JP6686605B2 - Binder composition for non-aqueous secondary battery positive electrode, slurry composition for non-aqueous secondary battery positive electrode, non-aqueous secondary battery positive electrode, and non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a binder composition for a non-aqueous secondary battery positive electrode, a slurry composition for a non-aqueous secondary battery positive electrode, a non-aqueous secondary battery positive electrode, and a non-aqueous secondary battery.

  A non-aqueous secondary battery such as a lithium-ion secondary battery (hereinafter sometimes simply referred to as “secondary battery”) has characteristics that it is small and lightweight, has high energy density, and can be repeatedly charged and discharged. Yes, it is used for a wide range of purposes. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of non-aqueous secondary batteries.

  Here, the positive electrode for a non-aqueous secondary battery usually includes a current collector and an electrode mixture layer (positive electrode mixture layer) formed on the current collector. The positive electrode mixture layer is formed using, for example, a slurry composition obtained by dispersing a positive electrode active material and a binder composition containing a binder in a dispersion medium.

Therefore, in recent years, in order to further improve the performance of the non-aqueous secondary battery, attempts have been made to improve the binder composition used for forming the positive electrode mixture layer.
Specifically, for example, Patent Document 1 proposes a technique for improving the cycle characteristics of a non-aqueous secondary battery by using a mixture of a fluoropolymer and hydrogenated nitrile rubber as a binder.

JP, 9-63590, A

  However, it may be difficult to make the secondary battery exhibit sufficiently excellent cycle characteristics even by using the above-mentioned conventional technique. For example, in recent years, attempts have been made to improve the performance of secondary batteries by increasing the density of the positive electrode mixture layer of secondary batteries. Here, in order to sufficiently permeate the electrolyte solution into the densified positive electrode mixture layer, it is preferable to adjust the composition of the electrolyte solution to reduce the viscosity. However, the difference in SP value between the low-viscosity electrolytic solution and the hydrogenated nitrile rubber used as the binder (also referred to as “solubility parameter”) is likely to be small, and the hydrogenated nitrile rubber is eluted in the electrolytic solution. easy. Therefore, there is a problem that the cycle characteristics of the secondary battery deteriorate.

Therefore, the present invention aims to provide a binder composition for a non-aqueous secondary battery positive electrode and a slurry composition for a non-aqueous secondary battery positive electrode capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery. And
Another object of the present invention is to provide a positive electrode for a non-aqueous secondary battery, which is capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery.
Another object of the present invention is to provide a non-aqueous secondary battery having excellent cycle characteristics.

  The present inventor has conducted earnest studies for the purpose of solving the above problems. Then, the present inventors, by adding a crosslinking agent to the binder composition comprising hydrogenated nitrile rubber in the solvent, the hydrogenated nitrile rubber in the obtained positive electrode mixture layer is eluted into the electrolytic solution. The idea was to suppress Then, a binder film formed from this binder composition was vacuum dried in a high temperature (150 ° C.) environment and then immersed in a predetermined electrolytic solution, and the elution rate was measured after the binder film was vacuum dried in a low temperature (25 ° C.) environment. Comparing the elution rate when immersed in a predetermined electrolytic solution, if the ratio of these elution rates is a predetermined value or less, found that it is possible to exhibit excellent cycle characteristics in the secondary battery, the present Completed the invention.

That is, the present invention is intended to advantageously solve the above problems, the binder composition for a non-aqueous secondary battery positive electrode of the present invention comprises a hydrogenated nitrile rubber, a crosslinking agent, and a solvent, The dissolution rate ratio calculated by the following equation (1) is 0.45 or less.
Dissolution rate ratio = Dissolution rate A / Dissolution rate B (1)
In formula (1),
The elution rate A was determined by vacuum-drying a binder film formed from the binder composition for a non-aqueous secondary battery positive electrode at 150 ° C. for 6 hours, and then subjecting the binder film after vacuum drying to ethylene carbonate (EC) and propylene carbonate (PC). ), Ethyl methyl carbonate (EMC), and n-propyl propionate (PP) in a mass ratio of EC: PC: EMC: PP = 2: 1: 1: 6, and LiPF ₆ is added to a solvent obtained by adding 1. It represents the dissolution rate when immersed in a measuring electrolyte solution having a concentration of 0 mol / liter for 72 hours at 60 ° C.,
The elution rate B was determined by vacuum-drying a binder film formed from the binder composition for a non-aqueous secondary battery positive electrode at 25 ° C. for 6 hours, and applying the vacuum-dried binder film to the measuring electrolyte at 60 ° C. Represents the dissolution rate when immersed for 72 hours. By using such a binder composition, it is possible to form a positive electrode mixture layer capable of exhibiting excellent cycle characteristics in a secondary battery.
In addition, in this invention, a "crosslinking agent" means the compound which produces | generates a free radical and advances a crosslinking reaction. Further, in the present invention, “vacuum drying” means performing drying under a reduced pressure environment of 10 kPa or less.

Here, in the binder composition for a non-aqueous secondary battery positive electrode of the present invention, the 10-hour half-life temperature of the cross-linking agent is preferably 80 ° C. or higher and 160 ° C. or lower. If a crosslinking agent having a 10-hour half-life temperature within the above range is used, the storage stability of the binder composition and the peel strength of the positive electrode (adhesion strength between the positive electrode mixture layer and the current collector) are increased, and the secondary battery is used. The cycle characteristics of can be further improved.
In the present invention, the “10-hour half-life temperature” means the temperature at which the time (half-life) until the concentration of the cross-linking agent is reduced to half the initial time is 10 hours.

  Moreover, in the binder composition for a non-aqueous secondary battery positive electrode of the present invention, the cross-linking agent is preferably an organic peroxide. When the crosslinking agent is an organic peroxide, the peel strength of the positive electrode can be increased and the cycle characteristics of the secondary battery can be further improved.

  Furthermore, the binder composition for a non-aqueous secondary battery positive electrode of the present invention preferably contains 1 part by mass or more and 3 parts by mass or less of the crosslinking agent per 100 parts by mass of the hydrogenated nitrile rubber. When the content of the cross-linking agent is within the above range, the flexibility and peel strength of the positive electrode and the stability of the binder composition can be increased, and the cycle characteristics of the secondary battery can be further improved.

The binder composition for a non-aqueous secondary battery positive electrode of the present invention preferably further contains a co-crosslinking agent. By using a binder composition containing a co-crosslinking agent in addition to the crosslinking agent, the peel strength of the positive electrode can be increased and the cycle characteristics of the secondary battery can be further improved.
In the present invention, the “co-crosslinking agent” refers to a compound having a plurality of radically reactive unsaturated groups such as ethylenic unsaturated bonds in one molecule.

  Here, the binder composition for a non-aqueous secondary battery positive electrode of the present invention preferably contains 1 part by mass or more and 5 parts by mass or less of the co-crosslinking agent per 100 parts by mass of the hydrogenated nitrile rubber. When the content of the co-crosslinking agent is within the above range, it is possible to increase the flexibility and peel strength of the positive electrode and further improve the cycle characteristics of the secondary battery.

  Moreover, this invention aims at solving the said subject advantageously, and the slurry composition for non-aqueous secondary battery positive electrodes of this invention is a positive electrode active material, and any non-aqueous secondary battery mentioned above. And a binder composition for a secondary battery positive electrode. By using such a slurry composition, it is possible to form a positive electrode mixture layer capable of exhibiting excellent cycle characteristics in a secondary battery.

  Moreover, this invention aims at solving the said subject advantageously, and the positive electrode for non-aqueous secondary batteries of this invention is formed using the slurry composition for non-aqueous secondary batteries positive electrode mentioned above. It is characterized by including the positive electrode mixture layer. As described above, when the positive electrode having the positive electrode mixture layer formed by using the above-mentioned slurry composition is used, the secondary battery can exhibit excellent cycle characteristics.

  Furthermore, the present invention is intended to advantageously solve the above problems, the non-aqueous secondary battery of the present invention, the positive electrode for a non-aqueous secondary battery described above, a negative electrode, and an electrolyte solution, And a separator. Thus, by using the positive electrode for a non-aqueous secondary battery described above, a secondary battery having excellent cycle characteristics can be obtained.

Here, in the non-aqueous secondary battery of the present invention, the SP value of the electrolytic solution is preferably 22.0 or more and 23.0 or less. The secondary battery using the electrolytic solution having the SP value within the above range is more excellent in battery characteristics such as cycle characteristics.
In the present invention, the “SP value” of the electrolytic solution is the SP value of each solvent contained in the electrolytic solution according to the Hoy calculation method (HLHoy Journal of Painting, 1970, Vol. 42, 76-118). It can be calculated by dividing the sum of those calculated by multiplying the SP value by the volume fraction (more than 0% and less than 100%) at 25 ° C. of each solvent by 100.

According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery positive electrode and a slurry composition for a non-aqueous secondary battery positive electrode capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery. .
Further, according to the present invention, it is possible to provide a positive electrode for a non-aqueous secondary battery, which is capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery.
Furthermore, according to the present invention, a non-aqueous secondary battery having excellent cycle characteristics can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder composition for a positive electrode of a non-aqueous secondary battery of the present invention can be used when preparing a slurry composition for a positive electrode of a non-aqueous secondary battery. Then, the slurry composition for a non-aqueous secondary battery positive electrode prepared using the binder composition for a non-aqueous secondary battery positive electrode of the present invention is used when forming a positive electrode of a non-aqueous secondary battery such as a lithium ion secondary battery. Can be used for. Furthermore, the non-aqueous secondary battery of the present invention is characterized by using a non-aqueous secondary battery positive electrode formed by using the non-aqueous secondary battery positive electrode slurry composition of the present invention.

(Binder composition for non-aqueous secondary battery positive electrode)
The binder composition for a non-aqueous secondary battery positive electrode of the present invention contains a hydrogenated nitrile rubber, a cross-linking agent, and a solvent, and optionally, a co-cross-linking agent and other components that can be blended in the positive electrode of the secondary battery. And are further contained. The binder composition of the present invention is characterized in that the elution rate ratio calculated by the following formula (1) is 0.45 or less.
Dissolution rate ratio = Dissolution rate A / Dissolution rate B (1)
In the formula (1), the elution rate A was obtained by vacuum-drying a binder film formed from the binder composition at 150 ° C. for 6 hours, and measuring the binder film after vacuum drying with an electrolytic solution for measurement (EC: PC: EMC). : PP = 2: 1: 1: 6 (mass basis) in a mixed solvent of LiPF ₆ at a concentration of 1.0 mol / liter), and the elution rate when immersed for 72 hours at 60 ° C. The elution rate B was obtained by vacuum-drying a binder film formed from the binder composition at 25 ° C. for 6 hours, and immersing the vacuum-dried binder film in a measuring electrolyte solution at 60 ° C. for 72 hours. The elution rate is shown.

Then, the positive electrode including the positive electrode mixture layer obtained by using the binder composition of the present invention can exhibit excellent cycle characteristics in the secondary battery.
Here, the reason why the positive electrode mixture layer that improves the cycle characteristics of the secondary battery can be obtained by using the binder composition of the present invention is not clear, but is presumed to be as follows.
That is, since the binder composition of the present invention contains a hydrogenated nitrile rubber, a cross-linking agent, and a solvent, when the slurry composition prepared using the binder composition of the present invention is dried to form the positive electrode mixture layer. , The solvent is removed, and the free radicals generated from the cross-linking agent are generated on the hydrogen atom in the hydrogenated nitrile rubber (especially on the carbon atom (allyl position) adjacent to the residual double bond of the hydrogenated nitrile rubber. Rigid cross-linked network is formed in the positive electrode mixture layer by the radical reaction by extracting the located hydrogen atom). This cross-linked network can suppress the elution of hydrogenated nitrile rubber into the electrolytic solution, and can prevent the positive electrode mixture layer from swelling and cutting the conductive path. In addition, since the binder composition of the present invention has a value of the above-mentioned dissolution rate ratio of 0.45 or less, the reaction between the cross-linking agent and the hydrogenated nitrile rubber is suppressed at a relatively low temperature, while the temperature at a relatively high temperature. Then, the reaction between the crosslinking agent and the hydrogenated nitrile rubber proceeds well. Therefore, the binder composition of the present invention, while maintaining the storage stability as a binder composition, can form a good cross-linked network during the formation of the positive electrode mixture layer, and can suppress the cutting of the conductive path. . Therefore, when the positive electrode mixture layer is formed by using the binder composition of the present invention, the secondary battery can exhibit excellent cycle characteristics.

<Hydrogenated nitrile rubber>
The hydrogenated nitrile rubber is a positive electrode mixture prepared by forming a positive electrode mixture layer on a current collector using a slurry composition for a non-aqueous secondary battery positive electrode prepared using a binder composition. The components contained in the layer are retained so as not to be released from the positive electrode mixture layer (that is, function as a binder). The hydrogenated nitrile rubber can be obtained by hydrogenating a copolymer (nitrile rubber) containing a conjugated diene monomer unit and a nitrile group-containing monomer unit. That is, a hydride of a copolymer containing a conjugated diene monomer unit and a nitrile group-containing monomer unit can be used as the hydrogenated nitrile rubber.
In addition, in the present invention, “containing a monomer unit” means “a repeating unit derived from a monomer is contained in a polymer obtained by using the monomer”.

[Copolymer Containing Conjugated Diene Monomer Unit and Nitrile Group-Containing Monomer Unit]
The above-mentioned copolymer used for preparing the hydrogenated nitrile rubber contains a conjugated diene monomer unit, a nitrile group-containing monomer unit, and optionally other repeating units.

[[Conjugated diene monomer unit]]
Examples of the conjugated diene monomer capable of forming the conjugated diene monomer unit include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, Examples thereof include conjugated diene compounds having 4 or more carbon atoms such as 1,3-pentadiene. Of these, 1,3-butadiene is preferable. These may be used alone or in combination of two or more.

  And the content ratio of the conjugated diene monomer unit in the copolymer is preferably 30% by mass or more, and preferably 98% by mass or less, when all the repeating units in the copolymer are 100% by mass. It is more preferably 80% by mass or less. When the content ratio of the conjugated diene monomer unit in the copolymer is at least the lower limit value of the above range, the flexibility of the positive electrode using the binder composition containing the hydrogenated nitrile rubber obtained from the copolymer is improved. Can be made. Further, when the content ratio of the conjugated diene monomer unit in the copolymer is not more than the upper limit value of the above range, the solubility of the hydrogenated nitrile rubber obtained from the copolymer in the solvent is secured. Therefore, the hydrogenated nitrile rubber can well disperse the conductive material and the like in the slurry composition, and can improve the battery characteristics (cycle characteristics and the like) of the secondary battery.

[[Nitrile group-containing monomer unit]]
Examples of the nitrile group-containing monomer capable of forming the nitrile group-containing monomer unit include α, β-ethylenically unsaturated nitrile monomers. The α, β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α, β-ethylenically unsaturated compound having a nitrile group, for example, acrylonitrile; α-chloroacrylonitrile, α-bromo. And α-halogenoacrylonitrile such as acrylonitrile; α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile; and the like. Among them, from the viewpoint of increasing the binding force of the hydrogenated nitrile rubber obtained from the copolymer and increasing the mechanical strength of the positive electrode, acrylonitrile and methacrylonitrile are preferable as the nitrile group-containing monomer, and acrylonitrile is more preferable. preferable. These may be used alone or in combination of two or more.

  And the content ratio of the nitrile group-containing monomer unit in the copolymer is preferably 5% by mass or more, and more preferably 15% by mass or more, when all the repeating units in the copolymer are 100% by mass. 20 mass% or more is more preferable, 60 mass% or less is preferable, 50 mass% or less is more preferable, and 40 mass% or less is further preferable. When the content ratio of the nitrile group-containing monomer unit in the copolymer is at least the lower limit value of the above range, the hydrogenated nitrile rubber satisfactorily disperses the conductive material and the like in the slurry composition to give a secondary battery. The battery characteristics (cycle characteristics, etc.) can be improved. Further, if the content ratio of the conjugated diene monomer unit in the copolymer is not more than the upper limit value of the above range, the flexibility of the positive electrode using the binder composition containing the hydrogenated nitrile rubber obtained from the copolymer Can be secured.

[[Other repeating units]]
Further, the monomer capable of forming other repeating units (hereinafter sometimes referred to as “other monomer”) is not particularly limited, and includes (meth) acrylic acid ester monomer, hydrophilic Examples thereof include polymerizable monomers having a functional group, aromatic vinyl monomers and the like.
In addition, these monomers can be used individually by 1 type or in combination of 2 or more types. Further, in the present invention, “(meth) acryl” means acryl and / or methacryl.

  Here, as the (meth) acrylic acid ester monomer, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate. , Acrylic acid alkyl esters such as hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, Isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, a Butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate and the like alkyl methacrylates; And so on. Among these, as the (meth) acrylic acid ester monomer, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are preferable, and n-butyl acrylate is more preferable.

  Further, as the polymerizable monomer having a hydrophilic group, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, a monomer having a hydroxyl group Can be mentioned. From the viewpoint of increasing the binding strength of the hydrogenated nitrile rubber obtained from the copolymer, the hydrophilic group is preferably a carboxylic acid group or a sulfonic acid group, and more preferably a carboxylic acid group.

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and its derivative, dicarboxylic acid and its acid anhydride, and their derivatives.
Examples of the monocarboxylic acid include acrylic acid, methacrylic acid and crotonic acid.
Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid and β-diaminoacrylic acid. Can be mentioned.
Examples of the dicarboxylic acid include maleic acid, fumaric acid and itaconic acid.
Examples of the dicarboxylic acid derivative include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate. , Maleic acid esters such as 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.
Further, as the monomer having a carboxylic acid group, an acid anhydride that produces a carboxyl group by hydrolysis can also be used.
Others, monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate And monoesters and diesters of α, β-ethylenically unsaturated polycarboxylic acids such as monobutyl itaconate and dibutyl itaconate.

Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, and 2-acrylamido-2-methyl. Examples thereof include propane sulfonic acid and 3-allyloxy-2-hydroxypropane sulfonic acid.
In addition, in this invention, "(meth) allyl" means allyl and / or methallyl.

Examples of the monomer having a phosphate group include 2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, ethyl phosphate- (meth) acryloyloxyethyl, and the like. .
In addition, in this invention, "(meth) acryloyl" means acryloyl and / or methacryloyl.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, and 5-hexen-1-ol; 2-hydroxyethyl acrylate, acrylic acid-2 -Ethylenic such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconic acid alkanol esters of unsaturated carboxylic acids; general ^{_{formula: CH 2 = CR 1 -COO- (}} C n H 2n O) m -H ( wherein, m is 2-9 integer, n represents an integer of 2 to 4, esters R ¹ is a polyalkylene glycol and (meth) acrylic acid represented by hydrogen or a methyl group); 2- hydro Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as cyethyl-2 '-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2'-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether, Vinyl ethers such as 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2- Alkylene glycol mono (meth) allyl ethers such as hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether Polyoxyalkylene glycol mono (meth) allyl ethers such as diethylene glycol mono (meth) allyl ether, dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro Halogen- and hydroxy-substituted mono (meth) allyl ethers of (poly) alkylene glycols such as 3-hydroxypropyl ether and (meth) allyl-2-hydroxy-3-chloropropyl ether; and eugenol and isoeugenol Mono (meth) allyl ethers of dihydric phenols and halogen-substituted products thereof; (meth) allyl ethers of alkylene glycols such as (meth) allyl-2-hydroxyethyl thioether and (meth) allyl-2-hydroxypropyl thioether. Thioether ethers; and the like.

  Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinyltoluene, divinylbenzene and the like.

  The content of the other repeating units in the copolymer is preferably 10% by mass or less, and 5% by mass or less, based on 100% by mass of all repeating units in the copolymer. It is more preferable that it is 0% by mass, and it is further preferable.

[[Copolymer Preparation Method]]
The method for producing a copolymer containing a conjugated diene monomer unit and a nitrile group-containing monomer unit is not particularly limited, and examples thereof include solution polymerization method, suspension polymerization method, bulk polymerization method and emulsion polymerization method. The method of can also be used. In each polymerization method, known emulsifiers and polymerization initiators can be used if necessary. As the polymerization method, addition polymerization such as ionic polymerization, radical polymerization and living radical polymerization can be used.

[Hydrogen addition to copolymer]
Hydrogenation can be performed on the copolymer (nitrile rubber) obtained as described above to prepare a hydrogenated nitrile rubber. Here, the method of hydrogenation is not particularly limited, and a general method using a catalyst (see, for example, International Publication No. 2012/165120, International Publication No. 2013/080989 and JP2013-8485A) is used. can do.
The hydrogenated nitrile rubber thus obtained contains an alkylene structural unit formed by hydrogenation of a conjugated diene monomer unit and a nitrile group-containing monomer unit, while the hydrogenated nitrile rubber is Usually, some conjugated diene monomer units remain without being hydrogenated. That is, the hydrogenated nitrile rubber usually contains at least an alkylene structural unit, a nitrile group-containing monomer unit, and a conjugated diene monomer unit. Here, the alkylene structural unit is a repeating unit composed only of an alkylene structure represented by the general formula: —C _n H _2n — [where n is an integer of 2 or more].

Here, the hydrogenated nitrile rubber preferably has an iodine value of 5 mg / 100 mg or more, and preferably 100 mg / 100 mg or less. When the iodine value of the hydrogenated nitrile rubber is within the above range, the hydrogenated nitrile rubber forms a more rigid crosslinked network in the positive electrode mixture layer, and the cycle characteristics of the secondary battery can be further improved.
In the present invention, "iodine value" means the iodine value of a dried polymer obtained by coagulating 100 g of an aqueous dispersion of hydrogenated nitrile rubber with 1 liter of methanol and vacuum-drying at 60 ° C for 12 hours. It can be obtained by measuring according to JIS K6235 (2006).

<Crosslinking agent>
The crosslinking agent is not particularly limited, but examples thereof include organic peroxides and azo compounds. Examples of the organic peroxide include dicumyl peroxide, cumene hydroperoxide, t-butyl cumyl peroxide, paramenthane hydroperoxide, di-t-butyl peroxide, 1,3-bis (t-butylperoxy). Isopropyl) benzene, 1,4-bis (t-butylperoxyisopropyl) benzene, 1,1-di-t-hexylperoxy-cyclohexane, 1,1-di-t-butylperoxy-3,3-trimethylcyclohexane, 4 , 4-Bis- (t-butyl-peroxy) -n-butylvalerate, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t -Butylperoxyhexyne-3,1,1-di-t-butylperoxy-3,5,5-trimethylcyclo Hexane, p-chlorobenzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate can be mentioned. Examples of the azo compound include azobisisobutyronitrile and dimethyl-2,2′-azobis (2-methylpropionate). Among them, organic peroxides are preferable from the viewpoint of enhancing the peel strength of the positive electrode and further improving the cycle characteristics of the secondary battery, and dicumyl peroxide, cumene hydroperoxide, 1,1-di-t-hexylperoxy are preferred. -Cyclohexane is more preferred, and dicumyl peroxide is even more preferred. If dicumyl peroxide is used as the crosslinking agent, the storage stability of the binder composition can be increased. These cross-linking agents can be used alone or in combination of two or more.

Here, the 10-hour half-life temperature of the cross-linking agent is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, further preferably 95 ° C. or higher, and preferably 160 ° C. or lower. , 150 ° C. or lower, more preferably 130 ° C. or lower. When the 10-hour half-life temperature of the cross-linking agent is at least the lower limit value of the above range, the cross-linking agent does not have excessive reactivity and the storage stability of the binder composition can be secured. Further, when the 10-hour half-life temperature of the cross-linking agent is not more than the upper limit value of the above range, the cross-linking reaction can be sufficiently advanced during the formation of the positive electrode mixture layer. Therefore, the peel strength of the positive electrode can be increased and the cycle characteristics of the secondary battery can be further improved.
The 10-hour half-life temperature of the crosslinking agent can be determined as follows.
First, a solvent (for example, benzene) that is relatively inert to radicals is used to prepare a crosslinking agent solution having a concentration of the crosslinking agent of 0.1 mol / liter. This cross-linking agent solution is sealed in a glass tube that has been subjected to nitrogen substitution, and the glass tube is immersed in a constant temperature bath set at a predetermined temperature to thermally decompose the cross-linking agent in the cross-linking agent solution.
Here, in general, the decomposition of the cross-linking agent in a dilute solution can be treated approximately as a first-order reaction. Therefore, assuming that the amount x of the decomposition crosslinking agent, the decomposition rate constant k, the time t, and the initial concentration a of the crosslinking agent, the following relationships are established among them.
dx / dt = k (ax) ... (2)
ln {a / (ax)} = kt (3)
Here, the half-life is the time until the concentration of the cross-linking agent is reduced to half of the initial value due to decomposition, so the half-life is represented by t _1/2 and substituting a / 2 for x in equation (3) gives The following equation (4) can be derived.
kt _1/2 = ln2 (4)
As described above, the cross-linking agent in the cross-linking agent solution is pyrolyzed at a predetermined temperature, a plurality of relationships between time (t) and ln {a / (ax)} are plotted, and the decomposition rate is determined from the slope of the obtained straight line. Calculate the constant k. Then, the half-life t _1/2 at the predetermined temperature can be obtained from the equation (4).
On the other hand, for the decomposition rate constant k, the frequency factor A (1 / h), activation energy ΔE (J / mol), gas constant R (= 8.314 J / mol · K), and absolute temperature T (K) are used. Then, it can be expressed by the following formula.
k = Aexp (-ΔE / RT) (5)
lnk = lnA-ΔE / RT (6)
When the value of ln2 in the expression (4) is L (approximately 0.693) and k = L / t _1/2 is substituted into the expression (6), the following expression (7) is obtained.
lnt _1/2 = ΔE / RT + ln (L / A) (7)
Then, the half-life is calculated for a plurality of temperatures T (K), and the value of 1 / T when t _1/2 is 10 hours is calculated on the straight line obtained by plotting the relationship between lnt _1/2 and 1 / T. By reading and converting the value of T (K) into Celsius (° C.), the 10-hour half-life temperature can be obtained.

  And, the compounding amount of the cross-linking agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and preferably 3 parts by mass or less per 100 parts by mass of the hydrogenated nitrile rubber. More preferably 2.5 parts by mass or less. When the blending amount of the cross-linking agent is not less than the lower limit value of the above range, the cross-linking reaction can be sufficiently advanced when forming the positive electrode mixture layer. Therefore, the peel strength of the positive electrode can be increased and the cycle characteristics of the secondary battery can be further improved. On the other hand, when the blending amount of the crosslinking agent is not more than the upper limit value of the above range, it is possible to increase the flexibility of the positive electrode while ensuring the storage stability of the binder composition.

<Co-crosslinking agent>
The binder composition of the present invention may optionally contain a co-crosslinking agent. If a co-crosslinking agent is used in combination with the above-described crosslinking agent, when a slurry composition prepared using a binder composition is dried to form a positive electrode mixture layer, a more rigid crosslinked network is formed, It is possible to sufficiently suppress the elution of the hydrogenated nitrile rubber into the electrolytic solution while increasing the peel strength of the positive electrode. Therefore, the use of the co-crosslinking agent can further improve the cycle characteristics of the secondary battery.
Here, the co-crosslinking agent is not particularly limited, but examples thereof include polyfunctional aromatic vinyl compounds such as divinylbenzene and divinylnaphthalene; isocyanurates such as triallyl isocyanurate and trimetallyl isocyanurate; and triallyl cyanurate. Cyanurates; maleimides such as N, N'-m-phenylene dimaleimide; allyl esters of polyvalent acids such as diallyl phthalate, diallyl isophthalate, diallyl maleate, diallyl fumarate, diallyl sebacate, triallyl phosphate; Diethylene glycol bisallyl carbonate; ethylene glycol diallyl ether, triallyl ether obtained by allylating trimethylolpropane, and allyl ether obtained by partially allylating pentaerythritol. Examples thereof include ril ethers; tri- to 5-functional methacrylate compounds and acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate. Among them, isocyanurates are preferable, and triallyl isocyanurate is more preferable, from the viewpoint of further improving the cycle characteristics of the secondary battery. These may be used alone or in combination of two or more.

  And, the compounding amount of the co-crosslinking agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and further preferably 5 parts by mass or less, per 100 parts by mass of the hydrogenated nitrile rubber. It is more preferably 4 parts by mass or less. When the blending amount of the co-crosslinking agent is at least the lower limit value of the above range, the crosslinking reaction can be sufficiently advanced during the formation of the positive electrode mixture layer. Therefore, the peel strength of the positive electrode can be further increased, and the cycle characteristics of the secondary battery can be further improved. On the other hand, when the blending amount of the co-crosslinking agent is not more than the upper limit of the above range, the flexibility of the positive electrode can be increased while ensuring the storage stability of the binder composition.

<Solvent>
The solvent of the binder composition of the present invention is preferably an organic solvent. The organic solvent is not particularly limited and includes, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol. Alcohols such as; ketones such as acetone, methyl ethyl ketone, cyclohexanone; esters such as ethyl acetate, butyl acetate; ethers such as diethyl ether, dioxane, tetrahydrofuran; N, N-dimethylformamide, N-methylpyrrolidone (NMP) And the like; aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene; and the like. These may be used alone or in combination of two or more. Among them, NMP is more preferable as the solvent.

<Other ingredients>
In addition to the above components, the binder composition may be a binder other than hydrogenated nitrile rubber (polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, etc.), a reinforcing material, a leveling agent, a viscosity modifier, an electrolyte additive, etc. You may contain the component. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. Moreover, these components may be used individually by 1 type, and may be used in combination of 2 or more types in arbitrary ratios.
When the binder composition contains a binder (other binder) other than hydrogenated nitrile rubber, the ratio of the amount of the other binder in the total amount of the hydrogenated nitrile rubber and the other binder. Is preferably 40.0 mass% or more, more preferably 50.0 mass% or more, preferably 99.9 mass% or less, and more preferably 90.0 mass% or less. preferable. When the ratio of the amount of the other binder is at least the lower limit value of the above range, the internal resistance of the secondary battery can be reduced and the cycle characteristics can be secured. On the other hand, when the ratio of the amount of the other binder is equal to or less than the upper limit value of the above range, the flexibility of the positive electrode can be secured.

<Preparation of binder composition>
Then, the binder composition can be prepared by dissolving or dispersing a hydrogenated nitrile rubber, a crosslinking agent, and optionally a co-crosslinking agent and other components in a solvent such as an organic solvent. . The mixing method is not particularly limited, but the container itself is shaken, rotated, or vibrated to mix the contents, and a container stirring method using a rocking mixer, a tumbler mixer, or the like; A mixer (horizontal cylinder type mixer, V type mixer, rotation) in which a stirring shaft, a rotating disk, or a screw is attached to a rotating shaft (for example, extending horizontally or vertically to the wall surface of the container). Mechanical stirring method using a disk-type mixer and a high-speed rotary blade mixer, etc., and the like.
When the hydrogenated nitrile rubber is prepared as an aqueous dispersion, it is preferable to mix the aqueous dispersion and the solvent and then remove water to use for preparing the binder composition.
The solid content concentration of the binder composition thus prepared is not particularly limited, but is preferably 5% by mass or more, and preferably 20% by mass or less.

<Elution rate ratio>
The dissolution rate ratio (= dissolution rate A / dissolution rate B) of the binder composition of the present invention obtained as described above needs to be 0.45 or less, preferably 0.20 or less. , 0.10 or less is more preferable. If the elution rate ratio exceeds 0.45, the crosslinking reaction cannot be sufficiently promoted when the positive electrode mixture layer is formed. Therefore, the disconnection of the conductive path due to the swelling of the positive electrode cannot be suppressed, and the battery characteristics such as the cycle characteristics of the secondary battery deteriorate. The lower limit of the dissolution rate ratio of the binder composition of the present invention is not particularly limited, but is preferably 0.03 or more from the viewpoint of ensuring storage stability of the binder composition and flexibility of the positive electrode, and 0 It is more preferably at least 0.04.

  Here, the values of the dissolution rate A and the dissolution rate B are not particularly limited as long as the dissolution rate ratio is equal to or less than the above upper limit value. For example, the elution rate A is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, preferably 40% by mass or less, and 20% by mass or less. More preferably, it is still more preferably 10 mass% or less. The elution rate B is preferably 80% by mass or more, more preferably 85% by mass or more, 100% by mass or less, and preferably 95% by mass or less. When the elution rate B is less than 80% by mass, the solid content in the binder composition becomes difficult to dissolve in a solvent such as NMP, which may make the preparation of the binder composition itself difficult.

(Slurry composition for non-aqueous secondary battery positive electrode)
The slurry composition for a non-aqueous secondary battery positive electrode of the present invention contains the positive electrode active material and the binder composition described above, and optionally further contains a conductive material and other components. That is, the slurry composition of the present invention contains a positive electrode active material, a hydrogenated nitrile rubber, a crosslinking agent, and a solvent, and optionally further contains a co-crosslinking agent, a conductive material, and other components. . And since the slurry composition of the present invention contains the above-mentioned binder composition, the positive electrode mixture layer formed using the slurry composition of the present invention should exhibit excellent cycle characteristics in a secondary battery. You can

<Cathode active material>
The positive electrode active material is a substance that transfers electrons in the positive electrode of the secondary battery. Then, for example, as a positive electrode active material for a lithium ion secondary battery, a material capable of inserting and extracting lithium is usually used.
The positive electrode active material in the case where the non-aqueous secondary battery is a lithium ion secondary battery will be described below as an example, but the present invention is not limited to the following example.

  Specifically, as the positive electrode active material for a lithium ion secondary battery, a compound containing a transition metal, for example, a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and a transition metal, or the like is used. be able to. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, and the like.

Examples of the transition metal oxides, for example _{MnO, MnO 2, V 2 O} 5, V 6 O 13, TiO 2, Cu 2 V 2 O 3, amorphous _{V 2 O-P 2 O 5} , amorphous Examples thereof include quality MoO ₃ , amorphous V ₂ O ₅ , and amorphous V ₆ O ₁₃ .
Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS and the like.
Examples of the composite metal oxide of lithium and a transition metal include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, a lithium-containing composite metal oxide having an olivine structure, and the like. To be

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ (lithium cobalt oxide)), lithium-containing nickel oxide (LiNiO ₂ ), and Co—Ni—Mn lithium-containing composite oxide. (Li (Co Mn Ni) O ₂ ), a lithium-containing composite oxide of Ni—Mn—Al, a lithium-containing composite oxide of Ni—Co—Al, a solid solution of LiMaO ₂ and Li ₂ MbO _3, and the like. . The lithium-containing composite oxide of Co—Ni—Mn includes Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O. _{2 and the} like. Moreover, as a solid solution of LiMaO ₂ and Li ₂ MbO ₃ , for example, xLiMaO ₂ · (1-x) Li ₂ MbO _{3 and the} like can be mentioned. Here, x represents a number satisfying 0 <x <1, Ma represents one or more kinds of transition metals having an average oxidation state of 3+, and Mb represents one or more kinds of transition metals having an average oxidation state of 4+. Represent Examples of such a solid solution include Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O _{2 and the} like.
In the present specification, the “average oxidation state” refers to the average oxidation state of the “one or more kinds of transition metals” and is calculated from the molar amount of transition metal and the valence. For example, when the “one or more transition metals” is composed of 50 mol% Ni ²⁺ and 50 mol% Mn ⁴⁺ , the average oxidation state of the “one or more transition metals” is (0.5). × (2 +) + (0.5) × (4 +) = 3+.

Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and compounds obtained by substituting a part of Mn of lithium manganate (LiMn ₂ O ₄ ) with another transition metal. Is mentioned. Specific examples _{include Li s [Mn 2-t Mc} t] O 4 , such as LiNi _{0.5 Mn} 1.5 _{O 4.} Here, Mc represents one or more kinds of transition metals having an average oxidation state of 4+. Specific examples of Mc include Ni, Co, Fe, Cu, Cr and the like. Further, t represents a number satisfying 0 <t <1, and s represents a number satisfying 0 ≦ s ≦ 1. As the positive electrode active material, a lithium-excess spinel compound represented by Li _{1 + x} Mn _2-x O ₄ (0 <X <2) can also be used.

Examples of the lithium-containing mixed metal oxide having an olivine type structure include olivine type phosphorus represented by Li _y MdPO ₄ such as olivine type lithium iron phosphate (LiFePO ₄ ), olivine type lithium manganese phosphate (LiMnPO ₄ ). Examples thereof include lithium acid compounds. Here, Md represents one or more kinds of transition metals having an average oxidation state of 3+, and examples thereof include Mn, Fe, and Co. Further, y represents a number satisfying 0 ≦ y ≦ 2. Furthermore, in the olivine-type lithium phosphate compound represented by Li _y MdPO ₄ , Md may be partially substituted with another metal. Examples of the replaceable metal include Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B and Mo.

Among the above, from the viewpoint of enabling the lithium-ion secondary battery to have a higher potential, the positive electrode active material may be a lithium-containing cobalt oxide (LiCoO ₂ ), or a lithium-containing composite oxide of Co—Ni—Mn (Li. (Co Mn Ni) O ₂ ), a solid solution of LiMaO ₂ and Li ₂ MbO ₃ , Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ , Li [Ni _1/3 Co _1/3 Mn _{1 / 3]} such as _{O 2, LiNi 0.5 Mn 1.5 O} 4 are preferred.
The amount and particle size of the positive electrode active material blended are not particularly limited and may be the same as those of conventionally used positive electrode active materials.

<Binder composition>
As the binder composition, the above-mentioned binder composition for a non-aqueous secondary battery positive electrode of the present invention containing hydrogenated nitrile rubber, a crosslinking agent, and a solvent is used.

  Here, the content ratio of the binder composition in the non-aqueous secondary battery electrode slurry composition is such that the amount of hydrogenated nitrile rubber is 0.1 parts by mass or more per 100 parts by mass of the positive electrode active material. Is preferable, the amount is preferably 0.3 parts by mass or more, more preferably 3 parts by mass or less, and further preferably 1.5 parts by mass or less. If the binder composition is contained in the slurry composition in an amount such that the amount of hydrogenated nitrile rubber falls within the above range, while improving the peel strength and flexibility of the positive electrode in a well-balanced manner, the cycle characteristics of the secondary battery are further improved. Can be increased.

<Conductive material>
The conductive material is for ensuring electrical contact between the positive electrode active materials. Then, as the conductive material, carbon black (for example, acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite, carbon fiber, carbon flake, carbon ultrashort fiber (for example, carbon nanotube or vapor grown carbon). Conductive carbon materials such as fibers); fibers and foils of various metals can be used.
These may be used alone or in combination of two or more.

  And, the compounding amount of the conductive material is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and 5.0 parts by mass or less per 100 parts by mass of the positive electrode active material. The amount is preferably 4.5 parts by mass or less, and more preferably 4.5 parts by mass or less. When the amount of the conductive material is within the above range, good electrical contact between the positive electrode active materials can be ensured and the secondary battery can exhibit excellent battery characteristics (cycle characteristics, output characteristics, etc.).

<Other ingredients>
Other components that can be blended with the slurry composition for a non-aqueous secondary battery positive electrode are not particularly limited, and include the same components as the other components that can be blended with the binder composition described above. Further, other components may be used alone or in combination of two or more at an arbitrary ratio.

<Preparation of slurry composition>
The above-mentioned slurry composition can be prepared by dissolving or dispersing each of the above components in a solvent such as an organic solvent. Specifically, a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a mix such as a fill mix is used to mix the above components and the solvent. , A slurry composition can be prepared. The solvent used in the preparation of the slurry composition may be the solvent contained in the binder composition.

(Cathode for non-aqueous secondary battery)
The positive electrode for a non-aqueous secondary battery of the present invention usually comprises a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer is a slurry composition for the non-aqueous secondary battery positive electrode. It is formed by using things. Here, the cross-linking agent and the optionally used co-cross-linking agent in the slurry composition (hereinafter, these may be collectively referred to as “cross-linking agent etc.”) are usually used in forming the positive electrode mixture layer. Although consumed by the crosslinking reaction, the crosslinking agent and the like may remain in the positive electrode mixture layer. That is, the positive electrode mixture layer contains at least a positive electrode active material and a hydrogenated nitrile rubber and / or a crosslinked product of hydrogenated nitrile rubber, and may contain an unreacted crosslinking agent or the like. .
And, in the positive electrode for a non-aqueous secondary battery of the present invention, since the slurry composition containing the binder composition for a non-aqueous secondary battery positive electrode of the present invention is used, a positive electrode mixture material in which a crosslinked network is well formed. The layer can be well formed on the current collector. Therefore, when the positive electrode is used, a secondary battery having excellent battery characteristics such as cycle characteristics can be obtained.

<Production method of positive electrode>
The positive electrode for a non-aqueous secondary battery of the present invention includes, for example, a step of applying the above-mentioned slurry composition on a current collector (application step), and drying the slurry composition applied on the current collector. And a step of forming a positive electrode mixture layer on the current collector (drying step).

[Coating process]
The method for applying the slurry composition onto the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method or the like can be used. At this time, the slurry composition may be applied to only one surface of the current collector, or may be applied to both surfaces. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the positive electrode mixture layer obtained by drying.

  Here, as the current collector for applying the slurry composition, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. In addition, the said material may be used individually by 1 type and may be used in combination of 2 or more types by arbitrary ratios.

[Drying process]
The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used, for example, hot air, hot air, low-humid air drying methods, vacuum drying methods, infrared rays, electron beams, and the like. A drying method by irradiation can be mentioned. By thus drying the slurry composition on the current collector, a positive electrode mixture layer is formed on the current collector, and a positive electrode for a non-aqueous secondary battery including the current collector and the positive electrode mixture layer is obtained. be able to.

  The drying step preferably includes an operation of drying the slurry composition for a non-aqueous secondary battery positive electrode on the current collector at a temperature of 110 ° C or higher. When the drying temperature is 110 ° C. or higher, the crosslinking reaction with a crosslinking agent or the like can proceed, and the cycle characteristics of the secondary battery can be further improved.

Here, after the drying step, the positive electrode mixture layer may be subjected to a pressure treatment using a die press or a roll press. The pressure treatment can improve the adhesion between the positive electrode mixture layer and the current collector. When the positive electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after forming the positive electrode mixture layer.
In addition, after the drying step, it is preferable that the crosslinking step includes an operation of vacuum drying the positive electrode mixture layer on the current collector at a temperature of 140 ° C. or higher. By vacuum-drying the positive electrode mixture layer at 140 ° C. or higher, the cross-linking reaction with the cross-linking agent or the like can be sufficiently advanced, and the cycle characteristics of the secondary battery can be further improved.

The bulk density of the positive electrode mixture layer (= basis weight of the positive electrode mixture layer / thickness of the positive electrode mixture layer) formed on the current collector is not particularly limited, but is 3.6 g / cm ³ or more. it is preferred, more preferably preferably it is at 3.8 g / cm ³ or more is more or less preferably 4.2 g / cm ^3, is 4.0 g / cm ³ or less. The nonaqueous secondary battery positive electrode of the present invention uses the slurry composition containing the binder composition of the present invention for the preparation of the positive electrode mixture layer, and therefore the hydrogenated nitrile rubber is difficult to elute in the electrolytic solution. Therefore, even when the bulk density of the positive electrode mixture layer is set to a relatively high value within the above range and a low-viscosity electrolytic solution is used, it is possible to suppress disconnection of the conductive path due to swelling of the positive electrode. it can. Therefore, the secondary battery can exhibit sufficiently excellent cycle characteristics while receiving benefits such as an increase in energy density due to the higher density of the positive electrode mixture layer.
A rubber composition containing hydrogenated nitrile rubber and a cross-linking agent, but containing substantially no solvent, the positive electrode active material, and optionally a powder mixture obtained by adding a co-cross-linking agent, a conductive material and the like are heated. By compressing, the positive electrode mixture layer can be formed on the current collector. However, even if the positive electrode mixture layer is formed in the absence of a solvent as described above, the variation in the thickness of the positive electrode mixture layer increases. Even if such a positive electrode having a large variation in the thickness of the positive electrode mixture layer is used, the secondary battery cannot exhibit excellent battery characteristics (cycle characteristics, etc.).

(Non-aqueous secondary battery)
The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and uses the positive electrode for a non-aqueous secondary battery of the present invention as the positive electrode. Since the non-aqueous secondary battery of the present invention includes the positive electrode for a non-aqueous secondary battery of the present invention, it has excellent battery characteristics such as cycle characteristics.
In addition, although the case where the non-aqueous secondary battery is a lithium ion secondary battery will be described below as an example, the present invention is not limited to the following example.

<Negative electrode>
A known negative electrode can be used as the negative electrode. Specifically, as the negative electrode, for example, a negative electrode formed of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode mixture layer on a current collector can be used.
As the current collector, one made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum can be used. As the negative electrode mixture layer, a layer containing a negative electrode active material and a binder can be used. Furthermore, the binder is not particularly limited, and any known material can be used.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution prepared by dissolving a supporting electrolyte in an organic solvent is usually used. For example, a lithium salt is used as the supporting electrolyte of the lithium ion secondary battery. 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, and LiPF ₆ is particularly preferable, because it is easily dissolved in a solvent and exhibits a high dissociation degree. The electrolytes may be used alone or in combination of two or more at an arbitrary ratio. Generally, the higher the dissociation degree of the supporting electrolyte, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, and examples thereof include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and ethylmethyl carbonate (EMC); esters such as n-propylpropionate (PP), γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. Moreover, you may use the mixed liquid of these solvents. Of these, carbonates are preferably used because they have a high dielectric constant and a wide stable potential region.
The concentration of the electrolyte in the electrolytic solution can be adjusted appropriately. Further, known additives can be added to the electrolytic solution.

  Here, the SP value of the electrolytic solution is preferably 22.0 or more and 23.0 or less. An electrolyte solution having an SP value within the above range usually has a low viscosity and can well penetrate into a densified positive electrode mixture layer. On the other hand, an electrolytic solution having an SP value of 22.0 or more and 23.0 or less usually has a high solubility for hydrogenated nitrile rubber. However, since the secondary battery of the present invention uses the positive electrode for a non-aqueous secondary battery of the present invention as the positive electrode, even when the electrolytic solution having the above SP value is used, the hydrogenated nitrile rubber Elution can be suppressed and the conductive path in the positive electrode mixture layer can be retained. Therefore, by using an electrolytic solution having an SP value within the above range, the battery characteristics (cycle characteristics, etc.) of the secondary battery can be further improved.

<Separator>
The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among them, the film thickness of the entire separator can be reduced, whereby the ratio of the electrode active material in the secondary battery can be increased and the capacity per volume can be increased. A microporous membrane made of a resin of polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferable.

<Method of manufacturing secondary battery>
The secondary battery of the present invention includes, for example, a positive electrode and a negative electrode, which are superposed with a separator interposed therebetween, and which are wound or folded according to the shape of the battery, if necessary, and put into a battery container to be electrolyzed into the battery container. It can be manufactured by injecting a liquid and sealing. If necessary, a fuse, an overcurrent preventing element such as a PTC element, an expanded metal, a lead plate, or the like may be provided in order to prevent an increase in pressure inside the secondary battery, an occurrence of overcharge, and the like. The shape of the secondary battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a prismatic type, a flat type or the like.

Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples. In the following description, “%” and “part” representing the amount are based on mass unless otherwise specified.
Further, in a polymer produced by copolymerizing a plurality of kinds of monomers, the ratio of the monomer unit formed by polymerizing a certain monomer in the polymer is usually unless otherwise specified. This is the same as the ratio (feeding ratio) of the certain monomer to all the monomers used for the polymerization of the polymer.
In the examples and comparative examples, the elution ratio and storage stability of the binder composition, the flexibility and peel strength of the positive electrode, and the cycle characteristics of the secondary battery were evaluated using the following methods, respectively.

<Elution rate ratio>
About 1 g of the binder composition adjusted to a solid content concentration of 8% by mass was dried in an oven at 100 ° C. for 1 hour to obtain a binder film A having a thickness of about 120 μm. The initial weight W _A0 of this binder film A was measured.
The binder film A was vacuum dried (0.6 kPa) at 150 ° C. for 6 hours, and then LiPF ₆ was added to a mixed solvent of the measurement electrolytic solution (EC: PC: EMC: PP = 2: 1: 1: 6 (mass standard)). Was dissolved at a concentration of 1.0 mol / liter) at 60 ° C. for 72 hours. The binder film A pulled up from the electrolytic solution was washed with methanol, dried in an oven at 25 ° C. for 24 hours, and the weight W _A1 of the binder film A after immersion was measured. Then, the dissolution rate A was calculated from the following formula.
Dissolution rate _{A = (W A0 -W A1)} / W A0
Separately, about 1 g of the binder composition adjusted to have a solid content concentration of 8% by mass was dried in an oven at 100 ° C. for 1 hour to obtain a binder film B having a thickness of about 120 μm. The initial weight W _B0 of this binder film B was measured.
Binder film B was vacuum dried (0.6 kPa) at 25 ° C. for 6 hours, and then immersed in a measuring electrolyte solution having the same composition as above at 60 ° C. for 72 hours. The binder film B pulled up from the electrolytic solution was washed with methanol, dried in an oven at 25 ° C. for 24 hours, and the weight W _B1 of the binder film B after immersion was measured. Then, the dissolution rate B was calculated from the following formula.
Dissolution rate _{B = (W B0 -W B1)} / W B0
From the values of the obtained dissolution rate A and dissolution rate B, the dissolution rate ratio (= dissolution rate A / dissolution rate B) was calculated.
<Storage stability>
The viscosity M ₀ immediately after preparation of the binder composition and the viscosity M ₁ after storage at 40 ° C. for 7 days were measured. The viscosity was measured using a B-type viscometer, temperature: 25 ° C., rotor: No. 4. Rotational speed of rotor: 60 rpm.
Then, the rate of viscosity change ΔM (= M ₁ / M ₀ × 100 (%)) was calculated and evaluated according to the following criteria. The smaller the value of the rate of change in viscosity ΔM, the higher the viscosity stability of the binder composition.
A: Viscosity change rate ΔM is less than 110% B: Viscosity change rate ΔM is 110% or more and less than 120% C: Viscosity change rate ΔM is 120% or more <Flexibility>
Using the produced positive electrode, a bending resistance test was performed according to JIS K 5600 (mandrel test). The positive electrode was wound around a mandrel (diameter: 3 mm) so that the positive electrode mixture layer was on the outside, and the presence or absence of cracks in the positive electrode mixture layer was observed with a digital microscope (magnification: 30 times). This operation was performed on 10 positive electrodes and evaluated according to the following criteria.
A: No crack was observed on any of the 10 positive electrodes.
B: Cracks were observed in 1 to 3 sheets of 10 sheets of positive electrode.
C: Cracks were observed in 4 or more and 9 or less of 10 positive electrodes.
D: Cracks were observed on all 10 positive electrodes.
<Peel strength>
The produced positive electrode was cut into a rectangular piece having a width of 1.0 cm and a length of 10 cm to obtain a test piece. Then, cellophane tape was attached to the surface of the test piece on the positive electrode mixture layer side. At this time, the cellophane tape used was specified in JIS Z1522. Then, the stress when the test piece was peeled off from the one end side toward the other end side at a speed of 50 mm / min while the cellophane tape was fixed to the test table was measured. The measurement was performed 10 times, the average value of stress was calculated | required, this was made into peel strength, and it evaluated by the following criteria. The higher the peel strength, the better the adhesion of the positive electrode mixture layer to the current collector.
A: Peel strength is 50 N / m or more B: Peel strength is 10 N / m or more and less than 50 N / m C: Peel strength is less than 10 N / m <Cycle characteristics>
The produced secondary battery was allowed to stand for 5 hours in an environment of 25 ° C. After that, in a 25 ° C environment, the constant current method with a charging rate of 0.2C is used to charge the battery at a constant current until it reaches 4.4V, and at 4.4V, a constant voltage is charged until the charging current reaches 0.02C. I went. Furthermore, it was discharged to 3.0 V at a discharge rate of 0.2 C. After that, in an environment of 45 ° C., charging / discharging operation of charging to 4.4 V and discharging to 3.0 V was performed by a constant current method of 1.0 C, and an initial capacity C0 was measured. Furthermore, the same charge and discharge as the above was repeated 199 times for this lithium ion secondary battery, and the capacity C1 after 200 cycles in total was measured.
Regarding the cycle characteristics (high temperature cycle characteristics), the capacity retention rate ΔC represented by ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. The higher the value of the capacity retention ratio ΔC, the better the cycle characteristics.
A: Capacity maintenance ratio ΔC is 85% or more B: Capacity maintenance ratio ΔC is 80% or more and less than 85% C: Capacity maintenance ratio ΔC is 75% or more and less than 80% D: Capacity maintenance ratio ΔC is less than 75%

(Example 1)
<Preparation of hydrogenated nitrile rubber>
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate as an emulsifier, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 0.25 parts of t-dodecyl mercaptan as a chain transfer agent are added. After sequentially charging the inside of the bottle with nitrogen, 65 parts of 1,3-butadiene as a conjugated diene monomer was press-fitted, 0.25 part of ammonium persulfate was added as a polymerization initiator, and polymerization was carried out at a reaction temperature of 40 ° C. The reaction was carried out to obtain a polymer (nitrile rubber) containing a conjugated diene monomer unit and a nitrile group-containing monomer unit. The polymerization conversion rate was 85%.

  Ion-exchanged water was added to the obtained polymer to adjust the total solid content concentration to 12% by mass, and 400 ml (total solid content 48 g) of the solution was charged into a 1-liter autoclave equipped with a stirrer. After nitrogen gas was flowed for 10 minutes to remove dissolved oxygen in the solution, 50 mg of palladium acetate was dissolved as a hydrogenation reaction catalyst in 180 mL of ion-exchanged water containing 4-fold molar nitric acid with respect to palladium (Pd). And added. After the system was replaced with hydrogen gas twice, the content of the autoclave was heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and hydrogenation reaction (hydrogenation reaction of the first step) was performed for 6 hours. .

  Then, the autoclave was returned to atmospheric pressure, and further 25 mg of palladium acetate was dissolved in 60 ml of ion-exchanged water containing 4 times mol of nitric acid with respect to Pd as a hydrogenation reaction catalyst and added. After the system was replaced with hydrogen gas twice, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and a hydrogenation reaction (second-stage hydrogenation reaction) was performed for 6 hours. .

  Then, the contents were returned to room temperature, the system was made a nitrogen atmosphere, and then concentrated using an evaporator until the solid content concentration became 40% to obtain an aqueous dispersion of hydrogenated nitrile rubber. NMP as a solvent was added to this aqueous dispersion so that the solid content concentration of the hydrogenated nitrile rubber was 7%. Then, vacuum distillation was carried out at 90 ° C. to remove water and excess NMP to obtain an NMP solution of hydrogenated nitrile rubber having a solid content concentration of 8%. The iodine value of the obtained hydrogenated nitrile rubber was 50 mg / 100 mg.

<Preparation of binder composition for positive electrode>
2 parts of dicumyl peroxide (10-hour half-life temperature: 116.4 ° C.) as a crosslinking agent and 100 parts of a co-crosslinking agent with respect to 100 parts (solid content conversion) of the obtained hydrogenated nitrile rubber in NMP. 3 parts of allyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., trade name “TAIC”) and an appropriate amount of NMP are added, and the mixture is agitated and mixed at room temperature by a container agitation method so that the solid content concentration is 8% by mass for the positive electrode binder A composition was obtained. Using this positive electrode binder composition, storage stability was evaluated. The results are shown in Table 1.

<Preparation of slurry composition for positive electrode>
96 parts of lithium cobalt oxide LCO (LiCoO ₂ ) as a positive electrode active material, ₂ parts of acetylene black (BET specific surface area: 39 m ² / g) as a conductive material, and amounts of hydrogenated nitrile rubber, a crosslinking agent and a co-crosslinking agent Of 0.4 parts (solid content) of the positive electrode binder composition, and polyvinylidene fluoride (PVDF) NMP solution 1.52 parts (solid content) as a binder, and A slurry composition for a positive electrode was prepared by mixing NMP as a solvent with a planetary mixer. The amount of additional NMP is in the range of 4000 ± 200 mPa · s in the viscosity of the obtained positive electrode slurry composition (using a B-type viscometer. Temperature: 25 ° C., rotor: No. 4, rotor rotation speed: 60 rpm). Adjusted to be within.
<Production of positive electrode for secondary battery>
The obtained positive electrode slurry composition was applied to one side of an aluminum foil (thickness: 20 μm) as a current collector by a doctor blade method so that the applied amount after drying was 25 mg / cm ² , and the temperature was 60 ° C. 20 minutes and dried at 120 ° C. for 20 minutes to obtain a positive electrode raw material. Then, it was compressed with a biaxial roll press to produce a sheet-shaped positive electrode. A secondary battery in which this sheet-shaped positive electrode is vacuum-dried (0.6 kPa) at 150 ° C. for 10 hours, and a positive electrode mixture layer having a bulk density of 4.0 g / cm ³ is provided on an aluminum foil (current collector). A positive electrode for use was obtained. Using this positive electrode for secondary battery, flexibility and peel strength were evaluated. The results are shown in Table 1.
<Preparation of negative electrode for secondary battery>
In a planetary mixer equipped with a disperser, 100 parts of artificial graphite (volume average particle diameter: 24.5 μm, specific surface area: 4 m ² / g) as a negative electrode active material, and a 1% aqueous solution of carboxymethyl cellulose as a dispersant (first 1 part (in terms of solid content) (manufactured by Kogyo Seiyaku Co., Ltd., BSH-12) was added, and the solid content concentration was adjusted to 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Then, the solid content concentration was adjusted to 52% with ion-exchanged water, and then the mixture was mixed at 25 ° C. for 15 minutes to obtain a mixed liquid. To the obtained mixed liquid, 1.0 part (solid content conversion) of 40% aqueous dispersion of styrene-butadiene copolymer (glass transition temperature of -15 ° C) as a binder and ion-exchanged water were added. The mixture was added and adjusted so that the final solid content concentration was 50%, and mixed for 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition having good fluidity.
The obtained negative electrode slurry composition was applied with a comma coater to one side of a copper foil (thickness: 18 μm) as a current collector so that the applied amount after drying was about 14.7 mg / cm ^2. And dried. This drying was performed by transporting the copper foil at a rate of 0.5 m / min in an oven at 60 ° C. for 2 minutes. Then, it heat-processed at 120 degreeC for 2 minutes, and obtained the negative electrode original fabric. The negative electrode raw material was rolled by a roll press to obtain a negative electrode for a secondary battery in which a negative electrode mixture layer having a bulk density of 1.6 g / cm ³ was provided on a copper foil (current collector).
<Preparation of secondary battery separator>
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by dry method, porosity 55%) was cut out into a square of 5 cm × 5 cm.
<Manufacture of secondary battery>
An aluminum packaging material exterior was prepared as the exterior of the battery. Then, the positive electrode obtained above was cut into a square of 4 cm × 4 cm, and arranged so that the surface of the current collector side was in contact with the aluminum packaging material exterior. The square separator obtained above was placed on the positive electrode mixture layer of the positive electrode. Further, the negative electrode obtained above was cut into a square of 4.2 cm × 4.2 cm, and the square was placed on a separator so that the surface of the negative electrode mixture layer side faced the separator. Furthermore, in order to seal the opening of the aluminum packaging material exterior | packing after filling with electrolyte solution, 150 degreeC heat sealing was performed and the aluminum packaging exterior was closed, and the lithium ion secondary battery was obtained. As the electrolytic solution, LiPF ₆ was mixed in a mixed solvent of EC, PC, EMC, and PP in a mass ratio of EC: PC: EMC: PP = 2: 1: 1: ₆ with 1.0 mol / mol. The solution was dissolved at a concentration of 1 liter, and 1.5% by volume of vinylene carbonate was added as an additive. The SP value of the electrolytic solution was 22.20.
Then, the obtained lithium ion secondary battery was used to evaluate the cycle characteristics. The results are shown in Table 1.

(Example 2)
Hydrogenated nitrile rubber, a positive electrode binder composition, and a positive electrode slurry composition were prepared in the same manner as in Example 1 except that triallyl isocyanurate as a co-crosslinking agent was not added during preparation of the positive electrode binder composition. , A secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Examples 3 and 4)
When preparing the binder composition for the positive electrode, 1,1-di-t-hexylperoxy-cyclohexane (10-hour half-life temperature: 87.1 ° C.) and cumene hydroper were used instead of dicumyl peroxide as the cross-linking agent. Hydrogenated nitrile rubber, a positive electrode binder composition, a positive electrode slurry composition, a positive electrode for a secondary battery, in the same manner as in Example 1 except that oxide (10-hour half-life temperature: 157.9 ° C.) was used. A negative electrode for a secondary battery and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
Hydrogenated nitrile rubber and positive electrode binder composition were prepared in the same manner as in Example 1 except that trimethylolpropane triacrylate was used instead of triallyl isocyanurate as a co-crosslinking agent when preparing the positive electrode binder composition. And a slurry composition for a positive electrode, a positive electrode for a secondary battery, a negative electrode for a secondary battery, and a secondary battery. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Examples 6 and 7)
At the time of preparing the binder composition for a positive electrode, the hydrogenated nitrile rubber, the binder composition for a positive electrode, the positive electrode for a positive electrode were prepared in the same manner as in Example 1 except that the amounts of the crosslinking agent and the co-crosslinking agent were changed as shown in Table 1. A slurry composition, a secondary battery positive electrode, a secondary battery negative electrode and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 8)
At the time of producing the secondary battery, as an electrolytic solution, an electrolytic solution having an SP value of 24.18 (a mixed solvent obtained by mixing EC and EMC at a mass ratio EC: EMC = 3: 7, was added with 1.0 mol of LiPF ₆ ). / L and dissolved in vinylene carbonate 1.5% by volume), and hydrogenated nitrile rubber, binder composition for positive electrode, positive electrode were prepared in the same manner as in Example 1. A slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Hydrogenated nitrile rubber was prepared in the same manner as in Example 1 except that neither dicumyl peroxide as a crosslinking agent nor triallyl isocyanurate as a co-crosslinking agent was added during the preparation of the binder composition for a positive electrode. A binder composition for a positive electrode, a slurry composition for a positive electrode, a positive electrode for a secondary battery, a negative electrode for a secondary battery and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 2)
The NMP solution of hydrogenated nitrile rubber was poured into methanol to precipitate and solidify the hydrogenated nitrile rubber. Next, the precipitate was washed with methanol to remove NMP, and then methanol was further removed by drying to obtain a solid product of hydrogenated nitrile rubber. 100 parts of the obtained hydrogenated nitrile rubber solid matter and 5 parts of 40% 1,3-bis (t-butylperoxyisopropyl) benzene as a cross-linking agent (Arkema, trade name "Vul-Cup40KE") ( By kneading 2 parts of the active ingredient of the crosslinking agent) and 3 parts of triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., trade name “TAIC”) as a co-crosslinking agent at 50 ° C. for 5 minutes using an open roll, A crosslinked rubber composition was obtained.
An attempt was made to dissolve the crosslinked rubber composition in NMP to prepare a binder composition, but the crosslinked rubber composition was not dissolved in NMP, and the binder composition could not be prepared.
In addition, except that the crosslinked rubber composition (granular) was used as a measurement sample, and this measurement sample was handled as a binder film (A, B), the elution rates A and B were determined and the elution rate was obtained in the same manner as in Example 1. The ratio was calculated. The results are shown in Table 1.

(Comparative example 3)
When preparing the binder composition for a positive electrode, the binder composition for a positive electrode and the slurry for a positive electrode were prepared in the same manner as in Example 1 except that the acrylic polymer prepared as described below was used instead of the hydrogenated nitrile rubber. A composition, a positive electrode for secondary battery, a negative electrode for secondary battery, and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of acrylic polymer>
In a reactor A equipped with a mechanical stirrer and a condenser, 210 parts of ion-exchanged water and a 30% concentration of alkyldiphenyl oxide disulfonate as an emulsifier (Dow Fax (registered trademark) manufactured by Dow Chemical Co., Ltd.) were used as an emulsifier in a reactor. 2A1 ″) was charged in an amount of 0.5 part (as solid content), and then heated to 70 ° C. with stirring, and 25.5 parts of a 1.96% potassium persulfate aqueous solution was added to the reactor A. Then, in a container B separate from the reactor A, under a nitrogen atmosphere, 20 parts of 2-ethylhexyl acrylate as a (meth) acrylic acid ester monomer, 70 parts of styrene as an aromatic vinyl monomer, and a nitrile group-containing 10 parts of acrylonitrile as a monomer, 0.5 parts of a 30% concentration of alkyldiphenyl oxide disulfonate (“Dowfax (registered trademark) 2A1” manufactured by Dow Chemical Co.) as an emulsifier (solid content conversion), and 22.7 parts of ion-exchanged water was added, and this was emulsified with stirring to prepare a monomer mixture liquid. Then, in a state in which this monomer mixed liquid was emulsified with stirring, it was added to a reactor A charged with 210 parts of ion-exchanged water and an aqueous potassium persulfate solution at a constant rate over 2.5 hours. The reaction was carried out until the conversion of polymerization reached 95% to obtain an aqueous dispersion of an acrylic polymer. NMP as a solvent was added to this aqueous dispersion so that the solid content concentration of the acrylic polymer was 7%. Then, vacuum distillation was carried out at 90 ° C. to remove water and excess NMP to obtain an NMP solution of an acrylic polymer having a solid content concentration of 8%.

(Comparative example 4)
At the time of producing the secondary battery, as an electrolytic solution, an electrolytic solution having an SP value of 24.18 (a mixed solvent obtained by mixing EC and EMC at a mass ratio EC: EMC = 3: 7, was added with 1.0 mol of LiPF ₆ ). / L concentration, and vinylene carbonate (1.5% by volume) was added as an additive), in the same manner as in Comparative Example 1 except that hydrogenated nitrile rubber, positive electrode binder composition, and positive electrode were used. A slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced. Then, the evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

In addition, "HNBR" in Table 1 represents hydrogenated nitric rubber,
“ACL” indicates an acrylic polymer,
“DPO” indicates dicumyl peroxide,
“DHPC” refers to 1,1-di-t-hexylperoxy-cyclohexane,
“CHP” indicates cumene hydroperoxide,
"TAIC" indicates triallyl isocyanurate,
"TMPT" means trimethylolpropane triacrylate,
“PVDF” refers to polyvinylidene fluoride.

From Table 1, in Examples 1 to 8 using a binder composition containing a hydrogenated nitrile rubber, a cross-linking agent, and a solvent, and having an elution rate ratio of 0.45 or less, the binder composition had a stable viscosity. It can be seen that it is possible to manufacture a positive electrode which is excellent in durability, and which has flexibility and peel strength secured, and a secondary battery which is excellent in cycle characteristics.
Further, from Table 1, in Comparative Examples 1 and 4 using the binder composition containing no crosslinking agent and having an elution rate ratio of more than 0.45, the peel strength of the positive electrode was decreased, and It can be seen that the cycle characteristics deteriorate. Further, from Table 1, it is speculated that Comparative Example 3 using an acrylic polymer instead of hydrogenated nitrile rubber deteriorates the dispersed state of the conductive material, but the cycle characteristics of the secondary battery deteriorate. You can see that In addition, comparing Example 1 using an electrolytic solution having an SP value of 22.20 and Example 8 using an electrolytic solution having an SP value of 24.18, Example 1 is superior in cycle characteristics. There is. It is considered that this is because the electrolytic solution having an SP value of 22.20 has a lower viscosity than the electrolytic solution having an SP value of 24.18, and thus penetrates better into the positive electrode mixture layer. On the other hand, on the other hand, comparing Comparative Example 1 using an electrolytic solution having an SP value of 22.20 with Comparative Example 4 using an electrolytic solution having an SP value of 24.18, Comparative Example 1 has a cycle characteristic. It is falling. This is because Comparative Examples 1 and 4 do not use a cross-linking agent, and therefore, when an electrolytic solution having an SP value of 22.20 is used as in Comparative Example 1, the electrolytic solution satisfactorily penetrates into the positive electrode mixture layer. It is considered that the elution of the hydrogenated nitrile rubber into the electrolytic solution becomes remarkable.

According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery positive electrode and a slurry composition for a non-aqueous secondary battery positive electrode capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery. .
Further, according to the present invention, it is possible to provide a positive electrode for a non-aqueous secondary battery, which is capable of exhibiting excellent cycle characteristics in the non-aqueous secondary battery.
Furthermore, according to the present invention, a non-aqueous secondary battery having excellent cycle characteristics can be provided.

Claims (9)

Including hydrogenated nitrile rubber, cross-linking agent, and solvent,
A binder composition for a non-aqueous secondary battery positive electrode having an elution rate ratio of 0.45 or less calculated by the following formula (1).
Dissolution rate ratio = Dissolution rate A / Dissolution rate B (1)
In formula (1),
The elution rate A was determined by vacuum-drying a binder film formed from the binder composition for a non-aqueous secondary battery positive electrode at 150 ° C. for 6 hours, and then subjecting the binder film after vacuum drying to ethylene carbonate (EC) and propylene carbonate (PC). ), Ethylmethyl carbonate (EMC), and n-propylpropionate (PP) in a mass ratio of EC: PC: EMC: PP = 2: 1: 1: 6, and LiPF ₆ is added to a solvent obtained by adding 1. It represents the dissolution rate when immersed in a measuring electrolyte solution having a concentration of 0 mol / liter for 72 hours at 60 ° C.,
The elution rate B was determined by vacuum-drying a binder film formed from the binder composition for a non-aqueous secondary battery positive electrode at 25 ° C. for 6 hours, and applying the vacuum-dried binder film to the measuring electrolyte at 60 ° C. Represents the dissolution rate when immersed for 72 hours.   The binder composition for a non-aqueous secondary battery positive electrode according to claim 1, wherein the 10-hour half-life temperature of the cross-linking agent is 80 ° C or higher and 160 ° C or lower.   The binder composition for a non-aqueous secondary battery positive electrode according to claim 1, wherein the cross-linking agent is an organic peroxide.   The binder composition for a non-aqueous secondary battery positive electrode according to claim 1, wherein the crosslinking agent is contained in an amount of 1 part by mass or more and 3 parts by mass or less per 100 parts by mass of the hydrogenated nitrile rubber.   The binder composition for a non-aqueous secondary battery positive electrode according to claim 1, further comprising a co-crosslinking agent.   The binder composition for a non-aqueous secondary battery positive electrode according to claim 5, comprising 1 part by mass or more and 5 parts by mass or less of the co-crosslinking agent per 100 parts by mass of the hydrogenated nitrile rubber.   A slurry composition for a non-aqueous secondary battery positive electrode, comprising a positive electrode active material and the binder composition for a non-aqueous secondary battery positive electrode according to any one of claims 1 to 6.   A positive electrode for a non-aqueous secondary battery, comprising a positive electrode mixture layer formed by using the slurry composition for a non-aqueous secondary battery positive electrode according to claim 7.   A non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery according to claim 8, a negative electrode, an electrolytic solution, and a separator.