Electrochemical performances of Bi based compound film-coated ZnO as anodic materials of Ni–Zn secondary batteries

Microstructures and electrochemical performances of Bi based compound film-coated ZnO are investigated and compared with those of Ni film-coated ZnO and Bi nanocompound-modified ZnO in order to illuminate the coating effect of Bi based compound film. Bi based compound film is composed of nanoparticles (1–2 nm in diameter) of Bi6(NO3)4(OH)2O6, BiO and Bi2O3, containing lots of micropores. In comparison with Bi nanocompound-modified ZnO and Ni film-coated ZnO, Bi based compound film-coated ZnO shows higher discharge capacity and more stable cycling performance. The highest average discharge capacity is as high as 535 mAh g−1, and the discharge capacity does not obviously decrease during the cycling tests. Cyclic voltammograms indicates that Bi based compound film can limit transfer of H2O, OH−, and enhance electrochemical activity of ZnO. The improvement of cycling performance is due to: (1) the coating film structure avoids the direct contact between ZnO/Zn with the electrolyte, and suppresses the dissolution of ZnO/Zn; (2) the micropores in the film is beneficial to adequate diffusion of H2O, OH− and zincates ions, leading to high discharge capacity and good cycling performance; (3) the light weight of the film also has a contribution to high specific discharge capacity.