Rechargeable alkaline manganese dioxide-zinc cell having improved

Abstract

This invention relates to rechargeable alkaline electrochemical cells, having manganese dioxide cathodes. Generally, those cells have zinc anodes and an alkaline electrolyte, but several other options are considered. In any event, the present invention provides an improved cell by providing a pre-conditioned manganese dioxide cathode, where the net oxidation state of the cathode at the time that the cell is finally assembled and sealed is such that the manganese dioxide is, in fact, MnOx where x is between 1.70 and 1.90. The preconditioned cell may be preconditioned by cycling the cathode in a unsealed cell, then replacing the zinc anode and sealing the cell; or by adding a reduction agent to the manganese dioxide cathode prior to the time when the cell is finally assembled and sealed; or by adding an overcharge reserve material to the cathode. By pre-conditioning the active cathode material, essentially partially reducing the oxidation state, the cumulative capacity of the cell, and its cycle life, are improved. Since the first cycle of a sealed manganese dioxide-zinc cell is a discharge, followed by a re-charge, the present invention assures that the re-charge efficiency of the cell is improved. In that manner, essentially a complete re-charge of the cell can be effected, even following the first discharge cycle. The invention also contemplates that the preconditioned manganese dioxide cathode may also be utilized, with a suitable non-aqueous electrolyte, in a rechargeable manganese dioxide-lithium cell.