JP2011060424A - Separator for power storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator used for an alkaline battery such as a nickel cadmium battery and a nickel hydrogen battery, which is a thin film, has alkali resistance, mechanical strength, and dimensional stability. <P>SOLUTION: The separator does not deteriorate in an electrolyte using a concentrated alkaline aqueous solution such as 30 mass% by containing polyphenylene-sulfide fiber and sheath core yarn conjugated fibers, and has excellent mechanical strength, dimensional stability, and ionic conductivity. Preferably, polyphenylene-sulfide fibers heat-treated at a temperature of glass transition point or higher is used. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a separator (hereinafter referred to as “separator”) used in alkaline batteries such as nickel cadmium batteries and nickel metal hydride batteries.

  Conventionally, the functions required of a separator are to separate a positive electrode and a negative electrode to prevent a short circuit and to hold an electrolyte so that an electromotive reaction can be smoothly performed. Since a concentrated alkaline aqueous solution of about 30% by mass is used as the electrolytic solution, a separator material having excellent alkali resistance is required. In recent years, demands for higher capacity and longer life are increasing with increasing needs, and improvements in separators are required.

  As the separator, a nonwoven fabric made of polyamide fiber or a nonwoven fabric made of polypropylene fiber is generally used. However, the nonwoven fabric made of polyamide fiber is oxidized by oxygen gas generated from the positive electrode during charging, and the product of decomposition repeatedly undergoes redox between the positive and negative electrodes of the battery, increasing the self-discharge of the battery. In addition, a separator made of a nonwoven fabric made of polypropylene fiber with excellent alkali resistance is subjected to sulfonation treatment to impart hydrophilicity. After immersing the separator in concentrated sulfuric acid, neutralize, wash with a large amount of water and dry. Therefore, the treatment is complicated, takes time, and increases the cost. Further, the carbon-carbon bond of the polyolefin is broken by the sulfonation treatment, so that the strength of the separator is lowered.

  For the purpose of solving these problems, for example, Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4 propose alkaline battery separators using polyphenylene sulfide fibers. However, the proposed separator is made of 100% polyphenylene sulfide fiber, and is, for example, a nonwoven fabric in which stretched polyphenylene sulfide fiber is fixed by thermocompression bonding of unstretched polyphenylene sulfide fiber. Since it cannot adhere to an electrode, it is difficult to produce a smooth electromotive reaction.

  Patent Document 5 proposes an alkaline battery separator using polyphenylene sulfide fiber and fibrillated aramid fiber. Since it contains an aramid fiber, it is more elastic than that made of 100% polyphenylene sulfide fiber, so that it can be in close contact with the electrode. However, since an aramid fiber is used, it is oxidized by oxygen gas generated from the positive electrode during charging, and the products resulting from the decomposition are repeatedly oxidized and reduced between the positive and negative electrodes of the battery, increasing the self-discharge of the battery.

Patent Document 6 proposes a battery separator using polyphenylene sulfide fibers that are not fibrillated, a Young's modulus of 6000 kg / mm ^2, and fused fibers. By combining polyphenylene sulfide fiber and rigid high Young's modulus fiber, it can be an elastic separator and can be in close contact with the electrode. However, since fibers that are not fibrillated are used, the hole diameter tends to be large, and a through hole such as a pinhole is generated, causing an internal short circuit between the electrodes.

  On the other hand, Patent Document 7 proposes an alkaline battery separator in which a plurality of hydroentangled nonwoven fabrics made of card webs of polyolefin diameter fibers and core-sheath composite fibers are laminated and integrated by thermocompression bonding. However, since the core-sheath type composite fiber is the main fiber, the piercing strength is weak, so that the electrode burr easily penetrates and an internal short circuit is likely to occur. In addition, the hole diameter tends to be large, and a through hole such as a pinhole is generated, causing an internal short circuit between the electrodes.

JP-A-7-262980 JP-A-9-67786 JP-A-10-64502 JP 2004-285536 A Japanese Patent Laid-Open No. 2001-40597 JP 2002-279958 A JP-A-2005-116514

  The present invention provides a separator used for an alkaline battery such as a nickel cadmium battery or a nickel metal hydride battery, which is a thin film and has alkali resistance, mechanical strength, and dimensional stability.

The separator of the present invention includes polyphenylene sulfide fibers and core-sheath type composite fibers.
The polyphenylene sulfide fiber is preferably heat-treated at a temperature not lower than the glass transition temperature.
The polyphenylene sulfide fiber preferably has a fiber diameter of 10 μm or less and a fiber length of 10 mm or less.
In the core-sheath type composite fiber, the sheath component is preferably polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the core component is preferably polypropylene or polyethylene.
Further, the core-sheath type composite fiber is preferably fibrillated to have a fiber diameter of 2.5 μm or less and a fiber length of 15 mm or less.

Moreover, it is preferable that melting | fusing point of the sheath component of the said core-sheath-type composite fiber is 80-130 degreeC.
Moreover, it is preferable that the said polyphenylene sulfide fiber is 65-20 mass%, and the said core-sheath-type composite fiber is 35-80 mass%.
Moreover, it is preferable that the said separator is comprised by the heat sealing | fusion or thermocompression bonding of the core-sheath-type composite fiber.
Moreover, it is preferable that the film thickness of the said separator is 100 micrometers or less.
Moreover, it is preferable that the density of the said separator is 0.2-0.9 g / cm < ³ >.
Moreover, it is preferable that the air permeability of the separator is 100 seconds / 100 ml or less.

  In addition to being a thin film, the separator of the present invention is extremely excellent in alkali resistance, mechanical strength, dimensional stability, and ion conductivity, and is suitably used for alkaline batteries such as nickel cadmium batteries and nickel hydrogen batteries.

  The present invention includes a polyphenylene sulfide fiber and a core-sheath type composite fiber, so that mechanical strength, dimensional stability and ionic conduction are not deteriorated in an electrolytic solution in which a concentrated alkaline aqueous solution of about 30% by mass is used. It is possible to provide a separator that is extremely excellent in performance.

  In the present invention, it is preferable to use polyphenylene sulfide fiber that has been heat-treated at a temperature equal to or higher than the glass transition temperature. Polyphenylene sulfide fibers that have been heat-treated at a temperature equal to or higher than the glass transition temperature have a small dimensional change rate, so there is no wrinkling or breakage due to shrinkage in the reliability test temperature range of 80 to 100 ° C. Excellent separator.

  The core-sheath type composite fiber is a fiber comprising a “core” having a cross section in the center and a “sheath” in the outer layer portion. In the present invention, the sheath component is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the core The component is preferably polypropylene or polyethylene. This is because the core component can maintain the fiber shape, and when thermally bonded, the tensile strength and piercing strength of the separator can be maintained high, and the gap between fibers can be maintained and cheap, so the hole diameter can be easily controlled. become. The cross-sectional shape of the core-sheath type composite fiber may be, for example, a circular shape or an irregular shape.

  In the present invention, the core-sheath type composite fiber has a fiber diameter of 2.5 μm or less and a fiber length of preferably 15 mm or less, particularly preferably a fiber length of 10 mm or less. When the fiber diameter is more than 2.5 μm and the fiber length is more than 15 mm, twisting occurs in the fiber, and uneven formation tends to occur.

  In the present invention, the polyphenylene sulfide fiber has a fiber diameter of 10 μm or less and a fiber length of preferably 10 mm or less, particularly preferably a fiber diameter of 5 μm or less and a fiber length of 7 mm or less. When the fiber diameter is more than 10 μm and the fiber length is more than 10 mm, the fiber is distorted and uneven formation tends to occur.

  In this invention, it is preferable that the polyphenylene sulfide fiber is mixed in the range of 20 to 65% by mass of the total fibers constituting the separator. If it is less than 20% by mass, the tensile strength and piercing strength of the separator cannot be maintained high, and if it exceeds 65%, the pore diameter of the separator cannot be controlled, resulting in an internal short circuit.

  In this invention, it is preferable that the core-sheath-type composite fiber is mixed in the range of 35-80 mass% of all the fibers which comprise a separator. If it is less than 35% by mass, the entanglement between the fibers tends to be weak and the mechanical strength tends to be weak. If it exceeds 80% by mass, the tensile strength and piercing strength of the separator cannot be maintained high.

  In order to obtain sufficient tensile strength and piercing strength, the separator of the present invention preferably uses a core-sheath type composite fiber having a sheath component having a melting point of 80 to 130 ° C. and is heat-sealed or thermocompression bonded. When the melting point is lower than 80 ° C., the core-sheath type composite fiber is dissolved in the reliability test temperature range, and the reliability is lowered. If the temperature exceeds 130 ° C., the temperature to be fused becomes high, so that the fiber is deformed and it becomes difficult to control the pore diameter.

  The thickness of the separator of the present invention is preferably 100 μm or less. When the thickness of the separator exceeds 100 μm, it is 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 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 ~0.90g / cm 3} . More preferably from ^{0.25g / cm 3 ~0.85g / cm 3} , particularly preferably ^{0.30g / cm 3 ~0.80g / cm 3} . If it is less than 0.20 g / cm ³ , the void portion of the separator becomes excessive, the amount of impregnation of the electrolyte for driving the electricity storage device increases, and the cost of the electricity storage device is increased. On the other hand, if the density is larger than 0.90 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.

  In the present invention, the pore diameter of the separator is preferably 3 μm to 40 μm, more preferably 5 μm to 30 μm, as the average pore diameter determined by the bubble point method. When the average pore diameter is smaller than 3 μm, the ion conductivity is lowered, the internal resistance is likely to be increased, the gas permeability is deteriorated, and the durability is lowered. If it exceeds 40 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.

  As described above, the separator of the present invention includes a polyphenylene sulfide fiber and a core-sheath type composite fiber, so that it does not deteriorate in an electrolytic solution in which a concentrated alkaline aqueous solution of about 30% by mass is used. In addition, it has excellent mechanical strength, dimensional stability and ionic conductivity, and is suitably used for alkaline batteries such as nickel cadmium batteries and nickel metal hydride batteries. In the case of producing an electricity storage device using the separator of the present invention, any material that constitutes the electricity storage device such as a positive electrode, a negative electrode, and an electrolytic solution can be used as long as it is conventionally known.

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, a polyphenylene sulfide fiber cut to a fiber diameter of 10 μm or less and a fiber length of 10 mm or less and a core-sheath type composite fiber cut to a fiber diameter of 2.5 μm or less and a fiber length of 15 mm or less are 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 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 or pure water in order to reduce ionic impurities as much as possible.

  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 overlapping the sheets, the dried and core-sheath type composite fibers are fused by passing through a drying part such as a multi-cylinder type or Yankee type dryer to produce a separator.

When the electrolyte solution retainability of the separator manufactured as described above is insufficient, it is preferable to perform a hydrophilization treatment in order to improve the electrolyte solution retainability.
As the hydrophilization treatment, for example, at least one hydrophilization treatment such as sulfonation treatment, fluorine gas treatment, graft treatment, surfactant treatment, discharge treatment, hydrophilic resin adhesion treatment, etc. is performed on the fiber surface. , Oxygen and / or sulfur-containing functional groups (for example, sulfonic acid groups, sulfonate groups, sulfofluoride groups, carboxyl groups, carbonyl groups, etc.), graft polymerization of hydrophilic monomers, surfactants It is preferable to adhere or to attach a hydrophilic resin. Such a hydrophilization treatment may be performed at the fiber stage. However, the hydrophilization treatment after the separator paper making is superior in workability. Hereinafter, although the method to hydrophilize after separator papermaking is demonstrated, it can implement in the same manner also in other cases.

  Examples of the sulfonation treatment include a method of introducing a sulfonic acid group by immersing a separator as described above in a solution composed of fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, sulfuryl chloride, or the like, as described above for sulfur trioxide gas. There are a method of introducing a sulfonic acid group by bringing a separator into contact, a method of introducing a sulfonic acid group by causing a discharge in the presence of sulfur monoxide gas or sulfur dioxide gas, and the like.

  As the fluorine gas treatment, for example, fluorine gas diluted with an inert gas (for example, nitrogen gas, argon gas, etc.) and at least one kind of gas selected from oxygen gas, carbon dioxide gas, sulfur dioxide gas, etc. The nonwoven fabric can be hydrophilized by exposing the nonwoven fabric to the mixed gas.

  Examples of the graft polymerization treatment of the vinyl monomer include, for example, a method in which the separator is immersed in a solution containing the vinyl monomer and the polymerization initiator, a method in which the separator is irradiated with radiation after the vinyl monomer is applied to the separator, and a radiation in the separator. There are a method of bringing it into contact with a vinyl monomer, a method of irradiating ultraviolet rays after applying a vinyl monomer solution containing a sensitizer to a separator, and the like. As this vinyl monomer, for example, acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl pyridine, vinyl pyrrolidone, or styrene can be used. When styrene is graft-polymerized, it is preferably sulfonated so as to have excellent affinity with the electrolytic solution. If the separator is modified by ultraviolet irradiation, corona discharge, plasma discharge or the like before the vinyl monomer solution is brought into contact with the separator, the affinity with the vinyl monomer solution is increased, so that graft polymerization can be efficiently performed.

  Examples of the surfactant treatment include an anionic surfactant (for example, an alkali metal salt of a higher fatty acid, an alkyl sulfonate, or a sulfosuccinate ester salt), or a nonionic surfactant (for example, a polyoxyethylene alkyl). The separator can be immersed in a solution of ether or polyoxyethylene alkylphenol ether), or the solution can be applied to or sprayed on the separator.

  Examples of the discharge treatment include corona discharge treatment, plasma treatment, glow discharge treatment, and electron beam treatment. In addition, under atmospheric pressure in the air, between each pair of electrodes carrying a dielectric, a separator is disposed so as to be in contact with both of these dielectrics, and an AC voltage is applied between these two electrodes, In the method of generating discharge in the internal voids of the separator, the fiber surface inside the separator can be hydrophilized, and thus a separator having excellent internal pressure characteristics can be manufactured.

  As hydrophilic resin provision processing, hydrophilic resins, such as carboxymethylcellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol, or polyacrylic acid, can be made to adhere, for example. These hydrophilic resins can be dissolved or dispersed in a suitable solvent, and then the separator can be immersed in the solvent, or the solvent can be applied or dispersed on the separator and dried to be adhered.

Examples of the crosslinkable polyvinyl alcohol include polyvinyl alcohol in which a part of the hydroxyl group is substituted with a photosensitive group. More specifically, the photosensitive group is a styrylpyridinium type or styrylquinolinium type. There is polyvinyl alcohol in which a part of the hydroxyl group is substituted with a styrylbenzothiazolium type. This crosslinkable polyvinyl alcohol can also be crosslinked by being irradiated with light after being attached to the separator in the same manner as other hydrophilic resins. Polyvinyl alcohol in which a part of such hydroxyl groups is substituted with a photosensitive group is excellent in alkali resistance and contains many hydroxyl groups that can form chelates with ions, and is dendritic on the electrode plate during discharge and / or charge. It can be preferably used because it can form a chelate with an ion before the metal is deposited and can prevent a short circuit between the electrodes.
EXAMPLES Hereinafter, although the separator of this invention and its manufacturing method are demonstrated by an Example, this invention is not limited by these Examples.

A core-sheath type composite fiber comprising a polyphenylene sulfide fiber having a fiber diameter of 9.5 μm and a fiber length of 6 mm, a sheath component having a fiber diameter of 1.7 μm and a fiber length of 10 mm of polyvinyl alcohol having a melting point of 80 ° C., and a core component comprising polypropylene. Each of them was put in ion exchange water at a mass ratio of 50:50 in a pulper at a concentration of 0.05% by mass and dispersed for 30 minutes to prepare a papermaking material comprising a fiber dispersion.
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 120 ° 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 99 μm, the density was 0.42 g / cm ³ , and the air permeability was 8 seconds / 100 ml.

The present invention was carried out in the same manner as in Example 1 except that the core-sheath composite fiber was replaced with a core-sheath composite fiber whose sheath component was an ethylene-vinyl alcohol copolymer having a melting point of 100 ° C. and whose core component was polypropylene. A separator was obtained.
Regarding the physical properties of the obtained separator, the thickness of the separator was 100 μm, the density was 0.40 g / cm ³ , and the air permeability was 9 seconds / 100 ml.

In the same manner as in Example 1, a separator of the present invention having a thickness of 50 μm was obtained.
As for the physical properties of the obtained separator, the density was 0.52 g / cm ³ and the air permeability was 12 seconds / 100 ml.

In the same manner as in Example 1, a separator of the present invention having a density of 0.67 g / cm ³ was obtained.
Regarding the physical properties of the obtained separator, the thickness of the separator was 98 μm, and the air permeability was 18 seconds / 100 ml.

A separator of the present invention was obtained in the same manner as in Example 1 except that the mass ratio of the polyphenylene sulfide fiber and the core-sheath composite fiber was 65:35.
Regarding the physical properties of the obtained separator, the thickness of the separator was 100 μm, the density was 0.45 g / cm ³ , and the air permeability was 10 seconds / 100 ml.

[Comparative Example 1]
A polypropylene non-woven fabric with a thickness of 100 μm, which is commercially available for nickel metal hydride batteries, was used as the separator.

[Comparative Example 2]
A nonwoven fabric made of stretched polyphenylene sulfide fiber and unstretched polyphenylene sulfide fiber having a thickness of 100 μm, which is commercially available for nickel metal hydride batteries, was used as a separator.
The following characteristics were evaluated for the separators obtained in Examples 1-5 and Comparative Examples 1-2.

<High-temperature long-term test>
As the electrode current collector, a paste type nickel positive electrode (33 mm width, 182 mm length) using a foamed nickel base material and a paste type hydrogen storage alloy negative electrode (mesh metal alloy, 33 mm width, 247 mm length) were prepared.
Next, each separator was cut into a width of 33 mm and a length of 410 mm, and each was sandwiched between a positive electrode and a negative electrode, and wound in a spiral shape to prepare an electrode group corresponding to SC (sub-C) type. This electrode group was housed in an outer can, and 5N potassium hydroxide and 1N lithium hydroxide as electrolytes were poured into the outer can and sealed to prepare a cylindrical nickel-hydrogen battery having a capacity of 2000 mAh.
For the produced cylindrical nickel-metal hydride battery, a charge / discharge cycle consisting of charging at 0.33 C and discharging to a final voltage of 1 V at 10 C is repeated at a temperature of 80 ° C. until the capacity reaches 50% of the initial capacity. The number of cycles was defined as the life.
The obtained results are shown in Table 1. In Table 1, ◎ indicates a value exceeding 500 cycles, and × indicates a value not exceeding 500 cycles.

  As is apparent from the results in Table 1, it was confirmed that the nickel metal hydride battery using the separator of the present invention maintained a sufficient discharge capacity even in a high-temperature long-term test at 80 ° C. and had a long battery life. On the other hand, the nickel-metal hydride batteries using the separators of Comparative Examples 1 and 2 have a very large decrease in discharge capacity, and some of them cause an internal short circuit from the beginning, and the characteristics are extremely inferior.

Claims (12)

  A separator for an electricity storage device comprising polyphenylene sulfide fiber and core-sheath type composite fiber.   The power storage device separator according to claim 1, wherein the polyphenylene sulfide fiber is heat-treated at a temperature equal to or higher than a glass transition temperature.   The fiber diameter of the said polyphenylene sulfide fiber is 10 micrometers or less, Fiber length is 10 mm or less, The separator for electrical storage devices of Claim 1 or Claim 2 characterized by the above-mentioned.   4. The core-sheath type composite fiber according to claim 1, wherein the sheath component is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the core component is polypropylene or polyethylene. 5. For electricity storage devices.   The electrical storage device separator according to any one of claims 1 to 4, wherein the core-sheath type composite fiber has a fiber diameter of 2.5 µm or less and a fiber length of 15 mm or less.   The separator for an electricity storage device according to any one of claims 1 to 5, wherein a melting point of a sheath component of the core-sheath composite fiber is 80 to 130 ° C.   7. The electricity storage device separator according to claim 1, wherein the polyphenylene sulfide fiber is 65 to 20% by mass and the core-sheath type composite fiber is 35 to 80% by mass. .   The separator for an electricity storage device according to any one of claims 1 to 7, wherein the separator is configured by heat fusion or thermocompression bonding of a core-sheath type composite fiber.   The electrical storage device separator according to any one of claims 1 to 8, wherein the separator has a thickness of 100 µm or less. The density | concentration of the said separator is 0.2-0.9 g / cm < ³ >, The separator for electrical storage devices in any one of the Claims 1 thru | or 9 characterized by the above-mentioned.   11. The electricity storage device separator according to claim 1, wherein the separator has an air permeability of 100 seconds / 100 ml or less.   The power storage device separator according to any one of claims 1 to 11, wherein the power storage device is a nickel cadmium battery or a nickel metal hydride battery.