Electrochemical impedance studies of Na/MnO 2 primary cells

Primary Na/MnO 2 cells are expected to gain importance for replacement of primary Li/MnO 2 cells in future akin to the Na-ion cells as alternative for Li-ion cells. Amorphous MnO 2 is prepared by a drop-wise addition of KMnO 4 solution to MnSO 4 solution, and coin cells of Na/MnO 2 are fabricated in a non-aqueous electrolyte of Na salt. The electrochemical impedance spectroscopy (EIS) data provides a high resistance of Na metal due to the surface passive film. On subjecting the cell for discharge, the surface film causes a delay response of the cell voltage and the closed circuit voltage reaches the normal discharge level following dielectric breakdown of the film. The EIS data measured at different stages of cell discharge are subjected to non-linear least square fitting with the aid of an appropriate equivalent circuit. The impedance parameters are examined to throw light on state-of-charge of Na/MnO 2 primary cells.