JP2006179278A - Battery separator and battery manufacturing method using the same - Google Patents

Abstract

A battery separator with high safety is provided.
A crosslinkable polymer having a radical polymerizable ethylenic double bond together with at least one functional group selected from a hydroxy group and a carboxyl group comprises a polyfunctional compound having reactivity with the functional group. Provided is a battery separator comprising a foamed sheet of a reactive polymer obtained by reacting a crosslinking agent. Also, an electrode sheet is laminated and pressure-bonded to this separator to form an electrode sheet / separator laminate, and after this laminate is charged into the battery container, an electrolyte solution in which a radical polymerization initiator is dissolved is placed in the battery container. A method for producing a battery in which an electrode sheet is bonded to a separator by injecting and heating to crosslink and cure the reactive polymer by a radically polymerizable ethylenic double bond in the reactive polymer forming the separator. provide.
[Selection figure] None

Description

  The present invention relates to a battery separator that is useful for battery production and can contribute to safety during use of the battery thus produced, and a battery production method using the battery separator.

  Conventionally, as a battery manufacturing method, a positive electrode sheet and a negative electrode sheet are laminated with a separator for preventing a short circuit between the electrodes, or a positive (negative) electrode sheet, a separator, and a negative (positive) electrode sheet. And separators are laminated in this order and wound to form an electrode sheet / separator laminate. After the electrode / separator laminate is charged into the battery container, an electrolyte is injected into the battery container and sealed. Methods are known (see, for example, Patent Documents 1 and 2).

  However, in such a battery manufacturing method, the electrode sheet and the separator are liable to shift each other during storage and transportation of the electrode sheet / separator laminate, resulting in low battery manufacturing productivity, There were problems such as the occurrence of defective products. Further, according to the battery thus obtained, the electrode expands or contracts at the time of use, the adhesion between the electrode sheet and the separator is deteriorated, and the battery characteristics are deteriorated. A short circuit occurred, and the battery was heated and heated. In some cases, the battery could even be destroyed.

  On the other hand, porous films for battery separators are conventionally produced by various production methods. For example, as one method, a method of manufacturing a sheet made of polyolefin resin and stretching it at a high magnification is known (see, for example, Patent Document 3). However, the battery separator made of a porous membrane obtained by stretching at a high magnification in this way is significantly shrunk under a high temperature environment such as when the battery is abnormally heated due to an internal short circuit or the like. There is a problem that it does not function as a partition between electrodes.

Therefore, in order to improve the safety of the battery, reduction of the thermal contraction rate of the battery separator under such a high temperature environment is an important issue. In this regard, for example, in order to suppress the thermal shrinkage of the battery separator in a high-temperature environment, for example, ultrahigh molecular weight polyethylene and a plasticizer are melt-kneaded and extruded into a sheet form from a die, and then the plasticizer is extracted and removed. And the method of manufacturing the porous film | membrane used for a battery separator is also known (refer patent document 4). However, according to this method, contrary to the above method, the obtained porous film has not been stretched, and thus there is a problem that the strength is not sufficient.
JP 09-161814 A JP 11-329439 A Japanese Patent Application Laid-Open No. 09-012756 Japanese Patent Laid-Open No. 05-310989

  The present invention has been made to solve the above-described problems in the manufacture of a conventional battery. In the manufacture of a battery, an electrode sheet and a separator are temporarily bonded together to form an electrode sheet / separator laminate. As a result, the battery can be efficiently manufactured without the mutual movement of the electrode sheet and the separator, and after the battery is manufactured, the electrode sheet is not only superior in both ion permeability and electric insulation. It is an object of the present invention to provide a battery separator that functions as an electrode sheet / separator assembly having strong adhesion to the battery and provides a battery with high performance and excellent safety. Furthermore, this invention aims at providing the manufacturing method of a battery using such a battery separator.

  According to the present invention, a polyfunctional compound having reactivity with the above functional group to a crosslinkable polymer having a radical polymerizable ethylenic double bond together with at least one functional group selected from a hydroxy group and a carboxyl group There is provided a battery separator comprising a reactive polymer foam sheet obtained by reacting a crosslinking agent comprising:

  Furthermore, according to the present invention, the electrode sheet is laminated on the separator, and the electrode sheet / separator laminate is formed by pressure bonding. After the laminate is charged into the battery container, the radical polymerization initiator is dissolved. The electrolytic solution is injected into the battery container, heated, and the reactive polymer is crosslinked and cured by radical polymerizable ethylenic double bonds in the reactive polymer forming the separator, whereby the electrode sheet is separated from the separator. There is provided a method for manufacturing a battery, characterized in that the battery is adhered to a battery.

  The battery separator according to the present invention is a crosslinkable polymer having a radical polymerizable ethylenic double bond together with at least one functional group selected from a hydroxy group and a carboxyl group, and having a reactivity with the functional group. It consists of a reactive polymer foamed sheet obtained by reacting a cross-linking agent composed of a functional compound and cross-linking it. If the electrode sheet is pressure-bonded to this separator while heating as necessary, the electrode sheet is used as the separator. It can be easily temporarily bonded, and an electrode sheet / separator laminate can be obtained.

  Therefore, by using such an electrode sheet / separator laminate in the production of a battery, it is possible to efficiently produce a battery without shear movement between the electrode sheet and the separator. In addition, even when such a laminate is prepared in a battery container and an electrolyte solution is injected into the battery container, the reactive polymer that forms the separator has already been reduced by the reaction between the functional group and the crosslinking agent. Since it is partly cross-linked, it does not elute in the electrolyte solution and the temporary adhesion with the electrode / separator is maintained. Furthermore, if a radical polymerization initiator is dissolved in the electrolytic solution, the electrode sheet / separator laminate is charged into the battery container, and the electrolytic solution is injected into the battery container and heated to convert the reactive polymer into the radical polymer. By radical polymerization of polymerizable double bonds, further cross-linking is performed so that the separator is more strongly adhered to the electrode sheet to form an electrode / separator assembly, thus keeping the battery performance high and battery safety. Can contribute to sex.

  Moreover, since the battery separator of the present invention is made of a polymer foam sheet, if the electrolyte is poured into the battery container after being charged into the battery container, the electrolyte quickly penetrates and spreads through the separator. Therefore, the electrolyte solution can be quickly injected into the battery container. In addition, since the battery separator of the present invention is made of a polymer foam sheet, it is excellent in both ion permeability and electrical insulation, and provides a high-performance battery.

  In the present invention, the crosslinkable polymer has a radically polymerizable ethylenic double bond together with at least one functional group selected from a hydroxy group and a carboxyl group, and is reactive to the functional group. A polymer that can be cross-linked by reacting a cross-linking agent comprising a functional compound. The reactive polymer means a product obtained by reacting the crosslinkable polymer with the functional group and the crosslinker to crosslink the crosslinkable polymer. Thus, the reactive polymer already has a crosslinked structure by itself.

  Further, in the present invention, the electrode sheet / separator laminate refers to a laminate in which an electrode sheet is pressure-bonded, temporarily bonded, and bonded to a separator made of a reactive polymer foam sheet as described above. An electrode sheet / separator assembly means that in such an electrode sheet / separator laminate, the reactive polymer forming the separator is radically polymerized by its ethylenic double bonds and crosslinked to bond the electrode sheet to the separator. What you did.

  In the present invention, the crosslinkable polymer is, for example, a radical polymerizable monomer having at least one functional group selected from a hydroxy group and a carboxyl group, for example, a radical polymerizable monomer having a hydroxy group and other radical polymerizable monomers. A monomer is radically copolymerized according to a conventional method to obtain a copolymer, and then at least a part of the hydroxy group of the copolymer is reacted with (meth) acryloyloxyethyl isocyanate, so that at least one of the hydroxy groups is reacted. If the part is converted to a group having a (meth) acryloyl group, a crosslinkable polymer having the (meth) acryloyl group as a group having a radical polymerizable ethylenic double bond can be obtained together with the hydroxy group. According to the present invention, the crosslinkable polymer thus obtained preferably has a weight average molecular weight in the range of 200,000 to 3,000,000. However, the ethylenic double bond capable of radical polymerization possessed by the crosslinkable polymer is not limited to the double bond possessed by the (meth) acryloyl group, and the method for producing the crosslinkable polymer is also limited to the above examples. Is not to be done.

  Similarly, a radical polymerizable monomer having a carboxyl group and another radical polymerizable monomer are radically copolymerized according to a conventional method to obtain a copolymer, and then at least a part of the carboxyl group of the copolymer is ( By reacting with (meth) acryloyloxyethyl isocyanate and converting at least a part of the carboxyl group to a group having a (meth) acryloyl group, the above group as a group having a radical polymerizable ethylenic double bond together with the carboxyl group A crosslinkable polymer having a (meth) acryloyl group can be obtained.

  Examples of the radical polymerizable monomer having a hydroxy group include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and the like, and examples of the radical polymerizable monomer having a carboxyl group include For example, (meth) acrylic acid, itaconic acid, etc. can be mentioned.

  Examples of the other radical polymerizable monomer other than the at least one radical polymerizable monomer selected from the hydroxy group and the carboxyl group include, for example, alkyl (meth) acrylate, (meth) acrylamide, and (meth) acrylic acid polyethylene glycol alkyl ether. Etc. As the alkyl (meth) acrylate, for example, preferably methyl (meth) acrylate having 1 to 20 carbon atoms in the alkyl group, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Examples include dodecyl (meth) acrylate and isostearyl (meth) acrylate. The alkyl group may be linear or branched.

  Examples of (meth) acrylamide include N, N-dimethylacrylamide, N-isopropylacrylamide, N- (meth) acryloylmorpholine, N- (meth) acryloylpyrrolidone, N- (meth) acryloylpiperidine, N- (meth). Examples include acryloylpyrrolidine and N- (meth) acryloylpiperidone. As the (meth) acrylic acid polyethylene glycol alkyl ether, methyl ether or ethyl ether having 3 to 100, preferably 5 to 30, oxyethylene units is preferably used.

  In the present invention, the above (meth) acrylic acid means acrylic acid or methacrylic acid, (meth) acrylate means acrylate or methacrylate, and (meth) acryloyl means acryloyl or methacryloyl.

  Furthermore, in addition to the (meth) acrylate monomers, various vinyl monomers can be used as other radical polymerizable monomers. Examples of such vinyl monomers include (meth) acrylonitrile, styrene, vinyl acetate, and the like.

  In the present invention, in the production of the crosslinkable polymer, it is preferable that at least one radical polymerizable monomer selected from the hydroxy group and the carboxyl group occupies a ratio of 0.1 to 30% by weight in the total monomers. When the proportion of at least one radical polymerizable monomer selected from the hydroxy group and carboxyl group is less than 0.1% by weight in all monomers, at least a part of the functional group of the polymer obtained therefrom is added. Using a crosslinkable polymer having a radically polymerizable (meth) acryloyl group, this is cross-linked and foamed to form a separator, and an electrode sheet is laminated thereon to form an electrode sheet / separator laminate. Even if the separator in the body is radically polymerized in the presence of a radical polymerization initiator in the electrolyte, the reactive polymer that forms the base material of the separator does not sufficiently crosslink and cure, so the electrode sheet should be strongly adhered to the separator. I can't.

  On the other hand, when the proportion of at least one radical polymerizable monomer selected from the above hydroxy group and carboxyl group in all the monomers is more than 30% by weight, a gel is easily generated during the production of the crosslinkable polymer. Thus, it seems that crosslinking is excessive when the separator in the electrode sheet / separator laminate is radically polymerized and cured in the presence of a radical polymerization initiator in the electrolyte solution. The characteristics of the decrease.

  According to the present invention, the crosslinkable polymer usually preferably has a glass transition temperature in the range of −30 ° C. to 100 ° C., particularly preferably in the range of 0 ° C. to 80 ° C. When the glass transition temperature of the crosslinkable polymer is 0 ° C. or lower, if the electrode sheet is pressure-bonded to a reactive polymer foam sheet (separator) obtained from such a crosslinkable polymer at room temperature, the electrode sheet is used as the separator. The electrode sheet / separator laminate can be obtained immediately after temporary bonding.

  When the glass transition temperature of the crosslinkable polymer is in the range of 0 to 100 ° C., the electrode sheet is usually temporarily bonded to the reactive polymer foam sheet (separator) obtained from such a crosslinkable polymer. It is necessary to heat and heat and crimp an electrode sheet to this. However, when the glass transition temperature of the crosslinkable polymer is in the range of 0 to 100 ° C., particularly at room temperature or higher, most preferably 50 ° C. or higher, the separator has no blocking property at room temperature, There is an advantage that when a separator is laminated or wound on a roll, it is not necessary to sandwich a release sheet therebetween.

  According to the present invention, in order to crosslink such a crosslinkable polymer into a reactive polymer, a crosslinker composed of a polyfunctional compound is used. As such a crosslinking agent, a polyfunctional isocyanate is preferably used. Polyfunctional isocyanates include phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, diphenyl ether diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, and other aromatic, araliphatic, alicyclic, and aliphatic diisocyanates, as well as trimethylolpropane. So-called isocyanate adducts obtained by adding these diisocyanates to simple polyols are also preferably used. Such polyfunctional isocyanate is used in the range of 0.1 to 10 parts by weight per 100 parts by weight of the crosslinkable polymer.

  The battery separator according to the present invention comprises a foamed sheet of a reactive polymer obtained by reacting the crosslinkable polymer as described above with the above-mentioned crosslinker. Here, as means and method for foaming the crosslinkable polymer, chemical foaming using a foaming agent is preferably employed. However, the means and method for foaming the cross-linkable polymer are not limited to those using such a foaming agent. For example, the solution of the cross-linkable polymer is stirred at a high speed so that bubbles are held in the solution. A crosslinkable polymer may be formed from such a solution and crosslinked. Moreover, it can also be based on foaming using a supercritical liquid such as carbon dioxide gas.

  In chemical foaming using a foaming agent, examples of the foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, oxybis (benzenesulfonylhydrazide), sodium bicarbonate, and the like, but are not limited thereto. is not. These foaming agents are usually used in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the crosslinkable polymer, depending on the foaming ratio of the foamed sheet to be obtained. Although it depends on the expansion ratio of the foam sheet, the foam sheet can be obtained by heating the crosslinkable polymer containing these foaming agents to 100 to 200 ° C.

  Thus, when a foaming agent is used, a foaming aid such as zinc oxide, zinc carbonate, zinc stearate, or a core such as silica fine powder is used to adjust the foaming temperature and to make the generated bubbles uniform or fine. An agent, a fluorosurfactant, an alcohol, a polyol compound, or the like can be used in combination.

  The battery separator according to the present invention comprises a reactive polymer foamed sheet obtained by crosslinking the aforementioned crosslinkable polymer, and such a separator can be obtained by various methods. As an example, for example, the cross-linking agent as described above is dissolved in the solution of the cross-linkable polymer described above, and, for example, in the case of chemical foaming, the foaming agent as described above is blended, and the obtained mixture solution is appropriately used. After being cast on a releasable support, such as a stretched polypropylene film or a release-treated paper, the solvent is removed from the crosslinkable polymer solution by heating. A sheet of a mixture containing a cross-linking agent and a foaming agent is obtained. Next, the sheet is heated between, for example, a gas-impermeable film to foam the foaming agent to obtain a foamed sheet of a crosslinkable polymer, and the crosslinkable polymer is reacted with the crosslinker. Thus, by crosslinking, a battery separator comprising a foamed sheet of a reactive polymer can be obtained. If necessary, after obtaining a foamed sheet of a crosslinkable polymer, the crosslinkable polymer may be postcrosslinked.

  According to the present invention, the separator made of the foamed sheet of the reactive polymer thus obtained has a foaming ratio in the range of 2 to 20 times, a thickness in the range of 5 to 500 μm, and a foam diameter of 500 μm or less, preferably 200 μm. The following is preferable. Here, the expansion ratio refers to the ratio of the thickness of the foamed sheet to the thickness of the crosslinkable polymer sheet before foaming. When the thickness of the separator made of the reactive polymer foam sheet is thinner than 5 μm, the strength is insufficient, and an internal short circuit may occur in the battery. However, when the thickness exceeds 500 μm, the internal resistance of the battery becomes excessive as a result of the distance between the electrodes being too large.

Furthermore, the separator made of such a reactive polymer foam sheet according to the present invention has a gel fraction in the range of 20-100%, preferably a gel fraction in the range of 25-80%. Here, the gel fraction refers to a mixture of a crosslinkable polymer A part by weight, a polyfunctional compound B part by weight and a foaming agent , cast on a peelable support, remove the solvent, and then heat, While foaming or after foaming the crosslinkable polymer, it is partially crosslinked to form a foamed sheet made of a reactive polymer. This foamed sheet is used as a non-aqueous solvent for an electrolyte used in a battery at a temperature of 23 ° C. After dipping for 7 days, the non-aqueous solvent was replaced with a readily volatile solvent such as ethyl acetate or tetrahydrofuran and dried, and the remaining reactive polymer was C parts by weight, (C / (A + B )) × 100 (%).

  In the present invention, to obtain a foamed sheet of a reactive polymer having a gel fraction in the range of 20 to 100%, although it is not limited, as described above, usually 100 wt. The polyfunctional compound is blended in the range of 0.1 to 10 parts by weight with respect to part, heated to foam the crosslinkable polymer, and further crosslinked until the resulting reactive polymer is stabilized characteristically. It can be obtained by carrying out the reaction. Although the heating temperature for crosslinking of the crosslinkable polymer and the reaction time therefor depend on the crosslinkable polymer used, the polyfunctional compound, the type thereof, and the like, these reaction conditions can be determined by experiments. For example, heating and reacting at a temperature of 50 ° C. for 7 days usually completes the cross-linking reaction of the cross-linkable polymer with the polyfunctional compound and stabilizes the resulting reactive polymer in terms of properties.

  Furthermore, according to the present invention, the separator made of a foamed sheet of reactive polymer preferably has a degree of swelling of 5 times or more, particularly 10 times or more. Here, the degree of swelling means that a mixture of A part by weight of crosslinkable polymer B, part by weight of polyfunctional compound B and a foaming agent is cast on a peelable support, and after removing the solvent, Heating to foam the crosslinkable polymer, or after foaming, partially cross-linking to form a foamed sheet made of a reactive polymer, and this foamed sheet becomes a non-aqueous solvent for the electrolyte used in the battery A value defined as D / C, assuming that the weight in the swollen state when immersed at a temperature of 23 ° C. for 7 days is D, and then the remaining reactive polymer is C parts by weight after the separator is dried. It is. This degree of swelling can be appropriately adjusted depending on the monomer composition and molecular weight distribution of the crosslinkable polymer, the amount of functional groups possessed by the crosslinkable polymer, the amount of crosslinker used, and the like. According to the present invention, when the swelling degree of the reactive polymer is less than 5 times, the obtained battery may be inferior in characteristics.

  A separator made of a foamed sheet of such a reactive polymer is not allowed to react or crosslink in the absence of a crosslinking agent or until heated in the presence of a radical polymerization initiator in an electrolyte. Therefore, it is stable and does not deteriorate even when stored for a long period of time.

  According to the present invention, if an electrode sheet is pressure-bonded to a separator made of a foamed sheet of such a reactive polymer under heating as necessary, the electrode sheet can be easily temporarily bonded and bonded to the separator. Thus, an electrode sheet / separator laminate can be obtained.

  According to the present invention, an electrode sheet, that is, a negative electrode sheet and a positive electrode sheet are respectively pressure-bonded to the front and back surfaces of the separator, temporarily bonded, and bonded together to form an electrode sheet / separator laminate. Only the electrode sheet, that is, either the negative electrode sheet or the positive electrode sheet may be pressure-bonded and temporarily bonded to form an electrode sheet / separator laminate. Of course, it can also be set as the laminated body which has the structure of a positive (negative) electrode sheet / separator / negative (positive) electrode sheet / separator.

  In the present invention, the electrode sheet, that is, the negative electrode sheet and the positive electrode sheet are different depending on the battery, but in general, an active material and, if necessary, a conductive agent are usually provided on a conductive substrate as a current collector. It can be obtained by fixing on the conductive substrate using a vinylidene fluoride resin as a binder.

  According to the present invention, by using such an electrode sheet / separator laminate, there is no mutual movement of the electrode sheet and the separator, and the battery can be efficiently manufactured. The separator contributes to the safety of the battery as an electrode sheet / separator assembly bonded to the electrode sheet.

  That is, after the electrode sheet / separator laminate is prepared in the battery container, an electrolyte solution in which a radical polymerization initiator is dissolved is injected into the battery container and heated, whereby the electrode sheet / separator laminate is temporarily prepared. While maintaining the adhesion, the reactive polymer is swollen, the radical polymerizable double bond of the reactive polymer forming the separator is polymerized by the action of the radical polymerization initiator, and further crosslinked to form an electrode sheet. A battery having an electrode sheet / separator assembly formed by bonding and integrating with a separator and firmly bonding the electrode sheet to the separator can be obtained.

  According to the present invention, as described above, the reactive polymer is previously cross-linked so as to have a gel fraction in the range of 5 to 100%, so that the electrode sheet / separator laminate is placed in the electrolyte solution. Even when immersed, elution of the reactive polymer into the electrolytic solution is prevented or reduced, so that it is effectively used for adhesion of the electrode sheet. Moreover, since the reactive polymer has a degree of swelling of 5 times or more, it is further crosslinked by its radical polymerizable double bond while swelling so as to enclose these at the interface between the separator and the electrode sheet temporarily adhered thereto. Thus, the electrode sheet is more firmly bonded to the separator to give an electrode sheet / separator assembly. According to the present invention, the degree of swelling of the reactive polymer is almost the same as that before the crosslinking even after crosslinking by the reaction of the radical polymerizable double bond. The characteristics of the obtained battery are superior as the degree of swelling increases.

  According to the present invention, the electrode is placed along the surface of the separator made of the foamed sheet of the reactive polymer obtained by crosslinking the crosslinkable polymer in advance, and heated to a temperature at which the deformation of the separator does not occur. The electrode sheet is preferably partially pressed into the separator, so that the electrode sheet is temporarily bonded to the separator to form an electrode sheet / separator laminate, and the laminate is then applied to the battery container. After charging, an electrolytic solution in which a radical polymerization initiator is dissolved is poured into this battery container, heated, and the above-mentioned separator is polymerized by a radical polymerization double bond polymerization reaction of the reactive polymer. Further, crosslinking is performed to obtain an electrode sheet / separator assembly. That is, the electrode sheet is actually bonded to the separator.

  As in the case of the electrode sheet / separator laminate described above, in the present invention, the electrode sheet / separator assembly is not limited to the negative electrode sheet / separator / positive electrode sheet assembly, but either the negative electrode sheet or the positive electrode sheet / A separator assembly and a configuration of positive (negative) electrode sheet / separator / negative (positive) electrode sheet / separator are also included.

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

  Any solvent can be used as the solvent for the electrolytic solution as long as it dissolves the above electrolyte salt. Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone. Cyclic esters such as tetrahydrofuran, ethers such as dimethoxyethane, and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These solvents are used alone or as a mixture of two or more.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Measurement of glass transition temperature of crosslinkable polymer)
After the solution of the crosslinkable polymer was cast on a release paper and dried, a sheet having a thickness of 0.2 to 0.5 mm and a width of 5 mm was obtained. The sheet was made a distance of 10 mm between chucks, manufactured by Seiko Electronics Industry Co., Ltd. Using DSM120, the storage elastic modulus (E ′) and loss elastic modulus (E ″) were measured at 10 Hz in a bending mode at a temperature range of −50 ° C. to 200 ° C. and a heating rate of 5 ° C./min. The peak temperature of E ″ / E ′) was taken as the glass transition temperature.

(Preparation of electrode)
Lithium cobaltate (LiCoO ₂ ) having an average particle size of 15 μm, graphite powder and polyvinylidene fluoride resin were mixed at a weight ratio of 85: 10: 5, and this was added to N-methyl-2-pyrrolidone to obtain a solid content concentration of 15 wt. % Slurry was prepared. This slurry was applied to the surface of an aluminum foil having a thickness of 20 μm to a thickness of 200 μm, and then dried at 80 ° C. for 1 hour. Thereafter, the slurry was similarly applied to the back surface of the aluminum foil to a thickness of 200 μm, dried at 120 ° C. for 2 hours, and then passed through a roll press to prepare a positive electrode sheet having a thickness of 200 μm.

  Graphite powder and polyvinylidene fluoride resin were mixed at a weight ratio of 95: 5 and added to N-methyl-2-pyrrolidone to prepare a slurry having a solid content concentration of 15% by weight. This slurry was applied to the surface of a 20 μm thick copper foil to a thickness of 200 μm and then dried at 80 ° C. for 1 hour. Thereafter, the slurry was similarly applied to the back surface of the copper foil to a thickness of 200 μm, dried at 120 ° C. for 2 hours, and then passed through a roll press to prepare a negative electrode sheet having a thickness of 200 μm.

(Evaluation of adhesion between separator and electrode sheet)
The positive electrode sheet / separator / negative electrode sheet laminate punched out to a predetermined size is impregnated with an electrolytic solution in which benzoyl peroxide is dissolved (the same as that used in the following examples), and is then sandwiched between glass plates. In order to suppress the volatilization of the electrolyte, it is placed in a desiccator saturated with an electrolyte vapor and heated at a temperature of 70 ° C. for 24 hours to further crosslink the reactive polymer forming the separator in the positive electrode sheet / separator / negative electrode sheet laminate. By reacting, the positive and negative electrode sheets were bonded to the separator to obtain a positive electrode sheet / separator / negative electrode sheet assembly.

  The positive electrode / separator / negative electrode sheet assembly thus obtained was cut to a width of 1 cm and then immersed in an electrolytic solution at room temperature for 24 hours. Thereafter, when the positive and negative electrode sheets were peeled off from the positive electrode sheet / separator / negative electrode sheet assembly in a wet state, the case where there was resistance was marked with ◯, and the case where the electrodes had already been peeled was marked with x.

(Evaluation of battery performance)
After charging and discharging 5 times at a rate of 0.2 CmA, charging was performed at a rate of 0.2 CmA, and thereafter, discharging was performed at a rate of 2.0 CmA, and a discharge capacity at 2.0 CmA / 0 The discharge load characteristics were evaluated by the discharge capacity ratio at a rate of 2 CmA.

(Battery heat resistance)
After heating the battery at 150 ° C. for 1 hour, the presence or absence of a short circuit between the electrodes was examined.

(Foam diameter and expansion ratio in the foam sheet)
Ten points of the foam diameter on the surface of the foam sheet were observed with a microscope, and the average value was taken as the foam diameter. Moreover, the value which remove | divided the thickness of the sheet | seat after foaming by the thickness of the sheet | seat before foaming was made into the foaming ratio.

Example 1
(Preparation of crosslinkable polymer)
N, N-dimethylacrylamide 50 parts by weight Acrylonitrile 10 parts by weight 2-hydroxyethyl acrylate 4 parts by weight Methyl methacrylate 15 parts by weight Butyl acrylate 21 parts by weight Azobisisobutyronitrile 0.3 part by weight Ethyl acetate 150 parts by weight

The monomer, polymerization initiator, and solvent were charged into a four-necked flask equipped with a stirrer, a nitrogen inlet tube, and a condenser, and the inside of the flask was purged with nitrogen under stirring. Next, polymerization is carried out at 62 ° C. for 8 hours with stirring in a warm water bath, and further heated to 75 ° C. and held at this temperature for 3 hours. A solution of a functional polymer was obtained. The weight average molecular weight of this crosslinkable polymer was 4.5 × 10 ⁵ .

  The ethyl acetate solution of the crosslinkable polymer is placed in a flask purged with nitrogen, 0.5 equivalent of methacryloyloxyethyl isocyanate of the hydroxy group of the crosslinkable polymer is added, and the mixture is reacted at 40 ° C. with stirring for 24 hours. As a result, a crosslinkable polymer having a methacryloyl group together with a hydroxy group was obtained. The glass transition temperature of this crosslinkable polymer was 65 ° C.

(Preparation of separator)
1 part by weight of trimethylolpropane and 3 parts by weight of hexamethylene diisocyanate added to 3 parts by weight of trifunctional isocyanate, 5 parts by weight of blowing agent (Neocelbon 1000S manufactured by Eiwa Kasei Kogyo Co., Ltd.), 3 parts by weight of zinc oxide and fine silica 1 part by weight of powder was added to 100 parts by weight of the crosslinkable polymer to the solution of the crosslinkable polymer to obtain a solution of a crosslinkable polymer / crosslinking agent / foaming agent mixture. This crosslinkable polymer / crosslinking agent / foaming agent mixture solution was applied onto a release film having a thickness of 40 μm made of a release-treated polyester film, dried at 70 ° C., and then having a thickness of 3 μm on the release sheet. A sheet comprising a mixture of / crosslinking agent / foaming agent was obtained.

  Next, a peelable sheet having a thickness of 40 μm made of the same polyester film as described above was further laminated on the sheet made of the crosslinkable polymer / crosslinker / foaming agent mixture on the peelable sheet, and the resulting laminate was 150. The foamed sheet was obtained by heating at 0 ° C. for 10 minutes. Thereafter, this was further put into a thermostatic chamber at 50 ° C. for 3 days to obtain a laminate including a separator made of a foamed sheet of a reactive polymer.

  One peelable sheet is peeled off from the laminate, the separator is exposed on the other peelable sheet, the positive electrode sheet is overlaid on the surface of the separator, and a heating laminating roll with a temperature of 85 ° C. is used. The positive electrode sheet was pressure-bonded to the separator. Next, the other peelable sheet is peeled and removed to expose the back surface of the separator, and the negative electrode sheet is overlaid on the back surface of the separator. Similarly, using a heat bonding roll at a temperature of 85 ° C., the separator The negative electrode sheet was pressure-bonded to the electrode sheet / separator laminate.

(Assembly of battery and evaluation of battery performance)
In an argon-substituted glove box, electrolyte salt lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an ethylene carbonate / ethyl methyl carbonate mixed solvent (volume ratio 1/2) to a concentration of 1.2 mol / L, Furthermore, 1 part by weight of benzoyl peroxide was dissolved in 100 parts by weight of this solution to prepare an electrolytic solution.

  The electrode sheet / separator laminate is loaded into a 2016-size coin-type battery can that also serves as a positive and negative electrode plate, and an electrolytic solution in which the benzoyl peroxide is dissolved is injected into the coin-type battery can. The work in process was made. Thereafter, this work-in-process was heated at a temperature of 70 ° C. for 24 hours to obtain a coin-type lithium ion secondary battery having an electrode sheet / separator assembly.

  Table 1 shows the gel fraction, thickness, foaming ratio, foaming diameter, and degree of swelling of the separator, and further, the separator in the electrode sheet / separator laminate used for the battery discharge load characteristics, heat resistance, and battery production. Table 1 shows the adhesion between the electrode sheet and the electrode sheet.

Example 2
The solution of the crosslinkable polymer / crosslinking agent / foaming agent mixture obtained in Example 1 was applied onto a peelable sheet made of a polyester film having a thickness of 40 μm and dried at 70 ° C., and then on the peelable sheet. A sheet having a thickness of 12 μm was obtained. A 40 μm thick peelable sheet made of the same polyester film as described above was further superimposed on the sheet on the peelable sheet, and the resulting laminate was heated at 150 ° C. for 10 minutes to obtain a foamed sheet.

  Hereinafter, in the same manner as in Example 1, an electrode sheet / separator laminate was obtained using this foam sheet, and a coin-type lithium ion secondary battery having an electrode sheet / separator assembly was obtained using this foam sheet.

  Table 1 shows the gel fraction, thickness, foaming ratio, foaming diameter, and degree of swelling of the separator, and further, the separator in the electrode sheet / separator laminate used for the battery discharge load characteristics, heat resistance, and battery production. Table 1 shows the adhesion between the electrode sheet and the electrode sheet.

Example 3
The crosslinkable polymer obtained in Example 1 was reacted with 0.8 equivalent of methacryloyloxyethyl isocyanate of the hydroxy group to obtain a crosslinkable polymer having a methacryloyloxy group together with a hydroxy group as a functional group. It was.

  0.5 parts by weight of a trifunctional isocyanate obtained by adding 3 parts by mole of hexamethylene diisocyanate to 1 part by weight of trimethylolpropane, 5 parts by weight of a foaming agent (Neocelbon 1000S manufactured by Eiwa Chemical Industry Co., Ltd.), 3 parts by weight of zinc oxide, and 1 part by weight of silica fine powder was added to 100 parts by weight of the crosslinkable polymer to the solution of the crosslinkable polymer to obtain a solution of a crosslinkable polymer / crosslinking agent / foaming agent mixture. This crosslinkable polymer / crosslinking agent / foaming agent mixture solution was applied onto a release film having a thickness of 40 μm made of a release-treated polyester film, dried at 70 ° C., and then having a thickness of 3 μm on the release sheet. A sheet comprising a mixture of / crosslinking agent / foaming agent was obtained.

  Hereinafter, a foamed sheet was obtained in the same manner as in Example 1, and an electrode sheet / separator laminate was obtained using the foamed sheet. Using this, a coin-type lithium ion secondary battery having an electrode sheet / separator assembly was obtained. Obtained.

  Table 1 shows the gel fraction, thickness, foaming ratio, foaming diameter, and degree of swelling of the separator, and further, the separator in the electrode sheet / separator laminate used for the battery discharge load characteristics, heat resistance, and battery production. Table 1 shows the adhesion between the electrode sheet and the electrode sheet.

Comparative Example 1
In Example 1, a solution of a crosslinkable polymer / foaming agent mixture was obtained without using the trifunctional isocyanate. That is, with respect to 100 parts by weight of the crosslinkable polymer in the ethyl acetate solution of the crosslinkable polymer obtained in Example 1, 5 parts by weight of a foaming agent (Neocelbon 1000S manufactured by Eiwa Kasei Kogyo Co., Ltd.), 3 parts by weight of zinc oxide, and 1 part by weight of silica fine powder was added to obtain a solution of a crosslinkable polymer / foaming agent mixture.

  The solution of the crosslinkable polymer / foaming agent mixture was applied onto a peelable sheet made of a polyester film having a thickness of 40 μm and dried at 70 ° C. to obtain a sheet having a thickness of 3 μm on the peelable sheet. A 40 μm thick peelable sheet made of the same polyester film as described above was further superimposed on the sheet on the peelable sheet, and the resulting laminate was heated at 150 ° C. for 10 minutes to obtain a foamed sheet.

  The positive and negative electrode sheets are pressure-bonded to the front and back of the foam sheet and bonded together to obtain an electrode sheet / separator laminate, which is used to form a coin-type lithium ion having an electrode sheet / separator assembly. A secondary battery was obtained.

  Table 1 shows the gel fraction, thickness, foaming ratio, foaming diameter, and degree of swelling of the separator, and further, the separator in the electrode sheet / separator laminate used for the battery discharge load characteristics, heat resistance, and battery production. Table 1 shows the adhesion between the electrode sheet and the electrode sheet.

Comparative Example 2
In Example 1, a solution of a crosslinkable polymer / crosslinker mixture was obtained without using a blowing agent. That is, 1 weight of trifunctional isocyanate obtained by adding 3 mole parts of hexamethylene diisocyanate to 1 mole part of trimethylolpropane with respect to 100 weight parts of the crosslinkable polymer to the ethyl acetate solution of the crosslinkable polymer obtained in Example 1. Part by weight, 3 parts by weight of zinc oxide and 1 part by weight of silica fine powder were added to obtain a solution of a crosslinkable polymer / crosslinking agent mixture.

  The solution of the crosslinkable polymer / crosslinking agent mixture was applied onto a peelable sheet made of a polyester film having a thickness of 40 μm and dried at 70 ° C. to obtain a sheet having a thickness of 3 μm on the peelable sheet. A 40 μm-thick peelable sheet made of the same polyester film as described above is further superimposed on the sheet on this peelable sheet, and placed in a temperature-controlled room at 50 ° C. for 3 days, and the hydroxy group of the crosslinkable polymer contained in the foamed sheet is added. By reacting with the above trifunctional isocyanate and crosslinking, a laminate including a separator made of a reactive polymer sheet was obtained.

  Next, an electrode sheet / separator laminate was obtained from the laminate, and a coin-type lithium ion secondary battery having an electrode sheet / separator assembly was obtained using this in the same manner as in Example 1.

  Table 1 shows the gel fraction, thickness, and degree of swelling of the separator. Further, the discharge load characteristics and heat resistance of the battery, and the adhesion between the separator and the electrode sheet in the electrode sheet / separator laminate used for battery manufacture. The properties are shown in Table 1.

Comparative Example 3
In Example 1, a battery was assembled using an electrolytic solution containing no benzoyl peroxide. That is, the electrode sheet / separator laminate obtained in Example 1 was charged into a 2016-size coin-type battery can that also serves as a positive and negative electrode plate, and an electrolyte containing no benzoyl peroxide was injected into the coin-type battery can. After that, the battery can was sealed to produce a work in process. Thereafter, this work-in-process was heated at a temperature of 70 ° C. for 24 hours to obtain a coin-type lithium ion secondary battery.

  Table 1 shows the gel fraction, thickness, foaming ratio, foaming diameter, and degree of swelling of the separator, and further, the separator in the electrode sheet / separator laminate used for the battery discharge load characteristics, heat resistance, and battery production. Table 1 shows the adhesion between the electrode sheet and the electrode sheet.

  As shown in Table 1, the battery separator according to the present invention is excellent in adhesion to the electrode sheet, and thus provides a high-performance battery excellent in heat resistance.

  On the other hand, according to Comparative Example 1, the crosslinkable polymer was not previously cross-linked, but was used as it was as a foam sheet, and the electrode sheet was pressure-bonded to the electrode sheet / separator laminate. The obtained battery has poor adhesion between the separator and the electrode sheet, and therefore has poor heat resistance.

According to Comparative Example 2, since the separator is not made of a foam sheet, the battery characteristics are inferior. According to Comparative Example 3, since the reactive polymer has no further cross-linking of the reactive polymer of the separator in the battery container, the resulting battery has no adhesion between the separator and the electrode sheet, and is therefore heat resistant. Inferior.

Claims (4)

  A crosslinking agent comprising a polyfunctional compound having reactivity with the functional group is reacted with a crosslinkable polymer having a radical polymerizable ethylenic double bond together with at least one functional group selected from a hydroxy group and a carboxyl group. A separator for a battery comprising a foamed sheet of a reactive polymer obtained by cross-linking.   The battery separator according to claim 1, wherein the ethylenic double bond having radical polymerizability is a double bond of an acryloyl group or a methacryloyl group.   The battery separator according to claim 1, wherein the crosslinking agent is a polyfunctional isocyanate. An electrode sheet is laminated on the separator according to claims 1 to 3 and pressed to form an electrode sheet / separator laminate. After the laminate is charged into a battery container, an electrolytic solution in which a radical polymerization initiator is dissolved is prepared. The solution is poured into the battery container and heated to crosslink and cure the reactive polymer by radically polymerizable ethylenic double bonds in the reactive polymer forming the separator, and the electrode sheet is used as a separator. A battery manufacturing method comprising bonding.