Engineering Surface Structure and Defect Chemistry of Nanoscale Cubic Co₃O₄ Crystallites for Enhanced Lithium and Sodium Storage

Transition metal oxide nanostructures are drawing much attention as promising electrodes for advanced rechargeable batteries. However, due to the intrinsic low electronic conductivity and substantial volume change during cycling, the electrodes usually show low rate capability and poor cycling life. Herein, we report a route combining surface/interface engineering and defect chemistry to tune the lithium storage properties in nanoscale cubic Co₃O₄ crystallites. The Co₃O₄ crystallites were annealed in an inert atmosphere by carefully controlling the temperature, which induces the conformal formation of CoO layers with a tunable thickness on the surface of initial cubes. Microstructural characterizations and electrochemical measurements indicate that the optimized sample possesses a CoO thickness of ∼1.1 nm and shows a reversible lithium storage capacity of 1069.4 mAh·g^–1 after 100 cycles of a current density of 0.1 A·g^–1. A capacity of 807.9 mAh·g^–1 can be obtained at a rate of 5 A·g^–1. The improved lithium storage performance is attributed to the unique CoO–Co₃O₄ interface structure and defect chemistry, which induces a strong electric field at the sharp Co₃O₄–CoO interface according to density functional theory calculations. The optimized sample also shows it improved sodium storage properties. This work thus provides an effective strategy for the design and synthesis of advanced electrode materials for energy applications.