Dual Fluorination Molecular Design Enabling Polyether Solid Electrolytes for 5.0 V Lithium‐Metal Batteries With Aggressive Chemistries

Abstract Polyether‐based solid electrolytes (PESEs) are uniquely advantageous for solid‐state batteries owed to their segmental flexibility and compatibility with lithium metal anodes (LMAs). However, PESEs face challenges with poor ionic conductivity, low Li ⁺ transference number, and low oxidation stability. Here it is reported a dual fluorination strategy by incorporating two types of fluorine, bound and exchangeable states, which enables PESEs with excellent physiochemical properties and stability with aggressive high‐voltage cathodes and LMAs at 25 °C. While a stiff pentafluorobenzene unit − as the bound fluorine − is integrated into the flexible polyether backbone to enhance oxidation stability, mechanical properties, and the Li ⁺ transference number (via anion‐π interactions), a solid‐state organic molecule 2,2,2‐trifluoro‐N‐methylacetamide – as the exchangeable fluorine – serves to construct a fluorine‐rich solid‐electrolyte interphase. As a result, the PESE enables high‐stability 5.0‐V class Li|LiNi _0.5 Mn _1.5 O ₄ cells maintaining 85.6% capacity over 600 cycles. The described dual fluorination strategy, applicable to PESEs herein and possibly beyond, is expected to pave the way toward practical, long‐life, and high‐energy solid‐state lithium‐metal batteries.