JPWO2010134501A1 - Porous membrane and secondary battery - Google Patents

Abstract

The present invention relates to a porous film comprising non-conductive particles and a graft polymer, and a porous film slurry comprising non-conductive particles, a graft polymer and a solvent, and an electrode mixture layer comprising a binder and an electrode active material Is an electrode for a secondary battery that is attached to a current collector and in which the porous film is laminated on the surface of the electrode mixture layer. The present invention has a high dispersibility of non-conductive particles and moderate electrolyte retention while maintaining a high level of electrical short-circuit prevention and thermal shrinkage suppression effects, and high temperature characteristics and a high rate by introducing a porous membrane layer. A porous membrane exhibiting properties is provided.

Description

  The present invention relates to a porous membrane, and more particularly to a porous membrane having high rate characteristics used for a lithium ion secondary battery or the like. The present invention also relates to a secondary battery having such a porous film.

  Among batteries in practical use, lithium ion secondary batteries exhibit the highest energy density, and are often used particularly for small electronics. In addition to small-sized applications, it is also expected to expand to automotive applications. Among them, there is a demand for higher capacity and longer life of lithium ion secondary batteries and further improvement of safety.

  Lithium ion secondary batteries generally use polyolefin-based organic separators such as polyethylene and polypropylene in order to prevent a short circuit between the positive electrode and the negative electrode. Since polyolefin-based organic separators have physical properties that melt at 200 ° C. or lower, volume changes such as shrinkage and melting occur when the battery becomes hot due to internal and / or external stimuli. As a result, positive and negative electrodes There is a risk of explosion due to short circuit of the battery or release of electrical energy.

Therefore, in order to solve such problems, it has been proposed to laminate a layer containing non-conductive particles such as inorganic particles on a polyethylene organic separator or on an electrode.
For example, in Patent Document 1, BaTiO ₃ powder that is inorganic particles is dispersed in a dispersion medium and slurried together with a polyvinylidene fluoride-chlorotrifluoroethylene copolymer polymer compound (PVDF-CTFE) that is a binder, A method of applying and drying this on a porous substrate made of polyethylene terephthalate, which is an organic separator, is disclosed. In the case of this method, the thermal contraction of the organic separator due to heat of 150 ° C. or more can be suppressed by containing inorganic particles. However, when the coating is applied on the surface of the organic separator so as not to drop the inorganic particles, the polymer compound However, by covering the surface of the organic separator, lithium migration is inhibited and the rate characteristics are lowered.
Patent Document 2 discloses a porous protective film formed using a fine particle slurry containing fine particles such as alumina, silica, and polyethylene resin on an electrode.
Further, in Patent Document 3, a layer containing a binder and inorganic particles having various particle diameters in the range of 0.2 to 1.5 μm in average particle diameter is formed on the electrode as a porous film layer. Studies have also been made to control the movement of lithium by controlling the pore diameter state by changing the particle diameters of the inorganic particles present on the surface side and electrode side of the layer.
However, in the case of Patent Documents 2 and 3, as in Patent Document 1, when coating on the electrode surface without dropping off the inorganic particles, the binder covers the electrode surface, thereby causing lithium migration. Is inhibited and the rate characteristics are lowered.

  Thus, according to Patent Documents 1 to 3, it is possible to prevent electrical short circuit and suppress thermal contraction by forming a porous film containing non-conductive particles such as inorganic particles. There is a problem that the deterioration of the rate characteristic due to the layer introduction cannot be prevented.

Japanese translation of PCT publication No. 2008-503049 (corresponding US Pat. No. 7,704,641) Japanese Patent Laid-Open No. 7-220759 Japanese Patent No. 2005-294139

  Therefore, the present invention has been made in view of the above prior art, and in lithium ion secondary batteries and the like, while maintaining a high level of electrical short-circuit prevention and thermal shrinkage suppression effects, rate characteristics are achieved. It aims at providing the porous membrane which has the binder which can contribute.

  As a result of intensive studies to solve the above problems, the present inventors have made a porous film containing non-conductive particles such as inorganic particles contain a specific binder, thereby preventing electrical short circuit and heat. In order to complete the present invention, it has been found that the deterioration of rate characteristics due to the introduction of a porous membrane layer can be suppressed with high dispersibility of non-conductive particles and moderate electrolyte solution retention while maintaining a high degree of mechanical shrinkage suppression effect. It came.

The present invention for solving the above-mentioned problems includes the following matters as a gist.
(1) A porous film comprising non-conductive particles and a graft polymer.
(2) The porous membrane according to (1), wherein the degree of swelling of the graft polymer with respect to the electrolytic solution is in the range of 100% to 300%.
(3) The porous membrane according to the above (1) or (2), wherein the graft polymer is composed of a component exhibiting swellability with respect to an electrolytic solution and a component not exhibiting swellability with respect to the electrolytic solution.
(4) The porous membrane according to any one of (1) to (3), wherein the graft polymer has a weight average molecular weight in the range of 1,000 to 500,000.
(5) A slurry for a porous membrane containing non-conductive particles, a graft polymer and a solvent.
(6) A method for producing a porous membrane, comprising a step of applying the slurry for porous membrane according to (5) above to a substrate and then drying.
(7) An electrode mixture layer comprising a binder and an electrode active material is attached to the current collector, and on the surface of the electrode mixture layer, any one of (1) to (4) The electrode for secondary batteries formed by laminating | stacking the porous film of description.
(8) A separator for a secondary battery in which the porous film according to any one of (1) to (4) is laminated on an organic separator.
(9) A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the porous film according to any one of (1) to (4) is laminated on at least one of the positive electrode, the negative electrode, and the separator. Secondary battery.
In particular, in the present invention, the porous film contains 50 to 99% by weight of the non-conductive particles and 0.1 to 10% by weight of the graft polymer, and the degree of swelling of the graft polymer with respect to the electrolytic solution is 100% to 300%. It is as follows. Further, the slurry for the porous membrane contains 50 to 99% by weight of the non-conductive particles and 0.1 to 10% by weight of the graft polymer in the total solid content, and the degree of swelling of the graft polymer with respect to the electrolytic solution is 100. % Or more and 300% or less.
In a preferred embodiment of the present invention, the non-conductive particles are organic particles.
In another preferred embodiment, the particle size distribution of the non-conductive particles is in the range of 0.5 to 40%.

  According to the present invention, while maintaining a high level of electrical short-circuit prevention and thermal shrinkage suppression effects, it has high dispersibility of non-conductive particles and moderate electrolyte solution retention, and high temperature characteristics by introducing a porous membrane layer. A porous membrane exhibiting high rate characteristics is provided. Such a porous film contains a specific binder and exhibits high rate characteristics while exhibiting low electrolyte swellability, and can also exhibit higher high temperature characteristics.

The present invention is described in detail below.
The porous film of the present invention includes non-conductive particles and a graft polymer.

(Non-conductive particles)
It is desired that the non-conductive particles used in the present invention are stably present in a use environment such as a lithium ion secondary battery or a nickel hydride secondary battery, and are electrochemically stable. For example, various inorganic particles and organic particles can be used. Organic particles are preferable from the viewpoint of producing particles with low metal contamination that adversely affect battery performance at low cost.
Examples of inorganic particles include oxide particles such as aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, BaTiO ₂ , ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; silicon, diamond, and the like Covalent crystal particles; poorly soluble ion crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite are used. These particles may be subjected to element substitution, surface treatment, solid solution, or the like, if necessary, or may be a single or a combination of two or more. Among these, oxide particles are preferable from the viewpoints of stability in an electrolytic solution and potential stability.
Examples of organic particles include cross-linked polymethyl methacrylate, cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked product, polyimide, polyamide, polyamideimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include crosslinked polymer particles, heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).
In addition, by electrically treating the surface of conductive metal such as carbon black, graphite, SnO ₂ , ITO, metal powder and fine powders of conductive compounds and oxides with a non-electrically conductive material, electrical insulation is achieved. It is also possible to use it with a certain character. These non-electrically conductive particles may be used in combination of two or more.

  In the present invention, it is preferable to use non-conductive particles having a foreign metal content of 100 ppm or less. When non-conductive particles containing a large amount of metal foreign matter or metal ions are used, in the slurry for porous film described later, the metal foreign matter or metal ion is eluted, which causes ionic crosslinking with the polymer in the slurry for porous film, There is a risk that the slurry for the porous film aggregates, resulting in a decrease in the porosity of the porous film and deterioration of the rate characteristics. As the metal, it is most preferable to contain Fe, Ni, Cr and the like which are particularly easily ionized. Accordingly, the metal content in the non-conductive particles is preferably 100 ppm or less, more preferably 50 ppm or less. The smaller the content, the less likely the battery characteristics will deteriorate. The term “metal foreign matter” as used herein means a simple metal other than non-conductive particles. The content of metal foreign matter in the non-conductive particles can be measured using ICP (Inductively Coupled Plasma).

The lower limit of the average particle size (volume average D50 average particle size) of the non-conductive particles used in the present invention is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 100 nm or more. On the other hand, the upper limit is preferably 10 μm or less, more preferably 5 μm or less. By controlling the average particle diameter of the non-conductive particles within the above range, it becomes easy to obtain a film having a predetermined thickness that is uniform in controlling the dispersion state. For example, by setting the average particle diameter of the non-conductive particles to be equal to or greater than the lower limit, it is possible to suppress the particle filling rate from becoming higher than desired, and thus to suppress the decrease in ionic conductivity. Can do. On the other hand, by setting the average particle diameter of the non-conductive particles to the upper limit or less, the porous film can be thinned, and the decrease in ion conductivity can be suppressed. It is particularly preferable that the average particle diameter of the non-conductive particles be in the range of 50 nm or more and 2 μm or less because the dispersion, the ease of coating, and the controllability of voids are excellent.
In addition, the BET specific surface area of these particles is specifically 0.9 to ²⁰⁰ m ² / g from the viewpoint of suppressing aggregation of the particles and optimizing the fluidity of the slurry for a porous film described later. Preferably, it is 1.5-150 m < ² > / g.
When the non-conductive particles are organic particles, the organic fine particles preferably have high heat resistance from the viewpoint of imparting heat resistance to the porous film and improving the stability of the battery. Specifically, the temperature at which the weight is reduced by 10% by weight when heated at a heating rate of 10 ° C./min in thermobalance analysis is preferably 250 ° C. or higher, more preferably 300 ° C. or higher, and even more preferably 350 ° C. or higher. is there. On the other hand, the upper limit of the temperature is not particularly limited, but can be, for example, 450 ° C. or less.
The lower limit of the particle size distribution (CV value) of the non-conductive particles is preferably 0.5% or more, and the upper limit is preferably 40% or less, more preferably 30% or less, and even more preferably 20 % Or less. By setting it within the range, it is possible to suppress the increase in resistance by inhibiting the movement of lithium without filling the voids of the non-conductive particle layer.

  The shape of the nonconductive powder used in the present invention is not particularly limited, such as a spherical shape, a needle shape, a rod shape, a spindle shape, and a plate shape, but a spherical shape, a needle shape, and a spindle shape are preferable. Moreover, porous particles can also be used as the non-conductive particles. The lower limit of the content of nonconductive particles in the porous film is 50% by weight, preferably 60% by weight, and more preferably 70% by weight. On the other hand, the upper limit is 99% by weight, preferably 98% by weight. By setting the content of non-conductive particles in the porous film within the above range, a porous film exhibiting high thermal stability and strength can be obtained. For example, heat resistance can be improved by making content of nonelectroconductive particle more than the said minimum. By making the content of the nonconductive particles not more than the above upper limit, the detachment of the nonconductive particles can be suppressed.

(Graft polymer)
The graft polymer used in the present invention comprises two segments (a first segment and a second segment), and one of the first segment and the second segment constitutes a main chain, and the other is a graft portion (side chain). Is a branched polymer.
In addition to comprising a first segment and a second segment, the graft polymer may further comprise one or more optional segments. Further, each of the first segment and the second segment may be a segment based on only one type of polymerization unit, or may be a segment based on two or more types of polymerization units.

The structure of the graft polymer used in the present invention is such that the first segment of the two segments is an electrolyte solution so that it has a high rate characteristic while controlling the degree of swelling into the electrolyte solution within a predetermined range. It is preferable that the second segment is composed of a component that does not exhibit swelling with respect to the electrolyte solution. When the graft polymer is composed of a component exhibiting swellability with respect to the electrolytic solution and a component that does not exhibit swellability with respect to the electrolytic solution, the first segment and the second segment are formed when the porous membrane containing the graft polymer is used inside the battery. The two islands form a sea-island structure, whereby the graft polymer shows moderate swelling to the electrolyte and retains the electrolyte without causing the porous membrane to peel off due to excessive swelling. Lithium conductivity can be exhibited.
In the graft polymer used in the present invention, the first segment may constitute the main chain, the second segment may constitute the graft portion (side chain), or the second segment may constitute the main chain, May constitute a graft portion (side chain).

As the component (first segment) exhibiting swellability with respect to the electrolytic solution, one having a monomer component having a solubility parameter (SP) of 8.0 or more and less than 11, or -OH group (hydroxyl group), -COOH group ( A carboxylic acid group), a —SO ₃ H group (phosphoric acid group), a —PO ₃ H ₂ group, a —PO (OH) (OR) group (R represents a hydrocarbon group), and a lower polyoxyalkylene group. It is preferably composed of a monomer component having at least one hydrophilic group selected from the group.

  Examples of the monomer having the solubility parameter of 8.0 or more and less than 11 include alkenes such as ethylene and propylene; methacrylic acid alkyl esters such as butyl methacrylate; acrylic acid alkyl esters such as butyl acrylate, and the like. Among these, alkyl acrylates and alkyl methacrylates are preferred, and since they swell in the electrolyte and are less likely to cause bridging aggregation due to the polymer when dispersed with a small particle size, the carbon of the alkyl group that binds to non-carbonyl oxygen atoms. Acrylic acid alkyl ester or methacrylic acid alkyl ester having a number of 1 to 5 is more preferred.

  Examples of the alkyl acrylate ester or methacrylic acid alkyl ester in which the alkyl group bonded to the non-carbonyl oxygen atom has 1 to 5 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, acrylic Acrylic acid alkyl esters such as n-butyl acid and t-butyl acrylate; 2- (perfluoroalkyl) acrylic acid such as 2- (perfluorobutyl) ethyl acrylate and 2- (perfluoropentyl) ethyl acrylate Ethyl; methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and t-butyl methacrylate; 2- (perfluorobutyl) ethyl methacrylate; Me Methacrylate 2- (perfluoroalkyl) ethyl, such as acrylic acid 2- (perfluorobutyl) ethyl methacrylate 2- (perfluoroalkyl) ethyl; and the like.

  The solubility parameter (SP) in the first segment when the component (first segment) exhibiting swellability with respect to the electrolytic solution has a monomer component having a solubility parameter (SP) of 8.0 or more and less than 11. The content of the monomer component in which) is 8.0 or more and less than 11 is preferably 30% by weight or more, more preferably 50 to 90% by weight with respect to 100% by weight of the total amount of monomers. The content of the monomer component having a solubility parameter (SP) in the first segment of 8.0 or more and less than 11 can be controlled by the monomer charge ratio at the time of producing the graft polymer. The content of the monomer component having a solubility parameter (SP) of 8.0 or more and less than 11 is in an appropriate range, so that it does not dissolve but exhibits elution inside the battery while exhibiting swelling property to the electrolyte. It does not occur and exhibits high temperature characteristics.

The solubility parameter of the polymer can be determined according to the method described in Polymer Handbook, but those not described in this publication can be determined according to the “molecular attractive constant method” proposed by Small. In this method, the SP value (δ) ((cal / cm ³ ) ¹ according to the following equation is obtained from the characteristic value of the functional group (atomic group) constituting the compound molecule, that is, the statistics of the molecular attraction constant (G) and the molecular volume. ^{/ 2} ).
δ = ΣG / V = dΣG / M
ΣG: Total of molecular attractive constant G V: Specific volume M: Molecular weight d: Specific gravity

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and derivatives thereof, dicarboxylic acid, acid anhydrides thereof, and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Monocarboxylic acid derivatives include 2-ethylacrylic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β -Diamino acrylic acid etc. are mentioned. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
Dicarboxylic acid derivatives include methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid and the like methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, And maleate esters such as octadecyl maleate and fluoroalkyl maleate.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; 2-hydroxyethyl acrylate, acrylic acid-2 Ethylene such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate alkanol esters of sexual unsaturated carboxylic acids; formula ^{_{CH 2 = CR 1 -COO- (CnH}} 2 nO) m-H (m is 2 to 9 integer, n represents 2 to 4 integer, R1 is hydrogen or methyl An ester of a polyalkylene glycol represented by (meth) acrylic acid represented by 2-hydroxy; Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as ethyl-2 ′-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether; Vinyl ethers such as 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2- Mono (meth) allylate of alkylene glycol such as hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro Mono (meth) allyl ethers of halogen and hydroxy-substituted products of (poly) alkylene glycols such as -3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; eugenol, isoeugenol Mono (meth) allyl ether of monohydric phenol and its halogen-substituted product; (meth) allylthiol of alkylene glycol such as (meth) allyl-2-hydroxyethylthioether, (meth) allyl-2-hydroxypropylthioether Ethers; and the like.

  Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamide-2. -Methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid and the like.

As a monomer having a —PO ₃ H ₂ group and / or —PO (OH) (OR) group (R represents a hydrocarbon group), 2- (meth) acryloyloxyethyl phosphate, methyl phosphate -2- (meth) acryloyloxyethyl, ethyl phosphate- (meth) acryloyloxyethyl, and the like.
Examples of the monomer containing a lower polyoxyalkylene group-containing group include poly (alkylene oxide) such as poly (ethylene oxide).

  In the case where the component (first segment) exhibiting swellability with respect to the electrolytic solution is composed of those having the monomer component having the hydrophilic group, among these monomers having the hydrophilic group, non-conductive From the viewpoint of further improving the dispersibility of the conductive particles, a monomer having a carboxylic acid group is preferred.

  Including a monomer having a hydrophilic group in the first segment when the component (first segment) exhibiting swellability with respect to the electrolytic solution is composed of a monomer component having the hydrophilic group The amount is preferably in the range of 0.5 to 40% by weight, more preferably 3 to 20% by weight, based on 100% by weight of the total amount of monomers having the hydrophilic group during polymerization. The content of the monomer having a hydrophilic group in the first segment can be controlled by the monomer charging ratio at the time of producing the graft polymer. If the content of the monomer having a hydrophilic group in the first segment is too small, the swelling property to the electrolytic solution may not be exhibited. On the other hand, if the content of the hydrophilic group in the first segment is too large, the solubility in the electrolytic solution is increased, and the elution inside the battery may be a concern.

  The second segment that does not exhibit swellability with respect to the electrolytic solution includes a monomer component having a solubility parameter of less than 8.0 or 11 or more, or a monomer component having a hydrophobic portion. desirable.

  Examples of the monomer component having a solubility parameter of less than 8.0 or 11 or more include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile.

  Monomer having a solubility parameter (SP) of less than 8.0 or 11 or more when the second segment contains a monomer component having a solubility parameter (SP) of less than 8.0 or 11 or more The content of the components is preferably in the range of 30% to 100% by weight, more preferably 50% to 100% by weight, based on 100% by weight of the total amount of monomers. The content of the monomer component whose solubility parameter (SP) in the second segment is less than 8.0 or 11 or more can be controlled by the monomer charge ratio at the time of graft polymer production. When the content ratio of the monomer component having a solubility parameter (SP) of less than 8.0 and 11 or more in the second segment is in the above range, higher electrolyte solution resistance and high temperature characteristics are exhibited.

Examples of the monomer component having a hydrophobic part include acrylic acid ester having 6 or more carbon atoms of an alkyl group bonded to a noncarbonyl oxygen atom such as -2-ethylhexyl acrylate and benzyl acrylate; -2-ethylhexyl methacrylate Methacrylic acid ester having 6 or more carbon atoms of alkyl group bonded to non-carbonyl oxygen atom (on ester bond) such as lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, benzyl methacrylate, etc .; styrene, α-styrene And aromatic vinyl compounds such as chlorostyrene, vinyl toluene, methyl t-butylstyrene vinyl benzoate, vinyl naphthalene, chloromethyl styrene, α-methyl styrene, and divinyl benzene.
In the present invention, the monomer component having a hydrophobic portion is preferably an aromatic vinyl compound because it does not show any swellability to an electrolytic solution.

  When the second segment is composed of a monomer component having a hydrophobic portion, the content of the monomer component having the hydrophobic portion in the second segment is a single amount having the hydrophobic portion at the time of polymerization. The body weight is preferably 10% by weight or more and 100% by weight or less, more preferably 20% by weight or more and 100% by weight or less, with respect to 100% by weight of the total amount of monomers. The content of the monomer component having a hydrophobic portion in the second segment can be controlled by the monomer charge ratio at the time of producing the graft polymer. When the content of the monomer component having the hydrophobic portion in the second segment is in the above range, higher resistance to electrolytic solution and high temperature characteristics are exhibited.

  The ratio of the first segment to the second segment in the graft polymer varies depending on the composition, the degree of crosslinking, etc. in order to have high rate characteristics while controlling the degree of swelling into the electrolyte within a predetermined range. In the case where the polymer does not have a copolymer component other than the first segment and the second segment, the ratio of the first segment: the ratio of the second segment is 10:90 to 90:10, more preferably 30: 70-70: 30. In particular, when acrylic and styrene materials are used as the first segment and the second segment, respectively, when these ratios are in the above range, the characteristics such as the degree of swelling and the rate characteristics should be in a good range. Can do.

  In the present invention, the degree of swelling of the graft polymer with respect to the electrolytic solution is in the range of 100% to 300%, and preferably in the range of 100% to 200%. When the degree of swelling of the graft polymer with respect to the electrolyte solution is in the above-described range, the degree of swelling in the electrolyte solution is exhibited while exhibiting the binding property in the porous membrane layer at the time of battery production, and non-conductive particles are dropped off. Rate characteristics can be developed without any problem.

In the present invention, the degree of swelling is a value obtained by measurement by the following method.
The graft polymer is formed into a film having a thickness of about 0.1 mm, and the film is cut into about 2 cm square and the weight (weight before immersion) is measured. Thereafter, it is immersed in an electrolytic solution at a temperature of 60 ° C. for 72 hours. The soaked film is pulled up, the weight immediately after wiping off the electrolytic solution (weight after soaking) is measured, and the value of (weight after soaking) / (weight before soaking) × 100 (%) is defined as the degree of swelling.
As an electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at EC: DEC = 1: 2 (volume ratio, where EC is a volume at 40 ° C., DEC is a volume at 20 ° C.). A solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent is used.

The degree of swelling of the graft polymer with respect to the electrolytic solution can be adjusted by controlling the above-described graft polymer composition, molecular weight, and degree of crosslinking.
The degree of swelling of the graft polymer with respect to the electrolytic solution tends to increase as the molecular weight decreases and decrease as the molecular weight increases. Therefore, the range of the weight average molecular weight of the graft polymer for obtaining a suitable degree of swelling varies depending on the structure and the degree of crosslinking, but is measured by, for example, gel permeation chromatography using tetrahydrofuran (THF) as a developing solvent. The standard polystyrene conversion value is 1,000 to 500,000, more preferably 2,000 to 100,000. The weight average molecular weight is more preferably 5,000 to 500,000, still more preferably 10,000 to 400,000, and even more preferably 30,000 to 300,000. When the weight average molecular weight of the graft polymer is within the above range, the adsorption stability of the polymer to the non-conductive particles is high, and the polymer does not cause cross-linking and aggregation, and exhibits excellent dispersibility. For example, when the weight average molecular weight is equal to or more than the above lower limit, desorption of non-conductive particles can be reduced. When the weight average molecular weight is not more than the above upper limit, the film thickness can be made uniform, and as a result, the rate characteristics can be kept in a favorable range.

When the degree of swelling is controlled by the degree of crosslinking of the graft polymer, the preferred range of the degree of crosslinking varies depending on the structure, molecular weight, etc., but for example, when immersed in a polar solvent such as tetrahydrofuran for 24 hours, A degree of cross-linking that swells to at least% is preferred.
Examples of the crosslinking method of the graft polymer include a method of crosslinking by heating or energy ray irradiation. By using a graft polymer that can be crosslinked by heating or irradiation with energy rays, the degree of crosslinking can be adjusted by heating conditions or irradiation conditions (intensity, etc.) of irradiation with energy rays. Further, since the degree of swelling tends to decrease as the degree of crosslinking increases, the degree of swelling can be adjusted by changing the degree of crosslinking.
Examples of the method for obtaining a graft polymer that can be crosslinked by heating or energy ray irradiation include a method of introducing a crosslinkable group into the graft polymer and a method of using a crosslinking agent in combination.

  Examples of the method for introducing a crosslinkable group into the graft polymer include a method for introducing a photocrosslinkable crosslinkable group into the graft polymer and a method for introducing a heat crosslinkable crosslinkable group. Among these methods, the method of introducing a heat-crosslinkable crosslinkable group into the graft polymer can crosslink the porous film by performing a heat treatment on the porous film after forming the porous film, and further dissolve in the electrolyte solution. It can be suppressed, and a tough and flexible porous membrane is obtained, which is preferable. In the case of introducing a thermally crosslinkable group into the graft polymer, the thermally crosslinkable group is selected from the group consisting of an epoxy group, a hydroxyl group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. At least one selected from the group consisting of epoxy groups is preferable, and an epoxy group is more preferable in terms of easy crosslinking and adjustment of the crosslinking density.

Examples of the monomer containing an epoxy group include a monomer containing a carbon-carbon double bond and an epoxy group, and a monomer containing a halogen atom and an epoxy group.
Examples of the monomer containing a carbon-carbon double bond and an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl ether; butadiene monoepoxide, Diene or polyene monoepoxides such as chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; Alkenyl epoxides such as epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycy Glycidyl esters of unsaturated carboxylic acids such as rubsorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid; It is done.

  Examples of the monomer having a halogen atom and an epoxy group include epihalohydrins such as epichlorohydrin, epibromohydrin, epiiodohydrin, epifluorohydrin, β-methylepichlorohydrin; p-chlorostyrene oxide; dibromo Phenyl glycidyl ether;

Examples of the monomer containing a hydroxyl group include unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; -2-hydroxyethyl acrylate, acrylate-2 -Unsaturation such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate alkanol esters of carboxylic acids; formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m-H (m is 2 to 9 integer, n represents 2 to 4 integer, ^{R 1} is hydrogen or methyl 2-hydroxyethyl- ester of polyalkylene glycol and (meth) acrylic acid represented by Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as '-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2'-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether, 2-hydroxy Vinyl ethers such as propyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, Mono (meth) allyl ethers of alkylene glycols such as (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether; Polyoxyalkylene glycol (meth) monoallyl ethers such as tylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3 -Mono (meth) allyl ethers of halogen and hydroxy-substituted products of (poly) alkylene glycols, such as hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; polyphenols such as eugenol, isoeugenol Mono (meth) allyl ether and its halogen-substituted product; (meth) allylthioether of alkylene glycol such as (meth) allyl-2-hydroxyethylthioether and (meth) allyl-2-hydroxypropylthioether Le acids; and the like.

  Examples of the monomer containing an N-methylolamide group include (meth) acrylamides having a methylol group such as N-methylol (meth) acrylamide.

  Examples of the monomer containing an oxetanyl group include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) acryloyloxymethyl) -2-trifluoromethyloxetane, and 3-((meth) acryloyloxymethyl. ) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, 2-((meth) acryloyloxymethyl) -4-trifluoromethyloxetane, and the like.

  Examples of the monomer containing an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2- Examples include oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

  The content of the heat-crosslinkable crosslinkable group in the graft polymer is preferably 0.1% with respect to 100% by weight of the total amount of monomers as the amount of the monomer containing the heat-crosslinkable crosslinkable group at the time of polymerization. It is in the range of 1 to 10% by weight, more preferably 0.1 to 5% by weight. The content ratio of the heat-crosslinkable crosslinkable group in the graft polymer can be controlled by the monomer charge ratio when the graft polymer is produced. When the content of the heat-crosslinkable crosslinking group in the graft polymer is within the above range, elution into the electrolytic solution can be suppressed, and excellent porous film strength and long-term cycle characteristics can be exhibited.

  In the production of the graft polymer, the heat-crosslinkable crosslinkable group is a monomer containing a heat-crosslinkable crosslinkable group in addition to the above-mentioned monomer, and / or other copolymerizable with these monomers. It can introduce | transduce in a graft polymer by copolymerizing with a monomer.

  The graft polymer used for this invention may contain the monomer copolymerizable with these other than the monomer component mentioned above. Monomers copolymerizable with these include halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; methyl vinyl ether, ethyl vinyl ether, butyl vinyl Vinyl ethers such as ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; Heterocycle-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; Acrylamide And amide monomers such as N-methylolacrylamide. By graft copolymerizing these monomers by an appropriate technique, the graft polymer having the above-described structure can be obtained.

  In the present invention, the glass transition temperature of the graft polymer can impart flexibility to the porous film at room temperature, and suppress cracks during winding and winding of the porous film, chipping of the porous film layer, and the like. From the viewpoint of being able to reduce the temperature, it is preferably 20 ° C or lower, more preferably 0 ° C or lower. The glass transition temperature of the graft polymer can be adjusted by changing the use ratio of the constituent monomers.

The graft polymer used in the present invention is synthesized by 1) a method of copolymerizing to form a branched structure, or 2) a method of modifying the obtained polymer to generate a branched structure. Among them, the method 1) is preferable because the desired structure can be obtained in one step.
As a method of copolymerizing so as to constitute 1) the branched structure, for example, a graft polymer can be obtained by a chain transfer reaction by polymerizing a graft monomer in the presence of a trunk polymer by a known polymerization method. Also, a graft polymer can be obtained by introducing a functional group capable of generating radicals and ions into the trunk polymer and initiating a polymerization reaction of the graft monomer from the functional group. In addition, a branch polymer obtained by polymerizing a graft monomer capable of forming a branched structure at the time of polymerization by a known polymerization method may be added to the trunk polymer by a radical addition reaction or the like. In this case, even if a part of the branch polymer remains ungrafted, it can be used as it is as a graft polymer. Specifically, the graft polymer can be produced by a method described in JP-B-6-51767.
Among these, the structure control is most easily controlled by a method in which a branched polymer obtained by polymerizing a graft monomer capable of forming a branched structure at the time of polymerization by a known polymerization method is added to a trunk polymer by a radical addition reaction or the like. This is preferable because the slurry for a porous film described later is easily stabilized. Specifically, a method of copolymerizing using a macromonomer as a branch polymer can be mentioned.

  The macromonomer has a (meth) acryloyl group at one end of the polymer, for example, one-end methacryloylated polystyrene oligomer (manufactured by Toa Gosei Chemical Co., Ltd., “AS-6”, Mn = 6000), one-end methacryloylation. Polymethyl methacrylate oligomer (manufactured by Toa Gosei Chemical Co., Ltd., “AA-6”, Mn = 6000), one-end methacryloylated polybutyl acrylate oligomer (manufactured by Toa Gosei Chemical Co., Ltd., “AB-6”, Mn = 6000) ), One-end methacryloylated polystyrene-acrylonitrile oligomer (manufactured by Toagosei Chemical Industry Co., Ltd., “AN-6S”).

  In addition, a polymer having a functional group such as a hydroxyl group at one end such as polyoxyethylene monomethyl ether may be used such as isocyanate ethyl methacrylate, (meth) acrylic acid, (meth) acrylic acid chloride, glycidyl (meth) acrylate, etc. Various macromonomers can also be obtained by reacting an ethylenically unsaturated monomer having a functional group. A graft polymer can be obtained by copolymerizing these macromonomers and other ethylenically unsaturated monomers.

  The polymerization method of the graft polymer 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. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Examples of the polymerization initiator used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

The graft polymer used in the present invention is preferably obtained through a particulate metal removal step of removing particulate metal contained in the polymer solution or polymer dispersion in the graft polymer production step. When the content of the particulate metal component contained in the graft polymer composition is 10 ppm or less, it is possible to prevent metal ion cross-linking between polymers in the porous membrane slurry described later and to prevent an increase in viscosity. . Furthermore, there is little concern about self-discharge increase due to internal short circuit of the secondary battery or dissolution / precipitation during charging, and the cycle characteristics and safety of the battery are improved.
The method for removing the particulate metal component from the polymer solution or polymer dispersion in the particulate metal removal step is not particularly limited. For example, the removal method by filtration using a filtration filter, the removal method using a vibrating screen, or centrifugation. Examples thereof include a removal method and a removal method using magnetic force. Especially, since the removal object is a metal component, the method of removing by magnetic force is preferable. The method for removing by magnetic force is not particularly limited as long as it is a method capable of removing a metal component, but in consideration of productivity and removal efficiency, it is preferably performed by placing a magnetic filter in the graft polymer production line. .

  The content ratio of the graft polymer in the porous membrane is 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably 0.5 to 3% by weight. When the content ratio of the binder in the porous film is in the above range, the migration of lithium is inhibited while maintaining the binding property between the non-conductive particles and the binding property to the electrode or the separator. And it can suppress that resistance increases.

  In addition to the above components, the porous membrane may further contain an arbitrary component. Such optional components include components such as dispersants, leveling agents, antioxidants, binders other than graft polymers, thickeners, antifoaming agents, and electrolyte additives having functions such as electrolyte decomposition inhibition. Can be mentioned. These are not particularly limited as long as they do not affect the battery reaction.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. A dispersing agent is selected according to the nonelectroconductive particle to be used. The content ratio of the dispersing agent in the porous film is preferably within a range that does not affect the battery characteristics, and specifically 10% by weight or less.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode.

  Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer type phenol compound is a polymer having a phenol structure in the molecule, and a polymer type phenol compound having a weight average molecular weight of 200 to 1000, preferably 600 to 700 is preferably used.

  As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a polyacrylic acid derivative, a polyacrylonitrile derivative, a soft polymer, or the like used for the electrode binder described later can be used.

  Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. When the use amount of the thickener is within this range, the coating property and the adhesion with the electrode mixture layer and the organic separator are good. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”.

  Other examples include nano-particles such as fumed silica and fumed alumina: surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the nanoparticles, the thixotropy of the slurry for forming a porous film can be controlled, and the leveling property of the porous film obtained thereby can be improved.

  The content ratio of the optional component in the porous film is preferably within a range that does not affect the battery characteristics. Specifically, each component is 10% by weight or less, and the total content of the optional components is 40% by weight. Below, more preferably 20% by weight or less. However, if the total of the non-conductive particles, the predetermined graft polymer, and any component (excluding the binder) is less than 100% by weight, the content of the binder as the optional component is increased appropriately. And a composition can be obtained.

(Method for producing porous membrane)
As a method for producing the porous membrane of the present invention, 1) a method of applying a slurry for porous membrane containing non-conductive particles, a graft polymer and a solvent on a predetermined substrate and then drying; 2) non-conductive particles A method for drying a slurry for a porous membrane containing a graft polymer and a solvent after immersing the substrate; 3) applying a slurry for a porous membrane containing non-conductive particles, a graft polymer and a solvent on a release film; And a method of transferring the obtained porous film onto a predetermined substrate. Among these, 1) The method of applying the slurry for porous film to the substrate and then drying is most preferable because the film thickness of the porous film can be easily controlled.

The porous membrane production method of the present invention is characterized in that the porous membrane slurry is applied to a substrate and then dried.
(Porous membrane slurry)
The slurry for a porous membrane of the present invention contains non-conductive particles, a graft polymer, and a solvent. Examples of the non-conductive particles and the graft polymer include the same as those described for the porous film.

The solvent is not particularly limited as long as it can uniformly disperse the solid content (non-conductive particles, graft polymer and the optional component).
As the solvent used for the slurry for the porous membrane, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as acetone, ethylmethylketone, diisopropylketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; N-methyl Amides such as lupyrrolidone and N, N-dimethylformamide are exemplified.
These solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent. Among these, a solvent having excellent dispersibility of non-conductive particles and having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. Specifically, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable.

The solid content concentration of the slurry for the porous membrane is not particularly limited as long as the slurry can be applied and immersed, and has a fluid viscosity, but is generally about 10 to 50% by weight.
Components other than solid components are components that volatilize in the drying process, and include, in addition to the solvent, for example, a medium in which these are dissolved or dispersed during preparation and addition of non-conductive particles and graft polymer.
Since the slurry for the porous membrane of the present invention is for forming the porous membrane of the present invention, the content ratio of the non-conductive particles and the graft polymer in the total solid content of the slurry for the porous membrane is, of course, The porous membrane of the present invention is as described above. That is, the content ratio of the non-conductive particles is 50 to 99% by weight, and the content ratio of the graft polymer is 0.1 to 10% by weight.

  Moreover, the slurry for the porous film may contain any component such as a dispersant and an electrolyte additive having a function of inhibiting the decomposition of the electrolyte, in addition to the nonconductive particles, the graft polymer, and the solvent. Good. These are not particularly limited as long as they do not affect the battery reaction.

(Porous membrane slurry manufacturing method)
The manufacturing method of the slurry for porous membranes is not particularly limited, and can be obtained by mixing the non-conductive particles, the graft polymer, and the solvent and optional components added as necessary.
In the present invention, a porous film slurry in which non-conductive particles are highly dispersed can be obtained by using the above components, regardless of the mixing method and mixing order. The mixing device is not particularly limited as long as it can uniformly mix the above components, and a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and the like can be used. In particular, it is particularly preferable to use a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix that can add a high dispersion share.
The viscosity of the slurry for the porous membrane is preferably 10 mPa · S to 10,000 mPa · S, more preferably 50 to 500 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

In the method for producing a porous membrane of the present invention, the substrate is not particularly limited, but the porous membrane of the present invention is particularly preferably formed on an electrode for a secondary battery or an organic separator. Among these, it is more preferable to form on the electrode surface for secondary batteries. By forming the porous film of the present invention on the electrode surface, high safety is maintained without causing a short circuit between the positive electrode and the negative electrode even when the organic separator shrinks due to heat. In addition, by forming the porous film of the present invention on the electrode surface, the porous film can function as a separator without an organic separator, and a battery can be manufactured at low cost. Even when an organic separator is used, higher rate characteristics can be expressed without filling the holes formed on the surface of the organic separator.
In the manufacturing method of the porous film of this invention, you may form on base materials other than an electrode and an organic separator. When the porous membrane of the present invention is formed on a substrate other than an electrode or an organic separator, it is used by peeling the porous membrane from the substrate and directly laminating it on the electrode or the organic separator when assembling the battery. I can do it.

The method for applying the slurry for the porous film onto the substrate is not particularly limited. Examples thereof 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 them, the dip method and the gravure method are preferable in that a uniform porous film can be obtained.
Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying temperature can be changed depending on the type of solvent used. In order to completely remove the solvent, for example, when a low-volatility solvent such as N-methylpyrrolidone is used, it is preferably dried at a high temperature of 120 ° C. or higher with a blower-type dryer. Conversely, when a highly volatile solvent is used, it can be dried at a low temperature of 100 ° C. or lower. When forming a porous film on the organic separator mentioned later, since it is necessary to dry without causing shrinkage of the organic separator, drying at a low temperature of 100 ° C. or lower is preferable.

  Next, if necessary, the adhesion between the electrode mixture layer and the porous film can be improved by pressure treatment using a mold press or a roll press. However, at this time, if the pressure treatment is excessively performed, the porosity of the porous film may be impaired, so the pressure and the pressure time are controlled appropriately.

  The film thickness of the porous film is not particularly limited and is appropriately set according to the use or application field of the porous film. However, if the film is too thin, a uniform film cannot be formed. Since the capacity per volume (weight) decreases, 0.5 to 50 μm is preferable, and 0.5 to 10 μm is more preferable.

  The porous membrane of the present invention is formed on the surface of the electrode mixture layer or organic separator of the secondary battery electrode, and is particularly preferably used as a protective film or separator for the electrode mixture layer. The secondary battery electrode on which the porous film is formed is not particularly limited, and the porous film of the present invention can be formed on electrodes having various configurations. Moreover, the porous film may be formed on any surface of the positive electrode and the negative electrode of the secondary battery, or may be formed on both the positive electrode and the negative electrode.

(Electrode for secondary battery)
In the secondary battery electrode of the present invention, an electrode mixture layer containing a binder and an electrode active material is attached to a current collector, and the porous film is laminated on the surface of the electrode mixture layer. Being done. That is, the electrode for a secondary battery of the present invention includes a current collector; an electrode mixture layer that includes a binder and an electrode active material and adheres to the current collector; and is laminated on a surface of the electrode mixture layer. The porous membrane of the present invention is also included.

(Electrode active material)
What is necessary is just to select the electrode active material used for the electrode for secondary batteries of this invention according to the secondary battery in which an electrode is utilized. Examples of the secondary battery include a lithium ion secondary battery and a nickel hydride secondary battery.

When the secondary battery electrode of the present invention is used for a lithium ion secondary battery positive electrode, the electrode active material (positive electrode active material) for the lithium ion secondary battery positive electrode is composed of an inorganic compound and an organic compound. It is roughly divided into
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. As the transition metal, Fe, Co, Ni, Mn and the like are used. 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 It is done. These compounds may be partially element-substituted. As the positive electrode active material made of an organic compound, for example, a conductive polymer compound such as polyacetylene or poly-p-phenylene can be used. An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted.

  The positive electrode active material for a lithium ion secondary battery may be a mixture of the above inorganic compound and organic compound. The particle diameter of the positive electrode active material is appropriately selected in consideration of the arbitrary constituent requirements of the battery. From the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the 50% volume cumulative diameter is usually 0.1. -50 μm, preferably 1-20 μm. When the 50% volume cumulative diameter is within this range, a secondary battery having a large charge / discharge capacity can be obtained, and handling of the slurry for electrodes and the electrodes is easy. The 50% volume cumulative diameter can be determined by measuring the particle size distribution by laser diffraction.

  When the secondary battery electrode of the present invention is used for a lithium ion secondary battery negative electrode, examples of the electrode active material (negative electrode active material) for the lithium ion secondary battery negative electrode include amorphous carbon, graphite, natural graphite, Examples thereof include carbonaceous materials such as mesocarbon microbeads and pitch-based carbon fibers, and conductive polymer compounds such as polyacene. In addition, as the negative electrode active material, metals such as silicon, tin, zinc, manganese, iron, nickel, alloys thereof, oxides or sulfates of the metals or alloys are used. In addition, lithium alloys such as lithium metal, Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitride, silicon, and the like can be used. As the electrode active material, a material obtained by attaching a conductivity imparting material to the surface by a mechanical modification method can also be used. The particle size of the negative electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics, a 50% volume cumulative diameter is usually The thickness is 1 to 50 μm, preferably 15 to 30 μm.

  When the secondary battery electrode of the present invention is used for a nickel metal hydride secondary battery positive electrode, the electrode active material (positive electrode active material) for the nickel metal hydride secondary battery positive electrode includes nickel hydroxide particles. The nickel hydroxide particles may be dissolved in cobalt, zinc, cadmium, or the like, or may be coated with a cobalt compound whose surface is subjected to an alkali heat treatment. In addition to yttrium oxide, nickel hydroxide particles include cobalt compounds such as cobalt oxide, metal cobalt and cobalt hydroxide, zinc compounds such as metal zinc, zinc oxide and zinc hydroxide, and rare earth compounds such as erbium oxide. The additive may be contained.

  When the secondary battery electrode of the present invention is used for a negative electrode of a nickel metal hydride secondary battery, as an electrode active material (negative electrode active material) for the negative electrode of a nickel metal hydride secondary battery, the hydrogen storage alloy particles are used when charging the battery. There is no particular limitation as long as it can occlude electrochemically generated hydrogen in an alkaline electrolyte and can easily release the occluded hydrogen during discharge, and is not particularly limited. Particles made of a hydrogen storage alloy are preferred. Specifically, for example, LaNi5, MmNi5 (Mm is a misch metal), LmNi5 (Lm is at least one selected from rare earth elements including La), and a part of Ni of these alloys may be Al, Mn, Co, Ti, Multi-element hydrogen storage alloy particles substituted with one or more elements selected from Cu, Zn, Zr, Cr, and B can be used. In particular, hydrogen storage alloy particles having a composition represented by the general formula: LmNiwCoxMnyAlz (the total value of atomic ratios w, x, y, z is 4.80 ≦ w + x + y + z ≦ 5.40) This is suitable because the pulverization associated with is suppressed and the charge / discharge cycle life is improved.

(Binder)
In the present invention, the electrode mixture layer contains a binder in addition to the electrode active material. By including the binder, the binding property of the electrode mixture layer in the electrode is improved, the strength against mechanical force applied during the process of winding the electrode is increased, and the electrode mixture layer in the electrode Since it becomes difficult to detach | desorb, danger, such as a short circuit by detachment | desorption material, becomes small.

  Various resin components can be used as the binder. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, and the like can be used. These may be used alone or in combination of two or more.

Furthermore, the soft polymer illustrated below can also be used as a binder.
Acrylic acid such as polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer Or an acrylic soft polymer which is a homopolymer of a methacrylic acid derivative or a copolymer with a monomer copolymerizable therewith;
Isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene / butadiene / Diene-based soft polymers such as styrene block copolymer, isoprene / styrene block copolymer, styrene / isoprene / styrene block copolymer;
Silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer, etc. Olefinic soft polymers of
Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
Epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
Examples thereof include other soft polymers such as natural rubber, polypeptide, protein, polyester-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer. These soft polymers may have a cross-linked structure or may have a functional group introduced by modification.

  The amount of the binder in the electrode mixture layer is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, particularly preferably 0.5 to 100 parts by weight of the electrode active material. 3 parts by weight. When the amount of the binder is within the above range, it is possible to prevent the active material from dropping from the electrode without inhibiting the battery reaction.

  The binder is prepared as a solution or dispersion to produce an electrode. The viscosity at that time is usually in the range of 1 mPa · S to 300,000 mPa · S, preferably 50 mPa · S to 10,000 mPa · S. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

  In the present invention, the electrode mixture layer may contain a conductivity imparting material or a reinforcing material. As the conductivity-imparting material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. Examples thereof include carbon powders such as graphite, and fibers and foils of various metals. As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved. In particular, when used in a lithium ion secondary battery, the discharge rate characteristics can be improved. The usage-amount of an electroconductivity imparting material or a reinforcing agent is 0-20 weight part normally with respect to 100 weight part of electrode active materials, Preferably it is 1-10 weight part.

  The electrode mixture layer can be formed by adhering a slurry containing a binder, an electrode active material, and a solvent (hereinafter sometimes referred to as “electrode mixture layer forming slurry”) to a current collector. .

  Any solvent may be used as long as it dissolves or disperses the binder in the form of particles. When a solvent that dissolves the binder is used, the binder is adsorbed on the surface, thereby stabilizing the dispersion of the electrode active material and the like.

  As the solvent used for the electrode mixture layer forming slurry, either water or an organic solvent can be used. Examples of the organic solvent include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate, γ-butyrolactone, ε -Esters such as caprolactone; Acylonitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: Alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methyl Amides such as pyrrolidone and N, N-dimethylformamide are exemplified. These solvents may be used alone or in admixture of two or more and appropriately selected from the viewpoint of drying speed and environment.

  The electrode mixture layer forming slurry may contain a thickener. A polymer soluble in the solvent used for the slurry for forming the electrode mixture layer is used. As the thickener, the thickener exemplified in the porous film of the present invention can be used. As for the usage-amount of a thickener, 0.5-1.5 weight part is preferable with respect to 100 weight part of electrode active materials. When the use amount of the thickener is within this range, the coating property and the adhesion with the current collector are good.

  Further, in addition to the above components, the electrode mixture layer forming slurry includes trifluoropropylene carbonate, vinylene carbonate, catechol carbonate, 1,6-dioxaspiro [4,4] nonane in order to increase the stability and life of the battery. -2,7-dione, 12-crown-4-ether and the like can be used. These may be used by being contained in an electrolyte solution described later.

  The amount of the solvent in the electrode mixture layer forming slurry is adjusted so as to have a viscosity suitable for coating according to the type of the electrode active material, the binder and the like. Specifically, in the slurry for forming an electrode mixture layer, the solid content concentration of any additive such as an electrode active material, a binder and a conductivity imparting agent is preferably 30 to 90% by weight, More preferably, it is used by adjusting to an amount of 40 to 80% by weight.

  The slurry for forming an electrode mixture layer is obtained by mixing an electrode active material, a binder, an optional additive such as a conductivity-imparting material added as necessary, and a solvent using a mixer. Mixing may be performed by supplying the above components all at once to a mixer. When an electrode active material, a binder, a conductivity-imparting material, and a thickener are used as constituents of the electrode mixture layer forming slurry, the conductivity-imparting material and the thickener are mixed in a solvent to conduct electricity. It is preferable to disperse the imparting material in the form of fine particles, and then add a binder and an electrode active material and further mix, since the dispersibility of the resulting slurry can be improved. As the mixer, a ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer, etc. can be used. It is preferable because aggregation of the resin can be suppressed.

  The particle size of the electrode mixture layer forming slurry is preferably 35 μm or less, and more preferably 25 μm or less. When the particle size of the slurry is in the above range, the conductive material is highly dispersible and a homogeneous electrode can be obtained.

The current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material. From the viewpoint of having heat resistance, for example, iron, copper, aluminum, nickel, stainless steel, etc. Metal materials such as titanium, tantalum, gold, and platinum are preferable. Among these, aluminum is particularly preferable for the positive electrode of the lithium ion secondary battery, and copper is particularly preferable for the negative electrode of the lithium ion secondary battery. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength of the electrode mixture layer, the current collector is preferably used after being roughened. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used.
Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity of the electrode mixture layer.

  The method for producing the electrode mixture layer may be any method in which the electrode mixture layer is bound in layers on at least one side, preferably both sides of the current collector. For example, the electrode mixture layer forming slurry is applied to a current collector, dried, and then heated at 120 ° C. or higher for 1 hour or longer to form an electrode mixture layer. The method for applying the electrode mixture layer forming slurry to the current collector is not particularly limited. Examples thereof 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. Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.

  Next, it is preferable to lower the porosity of the electrode mixture layer of the electrode by pressure treatment using a mold press or a roll press. The preferable range of the porosity is 5% to 15%, more preferably 7% to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, there are problems that it is difficult to obtain a high volume capacity or that the electrode mixture layer is easily peeled off and a defect is likely to occur. Further, when a curable polymer is used, it is preferably cured.

  The thickness of the electrode mixture layer is usually 5 to 300 μm, preferably 10 to 250 μm, for both the positive electrode and the negative electrode.

(Separator for secondary battery)
The separator for a secondary battery of the present invention is formed by laminating the porous film on an organic separator layer. That is, the separator for secondary batteries of this invention has an organic separator layer and the porous film of this invention laminated | stacked on the said organic separator layer.

As the organic separator layer, a known one such as a separator containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin is used.
As the organic separator layer used in the present invention, a porous membrane having a fine pore size and having no electron conductivity and ionic conductivity and high resistance to organic solvents is used. For example, polyolefin-based (polyethylene, polypropylene, polybutene, poly (Vinyl chloride), and microporous membranes made of resins such as mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoro Examples thereof include a microporous membrane made of a resin such as ethylene or a woven polyolefin-based fiber, a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like. Among these, since the coating properties of the aforementioned slurry for porous membranes are excellent, the thickness of the entire separator can be reduced, the active material ratio in the battery can be increased, and the capacity per volume can be increased. A microporous membrane is preferred.
The thickness of the organic separator layer is usually 0.5 to 40 μm, preferably 1 to 30 μm, more preferably 1 to 10 μm. Within this range, the resistance due to the separator in the battery is reduced, and the workability at the time of coating on the organic separator layer is good.

  In the present invention, examples of the polyolefin resin used as the material for the organic separator layer include homopolymers such as polyethylene and polypropylene, copolymers, and mixtures thereof. Examples of the polyethylene include low density, medium density, and high density polyethylene, and high density polyethylene is preferable from the viewpoint of piercing strength and mechanical strength. These polyethylenes may be mixed in two or more types for the purpose of imparting flexibility. The polymerization catalyst used for these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. From the viewpoint of achieving both mechanical strength and high permeability, the viscosity average molecular weight of polyethylene is preferably from 100,000 to 12 million, more preferably from 200,000 to 3 million. Examples of polypropylene include homopolymers, random copolymers, and block copolymers, and one kind or a mixture of two or more kinds can be used. The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts. The stereoregularity is not particularly limited, and isotactic, syndiotactic or atactic can be used. However, it is desirable to use isotactic polypropylene because it is inexpensive. Furthermore, an appropriate amount of a polyolefin other than polyethylene or polypropylene, and an additive such as an antioxidant or a nucleating agent may be added to the polyolefin as long as the effects of the present invention are not impaired.

  As a method for producing a polyolefin-based organic separator layer, known and publicly used methods are used. For example, after polypropylene and polyethylene are melt-extruded to form a film, they are annealed at a low temperature to grow a crystal domain and stretched in this state. A dry process for forming a microporous film by extending the amorphous region; mixing a hydrocarbon solvent or other low molecular weight material with polypropylene or polyethylene, forming a film, and then forming a solvent or low molecular weight into the amorphous phase A wet method in which a microporous film is formed by removing the film that has started to form an island phase by using this solvent or low-molecular solvent with another volatile solvent is selected. Among these, a dry method is preferable in that a large void can be easily obtained for the purpose of reducing the resistance.

  The organic separator layer used in the present invention may contain any filler or fiber compound for the purpose of controlling strength, hardness, and heat shrinkage. In addition, when laminating the porous film, it may be coated with a low molecular weight compound or a high molecular compound in advance for the purpose of improving the adhesion or improving the liquid impregnation property by lowering the surface tension with the electrolytic solution. Further, electromagnetic radiation treatment such as ultraviolet rays, plasma treatment such as corona discharge and plasma gas may be performed. In particular, the coating treatment is preferably performed with a polymer compound containing a polar group such as a carboxylic acid group, a hydroxyl group, and a sulfonic acid group from the viewpoint that the impregnation property of the electrolytic solution is high and the adhesion with the porous film is easily obtained.

(Secondary battery)
The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the porous film is laminated on at least one of the positive electrode, the negative electrode, and the separator. That is, the secondary battery of the present invention is a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution, and at least one of the positive electrode, the negative electrode, and the separator has the porous film of the present invention.

  Examples of the secondary battery include a lithium ion secondary battery and a nickel hydride secondary battery. However, improvement of safety is most demanded and the effect of introducing a porous film is the highest, and improvement of rate characteristics is also cited as an issue. Therefore, a lithium ion secondary battery is preferable. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

(Electrolyte)
As the electrolytic solution for the lithium ion secondary battery, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. A lithium salt is used as the supporting electrolyte. The lithium salt is not particularly _{limited, 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. Among these, 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 preferable. Two or more of these may be used in combination. Since the lithium ion conductivity increases as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

  The organic solvent used in the electrolyte for the lithium ion secondary battery is not particularly limited as long as it can dissolve the supporting electrolyte, but dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene Carbonates such as carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane, dimethyl sulfoxide Sulfur-containing compounds such as are preferably used. Moreover, you may use the liquid mixture of these solvents. Among these, carbonates are preferable because they have a high dielectric constant and a wide stable potential region. Since the lithium ion conductivity increases as the viscosity of the solvent used decreases, the lithium ion conductivity can be adjusted depending on the type of the solvent.

  The concentration of the supporting electrolyte in the electrolytic solution for a lithium ion secondary battery is usually 1 to 30% by weight, preferably 5% to 20% by weight. Further, it is usually used at a concentration of 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease. Since the degree of swelling of the polymer particles increases as the concentration of the electrolytic solution used decreases, the lithium ion conductivity can be adjusted by the concentration of the electrolytic solution.

As a separator, the organic separator illustrated by the above-mentioned separator for secondary batteries is mentioned. Examples of the positive electrode and the negative electrode include those in which an electrode mixture layer containing a binder and an electrode active material exemplified in the secondary battery electrode is attached to a current collector.
In the secondary battery of the present invention, the positive electrode or the negative electrode in which the porous film is laminated may be used as the positive electrode or the negative electrode, and the separator in which the porous film is laminated may be the secondary battery. A battery separator may be used as the separator.

  As a specific method for producing a lithium ion secondary battery, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the shape of the battery. The method of injecting and sealing is mentioned. The porous film of the present invention is formed on either the positive electrode, the negative electrode, or the separator. In addition, lamination with only a porous film is possible. If necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In the examples, parts and percentages relating to the quantity ratio of materials are based on weight unless otherwise specified.
In the examples and comparative examples, various physical properties were evaluated as follows.

<Polymer characteristics: degree of swelling>
A film of about 0.1 mm thick grafted polymer or non-grafted binder polymer is cut into about 2 cm square and the weight (weight before immersion) is measured. Thereafter, it is immersed in an electrolytic solution at a temperature of 60 ° C. for 72 hours. Pull up the immersed film, wipe off the electrolyte, measure the weight (weight after immersion), (weight after immersion) / (weight before immersion) x 100 (%) as the degree of swelling, and judge according to the following criteria To do. As the electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at EC: DEC = 1: 2 (volume ratio, where EC is the volume at 40 ° C., DEC is the volume at 20 ° C.). A solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / liter in the mixed solvent is used. The smaller the swelling degree, the higher the electrolyte resistance of the polymer.
A: 100% to 200% B: 200% to 300% or less C: 300% to 400% or less D: 400% to 600% or less E: 600% or more

<Slurry characteristics for porous membrane: sedimentation>
Put the slurry for porous membranes up to a height of 5 cm in a test tube with a diameter of 1 cm, and use 5 test samples each. The test sample is placed vertically on a desk. The state of the installed slurry for the porous membrane is observed for 10 days, and judged according to the following criteria. It shows that the dispersibility is so excellent that two-phase separation is not observed.
A: Two-phase separation is not observed even after 10 days.
B: Two-phase separation is observed after 6 to 10 days.
C: Two-phase separation is observed after 2 to 5 days.
D: Two-phase separation is observed after 1 day.
E: Two-phase separation is observed within 3 hours.

<Battery characteristics: Rate characteristics>
A full cell coin type lithium ion secondary battery is charged to 4.3 V by a constant current method of 0.1 C, and then discharged to 3.0 V at 0.1 C, and a 0.1 C discharge capacity is obtained. Thereafter, the battery is charged to 4.3 V at 0.1 C and then discharged to 3.0 V at 1 C, and the 1 C discharge capacity is obtained. These measurements are performed on 10 cells of a full-cell coin type lithium ion secondary battery, and the average value of each measurement value is defined as 0.1 C discharge capacity a and 1 C discharge capacity b. The capacity retention represented by the ratio (b / a (%)) of the electric capacity between the 1C discharge capacity b and the 0.1C discharge capacity a is obtained, and this is used as an evaluation criterion for rate characteristics, and is determined according to the following criteria. The higher this value, the better the rate characteristics.
SA: 93% or more A: 90% or more and less than 93% B: 80% or more and less than 90% C: 50% or more and less than 80% D: Less than 50%

<Battery characteristics: High temperature characteristics>
For a full-cell coin type lithium ion secondary battery, charging / discharging at 30 ° C. from 3 V to 4.3 V at 0.1 C and then discharging from 4.3 V to 3 V at 0.1 C is repeated 50 cycles. A value obtained by calculating the percentage of the 0.1C discharge capacity at the 50th cycle with respect to the 0.1C discharge capacity at the cycle as a percentage was determined as the capacity maintenance rate, and was judged according to the following criteria. The larger this value, the lower the discharge capacity and the better the high temperature characteristics.
A: 60% or more B: 50% or more and less than 60% C: 30% or more and less than 50% D: 10% or more and less than 30% E: Less than 10%

(Production Example 1: Cross-linked styrene particles 1)
A material consisting of 98 parts of styrene, 2 parts of methacrylic acid, 10 parts of t-dodecyl mercaptan, 0.8 part of sodium dodecylbenzenesulfonate, 0.4 part of potassium persulfate, and 200 parts of water is placed in a 2 L flask. It was. While stirring the material, the temperature was raised to 70 ° C. in nitrogen gas and polymerization was performed for 6 hours to obtain seed polymer particles 1. The polymerization yield was 98%. The average particle size of the seed polymer particles 1 was 0.17 μm, and the standard deviation value of the particle size was 0.08 μm. The average particle diameter is an average value of values measured for 100 polymer particles from a transmission electron micrograph. The toluene dissolved content of the seed polymer particles 1 was 98%. When the molecular weight of the seed polymer particles 1 was measured by gel permeation chromatography (standard material: polystyrene), the weight average molecular weight (Mw) = 5,000 and the number average molecular weight (Mn) = 3,100.

  Seed polymer particles 1 (aqueous dispersion) 8 parts (in terms of solid content), sodium lauryl sulfate 1.0 part, potassium persulfate 0.5 part, water 500 parts, and divinylbenzene 100 parts (commercial product, purity 55% by weight) The remaining monofunctional vinyl monomer) was stirred at 30 ° C. for 10 minutes to allow the seed polymer particles 1 to absorb other components. The concentration of the sodium lauryl sulfate in water is C.I. M.M. C. 87% of (critical micelle concentration).

  Next, the system was heated to 70 ° C. and polymerized for 3 hours to obtain crosslinked styrene particles 1. The polymerization yield was 99%. After the reaction, the reaction mixture containing crosslinked styrene particles was passed through a 200-mesh filter. The polymerized coagulum remaining on the filter was 0.02% (based on the solid content of polymerization), which indicates good polymerization stability. It was found that polymer particles were obtained.

  When the obtained crosslinked styrene particles 1 were observed with a scanning electron microscope, the average particle diameter of the crosslinked styrene particles 1 was 0.38 μm, and particles belonging to a range of ± 10% of the average particle diameter were 91% of all particles. % By weight. The particle size distribution (CV value) of the crosslinked styrene particles 1 was 10%. The shape of the crosslinked styrene particles 1 was spherical.

  When 1 g of the obtained crosslinked styrene particles 1 was placed in 100 ml each of toluene, cyclohexane, tetrahydrofuran, cresol, and methyl ethyl ketone and observed for 24 hours, the particles showed no sign of dissolution or swelling.

  In order to know the thermal properties of the obtained crosslinked styrene particles 1, differential thermal analysis and thermobalance analysis were performed in a nitrogen gas atmosphere. According to differential thermal analysis, when heated at a heating rate of 10 ° C./min, it did not melt or soften from room temperature to 450 ° C. Further, according to thermobalance analysis, the temperature at which the crosslinked styrene particles 1 are reduced by 10% by weight when heated at a heating rate of 10 ° C./min (hereinafter, this reduction starting temperature is expressed as “T10”) is 415 ° C. Met. In thermobalance analysis, when 10 g of the crosslinked styrene particles 1 were heated at 300 ° C. for 5 hours, the weight loss ratio was 8 wt%.

(Production Example 2: Cross-linked styrene particles 2)
(P2-1) A 2 L reactor equipped with a stirring blade, a cooling condenser, a nitrogen gas inlet tube, and a thermometer was previously purged with nitrogen. In this reactor, 840 g of ethanol, 360 g of distilled water, 13.3 g of methacrylic acid and 0.95 g of 2,2-azobisisobutyronitrile were added, and stirring was added until the system became uniform. After that, bubbling with nitrogen was performed, and then the reactor was heated to 70 ° C. to start the reaction, and kept for 6 hours. Thereafter, 66.7 g of styrene was added to the system, and the reaction was further continued for 16 hours to carry out polymerization. The polymerization conversion was 98.3% by weight method. Thereafter, the reactor was cooled to room temperature to obtain a suspension of polymer particles.

  (P2-2) The suspension obtained in (P2-1) was centrifuged to precipitate polymer particles, and decantation was performed to recover the polymer particles. The polymer particles were put into distilled water, sufficiently stirred and centrifuged. Thereafter, operations from decantation to centrifugation were performed once again, and the polymer particles were washed and purified by these operations. About the obtained polymer particle, the particle diameter was measured with the Coulter multisizer (Coulter company make). The obtained polymer particles had a weight average particle size of 2.05 μm, a number average particle size of 2.01 μm, a particle size distribution of monodisperse, and a particle shape of a spherical shape. It was.

To 50 g (solid content 2 g) of the obtained polymer particles suspended in distilled water, a 0.1 N / NaOH solution was added until pH 12 and stirred for 6 minutes, and then a 0.1 N / HCl solution was added to 0.5 cm. Conductive titration was carried out by adding ³ units every 30 seconds (Kyoto Electronics CM-117 conductivity meter), and the acid amount on the particle surface was measured, but no acid was detected on the particle surface, and the particle surface was made of polystyrene. It was found that a hydrophobic surface was maintained.

  (P2-3) To the total amount of the suspension obtained by performing the above (P2-1) again, 50 g of styrene, 50 g of divinylbenzene (manufactured by Wako Pure Chemicals, purity 55%), 2,2-azobisisobutyro 0.50 g of nitrile was added and the polymerization reaction was continued for 10 hours to obtain crosslinked styrene particles 2. The polymerization conversion rate was 94.8%. The crosslinked styrene particles 2 were spherical particles having a monodispersed particle size distribution with a particle size of 2.50 μm in weight average and 2.22 μm in number average. The particle size distribution of the crosslinked styrene particles 2 was 15%. T10 of the crosslinked styrene particles 2 was 375 ° C. Further, the acid amount on the particle surface was measured by conductometric titration, but no acid was detected on the particle surface, and it was found that the particle surface was hydrophobic polystyrene. When the obtained particles were dropped into a toluene solvent, the solution became white and turbid, and the particles were insoluble in the toluene solvent. Therefore, it was confirmed that a crosslinked structure was introduced into the particles.

Example 1
<Production of graft polymer>
In an autoclave with a stirrer, 230 parts of toluene, 50 parts of n-butyl acrylate, 50 parts of a styrene macromonomer (single-end methacryloylated polystyrene oligomer, “AS-6” manufactured by Toagosei Co., Ltd.), as a polymerization initiator After adding 1 part of t-butylperoxy-2-ethylhexanate and stirring sufficiently, the mixture was heated to 90 ° C. for polymerization to obtain a polymer (hereinafter referred to as “graft polymer 1”) solution. The polymerization conversion rate determined from the solid content concentration was approximately 98%. The graft polymer 1 had a glass transition temperature of 25 ° C. and a weight average molecular weight of about 50,000. In the obtained graft polymer, the main chain is composed of n-butyl acrylate (a component exhibiting swelling property with respect to the electrolytic solution), and the side chain is composed of styrene (a component not exhibiting swelling property with respect to the electrolytic solution). The obtained toluene solution of graft polymer 1 was dried at 120 ° C. for 10 hours under a nitrogen atmosphere to prepare a polymer film, and the degree of swelling was measured. The results are shown in Table 1.

<Creation of slurry for porous membrane>
Non-conductive particles (cross-linked styrene particles 1 obtained in Production Example 1) and the solution of graft polymer 1 are mixed so as to have a content ratio of 100: 2.5 (solid content equivalent ratio), and further acetone is added. The mixture was mixed so that the solid content concentration was 30%, and dispersed using a bead mill to prepare slurry 1 for porous membrane. The sedimentation property of the obtained slurry for porous membrane was measured. The results are shown in Table 1.

<Production of negative electrode composition and negative electrode>
98 parts of graphite having a particle size of 20 μm and a specific surface area of 4.2 m ² / g as a negative electrode active material, and 5 parts of PVDF (polyvinylidene fluoride) as a binder are mixed, and N-methylpyrrolidone is further mixed. In addition, the mixture was mixed with a planetary mixer to prepare a slurry-like electrode composition for negative electrode (slurry for forming a negative electrode mixture layer). This negative electrode composition was applied to one side of a 10 μm thick copper foil, dried at 110 ° C. for 3 hours, and then roll-pressed to form a negative electrode mixture layer having a thickness of 60 μm.
Furthermore, on this negative electrode mixture layer, the slurry 1 for porous membrane is applied using a wire bar so that the thickness of the porous membrane layer after drying becomes 5 μm, and then dried at 60 ° C. for 30 seconds. By forming a porous film, a negative electrode having a copper foil, a negative electrode mixture layer and a porous film was obtained.

<Production of electrode composition for positive electrode and positive electrode>
Mix 95 parts of LiCoO ₂ (manufactured by Nippon Kagaku Kogyo Co., Ltd.) having a spinel structure as a positive electrode active material and 3 parts of PVDF (polyvinylidene fluoride) as a binder, corresponding to a solid content, and further acetylene black (Electrochemical Industry) 2 parts) and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to prepare a slurry-like electrode composition for a positive electrode (a slurry for forming a positive electrode mixture layer). This positive electrode composition was applied to an aluminum foil having a thickness of 18 μm, dried at 120 ° C. for 3 hours, and then roll-pressed to obtain a positive electrode having a positive electrode mixture layer having a thickness of 70 μm.

<Separator>
A single-layer polypropylene separator (porosity 55%, manufactured by Celgard) manufactured by a dry method having a width of 65 mm, a length of 500 mm, and a thickness of 25 μm was used as a separator as it was.

<Production of battery>
Next, the positive electrode obtained was cut into a circle having a diameter of 13 mm, the negative electrode having a diameter of 14 mm, and the separator having a diameter of 18 mm. The positive electrode mixture layer side surface of the positive electrode and the porous film side surface of the negative electrode face each other with a separator interposed therebetween, and the positive electrode aluminum foil was placed in contact with the bottom surface of the outer container. Further, an expanded metal was put on the copper foil of the negative electrode and stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. Inject the electrolyte (EC / DEC = 1/2, 1M LiPF ₆ ) into this container so that no air remains, and cover the outer container with a 0.2 mm thick stainless steel cap via polypropylene packing. The battery can was sealed, and a lithium ion secondary battery having a diameter of 20 mm and a thickness of about 3.2 mm was manufactured (coin cell CR2032). The obtained battery was measured for rate characteristics and high temperature characteristics. The results are shown in Table 1.

(Example 2)
In the preparation of the slurry for the porous film, instead of the crosslinked styrene particles 1 as non-conductive particles, aluminum oxide particles (Al ₂ O ₃ , average particle size 0.3 μm, iron content <20 ppm, particle size distribution (CV value) The polymer film, the slurry for the porous film, the negative electrode having the porous film, and the battery were produced in the same manner as in Example 1 except that 30)) was used. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

(Example 3)
In an autoclave equipped with a stirrer, 230 parts of toluene, 50 parts of styrene, n-butyl acrylate macromonomer (single-end methacryloylated polybutyl acrylate oligomer, manufactured by Toagosei Co., Ltd., “AB-6”), polymerization 1 part of t-butylperoxy-2-ethylhexanate is added as an initiator, and after sufficiently stirring, the mixture is heated to 90 ° C. to polymerize, and a polymer (hereinafter referred to as “graft polymer 2”) solution is obtained. Obtained. The polymerization conversion rate determined from the solid content concentration was approximately 98%. The graft polymer 2 had a glass transition temperature of 25 ° C. and a weight average molecular weight of about 50,000. In the obtained graft polymer, the main chain is composed of styrene (a component that does not exhibit swelling with respect to the electrolytic solution), and the side chain is composed of n-butyl acrylate (a component that exhibits swelling with respect to the electrolytic solution).
A polymer film, a slurry for a porous film, a negative electrode having a porous film, and a battery were prepared in the same manner as in Example 1 except that the graft polymer 2 was used instead of the graft polymer 1 as a binder constituting the porous film. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

Example 4
In an autoclave with a stirrer, 230 parts of toluene, 65 parts of n-butyl acrylate, 35 parts of a styrene macromonomer (single-end methacryloylated polystyrene oligomer, “AS-6” manufactured by Toagosei Co., Ltd.), as a polymerization initiator 1 part of t-butylperoxy-2-ethylhexanate was added, and after sufficiently stirring, it was polymerized by heating to 90 ° C. to obtain a polymer (hereinafter referred to as “graft polymer 3”) solution. The polymerization conversion rate determined from the solid content concentration was 98%. The graft polymer 3 had a glass transition temperature of −7 ° C. and a weight average molecular weight of about 50,000. In the obtained graft polymer, the main chain is composed of n-butyl acrylate (a component exhibiting swelling property with respect to the electrolytic solution), and the side chain is composed of styrene (a component not exhibiting swelling property with respect to the electrolytic solution).
A polymer film, a slurry for a porous film, a negative electrode having a porous film, and a battery were prepared in the same manner as in Example 1 except that the graft polymer 3 was used instead of the graft polymer 1 as a binder constituting the porous film. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

(Example 5)
In the preparation of the slurry for the porous membrane, titanium oxide particles (TiO ₂ , trade name “PT-308 CR-EL”, manufactured by Ishihara Sangyo Co., Ltd. A polymer film, a slurry for a porous membrane, a negative electrode having a porous membrane, and a battery were prepared in the same manner as in Example 1 except that the particle size was 0.25 μm and the particle size distribution (CV value) was 35%. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

(Example 6)
In the preparation of the slurry for the porous membrane, a polymer film, a porous film were produced in the same manner as in Example 1 except that the crosslinked styrene particles 2 obtained in Production Example 2 were used as non-conductive particles instead of the crosslinked styrene particles 1. A slurry for membrane, a negative electrode having a porous membrane, and a battery were produced. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

(Example 7)
In the preparation of the slurry for the porous membrane, in place of the crosslinked styrene particles 1 as non-conductive particles, crosslinked polymethyl methacrylate particles (trade name “SSX-101” manufactured by Sekisui Chemical Co., Ltd., true specific gravity: 1.20, refractive index: 1.49, heat resistance: 250 to 270 ° C., average particle size 1.0 μm, particle size distribution (CV value) 15%) A negative electrode having a porous film and a battery were produced. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 1.

(Example 8)
<Production of graft polymer>
In an autoclave with a stirrer, 230 parts of toluene, 40 parts of ethyl acrylate, 60 parts of styrene-acrylonitrile macromonomer (manufactured by Toagosei Chemical Industry Co., Ltd., “AN-6S”, toluene solution) in terms of solid content, polymerization initiator 1 part of t-butylperoxy-2-ethylhexanate was added and sufficiently stirred, and then heated to 90 ° C. for polymerization to obtain a polymer (hereinafter referred to as “graft polymer 5”) solution. . The polymerization conversion rate determined from the solid content concentration was approximately 98%. The graft polymer 5 had a glass transition temperature of 50 ° C. and a weight average molecular weight of about 100,000. In the obtained graft polymer, the main chain is composed of ethyl acrylate (a component exhibiting swelling property with respect to the electrolytic solution), and the side chain is composed of styrene-acrylonitrile (a component not exhibiting swelling property with respect to the electrolytic solution).
The obtained toluene solution of graft polymer 5 was dried at 120 ° C. for 10 hours under a nitrogen atmosphere to prepare a polymer film, and the degree of swelling was measured. The results are shown in Table 2.

<Creation of slurry for porous membrane>
Mixing non-conductive particles (aluminum oxide, average particle size 0.3 μm, iron content <20 ppm) and a solution of graft polymer 5 to a content ratio (solid content equivalent ratio) of 100: 2.5 Further, acetone was mixed so as to have a solid content concentration of 30% and dispersed using a bead mill to prepare slurry 2 for porous membrane. The sedimentation property of the obtained slurry for porous membrane was measured. The results are shown in Table 2.

<Production of negative electrode composition and negative electrode>
98 parts of graphite having a particle size of 20 μm and a specific surface area of 4.2 m ² / g as a negative electrode active material, and 5 parts of PVDF (polyvinylidene fluoride) as a binder are mixed, and N-methylpyrrolidone is further mixed. In addition, the mixture was mixed with a planetary mixer to prepare a slurry-like electrode composition for negative electrode (slurry for forming a negative electrode mixture layer). This negative electrode composition was applied to one side of a 10 μm thick copper foil, dried at 110 ° C. for 3 hours, and then roll pressed to obtain a negative electrode having a negative electrode mixture layer having a thickness of 60 μm.

<Production of electrode composition for positive electrode and positive electrode>
Mix 95 parts of LiCoO ₂ (manufactured by Nippon Kagaku Kogyo Co., Ltd.) having a spinel structure as a positive electrode active material and 3 parts of PVDF (polyvinylidene fluoride) as a binder, corresponding to a solid content, and further acetylene black (Electrochemical Industry) 2 parts) and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to prepare a slurry-like electrode composition for a positive electrode (a slurry for forming a positive electrode mixture layer). This positive electrode composition was applied to an aluminum foil having a thickness of 18 μm, dried at 120 ° C. for 3 hours, and then roll-pressed to obtain a positive electrode having a positive electrode mixture layer having a thickness of 70 μm.

<Creation of separator with porous membrane>
A single-layer polypropylene separator (porosity 55%, manufactured by Celgard) manufactured by a dry method having a width of 65 mm, a length of 500 mm, and a thickness of 25 μm was used as the organic separator layer. On top of this, the porous membrane slurry 2 is applied using a wire bar so that the thickness of the porous membrane layer after drying is 5 μm, and then dried at 60 ° C. for 30 seconds to form a porous membrane. Thus, a separator 2 with a porous film was obtained.

<Production of battery>
Next, the obtained positive electrode was cut out into a circle having a diameter of 13 mm, the negative electrode was cut into a diameter of 14 mm, and the porous membrane separator 2 was cut into a circle having a diameter of 18 mm. The surface of the positive electrode mixture layer side of the positive electrode and the surface of the negative electrode mixture layer side of the negative electrode face each other via the separator 2 with a porous film, and the aluminum foil of the positive electrode is in contact with the bottom surface of the outer container. These were arranged. The separator 2 with a porous film was disposed so that the porous film layer was opposed to the positive electrode mixture layer side. Further, an expanded metal was put on the copper foil of the negative electrode and stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. Inject the electrolyte (EC / DEC = 1/2, 1M LiPF ₆ ) into this container so that no air remains, and cover the outer container with a 0.2 mm thick stainless steel cap via polypropylene packing. The battery can was sealed, and a lithium ion secondary battery having a diameter of 20 mm and a thickness of about 3.2 mm was manufactured (coin cell CR2032). The obtained battery was measured for rate characteristics and high temperature characteristics. The results are shown in Table 2.

Example 9
In the preparation of the slurry for the porous membrane, a polymer film and a porous membrane were obtained in the same manner as in Example 8, except that the crosslinked styrene particles 1 obtained in Production Example 1 were used as the nonconductive particles instead of the aluminum oxide particles. Slurry, a negative electrode having a porous film, and a battery were prepared. The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 2.

(Example 10)
A polymer film, a slurry for a porous membrane, a separator, and a polymer as in Example 8, except that the same graft polymer 1 as that obtained in Example 1 was used instead of the graft polymer 5 as a binder constituting the porous membrane. A battery was produced.
The obtained battery had the same configuration as the battery of Example 2, except that the separator was not a negative electrode but had a porous film.
The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 2.

(Example 11)
A polymer film, a slurry for a porous membrane, a separator, and a battery were produced in the same manner as in Example 8 except that the following points were changed.
The same graft polymer 2 as that obtained in Example 3 was used in place of the graft polymer 5 as a binder constituting the porous membrane.
In the preparation of the slurry for the porous membrane, the crosslinked styrene particles 1 obtained in Production Example 1 were used as the nonconductive particles instead of the aluminum oxide particles.
In the preparation of the slurry for the porous membrane, instead of mixing the non-conductive particles and the solution of the graft polymer 2 so as to have a content ratio (solid content equivalent ratio) of 100: 2.5, the crosslinked styrene particles 1 and The solution of graft polymer 2 and PVDF were mixed so that the ratio was 77: 2.5: 23 (solid content equivalent ratio).
The obtained battery had the same configuration as the battery of Example 3 except that the separator was not a negative electrode but had a porous film.
The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 2.

(Example 12)
A polymer film, a slurry for a porous membrane, a separator, and a battery were produced in the same manner as in Example 8 except that the following points were changed.
The same graft polymer 3 as that obtained in Example 4 was used in place of the graft polymer 5 as a binder constituting the porous membrane.
In the preparation of the slurry for the porous membrane, the crosslinked styrene particles 1 obtained in Production Example 1 were used as the nonconductive particles instead of the aluminum oxide particles.
The obtained battery had the same configuration as the battery of Example 4 except that the separator had a porous membrane instead of the negative electrode.
The swelling degree of the polymer film, the sedimentation property in the slurry for the porous film, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 2.

(Comparative Example 1)
In an autoclave equipped with a stirrer, 230 parts of toluene, 50 parts of n-butyl acrylate, 50 parts of styrene monomer, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added and stirred sufficiently. Polymerization was conducted by heating to 0 ° C. to obtain a polymer (hereinafter referred to as “copolymer 1”) solution. The polymerization conversion rate determined from the solid content concentration was approximately 98%. The copolymer 1 had a glass transition temperature of 25 ° C. and a weight average molecular weight of about 50,000. The obtained copolymer 1 is a random copolymer of n-butyl acrylate and styrene.
A polymer film, a slurry for a porous film, a separator, and a battery were prepared in the same manner as in Example 1 except that the copolymer 1 was used instead of the graft polymer 1 as a binder constituting the porous film. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 2.

(Comparative Example 2)
A polymer film, a slurry for a porous membrane, a separator as in Example 2 except that the same copolymer 1 as that obtained in Comparative Example 1 was used instead of the graft polymer 1 as a binder constituting the porous membrane. And a battery was fabricated. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

(Comparative Example 3)
Non-conductive particles (aluminum oxide, average particle size 0.3 μm, iron content <20 ppm), graft polymer 1 solution and PVDF, 46: 2.5: 54 content ratio (solid content equivalent ratio) Then, acetone was further mixed so that the solid content concentration became 30%, and dispersed using a bead mill to prepare slurry 3 for porous membrane.
As a porous membrane slurry, a polymer film, a porous membrane slurry, a separator and a battery were prepared in the same manner as in Example 2 except that the porous membrane slurry 3 obtained above was used instead of the porous membrane slurry 1. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

(Comparative Example 4)
A polymer film, a slurry for a porous membrane, a separator as in Example 12, except that the same copolymer 1 as that obtained in Comparative Example 1 was used instead of the graft polymer 2 as a binder constituting the porous membrane. And a battery was fabricated. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

(Comparative Example 5)
A polymer film, a slurry for a porous membrane, a separator as in Example 11 except that the same copolymer 1 as that obtained in Comparative Example 1 was used instead of the graft polymer 1 as a binder constituting the porous membrane. And a battery was fabricated. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

(Comparative Example 6)
As the porous membrane slurry, a polymer film, a porous membrane slurry, a separator were obtained in the same manner as in Example 11 except that the same porous membrane slurry 3 as that obtained in Comparative Example 3 was used instead of the porous membrane slurry 1. And a battery was fabricated. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

(Comparative Examples 7-8)
A polymer film as in Example 2 except that polyacrylonitrile (Comparative Example 7: manufactured by Nippon Zeon) or polyvinylidene fluoride (Comparative Example 8) was used instead of the graft polymer 1 as a binder constituting the porous film. A slurry for a porous membrane, a separator, and a battery were prepared. And the swelling degree of the polymer film, the sedimentation property in the slurry for porous films, the rate characteristics of the battery, and the high temperature characteristics were evaluated. The results are shown in Table 3.

  The Fe content in the slurry for the porous membrane was 30 ppm or less in all the examples and comparative examples.

The abbreviations shown in the table are as follows.
ST macromer: Styrene macromonomer ratio (parts) in the binder polymer (graft polymer) raw material
BA macromer: n-butyl acrylate macromonomer ratio (parts) in the raw material for the polymer (graft polymer) for binder
ST-AN Macromer: Ratio of styrene-acrylonitrile macromonomer in the raw material for polymer (graft polymer) for binder (part)
ST: Styrene ratio (parts) in the polymer (graft polymer) material for binder
BA: n-butyl acrylate ratio (parts) in polymer (graft polymer) raw material for binder
EA: Percentage of ethyl acrylate in the polymer (graft polymer) material for binder
GMA: Glycidyl methacrylate ratio (parts) in the binder polymer (graft polymer) raw material

As apparent from the results of Tables 1 to 3, by using the graft polymer as the binder constituting the porous film, high rate characteristics and high temperature characteristics can be exhibited while controlling the degree of swelling with respect to the electrolytic solution. Furthermore, by controlling the degree of swelling by molecular weight, graft structure, and degree of crosslinking, both dispersibility and rate characteristics are excellent, and among the examples, the graft structure is further included, and the degree of swelling with respect to the electrolytic solution is 100% or more 200 In Example 2 in which a porous film is formed on the electrode using a graft polymer of not more than%, the sedimentation property, the rate property, and the high temperature property are particularly excellent.
Furthermore, as is clear from the comparison between Example 1 and Example 2 and the comparison between Example 8 and Example 9, when cross-linked styrene which is an organic particle is employed as the non-conductive particle, rate characteristics and high temperature characteristics A further improvement was seen in. This can be said to be a remarkable effect of organic particles, considering that organic particles are advantageous from the viewpoint of producing low-cost particles with less metal contamination that adversely affects battery performance.

Claims (9)

Comprising 50-99 wt% non-conductive particles and 0.1-10 wt% graft polymer,
The porous membrane for secondary batteries whose swelling degree with respect to electrolyte solution of the said graft polymer is 100% or more and 300% or less.   The porous film according to claim 1, wherein the non-conductive particles are organic particles.   The porous membrane according to claim 1 or 2, wherein the graft polymer is composed of a component exhibiting swelling property with respect to an electrolytic solution and a component not exhibiting swelling property with respect to the electrolytic solution.   The porous membrane according to any one of claims 1 to 3, wherein the graft polymer has a weight average molecular weight in the range of 1,000 to 500,000. Including non-conductive particles, graft polymer and solvent,
The content ratio of the non-conductive particles in the total solid content is 50 to 99% by weight, the content ratio of the graft polymer is 0.1 to 10% by weight,
A slurry for a porous membrane of a secondary battery porous membrane, wherein the degree of swelling of the graft polymer with respect to the electrolytic solution is 100% or more and 300% or less.   The manufacturing method of the porous film for secondary batteries including the process of apply | coating the slurry for porous films of Claim 6 to a base material, and then drying. Current collector,
5. The porous material according to claim 1, comprising a binder and an electrode active material, the electrode mixture layer adhering onto the current collector, and the porous material laminated on a surface of the electrode mixture layer. An electrode for a secondary battery having a membrane.   The separator for secondary batteries which has an organic separator layer and the porous film of any one of Claims 1-4 laminated | stacked on the said organic separator layer.   A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein at least one of the positive electrode, the negative electrode, and the separator has the porous film according to any one of claims 1 to 4. .