The impedance of alkaline manganese cells and their relationship to cell performance. I. Interpretation of the basic impedance spectrum

The impedance characteristics of undischarged alkaline manganese cells of various sizes (LR20, LR6 and LR03) have been investigated over the frequency range 100 kHz to 1 mHz. Specially constructed reference electrode probes have been inserted into the cells in two basic positions such as to obtain a complete analysis of the contribution to the total impedance from the individual cell components. It is shown that the impedance of standard cells is determined by the cathode-can assembly, the anode-separator impedance being negligible by comparison. The cathode-can impedance is further resolved into two components. Firstly, a component due to a nickel oxide layer present on the surface of the nickel-plated steel can. This takes the form of a high frequency semicircle in the complex plane. Secondly, a component due to the cathode itself (manganese dioxide + graphite mixture) which takes the form of a higher frequency semicircle and a low-frequency straight line of slope ∼32°. The latter is interpreted in terms of porous electrode behaviour involving slow proton diffusion in the solid state. Some evidence for a porous-planar transition has also been obtained at a critical frequency of ∼3 mHz.