Differential voltage analyses of high-power lithium-ion cells

We characterized high-power lithium-ion cells in terms of performance and cycle- and calendar life at 45 °C. Among other parameters, we measured the C/25 capacity every 4 weeks during the test. Differentiation of the C/25 voltage versus capacity data with respect to capacity yielded dV/dQ curves. Analysis of Q0 dV/dQ curves has shown that capacity fade in high-power lithium-ion cells can be complex. From the analysis, the anode material in a significant fraction of the cells showed two types of capacity loss. The loss of accessible material tended to happen early in cell life, either during formation or during the first 4 weeks of testing. Most likely this was caused by a physical rather than chemical process. After 4 weeks, the principal cause of capacity loss was side reactions.