All‐Solid‐State Lithium Metal Batteries with Microdomain‐Regulated Polycationic Solid Electrolytes

Abstract Solid polymer electrolytes (SPEs) are promising for high‐energy and high‐safety solid‐state lithium metal batteries (LMBs). Here, a polycationic solid electrolyte (PCSE) is described that leverages the inherent high thermal/chemical stability of the polycationic domain and the anion trapping (FMAT) effect of another fluorinated microdomain for stable and fast‐charging high‐voltage LMBs. Specifically, while the polycationic imidazolium backbone ensures high segmental flexibility facilitating the Li⁺ mobility, the fluorinated microdomain effectively traps the bis(trifluoromethanesulfonyl)imide anions by strong dipole interactions, imparting localized solvation and restricted mobility of the anions, as well as improved oxidation stability. As a result, the PCSE exhibits a high ionic conductivity of 1.4 mS cm⁻¹, a high Li⁺ transference number of 0.50, and a wide electrochemical window of ∼5.5 V at 25 °C. By way of in situ thermal polymerization of the electrolyte within assembled cells, the PCSE enables ultra‐stable cycling of Li|LiNi_0.8Co_0.1Mn_0.1O₂ cells with a capacity retention of 98.1% after 500 cycles at 0.2 C at ambient temperatures. The work on the molecular design of PCSEs represents a fundamentally unique perspective for the rational design of SPEs with balanced properties that are historically challenging for high‐energy, long‐life, ambient‐temperature solid‐state LMBs.