Regulation of ferric iron vacancy for Prussian blue analogue cathode to realize high-performance potassium ion storage

Prussian blue analogs (PBAs) cathode materials undergo a phase change from cubic to tetragonal phase during potassiation-depotassiation processes, leading to the poor reversibility and cycling stability. Therefore, we introduced chelating agent of ethylenediaminetetraacetic acid dipotassium salt to synthesize PBAs with Fe^III vacancies, which has been demonstrated by the X-ray photoelectron spectroscopy and synchrotron radiation X ray absorption spectrum. Our calculation suggests that the Fe^III vacancies in PBAs can inhibit the movement of the Fe-C bond. This behavior helps to reduce the lattice distortion of Fe-C octahedron, in favour of the high reversibility and cycling stability of PBAs. After treatments, our specimens present a high initial Coulomb efficiency of 97% with a discharge capacity of 66 mAh g^-1 at 25 mA g^-1 after 50 cycles and a stable discharge capacity of 40 mAh g^-1 at 100 mA g^-1 after 250 cycles. This work demonstrates a new approach to improve PBAs cathode by tunneling Fe-C octahedrons fine structure and provides a guidance for developing high-performance potassium-ion batteries in the future.