Fluorinated Gel Polymer Electrolytes Based on Deep Eutectic Electrolytes for High-Voltage Lithium Metal Batteries

The instability of eutectic electrolytes under high-voltage operation and their poor compatibility with lithium metal limit their application in lithium metal batteries. In this work, a fluorinated gel polymer electrolyte based on deep eutectic electrolytes (FEGPE) was constructed via in situ polymerization of trifluoroethyl methacrylate (TFEMA) within a methylacetamide (MAc)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/fluoroethylene carbonate (FEC)-based deep eutectic solvent (DES) electrolyte. The resulting cross-linked polymer framework immobilizes the eutectic liquid phase while preserving rapid Li + transport. Incorporation of the fluorinated polymer backbone modifies intermolecular interactions in the eutectic matrix, promoting lithium salt dissociation and altering the Li + solvation structure. The incorporated fluorinated polymer backbones enhance the interfacial stability between the FEGPE and lithium metal, enabling a symmetric Li battery to maintain stable lithium plating/stripping for over 1300 h. The LiFePO 4 |Li battery with the FEGPE electrolyte delivers a high capacity retention of 82.1% after 800 cycles at 0.5C. In addition, the fluorinated polymer backbone improves the electrochemical stability of the electrolyte and, together with the gelation strategy, results in improved cycling stability of the LiMn 2 O 4 |Li battery with the FEGPE electrolyte compared to the DES electrolyte. This work demonstrates that polymer backbone fluorination provides an effective strategy to stabilize eutectic gel polymer electrolytes for high-voltage lithium metal batteries.