JP6665857B2 - Composition for non-aqueous electrolyte secondary battery electrode mixture layer, method for producing the same, and use thereof - Google Patents

Description

  The present invention uses a composition for a non-aqueous electrolyte secondary battery electrode mixture layer and a method for producing the same, which can be used for a lithium ion secondary battery and the like, and using the composition for a non-aqueous electrolyte secondary battery electrode mixture layer. The present invention relates to a nonaqueous electrolyte secondary battery electrode and a nonaqueous electrolyte secondary battery obtained.

  As the non-aqueous electrolyte secondary battery, for example, a lithium ion secondary battery is well known. Lithium-ion secondary batteries are superior in energy density, output density, charge / discharge cycle characteristics, etc., compared to other secondary batteries such as lead-acid batteries. It is used in terminals and contributes to downsizing, lightening and high performance of terminals. On the other hand, as a secondary battery for an electric vehicle or a hybrid vehicle (on-board secondary battery), sufficient performance has not yet been achieved in terms of output, charging time, and the like. For this reason, studies are being made to improve the charge / discharge characteristics (high-rate characteristics) at high current densities with the aim of increasing the output of the nonaqueous electrolyte secondary battery and shortening the charging time. Similarly, since high durability is required for in-vehicle applications, compatibility with cycle characteristics is also required.

A non-aqueous electrolyte secondary battery includes a pair of electrodes arranged via a separator, and a non-aqueous electrolyte solution. The electrode comprises a current collector and a mixture layer formed on the surface of the current collector. The mixture layer is formed by coating a composition (slurry) for an electrode mixture layer containing an active material and a binder on the current collector. Formed by drying and drying.
On the other hand, in recent years, there has been an increasing demand for an aqueous mixture of the composition for an electrode mixture layer from the viewpoint of environmental protection and cost reduction. In this regard, in the lithium ion secondary battery, an aqueous material using styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder for a composition for an electrode mixture layer for a negative electrode using a carbon-based material such as graphite as an active material. Binder is used. However, further improvement is desired in order to cope with advanced high-rate characteristics and cycle characteristics required for in-vehicle applications. As for the positive electrode of a lithium ion secondary battery, a solvent-based binder such as polyvinylidene fluoride (PVDF) using an organic solvent such as N-methyl-2-pyrrolidone (NMP) is mainly used, and the above requirements are sufficiently satisfied. No aqueous binder has been proposed yet.

The components constituting the lithium ion secondary battery electrode include active materials such as graphite and hard carbon (HC), and carbon-based materials such as conductive aids such as Ketjen black (KC) and acetylene black (AB). Often used. In general, these carbon-based materials have poor wettability to an aqueous medium, and in order to obtain a composition for an electrode mixture layer having excellent uniformity and dispersion stability, an aqueous-based material having an excellent dispersion stabilizing effect of the carbon-based material is required. A binder is desired. As an aqueous binder applicable to a lithium ion secondary battery electrode, as shown below, an aqueous binder containing crosslinked polyacrylic acid has been proposed.
Patent Document 1 discloses an acrylic acid polymer crosslinked with polyalkenyl ether as a binder for forming a negative electrode coating film of a lithium ion secondary battery. Patent Document 2 discloses that by using a polymer obtained by crosslinking polyacrylic acid with a specific crosslinking agent as a binder, the electrode structure is not destroyed even when an active material containing silicon is used. It is described that an excellent capacity retention ratio can be obtained.

JP 2000-294247 A International Publication No. WO 2014/065407

An example of Patent Document 1 discloses a binder composition containing an acrylic acid polymer crosslinked with a polyalkenyl polyether. However, the binder composition containing the acrylic acid polymer has a high viscosity, and it is difficult to ensure uniformity when kneading and preparing a mixture layer composition by mixing with an active material or the like. There was a possibility that this would occur. Further, in the detailed description of the invention of Patent Document 1, when the composition ratio of the acrylic acid polymer in the binder exceeds 95% by weight, the surface of the particles of the carbon material is coated, and the conductivity is reduced. And has the problem of inhibiting the transfer of lithium ions.
An example of Patent Document 2 discloses a binder composed of cross-linked polyacrylic acid having different types of cross-linking agents and different amounts of cross-linking agents, and a 1 wt% slurry of the cross-linked polyacrylic acid at 0.6 rpm or 60 rpm is used. The viscosity is described ([Table 3] and others). However, the binder composition containing a crosslinked polyacrylic acid specifically having a viscosity value of 60 rpm has a low viscosity, and there is a concern about dispersion stability and binding properties of an active material and the like. . On the other hand, the binder composition containing a crosslinked polyacrylic acid specifically having a viscosity value of 0.6 rpm has a high viscosity, and the uniformity in kneading and preparing the composition for a mixture layer is reduced. Therefore, there is a possibility that the electrode characteristics may be adversely affected.
Further, neither of Patent Documents 1 and 2 disclose a high-rate characteristic.

  The present invention has been made in view of such circumstances, and a non-aqueous electrolyte secondary battery containing an aqueous binder that can satisfy both electrode characteristics such as high-rate characteristics and durability (cycle characteristics). An object of the present invention is to provide a composition for an electrode mixture layer and a method for producing the same. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery obtained by using the composition for an aqueous electrode mixture layer.

Generally, in order to realize high high-rate characteristics, it is desirable that the amount of a binder serving as a resistance component be as small as possible. Therefore, it is possible to stably disperse the active material and the conductive auxiliary agent even in a small amount, and the binding force between the active materials and between the active material and the current collector is large (as a result, the mixture layer and the current collector may be separated). Is desired), and a binder which is excellent in durability of the obtained electrode is desired.
Further, the binder is required to be one that does not hinder the intrusion and escape of lithium ions even when present on the active material surface. That is, a binder which has a low desolvation effect of lithium ions and excellent lithium ion conductivity and thus has a small resistance (= interfacial resistance) due to penetration of lithium ions into the active material or escape from the active material is preferable. .

  The present inventors have conducted intensive studies to solve the above-described problems, and as a result, have found that a 0.5% by weight aqueous dispersion of an ethylenically unsaturated carboxylic acid monomer having a specific viscosity range has a crosslinked polymer and a salt thereof. It has been found that a binder containing the compound exhibits excellent binding properties even in a small amount, so that high-rate characteristics can be improved. In addition, it has been found that the binder is effective in improving the durability (cycle characteristics) of the electrode because the binder has excellent binding properties. Furthermore, since the composition for a mixture layer containing the above binder has a viscosity suitable for forming an electrode, it is possible to obtain a non-aqueous electrolyte secondary battery electrode having a uniform mixture layer and good electrode characteristics. Was. The present invention has been completed based on these findings.

The present invention is as follows.
[1] An active material, a composition for a non-aqueous electrolyte secondary battery electrode mixture layer containing water and a binder,
The binder contains a crosslinked polymer of a monomer component containing an ethylenically unsaturated carboxylic acid monomer and a salt thereof,
The viscosity of a 0.5% by weight aqueous dispersion of the crosslinked polymer at a degree of neutralization of 90 mol% is 5,000 to 40,000 mPa · s,
The composition for a non-aqueous electrolyte secondary battery electrode mixture layer, wherein the content of the crosslinked polymer and its salt is 0.5 to 5.0% by weight based on the active material.
[2] The cross-linked polymer is cross-linked by a cross-linkable monomer, and the amount of the cross-linkable monomer to be used is 0.05 to less than the total amount of monomers other than the cross-linkable monomer. The composition for an electrode mixture layer for a nonaqueous electrolyte secondary battery according to the above [1], which is 1.0 mol%.
[3] The composition for an electrode mixture layer of a nonaqueous electrolyte secondary battery according to the above [1] or [2], wherein the crosslinkable monomer has both a (meth) acryloyl group and an alkenyl group. .
[4] The composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to any of the above [1] to [3], wherein the degree of neutralization of the crosslinked polymer is 20 to 100 mol%.
[5] A method for producing a composition for a non-aqueous electrolyte secondary battery electrode mixture layer,
A monomer component containing an ethylenically unsaturated carboxylic acid monomer and a crosslinkable monomer is subjected to precipitation polymerization in an aqueous medium, and the viscosity of a 0.5% by weight aqueous dispersion at a degree of neutralization of 90 mol% is 5, After obtaining a crosslinked polymer of 000 to 40,000 mPa · s,
A method for producing a composition for a non-aqueous electrolyte secondary battery electrode mixture layer by mixing with an active material and water.
[6] A non-aqueous electrolyte secondary battery provided with a mixture layer formed on the surface of the current collector from the composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to any one of [1] to [4] above. Next battery electrode.
[1] A non-aqueous electrolyte secondary battery including the non-aqueous electrolyte secondary battery electrode according to [6], a separator, and a non-aqueous electrolyte solution.

  The binder used in the composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention exhibits excellent binding properties even in a small amount. For this reason, it becomes possible to reduce the binder content in the composition for a mixture layer, and it is possible to obtain an electrode having high high-rate characteristics and excellent durability (cycle characteristics). In addition, since the composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention has a viscosity suitable for electrode production, the non-aqueous electrolyte secondary battery electrode having a uniform mixture layer and good electrode characteristics. Can be obtained.

  Hereinafter, the present invention will be described in detail. In the present specification, “(meth) acryl” means acryl and / or methacryl, and “(meth) acrylate” means acrylate and / or methacrylate. Further, “(meth) acryloyl group” means an acryloyl group and / or a methacryloyl group.

The composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention is a binder containing a crosslinked polymer of a monomer component containing an ethylenically unsaturated carboxylic acid monomer and a salt thereof, an active material, and water. It contains. The above-mentioned composition may be in a slurry state that can be applied to the current collector, or may be prepared as a wet powder state so as to be able to cope with press working on the surface of the current collector. By forming a mixture layer formed from the above composition on the surface of a current collector such as a copper foil or an aluminum foil, the nonaqueous electrolyte secondary battery electrode of the present invention is obtained. The composition for a secondary battery electrode mixture layer and a method for producing the same, and the components of a non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery obtained using the composition will be described in detail. .

<Binder>
The binder of the present invention contains a crosslinked polymer of a monomer component containing an ethylenically unsaturated carboxylic acid monomer and a salt thereof. Specific compounds of the above-mentioned ethylenically unsaturated carboxylic acid monomer include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, monobutyl itaconate, monobutyl maleate, and cyclohexanedicarboxylic acid. Examples thereof include a vinyl monomer having a carboxyl group such as an acid or a (partial) alkali neutralized product thereof. One of these may be used alone, or two or more may be used in combination. You may. Among the above, in the point that the primary chain length of the obtained polymer is long and the binding power of the binder is good, carbon such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride and fumaric acid is used. Several to five ethylenically unsaturated carboxylic acid monomers and salts thereof are preferred, and acrylic acid is more preferred.
Examples of the salt include alkali metal salts such as lithium, sodium and potassium; alkaline earth metal salts such as calcium salt and barium salt; other metal salts such as magnesium salt and aluminum salt; ammonium salt and organic amine salt. Is mentioned. Among these, alkali metal salts and magnesium salts are preferred because they do not easily adversely affect battery characteristics, and alkali metal salts are more preferred.

  As long as the effects of the present invention are not impaired, it is also possible to use a non-crosslinkable monomer other than the above ethylenically unsaturated carboxylic acid monomer as a monomer component. Other non-crosslinkable monomers include (meth) acrylic acid alkyl ester, (meth) acrylic acid hydroxyalkyl ester, aromatic vinyl compound, amino group-containing vinyl compound, amide group-containing vinyl compound, sulfonic acid group-containing vinyl Compounds, vinyl compounds containing a polyoxyalkylene group, vinyl compounds containing an alkoxyl group, and the like. These compounds can be used alone or in combination of two or more.

  Specific examples of the above-mentioned alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and (meth) acryl. N-butyl acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-pentyl (meth) acrylate, isoamyl (meth) acrylate, (meth) acrylic (Meth) acrylic ester compounds having a linear, branched or cyclic alkyl group such as hexyl acid, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and octyl (meth) acrylate.

  Specific examples of the hydroxyalkyl (meth) acrylate include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and (meth) acrylate. And ε-caprolactone adduct of 2-hydroxyethyl acrylate.

  Examples of the aromatic vinyl compound include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, and 4-tert-butylstyrene. Tert-butoxystyrene, vinyltoluene, vinylnaphthalene, halogenated styrene, styrenesulfonic acid, α-methylstyrenesulfonic acid and the like.

  Examples of the amino group-containing vinyl compound include dimethylaminomethyl (meth) acrylate, diethylaminomethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, and (meth) acrylate. 2- (di-n-propylamino) ethyl acrylate, 2-dimethylaminopropyl (meth) acrylate, 2-diethylaminopropyl (meth) acrylate, 2- (di-n-propylamino) (meth) acrylate Propyl, 3-dimethylaminopropyl (meth) acrylate, 3-diethylaminopropyl (meth) acrylate, 3- (di-n-propylamino) propyl (meth) acrylate, and the like.

  Examples of the amide group-containing vinyl compound include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-isopropylacrylamide, and Nt-butylacrylamide. Can be

  Examples of the sulfonic acid group-containing vinyl compound include methallyl sulfonic acid and (meth) acrylamido-2-methyl-2-propanesulfonic acid.

  Examples of the polyoxyalkylene group-containing vinyl compound include a (meth) acrylate ester of an alcohol having a polyoxyethylene group and / or a polyoxypropylene group.

  Examples of the alkoxyl group-containing vinyl compound include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (n-propoxy) ethyl (meth) acrylate, and 2- (n-propoxy) ethyl (meth) acrylate. (N-butoxy) ethyl, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 2- (n-propoxy) propyl (meth) acrylate, 2- (n) (meth) acrylate -Butoxy) propyl and the like.

  The proportion of the ethylenically unsaturated carboxylic acid monomer in the total amount of the non-crosslinkable monomer is preferably in the range of 50 to 100% by weight, more preferably in the range of 70 to 100% by weight, and more preferably in the range of 90 to 100% by weight. The range is more preferable, and the range of 95 to 100% by weight is more preferable. When the polymer has a carboxyl group, the electrode is excellent in desolvation effect of lithium ion and ion conductivity, so that an electrode having low resistance and excellent in high-rate characteristics can be obtained. When the proportion of the ethylenically unsaturated carboxylic acid monomer in the total amount of the non-crosslinkable monomer is 50% by weight or more, the effect of the carboxyl group can be sufficiently provided.

As the monomer component, a crosslinkable monomer other than the above non-crosslinkable monomer may be used. Examples of the crosslinkable monomer include a polyfunctional polymerizable monomer having two or more polymerizable unsaturated groups, and a monomer having a self-crosslinkable crosslinkable functional group such as a hydrolyzable silyl group. No.
The polyfunctional polymerizable monomer is a compound having two or more polymerizable functional groups such as a (meth) acryloyl group and an alkenyl group in a molecule, and includes a polyfunctional (meth) acrylate compound, a polyfunctional alkenyl compound, Compounds having both a (meth) acryloyl group and an alkenyl group are exemplified. One of these compounds may be used alone, or two or more thereof may be used in combination. Among them, polyfunctional alkenyl compounds and compounds having one or more alkenyl groups in the molecule, such as compounds having both (meth) acryloyl group and alkenyl group, are preferable in that a uniform crosslinked structure is easily obtained. Further, a compound having both a (meth) acryloyl group and an alkenyl group is more preferable since the reactivity is good and unreacted substances are hardly left. Further, when a compound having a plurality of allyl ether groups in the molecule and a compound having both (meth) acryloyl group and alkenyl group are used in combination as a crosslinkable monomer, the coating properties of the mixture layer composition and It is particularly preferable because the binding property and the bending resistance of the obtained electrode are more excellent.

  Examples of the polyfunctional (meth) acrylate compound include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and polypropylene glycol di ( Di (meth) acrylates of dihydric alcohols such as (meth) acrylate; trimethylolpropane tri (meth) acrylate, trimethylolpropane ethylene oxide modified tri (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tri ( Poly (meth) acrylates such as tri (meth) acrylate and tetra (meth) acrylate of trihydric or higher polyhydric alcohols such as meth) acrylate and pentaerythritol tetra (meth) acrylate. Mention may be made of the rate.

  Examples of the polyfunctional alkenyl compound include polyfunctional allyl ether compounds such as trimethylolpropane diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl saccharose; polyfunctional allyl compounds such as diallyl phthalate; divinyl Examples thereof include polyfunctional vinyl compounds such as benzene.

Examples of the compound having both the (meth) acryloyl group and the alkenyl group include allyl (meth) acrylate, isopropenyl (meth) acrylate, butenyl (meth) acrylate, pentenyl (meth) acrylate, and (meth) acrylic acid. 2- (2-vinyloxyethoxy) ethyl and the like can be mentioned.
Examples of other polyfunctional polymerizable monomers include bisamides such as methylene bisacrylamide and hydroxyethylene bisacrylamide.

  Specific examples of the monomer having a self-crosslinkable crosslinkable functional group include a hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth) acrylamide, N-methoxyalkyl (meth) acrylate, and the like. Is mentioned. These compounds can be used alone or in combination of two or more.

  The hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group. For example, vinylsilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane; silyl such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, and methyldimethoxysilylpropyl acrylate Group-containing acrylates; silyl group-containing methacrylates such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, and dimethylmethoxysilylpropyl methacrylate; trimethoxysilylpropyl vinyl ether and the like And silyl group-containing vinyl esters such as vinyl trimethoxysilylundecanoate.

The crosslinking degree of the crosslinked polymer of the present invention is relatively low. When the cross-linked polymer is cross-linked by a cross-linkable monomer, the amount of the cross-linkable monomer used is based on the total amount of monomers (non-cross-linkable monomers) other than the cross-linkable monomer. On the other hand, the content is preferably 0.05 to 1.0 mol%, more preferably 0.1 to 0.8 mol%. When the amount of the crosslinkable monomer used is in the above range, a binder having more excellent binding power can be obtained.
Here, when a crosslinkable monomer having both a (meth) acryloyl group and an alkenyl group is used as the crosslinkable monomer, the amount of the crosslinkable monomer used is 0.05 to 0.5 mol%. And more preferably 0.2 to 0.5 mol%. When a polyfunctional allyl compound is used as the crosslinkable monomer, the amount of the crosslinkable monomer used is preferably 0.1 to 1.0 mol%, and 0.3 to 0.8 mol%. % Is more preferable.

The crosslinked polymer of the present invention may be crosslinked with a compound having two or more functional groups capable of reacting with a carboxyl group introduced into the polymer, in addition to the above-mentioned crosslinkable monomer.
Examples of the compound having two or more functional groups capable of reacting with a carboxyl group include the following compounds.
i) A compound that forms a covalent bond with a carboxyl group such as an epoxy group, a carbodiimide group, and an oxazoline group.
ii) A compound having Ca ²⁺ , Mg ^2+, etc. and forming an ionic bond with a carboxyl group.
iii) A compound having Zn ²⁺ , Al ³⁺ , Fe ^3+, etc., and forming a coordination bond with a carboxyl group.

When the degree of neutralization of the crosslinked polymer is adjusted to 90 mol% and a 0.5% by weight aqueous dispersion is obtained, its viscosity is in the range of 5,000 to 40,000 mPa · s. Here, the viscosity is measured by a B-type viscosity at a liquid temperature of 25 (rotor rotation speed: 20 rpm). The viscosity of the 0.5% by weight aqueous dispersion is preferably in the range of 10,000 to 40,000 mPa · s, more preferably in the range of 20,000 to 40,000 mPa · s, and still more preferably in the range of 30 to 40,000 mPa · s. 4,000 to 40,000 mPa · s. When the viscosity is less than 5,000 mPa · s, the dispersion stability of the active material is not sufficient, and an electrode having a uniform mixture layer may not be obtained. In addition, sufficient binding properties may not be obtained. On the other hand, when the viscosity exceeds 40,000 mPa · s, kneading at the time of preparing the composition for an electrode mixture layer may be difficult, and the uniformity of the obtained composition for a mixture layer may decrease. There is a possibility that battery characteristics may be adversely affected.
When the crosslinked polymer is unneutralized or has a degree of neutralization of less than 90 mol%, it is neutralized to a degree of neutralization of 90 mol% with an alkali compound in an aqueous medium to obtain a 0.5% by weight aqueous dispersion, and then the viscosity is reduced. Measure. When the degree of neutralization of the crosslinked polymer exceeds 90 mol%, the neutralization degree is adjusted to 90 mol% by maintaining the degree of neutralization or adding an appropriate acid such as sulfuric acid. The viscosity of the% aqueous dispersion is measured.

In general, the longer the length of the polymer chain (primary chain length) of the crosslinked polymer, the higher the toughness, the higher the binding ability, and the higher the viscosity of the aqueous dispersion. A crosslinked polymer (salt) obtained by subjecting a polymer having a long primary chain length to a relatively small amount of crosslinking exists in water as a microgel body swollen in water. As the degree of crosslinking increases, the viscosity of the aqueous dispersion also increases. However, when excessive crosslinking is performed, the water swellability of the crosslinked polymer is limited, and the viscosity of the aqueous dispersion tends to decrease. In the composition for an electrode mixture layer of the present invention, the interaction between the microgels exhibits a thickening effect and a dispersion stabilizing effect. The interaction of the microgel varies with the degree of water swelling of the microgel and the strength of the microgel, which are controlled by the degree of crosslinking of the crosslinked polymer. If the degree of crosslinking is too low, the strength of the microgel may be insufficient, and the dispersion stabilizing effect and the binding property may be insufficient. On the other hand, if the degree of crosslinking is too high, the swelling degree of the microgel may be insufficient, and the dispersion stabilizing effect and the binding property may be insufficient. That is, the crosslinked polymer is desirably a finely crosslinked polymer obtained by subjecting a polymer having a sufficiently long primary chain length to appropriate crosslinking.
As described above, although the degree of crosslinking of the crosslinked polymer of the present invention is relatively low, even a water dispersion having a low concentration of 0.5% by weight exhibits a viscosity of 5,000 mPa · s or more due to microgel packing. Therefore, it is presumed that the primary chain length is sufficiently long and the degree of crosslinking is appropriate. Since the binder comprising such a crosslinked polymer exhibits excellent binding properties, the amount of the binder used can be reduced, and the high-rate characteristics of the electrode can be improved.

  In the crosslinked polymer of the present invention, an acid group such as a carboxyl group derived from an ethylenically unsaturated carboxylic acid monomer is neutralized so as to have a degree of neutralization of 20 to 100 mol%, and used as a salt embodiment. Is preferred. The degree of neutralization is more preferably from 50 to 100 mol%, even more preferably from 60 to 95 mol%. When the degree of neutralization is 20 mol% or more, the water swelling property is good and the dispersion stabilizing effect is easily obtained, which is preferable.

The amount of the crosslinked polymer and its salt used in the composition for an electrode mixture layer of the present invention is 0.5 to 5.0% by weight based on the total amount of the active material. The use amount is preferably 1.0 to 5.0% by weight, more preferably 1.5 to 5.0% by weight, and further preferably 2.0 to 5.0% by weight. When the amount of the crosslinked polymer and its salt is less than 0.5% by weight, sufficient binding properties may not be obtained. Further, the dispersion stability of the active material or the like may be insufficient, and the uniformity of the formed mixture layer may decrease. On the other hand, when the use amount of the crosslinked polymer and its salt exceeds 5.0% by weight, the composition for the electrode mixture layer becomes high in viscosity, and the coatability to the current collector may be reduced. As a result, bumps and irregularities may occur in the obtained mixture layer, which may adversely affect the electrode characteristics. In addition, the interface resistance increases, and there is a concern that the high-rate characteristics may deteriorate.
If the amount of the crosslinked polymer and its salt is within the above range, a composition having excellent dispersion stability can be obtained, and a mixture layer having extremely high adhesion to the current collector can be obtained. As a result, the durability of the battery is improved. Furthermore, since the used amount is as small as 0.5 to 5.0% by weight based on the active material and the polymer has a carboxy anion, an electrode having low interface resistance and excellent high-rate characteristics can be obtained. .

<Method for producing crosslinked polymer and salt thereof>
The crosslinked polymer of the present invention can use a known polymerization method such as solution polymerization, precipitation polymerization, suspension polymerization, and inverse emulsion polymerization, but has a long primary chain length and is appropriately crosslinked. Precipitation polymerization is preferred because a polymer can be efficiently produced.
Precipitation polymerization is a method for producing a polymer by performing a polymerization reaction in a solvent that dissolves the unsaturated monomer as a raw material but does not substantially dissolve the produced polymer. As the polymerization proceeds, the polymer particles become larger due to aggregation and growth, and a dispersion of polymer particles in which primary particles of several tens nm to several hundreds of nm are aggregated to several μm to several tens μm is obtained. Dispersion stabilizers can also be used to control the particle size of the polymer. After the polymerization, the polymer particles may be separated from the solvent by subjecting the reaction solution to a treatment such as filtration or centrifugation.

In the case of precipitation polymerization, a solvent selected from water and various organic solvents can be used as the polymerization solvent in consideration of the type of the monomer to be used and the like. In order to obtain a polymer having a longer primary chain length, it is preferable to use a solvent having a small chain transfer constant.
As a specific polymerization solvent, when polymerizing an ethylenically unsaturated carboxylic acid monomer in an unneutralized state, benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane, n-heptane, and the like, and the like. Can be used alone or in combination of two or more.
In the case of polymerizing a (partially) neutralized product of an ethylenically unsaturated carboxylic acid monomer, a water-soluble solvent such as methanol, t-butyl alcohol, acetone and tetrahydrofuran may be used. More than one species can be used in combination. Alternatively, they may be used as a mixed solvent of these and water. In the present invention, the water-soluble solvent refers to a solvent having a solubility in water at 20 ° C. of more than 10 g / 100 ml.
Among these, a (partial) neutralized product of an ethylenically unsaturated carboxylic acid monomer is precipitated in an aqueous medium containing water and a water-soluble solvent because a polymer having excellent dispersion stability of the active material is obtained. Polymerization is preferred. At this time, by adjusting the amount of water according to the type and amount of the monomer used, it is possible to control the precipitation and aggregation of the polymer, and to stably complete the polymerization by ensuring the dispersion stability of the precipitated particles. it can. The proportion of the water-soluble solvent contained in the aqueous medium is preferably from 50 to 100% by weight, more preferably from 70 to 100% by weight, even more preferably from 90 to 100% by weight, based on the total amount of the aqueous medium.

  As the polymerization initiator, a known polymerization initiator such as an azo compound, an organic peroxide, or an inorganic peroxide can be used, but is not particularly limited. Use conditions can be adjusted by a known method such as heat initiation, redox initiation using a reducing agent in combination, UV initiation, etc., so that an appropriate amount of radicals is generated. In order to obtain a crosslinked polymer having a long primary chain length, it is preferable to set conditions so that the amount of generated radicals is reduced within a range where the production time is allowed.

  Examples of the azo compound include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (N-butyl-2-methylpropionamide), and 2- (tert-butylazo) -2. -Cyanopropane, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane) and the like, and one or more of these are used. be able to.

  Examples of the organic peroxide include 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane (trade name "Pertetra A" manufactured by NOF Corporation), 1,1-di (t- Hexylperoxy) cyclohexane (same as “perhexa HC”), 1,1-di (t-butylperoxy) cyclohexane (same as “perhexa C”), n-butyl-4,4-di (t-butylperoxy) Valerate (perhexa V), 2,2-di (t-butylperoxy) butane (perhexa22), t-butyl hydroperoxide (perbutyl H), cumene hydroperoxide (JP) Oil Company, trade name "Parkmill H"), 1,1,3,3-tetramethylbutyl hydroperoxide ("Perocta H"), t-butylcumyl peroxide ("" -Butyl C "), di-t-butyl peroxide (same as" perbutyl D "), di-t-hexyl peroxide (same as" perhexyl D "), di (3,5,5-trimethylhexanoyl) peroxide ( "Perloyl 355"), dilauroyl peroxide ("Perloyl L"), bis (4-t-butylcyclohexyl) peroxydicarbonate ("Perloyl TCP"), di-2-ethylhexyl peroxydicarbonate ( "Perloyl OPP"), di-sec-butyl peroxydicarbonate ("Perloyl SBP"), cumyl peroxy neodecanoate ("Parkmill ND"), 1,1,3,3-tetramethylbutyl Peroxyneodecanoate (same as “perocta ND”), t-hexylperoxyneodecanoate (Perhexyl ND), t-butylperoxy neodecanoate (perbutyl ND), t-butyl peroxyneoheptanoate (perbutyl NHP), t-hexylperoxypi Valate ("perhexyl PV"), t-butyl peroxypivalate ("perbutyl PV"), 2,5-dimethyl-2,5-di (2-ethylhexanoyl) hexane ("perhexa 250") 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (the same as “peroctyl O”), t-hexylperoxy-2-ethylhexanoate (the same as “perhexyl O”), t -Butylperoxy-2-ethylhexanoate (perbutyl O); t-butylperoxylaurate (perbutyl L); t-butyl Luperoxy-3,5,5-trimethylhexanoate ("Perbutyl 355"), t-hexylperoxyisopropyl monocarbonate ("Perhexyl I"), t-butyl peroxyisopropyl monocarbonate ("Perbutyl I") ), T-butyl peroxy-2-ethylhexyl monocarbonate ("Perbutyl E"), t-butyl peroxyacetate ("Perbutyl A"), t-hexyl peroxybenzoate ("Perhexyl Z") and t -Butyl peroxybenzoate (the same as "perbutyl Z"), and one or more of these can be used.

Examples of the inorganic peroxide include potassium persulfate, sodium persulfate, and ammonium persulfate.
In the case of redox initiation, sodium sulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ascorbic acid, sulfur dioxide (SO ₂ ), ferrous sulfate and the like can be used as a reducing agent.

  The preferred amount of the polymerization initiator to be used is 0.001 to 2 parts by weight, more preferably 0.005 to 1 part by weight, more preferably 0.005 to 1 part by weight, when the total amount of the monomer components used is 100 parts by weight. Is 0.01 to 0.1 part by weight. When the amount of the polymerization initiator used is 0.001 part or more, the polymerization reaction can be stably performed. When the amount is 2 parts or less, a polymer having a long primary chain length is easily obtained.

The concentration of the monomer component during polymerization is preferably higher from the viewpoint of obtaining a polymer having a longer primary chain length. However, if the concentration of the monomer component is too high, it is difficult to control the heat of polymerization, and the polymerization reaction may run away. Therefore, the monomer concentration at the start of the polymerization is usually in the range of about 2 to 30% by weight. The polymerization is carried out. The monomer concentration at the start of the polymerization is preferably 5 to 30% by weight, more preferably 15 to 30% by weight, and still more preferably 20 to 30% by weight.
The polymerization temperature is preferably from 0 to 100 ° C, more preferably from 20 to 80 ° C, depending on conditions such as the type and concentration of the monomer used. The polymerization temperature may be constant or may change during the polymerization reaction. The polymerization time is preferably 1 minute to 10 hours, more preferably 10 minutes to 5 hours, and even more preferably 30 minutes to 2 hours.

  The binder of the present invention comprises a crosslinked polymer of a monomer component containing the above-mentioned ethylenically unsaturated carboxylic acid monomer, a crosslinked polymer and a salt thereof. In addition, a styrene / butadiene-based latex (SBR) ), Other latex components such as acrylic latex and polyvinylidene fluoride-based latex. When other binder components are used in combination, the amount used is preferably 5% by weight or less, more preferably 2% by weight or less, further preferably 1% by weight or less based on the active material. . If the amount of the other binder component exceeds 5% by weight, the resistance increases, and the high-rate characteristics may be insufficient.

<Active material>
The mixture layer composition for a non-aqueous electrolyte secondary battery of the present invention contains the above-mentioned crosslinked polymer and a binder comprising the salt thereof, an active material, and water.
Among the above active materials, a lithium salt of a transition metal oxide is mainly used as a positive electrode active material, and for example, a layered rock salt type and a spinel type lithium-containing metal oxide can be used. Specific compounds of the layered rock salt type positive electrode active material include lithium cobaltate, lithium nickelate, and NCM {Li (Ni _x , Co _y , Mn _z ) called a ternary system, x + y + x = 1} and NCA {Li (Ni _1-ab Co _a Al _b )} and the like. In addition, examples of the spinel-type positive electrode active material include lithium manganate. In addition to oxides, phosphates, silicates, sulfur, and the like are used, and examples of the phosphates include olivine-type lithium iron phosphate. As the positive electrode active material, one of the above may be used alone, or two or more may be used in combination as a mixture or a composite.
When the layered rock salt-type positive electrode active material is dispersed in water, lithium ions on the surface of the active material are exchanged with hydrogen ions in the water, so that the dispersion exhibits alkalinity. For this reason, there is a possibility that aluminum foil (Al), which is a general positive electrode current collector material, may be corroded. In such a case, it is preferable to use an unneutralized or partially neutralized crosslinked polymer as a binder to neutralize alkalis eluted from the active material. The amount of the unneutralized or partially neutralized crosslinked polymer is used such that the amount of the unneutralized carboxyl group of the crosslinked polymer is equal to or more than the amount of the alkali eluted from the active material. Is preferred.

Since all positive electrode active materials have low electric conductivity, they are generally used by adding a conductive additive. Examples of the conductive auxiliary agent include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite fine powder, and carbon fibers. Of these, carbon black, carbon nanotubes, and carbon fibers are preferable in that excellent conductivity is easily obtained. Is preferred. As carbon black, Ketjen black and acetylene black are preferable. As the conductive auxiliary agent, one of the above-described conductive agents may be used alone, or two or more conductive auxiliary agents may be used in combination. The amount of the conductive auxiliary agent used is preferably 2 to 20% by weight, more preferably 2 to 10% by weight, based on the total amount of the active material, from the viewpoint of achieving both conductivity and energy density.
The positive electrode active material may be one whose surface is coated with a conductive carbon-based material.

On the other hand, examples of the negative electrode active material include a carbon-based material, a lithium metal, a lithium alloy, and a metal oxide, and one or more of these can be used in combination. Among these, natural graphite, artificial graphite, active materials composed of carbon-based materials such as hard carbon and soft carbon (hereinafter, also referred to as "carbon-based active material") are preferred, graphite such as natural graphite and artificial graphite, and Hard carbon is more preferred. In the case of graphite, spheroidized graphite is suitably used from the viewpoint of battery performance, and the preferable range of the particle size is 1 to 20 μm, and the more preferable range is 5 to 15 μm.
Further, in order to increase the energy density, it is also preferable to use a metal or a metal oxide such as silicon or tin which can store lithium as the negative electrode active material. Among them, silicon has a higher capacity than graphite, and an active material composed of silicon-based material such as silicon, silicon alloy, and silicon oxide such as silicon monoxide (SiO) (hereinafter also referred to as “silicon-based active material”). ) Can be used. However, the silicon-based active material has a high capacity, but has a large volume change due to charge and discharge. For this reason, it is preferable to use together with the carbon-based active material. In this case, if the blending amount of the silicon-based active material is large, the electrode material may be broken, and the cycle characteristics (durability) may be significantly reduced. From such a viewpoint, when the silicon-based active material is used in combination, the amount of use is preferably 60% by mass or less, more preferably 30% by mass or less based on the carbon-based active material.

  Since the carbon-based active material itself has good electric conductivity, it is not always necessary to add a conductive auxiliary. When a conductive additive is added for the purpose of further reducing the resistance, the amount of use is preferably 10% by weight or less, and more preferably 5% by weight or less based on the total amount of active materials from the viewpoint of energy density. Is more preferred.

When the composition for a non-aqueous electrolyte secondary battery electrode mixture layer is in a slurry state, the amount of the active material used is preferably in the range of 10 to 75% by weight, and more preferably 30 to 65% by weight based on the total amount of the composition. More preferably, it is within the range. When the amount of the active material used is 10% by weight or more, migration of a binder or the like can be suppressed, and it is advantageous in terms of the drying cost of the medium. On the other hand, if it is 75% by weight or less, the fluidity and coatability of the composition can be secured, and a uniform mixture layer can be formed.
When the composition for an electrode mixture layer is prepared in a wet powder state, the amount of the active material used is preferably in the range of 60 to 97% by weight, preferably 70 to 90% by weight, based on the total amount of the composition. More preferably, it is within the range.
Further, from the viewpoint of energy density, it is preferable that the amount of the non-volatile components other than the active material such as the binder and the conductive auxiliary agent is as small as possible as long as the necessary binding property and conductivity are secured.

<Water>
The composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention uses water as a medium. Further, for the purpose of adjusting the properties and drying properties of the composition, lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, tetrahydrofuran, and water-soluble organic solvents such as N-methylpyrrolidone. May be used as a mixed solvent. The proportion of water in the mixed medium is preferably at least 50% by weight, more preferably at least 70% by weight.
When the composition for an electrode mixture layer is made into a slurry state that can be applied, the content of the medium containing water in the entire composition is determined based on the applicability of the slurry, the energy cost required for drying, and the viewpoint of productivity. To 25 to 90% by weight, more preferably 35 to 70% by weight. In the case of a wet powder state that can be pressed, the content of the medium is preferably in the range of 3 to 40% by weight, more preferably 10 to 30% by weight, from the viewpoint of uniformity of the mixture layer after pressing. .

<Non-aqueous electrolyte secondary battery electrode mixture layer composition and production method thereof>
The composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention has the above-mentioned active material, water and a binder as essential components, and by mixing each component using a known means. can get. The mixing method of each component is not particularly limited, and a known method can be adopted.However, after dry-blending powder components such as crosslinked polymer particles as an active material, a conductive auxiliary agent and a binder, water is added. A method of mixing with a dispersing medium such as described above and dispersing and kneading is preferred.
When the composition for an electrode mixture layer is obtained in a slurry state, it is preferable to finish the slurry without poor dispersion or aggregation. As the mixing means, known mixers such as a planetary mixer, a thin-film whirl mixer and a self-revolving mixer can be used, but a thin-film whirl mixer is used because a good dispersion state can be obtained in a short time. It is preferable to carry out. When a thin-film swirling mixer is used, it is preferable to perform preliminary dispersion using a stirrer such as a disperser in advance.
The viscosity of the slurry is preferably in the range of 500 to 100,000 mPa · s, more preferably 1,000 to 50,000 mPa · s, as the B-type viscosity at 60 rpm.

  On the other hand, when the composition for an electrode mixture layer is obtained in a wet powder state, it is preferable to knead the mixture to a uniform state without concentration unevenness using a planetary mixer, a twin-screw kneader or the like.

<Electrode for non-aqueous electrolyte secondary battery>
The electrode for a non-aqueous electrolyte secondary battery of the present invention is provided with a mixture layer formed from the composition for an electrode mixture layer on the surface of a current collector such as copper or aluminum. The mixture layer is formed by applying the composition for an electrode mixture layer of the present invention to the surface of a current collector and then drying and removing a medium such as water. The method of applying the mixture layer composition is not particularly limited, and a known method such as a doctor blade method, a dip method, a roll coat method, a comma coat method, a curtain coat method, a gravure coat method, and an extrusion method is employed. be able to. Further, the drying can be performed by a known method such as hot air blowing, reduced pressure, (far) infrared ray, microwave irradiation, or the like.
Usually, the mixture layer obtained after drying is subjected to a compression treatment by a mold press, a roll press, or the like. By compressing, the active material and the binder are brought into close contact, and the strength of the mixture layer and the adhesion to the current collector can be improved. It is preferable to adjust the thickness of the mixture layer to about 30 to 80% before compression by compression, and the thickness of the mixture layer after compression is generally about 4 to 200 μm.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention will be described. A non-aqueous electrolyte secondary battery of the present invention includes the electrode for a non-aqueous electrolyte secondary battery according to the present invention, a separator, and a non-aqueous electrolyte solution.
The separator is disposed between the positive electrode and the negative electrode of the battery, and plays a role of preventing a short circuit due to contact between the two electrodes and holding an electrolytic solution to secure ionic conductivity. The separator is preferably a film-shaped insulating microporous film having good ion permeability and mechanical strength. As specific materials, polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene, and the like can be used.

As the non-aqueous electrolyte solution, known ones generally used for non-aqueous electrolyte secondary batteries can be used. Specific solvents include cyclic carbonates having a high dielectric constant and a high solubility for electrolytes such as propylene carbonate and ethylene carbonate, and low-chain viscosity carbonates such as ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate. These can be used alone or as a mixed solvent. The non-aqueous electrolyte solution is used by dissolving a lithium salt such as LiPF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , LiAlO ₄ in these solvents.
The nonaqueous electrolyte secondary battery of the present invention is obtained by storing a positive electrode plate and a negative electrode plate separated by a separator in a spiral or laminated structure in a case or the like.

  Hereinafter, the present invention will be specifically described based on examples. Note that the present invention is not limited by these examples. In the following, "parts" and "%" mean parts by weight and% by weight, respectively, unless otherwise specified.

(Production Example 1: Production of crosslinked polymer R-1)
For the polymerization, a reactor equipped with a stirring blade, a thermometer, a reflux condenser, and a nitrogen inlet tube was used.
295 parts of methanol, 100 parts of acrylic acid (hereinafter, referred to as "AA"), and 0.42 parts of allyl methacrylate (manufactured by Mitsubishi Gas Chemical Company, hereinafter, referred to as "AMA") were charged into the reactor. Next, 18 parts of caustic soda flake and 10 parts of ion-exchanged water were slowly added under stirring so that the internal temperature was maintained at 40 ° C. or lower.
After sufficiently replacing the inside of the reactor with nitrogen, the reactor was heated to raise the internal temperature to 68 ° C. After confirming that the internal temperature was stabilized at 68 ° C., 0.08 parts of 4,4′-azobiscyanovaleric acid (trade name “ACVA” manufactured by Otsuka Chemical Co., Ltd.) was added as a polymerization initiator, and the reaction solution was added. Since cloudiness was observed, this point was taken as the polymerization initiation point. The polymerization reaction was continued while adjusting the external temperature (water bath temperature) so that the solvent was gently refluxed. When 4 hours had passed from the polymerization starting point, 0.07 part of ACVA was additionally added, and the solvent was continuously refluxed. Was maintained. After 8 hours from the polymerization start point, cooling of the reaction solution was started. After the internal temperature was lowered to 30 ° C., 32 parts of caustic soda flake was slowly added so that the internal temperature did not exceed 50 ° C. After the addition of the caustic soda flake was completed and the internal temperature was cooled to 30 ° C. or lower, the polymerization reaction liquid (polymer slurry) was filtered by suction filtration. After the polymer separated by filtration was washed with methanol twice the amount of the polymerization reaction liquid, the filter cake was recovered and dried in vacuum at 100 ° C. for 6 hours to obtain a powdery crosslinked polymer R-1. The degree of neutralization of the crosslinked polymer R-1 is 90 mol%. Since the crosslinked polymer R-1 has a hygroscopic property, it was sealed and stored in a container having a water vapor barrier property.

  It was mixed with water so that the concentration of the crosslinked polymer R-1 obtained above became 0.5% by weight, and the mixture was stirred until it became a transparent and homogeneously dispersed (swelled) state. After adjusting the obtained dispersion to 25 ± 1 ° C., the viscosity at a rotor rotation speed of 20 rpm was measured using a B-type viscometer TVB-10 (manufactured by Toki Sangyo Co., Ltd.), and the results are shown in Table 1.

(Production Examples 2 to 10: Production of Crosslinked Polymers R-2 to R-10)
The same operation as in Production Example 1 was performed except that the charged amounts of the respective raw materials were as shown in Table 1, to obtain powdery crosslinked polymers R-2 to R-10.
The viscosity of the 0.5% by weight aqueous dispersion of each crosslinked polymer was measured in the same manner as in Production Example 1. However, since the degree of neutralization of the crosslinked polymer R-8 was 32.4 mol%, an aqueous dispersion having a degree of neutralization of 90 mol% by adding caustic soda was prepared, and the viscosity was measured. Table 1 shows the results.

(Production Example 11: Production of Crosslinked Polymer R-11)
For the polymerization, a reactor equipped with a stirring blade, a thermometer, a reflux condenser, and a nitrogen inlet tube was used.
300 parts of n-hexane, 140 parts of ethyl acetate, 100 parts of AA, and 0.70 part of pentaerythritol triallyl ether (manufactured by Daiso Corporation, trade name "Neoallyl P-30") were charged into the reactor.
After sufficiently replacing the inside of the reactor with nitrogen, the reactor was heated to raise the internal temperature to 60 ° C. After confirming that the internal temperature was stabilized at 60 ° C., 2,2′-azobis (2,4-dimethylvaleronitrile) (trade name “V-65” manufactured by Wako Pure Chemical Industries, Ltd.) was used as a polymerization initiator. When 01 parts were added, cloudiness was observed in the reaction solution, and this point was regarded as the polymerization initiation point. The polymerization reaction was continued while maintaining the internal temperature at 60 ° C., and at the time point of 3, 6, 9, and 12 hours from the polymerization initiation point, 0.01 part of V-65 was added at a time. At the lapse of 20 hours from the polymerization start point, the cooling of the reaction solution was started to complete the polymerization. After cooling to an internal temperature of 30 ° C. or lower, the polymerization reaction liquid (polymer slurry) was filtered by suction filtration. After the polymer separated by filtration was washed with twice the amount of ethyl acetate as the polymerization reaction liquid, the filter cake was recovered and dried in vacuum at 100 ° C. for 6 hours to obtain a powdery crosslinked polymer R-11. Since the crosslinked polymer R-11 has a hygroscopic property, it was sealed and stored in a container having a water vapor barrier property.
Further, since the degree of neutralization of the crosslinked polymer R-11 was 0 mol%, an aqueous dispersion having a degree of neutralization of 90 mol% by adding caustic soda was prepared, and the viscosity was measured. Table 1 shows the results.

The details of the compounds used in Table 1 are shown below.
AA: Acrylic acid AAM: Acrylamide AMA: Allyl methacrylate P-30: Pentaerythritol triallyl ether (manufactured by Daiso Corporation, trade name "Neoallyl P-30")
T-20: Trimethylolpropane diallyl ether (manufactured by Daiso Co., Ltd., trade name "Neoallyl T-20")
ACVA: 4,4'-azobiscyanovaleric acid (Otsuka Chemical Co., Ltd.)
V-65: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

Production and Evaluation of Nonaqueous Electrolyte Secondary Battery Electrode Example 1-1
For the composition for a mixture layer using graphite as a negative electrode active material and a crosslinked polymer R-1 as a binder, its coatability and peel strength between the formed mixture layer / current collector (ie, binder binding) G) was measured.
Take 100 parts of artificial graphite (manufactured by Nippon Graphite Co., trade name "CGB-10") and 3 parts of powdered crosslinked polymer R-1 and mix well beforehand, then add 126 parts of ion-exchanged water and disperse. After the preliminary dispersion, the main dispersion is performed for 15 seconds at a peripheral speed of 20 m / sec using a thin film swirling mixer (manufactured by Primix, FM-56-30) to obtain a slurry-like negative electrode mixture layer. A composition for use was obtained.
Using a variable-type applicator, the composition for a mixture layer was applied on a 20-μm-thick copper foil (manufactured by Nippon Foil Co., Ltd.) so that the film thickness after drying would be 50 μm, and immediately in a ventilation dryer. The mixture was dried at 100 ° C. for 10 minutes to form a mixture layer. The external appearance of the resulting mixture layer was visually observed, and the coatability was evaluated based on the following criteria.
<Coating property judgment criteria>
：: No appearance abnormality such as stripe unevenness or spots was observed on the surface.
Δ: Slight irregularities such as stripe unevenness and spots are observed on the surface.
X: Appearance abnormalities such as stripe unevenness and spots are remarkably observed on the surface.

<90 ° peel strength (binding property)>
Furthermore, after adjusting the mixture layer density to 1.7 ± 0.05 g / cm ³ with a roll press machine to prepare an electrode, the electrode was cut into a 25 mm wide strip to prepare a sample for a peeling test. The surface of the mixture layer of the above sample was adhered to a double-sided tape fixed to a horizontal plane, peeled at 90 ° at a pulling speed of 50 mm / min, and the peel strength between the mixture layer and the copper foil was measured. The peel strength was as high as 4.5 N / m, which was good.
Generally, when an electrode is cut and processed to assemble a battery cell, a peel strength of 1.0 N / m or more is required to avoid a problem that the mixture layer peels off from the current collector (copper foil). It is said. Higher peel strength means that the binder used is excellent in binding between the active material and between the active material and the electrode. It was suggested that a battery having excellent properties could be obtained.

Examples 1-2 to 1-12 and Comparative Examples 1-1 to 1-5
A composition for a mixture layer was prepared by performing the same operation as in Example 1-1, except that the crosslinked polymer used as the binder was used as shown in Tables 2 and 3, and the coatability and 90 ° peel strength were measured. Was evaluated. The results are shown in Tables 2 and 3.
In Examples 1-9 and Comparative Examples 1-4, a 48% aqueous NaOH solution was added so that the degree of neutralization of the crosslinked polymer was 90 mol%. Parts corresponding to parts were used.

In Examples 1-1 to 1-12, electrodes were produced using the composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to the present invention. The coatability of each composition (slurry) is good, and the peel strength between the obtained mixture layer and the current collector (copper foil) is 1.0 N / m or more in each case. It exhibited excellent binding properties. In Examples 1-1 to 1-7 in which 3 parts by weight of the crosslinked polymer neutralized by 90 mol% with respect to the active material were used, (meth) acryloyl group and alkenyl group were used as crosslinkable monomers. The peel strength of Examples 1-1, 1-2 and 1-4 to 1-6 using the crosslinked polymer using allyl methacrylate having both Higher results were obtained compared to Examples 1-3 and 1-7.
On the other hand, in Comparative Examples 1-1 and 1-2 using the crosslinked polymer having a low viscosity of 0.5% by weight, sufficient binding property was not obtained. In addition, the composition for a mixture layer containing the high-viscosity crosslinked polymer R-11 had poor coatability even when the degree of neutralization was adjusted (Comparative Examples 1-3 and 1-4). Further, Comparative Example 1-5, in which the blending amount of the crosslinked polymer with respect to the active material is small, has almost no binding property of the mixture layer, and the mixture layer is cut when the electrode is cut to prepare a sample for a peeling test. Because of the peeling, the peel strength could not be measured.

Example 2-1
A lithium ion secondary battery was prepared using a mixture layer composition containing hard carbon as a negative electrode material, acetylene black as a conductive aid, and a crosslinked polymer R-1 as a binder, and the battery characteristics thereof were evaluated.
100 parts of hard carbon (trade name "LBV-1001" manufactured by Sumitomo Bakelite Co., Ltd.), 2 parts of acetylene black (trade name "HS-100" manufactured by Denki Kagaku Kogyo Co., Ltd.), and powdered crosslinked polymer R-1 Take 3 parts, mix well beforehand, add 132 parts of ion-exchanged water, pre-disperse with a disper, and use a thin-film swirling mixer (manufactured by Primix, FM-56-30) to achieve a peripheral speed of 20 m / sec. This dispersion was carried out for 15 seconds under the conditions described above to obtain a slurry-like negative electrode mixture layer composition.
Using a direct coat type coating machine having a drying oven, the above mixture layer composition was coated on both sides of a 20 μm-thick copper foil (manufactured by Nippon Foil Co.) with a coating width of 120 mm. After drying, a roll press treatment was performed to produce a negative electrode having a mixture layer on both surfaces of the current collector. The adhesion amount of the mixture layer was 4.96 mg / cm ² (for one side), and the density was 1.0 g / cm ³ .
For the positive electrode, 85.5 / 4 of NCM (manufactured by Nippon Chemical Industry Co., Ltd.) as an active material, HS-100 as a conductive aid, and polyvinylidene fluoride (manufactured by Kureha Corporation, trade name “KF # 1000”) as a binder. A mixture having a mixture layer composition formed at a ratio of 0.5 / 10 (weight ratio) on both surfaces of a 15 μm-thick aluminum foil (made by Nippon Foil Co., Ltd.) serving as a current collector. used. The attached amount of the mixture layer of the positive electrode was 6.80 mg / cm ² (for one side), and the density was 2.78 g / cm ³ .

After vacuum drying at 120 ° C. for 12 hours for both the positive electrode and the negative electrode, the positive electrode was slit to a size of 96 × 84 mm, and the negative electrode was slit to a size of 100 × 88 mm. The slit electrodes (seven positive electrodes and eight negative electrodes) were stacked with a polyethylene separator interposed therebetween to assemble a laminate cell. After vacuum-drying the three-side sealed laminate cell at 60 ° C. for 5 hours, an electrolyte solution (1M, LiPF6 in EC / EMC = 3/7 (v / v)) was injected to perform vacuum sealing. The production of the laminate cells was all performed in a dry room.
The following battery characteristics evaluation was performed about the laminated cell produced above.

<Initial charge / discharge test>
Using a charge / discharge device SD8 (manufactured by Hokuto Denko), the initial charge / discharge capacity was measured under the following conditions.
At the time of measurement, after charging / discharging for one cycle to stabilize the battery state, charging / discharging for the second cycle was performed, and it was confirmed that the charge / discharge capacity was stable within the design capacity (700 to 800 mAh).
Measurement temperature: 25 ° C
Charging: 0.1C-CC / Cut-off 4.2V ⇒ CV / Cut-off rate 0.01C
Discharge: 0.1 C-CC / Cut-off 3.0 V
Second cycle The charge capacity in the first cycle was 1142 mAh, the discharge capacity was 769 mAh, the charge capacity in the second cycle was 778 mAh, and the discharge capacity was 755 mAh.

<Low-temperature rate test and AC impedance measurement>
A low-temperature rate test and an AC impedance measurement were performed on the cells subjected to the initial charge / discharge test under the following conditions and in the following order. For the measurement, a charge / discharge device SD8 (manufactured by Hokuto Denko) and an AC impedance measuring device VSP (manufactured by Bio-Logic) were used.
Measurement temperature: -15 ° C
(1) 0.1C charge / discharge (low temperature initial charge / discharge)
Charge: 0.1C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 0.1 C-CC / Cut-off 3.0 V
(2) AC impedance measurement Charge: 0.1 C, 2 hours Applied voltage: 10 mV
Frequency: 1000kHz-10mHz
(Residual discharge treatment 0.1 C up to 3 V)
(3) 0.5C charge / discharge Charge: 0.5C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 0.5 C-CC / Cut-off 3.0 V
(Residual discharge treatment 0.1 C up to 3 V)
(4) 1C charge / discharge Charge: 1C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 1 C-CC / Cut-off 3.0 V
(Residual discharge treatment 0.1 C up to 3 V)
(5) 2C charge / discharge Charge: 2C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 2C-CC / Cut-off 3.0V
(Residual discharge treatment 0.1 C up to 3 V)
(6) 3C charge / discharge Charge: 3C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 3C-CC / Cut-off 3.0 V
(Residual discharge treatment 0.1 C up to 3 V)
(7) 4C charge / discharge Charge: 4C-CC / Cut-off 4.2V
(Pause time 10 minutes)
Discharge: 4C-CC / Cut-off 3.0 V
(Residual discharge treatment 0.1 C up to 3 V)
The measurement result of the above (1) was a low-temperature initial charge / discharge capacity of 605 mAh and a discharge capacity of 598 mAh.
A Nyquist plot was created from the measurement result of the above (2), and as a result of estimating the interface resistance value from the size of the arc, the value was 0.38Ω.
The result of calculating the discharge capacity retention ratio at each C rate by dividing the discharge capacity obtained by the above (3) to (7) by the discharge capacity obtained by the above (1). , 0.5C: 67%, 1C: 44%, 2C: 15%, 3C: 3%, 4C: 0%. Note that 0% means that the voltage reaches the Cut-off voltage (3.0 V) immediately after the start of discharge due to a voltage drop due to an overvoltage.

<Cycle test>
A cycle test was performed on the cells subjected to the initial charge / discharge test under the following conditions.
Measurement temperature: 25 ° C
Charge: 1C-CC / Cut-off 4.2V
Discharge: 1 C-CC / Cut-off 3.0 V
200 Cycles The discharge capacity at the 200th cycle was calculated by dividing the discharge capacity at the 200th cycle by the discharge capacity at the 1st cycle, and as a result, it was 93%.

Examples 2-2 to 2-4 and Comparative examples 2-1 to 2-4
A laminate cell was assembled by performing the same operation as in Example 2-1 except that the crosslinked polymer used as the binder was used as shown in Table 4, and the battery characteristics were evaluated. Table 4 shows the results.
In Comparative Example 2-3, a 48% aqueous NaOH solution was added so that the degree of neutralization of the crosslinked polymer was 90 mol%, and the crosslinked polymer was in an amount equivalent to 3 parts as a 90 mol% neutralized product. It was used. In Comparative Example 2-4, the following styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) were used as binders.
SBR: manufactured by JSR, trade name "TRD2001", using 1.5 parts as solids CMC: manufactured by Daicel Finechem, trade name "CMC2200", used 1.5 parts as solids

The details of the compounds used in Table 4 are shown below.
LBV-1001: Hard carbon (Sumitomo Bakelite)
HS-100: Acetylene black (manufactured by Denki Kagaku Kogyo)

Examples 2-1 to 2-4 belong to the non-aqueous electrolyte secondary battery of the present invention, and the discharge capacity retention rate after the cycle test was as high as 93 to 95%, and results excellent in cycle characteristics were obtained. . Further, each of the examples exhibited good high-rate characteristics. This is because, due to the properties of the cross-linked polymer used, the interface resistance is reduced, the uniform dispersion of the active material and the conductive auxiliary agent is good, and the electronic resistance is reduced, so that the internal resistance of the battery is reduced. It is inferred that this has happened. Above all, when comparing Example 2-1 and Example 2-3 in which the amount of the crosslinked polymer used is the same, Example 2 using the crosslinked polymer R-6 having a high viscosity of the 0.5% by weight aqueous dispersion was used. No. 3 had a higher discharge capacity retention ratio under a high current density condition, and obtained a result excellent in high rate characteristics.
On the other hand, the cycle characteristics of Comparative Examples 2-2 and 2-3 using the crosslinked polymers R-9 and R-11 in which the viscosity of the 0.5% by weight aqueous dispersion is out of the range specified in the present invention are as follows. , 82% and 88%. In addition, it can be seen that Comparative Example 2-3 and Comparative Example 2-4 using SBR and CMC as the binder have inferior high-rate characteristics as compared with the examples. In Comparative Example 2-3, it is considered that the dispersion of the active material and the conductive additive was insufficient, and the electronic resistance was increased. In Comparative Example 2-4, it is inferred that the interface resistance was increased because the binder did not have a sufficient carboxyl group, and as a result, the high-rate characteristics were reduced. Similarly, Comparative Example 2-1 having a large content of the crosslinked polymer also had insufficient high-rate characteristics.

  The electrode obtained from the composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention has an excellent binding force and an effect of reducing battery resistance. For this reason, the non-aqueous electrolyte secondary battery provided with the above-mentioned electrode exhibits excellent high-rate characteristics and durability (cycle characteristics), and is expected to be applied to a vehicle-mounted secondary battery.

Claims (6)

An active material, a composition for a non-aqueous electrolyte secondary battery electrode mixture layer containing water and a binder,
The binder contains a crosslinked polymer of a monomer component containing an ethylenically unsaturated carboxylic acid monomer and a salt thereof,
The viscosity of a 0.5% by weight aqueous dispersion of the crosslinked polymer at a degree of neutralization of 90 mol% is 12,000 to 40, as a value measured by a B-type viscosity at a liquid temperature of 25 ° C. (rotor rotation speed: 20 rpm). 000 mPa · s,
The cross-linked polymer is cross-linked by a cross-linkable monomer,
Crosslinkable monomer, look-containing compound, and at least one selected from polyfunctional allyl ether compound or Ranaru group having both of (meth) acryloyl group and an alkenyl group,
The composition for a non-aqueous electrolyte secondary battery electrode mixture layer, wherein the content of the crosslinked polymer and its salt is 0.5 to 5.0% by weight based on the active material.   The non-aqueous electrolyte secondary battery electrode assembly according to claim 1, wherein the amount of the crosslinkable monomer used is 0.05 to 1.0 mol% based on the total amount of monomers other than the crosslinkable monomer. Composition for agent layer.   The composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to claim 1 or 2, wherein the degree of neutralization of the crosslinked polymer is 20 to 100 mol%. A method for producing a composition for a non-aqueous electrolyte secondary battery electrode mixture layer,
Include ethylenically unsaturated carboxylic acid monomer and a crosslinkable monomer in an aqueous medium, the crosslinkable monomer is a compound having both a (meth) acryloyl group and an alkenyl group, and polyfunctional allyl ethers a monomer component containing at least one selected from the compounds or Ranaru group is precipitation polymerization, viscosity of 0.5 wt% aqueous dispersion of the degree of neutralization of 90 mol%, B-type at a liquid temperature of 25 ° C. After obtaining a cross-linked polymer cross-linked by the cross-linkable monomer, having a value of 12,000 to 40,000 mPa · s as measured by viscosity (rotor rotation speed 20 rpm),
A method for producing a composition for a non-aqueous electrolyte secondary battery electrode mixture layer by mixing with an active material and water.   A non-aqueous electrolyte secondary battery electrode comprising, on a current collector surface, a mixture layer formed from the composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to claim 1.   A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte secondary battery electrode according to claim 5, a separator, and a non-aqueous electrolyte solution.