Polyoxometalates enable cross-scale interfacial engineering of polyimide cathodes toward enhanced energy density and...

Organic cathode materials suffer from low electrical conductivity, sluggish ion transport, and poor accessibility of active sites, which severely restrict their practical application in sodium-ion batteries (SIBs). Herein, we realize the simultaneous regulation of spatial and electronic structures of polyimide (PI) via polyoxometalate molecular engineering. The covalently anchored PMA (phosphomolybdic acid) clusters expose abundant CO groups with enhanced redox kinetics and create continuous charge transfer channels across the PI-PMA heteromolecular interface, thereby facilitating electron transport and improving electrode conductivity. Moreover, the strong electron-withdrawing nature of PMA significantly lowers the LUMO level of PI, which not only strengthens the binding affinity between carbonyl groups and Na⁺ to enhance reversible capacity, but also elevates the discharge voltage plateau to substantially boost the energy density of the composite. Consequently, the PI-PMA electrode exhibits high reversible capacity, superior rate capability, and excellent long-term cycling stability. This work establishes a multi-scale molecular engineering paradigm for overcoming the intrinsic limitations of organic cathodes for high-energy-density SIBs.