JP2015115281A - Method for manufacturing battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery separator superior in internal resistance.SOLUTION: A method for manufacturing a battery separator by making a composite of a base, and a porous ceramic layer including ceramic fine particles, provided that the ceramic fine particles include ceramic fine particles A, which are irregular-shaped silica formed by binding microparticles of particle sizes of 30 nm or smaller, and ceramic fine particles B having particle sizes of 0.1-1.0 μm, comprises the step of forming the porous ceramic layer by applying or casting a coating liquid including the ceramic fine particles A and B to the base. In the method, the coating liquid arranged by concurrently dispersing the ceramic fine particles A and B is used.

Description

  The present invention relates to a battery separator.

  Conventionally, as a separator of a lithium secondary battery, a polyolefin porous film having fine pores that have penetrated has been used. These separators suppress heat generation by increasing the internal resistance of the battery when the battery malfunctions and generate heat, and the through-holes are melted and closed. It has been responsible for suppressing battery explosion due to runaway.

  However, in applications that require charging and discharging with a large current, such as batteries for hybrid vehicles and uninterruptible power supplies, research on electrode composition has made it possible to suppress thermal runaway explosions, and conversely, rapid battery internals Due to the increase in temperature, in order to avoid electrode contact due to thermal contraction of the separator, there is an increasing demand for a separator having high heat resistance and low internal resistance.

  In response to this demand, Patent Document 1 discloses that the battery is thermally runaway by combining a porous ceramic layer containing porous ceramic fine particles with a porous support such as a nonwoven fabric. There has been proposed a method capable of suppressing electrode contact without causing thermal contraction of the separator even in the case of occurrence of heat. This method is an excellent method because the porous ceramic layer can permeate the surface and the inside of the separator and can impart high electrolyte retention and heat resistance.

  On the other hand, Patent Documents 2 and 3 propose a method of providing heat resistance by providing a porous ceramic layer containing ceramic fine particles on one side of a porous film. In particular, Patent Document 2 describes that titanium oxides such as alumina, zirconia, silica, titania, barium titanate, lead titanate, strontium titanate, and composite oxides thereof are effective for the porous ceramic layer.

  In particular, silica having a high insulating property is an inexpensive and very promising material, but if it is simply granular, the internal resistance cannot be lowered, leaving a problem.

Japanese Patent No. 4594098 Special table 2008-503049 gazette Japanese Patent No. 4499851

  An object of the present invention is to provide a battery separator having excellent internal resistance.

  As a result of intensive studies, the present inventor has found that the above-described problems can be solved by the present invention described below.

  In a method for manufacturing a battery separator comprising a composite of a porous ceramic layer containing ceramic fine particles and a support, the ceramic fine particles A are deformed silica bonded with fine particles having a particle size of 30 nm or less, and the ceramic fine particles B have a particle size. A ceramic fine particle of 0.1 μm or more and 1.0 μm or less is formed by applying or casting a coating liquid containing ceramic fine particles A and B on a support, and a porous ceramic layer is formed. Ceramic fine particles A and ceramic fine particles B A separator for a battery, wherein a coating liquid in which and are dispersed simultaneously is used.

  In the present invention, a battery separator having excellent internal resistance can be obtained.

It is a SEM image of the surface of the separator obtained in the Example. It is a SEM image of the surface of the separator obtained by the comparative example.

  The present invention is a method for producing a battery separator in which a porous ceramic layer containing ceramic fine particles and a support are combined. Ceramic fine particles A are deformed silica bonded with fine particles having a particle size of 30 nm or less, and ceramic fine particles B are ceramic particles having a particle size of 0.1 μm or more and 1.0 μm or less. In the method for producing a battery separator according to the present invention, a porous ceramic layer is formed by applying or casting a coating liquid containing ceramic fine particles A and B on a support, and the ceramic fine particles A and the ceramic fine particles B are simultaneously formed. It is characterized by using a dispersed coating liquid. In the battery separator manufactured by the battery separator manufacturing method of the present invention, the porous ceramic layer is composed of a composite of ceramic fine particles A and ceramic fine particles B.

  The ceramic fine particles A are irregular-shaped silica in which fine particles (colloidal silica) having a particle size of 30 nm or less are bonded. The particle size of the microparticles is an average value of 10 microparticles measured with a transmission electron microscope (TEM). When the microscopic image of the fine particles is not circular, the diameter of a perfect circle converted to the same area is used. The irregular-shaped silica is obtained by hydrothermal synthesis by adding a salt that forms a basic oxide to active silicic acid that is a raw material silica, and is an elongated silica having a rod shape, a bent shape, a branched shape, or the like. The active silicic acid is a silica sol obtained by subjecting water glass to a cation exchange treatment and adjusting the pH to an acidic atmosphere, and a salt forming a basic oxide is added thereto. As such salts, calcium, magnesium chloride, nitrate, sulfamate, formate, acetate and the like are preferable materials. The amount of salt added is preferably 0.15% by mass to 1.5% by mass in terms of CaO and MgO (basic oxide). Salt is added to return the pH from neutral to alkaline, and preferably heated at a temperature of 85 ° C. to 200 ° C. for 0.5 to 20 hours to obtain a deformed silica. If the silica concentration is too high during hydrothermal synthesis, the silica sol may gel, or problems such as sudden bond bonding and loss of reaction may occur. It is 10-40 mass%, More preferably, it is 15-30 mass%. Such deformed silica is, for example, a product with a special shape, such as ST-UP, ST-UP-S, ST-UP-M, manufactured by NISSAN CHEMICAL INDUSTRIES, under the trade name: Snowtex (registered trademark). Available in grades such as ST-OUP, ST-UP-SO, and ST-UP-MO.

  In the present invention, a composite of ceramic fine particles A which are irregularly shaped silica and ceramic fine particles B having a particle size of 0.1 μm or more and 1.0 μm or less constitutes a porous ceramic layer. The particle diameter of the ceramic fine particles B is an average value of the particle diameters of the ceramic fine particles B measured with a TEM or a scanning electron microscope (SEM). When the microscopic image of the ceramic fine particle B is not circular, the diameter of a perfect circle converted to the same area is used. The ceramic fine particles B are fine particles of a granular shape or a plate shape, and form an aggregated structure on the surface of the support to adjust the pore distribution of the support. When the silica-based material reacts with hydrogen fluoride produced by decomposition of the electrolyte, the silicon-oxygen bond is broken to produce gaseous silicon fluoride, causing serious problems in battery life. There is. In order to remove this hydrogen fluoride, the ceramic fine particles B are preferably a basic oxide. Examples of the basic oxide include calcium oxide, magnesium oxide, magnesium hydroxide and the like. A basic oxide of magnesium such as magnesium oxide or magnesium hydroxide is a particularly preferable material because the fluoride can be stably fixed on the surface.

  The particle diameter of the ceramic fine particles B is 0.1 μm or more and 1.0 μm or less. Fine particles with a particle size smaller than 0.1 μm form dense ceramic aggregates with irregular shaped silica in the support, and the porous ceramic layer does not spread over the entire support, but is localized on the support surface. As a result, the maximum pore diameter becomes too large, and the battery characteristics are deteriorated. On the other hand, when the particle diameter exceeds 1.0 μm, the coating amount of the porous ceramic layer necessary for stabilizing the battery characteristics is increased, and the thickness of the separator is increased. A more preferable particle size is 0.2 μm or more and 1.0 μm or less.

  A feature of the present invention is that a porous ceramic layer is formed by applying or casting a coating liquid containing ceramic fine particles A and B on a support, and the ceramic fine particles A and ceramic fine particles B are simultaneously dispersed. It is characterized by using. The ceramic fine particles A and ceramic fine particles B are dispersed at the same time. When the coating liquid is manufactured, the two fine particles are mixed and mechanical share is added so that the fine particles are stably dispersed in water. It means that the state that has been achieved is obtained. In general, in the case of a coating liquid containing two or more kinds of ceramic fine particles, first, aggregation occurs between the same particles during drying. When this phenomenon occurs, a high-density porous ceramic layer composed of fine particles and a low-density porous ceramic layer composed of large particles are separately formed. In particular, when a high-density layer made of deformed silica (ceramic fine particles A) is formed inside the separator, the internal resistance of the separator increases. However, when two kinds of ceramic fine particles are mixed at the same time and shear is applied, fine particles are dispersed so as to cover the surface of the large particles, so that the formed porous ceramic layer is locally high. A structure in which it is difficult to have a density layer can be taken, and a high porosity can be formed as a whole separator.

  In the present invention, the content of the ceramic fine particles A is preferably 30 to 60% by mass of the whole ceramic fine particles. When the content of the ceramic fine particles A is less than 30% by mass, the pores of the separator are expanded, and the ratio of the discharge capacity to the charge capacity (charge / discharge capacity ratio, discharge capacity / charge / discharge capacity) may be excessively reduced. Moreover, when it exceeds 60 mass%, the density of a separator will increase and the internal resistance of a battery may become large too much.

  In the present invention, the porous ceramic layer can contain a water-soluble cellulose derivative. The ceramic fine particles are dispersed in water to form a coating liquid that forms a porous ceramic layer. In this case, if a water-soluble cellulose derivative is contained, the water-soluble cellulose derivative becomes a dispersibility aid in water, and the coating liquid is thickened to improve the setting property of the coating liquid on the support. be able to.

  The water-soluble cellulose derivative in the present invention is a cellulose derivative synthesized by modifying a part of hydroxyl groups of β-glucose molecules bonded linearly by glycosidic bonds so as to be water-soluble. , A compound modified with a carboxymethoxy group, a methoxy group, a hydroxyethoxy group, or a hydroxyproxy group. A derivative substituted with a carboxymethoxy group is called carboxymethylcellulose (CMC), and can be water-solubilized with sodium salt or ammonium salt. Methylcellulose containing only methoxy groups dissolves only in low-temperature water and has a thermal gel property that gels an aqueous solution when the temperature rises. Moreover, it is excellent in foaming property and foaming property, and can behave like a nonionic polymer surfactant. In general, solubility and thermal gel properties can be controlled by combining a hydroxyethoxy group or a hydroxypropoxy group with a methoxy group. In addition, water-soluble cationized cellulose can also be used. However, cellulose derivatives such as cellulose acetate and ethyl cellulose cannot be used because they are water-insoluble cellulose derivatives that do not dissolve in water. The water-soluble cellulose derivative can be used in combination with ceramic fine particles to form a porous ceramic layer and reduce internal resistance. If the content of the water-soluble cellulose derivative is too large, a film is formed around the voids in the drying step to form independent voids, so that it is preferably 10% by mass or less of the porous ceramic layer, more preferably 5%. It is below mass%.

  In order to improve the adhesion between the ceramic fine particles and the adhesion between the support and the ceramic fine particles, various polymer binders can be used in combination as the organic binder. In particular, when polyester or polypropylene, which is difficult to bond, is used for the support, it is preferable to use a latex polymer binder as the polymer binder. As the polymer binder, polyolefin, styrene-butadiene, acrylic, or the like can be used. The content of the polymer binder is preferably 0.5 to 20% by mass of the porous ceramic layer, and more preferably 1 to 6% by mass. Furthermore, in order to improve the dispersibility of the ceramic fine particles and the affinity with the support, various surfactants such as nonionic, anionic and cationic can be used in combination. Examples of the surfactant include sodium laurate and dodecylbenzene sulfonic acid. Moreover, salts for imparting electric charge to the ceramic fine particles can be used in combination.

  In the present invention, a porous ceramic layer is formed on a support. Examples of the support include a porous film, a woven fabric, a nonwoven fabric, and a knitted fabric. Examples of the material for the support include polyester, polyolefin, polyamide, aramid, and cellulose. The support is a non-woven fabric using fibers such as polyester, polyolefin, polyamide, aramid, cellulose, etc., and is particularly excellent in heat resistance and easy to obtain fine fibers, using non-woven fabric using polyester or polyolefin fibers. Is preferred. The nonwoven fabric can be produced by various methods such as a wet method, a dry method, and an electrostatic spinning method. As a support body, it is preferable that it is 10-25 micrometers in thickness, and it is preferable that a porosity is 40-80%. More preferably, the thickness is 12 to 18 μm, and the porosity is 50 to 75%.

  When a wet nonwoven fabric produced by a wet method is used as a support, the surface of the support is hydrophilized by the surfactant remaining on the fiber surface during papermaking, and the above-mentioned deformed silica is formed on the surface. A composite having an aggregate structure stabilized with (ceramic fine particles A) appears. Therefore, a wet nonwoven fabric is more preferable as the support. The size of the composite is about submicron to several microns, and grows while adhering to the fiber surface with anisotropic silica.

The porous ceramic layer can be obtained by applying or casting a coating liquid containing ceramic fine particles on a support, gelling in some cases, and then drying. As an application or casting method, an air doctor coater, blade coater, knife coater, rod coater, squeeze coater, impregnation coater, gravure coater, kiss roll coater, die coater, reverse roll coater, transfer roll coater, spray coater, etc. The method used can be used. The coating amount of the porous ceramic layer is preferably 0.5 to 20 g / m ² by dry mass, and more preferably 1 to 10 g / m ² . The preferable thickness of the battery separator having a support is 10 to 30 μm, more preferably 12 to 25 μm.

  The obtained battery separator is cut and sandwiched between electrode materials for a lithium secondary battery, an electrolyte is injected, the battery is sealed, and a lithium secondary battery is obtained. The material constituting the positive electrode is mainly an active material and a conductive agent such as carbon black, a binder such as polyvinylidene fluoride and styrene butadiene rubber, and as the active material, lithium cobaltate, lithium nickelate, lithium manganate, A lithium manganese composite oxide such as lithium nickel manganese cobaltate (NMC) or lithium aluminum manganate (AMO), lithium iron phosphate, or the like is used. These are mixed and applied onto an aluminum foil as a current collector to form a positive electrode.

The material constituting the negative electrode is mainly an active material, a conductive agent, and a binder. As the active material, graphite, amorphous carbon material, silicon, lithium, lithium alloy and the like are used. These are mixed and applied onto a copper foil as a current collector to form a negative electrode. In a lithium secondary battery, a separator is sandwiched between a positive electrode and a negative electrode, and an electrolytic solution is impregnated therein to provide ionic conductivity and conduct. In the lithium secondary battery, a non-aqueous electrolyte solution is used. Generally, this is composed of a solvent and a supporting electrolyte. As the solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and vinylene carbonate having an additive function, vinyl Carbonate type such as ethylene carbonate. Dimethoxyethane (DME) can also be used. As the supporting electrolyte, in addition to lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ), an organic lithium salt such as LiN (SO ₂ CF ₃ ) ₂ is also used. Ionic liquids can also be used. Further, a gel electrolyte in which a lithium salt is dissolved in a gel polymer such as polyethylene glycol or a derivative thereof, polymethacrylic acid derivative, polysiloxane or a derivative thereof, or polyvinylidene fluoride can also be used.

  As the exterior body, a metal cylindrical can such as aluminum or stainless steel, a rectangular can, a sheet-type exterior body using a laminate film obtained by laminating aluminum foil with polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, or the like can be used. Further, it can be used by stacking and stacking, or it can be used by rotating in a cylindrical shape.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these at all.

[Production of support]
The composition is composed of 65 parts by mass of stretched regular polyethylene terephthalate (PET) fiber (0.1 dtex, length 3 mm) and 35 parts by mass of unstretched PET fiber (0.2 dtex, length 4 mm). An m ² web was prepared. The drying temperature at this time was 130 ° C. Next, a thermal calendar process was performed on the web at 220 ° C. to prepare a support body that was a wet nonwoven fabric having a thickness of 16 μm.

(Example)
Water 100 parts by mass Sodium laurate 0.03 parts by mass Deformed silica (Ceramic fine particles A, manufactured by Nissan Chemical Industries, trade name: Snowtex (registered trademark) ST-UP, elongated shape, fine particle size 30 nm or less, dynamic Particle size of irregularly shaped silica by scattering method 40 to 100 nm, concentration 20% by mass) 100 parts by mass of magnesium hydroxide (ceramic fine particles B, manufactured by Kyowa Chemical Industry, trade name: 200-06H,
Particle size 0.6μm) 20 parts by mass

  The above materials are manufactured by Tokushu Kika Kogyo Co., Ltd. K. Using a HOMO MIXER, the mixture was stirred at a rotational speed of 7000 rpm for 60 minutes to prepare a dispersion. The following materials were added to this dispersion to prepare a coating solution, impregnated into a support, and dried at 100 ° C. to prepare a separator having a thickness of 20 μm.

0.6% by weight sodium carboxymethylcellulose (Nippon Paper Industries, trade name: Sunrose (registered trademark) MAC500LC) 100 parts by weight 40% by weight acrylic latex (JSR, trade name: TRD202A) 3 parts by weight

  The above materials were mixed to prepare a coating liquid, impregnated into a support, and dried at 100 ° C. to prepare a separator having a thickness of 20 μm.

(Comparative example)
Water 100 parts by mass Sodium laurate 0.03 parts by mass Magnesium hydroxide (Ceramic fine particles B, manufactured by Kyowa Chemical Industry, trade name: 200-06H,
Particle size 0.6μm) 20 parts by mass

  The above materials are manufactured by Tokushu Kika Kogyo Co., Ltd. K. Using a HOMO MIXER, the mixture was stirred at a rotational speed of 7000 rpm for 60 minutes to prepare a dispersion. The following materials were added to this dispersion to prepare a coating solution, impregnated into a support, and dried at 100 ° C. to prepare a separator having a thickness of 20 μm.

Deformed silica (ceramic fine particles A, manufactured by Nissan Chemical Industries, trade name: Snowtex (registered trademark) ST-UP, elongated shape, fine particle diameter of 30 nm or less, irregular silica particle diameter of 40 to 100 nm by dynamic scattering method, Concentration 20% by mass) 100 parts by mass 0.6% by mass sodium carboxymethylcellulose (Nippon Paper Industries, trade name: Sunrose (registered trademark) MAC500LC) 100 parts by mass 40% by mass acrylic latex (manufactured by JSR, trade name: TRD202A) 3 parts by mass

[Measurement of air permeability]
The air permeability of the obtained separator was measured with a Gurley densometer manufactured by Toyo Seiki.

[SEM]
The SEM image was observed about the surface of the obtained separator, and the surface by the Example was given to FIG. 1, and the surface by the comparative example was given to FIG.

[Evaluation of battery characteristics]
On the aluminum foil, 200 g / m ^{2 of} lithium manganate, acetylene black, and polyvinylidene fluoride were applied at a mass ratio of 100/5/3, the solvent was dried, and further pressed to produce a positive electrode. On the other hand, spherical artificial graphite, acetylene black, and polyvinylidene fluoride were coated at a mass ratio of 85/15/5 on a copper foil at a rate of 100 g / m ² , dried and pressed to prepare a negative electrode.

  A separator was sandwiched between the obtained electrodes and heated at 95 ° C. under reduced pressure of 0.01 MPa or less for 12 hours, and then an electrolyte for a lithium secondary battery manufactured by Ube Industries (trade name: Purelite, solvent: EC / DEC / DME = 1/1/1 (volume ratio), supporting electrolyte: lithium hexafluorophosphate 1 mol / l) was dropped, and sealed in an aluminum foil laminate film by reducing the pressure, and the lithium secondary battery was Produced. Next, the produced lithium secondary battery was charged to 4.2 V at 0.2 C, and then discharged at 0.2 C. At this time, the ratio of the discharge capacity initially performed under the condition of 0.2 C to the charge capacity was measured. Further, the internal resistance was measured with the voltage drop value taken as the voltage 30 minutes after the start of discharge under the condition of 0.2 C (discharge time of 300 minutes). The results are given in Table 1.

  In the examples, the air permeability was low and the internal resistance was low and good as compared with the comparative example. From the SEM image, the high-density layer due to the aggregated structure (particle diameter of about 2 to 4 μm) made of deformed silica (ceramic fine particles A), which was seen in the comparative example, is reduced in the examples. In the example, it can be seen that the composite of ceramic fine particles A and magnesium hydroxide (ceramic fine particles B) has progressed, and it has a structure in which it is difficult to have a local high-density layer, and the entire separator is made uniform. As described above, according to the present invention, a separator excellent in internal resistance could be obtained.

  The battery separator of the present invention can be used as a capacitor separator in addition to a lithium secondary battery separator.

Claims (1)

  In a method for manufacturing a battery separator comprising a composite of a porous ceramic layer containing ceramic fine particles and a support, the ceramic fine particles A are deformed silica bonded with fine particles having a particle size of 30 nm or less, and the ceramic fine particles B have a particle size. A ceramic fine particle of 0.1 μm or more and 1.0 μm or less is formed by applying or casting a coating liquid containing ceramic fine particles A and B on a support, and a porous ceramic layer is formed. Ceramic fine particles A and ceramic fine particles B A separator for a battery, wherein a coating liquid in which and are dispersed simultaneously is used.