Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Reexamination Certificate
1999-03-03
2001-10-23
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
C429S225000, C429S142000, C429S141000, C429S129000, C429S251000, C429S249000, C429S248000, C429S247000
Reexamination Certificate
active
06306539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of batteries and, more specifically, to batteries in which mat containing glass fibers, commonly called separators, are positioned between the positive and negative plates and to a method for producing such mats or separators and batteries. As is subsequently discussed in more detail, separators containing glass fibers are well known. Long before glass fiber separators, however, cedar veneers were used as a separator material, and were replaced by microporous, hard rubbery separators and cellulose separators impregnated with resins.
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 which can be a prismatic flat plate, or in 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 wet laid nonwoven glass fibers, is an inert material; it stores battery acid, 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 against the plate paste or active material which forces the paste into contact with the plate, and causes a pressure between the positive active material and the positive grid and between the plates, ensuring that there is not an interface at which corrosion. which would cause premature capacity loss (PCL), can occur.
Glass fiber separator material has been produced commercially by wet processes 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 microglass fibers serves to maintain the sheet in a cohesive structure, and water glass or any of various sulfate salts, which sometimes form 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 a filler, e.g., silica, or another siciciferous material, to provide separators which are comparable to all glass fiber separators, at a lower cost. Separators made from glass fibers to which cellulose has been added and polyolefin fibers to which cellulose has been added have also been suggested. 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 &mgr;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.), discloses glass fiber sheet material for use as a plate separator in a battery, and made from 50 to 95 percent w/w of glass fibers less than 1 &mgr;m in diameter and 50 to 5 percent w/w of coarser glass fibers. The coarser glass fibers, the reference says, have a fiber diameter larger than 5 &mgr;m, preferably larger than 10 &mgr;m , and it is advantageous for some of the coarser fibers to have diameters of 10 &mgr;m to 30 &mgr;m.
U.S. Pat. No. 4,205,122 (Minra et al.) discloses a battery separator of reduced electric resistance comprising a self supporting, non woven mat consisting essentially of a mixture of olefinic resin fibers having a coarseness of from 4 to 13 decigrex and olefinic resin fibers having a coarseness of less than 4 decigrex, the latter fibers being present in an amount of not less than 3 parts by weight per 100 parts by weight of fibers; up to about 600 parts by weight of inert filler materials per 100 parts by weight of fibers can also be used. The battery separator is produced by subjecting a suitable aqueous dispersion to a sheet-forming operation, drying the resulting wet, non-woven mat, and heat treating the dried mat at a temperature ranging from a point 20° C. lower than the melting point of the aforementioned fibers to a point about 50° C. higher than the melting point.
U.S. Pat. No. 4,216,281 (O'Rell et al.) discloses a separator material produced from a furnish containing 30 to 70 percent w/w of polyolefin synthetic pulp, 15 to 65 percent w/w of a siliceous filler and 1 to 35 percent w/w of “long” fibers which can be polyester fibers, glass fibers, or a mixture of the two. Cellulose in an amount up to about 10 percent w/w is disclosed as an optional ingredient of the furnish.
U.S. Pat. No. 4,336,314 (Yonnezu, et al), assigned to Japan Storage Battery Company, discloses a pasted lead acid battery with greatly extended service life and capacity over the usuable service life therof. The battery has a glass mat, which may be of a dual layer construction, disposed adjacent positive plates of assembled elements. This patent teaches the importance of pressure that must be applied to the assembled elements, for example by a binding band, or from outside the battery container. As the pressure applied to the elements increases, the patent says, the charge and discharge cycle life increases although the relationship is said not to be linear. That is, in a pressure range of from 40 to 60 g/dm
2
, the life is abruptly increased by a factor of 2 to 2.5 as the pressure increased. Therefore, up to about 100 kg/dm
2
, the life remains substantially unchanged. However, if pressure exceeds about 100 kg/dm
2
, the life decreases. The tendency to decrease depends on the type of glass mat used. The life of the lead acid cell using the glass mat having a dual layer structure was found to be excellent at a low pressure range while the life of such cell increases by a fator of about two at a pressure of 20 kg/dm
2
.
The patent also states that the pressure applied to the assembled element presses on each plate and prevents the aforementioned expansion effect attributed to changes in structure of the active material layer. During use, it is necessary to prevent a reduction of the degree of pressure. It was found that the greatest cause for the reduction of the pressure applied to the assembled element is that, when the glass mat is wetted, its thickness decreases. The patent discloses that the degree of reduction of pressure applied to the glass mat depends upon the technique used in fabricating the glass mat. In general it is stated that it is desirable in a glass mat employed in a lead acid battery for the degree of pressure applied when the mat is immersed in dilute sulfuric acid to be more than 70% of the degree of pressured applied in the dry state. The importance of pressure was clearly noted and the main solution was external pressure devices. The method of making the glass material was not stated but a Japanese disclosure, No. 5505306 JPA1 issued to applicant: Japan Storage Battery Company Ltd., discloses a dual layer glass mat produced by a wet laid process. U.S
Brouillette Gabrielle
KVG Technologies, Inc.
Martin Angela J.
Purdue David C.
Purdue John C.
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