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

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_xO_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.