JP2010098074A - Separator for electric storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for an electric storage device which has thermal resistance, solvent resistance, and a dimensionally stable thin film form. <P>SOLUTION: The separator for electric storage device contains thermoplastic synthetic fiber A, heat-resistant synthetic fiber B, and a natural fiber C, and the thermoplastic synthetic fiber A is made of polyester fiber with 50% crystallinity or more. Preferably, the thermoplastic synthetic fiber A is made of at least one selected from polyethylene terephthalate, polybutylene terephthalate, and wholly aromatic polyarylate with 50% crystallinity or more, and the heat-resistant synthetic fiber B is made of at least one selected from wholly aromatic polyamide, wholly aromatic polyester, semiaromatic polyamide, polyphenylene sulfide, and polyparaphenylene benzobisoxazole. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separator for an electricity storage device 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 in a separator such as cellulose, the discharge capacity is reduced or the film is subjected to a long-term durability test at a high temperature. There was a problem that caused deterioration with a decrease in thickness.

  As a method for manufacturing such a separator, there are a spunbond method using a dry nonwoven fabric or a woven fabric using an olefin resin such as polyethylene or polypropylene as a material, and a wet papermaking method using cellulose or the like as a material. Specifically, there has been proposed a wet manufacturing method in which a fluid flow is applied to a fiber web formed of split type 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, there has been proposed a wet papermaking method in which fibrillated polymer and fibrillated natural fiber are mixed or laminated (see, for example, 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 an internal short circuit between the electrodes.

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

  The present invention provides a thin film separator for an electricity storage device having heat resistance, solvent resistance, and dimensional stability.

  The separator for an electricity storage device of the present invention (hereinafter referred to as “separator”) includes at least a thermoplastic synthetic fiber A (hereinafter referred to as “fiber A”) and a heat-resistant synthetic fiber B (hereinafter referred to as “fiber B”). And natural fiber C (hereinafter referred to as fiber “C”), wherein fiber A is made of a polyester fiber having a crystallinity of 50% or more.

  The separator for an electricity storage device of the present invention is a thin film, and is excellent in durability during long-term use in a high temperature environment in the presence of an organic solvent or an ionic liquid, and an electricity storage device such as an electric double layer capacitor And is excellent in prevention of short circuit between electrodes and suppression of self-discharge. In addition, it has good heat resistance and solvent resistance and is stable for long-term use at high temperatures.

  The fiber A used in the present invention is preferably made of a resin selected from polyester fibers such as polyethylene terephthalate, polybutylene terephthalate, wholly aromatic polyarylate having a crystallinity of 50% or more. When the fiber A has a crystallinity of 50% or more, it is highly resistant to organic solvents, ionic liquids, and high-temperature conditions, and provides a separator that does not deteriorate even if it is used in a high-temperature atmosphere for a long period of time. can do.

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. These materials can be fibrillated into fine fibers without dissolving in the organic solvent or ionic liquid used for 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. Further, the crystallinity of the fiber A is 50% or more, and particularly preferably 70% or more. When the degree of crystallinity is less than 50%, it becomes easy to dissolve in an organic solvent or an ionic liquid, and when used in a high temperature atmosphere for a long time, it causes deterioration.

The crystallinity of the polyester fiber can be measured by quantifying the endothermic peak derived from crystallization using a DSC (differential scanning calorimeter). Moreover, it can measure by obtaining the correlation of the peak band and the density which show the difference in crystallinity using FT-Raman spectroscopy.
In the present invention, the fiber diameter of the fibrillated fiber B is 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.

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. In addition, it is difficult to obtain sufficient electrolyte impregnation.
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. Furthermore, the amount of fibrillated fine fibers in the separator is less than 50% by mass, the pore diameter of the separator cannot be controlled, and an internal short circuit is likely to occur.
Moreover, it is preferable that the fiber B is mixed in the range of 60 to 10% by mass of the total fibers constituting the separator. If the amount is less than 10% by mass, the amount of fine fibers fibrillated is insufficient, the pore diameter of the separator cannot be controlled, and an internal short circuit tends to occur. 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 of the total fibers 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 is hardly obtained. When it exceeds 40% by mass, durability tends to be lowered due to an organic solvent or an ionic liquid under a high-temperature atmosphere condition.

  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 separator of the present invention has sufficient tensile strength and compressive strength, but it is also possible to mix a binder resin or binder fiber in order to obtain higher strength. The binder resin or binder fiber includes various materials such as polyvinyl alcohol, polyacrylonitrile, polyethylene, and derivatives thereof, but is not limited thereto.

The film thickness of the separator of the present invention is preferably 60 μm or less. If the thickness of the separator exceeds 60 μm, it will be disadvantageous for thinning of the electricity storage device, and at the same time, the amount of electrode material that can be put in a certain cell volume will be reduced, the capacity will be reduced, and the resistance will be increased. It is not preferable.
The density of the separator of the present invention ^is preferably ^{0.20g / cm 3 ~0.70g / cm 3} . More preferably from ^{0.25g / cm 3 ~0.65g / cm 3} , particularly preferably ^{0.30g / cm 3 ~0.60g / 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 0.70 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 contains fibers A, fibers B and fibers C, and the fibers A are made of polyester fibers having a crystallinity of 50% or more. It is difficult to deteriorate into an ionic liquid, and can be suitably used for power storage devices such as lithium ion secondary batteries, lithium ion capacitors, polymer batteries, and electric double layer capacitors. 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 water is not fixed. 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, the separator of the present invention can be obtained by passing through a drying part such as a multi-cylinder type or Yankee type dryer.

  By passing the drying part, heat fusion of the fiber A occurs, and the fiber A is entangled with the fibrillated fiber B and / or the fibrillated fiber C. Thereby, a separator excellent in mechanical strength can be provided.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 2.5 μm, a fiber length of 6 mm, and a crystallinity of 55%; and 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; Fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into the pulper at a mass ratio of 25:60:15 in ion-exchanged water at a concentration of 0.05% by mass. Then, a paper-making material comprising a fiber dispersion was produced by dispersing for 30 minutes.
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 to obtain the separator of the present invention. As for 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 2.5 μm, a fiber length of 6 mm, and a crystallinity of 73%; and 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; Fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into the pulper at a mass ratio of 25:60:15 in ion-exchanged water at a concentration of 0.05% by mass. Then, a paper-making material comprising a fiber dispersion was produced by dispersing for 30 minutes.
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 to obtain the separator of the present invention. As for 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.

A fiber A made of polyethylene terephthalate fiber having a fiber diameter of 3.2 μm, a fiber length of 6 mm, and a crystallinity of 55%; and 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; Fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm is charged into the pulper at a concentration of 0.05% by mass in ion-exchanged water at a mass ratio of 40:40:20, respectively. Then, a paper-making material comprising a fiber dispersion was produced by dispersing for 30 minutes. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1. 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, fiber length of 6 mm, and crystallinity of 55%, Fiber B made of polyphenylene sulfide fibrillated to a fiber diameter of 0.8 μm and fiber length of 1.5 mm, and fiber Fibers C made of solvent-spun cellulose fibrillated to a diameter of 0.5 μm and a fiber length of 1 mm were charged in ion exchange water at a mass ratio of 30:30:40, respectively, into a pulper at a concentration of 0.05% by mass. A papermaking material made of a fiber dispersion was prepared by dispersing for a minute. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1. 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 polybutylene terephthalate fiber having a fiber diameter of 3 μm, a fiber length of 6 mm, and a crystallinity of 55%; and 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; Fibers C made of solvent-spun cellulose fibrillated with a fiber diameter of 0.5 μm and a fiber length of 1 mm were introduced into the pulper at a mass ratio of 50:30:20 in ion exchange water at a concentration of 0.05% by mass. A papermaking material made of a fiber dispersion was prepared by dispersing for 30 minutes. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1. 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 composed of wholly aromatic polyarylate fibers having a fiber diameter of 3 μm, a fiber length of 6 mm, and a crystallinity of 55%; and a fiber B composed of wholly aromatic polyester fibrillated to a fiber diameter of 0.4 μm and a fiber length of 1 mm; Fibers C made of solvent-spun cellulose fibrillated with a fiber diameter of 0.5 μm and a fiber length of 1 mm were introduced into the pulper at a mass ratio of 25:60:15 in ion exchange water at a concentration of 0.05% by mass. A papermaking material made of a fiber dispersion was prepared by dispersing for 30 minutes. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1. Regarding the physical properties of the obtained separator, the film 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, a fiber length of 6 mm, and a crystallinity of 55%; and a fiber B made of polyparaphenylenebenzobisoxazole fibrillated to a fiber diameter of 0.3 μm and a fiber length of 1 mm; The fibers C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm were charged into the pulper at a mass ratio of 25:50:25 in ion exchange water at a concentration of 0.05% by mass. Then, a paper-making material comprising a fiber dispersion was produced by dispersing for 30 minutes. Thereafter, the separator of the present invention was obtained in the same manner as in Example 1. 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, a fiber length of 6 mm, and a crystallinity of 20%; and 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; Fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm was charged into the pulper at a mass ratio of 25:60:15 in ion-exchanged water at a concentration of 0.05% by mass. Then, a paper-making material comprising a fiber dispersion was produced by dispersing for 30 minutes.
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 to obtain the separator of the present invention. As for 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.

(Comparative Example 2)
A fiber C made of solvent-spun cellulose fibrillated to a fiber diameter of 0.5 μm and a fiber length of 1 mm is charged into ion exchange water at a concentration of 0.05% by mass in a pulper and dispersed for 30 minutes. A papermaking material consisting of a dispersion of only fibers C not containing was prepared. Thereafter, a comparative separator was obtained in the same manner as in Example 1. Regarding the physical 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, a fiber length of 6 mm, and a crystallinity of 55%, 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 were each 80 : A papermaking material composed of a dispersion of fibers A and C not containing fiber B was prepared by adding it into a pulper at a mass ratio of 20 in ion exchange water at a concentration of 0.05% by mass and dispersing for 30 minutes. Thereafter, a comparative separator was obtained in the same manner as in Example 1. Regarding the physical properties of the obtained separator, the film thickness of the separator was 70 μm, the density was 0.32 g / cm ³ , and the air permeability was 39 seconds / 100 ml.

(Comparative Example 4)
Fiber C made of polyethylene fiber having a fiber diameter of 3 μm, a fiber length of 6 mm, and a crystallinity of 55% and solvent-spun cellulose fibrillated to a fiber diameter of 0.4 μm and a fiber length of 1 mm is ionized at a mass ratio of 30:70, respectively. A papermaking material composed of a dispersion of polyethylene fibers not containing fiber B and fibers C was prepared by adding the dispersion water to the pulper at a concentration of 0.05 mass% and dispersing for 30 minutes. Thereafter, a comparative separator was obtained in the same manner as in Example 1. Regarding the physical properties of the obtained separator, the film thickness of the separator was 51 μm, the density was 0.72 g / cm ³ , and the air permeability was 104 seconds / 100 ml.

  The following evaluation was performed on the separators obtained in Examples 1 to 7 and Comparative Examples 1 to 4, and the characteristics as the separator for an electricity storage device were evaluated. In addition, about each separator, the physical-property value of the mixture ratio of a fiber, a film thickness, a 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 1-7 and Comparative Examples 1-4, 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 8.9 F or more even after 40000 hours of application of a voltage of 2.5 V at 80 ° C. and durability. It was confirmed that it was excellent. On the other hand, the electric double layer capacitors using the separators of Comparative Examples 1 to 4 have a very large decrease in discharge capacity, and some of them cause an internal short circuit, and the characteristics are extremely inferior.

<Comparison of separator film thickness after 4000 hours of high-temperature long-term test>
The electric double layer capacitor after the high temperature long-term test of 4000 hours was disassembled, the separator was taken out from the device, washed with methanol and dried, and then the thickness of the separator was measured. The obtained results are shown in Table 3.

  As is clear from the results in Table 3, the separator of the present invention maintains a difference from the initial film thickness within 3 μm even after application of a voltage of 80 ° C., 2.5 V, and 4000 hours. It was confirmed that the property was good and stable in the high-temperature long-term test. On the other hand, the separators of Comparative Examples 1 to 4 have a difference between the film thickness after application of a voltage for 4000 hours and the initial film thickness of 6 μm or more and are significantly thin, and are inferior in stability to a high-temperature long-term test.

Claims (12)

  A separator for an electricity storage device, comprising a thermoplastic synthetic fiber A, a heat resistant synthetic fiber B, and a natural fiber C, wherein the thermoplastic synthetic fiber A is made of a polyester fiber having a crystallinity of 50% or more.   2. The electricity storage device according to claim 1, wherein the thermoplastic synthetic fiber A is composed of at least one selected from polyethylene terephthalate, polybutylene terephthalate, and wholly aromatic polyarylate having a crystallinity of 50% or more. Separator for use.   The heat-resistant synthetic fiber B is made of at least one selected from wholly aromatic polyamide, wholly aromatic polyester, semi-aromatic polyamide, polyphenylene sulfide, and polyparaphenylene benzobisoxazole. The separator for electrical storage devices as described.   The thermoplastic synthetic fiber A is composed of 25 to 50% by mass, the heat resistant synthetic fiber B is composed of 60 to 10% by mass, and the natural fiber C is composed of 15 to 40% by mass. The separator for electrical storage devices as described.   2. 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.   2. The electricity storage device separator according to claim 1, wherein the heat resistant synthetic fiber B has a fiber diameter of 1 μm or less and a fiber length of 3 mm or less.   2. The electricity storage device separator according to claim 1, wherein the natural fiber C is a solvent-spun cellulose having a fiber diameter of 1 μm or less and a fiber length of 3 mm or less.   The said separator is comprised by the thermal entanglement of the thermoplastic synthetic fiber A, and the entanglement of the fiber of the fibrillated heat resistant synthetic fiber B and / or the fibrillated natural fiber C, It is characterized by the above-mentioned. The separator for electrical storage devices in any one of 1 thru | or 7.   The power storage device separator according to claim 1, wherein the separator has a thickness of 60 μm or less. The density | concentration of the said separator is 0.2-0.7 g / cm < ³ >, The separator for electrical storage devices in any one of the Claims 1 thru | or 9 characterized by the above-mentioned.   The separator for an electricity storage device according to any one of claims 1 to 10, wherein the separator has an air permeability of 100 seconds / 100 ml or less.   12. The separator for an electricity storage device according to claim 1, wherein the electricity storage device is a lithium ion secondary battery, a lithium ion capacitor, a polymer battery, or an electric double layer capacitor.