Surface Mn Oxidation State Controlled Spinel LiMn2O4 as a Cathode Material for High‐Energy Li‐Ion Batteries

Spinel lithium manganese oxide (LiMn 2 O 4 ) has attracted much attention as a promising cathode material for large‐scale lithium ion batteries. However, its continuous capacity fading at elevated temperature is an obstacle to extended cycling in large‐scale applications. Here, surface Mn oxidation state controlled LiMn 2 O 4 is synthesized by coating stoichiometric LiMn 2 O 4 with a cobalt‐substituted spinel, for which stoichiometric LiMn 2 O 4 is used as the starting material and onto which a Li x Mn y Co z O 4 layer is coated from an acetate‐based precursor solution. In the coated material, the concentrations of both cobalt and Mn 4+ ions vary from the surface to the core. the former without any lattice mismatch between the coating layer and host material. Cycle tests are performed under severe conditions, namely, high temperature and intermittent high current load. During the first discharge cycle at 7 C and 60 °C, a high energy and power density are measured for the coated material, 419 and 3.16 Wh kg −1 , respectively, compared with 343 and 3.03 Wh kg −1 , respectively, for the bare material. After 65 cycles under severe conditions, the coated material retains 82% and ≈100% of the initial energy and power density, respectively, whereas the bare material retains only ≈68% and ≈97% thereof.