SEPARATOR FOR STARVED ELECTROLYTE LEAD/ACID BATTERY

Abstract: Compositions and papers made therefrom useful as separator materials in starved electrolyte lead/acid batteries. The compositions comprise a mixture of 30 percent to 80 percent by weight of perlite and 20 percent to 70 percent by weight of glass fibers. The glass fibers have diameters in the range of from 0.3 to 1.0 micrometers while the perlite has particle sizes in the range of from about 3 to about 100 micrometers. Higher tensile strength papers are formed from an embodiment in which the compositions comprise a mixture of 15 percent to 75 percent by weight of perlite, 20 percent to 70 percent by weight of glass fibers and 5 percent to 20 percent by weight of acid-insoluble thermoplastic fibers, the latter preferably in the form of staple fibers.

Description: SEPARATOR FOR STARVED ELECTROLYTE LEAD/ACID BA2TEKY Technical Field The invention herein relates to lead/acid electric storage batteries. More particularly it relates to separators for such batteries. 5 Background of the Prior .Art Recently efficient maintenance-free rechargeable sealed lead/acid storage batteries utilizing a "starved electrolyte" concept have been introduced ∞mmerically. Various aspects of batteries of this type are disclosed in a number of patents, most notably U.S. 10 Patent No. 3,862,861. Such batteries normally utilize as separators materials such as -microporous rubber, polyvinyl chloride, polyolefins, phenolic resin impregnated paper or (preferably) glass paper m__de from microfiber diameter, unwoven, short staple glass fibers. These batteries, while useful in a wide variety of applications, have been 15 severely limited in the practical sizes which can be commercially utilized because of the high cost of these batteries per unit of energy density. __hus. while cells of the common C, D, "beer can" and similar sizes are practical for some purposes commercially, larger sizes such as the typical automotive battery size are far too costly for 20 commercial practicality. Similarly, the high unit density cost of even the smaller size batteries have restricted these types of batteries to high value end uses such as in spacecraft and emergency equipment, effectively eliminating the batteries from the fields of conventional consumer use such as flashlights, radios and the like. 25 In these types of batteries a very high proportion of the cost of battery materials lies in the cost of the separator. The preferred microfiber glass paper separators are extremely costly. In the past, however, all attempts to substitute lower cost materials WIPO have led to battery structures with significantly poorer electrica characteristics. It would therefore be highly desirable to have a separato material (as defined herein) suitable for use in batteries of the typ described which will provide equivalent or superior electrica characteristics as compared to the present high cost materials, bu which would utilize materials having a markedly lower cost than th present materials, thus making the batteries economically feasibl for use in a much wider range of aplication, particularly includin the automotive ("SLI") battery market. Brief Summary of the Invention The invention herein includes a separator composition fo use in a starved electrolyte lead/acid battery which comprises mixture of 30 percent to 80 percent by weight of expanded perlite an 20 percent to 70 percent by weight of glass fiber, wherein the glas fibers have diameters in the range of from about 0.3 to about 1. micrometers and the perlite has particle sizes in the range of fro about 3 to about 100 micrometers. where higher tensile strength i desired a portion of the perlite may be replaced by substantially acid insoluble thermoplastic fibers, to give a composition for use as separator in a starved electrolyte lead/acid battery which comprise a mixture of 15 percent to 75 percent by weight of expanded perlite the perlite having particle sizes in the range of from about 30 t about 100 micrometers; 20 percent to 70 percent by weight of glas fibers, wherein the glass fibers have diameters in the range of fro about 0.3 to about 1.0 micrometers and 50 percent to 20 percent b weight of substantially acid-insoluble thermoplastic fibers. Thes compositions have been found to be essentially equivalent in al important physical, chemcial and electrical properties to th microporous glass papers but are of approximately only half the cost The invention also includes paper articles made from these composition and battery separators made from the papers. Detailed Description of the Invention The articles .utilizing the compositions of this inventio are denominated "separators" for the starved electrolyte lead/aci batteries, following the nomenclature of the prior patents, especiall the aforesaid U.S. Patent No. 3,862,861. However, it will b < . OMPI , V.IrO recognized from the structure of these starved electrolyte batteries that the articles, unlike separators in conventional batteries, are multifunctional, in that they possess not only a separator function but also a reservoir function, wherein they serve to retain the electrolyte within the battery. It is believed that the microporous nature and the high specific surface area of the present articles, with their myriads of minute passageways and interstices, impart to the articles their ability to combine these different functions. For the purposes of this specification, therefore, the practice of the aforesaid prior patents in labeling these articles "separators" will be adhered to, but the difference between the present multifunctional articles (witn their "separator/reservoir" nature) and conventional battery separators should be recognized. The compositions herein are foremd from a mixture of expanded perlite granules and small diameter glass fibers. Perlite is a rhyolitic glassy rock formed by volcanic action. Perlite is unique among the glassy materials in that it contains a significant proportion of combined water which, when the perlite is crushed and rapidly heated, is converted to steam and causes the perlite granules to expand of "pop" to from expanded perlite granules with volumes some 4 to 20 times greater than the volume of the original unexpended particles. Bulk densities of the expanded materials are commonly in the range of from about 0.03 to about 0.25 g/αn . The high volume low bulk density expanded perlite has in the past been used in a variety of applications, including as filter aids, the mal insulation, lightweight concrete aggregates and for horticultural use. However, expanded perlite has never before been considered as having utility in electric batteries. In the compositions of this invention the perlite will be present in the form of generally irregular particles having nominal particle sizes in the range of from about 3 to about 100 micrometers. Most suitable for use in the present invention are those grades of perlite havin gparticle sizes in the range of from about 10 to about 35 micrometers. Suitable grades of perlite are available commercially from Johns-Manville Corporation. In the basic two-component composition, the perlite will be present as from about 15 percent to about 80 percent, preferably 50 percent to 70 percent, of the composition. (Unless otherwise states, all percentages herein are by weight.) Since perlite is a natural material, the composition sof batches taken from different ore bodies or even different parts of the same ore body will normally vary, sometimes widely, but normally within fairly well defined limits. Typical perlite chemical analyses show 71 percent to 75 percent SiO , 12 percent to 18 percent Al 0 . 7 percent to 9 percent K 0 and Na 0 with the remainder being a wide variety of other oxides and elements including materials such as calcium, iron, magnesium and titanium oxides. Typical analyses are described in Industrial Minerals, page 17 (May, 1977). The exact composition of the perlite is not critical in this invention, as long as the perlite used is chamically and electrically compatible with the other materials in the present separator compositions and also in the assembled batteries. The glass fibers used in the present compositions may be any of a wide variety of glass fiber forming compositions. The fibers formed from such compositions must have average volume surface diameters in the range of from 0.3 to 1.0 micrometers. Typical glass compositions for glass fibers useful ' in this invention include those shown in U.S. Patent No. 3,085,887. The glass fibers will be present in the composition as from about 20 percent to about 70 percent, preferbly 30 percent to 50 percent, of the composition. Compositions containins less than about 20 percent of glass fiber do not produce papers with adequate physical -_-.tegi_.ty "to 'w i stand handling, while those with more than about 85 percent glass fiber give no added electrical properties but are significantly costlier. For sane uses it may be desirable to have increased tensile strength in the papers. For example, in sane battery production methods, the separator is in the form of a long paper strip which is wound in a spiral fashion with the electrical plate materials to form cylindrical batteries. Typical of this type of construction are the batteries shown in the aforementioned U.S. Patent No. 3,862,861. The winding operations to form such batteries are performed at high speed and_ under high tensile loads. In 'Such cases it has been found appropriate to replace a portion of the perlite with a quantity of substantially acid-insoluble thermoplastic fibers. These fibers are _ s OM Λ. WIP present as 5 percent to 20 percent, preferably 10 percent to 15 percent, of the composition and the corresponding perlite contents are 15 percent to 75 percent, preferably 40 percent to 60 percent, of the composition. Minimum glass fiber content is not changed. The fibers may be staple or chopped form. Typical among the fibers which are useful in this composition are polypropylene fibers, saran fibers (predominantly polyvinylidene chloride units in the polymer), ethylene/propylene copolymer fibers, polyethylene fiber and vinyon fibers, such as fibers of copolymers of p . olyvinyi chloride and polyvinyl acetate. The staple fibers or chopped fibers should have an aspect ratio (i.e., length:diameter ratio) on the order of about 1000:1. The aspect ratio may vary widely, however, as long as the staple or chopped fibers have sufficient length to provide significant increases in tensile strength to the papers and sepaarators as compared to papers and separators of the prior invention not containing such staple or chopped fibers. Since the papers are normally wet-laid from slurries of fibers and perlite, the thermoplastic fibers should not be of undue length so that clumping and other formation problems can be avoided. Those skilled in the art of paper making will be iπmediately aware of. the maximum and minimum practical lengths for chopped fibers or staple fibers in order to get good formation during the paper making process as described below and have good tensile strength in the finished products. The separator articles of the present invention may also contain small amounts (up to a few perent by weight) of other mat≤ri&ls such as unexpanded perlite, glass fragments, silica particles and the like. Because the nature of the separator is vitally important to the electrical performance of the finishjed battery, however, such materials should be present only if they do not detrimentally affect that electrical performance. Since the effect on electrical performance of the various types of potential impurities cannot be readily determined, it is preferred that the amount of impurities be minimized and the compositions herein be composed essentially entirely of the expanded perlite, glass fiber and, if present, the thermoplastic fibers. The compositions of the present invention are formed into sheets of paper, from which the separator materials of the present invention are made, in the manner of conventional paper making. The glass fibers, expanded perlite and thermoplastic fibers are dispersed in water, or preferably an aqueous acid slurry (pH of about 3), ' which is stirred so as to cause the perlite and fibers to become thorougly 5. and randomly mixe -with each other. The perlitε/fiber mixture is then deposited from the slurry onto a conventional paper making screen or wire as in a Fourdrinier machine or a Rotoformer machine to form a matted paper. For these purposes the perlite in the furnish should not contain more than about 5 percent, preferably not more than about 0 1 percent, of "floaters," which are perlite particles which float on the surface of the water slurry. Floaters are detrimental because they do not get incorporated into the fiber matrix of the paper, but are deposited .last as the slurry drains and thus form a loose dusty layer on the surface of the paper. Quanitites of floaters greater 5 than those mentioned above merely increase the problem. __he paper formed of che fibers and perlite particles is then dried and collected in a conventional manner. If thermoplastic fibers are present, following collection of the dry paper the paper is heat treated to "seal in" the fibers. This is accomplished by heating the paper at 0 a temperature of approximately 260°F to 280°F (125°C to 135 * C) for a short period. In commerical operation, this would normally be carried on by passing the dry paper through hot press rolls where the paper would be in contact with the rolls for a few seconds. Thereafter, the paper may be cut to sizes appropriate for the various 5 size batteries in which the separator materials are to be used. Statement of Industrial Application The materials of the present invention find application as separators and reservoirs in starved electrolyte lead/acid storage batteries. Batteries using such materials will in turn find 0 application for many electrical power generating uses including automotive electrical systems.

Claims: *- Claims 1. A composition, useful as a separator material in starved electrolyte lead/acid batteries, which comprises a mixture of 30 percent to 80 percent by weight of expanded perlite and 20 percent 5 to 70 percent by weight of glass fiber, said glass fibers having diameters in the range of from about 0.3 to about 1.0 micrometers and said perlite having particle sizes in the range of from about 3 to about 100 micrometers. 2. A composition as in Claim 1 consisting essentially of 10 said expanded perlite and said glass fibers. 3. A composition as in Claims 1 or 2 wherein said expanded perlite is present as from 50 percent to 70 percent by weight of the composition and .said glass fiber is present as from 30 percent to 50 percent by weight of the composition. 15 4. A composition as in any of Claims 1, 2 or 3 wherein said expanded perlite has particle sizes in the range of from about 10 to about 35 micrometers. 5. A paper useful as separator material in a starved electrolyte lead/acid battery comprising the composition of any of 20 Claims 1 through 4 in matted form. 6. A battery separator for a starved electrolyte lead/acid battery formed from a paper as in Claim 5. 7. A composition, useful as a separator mterial in starved electrolyte lead/acid batteries, which comprises a mixture of 15 25 p ercent to 75 percent by weight of expndeό? perlite, 20 percent to 70 percent by weight of glass fibers and 5 percent to 20 percent by weight of acid-insoluble thermoplastic fibers, said glass fibers having diameters in the range of from about 0.3 to about 1.0 micrometers and said perlite having particle sizes in the range of from about 3 to 30 about 100 micrometers. 8. A composition as in Claim 7 consisting essentially of said expanded perlite, glass fibers and thermoplastic fibers. 9. A composition as in Claims 7 or 8 wherein said expanded perlite is present as from 40 percent to 60 percent by weight of the 35 composition, said glass fibers are present as from 30 percent to 50 percent by weight of the composition, and said thermoplastic fibers are present as on the order of about 10 to 15 percent by weight. 10. A composition as in any of Claims 7, 8 or 9 wherein said expanded perlite has particle sizes in the range of from about 10 to about 35 micrometers. 11. A composition as in any of Claims 7 through 10 wherein said thermoplastic fibers are selected from the group consisting of saran fibers, polypropylene fibers, ethylene/propylene copolymer fibers, vinyon fibers and polyethylene fibers. 12. A composition as in Claim 11 wherein said thermoplastic fibers are in the form of staple fibers. 13. A paper useful as a separator material in a starved ' electrolyte lead/acid battery comprising the composition of ' any of Claims 7 through 12 in matted form. 14. A battery separator for a starved electrolyte lead/acid battery formed from a paper as in Claim 13.

Inventors: BILAWSKY P, CAIN C, GROSS S, SCHEFFEL N
Applicants: JOHNS MANVILLE, JOHNS MANVILLE CORP
Application year: 1980
Main classification: H01M2
IPC codes: H01M2