Patent GB-590466-A (GB)
Title: Improvement in dry primary cells
IPC: H01M6/10
Filed: 1944-05-03
Abstract: 590,466. Primary batteries. MALLORY & CO., Inc., P. R. May 3, 1944, No. 8394. Convention date, Dec. 9, 1942. [Class 53] A primary cell is provided with electrodes separated by an absorbent spacer which is impregnated with a solid crystalline electrolyte containing at least' 30 per cent of water of crystallization. Potassium hydroxide is the preferred substance and the electrolyte is prepared by dissolving between 200 and 400 grams of potassium hydroxide, containing about 13 per cent water, in a litre of water at 120‹ C. The solution on cooling becomes a hard solid mass. Sodium and lithium hydroxides can also be used either alone or mixed with potassium hydroxide. The voltage of the cell on open circuit may be increased by adding a small amount of sulphur or a sulphide such as ammonium sulphide to the hydroxide before the water is added. The addition of selenium is said to have a similar effect. The voltage may also be raised and the internal resistance of the cell reduced by using spacers between the electrodes made of porous cotton paper in combination with sheets of regenerated cellulose. Bentonite may be added to the electrolyte for the same purpose. Fig. 1 shows the method of making a dry cell having strip electrodes 11, 14 of steel and zinc. The steel strip 11 is coated with a depolarizing mixture 15 and is welded at one end to a steel rod 10. The strip is covered on each side with two layers 12, 13 of regenerated sheet cellulose and wound into a roll with a strip 14 of corrugated zinc having a zinc terminal strip 16 welded to it. The depolarizer 15 may consist of a mixture of copper oxide and graphite and a solution of polymerized vinyl chloride in ether, and is painted or sprayed on both sides of the steel strip 11. After drying, the strip is baked at 130‹ C. and then passed between steel rollers at a temperature of 125‹ C. Alternatively, the depolarizing electrode may be produced by oxidizing a copper or copper-plated foil. After the roll has been completed it is placed on an insulating disc 20 in a zinc can 18, Fig. 2, and the strip 16 welded to the can at a point 19. The whole is then heated to 100‹ C. and immersed in the hot liquid electrolyte in a partial vacuum. The spaces between the electrodes become filled with the electrolyte which also impregnates the cellulose spacing strips which swell and fill any remaining space provided by the corrugations in the zinc electrode. The cell is then removed and allowed to cool. At 80‹ C. the electrolyte crystallizes and at room temperature it becomes a hard solid mass in which the elements of the cell are imbedded. The cell is closed by an insulating washer 22 and a rubber disc 23 which acts as a valve to allow gas to escape through its central aperture, but prevents the entry into the cell of carbon dioxide and moisture from the atmosphere. Instead of the discs 22, 23, a layer of pitch may be used to seal the cell. A number of cells may be connected to form a battery in which case the zinc can 18 is dispensed with. The individual rolled-up elements shown in Fig. 1 are impregnated with electrolyte in vacuo at 110‹ C. and then inserted in insulating containers closed by a layer of wax. The zinc strip 16 of each cell is connected to the rod 10 of the adjacent cell and all the cells are placed in a box closed by a wax layer. In a modified form of cell, the zinc strip 14 is not corrugated and is separated from the steel strip 11 by layers of nylon cloth or glass cloth and cellulose. Fig. 4 shows a further modification in which the cell is of disc form. One electrode consists of a steel disc 41 carrying a copper oxide depolarizer 42 and an insulating ring 44 cemented to the layer 42. Two cellulose discs 43 impregnated with electrolyte are placed in the ring 44 to which the zinc disc electrode 40 is then cemented. Several cells may be stacked and held together by a rubber band or the stack may be enclosed in a cardboard tube closed at the ends by cardboard discs through the centres of which the terminals project. Depolarizers other than copper oxide may be used such as sulphide of copper or lead sulphide or lead oxide and cadmium may be substituted for the zinc electrode. Specification 579,849 is referred to.