JP2019096401A - Binder for lithium ion secondary battery production, and lithium ion secondary battery using the same - Google Patents

Abstract

To provide a binder for lithium ion secondary battery production, which enables the manufacturing of an electrode with good adhesion among an electrode active substance, and satisfying contactness between an electrode mixture layer and a collector, and enables the manufacturing of a lithium ion secondary battery superior in cycle characteristic.SOLUTION: A binder for a lithium ion secondary battery production, an electrode, and a separator and a lithium ion secondary battery each arranged by use thereof are provided according to the present invention. The binder for lithium ion secondary battery production comprises a polyimide soluble in solvent. The polyimide is such a polyimide that the degree of swelling of a film fabricated from the polyimide, which has been immersed in an electrolyte solution for a lithium ion secondary battery and then subjected to a treatment at 80°C for 72 hours, is 50 wt.% or less.SELECTED DRAWING: None

Description

  The present invention relates to a binder used for producing a lithium ion secondary battery, an electrode using the same, a separator, and a lithium ion secondary battery using the same.

  Among secondary batteries, lithium ion secondary batteries are widely used as power sources for mobile electronic devices such as smart phones, because they are lighter and have higher capacity than nickel cadmium batteries and nickel hydrogen batteries. In addition, in recent years, the power source for hybrid vehicles and electric vehicles is also becoming widespread. As these power sources, lithium ion secondary batteries are expected to further increase the capacity and life.

  With regard to the negative electrode of a lithium ion secondary battery, many negative electrode active materials of alloy type such as silicon and silicon oxide having a large discharge capacity have been studied as a negative electrode active material capable of increasing the capacity. However, since the silicon-based negative electrode active material has a large expansion and contraction at the time of charge and discharge, cutting of the conductive path between the negative electrode active material particles in the negative electrode mixture layer by repetition of charge and discharge, the negative electrode mixture layer and the current collector There is concern that the separation between the layers may occur and the life characteristics may deteriorate. On the other hand, an electrode using a highly elastic polyimide having high adhesive strength as a binder for a negative electrode has been reported (Patent Document 1).

  In addition, as for the positive electrode, there are increasing examples of using a ternary composite oxide (hereinafter also referred to as "NCM positive electrode material") composed of nickel, cobalt and manganese having a large amount of nickel excellent in capacity expression amount as a positive electrode active material . However, when the nickel content of the NCM positive electrode active material is increased to increase the capacity, there is a problem that the dehydrofluorination reaction proceeds when PVDF is used as a binder and a slurry for a stable positive electrode can not be prepared. The In addition, PVDF is swollen by the electrolyte when the temperature of the battery becomes high, and cutting of the conductive path between the positive electrode active material and peeling of the positive electrode mixture layer and the current collector occur, resulting in deterioration of the life characteristics. There's a problem. In order to solve the problem of such PVDF, the electrode which uses a polyimide as a binder for positive electrodes is reported (patent document 2).

  Moreover, the binder for lithium ion secondary batteries containing a polyamic acid is also reported (patent documents 1, 3). However, since polyamic acid is easily hydrolyzed by water and easily changes at room temperature, there is a problem that the characteristic is easily varied. Furthermore, when using a binder containing a polyamic acid, a high temperature treatment such as 350 ° C. is required to make the imidization proceed completely. Therefore, the copper foil is oxidized at the time of manufacturing the electrode, and the resistance is increased. Therefore, there is a problem that the practical use is difficult unless it is a special atmosphere such as an inert gas atmosphere.

  Furthermore, a lithium ion secondary battery using a solvent-soluble block copolymerized polyimide which completes imidization as a binder for electrodes has also been reported (patent documents 4, 5, 6), and a polyimide water as a binder for electrodes A lithium ion secondary battery using a dispersion has also been reported (Patent Document 7).

Japanese Patent Application Publication No. 2014-067592 Japanese Patent Application Laid-Open No. 2002-124264 JP 2012-209219 JP-A-11-097028 JP, 2009-283284, A International Publication No. 2013/115219 JP 2017-190409

  Originally, polyimide is excellent in solvent resistance, but it is soluble in solvents such as N-methyl pyrrolidone, dimethyl acetamide, dimethylformamide, dimethyl sulfoxide and the like by controlling the imide group concentration in the polyimide, refraction and bending bond. Can be synthesized.

  In order to use such solvent-soluble polyimide as a binder for electrode production of a lithium ion battery, the solubility of the polyimide in the solvent is maintained and the polyimide is not dissolved in the electrolyte solution of the lithium ion secondary battery. It is necessary that the degree of swelling of the polyimide with respect to the electrolytic solution is small.

  However, when the present inventors try to increase the solubility of polyimide in the above-mentioned solvent, the solvent resistance of polyimide to the electrolyte used in the lithium ion secondary battery becomes insufficient, and the degree of swelling to the electrolyte increases. I found out. In addition, it was found that when the degree of swelling of the polyimide in the electrolytic solution was reduced, the solubility of the polyimide in the solvent was reduced. That is, in the case of a solvent-soluble polyimide synthesized from a combination of conventional tetracarboxylic acid dianhydride and diamine, it has been difficult to simultaneously achieve high solvent solubility in the solvent and low swelling degree in the electrolyte.

  As a result of intensive investigations in view of the above problems, the present inventors control the molecular weight of tetracarboxylic acid dianhydride and diamine used in the synthesis of polyimide to achieve high solvent solubility in solvents and low swelling degree in electrolytes. The inventors have found that it is possible to synthesize a solvent-soluble polyimide that can be compatible and suitable as a binder for lithium ion secondary batteries for the first time, and the present invention has been completed.

  That is, the present invention is a binder for producing a lithium ion secondary battery containing a solvent-soluble polyimide, wherein the polyimide immerses a film produced from the polyimide in an electrolyte for a lithium ion secondary battery, and A binder for producing a lithium ion secondary battery, which is a polyimide having a degree of swelling (hereinafter also referred to as “electrolyte solution swelling degree”) after time treatment of not more than 50% by weight.

  The present invention is also a binder for producing a lithium ion secondary battery, which comprises a solvent-soluble polyimide synthesized from tetracarboxylic acid dianhydride and a diamine, wherein the polyimide is a block copolymer, and the polyimide is constituted. It is a polyimide in which the molecular weight of all the tetracarboxylic acid dianhydride components is 360 or less, and the proportion of the diamine component having a molecular weight of 220 or less among all the diamine components constituting the polyimide is at least 30 mol%. Provided is a binder for producing a lithium ion secondary battery.

  Furthermore, the present invention is a method for producing a solvent-soluble polyimide for use in a binder for producing a lithium ion secondary battery by reacting tetracarboxylic acid dianhydride with diamine to obtain all solvent used for the reaction. A method for producing a binder for a lithium ion secondary battery, wherein the molecular weight of tetracarboxylic dianhydride is 360 or less, and the proportion of diamine having a molecular weight of 220 or less among all the diamines used in the reaction is at least 30 mol%. ,I will provide a.

  By synthesizing a specific solvent-soluble polyimide in the present invention in which the molecular weight of the tetracarboxylic acid dianhydride component and the diamine component constituting the polyimide is controlled, a solvent-soluble polyimide having an electrolyte solution swelling degree of 50% by weight or less is synthesized for the first time It became possible. In addition, adhesion between electrode active materials is achieved by using the binder for producing a lithium ion secondary battery of the present invention, which contains a polyimide capable of achieving both high solvent solubility to such solvent and low swelling degree to the electrolyte. It is possible to produce an electrode having good adhesion and adhesion between the electrode mixture layer and the current collector. Moreover, by using such an electrode, it becomes possible to produce a lithium ion secondary battery excellent in the life characteristics (cycle characteristics).

  The binder for a lithium ion secondary battery of the present invention contains a solvent-soluble polyimide. The features of the solvent-soluble polyimide in the present invention and the method for synthesizing the same will be specifically described below.

<Solvent soluble polyimide>
The solvent-soluble polyimide in the present invention is a polyimide having a degree of swelling of 50% by weight or less when immersed in an electrolyte for a lithium ion secondary battery and treated at 80 ° C. for 72 hours.

The specific measuring method of the swelling degree in this invention is as follows. That is, a solvent-soluble polyimide is poured into a dish-like container and dried at 120 ° C. for 15 hours to prepare a 3 cm × 3 cm test piece from a film having a thickness of about 50 μm. Then, the test piece is immersed in an electrolyte solution obtained by dissolving 1 mol / L of lithium hexafluorophosphate (LiPF ₆ ) in an electrolyte solution solvent consisting of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3: 3: 4, After heating the electrolytic solution to 80 ° C., the test piece is subjected to immersion treatment at 80 ° C. for 72 hours. The weight increase rate (%) of the film obtained by measuring the weight of the polyimide film before and after the immersion treatment in the electrolytic solution is taken as the degree of swelling (also referred to as "the degree of electrolytic solution swelling") in the present invention. Here, the method of producing the film does not affect the value of the degree of swelling of the electrolyte, and the weight of the film after the immersion treatment is such that the test piece is taken out of the electrolyte and the surface of the tissue is quickly not to be dried. It was measured after wiping off the electrolyte adhering to the.

  In the present invention, the degree of swelling of the polyimide film measured by the above method is preferably 50% by weight or less, more preferably 40% by weight or less, and particularly preferably 30% by weight or less. When the degree of swelling with respect to the electrolyte is large, adhesion between the active material tends to be insufficient, and adhesion between the electrode mixture layer and the current collector tends to be insufficient, and when used as a battery binder, the battery There is a tendency for the life characteristics of The lower the degree of swelling of the polyimide film, the better, but the lower limit of the degree of swelling is 15% by weight or more, further 17% by weight or more, and particularly 19% by weight or more. Can be achieved

  The term "solvent soluble" in the present invention is a term used for organic polar solvents used in the synthesis of polyimides and solvents used for the mixture described later, and is a polyimide which dissolves 5 g or more in 100 g of solvent. It means that there is. As the solvent, at least one organic solvent selected from the group consisting of N-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide and dimethylsulfoxide is preferable. The synthetic | combination polyimide can be used as a binder of a lithium ion secondary battery in the state of the solution which it was made to melt | dissolve in the said solvent, for example, so that solid content might be 10 to 30 weight%.

(Method of synthesizing solvent-soluble polyimide)
The solvent-soluble polyimide in the present invention can be synthesized by subjecting tetracarboxylic acid dianhydride and diamine to a catalytic dehydration / ring closure reaction in a solvent.
Examples of the catalyst include acid catalysts such as sulfuric acid, phosphoric acid and toluenesulfonic acid, and tetracarboxylic acid dianhydride and diamine can be heated to 160 to 200 ° C. to promote imidation using an acid catalyst. .

  If an acid catalyst remains in the formed polyimide solution, it causes discoloration or deterioration of the polymer product, so an insoluble solvent such as methanol or butanone is added to the formed polyimide solution to precipitate the polyimide, and it is separated and circulated. By re-dissolving, separation of polyimide and catalyst is performed (WH Miller, USP 4,927,736).

  As a further preferable synthesis method of the solvent-soluble polyimide in the present invention, there is a method of promoting a dehydration imidization reaction using a two-component acid-base catalyst utilizing an equilibrium reaction of lactone (US Pat. No. 5502143). In this method, a binary catalyst of γ-valerolactone and pyridine or N-methylmorpholine is used. As the imidization proceeds, water is produced, and the produced water participates in the lactone equilibrium to become an acid / base catalyst and exhibits a catalytic action.

  Water generated by the imidization reaction is removed out of the system by azeotropic distillation with toluene or xylene coexisting in a polar solvent. When the imidization reaction is completed, water in the solution is removed, and the acid / base catalyst becomes γ-valerolactone and pyridine or N-methylmorpholine and is removed out of the system. Thus, a highly pure polyimide solution can be obtained.

  As another two-component catalyst, oxalic acid or malonic acid and pyridine or N-methylmorpholine are used. In the reaction solution at 160 to 200 ° C., oxalate or malonate accelerates the imidization reaction as an acid catalyst. A catalytic amount of oxalic acid or malonic acid remains in the formed polyimide solution. When the polyimide solution is applied and heated to 200 ° C. or higher to remove the solvent and form a film, oxalic acid or malonic acid remaining in the polyimide is thermally decomposed and removed as a gas to the outside of the system. Thus, a high purity polyimide product can be obtained. The oxalic acid-pyridine based catalyst is more active than the valerolactone-pyridine based catalyst, and can generate a high molecular weight polyimide in a short time.

(Tetracarboxylic acid dianhydride)
Examples of tetracarboxylic acid dianhydrides used in the present invention include pyromellitic acid dianhydride (PMDA), 1,2,5,6-, and the like as tetracarboxylic acid dianhydrides for inducing formation of a tetracarboxylic acid ester compound. Naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 2,2 ', 3,3'- Biphenyl tetracarboxylic acid dianhydride, 2,3,3 ′, 4′-biphenyl tetracarboxylic acid dianhydride, 3,3 ′, 4,4′-biphenyl tetracarboxylic acid dianhydride (BPDA), 2,2 ', 3,3'-benzophenonetetracarboxylic acid dianhydride, 2,3,3', 4'-benzophenonetetracarboxylic acid dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic acid dianhydride ( TDA), bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 1, 1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 2,2-bis [3,4- (dicarboxyphenoxy) ) Phenyl] propane dianhydride (BPADA), 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) Sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfoxide dianhydride, thiodiphthalic acid dianhydride, 3,4,9,10-perylene tetracarboxylic acid Water, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride, 9,9-bis (3,4-dicarboxyphenyl) fluorene Aromatic tetracarboxylic acid dianhydrides such as dianhydrides, 9,9-bis [4- (3,4'-dicarboxyphenoxy) phenyl] fluorene dianhydrides, cyclobutane tetracarboxylic acid dianhydrides, 1,2 , 3,4-cyclopentane tetracarboxylic dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 3,4- Examples include dicarboxy-1-cyclohexyl succinic dianhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride, etc. It is not limited to these. These tetracarboxylic acid dianhydrides may be used alone or as a mixture of two or more.

  In the present invention, as the tetracarboxylic acid dianhydride, it is preferable to use one having a molecular weight of 360 or less, further 350 or less, and particularly 330 or less. As a tetracarboxylic acid dianhydride having a molecular weight of 360 or less, pyromellitic dianhydride (PMDA; molecular weight 218.1), 4,4'-oxydiphthalic anhydride (ODPA; molecular weight 310.2), 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride (BPDA; 294.2), 3,3', 4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA; molecular weight 322.2), etc. Be

  When the molecular weight of tetracarboxylic dianhydride is greater than 360, the solubility of the resulting polyimide in N-methylpyrrolidone and dimethylacetamide is improved, but the degree of swelling of the lithium ion secondary battery in the electrolyte is more than 50%. When it becomes large and it uses as a binder for electrodes of a lithium ion secondary battery, there exists a tendency for cycle characteristics to deteriorate.

  In the present invention, by reacting tetracarboxylic acid dianhydride having a molecular weight of 360 or less with a diamine in this way, a polyimide having a structure in which the molecular weight of all tetracarboxylic acid dianhydride components constituting the polyimide becomes 360 or less. Can be synthesized to provide a polyimide capable of achieving both high solvent solubility and low electrolyte swelling degree.

(Diamine)
As the diamine used in the present invention, paraphenylene diamine (PPD), metaphenylene diamine (MPDA), 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 2,5-dimethyl 1 , 4-phenylenediamine (DMPDA), 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 2,2 -Bis (trifluoromethyl) -4,4'-diaminobiphenyl, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (MDA), 2,2-bis- (4-aminophenyl) propane, 3 , 3'-diaminodiphenylsulfone (33DDS), 4,4'-diaminodiphenylsulfone (44DDS), 3,3'- Aminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,4-diaminodiphenyl ether (m-DADE), 4,4'-diaminodiphenyl ether (p-DADE), 1,5-diaminonaphthalene, 4,4'- Diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethyl phosphine oxide, 1,3-bis (3-aminophenoxy) benzene (APB), 1,3-bis (4-amino) Phenoxy) benzene (TPE-R), 1,4-bis (4-aminophenoxy) benzene, bis [4- (3-aminophenoxy) phenyl] sulfone (BAPSM), bis [4- (4-aminophenoxy) phenyl ] Sulfone (BAPS), 2,2-bis [4- (4-aminophenoxy) ) Phenyl] propane (BAPP), 3,3-diamino-4,4-dihydroxydiphenyl sulfone (ABPS), hydroxybenzidine (HAB), 2-bis (3-aminophenyl) 1,1,1,3,3,3 3-hexafluoropropane, 2,2-bis (4-aminophenyl) 1,1,1,3,3,3-hexafluoropropane, 9,9-bis (4-aminophenyl) fluorene and the like can be exemplified. Not limited to these. These diamines may be used alone or as a mixture of two or more.

In the present invention, as the diamine, the proportion of the diamine component having a molecular weight of 220 or less is at least 30 mol% or more, further 40 mol% or more, particularly 50 mol% or more of all diamine components used in the synthesis of polyimide. Is preferred.

  As diamines having a molecular weight of 220 or less, 4,4'-diaminobiphenyl, 2,5-dimethyl 1,4-phenylenediamine (DMPDA; molecular weight 136.19), diaminobenzoic acid (molecular weight 152.15), isophorone diamine (molecular weight 170.3), 4,4-diaminodiphenylmethane (MDA; molecular weight 198.26), 3,4-diaminodiphenyl ether (3,4-DADE; molecular weight 200.24), 4,4'-diaminodiphenyl ether (4,4) Molecular weight 200.24), 3,3'-dihydroxybenzidine (HAB; molecular weight 216.24), bis (4-aminophenyl) sulfide (ASD; molecular weight 216.3), and the like.

  When the proportion of the diamine component having a molecular weight of 220 or less is less than 30 mol%, the solubility of the resulting polyimide in N-methylpyrrolidone and dimethylacetamide is improved, but the degree of swelling of the lithium ion secondary battery in the electrolyte is It tends to be greater than 50%, and when used as a binder for an electrode of a lithium ion secondary battery, the cycle characteristics tend to deteriorate.

(Preferred embodiment of solvent soluble polyimide)
In the present invention, it is preferable to react the tetracarboxylic acid dianhydride having a molecular weight of 360 or less as described above with a diamine in which the proportion of a diamine having a molecular weight of 220 or less is at least 30% by mole of the total diamine. Thus, a polyimide having a structure in which the molecular weight of all tetracarboxylic acid dianhydride components constituting the polyimide is 360 or less and the proportion of the diamine component having a molecular weight of 220 or less is at least 30 mol% or more of all diamine components. It is possible to provide a polyimide that can be synthesized, has better solubility in a solvent, and has a smaller degree of swelling in a lithium ion secondary battery electrolyte.

(Imide group concentration)
In the present invention, setting the molecular weight of the carboxylic acid dianhydride or diamine used in the synthesis of the polyimide to a specific range means controlling the imide group concentration of the polyimide to be synthesized.
In the present invention, the imide group concentration in the polyimide resin is a value calculated by the following formula (1).
Imido group concentration = [(molecular weight of imide group portion 140) / (molecular weight of polyimide)] × 100 (1)

Since one mole of water is taken when an imide ring is formed by the reaction of a carboxylic acid dianhydride and a diamine, two imide rings are formed by the reaction of a pair of the carboxylic acid dianhydride and the diamine. (1) can be represented by the following formula (2).
[(Molecular weight 140 of imide group portion) / (molecular weight of tetracarboxylic acid dianhydride + molecular weight of diamine−molecular weight of water of 2 moles)] × 100 (2)

  When using a plurality of tetracarboxylic acid dianhydrides or diamines, as the molecular weight of the tetracarboxylic acid dianhydride and diamine in the above-mentioned formula (2), an average molecular weight calculated from the used amount of each component is used. Here, when the total amount of tetracarboxylic dianhydride used is 1, the average molecular weight of tetracarboxylic dianhydride is determined as the sum of the product of the ratio of each component used multiplied by the molecular weight of that component. be able to. Similarly, when the total amount of diamine used is 1, the average molecular weight of the diamine can be determined as the sum of the ratio of each component used multiplied by the molecular weight of that component.

  As can be seen from the above formula (2), the use of a low molecular weight tetracarboxylic acid dianhydride or a low molecular weight diamine increases the imide group concentration of the resulting polyimide. As described above, a polyimide varnish is prepared by incorporating a specific amount of a tetracarboxylic acid dianhydride having a specific molecular weight or less and a diamine having a specific molecular weight or less to synthesize a polyimide varnish, thereby dissolving the solvent in the solvent and having a low degree of swelling of the electrolyte. You can get Therefore, the lower limit value of the imide group concentration of the polyimide is 20% or more, further 25% or more, particularly, in that polyimide having a good solubility in a solvent and a low degree of swelling of the electrolyte can be obtained. 28% or more is preferable.

A polyimide having a high concentration of imide groups has a large irreversible capacity when used in a lithium ion secondary battery. Therefore, considering the irreversible capacity, the imide group concentration of the polyimide used as the binder for the electrode of the lithium ion secondary battery is preferably 33% or less, more preferably 32.5% or less, and particularly preferably 32% or less. When the imide group concentration of the polyimide exceeds 33%, the irreversible capacity of the lithium ion secondary battery tends to be large.
As described above, the imide group concentration of the solvent-soluble polyimide can be set to an optimum range in consideration of the electrolyte swelling degree and the irreversible capacity.

  In order to obtain a solvent-soluble varnish in which the imide group concentration is in the optimum range, block co-coefficients can be introduced in that tetracarboxylic acid dianhydrides of low molecular weight and diamines of low molecular weight can be introduced into different block structures. It is preferred to use a polymerization method. By using the block copolymerization method, it is possible to easily dissolve in a solvent and obtain a polyimide having a low degree of swelling of the electrolyte.

  On the other hand, if the synthesis is carried out by random polymerization without introducing a tetracarboxylic acid dianhydride having a small molecular weight and a diamine having a small molecular weight into different block structures, the reaction solution becomes turbid or gelates during the synthesis to obtain a solvent soluble polyimide. Things are difficult.

(Block copolymer)
Furthermore, the solvent-soluble polyimide of the present invention is preferably a block copolymer. In the case of the block copolymer, it is possible to expand the range of the polyimide compatible with the high solvent solubility in the solvent and the electrolyte swelling degree of 50% by weight or less.

  Originally, polyimide is difficult to dissolve in solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylsulfoxide, and in random polymerization, it is difficult to ensure the solubility in the solvent. However, in the case of a block copolymer, since it is possible to introduce tetracarboxylic acid dianhydride and diamine in a combination in which it is difficult to secure solubility in separate block structures, solubility in a solvent can be secured. Conceivable.

In addition, when the solvent-soluble polyimide of the present invention is a block copolymer, in a film obtained by drying the polyimide, an intermolecular interaction between tetracarboxylic acid dianhydride introduced in separate block structures and diamine. It is thought that a small degree of swelling of the electrolyte can be achieved because
The synthesis method of block copolymerized polyimide can be referred to the method described in WO2006 / 057036.

  In the present invention, the weight average molecular weight of the soluble polyimide is preferably 100,000 or more, and more preferably 130,000 or more. If the weight average molecular weight is less than 100,000, the stability of the electrode slurry composition produced using the polyimide tends to deteriorate. On the other hand, the upper limit of the weight average molecular weight is not particularly limited as long as it can be manufactured, but when the molecular weight is too large, the resistance of the lithium ion battery tends to increase, so the amount used as a binder needs to be reduced.

  The solvent-soluble polyimide in the present invention preferably has a B-type viscosity of 2000 cps or more in an 8% NMP solution. When the B-type viscosity is lower than 2000 cps, the stability of the electrode slurry tends to deteriorate. The B-type viscosity of the 8% NMP solution is more preferably 3000 cps or more, particularly preferably 5000 cps or more.

<Binder for lithium ion secondary battery>
The solvent-soluble polyimide in the present invention can be used as a binder for a positive electrode of a lithium ion battery or as a binder for a negative electrode. Also in the binder for ceramic coating, the degree of swelling with respect to the electrolyte is important, so the solvent-soluble polyimide of the present invention can also be suitably used as a binder for ceramic coating.

(The amount of binder used)
When the solvent-soluble polyimide of the present invention is used as a binder for a positive electrode of a lithium ion secondary battery, the solvent-soluble polyimide is 0.5 parts by mass to 10 parts by mass, preferably 1 part by mass per 100 parts by mass of the electrode active material. A part to 5 parts by mass, more preferably 1.5 parts by mass to 3 parts by mass can be used. When the amount of the solvent-soluble polyimide of the present invention used is less than 0.5 parts by mass, the adhesion between the active materials and the adhesion between the electrode layer and the current collector tend to be lowered and the peel strength tends to be lowered.

  When the solvent-soluble polyimide of the present invention is used as a binder for the negative electrode of a lithium ion secondary battery and a carbon material is used as an electrode active material, the solvent-soluble polyimide is 0.5 mass per 100 mass parts of the electrode active material Part to 10 parts by mass, preferably 1 to 5 parts by mass, and more preferably 1.5 to 3 parts by mass can be used. When the amount of the solvent-soluble polyimide of the present invention used is less than 0.5 parts by mass, the adhesion between the active materials and the adhesion between the electrode layer and the current collector tend to be lowered and the peel strength tends to be lowered.

  When a silicon material is used alone or in combination with a carbon material and used as a negative electrode active material, the solvent-soluble polyimide is 2 parts by mass to 20 parts by mass, preferably 1 part by mass, per 100 parts by mass of the electrode active material. ~ 10 parts by weight can be used. The amount of the solvent-soluble polyimide used as the binder varies depending on the use ratio of the silicon material and is appropriately determined.

<Electrode for Lithium Ion Secondary Battery and Method of Manufacturing the Same>
The material used for the electrode for lithium ion secondary batteries is demonstrated.
(Positive electrode active material)
The positive electrode active material for lithium ion secondary batteries is not particularly limited, but lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), Co- Lithium-containing composite oxide of Ni-Mn (Li (CoMnNi) O ₂ ), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, lithium olivine type lithium iron phosphate (LiFePO 4 ₄ ), olivine type lithium manganese phosphate (LiMnPO ₄ ), Li ₂ MnO ₃ -LiNiO ₂ based solid solution, lithium excess spinel compound represented by Li _{1 + x} Mn _2-x O ₄ (0 <X <2), Li _{[Ni 0.17 Li 0.2 Co 0.07 Mn} 0.56] O 2, LiNi 0.5 Mn 1 ₅ known positive electrode active material O ₄ and the like. The compounding quantity and particle size of a positive electrode active material are not specifically limited, The thing of a well-known range can be used.

(Anode active material)
The polar active material for lithium ion secondary batteries is not particularly limited, but coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fiber, pyrolytic vapor grown carbon fiber, phenol resin fired body, polyacrylonitrile type Carbon-based negative electrode active material such as carbon fiber, quasi-isotropic carbon, furfuryl alcohol resin fired body (PFA), hard carbon, natural graphite, artificial graphite, etc .; silicon (Si), alloy containing silicon, SiO, SiOx, Si A non-carbon-based negative electrode active material such as a composite of a conductive carbon and a Si-containing material formed by coating or complexing a contained material with conductive carbon may, for example, be mentioned. The compounding quantity and particle size of a negative electrode active material are not specifically limited, The thing of a well-known range can be used.

(Conductive material)
The slurry composition for electrodes obtained by disperse | distributing an electrode active material using a binder may contain the electrically conductive material. The conductive material is for securing electrical contact between the electrode active materials. As the conductive material, carbon black (eg, acetylene black, ketjen black (registered trademark), furnace black, etc.), graphite, carbon fiber, carbon flake, carbon ultrashort fiber (eg, carbon nanotube, vapor grown carbon fiber, etc.) And the like; fibers of various metals, foils, and the like can be used. Among them, carbon black is preferable as the conductive material, and acetylene black is more preferable. These can be used individually by 1 type or in combination of 2 or more types.

  Although the compounding quantity of the electrically conductive material in a slurry composition is not specifically limited, It is preferable that it is 1 mass part or more per 100 mass parts of electrode active materials, and it is preferable that it is 10 mass parts or less. When the slurry composition contains the conductive material in an amount within the above range, a good conductive path is formed in the mixture layer of the electrode manufactured using the slurry composition, and in particular, the slurry composition is used for the positive electrode. When used, battery characteristics such as rate characteristics of the lithium ion secondary battery can be improved.

  In the case of a slurry composition for slurry ceramic coating, the conductive material is used in an amount of 2 parts by mass to 10 parts by mass with respect to 100 parts by mass of an inorganic filler such as alumina. If the amount of the conductive material used is less than 2 parts by mass, the heat resistance of the separator tends to decrease. When the amount of the conductive material used is more than 10 parts by mass, the air permeability of the heat-resistant separator having the heat-resistant layer coated with the ceramic slurry decreases, and when used in the battery, the resistance of the battery tends to increase. .

(Slurry composition for electrode)
The slurry composition for electrodes (resin composition for electrodes) can be prepared by dispersing the above-mentioned components together with the solvent-soluble polyimide binder of the present invention in a dispersion medium such as N-methyl pyrrolidone (NMP). Specifically, the above components, the solvent-soluble polyimide binder, and the dispersion medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a leash, an ultrasonic disperser, a homogenizer, a planetary mixer, and film mix. The slurry composition can be prepared by mixing

  It is preferable that solid content concentration of the obtained slurry composition for electrodes is 40 to 80 mass%. If the solid content concentration of the slurry composition for electrodes is within the above range, the drying efficiency at the time of producing the electrode mixture layer by removing the dispersion medium from the slurry composition for electrodes can be enhanced. Moreover, since the slurry composition for electrodes contains a solvent-soluble polyimide, it exhibits excellent coatability even when the solid content concentration is relatively high.

  It is preferable that the viscosity of the slurry composition for electrodes is 3000 mPa * s or more and 8000 mPa * s or less. If the viscosity of the slurry composition for electrodes is within the above range, the coatability will be good, and holes and coating unevenness formed by air entrainment at the time of preparation of the slurry composition will be sufficiently suppressed, and have uniform thickness. An electrode mixture layer can be formed. In addition, the "viscosity" of the slurry composition for electrodes of a lithium ion secondary battery is a viscosity measured using a single cylindrical rotational viscometer (B-type viscometer), and specifically, in the following examples It can be measured using the method described.

(Electrode for lithium ion secondary battery)
The electrode for a lithium ion secondary battery of the present invention comprises a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed using the slurry composition for an electrode of the lithium ion secondary battery, and specifically, it is formed by applying and drying the slurry composition for an electrode on a current collector. it can. That is, the electrode mixture layer is made of the dried product of the slurry composition for electrodes, and usually contains the solvent-soluble polyimide of the present invention and the electrode active material, and optionally contains the conductive material. The electrode mixture layer contains, as other components, a polymer such as PVDF, epoxy resin or synthetic rubber as a binder other than the solvent-soluble polyimide of the present invention, an antifoamer, a leveling agent, a flame retardant, etc. It may be

The preferred abundance ratio of each component contained in the electrode mixture layer is the same as the preferred abundance ratio of each component in the slurry composition.
The electrode for a lithium ion secondary battery of the present invention is manufactured using the slurry composition of the present invention, and thus is excellent in peel strength. By using the electrode of the present invention, a lithium ion secondary battery excellent in battery characteristics such as cycle characteristics can be obtained.

(Method of manufacturing electrode for lithium ion secondary battery)
The electrode for a lithium ion secondary battery of the present invention includes, for example, a step of applying the above-described slurry composition on a current collector (coating step), and drying and collecting the slurry composition applied on the current collector. It manufactures through the process (drying process) of forming an electrode compound material layer on a collector.

[Coating process]
It does not specifically limit as method to apply | coat the slurry composition for electrodes on a collector, A well-known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application of the slurry composition and before drying may be appropriately set according to the thickness of the electrode mixture layer obtained by drying.

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

[Drying process]
The method for drying the slurry composition on the current collector is not particularly limited, and any known method can be used. For example, drying with warm air, hot air, low humidity air, vacuum drying, irradiation with infrared rays, electron beam, etc. The drying method is mentioned. Thus, by drying the slurry composition on the current collector, an electrode mixture layer is formed on the current collector, and an electrode for a lithium ion secondary battery comprising the current collector and the electrode mixture layer is obtained. be able to.
The electrode mixture layer may be subjected to pressure treatment using a die press or a roll press after the drying step. While the adhesion between the electrode mixture layer and the current collector can be improved by the pressure treatment, the density of the electrode mixture layer can be increased.

Lithium-Ion Secondary Battery and Method of Manufacturing the Same
The lithium ion secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the lithium ion secondary battery electrode of the present invention is used as at least one of the positive electrode and the negative electrode. And since the lithium ion secondary battery of this invention is equipped with the electrode for lithium ion secondary batteries of this invention, it is excellent in battery characteristics, such as cycling characteristics.

(electrode)
In the lithium ion secondary battery of the present invention, an electrode other than the electrode of the above-described lithium ion secondary battery of the present invention can be used. Although it does not specifically limit as electrodes other than the electrode of this invention, The well-known electrode used for manufacture of a lithium ion secondary battery can be used. Specifically, an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.

(Electrolyte solution)
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As a supporting electrolyte of a lithium ion secondary battery, for example, a lithium salt is used. Examples of lithium salts include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable, from the viewpoint of being easily soluble in a solvent and exhibiting a high degree of dissociation. The electrolyte may be used alone or in combination of two or more at an arbitrary ratio. Usually, the lithium ion conductivity tends to be higher as the supporting electrolyte having a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of the supporting electrolyte.

  The organic solvent used for the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, and examples thereof include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and ethyl methyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide And the like are preferably used. Also, a mixture of these solvents may be used. Among them, carbonates are preferably used from the viewpoint of a high dielectric constant and a wide stable potential region.

  The concentration of the electrolyte in the electrolytic solution can be properly adjusted, and is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. More preferable. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone can be added to the electrolytic solution.

(Separator)
The separator is not particularly limited, but is preferably a microporous film made of a resin such as polyolefin (polyethylene, polypropylene), polyamide, polyimide or the like. In addition, a heat resistant separator provided with a ceramic coating layer on one side or both sides of the microporous membrane may be used. The solvent-soluble polyimide of the present invention can also be suitably used as a binder used in this ceramic coating layer.

(Method of manufacturing lithium ion secondary battery)
In the lithium ion secondary battery of the present invention, for example, one obtained by overlapping a positive electrode and a negative electrode with a separator interposed therebetween is wound according to the battery shape as needed, or the positive electrode and the negative electrode are It can be manufactured by putting a plurality of sheets sandwiching a separator, etc. and putting them in a battery container, injecting an electrolytic solution into the battery container and sealing it. A fuse, an over current protection element such as a PTC element, an expanded metal, a lead plate, etc. may be provided if necessary to prevent the pressure rise inside the lithium ion secondary battery and the occurrence of overcharge and discharge and the like. . The shape of the lithium ion secondary battery may be, for example, a coin, a button, a sheet, a cylinder, a square, or a flat.

  EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified.

Abbreviations of raw material compounds used in the following synthesis examples and synthesis comparative examples and their compound names are described below.
s-BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic acid dianhydride (molecular weight: 294.2)
ODPA: 4,4'-oxydiphthalic dianhydride (molecular weight: 310.2)
PMDA: pyromellitic anhydride (molecular weight: 218.1)
BTDA: benzophenone tetracarboxylic acid dianhydride (molecular weight: 322.2)
DMPDA: 2,5-dimethyl-1,4-phenylenediamine (molecular weight: 136.19)
DETDA: Diethylmethylbenzenediamine (molecular weight: 178.28)
m-DADE: 3,4-diaminodiphenyl ether (molecular weight: 200.24)
TPE-R: 1,3-bis (4-aminophenoxy) benzene (molecular weight: 292.33)
ABPS: 3, 3-diamino-4, 4-dihydroxydiphenyl sulfone (molecular weight: 280.33)
p-DADE: diaminodiphenyl ether (molecular weight: 200.24)
APB: 1,3-bis (3-aminophenoxy) benzene (molecular weight: 292.33)
BAPS: bis [4- (4-aminophenoxy) phenyl] sulfone (molecular weight: 432.49)

<Synthesis of Polyimide>
Synthesis Example 1
A beaded condenser equipped with a water separation trap was attached to a glass separable three-necked flask equipped with a stainless steel vertical stirrer. 10.86 g (35 mmol) of 4,4'-oxydiphthalic dianhydride (ODPA, molecular weight: 310.2), 9.53 g of 2,5-dimethyl-1,4-phenylenediamine (DMPDA, molecular weight: 136.19) (70 mmol), 1.40 g of γ-valerolactone, 2.22 g of pyridine, 109 g of N-methylpyrrolidone (NMP) and 45 g of toluene were added to a three-necked flask. Under a nitrogen atmosphere, the silicon bath was heated and stirred at 180 ° C. and 180 rpm for 1.5 hours. Furthermore, it air-cooled to room temperature and stirred for 15 minutes. Subsequently, 7.01 g (35 mmol) of 3,4-diaminodiphenyl ether (m-DADE, molecular weight: 200.24) and 1,3-bis (4-aminophenoxy) benzene (TPE-R, molecular weight: 292.33) 10 A good mixture of .23 g (35 mmol) was added to the three-necked flask little by little. Further, 30.99 g (105 mmol) of 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA, molecular weight: 294.2), 146 g of NMP, and 10 g of toluene are added, and the mixture is heated to 180 ° C. under a nitrogen atmosphere. The mixture was heated and stirred at 180 rpm. The reaction was stopped after 6 hours to obtain a 20% by weight polyimide solution. Further, 106 g of NMP was added and stirred for 30 minutes to obtain a 15% by weight polyimide solution.

  The molar ratio of each component used for polyimide synthesis was ODPA: s-BPDA = 1: 3, DMPDA: m-DADE: TPE-R = 2: 1: 1. The molecular weight of all tetracarboxylic acid dianhydride components used in the synthesis of the polyimide was 360 or less, and the proportion of the diamine component having a molecular weight of 220 or less was 75 mol% of the total diamine components.

The imide group concentration of the polyimide was 30.9 according to the following formula.
(Calculation formula of imide group concentration)
Average molecular weight of tetracarboxylic acid dianhydride:
0.25 × 310.2 + 0.75 × 294.2 = 298.2
-Average molecular weight of diamine:
0.5 × 136.19 + 0.25 × 200.24 + 0.25 × 292.33
= 191.18
・ Imide group concentration:
[140 / (298.2 + 191.18-2 × 18)] × 100 = 30.9

The measurement results of the molecular weight and glass transition temperature (Tg) of the obtained polyimide are as follows.
Molecular weight Mw: 144,478
Tg: 296 ° C.

Synthetic Example 2
The same apparatus as in Synthesis Example 1 was used. 10.86 g (35 mmol) of ODPA (molecular weight: 310.2), 9.53 g (70 mmol) of DMPDA (molecular weight: 136.19), 1.40 g of γ-valerolactone, 2.22 g of pyridine, 109 g of NMP, 45 g of toluene Add to mouth flask. Under a nitrogen atmosphere, the silicon bath was heated and stirred at 180 ° C. and 180 rpm for 1.5 hours. Furthermore, it air-cooled to room temperature and stirred for 15 minutes. Then, 10.23 g (35 mmol) of TPE-R (molecular weight: 292.33) and 9.81 g (35 mmol) of 3,3-diamino-4,4-dihydroxydiphenyl sulfone (ABPS, molecular weight: 280.33) are mixed well Add little by little to the three-necked flask. Further, 30.99 g (105 mmol) of 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA, molecular weight: 294.2), 146 g of NMP, and 10 g of toluene are added, and the mixture is heated to 180 ° C. under a nitrogen atmosphere. The mixture was heated and stirred at 180 rpm. The reaction was stopped after 6 hours and 30 minutes to obtain a 20% by weight polyimide solution. Further, 106 g of NMP was added and stirred for 30 minutes to obtain a 15% by weight polyimide solution.

The molar ratio of each component used for polyimide synthesis was ODPA: DMPDA = 1: 2, s-BPDA: TPE-R: ABPS = 3: 1: 1. The molecular weight of all tetracarboxylic acid dianhydride components used in the synthesis of the polyimide is 360 or less, the proportion of the diamine component having a molecular weight of 220 or less is 50 mol% of the total diamine component, and the imide group concentration of the polyimide is It was 29.6%.
The measurement results of the molecular weight and glass transition temperature (Tg) of the obtained polyimide are as follows.
Molecular weight Mw: 172, 691
Tg: 328.4 ° C.

Synthetic Example 3
The same apparatus as in Synthesis Example 1 was used. 15.27 g (70 mmol) of PMDA (molecular weight: 218.1), 18.72 g (105 mmol) of DETDA (molecular weight: 178.28), 0.9 g of anhydrous oxalic acid, 1.9 g of pyridine, 130 g of NMP, 30 g of toluene One neck flask was added. The reaction was conducted at 180 ° C. and 175 rpm for 1 hour in a nitrogen atmosphere. Furthermore, the reaction was carried out at 180 ° C. and 165 rpm for 4 hours and 20 minutes. Then, 22.55 g (70 mmol) of BTDA (molecular weight: 322.2), 7.01 g (35 mmol) of p-DADE (molecular weight: 200.24), 102 g of NMP are added, and the mixture is heated at 180 ° C. and 165 rpm for 6 hours and 20 minutes. The reaction gave a 20% by weight polyimide solution.

The molar ratio of each component used for polyimide synthesis was PMDA: DETDA = 2: 3, BTDA: p-DADE = 2: 1. The molecular weight of all tetracarboxylic acid dianhydride components used in the synthesis of the polyimide is 360 or less, the proportion of the diamine component having a molecular weight of 220 or less is 100 mol% of the total diamine component, and the imide group concentration of the polyimide is It was 33.5%.
The measurement results of the molecular weight of the obtained polyimide are as follows.
Molecular weight Mw: 199, 610
Tg: 319.5 ° C.

Synthesis Comparative Example 1 (Random Polymerization Example)
Synthesis Example 3 was performed by random polymerization using the same apparatus as in Synthesis Example 1. Three mouths of 21.79 g (160 mmol) of DMPDA (molecular weight: 136.19), 23.39 g (80 mmol) of TPE-R (molecular weight: 292.33), 22.42 g (80 mmol) of ABPS (molecular weight: 280.33) Added to the flask. It was made to melt | dissolve in NMP, stirring at 180 rpm for 10 minutes under nitrogen atmosphere. Then, 24.82 g (80 mmol) of ODPA (molecular weight: 310.2), 70.61 g (240 mmol) of s-BPDA (molecular weight: 294.2), 3.20 g of γ-VL, 5.06 g of pyridine, NMP, 45 g of toluene In addition, it was stirred and heated at 180 rpm and 180 rpm in a silicon bath under a nitrogen atmosphere. The total amount of NMP introduced at this stage was 858 g. The reaction was terminated after 4 hours as the solution became turbid.

Synthetic Comparative Example 2
Using the same apparatus as in Synthesis Example 1, 34.60 g (80 mmol) of BAPS (molecular weight: 432.49) was added to a three-necked flask. It was made to melt | dissolve in NMP, stirring at 180 rpm for 10 minutes under nitrogen atmosphere. Then, 47.1 g (160 mmol) of s-BPDA (molecular weight: 294.2), 24.82 g (80 mmol) of ODPA (molecular weight: 310.2), 3.20 g of γ-VL, 5.06 g of pyridine, NMP, 45 g of toluene In addition, it was stirred and heated at 180 rpm and 180 rpm in a silicon bath under a nitrogen atmosphere. The total amount of NMP introduced at this stage was 390 g. The reaction was carried out for 5 hours and 30 minutes to obtain a 20% by weight polyimide solution.

The molar ratio of each component used for the synthesis of the polyimide was ODPA: BPDA = 1: 2, and the diamine was 100% BAPS. The molecular weight of all tetracarboxylic acid dianhydride components used in the synthesis of the polyimide is 360 or less, the proportion of the diamine component having a molecular weight of 220 or less is 0 mol% of the total diamine component, and the imide group concentration of the polyimide is It was 20.1%.
The measurement results of the molecular weight and glass transition temperature (Tg) of the obtained polyimide are as follows.
Molecular weight Mw: 123680
Tg: 272 ° C.

Synthetic Comparative Example 3
The same apparatus as in Synthesis Example 1 was used. 58.84 g (200 mmol) of s-BPDA (molecular weight: 294.2), 15.21 g (100 mmol) of 1,3-diaminobenzoic acid (molecular weight: 151.15), 1.50 g of γ-valerolactone, 2.4 g of pyridine , 200 g of NMP and 30 g of toluene were added to a three-necked flask. Under a nitrogen atmosphere, the silicon bath was heated and stirred at 180 ° C. and 180 rpm for 1.0 hour. Furthermore, it air-cooled to room temperature and stirred for 15 minutes. Next, 46.53 g (150 mmol) of ODPA (molecular weight: 310.2), 73.08 g (250 mmol) of TPE-R (molecular weight: 292.33), 360 g of NMP, and 90 g of toluene are added, and 180 ° C. at 180 rpm under a nitrogen atmosphere. Heated and stirred. The reaction was stopped after 2 hours and 30 minutes, NMP was added, and the mixture was stirred for 30 minutes to obtain a 20% by weight polyimide solution.

The molar ratio of each component used for polyimide synthesis was s-BPDA: ODPA = 57.1: 42.9, and diaminobenzoic acid: TPE-R = 28.6: 71.4.
Further, the molecular weight of the tetracarboxylic acid dianhydride component used in the synthesis of the polyimide is 360 or less, the proportion of the diamine component having a molecular weight of 220 or less is 28.6 mol% of the total diamine component, and the imide group concentration of the polyimide is It was 27.1%.
The measurement results of the molecular weight and glass transition temperature (Tg) of the obtained polyimide are as follows.
Molecular weight Mw: 80,000
Tg: 230 ° C.

Examples 1 to 3, Comparative Examples 1 to 3
A slurry composition for a positive electrode, a positive electrode for a lithium ion secondary battery, a separator, and a lithium ion secondary battery using the polyimides synthesized in the above Synthetic Examples 1 to 3 and Synthetic Comparative Examples 1 to 3 by the following method Made.

<Preparation of Slurry Composition for Positive Electrode>
1000 parts by mass of NCM (nickel-cobalt-manganese composite oxide, N: C: M = 5: 3: 2) manufactured by China, 20 parts by mass of conductive agent denka black, solvent-soluble polyimide of the present invention (8% by mass N- 250 parts by mass of methyl pyrrolidone solution) was mixed by a planetary mixer, N-methyl pyrrolidone (NMP) was added in several portions until reaching the target viscosity, and stirring was repeated to prepare a slurry composition.

<Fabrication of positive electrode for lithium ion secondary battery>
An aluminum foil having a thickness of 18 μm was prepared as a current collector. The slurry composition prepared above was applied to one side of an aluminum foil with a comma coater and dried to obtain a positive electrode. This drying was carried out by transporting the aluminum foil provided with the coating film at a speed of 0.5 m / min in an oven at 120 ° C. for 2 minutes and then heat-treating it in an oven at 120 ° C. for 2 minutes. . The obtained positive electrode material sheet was rolled by a roll press to obtain a lithium ion secondary battery electrode having a thickness of 60 μm of the positive electrode mixture layer.

Preparation of Separator for Lithium Ion Secondary Battery
A single-layered polypropylene separator ("CELGARD (registered trademark) 2500" manufactured by Celgard) was punched out and used as a separator.

<Manufacturing of lithium ion secondary battery>
As a positive electrode, the positive electrode manufactured above was heat-treated in a vacuum oven at 150 ° C. for 5 hours, and a 2032 coin cell was produced by a usual method. A Li foil was used for the negative electrode, and a porous polyolefin membrane of 20 μm thickness was used for the separator. As an electrolytic solution, ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3: 3: LiPF ₆ was used 1 mol / L dissolved electrolyte in the electrolyte solvent of 4.

  Molecular weight, glass transition temperature (Tg), viscosity of 8% solution, solvent-swelling degree of film obtained by drying, solvent-soluble polyimide prepared in the above-mentioned Synthesis Examples 1 to 3 and Synthesis Comparative Examples 1 to 3, The viscosity of the slurry composition, the peel strength of the electrode, the cycle characteristics of the lithium ion secondary battery, and the irreversible capacity were measured and evaluated by the following methods.

Molecular weight of solvent-soluble polyimide
The solvent-soluble polyimide was diluted with NMP, and the weight average molecular weight was measured using a high performance liquid chromatograph (manufactured by Tosoh Corporation).

<Glass transition temperature (Tg) of solvent-soluble polyimide>
Measured by using DSG-50 manufactured by Shimadzu Corporation after heating up to 400 ° C at a heating rate of 10 ° C / min, air cooling the sample, and heating up to 420 ° C at a heating rate of 10 ° C / min again The glass transition temperature (Tg) was determined.

<Electrolyte swelling degree of solvent soluble polyimide>
The solvent-soluble polyimide was poured into a petri dish made of PTX resin and dried at 120 ° C. for 15 hours to obtain a film having a thickness of about 50 μm. A test piece of 3 cm × 3 cm is prepared from the film, and the test piece is dissolved in an electrolyte solution obtained by dissolving 1 mol / L of LiPF _{6 in an} electrolyte solvent consisting of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3: 3: 4. Soaked. After heating the electrolytic solution to 80 ° C., the test piece was subjected to immersion treatment at 80 ° C. for 72 hours. The weight change of the test piece before and after the immersion treatment was measured, the weight increase rate (%) was determined, and the swelling degree of the electrolyte was obtained. Here, the method of producing the film does not affect the value of the degree of swelling of the electrolyte, and the weight of the film after the immersion treatment is such that the test piece is taken out of the electrolyte and the surface of the tissue is quickly not to be dried. It was measured after wiping off the electrolyte adhering to the.

<Viscosity of solvent-soluble polyimide 8% solution)
In accordance with JIS Z8803: 1991, it was measured by a B-type viscometer (25 ° C., rotation number = 60 rpm, spindle shape: 4), and the value 60 seconds after the start of measurement was taken as the B-type viscosity of the 8% polyimide solution.

<Viscosity of Slurry Composition>
According to JIS Z8803: 1991, it measured by B-type viscosity meter (25 degreeC, rotation speed = 60 rpm, spindle shape: 4), and made the value of B-type viscosity of a slurry composition 60 second after a measurement start.

<Peel strength of electrode>
The prepared electrode for lithium ion secondary battery is cut into a rectangle of 100 mm in length and 10 mm in width to form a test piece, and the surface having the electrode mixture layer is on the surface of the electrode mixture layer with cellophane tape (specified in JIS Z1522 ) And the end of the current collector was pulled vertically at a tensile speed of 50 mm / min to measure the stress (cellophane tape was fixed to the test stand). The measurement was performed 5 times, the average value was calculated | required, and this was made into peel strength. The larger the peel strength value, the better the adhesion between the electrode mixture layer and the current collector.

<Cycle characteristics of lithium ion secondary battery>
The produced lithium ion secondary battery half cell was allowed to stand for 24 hours in an environment of 25 ° C. After that, the battery was charged to 4.2 V by a low current method of 0.5 C under an environment of 25 ° C., charge and discharge operations were performed to discharge to 3.0 V, and the initial capacity Cs was measured. Furthermore, charge and discharge similar to the above were repeated 200 times (200 cycles) in the environment of 25 ° C. of this lithium ion secondary battery, and the capacity Cf after 200 cycles was measured.
The cycle characteristic was calculated by ΔC = (Cf / Cs) × 100 (%), and was used as the capacity retention rate. The higher the value of the capacity retention rate, the better the cycle characteristics.

<Presence of irreversible capacity>
The produced lithium ion secondary battery was allowed to stand for 24 hours under an environment of 25 ° C. After that, charge to 4.2 V with a low current method of 0.1 C and discharge to 3.0 V under an environment of 25 ° C., and use PVDF (Arkema HSV 900) as a binder as a binder. In comparison with the capacity of the lithium ion secondary battery manufactured with the amount of the electrode used, the case of showing a small capacity was regarded as having irreversible capacity. The case where the irreversible capacity is not shown is indicated by 〇, and the case where the irreversible capacity is indicated is indicated by x.

  The physical properties of the solvent-soluble polyimides produced in Synthesis Examples 1 to 3 and Synthesis Comparative Examples 1 to 3 above, and the evaluation results of the characteristics of the slurry composition, the electrode, and the lithium ion secondary battery are shown in Table 1 below.

  From the results in Table 1 above, it is understood that the block copolymer having a molecular weight of 360 or less of all tetracarboxylic acid dianhydride components constituting the solvent-soluble polyimide and a proportion of a diamine component having a molecular weight of 220 or less is 30 mol% or more In the case of using the combined polyimide (Examples 1 to 3), it can be seen that a low electrolyte swelling degree of 50% by weight or less can be achieved. Moreover, in the case of these Examples 1-3, it turns out that the lithium ion secondary battery excellent in cycling characteristics can be produced.

  The solvent-soluble polyimide in the present invention is a polyimide which is compatible with high solvent solubility in solvents such as N-methyl pyrrolidone, dimethyl acetamide, dimethylformamide, dimethyl sulfoxide and the like and a low degree of swelling in the electrolyte used in lithium ion secondary batteries. is there. By using such solvent-soluble polyimide as a binder for a lithium ion secondary battery, it is possible to produce an electrode having good adhesion between electrode active materials and adhesion between an electrode mixture layer and a current collector. It becomes possible. Moreover, by using such an electrode, it becomes possible to produce a lithium ion secondary battery excellent in the life characteristics (cycle characteristics).

Claims (18)

  It is a binder for lithium ion secondary battery manufacture containing solvent-soluble polyimide, Comprising: The swelling at the time of immersing the film produced from the said polyimide in the electrolyte solution for lithium ion secondary batteries for 72 hours at 80 degreeC. A binder for producing a lithium ion secondary battery, which is a polyimide having a degree of 50% by weight or less. The electrolyte for lithium ion secondary battery is prepared by dissolving 1 mol / L of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate (volume ratio 3: 3: 4) The binder for lithium ion secondary battery manufacture of Claim 1 which is an electrolyte solution.   The lithium ion secondary battery according to claim 1 or 2, wherein the solvent-soluble polyimide is soluble in at least one solvent selected from the group consisting of N-methyl pyrrolidone, dimethyl acetamide, dimethylformamide and dimethyl sulfoxide. Binder.   The polyimide is a block copolymer, and the molecular weight of all tetracarboxylic acid dianhydride components constituting the polyimide is 360 or less, and the molecular weight of all diamine components constituting the polyimide is 220 The binder for lithium ion secondary battery manufacture of any one of Claims 1-3 which is a polyimide which the ratio of the following diamine components becomes at least 30 mol%.   The binder for lithium ion secondary battery manufacture of any one of Claims 1-4 whose weight average molecular weight of the said polyimide is 100,000 or more.   The binder for lithium ion battery manufacture of any one of Claims 1-5 whose imide group density | concentration of the said polyimide is 33% or less.   The binder for lithium ion secondary battery manufacture of any one of Claims 1-6 whose B-type viscosity of the 8% NMP solution of the said polyimide is 2000 cps or more.   It is a binder for lithium ion secondary battery manufacture containing the solvent-soluble polyimide synthesize | combined from tetracarboxylic dianhydride and diamine, Comprising: The said polyimide is a block copolymer and all the tetracarboxylic acids which comprise the said polyimide A lithium ion secondary battery which is a polyimide in which the molecular weight of the dianhydride component is 360 or less and the proportion of the diamine component having a molecular weight of 220 or less among all the diamine components constituting the polyimide is at least 30 mol%. Manufacturing binder.   The resin composition for lithium ion secondary batteries containing an active material and the binder for lithium ion secondary battery manufacture of any one of Claims 1-8.   The electrode for lithium ion secondary batteries by which the resin composition containing the active material and the binder for lithium ion secondary battery manufacture of any one of Claims 1-8 is adhered on a collector.   11. The electrode for a lithium ion secondary battery according to claim 10, wherein the active material is a nickel, cobalt, manganese ternary active material for positive electrode, and the electrode is a positive electrode.   The electrode for a lithium ion secondary battery according to claim 10, wherein the active material is a negative electrode active material containing a Si material, and the electrode is a negative electrode.   The lithium ion secondary battery provided with the electrode of any one of Claims 10-12.   The separator for lithium ion secondary batteries which used the binder for lithium ion secondary battery manufacture of any one of Claims 1-8 as a binder for ceramic coatings.   A lithium ion secondary battery using the separator according to claim 14.   A method for producing a solvent-soluble polyimide for use in a binder for producing a lithium ion secondary battery by reacting a tetracarboxylic acid dianhydride with a diamine, which is all tetracarboxylic acid dianhydride used in the reaction. A method for producing a binder for producing a lithium ion secondary battery, wherein the molecular weight of the polymer is 360 or less and the proportion of diamine having a molecular weight of 220 or less among all the diamines used in the reaction is at least 30 mol%.   A production of an electrode for a lithium ion secondary battery, which comprises applying a resin composition containing an active material and a binder for producing a lithium ion secondary battery produced by the method according to claim 16 on a current collector and drying it. Method.   A method for producing a lithium ion secondary battery using an electrode produced by the method according to claim 17.