CH619321A5 - Method of manufacturing a microporous separator for accumulators - Google Patents

Abstract

The microporous separator for batteries is manufactured in the following manner: A master batch is first formed by mixing at room temperature and under low shear, a thermoplastic binder such polyvinyl chloride, with a plastifier such as dioctyl phthalate or adipate. Still under the aforementioned conditions, an inorganic filler, for example silica, a solvent (cyclohexanone) and a non-solvent (water) are added. The mixture is extruded and calendered, and the sheet obtained is passed into a water bath where the solvent is removed from the sheet. The latter is then dried in order to remove the non-solvent and the water of the bath. The separator thus obtained has micropores, is wettable, has an electrical resistance <0.01 OMEGA /cm<2>, an extension >40%, a pore diameter of approximately 1 mu and a tensile strength >10.5 kg/cm<2>.

Description

This invention relates to a process for manufacturing separators made of microporous and flexible sheets of plastic which are used as separators between the plates of electric accumulators.

As is known in the art, an accumulator separator must be porous to allow the passage of ions between the plates as well as the free diffusion of the acid. In addition, the battery separator must be resistant to acid attack and electrochemical oxidation and it must also be resistant and durable. More particularly, it is highly recommended that the separator be flexible enough to resist the formation of cracks during assembly because even small cracks if allowed to spread during use of the battery could lead to premature failure of the accumulator. In addition, the separator must be naturally hydrophilic since such separators for accumulators do not require the addition of a wetting agent.

As described, for example, in U.S. patents of Witt No. 2,772,322 and Selsor et al. No. 3,696,061, it is known in the art to manufacture separators for accumulators from compositons comprising a mixture of a plastic resin, a mineral filler and a solvent, so as to produce a semi-rigid and microporous sheet.

Attempts have been made to modify these plastic-based separators of the prior art to increase their flexibility and thus avoid the formation of cracks during assembly and handling, by adding plasticizers to the composition that is being treated.

However, it has been found that the simple addition of plasticizers to these compositions results in separators having significantly lower physical properties, and in particular significantly lower electrochemical properties when compared to unplasticized separators. It has been observed specifically that when plasticizers are added to these compositions the electrical resistance of the battery separator increases while the acid resistance of the resulting separator decreases.

Because of the above, it is an essential object of the present invention to provide a method for manufacturing a separator for a microporous accumulator, based on plastic and flexible material, resistant to the formation of cracks,

having good electrical properties and good resistance properties and which resists attack by acids and oxidation by electrochemicals, and which moreover is normally hydrophilic and wets easily without requiring the addition of a wetting agent, in which the plasticizer is not leached out during processing or use, and which is less prone to premature failure than the accumulator separators used so far.

The method according to the present invention is defined in independent claim 1. This method can in practice be carried out as follows:

The work consists of:

a) Combining, at room temperature in a low shear mixer, the binder which is a thermoplastic resin and the plasticizer in the quantities indicated above;

b) To add to said mixture the mineral filler, the solvent and the non-solvent, also in the preceding quantities;

c) mixing said ingredients until all the constituent parts are uniformly dispersed;

d) extruding or calendering said composition to form a sheet, microporous and flexible article;

e) passing said article through an extraction bath, and f) drying said article.

The composition which is described here and which can be transformed into a separator for accumulator, microporous, based

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of plastic and flexible material, consists of the ingredients being preferred. The following essential essential results are obtained: when the amount of solvent constitutes between 27% and 28% of a) a binder which is a thermoplastic resin; weight of the total composition.

b) a solvent which serves to dissolve the binder of thermoplastic resin; s The non-solvent, preferably water, represents between 28%

c) a mineral filler such as silica; and 34% by weight of the total composition, the range included d) a non-solvent such as water, and between 29% and 33% being preferred. We found that a quantity

e) a plasticizer. of non-solvent between 31% and 33% of the total weight of the

The binder, which is a thermoplastic resin, which composition is used gives particularly physical properties is preferably a good type m vinyl chloride resin binder and it is therefore preferred to use it within this range.

"EP" ("easy processing") that is to say easy to process, which is The plasticizer chosen must normally be compatible with porous and very absorbent. This thermoplastic resin binder in the system and thus, when mixed with the compositions may be a homopolymer of gamma vinyl chloride not mentioned above, must be able to improve the properties.

plasticized or a vinyl chloride copolymer mixed with an elongation tee of 1 resulting article without harming the properties small amount (less than about 15%) of a physical ethylene monomer such as electrical resistance and resistance to

such as, for example, vinyl acetate, chloride from acid attack or resistance to oxidation by vinylidene, ethylene propylene. A thermoplastic resin for electrochemical products. In this regard, any mono- plasticizer

particularly preferred as a binder is the mother homopolymer or polymer which achieves these objectives will be acceptable. This gamma vinyl chloride sold by Continental Oil Com- would include monomeric plasticizers such as, for example,

pany under the trade mark Conco 5385 although there is 20 'dioctyl sebaçate, as well as polymeric plasticizers obtained good results with homopolymers of chloride such as, for example, chlorinated polyethylene elastomer. The use

Gamma vinyl sold by the B.F. Goodrich Company under the sation of a monomeric plasticizer, and in particular of the phthalate trademark Geon 103 EP and by Solvey & Cie S.A. of dioctyl and dioctyl adipate, is preferred. We found

Belgium under the brand name Solvic 229. In addition, articles made from compositions containing other thermoplastic resins as binders can be used, if when one or the other of these two monomeric plasticizers is mixed with a solvent, they transform into a semi-mass with excellent physical and electrochemical properties.

pasty plastic for easy treatment and if by elimination The plasticizer must constitute between 4% and 10% of the weight of the solvent they are "deplasticized". In addition, the total thermosetting resin, the range between 4% and 8% being plastic chosen as a binder must be chemically and physically preferred. Particularly stable physical properties are observed under the conditions in which it must be good in the resulting article when the phthalate used is used. dioctyl in an amount between 6% and 7% of the weight of the

The thermoplastic resin used as a binder must re-total composition, and therefore when the dioctyl phthalate smell 10% to 16% of the weight of the total composition, the interval is P ^ ant, interval is much preferred. When between 11% and 15% being preferred. The plasticizer is obtained, however, is 1 ad. Dioctyl paste, particularly good results are preferred when the amount of resin "clearly ranges from 4.5% to 55%.

thermoplastic represents between 11% and 12% of the weight of the Pl "s of the previous" "g ^ 'ents, it is obvious for total composition and therefore we clearly prefer this inter-rhomme de1 art ^ on Can be used in other ingredients that do not change the essential nature of the resulting product.

The mineral filler may be an inorganic solid which may in fact contain many such ingredients as 30 parts of water or other volatile matter per 100 "" "Products for the purpose of improving other properties or in parts of non-volatile matter and must be able to release matter J * d ame, horer 1 accePtatl0n des Prodults sufle Plan m ^ nel.

volatile by heating to a temperature below the point of Typical ingredients understand but are not theirs.

decomposition of the thermoplastic resin. Although you are modifying or stabilizing droppings, for example, you can use any load satisfying these requirements, black and on one side.

't-, j 1J1- .... . . . . . = An important characteristic of the present invention is preferred a silica hydrogel or a hydrated silica precipi-, ..,> „, y. .. ^

tee. Precipitated hydrated silica is particularly preferred to manfe according to which one ml ml ™ ee * ingredients for and one can obtain it, for example, at PPG Coporation form ia C0mP0S1 / 10n Allowing to manufacture an artlde h under the trade mark Hi Sil 233 or at Chemische Fabrik as a separator for microporous accumulator, based

Hoechst from Germany under the brand name KS-300. from Iftiere P ftKlue ehtsoi! ple. ' P ^ mple: f. ,,

T,. t,, ...,. ry rri j su When I combine the ingredients mentioned above in

■ at <ar ^ e ms. ^? e rePyfsen eren re .06 ° u the quantities and intervals specified, it was found that the weight modes of the total composition, 1 interval included entée 20% and é4mtoires described in] e bFrevet des RU.A. ^ 3,696,061

23% of the weight of the total composition is preferred. When the, v ..., .., .f.

. ".J. -, * • / (above mentioned) can be used with certain modifications

amount of mineral charge is between 22% and 23%, on 2- tu /. „T,. XTO -, *,

n .., 6. . ... K,. . -,. tions. The U.S. Patent N 3 696 061 belonging to the product an article having physical and electrochemical properties ...,, c.

r. 1 x j i .r * c * ^ s 5 holder is cited here for reference.

particularly good miques and therefore we prefer net- „, ,,,. . t, ,, ^ ^ \ a

. ,, r We first prepare a starting batch (“masterbatch”) of this interval between the thermoplastic resinous binder and the plasticizer, by mixing

The solvent used, preferably an organic solvent, must for example dry at room temperature the parts

have a solvating action on the thermoplastic resinous binder in a low shear solid mixer, as a tick and must be able to be absorbed by the load. Although 1 on M, for example, a high intensity "liquid / solid" mixer can use organic solvents such as, for example, patterson-Kelley, for about 20 minutes. This can be

1 acetone, 1 ether, dimethylformamide, 1 orthochlorobenzene, to differentiate from the process used until now where tetrahydrofuran and certain ketones were used, cyclo is a high shear kneader, for example a hexanone kneader because it dissolves polyvinyl chloride and n is Henschel. Furthermore, in the processes used so far,

only slightly soluble in water. ft5 the thermoplastic resinous binder is mixed with the plasticizer

The solvent used, preferably cyclohexanone, is in the presence of heat to allow better absorption used in an amount between 26% and 32% of the weight of the plasticizer in the thermoplastic resinous binder. The total composition, with an interval of between 26% and 30% "Liquids / Solids" mixer of high intensity Patterson-Kel-

619,321

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2 (1

There is a preferred V-shaped section, although it is recognized that other mixing devices can be used for this purpose. The more an aliquot part of this starting batch, which is in the form of wet powder, is placed in a clean mixer and the mineral filler is added in the prescribed amount. Then we mix all the mixture, which then looks like a dry powder, until all the ingredients are evenly dispersed.

The prescribed amount of organic solvent is then added. The rate at which the solvent is added is of some importance, however, since the maximum rate of absorption of the solvent by the mineral filler must generally not be exceeded, otherwise part of the thermoplastic resin will not be dissolved.

The prescribed amount of non-solvent (eg, water) is then added usually at a rate less than the maximum absorption rate of the silica laden with solvent. The resulting composition is then in the form of a fluid, moist and stable powder.

To transform this composition into a usable article such as, for example, a separator for a microporous accumulator, based on plastic and flexible, the composition is introduced into an extruder, preferably having a vertical screw structure, where the fluid powder is transformed into a pasty mixture, formed by a leaf-forming matrix and calendered into a continuous sheet. 25

Extrusion temperatures can range from 27 ° C to 70 ° C, with a narrower range between 45 ° C and 55 ° C being preferred. The die temperature can be between 27 ° C and 70 ° C. The extruder back pressure can be between 14 kg / cm2 effective and 35 kg / cm2 effective, a 1 "pressure range between 14 and 21 kg / cm2 effective being preferred, it is obviously possible to use other extruders.

In practice, the pasty mass formed in the extruder then passes through a sieve of approximately 420 microns and a film-forming matrix before entering a multiplied calender which is maintained at a temperature between 4 ° C and 16 ° C, preferably between 4 ° C and 8 ° C. The die is hung in the grille to prevent evaporation. The calender used is an 80 cm calender preferably comprising rollers with a separator model. The composition, now in the form of sheets, is then carried by a transport sieve and passes into a water extraction bath whose temperature is normally maintained between 50 ° C and 93 ° C although we prefer a range narrower between 70 ° C and 80 ° C. The sheet remains in the bath until the solvent is removed and then it is dried by conventional means. The drying temperature should generally not exceed 135 ° C and a temperature of around 108 ° C is preferred.

It will be seen that the resulting article, after having removed during the treatment the solvent and the non-solvent, comprises a thermoplastic resinous binder suitably plasticized and forming a matrix, in which are distributed particles of mineral filler. A network of microvides or micropores is present in the article, and is formed between the adjacent particles of dispersed charges, between the various particles of charges and the matrix as well as in the matrix itself. These microvides or micro-pores do not have a uniform size, and it f, o is generally between 0.01 micron and 100 microns, and these micro-pores have a typical average pore diameter of about 1 micron, as it is determined by porosimetry by the well-known method of mercury penetration the porosity of the resulting article when it is measured in alcohol is between 50% and 75%.

The resulting article has physical properties which make it ideal for its application as a battery separator.

45

reader. In particular, not only is the resulting article very porous having a total porosity of at least about 50% when measured in alcohol, but it is both resistant and flexible, as shown by its resistance to tension which is generally greater than 14 kg / cm2 and its elongation which is generally greater than 40%. In addition, its electrical resistance, which is a characteristic of great importance when it comes to separators for accumulators, is generally not more than 0.010 ohm / cm2 and is normally less than 0.006 ohm / cm2. When the thickness of the resulting article is reduced to about 0.6 mm, for example, the electrical resistance further decreases to about 0.003 ohm / cm2.

The following examples illustrate certain preferred embodiments of the present composition and of the present process.

Example 1

To illustrate the preparation of a composition convertible into an article which can be used, for example, a separator for a micro-porous accumulator based on plastic and flexible material, according to the principles of this invention, a composition is prepared which comprises a plasticizer such as one of its constituent parts, according to a ratio of 60 parts of plasticizer per 100 parts of thermoplastic resinous binder. This composition comprises the following ingredients, the respective amounts being given as a percentage by weight of the total weight of the composition.

Ingredients percentage by weight

Conoco 5385, homopolymer

gamma vinyl chloride

11.17%

Dioctyl phthalate

6.67%

Hi Sil 233, filler, silica

hydrated precipitate

22.20%

Cyclohexanone

27.76%

Water

32.20%

Charcoal black

0.001%

The composition is prepared by first dry mixing in a "liquid / solid" mixer of high intensity Patter-son-Kelley, Conoco 5385 with dioctyl phthalate to form a starting batch, then adding Hi Sil 233 then cyclohexanone, water and carbon black.

Then the resulting composition is introduced into a vertical Aragon extruder with a stainless steel screw having a compression ratio of about 1.4 / 1. The composition is extracted at a temperature of about 50 ° C and a pressure of about 17.5 kg / cm2 effective. An 80 cm calender is used with an upper separator pattern calender cylinder to produce a separator pattern sheet with a thickness of about 2.5 mm. Then the resulting sheet is passed through a water extraction tank in which the water temperature is maintained at about 70 ° C and then dried in an air dryer at an air temperature of about 109 ° C.

The resulting manufactured article, in this case a separator for a micro-porous and flexible accumulator, has the following physical properties:

65

Tensile strength Elongation Mullen resistance Electrical resistance Total porosity

(mercury penetration technique) Average pore diameter% pore> 20 fi

14.7 kg / cm2 65%

4.48 kg / cm2 0.00835 Q / cm2 1.04 ml / g

0.085 2.5%

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Among the tests carried out, the tensile strength, elongation and Mullen strength data indicate that the resulting article is sufficiently strong and flexible to withstand any damage occurring during assembly and use.

The electrical resistance and porosity data show that it is a product with a small pore size which has excellent electrochemical properties. For use as a battery separator, the electrical resistance should be as low as possible, preferably less than about 0.01 ohms / cm2. The electrical resistance of the resulting product which is 0.0083 ohms / cm2 is therefore more than sufficient. In addition, data regarding pore size and total porosity indicate that the pore size and distribution is in the range corresponding to micro-porous products, the resulting article is very porous. An average pore diameter of 1 micro or less is preferred. In addition, these data indicate that virtually no plasticizer is removed by leaching during processing. The resulting product is hydrophilic and has good acid resistance. 2

Example 2

To demonstrate the effects of the implementation of the present invention with a low ratio of plasticizer to thermoplastic resin, the same procedure is repeated as that of Example 1, with the following ingredients according to the following percentage, the ratio of the plasticizer to the thermoplastic resin being 50 parts of plasticizer per 100 parts of resin:

thermoplastic resins and mineral fillers, although using the same ratio of resin to plasticizer as in Example 2, the procedure described in Example 1 is repeated with the following ingredients in the following percentages:

Ingredients

Conoco 5385, gamma vinyl chloride homopolymer Dioctyl phthalate Hi Sil 233, filler, precipitated hydrated silica Cyclohexanone Water

Charcoal black

10.98% 5.49%

21.97% 28.61% 32.95% 0.001%

The resulting composition is produced to obtain an article which can be used, for example, a separator for a micro-porous and flexible accumulator, in the same manner as in Example 1 and the resulting article has the following physical properties:

Tensile strength Elongation Mullen resistance Electrical resistance Total porosity

(mercury penetration test) Average pore diameter% of pores> 20 [i

15.3 kg / cm2 54% 3.7 kg / cm2 0.0063 fi / cm2 0.99 ml / g

0.095 [i 2.5%

Ingredients

Solvic 229 vinyl chloride homopolymer 1 Dioctyl phthalate KS 300, filler, precipitated hydrated silica Cyclohexanone Water

Charcoal black

Percentage by weight

14.23% 7.11%

19.96% 28.22% 30.48% 0.001%

An article which can be used, such as, for example, a separator for a micro-porous and flexible accumulator, is produced from the resulting composition, in the same manner as in Example 1, and the resulting article has the following physical properties. :

percentage 3 (1 by weight

Tensile strength Elongation Mullen resistance Electrical resistance Total porosity

(mercury penetration test) Average pore diameter% pore> 20 (i

20.3 kg / cm2 57% 4.76 kg / cm2 0.0069 Q / cm2 0.87 ml / g

0.11 ft 3.5%

If we compare the physical data of this article with that of the article produced in example 1, we see that the tensile strength of the article is higher than that of the article of example 1 although its elongation is lower, which indicates a more resistant but less flexible product. The electrical resistance of the article is less than the electrical resistance of the article of example 1. In addition, the porosity of the article ■ t "is less than the porosity of the article of example 1 well that the pore size is generally larger.

Example 4

To illustrate the preparation of a composition according to the present invention in which the type of plasticizer is changed, the procedure of Example 1 is repeated, choosing dioctyl adipate as the plasticizer and using it at a rate of 50 parts of plasticizer per 100 parts of resin. In addition, a different thermoplastic resin is used. The following 50 ingredients are used in the following percentages:

Ingredients

55

The results of these physical tests show that it is a product whose properties are essentially similar to those of the composition of Example 1, although the value of the elongation reflects the fact that the resulting article is somewhat less flexible than the article of Example 1 and has a slightly higher electrical result. However, the resulting article is a separator for accumulator, micro-porous, based on plastic and flexible, commercially acceptable.

Example 3

To illustrate the preparation of a composition according to the present invention, in which different types of

Geon 103EPF10, thermoplastic resin Dioctyl adipate Hi Sil 233, filler, silica precipitated hydyatce M) Cyclohexanone Water

Charcoal black

Percentage by weight

11.01% 4.96%

22.03% 29.52% 32.48% 0.001%

65 An article which can be used, for example a separator for a micro-porous and flexible accumulator, is prepared from the resulting composition, in the same manner as in Example 1 and the resulting article has the following physical properties:

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Tensile strength Elongation Mullen resistance Electrical resistance Total porosity

(mercury penetration test)% of pores> 20 \ i

13.1 kg / cm2 62%

4.2 kg / cm2 0.0047 Q / cm2 0.07 ml / g

1.3%

The physical data show that the use of dioctyl adipate as plasticizer produces an article whose physical and electrochemical properties are similar to those of the article of Example 1 where dioctyl phthalate is used as plasticizer.

VS

Claims (12)

619,321 2 1. Method for manufacturing a microporous separator for an accumulator from a composition comprising between 10 and 16% of a resinous thermoplastic binder, between 4 and 10% of a plasticizer, between 19 and 23% of a mineral filler, between s 26 and 32% of a solvent, and between 28 and 34% of a non-solvent, the percentages referring to the total weight of the composition , characterized in that a starting charge is first formed by mixing the binder and the plasticizer, then a mixture capable of being extruded is obtained by the addition of the mineral filler, m of the solvent and of the non-solvent to the initial charge, this mixture is extruded to produce a sheet-shaped article, this article is passed through an extraction medium to remove only the solvent therefrom, and finally the article is dried to remove only the medium therefrom and the non-solvent. ' 2. Method according to claim 1, characterized in that the components of the starting charge are mixed under low shear and without addition of heat. 3. Method according to claim 2, characterized in that the 211 components of the mixture to be extruded are mixed under low shear and without heat input. 4. Method according to claim 3, characterized in that the extrudate is calendered to form the sheet-shaped article. 5. Method according to claim 4, characterized in that the steps of mixing at low shear are carried out at room temperature, the extrusion step between 27 and 70 ° C at an effective back pressure between 14 and 21 kg / cm2, and that the extraction medium is a water bath maintained at a temperature between 50 and 93 ° C. m 6. Method according to claim 1, characterized in that phthalate or dioctyl adipate is used as plasticizer. 7. Method according to claim 6, characterized in that the thermoplastic resinous binder is a polyvinyl chloride resin, the mineral filler is silica, the solvent is ss cyclohexanone, and the non-solvent is water. 8. Method according to claim 7, characterized in that the polyvinyl chloride is a gamma homopolymer in an amount between 11 and 12%, the plasticizer is dioctyl phthalate in an amount between 6 and 7%, the silica is 4 ( 1 present in an amount between 22 and 23%, cyclohexanone is present in an amount between 27 and 28%, and water is present in an amount of 31 to 33%, these percentages relating to the total weight of the composition. 9. Method according to claim 7, characterized in that the polyvinyl chloride is a gamma homopolymer in an amount of 11 to 12%, the plasticizer is dioctyl adipate in an amount of 4.5 to 5.5%, the silica is present at 22 to 23%, cyclohexanone is present at 26 to 30%, and water is present at 31 to 33%, these percentages relate to the total weight of the composition. 10. Flexible and micro-porous separator comprising a matrix of plasticized resin and a mineral filler, obtained by the method according to claim 1, said article comprising a network of pores formed in the matrix of plasticized resin between 55 particles of mineral filler and the matrix, between the adjacent particles of the mineral filler and in the matrix itself, the sheet having an electrical resistance less than 0.01 ohm / cm2 and an elongation greater than 40%. 11. The separator of claim 10, wherein the average pore diameter 60 is about 1 micron. 12. Separator according to claim 10, characterized in that its tensile strength is greater than 10.5 kg / cm2.