AbstractMnOx‐surface‐modified Li1.2Ni0.4/3Co0.4/3Mn1.6/3O2 cathode materials have been prepared by solid‐state reaction with varying post‐annealing temperatures. The MnOx coating layers are homogeneous and crystalline with a thickness of 10 nm. Below a current rate of 0.1 C and in the voltage range of 2.0–4.8 V, the MnOx‐modified material, which has been post‐annealed at 300 °C, shows high discharge capacities of 308, 320, and 363 mAh g−1 at 20, 40, and 60 °C, respectively. Meanwhile, this sample shows good rate capability that can deliver discharge capacities of 278 and 178 mAh g−1, respectively, at 1 C and 10 C, both tested at 20 °C. However, the modified sample displays more serious capacity degradation compared to the pristine sample. The significantly higher extent of the transition metal dissolution from the modified sample is proved by compositional analysis. Cycling performance could be improved by replacing the conventional electrolyte with an ionic‐liquid‐based electrolyte.