Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035 (2021) / Chapter Skim
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5 Battery Electric Vehicles
5 Battery Electric Vehicles
Pages 72-143
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The assumption throughout the chapter is that vehicle electrification improves fuel economy (e.g., in hybrid electric vehicles [HEVs] and plug-in hybrid electric vehicles [PHEVs]
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The aver age EV emissions assume a 70 kWh capacity battery pack with manufacturing emissions of 75 kilograms CO2 per kWh, and average U.S. 2018 electricity emissions of 449 grams CO2 per kWh for electric vehicle charging.
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After summarizing cost reduction opportunities in each technology section, overall vehicle cost estimates that are expected to be realized in 2025–2035 are provided. 5.2 THE ELECTRIC DRIVE Several electric drive technologies, including brush and brushless direct current (DC)
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BATTERY ELECTRIC VEHICLES 75 FIGURE 5.2 Brushless PMSM -- power and control electronics. SOURCE: Rajashekara (2013)
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5.2.1 Motors -- Current Status and Future Developments Electric motor technology is a mature one; however, intensive efforts have been made over the past decade to optimize the motor design in order to meet the specific needs of automotive propulsion, as depicted by the torquespeed characteristic chart in Figure 5.4. These are as follows: • High motor torque at low motor speeds, for adequate vehicle acceleration and hill climbing; • High maximum motor power, for high-speed cruising; • Wide speed range, 3–4 times base speed, at the maximum motor power level, for cruising performance; • High torque and power density, for low motor weight and longer range; • High efficiency over the most frequently used range of operation, for longer E-range; • Reasonable cost (parity with internal combustion engines [ICE]
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while maintaining a low total motor cost, a single-stage gearbox with a gear ratio of about 7:1 to 10:1 is being used by most automakers. Increasing motor speed would result in unacceptable levels of the gear (a)
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Comparing the three vehicles in Table 5.1 reveals that the motor power density and specific cost, which are based on the motor weight and cost without the gearbox, improve with increasing the gear ratio. Adding the gearbox weight and cost, which increase with the gear ratio, will offset this improvement but still show cost improvement, as shown in Table 5.2.
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One should also keep in mind that operating at higher speed and reduced motor size will also result in a decreased cooling surface, which should be taken into account in sizing the motor cooling system for proper thermal management of the motor. Table 5.3 provides a summary of estimated potential cost and effectiveness impact of the above technologies by 2025 on the various vehicle classes.
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The direct connection between the power electronics and electric motor claimed to be responsible for reducing the overall weight of the drivetrain by about 1.5 kg owing to reduced cabling length (Green Car Congress, 2013)
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Research organizations of automakers and suppliers are active in research to understand the ultra-fast switching of WBG devices and are developing high-frequency circuitry and high-temperature components necessary to sustain and take advantage of WBG devices. Some of these research areas include WBG device characterization, as well as evaluating converter and inverter technologies.
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program is an extension of SWITCHES focusing specifically on developing selective-area doping processes for GaN power electronics. While research toward resolving the issues associated with GaN continues, the debate among proponents of GaN versus SiC fills the literature (Boutros et al., 2012; Patterson, 2015; Allan, 2017; Ferdowsi et al., 2017; Green Car Congress, 2017; Guerra, 2017; Slovick, 2017; Transphorm Inc., 2017; Wolfspeed, 2017; Els, 2018; Li, 2018; Business Wire, 2019; Davis, 2019; Semiconductor Today, 2019; Arrow Electronics, 2020; Bakeroot, 2020; Schweber, 2020)
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5.2.3 Findings and Recommendation for Motors and Power Electronics FINDING 5.1: The majority of automakers have converged on using permanent magnet synchronous motors with rare earth magnets as the drive motor for electrified vehicles owing to their superior efficiency, torque, and power density. Although permanent magnet synchronous motors are more costly (approx.
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, lifetime, safety, and cost. The cell energy density is the determining factor for driving range and will depend upon the active materials used within the cell, which define the cell voltage and capacity, as well as the inactive materials, which add weight and volume to the battery.
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Energy Density (Wh/L) Tesla Model 3 BEV Cylindrical 21700 250 721a Nissan Leaf BEV Pouch 33Ah 224 460b BMW i3 BEV Prismatic 94Ah 174 352c Chevy Bolt BEV Pouch 60 Ah 237 444d a Field (2019)
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5.3.3.1 Cathode Materials The composition of the cathode relates to the energy density of the battery. Commercial cathodes used in lithium-ion batteries are generally intercalation materials, wherein lithium ions can move into (intercalate)
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Lithium-ion batteries using graphite intercalation anode materials suffer from lithium plating during charge at high current densities. Plating of lithium metal results in reduced battery lifetimes and safety concerns.
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cathode or cell material) , cell energy density watt-hours per liter (Wh/L)
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are used as low viscosity diluents. TABLE 5.7 Important Separator Properties for Automotive Applications Property Typical Values Comments Thickness 10–40 microns Trend is thinner to improve cell energy density, but need to balance with safety Air permeability (Gurley value)
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As shown in Figure 5.11, 70% of the battery cost is owing to the material costs, with the remainder being factors such as manufacturing labor, R&D, and overhead. Efforts to reduce overall BEV costs must focus on reducing the cell cost -- which translates to use of cheaper higher energy density materials and more efficient manufacturing methods.
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can reduce materials costs from $80 to near $70/kWh, primarily owing to the improved energy density of the higher nickel materials and reduced cost owing to minimization of cobalt content. Figure 5.12b shows the sensitivity of various cathode costs to base cobalt market price.
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In addition to improving cell-level energy density, this also reduces cell costs, as shown in Figure 5.14. Improvements in technology of cathode coating for designed electrodes can enable cost reduction while maintaining performance.
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. FIGURE 5.15 Schematic of pouch cell battery manufacturing process.
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. As battery costs continue to come down, various studies suggest cell costs will be 73% to 84% of the total battery pack cost with higher production volume in the 2025–2030 time frame (Anderman, 2017; Pillot, 2019; UBS, 2017)
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Battery • ~42V Battery • ~300V Battery • ~300V Battery • >300V Battery • Various cathode • NMC cathode • NMC cathode • Ni-based cathode materials • Electric motor can power car • Electric motor can power car • Electric motor only power for • Electric motor cannot on its own at slow cruising through a specified range car power car on its own speeds SOC SOC SOC 100% 100% 100% State of Charge Characteristics Time Time Time HEV mode PHEV mode BEV mode FIGURE 5.17 Summary of battery differences along the spectrum of mild hybrid to BEV. HEV, PHEV, and BEV batteries vary dramatically in their size and SOC characteristics.
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In order to realize the maximum energy density benefit of a lithium metal anode, no lithium would be theoretically built into the anode. A copper current collector would FIGURE 5.18 Challenges with the use of lithium metal anodes.
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Safer materials may allow a reduction in system-level thermal management, allowing for improved system-level energy density and reduced costs. In addition, solid electrolytes may enable safer use of lithium metal anodes by mitigating growth and penetration of dendrites -- which ultimately results in energy density improvements.
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• Lithium metal anodes are used to improve cell energy density, and the solid electrolyte needs to be wetted by the lithium metal in order to minimize formation of high surface area lithium and lithium dendrites. Ideally, the shear modulus of the solid electrolyte should be a factor of eight higher than that of lithium metal to avoid puncture by dendrites.
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Owing to the low densities of both sulfur and lithium metal, the volumetric energy densities of these cells are lower than those of today's lithium-ion batteries. Owing to the technical challenges of safety and life of lithium-sulfur batteries as well as the commercial challenges of low-cost lithium electrodes, it is not anticipated that these will have any significant penetration into automotive markets before 2035.
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In an open system with oxygen coming from the environment, the battery would mainly consist of just the lithium anode. In theory, lithium-air architectures would present a substantial energy density improvement.
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To ease range-anxiety, modern PHEVs and BEVs have complex estimation algorithms for the SOC and SOH to translate the remaining battery energy to miles based on recognizing driving and terrain patterns. The performance and longevity of EV battery packs relies on constraining their operation so that current, SOC, and temperature are regulated within prescribed limits.
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5.3.4.1 State of Charge Battery SOC describes the remaining battery capacity and, therefore, remaining driving range. Since battery behavior is affected by several factors such as operating temperature, current direction, and history, battery SOC is a function of these factors.
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FIGURE 5.23 Schematic of an SOC estimation method in the form of a flow chart that integrates measurable outputs with models and algorithmic corrections. SOURCE: Reprinted from Zheng et al., Investigating the error sources of the online state of charge estimation methods for lithium-ion batteries in electric vehicles, Journal of Power Sources 377: 161–188, © 2018 with permission from Elsevier.
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. Battery SOP estimation is also important for battery thermal management (Kim et al., 2013, 2014)
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Electronic devices are fully charged and discharged more often than most EVs. Assuming the median driving distance, most large battery packs do not utilize more than 20% of their stored energy, which begs for other methods that will provide accurate estimation of the remaining capacity on board the vehicle.
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. It is also reported that the BEV leasing company Tesloop has its Tesla Model S vehicles driven more than 400,000 miles without significant battery capacity degradation (Tesloop, 2018)
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• Transportation of vehicles will require additional care to avoid damage to the battery pack. Tow truck drivers need to be familiar with BEV design and safety concerns.
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FIGURE 5.26 Fire heat release for EV and gasoline vehicles by range. SOURCE: Reprinted by permission from Springer Nature: Sun et al., 2020, A review of battery fires in electric vehicles, Fire Technology 56(4)
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5.3.5 Thermal Management Lithium-ion batteries' cycle life or capacity is considerably affected by operating temperature owing to irreversible chemical reactions. Thermal management systems monitor and control the battery pack temperature at certain locations.
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5.3.5.2 Cooling Systems Thermal management for heating and cooling of lithium-ion batteries relies on the existence of auxiliary systems using a medium such as fluid (air or liquid) , solid, or phase change material.
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. The Cold Weather Package usually consists of a dedicated battery heater, a heat pump system, and multimode thermal management.
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estimated that average battery costs would still be $200–$250/kWh in 2030 and reach $175–$200/kWh by 2050. Table 5.10 summarizes recent applicable technical studies that quantify EV battery pack costs for continued advances in battery technology and volume.
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. Although battery costs are reduced by 7% per year from 2018 through 2030, the precise cell and pack costs will differ by battery pack size.
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FINDING 5.8: With an increasing emphasis on improving battery energy density, and extending range and performance, some automakers are currently considering new chemistries and new battery management sys tems to address safety concerns, which could result in increased battery costs. FINDING 5.9: Although EV fires have attracted attention and raised safety concerns among some consumers, statistical comparison of fire incidents (between battery electric vehicles and internal combustion engine vehicles of all ages)
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The key questions are when, where, how many, and with what technologies to invest and deploy more chargers to achieve the most cost-effective energy impact. 5.4.1 Electric Charging Infrastructure Technologies and Costs 5.4.1.1 AC Level 1, AC Level 2, and DC Fast Chargers For a given electric range, longer available charging time at some locations (e.g., at-home overnight charging)
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In a sense, the electric charging infrastructure is already ubiquitous for Level 1 AC, as PEVs can charge directly with a regular 120 V power plug. Level 2 AC requires a 240 V power plug, which is available with commercial buildings and in residential units, usually for electric dryers but also in garages outfitted for PEV readiness.
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For example, "Electric vehicle charging stations in open parking lots and parking garages," a law passed in 2013 by the City Council in New York, requires that a minimum of 20% of parking spaces in new-construction open lots (or older lots being upgraded) be readied for EV charging (New York City Council, 2013)
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The total cost of the charging infrastructure system also depends on its scale, the number of PEVs, and the total electric vehicle miles traveled (eVMT)
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After all, profitable business models for 100 kW DC fast chargers are yet to be proved, not to mention for 400 kW xFC, which are presumably more expensive than the current DC fast charging systems. Two types of xFC systems are being pursued, with important cost implications.
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; PV = photovoltaic. SOURCE: Reprinted with permission from Tu et al., 2019, Extreme fast charging of electric vehicles: A technology overview, IEEE Transactions on Transportation Electrification 5(4)
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Overall, charging activities could increase when the charging infrastructure becomes more powerful, affordable, available, and convenient. Charging behavior may be reflected in charging activities.
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Availability of charging infrastructure has been found to significantly affect adoption of PEVs, but the impact of charging convenience on PEV adoption and charging behavior requires further research.
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. According to ICCT, by 2025, about 2.2 million chargers (including 1% 8% Public DC Fast Charging Public Level 2 Charging 100,000 Ports 800,000 Ports 13% Workplace Level 2 Charging 1,200,000 Ports 9.6 Million 78% Charge Ports Home Level 2 Charging 7,500,000 Needed by 2030 FIGURE 5.31 Projected EV charging infrastructure needs in 2030.
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Many studies have concluded that home charging is more cost-effective and important than workplace and public charging (Lin and Greene, 2011; Hardman et al., 2018; Lee et al., 2020a)
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. For BEVs, a better charging infrastructure increases the daily effective driving range and usability, which reduces dependence on a backup vehicle for long trips and increases eVMT.
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. Nissan Leaf eVMT by % of DC Charge Events Annualized Vehicle Miles or Vehicle Counts 14000 Average Annualized VMT 12000 Vehicle Counts 10000 8000 6000 4000 2000 None <1% 1% >5% >10% >15% >25% >50% to 5% to 10% to 15% to 25% to 50% Percentage of DC Charging Events by Vehicle FIGURE 5.34 Better charging infrastructure leads to more eVMT.
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Better charging infrastructure can increase the usability of the electric portion of plug-in hybrid vehicle propulsion and of limited-range battery electric vehicles. Better charging infrastructure can also encourage adoption of plug-in vehicles and further improve the fleet fuel economy.
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FINDING 5.15: Charging behavior, in terms of likelihood of plugging in when a charger is available, has been studied, but strategies to make charging more convenient and increase charging events are less studied. Electric vehicle automakers are trying to make charging more convenient and available.
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60000 Indirect cost Vehicle assembly Engine 50000 Engine auxiliaries Transmission 40000 Exhaust Engine control unit Charging cord 30000 On-board charger High voltage cables 20000 Control module Controller 10000 DC converter Electric drive module Inverter/converter 0 Power distribution module Thermal management Conventional BEV150 BEV200 BEV250 BEV300 Conventional BEV150 BEV200 BEV250 BEV300 Conventional BEV150 BEV200 BEV250 BEV300 Conventional BEV150 BEV200 BEV250 BEV300 Battery pack Medium car Sport utility vehicle Medium car Sport utility vehicle 2018 2025 FIGURE 5.36 Vehicle technology costs for ICEs and BEVs for 2018 and 2025 for the medium car and SUV classes. The figure shows the level of detail for the cost analysis's engine-related components (yellow)
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The BEV150 vehicles achieve price parity soonest, crossing the conventional vehicle line by 2023–2026. The longer-range BEV300s achieve price parity 4–5 years later than the BEV150s in each case: this is primarily owing to longer-range BEVs having larger battery packs, thus adding substantial costs over the shorter-electric-range versions of the same vehicle type.
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132 ASSESSMENT OF TECHNOLOGIES FOR IMPROVING LIGHT-DUTY VEHICLE FUEL ECONOMY -- 2025–2035 Conventional PHEV20 PHEV40 PHEV60 BEV150 BEV200 $35,000 Small car Vehicle price $30,000 $25,000 $20,000 $15,000 2020 2022 2024 2026 2028 2030 $50,000 Medium car $45,000 Vehicle price $40,000 $35,000 $30,000 $25,000 2020 2022 2024 2026 2028 2030 $50,000 Crossover $45,000 Vehicle price $40,000 $35,000 $30,000 $25,000 2020 2022 2024 2026 2028 2030 $70,000 Sport utility vehicle $60,000 Vehicle price $50,000 $40,000 $30,000 2020 2022 2024 2026 2028 2030 Pickup $60,000 Vehicle price $50,000 $40,000 $30,000 2020 2022 2024 2026 2028 2030 FIGURE 5.37 Price of conventional and electric vehicles for five classes for 2020–2030.
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FINDING 5.18: Battery electric vehicles with increasing electric range are expected to reach first-cost parity with combustion vehicles during 2025–2030 for companies moving to high-production volume. Reducing battery cost in addition to meeting specifications for greater durability and rapid charging capabilities will widen their appeal.
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Slow Charging: Pros and Cons for the New Age of Electric Vehicles." In EVS24 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium. Stavanger, Norway.
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2018. "Electric Vehicle Sales Forecast and the Charging Infrastructure Required Through 2030." Edison Electric Institute.
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2020. Public charging infrastructure for plug-in electric vehicles: What is it worth?
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2018. A review of consumer preferences of and interac tions with electric vehicle charging infrastructure.
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2020a. Exploring electric vehicle charging patterns: Mixed usage of charging infrastructure.
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2019. Estimating Electric Vehicle Charging Infrastructure Costs Across Major U.S.
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2013. Cost-effectiveness of plug-in hybrid electric vehicle battery capacity and charging infrastructure investment for reducing US gasoline consumption.
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2012. Battery electric vehicle driving and charging behavior observed early in the EV Project.
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2019. Battery versus infrastructure: Tradeoffs between battery capacity and charging infrastructure for plug-in hybrid electric vehicles.
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2018. A real-time battery thermal management strategy for connected and automated hybrid electric vehicles (CAHEVs)
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