Unlocking the intrinsic mechanisms of A-site K/Na doped perovskite fluorides pseudocapacitive cathode materials for enhanced aqueous zinc-based batteries

Here, we explored an A-site K/Na doped Ni-Co-Zn-Mn multimetallic perovskite fluoride (ABF3) electrode material (denoted as K/Na(3/1)-NCZMF) and applied it in an advanced aqueous zinc-based battery (AZB) energy storage system. This work mainly clarifies the intrinsic reasons for positive effect of A-site K/Na doping on the performance of ABF3 materials by comparing three materials K-NCZMF, Na-NCZMF and K/Na(3/1)-NCZMF via the electrochemical tests and density functional theory (DFT) calculations, largely owing to the superior pseudocapacitive contribution, adsorption of OH− and charge transfer ability of surface redox-active Ni/Co/Mn atoms by A-site K/Na doping of the ABF3 materials. Further, a typical bulk phase conversion mechanism of K/Na(3/1)-NCZMF electrode material in alkaline solution is deeply revealed via various ex-situ characterizations, which verifies that the crystalline K/Na(3/1)-NCZMF ABF3 material is converted into amorphous metal (hydro)oxides/oxyhydroxides via bulk reaction after charge/discharge in alkaline medium. In conclusion, this work reveals the charge storage mechanism and structure-activity relationship of A-site doped ABF3 cathode materials for aqueous zinc-based batteries, providing new ideas and inspiration for the further development of high-efficiency aqueous energy storage devices.