Triphenylamine-containing dihydrophenazine copolymers with adjustable multi-electron redox characteristics and their application as cathodes in lithium-organic batteries

Abstract

Arylamine p-type cathode materials have high redox potentials and rate capabilities, which have attracted increasing attention recently. However, the one-electron redox characteristic of most of the p-type cathodes makes them suffer from limited stability and low specific capacity (<150 mA h g⁻¹). Herein, two new triphenylamine-containing phenazine copolymers, a linear molecular structure of poly(4,4′-dibromotriphenylaminedihydrophenazine) (p-DTPAPZ) and a cross-linked molecular structure of poly(tris(4-bromophenyl)aminedihydrophenazine) (p-TTPAPZ) theoretically possessing multi-electron redox characteristics, were developed as p-type cathode materials. It was found that the different triphenylamine electroactive linkages present in the copolymers have different effects on the morphology and electrochemical performances of the copolymers. In addition, the linear copolymer of p-DTPAPZ displayed an aggregated fiber morphology and a relatively outstanding electrochemical and battery performance in which it exhibited three pairs of redox characteristics and delivered a higher specific capacity of 160.1 mA h g⁻¹ at the sixth cycle with excellent cycling stability. Comparatively, the cross-linked copolymer of p-TTPAPZ with high theoretical specific capacity exhibited a relatively low discharge capacity of 126.8 mA h g⁻¹ and two pairs of redox characteristics in which the redox process for the triphenylamine units in the copolymer disappeared. This work sheds light on the design of organic battery materials with multi-electron redox characteristics by regulating the molecular structure and conformation.