Borate‐Based Surface Coating of Li‐Rich Mn‐Based Disordered Rocksalt Cathode Materials

Upon cycling, Li‐rich Mn‐based disordered rocksalt (DRS) oxyfluoride cathode materials undergo unwanted degradation processes, which are triggered by chemical side reactions or irreversible oxygen redox activity, especially at high voltages and in contact with the electrolyte. A surface coating can be an effective strategy to mitigate these parasitic reactions. However, oxyfluorides generally experience limited stability, which makes the application of coatings requiring high temperatures challenging. For this purpose, this study is dealing with the implementation of a chemically inert and Li ion conducting borate‐based coating at mild‐temperature (300 °C), following a dry process on the Li2Mn2/3Ti1/3O2F particles. Electrochemical characterization, as function of the amount of coating, C‐rate and temperature, indicate that the coated samples possess considerably improved capacity retention and reduced Mn‐dissolution, however, at the cost of a measurable initial capacity loss. The authors further demonstrate that the presence of the coating reduces the interfacial resistance, which is beneficial for Li ion transfer. The 3 wt%‐coated sample loses only 27% of the capacity, where around 130 mAh g−1 after 100 cycles is retained. The utilization of surface modification can open up a path for further development of DRS cathode materials with high performance for Li‐ion batteries. The effect of borate‐based surface coating on the electrochemical performance of a Mn‐based disordered rocksalt oxyfluoride cathode material is demonstrated. A narrow B2O3 layer on top of the particles is formed, contributing significantly to improve the cycling performance with higher Coulombic efficiencies. This feature is likely attributed to preventing direct electrode–electrolyte interaction, resulting in reduced Mn‐dissolution at high voltage.