Effect of the reactants concentration on the synthesis and cycle life of copper hexacyanoferrate for aqueous Zn-ion batteries

Copper hexacyanoferrate (CuHCF) is a promising Zn2+ insertion material as positive electrode in mild aqueous Zn-ion batteries for power grid applications, due to its excellent power capability, non-toxicity, low cost and easy synthesis route. Here, the effect of the reactants' concentration and ratio during the synthesis of the CuHCF on the performance of the resulting material has been investigated through morphological, crystallographic and compositional analysis. Despite the different reaction's conditions, the synthesised CuHCF powders did not show any significant change in their average particle size and morphology. Nevertheless, different structural and compositional characteristics have been observed for the different samples. In particular, different amounts of potassium have been found in the crystal structure of the investigated CuHCF materials. Subsequent electrochemical analysis demonstrated that the CuHCF with higher initial potassium content showed higher stability and therefore achieved longer cycle life.