Zinc hexacyanoferrate with a highly reversible open framework for fast aqueous nickel-ion storage

Abstract

Rechargeable aqueous Ni-ion batteries are potential candidates for future large-scale energy storage owing to their low-cost aqueous electrolytes. In this study, we report K₂Zn₃[Fe(CN)₆]₂ (K-ZnHCF) as a possible Ni²⁺ storage material in aqueous batteries. The reversible capacity of K-ZnHCF is found to be 54.3 mA h g⁻¹ over 2500 cycles with a low capacity decay of 0.0023% per cycle at 1 C. Even under the higher rate (10 C), the specific capacity can maintain about 50 mA h g⁻¹. The open and stable framework of K-ZnHCF with large ionic channels is benefitial for high rate Ni²⁺ extraction/insertion capability. The calculated high diffusion coefficient convincingly proves the favorable rate performance of K-ZnHCF in nickel ion batteries. Furthermore, the reversible nickel ion storage mechanism in K-ZnHCF is investigated by XPS, FTIR spectroscopy, Raman spectroscopy, and XRD, revealing the origin of a stable host structure during the charge/discharge process. Therefore, K-ZnHCF with a highly reversible open framework is a suitable host material for repeated nickel ion storage in rechargeable batteries.