High Capacity and Stable Lithium‐Ion Cathodes Based on a Mellitic Trianhydride–Phenylenediamine Porous Polyimide

Organic redox polymers are promising cathode materials for lithium‐ion batteries because they can be built from earth‐abundant elements and offer tunable redox properties, yet many suffer from dissolution, slow kinetics, and limited cycling stability. Porous organic polymers (POPs) present a promising platform to circumvent these issues by incorporating redox‐active units into insoluble, robust frameworks. Herein, we report a polyimide‐based POP, PI(MTA‐PDA), synthesized via polycondensation of mellitic trianhydride (MTA) and 1,4‐phenylenediamine (PDA), as a high‐capacity cathode. The resulting carbonyl‐rich, π ‐conjugated network is predominantly amorphous with short‐range structural ordering and exhibits good structural stability and efficient charge transport. After electrochemical activation, the PI(MTA‐PDA) cathode delivers a high reversible capacity of 229.9 mAh g −1 and demonstrates stable long‐term cycling performance, retaining ~95% of its peak capacity after 600 cycles at 0.1 C. It also exhibits robust rate performance, delivering 119.6 mAh g −1 at a high rate of 4 C. Electrochemical analysis reveals a three‐electron redox process per repeating unit, involving sequential lithium‐ketyl radical formation and enolization of the imide carbonyls. These results highlight imide‐linked POPs based on MTA and PDA as attractive organic cathode platforms that couple high capacity with long‐term cycling stability and good rate performance.