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.