Differential voltage analyses of high-power lithium-ion cells. 4. Cells containing NMC

Cells with and without a LiC(2)O(4)BF(2) electrolyte additive and that contained Li(1.05)(Mn(1/3)Co(1/3)Ni(1/3))(0.95)O(2) (NMC) positive electrodes were tested for calendar and cycle life at 60% state of charge. The temperatures used in these tests were 25 and 45 degrees C (cycle life) and 45 and 55 degrees C (calendar life). An analysis of the C/25 capacity data shows that the C/25 capacity decreases with the square root of time. The additive slowed down the rate of capacity decline. The C/25 data were subjected to differential voltage analysis to determine the possible cause of the capacity decrease and at which electrode the capacity decrease was occurring. Data from full cells and half-cells were compared to elucidate individual electrode contributions. This analysis indicated that lithium-capacity-consuming side reactions were Occurring primarily at the negative electrode. (C) 2009 Elsevier B.V. All rights reserved.