Additive effect of Li on electrical property of ZnO passivation layer to control dendritic growth of Zn during recharge processes

Abstract

This study investigates the effect of Li⁺ on the dendritic growth of Zn anodes in the presence of a ZnO passivation layer formed after discharge, with particular attention to the initial recharge process. 0.1 mol dm⁻³ Li⁺ effectively suppresses dendrites, while 2 mol dm⁻³ Li⁺ addition facilitates the same. The difference in Zn dendrite formation behavior is also indicated by the attenuation tendency of the potential oscillation accompanied by hydrogen evolution reaction during recharge. This is attributed to Li⁺ concentration dependence of the properties of the ZnO passivation layer formed during Zn anode discharge. Li⁺ modulates the carrier density of ZnO by altering its crystalline defect characteristics; the carrier density of ZnO with 0.1 mol dm⁻³ Li⁺ addition becomes approximately three times as high as that without additive owing to the oxygen vacancies and interstitial zinc that form additional donor level. By contrast, 2 mol dm⁻³ Li⁺ reduces the carrier density of ZnO by inducing zinc vacancies to form acceptor levels. The highly conductive ZnO produced by adding 0.1 mol dm⁻³ Li⁺ improves the reaction uniformity during recharge, which suppresses dendrite formation. This study provides valuable insight into the mechanisms and control strategies of Zn dendrite growth during the charge-discharge cycling of alkaline Zn rechargeable batteries.