Effect of Tin Oxide Additive on the Suppression of Dendrite Growth of Zinc Electrodeposits

Unlike the market acceptance of Zn-air primary battery, the Zn-air secondary battery is not yet commercialized, mainly due to its poor cycling stability. Although a number of issues have been raised as possible reasons for its low electrical rechargeability, the dendrite growth of Zn during charging process might be most critical because it leads to short circuits and thereby catastrophic failure. Many inorganic additives have been reported for the suppression of the dendritic growth of Zn electrodeposits. For example, it is known that a small amount of Pb ions in an alkaline solution effectively suppresses the Zn dendritic growth. Nevertheless, the environmental issues of Pb-containing additive drive the researchers to search for its alternatives.

Sn is cost effective as well as environmentally friendly. Since it has higher reduction potential than Zn, it might be co-deposited with Zn to possibly change the growth habit of Zn dendrite. In fact, it has been reported that Sn ions affected the Zn deposition on a Zn single crystal at the very low Sn content, implying that Sn can be a possible option to toxic and expensive additives. In this work, we report that SnO additive significantly changes the morphology of Zn electrodeposits and suppresses quite well its dendritic growth. From the cyclic voltammograms at different SnO contents, it is proved that a few milli-moles of Sn ions in the electrolyte have a strong effect on the Sn deposition process. Moreover, the microscopic observation reveals that the non-uniform and dendritic growth of Zn electrodeposits is considerably suppressed at high content of SnO additive. From the depth profiling of the composition of Zn electrodeposit, it is confirmed that Sn is co-deposited with Zn during the course of deposition process, strongly indicating that the incorporated Sn interferes the dendritic growth of Zn. However, the addition of excess SnO resulted in a rough surface and crumbling porous particles containing large amount of Sn phase. 

In this presentation, an optimal SnO content required for the creation of dense Zn electrodeposits will be highlighted. Moreover, the possible mechanism of dendrite growth suppression by Sn ions will be further discussed.