Effect of indium and tin additives on the surface morphology of zinc negative electrodes for Zn-Ni flow-assisted batteries

The effects of In and Sn additives on the charging behavior of Zn negative electrodes for Zn-Ni flow-assisted batteries were investigated. The addition of InCl₃･4H₂O or K₂SnO₃･3H₂O to the electrolyte suppressed the formation of mossy shaped Zn, which was highly filamentous electrodeposit and a typical cause of a battery failure. In was effective even at concentrations as low as 1.0 mmol dm⁻³, while more than 25 mmol dm⁻³ was required for the case of Sn. The results of ICP-AES measurements indicated that the difference was explained by higher reduced amount of In than that of Sn during the charging process. The In additive did not show any negative effects on the Coulombic and voltaic efficiencies, which was in accordance with the polarization behavior of Zn in the In containing solution; electrodeposited In had high overpotential for hydrogen evolution and minor influences on the Zn deposition potential. From SEM observation at the early stages of electrodeposition, the compact Zn deposits were formed by mitigating the localized deposition on layer-like Zn structures. As a mechanism behind such a uniform deposition by In, a compositional analysis in depth showed deposited In was accumulated at the surface of the deposits.