The structural and thermal stabilities of the layered Li(Ni1/3Co1/3Mn1/3)O2 cathode materials under high rate cycling and abusive conditions are investigated using the commercial 18650 Li(Ni1/3Co1/3Mn1/3)O2/graphite high power batteries. The Li(Ni1/3Co1/3Mn1/3)O2 materials maintain their layered structure even when the power batteries are subjected to 200 cycles with 10C discharge rate at temperatures of 25 and 50°C, whereas their microstructure undergoes obvious distortion, which leads to the relatively poor cycling performance of power batteries at high charge/discharge rates and working temperature. Under abusive conditions, the increase in the battery temperature during overcharge is attributed to both the reactions of electrolyte solvents with overcharged graphite anode and Li(Ni1/3Co1/3Mn1/3)O2 cathode and the Joule heat that results from the great increase in the total resistance (R cell) of batteries. The reactions of fully charged Li(Ni1/3Co1/3Mn1/3)O2 cathodes and graphite anodes with electrolyte cannot be activated during short current test in the fully charged batteries. However, these reactions occur at around 140°C in the fully charged batteries during oven test, which is much lower than the temperature of about 240°C required for the reactions outside batteries.