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

TLDR

Li metal‑based high‑voltage batteries with solid polymer electrolytes are a promising route to safe, high‑energy batteries, but dendrite growth on Li anodes and oxidative degradation at high‑voltage cathodes pose major challenges. The authors synthesize a new family of main‑chain fluorinated solid polymer electrolytes (MCF‑SPEs) designed to be compatible with both Li metal anodes and high‑voltage cathodes. They probe the unique solvation structure between MCF‑SPEs and Li⁺ and systematically vary fluorinated segment lengths to elucidate how contact ion pairs and ion aggregates influence electrode–electrolyte interfaces. The fluoropolymer’s weak‑solvating capability expands the electrochemical window to 5.3 V, markedly suppresses dendrite growth, and improves compatibility with cathodes such as LiNi₀.₆Co₀.₂Mn₀.₂O₂, LiCoO₂, and LiNi₀.₈Co₀.₁Mn₀.₁O₂.

Abstract

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.