Enhanced Cycling Stability of NCM811 Cathodes at High C-Rates and Voltages via LiMTFSI-Based Polymer Coating

Improving the cycling stability in Ni-rich LiNi_xCo_yMn_1-x-yO₂ (NCM) cathodes, particularly under high C-rates and elevated voltages, remains a significant challenge in lithium battery technology. A novel polymer coating based on lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate (LiMTFSI), a material commonly used in solid polymer electrolytes (SPEs), is applied to LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes. This coating improves electrochemical stability at high C-rates (2C and 4C) and voltages up to 4.5 V, compared to uncoated cathodes, enabling reduced charging times (e.g., 1 h at 1C to 15 min at 4C) while maintaining relatively enhanced cycling performance. Mechanistically, the coating helps suppress surface phase transitions to the rock-salt phase, mitigates transition metal dissolution, and facilitates lithium-ion transport at the cathode-electrolyte interface. These combined effects contribute to enhanced cycling durability under demanding conditions. Galvanostatic intermittent titration technique (GITT) analysis further supports that the coating promotes interfacial lithium-ion conduction without acting as an insulating barrier. Additionally, the coated NCM811 electrodes exhibit improved rate performance. This study shows that repurposing SPE-derived monomers as cathode surface modifiers provides a practical route to improving rapid-charging capability, energy utilization, and long-term operational stability in lithium batteries.