Through a simple mechanical mixing and heating treatment, the surface of commercial LiCoO2 particles was modified by forming a phosphorus-containing surface layer. X-ray diffraction results proved that no second crystalline phase was present after modification. X-ray absorption near edge structure showed that the valence of Co ions decreased with increased heat-treatment temperature. A higher 3.6 V plateau efficiency was observed for the modified powders. Between 2.8 and 4.5 V, the modified powders showed significantly better capacity retention than pristine LiCoO2. After heat-treatment at the optimal temperature of 450 degrees C, the modified LiCoO2 can deliver a reversible 1 C-rate capacity of 164 mAh/g after 50 cycles.