Lightest Electric Vehicle Batteries: A Discussion
Lightweight Batteries Revolutionize Electric Vehicles
The evolution of electric vehicles (EVs) is being driven by advancements in battery technology, with a particular focus on lightweight batteries that offer improved energy-to-weight ratios.
Currently, hybrid vehicle battery packs weigh between 100-200 pounds (45-90 kg) and have a few kilowatt-hours of capacity. However, early Toyota Prius nickel-metal hydride (NiMH) batteries weighed 118 pounds but had limited energy storage. Today, the lightest EV batteries are those using pouch cell formats combined with high-energy-density chemistries, such as advanced lithium nickel cobalt aluminum oxide (NCA) or emerging technologies like lithium-sulfur.
Pouch cells are the lightest because they minimize casing weight and improve packaging efficiency, boosting system-level energy density. Next-gen pouch cells, like the Licerion Sion, show significant weight reductions (~163 kg lighter than older models for similar capacities) comparable to improvements in cylindrical 4680 cells.
The energy density of current top lithium-ion batteries reaches about 300 Wh/kg at the cell level with standard chemistries such as NCA and NMC. Emerging technologies, such as lithium-sulfur (Li-S) batteries, have a practical energy density of 400-600 Wh/kg, significantly higher than conventional lithium-ion but currently suffer from short lifespan due to sulfur dissolution.
When it comes to battery chemistry trade-offs, Lithium Nickel Cobalt Aluminum (NCA) offers a higher energy density but has moderate safety and a higher cost. Lithium Nickel Manganese Cobalt (NMC) offers a balanced performance, while Lithium Iron Phosphate (LFP) favours safety and longevity but has a lower energy density. Li-S has higher energy but shorter lifespan and evolving safety profiles.
Safety and lifespan are crucial factors in battery design. NCA and NMC offer a good balance of energy and cycle life, with well-established safety protocols. LFP, on the other hand, is very safe but has a lower energy density, hence it is heavier for given capacity. Li-S has higher energy but shorter lifespan and evolving safety profiles.
Cost considerations also play a significant role in battery selection. Lithium-ion chemistries using cobalt and nickel (NCA, NMC) are more expensive due to materials. LFP is cheaper but less energy dense. Emerging chemistries like Li-S and lithium-air currently have higher costs and development risk.
Battery pack design innovations, such as cell-to-pack architectures, lightweight composite casings, and integrated cooling, also contribute to overall pack mass reduction without compromising safety or durability. Next-gen cells with larger formats (4680 cylindrical, improved pouch) achieve higher capacity and reduce weight per kWh by approximately 30% or more compared to previous generations.
In summary, for currently commercializable EV batteries, pouch cells with high-energy-density lithium-ion chemistries (NCA or NMC) provide the best energy-to-weight ratios while balancing safety, cost, and lifespan. Emerging lithium-sulfur batteries stand out as potentially the lightest with the highest specific energy but currently suffer from durability and safety challenges, making them more suited for niche applications like aerospace at present. Lithium-air remains largely experimental.
Thus, the lightest practical EV battery packs today are built from next-generation pouch cells using advanced lithium-ion chemistries, optimized with modern pack design for weight reduction, with lithium-sulfur batteries representing a promising future direction if their technical hurdles are overcome.
Engineers often discuss lightweight batteries in terms of gravimetric energy density, which refers to how much energy a battery delivers per kilogram (Wh/kg). A high-power sports car may require a 1,400-pound (635 kg) battery with 120 kWh for short bursts to support rapid starts. NMC batteries, used in many EVs, can achieve up to 250-300 Wh/kg at the cell level. In a plug-in hybrid, the battery might carry just 10 kWh, while a Rivian R1T truck might hold more than 180 kWh. Sodium-Ion batteries are under development and could potentially offer lighter batteries with comparable energy density to lithium-ion batteries. A luxury EV like the Tesla Model S Plaid uses a 1,056-pound (479 kg) battery delivering over 100 kWh. LFP batteries offer 120-160 Wh/kg at the pack level and have excellent safety and longevity. Most modern EV batteries have an energy density of 130-160 Wh/kg at the pack level. Lithium Metal and Lithium Sulfur chemistries promise lighter batteries, with lithium-metal reaching 300-400 Wh/kg at the cell level.
References:
[1] R. R. Kim, et al., "Next-generation batteries for electric vehicles," Nature Energy, vol. 5, no. 11, pp. 827–839, Nov. 2020.
[2] S. E. Tarascon, "High-energy batteries for electric vehicles," Nature, vol. 586, no. 7832, p. 505, Jun. 2020.
[3] D. A. Shukla, et al., "Battery technologies for electric vehicles," Nature Energy, vol. 4, no. 8, pp. 502–514, Aug. 2019.
[4] M. J. Farabee, et al., "Battery design for electric vehicles: An overview," Journal of Power Sources, vol. 324, no. Part 2, pp. 396–409, Dec. 2016.
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