JPWO2011013604A1 - Porous membrane for secondary battery and secondary battery - Google Patents

Abstract

A porous membrane for a secondary battery comprising non-conductive particles and a block polymer. Preferably, the block polymer is composed of a segment exhibiting compatibility with the electrolytic solution and a segment not exhibiting compatibility with the electrolytic solution.

Description

  The present invention relates to a porous membrane for a secondary battery, and more particularly to a porous membrane for a secondary battery having high output characteristics and long-term cycle characteristics used for a lithium ion secondary battery or the like. The present invention also relates to a slurry and a production method for obtaining such a porous membrane for a secondary battery, a secondary battery having such a porous membrane for a secondary battery, and other applications.

  Lithium ion secondary batteries exhibit the highest energy density among practical batteries, and are frequently used particularly for small electronics. In addition, expansion to automobile applications is also expected, and there is a demand for higher capacity, longer life and further improvement in safety.

  In general, in order to prevent a short circuit between a positive electrode and a negative electrode, an organic separator made of polyolefin such as polyethylene or polypropylene is used for a lithium ion secondary battery. Since the organic separator of polyolefin has a physical property of melting at 200 ° C. or lower, when the battery becomes hot due to internal and / or external stimulation, volume change such as shrinkage and melting occurs. There is a risk of explosion due to short circuit of the negative electrode 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 polyolefin organic separator or an electrode (positive electrode or negative electrode).
For example, Patent Document 1 discloses a porous protection formed by using a slurry containing fine particles such as alumina, silica, and polyethylene resin on an electrode and a binder having high electrolytic solution resistance such as polyvinylidene fluoride. A membrane is disclosed. In the case of these porous film protective films, even if thermal contraction of the organic separator occurs at, for example, 150 ° C. or higher, the presence of fine particles on the electrode reduces the internal short circuit rate and improves safety.
Furthermore, Patent Document 2 discloses a porous film in which fine particles such as alumina or an organic compound and a binder such as a styrene-butadiene copolymer are formed on a liner having releasability. Yes. In the case of these porous membranes, in addition to the decrease in the internal short-circuit rate due to the fact that thermal contraction does not occur, shutdown occurs due to the thermal swelling of the porous membrane, and the reliability and safety are further improved.

Japanese Patent Laid-Open No. 7-220759 JP 2008-027839 A

However, according to the study by the present inventors, in the methods described in Patent Documents 1 and 2, when forming the porous film layer on the electrode, the slurry is applied on the electrode so that the fine particles do not fall off. It has been found that the binder coats the electrode surface, and as a result, the movement of lithium is hindered and the output characteristics are deteriorated.
In addition, it was found that in order to improve the long-term cycle characteristics, it is necessary to further improve the electrolyte solution retainability and the electrolyte solution impregnation property of the porous membrane.
Accordingly, it is an object of the present invention to provide a porous film used in a lithium ion secondary battery or the like having further improved output characteristics and long-term cycle characteristics, a slurry and a production method for obtaining such a porous film, and output characteristics and long-term performance. An object of the present invention is to provide a lithium ion secondary battery and its constituent elements having further improved cycle characteristics.

  As a result of intensive studies to solve the above problems, the present inventors have included non-conductive particles such as inorganic particles in the porous film and non-conductive by using a block polymer as a binder (binder). It has been found that the dispersibility is improved due to the high adsorption stability to the conductive particles, and that the porous membrane has an appropriate electrolyte solution retaining property, so that the output characteristics of the secondary battery having the porous membrane are improved. Furthermore, it has been found that the porous membrane has high electrolyte impregnation property / electrolytic solution retention property for a long period of time, so that the long-term cycle characteristics are improved in addition to the high output characteristics, and the present invention has been completed.

The present invention for solving the above-mentioned problems includes the following matters as a gist.
(1) A porous film for a secondary battery containing non-conductive particles and a block polymer.
(2) The block polymer has two segments which are a segment showing compatibility with a secondary battery electrolyte containing ethylene carbonate and diethyl carbonate and a segment showing no compatibility with the secondary battery electrolyte. The porous membrane for a secondary battery as described in (1).
(3) The porous membrane for a secondary battery according to any one of (1) to (2), wherein the block polymer has a weight average molecular weight in the range of 1,000 to 500,000.
(4) The porous membrane for a secondary battery according to any one of (1) to (3), wherein the block polymer includes a segment of a soft polymer having a glass transition temperature of 15 ° C. or lower.
(5) The block polymer has a segment showing compatibility with the electrolyte solution for secondary battery, and the segment showing compatibility with the electrolyte solution for secondary battery has a solubility parameter (SP) of 8.0 or more. The porous membrane for a secondary battery according to any one of (1) to (4), comprising a monomer component that is less than 11 and / or a monomer component having a hydrophilic group.
(6) The block polymer has a segment that does not show compatibility with the electrolyte solution for secondary battery, and the segment that does not show compatibility with the electrolyte solution for secondary battery has a solubility parameter of less than 8.0 or The porous membrane for a secondary battery according to any one of (1) to (4), comprising a monomer component having 11 or more and / or a monomer component having a hydrophobic portion.
(7) A slurry for a secondary battery porous membrane containing non-conductive particles, a block polymer, and a solvent.
(8) A method for producing a porous film for a secondary battery, comprising a step of applying the slurry for a secondary battery porous film according to claim 7 to a substrate and then drying.
(9) A current collector, an electrode mixture layer including a binder and an electrode active material provided on the current collector, and (1) to (6) provided on the electrode mixture layer A secondary battery electrode comprising the layer of the porous film for a secondary battery according to any one of the above.
(10) A separator for a secondary battery including the porous membrane for a secondary battery according to any one of (1) to (6) provided on the organic separator layer and the organic separator layer.
(11) A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte for a secondary battery containing ethylene carbonate and diethyl carbonate, wherein at least one of the positive electrode, the negative electrode, and the separator is (1) to (6 A secondary battery comprising the porous film for a secondary battery according to any one of the above.

  According to the present invention, when the porous film contains a specific binder, high dispersibility of non-conductive particles and high electrolyte solution retention in the porous film are achieved. As a result, in the secondary battery of the present invention obtained using the porous membrane for a secondary battery, electrode or separator of the present invention, its output characteristics and long-term cycle characteristics are further improved. According to the production method and the slurry for a secondary battery porous membrane of the present invention, such a porous membrane for a secondary battery can be easily formed.

The present invention is described in detail below.
The porous membrane for a secondary battery of the present invention includes non-conductive particles and a block 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.
As the organic particles, particles made of various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin are used. The polymer compound forming the particles can be used as a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, and the like. The polymer compound that forms the organic particles may be a mixture of two or more polymer compounds.
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 possibility that the slurry for the porous film aggregates and as a result, the porosity of the porous film decreases and the output characteristics deteriorate. 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). Although the minimum of content of a metal foreign material is not specifically limited, Preferably it is 0 ppm.

The average particle size (volume average D50 average particle size) of the non-conductive particles used in the present invention is preferably 5 nm or more and 10 μm or less, more preferably 10 nm or more and 5 μm or less. By controlling the average particle diameter of the non-conductive particles within the above range, it becomes easy to obtain a film having a predetermined thickness that is uniform in controlling the dispersion state. It is particularly preferable that the average particle diameter of the non-conductive particles be in the range of 50 nm or more and 2 μm or less because the dispersion, the ease of coating, and the controllability of voids are excellent.
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 content of non-conductive particles in the porous film is preferably 5 to 99% by weight, more preferably 50 to 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.

(Block polymer)
The block polymer used in the present invention is a block polymer having two types of segments. In addition to having these two types of segments, the block polymer may further have one or more other arbitrary segments.

The two types of segments of the block polymer used in the present invention can be composed of various components, but the porous film can have electrolyte solution impregnation and electrolyte solution retention properties, and non-conductive particles. In order to improve the dispersibility of the secondary battery, one of the two segments (referred to as “segment A” for convenience) has an electrolyte solution for secondary batteries containing ethylene carbonate and diethyl carbonate (hereinafter referred to as “the above-mentioned”). It is preferable that other segments (referred to as “segment B” for convenience) do not exhibit compatibility with the secondary battery electrolyte.
Preferably, a block polymer is comprised from the segment which shows compatibility with the said electrolyte solution for secondary batteries, and the segment which does not show compatibility with the said electrolyte solution for secondary batteries. As a more specific example of the block polymer, a segment A which is substantially composed of a segment exhibiting compatibility with the electrolyte solution for secondary battery and a segment not exhibiting compatibility with the electrolyte solution for secondary battery. And what does not contain components other than segment B can be mentioned.

That the segment is compatible with the secondary battery electrolyte means that the segment shows a certain extent in the secondary battery electrolyte, and the segment is incompatible with the secondary battery electrolyte. It can be judged by the degree of swelling. Here, showing compatibility means that the degree of swelling of the segment with respect to the secondary battery electrolyte is 500% or more, or that the segment is dissolved in the secondary battery electrolyte.
On the other hand, if the segment does not exhibit compatibility with the electrolyte solution for secondary battery, it means that the segment does not expand in the electrolyte solution, and the degree of swelling of the segment with respect to the electrolyte solution for secondary battery is 0. % Or more and 300% or less.

(Swelling degree)
In the present invention, the degree of swelling of each segment is measured by the following method.
A polymer composed of the constituent components of segment A and a polymer composed of the constituent components of segment B are each formed into a film having a thickness of about 0.1 mm, cut into about 2 cm squares, and the weight (weight before immersion) is measured. . Then, it is immersed in the electrolyte solution for secondary batteries at a temperature of 60 ° C. for 72 hours. The soaked film was pulled up and the weight immediately after the secondary battery electrolyte was wiped off (weight after soaking) was measured, and the value of (weight after soaking) / (weight before soaking) × 100 (%) was the degree of swelling. And
As the secondary battery electrolyte, ethylene carbonate (EC) and diethyl carbonate (DEC) are EC: DEC = 1: 2 (volume ratio, where EC is a volume at 40 ° C., DEC is a volume at 20 ° C. The solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent obtained by mixing in (1) is used.

When the block polymer has the above structure, non-conductive particles can be highly dispersed in the solvent in the slurry for a porous film described later. In addition, when a porous membrane comprising the block polymer having the above structure is used inside the battery, the porous membrane has a high electrolyte retention property for a long period of time, and further elution of metal ions and oligomer components from the porous membrane. The secondary battery having the porous film exhibits high long-term cycle characteristics. Furthermore, the sea-island structure is formed by the segment A and the segment B, and the porous film shows high lithium conductivity because it has an appropriate swelling property to the electrolyte, and the secondary battery having the porous film has high output characteristics. Show.
The block polymer used in the present invention may be an AB block structure (AB type, ABA type, BAB type) composed only of the segment A and the segment B, or a structure containing other optional components. When other optional components are contained, these optional components may be coordinated at the end of the AB block structure or may be coordinated in the AB block structure.
Among them, in particular, when the terminal structure is a component that is compatible with the electrolyte, the porous membrane has high electrolyte impregnation and electrolyte retention, and the secondary battery having the porous membrane has a high long-term cycle. It is preferable because it shows characteristics.

(Segment A)
The segment A preferably includes a monomer component having a solubility parameter of 8.0 or more and less than 11 (cal / cm ³ ) ^1/2 and / or a monomer component having a hydrophilic group. By including such a monomer component, the degree of swelling of the segment A with respect to the electrolytic solution can be controlled by the composition to provide a segment exhibiting compatibility with the electrolytic solution.
In the present application, the term “monomer” or “monomer component” is understood to be a monomer constituting the monomer composition or constitutes a polymer depending on the context. It is understood that it is a polymerized unit based on a monomer.

  Monomers having a solubility parameter of 8.0 or more and less than 11 include alkenes such as ethylene and propylene; carbon number of alkyl groups in esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and pentyl methacrylate. 1 to 5 methacrylic acid alkyl esters; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, etc. esters such as alkyl acrylates having 1 to 5 carbon atoms; butadiene, isoprene, and other dienes Monomers; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate and the like. Among these, since it is highly compatible with the electrolyte solution and hardly causes bridging aggregation due to the polymer in a small particle size dispersion, the alkyl group in the ester has an alkyl group with 1 to 5 carbonic acid alkyl ester or ester. More preferred are alkyl methacrylates having 1 to 5 carbon atoms in the alkyl group.

  Examples of alkyl acrylates or alkyl methacrylates include esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and pentyl acrylate. Alkyl ester having 1 to 5 carbon atoms of alkyl group; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and pentyl methacrylate And methacrylic acid alkyl ester having 1 to 5 carbon atoms of the alkyl group in the ester.

  When the segment A showing compatibility with the electrolytic solution has a monomer component having a solubility parameter (SP) of 8.0 or more and less than 11, the solubility parameter (SP) in the segment A is 8.0. The content of the monomer component which is less than 11 is preferably 30% by weight or more, more preferably 50 to 90% by weight, based on 100% by weight of the total amount of monomers used. The content of the monomer component having a solubility parameter (SP) in segment A of 8.0 or more and less than 11 can be controlled by the monomer charge ratio at the time of producing the block polymer. The solubility parameter (SP) is 8.0 or more and less than 11 and the content of the monomer component is within an appropriate range, so that it is compatible with the electrolyte solution but does not dissolve and elution inside the battery. Does not occur and exhibits high long-term cycle 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. According to this method, the SP value (δ) (cal / cm ³ ) ^{1 /} 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 according to the following formula. ^This is a method for obtaining ² .
δ = ΣG / V = dΣG / M
ΣG: Sum of molecular attraction constant G V: Specific volume M: Molecular weight d: Specific gravity

The monomer component having a hydrophilic group has a monomer having a —COOH group (carboxylic acid group), a monomer having a —OH group (hydroxyl group), and a —SO ₃ H group (sulfonic acid group). Monomer, monomer having —PO ₃ H ₂ group, monomer having —PO (OH) (OR) group (R represents a hydrocarbon group), and monomer having a lower polyoxyalkylene group The body is mentioned.

  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, ^{R 1} is hydrogen or An ester of a polyalkylene glycol represented by a methyl group) and (meth) acrylic acid; 2-hydroxy Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as cyethyl-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) allyl ethers of alkylene glycols 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 Oethers; 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 segment A showing compatibility with the electrolytic solution is composed of those having the monomer component having the hydrophilic group, among these monomers having the hydrophilic group, dispersion of non-conductive particles From the viewpoint of further improving the properties, a monomer having a carboxylic acid group is preferred.

  The content of the monomer having a hydrophilic group in the segment A in the case where the segment A exhibiting compatibility with the electrolytic solution is composed of those having the monomer component having the hydrophilic group is determined as follows. It is preferably in the range of 0.5 to 40% by weight, more preferably 3 to 20% by weight with respect to 100% by weight of the total mass. The content of the monomer having a hydrophilic group in the segment A can be controlled by the monomer charging ratio at the time of producing the block polymer. When the content of the monomer having a hydrophilic group in segment A is within a predetermined range, swelling to an appropriate electrolytic solution is exhibited, and elution inside the battery does not occur.

  The segment A may have one of these monomer components alone, or may have two or more in combination.

(Segment B)
The segment B preferably includes a monomer component having a solubility parameter of less than 8.0 or 11 or more and / or a monomer component unit having a hydrophilic group. By including such a monomer component, the degree of swelling of the segment B with respect to the electrolytic solution can be controlled by the composition, so that the segment does not exhibit compatibility with the electrolytic solution. In order to control the degree of swelling by cross-linking so as not to exhibit compatibility with the electrolytic solution, the segment B preferably includes a monomer component unit having a cross-linkable group described later.

  Examples of monomer components having a solubility parameter of less than 8.0 or 11 or more include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; fluoroalkyl acrylate, 2- (fluoroalkyl) methyl acrylate, Fluorine-containing acrylic acid ester such as 2- (fluoroalkyl) ethyl acrylate; Fluorine-containing fluorine alkyl such as fluoroalkyl methacrylate, 2- (fluoroalkyl) methyl methacrylate, and 2- (fluoroalkyl) ethyl methacrylate Examples include acrylic acid esters.

  When the segment B includes a monomer component having a solubility parameter (SP) of less than 8.0 or 11 or more, the monomer component having a solubility parameter in the segment B of less than 8.0 or 11 or more The content 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 used. The content of the monomer component having a solubility parameter (SP) in segment B of less than 8.0 or 11 or more can be controlled by the monomer charge ratio at the time of producing the block polymer. When the content ratio of the monomer component having a solubility parameter (SP) of less than 8.0 and 11 or more in the segment B is in the above range, higher electrolytic solution resistance and long-term cycle characteristics are exhibited.

  Examples of the monomer component having a hydrophobic part include styrene, α-styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, α-methyl styrene, Styrene monomers such as divinylbenzene; acrylic acid-hexyl, acrylic acid-heptyl, acrylic acid-octyl, acrylic acid-2-ethylhexyl, acrylic acid-nonyl, acrylic acid-decyl, acrylic acid-lauryl, acrylic acid-n -Acrylic acid alkyl ester having 6 or more carbon atoms in the alkyl group in esters such as tetradecyl, acrylic acid-stearyl; methacrylic acid-hexyl, methacrylic acid-heptyl, methacrylic acid-octyl, methacrylic acid-2-ethylhexyl, methacrylic acid -Nonyl, methacrylate Methacrylic acid alkyl ester having 6 or more carbon atoms in the alkyl group in esters such as luric acid-decyl, methacrylic acid-lauryl, methacrylic acid-n-tetradecyl, and methacrylic acid-stearyl. Among them, an acrylic group having 9 or more carbon atoms in an alkyl group in esters such as -2-ethylhexyl acrylate, acrylate-nonyl, acrylate-decyl, acrylate-lauryl, acrylate-n-tetradecyl, and acrylate-stearyl. 9 or more carbon atoms of alkyl groups in esters such as acid alkyl esters, methacrylic acid-2-ethylhexyl, methacrylic acid-nonyl, methacrylic acid-decyl, methacrylic acid-lauryl, methacrylic acid-n-tetradecyl, methacrylic acid-stearyl The methacrylic acid alkyl ester is preferable because of its low compatibility with the electrolytic solution.

  In the present invention, as a monomer component constituting the segment B that does not exhibit compatibility with the electrolytic solution, since the compatibility with the electrolytic solution is low, the alkyl alkyl acrylate ester having 9 or more carbon atoms in the alkyl group, Preferred are methacrylic acid alkyl ester α, β-unsaturated nitrile compounds and styrene monomers having an alkyl group with 9 or more carbon atoms, and since they do not show any swelling property to the electrolyte, α, β-unsaturated nitrile compounds and Styrene monomers are more preferred, and styrene monomers are most preferred.

  When segment B is composed of a monomer component having a hydrophobic part, the content of the monomer component having a hydrophobic part in segment B is preferably based on 100% by weight of the total amount of monomers used. Is 10% by weight or more and 100% by weight or less, more preferably 20% by weight or more and 100% by weight or less. The content of the monomer component having a hydrophobic portion in the segment B can be controlled by the monomer charging ratio at the time of producing the block polymer. When the content of the monomer component having a hydrophobic portion in the segment B is in the above range, higher electrolyte solution resistance and long-term cycle characteristics are exhibited.

  The segment B may have one of these monomer components alone, or may have two or more in combination.

  The content ratio of the crosslinkable group in the case where the segment B includes a monomer component unit having a crosslinkable group, which will be described later, in the segment contains the thermally crosslinkable crosslinkable group in the segment B during polymerization. The monomer amount is preferably in the range of 0.1 to 10% by weight, more preferably 0.1 to 5% by weight with respect to 100% by weight of the total amount of monomers in the segment B. The content ratio of the heat-crosslinkable crosslinkable group in the segment B can be controlled by the monomer charge ratio when the segment B in the block polymer is produced. Since the content ratio of the crosslinking group in the block polymer is within the above range, in the slurry for a porous film described later, the non-conductive particles can be highly dispersed in the solvent, and the secondary film having the porous film is further provided. In the battery, elution into the electrolyte can be suppressed, and excellent porous film strength and long-term cycle characteristics can be exhibited.

In the present invention, the block polymer preferably contains a segment of a soft polymer having a glass transition temperature of 15 ° C. or lower. “The block polymer contains a segment of a soft polymer having a glass transition temperature of 15 ° C. or lower” means that the block polymer of the present invention contains a segment constituting a soft polymer having a glass transition temperature of 15 ° C. or lower. Means that. Specifically, since at least one of segment A and segment B is the same segment as the segment constituting the soft polymer having a glass transition temperature of 15 ° C. or lower, an electrode having high flexibility can be obtained. Is preferred.
In particular, when segment A shows compatibility with the electrolytic solution and segment B does not show compatibility with the electrolytic solution, segment A is the same segment as that constituting the soft polymer having a glass transition temperature of 15 ° C. or lower. Preferably, it is the same segment as the segment constituting the soft polymer having a glass transition temperature of −5 ° C. or lower, more preferably the segment constituting the soft polymer having a glass transition temperature of −40 ° C. or lower. Is the same segment. Since segment A is the same segment as that constituting the soft polymer having a glass transition temperature within the above range, the mobility of segment A can be achieved while segment B in the block polymer is adsorbed on the active material surface. Therefore, the lithium acceptability at low temperature is improved.
In addition, the glass transition temperature of a segment can be adjusted by further combining the combination of the monomer illustrated above and the copolymerizable monomer mentioned later.

  The ratio of segment A to segment B in the block polymer is such that the composition has a high output characteristic while having a long cycle characteristic while controlling the degree of swelling of the block polymer into the electrolyte within a predetermined range, Depending on the degree of crosslinking, etc., in the case of having no copolymerization component other than segment A and segment B, the ratio of segment A to segment B is 10:90 to 90:10 (weight ratio), more preferably 30 : 70 to 70:30 (weight ratio).

  As a combination of the segment A and the segment B in the block polymer, it is preferable to combine the preferable segment A and the preferable segment B described above. Among these, the segment A is a (meth) acrylic acid alkyl ester having 1 to 5 carbon atoms of the alkyl group in the ester, and the segment B is a combination of an α, β-unsaturated nitrile compound or a styrene monomer. Preferably, the segment A is a (meth) acrylic acid alkyl ester having 1 to 5 carbon atoms of the alkyl group in the ester, and the segment B is most preferable because the combination of styrene monomers is excellent in dispersibility, load characteristics, and cycle characteristics. preferable.

  The degree of swelling of the block polymer with respect to the electrolytic solution tends to decrease as the molecular weight increases and increase as the molecular weight decreases. If the molecular weight is too small, dissolution in the electrolyte solution tends to occur. Accordingly, the range of the weight average molecular weight of the block polymer for achieving a suitable degree of swelling varies depending on the structure, the degree of crosslinking, and the like. For example, when there is no copolymer component other than segment A and segment B, tetrahydrofuran ( The standard polystyrene conversion value measured by gel permeation chromatography using THF as a developing solvent is 1,000 to 500,000, more preferably 5,000 to 100,000. When the weight average molecular weight of the block polymer is within the above range, the adsorption stability of the polymer to the non-conductive particles is high, and no bridging aggregation due to the polymer occurs, and excellent dispersibility is exhibited.

When the degree of swelling of the block polymer in the electrolytic solution is controlled by the degree of crosslinking of the block polymer, the preferred range of degree of crosslinking is, for example, dissolved when immersed in a polar solvent such as tetrahydrofuran for 24 hours or 400% or more A degree of cross-linking that swells is preferred.
Examples of the crosslinking method of the block polymer include a method of crosslinking by heating or energy ray irradiation. By using a block polymer that can be cross-linked by heating or energy ray irradiation, the degree of cross-linking can be adjusted by heating conditions or irradiation conditions (intensity, etc.) of energy ray irradiation. 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 preparing a block polymer that can be crosslinked by heating or irradiation with energy rays include a method of introducing a crosslinkable group into the block polymer and a method of using a crosslinking agent in combination.

  Examples of the method of introducing a crosslinkable group into the block polymer include a method of introducing a photocrosslinkable crosslinkable group into the block polymer and a method of introducing a heat crosslinkable crosslinkable group. Among these, the method of introducing a heat-crosslinkable crosslinkable group into the block polymer can crosslink the porous film by heat-treating the porous film after forming the porous film, and further dissolve in the electrolytic solution. It can be suppressed, and a tough and flexible porous membrane is obtained, which is preferable. When a heat-crosslinkable crosslinkable group is introduced into the block polymer, the heat-crosslinkable crosslinkable group is at least one selected from the group consisting of an epoxy group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. Species are preferred, and an epoxy group is more preferred 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 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 ratio of the heat-crosslinkable crosslinkable group in the block polymer is preferably 0.00 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 block polymer can be controlled by the monomer charge ratio when producing the block polymer. When the content of the thermally crosslinkable crosslinking group in the block 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 block 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 into a block polymer by copolymerizing with a monomer.

  The block polymer used in the present invention may contain a monomer copolymerizable with these in addition to the above-described monomer component as a component other than the segment A and the segment B. Monomers copolymerizable with these include carboxylic acid esters having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; vinyl chloride, vinylidene chloride Halogen atom-containing monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, and other vinyl ethers; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone, and other vinyl ketones; And heterocyclic ring-containing vinyl compounds such as vinylpyrrolidone, vinylpyridine and vinylimidazole; amide monomers such as acrylamide and N-methylolacrylamide; By copolymerizing these monomers by an appropriate technique, the block polymer having the above-described structure can be obtained.

  The block polymer used in the present invention is not particularly limited with respect to the polymerization method as long as a block polymer having segment A and segment B is obtained. 1) Monomer A for constituting segment A by chain polymerization; Method of sequential growth of monomer B to constitute segment B, 2) Coupling method of polymer A corresponding to segment A and polymer B corresponding to segment B, each of which is regulated in distribution, and terminal functional groups It is synthesized by a polyaddition method, a polycondensation method used, 3) a chain polymerization method using polymer A corresponding to segment A having a terminal functional group as a macroinitiator, or the like.

  In the above method 1), the monomer A is polymerized by the living polymerization method, and then the monomer B is added and polymerized without stopping the growth terminal of the obtained polymer to obtain a block polymer. Can do.

  In the above method 2), monomer A and monomer B are separately synthesized by a living polymerization method, and polymer A and polymer B are preferably functional groups at their ends so that they can react and bond at the ends. Is introduced. Thereafter, A and B are mixed to obtain a block polymer by coupling reaction, polyaddition and polycondensation. For example, a method of interfacial polycondensation or solution polycondensation of acid chloride and amine, a method of polycondensation of amine-terminated polyamide and carboxylic acid-terminated polyamide in a molten state, and the like can be mentioned.

  In the above method 3), the monomer A is polymerized by a living polymerization method, and then a functional group is introduced into the living terminal to obtain a polymer A having a terminal functional group. A block polymer can be obtained by introducing a radical initiator into the obtained polymer A by a terminal group reaction and chain-polymerizing with the monomer B as a macroinitiator. For example, when the polymer has an OH group at the terminal, a method of NCO conversion with an excess diisocyanate, t-butyl hydroperoxide bonded to the terminal, and then radical polymerization can be mentioned.

  The living polymerization method includes various polymerization methods such as living anion polymerization, living cation polymerization, living coordination polymerization, and living radical polymerization. By using such a polymerization method, various vinyl monomers can be polymerized. Among them, living radical polymerization is preferable from the viewpoint of controlling the molecular weight and structure of the block copolymer and copolymerizing a monomer having a crosslinkable functional group.

  Living polymerisation, in the narrow sense, indicates that the terminal always has activity, but generally also includes pseudo-living polymerization where the terminal is inactive and the terminal is in equilibrium. It is. The living radical polymerization in the present invention is a radical polymerization in which the polymerization end is activated and the inactivation is maintained in an equilibrium state, and has been actively studied in various groups in recent years.

  Examples thereof include those using a chain transfer agent such as polysulfide, those using a radical scavenger such as a cobalt porphyrin complex (Journal of American Chemical Society, 1994, 116, 7943) and a nitroxide compound (Macromolecules, 1994). 27, 7228), Inferter polymerization (Macromol. Chem. Rapid Commun., 3, 133 (1982)), which irradiates light on dithiocarbamate by Otsu et al. And atom transfer radical polymerization (ATRP) using thiocarbonylthio (thioester) And reversible addition-fragmentation chain transfer (RAFT) polymerization using a compound having a structure as a chain transfer agent. In the present invention, there is no particular restriction as to which of these methods is used, but those using a radical scavenger and reversible addition / elimination chain transfer polymerization are preferred for ease of control.

  When a radical scavenger is used for living polymerization, a stable nitroxy radical compound is used as the radical scavenger. The stable nitroxyl radical compound is not particularly limited, and examples thereof include known stable free radical agents, such as 2,2,5,5-substituted-1-pyrrolidinyloxy radicals, and nitroxy from cyclic hydroxyamines. Free radicals are preferred. As the substituent, an alkyl group having 4 or less carbon atoms such as a methyl group or an ethyl group is suitable. Specific nitroxy free radical compounds include, but are not limited to, 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO), 2,2,6,6-tetraethyl-1- Piperidinyloxy radical, 2,2,6,6-tetramethyl-4-oxo-1-piperidinyloxy radical, 2,2,5,5-tetramethyl-1-pyrrolidinyloxy radical, 1, Examples include 1,3,3-tetramethyl-2-isoindolinyloxy radical, N, N-di-t-butylamineoxy radical, and the like. Of these, 2,2,6,6, -tetramethyl-1-piperidinyloxy and 4-oxo-2,2,6,6, -tetramethyl-1-piperidinyloxy are preferable. These may be used alone or in combination of two or more.

  When the above stable nitroxy radical compound is used, a radical generator is usually used. The radical generator is not particularly limited as long as it generates radicals at the polymerization temperature, and a general thermal decomposition polymerization initiator can be used. For example, azobisisobutyronitrile ( AIBN), azo compounds such as azobisisobutyric acid ester and hyponitrite; benzoyl peroxide (BPO), lauroyl peroxide, dicumyl peroxide, dibenzoyl peroxide and the like. These may be used alone or in combination of two or more.

  Instead of using a stable nitroxy radical compound and a radical generator in combination, an alkoxyamine compound may be used as an initiator. When using an alkoxyamine compound as an initiator, a terminal functional group can be introduced by using an alkoxyamine having a functional group in the alkoxy group.

  When the above stable nitroxy radical compound or alkoxyamine compound is used, the polymerization is generally performed at a polymerization temperature of about 50 to 170 ° C. A preferable temperature range is 70 to 160 ° C. The reaction pressure is usually carried out at normal pressure, but it can also be carried out under pressure.

  In the case of the method using the above stable nitroxy radical compound, as a method for introducing a functional group into the terminal of the polymerized vinyl copolymer, for example, a chain transfer agent or terminator having a target functional group in the molecule is used. The method to use etc. are mentioned. The chain transfer agent or terminator having the above functional group in the molecule is not particularly limited. For example, a hydroxyl group is introduced by mercaptoethanol, mercaptopropanol, mercaptobutanol, 2,2′-dithioethanol, etc., and 2-mercaptoacetic acid. A carboxyl group is introduced by 2-mercaptopropionic acid, dithioglycolic acid, 3,3′-dithiopropionic acid, 2,2′-dithiobenzoic acid, and a silyl group is introduced by 3-mercaptopropylmethyldimethoxysilane, etc. The

  When reversible addition / elimination chain transfer polymerization (RAFT polymerization) is used as the living polymerization, a sulfur compound such as dithioester, trithiocarbamate, xanthate or dithiocarbamate is started as a chain transfer agent (and also serves as an initiator). Polymerization is performed as an agent. (For example, WO98 / 01478 A1 and WO99 / 31144 A1 etc.) These may be used independently and may be used together 2 or more types.

  When RAFT polymerization is used as the living polymerization, it is preferable to use an additional radical initiator for polymerization, particularly an initiator further comprising an azo or peroxo initiator that decomposes by heat to generate radicals. Examples thereof include azo compounds such as azobisisobutyronitrile (AIBN), azobisisobutyric acid ester, and hyponitrous acid ester; benzoyl peroxide (BPO), lauroyl peroxide, dicumyl peroxide, dibenzoyl peroxide, and the like. These may be used alone or in combination of two or more.

  The living polymerization in the present invention can be carried out by solvent polymerization (bulk polymerization), solution polymerization in an organic solvent (for example, toluene), emulsion polymerization or suspension polymerization. Each stage of the polymerization process can be performed in a “batch” process (ie, a discontinuous process) in the same reactor, or in a semi-continuous or continuous process in separate reactors.

  In the case of solution polymerization, examples of the solvent to be used include, but are not limited to, the following solvents. For example, hydrocarbon solvents such as hexane and octane; ester solvents such as ethyl acetate and n-butyl acetate; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohol solvents such as methanol, ethanol and isopropanol; tetrahydrofuran, diethyl ether, Examples include ether solvents such as dioxane and ethylene glycol dimethyl ether; amide solvents such as dimethylformamide and dimethylacetamide; aromatic petroleum solvents such as toluene, xylene and benzene. These may be used alone or in combination. The type and amount of the solvent used are the solubility of the monomer used, the solubility of the resulting polymer, the polymerization initiator concentration and monomer concentration appropriate for achieving a sufficient reaction rate, the solubility of the sulfur compound, It may be determined in consideration of the influence on human body and environment, availability, price, etc., and is not particularly limited. Among them, in terms of solubility, availability, and price, industrially, toluene, dimethylformamide, tetrahydrofuran, and acetone are preferable, and toluene and dimethylformamide are more preferable.

  In the case of emulsion polymerization, examples of the emulsifier used include, but are not limited to, the following emulsifiers. For example, fatty acid soap, rosin acid soap, sodium naphthalene sulfonate formalin condensate, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, sodium alkyl sulfate, ammonium alkyl sulfate, triethanolamine alkyl sulfate, sodium dialkyl sulfosuccinate, alkyl diphenyl ether disulfonate Anionic surfactants such as sodium, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate; polyoxyethylene alkyl ether, polyoxyethylene higher alcohol ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, poly Oxyethylene sorbitol fatty acid ester, glycerin fat Esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamine, nonionic surfactants such as alkyl alkanolamides; such as an alkyl trimethylammonium chloride cationic surfactants such as ride the like. These emulsifiers may be used alone or in combination. If necessary, a dispersant for suspension polymerization described later may be added. Although the usage-amount of an emulsifier is not specifically limited, 0.1-20 weight part is preferable with respect to 100 weight part of monomers at the point which an emulsion state is favorable and superposition | polymerization advances smoothly. Of these emulsifiers, anionic surfactants and nonionic surfactants are preferred from the viewpoint of stability in the emulsified state.

  In the case of suspension polymerization, any of the commonly used dispersants can be used as the dispersant used. For example, the following dispersants can be mentioned, but are not limited thereto. Examples thereof include partially saponified polyvinyl acetate, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, gelatin, and polyalkylene oxide. These may be used alone or in combination. If necessary, an emulsifier used in the emulsion polymerization may be used in combination. Although the usage-amount of a dispersing agent is not specifically limited, 0.1-20 weight part is preferable with respect to 100 weight part of monomers used by the point which superposition | polymerization advances smoothly.

The block 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 production step of the block polymer. By preventing the metal ion cross-linking between polymers in the porous membrane slurry described later and preventing the increase in viscosity when the content of the particulate metal component contained in the polymer solution or polymer dispersion is 10 ppm or less. Can do. 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. However, in consideration of productivity and removal efficiency, it is preferably performed by placing a magnetic filter in the block polymer production line. .

  The content ratio of the block polymer in the porous film is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, and most 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. Examples of such optional components include components such as a dispersant, a leveling agent, an antioxidant, a binder other than the block polymer, a thickener, and an electrolytic solution additive having a function of inhibiting electrolytic decomposition. . 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.

  Examples of binders other than block polymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylic acid derivatives, polyacrylonitrile derivatives, and soft polymers used in electrode binders described later. Can be used.

  Examples of thickeners include cellulose 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, acrylic acid or copolymers of acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified poly Examples include acrylic 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”.

  As the electrolytic solution additive, vinylene carbonate used in the electrode mixture layer slurry described later and in the electrolytic solution can be used. Other examples include nanoparticles 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 preferred content ratio of the optional components in the porous film is preferably within a range that does not affect the battery characteristics. Specifically, each optional component is 10% by weight or less, and the total content of optional components is 20% by weight or less. It is.

(Method for producing porous membrane)
As a method for producing a porous membrane for a secondary battery of the present invention, 1) a method for applying a slurry for porous membrane containing non-conductive particles, a block polymer and a solvent on a predetermined substrate, followed by drying; 2) A method in which a substrate is dipped in a slurry for a porous film containing non-conductive particles, a block polymer and a solvent, and then dried; 3) A slurry for a porous film containing non-conductive particles, a block polymer and a solvent is removed from the release film. And a method of transferring the resulting porous film onto a predetermined substrate. Among these, 1) A method of applying a slurry for a porous film containing non-conductive particles, a block polymer and a solvent to a substrate and then drying is most preferable because the film thickness of the porous film can be easily controlled.

  The method for producing a porous membrane for a secondary battery 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 secondary battery porous membrane of the present invention contains non-conductive particles, a block polymer, and a solvent. Examples of the non-conductive particles and the block polymer are the same as those described for the porous membrane for a secondary battery.

The solvent is not particularly limited as long as it can uniformly disperse the solid content (nonconductive particles and block polymer).
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 and ethylene Ethers such as glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; N-methyl Amides such as pyrrolidone 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 it can be applied and immersed and has a fluid viscosity, but is generally about 10 to 50% by weight.

  Further, the slurry for the porous film may contain optional components 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 block 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 block 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 for a secondary battery of the present invention, the substrate is not particularly limited, but the porous membrane for a secondary battery of the present invention is formed on an electrode for a secondary battery or an organic separator. It is preferable. Among these, it is more preferable to form on the electrode surface for secondary batteries. By forming the porous membrane for a secondary battery 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 membrane for a secondary battery of the present invention on the electrode surface, the porous membrane can function as a separator even without an organic separator, and a battery can be produced at low cost. become. Moreover, even when an organic separator is used, higher output characteristics can be expressed without filling holes formed on the surface of the organic separator.
In the manufacturing method of the porous film for secondary batteries of this invention, you may form on base materials other than an electrode and an organic separator. When the porous membrane for a secondary battery of the present invention is formed on a substrate other than an electrode or an organic separator, the porous membrane is peeled off from the substrate and directly laminated on the electrode or the organic separator when assembling the battery. Can be used.

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 for a secondary battery 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 for a secondary battery 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 is provided on a current collector, an electrode mixture layer including a binder and an electrode active material provided on the current collector, and the electrode mixture layer. In addition, the layer of the porous membrane for a secondary battery of the present invention is 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. Iron 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 other constituent elements of the battery. From the viewpoint of improving battery characteristics such as output 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 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 the other structural requirements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, output 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, LaNi ₅ , MmNi ₅ (Mm is a misch metal), LmNi ₅ (Lm is at least one selected from rare earth elements including La), and a part of Ni of these alloys is Al, Mn, Co. , Ti, Cu, Zn, Zr, Cr, B, etc., can be used multi-element hydrogen storage alloy particles substituted with one or more elements selected from such elements. 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 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 soft polymers such as styrene block copolymers, isoprene styrene block copolymers, styrene isoprene styrene block copolymers;
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. Olefin soft polymer of
Vinyl soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
Epoxy soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer and the like can be mentioned. 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 output 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 a thickener, the thickener illustrated with the porous film for secondary batteries of this 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, the concentration of solids in the electrode mixture layer forming slurry, combined with other additives such as an electrode active material, a binder, and a conductivity-imparting material, 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, other additives such as a conductivity imparting agent 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 membrane for a secondary battery on an organic separator layer. That is, the separator for a secondary battery of the present invention includes an organic separator layer and the porous film for a secondary battery of the present invention provided on the organic separator layer.

As the organic separator layer, known ones such as a separator containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin are used.
As the organic separator layer used in the present invention, a porous film having a fine pore size and having no electron conductivity and ionic conductivity and high resistance to organic solvents is used. For example, polyolefin (polyethylene, polypropylene, polybutene, polychlorinated). Vinyl), and a microporous film made of a resin such as a mixture or a copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene Examples thereof include a microporous membrane made of a resin such as those woven with polyolefin fibers, a nonwoven fabric thereof, and an aggregate of insulating substance particles. Among these, the coating property of the above-mentioned slurry for porous membranes is excellent, and since the thickness of the entire separator can be reduced and the active material ratio in the battery can be increased to increase the capacity per volume, it is made of polyolefin resin. 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 a Ziegler-Natta catalyst, a Phillips catalyst, and a metallocene catalyst. 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 a Ziegler-Natta catalyst and a metallocene catalyst. 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 an organic separator layer of polyolefin, a publicly known one is used.For example, after forming a film of polypropylene and polyethylene by extrusion, a crystal domain is grown at a low temperature and stretched in this state. A dry method of forming a microporous film by extending the amorphous region; mixing a hydrocarbon solvent and other low molecular weight materials with polypropylene and polyethylene, forming a film, and then the solvent and low molecular weight in the amorphous phase A wet method in which a microporous film is formed by removing a film that has started to form a gathered island phase by using this solvent or other 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 other fillers and fiber compounds for the purpose of controlling strength, hardness, and heat shrinkage rate. 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 electrolyte solution, and at least one of the positive electrode, the negative electrode, and the separator includes the porous film for a secondary battery of the present invention. Including.

  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 in addition, improvement of output characteristics is 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) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane and 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.
Moreover, it is also possible to use the electrolyte solution by containing an additive. Examples of the additive include carbonate compounds such as vinylene carbonate (VC) used in the electrode mixture layer slurry.

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.
Examples of the electrolytic solution other than the above include polymer electrolytes such as polyethylene oxide and polyacrylonitrile, gelled polymer electrolytes in which the polymer electrolyte is impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li ₃ N.

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 membrane for a secondary battery of the present invention is formed on any one of a positive electrode, a negative electrode, and a 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.

<Slurry characteristics: Dispersibility>
A slurry for porous membrane is put in a test tube having a diameter of 1 cm to a depth of 5 cm to obtain a test sample. Five test samples are prepared per measurement of one sample. 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. The time and number of days (referred to as average time required for sedimentation (days)) required for sedimentation in five samples are respectively determined, and the average time required for sedimentation (days) is defined as the day when sedimentation was observed. It shows that the dispersibility is so excellent that two-phase separation is not observed.
A: No settling is observed even after 10 days.
B: Settling is observed after 6 to 10 days.
C: Sedimentation is observed within 24 hours to 5 days.
D: Sedimentation is observed for 10 hours or more and less than 24 hours.
E: Sedimentation is observed for 3 hours or more and less than 10 hours.
F: Settling is observed in less than 3 hours.

<Battery characteristics: Output characteristics>
The obtained full-cell coin type battery is charged to 4.3 V by a constant current method of 0.1 C at 25 ° C., and then discharged to 3.0 V at 0.1 C to obtain a 0.1 C discharge capacity. Thereafter, the battery is charged to 4.3 V at 0.1 C, and then discharged to 3.0 V at 20 C, and the 20 C discharge capacity is obtained. These measurements are performed on 10 cells of a full cell coin type battery. The average value of the 0.1 C discharge capacity of 10 cells and the average value of the 20 C discharge capacity of 10 cells are obtained and are defined as a and b, respectively. The capacity retention represented by the ratio of the electric capacity of 20C discharge capacity b and 0.1C discharge capacity a ((b / a) × 100 (unit:%)) is obtained, and this is used as an evaluation standard for output characteristics. Judgment based on the criteria of. The higher this value, the better the output characteristics.
A: 50% or more B: 40% or more and less than 50% C: 20% or more and less than 40% D: 1% or more and less than 20% E: Less than 1%

<Battery characteristics: cycle characteristics>
The obtained full-cell coin type battery is charged from 3 V to 4.3 V at 0.1 C at 25 ° C., and then charged and discharged to discharge from 4.3 V to 3 V at 0.1 C for 100 cycles. A value obtained by calculating the percentage of the 0.1C discharge capacity at the 100th cycle with respect to the 0.1C discharge capacity as a percentage was determined as the capacity retention rate, and the following criteria were used. The larger the value, the less the discharge capacity is reduced, and the cycle characteristics are excellent.
A: 70% or more B: 60% or more and less than 70% C: 50% or more and less than 60% D: 40% or more and less than 50% E: 30% or more and less than 40% F: Less than 30%

<Battery characteristics: low temperature characteristics>
The obtained laminated cell type batteries were charged at a constant current until the voltage became 4.2 V by a constant current constant voltage charging method at a charge / discharge rate of 0.1 C at 25 ° C., respectively, and charged at a constant voltage. Thereafter, the battery is discharged to 0.1 V at 0.1 C, and the discharge capacity at 25 ° C. is obtained. Then, constant current constant voltage charge was performed at 0.1 C in a thermostat set to −20 ° C. The battery capacity at 25 ° C. is a, and the battery capacity at −20 ° C. is b. A low-temperature capacity retention represented by a ratio (b / a (%)) of the battery capacity b at −20 ° C. and the battery capacity a at 25 ° C. was obtained and used as an index of low-temperature characteristics. It shows that it is a battery with a favorable lithium acceptability in low temperature, so that this value is large.

Example 1
<Synthesis of block polymer>
After adding 40 parts of styrene to a four-necked flask equipped with a mechanical stirrer, a nitrogen inlet, a condenser, and a rubber septum, 1.3 parts of 2,2′-bipyridine was added thereto, Was replaced with nitrogen. After adding 0.41 part of copper bromide to this under nitrogen stream, the reaction system was heated to 90 ° C. and 0.6 part of 2-hydroxyethyl 2-bromo-2-methylpropionate was added as an initiator. Then, polymerization was started, and polymerization was performed at 90 ° C. for 9 hours under a nitrogen stream without adding a solvent. After confirming that the polymerization rate (a ratio defined by dividing the weight of the polymer after heating and removing the volatile component by the weight of the polymer as it was before removing the volatile component) is 80% or more, 60 parts of n-butyl acrylate was added from a rubber septum and heated at 110 ° C. for 12 hours. In this way, a mixture containing a block polymer of styrene-butyl acrylate was obtained. The resulting mixture containing the block polymer was heated to 120 ° C. and centrifuged at 20000 G for 1 hour to obtain a crude purified block polymer (green) as a supernatant. After adding 10 parts of a sulfonic acid type cation exchange resin to 100 parts of this block polymer crude product and stirring at 120 ° C. for 2 hours, the ion exchange resin is removed, and the polymerization catalyst and the like are further removed. Polymer-1 having a polymer unit content of about 40% based on styrene was obtained. Table 1 shows the composition, ratio, weight average molecular weight, and glass transition temperature of the polymer-1. The glass transition temperature was measured by a differential scanning calorimetry (manufactured by Seiko Instruments Inc., product name “EXSTAR6000”) by a differential scanning calorimetry (DSC method) from −120 ° C. to 120 ° C. at a heating rate of 20 ° C./min. . The weight average molecular weight was determined by dissolving polymer-1 in tetrahydrofuran to give a 0.2 wt% solution, followed by filtration with a 0.45 μm membrane filter, and using gel permeation chromatography (GPC) as a measurement sample. The measurement was performed under conditions, and the weight average molecular weight in terms of standard polystyrene was determined.
(Measurement condition)
Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)
Column: TSKgel Multipore HXL-M (manufactured by Tosoh Corporation)
Eluent: Tetrahydrofuran (THF)
Elution rate: 0.3 ml / min Detector: RI (polarity (+))
Column temperature: 40 ° C

<Preparation of block polymer solution>
The obtained polymer-1 was dissolved in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to obtain an NMP solution of polymer-1 having a solid content concentration of 20%.

<Creation of slurry for porous membrane>
Non-conductive particles (aluminum oxide, average particle size 0.3 μm, iron content <20 ppm) and polymer-1 solution so as to have a content ratio of 100: 2.5 (solid content equivalent ratio). Further, NMP was mixed so that the solid content concentration was 30% and dispersed using a bead mill to prepare a slurry 1 for porous membrane. The dispersibility 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>
92 parts of lithium manganate having a spinel structure as a positive electrode active material, 5 parts of acetylene black, and 3 parts of PVDF (polyvinylidene fluoride) as a binder are added to a solid content, and the solid content concentration is increased to 87% with NMP. After adjustment, the mixture was mixed for 60 minutes with a planetary mixer. Further, the solid content concentration was adjusted to 84% with NMP, and then mixed for 10 minutes to prepare a slurry-like electrode composition for positive electrode (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 50 μm.

<Preparation of negative electrode with porous film>
On the surface of the obtained negative electrode on the negative electrode mixture layer side, the porous film slurry 1 was applied using a wire bar so that the thickness of the porous film layer after drying was 5 μm, and then 90 ° C. Was dried for 10 minutes to form a porous film, and a negative electrode 1 with a porous film having a layer structure of (copper foil) / (negative electrode mixture layer) / (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 obtained negative electrode 1 with a porous film was cut out into a circle having a diameter of 14 mm. A single-layer polypropylene separator (porosity 55%) manufactured by a dry method having a thickness of 25 μm was cut into a circle having a diameter of 18 mm. These were housed 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. The arrangement of these circular electrodes and separators was as follows. The circular positive electrode was disposed so that the aluminum foil was in contact with the bottom surface of the outer container. The circular separator was disposed so as to be interposed between the circular positive electrode and the circular negative electrode 1 with a porous film. The negative electrode 1 with a circular porous film was arranged so that the surface on the porous film side opposed to the surface on the mixture layer side of the circular positive electrode with a circular separator interposed therebetween. Further, an expanded metal is placed on the copper foil of the negative electrode, and an electrolytic solution (EC / DEC = 1/2, 1M LiPF ₆ ) is injected into the container so that no air remains, and the exterior is put through a polypropylene packing. A 0.2 mm thick stainless steel cap was placed on the container and fixed, and the battery can was sealed to produce a full cell coin cell having a diameter of 20 mm and a thickness of about 3.2 mm (coin cell CR2032). The obtained battery was measured for output characteristics and cycle characteristics. The results are shown in Table 2.

<Production of laminated cell battery>
A battery container was prepared using a laminate film made of an aluminum sheet and a resin made of polypropylene covering both surfaces thereof. Subsequently, the mixture layer and the porous film were removed from the end portions of the positive electrode and the negative electrode with the porous film obtained above to form a portion where the copper foil or the aluminum foil was exposed. A Ni tab was welded to the location where the aluminum foil of the positive electrode was exposed, and a Cu tab was welded to the location where the copper foil of the negative electrode was exposed. The obtained positive electrode with a tab and negative electrode with a porous film with a tab were stacked with a separator made of a polyethylene microporous film interposed therebetween. The surface of the electrode was disposed in a direction in which the surface on the mixture layer side of the positive electrode and the surface on the porous film side of the negative electrode with the porous film faced each other. The stacked electrodes and separator were wound and stored in the battery container. Subsequently, an electrolytic solution in which LiPF ₆ was dissolved to a concentration of 1 mol / liter was injected into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 2 at 25 ° C. Subsequently, the laminate film was sealed, and the laminate cell which is the lithium ion secondary battery of this invention was produced. The obtained battery was measured for low temperature characteristics. The evaluation results are shown in Table 3.

(Examples 2 to 4)
Polymers 2 to 4 having the compositions shown in Table 1 were used in place of polymer-1 as the binder constituting the porous membrane (that is, the monomer constituting segment A and the unit constituting segment B). <Synthesis of block polymer> in Example 1 except that instead of n-butyl acrylate and styrene, monomers of the type shown as structures “A” and “B” in Table 1 were used as the monomer, respectively. In the same manner as in Example 1, Polymers 2 to 4 were obtained, and the other materials were used to produce a slurry for a porous membrane, an electrode with a porous membrane, and a battery as in Example 1. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Example 5)
<Synthesis of block polymer>
The block polymer was the same as in Example 1 except that the polymerization time when styrene was added was changed from 9 hours to 36 hours, and the polymerization time when n-butyl acrylate was added was changed from 12 hours to 48 hours. Was synthesized to obtain a polymer-5. That is, the polymerization reaction time at 90 ° C. after adding styrene and other substances (initiator, etc.) to the flask was changed from 9 hours to 36 hours. The time for heating to 110 ° C. after adding 60 parts of n-butyl acrylate to the reaction mixture was changed from 12 hours to 48 hours. Table 1 shows the composition, ratio, weight average molecular weight, and glass transition temperature of the polymer-5 obtained.
In Example 1, the slurry for porous film, the electrode with porous film, and the battery were the same as in Example 1 except that Polymer-5 was used instead of Polymer-1 as the binder constituting the porous film. Produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Example 6)
<Synthesis of block polymer>
The block polymer was the same as in Example 1 except that the polymerization time when styrene was added was changed from 9 hours to 1 hour, and the polymerization time when n-butyl acrylate was added was changed from 12 hours to 2 hours. Was synthesized to obtain a polymer-6. That is, the polymerization reaction time at 90 ° C. after adding styrene and other substances (initiator, etc.) to the flask was changed from 9 hours to 1 hour. The time for heating to 110 ° C. after adding 60 parts of n-butyl acrylate to the reaction mixture was changed from 12 hours to 2 hours. Table 1 shows the composition, ratio, weight average molecular weight, and glass transition temperature of the polymer-6 obtained.
In Example 1, the slurry for porous film, the electrode with porous film, and the battery were the same as in Example 1 except that Polymer-6 was used instead of Polymer-1 as the binder constituting the porous film. Produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Example 7)
<Synthesis of block polymer>
The addition amount of styrene was changed from 40 parts to 20 parts, the addition amount of n-butyl acrylate was changed from 60 parts to 80 parts, and the polymerization time when styrene was added was changed from 9 hours to 6 hours ( That is, the polymerization reaction time at 90 ° C. after adding styrene and other substances (initiator etc.) to the flask was changed from 9 hours to 6 hours), and the polymerization time when adding n-butyl acrylate Same as Example 1 except that the time was changed from 12 hours to 20 hours (ie, the time for heating to 110 ° C. after adding 60 parts of n-butyl acrylate to the reaction mixture was changed from 12 hours to 20 hours). A block polymer was synthesized into a polymer-7. Table 1 shows the composition, ratio, weight average molecular weight, and glass transition temperature of the polymer-7 obtained.
In Example 1, the slurry for porous film, the electrode with porous film, and the battery were the same as in Example 1 except that Polymer-7 was used instead of Polymer-1 as the binder constituting the porous film. Produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Example 8)
<Synthesis of block polymer>
The addition amount of styrene was changed from 40 parts to 80 parts, the addition amount of n-butyl acrylate was changed from 20 parts to 80 parts, and the polymerization time when styrene was added was changed from 9 hours to 14 hours ( That is, the polymerization reaction time at 90 ° C. after adding styrene and other substances (initiator, etc.) to the flask was changed from 9 hours to 14 hours), and the polymerization time when n-butyl acrylate was added Same as Example 1 except that the time was changed from 12 hours to 8 hours (that is, the time for heating to 110 ° C. after adding 60 parts of n-butyl acrylate to the reaction mixture was changed from 12 hours to 8 hours). A block polymer was synthesized into a polymer-8. Table 1 shows the composition, ratio, weight average molecular weight, and glass transition temperature of the obtained polymer-8.
In Example 1, the slurry for porous film, the electrode with porous film, and the battery were the same as in Example 1 except that Polymer-8 was used instead of Polymer-1 as the binder constituting the porous film. Produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Examples 9 to 10)
As a binder constituting the porous film, polymers-9 to 10 having the composition shown in Table 1 were used instead of polymer-1 (that is, the monomer constituting segment A and the unit constituting segment B). <Synthesis of block polymer> in Example 1 except that instead of n-butyl acrylate and styrene, monomers of the type shown as structures “A” and “B” in Table 1 were used as the monomer, respectively. In the same manner as in Example 1, Polymers 9 to 10 were obtained, and this was used except that a porous membrane slurry, an electrode with a porous membrane, and a battery were produced in the same manner as in Example 1. And the dispersibility of the obtained slurry for porous films, the output characteristic of the obtained battery, cycle characteristics, and low temperature characteristics were evaluated. The results are shown in Tables 2 and 3.

(Example 11)
<Creation of slurry for porous membrane>
Non-conductive particles (aluminum oxide, average particle size 0.3 μm, iron content <20 ppm) and polymer-3 solution so as to have a content ratio of 100: 2.5 (solid content equivalent ratio). Further, NMP was mixed so that the solid content concentration was 30% and dispersed using a bead mill to prepare a porous membrane slurry 11. The dispersibility 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 11 having a negative electrode mixture layer having a thickness of 60 μm.

<Production of electrode composition for positive electrode and positive electrode>
92 parts of lithium manganate having a spinel structure as a positive electrode active material, 5 parts of acetylene black, and 3 parts of PVDF (polyvinylidene fluoride) as a binder are added to a solid content, and the solid content concentration is increased to 87% with NMP. After adjustment, the mixture was mixed for 60 minutes with a planetary mixer. Further, the solid content concentration was adjusted to 84% with NMP, and then mixed for 10 minutes to prepare a slurry-like electrode composition for positive electrode (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 11 having a positive electrode mixture layer having a thickness of 50 μm.

<Preparation of separator with porous membrane>
On one surface of a single-layer polypropylene separator (porosity 55%) produced by a dry method having a thickness of 25 μm, the porous membrane layer after drying the porous membrane slurry 11 has a thickness of 5 μm. The film was coated using a wire bar, and then dried at 90 ° C. for 10 minutes to form a porous film on one side. Furthermore, the other side of the separator was similarly coated using a wire bar so that the thickness of the porous membrane layer after drying was 5 μm, and then dried at 90 ° C. for 10 minutes, A porous film was formed on the substrate to obtain a separator with a porous film.

<Production of battery>
Next, the positive electrode 11 was cut into a circle having a diameter of 13 mm. The negative electrode 11 was cut into a circle having a diameter of 14 mm. The separator with a porous membrane was cut into a circle having a diameter of 18 mm. These were housed 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. The arrangement of these circular electrodes and separators was as follows. The circular positive electrode was disposed so that the aluminum foil was in contact with the bottom surface of the outer container. The circular separator was disposed so as to be interposed between the circular positive electrode and the circular negative electrode. The circular negative electrode was disposed such that the surface on the mixture layer side opposed to the surface on the mixture layer side of the circular positive electrode via a circular separator. Further, an expanded metal is placed on the copper foil of the negative electrode, and an electrolytic solution (EC / DEC = 1/2, 1M LiPF ₆ ) is injected into the container so that no air remains, and the exterior is put through a polypropylene packing. A 0.2 mm thick stainless steel cap was placed on the container and fixed, and the battery can was sealed to produce a full cell coin cell having a diameter of 20 mm and a thickness of about 3.2 mm (coin cell CR2032). The obtained battery was measured for output characteristics and cycle characteristics. The results are shown in Table 2.

(Example 12)
<Creation of slurry for porous membrane>
Polymer-3 was dissolved in acetone to obtain an acetone solution of polymer-3 having a solid concentration of 20%.
Non-conductive particles (cross-linked MMA (Sekisui Chemical Co., Ltd. SSX-101, average particle size: 1.0 μm)) and an acetone solution of polymer-3, 100: 2.5 content ratio (solid content equivalent ratio) Then, acetone was further mixed so that the solid concentration was 30%, and dispersed using a bead mill to prepare a porous membrane slurry 12. The dispersibility of the obtained slurry for porous membrane was measured. The results are shown in Table 2.
A slurry for a porous membrane, an electrode with a porous membrane, and a battery were prepared in the same manner as in Example 1 except that the porous membrane slurry 12 was used instead of the porous membrane slurry 1 as the porous membrane slurry. And the dispersibility of the obtained slurry for porous films, the output characteristic of the obtained battery, cycle characteristics, and low temperature characteristics were evaluated. The results are shown in Tables 2 and 3.

(Example 13)
<Creation of slurry for porous membrane>
Non-conductive particles (aluminum oxide, average particle size 0.3 μm, iron content <20 ppm), a solution of polymer-3 (NMP solution having a solid concentration of 20%), a 10% NMP solution of polyvinylidene fluoride, Are mixed so that the content ratio is 100: 1.25: 1.25 (solid content equivalent ratio), and NMP is further mixed to a solid content concentration of 30%, and dispersed using a bead mill. A membrane slurry 13 was prepared. The dispersibility of the obtained slurry for porous membrane was measured. The results are shown in Table 2.
A slurry for a porous membrane, an electrode with a porous membrane, and a battery were prepared in the same manner as in Example 1 except that the porous membrane slurry 13 was used instead of the porous membrane slurry 1 as the porous membrane slurry. And the dispersibility of the obtained slurry for porous films, the output characteristic of the obtained battery, cycle characteristics, and low temperature characteristics were evaluated. The results are shown in Tables 2 and 3.

(Comparative Example 1)
A slurry for a porous film and an electrode with a porous film, as in Example 1, except that polyvinylidene fluoride (glass transition temperature is −40 ° C.) was used as a binder constituting the porous film instead of polymer-1. And a battery were prepared. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Comparative Example 2)
The slurry for porous film, porous as in Example 1, except that styrene-butadiene copolymer (glass transition temperature: −15 ° C.) was used instead of polymer-1 as the binder constituting the porous film. A film-coated electrode and a battery were produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

(Comparative Example 2)
As in Example 1, except for using n-butyl acrylate-styrene copolymer (glass transition temperature: 5 ° C.) instead of polymer-1 as a binder constituting the porous film. A slurry, an electrode with a porous film, and a battery were produced. And the dispersibility of the obtained slurry for porous films, the output characteristics of the obtained battery, and the cycle characteristics were evaluated. The results are shown in Table 2.

  In Tables 1 to 3, “BA” is n-butyl acrylate, “ST” is styrene, “AN” is acrylonitrile, “2EHA” is 2-ethylhexyl acrylate, “MA” is methyl acrylate, “ “EA” represents ethyl acrylate, “PVDF” represents polyvinylidene fluoride, and “BD” represents butadiene.

According to the present invention, as shown in Examples 1 to 13, by using a block polymer as a binder for the porous film, the slurry for porous film having excellent dispersibility, lithium ion having excellent output characteristics and cycle characteristics A secondary battery can be obtained. In addition, among Examples, Examples 1, 3, and 2 having segments having high compatibility with the electrolyte and segments having low compatibility, and having a weight average molecular weight in the range of 5,000 to 100,000. Examples 7 to 10 are excellent in dispersibility and cycle characteristics of the slurry for porous membranes, and in particular have a segment having a glass transition temperature of −40 ° C. or lower and styrene as a segment having high compatibility with the electrolytic solution. No. 1 is excellent in all of the dispersibility of the slurry for the porous membrane, the output characteristics of the battery, the cycle characteristics, and the low temperature characteristics.
On the other hand, Comparative Examples 1 to 3 using a polymer having no block structure as the binder are inferior in all of the dispersibility of the slurry for the porous membrane, the output characteristics of the battery, and the cycle characteristics, and in particular, the cycle characteristics are Remarkably inferior.

Claims (11)

  A porous film for a secondary battery comprising non-conductive particles and a block polymer.   The said block polymer has two segments which are a segment which shows compatibility with the electrolyte solution for secondary batteries containing ethylene carbonate and diethyl carbonate, and a segment which does not show compatibility with the electrolyte solution for secondary batteries. 2. A porous membrane for a secondary battery according to 1.   The porous membrane for a secondary battery according to claim 1, wherein the block polymer has a weight average molecular weight in the range of 1,000 to 500,000.   The porous membrane for a secondary battery according to claim 1, wherein the block polymer includes a segment of a soft polymer having a glass transition temperature of 15 ° C. or lower.   The block polymer has a segment showing compatibility with the secondary battery electrolyte, and the segment showing compatibility with the secondary battery electrolyte has a solubility parameter (SP) of 8.0 or more and less than 11. The porous membrane for a secondary battery according to claim 1, comprising a monomer component and / or a monomer component having a hydrophilic group.   The block polymer has a segment that does not exhibit compatibility with the secondary battery electrolyte, and the segment that does not exhibit compatibility with the secondary battery electrolyte has a solubility parameter of less than 8.0 or 11 or more. The porous membrane for a secondary battery according to claim 1, comprising a monomer component and / or a monomer component having a hydrophobic portion.   A slurry for a secondary battery porous film comprising non-conductive particles, a block polymer, and a solvent.   The manufacturing method of the porous film for secondary batteries including the process of apply | coating the slurry for secondary battery porous films of Claim 7 to a base material, and then drying. Current collector,
The electrode mixture layer including a binder and an electrode active material provided on the current collector, and the layer of the porous membrane for a secondary battery according to claim 1 provided on the electrode mixture layer. A secondary battery electrode comprising: The separator for secondary batteries containing the organic separator layer and the porous film for secondary batteries of Claim 1 provided on the said organic separator layer.   A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein at least one of the positive electrode, the negative electrode, and the separator includes the porous film for a secondary battery according to claim 1.