JP6340826B2 - Secondary battery porous membrane slurry, manufacturing method, secondary battery porous membrane, and secondary battery - Google Patents

Description

  The present invention relates to a slurry for a secondary battery porous film, a method for producing a slurry for a secondary battery porous film, a porous film for a secondary battery, and a secondary battery.

  Secondary batteries have been widely used in recent years as power sources for portable devices. In particular, lithium ion secondary batteries have characteristics such as being small and light, having high energy density, and being capable of repeated charge and discharge, and are expected to expand demand. Lithium ion secondary batteries are used in devices such as mobile phones and notebook personal computers, taking advantage of their high energy density. Secondary batteries are required to further improve performance in order to improve the performance of the devices used. For example, it is required to improve performance such as the ability to maintain capacity (high temperature cycle characteristics) even when charging and discharging are repeated in a high temperature environment.

  In secondary batteries, a separator is provided between a positive electrode and a negative electrode in order to improve performance. As a separator, a porous film obtained by applying a slurry layer containing non-conductive particles and a polymer to a substrate to form a layer and drying the layer is known. As the slurry for forming a porous film, a so-called aqueous slurry prepared using water as a solvent for reducing the environmental load is becoming widespread. Moreover, as a polymer as a component of the slurry for forming a porous film, for example, it is known to use a polymer of (meth) acrylic acid and (meth) acrylic acid ester (Patent Document 1).

International Publication No. WO2013 / 100023

  In order to improve the performance of the battery, the porous film is required to have sufficient strength in terms of peel strength and heat shrinkage resistance. As the polymer contained in the slurry for forming such a porous film, a polymer having a large molecular weight is preferable. However, since a slurry containing such a polymer having a high molecular weight usually has a high viscosity, it has fluid properties that are not suitable for application to a substrate. Therefore, a porous film obtained by applying such a slurry is applied to a slurry. There is a problem that it may have a defect due to the unevenness of. Specifically, after applying the slurry to the substrate, a phenomenon called leveling in which unevenness in thickness is averaged may occur, but when the viscosity exceeds a level suitable for application, such leveling does not occur, There arises a problem that uneven coating thickness is manifested in the film. In addition, when such a polymer is used in an aqueous slurry, there is also a problem that moisture tends to remain in the porous film because of the high hydrophilicity of the polymer.

  Therefore, the object of the present invention is that uniform coating is possible, the strength in terms of peel strength and heat shrinkage can be sufficiently expressed, and the amount of residual water when a porous film is formed is small, and coating is easy. An object of the present invention is to provide a slurry for a porous membrane of a secondary battery, which can be produced at the same time and can produce a porous membrane that can function as a separator that can improve battery performance such as high-temperature cycle characteristics.

  Further objects of the present invention are that it can be produced with a uniform thickness, has sufficient strength in terms of peel strength, heat shrinkage resistance, has a small amount of residual moisture, can be easily produced, and has high temperature cycle characteristics, etc. It is an object of the present invention to provide a secondary battery porous membrane that can function as a separator capable of improving the performance of the battery; and a secondary battery including such a porous membrane.

  The inventor has studied to achieve the above object. And this inventor can reduce a residual water content by employ | adopting specific polycarboxylic acid as a polymer added to the aqueous slurry for porous membranes, and making pH of a slurry into a predetermined range. In addition, it is possible to give the slurry physical properties that can be applied easily and cause good leveling, and can impart peel strength and heat shrinkage resistance to the porous film, resulting in improved battery performance such as high-temperature cycle characteristics. As a result, the present invention was completed. That is, according to the present invention, the following [1] to [7] are provided.

[1] A slurry for a secondary battery porous film comprising non-conductive particles and a polycarboxylic acid (A),
The polycarboxylic acid (A) contains a carboxylic acid group-containing monomer unit in an amount of 20% by weight to 50% by weight and has a weight average molecular weight of 50,000 to 300,000,
A part of the carboxylic acid group in the carboxylic acid group-containing monomer unit of the polycarboxylic acid (A) is an ammonium salt or an alkali metal salt,
A slurry for a secondary battery porous membrane, wherein the slurry has a pH of 6.0 to 8.0.
[2] The polycarboxylic acid (A) further contains a crosslinkable monomer unit,
The slurry for secondary battery porous membrane according to [1], wherein the ratio of the crosslinkable monomer unit in the polycarboxylic acid (A) is 0.1 wt% or more and 5 wt% or less.
[3] Further, polycarboxylic acid (B) is included,
The polycarboxylic acid (B) has a weight average molecular weight of 2,000 or more and 30,000 or less, and the polycarboxylic acid (B) has a carboxylic acid group, and a part of the carboxylic acid group is an ammonium salt. Or an alkali metal salt,
The slurry for a secondary battery porous membrane according to [1] or [2].
[4] The slurry for a secondary battery porous film according to any one of [1] to [3], wherein the viscosity measured with a B-type viscometer at 25 ° C. is 5 to 200 mPa · s.
[5] Step (I) of preparing a non-conductive particle dispersion containing non-conductive particles;
A process for producing a slurry for a secondary battery porous membrane comprising the step (II) of mixing the non-conductive particle dispersion and the polycarboxylic acid (A),
In the step (I),
The pH of the non-conductive particle dispersion is more than 6.0 and not more than 12.0,
In the step (II),
The polycarboxylic acid (A) contains a carboxylic acid group-containing monomer unit in an amount of 20% by weight to 50% by weight and has a weight average molecular weight of 50,000 to 300,000,
A part of the carboxylic acid group in the carboxylic acid group-containing monomer unit of the polycarboxylic acid (A) is an ammonium salt or an alkali metal salt,
The manufacturing method of the slurry for secondary battery porous films whose pH of the said slurry obtained is 6.0 or more and 8.0 or less.
[6] A porous membrane for a secondary battery, which is formed by forming a layer of the slurry for a secondary battery porous membrane according to any one of [1] to [4] and drying the layer.
[7] A secondary battery comprising the porous membrane for a secondary battery according to [6].

  When the slurry for a secondary battery porous membrane of the present invention is used, uniform coating is possible, and sufficient strength in terms of peel strength and heat shrinkage resistance can be expressed. The porous membrane of the present invention can be produced, and can be easily applied, and can function as a separator that can improve battery performance such as high-temperature cycle characteristics. A secondary battery can be manufactured.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the present application, the term “(meth) acryl” means either or both of acrylic and methacrylic. For example, (meth) acrylic acid means acrylic acid, methacrylic acid or a combination thereof. The term “(meth) acryloyl” means acryloyl, methacryloyl or a combination thereof.

[1. (Slurry for porous film)
The slurry for secondary battery porous membrane of the present invention (hereinafter sometimes referred to as “slurry for porous membrane”) includes non-conductive particles and a specific water-soluble polymer. The slurry for a porous membrane usually further contains water.

[1.1. Non-conductive particles
It is desired that the nonconductive particles used in the present invention exist stably under the usage environment of the secondary battery and are also stable electrochemically. For example, various non-conductive inorganic particles and organic particles can be used.

  As inorganic particles, oxide particles such as iron oxide, silicon oxide, aluminum oxide, magnesium oxide, and titanium oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; barium sulfate, Insoluble ion crystal particles such as calcium fluoride and barium fluoride are used. These particles may be subjected to element substitution, surface treatment, or solid solution as necessary, and may be used alone or in combination of two or more. Among these, aluminum oxide and barium sulfate are preferable from the viewpoint of stability in the electrolytic solution and potential stability, and barium sulfate is more preferable from the viewpoint of low water absorption and excellent battery characteristics.

The organic particles are usually polymer particles having no glass transition temperature or polymer particles having a high glass transition temperature. When the polymer has a glass transition temperature, the glass transition temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, particularly preferably 250 ° C. or higher, and usually 500 ° C. or lower. Examples of the organic particles include particles made of various polymers such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer forming the particles can be used as a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, and the like. The particles may be composed of two or more kinds of polymers. In addition, by electrically treating the surface of conductive metal such as carbon black, graphite, SnO ₂ , ITO, metal powder, and fine powder of conductive compounds and oxides with a non-conductive substance, electrical insulation can be achieved. It can also be used. These non-conductive particles may be used in combination of two or more.

  The average particle size (volume average D50 average particle size) of the non-conductive particles used in the present invention is preferably 5 nm or more and 10 μm or less, more preferably 10 nm or more and 5 μm or less. By controlling the average particle diameter of the non-conductive particles within the above range, it becomes easy to obtain a film having a predetermined thickness that is uniform in controlling the dispersion state. It is particularly preferable that the average particle diameter of the non-conductive particles be in the range of 50 nm or more and 2 μm or less because the dispersion, the ease of coating, and the controllability of voids are excellent.

Further, the BET specific surface area of these particles is preferably 0.5 to ²⁰⁰ m ² / g from the viewpoint of suppressing the aggregation of the particles and optimizing the fluidity of the slurry. More preferably, it is -50m < ² > / g.

  The shape of the non-conductive particles used in the present invention is not particularly limited, such as a spherical shape, a needle shape, a rod shape, a conical shape, a plate shape, and a scale shape, but a spherical shape, a needle shape, a conical shape, and the like are preferable. Porous particles can also be used.

[1.2. Polycarboxylic acid (A)]
The slurry for a porous membrane of the present invention contains a polycarboxylic acid (A). The polycarboxylic acid (A) binds the nonconductive particles by interposing between the nonconductive particles in the porous film, and between the nonconductive particles and the separator substrate or the electrode plate. By intervening, the effect of binding the porous film and the separator substrate or the electrode plate can be achieved.

[1.2.1. Polycarboxylic acid (A): carboxylic acid group-containing monomer unit]
The polycarboxylic acid (A) includes a carboxylic acid group-containing monomer unit. The term “carboxylic acid group-containing monomer unit” refers to a structural unit having a structure formed by polymerizing a carboxylic acid group-containing monomer.

  The carboxylic acid group-containing monomer may be a compound having a —COOH group (carboxylic acid group) and a group capable of undergoing a polymerization reaction. For example, a monomer capable of generating a carboxylic acid group by hydrolysis can also be used as the carboxylic acid group-containing monomer. Specific examples of such carboxylic acid group-containing monomers include acid anhydrides that can generate carboxylic acid groups by hydrolysis.

  Examples of the carboxylic acid group-containing monomer include the following ethylenically unsaturated carboxylic acid monomers. Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid and the like can be mentioned. Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; diphenyl maleate, nonyl maleate, Examples thereof include maleic acid esters such as decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate. Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable because the dispersibility of the polycarboxylic acid (A) in water can be further improved. Further, one type of ethylenically unsaturated carboxylic acid monomer may be used alone, or two or more types may be used in combination at any ratio.

  The proportion of the carboxylic acid group-containing monomer unit in the polycarboxylic acid (A) is 20% by weight or more, preferably 25% by weight or more, more preferably 30% by weight or more, while 50% by weight or less, preferably 45%. % By weight or less, more preferably 40% by weight or less. By setting the ratio of the carboxylic acid group-containing monomer unit in the polycarboxylic acid (A) to be the above lower limit or more, the desired water solubility of the polycarboxylic acid (A) can be obtained, and entanglement of polymer chains is formed. The heat shrinkage resistance can be improved. By setting the ratio of the carboxylic acid group-containing monomer unit in the polycarboxylic acid (A) to be equal to or less than the above upper limit, the amount of water adsorbed on the porous film can be kept in an appropriate small range.

[1.2.2. Polycarboxylic acid (A): crosslinkable monomer unit]
The polycarboxylic acid (A) preferably contains a crosslinkable monomer unit. A crosslinkable monomer unit is a structural unit having a structure obtained by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization. By including a crosslinkable monomer unit, the degree of swelling of the polycarboxylic acid (A) into the electrolyte can be kept at an appropriate low value, and the lithium ion permeability of the porous membrane can be improved.

  Examples of the crosslinkable monomer as the material of the polycarboxylic acid (A) include monomers having two or more reactive groups per molecule. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

  Examples of the thermally crosslinkable group contained in the monofunctional monomer include an N-methylolamide group, an epoxy group, an oxetanyl group, an oxazoline group, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, glycidyl Unsaturated carboxylic acids such as -4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Glycidyl ester compounds; and the like.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and And 2-isopropenyl-5-ethyl-2-oxazoline.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Examples include ethers, allyls or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, and divinylbenzene.

Among these, as the crosslinkable monomer, N-methylol acrylamide, allyl methacrylate, ethylene dimethacrylate, allyl glycidyl ether, glycidyl methacrylate, and ethylene glycol dimethacrylate are preferable, and N-methylol acrylamide, allyl methacrylate, ethylene dimethacrylate, Allyl glycidyl ether and glycidyl methacrylate are more preferred.
Moreover, a crosslinking | crosslinked monomer and a crosslinking | crosslinked monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the crosslinkable monomer unit in the polycarboxylic acid (A) is preferably 0.1% by weight or more, and preferably 5% by weight or less. When the ratio of the crosslinkable monomer unit in the polycarboxylic acid (A) is not less than the above lower limit, the degree of swelling of the polycarboxylic acid (A) in the electrolyte solution is kept at an appropriate low value, and the lithium ion of the porous film The permeability can be improved. When the ratio of the crosslinkable monomer unit in the polycarboxylic acid (A) is not more than the above upper limit, the molecular weight can be prevented from becoming excessively high, and the slurry viscosity can be kept at a reasonably low value suitable for coating. .

[1.2.3. Polycarboxylic acid (A): Reactive surfactant unit]
The polycarboxylic acid (A) may contain a reactive surfactant unit. The reactive surfactant unit is a structural unit having a structure formed by polymerizing a reactive surfactant. The reactive surfactant unit forms part of the molecule of the polycarboxylic acid (A) and can function as a surfactant.

  The reactive surfactant is a monomer having a polymerizable group that can be copolymerized with another monomer and having a surface active group (hydrophilic group and hydrophobic group). Usually, the reactive surfactant has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group that the reactive surfactant has include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group. One kind of the polymerizable unsaturated group may be used alone, or two or more kinds may be used in combination at any ratio.

  The reactive surfactant usually has a hydrophilic group as a portion that exhibits hydrophilicity. Reactive surfactants are classified into anionic, cationic and nonionic surfactants depending on the type of hydrophilic group.

Examples of the anionic hydrophilic group include —SO ₃ M, —COOM, and —PO (OM) ₂ . Here, M represents a hydrogen atom or a cation. Examples of cations include alkali metal ions such as lithium, sodium and potassium; alkaline earth metal ions such as calcium and magnesium; ammonium ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; and And ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.
Examples of cationic hydrophilic groups include primary amine salts such as —NH ₂ HX, secondary amine salts such as —NHCH ₃ HX, tertiary amine salts such as —N (CH ₃ ) ₂ HX, A quaternary amine salt such as —N ⁺ (CH ₃ ) ₃ X ^— ; Here, X represents a halogen group.
-OH is mentioned as an example of a nonionic hydrophilic group.

  Examples of suitable reactive surfactants include compounds represented by the following formula (II).

In the formula (II), R represents a divalent linking group. Examples of R include -Si-O- group, methylene group and phenylene group.
In the formula (II), R ³ represents a hydrophilic group. An example of R ³ includes —SO ₃ NH ₄ .
In the formula (II), n represents an integer of 1 to 100.

Another example of a suitable reactive surfactant has a structural unit having a structure formed by polymerizing ethylene oxide and a structural unit having a structure formed by polymerizing butylene oxide. Examples thereof include compounds having an alkenyl group having a terminal double bond and —SO ₃ NH ₄ (for example, trade names “Latemul PD-104” and “Latemul PD-105”, manufactured by Kao Corporation).
As the reactive surfactant and the reactive surfactant unit, one type may be used alone, or two or more types may be used in combination at any ratio.

  The ratio of the reactive surfactant unit in the polycarboxylic acid (A) is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and particularly preferably 0.5% by weight or more. Preferably it is 5 weight% or less, More preferably, it is 4 weight% or less, Most preferably, it is 2 weight% or less. By making the ratio of the reactive surfactant unit in the polycarboxylic acid (A) equal to or higher than the lower limit, the dispersibility of the slurry for the porous membrane can be improved. By setting the ratio of the reactive surfactant unit in the polycarboxylic acid (A) to the upper limit or less, the durability of the porous film can be improved.

[1.2.4. Polycarboxylic acid (A): other units]
The polycarboxylic acid (A) may contain a (meth) acrylic acid ester monomer unit. The (meth) acrylic acid ester monomer unit refers to a structural unit having a structure formed by polymerizing (meth) acrylic acid ester.

Examples of (meth) acrylic acid esters include alkyl (meth) acrylates, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, Alkyl acrylates such as heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl Methacrylate, t-butyl methacrylate, pentyl methacrylate, hex Methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, and alkyl methacrylates such as stearyl methacrylate. Moreover, these may use only 1 type and may be used combining two or more types by arbitrary ratios.
Among them, the alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl (meth) acrylate having an alkyl group having 1 to 6 carbon atoms. More preferably.
In a particularly preferred embodiment, the polycarboxylic acid (A) is an alkyl (meth) acrylate unit having an alkyl (meth) acrylate unit (U1) having an alkyl group having 1 to 3 carbon atoms and an alkyl group having 4 to 6 carbon atoms. And an alkyl (meth) acrylate unit (U2). Thus, combining the unit (U1) and the unit (U2) makes it possible to highly balance slurry coating properties and porous membrane strength. In particular, it is preferable to combine ethyl (meth) acrylate and butyl (meth) acrylate as monomers that give units (U1) and units (U2).

  In this case, the weight ratio U1 / U2 between the units (U1) and units (U2) in the polycarboxylic acid is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 2.5 or more. On the other hand, it is preferably 30.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less.

The proportion of the (meth) acrylic acid ester monomer unit in the polycarboxylic acid (A) is preferably 30% by weight or more, more preferably 40% by weight or more, particularly preferably 45% by weight or more, and preferably It is 80% by weight or less, more preferably 75% by weight or less, and particularly preferably 70% by weight or less. By making the amount of the (meth) acrylic acid ester monomer unit in the polycarboxylic acid (A) equal to or higher than the lower limit of the above range, the binding property between the porous membrane and the separator substrate or the electrode plate can be increased. it can. Moreover, the softness | flexibility of a porous film can be improved by making it into an upper limit or less.
Furthermore, polycarboxylic acid (A) can contain arbitrary structural units in addition to the structural units described above. Examples of arbitrary structural units that can be contained in the polycarboxylic acid (A) are the same examples as those exemplified later as structural units that can be contained in the particulate binder, and those other than the monomer units described above Is mentioned. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The polycarboxylic acid (A) may contain a structural unit other than the units described above as long as the effects of the present invention are not significantly impaired. Such a structural unit may be a structural unit formed by polymerizing a monomer copolymerizable with the above-described monomer. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. For example, the polycarboxylic acid (A) can contain a fluorine-containing (meth) acrylic acid ester monomer unit. However, from the viewpoint of satisfactorily applying the porous film slurry to the substrate, the proportion of the fluorine-containing (meth) acrylic acid ester monomer unit in the polycarboxylic acid (A) is less than 1% by weight. Is preferred.

[1.2.5. Properties of polycarboxylic acid (A)]
The weight average molecular weight of the polycarboxylic acid (A) is preferably 50,000 or more, more preferably 75,000 or more, even more preferably 100,000 or more, while preferably 300,000 or less, more preferably 200. Or less, more preferably 150,000 or less. By setting the weight average molecular weight of the polycarboxylic acid (A) to the lower limit or more, the viscosity of the slurry for the porous film is kept at a reasonably high value, and coating unevenness is prevented from occurring due to dripping of the slurry during coating. Can do. By keeping the weight average molecular weight of the polycarboxylic acid (A) below the upper limit, the viscosity of the slurry for the porous membrane is kept at a moderately low value, and the layer of the slurry for the porous membrane is leveled after the application of the slurry for the porous membrane. As a result, undesired stripes formed by coating can be reduced. The molecular weight of the polycarboxylic acid (A) may be set to a desired value by appropriately adjusting the ratio of the crosslinkable monomer and other monomers and the polymerization conditions (addition amount of the molecular weight modifier, etc.). it can.

In the slurry for a secondary battery porous membrane of the present invention, the polycarboxylic acid (A) has a part of its carboxylic acid group as an ammonium salt or an alkali metal salt. That is, in the slurry for porous membranes, the polycarboxylic acid (A) and ammonium ions and / or alkali metals coexist. Thereby, physical properties, such as pH and a viscosity, of a slurry composition can be made into an appropriate range.
In addition, when a part of the carboxylic acid group of the polycarboxylic acid (A) is an ammonium salt, the polycarboxylic acid (A) becomes water-insoluble because it volatilizes as ammonia during drying. As a result, even if a coating agent such as an adhesive containing an aqueous medium is applied on the formed porous film, the porous film is not attacked and the resistance of the polycarboxylic acid (A) to the electrolytic solution is also improved. In order to improve, the intensity | strength in the electrolyte solution of a porous film comes to improve.

[1.2.6. Content ratio of polycarboxylic acid (A)]
The content ratio of the polycarboxylic acid (A) in the slurry for the porous membrane of the present invention is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, further with respect to 100 parts by weight of the non-conductive particles. More preferably it is 0.5 parts by weight or more, while it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 8 parts by weight or less. By making the content rate of polycarboxylic acid (A) more than the said minimum, it can prevent that a slurry droops at the time of application | coating of the slurry for porous films, and a nonuniformity arises in application | coating. Further, the strength of the obtained porous film can be improved, and in particular, the heat shrinkage resistance can be improved. By setting the content ratio of the polycarboxylic acid (A) to the above upper limit or less, the viscosity of the slurry for the porous membrane can be kept at a moderately low value. As a result, the slurry for the porous membrane is applied after the application of the slurry for the porous membrane. Are layered, thereby reducing unwanted streaks formed by coating.

[1.2.7. Method for producing polycarboxylic acid (A)]
The polycarboxylic acid (A) can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. At this time, the ratio of each monomer in the monomer composition is usually the same as the ratio of the structural units in the polycarboxylic acid (A).

  As the aqueous solvent, a solvent capable of dispersing the polycarboxylic acid (A) can be used. Usually, the boiling point at normal pressure is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and preferably 350 ° C. or lower, more preferably 300 ° C. or lower. Examples of the aqueous solvent include those similar to those used for the production of the particulate binder. Among these, water is particularly preferable from the viewpoint that it is not flammable and a polymer dispersion can be easily obtained. Further, water may be used as the main solvent, and an aqueous solvent other than water may be mixed and used within a range in which the dispersion state of the polymer can be ensured.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. The reaction mode of the polymerization may be any of ionic polymerization, radical polymerization, living radical polymerization and the like. It is easy to obtain a high molecular weight body, and since the polymer is obtained in a state of being dispersed in water as it is, redispersion treatment is unnecessary, and it can be used for production of a slurry for a porous membrane as it is. From the viewpoint, the emulsion polymerization method is particularly preferable. Emulsion polymerization can be performed according to a conventional method.

Commonly used additives may be used as the emulsifier, dispersant, polymerization initiator, polymerization aid and the like used in the polymerization. The amount of these additives used may also be a commonly used amount. The polymerization conditions can be appropriately adjusted according to the polymerization method and the type of polymerization initiator.
In particular, the molecular weight of the polycarboxylic acid (A) can be adjusted to a desired range by adding a molecular weight modifier to the reaction system during the polymerization. Examples of such molecular weight modifiers include t-dodecyl mercaptan, α-methylstyrene dimer, terpinolene, allyl alcohol, allylamine, (meth) allyl sulfonic acid soda, and potassium (meth) allyl sulfonate.

[1.3. Polycarboxylic acid (B)]
The slurry for a porous membrane of the present invention preferably contains a polycarboxylic acid (B) in addition to the polycarboxylic acid (A).

The polycarboxylic acid (B) is a polymer having a carboxylic acid group, and has a weight average molecular weight of 2,000 or more and 30,000 or less. The weight average molecular weight of the polycarboxylic acid (B) is preferably 5,000 or more, more preferably 10,000 or more, and preferably 25,000 or less, more preferably 20,000 or less. In the slurry for a secondary battery porous membrane of the present invention, the polycarboxylic acid (B) has a part of its carboxylic acid group as an ammonium salt or an alkali metal salt. That is, in the porous membrane slurry, the polycarboxylic acid (B) and ammonium ions and / or alkali metals coexist. By containing such a low molecular weight polycarboxylic acid (B) in addition to the polycarboxylic acid (A), the non-conductive particles can be dispersed well in the slurry, and a good slurry can be applied. And the uniformity of the porous membrane can be improved.
Moreover, when the polycarboxylic acid (B) is adsorbed on the surface of the non-conductive particles, the binding force between the polycarboxylic acid (A) and the non-conductive particles is improved, and the strength of the porous film can be increased.
Moreover, the effect can be heightened more by mixing a nonelectroconductive particle and polycarboxylic acid (B) previously.

  Examples of the monomer unit constituting the polycarboxylic acid (B) and the monomer serving as the material for the polycarboxylic acid (B) include the same examples as in the polycarboxylic acid (A). The molecular weight of the polycarboxylic acid (B) is adjusted as appropriate in the preparation of the polycarboxylic acid (B), the ratio of the crosslinkable monomer and other monomers, and the polymerization conditions (addition amount of molecular weight modifier, etc.). Thus, a desired value can be obtained.

The content ratio of the polycarboxylic acid (B) in the slurry for the porous membrane of the present invention is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, further with respect to 100 parts by weight of the non-conductive particles. More preferably it is 0.2 parts by weight or more, while preferably 5.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 1.0 parts by weight or less. By making the content rate of polycarboxylic acid (B) more than the said minimum, a nonelectroconductive particle can be favorably disperse | distributed within a slurry and application | coating of a favorable external appearance can be achieved. By making the content rate of polycarboxylic acid (B) below the said upper limit, the moisture content which adsorb | sucks to a porous film can be kept in a suitable small range.
In the present invention, polycarboxylic acid (B) is preferably used, but a dispersant such as polysulfonic acid, polystyrene sulfonic acid, naphthalene sulfonic acid formalin condensate, and polyethylene glycol can also be used. The content ratio of the dispersant in the slurry for the porous membrane of the present invention is the same as the content ratio of the polycarboxylic acid (B).

[1.4. (Particulate binder)
The slurry for a porous membrane of the present invention may contain a particulate binder in addition to the polycarboxylic acid (polycarboxylic acid (A) and polycarboxylic acid (B) if contained). The particulate binder can be polymer particles. When the slurry for a porous membrane contains a particulate binder, the following advantages are usually obtained. That is, the binding property of the porous membrane is improved, and the strength against mechanical force applied to the separator or electrode provided with the porous membrane for a secondary battery of the present invention at the time of handling such as winding and transportation can be improved. . Further, since the particulate binder has a particulate shape, the particulate binder can bind to the non-conductive particles with a point instead of a surface. For this reason, since the hole in a porous film can be enlarged, the internal resistance of a secondary battery can be made small.

  Usually, the particulate binder is insoluble in water, and at least does not dissolve in the slurry for the porous membrane, and may exist in a dispersed state in a particle shape. In the porous membrane, the particulate binder can be present while maintaining part or all of the particle shape. Such a particulate polymer can be obtained by appropriately adjusting the proportion of the monomer units as constituent elements.

  The particulate binder can include an acid group-containing monomer unit. The acid group-containing monomer unit in the particulate binder refers to a structural unit having a structure formed by polymerizing an acid group-containing monomer. Moreover, an acid group containing monomer shows the monomer containing an acid group. Therefore, the particulate binder having an acid group-containing monomer unit contains an acid group.

Examples of acid groups that can be included in the particulate binder include: —COOH group (carboxylic acid group); —SO ₃ H group (sulfonic acid group); —PO ₃ H ₂ group and —PO (OH) (OR) Phosphonic acid groups such as groups (R represents a hydrocarbon group); and combinations thereof. Accordingly, examples of the acid group-containing monomer include monomers having these acid groups. In addition, for example, a monomer capable of generating the acid group by hydrolysis is also exemplified as the acid group-containing monomer. Specific examples of such acid group-containing monomers include acid anhydrides that can generate carboxylic acid groups by hydrolysis.

  Examples of the monomer having a carboxylic acid group (carboxylic acid monomer) include monocarboxylic acid, dicarboxylic acid, dicarboxylic acid anhydride, and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Among these, monocarboxylic acid is preferable, and acrylic acid and methacrylic acid are more preferable.

  Examples of monomers having a sulfonic acid group (sulfonic acid monomer) include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-sulfonic acid Examples include ethyl, 2-acrylamido-2-methylpropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and 2- (N-acryloyl) amino-2-methyl-1,3-propane-disulfonic acid. Among these, 2-acrylamido-2-methylpropanesulfonic acid is preferable.

  Examples of the monomer having a phosphonic acid group (phosphonic acid monomer) include 2- (meth) acryloyloxyethyl phosphate, 2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (Meth) acryloyloxyethyl is mentioned.

Moreover, you may use the salt of the monomer mentioned above as an acid group containing monomer. Examples of such salts include sodium salts of styrene sulfonic acid such as p-styrene sulfonic acid.
Moreover, an acid group containing monomer and an acid group containing monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The acid group may be introduced by polymerization of the acid group-containing monomer as described above, but after polymerizing the particulate binder having no acid group, the functional group in the particulate binder is You may introduce | transduce by substituting a part or all to an acid group. The repeating unit in the particulate binder having an acid group thus introduced is also included in the acid group-containing monomer unit.

  The ratio of the acid group-containing monomer unit in the particulate binder is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably It is 50% by weight or less, more preferably 20% by weight or less, and particularly preferably 10% by weight or less. By setting the ratio of the acid group-containing monomer unit in the particulate binder to be not less than the lower limit of the above range, the binding property between the porous membrane and the separator substrate or the electrode plate can be effectively enhanced. Moreover, durability of a porous film can be improved by making it into an upper limit or less.

  The particulate binder can include carboxylic acid primary amide monomer units. A carboxylic acid primary amide monomer unit means a structural unit having a structure formed by polymerizing a carboxylic acid primary amide monomer. Further, the carboxylic acid primary amide monomer means a compound having a structure formed by condensation of carboxylic acid and primary amide. In the secondary battery including the porous film formed using the slurry for the porous film of the present invention, the particulate binder contains the carboxylic acid primary amide monomer unit at a predetermined ratio, thereby generating gas. Can be reduced, thereby improving battery performance.

  Examples of the carboxylic acid primary amide monomer include unsaturated carboxylic acid primary amide compounds such as (meth) acrylamide, α-chloroacrylamide, crotonic acid amide, maleic acid diamide, and fumaric acid diamide. Of these, (meth) acrylamide is preferred. As the carboxylic acid primary amide monomer and the carboxylic acid primary amide monomer unit, one type may be used alone, or two or more types may be used in combination at any ratio.

  The ratio of the carboxylic acid primary amide monomer unit in the particulate binder is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1.0% by weight or more, and usually 10%. % By weight or less, preferably 7% by weight or less, more preferably 5% by weight or less. By setting the proportion of the carboxylic acid primary amide monomer unit in the particulate binder to be equal to or higher than the lower limit of the above range, halide ions in the electrolytic solution can be effectively captured by the particulate binder. Moreover, the rate characteristic of a secondary battery can be improved by making it below an upper limit.

  The particulate binder can contain a crosslinkable monomer unit. Here, the crosslinkable monomer unit is a structural unit having a structure obtained by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization. By including a crosslinkable monomer unit, the particulate binder can be cross-linked, so that the strength and stability of the porous membrane can be increased. Thereby, it is possible to stably exhibit the action of the particulate binder. In addition, since the degree of swelling of the particulate binder caused by the electrolytic solution can be prevented from becoming excessively high, normally the output characteristics of the secondary battery can be improved.

  Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

  Examples of the thermally crosslinkable group contained in the monofunctional monomer include an N-methylolamide group, an epoxy group, an oxetanyl group, an oxazoline group, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, glycidyl Unsaturated carboxylic acids such as -4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Glycidyl ester compounds; and the like.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and And 2-isopropenyl-5-ethyl-2-oxazoline.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Examples include ethers, allyls or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, and divinylbenzene.

Among these, as the crosslinkable monomer, N-methylol acrylamide, allyl methacrylate, ethylene dimethacrylate, allyl glycidyl ether, glycidyl methacrylate, and ethylene glycol dimethacrylate are preferable, and N-methylol acrylamide, allyl methacrylate, ethylene dimethacrylate, Allyl glycidyl ether and glycidyl methacrylate are more preferred.
Moreover, a crosslinking | crosslinked monomer and a crosslinking | crosslinked monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the crosslinkable monomer unit in the particulate binder is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, particularly preferably 1.0% by weight or more, preferably 5%. 0.0% by weight or less, more preferably 4.0% by weight or less, and particularly preferably 3.0% by weight or less. By making the ratio of the crosslinkable monomer unit in the particulate binder equal to or higher than the lower limit of the above range, the mechanical strength of the particulate binder can be increased, so that the porous membrane and the separator substrate or electrode plate The binding property can be increased. Moreover, durability of a porous film can be improved by making it into an upper limit or less.

  The particulate coalescence may contain (meth) acrylic acid ester monomer units. The (meth) acrylic acid ester monomer unit is a structural unit having a structure formed by polymerizing a (meth) acrylic acid ester monomer. Since the (meth) acrylic acid ester monomer unit has high strength, it is possible to stabilize the molecules of the particulate binder.

  Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, Acrylic acid alkyl esters such as 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t -Butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl Methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. As for the (meth) acrylic acid ester monomer and the (meth) acrylic acid ester monomer unit, one type may be used alone, or two or more types may be used in combination at any ratio.

  The proportion of the (meth) acrylic acid ester monomer unit in the particulate binder is preferably 50% by weight or more, more preferably 55% by weight or more, particularly preferably 58% by weight or more, and preferably 98% by weight. Hereinafter, it is more preferably 97% by weight or less, particularly preferably 96% by weight or less. By making the ratio of the (meth) acrylic acid ester monomer unit in the particulate binder equal to or higher than the lower limit of the above range, the binding property of the porous membrane to the separator substrate or electrode plate can be increased. . Moreover, the softness | flexibility of a porous film can be improved by making it into an upper limit or less.

  Furthermore, the particulate binder can contain an arbitrary structural unit in addition to the structural units described above. Examples of an arbitrary structural unit that the particulate binder may contain include a structural unit having a structure formed by polymerizing the following monomers. That is, aliphatic conjugated diene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene; styrene Aromatic vinyl monomers such as chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl benzene; Α, β-unsaturated nitrile compound monomers such as methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile; olefin monomers such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride ; Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc. Nyl ester monomers; Vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; Vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; and N -Structural units having a structure formed by polymerizing one or more of a heterocyclic compound containing a heterocyclic compound such as vinylpyrrolidone, vinylpyridine, and vinylimidazole. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, a particulate binder may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The weight average molecular weight of the polymer constituting the particulate binder is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less. is there. By keeping the weight average molecular weight of the polymer constituting the particulate binder within the above range, the strength of the porous film and the dispersibility of the non-conductive particles can be easily improved. Here, the weight average molecular weight of the polymer constituting the particulate binder can be determined by gel permeation chromatography (GPC) as a value in terms of polystyrene using tetrahydrofuran as a developing solvent.

  The glass transition temperature of the particulate binder is preferably −75 ° C. or higher, more preferably −55 ° C. or higher, particularly preferably −45 ° C. or higher, preferably 40 ° C. or lower, more preferably 30 ° C. or lower. More preferably, it is 20 degrees C or less, Most preferably, it is 15 degrees C or less. By keeping the glass transition temperature of the particulate binder within the above range, the flexibility and winding properties of the separator and electrode provided with the porous membrane, and the binding property between the porous membrane and the separator substrate or the electrode plate, etc. The properties are highly balanced and suitable. The glass transition temperature of the particulate binder can be adjusted, for example, by combining various monomers.

  The volume average particle diameter D50 of the particulate binder is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, while preferably 1.0 μm or less, more preferably It is 0.8 μm or less, more preferably 0.5 μm or less. By keeping the volume average particle diameter of the particulate binder within the above range, the strength and flexibility of the porous film can be improved.

  The amount of the particulate binder in the slurry for a porous membrane of the present invention is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more with respect to 100 parts by weight of the non-conductive particles. More preferably it is 1 part by weight or more, while preferably it is 15 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less. By making the amount of the particulate binder equal to or higher than the lower limit, non-conductive particles and between non-conductive particles and the base material are improved, and problems such as powder falling from the porous film occur. Can be reduced. Moreover, it can suppress that a particulate-form binder block | closes the hole of a base material, and a Gurley value increases by making it below an upper limit.

  The particulate binder can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. The content ratio of each monomer in the monomer composition in the polymerization reaction is usually the same as the content ratio of the repeating unit in the desired particulate binder.

  As the aqueous solvent, a solvent in which the particulate binder can be dispersed in a particle state can be selected. An aqueous solvent having a boiling point at normal pressure of preferably 80 to 350 ° C, more preferably 100 to 300 ° C can be selected.

  Examples of aqueous solvents include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol tertiary Glycol ethers such as butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; 1,3-dioxolane, 1 , 4-dioxolane, ethers such as tetrahydrofuran; and the like. Among these, water is particularly preferable from the viewpoint that it is not flammable and a dispersion of particulate binder particles can be easily obtained. In addition, water may be used as the main solvent, and an aqueous solvent other than the above water may be mixed and used as long as the dispersed state of the particles of the particulate binder can be ensured.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. The reaction mode of the polymerization may be any of ionic polymerization, radical polymerization, living radical polymerization, and the like. It is easy to obtain a high molecular weight product, and since the polymer is obtained as it is dispersed in water, redispersion treatment is unnecessary, and it can be used for production of the slurry for a porous film of the present invention as it is. From the viewpoint of production efficiency, an emulsion polymerization method is particularly preferred. Emulsion polymerization can be performed according to a conventional method.

  Commonly used additives may be used as the emulsifier, dispersant, polymerization initiator, polymerization aid and the like used in the polymerization. The amount of these additives used may also be a commonly used amount. The polymerization conditions can be appropriately adjusted according to the polymerization method and the type of polymerization initiator.

[1.5. water〕
The slurry for porous membrane of the present invention usually contains water. Water functions as a medium, that is, a solvent or a dispersion medium in the slurry for the porous membrane. Usually, in the slurry for porous films, the nonconductive particles and the particulate binder are dispersed in water, and the polycarboxylic acid is dissolved in water.

  Further, as a medium, a medium other than water may be used in combination with water. Examples of media that can be used in combination with water include cycloaliphatic hydrocarbon compounds such as cyclopentane and cyclohexane; aromatic hydrocarbon compounds such as toluene and xylene; ketone compounds such as ethyl methyl ketone and cyclohexanone; ethyl acetate and acetic acid Ester compounds such as butyl, γ-butyrolactone, ε-caprolactone; nitrile compounds such as acetonitrile and propionitrile; ether compounds such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, and the like And alcohol compounds; amide compounds such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide; One of these may be used alone, or two or more of these may be used in combination at any ratio. The amount of medium other than water is preferably 5 parts by weight or less with respect to 100 parts by weight of water.

  The amount of the solvent in the porous membrane slurry is preferably set so that the solid content concentration of the porous membrane slurry is within a desired range. The solid content concentration of the specific slurry for the porous membrane is preferably 10% by weight or more, more preferably 15% by weight or more, still more preferably 20% by weight or more, preferably 80% by weight or less, more preferably 75%. % By weight or less, still more preferably 70% by weight or less, particularly preferably 65% by weight or less. Here, the solid content of the composition means a substance remaining after the composition is dried. By setting the solid content concentration to be equal to or higher than the lower limit, water can be easily removed during the production of the porous membrane, and the amount of water in the porous membrane can be reduced. By setting the solid content concentration to be equal to or lower than the above upper limit, good coating can be performed.

[1.6. Other optional ingredients]
The slurry for a porous membrane of the present invention can contain any component in addition to the components described above. As such optional components, those which do not exert an excessively unfavorable influence on the battery reaction can be used. Arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. For example, a binder and a dispersant other than polycarboxylic acid, and a leveling agent, an antioxidant, an antifoaming agent, a wetting agent, and an electrolytic solution additive having a function of inhibiting decomposition of the electrolytic solution may be included. The slurry for a porous membrane of the present invention may further contain an acid and / or a base for adjusting the pH. Examples of such acids and bases include ammonia water (ammonium hydroxide aqueous solution); alkali metal aqueous solutions such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution; alkalis such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution. An earth metal aqueous solution may be mentioned. These acids and bases may be used alone or in combination of two or more at any ratio.

[1.7. Properties of porous membrane slurry]
The pH of the slurry for a porous membrane of the present invention is 6 or more, preferably 6.3 or more, more preferably 6.5 or more, while 8 or less, preferably 7.8 or less, more preferably 7.5 or less. is there. When the pH of the slurry for a porous membrane is not less than the lower limit, the stability of the slurry can be improved. Specifically, the polycarboxylic acid can be present in a stable dissolved state, thereby suppressing the generation of aggregates. When the pH of the slurry for the porous membrane is not more than the above upper limit, the viscosity of the slurry for the porous membrane is kept at a moderately low value, and after applying the slurry for the porous membrane, the layer of the slurry for the porous membrane is leveled, Undesired streaks formed by application can be reduced. Moreover, when the polycarboxylic acid is appropriately entangled, the peel strength and heat shrinkage of the porous film can be improved. The pH of the slurry for the porous membrane can be adjusted by adjusting the contents of the polycarboxylic acid and other components and, if necessary, by adding an acid or base that adjusts the pH.

  In the slurry for a porous membrane of the present invention, the polycarboxylic acid is usually present in a partially dissolved state. Specifically, the polycarboxylic acid is usually present in a state where a part of the polycarboxylic acid is dissolved in water as a solvent in the slurry. When the polycarboxylic acid is acidic at a pH of less than 6, it usually does not dissolve and becomes water-insoluble, but by adjusting the pH of the porous membrane slurry within the preferred range described above, a part of the polycarboxylic acid is dissolved, The viscosity can be adjusted to a value suitable for coating.

  The slurry for porous film of the present invention can be prepared to have a viscosity suitable for coating. The viscosity of the slurry for a porous membrane of the present invention is preferably 5 mPa · s or more, more preferably 10 mPa · s or more, even more preferably 15 mPa · s or more, while preferably 200 mPa · s or less, more preferably 150 mPa · s. s or less, more preferably 100 mPa · s or less, and particularly preferably 60 mPa · s or less. By setting the viscosity of the slurry for the porous film to the lower limit or more, it is possible to prevent the slurry from dripping during the application of the slurry for the porous film and causing unevenness in the application. By setting the viscosity of the slurry for the porous film to the above upper limit or less, the viscosity of the slurry for the porous film is kept at a moderately low value, and after the application of the slurry for the porous film, the layer of the slurry for the porous film is leveled. Undesired streaks formed by application can be reduced. The viscosity of the slurry for a porous membrane is a value measured using a B-type viscometer at a temperature of 25 ° C. and a rotation speed of 60 rpm. The viscosity of the slurry for the porous membrane can be adjusted by adjusting the molecular weight of the polycarboxylic acid and the content of components such as polycarboxylic acid, acid and base for pH adjustment.

[2. Method for producing slurry for porous membrane]
Although the slurry for porous membranes of the present invention can be produced by any production method, it can be preferably produced by the production method described below. That is:
Preparing a non-conductive particle dispersion containing non-conductive particles (I);
Preferably, it can be produced by a production method comprising the step (II) of mixing the non-conductive particle dispersion and the polycarboxylic acid (A). Below, this manufacturing method is demonstrated as a manufacturing method of the slurry for porous films of this invention.

  In the manufacturing method of the slurry for porous films of this invention, the nonelectroconductive particle dispersion solution containing a nonelectroconductive particle is prepared (process (I)). Such a non-conductive particle dispersion solution preferably contains a dispersant and / or polycarboxylic acid (B), is excellent in dispersibility of inorganic particles, and is excellent in physical properties of the resulting porous film. More preferably, B) is included. A part of the carboxylic acid group of the polycarboxylic acid (B) may be an ammonium salt or an alkali metal salt.

  The pH of the non-conductive particle dispersion is more than 6.0 and not more than 12.0. The pH of the non-conductive particle dispersion is preferably 6.5 or higher, more preferably 7.0 or higher, while preferably 11 or lower. By having a pH in such a range, a good dispersion of non-conductive particles can be obtained, and a slurry for a porous film having a desired pH can be easily obtained in step (II).

  The specific operation for preparing such a non-conductive particle dispersion solution is not particularly limited, and non-conductive particles and water are mixed, and an acid or a base is added as necessary to adjust the pH. As a result, a non-conductive particle dispersion solution can be prepared. As the non-conductive particles, the dispersant, and the polycarboxylic acid (B), those exemplified above can be appropriately selected and used. Further, the amount thereof can be appropriately adjusted so that the concentration in the final slurry for a porous membrane is in the range exemplified above.

  In the method for producing a slurry for a porous membrane of the present invention, the nonconductive particle dispersion obtained in step (I) and the polycarboxylic acid (A) are mixed (step (II)). As the polycarboxylic acid (A), those exemplified above can be appropriately selected and used. Further, the amount can be appropriately adjusted so that the concentration in the final slurry for a porous membrane is in the range exemplified above.

  In the method for producing a slurry for a porous membrane of the present invention, an optional step may be additionally performed in addition to steps (I) and (II). For example, after the step (II), an acid or a base for adjusting the pH of the slurry may be added to adjust the pH of the resulting slurry to 6.0 or more and 8.0 or less.

  In the method for producing a slurry for a porous membrane of the present invention, the non-conductive particle dispersion is prepared in advance in the step (I) described above, and the inorganic dispersion and the polycarboxylic acid (A) are mixed. The dispersibility of such non-conductive particles and the desired physical properties of the slurry can both be achieved.

  In step (I) and / or step (II), if necessary, the above-mentioned components, particularly non-conductive particles, are dispersed in the non-conductive particle dispersion solution and / or the slurry for the porous membrane using a disperser, if necessary. Can be made. As the disperser, it is preferable to use a medialess disperser because the particle size of the non-conductive particles is hardly reduced undesirably.

[3. (Porous membrane)
The porous membrane for a secondary battery of the present invention (hereinafter sometimes simply referred to as the porous membrane of the present invention) forms a layer of the slurry for a secondary battery porous membrane of the present invention and is dried.

  The porous membrane slurry layer can be obtained by applying a porous membrane slurry onto a substrate. A base material is a member used as the object which forms the film | membrane of the slurry for porous films. There is no restriction | limiting in a base material, For example, the film | membrane of the slurry for porous films is formed in the surface of a peeling film, A solvent is removed from the film | membrane, a porous film may be formed, and a porous film may be peeled from a peeling film. However, normally, from the viewpoint of improving the production efficiency by omitting the step of peeling the porous film, the constituent elements of the battery are used as the base material. Examples of such battery components include separator substrates and electrode plates.

  Examples of the coating method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the dip method and the gravure method are preferable in that a uniform porous film can be obtained. Since the slurry for porous film of the present invention contains a specific composition and physical properties, its application is easy, a high-quality layer can be easily obtained, and the amount of water remaining in the porous film is reduced. Can be reduced.

  Specific examples of the method for drying the porous membrane slurry layer include drying with warm air, hot air, low-humidity air, etc .; vacuum drying; drying by irradiation with infrared rays, far infrared rays, and electron beams. It is done.

  The temperature during drying is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, particularly preferably 50 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower. By setting the drying temperature to be equal to or higher than the lower limit of the above range, the solvent and the low molecular weight compound can be efficiently removed from the slurry for the porous membrane. Moreover, the deformation | transformation by the heat | fever of a base material can be suppressed by setting it as below an upper limit.

  The drying time is preferably 5 seconds or more, more preferably 10 seconds or more, particularly preferably 15 seconds or more, preferably 3 minutes or less, more preferably 2 minutes or less. By setting the drying time to be equal to or more than the lower limit of the above range, the solvent can be sufficiently removed from the slurry for the porous membrane, so that the output characteristics of the battery can be improved. Moreover, manufacturing efficiency can be improved by setting it as an upper limit or less.

In the method for producing a porous membrane of the present invention, any operation other than those described above may be performed.
For example, the porous film may be subjected to pressure treatment by a pressing method such as a mold press and a roll press. By performing the pressure treatment, the binding property between the substrate and the porous film can be improved. However, from the viewpoint of keeping the porosity of the porous film within a preferable range, it is preferable to appropriately control the pressure and the pressurization time so as not to become excessively large.
In order to remove residual moisture, it is preferable to dry in, for example, vacuum drying or a dry room.

  The thickness of the porous membrane of the present invention is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.3 μm or more, preferably 20 μm or less, more preferably 15 μm or less, particularly preferably 10 μm or less. It is. By setting the thickness of the porous film to be equal to or more than the lower limit of the above range, the heat resistance of the porous film can be increased. Moreover, the fall of the ionic conductivity by a porous film can be suppressed by setting it as an upper limit or less.

[4. (Separator for secondary battery)
When a separator base material is used as the base material, a separator for a secondary battery including the separator base material and the porous membrane of the present invention is obtained. The porous membrane of the present invention may be provided on only one side of the separator substrate, or may be provided on both sides.
In the secondary battery, when the separator provided with the porous membrane of the present invention is used as the separator, the residual moisture content in the porous membrane is small, the thermal contraction of the porous membrane is small, and high peel strength can be exhibited. The high-temperature cycle characteristics of the battery can be improved.

  As the separator substrate, for example, a porous substrate having fine pores can be used. By using such a separator base material, it is possible to prevent a short circuit without interfering with charge / discharge of the battery in the secondary battery. When the specific example of a separator base material is given, the microporous film or nonwoven fabric containing polyolefin resin, such as polyethylene resin and a polypropylene resin, an aromatic polyamide resin, etc. are mentioned.

  The thickness of the separator substrate is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 40 μm or less, more preferably 30 μm or less. Within this range, the resistance due to the separator substrate in the secondary battery is reduced, and the workability during battery production is excellent.

[5. Secondary battery electrode)
When an electrode plate is used as the substrate, an electrode for a secondary battery comprising the electrode plate and the porous film of the present invention is obtained. In the present application, the “electrode plate” refers to a member other than the porous film among the electrodes including the porous film. The electrode plate usually includes a current collector and an electrode active material layer. The electrode for a secondary battery including the electrode plate and the porous film of the present invention usually includes a current collector, an electrode active material layer, and the porous film of the present invention in this order. For example, when the electrode active material layer is provided only on one side of the current collector in the electrode plate, a layer configuration of current collector / electrode active material layer / porous film can be taken. Further, for example, in the electrode plate, when electrode active material layers are provided on both sides of the current collector, a layer configuration of porous film / electrode active material layer / current collector / electrode active material layer / porous film can be taken.

  In the secondary battery, when the electrode provided with the porous film of the present invention is used as the electrode, the residual moisture amount in the porous film is small, the thermal contraction of the porous film is small, and high peel strength can be exhibited. The high-temperature cycle characteristics of the battery can be improved.

[5.1. Current collector]
As the current collector of the electrode plate, an electrically conductive and electrochemically durable material can be used. Usually, a metal material is used as the material of the current collector. Examples thereof include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, the current collector used for the positive electrode is preferably aluminum, and the current collector used for the negative electrode is preferably copper. Moreover, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.

[5.2. Electrode active material layer
The electrode active material layer is a layer provided on the current collector and includes an electrode active material. There are various types of electrode active materials depending on the types of secondary batteries. Here, electrode active materials for lithium ion secondary batteries will be described in particular. However, the electrode active material is not limited to those listed below.

  As the electrode active material of the lithium ion secondary battery, a material capable of reversibly inserting or releasing lithium ions by applying a potential in an electrolytic solution can be used. As the electrode active material, an inorganic compound or an organic compound may be used.

The positive electrode active material is roughly classified into those made of inorganic compounds and those made of organic compounds. Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, and Mn. Specific examples of the inorganic compound used for the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO _{4 and} other lithium-containing composite metal oxides; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _13, etc. Can be mentioned. On the other hand, examples of the positive electrode active material made of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.

Furthermore, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
These positive electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Moreover, you may use the mixture of the above-mentioned inorganic compound and organic compound as a positive electrode active material.

  The particle diameter of the positive electrode active material can be selected in consideration of other constituent elements of the secondary battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the volume average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 50 μm or less, more preferably 20 μm or less. It is. When the volume average particle diameter of the positive electrode active material is within this range, a battery having a large charge / discharge capacity can be obtained, and handling of the electrode slurry composition and the electrode is easy.

  The ratio of the positive electrode active material in the electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, and preferably 99.9% by weight or less, more preferably 99% by weight or less. By setting the amount of the positive electrode active material in the above range, the capacity of the secondary battery can be increased, and the flexibility of the positive electrode and the binding property between the current collector and the positive electrode active material layer can be improved.

  Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, artificial graphite, mesocarbon microbeads, pitch-based carbon fibers, and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used. Furthermore, an electrode active material having a conductive material attached to the surface by a mechanical modification method may be used. These negative electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the secondary battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, the volume average particle diameter of the negative electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more. Is 100 μm or less, more preferably 50 μm or less, and still more preferably 20 μm or less.

The specific surface area of the negative electrode active material, the output from the viewpoint of improving the density, preferably ^2m 2 / g or more, more preferably ^3m 2 / g or more, more preferably ^{5 m} 2 / g or more, and preferably ^{20 m} 2 / g or less, more preferably 15 m ² / g or less, and further preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

  The ratio of the negative electrode active material in the electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, and preferably 99% by weight or less, more preferably 97% by weight or less. By setting the amount of the negative electrode active material in the above range, it is possible to realize a negative electrode that exhibits excellent flexibility and binding properties while exhibiting high capacity.

  The electrode active material layer preferably contains an electrode binder in addition to the electrode active material. By including the binder for the electrode, the binding property of the electrode active material layer is improved, and the strength against the mechanical force applied in the process of winding the electrode is increased. In addition, since the electrode active material layer is less likely to be peeled off from the current collector and the porous film, the risk of short-circuiting due to the detached desorbed material is reduced.

  As the electrode binder, for example, a polymer can be used. Examples of the polymer that can be used as an electrode binder include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, poly An acrylonitrile derivative or the like may be used.

Furthermore, you may use the particle | grains of the soft polymer illustrated below as a particulate-form binder. As a soft polymer, for example,
(I) Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer, etc. An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative or a copolymer thereof with a monomer copolymerizable therewith;
(Ii) isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
(Iii) Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene・ Diene-based soft polymers such as butadiene, styrene, block copolymers, isoprene, styrene, block copolymers, styrene, isoprene, styrene, block copolymers;
(Iv) silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
(V) Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer Olefinic soft polymers such as polymers;
(Vi) Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
(Vii) epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
(Viii) Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
(Ix) Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer, and the like. These soft polymers may have a cross-linked structure or may have a functional group introduced by modification.
The polymer may be in the form of particles or non-particulates.
Furthermore, the binder for electrodes may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the binder for the electrode in the electrode active material layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the electrode active material. It is preferably 5 parts by weight or less, more preferably 3 parts by weight or less. When the amount of the electrode binder is within the above range, it is possible to prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction.

  The electrode active material layer may contain any component other than the electrode active material and the electrode binder as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductive material and a reinforcing material. Moreover, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube; carbon powder such as graphite; fibers and foils of various metals; . By using a conductive material, electrical contact between electrode active materials can be improved, and battery characteristics such as cycle characteristics can be improved.

The specific surface area of the conductive material is preferably 50 m ² / g or more, more preferably 60 m ² / g or more, particularly preferably 70 m ² / g or more, preferably 1500 m ² / g or less, more preferably 1200 m ² / g. Hereinafter, it is particularly preferably 1000 m ² / g or less. By setting the specific surface area of the conductive material to be equal to or higher than the lower limit of the above range, the low-temperature output characteristics of the secondary battery can be improved. Moreover, the binding property of an electrode active material layer and an electrical power collector can be improved by setting it as an upper limit or less.

  As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using the reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be obtained.

  The amount of the conductive material and the reinforcing agent used is usually 0 part by weight or more, preferably 1 part by weight or more, preferably 20 parts by weight or less, more preferably 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is as follows.

  The thickness of the electrode active material layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 300 μm or less, more preferably 250 μm or less for both the positive electrode and the negative electrode.

  The method for producing the electrode active material layer is not particularly limited. The electrode active material layer can be produced by, for example, applying an electrode active material and a solvent, and, if necessary, an electrode slurry composition containing an electrode binder and optional components onto a current collector and drying it. As the solvent, either water or an organic solvent can be used.

[6. Secondary battery)
The secondary battery of the present invention includes the porous film of the present invention. A secondary battery usually includes a positive electrode, a negative electrode, and an electrolyte, and satisfies the following requirement (A), the requirement (B), or both the requirements (A) and (B).
(A) At least one of the positive electrode and the negative electrode of the secondary battery of the present invention is an electrode including the electrode plate and the porous film of the present invention.
(B) The secondary battery of the present invention includes a separator, and the separator includes a separator base material and the porous film of the present invention.

  The porous membrane of the present invention has a small amount of residual water, a small thermal shrinkage, and can exhibit high peel strength. Therefore, when the electrode and / or separator provided with the porous film of the present invention is used as a constituent element of a secondary battery, the high-temperature cycle characteristics of the secondary battery can be improved.

[6.1. separator〕
In principle, the secondary battery of the present invention includes a separator including the porous film of the present invention as a separator. However, in the case where the secondary battery of the present invention includes a battery including the porous film of the present invention as at least one of a positive electrode and a negative electrode, a separator other than the separator including the porous film of the present invention may be provided as a separator. Moreover, since the porous film in the electrode provided with the porous film of the present invention has a function as a separator, the separator may be omitted when the electrode includes the porous film of the present invention.

[6.2. electrode〕
In principle, the secondary battery of the present invention includes an electrode including the porous film of the present invention as one or both of a positive electrode and a negative electrode. However, when the secondary battery of the present invention includes a separator including the porous film of the present invention as a separator, an electrode that does not include the porous film of the present invention may be provided as both a positive electrode and a negative electrode.

[6.3. Electrolyte)
As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the supporting electrolyte is preferably 1% by weight or more, more preferably 5% by weight or more, preferably 30% by weight or less, more preferably 20% by weight or less, as the concentration in the electrolytic solution. By keeping the amount of the supporting electrolyte within this range, the ion conductivity can be increased and the charging characteristics and discharging characteristics of the secondary battery can be improved.

  As a solvent used for the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of such a solvent include alkyl carbonate compounds such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC). Ester compounds such as γ-butyrolactone and methyl formate; ether compounds such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. A solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, electrolyte solution may contain an additive as needed. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

[6.4. Secondary battery manufacturing method)
The manufacturing method of the secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode may be overlapped via a separator, and this may be wound or folded in accordance with the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed. Furthermore, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily set within the scope of the claims and equivalents of the present invention. Can be changed and implemented. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified.

  In Examples and Comparative Examples, measurement of molecular weight of polycarboxylic acid (A), measurement of viscosity of slurry for porous film, measurement of pH, measurement of particle size of non-conductive particles, evaluation of applicability of slurry for porous film Evaluation of peel strength, measurement of moisture content of the porous film, evaluation of heat shrinkage resistance of the porous film, and evaluation of high temperature cycle characteristics in the secondary battery were performed as follows.

[Molecular weight measurement method]
The concentration of the aqueous dispersion of the polycarboxylic acid (A) obtained in Examples and Comparative Examples was adjusted as necessary so that the solid content was 40%, and this was further dissolved in THF. % Solution. This solution was filtered through a 0.45 μm membrane filter to obtain a measurement sample. This measurement sample was analyzed under the following conditions using gel permeation chromatography (GPC), and the weight average molecular weight was determined from the analysis results.
Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)
Column: TSKgel Multipore HXL-M (manufactured by Tosoh Corporation)
Eluent: Tetrahydrofuran (THF)
Elution rate: 0.3 ml / min Detector: RI (polarity (+))
Column temperature: 40 ° C
Reference material: Polymethylmethacrylate

[viscosity]
The viscosity of the slurry for porous membrane was measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

[PH measurement method]
After calibrating a desktop pH meter (HORIBA F-51) with a pH standard solution (pH 4, pH 7 and pH 9), the pH of the dispersion of non-conductive particles and the slurry for the porous membrane was measured. .

[Method for measuring particle diameter of non-conductive particles]
The nonconductive particles are ultrasonically dispersed using an aqueous solution of sodium hexametaphosphate, and then analyzed by a laser diffraction particle size distribution measuring device (“SALD-7100” manufactured by Shimadzu Corporation). Asked.

[Applicability evaluation]
The state of the porous film of the separator (the separator base material and the porous film formed on one surface thereof) obtained in the examples and comparative examples was irradiated with light from the surface on the separator base side, and the porous film side And the presence or absence of streaks or coating unevenness was evaluated by observing whether or not the light transmission was uneven.

[Peel strength]
The separators obtained in the examples and comparative examples were cut into rectangles having a width of 10 mm and a length of 100 mm to obtain test pieces. Cellophane tape (specified in JIS Z1522) was attached to the porous film surface of the test piece. The cellophane tape is fixed to the horizontal surface of the test table in a flat state, and one end of the separator is pulled at a pulling speed of 10 mm / min in the 180 ° direction toward the end opposite to the one end of the separator. Stress was measured. The measurement was performed three times, the average value was obtained, and this was taken as the peel strength, and evaluated according to the following criteria. The higher the peel strength, the greater the binding force between the porous membrane and the separator substrate, that is, the higher the adhesion strength.

A: Peel strength is 100 N / m or more B: Peel strength is 75 N / m or more and less than 100 N / m C: Peel strength is 50 N / m or more and less than 75 N / m D: Peel strength is less than 50 N / m

[Moisture content measurement]
The separators obtained in the examples and comparative examples were cut out in a size of 10 cm width × 10 cm length to obtain test pieces. This test piece was left at a temperature of 25 ° C. and a humidity of 50% for 24 hours. Thereafter, the moisture content of the test piece was measured by a Karl Fischer method (JIS K-0068 (2001) moisture vaporization method, vaporization temperature 150 ° C.) using a coulometric titration moisture meter. This was evaluated according to the following criteria as the moisture content of the porous membrane.

A: The moisture content of the porous membrane is less than 1500 ppm B: The moisture content of the porous membrane is 1500 ppm or more and less than 2000 ppm C: The moisture content of the porous membrane is 2000 ppm or more and less than 3000 ppm D: The moisture content of the porous membrane is 3000 ppm or more

[Heat-resistant shrinkage]
The separators obtained in the examples and comparative examples were cut into squares having a width of 12 cm and a length of 12 cm, and a square having a side of 10 cm was drawn inside the square to obtain a test piece. The test piece was heated in a constant temperature bath at 150 ° C. for 1 hour. After the heat treatment, the area of the square drawn inside was measured, the change in the area before and after the heat treatment was determined as the heat shrinkage rate, and evaluated according to the following criteria. The smaller the heat shrinkage rate, the better the heat shrinkage of the separator.

A: The heat shrinkage rate is less than 1% B: The heat shrinkage rate is 1% or more and less than 5% C: The heat shrinkage rate is 5% or more and less than 10% D: The heat shrinkage rate is 10% or more

[High temperature cycle characteristics]
10 batteries obtained in Examples and Comparative Examples were charged to 4.2 V by a constant current method of 0.2 C in an atmosphere of 60 ° C., and charging / discharging to 3 V was repeated 50 times (= 50 cycles), The capacity was measured. The average value of the measurement results of 10 batteries is taken as the measured value, the ratio of the electric capacity at the end of 200 cycles to the electric capacity at the end of 5 cycles is calculated as a percentage to obtain the charge / discharge capacity retention rate, and this is the high temperature cycle. Evaluation was made according to the following criteria as evaluation criteria for characteristics. Higher values indicate better high temperature cycle characteristics.

A: The charge / discharge capacity retention is 80% or more.
B: The charge / discharge capacity retention is 70% or more and less than 80%.
C: The charge / discharge capacity retention is 60% or more and less than 70%.
D: The charge / discharge capacity retention is less than 60%.

<Example 1>
(1-1. Production of polycarboxylic acid (A))
In a 5 MPa pressure vessel equipped with a stirrer, 100 parts of the monomer composition, 0.6 part of t-dodecyl mercaptan as a molecular weight regulator, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator, After stirring, the polymerization was started by heating to 60 ° C. The monomer composition comprises 11 parts of butyl acrylate butyl acrylate, 57 parts of ethyl acrylate, 30 parts of methacrylic acid, 0.8 part of ethylene dimethacrylate, and polyoxyalkenyl ether ammonium sulfate as a reactive surfactant (trade name “Latemul PD-104 "(manufactured by Kao Corporation)) and 1.2 parts. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion of polycarboxylic acid (A). Using this as a sample, the weight average molecular weight of the obtained polycarboxylic acid (A) was measured.

(1-2. Production of particulate binder)
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (manufactured by Kao Chemicals, product name: Emar (registered trademark) 2F) as an emulsifier, and ammonium peroxodisulfate 0 as a polymerization initiator .5 parts were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94.8 parts of n-butyl acrylate as a monomer composition, 1 part of methacrylic acid, N-methylol A monomer mixture was obtained by mixing 1.2 parts of acrylamide, 2 parts of acrylonitrile, and 1 part of allyl glycidyl ether. This monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to produce an aqueous dispersion containing a particulate binder.
The obtained particulate binder had a volume average particle diameter D50 of 370 nm and a glass transition temperature of −45 ° C.

(1-3. Production of slurry for porous membrane)
100 parts of barium sulfate (volume average particle diameter of 0.5 μm, specific surface area of 5.5 g / m ² ), ammonium salt of polycarboxylic acid (B) (dispersant, manufactured by Toagosei Co., Ltd., trade name “Aron A6114”), weight An average molecular weight of 15,200) was mixed with 0.5 part of polycarboxylic acid and water. The amount of water was adjusted so that the solid concentration was 50%. The mixture was processed using a medialess dispersion apparatus to disperse barium sulfate, thereby obtaining a non-conductive particle dispersion solution. When this pH was measured, the pH was 7.3.
To the obtained non-conductive particle dispersion, 1.5 parts (corresponding to the solid content) of the 40% solid content polycarboxylic acid (A) dispersion obtained in the step (1-1) was added and mixed. . Subsequently, 5 parts (corresponding to solid content) of the particulate binder obtained in the step (1-2) is added, and further an aqueous 12% ammonium hydroxide solution and water are added, and the solid content concentration is 7.2. Was mixed to make a slurry for a porous membrane.
About the obtained slurry for porous films, pH and a viscosity were measured.

(1-4. Manufacture of separator)
A single-layer polyethylene separator substrate having a width of 250 mm, a length of 1000 m, and a thickness of 12 μm was prepared. The slurry for the porous membrane obtained in the step (1-3) is applied on one surface of the separator substrate at a speed of 20 m / min using a gravure coater so that the thickness after drying becomes 4 μm. Next, it was dried in a drying furnace at 50 ° C. and wound up to produce a separator having a separator substrate and a porous film formed on one surface thereof.

  About the obtained separator, applicability | paintability, peel strength, moisture content, and heat shrinkage were evaluated.

(1-5. Production of positive electrode)
100 parts of LiCoO ₂ (volume average particle diameter D50: 12 μm) as the positive electrode active material, ₂ parts of acetylene black (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and PVDF (binder for the positive electrode active material layer) Polyvinylidene fluoride, manufactured by Kureha Co., Ltd., # 7208) was mixed with 2 parts corresponding to the solid content and NMP (N-methylpyrrolidone) to make the total solid content concentration 70%. These were mixed by a planetary mixer to obtain a positive electrode slurry composition.
The obtained positive electrode slurry composition was applied onto a 20 μm-thick aluminum foil as a current collector by a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by transporting the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, the positive electrode raw material was rolled by a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 95 μm.

(1-6. Production of negative electrode)
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, ion exchange After adding 150 parts of water and 0.5 part of potassium peroxodisulfate as a polymerization initiator and stirring sufficiently, the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the negative electrode active material layer binder (SBR). A 5% aqueous sodium hydroxide solution was added to the mixture containing the negative electrode active material layer binder, and the pH was adjusted to 8. Then, unreacted monomers were removed by heating under reduced pressure. Then, it cooled to 30 degrees C or less, and obtained the water dispersion liquid containing the binder for desired negative electrode active material layers.
A mixture of 100 parts of artificial graphite (volume average particle diameter D50: 15.6 μm) and 1 part of a 2% aqueous solution of sodium salt of carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC350HC) as a thickener. The solid content was adjusted to 68% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Furthermore, after adjusting to 62% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC. The above-mentioned binder for negative electrode active material layer (SBR) was added in an amount corresponding to a solid content of 1.5 parts and ion-exchanged water, adjusted to a final solid content concentration of 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to prepare a slurry composition for negative electrode having good fluidity.
The obtained negative electrode slurry composition was applied on a copper foil having a thickness of 20 μm, which was a current collector, with a comma coater so that the film thickness after drying was about 150 μm, and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was rolled by a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 100 μm.

(1-7. Production of lithium ion secondary battery)
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained in the step (1-5) was cut into a rectangle with an electrode area of 3 cm × 4 cm to obtain a rectangular positive electrode. The separator obtained in the step (1-4) was cut into a 3.5 cm × 4.5 cm rectangle to obtain a rectangular separator. Further, the negative electrode obtained in the step (1-6) was cut into a rectangle having an electrode area of 3.2 cm × 4.2 cm to obtain a rectangular negative electrode. A rectangular positive electrode was placed in the packaging material exterior so that the current collector-side surface was in contact with the aluminum packaging exterior. On the surface of the rectangular positive electrode on the positive electrode active material layer side, a rectangular separator was disposed so that the surface on the porous membrane side was in contact with the rectangular positive electrode. Further, a rectangular negative electrode was placed on the separator so that the surface on the negative electrode active material layer side faces the separator. An electrolytic solution (solvent: EC / EMC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF ₆ having a concentration of 1 M) was injected so that no air remained. Further, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the exterior of the aluminum packaging material, and a lithium ion secondary battery was manufactured.
The lithium ion secondary battery was evaluated for high-temperature cycle characteristics.

<Example 2>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In the production of the polycarboxylic acid (A) in the step (1-1), the monomer composition is composed of 1 part of butyl acrylate, 57 parts of ethyl acrylate, 40 parts of methacrylic acid, 0.8 part of ethylene dimethacrylate, and It changed into what consists of 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be set to 7.0.

<Example 3>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the polycarboxylic acid (A) in the step (1-1), the monomer composition is composed of 6 parts of butyl acrylate, 57 parts of ethyl acrylate, 25 parts of methacrylic acid, 0.8 part of ethylene dimethacrylate, and It changed into what consists of 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be 7.3.

<Example 4>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of polycarboxylic acid (A) of a process (1-1), a monomer composition is 20 parts of butyl acrylate, 28.0 parts of ethyl acrylate, 50 parts of methacrylic acid, and 0.8 parts of ethylene dimethacrylate. And 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be set to 7.05.

<Example 5>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the polycarboxylic acid (A) in the step (1-1), the monomer composition is composed of 31 parts of butyl acrylate, 47.0 parts of ethyl acrylate, 20 parts of methacrylic acid, 0.8 part of ethylene dimethacrylate. And 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be 7.3.

<Example 6>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the polycarboxylic acid (A) in the step (1-1), the monomer composition is prepared by adding 11.8 parts of butyl acrylate, 57 parts of ethyl acrylate, 30 parts of methacrylic acid, 0 part of ethylene dimethacrylate (addition) ), And 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant, and the addition amount of t-dodecyl mercaptan as a molecular weight regulator was changed to 1.2 parts. .
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be 7.3.

<Example 7>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the polycarboxylic acid (A) of a process (1-1), 9.4 parts of butyl acrylate, 57.0 parts of ethyl acrylate, 30 parts of methacrylic acid, ethylene dimethacrylate 2. The composition was changed to 4 parts and 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.

<Example 8>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be 6.2.

<Example 9>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be 7.7.

<Example 10>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-The addition amount of polycarboxylic acid (B) was changed to 0.75 part.
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be 7.4.

<Example 11>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-The addition amount of polycarboxylic acid (B) was changed to 0.25 part.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be set to 6.5.

<Example 12>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
Step (1-3) In the production of the slurry for the porous membrane, alumina (volume average particle size 0.45 μm, specific surface area 6.0 g / m ² ) was used instead of barium sulfate.

<Example 13>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-Instead of polycarboxylic acid (B), β-naphthalenesulfonic acid formalin condensate sodium salt (trade name “Demol NL”, manufactured by Kao Corporation) was used.

<Example 14>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-The addition amount of polycarboxylic acid (A) was changed into 5.0 parts.
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be 6.8.

<Example 15>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-The polycarboxylic acid (B) was changed to one having a polymerization average molecular weight of 25,000.

<Comparative Example 1>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the polycarboxylic acid (A) in the step (1-1), the monomer composition is composed of 42.2 parts of butyl acrylate, 47 parts of ethyl acrylate, 10 parts of methacrylic acid, 0.8 part of ethylene dimethacrylate And 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.

<Comparative example 2>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the polycarboxylic acid (A) of a process (1-1), a monomer composition is 13.2 parts of butyl acrylate, 16.0 parts of ethyl acrylate, 70 parts of methacrylic acid, ethylene dimethacrylate 0. The composition was changed to 8 parts and 1.2 parts of polyoxyalkenyl ether ammonium sulfate as a reactive surfactant.

<Comparative Example 3>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurement and evaluation of the lithium ion secondary battery and its components were attempted.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be set to 9.
However, the streaks at the time of application were large, and a porous film could not be formed. As a result, the porous film and the battery could not be evaluated.

<Comparative Example 4>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the slurry for porous films of a process (1-3), the addition amount of polycarboxylic acid (B) was changed to 0.1 part.
-In manufacture of the slurry for porous films of a process (1-3), adjustment of pH of the slurry for porous films was performed so that pH might be set to 5.

<Comparative Example 5>
A lithium ion secondary battery was produced in the same manner as in Steps (1-2) to (1-7) of Example 1 except that the following matters were changed, and the lithium ion secondary battery and its constituent elements were manufactured. Measurement and evaluation were performed.
-In manufacture of the slurry for porous membranes of a process (1-3), it replaces with the aqueous solution of the polycarboxylic acid (A) obtained at the process (1-1), carboxymethylcellulose sodium salt (Product name "Daicel D1220", Daicel) 1.5 parts (corresponding to solid content) of Fine Chem, etherification degree 0.8 to 1.0) was added.
-In manufacture of the slurry for porous films of a process (1-3), pH adjustment of the slurry for porous films was performed so that pH might be set to 10.

  Evaluation results in Examples and Comparative Examples are shown in Tables 1 to 3.

The meanings of the abbreviations in the table are as follows.
Particle size: Particle size of non-conductive particles, unit μm.
MAA amount: ratio of methacrylic acid added for preparation of polycarboxylic acid (A), unit by weight.
EA amount: ratio of ethyl acrylate added for the preparation of polycarboxylic acid (A), unit by weight.
BA amount: ratio of butyl acrylate added for the preparation of polycarboxylic acid (A), unit by weight.
EDMA amount: ratio of ethylene dimethacrylate added for preparation of polycarboxylic acid (A), unit by weight.
TDM amount: ratio of t-dodecyl mercaptan added for preparation of polycarboxylic acid (A), unit by weight.
(A) Molecular weight: Measurement result of the weight average molecular weight of the polycarboxylic acid (A).
(A) Amount added: ratio of polycarboxylic acid (A) added during the production of the slurry for porous membrane, unit: parts by weight relative to 100 parts by weight of non-conductive particles.
(B) Type: The type of polycarboxylic acid (B) or dispersant added during the production of the slurry for the porous membrane. PC (B): polycarboxylic acid (B). Demol NL: β-naphthalenesulfonic acid formalin condensate sodium salt.
(B) Amount added: ratio of polycarboxylic acid (B) or dispersant added during the production of the slurry for porous membrane, unit: parts by weight relative to 100 parts by weight of non-conductive particles.
Non-conductive particles Non-conductive particle dispersion solution pH: pH of the non-conductive particle dispersion prepared in the production of the slurry for the porous membrane.
Slurry pH: pH of the slurry for the porous membrane.
Viscosity: Viscosity of the slurry for porous membrane, unit mPa · s.
* 1: Some streaks occurred.
* 2: A large amount of streaks occurred.
* 3: Slight coating unevenness was observed.

  As shown by the results in Tables 1 to 3, in the examples using the slurry for the porous film containing the specific polycarboxylic acid (A), the applicability of the slurry for the porous film is good, and the peel of the porous film The strength was high, the moisture content of the porous membrane was low, the heat shrinkage resistance of the porous membrane was good, and the obtained battery had good high-temperature cycle characteristics. On the other hand, in Comparative Example 1 in which the amount of carboxylic acid groups in the polycarboxylic acid (A) is lower than the specified range of the present application, a porous film having poor peel strength and heat shrinkage resistance was obtained. In Comparative Example 2 in which the amount of carboxylic acid groups in the polycarboxylic acid (A) is higher than the specified range of the present application, the moisture content of the porous film was large, and as a result, the high temperature cycle characteristics of the battery were insufficient. In addition, in Comparative Examples 3 and 4 in which the pH of the slurry was outside the range specified in the present application, and as a result, the viscosity became unsuitable for coating, a good porous film could not be obtained.

Claims (6)

A slurry for a secondary battery porous membrane comprising non-conductive particles, polycarboxylic acid (A) and polycarboxylic acid (B) ,
The polycarboxylic acid (A) contains 20% by weight or more and 50% by weight or less of a carboxylic acid group-containing monomer unit and has a weight average molecular weight of 50,000 or more and 300,000 or less. The polycarboxylic acid (A) A part of the carboxylic acid group in the carboxylic acid group-containing monomer unit is an ammonium salt or an alkali metal salt,
The polycarboxylic acid (B) has a weight average molecular weight of 2,000 or more and 30,000 or less, and the polycarboxylic acid (B) has a carboxylic acid group, and a part of the carboxylic acid group is an ammonium salt. Or an alkali metal salt,
A slurry for a secondary battery porous membrane, wherein the slurry has a pH of 6.0 to 8.0. The polycarboxylic acid (A) further contains a crosslinkable monomer unit,
The slurry for secondary battery porous membranes of Claim 1 whose ratio of the crosslinkable monomer unit in the said polycarboxylic acid (A) is 0.1 to 5 weight%. The slurry for secondary battery porous membranes of Claim 1 or 2 whose viscosity measured with a B-type viscometer in 25 degreeC is 5-200 mPa * s. Preparing a non-conductive particle dispersion containing non-conductive particles (I);
A process for producing a slurry for a secondary battery porous membrane comprising the step (II) of mixing the non-conductive particle dispersion and the polycarboxylic acid (A),
In the step (I),
The pH of the non-conductive particle dispersion is more than 6.0 and not more than 12.0,
In the step (II),
The polycarboxylic acid (A) contains a carboxylic acid group-containing monomer unit in an amount of 20% by weight to 50% by weight and has a weight average molecular weight of 50,000 to 300,000,
A part of the carboxylic acid group in the carboxylic acid group-containing monomer unit of the polycarboxylic acid (A) is an ammonium salt or an alkali metal salt,
The manufacturing method of the slurry for secondary battery porous films whose pH of the said slurry obtained is 6.0 or more and 8.0 or less. The porous membrane for secondary batteries formed by forming the layer of the slurry for secondary battery porous membranes of any one of Claims 1-3 , and drying the said layer. A secondary battery comprising the porous membrane for a secondary battery according to claim 5 .