JP5733219B2 - Positive electrode for secondary battery and secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a secondary battery, and more particularly relates to a positive electrode for a secondary battery having high rate characteristics and cycle characteristics used for a lithium ion secondary battery and the like, and a slurry for a secondary battery positive electrode used therefor. The present invention also relates to a secondary battery having such an electrode.

Among batteries in practical use, lithium ion secondary batteries exhibit the highest energy density, and are often used particularly for small electronics. In addition to small-sized applications, it is also expected to expand to automotive applications. Among them, there is a demand for higher output of lithium ion secondary batteries and further improvement in reliability such as cycle characteristics.
The positive electrode active material that is a constituent material of the lithium ion secondary battery is an inexpensive lithium, nickel, manganese, and iron-containing lithium, because the price of cobalt-based active materials used as the mainstream is limited and the amount of reserves is limited. Transition to active materials is progressing.
However, lithium nickel oxide that achieves a high capacity has a problem of reducing the safety of the battery during charging, and lithium manganese oxide, which is safe and inexpensive, is 3 at the time of charge / discharge at high temperature (about 60 ° C.). There is a problem in that valent manganese is eluted in the electrolyte, which significantly deteriorates battery performance such as a long charge / discharge cycle, and the substitution to these materials has not progressed much.

In order to solve these problems, Patent Document 1 discloses that a long discharge / discharge cycle can maintain an average discharge voltage of 3 V or more and a discharge capacity equal to or higher than that of a lithium cobalt oxide-based positive electrode material. A lithium ferrite composite oxide containing a crystal phase having a layered rock salt structure is disclosed.
However, the lithium ferrite composite oxide disclosed in Patent Document 1 has poor charge / discharge characteristics, the initial charge / discharge efficiency is remarkably low, and an irreversible capacity of about 40% occurs. Yes.

On the other hand, an electrode used in a lithium ion secondary battery usually has a structure in which an electrode active material layer is laminated on a current collector, and the electrode active material layer includes an electrode active material in addition to the electrode active material. Binders are used to bind materials, electrode active materials, and current collectors. As a binder for lithium ion secondary batteries, in particular, a positive electrode binder, a fluororesin (PVDF) or a synthetic rubber polymer particle binder has been proposed.
As the synthetic rubber polymer particle type binder, a (meth) acrylate soft polymer is disclosed. (See Patent Documents 2 and 3)

JP 2003-48718 A JP-A-8-287915 (corresponding foreign publication: US Pat. No. 5,595,841) JP-A-11-149929

According to the study by the present inventors, a battery was prepared using the above-mentioned fluororesin (PVDF) or a commonly used synthetic rubber binder as a binder and a lithium ferrite composite oxide as an electrode active material. However, it was found that the above-described decrease in charge / discharge efficiency was not solved. However, by including a polymer unit of a vinyl monomer having an acid component in the synthetic rubber polymer particles, the polymer particles are adsorbed on the surface of the positive electrode active material, and the decomposition of the electrolytic solution generated on the surface of the active material is suppressed, It was found that the charge / discharge efficiency of the obtained battery can be remarkably improved.
However, even if a synthetic rubber-based binder disclosed in Patent Documents 2 and 3 including a vinyl monomer polymerization unit having such an acid component is used, the vinyl monomer unit having an acid component constituting the binder is contained. It was confirmed that depending on the amount, the storage stability of the binder was lowered, the stability of the slurry used for forming the electrode active material layer, and the binding property of the obtained electrode plate were lowered.
Therefore, the object of the present invention is to provide secondary battery positive electrode slurry having excellent binder storage stability and slurry stability, as well as excellent electrode binding properties, and the resulting battery can achieve high initial charge / discharge efficiency. Furthermore, another object of the present invention is to provide a positive electrode for a secondary battery that can achieve a reduction in capacity reduction due to repeated charge and discharge.

  As a result of intensive studies to solve the above problems, the present inventors have not only reduced storage stability of the binder and stability of the slurry, but also reduced battery capacity and output characteristics. It was found that this was due to the content ratio of the polymerization units of the vinyl monomer. Therefore, as a result of further investigation, as a binder, a polymer containing a polymerization unit of (meth) acrylic acid ester monomer, a polymerization unit of vinyl monomer having an acid component, and a polymerization unit of α, β unsaturated nitrile monomer, By using a vinyl monomer polymer unit having the acid component in a specific proportion of the total polymer units of the polymer, the slurry for lithium ion secondary battery positive electrode having excellent storage stability, and excellent binding properties, and It has been found that the obtained battery has a high initial charge / discharge efficiency, and that it is possible to produce a positive electrode for a lithium ion secondary battery with little capacity decrease due to repeated charge / discharge, and the present invention has been completed based on this. It came to do.

The present invention for solving the above-mentioned problems includes the following matters as a gist.
(1) A current collector and a positive electrode active material layer containing a positive electrode active material and a binder provided on the current collector, wherein the positive electrode active material has a composition formula Li _2-x (Mn _{1− mn} Fe _n Ni _m ) O _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0.30, 0.05 ≦ n ≦ 0.75, 0.06) ≦ m + n <1), and a lithium ferrite composite oxide having a layered rock salt structure,
The binder is a polymer including a polymerization unit of (meth) acrylic acid ester monomer, a polymerization unit of vinyl monomer having an acid component, and a polymerization unit of α, β unsaturated nitrile monomer, and polymerization of the vinyl monomer having the acid component The positive electrode for secondary batteries whose content rate of a unit is 1.0 to 3.0 weight% in all the polymerization units of a polymer.
(2) The positive electrode for a secondary battery according to (1), wherein the binder further includes a structural unit having crosslinkability.
(3) The positive electrode for a secondary battery according to the above (2), wherein the content ratio of the structural unit having crosslinkability is 0.05 to 2.0% by weight.
(4) The polymerization unit of the (meth) acrylic acid ester monomer is a polymerization unit of a (meth) acrylic acid alkyl ester monomer,
The polymerization unit of the vinyl monomer having an acid component is a polymerization unit of a monomer having a carboxylic acid group, a polymerization unit of a monomer having a sulfonic acid group, or a combination thereof.
The secondary according to any one of (1) to (3) above, wherein the polymerization unit of the α, β unsaturated nitrile monomer is a polymerization unit of acrylonitrile, a polymerization unit of methacrylonitrile, or a combination thereof. Battery positive electrode.
(5) The binder further includes a structural unit having crosslinkability,
The positive electrode for a secondary battery according to (4), wherein the structural unit having crosslinkability is a structural unit having an allyl group, a structural unit having an epoxy group, or a combination thereof.
(6) A positive electrode active material, a binder, and a solvent are contained, and the positive electrode active material has a composition formula Li _2-x (Mn _1-mn F _n Ni _m ) O _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0.30, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1) and a lithium ferrite having a layered rock salt structure A composite oxide, wherein the binder is a polymer containing a polymer unit of a (meth) acrylic acid ester monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β unsaturated nitrile monomer, The slurry for secondary battery positive electrodes whose content rate of the polymerization unit of the vinyl monomer which has a component is 1.0 to 3.0 weight% in all the polymerization units of a polymer.
(7) The polymerization unit of the (meth) acrylic acid ester monomer is a polymerization unit of a (meth) acrylic acid alkyl ester monomer,
The polymerization unit of the vinyl monomer having an acid component is a polymerization unit of a monomer having a carboxylic acid group, a polymerization unit of a monomer having a sulfonic acid group, or a combination thereof.
The slurry for secondary battery positive electrode according to (6), wherein the polymerization unit of the α, β unsaturated nitrile monomer is a polymerization unit of acrylonitrile, a polymerization unit of methacrylonitrile, or a combination thereof.
(8) The binder further includes a structural unit having crosslinkability,
The slurry for secondary battery positive electrode according to (7), wherein the structural unit having crosslinkability is a structural unit having an allyl group, a structural unit having an epoxy group, or a combination thereof.
(9) A secondary battery comprising a positive electrode, an electrolytic solution, a separator, and a negative electrode, wherein the positive electrode is the positive electrode for a secondary battery according to any one of (1) to (5).

  According to the present invention, the secondary battery positive electrode slurry having excellent stability and the binding property are excellent, and the obtained secondary battery has high charge / discharge efficiency, and further has a small capacity decrease due to repeated charge / discharge. It becomes possible to produce an electrode for a secondary battery.

The present invention is described in detail below.
The positive electrode for a secondary battery of the present invention has a current collector and a positive electrode active material layer containing a positive electrode active material and a binder provided on the current collector, and the positive electrode active material has a composition formula Li _{2. -x (Mn 1-m-n} Fe n Ni m) O 3-y ( where, 0 ≦ x <2,0 ≦ y ≦ 1,0.01 ≦ m ≦ 0.30,0.05 ≦ n ≦ 0 .75, 0.06 ≦ m + n <1), and a lithium ferrite composite oxide having a layered rock salt structure, wherein the binder is a polymer having a polymerization unit of (meth) acrylic acid ester monomer and an acid component It is a polymer containing a polymerized unit of a monomer and a polymerized unit of an α, β unsaturated nitrile monomer, and the content ratio of the polymerized unit of the vinyl monomer having the acid component is 1.0 to 3.0 in the total polymerized units of the polymer. % By weight.

(Positive electrode active material)
In the present invention, the lithium ferrite composite oxide used as the positive electrode active material has a composition formula of Li _2-x (Mn _1-mn Fe _n Ni _m ) O _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0.30, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1), and has a layered rock salt structure.
The lithium ferrite composite oxide is characterized in that Fe ions and Ni ions partially replace the Mn layer corresponding to the Co layer of LiCoO ₂ . That is, Fe ions and Ni ions are diluted by the coexistence of Li ions and Mn ions in the containing layer. The LiCoO _{2 in which} the entire Co layer is replaced by Fe ions is layered rock salt type LiFeO ₂ , but this material has almost no charge / discharge capacity. In order to obtain a complex oxide having a sufficient charge / discharge capacity, Fe ions and Ni ions need to partially replace the Mn layer corresponding to the Co layer of LiCoO _2. The amount of Fe ions to be dissolved in the lithium ferrite composite oxide is 5 to 75 mol% (0.05 ≦ n ≦ 0.75) of the amount of metal ions other than Li ions, and is 20 to 60 mol% (0. 20 ≦ n ≦ 0.60) is preferable. When the amount of Fe ion solid solution is excessive, Fe ions that do not participate in charge / discharge increase, which is not preferable in terms of battery characteristics. On the other hand, when the amount of Fe ion solid solution is too small, the charge / discharge capacity becomes small, which is also not preferable.

  In the lithium ferrite-based composite oxide used in the present invention, Ni ions to be dissolved in the lithium ferrite complex oxide are also present in the layered rock salt structure in the form of replacing Mn ions in the same manner as Fe ions. Ni ions are presumed to exist in a divalent to trivalent mixed valence state, and contribute to an improvement in the electronic conductivity of the composite oxide. The amount of Ni ions dissolved in the lithium ferrite composite oxide is 1 to 30 mol% (0.01 ≦ m ≦ 0.30) of the amount of metal ions other than Li ions, and 5 to 25 mol% (0. 05 ≦ m ≦ 0.25) is preferable. When a large amount of expensive Ni is used compared to Mn and Fe, it is economically disadvantageous. On the other hand, when the amount of Ni ions in the solid solution is too small, effects such as improvement of electron conductivity achieved by addition of Ni may not be sufficiently exhibited.

Furthermore, the total amount of Fe ions and Ni ions to be dissolved in the lithium ferrite composite oxide used in the present invention is as follows in the composition formula Li _2-x (Mn _1-mn Fe _n Ni _m ) O _3-y 0.06 ≦ m + n <1 or less, preferably 0.3 ≦ m + n ≦ 0.8. In addition, in the lithium ferrite composite oxide used in the present invention, as long as the layered rock salt type crystal structure can be maintained, x and y of Li _2-x MnO _3-y are positive values up to about 1 each. Can be taken. However, from the viewpoint of charge capacity, it is preferable to be as close to 0 as possible. Furthermore, the composite oxide used in the present invention may contain an impurity phase such as Li ₂ CO _{3 in a} range that does not significantly affect the charge / discharge characteristics (up to about 10 mol%).

  The lithium ferrite composite oxide used in the present invention can be produced by a hydrothermal reaction method, a solid phase reaction method, or the like, which is a common composite oxide synthesis method. However, in general, in a solid-phase reaction method using a dry mixing process, homogeneous mixing between metal ions (particularly mixing of Fe ions, Mn ions, and Ni ions) is difficult. Therefore, the lithium ferrite composite oxide used in the present invention can be produced by a hydrothermal reaction method using a mixed solution in which a metal salt that is a source of each ion is dissolved in water, a water / alcohol mixture, or the like. More preferable.

  The amount of the positive electrode active material contained in the electrode active material layer of the secondary battery positive electrode of the present invention is 50 to 99% by weight, more preferably 70 to 99% by weight, and the most preferable range is 80%. ~ 99% by weight. By setting it as the said range, a high capacity | capacitance lithium secondary battery is producible.

(binder)
The binder used in the present invention is a polymer containing a polymer unit of a (meth) acrylic acid ester monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β unsaturated nitrile monomer.

In the present invention, examples of the (meth) acrylic acid ester monomer constituting the polymerization unit of the (meth) acrylic acid ester monomer include (meth) acrylic acid alkyl ester, that is, acrylic acid alkyl ester and / or methacrylic acid alkyl ester. it can. For example, the general formula _{^{CH 2 = CR 1 -COO-R}} 2 (R 1 represents hydrogen or a methyl group, ^{R 2} represents an alkyl group) can be exemplified compounds represented by.
Examples of alkyl acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, Nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate and the like can be mentioned. Examples of the methacrylic acid alkyl ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, Nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate and the like can be mentioned.
Among these, the alkyl acrylate ester has a lithium ion conductivity by moderate swelling into the electrolyte without eluting into the electrolyte, and in addition, it is difficult to cause bridging and aggregation by the polymer in the dispersion of the active material. Preferred are heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, and lauryl acrylate, which are alkyl acrylates having 7 to 13 carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom. Octyl acrylate, 2-ethylhexyl acrylate, and nonyl acrylate having 8 to 10 carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom are more preferable because they do not swell in the electrolytic solution.

  In the present invention, the content ratio of the polymer units of the (meth) acrylic acid ester monomer in the binder is preferably 50 to 95% by weight, more preferably 60 to 90% by weight, based on the total polymer units of the polymer. . When the content ratio of the polymerization unit of the (meth) acrylic acid ester monomer in the binder is within the above range, a binder having excellent flexibility of the electrode plate and excellent oxidation resistance in the battery can be obtained.

In the present invention, the monomer constituting the polymerization unit of the vinyl monomer having an acid component includes a monomer having a —COOH group (carboxylic acid group), a monomer having an —OH group (hydroxyl group), and —SO _3. A monomer having an H group (sulfonic acid group), a monomer having a —PO ₃ H ₂ group, a monomer having a —PO (OH) (OR) group (R represents a hydrocarbon group), and Examples include monomers having a lower polyoxyalkylene group. Among them, a monomer having a —COOH group (carboxylic acid group), a monomer having an —OH group (hydroxyl group), a —SO ₃ H group (sulfonic acid group). ) Is more preferable because the binder can have high binding properties. In particular, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, or a combination thereof is particularly preferable.

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

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

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

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

  Among these, a monomer having a carboxylic acid group is preferable because of excellent adhesion to the current collector and efficient capture of manganese ions eluted from the positive electrode active material, among which acrylic acid and methacrylic acid are preferred. A monocarboxylic acid having a carboxylic acid group having 5 or less carbon atoms such as a dicarboxylic acid having 2 or less carboxylic acid groups having 5 or less carbon atoms such as maleic acid or itaconic acid is preferred. Furthermore, acrylic acid and methacrylic acid are particularly preferable from the viewpoint that the prepared binder has high storage stability.

In this invention, the content rate of the polymerization unit of the vinyl monomer which has an acid component in a binder needs to be 1.0 to 3.0 weight% in all the polymerization units of a polymer. When the content ratio of the polymer units of the vinyl monomer having an acid component in the binder is 1.0 to 3.0% by weight in the total polymer units of the polymer, the initial charge / discharge efficiency is high, and further charge / discharge is repeated. A battery with a small capacity drop due to the above can be obtained. In the present invention, if the content ratio of the polymerization unit of the vinyl monomer having an acid component in the binder is less than 1.0% by weight, the initial charge / discharge efficiency is small, and the capacity decrease due to repeated charge / discharge increases, conversely If it exceeds 3.0% by weight, the storage stability of the binder and the stability of the positive electrode slurry described later are lowered.
In this invention, it is preferable that the content rate of the polymerization unit of the vinyl monomer which has an acid component in a binder is 1.5 to 2.5 weight% in all the polymerization units of a polymer. When the content ratio of the polymerization unit of the vinyl monomer having an acid component in the binder is within the above range, a binder having excellent storage stability, a positive electrode slurry having excellent stability can be obtained, and further, initial charge / discharge efficiency Thus, a battery having a higher capacity and smaller capacity reduction due to repeated charge and discharge can be produced.

In the present invention, examples of the monomer constituting the polymerization unit of the α, β unsaturated nitrile monomer include acrylonitrile and methacrylonitrile.
In the present invention, the content of the polymerization units of the α, β unsaturated nitrile monomer in the binder is preferably 3 to 40% by weight, more preferably 5 to 30% by weight, based on the total polymerization units of the polymer. . When the content ratio of the polymerization unit of the α, β unsaturated nitrile monomer in the binder is within the above range, an electrode excellent in adhesion to the current collector, that is, binding property can be obtained.

The binder used in the present invention preferably further contains a structural unit having crosslinkability in addition to the above polymerized units. By including a structural unit having crosslinkability in the binder, the electrode strength can be further improved, which contributes to an improvement in yield in the battery manufacturing process.
Examples of a method for introducing a structural unit having crosslinkability into the binder include a method for introducing a photocrosslinkable crosslinkable group into the binder and a method for introducing a heat crosslinkable crosslinkable group. Among these, the method of introducing a heat-crosslinkable crosslinkable group into the binder can crosslink the binder by applying heat treatment to the electrode plate after coating, and can further suppress dissolution in the electrolyte. It is preferable because a strong and flexible electrode plate can be obtained. A method of using a monofunctional monomer having one olefinic double bond having a heat-crosslinkable crosslinkable group when introducing a heat-crosslinkable crosslinkable group into the binder, and at least two olefinic properties There is a method using a polyfunctional monomer having a double bond. The heat-crosslinkable crosslinkable group contained in the monofunctional monomer having one olefinic double bond is selected from the group consisting of epoxy group, hydroxyl group, N-methylolamide group, oxetanyl group, and oxazoline group. At least one selected from the above is preferable, and an epoxy group is more preferable in terms of easy crosslinking and adjustment of the crosslinking density.

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

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

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

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

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

Polyfunctional monomers having at least two olefinic double bonds include allyl acrylate or allyl methacrylate, ethylene glycol dimethacrylate, trimethylolpropane-triacrylate, trimethylolpropane-trimethacrylate, dipropylene glycol diallyl ether, poly Glycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, or allyl or vinyl ethers of other multifunctional alcohols, tetraethylene glycol diacrylate, triallylamine, trimethylolpropane-diallyl ether, methylene bis Acrylamide and / or divinylbenzene are preferred. In particular, allyl acrylate, allyl methacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate and / or trimethylolpropane-methacrylate and the like can be mentioned.
Of these, polyfunctional monomers having at least two olefinic double bonds are preferred because the crosslinking density is likely to be improved, and allyl acrylate is also preferred because of improved crosslinking density and high copolymerizability. Allyl methacrylate or ethylene glycol dimethacrylate is preferred.

  Among these, as the structural unit having crosslinkability, an allyl methacrylate polymer unit, an ethylene glycol dimethacrylate polymer unit, or a combination thereof is particularly preferable. In particular, polymerized units of allyl methacrylate are preferable because a high crosslinking effect can be obtained with a small amount.

  The content ratio of the structural unit having crosslinkability in the binder is preferably 0.05 to 100% by weight with respect to the total amount of the polymer as the amount of the structural unit based on the monomer containing the heat crosslinkable crosslinkable group. It is 2.0 weight%, More preferably, it is the range of 0.1-1.0 weight%. By making the content ratio of the structural unit having crosslinkability in the binder within the above range, the binding property of the electrode plate is further improved, and further, the excessive swelling to the electrolytic solution is suppressed, and the capacity decreases due to repeated charge and discharge. Can be made smaller. The content ratio of the structural unit having crosslinkability in the binder can be controlled by the monomer charge ratio when the binder is produced. When the content ratio of the structural unit having crosslinkability in the binder is within the above range, it is possible to show swelling property with respect to an appropriate electrolytic solution, higher initial charge / discharge efficiency, and capacity reduction due to repeated charge / discharge. It can be made smaller.

  The binder used in the present invention may contain an arbitrary polymerization unit in addition to the above components. Arbitrary polymer units are polymer units other than (meth) acrylic acid ester monomer polymer units, vinyl monomer polymer units having acid components, α, β unsaturated nitrile monomer polymer units, and crosslinkable structural units. is there. As monomers constituting such polymerized units, (meth) acrylic acid ester monomers, vinyl monomers having an acid component, α, β unsaturated nitrile monomers, and monomers other than those constituting structural units having crosslinkability The vinyl monomer can be mentioned. Specifically, halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; methyl And vinyl ketones such as vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; and acrylamide. The content ratio of these polymerized units is 10% by weight or less in the total polymerized units of the polymer.

The binder used in the present invention is used in the state of a dispersion liquid or a dissolved solution dispersed in a dispersion medium. Among these, it is preferable that it is dispersed in the dispersion medium in the form of particles because the swelling property of the electrolytic solution is suppressed.
When the binder is dispersed in a particulate form in the dispersion medium, the number average particle size of the binder dispersed in the particulate form is preferably 50 nm to 500 nm, more preferably 70 nm to 400 nm, and most preferably 100 nm to 250 nm. is there. When the average particle size of the binder is within this range, the strength and flexibility of the obtained electrode are improved. In addition, an organic solvent or water is used as the dispersion medium, but it is preferable to use water as the dispersion medium because of the high drying speed.

  When the binder is dispersed in the dispersion medium in the form of particles, the solid content concentration of the dispersion is usually 15 to 70% by weight, preferably 20 to 65% by weight, and more preferably 30 to 60% by weight. When the solid content concentration is within this range, workability in the production of the slurry for electrodes is good.

  The glass transition temperature (Tg) of the binder used in the present invention is preferably −50 to 25 ° C., more preferably −45 to 15 ° C., and particularly preferably −40 to 5 ° C. When the Tg of the binder is in the above range, a secondary battery electrode having excellent strength and flexibility and high output characteristics can be obtained. The glass transition temperature of the binder can be adjusted by combining various monomers.

The method for producing the binder used in the present invention is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Examples of the polymerization initiator used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.
The proportion of polymerized units in the binder can be adjusted by adjusting the proportion of the corresponding monomer.

  The dispersant used in the case where the binder used in the present invention is produced by a polymerization method such as emulsion polymerization or suspension polymerization may be used in ordinary synthesis. Specific examples include sodium dodecylbenzenesulfonate and dodecyl. Benzene sulfonates such as sodium phenyl ether sulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate; fatty acid salts such as sodium laurate; poly Ethoxy sulfate salts such as oxyethylene lauryl ether sulfate sodium salt and polyoxyethylene nonylphenyl ether sulfate sodium salt; alkane sulfonate; alkyl ether phosphate ester Tersodium salt; Nonionic emulsifier such as polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, polyoxyethylene-polyoxypropylene block copolymer; gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, Examples thereof include water-soluble polymers such as sodium polyacrylate, polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more, and these may be used alone or in combination of two or more. Among these, benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecylsulfate are preferable, and oxidation resistance is more preferable. From this point, it is a benzenesulfonate such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate. The addition amount of the dispersing agent can be arbitrarily set, and is usually about 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of monomers.

  The pH when the binder used in the present invention is dispersed in the dispersion medium is preferably 5 to 13, more preferably 5 to 12, and most preferably 10 to 12. When the pH of the binder is in the above range, the storage stability of the binder is improved, and further, the mechanical stability is improved.

  PH adjusting agents for adjusting the pH of the binder include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, alkaline earth metal oxides such as calcium hydroxide, magnesium hydroxide and barium hydroxide, Hydroxides such as hydroxides of metals belonging to Group IIIA in a long periodic table such as aluminum hydroxide; carbonates such as alkali metal carbonates such as sodium carbonate and potassium carbonate, alkaline earth metal carbonates such as magnesium carbonate Examples of organic amines include alkylamines such as ethylamine, diethylamine and propylamine; alcohol amines such as monomethanolamine, monoethanolamine and monopropanolamine; ammonia such as ammonia water; Can be mentioned. Among these, alkali metal hydroxides are preferable from the viewpoints of binding properties and operability, and sodium hydroxide, potassium hydroxide, and lithium hydroxide are particularly preferable.

  Content of the binder in a positive electrode active material layer is 0.1-10 weight part with respect to 100 weight part of positive electrode active materials, More preferably, it is 0.5-5 weight part. The content of the binder in the positive electrode of the secondary battery is within the above range, so that the positive electrode active materials are excellent in binding property to the current collector and the current collector. Does not increase.

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

  In addition to the above components, the positive electrode active material layer used in the present invention further has electroconductivity imparting material, reinforcing material, dispersing agent, leveling agent, antioxidant, thickener, electrolytic solution having functions such as inhibiting decomposition of the electrolyte. Optional components such as liquid additives and other binders may be contained. These components may also be contained in a slurry for a secondary battery positive electrode described later. These are not particularly limited as long as they do not affect the battery reaction.

  As the conductivity-imparting material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. Examples thereof include carbon powders such as graphite, and fibers and foils of various metals. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved. In particular, when used in a lithium ion secondary battery, the discharge load characteristics can be improved. As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The usage-amount of an electroconductivity imparting material or a reinforcing agent is 0.01-20 weight part normally with respect to 100 weight part of electrode active materials, Preferably it is 1-10 weight part. By being included in the said range, a high capacity | capacitance and a high load characteristic can be shown.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. A dispersing agent is selected according to the electrode active material and electrically conductive agent to be used. The content ratio of the dispersant in the positive electrode active material layer is preferably 0.01 to 10% by weight. When the amount of the dispersant is in the above range, the positive electrode slurry described later is excellent in stability, a smooth electrode can be obtained, and a high battery capacity can be exhibited.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode. The content ratio of the leveling agent in the positive electrode active material layer is preferably 0.01 to 10% by weight. When the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.

  Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer type phenol compound is a polymer having a phenol structure in the molecule, and a polymer type phenol compound having a weight average molecular weight of 200 to 1000, preferably 600 to 700 is preferably used. The content ratio of the antioxidant in the positive electrode active material layer is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight. When the antioxidant is within the above range, the positive electrode slurry described later is excellent in stability, battery capacity, and cycle characteristics.

  Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. When the use amount of the thickener is within this range, the coating property and the adhesion with the electrode and the organic separator are good. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”. The content ratio of the thickener in the positive electrode active material layer is preferably 0.01 to 10% by weight. When the thickener is in the above range, a smooth electrode having excellent dispersibility of the active material in the positive electrode slurry described later can be obtained, and excellent load characteristics and cycle characteristics are exhibited.

  As the electrolytic solution additive, vinylene carbonate used in the positive electrode slurry and the electrolytic solution described later can be used. The content ratio of the electrolytic solution additive in the positive electrode active material layer is preferably 0.01 to 10% by weight. When the electrolytic solution additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the electrode forming slurry can be controlled, and the leveling property of the resulting electrode can be improved. The content ratio of nanoparticles and the like in the positive electrode active material layer is preferably 0.01 to 10% by weight. When the nanoparticles are in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

  As a method for producing the positive electrode for a secondary battery of the present invention, any method may be used as long as the positive electrode active material layer is bound in layers on at least one surface, preferably both surfaces of the current collector. For example, a slurry for a lithium secondary battery positive electrode, which will be described later, is applied to a current collector and dried, and then heated at 120 ° C. or higher for 1 hour or longer to form an electrode. Although the upper limit of heat processing temperature is not specifically limited, Preferably it can be 300 degrees C or less. The upper limit of the heating time is not particularly limited, but can be preferably 200 ° C. or lower. The method for applying the positive electrode slurry to the current collector is not particularly limited. Examples thereof include a doctor blade method, a zip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.

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

  The thickness of the positive electrode for secondary batteries of the present invention is usually 5 to 300 μm, preferably 10 to 250 μm. When the electrode thickness is in the above range, both load characteristics and energy density are high.

(Slurry for secondary battery positive electrode)
The slurry for a secondary battery positive electrode used in the present invention contains a positive electrode active material, a binder, and a solvent, and the positive electrode active material has a composition formula Li _2-x (Mn _1-mn Fe _n Ni _m ) O. _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0.30, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1), And a lithium ferrite composite oxide having a layered rock salt structure, wherein the binder is a polymerization unit of (meth) acrylate monomer, a polymerization unit of vinyl monomer having an acid component, and a polymerization unit of α, β unsaturated nitrile monomer The content ratio of the polymer units of the vinyl monomer having the acid component is 1.0 to 3.0% by weight in the total polymer units of the polymer. As a binder and a positive electrode active material, what was demonstrated by the positive electrode for secondary batteries is used.

(solvent)
The solvent is not particularly limited as long as it can uniformly dissolve or disperse the binder used in the present invention.
As the solvent used for the positive electrode slurry, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Ketones; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; Amides such as loridone and N, N-dimethylformamide are exemplified.
These solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent. Among these, a solvent having excellent dispersibility of the electrode active material and the conductive agent and having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. Acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable. In addition, since the effect of the present invention is noticeable when a water-dispersed particulate polymer is used as a binder, water is particularly preferable as a solvent.

  The solid content concentration of the slurry for the secondary battery positive electrode used in the present invention is not particularly limited as long as it can be applied and immersed and has a fluid viscosity, but is generally about 10 to 80% by weight. It is.

  In addition to the binder, the lithium ferrite composite oxide and the solvent, the slurry for the secondary battery positive electrode further functions as a dispersant used in the above-mentioned positive electrode for the secondary battery and the electrolytic solution decomposition suppression. Arbitrary components, such as electrolyte solution additive which has this, may be contained. These are not particularly limited as long as they do not affect the battery reaction.

(Slurry manufacturing method for secondary battery positive electrode)
In the present invention, the method for producing the slurry for the secondary battery positive electrode is not particularly limited, and can be obtained by mixing the binder, the lithium ferrite composite oxide, and the solvent and optional components added as necessary.
In the present invention, a positive electrode slurry in which the above components are highly dispersed can be obtained regardless of the mixing method and mixing order by using the above components. The mixing device is not particularly limited as long as it can uniformly mix the above-mentioned components. Bead mill, ball mill, roll mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, fill mix, etc. Among them, it is particularly preferable to use a ball mill, a roll mill, a pigment disperser, a crusher, or a planetary mixer because dispersion at a high concentration is possible.
The viscosity of the positive electrode slurry is preferably 10 mPa · s to 100,000 mPa · s, more preferably 100 to 50,000 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

(Secondary battery)
The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the positive electrode is the positive electrode for the secondary battery.

  Examples of the secondary battery include a lithium ion secondary battery and a nickel hydride secondary battery. However, since the most demanded performance improvement such as improvement of long-term cycle characteristics / improvement of output characteristics, lithium ion secondary batteries are used as applications. Secondary batteries are preferred. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

(Electrolyte for lithium ion secondary battery)
As the electrolytic solution for the lithium ion secondary battery, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. A lithium salt is used as the supporting electrolyte. The lithium salt is not particularly _{limited, LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferable. Two or more of these may be used in combination. Since the lithium ion conductivity increases as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

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

The concentration of the supporting electrolyte in the electrolytic solution for a lithium ion secondary battery is usually 1 to 30% by weight, preferably 5% to 20% by weight. Further, it is usually used at a concentration of 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease.
Examples of the electrolytic solution other than the above include polymer electrolytes such as polyethylene oxide and polyacrylonitrile, gelled polymer electrolytes in which the polymer electrolyte is impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li ₃ N.

(Separator for lithium ion secondary battery)
As a separator for a lithium ion secondary battery, known ones such as a microporous film or non-woven fabric containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder can be used. . For example, a polyolefin film (polyethylene, polypropylene, polybutene, polyvinyl chloride), a microporous film made of a resin such as a mixture or copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, Examples thereof include a microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like. Among these, a microporous film made of a polyolefin-based resin is preferable because the thickness of the entire separator can be reduced and the active material ratio in the battery can be increased to increase the capacity per volume.
The thickness of a separator is 0.5-40 micrometers normally, Preferably it is 1-30 micrometers, More preferably, it is 1-10 micrometers. Within this range, the resistance due to the separator in the battery is reduced, and the workability during battery production is excellent.

(Lithium ion secondary battery negative electrode)
The negative electrode for a lithium ion secondary battery is formed by laminating a negative electrode active material layer containing a negative electrode active material and a binder on a current collector. Examples of the binder and the current collector are the same as those described for the positive electrode for the secondary battery.

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

  The content ratio of the negative electrode active material in the negative electrode active material layer is preferably 90 to 99.9% by weight, more preferably 95 to 99% by weight. By setting the content of the negative electrode active material in the negative electrode active material layer within the above range, flexibility and binding properties can be exhibited while exhibiting high capacity.

  In addition to the above components, the negative electrode for a lithium ion secondary battery further includes optional components such as a dispersant used in the above-described positive electrode for a secondary battery and an electrolyte additive having a function of inhibiting electrolyte decomposition and the like. It may be included. These are not particularly limited as long as they do not affect the battery reaction.

(Binder for lithium ion secondary battery negative electrode)
The binder for the negative electrode of the lithium ion secondary battery is not particularly limited and a known binder can be used. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid, which are used for the above-described lithium ion secondary battery positive electrode Resins such as derivatives and polyacrylonitrile derivatives, and soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, and vinyl soft polymers can be used. These may be used alone or in combination of two or more.

  As the current collector, the current collector used for the secondary battery positive electrode described above can be used, and is not particularly limited as long as the material has electrical conductivity and is electrochemically durable. Copper is particularly preferable for the negative electrode of a lithium ion secondary battery.

  The thickness of the lithium ion secondary battery negative electrode is usually 5 to 300 μm, preferably 10 to 250 μm. When the electrode thickness is in the above range, both load characteristics and energy density are high.

  The lithium ion secondary battery negative electrode can be produced by the same method as that for the lithium ion secondary battery positive electrode described above.

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

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

<Binder properties: storage stability>
The obtained aqueous dispersion of the binder is stored for 50 days in a cool dark place (the weight of the aqueous dispersion before storage is a). The polymer aqueous dispersion after 50 days was filtered through 200 mesh, the dry weight of the solid matter remaining on the mesh was determined (the weight of the residue is b), and the weight of the aqueous dispersion before storage (a ) And the dry weight (b) of the solid matter remaining on the mesh, the ratio (%) is determined, and this is used as an evaluation criterion for the storage stability of the binder, and is evaluated according to the following criteria. It shows that it is excellent in storage stability, so that this value is small.
A: Less than 0.001% B: 0.001% or more and less than 0.01% C: 0.01% or more and less than 0.1% D: 0.1% or more

<Slurry stability: Viscosity change rate>
From the slurry viscosity (η _1h ) 1 hour after the production of the positive electrode slurry and the slurry viscosity (η _5h ) after 5 hours, the rate of change in slurry viscosity is determined by the following formula, and the following criteria are used.
Slurry viscosity change rate (%) = 100 × (η _5h −η _1h ) / η _1h
It shows that stability of a slurry is so high that this value is small.
A: Less than 10% B: 10% or more and less than 20% C: 20% or more and less than 30% D: 30% or more The viscosity of the slurry is a single cylindrical rotational viscometer (25 ° C. according to JIS Z8803: 1991). Rotational speed = 60 rpm, spindle shape: 4)

<Electrode characteristics: peel strength>
The positive electrode on which the electrode active material layer is formed is cut into a rectangle having a width of 2.5 cm and a length of 10 cm to form a test piece, which is fixed with the electrode active material layer surface facing up. After applying the cellophane tape to the surface of the electrode active material layer of the test piece, the stress is measured when the cellophane tape is peeled off from one end of the test piece in the direction of 180 ° at a speed of 50 mm / min. The measurement is performed 10 times, an average value thereof is obtained, and this is defined as peel strength (N / m), which is used as an evaluation standard for peel strength, and evaluated according to the following criteria. It shows that it is excellent in the binding property of an electrode, so that this value is large.
A: 15 N / m or more B: 10 N / m or more to less than 15 N / m C: 5.0 N / m or more to less than 10 N / m D: less than 5.0 N / m

<Battery characteristics: Initial charge / discharge efficiency>
A 10-cell half-cell coin-type battery was charged to 4.3 V by a constant current method of 0.2 C in a 25 ° C. atmosphere, charged and discharged to 3.0 V, and the electric capacity was measured. The charge / discharge efficiency is the ratio of the discharge capacity b of the first cycle to the charge capacity a of the first cycle (b / a (%)), with the average value of 10 cells as the measured value, the electric capacity at the end of 50 cycles and the 5 cycles The charge / discharge capacity retention ratio represented by the ratio (%) of the electric capacity at the end is obtained, and this is used as an evaluation criterion for cycle characteristics, and evaluated according to the following criteria. It shows that it is excellent in initial stage charge / discharge efficiency, so that this value is large.
A: 60% or more B: 40% or more and less than 50% C: 30% or more and less than 40% D: 20% or more and less than 30% E: Less than 20% <Battery characteristics: cycle characteristics>
A 10-cell half-cell coin-type battery was charged to 4.3 V by a constant current method of 0.2 C in an atmosphere at 60 ° C., and the electric capacity was repeatedly measured by charging and discharging to 3.0 V. Using the average value of 10 cells as the measured value, the charge / discharge capacity retention ratio represented by the ratio (%) of the electric capacity at the end of 50 cycles and the electric capacity at the end of 5 cycles is obtained, and this is used as an evaluation criterion for cycle characteristics. Evaluation is based on the following criteria. The higher this value, the better the cycle characteristics, that is, the smaller the capacity drop due to repeated charge and discharge.
A: 80% or more B: 70% or more and less than 80% C: 50% or more and less than 70% D: 30% or more and less than 50% E: Less than 30%

Example 1
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water are added to the polymerization can A, and 0. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, another polymerization vessel B was charged with 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, sodium lauryl sulfate 0 7 parts and 46 parts of ion-exchanged water were added to the emulsion prepared by stirring for about 180 minutes, and then added to the polymerization can A sequentially from the polymerization can B. After stirring for about 120 minutes, the monomer consumption was 95%. Then, the reaction was terminated by cooling to obtain an aqueous dispersion of binder A. The obtained binder A had a glass transition temperature of −32 ° C. and a number average particle size of 0.15 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder A, the content ratio of the polymer units of the (meth) acrylate monomer is 79% of the total polymer units of the polymer, and the content rate of the polymer units of the vinyl monomer having an acid component is 2% in the total polymer units of the polymer. 0.0%, the content of polymerization units of α, β-unsaturated nitrile monomer was 18%, and the content of structural units having crosslinkability was 0%.
The pH of the obtained binder A was 10.5 after adjusting with 4 wt% NaOH aqueous solution.

(B) Production of slurry for positive electrode and positive electrode Based on Example 1 of Japanese Patent Application Laid-Open No. 2003-48718, it is represented by Li _2-x MnO _3-y containing 10% Ni-40% Fe having a layered rock salt structure. A lithium ferrite composite oxide was synthesized. 100 parts of the obtained lithium ferrite-based composite oxide, 2.0 parts of acetylene black (HS-100: Electrochemical Industry), 2.5 parts of the aqueous dispersion of the binder A (solid content concentration 40%), A slurry for positive electrode was prepared by stirring 40 parts of a carboxymethylcellulose aqueous solution (solid content concentration 2%) having a degree of etherification of 0.8 as a thickener with a planetary mixer. Slurry stability was evaluated using the obtained positive electrode slurry. The results are shown in Tables 1 and 2. The positive electrode slurry is applied on an aluminum foil having a thickness of 20 μm with a comma coater so that the film thickness after drying becomes about 70 μm, dried at 60 ° C. for 20 minutes, and then heat-treated at 150 ° C. for 2 hours to form an electrode substrate. Got anti. This electrode original fabric was rolled with a roll press to produce a positive electrode plate with a density of 2.1 g / cm ³ and a thickness of aluminum foil and an electrode active material layer controlled to 65 μm. Peel strength measurement was performed using the produced electrode plate. The results are shown in Tables 1 and 2.

(C) Production of battery The positive electrode plate was cut into a disk shape having a diameter of 16 mm. A separator made of a disc-shaped polypropylene porous film having a diameter of 18 mm and a thickness of 25 μm, and a negative electrode of metallic lithium were prepared. A disc-shaped positive electrode plate, separator, negative electrode, and expanded metal are laminated in order, and this is a stainless steel coin-type outer container with a polypropylene packing (diameter 20 mm, height 1.8 mm, stainless steel thickness 0 .25 mm). The disc-shaped positive electrode plate was disposed so that the surface on the active material layer side faced the separator. The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A lithium ion coin battery (half cell) having a thickness of 20 mm and a thickness of about 2 mm was produced.
In addition, as an electrolytic solution, LiPF ₆ was added at 1 mol / liter in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). A solution dissolved at a concentration was used.
The initial charge / discharge efficiency and cycle characteristics were evaluated using this battery. The results are shown in Tables 1 and 2.

(Example 2)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water are added to Polymerization Can A, and 0.2% of ammonium persulfate is used as a polymerization initiator. And 10 parts of ion-exchanged water were added and heated to 60 ° C. and stirred for 90 minutes. Then, another polymerization vessel B was charged with 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of itaconic acid, 0. 7 parts and an emulsion prepared by adding 46 parts of ion-exchanged water and stirring were sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes, resulting in a monomer consumption of 95%. The reaction was terminated after cooling to obtain an aqueous dispersion of binder B. The obtained binder B had a glass transition temperature of −29 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
The content ratio of the polymer units of the (meth) acrylic acid ester monomer in the binder B is 79% of the total polymer units of the polymer, and the polymer unit of the vinyl monomer having an acid component is 2. The content of polymer units of 0%, α, β unsaturated nitrile monomer was 18% of the total polymer units of the polymer, and the content of cross-linkable structural units was 0%.
The pH of the obtained binder B was 10.6 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder B was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 3)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water are added to Polymerization Can A, and 0.2% of ammonium persulfate is used as a polymerization initiator. And 10 parts of ion-exchanged water were added and heated to 60 ° C. and stirred for 90 minutes. Then, another polymerization vessel B was charged with 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 1.0 part of methacrylic acid, 0. 7 parts and an emulsion prepared by adding 46 parts of ion-exchanged water and stirring were sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes, resulting in a monomer consumption of 95%. The reaction was terminated by cooling to obtain an aqueous dispersion of binder C. The obtained binder C had a glass transition temperature of −32 ° C. and a number average particle size of 0.15 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
The content ratio of polymer units of (meth) acrylic acid ester monomer in binder C is 78% of the total polymer units of the polymer, and the polymer unit of vinyl monomers having an acid component is 1.0% of the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 20% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0%.
The pH of the obtained binder C was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder C was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

Example 4
(A) Production of Binder 10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water are added to Polymerization Can A, 0.2 parts of ammonium persulfate as a polymerization initiator, After adding 10 parts of ion exchange water and heating to 60 ° C. and stirring for 90 minutes, 67 parts of ethyl acrylate, 19 parts of acrylonitrile, 1.0 part of itaconic acid, 0.7 part of sodium lauryl sulfate, The emulsion prepared by adding 46 parts of exchange water and stirring was added sequentially from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes and cooled when the monomer consumption reached 95%. Thus, the reaction was completed, and an aqueous dispersion of binder D was obtained. The obtained binder D had a glass transition temperature of 5 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder D, the content ratio of the polymer units of the (meth) acrylate monomer is 79% in the total polymer units of the polymer, and the polymer unit of the vinyl monomer having an acid component is 1.0% in the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 19% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0%.
The pH of the obtained binder D was 10.3 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder D was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 5)
(A) Production of Binder 10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water are added to Polymerization Can A, 0.2 parts of ammonium persulfate as a polymerization initiator, After adding 10 parts of ion-exchanged water and heating to 60 ° C. and stirring for 90 minutes, 67 parts of ethyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.2 part of allyl methacrylate, 0.2 parts of lauryl sulfate are added to another polymerization vessel B. An emulsion prepared by adding 0.7 parts of sodium and 46 parts of ion-exchanged water and stirring is sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to achieve a monomer consumption of 95. The reaction was terminated by cooling at the time when the water content reached%, and an aqueous dispersion of binder E was obtained. The obtained binder E had a glass transition temperature of 2 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder E, the content ratio of the polymer units of the (meth) acrylate monomer is 78% of the total polymer units of the polymer, and the polymer unit of the vinyl monomer having an acid component is 2.0% of the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 19% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0.2%.
The pH of the obtained binder E was 10.5 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder E was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 6)
(A) Production of Binder 10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water are added to Polymerization Can A, 0.2 parts of ammonium persulfate as a polymerization initiator, After adding 10 parts of ion exchanged water and heating to 60 ° C. and stirring for 90 minutes, 67 parts of ethyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.1 part of allyl methacrylate, lauryl sulfate are added to another polymerization vessel B. An emulsion prepared by adding 0.7 parts of sodium and 46 parts of ion-exchanged water and stirring is sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to achieve a monomer consumption of 95. The reaction was terminated by cooling at the time when the water content reached%, and an aqueous dispersion of binder F was obtained. The obtained binder F had a glass transition temperature of 2 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder F, the content of polymer units of (meth) acrylate monomer is 78% of the total polymer units of the polymer, and the polymer unit of vinyl monomers having an acid component is 2.0% of the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 19% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0.1%.
The pH of the obtained binder F was 10.5 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder F was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Comparative Example 1)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, and 0.2 part of ammonium persulfate and 10 parts of ion-exchanged water were used as polymerization initiators. After adding 90 parts and heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 0.7 part of sodium lauryl sulfate and 46 parts of ion-exchanged water were added to another polymerization vessel B and stirred. The emulsion prepared in this manner was sequentially added from polymerization vessel B to polymerization vessel A over about 180 minutes, and stirred for about 120 minutes to cool the monomer consumption amount to 95%, and the reaction was terminated. An aqueous dispersion was obtained. The obtained binder G had a glass transition temperature of −10 ° C. and a number average particle size of 0.15 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder G, the content ratio of the polymer units of the (meth) acrylate monomer is 79% of the total polymer units of the polymer, the polymer unit of the vinyl monomer having an acid component is 0% of the total polymer units of the polymer, α The content ratio of the polymer units of the β-unsaturated nitrile monomer was 20% of the total polymer units of the polymer, and the content ratio of the structural unit having crosslinkability was 0%.
The pH of the obtained binder G was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder G was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Comparative Example 2)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, and 0.2 part of ammonium persulfate and 10 parts of ion-exchanged water were used as polymerization initiators. And heated to 60 ° C. and stirred for 90 minutes, and then in another polymerization vessel B, 67 parts 2-ethylhexyl acrylate, 19 parts acrylonitrile, 5.0 parts methacrylic acid, 0.7 parts sodium lauryl sulfate, ion-exchanged water The emulsion prepared by adding 46 parts and stirring was sequentially added from the polymerization can B to the polymerization can A over about 180 minutes, and then stirred for about 120 minutes to cool and react when the monomer consumption reached 95%. And an aqueous dispersion of binder H was obtained. The obtained binder H had a glass transition temperature of −10 ° C. and a number average particle size of 0.15 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder H, the content ratio of the polymer units of the (meth) acrylic acid ester monomer is 77% of the total polymer units of the polymer, and the polymer unit of the vinyl monomer having an acid component is 5.0% of the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 17% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0%.
The pH of the obtained binder H was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder H was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Comparative Example 3)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, and 0.2 part of ammonium persulfate and 10 parts of ion-exchanged water were used as polymerization initiators. And then heated to 60 ° C. and stirred for 90 minutes, and then in another polymerization vessel B, 67 parts 2-ethylhexyl acrylate, 19 parts acrylonitrile, 0.5 parts methacrylic acid, 0.7 parts sodium lauryl sulfate, ion-exchanged water The emulsion prepared by adding 46 parts and stirring was sequentially added from the polymerization can B to the polymerization can A over about 180 minutes, and then stirred for about 120 minutes to cool and react when the monomer consumption reached 95%. And an aqueous dispersion of binder I was obtained. The obtained binder I had a glass transition temperature of −10 ° C. and a number average particle size of 0.15 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder I, the content of polymer units of the (meth) acrylate monomer is 79% of the total polymer units of the polymer, and the content of the polymer units of the vinyl monomer having an acid component is 0% of the total polymer units of the polymer. The content of the polymerized units of the α, β unsaturated nitrile monomer was 19.5% of the total polymerized units of the polymer, and the content of the structural unit having crosslinkability was 0%.
The pH of the obtained binder I was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder I was used instead of the aqueous dispersion of binder A. Then, the slurry stability was evaluated using the positive electrode slurry, and the initial charge / discharge efficiency and cycle characteristics were evaluated using the peel strength of the electrode plate and the lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 7)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After 10 parts were added and heated to 60 ° C. and stirred for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of 2-acrylamido-2-methylpropanesulfonic acid, allyl methacrylate were added to another polymerization vessel B. The emulsion prepared by adding 0.2 part, 0.7 part of sodium lauryl sulfate and 46 parts of ion-exchanged water and stirring the mixture was sequentially added from the polymerization vessel B to the polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reached 95%, the reaction was terminated by cooling, and an aqueous dispersion of binder J was obtained. The obtained binder J had a glass transition temperature of −31 ° C. and a number average particle size of 0.19 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder J, the content ratio of the polymer units of the (meth) acrylic acid ester monomer is 78% of the total polymer units of the polymer, and the content rate of the polymer units of the vinyl monomer having an acid component is 2% in the total polymer units of the polymer. 0.0%, the content of polymerization units of α, β-unsaturated nitrile monomer was 19%, and the content of structural units having crosslinkability was 0.2%.
The pH of the obtained binder J was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder J was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 8)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After adding 10 parts and heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of acrylic acid, 0.2 part of allyl methacrylate, sodium lauryl sulfate are added to another polymerization vessel B. An emulsion prepared by adding 0.7 parts and 46 parts of ion-exchanged water and stirring the mixture is sequentially added from the polymerization can B to the polymerization can A over about 180 minutes, and then stirred for about 120 minutes and the monomer consumption is 95%. Then, the reaction was terminated by cooling to obtain an aqueous dispersion of binder K. The obtained binder K had a glass transition temperature of −32 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder K, the content of polymer units of (meth) acrylate monomer is 78% of the total polymer units of the polymer, and the content of polymer units of vinyl monomer having an acid component is 2% of the total polymer units of the polymer. 0.0%, the content of polymerization units of α, β-unsaturated nitrile monomer was 19%, and the content of structural units having crosslinkability was 0.2%.
The pH of the obtained binder K was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder K was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

Example 9
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After adding 10 parts and heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.5 parts of methacrylic acid, 0.7 parts of sodium lauryl sulfate, ion exchange are added to another polymerization vessel B. The emulsion prepared by adding 46 parts of water and stirring was sequentially added from the polymerization can B to the polymerization can A over about 180 minutes, and then stirred for about 120 minutes and cooled when the monomer consumption reached 95%. The reaction was terminated, and an aqueous dispersion of binder L was obtained. The obtained binder L had a glass transition temperature of −30 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder L, the content ratio of the polymer units of the (meth) acrylate monomer is 78.5% of the total polymer units of the polymer, and the content of the polymer units of the vinyl monomer having an acid component is the total polymer units of the polymer. Among them, the content of polymerization units of α, β unsaturated nitrile monomer was 18.0%, and the content of structural units having crosslinkability was 0%.
The pH of the obtained binder L was 10.0 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder L was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 10)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After adding 10 parts and heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.5 parts of itaconic acid, 0.7 parts of sodium lauryl sulfate, ion exchange are added to another polymerization vessel B. The emulsion prepared by adding 46 parts of water and stirring was sequentially added from the polymerization can B to the polymerization can A over about 180 minutes, and then stirred for about 120 minutes and cooled when the monomer consumption reached 95%. The reaction was terminated, and an aqueous dispersion of binder M was obtained. The obtained binder M had a glass transition temperature of −29 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder M, the content of polymer units of (meth) acrylic acid ester monomer is 78.5% of the total polymer units of the polymer, and the content of polymer units of vinyl monomer having an acid component is the total polymer units of the polymer. Among them, the content of polymerization units of α, β unsaturated nitrile monomer was 18.0%, and the content of structural units having crosslinkability was 0%.
The pH of the obtained binder M was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder M was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 11)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After 10 parts were added and heated to 60 ° C. and stirred for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.8 part of ethylene glycol dimethacrylate, lauryl were added to another polymerization vessel B. An emulsion prepared by adding 0.7 parts of sodium sulfate and 46 parts of ion-exchanged water and stirring is sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to reduce monomer consumption. When it reached 95%, the reaction was terminated by cooling to obtain an aqueous dispersion of binder N. The obtained binder N had a glass transition temperature of −30 ° C. and a number average particle size of 0.18 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder N, the content ratio of the polymer units of the (meth) acrylate monomer is 78.5% of the total polymer units of the polymer, and the content of the polymer units of the vinyl monomer having an acid component is the total polymer units of the polymer. Among them, the content ratio of 2.1% of polymerization units of α, β unsaturated nitrile monomers was 17.5%, and the content ratio of structural units having crosslinkability was 0.9%.
The pH of the obtained binder N was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder N was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 12)
To polymerization can A, 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 parts of ammonium persulfate as the polymerization initiator, and ion-exchanged water After 10 parts were added and heated to 60 ° C. and stirred for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 1.8 parts of ethylene glycol dimethacrylate, lauryl were added to another polymerization vessel B. An emulsion prepared by adding 0.7 parts of sodium sulfate and 46 parts of ion-exchanged water and stirring is sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to reduce monomer consumption. When it reached 95%, the reaction was terminated by cooling to obtain an aqueous dispersion of binder O. The obtained binder O had a glass transition temperature of −29 ° C. and a number average particle size of 0.17 μm. Binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.
In the binder O, the content of the polymer units of the (meth) acrylate monomer is 78.0% of the total polymer units of the polymer, and the content of the polymer units of the vinyl monomer having an acid component is the total polymer units of the polymer. Among them, the content of polymer units of α, β unsaturated nitrile monomer was 17.0%, and the content of structural units having crosslinkability was 2.0%.
The pH of the obtained binder O was 10.1 after adjusting with 4 wt% NaOH aqueous solution.
A positive electrode slurry, a positive electrode plate, and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder O was used instead of the aqueous dispersion of binder A. Then, slurry stability was evaluated using this positive electrode slurry, peel strength was evaluated using this electrode plate, and initial charge / discharge efficiency and cycle characteristics were evaluated using a lithium ion coin battery. It shows in Table 1 and Table 2.

From the results shown in Tables 1 and 2, a lithium ferrite composite oxide having a layered rock salt structure is used as the positive electrode active material, and a polymerization unit of (meth) acrylate monomer and a polymerization of vinyl monomer having an acid component as a binder. A polymer containing a unit and a polymerized unit of an α, β unsaturated nitrile monomer, and the content of the polymerized unit of the vinyl monomer having an acid component is within a predetermined range in all polymerized units of the polymer By using the coalescence, the storage stability of the binder and the stability of the slurry are excellent, the electrode is excellent in peel strength (that is, the binding property of the electrode), the initial charge / discharge efficiency and the cycle characteristics are excellent (that is, the charge and discharge are A lithium secondary battery can be obtained in which the capacity is not reduced by repetition.
On the other hand, when the thing which does not contain the polymerization unit of the vinyl monomer which has an acid component is used as a binder (comparative example 1), or the content rate of the polymerization unit of the vinyl monomer which has an acid component is out of the range as a binder When used (Comparative Examples 2 and 3), at least one of the storage stability of the binder, the stability of the slurry, the peel strength, the initial charge / discharge efficiency, and the cycle characteristics is inferior.

Claims (9)

A current collector, and a positive electrode active material layer provided on the current collector and containing a positive electrode active material and a binder;
The positive electrode active material has a composition formula Li _2-x (Mn _1-mn F _n Ni _m ) O _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0). .30, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1), and a lithium ferrite composite oxide having a layered rock salt structure,
The binder comprises a polymer containing 60 to 90% by weight of a polymer unit of (meth) acrylate monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of 5 to 30% by weight of an α, β unsaturated nitrile monomer. The positive electrode for secondary batteries whose content rate of the polymerization unit of the vinyl monomer which has the said acid component is 1.0 to 3.0 weight% in all the polymerization units of a polymer.   The positive electrode for a secondary battery according to claim 1, wherein the binder further includes a structural unit having crosslinkability.   The positive electrode for a secondary battery according to claim 2, wherein a content ratio of the cross-linking structural unit is 0.05 to 2% by weight. The polymerization unit of the (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic acid alkyl ester monomer,
The polymerization unit of the vinyl monomer having an acid component is a polymerization unit of a monomer having a carboxylic acid group, a polymerization unit of a monomer having a sulfonic acid group, or a combination thereof.
The positive electrode for a secondary battery according to claim 1, wherein the polymerization unit of the α, β unsaturated nitrile monomer is a polymerization unit of acrylonitrile, a polymerization unit of methacrylonitrile, or a combination thereof. The binder further includes a structural unit having crosslinkability,
The positive electrode for a secondary battery according to claim 4, wherein the structural unit having crosslinkability is a polymerization unit of allyl acrylate, a polymerization unit of ethylene glycol dimethacrylate, or a combination thereof. Containing a positive electrode active material, a binder and a solvent;
The positive electrode active material has a composition formula Li _2-x (Mn _1-mn F _n Ni _m ) O _3-y (where 0 ≦ x <2, 0 ≦ y ≦ 1, 0.01 ≦ m ≦ 0). .30, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1), and a lithium ferrite composite oxide having a layered rock salt structure,
The binder comprises a polymer containing 60 to 90% by weight of a polymer unit of (meth) acrylate monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of 5 to 30% by weight of an α, β unsaturated nitrile monomer. The slurry for secondary battery positive electrodes whose content rate of the polymerization unit of the vinyl monomer which has the said acid component is 1.0 to 3.0 weight% in all the polymerization units of a polymer. The polymerization unit of the (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic acid alkyl ester monomer,
The polymerization unit of the vinyl monomer having an acid component is a polymerization unit of a monomer having a carboxylic acid group, a polymerization unit of a monomer having a sulfonic acid group, or a combination thereof.
The slurry for a secondary battery positive electrode according to claim 6, wherein the polymerization unit of the α, β unsaturated nitrile monomer is a polymerization unit of acrylonitrile, a polymerization unit of methacrylonitrile, or a combination thereof. The binder further includes a structural unit having crosslinkability,
The slurry for secondary battery positive electrode of Claim 7 whose structural unit which has the said crosslinking | crosslinked property is a polymerization unit of allyl acrylate, a polymerization unit of ethylene glycol dimethacrylate, or these combination. A secondary battery comprising a positive electrode, an electrolyte, a separator and a negative electrode,
The secondary battery whose said positive electrode is a positive electrode for secondary batteries as described in any one of Claims 1-5.