JP2015050090A - Separator for battery - Google Patents

Abstract

An object of the present invention is to provide a porous ceramic layer which is thinned, has excellent battery characteristics, and is stable in a battery separator composed of a porous ceramic layer containing an alumina-based material and a nonwoven fabric substrate. It is providing the battery separator which has this.
In a battery separator comprising a porous ceramic layer containing an alumina material and a nonwoven fabric substrate, the nonwoven fabric substrate is coated with a crosslinked cationic polymer and is porous. A battery separator comprising a cationic polymer having a crosslinked ceramic layer.
[Selection figure] None

Description

  The present invention relates to a battery separator that can be stably manufactured.

  Conventionally, as a battery separator for a lithium battery (hereinafter sometimes abbreviated as “separator”), a polyolefin 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 In order to avoid electrode contact due to thermal contraction of the separator due to an increase in temperature, there is an increasing demand for a separator having high heat resistance and low internal resistance.

  In response to this demand, Patent Document 1 proposes a separator including a support having a hole and a porous ceramic layer that closes the hole. A nonwoven fabric containing polymer fibers is used for the support, and ceramics such as zirconium, silica, and alumina are mainly used for the porous ceramic layer. By using the low-density support and the porous ceramic layer in combination, the porosity in the separator and the heat resistance can be improved.

  However, since such a separator is produced by coating a dispersion of a porous ceramic layer on a support, if the polymer fiber density of the support is low, the strength of the support is reduced and the coating is applied. As a result, the porous ceramic layer dispersion was detached from the support, and a porous ceramic layer uniform in the surface direction could not be obtained, resulting in a defect of the separator and an internal short circuit. Moreover, when the fiber density is too high, a problem that the thickness is increased occurs. In order to impart an appropriate fiber density and suppress an increase in thickness, Patent Document 2 is manufactured by a wet papermaking method excellent in fiber dispersibility, and uses an ultrafine fiber to balance strength and thickness. A support made of a nonwoven fabric substrate has been proposed.

  As the ceramic used for the porous ceramic layer, alumina-based materials such as alumina and boehmite are preferably used. However, there is room for improvement in the adhesion between the polymer fibers used in the nonwoven fabric substrate and the alumina-based material, and in order to obtain a thin battery separator with excellent battery characteristics, a more stable porous ceramic layer Improvements are expected to achieve this.

Japanese Patent No. 4594098 JP 2009-230975 A

  An object of the present invention is a battery separator composed of a porous ceramic layer containing an alumina-based material and a nonwoven fabric base material, and a battery having a stable porous ceramic layer that is thinned and has excellent battery characteristics. Is to provide a separator.

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

[1] In a battery separator composed of a porous ceramic layer containing an alumina-based material and a nonwoven fabric substrate, the nonwoven fabric substrate is covered with a crosslinked cationic polymer, and the porous ceramic A battery separator comprising a cationic polymer having a crosslinked layer.

  According to the present invention, in a battery separator composed of a porous ceramic layer containing an alumina-based material and a nonwoven fabric substrate, the battery separator has a stable porous ceramic layer that is thinned and has excellent battery characteristics. Is to get.

  Examples of the alumina-based material include α, β, γ-alumina typified by alumina oxide, boehmite, pseudoboehmite typified by hydroxide alumina, and the like. In particular, boehmite is a preferable material because various forms such as a plate shape, a granular shape, and a fiber shape can be obtained by a hydrothermal synthesis method. The alumina-based material is preferably used as fine particles. The particle diameter is preferably 10 nm to 10 μm, more preferably 12 nm to 5 μm. The particle size is obtained by sufficiently diluting the alumina material with water and measuring this with a laser scattering type particle size measuring device (trade name: 3300EX2 manufactured by Microtrac Co., Ltd.), and the obtained center particle size (D50, volume average). ) As the particle size.

  The nonwoven fabric substrate is produced by a dry or wet papermaking method. The dry method is a melt blow method in which fibers are blown from a nozzle to produce a web, a spunbond method in which the web is composed of long fibers obtained from the nozzle, and a dissolved polymer is charged to form a fine fiber web. There is an electrospinning method, a method of forming a web while defibrating 30 to 100 mm fibers in air. On the other hand, in the wet papermaking method, short fibers are dispersed in water at a low concentration of about 0.01 to 0.2% by mass, and then made from water with a net such as a long net, a short net, or a round net, A fiber web can be formed. In this case, the preferable short fiber length is 1 to 30 mm. Moreover, although it is preferable to contain the short fiber of a fineness 1.0 decitex (dt) or less, when producing a thinner battery separator, it is more preferable to contain the short fiber of 0.6 dt or less. The wet papermaking method is a preferable production method because a nonwoven fabric base material having a good balance between strength and thickness can be obtained.

  As fibers used for the nonwoven fabric substrate, there are various types such as cellulose, polyethylene, polypropylene, polyester, and polyamide, and cellulose, polypropylene, polyester, and the like are particularly preferable materials. The nonwoven fabric substrate composed of these fibers is optionally abbreviated as “crosslinked polymer” (hereinafter referred to as “crosslinked polymer”), which is subjected to heat pressure treatment or pressure treatment to adjust the thickness, and then the fiber surface is crosslinked. In some cases).

As a coating method, it is preferable that a cationic polymer and a crosslinking agent are dissolved in water or a solvent in advance and treated by an impregnation method or the like. At this time, in the nonwoven fabric substrate manufactured by the dry method, the fiber surface is hydrophobic, and it is difficult to coat with an aqueous impregnation method, so a hydrophilic treatment such as a corona treatment is performed before the impregnation method. Is preferred. The coating amount of the crosslinked polymer, in terms of solid content (dry weight), preferably 0.01~10.0g / ^{m 2,} more preferably from 0.1 to 2.0 g / ^{m 2.}

  Examples of the cationic polymer include acrylic resins containing amino groups and quaternary ammonium salts, polyacrylamide, polyethylene glycol, polyvinyl alcohol, and the like; chitosan, modified chitosan, polydiallyldimethylammonium salt, and the like. Among these, acrylic resins having an amino group that can be easily cross-linked, polyacrylamide, polyvinyl alcohol; chitosan is preferable, and chitosan having particularly good oxidation resistance is a more preferable cationic polymer. As a crosslinking method, a nucleophilic addition reaction of an amino group to a nitrogen lone pair proceeds easily. A vinylsulfone-based crosslinking agent, a triazine-based crosslinking agent, a catechol such as dopamine, a carbodiimide, an alkyl halide, or a urethane is used as a crosslinking agent. A method is known. In particular, vinyl sulfone cross-linking agents that have a sufficient reaction rate even at room temperature, and dopamine that cross-links with oxygen in the atmosphere selectively reacts with the amino group of the cationic polymer and has excellent cross-linking without side reactions. It is an agent.

  As the vinyl sulfone-based crosslinking agent, for example, the following compounds can be used.

In order to produce the battery separator of the present invention, the nonwoven fabric substrate preferably has a thickness of 10 to 25 μm and a porosity of 30 to 80%. More preferably, the thickness is 12 to 18 μm and the porosity is 40 to 70%. Preferably the weight per unit area is 5~18g / ^{m 2,} more preferably from 8~15g / ^{m 2.} The heating temperature at the time of the hot-press treatment is preferably 180 to 250 ° C, more preferably 200 to 245 ° C. In order to impart smoothness, the nip pressure between the rolls is preferably 190 to 1800 N / cm, and more preferably 400 to 1500 N / cm.

  In the present invention, a porous ceramic film layer containing an alumina-based material is provided on a nonwoven fabric substrate. The alumina-based material may penetrate into the nonwoven fabric substrate. Alumina-based material is prepared by first preparing a dispersion using a dispersant in combination with a thickening agent such as a cationic polymer and a cationic polymer latex and a binder, and preparing a coating solution. It is applied onto a nonwoven substrate.

  Preferred dispersants are water-soluble organic acids such as acetic acid, lactic acid, propionic acid, and gluconic acid, and acid compounds such as nitric acid, nitric acid amide, and sulfamic acid, and particularly preferred dispersant is acetic acid. In the present invention, chitosan is preferable as the cationic polymer that behaves as a dispersion aid and a thickener, and is used in combination with a crosslinking agent in the same manner as the coating of the nonwoven fabric substrate described above. In the present invention, the surface of the nonwoven fabric substrate is coated with a cationic polymer, and the porous ceramic layer also contains a crosslinked cationic polymer, so that the cationic polymer on the porous ceramic layer side is nonwoven fabric. By further cross-linking with the substrate surface, excellent adhesion is exhibited. Preferable binders include cationic acrylic resins, styrene-acrylic resins, and latexes thereof.

  As a dispersion method, mixing with a stirrer is sufficient when the concentration is low. However, when the concentration exceeds several percent, the overall viscosity is increased, and therefore, it is preferable to use a homogenizer or a bead mill. A preferable stirring and mixing time is about several minutes to 40 hours, more preferably about 1 hour to 20 hours.

The porous ceramic layer can be obtained by applying or casting a coating liquid containing an alumina-based material on a nonwoven fabric substrate and drying it. As an application or casting method, 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 50 g / ^{m 2} by dry weight, more preferably from 1 to 30 g / ^{m 2.} It is also possible to adjust the thickness of the obtained battery separator by further applying a heat calendering treatment after drying. The preferable thickness of the battery separator is 10 to 30 μm, and 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 system such as ethylene carbonate. Dimethoxyethane (DME) can also be used. As the supporting electrolyte, in addition to lithium hexafluorophosphate and lithium tetrafluoroborate, 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.

(Example 1)
[Manufacture of nonwoven fabric substrate]
The fiber was dispersed in water with the following configuration.
Stretched polyethylene terephthalate (PET) short fiber (fineness 0.1 dt, fiber length 3 mm) 40.0 parts by weight Stretched polyethylene terephthalate fiber (fineness 0.06 dt, fiber length 3 mm) 30.0 parts by weight Unstretched PET short fiber (fineness 0) .2 dt, fiber length 4 mm) 30.0 parts by mass Papermaking adhesive (Daiichi Kogyo Seiyaku, trade name: Serogen (registered trademark) BSH-12) 0.1 parts by mass

This was rolled up with a circular net to prepare a web having a basis weight of 9 g / m ² , subjected to thermal calendering at 220 ° C. and adjusted to a thickness of 15 μm, and a nonwoven fabric substrate was prepared.

Next, as a cationic polymer, a mixed coating liquid in which chitosan (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200) and a vinyl sulfone compound (compound 2) in a mass part ratio of 100/3 is obtained by dry mass. It impregnated so that it might become 0.3 g / m < ² >, and the fiber of the nonwoven fabric base material was coat | covered, and the base material (1) was obtained.

(Preparation of cationic acrylic latex)
0.1 parts by mass of sodium persulfate was added to 300 parts by mass of a 1.0% by mass acetic acid aqueous solution, and after nitrogen substitution, the mixture was heated to 80 ° C. To this aqueous solution, 5 parts by mass of NN-dimethylaminoethyl methacrylate, 2 parts by mass of ethyl methacrylate and 1 part by mass of methacrylic acid were slowly added over 2 hours. Furthermore, 0.15 parts by mass of sodium persulfate was added, 20 parts by mass of butyl methacrylate and 20 parts by mass of ethyl acrylate were added, and the mixture was further heated for 6 hours. Further, 0.15 parts by mass of sodium persulfate was added, Cationic acrylic latex was prepared by heating for 6 hours.

[Production of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemical Co., Ltd., trade name: C06) 60.0 parts by mass pure water 100.0 parts by mass acetic acid 1.0 part by mass acetylacetone 0.5 parts by mass or more is dispersed with a homomixer to obtain a dispersion. (1) was obtained.

  Next, the binder and thickener and the dispersion liquid (1) were combined with the following formulation to prepare a coating liquid (1).

Dispersion (1) 160.0 parts by mass 0.6 mass% chitosan aqueous solution (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200 1.0 mass% acetic acid contained)
100.0 parts by mass Vinylsulfonic acid compound (Compound 1) 0.12 parts by mass Cationic acrylic latex 12.0 parts by mass

[Manufacture of battery separators]
The obtained coating liquid (1) was impregnated into the substrate (1) and dried at 120 ° C. to produce a battery separator (1) having a thickness of 25 μm.

(Example 2)
In the nonwoven fabric base material used in Example 1, as a cationic polymer, a mixed coating liquid containing chitosan (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200) and dopamine in a mass part ratio of 100/4 was dried. It impregnated so that it might become 0.3 g / m < ² > by mass, and the fiber of the nonwoven fabric base material was coat | covered, and the base material (2) was obtained.

[Production of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemical Co., Ltd., trade name: C06) 60.0 parts by mass pure water 100.0 parts by mass acetic acid 1.0 part by mass acetylacetone 0.5 parts by mass or more is dispersed with a homomixer to obtain a dispersion. (2) was obtained.

  Next, latex and a thickener were combined with the dispersion liquid (2) according to the following formulation to prepare a coating liquid (1).

Dispersion liquid (1) 100.0 parts by mass 0.6 mass% chitosan aqueous solution (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200 1.0 mass% acetic acid contained)
100.0 parts by mass Dopamine 0.16 parts by mass Cationic acrylic latex 12.0 parts by mass

[Manufacture of battery separators]
The obtained coating liquid (2) was impregnated into the substrate (1) and dried at 120 ° C. to produce a battery separator (2) having a thickness of 25 μm.

(Comparative Example 1)
In Example 1, the non-woven fabric substrate was not coated with the cationic polymer, and the coating liquid (1) was applied in the same manner to prepare a comparative separator (1) having a thickness of 25 μm.

(Comparative Example 2)
In Example 1, the nonwoven fabric base material was impregnated with a cationic polymer, chitosan (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200) so as to have a dry mass of 0.3 g / m ² , The non-woven fabric substrate was coated to obtain a comparative substrate (1). Next, the coating liquid (1) was impregnated in the same manner to produce a comparative separator (2) having a thickness of 25 μm.

(Comparative Example 3)
[Production of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemical Co., Ltd., trade name: C06) 60.0 parts by mass Pure water 100.0 parts by mass Acetic acid 1.0 part by mass Acetylacetone 0.5 parts by mass or more of a mixed solution was dispersed with a homomixer for comparative dispersion A liquid (1) was obtained.

  Next, a comparative coating liquid (1) was prepared by combining the latex and thickener and the dispersion liquid (1) with the following formulation.

Comparative dispersion (1) 160.0 parts by mass 0.6 mass% chitosan aqueous solution (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200 1.0 mass% acetic acid contained)
100.0 parts by mass Cationic acrylic latex 12.0 parts by mass

[Manufacture of battery separators]
The obtained comparative coating liquid (1) was impregnated into the base material (1) prepared in Example 1, applied and dried at 120 ° C. to prepare a comparative separator (3) having a thickness of 25 μm.

(Comparative Example 4)
[Production of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemical Co., Ltd., trade name: C06) 60.0 parts by mass pure water 100.0 parts by mass sodium laurate 0.02 parts by mass Sodium polycarboxylate (product name: Poaz 520, concentration 40% by mass) 0 The mixed liquid of 5 parts by mass or more was dispersed with a homomixer to obtain a comparative dispersion liquid (2).

  Next, the latex and thickener were combined with the comparative dispersion liquid (2) with the following formulation to prepare a comparative coating liquid (2).

Comparative dispersion (2) 160.0 parts by mass 0.6 mass% carboxymethyl cellulose aqueous solution (Nippon Paper Industries, trade name: MAC500LC) 100.0 parts by mass acrylic latex (JSR, trade name: TRD202A, concentration: 40.2 mass%) 4.0 parts by mass

[Manufacture of battery separators]
Although the obtained comparative coating liquid (2) was impregnated into the base material (1) produced in Example 1, unevenness of the coating liquid occurred and a uniform separator could not be obtained.

(Comparative Example 5)
The nonwoven fabric substrate obtained in Example 1 was directly impregnated with the comparative coating liquid (2) and dried at 120 ° C. to prepare a comparative separator (4).

[Measurement of air permeability and average pore diameter]
The air permeability of the obtained separator was measured with a Gurley densometer manufactured by Toyo Seiki. Also, the average pore size was measured by Porous Materials Inc. Measured with a Capillary Flow Porometer CEP-1500A. The results are given in Table 1.

[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, and the solvent was dried and further pressed to prepare 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 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 added dropwise and sealed in an aluminum foil laminate film under reduced pressure to produce a lithium secondary battery. 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 value 30 minutes after the start of discharge under the condition of 0.2 C (discharge time of 300 minutes) as the voltage drop value. The results are given in Table 1. Further, the prepared lithium secondary battery was heated at 90 ° C. for 24 hours, charged and discharged again, the ratio of the discharge capacity to the charge capacity was measured in the same manner, and the results are given in Table 1.

  Since the battery separators obtained in Examples 1 and 2 are coated with a crosslinked cationic polymer on the nonwoven fabric substrate and contain a cationic polymer with a crosslinked porous ceramic layer. The adhesion between the nonwoven fabric substrate and the porous ceramic layer was good, and the battery characteristics were excellent.

  In Comparative Example 1, since the nonwoven fabric substrate is not covered with the crosslinked cationic polymer, the adhesion between the nonwoven fabric substrate and the porous ceramic layer is not sufficient, the air permeability is reduced, and the average pore diameter is reduced. Is spreading. In Comparative Example 2, since the cationic polymer on the surface of the nonwoven fabric substrate was not crosslinked, the effect was not sufficient, and the cation that had coated the nonwoven fabric substrate when impregnating the coating solution of the porous ceramic layer It is thought that the polymer was redissolved. Further, in Comparative Example 3, since the cationic polymer in the porous ceramic layer is not crosslinked, deterioration of the battery characteristics over time is observed, and there is a problem such as dissolution of the cationic polymer in the electrolytic solution. It was speculated. In Comparative Example 5, the porous ceramic layer contains an anionic polymer. The air permeability is small, the average pore diameter is widened, and sufficient battery characteristics are not obtained.

  In any of the examples, the adhesion between the nonwoven fabric substrate and the porous ceramic layer is good, the average pore diameter and the battery characteristics are superior to those of the comparative examples, and the thin film separator has excellent characteristics. .

  The battery separator of the present invention can be used as a thin film battery separator having excellent battery characteristics as a capacitor separator in addition to a lithium secondary battery separator.

Claims (1)

  In a battery separator composed of a porous ceramic layer containing an alumina-based material and a nonwoven fabric substrate, the nonwoven fabric substrate is coated with a crosslinked cationic polymer, and the porous ceramic layer is crosslinked A battery separator characterized by containing a cationic polymer.