Electrolyte Anion-Initiated In Situ Polymerization of Dioxolane-Derived Gel Electrolytes for Dendrite-Resistant and Separator-Free Lithium Metal Batteries

The practicality of solid-state lithium metal batteries is limited by poor interfacial contact and low ion conductivity of solid-state electrolytes. Herein, we report a gel polymer electrolyte composed of LiN(SO₂F)₂ and polymerized dioxolane prepared via in situ ring-opening polymerization triggered by radicals without the need for additional initiators and separators. Theoretical and experimental studies revealed a polymerization mechanism involving S-F bond rupture in LiN(SO₂F)₂, followed by attack of a Lewis-acidic S atom in the •(SO₂)(FSO₂)N^- radical on a Lewis-basic O atom in dioxolane. The electrolyte demonstrated high ion conductivity (1.836 mS cm^-1) and Li-ion transference number (0.705), significantly improving the Li plating/stripping uniformity and long-term stability. Batteries with such electrolytes exhibited high-rate capability, high Coulombic efficiency, high capacity retention (75.1% after 3000 cycles), and broad temperature tolerance (-15 to 70 °C). Our research underscores the potential of in situ polymerization in fabricating gel polymer electrolytes to promote the development of secondary alkali metal batteries with exceptional energy density and stability.