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

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_0.5Mn_1.5O₄ 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.