Cells with and without a LiC2O4BF2 electrolyte additive and that contained Li1.05(Mn1/3Co1/3Ni1/3)0.95O2 (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°C (cycle life) and 45 and 55°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.