Unwanted electroless zinc plating on current collectors in zinc air batteries

TL;DR

This study investigates spontaneous zinc film formation on copper current collectors in zinc air batteries, revealing zinc oxidation and proposing a reversible deposition mechanism.

Contribution

It provides new insights into unwanted zinc deposition on copper in zinc air batteries and elucidates the underlying reaction mechanism.

Findings

Zinc coating forms on copper and noble metals in zinc slurry.

The coating is mainly zinc with surface oxidation.

A reversible zinc film deposition mechanism is proposed.

Abstract

The occurrence of metallic film deposition without external power supply on the copper current collector of a zinc air battery half-cell containing zinc slurry is investigated. Therefore, test specimens of miscellaneous materials representing the current collector are immersed in a commercial available zinc slurry as well as an in self-prepared zinc slurry. In case of copper and metals which are more noble (silver and gold), a coating on the respective specimen is obtained. An element mapping of the coated copper specimen is performed by means of scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) identifying that the coating layer consists of zinc and oxygen. In order to clarify the crystal structure and the exact composition, focused ion beam (FIB) and x-ray photoelectron spectroscopy (XPS) measurements are applied, proving that the layer consists of elemental zinc, which, is merely oxidized on the surface. Finally, a reaction mechanism for the reversible zinc film deposition is proposed.