Rate dependent structural changes, cycling stability, and Li-ion diffusivity in a layered–layered oxide cathode material after prolonged cycling

Abstract

Li-Rich layered oxide (LLO) cathode materials, xLi₂MnO₃·(1 − x)LiCoO₂ (0 < x < 1, M = Mn, Ni, Co, etc.) are considered promising cathode materials in Li-ion batteries for large scale applications. This is because they provide high specific capacities of up to 250 mA h g⁻¹. An electrode material with high energy density and high rate capability (fast charging) is required in EVs to enhance mileage and reduce charging time, respectively. The fast-charging capability of Li-ion batteries is largely determined by the electrochemical kinetic behaviors of their electrodes. Therefore, a deeper understanding about the relationship between cycling rate, structural stability, cyclability, and Li-ion diffusivity behaviors of electrode materials is a critical key to explore high-performance electrode materials for EVs and other high rate applications. In this work, the effects of cycling rates on the structural changes, cycling stability and Li-ion diffusion coefficients of a 0.5Li₂MnO₃·0.5LiCoO₂ material were investigated. The results show that the activation of the Li₂MnO₃ component was controlled by the cycling rate. A high cycling rate effectively reduced the Li₂MnO₃ activation and spinel phase evolution, bringing about better cycling stability, and faster Li-ion diffusion after prolonged cycling.