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One important approach to access safe and high-energy batteries is to develop Li metal-based high-voltage batteries with a solid polymer electrolyte (SPE). However, it is notably difficult to construct such systems owing to the simultaneous occurrence of dendrite formation on the Li anode and severe oxidative decomposition against high-voltage cathodes. We here synthesize a new family of main-chain fluorinated solid polymer electrolytes (MCF-SPEs) that are compatible with both Li metal and high-voltage cathodes. Taking advantage of the synergistic weakly solvating capability and outstanding stability of the fluoropolymer, the electrochemical window is increased to 5.3 V, showing significantly mitigated dendrite proliferation and enhanced compatibility with various cathodes, including LiNi0.6Co0.2Mn0.2O2, LiCoO2, LiNi0.8Co0.1Mn0.1O2, etc. The unique solvation structure between MCF-SPEs and Li+ is probed to elucidate fundamental effects of fluoropolymers at electrode/electrolyte interfaces. Additionally, systematic study of varied fluorinated segment lengths that afford different contact ion pairs/ion aggregate solvation structures can guide further development of high-performance SPEs.

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 ≈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.