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

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.