In-situ electro-polymerization of aromatic diimide bridged N-phenylcarbazole as high-voltage cathode materials for long-lasting cationic and anionic co-storage batteries

Abstract

Organic electrode materials with large π electron-deficient backbones and inherently electroactive functional groups hold great promise for serving as advanced cathode materials in secondary batteries. However, conventional organic cathodes were usually plagued by low specific capacity, poor electronic/ionic conductivity, and high solubility in electrolytes. In this study, we report an efficient molecule engineering strategy to incorporate N-phenylcarbazole (NPC) groups as N-substituents on both sides of aromatic diimides to obtain di(N-phenylcarbazole) naphthalene/benzene diimides (namely DNPC-XDI, where X = N, B). The introduced electron-deficient NPC groups could induce the in-situ electro-polymerization of DNPC-XDI under applied field conditions, and also function as p-type anion-storage sites to achieve exceptional cationic and anionic co-storage with significantly enhanced operation voltage, specific capacity and rate capability. Comprehensive characterizations unveiled that the Poly(DNPC-XDI) cathodes operate through a hybrid cation–anion co-redox mechanism, involving the loading/detaching of Li⁺ cations on C=O functional groups and the concurrent doping/de-doping behavior of PF₆⁻ anions on Poly-carbazole backbones. The resultant Poly(DNPC-XDI) (X = N, B) displayed remarkable electrochemical performances, including a high cut-off voltage of 4.3 V and reversible specific capacities of 359.2 and 237.5 mAh g⁻¹ at a current density of 100 mA g⁻¹. Impressively, even at a significantly higher current density of 10 A g⁻¹, the Poly(DNPC-XDI) (X = N, B) still maintained reversible specific capacities of 100.5 and 75.0 mAh g⁻¹ after 10,000 cycles, confirming their outstanding rate performance and cycling stability. Theoretical calculations revealed that the lithiation process was energetically favourable and without the formation of π-π stacking structures. This study offers valuable insights into the rational design of molecular structures and efficient in-situ electrochemical polymerization methods for optimizing organic cathode materials to achieve high-performance cationic-anionic synergistic secondary batteries.