Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Patent
1998-03-19
2000-11-07
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
429225, H01M 414
Patent
active
061434418
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of batteries and, more specifically, to separators containing glass fibers which are positioned between the positive and negative plates of batteries and to a method for producing such separators.
DEFINITIONS
Subsequently herein, the term "percent v/v" means percent by volume; the term "percent w/w" and the symbol % mean percent by weight; the term "wire", as applied to a paper making machine, means the surface of the machine on which a furnish is cast in producing paper, and can be, for example, the screen of a Fourdrinier machine or the vacuum drum of a rotoformer machine; all temperatures are in .degree. C.; and the following abbreviations have the meanings indicated: psi means pounds per square inch, .mu.m=micron or microns; mg=milligram or milligrams; g=gram or grams; kg=kilogram or kilograms; l=liter or liters; ml=milliliter or milliliters; cc=cubic centimeter or cubic centimeters; pcf=pound per cubic foot or pounds per cubic foot; m=meter or meters; cm=centimeter or centimeters; KPa=pressure in thousands of Newtons per square meter; and KN=force in thousands of Newtons.
2. Description of the Prior Art
Valve regulated ("sealed"--"recombinant") lead acid (VRLA) batteries are known; they usually comprise a plurality of positive and negative plates, as in a prismatic cell, or layers of separator and positive and negative electrodes wound together, as in a "jelly roll" cell. The plates are arranged so that they alternate, negative--positive--negative, etc., with separator material separating each plate from adjacent plates. The separator, typically composed of a mat of glass fibers, is an inert material; it stores battery acid without stratification, and provides low electric resistance. In addition, in VRLA batteries, the separator material provides innumerable gas channels between the plates through which oxygen can migrate from the positive electrode, when generated there, to the negative electrode where it can be recombined with hydrogen, according to the oxygen cycle. Another important function of a separator is to exert pressure between the plates, ensuring that there is an interface, along the faces of the plates, among the plate paste or active material, the electrolyte and oxygen.
Glass fiber separator material is produced commercially on paper making equipment including fourdrinier machines and rotoformers, inclined fourdrinier machines and extended wire rotoformers. In the production of separator made of glass fibers for VRLA batteries, it is preferred that no organic binder be added to a furnish from which separator sheets are made; the entanglement of individual fibers serves to maintain the sheet in a cohesive structure, and water glass, which sometimes forms on the fiber surfaces, serves as a binder. Organic binders, however, tend to decrease the ability of a separator to wick acid, and to decrease the amount of acid a separator can hold. A great deal of work has been directed to modifying the glass fiber furnish from which separators are produced to improve battery performance and/or lower the cost of the separator. Some of the work has entailed the addition of synthetic fibers for various reasons, such as the use of thermoformable plastic fibers so that the separator can be heat sealed on its edges to envelop a plate. Other work, which pertains to the field of this invention, has been directed to the use of filler, e.g., silica, to provide separators which are comparable to all glass fiber separators, at a lower cost. Prior art patents are discussed below.
U.S. Pat. No. 4,465,748 (Harris) discloses glass fiber sheet material for use as a separator in an electrochemical cell, and made from 5 to 35 percent w/w of glass fibers less than 1 .mu.m in diameter; the patent also discloses a glass fiber sheet for such use wherein there are fibers of a continuous range of fiber diameters and lengths, and most of the fibers are not over 5 mm in length.
U.S. Pat. No. 4,216,280, (Kono et al.)
REFERENCES:
patent: 4137377 (1979-01-01), McClelland
patent: 4262068 (1981-04-01), Kono et al.
patent: 4414295 (1983-11-01), Uba
patent: 5225298 (1993-07-01), Nakayama et al.
patent: 5468572 (1995-11-01), Zguris et al.
Harmon, Jr. Frank C.
Zguris George C.
Hollingsworth & Vose Company
Nuzzolillo Maria
Purdue David C.
Purdue John C.
Wills M.
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