Regulating Li ⁺ Solvation, Transport, and Interfacial Robustness via Voltage Resistant Cationic Copolymer Design for Safe Lithium Metal Batteries

Abstract The application of polymer electrolytes in high‐performance lithium metal batteries (LMBs) is usually restricted by their sluggish ion conduction, and inferior electrochemical stability compatibility with electrodes. Here, a cationic copolymer‐based electrolyte PMC is developed. The copolymer of acryloyloxyethyl trimethylammonium bis(trifluoromethanesulfonyl)imide (AET⁺TFSI⁻), hexafluorobutyl acrylate (HFBA), and N, N′‐methylenebisacrylamide (MBA) is synthesized by photopolymerization with carbonate electrolytes. The copolymer facilitates the lithium salt dissociation, adjusts Li ⁺ interaction with the polymer chain, regulates Li ⁺ solvation environment, and thus promotes fast ion transport (ionic conductivity of 7.19 × 10 ⁻⁴ S cm ⁻¹ , Li ⁺ transference number of 0.84) and uniform Li deposition. PMC is electrochemically stable up 4.43 V versus Li ⁺ /Li and forms stable solid electrolyte interphase (SEI) with the anode, supporting long‐term stability (1500 h) of lithium plating/stripping test at 0.2 mA cm ⁻² , 0.2 mAh cm ⁻² . The Li/PMC/LiFePO ₄ cell shows excellent stability at 1C and a high specific capacity of 134.2 mAh g ⁻¹ even at 5C. PMC forms voltage‐resisting, LiF‐rich cathode electrolyte interface (CEI) with LiCoO ₂ . The Li/PMC/LiCoO ₂ cell shows excellent stability over 100 cycles with a capacity retention of 96%. Nonflammability of PMC and high safety of PMC‐based pouch type cells are confirmed. This work provides a facile method toward high‐performance and safe LMBs.