The Advanced Lead Acid Battery Development project was funded for a total of $67,000 over a two-year period. Researchers at the University of Idaho have been investigating the possibility of using lead acid batteries in electric and hybrid vehicles for more than ten years, and the funding from University Transportation Centers Program through NIATT helped support this continuing effort.
The ultimate objective of the funded work was to develop a high performance, long life, lead acid battery for a range-extended hybrid electric vehicle (REHEV). Although we realized that the amount of funding available through UTC was completely inadequate for achieving our objective, we were hopeful that we could use the funds to generate additional outside funding with which we could develop a larger program.
The lead acid battery uses horizontal plates and improved conductor structures to provide high power discharge capabilities (Fig. 1). Our first task was to design a baseline cell to provide 35 w-hr/kg at the two-hour discharge rate, 200 w-hr/kg at 100 percent state of charge (SOC) and 1000 cycles at 80 percent depth of discharge (DOD). This initial design was developed with the expectation of establishing a cell development program with battery manufacturers. The baseline cells, as developed, could serve as the foundation for the future development of advanced cells and eventually, the commercialization of a REHEV.
In the work performed to date, we used conductivity and diffusion computer models previously developed at the University of Idaho, to evaluate the performance of advanced cells having high performance plates. These plates had various conductive and non-conductive additives incorporated into the positive paste to improve the energy performance of the battery. Our models show that, in theory, we should be able to increase the energy performance of the baseline cells from 30-35 w-hr/kg to 60-65w-hr/kg.
Our project also involved improving the conductivity and diffusion models. The improved models were then used to evaluate the occurrence of oxygen evolution in the positive plate so we could understand how the positive active material deteriorates with cycling.
Further development of these models could ultimately be used to understand the failure mechanisms associated with sealed, lead acid batteries and to investigate methods for increasing their life.