Preparation and electrochemical performance of nanosized Bi compounds-modified ZnO for Zn/Ni secondary cell

Surface-modified ZnO with nanosized Bi compounds was prepared on the basis of the hydrolysis of Bi(NO3)3. Transmission electron microscopy images revealed that some nanoparticles with about 40 nm in diameter were modified on ZnO. X-ray diffraction indicated that Bi compounds consisted of Bi2O3 and BiO. Electrochemical performances of the surface-modified ZnO were analyzed by charge/discharge cycle test and slow rate cyclic voltammetry (CV). Compared with Bi2O3–physically mixed ZnO, nanosized Bi compounds-modified ZnO showed the improved cycle performance, higher discharge capacity and utilization ratio of ZnO. The discharge capacity of the modified ZnO with 9.3 wt.% Bi was the most stable among all tested electrode material and maintained 450 mAh g−1. In comparison with the average utilization ratio (53%) of the physically mixed ZnO, the average utilization ratio of the modified ZnO could reach 80%. The improvement of electrochemical performance resulted from the fact that surface modification with Bi compounds slowed dissolution of ZnO in the electrolyte and maintained the electrochemical activity of ZnO. Cyclic voltammograms clearly illuminated that the modifying agent could decrease polarization, maintain the electrochemical activity, and enhance the discharge capacity of ZnO.