JP2012207196A - Binder resin composition for electrode, electrode compound paste, and electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder resin composition for an electrode, having good environmental adaptability by using an aqueous solvent, having excellent characteristics such as heat resistance, mechanical strength, electric characteristics and solvent resistance, as an aromatic polyimide obtained from the composition shows high crystallinity, and having a low swelling degree even in a battery environment and having excellent toughness.SOLUTION: The binder resin composition for an electrode is obtained by uniformly dissolving in an aqueous medium, a polyamic acid comprising a repeating unit expressed by chemical formula (1) together with imidazoles having two or more alkyl groups as substituents, the imidazoles in an amount as 0.8 times or more equivalent as carboxyl groups of the polyamic acid. In chemical formula (1), A represents a group derived from an aromatic tetracarboxylic acid; and B represents a group derived from an aromatic diamine.

Description

The present invention relates to a binder resin composition for electrodes of electrochemical devices such as lithium ion secondary batteries and electric double layer capacitors using the binder resin composition for electrodes.
This binder resin composition for electrodes is suitable because it has higher environmental adaptability than a polyimide precursor solution composition using an organic solvent. Moreover, the aromatic polyimide obtained by using this electrode binder resin composition has high crystallinity, and therefore has excellent characteristics such as heat resistance, mechanical strength, electrical characteristics, and solvent resistance. It can be suitably used as a binder resin composition for electrodes of electrochemical devices such as ion secondary batteries and electric double layer capacitors.

  Aromatic polyimides obtained from aromatic tetracarboxylic dianhydrides and aromatic diamines have excellent heat resistance, mechanical strength, electrical properties, solvent resistance, and other properties, so they are widely used in the electrical and electronics industries. ing. However, since aromatic polyimides have poor solubility in organic solvents, a solution composition in which a polyimide precursor polyamic acid is dissolved in an organic solvent is usually applied onto a substrate surface, and then heated at a high temperature. Thus, aromatic polyimide is obtained by dehydration ring closure (imidization). As described above, the use of an organic solvent and the heat treatment at a high temperature are necessary, so that it is not necessarily suitable in terms of the environment, and the use may be limited in some cases.

  For this reason, a water-soluble polyimide precursor has been proposed. For example, in Patent Document 1, a polyamic acid obtained in an organic solvent is hydrolyzed and then poured into water to obtain a polyamic acid powder, and the polyamic acid powder is further pulverized or washed in warm water. Later, it has been proposed to obtain a water-soluble polyamic acid salt by mixing with a specific amine compound such as 2-methylaminodiethanol. However, the polyimide precursor composition comprising this water-soluble polyamic acid salt is difficult to have a high molecular weight, and there is room for improvement in the properties of the resulting polyimide. Furthermore, the water-soluble polyimide precursor proposed here has been suitably used as a varnish for forming an insulating layer of an electronic device such as a multichip module, a thin film magnetic head, or a semiconductor device.

  Patent Document 2 discloses a water-soluble polyimide precursor obtained separately from a reaction mixture of a polyamic acid obtained in an organic solvent and 1,2-dimethylimidazole and / or 1-methyl-2-ethylimidazole. Has been proposed. However, this water-soluble polyimide precursor can be obtained by preparing a water-soluble polyimide precursor in an organic solvent and then separating it. The obtained water-soluble polyimide precursor is dissolved in an aqueous solvent to obtain an aqueous solution composition, but the organic solvent cannot be completely removed from the water-soluble polyimide precursor prepared in the organic solvent (heating to remove completely). When treated, imidization occurs and the solubility is lost), and there is a problem that an organic solvent is accompanied in the aqueous solution composition. Furthermore, the water-soluble polyimide precursor proposed here has a non-crystalline and heat-fusible polyimide, and is suitably used as a binder for woven or non-woven fabrics made of organic or inorganic fibers. Met.

  That is, in these documents, there is no description about manufacturing electrodes of electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors using the polyimide precursor water-soluble composition.

  On the other hand, Non-Patent Document 1 shows that the smaller the degree of swelling of the binder resin for electrodes with respect to the electrolytic solution, the higher the discharge capacity retention rate associated with the charge / discharge cycle, which is preferable.

  Further, in Non-Patent Document 2, the reductive decomposition reaction of the electrolytic solution in the lithium battery has been analyzed, and it has been confirmed that methoxylithium or the like is generated on the electrode surface. That is, in a battery environment, methoxylithium that is strongly alkaline and may adversely affect the binder resin is contained in the electrolytic solution.

JP-A-8-59832 JP 2002-226582 A

Hitachi Chemical Technical Report No. 45 (July 2005) Yoshiaki Hiroaki et al., Decomposition of carbonate ester mixed electrolyte for lithium batteries, 35th Battery Symposium Abstracts, Japan, Battery Association of Electrochemical Society, November 14, 1994, p. 75-76

  The object of the present invention is that environmental adaptability is good by using an aqueous solvent, and the aromatic polyimide obtained by using the solvent has high crystallinity, so that it has heat resistance, mechanical strength, and electrical characteristics. Binder resin composition for an electrode having excellent characteristics such as solvent resistance, low swelling under battery environment, and excellent toughness, preferably high molecular weight and containing no organic solvent other than water. Is to provide things.

  The present invention particularly relates to the following items.

1. A polyamic acid comprising a repeating unit represented by the following chemical formula (1) obtained by reacting a tetracarboxylic acid component and a diamine component is 1.6 times mol or more with respect to the tetracarboxylic acid component of the polyamic acid. A binder resin composition for electrodes, which is dissolved in an aqueous solvent together with imidazoles.

化学式（１）において、Ａは芳香族テトラカルボン酸からカルボキシル基を除いた４価の基であり、Ｂは２５℃の水に対する溶解度が０．１ｇ／Ｌ以上である芳香族ジアミンからアミノ基を除いた２価の基である。

In the chemical formula (1), A is a tetravalent group obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, and B is an amino group derived from an aromatic diamine having a solubility in water at 25 ° C. of 0.1 g / L or more. Excluded divalent groups.

2. 2. The binder resin composition for an electrode according to item 1, wherein A is any one of the following chemical formulas (2) to (7) or a mixture thereof.

3. Imidazoles having two or more alkyl groups as substituents are from 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole. Item 3. The binder resin composition for electrodes according to Item 1 or 2, which is an imidazole selected from the group consisting of:

4). The binder resin composition for an electrode according to any one of Items 1 to 3, wherein B in the chemical formula (1) is the following chemical formulas (8) to (9) or a mixture thereof.

5). Item 5. A binder resin composition for an electrode according to any one of Items 1 to 4, wherein the logarithmic viscosity is 0.2 or more.

6). Item 6. The binder resin composition for electrodes according to any one of Items 1 to 5, wherein the aqueous solvent does not contain an organic solvent other than water.

7). Item 7. The electrode according to any one of Items 1 to 6, wherein the binder resin obtained by heat treatment has a mass increase of 2.0% by mass or less when immersed in dimethyl carbonate at 25 ° C. for 24 hours. Binder resin composition.

8). The electrode mixture paste containing an electrode active material and the binder resin composition for electrodes according to any one of Items 1 to 7.

9. Item 9. The electrode mixture paste according to Item 8, wherein the electrode active material is carbon powder, silicon powder, tin powder, or an alloy powder containing silicon or tin.

10. 10. An electrode obtained by applying the electrode mixture paste according to Item 8 or 9 on a current collector, removing the solvent by heat treatment, and imidizing.

11. Item 11. The electrode according to Item 10, wherein the heat treatment temperature is 250 ° C. or lower.

12 Item 12. The electrode according to Item 10 or 11, wherein the electrode is a negative electrode for a lithium ion secondary battery.

  According to the present invention, the environmental adaptability is good by using an aqueous solvent, and the aromatic polyimide obtained by using the water solvent has high crystallinity, so that it has heat resistance, mechanical strength, electrical properties, resistance to resistance. A binder resin composition for an electrode having excellent properties such as solvent properties, low swelling under battery environment, and excellent toughness, preferably having a high molecular weight and containing no organic solvent other than water. Can be provided.

  The polyamic acid which comprises the binder resin composition for electrodes of this invention consists of a repeating unit represented by the said Chemical formula (1).

  A in the chemical formula (1) is a tetravalent group obtained by removing a carboxyl group from tetracarboxylic acid, and is preferably the chemical formulas (2) to (7) or a mixture thereof, more preferably the chemical formula (2). ) To (4) or a mixture thereof, particularly preferably the chemical formulas (2) to (3) or a mixture thereof. That is, the tetracarboxylic acid component of the polyamic acid used in the present invention is a tetracarboxylic acid (tetracarboxylic acid, dianhydride or esterified product thereof) having 2 to 3 aromatic rings, for example, 3, 3 ′, 4,4′-biphenyltetracarboxylic acids, 2,3,3 ′, 4′-biphenyltetracarboxylic acids, 2,2 ′, 3,3′-biphenyltetracarboxylic acids, 4,4′-oxydiphthalic acids 3,3 ′, 4,4′-benzophenone tetracarboxylic acids, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic acids, p-terphenyl tetracarboxylic acids, m-terphenyl tetracarboxylic acids, and the like, and A mixture thereof can be preferably exemplified. If a tetracarboxylic acid component other than these is used, it may be difficult to obtain a water-soluble polyimide precursor, or the crystallinity of the resulting polyimide may be reduced, and high characteristics may not be obtained.

B in the chemical formula (1) is a divalent group obtained by removing an amino group from an aromatic diamine, and preferably a divalent group obtained by removing an amino group from an aromatic diamine having 1 to 2 aromatic rings. The aromatic diamine has a solubility in water at 25 ° C. of 0.1 g / L or more. That is, the aromatic diamine component of the polyamic acid used in the present invention is a divalent group obtained by removing an amino group from an aromatic diamine, preferably an aromatic diamine having 1 to 2 aromatic rings, The aromatic diamine has a solubility in water at 25 ° C. of 0.1 g / L or more.
When the aromatic diamine has more than two aromatic rings, since the aromatic diamine molecule usually contains a plurality of highly flexible bonds, the aromatic polyimide obtained from such an aromatic diamine is crystalline. It becomes difficult to obtain high characteristics due to a decrease in properties.
Further, the solubility of the aromatic diamine in water at 25 ° C. is 0.1 g / L or more, which is a particularly necessary characteristic for obtaining a binder resin composition for electrodes, and the solubility in water is 0.1 g / L. If it is less than L, it is difficult to obtain a uniformly dissolved binder resin composition for electrodes, which is not preferable.

Examples of the aromatic diamine component used in the present invention include p-phenylenediamine (the solubility in water at 25 ° C. is 120 g / L, the same applies hereinafter), m-phenylenediamine (77 g / L), 4,4′-diaminodiphenyl ether (0 19 g / L), 3,4′-diaminodiphenyl ether (0.24 g / L), 4,4′-diaminodiphenylmethane (0.54 g / L), 2,4-toluenediamine (62 g / L), 3, Examples thereof include 3′-dihydroxy-4,4′-diaminobiphenyl (1.3 g / L) and bis (4-amino-3-carboxyphenyl) methane (200 g / L). These aromatic diamines can be suitably used alone or as a mixture. In addition, these aromatic diamines having high solubility in water and other aromatic diamines may be used in combination so that the total aromatic diamine component has a solubility in water at 25 ° C. of 0.1 g / L or more. it can.
Since these aromatic diamines have high water solubility and the resulting polyimide has high crystallinity and excellent characteristics, p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenyl ether, 3 4,4′-diaminodiphenyl ether and mixtures thereof are preferred, and p-phenylenediamine, 4,4′-diaminodiphenyl ether, and mixtures thereof are more preferred.
In addition, the solubility with respect to the water in 25 degreeC means the limit amount (g) which the said substance melt | dissolves in 1 L (liter) of water of 25 degreeC. This value can be easily searched by SciFinder (registered trademark) known as a search service based on a beta base such as a chemical abstract. Here, among the solubility under various conditions, the value at pH 7 calculated by Advanced Chemistry Development (ACD / Labs) Software V11.02 (Copyright 1994-2011 ACD / Labs) was adopted.

  As the imidazole (compound) having two or more alkyl groups as a substituent used in the present invention, a compound represented by the following chemical formula (7) is preferable.

化学式（７）において、Ｘ_１〜Ｘ_４は、それぞれ独立に、水素原子、或いは炭素数が１〜５のアルキル基であって、Ｘ_１〜Ｘ_４のうち少なくとも２個は炭素数が１〜５のアルキル基である。

In Chemical Formula (7), X _{1 to} X ₄ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and at least two of X _{1 to} X ₄ have _{1 to} C carbon atoms. 5 alkyl groups.

Since imidazoles having two or more alkyl groups as substituents are highly soluble in water, a polyimide precursor composition can be easily produced by using them. As these imidazoles, 1,2-dimethylimidazole (solubility in water at 25 ° C. is 239 g / L, hereinafter the same), 2-ethyl-4-methylimidazole (1000 g / L), 4-ethyl-2-methyl Imidazole (1000 g / L), 1-methyl-4-ethylimidazole (54 g / L), and the like are preferable.
In addition, the solubility with respect to the water in 25 degreeC means the limit amount (g) which the said substance melt | dissolves in 1 L (liter) of water of 25 degreeC. This value can be easily searched by SciFinder (registered trademark) known as a search service based on a beta base such as a chemical abstract. Here, among the solubility under various conditions, the value at pH 7 calculated by Advanced Chemistry Development (ACD / Labs) Software V11.02 (Copyright 1994-2011 ACD / Labs) was adopted.

The amount of the imidazole having two or more alkyl groups as a substituent used in the present invention is 0.8 times equivalent or more, preferably 1.0 times equivalent or more, more preferably 1 with respect to the carboxyl group of the polyamic acid. It is preferable that it is 2 times equivalent or more. If the amount of imidazole used is less than 0.8 equivalent to the carboxyl group of the polyamic acid, it is difficult to obtain a uniformly dissolved binder resin composition for an electrode, which is not preferable. Moreover, although the upper limit of the usage-amount of imidazoles is not specifically limited, Usually, it is less than 10 times equivalent, Preferably it is less than 5 times equivalent, More preferably, it is less than 3 times equivalent. If the amount of imidazole used is too large, it may be uneconomical and the storage stability of the composition may be deteriorated.
In the present invention, the double equivalent to the carboxyl group of the polyamic acid that defines the amount of imidazoles is the number (number of molecules) of imidazoles in one carboxyl group that forms the amic acid group of the polyamic acid. Indicates whether to use. The number of carboxyl groups forming the amic acid group of the polyamic acid is calculated on the assumption that two carboxyl groups are formed per molecule of the starting tetracarboxylic acid component.

  The characteristics of imidazoles used in the present invention are not only to increase the solubility in water by forming a salt with a carboxyl group of polyamic acid, but also when imidizing (dehydrating cyclization) the polyimide precursor into a polyimide, It has an extremely high catalytic action. As a result, when the binder resin composition for electrodes of the present invention is used, it is possible to easily obtain an aromatic polyimide having extremely high physical properties, for example, even by a heat treatment at a lower temperature for a shorter time.

The electrode binder resin composition of the present invention conforms to the methods of Patent Documents 1 and 2,
(i) Polyamic acid obtained by reacting a tetracarboxylic acid component with a diamine component using an organic solvent as a reaction solvent is poured into water to obtain a polyamic acid powder, and the polyamic acid powder is imidazoles in an aqueous solvent. (Preferably a method of obtaining an aqueous solution composition by mixing and dissolving together with imidazoles having two or more alkyl groups),
(ii) A water-soluble polyimide precursor is obtained by reacting a tetracarboxylic acid component and a diamine component in the presence of imidazoles (preferably imidazoles having two or more alkyl groups) using an organic solvent as a reaction solvent, A method of dissolving it in an aqueous solvent after separating it, or
(iii) A polyamic acid is obtained by reacting a tetracarboxylic acid component and a diamine component using an organic solvent as a reaction solvent, and the polyamic acid is converted into an imidazole (preferably two or more alkyl groups) using the organic solvent as a reaction solvent. It can also be obtained by a method in which a water-soluble polyimide precursor is obtained by reacting with an imidazole having a solvent, and is separated and then dissolved in an aqueous solvent. However, as described above, it is not preferable to prepare the polyimide precursor in an organic solvent in order to obtain a polyimide precursor aqueous solution composition having an extremely small organic solvent content and further not containing an organic solvent.

  The binder resin composition for electrodes of the present invention preferably reacts a tetracarboxylic acid component with an aromatic diamine component in the presence of imidazoles having two or more alkyl groups as substituents using water as a reaction solvent. By doing so, it is possible to manufacture very simply (directly).

This reaction is carried out at a relatively low temperature of 100 ° C. or less, preferably 80 ° C. or less in order to suppress the imidization reaction, using approximately equimolar amounts of a tetracarboxylic acid component and an aromatic diamine component. Although not limited, the normal reaction temperature is 25 ° C to 100 ° C, preferably 40 ° C to 80 ° C, more preferably 50 ° C to 80 ° C, and the reaction time is about 0.1 to 24 hours, preferably Is preferably about 2 to 12 hours. By setting the reaction temperature and the reaction time within the above ranges, a high-molecular-weight electrode binder resin composition can be easily obtained with high production efficiency. The reaction may be performed in an air atmosphere, but is usually suitably performed in an inert gas atmosphere, preferably a nitrogen gas atmosphere.
Further, the substantially equimolar amount of the tetracarboxylic acid component and the aromatic diamine component specifically refers to a molar ratio [tetracarboxylic acid component / diamine component] of about 0.90 to 1.10, preferably 0.95 to 1. .05 or so.

  In the binder resin composition for electrodes of the present invention, logarithmic viscosity measured at a temperature of 30 ° C. and a concentration of 0.5 g / 100 mL (dissolved in water) based on the solid content concentration resulting from the polyimide precursor (substantially polyamic acid). Is 0.2 or more, preferably 0.4 or more, more preferably 0.6 or more, still more preferably 0.8 or more, and particularly preferably 1.0 or more, or a high molecular weight. When the logarithmic viscosity is lower than the above range, the molecular weight of the polyimide precursor is low, so that it is difficult to obtain a high-quality aromatic polyimide even if the binder resin composition for electrodes of the present invention is used. There is.

  “Water as a reaction solvent” means that water is used as a main component of the solvent. Therefore, the binder resin composition for an electrode of the present invention uses an aqueous solvent, but a known organic solvent used when preparing a polyamic acid other than water is 50% by mass or less, preferably 30% by mass or less in the total solvent. More preferably, you may use in the ratio of 10 mass% or less. The organic solvent mentioned here does not include tetracarboxylic acid components such as tetracarboxylic dianhydride, diamine components, polyimide precursors such as polyamic acid, and imidazoles.

  Examples of the organic solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl- 2-imidazolidinone, N-methylcaprolactam, hexamethylphosphorotriamide, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, tetrahydrofuran, bis [ 2- (2-methoxyethoxy) ethyl] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethyl urea, anisole, m-cresol, phenol, γ-butyrolactone, and the like. .

  In the manufacturing method of the polyimide precursor aqueous solution composition of the present invention, since the environmental adaptability is high, the reaction solvent is preferably a solvent having an organic solvent content of less than 5%, and an organic solvent other than water is used. It is particularly preferable that the aqueous solvent does not contain. The composition of the reaction solvent can be appropriately selected according to the desired solvent composition of the polyimide precursor aqueous solution composition to be produced, and may be preferably the same as the desired solvent composition of the polyimide precursor aqueous solution composition. .

The binder resin composition for electrodes of the present invention is not limited in the solid content concentration due to the polyimide precursor (substantially polyamic acid), but is preferably 5 mass with respect to the total amount of the polyimide precursor and the solvent. % To 45% by mass, more preferably 7% to 40% by mass, and further preferably more than 10% by mass to 30% by mass. If the solid content concentration is lower than 5% by mass, the productivity may be remarkably deteriorated, and if it is higher than 45% by mass, the fluidity of the solution may be lost. The solution viscosity at 30 ° C. of the binder resin composition for electrodes of the present invention is not limited, but is preferably 1000 Pa · sec or less, more preferably 0.5 to 500 Pa · sec, still more preferably 1 to 300 Pa · sec, particularly The handling is preferably 3 to 200 Pa · sec.
If the solution viscosity exceeds 1000 Pa · sec, the fluidity is lost, so that uniform application to a current collector foil or the like becomes difficult, and if it is lower than 0.5 Pa · sec, it may cause dripping during application to the current collector foil or the like. Since cissing and the like occur, it is not preferable, and it may be difficult to obtain an aromatic polyimide having high characteristics.

In the electrode binder resin composition of the present invention, an aromatic polyimide can be suitably obtained by removing an aqueous solvent by heat treatment and imidizing (dehydrating ring closure). The heat treatment conditions are not particularly limited, but are generally 100 ° C. or higher, preferably 120 ° C. to 600 ° C., more preferably 150 ° C. to 500 ° C., 0.01 hours to 30 hours, preferably 0.01 to 10 hours. is there.
The characteristics of the aromatic polyimide obtained using the binder resin composition for an electrode of the present invention are as follows. The organic polyimide can be obtained by merely heat-treating at a relatively low temperature (for example, 150 to 300 ° C., preferably 200 to 280 ° C.) Compared to the binder resin composition for electrodes using a solvent, it is possible to exhibit excellent characteristics such as high adhesiveness to metal, for example.

  The electrode binder resin composition of the present invention has a mass increase of preferably 3% by weight or less when the polyimide resin obtained by the above heat treatment is immersed in dimethyl carbonate at 25 ° C. for 24 hours. Since it is preferably 2% by mass or less, more preferably 1% by mass or less, it can be suitably used as a binder resin composition for batteries.

  Dimethyl carbonate is a compound that is frequently used as a battery electrolyte component, and methoxy lithium is often produced in a battery environment. Further, the increase in the mass of the binder resin (swelling ratio when immersed at 25 ° C. for 24 hours) due to swelling with the electrolytic solution in the electrolytic solution is 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. If it exists, the influence of the volume change of an electrode can be suppressed suitably. The polyimide resin obtained from the binder resin composition for an electrode of the present invention preferably has a mass increase (swelling ratio when immersed for 24 hours at 25 ° C.) in an electrolytic solution containing methoxy lithium, more preferably 5% by mass or less. Is 3% by mass or less, particularly preferably 2% by mass or less.

  Although at least an electrode active material is not limited to the binder resin composition for electrodes of this invention, Preferably it mixes in the temperature range of 10 to 60 degreeC, and prepares an electrode mixture paste suitably. Can do. Known electrode active materials can be preferably used, but lithium-containing metal composite oxides, carbon powders, silicon powders, tin powders, or alloy powders containing silicon or tin are preferable. The amount of the electrode active material in the electrode mixture paste is not particularly limited, but is usually 0.1 to 1000 times, preferably 1 to 1000 times, on a mass basis with respect to the solid mass due to the polyamic acid. Preferably it is 5-1000 times, More preferably, it is 10-1000 times. When the amount of the active material is too small, an inactive portion is increased in the active material layer formed on the current collector, and the function as an electrode may be insufficient. On the other hand, when the amount of the active material is too large, the active material is not sufficiently bound to the current collector and easily falls off. In the electrode mixture paste, additives such as a surfactant, a viscosity modifier and a conductive additive can be added as necessary. Moreover, it is preferable to mix so that the solid content resulting from a polyamic acid may be 1-15 mass% in the total solid content of a paste. Outside this range, the electrode performance may deteriorate.

An electrode mixture paste obtained by using an electrode active material such as a lithium-containing metal composite oxide capable of reversibly inserting and releasing lithium ions by charging and discharging is cast on a conductive current collector such as aluminum. Alternatively, the electrode can be obtained by coating and removing the solvent by heat treatment at a temperature range of 80 to 400 ° C., more preferably 120 to 380 ° C., particularly preferably 150 to 350 ° C., and imidization reaction. .
When the heat treatment temperature is outside the above range, the imidization reaction may not proceed sufficiently or the physical properties of the electrode molded body may be deteriorated. The heat treatment may be performed in multiple stages to prevent foaming or powdering. The heat treatment time is preferably in the range of 3 minutes to 48 hours. 48 hours or longer is not preferable from the viewpoint of productivity, and if it is shorter than 3 minutes, imidation reaction or solvent removal may be insufficient, which is not preferable.
The obtained electrode can be particularly suitably used as a positive electrode of a lithium ion secondary battery.

Further, an electrode mixture paste obtained by using an electrode active material such as carbon powder, silicon powder, tin powder, or an alloy powder containing silicon or tin capable of reversibly inserting and releasing lithium ions by charging and discharging, When cast or coated on a conductive current collector such as copper, the solvent is removed by heat treatment at a temperature of 80 to 300 ° C., more preferably 120 to 280 ° C., particularly preferably 150 to 250 ° C. An electrode can be obtained by imidization reaction together. When the heat treatment temperature is lower than 80 ° C., the imidization reaction does not proceed sufficiently and the physical properties of the electrode molded body may be lowered. If heat treatment is performed at a temperature higher than 300 ° C., copper may be deformed and cannot be used as an electrode. Also in this case, the heat treatment may be performed in multiple stages in order to prevent foaming and powdering. The heat treatment time is preferably in the range of 3 minutes to 48 hours. 48 hours or longer is not preferable from the viewpoint of productivity, and if it is shorter than 3 minutes, imidation reaction or solvent removal may be insufficient, which is not preferable.
The obtained electrode can be particularly suitably used as a negative electrode of a lithium ion secondary battery.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples.

A method for measuring the characteristics used in the following examples is shown below.
<Concentration of solid content>
The sample solution (whose mass is designated as w1) is heat-treated in a hot air dryer at 120 ° C. for 10 minutes, 250 ° C. for 10 minutes, and then at 350 ° C. for 30 minutes. Measure). Solid content concentration [mass%] was computed by the following formula.
Solid content concentration [% by mass] = (w2 / w1) × 100

<Logarithmic viscosity>
The sample solution was diluted to a concentration of 0.5 g / dl (solvent is water) based on the solid content concentration. This diluted solution was added to Cannon Fenceke No. The flow-down time (T ₁ ) was measured using 100. The logarithmic viscosity was calculated from the following equation using the flow time (T ₀ ) of blank water.
Logarithmic viscosity = {ln (T ₁ / T ₀ )} / 0.5

<Solution viscosity (rotational viscosity)>
It measured at 30 degreeC using the Tokimec E-type viscosity meter.

<Preparation of polyimide film sample>
The obtained binder resin composition for an electrode was applied on a glass plate of a substrate by a bar coater, and the coating film was defoamed and pre-dried at 25 ° C. under reduced pressure for 30 minutes, and then heated under normal pressure under hot air. It put into the drier and heat-processed at 80 degreeC for 30 minutes, 120 degreeC for 30 minutes, 200 degreeC for 10 minutes, and then 250 degreeC for 10 minutes, and formed the 25-micrometer-thick polyimide film. Properties were evaluated using this polyimide film.

<Mechanical properties (tensile test)>
Using a tensile tester (Orientec RTC-1225A), a tensile test was performed in accordance with ASTM D882 to determine the tensile modulus, tensile break elongation, and tensile break strength.

<Swelling test>
A sample obtained by cutting a polyimide film obtained from the binder resin composition for electrodes into 5 cm square (thickness: 25 μm) was used as a sample. The mass after vacuum drying at 60 ° C. for 24 hours is defined as the dry mass (Wd), and the mass after being immersed in a DMC solution or 10% by mass methanol solution of methoxy lithium at 25 ° C. for 24 hours is defined as the swelling mass (Ww). The swelling ratio S was calculated by the following formula.
S [mass%] = (Ww−Wd) / Ww × 100

<Glass transition temperature measurement>
TA Instruments Co., Ltd. solid viscoelasticity analyzer RSAIII (compression mode dynamic measurement, frequency 62.8 rad / sec (10 Hz), strain amount set to 3% of sample height), −140 Measure from 30 ° C to 450 ° C at a temperature step of 3 ° C, measure 30 seconds after reaching each temperature, raise the temperature to the next temperature and repeat the measurement to obtain the maximum point of loss elastic modulus (E ''), The temperature was determined as the glass transition point (Tg).

The abbreviations of the compounds used in the following examples are described.
s-BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride ODPA: 4,4′-oxydiphthalic dianhydride PMDA: pyromellitic dianhydride a-BPDA: 2,3 ′ 3,4′-biphenyltetracarboxylic dianhydride PPD: p-phenylenediamine (solubility in water at 25 ° C .: 120 g / L, the same applies hereinafter)
ODA: 4,4′-diaminodiphenyl ether (0.19 g / L)
MPD: m-phenylenediamine (77 g / L)
BAPP: 2,2-bis [4- (4-aminophenoxy) phenyl] propane (0.000019 g / L)
TPE-R: 1,3-bis (4-aminophenoxy) benzene (0.0018 g / L)
1,2-DMZ: 1,2-dimethylimidazole 2E4MZ: 2-ethyl-4-methylimidazole 2MZ: 2-methylimidazole DBU: 1,8-diazabicyclo [5,4,0] undec-7- En NMP: N-methyl-2-pyrrolidone

[Example 1]
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 1,2-DMZ were added thereto. Of 29.87 g (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 36.56 g (0.124 mol) of s-BPDA was added and stirred at 25 ° C. for 12 hours. The solid content concentration was 9.0% by mass, the solution viscosity was 16.3 Pa · s, and the logarithmic viscosity was 0.95. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Also, 8.89 g of the obtained binder resin composition for electrodes (solid content mass after imidization) and 9.2 g of 300 mesh silicon powder were kneaded so as to be ground in a mortar, and an electrode mixture paste Was prepared. The obtained paste could be thinly spread on the copper foil with a glass rod. The copper foil coated with the paste is fixed on the substrate and heated in a nitrogen atmosphere at 120 ° C. for 1 hour, 200 ° C. for 10 minutes, 220 ° C. for 10 minutes, and 250 ° C. for 10 minutes. An electrode having a thickness of 100 μm could be suitably produced.

[Example 2]
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 1,2-DMZ were added thereto. Of 29.87 g (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 36.56 g (0.124 mol) of s-BPDA was added to this solution, and the mixture was stirred at 50 ° C. for 8 hours. The solid content concentration was 9.1% by mass, the solution viscosity was 35.5 Pa · s, and the logarithmic viscosity was 1.25. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 3
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 1,2-DMZ were added thereto. Of 29.87 g (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 36.56 g (0.124 mol) of s-BPDA was added and stirred at 70 ° C. for 4 hours. The solid content concentration was 9.1% by mass, the solution viscosity was 63.0 Pa · s, and the logarithmic viscosity was 1.86. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 4
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 34.23 g of 2E4MZ were added thereto. (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 36.56 g (0.124 mol) of s-BPDA was added and stirred at 70 ° C. for 4 hours to obtain a solid content concentration of 9.6% by mass, a solution viscosity of 10.3 Pa · s, and a logarithmic viscosity of 0.64. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 5
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas introduction / discharge tube, and 10.97 g (0.055 mol) of ODA and 5.92 g of PPD ( 0.055 mol) and 20.43 g of 1,2-DMZ (1.25 times equivalent to the carboxyl group) were added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 16.12 g (0.055 mol) of s-BPDA and 16.99 g (0.055 mol) of ODPA were added and stirred at 70 ° C. for 4 hours to obtain a solid content concentration of 9.1% by mass. An aqueous binder resin composition composition for an electrode having a viscosity of 6.5 Pa · s and a logarithmic viscosity of 0.50 was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 6
450 g of water was added as a solvent to a glass reaction vessel having an internal volume of 500 mL equipped with a stirrer and a nitrogen gas introduction / discharge tube, and 14.86 g (0.074 mol) of ODA and 3.44 g of PPD ( 0.032 mol) and 20.43 g of 1,2-DMZ (1.25 times equivalent to carboxyl group) were added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 21.83 g (0.074 mol) of s-BPDA and 9.87 g (0.032 mol) of ODPA were added and stirred at 70 ° C. for 4 hours to obtain a solid content of 9.0% by mass. An aqueous binder resin composition composition for an electrode having a viscosity of 5.2 Pa · s and a logarithmic viscosity of 0.46 was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 7
450 g of water as a solvent was added to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 20.25 g (0.101 mol) of ODA and 1,2-DMZ were added thereto. Of 24.31 g (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 29.75 g (0.101 mol) of s-BPDA was added and stirred at 70 ° C. for 4 hours. The solid content concentration was 8.7% by mass, the solution viscosity was 32.0 Pa · s, and the logarithmic viscosity was 0.42. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

Example 8
450 g of water as a solvent was added to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of MPD and 1,2-DMZ were added thereto. Of 29.87 g (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 36.56 g (0.124 mol) of s-BPDA was added and stirred at 70 ° C. for 4 hours. The solid content concentration was 8.9% by mass, the solution viscosity was 13.5 Pa · s, and the logarithmic viscosity was 0.75. An electrode binder resin composition aqueous solution was obtained.
The properties of the obtained binder resin composition for electrodes and binder polyimide for electrodes are shown in Table 1.

  Moreover, the obtained binder resin composition for electrodes was treated in the same manner as in Example 1 to suitably prepare electrodes.

[Comparative Example 1]
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 1,2-DMZ were added thereto. Of 17.92 g (0.75 equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 36.56 g (0.124 mol) of s-BPDA was added to this solution and stirred for 4 hours at 70 ° C., but it did not dissolve uniformly, and an aqueous binder resin composition solution for electrodes could not be obtained. .
The results are shown in Table 2.

[Comparative Example 2]
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas introduction / discharge tube, and 13.44 g (0.124 mol) of PPD and 25.50 g of 2MZ were added thereto. (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 36.56 g (0.124 mol) of s-BPDA was added to this solution and stirred for 4 hours at 70 ° C., but it did not dissolve uniformly, and an aqueous binder resin composition solution for electrodes could not be obtained. .
The results are shown in Table 2.

[Comparative Example 3]
450 g of water as a solvent was added to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 13.44 g (0.124 mol) of PPD and 47.29 g of DBU were added thereto. (1.25 times equivalent to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 36.56 g (0.124 mol) of s-BPDA was added to this solution and stirred for 4 hours at 70 ° C., but it did not dissolve uniformly, and an aqueous binder resin composition solution for electrodes could not be obtained. .
The results are shown in Table 2.

[Comparative Example 4]
450 g of water as a solvent was added to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 29.13 g (0.071 mol) of BAPP and 1,2-DMZ were added thereto. Of 17.05 g (1.25 equivalents relative to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 20.87 g (0.071 mol) of s-BPDA was added to this solution and stirred at 70 ° C. for 4 hours, but it did not dissolve uniformly and an electrode binder resin composition aqueous solution could not be obtained. .
The results are shown in Table 2.

[Comparative Example 5]
450 g of water was added as a solvent to a glass reaction vessel having an internal volume of 500 mL equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 24.92 g (0.085 mol) of TPE-R was added to the reaction vessel. -20.49 g of DMZ (1.25 equivalents relative to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. 25.08 g (0.085 mol) of a-BPDA was added to this solution and stirred for 4 hours at 70 ° C., but it did not dissolve uniformly, and an aqueous binder resin composition solution for electrodes could not be obtained. .
The results are shown in Table 2.

[Comparative Example 6]
450 g of water as a solvent was added to a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, and 23.93 g (0.120 mol) of ODA and 1,2-DMZ were added thereto. Of 28.73 g (1.25 equivalents relative to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 26.07 g (0.120 mol) of PMDA was added and stirred at 70 ° C. for 4 hours. However, the solution did not dissolve uniformly, and an electrode binder resin composition aqueous solution could not be obtained.
The results are shown in Table 2.

[Comparative Example 7]
To a 500 mL glass reaction vessel equipped with a stirrer and a nitrogen gas inlet / outlet tube, 450 g of water was added as a solvent, and 24.26 g (0.083 mol) of TPE-R and 2E4MZ 22 .86 g (1.25 equivalents relative to the carboxyl group) was added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 25.74 g (0.083 mol) of ODPA was added and stirred at 70 ° C. for 4 hours. However, the solution was not uniformly dissolved, and water solubility of the polyimide precursor could not be obtained.
The results are shown in Table 2.

[Comparative Example 8]
450 g of water was added as a solvent to a 500 mL glass reaction vessel equipped with a stirrer and nitrogen gas inlet / outlet tube, and 8.94 g (0.083 mol) of PPD and 11.03 g of ODA were added thereto. (0.055 mol) and 33.10 g of 1,2-DMZ (1.25 equivalents relative to the carboxyl group) were added and stirred at 25 ° C. for 1 hour to dissolve. To this solution, 30.03 g (0.138 mol) of PMDA was added and stirred at 70 ° C. for 4 hours. However, the solution did not dissolve uniformly, and an electrode binder resin composition aqueous solution could not be obtained.
The results are shown in Table 2.

  According to the present invention, the environmental adaptability is good by using an aqueous solvent, and the aromatic polyimide obtained by using the water solvent has high crystallinity, so that it has heat resistance, mechanical strength, electrical properties, resistance to resistance. A binder resin composition for an electrode having excellent properties such as solvent properties, low swelling under battery environment, and excellent toughness, preferably having a high molecular weight and containing no organic solvent other than water. Can be provided.

Claims (12)

A polyamic acid comprising a repeating unit represented by the following chemical formula (1) obtained by reacting a tetracarboxylic acid component and a diamine component is 1.6 times mol or more with respect to the tetracarboxylic acid component of the polyamic acid. A binder resin composition for electrodes, which is dissolved in an aqueous solvent together with imidazoles.

In the chemical formula (1), A is a tetravalent group obtained by removing a carboxyl group from an aromatic tetracarboxylic acid, and B is an amino group derived from an aromatic diamine having a solubility in water at 25 ° C. of 0.1 g / L or more. Excluded divalent groups. The binder resin composition for electrodes according to claim 1, wherein A is any one of the following chemical formulas (2) to (7) or a mixture thereof.

  Imidazoles having two or more alkyl groups as substituents are from 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole. The binder resin composition for an electrode according to claim 1, wherein the binder resin composition is an imidazole selected from the group consisting of: B of chemical formula (1) is following chemical formula (8)-(9) or those mixtures, The binder resin composition for electrodes in any one of Claims 1-3 characterized by the above-mentioned.

  The binder resin composition for electrodes according to any one of claims 1 to 4, wherein the logarithmic viscosity is 0.2 or more.   The binder resin composition for an electrode according to any one of claims 1 to 5, wherein the aqueous solvent does not contain an organic solvent other than water.   The electrode according to any one of claims 1 to 6, wherein the binder resin obtained by the heat treatment has a mass increase of 2.0% by mass or less when immersed in dimethyl carbonate at 25 ° C for 24 hours. Binder resin composition.   The electrode mixture paste containing an electrode active material and the binder resin composition for electrodes in any one of Claims 1-7.   The electrode mixture paste according to claim 8, wherein the electrode active material is carbon powder, silicon powder, tin powder, or an alloy powder containing silicon or tin.   An electrode obtained by applying the electrode mixture paste according to claim 8 or 9 on a current collector, removing the solvent by heat treatment, and imidizing.   The electrode according to claim 10, wherein the heat treatment temperature is 250 ° C or lower.   The electrode according to claim 10, wherein the electrode is a negative electrode for a lithium ion secondary battery.