In our efforts to develop low cost high-power Li-ion batteries with excellent safety, as well as long cycle and calendar life, lithium manganese oxide spinel and layered lithium nickel cobalt manganese oxide cathode materials were investigated. Our studies with the graphite/LiPF6/spinel cells indicated a very significant degradation of capacity with cycling at 55°C. This degradation was caused by the reduction of manganese ions on the graphite surface which resulted in a significant increase of the charge-transfer impedance at the anode/electrolyte interface. To improve the stability of the spinel, we investigated an alternative salt that would not generate HF acid that may attack the spinel. The alternative salt we selected for this work was lithium bisoxalatoborate, LiB(C2O4)2 (“LiBoB”). In this case, the graphite/LiBoB/spinel Li-ion cells exhibited much improved cycle/calendar life at 55°C and better abuse tolerance, as well as excellent power. A second system based on LiNi1/3Co1/3Mn1/3O2 layered material was also investigated and its performance was compared to commercial LiNi0.8Co0.15Al0.05O2. Cells based on LiNi1/3Co1/3Mn1/3O2 showed lower power fade and better thermal safety than the LiNi0.8Co0.15Al0.05O2-based commercial cells under similar test conditions. Li-ion cells based on the material with excess lithium (Li1.1Ni1/3Co1/3Mn1/3O2) exhibited excellent power performance that exceeded the FreedomCAR requirements.