The storage process of Zn2+ ion into alpha-MnO2 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 Zn2+ ion into alpha-MnO2. It is found that the storage process of Zn2+ ions is mainly determined by the phase change. With the decrease of potential, Zn2+ ions begin to insert into MnO2 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 (|Phi|(0)) at low frequency domain shows a logarithmic dependence on R-T, which is confirmed by the experimental results. By using |Phi|(0) directly from Bode plot, we can easily monitor the phase change and the storage process of zinc ion into MnO2. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.008302jes] All rights reserved.