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

摘要

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 Bi_6(NO_3)_4(OH)_2O_6, BiO and Bi_2O_3, 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 H_2O, 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 H_2O, 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.