The battery is the critical technology for electric vehicles, providing both energy and power storage. Unfortunately, the weak link of batteries has been their low energy storage capacity-on a weight basis, lower than gasoline by a factor of 100 to 400. Power capacity may also be a problem, especially for some of the higher temperature and higher energy batteries. In fact, power capacity is the more crucial factor for hybrid vehicles, where the battery’s major function is to be a load leveler for the engine, not to store energy.1 Aside from increasing energy and power storage, other key goals of battery R&D are increasing longevity and efficiency and reducing costs.
Numerous battery types are in various stages of development. Although there are multiple claims for the efficacy of each type, there is a large difference between the performance of small modules or even full battery packs under nondemanding laboratory tests, and performance in the challenging environment of actual vehicle service or tests designed to duplicate this situation. Although the U.S. Advanced Battery Consortium is sponsoring such tests, the key results are confidential, and much of the publicly available information comes from the battery manufacturers themselves, and may be unreliable. Nevertheless, it is quite clear that a number of the batteries in development will prove superior to the dominant conventional lead acid battery,2 though at a higher purchase price. Promising candidates include advanced lead acid (e.g., woven-grid semi-bipolar and bipolar) with specific energy of 35 to 50 Wh/kg, specific power of 200 to 900 W/kg,3 and claimed lifetimes of five years and longer; nickel metal hydride with 80 Wh/kg and 200 W/kg specific energy and power, and claimed very long lifetimes; lithium polymer, considered potentially to be an especially “EV friendly” battery (they are spillage proof and maintenance free), that claims specific energy and power of 200 or more Wh/kg and 100 or more W/kg; lithium-ion, which has demonstrated specific energy of 100 to 110 Wh/kg; and many others. The claimed values of battery lifetime in vehicle applications should be considered extremely uncertain. With the possible exception of some of the very near-term advanced lead acid batteries, each of the battery types has significant remaining challenges to commercialization—high costs, corrosion and thermal management problems, gas buildup during charging, and so forth. Further, the history of battery commercialization demonstrates that bringing a battery to market demands an extensive probationary period: once a battery has moved beyond the single cell stage, it will require a testing time of nearly a decade or more before it can be considered a proven production model.
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Advanced Automotive Technology: Visions
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