KR20120112397A - Positive electrode for secondary battery, and secondary battery - Google Patents

Abstract

On a collector, it has a positive electrode active material layer containing a positive electrode active material and a binder, the said positive electrode active material is a lithium ferrite type complex oxide which has a specific composition, and has a layered rock salt structure, The said binder is a (meth) acrylic acid ester monomer A polymer containing a polymer unit, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β unsaturated nitrile monomer, and the content ratio of the polymer unit of a vinyl monomer having the acid component is 1.0 in all polymer units of the polymer. ? 3.0 wt% positive electrode for secondary batteries.

Description

POSITIVE ELECTRODE FOR SECONDARY BATTERY, AND SECONDARY BATTERY}

TECHNICAL FIELD The present invention relates to a positive electrode for a secondary battery, and more particularly, 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 therein. Moreover, this invention relates to the secondary battery which has such an electrode.

Among the batteries that have been put to practical use, lithium ion secondary batteries exhibit the highest energy density and are particularly used for small electronics. In addition, it is also expected to be used in automobiles in addition to small applications. Among them, further improvement of reliability, such as high output of a lithium ion secondary battery and cycling characteristics, is desired.

The positive electrode active material, which is a constituent material of a lithium ion secondary battery, has a limitation in the high price and the reserve of the cobalt-based active material used as a mainstream, and thus the transition to a cheaper lithium-based active material containing nickel, manganese, and iron is difficult. It's going on.

However, lithium nickel oxide that achieves a high capacity has a problem of lowering battery safety during charging, and high safety and inexpensive lithium manganese oxide elutes trivalent manganese in the electrolyte at high temperatures (about 60 ° C.). There is a problem that it significantly deteriorates battery performance such as a long time charge / discharge cycle, and the replacement of these materials has not proceeded much.

In terms of these problems, Patent Document 1 discloses a layered rock salt type structure having an average discharge voltage of 3 V or more in a long charge / discharge cycle, and having a discharge capacity equivalent to or higher than that of a lithium cobalt oxide-based positive electrode material. A lithium ferrite composite oxide containing a crystalline phase is disclosed.

However, the lithium ferrite-based composite oxide disclosed in Patent Document 1 has poor charge and discharge characteristics, significantly lower initial charge and discharge efficiency, and has a major problem of generating an irreversible capacity of about 40%.

On the other hand, an electrode used in a lithium ion secondary battery has a structure in which an electrode active material layer is laminated | stacked on the electrical power collector normally, and it binds to the said electrode active material layer in order to bind electrode active materials, an electrode active material, and an electrical power collector in addition to an electrode active material. I am used. Fluorine resin (PVDF) and a synthetic rubber polymer particle binder are proposed as a binder for lithium ion secondary batteries, especially a positive electrode.

As a synthetic rubber polymer particle binder, a (meth) acrylate type soft polymer etc. are disclosed (refer patent document 2 or 3).

Japanese Laid-Open Patent Publication 2003-48718 Japanese Patent Application Laid-Open No. 8-287915 (corresponding foreign publication: US Patent Publication No. 5595841) Japanese Patent Application Laid-Open No. 11-149929

According to the studies of the present inventors, even when a battery is manufactured using the above-mentioned fluorine resin (PVDF) or a synthetic rubber binder commonly used as a binder and a lithium ferrite composite oxide as an electrode active material, The degradation was found to be unresolved. However, by including the polymerized unit of the 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, thereby suppressing decomposition of the electrolyte solution generated on the surface of the active material, thereby remarkably increasing the charge and discharge efficiency of the battery obtained. I could figure out what could be improved.

However, depending on the content of the vinyl monomer unit having an acid component constituting the binder, even when the synthetic rubber binders disclosed in Patent Literatures 2 and 3 containing the polymer unit of the vinyl monomer having such an acid component are used, the binder It was confirmed that the problem that the storage stability of the resin was lowered or that the stability of the slurry used to form the electrode active material layer and the binding property of the resulting electrode plate were lowered.

Therefore, the objective of this invention is the slurry for secondary battery positive electrodes which is excellent in the storage stability of a binder, the stability of a slurry, and the binding property of an electrode, and the obtained battery can achieve the initial stage charging and discharging efficiency, It is providing the positive electrode for secondary batteries which can achieve reducing the capacity | capacitance fall by repetition of charging / discharging.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, the polymer unit of the vinyl monomer which has the acid component which comprises not only the fall of the storage stability of a binder, the fall of the stability of a slurry, but also the fall of a battery capacity and an output characteristic, and a binder. It turns out that it originates in the content rate of. Therefore, as a result of further examination, it is a polymer containing the polymer unit of the (meth) acrylic acid ester monomer, the polymer unit of the vinyl monomer which has an acid component, and the polymer unit of the (alpha), (beta) unsaturated nitrile monomer as said binder, By using the polymer unit of the vinyl monomer which has a specific ratio among all the polymer units of a polymer, the slurry for lithium ion secondary battery positive electrodes which was excellent in storage stability, and the battery which is excellent in binding property and the obtained battery has high initial stage charge and discharge It was found out that it was possible to produce a positive electrode for a lithium ion secondary battery that had efficiency and had a small capacity drop due to repeated charge and discharge, and completed the present invention based thereon.

MEANS TO SOLVE THE PROBLEM This invention which solves the said subject includes the following matter as a summary.

(1) A current collector and a positive electrode active material layer containing a positive electrode active material and a binder formed on the current collector, wherein the positive electrode active material is 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 system having a layered rock salt structure Complex oxide,

The binder is a polymer containing a polymerized unit of a (meth) acrylic acid ester monomer, a polymerized unit of a vinyl monomer having an acid component and a polymerized unit of an α, β unsaturated nitrile monomer, and containing a polymerized unit of a vinyl monomer having the acid component. The proportion is 1.0? 3.0 wt% positive electrode for secondary batteries.

(2) The positive electrode for secondary batteries as described in said (1) in which the said binder contains the structural unit which has crosslinkability further.

(3) The content ratio of the structural unit having the crosslinkability is 0.05? The positive electrode for secondary batteries as described in said (2) which is 2.0 weight%.

(4) The polymerization unit of the said (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic-acid alkylester monomer,

The polymer unit of the vinyl monomer which has the said acid component is the polymer unit of the monomer which has a carboxylic acid group, the polymer unit of the monomer which has a sulfonic acid group, or a combination thereof,

(1)? The polymerized unit of the α and β unsaturated nitrile monomers is a polymerized unit of acrylonitrile, a polymerized unit of methacrylonitrile, or a combination thereof. The positive electrode for secondary batteries in any one of (3).

(5) the binder further contains a structural unit having crosslinkability,

The positive electrode for secondary batteries as described in said (4) whose structural unit which has the said crosslinkability is a structural unit which has an allyl group, a structural unit which has 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 is composed of the 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 is a lithium ferrite composite oxide having a layered rock salt structure, wherein the binder is a (meth) acrylic acid ester It is a polymer containing the polymer unit of a monomer, the polymer unit of a vinyl monomer which has an acid component, and the polymer unit of the (alpha), (beta) unsaturated nitrile monomer, and the content rate of the polymer unit of the vinyl monomer which has the said acid component is in all the polymer units of a polymer. 1.0? Slurry for secondary battery positive electrode, 3.0 wt%.

(7) The polymerization unit of the said (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic-acid alkylester monomer,

The polymer unit of the vinyl monomer which has the said acid component is the polymer unit of the monomer which has a carboxylic acid group, the polymer unit of the monomer which has a sulfonic acid group, or a combination thereof,

The slurry for secondary battery positive electrodes as described in (6) whose polymer unit of the said (alpha), (beta) unsaturated nitrile monomer is a polymer unit of acrylonitrile, the polymer unit of methacrylonitrile, or a combination thereof.

(8) the binder further contains a structural unit having crosslinkability,

The slurry for secondary battery positive electrodes as described in (7) whose structural unit which has the said crosslinkability is a structural unit which has an allyl group, a structural unit which has an epoxy group, or a combination thereof.

(9) A secondary battery comprising a positive electrode, an electrolyte solution, a separator, and a negative electrode, wherein the positive electrode is (1)? The secondary battery which is the positive electrode for secondary batteries in any one of (5).

ADVANTAGE OF THE INVENTION According to this invention, the slurry for secondary battery positive electrodes which is excellent in stability, and the secondary battery obtained which is excellent in binding property has a high charge / discharge efficiency, Furthermore, the electrode for secondary batteries which can reduce the capacity | capacitance decrease by repeated charge / discharge can be manufactured. Will be.

The present invention is described in detail below.

A secondary battery of the present invention is a positive electrode, current collector, and the collector formed, has a positive electrode active material layer containing a positive electrode active material and a binder, wherein the positive electrode active material, the composition formula Li _{2 -x (1-mn} Mn Fe Ni _{n 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 also have a layered rock salt structure Vinyl having ferric composite oxide, wherein the binder is a polymer containing a polymerized unit of a (meth) acrylic acid ester monomer, a polymerized unit of a vinyl monomer having an acid component, and a polymerized unit of an α, β unsaturated nitrile monomer. The content rate of the polymerized unit of a monomer is 1.0? 3.0 wt%.

(Positive electrode active material)

In the present invention, the lithium ferrite composite oxide used as the positive electrode active material is composed of the 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 also 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. Although all of the Co layers of LiCoO ₂ are substituted by Fe ions, the layered rock salt type LiFeO ₂ has little charge / discharge capacity. In order to obtain a composite oxide having a sufficient charge and discharge capacity, since the Fe ions and Ni ions need to partially replace the Mn layer corresponding to the Co layer of LiCoO ₂ , the lithium ferrite composite oxide used in the present invention. The amount of Fe ions to be dissolved in the solution is 5? 75 mol% (0.05 ≦ n ≦ 0.75), and 20? It is preferable that it is 60 mol% (0.20 ≦ n ≦ 0.60). When the solid solution amount of Fe ions becomes excessive, Fe ions which are not involved in charging and discharging increase, which is not preferable in view of battery characteristics. On the other hand, when the solid solution amount of Fe ion is too small, since the charge / discharge capacity becomes small, it is also not preferable.

In the lithium ferrite composite oxide used in the present invention, Ni ions to be dissolved in the solution are also present in the layered rock salt structure in the form of substituting Mn ions, similarly to Fe ions. It is estimated that Ni ion exists in the bivalent trivalent mixed valence state, and contributes to the improvement of the electronic conductivity of a composite oxide, etc. The amount of Ni ions to be dissolved in the lithium ferrite composite oxide is 1? Of the amount of metal ions other than Li ions. 30 mol% (0.01 ≦ m ≦ 0.30), and 5? It is preferred that it is 25 mol% (0.05 ≦ m ≦ 0.25). It is economically disadvantageous when using Ni which is expensive compared with Mn and Fe in large quantities. On the other hand, when the solid solution amount of Ni ion is too small, effects, such as the improvement of the electronic conductivity achieved by Ni addition, may not fully be expressed.

The total amount of Fe ions and Ni ions to be dissolved in the lithium ferrite composite oxide used in the present invention is 0.06 ≦ in the composition formula Li _{2 -x} (Mn _{1 -m- n} Fe _n Ni _m ) O _3-y . m + n <1, Preferably it exists in the range of 0.3 <= m + n <= 0.8. In addition, the lithium ferrite composite oxide used in the present invention, one can maintain the crystal structure of the layered rock-salt type, Li _{2 - x} MnO _{3 - y} of x and y is positive (正) of up to one degree, respectively Can take the value of. However, it is preferable to be as close to zero as possible in view of the charging capacity. Further, it is even, and the complex oxide used in the invention, containing the impurity phase, such as Li ₂ CO ₃ charging and discharging range that does not significantly affect the properties (up to 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 conventional composite oxide synthesis method. In general, however, in the 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, it is more preferable that the lithium ferrite composite oxide used in the present invention is produced by a hydrothermal reaction method using a mixed solution in which a metal salt serving as a generation source of each ion is dissolved in water, a water / alcohol mixture, or the like.

The amount of the positive electrode active material contained in the electrode active material layer of the positive electrode for secondary batteries of the present invention is 50? 99 wt%, more preferably 70? 99 wt%, and the most preferable range is 80? 99 wt%. By setting it as the said range, the lithium secondary battery of high capacity can be manufactured.

(bookbinder)

The binder used for this invention is a polymer containing the polymer unit of the (meth) acrylic acid ester monomer, the polymer unit of the vinyl monomer which has an acid component, and the polymer unit of the (alpha), (beta) unsaturated nitrile monomer.

In this invention, (meth) acrylic-acid alkylester, ie, alkyl acrylate and / or alkyl methacrylate, is mentioned as a (meth) acrylic acid ester monomer which comprises the polymer unit of a (meth) acrylic acid ester monomer. For example, the general formula ^{_{CH 2 = CR 1 -COO-R}} 2 can be given a compound represented by (R ¹ is a hydrogen or a methyl group, R ² represents an alkyl group).

Examples of the alkyl acrylate esters 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. Examples of the alkyl methacrylate esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate and 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.

Among these, alkyl acrylate esters are preferred because they exhibit the conductivity of lithium ions due to proper swelling into the electrolyte without being eluted into the electrolyte, and are unlikely to cause crosslinking aggregation with the polymer in the dispersion of the active material. 7 to 6 carbon atoms of the alkyl group bonded to the carbonyl oxygen atom. Heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, and lauryl acrylate which are alkyl phosphate of 13 are preferable, and carbon number of the alkyl group couple | bonded with a noncarbonyl oxygen atom 8? Since octal acrylate, 2-ethylhexyl acrylate, and nonyl acrylate do not swell in electrolyte solution, they are more preferable.

In this invention, the content rate of the polymer unit of the (meth) acrylic acid ester monomer in a binder is 50? In all the polymer units of a polymer. It is preferable that it is 95 weight%, and is 60? It is more preferable that it is 90 weight%. When the content rate of the polymerization unit of the (meth) acrylic acid ester monomer in a binder is the said range, the binder excellent in the flexibility of an electrode plate, and excellent in oxidation resistance in a battery can be obtained.

Monomers that comprise polymerized units of a vinyl monomer having an acid component according to the present invention, -COOH group (carboxylic acid group) with a monomer, -OH monomer group, -SO ₃ H group having (hydroxy) (sulfonic acid group And a monomer having a -PO ₃ H ₂ group, a monomer having a -PO (OH) (OR) group (R represents a hydrocarbon group), and a monomer having a lower polyoxyalkylene group. is more preferable because the -COOH group (carboxylic acid group) with a monomer, monomer having a -OH group monomer, -SO ₃ H group (sulfonic acid group) with an (hydroxyl group) to increase the binding of the binder. It is especially preferable that it is a monomer which has a carboxylic acid group, the monomer which has a sulfonic acid group, or a combination thereof.

As a monomer which has a carboxylic acid group, monocarboxylic acid, its derivative (s), dicarboxylic acid, its acid anhydride, these derivatives, etc. are mentioned. Acrylic acid, methacrylic acid, crotonic acid, etc. are mentioned as monocarboxylic acid. Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, and the like. Can be. Maleic acid, fumaric acid, itaconic acid, etc. are mentioned as dicarboxylic acid. As an acid anhydride of dicarboxylic acid, maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, etc. are mentioned. Examples of the dicarboxylic acid derivatives include methyl maleic acid, dimethyl maleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, nonyl maleic acid, maleic acid decyl, maleic acid dodecyl, maleic acid octadecyl, Maleic acid esters such as fluoroalkyl maleate; .

As a monomer which has a hydroxyl group, Ethylenic unsaturated alcohols, such as (meth) allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, maleic acid-di-2-hydroxyethyl, maleic acid- Alkanol esters of ethylenically unsaturated carboxylic acids such as 4-hydroxybutyl and di-2-hydroxypropyl itaconic acid; Polyalkylene glycol represented by the general formula CH ₂ = CR ¹ -COO- (CnH ₂ nO) mH (m is an integer from 2 to 9, n is an integer from 2 to 4, R ¹ represents hydrogen or a methyl group) Esters of (meth) acrylic acid; Mono of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2 '-(meth) acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth) acryloyloxysuccinate Meth) acrylic acid esters; Vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth Mono (meth) allyl ethers of alkylene glycols such as allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, and (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; Halogen of (poly) alkylene glycols such as glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether and (meth) allyl-2-hydroxy-3-chloropropyl ether; Mono (meth) allyl ether of a hydroxy substituent; Mono (meth) allyl ethers of polyhydric phenols such as eugenol and isoeugenol and halogen substituents thereof; (Meth) allylthio ethers of alkylene glycols such as (meth) allyl-2-hydroxyethylthioether and (meth) allyl-2-hydroxypropylthioether; And the like.

Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylic acid-2-sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and 3-allyloxy-2. -Hydroxypropanesulfonic acid, etc. are mentioned.

-PO ₃ H ₂ group and / or -PO (OH) (OR) group of the monomer having the (R represents a hydrocarbon group) is phosphate-2- (meth) acryloyloxyethyl phosphate, methyl-2- ( (Meth) acryloyloxyethyl, ethyl phosphate ((meth) acryloyloxyethyl, etc. are mentioned.

As a monomer containing a lower polyoxyalkylene group containing group, poly (alkylene oxide), such as poly (ethylene oxide), etc. are mentioned.

Among these, the monomer which has a carboxylic acid group is preferable from the thing which is excellent in adhesiveness with respect to an electrical power collector, and the manganese ion eluted from the positive electrode active material efficiently, Especially, C5 or less, such as acrylic acid and methacrylic acid, is preferable. The monocarboxylic acid which has a carboxylic acid group of this, and the dicarboxylic acid which has two C5 or less carboxylic acid groups, such as maleic acid and itaconic acid, are preferable. Furthermore, acrylic acid and methacrylic acid are especially preferable from the viewpoint of the high storage stability of the produced binder.

In this invention, the content rate of the polymer unit of the vinyl monomer which has an acid component in a binder is 1.0-? In all the polymer units of a polymer. It is necessary to be 3.0% by weight. The content rate of the polymer unit of the vinyl monomer which has an acid component in a binder is 1.0? In all the polymer units of a polymer. By 3.0 wt%, a battery having a high initial charge / discharge efficiency and further a small capacity drop due to repeated charge / discharge can be obtained. In this invention, when the content rate of the polymer unit of the vinyl monomer which has an acid component in a binder is less than 1.0 weight%, initial stage charging / discharging efficiency is small, and capacity | capacitance fall by repetition of charging / discharging becomes large, On the contrary, 3.0 When it exceeds weight%, the storage stability of a binder and the stability of the slurry for positive electrodes mentioned later will fall.

In this invention, the content rate of the polymer unit of the vinyl monomer which has an acid component in a binder is 1.5? In all the polymer units of a polymer. It is preferred that it is 2.5% by weight. When the content rate of the polymer unit of the vinyl monomer which has an acid component in a binder is the said range, the binder for excellent storage stability and the slurry for positive electrodes which are excellent in stability can be obtained, Furthermore, initial stage charging and discharging efficiency is higher, A battery having a smaller capacity drop due to repetition of discharge can be produced.

In this invention, an acrylonitrile and methacrylonitrile are mentioned as a monomer which comprises the polymer unit of the (alpha), (beta) unsaturated nitrile monomer.

In this invention, the content rate of the polymer unit of the (alpha), (beta) unsaturated nitrile monomer in a binder is 3 to 3 in all the polymer units of a polymer. It is preferable that it is 40 weight%, and 5? More preferably, it is 30 weight%. When the content rate of the polymer unit of the (alpha), (beta) unsaturated nitrile monomer in a binder is the said range, the electrode excellent in adhesiveness to an electrical power collector, ie, binding property, can be obtained.

It is preferable that the binder used in this invention contains the structural unit which has crosslinkability further in addition to said polymer unit. By containing the structural unit which has crosslinkability in a binder, electrode strength can be improved more and it contributes to the improvement of the yield in the manufacturing process of a battery.

As a method of introducing a crosslinkable structural unit into the binder, a method of introducing a photocrosslinkable crosslinkable group or a method of introducing a thermal crosslinkable crosslinkable group into the binder may be mentioned. Among these, the method of introducing a heat crosslinkable crosslinkable group into a binder can crosslink a binder by heat-processing a pole plate after electrode plate application, and can further suppress dissolution to electrolyte solution, and is strong and flexible electrode plate It is preferable because it is obtained. In the case of introducing a crosslinkable crosslinkable group into the binder, a method of using a monofunctional monomer having one olefinic double bond having a crosslinkable crosslinkable group, and a polyfunctional monomer having at least two olefinic double bonds There is a way to use it. The thermally crosslinkable crosslinkable group contained in the monofunctional monomer having one olefinic double bond is at least 1 selected from the group consisting of an epoxy group, a hydroxyl group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. A species is preferable and an epoxy group is more preferable at the point which adjusts crosslinking and a crosslinking density easily.

As a monomer containing an epoxy group, the monomer containing a carbon-carbon double bond and an epoxy group, and the monomer containing a halogen atom and an epoxy group are mentioned.

As a monomer containing a carbon-carbon double bond and an epoxy group, For example, unsaturated glycy, such as vinylglycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl ether, etc. Dyl ether; Butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes; Alkenylepoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2-epoxy-9-decene; Glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl- Glycidyl esters of unsaturated carboxylic acids such as glycidyl ester of 3-pentenoate, 3-cyclohexene carboxylic acid and glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid; .

As a monomer which has a halogen atom and an epoxy group, for example, epihalohydrin, such as epichlorohydrin, epibromohydrin, epiiodhydrin, epifluorohydrin, (beta) -methyl epichlorohydrin, etc. ; p-chloro styrene oxide; Dibromophenyl glycidyl ether; .

As a monomer containing an N-methylolamide group, (meth) acrylamide which has methylol groups, such as N-methylol (meth) acrylamide, is mentioned.

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-trifluoromethyl jade Cetane 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, and 2-isopropenyl- 2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. Can be mentioned.

Polyfunctional monomers having at least two olefinic double bonds include allyl acrylate or allyl methacrylate, ethylene glycol dimethacrylate, trimethylolpropane-triacrylate, trimethylolpropane-trimethacrylate, dipropylene glycol Allyl or vinyl ether of diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxy ethane, or polyfunctional alcohols other than these, tetraethylene glycol diacrylate, triallyl Preference is given to amines, trimethylolpropane-diallylether, methylenebisacrylamide and / or divinylbenzene. In particular, allyl acrylate, allyl methacrylate, ethylene glycol dimethacrylate, trimethylol propane triacrylate, and / or trimethylol propane-methacrylate, etc. are mentioned.

Among these, since the crosslinking density tends to improve, the polyfunctional monomer which has at least 2 olefinic double bond is preferable, and allyl acrylate, allyl methacrylate, from the viewpoint of improving the crosslinking density and high copolymerizability, Or ethylene glycol dimethacrylate is preferred.

Among the above-mentioned, as a structural unit which has crosslinkability, the polymer unit of allyl methacrylate, the polymer unit of ethylene glycol dimethacrylate, or a combination thereof is especially preferable. In particular, the polymerization unit of allyl methacrylate is preferable because a high crosslinking effect can be obtained in a small amount.

As for the content rate of the structural unit which has a crosslinkability in a binder, as a quantity of the structural unit based on the monomer containing a crosslinkable crosslinkable group, it is 0.05? 2.0% by weight, more preferably 0.1? It is the range of 1.0 weight%. By making the content rate of the structural unit which has crosslinkability in a binder into the said range, the binding property of an electrode plate improves more, and also excessive swelling with respect to electrolyte solution is suppressed, and the capacity | capacitance fall by repetition of charge / discharge is made smaller. can do. The content rate of the structural unit which has crosslinkability in a binder can be controlled by the monomer injection ratio at the time of manufacturing a binder. By the content rate of the structural unit which has a crosslinking | crosslinked property in a binder being in the said range, swelling property with respect to a suitable electrolyte solution can be exhibited, the initial charge / discharge efficiency can be made higher, and the capacity | capacitance fall by repetition of charge / discharge can be made smaller. .

The binder used for this invention may contain arbitrary polymerization units other than said component. Arbitrary polymer units are polymer units other than the polymer unit of a (meth) acrylic acid ester monomer, the polymer unit of a vinyl monomer which has an acid component, the polymer unit of (alpha), (beta) unsaturated nitrile monomer, and the structural unit which has crosslinkability. As a monomer which comprises such a polymerization unit, vinyl monomers other than the monomer which comprises the (meth) acrylic acid ester monomer, the vinyl monomer which has an acid component, the (alpha), (beta) unsaturated nitrile monomer, and the structural unit which has crosslinkability are mentioned. have. 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; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; Heterocyclic ring-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; Acrylamide is mentioned. The content rate of these polymer units is 10 weight% or less in all the polymer units of a polymer.

The binder used for this invention is used in the state of the dispersion liquid melt | dissolved in the dispersion medium, or the dissolved solution state. Especially, it is preferable to disperse | distribute in particulate form to a dispersion medium from the reason of suppressing swelling property of electrolyte solution.

In the case where the binder is dispersed in the dispersion medium in the form of particles, the number average particle diameter of the binder dispersed in the form of particles is 50 nm? 500 nm is preferable and 70 nm? 400 nm is more preferable, Most preferably, it is 100 nm? 250 nm. If the average particle diameter of a binder is this range, the intensity | strength and flexibility of the electrode obtained will become favorable. Moreover, although an organic solvent and water are used as a dispersion medium, it is preferable to use water as a dispersion medium from the reason that a drying rate is quick especially.

In the case where the binder is dispersed in the dispersion medium in the form of particles, the solid content concentration of the dispersion is usually 15? 70 wt%, 20? 65 weight% is preferable and 30? More preferred is 60% by weight. When solid content concentration is this range, workability in electrode slurry manufacture is favorable.

The glass transition temperature (Tg) of the binder used for the present invention is preferably -50? 25 ° C., more preferably -45? 15 ° C., particularly preferably -40? 5 ° C. When Tg of a binder exists in the said range, the electrode for secondary batteries which has the outstanding strength and flexibility, and has high output characteristics can be obtained. In addition, the glass transition temperature of a binder can be prepared by combining various monomers.

The manufacturing method of the binder used for this invention is not specifically limited, Any method, such as solution polymerization method, suspension polymerization method, block polymerization method, emulsion polymerization method, can also be used. As the polymerization method, any method such as ionic polymerization, radical polymerization or living radical polymerization can be used. As a polymerization initiator used for superposition | polymerization, a lauroyl peroxide, diisopropyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, t-butylperoxy pivalate, 3,3,5-trimethyl hexa, for example Organic peroxides, such as a noyl peroxide, Azo compounds, such as (alpha), (alpha) '-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, etc. are mentioned.

The ratio of the polymer unit in a binder can be adjusted by adjusting the ratio of the corresponding monomer.

The dispersing agent used when manufacturing the binder used by this invention by superposition | polymerization methods, such as emulsion polymerization and suspension polymerization, may be used by normal synthesis, As a specific example, sodium dodecylbenzenesulfonate, dode 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; Ethoxy sulfate salts such as polyoxyethylene lauryl ether sulfate sodium salt and polyoxyethylene nonylphenyl ether sulfate sodium salt; Alkanesulfonates; Alkyl ether phosphate ester sodium salt; Nonionic emulsifiers such as polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, and polyoxyethylene-polyoxypropylene block copolymers; Water-soluble polymers, such as gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, sodium polyacrylate, degree of polymerization 700 or more, and saponification degree 75% or more, are illustrated, and these may be individual, and these may be two or more types. You may use it together. Among these, Preferably, benzene sulfonate, such as sodium dodecyl benzene sulfonate and sodium dodecyl phenyl ether sulfonate; Alkyl sulfates, such as sodium lauryl sulfate and sodium tetradodecyl sulfate, More preferably, they are benzene sulfonates, such as sodium dodecyl benzene sulfonate and sodium dodecyl phenyl ether sulfonate from the point which is excellent in oxidation resistance. The addition amount of a dispersing agent can be set arbitrarily and it is 0.01-0 with respect to 100 weight part of monomer total amounts normally. It is about 10 parts by weight.

PH when the binder used for this invention is disperse | distributed to a dispersion medium is 5? 13 is preferred, and 5? 12, most preferably 10? 12 is. By the pH of a binder being in the said range, the storage stability of a binder improves and also mechanical stability improves.

The pH adjusting agent for adjusting the pH of the binder includes 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, and hydroxides of metals belonging to IIIA in long periods such as aluminum hydroxide. Hydroxides such as these; Carbonates such as alkali metal carbonates such as sodium carbonate and potassium carbonate, and alkaline earth metal carbonates such as magnesium carbonate; Examples thereof include alkylamines such as ethylamine, diethylamine and propylamine; Alcohol amines such as monomethanolamine, monoethanolamine and monopropanolamine; Ammonia such as ammonia water; And the like. Among these, an alkali metal hydroxide is preferable from a viewpoint of binding property and operability, and sodium hydroxide, potassium hydroxide, and lithium hydroxide are especially preferable.

The content of the binder in the positive electrode active material layer is 0.1? To 100 parts by weight of the positive electrode active material. 10 parts by weight, more preferably 0.5? 5 parts by weight. When content of the binder in a secondary battery positive electrode exists in the said range, while being excellent in binding property with respect to positive electrode active materials and an electrical power collector, and maintaining flexibility, resistance does not increase without inhibiting Li movement.

(Current collector)

The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. For example, iron, copper, aluminum, nickel, stainless steel, or titanium from the viewpoint of heat resistance. Metal materials such as tantalum, gold and platinum are preferred. Especially, aluminum is especially preferable for the positive electrode of a lithium ion secondary battery. The shape of the current collector is not particularly limited, but the thickness is 0.001? It is preferable that it is a sheet form of about 0.5 mm. In order that a collector may raise the adhesive strength of a positive electrode active material layer, it is preferable to use it, roughening previously. Examples of the roughening method include mechanical roughening, electrolytic roughening, and chemical roughening. In the mechanical polishing method, a wire brush provided with abrasive cloth, a grindstone, an emery buff, a steel wire or the like to which abrasive particles are fixed are used. Moreover, in order to improve the adhesive strength and electroconductivity of a positive electrode active material layer, you may form an intermediate | middle layer in the electrical power collector surface.

In addition to the above components, the positive electrode active material layer used in the present invention may further include an electrolytic solution additive having a function such as a conductivity providing agent, a reinforcing material, a dispersant, a leveling agent, an antioxidant, a thickener, and electrolyte solution decomposition suppression, and other binders. A component may contain. These components may also contain in the slurry for secondary battery positive electrodes mentioned later. These are not particularly limited as long as they do not affect the battery reaction.

As the conductive imparting material, conductive carbon such as acetylene black, Ketjen black, carbon black, graphite, vapor grown carbon fiber, and carbon nanotube can be used. Carbon powder, such as graphite, a fiber, foil of various metals, etc. are mentioned. By using an electroconductivity imparting material, the electrical contact of electrode active materials can be improved, and discharge load characteristics can be improved especially when using for a lithium ion secondary battery. As the reinforcing material, various inorganic and organic spherical, plate-like, plate-like or fibrous fillers can be used. By using the reinforcing material, a strong and flexible electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The usage-amount of electroconductivity imparting material and a reinforcing agent is 0.01-100 normally with respect to 100 weight part of electrode active materials. 20 parts by weight, preferably 1? 10 parts by weight. By being included in the above range, it is possible to exhibit high capacity and many load characteristics.

Examples of the dispersant include anionic compounds, cationic compounds, nonionic compounds, and high molecular compounds. The dispersant is selected according to the electrode active material and the conductive agent to be used. Preferably the content rate of the dispersing agent in a positive electrode active material layer is 0.01? 10 wt%. When the amount of the dispersant is within the above range, the stability of the slurry for the positive electrode described later is excellent, a smooth electrode can be obtained, and high battery capacity can be exhibited.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the said surfactant, the cratering which arises at the time of coating can be prevented, or the smoothness of an electrode can be improved. The content ratio of the leveling agent in the positive electrode active material layer is preferably 0.01? 10 wt%. When the leveling agent is in the above range, the productivity, smoothness and battery characteristics at the time of electrode production are excellent.

Examples of the antioxidant include phenol compounds, hydroquinone compounds, organophosphorus compounds, sulfur compounds, phenylenediamine compounds, and polymer type phenol compounds. A polymer type phenol compound is a polymer which has a phenol structure in a molecule | numerator, and a weight average molecular weight is 200? 1000, preferably 600? Polymeric phenol compounds which are 700 are preferably used. The content ratio of the antioxidant in the positive electrode active material layer is preferably 0.01? 10% by weight, more preferably 0.05? 5 wt%. When antioxidant is the said range, it is excellent in stability, battery capacity, and cycling characteristics of the slurry for positive electrodes mentioned later.

As a thickener, Cellulose polymers, such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, these ammonium salts, and alkali metal salt; (Modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; (Modified) polyvinyl alcohols such as a copolymer of polyvinyl alcohol, acrylic acid or acrylate and vinyl alcohol, a copolymer of maleic anhydride or maleic acid, or fumaric acid and vinyl alcohol; Polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, various modified starches, acrylonitrile-butadiene copolymer hydride and the like. If the usage-amount of a thickener is this range, coatability and adhesiveness with an electrode or an organic separator are favorable. 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? 10 wt%. When the thickener is in the above range, excellent dispersibility of an active material and the like in the slurry for the positive electrode described later can be obtained, and a smooth electrode can be obtained, thereby exhibiting excellent load characteristics and cycle characteristics.

As an electrolyte solution additive, the vinylene carbonate etc. which are used in the slurry for positive electrodes mentioned later and in electrolyte solution can be used. The content ratio of the electrolyte solution additive in the positive electrode active material layer is preferably 0.01? 10 wt%. By the electrolyte additive being in the above range, the cycle characteristics and the high temperature characteristics are excellent. In addition, nano fine particles, such as fumed silica and fumed alumina, are mentioned. By mixing the said nanoparticles, the thixotropy of the slurry for electrode formation can be controlled, and the leveling property of the electrode obtained by it can be improved. The content ratio of the nano fine particles in the positive electrode active material layer is preferably 0.01? 10 wt%. When nanoparticles are in the said range, it is excellent in slurry stability and productivity, and shows high battery characteristics.

As a method of manufacturing the positive electrode for secondary batteries of this invention, what is necessary is just a method of binding a positive electrode active material layer in layer form on at least one side, preferably both surfaces of the said electrical power collector. For example, the slurry for lithium secondary battery positive electrodes mentioned later is apply | coated to an electrical power collector, and it dries, and then heat-processes at 120 degreeC or more for 1 hour or more, and forms an electrode. Although the upper limit of heat processing temperature is not specifically limited, Preferably it can be 300 degrees C or less. Although the upper limit of heating time is not specifically limited, either, Preferably it can be 200 degrees C or less. The method of apply | coating the slurry for positive electrodes to an electrical power collector is not specifically limited. For example, methods, such as a doctor blade method, a collection method, a reverse roll method, the direct roll method, the gravure method, an extrusion method, the brushing method, are mentioned. As a drying method, the drying method by irradiation with warm air, hot air, low humidity wind, vacuum drying, (far) infrared rays, an electron beam, etc. are mentioned, for example.

Subsequently, it is preferable to lower the porosity of the electrode by pressure treatment using a mold press or a roll press. The preferred range of porosity is 5%? 15%, more preferably 7%? 13%. If the porosity is too high, the charging efficiency and the discharge efficiency deteriorate. If the porosity is too low, a high volume capacity is hardly obtained, or the electrode is likely to peel off, causing a problem of easily causing defects. In addition, when using a curable polymer, it is preferable to harden.

The thickness of the positive electrode for secondary batteries of this invention is 5? 300 µm, preferably 10? 250 μm. By the electrode thickness being in the above range, both the load characteristics and the energy density exhibit high characteristics.

(Slurry for Secondary Battery Positive Electrode)

Secondary battery positive electrode slurry to be used in the present invention is composed by containing a positive electrode active material, a binder and a solvent, wherein the positive electrode active material, the composition formula _{Li 2 -x (Mn 1 -m- n} Fe n Ni m) O 3-y (Wherein 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 containing a polymerized unit of a (meth) acrylic acid ester monomer, a polymerized unit of a vinyl monomer having an acid component, and a polymerized unit of an α, β unsaturated nitrile monomer, and a polymerized unit of a vinyl monomer having the acid component. The content rate is 1.0? 3.0 wt%. As a binder and a positive electrode active material, the thing demonstrated by the positive electrode for secondary batteries is used.

(menstruum)

The solvent is not particularly limited as long as it can uniformly dissolve or disperse the binder used in the present invention.

As a solvent used for the slurry for positive electrodes, both water and an organic solvent can be used. As an organic solvent, Cycloaliphatic hydrocarbons, such as cyclopentane and a cyclohexane; Aromatic hydrocarbons such as toluene, xylene and ethylbenzene; Ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane and ethylcyclohexane; Chlorine aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; Esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; Acyl nitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; Amides, such as N-methylpyrrolidone and N, N- dimethylformamide, are mentioned.

These solvents may be used alone, or two or more thereof may be mixed and used as a mixed solvent. Among these, especially the solvent which is excellent in the dispersibility of an electrode active material and a conductive agent, and has a low boiling point and high volatility can be removed in a short time and at low temperature, It is preferable. Acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, or N-methylpyrrolidone, or a mixed solvent thereof is preferable. Moreover, since the effect of this invention is remarkable when a water dispersion type particulate polymer is used as a binder, water is especially preferable as a solvent.

Solid content concentration of the slurry for secondary battery positive electrodes used for this invention is a grade which can apply | coat and immerse, and it will not specifically limit, if it becomes a viscosity which has fluidity, but is generally 10? About 80% by weight.

In addition to the binder, the lithium ferrite-based composite oxide and the solvent, an optional component such as an electrolyte solution additive having a function such as a dispersant or an electrolyte solution decomposition suppression used in the above-described positive electrode for secondary batteries is further included in the slurry for the secondary battery positive electrode. You may contain it. These are not particularly limited as long as they do not affect the battery reaction.

(Slurry Production Method for Positive Electrode for Secondary Battery)

In this invention, the manufacturing method of the slurry for secondary battery positive electrodes is not specifically limited, It is obtained by mixing the said binder, a lithium ferrite type complex oxide, and a solvent and arbitrary components added as needed.

In the present invention, by using the above components, a slurry for the positive electrode in which the above components are highly dispersed can be obtained regardless of the mixing method and the mixing order. The mixing device is not particularly limited as long as it is a device capable of uniformly mixing the above components, and is preferably a bead mill, ball mill, roll mill, sand mill, pigment disperser, brain trajectory, ultrasonic disperser, homogenizer, planetary mixer, peel Although a mix etc. can be used, it is especially preferable to use a ball mill, a roll mill, a pigment disperser, a brain trajectory, and a planetary mixer from the point which can disperse | distribute at high concentration among these.

The viscosity of the slurry for the positive electrode is preferably 10 mPa? S? From the viewpoint of uniform coatability and slurry time course stability. 100,000 mPa? S, more preferably 100? 50,000 mPa? S. The said viscosity is a value when it measures by 25 degreeC and rotation amount 60rpm using a Brookfield viscometer.

(Secondary battery)

The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolyte solution, and the positive electrode is the positive electrode for secondary batteries.

Examples of the secondary battery include a lithium ion secondary battery, a nickel hydride secondary battery, and the like. A lithium ion secondary battery is preferable for the purpose of improving performance such as improvement in long-term cycle characteristics and improvement in output characteristics. Do. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

(Electrolyte for lithium ion secondary battery)

As an electrolyte solution for lithium ion secondary batteries, the organic electrolyte solution which melt | dissolved the supporting electrolyte in the organic solvent is used. Lithium salt is used as a supporting electrolyte. Lithium salts include, but are not particularly limited to, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO ) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily dissolved in a solvent and exhibit high dissociation degree are preferable. These may use 2 or more types together. Since the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity is, the lithium ion conductivity can be adjusted according to the type of the supporting electrolyte.

The organic solvent used in the electrolyte solution for the lithium ion secondary battery is not particularly limited as long as it can dissolve the supporting electrolyte. Dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds such as sulfolane and dimethylsulfoxide; Is preferably used. Moreover, you may use the liquid mixture of these solvent. Among them, carbonates are preferable because the dielectric constant is high and the stable potential region is wide. Since the lower the viscosity of the solvent used, the higher the lithium ion conductivity is, so that the lithium ion conductivity can be adjusted according to the type of the solvent.

Moreover, you may use it, containing an additive in the said electrolyte solution. As an additive, carbonate type compounds, such as vinylene carbonate (VC) used in the slurry for secondary battery positive electrodes mentioned above, are mentioned.

The concentration of the supporting electrolyte in the electrolyte solution for lithium ion secondary batteries is usually 1 ?. 30 wt%, preferably 5 wt%? 20 wt%. In addition, depending on the type of the supporting electrolyte, it is usually 0.5? Used at a concentration of 2.5 mol / l. Even if the concentration of the supporting electrolyte is too low or too high, the ion conductivity tends to be lowered.

In other than the electrolytic solution, there may be mentioned an inorganic solid electrolyte of polyethylene oxide, a gel polymer electrolyte impregnated with an electrolytic solution in the polymer electrolyte or the polymer electrolyte, such as polyacrylonitrile, or, such as LiI, Li ₃ N.

(Separator for lithium ion secondary battery)

As a separator for lithium ion secondary batteries, Microporous film or nonwoven fabric containing polyolefin resin, such as polyethylene and a polypropylene, and aromatic polyamide resin; Porous resin coat containing inorganic ceramic powder; And the like can be used. For example, a microporous membrane made of resin such as polyolefin-based (polyethylene, polypropylene, polybutene, polyvinyl chloride), and mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, poly Woven microporous membranes or polyolefin fibers made of resins such as meads, polyimideamides, polyaramids, polycycloolefins, nylons, and polytetrafluoroethylene, or aggregates of nonwoven fabrics and insulating material particles thereof. Among these, the microporous membrane which consists of polyolefin resin is preferable, since the film thickness of the whole separator can be made thin and the ratio of the active material in a battery can be raised and a capacity per volume can be raised.

The thickness of the separator is usually 0.5? 40 μm, preferably 1? 30 µm, more preferably 1? 10 μm. If it is this range, resistance by the separator in a battery will become small and it is excellent in workability at the time of battery manufacture.

(Lithium ion secondary battery negative electrode)

In the negative electrode for lithium ion secondary batteries, the negative electrode active material layer containing a negative electrode active material and a binder is laminated | stacked on an electrical power collector. As a binder and an electrical power collector, the thing similar to what was demonstrated by the positive electrode for secondary batteries is mentioned.

(Negative electrode active material for lithium ion secondary battery)

As an electrode active material (negative electrode active material) for lithium ion secondary battery negative electrodes, carbonaceous materials, such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, pitch-type carbon fiber, conductive polymers, such as polyacene, etc. are mentioned, for example. Can be mentioned. Moreover, as a negative electrode active material, metals, such as silicon, tin, zinc, manganese, iron, nickel, these alloys, the oxide or sulfate of the said metal or alloy are used. Moreover, lithium alloys, such as metallic lithium, Li-Al, Li-Bi-Cd, Li-Sn-Cd, lithium transition metal nitride, silicon, etc. can be used. The electrode active material can also use the thing which made the electrically conductive provision material adhere to the surface by a mechanical modification method. The particle size of the negative electrode active material is appropriately selected in consideration of balance with other constituent requirements of the battery. From the viewpoint of improvement of battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, a 50% volume cumulative diameter is usually 1? 50 μm, preferably 15? 30 μm.

The content ratio of the negative electrode active material in the negative electrode active material layer is preferably 90? 99.9% by weight, more preferably 95? 99 wt%. By making content of the negative electrode active material in a negative electrode active material layer into the said range, flexibility and binding property can be exhibited, showing a high capacity | capacitance.

In addition to the said component, the negative electrode for lithium ion secondary batteries may further contain arbitrary components, such as the electrolyte solution additive which has a function, such as a dispersing agent used in the positive electrode for secondary batteries mentioned above, and electrolyte solution decomposition suppression. These are not particularly limited as long as they do not affect the battery reaction.

(Binder for lithium ion secondary battery negative electrode)

It does not specifically limit as a binder for lithium ion secondary battery negative electrodes, A well-known thing can be used. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) used for the above-mentioned lithium ion secondary battery positive electrode Resins such as polyacrylic acid derivatives and polyacrylonitrile derivatives, and soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers and vinyl soft polymers. These may be used independently and may use 2 or more types together.

As the current collector, any of the current collectors used for the secondary battery positive electrode described above can be used, and it is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but the copper for the negative electrode of a lithium ion secondary battery Is particularly preferred.

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

The lithium ion secondary battery negative electrode can be manufactured by the same method as for the lithium ion secondary battery positive electrode mentioned above.

As a specific manufacturing method of a lithium ion secondary battery, a positive electrode and a negative electrode are superposed | superposed through a separator, it is wound in a battery container by winding or bending according to a battery shape, an electrolyte solution is inject | poured into a battery container, and it is sealed. How to do this. If necessary, an overcurrent prevention device such as an expanded metal, a fuse, a PTC device, a lead plate, or the like may be placed to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat type.

Example

Although an Example is given to the following and this invention is demonstrated, this invention is not limited to this. In addition, the part and% in a present Example are a basis of weight unless there is particular notice.

In Examples and Comparative Examples, various physical properties were evaluated as follows.

<Binder characteristics: storage stability>

The aqueous dispersion of the obtained binder is stored under cold dark place for 50 days (the weight of the aqueous dispersion before storage is a). The aqueous dispersion of the polymer after 50 days has been filtered through 200 mesh, the dry weight of the solid remaining on the mesh (the weight of the residue is b), and the weight (a) of the aqueous dispersion before storage and the residue on the mesh The ratio (%) of the dry weight (b) of the solid is determined, and this is evaluated based on the following criteria, based on the evaluation criteria for the storage stability of the binder. The smaller this value, the better the storage stability.

A: less than 0.001%

B: 0.001% or more but less than 0.01%

C: 0.01% or more and less than 0.1%

D: 0.1% or more

<Slurry stability: Viscosity change rate>

The slurry viscosity change rate is calculated | required by the following formula from the slurry viscosity ((eta) _h ) 1 hour after the slurry preparation for positive electrodes, and the slurry viscosity ((eta) _5h ) after 5 hours, and it determines on the following references | standards.

Slurry Viscosity Change (%) = 100 × (η _5h -η _1h ) / η _1h

The smaller this value, the higher the stability of the slurry.

A: less than 10%

B: 10% or more but less than 20%

C: 20% or more but less than 30%

D: 30% or more

In addition, the viscosity of a slurry is measured with a single cylindrical rotational viscometer (25 degreeC, rotation speed = 60 rpm, spindle shape: 4) according to JISZ 8803: 1991.

<Electrode characteristics: peel strength>

The positive electrode on which the electrode active material layer was formed was cut into a rectangle of 2.5 cm in width x 10 cm in length to form a test piece, and the electrode active material layer surface was fixed upward. After affixing a cellophane tape on the electrode active material layer surface of a test piece, the stress at the time of peeling a cellophane tape in 180 degree direction at a speed of 50 mm / min from one end of a test piece is measured. The measurement is performed 10 times, the average value is obtained, and this is set as the peel strength (N / m), and this is evaluated based on the following criteria using the evaluation criteria of the peel strength. The larger this value, the better the binding property of the electrode.

A: 15 N / m or more

B: 10 N / m or more? Less than 15 N / m

C: 5.0 N / m or more? Less than 10 N / m

D: less than 5.0 N / m

<Battery characteristics: initial charge and discharge efficiency>

A 10-cell half cell coin-type battery was charged to 4.3 V by a 0.2 C constant current method in a 25 ° C. atmosphere, and charged and discharged to discharge to 3.0 V, and then the electric capacity was measured. The charge / discharge efficiency is a measure of the average value of 10 cells using the ratio (b / a (%)) of the discharge capacity b at the first cycle to the charge capacity a at the first cycle, and at the end of 50 cycles and at the end of 5 cycles. The charge / discharge capacity retention rate expressed by the ratio (%) of the capacitance is obtained, and this is evaluated based on the following criteria, based on the evaluation criteria for the cycle characteristics. The larger this value, the better the initial charge / discharge efficiency.

A: 60% or more

B: 40% or more but 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>

The 10-cell half cell coin-type battery was charged to 4.3 V by a 0.2 C constant current method under a 60 ° C. atmosphere, and the charge and discharge discharged to 3.0 V were repeated to measure the electric capacity. The average value of 10 cells is used as a measured value, and the charge / discharge capacity retention rate expressed by the ratio (%) of the capacitance at the end of 50 cycles and the cycle at the end of 5 cycles is obtained. Evaluate. The higher this value, the more excellent the cycle characteristics, that is, the smaller the capacity decrease due to repetition of charge and discharge.

A: 80% or more

B: more than 70% less than 80%

C: 50% or more but less than 70%

D: 30% or more and less than 50%

E: less than 30%

(Example 1)

(A) Preparation of Binder

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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 60 DEG C and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B. The stirred emulsion was added sequentially from the polymerization can B to the polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated. The aqueous dispersion of binder A was obtained. Got. The glass transition temperature of the obtained binder A was -32 degreeC, and the number average particle diameter was 0.15 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder A is 79% among all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 18%, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder A was 10.5 after adjustment in 4weight% of NaOH aqueous solution.

(B) Preparation of the slurry for the positive electrode and the positive electrode

Based on Example 1 of Japanese Unexamined Patent Application Publication No. 2003-48718, 10% Ni-40% Fe -containing Li ₂ having a layered rock-salt type _structure was synthesized by lithium ferrite composite oxide represented by the _y-x MnO _3. 100 parts of the obtained lithium ferrite composite oxide, 2.0 parts of acetylene black (HS-100: Denki Chemical Industry), 2.5 parts of aqueous dispersion of the binder A (solid content concentration 40%), and carboxymethyl having an etherification degree of 0.8 as a thickener. 40 parts of cellulose aqueous solution (solid content concentration 2%) and appropriate amount of water were stirred with the planetary mixer, and the slurry for positive electrodes was prepared. Slurry stability was evaluated using the obtained slurry for positive electrodes. The results are shown in Table 1 and Table 2. The slurry for the positive electrode was coated on a aluminum foil having a thickness of 20 μm with a comma coater so that the film thickness after drying was about 70 μm, dried at 60 ° C. for 20 minutes, and then heated at 150 ° C. for 2 hours to prepare an electrode disk. ) This electrode disk was rolled by the roll press, and the positive electrode plate whose density was controlled to 65 micrometers which consists of 2.1 g / cm <3>, aluminum foil, and an electrode active material layer was produced. Peel strength measurement was performed using the produced electrode plate. The results are shown in Table 1 and Table 2.

(C) Fabrication of Batteries

The positive electrode plate was cut out into a disk shape having a diameter of 16 mm. The separator which consists of a disk-shaped porous polypropylene film of 18 mm in diameter and 25 micrometers in thickness, and the negative electrode of metal lithium were prepared. A disk-shaped positive electrode plate, a separator, a negative electrode, and an expansive metal were laminated in this order, and this was placed in a stainless steel coin-type outer container (20 mm in diameter, 1.8 mm in height, 0.25 mm in stainless steel thickness) provided with a polypropylene packing. Housed. The disk-shaped positive electrode plate was arranged in the direction in which the surface on the active material layer side faces the separator. The electrolyte is injected into the container so that no air is left, 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. A lithium battery having a diameter of 20 mm and a thickness of about 2 mm is sealed. An ion coin battery (half cell) was produced.

In addition, LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in an EC: DEC = 1: 2 (volume ratio at 20 ° C) as an electrolyte. Solution was used.

This battery was used to evaluate initial charge and discharge efficiency and cycle characteristics. The results are shown in Table 1 and Table 2.

(Example 2)

(A) Preparation of Binder

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, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 90 DEG C and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of itaconic acid, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added and stirred to another polymerization can B. The prepared emulsion was sequentially added from polymerization can B to polymerization can A over about 180 minutes, stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated to obtain an aqueous dispersion of binder B. . The glass transition temperature of the obtained binder B was -29 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

In addition, the content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder B is 79% in all the polymer units of a polymer, and the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), (beta) The content rate of the polymer unit of an unsaturated nitrile monomer was 18% in all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder B was 10.6 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder B was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 3)

(A) Preparation of Binder

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, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 90 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 1.0 part of methacrylic acid, 0.7 part of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B and stirred. The resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated. Thus, the aqueous dispersion of binder C was prepared. Got it. The glass transition temperature of the obtained binder C was -32 degreeC, and the number average particle diameter was 0.15 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder C is 78% of all the polymer units of a polymer, and the polymer unit of the vinyl monomer which has an acid component is 1.0% of all the polymer units of a polymer, (alpha), (beta) unsaturated nitrile. The content rate of the polymer unit of a monomer was 20% of all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder C was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder C was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 4)

(A) Preparation of Binder

10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to the polymerization can A, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator, and the mixture was heated to 60 ° C. After stirring for 90 minutes, 67 parts of ethyl acrylate, 19 parts of acrylonitrile, 1.0 part of itaconic acid, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to the other polymerization can B, and the resulting emulsion was stirred for about 180 minutes. After sequentially adding to polymerization can A from polymerization can B over minutes, it stirred for about 120 minutes, cooled when monomer consumption reached 95%, and reaction was complete | finished, and the aqueous dispersion of binder D was obtained. The glass transition temperature of the obtained binder D was 5 degreeC, and the number average particle diameter was 0.18 micrometer. The 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 polymerized unit of the (meth) acrylic acid ester monomer is 79% in the total polymerized units of the polymer, and the polymerized unit of the vinyl monomer having an acid component is 1.0% in the total polymerized units of the polymer, α, β unsaturated nitrile. The content rate of the polymer unit of a monomer was 19% in all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder D was 10.3 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder D was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 5)

(A) Preparation of Binder

10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to the polymerization can A, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator, and the mixture was heated to 60 ° C. After stirring for 90 minutes, 67 parts of ethyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.2 parts of allyl methacrylate, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B. The stirred emulsion was added sequentially from the polymerization can B to the polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated, resulting in an aqueous dispersion of binder E. Got. The glass transition temperature of the obtained binder E was 2 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

In binder E, the content rate of the polymer unit of a (meth) acrylic acid ester monomer is 78% in all the polymer units of a polymer, and the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), (beta) unsaturated nitrile The content rate of the polymer unit of a monomer was 19% in all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0.2%.

PH of the obtained binder E was 10.5 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder E was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the lithium ion coin battery. It shows in Table 1 and Table 2.

(Example 6)

(A) Preparation of Binder

10.75 parts of ethyl acrylate, 1.25 parts of acrylonitrile, 0.12 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to the polymerization can A, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator, and the mixture was heated to 60 ° C. After 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, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B. The stirred emulsion was added sequentially from the polymerization can B to the polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated, resulting in an aqueous dispersion of the binder F. Got. The glass transition temperature of the obtained binder F was 2 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder F is 78% in all the polymer units of a polymer, and the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), (beta) unsaturated nitrile. The content rate of the polymer unit of a monomer was 19% in all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0.1%.

PH of the obtained binder F was 10.5 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder F was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 90 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B, and the resulting emulsion was stirred. After sequentially adding to polymerization can A from polymerization can B over 180 minutes, it stirred for about 120 minutes, cooled when monomer consumption became 95%, reaction was complete | finished, and the aqueous dispersion of binder G was obtained. The glass transition temperature of the obtained binder G was -10 degreeC, and the number average particle diameter was 0.15 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content ratio of the polymerized unit of the (meth) acrylic acid ester monomer in the binder G is 79% in the total polymerized units of the polymer, and the polymerized unit of the vinyl monomer having an acid component is 0% in the total polymerized units of the polymer, α, β unsaturated nitrile. The content rate of the polymer unit of a monomer was 20% of all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder G was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for a positive electrode, 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. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 90 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 5.0 parts of methacrylic acid, 0.7 parts of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B and stirred. The resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated. Got it. The glass transition temperature of the obtained binder H was -10 degreeC, and the number average particle diameter was 0.15 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

In binder H, the content rate of the polymer unit of a (meth) acrylic acid ester monomer is 77% in all the polymer units of a polymer, and the polymer unit of the vinyl monomer which has an acid component is 5.0% in all the polymer units of a polymer, (alpha), (beta) unsaturated nitrile The content rate of the polymer unit of a monomer was 17% of all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder H was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder H was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 parts of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added, and 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 90 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 0.5 part of methacrylic acid, 0.7 part of sodium lauryl sulfate, and 46 parts of ion-exchanged water were added to another polymerization can B and stirred. The resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated, thereby obtaining the aqueous dispersion of binder I. Got it. The glass transition temperature of the obtained binder I was -10 degreeC, and the number average particle diameter was 0.15 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder I is 79% of all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 0.5% of all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 19.5% of all the polymer units of a polymer, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder I was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder I was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, and the initial charge-discharge efficiency and cycling characteristics were evaluated using the peeling strength of this electrode plate and a 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of 2-acrylamide-2-methylpropanesulfonic acid, and 0.2 parts of allyl methacrylate to another polymerization can B , 0.7 parts of sodium lauryl sulfate and 46 parts of ion-exchanged water were added, and the emulsion prepared by stirring was sequentially added from polymerization can B to polymerization can A over about 180 minutes, followed by stirring for about 120 minutes, resulting in 95% monomer consumption. When it cooled, it cooled, the reaction ended, and the aqueous dispersion of binder J was obtained. The glass transition temperature of the obtained binder J was -31 degreeC, and the number average particle diameter was 0.19 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder J is 78% among all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 19%, and the content rate of the structural unit which has crosslinkability was 0.2%.

PH of the obtained binder J was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 J was used instead of the aqueous dispersion of binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After 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 parts of allyl methacrylate, 0.7 parts of sodium lauryl sulfate, and ion exchange to another polymerization can B 46 parts of water were added and the resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to cool down when the monomer consumption reached 95% to terminate the reaction. An aqueous dispersion of binder K was obtained. The glass transition temperature of the obtained binder K was -32 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder K is 78% in all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.0% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 19%, and the content rate of the structural unit which has crosslinkability was 0.2%.

PH of the obtained binder K was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for a positive electrode, 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. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After 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, and 46 parts of ion-exchanged water were added to another polymerization can B The stirred emulsion was sequentially added from polymerization can B to polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated, resulting in an aqueous dispersion of binder L. Got. The glass transition temperature of the obtained binder L was -30 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder L is 78.5% in all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.5% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 18.0%, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder L was 10.0 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for a positive electrode, 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 the binder L was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After 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, and 46 parts of ion-exchanged water were added to another polymerization can B and stirred. The prepared emulsion was sequentially added from polymerization can B to polymerization can A over about 180 minutes, then stirred for about 120 minutes, cooled when the monomer consumption reached 95%, and the reaction was terminated. Thus, the aqueous dispersion of binder M was prepared. Got it. The glass transition temperature of the obtained binder M was -29 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder M is 78.5% in all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.5% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 18.0%, and the content rate of the structural unit which has crosslinkability was 0%.

PH of the obtained binder M was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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 the binder M was used instead of the aqueous dispersion of the binder A. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 60 ° C. and stirring for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0.8 parts of ethylene glycol dimethacrylate, and sodium lauryl sulfate were added to another polymerization can B. Particularly, 46 parts of ion-exchanged water was added and stirred, and the resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to cool when the monomer consumption reached 95%. Then, the aqueous dispersion of binder N was obtained. The glass transition temperature of the obtained binder N was -30 degreeC, and the number average particle diameter was 0.18 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder N is 78.5% in all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.1% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of the (beta) unsaturated nitrile monomer was 17.5%, and the content rate of the structural unit which has crosslinkability was 0.9%.

PH of the obtained binder N was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the 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 and 10 parts of ion-exchanged water were added as a polymerization initiator. After heating to 60 ° C. and stirring 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, sodium lauryl sulfate to another polymerization can B Particularly, 46 parts of ion-exchanged water was added and stirred, and the resulting emulsion was added sequentially from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes to cool when the monomer consumption reached 95%. Then, the aqueous dispersion of binder O was obtained. The glass transition temperature of the obtained binder O was -29 degreeC, and the number average particle diameter was 0.17 micrometer. The binder storage stability was evaluated using the obtained aqueous dispersion. The results are shown in Tables 1 and 2.

The content rate of the polymer unit of the (meth) acrylic acid ester monomer in binder O is 78.0% in all the polymer units of a polymer, and the content rate of the polymer unit of the vinyl monomer which has an acid component is 2.2% in all the polymer units of a polymer, (alpha), The content rate of the polymer unit of a (beta) unsaturated nitrile monomer was 17.0%, and the content rate of the structural unit which has crosslinkability was 2.0%.

PH of the obtained binder O was 10.1 after adjustment in 4weight% of NaOH aqueous solution.

A slurry for the positive electrode, 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. And the slurry stability was evaluated using this slurry for positive electrodes, the peeling strength was evaluated using this electrode plate, and the initial stage charging and discharging efficiency and cycling characteristics were evaluated using the lithium ion coin battery. It shows in Table 1 and Table 2.

From the results of Tables 1 and 2, a lithium ferrite composite oxide having a layered rock salt structure was used as the positive electrode active material, and as a binder, a polymerization unit of a (meth) acrylic acid ester monomer, a polymerization unit of a vinyl monomer having an acid component, and α and the storage stability of the binder by using a copolymer containing a polymerized unit of a β unsaturated nitrile monomer and having a content ratio of the polymerized unit of a vinyl monomer having an acid component in a predetermined range in all polymerized units of the polymer. An electrode having excellent slurry stability and excellent peeling strength (ie, electrode binding property), excellent initial charging and discharging efficiency, and cycle characteristics (that is, a small capacity decrease due to repeated charging and discharging) can be obtained. have.

On the other hand, when the thing which does not contain the polymer unit of the vinyl monomer which has an acid component is used as a binder (comparative example 1), and when the content rate of the polymer unit of the vinyl monomer which has an acid component is outside the range as a binder (comparatively) At least any of the storage stability of the binder, the stability of the slurry, the peel strength, the initial charge and discharge efficiency, and the cycle characteristics are inferior to the example 2 and the comparative example 3).

Claims (9)

A current collector and a positive electrode active material layer containing a positive electrode active material and a binder formed on the current collector,
The positive electrode active material is 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,
The binder is a polymer containing a polymerized unit of a (meth) acrylic acid ester monomer, a polymerized unit of a vinyl monomer having an acid component and a polymerized unit of an α, β unsaturated nitrile monomer, and containing a polymerized unit of a vinyl monomer having the acid component. The proportion is 1.0? 3.0% by weight of a positive electrode for a secondary battery. The method of claim 1,
The positive electrode for secondary batteries in which the said binder further contains the structural unit which has crosslinkability. The method of claim 2,
The content ratio of the structural unit having the crosslinkability is 0.05? 2% by weight of a positive electrode for a secondary battery. The method of claim 1,
The polymerization unit of the said (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic-acid alkylester monomer,
The polymer unit of the vinyl monomer which has the said acid component is the polymer unit of the monomer which has a carboxylic acid group, the polymer unit of the monomer which has a sulfonic acid group, or a combination thereof,
The positive electrode for secondary batteries whose polymer unit of the said (alpha), (beta) unsaturated nitrile monomer is a polymer unit of acrylonitrile, the polymer unit of methacrylonitrile, or a combination thereof. The method of claim 4, wherein
The binder further contains a structural unit having crosslinkability,
The positive electrode for secondary batteries whose structural unit which has the said crosslinkability is a polymer unit of allyl acrylate, a polymer unit of ethylene glycol dimethacrylate, or a combination thereof. It contains a positive electrode active material, a binder, and a solvent,
The positive electrode active material is 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,
The binder is a polymer containing a polymerized unit of a (meth) acrylic acid ester monomer, a polymerized unit of a vinyl monomer having an acid component and a polymerized unit of an α, β unsaturated nitrile monomer, and containing a polymerized unit of a vinyl monomer having the acid component. The proportion is 1.0? Slurry for secondary battery positive electrode, which is 3.0 weight%. The method according to claim 6,
The polymerization unit of the said (meth) acrylic acid ester monomer is a polymerization unit of the (meth) acrylic-acid alkylester monomer,
The polymer unit of the vinyl monomer which has the said acid component is the polymer unit of the monomer which has a carboxylic acid group, the polymer unit of the monomer which has a sulfonic acid group, or a combination thereof,
The slurry for secondary battery positive electrodes whose said polymer unit of the (alpha), (beta) unsaturated nitrile monomer is a polymer unit of acrylonitrile, a polymer unit of methacrylonitrile, or a combination thereof. The method of claim 7, wherein
The binder further contains a structural unit having crosslinkability,
The slurry for secondary battery positive electrodes whose structural unit which has the said crosslinkability is a polymerization unit of allyl acrylate, a polymerization unit of ethylene glycol dimethacrylate, or a combination thereof. A secondary battery comprising a positive electrode, an electrolyte, a separator, and a negative electrode,
The secondary battery is a positive electrode for secondary batteries according to any one of claims 1 to 5.