Fluorinated Deep Eutectic Gel Electrolytes with Simultaneously Enhanced Mechanical Strength and Ionic Conductivity for Solid-State Lithium Metal Batteries.

Abstract

Gel polymer electrolytes for lithium-metal batteries face an inherent trade-off between mechanical strength and ionic conductivity. Herein, we present a molecular-level strategy that harnesses competitive hydrogen-bonding interactions to spontaneously generate a nanoscale phase-separated architecture in the deep eutectic gel (DEG) electrolyte. Through one-step in-situ copolymerization of acrylamide and N,N-dimethylacrylamide within a trifluoromethyl-functionalized deep eutectic solvent comprising N-methyl-2,2,2-trifluoroacetamide (TNMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), an interpenetrating network is formed, in which rigid polyacrylamide-rich domains reinforce the matrix while polydimethylacrylamide-rich channels facilitate ion transport. Driven by the competition between polymer-polymer and polymer-solvent hydrogen bonds, the resulting DEG electrolyte achieves an exceptional ionic conductivity of 2.99 mS cm^-1 at 30°C, an excellent Li⁺ transference number of 0.78, and a remarkable tensile strength of 11.4 MPa with 473% elongation. Meanwhile, TNMA, together with TFSI^-, regulates the Li⁺ solvation structure and interfacial chemistry, promoting the formation of a LiF-rich interphase through fluorinated-solvent- and anion-involved interfacial reactions. The resulting Li||Li symmetric cells operate for over 3500 hours (0.1 mA cm^-2), and Li|DEG|NCM811 cells retain 77.5% capacity after 400 cycles at 2 C. This work establishes competitive molecular interactions as a design principle for next-generation gel polymer electrolytes.