JP2015144084A - Composition for lithium ion secondary battery porous films, porous film for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a composition for lithium ion secondary battery porous films which enables the manufacturing of a porous film capable of functioning as a separator having a high strength, and never causing an undesired phenomenon, such as gas generation in a lithium ion secondary battery and therefore, making possible to enhance the battery performances including low-temperature output and high-temperature cycle characteristics; such a porous film; and a secondary battery.SOLUTION: A composition for lithium ion secondary battery porous films comprises: non-conductive particles; a polymer including an acid group; and a carbodiimide compound. The total acid group amount measured in aqueous medium of the polymer including an acid group is 1-40 mmol to 100 g of the non-conductive particles. A porous film and a secondary battery are each arranged by use of the composition.

Description

  The present invention relates to a composition for a porous membrane of a lithium ion secondary battery, a porous membrane for a lithium ion secondary battery, and a lithium ion secondary battery.

  A lithium ion secondary battery has characteristics such as being small and light, having a high energy density, and capable of repeated charge and discharge, and is 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. Lithium ion secondary batteries are required to further improve performance in order to improve the performance of devices used. For example, it is required to improve performance such as the ability to maintain high output even in low temperature environments (low temperature output characteristics) and the ability to maintain capacity even after repeated charge and discharge in high temperature environments (high temperature cycle characteristics). Yes.

  In order to improve the performance of the lithium ion secondary battery, it has been proposed to use a specific material as a separator material constituting the battery. For example, Patent Document 1 proposes a separator made of a polymer obtained by reacting a crosslinkable polymer having a specific crosslinkable group and a compound having a functional group that reacts with the crosslinkable group. ing. By using a polymer obtained by such a crosslinking reaction as a material for the separator, it can be expected that the strength of the separator can be increased and, in turn, durability during use of the battery can be improved.

  A technique such as that disclosed in Patent Document 2 is also known.

JP 2006-179279 A JP 2010-27549 A

  However, when the polymer using the crosslinking agent described in Patent Document 1 is used for a separator of a lithium ion secondary battery, gas is generated in the battery when the lithium ion secondary battery is used. The performance may not be improved.

  The object of the present invention is high strength and does not cause undesired phenomena such as gas generation in a lithium ion secondary battery, and as a result, improves battery performance such as low temperature output characteristics and high temperature cycle characteristics. An object of the present invention is to provide a composition for a porous membrane of a lithium ion secondary battery that can produce a porous membrane that can function as a separator.

  A further object of the present invention is high strength and does not cause undesired phenomena such as gas generation in a lithium ion secondary battery, and as a result, improves battery performance such as low temperature output characteristics and high temperature cycle characteristics. An object of the present invention is to provide a porous membrane for a lithium ion secondary battery, which can be a constituent element of a separator that can be made to operate.

  A further object of the present invention is to provide a lithium ion secondary battery that does not cause undesired phenomena such as gas generation and has improved performance such as low temperature output characteristics and high temperature cycle characteristics.

  The inventor has studied to achieve the above object. And this inventor uses what contains a nonelectroconductive particle, an acid group containing polymer, and a carbodiimide compound as a composition for manufacturing a lithium ion secondary battery porous film, and also a nonelectroconductive The inventors have found that the above object can be achieved by setting the total acid group amount of the acid group-containing polymer in a specific range with respect to the particles, thereby completing the present invention. That is, according to the present invention, the following [1] to [5] are provided.

[1] A composition for a porous membrane of a lithium ion secondary battery comprising non-conductive particles, an acid group-containing polymer, and a carbodiimide compound,
A composition for a porous membrane of a lithium ion secondary battery, wherein a total acid group amount measured in an aqueous medium of the acid group-containing polymer with respect to 100 g of the nonconductive particles is 1 mmol or more and 40 mmol or less.
[2] The ratio of the total acid group amount measured in the aqueous medium of the acid group-containing polymer to the carbodiimide group amount of the carbodiimide compound (total acid group mmol / carbodiimide compound NCNmol) is 1.0 × 10 ^The composition for a porous membrane of a lithium ion secondary battery according to [1], which is ³ or more and 1.0 × 10 ⁵ or less.
[3] A layer of the composition for a lithium ion secondary battery porous membrane according to [1] or [2] is formed,
A porous membrane for a lithium ion secondary battery, wherein the acid group-containing polymer and the carbodiimide compound are crosslinked in the layer.
[4] The layer is a layer obtained by applying the composition for a lithium ion secondary battery porous membrane on a substrate,
The porous membrane for a lithium ion secondary battery according to [3], wherein the substrate is an electrode plate or a separator substrate.
[5] A lithium ion secondary battery comprising the porous membrane for a lithium ion secondary battery according to any one of [1] to [4].

  According to the composition for a porous membrane of a lithium ion secondary battery of the present invention, the strength is high and an undesirable phenomenon such as gas generation in the lithium ion secondary battery is not caused. The porous membrane for lithium ion secondary battery of the present invention, which can function as a separator that can improve battery performance such as high temperature cycle characteristics, and low temperature output characteristics, high temperature cycle without causing undesirable phenomena such as gas generation The lithium ion secondary battery of the present invention with improved performance such as characteristics 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.

[1. Composition for porous membrane]
The composition for a porous membrane of a lithium ion secondary battery of the present invention (hereinafter sometimes referred to as “a composition for a porous membrane”) includes non-conductive particles, an acid group-containing polymer, and a carbodiimide compound. The composition for porous membranes usually further contains water.

[1.1. Non-conductive particles
Non-conductive particles are components filled in the porous film, and the gaps between the non-conductive particles can form pores of the porous film. Since the non-conductive particles have non-conductivity, the porous film can be made insulative, and therefore a short circuit in the secondary battery can be prevented. In general, non-conductive particles have high rigidity, which can increase the mechanical strength of the porous membrane. For this reason, even if stress that causes shrinkage occurs in the base material such as the separator base material due to heat, the porous film can resist the stress, so it is possible to prevent the occurrence of a short circuit due to the shrinkage of the base material. It is.
As the non-conductive particles, inorganic particles or organic particles may be used.

  Inorganic particles are usually excellent in dispersion stability in water, hardly settled in the composition for porous membranes, and can maintain a uniform slurry state for a long time. In addition, when inorganic particles are used, the heat resistance of the porous film can usually be increased.

As the material for the non-conductive particles, an electrochemically stable material is preferable. From this point of view, preferable examples of inorganic materials for non-conductive particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ ), bakelite, oxidation. Oxide particles such as iron, silicon oxide, magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO, alumina-silica composite oxide; aluminum nitride, silicon nitride, boron nitride, etc. Nitride particles; covalently-bonded crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as barium sulfate, calcium fluoride and barium fluoride; clay fine particles such as silica, talc and montmorillonite;

  Among these, alumina, boehmite, and barium sulfate are preferable from the viewpoint of low water absorption and excellent heat resistance (for example, resistance to a high temperature of 180 ° C. or higher), and barium sulfate is particularly preferable.

  As the organic particles, polymer particles are usually used. The organic particles can control the affinity for water by adjusting the type and amount of the functional group on the surface of the organic particles, and thus can control the amount of water contained in the porous film. Organic particles are excellent in that they usually have less metal ion elution.

  Examples of the polymer that forms the non-conductive particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, phenol resin, and acrylic resin. The polymer compound forming the particles may be a homopolymer or a copolymer. In the case of a copolymer, any of a block copolymer, a random copolymer, a graft copolymer, and an alternating copolymer is used. it can. Furthermore, it may be at least partially modified or a crosslinked product. And a mixture of these may be sufficient. In the case of a cross-linked product, the cross-linking agent includes a cross-linked product having an aromatic ring such as divinylbenzene, a polyfunctional acrylate cross-linked product such as ethylene glycol dimethacrylate, and a cross-linked product having an epoxy group such as glycidyl acrylate and glycidyl methacrylate. Can be mentioned.

  When organic particles are used as the non-conductive particles, 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, and particularly preferably 250 ° C. or higher.

  The method for producing the organic particles as the non-conductive particles is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among them, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as a material for the composition for a porous membrane. Moreover, when manufacturing organic particles, it is preferable to include a dispersant in the reaction system. The organic particles are generally composed of a polymer that substantially constitutes the organic particles, but may be accompanied by any component such as an additive added during the polymerization.

  The non-conductive particles may be subjected to, for example, element substitution, surface treatment, solid solution, or the like as necessary. Further, the non-conductive particles may include one kind of the above materials alone in one particle, or may contain two or more kinds in combination at an arbitrary ratio. . Further, the non-conductive particles may be used in combination of two or more kinds of particles formed of different materials.

  Examples of the shape of the nonconductive particles include a spherical shape, an elliptical spherical shape, a polygonal shape, a tetrapod (registered trademark) shape, a plate shape, and a scale shape. Among these, from the viewpoint of increasing the porosity of the porous film and suppressing the decrease in ionic conductivity due to the porous film, a tetrapod (registered trademark) shape, a plate shape, and a scale shape are preferable.

  The volume average particle diameter of the non-conductive particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, preferably 5 μm or less, more preferably 1 μm or less. By making the volume average particle diameter of the non-conductive particles equal to or more than the lower limit of the above range, the dispersibility of the non-conductive particles in the porous film can be improved, and thus a porous film having excellent uniformity can be obtained. . Moreover, the porous film excellent in durability can be obtained by making it into an upper limit or less. Here, the volume average particle diameter of the particles represents a particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle diameter distribution measured by the laser diffraction method.

[1.2. Acid group-containing polymer)
The composition for a porous membrane of a lithium ion secondary battery of the present invention contains an acid group-containing polymer. The acid group-containing polymer is a compound different from the carbodiimide compound, and can be a particulate polymer or a water-soluble polymer. In a preferred embodiment, the composition for a porous membrane of the present invention contains both a water-soluble polymer and a particulate polymer as the acid group-containing polymer.

[1.2.1. (Particulate polymer)
The particulate polymer is a polymer particle containing an acid group. When the composition for porous membranes contains a particulate polymer, 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 lithium ion secondary battery of the present invention at the time of handling such as winding and transportation is improved. Can do. Further, since the shape of the particulate polymer is particulate, the particulate polymer can be bound to the non-conductive particles by 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 polymer is insoluble in water. Therefore, normally, the particulate polymer can be present in a dispersed state in a particle shape in the aqueous porous membrane composition. In the porous membrane, the particulate polymer can exist while maintaining a part or all of the particle shape.

  The particulate polymer usually contains an acid group-containing monomer unit, and can thereby become an acid group-containing polymer. The acid group-containing monomer unit 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 polymer having an acid group-containing monomer unit contains an acid group.

The acid group, for example, -COOH group (carboxylic acid group); - SO ₃ H group (sulfonic acid group); - _PO 3 _{H 2} group and -PO (OH) (OR) group (R is a hydrocarbon radical Phosphonic acid groups; and the like. 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 acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Among these, monocarboxylic acid is preferable, and acrylic acid and methacrylic acid are more preferable.

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

  Examples of the monomer having a phosphonic acid group (phosphonic acid monomer) include phosphoric acid-2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, ethyl phosphate- ( And (meth) acryloyloxyethyl.

Moreover, you may use the salt of the monomer mentioned above as an acid group containing monomer. Examples of such a salt include a sodium salt 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 polymer having no acid group, a part of the functional group in the particulate polymer. Or you may introduce | transduce by substituting the whole for an acid group. The repeating unit in the particulate polymer 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 polymer can be appropriately adjusted so that a desired total acid group amount is obtained. Specifically, the ratio of the acid group-containing monomer unit in the particulate polymer 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. Yes, preferably 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 polymer to be equal to or higher than the lower limit of the above range, the binding property between the porous film 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 polymer may contain 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 composition for porous film of the present invention, the particulate polymer contains a carboxylic acid primary amide monomer unit at a predetermined ratio. 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 proportion of the carboxylic acid primary amide monomer unit in the particulate polymer 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 ratio of the carboxylic acid primary amide monomer unit in the particulate polymer 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 polymer. Moreover, the rate characteristic of a secondary battery can be improved by making it below an upper limit.

  The particulate polymer may 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 heating or irradiation with energy rays. By including a crosslinkable monomer unit, the particulate polymer can be crosslinked, so that the strength and stability of the porous film can be increased. Thereby, it becomes possible to exhibit the effect | action by a particulate polymer stably. In addition, since the degree of swelling of the particulate polymer by the electrolytic solution can be prevented from becoming excessively high, normally the output characteristics of the secondary battery can be improved.

  As the crosslinkable monomer, a monomer capable of forming a crosslinked structure upon polymerization can be used. 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 polymer 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. It is 0 wt% or less, more preferably 4.0 wt% or less, and particularly preferably 3.0 wt% or less. Since the mechanical strength of the particulate polymer can be increased by setting the ratio of the crosslinkable monomer unit in the particulate polymer to be equal to or higher than the lower limit of the above range, the bonding between the porous membrane and the separator substrate or the electrode plate is possible. Wearability can be improved. 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, the molecules of the particulate polymer can be stabilized.

  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 polymer 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 or less. More preferably, it is 97% by weight or less, particularly preferably 96% by weight or less. By setting the ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer to be 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 polymer may contain an arbitrary structural unit in addition to the above-described structural unit. Examples of arbitrary structural units that can be included in the particulate polymer include structural units 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 polymer 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 polymer is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less. . By keeping the weight average molecular weight of the polymer constituting the particulate polymer in 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 polymer 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 polymer 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, and even 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 polymer within the above range, characteristics such as flexibility and winding properties of the separator and electrode provided with the porous membrane, and binding properties between the porous membrane and the separator substrate or electrode plate, etc. Is highly balanced and suitable. The glass transition temperature of the particulate polymer can be adjusted, for example, by combining various monomers.

  The volume average particle diameter D50 of the particulate polymer is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. By keeping the volume average particle diameter of the particulate polymer in the above range, the strength and flexibility of the porous film can be improved.

  The amount of acid groups measured in the aqueous medium of the particulate polymer is preferably 0.01 mmol / g or more, more preferably 0.05 mmol / g or more, and even more as the amount of acid groups per gram of the particulate polymer. Preferably it is 0.1 mmol / g or more, while preferably 15.0 mmol / g or less, more preferably 5.0 mmol / g or less, and even more preferably 1.0 mmol / g or less. The amount of acid groups measured in the aqueous medium of the particulate polymer in the composition for porous membrane is preferably 0.1 mmol / 100 g or more as the amount of acid groups with respect to 100 g of non-conductive particles, on the other hand, preferably Is 6 mmol / 100 g or less, more preferably 5 mmol / 100 g or less, and even more preferably 3 mmol / 100 g or less. When the amount of the acid group of the particulate polymer is not less than the above lower limit, the acid group can be polymerized with the carbodiimide compound to form a crosslink when the porous film is formed. Thereby, effects, such as an improvement of peel strength, can be acquired, and the performance of a secondary battery can be improved by extension. On the other hand, when the amount of acid groups in the particulate polymer is not more than the above upper limit, the proportion of uncrosslinked acid remaining in the porous membrane can be reduced, and consequently the amount of water in the porous membrane can be reduced.

  The amount of the particulate polymer in the composition 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 setting the amount of the particulate polymer to the lower limit value or more, it is possible to reduce the occurrence of problems such as powder falling from the porous film. Moreover, the air permeability and resistance of a porous film can be suppressed by making it below an upper limit. In addition, the amount of the particulate polymer in the above range usually has a high binding property between the non-conductive particles and the binding property between the porous membrane and the separator substrate or the electrode plate, It is also significant in that the flexibility of the porous membrane can be increased and the ion conductivity of the porous membrane can be increased.

The particulate polymer 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 polymer.

  As the aqueous solvent, a solvent in which the particulate polymer 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 preferred from the viewpoint that it is not flammable and a dispersion of particulate polymer 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 within a range in which the dispersed state of the particulate polymer particles 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, 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 as it is for producing the porous membrane composition of the present invention. From the viewpoint of production efficiency, 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.

[1.2.2. Water-soluble polymer)
The water-soluble polymer is a water-soluble polymer containing an acid group. When the composition for porous membrane contains a water-soluble polymer, the viscosity of the composition for porous membrane is in an appropriate range, and the operation for forming the layer of the composition for porous membrane is performed well, and a homogeneous porous membrane can be easily formed. Can be manufactured. In addition, the water-soluble polymer has a function of binding non-conductive particles by interposing between non-conductive particles in the porous film, and between the non-conductive 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. A water-soluble polymer means a polymer that satisfies the following criteria.
An aqueous solution of pH 8.0 having a polymer concentration of 40% by mass is prepared, and stirred at 25 ° C. for 1 hour to obtain an evaluation solution. The evaluation solution is transferred to a cell having an optical path length of 30 mm, and the haze of the evaluation solution is measured using a haze meter. When the haze of the evaluation solution is 60% or less, the polymer is a water-soluble polymer. .
In addition, the cloudiness of the said solution is a value calculated | required by the following Formula.
Haze = diffuse transmitted light rate / total light transmitted light × 100 (%)

  Examples of the water-soluble polymer include carboxymethyl cellulose and a water-soluble polymer containing an ethylenically unsaturated carboxylic acid monomer unit.

[1.2.2.1. (Carboxymethylcellulose)
The degree of etherification of carboxymethylcellulose is preferably 0.5 or more, more preferably 0.8 or more, preferably 1.8 or less, more preferably 1.5 or less. Here, the degree of etherification refers to the degree of substitution of hydroxyl groups (three) per anhydroglucose unit in cellulose with a substitution product such as a carboxymethyl group. The degree of etherification can theoretically take a value of 0-3. When the degree of etherification is in the above range, carboxymethylcellulose is adsorbed on the surface of the non-conductive particles and also compatible with water, so it has excellent dispersibility and the non-conductive particles are finely dispersed to the primary particle level. it can.

[1.2.2.2. Water-soluble polymer containing ethylenically unsaturated carboxylic acid monomer unit]
A water-soluble polymer containing an ethylenically unsaturated carboxylic acid monomer unit (hereinafter, this water-soluble polymer may be simply referred to as “carboxylic acid group-containing water-soluble polymer”) is used as an acid group. It contains an acid group of an ethylenically unsaturated carboxylic acid monomer, and thereby becomes an acid group-containing polymer. The ethylenically unsaturated carboxylic acid monomer unit refers to a structural unit having a structure formed by polymerizing an ethylenically unsaturated carboxylic acid monomer.
Examples of the ethylenically unsaturated carboxylic acid monomer include monocarboxylic acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof having an ethylene structure. Specific examples thereof include those similar to the carboxylic acid monomer constituting the particulate polymer. An ethylenically unsaturated carboxylic acid monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ratio of the ethylenically unsaturated carboxylic acid monomer unit in the carboxylic acid group-containing water-soluble polymer is preferably 20% by weight or more, preferably 80% by weight or less, more preferably 60% by weight or less, particularly preferably. 40% by weight or less. By increasing the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the carboxylic acid group-containing water-soluble polymer to be 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 is improved. Can do. Moreover, it can prevent that the viscosity of the composition for porous films becomes high too much by making it into an upper limit or less. Therefore, the porous film composition can be applied satisfactorily, and the rate characteristics of the secondary battery can be improved.

  The carboxylic acid group-containing water-soluble polymer may contain a (meth) acrylic acid ester monomer unit. Examples of the (meth) acrylic acid ester monomer include the same examples as those exemplified in the section of the particulate polymer. Moreover, a (meth) acrylic acid ester monomer and a (meth) acrylic acid ester monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ratio of the (meth) acrylic acid ester monomer unit in the carboxylic acid group-containing water-soluble polymer is preferably 25% by weight or more, more preferably 30% by weight or more, and particularly preferably 35% by weight or more. Preferably it is 75 weight% or less, More preferably, it is 70 weight% or less, Most preferably, it is 65 weight% or less. By setting the amount of the (meth) acrylic acid ester monomer unit in the water-soluble polymer 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 increased. Moreover, the softness | flexibility of a porous film can be improved by making it into an upper limit or less.

  The carboxylic acid group-containing water-soluble polymer may contain any structural unit in addition to the structural units described above. Examples of arbitrary structural units that can be contained in the carboxylic acid group-containing water-soluble polymer are the same as those exemplified as the structural units that can be contained in the particulate polymer, and are ethylenically unsaturated carboxylic acid monomers. Examples other than the unit and the (meth) acrylic acid ester monomer unit. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The carboxylic acid group-containing water-soluble polymer can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. In this case, the ratio of each monomer in the monomer composition is usually the same as the ratio of the structural units in the carboxylic acid group-containing water-soluble polymer.

  As an aqueous solvent, the thing similar to what is used for manufacture of a particulate polymer can be used.

  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. Of these, emulsion polymerization is 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.

[1.2.2.3. Properties of water-soluble polymer etc.)
The weight average molecular weight of the water-soluble polymer is preferably 5,000 or more, more preferably 10,000 or more, particularly preferably 20,000 or more, preferably 1,000,000 or less, more preferably 750,000. Hereinafter, it is particularly preferably 500,000 or less. By setting the weight average molecular weight of the water-soluble polymer to be 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 enhanced. Moreover, the cycle characteristic of a secondary battery can be improved by making it below an upper limit. Here, the weight average molecular weight of the water-soluble polymer can be determined by GPC as a value in terms of polystyrene using, as a developing solvent, a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide.

  The water-soluble polymer has a 2% by weight aqueous solution preferably having a viscosity of 15 mPa · s or higher, more preferably 50 mPa · s or higher, even more preferably 100 mPa · s or higher, while preferably 10000 mPa · s or lower, and more. Preferably it is 1000 mPa * s or less, More preferably, it is 500 mPa * s or less. When the viscosity of the aqueous solution of the water-soluble polymer is equal to or higher than the lower limit, the composition for a porous membrane can be made to exhibit a viscosity and can exhibit a good porous membrane peel strength. When the viscosity of the aqueous solution of the water-soluble polymer is not more than the above upper limit, the amount of water in the porous film can be set to a desired low value. The viscosity of the aqueous solution of the water-soluble polymer is a value measured using a B-type viscometer at 25 ° C. and a rotational speed of 60 rpm.

  The amount of acid groups measured in an aqueous medium of the water-soluble polymer is preferably 0.01 mmol / g or more, more preferably 0.5 mmol / g or more, and even more as the amount of acid groups per 1 g of the water-soluble polymer. Preferably it is 1.0 mmol / g or more, while preferably 15.0 mmol / g or less, more preferably 10.0 mmol / g or less, and even more preferably 7.0 mmol / g or less. Further, the amount of acid groups measured in the aqueous medium of the water-soluble polymer in the composition for porous membrane is preferably 1 mmol / 100 g or more, preferably 30 mmol as the amount of acid groups with respect to 100 g of non-conductive particles. / 100 g or less, more preferably 25 mmol / 100 g or less, still more preferably 20 mmol / 100 g or less. When the amount of the acid group of the water-soluble polymer is not less than the above lower limit, the acid group can be polymerized with the carbodiimide compound to form a crosslink when forming the porous film. Thereby, effects, such as an improvement of peel strength, can be acquired, and the performance of a secondary battery can be improved by extension. On the other hand, when the amount of acid groups in the water-soluble polymer is not more than the above upper limit, the proportion of uncrosslinked acid remaining in the porous membrane can be reduced, and consequently the amount of water in the porous membrane can be reduced.

  The amount of the water-soluble polymer in the composition for a porous membrane of the present invention is preferably 0.01 to 5.5 parts by weight with respect to 100 parts by weight of the non-conductive particles. By setting the amount of the water-soluble polymer within this range, the viscosity of the composition for the porous membrane is in an appropriate range, and the operation for forming the layer of the composition for the porous membrane is performed well, and a homogeneous porous membrane can be easily formed. It can be manufactured.

[1.2.3. Total acid group content of acid group-containing polymer]
In the composition for a porous membrane of a lithium ion secondary battery of the present invention, the total acid group amount measured in an aqueous medium of the acid group-containing polymer with respect to 100 g of non-conductive particles is 1 mmol or more, preferably 2 mmol or more. Preferably it is 3 mmol or more, while it is 40 mmol or less, preferably 25 mmol or less, more preferably 20 mmol or less.
When the porous membrane composition contains an acid group-containing polymer having a total acid group amount equal to or more than the lower limit together with the carbodiimide compound, the acid group is polymerized with the carbodiimide compound to form a crosslink when forming the porous membrane. Can do. Thereby, effects, such as an improvement of peel strength, can be acquired, and the performance of a secondary battery can be improved by extension. On the other hand, when the total acid group amount of the acid group-containing polymer is equal to or less than the above upper limit, the proportion of non-crosslinked acid remaining in the porous film can be reduced, and consequently the water content in the porous film can be reduced.

The amount of acid groups in the aqueous medium can be measured by titration in which the electric conductivity of the aqueous solution or aqueous dispersion containing the sample is adjusted and then a small amount of acid is added to measure the electric conductivity. Specifically, it can be performed by the same method as in the present embodiment.
Here, as the sample, a material containing an acid group-containing polymer and substantially free of an acid other than the acid group-containing polymer can be used. Specifically, an aqueous solution or aqueous dispersion of an acid group-containing polymer obtained by preparing an acid group-containing polymer can be used. When the aqueous solution or aqueous dispersion of the acid group-containing polymer contains a substance having an acid group in addition to the acid-containing polymer, the measurement can be performed after removing the acid group-containing polymer as necessary. Or when the density | concentration of this substance is known, the acid amount resulting from this substance can be subtracted from a measured value, and the acid amount of an acid group containing polymer can be calculated | required.

  When the porous membrane composition contains both the particulate polymer and the water-soluble polymer as the acid group-containing polymer, the total acid group amount is measured by mixing them in the production process of the porous membrane composition. However, it may be performed separately before mixing them. That is, the acid group amount was measured separately for each of the particulate polymer and the water-soluble polymer, and the total acid group amount of the acid group-containing polymer in the porous membrane composition was determined from the respective measured values and addition amounts. It can be sought.

[1.3. (Carbodiimide compound)
The composition for a porous membrane of a lithium ion secondary battery of the present invention contains a carbodiimide compound. The carbodiimide compound has a carbodiimide group represented by the general formula (1): —N═C═N— (1) in the molecule. The carbodiimide compound can react with the acid group of the acid group-containing polymer to form a crosslinked structure.
As an example of a carbodiimide compound, a compound having two or more carbodiimide groups per molecule, specifically, a general formula (2): —N═C═N—R ¹ — (2) [General formula ( In 2), R ¹ represents a divalent organic group. Suitable examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by the formula: In this specification, the modified polycarbodiimide refers to a compound obtained by reacting a reactive compound described later with polycarbodiimide.

[1.3.1. Synthesis of polycarbodiimide)
The method for synthesizing the polycarbodiimide is not particularly limited. For example, the organic polyisocyanate is reacted in the presence of a catalyst for promoting the carbodiimidization reaction of the isocyanate group (hereinafter referred to as “carbodiimidization catalyst”). Polycarbodiimide can be synthesized. The polycarbodiimide having a repeating unit represented by the general formula (2) is a copolymer of an oligomer obtained by reacting an organic polyisocyanate (carbodiimide oligomer) and a monomer copolymerizable with the oligomer. Can also be synthesized. As the organic polyisocyanate used for the synthesis of the polycarbodiimide, an organic diisocyanate is preferable.

  As an example of the organic diisocyanate used for the synthesis | combination of polycarbodiimide, the thing of Unexamined-Japanese-Patent No. 2005-49370 is mentioned, for example. Among these, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are particularly preferable from the viewpoint of storage stability of a composition for a porous membrane containing polycarbodiimide as a carbodiimide compound. An organic diisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In addition to the above organic diisocyanates, organic polyisocyanates having three or more isocyanate groups (trifunctional or higher functional organic polyisocyanates), and stoichiometric excesses of trifunctional or higher organic polyisocyanates and difunctional or higher polyfunctionality. Terminal isocyanate prepolymer obtained by reaction with a reactive active hydrogen-containing compound (hereinafter, the trifunctional or higher functional organic polyisocyanate and the terminal isocyanate prepolymer are collectively referred to as “trifunctional or higher functional organic polyisocyanates”). May be used. Examples of such trifunctional or higher functional organic polyisocyanates include those described in JP-A-2005-49370. Trifunctional or higher functional organic polyisocyanates may be used alone or in combination of two or more at any ratio. The amount of the trifunctional or higher functional organic polyisocyanate used in the polycarbodiimide synthesis reaction is preferably 40 parts by weight or less, more preferably 20 parts by weight or less per 100 parts by weight of the organic diisocyanate.

  Further, in the synthesis of polycarbodiimide, an organic monoisocyanate can be added as necessary. By adding an organic monoisocyanate, when the organic polyisocyanate contains organic polyisocyanates having a functionality of 3 or more, the molecular weight of the resulting polycarbodiimide can be appropriately regulated, and the organic diisocyanate is used in combination with the organic monoisocyanate. By doing so, a polycarbodiimide having a relatively small molecular weight can be obtained. Examples of such organic monoisocyanates include those described in JP-A-2005-49370. An organic monoisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the organic monoisocyanate used in the synthesis reaction of the polycarbodiimide depends on the molecular weight required for the polycarbodiimide to be obtained and the presence or absence of the use of trifunctional or higher functional organic polyisocyanates. It is preferably 40 parts by weight or less, more preferably 20 parts by weight or less per 100 parts by weight of the functional or higher organic polyisocyanate) component.

  Examples of carbodiimidization catalysts include phospholene compounds, metal carbonyl complexes, metal acetylacetone complexes, and phosphate esters. Specific examples of these are disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-49370. A carbodiimidization catalyst may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the carbodiimidization catalyst used is preferably 0.001 to 30 parts by weight, more preferably 0, per 100 parts by weight of the total organic isocyanate (organic monoisocyanate, organic diisocyanate, and trifunctional or higher organic polyisocyanate) component. 0.01 to 10 parts by weight.

  The carbodiimidization reaction of organic polyisocyanate can be carried out in the absence of a solvent or in a suitable solvent. As a solvent for carrying out the synthesis reaction in a solvent, a solvent capable of dissolving the polycarbodiimide or carbodiimide oligomer generated by heating during the synthesis reaction can be appropriately selected. Examples of the solvent include halogenated hydrocarbon solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, amide solvents, aprotic polar solvents, and acetate solvents. Specific examples of these are disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-49370. These solvents may be used alone or in combination of two or more at any ratio. The amount of the solvent used in the polycarbodiimide synthesis reaction is such that the concentration of the total organic isocyanate component is preferably 0.5 to 60% by weight, more preferably 5 to 50% by weight. If the concentration of the total organic isocyanate component in the solvent is too high, the resulting polycarbodiimide or carbodiimide oligomer may gel during the synthesis reaction. Moreover, when the density | concentration of all the organic isocyanate components in a solvent is too low, reaction rate will become slow and productivity may fall.

  The temperature of the carbodiimidization reaction of the organic polyisocyanate is appropriately selected according to the type of the organic isocyanate component and the carbodiimidization catalyst, but is preferably 20 to 200 ° C. In the carbodiimidization reaction of the organic polyisocyanate, the organic isocyanate component may be added in the whole amount before the reaction, or a part or the whole thereof may be added continuously or stepwise during the reaction. Further, in the present invention, a compound capable of reacting with an isocyanate group is added at an appropriate reaction stage from the initial stage to the late stage of the carbodiimidization reaction of the organic polyisocyanate, and the terminal isocyanate group of the polycarbodiimide is sealed. The molecular weight of the polycarbodiimide can also be adjusted. Further, the molecular weight of the resulting polycarbodiimide can be regulated to a predetermined value by adding in the latter stage of the carbodiimidization reaction of the organic polyisocyanate. Examples of such a compound capable of reacting with an isocyanate group include alcohols such as methanol, ethanol, i-propanol and cyclohexanol; and amines such as dimethylamine, diethylamine and benzylamine.

  As a monomer copolymerizable with a carbodiimide oligomer, an oligomer obtained by using a bivalent or higher alcohol as a monomer and an ester thereof, for example, a divalent such as ethylene glycol or propylene glycol Alcohol or polyalkylene oxide, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monoacrylate, and polypropylene glycol monoacrylate are preferred.

  For example, polycarbodiimide having a polycarbodiimide group and a monomer unit derived from a divalent alcohol is synthesized by copolymerizing a divalent alcohol having a hydroxyl group at both ends of the molecular chain with a carbodiimide oligomer by a known method. can do. Thus, when the polycarbodiimide as the carbodiimide compound has a monomer unit derived from a divalent or higher alcohol, preferably a monomer unit derived from a divalent alcohol, the composition for porous membrane containing the polycarbodiimide is used. The wettability of the formed porous membrane with respect to the electrolytic solution is improved, and the pouring property of the electrolytic solution in the production of the secondary battery can be improved. In addition, when the above-mentioned alcohol is copolymerized, the water solubility of the polycarbodiimide can be increased, and the polycarbodiimide is self-micelleized in water (the hydrophobic carbodiimide group is covered with a hydrophilic ethylene glycol chain). Therefore, chemical stability can be improved.

  The polycarbodiimide compound cross-linking agent described above can be used as a solution or as a solid separated from the solution for the preparation of the composition for a porous membrane of the present invention. As a method for separating polycarbodiimide from a solution, for example, a polycarbodiimide solution is added to a non-solvent inert to the polycarbodiimide, and the resulting precipitate or oil is separated and collected by filtration or decantation. A method of separating and collecting by spray drying; a method of separating and collecting by using a change in solubility with respect to the temperature of the solvent used in the synthesis of the obtained polycarbodiimide, that is, immediately after the synthesis, the solvent is dissolved in the solvent In the case where polycarbodiimide is precipitated by lowering the temperature of the system, a method of separating and collecting from the turbid liquid by filtration or the like can be exemplified, and further, these separation and collecting methods can be appropriately combined. The number average molecular weight in terms of polystyrene (hereinafter referred to as “Mn”) determined by gel permeation chromatography (GPC) of polycarbodiimide in the present invention is preferably 1 from the viewpoint of increasing the crosslinking rate with the acid group-containing polymer. 1,000 to 200,000, more preferably 2,000 to 100,000 or less.

[1.3.2. Synthesis of modified polycarbodiimide)
Next, a method for synthesizing the modified polycarbodiimide will be described. The modified polycarbodiimide is prepared by adding at least one reactive compound to at least one polycarbodiimide having a repeating unit represented by the general formula (2) at an appropriate temperature in the presence or absence of a suitable catalyst. It can be synthesized by reaction (hereinafter referred to as “denaturation reaction”).

  As a reactive compound used for the synthesis of the modified polycarbodiimide, one group having reactivity with polycarbodiimide (hereinafter, simply referred to as “reactive group”) is included in one molecule, and another functional group. A compound having a group may be used. This reactive compound can be an aromatic compound, an aliphatic compound or an alicyclic compound, and the ring structure in the aromatic compound and the alicyclic compound may be a carbocyclic ring or a heterocyclic ring. Examples of the reactive group in the reactive compound include a group having active hydrogen. Examples of reactive groups include carboxyl groups, primary amino groups, and secondary amino groups. The reactive compound may further have another functional group in the molecule in addition to one reactive group. Examples of functional groups other than reactive groups possessed by the reactive compound include groups having the action of promoting the crosslinking reaction of polycarbodiimide and / or modified polycarbodiimide, and the second and subsequent ( That is, a group having the above-mentioned active hydrogen may be mentioned, which is different from the reactive group described above. Examples thereof include a carboxylic acid anhydride group and a tertiary amino group, and a carboxyl group and a primary or secondary amino group exemplified as a group having active hydrogen. As these other functional groups, two or more identical or different groups may exist in one molecule of the reactive compound.

  Examples of the reactive compound include those described in JP-A-2005-49370. Of these, trimellitic anhydride and nicotinic acid are preferable. A reactive compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the reactive compound used in the modification reaction for synthesizing the modified polycarbodiimide can be appropriately adjusted according to the kind of polycarbodiimide and the reactive compound, the physical properties required for the resulting modified polycarbodiimide, and the like. The ratio of the reactive group in the reactive compound to 1 mol of the repeating unit represented by the general formula (2) of the polycarbodiimide is preferably 0.01 mol or more, more preferably 0.02 mol or more, while preferably Is 1 mol or less, more preferably 0.8 mol or less. There exists a possibility that the storage stability of the composition for porous films containing a modified polycarbodiimide may fall that the said ratio is less than 0.01 mol. On the other hand, when the ratio exceeds 1 mol, the original properties of polycarbodiimide may be impaired.

  In the modification reaction, the reaction between the reactive group in the reactive compound and the repeating unit represented by the general formula (2) of the polycarbodiimide usually proceeds quantitatively, and the functionality commensurate with the amount of the reactive compound used. Groups can be introduced into the modified polycarbodiimide. The modification reaction can be carried out in the absence of a solvent, but is preferably carried out in a suitable solvent. As such a solvent, a solvent which is inactive with respect to polycarbodiimide and a reactive compound and can dissolve them can be appropriately selected. Examples of the solvent include ether solvents, amide solvents, ketone solvents, aromatic hydrocarbon solvents, and aprotic polar solvents that can be used for the synthesis of the above-described polycarbodiimide. These solvents may be used alone or in combination of two or more at any ratio. Moreover, when the solvent used at the time of the synthesis | combination of polycarbodiimide can be used for modification | denaturation reaction, the polycarbodiimide solution obtained by the synthesis | combination can also be used as it is. The amount of the solvent used in the modification reaction is preferably 10 to 10,000 parts by weight, preferably 50 to 5,000 parts by weight per 100 parts by weight of the total reaction raw material.

  The temperature of the modification reaction is appropriately selected according to the type of polycarbodiimide or reactive compound, but is preferably −10 to 100 ° C. or less, more preferably −10 to 80 ° C. The Mn of the modified polycarbodiimide in the present invention is preferably 1,000 to 200,000, more preferably 2,000 to 400,000, from the viewpoint of increasing the crosslinking rate with the acid group-containing polymer.

[1.3.3. Properties of carbodiimide compound etc.)
The chemical formula amount (NCN equivalent) per carbodiimide group (—N═C═N—) of the carbodiimide compound is preferably 300 to 600, more preferably 400 to 500. When the NCN equivalent of the carbodiimide compound is too small, the storage stability of the composition for a porous membrane is lowered. On the other hand, if the NCN equivalent of the carbodiimide compound is too large, the crosslinking reaction will not proceed sufficiently.

The NCN equivalent of the carbodiimide compound is obtained, for example, by obtaining the polystyrene-equivalent number average molecular weight of the carbodiimide compound using GPC (gel permeation chromatography) and using IR (infrared spectroscopy) of the carbodiimide group per molecule of the carbodiimide compound. The number can be quantitatively analyzed and calculated using the following formula.
NCN equivalent = (Number average molecular weight in terms of polystyrene of carbodiimide compound) / (Number of carbodiimide groups per molecule of carbodiimide compound)

  The viscosity of the 1% by weight aqueous solution of the carbodiimide compound is preferably 5000 mPa · s or less, more preferably 700 mPa · s or less, particularly preferably 150 mPa · s or less, from the viewpoint that the adhesion strength of the porous film can be improved. It is. The viscosity of a 1% by weight aqueous solution of a carbodiimide compound is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

The content ratio of the carbodiimide compound in the composition for a porous membrane of a lithium ion secondary battery of the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts per 100 parts by weight of the non-conductive particles. Part by weight, more preferably 0.01 to 1 part by weight. The amount of the carbodiimide group of the carbodiimide compound in the porous membrane composition is preferably 5.0 × 10 ³ mol / 100 g or more, more preferably 8.0 × 10, as the amount of carbodiimide group with respect to 100 g of non-conductive particles. ³ mol / 100 g or more, even more preferably 1.0 × 10 ⁴ mol / 100 g or more, while preferably 1.5 × 10 ⁶ mol / 100 g or less, more preferably 1.3 × 10 ⁶ mol / 100 g or less. Even more preferably, it is 3.0 × 10 ⁵ mol / 100 g or less. By setting the content ratio of the carbodiimide compound in the composition for a porous film within the above range, the strength of the porous film and the adhesion strength between the porous film and the substrate can be increased, and the cycle characteristics of the secondary battery can be improved.

[1.3.4. Carbodiimide compound content)
In the composition for a porous membrane of a lithium ion secondary battery of the present invention, the ratio of the total acid group amount of the acid group-containing polymer to the carbodiimide group amount of the carbodiimide compound is the value of total acid group amount mmol / carbodiimide compound NCNmol. 1.0 × 10 ^{3 to} 1.0 × 10 ⁵ is preferable, 5.0 × 10 ^{3 to} 7.0 × 10 ⁴ is more preferable, and 1.0 × 10 ^{4 to} 5.0 is preferable. × and more preferably 10 ^4.
In the composition for a porous membrane, when the ratio of the acid group-containing polymer to the carbodiimide compound is equal to or more than the lower limit of the above range, the acid group is polymerized with the carbodiimide compound to form a sufficient amount of crosslinks when forming the porous membrane. can do. Thereby, effects, such as an improvement of peel strength, can be acquired, and the performance of a secondary battery can be improved by extension. On the other hand, when the ratio of the acid group-containing polymer is not more than the above upper limit, the ratio of the non-crosslinked acid remaining in the porous film can be reduced, and the water content in the porous film can be reduced.

[1.4. water〕
The composition for a porous membrane of the present invention usually contains water. Water functions as a medium, that is, a solvent or a dispersion medium in the porous membrane composition. Usually, in the composition for porous membranes, the nonconductive particles and the particulate polymer are dispersed in water, and a part or all of the water-soluble polymer and the carbodiimide compound are 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 composition is preferably set so that the solid content concentration of the porous membrane composition falls within a desired range. The solid content concentration of the specific porous membrane composition 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 wt% or less, even more preferably 70 wt% or less, and particularly preferably 65 wt% 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.

[1.5. (Dispersant)
The composition for porous membranes may contain a dispersant. By including a dispersant, components such as non-conductive particles and particulate polymer can be stably dispersed in the composition for a porous membrane. As the dispersant, known dispersants such as sodium dodecylbenzenesulfonate and sodium polyacrylate can be used.

  As the dispersing agent, a dispersing agent whose viscosity is lower than a predetermined value is usually used. Specifically, the viscosity of the 2% by weight aqueous solution of the dispersant is preferably less than 15 mPa · s, more preferably 10 mPa · s or less, and even more preferably 5 mPa · s or less. Dispersibility can be improved by using such a low-viscosity dispersant. The viscosity of the aqueous solution of the dispersant is a value measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer.

  The amount of the dispersant in the composition for a porous membrane can be appropriately adjusted so as to obtain an appropriate dispersion. Specifically, the ratio of the dispersant to 100 parts by weight of the nonconductive particles can be 0.1 to 5 parts by weight.

[1.6. Other optional ingredients]
The composition for porous membranes can contain arbitrary components 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, it may contain a binder and a dispersant other than the acid group-containing polymer, 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. .

[1.7. Properties of porous film composition]
The viscosity of the composition for a porous membrane is preferably 15 to 500 mPa · s. By setting the viscosity of the composition for a porous film within this range, it is possible to apply a good composition for a porous film. The viscosity of the composition 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.

[1.8. Method for producing composition for porous membrane]
Although the manufacturing method of the composition for porous membranes is not specifically limited, Usually, each component mentioned above is mixed and obtained. There is no particular limitation on the mixing order. There is no particular limitation on the mixing method. Usually, in order to disperse non-conductive particles quickly, mixing is performed using a disperser as a mixing device.

  The disperser is preferably an apparatus capable of uniformly dispersing and mixing the above components. Examples of the disperser include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Among them, a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix is particularly preferable because a high dispersion share can be added.

[2. (Porous membrane)
The porous membrane for a lithium ion secondary battery of the present invention (hereinafter sometimes simply referred to as the porous membrane of the present invention) forms a layer of the composition for a porous membrane of the lithium ion secondary battery of the present invention. Inside, an acid group containing polymer and a carbodiimide compound are cross-linked.
The layer of the porous membrane composition can be obtained by applying the porous membrane composition on a substrate. A base material is a member used as the object which forms the film | membrane of the composition for porous films. There is no restriction | limiting in a base material, For example, the film | membrane of the composition for porous films may be formed in the surface of a peeling film, a solvent may be 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.

  The porous film of the present invention can be formed by cross-linking the acid group-containing polymer and the carbodiimide compound in the layer of the composition for porous film. Since the crosslinking reaction usually proceeds when the composition for porous membrane is dried, it can be performed by drying the layer of the composition for porous membrane. Specific examples of the drying method include drying with warm air, hot air, low-humidity air, and the like; vacuum drying; drying method by irradiation with infrared rays, far infrared rays, and electron beams.

  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 compound from the porous membrane composition can be efficiently removed. 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 porous membrane composition, 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.

[3. (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.
The separator provided with the porous film of the present invention has a high peel strength because it has a crosslinked structure formed by a crosslinking reaction between an acid group-containing polymer and a carbodiimide compound. The separator provided with the porous membrane of the present invention can further reduce the amount of water remaining by setting the total acid group amount of the acid group-containing polymer within a specific range. Low tendency to cause undesired phenomena. Therefore, when the separator provided with the porous membrane of the present invention is used as a constituent element of a secondary battery, such secondary batteries have less undesirable phenomena such as gas generation, and low temperature output characteristics, high temperature cycle characteristics, etc. Performance 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.

[4. 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.

  An electrode provided with the porous film of the present invention has a high peel strength by having a cross-linked structure formed by a cross-linking reaction between an acid group-containing polymer and a carbodiimide compound. The electrode provided with the porous membrane of the present invention can further reduce the amount of water remaining by setting the total acid group amount of the acid group-containing polymer within a specific range. Low tendency to cause undesired phenomena. Therefore, when the electrode having the porous membrane of the present invention is used as a constituent element of a secondary battery, such secondary battery has less undesirable phenomena such as gas generation, and has low temperature output characteristics, high temperature cycle characteristics, etc. Performance can be improved.

[4.1. 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.

[4.2. 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, the soft polymer particles exemplified below may be used as the particulate polymer. 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.

[5. 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 is high in strength and has a low tendency to cause undesired phenomena such as gas generation in the secondary battery. Therefore, when the electrode and / or separator provided with the porous membrane of the present invention is used as a constituent element of a secondary battery, such secondary battery has less undesirable phenomena such as gas generation, low temperature output characteristics, high temperature Performance such as cycle characteristics can be improved.

[5.1. 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.

[5.2. 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.

[5.3. 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 methyl ethyl carbonate (MEC). 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 methyl ethyl 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.

[5.4. 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, measurements and evaluations regarding peel strength, porous film moisture content, low temperature output characteristics, cell volume change, high temperature cycle characteristics, acid group content, and viscosity were performed as follows.

(1) Peel strength (peel strength between separator substrate and porous film)
A separator provided with a porous film was cut into a rectangle having a width of 10 mm and a length of 100 mm to obtain a test piece. Cellophane tape (specified in JIS Z1522) was attached to the porous film surface of the test piece. The cellophane tape was fixed flat on the horizontal surface of the test bench, and one end of the separator was peeled off by pulling at a pulling speed of 10 mm / min in the direction perpendicular to the cellophane tape surface, and the stress at that time 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

(2) Moisture content of porous membrane A separator provided with a porous membrane was cut into a size of 10 cm width x 10 cm length to obtain a test piece. This test piece was left for 24 hours in an environment of a temperature of 25 ° C. and a dew point temperature of −60 ° C. 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 regarded as the moisture content of the porous film and evaluated according to the following criteria.

A: The moisture content of the porous membrane is less than 200 ppm B: The moisture content of the porous membrane is 200 ppm or more and less than 300 ppm C: The moisture content of the porous membrane is 300 ppm or more and less than 400 ppm D: The moisture content of the porous membrane is 400 ppm or more

(3) Low temperature output characteristics The 800 mAh wound type lithium ion secondary battery produced in the examples and comparative examples was allowed to stand for 24 hours in an environment at 25 ° C, and then 4.35V in an environment at 25 ° C. , 0.1 C, 5 hours charging operation was performed, and the voltage Vt0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., the voltage Vt1 15 seconds after the start of discharge was measured, and the voltage drop ΔVt was calculated by the equation ΔVt = Vt0−Vt1. The calculated voltage drop amount ΔVt was evaluated according to the following criteria. It shows that it is excellent in low temperature output characteristics, so that voltage drop amount (DELTA) Vt is small.

A: Voltage drop amount ΔVt is less than 120 mV B: Voltage drop amount ΔVt is 120 mV or more and less than 140 mV C: Voltage drop amount ΔVt is 140 mV or more and less than 160 mV D: Voltage drop amount ΔVt is 160 mV or more

(4) Cell volume change before and after high-temperature cycle charge / discharge After the lithium ion secondary battery of the 800 mAh wound-type cell produced in Examples and Comparative Examples was allowed to stand in an environment of 25 ° C. for 24 hours, 25 ° C. After charging and discharging with 4.35V, 0.1C charge, 2.75V, 0.1C discharge, the wound cell was immersed in liquid paraffin and the volume Vm0 was It was measured. Furthermore, in a 60 ° C environment, charging and discharging with one cycle of 4.35 V and 0.1 C charging and subsequent 2.75 V and 0.1 C discharging are repeated, and the wound cell after 1000 cycles flows. It was immersed in paraffin and its volume Vm1 was measured. The cell volume increase rate ΔVm (%) before and after the high temperature cycle charge / discharge was calculated by the formula ΔVm = (Vm1−Vm0) / Vm0 × 100. The calculated cell volume increase rate ΔVm was evaluated according to the following criteria. It shows that it is excellent in gas generation | occurrence | production suppression, so that this value is small.

A: Volume increase rate ΔVm is less than 20% B: Volume increase rate ΔVm is 20% or more and less than 30% C: Volume increase rate ΔVm is 30% or more and less than 40% D: Volume increase rate ΔVm is 40% or more

(5) High-temperature cycle characteristics The lithium ion secondary battery of the 800 mAh wound type cell produced in the examples and comparative examples was allowed to stand for 24 hours in an environment at 25 ° C, and then in an environment at 25 ° C. Charging / discharging operation was performed at 35V, 0.1C charge, 2.75V, 0.1C discharge, and the initial capacity C0 was measured. Further, in a 60 ° C. environment, charging and discharging with one cycle of 4.35 V and 0.1 C charging and subsequent 2.75 V and 0.1 C discharging were repeated, and the capacity C1 after 1000 cycles was measured. The capacity retention rate ΔC (%) was calculated by the formula ΔC = C1 / C0 × 100. The calculated capacity retention rate ΔC was evaluated according to the following criteria. It shows that it is excellent in high temperature cycling characteristics, so that this value is large.

A: Capacity maintenance ratio ΔC is 70% or more B: Capacity maintenance ratio ΔC is 60% or more and less than 70% C: Capacity maintenance ratio ΔC is 50% or more and less than 60% D: Capacity maintenance ratio ΔC is less than 50%

(6) Method for measuring the amount of acid groups in an aqueous medium As a sample, an aqueous solution or aqueous dispersion of an acid group-containing polymer (water-soluble polymer or particulate polymer) (solid content concentration adjusted to 2%) Was used. The sample was placed in a glass container having a capacity of 150 ml washed with distilled water so that the weight of the acid group-containing polymer was 50 g, and a solution conductivity meter (manufactured by Kyoto Electronics Co., Ltd .: CM-117, used cell type: K- 121) and stirred. Thereafter, stirring was continued until the addition of hydrochloric acid was completed.
0.1 N sodium hydroxide was added to the sample so that the electrical conductivity of the sample was 2.5 mS to 3.0 mS. Thereafter, after 6 minutes, the electrical conductivity was measured. This value was taken as the electrical conductivity at the start of measurement. Immediately after this measurement, 0.5 ml of 0.1 N hydrochloric acid was added to the sample, and the electrical conductivity was measured after 30 seconds. As described above, the addition of hydrochloric acid immediately after the measurement in the previous stage and the measurement of the electric conductivity after 30 seconds were repeated until the electric conductivity of the sample became equal to or higher than the electric conductivity at the start of the measurement.

The obtained electric conductivity data is plotted on a graph with the electric conductivity (unit “mS”) on the vertical axis (Y coordinate axis) and the cumulative amount of added hydrochloric acid (unit “mmol”) on the horizontal axis (X coordinate axis). Plotted. Thus, a hydrochloric acid amount-electric conductivity curve having three change points (the points at which the graph bends) was obtained. The X coordinate of the three change points and the X coordinate at the end of the addition of hydrochloric acid are respectively set to P ₁ , P ₂ , P ₃ and P _{4 in} order from the smallest value. X coordinate, divided from zero to coordinate _{P 1,} segment from the coordinates _{P 1} to the coordinates _{P 2,} segment from the coordinates _{P j} to the coordinates _{P 3,} and four categories of classification from the coordinate _{P 3} to the coordinates _{P 4} For each of the data, approximate straight lines L ₁ , L ₂ , L ₃ and L ₄ were obtained by the method of least squares. The X coordinate of the intersection of the approximate line L ₁ and the approximate line L ₂ is A ₁ (mmol), the X coordinate of the intersection of the approximate line L ₂ and the approximate line L ₃ is A ₂ (mmol), and the approximate line L ₃ is approximated The X coordinate of the intersection with the straight line L ₄ was defined as A ₃ (mmol).
Acid groups per acid group-containing polymer 1g of (mmol), was calculated by subtracting the _{A 1} from _{A 3.}

(7) Viscosity A 2% aqueous solution of a water-soluble polymer or dispersant was prepared, and the viscosity was measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer. Sodium polyacrylate, which is a dispersant, was common in all Examples and Comparative Examples, and the viscosity of a 2% aqueous solution was 3 mPa · s.

(8) Turbidity of aqueous polymer solution (determination of water solubility)
An aqueous solution of pH 8.0 having a polymer concentration of 40% by mass was prepared, and stirred at 25 ° C. for 1 hour to prepare an evaluation solution.
The evaluation solution was transferred to a cell having an optical path length of 30 mm, and the haze of the evaluation solution was measured using a haze meter. When the haze of the evaluation solution was 60% or less, the polymer was regarded as a water-soluble polymer. .
In addition, the cloudiness of the said solution is a value calculated | required by the following Formula.
Haze = diffuse transmitted light rate / total light transmitted light × 100 (%)

<Example 1>
(1-1. Production of water-soluble polymer)
In a 5 MPa pressure vessel equipped with a stirrer, as a monomer composition, 30 parts of methacrylic acid, 57 parts of ethyl acrylate, 13 parts of butyl acrylate; 1 part of sodium dodecylbenzenesulfonate as an emulsifier; 150 parts of ion-exchanged water; As a polymerization initiator, 0.5 part of potassium persulfate was added and sufficiently stirred. Then, it heated to 60 degreeC and superposition | polymerization was started. By continuing the polymerization until the polymerization conversion rate reached 96%, an aqueous solution of a water-soluble polymer was obtained.
A part of the aqueous solution of the obtained water-soluble polymer was taken, and ion exchange water was further added thereto to adjust the solid content concentration to 2%. Using this as a sample, the amount of acid groups and the viscosity were measured.
Moreover, pH 8.0 aqueous solution of the obtained water-soluble polymer was adjusted, and turbidity was measured.

(1-2. Preparation of dispersion of non-conductive particles)
100 parts of barium sulfate (volume average particle diameter 0.4 μm, BET specific surface area 4.5 g / m ² ) as non-conductive particles, 1.0 part of sodium polyacrylate as a dispersant, and step (1-1) 1.6 parts of the aqueous solution of the water-soluble polymer obtained in (1) was mixed on the basis of the solid content, and water having an electric conductivity of 10 μS / cm was added to the mixture to make the solid content concentration 50% by weight. Then, it was dispersed for 1 hour at 4000 rpm and 5.4 Wh / kg using a medialess dispersion apparatus (manufactured by IKA, in-line type pulverizer MKO) to obtain a dispersion of non-conductive particles.

(1-3. Production of water-insoluble particulate polymer)
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (product name “Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate, The gas phase portion 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 exchange water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94 parts of butyl acrylate, 2 parts of acrylonitrile, 2 parts of methacrylic acid, N- A monomer mixture was obtained by mixing 1 part of methylolacrylamide and 1 part of acrylamide. 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 particles of (meth) acrylic polymer as a particulate polymer.
The obtained particulate polymer had a volume average particle diameter D50 of 0.36 μm and a glass transition temperature of −45 ° C.
A part of the aqueous dispersion of the obtained particulate polymer was taken, and ion exchanged water was further added thereto to adjust the solid content concentration to 2%. Using this as a sample, the amount of acid groups was measured.

(1-4. Production of composition for porous membrane)
A carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark)) as a crosslinking agent in a predetermined amount (non-conductive particle content: 100 parts) of the non-conductive particle dispersion obtained in step (1-2). ) SV-02, NCN equivalent 429, one-phase water-soluble) was added in an amount of 0.1 part, and an aqueous dispersion of the particulate polymer obtained in step (1-3) was added in an amount of 6 parts (based on solid content). Furthermore, 0.2 part of a polyethylene glycol type surfactant (San Nopco SN wet 366) was mixed to obtain a slurry of the composition for a porous membrane.

(1-5. Production of separator)
A separator base material (thickness 16 μm, Gurley value 210 s / 100 cc) made of a polyethylene porous base material was prepared. The porous membrane composition obtained in the step (1-4) was applied to both surfaces of the prepared separator substrate and dried at 80 ° C. for 2 minutes. This obtained the separator provided with a separator base material and the porous membrane provided in the both surfaces. Each thickness of the porous film on both sides of the obtained separator was 3 μm.
About the obtained separator, peel strength and the moisture content of the porous film were measured.

(1-6. Production of negative electrode)
Artificial graphite (volume average particle size: 15.6 μm) 100 parts, 1 part of a 2% aqueous solution of carboxymethyl cellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener, and a predetermined amount of ions Exchanged water (in a solid content concentration of 68%) was mixed at 25 ° C. for 60 minutes. Further, ion-exchanged water was added to adjust the solid content concentration to 62%, and the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.
Particulate styrene-butadiene rubber (1,3-butadiene / styrene / itaconic acid / 2-hydroxyethyl acrylate = 33.5 parts / 62 parts / 3.5 parts / 1 part) 1.5 wt. Parts (solid content basis) and ion-exchanged water were added, adjusted to a final solid content concentration of 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode having good fluidity.
The obtained slurry composition for secondary battery negative electrode was applied on a copper foil having a thickness of 20 μm 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 conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material before pressing. The negative electrode raw material before pressing was rolled with a roll press to obtain a negative electrode after pressing with a negative electrode active material layer thickness of 80 μm.

(1-7. Production of positive electrode)
100 parts of LiCoO ₂ having a volume average particle size of 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 solid PVDF (manufactured by Kureha, # 7208) as the binder In an amount corresponding to 2 minutes, 2 parts and NMP were mixed so that the total solid concentration was 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, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material before pressing. The positive electrode raw material before pressing was rolled by a roll press to obtain a positive electrode after pressing with a positive electrode active material layer thickness of 100 μm.

(1-8. Production of lithium ion secondary battery)
The pressed positive electrode obtained in the step (1-7) was cut into a size of 49 cm × 5 cm to obtain a rectangular positive electrode. The separator obtained in step (1-5) was cut into a size of 55 cm × 5.5 cm to obtain a rectangular separator. Furthermore, the negative electrode after pressing obtained in the step (1-6) was cut into a size of 50 cm × 5.2 cm to obtain a rectangular negative electrode. A rectangular separator was disposed on the surface of the rectangular positive electrode on the positive electrode active material layer side. Furthermore, a rectangular negative electrode was disposed on the surface of the rectangular separator opposite to the positive electrode side so that the surface on the negative electrode active material layer side faces the separator. This was wound by a winding machine to obtain a wound body. The wound body was pressed at 60 ° C. and 0.5 MPa to obtain a flat body. The flat body is wrapped with an aluminum wrapping case as a battery case, and an electrolytic solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF _{6 with a} concentration of 1 M) is air. Injected so as not to remain. Further, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior. Thus, an 800 mAh wound type lithium ion secondary battery was manufactured.
About the obtained lithium ion secondary battery, the low temperature output characteristic, the cell volume change before and after a high temperature cycle test, and the high temperature cycle characteristic were evaluated.

<Example 2>
In the production of the water-soluble polymer in the step (1-1), the components of the monomer composition and their amounts were changed to 50 parts of methacrylic acid, 30 parts of ethyl acrylate, 10 parts of butyl acrylate, and 10 parts of methyl methacrylate. A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the measurement was performed and evaluated for the lithium ion secondary battery and its components.

<Example 3>
In the production of the water-soluble polymer in step (1-1), the components of the monomer composition and the amounts thereof were changed to 10 parts methacrylic acid, 40 parts methyl methacrylate, 40 parts ethyl acrylate, and 10 butyl acrylate. A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the measurement was performed and evaluated for the lithium ion secondary battery and its components.

<Example 4>
In the preparation of the dispersion of nonconductive particles in the step (1-2), an acrylic polymer (ethylene glycol dimethacrylate / acrylic acid = 99) having a volume average particle diameter of 0.65 μm was used as the nonconductive particles instead of barium sulfate. A lithium ion secondary battery was produced in the same manner as in Example 1 except that a part / 1.0 part monomer composition was polymerized to form particles). The element was measured and evaluated.

<Example 5>
In the preparation of the dispersion of non-conductive particles in the step (1-2), lithium was added in the same manner as in Example 1 except that the amount of the aqueous solution of the water-soluble polymer was changed to 0.5 part on the basis of the solid content. An ion secondary battery was manufactured, and the lithium ion secondary battery and its constituent elements were measured and evaluated.

<Example 6>
In the preparation of the dispersion of non-conductive particles in the step (1-2), the amount of the aqueous solution of the water-soluble polymer is changed to 5.0 parts on the basis of the solid content, and the amount of the crosslinking agent added is 0.5 parts. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the lithium ion secondary battery and its constituent elements were measured and evaluated.

<Example 7>
In the production of the porous membrane composition in the step (1-4), a lithium ion secondary battery was produced in the same manner as in Example 1 except that the addition amount of the crosslinking agent was changed to 0.05 part. The secondary battery and its constituent elements were measured and evaluated.

<Example 8>
In the production of the porous membrane composition in the step (1-4), a lithium ion secondary battery was produced in the same manner as in Example 1 except that the addition amount of the crosslinking agent was changed to 5 parts. The battery and its components were measured and evaluated.

<Example 9>
In the production of the porous membrane composition in the step (1-4), the product type of the carbodiimide compound as a cross-linking agent is Carbodilite (registered trademark) V-02 (Nisshinbo Chemical Co., Ltd., NCN equivalent 600, one-phase water-soluble The lithium ion secondary battery was produced in the same manner as in Example 1 except that the measurement was performed on the lithium ion secondary battery and its components.

<Example 10>
In the production of the porous membrane composition in the step (1-4), the product type of the carbodiimide compound as a cross-linking agent is Carbodilite (registered trademark) V-04 (Nisshinbo Chemical Co., Ltd., NCN equivalent 335, one-phase water-soluble The lithium ion secondary battery was produced in the same manner as in Example 1 except that the measurement was performed on the lithium ion secondary battery and its components.

<Example 11>
In the preparation of the dispersion of non-conductive particles in the step (1-2), instead of the water-soluble polymer obtained in the step (1-1), carboxymethylcellulose sodium salt (product name “Daicel 1220”, A lithium ion secondary battery was produced in the same manner as in Example 1 except that Daicel Finechem Co., Ltd., with a degree of etherification of 0.8 to 1.0) was used, and measurements were made on the lithium ion secondary battery and its components. And evaluation.

<Example 12>
In the preparation of the dispersion of non-conductive particles in the step (1-2), as a water-soluble polymer, instead of the one obtained in the step (1-1), carboxymethylcellulose sodium salt (product name “Daicel 1380”, A lithium ion secondary battery was produced in the same manner as in Example 1 except that Daicel Finechem Co., Ltd. (degree of etherification: 1.0 to 1.5) was used, and measurement of the lithium ion secondary battery and its components And evaluation.

<Example 13>
In the preparation of the dispersion of non-conductive particles in the step (1-2), an example was used except that α-alumina particles (volume average particle diameter 0.6 μm) were used as the non-conductive particles instead of barium sulfate. A lithium ion secondary battery was produced in the same manner as in Example 1, and measurements and evaluations were made on the lithium ion secondary battery and its constituent elements.

<Example 14>
In the production of the water-insoluble particulate polymer in the step (1-3), a lithium ion secondary battery was obtained in the same manner as in Example 1 except that 95.3 parts of butyl acrylate and 0.7 parts of methacrylic acid were changed. The lithium ion secondary battery and its constituent elements were measured and evaluated.

<Example 15>
In the production of the water-insoluble particulate polymer in the step (1-3), a lithium ion secondary battery was prepared in the same manner as in Example 1 except that 93.4 parts of butyl acrylate and 2.6 parts of methacrylic acid were changed. The lithium ion secondary battery and its constituent elements were measured and evaluated.

<Example 16>
The composition for porous membrane obtained in step (1-4) is applied to the surface of the positive electrode active material layer of the positive electrode after pressing obtained in the production of the positive electrode in step (1-7), and dried at 80 ° C. for 2 minutes. It was. Thereby, the positive electrode provided with the porous film on one side of the positive electrode was obtained. The thickness of the porous film provided in the obtained positive electrode was 3 μm.
In the production of the lithium ion secondary battery in step (1-8), the separator base material is used as it is instead of the separator obtained in step (1-5), and the press obtained in step (1-7). Instead of the later positive electrode, a positive electrode having a porous film on one side of the positive electrode was used.
Except for the above, a lithium ion secondary battery was produced in the same manner as in Example 1, and measurement and evaluation of the lithium ion secondary battery and its components were performed.

<Comparative Example 1>
In the production of the porous membrane composition in the step (1-4), a lithium ion secondary battery was produced in the same manner as in Example 1 except that the carbodiimide compound as a crosslinking agent was not added. The battery and its components were measured and evaluated.

<Comparative Example 2>
Except for the following changes, a lithium ion secondary battery was produced in the same manner as in Example 1, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the water-soluble polymer in the step (1-1), the components of the monomer composition and the amounts thereof are 50 parts of methacrylic acid, 30 parts of ethyl acrylate, 10 parts of butyl acrylate, and methyl methacrylate. Changed to 10 copies.
-In preparation of the dispersion liquid of the nonelectroconductive particle of a process (1-2), the addition amount of the aqueous solution of a water-soluble polymer was changed into 8 parts on the solid content basis.

  The measurement and 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.
Water-soluble polymer composition: The type and weight part of the monomer constituting the monomer composition used in the production of the water-soluble polymer, or the trade name of a commercially available water-soluble polymer. MAA: methacrylic acid. EA: ethyl acrylate. BA: butyl acrylate. MMA: methyl methacrylate. D1220: Product name “Daicel 1220” (manufactured by Daicel Finechem, degree of etherification: 0.8 to 1.0). D1380: Product name “Daicel 1380” (manufactured by Daicel Finechem, degree of etherification of 1.0 to 1.5).
Water-soluble polymer acid group amount: Amount of acid group (mmol) measured in an aqueous medium per 1 g of water-soluble polymer.
Water-soluble polymer content: content (parts) of water-soluble polymer with respect to 100 parts of non-conductive particles.
Water-soluble polymer acid group ratio: Ratio of acid group (mmol / 100 g) measured in an aqueous medium of the water-soluble polymer with respect to 100 g of non-conductive particles.
Water-soluble polymer viscosity: Viscosity of a 2% aqueous solution of a water-soluble polymer (mPa · s, measured at 25 ° C. and 60 rpm).
Amount of particulate polymer acid group: Amount of acid group (mmol) measured in an aqueous medium per gram of particulate polymer.
Particulate polymer content: Content (parts) of particulate polymer with respect to 100 parts of non-conductive particles.
Particulate polymer acid group ratio: The ratio of the acid group of the particulate polymer to 100 g of non-conductive particles (mmol / 100 g).
Total acid group amount: The ratio (mmol / 100 g) of acid groups of the acid group-containing polymer (water-soluble polymer and particulate polymer) to 100 g of non-conductive particles.
Crosslinking agent type: The type of crosslinking agent used in the production of the composition for porous membrane. SV-02: Product name “carbodilite (registered trademark) SV-02” (carbodiimide compound, manufactured by Nisshinbo Chemical Co., Ltd., NCN equivalent 429, one-phase water-soluble). V-02: Product name “Carbodilite (registered trademark) V-02” (carbodiimide compound, manufactured by Nisshinbo Chemical Co., Ltd., NCN equivalent 600, one-phase water-soluble). V-04: Product name “Carbodilite (registered trademark) V-04” (carbodiimide compound, manufactured by Nisshinbo Chemical Co., Ltd., NCN equivalent 335, one-phase water-soluble).
Weight of crosslinking agent: Weight (parts) of crosslinking agent used in the production of the composition for porous membrane.
NCNmol × 10 ^4: for the non-conductive particles 100 g, the number of carbodiimide groups in the crosslinking agent (mol × ¹⁰ 4 / 100g)
(Total acid group amount / NCN mol) × 10 ⁻⁴ : Acid group-containing polymer (water-soluble polymer and particulate polymer) relative to the number of moles of carbodiimide groups in the crosslinking agent used in the production of the composition for porous membrane Of acid groups ((mmol / NCNmol) × 10 ⁻⁴ ).

  As shown by the results in Tables 1 to 3, the porous film obtained using the composition for a porous film containing an acid group-containing polymer containing a predetermined amount of acid groups and a carbodiimide compound has good peel strength and The secondary battery having a low water content and obtained using the same showed good results in low-temperature output characteristics, cell volume changes, and cycle characteristics.

Claims (5)

A composition for a porous membrane of a lithium ion secondary battery comprising non-conductive particles, an acid group-containing polymer, and a carbodiimide compound,
A composition for a porous membrane of a lithium ion secondary battery, wherein a total acid group amount measured in an aqueous medium of the acid group-containing polymer with respect to 100 g of the nonconductive particles is 1 mmol or more and 40 mmol or less. The ratio of the total acid group amount measured in the aqueous medium of the acid group-containing polymer to the carbodiimide group amount of the carbodiimide compound (total acid group amount mmol / carbodiimide compound NCNmol) is 1.0 × 10 ³ or more 1 The composition for a porous membrane of a lithium ion secondary battery according to claim 1, wherein the composition is 0.0 × 10 ⁵ or less. A layer of the composition for a lithium ion secondary battery porous film according to claim 1 or 2 is formed,
A porous membrane for a lithium ion secondary battery, wherein the acid group-containing polymer and the carbodiimide compound are crosslinked in the layer. The layer is a layer obtained by applying the composition for a lithium ion secondary battery porous membrane on a substrate,
The porous membrane for a lithium ion secondary battery according to claim 3, wherein the substrate is an electrode plate or a separator substrate.   A lithium ion secondary battery comprising the porous membrane for a lithium ion secondary battery according to claim 3 or 4.