Electrode formation material, electrode mixture, energy device electrode, and energy device

Abstract

To provide an electrode formation material that can produce an electrode for an energy device with excellent cycle characteristics.SOLUTION: An electrode formation material contains polyamide-imide and is used for forming an electrode containing an active material that includes silicon-based active material and 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 power sources for electric vehicles. A lithium-ion secondary battery is a non-aqueous electrolyte-based energy device having a high energy density.

[0003] The electrodes of lithium-ion secondary batteries are produced, for example, as follows. First, an active material, a binder, and a solvent are kneaded to prepare a slurry-like electrode binder. This electrode binder is applied to one or both sides of a metal foil, which is a current collector, using a transfer roll or the like, and the solvent is removed to form an electrode binder layer. Then, the electrode is produced through a step of compression molding the electrode binder layer using a roll press or the like.

[0004] Patent Document 1 describes a binder resin material for an energy device electrode containing a copolymer including 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 copolymer for an energy device electrode 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.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Binders used in the production of electrodes are required to be excellent in properties such as adhesion between active materials and between the active material and the current collector, and electrochemical stability. Further, in order to increase the capacity of lithium-ion secondary batteries, it is required to satisfy these properties with a smaller addition amount.

[0007] On the other hand, in recent years, against the background of the increase in the capacity of lithium-ion secondary batteries, the use of silicon-based active materials as negative electrode active materials has been studied. When a silicon-based active material is used as the negative electrode active material, a significant improvement in the discharge capacity of the lithium-ion secondary battery can be expected.

[0008] Under such circumstances, an embodiment of the present invention aims to provide a material for forming an electrode and an electrode binder that can produce an electrode of an energy device having excellent cycle characteristics. Another object of an embodiment of the present invention is to provide an electrode that can produce an energy device having excellent cycle characteristics. Still another object of an embodiment of the present invention is to provide an energy device having excellent cycle characteristics.

Means for Solving the Problems

[0009] Examples of embodiments of the present invention are listed below. The present invention is not limited to the following embodiments. (1) A material for forming an electrode, which contains polyamideimide and contains an active material including a silicon-based active material and a carbon-based active material, and is used to form an electrode. (2) The material for forming an electrode according to (1) above, wherein the number average molecular weight of the polyamideimide is 3,000 to 100,000. (3) The material for forming an electrode according to (1) or (2) above, which is used for forming an electrode in which the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material.

[0010] (4) An electrode binder containing the electrode-forming material according to any one of the above (1) to (3) and an active material containing a silicon-based active material and a carbon-based active material. (5) The electrode binder according to the above (4), wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material.

[0011] (6) 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 the above (4) or (5). (7) 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 the above (6).

Advantages of the Invention

[0012] According to the embodiments of the present invention, it is possible to provide an electrode-forming material and an electrode binder capable of manufacturing an electrode of an energy device having excellent cycle characteristics. Further, according to the embodiments of the present invention, it is possible to provide an electrode capable of manufacturing an energy device having excellent cycle characteristics. Furthermore, according to the embodiments of the present invention, it is possible to provide an energy device having excellent cycle characteristics.

Modes for Carrying Out the Invention

[0013] Embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

[0014] <Electrode-Forming Material> The electrode-forming material according to an embodiment of the present invention is used for forming an electrode containing an active material containing a silicon-based active material and a carbon-based active material. The electrode-forming material contains at least polyamideimide.

[0015] As silicon-based active materials, silicon-containing alloys, silicon oxides, etc. are known. While lithium-ion secondary batteries using silicon-based active materials are expected to significantly improve the discharge capacity, they tend to have difficulty obtaining sufficiently good cycle characteristics. One of the presumed causes is that since silicon-based active materials have large volume expansion and contraction during charge and discharge, sufficient adhesion between the active materials or between the active materials and the current collector may not be obtained, and detachment of the active material from the electrode, deformation or cracking of the electrode, etc. may occur. Further, as another cause, cracking, peeling, etc. of the protective film (hereinafter sometimes referred to as "SEI" (Solid Electrolyte Interphase, SEI)) formed on the surface of the active material during charge and discharge may occur, resulting in the formation of an active surface, and the decomposition of the electrolyte may progress.

[0016] As a measure to solve the above problems, it is conceivable to use a binder that can ensure sufficient adhesion between the active materials or between the active materials and the current collector even when volume expansion and contraction due to charge and discharge occur, and can sufficiently suppress cracking of the SEI, etc. In an embodiment of the present invention, the electrode-forming material contains polyamideimide as such a binder.

[0017] Polyamideimide is a polymer having an amide bond and an imide bond in the molecule. Polyamideimide is obtained by reacting at least a tricarboxylic anhydride or its derivative (hereinafter sometimes referred to as "acid component") with a diisocyanate compound and / or a diamine compound. Other arbitrary compounds may be reacted. For the reaction, only one kind of each raw material compound may be used, or two or more kinds may be used in combination.

[0018] As the acid component, there is no particular limitation as long as it is a trivalent carboxylic acid having an acid anhydride group that reacts with an isocyanate group or an amino group, including its derivatives. Considering heat resistance, a compound having an aromatic ring group is preferable. Examples of the tricarboxylic acid anhydride include compounds represented by the following formula (I) or (II). Considering heat resistance, cost, etc., it is particularly preferable that the acid component contains trimellitic anhydride. The acid component is used alone or in combination according to the purpose.

[0019]

Chemical formula

[0020] Y represents -CH2-, -CO-, -SO2-, or -O-.

[0021]

Chemical formula

[0022] The acid component may optionally contain a tetracarboxylic dianhydride. Examples of the tetracarboxylic dianhydride include tetracarboxylic dianhydrides (pyromellitic dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4′-sulfonyldiphthalic dianhydride, m-terphenyl-3,3′,4,4′-tetracarboxylic dianhydride, 4,4′-oxydiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, butanetetracarboxylic dianhydride, bicyclo-[2,2,2]-oct-7-ene-2:3:5:6-tetracarboxylic dianhydride, etc.).

[0023] Examples of the diisocyanate compound and / or diamine compound include compounds represented by the following formula (III), (IV), or (V). The diisocyanate compound and / or diamine compound may be used alone or in combination according to the purpose.

[0024]

Chemical formula

[0025]

Chemical formula

[0026] [Chemical formula]

[0027] In these formulas, R 2 is a hydrogen atom, an alkyl group, a hydroxyl group, or an alkoxy group, and R 3 is an isocyanate group or an amino group. Here, the alkyl group and alkoxy group where R 2 is preferably a C1-C20 alkyl group or alkoxy group.

[0028] Examples of the compound represented by formula (III), (IV) or (V) 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, 1,5-diisocyanatonaphthalene, 2,6-diisocyanatonaphthalene, 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, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, and the like.

[0029] As the diisocyanate compound and / or diamine compound, other aromatic diisocyanate compounds or aromatic diamine compounds other than the compounds represented by formula (III), (IV) or (V) can be used. Examples of other aromatic diisocyanate compounds or aromatic diamine compounds include tolylene diisocyanate, xylylene diisocyanate, 4,4'-diisocyanatodiphenyl ether, 2,2-bis[4-(4'-isocyanatophenoxy)phenyl]propane, tolylene diamine, xylylene diamine, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4'-aminophenoxy)phenyl]propane, and the like.

[0030] As the diisocyanate compound and / or diamine compound, an aliphatic or alicyclic diisocyanate compound and / or an aliphatic or alicyclic diamine compound can be used. Examples of these compounds include hexamethylene diamine, 2,2,4-trimethylhexamethylene diamine, diaminoisophorone, bis(4-aminocyclohexyl)methane, 1,4-diaminotranscyclohexane, hydrogenated m-xylylene diamine, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, diisocyanatoisophorone, bis(4-isocyanatocyclohexyl)methane, 1,4-diisocyanatotranscyclohexane, hydrogenated m-xylylene diisocyanate, and the like. When using an aliphatic or alicyclic diisocyanate compound and / or an aliphatic or alicyclic diamine compound, it is preferable to use them in combination with an aromatic diisocyanate compound and / or an aromatic diamine compound. From the viewpoint of the heat resistance of the resulting polyamideimide, etc., the content of these compounds in the total amount of the diisocyanate compound and / or diamine compound is preferably 50 mol% or less.

[0031] Considering the balance of heat resistance, solubility, mechanical properties, cost, etc., it is particularly preferable that the diisocyanate compound and / or diamine compound contains 4,4'-diphenylmethane diisocyanate. A polyfunctional isocyanate compound and / or amine compound having a functionality of 3 or more can also be used in combination with the diisocyanate compound and / or diamine compound.

[0032] When necessary to avoid daily changes, a compound in which the isocyanate group is stabilized with a blocking agent may be used. Examples of the blocking agent include alcohols, phenols, oximes, etc., but there is no particular limitation.

[0033] When the acid component (hereinafter sometimes referred to as component (a)) and the diisocyanate compound and / or diamine compound (hereinafter sometimes referred to as component (b)) have a carboxyl group, an acid anhydride group, and a reactive hydroxyl group, 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 even more preferably 0.8 to 1.2. It is preferable to react so that. When this ratio is 0.6 or more, the molecular weight of the polyamideimide tends to be easily increased. 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 good stability of the polyamideimide tends to be easily obtained.

[0034] 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 component (a) and component (b). When the amount of the solvent used is 100 parts by mass or more, the reaction accompanied by foaming tends to 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 the synthesis tends to be sufficient. Examples of the solvent include polar solvents such as N-methyl-2-pyrrolidone, N,N'-dimethylformamide, γ-butyrolactone, 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; and ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone.

[0035] For the reaction between component (a) and component (b), 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 a polyamideimide excellent in characteristics such as electrochemical stability can be obtained.

[0036] The synthesis conditions of the polyamideimide 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 of nitrogen or the like in order to reduce the influence of moisture in the air.

[0037] The synthesized polyamideimide can be obtained, for example, as a polyamideimide solution dissolved in the solvent used in the reaction.

[0038] The polyamideimide preferably has a number average molecular weight of 3,000 to 100,000. When the number average molecular weight is 3,000 or more, various properties such as viscosity and strength tend to improve. The number average molecular weight of the polyamideimide may be 5,000 or more, 8,000 or more, 15,000 or more, or 20,000 or more. When the number average molecular weight is 100,000 or less, good adhesion to the current collector is likely to be obtained. The number average molecular weight of the polyamideimide may be 80,000 or less, 50,000 or less, 30,000, or 27,000 or less.

[0039] The polyamideimide preferably has a weight average molecular weight of 3,000 to 300,000. When the weight average molecular weight is 3,000 or more, various properties such as viscosity and strength tend to improve. The weight average molecular weight of the polyamideimide may be 5,000 or more, 8,000 or more, or 20,000 or more. When the weight average molecular weight is 300,000 or less, good adhesion to the current collector is likely to be obtained. The weight average molecular weight of the polyamideimide may be 240,000 or less, 150,000 or less, 90,000 or less, or 80,000 or less.

[0040] The polyamideimide preferably has a dispersity (Mw / Mn) 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 polyamideimide is more preferably 1.1 to 2.5, and even more preferably 1.1 to 2.3.

[0041] The number average molecular weight and weight average molecular weight of the polyamideimide 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 polyamideimide 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.

[0042] The polyamideimide may have a tensile elastic modulus of 1.8 GPa or more, 2.0 GPa or more, 2.1 GPa or more, 2.5 GPa or more, 2.7 GPa or more, or 3.0 GPa or more. When using a polyamideimide with a tensile elastic modulus of 1.8 GPa or more, the adhesion between the active materials and between the active material and the current collector can be further improved, and the reliability tends to be further improved. The upper limit of the tensile elastic modulus is not particularly limited, but for example, it is 3.5 GPa or less, 3.4 GPa or less, 3.3 GPa or less, or 3.0 GPa or less. The tensile elastic modulus of the polyamideimide is measured using a polyamideimide film with a thickness of 20 μm formed using the polyamideimide. Specifically, it can be measured using an autograph at room temperature according to the method described in the examples.

[0043] The polyamideimide may have a tensile strength of 80 MPa or more, 90 MPa or more, 100 MPa or more, 110 MPa or more, or 120 MPa or more. When the tensile strength is 80 MPa or more, the adhesion between the active materials and between the active material and the current collector can be further improved, and the reliability tends to be further improved. The upper limit of the tensile strength is not particularly limited, but for example, it is 150 MPa or less, 140 MPa or less, or 130 MPa or less. The tensile strength of the polyamideimide is measured using a polyamideimide film with a thickness of 20 μm formed using the polyamideimide. Specifically, it can be measured using an autograph according to the method described in the examples.

[0044] The electrode-forming material contains at least polyamideimide and may further contain materials known as binders for electrodes such as polyolefins and acrylic polymers. Since the polyamideimide is difficult to follow the volume change of the silicon-based active material, it can prevent deformation of the electrode, etc., and can improve the reliability of the electrode because it exhibits excellent adhesiveness. Also, since the polyamideimide has good chemical resistance, it is less affected by the electrolyte.

[0045] <Electrode mixture> The electrode mixture which is an embodiment of the present invention contains at least an active material including a silicon-based active material and a carbon-based active material, and a material for forming an electrode of the above 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.

[0046] 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.

[0047] 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 a coating of an amorphous carbon material 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.

[0048] 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, a decrease in cycle performance can be prevented, and the handleability 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.

[0049] 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 more 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.

[0050] 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.

[0051] <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.

[0052] 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 viewpoints of improving adhesiveness, conductivity, and reduction resistance. Examples of the shape of the current collector include a plate and a film.

[0053] 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, an electrode 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 volatilizing the solvent, the coating film is compression molded. Examples of the coating method include the doctor blade method, the dipping method, the spraying method, the transfer roll method, etc. Examples of the compression molding method include the method of roll pressing.

[0054] Compression molding can be performed while heating the coating film. After performing compression molding 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 about 30 to 100 °C lower than when using polyimide as a binder.

[0055] <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.

[0056] 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.).

[0057] 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.

[0058] 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, or the like. The electrolytic solution may contain an additive such as vinylene carbonate.

[0059] 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.

[0060] 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.

Example

[0061] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.

[0062] <Example 1> (Preparation of material for electrode formation (polyamideimide resin)) 120.0 g of trimellitic anhydride, 158.0 g of 4,4'-diphenylmethane diisocyanate, and 525.3 g of N-methyl-2-pyrrolidone (NMP) were placed in a flask equipped with a thermometer, a stirrer, and a condenser tube, and gradually heated to 130° C. over 2 hours while stirring in a dried nitrogen stream. While paying attention to the rapid 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 polyamideimide solution.

[0063] The non-volatile content (200 °C - 2 h) of the obtained polyamide-imide solution was 31.8 mass%, and the viscosity (25 °C) was 5.0 Pa·s. Also, the number average molecular weight of the polyamide-imide was 18,000. The number average molecular weight was measured by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene under the following conditions.

[0064] 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 Chemical Co., Ltd. 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: 4.8×106 Pa (49 kgf / cm 2 ) Flow rate: 1.0 ml / min

[0065] The obtained polyamide-imide solution was applied to a glass substrate to form a coating film. After drying the coating film by heating under the conditions of 80 °C for 30 minutes, a polyamide-imide film with a film thickness of 20 μm was prepared by heating under the conditions of 270 °C for 30 minutes. The polyamide-imide film was peeled off from the glass substrate, and a strip-shaped test piece with a length of 60 mm and a width of 10 mm was cut out. The tensile test of the obtained test piece was carried out at room temperature using an autograph (AGS-5kNG manufactured by Shimadzu Corporation), and the mechanical properties (tensile strength, elastic modulus) were determined. The tensile test was carried out under the conditions of a chuck distance of 20 mm and a tensile speed of 5 m / min. The tensile strength was 116 MPa, and the tensile elastic modulus was 2.1 GPa.

[0066] (Fabrication of the 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 solid content ratio (carbon-based active material: silicon-based active material: polyamideimide) was 66.5 mass%: 28.5 mass%: 5.00 mass% so that the volumetric density became 600 mAh / kg. Further, NMP was added to adjust the viscosity to obtain a slurry-like negative electrode binder. The obtained negative electrode binder was applied substantially evenly and homogeneously on one side of a current collector (metal foil (Cu, 10 μm)). Then, 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.

[0067] (Fabrication and Evaluation of Battery) A positive electrode having a positive electrode binder 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 battery containing an electrolytic solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (1 vol / 2 vol) + vinylene carbonate (VC) (1 wt%)) was fabricated. When the charge-discharge cycle characteristics of the battery were measured, the capacity retention rate after 100 cycles was 83.2%.

[0068] <Example 2> (Preparation of Electrode Forming Material (Polyamideimide Resin)) 134.5 g of trimellitic anhydride, 176.9 g of 4,4'-diphenylmethane diisocyanate, and 586.9 g of N-methyl-2-pyrrolidone were placed in a flask equipped with a thermometer, a stirrer, and a condenser tube, and gradually heated 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, it was maintained at 130 °C and heating was continued for 6.5 hours as it was, and then the reaction was stopped to obtain a polyamideimide solution.

[0069] The non-volatile content (200 °C - 2 h) of the obtained polyamideimide solution was 33.1% by mass, and the viscosity (25 °C) was 15.0 Pa·s. The number average molecular weight of the polyamideimide was 24,000.

[0070] (Fabrication and Evaluation of Lithium-Ion Secondary Batteries) A battery was fabricated in the same manner as in Example 1, and the charge-discharge cycle characteristics of the battery were measured. As a result, the capacity retention rate after 100 cycles was 73.0%.

[0071] <Example 3> (Preparation of Material for Electrode Formation (Polyamideimide Resin)) 88.4 g of trimellitic anhydride, 46.5 g of 4,4'-diphenylmethane diisocyanate, 73.7 g of 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and 679.3 g of N-methyl-2-pyrrolidone were placed in a flask equipped with a thermometer, a stirrer, and a condenser tube, and gradually heated to 130 °C over 2 hours while stirring in a stream of dried nitrogen. While paying attention to the rapid 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. Then, the reaction was stopped to obtain a polyamideimide solution.

[0072] The non-volatile content (200 °C - 2 h) of the obtained polyamideimide solution was 21.2% by mass, and the viscosity (25 °C) was 7.4 Pa·s. The number average molecular weight of the polyamideimide was 28,000.

[0073] (Fabrication and Evaluation of Batteries) A battery was fabricated in the same manner as in Example 1, and the charge-discharge cycle characteristics of the battery were measured. As a result, the capacity retention rate after 100 cycles was 84.4%.

[0074] <Comparative Example 1> A commercially available water-soluble resin was used, and a battery was fabricated in the same manner as in Example 1. When the charge-discharge cycle characteristics of the battery were confirmed, the capacity retention rate after 100 cycles was 1.6%.

[0075] <Comparative Example 2> A battery was fabricated in the same manner as in Example 1, except that a polyimide solution (a polyamic acid type polyimide resin, "HCI-7000" manufactured by Hitachi Chemical Co., Ltd.) was used. When the charge-discharge cycle characteristics of the battery were examined, the capacity retention rate after 100 cycles was 65.0%.

[0076] Table 1 shows the capacity retention rates of the batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2. The batteries obtained in Examples 1 to 3 had good charge-discharge cycle characteristics.

[0077]

Table 1

[0078] As can be seen from Table 1, by using an electrode-forming material containing polyamideimide and an electrode containing an active material including a silicon-based active material and a carbon-based active material, the charge-discharge cycle characteristics of a lithium-ion secondary battery can be improved.

Claims

1. It contains polyamideimide and is used to form an electrode containing an active material comprising a silicon-based active material and a carbon-based active material, a material for electrode formation.

2. The material for electrode formation according to Claim 1, wherein the number average molecular weight of the polyamideimide is 3,000 to 100,000.

3. The material for electrode formation according to Claim 1 or 2, wherein the content of the silicon-based active material is 10 to 50% by mass based on the mass of the active material.

4. An electrode binder containing the material for electrode formation according to any one of Claims 1 to 3 and an active material containing a silicon-based active material and a carbon-based active material.

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

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

7. 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 6. ​

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