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All‐solid‐state lithium ion batteries (LIBs) are ideal for energy storage given their safety and long‐term stability. However, there is a limited availability of viable electrode active materials. Herein, we report a truxenone‐based covalent organic framework (COF‐TRO) as cathode materials for all‐solid‐state LIBs. The high‐density carbonyl groups combined with the ordered crystalline COF structure greatly facilitate lithium ion storage via reversible redox reactions. As a result, a high specific capacity of 268 mAh g⁻¹, almost 97.5 % of the calculated theoretical capacity was achieved. To the best of our knowledge, this is the highest capacity among all COF‐based cathode materials for all‐solid‐state LIBs reported so far. Moreover, the excellent cycling stability (99.9 % capacity retention after 100 cycles at 0.1 C rate) shown by COF‐TRO suggests such truxenone‐based COFs have great potential in energy storage …