JP2010219335A - Separator for storage device, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator which has heat resistance, mechanical strength, and size stability and is made into a thin film, the separator having superior ion transmissivity and low resistance, seldom causing a short circuit between electrodes or a self-discharge and being superior in durability even after being used for a long period in a high-temperature environment in the presence of an organic solvent and an ionic liquid. <P>SOLUTION: The separator for a storage device is formed by laminating two or more fiber layers, and at least one or more of the fiber layers contain synthetic fiber and a synthetic resin-based binding agent. Further, the synthetic resin-based binding agent is preferably composed of at least one kind selected between carboxymethyl cellulose and styrene butadiene rubber, and the fiber layers are preferably laminated one over another on a paper making net by using an inclined wire paper making machine having two or more heads. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separator for an electricity storage device, and in particular, a separator for an electricity storage device such as a lithium ion secondary battery, a polymer lithium secondary battery, an electric double layer capacitor or an aluminum electrolytic capacitor (hereinafter referred to as “separator”). )

  In recent years, due to the increasing demand for electrical and electronic equipment regardless of industrial equipment and consumer equipment and the development of hybrid vehicles, etc., lithium-ion secondary batteries, polymer lithium secondary batteries, electric double layer capacitors and aluminum electrolytic capacitors, which are electronic components, have been developed. Demand has increased significantly. These electric and electronic devices are steadily increasing in capacity and functionality. Lithium ion secondary batteries, polymer lithium secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors also have higher capacities and higher functions. The use in severe environments is increasing.

  A lithium ion secondary battery and a polymer lithium secondary battery include a positive electrode in which an active material, a lithium-containing oxide, and a binder such as polyvinylidene fluoride are mixed with 1-methyl-2-pyrrolidone to form a sheet on an aluminum current collector. , A negative electrode formed by mixing a carbonaceous material capable of inserting and extracting lithium ions and a binder such as polyvinylidene fluoride with 1-methyl-2-pyrrolidone into a sheet on a copper current collector, and a porous electrolyte made of polyethylene, polypropylene, or the like An electrode body obtained by winding or laminating a membrane in the order of a positive electrode, an electrolyte membrane, and a negative electrode is impregnated with a driving electrolyte solution and sealed with an aluminum case.

  An electric double layer capacitor is a mixture of activated carbon, conductive agent and binder, which is attached to both sides of the positive and negative current collectors made of aluminum and driven to a wound or laminated electrode body via a separator made of cellulose or the like. In this structure, the positive electrode lead and the negative electrode lead are passed through the sealing body so as not to be short-circuited by being impregnated with an electrolytic solution and packed with an aluminum case and a sealing body.

  An aluminum electrolytic capacitor is an electrode obtained by etching or laminating an aluminum positive foil having a dielectric film formed thereon by etching, and an etched aluminum negative foil through a separator made of cellulose or the like. The body is impregnated with a driving electrolyte solution, packed with an aluminum case and a sealing body, and has a structure in which a positive electrode lead and a negative electrode lead are passed through the sealing body and pulled out so as not to be short-circuited.

  Conventionally, porous membranes such as polyethylene and polypropylene have been used as separators for lithium ion secondary batteries and polymer lithium secondary batteries, and paper made of cellulose pulp has been used as separators for electric double layer capacitors and aluminum electrolytic capacitors. Moreover, the nonwoven fabric which consists of a cellulose fiber is used.

  By the way, electronic parts as described above are increasingly demanded for higher capacity and higher functionality. In order to increase the capacity, a separator having heat resistance, mechanical strength, and dimensional stability to withstand abnormal heat generation such as self-heating during charging / discharging or abnormal charging is required. On the other hand, improvement of rapid charge / discharge characteristics, improvement of high output characteristics, use in high-temperature atmosphere, etc. are required as one of higher functions, and separators are made thinner, more uniform, and more resistant to heat. It is requested. However, in the conventional separator, not only the heat resistance is insufficient, but through-holes are likely to exist due to the thin film, and the mechanical strength is lowered. As a result, internal short circuit occurs between the electrodes, and the uniformity is not good. There is a problem that a portion where ion movement is sufficiently concentrated and locally concentrated is likely to occur, resulting in a decrease in reliability. In addition, the above-described lithium ion secondary battery, polymer lithium secondary battery, electric double layer capacitor, and aluminum electrolytic capacitor use an organic solvent or ionic liquid as a driving electrolyte, and a separator such as cellulose has a high temperature. There was a problem that it deteriorated considerably in the long-term durability test.

  In response to the demand for such a separator, for example, a microporous resin film (stretched film) produced by stretching polyolefin and having a relatively high air permeability value provided with a through hole with a needle or a laser is used as the separator. It is proposed to use as (for example, refer patent document 1). However, when such a microporous resin film is used alone, there is a possibility that a short circuit occurs between the positive electrode and the negative electrode because there are through holes. Moreover, it has the property of being easily shrunk in a meltdown temperature range higher than the shutdown temperature, and as a result, it has a problem that a short circuit between the electrodes tends to occur when the temperature becomes high.

  In addition, it has been proposed to use a separator containing chemical fibers with little thermal deterioration in the driving electrolyte solution to increase heat resistance and extend the life when used at high temperatures (see, for example, Patent Document 2). ). This document has a description that the compounding ratio of the chemical fiber in the separator is about 10%, and the remaining fiber such as cellulose fiber can be used. However, the separator tends to be deteriorated in strength and durability due to mass reduction of the separator in a high temperature environment in the presence of an organic solvent or an ionic liquid. In addition, since highly durable chemical fibers and lowly durable cellulose fibers are randomly made, the separator is deteriorated unevenly with respect to the organic solvent, and current concentration tends to occur. Furthermore, since the separator has a single-layer structure, an internal short circuit is likely to occur when the separator is thinned.

  Further, as another document, in order to prevent an internal short circuit, it has been proposed to combine two or more layers into one layer using a circular paper machine (see, for example, Patent Document 3). However, in the conventional one, since all layers are composed of natural fibers, in a high temperature environment in the presence of an organic solvent or an ionic liquid, deterioration in strength and durability occurs due to a decrease in mass of the separator, There was a problem that the product characteristics could not be maintained. In addition, since the layers made individually by the circular net paper machine are bonded together, a boundary is generated between the layers, which tends to hinder the movement of ions.

  In addition, a method has been proposed in which a fibrillated natural fiber is subjected to wet papermaking, and after paper making, a paper strength enhancer is impregnated to form a thin film to reduce the resistance of the separator (see, for example, Patent Document 4). However, a separator made of only natural fibers such as cellulose has a problem of causing deterioration accompanying a decrease in discharge capacity and a decrease in film thickness in a long-term durability test at a high temperature.

International Publication No. WO01 / 67536 JP 2002-367863 A Japanese Patent No. 2892412 JP-A-8-273984

  The present invention is a thinned separator having heat resistance, mechanical strength, and dimensional stability, excellent ion permeability, low resistance, hardly causing short circuit and self-discharge between electrodes, and organic solvent. A separator for an electricity storage device that is excellent in durability even after long-term use in a high-temperature environment in the presence of an ionic liquid and a method for producing the same.

The separator of the present invention is a separator formed by laminating two or more fiber layers, wherein at least one of the fiber layers contains a synthetic fiber and a synthetic resin binder.
The synthetic resin binder is preferably at least one selected from carboxymethylcellulose and styrene-butadiene rubber.
Moreover, it is preferable that the synthetic resin binder is fused by heat treatment.
The synthetic fiber is selected from polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyamide, wholly aromatic polyester, semi-aromatic polyamide, polyphenylene sulfide, polyparaphenylene benzobisoxazole, polyethylene, polypropylene, aramid, and polyarylate. It is preferable that it is at least one or more.
Moreover, it is preferable that the synthetic fiber has a fiber diameter of 5 μm or less and a fiber length of 10 mm or less.
Moreover, it is preferable that the fiber layer is formed by overlapping and making a paper-making net using an inclined wire paper machine having two or more heads.
Further, the multi-tank inclined type wet paper machine in which the fiber layer can simultaneously form a plurality of layers having a structure in which the lower part of the second flow box is located in the vicinity of the intersection of the waterline and the paper making net in the first flow box. It is preferable that the sheet is overlapped on the papermaking net.
Moreover, it is preferable that the said electrical storage device is any one of a lithium ion secondary battery, a polymer lithium secondary battery, an electric double layer capacitor, and an aluminum electrolytic capacitor.
Moreover, the manufacturing method of the separator for electrical storage devices of this invention is obtained by apply | coating the said synthetic resin type binder to the fiber layer of a dry state or a wet paper state by spray application.

  The separator of the present invention is a thin film separator having heat resistance, mechanical strength and dimensional stability, excellent ion permeability and low resistance, and excellent in prevention of short circuit between electrodes and suppression of self-discharge. In addition, it has excellent durability after long-term use at high temperatures in the presence of organic solvents and ionic liquids. Therefore, the separator of the present invention can be suitably used for power storage devices, particularly for lithium ion secondary batteries, polymer lithium secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors.

It is sectional drawing which shows the structure of the multi-tank inclination type wet paper machine concerning this invention.

The separator of the present invention is a separator formed by laminating two or more fiber layers, and at least one of the fiber layers contains a synthetic fiber, and contains a synthetic resin binder. It is characterized by that.
In the present invention, a synthetic resin binder is applied to a dry separator after papermaking, or a synthetic resin binder is applied to a wet paper separator, and then the binder is fused by heat treatment. As a result, the bond between fibers is strengthened, so that the piercing strength is improved, and further, the fibers are fixed to each other by the fused binder, so that the crushing strength in the film thickness direction (Z-axis direction) is improved. It is possible to provide a separator having excellent short-circuit resistance.

  In addition, since the fibers are coated with a binder resin, the durability against organic solvents, ionic liquids, and high-temperature conditions is high, and high-temperature and long-term use is unlikely to deteriorate even if used in a high-temperature atmosphere for a long period of time. It is possible to provide a separator having excellent durability.

  Synthetic resin binders include ethylene-propylene-diene terpolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, polyvinylidene fluoride, polyethylene, polypropylene, poly At least one selected from tetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC) is used. Styrene-butadiene rubber (SBR) or water-soluble carboxymethylcellulose (CMC), which is commercially available as an aqueous emulsion, can contain organic solvents in the separator. Particularly preferred because they do not cut.

The synthetic resin binder is preferably applied in an amount of 5 to 200 parts by weight, particularly preferably 10 to 150 parts by weight, based on 100 parts by weight of the fiber. If it is less than 5 parts by mass, the effect of the present invention is hardly exhibited, and if it exceeds 200 parts by mass, the pores are filled with the synthetic resin binder, and the separator becomes a film.
As a solvent used when mixing or applying the binder, either a non-aqueous solvent or an aqueous solution can be used. Non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. Can be used. On the other hand, a dispersing agent, a thickener, etc. can be added and used for aqueous solution.

  Synthetic fibers used in the present invention are polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyamide, wholly aromatic polyester, semi-aromatic polyamide, polyphenylene sulfide, polyparaphenylene benzobisoxazole, polyethylene, polypropylene, aramid, polyarylate Those selected from the group consisting of resins selected from the above are preferably used, but are not necessarily limited to these, as long as they have high heat resistance and do not dissolve in organic solvents or ionic liquids used in driving electrolytes. Any one can be used. By laminating the fiber layer containing the synthetic fiber, durability against an organic solvent or an ionic liquid is increased, and even when the fiber layer is used in a high temperature atmosphere for a long period of time, it does not easily deteriorate.

  In the present invention, the fiber layer containing the synthetic fiber and the other fiber used in the fiber layer laminated with the fiber layer may be selected from the synthetic fibers. Any of synthetic fibers or cellulose fibers made of natural pulp can be used. These synthetic fibers, cellulose fibers, and the like are preferably beaten in order to improve the retention of the electrolytic solution and to form a uniform fiber layer.

In the present invention, the synthetic fiber has a fiber diameter of 5 μm or less and a fiber length of preferably 10 mm or less, particularly preferably a fiber diameter of 3 μm or less and a fiber length of 3 mm or less. When the fiber diameter exceeds 5 μm or the fiber length exceeds 10 mm, there is a high possibility that a through hole will be formed when the film is thinned, which is likely to cause an internal short circuit.
In the present invention, the pore diameter of the fiber layer is preferably 0.1 μm to 15 μm, more preferably 0.1 μm to 5.0 μm, as the average pore diameter measured by the bubble point method. When the average pore diameter is smaller than 0.1 μm, the ionic conductivity is lowered and the internal resistance tends to be high. Further, since it is difficult for water to escape during the production of the separator, it is difficult to produce the separator. If it exceeds 15 μm, an internal short circuit is likely to occur when the film is thinned. In addition, the measurement of the hole diameter by the bubble point method may be performed by using a porometer manufactured by Seika Sangyo Co., Ltd.

The thickness of the separator of the present invention is preferably 50 μm or less. When the thickness of the separator exceeds 50 μm, it is difficult to reduce the thickness of the electrochemical element, and at the same time, the amount of electrode material that can be put in a certain cell volume is reduced, the capacity is reduced, and the resistance is increased. It is not preferable.
The density of the separator of the present invention ^is preferably ^{0.20g / cm 3 ~0.75g / cm 3} . If it is less than 0.20 g / cm ³ , the void portion of the separator becomes excessive, and problems such as occurrence of short circuits and deterioration of self-discharge resistance are likely to occur. On the other hand, if the density is larger than 0.75 g / cm ³ , the material constituting the separator becomes excessively clogged, so that ion migration is hindered and resistance is likely to increase.

The porosity of the separator of the present invention is preferably in the range of 30% to 90% in order to achieve both prevention of short circuit and suppression of increase in resistance. The porosity here is calculated | required by following Formula using basis weight M (g / cm < ² >), thickness T (micrometer), and density D (g / cm < ³ >).
Porosity (%) = [1- (M / T) / D] × 100

  As described above, the separator of the present invention has a laminated structure in which two or more fiber layers are laminated, and at least one layer is composed of a fiber layer containing the above-described synthetic fiber having heat resistance, and is a synthetic resin. Because it contains a binder, it is difficult to deteriorate into an organic solvent or ionic liquid in a high-temperature atmosphere, and power storage such as lithium ion secondary batteries, polymer lithium secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors It can be suitably used for a device. In addition, when producing an electrical storage device using the separator of this invention, what is conventionally well-known can be used for the materials which comprise electrochemical elements, such as a positive electrode, a negative electrode, and electrolyte solution.

  Next, although the manufacturing method of the separator of this invention is demonstrated, it is not limited only to this, The separator of this invention can be manufactured also by another method.

  First, one or more kinds of synthetic fibers cut or beaten to have a fiber diameter of 5 μm or less and a fiber length of 10 mm or less are dispersed in water. Since the fibers used in the present invention are very fine and difficult to disperse uniformly in the disaggregation process, good dispersion is possible by using a dispersing device such as a pulper or an agitator or an ultrasonic dispersing device. The water used in this dispersion step is preferably ion-exchanged water in order to minimize ionic impurities. Next, the same synthetic fiber or different fiber as described above is dispersed in water by a dispersing device such as a pulper or agitator different from the above. The beating may be performed using a general beating machine such as a ball mill, beater, lampel mill, PFI mill, SDR (single disc refiner), DDR (double disc refiner), high pressure homogenizer, homomixer, or other refiner. it can.

  The fiber dispersion obtained above is made by applying a wet paper machine such as a long-mesh type, a short-mesh type, a circular net type, or an inclined type. Dehydrate in a continuous wire mesh dewatering part. When using an inclined wire paper machine with two heads in a wet paper machine, when two or more fiber layers are laminated together, it is difficult to create a boundary between fiber layers, and there is no pinhole. A separator is obtained. After the sheets are overlaid, a dried separator can be obtained by passing through a drying part such as a multi-cylinder type or Yankee type dryer. A synthetic resin binder solution diluted according to the target strength is impregnated and applied to the dry paper separator after the paper making. As a coating method, a separator is manufactured by dipping in a coating method such as a direct roll coater, a dip coater, a spray coater, or a kiss roll coater, and drying by passing through a drying part such as a multi-cylinder type or a Yankee type dryer.

  In addition, it is more preferable that the synthetic resin binder solution is impregnated and sprayed on a wire part in which the separator is in a wet paper state, on a felt or canvas, or on a carrier having good drainage and air permeability. In the impregnation coating method on the separator in the dry state, the separator is likely to be cut or wrinkled. Therefore, spray coating is suitable as the coating method.

  In particular, as a papermaking method, a multi-tank wet type wet paper machine capable of simultaneously forming a plurality of layers having a structure in which the lower part of the second flow box is located in the vicinity of the intersection of the floodline in the first flow box and the papermaking net. A method in which the fiber layers are stacked on the papermaking net and used together is more preferable because the fibers of the fiber layers are not easily entangled and peeled between the layers. In addition, the separator obtained by the multi-tank inclined type wet paper machine is difficult to form a boundary between fiber layers, and a uniform separator without a pinhole is obtained.

  Such a multi-tank inclined type wet paper machine has a configuration as shown in FIG. As shown in FIG. 1, the papermaking net 10 travels in the arrow α direction by a plurality of guide rollers. The inclined paper making net 10 between the guide roller 11 and the guide roller 12 is referred to as an inclined traveling unit 13. In the present invention, the lower part of the second flow box 15 is located in the vicinity A of the intersection of the floodline WL and the inclined traveling part 13 in the first flow box 14. In the vicinity A of the intersection, the dispersion 16 containing the fibers in the first flow box 14 and the dispersion 17 containing the fibers in the second flow box 15 are adjacent to each other with a partition wall 18 therebetween. There is a gap between the partition wall 18 and the inclined traveling part 13 in the vicinity A of the intersection, and the dispersion 16 that has flowed out from the first flow box 14 as the papermaking net 10 travels passes through this gap to the first position. 2 is mixed with the dispersion 17 in the flow box 15.

A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was placed in a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare a fiber dispersion A. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The fibers were mixed at a ratio, charged in ion-exchanged water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion B.
The dispersion A was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, Dispersion B was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness of the separator was 30 μm.

In Example 1, the separator of the present invention was obtained in the same manner except that the aqueous carboxymethylcellulose solution was changed to an SBR aqueous emulsion.
Regarding the physical properties of the obtained separator, the density was 0.43 g / cm ³ , the porosity was 75%, and the thickness of the separator was 32 μm.

In Example 1, the separator of this invention was obtained similarly except having changed the spray application quantity after drying of carboxymethylcellulose aqueous solution into 10 mass parts.
Regarding the physical properties of the obtained separator, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness of the separator was 30 μm.

In Example 1, the separator of this invention was obtained similarly except having changed the spray application amount after drying of carboxymethylcellulose aqueous solution into 60 mass parts.
Regarding the physical properties of the obtained separator, the density was 0.52 g / cm ³ , the porosity was 70%, and the thickness of the separator was 33 μm.

In Example 1, the separator of this invention was obtained similarly except having changed the spray application amount after drying of carboxymethylcellulose aqueous solution into 150 mass parts.
Regarding the physical properties of the obtained separator, the density was 0.55 g / cm ³ , the porosity was 69%, and the thickness of the separator was 35 μm.

  A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was placed in a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare a fiber dispersion A. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The fibers were mixed at a ratio, charged in ion-exchanged water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion B.

The dispersion A was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, Dispersion B was made on the sheet. Thereafter, the obtained wet sheet is taken out from the hand-making apparatus and dried at 130 ° C. with a Yankee dryer, and then the applied amount after drying becomes 20 parts by mass with respect to 100 parts by mass as the total mass of the dry fibers. Thus, the aqueous solution of carboxymethylcellulose was applied by spraying and dried at 130 ° C. with a Yankee dryer to obtain the separator of the present invention.
Regarding the physical properties of the obtained separator, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness of the separator was 30 μm.

  Polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm and a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm are mixed at a mass ratio of 1: 1, and ion-exchanged water. Was added to a pulper at a concentration of 0.05 mass% and dispersed for 30 minutes to prepare a fiber dispersion E. Next, solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into ion-exchanged water at a concentration of 0.05% by mass in a different pulper and dispersed for 30 minutes. Dispersion F was produced.

The dispersion E was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, Dispersion F was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.39 g / cm ³ , the porosity was 74%, and the thickness of the separator was 30 μm.

  A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm and polyphenylene sulfide fibrillated to a fiber diameter of 0.8 μm and a fiber length of 1.5 mm are mixed at a mass ratio of 1: 1, and 0 in ion-exchanged water. A fiber dispersion G was prepared by putting it into a pulper at a concentration of 0.05 mass% and dispersing it for 30 minutes. Next, solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into ion-exchanged water at a concentration of 0.05% by mass in a different pulper and dispersed for 30 minutes. Dispersion H was produced.

The dispersion G was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, a dispersion H was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.44 g / cm ³ , the porosity was 74%, and the thickness of the separator was 31 μm.

  A fully aromatic polyester fiber fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm is charged into ion exchange water at a concentration of 0.05% by mass in a pulper and dispersed for 30 minutes. Was made. Next, solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into ion-exchanged water at a concentration of 0.05% by mass in a different pulper and dispersed for 30 minutes. Dispersion J was prepared.

The dispersion I was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, the dispersion J was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.42 g / cm ³ , the porosity was 73%, and the thickness of the separator was 29 μm.

  A fully aromatic polyester fiber fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm is charged into ion exchange water at a concentration of 0.05% by mass in a pulper and dispersed for 30 minutes. Was made. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The mixture was mixed at a ratio, charged in deionized water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion L.

The dispersion K was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, the dispersion L was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness of the separator was 34 μm.

  A polyethylene terephthalate fiber having a fiber diameter of 0.5 μm and a fiber length of 5 mm was placed in a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare a fiber dispersion M. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The mixture was mixed at a ratio, and charged into ion-exchanged water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion N.

The dispersion M was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, the dispersion N was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.41 g / cm ³ , the porosity was 73%, and the thickness of the separator was 29 μm.

  A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was placed in a pulper at a concentration of 0.05% by mass in ion exchange water and dispersed for 30 minutes to prepare a fiber dispersion P. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The fibers were mixed at a ratio, charged in deionized water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion Q.

The dispersion P was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Furthermore, the dispersion Q was made on the sheet. Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, The separator of the present invention was obtained by drying at 130 ° C. with a Yankee dryer.
Regarding the physical properties of the obtained separator, the density was 0.41 g / cm ³ , the porosity was 73%, and the thickness of the separator was 19 μm.

A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was placed in a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare a fiber dispersion R. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.6 μm and a fiber length of 1.5 mm is charged into ion exchange water at a concentration of 0.05% by mass in a pulper and dispersed for 30 minutes to obtain a fiber dispersion. S was produced.
Further, the solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm is charged into ion-exchanged water at a concentration of 0.05% by mass in a pulper different from the above and dispersed for 30 minutes to disperse the fiber. A body T was prepared.

The dispersion R was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Furthermore, the dispersion S was made on the sheet. Thereafter, the dispersion T was made on the sheet. The obtained wet sheet is taken out from the hand-drawing apparatus, and the carboxymethyl cellulose aqueous solution is spray-applied so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fibers, and then a Yankee dryer. The separator of the present invention was obtained by drying at 130 ° C.
Regarding the physical properties of the obtained separator, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness of the separator was 35 μm.

  A fiber made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm, a fiber made of wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm, a fiber diameter of 0.5 μm, and a fiber Fibers made of solvent-spun cellulose fibrillated to a length of 1 mm are charged into a pulper at a concentration of 0.05% by mass in ion exchange water at a mass ratio of 25:60:15, respectively, and dispersed for 30 minutes. Was made.

The dispersion U is supplied to both the first flow box 14 and the second flow box 15 in the multi-tank inclined wet paper machine shown in FIG. Shed from. Thus, a wet sheet in which fiber layers of the same fiber composition are sequentially laminated is made, and on the felt, the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the total mass of the dry fibers. After spray-applying an aqueous solution of carboxymethylcellulose, it was dried with a Yankee dryer at 130 ° C. to obtain a separator having no pinholes having a thickness of 20 μm, a density of 0.45 g / cm ³ , and a porosity of 70%.

  A fiber made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was put into a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare dispersion V. A fiber made of wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a fiber made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm were each 80: Dispersion W was prepared by charging the ion exchange water at a mass ratio of 20 into the pulper at a concentration of 0.05 mass% and dispersing for 30 minutes.

The dispersion V was supplied to the first flow box 14 of the multi-tank inclined wet paper machine in FIG. 1, and the dispersion W was supplied to the second flow box 15. Next, the papermaking net 10 was run, and the dispersion was poured out from each flow box to the inclined running unit 13. In this way, a wet sheet in which fiber layers of different fiber types are sequentially laminated is made, and on the felt, the coating amount after drying is 20 parts by mass with respect to the total mass of 100 parts by mass of the dry fibers. After spraying a carboxymethylcellulose aqueous solution onto the surface, it was dried at 130 ° C. with a Yankee dryer, the thickness was 20 μm, the density was 0.45 g / cm ³ , and the porosity was 69% without pinholes. A separator was obtained.

(Comparative Example 1)
A polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm was placed in a pulper at a concentration of 0.05% by mass in ion-exchanged water and dispersed for 30 minutes to prepare a fiber dispersion A. Next, a wholly aromatic polyamide fibrillated to a fiber diameter of 0.2 μm and a fiber length of 0.6 mm and a solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are in a mass ratio of 1: 1. The fibers were mixed at a ratio, charged in ion-exchanged water at a concentration of 0.05% by mass in a pulper different from the above, and dispersed for 30 minutes to prepare a fiber dispersion B.

The dispersion A was made using a standard hand-making device specified in JIS P8222 to obtain a wet paper sheet. Further, Dispersion B was made on the sheet. Thereafter, the obtained wet sheet was taken out from the hand-making apparatus and then dried at 130 ° C. with a Yankee dryer to obtain a comparative separator.
Regarding the physical properties of the comparative separator obtained, the density was 0.40 g / cm ³ , the porosity was 73%, and the thickness was 30 μm.

(Comparative Example 2)
Solvent-spun cellulose, which is not a synthetic fiber fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm, is placed in ion exchange water at a concentration of 0.05% by mass in a pulper and dispersed for 30 minutes to produce a fiber dispersion c. did.
The dispersion c was made using a standard handmaking apparatus defined in JIS P8222 to obtain a wet paper sheet having a basis weight of 6 g / cm ² . Then, after taking out the obtained wet sheet from the hand-pickup device, spray application of the carboxymethyl cellulose aqueous solution so that the coating amount after drying is 20 parts by mass with respect to 100 parts by mass of the dry fiber, A comparative separator was obtained by drying at 130 ° C. with a Yankee dryer.
As for the physical properties of the comparative separator obtained, the density was 0.41 g / cm ³ , the porosity was 74%, and the thickness was 32 μm.
The following evaluation was performed in the separators obtained in Examples 1 to 15 and Comparative Examples 1 and 2, and the characteristics as the separator were evaluated. In addition, about each separator, the physical-property value of a film thickness, a density, and a porosity is shown in Table 1.

<Assembly of electric double layer capacitor and evaluation of discharge capacity and voltage retention>
About the separator of Examples 1-15 and Comparative Examples 1-2, the electric double layer capacitor was assembled using the electrode of a positive electrode and a negative electrode, and 100 each wound type cells were produced. In the production of the wound cell, an activated carbon electrode for electric double layer capacitor (made by Hosen Co., Ltd.) was used as the electrode. Moreover, what melt | dissolved the tetraethylammonium tetrafluoroborate (made by Kishida-Chemical Co., Ltd.) was used for the electrolyte solution in propylene carbonate so that it might become 1 mol / L.
About the produced wound cell, the initial discharge capacity, the discharge capacity after 2000 hours test, and the discharge capacity after 4000 hours test were measured with an LCR meter. Each cell was charged at 2.5 V after 2000 hours of testing, and then the electric circuit was opened and the holding voltage after 24 hours was examined. The test conditions were 80 ° C. and 2.5 V applied.
The obtained results are shown in Table 2.

<Comparison of crushing strength of separator>
The thickness after crushing the separators of Examples 1 to 15 and Comparative Examples 1 and ^{2 at} a pressure of 1 N / cm ² at 170 ° C. was measured.
The obtained results are shown in Table 3.

As is clear from the results in Tables 2 and 3, the electric double layer capacitor using the separator of the present invention maintains a sufficient discharge capacity of 8.5 F or more even after a 4000 hour test at 80 ° C. and 2.5 V. In addition, a voltage of 2.26 V or more was maintained, and the crushing strength was also maintained at an initial value, confirming that it had excellent performance. On the other hand, the electric double layer capacitor using the separators of Comparative Examples 1 and 2 was significantly inferior in discharge capacity. Moreover, the separators of Comparative Examples 1 and 2 significantly reduced the film thickness in the crushing test.
From the above results, it was found that the separator of the present invention is a thin film and very excellent in durability under a high temperature environment in the presence of an organic solvent or an ionic liquid. Therefore, the separator of the present invention is suitably used for an electricity storage device such as an electric double layer capacitor, and is excellent in preventing a short circuit between electrodes and suppressing self-discharge.

10 Papermaking Net 11 Guide Roller 12 Guide Roller 13 Inclined Traveling Section 14 First Flow Box 15 Second Flow Box 16 Dispersion 17 Dispersion 18 Partition

Claims (9)

  A separator for an electricity storage device formed by laminating two or more fiber layers, wherein at least one of the fiber layers contains a synthetic fiber and a synthetic resin binder.   The power storage device separator according to claim 1, wherein the synthetic resin binder is at least one selected from carboxymethylcellulose and styrene-butadiene rubber.   The power storage device separator according to claim 1, wherein the synthetic resin binder is fused by heat treatment.   The synthetic fiber is at least one selected from polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyamide, wholly aromatic polyester, semi-aromatic polyamide, polyphenylene sulfide, polyparaphenylene benzobisoxazole, polyethylene, polypropylene, aramid, and polyarylate. The separator for an electrochemical element according to any one of claims 1 to 3, wherein the separator is one or more species.   5. The electricity storage device separator according to claim 1, wherein the synthetic fiber has a fiber diameter of 5 μm or less and a fiber length of 10 mm or less.   The electrical storage device separator according to any one of claims 1 to 5, wherein the fiber layer is formed by overlapping and making paper sheets on a papermaking net using an inclined wire paper machine having two or more heads. .   Using a multi-tank slanting wet paper machine capable of simultaneously forming a plurality of layers having a structure in which the lower part of the second flow box is located in the vicinity of the intersection of the floodline and the paper making net in the first flow box. The separator for an electricity storage device according to any one of claims 1 to 5, wherein the separator is made by overlapping and making a sheet on a papermaking net.   The power storage device separator according to any one of claims 1 to 7, wherein the power storage device is any one of a lithium ion secondary battery, a polymer lithium secondary battery, an electric double layer capacitor, and an aluminum electrolytic capacitor. .   9. A power storage device according to claim 1, wherein a synthetic resin-based binder is applied to a dry fiber layer or a wet paper fiber layer by spray coating to obtain the power storage device separator according to claim 1. Manufacturing method for the separator.

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