Covalent organic frameworks (COFs) have been regarded as promising cathode materials for lithium batteries. However, they generally show low practical capacity. Here, the design, preparation, and battery application of a highly crystalline 2D truxenone-based COF (TRO-BT-COF) with rich redox active sites, realizing a high practical capacity is reported. In situ characterizations and theoretical calculations indicate that the lithiation reaction proceeds successively on C═O and C═N groups of TRO-BT-COF. One ring of TRO-BT-COF can theoretically store 27 Li