JP2015005391A - Binder resin composition used in manufacturing lithium ion secondary battery, electrode mixed material paste, manufacturing method thereof, lithium ion secondary battery electrode, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder resin composition and others for obtaining a lithium ion secondary battery sufficiently reduced in battery internal resistance and having good cycle characteristics.SOLUTION: A binder resin composition for a lithium ion secondary battery comprises: a polyamide acid including a diamine compound and a tetracarboxylic dianhydride; and at least one monoalkali metal salt selected from a group consisting of a lithium salt, a sodium salt and a potassium salt. The tetracarboxylic dianhydride includes 3,3',4,4'-biphenyl tetracarboxylic dianhydride or 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The binder resin composition for a lithium ion secondary battery includes 4-20 mol% of the monoalkali metal salt to 100 mol% of the tetracarboxylic dianhydride.

Description

  The present invention relates to a binder resin composition, an electrode mixture paste, and a method for producing the same, which are used for producing a lithium ion secondary battery. The present invention also relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery.

In recent years, electronic devices have been reduced in size and weight, and a secondary battery with high energy density is desired as a power source. A secondary battery uses chemical energy generated by a chemical reaction between a positive electrode active material and a negative electrode active material via an electrolyte as electrical energy.
Among such secondary batteries, lithium ion secondary batteries have been put into practical use as those having a high energy density. A lithium-containing metal composite oxide such as lithium cobalt composite oxide is mainly used as a positive electrode active material of a lithium ion secondary battery, and a carbon material is mainly used as a negative electrode active material.

In the lithium ion secondary battery or other secondary batteries, as a binder for fixing the active material to the current collector, polyvinylidene fluoride (hereinafter abbreviated as “PVdF”) or styrene butadiene rubber (hereinafter referred to as “SBR”). Abbreviated).
In recent years, the development of next-generation negative electrode active materials having charge / discharge capacities that greatly exceed the theoretical capacity of carbon materials has been promoted as negative electrode active materials for lithium ion secondary batteries. In particular, negative electrode active materials using silicon atoms, tin atoms, and the like are expected to be put to practical use because they have a large charge / discharge capacity. However, silicon and tin atoms have a very large volume change accompanying the insertion and extraction of lithium ions, and repeat expansion and contraction with charge / discharge cycles. Therefore, when these are used as a negative electrode active material and conventional PVdF, SBR, or the like is used as a binder, there is a disadvantage that the active material particles are pulverized or detached from the binder, so that cycle deterioration is likely to occur. In addition, when charging / discharging in a short time, heat is generated due to rapid movement of ions, so that the binder is required to have heat resistance. Therefore, an electrode using polyimide, which is excellent in mechanical strength and heat resistance, as a binder has been proposed (Patent Documents 1-6).
However, since the polyimide binder covers the active material surface more widely than conventional binders such as PVdF and SBR, there is a problem that the internal resistance of the battery increases and the cycle characteristics deteriorate.

JP 2011-40326 A JP 2010-238562 A JP 2011-86480 A International Publication No. 2010/150513 International Publication No. 2011/040308 JP 2011-142068 A JP 2008-251223 A JP-A-8-203499 Japanese Patent No. 5099394

  In Patent Document 7, it has been proposed to introduce a compound having a carboxyl group into the negative electrode in order to reduce the internal resistance of the battery. As a specific example thereof, a salt of polyamic acid which is a precursor of polyimide is proposed. Compounds are mentioned. However, the conductive composition of Patent Document 7 uses a carbon material as a negative electrode active material, and does not correspond to the next generation negative electrode active material. Further, when the polyamic acid is neutralized with a base, the swelling resistance to the electrolytic solution is lowered, so that the binding property to the active material and the current collector foil is lowered, and conversely, the cycle characteristics are lowered.

  In Patent Document 8, when used as a mixture of electrodes, an alkali metal salt of an organic polymer compound having a carboxyl group for suppressing peeling between the electrode and the aggregate, conductive carbon particles, , And a conductive composition containing the same is disclosed. However, the conductive composition of Patent Document 8 uses a carbon material as the negative electrode active material, as in Patent Document 7, and does not correspond to the next generation negative electrode active material. In addition, the alkali metal salt of the organic polymer compound has a low degree of carboxylic acid neutralization, so that the swelling resistance to the electrolytic solution is reduced, so that the binding property with the active material and the current collector foil is reduced, and the cycle characteristics However, in Patent Document 8, there is no provision regarding the degree of neutralization of carboxylic acid.

  Further, Patent Document 9 discloses a binder composition for an electrode of an electricity storage device that has a large charge / discharge capacity and a small degree of capacity deterioration due to repeated charge / discharge cycles. As a specific example, a composition containing (A) an imidized polymer, (B) water, (C) a compound having a plurality of carboxy groups, and an anhydride thereof is disclosed. It is also disclosed that the compound (C) may be used in the form of a salt. According to such a composition, (A) by containing water (B) in a specific ratio with respect to the imidized polymer, the adhesion with the electrode active material is improved, and the electric characteristics of the obtained electrode layer are good. It is also disclosed that. However, (C) a salt compound of a compound having a plurality of carboxy groups has low solubility in an organic solvent and is difficult to uniformly dissolve in a polyamic acid solution. For this reason, the binding properties with the active material and the current collector foil are lowered, and thus the cycle characteristics are lowered. However, in Patent Document 9, preferred specific examples and optimal contents of the compound (C), which can achieve both the adhesion of the binder composition to the electrode active material and the solubility of the compound (C) in the polyamic acid solution, (A) The specific example of the preferable monomer which comprises an imidation polymer was not suggested.

  The present invention has been made in view of the above-mentioned problems of the prior art, and a binder resin composition and a composite for obtaining a lithium ion secondary battery in which the internal resistance of the battery is sufficiently reduced and which has good cycle characteristics. An object of the present invention is to provide a material paste, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery obtained therefrom.

（化学式１）
（式中、Ａ_１は直結、イソプロピリデン基、六フッ素化されたイソプロピリデン基、カルボニル基、チオ基および／またはスルホニル基を表す。ｎは１〜４の整数である。）
７.モノアルカリ金属塩が、フッ素を含まない上記１記載のリチウムイオン二次電池用バインダー樹脂組成物。
８.テトラカルボン酸二無水物のうち３０〜１００モル％が、３,３’,４,４’-ビフェニルテトラカルボン酸二無水物である上記１記載のリチウムイオン二次電池用バインダー樹脂組成物。
９.ケイ素原子、スズ原子またはゲルマニウム原子から選ばれる少なくとも一種の負極活物質と、上記１記載のバインダー樹脂組成物とを含む、リチウムイオン二次電池電極合材ペースト。
１０.上記９記載のリチウムイオン二次電池電極合材ペーストを、集電体上に塗布し、加熱処理してイミド化反応することにより得られるリチウムイオン二次電池用電極。
１１.リチウムイオンを吸蔵・放出可能な正極及び負極、並びに電解質を備えたリチウムイオン二次電池であって、負極が上記１０記載のリチウムイオン二次電池用電極であるリチウムイオン二次電池。
１２.ジアミン化合物とテトラカルボン酸二無水物から構成されるポリアミド酸と、リチウム塩、ナトリウム塩またはカリウム塩からなる群から選ばれる少なくとも一種のモノアルカリ金属塩と、ケイ素原子、スズ原子またはゲルマニウム原子から選ばれる少なくとも一種の負極活物質と、を含む、リチウムイオン二次電池電極合材ペーストの製造方法であって、ポリアミド酸と、テトラカルボン酸二無水物１００モル％に対して４〜２０モル％のモノアルカリ金属塩と、を混合する工程を有するリチウムイオン二次電池電極合材ペーストの製造方法。
１３.上記９記載のリチウムイオン二次電池電極合材ペーストを、集電体上に、塗布し、加熱処理してイミド化反応することにより得られるリチウムイオン二次電池用電極の製造方法。 1. A lithium ion secondary battery comprising a polyamic acid composed of a diamine compound and tetracarboxylic dianhydride, and at least one monoalkali metal salt selected from the group consisting of a lithium salt, a sodium salt or a potassium salt Binder resin composition, wherein tetracarboxylic dianhydride is 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride or 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride The binder resin composition for lithium ion secondary batteries in which a monoalkali metal salt is contained in an amount of 4 to 20 mol% with respect to 100 mol% of tetracarboxylic dianhydride.
2. The binder resin composition for a lithium ion secondary battery as described in 1 above, wherein the monoalkali metal salt contains water as a ligand.
3. The monoalkali metal salt includes a ligand having a molecular weight of 200 or less as a ligand, and at least one of the ligands having a molecular weight of 200 or less has a carboxyl group, the binder resin for a lithium ion secondary battery according to 1 above Composition.
4. The film obtained by heating the resin composition is immersed in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1 mixture), and the swelling degree after holding at 60 ° C. for 3 days is 20% or less. 2. The binder resin composition for lithium ion secondary batteries according to 1 above.
5. The binder resin composition for lithium ion secondary batteries as described in 1 above, wherein the charging ratio of the tetracarboxylic dianhydride and the diamine compound is 0.95 to 0.99: 1.00.
6. The binder resin composition for a lithium ion secondary battery according to 1 above, wherein 25 to 100 mol% of the diamine compound is a compound represented by the following chemical formula 1.

(Chemical formula 1)
(In the formula, A ₁ represents a direct bond, an isopropylidene group, a hexafluorinated isopropylidene group, a carbonyl group, a thio group and / or a sulfonyl group. N is an integer of 1 to 4.)
7. The binder resin composition for a lithium ion secondary battery as described in 1 above, wherein the monoalkali metal salt does not contain fluorine.
8. The binder resin composition for a lithium ion secondary battery as described in 1 above, wherein 30 to 100 mol% of tetracarboxylic dianhydride is 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride .
9. A lithium ion secondary battery electrode mixture paste comprising at least one negative electrode active material selected from silicon atoms, tin atoms or germanium atoms, and the binder resin composition described in 1 above.
10. An electrode for a lithium ion secondary battery obtained by applying the lithium ion secondary battery electrode mixture paste according to 9 above on a current collector and subjecting it to an imidization reaction by heat treatment.
11. A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is an electrode for a lithium ion secondary battery as described in 10 above.
12. Polyamic acid composed of diamine compound and tetracarboxylic dianhydride, at least one monoalkali metal salt selected from the group consisting of lithium salt, sodium salt or potassium salt, silicon atom, tin atom or germanium atom A method for producing a lithium ion secondary battery electrode mixture paste comprising at least one negative electrode active material selected from the group consisting of 4 to 20 mol of polyamic acid and 100 mol% of tetracarboxylic dianhydride % Monoalkali metal salt and a method for producing a lithium ion secondary battery electrode mixture paste.
13. A method for producing an electrode for a lithium ion secondary battery obtained by applying the lithium ion secondary battery electrode mixture paste described in 9 above onto a current collector and subjecting it to an imidization reaction by heat treatment.

  According to the present invention, the binder resin composition and the composite paste for obtaining a lithium ion secondary battery having good cycle characteristics with sufficiently reduced internal resistance of the battery, and the lithium ion secondary battery obtained therefrom An electrode and a lithium ion secondary battery are provided.

Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments.
First, the binder resin composition for a lithium ion secondary battery according to the embodiment will be described.

[Binder resin composition for lithium ion secondary battery]
1. Examples of diamine compounds include m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3, 3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl Sulfone, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 2,2-bis (3-aminophenyl) propane, 2,2 -Bis (4-aminophenyl) pro 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-bis (4-aminophenyl) -1,1,1,3 3,3-hexafluoropropane, 3,3′-diaminodiphenyl sulfoxide, 3,4′-diaminodiphenyl sulfoxide, 4,4′-diaminodiphenyl sulfoxide, 1,3-bis (3-aminophenyl) benzene, 1, 3-bis (4-aminophenyl) benzene, 1,4-bis (3-aminophenyl) benzene, 1,4-bis (4-aminophenyl) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenyl sulfide) benzene, 1,3-bis (4-aminophenyl sulfide) benzene, 1,4-bis (4-aminophenyl sulfide) benzene, 1,3-bis (3-aminophenylsulfone) benzene 1,3-bis (4-aminophenylsulfone) benzene, 1,4-bis (4-aminophenylsulfone) benzene, 1,3-bis (3-aminobenzyl) benzene, 1,3-bis (4- Aminobenzyl) benzene, 1,4-bis (4-aminobenzyl) benzene, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 3,3′-bis (3-aminophenoxy) biphenyl, 3 , 3′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis (4-a Minophenoxy) biphenyl, bis [3- (3-aminophenoxy) phenyl] ether, bis [3- (4-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ether, bis [4 -(4-aminophenoxy) phenyl] ether, bis [3- (3-aminophenoxy) phenyl] ketone, bis [3- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl ] Ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [3- (3-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl] sulfide, bis [4- ( 3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide Fido, bis [3- (3-aminophenoxy) phenyl] sulfone, bis [3- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4 -Aminophenoxy) phenyl] sulfone, bis [3- (3-aminophenoxy) phenyl] methane, bis [3- (4-aminophenoxy) phenyl] methane, bis [4- (3-aminophenoxy) phenyl] methane, Bis [4- (4-aminophenoxy) phenyl] methane, 2,2-bis [3- (3-aminophenoxy) phenyl] propane, 2,2-bis [3- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phene Ru] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [3- (4-aminophenoxy) ) Phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexa Fluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 9,9-bis (4-aminophenyl) fluorene, 9 , 9-bis (2-methyl-4-aminophenyl) fluorene, 9,9-bis (3-methyl-4-aminophenyl) fluorene, 9,9-bis (2-ethyl-4-aminophenyl) fluorene, 9,9-bis (3-ethyl -4-aminophenyl) fluorene, 9,9-bis (4-aminophenyl) -1-methylfluorene, 9,9-bis (4-aminophenyl) -2-methylfluorene, 9,9-bis (4- Aromatic diamine compounds such as aminophenyl) -3-methylfluorene and 9,9-bis (4-aminophenyl) -4-methylfluorene are included. These may be used alone or in combination of two or more.

The diamine compound may contain a divalent group derived from another aliphatic diamine other than the divalent group derived from the aromatic diamine compound.
Examples of other aliphatic diamines include 1,3-bis (3-aminopropyl) tetramethyldisiloxane, 1,3-bis (4-aminobutyl) tetramethyldisiloxane, α, ω-bis (3- Aminopropyl) polydimethylsiloxane, α, ω-bis (3-aminobutyl) polydimethylsiloxane, bis (aminomethyl) ether, 1,2-bis (aminomethoxy) ethane, bis [(2-aminomethoxy) ethyl] Ether, 1,2-bis [(2-aminomethoxy) ethoxy] ethane, bis (2-aminoethyl) ether, 1,2-bis (2-aminoethoxy) ethane, bis [2- (2-aminoethoxy) Ethyl] ether, bis [2- (2-aminoethoxy) ethoxy] ethane, bis (3-aminopropyl) ether, ethylene glycol bis (3- Minopropyl) ether, diethylene glycol bis (3-aminopropyl) ether, triethylene glycol bis (3-aminopropyl) ether, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1 , 6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,2 -Diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, 1,2-diaminomethylcyclohexane, 1,2-di (2- Aminoethyl) cyclohe Xanthine, 1,3-di (2-aminoethyl) cyclohexane, 1,4-di (2-aminoethyl) cyclohexane, bis (4-aminocyclohexyl) methane, 2,6-bis (aminomethyl) bicyclo [2. 2.1] heptane, 2,5-bis (aminomethyl) bicyclo [2.2.1] heptane, and the like. These may be used alone or in combination of two or more.

（化学式２）
化学式２におけるＹは、炭素数６〜２７の４価の芳香族基であり、芳香環、縮合多環式芳香族基、芳香族基が直接または架橋員により相互に連結された非縮合多環式芳香族基から選ばれる。特に芳香環が直接結合により相互に連結された非縮合多環式芳香族基が好ましい。 2. Tetracarboxylic dianhydride The tetracarboxylic dianhydride used in the embodiment is 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride or 3,3 ′, 4,4′-benzophenonetetracarboxylic acid. Contains acid dianhydride. In addition to the tetracarboxylic dianhydride, an aromatic tetracarboxylic dianhydride represented by (Chemical Formula 2) can be used.

(Chemical formula 2)
Y in Chemical Formula 2 is a tetravalent aromatic group having 6 to 27 carbon atoms, and is an aromatic ring, a condensed polycyclic aromatic group, or a non-condensed polycycle in which aromatic groups are connected to each other directly or by a bridging member Selected from the formula aromatic groups. In particular, non-condensed polycyclic aromatic groups in which aromatic rings are connected to each other by a direct bond are preferable.

  As aromatic tetracarboxylic dianhydride, pyromellitic dianhydride, merophanic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3 '-Biphenyltetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) Sulfide dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane Dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis (3,4-dicarboxy) Enoxy) benzene dianhydride, 1,4-bis (3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis (3,4-dicarboxyphenoxy) biphenyl dianhydride, 2,2-bis [(3,4-dicarboxyphenoxy) phenyl] propane dianhydride, oxydiphthalic dianhydride, and the like. These may be used alone or in combination of two or more.

3. Polyamic acid Polyamic acid can be obtained by condensing the aromatic diamine compound and aromatic tetracarboxylic dianhydride described above.

（１）
例えば下記一般式（２）で表されるジアミンと、

（２）
下記一般式（３）で表されるテトラカルボン酸二無水物と

（３）
を反応させて得られる。 The polyamic acid represented by the general formula (1) is

(1)
For example, a diamine represented by the following general formula (2),

(2)
Tetracarboxylic dianhydride represented by the following general formula (3)

(3)
It is obtained by reacting.

At this time, the charging ratio of tetracarboxylic dianhydride and diamine was M1: M2 = 0.90-1.10: 1.00 (M1: number of moles of tetracarboxylic dianhydride, M2: number of moles of diamine) ) Is preferably satisfied. M1: M2 is more preferably 0.92 to 1.03: 1.00, and further preferably 0.95 to 0.99: 1.00. In the case of 0.95 to 0.99: 1.00, the terminal of the polyamic acid is an amino group. The amino group at the end is easier to handle than the acid dianhydride, since there is no change in the viscosity of the paste due to water mixing when preparing the electrode mixture paste.
The weight average molecular weight of the polyamic acid is preferably 1.0 × 10 ^{3 to} 5.0 × 10 ⁵ . If the weight average molecular weight is less than 1.0 × 10 ³ , the mechanical strength of the layer obtained by curing the binder resin composition may be reduced, and if the weight average molecular weight exceeds 5.0 × 10 ⁵ , Work becomes difficult. The weight average molecular weight of the polyimide or its precursor can be measured by gel permeation chromatography (GPC).

  The polyamic acid is aminopropyltrimethoxysilane, aminopropyltriethoxysilane, glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, trimethoxyvinylsilane, triethoxyvinylsilane, trimethoxyglycidoxysilane, You may contain 0.1-20 mass parts of silane coupling agents, such as a triethoxyglycidoxy silane, a triazine type compound, a phenanthroline type compound, a triazole type compound, with respect to 100 mass parts of total amounts of a polyamic acid. By containing these, adhesiveness with an active material and a collector can further be improved. Among the silane coupling agents, 3-aminopropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane are preferable.

  A film obtained by heating the resin composition is immersed in an electrolytic solution (Ethylene Carbonate (EC) / Diethylcarbonate (DEC) = 1/1 (vol / vol)), and 3 at 60 ° C. The degree of swelling after holding for one day is preferably 20% or less, and more preferably 15% or less. When the degree of swelling is 15% or less, the binding property between the active material and the binder is maintained, so that good cycle characteristics can be obtained.

（化学式１）
（式中、Ａ_１は直結、イソプロピリデン基、六フッ素化されたイソプロピリデン基、カルボニル基、チオ基および／またはスルホニル基を表す。ｎは１〜４の整数である。） It is preferable that 25-100 mol% is a compound shown by following Chemical formula 1 among the said diamine compounds. If it is the said range, high binding property with respect to an active material will express.

(Chemical formula 1)
(In the formula, A ₁ represents a direct bond, an isopropylidene group, a hexafluorinated isopropylidene group, a carbonyl group, a thio group and / or a sulfonyl group. N is an integer of 1 to 4.)

4). Monoalkali metal salt The monoalkali metal salt preferably contains at least one selected from the group consisting of lithium salts, sodium salts and potassium salts.
Examples of the monoalkali metal salt include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and sodium hydroxide; alkali metal carbonates such as lithium carbonate, potassium carbonate, and sodium carbonate; potassium-t-butoxide, sodium Examples include alkoxides of alkali metals such as methoxide; metal acetates such as magnesium acetate, calcium acetate, aluminum acetate, lithium acetate or sodium acetate. Of the above monoalkali metal salts, lithium acetate or sodium acetate is preferably used. This is because the solubility in an organic solvent is high.

The monoalkali metal salt is preferably a hydrate or contains water as a ligand. This is because the solubility in an organic solvent is high. Monoalkali metal salt so that the A / B value is less than 500 when the content of polyamic acid is A part by mass and the content of water is B part by mass relative to the total mass of the composition according to the embodiment. Is preferably added. The value of A / B is preferably 50 or more and less than 500, and more preferably 100 or more and less than 500.
In the technical field of the binder resin composition for secondary batteries, water is considered as an impurity that erodes the electrode active material, so that mixing of water into the binder resin composition has been avoided. However, by including water in the above-mentioned range in the binder resin composition, the adhesion of the binder resin composition to the electrode active material, the internal resistance of the battery is reduced, and the solubility of the monoalkali metal salt in the polyamic acid solution is reduced. Can be achieved.

  The monoalkali metal salt preferably contains a ligand having a molecular weight of 200 or less, preferably 150 or less. This is because, when the molecular weight is smaller, the ligand is decomposed and disappears from the electrode when the high temperature treatment (imidization) is performed, so that deterioration of battery characteristics due to dissolution in the electrolytic solution can be suppressed. In the monoalkali metal salt, it is more preferable that at least one of the above-mentioned ligands having a molecular weight of 200 or less has a carboxyl group. This is because it has high solubility in an organic solvent and is easily decomposed by high-temperature treatment. The lower limit of the molecular weight of the monoalkali metal salt is not particularly limited, but is about 15.

  Here, the “ligand” refers to a molecule or ion bonded to a certain atom by a coordinate bond. An atom that can be regarded as directly related to a bond (donation of an electron pair) is called a coordination atom. When the monoalkali metal salt is, for example, lithium acetate or a hydrate thereof, the coordination atom is a lithium ion, and the ligand includes acetate ion and water. In addition to the water in the monoalkali metal salt hydrate, the water as the ligand is a case where a part of the monoalkali metal salt added to the composition according to the embodiment is hydrated. Contains water.

  The alkali metal salt preferably does not contain fluorine. This is because it is difficult to decompose and easily remains in the electrode. The alkali metal salt is preferably soluble in the polyamic acid solution. This is because a uniform solution of the alkali metal salt and the solution can be obtained.

  The addition amount of the alkali metal salt is preferably 4 to 20 mol%, more preferably 6 to 20 mol%, and still more preferably 8 to 20 mol% with respect to 100 mol% of tetracarboxylic dianhydride.

[Electrode compound paste for lithium ion secondary batteries]
The electrode mixture paste for a lithium ion secondary battery according to the embodiment comprises the binder resin composition and the negative electrode active material described above. The electrode mixture paste for a lithium ion secondary battery according to the embodiment is obtained by mixing a negative electrode active material and, if necessary, a conductive additive, a solvent, etc., into an electrode binder resin composition for a lithium ion secondary battery or a varnish containing the same. And can be produced by stirring or kneading. Examples of the mixing method of the raw materials include the following two methods, but are not limited thereto.

  i) An active material and a solvent are added to a varnish containing an electrode binder resin composition for a lithium ion secondary battery to obtain an electrode mixture paste.

ii) An active material is added to the varnish containing the electrode binder resin composition for a lithium ion secondary battery and kneaded. A solvent is added to the kneaded material obtained and stirred to obtain an electrode mixture paste.
The stirring may be normal stirring using a stirring blade or the like, or stirring using a rotation / revolution mixer or the like. For the kneading operation, a kneader or the like can be used.

1. Negative electrode active material Although it does not specifically limit as a negative electrode active material, The effect of this invention is exhibited more with respect to the active material with a large volume change accompanying charging / discharging. Those having a volume expansion coefficient of greater than 110% during lithium ion storage and / or insertion can be preferably used. Even if the volume expansion coefficient accompanying charging / discharging is large, the resin for binders used for embodiment shows favorable binding property. The value of the volume expansion coefficient is disclosed in, for example, “Development Trend of Automotive Lithium Ion Batteries”, Kinki University Faculty of Engineering Research Public Forum, October 27, 2010, and the like.
As the negative electrode active material, an active material containing a silicon atom, a tin atom or a germanium atom having a large charge / discharge capacity can be preferably used. Since the volume change accompanying charging / discharging is large in these, the effect of this invention is exhibited more. Among these, silicon particles and / or silicon alloys are more preferable.

Examples of the negative electrode active material containing silicon atoms include (i) silicon fine particles, (ii) tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium, Examples thereof include alloys with silicon, (iii) compounds of boron, nitrogen, oxygen or carbon and silicon, and those having the metal exemplified in (ii). Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiOx (0 <x ≦ 2) or LiSiO.

Examples of the negative electrode active material containing tin atoms include (i) alloys of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium and tin, ( ii) Oxygen or a compound of carbon and tin, and those having the metal exemplified in (i). Examples of tin alloys or compounds include SnOw (0 <w ≦ 2), SnSiO ₃ , LiSnO, Mg ₂ Sn, and the like.

Examples of the negative electrode active material containing germanium include germanium oxide, carbide, nitride, and carbonitride.
The negative electrode active material may be used by mixing with an active material having a volume expansion coefficient of 110% or less, and can be preferably used as long as the volume expansion coefficient of the entire mixture is greater than 110%. Examples of the active material having a volume expansion coefficient of 110% or less include graphite, non-graphitizable carbon, mesocarbon microbeads, and lithium titanate. Of these, one or two of them can be mixed with the negative electrode active material.

The surface of these negative electrode active materials may be covered with a conductive material such as carbon or copper for the purpose of improving the conductivity.
The average particle size (average median particle size) of the active material is preferably 0.1 to 20 μm. The surface of the active material may be treated with a silane coupling agent or the like.

2. Solvent The electrode mixture paste for a lithium ion secondary battery according to the embodiment may contain a solvent. The type of the solvent is not particularly limited as long as it can uniformly dissolve or disperse the electrode binder resin composition for a lithium ion secondary battery and the active material. As such a solvent, an aprotic polar solvent is preferable, and an aprotic amide solvent is more preferable. Examples of aprotic amide solvents include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazo Lysinone etc. are included. These solvents may be used alone or in combination of two or more.

In addition to these solvents, other solvents may coexist as necessary. Examples of other solvents include benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, o-cresol, m-cresol, p-cresol, o-chlorotoluene, m-chlorotoluene, p- Examples include chlorotoluene, o-bromotoluene, m-bromotoluene, p-bromotoluene, chlorobenzene, bromobenzene, methanol, ethanol, n-propanol, isopropyl alcohol and n-butanol.
The amount of the solvent is appropriately selected in consideration of the viscosity of the electrode mixture paste for lithium ion secondary batteries. Usually, it is preferable to mix | blend 50-900 mass parts with respect to 100 mass parts of solid content contained in a composite paste, and it is more preferable to mix | blend 65-500 mass parts.

3. Conductive auxiliary agent The electrode mixture paste for lithium ion secondary batteries according to the embodiment may contain a conductive auxiliary agent together with an active material. The conductive assistant is blended for the purpose of reducing the electrical resistance of the electrode. A carbon material can be used as the conductive assistant. There are no particular restrictions on the type of carbon material, but graphite such as artificial graphite and natural graphite (graphite), carbon fibers (carbon nanotubes, vapor-grown carbon fibers, etc.), and organic materials under various pyrolysis conditions A thermal decomposition product is mentioned.
Examples of pyrolysis products of organic matter include coal-based coke; petroleum-based coke; carbides from coal-based pitch; carbides from petroleum-based pitch; or carbides obtained by oxidizing these pitches; needle coke; pitch coke; phenol resin, crystalline cellulose And carbon materials obtained by partially graphitizing these; furnace black; acetylene black; pitch-based carbon fiber; and the like. Among these, graphite is preferable, and artificial graphite, purified natural graphite, or those obtained by subjecting these graphites to various surface treatments, which are produced by subjecting easy-graphite pitches obtained from various raw materials to high-temperature heat treatment, are particularly preferable.

One of these carbon materials may be used alone, or two or more thereof may be used in combination.
In addition to the above carbon material, the electrode mixture paste for lithium ion secondary batteries contains metal oxides such as tin oxide, sulfides and nitrides, lithium alloys such as lithium alone and lithium aluminum alloys, and the like. Also good. As for materials other than these carbon materials, one kind may be used alone, or two or more kinds may be used in combination. Moreover, you may use in combination with the above-mentioned carbon material.
The blending amount (mass) of the conductive assistant with respect to the total amount (mass) of the solid content in the electrode mixture paste for a lithium ion secondary battery is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, More preferably, it is 0.1 mass% or more. Moreover, 20 mass% or less is preferable normally, and 10 mass% or less is more preferable.

[Electrode for lithium ion secondary battery]
The electrode for a lithium ion secondary battery according to the embodiment is a laminate of a current collector and a negative electrode active material layer. This active material layer is a cured product of an electrode mixture paste for a lithium ion secondary battery containing a binder resin composition. The electrode for a lithium ion secondary battery includes a sheet-like electrode.

1. Current collector The material of the negative electrode current collector includes metal materials such as silicon and / or silicon alloys, tin and alloys thereof, silicon-copper alloys, copper, nickel, stainless steel, nickel-plated steel, carbon cloth, and carbon paper. A carbon material such as is used.

  Examples of the shape of the negative electrode current collector include a metal foil, a metal cylinder, a metal coil, a metal plate, and a metal thin film in the case of a metal material, and a carbon plate, a carbon thin film, and a carbon cylinder in the case of a carbon material. Although there is no restriction | limiting in particular in the thickness of an electrical power collector, For example, it is 5-30 micrometers normally, Preferably it is 9-20 micrometers.

2. Negative electrode active material layer The active material layer is obtained by applying an electrode mixture paste for a lithium ion secondary battery containing a binder resin composition to a current collector and curing it by heating.

  Application | coating of an electrode compound paste can be performed by methods, such as screen printing, roll coating, and slit coating, for example. At this time, the electrode mixture paste may be applied onto the pattern so that the binder (cured product) has a mesh shape. The thickness of the active material layer is not particularly limited, and for example, the thickness after curing is preferably 5 μm or more, and more preferably 10 μm or more. Moreover, 200 micrometers or less are preferable, 100 micrometers or less are more preferable, and 75 micrometers or less are still more preferable. When the active material layer is too thin, the practicality as a positive electrode or a negative electrode is lacking from the balance with the particle size of the active material. On the other hand, if the thickness is too thick, it may be difficult to obtain a sufficient Li storage / release function for high-density current values.

Heating and curing of the electrode mixture paste can usually be performed under atmospheric pressure, but may be performed under pressure or under vacuum. The atmosphere at the time of heating and drying is not particularly limited, but is usually preferably performed in an atmosphere of air, nitrogen, helium, neon, argon, or the like, and more preferably in an atmosphere of nitrogen or argon as an inert gas.
Moreover, the heating temperature in the heat curing of the electrode mixture paste is usually 150 ° C. to 500 ° C. for 1 minute to 24 hours to perform a ring closure reaction of the polyimide precursor to the polyimide, thereby obtaining a reliable negative electrode. be able to. Preferably, it is 200 ° C. to 450 ° C. for 5 minutes to 20 hours.

[Lithium ion secondary battery]
The negative electrode thus obtained can be used for a lithium ion secondary battery.
The basic configuration of the lithium ion secondary battery according to the embodiment is the same as that of a conventionally known lithium ion secondary battery, and usually includes a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte. The hardened | cured material of the binder resin composition mentioned above is good also as any active material layer of a positive electrode and a negative electrode, and may be used only for any one. In the present invention, it is particularly preferable to use a cured product of the binder resin composition described above as an active material layer of a negative electrode containing silicon atoms or tin atoms as a negative electrode active material.

  The form of the lithium ion secondary battery according to the embodiment is not particularly limited. Examples of the form of the lithium ion secondary battery include a cylinder type in which the sheet electrode and the separator are spiral, a cylinder type having an inside-out structure in which the pellet electrode and the separator are combined, a coin type in which the pellet electrode and the separator are stacked, and the like. It is done. Moreover, it is good also as arbitrary shapes, such as a coin shape, a cylindrical shape, and a square shape, by accommodating the battery of these forms in arbitrary exterior cases.

  The procedure for assembling the lithium ion secondary battery according to the embodiment is not particularly limited, and may be assembled by an appropriate procedure according to the structure of the battery. For example, a negative electrode is placed on an outer case, an electrolyte and a separator are provided on the outer case, and a positive electrode is placed so as to face the negative electrode. The battery is then caulked together with a gasket and a sealing plate.

1. Electrolytic solution As an electrolytic solution for a lithium ion secondary battery, a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent, or a non-aqueous electrolytic solution gelled, rubbery, or solid sheet with an organic polymer compound or the like The one made into a shape is used.

For example, a non-aqueous solvent in which a lithium salt is dissolved is used for the electrolytic solution. The lithium salt can be appropriately selected from known lithium salts. For example, halides such as LiCl and LiBr; perhalogenates such as LiClO ₄ and LiBrO ₄ ; inorganic fluoride salts such as LiPF ₆ , LiBF ₄ and LiAsF ₆ ; lithium bis (oxalatoborate) LiBC ₄ O _{8 and the} like Inorganic lithium salts of: Perfluoroalkane sulfonates such as LiCF ₃ SO ₃ and LiC ₄ F ₉ SO ₃ ; Perfluoroalkane sulfonic acid imide salts such as Li trifluorosulfonimide ((CF ₃ SO ₂ ) ₂ NLi); And fluorine-containing organic lithium salts. Lithium salts may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte is usually in the range of 0.5M to 2.0M.

  Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, and γ-lactones such as γ-butyrolactone Chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethylsulfate Hoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl -2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methylpyrrolidone, butyl diglyme, methyl tetraglyme Aprotic organic solvents such as these may be used, and these may be used alone or in combination of two or more.

  It is also possible to include an organic polymer compound in the electrolytic solution to form a gel, rubber, or solid sheet. Specific examples of such organic polymer compounds include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymers such as polyvinyl alcohol and polyvinyl butyral. Compound; insolubilized product of vinyl alcohol polymer; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer such as polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), And polymer copolymers such as poly (ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate) and poly (hexafluoropropylene-vinylidene fluoride). .

  Further, the electrolytic solution may further contain a film forming agent. Specific examples of the film forming agent include vinylene carbonate, vinyl ethylene carbonate, vinyl ethyl carbonate, methyl phenyl carbonate and other carbonate compounds, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, bis (trifluoromethyl) ethylene carbonate. 1-fluoroethyl methyl carbonate, ethyl 1-fluoroethyl carbonate, fluoromethyl methyl carbonate, bis (1-fluoroethyl) carbonate, bis (fluoromethyl) carbonate, ethyl 2-fluoroethyl carbonate, bis (2-fluoroethyl) Carbonate, methyl 1,1,1-trifluoropropan-2-yl carbonate, ethyl 1,1,1-trifluoropro N-2-yl carbonate, methyl 2,2,2-trifluoroethyl carbonate, bis (1,1,1-trifluoropropan-2-yl) carbonate, bis (2,2,2-trifluoroethyl) carbonate , Fluorinated carbonate compounds such as ethyl 3,3,3-trifluoropropyl carbonate, bis (3,3,3-trifluoropropyl) carbonate, alkene sulfides such as ethylene sulfide and propylene sulfide; 1,3-propane sultone, Examples include sultone compounds such as 1,4-butane sultone; acid anhydrides such as maleic anhydride and succinic anhydride.

  Moreover, when using a film forming agent, the content thereof is usually 30% by mass or less, particularly 15% by mass or less, more preferably 10% by mass or less, based on the total amount (mass) of the constituent components of the electrolytic solution. In particular, it is preferably 5% by mass or less. If the content of the film forming agent is too large, other battery characteristics such as an increase in initial irreversible capacity, low temperature characteristics, and deterioration in rate characteristics of the lithium ion secondary battery may be adversely affected.

2. Positive electrode The positive electrode may have a structure in which a current collector and a positive electrode active material layer are laminated.
As the material for the positive electrode current collector, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper are usually used. Of these, metal materials are preferable, and aluminum is particularly preferable. As for the shape, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foam metal, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder Etc. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape. When a thin film is used as the positive electrode current collector, its thickness is arbitrary, but the lower limit is usually 1 μm, preferably 3 μm, more preferably 5 μm, and the upper limit is usually 100 mm, preferably 1 mm, more preferably 50 μm. It is a range. If the thickness is less than the above range, the strength required for the current collector may be insufficient. On the other hand, if it is thicker than the above range, the handleability may be impaired.

The positive electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used for a lithium ion secondary battery can be used. Specifically, lithium-manganese composite oxide (LiMn ₂ O ₄ etc.), lithium-nickel composite oxide (LiNiO ₂ etc.), lithium-cobalt composite oxide (LiCoO ₂ etc.), lithium-iron composite oxide ( LiFeO ₂ etc.), lithium-nickel-manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ etc.), lithium-nickel-cobalt composite oxide (LiNi _0.8 Co _0.2 O ₂ etc.), lithium - nickel - cobalt - manganese composite oxide, lithium - transition metal phosphate compound (such as LiFePO _4), and lithium - transition metal sulfate compound _{(LixFe 2 (SO 4) 3} ) , and the like.

  These positive electrode active materials may be used alone or in combination. The lower limit of the content ratio of the positive electrode active material in the positive electrode active material layer is usually 10% by mass, preferably 30% by mass, more preferably 50% by mass, and the upper limit is usually 99.9% by mass, preferably 99%. % By mass.

  As the binder resin for binding the positive electrode active material, a known resin can be arbitrarily selected and used in addition to the binder resin composition described above. Examples thereof include inorganic compounds such as silicate and water glass, polyvinylidene fluoride, Teflon (registered trademark), and polymers having no unsaturated bond. The lower limit of the weight average molecular weight of these polymers is usually 10,000, preferably 100,000, and the upper limit is usually 3 million, preferably 1 million.

  As for the ratio of the binder resin (mass) to the mass of all components constituting the positive electrode active material layer, the lower limit is usually 0.1% by mass, preferably 1% by mass, more preferably 5% by mass, and the upper limit is usually 80%. % By mass, preferably 60% by mass, more preferably 40% by mass, particularly preferably 10% by mass. When the ratio of the binder resin is too low, the positive electrode active material cannot be sufficiently retained, and the mechanical strength of the positive electrode is insufficient, which may deteriorate battery performance such as cycle characteristics. On the other hand, when the ratio of binder resin is too high, there exists a possibility of leading to a battery capacity and electroconductivity fall.

The positive electrode active material layer may contain a conductive material in order to improve the conductivity of the electrode. The conductive agent is not particularly limited as long as it can be mixed with an active material in an appropriate amount to impart conductivity, but is usually carbon powder such as acetylene black, carbon black, and graphite, various metal fibers, powder, and foil. Etc.
The thickness of the positive electrode active material layer is usually about 10 to 200 μm. The positive electrode is obtained by forming a positive electrode active material and a binder resin composition containing the binder resin on a current collector. The positive electrode active material layer is usually formed by mixing a positive electrode material, a binder, and a conductive material and a thickener, which are used if necessary, in a dry form into a sheet shape, and then pressing the positive electrode current collector on the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a paste, which is then applied to the positive electrode current collector and dried. Note that the positive electrode active material layer obtained by applying and drying the paste on the positive electrode current collector is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.

  As a liquid medium for forming the paste, a positive electrode active material, a binder resin, and a conductive material and a thickener that can be used as necessary can be dissolved or dispersed in the solvent, in particular. There is no restriction, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N -N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. be able to. In particular, when an aqueous solvent is used, a dispersant is added in addition to the thickener, and a paste is formed using a latex such as SBR. In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

3. Separator Normally, a porous separator such as a porous film or a nonwoven fabric is interposed between the positive electrode and the negative electrode in order to prevent a short circuit between the electrodes. As the separator, for example, a microporous film having excellent ion permeability, a glass fiber sheet, a nonwoven fabric, a woven fabric, or the like is used. Also, from the viewpoint of organic solvent resistance and hydrophobicity, as a material for the separator, polypropylene, polyethylene, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polymethylpentene, polyamide, polyimide, or the like is used. These may be used alone or in combination of two or more. In addition, inexpensive polypropylene is usually used, but when reflow resistance is imparted to the lithium ion secondary battery, among these, polypropylene sulfide, polyethylene terephthalate, polyamide, polyimide, etc. having a heat distortion temperature of 230 ° C. or higher are used. It is preferable. The thickness of the separator is, for example, 10 to 300 μm. Further, the porosity of the separator may be appropriately determined according to the permeability of electrons and ions, the material of the separator, and the like, but generally 30 to 80% is desirable.

In the following, the present invention will be described in more detail with reference to examples. The scope of the invention should not be construed as limited by these examples. The contents of the abbreviations used in the examples and comparative examples are shown.
NMP: N-methyl-2-pyrrolidone m-BP: 4,4′-bis (3-aminophenoxy) biphenyl PMDA: pyromellitic dianhydride BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic acid The dianhydride The measuring method of the characteristic used in the Example is shown below.
<Concentration of solid content>
The sample solution (whose mass is designated as w1) is heat-treated at 330 ° C. for 120 minutes in a hot air dryer, and the mass after the heat treatment (its mass is designated as w2) is measured.
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 NMP) based on the solid content concentration. The flow down time (T1) of this diluted solution was measured at 35 ° C. using an automatic kinematic viscosity measuring device PVS manufactured by Lauda. The logarithmic viscosity was calculated from the following equation using the flow time (T0) of blank NMP.
Logarithmic viscosity = {ln (T1 / T0)} / 0.5
<Swelling rate>
A 20 cm thick polyimide film obtained from the electrode binder resin composition was cut into 10 cm square, and the mass after vacuum drying at 100 ° C. for 3 hours was defined as the dry mass (Wd). The mass after immersing this film in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1 mixture) at 60 ° C. for 72 hours was defined as the swelling mass (Ww), and the swelling rate S was calculated by the following formula, respectively. .
S [mass%] = Ww / Wd × 100
<Charge / discharge cycle test using coin cell>
In order to evaluate the electrode characteristics of the negative electrode single electrode, a test lithium secondary battery was produced as follows. For the counter electrode, 16 mm diameter metallic lithium was used. In addition, a coin cell was prepared by using a solution of LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio of 1: 1) as the electrolytic solution at a concentration of 1 mol / l, and using a porous polypropylene film as a separator. did.
Using the obtained coin cell, a constant voltage of 0.2 C was obtained at a constant temperature of 25 ° C., with a terminal voltage lower limit voltage of 0.01 V and a discharge upper limit voltage of 1.2 V. The discharge capacity after 20 cycles of current charging and discharging and the change in capacity retention rate with respect to the discharge capacity at the first cycle were examined. Thereafter, in the 21st cycle, the current value was reduced to 0.1 C to charge and discharge, and the load characteristics were calculated from the following equation.
Load characteristics (%) = [{Discharge capacity at 20th cycle (current value 0.2 C)} / {Discharge capacity at 21st cycle (current value 0.1 C)}] × 100
The initial efficiency and discharge capacity retention rate were calculated from the following formulas.
Initial efficiency (%) = [(discharge capacity at the first cycle) / (charge capacity at the first cycle)] × 100
Discharge capacity retention rate (%) = [(discharge capacity at 20th cycle) / (discharge capacity at 1st cycle)] × 100

(Synthesis Example 1)
A container equipped with a stirrer and a nitrogen introduction tube was charged with 66.32 g (0.18 mol) of m-BP and 475.9 g of NMP as a solvent. After stirring until m-BP was dissolved, 51.9 g of BPDA (0.176 mol) was added over about 30 minutes, 204 g of NMP was further added, and the mixture was stirred for 20 hours to obtain polyamic acid varnish A. . The obtained polyamic acid varnish had a solid content concentration of 14% by mass and a logarithmic viscosity of 0.75 dl / g.

(Synthesis Example 2)
A container equipped with a stirrer and a nitrogen introduction tube was charged with 66.32 g of m-BP (0.18 mol) and 456 g of NMP as a solvent. After stirring until m-BP is dissolved, 38.47 g of PMDA (0.176 mol) is added over about 30 minutes, 195.4 g of NMP is further added, and the mixture is stirred for 20 hours to obtain polyamic acid varnish B. Obtained. The obtained polyamic acid varnish had a solid content concentration of 13% by mass and a logarithmic viscosity of 0.77 dl / g.

(Synthesis Example 3)
A container equipped with a stirrer and a nitrogen introduction tube was charged with 66.31 g of m-BP (0.18 mol) and 412.1 g of NMP as a solvent. After stirring until m-BP was dissolved, 25.95 g (0.088 mol) of BPDA and 19.24 (0.088 mol) g of PMDA were added over 30 minutes, and 176.6 g of NMP was further added. The polyamic acid varnish C was obtained by stirring for 20 hours. The obtained polyamic acid varnish had a solid content concentration of 15% by mass and a logarithmic viscosity of 0.80 dl / g.

Example 1
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate.
The above ethanol solution was added to 68.73 g of polyamic acid varnish A (polyamic acid, 0.015 mol) so that the amount of lithium acetate added was 10 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting polyamic acid. 3.1 g (lithium acetate, 0.0015 mol) was added. And the binder varnish 1 was obtained by stirring the obtained solution for 3 minutes with an autorotation revolution mixer (Shinky Co., Ltd. Awatori Kentaro AR-250) (autorotation 800rpm, revolution 2000rpm). The obtained binder varnish had a solid content concentration of 13.4% by mass.
Preparation of binder film The obtained binder varnish 1 was applied on a glass plate of a substrate by an applicator, and the coating film was baked at 330 ° C. for 2 hours in a nitrogen atmosphere to form a binder resin film having a thickness of 15 μm. did. The swelling ratio of the obtained film is shown in Table 1.
Production of negative electrode 2% by mass, 3.7% by mass, 41.4% by mass of Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle diameter of 3 μm), acetylene black, binder varnish 1 and NMP, respectively. And 27.1% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Example 2)
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The above ethanol solution was added to 68.63 g of polyamic acid varnish A (polyamic acid, 0.015 mol) so that the amount of lithium acetate added was 20 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting polyamic acid. 6.28 g (lithium acetate, 0.003 mol) was added. And the binder varnish 2 was obtained by agitating and rotating the obtained solution for 3 minutes (autorotation 800rpm, revolution 2000rpm) with the autorotation revolution mixer (Shinky Co., Ltd. foaming Netaro AR-250). The obtained binder varnish had a solid content of 13% by mass.
Using the obtained binder varnish 2, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle size of 10 μm), acetylene black, binder varnish 2 and NMP were respectively 27.8% by mass, 3.7% by mass and 42.7% by mass. And a mixture of 25.9% by mass and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

Example 3
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The above ethanol solution was added to 58.35 g of polyamic acid varnish C (polyamic acid, 0.015 mol) so that the amount of lithium acetate added was 10 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting the polyamic acid. 3 g (lithium acetate, 0.0015 mol) was added. And the binder varnish 3 was obtained by stirring the obtained solution for 3 minutes (autorotated 800 rpm, revolution 2000 rpm) with the autorotation revolution mixer (Shinky Co., Ltd. foaming Netaro AR-250). The obtained binder varnish had a solid content concentration of 14.3% by mass.
Using the obtained binder varnish 3, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle diameter of 10 μm), acetylene black, binder varnish 3 and NMP were respectively 27.8% by mass, 3.7% by mass and 38.8% by mass. And 29.7% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 1)
Using the polyamic acid varnish A prepared in Synthesis Example 1, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle size of 3 μm), acetylene black, polyamic acid varnish A and NMP were respectively 27.8% by mass, 3.7% by mass and 39.6% by mass. % And 28.9% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 2)
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The ethanol solution was added so that the amount of lithium acetate added to 68.6 g of polyamic acid varnish A (polyamic acid, 0.015 mol) was 50 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting the polyamic acid. 15.7 g (lithium acetate, 0.0075 mol) was added. Then, the obtained solution was stirred for 3 minutes (autorotation 800 rpm, revolution 2000 rpm) with a rotation and revolution mixer (Shinky Co., Ltd., Awatori Nertaro AR-250). The electrode could not be produced because insoluble material was deposited.

(Comparative Example 3)
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The above ethanol solution was added to 68.63 g of polyamic acid varnish A (polyamic acid, 0.015 mol) such that the addition amount of lithium acetate was 30 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting polyamic acid. 9.42 g (lithium acetate, 0.0045 mol) was added. And the binder varnish 4 was obtained by agitating and rotating the obtained solution for 3 minutes with a rotation revolution mixer (Shinky Co., Ltd. Awatori Kentaro AR-250) (rotation 800rpm, revolution 2000rpm). The obtained binder varnish had a solid content concentration of 12.5% by mass.
Using the obtained binder varnish 4, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle diameter of 3 μm), acetylene black, binder varnish 4 and NMP were respectively 27.8% by mass, 3.7% by mass and 44.4% by mass. And a mixture of 24.2% by mass and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 4)
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The above ethanol solution was added to 72.26 g of polyamic acid varnish B (polyamic acid, 0.015 mol) so that the amount of lithium acetate added was 10 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting the polyamic acid. 3.44 g (lithium acetate, 0.0015 mol) was added. And the binder varnish 5 was obtained by agitating and rotating the obtained solution for 3 minutes with a rotation revolution mixer (Shinky Co., Ltd. Awatori Netaro AR-250) (rotation 800rpm, revolution 2000rpm). The obtained binder varnish had a solid content concentration of 12.4% by mass.
Using the obtained binder varnish 5, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder with an average particle size of 10 μm), acetylene black, binder varnish 5 and NMP were respectively 27.8% by mass, 3.7% by mass and 45.5% by mass. And 23.1% by mass and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 5)
A binder resin film was formed in the same manner as in Example 1 using the polyamic acid varnish B prepared in Synthesis Example 2. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle size of 10 μm), acetylene black, polyamic acid varnish B and NMP were respectively 27.8% by mass, 3.7% by mass and 42.7% by mass. % And 25.9% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 6)
A binder resin film was formed in the same manner as in Example 1 using the polyamic acid varnish C produced in Synthesis Example 3. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle diameter of 3 μm), acetylene black, polyamic acid varnish C and NMP were respectively 27.8% by mass, 3.7% by mass and 37.0% by mass. % And 31.6% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

(Comparative Example 7)
5 parts by mass of lithium acetate dihydrate was dissolved in 95 parts by mass of ethanol to prepare an ethanol solution of lithium acetate. The above ethanol solution was added to 68.63 g of polyamic acid varnish A (polyamic acid, 0.015 mol) so that the amount of lithium acetate added was 2 mol% with respect to 100 mol% of tetracarboxylic dianhydride constituting polyamic acid. 0.63 g (lithium acetate, 0.0003 mol) was added. And the binder varnish 6 was obtained by stirring the obtained solution for 3 minutes (autorotated 800 rpm, revolution 2000 rpm) with the autorotation revolution type | formula mixer (Shinky Co., Ltd. foaming Netaro AR-250). The obtained binder varnish had a solid content concentration of 14.1% by mass.
Using the obtained binder varnish 6, a binder resin film was formed in the same manner as in Example 1. The swelling ratio of the obtained film is shown in Table 1.
Production of Negative Electrode Si active material (manufactured by Yamaishi Metal, metal silicon powder having an average particle size of 3 μm), acetylene black, binder varnish 6 and NMP were respectively 27.8 mass%, 3.7 mass% and 39.4 mass%. And 29.2% by mass, and kneaded to prepare a slurry. This was applied to a rolled copper foil having a thickness of 18 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 20 minutes in a nitrogen atmosphere to form an electrode sheet. A negative electrode was obtained by cutting the sheet into a circle having a diameter of 14.5 mmΦ. Table 1 shows the results of a charge / discharge cycle test using a coin cell produced using the obtained negative electrode.

In Examples 1 to 3 in which the alkali metal salt was added to the polyamic acid, compared to Comparative Examples 1 and 6 to which no alkali metal salt was added, the discharge capacity after 20 cycles and the discharge capacity retention rate were high, and good cycle characteristics were obtained. Indicated. Moreover, Examples 1-3 showed a large load characteristic value compared with the comparative examples 1, 5, and 6, and showed the outstanding rate characteristic.
Example 1 in which 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride or 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride was used as tetracarboxylic dianhydride 3 had a high discharge capacity after 20 cycles and a discharge capacity retention rate as compared with Comparative Example 4 in which the tetracarboxylic dianhydride was not used, and showed good cycle characteristics. It is considered that Examples 1 to 3 had a lower swelling rate than Comparative Example 4 and the binder was less likely to swell with the electrolyte solution, and thus exhibited good binding properties even after the cycle test.
Comparative Examples 1 to 3 and 5 to 7 in which the addition amount of the alkali metal salt with respect to 100 mol% of tetracarboxylic dianhydride is not included in the range of 4 to 20 mol% are the discharge capacity and the discharge capacity maintenance after 20 cycles. In both items of rate and load characteristic value, results were inferior to those of Examples 1 to 3.

Claims (13)

A polyamic acid composed of a diamine compound and tetracarboxylic dianhydride;
A binder resin composition for a lithium ion secondary battery, comprising at least one monoalkali metal salt selected from the group consisting of a lithium salt, a sodium salt or a potassium salt,
The tetracarboxylic dianhydride comprises 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride or 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride;
The binder resin composition for a lithium ion secondary battery, wherein the monoalkali metal salt is contained in an amount of 4 to 20 mol% with respect to 100 mol% of the tetracarboxylic dianhydride.   The binder resin composition for a lithium ion secondary battery according to claim 1, wherein the monoalkali metal salt contains water as a ligand.   The lithium ion according to claim 1, wherein the monoalkali metal salt includes a ligand having a molecular weight of 200 or less as a ligand, and at least one of the ligands having a molecular weight of 200 or less has a carboxyl group. A binder resin composition for a secondary battery.   The film obtained by heating the resin composition is immersed in a mixed solvent of ethylene carbonate and diethyl carbonate (1: 1 volume ratio), and the swelling degree after holding at 60 ° C. for 3 days is 20% or less. The binder resin composition for lithium ion secondary batteries according to claim 1.   The binder resin composition for a lithium ion secondary battery according to claim 1, wherein a charging ratio of the tetracarboxylic dianhydride and the diamine compound is 0.95 to 0.99: 1.00. The binder resin composition for a lithium ion secondary battery according to claim 1, wherein 25 to 100 mol% of the diamine compound is a compound represented by the following chemical formula 1.

(Chemical formula 1)
(In the formula, A ₁ represents a direct bond, an isopropylidene group, a hexafluorinated isopropylidene group, a carbonyl group, a thio group and / or a sulfonyl group. N is an integer of 1 to 4.)   The binder resin composition for a lithium ion secondary battery according to claim 1, wherein the monoalkali metal salt does not contain fluorine.   The lithium ion secondary battery according to claim 1, wherein 30 to 100 mol% of the tetracarboxylic dianhydride is 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride. Binder resin composition.   A lithium ion secondary battery electrode mixture paste comprising at least one negative electrode active material selected from silicon atoms, tin atoms or germanium atoms, and the binder resin composition according to claim 1.   An electrode for a lithium ion secondary battery obtained by applying the lithium ion secondary battery electrode mixture paste according to claim 9 on a current collector and subjecting it to an imidization reaction by heat treatment.   A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is an electrode for a lithium ion secondary battery according to claim 10. A polyamic acid composed of a diamine compound and tetracarboxylic dianhydride;
At least one monoalkali metal salt selected from the group consisting of lithium salt, sodium salt or potassium salt;
A method for producing a lithium ion secondary battery electrode mixture paste, comprising at least one negative electrode active material selected from silicon atoms, tin atoms, or germanium atoms,
The polyamic acid;
The manufacturing method of the lithium ion secondary battery electrode compound paste which has a process which mixes 4-20 mol% of the said monoalkali metal salt with respect to 100 mol% of said tetracarboxylic dianhydrides.   The manufacturing method of the electrode for lithium ion secondary batteries obtained by apply | coating the lithium ion secondary battery electrode compound paste of Claim 9 on a collector, and heat-treating and imidating.