Selectively fluorinated aromatic lithium salts regulate the solvation structure and interfacial chemistry for...

Solid polymer electrolytes suffer from the polymer-dominated Li⁺ solvation structure, causing unstable electrolyte/electrode interphases and deteriorated battery performance. Here, we design a class of selectively fluorinated aromatic lithium salts (SFALS) as single conducting lithium salts to regulate the solvation structure and interfacial chemistry for all-solid-state lithium metal batteries. By tuning the anionic structure, the Li⁺-polyether coupling is weakened, and the Li⁺-anion coordination is enhanced. The hydrogen bonding between the SFALS and polymer matrix induces a special "triad"-type solvation structure, which improves the electrolyte homogeneity and mechanical strength, and promotes the formation of an ultrathin and robust Li₂O-rich solid electrolyte interphase. Therefore, the stable cycling of more than 1650 cycles (Coulombic efficiency, 99.8%) for LiFePO₄/Li half cells and 580 cycles (97.4% capacity retention) for full cells is achieved. This molecular engineering strategy could inspire further advancements of functional lithium salts for practical application of all-solid-state lithium metal batteries.