Semi in-situ measurement of zincate ion concentration near zinc anode using background-oriented Schlieren technique

Abstract

In metal-anode batteries such as zinc, the concentration of metal ions in the electrolyte usually plays a significant role in the metal electrodeposition upon charging. This study aims to clarify the concentration of zincate ions near the zinc anode. After preliminary experiments in a minichannel were conducted to identify the system parameters, galvanostatic charging experiments in a zinc battery cell were conducted at current densities of 20 and 40 mA cm −2. The bulk concentrations of zincate ions were set to 0.49 and 0.98 mol L −1. Images near the zinc anode were captured using an optical microscope to calculate the zincate ion concentration distribution through the background-oriented Schlieren (BOS) technique. They were taken at an equal time intervals to investigate the transition of the concentration diffusion layer. It was confirmed that the BOS technique enables us to quantitatively measure the zincate ion concentration in zinc anode batteries. The results are consistent with the theoretical expectation. The applied current density basically determines the concentration gradient near the anode surface, although it takes time to reach a steady state. The spatial variance in the zincate ion concentration at the anode surface increases with the distance from equilibrium.