Investigation on Zinc Ion Storage in Alpha Manganese Dioxide for Zinc Ion Battery by Electrochemical Impedance Spectrum

The storage process of Zn 2+ ion into α-MnO 2 has been investigated by electrochemical impedance spectrum. A new phase formation process has been recognized. The equivalent circuit model and the impedance expression have been built up to characterize the storage of Zn 2+ ion into α-MnO 2 . It is found that the storage process of Zn 2+ ions is mainly determined by the phase change. With the decrease of potential, Zn 2+ ions begin to insert into MnO 2 and phase change occurs, which leads to a significant increase on phase change resistance ( R T ). We also investigated the relationship between the phase change and the phase angle. It is mathematically calculated that maximum phase angle ( | Φ | 0 ) at low frequency domain shows a logarithmic dependence on R T , which is confirmed by the experimental results. By using | Φ | 0 directly from Bode plot, we can easily monitor the phase change and the storage process of zinc ion into MnO 2 .