JP5682737B2 - Porous membrane for secondary battery and method for producing the same, electrode for secondary battery, separator for secondary battery, and secondary battery - Google Patents

Description

  The present invention relates to a porous membrane for a secondary battery, a method for producing the same, and an electrode for a secondary battery, a separator for a secondary battery, and a secondary battery provided with the porous membrane for a secondary battery.

  In secondary batteries, a separator is generally used to prevent a short circuit between the positive electrode and the negative electrode. The separator may affect the performance of the secondary battery. For this reason, various investigations have conventionally been made on separators (see Patent Documents 1 to 3).

JP 2006-182925 A JP 2011-54502 A JP 2011-23186 A

  A normal separator is composed of, for example, a polyolefin-based organic separator such as polyethylene and polypropylene. These separators may shrink when the secondary battery becomes hot due to internal and external stimuli. Such shrinkage may cause a short circuit between the positive electrode and the negative electrode, release of electrical energy, and the like.

  Therefore, in order to suppress the above-described shrinkage at a high temperature, it has been studied to provide a porous film containing non-conductive particles in the separator. By providing a porous film on the separator, the strength of the separator is increased and safety is improved.

  It has also been proposed to provide the porous film on the surface of the electrode. Usually, since the porous film is unlikely to shrink due to heat, if a porous film is provided on the surface of the electrode, the risk of short circuit is greatly reduced, and a significant improvement in safety is expected. Further, by providing the porous film, it is possible to prevent the electrode active material from falling off during the battery manufacturing process. Furthermore, since the porous film has pores, the electrolytic solution can penetrate into the porous film, and the battery reaction is not hindered.

  In the separator and electrode provided with the porous film as described above, the porous film is required to have excellent adhesiveness. Therefore, it is conceivable to include a binder in the porous film. However, when a large amount of the binder is contained in the porous film, blocking tends to occur. Generally, a separator and an electrode provided with a porous film have a sheet-like shape. In addition, these sheet-like separators and electrodes are usually transported or stored in a state of being wound in a roll. However, when the porous film contains a large amount of a binder, the porous film is excellent in adhesiveness, but the separators and the electrodes that overlap each other may be blocked when they become rolls.

  In addition, the porous film is required to prevent non-conductive particles from separating from the porous film from the viewpoint of stably preventing a short circuit. Here, the phenomenon that the non-conductive particles are detached from the porous film is also called “powder falling”.

  The present invention was devised in view of the above-mentioned problems, is excellent in adhesiveness and anti-blocking property, hardly causes powder falling, and can suppress the shrinkage of the separator when configured in combination with an organic separator. It is an object of the present invention to provide a porous film for a secondary battery and a method for producing the same, and an electrode for a secondary battery, a separator for a secondary battery, and a secondary battery provided with the porous film for a secondary battery.

The inventor has intensively studied to solve the above-described problems. As a result, the present inventor uses the polymer particles having a predetermined core-shell structure as the non-conductive particles in the porous film containing the non-conductive particles, the particulate polymer, and the water-soluble polymer, thereby improving the adhesion. And it discovered that it was excellent in blocking resistance, it was hard to produce powder fall, and when a separator was constituted combining with an organic separator, a porous membrane which can control contraction of a separator was realized, and the present invention was completed.
That is, the present invention is as follows.

[1] including non-conductive particles, a particulate polymer and a water-soluble polymer,
The non-conductive particles are polymer particles having a core-shell structure;
The softening start point or decomposition point of the core part of the non-conductive particles is 175 ° C. or higher,
A porous membrane for a secondary battery, wherein the shell portion of the nonconductive particles has a softening start point at 85 ° C to 145 ° C.
[2] The glass transition point of the particulate polymer is −80 ° C. to 60 ° C.,
The porous membrane for a secondary battery according to [1], wherein the softening start point of the water-soluble polymer is 85 ° C or higher.
[3] The porous membrane for a secondary battery according to [1] or [2], wherein the shell part of the nonconductive particles and the particulate polymer contain 50% by weight or more of (meth) acrylate units.
[4] In any one of [1] to [3], the shell portion of the nonconductive particles has a thickness of 3% to 18% with respect to the number average particle diameter of the nonconductive particles. The porous membrane for secondary batteries as described.
[5] The porous membrane for a secondary battery according to any one of [1] to [4], wherein the number average particle diameter of the nonconductive particles is 100 nm to 1500 nm.
[6] A method for producing a porous film for a secondary battery according to any one of [1] to [5],
The non-conductive particles, the particulate polymer, the water-soluble polymer and the medium are mixed to obtain a slurry for a porous film,
Applying the slurry for porous film on a substrate to obtain a slurry layer,
The manufacturing method of the porous film for secondary batteries including drying the said slurry layer.
[7] The medium is an aqueous medium,
The method for producing a porous film for a secondary battery according to [6], wherein the slurry for the porous film is an aqueous dispersion.
[8] Current collector,
An electrode mixture layer that includes an electrode active material and an electrode mixture layer binder, and is attached to the current collector; and
An electrode for a secondary battery, comprising the porous film according to any one of [1] to [5] formed on the electrode mixture layer.
[9] A separator for a secondary battery, comprising the organic separator, and the porous film according to any one of [1] to [5] formed on the organic separator.
[10] A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte solution,
A secondary battery in which at least one of the positive electrode, the negative electrode, and the separator includes the porous film according to any one of [1] to [5].

  ADVANTAGE OF THE INVENTION According to this invention, the porous film for secondary batteries which is excellent in adhesiveness and anti-blocking property, is hard to produce powder falling, and can suppress shrinkage | contraction of a separator when it comprises a separator in combination with an organic separator, and its manufacture The method, and the secondary battery electrode, secondary battery separator and secondary battery provided with the porous membrane for the secondary battery can be realized.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be arbitrarily modified within the scope of the claims of the present invention and its equivalents.
In the following description, (meth) acrylic acid includes both acrylic acid and methacrylic acid.
Further, (meth) acrylate includes both acrylate and methacrylate.
Further, (meth) acrylonitrile includes both acrylonitrile and methacrylonitrile.
Furthermore, that a substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. On the other hand, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.

[1. Porous membrane]
The porous membrane for a secondary battery of the present invention (hereinafter sometimes referred to as “porous membrane” as appropriate) includes non-conductive particles, a particulate polymer, and a water-soluble polymer. The non-conductive particles are polymer particles having a core-shell structure. Here, the core-shell structure refers to a particle structure including a core part inside the particle and a shell part covering the core part. In the non-conductive particles according to the present invention, the softening start point or decomposition point of the core portion is as high as a predetermined temperature or higher, and the shell portion has a softening start point in a predetermined low temperature range. With such a configuration, the porous film of the present invention is excellent in adhesiveness and blocking resistance, hardly causes powder falling, and can suppress the shrinkage of the separator when the separator is configured in combination with an organic separator. The reason why the porous film of the present invention can exhibit such excellent effects is not clear, but according to the study of the present inventor, it is presumed as follows.

i. Adhesiveness The shell portion of the non-conductive particles according to the present invention has a softening start point in a low temperature range. For this reason, it melts easily when heated. Therefore, when the organic separator, the porous film, and the electrode are stacked in this order and heat-pressed, the polymer in the shell portion of the nonconductive particles is melted, and the melted polymer adheres to the organic separator and the electrode. Thereafter, when the porous film is cooled, the melted polymer is cured again while maintaining a close contact state. Thereby, since nonelectroconductive particle adheres to an organic separator and an electrode firmly, the adhesiveness of a porous film can be improved. The particulate polymer generally has binding properties. Therefore, the adhesiveness of the porous film can be enhanced also by the binding property of the particulate polymer.
Here, since the core part of a nonelectroconductive particle has a high softening start point or decomposition | disassembly point, even if it heats in the case of heat press, it does not melt | dissolve and maintains particle shape. For this reason, the pores of the porous membrane are not blocked.

ii. Blocking resistance Since the particulate polymer generally has binding properties, if the content of the particulate polymer in the porous film is large, the adhesion of the porous film is improved, but blocking is likely to occur. On the other hand, in the porous film of the present invention, the shell part of the non-conductive particles can be melted to improve the adhesiveness, so that the amount of the particulate polymer can be reduced. Further, since the shell portion of the nonconductive particles is in a cured state with low friction when not melted, the nonconductive particles are unlikely to cause blocking in a normal use state. For this reason, the electrode for a secondary battery of the present invention (hereinafter sometimes referred to as “the battery of the present invention”) provided with a porous film or the separator for a secondary battery of the present invention (hereinafter referred to as “the separator of the present invention” as appropriate). In some cases, the friction force between the stacked electrodes of the present invention or the separators of the present invention hardly increases, so that the porous film of the present invention is excellent in blocking resistance.

iii. Powder fall The non-conductive particles are firmly bound to each other by the action of the shell portion of the non-conductive particles and the particulate polymer. Therefore, the nonconductive particles are difficult to leave from the porous film. For this reason, the porous film of the present invention is less prone to powder falling.

iv. Inhibition of separator shrinkage The core portion of the non-conductive particles has a high softening start point or decomposition point. For this reason, even if it becomes high temperature, it does not melt and is not easily deformed. Further, the shell portion of the non-conductive particles is not melted in a normal use state. Therefore, the porous film is not easily deformed even when the temperature is high, and maintains high rigidity. Furthermore, in the porous film, the water-soluble polymer covers the surfaces of the non-conductive particles and the particulate polymer. For this reason, the rigidity of the porous membrane is also increased by the water-soluble polymer. Here, the porous film can be firmly adhered to the organic separator as described above. When the porous film having high rigidity without being deformed even at a high temperature is firmly bonded to the organic separator, the organic separator is also difficult to deform. Therefore, even if stress due to heating is generated in the organic separator, the porous film resists the stress, so that the shrinkage of the separator can be suppressed.

[1.1. Non-conductive particles]
The non-conductive particles are polymer particles and have a core-shell structure. That is, a nonelectroconductive particle is equipped with the core part containing a polymer and the shell part containing a polymer.

(Core part)
The core part of nonelectroconductive particle has a softening start point or a decomposition point normally at 175 degreeC or more, Preferably it is 220 degreeC or more, More preferably, it is 225 degreeC or more. Thus, the core part which has a softening start point or a decomposition point in a high temperature range is hard to deform | transform at the use environment and heat press of a secondary battery. Therefore, it is possible to prevent the pores of the porous film from being blocked. Moreover, since it can prevent that the rigidity of a porous film falls, shrinkage | contraction of a separator can be suppressed. Therefore, it is possible to stably prevent a short circuit in a high temperature environment. Moreover, although there is no restriction | limiting in the upper limit of the softening start point or decomposition point of a core part, Usually, it is 450 degrees C or less.

Here, the softening start point can be measured as follows. First, 10 mg of a measurement sample was weighed into an aluminum pan, and an empty aluminum pan was used as a reference with a differential thermal analysis measurement device. The measurement temperature range was −100 ° C. to 500 ° C. The DSC curve is measured under normal temperature and humidity. During this temperature rising process, the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) is 0.05 mW / min / mg or more and the tangent line of the DSC curve at the first inflection point after the endothermic peak The point of intersection with is the glass transition point (Tg). And the temperature 25 degreeC higher than the glass transition point is made into a softening start point.
In addition, when the decomposition point is lower than the softening start point of the core portion of the nonconductive particles, the softening start point may not be observed due to decomposition.

The decomposition point can be measured as follows. Under a nitrogen atmosphere, the measurement sample is heated from 30 ° C. at a rate of temperature increase of 10 ° C./min with a differential thermogravimetric simultaneous measurement apparatus. At this time, the temperature at which the weight loss ratio reaches 10% by weight is defined as the decomposition point.
When both the softening start point and the decomposition point of the core portion of the nonconductive particles are observed, the lower temperature is treated as the softening start point or the decomposition point of the core portion of the nonconductive particle.

  As a polymer which forms a core part, the highly crosslinked polymer is mentioned, for example. By highly crosslinking, molecular motion of the polymer is suppressed even at a temperature equal to or higher than the glass transition point of the polymer, so that the core portion can maintain its shape.

  The polymer forming the core part can be obtained, for example, by polymerizing a crosslinkable vinyl monomer. Examples of the crosslinkable vinyl monomer include compounds having usually 2 or more, preferably 2 copolymerizable double bonds. Moreover, a crosslinking | crosslinked vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of suitable crosslinkable vinyl monomers include non-conjugated divinyl compounds and polyvalent acrylate compounds.
Examples of non-conjugated divinyl compounds include divinylbenzene.
Examples of polyvalent acrylates include polyethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexane glycol diacrylate, neopentyl glycol diacrylate, polypropylene glycol diacrylate, 2,2′-bis (4 -Diacrylate compounds such as acryloxypropyloxyphenyl) propane and 2,2'-bis (4-acryloxydiethoxyphenyl) propane; trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate, etc. Triacrylate compounds; tetraacrylate compounds such as tetramethylolmethane tetraacrylate; ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, Liethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexane glycol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene And dimethacrylate compounds such as glycol dimethacrylate and 2,2′-bis (4-methacryloxydiethoxyphenyl) propane; and tomimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate;
Among these, divinylbenzene, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate are preferable, and ethylene glycol dimethacrylate is particularly preferable.

  The ratio of the crosslinkable vinyl monomer is usually 20% by weight or more, preferably 25% by weight or more, and more preferably 30% by weight or more with respect to all monomers of the polymer forming the core part. By setting the ratio of the crosslinkable vinyl monomer to 20% by weight or more, the hardness, heat resistance, and solvent resistance of the core part can be improved. Moreover, an upper limit is 100 weight% or less normally, Preferably it is 98 weight% or less, More preferably, it is 95 weight% or less. Here, the amount of the crosslinkable vinyl monomer is, for example, in terms of a pure product excluding diluents and impurities.

  As the monomer for the polymer forming the core, only a crosslinkable vinyl monomer may be used. However, monomers other than the crosslinkable vinyl monomer may be used in combination as long as the effects of the present invention are not significantly impaired. Examples of monomers other than the crosslinkable vinyl monomer include polymerizable monovinyl monomers.

  Examples of the polymerizable monomer that can be used in combination with the crosslinkable vinyl monomer include aromatic monovinyl compounds such as styrene, ethylvinylbenzene, α-methylstyrene, fluorostyrene, and vinylpyrine; vinyl cyanide such as acrylonitrile and methacrylonitrile. Compound: Acrylic acid ester monomer such as butyl acrylate, 2-ethylhexyl ethyl acrylate, glycidyl acrylate, N, N′-dimethylaminoethyl acrylate; butyl methacrylate, 2-ethylhexyl methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, N, N '-Dimethylaminoethyl methacrylate and other methacrylic acid ester monomers; acrylic acid, methacrylic acid, maleic acid, itaconic acid and other mono- or dicarbo Acids and acid anhydrides of dicarboxylic acids; amide monomers such as acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide; containing carbon-carbon double bonds and epoxy groups such as allyl glycidyl ether and glycidyl methacrylate Monomers to be used. Moreover, within the range permitted in terms of polymerization rate and polymerization stability, for example, conjugated double bond compounds such as butadiene and isoprene; vinyl ester compounds such as vinyl acetate; 4-methyl-1-pentene; α-olefins A compound or the like may be used in combination with a crosslinkable vinyl monomer. However, the specific type of the polymerizable monomer that can be used in combination with the crosslinkable vinyl monomer usually varies depending on the type of the crosslinkable vinyl monomer. For example, when divinylbenzene is used as the crosslinkable monomer, ethyl vinylbenzene and styrene are preferable. For example, when ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate is used as the crosslinkable monomer, an acrylate monomer and a methacrylic acid ester monomer are preferred. Moreover, these monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Furthermore, as a polymer which forms a core part, you may use amorphous heat-resistant polymers, such as a polysulfone, polyether sulfone, polyarylate, polyamideimide, polyetherimide, a polyimide, for example.

(Shell part)
The shell part of the non-conductive particles is usually in a temperature range of 85 ° C. or higher, preferably 87 ° C. or higher, more preferably 89 ° C. or higher, and usually 145 ° C. or lower, preferably 125 ° C. or lower, more preferably 115 ° C. or lower. Has a softening start point. When the softening start point is not less than the lower limit of the above range, the blocking resistance of the porous film can be improved. In addition, since the shell portion hardly melts at the use temperature of the secondary battery, it is possible to stably prevent the pores of the porous film from being blocked. For this reason, it is possible to improve the rate characteristics of the secondary battery. Moreover, since a shell part can be easily melt | dissolved in the case of heat press because a softening start point is below the upper limit of the said range, the adhesiveness of a porous film can be improved. For this reason, the cycling characteristics of a secondary battery can be improved.

  As the polymer forming the shell part, it is preferable to use a polymer containing a (meth) acrylate unit. Here, the (meth) acrylate unit refers to a structural unit formed by polymerizing one or both of acrylate and methacrylate. By forming the shell portion with a polymer containing a (meth) acrylate unit, the electrical stability of the porous film can be improved. Moreover, when both a shell part and a particulate polymer contain a (meth) acrylate unit, the affinity of a shell part and a particulate polymer can improve, and it can improve dust-proof property.

Examples of the acrylate include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl ethyl acrylate, and the like.
Examples of the methacrylate include methyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate.
One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The ratio of the (meth) acrylate unit in the polymer forming the shell part is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and 100% by weight or less. Thereby, the electrical stability of the porous film can be improved. Moreover, when both a shell part and a particulate polymer contain a (meth) acrylate unit, anti-powder resistance can be improved. The ratio of the (meth) acrylate unit in the polymer forming the shell part is usually the same as the ratio (preparation ratio) of acrylate and methacrylate in all monomers of the polymer forming the shell part.

  The shell part may be a polymer of a monomer other than acrylate and methacrylate, or may be a copolymer of one or both of acrylate and methacrylate and another monomer. Examples of monomers other than acrylate and methacrylate include fats such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3 butadiene, and 2-chloro-1,3-butadiene. Group conjugated diene monomers; aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and divinylbenzene; One of these may be used alone, or two or more of these may be used in combination at any ratio.

(Size of non-conductive particles)
The number average particle diameter of the non-conductive particles is usually 100 nm or more, preferably 200 nm or more, more preferably 300 nm or more, and usually 1500 nm or less, preferably 1200 nm or less, more preferably 1000 nm or less. By setting the number average particle diameter of the non-conductive particles in such a range, a gap between the non-conductive particles is formed to such an extent that the non-conductive particles have contact portions and the movement of ions is not hindered. it can. Therefore, the strength of the porous film can be improved and a short circuit of the battery can be prevented. It is also possible to improve the cycle characteristics of the secondary battery.

  The number average particle diameter of the particles can be measured as follows. 200 particles are arbitrarily selected from a photograph taken at a magnification of 25000 times with a field emission scanning electron microscope. When the longest side of the particle image is La and the shortest side is Lb, the particle size is (La + Lb) / 2. The average particle size of 200 particles is determined as the average particle size.

  The thickness of the shell part is usually 3% or more, preferably 5% or more, more preferably 7% or more, and usually 18% or less, preferably 16% with respect to the number average particle diameter of the non-conductive particles. Below, more preferably 14% or less. By setting the thickness of the shell part to be equal to or more than the lower limit of the above range, the adhesion of the porous film can be enhanced and the cycle characteristics of the secondary battery can be improved. Further, by setting the thickness of the shell portion to be equal to or less than the upper limit of the above range, the size of the pores of the porous membrane can be increased to an extent that does not hinder the movement of ions. For this reason, the rate characteristic of a secondary battery can be improved. Moreover, since a core part can be enlarged relatively by making a shell part thin, the rigidity of a nonelectroconductive particle can be improved. For this reason, the rigidity of a porous membrane can be improved and shrinkage | contraction of a separator can be suppressed.

The thickness (S) of the shell part is, for example, from the number average particle diameter (D1) of the seed polymer particles before forming the shell part and the number average particle diameter (D2) of non-conductive particles after forming the shell part. And can be calculated by the following equation.
(D2-D1) / 2 = S

(Amount of non-conductive particles)
The content ratio of non-conductive particles in the porous membrane of the present invention is usually 70% by weight or more, preferably 75% by weight or more, more preferably 80% by weight or more, and usually 98% by weight or less, preferably 96% by weight or less. More preferably, it is 94 weight% or less. By setting the content ratio of the non-conductive particles in the porous film of the present invention within this range, the non-conductive particles have a contact portion and the non-conductive particles do not hinder the movement of ions. A gap can be formed. Therefore, if the content rate of nonelectroconductive particle is in the said range, the intensity | strength of the porous film of this invention can be improved and the short circuit of a battery can be prevented stably.

(Method for producing non-conductive particles)
Non-conductive particles having a core-shell structure are polymerized stepwise by using, for example, a polymer monomer that forms the core part and a polymer monomer that forms the shell part, and changing the ratio of these monomers over time. Can be manufactured. As a specific example, first, seed polymer particles are produced by polymerizing a polymer monomer that forms the core. This seed polymer particle becomes a core part of a nonelectroconductive particle. Thereafter, in a polymerization system including seed polymer particles, a polymer monomer that forms a shell portion is polymerized. Thereby, since a shell part is formed in the surface of a core part, the nonelectroconductive particle which has a core shell structure is obtained. At this time, if necessary, for example, a reaction medium, a polymerization initiator, a surfactant, or the like may be used.

[1.2. Particulate polymer]
The particulate polymer is a component that can function as a binder in the porous film. As the polymer forming the particulate polymer, various polymers can be used as long as they have binding properties. Especially, it is preferable to use the polymer containing a (meth) acrylate unit from a viewpoint of improving affinity with the shell part of nonelectroconductive particle and improving powder-proof property. Examples of the acrylate and methacrylate forming the (meth) acrylate unit include the same examples as those described in the description of the non-conductive particles. Moreover, an acrylate and a methacrylate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ratio of the (meth) acrylate unit in the particulate polymer is usually 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and 100% by weight or less. Thereby, the electrical stability of the porous film can be improved. Moreover, when both a shell part and a particulate polymer contain a (meth) acrylate unit, anti-powder resistance can be improved. The ratio of (meth) acrylate units in the particulate polymer usually matches the ratio of acrylate and methacrylate (charge ratio) in all monomers of the particulate polymer.

  The particulate polymer may be a polymer of monomers other than acrylate and methacrylate, or may be a copolymer of one or both of acrylate and methacrylate and other monomers. Examples of monomers other than acrylates and methacrylates include vinyl monomers having an acidic group, α, β-unsaturated nitrile monomers, monomers having a crosslinkable group, and the like. These are preferably copolymerized with acrylates or methacrylates. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

In the vinyl monomer having an acidic group, the acidic group, e.g., -COOH group (carboxylic acid group), - OH group (hydroxyl group), - SO ₃ H group (sulfonic acid group), - _PO 3 _{H 2} group, - And PO (OH) (OR) group (R represents a hydrocarbon group). As the vinyl monomer having an acidic group, any vinyl monomer having these acidic groups can be used. Further, for example, a monomer having a lower polyoxyalkylene group and an acid anhydride that generates a carboxylic acid group by hydrolysis can also be used as the vinyl monomer having an acidic group. Especially, it is preferable to use the monomer which has a carboxylic acid group from the reason that it is excellent in the binding property to an electrode mixture layer or an organic separator, and the transition metal ion eluted from the positive electrode active material can be capture | acquired efficiently.

  Examples of the monomer having a carboxylic acid group include monocarboxylic acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxy. Examples include acrylic acid and β-diaminoacrylic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenyl maleate, and maleic acid. Examples thereof include maleyl esters such as nonyl, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Among these, for example, monocarboxylic acids having 5 or less carbon atoms having carboxylic acid groups such as acrylic acid and methacrylic acid; and dicarboxylic acids having 5 or less carbon atoms having two carboxylic acid groups such as maleic acid and itaconic acid are preferable. . Furthermore, acrylic acid, methacrylic acid, and itaconic acid are preferable from the viewpoint that the storage stability of the prepared slurry for porous membrane is high. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The ratio (charge ratio) of the vinyl monomer having an acidic group to the total monomer of the particulate polymer is preferably 1.0% by weight or more, more preferably 1.5% by weight or more, preferably 3.0% by weight. Below, more preferably 2.5% by weight or less.

  Examples of the α, β-unsaturated nitrile monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and the like. Among these, acrylonitrile and methacrylonitrile are preferable from the viewpoint of improving the mechanical strength of the porous film and the binding force in the porous film. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The ratio (charge ratio) of the α, β-unsaturated nitrile monomer to the total monomer of the particulate polymer is preferably 1.0% by weight or more, preferably 50% by weight or less, more preferably 40% by weight or less, Particularly preferred is 30% by weight or less.

Examples of the monomer having a crosslinkable group include a monofunctional monomer having a crosslinkable group and having one olefinic double bond, and a polyfunctional monomer having at least two olefinic double bonds.
The crosslinkable group is preferably at least one selected from the group consisting of an epoxy group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. Among these, an epoxy group and an N-methylolamide group are more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the monomer having an epoxy group as a crosslinkable 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, chloroprene mono Monoepoxides of dienes or polyenes such as epoxides, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; 3,4-epoxy Alkenyl epoxides such as -1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate Glycidyl esters of unsaturated carboxylic acids such as glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid; Can be mentioned.

  Examples of the monomer having a halogen atom and an epoxy group include epihalohydrin such as epichlorohydrin, epibromohydrin, epiiodohydrin, epifluorohydrin, β-methylepichlorohydrin; p-chlorostyrene oxide; dibromophenylglycidyl. Ether; and the like.

  Examples of the monomer having an N-methylolamide group as a crosslinkable group include N-methylolacrylamide and N-methylolmethacrylamide.

Examples of the polyfunctional monomer having at least two olefinic double bonds include allyl acrylate, allyl methacrylate, trimethylol propane-triacrylate, trimethylol propane-methacrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triglyceride. Examples include ethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, other allyl or vinyl ethers of polyfunctional alcohols, tetraethylene glycol diacrylate, triallylamine, trimethylolpropane-diallyl ether, methylenebisacrylamide, divinylbenzene, etc. It is done. Of these, allyl acrylate, allyl methacrylate, trimethylolpropane-triacrylate, and trimethylolpropane-methacrylate are preferable. Among them, acrylates and methacrylates having an allyl group such as allyl acrylate and allyl methacrylate are preferable because the crosslinking density is easily improved and the crosslinking density is improved and copolymerization is high.
Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The ratio (charge ratio) of the monomer having a crosslinkable group to the total monomer of the particulate polymer is preferably 0.02% by weight or more, more preferably 0.1% by weight or more, and particularly preferably 0.2% by weight or more. Preferably 4.0% by weight or less, more preferably 3.5% by weight or less, and particularly preferably 3.0% by weight or less. Thereby, the elution to the electrolyte solution of a particulate polymer is suppressed, and the outstanding porous film intensity | strength and long-term cycling characteristics are realizable.

  The glass transition point of the particulate polymer is usually −80 ° C. or higher, preferably −70 ° C. or higher, more preferably −60 ° C. or higher, and usually 60 ° C. or lower, preferably 30 ° C. or lower, more preferably 0. It is below ℃. By making the glass transition point of a particulate polymer more than the lower limit of the said range, it can prevent that the hole of a porous film is block | closed and can improve liquid permeability. For this reason, the rate characteristic of a secondary battery can be made high. Moreover, by setting it as an upper limit or less, the binding property of a particulate polymer can be made high and the powder-off of a nonelectroconductive particle can be prevented stably.

  The number average particle size of the particulate polymer is usually 50 nm or more, preferably 100 nm or more, more preferably 150 nm or more, and usually 1000 nm or less, preferably 800 nm or less, more preferably 600 nm or less. By setting the number average particle diameter of the particulate polymer to be equal to or greater than the lower limit of the above range, the porosity of the porous film can be kept high, the resistance of the porous film can be suppressed, and the battery physical properties can be kept good. Moreover, by making it below the upper limit of the said range, the adhesion point of a nonelectroconductive particle and a base material, and a particulate polymer can be increased, and powder fall can be prevented stably.

  The amount of the particulate polymer is usually 3 parts by weight or more, preferably 7 parts by weight or more, more preferably 11 parts by weight or more, and usually 26 parts by weight or less, preferably 100 parts by weight of the non-conductive particles. It is 22 parts by weight or less, more preferably 18 parts by weight or less. By setting the amount of the particulate polymer to be equal to or higher than the lower limit of the above range, it is possible to stably prevent the nonconductive particles from falling off. Moreover, by setting it as the upper limit value or less of the above range, the porosity of the porous film can be kept high, the resistance of the porous film can be suppressed, and the battery physical properties can be kept good.

  The production method of the particulate polymer is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as the material for the slurry for the porous membrane.

[1.3. Water-soluble polymer]
The water-soluble polymer has a function of binding nonconductive particles to each other in the porous film. In addition, since the water-soluble polymer usually covers the surfaces of the non-conductive particles and the particulate polymer in a cured state, it has an action of increasing the rigidity of the porous film and suppressing blocking. Furthermore, in the slurry for porous membranes, the water-soluble polymer usually functions as a thickener that can adjust the viscosity of the slurry.

  Examples of the water-soluble polymer include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, 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 (modified) polyvinyl alcohol, acrylic acid or copolymers of acrylic acid salt and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl Examples include pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches. Here, “(modified) poly” includes both “unmodified poly” and “modified poly”. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The softening start point of the water-soluble polymer is usually 85 ° C or higher, preferably 175 ° C or higher, more preferably 200 ° C or higher. By increasing the softening start point of the water-soluble polymer in this way, the heat resistance of the porous film can be improved and the anti-powder resistance can be improved. Furthermore, blocking resistance can also be improved. Moreover, although there is no restriction | limiting in the upper limit of the softening start point of a water-soluble polymer, Usually, it is 450 degrees C or less.

  The amount of the water-soluble polymer is usually 0.03 parts by weight or more, preferably 0.18 parts by weight or more, more preferably 0.3 parts by weight or more with respect to 100 parts by weight of the nonconductive particles. It is not more than parts by weight, preferably not more than 15 parts by weight, more preferably not more than 12 parts by weight. By setting the amount of the water-soluble polymer to be equal to or higher than the lower limit of the above range, the heat resistance of the porous membrane can be improved, and the dust resistance can be improved. Moreover, by setting it as the upper limit value or less of the above range, the porosity of the porous film can be kept high, the resistance of the porous film can be suppressed, and the battery physical properties can be kept good.

[1.4. Arbitrary ingredients]
The porous film of the present invention may contain any component other than the components described above. The optional component is not particularly limited as long as it does not have an excessively unfavorable effect on the battery reaction in the secondary battery of the present invention. Moreover, the kind of arbitrary component may be one, and two or more kinds may be sufficient as it.

[1.5. Production method of porous membrane]
The porous film of the present invention includes, for example, a step of mixing a non-conductive particle, a particulate polymer, a water-soluble polymer and a medium to obtain a porous film slurry, and applying the porous film slurry onto a substrate. It can manufacture by the manufacturing method including the process of obtaining a slurry layer, and the process of drying a slurry layer. Hereinafter, this manufacturing method will be described.

  The slurry for a porous film is a fluid composition containing non-conductive particles, a particulate polymer, a water-soluble polymer, and a medium. Usually, in the slurry for porous films, the nonconductive particles and the particulate polymer are dispersed in the medium. Further, in the slurry for porous membrane, when an aqueous medium is used as a medium, some water-soluble polymers are dissolved in the medium, but another part of the water-soluble polymers are non-conductive particles and particulates. Adsorbs on the surface of the polymer. As a result, the non-conductive particles and the particulate polymer are covered with the water-soluble polymer layer (dispersion stable layer), and the dispersibility of the non-conductive particles and the particulate polymer in water is improved.

As the medium, an aqueous medium is usually used. Thereby, the slurry for porous films is obtained as an aqueous dispersion. As the aqueous medium, water is usually used.
The amount of the medium contained in the porous membrane slurry is usually arbitrarily set within a range in which the porous membrane slurry has a viscosity that does not impair workability when producing the porous membrane of the present invention. Specifically, the amount of the medium is set so that the solid content concentration of the slurry for the porous membrane is usually 5 wt% to 30 wt%.

  The slurry for a porous film may contain an arbitrary component other than the nonconductive particles, the particulate polymer, the water-soluble polymer and the medium. The optional component is not particularly limited as long as it does not have an excessively unfavorable effect on the battery reaction in the secondary battery. Moreover, the kind of arbitrary component may be one, and two or more kinds may be sufficient as it.

As an arbitrary component, a dispersing agent, electrolyte solution dispersion inhibitor, etc. are mentioned, for example.
Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. The specific type of the dispersant is usually selected according to the configuration of the non-conductive particles.

  Moreover, the slurry for porous films may contain surfactants, such as an alkyl type surfactant, a silicon type surfactant, a fluorine type surfactant, a metal type surfactant, for example. By including the surfactant, it is possible to prevent repelling when applying the slurry for the porous film, or to improve the smoothness of the electrode of the present invention. The amount of the surfactant is preferably within a range that does not affect the battery characteristics, and is preferably 10% by weight or less in the porous membrane of the present invention.

  Moreover, the slurry for porous films may contain nanoparticles having a volume average particle diameter of less than 100 nm, such as fumed silica and fumed alumina. By including the nano fine particles, the thixotropy of the slurry for the porous membrane can be controlled, and the leveling property of the porous membrane of the present invention can be further improved.

  In the production of the slurry for the porous membrane, there is no particular limitation on the mixing order of the non-conductive particles, the particulate polymer, the water-soluble polymer and the medium, and any components used as necessary. There is no particular limitation on the mixing method. Usually, in order to disperse non-conductive particles quickly, mixing is performed using a disperser as a mixing device.

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

  After preparing the slurry for porous membrane, the slurry for porous membrane is apply | coated on a base material, and a slurry layer is obtained. A base material is a member used as the object which forms a slurry layer as a film | membrane of the slurry for porous films. There is no restriction | limiting in a base material, For example, you may use a peeling film. In this case, the slurry for the porous film may be applied to the surface of the release film to obtain a slurry layer, and after the slurry layer is dried to obtain the porous film, the porous film may be peeled off from the release film. However, normally, a battery element is used as a base material from the viewpoint of improving the production efficiency by omitting the step of peeling the porous film of the present invention. Specific examples of such battery elements include electrodes and organic separators.

  Examples of the method for applying the slurry for the porous membrane include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the dip method and the gravure method are preferable in that a uniform porous film can be obtained.

  After obtaining the slurry layer, the slurry layer is dried. Thereby, the porous film of the present invention is obtained. Examples of the drying method include drying with warm air, hot air, low-humidity air, and the like; vacuum drying; drying method by irradiation with energy rays such as infrared rays, far infrared rays, and electron beams. The drying temperature is a temperature at which the medium is vaporized and removed from the coating film. In addition, when the particulate polymer has a thermally crosslinkable group, it is preferable to perform drying at a temperature higher than the temperature at which the thermally crosslinkable group causes a crosslinking reaction. By simultaneously performing the drying and the crosslinking reaction, the number of steps can be reduced and the production efficiency can be improved. Usually, it is dried at 40 ° C to 120 ° C.

  In the above-described method for manufacturing a porous membrane, another step may be performed. For example, the pressing process may be performed using a mold press, a roll press, or the like. Thereby, the adhesiveness of a base material and the porous film of this invention can be improved. Such pressure treatment is particularly useful when an electrode, an organic separator, or the like is used as the base material. However, if the pressure treatment is excessively performed, the porosity of the porous membrane of the present invention may be impaired, so it is preferable to appropriately control the pressure and the pressure time.

[1.6. Other matters related to porous membrane]
The porous film of the present invention has moderate porosity by having voids between the non-conductive particles, and can absorb the electrolytic solution. Thus, since the electrolytic solution can penetrate into the porous film of the present invention, even if the porous film of the present invention is provided on the electrode of the present invention or the separator of the present invention, the battery reaction is not hindered, and the rate characteristics are improved. A high secondary battery can be realized.

  The thickness of the porous membrane of the present invention is preferably 0.5 μm to 20 μm. Moreover, when providing the porous film of this invention on the surface of an electrode, the thickness of a porous film has preferable 1 micrometer-10 micrometers. By setting the thickness of the porous film to be equal to or more than the lower limit of the above range, the thickness of the film can be made uniform. Moreover, the capacity | capacitance (capacity) per volume in a battery or weight can be made high by setting it as below an upper limit.

[2. Secondary battery electrode]
The electrode of the present invention (secondary battery electrode) includes a current collector, an electrode mixture layer attached on the current collector, and a porous film of the present invention formed on the electrode mixture layer. The electrode mixture layer includes an electrode active material and an electrode mixture layer binder. Even if the porous film of the present invention is provided on the surface of the electrode mixture layer, the electrolyte solution can permeate the porous film of the present invention, so that the rate characteristics are not adversely affected. In addition, since the porous film of the present invention has an appropriate strength, it functions as a protective film when provided on the surface of the electrode mixture layer, prevents the electrode active material from falling off during the manufacturing process of the secondary battery, and shorts during battery operation. It can be prevented. Furthermore, since the porous membrane of the present invention is provided, the electrode of the present invention is less likely to cause blocking.

[2.1. Current collector]
The current collector is not particularly limited as long as it is a material having electrical conductivity and electrochemical durability. Among these, metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum are preferable from the viewpoint of heat resistance. Among these, aluminum is particularly preferable for the positive electrode of the nonaqueous electrolyte secondary battery, and copper is particularly preferable for the negative electrode.

The shape of the current collector is not particularly limited, but a sheet having a thickness of 0.001 mm to 0.5 mm is preferable.
In order to increase the adhesive strength with the electrode mixture layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, 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 surface of the current collector in order to increase the adhesive strength and conductivity with the electrode mixture layer.

[2.2. Electrode mixture layer]
(Electrode active material)
The electrode mixture layer includes an electrode active material. In the following description, among the electrode active materials, an electrode active material for a positive electrode may be referred to as a “positive electrode active material”, and an electrode active material for a negative electrode may be referred to as a “negative electrode active material”. Since the electrode of the present invention is usually used in a lithium secondary battery, an electrode active material for a lithium secondary battery will be described in particular.

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

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

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

  The particle diameter of the positive electrode active material is appropriately selected in view of other constituent requirements of the battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the volume average particle diameter D50 of the positive electrode active material is usually 0.1 μm or more, preferably 1 μm or more, and usually 50 μm or less, preferably 20 μm or less. When the volume average particle diameter D50 of the positive electrode active material is within this range, a secondary battery having a large charge / discharge capacity can be obtained, and handling of the mixture slurry and the electrode of the present invention is easy. Here, the volume average particle diameter D50 represents a particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle size distribution measured by the laser diffraction method.

  Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers; and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used. Furthermore, as the electrode active material, a material obtained by attaching a conductivity imparting material to the surface by a mechanical modification method may be used. These negative electrode active materials may be used alone or in combination of two or more at any ratio.

  The particle size of the negative electrode active material is appropriately selected in view of other constituent requirements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, the volume average particle diameter D50 of the negative electrode active material is usually 1 μm or more, preferably 15 μm or more, and usually 50 μm or less, preferably 30 μm or less. .

(Binder for electrode mixture layer)
The electrode mixture layer includes a binder for the electrode mixture layer. By including the binder for the electrode mixture layer, the adhesion of the electrode mixture layer is improved, and the strength against the mechanical force is increased in the process of winding the electrode of the present invention. In addition, since the electrode mixture layer is difficult to be detached, the possibility of a short circuit due to the desorbed material is reduced.

  Various polymer components can be used as the binder for the electrode mixture layer. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, and the like may be used.

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

  The binder for electrode mixture layers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the binder for the electrode mixture layer in the electrode mixture layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0, relative to 100 parts by weight of the electrode active material. 0.5 parts by weight or more, preferably 5 parts by weight or less, more preferably 4 parts by weight or less, and particularly preferably 3 parts by weight or less. When the amount of the binder for the electrode mixture layer is within the above range, it is possible to prevent the electrode active material from dropping from the electrode mixture layer without inhibiting the battery reaction.

  The binder for electrode mixture layers is normally prepared in the state contained in the solution or the dispersion liquid in order to produce an electrode mixture layer. The viscosity of the solution or dispersion at that time is usually 1 mPa · s or more, preferably 50 mPa · s or more, and usually 300,000 mPa · s or less, preferably 10,000 mPa · s or less. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

(Any component that may be contained in the electrode mixture layer)
The electrode mixture layer may contain any component other than the electrode active material and the electrode mixture layer binder, as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductivity imparting material (also referred to as a conductive material), a reinforcing material, and the like. Arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the conductivity-imparting material include acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, carbon nanotube and other conductive carbon; graphite and other carbon powders; various metal fibers and foils; Can be mentioned. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved. In particular, when used for a lithium secondary battery, the discharge rate characteristics can be improved.

As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.
The amount of the conductivity-imparting material and the reinforcing agent used is usually 0 parts by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is as follows.

(Mixture slurry)
In general, the electrode mixture layer is a current collector made of an electrode active material, a binder for the electrode mixture layer and a solvent, and a slurry containing optional components as necessary (hereinafter referred to as “mixture slurry” as appropriate). It is made to adhere to.

  The mixture slurry usually contains a solvent, and dissolves or disperses the electrode active material, the binder for the electrode mixture layer, and optional components. As the solvent, it is preferable to use a solvent that can dissolve the binder for the electrode mixture layer because the dispersibility of the electrode active material and the conductivity-imparting material is excellent. By using the binder for the electrode mixture layer dissolved in a solvent, the binder for the electrode mixture layer is adsorbed on the surface of the electrode active material and the like, and the dispersion is stabilized by the volume effect. Guessed.

  As a solvent used for the mixture 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, and γ-butyrolactone Esters such as ε-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 -Amides such as methylpyrrolidone and N, N-dimethylformamide. These solvents may be used alone or in combination of two or more at any ratio. The specific type of solvent is preferably selected as appropriate from the viewpoints of drying speed and environment. Especially, it is preferable to use a non-aqueous solvent from a viewpoint of the electrode expansion | swelling characteristic to water.

  The mixture slurry may further contain additives that exhibit various functions such as a thickener. As the thickener, a polymer that is soluble in an organic solvent used for the mixture slurry is usually used. Specific examples thereof include acrylonitrile-butadiene copolymer hydride.

  Further, in the mixture slurry, in order to increase the stability and life of the battery, for example, trifluoropropylene carbonate, vinylene carbonate, catechol carbonate, 1,6-dioxaspiro [4,4] nonane-2,7-dione, 12 -Crown-4-ether etc. may be included. Moreover, you may include these in electrolyte solution.

  The amount of the solvent in the mixture slurry is preferably adjusted so as to have a viscosity suitable for coating depending on the types of the electrode active material and the binder for the electrode mixture layer. Specifically, the concentration of the solid content of the electrode active material, the binder for the electrode mixture layer and the optional components is preferably 30% by weight or more, more preferably 40% by weight or more, and preferably 90%. It is used by adjusting the amount to be not more than wt%, more preferably not more than 80 wt%.

  The mixture slurry is obtained by mixing an electrode active material and a solvent, and a binder for an electrode mixture layer and optional components, which are included as necessary, using a mixer. Mixing may be performed by supplying the above components all at once to a mixer. Moreover, when using an electrode active material, a binder for electrode mixture layers, a conductivity-imparting material, and a thickener as components of the mixture slurry, the conductivity-imparting material and the thickener are mixed in a solvent. Then, it is preferable to disperse the conductivity-imparting material in the form of fine particles and then mix the binder for the electrode mixture layer and the electrode active material because the dispersibility of the slurry is improved. As the mixer, for example, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, or the like may be used. Among these, use of a ball mill is preferable because aggregation of the conductivity imparting material and the electrode active material can be suppressed.

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

(Method for producing electrode mixture layer)
The electrode mixture layer may be produced, for example, by adhering the electrode mixture layer in layers on at least one side, preferably both sides, of the current collector. As a specific example, the electrode mixture layer may be produced by applying and drying the mixture slurry on a current collector and then heat-treating the mixture at 120 ° C. or more for 1 hour or more.

  Examples of methods for applying the mixture slurry to the current collector include methods such as 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 with warm air, hot air, and low-humidity air; vacuum drying; drying by irradiation with energy rays such as infrared rays, far infrared rays, and electron beams.

Thereafter, the electrode mixture layer is preferably subjected to pressure treatment using, for example, a mold press and a roll press. By performing the pressure treatment, the porosity of the electrode mixture layer can be lowered. The porosity of the electrode mixture layer is preferably 5% or more, more preferably 7% or more, preferably 15% or less, more preferably 13% or less. By setting the porosity to be equal to or higher than the lower limit of the above range, the volume capacity can be increased, or peeling of the electrode mixture layer can be prevented. Moreover, charge efficiency and discharge efficiency can be improved by making a porosity into below the upper limit of the said range.
Moreover, when using a curable polymer as a binder for electrode mixture layers, it is preferable to harden the binder for electrode mixture layers at the appropriate time after apply | coating a mixture slurry.

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

[2.3. Porous membrane]
The electrode of the present invention includes the porous film of the present invention on an electrode mixture layer. Thereby, detachment | desorption of the electrode active material etc. from an electrode mixture layer, peeling of an electrode mixture layer, an internal short circuit of a battery, etc. can be prevented.

As a method for providing the porous film of the present invention on the electrode mixture layer, for example, the method for producing the porous film of the present invention may be performed using the electrode mixture layer as a base material. An example of a specific method is:
1) A method in which a slurry for a porous membrane is applied to the surface of an electrode mixture layer and then dried;
2) A method of drying the electrode mixture layer after immersing the electrode mixture layer in the slurry for the porous membrane;
3) A method for transferring the slurry for porous film of the present invention to the surface of the electrode mixture layer by applying the slurry for porous film on a release film and drying to produce the porous film of the present invention;
Etc. Among these, the method 1) is particularly preferable because the film thickness of the porous film of the present invention can be easily controlled.

[2.4. Other components]
The electrode of the present invention may include components other than the current collector, the electrode mixture layer, and the porous film of the present invention as long as the effects of the present invention are not significantly impaired. For example, another layer may be provided between the electrode mixture layer and the porous film of the present invention as necessary. In this case, the porous film of the present invention is indirectly provided on the electrode mixture layer. Further, another layer may be provided on the porous film of the present invention.

[3. Secondary battery separator]
The separator of the present invention (secondary battery separator) includes an organic separator and the porous film of the present invention formed on the organic separator. Even if the separator of the present invention is provided with the porous film of the present invention, the electrolyte solution can penetrate into the porous film of the present invention, so that the rate characteristics and the like are not adversely affected. Moreover, since the separator of this invention is equipped with the porous film of this invention which does not deform | transform even at high temperature and can have high rigidity, it is hard to shrink | contract also in a high temperature environment. Furthermore, since the porous membrane of the present invention is provided, the separator of the present invention is less likely to cause blocking.

  In general, an organic separator is a member provided between a positive electrode and a negative electrode in order to prevent a short circuit between electrodes. As the organic separator, for example, a porous substrate having fine pores is used, and a porous substrate made of an organic material is usually used. Specific examples of the organic separator include microporous membranes and nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, and the like.

  The thickness of the organic separator is usually 0.5 μm or more, preferably 1 μm or more, and is usually 40 μm or less, preferably 30 μm or less, more preferably 10 μm or less. Within this range, the resistance of the separator of the present invention in the battery is reduced, and the workability during battery production is excellent.

The separator of the present invention includes the porous film of the present invention on an organic separator. As a method of providing the porous membrane of the present invention on the organic separator, for example, the method for producing the porous membrane of the present invention may be performed using the organic separator as a substrate. An example of a specific method is:
1) A method in which a slurry for a porous membrane is applied to the surface of an organic separator and then dried;
2) A method of drying an organic separator after immersing it in a slurry for a porous membrane;
3) A method for producing a porous film of the present invention by applying a slurry for a porous film onto a release film and drying it, and transferring the resulting porous film of the present invention to the surface of an organic separator;
Etc. Among these, the method 1) is particularly preferable because the film thickness of the porous film of the present invention can be easily controlled.

  The separator of the present invention may include components other than the organic separator and the porous membrane of the present invention as long as the effects of the present invention are not significantly impaired. For example, another layer may be provided on the porous film of the present invention.

[4. Secondary battery]
The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution. In the secondary battery of the present invention, at least one of the positive electrode, the negative electrode, and the separator includes the porous film of the present invention. That is, the secondary battery of the present invention satisfies one or both of the following requirements (A) and (B).
(A) The electrode of the present invention is provided as at least one of the positive electrode and the negative electrode.
(B) The separator of the present invention is provided as a separator.

Since the porous film of the present invention is excellent in adhesiveness and anti-powder resistance, the porous film of the present invention is hardly peeled off from the electrode mixture layer and the organic separator even if charging and discharging are repeated in the secondary battery of the present invention. ing. For this reason, the secondary battery of this invention is excellent in cycling characteristics.
In addition, since the porous film of the present invention does not easily close the pores even in a high temperature environment, the secondary battery of the present invention is excellent in rate characteristics.
Furthermore, by using the porous membrane of the present invention, the separator of the secondary battery of the present invention hardly shrinks even at high temperatures. Further, in the porous film of the present invention, non-conductive particles are hardly detached even in a high temperature environment. For this reason, the secondary battery of the present invention is a highly reliable battery which is unlikely to cause a short circuit even in a high temperature environment.

[4.1. electrode]
In principle, the secondary battery of the present invention includes the electrode of the present invention as one or both of a positive electrode and a negative electrode. However, when the secondary battery of the present invention includes the separator of the present invention as a separator, an electrode other than the electrode of the present invention may be provided as both the positive electrode and the negative electrode.

[4.2. separator]
In principle, the secondary battery of the present invention includes the separator of the present invention as a separator. However, when the secondary battery of the present invention includes the electrode of the present invention as one or both of the positive electrode and the negative electrode, a separator other than the separator of the present invention may be provided as a separator.

[4.3. Electrolyte]
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, a lithium salt is used as the supporting electrolyte. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable because they are easily soluble in a solvent and exhibit a high degree of dissociation. Further, one type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Usually, the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, so that the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

  The organic solvent used for the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC); γ-butyrolactone, methyl formate, etc. Esters of the following: ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; 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. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted depending on the type of solvent.

  The concentration of the supporting electrolyte in the electrolytic solution is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less. Further, depending on the type of the supporting electrolyte, it may be used usually at a concentration of 0.5 mol / L to 2.5 mol / L. Even if the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease. Usually, the lower the concentration of the electrolytic solution, the higher the degree of swelling of the polymer particles such as the binder for the electrode mixture layer. Therefore, the lithium ion conductivity can be adjusted by adjusting the concentration of the electrolytic solution.

  Furthermore, you may include an additive etc. in electrolyte solution as needed.

[4.4. Secondary battery manufacturing method]
As a manufacturing method of the secondary battery of this invention, the following methods are mentioned, for example.
First, a positive electrode and a negative electrode are overlapped via a separator. Thereby, a laminated body provided with a positive electrode, a separator, and a negative electrode in this order is obtained. This laminate has the porous film of the present invention between the electrode mixture layer and the organic separator.

  Thereafter, this laminate is subjected to heat press. The polymer that forms the shell portion of the nonconductive particles in the porous film of the present invention is melted by heat pressing, and the electrode mixture layer and the organic separator are firmly bonded to the porous film of the present invention.

  The temperature of the heat press is usually equal to or higher than the softening start point of the shell part and lower than the softening start point and the decomposition point of the core part. Specifically, it is preferably 85 ° C. or higher, more preferably 87 ° C. or higher, particularly preferably 89 ° C. or higher, preferably 110 ° C. or lower, more preferably 105 ° C. or lower, particularly preferably 100 ° C. or lower.

  The pressure of the heat press is usually 0.1 MPa or more, preferably 0.3 MPa or more, more preferably 0.5 MPa or more, and usually 10 MPa or less, preferably 5 MPa or less, more preferably 3 MPa or less. The electrode mixture layer and the organic separator can be firmly bonded by setting the pressure of the heat press to the lower limit value or more of the above range, and the porosity of the organic separator can be maintained by setting the pressure of the heat press to the upper limit value or less.

  The time for applying the heat press is usually 2 seconds or longer, preferably 5 seconds or longer, more preferably 8 seconds or longer, and usually 60 seconds or shorter, preferably 40 seconds or shorter, more preferably 20 seconds or shorter. The electrode mixture layer and the organic separator can be firmly bonded by setting the time for performing heat press to the lower limit value or more of the above range, and high productivity can be ensured by setting the time to the upper limit value or less.

Thereafter, the obtained laminate is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed. Thereby, the secondary battery of the present invention is obtained.
In addition, if necessary, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, an expanded metal, or the like may be inserted to prevent overcharging / discharging or an increase in pressure inside the battery. 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 specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily modified within the scope of the claims of the present invention and its equivalents. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified. Further, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation method]
[Calculation method of number average particle diameter]
200 particles were arbitrarily selected from a photograph taken at a magnification of 25000 times with a field emission scanning electron microscope (Hitachi S-4700, manufactured by Hitachi High-Tech). When the longest side of the particle image is La and the shortest side is Lb, the particle size is (La + Lb) / 2, and the average particle size is calculated from the average of 200 particles.

[Calculation method of glass transition point (Tg) and softening start point]
10 mg of a measurement sample is weighed into an aluminum pan, and an empty aluminum pan is used as a reference with a differential thermal analysis measuring device (“EXSTAR DSC6220” manufactured by SII Nano Technology), and the measurement temperature range is −100 ° C. to 500 ° C. In the meantime, the DSC curve was measured at a heating rate of 10 ° C./min and at normal temperature and humidity. During this temperature rising process, the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) is 0.05 mW / min / mg or more and the tangent line of the DSC curve at the first inflection point after the endothermic peak Was determined as the glass transition point (Tg). Furthermore, a temperature 25 ° C. higher than the glass transition point was taken as the softening start point.
In the table below, the softening start point of the water-soluble polymer is “none”, and the softening start point is not observed below 200 ° C., and the softening start point is due to decomposition of the water-soluble polymer above 200 ° C. Indicates that no points were observed.

[Calculation method of decomposition point]
Under a nitrogen atmosphere, it is heated from 30 ° C. at a heating rate of 10 ° C./min with a differential thermothermogravimetric simultaneous measurement device (“EXSTAR TG / DTA6000” manufactured by SII Nanotechnology Inc.), and the weight loss rate reaches 10% by weight. The temperature was taken as the decomposition point.

[Calculation method of thickness of shell part of non-conductive particles]
The thickness (S) of the shell part of the nonconductive particles is determined by the number average particle diameter (D1) of the seed polymer particles A before the formation of the shell part and the number average particle diameter (D2) of the nonconductive particles after the formation of the shell part. ) And was calculated from the following equation.
(D2-D1) / 2 = S

[Heat shrinkage test of secondary battery separator]
A separator for a secondary battery (organic separator with a porous film) is cut into a width of 10 cm and a length of 10 cm to obtain a test piece. After leaving the test piece in an oven adjusted to a temperature of 150 ° C. for 1 hour, the length of each side was measured, and the shrinkage rate of the side having the largest shrinkage rate was evaluated according to the following criteria. The smaller the heat shrinkage rate, the better the safety of the secondary battery.
(Evaluation criteria)
A: Less than 3.0% B: 3.0% or more and less than 5.0% C: 5.0% or more and less than 10.0% D: 10% or more

[Powder removal test of secondary battery separator and secondary battery electrode]
The separator with the porous film and the electrode with the porous film were punched out into a circle having a diameter of 19 mm with an electrode punching machine, and the presence or absence of the porous film piece adhering to the punching blade was visually observed and judged according to the following criteria. It shows that the powder generation | occurrence | production of the porous film layer formed on the electrode mixture layer or the organic separator layer is excellent, so that adhesion | attachment generation | occurrence | production of the porous film piece to a punching blade is slow. In addition, the presence or absence of porous membrane piece adhesion was performed every 100 times of punching, and was confirmed up to 1000 times.
(Evaluation criteria)
A: The porous film piece does not adhere even after punching 1000 times.
B: Adhesion of porous membrane pieces occurred after punching 501 to 999 times.
C: Adhesion of porous membrane pieces occurs after punching 101 to 500 times.
D: Adhesion of the porous membrane piece occurred by punching 100 times or less.

[Blocking test of secondary battery separator and secondary battery electrode]
An electrode with a porous film or a separator with a porous film is cut into a width of 5 cm and a length of 5 cm to obtain a test piece. Two sheets of this were stacked, and the adhesion state (blocking state) of the electrode with a porous film or the separator with a porous film after pressing at 60 ° C. for 1 hour under the condition of 1 MPa was visually confirmed.
(Evaluation criteria)
A: Not adhered at all.
B: Although it adheres slightly, it peels off only by touching with a hand.
C: Although slightly adhered, it can be easily peeled off.
D: Adhering.

[Electrode adhesion test of separator for secondary battery]
A separator with a porous film is cut into a width of 5 cm × a length of 5 cm, and a positive electrode and a negative electrode are cut into a width of 3 cm × a length of 3 cm, respectively. A separator with a porous film was disposed on the surface of the positive electrode on the positive electrode mixture layer side. Furthermore, the negative electrode was disposed on the separator so that the surface on the negative electrode mixture layer side faced the separator. This laminate was subjected to heat press using a desktop test press under conditions of a temperature of 90 ° C., a time of 10 seconds, and a pressure of 1 MPa. By calculating the ratio (R1) of the electrode mixture layer remaining adhered to the separator with the porous film when each electrode was peeled off at a speed of 50 mm / sec and an angle of 90 ° from this laminate, The adhesion of the separator with a porous membrane to the electrode was evaluated. It shows that it is excellent in adhesiveness, so that this ratio is high.
(R1) = (area of electrode mixture layer remaining adhered to separator with porous film / area of electrode mixture layer used) × 100
(Evaluation criteria)
A: 50% or more B: 30% or more and less than 50% C: 10% or more and less than 30% D: Less than 10%

[Secondary battery electrode separator adhesion test]
An organic separator is cut into a width of 5 cm × a length of 5 cm, a positive electrode with a porous film and a negative electrode with a porous film are each cut into a width of 3 cm × a length of 3 cm to form a test piece. An organic separator was disposed on the porous membrane layer side surface of the positive electrode with the porous membrane. Furthermore, the negative electrode with a porous film was arrange | positioned on an organic separator so that the surface by the side of a porous film layer might oppose an organic separator. This laminate was subjected to heat press using a desktop test press under conditions of a temperature of 90 ° C., a time of 10 seconds, and a pressure of 1 MPa. By calculating the ratio (R2) of the electrode mixture layer remaining adhered to the organic separator when each electrode was peeled off from this laminate at a speed of 50 mm / sec and an angle of 90 °, the porous film The adhesion of the attached electrode to the organic separator was evaluated. It shows that it is excellent in adhesiveness, so that this ratio is high.
(R2) = (Area of electrode mixture layer with porous film remaining adhered to organic separator / area of electrode mixture layer used) × 100
(Evaluation criteria)
A: 50% or more B: 30% or more and less than 50% C: 10% or more and less than 30% D: Less than 10%

[Evaluation test of rate characteristics of secondary battery]
After the laminate-type lithium ion secondary battery was allowed to stand for 24 hours, a charge / discharge operation of charging to 4.2 V and discharging to 3.0 V at a charge / discharge rate of 25 ° C. and 0.1 C was performed. Thereafter, the battery is charged to 4.2 V at a charge rate of 0.1 C at 25 ° C., discharged to 3.0 V at a discharge rate of 1.0 C, and discharged to 3.0 V at a discharge rate of 3.0 C. Each charge / discharge cycle was performed. The ratio of the battery capacity at 3.0C to the battery capacity at 1.0C was calculated as a percentage to obtain the charge / discharge rate characteristics, and was judged according to the following criteria. The higher this value, the smaller the internal resistance, indicating that high speed charge / discharge is possible.
(Evaluation criteria)
A: 70% or more B: 65% or more and less than 70% C: 60% or more and less than 65% D: Less than 60%

[Evaluation test of high-temperature cycle characteristics of secondary batteries]
After the laminate-type lithium ion secondary battery was allowed to stand for 24 hours, charge / discharge operation was performed at a charge / discharge rate of 25 ° C., 4.2 V, and 0.1 C, and the initial capacity C0 was measured. Furthermore, in a 60 degreeC environment, it charged to 4.2V with the charging / discharging rate of 0.1C, charging / discharging discharged to 3.0V was repeated, and the capacity | capacitance C1 after 100 cycles was measured. The high-temperature cycle characteristics were evaluated by a capacity retention rate represented by ΔC = C1 / C0 × 100 (%). The higher this value, the lower the discharge capacity and the better the cycle characteristics.
(Evaluation criteria)
A: 80% or more B: 75% or more and less than 80% C: 70% or more and less than 75% D: Less than 70%

[Reliability test of secondary battery]
After the laminate-type lithium ion secondary battery was allowed to stand for 24 hours, a charge / discharge operation of charging to 4.2 V and discharging to 3.0 V was performed at a charge / discharge rate of 25 ° C. and 0.1 C. The battery was charged to 4.2 V at a charging rate of 0.1 C. This battery was placed in a thermostatic bath, heated to 150 ° C. at 5 ° C./min, and further left at 150 ° C. for 1 hour. Then, the presence or absence of a short circuit of each battery was examined. A battery that is not short-circuited is excellent in reliability.
(Evaluation criteria)
Good: No short circuit Bad: Short circuit

[Example 1]
(1-1. Production of seed polymer particles a)
In a reactor equipped with a stirrer, 0.08 part of sodium dodecyl sulfate, 0.23 part of ammonium persulfate and 100 parts of ion-exchanged water were added and mixed to obtain a mixture A, which was heated to 80 ° C.
On the other hand, 93.8 parts of butyl acrylate, 2.0 parts of methacrylic acid, 2.0 parts of acrylonitrile, 1.0 part of allyl glycidyl ether, 1.2 parts of N-methylol acrylamide, sodium dodecyl sulfate 0. 1 part and 100 parts of ion-exchanged water were mixed to prepare a dispersion of monomer mixture 1.
The dispersion of the monomer mixture 1 was continuously added to the mixture A for 4 hours and polymerized. The temperature of the reaction system during the continuous addition of the dispersion of the monomer mixture 1 was maintained at 80 ° C. to carry out the reaction. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours.
Thereby, an aqueous dispersion of seed polymer particles a having a number average particle diameter of 284 nm was obtained.

(1-2. Production of seed polymer particle A)
Next, in a reactor equipped with a stirrer, 20 parts by weight of the aqueous dispersion of the seed polymer particles a obtained in the step (1-1) based on the solid content (that is, based on the weight of the seed polymer particles a). 100 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. “Light Ester EG”) as a body, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and t-butylperoxy-2-ethylhexanoate as a polymerization initiator 4.0 parts of NOF (“Perbutyl O” manufactured by NOF Corporation) and 200 parts of ion-exchanged water are added and stirred for 12 hours at 35 ° C., so that the monomer and the polymerization initiator are completely added to the seed polymer particles a. Absorbed. Thereafter, this was polymerized at 90 ° C. for 5 hours. Thereafter, steam was introduced to remove unreacted monomers and initiator decomposition products.
Thereby, an aqueous dispersion of seed polymer particles A having a number average particle diameter of 516 nm was obtained.

(1-3. Production of non-conductive particles A)
Next, in a reactor equipped with a stirrer, 87.0 parts of methyl methacrylate and 13.0 parts of butyl acrylate as monomers, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and polymerization initiator 4.0 parts of t-butyl peroxy-2-ethylhexanoate (“Perbutyl O” manufactured by NOF Corporation) and 200 parts of ion-exchanged water were added and stirred until coarse droplets could not be visually confirmed. This was subjected to high-speed shearing stirring for 1 minute at a rotational speed of 15,000 rpm using an in-line type emulsifying disperser (“Cabitron” manufactured by Taiheiyo Kiko Co., Ltd.) to obtain a dispersion of a polymerizable monomer composition. Into this, 100 parts of the aqueous dispersion of the seed polymer particles A obtained in the step (1-2) is added on a solid basis (that is, based on the weight of the seed polymer particles A), and stirred at 35 ° C. for 12 hours. The seed polymer particles A were completely absorbed with the monomer and the polymerization initiator. Thereafter, this was polymerized at 90 ° C. for 5 hours. Thereafter, steam was introduced to remove unreacted monomers and initiator decomposition products.
As a result, an aqueous dispersion of non-conductive particles A having a core-shell structure with a number average particle diameter of 650 nm was obtained.

(1-4. Production of particulate polymer)
In a reactor equipped with a stirrer, 0.06 part of sodium dodecyl sulfate, 0.23 part of ammonium persulfate and 100 parts of ion-exchanged water were added and mixed to obtain a mixture B, which was heated to 80 ° C.
Meanwhile, in another container, 66.8 parts of butyl acrylate, 17.0 parts of ethyl acrylate, 2.0 parts of methacrylic acid, 12.0 parts of acrylonitrile, 1.0 part of allyl glycidyl ether, 1. 2 parts of sodium dodecyl sulfate 0.1 part and 100 parts of ion-exchanged water were mixed to prepare a dispersion of monomer mixture 2.
This dispersion of the monomer mixture 2 was continuously added and polymerized in the mixture B obtained above over 4 hours. The temperature of the reaction system during the continuous addition of the dispersion of the monomer mixture 2 was maintained at 80 ° C. to carry out the reaction. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours. Thereby, an aqueous dispersion of a particulate polymer was obtained.
The obtained aqueous dispersion of the particulate polymer was cooled to 25 ° C., ammonia water was added thereto to adjust the pH to 7, and then steam was introduced to remove unreacted monomers. Thereafter, filtration was performed with a 200 mesh (pore diameter: about 77 μm) stainless steel wire mesh while further adjusting the solid content concentration with ion-exchanged water. As a result, an aqueous dispersion of a particulate polymer having an average particle diameter of 370 nm and a solid content concentration of 40% was obtained.

(1-5. Production of slurry for porous membrane)
An aqueous dispersion of non-conductive particles A obtained in the step (1-3), an aqueous dispersion of the particulate polymer obtained in the step (1-4), and carboxymethyl cellulose (manufactured by Daicel Chemical Industries, Ltd.) Daicel 1220 ") and a wetting agent (" SN Wet 980 "manufactured by San Nopco Co., Ltd.) are mixed in water so that the solid content weight ratio is 82: 12: 5: 1. A membrane slurry was obtained.

(1-6. Production of secondary battery separator (separator with porous membrane))
A single-layer polyethylene separator (thickness 16 μm) produced by a wet method was prepared as an organic separator. The slurry for the secondary battery obtained in the step (1-5) was applied to one surface of the organic separator so that the thickness after drying was 4 μm to obtain a slurry layer. Thereafter, the slurry layer was dried at 50 ° C. for 10 minutes to form a porous film. Subsequently, a porous film was similarly formed on the other surface of the organic separator, and a separator with a porous film having a porous film on both surfaces was obtained.

(1-7. Production of positive electrode)
95 parts of LiCoO ₂ is prepared as a positive electrode active material, and PVDF (polyvinylidene fluoride; “KF-1100” manufactured by Kureha Chemical Co., Ltd.) as a positive electrode binder is 3 parts in terms of solid content. In addition, 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to obtain a slurry for positive electrode. This positive electrode slurry was applied to one side of an aluminum foil having a thickness of 18 μm and dried at 120 ° C. for 3 hours. Then, it roll-pressed and the positive electrode which has a positive mix layer whose total thickness is 100 micrometers was obtained.

(1-8. Production of negative electrode)
98 parts of graphite having a particle size of 20 μm and a specific surface area of 4.2 m ² / g were prepared as the negative electrode active material. This and 1 part of SBR (styrene-butadiene rubber having a glass transition point of −10 ° C.) as a binder for the negative electrode were mixed in a solid content conversion amount. 1.0 parts of carboxymethylcellulose was further added to this mixture, and these were mixed with a planetary mixer to prepare a slurry for a negative electrode. This negative electrode slurry was applied to one side of a 18 μm thick copper foil and dried at 120 ° C. for 3 hours. Thereafter, roll pressing was performed to obtain a negative electrode having a negative electrode mixture layer with a total thickness of 100 μm.

(1-9. Production of secondary battery)
The positive electrode obtained in the step (1-7) was cut into a width of 40 mm and a length of 40 mm to obtain a square positive electrode. The negative electrode obtained in the step (1-8) was cut into a width of 42 mm and a length of 42 mm to obtain a square negative electrode. Moreover, the separator with a porous film obtained in the step (1-6) was cut into a width of 46 mm and a length of 46 mm to obtain a square separator with a porous film.

  On the surface of the square positive electrode on the positive electrode mixture layer side, a square separator with a porous film was disposed. Furthermore, a square negative electrode was arranged on the separator with a porous film so that the surface on the negative electrode mixture layer side was opposed to the separator with a porous film. This laminate was heat-pressed with a desktop test press under the conditions of a temperature of 90 ° C., a time of 10 seconds, and a pressure of 1 MPa to obtain a laminate in which the separator was bonded and integrated with the positive electrode and the negative electrode.

The above laminate was placed on an aluminum wrapping material. The electrolyte was poured into the aluminum packaging material so that no air remained. Furthermore, by performing heat sealing at 150 ° C., the opening of the aluminum packaging material was sealed to manufacture a laminate type lithium ion secondary battery. Incidentally, the electrolyte used was a VC (vinylene carbonate) to LiPF ₆ solution with a concentration of 1.0M was added 2% by volume. The solvent of the LiPF ₆ solution is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC / DEC = 1/2 volume ratio).

(1-10. Evaluation)
About the obtained separator with a porous film, the heat shrink test, the blocking test, the powder fall test, and the adhesion test to an electrode were done. Moreover, the evaluation test of the rate characteristic of the obtained secondary battery, a high temperature cycling characteristic, and reliability was done.

[Example 2]
In the step (1-3), a separator with a porous membrane was prepared in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 84.0 parts and the amount of butyl acrylate was changed to 16.0 parts. A secondary battery was manufactured and evaluated.

[Example 3]
In the step (1-4), the amount of butyl acrylate was changed to 93.8 parts, ethyl acrylate was not used, and the amount of acrylonitrile was changed to 2.0 parts. A separator with a porous membrane and a secondary battery were manufactured and evaluated.

[Example 4]
In the step (1-5), a separator with a porous membrane and a secondary battery were produced and evaluated in the same manner as in Example 1 except that polyvinylpyrrolidone was used instead of carboxymethylcellulose as the water-soluble polymer.

[Example 5]
In the step (1-3), a separator with a porous membrane was prepared in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 82.0 parts and the amount of butyl acrylate was changed to 18.0 parts. A secondary battery was manufactured and evaluated.

[Example 6]
In the step (1-3), the amount of methyl methacrylate was changed to 100.0 parts, and a separator with a porous membrane and a secondary battery were prepared in the same manner as in Example 1 except that butyl acrylate was not used. Manufactured and evaluated.

[Example 7]
In the step (1-4), the amount of butyl acrylate was changed to 22.8 parts, and in the same manner as in Example 1 except that 61.0 parts of methyl methacrylate was used instead of ethyl acrylate, the porosity was changed. A membrane separator and a secondary battery were manufactured and evaluated.

[Example 8]
In the step (1-5), except that saponified polyvinyl alcohol (“NH-26” manufactured by Nippon Gosei Kagaku) was used instead of carboxymethylcellulose as the water-soluble polymer, the same as in Example 1, A separator with a porous membrane and a secondary battery were manufactured and evaluated.

[Example 9]
(9-1. Production of positive electrode with porous film)
On the surface of the positive electrode mixture layer side of the positive electrode obtained in the step (1-7) of Example 1, the thickness of the porous film slurry obtained in the step (1-5) of Example 1 after drying is 4 μm. This was applied to obtain a slurry layer. At this time, the slurry for the porous film was applied so as to completely cover the positive electrode mixture layer. Thereafter, the slurry layer was dried at 50 ° C. for 10 minutes to form a porous film, whereby a positive electrode with a porous film was obtained. The obtained positive electrode with a porous film had a layer structure of (porous film) / (positive electrode mixture layer) / (aluminum foil).

(9-2. Production of negative electrode with porous film)
On the surface of the negative electrode mixture layer side of the negative electrode obtained in the step (1-8) of Example 1, the slurry for the porous film obtained in the step (1-5) of Example 1 has a thickness after drying of 4 μm. This was applied to obtain a slurry layer. At this time, the slurry for the porous film was applied so as to completely cover the negative electrode mixture layer. Thereafter, the slurry layer was dried at 50 ° C. for 10 minutes to form a porous film, and a negative electrode with a porous film was obtained. The obtained negative electrode with a porous film had a layer structure of (porous film) / (negative electrode mixture layer) / (copper foil).

(9-3. Manufacture and evaluation of secondary batteries, etc.)
I. ~ Iv. A secondary battery was manufactured in the same manner as in step (1-9) of Example 1 except that the above was changed.
i. Instead of the separator with a porous membrane, an organic separator (a single-layer polyethylene separator manufactured by a wet method, thickness 16 μm) was used as it was.
ii. Instead of the positive electrode, the positive electrode with a porous film obtained in the step (9-1) was used.
iii. Instead of the negative electrode, the negative electrode with a porous film obtained in the step (9-2) was used.
iv. The organic separator was arrange | positioned on the surface at the side of the porous membrane layer of the positive electrode with a porous membrane. Furthermore, the negative electrode with a porous film was arrange | positioned on an organic separator so that the surface by the side of a porous film layer might oppose an organic separator.

  The obtained secondary battery and other materials were evaluated in the same manner as in Example 1. However, the thermal contraction test of the separator was not performed, and the reliability test of the electrode with a porous film was performed instead. The result of the reliability test was “good”.

[Example 10]
In the step (1-3), a porous membrane was prepared in the same manner as in Example 1 except that 90.0 parts of styrene and 10.0 parts of 1,3-butadiene were used instead of methyl methacrylate and butyl acrylate. A separator and a secondary battery were manufactured and evaluated.

[Example 11]
In the step (1-4), a porous membrane was prepared in the same manner as in Example 1 except that 21.8 parts of styrene and 62.0 parts of 1,3-butadiene were used instead of butyl acrylate and ethyl acrylate. A separator and a secondary battery were manufactured and evaluated.

[Example 12]
In the step (1-3), the amount of the aqueous dispersion of the seed polymer particles A was changed to 357.0 parts on the basis of the solid content (that is, based on the weight of the seed polymer particles A). Thus, a separator with a porous membrane and a secondary battery were produced and evaluated.

[Example 13]
In the step (1-3), the amount of the aqueous dispersion of the seed polymer particles A was changed to 27.0 parts on the basis of the solid content (that is, based on the weight of the seed polymer particles A). Thus, a separator with a porous membrane and a secondary battery were produced and evaluated.

[Example 14]
In the step (1-2), a porous membrane was prepared in the same manner as in Example 1 except that 75 parts of ethylene glycol dimethacrylate and 25 parts of methyl methacrylate were used as monomers instead of 100 parts of ethylene glycol dimethacrylate. A separator and a secondary battery were manufactured and evaluated.

[Example 15]
In the step (1-2), a porous membrane was prepared in the same manner as in Example 1 except that 50 parts of ethylene glycol dimethacrylate and 50 parts of methyl methacrylate were used as monomers instead of 100 parts of ethylene glycol dimethacrylate. A separator and a secondary battery were manufactured and evaluated.

[Example 16]
In the step (1-3), a separator with a porous membrane was prepared in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 92.0 parts and the amount of butyl acrylate was changed to 8.0 parts. A secondary battery was manufactured and evaluated.

[Example 17]
In the step (1-4), the amount of butyl acrylate was changed to 51.4 parts, and the same procedure as in Example 1 except that 32.4 parts of methyl methacrylate was used instead of ethyl acrylate. A membrane separator and a secondary battery were manufactured and evaluated.

[Example 18]
In step (1-4), the amount of butyl acrylate was changed to 39.0 parts, and 44.8 parts of methyl methacrylate was used instead of ethyl acrylate. A membrane separator and a secondary battery were manufactured and evaluated.

[Example 19]
In the step (1-3), a separator with a porous film was used in the same manner as in Example 1 except that 37.0 parts of methyl methacrylate and 50.0 parts of styrene were used instead of 87.0 parts of methyl methacrylate. A secondary battery was manufactured and evaluated.

[Example 20]
In step (1-4), instead of 66.8 parts of butyl acrylate and 17.0 parts of ethyl acrylate, 39.9 parts of butyl acrylate, 10.1 parts of ethyl acrylate, 2.8 parts of styrene and 1 A separator with a porous membrane and a secondary battery were produced and evaluated in the same manner as in Example 1 except that 31.0 parts of 1,3-butadiene was used.

[Comparative Example 1]
In the step (1-3), a separator with a porous membrane was prepared in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 80.0 parts and the amount of butyl acrylate was changed to 20.0 parts. A secondary battery was manufactured and evaluated.

[Comparative Example 2]
In the step (1-3), the porous membrane was changed in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 70.0 parts and 30.0 parts of methacrylic acid was used instead of butyl acrylate. A separator and a secondary battery were manufactured and evaluated.

[Comparative Example 3]
In the step (1-2), a separator with a porous membrane and a secondary battery were produced and evaluated in the same manner as in Example 1 except that 100 parts of styrene was used instead of ethylene glycol dimethacrylate.

[result]
Tables 1 to 8 show the configurations of Examples and Comparative Examples, and Tables 9 to 16 show the results of Examples and Comparative Examples.
In the table, the meaning of each abbreviation is as follows.
EGDMA: ethylene glycol dimethacrylate ST: styrene LASNa: sodium dodecylbenzenesulfonate PBO: t-butylperoxy-2-ethylhexanoate MMA: methyl methacrylate BA: butyl acrylate MAA: methacrylic acid BD: 1,3- Butadiene EA: Ethyl acrylate AN: Acrylonitrile NMA: N-methylolacrylamide AGE: Allyl glycidyl ether SDS Na: Sodium dodecyl sulfate ASP: Ammonium persulfate Shell thickness: Shell thickness relative to the number average particle diameter of non-conductive particles Ratio (Meth) acrylate ratio: Ratio of (Meth) acrylate units Sepa: Separator

[Consideration]
As can be seen from the above table, in the Examples, good results were obtained in any of the adhesion test, the blocking test, the powder falling test, and the heat shrink test of the separator. From this, according to the present invention, the porosity for a secondary battery is excellent in adhesiveness and blocking resistance, hardly causes powder falling, and can suppress the shrinkage of the separator when the separator is configured in combination with the organic separator. It was confirmed that a film could be realized.

Claims (10)

Non-conductive particles, a porous membrane for including rechargeable batteries particulate polymer and a water-soluble polymer,
The non-conductive particles are polymer particles having a core-shell structure;
The softening start point or decomposition point of the core part of the non-conductive particles is 175 ° C. or higher,
The shell portion of the non-conductive particles have a softening starting point 85 ° C. to 145 ° C.,
The amount of the particulate polymer is 3 parts by weight or more with respect to 100 parts by weight of the non-conductive particles,
The amount of the water-soluble polymer is 0.03 parts by weight or more with respect to 100 parts by weight of the non-conductive particles,
The content of the non-conductive particles, Ru der 70 wt% or more, the secondary battery porous membrane in the porous film for a secondary battery. The glass transition point of the particulate polymer is −80 ° C. to 60 ° C.,
The porous membrane for a secondary battery according to claim 1, wherein a softening start point of the water-soluble polymer is 85 ° C or higher.   The porous membrane for a secondary battery according to claim 1 or 2, wherein the shell part of the non-conductive particles and the particulate polymer contain 50% by weight or more of (meth) acrylate units.   The secondary battery according to claim 1, wherein the shell portion of the nonconductive particles has a thickness of 3% to 18% with respect to the number average particle diameter of the nonconductive particles. Porous membrane.   The porous membrane for a secondary battery according to any one of claims 1 to 4, wherein the number average particle diameter of the non-conductive particles is 100 nm to 1500 nm. A method for producing a porous membrane for a secondary battery according to any one of claims 1 to 5,
The non-conductive particles, the particulate polymer, the water-soluble polymer and the medium are mixed to obtain a slurry for a porous film,
Applying the slurry for porous film on a substrate to obtain a slurry layer,
The manufacturing method of the porous film for secondary batteries including drying the said slurry layer. The medium is an aqueous medium;
The manufacturing method of the porous film for secondary batteries of Claim 6 whose said slurry for porous films is an aqueous dispersion. Current collector,
An electrode mixture layer that includes an electrode active material and an electrode mixture layer binder, and is attached to the current collector; and
The electrode for secondary batteries provided with the porous film as described in any one of Claims 1-5 formed on the said electrode mixture layer. The separator for secondary batteries provided with the organic membrane and the porous film as described in any one of Claims 1-5 formed on the said organic separator. A secondary battery including a positive electrode, a negative electrode, a separator and an electrolyte solution,
A secondary battery in which at least one of the positive electrode, the negative electrode, and the separator includes the porous film according to claim 1.