High-performance aqueous zinc-ion batteries with air self-charging capability based on azo-based covalent organic...

Air self-charging aqueous zinc-ion batteries (AZIBs), as a structurally simple self-powered system, have application prospects in harsh environments lacking power supply. But, the absence of suitable cathode material leads to unsatisfactory self-charging capability. Here, we develop a novel azo-based covalent organic framework (HTAzo-COF) containing triple-active centers (NN, CN and CO) as the cathode material of AZIBs. Owing to its π-conjugated porous structure including abundant active sites, and large specific surface area, the energy densities of coin-type and flexible Zn//HTAzo-COF AZIBs can reach at 123.4 Wh kg^-1 and 18.4 mWh cm^-3, respectively. Ex-situ experiments combined with theory calculations elucidate the redox reaction occurring in the HTAzo-COF cathode is related to the intercalation and extraction of Zn²⁺ and H⁺. Encouragingly, due to the spontaneous oxidation of the discharged HTAzo-COF cathode by O₂ in air, the flexible Zn//HTAzo-COF battery that had exhausted its electrical energy can regain energy through air self-charging. After air oxidization of 20 h, this flexible battery demonstrates a superior discharging capacity (366 mAh g^-1 at 0.5 A g^-1), outstanding rate capability (111 mAh g^-1 at 20 A g^-1), and better stability in air self-charging cycles (20 cycles). This study offers a promising avenue for developing high-performance organic cathode materials for AZIBs with air self-charging ability.