GB1088271A - Electric cells - Google Patents

Abstract

1,088,271. Sealed alkaline electrolyte secondary cells. BURNDEPT Ltd. April 7, 1964 [April 4, 1963], No. 3904/63. Heading H1B. In a sealed, alkaline electrolyte, secondary cell which is designed to deliver substantially its whole theoretical capacity in not more than two hours, the negative electrode system has a greater theoretical capacity than the positive, and, at the moment of sealing, the positive electrode system has material in the uncharged state, while the negative electrode system has a main body of uncharged cadmium oxide or hydroxide, together with such a reserve of charged cadmium metal that the total charge on the negative electrode system exceeds that on the positive. If desired an additional reserve of charged material may be included in the negative electrode to compensate for deterioration of the electrode during its lifetime. Preferably the action materials on the electrodes are bound with elastomers, e.g. polyisobutylene. The active materials of the positive electrode may be nickel, nickel hydroxide and a small proportion of cobalt hydroxide. Graphite may also be included. The negative electrode contains calcium oxide, nickel powder, and if desired graphite and iron oxide. The mixtures may be coated on to nickel gauge or expanded foil. The electrodes may be of sintered construction. The negative electrode system may be prepared as two strips one for the main body and the other an auxiliary electrode for the reserve of charged material. Strips of positive electrode material 10, separators 16, 18, main negative electrodes 12, and auxiliary negative electrodes 14 are superimposed and wound on a slotted mandrel into a spiral which is enclosed in a can 20 between insulating end discs 22, 24, which are apertured to allow contact strips 26 and 28, 29 to pass through from the electrodes and be connected to the terminals 30, and the bottom of can 20. The auxiliary negative electrode is fully precharged before incorporation in the cell. In a modification the slotted mandrel is applied to the middle of the pack of electrode strip and separators. A button cell construction is also described with the electrodes and auxiliary electrodes and separators as superimposed flat plates. A safety device to prevent bursting of the cell if gas pressure accumulates may consist of a diaphragm structure across the top of the electrodes with an inturned pointer by constituting a piercer on the top cap of the cell. If cells are to be connected together as batteries, overdischarge of a weak cell can be avoided by connecting an auxiliary electrode of uncharged negative material to the positive electrode.