suggested that sodium-polymer batteries may be superior to lithium-polymer versions, and could
have lower costs. However, even a prototype EV size battery is possibly several years away.^85As noted, the previous discussion covers only those battery types that are highly regarded
today, but there are numerous other electrochemical couples in various stages of development
with the potential to meet USABC goals. These include nickel-zinc, zinc-bromine, and sodium-
polydisulfide systems; these are being actively researched but need considerable development
before they can become serious contenders. Nickel-zinc and zinc-bromine batteries have energy
densities comparable to Ni-MH batteries but significantly lower power densities of about 100
W/kg, so that they can compete only if costs are low and they have long life.^86 Sodium-
polydisulfide batteries are in a very early stage of development and little is publicly known about
their performance parameters.
Table 3-12 provides a summary of the state-of-the-art for batteries of different types. It is
important to note that the actual usable specific energy and power can differ significantly from the
values listed for some batteries. Lead acid batteries should not be discharged to below 80 percent
DoD, for example, so that usable specific energy is only (40x 0.8) or 32 Wh/kg for the advanced
lead acid battery.
Bringing an Advanced Battery to Market.
Table 3-12 also shows the development status of the batteries, which differs considerably
between battery types. Initial testing of a simple cell at the laboratory is basically a proof-of-
concept, and is utilized to test the stability and output under carefully controlled conditions. A
group of cells aggregated into a module is the first step toward a functional battery, and scaleup,
cell packaging, interconnections between cells, and multiple cell charge and discharge control are
demonstrated in this phase. The development of a prototype EV battery with an overall energy
storage capability of 20 to 40 kwh at a voltage of 200 to 300 V involves collections of modules in
an enclosure with appropriate electrical and thermal management. These batteries typically must
be tested extensively in the real world EV environment to understand the effect of severe
ambients, vibration, cell failures, and cyclically varying discharge rates--all which can have
significant effects on the usable power, energy, and life of a battery that is not properly designed.
A preproduction battery is one that has been redesigned to account for the real world experience,
and is also suitable for mass production. Typically, preproduction batteries are built at modest
volumes of a few hundred per year to ascertain whether the production process is suitable for
high-volume output with low-production variability.
Many new entrants in the advanced battery arena have made bold claims about the availability
of their particular battery designs for commercial use in time to meet the California “ZEV”
requirements for 1998. More established battery manufacturers contest their claims, and have
stated that several years of in-vehicle durability testing is required before a preproduction design
can be completed, as batteries often fail in the severe EV environment. The case of ABB’s
85 There are rumorsof a breakthrough by Valence, Inc., which has a joint venture with Delco Remy in the development of a commercially viable
lithium-polymer prototype battery, but no information 86 is publicly available on actual battery performance.
G.L. Henriksenet al., "Advanced Batteries for Electric Vehicles,” CHEMTECH, November, 1994.