A case study on storage and capacity fading mechanism of poly(perylene diimides) cathode in aqueous zinc ion battery

Organic electroactive compounds can be applied as alternative cathodes in aqueous zinc ion batteries (AZIBs) with high stability and low toxicity. In the present study, the storage and capacity fading mechanism of a poly(perylene diimides) named OAP and its monomer, 3,4,9,10-perylene-tetracarboxylicacid-dianhydride (PTCDA), is studied. As disclosed by the structural and electrochemical characterization, OAP exhibits larger capacity, better cycling stability and rate performance compared with the monomer PTCDA, which is due to the reduced solubility in the electrolyte, rougher surface and better tolerance to volume expansion. Electrochemical measurements and ex-situ characterization show that there are two storage ways in OAP-based AZIBs: (1) the redox reaction of the carbonyl groups. Compared with carbonyls in anhydrite groups, the redox reaction of carbonyls in imide groups exhibited better reversibility. (2) partially reversible intercalation and de-intercalation of zinc ion/proton between perylene structures. This work is meaningful for design novel and stable organic electrode materials for AZIBs.