Abstract: Rechargeable lithium-oxygen batteries (LOBs) have received incremental attention owing to their high energy density and applicability to mobile devices and electric vehicles. However, the lack of robust, low-cost, and environmentally benign bifunctional catalysts is a major impediment to the commercial application. The introduction of vacancies is one of the effective strategies to enhance the performance of cathode catalysts for lithium-oxygen batteries, but the preparation is complicated. In this work, needle-like microsphere cathode catalysts of nickel-cobalt oxide containing cationic vacancies are constructed by controlling the annealing temperature. It is demonstrated that the presence of cationic vacancies can modulate the electronic structure of the catalyst, reduce the energy barrier for the oxygen electrode reaction, meanwhile enhance the bifunctional catalytic activity. Impressively, the nickel-cobalt oxide-based LOB with cationic vacancies exhibits large specific capacity (12,205 mAh g^-1 at 200 mA g^-1) and good durability. This work provides worthwhile insight into the formation and catalytic enhancement mechanism of transition metal oxide catalysts with cationic vacancies, and to some extent, the creation of efficient and low-cost oxygen electrocatalysts for LOBs.

Key words: Li-O₂ batteries, Metal oxides, Cation vacancies, Catalytic kinetic