Influence of the Thermal Treatment on the Structure and Cycle Life of Copper Hexacyanoferrate for Aqueous Zinc-Ion Batteries

Copper hexacyanoferrate (CuHCF) has become an attractive Zn2+ insertion material as a positive electrode in aqueous zinc-ion batteries thanks to its high reversibility towards Zn2+ (de-)insertion, its simple, inexpensive and easily scalable synthesis route, its low toxicity, and its high working potential. It is known that the physiochemical properties of CuHCF can be modified by manipulating its synthesis parameters. However, the effect of these parameters on the material’s electrochemical performance and cycle life needs further investigation. Here, the structure and composition of CuHCF treated at different temperatures are studied through crystallographic, compositional, and thermogravimetric analyses. The resulting CuHCF powders were galvanostatically cycled to assess their electrochemical performance in relation to their annealing temperature. The results showed that the annealed CuHCF electrodes exhibited longer cycle life while maintaining a coulombic efficiency ≥ 99.5%. The longest cycle life was achieved by annealing the CuHCF electrodes at 100 °C.