A chemically self-charging flexible aqueous Zinc battery using a covalent organic framework cathode

The development of novel high performance organic cathode materials is the focus of research in aqueous Zn-organic batteries. Covalent organic framework (COF) is a new type of crystalline porous polymer with the advantages of large capacity, flexible structural design and low solubility in electrolyte. It is considered as a promising cathode material for zinc battery. In this study, a novel nitrogen-heterocyclic covalent organic framework COF material (HTAQ-COF) with abundant redox active sites of C═N and C═O was designed and synthesized, which was successfully applied to the cathode of aqueous Zn battery. The constructed HTAQ-COF cathode exhibits a high discharge specific capacity of 305 mA h g-1 at 0.04 A g-1 with excellent cycle life and high rate-performance, and a high energy density of 135 Wh kg-1. In addition, the fabricated flexible aqueous Zn//HTAQ-COF batteries also exhibited excellent long-cycle stability (about 87% capacity retention after 1000 cycles at 2.0 A g-1). At the same time, the flexible aqueous Zinc battery can be effectively charged by harvesting pervasive energy from the ambient air. After air-charging for 30 h, the discharged flexible Zn//HTAQ-COF battery can be self-charged to 1.2 V around without any external power supply, deliver a considerable discharge capacity of 279 mA h g-1, display a high-rate performance and the higher chemically self-charging stability. More importantly, this air-rechargeable flexible Zn//HTAQ-COF batteries are compatible with different chemical or/and galvanostatic charging hybrid modes. This work provides a new way to develop energy storage systems that are not limited by the power supply environment.