Designing Weakly Solvating Solid Main-Chain Fluoropolymer Electrolytes: Synergistically Enhancing Stability toward Li Anodes and High-Voltage Cathodes

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.