Solvent-soluble polyimide resin

Abstract

To provide a polyimide resin which is excellent in heat resistance and mechanical strength, has solvent solubility and a low swelling degree to an electrolyte, has a coefficient of thermal expansion of 15-30 ppm / °C, and has a high retention ratio of tensile strength after immersion of the electrolyte, and an adhesive containing the same, a laminate, and a member for a battery.SOLUTION: There are provided a solvent-soluble polyimide resin which has a repeating unit containing (a) a 3,3'-4,4'- biphenyltetracarboxylic acid dianhydride (s-BPDA), and (b) 2,2'-dimethyl-4,4-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE), and a repeating unit containing (c) a 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylene diamine (DMPDA) in a main chain, and a method for producing the same.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a solvent-soluble polyimide resin, an adhesive containing the same, a laminate, and a battery member.

Background Art

[0002] Conventionally, in lithium-ion batteries, rolled copper foil is used as a negative electrode current collector, and aluminum foil is used as a positive electrode current collector. In recent years, as a new current collector replacing metal foil, a laminated film using an organic film having advantages in terms of lightness, thickness, and strength compared to metal foil as a support has been studied.

[0003] A laminated film using an organic film as a support is produced by laminating metal layers on both sides of an organic film such as PP, PE, or PET. However, these laminated films have many points to be improved in terms of heat resistance and thermal expansion coefficient, and a film made of polyimide resin has been proposed as an organic film capable of improving heat resistance and thermal expansion coefficient.

[0004] Such a polyimide resin is an aromatic polyimide obtained by polymerizing an aromatic tetracarboxylic acid compound and an aromatic diamine compound, and is particularly widely used as a material for electronic devices because it is excellent in mechanical strength, heat resistance, electrical insulation, chemical resistance, dimensional stability, etc. On the other hand, aromatic polyimide has poor solvent solubility due to its rigid molecular structure and strong interaction of imide bonds connecting them. Therefore, the film formation of aromatic polyimide needs to be carried out in the form of a solvent-soluble polyimide or a polyamic acid varnish which is a precursor, and it is required to be excellent in solubility in a solvent (varnish solubility) in this form.

[0005] Furthermore, lithium-ion batteries contain, along with positive and negative electrode materials, an electrolyte layer consisting of an electrolyte solution in which lithium salts are dissolved in an aprotic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate, or a polymer gel impregnated with such an electrolyte. In addition, substances such as LiPF6 and LiBF4 are used as lithium salts for the electrolyte in batteries, but these salts generate corrosive hydrofluoric acid through hydrolysis reactions with water. Therefore, the organic film used as a support for the battery's current collector needs to have resistance to the electrolyte. Specifically, the organic film is required to have a low degree of swelling in the electrolyte and a high retention rate of tensile strength after immersion in the electrolyte.

[0006] Various methods for producing polyimide films have been proposed. For example, Patent Document 1 discloses a method for producing a polyimide film by synthesizing a 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA)-p-phenylenediamine (PPD) polyamic acid in a single reaction and then heating the resulting polyamic acid at a high temperature.

[0007] Patent Document 2 discloses a method for synthesizing pyromellitic dianhydride (PMDA)-4,4'-diaminodiphenyl ether (p-DADE)-based polyamic acid in a single reaction and for producing a polyamic acid film.

[0008] Patent Document 3 discloses a method for synthesizing three-component or four-component polyamic acids by copolymerizing the above monomers in any ratio, and then producing a polyimide film by forming the obtained polyamic acid into a film and heating it at a high temperature.

[0009] Patent Document 4 discloses a method for synthesizing polyamic acid by reacting 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), paraphenylenediamine (PDA), and 4,4-diaminodiphenyl ether, and then heating the resulting polyamic acid at a high temperature to produce a polyimide film for flexible devices. The linear expansion coefficient of the polyimide film obtained in Patent Document 4 is 0 to 10 ppm / °C, which is suitable for flexible devices.

[0010] Patent Document 5 discloses a method for synthesizing polyamic acid by reacting 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), pyromellitic acid dianhydride (PMDA), paraphenylenediamine (PDA), 4,4-diaminodiphenyl ether, etc., and then heating the obtained polyamic acid at a high temperature to produce a polyimide film for flexible devices.

[0011] Patent Document 6 discloses a method for synthesizing polyamic acid by polymerizing 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and paraphenylenediamine (PDA) in a single reaction, and then heating the obtained polyamic acid at a high temperature to produce a polyimide film with a coefficient of thermal expansion of 10 ppm or less.

[0012] Patent Document 7 discloses a method for synthesizing polyamic acid by polymerizing 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), paraphenylenediamine (PDA), and 2,2'-bis(trifluoromethyl)benzidine (TFMB) in a single reaction, and then producing a polyimide film by heating the obtained polyamic acid at a high temperature.

[0013] Patent Document 8 discloses a polyimide resin containing a reaction block of ODPA and DMPDA and a reaction block of m-DADE,TPE-R,3,3'-4,4'-biphenyltetracarboxylic acid as a binder for manufacturing lithium-ion secondary batteries. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 55-7805 [Patent Document 2] Special Publication No. 36-10999 [Patent Document 3] Japanese Patent Application Publication No. 9-235373 [Patent Document 4] Japanese Patent Publication No. 2012-102155 [Patent Document 5] Japanese Patent Publication No. 2014-9305 [Patent Document 6] Japanese Patent Publication No. 2016-204457 [Patent Document 7] Japanese Patent Publication No. 2013-14727 [Patent Document 8] Japanese Patent Publication No. 2019-96401 [Overview of the project] [Problems that the invention aims to solve]

[0015] However, Patent Documents 1 to 7 all describe methods for producing polyimide films by synthesizing polyamic acid, forming a film of polyamic acid, and then heating it at high temperatures. Polyamic acid is prone to hydrolysis by water and changes easily at room temperature, so polyimide films produced via polyamic acid tend to have variations in properties. Furthermore, when producing polyimide films from polyamic acid, high-temperature treatment such as 350°C is required to completely carry out imidation. As a result, problems such as warping of the polyimide film during manufacturing and poor dimensional stability occurred. Moreover, Patent Documents 1 to 7 do not disclose a polyimide film that has a thermal expansion coefficient of 15 to 30 ppm / °C, which is considered necessary for laminated films for battery current collectors, and that is resistant to electrolytes.

[0016] In addition, the polyimide resin of Patent Document 8 discloses a polyimide resin used as a binder resin for a coating layer formed on a current collector made of a metal foil. Although the swelling degree is low, further improvement has been demanded for the retention rate of the tensile strength after immersion in an electrolytic solution. Also, with the polyimide resin of Patent Document 8, a polyimide film having a coefficient of thermal expansion of 15 to 30 ppm / °C suitable for an organic film as a support for a current collector of a battery has not been obtained.

[0017] That is, conventionally, without going through polyamic acid, a method for producing a polyimide film that is excellent in heat resistance and mechanical strength, has solvent solubility and a low swelling degree with respect to an electrolytic solution, and has a coefficient of thermal expansion in the range of 15 to 30 ppm / °C that matches both the coefficient of thermal expansion of copper of 16.8 ppm / °C and the coefficient of thermal expansion of aluminum of 23.8 ppm / °C laminated on both sides of an organic film, and has a high retention rate of tensile strength after immersion in an electrolytic solution has not been found. In particular, it has been difficult to concurrently achieve solvent solubility, swelling resistance to an electrolytic solution, and a coefficient of thermal expansion in the range of 15 to 30 ppm / °C in a polyimide resin.

[0018] As a result of intensive studies in view of the above problems, the inventors have found that a polyimide resin of a block copolymer having a repeating unit with a specific structure is excellent in heat resistance and mechanical strength, has solvent solubility and a low swelling degree with respect to an electrolytic solution, has a coefficient of thermal expansion in the range of 15 to 30 ppm / °C, and has a high retention rate of tensile strength after immersion in an electrolytic solution. And it has been found that a polyimide film formed from such a polyimide resin can be used as a battery member such as a current collector for a positive electrode or a negative electrode of a lithium ion secondary battery, and the present invention has been completed.

Means for Solving the Problems

[0019] That is, the present invention has in the main chain a repeating unit containing (a) 3,3'-4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE), and a repeating unit containing (c) 4,4'-oxydiphthalic dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA). Furthermore, the content of (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride is 65 to 82.0 mol% of all acid dianhydrides, the content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) is 8 to 25.0 mol% of all diamines, and the content of (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 47 to 80.0 mol% of all diamines. The present invention provides a solvent-soluble polyimide resin, characterized by the above.

[0020] Further, the present invention includes a first step of reacting (c) 4,4'-oxydiphthalic dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA), and a second step of adding and reacting (a) 3,3'-4,4'-biphenyltetracarboxylic dianhydride (s-BPDA (4,4'-biphthalic anhydride)) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) to the reaction product obtained in the first step. Furthermore, in the solvent-soluble polyimide resin obtained by the first and second steps, the content of (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride is 65 to 82.0 mol% of all acid dianhydrides, the content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) is 8 to 25.0 mol% of all diamines, and the content of (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 47 to 80.0 mol% of all diamines. The present invention provides a method for producing a solvent-soluble polyimide resin, characterized by the above.

Advantages of the Invention

[0021] The polyimide resin of the present invention has high heat resistance, solvent solubility, and a low degree of swelling in electrolytes, as well as a thermal expansion coefficient in the range of 15 to 30 ppm / °C, and retains high tensile strength after immersion in an electrolyte. Therefore, a laminate made by laminating metal layers such as copper or aluminum on both sides of a polyimide film made from the polyimide resin of the present invention as a support can be used as a current collector in a lithium-ion secondary battery for a long period of time without delamination, even when used in contact with the electrolyte in the battery. As a result, the current collector of the battery can be made thinner and lighter, increasing the battery capacity per unit volume while simultaneously reducing the weight of the battery. Furthermore, the polyimide resin of the present invention can be suitably used not only as a current collector in a battery, but also as a battery component (adhesive layer) such as a battery electrolyte sealing film or a battery electrode protective film. [Modes for carrying out the invention]

[0022] The solvent-soluble polyimide resin of the present invention is a block copolymer having repeating units in its main chain that contain specific tetracarboxylic dianhydride residues and diamine residues.

[0023] <Solvent-soluble polyimide resin> The polyimide resin of the present invention is characterized by having in its main chain repeating units (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE), and (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA).

[0024] In the present invention, a repeating unit comprising (a) 3,3'-4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) is a constituent unit obtained by a condensation reaction and dehydration of component (a) and component (b), and only needs to contain at least component (a) and component (b).

[0025] Furthermore, from the viewpoint of providing optimal solvent solubility to the polyimide resin, it is preferable that the repeating unit containing components (a) and (b) further contains 3,4-diaminodiphenyl ether or 1,3-bis(4-aminophenoxy)benzene as a constituent component.

[0026] In the present invention, a repeating unit comprising (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is a constituent unit obtained by a condensation reaction and dehydration of component (c) and component (d), and only needs to contain at least component (c) and component (d).

[0027] The polyimide resin of the present invention may contain tetracarboxylic dianhydride residues and diamine residues other than those mentioned above, but from the viewpoint of resistance to electrolyte swelling, it is preferable that the diamine residues other than those mentioned above do not contain fluorine or sulfur atoms.

[0028] In the present invention, the content of (a) 3,3'-4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in the polyimide resin is preferably 65 mol% or more of all acid dianhydrides, more preferably 66.0 to 82.0 mol%, more preferably 67.0 to 80.0 mol%, and particularly preferably 68.0 to 78.0 mol%.

[0029] In the present invention, the total content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) contained in the polyimide resin is preferably 55 mol% or more of all diamines, more preferably 56.0 to 86.0 mol%, more preferably 57.0 to 84.0 mol%, and particularly preferably 58.0 to 82.0 mol%, from the viewpoint of exhibiting an optimal range of thermal expansion coefficient (15 to 30 ppm / °C).

[0030] In the present invention, the content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) contained in the polyimide resin is preferably 8 mol% or more of all diamines, more preferably 8.5 to 25.0 mol%, more preferably 8.8 to 22.0 mol%, and particularly preferably 9.0 to 20.0 mol%, from the viewpoint of exhibiting an optimal range of thermal expansion coefficient (15 to 30 ppm / °C) and solubility.

[0031] In the present invention, the content of (d)2,5-dimethyl-1,4-phenylenediamine (DMPDA) in the polyimide resin is preferably 47 mol% or more of all diamines, more preferably 48.0 to 80.0 mol%, more preferably 48.5 to 78.0 mol%, and particularly preferably 49.0 to 75.0 mol%.

[0032] The polyimide resin of the present invention, having repeating units in its main chain containing specific tetracarboxylic dianhydride residues and diamine residues as described above, has a coefficient of thermal expansion in the range of 15 to 30 ppm / °C, preferably 16 to 25 ppm / °C. Therefore, by using a polyimide film made from the polyimide resin of the present invention as a support, and a laminate formed by laminating metal layers such as copper or aluminum on both sides thereof as a current collector for a battery, peeling of the current collector film can be prevented.

[0033] In this invention, the term "solvent-soluble" refers to an organic polar solvent used in the synthesis of polyimide, meaning a polyimide that dissolves in 5 g or more of the solvent in 100 g of the solvent. Therefore, the solvent-soluble polyimide resin of this invention can be made into a solution suitable for film formation. As the solvent in which the polyimide dissolves, polar solvents such as N-methyl-2-pyrrolidone, γ-butyrolactone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, sulfolane, and tetramethylurea, which are used as solvents in imidation reactions, can be used. The concentration of polyimide (solid content) in the solution is preferably 3% to 50% by weight, and more preferably 5% to 40% by weight. Polyimide obtained by a direct imidation reaction using a catalyst system consisting of lactone and a base, as described later, is obtained in the form of a solution dissolved in a polar solvent, and the concentration of polyimide is also obtained within the above preferred range, so the polyimide solution produced by the above method can preferably be used as is. If desired, the produced polyimide solution can be further diluted with a diluent. Suitable diluents include, but are not limited to, solvents that do not significantly reduce solubility, such as dioxane, dioxolane, N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, cyclopentanone, propylene glycol monomethyl ether acetate, methyl lactate, anisole, methyl benzoate, and ethyl acetate.

[0034] The solvent-soluble polyimide resin of the present invention has a low degree of swelling in relation to the electrolyte. Specifically, when a film made from the polyimide resin of the present invention is immersed in an electrolyte for lithium-ion secondary batteries and treated at 80°C for 72 hours, the degree of swelling is 50% by weight or less, preferably 45% by weight or less, and more preferably 40% by weight or less. If the degree of swelling of the polyimide film in relation to the electrolyte is high, the adhesion between the polyimide film and the conductive material layer tends to be insufficient, and when the polyimide film is used as a support for the current collector of the battery, the battery life characteristics tend to deteriorate. In this case, the electrolyte used to immerse the polyimide film can be the electrolyte described later as a battery component. Furthermore, the film made from the solvent-soluble polyimide resin of the present invention can maintain a high retention rate of tensile strength after immersion in an electrolyte solution.

[0035] The weight-average molecular weight of the polyimide resin of the present invention is preferably 10,000 to 100,000 in terms of polystyrene equivalent. When the weight-average molecular weight is within this range, good solvent solubility, film properties, and insulating properties of the polyimide resin can be achieved.

[0036] <Method for synthesizing solvent-soluble polyimide resins> The solvent-soluble polyimide resin of the present invention can be synthesized by a block copolymerization reaction. Specifically, a block copolymerized polyimide resin can be synthesized by carrying out a first step of polycondensation reaction of (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA), and then a second step of adding (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA (4,4'-biphthalic acid anhydride)) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) or 4,4-diaminodiphenyl ether (p-DADE) to the reaction product obtained in the first step and carrying out a polycondensation reaction.

[0037] As a catalyst for block copolymerization reactions, a two-component acid-base catalyst utilizing the equilibrium reaction of lactones can be used to accelerate the dehydration imidation reaction. Specifically, a two-component catalyst of γ-valerolactone and pyridine or N-methylmorpholine is used. As shown in the formula below, water is generated as imidation progresses, and this generated water participates in the equilibrium of the lactones, becoming an acid-base catalyst and exhibiting catalytic activity.

[0038] [ka]

[0039] The water produced by the imidation reaction is removed from the system by azeotropic reaction with a dehydrating agent such as toluene or xylene present in the polar solvent. Once the reaction is complete, the water in the solution is removed, and the acid-base catalyst becomes γ-valerolactone and pyridine or N-methylmorpholine, which are then removed from the system. In this way, a high-purity polyimide solution can be obtained.

[0040] Other two-component catalysts include oxalic acid or malonic acid and pyridine or N-methylmorpholine. In the reaction solution at 160-200°C, the oxalate or malonic acid acts as an acid catalyst to promote the imidation reaction. A catalytic amount of oxalic acid or malonic acid remains in the resulting polyimide solvent. When this polyimide solution is applied to a substrate and heated to over 200°C to desolvate and form a film, the oxalic acid or malonic acid remaining in the polyimide is thermally decomposed as shown in the following formula and removed from the system as a gas.

[0041] [ka]

[0042] By the above method, high-purity solvent-soluble polyimide can be obtained. The oxalic acid-pyridine catalyst is more active than the valerolactone-pyridine catalyst, and high molecular weight polyimide can be produced in a short time. The method for synthesizing the polyimide resin of the present invention can be based, for example, on the method described in WO2006 / 057036.

[0043] <Adhesive> The solvent-soluble polyimide resin of the present invention can be used as various adhesives in a solvent-containing form. Adhesives containing the solvent-soluble polyimide resin of the present invention also exhibit excellent electrolyte resistance, making them suitable as battery adhesives. They are also suitable as adhesives for various metals. When using the polyimide resin of the present invention as an adhesive, it can be used as a polyimide resin composition containing polyamide-imide resin, polyamide resin, epoxy resin, acrylic resin, phenolic resin, etc., in addition to the polyimide resin itself.

[0044] <Method for producing polyimide film> The polyimide resin of the present invention can form an adhesive layer with adhesive properties by being formed into a film, and can be used as a support for the current collector of a lithium-ion battery (an intermediate layer on which metal layers or the like are formed on both sides). As a method for forming the polyimide resin into a film, for example, a method of coating the polyimide resin onto a conductive material layer such as copper or aluminum, which will be described later, can be used. In this case, there are no particular limitations on the method of coating the polyimide resin, and examples include spray method, spin coating method, dip method, roll coating method, blade coating method, doctor roll method, doctor blade method, curtain coating method, slit coating method, screen printing method, inkjet method, etc.

[0045] Furthermore, when the polyimide film is a thin film, a method for forming a polyimide resin film involves coating a peelable support with the polyimide resin to form an organic film, and then peeling off the support. The coating method for the polyimide resin in this case depends on the film thickness, but examples include gravure coating and precision die coating. Examples of peelable supports include polyimide film and aluminum foil. The polyimide resin of the present invention is a ring-closed polyimide, and the drying temperature of the polyimide film is preferably 200°C to 300°C due to solvent drying. The polyimide resin of the present invention exhibits excellent resistance to electrolyte swelling and has a thermal expansion coefficient close to that of copper and aluminum, making it suitable as an organic film for positive or negative electrodes.

[0046] <Laminate> The polyimide film formed from the polyimide resin of the present invention functions as a support and adhesive layer (intermediate layer) of a laminate, and can be formed into a laminate (laminated film) by forming an upper layer and a lower layer on both sides. The upper and lower layers can be selected according to the application. For example, conductive material layers composed of metals such as copper, aluminum, iron, silver, and titanium, metal oxides, or composites thereof can be used. Particularly preferred is a metal layer composed of copper or aluminum. The thickness of the upper and lower layers formed on both sides of the polyimide film formed from the polyimide resin of the present invention is not particularly limited as long as it satisfies the properties of the laminate used, but it is preferable that they be as thin as possible.

[0047] One method for producing the laminate is to coat the polyimide resin of the present invention onto a metal foil such as copper foil or aluminum foil to form a polyimide film, and then further bond the polyimide film to the metal foil such as copper foil or aluminum foil. Another method for forming an ultrathin conductive material layer (upper or lower layer) is to deposit a film on both sides of an adhesive layer (intermediate layer) made of polyimide film by vacuum deposition or sputtering. The laminate produced in the above manner can be used for a long period of time without delamination between the conductive material layer and the polyimide film layer, even when used in contact with polar solvents and / or salts, especially non-aqueous electrolytes which are mixtures thereof. Therefore, it can be suitably used as a laminated film for the positive or negative electrode of a battery, an electrolyte sealing film, or an electrode protective film.

[0048] <Electrodes for lithium-ion secondary batteries> The laminate produced as described above can be used as a current collector (laminated film) for the positive or negative electrode of a lithium-ion secondary battery.

[0049] <Manufacturing method for lithium-ion secondary batteries> The lithium-ion secondary battery of the present invention can be manufactured according to a conventional method by coating a paste layer containing a positive electrode active material, a conductive material, and a binder on the laminated film (current collector), which is the positive electrode and the negative electrode described above, drying it, and combining it with an electrolytic solution, a separator, etc.

[0050] (Positive electrode active material) The positive electrode active material for the lithium-ion secondary battery is not particularly limited, but includes lithium-containing cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxide of Co-Ni-Mn (Li(CoMnNi)O2), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li2MnO3-LiNiO2-based solid solution, Li 1+x Mn 2-x excess spinel compound represented by O4 (0 <X <2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4 and other known positive electrode active materials. The blending amount and particle size of the positive electrode active material are not particularly limited, and those within a known range can be used.

[0051] (Negative electrode active material) The negative electrode active material for the lithium-ion secondary battery is not particularly limited, but includes carbon-based negative electrode active materials such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, pyrolytic vapor-grown carbon fiber, phenolic resin fired body, polyacrylonitrile-based carbon fiber, quasi-isotropic carbon, furfuryl alcohol resin fired body (PFA), hard carbon, natural graphite, artificial graphite; non-carbon-based negative electrode active materials such as silicon (Si), an alloy containing silicon, SiO, SiOx, and a composite of a Si-containing material coated or compounded with conductive carbon and conductive carbon. The blending amount and particle size of the negative electrode active material are not particularly limited, and those within a known range can be used.

[0052] (Conductive material) The conductive material is used to ensure electrical contact between the electrode active materials. Suitable conductive materials include conductive carbon materials such as carbon black (e.g., acetylene black, Ketjenblack®, furnace black, etc.), graphite, carbon fibers, carbon flakes, and carbon short fibers (e.g., carbon nanotubes and vapor-grown carbon fibers); as well as various metal fibers and foils. Among these, carbon black is preferred as the conductive material, and acetylene black is more preferred. These can be used individually or in combination of two or more.

[0053] (electrolyte) Typically, an organic electrolyte is used as the electrolyte, obtained by dissolving a supporting electrolyte in an organic solvent. For lithium-ion secondary batteries, lithium salts are used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9S O3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, from the viewpoint of being easily soluble in the solvent and exhibiting a high degree of dissociation. One type of electrolyte may be used alone, or two or more types may be used in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0054] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. However, suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. A mixture of these solvents may also be used. Among these, carbonates are preferred from the viewpoint of having a high dielectric constant and a wide stable potential range. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate, and a solution of 0.5 to 3 mmol / L is preferred. In addition, known additives, such as fluoroethylene carbonate and ethyl methyl sulfone, can be added to the electrolyte. [Examples]

[0055] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0056] <Synthesis of polyimide resin> Example 1 A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 23.38 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.172 mol), 26.63 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.085 mol), 266 g of N-methyl-2-pyrrolidone, 70 g of toluene, 5.43 g of pyridine, and 3.44 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 27.5 g (0.137 mol) of 3,4-diaminodiphenyl ether, 7.29 g (component (b): 0.034 mol) of 2,2'-dimethyl-4,4'-biphenyldiamine, 77.58 g (component (a): 0.264 mol) of 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride, and 441 g of N-methyl-2-pyrrolidone were added to the system. The reaction was carried out under the same conditions as the first step, and the second step was completed after 6.0 hours from the start of the reaction. After the reaction was complete, 143 g of N-methyl-2-pyrrolidone was added to obtain a polyimide solution with a solid content of 15 wt%.

[0057] Example 2 A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 26.83 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.197 mol), 30.56 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.099 mol), 305 g of N-methyl-2-pyrrolidone, 70 g of toluene, 6.23 g of pyridine, and 3.95 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 27.61 g (0.138 mol) of 3,4-diaminodiphenyl ether, 16.21 g (component (b): 0.059 mol) of 2,2'-dimethyl-4,4'-biphenyldiamine, 87.99 g (component (a): 0.299 mol) of 3,3'-4,4'-biphenyltetracarboxylic dianhydride, and 520 g of N-methyl-2-pyrrolidone were added to the system. The reaction was carried out under the same conditions as the first step, and the second step was completed after 6.0 hours from the start of the reaction. After the reaction was completed, a polyimide solution with a solid content of 17.5 wt% was obtained by cooling.

[0058] Example 3 A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 32.67 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.240 mol), 37.21 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.120 mol), 371 g of N-methyl-2-pyrrolidone, 70 g of toluene, 5.42 g of pyridine, and 3.43 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 6.85 g of 4,4-diaminodiphenyl ether (component (b): 0.034 mol), 20.04 g of 1,3-bis(4-aminophenoxy)benzene (0.069 mol), 65.58 g of 3,3'-4,4'-biphenyltetracarboxylic dianhydride (component (a): 0.223 mol), and 479 g of N-methyl-2-pyrrolidone were added to the system, and the reaction was carried out under the same conditions as the first step. The second step was completed after 6.0 hours from the start of the reaction, and a polyimide solution with a solid content of 15 wt% was obtained.

[0059] Comparative Example 1 A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 27.99 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.205 mol), 31.87 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.103 mol), 318 g of N-methyl-2-pyrrolidone, 70 g of toluene, 5.01 g of pyridine, and 3.17 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 18.51 g (0.043 mol) of bis[4-(4-aminophenoxy)phenyl]sulfone, 20.02 g (0.069 mol) of 1,3-bis(4-aminophenoxy)benzene, 63.02 g (component (a): 0.214 mol) of 3,3'-4,4'-biphenyltetracarboxylic dianhydride, and 282 g of N-methyl-2-pyrrolidone were added to the system. The reaction was carried out under the same conditions as the first step, and the second step was completed after 6.0 hours from the start of the reaction. The obtained product was diluted with 250 g of NMP to obtain a polyimide solution with a solid content of 15 wt%.

[0060] Comparative Example 2 (An example of polyimide production under the same conditions as in Example 1, except that TPE-R was used instead of m-TOLIDINE.) A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 23.38 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.172 mol), 26.63 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.085 mol), 266 g of N-methyl-2-pyrrolidone, 70 g of toluene, 5.43 g of pyridine, and 3.44 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 27.5 g (0.137 mol) of 3,4-diaminodiphenyl ether, 9.94 g (0.034 mol) of 1,3-bis(4-aminophenoxy)benzene, 77.58 g (component (a): 0.264 mol) of 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride, and 441 g of N-methyl-2-pyrrolidone were added to the system. The reaction was carried out under the same conditions as the first step, and the second step was completed after 6.0 hours from the start of the reaction. After the reaction was complete, 143 g of N-methyl-2-pyrrolidone was added to obtain a polyimide solution with a solid content of 15 wt%.

[0061] Comparative Example 3 (An example in which polyimide was produced under the same conditions as in Example 3, except that m-DADE was used instead of p-DADE.) A glass separable three-necked flask was fitted with a stirrer, nitrogen inlet tube, and Dean-Stark apparatus. 32.67 g of 2,5-dimethyl-1,4-phenylenediamine (component (d): 0.240 mol), 37.21 g of 4,4-oxydiphthalic acid dianhydride (component (c): 0.120 mol), 371 g of N-methyl-2-pyrrolidone, 70 g of toluene, 5.42 g of pyridine, and 3.43 g of γ-valerolactone were charged and reacted under a nitrogen atmosphere at an oil bath temperature of 180°C and 180 rpm. After 1.5 hours following the evaporation of water, the mixture was removed from the oil bath and cooled to complete the first stage of the reaction. 6.85 g (0.034 mol) of 3,4-diaminodiphenyl ether, 20.04 g (0.069 mol) of 1,3-bis(4-aminophenoxy)benzene, 65.58 g (component (a): 0.223 mol) of 3,3'-4,4'-biphenyltetracarboxylic dianhydride, and 479 g of N-methyl-2-pyrrolidone were added to the system. The reaction was carried out under the same conditions as the first step, and the second step was completed after 6.0 hours from the start of the reaction to obtain a polyimide solution with a solid content of 15 wt%.

[0062] Table 1 shows the results of measuring various properties of the polyimide solutions synthesized in Examples 1-3 and Comparative Examples 1-3 using the following methods.

[0063] <Glass transition temperature (Tg), mechanical strength, coefficient of thermal expansion, and 5% thermogravimetric loss temperature> The polyimide solutions of each of the above examples and comparative examples were spin-coated onto rolled copper foil to a final drying thickness of 15 μm. After pre-baking at 90°C for 360 seconds, the films were heated and dried at 250°C for 60 minutes to produce copper foil-coated dried resin films. The copper foil-coated dried resin films were then etched and heated and dried at 80°C for 30 minutes to obtain test samples for measuring glass transition temperature (Tg), mechanical strength, thermal expansion coefficient, and 5% thermogravimetric loss temperature. The glass transition temperature (Tg) was measured according to IPC-TM-650-2.4.24.3, the mechanical strength (tensile strength) according to IPC-TM-650-2.4.19, the coefficient of thermal expansion according to IPC-TM-650-2.4.41.3, and the 5% thermogravimetric loss temperature according to IPC-TM-650-2.4.24.6.

[0064] <Electrolyte swelling properties> The polyimide solutions of each of the above examples and comparative examples were spin-coated onto rolled copper foil to achieve a final drying thickness of 15 μm. After pre-baking at 90°C for 360 seconds, the films were heated and dried at 250°C for 60 minutes to produce copper foil-coated dried resin films. The copper foil-coated resin film was etched, and the resulting film was heated and dried at 80°C for 30 minutes to obtain a film with a thickness of approximately 15 μm. A 30 mm × 30 mm test specimen was prepared from the film, and the specimen was immersed in an electrolyte solution prepared by dissolving 1 mol / L of LiPF6 in an electrolyte solvent consisting of ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate = 3:3:4. After heating the electrolyte solution to 80°C, the specimen was immersed at 80°C for 72 hours. The weight change of the specimen before and after the immersion treatment was measured, and the weight increase rate (%) was determined as the degree of swelling. Here, the method of preparing the film did not affect the value of the degree of swelling, and the weight of the film after the immersion treatment was measured after removing the specimen from the electrolyte solution and quickly wiping off the electrolyte adhering to the surface with a tissue to prevent drying. Furthermore, the mechanical strength (tensile strength) after immersion was measured using test pieces (10 mm x 150 mm) that had been similarly wiped after being immersed in the electrolyte solution.

[0065] Table 1 below shows the resin composition of the solvent-soluble polyimides produced in Synthesis Examples 1-3 and Comparative Examples 1-3, and the evaluation results of the properties required for laminated films for lithium-ion secondary batteries of the polyimide films produced therefrom.

[0066] [Table 1]

[0067] In Table 1 above, comparing the polyimide solution of Example 1 with the polyimide solution of Comparative Example 2 (corresponding to Synthesis Example 1 of Japanese Patent Application Publication No. 2019-96401 (Patent Document 8)), which was prepared under the same conditions as in Example 1 except that TPE-R was used instead of m-TOLIDINE, it can be seen that the thermal expansion coefficient of Example 1 (thermal expansion coefficient: 22.4 ppm / °C, tensile strength retention rate after immersion in electrolyte: 91.4%) is significantly lower than that of Comparative Example 2 (thermal expansion coefficient: 41.5 ppm / °C, tensile strength retention rate after immersion in electrolyte: 89.3%), exhibiting a thermal expansion coefficient in the range of 15 to 30 ppm / °C, and that the retention rate of tensile strength after immersion in electrolyte is improved.

[0068] Furthermore, comparing the polyimide solution of Example 3 with the polyimide solution of Comparative Example 3, which was prepared under the same conditions as in Example 3 except that m-DADE was used instead of p-DADE, it can be seen that the thermal expansion coefficient of Example 3 (thermal expansion coefficient: 18.1 ppm / °C, tensile strength retention rate after immersion in electrolyte: 92.0%) is significantly lower than that of Comparative Example 3 (thermal expansion coefficient: 40.2 ppm / °C, tensile strength retention rate after immersion in electrolyte: 89.7%), exhibiting a thermal expansion coefficient in the range of 15 to 30 ppm / °C, and that the retention rate of tensile strength after immersion in electrolyte is improved.

[0069] The results above demonstrate that the block copolymerized polyimide resin containing the specific components of the present invention achieves a thermal expansion coefficient in the range of 15 to 30 ppm / °C and maintains high tensile strength after immersion in an electrolyte solution. [Industrial applicability]

[0070] The solvent-soluble polyimide resin of the present invention can be suitably used in the fields of various adhesives, laminated films for positive or negative electrodes of lithium-ion batteries, battery electrolyte sealing films, battery electrode protective films, and batteries using these.

Claims

1. The main chain has repeating units comprising (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE), and (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA), The content of (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride is 65 to 82.0 mol% of all acid dianhydrides. The content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) is 8 to 25.0 mol% of all diamines. A solvent-soluble polyimide resin characterized in that the content of (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 47 to 80.0 mol% of all diamines.

2. The solvent-soluble polyimide resin according to claim 1, having in its main chain a repeating unit comprising (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE), and a repeating unit comprising (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA).

3. The solvent-soluble polyimide resin according to claim 1, having in its main chain a repeating unit comprising (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) and (b) 4,4-diaminodiphenyl ether (p-DADE), and a repeating unit comprising (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA).

4. The solvent-soluble polyimide resin according to any one of claims 1 to 3, wherein the repeating unit comprising (a) and (b) comprises 3,4-diaminodiphenyl ether.

5. The solvent-soluble polyimide resin according to any one of claims 1 to 4, wherein the repeating unit comprising (a) and (b) comprises 1,3-bis(4-aminophenoxy)benzene.

6. The solvent-soluble polyimide resin according to any one of claims 1 to 5, wherein the content of (a) 3,3'-4,4'-biphenyltetracarboxylic dianhydride is 66.0 to 82.0 mol% of all acid dianhydrides.

7. The solvent-soluble polyimide resin according to any one of claims 1 to 6, wherein the total content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) or 4,4-diaminodiphenyl ether (p-DADE) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 55 mol% or more of all diamines.

8. The solvent-soluble polyimide resin according to any one of claims 1 to 7, wherein the content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) or 4,4-diaminodiphenyl ether (p-DADE) is 8.5 to 25.0 mol% of all diamines.

9. The solvent-soluble polyimide resin according to any one of claims 1 to 8, wherein the content of (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 48.0 to 80.0 mol% of all diamines.

10. The solvent-soluble polyimide resin according to any one of claims 1 to 9, wherein the coefficient of thermal expansion of the solvent-soluble polyimide resin is 15 to 30 ppm / °C.

11. A polyimide resin composition comprising a solvent-soluble polyimide resin according to any one of claims 1 to 10, and at least one solvent selected from the group consisting of N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide.

12. A battery adhesive comprising a solvent-soluble polyimide resin according to any one of claims 1 to 10.

13. Adhesive for metals or metal oxides comprising a solvent-soluble polyimide resin according to any one of claims 1 to 10.

14. A laminate having an adhesive layer containing the adhesive described in claim 12 or 13 as an intermediate layer.

15. A laminate having a metal layer and a polyimide film layer made of a solvent-soluble polyimide resin according to any one of claims 1 to 10.

16. The laminate according to claim 15, wherein the metal layer is composed of copper or aluminum.

17. A battery component having a laminate according to any one of claims 14 to 16.

18. A battery having the battery component described in claim 17.

19. The process includes a first step of reacting (c) 4,4-oxydiphthalic acid dianhydride (ODPA) and (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA), and a second step of adding (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA (4,4'-biphthalic acid anhydride)) and (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) to the reaction product obtained in the first step and reacting them, In the solvent-soluble polyimide resin obtained by the first and second steps, The content of (a) 3,3'-4,4'-biphenyltetracarboxylic acid dianhydride is 65 to 82.0 mol% of all acid dianhydrides. The content of (b) 2,2'-dimethyl-4,4'-biphenyldiamine (m-TOLIDINE) and / or 4,4-diaminodiphenyl ether (p-DADE) is 8 to 25.0 mol% of all diamines. A method for producing a solvent-soluble polyimide resin, characterized in that the content of (d) 2,5-dimethyl-1,4-phenylenediamine (DMPDA) is 47 to 80.0 mol% of all diamines.

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