Chemistry: electrical current producing apparatus – product – and – Sealed cell having gas prevention or elimation means
Patent
1981-01-09
1983-02-08
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Sealed cell having gas prevention or elimation means
429204, 429225, 429250, H01M 1006
Patent
active
043730159
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to lead acid electric storage batteries, and is particularly concerned with such batteries of sealed or recombinant type in which the gas evolved during operation or charging is induced to recombine within the battery at the battery electrodes.
BACKGROUND ART
Recombinant lead acid batteries are known. An object of the present invention is to provide such a battery having improved separator characteristics.
The invention, although described with reference to batteries, is not restricted to batteries but is also applicable to single cells e.g. spirally wound cells, and the claims to batteries thus include single cells within their scope.
DISCLOSURE OF THE INVENTION
According to the present invention there is provided a recombinant lead acid electric storage battery in which the positive and negative plates in each cell are separated by separators of electrolyte and gas permeable compressible fibrous separator material comprising organic polymeric fibres, the separator material having an electrolyte absorption ratio of at least 100%, the volume E of electrolyte in the battery preferably being at least 0.8 (X+Y) where X is the total pore volume of the separators in the dry state and Y is the total pore volume of the positive and negative active materials in the dry fully charged state, the battery at least when fully charged having substantially no free unabsorbed electrolyte whereby substantial oxygen gas recombination occurs in the battery at charging rates not in excess of C/20.
The ratio of X to Y may be in the range 6:1 to 1:1 e.g. 5.5:1 to 1.5:1 or more preferably 4:1 to 1.5:1.
The charging rate is desirably kept at not greater than C/15 and preferably less than C/20 e.g. C/20 to C/60. The volume of electrolyte is desirably in the range 0.8 (X+Y) to 0.99 (X+Y) and especially at least 0.9 (X+Y) or even at least 0.95 (X+Y). These values enable the active material to be utilized more efficiently than when lower amounts of electrolyte are used.
We have found that surprisingly oxygen gas recombination can still occur at the negative electrodes at these very high levels of saturation of the pores which is contrary to what is conventional in recombinant sealed lead acid cells.
The electrolyte active material ratio is at least 0.05 e.g. at least 0.06 or at least 0.10 and is the ratio of H.sub.2 SO.sub.4 in grams to the lead in the active material on the positive and negative electrodes calculated as grams of lead.
It is preferably in the range 0.10 to 0.60 especially 0.11 to 0.55 e.g. 0.20 to 0.50.
The ratio of negative to positive active material (on a weight of lead basis) may be in the range 0.5:1 to 1.5:1 e.g. 0.6:1 to 1.4:1. The use of ratios below 1:1 is contrary to what is conventional but we find that recombinant operation can be achieved at these ratios and they have the advantage of providing more positive active material for the same cell volume. We thus prefer to use ratios in the range 0.6:1 to 0.99:1 e.g. 0.7:1 to 0.9:1.
As mentioned above the separator material is a compressible absorbent fibrous material having an electrolyte absorption ratio of at least 100% e.g. of 100 to 200% especially 110 to 170%. It is electrically non-conducting and electrolyte resistant.
Electrolyte absorption ratio is the ratio, as a percentage, of the volume of electrolyte absorbed by the wetted portion of the separator material to the dry volume of that portion of the separator material which is wetted, when a strip of the dry separator material is suspended vertically above a body of aqueous sulphuric acid electrolyte of 1.270 SG containing 0.01% by weight sodium lauryl sulphonate with 1 cm of the lower end of the strip immersed in the electrolyte, after a steady state wicking condition has been reached at 20.degree. C. at a relative humidity of less than 50%.
The thickness of the separator is measured with a micrometer at a loading of 10 kilpascals (1.45 psi) and a foot area of 200 square millimeters (in accordance with the method of British standard specification
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Culpin Barry
Peters Kenneth
Chloride Group Limited
Skapars Anthony
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