Understanding the Structure-Performance Relationship of Lithium-Rich Cathode Materials from an Oxygen-Vacancy Perspective.

Li-rich layered oxide cathode materials are regarded as an attractive candidate of next-generation Li-ion batteries (LIBs) to realize an energy density of >300 Wh kg-1. However, challenges such as capacity fade, cycle life, oxygen release, and structural transformation still restrain its practical application. Micro/nanotechnology is one of the effective strategies to enhance its structural stability and electrochemical performance. An in-depth understanding of the relationship between micro/nanostructures and the electrochemical performance of Li-rich layered oxides is undoubtedly important for developing high-performance cathode materials. Herein, Li1.2Ni0.13Co0.13Mn0.54O2 with different micro/nanostructures including irregular particles, microspheres, microrods, and orthogonal particles are synthesized. Starting from the amount of surface oxygen vacancies in the different structures, the influence of oxygen vacancies on every step during the charge-discharge processes is analyzed by experimental characterizations and theoretical calculations. It is indicated that intrinsic oxygen vacancies can enhance the electrical conductivity and decrease the energy barrier for ion migration, which exerts a significant influence on promoting the kinetics and capacity. Among the different micro/nanostructures, microrods with abundant oxygen vacancies can not only promote lithium ion transport but also stabilize a cathode electrolyte interface (CEI) film by adjusting the distribution of surface elements with lower nickel content. The microrods deliver an initial discharge capacity of up to 306.1 mAh g-1 at 0.1C rate and a superior cycle performance with a capacity retention of 91.0% after 200 cycles at 0.2C rate.