Ternary Inert Element Co‐Doping: a New Approach to Stable 4.7 V LiCoO ₂

LiCoO₂ (LCO) has long dominated the cathode materials in portable electronic batteries due to its high volumetric energy density. However, the pursuit of higher voltages to achieve larger capacities remains a challenge due to severer structural degradation. Herein, a ternary inert element co-doping strategy that can greatly improve the structure stability of LCOs at elevated voltages is reported. Mg and Ni doping at Li site support the layered structure in the highly delithiated state, while Ni also facilitates the separation of O 2p and Co 3d orbits, thereby suppressing oxygen loss. Meanwhile, Al doping at Co site suppresses the distortion of Co-O octahedra and stabilizes the Co layers. The synergistic effects of Al, Mg and Ni co-doping inhibit the irreversible H3-H1-3 phase transitions and mitigate internal stress accumulation. The Al-Mg-Ni co-doped LCO exhibits a capacity of 221 mAh g^-1 with a capacity retention of 65.5% after 1500 cycles at 4.6 V. At a higher voltage of 4.7 V, it delivers a capacity of 225.8 mAh g^-1 with a capacity retention of 58.6% after 600 cycles. This multiple inert elements co-doping strategy gives an effective method for stabilizing the high-voltage LCO and other related layered oxide materials.