Building a Rechargeable Zn-Cu Battery Through Employing a Monovalent Selective Cation Exchange Membrane

The Zn-Cu battery is plagued with both the problems of Cu2+ migration into the anodic chamber as well as the problem of shape change of zinc electrodes, where both of these processes together have historically prevented this type of battery technology from being rechargeable. We herein propose using a monovalent selective cation exchange membrane (CIEM) that through X-ray diffraction experiments was shown to be effective in preventing any substantial Cu2+ crossover on the charge process. By using Na+ based supporting electrolytes, Na+ can pass through this membrane and maintain electroneutrality in the battery, greatly alleviating the Cu2+ crossover process. For our electrolyte composition we compared sulphate, chloride, and nitrate based zinc and copper salts. We saw that overall for the zinc half-cell sulphate based electrolytes require a larger overpotential than analogous chloride ones due to their differing dissociation constants, whereas nitrate ions lead to complete passivation of the zinc electrode due to the formation of insoluble ZnO. As for the copper half-cells, the chloride-based electrolytes required the largest overpotential for copper electrodeposition since chloride ions are able to stabilize the cupric (Cu+) state of copper, and sulphate and nitrate based copper electrolytes required near identical overpotentials for electrodeposition. In the presence of 0.5 M background electrolyte, masstransfer limitations are alleviated in all electrolyte compositions when the concentration of active species is increased over 0.1 M, where the electrochemical process is then dominated by the kinetics of the electrochemical process.