JP2016119279A - Secondary battery electrode binder, secondary battery electrode slurry, secondary battery electrode and nonaqueous secondary battery - Google Patents

Abstract

An object of the present invention is to improve the adhesive force between a mixture layer forming an electrode and a current collector by adjusting the content of residual monomers within a certain range when preparing a binder by aqueous solution polymerization. It is to find out that an excellent binder can be obtained, and to provide this. A binder for a secondary battery electrode comprising a polymer (I) having a structural unit (A) represented by the general formula (1), wherein the structural unit (A) in the polymer (I) is A binder for a secondary battery electrode, wherein the content of the monomer (a) as a source of origin is 0.01 to 2.5 mass% and the polymer (I) is obtained by an aqueous solution polymerization method. [Selection diagram] None

Description

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

In recent years, secondary batteries have been used as storage batteries for portable devices such as mobile phones, video cameras, laptop computers, hybrid cars, electric cars, etc., and lithium ion secondary batteries are frequently used as secondary batteries. .
Generally, an electrode for a lithium ion secondary battery is provided on a current collector and a mixture in which an electrode active material (active material), a conductive auxiliary agent, etc. are held by a binder (binder). What is provided with a layer is used. Usually, a solvent is mixed with a mixture obtained by adding an appropriate amount of a binder to an active material to form an electrode slurry, which is applied to a current collector, dried, and then pressed to form an electrode layer.

As the binder, a material that satisfies the solvent resistance to the organic solvent used in the electrolyte of the secondary battery, the oxidation resistance and the reduction resistance within the driving voltage, and the like is used. As such a material, polyvinylidene fluoride is used.
On the other hand, as a solvent for making a mixture of an active material and a binder into a slurry, amides such as N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”) and nitrogen-containing organic solvents such as ureas are used. It is done.
However, nitrogen-containing organic solvents such as NMP have problems such as solvent recovery costs and high environmental load. In addition, since NMP has a high boiling point of 204 ° C., there is a problem that a large amount of energy is required during drying and solvent recovery and purification.

In order to solve these problems, it has been studied to produce an electrode by preparing an electrode slurry by using a nonionic water-soluble polymer as a binder and dissolving or dispersing it in water.
For example, styrene-butadiene rubber latex is used in combination with a thickener such as carboxymethyl cellulose (hereinafter referred to as “CMC”) as a binder for the negative electrode.

  However, since CMC is derived from a natural product, a problem has been pointed out that the quality of the electrode is not stable depending on the supply lot. Therefore, a non-natural water-soluble polymer that can be supplied with stable quality is desired. In addition, water-soluble polymers are required to have high battery performance.

Therefore, poly N-vinylformamide has been reported as a water-soluble binder derived from a non-natural product.
For example, Patent Document 1 discloses a battery electrode paste containing poly N-vinylformamide. Poly N-vinylformamide is excellent in performance such as binding properties and electrochemical stability, and is said to be able to improve the required performance in secondary batteries (especially non-aqueous secondary batteries).
However, in Patent Document 1, poly N-vinylformamide is prepared by adiabatic polymerization. In the adiabatic polymerization method, a polymer with a small amount of residual monomer is obtained, but since the polymer is obtained as a lump of gel, there are a step of crushing it into a powder and a step of dissolving the powder in water for use as a binder. Necessary. In addition, since the polymerization process proceeds, it is difficult to precisely control the molecular weight of the polymer, the residual monomer, and the like.

When poly N-vinylformamide is prepared by aqueous solution polymerization, the polymer is obtained in the state of an aqueous solution, so that it can be used directly as a binder or used in the next homogeneous reaction step. Further, the molecular weight and molecular weight distribution of the polymer can be controlled with an auxiliary agent such as a polymerization initiator or a chain transfer agent to be used.
However, in aqueous solution polymerization, as the polymerization proceeds, the apparent polymerization rate decreases, the molecular weight hardly increases, and the residual monomer tends to increase. When the polymer with the monomer remaining is used as a binder, the adhesion between the mixture layer constituting the electrode and the current collector foil is lowered due to low cohesive force and high solubility in the electrolyte. was there.

International Publication No. WO2012 / 176895 Pamphlet

The present invention has been made in view of the above circumstances, and when preparing a binder by aqueous solution polymerization, the content ratio of the residual monomer is kept within a certain range, whereby the mixture layer and the current collector constituting the electrode are collected. It has been found that a binder having excellent body adhesion can be obtained.
Since this manufacturing method has fewer manufacturing steps than the adiabatic polymerization method, it is possible to reduce the manufacturing cost and the contamination, and it is possible to obtain a polymer that is less expensive and contains less foreign matter.
The present invention relates to a secondary battery electrode binder and a secondary battery electrode slurry from which an electrode having high adhesion and less foreign matter can be obtained, a secondary battery electrode having high adhesion and little foreign matter, and a non-contact equipped with the same. An object is to provide a water secondary battery.

That is, this invention has the following aspects.
[1] A secondary battery electrode binder comprising a polymer (I) having a structural unit (A) represented by the following general formula (1), wherein the structural unit (A) in the polymer (I) The binder for secondary battery electrodes whose content rate of the monomer (a) used as the origin of is 0.01-2.5 mass%, and a polymer (I) is obtained by the aqueous solution polymerization method.

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group.)
[2] A binder for a secondary battery electrode comprising a polymer (II) having a structural unit (A) represented by the general formula (1) and a structural unit (B) represented by the following general formula (2). In the polymer (II), the content of the monomer (a) that is the source of the structural unit (A) and / or the monomer (b) that is the source of the structural unit (B) is The binder for secondary battery electrodes which is 0.01-2.5 mass% and a polymer (II) is obtained by the aqueous solution polymerization method.

(In Formula (2), R ³ is a hydrogen atom or an alkyl group.)
[3] The polymer (II) according to [2], wherein the polymer (II) is a polymer obtained by hydrolyzing a part of the structural unit (A) after obtaining the polymer (I) by an aqueous solution polymerization method. Secondary battery electrode binder.
[4] A secondary battery electrode slurry comprising the secondary battery electrode binder according to any one of [1] to [3], an active material, and a solvent.
[5] A current collector and a mixture layer provided on the current collector, wherein the mixture layer includes the binder for a secondary battery electrode according to any one of [1] to [3] and An electrode for a secondary battery containing an active material.
[6] A non-aqueous secondary battery comprising the secondary battery electrode according to [5].

  ADVANTAGE OF THE INVENTION According to this invention, control of molecular weight and residual monomer is easy, it is excellent in adhesiveness, there are few foreign materials, the binder for secondary battery electrodes, the slurry for secondary battery electrodes, the electrode for secondary batteries, and a non-aqueous secondary battery Can provide.

In this specification, “water-soluble” means that the binder is dissolved in water. Of course, all of the binder dissolves in water, but even when a part of the binder dissolves in water, it is considered water-soluble.
In this specification, “(meth) acryl” is a generic term for acrylic and methacrylic, “(meth) acrylate” is a generic term for acrylate and methacrylate, and “(meth) allyl” means allyl and methallyl. It is a generic name.

<Polymer (I)>
The polymer (I) of the present invention has a structural unit (A) represented by the following general formula (1).
The content rate of the monomer (a) used as the origin of a structural unit (A) in a polymer (I) is 0.01-2.5 mass%.

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group.)

The alkyl group is preferably an alkyl group having 1 to 5 carbon atoms.
The alkyl group may be linear or branched, and examples thereof include a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, t-butyl group, and pentyl group. .
From the viewpoint of increasing the water solubility of the polymer (I), when R ¹ and R ² are alkyl groups, a smaller number of carbon atoms is preferable, and R ¹ and R ² are each independently a hydrogen atom or a carbon number of 1 -3 alkyl groups are preferable, a hydrogen atom or a methyl group is more preferable, and a hydrogen atom is still more preferable.

  Examples of the monomer (a) that is a source of the structural unit (A) include N-vinylformamide and N-vinylacetamide. The monomer (a) may be used alone or in combination of two or more.

The polymer (I) is obtained by polymerizing the monomer (a), and the monomer (a) is contained as a residual monomer in the polymer (I).
The content rate of the monomer (a) in polymer (I) is 0.01-2.5 mass%. Here, let the polymer (I) containing the monomer (a) be 100 mass%.
When the content of the monomer (a) in the polymer (I) is within the above range, the total amount of the low molecular weight monomer or oligomer in the binder is suppressed, and the mixture layer and the current collector are collected. The adhesiveness of the foil can be kept high. In addition, since the total dissolved amount of these low molecular weight substances in the electrolyte is suppressed, battery characteristics (particularly cycle characteristics) can be kept good.

The content of the structural unit (A) in the polymer (I) is preferably 20 to 99.99% by mass, and more preferably 50 to 99.99% by mass.
If the content of the structural unit (A) is within the above range, it exhibits high water solubility and is less likely to swell against the electrolyte when used in an electrode, giving the battery good cycle characteristics and other characteristics. A binder that can be obtained is obtained.

The polymer (I) may contain an arbitrary structural unit in addition to the structural unit (A).
Examples of the monomer that is the source of the arbitrary structural unit (hereinafter referred to as “optional monomer”) include, for example, acrylonitrile, methacrylonitrile, α-cyanoacrylate, dicyanovinylidene, fumaronitrile ethyl, and the like. Vinyl cyanide monomer; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate; (meth) acrylic acid, itacon Carboxyl group-containing monomers such as acid, crotonic acid, maleic acid, maleic anhydride and salts thereof; aromatic vinyl monomers such as styrene and α-methylstyrene; maleimides such as maleimide and phenylmaleimide; (meth) Acrylamide, N, N-dimethyl (meth) acrylamide, N-isopropyl (Meth) acrylamides such as ru (meth) acrylamide; vinyls containing sulfonic acid groups such as (meth) allylsulfonic acid, (meth) allyloxybenzenesulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid Monomer and salt thereof; 2- (meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxyethyl acid phosphate monoethanolamine salt, diphenyl ((meth) acryloyloxyethyl) phosphate, (meth) acryloyloxy Propyl acid phosphate, 3-chloro-2-acid phosphooxypropyl (meth) acrylate, acid phosphooxypolyoxyethylene glycol mono (meth) acrylate, acid phosphooxypolyoxyp Phosphoric acid group-containing vinyl monomers such as pyrene glycol (meth) acrylate and salts thereof; dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide tertiary salt or quaternary ammonium salt; vinyl acetate, N- Vinylpyrrolidone is mentioned.
These monomers may be used individually by 1 type, and may use 2 or more types together.

0-77.5 mass% is preferable, and, as for the content rate of the arbitrary structural units in polymer (I), 0-47.5 mass% is more preferable.
When the content of any structural unit is within the above range, battery performance can be maintained satisfactorily.

The peak top molecular weight (Mp) of the polymer (I) is preferably 10,000 to 10,000,000, more preferably 100,000 to 5,000,000, and further preferably 200,000 to 3,000,000. When the peak top molecular weight is 10 million or less, the binder has good solubility in water and is suitable for aqueous solution polymerization. Moreover, the stability with respect to the elution and swelling of the binder in electrolyte solution as it is 10,000 or more increases.
The peak top molecular weight of the polymer (I) can be measured using gel permeation chromatography (GPC). For example, the calculated molecular weight can be obtained using a solvent such as tetrahydrofuran, water or acetonitrile as an eluent and pullulan as an internal standard sample.

<Polymer (II)>
The polymer (II) of the present invention has a structural unit (A) represented by the general formula (1) and a structural unit (B) represented by the following general formula (2).
In the polymer (II), the content of the monomer (a) that is the source of the structural unit (A) and / or the monomer (b) that is the source of the structural unit (B) is 0.01. It is -2.5 mass%.

(In Formula (2), R ³ is a hydrogen atom or an alkyl group.)
R ³ is the same as R ¹ .

Examples of the monomer (a) that is a source of the structural unit (A) include N-vinylformamide and N-vinylacetamide. The monomer (a) may be used alone or in combination of two or more.
As a monomer (b) used as the origin of a structural unit (B), N-vinylamine is mentioned, for example.

As will be described later, the polymer (II) is obtained by hydrolyzing the polymer (I). In the polymer (II), the monomer (a) and / or the monomer (b) is contained. It is contained as a residual monomer.
The content of the monomer (a) and / or the monomer (b) in the polymer (II) is 0.01 to 2.5% by mass. Here, let the polymer (II) in the state containing the monomer (a) and / or the monomer (b) be 100 mass%.
If the content of monomer (a) and / or monomer (b) in polymer (II) is within the above range, the total amount of low molecular weight monomers and oligomers in the binder will be It is suppressed and the adhesiveness of the mixture layer and the current collector foil can be kept high. In addition, since the total dissolved amount of these low molecular weight substances in the electrolyte is suppressed, battery characteristics (particularly cycle characteristics) can be kept good.

The content of the structural unit (A) in the polymer (II) is preferably 17.5 to 99.99% by mass, and more preferably 40.5 to 89.99% by mass.
If the content of the structural unit (A) is within the above range, it exhibits high water solubility and is less likely to swell against the electrolyte when used in an electrode, giving the battery good cycle characteristics and other characteristics. A binder that can be obtained is obtained.

The content of the structural unit (B) in the polymer (II) is preferably 1 to 80% by mass, and more preferably 10 to 50% by mass.
If the content rate of a structural unit (B) is in the said range, the binder which is excellent in the adhesiveness of a mixture layer and a collector and can maintain battery performance favorable will be obtained.

0-77.5 mass% is preferable, and, as for the content rate of the arbitrary structural unit in polymer (II), 0-47.5 mass% is more preferable.
When the content of any structural unit is within the above range, battery performance can be maintained satisfactorily.

  The peak top molecular weight of the polymer (II) is preferably 10,000 to 10,000,000, more preferably 100,000 to 5,000,000, and further preferably 200,000 to 3,000,000. When the peak top molecular weight is 10 million or less, the binder has good solubility in water and is suitable for aqueous solution polymerization. Moreover, the stability with respect to the elution and swelling of the binder in electrolyte solution as it is 10,000 or more increases.

<Manufacturing method>
Polymer (I) obtains monomer (a) and an optional monomer as required by an aqueous solution polymerization method. Aqueous solution polymerization is a method for obtaining a polymer (I) by dissolving a monomer as a raw material and a water-soluble polymerization initiator in water and heating with stirring. Therefore, it is limited to conditions where the reaction solution containing water is uniform.
After the polymerization, the obtained aqueous solution may be used as a binder as it is, or may be dried by heating, drying under reduced pressure, and a combination thereof to remove water to obtain a powdery polymer (I) as a binder. .

Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; water-soluble peroxides such as hydrogen peroxide; 2,2′-azobis [N- (2-carboxy Water-soluble azo compounds such as ethyl) -2-methylpropionamidine].
In carrying out the polymerization, a chain transfer agent may be used for the purpose of adjusting the molecular weight. Examples of the chain transfer agent include mercaptan compounds, thioglycol, carbon tetrachloride, α-methylstyrene dimer, and hypophosphite.

  The polymer (II) is obtained by obtaining a polymer (I) by an aqueous solution polymerization method and then hydrolyzing a part of the structural unit (A) of the polymer (I). Since polymerization and hydrolysis can be easily carried out, aqueous solution polymerization is optimal.

Examples of the hydrolysis method include hydrolysis with an acid, hydrolysis with an alkali, and hydrolysis by applying heat. Among these, hydrolysis with an alkali is preferable.
Examples of the alkali (base) used for the hydrolysis with an alkali include metal hydroxides of Group 1 and Group 2 metals of the periodic table. Specific examples include sodium hydroxide, lithium hydroxide, potassium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide.

As the alkali, ammonia and alkyl derivatives of ammonia, for example, amines such as alkylamine and allylamine are also suitable. Examples of amines include triethylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, and aniline.
Among these, as the alkali, sodium hydroxide, lithium hydroxide, and potassium hydroxide are preferable.

  When polymer (II) is produced by hydrolyzing polymer (I), the content of structural unit (A) and structural unit (B) in polymer (II) controls the degree of hydrolysis progress. You can adjust it. The degree of progress of hydrolysis can be controlled by the amount of alkali added as described above.

  When polymer (I) is hydrolyzed using acid or alkali, the pH of the resulting reaction solution becomes acidic or alkaline, but the reaction solution may be neutralized as necessary to obtain a neutral aqueous solution. . Moreover, the reaction liquid obtained by hydrolysis may be used as a binder as it is, or heat drying, drying under reduced pressure, and combining these to remove water to obtain a powdered polymer (II) as a binder. Also good.

<Binder for secondary battery electrode>
The binder for secondary battery electrodes of the present invention comprises polymer (I) or polymer (II). Polymer (I) may be used individually by 1 type, and may use 2 or more types together. Polymer (II) may be used individually by 1 type, and may use 2 or more types together.
The binder for secondary battery electrodes may contain other polymers as long as the effects of the present invention are not impaired.

Examples of other polymers include polyacrylic acid and salts thereof, polyvinyl alcohol, and polyacrylamide. These may be used alone or in combination of two or more.
The content of polymer (I) or polymer (II) in 100% by mass of the binder is preferably 50 to 100% by mass, and the content of other polymers is preferably 0 to 50% by mass.

<Form>
Examples of the form of the binder for the secondary battery electrode include a powder form and a dope form dissolved or dispersed in a solvent such as water.

<Effect>
The binder for secondary battery electrodes of the present invention described above is composed of the polymer (I) having a monomer (a) content of 0.01 to 2.5% by mass. Moreover, the binder for secondary battery electrodes of this invention consists of polymer (II) whose content rate of a monomer (a) and / or monomer (b) is 0.01-2.5 mass%. .
These polymers (I) and (II) are obtained by aqueous solution polymerization. Since the binder for secondary battery electrodes of the present invention obtained by aqueous solution polymerization can reduce the number of manufacturing steps, the cost can be reduced and the cleanliness of the product can be improved. And since the content rate of a monomer can be reduced, it is excellent in the adhesiveness of a mixture layer and current collection foil, and there is little melt | dissolution to electrolyte solution, and it is excellent in a battery characteristic.

  Therefore, the binder for secondary battery electrodes of the present invention comprising polymer (I) is a water-soluble binder with low impurities and low impurities, and is excellent in adhesion. Therefore, a battery including an electrode manufactured using the electrode slurry is excellent in battery performance. In addition to the above properties, the binder for a secondary battery electrode of the present invention comprising the polymer (II) is also easy to produce by being obtained by aqueous solution polymerization and subsequent hydrolysis.

<Slurry for secondary battery electrode>
The secondary battery electrode slurry of the present invention (hereinafter also simply referred to as “electrode slurry”) includes a secondary battery electrode binder, an active material, and a solvent.
The content of the binder in the electrode slurry is preferably 0.01 to 10% by mass and more preferably 0.1 to 7% by mass in the total solid content (all components excluding the solvent) of the electrode slurry. If it is 0.01 mass% or more, the adhesiveness (binding property) of the mixture layer formed using the electrode slurry and the current collector is further enhanced. If it is 10 mass% or less, since an active material, the conductive support agent added as needed, etc. can be contained enough, battery performance will improve.

As the active material used for the electrode slurry of the present invention, known materials can be used depending on the type of non-aqueous secondary battery used for the electrode produced using the electrode slurry.
For example, in the case of a lithium ion secondary battery, as the positive electrode active material (positive electrode active material), a material having a higher potential than the negative electrode active material (negative electrode active material) and capable of absorbing and desorbing lithium ions during charge and discharge is used. .

  Examples of the positive electrode active material include a lithium-containing metal composite oxide containing at least one metal selected from iron, cobalt, nickel, and manganese and lithium. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  Examples of the negative electrode active material include carbon materials such as graphite, amorphous carbon, carbon fiber, coke, and activated carbon; and composites of the carbon materials and metals such as silicon, tin, and silver, or oxides thereof. . These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  In the lithium ion secondary battery, it is preferable to use a lithium-containing metal composite oxide as the positive electrode active material and graphite as the negative electrode active material. By setting it as such a combination, the voltage of a lithium ion secondary battery can be raised, for example to 4V or more.

  The content of the active material in the electrode slurry is preferably 80 to 99.9% by mass and more preferably 85 to 99% by mass in the total solid content (all components excluding the solvent) of the electrode slurry. If it is 80 mass% or more, the function as a mixture layer will fully be exhibited. If it is 99.9 mass% or less, the adhesiveness of a mixture layer and a collector is favorable.

The electrode slurry may contain a conductive additive. In particular, when a positive electrode is produced using an electrode slurry, the electrode slurry preferably contains a conductive additive. By containing the conductive auxiliary agent, the electrical contact between the active materials and between the active material and the metal fine particles can be improved, and the battery performance such as the discharge rate characteristic of the non-aqueous secondary battery can be further improved.
Examples of the conductive assistant include graphite, carbon black, and acetylene black. These conductive auxiliary agents may be used individually by 1 type, and may use 2 or more types together.

  The content of the conductive additive in the electrode slurry is preferably 0.01 to 10% by mass and more preferably 0.1 to 7% by mass in the total solid content (all components excluding the solvent) of the electrode slurry. If it is 0.01 mass% or more, battery performance will be improved more. If it is 10 mass% or less, the adhesiveness of a mixture layer and a collector is favorable.

Examples of the solvent contained in the electrode slurry include water, a mixed solvent of water and an organic solvent, and the like.
Examples of organic solvents include NMP, mixed solutions of NMP and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.), NMP and glyme solvents (diglyme, triglyme, tetraglyme, etc.) A mixed solution of These organic solvents may be used individually by 1 type, and may use 2 or more types together.
However, since an organic solvent has a high environmental load, it is preferable to use water alone as the solvent.
Since the binder is water-soluble, it can be easily dissolved or dispersed in water.

  The content of the solvent in 100% by mass of the electrode slurry may be a minimum amount that can maintain the state in which the binder or the binder composition is dissolved or dispersed at room temperature. However, in the slurry preparation step described later, since the viscosity of the electrode slurry is usually adjusted while adding a solvent, it is preferable to use an arbitrary amount that is not excessively diluted. Specifically, 10 to 70% by mass is preferable, and 20 to 60% by mass is more preferable.

The electrode slurry can be produced by kneading a binder, an active material and a solvent, if necessary, with the addition of a conductive additive and optional components. Kneading can be performed by a known method.
At the time of slurry preparation, the binder on the aqueous solution obtained by the aqueous solution polymerization may be used as it is, or a powdered one may be used because there is merit in transportation.

  Since the electrode slurry described above contains the binder of the present invention, an excellent mixture layer with few impurities can be formed at low cost. The mixture layer is also excellent in binding properties with the current collector.

<Electrode for non-aqueous secondary battery>
An electrode for a non-aqueous secondary battery of the present invention (hereinafter also simply referred to as “electrode”) includes a current collector and a mixture layer provided on the current collector, and the mixture layer comprises: The electrode slurry of the present invention described above is applied to a current collector and dried. That is, the mixture layer contains the binder of the present invention and the active material.

The current collector may be any material having conductivity, and a metal can be used as the material. Specifically, aluminum, copper, nickel or the like can be used.
The shape of the current collector can be determined according to the shape of the target battery, and examples thereof include a thin film shape, a net shape, and a fiber shape. Among these, a thin film is preferable.
The thickness of the current collector is preferably 5 to 30 μm, more preferably 8 to 25 μm.

The electrode of the present invention can be produced using a known method. For example, the electrode slurry of the present invention is prepared (slurry preparation step), and the electrode slurry is applied to a current collector (coating). Step) and then drying to remove the solvent (drying step), rolling as necessary (rolling step), and forming a mixture layer on the current collector surface.
In addition, you may cut | disconnect the obtained electrode to arbitrary dimensions.

In the slurry preparation step, an electrode slurry is prepared by dispersing the binder of the present invention, an active material, and, if necessary, additives such as a conductive additive in a solvent.
In the coating process, the electrode slurry is applied to the current collector. The coating method is not particularly limited as long as the electrode slurry can be applied to the current collector with an arbitrary thickness. For example, a doctor blade or a comma coater can be used. The coating amount can be appropriately set according to the thickness of the mixture layer to be formed.

In the drying step, the solvent is removed. As the drying method, it is sufficient if the solvent can be removed. Examples thereof include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.
In the rolling process, the formed mixture layer is rolled. As a rolling method, the mixture layer may be rolled to an arbitrary thickness, and examples thereof include a die press and a roll press.

20-200 micrometers is preferable and, as for the thickness of a mixture layer, 30-120 micrometers is more preferable.
Since the positive electrode (positive electrode) has a smaller active material capacity than the negative electrode (negative electrode), the positive electrode mixture layer is preferably thicker than the negative electrode mixture layer.

  Since the mixture layer containing the binder of the present invention is formed on the current collector, the electrode of the present invention described above has high binding properties of the mixture layer to the current collector. Moreover, since the mixture layer has few impurities and little elution into the electrolyte, the battery performance is also excellent.

  The electrode of the present invention can be used for either a positive electrode or a negative electrode of a non-aqueous secondary battery, and is particularly suitable as an electrode for a lithium ion secondary battery.

<Non-aqueous secondary battery>
The nonaqueous secondary battery of the present invention comprises the above-described electrode of the present invention.
The “non-aqueous secondary battery” uses a non-aqueous electrolyte solution that does not contain water as the electrolyte solution, and includes, for example, a lithium ion secondary battery. A nonaqueous secondary battery usually includes electrodes (a positive electrode and a negative electrode), a nonaqueous electrolytic solution, and a separator. As a non-aqueous secondary battery, a positive electrode and a negative electrode are arranged with a permeable separator (for example, a porous film made of polyethylene or polypropylene) interposed therebetween, and this is impregnated with a non-aqueous electrolyte solution. Water secondary battery: A laminate of a negative electrode / separator / positive electrode with a mixture layer formed on both sides of a current collector and a positive electrode / separator with a mixture layer formed on both sides of the current collector The cylindrical non-aqueous secondary battery in which the wound body wound in (1) is housed in a battery can (a metal casing with a bottom) together with a non-aqueous electrolyte solution is exemplified.

The non-aqueous electrolytic solution is a solution in which an electrolyte is dissolved in an organic solvent.
Examples of the organic solvent include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; lactones such as γ-butyrolactone; trimethoxymethane, 1,2-dimethoxyethane, diethyl Ethers such as ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; acetonitrile, nitromethane, NMP Nitrogens such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, phosphate triester; diglyme, triglyme, tet Glymes such as glyme; ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone; sulfones such as sulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone, 4-butane sultone, Examples include sultone such as naphtha sultone. These organic solvents may be used individually by 1 type, and may use 2 or more types together.

As the electrolyte, for _{example, LiClO 4, LiBF 4, LiI} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH _{3 SO 3, LiC 4 F 9} SO 3, Li (CF 3 SO 2) 2 N, Li [(CO 2) 2] include ₂ B.
As the non-aqueous electrolyte, a solution in which LiPF ₆ is dissolved in carbonates is preferable, and the solution is particularly suitable as an electrolyte for a lithium ion secondary battery.

In the nonaqueous secondary battery of the present invention, the electrode of the present invention is used for one or both of the positive electrode and the negative electrode.
When either one of the positive electrode and the negative electrode is the electrode of the present invention, a known one can be used as the other electrode.

  A well-known thing can be used as a separator. For example, a porous polymer film produced from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer These can be used alone or in layers. In addition, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like can be used, but is not limited thereto.

The non-aqueous secondary battery of this invention can be manufactured using a well-known method. Below, an example of the manufacturing method of a lithium ion secondary battery is demonstrated.
First, the positive electrode and the negative electrode are wound spirally through a separator to obtain a wound body. The obtained wound body is inserted into a battery can, and a tab terminal previously welded to the current collector of the negative electrode is welded to the bottom of the battery can.
Next, a non-aqueous electrolyte solution is injected into the battery can, and a tab terminal previously welded to the current collector of the positive electrode is welded to the battery lid, and the lid is attached to the battery can via an insulating gasket. It arrange | positions at the upper part, the part which the lid | cover and the battery can contacted is crimped and sealed, and it is set as a lithium ion secondary battery.
The shape of the non-aqueous secondary battery may be any of a coin shape, a cylindrical shape, a square shape, a flat shape, and the like.

  Since the non-aqueous secondary battery of the present invention described above includes the electrode of the present invention, the battery performance is excellent. The battery performance is excellent because the electrode material has few impurities and the mixture layer contains the binder of the present invention, so that the mixture layer has a high binding property to the current collector. In addition, the binder is difficult to elute into the electrolyte solution, so that high battery performance can be maintained.

Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to the following examples.
In the examples, “part” represents “part by mass” and “%” represents “% by mass”.

<Production Example 1>
100 parts of deionized water was placed in a separable flask equipped with a thermometer, and aerated with nitrogen at room temperature for 1 hour. Subsequently, after the temperature was raised to 70 ° C., 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] (Wako Pure Chemical Industries, Ltd., “VA-057”) 1500 ppm (vs. Was added as a 5% aqueous solution.
Further, nitrogen explosion was performed for 20 minutes with respect to 10.0 parts of N-vinylformamide as the monomer (a), and then dropwise added over 1 hour. Next, 3000 ppm of “VA-057” was added after 2 hours, and 1500 ppm of “VA-057” was added after 2 hours as a 5% aqueous solution, and the mixture was further heated and stirred for 2 hours.

  Water was added thereto to make the reaction solution a 4% aqueous solution, and the internal temperature was raised to 75 ° C. A 10% lithium hydroxide aqueous solution was added so as to be 20 mol% of poly N-vinylformamide in terms of solid content, and the mixture was heated for 5 hours to carry out a hydrolysis reaction.

  The reaction solution after the hydrolysis reaction was cooled to obtain an aqueous solution containing a polymer. This was designated as binder aqueous solution 1. About the obtained binder aqueous solution 1, the content rate of the monomer in a polymer and the peak top molecular weight (Mp) were measured with the following measuring methods. The results are shown in Table 1.

(Monomer content)
The content of monomer (a) and / or monomer (b) in the polymer was measured using liquid chromatography (HPLC).

(Measurement of molecular weight)
Measurement was performed using GPC. NaCl (0.1 M) / phosphate buffer (10 mM, pH 6) was used as a carrier, and the flow rate was 0.5 mL / min. The detector used RID. Further, two SHODEX SB-807HQs were connected in series as GPC columns. Pullulan (Showa Denko) was used as an internal standard.

<Production Example 2>
100 parts of deionized water and 10.0 parts of N-vinylformamide as the monomer (a) were placed in a separable flask equipped with a thermometer, heated to 60 ° C., and subjected to nitrogen aeration for 1 hour. Subsequently, 750 ppm (based on monomer) of “VA-057” was dropped as a 0.1% aqueous solution over 3 hours. Then, after 1 hour, 1500 ppm of “VA-057” was added, and after 2 hours, 1500 ppm was added as a 5% aqueous solution, and the mixture was further stirred with heating for 2 hours.

  Water was added thereto to make the reaction solution a 3% aqueous solution, and the internal temperature was raised to 75 ° C. A 10% lithium hydroxide aqueous solution was added so as to be 20 mol% of poly N-vinylformamide in terms of solid content, and the mixture was heated for 5 hours to carry out a hydrolysis reaction.

  The reaction solution after the hydrolysis reaction was cooled to obtain an aqueous solution containing a polymer. This was designated as Binder aqueous solution 2. About the obtained binder aqueous solution 2, it carried out similarly to manufacture example 1, and measured the content rate of the monomer in a polymer, and the peak top molecular weight (Mp). The results are shown in Table 1.

<Production Example 3>
100 parts of deionized water and 10.0 parts of N-vinylformamide as the monomer (a) were put into a separable flask equipped with a thermometer, and the temperature was raised to 70 ° C., followed by nitrogen aeration for 1 hour. Subsequently, 750 ppm (based on monomer) of “VA-057” was dropped as a 0.1% aqueous solution over 3 hours. Then, after 1 hour, 1500 ppm of “VA-057” was added as a 5% aqueous solution, and the mixture was further heated and stirred for 2 hours.

  Water was added thereto to make the reaction solution a 3% aqueous solution, and the internal temperature was raised to 75 ° C. A 10% lithium hydroxide aqueous solution was added so as to be 40 mol% of poly N-vinylformamide in terms of solid content, and the reaction was hydrolyzed by heating for 5 hours.

  The reaction solution after the hydrolysis reaction was cooled to obtain an aqueous solution containing a polymer. This was designated as binder aqueous solution 3. About the obtained binder aqueous solution 3, it carried out similarly to manufacture example 1, and measured the content rate of the monomer in a polymer, and the peak top molecular weight (Mp). The results are shown in Table 1.

<Production Example 4>
7000 ppm of the addition timing and amount of the initiator were added before dropping the monomer, and the same operation as in Production Example 1 was carried out except that the monomer was not added after dropping the monomer to obtain an aqueous solution containing a polymer. This was designated as binder aqueous solution 4.
About the obtained binder aqueous solution 4, it carried out similarly to manufacture example 1, and measured the content rate of the monomer in a polymer, and the peak top molecular weight (Mp). The results are shown in Table 1.

<Production Example 5>
The same operation as in Production Example 1 was performed except that the addition timing and amount of the initiator were 1500 ppm before the monomer addition and 1500 ppm after 1 hour of the monomer addition to obtain an aqueous solution containing a polymer. This was designated as binder aqueous solution 5.
About the obtained binder aqueous solution 5, it carried out similarly to manufacture example 1, and measured the content rate of the monomer in a polymer, and the peak top molecular weight (Mp). The results are shown in Table 1.

<Example 1>
[Preparation of slurry for electrode]
2 parts of the binder aqueous solution 1 obtained in Production Example 1 in solids, 1 part of acetylene black (Electrochemical Industry Co., Ltd., “DENKA BLACK”), a natural graphite-based negative electrode active material (Mitsubishi Chemical Corporation) as the negative electrode active material ), “MPGC16”) 100 parts were kneaded under the conditions of rotation 1000 rpm and revolution 2000 rpm using a revolutionary stirrer (Thinky's “Tentaro Awatori”). After sufficiently kneading, the viscosity was adjusted using deionized water until the viscosity became coatable to obtain an electrode slurry.

[Preparation of negative electrode]
The obtained slurry for electrodes is prepared on a current collector (copper foil, 20 cm × 25 cm, thickness 18 μm) using a doctor blade, dried with a constant temperature dryer (80 ° C.), and further vacuum dried. It was dried under reduced pressure at 60 ° C. for 12 hours using a machine to obtain an electrode having a 90 μm-thick mixture layer formed on a current collector (copper foil).

[Evaluation]
(Evaluation of binding properties)
The electrode was cut out to be 20 mm wide and 80 mm long and pressed with a roll press so that the density of the mixture layer was 1.6 g / cm ³ . The electrode layer surface of the cut piece was fixed to a polycarbonate sheet (width 25 mm, length 100 mm, thickness 1 mm) with a double-sided tape (Sekisui Chemical Co., Ltd., “# 570”) to obtain a test piece.
The test piece was set in a tensile strength test Tensilon tester (Orientec Co., Ltd., “RTC-1210A”), the copper foil was peeled 180 ° at 10 mm / min, and the peel strength was measured. The results are shown in Table 1.

<Examples 2-3 and Comparative Examples 1-2>
A slurry for an electrode was prepared in the same manner as in Example 1 except that the binder aqueous solution was changed to the type shown in Table 1, and a negative electrode was prepared and evaluated. The results are shown in Table 1.

As shown in the results of Table 1, the negative electrode of each Example obtained by aqueous solution polymerization and using a binder having a monomer content of 0.01 to 2.5% by mass had high peel strength. That is, according to the binder of this invention, it was shown that it is excellent in adhesiveness.
On the other hand, even when the aqueous solution polymerization and hydrolysis were similarly performed, when the monomer content was out of the range, the peel strength was low. In order to increase the adhesion strength, it was useful to be within the scope of the present invention.

Claims (6)

A secondary battery electrode binder comprising a polymer (I) having a structural unit (A) represented by the following general formula (1):
In the polymer (I), the content of the monomer (a) that is the source of the structural unit (A) is 0.01 to 2.5% by mass,
A binder for secondary battery electrodes, wherein the polymer (I) is obtained by an aqueous solution polymerization method.

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group.) A binder for a secondary battery electrode comprising a polymer (II) having a structural unit (A) represented by the general formula (1) and a structural unit (B) represented by the following general formula (2),
In the polymer (II), the content of the monomer (a) that is the source of the structural unit (A) and / or the monomer (b) that is the source of the structural unit (B) is 0.01. ~ 2.5% by weight,
A binder for secondary battery electrodes, wherein the polymer (II) is obtained by an aqueous solution polymerization method.

(In Formula (2), R ³ is a hydrogen atom or an alkyl group.) The polymer (II) is
The binder for secondary battery electrodes according to claim 2, which is a polymer obtained by hydrolyzing a part of the structural unit (A) after obtaining the polymer (I) by an aqueous solution polymerization method.   The slurry for secondary battery electrodes containing the binder for secondary battery electrodes of any one of Claims 1-3, an active material, and a solvent. A current collector, and a mixture layer provided on the current collector,
The said mixture layer is an electrode for secondary batteries containing the binder for secondary battery electrodes and active material of any one of Claims 1-3. A non-aqueous secondary battery comprising the secondary battery electrode according to claim 5.