Li[Ni0.8Co0.15Al0.05]O2 particles are modified with AlF3 as a new coating material. Even though the initial discharge capacity of the coated Li[Ni0.8Co0.15Al0.05]O2 is almost the same as that of the pristine material, the capacity retention and the thermal stability, in a highly oxidized state are both significantly improved. This effect is attributed to the thin AlF3 coating layer protecting the oxidized cathode particles from attack by hydrogen fluoride in the electrolyte.