A Cyclosiloxane-Copolymerized Polyether Electrolyte for High-Voltage Solid-State Lithium Metal Batteries

Polyether-based solid polymer electrolytes (SPEs) hold great promise for solid-state batteries, yet they suffer from a fundamental trade-off among ionic conductivity, oxidative stability, and mechanical robustness. Herein, a cyclosiloxane-copolymerized polyether electrolyte (CS-PDOX) is developed via in situ ring-opening copolymerization between 1,3-dioxane (DOX) monomers and a cyclosiloxane cross-linker. The incorporation of cyclosiloxane redistributes the local electrostatic environment of the polyether electrolyte, weakens Li⁺-polymer coordination, and lowers the Li⁺ migration barrier, leading to a high room-temperature ionic conductivity of 8.45 × 10⁻⁴ S cm⁻¹. Simultaneously, the electron-deficient Si─O─Si downshifts the highest occupied molecular orbital (HOMO) energy level, expanding the oxidative stability to ∼4.76 V vs. Li⁺/Li and suppressing side reactions upon pairing with high-voltage cathodes. Moreover, the engineered weak-solvation, featuring a weakened Li⁺-polymer coordination environment, drives FSI⁻ anions into the solvation sheath, which favors the formation of an inorganic-rich solid electrolyte interphase. This interface provides uniform Li deposition and robust mechanical protection, enabling >2400 h lifespans in Li||Li cells. Consequently, the Li|CS-PDOX|NCM811 cell delivers exceptional cycling stability with 85.0% capacity retention over 400 cycles, and the ∼3.5 Ah Li─Cu||NCM811 pouch cell delivers a remarkable energy density of 445 Wh kg⁻¹, demonstrating the potential of this strategy for next-generation high-voltage solid-state batteries.