Material for forming electrode, and electrode mixture

Abstract

To provide a material for forming an electrode, by which an electrode of an energy device with a low resistance value can be manufactured.SOLUTION: A material for forming an electrode contains polyamideimide whose number-average molecular weight is 2000 to 17000, and is used to form an electrode including an active material containing a silicon-based active material and a carbon-based active material.SELECTED DRAWING: None

Description

Technical Field

[0001] Embodiments of the present invention relate to a material for forming an electrode, an electrode binder, an electrode for an energy device, and an energy device.

Background Art

[0002] Lithium-ion secondary batteries are widely used as power sources for portable information terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants), and as power sources for electric vehicles. A lithium-ion secondary battery is a non-aqueous electrolyte-based energy device having a high energy density. The electrodes of a lithium-ion secondary battery are produced, for example, using a slurry-like electrode binder containing an active material, a binder, and a solvent.

[0003] Patent Document 1 describes a composition containing a binder resin material for an energy device electrode containing a copolymer containing a structural unit derived from (meth)acrylonitrile and a structural unit derived from a compound having two or more ethylenically unsaturated bonds. Further, Patent Document 2 describes a composition containing a copolymer containing a structural unit derived from (meth)acrylonitrile and a structural unit derived from (meth)acrylate, and having a swelling degree of 200 to 400% with respect to an electrolytic solution of the copolymer.

[0004] With the background of expanding the use of lithium-ion secondary batteries to electric vehicles and the like, further improvement of battery characteristics is expected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] An embodiment of the present invention aims to provide a material for forming an electrode and an electrode paste that can manufacture an electrode of an energy device having a low resistance value. Another embodiment of the present invention aims to provide an electrode that can manufacture an energy device having a low resistance value. Further, an embodiment of the present invention aims to provide an energy device having a low resistance value.

Means for Solving the Problems

[0007] The present invention includes the following embodiments. The present invention is not limited to the following embodiments. [1] A material for forming an electrode, which contains polyamideimide, wherein the number average molecular weight of the polyamideimide is 2,000 to 17,000, and is used for forming an electrode containing an active material including a silicon-based active material and a carbon-based active material. [2] The material for forming an electrode according to [1] above, wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material. [3] An electrode paste containing the material for forming an electrode according to [1] or [2] above, and an active material including a silicon-based active material and a carbon-based active material. [4] The electrode paste according to [3] above, wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material. [5] An electrode for an energy device, which has a current collector and an electrode paste layer formed on at least a part of the surface of the current collector using the electrode paste according to [3] or [4] above. [6] An energy device, which has a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode includes the electrode for an energy device according to [5] above.

Advantages of the Invention

[0008] According to an embodiment of the present invention, it is possible to provide a material for forming an electrode and an electrode paste that can manufacture an electrode of an energy device having a low resistance value. Further, according to an embodiment of the present invention, it is possible to provide an electrode that can manufacture an energy device having a low resistance value. Furthermore, according to an embodiment of the present invention, it is possible to provide an energy device having a low resistance value.

Mode for Carrying Out the Invention

[0009] Embodiments of the present invention will be described. The present invention is not limited to the following embodiments. In the present disclosure, a numerical range indicated using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In a numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value of a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range. The upper limit value or the lower limit value of the numerical range described in the present disclosure may be replaced with the value shown in the examples. From the upper limit numerical value and the lower limit numerical value described stepwise in the present disclosure, a certain numerical value may be selected respectively to form a stepwise numerical range. The upper limit numerical value and the lower limit numerical value described in the present disclosure may be replaced with the values shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content or the content rate of each component means the total content or the content rate of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, each structure in the polymer may contain a plurality of corresponding structures. When there are a plurality of structures corresponding to each structure in the polymer, the content or the content rate of each structure means the total content or the content rate of the plurality of structures present in the polymer, unless otherwise specified. In the present disclosure, the "layer" includes a continuous layer and a discontinuous layer. The thickness of the "layer" may be uniform or non-uniform. The outer edge in the plane direction and the outer edge in the thickness direction of the "layer" may be clear or unclear, respectively. The same applies to the "film".

[0010] <Material for electrode formation> The material for electrode formation according to an embodiment of the present invention is used for forming an electrode containing an active material including a silicon-based active material and a carbon-based active material. The material for electrode formation contains at least polyamideimide. The number average molecular weight of the polyamideimide is 2,000 to 17,000.

[0011] [Polyamideimide] From the viewpoint of obtaining an energy device with a small resistance value, the polyamideimide preferably has a number average molecular weight of 2,000 to 17,000. When the number average molecular weight is 2,000 or more, various properties such as viscosity and strength are improved, and good cycle characteristics tend to be obtained. The number average molecular weight of the polyamideimide may be 4,000 or more, 6,000 or more, 7,000 or more, or 8,500 or more. When the number average molecular weight is 17,000 or less, the resistance value can be suppressed to be small, and good adhesion to the current collector tends to be obtained. The number average molecular weight of the polyamideimide may be 14,000 or less, 12,000 or less, or 10,000 or less. When the number average molecular weight is 10,000 or less, the resistance value can be made smaller, and good initial efficiency, capacity retention rate, and charge / discharge characteristics tend to be obtained.

[0012] In some embodiments, the polyamideimide may include, for example, a structure represented by the following formula (1-1). The polyamideimide may include the structure represented by the following formula (1-1) alone or in combination of two or more. [Chemical formula] (In the formula, R 1represents an organic group, R represents a carboxy group, and n represents an integer from 1 to 5. * represents the bonding position with other atoms.)

[0013] The polyamideimide may further contain a structure represented by the following formula (1-2). The polyamideimide may contain, alone or in combination of two or more, the structure represented by the following formula (1-2).

Chemical formula

[0014] In formula (1-1) and formula (1-2), the organic group is, for example, at least one group selected from the group consisting of a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, a saturated alicyclic hydrocarbon group, an unsaturated alicyclic hydrocarbon group, an aromatic hydrocarbon group, an aromatic heterocyclic compound group, and a group consisting of two or more selected from these. These groups may or may not have a substituent (excluding the carboxy group). In some embodiments, these groups do not have a substituent (excluding the carboxy group). The organic group may be a group containing an aromatic hydrocarbon group, and preferably a group containing a benzene ring. n may be, for example, from 1 to 4, and may be 1 or 2.

[0015] * represents the bonding position with other atoms. * may be, for example, the bonding position with a carbon atom, and * may each independently be the bonding position with a carbon atom contained in the structure represented by formula (2-1) (the C atom in “-CO-*”) or a carbon atom contained in another structure.

[0016] R 1 and (R) n Examples of the group represented by include the groups represented by the following formulae.

Chemical formula

[0017] The linking group may be, for example, an alkylene group (-CH2-, -C(CH3)2-, etc.), -CO-, -SO2-, or -O-.

[0018] Specific examples of the group represented by formula (1-3) include groups represented by the following formulas.

Chemical formula

Chemical formula

[0019] In some embodiments, the polyamideimide contains a structure represented by formula (1-1) (wherein the groups represented by R 1 and (R) n are groups represented by formula (1-3).), and preferably, the polyamideimide contains a structure represented by formula (1-1) (wherein the groups represented by R 1 and (R) n are groups represented by formula (1-4).). In some embodiments, the polyamideimide further contains a structure represented by formula (1-2) (wherein the groups represented by R 1 and (R) n are groups represented by formula (1-3).), and preferably, the polyamideimide further contains a structure represented by formula (1-2) (wherein the groups represented by R 1 and (R) n are groups represented by formula (1-4).).

[0020] The structure represented by formula (1-1) and the structure represented by formula (1-2) can be introduced into the polyamideimide using a diisocyanate compound having a carboxy group, a diamine compound having a carboxy group, or both, which will be described later.

[0021] In some embodiments, the polyamideimide may include, for example, a structure represented by the following formula (3-1). The polyamideimide may include the structure represented by the following formula (3-1) alone or in combination of two or more. The structure represented by the following formula (3-1) is a structure different from the structure represented by formula (1-1) and has no carboxy group in the structure.

Chemical formula

[0022] The polyamideimide may further include a structure represented by the following formula (3-2). The polyamideimide may include the structure represented by the following formula (3-2) alone or in combination of two or more. The structure represented by the following formula (3-2) is a structure different from the structure represented by formula (1-2) and has no carboxy group in the structure.

Chemical formula

[0023] In formula (3-1) and formula (3-2), the organic group is, for example, at least one group selected from the group consisting of a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, a saturated alicyclic hydrocarbon group, an unsaturated alicyclic hydrocarbon group, an aromatic hydrocarbon group, an aromatic heterocyclic compound group, and a group consisting of two or more selected from these. These groups may or may not have a substituent (provided that it is not a carboxy group). Examples of the substituent include an alkyl group (for example, having 1 to 20 or 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (for example, having 1 to 20 or 1 to 6 carbon atoms), etc. The substituent may be an alkyl group and may be a methyl group. The organic group may be a group containing an aromatic hydrocarbon group and preferably may be a group containing a benzene ring. The aromatic hydrocarbon group and the benzene ring may or may not have a substituent, respectively.

[0024] * represents the bonding position with other atoms. * may be, for example, the bonding position with a carbon atom, and each * may independently be the bonding position with a carbon atom (the C atom in “-C(O)-*”) contained in the structure represented by formula (2-1) or a carbon atom contained in another structure.

[0025] R 3 Examples of the group represented by include groups represented by the following formulae.

Chemical formula

[0026] The linking group may be, for example, an alkylene group (such as -CH2-, -C(CH3)2-), -CO-, -SO2-, or -O-.

[0027] Specific examples of the group represented by formula (3-3) include groups represented by the following formulae.

Chemical formula

Chemical formula

[0028] In some embodiments, the polyamideimide has a structure represented by formula (3-1) (wherein R 3 is a group represented by formula (3-3).) and a structure represented by formula (3-2) (wherein R 3is a group represented by the formula (3-3).) and contains at least one structure selected from the group consisting of 3 is a group represented by the formula (3-4).) and the structure represented by the formula (3-2) (wherein R 3 is a group represented by the formula (3-4).).

[0029] The structure represented by the formula (3-1) and the structure represented by the formula (3-2) can be introduced into the polyamideimide using the diisocyanate compound, diamine compound, or both described below.

[0030] Polyamideimide is a polymer having an amide bond and an imide bond in the molecule. The polyamideimide may contain at least one structure selected from the group consisting of the structure represented by the formula (1-1) and the structure represented by the formula (3-1), and may further contain at least one structure selected from the group consisting of the structure represented by the formula (1-2) and the structure represented by the formula (3-2).

[0031] When the polyamideimide contains at least one structure selected from the group consisting of the structure represented by the formula (1-1) and the structure represented by the formula (1-2) and at least one structure selected from the group consisting of the structure represented by the formula (3-1) and the structure represented by the formula (3-2), based on the total of the structure represented by the formula (1-1), the structure represented by the formula (1-2), the structure represented by the formula (3-1), and the structure represented by the formula (3-2), the total content ratio of the structure represented by the formula (1-1) and the structure represented by the formula (1-2) (when only one of them is contained, the content ratio of that one only) is, from the viewpoint of suppressing the resistance value, for example, 10 to 60% by mass, 15 to 50% by mass, or 20 to 45% by mass. The total content ratio of the structure represented by the formula (3-1) and the structure represented by the formula (3-2) (when only one of them is contained, the content ratio of that one only) is, for example, 40 to 90% by mass, 50 to 85% by mass, or 55 to 80% by mass.

[0032] When the polyamideimide contains at least one structure selected from the group consisting of the structure represented by formula (1-1) and the structure represented by formula (1-2) and at least one structure selected from the group consisting of the structure represented by formula (3-1) and the structure represented by formula (3-2), the total content ratio (molar ratio) of the structure represented by formula (1-1) and the structure represented by formula (1-2) based on the total of the structure represented by formula (1-1), the structure represented by formula (1-2), the structure represented by formula (3-1), and the structure represented by formula (3-2) (when only one of them is contained, the content ratio of only that one) is, from the viewpoint of suppressing the resistance value to a small level, for example, 0.05 to 0.60, 0.10 to 0.50, or 0.15 to 0.45. The total content ratio (molar ratio) of the structure represented by formula (3-1) and the structure represented by formula (3-2) (when only one of them is contained, the content ratio of only that one) is, for example, 0.40 to 0.95, 0.50 to 0.90, or 0.55 to 0.85.

[0033] The polyamideimide may further contain the structure represented by the following formula (2-1). The polyamideimide may contain the structure represented by the following formula (2-1) alone or in combination of two or more.

[0034] [Chemical formula] (In the formula, R 2 represents an organic group. * represents the bonding position with other atoms.)

[0035] In formula (2-1), the organic group is, for example, a group containing at least one selected from the group consisting of a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, a saturated alicyclic hydrocarbon group, an unsaturated alicyclic hydrocarbon group, an aromatic hydrocarbon group, an aromatic heterocyclic compound group, and a group composed of two or more selected from these. These groups may or may not have a substituent. Examples of the substituent include an alkyl group (e.g., having 1 to 20 or 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (e.g., having 1 to 20 or 1 to 6 carbon atoms), and the like. The organic group may be a group containing an aromatic hydrocarbon group, and preferably may be a group containing a benzene ring. The aromatic hydrocarbon group and the benzene ring may each have or may not have a substituent.

[0036] * represents the bonding position with another atom. * may be, for example, the bonding position with a nitrogen atom, and * may each independently be the bonding position with a nitrogen atom contained in the structure represented by formula (1-1), a nitrogen atom contained in the structure represented by formula (1-2) (the N atom in “-N(-*)-*”), or a nitrogen atom contained in another structure.

[0037] R 2 Examples of R include groups represented by the following formulas.

Chemical formula

Chemical formula

[0038] The linking group may be, for example, an alkylene group (-CH2-, -C(CH3)2-, etc.), -CO-, -SO2-, or -O-.

[0039] Preferably, the polyamideimide has a structure represented by formula (2-1) (wherein R2 is a group represented by the formula (2-3).) includes

[0040] The structure represented by the formula (2-1) can be introduced into polyamideimide using a tricarboxylic acid compound described later.

[0041] Polyamideimide can be obtained using at least a diisocyanate compound and / or a diamine compound and a tricarboxylic acid compound.

[0042] For example, as the diisocyanate compound and the diamine compound, a compound represented by the following formula (1-6) and a compound represented by the following formula (3-6) can be mentioned. The diisocyanate compound and the diamine compound are used alone or in combination.

[0043]

Chemical formula

Chemical formula

[0044] R 1 , R, n, and R 3 are as described above, and the preferred embodiments, specific examples, etc. are also as described above.

[0045] The compound represented by the formula (1-6) (in the formula, R 1 and (R) nThe group represented by is a group represented by formula (1-3) or a group represented by formula (1-4).) Examples of such compounds include 4,4'-diisocyanato-3,3'-dicarboxybiphenyl, 4,4'-diisocyanato-2,2'-dicarboxybiphenyl, bis(4-isocyanato-3-carboxyphenyl)methane, bis(4-isocyanato-2-carboxyphenyl)methane, 4,4'-diamino-3,3'-dicarboxybiphenyl, 4,4'-diamino-2,2'-dicarboxybiphenyl, bis(4-amino-3-carboxyphenyl)methane, bis(4-amino-2-carboxyphenyl)methane, and the like.

[0046] The compound represented by formula (3-6) (wherein R 3 The group represented by is a group represented by formula (3-3) or a group represented by formula (3-4).) Examples of such compounds include 4,4'-diisocyanatodiphenylmethane, 4,4'-diisocyanatobiphenyl, 3,3'-diisocyanatobiphenyl, 3,4'-diisocyanatobiphenyl, 4,4'-diisocyanato-3,3'-dimethylbiphenyl, 4,4'-diisocyanato-2,2'-dimethylbiphenyl, 4,4'-diisocyanato-3,3'-diethylbiphenyl, 4,4'-diisocyanato-2,2'-diethylbiphenyl, 4,4'-diisocyanato-3,3'-dimethoxybiphenyl, 4,4'-diisocyanato-2,2'-dimethoxybiphenyl, 4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3'-diethylbiphenyl, 4,4'-diamino-2,2'-diethylbiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 4,4'-diamino-2,2'-dimethoxybiphenyl, and the like.

[0047] As the compound represented by formula (3-6), other aromatic diisocyanate compounds and / or aromatic diamine compounds other than the above compounds can be used. Examples of other aromatic diisocyanate compounds or aromatic diamine compounds include 1,4-phenylene diisocyanate, 1,5-diisocyanato naphthalene, 2,6-diisocyanato naphthalene, tolylene diisocyanate, xylylene diisocyanate, 4,4'-diisocyanato diphenyl ether, 2,2-bis[4-(4'-isocyanatophenoxy)phenyl]propane, 1,4-phenylene diamine, 1,5-diamino naphthalene, 2,6-diamino naphthalene, tolylene diamine, xylylene diamine, 4,4'-diamino diphenyl ether, 2,2-bis[4-(4'-aminophenoxy)phenyl]propane, and the like.

[0048] As the compound represented by formula (3-6), an aliphatic or alicyclic diisocyanate compound and / or an aliphatic or alicyclic diamine compound can be used. Together with the diisocyanate compound and / or diamine compound, a monofunctional isocyanate compound and / or amine compound, a trifunctional or higher-functional isocyanate compound and / or amine compound, etc. can also be used in combination as necessary. If necessary to avoid changes over time, a compound in which the isocyanate group is stabilized with a blocking agent may be used. Examples of the blocking agent include alcohol, phenol, oxime, etc., but there is no particular limitation.

[0049] The usage amounts of the diisocyanate compound and the diamine compound based on the masses of the isocyanate compound and the amine compound are, for example, 90 to 100% by mass, 95 to 100% by mass, or 98 to 100% by mass. When using the compound represented by formula (1-6), the usage amount of the compound represented by formula (1-6) based on the masses of the diisocyanate compound and the diamine compound is, from the viewpoint of suppressing the resistance value to a small level, for example, 10 to 60% by mass, 15 to 50% by mass, or 20 to 45% by mass. When using the compound represented by formula (3-6), the usage amount of the compound represented by formula (3-6) based on the masses of the diisocyanate compound and the diamine compound is, for example, 40 to 90% by mass, 50 to 85% by mass, or 55 to 80% by mass.

[0050] When using the compound represented by formula (1-6), the usage ratio (molar ratio) of the compound represented by formula (1-6) based on the diisocyanate compound and the diamine compound is, from the viewpoint of suppressing the resistance value to a small level, for example, 0.05 to 0.60, 0.10 to 0.50, or 0.15 to 0.45. When using the compound represented by formula (3-6), the usage ratio (molar ratio) of the compound represented by formula (3-6) based on the diisocyanate compound and the diamine compound is, for example, 0.40 to 0.95, 0.50 to 0.90, or 0.55 to 0.85.

[0051] As the tricarboxylic acid compound, there is no particular limitation as long as it is a trivalent carboxylic acid having a carboxylic anhydride group capable of reacting with an isocyanate group or an amino group, including its derivatives. Examples of the derivatives include esters, halides, etc. Considering heat resistance, compounds having an aromatic ring group are preferred. The aromatic ring group may be an aromatic hydrocarbon group, an aromatic heterocyclic compound group, or a group composed of two or more selected from these. For example, as the tricarboxylic anhydride, the compounds represented by the following formula (2-4) and the compounds represented by the following formula (2-5) can be mentioned. The tricarboxylic acid compound is used alone or in combination. Considering heat resistance, cost, etc., it is particularly preferred that the acid component contains trimellitic anhydride.

[0052] [Chemical formula] (In the formula, Y represents -CH2-, -CO-, -SO2-, -O-, or a direct bond. Each benzene ring may be independently substituted or unsubstituted.) [Chemical formula] (In the formula, the benzene ring may be substituted or unsubstituted.)

[0053] Together with the tricarboxylic acid compound, a dicarboxylic acid compound and / or a tetracarboxylic acid compound can also be used in combination as needed. The tricarboxylic acid compound, dicarboxylic acid compound, and tetracarboxylic acid compound may be collectively referred to as a carboxylic acid compound. In this specification, a compound having a carboxy group and an isocyanate group or an amino group shall be regarded as corresponding to an isocyanate compound or an amine compound.

[0054] The amount of the tricarboxylic acid compound used based on the mass of the carboxylic acid compound is, for example, 90 to 100% by mass, 95 to 100% by mass, or 98 to 100% by mass. When using the compound represented by formula (2-5), the amount of the compound represented by formula (2-5) used based on the mass of the tricarboxylic acid compound is, for example, 30 to 100% by mass, 70 to 100% by mass, or 95 to 100% by mass.

[0055] When a carboxylic acid compound, an isocyanate compound, and an amine compound (when only one of them is used, the said one compound) are used, when a carboxy group, an acid anhydride group, and a reactive hydroxy group are present, the ratio of the total number of isocyanate groups and amino groups to the total number of these functional groups is preferably 0.6 to 1.4, more preferably 0.7 to 1.3, and still more preferably 0.8 to 1.2. It is preferable to carry out the reaction so that this ratio is obtained. When this ratio is 0.6 or more, there is a tendency that it becomes easy to increase the molecular weight of the polyamideimide. When this ratio is 1.4 or less, it is possible to prevent the reaction accompanied by foaming from becoming intense and the remaining amount of unreacted substances from increasing, and there is a tendency that good stability of the polyamideimide is easily obtained. In the polyamideimide, an amide group and an imide group are introduced by the reaction of a tricarboxylic acid compound, a diisocyanate compound, and / or a diamine compound. Since the compound represented by the formula (1-6) has a carboxy group and an isocyanate group or an amino group, when the compound represented by the formula (1-6) is used, an amide bond may be introduced into the polyamideimide by the reaction of the compounds represented by the formula (1-6). When the compound represented by the formula (1-6) and the compound represented by the formula (3-6) are used, an amide bond may be introduced by these reactions.

[0056] The amount of the solvent used during the reaction is preferably 100 to 300 parts by mass, more preferably 150 to 250 parts by mass, based on 100 parts by mass of the total amount of the carboxylic acid compound, the isocyanate compound, and the amine compound. When the amount of the solvent used is 100 parts by mass or more, the reaction accompanied by foaming can be easily prevented. When the amount of the solvent used is 300 parts by mass or less, the synthesis time can be prevented from becoming too long, and the concentration of the polyamideimide contained in the solution obtained after synthesis tends to be sufficient. Examples of the solvent include polar solvents such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), γ-butyrolactone (GBL), 3-methoxy-N,N-dimethylpropanamide (MPA), N,N'-dimethylformamide, N,N'-dimethylpropyleneurea [1,3-dimethyl-3,4,5,6-tetrahydropyrimidin-2(1H)-one], dimethyl sulfoxide, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, sulfolane; aromatic hydrocarbon solvents such as xylene and toluene; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, etc. The solvent preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), γ-butyrolactone (GBL), and 3-methoxy-N,N-dimethylpropanamide (MPA), and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), γ-butyrolactone (GBL), and 3-methoxy-N,N-dimethylpropanamide (MPA).

[0057] For the reaction, a catalyst may or may not be used from the viewpoint of reaction efficiency or from the viewpoint of reducing residual impurities. For example, when a fluorine-based catalyst such as potassium fluoride is not used, contamination by fluorine is prevented, and thus a polyamideimide excellent in characteristics such as electrochemical stability can be obtained.

[0058] The synthesis conditions of polyamide-imide are diverse and cannot be specified generally. For example, it can be carried out at a temperature of 80 to 180°C. The synthesis is preferably carried out under an atmosphere such as nitrogen to reduce the influence of moisture in the air.

[0059] The synthesized polyamide-imide can be obtained, for example, as a polyamide-imide solution dissolved in the solvent used in the reaction.

[0060] The polyamide-imide preferably has a dispersity (Mw (weight average molecular weight) / Mn (number average molecular weight)) of 2.8 or less. The smaller the dispersity, the more likely it is to form an electrode with excellent properties. The lower limit of the dispersity may be 1.0 or more. The dispersity of the polyamide-imide is more preferably 1.1 to 2.5, and even more preferably 1.1 to 2.3.

[0061] The number average molecular weight and weight average molecular weight of the polyamide-imide can be measured by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene. The number average molecular weight and weight average molecular weight of the polyamide-imide can be controlled and adjusted by repeating sampling and measurement during synthesis and continuing the synthesis until the target number average molecular weight is reached.

[0062] The material for forming an electrode contains at least polyamide-imide and may further contain materials known as binders for electrodes such as polyolefins and acrylic polymers. The polyamide-imide of the above embodiment can suppress the resistance value of the battery to a small level. When the active material contains a silicon-based active material, the polyamide-imide of the above embodiment can prevent deformation of the electrode because it is difficult to follow the volume change of the silicon-based active material, and can improve the reliability of the electrode because it exhibits excellent adhesiveness. In addition, since the polyamide-imide has good chemical resistance, it is also less affected by the electrolyte.

[0063] <Electrode mixture> The electrode mixture according to an embodiment of the present invention contains at least an active material containing a silicon-based active material and a carbon-based active material, and a material for forming an electrode according to the embodiment. The electrode mixture may be a slurry containing a solvent. The electrode mixture may contain optional components such as a conductive material and an additive.

[0064] The active material contains at least a silicon-based active material and a carbon-based active material. The silicon-based active material contains at least silicon, and examples thereof include a silicon-containing alloy, a silicon-containing oxide, a silicon-containing nitride, or a silicon-containing carbide. Examples of the silicon-containing alloy include an alloy containing silicon and at least one selected from the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Specific examples of the silicon-containing oxide include SiO, SiO2, LiSiO, etc., specific examples of the silicon-containing nitride include Si3N4, Si2N2O, etc., and examples of the silicon-containing carbide include SiC, etc.

[0065] The carbon-based active material may be a carbon material, and examples thereof include an amorphous carbon material, natural graphite, a composite carbon material in which an amorphous carbon material film is formed on natural graphite, artificial graphite (graphite obtained by firing a resin raw material such as an epoxy resin or a phenol resin, or a pitch-based raw material obtained from petroleum, coal, etc.). The carbon-based active material preferably contains natural graphite and / or artificial graphite.

[0066] The content of the silicon-based active material is preferably 10% by mass or more based on the mass of the active material. When the content of the silicon-based active material is 10% by mass or more, the discharge capacity tends to be larger. The content of the silicon-based active material may be 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more. The content of the silicon-based active material may be less than 100% by mass based on the mass of the active material. By including a carbon-based active material in the active material, it is possible to prevent a decrease in cycle characteristics and the handling property tends to be excellent. The content of the silicon-based active material may be 80% by mass or less, 70% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less.

[0067] Examples of the solvent include the solvents exemplified as solvents that can be used for the synthesis of polyamideimide. The solvent used for the synthesis of polyamideimide and the solvent contained in the electrode binder may be the same. The content of the active material is preferably 80% by mass or more based on the total mass of the components other than the solvent contained in the electrode binder. When the content of the active material is 80% by mass or more, the discharge capacity tends to be further improved. The content of the active material may be 85% by mass or more, 88% by mass or more, 90% by mass or more, 93% by mass or more, or 95% by mass or more. Considering the content of the binder, the content of the active material may be, for example, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less based on the total mass of the components other than the solvent contained in the electrode binder.

[0068] Examples of the conductive material include carbon materials such as acetylene black, ketjen black and other carbon blacks, graphite, graphene, and carbon nanotubes. As the active material, a material that can function as an active material, for example, a material having a structure capable of occluding and releasing an electrolyte such as lithium ions can be selected and used. In contrast, as the conductive material, a material that cannot function as an active material, for example, a material that does not have a structure capable of occluding and releasing an electrolyte such as lithium ions can be selected and used. When the electrode binder contains a conductive material, the content of the conductive material may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more based on the total mass of the components other than the solvent contained in the electrode binder. The content of the conductive material may be, for example, 50% by mass or less, 30% by mass or less, or 15% by mass or less based on the total mass of the components other than the solvent contained in the electrode binder.

[0069] <Electrode for energy device> The electrode for an energy device according to an embodiment of the present invention includes at least a current collector and an electrode binder layer formed on at least a part of the surface of the current collector. The electrode binder layer can be formed using the electrode binder of the above embodiment.

[0070] Examples of the material of the current collector include copper, stainless steel, nickel, aluminum, titanium, fired carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, and the like. The surface of the current collector may be treated with carbon, nickel, titanium, silver, etc. from the viewpoint of improving adhesiveness, conductivity, and reduction resistance. Examples of the shape of the current collector include a plate and a film.

[0071] When the current collector is in the form of a plate or a film, the electrode has at least the current collector and an electrode binder layer formed on one or both surfaces of the current collector. The electrode binder layer can be formed, for example, according to the following method. First, a binder is prepared by mixing at least an active material containing a silicon-based active material and a carbon-based active material, a material for forming an electrode, and a solvent. Next, the electrode binder is applied to at least one surface of the current collector to form a coating film. Then, the solvent contained in the coating film is volatilized. After the solvent is volatilized, the coating film is compression molded. Examples of the coating method include the doctor blade method, the dipping method, the spray method, the transfer roll method, etc. Examples of the compression molding method include the method of roll pressing.

[0072] Compression molding can be performed while heating the coating film. After compression molding is performed at room temperature or under heating, the coating film may be heated. The heating temperature may be, for example, 200 °C or higher, 250 °C or higher, or 260 °C or higher. The heating temperature may be 300 °C or lower, 290 °C or lower, or 280 °C or lower. By using the material for forming an electrode of the above embodiment, even when the heating temperature is low, an electrode binder layer with good adhesion between the active materials and between the active material and the current collector can be formed. For example, the heating temperature can be reduced by about 30 to 100 °C compared to the case where polyimide is used as the binder.

[0073] <Energy device> The energy device according to an embodiment of the present invention has a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode includes the electrode for an energy device of the above embodiment. Examples of the energy device include a non-aqueous electrolyte secondary battery, a capacitor, etc. The non-aqueous electrolyte secondary battery is preferably a lithium ion secondary battery.

[0074] The non-aqueous electrolyte secondary battery includes, for example, an electrode group including a positive electrode, a negative electrode, and a separator, and a battery exterior body that houses the electrode group. The battery exterior body is filled with an electrolyte. The non-aqueous electrolyte secondary battery may be a so-called laminate type battery or a battery having a shape other than the laminate type (coin type, cylindrical type, laminated type, etc.).

[0075] Examples of the separator include, but are not particularly limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment. Examples of the battery exterior body may be a container formed of a laminate film. Examples of the laminate film include a laminate film in which a resin film such as polyethylene terephthalate (PET film), a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

[0076] The electrolytic solution contains, for example, an electrolyte salt and a non-aqueous solvent. The electrolyte salt may be a lithium salt. Examples of the lithium salt may be at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (Li[FSI], lithium bis(fluorosulfonyl)imide), LiN(SO2CF3)2 (Li[TFSI], lithium bis(trifluoromethanesulfonyl)imide), and LiN(SO2CF2CF3)2. The non-aqueous solvent may be, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate, etc. The electrolytic solution may contain additives such as vinylene carbonate.

[0077] The energy device includes, as at least one of the positive electrode and the negative electrode, the electrode for an energy device of the above embodiment. Preferably, at least the negative electrode is the electrode for an energy device of the above embodiment. When the energy device includes an electrode other than the electrode for an energy device of the above embodiment, the electrode may be a general electrode used in the field of energy devices. For example, a general positive electrode has at least a current collector and a positive electrode mixture layer formed on at least a part of the surface of the current collector. The positive electrode mixture layer contains at least a positive electrode active material and a binder, and may further contain a conductive material or the like.

[0078] The positive electrode active material may be, for example, nickel cobalt manganese oxide (NCM), lithium cobalt dioxide (LCO), nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), or the like. Examples of the current collector and the conductive material include the current collector and the conductive material exemplified in the electrode for an energy device of the above embodiment.

Examples

[0079] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[0080] <Preparation of Electrode-Forming Material (Polyamide Imide)> [Example 1] 192.0 g of trimellitic anhydride, 114.5 g of bis(4-amino-3-carboxyphenyl)methane, 150.0 g of bis(4-isocyanatophenyl)methane, and 760 g of N-methyl-2-pyrrolidone (NMP) were placed in a flask equipped with a thermometer, a stirrer, and a condenser tube, and heated gradually to 130° C. over 2 hours while stirring in a dried nitrogen stream. While paying attention to the sudden foaming of carbon dioxide gas generated by the reaction, the temperature was maintained at 130° C., and heating was continued for 6 hours as it was, and then the reaction was stopped to obtain a polyamide imide solution.

[0081] The non-volatile content (200 °C - 2 h) of the obtained polyamideimide solution was 32% by mass. The number-average molecular weight of the polyamideimide was measured using a calibration curve of standard polystyrene under the following conditions by gel permeation chromatography (GPC). The number-average molecular weight is shown in Table 1.

[0082] Model: Manufactured by Hitachi, Ltd. Product name: L6000 Detector: Manufactured by Hitachi, Ltd. Product name: L4000 type UV Wavelength: 270 nm Data processor: ATT 8 Column: Manufactured by Hitachi High-Tech Corporation Product name: Gelpack GL-S300MDT-5×2 Column size: Diameter 8 mm × 300 mm Solvent: DMF / THF = 1 / 1 (liter) + 0.06 M phosphoric acid + 0.06 M lithium bromide Sample concentration: 5 mg / 1 mL Injection volume: 5 μL Pressure: 4.8×10 6 Pa (49 kgf / cm 2 ) Flow rate: 1.0 mL / min

[0083] [Examples 2 and Comparative Examples 1 and 2] A polyamideimide solution was obtained in the same manner as in Example 1, except that the types and amounts of the raw material monomers were changed as shown in Table 1. However, in Comparative Examples 1 and 2, the temperature was maintained at 130 °C and heating was continued for 8 hours as it was.

[0084] In Table 1, the abbreviations for the raw material monomers mean the following compounds. MBAA: 5,5'-methylenebis(2-aminobenzoic acid) (bis(4-amino-3-carboxyphenyl)methane) MDI: Diphenylmethane diisocyanate (bis(4-isocyanatophenyl)methane) TMAC: Trimellitic anhydride

[0085] [Fabrication and Evaluation of Lithium-Ion Secondary Batteries] [Fabrication of Negative Electrode] As the negative electrode active material, a silicon-based active material (Si alloy) and a carbon-based active material (graphite, "SMGYM2" manufactured by Hitachi Chemical Co., Ltd.) were used. The negative electrode active material, the electrode forming material obtained above, and a solution containing NMP (polyamideimide solution) were mixed so that the mass ratio of the solid content (carbon-based active material: silicon-based active material: polyamideimide) was 105:45:25 so that the volumetric density became 600 mAh / kg, and further NMP was added for viscosity adjustment to obtain a slurry-like negative electrode mixture. The obtained negative electrode mixture was applied substantially evenly and homogeneously to one side of a current collector (metal foil (Cu, 10 μm)). Thereafter, the coating film was dried, compression molded by pressing, and then heated at 270 °C for 30 minutes for curing treatment to obtain a negative electrode.

[0086] (Fabrication of Secondary Battery) A positive electrode having a positive electrode mixture layer containing NCM111 (nickel cobalt manganese oxide, manufactured by BASF Toda Battery Materials Co., Ltd.) as a positive electrode active material and a current collector (metal foil (Al, 15 μm)) was obtained. Using this positive electrode and the negative electrode obtained above, a secondary battery containing an electrolytic solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (1 vol / 2 vol) + vinylene carbonate (VC) (1 wt%)) was fabricated.

[0087] (Fabrication of Battery) Regarding the obtained secondary battery, the resistance value, initial efficiency, capacity retention rate, and rate characteristics were measured according to the following methods.

[0088] (Measurement of Resistance Value) The resistance value was calculated from the slope shown by the relationship between the voltage (V) drop when the obtained secondary battery was energized at 1C for 10 seconds and the current density (I) under the condition of a temperature of 25 °C (V-I method). "C" used as the unit of the current value means "current value (A) / battery capacity (Ah)".

[0089] (Measurement of Discharge Capacity Retention Rate) Regarding the obtained secondary battery, a charge-discharge cycle test of the battery was performed by the following method under the condition of a temperature of 25 °C. First, it was charged at a current of 0.5C until the voltage reached 4.2V (CC charging). Next, it was charged at a voltage of 4.2V until the current reached 0.01C (CV charging). After leaving it for 30 minutes, it was discharged at a current of 0.5C until the voltage reached 3.23V (CC discharging). Then, a series of operations of CC charging, CV charging, and CC discharging was defined as one cycle, and 100 cycles were performed. Next, the sum of the time integral values of the current in the CC charging and CV charging in the n-th cycle was defined as the charging capacity (mAh) in the n-th cycle, and the time integral value of the current in the CC discharging in the n-th cycle was defined as the discharging capacity (mAh) in the n-th cycle. The discharging capacity retention rate of the battery in the 100th cycle was obtained by the following formula. Discharging capacity retention rate in the 100th cycle (%) = (Discharging capacity in the 100th cycle / Discharging capacity in the 1st cycle) × 100

[0090] (Measurement of initial efficiency) For the obtained secondary battery, under the condition of a temperature of 25°C, constant current constant voltage (CC(0.05C)-CV(upper limit voltage 4.2V)) charging was performed. After leaving it for 30 minutes, it was discharged at a constant current (CC(0.05C)) until the lower limit voltage reached 2.5V. This was continued for 5 cycles, and the average value of the discharging capacity in the latter 2 cycles was defined as the initial capacity. The initial efficiency was calculated from the following calculation formula. Initial efficiency (%) = Initial capacity / Theoretical capacity × 100

[0091] (Measurement of discharge rate characteristics) Regarding the obtained secondary battery, the discharge rate characteristics at a temperature of 25°C were measured using a charge-discharge device under the following charge-discharge conditions. After performing constant current constant voltage (CCCV) charging at a termination voltage of 4.2V and 0.2C, a cycle of discharging at a constant current (CC) to a termination voltage of 2.5V at 0.2C was performed once. The capacity at the time of this discharge was defined as the discharge capacity at a current value of 0.2C. Next, after performing constant current constant voltage (CCCV) charging at a termination voltage of 4.2V and 1.5C, a cycle of discharging at a constant current (CC) to a termination voltage of 2.5V at 1.5C was performed once. The capacity at the time of this discharge was defined as the discharge capacity at a current value of 1.5C, and the discharge rate characteristics (%) were calculated by the following formula. Discharge rate characteristic (%) = (Discharge capacity at a current value of 0.5C) / (Discharge capacity at a current value of 0.2C) × 100

[0092]

Table 1

Claims

1. It contains polyamideimide, and the number average molecular weight of the polyamideimide is 2,000 to 17,000, and is used to form an electrode containing an active material including a silicon-based active material and a carbon-based active material. An electrode forming material.

2. The electrode forming material according to claim 1, wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material.

3. An electrode binder containing the electrode forming material according to claim 1 and an active material including a silicon-based active material and a carbon-based active material.

4. The electrode binder according to claim 3, wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material.

5. An electrode for an energy device, comprising a current collector and an electrode binder layer formed on at least a part of the surface of the current collector using the electrode binder according to claim 3 or 4.

6. An energy device having a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode includes the electrode for an energy device according to claim 5.

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