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

Various TiO 2 -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 TiO 2 domain as a coating layer. High-temperature annealing, however, results in the reaction of TiO 2 with ZnO, forming ZnTiO 3 and Zn 2 TiO 4 . Whereas TiO 2 -coated ZnO suppresses the dissolution of Zn by forming a passive surface layer, the performance of TiO 2 -coated ZnO is reduced due to the difficulty of transporting the Zn ions through the thicker TiO 2 surface layer as the amount of added titanium increases. Moreover, the samples annealed at high temperature have a surface layer containing highly crystalline Zn 2 TiO 4 with low conductivity. The results obtained in this study clearly demonstrate that the surface modification of ZnO with TiO 2 effectively suppresses the change in shape of the zinc electrode and maintains the cell performance.