Macromolecular Boron‐Based Salt Enables Dense Interphases for Long‐Cycling Lithium‐Sulfur Batteries

Abstract Lithium‐sulfur (Li‐S) batteries represent a compelling next‐generation energy storage system with practical energy densities exceeding 700 Wh kg −1 , offering a promising pathway beyond current lithium‐ion technology. However, their commercial viability remains constrained by deleterious interfacial reactions between lithium metal anodes and polysulfide‐containing electrolytes. Herein, it is presented a molecular engineering approach through a novel boron‐based salt, lithium perfluoropinacolatoborate (LiFPB), strategically designed to reinforce the solid electrolyte interphase (SEI) for long‐cycling Li‐S batteries. LiFPB anions, featuring higher specific charge (mass‐to‐charge ratio) and larger steric bulk compared to conventional salts, demonstrate enhanced resistance to Helmholtz double‐layer repulsion and increased susceptibility to lithium metal reduction, promoting the formation of a robust SEI enriched with LiF and LiB x O y species. The LiFPB‐containing electrolyte exhibits superior lithium metal compatibility, achieving a high coulombic efficiency of 99.59%. Consequently, Li‐S cells demonstrate markedly improved capacity retention from 50.9% to 75.7% over 200 cycles. This strategy has been successfully scaled to Ah‐level Li‐S pouch cells, achieving practical energy densities of 408 Wh kg −1 with stable cycling over 75 cycles. This work presents an effective approach to developing long‐cycling Li‐S batteries through the rational design of electrolyte salt.