This chapter discusses the vehicle systems technology areas that the Partnership is addressing in its research and development (R&D) programs, which include the following: (1) advanced combustion, emission control, and fuels for internal combustion engines (ICEs); (2) fuel cells; (3) hydrogen storage onboard a vehicle; (4) electrochemical energy storage or technologies for storing electricity onboard a vehicle; (5) electrical propulsion systems; and (6) materials for reducing the weight of a vehicle. The reader is referred to the presentations from the Partnership to the National Research Council’s (NRC’s) Committee on Review of the U.S. DRIVE Research Program, Phase 4, on the various technical areas (Appendix D provides a list of the presentations to the committee at its meetings). The presentations can all be found in the project’s Public Access File, available through the National Academies Public Access Records Office. Chapter 4 addresses issues associated with hydrogen, electricity, biomass-based fuels, and natural gas.
Introduction and Background
It will take decades to develop and integrate non-internal combustion engine propulsion systems into becoming a significant fraction of the total U.S. mobility fleet. The internal combustion engine will be the dominant power plant for mobility systems for at least the next 20 to 30 years (NRC, 2008, 2010). Consequently it is important to maintain a dedicated effort directed at ICE improvement within the U.S. DRIVE research portfolio.
Furthermore, there is reason for optimism that the drive-cycle-based efficiency of ICEs can be improved, both through engine-based advancements and through hybridization, such that the fuel consumption of engine-powered vehicles can be significantly reduced. Also, the engine has a sophisticated and mature manufacturing basis and is capable of using a range of fuels, from petroleum to liquid-based biofuels to gaseous fuels, derived from a variety of feedstocks. Liquid fuels offer the attractive characteristic of having very high energy per unit of mass and energy per unit of volume. This characteristic facilitates long-range and/or sustained high-power-output vehicle operation. There will be, for many decades, applications for which the ICE-powered vehicle is the best choice.
Life-cycle analyses reported in the literature, such as that shown in Figure 3-1, suggest that total greenhouse gas (GHG) emissions for future high-technology ICE-powered vehicles1 will be made competitive with non-ICE-powered vehicles on a basis of total GHG life-cycle emissions, while still meeting stringent air quality regulations (Weiss et al., 2000; Bandivadekar et al., 2008). Uncertainty bars in Figure 3-1 denote well-to-tank GHG emissions for electricity generated from coal (upper bound) and natural gas (lower bound). For the well-to-tank GHG emissions from hydrogen fuel cell vehicles (HFCVs; shown as “FCV” in Figure 3-1), it is assumed that the hydrogen fuel is steam-reformed from natural gas at distributed locations and compressed to 10,000 psi.
The advanced combustion and emission control (ACEC) technical team of U.S. DRIVE is the Partnership’s technical interface with the research community’s activities in advanced combustion and emission control. The goals, technical targets, and program structure of the ACEC technical team build on those from the FreedomCAR and Fuel Partnership, which in turn built on the goals and targets from the Partnership for a New Generation of Vehicles (PNGV). For the FreedomCAR program, the advanced combustion and emission control targets and results were as follows:2
• Peak engine brake thermal efficiency (BTE) of 45 percent
—This BTE was demonstrated with a light-duty diesel engine and an H2-fueled ICE.
• Oxides of nitrogen (NOx) and particulate matter (PM) emissions for light-duty diesel engines at Tier 2 Bin 5 (T2B5) standards
— Twelve vehicle models that met this target were commercially available in the 2012 model year (MY).
1 Hybrid electric vehicles and plug-in hybrid electric vehicles are included in this classification because the engine still plays a major role as the energy converter between the fuel energy and work delivered to the wheels.
2 R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
FIGURE 3-1 Predicted comparative total greenhouse gas emissions for current spark ignition engines (SIEs) and potential 2035 propulsion systems. NOTE: Acronyms are defined in Appendix E. SOURCE: Bandivadekar et al. (2008).
• Power-train cost of $30/kW
— This cost target guidance and status are currently under evaluation by U.S. DRIVE.
To push past the targets of the FreedomCAR and Fuel Partnership, the U.S. DRIVE Partnership addressed three engine technology pathways: (1) hybrid optimized (low-level power density), (2) naturally aspirated (mid-level power density), and (3) downsized and boosted (high-level power density); it identified engine efficiency metrics at three load conditions: peak efficiency; 2-bar brake mean effective pressure (BMEP)—2,000 revolutions per minute (rpm); and 20 percent of peak load—2,000 rpm.
The specific 2020 stretch targets were set relative to 2010 MY engines for each technology pathway. Table 3-1 shows a compilation of these targets for each engine technology pathway for each of the three metric conditions. Standard fuels, either gasoline or diesel, are considered in specifying the performance metrics.
For each of the three pathways being pursued to achieve the targets shown in Table 3-1, the fundamental approach and issues being addressed are these:
1. High-efficiency combustion with low engine-out emissions
— Low-temperature combustion (LTC)
|2010 Baselines||2020 Stretch|
|Technology Pathway||Fuel||Peak Efficiency (%)||Efficiencya @ 2-bar BMEP and 2,000 rpm (%)||Efficiencya @ 20% of Peak Load and 2,000 rpm (%)||Peak Loadb at 2,000 rpm||Peak Efficiency (%)c||Efficiencyc @ 2-bar BMEP and 2,000 rpm (%)||Efficiencyc @ 20% of Peak 2,000 rpm (%)|
aEntries in percent brake thermal efficiency (BTE).
bEntries in bar of brake mean effective pressure (BMEP).
cEntries in percent BTE that are equal to 1.2 times the corresponding baseline BTE.
SOURCE: R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
— Clean diesel
2. Improved efficiency with waste energy recovery
— Solid-state and mechanical approaches
— Improved air handling and lubricants
3. Efficient aftertreatment systems that reduce the energy penalty and meet emissions regulations
— NOx, PM, hydrocarbons (HC), and carbon monoxide (CO)
At first glance the above list of technology pathways appears to focus on development-type issues that would best be addressed by industry as part of product development. However, the barriers to achieving the targets given above are fundamental understandings of the controlling phenomena for each pathway, and this is the focus of the U.S. DRIVE activities. The optimization of the interaction among the following is very complicated: the ambient conditions; the details of the gas exchange processes (intake and exhaust processes, exhaust gas recirculation [EGR], boost, intercooling, manifold geometry, valving events, etc.); the in-cylinder processes (injection characteristics, in-cylinder flow, combustion chamber geometry, fuel chemistry, etc.); and the exhaust-gas aftertreatment system (PM traps, NOx reduction systems, CO and HC oxidation systems, etc.) for minimum fuel consumption while meeting emissions standards. To address these challenges, industry uses analysis-led design, in which computational fluid dynamics (CFD) is used to predict the optimum combinations of power-train system control parameters for each engine operating regime.
This process is only as good as the accuracy and fidelity of the CFD programs being used. Consequently, the lack of a detailed fundamental understanding of the various thermo-fluid-chemical processes and their incorporation into CFD submodels is a barrier to further engine system optimization. Certain aspects of the challenges that industry must deal with are not understood at this time: for example, there is no accepted explanation for how lubricating oil is involved in the particulate formation processes within the engine cylinder. This is a relevant example of the importance of a lack of fundamental understanding, because higher-efficiency engines will rely on controlled air-fuel heterogeneity within the cylinder, which can lead to significant nanoparticle formation. Lack of understanding of the detailed processes occurring in the combustion chamber, like the particulate formation, subsequently impedes the optimization of engine performance through simulation.
The engine combustion and emission research community is collaborating with industry to address these fundamental issues through experiment and simulation. To best duplicate the conditions in which to probe a deeper fundamental understanding of these phenomena, researchers perform experiments and simulations in representative engine geometries under real operating conditions.
The primary framework through which the U.S. DRIVE ACEC technical team engages with research activities on combustion and emission controls is through the U.S. Department of Energy’s (DOE’s) Office of Vehicle Technologies Program (VTP). This office supports fundamental research in combustion, energy recovery, and aftertreatment performance. Within these programs there is participation from industry, DOE national laboratories (Argonne National Laboratory [ANL], the Sandia National Laboratories [SNL] Combustion Research Facility, Oak Ridge National Laboratory [ORNL], Pacific Northwest National Laboratory [PNNL], Lawrence Livermore National Laboratory [LLNL], and Los Alamos National Laboratory [LANL]), and universities.
DOE’s vision of the collaborative activities between national laboratories, universities, and industry is a progression from fundamental to applied research to technology maturation and deployment. Fundamental R&D is the focus of activities at the following:
• Sandia National Laboratories
— E.g., Combustion Research Facility (lean-burn, LTC, advanced direct injection)
• Pacific Northwest National Laboratory
— E.g., catalyst characterization (NOx and PM control)
• Argonne National Laboratory
— E.g., x-ray fuel spray characterization
• Lawrence Livermore National Laboratory
— E.g., chemical kinetics models (LTC and emissions)
• Los Alamos National Laboratory
— E.g., CFD modeling of combustion (KIVA code development)
— Complementary research
The fundamental to applied bridging R&D is performed at the following:
• Oak Ridge National Laboratory
— E.g., experiments and simulation of engines and emission control systems (bench-scale to fully integrated systems)
• Argonne National Laboratory
— E.g., H2-fueled ICE, fuel-injector design
Finally, competitively awarded cost-shared industry R&D is done by the following:
• Automotive and engine companies and suppliers
— E.g., engine systems and enabling technologies (sensors, variable valve actuation, waste heat recovery)
The advanced combustion and emissions control program is well managed. The organizational structure of its activities involves memoranda of understanding between companies and government laboratories. It is usual for individual projects to include one or more of the national laboratories, a university, and an industrial partner. To ensure relevance, industry cofunding or matching is often required.
In addition to the regular research meetings within a specific project, two formal research reviews are held each year, one at the Sandia Combustion Research Facility in Livermore, California, and one at the U.S. Council for Automotive Research (USCAR) in Southfield, Michigan. The researchers also participate in the DOE Annual Merit Review.
Additional avenues for technical interchange are promoted through CLEERS (Crosscut Lean Exhaust Emission Reduction Simulation) and the Engine Combustion Network (ECN).
CLEERS sponsors monthly teleconferences and an annual workshop to promote the development of improved computational tools for simulating realistic full-system performance of lean-burn diesel/gasoline engine and associated emission control systems. This activity helps in the development of emission control models that are integrated into vehicle simulations for drive-cycle analysis within the vehicle systems and analysis technical team (VSATT).
The ECN supports a website and teleconferences to share and leverage research between experimenters and modelers on direct-injection fuel sprays and combustion.
Overview of Technologies Being Investigated
To implement new combustion strategies, effective exhaust-gas energy recovery, and aftertreatment systems that promote efficient engine operation, the air handling, combustion, and exhaust subsystem must be optimized as a system. Such optimization requires advanced computational fluid dynamics. It is now common that the design of a new power-train system is led by CFD. To extract increasingly better performance from the power train requires more accurate and detailed computational models. These models are developed through the coupling of fundamental experiments and computational submodel development. This is the interface at which the U.S. DRIVE effort is focused.
In the area of high-efficiency combustion, the emphasis continues to be on low-temperature combustion. LTC is in essence controlled knock, and it relies on the auto-ignition chemistry of the fuel. Regardless of the fuel, the underlying approach to achieving acceptable LTC is the same. One wants to get the fuel vaporized and partially mixed with the cylinder gases such that when the auto-ignition chemistry reaches the point of ignition, the energy release is volumetric. Furthermore there needs to be sufficient inhomogeneity of the mixture within the combustion chamber that the entire mixture does not auto-ignite all at once, which would lead to excessive rates of pressure rise. This inhomogeneity can be in
temperature, air-fuel ratio, or degree to which the local mixtures have kinetically traversed their auto-ignition pathway. If this is achieved, the engine efficiency is higher and the in-cylinder emissions are very low. The approach taken to control LTC will be dependent on the fuel type—gasoline-like, diesel-like, or dual fuels— and the load demanded of the engine. Since the NRC (2010) Phase 3 review of the FreedomCAR and Fuel Partnership carried out in 2009, five new combustion projects have been started to address these challenges.
Regardless of how efficient the engine is, there will always be some usable energy in the exhaust that leaves the cylinder. As the engine efficiency gets higher, the usable energy in the exhaust gets smaller. Thermodynamically, it is known that as the portion of recoverable energy in the exhaust decreases, the efficiency of an exhaust-gas energy recovery system also decreases. However, in the quest to maximize engine efficiency, gains can still be made by the inclusion of exhaust-gas energy recovery systems. This imposes challenging constraints on the cost-benefit assessment of implementing energy recovery systems in the exhaust, and on maintaining a highly efficient exhaust-gas aftertreatment system.
The fundamental research being pursued on exhaust-gas energy recovery within the ACEC technical team is to develop energy recovery systems that maximize the conversion of usable exhaust energy in ways that are economically viable. Research programs addressing exhaust-gas energy recovery involve electricity generation with thermoelectrics, as well as more efficient turbomachinery and air handling. In addition, work is being supported on advanced lubricants, improved friction management, and materials for higher operating pressures and temperatures.
Within the aftertreatment research programs, there are activities on developing efficient catalysts that operate at lower exhaust temperature, improved NOx and PM aftertreatment systems, reducing the platinum group metal (PGM) requirement for the aftertreatment systems, and combining multiple aftertreatment systems into a single unit.
The predictive capabilities of the current CFD programs are good. The simulation code used most widely at this time is KIVA III, developed by DOE. KIVA is an open-source-code program, which allows researchers to incorporate new understanding directly into the code for any aspect of the thermophysical processes occurring within the engine. For example, improved kinetic schemes for different fuel types or new submodels that more accurately represent liquid fuel-combustion chamber surface interactions can be implemented into the code and then exercised for more detailed predictions of combustion results. However, KIVA III is more than 12 years old and lacks important, modern numerical technologies such as parallel computing and using an object-oriented structure. Having an up-to-date, open-source CFD program for researchers to use is a critical aspect of achieving the improvement potential of the ICE and aftertreatment power trains.
The DOE is supporting work on a new version of the code, KIVA IV. To date the code has not been widely adopted. Discussions of committee members3 with academic users led to a list of possible reasons for the code not being widely adopted:
• A code with KIVA IV’s level of physics and geometry (engines) needs to be modular and needs to have a data structure that is object-oriented.
• The current effort allocated does not appear to provide the level of development support required for doing an acceptable job—an increased effort was suggested by academic users and submodel developers.
• Code development for KIVA needs to be strongly tied to the activities of its “customers,” which are predominantly the universities where the advanced submodels are being developed and implemented.
• Intellectual property (IP) issues associated with the code and submodels may be jeopardizing the open-source designation. If this key element is lost, the university following could disappear, which seems to be happening.
Perhaps if a more active interface could be established between researchers working on the code development, university and research groups developing submodels, and industry partners, who will be the ultimate users of the code, the adaptation of the new code could be expedited.
The energy companies continue to be engaged, and the program of Fuels for Advanced Combustion Engines (FACE), organized under the Coordinating Research Council (CRC), is supplying an important database for quantifying the impact of fuel characteristics on engine emission processes and alternative combustion process facilitation.
In response to questions from the committee, U.S. DRIVE Partnership officials commented that natural gas is not included in the Partnership’s technical scope. The committee believes that in light of the increased supply of natural gas and the high interest in using it to displace petroleum, an assessment should be made of whether natural gas is in any way an enabler for achieving U.S. DRIVE goals. For example, does natural gas facilitate the advanced combustion modes under investigation within U.S. DRIVE?
The ACEC technical team’s responses to the recommendation of the previous review were good. The team is continuing to look for opportunities to enhance collaboration and has a program in KIVA code development. As discussed above, the committee believes that the KIVA code development effort could be improved. The ACEC technical team is making more use of the vehicle simulation that is being developed by the VSATT, and although it is not engaged in biofuels research, the team is aware of activities in the field. Also, the approach being
3 In particular, David Foster, committee member, had discussions with academic users.
FIGURE 3-2 Department of Energy advanced combustion engine research and development (R&D) funding—FY 2010 to FY 2012. SOURCE: R. Peterson, General Motors, and K. Howden, Department of Energy, “Advanced Combustion and Emission Control Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
taken within the ACEC technical team’s programs in developing kinetic models for combustion process simulation is compatible with the inclusion of compositional changes that could occur to the fuel when biomass-derived compounds are blended with the fuel.
Even though the U.S. DRIVE Partnership’s ACEC technical team does not exercise control over a budget, it did offer to the committee an overview of the DOE funding within the advanced combustion and emission control programs for FY 2010 through FY 2012 (see Figure 3-2).
Within the scope of the U.S. DRIVE goals, the work allocation for the continued development of the ICE and vehicle electrification seems appropriate.
This section presents a summary of accomplishments related to R&D activities in the areas of advanced combustion, emission control, and fuels for internal combustion engines.4
Low-temperature combustion has proven to be an effective means of improving closed-cycle efficiency and reducing the formation of NOx and particulates. By reducing the formation of NOx, both the cost and the complexity of additional aftertreatment can be reduced. The benefits of LTC are known, and include dramatic reductions in the formation of NOx. However, controlling the in-cylinder processes leading to successful LTC operation is a challenge. The ACEC technical team has demonstrated a number of successes both in the control of LTC and in expanding its operational range within the engine duty cycle.
One example of this success is a project at ANL where researchers were able to use 87 research octane number (RON) gasoline in a 1.9-liter turbocharged engine while retaining a full load range and diesel levels of efficiency with substantially reduced NOx.
The Sandia National Laboratories achieved indicated thermal efficiencies as high as 48 percent by using partial fuel stratification in a boosted homogeneous charge compression ignition (HCCI) engine.
The ORNL has a project using E85 (a mixture of 85 percent ethanol and 15 percent gasoline) in a spark-assisted HCCI engine. A 17 percent increase in indicated thermal efficiency was achieved as compared to that of gasoline and over a wide range of loads.
The use of two fuels, while adding some complexities and costs, also adds to the capabilities of controlling combustion and emissions. Reactivity controlled compression ignition (RCCI) engines involve the in-cylinder blending of two fuels with differing reactivity in order to tailor the reactivity of the fuel charge. Researchers at ORNL and the University of Wisconsin have used a diesel/gasoline multicylinder engine RCCI to demonstrate efficiencies up to 5 percent greater than diesel efficiencies. To better understand how dual fuels provide the benefits, fuel mixing and RCCI combustion were imaged from inside an optical engine by researchers at SNL and the University of Wisconsin.
In other combustion research approaches, researchers from ANL, SNL, and the Ford Motor Company, using advanced direct injection of hydrogen, were able to achieve 45.5 percent peak brake thermal efficiency of a hydrogen-fueled ICE. Further, it is expected that minimal exhaust aftertreatment will be required to meet stringent emission goals. The researchers were also able to demonstrate a part-load efficiency of 31 percent while meeting T2B5 emissions standards.
4 A full summary of accomplishments can be found in U.S. DRIVE Highlights of Technical Accomplishments: 2011, available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/2011_usdrive_accomplishments_rpt.pdf.
Detailed CFD and supporting experimental activities are critical to achieving more efficient combustion modes. The Lawrence Livermore National Laboratory has developed new approaches to computing fuel combustion chemistry using desktop-scale workstations, containing graphical processing units (GPUs) in addition to conventional central processing units (CPUs), that result in about an order-of-magnitude decrease in computation time.
Additional accomplishments relate to improved understanding of engine lubrication, spray and combustion modeling, EGR control, and exhaust energy recovery. The ORNL, working with Cummins, Inc., has developed a fiber-optic probe with laser-induced fluorescence to provide an accurate measurement of fuel dilution in engine oil. This technology has already been licensed to industry.
Researchers at ANL, the University of Illinois at Chicago, and Caterpillar have developed a new spray model for diesel engines that accounts for effects such as cavitation and turbulence in addition to aerodynamic breakup.
There are several other ICE-related projects that have added to industry’s ability to produce more efficient engines with lower emissions. Among those, SNL established the ECN, an international, multi-institutional collaboration with goals of improving the understanding of spray nozzles and increasing the capability of developing predictive spray models. Also, ORNL, the University of Michigan, and Ford Motor Company have provided a new understanding of EGR fouling mechanisms that can lead to improved EGR heat exchanger designs.5
Other important projects include collaboration between Ford Motor Company, Wayne State University, and ConceptsNREC to improve turbocharger design so as to improve engine efficiency while increasing rated power. Finally, through DOE working with Ford Motor Company, an improved aftertreatment system to minimize NOx emissions with selective catalytic reduction (SCR) was developed.
The ACEC technical team is making good progress. It is doing a good job at maintaining a close and constructive working relationship with the stakeholders within the vehicle and energy community. It is critical for the technical team to maintain this collaboration and to look for ways to make it even stronger.
The major barrier to implementing advanced combustion, aftertreatment, and fuel technologies continues to be an insufficient knowledge base. For example, the understanding necessary to control low-temperature combustion over a large portion of the engine map is a fundamental area appropriate for federal support. Topic-specific understanding is critical to continued improvement of the ICE power train; also critical is understanding of the system-level interactions between
5 Further details on this work can be found at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2011/tuesday/presentations/deer11_styles.pdf.
the energy carrier, the energy release process, and the final emission cleanup.6 Continued close collaboration between DOE and industry is necessary to allow newly developed understandings to transition into the industrial laboratories and to enable the identification of new areas where enhanced understanding will be most beneficial. Even though the thrust of current activities within the U.S. DRIVE Partnership is to develop the technologies necessary to meet performance targets, being able to implement the technologies into vehicles that are affordable will ultimately determine their success.
The ACEC technical team is a well-managed activity and should be recognized for its accomplishments. However, the committee does have two recommendations that it believes will make the program stronger and more complete.
Because computational fluid dynamics plays an indispensable role in future engine-power train system development, having a robust, modern code in which researchers can integrate and exercise improved submodels is critical. The U.S. DRIVE Partnership is working on the next generation of KIVA, but KIVA IV may not be widely adopted by the research community.
Recommendation 3-1. The DOE should undertake a larger effort on the next generation of KIVA in order to be successful in facilitating such a resource. There should be a more formal collaboration established among the industry stakeholders, university stakeholders, and the DOE researchers doing the development work for KIVA IV. Efforts should be made to implement a modular and object-oriented structure to the code that is most useful to the ultimate stakeholders.
Domestic natural gas reserves and production are growing rapidly, providing for possible future use in ICE vehicles.
Recommendation 3-2. U.S. DRIVE should make an assessment of whether natural gas can be an enabler for achieving the advanced combustion modes currently being pursued in its research portfolio.
Fuel cell vehicles, under development globally, are based on a technology that can ultimately result in a zero-emissions and fossil-fuel-free option for transportation applications, and can help meet the vision of the U.S. DRIVE Partnership. Elegantly simple in concept, it has been a costly and daunting task to develop
6 Hybrid electric and even plug-in hybrid electric power trains are included in the general classification of power train.
fuel cell technology for vehicular applications. This has been partly due to the expectation that at the time of the rollout of such vehicles, the new technology would mimic current ICE vehicle operational standards and turn-key performance under all conditions at a competitive cost. The challenge has also partly rested with the fact that fuel cell power plant and ancillary subsystems are unrelated to any power-train technology previously used in conventional vehicular applications. In development for well over two decades, the vehicle original equipment manufacturers (OEMs) have now engineered, built, and tested fuel-cell-powered prototype vehicles, which appear to have met many consumer expectations with respect to vehicle performance. Automotive OEMs, with the assistance of suppliers and end users in the United States, have now begun to generate statistically significant on-road performance data leading to further confidence in the technology, engineering refinements, and identification of areas requiring further development. If the hydrogen fueling infrastructure, currently in its infancy, can evolve based on renewable hydrogen generation processes, there is a good chance that the vision of the U.S. DRIVE Partnership and its predecessor organizations will be achieved. Regardless of the source of the hydrogen, the development of a production and distribution infrastructure is clearly essential for the possible success of widespread hydrogen fuel cell vehicles (see Chapter 4).
The DOE’s primary role in fuel cell R&D is to facilitate the advancement of precompetitive technology that is considered longer term and high risk. These are projects that, if successful, will provide the OEMs with “next-generation” technical options. Assessment of the approximately 300 projects currently funded by DOE indicates that approximately 65 percent fall within the technology readiness levels (TRLs) of 2 and 4—that is, basic research efforts as well as activities related to analytical and experimental proof of concepts.7 Only a small percentage (7 percent) of funding is allocated to nearer-term initiatives (TRL 7).
The lifetime of the fuel cell stack is still a limiting factor. The current stack life is approximately half of the targeted lifetime as set forth by the Partnership. The 5,000-hour target required with minimal degradation has still not been achieved, as reported by the National Renewable Energy Laboratory (NREL) in on-road vehicle tests (Wipke et al., 2012); however, proton exchange membrane (PEM)-based bus stack lifetimes have exceeded 10,000 hours with similar technology. Advancements in systems engineering focusing on stack operation will also play a role in meeting the lifetime targets. Reports by NREL on fuel cell performance in on-road vehicle tests, based on 2009 vehicle technology, indicate that significant advancements have been achieved (Wipke et al., 2012).
Recent results presented at the 2011 and 2012 DOE Annual Merit Review meetings have indicated that the key issues impacting fuel cell performance are under investigation at the national laboratories, within academia, and in industry.8
7S. Satyapal, Department of Energy, “Fuel Cell Technologies Overview,” presentation to the committee, December 5, 2011, Washington, D.C.
Degradation mechanisms and performance limitations of the fuel cell power module are now the focus of such efforts, leading to a better understanding of the primary life-limiting issues. Reports from the Annual Merit Review over the past 3 years continue to show that laboratory tests of single cells have in many cases surpassed the program lifetime target (Debe, 2011, 2012), yet the laboratory and on-road test results are still in need of addressing operability and performance issues. As a result, technology and stack operating modes tested in the laboratory and those encountered during on-road vehicle tests are now being coordinated. The conclusions and outcomes of such efforts are essential to the delineation of the technical issues that need to be addressed when moving from the laboratory to real-world applications.
Assessment of the Program and Key Achievements
The fuel cell activities and resultant achievements can be grouped into three categories: (1) on-road vehicle performance, (2) longer-term R&D, and (3) near-term programs to support the secondary activities, including cost and engineering modeling, as well as programs focused on the adoption of the technology. All three areas have progressed at various paces since the Phase 3 NRC (2010) review.
Fuel Cell Vehicle Performance
On-road tests of hundreds of vehicles have been completed since the NRC (2010) Phase 3 review. Although it is difficult to state conclusively the magnitude and extent of the progress, such results are impressive, as reported by NREL (see Figure 3-3). It is significant that the results of the on-road field vehicle demonstration programs were generated with vehicles using 2009 or earlier technology. Additional progress has been made since then by the OEMs. The past and current status of selected metrics, including power density (W/l) and specific power (W/kg), cost, durability, start times at –20°C, and energy efficiency at 25 percent rated power are presented in the spider chart in Figure 3-3. It is clearly evident that all of the metrics have met or are approaching the 2017 targets except for cost and durability. Significant progress has been made in the past 8 years.
Long-term programs account for 65 percent of the fuel cell activities, ranging from proof of concept to applied engineering efforts. The topics addressed in this category are for the most part continuation and follow-on programs of prior efforts. This continuity is critical, as the programs that have survived the go/no-go decisions are the ones deemed to have the most significant potential.
FIGURE 3-3 Spider chart of fuel cell performance results versus targets for various years. SOURCE: C. Gittleman, General Motors, and K. Epping Martin, Department of Energy, “Fuel Cell Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
There are new programs, but the number and magnitude have been limited. Since the Phase 3 review, five proposed efforts have been funded. New research efforts have originated through other offices besides the Office of Energy Efficiency and Renewable Energy (EERE), including the Office of Basic Energy Sciences (BES) and Small Business Innovation Research (SBIR) programs.
The accomplishments and progress considered significant in the past few years focus on the two main barriers, durability and cost. With respect to the barriers, the primary emphasis has been on the membrane electrode assembly (MEA), consisting of catalysts and membranes sandwiched between two carbon-based gas diffusion layers. The assembly is then placed between two plates, resulting in anode and cathode compartments (the cell). The cells are then stacked on one another until the desired voltage-current specification is met. Catalysts, predominately platinum group-based, are formulated with binders and/or ionomeric materials (proton conducting polymer) and fabricated into an electrode layer, which is applied to either the membrane or gas diffusion media. The majority of the currently funded efforts are on performance and durability aspects of carbon-free supported catalysts, non-precious metal catalysts, the quantity of catalysts required per cell, as well as on lower-cost, durable membranes. If success is achieved in any one of the above areas, the attractiveness of the fuel cell from a cost and durability perspective would be greatly enhanced. As noted in its recommendations, the committee believes that these activities should be increased in scope and that the budget should be adjusted to reflect the change.
Recent progress at the laboratory level has been promising, but it in no way implies the successful viability or the adoption of the advancements in fuel cell stacks when used in vehicles. With that said, recent work reported by Argonne
National Laboratory (Myers et al., 2011, 2012) at the 2011 and 2012 DOE Annual Merit Review meetings on determining the fundamental degradation mechanisms of MEAs has provided invaluable insight into the science of the failure modes of the catalysts and membranes. A number of other efforts to change catalyst supports, the architecture of the catalyst layers, and the work to develop non-precious metal catalysts will benefit from the findings of this effort. As the MEA is a complex “system,” changes in any one component will impact the functionality and performance characteristics of the entire assembly. As a result, advancements and scientific findings in each area must be thoroughly communicated, including to the industrial partners who will ultimately fabricate the MEA in high volumes. An assessment of the interrelationships of the fuel cell technical team with associated organizations indicates that the dissemination of information is taking place at the appropriate level on the membrane and electrode topics.
The catalyst development efforts have resided mainly at the national laboratories, where steady progress has been made in enhancing the catalytic activity as a function of the amount of catalyst required to support the reactions. The development of carbon-free supported catalysts is also underway. Durability, stability, and poisoning issues remain, but the results are promising, and as such these activities are essential if the ultimate targets are to be met. For example, at the national laboratories, fundamental electrochemical-catalyst modeling to predict performance-cost benefits is underway, as are activities to improve the understanding of the platinum core shell catalysts and the promising Pt3Ni(111) alloys, among others, and the impact of processing and operating conditions on them. Non-precious metal catalysts are also being investigated. Industrial organizations, predominately the ones that will eventually be part of the backbone of the supply chain, are engaged, with 3M being an example. The 3M activity on the nanostructured thin film (NSTF) electrode is showing good progress, not only from a catalysis perspective but also from the electrode layer architecture and the impact of water dynamics in a functioning MEA. The contributions of 3M with respect to the effect of gas diffusion media on performance offer another example of the interrelationships of the different layers within the MEA.
Because catalysts are at the heart of the electrochemical process and are a major cost component of the stack, research activity in this area is considered significant and appropriate and should be continued. It should be noted that selected aspects of catalyst and electrode technology used in fuel cells may provide guidance and direction in other electrochemical processes as well (e.g., batteries).
Proton exchange membranes are composed of complex polymers that must be able to transport protons efficiently with minimal resistance and at the same time exhibit acceptable mechanical strength and low gas permeability. They must be low cost and be able to be easily manufactured. The polymer/membrane development is a long and costly process. The DOE is aware of this and has been appropriately supporting new membrane development for a number of years in academia and national laboratories and within industrial organizations.
|2010 Target||2011 Status||2017 Target|
|Fuel cell stack durability (hr)a||5,000||3,700||5,000|
|Fuel cell stack cost ($/kWe)b||25||22||15|
|Membrane electrode assembly (MEA) cost ($/kW)b||14||13||9|
|MEA total Pt group metal total content (g/kW)||0.15||0.19c||0.125|
|Non-Pt catalyst activity per volume of supported catalyst (A/cm3 @ 800 mVIR-free)||130||127d||300|
|Bipolar plate cost ($/kW)b||5||5||3|
aProjected time to 10 percent voltage degradation from the technology validation activity.
bCost status is from 2011 DTI study; costs are projected to high-volume production (500,000 stacks per year). Available at http://www.hydrogen.energy.gov/pdfs/review11/fc018_james_2011_o.pdf.
cM. Debe, U.S. Department of Energy Hydrogen and Fuel Cells Program 2011 Annual Merit Review Proceedings, May, 2011. Available at http://www.hydrogen.energy.gov/pdfs/review11/fc001_debe_2011_o.pdf.
dP. Zelenay, H. Chung, C. Johnston, N. Mack, M. Nelson, P. Turner, and G. Wu. 2011. FY 2010 Annual Progress Report for the DOE Hydrogen Program. DOE/GO-102011-3178. U.S. Department of Energy, February, p. 816.
SOURCE: C. Gittleman, General Motors, and K. Epping Martin, Department of Energy, “Fuel Cell Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
The focus has appropriately been on membranes that can operate with reduced hydration requirements and/or higher operating temperatures and at the same time exhibit higher conductivities. The committee sees less value in supporting membrane-based subsystem development—for example, in enthalpy exchange processes—as this is more of an engineering initiative and not deemed long-term, high-risk research. The financial resources used to fund the near-term engineering initiatives should be reallocated to topic areas that impact the durability and/or cost issues.
Table 3-2 summarizes the fuel cell stack and stack component progress against the 2010 and 2017 targets.
Near-Term Supporting Efforts
The DOE and the U.S. DRIVE Partnership have developed additional mechanisms by which the key fuel cell issues are addressed. Although the programs highlighted above are selected through the DOE solicitation-proposal process, working groups have been formed to facilitate better communication among the stakeholders and are also being asked to focus on the most critical needs (e.g., durability, modeling, and catalysis). The teams are led by national laboratory representatives and involve catalyst and membrane suppliers as well as fuel cell companies, vehicle OEMs, and other participants. As articulated by the
fuel cell technical team during the review process, the primary objectives are to (1) promote sharing in the learning, (2) prevent duplication of effort, and (3) disseminate the findings to the fuel cell community. The committee sees this activity as a valuable means to maximize progress and learning through such a coordinated effort. Cooperation among the team members on critical precompetitive research topics will accelerate and facilitate solutions for the entire industry.
The past three NRC reviews of this program have expressed concerns that the cost assessments as reported are difficult to endorse fully as the technology was still evolving, the supply chain immature, and the technology used by the OEMs unknown to the assessment committee. The Phase 3 report (NRC, 2010) noted that even with these uncertainties, the estimated costs for the fuel cell system (for 500,000 per year production) represented a reference point from which to measure cost-reduction progress. As the $30/kW target is still quite challenging, the technical development and cost-reduction efforts currently underway must be appropriately funded. Figure 3-4 presents the reported cost estimates for the fuel cell system for the last 5 years. The most recent estimate is also included (2011).
Although it is difficult to validate the absolute value of the reduction in system costs, the trend is quite apparent. New manufacturing initiatives will further impart greater certainty in the numbers, as will commitments to the OEMs by the
FIGURE 3-4 Cost estimate on a dollars per kilowatt ($/kW) basis for the fuel cell system, not including onboard hydrogen storage. SOURCE: C. Gittleman, General Motors, and K. Epping Martin, Department of Energy, “Fuel Cell Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
supply chain. As technology development efforts continue to progress, it is not possible to know at this time if there will be a significant impact on cost. High-volume vehicle production will not result in economies of scale with respect to the price of platinum. Platinum costs can be mitigated by recycling strategies, but the stack lifetime issue will impact maintenance and stack replacement costs until such time as durability issues are resolved. As it is not apparent that lifetime targets will be met any time soon, DOE should consider including, as part of its modeling efforts, not only the original bill of materials but also a realistic assessment of component replacement costs for the near term.
In addition to component costs, manufacturing processes must be efficient in leading to a high yield of finished goods. The membrane electrode assembly, the heart of the power generation unit, is a complicated and costly five-layer package composed of membranes and catalyst layers sandwiched between gas diffusion media. The intimate bonding of the various layers is critical, as are catalyst functionality and membrane conductivity. If any element of the five layers is jeopardized or incorrectly assembled and then incorporated into stacks, the problem is not likely to surface until preliminary stack qualification testing. At that point the entire stack would have to be rebuilt and the suspect cells removed. This is a costly and time-consuming process. Sophisticated electroanalytical methods are now currently used to assess small, laboratory single cells, especially alternating current (ac) impedance spectroscopy from which membrane and electrode viability can be assessed. These methods have not been fully developed for online, continuous, web-based, stand-alone membrane electrode assemblies.
The annual funding for hydrogen and fuel cell R&D since 2003 is presented in Figure 3-5(a). The breakdown of how the funds have been appropriated with respect to fuel cell R&D since the Phase 3 review is shown in Figure 3-5(b). In the latter years it is evident that fuel cell R&D has seen a significant reduction in funding. It is also evident from Figure 3-5(b) that the bulk of the funding has focused on the most critical technical issues, namely, catalysts and membranes. This trend continues as the proposed FY 2013 budget (DOE, 2012a) for the DOE hydrogen and fuel cell R&D has been further reduced by greater than 20 percent, to about $80 million, down from $104 million in FY 2011 and $170 million in FY 2010. The fuel cell systems R&D budget, relevant to this review, has seen a decrease in funding from $75 million in FY 2010 to $43 million in FY 2012.
The budget reductions have resulted in a limited but more focused and coordinated set of initiatives (Figure 3-5[b]). Although fuel cell technology has progressed, the current status is that further advancements are still needed. The funding reductions have impacted to varying degrees the approximately 300 hydrogen and fuel cell projects currently under contract with DOE, as well as the number of new awards made under recent solicitations. Offsetting this to some
FIGURE 3-5 Historical and current Department of Energy (DOE) budgets for hydrogen and fuel cell research and development (R&D), FY 2003 through FY 2012. (a) Annual DOE funding for hydrogen and fuel cell R&D, FY 2003 through FY 2012. (b) DOE funding for various fuel cell R&D areas, FY 2010 through FY 2012. SOURCE: C. Gittleman, General Motors, and K. Epping Martin, Department of Energy, “Fuel Cell Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.; and S. Satyapal, Department of Energy, “Fuel Cell Technologies Overview,” presentation to the committee, December 5, 2011, Washington, D.C.; Sunita (2011). (b) (b) Figure 3-5 (b)
extent is the coordination of activities with other organizations—for example, with the Office of Basic Energy Sciences, which has contributed to key fundamental learning and advancements. It is important that conclusions regarding the status and needs of the program not be improperly derived. The benefits of prior DOE funding are just now becoming apparent and quantifiable. Over the past decade, 183 prototype vehicles have been involved in actual on-road tests, more than 500,000 vehicle trips have been documented, and 3.5 million miles have been driven—all of which have contributed to the assessment and validation of the technology and the identification of areas requiring further technical enhancement. This learning impacts the supply chain as well because component suppliers are responsible for developing and ultimately manufacturing what goes into a vehicle. Given that suppliers are the predominant recipient of DOE funding, budget reductions may impact them as well.
Significant Barriers and Issues
As highlighted throughout this review, cost and durability issues remain significant impediments to meeting the fuel cell program targets. Both are technical issues and must ultimately be addressed through continued activities in fundamental and applied R&D efforts.
If progress toward meeting the targets is to continue in the aforementioned topic areas, the activities addressing them must remain intact, in some cases for extensive periods of time. Although the OEMs are making progress, what is reported to the committee is not necessarily derived from the most recent technical advancements, but rather from older vehicle performance test programs that take time to develop statistically significant and meaningful results. These results then provide direction to the fuel cell technical team, followed by DOE solicitations. It is important but difficult to maintain a coordinated, longer-term, proactive effort among the various stakeholders, including the OEMs, the national laboratories, private industry, and academia, especially in the face of uncertain funding. The majority of the Fuel Cell Technologies Program funding should be directed toward next-generation technical solutions that will be important in meeting the goals of the entire program. The lack of continuity of funding as a result of budget limitations is a serious issue.
Response to Phase 3 Recommendations
The Phase 3 review presented four recommendations regarding fuel cell activities (NRC, 2010). The recommendations addressed (1) increased funding levels and support for the enhancement of key system components, including stack technology; (2) ensuring that non-OEM cost and systems modeling activities utilize the most recent, up-to-date, vehicle technical know-how, design, and componentry; (3) the development of alternative pathways in the event that the primary paths fail
to yield desired results; and (4) the subjecting of currently funded nonperforming programs or efforts to an accelerated go/no-go assessment if they are deemed not to be of value to the vehicle program. It is noted by the committee that the majority of the recommendations were adequately addressed by DOE, some more so than others. Although not called out specifically in a formal response, in many cases elements of some of the recommendations can be found in existing funded programs. With that said, the recommendation to increase funding in the most critical area, specifically, stacks—that is, durability, catalyst, and membrane development—is not apparent from the FY 2010-2012 budget allocations.
Appropriateness of Federal Funding
The committee believes that R&D that has been supported by DOE related to fuel cells is appropriate for federal funding. R&D in this area is important for giving the nation a range of options for energy conversion across several applications and for providing needed energy savings and emissions reductions. Significant progress has been made to date; nonetheless, barriers that need to be addressed by research remain. Continued R&D support for fuel cells is necessary to make the progress needed to meet the ultimate goals set by DOE.
Observations and Conclusions
Based on the advancements that the automotive companies have made on their HFCVs and assuming that part of these advancements have been due to Partnership efforts, it can be concluded that significant progress has been made since the Phase 3 NRC (2010) report. It should be noted that such technologies were in part derived from DOE funding and coordinated efforts with the prior FreedomCAR and Fuel Partnership and current U.S. DRIVE Partnership programs. Furthermore, investigations on fundamental issues related to durability and performance have been expanded in scope and have begun to yield insight not only into degradation mechanisms but also in terms of providing guidance for developing next-generation catalysts and electrodes. Both are necessary if the performance targets are to be met. Progress has been made in other areas as well and should not be dismissed. It is important to provide continuous support for R&D in these areas if targets are to have any likelihood of being met.
Fuel cell stack cost and durability are still the two major areas that have not simultaneously met targeted levels. Stack lifetimes have exceeded 50 percent of the targeted 5,000 hours in real-world on-road vehicles. Fuel cell costs for a 500,000 per year production level have been projected to have dropped since the last report, from $60-$70/kW in 2009 to $49/kW in 2011.9 Further reductions
9 C. Gittleman, General Motors, and K. Epping Martin, Department of Energy, “Fuel Cell Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
will potentially come over time, as learning from on-road vehicle performance and technologies with reduced platinum loadings are adopted. Advanced catalysts have been and continue to be developed, including platinum-free systems. Such programs have emanated from academia, industry, and, most important, from the national laboratories. New developments take significant time and testing resources by the fuel cell OEMs before they can be fully adopted. This activity represents significant financial resources.
Statements by OEMs in this country and by other global automotive companies have indicated that vehicles in limited quantities will be placed in predetermined locations worldwide, partly gated by the availability of hydrogen refueling facilities, in the 2014-2016 time frame. This activity coincides with the timing of the original technology roadmap milestone of the FreedomCAR and Fuel Partnership whereby in 2015 there would be a commercialization readiness decision. Considering the global economic downturn and the budget constraints of late, the vehicle engineering accomplishments attest to the commitment of automotive manufacturers to fuel cell vehicles and thus to the importance of the Partnership’s enabling R&D. The expected onset of fuel cell vehicle deployment is impressive.
Activities within the program encompass not only the technical elements of the stack but also a number of focus areas that address market adoption and analyses, as well as a host of technical and nontechnical topics. In light of the budget data presented in Figure 3-5 and the criticality of the technical issues (durability and cost), the “balance” of the entire program as assessed by the percentage of funding in less critical areas over others of greater importance can be called into question.
The adoption of fuel cell vehicles is partly dependent on the durability and the cost of the technology. Fuel cell development is an important element of the U.S. DRIVE Partnership and, if successful, the chances of meeting the long-term goal of reducing greenhouse gas emissions and U.S. dependence on foreign oil are increased. Fuel cell R&D activities that address the remaining technical challenges and costs have decreased annually since the NRC’s Phase 3 review. This decline negatively impacts the development of future solutions that the developers will have available to meet the near- and long-term targets.
Enhanced catalyst, electrode, and membrane robustness would improve the likelihood that fuel cell stacks achieve the 5,000-hour life target. Such research efforts are generally long-term programs, as new catalysts, membranes, and related stack initiatives must progress from fundamental research activities all the way through lifetime and performance testing, and then vehicle qualification. These types of R&D activities must remain a high priority in order to ensure that next-generation robust stack component solutions become available.
Recommendation 3-3. The DOE should increase the efforts related to the development of new catalysts, membranes, and related membrane electrode assembly components for proton exchange membrane (PEM)-based fuel cells. The focus should be on materials, performance, durability, and, ultimately, on manufacturability.
As noted throughout this major section on fuel cells, cost is the other major challenge besides durability. There are two primary cost-reduction pathways: subsystem process optimization and specific component cost-reduction initiatives. For example, technical innovations might result in the simplification or elimination of subsystems or, when it comes to stack components, lower platinum loadings as well as lower-cost membranes and plate hardware. Emerging modeling capabilities can be used for sensitivity analysis and can guide resource allocation to the areas that will have the greatest impact on performance, endurance, and cost at the system level.
Recommendation 3-4. The DOE should increase efforts for the cost reduction initiatives for fuel cells taking into account the entire system, including balance of plant. Emerging modeling capabilities should be used for sensitivity analysis and for guiding resource allocation to the areas that will have the greatest impact on performance, endurance, and cost at the system level.
A number of emerging alternative fuel cell concepts, if successfully developed, may provide options for the OEMs in future generations of fuel cell vehicles. An alkaline fuel cell that uses membrane technology is one such example; a fuel cell concept that employs a flowing catholyte concept is another. Although PEM technology is well embraced by the automotive OEMs, it is imperative that novel fuel cell concepts be assessed critically and, if considered potentially attractive, also be explored and, as appropriate, directly or indirectly supported by DOE in its long-term, high-risk portfolio of projects.
Recommendation 3-5. Either in coordination with other organizations, such as the Office of Basic Energy Sciences or DOE’s Advanced Research Projects Agency-Energy (ARPA-E), or directly, DOE should consider supporting new and innovative alternative fuel cell concepts.
High-volume manufacturing methods for fuel cell stack components, in particular for the membrane and electrode assemblies, will need to incorporate (electro-) analytical quality-control methods to assess membrane and electrode viability prior to assembly into stacks. Such methods are utilized in laboratory fuel cells, but they are not currently developed for high-speed web-based manufacturing processes. If successfully developed, the information will be able to identify stacks that have inherent flaws within the membrane, interfacial region, and electrode layers.
Recommendation 3-6. U.S. DRIVE should encourage projects that address the use of real-time, in situ electroanalytical quality-control methods to assess membrane and electrode performance characteristics during the continuous manufacturing web-based process.
The mission of the hydrogen storage technical team is to “accelerate research and innovation to achieve commercially viable hydrogen storage technologies that meet U.S. Drive goals.”10 The onboard hydrogen storage goal is for “a >300 mile driving range across different vehicle platforms without compromising cargo space or performance.” The program scope is to “review and evaluate materials and systems research regarding hydrogen storage onboard light-duty vehicles and provide feedback to DOE and partnership stakeholders … generate goals and performance targets for hydrogen storage onboard vehicles … collaborate with other technical teams and assist the partnership in regards to hydrogen storage.” The work of the hydrogen storage technical team on onboard storage is most important to the U.S. DRIVE Partnership as a whole given the criticality of hydrogen storage to the performance of PEM fuel-cell-powered vehicles. The hydrogen storage system characteristics determine the amount of hydrogen that can be stored on the vehicle and the corresponding miles traveled between refueling as well as fuel storage costs.11
Materials-based solutions are the long-term option for onboard hydrogen storage. In the past decade, DOE established four hydrogen storage centers of excellence (COEs). Three materials centers of excellence (Chemical Hydrogen Storage COE, Metal Hydrides COE, and Hydrogen Sorption COE) operated from 2005 through 2010 and are now closed; final reports were issued April 2012.12 The fourth is the Hydrogen Storage Engineering COE. The COE proved to be an outstanding management concept that enabled the assembly of the right skills and resources for good collaboration to be brought to the work, a systematic down-select decision process, high-quality and consistent communication among the partners, and the development of intellectual property. Through these centers of excellence more than 400 compounds were investigated for their hydrogen sorption and release characteristics, and computationally millions of materials were studied. The work of these centers and related independent projects was a
10 N. Stetson, Department of Energy, and S. Jorgensen, General Motors R&D, “Hydrogen Storage Tech Team,” presentation to the committee, January 26, 2012, Washington, D.C. Also see http://www.hydrogen.energy.gov/storage.html.
well-organized systematic effort. This work involved extensive collaborations. In total, 45 universities, 15 companies, and 15 federal laboratories participated. A number of materials identified in this work are still considered to have potential, but storage weight, volume, performance, and cost are still a challenge. A brief description of the center accomplishments follows.
• Chemical Hydrogen Storage COE. Los Alamos National Laboratory, the lead laboratory for the Chemical Hydrogen Storage COE, worked closely with PNNL and other partners. A major accomplishment of the center was to demonstrate that chemical reprocessing of spent fuel is feasible. The highest-capacity material identified was based on ammonia borane, which was shown to release 2 to 2.5 moles of hydrogen (13-16 weight percent [wt%]) below 200°C with good stability. Research studies led to new understanding of the kinetics and nucleation of dehydrogenation. Additional findings related to materials processing and materials modification for improved performance and for ease of regeneration at a favorable cost. The COE received 16 patents.
• Hydrogen Sorption COE. The Hydrogen Sorption COE, led by NREL, was challenged to obtain high gravimetric and volumetric storage of hydrogen compared with compressed storage and at ambient temperatures. Work was focused on materials that gave excess storage capacities greater than 6 wt% and 40 g/L at pressures less than 200 bar (ca. 20 MPa) and storage temperatures above 77 K. Major findings overall include new materials for cryogenic storage on high specific surface area sorbents by optimizing pore size distributions, metal organic frameworks that exhibit enhanced di-hydrogen binding, and ambient-temperature storage by means of spillover and coordinatively unsaturated metal clusters. Also, measurement capabilities were improved and materials design was accelerated with coupled theory and experimental efforts. The COE produced more than 200 peer-reviewed publications, stimulated progress worldwide, and fostered spin-off for other sorption applications.
• Metal Hydride COE. The Metal Hydride COE, which was led by SNL, had five projects: (1) destabilized hydrides with enhanced kinetics (LiBH4/Mg2NiH4); (2) complex anionic hydride materials (e.g., boron hydride); (3) amide/imide storage materials (e.g., LiMgN); (4) alane; and (5) engineering analysis and design. The COE expanded the knowledge of metal hydrides hydrogen storage material and issued 279 publications. The boron hydride system showed remarkable properties reversibly, storing 12 wt% hydrogen. In spite of these favorable properties, no single material was identified that meets all criteria. A breakthrough theoretical method was developed for the rapid screening of materials, and a new theoretical method, prototype electrostatic ground state, from the theory group enables the prediction of crystal structures of unknown compounds.
|Year||Budget ($ millions)|
|FY 2009 appropriated||59.20|
|FY 2010 appropriated||32.00|
|FY 2011 appropriated||15.00|
|FY 2012 appropriated||17.50|
|FY 2013 requested||13.00a|
aHydrogen Storage is included within the Hydrogen Fuel R&D request ($27 million).
SOURCES: DOE (2010a, 2011); Stetson (2010, 2011, 2012); S. Satyapal, Department of Energy,
“Fuel Cell Technologies Overview,” presentation to the committee, December 5, 2011, Washington, D.C.
• Hydrogen Storage Engineering COE. The more recently established Hydrogen Storage Engineering COE at Savannah River National Laboratory (SRNL) has as its mission to “address significant engineering challenges associated with the development of lower pressure materials based hydrogen storage systems for hydrogen fuel cell and internal combustion engines for light duty vehicles.”13 Reported accomplishments to date include the development of hydrogen storage system models, the establishment of a baseline for materials properties that is used to guide the development of storage systems, assessment of the current status of all storage system approaches versus targets, and the identification of technology gaps that help to focus R&D. Modeling work on metal hydride hydrogen storage systems was completed.
The coordination with the DOE Office of Basic Energy Sciences is continuing. Twenty BES-funded projects were included in the Annual Merit Review held in May 2012. Work is underway to strengthen all national collaborations (within the DOE and across agencies including the U.S. Department of Transportation [DOT], the U.S. Department of Defense [DOD-Defense Logistics Agency], the National Institute of Standards and Technology [NIST], and the National Science Foundation [NSF]).
The FY 2011 budget for the onboard hydrogen storage activities has seen a decrease of 75 percent from FY 2009 and a 60 percent decrease in the number of projects for the same time period. The materials development work has experienced the largest decrease, with the closing of three materials centers of excellence. New work on advanced compressed gas tanks is anticipated in the FY 2012 budget plan. See Table 3-3 for recent appropriations and the FY 2013 budget request for hydrogen storage R&D.
A new roadmap that will guide the research is in final development, having been last updated in 2007. The target levels for onboard hydrogen storage first established in 2003 are in review. The DOE is reevaluating the performance metrics in comparison to available fuel cell, hybrid, and electric vehicle performance data. The current and projected target levels are shown in Tables 3-4 and 3-5.
The capabilities of various storage systems have been determined from engineering models of the various technologies. Progress is being made, and several targets have been met for some technologies, but no technology meets all targets simultaneously. Cost is an issue for all technologies.
The key system issues and challenges have been identified in terms of the following criteria:
• Sufficient storage for driving range without impacting vehicle performance,
|System gravimetric density||wt%||4.5||5.5||7.5|
|System volumetric density||g/L||28||40||70|
|System fill time for 5-kg fill||min||4.2||3.3||2.5|
|Svstem cost||$/kg H2 $/kWhne[||TBD||TBD||TBD|
|Minimum delivery temperature||°C||–40||–40||–40|
|Maximum delivery temperature||°c||85||85||85|
|Minimum full flow rate||(g H2/s)/kW||0.02||0.02||0.02|
|Cycle life (1/4 tank to full)||Cycles||1,000||1,500||1,500|
|Fuel cost||$/gge at pump||3-7||2-4||2-4|
|Loss of usable H2||(g H2/hr)/kg H2||0.1||0.05||0.05|
|“Well” to power plant efficiency||%||60||60||60|
|Fuel purity||% dry basis||99.97||99.97||99.97|
|Start time to full flow (–20°C)||s||15||15||15|
|Start time to full flow (20°C)||s||5||5||5|
NOTE: TBD, to be determined.
SOURCE: See http://www1.eere.energy.gov/hydrogenandfuelcells/storage/pdfs/targets_onboard_hydro_storage.pdf; N. Stetson, Department of Energy, and S. Jorgensen, General Motors R&D, “Hydrogen Storage Tech Team (HSTT),” presentation to the committee, January 26, 2012, Washington, D.C.
|Current Status||Gravimetric (kWh/kg-system)||Volumetric (kWh/L-ystem)||Cost ($/kWh)|
|700 bar (ca. 70 MPa) compressed (Type IV)a||1.7||0.9||18.9|
|350 bar (ca. 35 MPa) compressed (Type IV)a||1.8||0.6||15.5|
|Cryo-compressed (276 bar)a||1.9||1.4||12|
|Metal hydride (NaAlH4)b||0.4||0.4||11.3|
|Sorbent (MOF-5; 200 bar)b||1.7||0.9||18|
|Off-board regenerable (AB)b||1.4||1.3||N/A|
NOTE: Cost targets are being finalized and are expected to be released soon. Also, the Environmental Protection Agency (EPA) defines 33.7 kWh of electricity as equivalent to 1 gallon of gasoline. AB, ammonia borane; N/A, not available.
aBased on TIAX/ANL projections.
bBased on Hydrogen Storage Engineering Center of Excellence projections
SOURCE: Stetson (2012).
• Heat management,
• Durability, and
• Engineering and manufacturing.
In spite of rather rapid and impressive advances in hydrogen storage capacity by metal organic frameworks (MOFs) and covalent organic frameworks (COFs), the temperature and pressure required to achieve high capacities are far from DOE’s targets, and there are no systems identified yet that can do so.
System cost has proven to be a challenge for all promising materials and systems. Currently 80 percent of the hydrogen sorption projects have been discontinued on the basis of budgets or project results. Down-selects (go/no-go points) led to a decision to stop hydrolysis program work. Project down-selects by the Hydrogen Storage Engineering COE have resulted in phasing out work on metal hydrides (75 percent discontinued) and solid-phase chemical hydrogen (95 percent discontinued) materials engineering. Clearly, creative ideas need to be developed, and a plan is needed that will lead to fundamentally new ideas.
Compressed gas storage is the near-term path to commercialization. Compressed gas storage levels at 35 MPa and 70 MPa are near to the 2015 target for gravimetric storage but are only about 45 percent and 66 percent, respectively, of the volumetric target. The 70 MPa is preferred by the automotive OEMs because it offers greater vehicle range and is becoming the de facto standard storage pressure, but it can lead to additional refueling costs for pre-cooling and higher compression energy. The National Aeronautics and Space Administration (NASA) White Sands Facility offers expertise in composite pressure vessel testing, including
pressure failure analysis, nondestructive evaluation, structural analysis, burst tests, and fire safety.14
Assessment of Progress and Key Achievements
Key achievements since the NRC (2010) Phase 3 review are in the area of cryo-compressed hydrogen, hydrogen sorbents, chemical hydrogen storage, and metal hydrides. The cryo-compressed system has demonstrated 10.4 kg of usable capacity that is greater than the 2017 target, but the cost is estimated to be $12/kWh. A smaller tank has been designed that delivers 5.6 kg of H2 (LLNL). The tank must be filled with liquid hydrogen to achieve maximum capacity, and the length of time that the tank is idle before venting hydrogen (dormancy) is an issue.
Two hydrogen sorbents have exhibited materials capacities greater than 8 wt% and 28 g/L at 77 K and 7 MPa. This work was done at Northwestern University (Cu-MOF, a copper-containing metal organic framework) and at Texas A&M University (PPN[porous polymer network]-4(Si)). PPN-4(Si) is a highly stable porous polymer network with ultrahigh gas uptake capacity. Chemical hydrogen storage systems are on a path to exceed the 2017 system targets, but off-board regeneration efficiency is still an issue. Ammonia borane and alane, chemical hydrogen storage materials, have demonstrated release kinetics and spent fuel regeneration. Both materials have greater than 10 wt% hydrogen (LANL/PNNL and Brookhaven National Laboratory [BNL]/SRNL). One metal hydride, Mg(BH4)2, has demonstrated a reversible material capacity of greater than 12 wt%, but the temperature and pressure are too extreme for onboard use (University of Hawaii and SNL).
The Hydrogen Storage Engineering COE provides a coordinated approach to the engineering R&D of materials-based hydrogen storage. This COE has completed an integrated system model for hydrogen storage and established a state-of-the-art baseline against the 2010 targets for all three materials classes. This modular approach allows each system to be run through simulated drive cycles to predict performance. This work has enabled the COE to down-select systems for further development.
Compressed hydrogen is the near-term option for onboard hydrogen storage. A major barrier, however, is the cost of the storage system, cited to be $2,800 for a 5-kg H2 system.15 The U.S. DRIVE Partnership defines 1 kg of hydrogen to be equivalent to 1 gallon of gasoline. A 300-mile driving range will thus require 5 to 10 kg of hydrogen depending on vehicle characteristics such as size and weight. Approximately 75 percent of the cost is the carbon-fiber composite and 50 percent of that cost is the precursor fiber. The DOE, in concert with the U.S.
15 N. Stetson, Department of Energy, and S. Jorgensen, General Motors R&D, “Hydrogen Storage Tech Team (HSTT),” presentation to the committee, January 26, 2012, Washington, D.C.
• Development of textile-grade polyacrylnitrile, PAN (ORNL),
• Development of melt spinable PAN (ORNL-Virginia Polytechnic Institute and State University),
• Development of nano-reinforced CFCs (Applied Nanotech, Inc.; SBIR), and
• Investigation of basalt glass fibers (Quantum Technologies; SBIR).
The first project aims to produce high-strength carbon fibers from commodity textile-grade PAN fibers.
A workshop with various stakeholders was held in February 2011 to address opportunities for cost reduction of composite storage tanks.16 In December 2011, DOE announced four projects totaling more than $7 million to advance hydrogen storage technologies for fuel cell electric vehicles. These 3-year projects are listed in Table 3-6.
Committee members conducted site visits with two DOE contractors for hydrogen storage tank development related to the U.S. DRIVE objectives: Lincoln Composites and Quantum Technologies. (See Appendix D, “Committee Meetings and Presentations.”) These visits provided an understanding both of the challenges and the costs of high-pressure storage and of the manufacturing processes. Lincoln Composites is working with the Engineering Center of Excellence on material filled tanks. Committee members also visited Structural Composites, Inc., a manufacturer of Type 3 tanks.17 Following these visits, the committee members are optimistic that the cost of hydrogen storage tanks (Type 4 tanks) can be reduced in the future through reduced materials and manufacturing costs. Cost reduction is not likely in the near term. These companies also manufacture tanks for natural gas storage, which is a rapidly growing business area.
Hydrogen storage is an area of keen interest within the various international fuel cell programs. These programs, which have representation from many countries, include the International Energy Agency, the International Partnership for a Hydrogen Economy, and the International Institute for Carbon-Neutral Energy Research (Japan). The DOE is an active participant in these programs and has a significant number of its projects “endorsed” by these groups. For example, an international task force was established to confirm whether excess
17 The Type 3 tank is composed of a metal liner reinforced by fiberglass or carbon fiber applied in a full wrapped pattern around the entire liner. The Type 4 tank is composed of a plastic gas-tight liner reinforced by carbon fiber or fiberglass around the entire liner.
|Institutions||Amount ($ millions)||Activity|
|PNNL with Lincoln Composites, Ford, Toray Carbon Fibers America, Inc., AOC, Inc.||2.10||Lower the cost of manufacturing of hydrogen storage tanks by more than 30 percent relative to current projections|
|HRL Laboratories, LLC||1.20||Innovative approach to hydrogen storage using engineered liquids that absorb and release hydrogen gas|
|LBNL with NIST, GM||2.10||Theory-guided synthesis of novel hydrogen storage materials|
|University of Oregon with University of Alabama, PNNL, Protonex Technology||2.00||Develop and test promising new chemical storage materials|
NOTE: PNNL, Pacific Northwest National Laboratory; LBNL, Lawrence Berkeley National Laboratory; NIST, National Institute of Standards and Technology.
SOURCE: See www.EERE.energy.gov/hydrogen&fuelcell/news.
adsorption at room temperature can be increased by hydrogen spillover from a catalyst site on a high-surface-area catalyst support material. Further progress on hydrogen storage in other countries supports the goals of the U.S. DRIVE program (Stetson, 2012).
Significant Barriers and Issues That Need to Be Addressed
Although progress continues to be made in solid-state storage, key characteristics have not all been met with any single material. Cost is a significant barrier for all systems. Given the cuts in the hydrogen storage budget, the Partnership is not on a path to overcome these barriers. Basic research and generation of new ideas are needed. One example is the need for R&D on liner materials for cryo-compressed hydrogen storage.
The development of a hydrogen fueling infrastructure that anticipates and leads vehicle introduction is in need of support to ensure that the fueling infrastructure is in place in advance of vehicle introduction. The timely build-out of the hydrogen refueling infrastructure is a potential significant barrier.
Responses to Recommendations from Phase 3 Review
The recommendations and responses to recommendations from the NRC (2010) Phase 3 review are listed below. These responses were written prior to the latest round of budget cuts, and DOE may no longer be in a position to follow
through on the cited plans. The full text of the responses to the recommendations is available in the file entitled “Actions, Evidence, and Responses to the Review of the Research Program of the FreedomCAR and Fuel Partnership: Third Report, December 2012,” which is available in the National Academies Public Access File for this Phase 4 review.
• NRC Phase 3 Recommendation 3-9. The NRC (2010) Phase 3 report recommended that the most promising approaches for hydrogen storage be continued, that the centers of excellence that were being closed document their findings for the completed R&D, that contractor reports be available through EERE, and that basic research activities on hydrogen storage continue. The DOE responded that it agrees with this committee recommendation. It will continue to fund independent projects that address applied materials work on H2 storage. The centers of excellence will complete summary reports, a database for materials performance data from the materials centers will be established, and the partner final reports will be public documents. The BES will continue to fund basic research in H2 storage materials and crosscutting research through its Hydrogen Fuel Initiative Projects and Core Research Programs.
• NRC Phase 3 Recommendation 3-10. The NRC (2010) Phase 3 report recommended that research on compressed gas storage be expanded to safety-related activities that determine cost and weight. The DOE agrees that safety is paramount and critical during the development of all hydrogen storage technologies. Safety is included in all development projects. One significant accomplishment involves the development of SAE J2579, “Recommended Practices for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles.” The DOE has participated in and hosted international workshops on hydrogen safety-related technologies including codes and standards.
• NRC Phase 3 Recommendation 3-11. The NRC (2010) Phase 3 report recommended that R&D continue on the reduction of the cost of aerospace-quality carbon fiber and alternative fibers for compressed hydrogen storage. The DOE agrees with this recommendation and cited several significant activities related to this effort.
• NRC Phase 3 Recommendation 3-12. The NRC (2010) Phase 3 report recommended that, given the critical part that hydrogen storage is to the hydrogen and fuel cell part of the FreedomCar and Fuel Partnership, it should continue to be funded, and the funding should include the work of the Hydrogen Storage Engineering COE. The Phase 3 report recommended that effort be directed to low-pressure materials storage and to compressed-gas storage to help achieve weight reductions while maintaining safety. The DOE agrees with this recommendation and cited projects and programs both underway and proposed.
• NRC Phase 3 Recommendation 3-13. The NRC (2010) Phase 3 report recommended that concepts beyond materials properties be explored for reducing refueling time. The DOE responded that it will continue to work on materials with favorable thermodynamic properties and improved sorption kinetics.
• NRC Phase 3 Recommendation 3-14. The NRC (2010) Phase 3 report recommended that effort be made to anticipate ways in which hydrogen storage material properties might impact system performance—for example, purity, lifetime, and safety. The DOE agrees with this recommendation and has programs in place that address this concern.
• NRC Phase 3 Recommendation 3-15. The NRC (2010) Phase 3 report recommended a balanced long-term/short-term joint portfolio for onboard hydrogen storage. The DOE agrees with the committee recommendation and states that it continues to fund both long-term and short-term projects and will give careful consideration to achieving a balanced portfolio.
Appropriate Federal Role
The work on onboard hydrogen storage is appropriate for federal support, given the critical importance of fuel cell vehicles to the goals for fuel savings and reduction in both criteria and greenhouse gas emissions. Advanced hydrogen storage technologies need to be developed in order to meet all of the performance metrics. Ongoing high-risk basic research is needed, given the complexity and scope of this challenge. The capabilities of the national laboratories, as well as of university laboratories given the necessary government support, are well equipped to contribute to addressing this challenge.
The U.S. DRIVE automotive OEMs have adopted 70 MPa compressed-gas storage for near-term onboard vehicle hydrogen storage.
Recommendation 3-7. The U.S. DRIVE Partnership should re-examine high-pressure compressed-gas storage and reach a consensus as to whether this is a long-term solution or just a transition technology. Short-term and medium-term performance targets should be developed specifically for compressed tanks because such tanks are expected to be used at least on the first generation of hydrogen fuel cell vehicles. Then there should be long-term general materials targets that basic research can use for benchmarking.
Recommendation 3-8. The U.S. DRIVE Partnership should investigate the relationship between the onboard hydrogen storage tank pressure and the hydrogen infrastructure so that trade-offs can be worked out.
Cost is an issue for the compressed-gas storage tanks.
Recommendation 3-9. The U.S. DRIVE Partnership should consider joint programs with the U.S. Department of Defense and the National Aeronautics and Space Administration, which undoubtedly have similar goals for lower-cost aerospace-quality carbon fibers. Work with the newly constructed ORNL Carbon Fiber Technology Facility should also be explored.
There is a potential relationship between tank cost and safety criteria.
Recommendation 3-10. The U.S. DRIVE Partnership should demonstrate the safety of lower-cost, lighter-weight compressed-hydrogen tanks with a rigorous testing program, for example, by statistically demonstrating stress rupture toughness, fatigue life, and fire safety. In implementing such an activity, it should consider cofunding the related tests proposed by the NASA White Sands facility.
Fundamental R&D directed to onboard hydrogen storage has contributed to progress and understanding that has aided decision making.
Recommendation 3-11. The DOE (e.g., the Office of Basic Energy Sciences, the Office of Energy Efficiency and Renewable Energy, the Advanced Research Projects Agency-Energy) should initiate a new program that builds on the excellent progress made to date and expands into fundamentally new hydrogen storage research areas. A critical assessment of prospects for, and barriers to, advanced storage techniques and concepts should form the first part of this initiative.
Electric drive vehicles have great promise of dramatically reducing or even eliminating U.S. dependence on imported petroleum and the harmful greenhouse gas emissions currently associated with light-duty vehicles (provided that GHG emissions in the production of electricity are controlled). Electrochemical energy storage technology (including batteries and supercapacitors) is a key enabler for all electric drive vehicles, including hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), and hydrogen fuel cell vehicles (HFCVs). (Fuel cell electric vehicles have evolved into fuel cell hybrid electric vehicles that utilize electrochemical energy storage systems to capture regenerative braking energy and to provide for a smaller fuel cell system with optimized efficiency operation.)
In the near term, HEVs utilizing high-power batteries have the best opportunity for substantial impact due to their lower cost and higher commercial
viability. An improved intermediate solution could be provided by plug-in hybrid electric vehicles (PHEVs) using high-energy batteries. In the long term, the full advantage of electric drive vehicles could be realized with BEVs and/or fuel cell hybrid electric vehicles (Wagner et al., 2010). Both would use batteries or similar devices, but fuel cell hybrid electric vehicles will require high-power batteries or supercapacitors, and BEVs will require high-energy batteries. Thus, both high-power and high-energy batteries are of interest for the short and long term.
The U.S. DRIVE Partnership has provided for an intensification of R&D efforts in a portfolio of high-energy and high-power battery and supercapacitor technologies. This effort has included a wide range of activities, from basic research at the materials level, to new device development, all the way to systems-level prototype development aimed at meeting performance and cost objectives. The status of manufacturing development and cost reduction of these technologies has also been advanced through large capital contracts issued through American Recovery and Reinvestment Act of 2009 (ARRA) funding for the building of battery plants for electric drive vehicle applications.
The past decade has seen the commercial development of HEVs, based in part on the previous successful development of high-power batteries supported by the U.S. DRIVE Partnership through the United States Advanced Battery Consortium (USABC). However, the HEV market share remains somewhat flat, at around 3 percent of U.S. new-car sales. Innovations are still needed, particularly to overcome battery cost impediments.
Due in part to more than a decade of extensive DOE-funded lithium-ion (Li-ion) battery R&D, this technology is now starting to show tangible commercial progress in automotive applications. High-energy Li-ion batteries are enabling several high-profile BEV and PHEV production programs, including the Tesla Model S, GM Volt, and Nissan Leaf. About 20,000 of these vehicles were sold in the United States in 2011. Additionally, Li-ion batteries are now being commercialized in hybrid vehicles, recently showcased in numerous automotive OEM models displayed at the 2012 North American International Auto Show. Most notably, Ford, the largest U.S. manufacturer of HEVs, is planning to discontinue nickel metal hydride batteries in its vehicles in favor of higher-power Li-ion batteries, starting in 2013. With GM also introducing Li-ion batteries in new HEV models, the U.S. automotive companies are at the forefront of advanced battery technology for electric drive vehicles.
The DOE Vehicle Technologies Program, in collaboration with the USABC, manages the electrochemical energy storage technology activities with a goal of the advancement of electrochemical energy storage technologies, to enable the U.S. DRIVE partners to introduce electric drive vehicles with the potential to reduce U.S. dependence on petroleum and harmful vehicle emissions (DOE, 2010b, 2012a,b). Technology development is undertaken by battery manufacturers, DOE national laboratories, and universities. As in recent years, the main effort is now composed of four main subactivities: (1) Battery Development, (2) Applied
Battery Research, (3) Exploratory Materials Research, and (4) Testing, Analysis, and Design (Howell, 2012).18
The Battery Development subactivity encompassing battery module and system hardware development and related activities was largely directed by USABC, funding more than a dozen major programs, with a variety of companies developing batteries, supercapacitors, components, and materials aimed at BEV, PHEV, and HEV applications. Applied Battery Research activities were directed and carried out by the national laboratories, with ANL in the lead role; these activities focused on the next-generation, high-energy Li-ion battery couples with a potential to meet challenging requirements for the 40-mile all-electric-range PHEV. Exploratory Battery Research (previously known as the Batteries for Advanced Transportation Technologies Program) addressed the fundamental understanding of specific electrochemical systems for lithium batteries and the development of newer couples with a potential for higher power and higher energy density. This exploratory work, directed by the Lawrence Berkeley National Laboratory, was carried through many top academic groups with the participation of national laboratories and industrial research groups as well. The newest program, Testing, Analysis, and Design, was initiated in 2011 to address testing, modeling, and computer design tool development.
In addition to the battery R&D activities of the DOE VTP and USABC, which U.S. DRIVE is most directly involved with, U.S. DRIVE longer-term objectives are being pursued by DOE-funded R&D in the new ARPA-E organization. These efforts are aimed at high-risk transformational (game-changing) technologies beyond the projected capabilities of Li-ion batteries that have been the central R&D focus for a decade. More broad fundamental R&D activities are also pursued by the DOE Basic Energy Sciences program. Finally, an Energy Innovation Hub on batteries is being formed in 2012 by DOE because of the perceived need for a multidisciplinary, multi-institutional integrated research organization to address this strategically important field.
In a related activity, funding from the ARRA enabled DOE to provide $1.5 billion in grants for producing batteries and their components. Since the Phase 3 NRC (2010) review, several of these plants are now in production. Very useful information related to manufacturing process technology and production costs is being provided to the program (DOE, 2012b).
Current Status Versus Goals and Targets
Overall the goal is to develop electrochemical energy storage systems that will enable electric drive vehicles that can substantially reduce both U.S. dependence on petroleum and GHG emissions without sacrificing vehicle performance.
18 D. Howell, Department of Energy, and R. Elder, Chrysler, “Electrochemical Energy Storage Technical Team (EEST),” presentation to the committee, January 26, 2012, Washington, D.C.
These vehicles include a progression of technology from HEVs to PHEVs to BEVs and HFCVs. DOE energy storage targets adapted from the USABC technical targets are provided in Table 3-7 (DOE, 2010a).
HEV Batteries Meet Performance Targets But Exceed Cost Targets
Although there remains some uncertainty about calendar life, at least the initial performance targets for high-power batteries for power-assist hybrid vehicles have been generally met by both nickel-metal hydride and Li-ion high-power battery technologies, with the exception of cost. High costs, exceeding targets by about 50 percent, remain a barrier for the more widespread commercialization of hybrid vehicles.
Supercapacitors may offer a more cost-effective solution for HEVs. However, they do not currently meet the available energy target of 0.3-0.5 kWh within the weight and volume restraints above. Recently, modeling and experimental R&D at NREL have scrutinized this target, providing strong evidence that only a fraction of this targeted available energy is needed for the HEV application. Consequently, USABC has added a new set of performance targets, called High Power Low Energy—Energy Storage System targets, and funded Maxwell Technologies to develop supercapacitors for HEV applications (U.S. DRIVE, 2011; Snyder, 2012).
|Storage Technology Characteristics||HEV (2010)||PHEV (2015)||EV (2020)|
|Equivalent electric range, mi||N/A||10-40||200-300|
|Discharge pulse power, kW||25-40 for 10 sec||38-50||80|
|Regen pulse power (10 s), kW||20-25||25-30||40|
|Recharge rate, kW||N/A||1.4-2.8||5-10|
|Cold cranking power @ –30°C (2 s), kW||5-7||7||N/A|
|Available energy, kWh||0.3-0.5||3.5-11.6||30-40|
|Calendar life, years||15||10+||10|
|Cycle life, cycles||300,000, shallow||3,000-5,000, deep discharge||750, deep discharge|
|Maximum system weight, kg||40-60||60-120||300|
|Maximum system volume, liters||32-45||40-80||133|
|Operating temperature range, °C||–30 to 52||–30 to 52||–40 to 85|
|Selling price at 100,000 units per year, $||500-800||1,700-3,400||4,000|
NOTE: N/A, not available.
SOURCE: DOE (2010b).
Lithium-ion high-energy battery technology has progressed to be capable of meeting the performance goals for PHEV applications at the systems level with the exception of cost, which still exceeds the cost target by a factor of two (DOE, 2012b).
BEV Batteries Fall Short on Specific Energy and Greatly Exceed Cost Targets
Lithium-ion high-energy battery technology has substantially exceeded the capabilities of previous battery technologies aimed at BEV applications, with substantial progress in the past decade, in part due to the concentrated efforts of DOE in coordination with the U.S. DRIVE Partnership. However, current Li-ion BEV batteries are too heavy by about a factor of two on a system basis. More seriously, they currently cost too much by a factor of four or more versus USABC cost targets. Yet there have been some optimistic cost projections for the rest of the decade, some at less than $300/kWh in the 2015-2020 time frame. However, these costs are still double the official USABC cost targets (DOE, 2012b). The status of BEV battery performance versus technical targets is given in Table 3-8.
Technical Targets Need Revision
Over the years, a variety of detailed technical targets for electrochemical energy storage systems for a variety of electric drive vehicle applications have
|Energy Storage Goals||AEV (2020)||Current|
|Equivalent electric range, mi||200-300||√|
|Discharge pulse power (10 s), kW||80-120||√|
|Regenerative pulse power (10 s), kW||40||√|
|Available energy, kWh||40-60||√|
|Recharge rate, kW||120||50|
|Calendar life, years||10+||TBD|
|Cycle life, cycles||1,000 deep cycles||TBD|
|Operating temperature range, °C||+40-60||0-40|
|System weight, kg||160-240||500-750|
|System volume, liters||80-120||200-400|
|Production cost at 100,000 units per year, $/kWh||125||<600|
NOTE: Initial electric vehicle (EV) battery development contracts were started in FY 2011. Focus on high-voltage/high-capacity cathodes and electric vehicle cell design optimization. Data based on initial work from USABC Envia Systems and Cobasys/SBLimotive contracts. TBD, to be determined.
SOURCE: D. Howell, Department of Energy, and R. Elder, Chrysler, “Electrochemical Energy Storage Technical Team (EEST),” presentation to the committee, January 26, 2012, Washington, D.C.
been developed by various organizations, including USABC, the Partnership for a New Generation of Vehicles, and DOE (DOE, 2010b; Snyder, 2012). These technical targets have played an important role in the development of battery technology beyond their use in various funding solicitations, which include DOE and USABC funding opportunity announcements and requests for proposals. These performance and cost criteria, goals, and targets have guided the industry in the development of technologies and products for electric drive vehicle applications.
Unfortunately, the technical targets for various applications crafted at various times over the past two decades are generally not consistent with one another in format or assumptions. Several key targets are in urgent need of revision. Most notably, the Goals for Advanced Batteries for BEVs have not been revised since their release in 1993. The technical targets for power-assist HEVs are more than a decade old. In particular, the BEV cost targets are no longer consistent with the changed factors that govern economic competitiveness, especially fuel costs but also the anticipated costs of future high-technology ICE vehicles that provide a benchmark. PHEV battery goals do not include targets for PHEVs with an all-electric range. (The targeted PHEVs with an equivalent electric range of 10 to 40 miles do not have sufficient power at 38 to 50 kW for any significant all-electric range but are designed for blended operation only.) Assumptions in the derivation of targets are generally not provided. There are no formal targets for electrochemical energy storage systems for fuel cell hybrid vehicles. There are inconsistencies in the criteria and even units (watts per kilogram for BEV batteries; watts and kilograms for HEV batteries). Production volumes on which cost projections are based are not consistent, nor are they consistent with the production volumes assumed for fuel cell vehicle cost projections.
It is time to take advantage of the past two decades of substantial progress, experience, and learning about electric drive vehicle applications to start over and develop a technically sound and consistent set of technical targets for electrochemical energy storage systems aimed at the key applications under development:
• Hybrid Electric Vehicles
— Stop-start micro HEVs
— Mild HEVs
— Full HEVs
— PHEVs, both blended and all-electric range types
• Battery Electric Vehicles
— Commuter BEVs (<100 mile range)
— Touring BEVs (300 mile range)
• Fuel Cell Hybrid Electric Vehicles
The electrochemical energy storage technology program has been a very comprehensive program aimed at all light-duty electric drive vehicle applications including HEVs, PHEVs, BEVs, and HFCVs. Projects aimed at these applications covered a wide scope, including battery development; applied battery research; exploratory materials research; and testing, analysis, and design. They ranged from basic materials development to battery systems development. Due in part to excellent progress toward goals for high-power batteries, the focus of battery development activities since the Phase 3 NRC (2010) review has shifted to high-energy batteries for PHEVs and BEVs. This is responsive to the recommendation in the NRC (2010) Phase 3 review and supports President Obama’s call for 1 million PHEVs by 2015.
Substantial progress has been achieved relative to the key performance and cost targets, including energy density, power, cycle and calendar life, and cost of Li-ion batteries. A special focus was placed on developing lower-cost technologies, with a key strategy being the development of higher-energy-density materials, cells, and systems that could reduce materials costs. In particular, higher-energy-density anodes and cathodes for Li-ion batteries and materials enabling higher-voltage operation were developed to increase cell energy density and to lower materials costs. This approach yields great promise of meeting PHEV energy density and cost targets this decade. There is also a realization that even more substantial improvements will be needed to meet BEV energy density and cost targets. Thus, exploratory R&D is now being performed toward lithium metal and lithium air battery concepts.
General U.S. DRIVE Partnership achievements in electrochemical energy storage (DOE, 2012b) include the following:
• Cost reduction of Li-ion PHEV battery technology, with $650/kWh feasible at 100,000 packs per year production volumes and on track for meeting the $300/kWh goal this decade.19
• High-energy-density cathode material licensed to General Motors, LG Chem Ltd., BASF, Toda, and Envia Systems.
• Lifetime of Li-ion batteries extended to 10 to 15 years and/or 3,000 to 5,000 deep cycles for some technologies on test by USABC at U.S. national laboratories.
• Performance and life and safety targets met for HEV batteries, and significant cost reduction toward targets accomplished.
Specific highlights from U.S. DRIVE R&D programs (U.S. DRIVE, 2011; FCFP, 2011) include the following:
19 D. Howell, Department of Energy, and R. Elder, Chrysler, “Electrochemical Energy Storage Technical Team (EEST),” presentation to the committee, January 26, 2012, Washington, D.C.
• New prismatic cell and system technology based on Li-ion NMC (nickel-managese-cobalt) chemistry developed by Johnson Controls demonstrated 40 percent volumetric energy density improvement and 13 percent cost reduction. PHEV hardware deliverables in this USABC program also met other performance, safety, and life requirements according to tests and projections.
• High-specific-energy cathodes developed by Envia Systems using Argonne National Laboratory-patented technology achieved greater than 200 Wh/kg in a 20-Ah PHEV Li-ion cell delivered to USABC. A record-setting 400 Wh/kg was achieved in a prototype with a silicon-carbon anode under development in an ARPA-E program. Work continues to move this promising technology ahead toward meeting cycle-life and calendar-life targets.
• New inorganic-filled separators developed by Entek International LLC demonstrated improved safety performance as well as improved low-temperature power and life performance. This USABC development offers potential cost reduction through the use of smaller batteries that can meet lifetime performance requirements.
• Advanced Gen 2 NMC (nickel-manganese-cobalt) mixed oxide PHEV cathode material developed by 3M lowered material costs 15 percent while increasing specific capacity 5 to 10 percent with thermal stability and cycle-life performance comparable to Gen 1 materials.
• An electrolyte additive developed by the Army Research Laboratory significantly improves the high-voltage stability of 4.8-V lithium cobalt phosphate cathodes, which are capable of providing 40 percent higher energy density than commercially available lithium iron phosphate cathodes.
• High-voltage (4.8 V) cathodes composed of nickel-manganese spinel oxides doped with chromium developed by PNNL exhibited stable cycle performance through the use of LiBOB (lithium bis[oxatlato] borate) electrolyte additive.
• Silicon-based anode technology developed by 3M provided for a 15 to 20 percent increase in an Li-ion cell energy density with a cycle-life capability of hundreds of cycles and is now being commercialized.
• A multiscale, multidimensional model framework developed by NREL was used to initiate programs in multiphysics battery modeling to provide computer-aided engineering tools to the Li-ion battery industry.
Significant Barriers and Issues
The most serious barrier in the area of electrochemical energy storage is the high cost of batteries, which generally comprises the highest cost component of
the electric propulsion system, with the exception of fuel cell systems. The cost targets for electric drive vehicles20 are as follows:
• $125/kWh for battery electric vehicles (DOE target for 2020),
• $300/kWh for plug-in hybrid electric vehicles (DOE target for 2015), and
• $20/kW for hybrid electric vehicles (DOE target for 2010).
None of these targets aimed at widespread commercialization has been met. HEV battery costs are still 50 percent over target, and the consequent cost premiums for HEVs have clearly limited the market share that these vehicles have achieved.
The PHEV battery high-volume cost feasibility is currently double the target. BEV battery costs exceed targets by a factor of four or more, generally making battery electric vehicles with a range of more than 100 miles unaffordable.
The second most serious barrier is the performance gap with respect to energy density for BEV applications. On a systems level, the gravimetric energy density is about half of the target. BEV battery cost and energy density are highly correlated, since higher specific energy systems will require fewer materials, reducing materials costs, and they will be smaller, reducing packaging costs.
There has been great progress in recent years in overcoming safety issues with Li-ion batteries, through the use of intrinsically safer materials and through design for safety on a systems level. However, as the 2011 incidents surrounding Chevy Volt PHEVs after crash testing indicate, continued vigilance with safety development is essential. Additionally, as higher-energy-density battery systems are developed, further diligence is needed owing to the intrinsic tendency for increased hazard with higher energy densities.
The technology barriers for Li-ion batteries are well understood. Barriers for more exotic new technologies with higher theoretical specific energy are now being uncovered and will become clearer as development advances. For example, issues with lithium air batteries now include low power, poor efficiency, short cycle life, and system complexities approaching those of fuel cells.
Response to Phase 3 Recommendations
NRC Phase 3 Recommendation 3-16. The Partnership should revisit and modify, as necessary, the goals and targets for battery electric vehicles in view of the changing market conditions and improvements in technologies. [NRC, 2010, p. 93.]
This recommendation for the revision of targets for BEVs was not acted on. The official targets remain those developed 20 years ago. With the renewed activities
20 D. Howell, Department of Energy, and R. Elder, Chrysler, “Electrochemical Energy Storage Technical Team (EEST),” presentation to the committee, January 26, 2012, Washington, D.C.
aimed at BEVs, including embryonic commercial programs with the Tesla Roadster and the Nissan Leaf, it is now even more urgent to revisit this matter. The revised goals and targets should be consistent with recent USABC targets for PHEV batteries and HEV batteries and should incorporate what has been learned in the past two decades. In addition to a long-term goal aimed at a 300-mile range, it would be useful to establish targets for 100-mile-range commuters. These vehicles, which have sufficient range to meet the needs of most U.S. commuters, are now starting to be introduced into the market. Furthermore, additional diligent efforts are needed to review targets for other applications and to provide a consistent and up-to-date set of technical targets across all key electric drive vehicle applications.
NRC Phase 3 Recommendation 3-17. The Partnership should significantly intensify its efforts to develop improved materials and systems for high-energy batteries for both plug-in electric vehicles and battery electric vehicles. [NRC, 2010, p. 93.]
Activities into the development of high-energy batteries were intensified as recommended. Significant progress has helped enable the embryonic introduction of PHEVs and the reintroduction of BEVs, albeit with limited range.
NRC Phase 3 Recommendation 3-18. The Partnership should conduct a study to determine the cost of recycling batteries and the potential savings from recycled materials. A research program on improved processes for recycling advanced batteries should be initiated in order to reduce the cost of the processes and recover useful materials and to reduce potentially hazardous toxic waste and, if necessary, to explore and develop new processes that preserve and recycle a much larger portion of the battery values. [NRC, 2010, p. 93.]
In response to the recommendation for a study on recycling batteries, U.S. DRIVE referred to an analysis by Argonne National Laboratory showing that recycling of Li-ion batteries can mitigate material supply issues and provide cost savings from recycled materials (Gaines, 2011). Battery recycling is also being studied in an ongoing effort by USCAR and remains an area of interest for the Vehicle Technologies Program of DOE. Additionally, with ARRA funds, DOE has supported Toxco in a cost-shared project for construction of a Li-ion battery recycling facility. Further process development for recycling Li-ion batteries is needed, as well as full-life-cycle assessment studies for all environmental externalities (see Chapter 2, Recommendation 2-10).
Appropriate Federal Role
Clearly, the long-term R&D aimed at fundamental discoveries on precompetitive technology development, as in the Applied Battery Research and Exploratory
Battery Research programs as well as the related activities funded through the Office of Basic Energy Sciences and ARPA-E, is completely appropriate for federal funding. Little of this work would be performed by private industry without government support.
The Battery Development effort of USABC is of a more near-term nature and benefits specific companies as well as the automotive OEMs, as hardware is developed that can be translated into products in a relatively short time frame. However, developers are typically required to provide a 50 percent cost share. Thus, it is a reasonable role for the government to assist companies in taking the risk to develop technologies that show promise for commercial success. The cost-share provision helps focus on the development of viable technologies.
Although not part of the U.S. DRIVE Partnership and the committee’s review, cost-shared programs were funded by the ARRA of 2009 for the building of battery plants to jump-start the Li-ion battery industry in the United States. A large investment of $1.5 billion was made in the manufacturing of Li-ion battery technologies developed through the U.S. DRIVE Partnership. The knowledge in manufacturing processes and product cost reduction gained from these programs will be invaluable.
Improvements in high-energy batteries as well as in high-power batteries and supercapacitors will be of benefit for many advanced vehicles.
Recommendation 3-12. While continuing mainstream efforts to increase energy density and reduce the cost of high-energy batteries for BEV and HEV applications, the U.S. DRIVE Partnership should intensify its development of high-power batteries and supercapacitors as such technology impacts all types of hybrid vehicles (HEVs, PHEVs, and HFCVs). It should also more closely integrate its efforts with other DOE offices and agencies to investigate new high-energy electrochemical couples for BEV applications.
The U.S. DRIVE Partnership technical targets for electrochemical energy storage systems are largely outdated and contain some significant inconsistencies and unclear constructions. Notably, the USABC targets for BEV batteries are more than 20 years old.
Recommendation 3-13. The USABC targets for BEV batteries are more than 20 years old and should be revised, as also recommended in the NRC’s Phase 3 review. U.S. DRIVE should also undertake a diligent effort to develop a consistent set of technical targets across the key electric drive vehicle applications.
Introduction and Background
The mission of the U.S. DRIVE Partnership’s electric propulsion and electrical systems effort is to “develop technologies to enable large market penetration of electric drive vehicles.”21 Thus, the accomplishments of this activity will impact all hybrid electric vehicles, mild or full hybrid, plug-in hybrid electric vehicles and extended-range electric vehicles (EREVs), battery electric vehicles, and hydrogen fuel cell (electric) vehicles. The architectures for these vehicles were schematically illustrated in Figures 3-6 through 3-10 in the NRC (2010, pp. 95-97) Phase 3 report and will not be repeated here. Since the Phase 3 review, there has been tremendous interest worldwide in electric propulsion and hybrid vehicles, with several new models of HEVs, PHEVs, EREVs, and BEVs introduced recently. This is due to a general awareness and to increased regulation to reduce fuel consumption and greenhouse gas emissions. Thus, there is significant development of electric motors and power electronics in private industry in addition to DOE-funded activities.
The electric propulsion development FY 2012 budget of $28.8 million is subdivided into four major subsections with the following associated budgets: (1) power electronics, $10 million; (2) electric motors, $7 million; (3) thermal management, $6 million; and (4) traction drive systems, $3 million. Another $3 million is unassigned as of this writing and is for new solicitations. The FY 2012 amount represents a small increase from $22.2 million spent in FY 2011 and FY 2010. The electrical propulsion development was also enhanced by ARRA funding in 200922 to accelerate the development of U.S. manufacturing of electric drive components and by several ARPA-E projects on charging systems and electric motors. In particular, 14 projects constitute ARPA-E REACT23 (Rare Earth Alternatives in Critical Technologies) for the development of cost-effective alternatives to rare-earth, magnetic materials used in electric motors. These activities are not under the U.S. DRIVE Partnership but do reflect the importance of the electric propulsion development effort.
The general objective of the program is to reduce the cost, weight, and volume of the various components and systems for electric propulsion. Since these systems have also been investigated for non-transportation applications, it is important that the electrical and electronics technical team be fully aware of the state of the art of the various technologies. Also it might be useful if the technical team conducted a careful analysis to determine that the investigation is precompetitive and involves breakthrough technologies relevant for U.S. DRIVE.
21 J. Czubay, General Motors, and S. Rogers, Department of Energy, “Electrical and Electronics Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
At the present time, the power electronics and electrical machine costs relative to the rest of the drive system depend on the type of drive. For mild HEVs the costs are relatively small, but as the power increases with full HEVs and PHEVs, the cost increases. EREVs, such as the Chevrolet Volt, and BEVs and HFCVs would be the most costly. Thus reducing the cost, weight, and volume is an important and worthwhile objective, and the funds allocated for this activity are appropriate.
Current Status Versus Targets
The electric propulsion and electrical systems targets have been met for 2010, including the cost, weight, and volume targets for the electric motor, power electronics, and traction drive system efficiency. Progress is continuing on the 2015 and 2020 targets, and preliminary data suggest that a General Motors (GM) integrated traction drive system meets the weight and volume target but not the efficiency or cost target for 2015. Since all of these properties are interrelated, meeting just some of the targets may not be sufficient. Also, several requirements for individual components emphasize performance at peak values only, which may be valuable for determining progress, but the final performance can only be judged on the basis of its effect on fuel economy—that is, performance of the component over the standardized driving cycles (city and highway).
Assessment of Progress and Key Achievements
The main achievement in the electric propulsion and electrical systems area was that of meeting all the 2010 and some of the 2015 targets with the GM and Delphi/GE traction drive and electric motor system. In addition, several important and promising initiatives are underway that should result in reduction of cost, size, and weight in power electronics, electric motors, thermal management, and traction drive systems.
The program involving power electronics has several projects on materials, components, and design topology for switches and circuits. Thin-film capacitors that can operate at higher temperatures have been developed; however, these have not been commercialized. Switches have been designed using wide-band-gap semiconductors, such as silicon carbide (SiC); however, such materials are very expensive, and the Partnership should leverage industry efforts to reduce the cost of manufacturing and should determine how best to utilize these in power electronics for vehicular applications. Projects on inverter topology24 are being funded
24 The term “inverter topology” is used to describe the arrangement of semiconductor switches, diodes, coils, and capacitors.
A proposed project is investigating the use of the same power switching devices for both the charger and the inverter. AC Propulsion is already marketing such a system, and it is being used in the Tesla and BMW Mini electric vehicles. It is hoped that the proposed project endeavors to improve on these production systems.
The cost of rare earths used for permanent magnets has increased substantially, some by as much as an order of magnitude,25 in the past few years, and the Partnership has initiated projects to develop magnets without, or with a minimum of, rare earths. Extensive research on this subject is being done at the national laboratories. It is too early to evaluate the results, but this activity should be encouraged. Recently Mitsubishi has claimed success with magnet alloys with 1 to 4 percent rare-earth content with performance comparable to the magnets in the Prius, which contain approximately 10 percent rare-earth.26
There is also a need for improved soft magnetic materials. Soft magnetic materials, which are used in motors, inductors, and transformers with higher permeability, high flux density, and low loss, are needed. The standard for decades has been high-silicon steel with a maximum of 4 percent Si. More recently a Japanese company27 has developed a new process for making 6.5 percent Si, which will have lower loss but perhaps lower peak flux density. The suitability of this development needs to be determined.
The program is also investigating new permanent-magnet motor designs. A possible design uses open slots to facilitate the insertion of formed coils, reducing costs and reducing resistance loss but increasing eddy current losses on the magnets. It is hoped that this and other such projects bring about improvements over production motors used in hybrid vehicles on the road. In the Phase 3 report (NRC, 2010), it was recommended that induction motors for electric propulsion be investigated. Several hybrid vehicles on the road, such as the GM Buick LaCrosse, Tesla, and BMW, are using induction motors. Thus it may be worthwhile to compare induction and permanent-magnet motors to determine the relative efficiency and cost trade-offs for the two systems. Switched reluctance motors are also being investigated; however, acoustical noise continues to be an issue with this design.
26 SAE, 2012, Powertrain Electric Motors Symposium for Electric and Hybrid Vehicles (April 20, 2012).
Heat removal from the silicon chip is a key determinant of the efficiency and size of the power electronics; thus thermal management plays an important role in meeting the program targets. Furthermore, matching differential expansion between the silicon chip and the (typically) aluminum heat sink is a tough problem, especially over the temperature range of –40°C to 200°C. There are many ways to minimize the thermal resistance from the silicon to the heat sink. One alternative is to use only aluminum and no copper plates to remove the heat. Other techniques consist of using direct sintering or double-sided cooling. The Oak Ridge National Laboratory claims to build a small, high-efficiency, planar bonded power electronic module for improved thermal management (Olszewski, 2011).28 A study to evaluate and compare the various alternative techniques and their relative merit to production units would be appropriate.
The Nissan Leaf battery is air cooled, and other vehicles use liquid cooling. For example, the Volt uses a 50/50 mix of ethylene glycol for cooling the battery and possibly the inverter, whereas other vehicles use transformer oil.
Traction Drive System
The emphasis on the traction drive system in this program seems to be on components rather than on investigating the traction drive as a system. In fact, a thorough systems analysis of the traction drive may result in more optimized targets for the necessary components. Such an analysis is highly encouraged. For example, it may be possible to trade off the cost of improving the motor efficiency versus increased battery cost. The electric motor efficiency is targeted to be 95 percent or higher over a range of torque of 20 to 100 percent and over speeds of 10 to 100 percent. Such high efficiency over such a wide range of load seems overly ambitious. It may be more cost-effective to improve the battery performance by 2 percent compared to the cost of raising the drive efficiency from 93 percent to 95 percent.
Also, there seems to be little work on “less costly mild hybrids.” Recently GM started selling the Buick LaCrosse Hybrid (Hawkins et al., 2012) with great improvements in the Environmental Protection Agency’s fuel economy (in miles per gallon) ratings.29 This remarkable result was achieved by a systems approach in which hybridization includes aggressive fuel cutoff during decelerations and stop-start.
28J. Czubay, General Motors, and S. Rogers, Department of Energy, “Electrical and Electronics Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
Although electric machines and power electronics have been developed for many years for a variety of commercial applications, there are significant barriers to their utilization in electric drive vehicles, including BEVs, HEVs, PHEVs, and HFCVs. Barriers include inadequate efficiency and inadequate volumetric and gravimetric power density, and, most importantly, excessive costs.
As discussed, a significant issue with this program is a lack of a thorough systems analysis of the complete traction drive system. Such an analysis not only would guide the program to which activity will provide the best results, but also would provide more optimized targets for efficiency, weight, volume, and cost for the various components constituting the system. Ideally, this should also include the battery, fuel cell, and internal combustion engine, so that the whole system can be optimized, and would involve separate analysis and targets for HEVs, PHEVs, BEVs, and HFCVs.
As noted, significant improvements in various components and systems are being made at the national laboratories in this program. However, not much of this effort is finding its way to commercial applications. Also, establishing a supplier base for the large number of components involved in building an electrical drive system is warranted.
Response to Recommendations from Phase 3 Review
NRC Phase 3 Recommendation 3-19. The Partnership should continue to focus on activities to reduce the cost, size, and losses in the power electronics and electrical machines. [NRC, 2010, p. 105.]
U.S. DRIVE seems to have pursued this recommendation. Prime examples are the GM, Delphi, and GE contracts that have improved on the state of the art.
NRC Phase 3 Recommendation 3-20. The Partnership should conduct a project to evaluate the effect of battery charging on lithium-ion battery packs as a function of the cell chemistries, cell geometries, and configurations in the pack; battery string voltages; and numbers of parallel strings. A standardized method for these evaluations should be developed to ensure the safety of battery packs during vehicle operation as well as during plug-in charging. [NRC, 2010, p. 105.]
The committee believes that this recommendation needs more attention. There is no evidence that the Partnership considered how high-rate charging affects the life of the battery.30 This issue needs to be addressed together with the
30 The following inaccurate and factually wrong sentence was removed from the report: “It is particularly surprising that nothing seems to have been done regarding safety even after the fires developed on the Volt in mid-2011.”
electrochemical energy storage team and affects not only the charging regimen but also the monitoring and equalizing of the voltage of the cells. The role of the electrical and electronics technical team would be to specify the charging rates; presumably it can meet the need. Lithium-ion batteries have a history of causing fires in several instances. In addition to safety, there is a need to worry about battery life, especially with “fast charging” at 440 V. The committee believes that continued work in this area is important and that the U.S. DRIVE Partnership should revisit Phase 3 (NRC, 2010), Recommendation 3-20.
NRC Phase 3 Recommendation 3-21. The Partnership should consider conducting a project to investigate induction motors as replacements for the permanent-magnet motors now almost universally used for electric propulsion. [NRC, 2010, p. 105.]
U.S. DRIVE seems to have relied on preliminary findings from an ongoing DOE motor assessment indicating that induction motors will not meet its targets.31 This is interesting in that a mild hybrid vehicle (2012 Buick LaCrosse using the eAssist mild hybrid system) on sale by one of the Partnership’s partners demonstrated great improvement in fuel consumption, as discussed above. Clearly other factors contributed, but induction motors will meet some of the targets. Also, one of the new partners, Tesla, uses an induction motor in its vehicles. BMW also uses induction motors in some of its BEVs.
Appropriateness of Federal Funding
There is tremendous interest in electric propulsion worldwide, and a great deal of money is spent on improving the state of the art. However, HFCVs, BEVs, PHEVs, and even HEVs are unlikely to capture a significant share of the market unless dramatic improvements take place in all elements of the drivetrain. In addition to the battery and fuel cell systems, which are discussed in other sections of this report, the cost, volume, and weight of power electronics and motors need significant breakthroughs. The Partnership is focusing on these three areas, which are interdependent. For example, better cooling of electronics reduces not only cost but also volume and weight; integrating the motor and electronics reduces not only cost but also volume; replacing rare-earth magnet materials has the potential of significantly reducing cost, although volume and weight may go up. Most of the funding goes to national laboratories, which will produce fresh thinking that would complement industry efforts, while the Partnership combines the best thinking of both. The fact that the electric propulsion components are used for all types of electric drive vehicles makes this a very strategically attractive R&D
31 J. Czubay, General Motors, and S. Rogers, Department of Energy, “Electrical and Electronics Technical Team,” presentation to the committee, January 26, 2012, Washington, D.C.
Recommendation 3-14. The U.S. DRIVE Partnership should leverage the various investigations on wide-band-gap materials such as silicon carbide (SiC) and should determine how best to utilize these in power electronics for vehicular applications.
Recommendation 3-15. The U.S. DRIVE Partnership should determine the potential and limitations of designing motors with permanent-magnet materials using less rare earth metal.
Recommendation 3-16. The U.S. DRIVE Partnership should make a comprehensive assessment of the various methods available (some of these are discussed in the section titled “Thermal Management” in this chapter) to reduce the thermal resistance between the chip and the heat sink and establish their relative value to existing techniques in production vehicles.
Goals and Challenges
A critical component of any automotive manufacturer’s strategy to reduce fuel consumption and meet increasingly stringent Corporate Average Fuel Economy (CAFE) standards and greenhouse gas emissions requirements is to reduce vehicle weight. For example, DOE has estimated that a 10 percent reduction in vehicle weight can result in up to a 6 to 8 percent improvement in fuel economy. Consequently, the U.S. DRIVE materials technical team (MTT), like the FreedomCAR and Fuel Partnership before it, has adopted a stretch goal of 50 percent reduction in vehicle weight (versus 2002 comparable vehicles) with equal affordability (emphasis added). Previous committees (NRC, 2008, 2010) found this goal unrealistic, and it remains so today.
Nevertheless, reducing vehicle weight is important, and doing so at the least incremental cost, while challenging, is worthy of pursuit, since achieving the 50 percent goal would result in up to a 35 percent fuel economy improvement. The DOE has developed a roadmap for a 30 percent weight reduction by 2025, which, if achieved, would result in up to a 21 percent fuel economy improvement.
One factor that potentially assists with the task of major weight reductions is that of mass decompounding. That is, a reduction of weight in basic vehicle structure permits secondary weight reduction in brakes, suspension, power train,
and other components. The materials technical team has estimated that each 1.0 lb of primary weight reduction may enable 1.0 to 1.5 lb of secondary weight reduction, provided that the entire vehicle can be redesigned to capture this opportunity. Nevertheless, large-scale weight reduction is an extremely challenging task, particularly since the addition of enhanced fuel-efficiency systems such as electrification results in the opposite effect, namely, mass compounding.
Broadly speaking, there are three obstacles to achieving the Partnership’s stated stretch goals regarding vehicle weight: increasing vehicle content, maintaining structural integrity, and managing cost.
• A 2011 Massachusetts Institute of Technology study (Zoepf, 2011) found that average passenger-car weight had increased by greater than 11 percent, or 160 kg, since 1990, despite the base car weight remaining unchanged. The entire weight increase was attributable to increasing comfort and convenience content and to added safety features and requirements. The pressure to keep adding feature content and more safety features will undoubtedly continue, in conflict with the need to reduce weight. Furthermore, the enhanced electrification of vehicles, while improving inherent fuel efficiency, adds considerable mass in batteries, motors, electronics, cooling, and so on, which must all be offset, including the mass compounding effect noted above, to yield the greatest fuel consumption benefits.
• Compliance with the full suite of Federal Motor Vehicle Safety Standards provides confidence in the overall safety performance of a vehicle, but it becomes increasingly challenging as weight is reduced. This has led to increased use of sophisticated structural analysis tools and demand for stronger, lighter materials such as high-strength steels and carbon fiber. This trend can only accelerate in the future.
• Cost is arguably the greatest challenge of the three: a detailed analysis in the NRC (2010) Phase 3 report illustrated both the high cost of weight reduction and the extent to which the reduction in fuel consumption can offset part of the cost to the ultimate consumer. However, the offset in fuel cost is only a fraction of the material cost penalty, and furthermore, much of the proverbial “low hanging fruit” has been harvested already.
In light of these challenges, having the Partnership’s activities focused as they are on enabling advanced high-strength lightweight materials and reducing their cost appears to be appropriate, even if the ultimate stretch goal is unrealistic.
In the materials area, the Partnership listed eight areas of major achievement in its presentations to the committee on January 26, 2012.32 These were as follows:
• Completed design and manufacturability assessment of a magnesium front-end structure.
• Completed design, tooling, fabrication, and testing of a one-piece composite underbody, saving 11.3 kg.
• Optimized engineering and manufacturing processes for advanced high- strength steel (AHSS).
• Developed a process for warm forming of aluminum and magnesium sheet.
• Enhanced the formability of aluminum at room temperature.
• Demonstrated a conversion technique for low-cost textile precursor for carbon fiber.
• Improved performance of AHSS welds.
• Developed a unique process for producing low-cost highly ductile magnesium sheet.
Response to Recommendations from the Phase 3 Review
Three recommendations on materials were made in the NRC Phase 3 report (NRC, 2010, pp. 108-109). The Partnership responses are shown below as “Updates.”
NRC Phase 3 Recommendation 3-22. The materials technical team should develop a systems-analysis methodology to determine the currently most cost-effective way for achieving a 50 percent weight reduction for hybrid and fuel cell vehicles. The materials team needs to evaluate how the cost penalty changes as a function of the percent weight reduction, assuming that the most effective mix of materials is used at each step in the weight-reduction process. The analysis should be updated on a regular basis as the cost structures change as a result of process research breakthroughs and commercial developments. [NRC, 2010, p. 108.]
Updates: DOE FY 2011 solicitation results for the multimaterial vehicle car (50 percent lighter than a midsized vehicle, design, build, and validate):
• Award to Vehma (Magna International)—project started in November 2011.
32 M. Zaluzec, Ford Motor Company, and C. Schutte, Department of Energy, “Materials Technical Team (MTT),” presentation to the committee, January 26, 2012, Washington, D.C.
NRC Phase 3 Recommendation 3-23. The magnesium castings study is completed, and no further technical effort is anticipated by the Partnership as recommended in the Phase 2 report. However, magnesium castings should be considered in completing the cost reduction recommendations listed above. [NRC, 2010, p. 109.]
• DOE award to MOxST, Inc., for a clean and low-cost domestic supply of magnesium (Mg). If successful, this technology will introduce a lower- cost feedstock for alloy production and die casting.
• DOE award to United States Automotive Materials Partnership (USAMP) on Magnesium Intensive Front End, which includes a focus on the characterization, optimization, and production of Mg die cast structural components.
• Cooperative Research and Development Agreement project involving the Pacific Northwest National Laboratory, Ford Motor Company, University of Michigan, and MagTech (die casting supplier) to develop and validate mechanistic-based ductility models for Mg die castings. This will provide a better understanding of how die-casting characteristics affect ductility, in turn providing insight for methods to improve ductility.
NRC Phase 3 Recommendation 3-24. Methods for the recycling of carbon-reinforced composites need to be developed. [NRC, 2010, p. 109.]
Updates: DOE cofunding of Small Business Innovation Research work with Materials Innovation Technologies (Fletcher, North Carolina) to research low-cost carbon-fiber composite manufacturing using recycled aerospace carbon-fiber.
Other global recycling efforts identified are as follows:
• Nottingham University, United Kingdom: Fluidised Bed, Supercritical Fluids, Microwave;
• Adherent Technologies, New Mexico, United States: Batch Thermo- chemical;
• Valley Stade Consortium, Germany: Batch Pyrolysis;
• Wells Specialty Products, Texas, United States: Fluidized Bed;
• Ruag, Switzerland;
• Firebird Advanced Materials, North Carolina, United States: Microwave; and
• Milled Carbon, United Kingdom: Continuous Pyrolysis.
As noted earlier, weight reduction is a crucial part of any balanced approach to achieving aggressive fuel consumption targets and will undoubtedly entail enhanced computational methods and widespread materials substitution. The work being performed under the auspices of the Partnership appears to be properly focused on relevant initiatives.
Although these initiatives appear relevant, the committee questions whether they all satisfy the criteria of high-risk, precompetitive research judged appropriate for federal involvement. Competition has raged among the steel, aluminum, and composites automotive supply base for many years in an effort to achieve low-cost weight reduction via materials substitution, and the aluminum, magnesium, high-strength steel, and composites content of production vehicles has been steadily rising for more than 20 years. Furthermore, numerous vehicle demonstration projects have been conducted in the past, both by materials trade associations and by industry consortia, some of which were sponsored by DOE.
As noted in Chapter 2, the committee applauds the appointment by each technical team of an associate member. However, the MTT has selected as its associate member a manufacturer of aluminum truck bodies; although the company no doubt is competent, this selection would seem to add little in the area of greatest need, namely, long-term high-risk research into low-cost lightweight alternative materials. It might be productive for MTT to consider adding another associate member with this type of expertise. Phase 3 Recommendation 3-22 emphasized the need for systems analysis focusing on the most cost-effective way to achieve a 50 percent weight reduction. While the analytical approach in process at ORNL is responsive to that task, it is less clear what value the $10 million award (over 4 years) to Vehma to build another prototype multimaterial vehicle offers, especially considering that the award abstract does not even mention cost.
Phase 3 Recommendation 3-23 reiterated the Phase 2 recommendation (NRC, 2008, p. 9) and essentially anticipated no further work on magnesium, other than inclusion in the analytical optimization process. The Partnership nevertheless listed in its response several continuing Mg projects within the 67 percent of DOE’s FY 2012 budget that is devoted to metals development.
Phase 3 Recommendation 3-24 urged the development of methods to recycle carbon-fiber composites. The Partnership is devoting 18 percent of its FY 2012 Lightweight Materials budget to carbon-fiber projects, including recycling. Although this is responsive to the committee recommendation, it can be argued that carbon fiber offers perhaps the greatest opportunity for weight reduction while maintaining structural integrity, and hence the huge challenge of doing so at low cost could deserve a greater share of the materials budget.
While increased emphasis on low-cost carbon fiber would be desirable, the committee continues to believe that much of the MTT work on light metals and materials substitution demonstrations is not precompetitive and would be best performed by the private sector. Funding currently allocated to these activities
Recommendation 3-17. The Partnership should expand its current work on low-cost carbon-fiber precursors, manufacturing, and recycling. This work could also potentially help to reduce the cost of high-pressure hydrogen storage tanks.
Recommendation 3-18. The materials technical team should expand its outreach to the other technical teams to determine the highest-priority collective Partnership needs, and the team should then reassess its research portfolio accordingly. Any necessary reallocation of resources could be enabled by delegating some of the highly competitive metals development work to the private sector.
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