JP2010219351A - Separator for storage device, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a storage device which has superior heat resistance, mechanical strength, and size stability and is made into a thin film, and a method of manufacturing the same. <P>SOLUTION: The separator for the storage device contains thermoplastic synthetic fiber A, heat-resisting synthetic fiber B, natural fiber C, and a synthetic resin-based binding agent. The synthetic resin-based binding agent is preferably composed of at least one selected between carboxymethyl cellulose and styrene butadiene rubber, and also preferably fused through a heat treatment. In the method of manufacturing the separator for the storage device, the synthetic resin-based binding agent is applied to fiber layers in a dry state or wet-paper state by spraying. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In recent years, electrical and electronic equipment has increased in both industrial and consumer use, and since hybrid vehicles have been put into practical use, power storage devices such as lithium ion secondary batteries and polymers mounted on them Demand for lithium secondary batteries, aluminum electrolytic capacitors, electric double layer capacitors, etc. has increased significantly. Electrical and electronic equipment has long life and high functionality, and power device separators are required to have long life and high functionality, and use in harsh environments is increasing. .

  A lithium ion secondary battery is 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, and lithium ions are occluded and released. A negative electrode formed by mixing a carbonaceous material and a binder such as polyvinylidene fluoride with 1-methyl-2-pyrrolidone into a sheet on a copper current collector, and a porous electrolyte membrane made of polyethylene, polypropylene, or the like, An electrode body wound or laminated in the order of 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.

Conventionally, porous membranes such as polyethylene and polypropylene have been used as separators for the lithium ion secondary battery, and paper made of cellulose pulp and nonwoven fabric made of cellulose fibers have been used as separators for electric double layer capacitors. ing.
The demand for higher capacity and higher functionality is increasing for the electricity storage devices as described above, and in order to increase the capacity, it can withstand abnormal heat generation such as self-heating during charging or discharging or abnormal charging. Therefore, a separator having heat resistance, mechanical strength, and dimensional stability 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 the above lithium ion secondary battery and electric double layer capacitor, an organic solvent or an ionic liquid is used as a driving electrolyte, and a separator such as cellulose has a reduced discharge capacity in a long-term durability test at a high temperature. There was a problem of causing deterioration accompanied by a decrease in film thickness.

  As a method for producing such a separator, there are a conventional card method using an olefin resin such as polyethylene or polypropylene, a spunbond method using a dry nonwoven fabric or a woven fabric, and a wet papermaking method using cellulose or the like as a material. For example, a wet manufacturing method has been proposed in which a fluid flow is applied to a fiber web formed of split composite fibers having a fiber length of 3 to 25 mm (see, for example, Patent Document 1). However, when a fluid flow is applied to a fiber web formed of split composite fibers, the action of jetting fluid at a high pressure to split the fibers creates through holes such as pinholes, causing internal short circuit between the electrodes. It was generated. In addition, a wet papermaking method in which fibrillated polymer and fibrillated natural fiber are mixed or laminated has been proposed (for example, see Patent Document 2). However, the fibrillated fiber is easy to embed air on the fiber surface, and pinholes caused by bubbles entrained in the nonwoven fabric layer cause defects such as internal short circuit between the electrodes.

JP-A-8-273654 JP 2003-168629 A

  The present invention provides a thinned separator for an electricity storage device having excellent heat resistance, mechanical strength, and dimensional stability, and a method for producing the same.

The separator of the present invention includes a thermoplastic synthetic fiber A (hereinafter referred to as “fiber A”), a heat-resistant synthetic fiber B (hereinafter referred to as “fiber B”), and a natural fiber C (hereinafter referred to as fiber “C”). And a synthetic resin-based 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 thermoplastic synthetic fiber A is preferably made of at least one selected from polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyarylate, polyethylene, and polypropylene.
The heat-resistant synthetic fiber B is preferably made of at least one selected from wholly aromatic polyamides, wholly aromatic polyesters, semi-aromatic polyamides, polyphenylene sulfide, and polyparaphenylene benzobisoxazole.
Moreover, it is preferable that the said thermoplastic synthetic fiber A consists of 25-50 mass%, the said heat resistant synthetic fiber B consists of 60-10 mass%, and the said natural fiber C consists of 15-40 mass%.

The fiber diameter of the thermoplastic synthetic fiber A is preferably 5 μm or less and the fiber length is 10 mm or less.
The heat-resistant synthetic fiber B is preferably fibrillated so that the fiber diameter is 1 μm or less and the fiber length is 10 mm or less.
The natural fiber C is preferably solvent-spun cellulose that is fibrillated with a fiber diameter of 1 μm or less and a fiber length of 3 mm or less.
Moreover, it is preferable that it is comprised by the entanglement of the said thermoplastic synthetic fiber A, the fiber of the fibrillated heat resistant synthetic fiber B, and / or the fibrillated natural fiber C. FIG.
Moreover, it is preferable that the film thickness of the electrical storage device separator is 60 μm or less.
The density of the electricity storage device separator is preferably 0.2 to 0.7 g / cm ³ .
The air permeability of the electricity storage device separator is preferably 100 seconds / 100 ml or less.
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.
The method for producing a separator for an electricity storage device of the present invention is characterized in that a synthetic resin binder is applied to a dry fiber layer or a wet fiber layer by spray coating to obtain an electricity storage device separator. To do.

  The separator for an electricity storage device of the present invention is a thin film and very excellent in durability in a high temperature environment in the presence of an organic solvent or an ionic liquid, and is suitably used for an electricity storage device such as an electric double layer capacitor. It is excellent in prevention of short circuit between electrodes and suppression of self-discharge.

  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. Since the bond between fibers is strengthened by this, the puncture strength is improved, and furthermore, the fibers are fixed to each other by the fused synthetic resin binder, so that the crushing strength in the film thickness direction (Z-axis direction) Thus, a separator having excellent short-circuit resistance can be provided.

  In addition, since the fibers are covered with a synthetic resin binder, the durability against organic solvents, ionic liquids, and even high-temperature conditions is high, and high-temperature and long-term resistance to deterioration even when used in a high-temperature atmosphere for a long period of time. A separator excellent in durability during use can be provided.

  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 contained in an amount of 5 parts by mass to 200 parts by mass, particularly preferably 10 parts by mass to 150 parts by mass with respect to 100 parts by mass of the total amount of fibers A, B, and C. If the amount 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 the solvent used when mixing or coating the synthetic resin 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.

The fiber A used in the present invention is preferably a fiber made of a resin selected from polyester fibers such as polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyarylate, polyethylene, and polypropylene.
The fiber B may be at least one selected from wholly aromatic polyamide, wholly aromatic polyester, semi-aromatic polyamide, polyphenylene sulfide, and polyparaphenylene benzobisoxazole, and may use two or more. The fiber B can be fibrillated into fine fibers without dissolving in the organic solvent or ionic liquid used in the driving electrolyte.

  By including the fiber B in the separator, durability against an organic solvent, an ionic liquid, and further a high temperature condition is increased, and it is difficult to deteriorate even if the separator is used for a long time in a high temperature atmosphere. Moreover, since it becomes difficult to generate | occur | produce a pinhole by using the fibrillated fiber B, it becomes a separator excellent in short circuit prevention.

  As the fiber C constituting the present invention, for example, cotton, hemp, kenaf, banana, pineapple, wool, silk, angora, cashmere, rayon, cupra, polynosic, solvent-spun cellulose and the like can be used. The material constituting the fiber C may be one type or two or more types. Separators using these materials have improved electrolyte impregnation properties. In the present invention, it is preferable to use fibrillated fibers as fiber C, and it is particularly preferable to use fibrillated solvent-spun cellulose. The fibrillated solvent-spun cellulose is excellent in electrolytic solution impregnation and has sufficient fiber entanglement, so that it becomes a separator excellent in mechanical strength.

  In the present invention, the fiber A 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 7 mm or less. When the fiber diameter is less than 5 μm and the fiber length is more than 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 fiber diameter of the fibrillated fiber B is 1 μm or less, the fiber length is preferably 10 mm or less, and particularly preferably the fiber length is 1 mm or less. When the fiber diameter exceeds 1 μm and the fiber length exceeds 10 mm, there is a high possibility that a through-hole will be formed when the film is thinned, which may cause an internal short circuit, and the entanglement between fibers becomes weak and the mechanical strength becomes weak. There is a tendency.
In the present invention, the fiber diameter of the fibrillated fiber C is preferably 1 μm or less, the fiber length is preferably 3 mm or less, and particularly preferably the fiber length is 1 mm or less. When the fiber diameter exceeds 1 μm and the fiber length exceeds 3 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, the entanglement between fibers becomes weak, and the mechanical strength becomes weak. There is a tendency, and the impregnation of the electrolytic solution is not sufficiently obtained.

In this invention, it is preferable that the fiber A, the fiber B, and the fiber C are the following compounding ratios in all the fibers.
That is, it is preferable that the fiber A is mixed in the range of 25 to 50% by mass of the total fibers constituting the separator. If it is less than 25% by mass, the effect of preventing the separator from being crushed in the Z-axis direction (spacer effect) cannot be sufficiently exhibited, and a short circuit is likely to occur due to compression. If it exceeds 50% by mass, the porosity is reduced and the pores are blocked, leading to an increase in internal resistance. In addition, because it is thermoplastic, it becomes unstable at high temperatures, leading to a decrease in durability. Further, the amount of fibrillated fine fibers in the separator becomes less than 50% by mass, and the pore diameter of the separator cannot be controlled, resulting in an internal short circuit.

  Moreover, it is preferable that the fiber B is mixed in the range of 60-10 mass% of all the fibers which comprise a separator. If it is less than 10% by mass, the amount of fine fibers fibrillated is insufficient, and the pore diameter of the separator cannot be controlled, resulting in an internal short circuit. If it exceeds 60% by mass, the amount of fibrillated fine fibers is too large and the separator becomes too dense, resulting in an increase in internal resistance.

  Furthermore, it is preferable that the fiber C is mixed in the range of 15 to 40% by mass constituting the separator. If it is less than 15% by mass, the entanglement between the fibers tends to be weak, the mechanical strength tends to be weak, and the impregnation property of the electrolytic solution cannot be sufficiently obtained. When it exceeds 40 mass%, durability will be reduced by the organic solvent and ionic liquid under high temperature atmosphere conditions.

In the present invention, the pore diameter of the fiber layer after the synthetic resin binder is preferably 0.1 μm to 15 μm, more preferably 0.1 μm to 5.0 μm in average pore diameter by the bubble point method. is there. 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 60 μm or less. When the thickness of the separator exceeds 60 μm, it is disadvantageous for thinning of the electricity storage device, and at the same time, the amount of the 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 ^{0.2g / cm 3 ~0.7g / cm 3} . More preferably from ^{0.25g / cm 3 ~0.65g / cm 3} , particularly preferably ^{0.3g / cm 3 ~0.6g / cm 3} . If it is less than 0.2 g / cm ³ , the void portion of the separator becomes excessive, and problems such as occurrence of short circuit and deterioration of self-discharge resistance are likely to occur. On the other hand, if the density is larger than 0.7 g / cm ³ , the material constituting the separator becomes excessively clogged, so that ion migration is hindered and resistance is likely to increase.

  The air permeability of the separator of the present invention is preferably 100 seconds / 100 ml or less. Ionic conductivity can be suitably maintained. In addition, the air permeability in the separator of this invention says the value measured using the Gurley air permeability measuring device.

  As described above, the separator of the present invention is composed of fiber A, fiber B, and fiber C and contains a synthetic resin-based binder, and the binder is fused by heat treatment. Lithium ion secondary battery, lithium ion capacitor, polymer battery, and electric double layer are resistant to crushing strength in the film thickness direction (Z-axis direction) and short circuit resistance, and are not easily degraded to organic solvents or ionic liquids even in high-temperature atmospheres. It can be suitably used for an electricity storage device such as a capacitor. 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 fibers A cut or beaten to a fiber diameter of 5 μm or less and a fiber length of 10 mm or less, a fiber B fibrillated to a fiber diameter of 1 μm or less and a fiber length of 3 mm or less, a fiber diameter of 1 μm or less, a fiber length Fiber C fibrillated to 3 mm or less is dispersed in water. The order in which it is put into the water is not fixed. Since the fibers used in the present invention are very fine and difficult to disperse uniformly in the disaggregation step, 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 or pure water in order to reduce ionic impurities as much as possible. 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, the impregnation application of the synthetic resin binder solution is performed by spraying the fiber layer on which the fiber dispersion is made on a wet paper wire part, a felt or a canvas, or a filtered water or a carrier having good air permeability. It is more preferable to apply. 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.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm, a fiber B 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 diameter of 0.5 μm The fibers C made of solvent-spun cellulose fibrillated to a fiber length of 1 mm are charged in ion exchange water at a concentration of 0.05% by mass in a mass ratio of 25:60:15, and dispersed for 30 minutes. A papermaking material consisting of a dispersion of fibers was prepared.
A wet sheet (fiber layer) was made from the above paper making material using a standard hand-making device specified in JIS P8222. 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 thickness of the separator was 31 μm, the density was 0.41 g / cm ³ , and the air permeability was 8 seconds / 100 ml.

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 thickness of the separator was 31 μm, the density was 0.45 g / cm ³ , and the air permeability was 8 seconds / 100 ml.

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.
As for the properties of the obtained separator, the thickness of the separator was 30 μm, the density was 0.40 g / cm ³ , and the air permeability was 12 seconds / 100 ml.

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 thickness of the separator was 33 μm, the density was 0.55 g / cm ³ , and the air permeability was 74 seconds / 100 ml.

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 thickness of the separator was 32 μm, the density was 0.63 g / cm ³ , and the air permeability was 82 seconds / 100 ml.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm, a fiber B 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 diameter of 0.5 μm The fibers C made of solvent-spun cellulose fibrillated to a fiber length of 1 mm are charged in ion exchange water at a concentration of 0.05% by mass in a mass ratio of 25:60:15, and dispersed for 30 minutes. A papermaking material consisting of a dispersion of fibers was prepared.
A wet sheet was made from the above papermaking material using a standard type handmaking apparatus defined in JIS P8222. 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 thickness of the separator was 31 μm, the density was 0.41 g / cm ³ , and the air permeability was 8 seconds / 100 ml.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 3.2 μm and a fiber length of 6 mm, a fiber B 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 diameter of 0.5 μm The fibers C made of solvent-spun cellulose fibrillated to a fiber length of 1 mm were charged into the pulper at a concentration of 0.05% by mass in ion-exchanged water at a mass ratio of 40:40:20, and dispersed for 30 minutes. A papermaking material consisting of a dispersion of fibers was prepared. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1 by papermaking, spray application of a synthetic resin-based binder, and drying treatment.
Regarding the physical properties of the obtained separator, the thickness of the separator was 49 μm, the density was 0.32 g / cm ³ , and the air permeability was 15 seconds / 100 ml.

Fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and fiber length of 6 mm, Fiber B made of polyphenylene sulfide fibrillated to a fiber diameter of 0.8 μm and fiber length of 1.5 mm, Fiber diameter of 0.5 μm, Fiber Fiber C made of solvent-spun cellulose fibrillated to a length of 1 mm was introduced into the pulper at a concentration of 0.05% by mass in ion exchange water at a mass ratio of 30:30:40, and dispersed for 30 minutes. A papermaking material consisting of a dispersion was prepared. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1 by papermaking, spray application of a synthetic resin-based binder, and drying treatment.
Regarding the physical properties of the obtained separator, the thickness of the separator was 22 μm, the density was 0.45 g / cm ³ , and the air permeability was 5 seconds / 100 ml.

A fiber A made of polyethylene fiber having a fiber diameter of 3 μm and a fiber length of 6 mm, a fiber B 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 length Fiber C made of solvent-spun cellulose fibrillated to 1 mm was introduced into a pulper at a concentration of 0.05% by mass in ion exchange water at a mass ratio of 50:30:20, and dispersed for 30 minutes. A papermaking material consisting of body was prepared. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1 by papermaking, spray application of a synthetic resin-based binder, and drying treatment.
Regarding the physical properties of the obtained separator, the thickness of the separator was 57 μm, the density was 0.36 g / cm ³ , and the air permeability was 19 seconds / 100 ml.

A fiber A made of polyethylene fiber having a fiber diameter of 3 μm and a fiber length of 6 mm, a fiber B made of wholly aromatic polyester fibrillated to a fiber diameter of 0.4 μm and a fiber length of 1 mm, a fiber diameter of 0.5 μm and a fiber length of 1 mm Fiber C composed of fibrillated solvent-spun cellulose is introduced into a pulper at a concentration of 0.05% by mass in ion exchange water at a mass ratio of 25:60:15, and dispersed for 30 minutes. A papermaking material was produced. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1 by papermaking, spray application of a synthetic resin-based binder, and drying treatment.
Regarding the physical properties of the obtained separator, the thickness of the separator was 32 μm, the density was 0.45 g / cm ³ , and the air permeability was 11 seconds / 100 ml.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm, a fiber B made of polyparaphenylenebenzobisoxazole fibrillated to a fiber diameter of 0.3 μm and a fiber length of 1 mm, and a fiber diameter of 0.5 μm The fibers C composed of solvent-spun cellulose fibrillated to a fiber length of 1 mm were charged in ion exchange water at a concentration of 0.05% by mass in a mass ratio of 25:50:25, and dispersed for 30 minutes. A papermaking material consisting of a dispersion of fibers was prepared. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1 by papermaking, spray application of a synthetic resin-based binder, and drying treatment.
Regarding the physical properties of the obtained separator, the thickness of the separator was 38 μm, the density was 0.62 g / cm ³ , and the air permeability was 42 seconds / 100 ml.

(Comparative Example 1)
A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm, a fiber B 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 diameter of 0.5 μm The fibers C made of solvent-spun cellulose fibrillated to a fiber length of 1 mm are charged in ion exchange water at a concentration of 0.05% by mass in a mass ratio of 25:60:15, and dispersed for 30 minutes. A papermaking material consisting of a dispersion of fibers was prepared.
A wet sheet was made from the above papermaking material using a standard type handmaking apparatus defined in JIS P8222. Thereafter, the obtained wet sheet was taken out from the hand-making apparatus and then dried at 130 ° C. with a Yankee dryer without any treatment to obtain a comparative separator.
Regarding the physical properties of the obtained separator, the thickness of the separator was 30 μm, the density was 0.41 g / cm ³ , and the air permeability was 8 seconds / 100 ml.
The data was filmed.

(Comparative Example 2)
A fiber C composed of 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 and dispersed for 30 minutes to form a fiber dispersion. Papermaking materials were prepared. Thereafter, papermaking, spray application of a synthetic resin binder and drying treatment were performed in the same manner as in Example 1 to obtain a comparative separator.
As for the properties of the obtained separator, the thickness of the separator was 35 μm, the density was 0.41 g / cm ³ , and the air permeability was 5 seconds / 100 ml.

(Comparative Example 3)
A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm and a fiber length of 6 mm and a fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm are each in a mass ratio of 80:20. Into the ion exchange water at a concentration of 0.05% by mass, it was put into a pulper and dispersed for 30 minutes to prepare a papermaking material comprising a fiber dispersion. Thereafter, papermaking, spray application of a synthetic resin binder and drying treatment were performed in the same manner as in Example 1 to obtain a comparative separator.
Regarding the physical properties of the obtained separator, the thickness of the separator was 70 μm, the density was 0.32 g / cm ³ , and the air permeability was 39 seconds / 100 ml.

  The following evaluation was performed in the separators obtained in Examples 1 to 11 and Comparative Examples 1 to 3, and the characteristics as a separator for an electricity storage device were evaluated. In addition, about each separator, the physical-property value of the mixture ratio of fiber, thickness, density, and air permeability is shown in Table 1.

<Assembly of electric double layer capacitor and evaluation of change in discharge capacity during long-term high temperature test>
About the separator of Examples 1-11 and Comparative Examples 1-3, the electric double layer capacitor was assembled using the electrode of a positive electrode and a negative electrode, and each 100 pieces each wound type cell was 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 discharge capacity of the produced wound type cell, it measured with the LCR meter after the initial stage, 2000 hours test, and 4000 hours test, respectively, and the change (decrease) of the discharge capacity after a high temperature long-term test was evaluated. The test conditions were 80 ° C. and 2.5 V applied.
The obtained results are shown in Table 2.

  As is apparent from the results in Table 2, the electric double layer capacitor using the separator of the present invention maintains a sufficient discharge capacity of 9.8 F or more even after 4000 hours of a 2.5 V voltage application test at 80 ° C. It was confirmed that On the other hand, the electric double layer capacitor using the separators of Comparative Examples 1 to 3 had a large decrease in discharge capacity and extremely poor characteristics.

<Comparison of crushing strength of separator>
The thicknesses after the separators of Examples 1 to 11 and Comparative Examples 1 to 3 were crushed at 170 ° C. with a pressure of 1 N / cm ² were measured.
The obtained results are shown in Table 3.

As is clear from the results in Table 3, it was confirmed that the electric double layer capacitor using the separator of the present invention has excellent crushing strength and an excellent performance. On the other hand, the electric double layer capacitor using the separators of Comparative Examples 1 to 3 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.

Claims (15)

  A separator for an electricity storage device, comprising thermoplastic synthetic fiber A, heat-resistant synthetic fiber B, natural fiber C, and a synthetic resin-based 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 electricity storage according to any one of claims 1 to 3, wherein the thermoplastic synthetic fiber A is composed of at least one selected from polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyarylate, polyethylene, and polypropylene. Device separator.   The heat-resistant synthetic fiber B comprises at least one selected from wholly aromatic polyamides, wholly aromatic polyesters, semi-aromatic polyamides, polyphenylene sulfide, and polyparaphenylene benzobisoxazole. 4. The electrical storage device separator according to any one of 3 above.   The thermoplastic synthetic fiber A comprises 25 to 50% by mass, the heat resistant synthetic fiber B comprises 60 to 10% by mass, and the natural fiber C comprises 15 to 40% by mass. 4. The electrical storage device separator according to any one of 3 above.   4. The electricity storage device separator according to claim 1, wherein the thermoplastic synthetic fiber A has a fiber diameter of 5 μm or less and a fiber length of 10 mm or less. 5.   The electrical storage device separator according to any one of claims 1 to 3, wherein the heat-resistant synthetic fiber B has a fiber diameter of 1 µm or less and a fiber length of 10 mm or less. .   The electricity storage device separator according to any one of claims 1 to 3, wherein the natural fiber C is solvent-spun cellulose fibrillated with a fiber diameter of 1 µm or less and a fiber length of 3 mm or less.   10. The fiber according to claim 1, wherein the thermoplastic synthetic fiber A is entangled with fibers of a fibrillated heat-resistant synthetic fiber B and / or a fibrillated natural fiber C. The separator for electrical storage devices as described.   The separator for an electricity storage device according to any one of claims 1 to 10, wherein the film thickness of the separator for an electricity storage device is 60 µm or less. The density of the separator for electrical storage devices is 0.2-0.7 g / cm < ³ >, The separator for electrical storage devices in any one of Claims 1 thru | or 11 characterized by the above-mentioned.   13. The electricity storage device separator according to claim 1, wherein the air permeability of the electricity storage device separator is 100 seconds / 100 ml or less.   The power storage device separator according to any one of claims 1 to 13, 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. .   15. The electricity storage device according to claim 1, wherein the synthetic resin binder is applied to a dry fiber layer or a wet paper fiber layer by spray application to obtain the electricity storage device separator according to claim 1. Manufacturing method for the separator.