WO2015129257A1

WO2015129257A1 - Binder composition for lithium ion secondary battery electrode, slurry composition for lithium ion secondary battery negative electrode, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Info

Publication number: WO2015129257A1
Application number: PCT/JP2015/000937
Authority: WO
Inventors: 徳一山本; 金田　拓也; 健太郎早坂
Original assignee: 日本ゼオン株式会社
Priority date: 2014-02-27
Filing date: 2015-02-24
Publication date: 2015-09-03
Also published as: JP6593320B2; JPWO2015129257A1

Abstract

The purpose of the present invention is to provide a binder composition for a lithium ion secondary battery electrode, said binder composition being capable of improving the cycle characteristic while suppressing swelling of an electrode of a lithium ion secondary battery. This binder composition for a lithium ion secondary battery electrode includes a particulate polymer and water. The surface acid amount of the particulate polymer is 0.5-3.0 mmol/g inclusive.

Description

Binder composition for lithium ion secondary battery electrode, slurry composition for negative electrode of lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to a binder composition for lithium ion secondary battery electrodes, a slurry composition for lithium ion secondary battery negative electrodes, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

Lithium ion secondary batteries are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.

Here, the electrode for lithium ion secondary batteries is normally provided with the electrical power collector and the electrode compound-material layer formed on the electrical power collector. The electrode mixture layer is formed on the current collector by, for example, a slurry composition obtained by dispersing a binder composition containing a particulate polymer as a binder and an electrode active material in a dispersion medium such as water. The electrode active material and the like are bound with a particulate polymer.
Therefore, in order to achieve further performance improvement of the lithium ion secondary battery, attempts have been made to improve a binder composition and a slurry composition using an aqueous medium as a dispersion medium, which is used for forming an electrode.

For example, in Patent Document 1, in a composition for forming a lithium secondary battery electrode including specific first and second active material particles, a dispersant, a binder, and a solvent, the acid value is in the range of 100 mgKOH / g to 600 mgKOH / g. It has been proposed to ensure the stability of the composition by using the anionic dispersant as a dispersant.
For example, in Patent Document 2, in a binder composition for an electrode containing polymer particles having a predetermined particle shape and a dispersion medium, a polymer containing a repeating unit derived from an unsaturated carboxylic acid at a predetermined ratio It has been proposed to improve the stability of an electrode slurry composition prepared using an electrode binder composition by using particles.

JP 2013-232313 A JP 2013-98123 A

However, the composition for forming a lithium secondary battery electrode using an anionic dispersant having a predetermined acid value and the polymer particles containing a repeating unit derived from an unsaturated carboxylic acid at a predetermined ratio are used. The electrode slurry composition only pays attention to the stability of the prepared composition.

The electrode and lithium ion secondary battery manufactured using the above conventional composition have a problem that the occurrence of swelling of the electrode cannot be sufficiently suppressed and a problem that excellent cycle characteristics cannot be obtained. there were.

Then, an object of this invention is to provide the binder composition for lithium ion secondary battery electrodes which can improve cycling characteristics, suppressing the swelling of the electrode of a lithium ion secondary battery.
Moreover, an object of this invention is to provide the slurry composition for lithium ion secondary battery negative electrodes which can improve cycling characteristics, suppressing the swelling of the negative electrode of a lithium ion secondary battery.
Furthermore, an object of the present invention is to provide a negative electrode for a lithium ion secondary battery in which swelling is suppressed and the lithium ion secondary battery can exhibit excellent cycle characteristics.
In addition, an object of the present invention is to provide a lithium ion secondary battery having excellent cycle characteristics.

The present inventors have intensively studied for the purpose of solving the above problems. Then, the present inventors use the particulate polymer having a surface acid amount within a predetermined range as a binder, thereby improving the strength (toughness, binding strength to the current collector, etc.) of the electrode mixture layer. The inventors have newly found that the cycle characteristics can be improved while suppressing swelling of the electrodes of the lithium ion secondary battery, and the present invention has been completed.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the binder composition for a lithium ion secondary battery electrode of the present invention comprises a particulate polymer and water, and the particulate weight The surface acid amount of the coalescence is 0.5 mmol / g or more and 3.0 mmol / g or less. Thus, if a particulate polymer having a surface acid amount within a predetermined range is used, the strength of the electrode mixture layer formed using the binder composition containing the particulate polymer is ensured, and the electrode A lithium ion secondary battery with suppressed swelling and excellent cycle characteristics can be obtained.

Here, in the binder composition for a lithium ion secondary battery electrode of the present invention, the acid amount in the aqueous phase of the particulate polymer is preferably 0.1 mmol / g or more and 0.7 mmol / g or less. By using a particulate polymer in which the amount of acid in the aqueous phase is within a predetermined range as described above, the binding strength of the electrode mixture layer to the current collector and the cycle characteristics of the lithium ion secondary battery can be further improved. Can do.

In the binder composition for a lithium ion secondary battery electrode according to the present invention, the value obtained by dividing the surface acid value of the particulate polymer by the acid value in the aqueous phase is 2.5 or more. preferable. If the value obtained by dividing the value of the surface acid amount of the particulate polymer by the value of the acid amount in the aqueous phase is not less than the above value, the swelling of the electrode is further suppressed, and the electrode mixture layer for the current collector The binding strength and the cycle characteristics of the lithium ion secondary battery can be further improved.

In the binder composition for a lithium ion secondary battery electrode of the present invention, the particulate polymer may contain a hydroxyl group-containing (meth) acrylic acid ester monomer unit in an amount of 0.5% by mass to 5% by mass. preferable. If the particulate polymer contains a hydroxyl group-containing (meth) acrylic acid ester monomer unit within the above range, it becomes easy to prepare a particulate polymer having a surface acid amount within a desired range.

Moreover, this invention aims at solving the said subject advantageously, The slurry composition for lithium ion secondary battery negative electrodes of this invention is the binder for any of the lithium ion secondary battery electrodes mentioned above. A composition and a negative electrode active material are included. Thus, if the slurry composition containing any one of the binder compositions for lithium ion secondary battery electrodes described above is used for forming the negative electrode mixture layer, the strength of the negative electrode mixture layer is ensured and swelling of the negative electrode is suppressed. In addition, a lithium ion secondary battery having excellent cycle characteristics can be obtained.

Here, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the negative electrode active material preferably contains a silicon-based negative electrode active material. If a silicon-based negative electrode active material is used as the negative electrode active material, the capacity of the lithium ion secondary battery can be increased. Even when a silicon-based negative electrode active material is used, the negative electrode formed from the slurry composition of the present invention is sufficiently suppressed from swelling.

Moreover, this invention aims at solving the said subject advantageously, The negative electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery negative electrodes mentioned above. It has the negative mix layer obtained by using, It is characterized by the above-mentioned. Thus, if the negative electrode composite material layer is formed using the above-described slurry composition for a negative electrode of a lithium ion secondary battery, the swelling is suppressed and lithium capable of exhibiting excellent cycle characteristics in the lithium ion secondary battery. A negative electrode for an ion secondary battery is obtained.

Furthermore, this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is equipped with a positive electrode, a negative electrode, a separator, and electrolyte solution, and the said negative electrode is the above-mentioned lithium ion. It is a negative electrode for secondary batteries. Thus, if the negative electrode is the above-described negative electrode for a lithium ion secondary battery, a lithium ion secondary battery having excellent cycle characteristics can be obtained.

ADVANTAGE OF THE INVENTION According to this invention, the binder composition for lithium ion secondary battery electrodes which can improve cycling characteristics, suppressing the swelling of the electrode of a lithium ion secondary battery can be provided.
Moreover, according to this invention, the slurry composition for lithium ion secondary battery negative electrodes which can improve cycling characteristics, suppressing the swelling of the negative electrode of a lithium ion secondary battery can be provided.
Furthermore, according to the present invention, it is possible to provide a negative electrode for a lithium ion secondary battery in which swelling is suppressed and the cycle characteristics excellent in the lithium ion secondary battery can be exhibited.
In addition, according to the present invention, a lithium ion secondary battery having excellent cycle characteristics can be provided.

3 is a graph showing a hydrochloric acid addition amount-electric conductivity curve created when calculating the surface acid amount of a particulate polymer and the acid amount in an aqueous phase.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder composition for a lithium ion secondary battery electrode of the present invention is used for preparing a slurry composition for a lithium ion secondary battery electrode, preferably a slurry composition for a lithium ion secondary battery negative electrode. Moreover, the slurry composition for lithium ion secondary battery negative electrodes of this invention is used for formation of the negative electrode of a lithium ion secondary battery. And the negative electrode for lithium ion secondary batteries of this invention is equipped with the negative mix layer formed from the slurry composition for lithium ion secondary battery negative electrodes of this invention, It is characterized by the above-mentioned. Furthermore, the lithium ion secondary battery of the present invention is characterized by using the negative electrode for a lithium ion secondary battery of the present invention.

(Binder composition for lithium ion secondary battery electrode)
The binder composition for a lithium ion secondary battery electrode of the present invention is a composition in which a particulate polymer having a surface acid amount of 0.5 mmol / g or more and 3.0 mmol / g or less is dispersed in an aqueous medium as a dispersion medium. It is.

<Particulate polymer>
In the electrode (positive electrode, negative electrode) provided with the electrode mixture layer formed using the binder composition for a lithium ion secondary battery electrode of the present invention, the particulate polymer is composed of each component in the electrode mixture layer or each component. And the current collector. As the particulate polymer, a polymer that can be dispersed in an aqueous medium such as water can be used.

[Properties of particulate polymer]
Hereinafter, the surface acid amount of the particulate polymer used in the present invention, the acid amount in the aqueous phase, the gel content, and the number average particle diameter will be described in detail.

[[Surface acid amount and acid amount in aqueous phase]]
In the present invention, the “surface acid amount” is the amount of acid present on the surface portion of the particulate polymer, and refers to the acid amount per gram of the solid content of the particulate polymer. The particulate polymer needs to have a surface acid amount of 0.5 mmol / g or more and 3.0 mmol / g or less, preferably 1.0 mmol / g or more, and 1.5 mmol / g. More preferably, it is preferably 2.8 mmol / g or less, more preferably 2.7 mmol / g or less, and particularly preferably 2.5 mmol / l or less. When the surface acid amount of the particulate polymer is less than 0.5 mmol / g, sufficient strength of the electrode mixture layer cannot be obtained, and the suppression of the swelling of the electrode becomes insufficient, and the lithium ion secondary battery Cycle characteristics cannot be ensured. On the other hand, if the surface acid amount of the particulate polymer is more than 3.0 mmol / g, the binding strength of the electrode mixture layer to the current collector cannot be sufficiently obtained, and the electrode and lithium ion two The productivity of the secondary battery and the cycle characteristics of the lithium ion secondary battery cannot be ensured.

In the present invention, the “acid amount in the aqueous phase” is the amount of acid present in the aqueous phase in the aqueous dispersion containing the particulate polymer, and the acid amount per gram of the solid content of the particulate polymer. Say. The particulate polymer preferably has an acid amount in the aqueous phase of 0.7 mmol / g or less, more preferably 0.65 mmol / g or less, and 0.6 mmol / g or less. Is more preferable, and 0.55 mmol / g or less is particularly preferable. Further, the lower limit of the range of the acid amount in the aqueous phase is not particularly limited, but is usually 0.1 mmol / g or more.
The amount of acid in the aqueous phase of the particulate polymer is 0.7 mmol / g or less, and a water-soluble acid component present in the aqueous phase, for example, a free oligomer produced during the preparation of the particulate polymer If the amount of such by-products is sufficiently small, adverse effects due to the water-soluble acid component can be suppressed. Specifically, inhibition of binding by the water-soluble acid component can be suppressed, and the binding strength of the electrode mixture layer to the current collector and the cycle characteristics of the lithium ion secondary battery can be further improved. In addition, the amount of the water-soluble acid component brought into the electrolyte of the lithium ion secondary battery can be reduced, and the rate characteristics of the lithium ion secondary battery can be improved. In addition, generation of gas generated by decomposition of a water-soluble acid component or the like can be suppressed, and swelling of cells of the lithium ion secondary battery can be suppressed.

Here, the value obtained by dividing the value of the surface acid amount of the particulate polymer by the value of the acid amount in the aqueous phase (surface acid amount / acid amount in the aqueous phase) is preferably 2.5 or more, It is more preferably 3 or more, more preferably 3.5 or more, more preferably 4 or more, still more preferably 4.5 or more, and particularly preferably 5 or more. The value of the surface acid amount / acid amount in the aqueous phase is 2.5 or more, so that the occurrence of adverse effects due to the water-soluble acid component is suppressed and the swelling of the electrode is further suppressed. The cycle characteristics can be further improved.

The surface acid amount of the particulate polymer and the acid amount in the aqueous phase can be calculated by the following method.
First, an aqueous dispersion containing a particulate polymer is prepared. An aqueous dispersion containing the particulate polymer is placed in a glass container washed with distilled water, and a solution conductivity meter is set and stirred. Stirring is continued until addition of hydrochloric acid described later is completed.
A 0.1 N aqueous sodium hydroxide solution is added to the aqueous dispersion containing the particulate polymer so that the electrical conductivity of the aqueous dispersion containing the particulate polymer is 2.5 to 3.0 mS. Thereafter, after 6 minutes, the electrical conductivity is measured. This value is the electrical conductivity at the start of measurement.
Further, 0.5 mL of 0.1 N hydrochloric acid is added to the aqueous dispersion containing the particulate polymer, and the electrical conductivity is measured after 30 seconds. Thereafter, 0.5 mL of 0.1 N hydrochloric acid is added again, and the electrical conductivity is measured after 30 seconds. This operation is repeated at intervals of 30 seconds until the electrical conductivity of the aqueous dispersion containing the particulate polymer becomes equal to or higher than the electrical conductivity at the start of measurement.
On the graph, the obtained electrical conductivity data is plotted with the electrical conductivity (unit “mS”) on the vertical axis (Y coordinate axis) and the cumulative amount of added hydrochloric acid (unit “mmol”) on the horizontal axis (X coordinate axis). Plot to. As a result, a hydrochloric acid addition amount-electric conductivity curve having three inflection points is obtained as shown in FIG. The X coordinate of the three inflection points and the X coordinate at the end of the addition of hydrochloric acid are P1, P2, P3, and P4 in order from the smallest value. For the data in the four sections of the X coordinate from zero to the coordinate P1, from the coordinate P1 to the coordinate P2, from the coordinate P2 to the coordinate P3, and from the coordinate P3 to the coordinate P4, the approximate straight line L1 by the least square method, respectively. , L2, L3, and L4. The X coordinate of the intersection of the approximate line L1 and the approximate line L2 is A1 (mmol), the X coordinate of the intersection of the approximate line L2 and the approximate line L3 is A2 (mmol), and the X point of the intersection of the approximate line L3 and the approximate line L4 The coordinates are A3 (mmol).
The surface acid amount per 1 g of the particulate polymer and the acid amount in the aqueous phase per 1 g of the particulate polymer are given as values (mmol / g) converted to hydrochloric acid from the following formulas (a) and (b). It is done. Further, the total acid amount per 1 g of the particulate polymer dispersed in water is the sum of the formula (a) and the formula (b) as represented by the following formula (c).
(A) Surface acid amount per gram of particulate polymer = (A2-A1) / Solid content of particulate polymer in aqueous dispersion (b) Acid amount in aqueous phase per gram of particulate polymer = ( A3-A2) / Solid content of particulate polymer in aqueous dispersion (c) Total acid amount per gram of particulate polymer dispersed in water = (A3-A1) / Particulate polymer in aqueous dispersion Solid content of

The surface acid amount of the particulate polymer can be controlled, for example, by changing the type and ratio of monomer units constituting the particulate polymer and the polymerization method. Specifically, for example, the amount of surface acid can be increased by increasing the amount of an acidic group-containing monomer such as an ethylenically unsaturated carboxylic acid monomer.
In addition, as will be described later, semi-batch polymerization is adopted for the preparation of the particulate polymer, more preferably, for example, a hydroxyl group-containing (meth) acrylic acid ester monomer is added in the latter half of the polymerization reaction, and ethylenically unsaturated By increasing the copolymerizability of acidic group-containing monomers such as carboxylic acid monomers with other monomers at the surface portion of the particulate polymer, water is increased while increasing the surface acid amount of the particulate polymer. The amount of acid in the phase can be reduced.

[[Gel content]]
Further, the particulate polymer preferably has a gel content of 80% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, and 99% by mass. Or less, more preferably 97% by mass or less, and still more preferably 94% by mass or less. If the gel content of the particulate polymer is 80% by mass or more, the degree of polymerization of the particulate polymer is increased and the strength of the particulate polymer itself is improved. Therefore, the strength of the electrode mixture layer is increased, and the swelling of the electrode is increased. Can be suppressed, and the size of the surface acid amount can be appropriately controlled on the particle surface. Further, if the gel content of the particulate polymer is 99% by mass or less, the particulate polymer is prevented from losing toughness and becoming brittle, and the components constituting the electrode mixture layer and the electrode mixture layer The current collector can be bound well.

In addition, in this invention, "gel content" can be measured using the measuring method as described in the Example of this specification.

The gel content of the particulate polymer can be adjusted by changing the polymerization conditions of the particulate polymer. For example, the amount of the chain transfer agent (eg, t-dodecyl mercaptan) used during the polymerization. If the amount is reduced, the gel content can be increased, and if the amount of the chain transfer agent used during polymerization is increased, the gel content can be decreased.

[[Number average particle diameter]]
The particulate polymer preferably has a number average particle diameter of 80 nm or more, more preferably 100 nm or more, particularly preferably 120 nm or more, and preferably 400 nm or less. It is more preferably 350 nm or less, and particularly preferably 300 nm or less. When the number average particle diameter is in the above range, the strength and flexibility of the obtained electrode mixture layer can be improved.

Here, in the present invention, the “number average particle diameter” means a particle diameter at which the value of the integrated distribution is 50% in the particle diameter-number integrated distribution measured using a laser diffraction / scattering particle size distribution measuring apparatus. Point to.

The number average particle diameter of the particulate polymer can be adjusted by changing the production conditions of the particulate polymer. Specifically, for example, when preparing a particulate polymer by seed polymerization, the number average particle diameter of the particulate polymer is controlled by adjusting the number and particle diameter of the seed particles used for the polymerization. Can do.

[Types of particulate polymer]
Here, examples of the particulate polymer include known polymers such as a diene polymer, an acrylic polymer, a fluorine polymer, and a silicon polymer. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Specifically, for example, when a binder composition for a lithium ion secondary battery electrode is used for forming a slurry composition for a negative electrode, the particulate polymer may be a diene polymer, particularly an aliphatic conjugated diene monomer unit. It is preferable to use a copolymer having an aromatic vinyl monomer unit or a hydrogenated product thereof. An aliphatic conjugated diene monomer unit that is a low-rigidity and flexible repeating unit that can enhance the binding property, and the solubility of the polymer in the electrolytic solution is reduced to form particles in the electrolytic solution. This is because the particulate polymer composed of a copolymer having an aromatic vinyl monomer unit capable of enhancing the stability of the polymer can satisfactorily function as a binder.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.

[[Monomer used for preparation of copolymer having aliphatic conjugated diene monomer unit and aromatic vinyl monomer unit]]
Here, when a copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit is used as a particulate polymer, an aliphatic conjugated diene unit capable of forming an aliphatic conjugated diene monomer unit is used. The monomer is not particularly limited, and 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, Substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like can be used. In addition, an aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

And in a particulate polymer, the content rate of an aliphatic conjugated diene monomer unit becomes like this. Preferably it is 30 mass% or more, More preferably, it is 40 mass% or more, Preferably it is 70 mass% or less, More preferably, it is 60 It is below mass%. It is because the flexibility of the electrode formed using a binder composition can be improved because the content rate of an aliphatic conjugated diene monomer unit is 30 mass% or more. Further, when the content ratio of the aliphatic conjugated diene monomer unit is 70% by mass or less, the binding force of the particulate polymer is sufficiently high, and the components constituting the electrode mixture layer and the electrode mixture layer This is because the current collector and the current collector can be favorably bound.

The aromatic vinyl monomer that can form an aromatic vinyl monomer unit is not particularly limited, and styrene, α-methylstyrene, vinyl toluene, divinylbenzene, and the like can be used. In addition, an aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In the particulate polymer, the content of the aromatic vinyl monomer unit is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 50% by mass or less, more preferably 40% by mass. % Or less. It is because the electrolyte solution resistance of the electrode formed using a binder composition can be improved because the content rate of an aromatic vinyl monomer unit is 20 mass% or more. Further, since the content ratio of the aromatic vinyl monomer unit is 50% by mass or less, the binding force of the particulate polymer made of the copolymer is sufficiently high, and the components constituting the electrode mixture layer and This is because the electrode mixture layer and the current collector can be favorably bound.

The copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit includes a 1,3-butadiene unit as the aliphatic conjugated diene monomer unit, and the aromatic vinyl monomer unit. It preferably contains a styrene unit (that is, a styrene-butadiene copolymer or a hydrogenated styrene-butadiene copolymer).

Further, from the viewpoint that the particulate polymer used in the present invention needs to have the above-mentioned surface acid amount, a copolymer (particulate polymer) having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit is used. The coalesced) preferably contains an acidic group-containing monomer unit. Examples of the acidic group-containing monomer unit include an ethylenically unsaturated carboxylic acid monomer unit and an unsaturated monomer unit having a sulfonic acid group. Especially, it is preferable that a particulate polymer contains an ethylenically unsaturated carboxylic acid monomer unit.

Here, the ethylenically unsaturated carboxylic acid monomer capable of forming an ethylenically unsaturated carboxylic acid monomer unit includes ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof. Products and derivatives thereof.
Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of the ethylenically unsaturated 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.
Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. In addition, examples of ethylenically unsaturated dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate , Dodecyl maleate, octadecyl maleate, fluoroalkyl maleate and the like. Among them, ethylenically unsaturated monocarboxylic acid is preferable, and acrylic acid is particularly preferable.
One of these may be used alone, or two or more of these may be used in combination at any ratio.

Examples of the unsaturated monomer having a sulfonic acid group capable of forming an unsaturated monomer unit having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) acryl sulfonic acid, and styrene sulfone. Examples include acids, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like. One of these may be used alone, or two or more of these may be used in combination at any ratio. In this specification, “(meth) acryl” means acrylic and / or methacrylic.

In the particulate polymer, the content ratio of the acidic group-containing monomer unit is preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 18% by mass or more. Is 30% by mass or less, more preferably 25% by mass or less, particularly preferably 23% by mass or less, and still more preferably 20% by mass or less. When the content ratio of the acidic group-containing monomer unit is 10% by mass or more, the surface acid amount of the particulate polymer can be easily increased to the desired range of the present application, and the lithium ion secondary can be suppressed while suppressing the swelling of the electrode. The cycle characteristics of the battery can be made excellent. On the other hand, when it is 30% by mass or less, the preparation of the particulate polymer becomes easy.

Further, the copolymer (particulate polymer) having the above-described aliphatic conjugated diene monomer unit and aromatic vinyl monomer unit preferably contains a hydroxyl group-containing (meth) acrylate monomer unit. .
Here, examples of the hydroxyl group-containing (meth) acrylate monomer that can form a hydroxyl group-containing (meth) acrylate monomer unit include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and hydroxypropyl acrylate. , Hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, and the like. Of these, 2-hydroxyethyl acrylate is preferred.
One of these may be used alone, or two or more of these may be used in combination at any ratio.

And in a particulate polymer, the content rate of a hydroxyl-containing (meth) acrylic acid ester monomer unit becomes like this. Preferably it is 0.5 mass% or more, More preferably, it is 0.7 mass% or more, Most preferably, it is 0.00. It is 8% by mass or more, preferably 5% by mass or less, more preferably 4% by mass or less, particularly preferably 3% by mass or less, and still more preferably 2% by mass or less. Acid group-containing monomers such as ethylenically unsaturated carboxylic acid monomers and other monomers because the content ratio of the hydroxyl group-containing (meth) acrylic acid ester monomer unit is 0.5% by mass or more The copolymerizability with can be enhanced. On the other hand, when the content ratio of the hydroxyl group-containing (meth) acrylate monomer unit is 5% by mass or less, the hydroxyl group-containing (meth) acrylate monomer is polymerized to form a polymer. And the copolymerization of the ethylenically unsaturated carboxylic acid monomer to the particulate polymer is improved, so that the copolymerization of the above-described monomer can proceed well.

In addition, the copolymer having the aliphatic conjugated diene monomer unit and the aromatic vinyl monomer unit described above includes any other repeating unit other than those described above as long as the effects of the present invention are not significantly impaired. You may go out.
The content of other repeating units is not particularly limited, but the upper limit is preferably 6% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less in total.

[Preparation method of particulate polymer]
The particulate polymer can be prepared by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent.
Here, in the present invention, the content ratio of each monomer in the monomer composition can be determined according to the content ratio of the monomer units (repeating units) in the particulate polymer.

The aqueous solvent is not particularly limited as long as the particulate polymer can be dispersed in a particulate state, but water is not flammable and a dispersion of particulate polymer particles is easily obtained. Particularly preferable from the viewpoint. In addition, water may be used as the main solvent, and an aqueous solvent other than water may be mixed and used as long as the dispersed state of the particulate polymer particles can be ensured.

The polymerization mode is not particularly limited, and any mode 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. In addition, since it is easy to obtain a high molecular weight substance and the polymer is obtained in a state of being dispersed in water as it is, no redispersion treatment is required, and the binder composition of the present invention or the slurry composition of the present invention is used as it is. From the viewpoint of production efficiency, such as being capable of being used for production, the emulsion polymerization method is particularly preferred. The emulsion polymerization can be performed according to a conventional method. In emulsion polymerization, seed polymerization using seed particles may be employed.

And generally used emulsifiers, dispersants, polymerization initiators, polymerization aids and the like used for polymerization can be used, and the amount used is also generally used.

In order to produce the particulate polymer used in the present invention, batch polymerization and semi-batch polymerization can be used, but it is preferable to use semi-batch polymerization in which a monomer is continuously or intermittently added to the reaction system. . By using semi-batch polymerization, compared with the case of using batch polymerization in which acidic group-containing monomers such as ethylenically unsaturated carboxylic acid monomers are added to the reaction system from the beginning, the particulate polymer The surface acid amount and the value of the surface acid amount / the acid amount in the aqueous phase can be easily controlled.

As a method for preparing a particulate polymer using semi-batch polymerization, for example, when the particulate polymer is a copolymer having the above-described aliphatic conjugated diene monomer unit and aromatic vinyl monomer unit, A primary monomer composition containing an aromatic conjugated diene monomer, an aromatic vinyl monomer and an acidic group-containing monomer is continuously or intermittently added to the reaction system, and the addition rate of the monomer composition Is 70% or more, a method of starting addition of a secondary monomer composition containing a hydroxyl group-containing (meth) acrylic acid monomer to obtain a particulate polymer is preferred. This preferred embodiment will be described in detail below.
Note that “added continuously or intermittently” means that the monomer composition is not added to the reaction system all at once, but added over a certain period of time (for example, 30 minutes or more).
The “addition rate of the monomer composition” refers to the ratio (mass%) of the monomer already added to the reaction system in the total monomer composition used for the polymerization.

The “primary monomer composition” is a monomer composition that is added to the reaction system from the initiation stage of polymerization, and is preferably 80 to 99% by mass, more preferably among all monomer compositions used for polymerization. 90 to 99% by mass is included in the primary monomer composition. The primary monomer composition preferably includes an aromatic vinyl monomer, an aliphatic conjugated diene monomer, an acidic group-containing monomer, and a hydroxyl group-containing (meth) acrylic acid ester monomer. It is preferable that it does not contain substantially.
In preparation of the particulate polymer using semi-batch polymerization, for example, a mixture obtained by appropriately adding an emulsifier, a chain transfer agent, and water to this primary monomer composition and a separately prepared polymerization initiator are combined. The polymerization reaction is started by adding to one reaction vessel. The reaction conditions at this time are not particularly limited, but the reaction temperature is preferably 60 to 90 ° C. The time from the start of polymerization until the addition rate of the monomer composition reaches 70% is not particularly limited, but is preferably 2 to 6 hours, more preferably 3 to 5 hours.

Then, after the addition rate of the monomer composition becomes 70% or more (that is, after the addition of 70% by mass of the total monomer composition used in the polymerization to the reaction system), the hydroxyl group content ( The addition of the secondary monomer composition containing the (meth) acrylate monomer is started. The time from the start of the addition of the secondary monomer composition to the end of the addition of the secondary monomer composition is not particularly limited, but is preferably 1 to 3 hours. Thus, by adding the hydroxyl group-containing (meth) acrylic acid ester monomer later, the copolymerization of the acidic group-containing monomer and other monomers proceeds well, and the surface acid amount is large. Can be controlled easily.

Moreover, the addition of the primary monomer composition and the secondary monomer composition may be completed separately or may be completed simultaneously. The time from the start of polymerization to the end of the addition of all monomer compositions is not particularly limited, but is preferably 3 to 8 hours, more preferably 4 to 7 hours. Then, after the addition of the whole monomer composition is completed, the reaction is preferably carried out at 0 to 90 ° C. for 3 to 9 hours.

Thereafter, when the polymerization conversion becomes sufficient (for example, 95% or more), the reaction is stopped by cooling.
Here, after the above-described polymerization, the obtained aqueous dispersion is, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (for example, NH ₄ Cl). And a basic aqueous solution containing an organic amine compound (for example, ethanolamine, diethylamine, etc.), and adjusted so that the pH is usually 5 or more, usually 10 or less, preferably 9 or less. An aqueous dispersion of a polymer may be used. Among these, pH adjustment with an alkali metal hydroxide is preferable because it improves the binding strength of the electrode mixture layer to the current collector.
Moreover, it is preferable to remove an unreacted monomer by heating and vacuum distillation after pH adjustment.

<Preparation of binder composition for lithium ion secondary battery electrode>
The binder composition of the present invention is prepared by adding water or any other component within a range not impairing the effects of the invention to the aqueous dispersion of the particulate polymer obtained by polymerizing the monomer composition. Although it may be prepared, it is preferable to use the aqueous dispersion of the particulate polymer obtained by emulsion polymerization (including any of the above-described pH adjustment and heating and vacuum distillation) as it is as the binder composition of the present invention. . That is, the binder composition for secondary battery electrodes of the present invention is preferably a binder composition obtained by emulsion polymerization of a monomer composition.
The binder composition of the present invention can be used for producing either a positive electrode or a negative electrode of a lithium ion secondary battery. However, the problem of swelling of the electrode plate is significant, and the strength of the electrode mixture layer is high. It is preferable to use it for the more demanded negative electrode. That is, the binder composition for lithium ion secondary battery electrodes of the present invention is preferably used for forming a slurry composition for lithium ion secondary battery negative electrodes.

(Slurry composition for negative electrode of lithium ion secondary battery)
The lithium ion battery negative electrode slurry composition of the present invention is an aqueous slurry composition containing a negative electrode active material and the above-described binder composition for lithium ion secondary battery electrodes of the present invention. In addition, the slurry composition for lithium ion secondary battery negative electrodes of this invention may contain the other component mentioned later other than the above-mentioned negative electrode active material and binder composition.

And according to the slurry composition for a lithium ion secondary battery negative electrode of the present invention, since the binder composition of the present invention containing the above-mentioned particulate polymer is included, the swelling of the negative electrode of the lithium ion secondary battery is reduced. It can suppress and can make cycling characteristics excellent.

<Negative electrode active material>
The negative electrode active material is a material that transfers electrons in the negative electrode of the lithium ion secondary battery. And as a negative electrode active material of a lithium ion secondary battery, the substance which can occlude and discharge | release lithium is used normally. Examples of the material that can occlude and release lithium include a carbon-based negative electrode active material, a metal-based negative electrode active material, and a negative electrode active material obtained by combining these materials.

Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite. Quality materials.

The carbonaceous material is a material having a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower. In addition, although the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. .
Here, as the graphitizable carbon, for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
In addition, examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.

The graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher. In addition, although the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
Examples of the graphite material include natural graphite and artificial graphite.
Here, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.

Further, the metal-based negative electrode active material is an active material containing a metal, and usually includes an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / The active material which is more than g. Examples of the metal active material include lithium metal and a single metal capable of forming a lithium alloy (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn). , Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof. Among these, as the metal-based negative electrode active material, an active material containing silicon (silicon-based negative electrode active material) is preferable. This is because the capacity of the lithium ion secondary battery can be increased by using the silicon-based negative electrode active material. In addition, the silicon-based negative electrode active material generally expands and contracts greatly as compared with the carbon-based negative electrode active material due to charging / discharging of the lithium ion secondary battery. However, since the slurry composition of the present invention uses the binder composition of the present invention, even if the negative electrode active material contains a silicon-based negative electrode active material, the swelling of the negative electrode due to charge / discharge is suitably suppressed. can do.

Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, SiO, SiO _x , and a composite of a Si-containing material obtained by coating or combining a Si-containing material with conductive carbon and conductive carbon. Etc. In addition, these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 types.

Examples of the alloy containing silicon include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium.

SiO _x is a compound containing at least one of SiO and SiO ₂ and Si, and x is usually 0.01 or more and less than 2. Then, SiO _x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO _x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or steam after grinding and mixing SiO and optionally a polymer.

As a composite of Si-containing material and conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam. Can be mentioned. In addition, such a composite is obtained by coating the surface of SiO particles by a chemical vapor deposition method using an organic gas or the like, or by combining SiO particles and graphite or artificial graphite by a mechanochemical method (granulation). It can also be obtained by a known method such as

<Binder composition for lithium ion secondary battery electrode>
The binder composition used for the slurry composition of the present invention is a binder composition for a lithium ion secondary battery electrode containing the above-described particulate polymer of the present invention. And as for the slurry composition of this invention, content of the particulate polymer in a slurry composition becomes like this. Preferably it is 0.1 mass part or more per 100 mass parts of negative electrode active materials, More preferably, it is 0.5 mass part or more, The binder composition is contained so that the amount is particularly preferably 1 part by mass or more, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. When the slurry composition contains the particulate polymer in the above amount, the amount of the particulate polymer becomes sufficient to suitably follow the expansion and contraction of the negative electrode active material, while suppressing the swelling of the negative electrode, The cycle characteristics of the lithium ion secondary battery can be made excellent.

<Other ingredients>
In addition to the above components, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention includes components such as a water-soluble polymer such as carboxymethyl cellulose and polyacrylic acid, a conductive material, a reinforcing material, a leveling agent, and an electrolyte additive. May be contained. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. In addition, these other components may be contained in the slurry composition of the present invention by using the binder composition of the present invention in which the components are blended.
The particulate polymer used in the present invention has a large amount of surface acid and has a relatively high affinity for water, so that it is well compatible with water-soluble polymers such as carboxymethyl cellulose and polyacrylic acid. Therefore, when a water-soluble polymer such as carboxymethyl cellulose or polyacrylic acid is blended with the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention, it is compared with the case where a particulate polymer having a small surface acid amount is used. And the intensity | strength of an electrode compound-material layer can further be raised by compatibility with a particulate polymer and a water-soluble polymer.

<Method for preparing slurry composition for negative electrode of lithium ion secondary battery>
The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, the above components and any aqueous medium are mixed using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crushed grinder, ultrasonic disperser, homogenizer, planetary mixer, or fill mix. By doing so, a slurry composition can be prepared.
Here, water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used. In addition, after preparing a binder composition, you may prepare a slurry composition by adding a negative electrode active material etc. to this binder composition. The aqueous medium in the slurry composition may be derived from the binder composition.

(Anode for lithium ion secondary battery)
The negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for negative electrodes of lithium ion secondary batteries of this invention.
Here, the negative electrode for a lithium ion secondary battery of the present invention includes a current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer is a lithium ion secondary battery of the present invention. Obtained from the negative electrode slurry composition. In addition, each component contained in the negative electrode composite material layer was contained in the slurry composition for a lithium ion secondary battery negative electrode of the present invention, and a suitable abundance ratio of each of these components is It is the same as the suitable abundance ratio of each component in the slurry composition for use.
And the negative electrode for lithium ion secondary batteries of this invention can suppress swelling, and can exhibit the cycling characteristics excellent in the lithium ion secondary battery.

<Method for producing negative electrode for lithium ion secondary battery>
The negative electrode for a lithium ion secondary battery of the present invention was applied on the current collector, for example, a step of applying the above-described slurry composition for a lithium ion secondary battery negative electrode on the current collector (application step). The slurry composition for a negative electrode of a lithium ion secondary battery is dried and then manufactured through a step (drying step) of forming a negative electrode mixture layer on the current collector.

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

Here, as the current collector to which the slurry composition for negative electrode is applied, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. Among these, a copper foil is particularly preferable as the current collector used for the negative electrode. In addition, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Drying process]
A method for drying the slurry composition for the negative electrode on the current collector is not particularly limited, and a known method can be used, for example, drying with hot air, hot air, low-humidity air, vacuum drying, infrared rays, electron beam, etc. The drying method by irradiation is mentioned. Thus, by drying the negative electrode slurry composition on the current collector, a negative electrode mixture layer is formed on the current collector, and the negative electrode for a lithium ion secondary battery comprising the current collector and the negative electrode mixture layer Can be obtained.

Note that after the drying step, the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressurization treatment, the binding strength of the negative electrode mixture layer to the current collector can be improved.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode for a lithium ion secondary battery of the present invention is used as the negative electrode. And since the lithium ion secondary battery of this invention uses the negative electrode for lithium ion secondary batteries of this invention, it is excellent in cycling characteristics.

<Positive electrode>
As a positive electrode of a lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used.
As the current collector, one made of a metal material such as aluminum can be used. As the positive electrode mixture layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used. Incidentally, the binder composition for a lithium ion secondary battery electrode of the present invention may be used for the preparation of the positive electrode mixture layer.

<Electrolyte>
As the electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, examples of the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
A lithium salt can be used as the electrolyte. As the lithium salt, for example, those described in JP 2012-204303 A can be used. Among these lithium salts, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.

<Separator>
As the separator, for example, those described in JP 2012-204303 A can be used. Among these, the thickness of the entire separator can be reduced, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume. A microporous film made of a series resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.

<Method for producing lithium ion secondary battery>
In the lithium ion secondary battery of the present invention, for example, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and put into a battery container. It can manufacture by inject | pouring electrolyte solution into and sealing. In order to prevent the occurrence of pressure rise and overcharge / discharge inside the lithium ion secondary battery, an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the surface acid amount of the particulate polymer, the acid amount in the aqueous phase, the gel content and the number average particle diameter, and the swelling resistance (initial) of the negative electrode of the lithium ion secondary battery, the cycle The properties, the swelling resistance of the negative electrode (after cycle), and the binding strength of the negative electrode mixture layer to the current collector were evaluated using the following methods, respectively.

<Surface acid amount and acid amount in aqueous phase>
In a glass container having a capacity of 150 mL washed with distilled water, 50 g of an aqueous dispersion containing the prepared particulate polymer (adjusted to a solid content concentration of 2%) was added, and a solution conductivity meter was set and stirred. Stirring was continued until the addition of hydrochloric acid described later was completed.
A 0.1 N aqueous sodium hydroxide solution was added to the aqueous dispersion containing the particulate polymer so that the electrical conductivity of the aqueous dispersion containing the particulate polymer was 2.5 to 3.0 mS. Thereafter, after 6 minutes, the electrical conductivity was measured. This value was taken as the electrical conductivity at the start of measurement.
Further, 0.5 mL of 0.1 N hydrochloric acid was added to the aqueous dispersion containing the particulate polymer, and the electrical conductivity was measured after 30 seconds. Thereafter, 0.5 mL of 0.1 N hydrochloric acid was added again, and the electrical conductivity was measured after 30 seconds. This operation was repeated at intervals of 30 seconds until the electrical conductivity of the aqueous dispersion containing the particulate polymer was equal to or higher than the electrical conductivity at the start of measurement.
The obtained electric conductivity data is plotted on a graph with the electric conductivity (unit “mS”) on the vertical axis (Y coordinate axis) and the cumulative amount of added hydrochloric acid (unit “mmol”) on the horizontal axis (X coordinate axis). Plotted. Thereby, a hydrochloric acid addition amount-electric conductivity curve having three inflection points as shown in FIG. 1 was obtained. The X coordinate of the three inflection points and the X coordinate at the end of the addition of hydrochloric acid were P1, P2, P3, and P4 in order from the smallest value. For the data in the four sections of the X coordinate from zero to the coordinate P1, from the coordinate P1 to the coordinate P2, from the coordinate P2 to the coordinate P3, and from the coordinate P3 to the coordinate P4, the approximate straight line L1 by the least square method, respectively. , L2, L3 and L4 were determined. The X coordinate of the intersection of the approximate line L1 and the approximate line L2 is A1 (mmol), the X coordinate of the intersection of the approximate line L2 and the approximate line L3 is A2 (mmol), and the X point of the intersection of the approximate line L3 and the approximate line L4 The coordinates were A3 (mmol).
The surface acid amount per 1 g of the particulate polymer and the acid amount in the aqueous phase per 1 g of the particulate polymer were each determined as a value (mmol / g) converted to hydrochloric acid from the following formula.
Surface acid amount per gram of particulate polymer = A2-A1
Acid amount in aqueous phase per gram of particulate polymer = A3-A2
<Gel content>
An aqueous dispersion containing a particulate polymer was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ± 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Thereafter, the dried film was cut into 3 to 5 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0.
This film piece was immersed in 50 g of tetrahydrofuran (THF) for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble matter was measured.
And gel content (mass%) was computed according to the following formula.
Gel content (mass%) = (w1 / w0) × 100
<Number average particle diameter>
For the aqueous dispersion containing the particulate polymer, the particle size-number cumulative distribution of the particulate polymer is measured using a laser diffraction / scattering particle size distribution analyzer (LS230, manufactured by Beckman Coulter, Inc.) The particle diameter at which the value was 50% was taken as the number average particle diameter of the particulate polymer.
<Swelling resistance of negative electrode (initial)>
The produced laminate cell type lithium ion secondary battery was allowed to stand in a 25 ° C. environment for 5 hours, and then charged at a rate of 4.2 V and 0.5 C in a 25 ° C. environment.
Thereafter, the charged cell was disassembled, the negative electrode was taken out, and the thickness (d1) of the negative electrode mixture layer was measured. Then, a change rate (initial swelling ratio = {(d1−d0) / d0} × 100 (%)) with respect to the thickness (d0) of the negative electrode mixture layer before the production of the lithium ion secondary battery was obtained, and the following criteria were used. Judged. It shows that it is excellent in the swelling resistance (initial) of a negative electrode, so that an initial swelling rate is small.
A: Initial swell rate is less than 30% B: Initial swell rate is 30% to less than 35% C: Initial swell rate is 35% to less than 40% D: Initial swell rate is 40% or more <Cycle characteristics>
The prepared laminate cell type lithium ion secondary battery was allowed to stand for 24 hours in an environment of 25 ° C., and then charged and discharged at a charge / discharge rate of 4.2 V and 0.5 C in an environment of 25 ° C. The initial capacity C1 was measured. Furthermore, charge / discharge was repeated under an environment of 45 ° C., and the capacity C2 after 300 cycles was measured.
For the cycle characteristics, a capacity change rate ΔC represented by ΔC = (C2 / C1) × 100 (%) was calculated and evaluated according to the following criteria. It shows that it is excellent in cycle characteristics, so that the value of this capacity | capacitance change rate (DELTA) C is high.
A: Capacity change rate ΔC is 75% or more B: Capacity change rate ΔC is 70% or more and less than 75% C: Capacity change rate ΔC is 65% or more and less than 70% D: Capacity change rate ΔC is less than 65% Swelling (after cycle)>
The lithium ion secondary battery after the cycle characteristics were evaluated as described above was charged at 0.5 C in a 25 ° C. environment, the charged cell was disassembled, the negative electrode was taken out, and the negative electrode mixture layer The thickness (d2) of was measured. Then, the rate of change with respect to the thickness (d0) of the negative electrode mixture layer before the production of the lithium ion secondary battery (swell rate after cycle = {(d2−d0) / d0} × 100 (%)) was obtained, and the following criteria were obtained: Judged by. It shows that it is excellent in the swelling resistance (after a cycle) of a negative electrode, so that the swelling rate after a cycle is small.
A: Swelling rate after cycle is less than 35% B: Swelling rate after cycle is 35% or more and less than 40% C: Swelling rate after cycle is 40% or more and less than 45% D: Swelling rate after cycle is 45% or more <Current collector Bonding strength of negative electrode composite layer to
The produced negative electrode was cut into a rectangle having a width of 1.0 cm and a length of 10 cm to obtain a test piece. Then, the negative electrode composite layer side surface of the test piece was fixed upward, and a cellophane tape was attached to the negative electrode composite layer side surface of the test piece. At this time, the cellophane tape defined in JIS Z1522 was used. Thereafter, the stress was measured when the cellophane tape was peeled from the one end of the test piece in the 180 ° direction (the other end side of the test piece) at a speed of 50 mm / min. The measurement was performed 10 times, the average value of the stress was determined, and this was defined as the peel strength (N / m). It shows that the binding strength of the negative mix layer with respect to a collector is excellent, so that peel strength is large.
A: Peel strength is 5 N / m or more B: Peel strength is 3 N / m or more and less than 5 N / m C: Peel strength is 2 N / m or more and less than 3 N / m D: Peel strength is less than 2 N / m

Example 1
<Preparation of binder composition for lithium ion secondary battery electrode>
33 parts of styrene as an aromatic vinyl monomer, 46 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 20 parts of acrylic acid as an acidic group-containing monomer, 0.25 tert-dodecyl mercaptan as a chain transfer agent The addition of these mixtures to the pressure vessel B from a container A containing 0.35 parts of sodium lauryl sulfate as an emulsifier, and at the same time, a pressure vessel of 1 part of potassium persulfate as a polymerization initiator The polymerization was started by starting the addition to B. The reaction temperature was maintained at 75 ° C.
Also, 4 hours after the start of polymerization (after 70% of the entire monomer composition was added), 1 part of 2-hydroxyethyl acrylate was added to the pressure vessel B as a hydroxyl group-containing (meth) acrylic acid ester monomer for 1 hour. Added over half.
After 5 and a half hours from the start of polymerization, the addition of all of these monomer compositions was completed, and then the mixture was further heated to 85 ° C. and reacted for 6 hours.
When the polymerization conversion reached 97%, the reaction was stopped by cooling to obtain a mixture containing a particulate polymer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the particulate polymer to adjust the pH to 8. Then, the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled after that and the aqueous dispersion (Binder composition for lithium ion secondary battery electrodes, solid content concentration: 30%) containing the desired particulate polymer was obtained. Using the aqueous dispersion containing the particulate polymer, the surface acid amount, the acid amount in the aqueous phase, the gel content, and the number average particle diameter were measured. The results are shown in Table 1.

<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
First, 100 parts of silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd.) and 20 parts of polyvinyl alcohol (reagent grade of Tokyo Chemical Industry Co., Ltd.) were added to a bead mill, and wet pulverization and surface coating of silicon monoxide particles were performed. Thereafter, after drying in a cake shape in a nitrogen atmosphere, heat treatment was performed at 950 ° C. in an argon atmosphere, and classification was performed to obtain a carbon coat SiOx (x = 1.1, volume average particle size: 5 μm) of less than 325 mesh. Produced.
Next, in a planetary mixer with a disper, 95 parts of artificial graphite (specific surface area: 4 m ² / g, volume average particle diameter: 24.5 μm) as a negative electrode active material, and 5 parts of the above-prepared carbon-coated SiOx As a water-soluble polymer, 1 part of a 1% aqueous solution of carboxymethyl cellulose in terms of solid content was added. These mixtures were adjusted to a solid content concentration of 60% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting the solid content concentration to 52% with ion-exchanged water, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.
In the above mixed liquid, an aqueous dispersion containing a particulate polymer (binder composition for a lithium ion secondary battery electrode), 1.5 parts in terms of solid content of the particulate polymer, and ion-exchanged water are added, The final solid concentration was adjusted to 50%, and the mixture was further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for a negative electrode of a lithium ion secondary battery.

<Manufacture of negative electrode for lithium ion secondary battery>
The slurry composition for a negative electrode of a lithium ion secondary battery was applied with a comma coater onto a 15 μm thick copper foil as a current collector so that the amount applied was 9 to 10 mg / cm ² . The copper foil coated with the lithium ion secondary battery negative electrode slurry composition was dried at a rate of 0.5 m / min in an oven at a temperature of 60 ° C. over 2 minutes. Thereafter, heat treatment was performed in an oven at a temperature of 120 ° C. for 2 minutes to obtain a negative electrode original fabric.
The obtained negative electrode original fabric was pressed with a roll press machine so that the density of the negative electrode mixture layer was 1.6 to 1.7 g / cm ³ , thereby obtaining a negative electrode for a lithium ion secondary battery. Using this negative electrode for a lithium ion secondary battery, the binding strength of the negative electrode mixture layer to the current collector was evaluated. The results are shown in Table 1.

<Manufacture of positive electrode for lithium ion secondary battery>
In a planetary mixer, 100 parts of LiCoO ₂ as a positive electrode active material, 2 parts of acetylene black as a conductive material (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride, as a binder) 2 parts of Kureha Chemical Co., Ltd., KF-1100), and further added 2-methylpyrrhodone so that the total solid content concentration was 67%, and mixed to prepare a slurry composition for a lithium ion secondary battery positive electrode.
The obtained slurry composition for a lithium ion secondary battery positive electrode was applied onto an aluminum foil having a thickness of 20 μm as a current collector with a comma coater. The aluminum foil coated with the lithium ion secondary battery positive electrode slurry composition was dried by transporting it in an oven at a temperature of 60 ° C. for 2 minutes at a speed of 0.5 m / min. Thereafter, heat treatment was performed for 2 minutes in an oven at a temperature of 120 ° C. to obtain a positive electrode raw material.
The obtained positive electrode fabric was pressed with a roll press machine so that the density of the positive electrode mixture layer was 3.40 to 3.50 g / cm ³ to obtain a positive electrode for a lithium ion secondary battery.

<Manufacture of lithium ion secondary batteries>
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by a dry method; porosity 55%) was prepared and cut into a 5 cm × 5 cm square. Moreover, the aluminum packaging material exterior was prepared as a battery exterior.
And the produced positive electrode was cut out into a 4 cm x 4 cm square, and it has arrange | positioned so that the surface at the side of a collector may contact | connect the aluminum packaging material exterior. Next, the above-described square separator was disposed on the surface of the positive electrode mixture layer of the positive electrode. Furthermore, the produced negative electrode was cut out into a square of 4.2 cm × 4.2 cm, and this was arranged on the separator so that the surface on the negative electrode mixture layer side faces the separator. Thereafter, a LiPF ₆ solution having a concentration of 1.0 M as an electrolytic solution (a solvent is a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3/7 (volume ratio), and 2% by mass of vinylene carbonate is added as an additive)) Filled. Further, heat sealing at 150 ° C. was performed to seal the opening of the aluminum packaging material exterior, and a lithium ion secondary battery was manufactured. Using the obtained lithium ion secondary battery, the swell resistance (initial) of the negative electrode, the cycle characteristics, and the swell resistance (after cycling) of the negative electrode were evaluated. The results are shown in Table 1.

(Examples 2 to 4)
A binder composition for a lithium ion secondary battery electrode in the same manner as in Example 1 except that the blending amount of 1,3-butadiene and acrylic acid was changed as shown in Table 1 when preparing the binder composition for a lithium ion secondary battery electrode. Product, a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were manufactured and evaluated by the method described above. The results are shown in Table 1.

(Examples 5 and 6)
A lithium ion secondary battery electrode was prepared in the same manner as in Example 1 except that the blending amounts of 1,3-butadiene and 2-hydroxyethyl acrylate were changed as shown in Table 1 when preparing the binder composition for a lithium ion secondary battery electrode. Binder composition, slurry composition for negative electrode of lithium ion secondary battery, negative electrode for lithium ion secondary battery, positive electrode for lithium ion secondary battery and lithium ion secondary battery, and evaluated by the method described above . The results are shown in Table 1.

(Example 7)
A slurry composition for a lithium ion secondary battery negative electrode, a negative electrode for a lithium ion secondary battery, a lithium ion secondary battery, as in Example 1, except that the binder composition for a lithium ion secondary battery electrode was prepared by the following method. A positive electrode for a battery and a lithium ion secondary battery were produced and evaluated by the method described above. The results are shown in Table 1.
<Preparation of binder composition for lithium ion secondary battery electrode>
33 parts of styrene as an aromatic vinyl monomer, 46 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 20 parts of acrylic acid as an acidic group-containing monomer, 2 parts as a (meth) acrylic acid ester monomer -Starting addition of these mixtures to pressure vessel B from container A containing 1 part of hydroxyethyl acrylate, 0.25 parts of tert-dodecyl mercaptan as chain transfer agent and 0.35 parts of sodium lauryl sulfate as emulsifier At the same time, the polymerization was started by starting the addition of 1 part of potassium persulfate to the pressure vessel B as a polymerization initiator. The reaction temperature was maintained at 75 ° C.
Five and a half hours after the start of the polymerization, the addition of the entire amount of the mixture containing these monomer compositions was completed, and then the mixture was further heated to 85 ° C. and reacted for 6 hours.
When the polymerization conversion reached 97%, the reaction was stopped by cooling to obtain a mixture containing a particulate polymer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the particulate polymer to adjust the pH to 8. Then, the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled after that and the aqueous dispersion (Binder composition for lithium ion secondary battery electrodes solid content concentration: 30%) containing the desired particulate polymer was obtained.

(Example 8)
Lithium ion secondary battery negative electrode was prepared in the same manner as in Example 1 except that artificial graphite 100 parts was used instead of artificial graphite 95 parts and carbon-coated SiOx 5 parts as the negative electrode active material when preparing the negative electrode slurry composition. Binder composition for ion secondary battery electrode, slurry composition for negative electrode of lithium ion secondary battery, negative electrode for lithium ion secondary battery, positive electrode for lithium ion secondary battery and lithium ion secondary battery, and the method described above Evaluation was performed. The results are shown in Table 1.

(Comparative Example 1)
The same as Example 1 except that the blending amount of 1,3-butadiene and acrylic acid was changed as shown in Table 1 and 2-hydroxyethyl acrylate was not used when preparing the binder composition for lithium ion secondary battery electrodes. A lithium ion secondary battery electrode binder composition, a lithium ion secondary battery negative electrode slurry composition, a lithium ion secondary battery negative electrode, a lithium ion secondary battery positive electrode and a lithium ion secondary battery, and Evaluation was performed by the method described above. The results are shown in Table 1.

(Comparative Example 2)
Example 1 except that the blending amount of 1,3-butadiene was changed as shown in Table 1 and 1 part of itaconic acid was used instead of 20 parts of acrylic acid when preparing the binder composition for lithium ion secondary battery electrodes. Similarly, a lithium ion secondary battery electrode binder composition, a lithium ion secondary battery negative electrode slurry composition, a lithium ion secondary battery negative electrode, a lithium ion secondary battery positive electrode, and a lithium ion secondary battery are manufactured. And evaluation was performed by the above-mentioned method. The results are shown in Table 1.

(Comparative Example 3)
Example 1 except that the blending amount of 1,3-butadiene was changed as shown in Table 1 and 30 parts of methacrylic acid was used instead of 20 parts of acrylic acid when preparing the binder composition for lithium ion secondary battery electrodes. Similarly, a lithium ion secondary battery electrode binder composition, a lithium ion secondary battery negative electrode slurry composition, a lithium ion secondary battery negative electrode, a lithium ion secondary battery positive electrode, and a lithium ion secondary battery are manufactured. And evaluation was performed by the above-mentioned method. The results are shown in Table 1.

(Comparative Example 4)
A binder composition was prepared by the following procedure.
Container containing 35 parts of butyl acrylate, 35 parts of ethyl acrylate, 30 parts of methacrylic acid as an acidic group-containing monomer, 0.25 part of tert-dodecyl mercaptan as a chain transfer agent, and 0.35 part of sodium lauryl sulfate as an emulsifier From A, addition of these mixtures to the pressure vessel B was started, and at the same time, addition of 1 part of potassium persulfate as a polymerization initiator to the pressure vessel B was started to initiate polymerization. The reaction temperature was maintained at 75 ° C.
Five and a half hours after the start of the polymerization, the addition of the entire amount of the mixture containing these monomer compositions was completed, and then the mixture was further heated to 85 ° C. and reacted for 6 hours.
When the polymerization conversion rate reached 97%, the reaction was stopped by cooling to obtain a mixture containing a polymer. The mixture containing this polymer was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, the unreacted monomer was removed by heating under reduced pressure, and then cooled to obtain a binder composition. The polymer in the obtained binder composition was water-soluble and did not form a particulate polymer. The gel content of this water-soluble polymer was measured.
Further, the number average particle diameter could not be measured because the polymer was not in the form of particles.
Similarly, the surface acid amount and the acid amount in the aqueous phase are all converted to the acid amount in the aqueous phase because the polymer is dissolved in water (that is, the value of A2 in FIG. 1 is specified). The surface acid amount could not be calculated.
A slurry composition for a lithium ion secondary battery negative electrode, a lithium ion secondary battery, and a lithium ion secondary battery negative electrode slurry, except that this water-soluble polymer-containing binder composition was used instead of the lithium ion secondary battery electrode binder composition. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were manufactured and evaluated by the above-described method. The results are shown in Table 1.

(Comparative Example 5)
Except that the amount of styrene and 1,3-butadiene was changed as shown in Table 1 when preparing the binder composition for lithium ion secondary battery electrodes, and 1 part of itaconic acid was used instead of 20 parts of acrylic acid. The lithium ion secondary battery electrode binder composition, the lithium ion secondary battery negative electrode slurry composition, the lithium ion secondary battery negative electrode, the lithium ion secondary battery positive electrode and the lithium ion secondary battery are produced in the same manner as in 1. Then, the evaluation was performed by the method described above. The results are shown in Table 1.

In Table 1, ST is styrene, BD is 1,3-butadiene, 2-HEA is 2-hydroxyethyl acrylate, AA is acrylic acid, IA is itaconic acid, MAA is methacrylic acid, and BA is Butyl acrylate and EA indicate ethyl acrylate.

From Table 1, in Examples 1 to 8, it is possible to obtain a lithium ion secondary battery in which swelling of the negative electrode at the initial stage and after the cycle is suppressed and the binding strength of the negative electrode mixture layer to the current collector and the cycle characteristics are excellent. I understand.
On the other hand, it can be seen from Table 1 that in Comparative Examples 1, 2, and 5, the surface acid amount is small, the swelling of the negative electrode after the initial stage and after the cycle is not suppressed, and the cycle characteristics are poor. Further, in Comparative Example 3, it can be seen that the surface acid amount is large, the swelling of the negative electrode after cycling is not particularly suppressed, and the binding strength and cycle characteristics of the negative electrode mixture layer to the current collector are inferior. Further, in Comparative Example 4, the polymer used as the binder is not in the form of particles, the swelling of the negative electrode at the initial stage and after the cycle is not suppressed, and the binding strength and cycle of the negative electrode mixture layer to the current collector It turns out that it is inferior to a characteristic.

From Examples 1 to 7, by changing the surface acid amount of the particulate polymer, the acid amount in the aqueous phase, and the surface acid amount / the acid amount in the aqueous phase, the negative electrode mixture layer for the current collector It can be seen that the binding strength, the swelling resistance (after cycle) of the negative electrode, and the cycle characteristics can be improved.

Claims

Containing particulate polymer and water,
The binder composition for lithium ion secondary battery electrodes whose surface acid amount of the said particulate polymer is 0.5 mmol / g or more and 3.0 mmol / g or less.
The binder composition for a lithium ion secondary battery electrode according to claim 1, wherein the acid amount in the aqueous phase of the particulate polymer is 0.1 mmol / g or more and 0.7 mmol / g or less.
The binder composition for a lithium ion secondary battery electrode according to claim 1 or 2, wherein a value obtained by dividing the value of the surface acid amount of the particulate polymer by the value of the acid amount in the aqueous phase is 2.5 or more. .
The lithium ion secondary battery according to any one of claims 1 to 3, wherein the particulate polymer contains a hydroxyl group-containing (meth) acrylic acid ester monomer unit in an amount of 0.5 mass% to 5 mass%. Electrode binder composition.
A slurry composition for a negative electrode of a lithium ion secondary battery, comprising the binder composition for a lithium ion secondary battery electrode according to any one of claims 1 to 4 and a negative electrode active material.
The slurry composition for a negative electrode of a lithium ion secondary battery according to claim 5, wherein the negative electrode active material contains a silicon-based negative electrode active material.
A negative electrode for a lithium ion secondary battery, comprising a negative electrode mixture layer obtained using the slurry composition for a negative electrode of a lithium ion secondary battery according to claim 5 or 6.
A positive electrode, a negative electrode, a separator and an electrolyte solution are provided.
The lithium ion secondary battery whose said negative electrode is a negative electrode for lithium ion secondary batteries of Claim 7.