Battery Technologies, Inc.

Varta Batterie Aktiengesellschaft

Josef Gsellmann

Karl Kordesch

Klaus Tomantschger

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.

Rechargeable alkaline manganese dioxide-zinc cell having improved

A rechargeable alkaline electrochemical cell has a manganese dioxide cathode and a zinc anode. The cathode is mixed with graphite or other conductive carbon and a binder, and is contained by a metallic screen which also serves as an oxygen evolution catalyst. The screen also serves to contain the cathode in place as it tends to expand under use. A diaphram is provided to separate the cathode and anode; an alkaline electrolyte contains the cathode and anode, and the other components of the cell.

Rechargeable alkaline manganese cells with zinc anodes

A rechargeable galvanic element with constant-volume positive manganese dioxide electrode. In a rechargeable galvanic element having an alkaline electrolyte and a positive manganese dioxide electrode the volumetric change of the electrode body caused by phase transformation, which entails undesired contact losses, is largely prevented by exertion of a steady pressure upon the electrode surfaces. For a concentric electrode arrangement, this can be done with particular effectiveness. For example, the pre-pressed MnO.sub.2 electrode can be forced into a rigid cylindrical metal cage, while the annular slot enclosed by the housing cup, lid and bottom insulation is occupied by the zinc electrode. In other cases, continuous take-off contact is preferable, using pressure springs or tensioned metal mesh which extend over the flat electrodes.

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Graz, Austria

Josef Gsellmann