The Synergetic Effects of Ru and Al Co-Doping for Improved Cyclability of LiCoO₂ at High Voltages

LiCoO₂ is one of the most extensively deployed cathode materials in commercial lithium-ion batteries. However, it remains a challenge to fulfill the potential specific capacity of LiCoO₂ during long-term cycling, due to the lattice degradations in deep delithiation states. Herein, a dual doping scheme based on Ru and Al is explored, which improves the cyclability of LiCoO₂ at high voltages through synergistically reconfiguring electronic structure and stabilizing lattice structure. It is well known that the doped Al will serve as a strong positively charged center and restrain the lattice distortion. The doping of Ru suppresses the occupied O:2p states below Fermi level and stabilizes oxygen redox during cycling. The proposed dual doping strategy improves the accessible energy density and cyclability of LiCoO₂ at increased voltages significantly. For example, the dual doped LiCoO₂ performs 19% higher energy density at 4.57 V versus Li⁺/Li than the pristine one. In addition, an initial capacity of 197 mAh g⁻¹ and 86% capacity retention after 100 cycles are achieved from 3.00 to 4.53 V versus Li⁺/Li. This study sheds a light on the fundamental principles for the development of high-voltage LiCoO₂ and other layered oxide cathode materials with high energy density and excellent cyclability.