JP2015060686A - Separator for molten salt battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for molten salt battery exhibiting high corrosion resistance for hydrogen fluoride, capable of suppressing short circuit due to dendrite, excellent in affinity with molten salt and retentivity, ensuring high dimensional stability even at high operating temperatures of the molten salt battery, and exhibiting enhanced short circuit resistance during compression.SOLUTION: A separator for molten salt battery consists of a porous layer containing insulating inorganic particles having particle size of 5.0 μm or less, and a polyolefin fiber wet-laid nonwoven fabric. The polyolefin fiber contains one kind or more of polyolefin selected from polypropylene and polymethylpentene, and the wet-laid nonwoven fabric is preferably dried by hot plate thermocompression.

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 corrosion of the separator widens the pore diameter, further increases the internal temperature, and may cause thermal runaway. 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, when sufficient liquid retention and strength are not secured in the separator, pressure is applied when the electrode expands with respect to the separator, so that the molten salt retention performance decreases. In some cases, it was compressed and destroyed.

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 to hydrogen fluoride, can suppress a short circuit due to dendrite, has excellent affinity and retention with molten salt, and high temperature at which a molten salt battery operates. However, it is to provide a molten salt battery separator having high dimensional stability and improved short circuit resistance during compression.

  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 porous layer containing insulating inorganic particles having a particle diameter of 5.0 μm or less and a polyolefin fiber wet nonwoven fabric.
(2) The separator for a molten salt battery according to (1), comprising at least one polyolefin selected from polypropylene and polymethylpentene as the polyolefin fiber.
(3) The separator for 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 batteries of the present invention is characterized by comprising a porous layer containing insulating inorganic particles having a particle diameter of 5.0 μm or less and a polyolefin-based fiber wet nonwoven fabric. Dimensional stability against heat is further improved by comprising a porous layer containing insulating inorganic particles and a polyolefin fiber nonwoven fabric, compared to the case where only a polyolefin fiber wet nonwoven fabric is used. Thus, it was found that the effect of withstanding the temperature rise when a part of the battery was short-circuited was obtained, and the short-circuit resistance during compression was improved. Further, the polyolefin fiber wet nonwoven fabric exhibits an effect of high corrosion resistance against hydrogen fluoride. 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.

  The separator for molten salt batteries of the present invention is characterized by comprising a porous layer containing insulating inorganic particles and a polyolefin fiber wet nonwoven fabric.

  In the battery separator of the present invention, the particle diameter of the insulating inorganic particles is 5.0 μm or less, preferably 0.02 μm or more and 3.0 μm or less, more preferably 0.7 μm or more and 2.0 μm or less. If the particle size is too large, it is difficult to produce a uniform aqueous slurry, and it may be difficult to form a porous layer with an appropriate thickness when applied to a nonwoven fabric, or the surface unevenness may be increased. is there. On the other hand, if the particle size is too small, the porous layer will be too dense, impeding the permeation of ions, making it easier for inorganic particles to fall off the nonwoven fabric, and increasing the amount of binder to prevent dropping. Sometimes. In addition, unless otherwise indicated, the particle diameter said by this invention represents the average particle diameter measured by the laser diffraction scattering method.

  In the battery separator of the present invention, when the content of insulating inorganic particles is too small, improvement in dendrite resistance is not observed, heat shrinkage during heating, and short circuit resistance when compression is applied Is no longer allowed. In addition, if the thickness and content of the porous layer containing insulating inorganic particles are too large, the mechanical strength of the layer itself becomes weak, or the layer becomes too dense and inhibits ion permeation. Sometimes.

  In addition, there is no restriction | limiting in particular in the method for manufacturing the insulating inorganic particle used for this invention.

  Examples of the insulating inorganic particles used in the present invention include inorganic oxides such as magnesium oxide, magnesium hydroxide, silica, titanium oxide, barium titanate, zirconium oxide, and aluminum oxide, or hydroxides, aluminum nitride, and silicon nitride. Inorganic nitrides such as zeolite, mica, boehmite and the like can be mentioned, but the present invention is not limited to these.

  Furthermore, in addition to the insulating inorganic particles, organic particles may be included as necessary. Examples of such organic fillers include polypropylene, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide, polystyrene, polyvinylidene fluoride, ethylene-vinyl monomer copolymer, polyolefin wax, and the like, but the present invention is not limited thereto. Is not to be done.

  The porous layer may contain a binder in addition to the insulating inorganic particles. Examples of the organic binder include acrylic resins, polyvinylidene fluoride and derivatives thereof, meta-type or para-type aromatic polyamide resins, polyimide resins such as aromatic polyimide, polysulfone resins, and ethylene-vinyl acetate copolymers ( In particular, vinyl acetate is a copolymer of 20 to 35 mol%), ethylene-acrylate copolymer, fluorine resin, styrene butadiene rubber (SBR) resin, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, Examples thereof include, but are not limited to, polyurethane resins and epoxy resins. Moreover, these binders may be used individually by 1 type, and may use 2 or more types together.

  As the inorganic binder, for example, 3-glycidyloxytrimethoxysilane, methacryloyloxy, which is also generally called a silane coupling agent and chemically bonds an inorganic oxide and an organic compound through a dehydration or dealcoholization reaction or the like. A mixture of a silicon compound having an organic functional group such as propyltrimethoxysilane and 3-aminopropyltriethoxysilane and an inorganic oxide sol such as silica and zirconium oxide is preferable because of excellent adhesion strength and heat resistance. It is not limited to this.

  The content of the binder in the porous layer is preferably 2% by mass or more and 200% by mass or less with respect to the total amount of the inorganic and organic fillers. 5 mass% or more and 50 mass% or less are especially preferable. If the amount of the binder is too small, the inorganic and organic fillers may be easily removed from the nonwoven fabric. Moreover, when there is too much quantity of a binder, a porous layer may become too dense and ion permeability may fall.

  The porous layer is provided on at least one surface of the polyolefin fiber wet nonwoven fabric. Moreover, the porous layer may be provided so that a porous layer may enter the inside of a polyolefin-type fiber wet nonwoven fabric. As a method of providing a porous layer, a slurry for forming a porous layer (porous layer coating solution) in which each component constituting the porous layer is dispersed or dissolved in a medium such as water or an organic solvent is prepared. This can be provided by coating it on the surface of the polyolefin fiber wet nonwoven fabric.

  The medium for preparing the slurry for forming the porous layer is not particularly limited as long as it can uniformly dissolve or disperse the binder, the insulating inorganic particles, and the like. For example, aromatic hydrocarbons such as toluene, Furans such as tetrahydrofuran, ketones such as methyl ethyl ketone, alcohols such as isopropyl alcohol, N-2-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl sulfoxide, water and the like can be used as necessary. Moreover, you may mix and use these media as needed. The medium to be used is preferably one that does not expand or dissolve the polyolefin fiber wet nonwoven fabric.

  As a method for forming a porous layer by coating a slurry for forming a porous layer on the surface of a polyolefin fiber wet nonwoven fabric, various coating methods such as blades, rods, reverse rolls, lips, dies, curtains, and air knives can be used. Various printing methods such as a construction method, flexo, screen, offset, gravure, and ink jet, a transfer method such as roll transfer and film transfer, a pulling method such as dipping, and the like can be selected and used as necessary.

Although the coating amount of the porous layer depends on the polyolefin fiber wet nonwoven fabric, the coating amount per one side of the polyolefin fiber wet nonwoven fabric (dry coating amount) is preferably 1 g / m ² or more and 30 g / m ² or less. , particularly preferably 2 g / ^{m 2} or more 15 g / ^{m 2} or less, further preferably 3 g / ^{m 2} or more 10 g / ^{m 2} or less. If the coating amount of the porous layer is too small, many of the various materials contained in the porous layer penetrate into the polyolefin fiber wet nonwoven fabric when the porous layer is provided, The quality layer may not be formed uniformly. Further, when the coating amount of the porous layer is too large, the pores of the polyolefin fiber wet nonwoven fabric may be filled, thereby inhibiting the ion permeability and battery characteristics.

  Next, fibers used in the polyolefin fiber wet nonwoven fabric will be described. The polyolefin fiber used in the present invention 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, and a copolymer composed of a copolymer of two or more different olefins. Examples include polyolefin fibers, core-sheath types, side-by-side types, eccentric types, orange-type composite fibers, and the like, 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). Furthermore, the nonwoven fabric of the present invention may contain inorganic fibers. Examples of inorganic fibers include ceramics and rock wool. When inorganic fibers are contained, heat-resistant dimensional stability and puncture strength may be improved.

  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.

  Although the fiber diameter of the fiber contained in the separator for molten salt batteries of the present invention is not particularly limited, the fiber diameter is preferably 1 μm or more and 20 μm or less from the denseness and manufacturability of the nonwoven fabric. When the fiber diameter is less than 1 μm, the strength of the fiber itself is low, and if the proportion of the fiber is high, sufficient mechanical strength may not be obtained, and the pores become too small, making it difficult for sodium ions to pass through. It may become. If the fiber length exceeds 20 μm, poor formation and sheet uniformity cannot be obtained, and there is a high possibility that the molten salt retention performance will be affected, or that a short circuit due to the occurrence of dendrites cannot be prevented. .

  The separator for a molten salt battery of the present invention comprises a porous layer containing insulating inorganic particles and a polyolefin fiber wet nonwoven fabric, and the nonwoven fabric portion is manufactured by a 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 wet papermaking method, an aqueous slurry containing fibers is prepared and made up. Specifically, the fibers are uniformly dispersed in water to form a uniform aqueous slurry for papermaking, and then passed through processes such as screen (removal of foreign matters, lumps, etc.), and the final fiber concentration is 0.01 to 0.50. The fiber web is formed and dried by adjusting the concentration to the mass% concentration, and the fiber in the fiber web is produced by a method of bonding, fusing and entanglement. In order to obtain a fiber web, a paper machine having at least one of a wire such as a circular net, a long net, and an inclined type can be used for the papermaking slurry. In order to obtain a uniform nonwoven fabric, chemicals such as a dispersion aid, an antifoaming agent, a hydrophilic agent, an antistatic agent, and a paper strength enhancing agent may be added in the process. Furthermore, in order to hold the inorganic particles between the fibers of the nonwoven fabric, an aggregating agent such as a cationic resin or a fixing agent may be added.

  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.

In the present invention, the polyolefin fiber wet nonwoven fabric can be used by adjusting the thickness by super calendering or thermal calendering treatment, if necessary. The basis weight of the polyolefin fiber wet nonwoven fabric is preferably in the range of 10 g / m ^{2 to} 80 g / m ² , and the thickness is preferably in the range of 30 μm to 250 μm. The basis weight and thickness of the polyolefin fiber wet nonwoven fabric 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.

  The separator for molten salt batteries of the present invention can be subjected to at least one hydrophilization treatment selected from a corona discharge treatment and a surfactant application treatment on a polyolefin fiber wet nonwoven fabric before providing a porous layer.

  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 molten salt is not provided. When the application amount exceeds 1.00% by mass, the sheet strength of the battery separator may be excessively lowered.

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. Moreover, if the maximum pore diameter is less than 1 μm, the retention of the molten salt 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 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. 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.

  100 parts by mass of magnesium oxide (particle diameter 2.1 μm) and 100 parts by mass of NMP are put in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle diameter measured by laser diffraction method becomes 0.8 μm. did. Next, 30 parts by mass of polyvinylidene fluoride (PVDF) was added and sufficiently mixed and stirred to prepare a coating solution for a porous layer.

  Using the nonwoven fabric produced above and the prepared coating liquid for the porous layer, the clearance between the two metal rolls is adjusted to 200 μm, and the nonwoven fabric for providing the porous layer is run between the two rolls. However, the porous layer coating solution is supplied to the side of the two rolls where the nonwoven fabric enters, and the excess coating solution is squeezed out by the two rolls. A porous coating solution was applied to both surfaces of the material to produce a molten salt battery separator.

(Examples 2 to 7)
A non-woven fabric was prepared by blending the fibers shown in Table 1, the insulating inorganic particles shown in Table 1 were used, and the porous layer was provided in the coating amount shown in Table 1, as in Example 1. Thus, a molten salt battery separator was produced.

(Example 8)
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. 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.

  100 parts by mass of magnesium oxide (particle diameter: 3.1 μm) and 100 parts by mass of NMP were put in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle diameter by laser diffraction method became 2.5 μm. Next, 30 parts by mass of PVDF was added and sufficiently mixed and stirred to prepare a coating liquid for porous layer.

  Using the nonwoven fabric produced above and the prepared coating liquid for the porous layer, the clearance between the two metal rolls is adjusted to 200 μm, and the nonwoven fabric for providing the porous layer is run between the two rolls. However, the porous layer coating solution is supplied to the side of the two rolls where the nonwoven fabric enters, and the excess coating solution is squeezed out by the two rolls, and the coating amount shown in Table 1 is applied. A porous coating solution was applied on both sides to produce a separator for a molten salt battery.

(Examples 9 to 10)
A non-woven fabric was prepared by blending the fibers shown in Table 1, the insulating inorganic particles shown in Table 1 were used, and the porous layer was provided in the coating amount shown in Table 1, as in Example 8. Thus, a molten salt battery separator was produced.

(Example 11)
70 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.), and PP single fiber (Average fiber diameter 10.5 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 using a wet paper making method with a circular paper machine, and using a band-type through dryer set at 135 ° C., the sheath portion of the PP / PE core-sheath type composite fiber is heat-melted and bonded. A nonwoven fabric having a width of 500 mm was produced.

  100 parts by mass of magnesium oxide (particle diameter 2.1 μm) and 100 parts by mass of NMP are put in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle diameter measured by laser diffraction method becomes 0.8 μm. did. Next, 30 parts by mass of PVDF was added and sufficiently mixed and stirred to prepare a coating liquid for porous layer.

  Using the nonwoven fabric produced above and the prepared coating liquid for the porous layer, the clearance between the two metal rolls is adjusted to 200 μm, and the nonwoven fabric for providing the porous layer is run between the two rolls. However, the porous layer coating solution is supplied to the side of the two rolls where the nonwoven fabric enters, and the excess coating solution is squeezed out by the two rolls, and the coating amount shown in Table 1 is applied. A porous coating solution was applied on both sides to produce a separator for a molten salt battery.

(Comparative Example 1)
A glass nonwoven fabric separator having a width of 500 mm was prepared using chopped strand glass fibers (fiber diameter 10.5 μm, fiber length 6 mm).

  100 parts by mass of magnesium oxide (particle diameter 2.1 μm) and 100 parts by mass of NMP are put in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle diameter measured by laser diffraction method becomes 0.8 μm. did. Next, 30 parts by mass of PVDF was added and sufficiently mixed and stirred to prepare a coating liquid for porous layer.

  Using the nonwoven fabric prepared above and the prepared coating liquid for the porous layer, the clearance of the two metal rolls is adjusted to 200 μm, and the nonwoven fabric for providing the porous layer is run between the two rolls. However, the porous layer coating solution is supplied to the side of the two rolls where the nonwoven fabric enters, and the excess coating solution is squeezed out by the two rolls, and the coating amount shown in Table 1 is applied. A porous coating solution was applied on both sides to produce a separator for a molten salt battery.

(Comparative Example 2)
100 parts by mass of magnesium oxide (particle diameter 2.1 μm) and 100 parts by mass of NMP are put in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle diameter measured by laser diffraction method becomes 0.8 μm. did. Next, 30 parts by mass of PVDF was added and sufficiently mixed and stirred to prepare a coating liquid for porous layer.

  Using a porous film made of PVDF resin having a thickness of 30 μm and an average pore diameter of 0.56 μm and the porous layer coating liquid prepared above, the clearance between the two metal rolls was adjusted to 40 μm, and two While running a porous film for providing a porous layer between two rolls, the porous layer coating solution is supplied to the side of the two rolls where the porous film enters, and the two rolls are excessive. As the coating solution was squeezed out, the porous coating solution was applied to both sides of the porous film in the coating amount shown in Table 1 to produce a molten salt battery separator.

(Comparative Example 3)
100 parts by mass of PP / PE core-sheath type composite fiber (average fiber diameter 10.7 μm, fiber length 5 mm) whose core component is polypropylene (melting point 165 ° C.) and whose sheath component is polyethylene (melting point 135 ° C.) 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 Co., Ltd., trade name: Elenite AB-100) and sodium alkyldiphenyl ether disulfonate (manufactured by Kao Corporation, trade name: Perex (registered trademark) SS-H ) Each of the solutions mixed at a mass ratio of 1: 1 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, A separator for a molten salt battery having a basis weight of 60.7 g / m ² was obtained.

(Comparative Example 4)
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. 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.

  100 parts by mass of magnesium oxide (particle size: 10.5 μm) and 100 parts by mass of NMP were placed in a container together with zirconia beads, and pulverized and dispersed with a paint conditioner until the average particle size by laser diffractometry was 5.1 μm. Next, 30 parts by mass of PVDF was added and sufficiently mixed and stirred to prepare a coating liquid for porous layer.

  Using the nonwoven fabric created above and the prepared porous layer coating solution, the clearance of the two metal rolls is adjusted to 200 μm, and the nonwoven fabric for running the porous layer between the two rolls is running The porous layer coating liquid is supplied to the side of the two rolls where the nonwoven fabric enters, and excess coating liquid is squeezed out by the two rolls. A porous coating solution was applied to the substrate to prepare a separator for a molten salt battery.

<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 and no problem at all.
(Triangle | delta): The state in which some change is seen.
X: State in which change is clearly understood.

[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 separator for molten salt battery of the present invention obtained in Examples 1 to 11 is composed of a porous layer containing insulating inorganic particles and a polyolefin fiber nonwoven fabric, the dimensional stability against heat is further improved. Thus, the effect of withstanding the temperature rise when a part of the battery was short-circuited was obtained, and good results were obtained such that the short-circuit resistance during compression was improved.

  From the comparison of Examples 1 to 11 and Comparative Example 3, by having a porous layer containing insulating inorganic particles, the puncture strength and short circuit resistance during compression, dimensional stability can be improved, In addition, the presence of a porous layer containing insulating inorganic particles made it possible to obtain appropriate air permeability and maximum pore diameter.

  From comparison between Examples 1 to 7 and Examples 8 to 10, the insulating inorganic particles were 0.7 μm or more and 2.0 μm or less, so that more appropriate air permeability and maximum pore diameter could be obtained.

  From comparison of Examples 1-7, the improvement of dimensional stability was seen by the compounding quantity of PP fiber and PMP fiber increasing. Further, by blending PP / PMP split fibers, a decrease in air permeability and a reduction in the maximum pore diameter were observed.

  From a comparison between Example 1 and Example 11, 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 method.

  From comparison between Examples 1 to 11 and Comparative Example 1, it was confirmed that hydrogen fluoride acid resistance was improved by using a polyolefin fiber wet nonwoven fabric instead of a glass nonwoven fabric.

  From the comparison between Examples 1 to 11 and Comparative Example 2, the separator for molten salt battery comprising a porous layer containing insulating inorganic particles and a polyolefin-based fiber wet nonwoven fabric is composed of insulating inorganic particles and a porous film. It was confirmed that the dimensional stability was excellent as compared with the obtained molten salt battery separator.

  From the comparison of Examples 1 to 11 and Comparative Example 4, when the insulating inorganic particles exceeding 5.0 μm are used, the non-uniformity shows that the maximum pore diameter is increased and the short circuit resistance is decreased. It was.

  As described above, the separator for a molten salt battery of the present invention is composed of a porous layer containing insulating inorganic particles having a particle diameter of 5.0 μm or less and a polyolefin fiber wet nonwoven fabric so that it can be compressed. Short-circuit resistance is improved, dimensional stability against heat is improved compared to the case of using only a polyolefin fiber wet nonwoven fabric, and the effect of withstanding the temperature rise when a part of the battery is short-circuited Accordingly, 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 porous layer containing insulating inorganic particles having a particle diameter of 5.0 μm or less and a polyolefin fiber wet nonwoven fabric.   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.