Performance of high-power lithium-ion cells under pulse discharge and charge conditions

Lithium-ion cells being designed for transportation applications must sustain high current pulses under rapid discharge and rapid charge conditions without significant degradation of cell performance. In this article we examine the pulse discharge and charge performance of cells, containing a LiNi0.8Co0.15Al0.05O2-based cathode, a graphite-based anode, and a LiPF6-bearing EC:EMC electrolyte, at current rates ranging from 3 to 25 C. Impedance data indicate that 18650-type cells containing this chemistry can withstand 18s discharge pulses at rates up to 17C in the 3.7-4.0V voltage window. Data from cells containing a LiSn micro-reference electrode show that the positive electrode impedance increases, whereas the negative electrode impedance decreases, with increasing magnitude of the discharge current pulse. The discharge pulse-current that can be sustained by the cell is limited by lithium diffusion into oxide particles of the positive electrode. Copyright (C) 2009 John Wiley & Sons, Ltd.