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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report 3 Vehicle Subsystems INTRODUCTION At the time of the Phase 1 review of the FreedomCAR and Fuel Partnership, the Partnership had been under way for a relatively short time, although it did have the advantage that a number of the technologies under development were part of the Partnership for a New Generation of Vehicles (PNGV) program, which had been initiated in 1993. Since the Phase 1 report was issued, there have been significant changes in some external influences, such as a large increase in the price of gasoline and heightened interest in carbon dioxide (CO2) contributions to global warming. These changes could make achieving the program goals even more beneficial in the long term and, consequently, more important to the nation. Since the program objectives are obviously in the national interest, and since most of the high-risk activities would not be undertaken without governmental support, DOE involvement is clearly justified. The long-range goals of the Partnership—to transition to a transportation system that uses sustainable energy resources and produces minimal criteria or net carbon emissions on a life-cycle or well-to-wheels basis—are extremely ambitious. The difficulties are compounded when the additional constraints associated with the Partnership are imposed: energy freedom, environmental freedom, and vehicle freedom. These goals and associated constraints effectively eliminate the continued simple evolution of the gasoline-fueled internal combustion engine (ICE) vehicle as a possible answer. “Sustainable energy resources” and “energy freedom” both suggest non-petroleum-based alternative fuels. The emphasis on “net carbon emissions” and “environmental freedom” suggests that CO2 and other emissions from the production and consumption of alternative fuels should
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report be reduced, through highly efficient processes, to minimize adverse environmental effects. Finally, “vehicle freedom” implies that the fuel and onboard energy conversion systems should not limit the options and choice that buyers expect to have available in their personal vehicles. These goals, if attained, are likely to require new transportation fuel(s) utilized in more efficient power plants in lighter vehicles having reduced power requirements and equivalent utility and safety. DOE envisions that the path to achieving the long-term goals of the FreedomCAR and Fuel Partnership involves improvements in ICEs, a transition from improved gasoline- and diesel-fueled ICE vehicles to a greater utilization of gasoline- and diesel-fueled hybrid electric vehicles (HEVs), the development and implementation of plug-in hybrid electric vehicles (PHEVs), more utilization of hydrogen-fueled ICEs and HEVs, and—finally—hydrogen-fueled fuel cell vehicles (FCVT, 2004). For this transition to take place, the industry will require enhanced technology in many areas so that it can develop new vehicle subsystems and vastly improved vehicles. The DOE-sponsored activities described in this section are intended to provide understanding that will enable the needed technologies to be successful. The scope of the technologies needed is broad and the timescales for implementation are short. Competitive pressures dictate that if a technology appears to be promising it will be rapidly integrated into industry’s implementation plans. Consequently, continued close collaboration between DOE and industry is necessary to allow these technologies to transition into the industrial laboratories and development programs and then to identify new critical areas where enhanced understanding will be most beneficial. An example of technology that has progressed from concept demonstration stage to implementation is exhaust gas aftertreatment from lean-burn engines. Various engine manufacturers and original equipment manufacturers (OEMs), both domestic and foreign, have or are planning to introduce lean oxides of nitrogen (NOx) traps, selective catalytic reduction, and diesel particulate filters to their production models. Therefore, it is appropriate that DOE funding for these activities should be curtailed and redirected to areas where fundamental understandings are lacking. This observation was made in the Phase 1 report and recommended that the Partnership redirect its pursuit of novel emission control technologies and plan for, analyze, and seek solutions for emission problems associated with emerging fuels, fuel infrastructure, and propulsion systems (see Recommendation 3-3 in Appendix D). In response to the recommendation, DOE initiated a solicitation (DE-PS26_07NT43103) to address (1) E85-optimized engines, (2) enabling technologies for fuels and lubricants, and (3) efficiency of clean combustion and fuels development. Since some of these technologies are in production (e.g., flex-fuel vehicles), it is important that the Partnership carefully coordinate with industry to maintain programs that contribute most to a new understanding of the physical, chemical, and thermal processes impacting performance of the engine, the fuel, and the aftertreatment system.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report The most direct way to enable near-term reductions in fuel consumption and emissions is by improving ICEs. Specifically, better understanding of the ICE combustion process and how emissions are produced could both increase efficiency and decrease engine-out emissions. Higher thermal efficiency reduces the fuel needed to produce a given power output, and lower engine-out emissions will allow the use of a simpler, probably less expensive exhaust aftertreatment system. Such improvements in ICEs, which could be implemented quickly, would benefit both conventional vehicles and HEVs. The fuel cell subsystem is an energy converter with the potential to be more efficient than an ICE. However, the only fuel cell systems currently appropriate for transportation systems use hydrogen as fuel. The hydrogen can be stored onboard the vehicle in pure form or it can be extracted from hydrocarbon fuels and water using an onboard fuel processor. However, DOE effectively eliminated the latter alternative from its R&D portfolio after years of research determined that there was little prospect of meeting essential cost and performance targets within the program time frames. This means that sufficient pure hydrogen must be carried onboard the vehicle to meet range requirements a very challenging task given the space and weight limits of typical light-duty vehicles. This, in turn, places a high premium on reducing the mass of the vehicle and maximizing the efficiency of the energy converter. Current experimental hydrogen-fueled fuel cell systems demonstrate efficiencies approaching 50 percent over a fairly wide range of operation. Further, such systems produce zero criteria emissions (occasional discharges of small quantities of hydrogen may occur). FreedomCAR and Fuel Partnership programs are addressing the performance, durability, and cost issues that need to be resolved so that fuel cells can become a viable option for personal transportation vehicles. HEVs require compact, efficient, and low-cost power electronics and energy storage systems as well as other advanced electrical components to make vehicle costs and weights competitive with conventional vehicles. Many of these same technologies are applicable to fuel cell vehicles and PHEVs. Consequently, advances in the power electronics and electrical subsystems are critical for improved viability of both the midterm as well as the longer-term vehicles envisioned by the Partnership. It is possible for HEVs and fuel cell vehicles to reduce fuel consumption by capturing some of the vehicle kinetic energy during deceleration and stopping. This requires some form of energy storage capable of accepting this energy and returning it to the drive train for propulsive power (called regenerative braking). The most likely form of such energy storage is electrochemical (batteries), but ultracapacitors are also being investigated. For such relatively small-scale energy storage, the most important parameters are cost per kilowatt ($/kW), specific power (kW/kg), cycle life, and calendar life. With increased electric energy storage onboard, the vehicle could run for a significant distance without using the fuel cell or engine. This would add design
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report flexibility to HEVs and reduce some of the performance requirements for fuel cells (e.g., start-up time and power ramp-up rate). Further increases in onboard energy storage capacity could enable PHEVs (vehicles whose batteries could be recharged by plugging them into a source of electricity while it is parked) and even all-electric vehicles. Both plug-in hybrids and all-electric vehicles would shift some transportation energy demand from petroleum-based fuels to the electric grid, which is mostly non-petroleum-based but not emissions free. The most important goals for research on these energy storage systems are to improve their cost per kilowatt-hour ($/kWh), specific energy (kWh/kg), cycle life, and calendar life. These storage systems also have to maintain adequate specific power (kW/kg) even at low states of charge. Irrespective of the propulsion technology, reducing the mass of a vehicle for a given mission will, with no other design changes, have the effect of reducing fuel consumption and increasing acceleration performance. However, to achieve the vehicle goals of the Partnership, any such mass reduction must be accomplished without compromising safety or overall vehicle utility. To accomplish significant weight reductions, several materials, including aluminum, high-strength steel (HSS), and carbon-fiber-reinforced polymer composites have been considered for replacing a large part of the (mostly) mild steel currently used. Other material substitutions, such as cast magnesium, in other vehicle components could further decrease vehicle weight. The challenge for all of these potential material substitutions is to reduce their cost. The following sections discuss in more detail the research approaches and issues associated with each of these technologies. ADVANCED COMBUSTION, EMISSIONS CONTROL, AND HYDROCARBON FUELS Introduction Even the most optimistic scenario for introducing fuel cell vehicles into the market requires several decades before market penetration becomes sufficient to have a measurable impact on petroleum consumption and CO2 emissions. During this transition the dominant powerplant for mobility systems will continue to be ICEs fueled with a hydrocarbon (gasoline, diesel fuel, or biofuel). Consequently, it is important to maintain an active R&D program at all levels of industry, academia, and government. The near-term introduction of such technologies could reduce the rate at which petroleum consumption for transportation grows during the transition to alternative powerplants and powertrain configurations. Adding electric components to a vehicle powertrain opens new ways to improve fuel economy. HEVs are being marketed today, and PHEVs, which offer greater vehicle range from the electricity stored in the onboard battery and can benefit from off-peak battery recharging, are being actively pursued. In hybrid
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report vehicles, the ICE can be operated more efficiently than it is with conventional mechanical or hydromechanical transmissions. Obviously, any improvements to the ICE will carry over directly into incremental improvements of these electrified vehicles. Maximizing efficiency under the constraint of meeting stringent emission standards complicates engine-powertrain systems. Efficiency improvements require understanding and precise control of every aspect of the engine operation as well as optimization of every component and its interaction within the powertrain system. The technologies currently being pursued with the intent of introducing them to the market for both diesel- and gasoline-fueled vehicles—for example, low-temperature combustion (LTC) and lean exhaust aftertreatment—tax the limits of the engine and powertrain community’s fundamental understanding of the controlling thermochemical processes. A greater knowledge of the controlling thermochemical phenomena will accelerate the introduction of these technologies into the marketplace. The urgent need to get vehicles with lower fuel consumption to market has spurred the effort to incorporate new technologies such as LTC or new lean exhaust aftertreatment systems into vehicle powertrains. After research is completed, system optimization through prototyping and the development of manufacturing procedures can take several years before the new technology reaches production. This time pressure has unified the traditionally separate pursuits of “research” and “development.” Researchers are now pursuing enhanced fundamental understanding of the controlling thermochemistry at the same time as engineers are investigating concept systems. Sophisticated research tools such as laser-based optical diagnostics, the detailed identification of chemical kinetic mechanisms and their subsequent simplification, and the implementation of advanced three-dimensional computational fluid dynamics (CFD) are being used to expand the fundamental knowledge base and also being applied to potential configurations for prototype engines and powertrains. To successfully conduct such a program requires close coordination among industry, government laboratories, and academia. In the opinion of the committee, the advanced combustion and emission control technical team is doing a good job with this close coordination. The organizational structure of their activities involves memoranda of understanding (MOUs) between companies and government labs, working group meetings, regular intergroup reviews, and an annual peer-reviewed research meeting. The committee is pleased with the responses of the technical team to the recommendations made in the Phase 1 report. In particular the team has succeeded in involving the energy companies in its programs. The energy companies are now actively engaged, and a program known as Fuels for Advanced Combustion Engines has been organized under the Coordinating Research Council. This program has the objective of providing a set of research fuels to discern fuel effects on LTC. The technical team is making good use of its resources. Requests for proposals (RFPs) have been issued for an E85-
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report optimized engine, for enabling technology for fuels and lubricants, and for clean combustion and fuels co-development. Funding FY07 funding for the advanced combustion and emission control technical team was $20.7 million, with the same amount requested for FY08. A breakdown of how the funding was dispensed to different organizations and technologies is shown in Figure 3-1. FIGURE 3-1 Distribution of DOE FY06 funding for the advanced combustion and emission control technical team. SOURCE: R. Peterson and K. Howden, DOE, “Advanced combustion and emission control,” Presentation to the committee on March 1, 2007. Goals and Targets The technical targets and roadmap remain the same as reported previously (NRC, 2005; DOE, 2004). To briefly summarize, the Partnership expects to achieve by 2010 an engine thermal efficiency of 45 percent, with a cost under $30/ kW, while meeting Tier 2, Bin 5, emissions. These are very challenging targets. The technical team is working hard to achieve them and is making progress. The focus of the research continues to be lean-burn, direct-injection engines for both diesel- and gasoline-fueled vehicles. Within this broad area, specific research areas include the following:
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report Low-temperature combustion Control, Expanding the load range, Coupling to fuel characteristics, Transient operation, and Combustion mode switching. Aftertreatment Modeling of a diesel particulate filter, Lean NOx traps, Selective catalytic reduction (SCR) NOx reduction, and Identification of a potential catalyst for hydrocarbon NOx catalysis. Tool development Improved CFD capabilities, Improved diagnostics capabilities, and Comparison of CFD and experimental results. Within each of the research areas discernable progress has been made. Highlights are documented in “FreedomCAR and Fuel Partnership 2005—Highlights of Technical Accomplishments” and can be found at the USCAR Web site: <www.uscar.org/commands/files_download.php?files_id=95>. Significant Barriers to Achieving Success The technologies being pursued by the advanced combustion and emission control technical team are very sophisticated. Making these technologies work in an engine-powertrain system under a range of operating conditions is very challenging. It pushes all the fundamental boundaries of understanding within the combustion and powertrain community. For example, trying to expand the LTC operating condition from an optimal operating point quickly leads to excessive unburned HC and carbon monoxide (CO) emissions, with an attendant reduction in combustion efficiency. The increase in HC and CO poses an additional problem because the exhaust temperatures during LTC are usually below the typical light-off temperatures of current catalysts. Extended-range catalytic converters to facilitate engine operation approaching the edge of the combustion stability regime may solve this problem. Expanding the LTC operating range of an engine will require optimal matching of the fuel, its distribution within the cylinder, the fluid mechanic mixing, and the temporal and spatial evolution of thermodynamic states within the cylinder. Combustion mode switching between regular spark or diesel combustion and LTC may affect emissions, and the emission behavior of the engine during transient operation within LTC operation is not well understood and could be a serious issue. Similar statements about the technical complexity of the problems can be
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report made for virtually all the technologies being investigated by the advanced combustion and emission control technical team. A critical prerequisite for achieving success is expanding the knowledge base of the processes that influence the performance of advanced combustion and emission reduction technologies and their interaction with the fuel being used as the energy carrier. Conclusions and Recommendations In light of the FreedomCAR and Fuel Partnership objectives, the funding and work allocation for continued development of the ICE and vehicle electrification seem appropriate. The advanced combustion and emission control technical team is doing a good job of maintaining a close and constructive working relationship with the stakeholders in the auto and energy communities. Since the distinction between research and development has blurred, it is critical for the technical team to maintain this collaboration and make it even stronger. The international competition is fierce, so maintaining a presence within that community and an awareness of technological developments outside the United States continue to be important to establish benchmarks and grow the knowledge base. The largest barrier to implementing advanced combustion, aftertreatment, and fuel technologies is an insufficient knowledge base. Not only topic-specific understanding but also understanding the system-level interactions between the energy carrier, the energy release process, and the final emission cleanup is critical to continued improvement of the ICE powertrain. Continued close collaboration between DOE and industry is necessary to allow these technologies to transition into industrial laboratories and to identify the areas where enhanced understanding will be most beneficial. Recommendation. The Partnership should formulate and implement a clear set of criteria to identify and provide support to ICE combustion and emission control projects that are precompetitive and show potential for improvements well beyond those currently being developed by industry. Recommendation. DOE should actively encourage collaborations among the national laboratories, industry, and academia to more effectively direct research efforts to areas where enhanced fundamental understanding is most needed. Transient LTC engine operation and combustion mode switching between conventional combustion and LTC could have significant impact on total vehicle drive cycle emissions and the necessary operating domain for catalytic exhaust treatment systems. This could also be relevant to the emissions for PHEVs, where the engine may be off for long periods of time before being started and engaged into the vehicle’s powertrain.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report Recommendation. The Partnership should investigate the impact on emissions of combustion mode switching and transient operation with LTC. As the engine is made more efficient and exhaust thermal energy is used for advanced turbocharging and the aftertreatment systems, the final exhaust temperature will become lower. This will reduce the theoretical maximum thermal efficiency of heat engine exhaust recovery systems. Given the projected conversion efficiency of the exhaust heat recovery systems under investigation, the committee questions how much exhaust energy can actually be recovered. In addition, it seems likely that the cost per kilowatt of the heat recovery systems will be high. Recommendation. The Partnership should perform a detailed analysis of the potential improvement in efficiency and the cost effectiveness of the exhaust gas heat recovery effort and make a go/no-go decision about this work. FUEL CELLS Introduction Hydrogen-based fuel cell powerplants promise to be one of the most efficient and least polluting way to power personal transportation vehicles while providing the potential for meeting the Partnership’s major goals. Consequently, the advancement of fuel cell technologies to the point where performance and costs can be compatible with mass-manufactured automobiles is a key element of the FreedomCAR and Fuel Partnership. Over the course of the Partnership, DOE-sponsored fuel cell activities have contributed to solid advances in many of the performance and engineering metrics as well as reductions in projected costs as described in the following section. Current projects are focused on advancing the science and engineering of the high-risk technical challenges that remain, including performance, durability, and lifetime. Initiatives that can lead to cost reductions through materials advancements, new concepts, or simplification of the engineering are also under way and are expected to eventually lead to a mass-manufactured product. Current Status of Key Parameters Fuel cell stack life currently limits the overall demonstrated powerplant durability to only about one fourth of what is needed to meet the performance targets set forth by the Partnership. A major reduction in stack life occurs in actual vehicle applications because of the many stops and starts and transients with vehicle operations, fuel composition, and related phenomena when compared to what is observed with the testing methods and conditions in laboratory development work.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report In addition, as laboratory fuel cell stack lifetimes lengthen, new failure modes are surfacing and must be better understood and resolved. One such example is platinum catalyst dissolution, which impairs long-term performance. The prompt resolution of these and new failure modes, as they are discovered, is critical to achieving 2010 and 2015 targets. Projected costs for high-volume (500,000 units/yr) fuel cell powerplant production are currently approximately $100/kW for relatively proven technologies and about $67/kW for a newer technology compared to the 2015 target of $30/kW (see Figure 3-2; also see James and Kalinoski, 2007; Lasher, 2007). The latter estimate includes recent advances by 3M (Debe, 2007) in membrane and electrode technology that result in lower projected costs. These new technologies are quite promising, yet there is still a need to demonstrate that laboratory performance can translate to similar results in full stacks and then, ultimately, in vehicle tests. It should also be noted that the manufacturing and supply chains have not been fully established to date because the technology continues to evolve. The numerous assumptions that underlie the aforementioned cost projections may have to change as the development process proceeds. The cost of the platinum catalyst used in the membrane electrode assembly (MEA) represents approximately 57 percent of projected stack costs (Lasher, 2007). The platinum metal contained in the electrode alone accounts for most of FIGURE 3-2 Two estimates of 2006 costs for fuel cell systems. The differences between the DTI and TIAX estimates are (1) the cost of the MEA and seals in stack balance of plant and (2) DTI included test and conditioning in its estimate. The 2015 cost target is $30/kW, for a total cost of $2,400. SOURCE: D. Tran and K. Epping, FreedomCAR fuel cell tech team, Presentation to the committee on March 1, 2007.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report the cost of the catalyst, and the price of precious metals has risen substantially in recent years. The spot market price was approximately $1,300 per troy ounce in June 2007, 18 percent higher than the price used for estimating stack costs as reported at the 2007 DOE Merit Review. It must be noted that this price is set by market forces and will not be impacted by the Partnership’s research program. Even though the fuel cell stack is the core of a fuel cell power generation system (and its most discussed element), it must be part of a carefully integrated system to achieve performance goals. The design, performance, and integration requirements of the ancillary components of the system depend heavily on the performance and engineering specifications of the stack, which means that the developmental progress of the entire system is highly dependent on the uncertainties and risks associated with meeting the long-term targets for each of these ancillary components. Of these components, onboard hydrogen storage—even though it does not affect power plant performance directly—is probably the most challenging goal. Major issues associated with this goal are discussed in detail in the next section of this report. The Partnership has achieved a significant improvement in the power density of the fuel cell stack without storage over the years: 440 W/l (2004), 500 W/l (2005), 580 W/l (2006) vs. the DOE target of 650 W/l in 2010 (Epping and Tran, 2007).1 Progress in power density, including the storage subsystem, has also been achieved (160 W/l in 2006) and is steadily progressing toward the 2010 target (220 W/l). The DOE’s Office of Basic Energy Sciences (BES) sponsors activities and programs at national laboratories and academic institutions that have used solid state and polymer sciences to study the atomic and molecular structure of catalysts and new polymers. These efforts have improved the knowledge base and could result in new and improved materials and processes for fuel cell components (e.g., membranes and electrocatalysts). The impact of these important efforts will most likely not be realized until after 2010. Lastly, water dynamics still remains challenging in that, if water distribution is mismanaged, it can reduce stack performance and lifetime. The neutron scattering in situ water imaging technique available at the National Institute of Standards and Technology (NIST) has yielded exceptionally valuable insights into water behavior in an operating fuel cell. With the detection equipment installed in the spring of 2007, it is possible to “see” the water not only in the plates but also under dynamic conditions in the MEA and the gas diffusion layer (Jacobson, 2007). DOE’s support for the development of new laboratory techniques such as these is commendable. 1 K. Epping and D. Tran, FreedomCAR Fuel Cell Tech Team, Presentation to the committee on March 1, 2007.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report life requirement of at least 300,000, and progress has been made in meeting the calendar life target of 15 years (more than 10 years has been demonstrated). Furthermore, the battery will operate over a wider temperature range, and its cold cranking power has been improved. FCVT and the larger battery community have recognized that safety issues are an important part of battery development, and safety-related issues are being worked on by all subgroups of the Li ion battery development program. This involves understanding the thermochemical and electrochemical stability of the individual materials and single cells and the abuse testing of battery modules. (Extensive testing of the battery component and systems are conducted not only within the window of operation of the battery, such as the voltage, current, temperature, and so forth, but also outside this window, and such testing is called “abuse” testing.) Over the last few years the abuse tolerance of the battery has continued to improve. Many abuse-related issues can also be addressed by external electronic control; however, it is imperative that researchers continue to look for battery chemistries that are resistant to voltage or thermal abuse. The recent rash of fires in laptops using Li ion batteries may have left the public with the idea that these batteries cannot be made safe. This perception should be balanced against the reality that such failures are very rare and Li ion batteries are still in the early stage of development. In the past, generally during early development, today’s safe lead acid and nickel metal hydride batteries were perceived to have safety issues. A safety concern has also been raised about the scale-up of Li ion batteries from the AA type cells used in cell phones and laptops to the larger cells used in automotive applications. Large Li ion batteries and other lithium-metal-based batteries have been safely deployed in military and space applications and, in Japan, in some trucks. The FCVT should continue to be forthright and transparent about all safety-related concerns, tests, and results, not only by making technical improvements but also by correcting any misperceptions. Performance improvements and the abuse tolerance issues of Li ion batteries are being addressed at all levels of development. Similar systems (nickel/cobalt oxide–carbon or manganese oxide–carbon) are being investigated at the level of the entire battery system by the battery technology development subactivity; single-cell performance is being investigated by the national laboratories as a part of the applied battery research subactivity; and a basic understanding of components and materials is being sought at universities in the long-term research subactivity. Similarly, more stable anodes, such as lithium iron phosphate (LiFePO4), and alternative cathodes, such as nano lithium titanium oxide (LiTi12O5), which prevents the deposition of metallic lithium, are being investigated to improve the abuse tolerance of the Li ion battery system. Again, this investigation is being conducted at the materials level in the long-term battery research subactivity and as cells and batteries in the advanced battery research subactivity. There appears to be coordination of efforts in investigating similar and related materials and systems issues across all three subactivities of the Li ion battery development
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report effort, and it is hoped that there is close communications between groups to accelerate progress. Although significant progress has been demonstrated in the performance of the Li ion battery, the cost of this battery remains a major barrier to its introduction in HEV applications. Currently, the cost for the HEV battery in volumes of 100,000 units per year is estimated to be between $750 and $900, which is almost twice the FreedomCAR’s 2010 target of $500. However, in comparison to the 2004 cost estimate of $1,200, there has been significant reduction in cost. Cost is a critical factor in the introduction of Li ion batteries in HEV applications since they will replace existing and presumably lower cost nickel metal hydride batteries. Going forward, it is generally expected that the cost of the mature nickel metal hydride battery will be tied to the commodity price of nickel, while the evolving Li ion battery technology, which can use a variety of lower cost materials, will eventually become much cheaper. In fact the main improvement in the cost of the Li ion battery over the last 2 years comes from replacing the expensive LiCoO2 by cheaper LiMn2O4 or LiFePO4 for the cathode in the battery. Another expensive material in Li ion batteries is the microporous separator, and FCVT has funded two programs to reduce the cost of the separator by half, to about $1/m2. FCVT should be commended for recognizing that cost reduction will primarily be achieved by investigating alternative low cost materials and aggressively pursuing various combinations of materials for the Li ion battery. Furthermore, the performance and abuse tolerance of these potentially lower cost materials are being simultaneously studied by the various subactivities at all levels, from basic research on understanding the materials themselves to research at the level of cells to determine their life-limiting processes. The fact that Li ion batteries can be made from a variety of materials is at one and the same time both the strength of this technology and its difficulty—namely, developing a viable commercial product. On the one hand, the variety of materials that can be used to make a battery suggest that there is significant room for increasing the battery’s energy density, improving other performance characteristics, and reducing cost. On the other hand, the development of the battery is made more difficult by the wide choice of materials, since not only do the individual materials have to be characterized but each electrochemical couple has to be characterized for its performance, abuse tolerance, and cost at the cell and battery module levels. Replacing expensive cobalt (LiCoO2) with low-cost manganese (LiMn2O4) or iron (LiFePO4) could significantly reduce the cost of the battery, but it would still be much higher than the target cost of $500 per battery. These estimates have a wide window ($750 to $900) at a production rate of 100,000 units per year. Thus, larger production volumes may be required to reduce the price of the battery, and a detailed study of the effect of production rate on battery cost should be undertaken. In fact, the cost study should be carried out to at least 500,000 units per year to allow a meaningful comparison against fuel cell production costs. It may also
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report be necessary to revisit the cost target established for the battery and substitute a more realistic target. It is possible that the initial assumptions, both market and technical, may have to be refined to reflect the present market conditions such as gasoline prices. In addition, the greater base of knowledge about materials and processing gained over the last few years should be factored in to obtain a more realistic cost target for these batteries. In any case, the impact of higher battery cost on the cost of an HEV should be determined. The cost of the battery will play a large role in the eventual success (or otherwise) of the PHEV, which operates in both the HEV mode, requiring high pulse power, and the electric mode, like an EV, where the increase in electric energy required is proportional to the electric mileage requirements. Thus, while an HEV requires a battery delivering only 1.5 to 2 kWh, a PHEV with a 10-mile electric range will require 5-7 kWh of energy from the battery and a PHEV with a 40-mile electric range will require 10-15 kWh (the energy and power requirements can depend on the charge depleting and sustaining modes chosen for the PHEV application). The FCVT’s cost goal for the high-power HEV battery is $250/ kWh; its goals for high-energy EV batteries are $150/kWh in the short term and $100/kWh in the long term. Since the PHEV battery needs both high power and high energy and the ratio of the power to energy changes with the desired electric range, a new normalized cost requirement needs to be established for PHEVs. Although the PHEV cost goal has not been finalized, the draft short-term goal is a 10-mile electric range at a battery cost of $300/kWh and the draft long-term goal (2016) is a 40-mile (or more) electric range at a battery cost of $200/kWh. The energy and power required from the battery for the PHEV application depend on the electric range and the relative charge-depleting and charge-sustaining modes. Some performance and cost goals that may be under consideration are listed in Table 3-1. The recognition of the potential benefit of PHEVs, a reduction in petroleum consumption, has led to growing support from the government and, in 2007, to $27.5 million in funding for the development of PHEV-related components and systems. However, progress has been extremely slow, and although the first discussions on a PHEV program began in May 2006, FCVT and its partners were unable to finalize the PHEV R&D plan by fall 2007. The latest draft plan states that the PHEV program goal and the development targets are expected to be completed sometime in 2008. There is a serious lack of urgency in executing this important plan, and the reasons for the delay are not clear. Furthermore, DOE is delivering inconsistent messages. On the one hand, the PHEV program has been presented as one of the elements in the transition to hydrogen-driven vehicles that are to be ready for a commercialization decision in 2015. On the other hand, the June 2007 draft plan for PHEVs calls for commercialization between 2016 and 2020. These mixed messages can only cause confusion among the interested parties. It is very important that DOE present a single and consistent R&D plan for PHEVs immediately.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report TABLE 3-1 USABC Goals for Advanced Batteries for PHEVs Characteristics at End of Life Unit High Power/Energy Ratio Battery High Energy/ Power Ratio Battery Reference equivalent electric range miles 10 40 Peak pulse discharge power at 2 sec/10 sec kW 50/45 46/38 Peak Regen pulse power (10 sec) kW 30 25 Available energy for CD mode, 10 kW rate kWh 3.4 11.6 Available energy for CS mode kWh 0.5 0.3 Minimum round-trip energy efficiency (USABC HEV cycle) % 90 90 Cold cranking power at −30°C, 2 sec-3 pulse kW 7 7 CD life/discharge throughput cycles/MWh 5,000/17 5,000/58 CS HEV cycle life, 50 Wh profile cycle 300,000 300,000 Calendar life, 35°C year 15 15 Maximum system weight kg 60 120 Maximum system volume liter 40 80 Maximum operating voltage Vdc >.55 * Vmax >.55 * Vmax Minimum operating voltage Wh/day 50 50 System recharge rate at 30°C kW 1.4 (120 V/15 A) 1.4 (120 V/15 A) Unassisted operating and charging temperature range °C −30 to +52 −30 to +52 Survival temperature range °C −46 to +66 −46 to +66 Maximum systems production price, 100,000 units/yr $ 1,700 3,400 NOTE: CD, charge depleting; CS, charge sustaining. SOURCE: USCAR Request for Proposal Information for Advanced High Performance for Plug-in Electric Vehicle Applications. Available on the Web at <http://www.uscar.org/guest/publications.php>.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report Recommendations Recommendation. The Partnership should conduct a thorough analysis of the cost of the Li ion battery for each application; hybrid electric vehicles (HEVs), PHEVs, battery electric vehicles (EVs), and hydrogen-fueled fuel cell HEVs. The analysis should re-examine the initial assumptions, including those for both market forces and technical issues, and refine them based on recent materials and process costs. It should also determine the effect of increasing production rates for the different systems under development. Recommendation. The Partnership should significantly intensify its efforts to develop high-energy batteries, particularly newer, higher specific energy electrochemical systems within the long-term battery research subactivity and in close coordination with BES. High-energy batteries provide the surest way to successful batteries for PHEVs. Recommendation. The Partnership should move forward aggressively with completing and executing its R&D plan for plug-in hybrid electric vehicles. ELECTRIC PROPULSION, ELECTRICAL SYSTEMS, AND POWER ELECTRONICS Introduction The scope of the FreedomCAR and Fuel Partnership includes R&D aimed at commercial advancement of HEVs, fuel cell HEVs, EVs, and PHEVs. Electrical systems in all these types of vehicles consist of electric propulsion systems and power electronics systems, along with appropriate electronic controllers. Electric propulsion systems convert electrical energy from the fuel cell and/or electrochemical energy storage device (e.g., a battery) into propulsive force interfaced to the wheels through appropriate drive trains and vice versa. Power electronic systems are used to convert the electrical energy among various forms (current, voltage, dc, ac, frequency) for energy flow between a fuel cell, and electrochemical energy storage device, a rotating electric machine, an internal combustion engine, and the electric utility. Electric machines and power electronic systems thus form an enabling technology critical for achieving the Partnership’s goal of clean and sustainable energy for transportation systems, cutting across the various approaches in both the near term and the long term. The relatively recent emphasis on PHEVs has raised additional technological concerns about interactions between the electric grid and the vehicle. Concomitantly, the budget appropriation for these activities has been essentially steady in recent years (for FY07, $15.6 million; for FY06, $13.6 million). HEVs are gradually becoming established and noticeable in the marketplace, spurred by increasing gasoline prices. Although the share of new vehicles sold
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report accounted for by HEVs is small, their absolute numbers are growing rapidly, and they are the segment with the fastest growth. The electric propulsion and power electronics technologies in these vehicles continue to improve, with new models introduced every year. The technologies of permanent magnet electric motors and power electronic converters are showing aggressive design and rapid progress in their performance. In recognition of the critical nature of these enabling technologies, there has been an increase in activities focused on them. A majority of the technical activities are being conducted by DOE national laboratories, by universities, and by automotive equipment vendors. During 2006, a comprehensive solicitation aimed at developing advanced technologies was issued and research awards were announced in May 2007. The projects include a significant amount of cost share from industry focused in four areas: (1) high-temperature, three-phase inverters, (2) high-speed motors, (3) integrated traction drive systems, and (4) bidirectional dc-to-dc converters. The goal in all four areas is to reduce the cost, weight, and package size of electric drive and power conversion devices while increasing vehicle efficiency. These projects represent are spending about $33.7 million, including the 50 percent cost sharing by industry. Program Status The current generation of HEV devices uses a permanent magnet ac motor, along with insulated gate bipolar transistor (IGBT)-based inverters and dc-dc power converters to manage the power flow among various energy sources and loads, with an appropriate cooling system. Improvements in the cost, weight, and volume of these systems are projected to come from developments in (1) the high-temperature operation of materials, components, and subsystems; (2) high-speed electric machines; (3) novel power converters that minimize the use of capacitors and magnetic elements; and (4) the integration of subsystems and components. Higher Temperature Operation Current-generation power conversion devices utilize a secondary coolant loop that operates at a lower temperature than the primary engine coolant loop. Advances in the technology to operate the devices at higher temperatures would lead to improvements in cost, reliability and power density. A variety of projects aimed at this include phase change cooling, compressed air cooling, spray cooling, high-temperature capacitors, high-temperature insulation, high-temperature packaging, wide band-gap materials such as silicon carbide power devices, high-temperature gate drives, high-temperature magnets, and thermal interface materials. While these projects are broadly aligned with the goals of the program, it is unclear whether there is a clear, quantifiable impact on meeting the performance and cost goals of the program.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report High-Speed Electric Machines The current generation of permanent magnet electric machines for vehicle propulsion operate at about 15,000 rpm. For a given power level, the general scaling laws of rotating electric machines lead to a proportionate reduction in the weight of the active materials, copper and iron, as the operating speed is increased. However, the accompanying design trade-offs involved in increasing the speed are related to various electrical and mechanical parameters such as voltage, current, losses, shear stress, fault tolerance, manufacturability, etc. The series of projects in progress that are aimed at high-speed machines include the development of design and optimization models, control without sensors, magnet materials, prototyping, and testing. An Oak Ridge National Laboratory technical report prepared by Unique Mobility indicates that the cost, volume, and mass goals for the Partnership are realizable with projected design developments and manufacturing improvements. Novel Power Converters Current-generation power electronic systems in HEVs include three-phase inverter modules to interface between the dc bus and the electric machine and possibly dc-to-dc converters between the battery and the dc bus. The capacitors at the dc bus and the inductor of the dc-to-dc converter represent major volume and cost elements as do the silicon power devices. Various projects are being conducted that are aimed at reducing the size of the dc-to-dc converter through high-frequency switching, integrated converters that incorporate the battery interface and the machine interface into one converter, and the use of switched capacitor converters, among other things. While progress and success in these projects are expected to lead to incremental improvements in the size and cost goals for the converters, their impact on meeting the goals of the Partnership in terms of performance and cost is unclear. Integration of Subsystems and Components The current generation of electrical systems, including electrical propulsion subsystems, power electronic subsystems, and thermal management subsystems, is packaged as discrete and separate elements and assembled together to realize the overall functional objectives. From a systems point of view, integrating these subsystems into a single package and specifying it as a single component can drive their cost and size lower and their reliability higher as the designs continue to evolve. However, the disparate constituent technologies and manufacturing involved in each of these subsystems cause such integration to be a significant challenge. Selected projects are aimed at various degrees of integration: the converter with the motor, the converter package with the thermal management, and so forth. Together, these integration projects are perhaps the riskiest projects in the
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report portfolio. Successful realization of their ambitious goals may lead to significant improvements in the electrical propulsion system performance across various measures. Summary Assessment The activities of this program have been multidisciplinary, and its portfolio is diverse: (1) materials development (thermal interfaces, high-temperature insulation, wide band-gap semiconductors, magnetic materials), (2) components development (high-temperature capacitors, silicon on insulator gate drives), (3) converter topologies (multilevel converters, switched capacitor converters), (4) manufacturing (high-temperature packaging), (5) machine control (sensorless operation, optimizing efficiency), and (6) design optimization and modeling (motor design and modeling tools, thermal modeling). Program review reports from 2005 and 2006 indicate a dispersed effort with diverse perspectives (Rogers, 2005; Wall and Rogers, 2006). By contrast, the recent solicitation and its selected projects with specific demonstration goals are aimed at realizing manufacturable engineering prototypes and designs by the selected technology vendors. Overall, these projects are aimed at incremental improvements relative to the state of the art in each of the constituent technologies. Recommendations Recommendation. The Partnership should conduct a meta-analysis and develop quantitative models to identify fundamental geometric limitations that ultimately set bounds on and lead to the realization of the size, mass, and cost of power converters and electric propulsion systems in relation to the physical properties of materials and processes such as dielectric strength, magnetic saturation, thermal conductivity, etc. This will allow the various ongoing and future efforts to be benchmarked against the theoretical boundaries of what is possible and enable the establishment of appropriate directions in research goals. Recommendation. In general, the Partnership should focus on the projects that address specific performance and cost goals of the program on the basis of the results of the meta-analysis recommended above. Specifically, it should (1) intensify packaging efforts; (2) commit additional resources to high-temperature electronics, including wide band-gap semiconductor devices such as SiC; and (3) redirect research on higher speed electrical machines to improve torque density. STRUCTURAL MATERIALS Substantial weight savings are a critical and key requirement of the FreedomCAR and Fuel Partnership. The vehicle weight reduction target has been set at
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report 50 percent, with the added criterion of cost parity (i.e., no increase in structural materials cost). This weight target is critical to vehicle design because the powerplant and fuel storage requirements are based on it. Any failure to meet the vehicle weight goal would necessitate a larger powerplant, increased fuel storage capacity, and larger components to achieve the overall vehicle functional goals—for example, driving range and acceleration. As noted in the Phase 1 report (NRC, 2005), the majority of the materials technical programs have been under way for some time, going back to the Partnership for a New Generation of Vehicles (PNGV) before the initiation of the FreedomCAR and Fuel Partnership (NRC, 2001). Thus detailed descriptions of the individual material studies would be superfluous here, and readers interested in specific details are referred to the earlier reports. In this report, the committee concentrates on reviewing the overall objectives and recommending some changes in the program targets and focus that appear to be more appropriate based on the progress to date. Assessment of the Program The lightweight materials programs have continued unabated, with only very small modifications to the activities described in the Phase 1 report. Thus the main structural weight savings are anticipated to be achieved through the widespread application of advanced high-strength steels, aluminum alloys (both sheet stock and castings), and cast magnesium. Lesser overall weight savings are also expected from specialized use of glass-fiber-reinforced plastics (GFRPs), titanium alloys, metal matrix composites, and stainless steel. From a technical perspective, all these materials are more than adequately covered in the current programs, from both an application viewpoint and an innovative manufacturing viewpoint. In addition to the above activities, there is a significant effort on carbon-fiber-reinforced plastic (CFRP) composites. While these materials potentially offer greater weight savings than any of the other candidate materials, the formidable challenges involved in meeting both cost and manufacturing requirements appear to be insurmountable in the time frame of this program, if indeed ever! In particular, the cost barrier is so great that the cost modeling results of the materials technical team apparently confirm the conclusion that CFRP composites will not be economically viable within the time frame of the Partnership. This is not to imply that some research activity in CFRP is not justified, but it does mean that the Partnership should not include such composites as part of its main program objectives and projections for vehicle design. By far the biggest question mark in the drive to achieve 50 percent weight reduction is the cost penalty for such a massive reduction. There is essentially zero possibility that such a reduction can be achieved at cost parity. However, failure to achieve the 50 percent goal would require redesigning the fuel cell to have a larger capacity; this would be accompanied by a significant increase in the size of the fuel storage system, not to mention an increase in the size and weight of
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report other components such as brakes and suspension. Such enlargements of the fuel cell powerplant and hydrogen storage capability would involve extraordinarily expensive materials and major cost increases, allowing the cost penalty for the structural materials to likely pale by comparison. Thus in the committee’s opinion, the 50 percent weight reduction is mandatory even with the associated cost penalty, because the alternative is likely to involve significantly greater cost! Overall, it seems clear that while the technical challenges to the successful application of lightweight materials are not trivial, a reduction in the associated large cost penalty is by far the bigger obstacle. Minimizing this cost penalty is primarily a matter of reducing the feedstock cost and is influenced to a much lesser extent by component manufacturing improvements, etc. This clearly gets into individual company proprietary matters (e.g., the cost of aluminum sheet stock), so cost modeling of structural materials in the context of the Partnership is unlikely to produce reliable information. However, it is the committee’s opinion that some realistic cost estimating to achieve the 50 percent weight reduction is needed if the Partnership is going to obtain anything close to a realistic evaluation of the overall cost/functionality trade-offs. Recommendations The technical programs are making good progress, and the team members are extremely competent and interacting very well. The main recommendation of the committee in the Phase 1 report is still pertinent—namely, that the funds supporting materials research should largely be diverted to higher priority areas such as fuel cells, hydrogen storage, high-energy batteries, and infrastructure transitions. The committee believes that the proportion of funding going to materials is still exceedingly high given the urgency of many of the other R&D areas (see Chapter 5). The committee also wants the materials effort to focus on what appears to be the most difficult issue for the materials program: recognition that while a 50 percent weight reduction not only must but also probably can be achieved, it will involve a significant cost penalty but, nonetheless, be the most cost-effective way of achieving the overall vehicle program objectives. Recommendation. Based on the goal of 50 percent weight reduction as a critical goal and the near-certainty that some (probably significant) cost penalty will be associated with it, the Partnership should develop a materials cost model (even if only an approximation) that can be used in a total systems model to spread this penalty in an optimal way across other vehicle components. Recommendation. The materials research funding should largely be redistributed to areas of higher potential payoff, such as high-energy batteries, fuel cells, hydrogen storage, and infrastructure issues. However, materials research for projects that show a high potential for enabling near-term, low-cost mass reduction should continue to be funded.
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Review of the Research Program of the FreedomCAR and Fuel Partnership: Second Report REFERENCES Debe, M. 2007. Advanced Cathode Catalysts and Supports for PEM Fuel Cells. Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fcp_25_debe.pdf>. Department of Energy (DOE). 2004. FreedomCAR and Vehicle Technologies Multi-Year Program Plan. Washington, D.C.: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Available on the Web at <http://www.eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.shtml>. Jacobson, D. 2007. Neutron Imaging Study of the Water Transport in Operating Fuel Cells. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fc_2_jacobson.pdf>. James, B.D., and J.A. Kalinoski. 2007. Mass Production Cost Estimation for Direct Hydrogen PEM Fuel Cell System for Automotive Applications. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fc_28_james.pdf>. Kung, H. 2007. Update on DOE Basic Hydrogen Research. 2007 Annual Merit Review. Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/pl_0_kung.pdf>. Lasher, S. 2007. Direct Hydrogen PEMFC Manufacturing Cost Estimation for Automotive Applications. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fc_27_lasher.pdf>. National Research Council (NRC). 2001. Review of the Research Program of the Partnership for a New Generation of Vehicles, Seventh Report. Washington, D.C.: National Academy Press. NRC. 2005. Review of the Research Program of the FreedomCAR and Fuel Partnership, First Report. Washington, D.C.: The National Academies Press. Rogers, S.A. 2005. Annual Program Report for the Advanced Power Electronics and Electric Machines Program (November). Washington, D.C.: U.S. Department of Energy, Office of FreedomCAR and Vehicle Technologies. Satyapal, S. 2007. Hydrogen Storage Session Review. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available online at <http://www.hydrogen.energy.gov/pdfs/review07/pl_3_satyapal.pdf>. Wall, E., and S.A. Rogers. 2006. Annual Program Report for the Advanced Power Electronics Technology Area. Washington, D.C.: Department of Energy, Office of FreedomCAR and Vehicle Technologies.