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 FeIII vacancies, which has been demonstrated by the X-ray photoelectron spectroscopy and synchrotron radiation X ray absorption spectrum. Our calculation suggests that the FeIII 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.