JP5904335B2 - Binder composition for negative electrode of electricity storage device - Google Patents

Description

  The present invention relates to a binder composition for a negative electrode of an electricity storage device. More specifically, the present invention relates to a negative electrode binder composition that can provide an electricity storage device having a large charge / discharge capacity and little capacity deterioration due to repeated charge / discharge cycles and is excellent in long-term storage stability.

As power sources for driving electronic devices, power storage devices with high voltage and high energy density are required. For this application, lithium ion batteries, lithium ion capacitors, and the like are expected.
The electrode used for an electrical storage device is normally manufactured by apply | coating and drying to a collector surface containing the composition (slurry for electrodes) containing an active material and the polymer which functions as a binder. The properties required for the polymer used as the binder for the electrode include the ability to bind the active materials and the adhesion between the active material and the current collector, the abrasion resistance in the process of winding the electrode, and subsequent cutting. In addition, there can be mentioned powder-off resistance, etc., in which fine powder of the active material does not fall off from the applied and dried composition coating film (hereinafter also simply referred to as “active material layer”). When the polymer satisfies these various required characteristics, the degree of freedom in structural design of the electricity storage device such as the method of folding the obtained electrode and setting the winding radius is increased, and the device can be miniaturized. it can. In addition, it has been empirically revealed that the quality of the active materials is substantially proportional to the ability to bond the active materials to each other, the adhesion between the active material and the current collector, and the powder fall resistance. Therefore, in the present specification, hereinafter, the term “adhesiveness” may be used in a comprehensive manner.

In recent years, in order to achieve the demand for higher output and higher energy density of such an electricity storage device, studies are being made to apply a material having a large lithium storage capacity. For example, silicon can reversibly occlude and release lithium by forming an intermetallic compound with lithium. The theoretical capacity of silicon is about 4,200 mAh / g at the maximum, which is much larger than the theoretical capacity of about 370 mAh / g of the carbon material conventionally used as the negative electrode material. Therefore, the silicon material is used as the negative electrode active material. As a result, the capacity of the electricity storage device should be greatly improved. However, since the volume change due to charging / discharging is large in silicon materials, when the binder material used in the past is applied to silicon materials, the initial adhesion cannot be maintained, and the capacity decreases significantly with charging / discharging. Occurs.
A method of applying polyimide as a negative electrode binder for holding such a silicon material in an active material layer has been proposed (Patent Documents 1 to 4). These techniques are technical ideas of restraining the volume change of the silicon material by constraining the silicon material with a rigid molecular structure of polyimide. In Patent Documents 1 to 4, by applying a slurry for negative electrode containing polyamic acid to the current collector surface to form a coating film, the coating film is heated at a high temperature to thermally imidize the polyamic acid. It is described that polyimide is formed. However, since the binder using these polyimides has insufficient adhesion, the electrode (negative electrode) is deteriorated by repeated charge and discharge, so that sufficient durability cannot be exhibited.
A negative electrode binder material that provides a negative electrode that can exhibit its expected performance over a long period of time when a silicon material is used as an active material has not been known so far.
Furthermore, the binder composition for an electrode may have a long storage period of several months to several years from its acceptance to use, even when the negative electrode binder composition after being stored for a long time is used. The performance of the obtained electricity storage device needs to be constant.

JP 2012-129068 A JP 2011-86480 A JP 2010-23862 A JP 2009-302046 A JP 2010-97188 A JP 2004-185810 A

Chemical Handbook (Revised 3rd Edition, The Chemical Society of Japan, June 25, 1984, Maruzen Co., Ltd.)

  The present invention has been made in an attempt to overcome the current situation as described above, and its purpose is to provide an electricity storage device having a large charge / discharge capacity and a low degree of capacity deterioration due to repeated charge / discharge cycles, An object of the present invention is to provide a negative electrode binder composition having excellent long-term storage stability.

According to the present invention, the above problems of the present invention are as follows.
A binder composition for a lithium ion secondary battery negative electrode of an electricity storage device containing at least (A) a polymer , (B) water, and (D) a liquid medium,
The polyamic acid obtained by reacting the polymer (A) with tetracarboxylic dianhydride a mole and diamine b mole, wherein the ratio a / b is 1.01 or more and less than 1.05 and its imide of at least 1 Tanedea Risoshite above (a) Ma parts by mass content of the polymer is selected from polymers group consisting, when a Mb parts by the content of the (B) water, both The ratio Ma / Mb is 500 to 5,000, and is achieved by the binder composition for a negative electrode of a lithium ion secondary battery .

ADVANTAGE OF THE INVENTION According to this invention, while being able to provide the electrical storage device with large charging / discharging capacity | capacitance and suppressing the deterioration of the capacity | capacitance by repetition of charging / discharging cycle as much as possible, the binder composition for negative electrodes excellent in long-term storage stability is provided. Provided.
Therefore, the electricity storage device manufactured using the negative electrode binder composition of the present invention has a high capacity and a long life. Moreover, the binder composition for negative electrodes of this invention can give the electrical storage device which exhibits the expected performance, even when it is used after long-term storage.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modified examples that are implemented without departing from the scope of the present invention.
1. Negative electrode binder composition The negative electrode binder composition of the present invention contains at least (A) a polymer , (B) water, and (D) a liquid medium. Negative electrode binder composition may further contain a compound having one or more (C) a carboxyl group.

1.1 (A) Polymer The (A) polymer contained in the negative electrode binder composition of the present invention is at least one polymer selected from the group consisting of polyamic acids and imidized polymers thereof. . The polymer serves as a binder in the active material layer constituting the negative electrode of the electricity storage device.
When the polymer (A) contained in the negative electrode binder composition of the present invention contains an imidized polymer of polyamic acid, the imidization rate of the imidized polymer is preferably 50% or less, More preferably, it is 20% or less. By adjusting the imidization rate of the imidized polymer contained in the negative electrode binder composition within the above range, the stability of the negative electrode slurry prepared using the binder composition is not impaired, and the adhesion In addition, a negative electrode having excellent charge / discharge characteristics can be produced, which is preferable. This imidation ratio represents the ratio of the number of imide ring structures to the total of the number of amic acid structures and the number of imide ring structures of the polyamic acid in percentage. The imidation ratio of the polyamic acid can be determined using ¹ H-NMR.
The polyamic acid and its imidized polymer can be used in combination. If the imidization rate of the imidized polymer is in the above preferred range, the use ratio of the polyamic acid and its imidized polymer is an arbitrary ratio. can do.
A polyamic acid can be obtained by reacting a tetracarboxylic dianhydride and a diamine. The imidized polymer of polyamic acid can be obtained by dehydrating and ring-closing a part of the amic acid structure of the polyamic acid to imidize it.

1.1.1 Tetracarboxylic acid dianhydride Examples of the tetracarboxylic acid dianhydride used for synthesizing the polyamic acid in the present invention include, for example, an aliphatic tetracarboxylic dianhydride and an alicyclic tetracarboxylic dianhydride. Products, aromatic tetracarboxylic dianhydrides and the like. Specific examples of these include aliphatic tetracarboxylic dianhydrides such as butane tetracarboxylic dianhydride;
Examples of the alicyclic tetracarboxylic dianhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 1,3,3a, 4, 5,9b-Hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5,9b- Hexahydro-8-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 3-oxabicyclo [3.2.1] octane -2,4-dione-6-spiro-3 '-(tetrahydrofuran-2', 5'-dione), 5- (2,5-dioxotetrahydro-3-furanyl) -3-methyl-3-cyclohexene- No 1,2-dicarboxylic acid 3,5,6-tricarboxy-2-carboxymethylnorbornane-2: 3,5: 6-dianhydride, 2,4,6,8-tetracarboxybicyclo [3.3.0] octane-2 : 4,6: 8-dianhydride, 4,9-dioxatricyclo [5.3.1.0 ^2,6 ] undecane-3,5,8,10-tetraone and the like;
As aromatic tetracarboxylic dianhydride, for example, pyromellitic dianhydride can be mentioned, respectively, and the tetracarboxylic dianhydride described in Patent Document 5 (Japanese Patent Laid-Open No. 2010-97188) is used. be able to.
Among these, the tetracarboxylic dianhydride used for synthesizing the polyamic acid preferably includes an aromatic tetracarboxylic dianhydride. The tetracarboxylic dianhydride in the present invention consists of only an aromatic tetracarboxylic dianhydride or a mixture of an aromatic tetracarboxylic dianhydride and an alicyclic tetracarboxylic dianhydride. It is preferable from the viewpoint of stability of the binder composition for a negative electrode of the present invention. In the latter case, the use ratio of the alicyclic tetracarboxylic dianhydride is preferably 30 mol% or less, more preferably 20 mol% or less, based on the total tetracarboxylic dianhydride.

1.1.2 Diamine Examples of the diamine used for synthesizing the polyamic acid in the present invention include aliphatic diamine, alicyclic diamine, aromatic diamine, and diaminoorganosiloxane. Specific examples thereof include aliphatic diamines such as 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine and the like;
Examples of alicyclic diamines include 1,4-diaminocyclohexane, 4,4′-methylenebis (cyclohexylamine), 1,3-bis (aminomethyl) cyclohexane and the like;
Examples of aromatic diamines include p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfide, 1,5-diaminonaphthalene, 2,2′-dimethyl-4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-bis (trifluoromethyl) biphenyl, 2,7-diaminofluorene, 4,4′-diaminodiphenyl ether, 2,2-bis [4- (4-aminophenoxy) phenyl ] Propane, 9,9-bis (4-aminophenyl) fluorene, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane 4,4 ′-(p-phenylenediisopropylidene) bisaniline, 4,4 ′-(m-phenylenediisopropylene Riden) bisaniline, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diamino Pyrimidine, 3,6-diaminoacridine, 3,6-diaminocarbazole, N-methyl-3,6-diaminocarbazole, N-ethyl-3,6-diaminocarbazole, N-phenyl-3,6-diaminocarbazole, N , N′-bis (4-aminophenyl) -benzidine, N, N′-bis (4-aminophenyl) -N, N′-dimethylbenzidine, 1,4-bis- (4-aminophenyl) -piperazine, 3,5-diaminobenzoic acid and the like;
Examples of the diaminoorganosiloxane include 1,3-bis (3-aminopropyl) -tetramethyldisiloxane, and the diamine described in Patent Document 5 (Japanese Patent Laid-Open No. 2010-97188). be able to.
The diamine used for synthesizing the polyamic acid in the present invention preferably contains 30% by mole or more, more preferably 50% by mole or more, especially 80 moles of the aromatic diamine with respect to the total diamine. % Or more is preferable.

1.1.3 Ratio of tetracarboxylic dianhydride and diamine In the present invention, the ratio of use of tetracarboxylic dianhydride and diamine is such that the amount of tetracarboxylic dianhydride used is a mole of diamine. When the amount used is b mol, the ratio a / b is 1.01 or more and less than 1.05. The ratio a / b is preferably 1.02 to 1.04.
By setting the ratio a / b within the above range, (A) the molecular weight of the polymer can be prevented from excessively increasing, and as a result, the viscosity of the resulting negative electrode binder composition is moderate. It becomes easy to adjust to a value, and since the applicability of the negative electrode slurry prepared using the negative electrode binder composition is improved, the formation of a uniform active material layer becomes easier.
Further, the ratio a / b being in the above range is attributed to the fact that the polymerization reaction is carried out in an excess of tetracarboxylic dianhydride relative to the diamine. Is expected to be a carboxy group. (A) Since many of the polymer terminals are carboxy groups, even when the negative electrode binder composition containing the (A) polymer is stored for a long period of time, the molecular weight increases due to reaction between the terminals. Therefore, it is possible to maintain the performance. Furthermore, (A) the terminal carboxy group of the polymer can be easily adsorbed on the surface of the active material, which improves adhesion and suppresses powder falling from the active material layer, which is preferable. In addition, since the reduction resistance during the exchange of electrons during charging / discharging of the electricity storage device is improved, deterioration of the binder component is suppressed even when charging / discharging is repeated, and deterioration of charging / discharging capacity over time is suppressed. Become.

1.1.4 (A) Synthesis of Polymer The polyamic acid synthesis reaction is preferably performed in an organic solvent, preferably at -20 ° C to 150 ° C, more preferably at 0 to 100 ° C, preferably 0.1 to 0.1 ° C. It is performed for 24 hours, more preferably 0.5 to 12 hours.
Here, as the organic solvent, for example, an aprotic polar solvent, a phenol and a derivative thereof, an alcohol, a ketone, an ether, an ester, a hydrocarbon, or the like, which can generally be used for a polyamic acid synthesis reaction, can be used. . Specific examples of these organic solvents include the above aprotic polar solvents such as N-methyl-2-pyrrolidone, Nt-butyl-2-pyrrolidone, N-methoxyethyl-2-pyrrolidone, N, N-dimethyl. Acetamide, N, N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, tetramethylurea, hexamethylphosphortriamide and the like;
Examples of the phenol derivative include m-cresol, xylenol, halogenated phenol and the like;
Examples of the alcohol include methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, propylene glycol, 1,4-butanediol, triethylene glycol, and ethylene glycol monomethyl ether;
Examples of the ketone include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Examples of the ether include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-i-propyl ether, ethylene glycol-mono-n-butyl ether, ethylene glycol-di-n-butyl ether, ethylene Examples thereof include glycol dimethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, and tetrahydrofuran.
Examples of the ester include ethyl lactate, butyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl methoxypropionate, ethyl ethoxypropionate, isoamyl propionate, isoamyl isobutyrate, diethyl oxalate, and malonic acid. Diethyl etc .;
Examples of the hydrocarbon include hexane, heptane, octane, benzene, toluene, xylene, and the like.

The polyamic acid dehydration ring-closing reaction is preferably performed by a method of heating the polyamic acid or a method of adding a dehydrating agent and a dehydrating ring-closing catalyst to a solution obtained by dissolving the polyamic acid in an organic solvent and heating as necessary.
The reaction temperature in the method for heating the polyamic acid is preferably 180 to 250 ° C, more preferably 180 to 220 ° C. When the reaction temperature is less than 50 ° C., the dehydration ring-closing reaction does not proceed sufficiently, and when the reaction temperature exceeds 250 ° C., the molecular weight of the imidized polymer obtained may decrease. The reaction time in the method of heating the polyamic acid is preferably 0.5 to 20 hours, more preferably 2 to 10 hours.
In the method of adding a dehydrating agent and a dehydrating ring-closing catalyst to the polyamic acid solution, for example, an acid anhydride such as acetic anhydride, propionic anhydride, or trifluoroacetic anhydride can be used as the dehydrating agent. The use ratio of the dehydrating agent is preferably 0.01 to 1.0 mol with respect to 1 mol of the amic acid structure of the polyamic acid. As the dehydration ring closure catalyst, for example, tertiary amines such as pyridine, collidine, lutidine, and triethylamine can be used. The use ratio of the dehydration ring closure catalyst is preferably 0.01 to 10 mol per 1 mol of the dehydrating agent to be used. Examples of the organic solvent used in the dehydration ring-closing reaction include the organic solvents exemplified as those used for the synthesis of polyamic acid. The reaction temperature of the dehydration ring closure reaction is preferably 0 to 180 ° C, more preferably 10 to 150 ° C. The reaction time is preferably 1 to 10 hours, more preferably 2 to 5 hours.

  The polyamic acid or imidized polymer obtained as described above preferably has a solution viscosity of 2,000 to 100,000 mPa · s when it is made into a solution having a concentration of 10% by weight. More preferably, it has a solution viscosity of 5,000 to 30,000 mPa · s. The solution viscosity (mPa · s) of this polymer is about 10% by weight of the polymer solution prepared using a good solvent for these polymers (for example, γ-butyrolactone, N-methyl-2-pyrrolidone, etc.). It is a value measured at 25 ° C. using an E-type rotational viscometer.

The polyamic acid or its imidized product obtained as described above is used as it is or after purification by a known method as necessary, to prepare a negative electrode slurry described later.
As the polyamic acid in the present invention, a commercially available polyamic acid solution may be used. As a commercially available polyamic acid solution, U-varnish A (made by Ube Industries, Ltd.) etc. can be mentioned, for example.

1.2 (B) a negative electrode binder composition of the water present invention, you containing (B) water.
The proportion of water used in the binder composition for negative electrode of the present invention is such that the content of (A) polymer in the composition is Ma parts by mass, and (B) the content of water is Mb parts by mass. The ratio Ma / Mb is 500 to 5,000, more preferably 1,000 to 4,000, and still more preferably 1,300 to 3,500. (B) By using water in the above range, the adhesion is improved, and the electrical properties of the resulting active material layer are improved.
In the field of power storage devices, conventionally, water is considered to erode the electrode active material. Therefore, it has been common knowledge in the industry to avoid mixing water as an impurity as much as possible when manufacturing an electrode binder. In the field of polymers, it is believed that when a polyamic acid and its imidized polymer come into contact with water, the amic acid structure or imide ring is hydrolyzed and the molecular weight decreases.

However, the negative electrode binder composition of the present invention contains (B) water in a specific ratio with respect to the polymer (A), so that the electricity storage device manufactured using the composition is extremely excellent charge / discharge. The characteristics will be shown. In particular, this effect is remarkable when an active material containing a silicon atom is used as the negative electrode active material. Although the expression mechanism of this is not clear, the present inventors presume that it is caused by the following actions.
When forming an active material layer, when a polyamic acid or an imidized polymer thereof approaches a metal atom (for example, Co) or a semimetal atom (for example, Si) on the surface of the active material, the metal atom or the half It is considered that a strong binder action is expressed by bonding the metal atom and the carboxy group of the polymer (A) as follows. The carboxy group of the (A) polymer may be at the end of the (A) polymer, or may be a carboxy group constituting an amic acid structure in the polymer chain.

(In the above formula, “Polymer” is a polymer chain, and M is a metal atom or a semimetal atom on the surface of the active material.)
And if the usage-amount ratio of the water in the binder composition for negative electrodes is said range, it turned out that the above disadvantageous effects which were a concern in this industry do not appear in the electrical storage device obtained. This is a surprising fact that goes against the common technical knowledge of the industry. Probably, water brought from the binder composition for the negative electrode by the heating preferably performed in the step of forming the active material layer, or water regenerated by the bonding of the metal atom or semimetal atom on the surface of the active material and the polymer (A). Will dissipate easily and will not remain in the active material layer.
By such an action mechanism, it is considered that (A) the binder effect of the polymer is maximized, and the adverse effect of water on the electrical characteristics of the active material layer is reduced as much as possible.
The content of (B) water in the negative electrode binder composition of the present invention can be measured, for example, by a Karl Fischer moisture meter.

1.3 (C) Compound The negative electrode binder composition of the present invention may optionally contain (C) a compound having one or more carboxy groups.
The compound (C) in the present invention preferably has a first acid dissociation constant (pKa1) of 2 to 5 at 25 ° C. This acid dissociation index can be measured, for example, by a method using a commercially available potentiometric titrator (eg, product name “COM-980Win” manufactured by Hiranuma Sangyo Co., Ltd.).
Non-Patent Document 1 (Chemical Handbook (Revised 3rd Edition, edited by The Chemical Society of Japan, June 25, 1984, Maruzen Co., Ltd.)) Acid dissociation index, database “pKaBASE” manufactured by Compudrug, etc. Can be investigated using.

Specific examples of such a compound (C) are those having one carboxyl group such as formic acid, acetic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, etc .;
As those having two carboxy groups, maleic acid, succinic acid, oxalic acid, itaconic acid, malonic acid and the like, and as compounds having three carboxyl groups, for example, trimellitic acid, 1,2,3-tricarboxypropane, Pyromellitic acid monoethyl ester, 3, 3 ′, 4, 4′-biphenyltetracarboxylic acid monoethyl ester, 3, 3 ′, 4, 4′-benzophenone tetracarboxylic acid monoethyl ester, etc .;
Examples of the compound having four carboxyl groups include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, and Patent Document 5 ( Examples thereof include tetracarboxylic acids obtained by hydrating tetracarboxylic dianhydrides described in JP 2010-97188 A).
(C) The compound may be used in the form of a salt. Examples of the counter cation in this salt include lithium ion, sodium ion, potassium ion, cesium ion, magnesium ion, calcium ion, ammonium ion, and alkylammonium ion.

When the binder composition for negative electrodes of this invention contains (C) compound, the electrical storage device manufactured using this composition will show the very outstanding charging / discharging characteristic. Although the manifestation mechanism of this effect is not clear, the present inventors presume that it is caused by the following action.
The polymer (A) in the present invention may have an amino group (primary amino group) at its end. This amino group is thought to erode metal atoms or metalloid atoms on the surface of the active material. Therefore, there is a concern that the charge / discharge characteristics of an electricity storage device using a polymer having an amino group as a binder deteriorates with time. In addition, the (A) polymer having an amino group at the end cannot form a bond with a metal atom or a semimetal atom on the surface of the active material even if water is present. The strong binder action described in the section “B) Water” does not appear.
However, when the negative electrode binder composition of the present invention contains the compound (C), the carboxy group is probably bonded to the amino group during heating in the formation process of the active material layer, and (A) It is thought that a carboxy group is formed at the terminal of the coalescence. Therefore, the presence of the compound (C) can avoid deterioration of metal atoms or metalloid atoms on the surface of the active material, and these can be bonded to the polymer chain to improve charge / discharge characteristics. Conceivable.
From the above viewpoint, the number of carboxy groups in the compound (C) is preferably 2 or more. (C) By using a compound having 3 or more carboxy groups as a compound, when (A) the polymer has two amino groups at its ends, it is between the metal atom or the semimetal atom on the surface of the active material. Since two bonds can be formed, the above-described effect is superimposed. (C) The number of carboxy groups in the compound is preferably 4 or less.
The compound (C) preferably has a molecular weight of about 40 to 1,000.

The proportion of the compound (C) used in the negative electrode binder composition of the present invention is such that the content of the polymer (A) in the composition is Ma parts by mass, and the content of the compound (C) is Mc parts by mass. The ratio Ma / Mc between the two is preferably 50 or more. The ratio Ma / Mc is more preferably 50 to 400, and further preferably 60 to 350. By using the compound (C) in the above range, the function of the compound (C) can be expressed under mild conditions, so that deterioration of each component due to excessive heating can be avoided, which is preferable.
The content of the compound (C) in the negative electrode binder composition of the present invention can be measured, for example, by liquid chromatography.

1.4 (D) Liquid medium The (D) liquid medium preferably used in the negative electrode binder composition of the present invention is a non-aqueous medium. Specific examples thereof include methanol, ethanol, propanol, isopropanol, and butanol. , Alcohols such as benzyl alcohol and glycerin;
Ketones such as acetone, methyl ethyl ketone, cyclopentanone, isophorone;
Ethers such as methyl ethyl ether, diethyl ether, tetrahydrofuran, dioxane;
lactones such as γ-butyrolactone and δ-butyrolactone;
lactams such as β-lactams;
Linear or cyclic amide compounds such as dimethylformamide, N-methylpyrrolidone, N, N-dimethylacetamide;
Compounds having a nitrile group, such as methylene cyanohydrin, ethylene cyanohydrin, 3,3′-thiodipropionitrile, acetonitrile;
Glycol compounds such as ethylene glycol and propylene glycol;
Examples thereof include diethylene glycol or derivatives such as diethylene glycol, diethylene glycol monoethyl ether, and diethylene glycol ethyl butyl ether, and one or more selected from these can be used.
In the binder composition for negative electrode of the present invention, the proportion of (D) the liquid medium used is the solid content concentration of the negative electrode binder composition (the total mass of components other than the liquid medium in the composition is based on the total mass of the composition). (Occupying ratio) is preferably a ratio of 5 to 70% by mass, and more preferably 10 to 55% by mass.

1.5 pH of binder composition for negative electrode
The pH of the negative electrode binder composition of the present invention is preferably from 3 to 9, and more preferably from 4 to 7. For adjusting the liquidity of the composition, a known acid (however, excluding those corresponding to the compound (C)) or a base can be used. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like;
Examples of the base include sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia.
Accordingly, the negative electrode binder composition of the present invention is not limited to the (A) polymer, (B) water, (C) compound, and (D) liquid medium, and the acid or base described above as other components is used to adjust the pH. You may contain in the required range.

1.6 Preparation Method of Negative Electrode Binder Composition The negative electrode binder composition of the present invention may be prepared by any method as long as it contains the above components.
In order to prepare the negative electrode binder composition of the present invention, for example, (1) a method of adding other components added as necessary to a polymerization mixture obtained by synthesizing (A) polymer (in this case, (A) The polymerization solvent used when synthesizing the union is used as it is (D) as a liquid medium);
(2) (A) A method of substituting part or all of the solvent in the polymerization mixture for synthesizing the polymer (in this case, other components added as necessary are added before or after solvent replacement);
(3) The polymer isolated from the polymerization mixture obtained by synthesizing the polymer (A) can be obtained by an appropriate method such as (D) a method of dissolving in a liquid medium together with other components added as necessary.
Of these, the method (1) is preferable because of convenience.
When the binder composition for negative electrodes of the present invention contains (B) water, the (B) water may be added as a single component, or (C) contained in a liquid medium or the like. It may be added as an impurity.

2. Negative electrode slurry A negative electrode slurry can be produced using the negative electrode binder composition of the present invention as described above. The negative electrode slurry refers to a dispersion used for forming a negative electrode active material layer on the surface of a current collector. The negative electrode slurry in the present invention contains at least the negative electrode binder composition of the present invention and a negative electrode active material.

2.1 Negative electrode active material Examples of the negative electrode active material used in the negative electrode slurry produced using the negative electrode binder composition of the present invention include carbon materials, active materials containing silicon atoms, lead compounds, tin compounds, Examples thereof include arsenic compounds, antimony compounds, and aluminum compounds.
Examples of the carbon material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.
Examples of the active material containing silicon atoms include silicon simple substance, silicon oxide, silicon alloy, and the like, and use a silicon material described in Patent Document 6 (Japanese Patent Laid-Open No. 2004-185810). Can do. The silicon oxide is preferably a silicon oxide represented by the composition formula SiO _x (0 <x <2, preferably 0.1 ≦ x ≦ 1). The silicon alloy is preferably an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron and molybdenum. These transition metal silicides are preferably used because they have high electronic conductivity and high strength. Moreover, since the transition metal existing on the surface of the active material is oxidized and becomes an oxide having a hydroxyl group on the surface when the active material contains these transition metals, the binding force with the binder is also improved. preferable. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The silicon content in the silicon alloy is preferably 10 mol% or more, and more preferably 20 to 70 mol%, based on all the metal elements in the alloy. The active material containing a silicon atom may be single crystal, polycrystalline, or amorphous.

As an active material which the slurry for negative electrodes in this invention contains, it is preferable to contain the active material containing a silicon atom. Since silicon atoms have a larger amount of lithium storage per unit weight than other active material groups, the active material contains an active material containing silicon atoms, thereby increasing the storage capacity of the resulting electricity storage device. As a result, the output and energy density of the electricity storage device can be increased. The active material for the negative electrode is preferably composed of a mixture of an active material containing silicon atoms and a carbon material. Since the volume change due to charging and discharging is small, the use of a mixture of an active material containing a silicon atom and a carbon material as an active material for a negative electrode alleviates the effect of the volume change of the active material containing a silicon atom. Thus, the adhesion between the active material layer and the current collector can be further improved. The negative electrode active material is particularly preferably composed of a mixture of an active material containing silicon atoms and graphite.
The proportion of the active material containing silicon atoms in 100% by mass of the active material is preferably 1% by mass or more, more preferably 1 to 50% by mass, and further preferably 5 to 45% by mass. Particularly preferred is 10 to 40% by mass.
The shape of the active material is preferably granular. The particle size (average median particle size) of the particles is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm.
The proportion of the active material used is preferably such that the amount of the polymer (A) in the negative electrode binder composition is 0.1 to 25 parts by mass with respect to 100 masses of the active material, 0.5 to More preferably, the ratio is 15 parts by mass. By setting it as such a usage rate, the negative electrode which is excellent in adhesiveness, and has small electrode resistance and excellent charge / discharge characteristics can be manufactured.

2.2 Other Components The negative electrode slurry in the present invention may contain other components as necessary in addition to the negative electrode binder composition and the negative electrode active material. Examples of such other components include a conductivity-imparting agent, a thickener, and a liquid medium.

2.2.1 Conductivity-imparting agent Specific examples of the conductivity-imparting agent include carbon in a lithium ion secondary battery. Examples of carbon include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black or ketjen black can be preferably used. The ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material.

2.2.2 Thickener The negative electrode slurry can contain a thickener from the viewpoint of improving its coatability. Specific examples of the thickener include, for example, cellulose derivatives such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose;
An ammonium salt or an alkali metal salt of the cellulose derivative;
Polycarboxylic acids such as poly (meth) acrylic acid, modified poly (meth) acrylic acid;
An alkali metal salt of the polycarboxylic acid;
Polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer;
Examples thereof include water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid and fumaric acid and vinyl esters.
The use ratio of the thickener is preferably such that the ratio Wv / Wa of the weight Wv of the thickener to the weight Wa of the active material in the negative electrode slurry is 0.001 to 0.1. More preferably, it is 0.005 to 0.05.

2.2.3 Liquid Medium Since the negative electrode slurry contains the negative electrode binder composition, the negative electrode binder composition contained (D) the liquid medium. However, the negative electrode slurry may additionally contain a further liquid medium in addition to the liquid medium (D) brought in from the negative electrode binder composition.
The liquid medium additionally contained in the negative electrode slurry may be the same as or different from the liquid medium contained in the negative electrode binder composition, but the liquid medium in the negative electrode binder composition has been described above. It is preferable to select and use from a liquid medium.
The use ratio of the liquid medium (including the amount brought in from the binder composition for the negative electrode) in the negative electrode slurry is the solid content concentration of the negative electrode slurry (the total mass of components other than the liquid medium in the negative electrode slurry is the negative electrode slurry) It is preferable to set it as the ratio used as 30-70 mass%, and it is more preferable to set it as the ratio used as 40-60 mass%.

2.3 Method for Producing Negative Electrode Slurry The negative electrode slurry may be produced by any method as long as it contains the above-described components.
However, from the viewpoint of producing a negative electrode slurry having better dispersibility and stability more efficiently and inexpensively, the negative electrode binder composition includes an active material and optional additional components used as necessary. In addition, it can manufacture by mixing these.
In order to mix the binder composition for negative electrodes and other components, it can carry out by stirring by a well-known method.
The preparation of the slurry for the negative electrode (mixing operation of each component) is preferably performed at least part of the process under reduced pressure. Thereby, it can prevent that a bubble arises in the active material layer obtained. The degree of pressure reduction is preferably about 5.0 × 10 ^{4 to} 5.0 × 10 ⁵ Pa as an absolute pressure.
As the mixing and stirring for producing the negative electrode slurry, it is necessary to select a mixer capable of stirring to such an extent that no agglomerates of active material particles remain in the slurry and a sufficient dispersion condition as necessary. The degree of dispersion can be measured by a particle gauge, but it is preferable to mix and disperse so that aggregates larger than at least 100 μm are eliminated. Examples of the mixer that meets such conditions include a ball mill, a bead mill, a sand mill, a defoamer, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer. it can.

3. Method for producing negative electrode for electricity storage device A negative electrode for electricity storage device can be produced using the above slurry for negative electrode.
The negative electrode for an electrical storage device is formed by coating the negative electrode slurry produced using the negative electrode binder composition of the present invention on the surface of an appropriate current collector such as a metal foil. It is manufactured by removing the liquid medium from The negative electrode produced in this manner is formed by binding an active material layer containing the above-described polymer (A) and active material, and optional additional components used as necessary, on a current collector. Is. It is considered that the water (B) contained in the negative electrode binder composition and the negative electrode slurry is removed during the liquid medium removing step, and the existing concentration in the resulting active material layer is low.
The negative electrode having a layer formed from the slurry for negative electrode produced using the binder composition for negative electrode of the present invention on the surface of the current collector has excellent binding properties between the current collector and the active material layer The degree of deterioration of the charge / discharge capacity when the charge / discharge cycle is repeated is small.

3.1 Current collector The current collector is not particularly limited as long as it is made of a conductive material. In a lithium ion secondary battery, a current collector made of metal such as iron, copper, aluminum, nickel, and stainless steel is used. Especially when aluminum is used for the positive electrode and copper is used for the negative electrode, the current collector for the negative electrode of the present invention is used. The effect of the slurry is most apparent. As the current collector in the nickel metal hydride secondary battery, a punching metal, an expanded metal, a wire mesh, a foam metal, a mesh metal fiber sintered body, a metal plated resin plate, or the like is used.
The shape and thickness of the current collector are not particularly limited. The thickness of the current collector is preferably 1 to 500 μm, more preferably 5 to 150 μm, and particularly preferably 10 to 50 μm. As the shape of the current collector, a sheet shape is preferably used.

3.2 Method for forming negative electrode for power storage device The negative electrode for power storage device of the present invention is formed on a current collector,
A negative electrode slurry containing at least an active material and a negative electrode binder composition is applied to form a coating film, and then the coating film is heated to remove the dispersion medium from the coating film on the substrate. It can manufacture by forming an active material layer. In the dispersion medium removing step, it is considered that (B) water is also removed if present.
There is no restriction | limiting in particular about the coating method to the electrical power collector of the slurry for negative electrodes. The coating can be performed by an appropriate method such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, or a brush coating method. The coating amount of the negative electrode slurry is not particularly limited, but the thickness of the active material layer formed after removing the liquid medium is preferably 5 to 250 μm, and preferably 20 to 100 μm. Is more preferable.
The method for removing the liquid medium from the coated film after coating is not particularly limited, and may be, for example, drying with hot air, hot air, low-humidity air; vacuum drying; (far) drying by irradiation with infrared rays, electron beams, or the like. . The drying speed is appropriately set so that the liquid medium can be removed as quickly as possible within a speed range in which the active material layer does not crack due to stress concentration or the active material layer does not peel from the current collector. be able to.
The heating temperature is preferably in a range in which the amic acid structure of the negative electrode binder composition in the coating film does not completely undergo thermal imidization. From such a request, the heating temperature in the step of removing the dispersion medium is preferably set to a temperature not exceeding 150 ° C., more preferably not exceeding 130 ° C. The heating time is preferably 0.5 to 30 minutes, and more preferably 1 to 15 minutes.

Furthermore, it is preferable to increase the density of the active material layer by pressing the current collector after removal of the liquid medium. Examples of the pressing method include a mold press and a roll press. The press conditions should be set appropriately depending on the type of press equipment used and the desired density of the active material layer. This condition can be easily set by a few preliminary experiments by those skilled in the art. For example, in the case of a roll press, either the gap type or the pressure type may be used, and the linear pressure is 0.1 to 10 t / cm, Preferably, at a pressure of 0.5 to 5 t / cm, for example, at a roll temperature of 20 to 100 ° C., the coating speed (roll rotation speed) after removal of the dispersion medium is 1 to 80 m / min, preferably 5 to 5 m / min. It can be carried out at 50 m / min.
Density of the active material layer after pressing is preferably in a 1.2~1.9g / cm ^3, and more preferably to 1.3~1.8g / cm ^3.
It is preferable that the pressed coating film is further heated under reduced pressure to completely remove the liquid medium. In this case, the degree of reduced pressure is preferably 50 to 200 Pa, more preferably 75 to 150 Pa as an absolute pressure. The heating temperature is preferably a temperature range in which the polyamic acid structure in the negative electrode binder composition is not thermally imidized, preferably 100 to 300 ° C, and more preferably 150 to 200 ° C. The heating time is preferably 2 to 12 hours, and more preferably 4 to 8 hours.

In any step for forming the active material layer on the current collector using the negative electrode slurry, the process temperature preferably does not exceed 200 ° C, and more preferably does not exceed 180 ° C. Here, the process for forming the active material layer refers to the application process of the negative electrode slurry and the removal process of the dispersion medium from the coating film, the optionally performed pressing process, the heating process under reduced pressure, and the pressing process. About all of the steps that those skilled in the art perform to form the active material layer. The above process temperature refers to the temperature of the slurry for the negative electrode, the current collector or the active material layer itself, the temperature of the surrounding atmosphere surrounding them, and the temperature of the device or instrument in contact with or in proximity to them.
The negative electrode for an electricity storage device manufactured in this way is excellent in the adhesion between the current collector and the active material layer, and has good cycle characteristics, which is one of the electrical characteristics.

4). Electric storage device An electric storage device can be produced using the negative electrode for an electric storage device of the present invention as described above.
The electricity storage device includes the above-described negative electrode, further contains an electrolytic solution, and can be manufactured according to a conventional method using components such as a separator. As a specific manufacturing method, for example, the above-described negative electrode and a positive electrode as its counter electrode are overlapped via a separator, and this is wound or folded according to the battery shape and stored in a battery container, and the battery The method of inject | pouring electrolyte solution into a container and sealing can be mentioned. The shape of the battery can be an appropriate shape such as a coin shape, a cylindrical shape, a square shape, or a laminate shape.
The electrolyte solution may be liquid or gel, and an electrolyte that effectively expresses the function as a battery may be selected from the known electrolytes used for the electricity storage device according to the type of the active material.
The electrolytic solution can be a solution in which an electrolyte is dissolved in a suitable solvent.

As the electrolyte, for example, in the lithium ion secondary battery, any conventionally known lithium salt can be used, and specific examples thereof include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO _2. , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂₎ 2 _N, and the like can be exemplified lower aliphatic lithium carboxylate.
The solvent for dissolving the electrolyte is not particularly limited, and specific examples thereof include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. Compound;
Lactone compounds such as γ-butyl lactone;
Ether compounds such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Examples thereof include sulfoxide compounds such as dimethyl sulfoxide, and one or more selected from these can be used.
The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
The solution viscosity of the polymer solution, the content of (B) water in the binder composition, and the content of the (C) compound in the binder composition were measured as follows.
<Solution viscosity of polymer solution>
The solution viscosity of the polymer solution obtained in each synthesis example is a value measured at 25 ° C. using an E-type rotational viscometer.
<(B) Water content in binder composition>
The content of (B) water in the binder compositions prepared in the following examples and comparative examples was measured with a Karl Fischer moisture meter (manufactured by Mitsubishi Chemical Corporation, model number “CA-100 type”).
<Content of Compound (C) in Binder Composition>
The content of the compound (C) in the binder composition prepared in each of the following Examples and Comparative Examples was measured by liquid chromatography under the following conditions.
Measuring apparatus: HLC-8220 (manufactured by Tosoh Corporation)
Degasser: SD-8000
Detector: UV8020 (ultraviolet absorption detector)
Column: TSKGEL α-M and α-2500 (both manufactured by Tosoh Corporation) are used in series. Developing solution: dimethylformamide solution containing LiBr ₃₀ mmol / L and H ₃ PO ₄ 10 mmol / L Flow rate: 1 mL / min

<Synthesis of polymer>
Synthesis example 1
The interior of a 3 L flask equipped with a stirrer, a thermometer and a condenser was heated with a heat gun under reduced pressure to remove residual moisture inside the container, and then filled with dry nitrogen gas. Into this flask, 1,166 g of N-methyl-2-pyrrolidone (NMP) subjected to dehydration by a dehydration distillation method using calcium hydride as a solvent in advance, and 3,3 ′, 4, as tetracarboxylic dianhydride 80.556 g (250.0 mmol) of 4′-benzophenone tetracarboxylic dianhydride and 49.058 g (245.0 mmol) of 4,4′-diaminodiphenyl ether as diamine were charged and reacted at 25 ° C. with stirring for 3 hours. To obtain a polymer solution containing 10% by mass of polyamic acid P1.
The solution viscosity of this polymer solution was 7,200 mPa · s.

Synthesis Examples 2-6 and Comparative Synthesis Examples 1-3
10% by mass of polyamic acids P2-6 and R1-3, respectively, in the same manner as in Synthesis Example 1 except that tetracarboxylic dianhydride and diamine were used in the composition shown in Table 1 in Synthesis Example 1 above. A polymer solution was obtained. The solution viscosities of these polymer solutions are shown in Table 1.

Synthesis example 7
In the same manner as in Synthesis Example 1, a polymer solution containing 10% by mass of polyamic acid was obtained. To this polymer solution, 3.96 g of pyridine and 5.11 g of acetic anhydride were added, and an imidization reaction was performed with stirring at 110 ° C. for 4 hours.
The obtained reaction solution was put into methanol, and the produced precipitate was recovered and dried under reduced pressure to obtain an imidized polymer P7 of polyamic acid as a white solid. The obtained imidized polymer acid was dissolved in NMP so as to have a concentration of 10% by mass to obtain a polymer solution.
The solution viscosity of this polymer solution was 8,200 mPa · s, and the imidization ratio of the polymer P7 contained in the polymer solution was 20%.
The imidation rate is a ¹ H-NMR chart obtained by dissolving a polymer recovered by removing the solvent from the obtained polymer solution under reduced pressure in deuterated dimethyl sulfoxide and measuring tetramethylsilane as a reference material at room temperature. From the following formula (1).
Imidation ratio (%) = (1−A1 / A2 × α) × 100 (1)
(In Formula (1), A1 is a peak area derived from protons of NH groups appearing near a chemical shift of 10 ppm, A2 is a peak area derived from other protons, and α is a polyamic that is a precursor of an imidized polymer. (This is the ratio of the number of other protons to one proton of the NH group in the acid.)

Abbreviations of each component in Table 1 have the following meanings.
<Tetracarboxylic dianhydride>
BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride PMDA: 1,2,4,5-benzenetetracarboxylic dianhydride TDA: 4- (2,5-dioxotetrahydrofuran-3 -Yl) -1,2,3,4-tetrahydronaphthalene-1,2-carboxylic anhydride <diamine>
DDE: 4,4′-diaminodiphenyl ether DDP: 4,4′-diaminobiphenyl

<Synthesis of active material>
Synthesis Example 9
A mixture of pulverized silicon dioxide powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was placed in an electric furnace adjusted to a temperature in the range of 1,100 to 1,600 ° C. under a nitrogen stream (0 0.5 NL / min), heat treatment was performed for 10 hours to obtain a silicon oxide powder (average particle size 8 μm) represented by the composition formula SiOx (x = 0.5 to 1.1).
300 g of this silicon oxide powder was charged into a batch-type heating furnace, and the temperature was increased from room temperature (25 ° C.) to 1,100 ° C. at a temperature increase rate of 300 ° C./h while maintaining a reduced pressure of 100 Pa with a vacuum pump. Warm up. Next, while maintaining the pressure in the heating furnace at 2,000 Pa, heat treatment (graphite coating treatment) was performed at 1,100 ° C. for 5 hours while introducing methane gas at a flow rate of 0.5 NL / min. After the completion of the graphite coating treatment, the powder was cooled to room temperature at a temperature decrease rate of 50 ° C./h to obtain about 330 g of graphite-coated silicon oxide powder.
This graphite-coated silicon oxide is a conductive powder (active material) in which the surface of silicon oxide is coated with graphite, and the average particle diameter thereof is 10.5 μm. The ratio of the graphite coating in the case of mass% was 2 mass%.

Example 1
(1) Binder composition 100 g of the polymer solution containing the polyamic acid P1 obtained in Synthesis Example 1 as a polymer (containing 10 g of the polyamic acid P1) was used as the binder composition as it was.
The water content in the binder composition was measured by the above method, but no water was detected.

(2) Adhesion test of binder composition The binder composition prepared above was applied on a 10 cm square copper plate and a glass plate so that the film thickness after removal of the solvent would be 90 μm, and 15 ° C. at 15 ° C. By thinly heating, a thin film of a binder was formed on each of the copper plate and the glass plate.
The two types of binder thin films formed above were each subjected to a cross-cut peel test in accordance with JIS K5400.
Specifically, using a cutter, 11 cuts were made from the surface of the thin film to the depth reaching the copper plate or the glass plate at 1 mm intervals, both vertically and horizontally, and the thin film was divided into a grid-like area of 100 squares. An adhesive tape (manufactured by Terraoka Co., Ltd., product number “650S”) was applied to the entire surface of these 100 square areas and immediately peeled off, and the number of remaining squares was counted.
The evaluation results are shown in Table 1 as the number of remaining cells in 100 cells.
When the number of remaining cells is 80 or more, it can be determined that the adhesion is good, and when the number of cells remaining is less than 80, the adhesion can be determined as poor.
In addition, from the examination by the present inventors, it is empirically clear that the adhesion between the active material layer and the current collector is proportional to the adhesion between the copper plate and the polymer film in this test. It has become. Further, it has been empirically revealed that the binding property as a binder for binding active materials is proportional to the adhesion between the glass plate and the polymer film in this test. For this reason, when the adhesion between the glass plate and the polymer film is good, it can be estimated that the adhesion as a binder of the polymer binding the active materials is good,
When the adhesion between the Cu plate and the polymer film is good, it can be estimated that the adhesion between the current collector and the active material layer is good.
In this case, if the number of remaining squares is 80 or more, it can be determined that the adhesion is good,
If this number is 90 or more, it can be determined that the adhesion is excellent. The number of remaining cells is most preferably 100 out of 100 grids.

(3) Preparation of slurry for negative electrode Graphite (Hitachi Chemical Industry Co., Ltd.) having an average particle size of 22 μm as a negative electrode active material in a biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) 80 parts by mass (in terms of solid content), 20 parts by mass of graphite-coated silicon oxide prepared in Synthesis Example 8 above, and acetylene black (Electrochemical Industry Co., Ltd.) 1 part by mass was added and mixed at 20 rpm for 3 minutes. Next, 100 parts by mass and 20 parts by mass of NMP were added to the binder composition prepared above, and the mixture was stirred at 60 rpm for 1 hour.
Then, the slurry for negative electrodes was prepared by stirring and mixing for 5 minutes at 600 rpm under the pressure reduction of 25 kPa of absolute pressures using the stirring deaerator (made by Shinkey, brand name "ARV930-TWIN").

(4) Manufacture of negative electrode for electricity storage device On the surface of a current collector made of copper foil having a thickness of 10 μm, the slurry for negative electrode prepared in “(3) Preparation of slurry for negative electrode” is applied to the active material layer after solvent removal. The film thickness was adjusted so that the mass was 4.50 mg / cm ² , and the film was uniformly applied by a doctor blade method, followed by drying at 120 ° C. for 5 minutes to form a coating film. Subsequently, the above-mentioned coating film was subjected to a roll temperature adjustment at a roll temperature of 30 ° C., a linear pressure of 1 t / cm, and a feed rate of 0.5 m / min. And the density of the negative electrode layer was adjusted to 1.60 g / cm ³ . Furthermore, the negative electrode for electrical storage devices was obtained by heating at 160 degreeC under reduced pressure of 100 Pa of absolute pressures for 6 hours, and forming an active material layer.

(5) Manufacture of electricity storage device In a glove box substituted with argon so that the dew point is −80 ° C. or less, the anode manufactured in the above “(4) Production of anode for electricity storage device” was punched into a diameter of 15.5 mm. The product was placed on a bipolar coin cell (trade name “HS Flat Cell” manufactured by Hosen Co., Ltd.) with the active material layer facing upward. Next, a separator (made by Celgard Co., Ltd., trade name “Celgard # 2400”) made of a polypropylene porous film punched to a diameter of 24 mm is placed on the above negative electrode, and the electrolyte solution is placed so that air does not enter. After injection of 500 μL, a 200 μm-thick lithium foil punched and molded to a diameter of 16.6 mm is placed as a counter electrode (positive electrode), and the outer body of the bipolar coin cell is closed with a screw and sealed. A lithium ion battery cell (electric storage device) was assembled.
The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).
This operation was repeated to produce a total of three power storage devices. One of these is "(6) Evaluation of power storage device (Evaluation of charge / discharge cycle characteristics)", "(7) Evaluation of film thickness change rate of active material layer" and "(8) Active material after charging" Each was used for “evaluation of rate of change in thickness of layer”.

(6) Evaluation of electricity storage device (Evaluation of charge / discharge cycle characteristics)
About the electricity storage device manufactured in the above “(5) Production of electricity storage device”, charging is started at a constant current (0.2 C), and when the voltage reaches 0.01 V, the charge continues to the constant voltage (0.01 V). Then, the charging was continued and the time when the current value reached 0.05 C was regarded as the completion of charging (cut-off). Next, discharging was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the initial charge / discharge was completed.
Next, 0.5 C charge / discharge was performed as follows for the above-described electricity storage device that was charged and discharged for the first time.
First, charging starts at a constant current (0.5C), and when the voltage reaches 0.01V, charging continues at a constant voltage (0.01V), and when the current value reaches 0.05C. Was charged (cut off). Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the discharge capacity at 0.5 C (0.5 C discharge capacity in the first cycle) = A) was measured.
This charge / discharge of 0.5C was repeated, and when the 0.5C discharge capacity at the 100th cycle was B, the capacity retention rate after 100 cycles was calculated by the following mathematical formula (2).
Capacity maintenance rate (%) = B / A × 100 (2)
The evaluation results are shown in Table 1.
If the capacity retention rate after 100 cycles is 90% or more and less than 95%, it can be determined that the charge / discharge cycle characteristics are excellent, and if it is 95% or more, the charge / discharge cycle characteristics are extremely excellent. Can be determined.

(7) Evaluation of electricity storage device using negative electrode binder after storage 1,000 g of the negative electrode binder composition obtained in the above "(1) Preparation of binder composition" was filled in a polybin and set at 2 ° C. Stored in refrigerator for 1 month. Using this negative electrode binder composition after storage, an electricity storage device was produced in the same manner as in the above-mentioned “(5) Production of electricity storage device”. Evaluation ”of the electricity storage device after storage (evaluation of charge / discharge cycle characteristics) was performed in the same manner as in“ Evaluation) ”.

(8) Evaluation of rate of change in thickness of active material layer after charging For the electricity storage device obtained in “(5) Production of electricity storage device”, charging was started at a constant current (0.2 C), and the voltage was 0. When the voltage reached 0.01 V, charging was continued at a constant voltage (0.01 V), and charging was completed (cut off) when the current value reached 0.05C. Next, discharging was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the initial charge / discharge was completed.
Next, about the said electrical storage device which performed initial charge / discharge, charge starts with a constant current (0.2C), and when a voltage becomes 0.01V, it charges with a constant voltage (0.01V) continuously. Continuing, the time when the current value reached 0.05 C was defined as the completion of charging (cut-off).
The electricity storage device was disassembled in a dry room (room temperature 25 ° C.) having a dew point of −60 ° C. or less, and the anode for the electricity storage device was taken out. Subsequently, this negative electrode was immersed in dimethyl carbonate for 1 minute in a dry room and washed. After taking out the negative electrode from dimethyl carbonate, the dimethyl carbonate was vaporized and removed by standing in a dry room for 30 minutes.
The thickness of the active material layer of the negative electrode after charging was measured, and the ratio of the thickness of the active material layer of the negative electrode after charging to the thickness of the active material layer of the negative electrode immediately after production (uncharged state) measured in advance. Was calculated by the following mathematical formula (3).
Film thickness ratio after charge (%) = (film thickness after charge) / (film thickness immediately after manufacture) × 100 (3)
The evaluation results are shown in Table 2.
When this value exceeds 120%, the active material layer indicates that the volume expansion of the active material accompanying charging is not relaxed, and there is a concern that the active material may be peeled off when mechanical stress is applied to the active material. is there. On the other hand, if this value is 120% or less, it indicates that the active material is firmly held in the active material layer despite the volume expansion of the active material with charging, and the active material is peeled off. It can be evaluated that the electrode is a good electrode with suppressed.

Examples 2 and 3 and Comparative Examples 2 and 3
In Example 1 above, Example 1 was used except that a solution containing the polymer described in Table 2 was used as the binder composition, and the type and amount of active material used were as described in Table 2. The negative electrode slurry was prepared in the same manner as described above, and an electricity storage device was produced and evaluated.
The evaluation results are shown in Table 2.

Examples 4-7 and Comparative Example 1
In a glove box substituted with argon, 100 g of a polymer solution containing each of the polymers shown in Table 2 as a polymer (containing 10 g of each polymer) was added with water using a microsyringe. A binder composition was prepared by adding only the amount described in.
The results of measuring the water content in the binder composition by the above method are shown in Table 2 as values for 100 parts by mass of the binder composition.
The negative electrode slurry was prepared in the same manner as in Example 1 except that the binder composition prepared above was used and the active material was used in the composition ratio of the types and amounts described in Table 2. Went.
The evaluation results are shown in Table 2.

Examples 8-12 and Comparative Examples 4 and 5
In a glove box substituted with argon, 100 g of a polymer solution containing each of the polymers shown in Table 2 as a polymer (containing 10 g of each polymer) was added with water using a microsyringe. A binder composition was prepared in the same manner as in Examples 4 to 7 except that the amount and amount of the compound (C) described in Table 2 were added. However, in Comparative Example 4, water was not added.
The negative electrode slurry was prepared in the same manner as in Example 1 except that the binder composition prepared above was used and the active material was used in the composition ratio of the types and amounts described in Table 2. Went.
The evaluation results are shown in Table 2.

Abbreviations of each component in Table 2 have the following meanings.
<(C) component>
C1: acetic acid C2: maleic acid C3: citric acid C4-1: 3,3 ′, 4,4′-benzophenone tetracarboxylic acid C4-2: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride <Active material>
C / Si: Graphite-coated silicon oxide prepared in Synthesis Example 9 Graphite: manufactured by Hitachi Chemical Co., Ltd., product name “SMG-HE1”
In addition, “ND” in the table indicates that the binder composition was analyzed, but the detection target substance (water) was not detected.

Claims (7)

A binder composition for a lithium ion secondary battery negative electrode of an electricity storage device containing at least (A) a polymer , (B) water, and (D) a liquid medium,
The polyamic acid obtained by reacting the polymer (A) with tetracarboxylic dianhydride a mole and diamine b mole, wherein the ratio a / b is 1.01 or more and less than 1.05 and its imide of at least 1 Tanedea Risoshite above (a) Ma parts by mass content of the polymer is selected from polymers group consisting, when a Mb parts by the content of the (B) water, both The binder composition for a lithium ion secondary battery negative electrode, wherein the ratio Ma / Mb is 500 to 5,000 . Further (C) contains a compound having at least one carboxyl group, the lithium ion secondary battery negative electrode binder composition of claim 1. Ma parts by the content of the polymer (A), the content of the compound (C) is taken as Mc parts by weight, both ratios Ma / Mc is 50 to 400, according to claim 2 A binder composition for a negative electrode of a lithium ion secondary battery . The binder composition for a lithium ion secondary battery negative electrode according to any one of claims 1 to 3 ,
A negative electrode active material;
A slurry for a negative electrode of a lithium ion secondary battery of an electricity storage device, comprising : The slurry for a negative electrode of a lithium ion secondary battery according to claim 4 , wherein the negative electrode active material contains an active material containing a silicon atom. The slurry for lithium ion secondary battery negative electrodes of Claim 5 whose active material containing the said silicon atom is at least 1 sort (s) selected from the group which consists of a silicon simple substance, a silicon oxide, and a silicon alloy. A current collector,
An active material layer formed on the current collector;
A lithium ion secondary battery negative electrode of an electricity storage device comprising :
The active material layer, characterized in that it is one that is formed of a lithium-ion secondary battery negative electrode slurry according to any one of claims 4-6, wherein the electric storage device a lithium ion secondary battery negative electrode .