Characteristics and Electrochemical Performance of the TiO2-Coated ZnO Anode for Ni−Zn Secondary Batteries

Various TiO2-coated ZnO samples were prepared by the sol−gel method for use as the anode active materials of Ni−Zn secondary batteries. At a low annealing temperature, the added titanium does not react with the host material, ZnO, but forms an independent TiO2 domain as a coating layer. High-temperature annealing, however, results in the reaction of TiO2 with ZnO, forming ZnTiO3 and Zn2TiO4. Whereas TiO2-coated ZnO suppresses the dissolution of Zn by forming a passive surface layer, the performance of TiO2-coated ZnO is reduced due to the difficulty of transporting the Zn ions through the thicker TiO2 surface layer as the amount of added titanium increases. Moreover, the samples annealed at high temperature have a surface layer containing highly crystalline Zn2TiO4 with low conductivity. The results obtained in this study clearly demonstrate that the surface modification of ZnO with TiO2 effectively suppresses the change in shape of the zinc electrode and maintains the cell performance.