2
Batteries and Battery Packs for PHEVs

Battery cells, and the packs into which they are assembled, are the key component that will largely determine the viability of PHEVs. The battery packs must be affordable, durable, and safe. No commercially available battery meets all these requirements. Rechargeable lithium-ion (Li-ion) batteries, made by the billions for small electronic devices, are the most promising technology for automotive propulsion and will be used in the first-generation PHEVs soon to be rolled out. This section reviews the relevant technologies and estimates how their characteristics may evolve over the coming years.

TYPES OF PHEVS

Several configurations are possible for PHEV drive trains. The two considered here represent those that may be introduced, as shown in Figure 2.1. A PHEV differs from a hybrid electric vehicle (HEV) in that the battery can be charged from the electrical grid and operate the vehicle independently of the internal combustion engine (ICE) for a limited all-electric range (AER). This is the charge-depleting mode of operation. The ICE starts when the battery reaches its minimum state of charge and operates the generator to charge the battery. This charge-sustaining mode of operation prevents the battery from being discharged too deeply.

The PHEV-10 is designed for an AER of 10 miles before the ICE must start. It is similar to the Toyota Prius but has a larger battery and modified control electronics. Its split-power blended (or parallel-drive) configuration can drive the car either with only the electric motor powered by the battery or with the gasoline engine. When the battery is discharged to its minimum allowable level, the engine starts and the vehicle operates in a charge-sustaining mode, as in a conventional HEV. The engine will also start and assist in driving the wheels when more power is needed than can be delivered by the electric motor for rapid acceleration or heavy-load hill climbing. The PHEV-10 requires a more robust battery than an HEV because it must operate over a wide state of charge (SOC) range, enduring many deep charge/discharge cycles.1

The PHEV-40 has its engine, battery, and electric motor in series. The engine only charges the battery, and all propulsion comes from the electric motor. Thus it has a larger battery and motor than the PHEV-10 but a longer AER. It is conceptually similar to the General Motors Volt in design.

The size of the battery required to provide propulsion depends on the size and weight of the vehicle and the AER desired. For simplicity, this report considers just one vehicle, a midsize car, as representative of the fleet of light-duty vehicles, as was done in the 2008 Hydrogen Report. While midsize cars may not perfectly represent the fleet, they are adequate to illustrate the critical issues. Various recent studies have reported a range of energy requirements for midsize cars: in a study of Prius conversions to PHEVs, on average the vehicles required 238 watt-hours (Wh) per mile (Francfort, 2009). A simulated driving analysis calculated 170-200 Wh per mile energy consumption.2 In addition, the GM Volt is expected to reach 40 miles on 8 kWh from its batteries, or 200 Wh per mile.3 The committee assumed that the vehicles it analyzed would initially require 200 Wh per mile in its calculations. Larger, heavier vehicles would require substantially more energy per mile and bigger, more-expensive batteries, but those are not considered in this report. All vehicles are expected to become more efficient over time, and PHEVs will require less gasoline and less electricity, as discussed in Chapter 4.

1

A rechargeable battery can be charged to 100 percent of its capacity and then discharged to 0 percent, but full charge would not allow regenerative braking, and full discharge typically would seriously damage its future performance. Early PHEV batteries may be limited to 80 percent of full charge and prevented from discharging to less than 30 percent. This is a 50 percent SOC range. Later generations may be able to operate with a wider range.

2

M. Wang, A. Elgowainy, A. Burnham, and A. Rousseau, Center for Transportation Research, Argonne National Laboratory, Well-to-wheels energy and greenhouse gas results of plug-in hybrid electric vehicles, presentation to the committee, June 18, 2009, Washington, D.C.

3

M. Verbrugge, General Motors, Extended-range electric vehicles, presentation to the committee, May 18, 2009, Washington, D.C.



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2 Batteries and Battery Packs for PHEVs Battery cells, and the packs into which they are assem- a wide state of charge (SOC) range, enduring many deep charge/discharge cycles.1 bled, are the key component that will largely determine the viability of PHEVs. The battery packs must be affordable, The PHEV-40 has its engine, battery, and electric motor in durable, and safe. No commercially available battery meets series. The engine only charges the battery, and all propulsion all these requirements. Rechargeable lithium-ion (Li-ion) comes from the electric motor. Thus it has a larger battery batteries, made by the billions for small electronic devices, and motor than the PHEV-10 but a longer AER. It is concep- are the most promising technology for automotive propul- tually similar to the General Motors Volt in design. sion and will be used in the first-generation PHEVs soon to The size of the battery required to provide propulsion be rolled out. This section reviews the relevant technologies depends on the size and weight of the vehicle and the AER and estimates how their characteristics may evolve over the desired. For simplicity, this report considers just one vehicle, coming years. a midsize car, as representative of the fleet of light-duty vehicles, as was done in the 2008 Hydrogen Report. While midsize cars may not perfectly represent the fleet, they TYPES OF PHEVS are adequate to illustrate the critical issues. Various recent Several configurations are possible for PHEV drive studies have reported a range of energy requirements for trains. The two considered here represent those that may be midsize cars: in a study of Prius conversions to PHEVs, on introduced, as shown in Figure 2.1. A PHEV differs from average the vehicles required 238 watt-hours (Wh) per mile a hybrid electric vehicle (HEV) in that the battery can be (Francfort, 2009). A simulated driving analysis calculated 170-200 Wh per mile energy consumption.2 In addition, charged from the electrical grid and operate the vehicle independently of the internal combustion engine (ICE) the GM Volt is expected to reach 40 miles on 8 kWh from its batteries, or 200 Wh per mile.3 The committee assumed for a limited all-electric range (AER). This is the charge- depleting mode of operation. The ICE starts when the that the vehicles it analyzed would initially require 200 Wh battery reaches its minimum state of charge and operates per mile in its calculations. Larger, heavier vehicles would the generator to charge the battery. This charge-sustaining require substantially more energy per mile and bigger, more- mode of operation prevents the battery from being dis- expensive batteries, but those are not considered in this charged too deeply. report. All vehicles are expected to become more efficient The PHEV-10 is designed for an AER of 10 miles before over time, and PHEVs will require less gasoline and less the ICE must start. It is similar to the Toyota Prius but has electricity, as discussed in Chapter 4. a larger battery and modified control electronics. Its split- power blended (or parallel-drive) configuration can drive 1A rechargeable battery can be charged to 100 percent of its capacity and the car either with only the electric motor powered by the then discharged to 0 percent, but full charge would not allow regenerative braking, and full discharge typically would seriously damage its future per- battery or with the gasoline engine. When the battery is formance. Early PHEV batteries may be limited to 80 percent of full charge discharged to its minimum allowable level, the engine starts and prevented from discharging to less than 30 percent. This is a 50 percent and the vehicle operates in a charge-sustaining mode, as in SOC range. Later generations may be able to operate with a wider range. a conventional HEV. The engine will also start and assist 2M. Wang, A. Elgowainy, A. Burnham, and A. Rousseau, Center for in driving the wheels when more power is needed than can Transportation Research, Argonne National Laboratory, Well-to-wheels energy and greenhouse gas results of plug-in hybrid electric vehicles, be delivered by the electric motor for rapid acceleration or presentation to the committee, June 18, 2009, Washington, D.C. heavy-load hill climbing. The PHEV-10 requires a more 3M. Verbrugge, General Motors, Extended-range electric vehicles, robust battery than an HEV because it must operate over presentation to the committee, May 18, 2009, Washington, D.C. 

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 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIES—PHEVS Series PHEV Toyota Bl en ded PHEV Electric flow Electric flow Traction flow Traction flow Battery Battery Generator Engine Motor Generator Engine Motor Mode AER Blended Charge-depleting Battery only mainly Battery + Engine if needed mainly Engine Charge-sustaining mainly Engine + Battery if needed FIGURE 2.1 Plug-in hybrid electric vehicle concepts. SOURCE: Toyota. Figure 2-1 R01653 Thus, the PHEV-10 requires 2.0 kWh of battery energy redrawn Li-ion batteries currently are the only serious option for (actually used) to drive its 10-mile AER. The PHEV-40 editable vectors They are smaller and lighter than other batteries, and draws PHEVs. 8 kWh of battery-stored energy to meet its 40-mile AER in they promise to withstand multiple large SOC swings while charge-depletion mode before the engine starts and begins maintaining their performance. They have more than twice supplying power to operate the vehicle in charge-sustaining the energy density and about three times the power density mode.4 For the 50 percent SOC assumed in this report for of the nickel-metal-hydride (NiMH) batteries used in current the first generation of vehicles, the nameplate capacities are HEVs, and four times the energy density of the lead-acid 4 kWh for the PHEV-10 and 16 kWh for the PHEV-40. batteries used in most vehicles today. What no Li-ion battery can do—yet—is simultaneously deliver both high power density and high energy density at LITHIUm-ION BATTERY CELL CHEmISTRIES a reasonable cost. To meet this challenge, several promising For PHEVs to be widely accepted by consumers, batteries Li-ion chemistries are being vigorously pursued by compa- must be significantly cheaper than they are now, durable nies, research institutions, and governments. The technology enough to have a long life, and safe. In addition, they will is advancing rapidly, but there is no guarantee that any Li-ion have to meet performance goals, which will require battery will be developed that meets all goals for vehicle use. Table 2.1 compares the attributes of four of the more promis- • High power density to deliver the current needed for ing Li-ion battery chemistries. demanding driving conditions; Li-ion battery manufacturing technology is essentially the • High energy density for storing the needed energy for same for all battery chemistries. Typically the electrodes of an extended all-electric range; and Li-ion batteries are coated on metal foils, usually copper foil • Wide range of SOC while maintaining a long cycle life. for the negative electrode and aluminum foil for the positive electrode, separated by an electrolyte (Nelson et al., 2009). Typical electrolytes are derived from solutions of LiPF6 salt 4The batteries for these two vehicles are not identical because they are in a solvent blend of ethylene carbonate and various linear optimized for different conditions. For example, the PHEV-10 is likely carbonates, such as dimethyl carbonate (Tikhonov and Koch, to operate more in a charge, sustaining mode at minimum SOC than the 2009; Zhang et al., 2002). PHEV-40.

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 BATTERIES AND BATTERY PACKS FOR PHEVS TABLE 2.1 Characteristics of Li-Ion Batteries Involving Different Chemistries Cathode/Anode Nickel Cobalt Aluminum Manganese Spinel/ Iron Phosphate/ Manganese Spinel/ Characteristics Oxide/Graphite Graphite Graphite Lithium Titanium Oxide Durability Good Fair Good TBD Power Fair Fair Good Good Energy Good Good Fair Poor Safety and abuse tolerance Poor; safety concerns Fair Good Good Cell voltage 3.6 3.8 3.3 2.5 Some battery developers Johnson Controls/Saft LG Chem Ltd. A123 EnerDel Associated vehicle manufacturers Toyota/Ford GM Daimler HEV buses NOTE: Cathode chemistries are frequently referred to as involving a spinel crystal structure. Actually there are no pure spinel structures present in Li-ion batteries; spinel-like would be more accurate. While the power density (W/kg) of the cell is fixed by the last 3 to 4 years, which is a function of both the number of surface area of the electrode foil, the energy density (Wh/kg) charge/discharge cycles and calendar life (Howell, 2009). can be varied over a limited, but significant, range simply by Some degradation is inevitable; for the purposes of this increasing or decreasing coating thickness. HEV batteries, report, about 20 percent over the warranty period is assumed. which require high power more than high energy storage, If the PHEV-40 is expected to still have its required 8 kWh have thin electrode coatings. By contrast, electric vehicle (actually used) of energy needed for an AER of 40 miles with (EV) batteries require high energy density and have thicker the same 50 percent SOC range in 10 years, it could be sized electrode coatings. Research has yielded new concepts for to provide 10 kWh (actually used) energy initially. The other better electrodes and electrolytes. For example, raising the option is to assume that the SOC range is increased over time cell voltage to 5 V would increase the battery’s energy den- to account for battery degradation, which could be adjusted sity. Could this lead to a better PHEV battery? It is simply every year when the vehicle is brought in for servicing. This too early to tell. is the approach that the committee chose for the estimations In this report overall properties such as energy density, that follow. If degradation is not too large or does not accel- power density, and total energy available refer to the full erate with larger SOC range, this should be satisfactory, but until demonstrated it remains a concern.5 range from 100 percent to 0 percent SOC. Energy and power density are intrinsic properties, and total available energy is Figure 2.2 compares the SOC variation for PHEV and the nameplate capacity of the cell or battery. For batteries in HEV batteries. In a PHEV, batteries must undergo multiple battery packs for vehicle operation, this report refers to the large SOC range cycles without significant degradation. A energy (kWh) actually used—that is, the nameplate capacity 10-year life would require the batteries to undergo at least of all the cells in the pack multiplied by the allowable SOC. 2,000 cycles and still stay within the prescribed performance range. At present, this requires limiting the SOC range. The right-hand figure shows the much narrower (and less LITHIUm-ION BATTERY PACKS demanding) SOC range of an HEV. For PHEV applications, about 100 Li-ion cells are con- This study assumes that SOC varies at most between nected in series to provide the design voltage to operate the 30 and 80 percent, or 50 percent of the total charge. The electrical propulsion motors. These cell groups are then 30 percent lower limit is near the minimum and serves to installed in parallel, as needed, to provide the energy to drive maintain power and energy during charge-sustaining mode. the motor for the distance desired. Battery packs consist of The upper limit allows charging from regenerative braking these groups of cells, the supporting frame, electronic con- while preventing overcharging and the resultant rapid battery trols, and cooling systems to protect the cells. The current degradation. A 50 percent range in SOC does, however, come focus is on improving battery durability, safety, and cost at a price: The battery must have a nameplate capacity twice competitiveness. as high as the amount of energy actually needed and delivered to meet performance targets. In other words, the PHEV-40 will need a nameplate battery rating of 16 kWh to supply Battery Durability 8 kWh of the energy actually used for its 40 miles of charge- Auto manufacturers have indicated that they intend to offer an 8-year warranty in 49 states and a 10-year warranty 5If after 10 years of operation the battery pack has lost 20 percent of its in California on PHEV battery systems as part of the drive- capacity (16 kWh down to 12.8 kWh for the PHEV-40), the SOC would have train warranty. Current commercial Li-ion batteries typically to be raised to 62.5 percent to maintain the required 8 kWh usable energy.

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0 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIES—PHEVS FIGURE 2.2 Differences in SOC requirements for PHEV batteries and HEV batteries. The PHEV is charged from an external source until it reaches its maximum state of charge, as shown on the left side of the figure. Its charge-depleting mode in AER takes it down to its minimum state of charge. The jagged portion of this curve is from regenerative braking, which partially recharges the battery. The level portion is charge-sustaining operation with the engine maintaining the battery charge around its lower SOC. The HEV also recharges from regenerative Figure 2-2 braking but operates in a much narrower SOC range. SOURCE: Toyota, presentation to the committee, May 18, 2009. R01653 uneditable bitmapped image one-column size below depleting driving (or 20 kWh if it is oversized to account for range in SOC with little reduction in performance under 20 percent degradation). Energy used is the product of the controlled test conditions.7 However, life prediction is dif- nameplate energy and the SOC range. Increasing the SOC ficult, and actual performance will not be known until many range will increase the fraction of the nameplate energy used vehicles are in service for many years. In the absence of this from a given battery pack size if that can be done without operational information, accelerated-age tests are used to compromising durability.6 Generally, however, the industry estimate the expected performance, but they may not capture believes that for the first 5 years or so, battery durability the full effect of actual aging. issues will require conservative battery management—that In addition, higher temperatures and other excursions is, keeping the SOC range at about 50 percent. outside the design envelope (e.g., SOC limits and rate of New technology may help meet the durability challenge. charging) detract from durability and battery life. Accord- One type of battery is claimed to have lasted 7,000 cycles ingly, cooling and temperature control systems will have to in accelerated aging tests covering a wide (70 to 90 percent) be included in the battery pack, and operation-control strate- gies must avoid excursions in operational performance. 6While increased SOC range is one of the factors leading to cost reduc - 7D. tions in the required battery pack (discussed later), it can also increase the Vieau, A123 Systems, Lithium-ion battery progress, presentation to rate of degradation. the committee, May 2009, Washington, D.C.

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 BATTERIES AND BATTERY PACKS FOR PHEVS Battery-Pack Safety volts. This balancing of charge is important to battery life and battery safety. Safety has been a concern with Li-ion batteries, which The non-cell portion of the battery pack (i.e., the structure can overheat and catch fire or even explode, emitting burn- and control systems) could account for around 50 percent ing gases. There appear to be two separate causes for these of the pack’s cost and is less likely to produce large future thermal runaways: contaminants and overcharging. cost reductions. However, with improved battery technology, Contaminants, particularly small metal particles, can operational experience, and better quality control in cell enter the cell during manufacturing, causing a short circuit manufacture, it might be possible to monitor some of the between the anode and the cathode, resulting in a fire. cells rather than all of them, as is done now, which would Improved manufacturing techniques and rigorous quality help reduce battery pack cost. In addition to adding to costs, control should manage this issue, albeit at an increased cooling and monitoring of the cells add significantly to the cost. Overcharging the cells or charging them too rapidly weight of the battery pack, reducing the power and energy can lead to overheating, which can degrade the battery and density of the battery pack. limit its service life. With some Li-ion chemistries, over- charging can result in thermal runaway and catastrophic Battery-Pack Performance and Cost failure. Control systems to prevent this are discussed in the following section. Tables 2.2 and 2.3 summarize the committee’s estimates Proper choice of Li-ion chemistry, controlled manufac- of Li-ion battery and battery-pack performance, and costs for turing procedures, and onboard monitoring and temperature the two PHEV types examined in three time periods, 2010 control should assure safe batteries and safe battery pack (current technology), 2020, and 2030. Additional detail on operation. Another safety concern, crashes, also must be the committee’s analysis of battery-pack cost can be found in resolved. Passengers and emergency workers must be safe Appendix F. These estimates were arrived at after literature from shocks and fumes. As with durability, battery and searches and discussions with industry experts. The values automotive manufacturers are confident that the safety in the tables represent the judgment of the committee of issues can be overcome and managed. The consequences of the most probable rate of anticipated progress based on the catastrophic failures would be too great for manufacturers to entirety of the data available to it.9 Future battery and battery- market PHEVs that do not meet very high safety standards. pack costs are quite uncertain at this point. For that reason the committee feels that it will be important to reevaluate Battery Pack Cooling and Control Electronics these costs in several years, when significant data on the first production cycle of PHEVs is available, which should allow The battery pack, in addition to containing a hundred or better projections. so interconnected Li-ion cells, includes two control systems Optimistic and conservative estimates also were made essential for the safety and durability of the batteries. Both for the production costs expected in 2010, 2020, and 2030. of these systems include significant electronics and other “Optimistic” means progress is faster than expected. “Con- equipment, located separate from, but connected to, the servative” means partial rather than “probable” success but battery pack. could also mean that additional battery capacity (and thus One of these systems monitors and controls the tem- cost) was necessary to account for degradation. The “prob- perature of the battery cells. With the current state of Li-ion able” and “optimistic” estimates form the basis for the pro- battery cell technology, the individual cell temperature jections that the committee modeled, as discussed in the next should not exceed 60°C (140°F) because the batteries section. Box 2.1 lists DOE’s battery targets for comparison.10 deteriorate at higher temperature.8 The electrically driven It is the committee’s opinion that these PHEV battery goals temperature-control unit uses cooling fluid to maintain are extremely aggressive and are unlikely to be reached by battery temperature. Liquid cooling is assumed to be required the target date or even for a significant time beyond. for larger battery packs; smaller battery packs, such as for a PHEV-10, may allow air cooling. 9The performance and cost numbers in Tables 2.2 and 2.3 are less The other system measures the voltage of each cell and optimistic than some others that have been claimed. Lithium-ion battery ensures that it does not exceed an upper limit during charging manufacturing is a well-developed technology. Worldwide over a billion or regenerative braking, which could lead to thermal runaway Li-ion cells are currently produced every year. They are made by coating (overheating). The voltage of each Li-ion cell should not large sheets that are then cut up in small pieces for cell phones and other exceed its specified value by more than a few tens of milli- electronic devices. Vehicle batteries will be conceptually similar, but the sheets will be cut in larger pieces. Also, a large part of the cost of automo- tive batteries is the packaging, which involves electronics for monitoring the cell voltage and state of charge the SOC, cooling systems and, their 8Damage can start at 50°C, but deterioration is slow. Vehicles are unlikely mechanical supports and sheet metal. These components are not expected to be exposed to such high ambient temperatures, but the heat given off by to decline greatly in cost. 10D. Howell, DOE, DOE targets for battery performance, presentation to charging and discharging can lead to high temperatures inside the pack. Thus cooling is necessary, particularly in hot climates. the committee, June 2009.

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 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIES—PHEVS TABLE 2.2 Estimates of Li-Ion Battery Performance Parameters for a PHEV-40 2010a Characteristic 2020 2030 Energy density at nameplate cell level, Wh/kg Probable 150 200 200 Power density at nameplate cell level, W/kg for 12 sec Probable 1,400 1,600 1,750 Energy density at nameplate battery pack level,b Wh/kg Probable 120 150 150 level,c Power density at nameplate battery pack W/kg for 12 sec Probable 1,150 1,250 1,400 Cycle life over SOC at 40°C ambient Probable 3,000 5,000 7,500 $/kWhd Battery pack cost per kWh over SOC variation (8 kWh actually used), Conservative 2,000 1,275 1,150 Probable 1,750 1,120 1,000 Optimistic 1,250 800 720 Battery pack cost per kWh for nameplate energy level (16 kWh), $/kWh Conservative 1,000 638 575 Probable 875 560 500 Optimistic 625 400 360 Battery calendar life, yr Conservative 3 7 9 Probable 5 10 10 Optimistic 8 12 15 NOTE: PHEV-40 nameplate battery rating 16 kWh (8 kWh usable); SOC variation range, 80-30 percent; 100+ kW peak power. aFirst production cycle. bBattery pack means the entire system, including packaging, cooling, and monitoring and control electronics. cPower density numbers for PHEVs are still variable since developers are engineering their cells to give optimum life and energy. dAs applied to SOC range actually used. Cost per kWh based on nameplate capacity would be half these. Additional information on the committee’s analysis of these costs is in Appendix F. TABLE 2.3 Estimated Battery Performance Properties for a PHEV-10 2010a Characteristic 2020 2030 Energy density at nameplate cell level, Wh/kg Probable 100 150 150 Power density at nameplate cell level, W/kg for 12 sec Probable 1,500 1,600 1,750 Energy density at nameplate battery pack level, Wh/kgb Probable 80 110 125 level,c W/kg Power density at nameplate battery pack for 12 sec Probable 1,250 1,350 1,400 Cycle life over SOC at 40oC ambient Probable 3,000 5,000 7,500 $/kWhd Battery pack cost per kWh over SOC variation (2 kWh actually used), Conservative 2500 1,600 1,450 Probable 1,650 1,050 950 Optimistic 1,250 800 725 Battery pack cost per kWh for nameplate energy level (4 kWh), $/kWh Conservative 1,250 800 725 Probable 825 525 475 Optimistic 625 400 363 Battery calendar life, yr Conservative 3 7 9 Probable 5 10 10 Optimistic 8 10 15 NOTE: PHEV-10 nameplate battery rating 4.0 kWh (2 kWh usable); SOC variation range, 80-30 percent; 50+ kW peak power. aFirst production cycle. bBattery pack means the entire system, including packaging, cooling, and monitoring and control electronics. cPower density numbers for PHEVs are still highly variable since developers are engineering their cells to give optimum life and energy. dAs applied to SOC range actually used. Cost per kWh based on nameplate capacity would be half these. Additional information on the committee’s analysis of these costs is in Appendix F.

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 BATTERIES AND BATTERY PACKS FOR PHEVS BOX 2.1 Department of Energy Targets for Battery Performance The Department of Energy has set several targets for battery performance: • Battery cost. — PHEV-10: (3.4 kWh available energy at end of life)1 $500/kWh or $1,700 battery cost2 achieved in 2012 vs. $1,000+/kWh today — PHEV-40: (11.6 kWh available energy at end of life) $300/kWh or $3,400 battery cost2 achieved in 2014 vs. $1,000+/kWh today • Battery life. — PHEV-10: 10+ years achieved in 2012 (5,000 cycles) vs. 3+ years today — PHEV-40: 10+ years achieved in 2014 (3,000-5,000 cycles) • Maximum system weight. — PHEV-10: 60 kg for in 2012 vs. 80-120 kg today — PHEV-40: 120 kg in 2014 1This PHEV-10 is a small SUV that requires more energy than the midsize car modeled in this study. 2At high volume production. SOURCE: Adapted from DOE (2009b). PROJECTED PHEV INCREmENTAL COSTS who provided valuable input to this table. There was good agreement on the expected rate of improvements, particularly Tables 2.4 and 2.5 compare the current incremental cost of for the non-battery components, where there is considerable components for a PHEV-40 and a PHEV-10 with those of a experience. There also was general agreement that battery conventional (nonhybrid) car. Savings from eliminating com- pack costs would decline significantly, but not dramatically, ponents or reducing size are shown as negative numbers; for for the first 10-15 years of commercial experience and would example, the automatic transmission can be eliminated when later slow. the drive is electric.11 These incremental numbers are for The reductions expected mirror the experience with the first round of PHEV production, including the estimated NiMH batteries for HEVs, where costs came down sig- cost of the battery pack, the least well defined of the costs. nificantly at first but then decreased much more slowly. The Initially, the PHEV-40 is expected to cost the vehicle manu- NiMH battery pack for HEVs saw a cost reduction of about facturer about $18,000 more than an equivalent conventional 11 percent from 2000 to 2006 but since has seen much less car and the PHEV-10 to cost about $6,300 more. The price change. Li-ion battery cost decreased by about 35 percent to the customer, before government subsidies, is likely to be from 2000 to 2008, but most of that was at the beginning of significantly higher once manufacturers’ additional expenses that period, with only about 5 percent after 2004 (Howell, and profit and dealers’ markup are added in. 2009). Manufacturers of Li-ion batteries with technology These costs are likely to decline over time. Table 2.6 sum- similar to consumer batteries are already considerably fur- marizes projections of cost reductions for the different com- ther along the learning curve than were manufacturers of ponents for the two PHEV types for 2015, 2020, and 2030. NiMH batteries when HEVs were introduced, so steep cost Reduction estimates are posited on technology improve- reductions seem unlikely. Nor does it seem likely that the ments, on experience gained over time through several cycles cost of materials will decline greatly. Indeed, some materi- of technology evolution, and from increased economies of als, including lithium, may increase in cost with additional scale. The committee held discussions with various experts demand, but the committee believes that the supply of lithium will be adequate for any plausible number of PHEVs manufactured worldwide. 11The PHEV-10 will require a transmission because the engine is con - nected directly to the wheels. However, the committee assumed that manu - It is likely that much of the reductions in Li-ion cell facturers would use a small, electronically controlled continuously variable costs will come from technology innovations, with smaller transmission (ECVT) such as used in the 2010 Prius. This cost is included reductions from manufacturing improvements and volume under power electronics in Table 2.5.

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 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIES—PHEVS TABLE 2.4 Projected Incremental Costa of Components for PHEV-40 for Production in 2010 Using Current Technology Compared with an Equivalent Current Nonhybrid Vehicle Price That a Supplier Cost Reductions in Incremental Cost of Charges the Vehicle Components due to PHEV-40 Vehicle vs. Manufacturer for the Vehicle Changes in Going Modern, Comparable Component Technology to PHEV-40 ICE Vehicle Motor/generator Probable 1,800 1,800 Power electronics, DC/DC converter Probable 2,500 2,500 (1.2 kW), and inverter Li-ion battery pack Conservative 16,000 16,000 8 kWh actually used Probable 14,000 14,000 16 kWh nameplate capacityb Optimistic 10,000 10,000 Electrical accessories Probable 100 100 Electric air conditioning Probable 400 400 Regenerative brakes Probable 180 180 Electric power steering/water pump Probable 200 200 Body/chassis/special components Probable 200 200 Automatic transmission Probable 850 −850 Starter and alternator Probable 95 −95 Engine simplification Probable 300 −300 Total Conservative 21,380 20,135 Probable 19,380 1,245 18,135 Optimistic 15,380 14,135 aSeries plug-in hybrid 40-mile AER, 100+ kW peak power, 8 kWh usable; 16 kWh nameplate capacity. bSee Appendix F for further information on the committee’s analysis of costs. TABLE 2.5 Projected Incremental Costa of Components for PHEV-10 for Production in 2010 Using Current Technology Compared with an Equivalent Current Nonhybrid Vehicle Price That a Supplier Cost Reductions in Incremental Cost of Charges the Vehicle Components due to PHEV-10 Vehicle vs. Manufacturer for the Vehicle Changes in Going Modern, Comparable Component Technology to PHEV-10 ICE Vehicle Motor/generator Probable 1,500 1,500 Power electronics, DC/DC converter Probable 1,500 1,500 (1.2 kW), and inverter Li-ion battery pack Conservative 4,000 4,000 2.0 kWh actually used Probable 3,300 3,300 (4 kWh nameplate capacity)b Optimistic 2,500 2,500 Electrical accessories Probable 100 100 Electrical air conditioning Probable 400 400 Regenerative brakes Probable 180 180 Electric power steering and water pump Probable 200 200 Body/chassis/special parts Probable 200 200 Automatic transmission Probable 850 −850 Starter and alternator Probable 95 −95 Engine simplification Probable 120 −120 Total Conservative 8,080 7,015 Probable 7,380 1,065 6,315 Optimistic 6,580 5,515 aSplit-power plug-in hybrid, 10-mile AER capacity, 50+ kW peak power, 2 kWh usable; 4 kWh nameplate capacity. bSee Appendix F for further information on the committee’s analysis of costs.

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 BATTERIES AND BATTERY PACKS FOR PHEVS TABLE 2.6 Percent Projected Cost Reductions for TABLE 2.7 Estimated PHEV Incremental Costs Different Components with Increased Production and 2011a 2015 2020 2030 Learning by Doing PHEV-40 14,100-18,100 11,200-14,200 9,600-12,200 8,800-11,000 Year Reduction Achieved/ PHEV-10 5,500-6,300 4,600-5,200 4,100-4,500 3,700-4,100 Year Against Which Compared NOTE: These are the incremental costs to manufacture the vehicle itself, 2015a/ 2020b/ 2030c/ relative to a conventional (nonhybrid) vehicle. They do not include engineer- 2015a 2020b Component 2010 ing, overhead, or other costs, or profit, and thus are not the total incremental prices to the customer. Ranges represent probable and optimistic assess - Motor/generator/gear set 5 5 5 ments of battery technology progress. Power electronics, AC/DC converter 10 15 5 aCosts for 2011 are based on low battery production rates in response Li-ion battery pack 25 15 10 to contracts initiated about 2 years earlier. Electrical accessories 5 5 5 Air conditioning 10 5 5 Regenerative brakes 5 5 5 Electric power steering + water pump 5 5 5 Body/chassis/special components 10 5 5 OTHER TECHNOLOGY OPTIONS AND POTENTIAL NOTE: Estimated cost reductions are based on increased production BREAKTHROUGHS volumes and anticipated improvements in technology and production tech - niques. Unanticipated technology advances (breakthroughs) could lead to The cost of Li-ion batteries is currently very high, making faster reductions. it difficult for PHEVs to be cost competitive when the cost aAssumed production, 25,000 vehicles per year. bAssumed production, 1 million vehicles per year. of gasoline is less than $4 per gallon. Although considerable cAssumed production, 1 million-plus vehicles per year. progress is expected in reducing battery costs, it is not clear that sufficient cost reductions can be achieved with Li-ion batteries or battery packs to make PHEVs cost competitive without substantial subsidies. Announcements continue from researchers about improve- ments in Li-ion batteries, including better electrodes and production.12 Although it is hard to quantify, about half of electrolytes and, possibly, higher cell voltages (to 5 V), the cell cost is estimated to be for materials, and the cells resulting in better energy density. Unfortunately, it is hard to account for about half the battery pack cost, further reducing evaluate the practicality of these concepts or to assess which, the impact of cell-only cost reductions. if any, will become commercial and when. The additional costs for changes in mechanical and Other Li-ion battery cell chemistries may offer better electrical components in going from a conventional vehicle performance than those currently projected for PHEV appli- to a PHEV are considered quite predictable and have the cations,13 but serious questions remain about their durability, expected impact on vehicle cost. These estimates (Table 2.4 safety, and costs. There appears to be little chance that any and Table 2.5) are only for the cost of the components to the of these could become commercially cost competitive in the vehicle manufacturer and do not include the cost for vehicle near future. engineering, R&D, or the automakers’ capital investments. A breakthrough in battery technology would definitely These and other markups to the vehicle price, which is what improve the prospect of PHEVs becoming economically the customer will see, are addressed in Chapter 4 of this competitive. It is not possible to predict or schedule scientific report. and technical breakthroughs, but a continued, substantial Overall, Li-ion battery-pack costs may decline by almost scientific research effort is needed to increase the chances 50 percent, as shown in Table 2.2, from $1,750 per kWh that this will occur. However, even if a breakthrough occurs, energy actually used in 2010 to about $1,000 per kWh in it will be decades before it has a great impact. Major battery 2030. Collectively, the reductions in component costs lead developments will require considerable work and time prior to future PHEV costs shown in Table 2.7. These estimates do to commercialization to confirm cost advantage, durability, not consider the possibility of technological breakthroughs, and safety, and years more to achieve significant penetration which, if they occur, could significantly reduce the costs and into the fleet. improve the viability of PHEVs. Table 2.7 and the scenarios Options such as the lithium-air battery and solid polymer that follow do not report the conservative estimates, for if Li-ion electrolyte batteries are under study. Several large costs remain that high, PHEVs are unlikely to achieve much U.S. corporations are working on lithium-air technology, success in the market. which could offer 5 to 10 times as much energy density as the Li-ion batteries discussed above. This battery is much 12D. Vieau, A123 13D. Vieau, A123 Systems, Lithium-ion battery progress, presentation to Systems, Lithium-ion battery progress, presentation to the committee, May 2009, Washington, D.C. the committee, May 2009, Washington, D.C.

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 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIES—PHEVS lighter, but there are issues of safety, primarily because of widely practical. Battery leasing is another proposal. Leas- lithium’s reactivity with water, and regeneration or recharg- ing could lower the initial cost to the consumer and perhaps ing needs to be developed. Solid polymer Li-ion electrolyte provide some reassurance about durability, but it would not batteries offer higher energy densities and more stability than necessarily lower overall costs. Li-ion batteries, but safety and operational challenges (such It should also be noted that higher CAFE standards or as achieving acceptable current density at ambient tempera- high oil prices will improve the competitiveness of PHEVs. tures) will be difficult to meet. There do not appear to be Conversely, HEV cost and performance characteristics will any other radically new battery technologies on the horizon continue to improve, reducing the fuel-saving advantage (the lithium metal-air battery concept has been around for of PHEVs. Although HEVs will be more expensive than many years) that could economically provide the enhanced n onhybrid vehicles, PHEVs will be significantly more performance needed, but the vibrant research and develop- expensive than HEVs. However, the low fuel consumption ment programs world-wide may produce a technology that of PHEVs, especially the PHEV-40 type, will be advanta - will overcome these barriers. geous in helping the United States reduce its dependence Also, totally different approaches are being considered. on imported oil. Also, once the carbon intensity of grid Swapping battery packs at stations that charge them for the electricity is reduced, PHEVs will be able to significantly next vehicle is one possibility, but it is not clear if pack and reduce greenhouse gas (GHG) emissions from the light- vehicle design will be sufficiently standardized to make this duty vehicle sector.