Effects of Electrolyte Concentration on Electrochemical Properties of an Iron Hexacyanoferrate Active Material

The effects of electrolyte concentration on the electrochemical properties of Fe4[Fe(CN6)]3 (FeHCF) as a novel active material for the electrode of aqueous zinc-ion batteries was investigated. The electrochemical reactions and structural stability of the FeHCF electrode were significantly affected by the electrolyte concentration. In the electrolyte solutions of 1.0-7.0 mol dm, the charge-discharge capacities increased with increasing electrolyte concentration, however gradually decreased as the cycle progressed. On the other hand, in the 9.0 mol dm electrolyte solution, the initial capacity was relatively small, however showed good cyclability. Additionally, the FeHCF electrode after five cycles in the former electrolyte solutions, had a change in crystal structure, whereas there was no change in the latter electrolyte solution. This suggests that the performance of the FeHCF electrode is greatly influenced by the hydration structure of zinc ions present in electrolyte solutions.