An electrochemical investigation of the aging of copper hexacyanoferrate during the operation in zinc-ion batteries

A nontoxic, noncorrosive, and environmentally friendly aqueous zinc-ion battery based on copper hexacyanoferrate (CuHCF) has been recently developed. In this work the effect of the electrolyte (nature and concentration), as well as current rate, on the aging of the positive electrode during the operation of the battery are investigated. By using differential charge curves, it is possible to observe how the reaction equilibrium potential and overpotential are changing during the cycling. In particular, it is possible to see a clear change of the reaction mechanism, identified through the simultaneous appearance of a second redox peak and decrease of the main redox peak upon cycling. Such shift of the reaction path is also accompanied by a decrease of the reversible specific charge of the material. ICP-MS data suggest that such fading of the performances is not related to the dissolution of the active material. The aging is occurring at a shorter number of cycles when the concentration of the electrolyte is higher and when the current rate is lower. A mechanism for the phase transformation is proposed. (C) 2016 Elsevier Ltd. All rights reserved.