Water-Induced Stable Structure of Zinc Hexacyanoferrate Enabling Superior Electrochemical Performance

Prussian blue analogues have an open and adjustable framework structure, and their stability and electrochemical performance depend on the occurrence state and content of structural water. Zinc ferricyanide (ZnHCF) is a promising cathode material for zinc-ion batteries. Although it has a good electrochemical potential, there is a problem of structural instability during the charge and discharge cycles. Structural water (especially coordinated water) is crucial to its crystal stability. Currently, there is still controversy over the structural modeling of the hydrated cubic-phase ZnHCF. In this study, ZnHCF materials were prepared by the coprecipitation method at room temperature. Combining X-ray diffraction and Fourier transform infrared spectroscopy characterization, it was confirmed that they were of cubic or rhombic phase. Meanwhile, a reasonable hydrated cubic-phase ZnHCF structure model was constructed through VESTA software to fill the missing [Fe(CN) 6 ] 3 − vacancies in the lattice with water molecules. Research shows that coordinating water can effectively buffer the lattice volume changes caused by the intercalation and deintercalation of Zn 2+, and interstitial water can support the lattice framework. The synergistic effect of the two significantly enhances the structural stability and cycling performance of the material, making the electrochemical performance of the hydrated cubic-phase ZnHCF superior to that of the anhydrous rhombic phase. The theoretical specific capacity of this aqueous cubic-phase material is 62 mAh g −1 . After 400 charge−discharge cycles, the capacity retention rate still reaches 96%. This work clarifies the regulatory effect of structural water on the intercalation and deintercalation behavior of Zn 2+, confirms that structural water can effectively alleviate the lattice volume deformation caused by Zn 2+ intercalation and deintercalation, and thereby reveals the origin of the excellent electrochemical performance of C-ZnHCF.