Morphology Control of Zinc Electrodeposition By Surfactant Addition for Alkaline-Based Rechargeable Batteries

Critical challenges have remained in practical realization of Zn-air batteries. Focusing on negative electrode, Zn grows in the form of mossy and dendrite structures in low and high current densities, respectively. The non-uniform Zn morphology prevents homogeneous Zn dissolution (discharge) reaction, which is responsible for deterioration of battery performance. In the present study, we used trimethyloctadecylammonium chloride (STAC / surfactants) as an inhibitor of the formation of mossy and dendrite Zn structures. The addition of surfactant to an electrolyte is not necessarily a new approach for improving Zn deposition morphology. However, the new insight in this study is that we found a leveling agent enabling to suppress the formation of not only mossy structure but also dendrite structure and highly flatten deposit in wide current densities (5−40 mA cm −2 ). The mechanism was systematically investigated by means of X-ray diffraction and measurements of zeta potential and kinetic current density for Zn-deposition. The obtained results indicate that quaternary ammonium cations (STAC) with bulky size adsorb to protrusions which are cause of shape change and suppress Zn deposition in the region to promote lateral growth. In charge−discharge test using an asymmetric Cu|Zn cell, Coulombic efficiency in an additive free electrolyte was less than 95%, whereas the addition of STAC with 1 mM achieved superior cycling performance without any capacity loss originated from the generation of dead Zn. These results demonstrate that the addition of STAC is a promising way of controlling Zn morphology and allows the efficient utilization of Zn metal electrode in large-scale batteries for important next-generation applications. Figure 1