We tested the effect of Al concentration on the performance of lithium-ion cells. One set of cells contained a LiNi0.8Co0.15Al0.05O2 cathode and the other, LiNi0.8Co0.10Al0.10O2. 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 1/25 capacity fade in the cells displayed t 1/2 dependence. The capacity fade of the 10% Al-doped cells tested at 45°C was similar to that of the 5% Al-doped cells at 25°C. The impedance rise and power fade were also sensitive to the Al concentration. For the one common temperature investigated (i.e., 45°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 1/2 and the final, on t. On the other hand, the 10% Al-doped cells depended on t 1/2 only.