Fluorinated Bifunctional Solid Polymer Electrolyte Synthesized under Visible Light for Stable Lithium Deposition and Dendrite-Free All-Solid-State Batteries

Solid polymer electrolytes (SPEs) that can offer flexible processability, highly tunable chemical functionality, and cost effectiveness are regarded as attractive alternatives for liquid electrolytes (LE) to address their safety and energy density limitations. However, it remains a great challenge for SPEs to stabilize Li+ deposition at the electrolyte-electrode interface and impede lithium dendrite proliferation compared with LE-based systems. Herein, a design of solid-state fluorinated bifunctional SPE (FB-SPE) that covalently tethers fluorinated chains with polyether-based segments is proposed and synthesized via photo-controlled radical polymerization (photo-CRP). In contrast to the conventional non-fluorinated polyether-derived SPEs, FB-SPE is able to provide conducting Li+ transport pathways up to approximate to 5.0 V, while simultaneously forming a Li-F interaction that can enhance Li anode compatibility and prevent Li dendrites growth. As a result, the FB-SPE exhibits outstanding cycling stability in Li||Li symmetrical cells of over 1500 operating hours at as high current density as 0.2 mA cm(-2). A thin and uniform Li deposition layer and LiF-rich SEI at the surface of Li anode are found, and stable cycling with average coulombic efficiencies of 99% is demonstrated in Li||LFP and Li||NCM all-solid-state batteries based on such bifunctional fluorinated SPEs. The interesting fluorine effect and effective self-suppression of lithium dendrites will inform rational molecular design of novel electrolytes and practical development of all-solid-state Li metal batteries.