JP2013020875A - Resin composition for electrode of lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition from which a lithium ion secondary battery having excellent cycle characteristics can be obtained, and an electrode having superior adhesion with a copper foil being a raw material of the electrode and also having superior flexibility can be obtained, and to provide a lithium ion secondary battery.SOLUTION: A resin composition for an electrode of a lithium ion secondary battery contains a straight chain polyimide resin (A) having a weight average molecular weight of 4,000 to 60,000 and an acid value of blocked carboxyl groups of 30 to 90 KOHmg/g, and a straight chain epoxy resin (B) having two epoxy groups in a molecule and an epoxy equivalent of 250 to 1,000. The lithium ion secondary battery includes a negative electrode which can be obtained by using the resin composition for the electrode and a carbon material.

Description

  The present invention relates to a composition for an electrode of a lithium ion secondary battery that can be suitably used as a power source for equipment that uses electricity as a power source, and particularly for power storage and electric vehicles that require cycle stability. The present invention also relates to a lithium ion secondary battery having an electrode using the composition.

  In recent years, the demand for high energy density secondary batteries has increased with the progress of high performance, miniaturization, and weight reduction of portable electronic devices and the progress of research and development for practical application of electric vehicles. Secondary batteries that have been widely used in the past include nickel-cadmium batteries and lead batteries, but these batteries have a small discharge capacity per volume or weight and a low discharge voltage. The battery requirement could not be met sufficiently.

  As a battery system that satisfies these requirements, a non-aqueous electrolyte secondary battery (lithium ion secondary battery) using a material capable of occluding and releasing lithium ions as a negative electrode has attracted attention.

  A material capable of occluding and releasing lithium ions as an electrode active material carrier, for example, a lithium ion secondary battery using a carbonaceous material as a negative electrode can obtain a high discharge voltage close to that when a metal lithium negative electrode is used. The adhesion between the carrier and the metal foil is small, peeling occurs during repeated charging and discharging, and the cycle characteristics are not sufficient, and further improvement has been demanded.

  In response to such a demand, an electrode material formed by forming a coating film comprising an electrode active material carrier and a binder component on the surface of a metal foil, the electrode active material carrier for the area (A) of the coating film Alternatively, when the percentage (B / A × 100) of the area (B) of the portion where the binder component is in close contact with the surface of the metal foil is defined as the degree of adhesion (Rc), Rc is 40% or more. A lithium ion secondary battery using an electrode material characterized by the above is disclosed (for example, see Patent Document 1). Examples of the electrode material disclosed in the patent literature include 96 g (0.5 mol) trimellitic anhydride, 101 g (1.01 mol) sebacic acid, and 4,4 as disclosed in Example 2. 100 parts by weight of a polyamideimide resin obtained by reacting 265 g (0.5 mol) of '-dicyclohexylmethane diisocyanate and 2.5 parts by weight of bisphenol A-diglycidyl ether (bisphenol A type epoxy resin, epoxy equivalent 188) There is an electrode material obtained by applying a paste mixture comprising a resin composition and a carbonaceous material on a copper foil.

The cycle characteristics of a lithium ion secondary battery obtained using the electrode material disclosed in Patent Document 1 are evaluated by performing a charge / discharge cycle test. Specifically, a charge / discharge cycle test is performed between a turn-back voltage of 0 V and 2 V at a constant current of a current density of 0.5 mA / cm ² , and the discharge capacity at the second cycle of the charge / discharge cycle test is 5 cycles. The value obtained by dividing the discharge capacity is evaluated as the capacity retention rate (%). According to this evaluation, the capacity retention rate of the lithium ion secondary battery obtained using the electrode material obtained in Example 2 is 100%, and the cycle characteristics are good. However, in this evaluation, the capacity maintenance rate is calculated by dividing the discharge capacity at the second cycle by the discharge capacity at the fifth cycle, and even if the capacity maintenance rate is 100%, the cycle interval is narrow, In this evaluation, when the cycle interval is wide, for example, when the discharge capacity at the 100th cycle is divided by the discharge capacity at the 10th cycle, the capacity retention rate is reduced to about 70%.

JP 2000-149921 A

  The present invention provides a lithium ion secondary battery having good cycle characteristics, a composition capable of obtaining an electrode having excellent adhesion to a copper foil as a raw material of the electrode, and also having excellent flexibility, and lithium ion It is to provide a secondary battery.

The present inventors have conducted intensive studies and found the following findings.
1) Since the polyamideimide resin used in Patent Document 1 is reacted under the condition that the isocyanate group becomes excessive as apparent from Example 1 and Example 2, the acid value (acid value of carboxyl group) Is substantially zero. The inventors have obtained a patent by using a linear polyimide resin having an acid value (acid value of carboxyl group) of 30 to 90 KOHmg / g and a weight average molecular weight of 4,000 to 60,000. Even if it does not have an amide structure as in Reference 1, it can be used as a resin for electrodes.

2) The epoxy resin used in Patent Document 1 has an epoxy equivalent of about 188. The present inventors obtained a composition obtained by using an epoxy resin having an epoxy equivalent of 250 to 1000 as an epoxy resin and the polyimide resin found in the above 1), in an adhesiveness with a copper foil which is a raw material of an electrode. A lithium ion secondary battery having an electrode that is excellent and has excellent flexibility and that has an electrode obtained by using this composition has good cycle characteristics.
The present invention has been completed based on the above findings.

  That is, the present invention relates to a linear polyimide resin (A) having a weight average molecular weight of 4,000 to 60,000 and an acid value of a carboxyl group of 30 to 90 KOHmg / g, and two epoxy groups in one molecule. And a linear epoxy resin (B) having an epoxy equivalent of 250 to 1000, and a resin composition for an electrode of a lithium ion secondary battery.

  The present invention also provides a lithium ion secondary battery comprising a negative electrode obtained by using the resin composition for an electrode of the lithium ion secondary battery and a carbon material.

  The lithium ion secondary battery electrode resin composition of the present invention provides a lithium ion secondary battery with good cycle characteristics. Moreover, since it is excellent in adhesiveness with the copper foil which is a raw material of an electrode, and is excellent in flexibility, it is also possible to store the manufactured electrode in a roll shape.

  The polyimide resin (A) used in the present invention is a linear polyimide resin having a weight average molecular weight of 4,000 to 60,000 and an acid value of 30 to 90 KOHmg / g. If the weight average molecular weight is less than 4,000, it is not preferable because it becomes difficult to obtain a sufficiently flexible electrode. When the weight average molecular weight is larger than 60,000, it becomes difficult to obtain a polyimide resin having an acid value in the range of 30 to 90 KOHmg / g. As a result, the adhesiveness with the copper foil is excellent, and the flexibility is also excellent. Since it becomes difficult to obtain an electrode, it is not preferable. The weight average molecular weight is more preferably in the range of 5,000 to 30,000.

  Further, when the acid value of the polyimide resin (A) used in the present invention is less than 30 KOHmg / g, it is not preferable because sufficient curability with the epoxy resin cannot be obtained and it is difficult to obtain an electrode having excellent flexibility. An acid value greater than 90 KOH mg / g is not preferred because the resulting electrode becomes hard and brittle and the flexibility decreases. The acid value is more preferably 50-80 KOH mg / g.

In the present invention, the weight average molecular weight was measured using a gel permeation chromatograph (GPC) under the following conditions.
Measuring device: Tosoh Corporation HLC-8320GPC, UV8320
Column: Super AWM-H × 2 manufactured by Tosoh Corporation Detector: RI (differential refractometer) and UV (254 nm)
Data processing: Tosoh Corporation EcoSEC-WorkStation
Measurement conditions: Column temperature 40 ° C
Solvent DMF
Flow rate 0.35 ml / min Standard: Calibration curve prepared with polystyrene standard sample Sample: 0.2% by weight DMF solution in terms of resin solid content filtered through a microfilter (injection volume: 10 μl)

  The polyimide resin (A) includes, for example, a polyisocyanate compound (a1) having a biphenyl structure and / or an acid anhydride (a2) having a biphenyl structure, and a polyisocyanate compound (a3) other than (a1) as necessary. It can be easily obtained by reacting an acid anhydride (a4) other than (a2).

  Examples of the polyisocyanate compound (a1) having a biphenyl structure include 4,4′-diisocyanate-3,3′-dimethyl-1,1′-biphenyl and 4,4′-diisocyanate-3,3′-diethyl. -1,1'-biphenyl, 4,4'-diisocyanate-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diisocyanate-2,2'-diethyl-1,1'-biphenyl, Examples include 4,4′-diisocyanate-3,3′-ditrifluoromethyl-1,1′-biphenyl, 4,4′-diisocyanate-2,2′-ditrifluoromethyl-1,1′-biphenyl, and the like.

  Examples of the acid anhydride (a2) having the biphenyl structure include biphenyl-3,3 ′, 4,4′-tetracarboxylic acid, biphenyl-2,3,3 ′, 4′-tetracarboxylic acid, and these Monoanhydrides, dianhydrides, and the like. These may be used alone or as a mixture of two or more.

  Examples of the polyisocyanate compound (a3) other than (a1) include aromatic polyisocyanates and aliphatic polyisocyanates other than (a1).

  Examples of the aromatic polyisocyanate other than (a1) include p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylene diisocyanate, m-xylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate. 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 3,3'-diethyldiphenyl-4,4'-diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, , 3-bis (α, α-dimethylisocyanatomethyl) benzene, tetramethylxylylene diisocyanate, diphenylene ether-4,4′-diisocyanate and naphthalene diisocyanate.

  Examples of the aliphatic polyisocyanate compound include hexamethylene diisocyanate, lysine diisocyanate, trimethylhexamethylenemethylene diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, hydrogenated xylene diisocyanate, and norbornene diisocyanate.

  As the polyisocyanate compound, it is also possible to use an isocyanate prepolymer obtained by reacting the polyisocyanate compound and various polyol components in advance with an excess of isocyanate groups.

  The polyimide resin used in the present invention may have a branched structure in order to improve solvent solubility and compatibility with other resins. As the branching method, as the polyisocyanate compound, for example, a tri- or higher functional polyisocyanate compound having an isocyanurate ring that is an isocyanurate body such as the diisocyanate compound, a burette body, an adduct body, an allohanate body of the diisocyanate, or Polymethylene polyphenyl polyisocyanate (crude MDI) or the like may be used.

  Examples of the acid anhydride (a4) other than (a2) include aromatic tricarboxylic acid anhydrides, alicyclic tricarboxylic acid anhydrides other than (a2), and tetracarboxylic acid anhydrides other than (a2). . Examples of aromatic tricarboxylic acid anhydrides other than (a2) include trimellitic anhydride and naphthalene-1,2,4-tricarboxylic acid anhydride.

  Examples of the alicyclic tricarboxylic acid anhydride include cyclohexane-1,3,4-tricarboxylic acid anhydride-3,4-anhydride, cyclohexane-1,3,5-tricarboxylic acid anhydride-3,5-anhydride, And cyclohexane-1,2,3-tricarboxylic acid anhydride-2,3-anhydride.

  Examples of tetracarboxylic acid anhydrides other than (a2) include pyromellitic dianhydride, benzophenone-3,3 ', 4,4'-tetracarboxylic dianhydride, diphenyl ether-3,3', 4. , 4'-tetracarboxylic dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, naphthalene-2,3,6,7-tetracarboxylic dianhydride, naphthalene-1,2 , 4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 4, 8-Dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8- Tetracarboxylic dianhydride, , 7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, phenanthrene- 1,3,9,10-tetracarboxylic dianhydride, berylene-3,4,9,10-tetracarboxylic 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 (2,3-dicarboxyphenyl) propane dianhydride, 2,3-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) sulfone Anhydride Bis (3,4-carboxyphenyl) ether dianhydride,

Ethylene glycol bisanhydro trimellitate, propylene glycol bis anhydro trimellitate, butanediol bis anhydro trimellitate, hexamethylene glycol bis anhydro trimellitate, polyethylene glycol bis anhydro trimellitate, polypropylene lenglycol bis Anhydro trimellitate, other alkylene glycol bisan hydroxy trimellitate, etc. are mentioned.

  By using a polyimide resin having a benzophenone structure as the polyimide (A) used in the present invention, an electrode exhibiting heat resistance and low linear expansion can be obtained. A polyimide resin having a benzophenone structure can be obtained, for example, by using benzophenone tetracarboxylic acid anhydride as an essential component in the production method.

  The content of the benzophenone structure is preferably from 1 to 30% by mass based on the mass of the polyimide resin, since a cured product having excellent heat resistance is obtained, and more preferably from 5 to 20% by mass is excellent in synthetic stability.

  The content of the benzophenone structure can be calculated from the ratio of the benzophenone structure to the total weight of the polyimide resin, with the molecular weight of the benzophenone structure having 4 bonding points to the polyimide resin main chain being 178.

  Further, by using a polyimide resin having a tolylene structure bonded to the main chain at the 2- and 4-positions as the polyimide (A) used in the present invention, an electrode exhibiting melt adhesion and low linear expansion can be obtained. A polyimide resin having a tolylene structure bonded to the main chain at positions 2 and 4 can be obtained, for example, by using toluene diisocyanate as an essential component in the production method.

  The content of the tolylene structure bonded to the main chain at the 2nd and 4th positions is based on the ratio of the tolylene structure to the total weight of the polyimide resin, assuming that the molecular weight of the tolylene structure bonded at the 2nd and 4th positions to the polyimide resin main chain is 150. Can be calculated.

  The content of the tolylene structure bonded to the main chain at positions 2 and 4 in the polyimide resin is preferably 1 to 20% by mass because it is excellent in synthetic stability, and 2 to 14% by weight is low in linear expansion and synthetic stability. More preferable.

  In the said manufacturing method, a polyisocyanate compound and the compound which has an acid anhydride group react. The ratio (ma) / (mb) of the number of moles of isocyanate groups in the polyisocyanate compound (ma) and the total number of moles of non-hydroxyl groups and carboxyl groups in the compound having an acid anhydride group (mb) is expressed as the molecular weight. A ratio of 0.7 to 1.2 is preferable, and a ratio of 0.8 to 1.2 is more preferable because a polyimide resin from which a large polyimide resin can be easily obtained and a cured product having excellent mechanical properties is obtained. Moreover, since it is easy to obtain the polyimide resin which is excellent in storage stability, the (ma) / (mb) is more preferably in the range of 0.9 to 1.1. In addition, when using together carboxylic anhydrides, such as trimellitic anhydride, said (mb) is the total number of moles of a hydroxyl-free group and a carboxyl group in all the carboxylic anhydrides.

  In the case of producing in a one-step reaction in the production method, for example, a reaction vessel is charged with a polyisocyanate compound and a compound having an acid anhydride group, and the reaction is allowed to proceed while decarboxylation by heating while stirring. .

  The reaction temperature can be in the range of 50 ° C. to 250 ° C., and is preferably performed at a temperature of 70 ° C. to 180 ° C. in terms of reaction rate and prevention of side reactions.

  The reaction is preferable because the stability of the resulting polyimide resin is improved when the reaction is performed until almost all isocyanate groups have reacted. Moreover, you may make it react by adding an alcohol and a phenol compound with respect to the isocyanate group which remains a little.

  In producing the polyimide resin (A) used in the present invention, it is preferable to use an organic solvent because a uniform reaction can proceed. Here, the organic solvent may be present after being present in the system in advance or may be introduced in the middle. In order to maintain an appropriate reaction rate, the proportion of the organic solvent in the system is preferably 98% by mass or less of the reaction system, more preferably 10 to 90% by mass, and more preferably 40 to 90% by mass. % Is more preferable. As such an organic solvent, since a compound containing an isocyanate group is used as a raw material component, an aprotic polar organic solvent having no active proton such as a hydroxyl group or an amino group is preferable.

  As the aprotic polar organic solvent, for example, polar organic solvents such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, and γ-butyrolactone can be used. In addition to the above solvents, ether solvents, ester solvents, ketone solvents, petroleum solvents and the like may be used as long as they are soluble. Various solvents may be mixed and used.

  In particular, use of dimethylacetamide is preferred from the viewpoint of reducing the amount of residual solvent when the coating film is dried and cured, and the solubility of the polyimide resin.

  Examples of ether solvents that can be used in the method for producing a polyimide resin used in the present invention include ethylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol dibutyl ether; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, Polyethylene glycol dialkyl ethers such as diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, and triethylene glycol dibutyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, etc. Polyethylene glycol monoalkyl ether acetates such as diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, triethylene glycol monomethyl ether acetate, triethylene glycol monoethyl ether acetate, triethylene glycol monobutyl ether acetate Alkyl ether acetates;

Propylene glycol dialkyl ethers such as propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dibutyl ether; dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol dibutyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol Polypropylene glycol dialkyl ethers such as propylene glycol dibutyl ether; propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate; Polypropylene glycol monoalkyl ether acetate such as triglycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monobutyl ether acetate, tripropylene glycol monomethyl ether acetate, tripropylene glycol monoethyl ether acetate, tripropylene glycol monobutyl ether acetate Dialkyl ethers of copolymerized polyether glycols such as low molecular weight ethylene-propylene copolymers; monoacetate monoalkyl ethers of copolymerized polyether glycols; alkyl esters of copolymerized polyether glycols; Examples include ether glycol monoalkyl esters and monoalkyl ethers. It is.

  Examples of the ester solvent include ethyl acetate and butyl acetate. Examples of the ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. In addition, as the petroleum solvent, it is also possible to use toluene, xylene, other high-boiling aromatic solvents, and aliphatic and alicyclic solvents such as hexane and cyclohexane.

  Whether or not the polyimide resin (A) used in the present invention is dissolved in an organic solvent was determined by adding the polyimide resin concentration of the present invention to 10% by mass in the organic solvent and allowing to stand at 25 ° C. for 7 days. Then, it can carry out by observing an external appearance visually.

  The polyimide resin (A) used in the present invention may be a polyimide resin having a linear structure or a polyimide resin having a branched structure. Further, the copolymer component may have a polyester-modified polyesterimide or urethane-modified polyurethaneimide structure.

  Examples of the terminal structure of the polyimide resin (A) used in the present invention include structures such as carboxylic acid, carboxylic acid anhydride, isocyanate group, and amine group. As the terminal structure, the structure of the carboxylic acid or its anhydride is preferable because the stability of the polyimide resin itself of the present invention and the stability after blending with an organic solvent or another resin are good. When the terminal structure is a carboxylic acid or its anhydride structure, the acid value is a polyimide resin with a solid content acid value of 1 to 200, which makes it easy to handle, and a film or molded product with excellent mechanical strength and dimensional stability can be obtained. To preferred.

  Moreover, the polyimide resin (A) used by this invention has a preferable polyimide resin which does not have an alkylene structure.

  The epoxy resin (B) used in the present invention needs to have two epoxy groups in one molecule and have an epoxy equivalent of 250 to 1,000. Use of an epoxy resin having more than two epoxy groups in one molecule is not preferable because the electrode becomes hard and brittle and flexibility decreases.

  On the other hand, if the epoxy equivalent is less than 250, the electrode coating film becomes hard and brittle and the flexibility is unfavorable. An epoxy equivalent greater than 1000 is not preferable because sufficient curability with the imide resin cannot be obtained and flexibility is lowered. The epoxy equivalent is more preferably 250 to 700.

  As the epoxy resin (B), for example, biphenyl type epoxy resin, naphthalene type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin and the like can be preferably used.

  Among the epoxy resins (B), an epoxy resin containing a polyalkylene glycol chain in the main chain is more preferable because an electrode having excellent flexibility and adhesiveness and excellent lithium ion conductivity can be obtained.

  As an epoxy resin containing a polyalkylene glycol chain in the main chain, for example, diglycidyl ether containing a polyethylene glycol chain in the main chain, diglycidyl ether having polypropylene glycol in the main chain, and polytetramethylene glycol in the main chain And diglycidyl ether.

  Examples of the diglycidyl ether containing a polyethylene glycol chain in the main chain include compounds represented by the following formula (1).

  In Formula 1, n is 1 to 30, preferably 2 to 15.

  Moreover, as a diglycidyl ether which has polypropylene glycol in a principal chain, the compound etc. which are represented by following formula (2) are mentioned, for example.

  In Formula 2, m is 1 to 30, preferably 2 to 15.

  As the bifunctional epoxy resin (B) used in the present invention, diglycidyl ether having a polyethylene glycol chain in the main chain and diglycidyl ether having polypropylene glycol in the main chain can improve the flexibility of the cured coating film. The diglycidyl ether containing a polyethylene glycol chain in the main chain is more preferable. Among the diglycidyl ethers containing a polyethylene glycol chain in the main chain, diglycidyl ethers having a polyethylene glycol chain repeating unit of 1 to 30 are preferable, and diglycidyl ethers having a polyethylene glycol chain repeating unit of 2 to 15 are more preferable.

  As a commercial item of the bifunctional epoxy compound (B) containing a polyalkylene glycol chain in the main chain used in the present invention, for example, Denacol EX-810, Denacol EX-811, Denacol EX-850, Denacol 851, Denacol EX -821, Denacol EX-830, Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-911, Denacol EX-941, Denacol EX-920, Denacol EX-931 (Nagase ChemteX Corporation) Product], Epiol E-400, Epiol E-1000 [manufactured by NOF Corporation] and the like. Two or more of these epoxy compounds may be mixed and used.

  The content of the epoxy resin (B) is 30 to 200% by mass with respect to 100 parts by mass of the polyimide resin (A), and the cured product has a low linear expansion, and has excellent thermosetting properties at low temperatures. The resin composition is preferably obtained, more preferably 50 to 150% by mass, and still more preferably 40 to 150% by mass.

  If necessary, various fillers, organic pigments, inorganic pigments, extender pigments, rust inhibitors and the like can be added to the resin composition for electrodes of the lithium ion secondary battery of the present invention. These may be used alone or in combination of two or more.

  Examples of the filler include barium sulfate, barium titanate, silicon oxide powder, finely divided silicon oxide, silica, talc, clay, magnesium carbonate, calcium carbonate, aluminum oxide, aluminum hydroxide, mica, and alumina. Is mentioned.

  As the filler, those having various particle sizes can be used, and can be added to such an extent that the physical properties of the present resin and its composition are not impaired. Such an appropriate amount is in the range of about 5 to 80% by mass, and preferably used after being uniformly dispersed. As a dispersion method, it is possible to carry out dispersion by a known roll, bead mill, high-speed dispersion or the like, and the surface of the particles may be modified in advance with a dispersion treatment agent.

  Examples of the organic pigment include azo pigments; copper phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, and quinacridone pigments.

  Examples of the inorganic pigment include chromates such as chrome lead, zinc chromate and molybdate orange; ferrocyanides such as bitumen, titanium oxide, zinc white, bengara, iron oxide; metal oxides such as chromium carbide green, Cadmium yellow, cadmium red; metal sulfides such as mercury sulfide; selenides; sulfates such as lead sulfate; silicates such as ultramarine; carbonates, cobalt biored; phosphates such as manganese purple; aluminum powder, zinc dust Metal powders such as brass powder, magnesium powder, iron powder, copper powder and nickel powder; carbon black and the like.

  In addition, any of other coloring, rust prevention, and extender pigments can be used. These may be used alone or in combination of two or more.

  The cured product of the present invention is obtained by curing the thermosetting polyimide resin composition of the present invention. Specifically, for example, the thermosetting polyimide resin composition of the present invention includes a cured product that is cured by heating at 100 to 300 ° C. after coating on a substrate.

  The substrate used in the method for forming the coating film can be used without any particular limitation. Examples of the substrate include plastic, metal, wood, glass, inorganic material, and composite materials thereof. There is no restriction | limiting in particular as a shape of a base material, A sheet | seat, a film-like thing, a chip | tip shape, a solid shape, etc. can be illustrated.

  The electrode material of the lithium ion secondary battery is prepared by, for example, applying a paste mixture prepared by mixing and dispersing the composition of the present invention and a granular electrode active material carrier in a solvent onto a metal foil to form a coating layer. After forming, it is formed by drying and pressure bonding.

  The solvent used for the mixture preferably contains at least one of N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, and xylene. Particularly preferred is N-methyl-2-pyrrolidone from the viewpoint of solubility.

  Among the steps of forming the electrode layer, at least the step of drying at a temperature of 125 ° C. or lower until the amount of the solvent contained in the coating layer is 40% or less of the initial content at least at the beginning of the drying step It is preferable to include. Thus, by drying at a low temperature of 125 ° C. or lower until the amount of the solvent is 40% or less of the initial content at least in the initial stage of the drying step, the distribution state of the binder component in the electrode layer is optimized, Through the subsequent drying and pressure-bonding steps, an optimal adhesion state between the electrode layer and the metal foil is obtained, and charge / discharge characteristics are improved.

  The weight ratio of the resin composition to the electrode active material carrier in the electrode material of the present invention is preferably 3:97 to 20:80, more preferably 5:95 to 10:90. When the content of the electrode active material carrier is more than the above range, the electrode mixture layer tends to crack or the electrode mixture layer tends to be peeled off from a current collector such as a metal foil. Moreover, when content of carbonaceous material is less than the said range, there exists a tendency for the charge / discharge cycle characteristic when it is set as a battery to fall easily.

  Examples of the non-aqueous solvent for the non-aqueous electrolyte used in the lithium ion secondary battery of the present invention include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, which are high dielectric constant solvents, and 1,1, which are low-viscosity solvents. 2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like can be used.

The electrolyte used when preparing the non-aqueous electrolyte by dissolving in the non-aqueous solvent as described above generally varies depending on the conductive ion species, but when the conductive ion species is lithium ion, LiClO ₄ , LiAsF. ₆ , LiPF ₆ , LiBF ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like can be preferably used. These may be used alone or in combination of two or more.

  Other configurations such as the separator, battery can, and PTC element of the lithium ion secondary battery of the present invention can be the same as those of a conventional lithium ion nonaqueous electrolyte secondary battery.

  The battery shape of the lithium ion secondary battery of the present invention is not particularly limited, and may be various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape as necessary.

  EXAMPLES Next, an Example is shown and this invention is demonstrated further in detail. Unless otherwise specified, “parts” and “%” are based on weight.

  To a flask equipped with a stirrer, a thermometer and a condenser, 213.2 g of DMAC (dimethylacetamide), 6.28 g (0.036 mol) of TDI (tolylene diisocyanate), TODI (4,4′-diisocyanate-3,3 '-Dimethyl-1,1'-biphenyl) 37.8 g (0.143 mol), TMA (trimellitic anhydride) 29.1 g (0.151 mol) and BTDA (benzophenone-3,3', 4,4) ′ -Tetracarboxylic dianhydride) and 12.2 g (0.038 mol) were added, the temperature was raised to 150 ° C. over 2 hours, taking note of heat generation while stirring, and the reaction was carried out at this temperature for 5 hours. I let you. The reaction proceeded with the foaming of carbon dioxide, and the system became a brown transparent liquid. A solution of a polyimide resin (A1) having a resin solid content of 25% with a viscosity of 2 Pa · s at 25 ° C. and a solution acid value of 16 (KOHmg / g) (resin composition in which the polyimide resin was dissolved in DMAC) was obtained. In addition, the solid content acid value of the resin calculated from the value was 64 (KOHmg / g). Moreover, it was the weight average molecular weight 10,000 as a result of the measurement of a gel permeation chromatography (GPC). Further, the polyimide resin (A1) was dried at 200 ° C. for 2 hours to obtain a solid content of the polyimide resin (A1), and 0.1 g of the solid content was dissolved in 20 cc of N-methyl-2-pyrrolidone. The logarithmic viscosity was measured at 0 ° C. and found to be 0.43 dl / g.

Synthesis example 2 (same as above)
In a flask equipped with a stirrer, a thermometer and a condenser, 547.0 g of DMAC (dimethylacetamide), 13.16 g (0.076 mol) of TDI (2,4-tolylene diisocyanate), DMBPDI (4,4′-diisocyanate) −3,3′-dimethyl-1,1′-biphenyl) 80.0 g (0.30 mol) and TMA (trimellitic anhydride) 76.8 g (0.40 mol) were charged and exothermic while stirring. The temperature was raised to 160 ° C. over 1 hour, and the reaction was carried out at this temperature for 10 hours. The reaction proceeded with the foaming of carbon dioxide, and the system became a brown transparent liquid. A solution of a polyimide resin (A2) having a resin solid content of 20% with a viscosity of 1.0 Pa · s at 25 ° C. and a solution acid value of 8 (KOHmg / g) (resin composition in which the polyimide resin is dissolved in DMAC) is obtained. It was. The solid content acid value of the resin was 40 (KOHmg / g). Moreover, it was the weight average molecular weight 35000 as a result of the measurement of a gel permeation chromatography (GPC). Further, the polyimide resin (A2) was dried at 200 ° C. for 2 hours to obtain a solid content of the polyimide resin (A2), and 0.1 g of the solid content was dissolved in 20 cc of N-methyl-2-pyrrolidone. The logarithmic viscosity was measured at 0 ° C. and found to be 0.60 dl / g.

Synthesis example 3 (same as above)
Into a flask equipped with a stirrer, a thermometer and a condenser, 204.6 g of DMAC (dimethylacetamide), 5.96 g (0.034 mol) of TDI (tolylene diisocyanate), TODI (4,4′-diisocyanate-3,3 '-Dimethyl-1,1'-biphenyl) 36.0 g (0.137 mol), TMA (trimellitic anhydride) 29.1 g (0.151 mol) and BTDA (benzophenone-3,3', 4,4) '-Tetracarboxylic dianhydride) and 12.2 g (0.038 mol) were added, the temperature was raised to 150 ° C. over 2 hours, taking note of heat generation while stirring, and then reacted at this temperature for 5 hours. I let you. The reaction proceeded with the foaming of carbon dioxide, and the system became a brown transparent liquid. A solution of a polyimide resin (A2) having a resin solid content of 25% with a viscosity of 1 Pa · s at 25 ° C. and a solution acid value of 20 (KOHmg / g) (resin composition in which the polyimide resin was dissolved in DMAC) was obtained. In addition, the solid content acid value of the resin calculated from the value was 80 (KOHmg / g). Moreover, it was the weight average molecular weight 5000 as a result of the measurement of a gel permeation chromatography (GPC). Further, the polyimide resin (A2) was dried at 200 ° C. for 2 hours to obtain a solid content of the polyimide resin (A2), and 0.1 g of the solid content was dissolved in 20 cc of N-methyl-2-pyrrolidone. The logarithmic viscosity was measured at 0 ° C. and found to be 0.29 dl / g.

Synthesis Example 4 (Synthesis of comparative polyimide resin)
A reaction vessel was charged with 96 g of trimellitic anhydride, 101 g of sebacic acid, 265 g of 4,4′-dicyclohexylmethane diisocyanate and 1 g of potassium fluoride together with 900 g of N-methyl-2-pyrrolidone, heated to 200 ° C. and reacted for 5 hours. After cooling, 950 g of N-methyl-2-pyrrolidone was further added while cooling to obtain a solution of polyamideimide resin (a1) having a solid content concentration of 20% by weight. The solid content acid value of the resin was 1.0 (KOH mg / g). Moreover, it was the weight average molecular weight 120,000 as a result of the measurement of a gel permeation chromatography (GPC).

Examples 1-6, Comparative Example 1
Polyimide resin and epoxy resin were mixed in the formulation shown in Table 1 to obtain electrode resin compositions 1-6 and comparative control resin composition 1 '.

Footnotes in Table 1 Epoxy resin B1: Denacol EX-830 (manufactured by Nagase ChemteX Corporation, polyethylene glycol diglycidyl ether, epoxy equivalent 268 g / eq)
Epoxy resin B2: Epicron 2055 (manufactured by DIC Corporation, solid BPA type epoxy resin, epoxy equivalent 628 g / eq)
Epoxy resin B3: Epicron EXA-4850-150 (manufactured by DIC Corporation, polyether-modified epoxy resin, epoxy equivalent of 437 g / eq)
Epoxy resin b1: bisphenol A diglycidyl ether. Epoxy equivalent 188 g / eq

  90 parts by weight of spherical graphite having an average particle size of 15 microns (manufactured by Chuetsu Graphite Industries Co., Ltd.) and 10 parts by weight of electrode resin composition (in terms of solid content) were mixed, and the solid content concentration was determined with N-methyl-2-pyrrolidone. Was diluted to be 59% by weight and dispersed and kneaded to prepare a paste-like mixture. The obtained paste mixture was applied to one side of a 30 μm thick copper foil, then dried in a hot air oven at 100 ° C. for 10 minutes, and further dried in a hot air oven at 170 ° C. for 60 minutes. Created. The prepared electrode was cooled to room temperature and then pressed so that the electrode density was 1.3 g / cm 3. The obtained electrode had a thickness of 90 μm including the copper foil.

  The flexibility of the obtained electrode and the adhesion between the copper foil of the electrode and the cured resin were evaluated according to the following methods. The evaluation results are shown in Table 2.

Electrode flexibility evaluation method The electrode was cut into a square of 8 cm square to obtain a test piece. This test piece was wound around a rod having a diameter of 2 mm and 10 mm, and the surface of the electrode was visually observed. Evaluation was made according to the following criteria.

(Double-circle): Even if it winds around a 2 mm diameter stick, peeling of copper foil and hardened resin is not seen.
○: The above-mentioned peeling occurs when wound on a rod having a diameter of 2 mm, but the above-mentioned peeling does not occur when wound on a rod having a diameter of 10 mm.
X: The above peeling occurs even when wound on a rod having a diameter of 10 mm.

Evaluation of Adhesiveness between Copper Foil of Electrode and Cured Resin The electrode was cut into an 8 cm square to obtain a test piece. Using this test piece, a cross-cut test and an adhesive tape test were conducted and evaluated according to the following criteria.

○: No peeling is observed in a cross cut (100 square) test of 1 mm × 1 mm, and the copper foil is not exposed by subsequent peeling of the adhesive tape.
Δ: No peeling is observed in the cross cut (100 square) test of 1 mm × 1 mm, and the copper foil is exposed partially or almost on the front surface in the subsequent peeling of the adhesive tape.
X: At the time of cross cut (100 squares) of 1 mm x 1 mm, peeling is observed and the copper foil is exposed.

The electrode was cut into a circle having an area of 1.539 cm ² and dried under vacuum at 80 ° C. for 24 hours. This electrode is placed in a nickel-plated iron battery can container so that the electrode layer surface faces a lithium foil through a porous polypropylene film having a thickness of 25 μm, and a six-volume mixture of ethylene carbonate and diethyl carbonate in an equal volume mixture. A non-aqueous electrolyte solution in which lithium phosphate LiPF6 was dissolved at a rate of 1 mol / liter was injected and sealed to prepare a lithium ion secondary battery. About the obtained lithium ion secondary battery, the capacity | capacitance maintenance factor (%) was measured with the following method.

<Measurement method of capacity retention rate (%)>
Charging capacity at the second cycle (unit = mAh / g (per active material)) and charging capacity at the 50th cycle (units) from 0V to 1.5V with a positive electrode made of metallic lithium and a constant current constant voltage charging method of 0.5C = MAh / g (per active material)), the ratio of the charge capacity at the 50th cycle to the charge capacity at the 2nd cycle is calculated as a percentage, and this is used as the capacity maintenance rate (%). The larger this value is, the better the result is.

Claims (8)

  A linear polyimide resin (A) having a weight average molecular weight of 4,000 to 60,000 and an acid value of a carboxyl group of 30 to 90 KOHmg / g, and having two epoxy groups in one molecule, epoxy equivalent A resin composition for an electrode of a lithium ion secondary battery, comprising: a linear epoxy resin (B) having a molecular weight of 250 to 1000.   The resin composition for an electrode of a lithium ion secondary battery according to claim 1, wherein the linear polyimide resin (A) has a weight average molecular weight of 5,000 to 40,000 and an acid value of a carboxyl group of 30 to 80. .   The linear polyimide resin (A) has a biphenyl skeleton directly linked to a 5-membered ring imide skeleton, the content of the biphenyl skeleton is 20 to 45% by mass, and the logarithmic viscosity is 0.2 to 0.00. 2. The resin composition for an electrode of a lithium ion secondary battery according to claim 1, which is an 8 dl / g polyimide resin.   The resin composition for an electrode of a lithium ion secondary battery according to claim 1, wherein the linear epoxy resin (B) is an epoxy resin containing a polyalkylene glycol chain in the main chain.   The resin composition for an electrode of a lithium ion secondary battery according to claim 4, wherein the linear epoxy resin (B) is an epoxy resin containing a polyethylene glycol chain and / or a polypropylene glycol chain in the main chain.   The lithium ion secondary battery according to claim 5, wherein the linear epoxy resin (B) is an epoxy resin containing a polyethylene glycol chain in the main chain and having a repeating unit of the polyethylene glycol chain of 1 to 30. The electrode resin composition.   Content of the said epoxy resin (B) is 50-150 mass parts with respect to 100 mass parts of said polyimide resins (A), For electrodes of the lithium ion secondary battery of any one of Claims 1-6. Resin composition.   A lithium ion secondary battery comprising a negative electrode obtained using the resin composition for an electrode of a lithium ion secondary battery according to any one of claims 1 to 7 and a carbon material.