Randy Ben Wright

Effect of cathode composition on capacity fade, impedance rise and power fade in high-power, lithium-ion cells ☆

We tested the effect of Al concentration on the performance of lithium-ion cells. One set of cells contained a LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathode and the other, LiNi{sub 0.8}Co{sub 0.10}Al{sub 0.10}O{sub 2}. The cells were calendar- and cycle-life tested at several temperatures, with periodic interruptions for reference performance tests that were used to gauge capacity and power fade as a function of time. The C{sub 1}/25 capacity fade in the cells displayed t{sup 1/2} dependence. The capacity fade of the 10% Al-doped cells tested at 45 {sup o}C was similar to that of the 5% Al-doped cells at 25 {sup o}C. The impedance rise and power fade were also sensitive to the Al concentration. For the one common temperature investigated (i.e., 45 {sup o}C), the 10% Al-doped cells displayed higher impedance rise and power fade than the 5% Al-doped cells. Additionally, the time dependence of the impedance rise displayed two distinct kinetic regimes; the initial portion depended on t{sup 1/2} and the final, on t. On the other hand, the 10% Al-doped cells depended on t{sup 1/2}2 only.

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

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.