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

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_0.8Co_0.1Mn_0.1O₂ (NCM811) quasi-solid-state batteries (QSSBs) are demonstrated. Meanwhile, the resulting 4.3 V Li||LiNi_0.5Co_0.2Mn_0.3O₂ 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.