Bringing an Advanced Battery to Market

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 ambient, 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 sodium-sulphur battery is illustrative. Early prototype batteries were available during the late- 1980s and tested by Mercedes and BMW. These prototypes had a calendar life of about six months and were plagued by excessive failures. Second generation prototypes were supplied to BMW and Ford, and these doubled calendar life to about one year. More recently, two of the Ford Ecostar vehicles have reported fires during charging. ABB is currently providing third generation prototypes to Ford, but even these are not considered production ready. ABB is willing to guarantee a calendar life of only one year in EV services for its latest sodium-sulfur prototypes, although actual life may be two to three years.

Although the sodium-sulfur battery may pose especially difficult development problems, such experiences are reported even for advanced lead acid batteries whose basic principles have been utilized introduction batteries for many decades. INEL reports that the Sonnenschein advanced lead acid battery has demonstrated very good cycle life in the laboratory, but that its in-use reliability is very poor.88 Once a battery has moved beyond the single-cell stage, manufacturers estimate that a minimum of three years per stage is required to move to the module, prototype battery, and preproduction battery stages, and a total testing time of nearly a decade will be necessary for a proven production model.

This estimate of time assumes that problems are successfully tackled in each stage and that manufacturing processes can replicate cells with very little variability in mass production--an assumption that remains unproven for almost all advanced battery types demonstrated to date. Based on this, it is reasonable to conclude that batteries whose status is listed “3” in Table 3-12 will not be mass produced until 2000 at the earliest.

Vehicle lifetime costs depend on the battery durability, an issue about which little is known except for the fact that usable lifetimes are quite different for different batteries. It should be noted that battery life depends on the desire of the battery system and its usage pattern. Also, there are tradeoffs between battery life and cost, specific energy, specific power, and user specification of end-of-life criteria. For example, a battery may have very different “life,” if the end-of-life criterion is set at 90 percent of initial energy density, or is set at 80 percent. Nevertheless, for almost any set of reasonable criteria for end-of-life that are acceptable to auto manufacturers, there are currently no advanced batteries that have demonstrated an average fiveyear life in the field, nor have any battery manufacturers been willing to warranty a battery for this period. Hence, even the prospect of five-year life in customer service is unproven and is an input assumption for most analyses of battery costs.

Cost per kilowatt-hour of storage capacity in table 3-9 is based on production rates of at least 10,000 modules per month and are estimated from the educated guesses of battery manufacturers, (except for the nickel-metal hydride battery where the cost controversy was noted earlier). The cost estimates in the table are based on both battery and auto manufacturer inputs. Although OTA has attempted to include only estimates that appear realistic given current knowledge, these estimates may still be unreliable as most battery types are not yet production ready.