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

Abstract

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.