JP2014241231A - Cell separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell separator that may be stably manufactured while preventing a part of a coating liquid from infiltrating to a back surface of a support body when a coating layer is provided on the porous support body.SOLUTION: The cell separator is composed of a porous layer containing an alumina based material and a non-woven fabric base material. The non-woven fabric base material is coated by a cationic polymer formed by cross-linking an acrylic resin containing an amino group or a quaternary ammonium salt, polyacrylamide, polyethylene glycol, polyvinyl alcohol, chitosan, modified chitosan, poly diallyl dimethyl ammonium salt, and such.

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 made of a flexible support having a hole and a porous ceramic material that closes the hole. Polymer fibers are used for the flexible support, and zirconium, silica, and alumina are used for the porous ceramic. By using a low density support and a porous ceramic in combination, the porosity in the separator and the heat resistance can be improved.

  However, since such a separator is prepared by coating a dispersion of a porous ceramic material on a flexible support, the strength of the support is reduced when the polymer fiber density of the flexible support is low. In addition, the dispersion of the coated porous ceramic material is detached from the support, and a uniform porous ceramic layer in the surface direction cannot be obtained, which may cause a separator and cause 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.

  In general, as a method of providing a coating layer on a support, gravure coating, reverse roll coating, die coating, fountain coating, etc. are used. When such a method is used on a porous support, The coating solution penetrates into the back surface of the support, causing a problem that a stable coating film cannot be formed.

Japanese Patent No. 4594098 JP 2009-230975 A

  An object of the present invention is to provide a battery separator that can be stably produced.

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 membrane layer containing an alumina material and a nonwoven fabric substrate, the nonwoven fabric substrate is covered with a crosslinked cationic polymer. Battery separator.

  According to the present invention, a battery separator that can be stably produced can be obtained.

  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.

  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 base material composed of these fibers is subjected to a hot-pressure treatment to adjust the thickness, and then the cationic surface polymer (hereinafter sometimes abbreviated as “crosslinked polymer”) whose fiber surface is crosslinked. Covered.

As a coating method, it is preferable that a cationic polymer is dissolved in water, a solvent or the like 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 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, a vinylsulfone-based crosslinking agent having a sufficient reaction rate even in a room temperature atmosphere and dopamine that performs crosslinking with oxygen in the atmosphere are excellent crosslinking agents without side reactions.

  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 base material preferably has a thickness of 10 to 25 μm, and the porosity is preferably 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 membrane layer containing an alumina material is provided on the nonwoven fabric substrate. The alumina-based material may penetrate into the nonwoven fabric substrate. For alumina-based materials, first, a dispersion using a surfactant or the like is prepared, and a coating solution is prepared by combining a binder such as a polymer latex and a thickener, and then applied onto the nonwoven fabric substrate. Is done.

  Preferred dispersing agents include anionic surfactants such as sodium polyacrylate, phosphates such as sodium metaphosphate and sodium hydrogenphosphate, organic acids such as acetic acid, lactic acid and gluconic acid, and salts thereof, in particular. A preferred dispersant is acetic acid. Preferred binders include acrylic resins, styrene-acrylic resins, styrene butadiene rubber (SBR) resins, modified polyolefin resins, and latexes thereof. Preferred thickeners are polycarboxylic acid, carboxymethylcellulose, other cellulose derivatives, gum thickeners and the like, and particularly preferred thickener is sodium salt of carboxymethylcellulose which is insoluble in the electrolytic solution.

  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 membrane 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 membrane 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 separator is cut and sandwiched between electrode materials for a lithium battery, an electrolyte is injected, the battery is sealed, and a lithium battery is obtained. The material constituting the positive electrode is mainly an active material and a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride and styrene butadiene rubber. The active material includes lithium cobaltate, lithium nickelate, and lithium manganate. In addition, lithium manganese composite oxides such as lithium nickel manganese cobaltate (NMC) and lithium aluminum manganate (AMO), and lithium iron phosphate are used. These are mixed and apply | coated on the aluminum foil which is a collector, and become 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 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 a lithium battery, a non-aqueous electrolyte solution is used. Generally, this is composed of a solvent and a supporting electrolyte. As the solvent, 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. 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.

  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) 60.0 parts by mass Unstretched PET short fiber (fineness 0.2 dt, fiber length 4 mm) 40.0 parts by weight Papermaking adhesive (first Product name: Serogen (registered trademark) BSH-12, manufactured by Kogyo Seiyaku Co., Ltd.

This was rolled up with a circular net to produce a web having a basis weight of 9 g / m ² and subjected to a heat calendar treatment at 220 ° C. to a thickness of 15 μm.

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. The nonwoven fabric substrate (1) was obtained by impregnating to 0.3 g / m ² to coat the fibers.

[Production of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemical Co., Ltd., trade name: C20) 80.0 parts by mass pure water 100.0 parts by mass sodium metaphosphate 0.1 part by mass The above mixture is dispersed with a homomixer, and dispersion (1) is prepared. Obtained.

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

Dispersion (1) 180.0 parts by mass 0.6 mass% carboxymethylcellulose aqueous solution (manufactured by Nippon Paper Chemicals, trade name: MAC500HC) 100.0 parts by mass 40% by mass binder dispersion (manufactured by JSR, acrylic latex, commodity Name: TDR202A) 5.0 parts by mass

[Manufacture of battery separators]
The obtained coating liquid (1) was applied to one side of the nonwoven fabric substrate (1) by a gravure coating method. The coating process was stable, and a battery separator having a thickness of 25 μm was obtained without problems.

(Example 2)
[Manufacture of nonwoven fabric substrate]
The fiber was dispersed in water with the following configuration.
Stretched polyethylene terephthalate (PET) short fibers (fineness 0.1 dt, fiber length 3 mm) 60.0 parts by mass Unstretched PET short fibers (fineness 0.2 dt, fiber length 4 mm) 40.0 parts by weight Product name: Alcox (registered trademark) R-400) 0.1 part by mass

This was rolled up with a circular net to produce a web having a basis weight of 10 g / m ² and heat calendered at 220 ° C. to a thickness of 15 μm.

Next, 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, with a dry mass of 0.3 g / m ^2. The nonwoven fabric base material (2) was obtained by impregnating so as to cover the fibers.

[Manufacture of coating liquid containing alumina material]
Boehmite (manufactured by Daimei Chemicals, trade name: C20) 80.0 parts by mass Pure water 100.0 parts by mass Acetic acid 0.8 parts by mass The above mixture was dispersed with a homogenizer to obtain dispersion (2).

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

Dispersion (2) 180.0 parts by mass 0.6 mass% carboxymethyl cellulose aqueous solution (manufactured by Nippon Paper Chemicals, trade name: MAC500LC) 100.0 parts by mass 40% by mass binder dispersion (manufactured by JSR, acrylic latex, commodity Name: TDR202A) 5.0 parts by mass

[Manufacture of battery separators]
The obtained coating liquid (2) was applied to one side of the nonwoven fabric substrate (2) by a gravure coating method. The coating process was stable, and a battery separator having a thickness of 23 μm was obtained without problems.

(Comparative Example 1)
The coating liquid (1) was applied in the same manner without coating with a crosslinked cationic polymer during the production of the nonwoven fabric substrate (1) in Example 1. At the time of coating, the coating liquid oozed out to the back surface, and alumina-based material accumulated on the roll, so that continuous coating could not be performed.

(Comparative Example 2)
During the production of the nonwoven fabric substrate (2) in Example 2, chitosan (manufactured by Koyo Chemical Co., Ltd., trade name: Koyo Chitosan SK-200) as a cationic polymer was impregnated so as to have a dry mass of 0.3 g / m ^2. Then, the fibers were coated to obtain a comparative nonwoven fabric substrate (2). Next, the coating liquid (2) was applied by the same method. A good coated surface was obtained at the initial stage of coating. However, the coating solution gradually gelled, causing a lot of streaks on the coated surface, making it difficult to apply continuously for a long time.

  As described above, in the battery separator composed of the porous membrane layer containing the alumina-based material and the nonwoven fabric base material, the nonwoven fabric base material is coated with the crosslinked cationic polymer. It was found that the separator can be manufactured stably.

  The battery separator of the present invention can be used as a separator for a lithium battery or a separator for a capacitor.

Claims (1)

  A battery separator comprising a porous membrane layer containing an alumina material and a nonwoven fabric substrate, wherein the nonwoven fabric substrate is coated with a crosslinked cationic polymer. .