JP2015046346A - Separator for molten salt battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a molten salt battery, high in corrosion resistance against hydrogen fluoride, capable of suppressing a short circuit due to dendrite, excellent in permeability and retention properties of a molten salt and also in short-circuit resistance during separator compression, and hardly causing deformation even at high temperatures at which a molten salt battery operates.SOLUTION: A separator for a molten salt battery is made of a wet-laid nonwoven fabric containing polyolefin-based fibers having an average fiber diameter of 8.0 μm or less. More preferably, one or more polyolefins selected from polypropylene and polymethyl pentene are contained as the polyolefin-based fibers, and the wet-laid nonwoven fabric is subjected to drying treatment using a hot plate compression bonding method.

Description

  The present invention relates to a separator used in a battery using a molten salt as an electrolyte.

  Currently, power storage systems are being commercialized for various purposes, and large storage batteries for power systems have improved performance to stabilize output fluctuations associated with the introduction of renewable energy (wind power generation, solar power generation). As one of them, development of a sodium-sulfur battery or the like is underway (for example, see Patent Document 1).

Other developed storage batteries include molten salt batteries. The molten salt battery is a battery using a molten salt as an electrolyte, and operates in a state where the molten salt is dissolved at a high temperature of 80 ° C. or higher. As the molten salt to be used, NaFSA (sodium bisfluorosulfonylamide) having sodium ion as a cation and FSA (bisfluorosulfonylamide; (FSO ₂ ) ₂ N ⁻ ) as an anion is used. The molten salt battery includes a positive electrode, a negative electrode, and a separator.

  The separator is a sheet-like member that separates the positive electrode and the negative electrode, and has a capability of holding a molten salt containing ions inside (see, for example, Patent Documents 2 to 4). In a conventional molten salt battery, a glass separator using a glass cloth or the like is used. In the molten salt battery, the internal temperature may rise abnormally due to a short circuit between a part of the positive electrode and the negative electrode during operation. When the internal temperature rises abnormally, a part of the molten salt may be thermally decomposed. When the molten salt containing a fluorine atom thermally decomposes, the fluorine atom and water may react to generate hydrogen fluoride. Since hydrogen fluoride corrodes silicon dioxide, when a glass separator is used, the pore diameter widens due to the corrosion of the separator, the internal temperature further increases, and thermal runaway may occur. Further, the glass separator has a problem that it has low strength with respect to processing such as bending, has poor workability, and is easily damaged. When the glass separator is broken, when dendrite is generated on the electrode, the dendrite growth cannot be suppressed, and the molten salt battery may be short-circuited.

  In order to solve the problem of these glass separators, a film separator using a resinous porous film has been proposed. As the resin, a fluorine-based resin or a polyolefin-based resin having excellent corrosion resistance against hydrogen fluoride is used. However, the film separator has a drawback in that the affinity for the molten salt is low and it is difficult to hold the molten salt. In addition, a film separator made of a polyolefin-based resin is deformed at a high temperature of 80 ° C. or higher at which the molten salt battery operates, and it is difficult to use it in the molten salt battery.

  Moreover, in a storage battery, a positive electrode and a negative electrode repeat expansion and contraction with a charge / discharge reaction. At that time, if sufficient molten salt retention performance and strength are not secured in the separator, pressure is applied when it expands, resulting in a decrease in electrolyte retention performance, short-circuit due to destruction of the separator, etc. Could happen.

JP 2007-273297 A JP 2012-018773 A International Publication No. 2011/126047 Pamphlet JP 2012-243417 A

  The problem of the present invention is that it has high corrosion resistance against hydrogen fluoride, can suppress a short circuit due to dendrite, has excellent affinity with molten salt and retainability, and has a short circuit resistance due to separator compression. An object of the present invention is to provide a separator for a molten salt battery which is excellent and hardly deforms even at a high temperature at which the molten salt battery operates.

  As a result of intensive studies to solve this problem, the present inventors have reached the following invention.

(1) A separator for a molten salt battery comprising a wet nonwoven fabric containing polyolefin fibers having an average fiber diameter of 8.0 μm or less.
(2) The separator for a molten salt battery according to (1), wherein the polyolefin fiber is a fiber comprising one or more polyolefins selected from polypropylene and polymethylpentene.
(3) The separator for a molten salt battery according to (1) or (2), wherein the wet nonwoven fabric is dried by a hot plate compression method.

  The separator for molten salt battery of the present invention is characterized by comprising a wet nonwoven fabric containing polyolefin fibers having an average fiber diameter of 8.0 μm or less. By comprising the polyolefin fiber, the effect of high corrosion resistance against hydrogen fluoride is exhibited. Moreover, since a wet nonwoven fabric is flexible, it is not damaged like a glass separator, and a short circuit caused by dendrite can be suppressed. Furthermore, by containing polyolefin fibers having an average fiber diameter of 8.0 μm or less, the retention of molten salt is improved compared to the case of using a nonwoven fabric containing only polyolefin fibers having an average fiber diameter of more than 8.0 μm. Therefore, the effect that the molten salt easily permeates and the ability to hold the molten salt is high can be obtained. Moreover, it discovered that the short circuit resistance at the time of the compression of a separator improved by mix | blending polyolefin fiber with an average fiber diameter of 8.0 micrometers or less. And because wet nonwoven fabrics are composed of fibers, they are structurally solid compared to film separators using the same polyolefin resin, so they are less susceptible to heat, so deformation is also suppressed. The effect that it is done is acquired.

  The separator for molten salt batteries of the present invention is characterized by comprising a wet nonwoven fabric containing polyolefin fibers having an average fiber diameter of 8.0 μm or less. Hereinafter, “polyolefin fiber having an average fiber diameter of 8.0 μm or less” may be referred to as “fine fiber”.

  In the molten salt battery separator of the present invention, the average fiber diameter of the fine fibers is 8.0 μm or less. More preferably, they are 1.0 micrometer or more and 8.0 micrometers or less, More preferably, they are 1.0 micrometer or more and less than 5.0 micrometers, Most preferably, they are 1.0 micrometer or more and less than 3.5 micrometers. When the average fiber diameter is less than 1.0 μm, there is a problem that it is difficult to obtain the fiber because it is difficult to manufacture the fiber. When the average fiber diameter is more than 8.0 μm, the average fiber diameter is too large, the air permeability and the maximum pore diameter become too high, the ability to retain the electrolyte solution, and the short-circuit resistance during compression decreases. There is a problem.

  In the separator for molten salt battery of the present invention, the blending ratio of the small-diameter fibers is preferably 20% by mass or more, more preferably 40% by mass or more, and further preferably 80% by mass or more with respect to the entire fibers constituting the wet nonwoven fabric. preferable. Moreover, the upper limit of a mixture ratio is 100 mass%. When the blending ratio is less than 20% by mass, the average fiber diameter of the entire fibers constituting the wet nonwoven fabric is too thick, so that the air permeability and the maximum pore diameter are too high, and the short ratio during battery production is high. Problems may occur.

  In addition, the average fiber diameter in the present invention is obtained by observing a cross section of a wet papermaking nonwoven fabric with a microscope, obtaining a cross-sectional area of 50 or more randomly selected fibers, and assuming that the cross section of the fiber is circular. It is the value converted into the fiber diameter.

  The polyolefin fiber is a polyolefin single fiber composed of a single polyolefin component, a mixed polyolefin fiber composed of a mixture of two or more different polyolefins, a copolymer polyolefin fiber composed of a copolymer of two or more different olefins, Examples of the composite fiber include a core-sheath type, a side-by-side type, an eccentric type, and an orange type, in which two or more different polyolefins are appropriately combined. The cross-sectional shape of the polyolefin-based fiber is preferably substantially circular rather than an irregular cross-section such as a wedge shape or a flat plate shape obtained by dividing a split-type composite fiber or a fiber shape such as a fibril. Examples of the polyolefin include polyethylene, polypropylene, polymethylpentene, polybutene and the like. Examples of other monomers copolymerizable with olefins include vinyl acetate, vinyl butyrate, and vinyl alcohol (vinyl acetate is polymerized and then saponified).

  The separator for molten salt battery of the present invention is a fiber containing at least one polyolefin selected from polypropylene (PP) and polymethylpentene (PMP) as the polyolefin fiber (hereinafter referred to as “PP, PMP”). It is preferable that “fibers containing one or more polyolefins” are sometimes abbreviated as “PP / PMP fibers”. When PP / PMP fiber is included, the melting point is high, so that an effect that the separator is hardly deformed can be obtained. It is more preferable to include a fiber containing PMP.

  The separator for a molten salt battery of the present invention can achieve the effects of the present invention without including PP / PMP fibers. However, when PP / PMP fibers are included, the content is based on the total fibers. Preferably, it is in the range of 5 to 70% by mass, more preferably in the range of 10 to 60% by mass, and still more preferably in the range of 10 to 50% by mass. is there. When the content is less than 5% by mass, the blending amount is too small, and the blending effect of PP / PMP fibers may not be seen. When it exceeds 70 mass%, the coupling | bonding between fibers becomes weak and a problem may be seen in an intensity | strength.

  The separator for molten salt battery of the present invention may be abbreviated as a core-sheath type composite fiber (hereinafter referred to as “PP / PE core-sheath type composite fiber”) having a polypropylene as a core component and polyethylene as a sheath component as a polyolefin fiber. It is preferable to contain at least. The PP / PE core-sheath type composite fiber is melt-spun using a melt spinning machine and using a core-sheath type composite spinning die. The spinning temperature is carried out at a temperature at which the polyethylene as the sheath component does not change, and the polymer is extruded at a spinning temperature of 200 ° C. or higher and 300 ° C. or lower to produce a spinning filament having a predetermined fineness. The spinning filament is subjected to a stretching treatment as necessary. The stretching treatment is carried out at a temperature at which the sheath component polyethylene is not fused. For example, it is preferable to treat the stretching component at a stretching temperature of 50 ° C. or more and 100 ° C. or less at a draw ratio of 2 times or more because the fiber strength is improved. The obtained filament is provided with a fiber treatment agent as necessary, and after controlling the hydrophilicity and dispersibility, it is cut into a predetermined length and used as a core-sheath type composite fiber for producing a nonwoven fabric.

  Polypropylene is used as the core component constituting the PP / PE core-sheath type composite fiber, but polyolefin such as polyethylene and polymethylpentene can be mixed as necessary in order to adjust the fiber properties. The mixing ratio of the polyolefin is preferably 10% by mass or less of the core component. Moreover, the resin additive used for normal polyolefin can be added as needed. Examples of the resin additive include various antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antistatic agents, and the like. It is used in the range of 0.01% by mass or more and 1.0% by mass or less.

  Polyethylene is used as the sheath component constituting the PP / PE core-sheath composite fiber, but polyolefin such as polypropylene or ethylene-propylene copolymer can be mixed as necessary in order to adjust fiber physical properties. . The mixing ratio of the polyolefin is preferably 10% by mass or less of the sheath component. Moreover, the resin additive used for normal polyolefin can be added as needed. Examples of the resin additive include various antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antistatic agents, and the like. It is used in the range of 0.01% by mass or more and 1.0% by mass or less.

  The content of the PP / PE core-sheath composite fiber contained in the molten salt battery separator of the present invention is preferably in the range of 30% by mass to 100% by mass, more preferably, based on the total fiber. , 40 mass% or more and 90 mass% or less, and more preferably 60 mass% or more and 80 mass% or less. When the content is less than 30% by mass, the defective rate during battery production may increase due to insufficient strength of the separator for a molten salt battery.

  In addition to polyolefin fibers, the fibers that can be included in the separator for molten salt batteries of the present invention include fully aromatic polyamides, semi-aromatic polyamides, aliphatic polyamides; ethylene-vinyl alcohol copolymers; polyethylene terephthalate, poly Examples thereof include polyesters such as butylene terephthalate and polycyclohexanedimethylene terephthalate; polyphenylene sulfide. When fibers other than polyolefin fibers are contained, the content thereof is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, based on the total fibers. .

  Although the fiber length of the fiber contained in the separator for molten salt batteries of this invention is not specifically limited, From the nonwoven fabric strength, manufacturability, etc., fiber length is 1 mm or more and 20 mm or less. When the fiber length is less than 1 mm, sufficient mechanical strength of the nonwoven fabric may not be obtained. Moreover, since the structure of the nonwoven fabric is not firm, it may be deformed during battery operation. If the fiber length exceeds 20 mm, the formation may be poor, and a good nonwoven fabric may not be formed. A short circuit may occur due to vibration between electrodes, or a short circuit may occur due to the occurrence of dendrites. is there. In particular, in a wet nonwoven fabric produced by a wet papermaking method, abnormal entanglement between fibers at the time of dispersion may occur, and a uniform dispersion state may not be achieved, resulting in poor formation.

  The separator for molten salt battery of this invention is a wet nonwoven fabric, and is manufactured by the wet papermaking method. The wet papermaking method has an advantage that the production speed is higher than that of the dry papermaking method, and fibers having different fiber diameters or a plurality of types of fibers can be mixed at an arbitrary ratio in the same apparatus. In other words, the fiber form can be selected from a wide range of staples, pulps, etc., and the usable fiber diameter can be used from ultrafine fibers to thick fibers. This is the method obtained. In addition, when split-type conjugate fibers are used, the split-type conjugate fibers can be almost completely divided by a disaggregation process and a dispersion process in a disaggregator such as a pulper, a high-speed mixer, and a beater. . Because of this, it is a nonwoven fabric forming method with a very wide application range. Therefore, the wet papermaking method is optimal as a method for producing the nonwoven fabric constituting the molten salt battery separator of the present invention.

  In the present invention, the wet nonwoven fabric can be treated by the hydroentanglement method. The water flow entanglement method is a method in which fibers are entangled three-dimensionally by applying a high-pressure water flow sprayed from a nozzle to the nonwoven fabric obtained as described above. Hydroentanglement treatment has the effect of improving the mechanical strength and liquid retention of the nonwoven fabric, imparting flexibility to the nonwoven fabric, and splitting the composite fiber when using split-type composite fibers. Moreover, it can suppress that a separator deform | transforms in the high-temperature state at the time of a battery operation because a fiber entangles.

  Further, in the wet papermaking method, when the nonwoven fabric is formed by a binder bonding method by heat-sealing of heat-bonding fibers, a step of causing heat-sealing simultaneously with heat drying of the wet fiber web is used. Examples of the heat drying method include a hot plate pressure bonding method represented by a cylinder dryer and a Yankee dryer, a band-type through dryer, and a hot air ventilation method represented by an air through dryer. In the present invention, heat drying by a hot plate pressure bonding method is more preferable. In the hot plate pressure bonding method, a non-woven fabric having high heat-seal efficiency of heat-sealable fibers and improved mechanical strength can be obtained, and the separator is not easily deformed even at a high temperature at which the molten salt battery operates. As the heat-sealing fiber, it is preferable to use a PP / PE core-sheath type composite fiber.

  The separator for molten salt battery of the present invention is a wet nonwoven fabric subjected to at least one hydrophilic treatment selected from hydrophilic monomer grafting treatment, corona discharge treatment, surfactant application treatment, and sulfonation treatment. Can do.

  The hydrophilic monomer graft polymerization treatment is, for example, a method in which a nonwoven fabric is immersed in a solution containing a hydrophilic monomer and a polymerization initiator and heated, and radiation is applied after the hydrophilic monomer is applied to the nonwoven fabric. There are a method of irradiating, a method of contacting a hydrophilic monomer after irradiating the nonwoven fabric with radiation, a method of irradiating ultraviolet rays after applying a hydrophilic monomer solution containing a sensitizer to the nonwoven fabric, and the like. As the hydrophilic monomer, for example, acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, vinyl pyridine, vinyl pyrrolidone and the like can be used. In addition, if the non-woven fabric is modified by ultraviolet irradiation, corona discharge, plasma discharge, etc. before the hydrophilic monomer solution is brought into contact with the non-woven fabric, the affinity with the hydrophilic monomer solution is increased, so that the efficiency is improved. Can be graft polymerized.

  In the corona discharge treatment, an appropriate gap is provided between an electrode connected to a high voltage generator and a metal roll coated with silicon rubber or the like, and a voltage of thousands to tens of thousands of volts is applied at a high frequency to generate corona discharge. , By running a nonwoven fabric in the gap and reacting ozone, nitric oxide, etc. generated by corona discharge on the nonwoven fabric surface to generate carboxyl groups, hydroxyl groups, peroxide groups, and thereby to the molten salt of the molten salt battery separator It is a surface modification method that improves affinity.

  Surfactants used in the surfactant application treatment include alkyl phosphate ester salts, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, polyoxyethylene alkyl ether phosphate ester salts, polyoxyethylene alkyl phenyl ethers. Phosphate ester salt, alkylbenzene sulfonate, dialkyl sulfosuccinate, alkyl diphenyl ether disulfonate, alkane sulfonate, long-chain fatty acid salt, sodium salt of β-naphthalene sulfonate formalin condensate, special aromatic sulfonate formalin condensation Sodium salts of products, anionic surfactants such as special polycarboxylic acid type polymer surfactants, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyalkylene alkenyl ethers Nonionic surfactants such as tellurium, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene hydrogenated castor oil Agents. From these groups, they can be used in combination. These surfactants can be applied to the nonwoven fabric by impregnation, coating, spraying, and drying.

  The applied amount of the surfactant is preferably 0.10% by mass or more and 1.00% by mass or less, more preferably 0.20% by mass or more and 0.80% by mass or less, and still more preferably 0% with respect to the nonwoven fabric. It is 30 mass% or more and 0.60 mass% or less. When the application amount is less than 0.10% by mass, it may be the same as the case where the affinity with the electrolytic solution is not provided. When the application amount exceeds 1.00% by mass, the sheet strength of the battery separator may be excessively lowered.

  As the sulfonation treatment, a gas phase treatment method using sulfur dioxide gas, sulfur trioxide gas or the like, or a liquid phase treatment method using hot concentrated sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, or the like can be used. Introduce a sulfonic acid group. In the battery separator of the present invention, sulfonation treatment by a gas phase treatment method is preferable. The sulfonation treatment by the liquid phase treatment method has a problem that it is difficult to set reaction conditions, and when the reaction time is excessively long or the temperature is excessively high, the nonwoven fabric is easily carbonized, contracted, and formed into a film. There is also a problem that a large amount of strongly acidic waste liquid is produced.

The separator for molten salt battery of the present invention can be used by adjusting the thickness by super calendering or thermal calendering treatment, if necessary. The basis weight of the molten salt battery separator of the present invention is preferably in the range of 30 g / m ^{2 to} 100 g / m ² , and the thickness is preferably in the range of 30 μm to 250 μm. The basis weight and thickness of the separator for a molten salt battery can be appropriately selected according to the characteristics of the applied battery. Here, the basis weight represents the basis weight defined in JIS P 8124, and the thickness represents the thickness defined in JIS P 8118.

  Moreover, the maximum pore diameter of the separator for a molten salt battery of the present invention is preferably in the range of 1 μm to 50 μm. When the maximum pore diameter is larger than 50 μm, short-circuiting is likely to occur, and the defect rate during battery manufacture may increase. In addition, when the maximum pore diameter is less than 1 μm, the molten salt retainability may be too low. Here, the maximum pore diameter represents the maximum pore diameter according to the bubble point method specified in JIS K3832.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example.

(Example 1)
100 parts by mass of PP / PE core-sheath type composite fiber (average fiber diameter 7.8 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) Then, the mixture was disaggregated and dispersed, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.5 g / An m ² battery separator was obtained.

(Example 2)
70 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.9 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and sheath component is polyethylene (melting point 135 ° C.), PP single fiber 30 parts by mass (average fiber diameter: 7.8 μm, fiber length: 5 mm) was disaggregated and dispersed in pulper water, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.4 g / An m ² battery separator was obtained.

Example 3
50 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and sheath component is polyethylene (melting point 135 ° C.), PP single fiber 50 parts by mass (average fiber diameter: 7.9 μm, fiber length: 5 mm) was disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.5 g / An m ² battery separator was obtained.

Example 4
70 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.7 mm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.), PMP single fiber 30 parts by mass (average fiber diameter: 7.9 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.5 g / An m ² battery separator was obtained.

(Example 5)
50 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.8 mm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.), PMP single fiber 50 parts by mass (average fiber diameter: 7.8 μm, fiber length: 5 mm) were disaggregated and dispersed in pulper water, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.0 g / An m ² battery separator was obtained.

(Example 6)
When dispersing 30 parts by mass of PP / PMP split type composite fibers (average fiber diameter after splitting: 3.1 μm, fiber length: 5 mm), pretreatment was performed in advance using a refiner in order to advance the splitting of the fibers. When processing with a refiner, after confirming that it is almost completely divided, a PP / PE core-sheath type in which the core component is polypropylene (melting point 165 ° C.) and the sheath component is polyethylene (melting point 135 ° C.) 70 parts by mass of composite fibers (average fiber diameter: 7.7 mm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.5 g / An m ² battery separator was obtained.

(Example 7)
When 50 parts by mass of PP / PMP split type composite fiber (average fiber diameter after splitting: 3.2 μm, fiber length: 5 mm) was dispersed, pretreatment was performed in advance using a refiner to advance the splitting of the fibers. When processing with a refiner, after confirming that it is almost completely divided, a PP / PE core-sheath type in which the core component is polypropylene (melting point 165 ° C.) and the sheath component is polyethylene (melting point 135 ° C.) 50 parts by mass of composite fibers (average fiber diameter 7.5 mm, fiber length 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core sheath. The sheath portion of the mold composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.3 g / An m ² battery separator was obtained.

(Example 8)
100 parts by mass of PP / PE core-sheath type composite fiber (average fiber diameter 7.9 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) Then, the mixture was disaggregated and dispersed, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine, and a band type through dryer set at 135 ° C. is used, and the sheath portion of the PP / PE core-sheath type composite fiber is heat-melted and bonded to a width of 500 mm. A non-woven fabric was prepared.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.1 g / An m ² battery separator was obtained.

Example 9
30 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 70 parts by mass of fibers (average fiber diameter: 7.6 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.1 g / An m ² battery separator was obtained.

(Example 10)
30 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 7.9 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 70 parts by mass of fibers (average fiber diameter: 7.9 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.0 g / An m ² battery separator was obtained.

(Example 11)
70 parts by mass of a PP / PE core-sheath composite fiber (average fiber diameter 7.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 30 parts by mass of fibers (average fiber diameter: 7.9 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

Grafting was performed using an acrylic acid monomer as the monomer, and the graft amount was 9.5% by mass. Thereafter, the thickness was adjusted with a super calendar to obtain a battery separator having a basis weight of 61.5 g / m ² .

(Example 12)
70 parts by mass of a PP / PE core-sheath composite fiber (average fiber diameter 7.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 30 parts by mass of fibers (average fiber diameter: 7.9 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

This nonwoven fabric is sulfonated for 25 seconds in 75 ° C dry air containing sulfur trioxide gas, neutralized with 2.5% by mass sodium hydroxide aqueous solution, washed thoroughly with ion-exchanged water, and dried. The thickness was adjusted with a super calender to obtain a battery separator having a basis weight of 61.2 g / m ² .

(Example 13)
70 parts by mass of a PP / PE core-sheath composite fiber (average fiber diameter 7.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 30 parts by mass of fibers (average fiber diameter: 7.9 μm, fiber length: 5 mm) were disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

Next, corona treatment was performed, and the thickness was adjusted with a super calender to obtain a battery separator having a basis weight of 60.4 g / m ² .

(Comparative Example 1)
Using a chopped strand glass fiber (fiber diameter 7.5 μm, fiber length 6 mm), a glass nonwoven fabric separator (basis weight 50.1 g / m ² , thickness 209 μm) having a width of 500 mm was produced.

(Comparative Example 2)
A film separator using a porous film made of PVDF resin having a thickness of 30 μm and an average pore diameter of 0.56 μm was used.

(Comparative Example 3)
100 parts by mass of PP / PE core-sheath type composite fiber (average fiber diameter 10.8 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) Then, the mixture was disaggregated and dispersed, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath part of the composite fiber was heat-melted and bonded to prepare a nonwoven fabric having a width of 500 mm, and the thickness was adjusted with a super calender to obtain a battery separator having a basis weight of 59.9 g / m ² .

(Comparative Example 4)
100 parts by mass of PP / PE core-sheath composite fiber (average fiber diameter 10.9 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) Then, the mixture was disaggregated and dispersed, and gently stirred with an agitator to prepare a uniform papermaking slurry. The slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer which is a hot plate pressure setting method set to 135 ° C., and also a PP / PE core-sheath type The sheath portion of the composite fiber was heat-melted and bonded to produce a nonwoven fabric having a width of 500 mm.

As surfactants, alkyl phosphate ester salt (manufactured by Takamatsu Yushi, trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (trade name: Perex (registered trademark) SS-H) are each 1: 1. The solution mixed at a mass ratio was impregnated and applied to the nonwoven fabric so that the applied amount of the surfactant was 0.30% by mass, and after drying, the thickness was adjusted with a super calender to obtain a basis weight of 60.3 g / An m ² battery separator was obtained.

<Evaluation method>
The following evaluations were performed on the molten salt battery separators obtained in Examples and Comparative Examples, and the results are shown in Table 1.

[Average fiber diameter]
The average fiber diameter of each fiber constituting the non-woven fabric is observed with a microscope, the cross section of the fiber, the area of 50 or more randomly selected fiber cross sections is calculated with image analysis software, and converted to the fiber diameter. Measurement data was used.

[Unit weight]
A 50 mm × 200 mm sample was measured with an electronic balance up to three digits after the decimal point, and converted to a mass per unit area of 1 m ² .

[Thickness]
A 50 mm × 200 mm sample was measured to 0.001 mm with a dial thickness gauge (Mitutoyo Corporation, trade name: 7321, 1 mm / 3 rotation).

[Puncture strength]
A metal needle with a diameter of 1 mm with a curvature of 1.6 at the tip is attached to a desktop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and 1 mm / s perpendicular to the sample surface. Until it penetrates at a constant speed. The maximum load (g) at this time was measured.

[Air permeability]
A sample of 50 mm × 50 mm was ventilated with a breathability tester (device name: KES-F8-AP1, manufactured by Kato Tech Co., Ltd.) according to the breathability method A (Fragile method) defined in JIS L 1096. The degree was measured.

[Dimensional stability]
A 50 mm × 50 mm sample was heated at 110 ° C. for 1 hour, and then the dimensions before and after cooling were measured to measure the dimensional change.

[Maximum pore size]
For the battery separator, the maximum pore diameter was determined by the bubble point method specified in JIS K3832.

[Hydrogen fluoride acid resistance]
Water was added to LiPF ₆ (lithium hexafluorophosphate) to evaluate the state after the sample was immersed for 1 hour in a state where hydrofluoric acid was generated.

○: No change in appearance, no problem at all.
(Triangle | delta): The state in which some change is seen.
×: State in which changes can be clearly seen

[Liquid permeability]
A test piece of 100 mm × 100 mm was collected, and the sample was spread in 23 ± 5 ° C. tap water and immersed for 1 minute to observe and evaluate the degree of water penetration.

○: Infiltration of water promptly and no mottled pattern is seen.
(Triangle | delta): Although water osmose | permeates, osmosis | permeation is mottled and the state which is not osmose | permeating uniformly.
X: The state which repels water and water penetration is not seen.

[Pressure retention volume]
A test piece of 100 mm × 100 mm is collected and its mass (W ₁ ) is measured. Next, the sample was spread in tap water at 23 ± 5 ° C. and immersed for 1 minute, taken out from the tap water, sandwiched with filter paper (Advantech No. 26), passed through a couch roll (mass 16 kg, diameter 98 mmφ), The mass (W ₂ ) of the sample is measured, and the pressurized liquid retention amount is calculated by the following equation (1).

Pressurized liquid retention amount (g / m ² ) = [(W ₂ −W ₁ ) ÷ (0.1 × 0.1)] (1)

[Short resistance test]
A test piece of 50 mm × 50 mm was taken, and the test piece was sandwiched with a press machine while applying a voltage of 2.5 V between both electrodes (diameter 30 mm, diameter 20 mm, material: copper, cylindrical shape), and a load was applied. The load when the voltage flowing between both electrodes was confirmed to be 1.0 V was measured.

  Since the separators for molten salt batteries of the present invention obtained in Examples 1 to 13 are wet nonwoven fabrics containing polyolefin fibers of fine fibers having an average fiber diameter of 8.0 μm or less, the separators are compressed. Excellent short-circuit resistance, excellent compatibility with molten salt and excellent retention, and retains molten salt more than when using non-woven fabrics containing polyolefin fibers with an average fiber diameter of more than 8.0 μm The capacity is improved, and the liquid permeability and pressurized liquid retention are excellent. Also. It is composed of polyolefin fiber diameters, hydrofluoric acid resistance, excellent puncture strength, dendrite resistance, dimensional stability, heat resistance, hydrophilization treatment, and Good results were obtained in the affinity and retention with the molten salt by having excellent air permeability and maximum pore diameter, and excellent liquid permeability and pressurized liquid retention.

  From the comparison between Examples 1 to 13 and Comparative Example 4, it was confirmed that by blending the small diameter fiber, it was excellent in liquid permeability and pressurized liquid retention, and short-circuit resistance during compression was improved.

  From the comparison of Examples 1 to 7, 9, and 10, an improvement in dimensional stability was observed as the blending amount of PP fiber and PMP fiber increased. Further, by blending PP / PMP split fibers, a decrease in air permeability and a reduction in the maximum pore diameter were observed.

  From the comparison of Examples 2 to 7, 9, and 10, a fiber having a high melting point such as PP or PMP is blended, the melting between the fibers is decreased, and the air gap between the fibers is increased so that the appropriate air permeability and the maximum pore diameter And the retention of the molten salt electrolyte was improved.

  From a comparison between Example 1 and Example 8, it was confirmed that when the drying treatment was performed by the hot plate pressure bonding method, the puncture strength was excellent as compared with the band type through dryer method.

  From the comparison between Examples 1 to 13 and Comparative Example 1, it was confirmed that the dendrite resistance was improved by improving the puncture strength.

  From the comparison between Examples 1 to 13 and Comparative Example 1, it was confirmed that hydrogen fluoride acid resistance was improved by using a wet nonwoven fabric using polyolefin fibers.

  From the comparison between Examples 1 to 13 and Comparative Example 2, it was confirmed that the sheet made of the wet nonwoven fabric was excellent in dimensional stability.

  From the comparison between Examples 1 to 13 and Comparative Examples 3 and 4, it was confirmed that the liquid permeability and the pressurized liquid retention amount were excellent by performing the hydrophilic treatment.

  As described above, the separator for molten salt battery of the present invention is blended with fine fibers having an average fiber diameter of 8.0 μm or less, so that the short-circuit resistance at the time of compressing the separator is improved. Excellent salt penetration and retention, and the use of olefin fibers has improved hydrofluoric acid resistance and dendrite resistance due to its high puncture strength, and excellent dimensional stability. Since it exhibits heat resistance, the molten salt battery using the separator for molten salt battery of the present invention has a low occurrence rate of short circuit, exhibits stable battery characteristics over a long period of time, and can be suitably used.

Claims (3)

  A separator for a molten salt battery, comprising a wet nonwoven fabric containing polyolefin fibers having an average fiber diameter of 8.0 μm or less.   The molten salt battery separator according to claim 1, comprising at least one polyolefin selected from polypropylene and polymethylpentene as the polyolefin fiber.   The separator for a molten salt battery according to claim 1 or 2, wherein the wet nonwoven fabric is dried by a hot plate compression method.