JP2009193755A - Reactive polymer supporting porous film for separator for battery and electrode/separator assembly obtained therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reactive polymer supporting porous film for a battery separator, providing the battery excellent in safety at high temperature because of sufficient adhesiveness to an electrode and excellent heat resistance and to provide an electrode/separator assembly obtained using such a reactive polymer supporting porous film. <P>SOLUTION: The reactive polymer supporting porous film for a battery separator includes a reactive polymeric layer supported on a porous film that includes a cross-linked body of a resin composition containing polyolefin and a styrene-butadiene copolymer, has a gel fraction of ≥5%, and has the reactivity polymer having a cation polymerizable functional group in a molecule. An electrode is stacked thereon to provide a layered product with the electrode, an electrolyte including a cation polymerizable catalyst is contacted therewith, and reactive polymers are cross-linked to provide the electrode/separator assembly having the porous film adhesively bonded to the electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reactive polymer-supported porous film for a battery separator and an electrode / separator assembly obtained therefrom.

  In recent years, lithium ion secondary batteries having a high energy density have been widely used as power sources for small to portable electronic devices such as mobile phones and notebook personal computers. Such a lithium ion secondary battery is obtained by laminating or winding sheet-like positive and negative electrodes and, for example, a polyolefin resin porous film, and charging the battery into a battery container made of, for example, a metal can. It is manufactured through a process of injecting an electrolytic solution into a container, sealing, and sealing.

  However, in recent years, there has been a strong demand for further downsizing and weight reduction of the above-described small or portable electronic devices. Therefore, further thinning and weight reduction of lithium ion secondary batteries are also required. In place of the conventional metal can container, a laminate seal type battery container is also used.

  According to such a laminated seal type battery container, since the surface pressure for maintaining the electrical connection between the separator and the electrode cannot be sufficiently applied to the electrode surface as compared with the conventional metal can container, Due to the expansion and contraction of the electrode active material during charging and discharging, the distance between the electrodes partially increases with time, the internal resistance of the battery increases, the battery characteristics deteriorate, and the resistance varies within the battery. However, there arises a problem that the battery characteristics are deteriorated.

  Further, when manufacturing a sheet battery having a large area, the distance between the electrodes cannot be kept constant, and there is a problem that battery characteristics cannot be sufficiently obtained due to variations in resistance inside the battery.

  Therefore, conventionally, in order to solve such problems, it has been proposed to join an electrode and a separator by an adhesive resin layer comprising an electrolyte phase, a polymer gel layer containing an electrolyte solution, and a polymer solid layer. (For example, refer to Patent Document 1). In addition, after applying a binder resin solution containing polyvinylidene fluoride resin as a main component to the separator, an electrode is superimposed on the separator and dried to form a battery laminate, and after charging the battery laminate into a battery container, It has also been proposed to obtain a battery in which an electrolyte is injected into a battery container and an electrode is bonded to a separator (see, for example, Patent Document 2).

  Further, the separator impregnated with the electrolytic solution and the positive and negative electrodes are joined and adhered by the porous adhesive resin layer, and the electrolytic solution is held in the through-hole in the adhesive resin layer, thereby separating the separator. It has also been proposed to use a battery in which an electrode is bonded to the battery (see, for example, Patent Document 3).

However, according to such a method, in order to obtain a sufficient adhesive force between the separator and the electrode, the thickness of the adhesive resin layer must be increased, and the electrolytic solution for the adhesive resin Since the amount cannot be increased, the resulting battery has a problem that the internal resistance becomes high and the cycle characteristics and the high rate discharge characteristics cannot be sufficiently obtained.
JP-A-10-177865 Japanese Patent Laid-Open No. 10-189054 JP-A-10-172606

  The present invention has been made to solve the above-described problems in the production of a battery in which an electrode is bonded to a separator, and has sufficient adhesiveness with the electrode and is excellent in heat resistance. Another object of the present invention is to provide a battery separator that provides a battery with excellent safety at high temperatures. Furthermore, an object of the present invention is to provide an electrode / separator assembly obtained from such a battery separator.

  According to the present invention, there is provided a battery separator having a reactive polymer layer supported on a porous film, wherein the porous film is formed from a crosslinked resin composition containing a polyolefin and a styrene-butadiene copolymer. A reactive polymer-supported porous film for a battery separator is provided, which has a gel fraction of 5% or more, and wherein the reactive polymer has a cationic polymerizable functional group in the molecule .

  The reactive polymer is preferably a radical copolymer of a radical polymerizable monomer having a cationic polymerizable functional group and another radical polymerizable monomer.

  According to the present invention, the cationically polymerizable functional group is preferably at least one selected from a 3-oxetanyl group and an epoxy group.

  Further, according to the present invention, an electrode is laminated on the reactive polymer-supported porous film to obtain an electrode / reactive polymer-supported porous film laminate, and the reactive polymer contained in the laminate is converted into a cationic polymerizable catalyst. There is provided an electrode / separator assembly obtained by bringing the porous film into contact with an electrolytic solution containing the above-mentioned reactive polymer via the reactive polymer.

  In the present invention, the cationic polymerization catalyst is preferably an onium salt, and the electrolytic solution is preferably selected from lithium hexafluorophosphate and lithium tetrafluoroborate as an electrolyte salt that also serves as the cationic polymerization catalyst. Contains at least one species.

  The reactive polymer-supported porous film for a battery separator according to the present invention provides an electrode / separator assembly excellent in adhesion therebetween, and is excellent in heat resistance by using such an electrode / separator assembly. Therefore, a battery excellent in safety at a high temperature can be obtained.

  A reactive polymer-supported porous film for a battery separator according to the present invention is a battery separator having a reactive polymer layer supported on a porous film, wherein the porous film comprises polyolefin and styrene-butadiene. It consists of a crosslinked product of a resin composition containing a copolymer, has a gel fraction of 5% or more, and the reactive polymer has a cationic polymerizable functional group in the molecule.

  In the reactive polymer-supported porous film for battery separator according to the present invention, the base porous film is a gel of 5% or more comprising a cross-linked product of a resin composition containing a polyolefin resin and a styrene-butadiene copolymer. It is a porous film having a fraction. Such a porous film is prepared by, for example, producing a porous film from a resin composition containing a polyolefin resin and a styrene-butadiene copolymer, heat-treating the film, or irradiating with an electron beam or an ultraviolet ray to form the double bond. Can be obtained by reacting to give a cross-linked structure.

  The polyolefin resin is preferably a polyethylene resin. For example, a high density polyethylene resin, an ultrahigh molecular weight polyethylene resin, or a mixture thereof is preferably used. The styrene-butadiene copolymer may be a random copolymer, but is preferably a block copolymer. The resin composition containing such a polyolefin resin and a styrene-butadiene copolymer may contain other resins as necessary in order to improve the molding processability and adhesion. An example of such a resin is a modified polyolefin resin obtained by graft polymerization of maleic anhydride onto polyethylene or polypropylene.

  In the present invention, such a porous film has a gel fraction of 5% or more. When the gel fraction is less than 5%, the film resistance at high temperatures is insufficient, and when the battery is exposed to high temperatures, the separator may be broken, leading to a short circuit of the electrodes. In the present invention, the gel fraction of the porous film is in the range of 5 to 90%, preferably in the range of 5 to 70%.

  According to the present invention, the porous film usually has pores having an average pore diameter of 0.01 to 5 μm and a porosity in the range of 20 to 95%. The porosity of the porous film is preferably in the range of 30 to 90%, and most preferably in the range of 40 to 85%. When the porosity of the porous film is too low, when used as a battery separator, the ion conduction path is reduced and sufficient battery characteristics cannot be obtained. On the other hand, when the porosity is too high, when used as a battery separator, the strength is insufficient, and in order to obtain the required strength, a thick substrate porous film must be used. This is not preferable because the internal resistance of the battery increases.

  Further, according to the present invention, the porous film usually has an air permeability of 1500 seconds / 100 cc or less, preferably 1000 seconds / 100 cc or less. When the air permeability is too high, ion conductivity is low when used as a battery separator, and sufficient battery characteristics cannot be obtained.

  The strength of the porous film is preferably 1 N or more in terms of piercing strength. This is because when the piercing strength is less than 1N, the base material may be broken when a surface pressure is applied between the electrodes, thereby causing an internal short circuit.

  The reactive polymer-supported porous film for a battery separator according to the present invention has a reactive polymer supported on the substrate porous film as described above, and this reactive polymer is cationically polymerizable in the molecule. The cation polymerizable functional group having a plurality of functional groups is preferably at least one selected from a 3-oxetanyl group and an epoxy group (2-oxiranyl group). That is, according to the present invention, the reactive polymer is a polymer having a plurality of at least one cationically polymerizable functional group selected from a 3-oxetanyl group and an epoxy group in the molecule. In this way, a reactive polymer having a plurality of 3-oxetanyl groups in the molecule (hereinafter referred to as a 3-oxetanyl group-containing reactive polymer) or a reactive polymer having a plurality of epoxy groups in the molecule (hereinafter referred to as an epoxy group). For example, as described in JP-A No. 2002-110245 and JP-A No. 2001-176555, it is already known.

  According to the present invention, the 3-oxetanyl group-containing reactive polymer is preferably a radical polymerizable monomer having a 3-oxetanyl group (hereinafter referred to as a 3-oxetanyl group-containing radical polymerizable monomer) and another radical polymerizable. It is a radical copolymer with a monomer, and the epoxy group-containing reactive polymer is preferably also preferably a radical polymerizable monomer having an epoxy group (hereinafter referred to as an epoxy group-containing radical polymerizable monomer) and the other. It is a radical copolymer with a radically polymerizable monomer.

  In particular, according to the present invention, the 3-oxetanyl group-containing radical polymerizable monomer is preferably represented by the general formula (I)

(In the formula, R ₁ represents a hydrogen atom or a methyl group, and R ₂ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)
The 3-oxetanyl group containing (meth) acrylate represented by these is used.

  Specific examples of such a 3-oxetanyl group-containing (meth) acrylate include, for example, 3-oxetanylmethyl (meth) acrylate, 3-methyl-3-oxetanylmethyl (meth) acrylate, 3-ethyl-3-oxetanylmethyl ( Mention may be made of (meth) acrylate, 3-butyl-3-oxetanylmethyl (meth) acrylate, 3-hexyl-3-oxetanylmethyl (meth) acrylate and the like. These (meth) acrylates are used alone or in combination of two or more.

  In the present invention, (meth) acrylate means acrylate or methacrylate.

  Further, according to the present invention, the epoxy group-containing radical polymerizable monomer is preferably represented by the general formula (II)

(In the formula, R ₃ represents a hydrogen atom or a methyl group, and R ₄ represents the formula (1)

Or formula (2)

The epoxy group containing group represented by these is shown. )
The epoxy group containing (meth) acrylate represented by these is used.

  Specific examples of such an epoxy group-containing (meth) acrylate include 3,4-epoxycyclohexylmethyl (meth) acrylate and glycidyl (meth) acrylate. These (meth) acrylates are used alone or in combination of two or more.

  The other radical polymerizable monomer copolymerized with such a 3-oxetanyl group-containing radical polymerizable monomer or an epoxy group-containing radical polymerizable monomer is preferably represented by the general formula (III)

(In the formula, R ₅ represents a hydrogen atom or a methyl group, A represents an oxyalkylene group having 2 or 3 carbon atoms (preferably an oxyethylene group or an oxypropylene group), and R ₆ represents 1 to 1 carbon atoms. 6 represents an alkyl group or a fluorinated alkyl group having 1 to 6 carbon atoms, and n represents an integer of 0 to 12.)
(Meth) acrylate represented by the general formula (IV)

(In the formula, R ₇ represents a methyl group or an ethyl group, and R ₈ represents a hydrogen atom or a methyl group.)
It is at least 1 sort (s) chosen from vinyl ester represented by these.

Specific examples of the (meth) acrylate represented by the general formula (III) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2,2,2 -Trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, etc. can be mentioned.
Besides these, for example,

(In each formula, R ₅ represents a hydrogen atom or a methyl group, and n represents an integer of 0 to 12.)
Etc.

  Specific examples of the vinyl ester represented by the general formula (IV) include vinyl acetate and vinyl propionate.

  As described above, the 3-oxetanyl group-containing reactive polymer or the epoxy group-containing reactive polymer is preferably a 3-oxetanyl group-containing radical polymerizable monomer, an epoxy group-containing radical polymerizable monomer, and another radical polymerizable monomer. Can be obtained as a radical copolymer by radical copolymerization using a radical polymerization initiator.

  This radical copolymerization may be carried out by any polymerization method such as solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc., but solution polymerization or suspension polymerization in terms of ease of polymerization, adjustment of molecular weight, post-treatment, etc. Is preferred.

  The radical polymerization initiator is not particularly limited, and examples thereof include N, N′-azobisisobutyronitrile, dimethyl N, N′-azobis (2-methylpropionate), and benzoyl peroxide. Lauroyl peroxide is used.

  In this radical copolymerization, a molecular weight modifier such as mercaptan can be used as necessary.

  According to the present invention, as will be described later, the reactive polymer having the reactive polymer-supported porous film is brought into contact with the electrolytic solution containing the cationic polymerization catalyst, and at least near the interface between the porous film and the electrode. Part is swollen in the electrolytic solution or eluted into the electrolytic solution, crosslinked by cationic polymerization, and the electrolytic solution is gelled in the vicinity of the interface between the porous film and the electrode. Adhere. Therefore, the gel formed by the reactive polymer together with the electrolytic solution needs to be able to bond the porous film and the electrode.

  Therefore, according to the present invention, when the 3-oxetanyl group-containing reactive polymer or the epoxy group-containing reactive polymer is obtained, the total amount of the 3-oxetanyl group-containing radical polymerizable monomer and the epoxy group-containing radical polymerizable monomer is the same. Is used in a range of 5 to 50% by weight, preferably 10 to 30% by weight of the total amount of monomers. Therefore, in the case of obtaining a 3-oxetanyl group-containing reactive polymer, the 3-oxetanyl group-containing radical polymerizable monomer is used in the range of 5 to 50% by weight, preferably 10 to 30% by weight of the total monomer amount. Similarly, in the case of obtaining an epoxy group-containing reactive polymer, the epoxy group-containing radical polymerizable monomer is used in the range of 5 to 50% by weight, preferably 10 to 30% by weight of the total monomer amount. .

  Further, a reactive polymer having a 3-oxetanyl group and an epoxy group by using a 3-oxetanyl group-containing radical polymerizable monomer and an epoxy group-containing radical polymerizable monomer together and copolymerizing them with other radical polymerizable monomers Is used such that the proportion of the epoxy group-containing radical polymerizable monomer in the total amount of the 3-oxetanyl group-containing radical polymerizable monomer and the epoxy group-containing radical polymerizable monomer is 90% by weight or less.

  In obtaining a 3-oxetanyl group-containing reactive polymer or an epoxy group-containing reactive polymer, the total amount of the 3-oxetanyl group-containing radical polymerizable monomer and the epoxy group-containing radical polymerizable monomer is more than 5% by weight of the total monomer amount. When the amount is small, as described above, the amount of the reactive polymer required for gelation of the electrolytic solution is increased, so that the performance of the obtained battery is deteriorated. On the other hand, when it is more than 50% by weight, the retention property of the electrolyte solution of the formed gel is lowered, and the adhesion between the electrode / separator in the obtained battery is lowered.

  In the present invention, the reactive polymer having a plurality of at least one selected from a 3-oxetanyl group and an epoxy group preferably has a weight average molecular weight of 10,000 or more. When the weight average molecular weight of the reactive polymer is smaller than 10,000, a large amount of the reactive polymer is required to gel the electrolytic solution, so that the characteristics of the obtained battery are deteriorated. On the other hand, the upper limit of the weight average molecular weight of the reactive polymer is not particularly limited, but is about 3 million, preferably about 2.5 million so that the electrolytic solution can be held as a gel. In particular, according to the present invention, the reactive polymer preferably has a weight average molecular weight in the range of 100,000 to 2,000,000.

A reactive polymer-supported porous film for a battery separator according to the present invention is formed by supporting a reactive polymer as described above on a substrate porous film as described above. Is not particularly limited, for example, a reactive polymer solution is dissolved in an appropriate organic solvent such as acetone, ethyl acetate, butyl acetate to prepare a reactive polymer solution. Appropriate means such as casting or spraying the functional polymer solution on the surface of the porous substrate film. After applying by the method or impregnating the base material porous film in the reactive polymer solution, the organic solvent used may be removed by drying.

  As another method, the reactive polymer may be formed into a film by melt extrusion, and this film may be bonded to a porous substrate film by thermal lamination or the like.

  Next, production of a battery using the reactive polymer-supported porous film thus obtained will be described.

  First, the electrode is laminated or wound on the reactive polymer-supported porous film, and preferably the electrode and the reactive polymer-supported porous film are thermocompression-bonded to form an electrode / reactive polymer-supported porous film laminate. Then, this laminate is placed in a battery container made of a metal can, a laminate film, etc., and if necessary, welding of the terminal is performed, and then the cationic polymerization catalyst is dissolved in the battery container. A predetermined amount of the electrolyte solution is injected, the electrolyte solution is brought into contact with the reactive polymer of the electrode / reactive polymer-supported porous film laminate, and then the battery container is sealed and sealed. A portion of the electrolyte film is swollen in the electrolyte solution at least in the vicinity of the interface between the porous film and the electrode, or eluted in the electrolyte solution and crosslinked by cationic polymerization to reduce the electrolyte solution. Ku and also partially, by gelling, an electrode through a reactive polymer adhered to the porous film, thus, it is possible to obtain a battery having an electrode / separator junction body a porous film as the separator.

  In the present invention, it is sufficient for the reactive polymer to function so as to adhere the electrode and the porous film by cross-linking by cationic polymerization. Therefore, it is not necessary to gel all of the electrolytic solution.

In the present invention, the reactive polymer can be cationically polymerized and crosslinked even at room temperature, although it depends on its structure, the amount supported on the porous film, and the type and amount of the cationic polymerization catalyst. Thus, cationic polymerization can be promoted. In this case, although it depends on the heat resistance and productivity of the material constituting the battery, the heating is usually performed at a temperature of about 40 to 100 ° C. for about 0.5 to 48 hours. Further, in order to swell or elute an amount of polymer sufficient to adhere the electrode to the porous film, the electrolyte may be poured into the battery container and then left at room temperature for several hours.

  In the present invention, the electrode / reactive polymer-supported porous film laminate only needs to have an electrode laminated on the reactive polymer-supported porous film. Therefore, depending on the structure and form of the battery, the electrode / reactive polymer Examples of the supported porous film laminate include negative electrode / porous film / positive electrode, negative electrode / porous film / positive electrode / porous film, and the like.

  The electrolytic solution is a solution obtained by dissolving an electrolyte salt in an appropriate organic solvent. Examples of the electrolyte salt include alkali metals such as hydrogen, lithium, sodium and potassium, alkali metals such as calcium and strontium, tertiary or quaternary ammonium salts, etc. as cation components, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid A salt containing an anionic component of an inorganic acid such as borohydrofluoric acid, hydrofluoric acid, hexafluorophosphoric acid or perchloric acid, or an organic acid such as carboxylic acid, organic sulfonic acid or fluorine-substituted organic sulfonic acid. it can. Among these, an electrolyte salt containing an alkali metal ion as a cation component is particularly preferably used.

  Specific examples of the electrolyte salt having such an alkali metal ion as a cation component include, for example, alkali perchlorate such as lithium perchlorate, sodium perchlorate, potassium perchlorate, lithium tetrafluoroborate, tetra Alkali metal tetrafluoroborate such as sodium fluoroborate and potassium tetrafluoroborate, alkali metal hexafluorophosphate such as lithium hexafluorophosphate and potassium hexafluorophosphate, alkali metal trifluoroacetate such as lithium trifluoroacetate And alkali metal trifluoromethanesulfonates such as lithium trifluoromethanesulfonate.

  In particular, when obtaining a lithium ion secondary battery according to the present invention, as the electrolyte salt, for example, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate and the like are preferably used.

  Furthermore, any solvent can be used as the solvent for the electrolyte salt used in the present invention as long as it dissolves the electrolyte salt. Examples of the non-aqueous solvent include ethylene carbonate and propylene carbonate. , Cyclic esters such as butylene carbonate and γ-Iptylolactone, industrial esters such as tetrahydrofuran and dimethoxyethane, and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate alone or in combination of two or more Can be used as a mixture.

  Moreover, although the said electrolyte salt is suitably determined according to the kind and quantity of the solvent to be used, normally the quantity used as the density | concentration of 1 to 50 weight% is used in the obtained electrolyte solution.

  In the present invention, an onium salt is preferably used as the cationic polymerization catalyst. Examples of such onium salts include ammonium salts, phosphonium salts, arsonium salts, stibonium salts, iodonium salts, and other cationic components, tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate, and perchloric acid. An onium salt comprising an anionic component such as a salt can be mentioned.

  However, according to the present invention, among the electrolyte salts described above, in particular, lithium tetrafluoroborate and lithium hexafluorophosphate also function as a cationic polymerization catalyst. It is preferably used as an agent. In this case, either lithium tetrafluoroborate or lithium hexafluorophosphate may be used alone, or both may be used in combination.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The characteristics of the porous film and the characteristics of the obtained battery were evaluated as follows.

(Thickness of porous film)
It was determined based on a measurement with a 1/10000 mm thickness gauge and a 10,000 times scanning electronic microscopic photograph of the cross section of the porous film.
(Porosity of porous film)
The weight was calculated from the weight W (g) per unit area S (cm ² ) of the porous film, the average thickness t (cm), and the density d (g / cm ³ ) of the resin constituting the porous film by the following equation.

Porosity (%) = (1− (100 W / S / t / d)) × 100
(Air permeability of porous film)
It calculated | required based on JISP8117.
(Puncture strength)
A piercing test was performed using a compression test kit KES-G5 manufactured by Kato Tech Co., Ltd. The maximum load was read from the load displacement curve obtained by the measurement, and the puncture strength was obtained. A needle having a diameter of 1.0 mm and a radius of curvature of the tip of 0.5 mm was used at a speed of 2 cm / second.

(Gel fraction of porous film)
A porous film cut out in a 10 cm square was folded and sandwiched between 5 cm × 10 cm metal meshes to prepare a 5 cm square sample. The initial weight P ₀ of this sample was measured. Subsequently, this sample was immersed in 100 mL of m-xylene (boiling point 139 ° C.) and then heated to boil xylene for 5 hours. Thereafter, the sample was taken out and dried, and the weight P after the boiling xylene treatment was measured in this way, and the gel fraction R was measured from the following equation.

R (%) = (P / P ₀ ) × 100
<Measurement of electrode / separator adhesion>
About each battery obtained by the Example and the comparative example, it decomposed | disassembled before performing a charging / discharging test, and measured the adhesive force between an electrode sheet / separator. That is, the battery is disassembled and the electrode sheet / separator assembly is taken out. Next, the interface of the electrode sheet / separator assembly is peeled off 5 mm from the end, and the end of the electrode sheet and the separator are mutually oriented at 180 °. The load at that time was measured by pulling. This load was divided by the width of the electrode sheet / separator to obtain the adhesive force between the electrode sheet / separator.

(Battery high temperature storage test)
Each battery obtained in Examples and Comparative Examples was fixed to a battery holder, applied with a certain surface pressure, and left in a thermostat at 160 ° C. The positive and negative terminals of the battery were connected to an ohmmeter, and the time when the resistance indicated by the ohmmeter suddenly decreased was measured. The test was up to 60 minutes. After 60 minutes, the battery was taken out of the incubator and allowed to cool, then the battery was disassembled, the area of the separator was measured, and the shrinkage was measured. However, since the separator usually has a larger area than the electrode sheet, the separator protrudes outward from the periphery of the electrode sheet. Therefore, when the battery was disassembled, the shrinkage rate was set to 0% when the area of the separator was equal to the area of the electrode sheet. Therefore, for example, if the area of the separator contracts to 80% of the area of the electrode sheet, the contraction rate of the separator in this case is 20%.

Reference example 1
(Preparation of electrode sheet)
85 parts by weight of lithium cobaltate (Nippon Chemical Industry Co., Ltd., Cellseed C-10) as a positive electrode active material and 10 parts by weight of acetylene black (Denka Black from Denki Kagaku Kogyo Co., Ltd.) as a conductive additive and a binder. 5 parts by weight of vinylidene fluoride resin (KF Polymer L # 1120 manufactured by Kureha Chemical Industry Co., Ltd.) was mixed, and this was made into a slurry using N-methyl-2-pyrrolidone so as to have a solid concentration of 15% by weight. .

  This slurry was applied to an aluminum foil (current collector) having a thickness of 20 μm to a thickness of 200 μm, dried at 80 ° C. for 1 hour, and then at 120 ° C. for 2 hours, and then pressed by a roll press, so that the thickness of the active material layer was A 100 μm positive electrode sheet was prepared.

  In addition, 80 parts by weight of mesocarbon microbeads (MCMB6-28 manufactured by Osaka Gas Chemical Co., Ltd.) as a negative electrode active material, 10 parts by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent, and a binder 10 parts by weight of vinylidene fluoride resin (KF Polymer L # 1120 manufactured by Kureha Chemical Industry Co., Ltd.) is mixed, and this is slurried with N-methyl-2-pyrrolidone so as to have a solid concentration of 15% by weight. It was.

  This slurry was applied to a copper foil (current collector) having a thickness of 20 μm to a thickness of 200 μm, dried at 80 ° C. for 1 hour, dried at 120 ° C. for 2 hours, and then pressed by a roll press to form an active material layer. A negative electrode sheet having a thickness of 100 μm was prepared.

Production Example 1
(Production of 3-oxetanyl group-containing reactive polymer A, 3-oxetanyl group-containing monomer component 25% by weight)
In a 500 mL three-necked flask equipped with a reflux condenser, 60.0 g of methyl methacrylate, 20.0 g of 3-ethyl-3-oxetanylmethyl methacrylate, 158.0 g of ethyl acetate and N, N′-azobisisobutyro The nitrile 0.16g was thrown in, stirred and mixed for 30 minutes while introducing nitrogen gas, and then heated to 60 ° C.

  When about 2 hours had elapsed, the viscosity of the reaction mixture began to rise, and then polymerization was continued for 8 hours. Thereafter, the mixture was cooled to about 10 ° C., and 0.16 g of N, N′-azobisisobutyronitrile was added again. After reheating to 70 ° C., polymerization was carried out for 8 hours.

  After completion of the reaction, the reaction mixture is cooled to about 40 ° C., 295 g of ethyl acetate is added, and the mixture is stirred and mixed until the whole becomes uniform to obtain an ethyl acetate solution (15 wt% concentration) of the oxetanyl group-containing reactive polymer A. It was.

  Next, 100 g of this polymer solution was added to 600 mL of methanol while stirring with a high-speed mixer to precipitate a polymer. The polymer was filtered off and washed several times with methanol, then placed in a drying tube, and a dry nitrogen gas (dew point temperature of −150 ° C. or lower) in which liquid nitrogen was vaporized was passed through the drying tube. Was dried in a desiccator for 6 hours under vacuum to obtain 3-oxetanyl group-containing reactive polymer A as a white powder. As a result of molecular weight measurement by GPC, this reactive polymer had a weight average molecular weight of 518,000 and a number average molecular weight of 231,000.

Production Example 2
(Production of 3-oxetanyl group-containing reactive polymer B, 3-oxetanyl group-containing monomer component 15% by weight)
In the same manner as in Production Example 1, a 500 mL three-necked flask equipped with a reflux condenser was charged with 68.0 g of methyl methacrylate, 12.0 g of 3-ethyl-3-oxetanylmethyl methacrylate, 158.0 g of ethyl acetate, and N, N ′. -0.15 g of azobisisobutyronitrile was added, mixed with stirring for 30 minutes while introducing nitrogen gas, and then heated to 70 ° C.

  When about 1.5 hours had elapsed, the viscosity of the reaction mixture began to rise, and then polymerization was continued for 8 hours. Thereafter, the mixture was cooled to about 40 ° C., 0.15 g of N, N′-azobisisobutyronitrile was added again, and then the mixture was reheated to 70 ° C., and polymerization was carried out for 8 hours.

  After completion of the reaction, the reaction mixture was cooled to about 40 ° C., 162 g of ethyl acetate was added, and the mixture was stirred and mixed until the whole became uniform to obtain an ethyl acetate solution (20 wt% concentration) of the oxetanyl group-containing reactive polymer B. It was. Then, it processed like the manufacture example 1 and obtained 3-oxetanyl group containing crosslinkable polymer B as white powder. As a result of molecular weight measurement by GPC, this reactive polymer had a weight average molecular weight of 253,000 and a number average molecular weight of 147,000.

Production Example 3
(Production of 3-oxetanyl group-containing reactive polymer C, 40% by weight of 3-oxetanyl group-containing monomer component)
In the same manner as in Production Example 1, a 500 mL three-necked flask equipped with a reflux condenser was charged with 48.0 g of methyl methacrylate, 32.0 g of 3-ethyl-3-oxetanylmethyl methacrylate, 58.0 g of ethyl acetate, and N, N ′. -0.36 g of azobisisobutyronitrile was added, mixed with stirring for 30 minutes while introducing nitrogen gas, and then heated to 70 ° C.

  When about 1.5 hours had elapsed, the viscosity of the reaction mixture began to increase, and then polymerization was continued for 8 hours. Thereafter, the mixture was cooled to about 40 ° C., 0.36 g of N, N′-azobisisobutyronitrile was added again, and then the mixture was reheated to 70 ° C., and polymerization was carried out for 8 hours.

  After completion of the reaction, the reaction mixture was cooled to about 40 ° C., 82 g of ethyl acetate was added, and the mixture was stirred and mixed until the whole became homogeneous, and an ethyl acetate solution of oxetanyl group-containing reactive polymer C (25% by weight concentration) Obtained. Then, it processed similarly to manufacture example 1 and obtained 3-oxetanyl group containing reactive polymer C as white powder. As a result of molecular weight measurement by GPC, this reactive polymer had a weight average molecular weight of 167,000 and a number average molecular weight of 80000.

Production Example 4
(Production of epoxy group-containing reactive polymer D, epoxy group-containing monomer component 25% by weight)
In the same manner as in Production Example 1, 60.0 g of methyl methacrylate, 20.0 g of 3,4-epoxycyclohexylmethyl acrylate, 158.0 g of ethyl acetate and N, N′— were added to a 500 mL three-necked flask equipped with a reflux condenser. Azobisisobutyronitrile (0.32 g) was added, and the mixture was stirred and mixed for 30 minutes while introducing nitrogen gas, and then heated to 70 ° C.

  When about 1 hour had elapsed, the viscosity of the reaction mixture began to rise, and then polymerization was continued for 8 hours. Thereafter, the mixture was cooled to about 40 ° C., 0.32 g of N, N′-azobisisobutyronitrile was added again, and then the mixture was reheated to 70 ° C. to carry out polymerization for 8 hours.

  After completion of the reaction, the reaction mixture is cooled to about 40 ° C., 162 g of ethyl acetate is added, and the mixture is stirred and mixed until the whole becomes uniform to obtain an ethyl acetate solution (15 wt% concentration) of the epoxy group-containing reactive polymer D. It was. Thereafter, the same treatment as in Example 1 was performed to obtain an epoxy group-containing reactive polymer D as a white powder. As a result of molecular weight measurement by GPC, this reactive polymer had a weight average molecular weight of 466,000 and a number average molecular weight of 228,000.

Production Example 5
(Production of 3-oxetanyl group-containing reactive polymer E, 25% by weight of 3-oxetanyl group-containing monomer component)
In a 500 mL three-necked flask equipped with a reflux condenser, 2.0 g of completely saponified polyvinyl alcohol (weight average molecular weight 2000, saponification degree 99 mol%), partially saponified polyvinyl alcohol (weight average molecular weight 2000, saponification degree) (80 mol%) 0.05 g and 210 g of pure water were added and stirred at 90 ° C. for 15 minutes to dissolve the polyvinyl alcohol, and then the solution was cooled to 40 ° C.

  Separately prepared 60.0 g of methyl methacrylate, 20.0 g of 3-ethyl-3-oxetanyl methyl methacrylate, 0.15 g of a 10% ethyl acetate solution of 1-dodecanethiol and N, N′-azobisisobutyronitrile 0 A mixture consisting of .8 g was added to the polyvinyl alcohol solution, stirred and mixed for 30 minutes while introducing nitrogen gas, and then subjected to radical polymerization at 70 ° C. for 8 hours while continuing strong stirring.

  After completion of the reaction, the mixture was cooled to about 40 ° C., filtered with suction, and washed with water to obtain a spherical fine particle polymer. Next, the polyvinyl alcohol adhering to the polymer was removed by washing. That is, the polymer is charged into a new 500 mL volumetric flask, 400 mL of pure water is added thereto, heated to 90 ° C., stirred at this temperature for about 15 minutes, cooled to about 40 ° C., suction filtered, purified water Washed with. This washing operation was repeated three times, followed by suction filtration, pure water washing, and finally methanol washing several times. Thereafter, a polymer is placed in a drying tube, and a dry nitrogen gas (dew point temperature of −150 ° C. or lower) in which liquid nitrogen is vaporized is passed through the drying tube to dry the polymer, and further in a desiccator. By vacuum drying for 6 hours, 3-oxetanyl group-containing reactive polymer E was obtained as white spherical fine particles. As a result of molecular weight measurement by GPC, this reactive polymer had a weight average molecular weight of 821400 and a number average molecular weight of 292400.

Production Example 6
(Preparation of porous film A)
Styrene-butadiene block copolymer (JSR Co., Ltd. JSR-TR2601K, styrene content 30 wt%) 5 wt%, modified polyolefin resin (Nippon Polyethylene Co., Ltd. Adtex DH0200, melting point 135 ° C.) 28.5 wt% %, A resin composition consisting of 66.5% by weight of ultra high molecular weight polyethylene having a weight average molecular weight of 2 million and 85 parts by weight of liquid paraffin are uniformly mixed in a slurry state, and at 160 ° C. using a small kneader, Dissolved and kneaded for 60 minutes. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. Subsequently, this resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the above thickness.

  Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 3 hours to obtain a porous film A. This porous film had a film thickness of 21 μm, a porosity of 44%, an air permeability of 186 seconds / dL, a puncture strength of 239 gf, and a gel fraction of 12.4%.

Production Example 7
(Preparation of porous film B)
The same styrene-butadiene block copolymer 2.5% by weight as in Production Example 6, high-density polyethylene (melting point 135 ° C.) 29.3% by weight, and ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 million 68.2% by weight. 15 parts by weight of the resin composition and 85 parts by weight of liquid paraffin were uniformly mixed in a slurry state, and dissolved and kneaded for 60 minutes at 160 ° C. using a small kneader. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. The resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the thickness.

  Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 3 hours to obtain a porous film B. This porous film had a film thickness of 19 μm, a porosity of 50%, an air permeability of 167 seconds / dL, a piercing strength of 311 gf, and a gel fraction of 5.3%.

Production Example 8
(Preparation of porous film C)
Resin comprising 5% by weight of the same styrene-butadiene block copolymer as in Production Example 6, 28.5% by weight of the same modified polyolefin resin as in Production Example 6, and 66.5% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 million. 15 parts by weight of the composition and 85 parts by weight of liquid paraffin were uniformly mixed in a slurry state and dissolved and kneaded at 160 ° C. using a small kneader for 60 minutes. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. The resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the thickness.

Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 1 hour. Furthermore, this porous film was immersed in a benzophenone / methanol solution at a concentration of 0.1% by weight, and then irradiated with ultraviolet rays at a dose of 0.2 J / cm ² to obtain a porous film C. This porous film had a thickness of 20 μm, a porosity of 50%, an air permeability of 175 seconds / dL, a puncture strength of 229 gf, and a gel fraction of 62%.

Production Example 9
(Preparation of porous film D)
15% by weight of a resin composition comprising 10% by weight of the same styrene-butadiene block copolymer as in Production Example 6, 27% by weight of the same modified polyolefin resin as in Production Example 6, and 63% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 million. And 85 parts by weight of liquid paraffin were uniformly mixed in a slurry state and dissolved and kneaded for 60 minutes at 160 ° C. using a small kneader. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. The resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the thickness.

  Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 3 hours to obtain a porous film D. This porous film had a film thickness of 23 μm, a porosity of 46%, an air permeability of 275 seconds / dL, a puncture strength of 273 gf, and a gel fraction of 23%.

Production Example 10
(Preparation of porous film X)
15 parts by weight of a resin composition comprising 30.0% by weight of the same modified polyolefin resin as in Production Example 6 and 70.0% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 million and 85 parts by weight of liquid paraffin are uniformly mixed in a slurry form. Then, the mixture was dissolved and kneaded at 160 ° C. for 60 minutes using a small kneader. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. The resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the thickness.

  Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 3 hours to obtain a porous film X. This porous film had a film thickness of 20 μm, a porosity of 41%, an air permeability of 200 seconds / dL, a puncture strength of 225 gf, and a gel fraction of 3%.

Production Example 11
(Preparation of porous film Y)
A slurry of 15 parts by weight of a resin composition comprising 30% by weight of a high-density polyethylene resin (3000B, Mitsui Chemicals Co., Ltd., melting point 135 ° C.) and 70% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2 million and 85 parts by weight of liquid paraffin The mixture was uniformly mixed and dissolved and kneaded at 160 ° C. using a small kneader for 60 minutes. Thereafter, the kneaded product was sandwiched between metal plates cooled to 0 ° C. and rapidly cooled to obtain a resin sheet. The resin sheet was heat-pressed at 115 ° C. until the thickness became 0.4 mm, and further press-molded at 20 ° C. while maintaining the thickness.

  Next, the obtained resin sheet was biaxially stretched 4.0 × 4.0 times in length and width simultaneously at a temperature of 120 ° C. and a speed of 10 mm / second, and then desolvated with heptane to obtain a porous film. It was. This porous film was heat-treated in air at 85 ° C. for 12 hours, and then heat-treated at 126 ° C. for 3 hours to obtain a porous film Y. This porous film had a thickness of 20 μm, a porosity of 41%, an air permeability of 200 seconds / dL, a puncture strength of 225 gf, and a gel fraction of 0%.

Examples 1-9
(Production of reactive polymer-supported porous films A to E)
Reactive polymers A to E obtained in Production Examples 1 to 5 were each dissolved in ethyl acetate to prepare a 10 wt% concentration of a reactive polymer solution. As shown in Table 1, the reactive polymer solution was applied to the porous films A to D obtained in Production Examples 6 to 9, and reactive polymer-supported porous films A to E were obtained, respectively. Here, when the reactive polymer was applied to both sides of the porous film and supported, it was first applied to one side of the porous film and then applied to the back side in the same manner. Table 1 shows the names and structures of the reactive polymer-supported porous films thus obtained.

Comparative Examples 1-5
(Production of reactive polymer-supported porous films X and Y)
Polymer A, D or E was dissolved in ethyl acetate to prepare a 10 wt% polymer solution. As shown in Table 2, the polymer solution was applied to the porous film X or Y obtained in Production Example 10 or 11, to obtain a reactive polymer-supported porous film X or Y, respectively. Table 2 shows the names of the reactive polymer-supported porous films thus obtained and their structures.

Examples 10-18
(Battery assembly)
Reactive polymer-supported porous films A to E obtained in Production Examples 1 to 9 were sandwiched between the positive electrode and the negative electrode obtained in Reference Example 1, respectively, and a reactive polymer was supported using a hot press at a temperature of 80 ° C. The porous film was pressure-bonded to both the positive and negative electrodes to produce electrode / separator laminates, respectively. The size of the battery separator was set to 1 mm at the portion protruding from the electrode.

  After each of these electrode / separator laminates was loaded into an aluminum laminate package, an electrolytic solution was injected into the package. The electrolytic solution used was a solution of lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate / diethyl carbonate (volume ratio 1: 1) at a concentration of 1.0 mol / L. Next, the aluminum laminate package is sealed, left at room temperature for 12 hours, and then heated at 50 ° C. for 24 hours to cause the reactive polymer in the separator to be cationically polymerized by the cationically polymerizable functional group that it has, to be crosslinked, thus Then, an electrode was bonded to the separator to produce a battery having an electrode / separator assembly. Table 3 shows the electrode / separator adhesion in these batteries and the results of the battery high-temperature storage test.

  The reactive polymer-supported porous film according to the present invention provides an electrode / separator assembly having a high adhesive force therebetween, and the resulting battery is excellent in high-temperature storage, the separator does not shrink, and the short circuit time is short. Also long.

Comparative Examples 6-10
In the above examples, batteries were produced in the same manner except that the reactive polymer-supported porous film X or Y was used as the reactive polymer-supported porous film. Table 4 shows the electrode / separator adhesive strength of these batteries and the results of the battery high-temperature storage test.

  The battery obtained using the separator according to the comparative example has a high adhesive strength with respect to the electrode / separator assembly, but is inferior in high-temperature storage and has a short-circuit time.

Comparative Examples 11-14
In the said Example, it replaced with the reactive polymer carrying | support porous film, and produced the battery respectively similarly except having used porous film AD obtained by manufacture examples 6-9. Table 4 shows the electrode / separator adhesion in these batteries and the results of the battery high-temperature storage test.

  A battery obtained by using a porous film as a separator has no adhesion between the electrode and the separator, and is inferior in high-temperature storage stability. The separator is significantly contracted, and the short-circuit time is short.

Claims (7)

  A battery separator having a reactive polymer layer supported on a porous film, wherein the porous film is a crosslinked product of a resin composition containing a polyolefin and a styrene-butadiene copolymer, and is 5% or more. A reactive polymer-supported porous film for a battery separator, having a gel fraction, wherein the reactive polymer has a cationic polymerizable functional group in a molecule.   The reactive polymer-supported porous film for a battery separator according to claim 1, wherein the reactive polymer is a radical copolymer of a radical polymerizable monomer having a cationic polymerizable functional group and another radical polymerizable monomer.   The reactive polymer-supported porous film for battery separator according to claim 1 or 2, which is at least one selected from a cationically polymerizable functional group 3-oxetanyl group and an epoxy group.   An electrode is laminated on the reactive polymer-supported porous film according to claim 1 to obtain an electrode / reactive polymer-supported porous film laminate, and the reactive polymer included in the laminate is subjected to cationic polymerization. Electrode / separator assembly obtained by bringing a porous film into contact with an electrolytic solution containing a reactive catalyst and bonding the porous film via a reactive polymer.   The electrode / separator assembly according to claim 4, wherein the cationic polymerization catalyst is an onium salt.   6. The electrode / separator assembly according to claim 5, wherein the electrolytic solution contains at least one selected from lithium hexafluorophosphate and lithium tetrafluoroborate as an electrolyte salt serving also as a cationic polymerization catalyst.   A battery comprising the electrode / separator assembly according to any one of claims 4 to 6.