WO2011148970A1

WO2011148970A1 - Positive electrode for secondary battery, and secondary battery

Info

Publication number: WO2011148970A1
Application number: PCT/JP2011/061963
Authority: WO
Inventors: 康尋脇坂; 庸介薮内
Original assignee: 日本ゼオン株式会社
Priority date: 2010-05-25
Filing date: 2011-05-25
Publication date: 2011-12-01
Also published as: JPWO2011148970A1; CN103026535A; JP5783172B2; CN103026535B

Abstract

Disclosed is a positive electrode for a secondary battery, which can be formed into a thick film and is capable of preventing occurrence of cracks. The positive electrode for a secondary battery is capable of providing a secondary battery that has improved cycle characteristics (especially high-temperature cycle characteristics) and improved safety. Specifically disclosed is a positive electrode for a secondary battery, which is characterized by being composed of a collector and a positive electrode active material layer that is arranged on the collector and contains fibrous carbon, a binder and a positive electrode active material containing manganese or iron. The positive electrode for a secondary battery is also characterized in that the binder is composed of a polymer that contains a (meth)acrylate monomer polymerization unit, a vinyl monomer polymerization unit having an acid component and an α,β-unsaturated nitrile monomer polymerization unit, and the content of the vinyl monomer polymerization unit having an acid component is 1.0-3.0% by mass of the total polymerization units of the polymer.

Description

Positive electrode for secondary battery and secondary battery

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. The present invention also relates to a secondary battery having such an electrode.

Among the batteries in practical use, lithium ion secondary batteries exhibit the highest energy density, and are often used especially for small electronics. In addition to small-sized applications, it is also expected to expand to automotive applications. Among them, there is a demand for higher output of lithium ion secondary batteries and further improvement in reliability such as cycle characteristics.

The positive electrode active material, which is a constituent material of lithium ion secondary batteries, has become a cheap active material containing manganese and nickel because the price of cobalt-based active materials used as the mainstream and the reserves are limited. The transition is progressing. However, in manganese-based active materials that are expected to become mainstream in the future, repeated charge and discharge at high temperatures, particularly 40 ° C or higher, may elute manganese ions into the electrolyte, resulting in a decrease in battery capacity. It has become a big issue.

In addition, manganese ions eluted from the positive electrode are reduced and deposited on the negative electrode surface, thereby forming a dendritic metal precipitate, which damages the separator and lowers the safety as a battery. Has been.

In addition, an electrode used in a lithium ion secondary battery usually has a structure in which an electrode active material layer is laminated on a current collector, and the electrode active material layer includes an electrode active material in addition to the electrode active material. A binder is used to bind each other and the electrode active material and the current collector.

Patent Document 1 describes a positive electrode containing LiFePO ₄ having an olivine structure as a positive electrode active material, carbon and a copolymer of (meth) acrylic acid ester and an α, β-unsaturated nitrile compound as a binder. .

Patent Document 2 describes a positive electrode containing LiFePO ₄ having an olivine crystal structure as a positive electrode active material, carbon fiber, and polyvinylidene fluoride (PVDF) as a binder.

WO 2006/038652 (corresponding US publication: US Patent Application Publication No. 2008/096109) JP 2005-222933 A (corresponding US publication: US Patent Application No. 2007/275302)

However, according to the study by the present inventors, in Patent Document 1, LiFePO ₄ having an olivine structure used as the positive electrode active material has a small particle size as the positive electrode active material, and thus the positive electrode active material layer is formed as a thick film. It has been found that there is a problem that cracks occur when it is converted. Further, in the positive electrode of Patent Document 2, as in the case where a manganese-based active material is used as the positive electrode active material described above, when charging / discharging is repeated at a high temperature, iron ions are eluted into the electrolytic solution, resulting in a decrease in battery capacity. It has been found that there is a problem that the safety of the battery is reduced due to the problem that the eluted iron ions are dendritically deposited on the negative electrode surface.

Therefore, the present invention can increase the film thickness, prevent the occurrence of cracks, and improve the cycle characteristics (especially high temperature cycle characteristics) and safety of the obtained secondary battery. The purpose is to provide a positive electrode for use. Moreover, this invention aims at providing a secondary battery provided with this positive electrode for secondary batteries.

The gist of the present invention aimed at solving such problems is as follows.
(1) A current collector and a positive electrode active material layer that is laminated on the current collector and contains manganese or iron, fibrous carbon, and a binder.
The binder comprises a polymer comprising a polymer unit of a (meth) acrylic acid ester monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β-unsaturated nitrile monomer,
A positive electrode for a secondary battery, wherein a content ratio of polymer units of the vinyl monomer having an acid component is 1.0 to 3.0% by mass in all polymer units of the polymer.

(2) The positive electrode for a secondary battery according to (1), wherein the positive electrode active material contains iron and further has an olivine structure.

(3) The positive electrode for a secondary battery according to (1) or (2), wherein the fibrous carbon has an average fiber diameter of 0.01 to 1.0 μm.

(4) The positive electrode for a secondary battery according to any one of (1) to (3), wherein the fibrous carbon has an average aspect ratio of 5 to 50000.

(5) The positive electrode for a secondary battery according to any one of (1) to (4), wherein the vinyl monomer having an acid component is a monomer having a carboxylic acid group.

(6) The positive electrode for a secondary battery according to any one of (1) to (5), wherein the binder further contains a polymer unit having crosslinkability.

(7) A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the positive electrode is the positive electrode for a secondary battery according to any one of (1) to (6).

According to the present invention, by including fibrous carbon in the positive electrode active material layer, the toughness of the positive electrode active material layer can be improved, so that the generation of cracks in the positive electrode active material layer is prevented, and the positive electrode active material layer Can be thickened. In addition, the binder contained in the positive electrode active material layer includes a polymer comprising a polymer unit of a (meth) acrylate monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β-unsaturated nitrile monomer. Since the metal ion (manganese ion or iron ion) eluted from the positive electrode active material can be captured by setting the content ratio of the polymerization unit of the vinyl monomer having an acid component to a predetermined ratio, the secondary battery Cycle characteristics (especially high-temperature cycle characteristics) and safety are improved.

The present invention is described in detail below. The positive electrode for secondary batteries of the present invention has a positive electrode active material layer containing a positive electrode active material containing manganese or iron, fibrous carbon, and a binder on a current collector.

(Positive electrode active material)
The positive electrode active material used in the present invention is not particularly limited as long as it contains manganese or iron and can reversibly insert and release lithium ions. Among them, a lithium-containing transition metal oxide is preferable.

Examples of the lithium-containing transition metal oxide containing manganese include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

The lithium-containing composite metal oxide having a layered structure, _Li X obtained by replacing a part of LiMnO ₂ and Mn in other transition metals _{_{[Mn y M 1-y]}} O 2 ( where x = 0.02 ~ 1 .2, 0 <y <1, M is Cr, Fe, Co, Ni, Cu, etc.).

The lithium-containing composite metal oxide having a spinel _{_{_{structure, Li X [Mn y M 2}}} -y] O 4 ( where x = 0.02 obtained by substituting a part of LiMn ₂ O ₄ and Mn in other transition metals -1.2, 0 <y <2, M is Cr, Fe, Co, Ni, Cu, V, etc.).

Examples of the lithium-containing composite metal oxide having an olivine structure include Li _x MnPO ₄ and Li _x Mn _y M _1-y PO _{4 in} which a part of Mn is substituted with another transition metal (where x = 0.02 to 1 .2, 0 <y <1, M is at least one selected from Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo) Olivine type lithium phosphate compound.

Among these, LiMnO ₂ having a layered structure that easily undergoes cycle deterioration due to elution of Mn ions and its substitute, LiMn ₂ O ₄ having a spinel structure and its substitute, most preferably LiMn ₂ O ₄ having a spinel structure. And the substitution thereof has a great effect of improving the cycle characteristics of the secondary battery of the present invention. In the present invention, two or more positive electrode active materials may be used, or a mixture of a positive electrode active material containing manganese and a positive electrode active material not containing manganese may be used. Furthermore, since the cycle deterioration due to elution of Mn ions is more likely to occur as the manganese content increases, the effect of improving the cycle characteristics by the positive electrode for secondary batteries of the present invention is greater. In the present invention, the manganese content in the positive electrode active material is preferably 10 to 80% by mass, more preferably 15 to 65% by mass. By setting the manganese content in the positive electrode active material within the above range, the manganese ion scavenging effect by the acid component of the binder in the present invention remarkably appears.

Examples of the lithium-containing transition metal oxide containing iron include Li _y FeXO ₄ (where X is at least one element selected from elements of Groups 4 to 7 and Groups 14 to 17 of the periodic table). Y represents 0 <y <2.).

The lithium-containing transition metal oxide containing iron usually has a structure in which the element X is located at a tetrahedral site and lithium is located at an octahedral site together with iron. The structure of the positive electrode active material is represented as {X} · [Li _y Fe] O ₄ when expressed up to the site (where {} indicates a tetrahedral site and [] indicates an octahedral site). As the element X which gives such a structure, for example, a Group 5 element such as vanadium or a Group 15 element such as phosphorus, arsenic, antimony, or bismuth is preferable.

The lithium-containing transition metal oxide containing iron preferably has an olivine structure having a hexagonal close-packed oxygen skeleton or a spinel or inverse spinel structure having a cubic close-packed oxygen skeleton, and particularly preferably an olivine-type structure. preferable. The difference between the olivine structure and the spinel structure including the reverse spinel is whether the oxygen ions are hexagonal close packed or cubic close packed, and the stable structure varies depending on the type of element of X. For example, LiFePO ₄ has a stable olivine structure, and LiFeVO ₄ has a reverse spinel structure as a stable phase.

Li _y FeXO ₄ having an olivine type structure or a spinel structure is prepared by mixing a lithium compound, a divalent iron compound and an ammonium salt of element (X), and then firing in an inert gas atmosphere or a reducing atmosphere. Can be manufactured. Examples of the lithium compound include Li ₂ CO ₃ , LiOH, LiNO _{3 and the} like.

Specific examples of the divalent iron compound include FeC ₂ O ₄ .2H ₂ O, Fe (CH ₃ COO) ₂ , FeCl _{2 and the} like. Specific examples of the ammonium salt of element (X) include phosphates such as (NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₃ PO ₄ ; NH ₄ HSO ₄ , (NH ₄ ) ₂ sulfates such as SO ₄ ; and the like.

In addition to the above, an iron compound having a NASICON structure can also be used as the positive electrode active material. The NASICON type iron compound is specifically represented by Li ₂ Fe _2-n V _n (XO ₄ ) ₃ (where 0 ≦ n <2, preferably 0 ≦ n ≦ 1). Compounds.

Among these, an olivine-type iron compound is more preferable in terms of manifesting the effect of the invention that an electrode using a positive electrode active material having a small particle diameter can be produced with good yield.

The amount of the positive electrode active material contained in the positive electrode active material layer of the positive electrode for a secondary battery of the present invention is preferably 80 to 99.5% by mass, more preferably 90 to 99% by mass. When the amount of the positive electrode active material exceeds 99.5% by mass, the ratio of the binder and the conductivity-imparting agent in the positive electrode active material layer becomes small. While the binding property with an electric body falls, the output characteristic of a battery may fall. Further, when the amount of the positive electrode active material is less than 80% by mass, the battery capacity may be reduced.

粒径 The particle size (average particle size) of the positive electrode active material contained in the positive electrode active material layer of the positive electrode for secondary battery of the present invention is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm. When the particle diameter of the positive electrode active material exceeds 10 μm, the dispersibility in the slurry is lowered, and it becomes difficult to produce a good slurry. Moreover, when the particle size of the positive electrode active material is less than 0.01 μm, the conductivity of the active material may be reduced, and the internal resistance of the battery may be increased.

(Fibrous carbon)
In the present invention, fibrous carbon is used. By using fibrous carbon, the toughness of the positive electrode active material layer can be improved, so that the generation of cracks in the positive electrode active material layer can be prevented and the positive electrode active material layer can be thickened. As a result, the safety of the secondary battery using the positive electrode for secondary battery of the present invention can be improved.
If the fibrous carbon used in the present invention is fibrous, the effect of the present invention can be achieved. However, if the fiber diameter of the fibrous carbon is too large, voids in the electrode become large and the electrode density cannot be increased, which is not preferable. . On the other hand, if the fiber diameter is too small, it is not preferable because it is buried between the active material particles, a network in the electrode cannot be formed, and void formation between the active materials becomes impossible. For the above reasons, the average fiber diameter of the fibrous carbon that can be used in the positive electrode for secondary battery of the present invention is preferably 0.01 to 1.0 μm, more preferably 0.01 to 0.2 μm. By using a fiber carbon having an average fiber diameter in the above range, the dispersion stability of the secondary battery positive electrode slurry described later can be improved, and a high-capacity secondary battery can be produced.

The higher the degree of crystallinity (so-called graphitization) of fibrous carbon is preferable. In general, the higher the degree of graphitization of the carbon material, the more the layered structure develops, the harder the carbon material is, and the higher the conductivity is. Therefore, it is suitable for use as a positive electrode for a secondary battery. In order to graphitize the carbon material, it is generally sufficient to treat it at a high temperature. In this case, the treatment temperature varies depending on the fibrous carbon used, but is preferably 2000 ° C. or higher, and more preferably 2500 ° C. or higher. In this case, it is effective to add boron or Si, which is a graphitization cocatalyst that works to promote the degree of graphitization, before the heat treatment. The addition amount of the cocatalyst is not particularly limited, but if the addition amount is too small, the effect is not obtained, and if it is too much, it remains as an impurity, which is not preferable. A preferable addition amount is 0.1 to 100,000 ppm, and more preferably 10 to 50,000 ppm.

The degree of crystallinity of these fibrous carbons is not particularly limited, but the average interplanar distance d ₀₀₂ by X-ray diffraction method is preferably 0.344 nm or less, more preferably 0.339 nm or less, and the crystallinity in the C-axis direction of the crystal The thickness Lc is 40 nm or less.

The longer the fiber length of the fibrous carbon, the better the conductivity in the electrode, the strength of the electrode, and the electrolyte solution retention, but if it is too long, the fiber dispersibility in the electrode is impaired. The range of the average fiber length varies depending on the type of fibrous carbon used and the fiber diameter, but is preferably 0.5 to 100 μm, more preferably 1 to 50 μm. A preferred range of this average fiber length is expressed in terms of an average aspect ratio (ratio of average fiber length to average fiber diameter), which is in the range of 5 to 50000, and more preferably in the range of 10 to 15000. By using a fiber carbon having an average fiber length and an average aspect ratio within the above ranges, the dispersion stability of a slurry for a secondary battery positive electrode, which will be described later, is improved, and the effect of suppressing cracks in the positive electrode active material layer and the positive electrode active The effect as a conductive path in the material layer can be further enhanced.

It is preferable that the fibrous carbon is branched (branched) because the conductivity of the whole electrode, the strength of the electrode, and the electrolyte solution retention are further increased. However, if there are too many branched fibers, the dispersibility in the electrode is impaired as in the fiber length. The proportion of these branched fibers can be controlled to some extent by the production method and the subsequent pulverization treatment.

The method for producing fibrous carbon is not particularly limited. For example, a method of heat-treating a precursor made of a polymer or pitch spun into a fiber, an organic vapor such as benzene is directly flowed on a substrate at about 1000 ° C., and iron Examples thereof include a method of growing carbon crystals using fine particles as a catalyst (vapor phase growth method).

The content of fibrous carbon is preferably 0.05 to 20% by mass, more preferably 0.1 to 15% by mass with respect to the total amount of the positive electrode active material, the binder and the thickener to be blended as necessary. Particularly preferred is 0.5 to 10% by mass. When the content exceeds 20% by mass, the active material ratio in the electrode becomes small, so that the battery capacity becomes small. If the content is less than 0.05% by mass, it is difficult to suppress the generation of cracks in the electrode. In order to adjust the content to the above range, it can be carried out by adding the same ratio in the production method.

Fibrous carbon that has been surface-treated to control the dispersion state in the electrode can also be used. The surface treatment method is not particularly limited, and examples thereof include those made hydrophilic by introducing an oxygen-containing functional group by oxidation treatment, and those made hydrophobic by fluorination treatment or silicon treatment. In addition, a phenol resin coating or a mechanochemical treatment may be used. If the surface treatment is too much, the conductivity and strength of the fibrous carbon will be remarkably impaired, and appropriate treatment is required. The oxidation treatment can be performed, for example, by heating fibrous carbon in air at 500 ° C. for about 1 hour. This treatment improves the hydrophilicity of the fibrous carbon.

(binder)
The positive electrode for a secondary battery of the present invention comprises, in a binder, a polymer unit of a (meth) acrylate monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β-unsaturated nitrile monomer. Including. Specifically, the polymer as the binder includes the respective polymer units.

In the present invention, polymerization units of (meth) acrylic acid ester monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl Acrylic acid alkyl esters such as acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl meta Relate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Among these, non-carbonyl oxygen is shown because it exhibits lithium ion conductivity by moderate swelling into the electrolyte without eluting into the electrolyte, and in addition, it is difficult to cause bridging aggregation by the polymer in the dispersion of the active material. Heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate and lauryl acrylate, which are alkyl acrylates having 7 to 13 carbon atoms in the alkyl group bonded to the atom, are preferred, and bonded to a non-carbonyl oxygen atom More preferred are octyl acrylate, 2-ethylhexyl acrylate, and nonyl acrylate having 8 to 10 carbon atoms in the alkyl group.

In the present invention, preferred as a polymerization unit of a vinyl monomer having an acid component is a monomer having a —COOH group (carboxylic acid group), a monomer having an —OH group (hydroxyl group), a —SO ₃ H group ( A monomer having a sulfonic acid group), a monomer having a —PO ₃ H ₂ group, a monomer having a —PO (OH) (OR) group (R represents a hydrocarbon group), and a lower polyoxy Examples include monomers having an alkylene group.

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and derivatives thereof, dicarboxylic acid, acid anhydrides thereof, and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of 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 mentioned. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Dicarboxylic acid derivatives include methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid and the like methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, And maleate esters such as octadecyl maleate and fluoroalkyl maleate.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol and 5-hexen-1-ol; 2-hydroxyethyl acrylate, acrylic acid-2 Ethylenic acid such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate Alkanol esters of unsaturated carboxylic acids; general formula CH ₂ ═CR ¹ —COO— (C _n H _2n O) _m —H (m is an integer from 2 to 9, n is an integer from 2 to 4, R ¹ is hydrogen Or an ester of a polyalkylene glycol represented by (meth) acrylic acid represented by 2-hydro; Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as cyethyl-2 ′-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether; Vinyl ethers such as 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2- Mono (meth) allyl ethers of alkylene glycols such as hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro -3-Hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether and the like (poly) alkylene glycol halogen and hydroxy-substituted mono (meth) allyl ethers; Eugenol, isoeugenol and many others Mono (meth) allyl ether of monohydric phenol and its halogen-substituted product; (meth) allyl of alkylene glycol such as (meth) allyl-2-hydroxyethylthioether, (meth) allyl-2-hydroxypropylthioether Thioether compounds; and the like.

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

Monomers having a —PO ₃ H ₂ group and / or —PO (OH) (OR) group (R represents a hydrocarbon group) include 2- (meth) acryloyloxyethyl phosphate, methyl phosphate -2- (Meth) acryloyloxyethyl, ethyl phosphate- (meth) acryloyloxyethyl, and the like.

Examples of the monomer having a lower polyoxyalkylene group include poly (alkylene oxide) such as poly (ethylene oxide).

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

In the present invention, the polymerization unit of the α, β-unsaturated nitrile monomer is preferably acrylonitrile or methacrylonitrile from the viewpoint of improving the mechanical strength and the binding force.

In the present invention, the content ratio of the polymerization units of the (meth) acrylic acid ester monomer in the binder (hereinafter sometimes referred to as “component A”) is preferably 50 to 95% by mass, more preferably 60 to 90% by mass. It is. The content of polymerized units of the α, β-unsaturated nitrile monomer (hereinafter sometimes referred to as “component B”) is preferably 3 to 40% by mass, more preferably 5 to 30% by mass. . Further, the content ratio of the polymerization unit of the vinyl monomer having an acid component (hereinafter sometimes referred to as “component C”) is 1.0 to 3.0% by mass, preferably 1.5 to 2.5% by mass. It is. When the content ratio of component A exceeds 95% by mass, the mechanical strength of the binder decreases. Moreover, since the softness | flexibility of a binder falls that the content rate of the component A is less than 50 mass%, and an electrode becomes hard, it becomes difficult to prevent generation | occurrence | production of a crack. When the content ratio of Component B exceeds 40% by mass, the flexibility of the binder is lowered and the electrode becomes hard, so that it is difficult to prevent the occurrence of cracks. Moreover, the mechanical strength of a binder falls that the content rate of the component B is less than 3 mass%, and the adhesiveness of an electrode falls. When the content of Component C exceeds 3.0% by mass, the production stability and storage stability of the binder are lowered. On the other hand, when the content ratio of Component C is less than 1.0% by mass, the binding property as a binder is insufficient, and the battery life characteristics are deteriorated.

In the present invention, it is preferable that the binder to be used further contains a polymerized unit having crosslinkability in addition to the above components A, B and C. Examples of the method for introducing a crosslinkable polymer unit into the binder include a method for introducing a photocrosslinkable crosslinkable group into the binder and a method for introducing a heat crosslinkable crosslinkable group. Among these, the method of introducing a heat-crosslinkable crosslinkable group into the binder can crosslink the binder by applying heat treatment to the electrode plate after coating, and can further suppress dissolution in the electrolyte. It is preferable because a tough and flexible electrode plate can be obtained and the life characteristics of the battery are improved. A method of using a monofunctional monomer having one olefinic double bond having a heat-crosslinkable crosslinkable group when introducing a heat-crosslinkable crosslinkable group into the binder, and at least two olefinic properties There is a method using a polyfunctional monomer having a double bond. The thermally crosslinkable group contained in the monofunctional monomer having one olefinic double bond is at least selected from the group consisting of an epoxy group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. One type is preferred, and an epoxy group is more preferred in terms of easy crosslinking and adjustment of the crosslinking density.

Examples of the monomer containing an epoxy group include a monomer containing a carbon-carbon double bond and an epoxy group, and a monomer containing a halogen atom and an epoxy group.

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

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

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

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

Monomers containing an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2- Examples thereof include oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline and the like.

Polyfunctional monomers having at least two olefinic double bonds include allyl acrylate or allyl methacrylate, trimethylolpropane-triacrylate, trimethylolpropane-methacrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene Glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, or other allyl or vinyl ethers of polyfunctional alcohols, tetraethylene glycol diacrylate, triallylamine, trimethylolpropane-diallyl ether, methylenebisacrylamide and / or divinylbenzene preferable. In particular, allyl acrylate, allyl methacrylate, trimethylolpropane-triacrylate and / or trimethylolpropane-methacrylate and the like can be mentioned.
Of these, polyfunctional monomers having at least two olefinic double bonds are preferred because the crosslinking density is likely to be improved, and allyl acrylate is also preferred because of improved crosslinking density and high copolymerizability. Or acrylate or methacrylate having an allyl group such as allyl methacrylate is preferable.

The content ratio of the heat-crosslinkable crosslinkable group in the binder is preferably 0.01 with respect to 100% by mass of the total amount of monomers as the amount of the monomer containing the heat-crosslinkable crosslinkable group at the time of polymerization. It is in the range of -0.5% by mass, more preferably 0.3-0.05% by mass. The content ratio of the heat-crosslinkable crosslinkable group in the binder can be controlled by the monomer charge ratio when the binder is produced. When the content ratio of the heat-crosslinkable crosslinking group in the binder is within the above range, the swelling property with respect to an appropriate electrolytic solution can be exhibited, and excellent rate characteristics and cycle characteristics can be exhibited.

The binder used in the present invention may contain other polymerization units in addition to the above components. The other polymerized unit is a polymerized unit derived from another vinyl monomer. For example, as a monomer copolymerizable with these, two or more carbon atoms such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, etc. Carboxylic acid esters having a carbon double bond; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, etc. Vinyl ethers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone and the like; heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole; It is.

The binder used in the present invention is used in the state of a dispersion liquid or a dissolved solution dispersed in a dispersion medium. Among these, it is preferable that it is dispersed in the dispersion medium in the form of particles because the swelling property of the electrolytic solution is suppressed.

When the binder is dispersed in the form of particles in the dispersion medium, the average particle size (dispersed particle size) of the binder dispersed in the form of particles is preferably 50 to 500 nm, more preferably 70 to 400 nm, and most preferably. 100 to 250 nm. When the average particle size of the binder is within this range, the strength and flexibility of the obtained electrode are improved. In addition, an organic solvent or water is used as the dispersion medium, but it is preferable to use water as the dispersion medium because of the high drying speed.

When the binder is dispersed in the dispersion medium in the form of particles, the solid content concentration of the dispersion is usually 15 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. When the solid content concentration is within this range, workability when producing a slurry for a secondary battery positive electrode, which will be described later, is good.

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

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

In the binder used in the present invention, the dispersant used in these polymerization methods may be those used in ordinary synthesis. Specific examples thereof include benzene such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate. Sulfonates; 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; polyoxyethylene lauryl ether sulfate sodium salt; Ethoxy sulfate salts such as polyoxyethylene nonylphenyl ether sulfate sodium salt; alkane sulfonate salt; alkyl ether phosphate sodium salt; Nonionic emulsifiers such as oxyethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, polyoxyethylene-polyoxypropylene block copolymer; gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, sodium polyacrylate, Examples thereof include water-soluble polymers such as polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more, and these may be used alone or in combination of two or more. Among these, benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecylsulfate are preferable, and oxidation resistance is more preferable. From this point, it is a benzenesulfonate such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate. The addition amount of the dispersant can be arbitrarily set, and is usually about 0.01 to 10 parts by mass with respect to 100 parts by mass of the total amount of monomers.

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

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

The content of the binder in the positive electrode active material layer is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material. The content of the binder in the positive electrode of the secondary battery is in the above range, so that the positive electrode active materials and the positive electrode active material and the current collector are excellent in binding properties while maintaining flexibility and the movement of lithium ions. Does not inhibit the resistance.

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

As the conductivity imparting material, conductive carbon such as acetylene black, ketjen black, carbon black and graphite can be used. Examples thereof include carbon powders such as graphite, and fibers and foils of various metals. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved. In particular, when used in a lithium ion secondary battery, the discharge load characteristics can be improved.

As the reinforcing material, various inorganic and organic spherical, plate-like, or rod-like fillers can be used. By using a reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The amount of the conductivity-imparting material and reinforcing agent used is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. By being included in the said range, a high capacity | capacitance and a high load characteristic can be shown.

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

Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs when applying a slurry for a secondary battery positive electrode, which will be described later, to the current collector, or to improve the smoothness of the electrode. The content of the leveling agent in the positive electrode active material layer is preferably 0.01 to 10% by mass. When the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.

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

Examples of thickeners include cellulose polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”. The content of the thickener in the positive electrode active material layer is preferably 0.01 to 10% by mass. When the thickener is in the above range, the coating property of the secondary battery positive electrode slurry, which will be described later, to the current collector is improved. Moreover, it is excellent in the dispersibility of the active material etc. in the positive electrode slurry mentioned later, a smooth electrode can be obtained, and the outstanding load characteristic and cycling characteristics are shown.

As the electrolytic solution additive, vinylene carbonate used in a slurry for a secondary battery positive electrode and an electrolytic solution described later can be used. The content ratio of the electrolytic solution additive in the positive electrode active material layer is preferably 0.01 to 10% by mass. When the electrolytic solution additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nano-particles such as fumed silica and fumed alumina: surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the nanoparticles, the thixotropy of the electrode forming slurry can be controlled, and the leveling property of the resulting electrode can be improved. The content ratio of the nanoparticles in the positive electrode active material layer is preferably 0.01 to 10% by mass. When the nanoparticles are in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited. By mixing the surfactant, the dispersibility of the active material and the like in the slurry for the secondary battery positive electrode can be improved, and the smoothness of the electrode obtained thereby can be improved. The content ratio of the surfactant in the positive electrode active material layer is preferably 0.01 to 10% by mass. When the surfactant is in the above range, the slurry for a secondary battery positive electrode described later is excellent in stability and electrode smoothness, and exhibits high productivity.

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

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

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

The thickness of the positive electrode for secondary battery of the present invention is usually 5 to 150 μm, preferably 10 to 100 μm. When the electrode thickness is in the above range, both load characteristics and energy density are high.

(Slurry for secondary battery positive electrode)
The slurry for secondary battery positive electrode used in the present invention is a positive electrode active material containing manganese or iron, fibrous carbon, (meth) acrylic acid ester monomer polymerization units, vinyl monomer polymerization units having an acid component, and α, A binder comprising a polymer containing polymerized units of β-unsaturated nitrile monomer and a solvent are included. As the binder containing the positive electrode active material, fibrous carbon, polymer unit of (meth) acrylate monomer, polymer unit of vinyl monomer having an acid component, and polymer unit of α, β-unsaturated nitrile monomer, those described above are used. Use.

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

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

In addition, the secondary battery positive electrode slurry includes a positive electrode active material containing manganese or iron, fibrous carbon, a polymerization unit of a (meth) acrylate monomer, a polymerization unit of a vinyl monomer having an acid component, and α, β -In addition to a binder comprising a polymer comprising polymerized units of an unsaturated nitrile monomer and a solvent, the electrolytic agent having functions such as a dispersant used in the above-mentioned positive electrode for a secondary battery and an electrolytic solution decomposition suppression Other components such as a liquid additive may be contained. These are not particularly limited as long as they do not affect the battery reaction.

(Production of slurry for secondary battery positive electrode)
In the present invention, the method for producing the slurry for the secondary battery positive electrode is not particularly limited, and can be obtained by mixing the positive electrode active material, fibrous carbon, binder, and solvent and other components added as necessary. . In the present invention, a positive electrode slurry in which the positive electrode active material and the fibrous carbon are highly dispersed can be obtained by using the above components regardless of the mixing method and the mixing order. The mixing device is not particularly limited as long as it can uniformly mix the above components, and bead mill, ball mill, roll mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, fill mix, etc. Among them, it is particularly preferable to use a ball mill, a roll mill, a pigment disperser, a crusher, or a planetary mixer because dispersion at a high concentration is possible.

The viscosity of the positive electrode slurry is preferably 10 to 100,000 mPa · s, more preferably 100 to 50,000 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The said viscosity is a value when it measures at 25 degreeC and rotation speed 60rpm using a B-type viscometer.

(Secondary battery)
The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode includes a positive electrode active material containing manganese or iron, fibrous carbon, and the binder on a current collector. It has a positive electrode active material layer formed.

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

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

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

Also, it is possible to use the electrolyte solution by adding an additive. Examples of the additive include carbonate compounds such as vinylene carbonate (VC) used in the slurry for a secondary battery positive electrode.

The concentration of the supporting electrolyte in the electrolytic solution for a lithium ion secondary battery is usually 1 to 30% by mass, preferably 5 to 20% by mass. The concentration is usually 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease.

Further, as the electrolytic solution, a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, a gel polymer electrolyte obtained by impregnating the polymer electrolyte with an electrolytic solution, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

(Separator for lithium ion secondary battery)
As the separator, known ones such as a microporous film or non-woven fabric made of polyolefin such as polyethylene and polypropylene; a porous resin coat containing inorganic ceramic powder; and the like can be used.

As a separator for a lithium ion secondary battery, a known one such as a microporous film or non-woven fabric containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder; Can do. For example, a polyolefin film (polyethylene, polypropylene, polybutene, polyvinyl chloride), a microporous film made of a resin such as a mixture or copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, Examples thereof include a microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like. Among these, a microporous film made of a polyolefin-based resin is preferable because the thickness of the entire separator can be reduced and the active material ratio in the battery can be increased to increase the capacity per volume.

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

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

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

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

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

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

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

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

The lithium ion secondary battery negative electrode can be produced in the same manner as the above-described lithium ion secondary battery positive electrode.

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

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard. In the examples and comparative examples, various physical properties are evaluated as follows.

<Battery characteristics: High-temperature cycle characteristics>
A 10-cell full-cell coin-type battery was charged to 4.3 V by a constant current method of 0.2 C in an atmosphere of 60 ° C., and was repeatedly charged and discharged to 3.0 V, and the electric capacity was measured. Using the average value of 10 cells as the measured value, the charge / discharge capacity retention ratio represented by the ratio (%) of the electric capacity at the end of 50 cycles and the electric capacity at the end of 5 cycles is obtained, and this is used as an evaluation criterion for cycle characteristics. Evaluation is based on the following criteria. The higher this value, the better the high-temperature cycle characteristics.
A: 80% or more B: 70% or more and less than 80% C: 50% or more and less than 70% D: 30% or more and less than 50% E: Less than 30%

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

<Electrode characteristics: crack measurement>
The electrode is cut into a rectangle 3 cm wide by 9 cm long to form a test piece. Place the test piece on the desk with the current collector side facing down, and lay a stainless steel rod 1 mm in diameter in the short direction on the center in the length direction (position 4.5 cm from the end). Install. The test piece was bent 180 ° around the stainless steel bar so that the active material layer was on the outside. Ten test pieces were tested, and the bent portions of the active material layer of each test piece were observed for cracking or peeling, and judged according to the following criteria. The fewer the cracks or peeling, the less the electrode is cracked and the better the safety.
A: No cracking or peeling is observed in all 10 sheets B: Cracking or peeling is observed in 1 to 3 of 10 sheets C: Cracking or peeling is observed in 4 to 9 out of 10 sheets D: 10 sheets All inside are cracked or peeled

Example 1
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0 parts of sodium lauryl sulfate were added to another polymerization vessel B. 7 parts and 46 parts of ion-exchanged water were added to the emulsion prepared by stirring for about 180 minutes, and then added to the polymerization can A sequentially from the polymerization can B. After stirring for about 120 minutes, the monomer consumption was 95%. Then, the reaction was terminated by cooling, and then the pH was adjusted with a 4% NaOH aqueous solution to obtain an aqueous dispersion of binder A. The obtained binder A had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder A having a pH of 10.5. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion.

The content of polymer units of (meth) acrylic acid ester monomer in binder A is 78%, the content of polymer units of vinyl monomer having an acid component is 2.0%, and the content of polymer units of α, β-unsaturated nitrile monomer The ratio was 20%, and the content ratio of the polymerized units having crosslinkability was 0%.

(B) Production of slurry for positive electrode and positive electrode As an electrode active material, 100 parts of LiFePO ₄ (particle diameter: 0.2 μm) having an olivine type crystal structure, carbon fiber (average fiber diameter: 150 nm, average fiber length: 8 μm, average aspect) Ratio: 53, hereinafter referred to as “carbon fiber 1”) 1 part, 5 parts of acetylene black (HS-100: Electrochemical Industry), 2.5 parts of aqueous dispersion of binder A (solid content) 40%), 40 parts of an aqueous carboxymethyl cellulose solution having a degree of etherification of 0.8 as a thickener (solid content concentration 2%), and an appropriate amount of water are stirred with a planetary mixer to obtain a slurry for positive electrode Was prepared. The positive electrode slurry is applied on an aluminum foil having a thickness of 20 μm with a comma coater so that the film thickness after drying becomes about 70 μm, dried at 60 ° C. for 20 minutes, and then heat-treated at 150 ° C. for 2 hours to form an electrode substrate. Got anti. This electrode original fabric was rolled with a roll press to produce a positive electrode plate with a density of 2.1 g / cm ³ and a thickness of aluminum foil and an electrode active material layer controlled to 65 μm. The occurrence of cracks was measured using the produced electrode plate. The results are shown in Table 1.

(C) Production of Battery The positive electrode plate was cut into a disk shape with a diameter of 16 mm, a separator made of a disk-shaped porous polypropylene film with a diameter of 18 mm and a thickness of 25 μm on the active material layer side of the positive electrode, and metallic lithium used as the negative electrode The expanded metal was laminated in order, and this was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A lithium ion coin battery having a thickness of 20 mm and a thickness of about 2 mm was produced. In addition, as an electrolytic solution, LiPF ₆ was added at 1 mol / liter in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). A solution dissolved at a concentration was used. Using this battery, the high-temperature cycle characteristics were evaluated. The results are shown in Table 1.

(Example 2)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, 0. 2 parts, 0.7 parts of sodium lauryl sulfate and 46 parts of ion-exchanged water were added and stirred, and the emulsion was sequentially added from polymerization vessel B to polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reached 95%, the reaction was terminated by cooling, and then the pH was adjusted with 4% NaOH aqueous solution. An aqueous dispersion was obtained. The obtained binder B had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder B having a pH of 10.1. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion. In the binder B, the content of polymer units of (meth) acrylic acid ester monomer is 78%, the content of polymer units of vinyl monomer having an acid component is 2.0%, the content of polymer units of α, β-unsaturated nitrile monomer The ratio was 20%, and the content ratio of the polymerized units having crosslinkability was 0.2%.

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 B was used as the positive electrode binder. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Example 3)
As carbon fiber, instead of carbon fiber 1, 1 part of carbon fiber having an average fiber diameter of 50 nm, an average fiber length of 1 μm, and an average aspect ratio of 20 (hereinafter sometimes referred to as “carbon fiber 2”). A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that they were used. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

Example 4
As carbon fiber, instead of carbon fiber 1, 1 part of carbon fiber having an average fiber diameter of 500 nm, an average fiber length of 100 μm, and an average aspect ratio of 200 (hereinafter sometimes referred to as “carbon fiber 3”). A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that they were used. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Example 5)
A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that the number of parts used of the carbon fiber 1 was 5 parts. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Example 6)
A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that the number of parts used of the carbon fiber 1 was 8 parts. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Example 7)
As in the case of Example 1, except that 100 parts of spinel manganese (LiMn ₂ O ₄ ; Mn content 60%, average particle diameter 8 μm) was used in place of LiFePO ₄ having an olivine type crystal structure as the positive electrode active material. A positive electrode plate and a lithium ion coin battery were prepared. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1. At this time, the density of the positive electrode active material layer was set to 2.5 g / cm ³ .

(Example 8)
A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 7, except that the aqueous dispersion of binder B was used instead of the aqueous dispersion of binder A as the positive electrode binder. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

Example 9
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, another polymerization vessel B was charged with 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, allyl glycidyl ether 0 The emulsion prepared by adding 2 parts, 0.7 parts of sodium lauryl sulfate and 46 parts of ion-exchanged water and stirring was sequentially added from polymerization vessel B to polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reaches 95%, the reaction is terminated by cooling, and then the pH is adjusted with 4% NaOH aqueous solution. An aqueous dispersion of -E was obtained. The obtained binder E had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder E having a pH of 10.1. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion. In binder E, the content of polymer units of (meth) acrylic acid ester monomer is 78%, the content of polymer units of vinyl monomer having an acid component is 2.0%, the content of polymer units of α, β-unsaturated nitrile monomer The ratio was 20%, and the content ratio of the polymerized units having crosslinkability was 0.2%.

A positive electrode plate and a lithium ion coin battery were prepared in the same manner as in Example 1 except that the aqueous dispersion of binder E was used as the positive electrode binder. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Example 10)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. 2 parts and 10 parts of ion-exchanged water were added and heated to 60 ° C. and stirred for 90 minutes. Then, in another polymerization vessel B, 67 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 2.0 parts of methacrylic acid, ethylene glycol dimethacrylate The emulsion prepared by adding 0.2 part, 0.7 part of sodium lauryl sulfate and 46 parts of ion-exchanged water and stirring the mixture was sequentially added from the polymerization vessel B to the polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reaches 95%, the reaction is terminated by cooling, and then the pH is adjusted with 4% NaOH aqueous solution. An aqueous dispersion of binder F was obtained. The obtained binder F had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder F having a pH of 10.1. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion. In the binder F, the content of polymer units of (meth) acrylic acid ester monomer is 78%, the content of polymer units of vinyl monomer having an acid component is 2.0%, the content of polymer units of α, β-unsaturated nitrile monomer The proportion was 20%, and the content of other polymerized units was 0.2%.

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 F was used as the positive electrode binder. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Comparative Example 1)
A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 2 except that no carbon fiber was used. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Comparative Example 2)
A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 8 except that no carbon fiber was used. And the high temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Comparative Example 3)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, 68 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 0.8 part of methacrylic acid, 0. 2 parts, 0.7 parts of sodium lauryl sulfate and 46 parts of ion-exchanged water were added and stirred, and the emulsion was sequentially added from polymerization vessel B to polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reached 95%, the reaction was terminated by cooling, and then the pH was adjusted with 4% NaOH aqueous solution. An aqueous dispersion was obtained. The obtained binder C had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder C having a pH of 10.1. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion. In the binder C, the content of polymer units of (meth) acrylic acid ester monomer is 79%, the content of polymer units of vinyl monomer having an acid component is 0.8%, the content of polymer units of α, β-unsaturated nitrile monomer The ratio was 20%, and the content ratio of the polymerized units having crosslinkability was 0.2%.

A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder C was used as the positive electrode binder. And the high-temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

(Comparative Example 4)
(A) Production of Binder 10.75 parts of 2-ethylhexyl acrylate, 1.25 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate, and 79 parts of ion-exchanged water were added to Polymerization Can A. After 2 parts and 10 parts of ion exchange water were added and heated to 60 ° C. and stirred for 90 minutes, another polymerization vessel B was charged with 65.3 parts of 2-ethylhexyl acrylate, 19 parts of acrylonitrile, 3.5 parts of methacrylic acid, allyl methacrylate. The emulsion prepared by adding 0.2 part, 0.7 part of sodium lauryl sulfate and 46 parts of ion-exchanged water and stirring the mixture was sequentially added from the polymerization vessel B to the polymerization vessel A over about 180 minutes, and then stirred for about 120 minutes. When the monomer consumption reaches 95%, the reaction is terminated by cooling, and then the pH is adjusted with a 4% NaOH aqueous solution. An aqueous dispersion of -D was obtained. The obtained binder D had a glass transition temperature of −32 ° C., a dispersed particle size of 0.15 μm, and an aqueous dispersion of binder D having a pH of 10.1. Table 1 shows the results of evaluating the storage stability of the binder using the obtained aqueous dispersion. The content ratio of polymer units of (meth) acrylic acid ester monomer in binder D is 76.3%, polymer units of vinyl monomer having an acid component is 3.5%, polymer units of α, β-unsaturated nitrile monomer The content ratio of was 20%, and the content ratio of the crosslinkable polymer units was 0.2%.

A positive electrode plate and a lithium ion coin battery were produced in the same manner as in Example 1 except that the aqueous dispersion of binder D was used as the positive electrode binder. And the high temperature cycling characteristic was evaluated using the crack measurement of this electrode plate, and the lithium ion coin battery. The results are shown in Table 1.

From the results shown in Table 1, the positive electrode active materials containing manganese or iron, fibrous carbon, polymerized units of (meth) acrylic acid ester monomers, polymerized units of vinyl monomers having an acid component, and α in Examples 1 to 10 In a positive electrode for a secondary battery having a positive electrode active material layer containing a binder composed of a polymer containing polymerized units of β, unsaturated nitrile monomer, the occurrence of cracks in the positive electrode active material layer can be prevented That is, it can be seen that the safety is improved and the high-temperature cycle characteristics of the battery are good. The binder has good storage stability.
On the other hand, the comparative example using what the content rate of the polymerization unit of the vinyl monomer which has the acid component in the positive electrode for secondary batteries and binder of the comparative examples 1 and 2 which does not contain fibrous carbon is less than 1.0 mass%. In the positive electrode for secondary battery of Comparative Example 4 using 3 or more than 3.0% by mass, it was difficult to prevent the occurrence of cracks in the positive electrode active material layer, and the high-temperature cycle characteristics of the battery were deteriorated.

Claims

A current collector and a positive electrode active material layer laminated on the current collector and containing manganese or iron, fibrous carbon, and a binder,
The binder comprises a polymer comprising a polymer unit of a (meth) acrylic acid ester monomer, a polymer unit of a vinyl monomer having an acid component, and a polymer unit of an α, β-unsaturated nitrile monomer,
A positive electrode for a secondary battery, wherein a content ratio of polymer units of the vinyl monomer having an acid component is 1.0 to 3.0% by mass in all polymer units of the polymer.
The positive electrode for a secondary battery according to claim 1, wherein the positive electrode active material contains iron and further has an olivine type structure.
3. The positive electrode for a secondary battery according to claim 1, wherein the fibrous carbon has an average fiber diameter of 0.01 to 1.0 μm.
The positive electrode for secondary battery according to any one of claims 1 to 3, wherein the fibrous carbon has an average aspect ratio of 5 to 50,000.
The positive electrode for a secondary battery according to any one of claims 1 to 4, wherein the vinyl monomer having an acid component is a monomer having a carboxylic acid group.
The positive electrode for a secondary battery according to any one of claims 1 to 5, wherein the binder further contains a polymerized unit having crosslinkability.
A secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode is a positive electrode for a secondary battery according to any one of claims 1 to 6.