Aromatic polyimides have been considered promising organic cathode materials for lithium-ion batteries (LIBs) due to their excellent solvent resistance, superior electrochemical capability and highly designable structure. However, the inferior intrinsic conductivity and limited redox-active sites lead to their suboptimal comprehensive electrochemical performance and restrict their applications in LIBs. Herein, a novel conjugated diketone-based polyimide (PTN) cathode material with multiple carbonyl redox sites is proposed and prepared for LIBs. The integration of electron-withdrawing π-conjugated diketone with naphthimide can effectively regulate the electronic structure and elevate the working potential of the polyimide-based cathode, and improve its comprehensive electrochemical performance. The PTN-based cathode delivers a high specific capacity of 213.4 mAh g⁻¹, excellent cycling stability (97.3% capacity retention after 2000 cycles at 2000 mA g⁻¹) and high rate performance (78.2% capacity retention at 2000 mA g⁻¹ vs. 50 mA g⁻¹), high gravimetric energy density (380 Wh kg⁻¹) at a high power density (4417 W kg⁻¹) simultaneously. This comprehensive electrochemical performance is among the best results of reported polyimide cathode materials and suggests that PTN has great potential in energy storage applications.