“Rigid Exterior, Soft Interior” Design Enables High‐Voltage Polyether Electrolytes for Quasi‐Solid‐State Batteries

Abstract Polyether electrolytes with high Li + conductivity and excellent interfacial contact have garnered significant attention. Yet further applications of such electrolytes in high‐voltage lithium metal batteries are severely hindered by the instability of the electrolyte and electrolyte/electrodes interphases. Here, we report a novel high‐voltage polyether electrolyte with a “rigid exterior, soft interior” design, which involves a 3D F‐contained network as a rigid exterior framework, and a unique solvation structure with intensified Li + ‐anion coordination as a soft interior within the framework. The achieved electrolyte demonstrates an ionic conductivity of 1.13 mS cm −1 at 25 °C, a Li + transference number of 0.85, and an extended electrochemical stability window of over 5 V. Besides, such a designed polyether electrolyte further induces salt‐philic, solvent‐phobic interfacial films for stabilizing electrolyte/electrode interphases. An exceptional cyclability in a Li||Li cell for over 4000 h, and a preferable capacity and cyclability in even 4.6 V Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) quasi‐solid‐state batteries (QSSBs) are demonstrated. Meanwhile, the resulting 4.3 V Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 QSSB shows a Coulombic efficiency of ∼100% and an extremely high capacity retention of 95.4% after 600 cycles at 3C. A capacity retention of over 96.3% after 400 cycles at 1C are further realized in 4.5 V Li||NCM811 QSSB.