By introducing lithiophilic groups and electrochemically stable quinolyl aromatic ring linkages, we prepared covalent organic frameworks (COFs) exhibiting a large band gap with an ultralow HOMO value (−6.2 eV under vacuum) and oxidative stability up to 5.6 V (versus Li+/Li) as solid‐state electrolytes (SSEs). The obtained flexible COF SSE thin films showed a holistically oriented arrangement along the (001) facet with remarkable ionic conductivity up to 1.5×10−4 S cm−1 at 60 °C and excellent mechanical strength with a high Young's modulus of 10.5 GPa. Molecular dynamic simulations showed that lithium ions are transmitted in this COF SSE by directional hopping paths with fast drift velocity. The COF SSE film was used to assemble all‐solid‐state lithium metal batteries with nickel‐rich cathodes (NMC811). The batteries demonstrated stable cycling performance over 400 cycles, high coulombic efficiency (>99 %), and could also withstand abuse tests, such as folding.

High-voltage polymer electrolytes play important roles in achieving high-energy-density polymer electrolyte-based batteries, but the pace of progress moves slowly, since oxidation-resistant polymer electrolytes at high voltages are rarely obtained. Herein, we reported a nonflammable and high-voltage-tolerated polymer electrolyte (HVTPE) with extended voltage of 5.5 V. The obtained HVTPE has lower HOMO energy indicating a higher antioxidation ability, which avoids the decomposition and depletion of electrolyte near the cathode. Significantly, the HVTPE-based 4.45 V-class LiCoO2 battery delivered a high capacity of 173.2 mA h g–1 at 0.05 C. Using 4.9 V-class LiNi0.5Mn1.5O4 as a cathode, the battery exhibited stable cycling performance. Moreover, HVTPE showed a high modulus of 2.3 GPa, which can efficiently restrain the penetration of Li dendrites, and desirable nonflammable feature, leading to the enhanced safety based on polymer electrolytes. The current work opens new avenues to realize high-voltage polymer electrolyte-based batteries with high safety.

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