Effect of Li+ addition on growth behavior of ZnO during anodic dissolution of Zn negative electrode

Abstract

Discharge behavior of the Zn negative electrode was investigated to elucidate the effects of Li+ as an additive in Zn batteries. Li+ influenced the dissolution of Zn as well as the formation of ZnO (passivation). The dissolution reaction was enhanced by Li+; step-flow dissolution at the Zn surface changed to dissolution from the entire surface. SEM observations of the ZnO formed due to the supersaturation of zincate ions showed morphological changes from acicular crystals to particulate clusters upon introduction of Li+; also, ZnO peaks in XRD patterns decreased. These changes indicated that Li+ suppressed the growth of ZnO, which was caused by the adsorption or incorporation of Li+ into the ZnO crystallites. In situ Raman analysis was carried out to monitor such a difference in the nucleation and growth processes. An E2 mode corresponding to crystalline wurtzite ZnO was dominant in the solution without Li+, while this mode diminished and an E1 (LO) mode corresponding to excess Zn in the interstitial sites of ZnO became strong in the presence of Li+. It was suggested that the Zn excess was introduced due to dominance of nucleation (reactions between zincate species) over the growth process (zincate decomposition at the surface).