Cycle Life Studies of Advanced Technology Development Program Gen 1 Lithium Ion Batteries

Abstract

This report presents the test results of a special calendar-life test conducted on 18650-size, prototype, lithium-ion battery cells developed to establish a baseline chemistry and performance for the Advanced Technology Development Program. As part of electrical performance testing, a new calendar-life test protocol was used. The test consisted of a once-per-day discharge and charge pulse designed to have minimal impact on the cell yet establish the performance of the cell over a period of time such that the calendar life of the cell could be determined. The calendar life test matrix included two states of charge (i.e., 60 and 80%) and four temperatures (40, 50, 60, and 70°C). Discharge and regen resistances were calculated from the test data. Results indicate that both discharge and regen resistance increased nonlinearly as a function of the test time. The magnitude of the discharge and regen resistance depended on the temperature and state of charge at which the test was conducted. The calculated discharge and regen resistances were then used to develop empirical models that may be useful to predict the calendar life or the cells.