Modulating Anion Solvation Competitiveness in Gel Polymer Electrolytes to Construct Robust Interphases for Long-Life Li-SPAN Batteries

Abstract

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for lithium-sulfur batteries, yet conventional ether/ester electrolytes exhibit poor compatibility with both SPAN and lithium metal, making it difficult to simultaneously achieve interfacial stability and safety. In this work, we propose a gel polymer electrolyte (FETB-GPE), synthesized via copolymerization of a fluorinated acrylate monomer and a multifunctional crosslinker within a weakly solvating electrolyte composed of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC). By introducing lithium difluoro(oxalato)borate (LiDFOB), the Li⁺ solvation structure is optimized, increasing the proportion of contact ion pairs (CIPs) and ion aggregates (AGGs), which facilitates the formation of a LiF and Li_xBO_yF_z rich anion-derived interphase. Molecular dynamics simulations and analyses confirm that FETB-GPE enables uniform Li deposition and enhances Li⁺ transport kinetics. Furthermore, symmetric Li||Li cells exhibit highly reversible Li plating/stripping for 4000 h, while Li||Cu cells deliver an average coulombic efficiency of 99.1% at 0.5 mA cm⁻². Consequently, Li||SPAN cells achieve exceptional cyclability with 90.29% capacity retention after 1500 cycles at 5 C and operate stably for over one year at 0.2 C. This work establishes a design principle for polymer electrolytes tailored to Li||SPAN batteries, paving the way for the development of solid-state lithium-sulfur systems.