Alternant P-Type/N-Type Conjugated Bipolar Copolymer Cathodes for Advanced Aqueous Zinc-Ion Batteries
Yanrong Wang, Shigui Qiu, Shengwen Tan, Huaizhu Wang, Xuemei Wang, Chenxi Zheng, Lubin Ni, Guowang Diao, Caixing Wang, Zhong Jin
Abstract
To synergistically combine the features of high specific capacity of n-type organic materials with the high voltage of p-type organic materials, bipolar phenolthiazine-based cathodes with p-type/n-type structures are gaining increased attention for aqueous zinc-ion batteries (AZIBs). Nevertheless, their small molecular structure often leads to dissolution during cycling. To address the challenge, a bipolar poly(phenothiazine iodide-3,3′-diaminobenzidine), abbreviated as P(PTD-DAB), was synthesized as a cathode material. Through comprehensive spectroscopic analyses, we elucidated a cooperative p-type/n-type dual-ion storage mechanism. Specifically, the N atom in the phenothiazine core stores Zn 2+ or H + cations via n-type reactions, while the N atoms connecting phenothiazinium tetraiodide and 3,3′-diaminobenzidine monomers, along with S atoms, act as p-type active sites for storing OTF – anions. The material delivers an average operating voltage of 1 V and achieves a high specific capacity of 211.8 mAh g –1 at a low current density of 0.1 A g –1 . Additionally, it shows 90% capacity over 3600 cycles at a high current density of 3 A g –1 while sustaining robust stability at a high mass loading of active cathode (10 mg cm –2 ). Furthermore, flexible belt-shaped cells maintain 88% capacity retention over 550 cycles at 3 A g –1 even when subjected to repeated bending conditions. This work represents a great advancement in developing bipolar polymers for high-performance AZIBs and offers valuable insights into their design principle and functionality.