BOX 1-3: Battery TechnologiesThe 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.