GB561056A - Improvements in or relating to electric secondary batteries of the so-called dry type - Google Patents

Abstract

561,056. Galvanic batteries. FULLER, L., and SUDLOW, E. W. Sept. 28, 1942, No. 13563: [Class 53] A lead-acid accumulator of the " dry " type, in which all the space in the container which is not occupied by the electrodes is filled with porous separating material. to form a porous block in which the whole of the electrolyte is absorbed, is characterized by the fact that either the porosity factor of the whole block comprising the electrodes and separating material, or the porosity factor of either the positive or negative electrode, or of both electrodes, is at least 50 per cent. The porosity factor is the ratio of the total free space within the mass to the total volume of the mass. By making the electrodes sufficiently porous substantially the whole of the active material may be used efficiently with little more than the theoretical minimum quantity of acid ; the rise in resistance of the battery during discharge is diminished, so improving the voltage characteristic ; the discharge rate may be increased; and " choking " of the active material by sulphate is diminished. The desired porosity may be obtained by mixing a salt with the electrode material which dissolves out when the pasted plates are formed leaving pores. Alternatively, particles of porous filling material may be used and remain in the plates, for example powdered ceramic, 'aluminium oxide or silicate, active carbon black or charcoal, or natural or synthetic fibrous material. Examples of pasting mixtures for negative electrodes containing carbon black, asbestos fibres, or aluminium oxide, and having porosities of from 40 to 60 per cent are given. A pasting mixture for positive electrodes containing asbestos fibre, and having a porosity factor of 50 per cent, and another in which a porosity of 60 to 70 per cent is obtained by the formation of a relatively large amount of sulphate in the material, are also given. The porous separating material may be made as described in Specification 537,377, [Group V], of glass wool consolidated by a mixture of kieselguhr and a binding agent and compressed, the porosity varying between 50 and 80 per cent. The electrodes may be assembled in the accumulator prior to forming them, as described in Specification 550,334. Specifications 432,775, 506,062 and 540,591 are also referred to.