Electrochemical impedance method was applied to pasted-type negative electrodes (current collector: metal core sheet) of Ni-MH batteries. The following information was obtained during a charge-discharge cycle test without disassembling the batteries; 1) the solution resistance, 2) the contact resistance between particles of the active material, 3) the impedance of the corrosion product, 4) the charge transfer resistance and capacitance of the electric double layer at the interface between the electrolyte and the active material, 5) Warburg impedance caused by hydrogen diffusion in the active material. It was also revealed that the property of porous electrode was very impotant to analyze impedance spectra measured by the pasted-type electrodes.

The factor impeding hydrogen diffusion from the inside of the active material to the surface reaction sites was clarified by analyzing the impedance components of the negative electrodes. Discharge characteristics were largely improved by the electrochemical impedance method.
�@