KR20160016642A - Method for producing separator for cell - Google Patents

Abstract

The present invention relates to a method to manufacture a separator for a battery, capable of laminating a reforming porous layer on both surfaces of a porous film, formed of polyolefin resin, assuming that a lithium ion secondary battery progresses at a lower cost in the future. Provided is a manufacturing method, capable of rapid processing and preventing application stripes even if a battery separator is thinned. The manufacturing method, laminating a reforming porous layer on both surfaces of a polyolefin porous film, includes: a process of applying application liquid to both surfaces at the same time; a coagulating step; a cleaning step; and a dry step. The manufacturing method is capable of making contact between a device for simultaneous application to both sides and a device for the prevention of shaking between the application device and a coagulation tub.

Description

METHOD FOR PRODUCING SEPARATOR FOR CELL [0002]

The present invention relates to a method of manufacturing a battery separator. In particular, it is useful as a method for producing a battery separator having a modified porous layer.

The thermoplastic resin microporous membrane is widely used as an insulator and a filter. Examples of the separator include a battery separator used for a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, or a polymer battery, a separator for an electric double layer capacitor, a reverse osmosis filtration membrane, an ultrafiltration membrane, . In addition, it is used for breathable waterproof medicine (medical), medical (medical) materials and so on. Particularly, as a separator for a lithium ion secondary battery, a separator having ion permeability by impregnation with an electrolyte is excellent in electric insulation, electrolytic solution resistance and oxidation resistance, and at the temperature of about 120 to 150 DEG C, A porous film made of polyethylene and having a hole-blocking effect for suppressing the hole-blocking effect is suitably used. However, if the temperature increase continues after the hole closure for some reason, the viscosity of the polyethylene constituting the film may be lowered or the film may be shrunk due to film shrinkage. This phenomenon is not a phenomenon confined to polyethylene, and even when other thermoplastic resin is used, it can not be avoided above the melting point of the resin constituting the porous film.

The separator for a lithium ion battery is deeply related to battery characteristics, battery productivity and battery safety, and it is required to have excellent mechanical properties, heat resistance, permeability, dimensional stability, hole closing property (shutdown property), melt breaking property (meltdown property) . Further, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion with the electrode material and the electrolyte permeability to improve the productivity. Therefore, a separator for laminating various modified porous layers on a porous film has been studied. A polyamide-imide resin, a polyimide resin, an aromatic polyamide resin, and a fluorine-based resin having excellent electrode adhesion properties are preferably used as the modified porous layer, together with heat resistance and electrolyte permeability. The modified porous layer in the present invention means a layer containing a resin which imparts or improves at least one or more of functions such as heat resistance, adhesion with an electrode material, electrolyte permeability, and the like.

In order to cope with the cost reduction of the battery separator, it is expected that the processing speed (conveying speed) is further increased in the film forming process of the porous film and the lamination process of the modified porous layer. In addition to the electrode sheet as well as the separator, it is necessary to increase the area that can be filled in the container in order to improve the battery capacity, and it is predicted that the separator will become thinner.

Various studies have been made to solve the above problems.

In Example 1 of Patent Document 1, a fluorinated resin solution is applied to both surfaces of a polyethylene microporous membrane, followed by entering a coagulation bath, followed by washing with water and drying to obtain a separator for a non-aqueous secondary battery.

In Example 1 of Patent Document 2, a fluorinated resin solution was placed in a tank in which two Meyer bars were arranged in parallel at the bottom, and a polypropylene microporous membrane was introduced into the tank from the top of the tank at a conveying speed of 3 m / The fluorine-based solution is applied on both sides by passing between the bars, and then the solution is allowed to enter the coagulation bath without being brought into contact with the other device, followed by washing with water and drying to obtain a composite porous film.

In Example 2 of Patent Document 3, a meta-type wholly aromatic polyamide resin solution containing alumina particles is placed in a tank in which two Meyer bars are arranged in parallel at the bottom, and a polyethylene microporous membrane is introduced into the tank from the top of the tank at 20 m / The resin solution is applied to both sides by passing through two Meyer bars and then passed through a precooler to enter a coagulation bath and washed with water and dried to obtain a battery separator.

In the future, the conveying speed at the time of coating tends to be increased more and more. In particular, a soft material such as a polyolefin porous film used for a battery separator tends to cause shaking during conveyance as the conveying speed increases. This tendency becomes more conspicuous as the thickness of the polyolefin porous film as the base becomes thinner.

In the application methods of Patent Documents 1 and 2, for example, at a transport speed of 30 m / min or more, coating streaks may occur in the longitudinal direction due to shaking of the polyolefin porous film as the base. As the speed increases, the clearance between the two Meyer bars needs to be made smaller in order to adjust the coating amount, and coating streaks are more likely to occur.

Japanese Patent No. 4988973 Japanese Patent Application Laid-Open No. 2011-012266 Japanese Patent Application Laid-Open No. 2010-149011

The present inventors assumed that lithium ion secondary batteries progressively become more and more inexpensive in the future, and in the process for producing a battery separator in which a modified porous layer is laminated on both surfaces of a porous film made of a polyolefin resin, even when the cell separator is made thin, It is difficult to generate streaks, and a manufacturing method capable of high-speed processing is provided. The above problem is a problem peculiar to a separator for a battery which is not seen in a step of applying a general thermoplastic resin film having a relatively high rigidity. The coated streaks referred to in the present specification are stripes extending in the transport direction of a visually detectable polyolefin porous film, and they have a length of about 5 to 100 cm, a plurality of stripes at intervals of 1 to 50 mm in the coating width direction, Striped defect refers to defects.

Means for Solving the Problems In order to solve the above-described problems, a manufacturing method of a separator for a battery of the present invention has the following constitution. In other words,

1. A method for producing a battery separator in which a modified porous layer is formed on the surface of a porous polyolefin membrane,

(1) a step of simultaneously applying a coating liquid obtained by dissolving a resin in a solvent on both surfaces of the polyolefin porous film,

(2) a step of solidifying the resin component in the applied coating liquid,

(3) a step of cleaning,

(4) a step of drying,

A method for manufacturing a battery separator (1), comprising the steps of: (1) contacting a polyolefin porous film applied between steps (1) and (2) .

2. The method for producing a separator for a battery according to 1 above, wherein the polyolefin porous film has a thickness of 25 mu m or less.

3. The method for producing a separator for a battery according to 1 or 2, wherein the resin is a fluorine-based resin or a polyamide-imide resin.

4. The method for producing a separator for a battery according to any one of 1 to 3 above, wherein the coating liquid comprises inorganic particles or crosslinked organic particles.

(Effects of the Invention)

According to the production method of the present invention, it is possible to obtain a separator for a battery having a high productivity and an excellent appearance quality obtained by laminating modified porous layers on both sides.

Fig. 1 shows an example of a device (coating device A) used for coating with a blade in the present invention.
Fig. 2 shows an example of a device (coating device B) used for coating with a die in the present invention.
Fig. 3 shows an example of a device (coating device C) used for coating by the dipping method in the present invention.
Fig. 4 shows an example of the anti-shake device (Y-shaped jig).
Fig. 5 shows an example of a combination of a device used when applying with a blade and a vibration preventing device (Y-shaped jig) in the present invention.

Hereinafter, a method of producing a separator for a battery having a modified porous layer on both surfaces of the polyolefin porous membrane of the present invention will be described, but the present invention is not limited thereto.

First, the polyolefin porous film of the present invention will be described.

The upper limit value of the thickness of the polyolefin porous film of the present invention is preferably 25 占 퐉, more preferably 20 占 퐉, and still more preferably 16 占 퐉. The lower limit value is preferably 3 占 퐉, more preferably 5 占 퐉. When the thickness of the polyolefin porous film is within the above-mentioned preferable range, it is possible to have a practical film strength and a hole closing function, and the area per unit volume of the battery case is not restricted, which is suitable for increasing the capacity of the battery.

The upper limit value of the durability of the polyolefin porous film is preferably 300 sec / 100ccAir, more preferably 200sec / 100ccAir, further preferably 150sec / 100ccAir, and the lower limit value is preferably 50sec / 100ccAir, more preferably 70sec / 100ccAir, More preferably, it is 100 sec / 100ccAir.

The porosity of the polyolefin porous film is preferably 70%, more preferably 60%, and still more preferably 55%. The lower limit value is preferably 30%, more preferably 35%, still more preferably 40%. When the durability and the porosity are in the above-described preferable ranges, a sufficient battery charge / discharge characteristic, especially ion permeability (charging / discharging operation voltage) and battery life (relating to adherence and adhesion to the electrolyte solution) It can be exercised sufficiently. In addition, since the mechanical strength and the insulating property are obtained, the possibility of a short circuit occurring during charging and discharging can be reduced.

The average pore diameter of the polyolefin porous film is preferably 0.01 to 1.0 占 퐉, more preferably 0.05 to 0.5 占 퐉, and still more preferably 0.1 to 0.3 占 퐉, because it largely affects the hole closing performance. When the average pore diameter of the polyolefin porous film is within the above preferable range, the peeling strength of the modified porous layer can be appropriately obtained by the anchor effect of the functional resin. In addition, when the modified porous layer is laminated, it is prevented that the durability of the durability is greatly deteriorated, so that the response to the temperature of the hole closing phenomenon is not gentle, and the hole closing temperature due to the heating rate does not shift to the higher temperature side.

The polyolefin resin constituting the polyolefin porous film is preferably polyethylene or polypropylene. Further, a single substance or a mixture of two or more different polyolefin resins may be used, for example, a mixture of polyethylene and polypropylene, or a copolymer of other olefins. The separator obtained by using the polyolefin resin can have a hole closing effect that cuts off the current at the time of abnormally increasing the battery temperature and suppresses the excessive increase in temperature, in addition to the basic characteristics such as electrical insulation and ion permeability. Among them, polyethylene is particularly preferable from the viewpoint of hole closing performance.

Hereinafter, polyethylene will be described as an example of the polyolefin resin used in the present invention. Examples of the polyethylene include ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene. There is no particular limitation on the polymerization catalyst, and examples thereof include a Chigler-type catalyst, a Phillips-type catalyst and a metallocene catalyst. These polyethylene may be not only homopolymers of ethylene but also copolymers containing small amounts of other? -Olefins. As the? -Olefins other than ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, esters of (meth) acrylic acid, . The polyethylene may be a single material, but is preferably a mixture of two or more kinds of polyethylene. As the polyethylene mixture, a mixture of two or more kinds of ultra-high molecular weight polyethylene having different weight average molecular weights (Mw), a mixture of high density polyethylene, medium density polyethylene and low density polyethylene may be used, and ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene and low density polyethylene A mixture of two or more kinds of polyethylene selected from the group consisting of polyethylene may be used.

As the polyethylene mixture, a mixture of an ultrahigh molecular weight polyethylene having an Mw of 5 x 10 5 or more and a polyethylene having an Mw of 1 x 10 4 or more and less than 5 x 10 5 is preferable. The Mw of the ultrahigh molecular weight polyethylene is preferably 5 × 10 5 to 1 × 10 7, more preferably 1 × 10 6 to 15 × 10 6, and particularly preferably 1 × 10 6 to 5 × 10 6. As the polyethylene having Mw of 1 x 10 < 4 > or more and less than 5 x 10 < 5 >, any of high density polyethylene, medium density polyethylene and low density polyethylene can be used, but it is particularly preferable to use high density polyethylene. As the polyethylene having Mw of 1 x 10 4 or more and less than 5 x 10 5, two or more different Mws may be used, or two or more different densities may be used. By setting the upper limit of the Mw of the polyethylene mixture to 15 x 10 < 6 > or less, melt extrusion can be facilitated.

In the present invention, the content of the ultrahigh molecular weight polyethylene is preferably 40% by weight, more preferably 30% by weight, still more preferably 10% by weight, and the lower limit is preferably 1% by weight, 2% by weight, more preferably 5% by weight. When the content of ultrahigh molecular weight polyethylene is within the above preferable range, sufficient tensile strength can be obtained even when the thickness of the polyethylene porous film is reduced. The tensile strength is preferably 100 MPa or more, and the upper limit is not particularly defined.

The ratio [(Mw / Mn)] of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyethylene resin is preferably in the range of 5 to 200, more preferably 10 to 100. When the range of Mw / Mn is within the above preferable range, extrusion of the polyethylene resin is easy and sufficient mechanical strength is obtained when the thickness of the polyethylene porous film is reduced. Mw / Mn is used as a measure of the molecular weight distribution, that is, in the case of polyethylene made of a single substance, the larger the value, the larger the molecular weight distribution is. The Mw / Mn of the single-component polyethylene can be suitably adjusted by the multi-terminal polymerization of polyethylene. Further, the Mw / Mn of the mixture of polyethylene can be appropriately adjusted by adjusting the molecular weight and mixing ratio of each component.

As long as the polyethylene porous film satisfies the above-described various characteristics, the manufacturing method according to the purpose can be freely selected. Examples of the method for producing the porous film include a foaming method, a phase separation method, a dissolution recrystallization method, a stretching method, a powder sintering method, and the like. Among these methods, a phase separation method is preferable in terms of uniformity of fine holes and cost.

Examples of the production method by the phase separation method include a method in which a molten mixture is heated and melted by, for example, polyethylene and a molding solvent, the molten mixture is extruded and cooled from the die to form a gel-like molded product, And a method in which the above-mentioned molding solvent is removed to obtain a porous film.

The polyethylene porous film may be a single layer film or a layer structure composed of two or more layers different in molecular weight or average pore diameter. In the case of a layer structure composed of two or more layers, it may be a laminate of a layer comprising a polyethylene porous layer and a polyolefin resin other than polyethylene.

As a method for producing a multilayered film composed of two or more layers, for example, each of polyethylene constituting the a layer and the b layer is melt-kneaded with a molding solvent, and the obtained molten mixture is supplied to one die from an extruder, A method of pneumatic shipment by integrating a gel sheet constituting each layer, and a method of polymerizing and heat-sealing the gel sheet constituting each layer. The coextrusion method is preferable because it is easy to obtain an interlaminar bond strength, easily forms a communication hole between the layers, easily maintains high permeability, and is excellent in productivity. In the case of a layer constitution of two or more layers, it is preferable that the molecular weight and the molecular weight distribution of the polyethylene resin in at least one outermost layer satisfy the above-mentioned.

It is necessary that the polyethylene porous film has a function of closing the hole at the time of abnormality of charge-discharge reaction. Therefore, the melting point (softening point) of the constituent resin is 70 to 150 占 폚, more preferably 80 to 140 占 폚, and still more preferably 100 to 130 占 폚. When the melting point of the constituting resin is in the above-described preferable range, the hole closing function is not exhibited at the time of normal use and the hole closing function is exhibited at the time of the abnormal reaction, whereby safety can be secured.

Next, a method for laminating the modified porous layer used in the present invention will be described.

The method for producing a separator for a battery of the present invention comprises a step of applying a coating liquid dissolved in a solvent which is soluble in a resin such as a fluorine resin or a polyamideimide resin and which is miscible with water at the same time on both sides of a polyolefin porous film, And the anti-shake device is brought into contact with the coagulation tank and the application device for applying both sides at the same time. As used herein, both sides of a substrate include a method of applying the substrate on one side within 10 seconds and coagulating, cleaning and drying the substrate on both sides simultaneously. As a coating apparatus for applying two-sided coating at the same time, for example, a coating apparatus as shown in Figs. 1 to 3 can be mentioned.

1 is a method of applying both sides using a blade. The coating amount can be adjusted by the clearance between the polyolefin porous film and the tip of the blade. In this case, it is preferable that the tip of the blade is not a rectangular shape but a rounded shape in the thickness direction of the blade. When the tip of the blade is prismatic, coating streaks tend to occur when the polyolefin porous film is in contact with the polyolefin porous film at the time of coating.

Fig. 2 is a method of applying using a die. The two dies disposed opposite to the both surfaces of the polyolefin porous film are slightly shifted from the application position and the backup roll is provided on the side opposite to the application surface of the polyolefin porous film as shown in Fig. desirable. In addition, it is preferable to provide an anti-shake device immediately after the downstream die.

3 is a method of applying a coating liquid to a tank in which two straight rods are arranged in parallel at the bottom of the tank and passing the polyolefin porous film from above the tank through a gap between two seamless rods arranged parallel to the tank bottom. The amount of coating can be adjusted by a clearance between the two swivels. It is preferable that the rotary shaft used herein has a smooth surface. When there is unevenness on the straight surface, coating streaks tend to occur when the polyolefin porous film is in contact with the coating film. The diameter of the circular bar is preferably 5 to 50 mm, and good applicability. In addition to the above, a gravure roll may be disposed on both sides of the polyolefin porous film to apply the coating to both surfaces, but the present invention is not limited thereto.

The shake prevention device is not particularly limited as long as it is an apparatus which is provided between the application device and the coagulation tank and can reduce the shaking of the polyolefin porous film at the time of application. For example, there can be mentioned a method of bringing a Y-shaped jig as shown in Fig. 4 into contact with both ends of the porous film immediately after the application, or both ends of the porous film immediately after application with a pinch roll. In the case of using a Y-shaped jig, it is preferable to install it obliquely as shown in Fig. 5, and to discharge the coating liquid attached to the Y-shaped jig so as not to return to the porous film.

The position of the anti-shake device is located closer to the application device, and the anti-shake effect is more easily obtained. The anti-shake device is positioned within a range of 50 mm to 500 mm on the basis of the application end point (the coating end point on the rear side in the case of two preceding application devices) do. The coating end point refers to, for example, the position of the tip of the blade of the coating apparatus in Fig. 1, the position of the tip of the die at the rear side in Fig. 2, and the position of the contact point of the flexible pole and the polyolefin porous film in Fig. The upper limit value of the anti-shake device is more preferably 400 mm, more preferably 300 mm, and the lower limit value is more preferably 80 mm, further preferably 100 mm. In addition to the above-described anti-shake device, a humidifying step may be provided between the coating device and the coagulation bath as needed. The shaking of the polyolefin porous film at the time of coating as used herein refers to the vibration of the polyolefin porous film caused by the mechanical vibration of the conveying device including the unwinding device and the winding device.

The resin component or the resin component and the inorganic particles coated by applying the coating liquid are immersed in an aqueous solution (coagulation liquid) in the coagulation bath and solidified into a three-dimensional mesh shape. The aqueous solution is an aqueous solution containing 1 to 20% by weight, more preferably 5 to 15% by weight, of a good solvent to be described later with respect to the resin component constituting the modified porous layer. The immersion time in the coagulation bath is preferably 3 seconds or more. If less than 3 seconds, the resin component may not be solidified sufficiently. The upper limit is not limited, but 10 seconds is enough. Further, a final battery separator can be obtained through a washing step using water and a drying step using hot air having a temperature of 100 DEG C or less.

The cleaning step for removing the solvent can also increase the cleaning efficiency by a general method such as heating, ultrasonic irradiation, or bubbling. Specifically, a method of extruding a solution in the porous layer with air or an inert gas, a method of physically squeezing the solution in the membrane by a guide roll, and the like can be given.

The conveying speed in the production method of the present invention is 30 m / min or more. According to the present invention, even when the conveying speed is 30 m / min or more, occurrence of coating streaks can be largely suppressed. The conveying speed is preferably 40 m / min or more, more preferably 50 m / min or more from the viewpoint of productivity.

Further, it is preferable that the modified porous layer is laminated on both surfaces of the porous film as a substrate. It is possible to reduce the curl by laminating it on both sides, thereby preventing a decrease in the productivity in the electrode pair assembly process. When the adhesion with the electrode material is to be improved, the adhesion between both the positive electrode side and the negative electrode side is improved, and when the heat resistance is improved, a significant effect of preventing heat shrinkage is obtained.

Next, the modified porous layer used in the present invention will be described.

The resin constituting the modified porous layer is not particularly limited as long as it is a resin capable of imparting adhesiveness to an electrode material and a heat shrinkage suppressing function (heat resistance). For example, a polyamideimide resin having excellent heat resistance, Based resin and the like are preferable. These resins may be used alone or in combination with other materials.

Hereinafter, the polyamide-imide resin and the fluorine-based resin will be described in detail.

(1) Polyamideimide resin

In general, the synthesis of a polyamide-imide resin is synthesized by an ordinary method such as an acid chloride method using trimellitic acid chloride and diamine or a diisocyanate method using trimellitic anhydride and diisocyanate, The isocyanate method is preferred.

The acid component used in the synthesis of the polyamideimide resin includes trimellitic acid anhydride (chloride), but a part thereof may be replaced with another polybasic acid or an anhydride thereof. For example, there can be mentioned pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfone tetracarboxylic acid, benzophenonetetracarboxylic acid, biphenyl ether tetracarboxylic acid, ethylene glycol bistrimellitate, propylene glycol bis Tetracarboxylic acids such as tartaric acid and their anhydrides and their anhydrides such as oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene) Alicyclic dicarboxylic acids such as carboxypoly (styrene-butadiene), and the like, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4'-dicyclohexylmethanedicarboxylic acid , Aromatic dicarboxylic acids such as aliphatic dicarboxylic acids such as dimer acid and terephthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid and naphthalene dicarboxylic acid. Of these, 1,3-cyclohexane dicarboxylic acid and 1,4-cyclohexane dicarboxylic acid are preferable from the standpoint of electrolyte resistance, dimer acid from the shutdown property, dicarboxylic polybutadiene having a molecular weight of 1000 or more, Poly (acrylonitrile butadiene), and dicarboxy poly (styrene-butadiene) are preferable.

Further, a urethane group may be introduced into the molecule by replacing a part of the trimellitic acid compound with glycol. Examples of the glycol include alkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol and hexanediol, polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, and one kind of the dicarboxylic acid Or a polyester of a terminal hydroxyl group synthesized from at least two kinds of these glycols and at least one of these glycols, and among these, polyethylene glycol and a polyester of a terminal hydroxyl group are preferable from the shutdown effect. The number average molecular weight is preferably 500 or more, and more preferably 1000 or more. The upper limit is not particularly limited, but is preferably less than 8,000.

When a part of the acid component is substituted with at least one member selected from the group consisting of dimer acid, polyalkylene ether, polyester and a butadiene rubber containing at least one of a carboxyl group, a hydroxyl group and an amino group at the terminal, 60 mol% is preferably substituted.

As the diamine (diisocyanate) component used in the synthesis of the polyamide-imide resin, it is preferable to use o-tolidine and tolylene diamine as the components. As a component for substituting a part of these diamines, ethylenediamine, propylenediamine, hexamethylenediamine Alicyclic diamines such as 1,4-cyclohexane diamine, 1,3-cyclohexane diamine and dicyclohexylmethane diamine, and diisocyanates thereof, m-phenylenediamine, p-phenyl Aromatic diamines such as rhenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, benzidine, xylylenediamine and naphthalenediamine, and Diisocyanate and the like. Among them, dicyclohexylmethanediamine and its diisocyanate are most preferable from the standpoints of reactivity, cost, and electrolyte resistance. Preferred are 4,4'-diaminodiphenylmethane, naphthalenediamine and their diisocyanates. Particularly, it is preferable that o-tolylidine diisocyanate (TODI), 2,4-tolylene diisocyanate (TDI) and blends thereof. Particularly, in order to improve the adhesion of the heat-resistant porous B, o-tolylidine diisocyanate (TODI) having high rigidity is contained in an amount of 50 mol% or more, preferably 60 mol% or more, and more preferably 70 mol% or more with respect to the total isocyanate.

The polyamideimide resin is heated in a polar solvent such as N, N'-dimethylformamide, N, N'-dimethylacetamide, N-methyl-2-pyrrolidone or? -Butyrolactone at 60 to 200 占 폚 While stirring. In this case, if necessary, amines such as triethylamine and diethylenetriamine, alkali metal salts such as sodium fluoride, potassium fluoride, cesium fluoride, and sodium methoxide may be used as a catalyst.

When the polyamide-imide resin is used in the present invention, the logarithmic viscosity is preferably 0.5 dl / g or more. If the logarithmic viscosity is less than 0.5 dl / g, the melt-down property may not be sufficiently obtained due to the lowering of the melting temperature and the molecular weight is low, so that the porous film is retracted and the anchor effect is lowered. On the other hand, the upper limit is preferably less than 2.0 dl / g in consideration of processability and solvent solubility.

(2) Fluorine-based resin

The fluororesin is preferably at least one selected from the group consisting of vinylidene fluoride homopolymer, vinylidene fluoride / fluoroolefin copolymer, vinyl fluoride homopolymer, and vinyl fluoride / fluoroolefin copolymer. Also, resins obtained by graft-polymerizing maleic acid or the like may be used. These polymers are excellent in adhesion to electrodes, have high affinity with non-aqueous electrolytes, have good heat resistance, and have high chemical and physical stability against non-aqueous electrolytes. Therefore, they can sufficiently maintain affinity with electrolytes even under high temperature use .

The melting point of the fluorine-based resin is preferably 150 占 폚 or higher, more preferably 180 占 폚 or higher, even more preferably 210 占 폚 or higher, and the upper limit is not particularly limited. When the melting point is higher than the decomposition temperature, the decomposition temperature may be within the above range. If the melting point is lower than 150 캜, a sufficient heat-resistant wave-film temperature can not be obtained and high safety may not be ensured.

The modified porous layer of the present invention is obtained by applying a coating liquid obtained by dissolving the resin in a solvent which is soluble and miscible with water to a predetermined polyolefin porous film to phase-separate the resin and the solvent, and further put into a coagulation bath to solidify the resin. If necessary, a phase separation auxiliary may be added.

Examples of the solvent (good solvent) usable for dissolving the resin include N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), hexamethyltriamide (HMPA) Dimethylformamide (DMF), dimethylsulfoxide (DMSO),? -Butyrolactone, chloroform, tetrachloroethane, dichloroethane, 3-chloronaphthalene, parachlorophenol, tetralin, acetone, acetonitrile and the like And can be freely selected in accordance with the solubility of the resin.

Examples of the phase separation auxiliary used in the present invention include water, alkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol and hexanediol, polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, Soluble polyurethane, water-soluble polyurethane, water-soluble polyurethane, polyvinyl alcohol, carboxymethylcellulose, and the like.

The addition amount of the phase separation auxiliary agent is preferably 1 to 9% by weight, more preferably 2 to 8% by weight, and still more preferably 3 to 7% by weight based on the solution weight of the coating liquid. By mixing these phase separation formulations with the coating liquid, it is possible to mainly control the durability, surface open area ratio, and formation rate of the layer structure. When the addition amount of the phase separation auxiliary agent is in the above preferable range, there is a case where the phase separation rate is remarkably increased. In addition, there is a case where the coating liquid is prevented from being clouded at the mixing stage and the resin component is prevented from being precipitated.

In the present invention, it is preferable to add inorganic particles or crosslinked polymer particles to the coating liquid. By adding inorganic particles or crosslinked polymer particles to the coating liquid, it is possible to prevent the internal short circuit (dendritic effect) caused by the growth of the dendrites of the electrode in the battery, reduce the heat shrinkage rate, Can be obtained. The upper limit value of the added amount of the particles is preferably 98% by weight, more preferably 95% by weight. The lower limit value is preferably 50% by weight, more preferably 60% by weight. By setting the lower limit of the added amount of the particles within the above preferable range, dendrites can be prevented. In addition, when the upper limit value is within the above preferable range, sufficient adhesion of the modified porous layer may be obtained.

The average particle diameter of the particles is preferably 1.5 times or more and 50 times or less the average pore diameter of the polyolefin porous film. More preferably 2.0 times or more and 20 times or less. The shape of the particles may be spheric, substantially spherical, plate-like, or scaly, but is not particularly limited. When the average particle diameter of the particles is less than 1.5 times the average pore diameter of the polyolefin porous film, the pores of the polyolefin porous film are blocked in a state where the resin and the particles are mixed depending on the particle size distribution, resulting in a significant increase in the durability There is a case. If the average particle diameter of the particles exceeds 50 times the average pore diameter of the polyolefin porous film, the particles may fall off during the battery assembling process, resulting in serious defects of the battery.

Examples of the inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, .

Examples of the crosslinked polymer particles include heat-resistant crosslinked polymer particles such as crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles.

The solid content concentration of the coating liquid is not particularly limited as long as it can be applied uniformly, but is preferably 10% by weight or more and 90% by weight or less, more preferably 20% by weight or more and 80% by weight or less. If the solid concentration is less than 10% by weight, the obtained heat resistant layer may be retreated. On the other hand, if it exceeds 80% by weight, the coatability decreases.

The upper limit of the total thickness of the battery separator obtained by laminating the modified porous layers is preferably 35 占 퐉, more preferably 30 占 퐉. The lower limit value is preferably 5 占 퐉, and more preferably 7 占 퐉. By setting the lower limit of the total film thickness of the battery separator within the above preferable range, sufficient mechanical strength and insulation can be ensured. Further, by setting the upper limit value within the above preferable range, the area of the electrode that can be filled in the container is reduced, so that the decrease in capacity can be avoided.

The film thickness of the modified porous layer is preferably 1 to 5 占 퐉, more preferably 1 to 4 占 퐉, and further preferably 1 to 3 占 퐉. When the film thickness is 1 탆 or more, adhesiveness to the electrode is ensured, and the polyolefin porous film is prevented from melting and shrinking to a melting point or more, thereby securing the strength of the film and the insulating property. When the thickness is 5 mu m or less, the winding volume can be suppressed, which is suitable for increasing the capacity of the battery to be advanced in the future. In addition, the curl is prevented from becoming large, leading to an improvement in productivity in a battery assembling process. In addition, by optimizing the ratio occupied by the polyolefin porous film, a sufficient hole closing function can be obtained and the adverse reaction can be suppressed.

The porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%. If the porosity of the modified porous layer is 30% or more, the increase of the electrical resistance of the film is prevented and the large current can be lost. If the porosity is 90% or less, the film strength can be maintained.

The permeation resistance of the modified porous layer is preferably 1 to 600 sec / 100 ccir measured by a method according to JIS-P8117. More preferably 50 to 500 sec / 100 ccir, and further preferably 100 to 400 sec / 100 ccir. When the durability is less than 1 sec / 100 cc Arcc, the film strength becomes weak. When the durability exceeds 600 sec / 100 cc Air, the cycle characteristics may be deteriorated.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by these Examples.

Evaluation method of coated stripes

The battery separator obtained in Examples and Comparative Examples was slit-processed to obtain a roll having a width of 300 mm and a length of 600 m. The rolls were visually observed under a fluorescent lamp at a conveying speed of 5 m / min while being observed with naked eyes. The rolls were stretched in the conveying direction, with a length of about 5 to 100 cm, a plurality of rollers at intervals of 1 to 50 mm, The number of occurrences per 500 m was counted.

Further, a length of about 5 to 100 cm, and a plurality of coating stripes extending over the entire width of the coating width in the coating width direction at intervals of 1 to 50 mm were counted as one place.

Example 1

(Adjustment of Coating Liquid)

A polyvinylidene fluoride-hexafluoropropylene copolymer [PVdF / HFP = 92/8 (weight ratio), weight average molecular weight of 1 million] was used as the fluororesin. Fluorine-based resin, alumina particles (average particle diameter: 1.0 탆) and N-methyl-2-pyrrolidone were blended in a weight ratio of 5:12:83, respectively. After completely dissolving the resin component, zirconium oxide beads ) Was put into a container made of polypropylene and dispersed with a paint shaker (Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. Subsequently, the solution was filtered with a filter having a filtration limit of 5 탆, and the coating liquid (a) was combined. The coating liquid was kept sealed so as not to contact with the outside air as much as possible until the application.

(Lamination of the modified porous layer)

The above coating liquid (a) was applied to both surfaces of a polyethylene porous film (thickness: 5 mu m, durability of 170 sec / 100 cAir) as a polyolefin porous film at a conveying speed of 30 m / min using a coating apparatus A by a blade coating method, (Coagulation bath), washed with pure water, and then dried by passing through a hot-air drying furnace at 70 ° C to obtain a battery separator having a final thickness of 13 μm. At this time, a Y-shaped jig (anti-shake device) shown in Fig. 4 was provided at both ends of a porous film coated with a coating liquid as shown in Fig. 5, at a position 50 mm below the blade tip of the application device.

Example 2

A separator for a battery was obtained in the same manner as in Example 1 except that a polyethylene porous film (thickness: 9 mu m, air resistance: 115 sec / 100ccAir) was used.

Example 3

A separator for a battery was obtained in the same manner as in Example 1 except that a polyethylene porous film (thickness: 16 mu m, durability 120 sec / 100 ccir) was used.

Example 4

A separator for a battery was obtained in the same manner as in Example 1 except that a polyethylene porous film (thickness: 20 mu m, durability of 150 sec / 100 ccir) was used.

Example 5

(Synthesis of polyamideimide resin)

(TODI) (0.8 mol), 2,4-tolylene diisocyanate (TDI) (0.2 mol), and fluorine (TMA) were added to a four-necked flask equipped with a thermometer, a cooling tube and a nitrogen gas introducing tube. 0.01 mol of potassium was added together with N-methyl-2-pyrrolidone so that the solid concentration became 20% by weight, and the mixture was stirred at 100 ° C for 5 hours. Then, N-methyl- And diluted with water to synthesize a polyamideimide resin solution.

(Adjustment of Coating Liquid)

Alumina particles (average particle size 0.5 mu m) and N-methyl-2-pyrrolidone were blended in a weight ratio of 16:20:64, respectively, and a zirconium oxide bead (manufactured by Toray Industries, (Registered trademark) beads, 0.5 mm in diameter] in a container made of polypropylene and dispersed for 6 hours with a paint shaker (Toyo Seiki Seisakusho Co., Ltd.) for 6 hours. Then, the solution was filtered with a filter having a filtration limit of 5 탆 to prepare a coating liquid (b).

(Lamination of the modified porous layer)

A separator for a battery was obtained in the same manner as in Example 2 except that the coating liquid (b) was used.

Example 6

(C) in which alumina particles were changed to polymethyl methacrylate crosslinked particles (Nippon Shokubai Co., Ltd., "Eposota" (registered trademark) MA, Type 1002, average particle diameter 2.5 μm) A separator for a battery was obtained in the same manner as in Example 2 except for the above.

Example 7

Except that a coating liquid (d) in which fluorine resin, alumina particles (average particle diameter: 0.5 μm) and N-methyl-2-pyrrolidone were blended in a weight ratio of 3:13:84 was used in place of the coating liquid A separator was obtained.

Example 8

A separator for a battery was obtained in the same manner as in Example 2 except that the conveying speed was 3 m / min.

Example 9

A separator for a battery was obtained in the same manner as in Example 2 except that the conveying speed was 10 m / min.

Example 10

A separator for a battery was obtained in the same manner as in Example 2 except that the conveying speed was 50 m / min.

Example 11

A separator for a battery was obtained in the same manner as in Example 2 except that the conveying speed was 80 m / min.

Example 12

As shown in Fig. 5, a Y-shaped jig (anti-shake device) shown in Fig. 4 was placed on the surface of the coating device B shown in Fig. A separator for a battery was obtained in the same manner as in Example 2 except that the separator was provided at both ends of the membrane.

Example 13

A Y-shaped jig (anti-shake device) shown in Fig. 4 was placed at a position 50 mm downward from the contact point of the polyurethane porous film and the flat surface of the coating device C, using the coating device C shown in Fig. A separator for a battery was obtained in the same manner as in Example 2 except that the separator was provided at both ends of a porous film coated with a coating liquid.

Comparative Example 1

A separator for a battery was obtained in the same manner as in Example 2 except that the shake prevention device was not used.

Comparative Example 2

A battery separator was obtained in the same manner as in Comparative Example 1 except that the shake prevention device was not used and the conveying speed was 3 m / min.

Comparative Example 3

A battery separator was obtained in the same manner as in Comparative Example 1 except that the shake prevention device was not used and the conveying speed was 80 m / min.

Table 1 shows the production conditions of Examples 1 to 13 and Comparative Examples 1 to 3 and the number of generated streaks.

1: polyolefin porous film 2: coating liquid
3: Blade 4: Porous film coated with a coating liquid
5: die 6: backup roll
7: tank 8:
9: Y-shaped jig (anti-shake device) 10: application device
11: dispensing end point

Claims (4)

A method for producing a battery separator in which a modified porous layer is formed on a surface of a porous polyolefin membrane,
(1) a step of simultaneously applying a coating liquid obtained by dissolving a resin in a solvent on both surfaces of the polyolefin porous film,
(2) a step of solidifying the resin component in the applied coating liquid,
(3) a step of cleaning,
(4) a step of drying,
And a step of bringing the coated polyolefin porous film between the step (1) and the step (2) into contact with the anti-shake device, wherein the conveying speeds of (1) to (4) A method of manufacturing a separator. The method according to claim 1,
Wherein the thickness of the polyolefin porous film is 25 占 퐉 or less. 3. The method according to claim 1 or 2,
Wherein the resin is a fluorine-based resin or a polyamide-imide resin. 4. The method according to any one of claims 1 to 3,
Wherein the coating liquid comprises inorganic particles or crosslinked organic particles.

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