RU2787681C1 - Composition for an electrochemical apparatus, mixture of a positive electrode, structure of a positive electrode and accumulator battery - Google Patents

Abstract

FIELD: batteries.

SUBSTANCE: group of inventions relates to a composition for an electrochemical apparatus, a mixture of a positive electrode, a structure of a positive electrode, and an accumulator battery. Composition for an electrochemical apparatus includes single-walled carbon nanotubes, a binder, and a solvent, wherein the binder contains a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit other than the vinylidene fluoride unit, and the content of the vinylidene fluoride unit in the fluorine-containing copolymer is 50.0 mol.% or more relative to the total number of monomer units.

EFFECT: viscosity rise resistance if the electrode mixture even after a long time after production, low resistance and excellent adhesion to the current collector, flexibility and absence of springback.

14 cl, 3 tbl, 28 ex

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to an electrochemical device composition, a positive electrode mixture, a positive electrode structure, and a storage battery.

BACKGROUND OF THE INVENTION

[0002] Rechargeable batteries, such as lithium-ion batteries, have advantages such as high voltage, high energy density, low self-discharge, low memory effect, and the potential for ultra-low weight; therefore, rechargeable batteries are used in electrical and electronic devices that are portable due to their small size, such as laptops, mobile phones, smartphones, tablets and ultrabooks, and they also find practical use in a wide range of power sources, from on-board drive power supplies , for example, automobile, to large-scale stationary sources of energy supply.

[0003] For example, Patent Document 1 describes a battery including a positive electrode, a negative electrode, and an electrolyte solution, wherein: the negative electrode comprises a first negative electrode active material, a second negative electrode active material, and a negative electrode bond; the first active substance of the negative electrode has a central part containing a material containing silicon (Si) as a constituent element, and a cover part located on the surface of the central part and containing a salt compound and an electrically conductive substance; the salt compound contains at least one of a polyacrylic acid salt and a carboxymethyl cellulose salt; the electrically conductive substance comprises at least one of a carbon material and a metal material; the second active substance of the negative electrode includes a material containing carbon (C) as a constituent element; the negative electrode binder contains at least one of polyvinylidene fluoride, polyimide, and aramid. In addition, Patent Document 1 mentions single-walled carbon nanotubes as one example of a carbon material.

[0004] Patent Document 2 describes a metal foil, the surface of which is provided with a conductive layer containing carbon nanotubes, characterized in that the conductive layer is applied in such a way that carbon nanotubes are arranged randomly on the surface of the foil and in an amount of 100 ng/cm ² - 10 μg /cm ² .

CITATED MATERIALS

PATENT DOCUMENTS

[0005] Patent Document 1: International Publication No. WO 2018/146865

Patent Document 2: European Patent Application Publication No. EP 3147919

SUMMARY OF THE INVENTION

Problem solved by the invention

[0006] It is an object of the present invention to provide a composition for an electrochemical device, the use of which makes it possible to obtain an electrode mixture resistant to viscosity increase even after a long time after preparation, and also makes it possible to form an electrode mixture layer with low resistance, and to form an electrode mixture layer with excellent adhesion to current collector and flexibility and lack of elastic return.

Means for solving the problem

[0007] The present invention provides an electrochemical device composition comprising single-walled carbon nanotubes, a binder and a solvent, wherein the binder contains a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit other than the vinylidene fluoride unit, and the content of the vinylidene fluoride unit in the fluorine-containing copolymer is 50, 0 mol.% or more relative to the total number of monomer units.

[0008] It is preferable that the average outer diameter of single-walled carbon nanotubes is 2.5 nm or less.

It is preferable that the average G/D ratio of single-walled carbon nanotubes is 2 or more.

It is preferable that the content of fluorinated monomer units in the fluorine-containing copolymer is 1.0 mol% or more relative to the total amount of monomer units.

It is preferred that the fluorinated monomer unit is at least one selected from the group consisting of a tetrafluoroethylene unit, a chlorotrifluoroethylene unit, a fluoroalkyl vinyl ether unit, and a hexafluoropropylene unit.

It is more preferred that the fluorinated monomer unit is at least one selected from the group consisting of a tetrafluoroethylene unit and a hexafluoropropylene unit.

It is preferable that the dynamic modulus (E') determined by analyzing the viscoelasticity of the fluorine-containing copolymer at 30°C is 100 to 1200 MPa, and the dynamic modulus (E') determined by analyzing the viscoelasticity of the fluorine-containing copolymer at 60°C, ranged from 50 to 600 MPa.

It is preferred that the binder additionally contains polyvinylidene fluoride.

It is preferred that the solvent is at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and β-alkoxypropionamides.

The composition for an electrochemical device of the present invention can be suitably used to form an electrode or separator of an electrochemical device.

[0009] The present invention also provides a positive electrode mixture comprising the electrochemical device composition described above and a positive electrode active material.

[0010] It is preferable that the content of single-walled carbon nanotubes in the positive electrode mixture is from 0.001 to 10 mass parts per 100 mass parts of positive electrode active material.

It is preferable that the content of the binder in the positive electrode mixture is 0.1 to 5.0 mass parts per 100 mass parts of the positive electrode active material.

[0011] The present invention also provides a positive electrode structure including a current collector and a positive electrode mixture layer provided on one or both sides of the current collector, the positive electrode mixture layer being made of the positive electrode mixture described above.

[0012] The present invention also provides a battery including the positive electrode structure described above.

EFFECTS OF THE INVENTION

[0013] The present invention can provide a composition for an electrochemical device, the use of which makes it possible to obtain an electrode mixture that is resistant to viscosity increase even after a long time after preparation, and also makes it possible to form an electrode mixture layer with low resistance, and to form an electrode mixture layer with excellent adhesion to the current collector. and flexibility and lack of springback.

DESCRIPTION OF EMBODIMENTS

[0014] Specific embodiments of the present invention will now be described in detail. The present invention is not limited to the embodiments described below.

[0015] Electrochemical Device Composition

The composition for an electrochemical device of the present invention includes single-walled carbon nanotubes, a binder and a solvent.

[0016] Single walled carbon nanotubes

The composition for an electrochemical device of the present invention contains single-walled carbon nanotubes. Single walled carbon nanotubes (SWCNTs or SWCNTs) are a special type of carbon materials known as one-dimensional material. A single-walled carbon nanotube consists of a layer of graphene that is rolled up to form a hollow tube with a wall one atom thick. Due to this chemical structure and size, single-walled carbon nanotubes have exceptional mechanical, electrical, thermal and optical properties. Since the electrochemical device composition of the present invention includes single-walled carbon nanotubes, the use of the electrochemical device composition of the present invention in the preparation of the electrode mixture and the use of the obtained electrode mixture in the formation of the electrode mixture layer can provide the formed electrode mixture layer with low resistance. Thus, when the electrode mixture layer is formed with the same resistance as the conventional electrode mixture layer, it becomes possible to reduce the total amount of the electrical conductive additive such as acetylene black and increase the amount of active material, and therefore an electrochemical device with a high energy density can be provided. . In addition, the use of single-walled carbon nanotubes with a special copolymer described below can guarantee both the adhesion between the electrode mixture layer and the current collector and the flexibility of the electrode design, including the electrode mixture layer and the current collector.

[0017] In addition, the electrode mixture layer obtained using the electrochemical device composition of the present invention provides the advantage of resistance to springback. When an electrode is formed to be included in an electrochemical device, it may be pressed to flatten the electrode or increase its density, and the pressing may be followed by a heat treatment. Conventional methods have a problem that the heat treatment after removal of the compressive compression load causes a phenomenon called springback, which is an increase in the thickness of the electrode or a decrease in its density. The use of single-walled nanotubes with a special copolymer described below can effectively prevent springback. In addition, by using the electrochemical device composition of the present invention, a battery excellent in output performance, cycle performance, and storage performance at 60°C can be obtained.

[0018] The average outer diameter of the single-wall carbon nanotube is preferably 1.0-2.5 nm, more preferably 1.1-2.0 nm, and even more preferably 1.2-1.8 nm. The average outer diameter of a single-walled carbon nanotube can be determined from the optical absorption spectrum obtained for single-walled carbon nanotubes by ultraviolet, visible and near infrared (UV-Vis-NIR) spectroscopy, from the Raman spectrum of single-walled carbon nanotubes, or from a transmission electron microscope (TEM) image of single-walled carbon nanotubes.

[0019] The average length of single-wall carbon nanotubes is preferably 0.1-50 µm, more preferably 0.5-20 µm, and even more preferably 1-10 µm. The average length of SWCNTs can be determined from an atomic force microscope (AFM) or transmission electron microscope (TEM) image of SWCNTs by measuring the length of each SWCNT and dividing the sum of the lengths by the number of SWCNTs subjected to measurement.

[0020] The average G/D ratio of single wall carbon nanotubes measured by Raman spectroscopy (532 nm wavelength) is preferably 2-250, more preferably 5-250, even more preferably 10-220, and particularly preferably 40-180. The G/D ratio means the intensity ratio of the G band and the D band (G/D) in the Raman spectrum of a single-walled carbon nanotube. A higher G/D ratio of the single wall carbon nanotube indicates higher crystallinity of the single wall carbon nanotube and less carbon impurities and defective carbon nanotubes.

[0021] The content of single-walled carbon nanotubes in the electrochemical device composition of the present invention is preferably 0.01-3 wt%, more preferably 0.01-2 wt%, even more preferably 0.01-1 wt%, especially preferably 0.1-0.8% by weight and most preferably 0.2-0.5% by weight of the composition. When the content of single-walled carbon nanotubes is within the above range, the composition for an electrochemical device has an appropriate level of viscosity, and an electrode mixture with well-dispersed components can be obtained without applying very high shear forces. Therefore, in the resulting electrode mixture layer, a three-dimensional network of single-wall carbon nanotubes is correctly formed, and an electrode mixture layer with lower resistance can be obtained.

[0022] Binder

The composition for an electrochemical device of the present invention contains, as a binder, a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit other than the vinylidene fluoride unit. By including a fluorine-containing copolymer, the electrochemical device composition of the present invention can be used to prepare an electrode mixture resistant to viscosity increase even after a long time after preparation. In particular, even when the electrochemical device composition of the present invention is mixed with a Ni-rich positive electrode active material, the resulting positive electrode mixture is resistant to viscosity increase. In addition, since the electrochemical device composition of the present invention includes the above fluorine-containing copolymer in combination with single-walled carbon nanotubes, the electrochemical device composition of the present invention can be used to prepare an electrode mixture, the use of which in forming the electrode mixture layer makes it possible to achieve both strong adhesion between the electrode mixture layer and the current collector, and high flexibility of the electrode structure, as well as the effective prevention of the elastic return of the electrode mixture layer.

[0023] It is preferred that the fluorine-containing copolymer is a fluororubber. By fluoroelastomer is meant a partially crystalline fluoropolymer which is a fluoroplastic rather than a fluoroelastomer. Fluororubber has a melting point and thermoplasticity and can be melt-produced or non-melt-processable. It is preferred that the fluoroelastomer is a melt-blown fluoroelastomer.

[0024] It is preferred that the fluorinated monomer (excluding VDF) is at least one selected from the group consisting of tetrafluoroethylene (TFE), vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene and trans-1,3,3,3-tetrafluoropropene to further reduce the increase in the viscosity of the electrode mixture and allow an electrode mixture layer with better adhesion to the current collector and flexibility and more resistant to elastic return. More preferably at least one monomer selected from the group consisting of TFE, CTFE, fluoroalkyl vinyl ether and HFP, even more preferably at least one monomer selected from the group consisting of TFE, fluoroalkyl vinyl ether and HFP, and particularly preferred at least one monomer selected from the group consisting of TFE and HFP. SPE is most preferred in terms of reducing the swelling of the electrode mixture layer when impregnated with an electrolyte solution and providing improved battery performance such as output and cycle performance and low resistivity.

[0025] The fluorinated monomer unit (excluding the VDF unit) may or may not have a polar group.

[0026] Examples of a fluoroalkyl vinyl ether (PAVE) include at least one selected from the group consisting of a monomer represented by the following formula:

CF ₂ \u003d CFO (CF ₂ CFX ¹ O) _p - (CF ₂ CF ₂ CF ₂ O) _q -Rf ¹ ,

where X ¹ means F or CF ₃ ; Rf ¹ is a perfluoroalkyl group having 1 to 5 carbon atoms; p means an integer from 0 to 5; and q is an integer from 0 to 5; and

monomer represented by the following formula:

CFX ² =CX ² OCF ₂ ORf ² ,

where X ² are the same or different and each represents H, F or CF ₃ ; Rf ² means a fluoroalkyl group having 1 to 6 carbon atoms, which may have 1 to 2 atoms selected from the group consisting of H, Cl, Br and I, and which may be linear or branched, or a cyclic fluoroalkyl group, having 5 or 6 carbon atoms, which may have 1 to 2 atoms selected from the group consisting of H, Cl, Br and I.

[0027] A preferred surfactant is at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PFMVE), perfluoro(ethyl vinyl ether) (PFEVE), and perfluoro(propyl vinyl ether) (PPVVE).

[0028] The content of the VDF unit in the fluorine-containing copolymer is 50.0 mol.% or more of the total number of monomer units. In order to be able to further reduce the increase in the viscosity of the electrode mixture and to be able to form an electrode mixture layer with lower resistance, improved adhesion to the current collector and flexibility, and more resistant to elastic return, the content of VDF units in the fluorine-containing copolymer is preferably 55.0 mol.% or more, and more preferably 60.0 mol% or more, and preferably 99.0 mol% or less, more preferably 97.0 mol% or less, even more preferably 95.0 mol% or less, and particularly preferably 90.0 mol% or less.

[0029] In order to be able to further reduce the increase in the viscosity of the electrode mixture and to be able to form an electrode mixture layer with lower resistance, improved adhesion to the current collector and flexibility, and more resistant to elastic return, the content of fluorinated monomer units (excluding VDF units) in the fluorine-containing copolymer is preferably is 1.0 mol% or more, more preferably 2.5 mol% or more, even more preferably 5.0 mol% or more, particularly preferably 8.0 mol% or more, and most preferably 10.0 mol% or more, and preferably 50.0 mol% or less, more preferably 49.5 mol% or less, even more preferably 45.0 mol% or less, and particularly preferably 40.0 mol% or less, relative to the total number of monomer units.

[0030] As used herein, compositional characteristics of the fluorocopolymer can be measured, for example, by ¹⁹ F-NMR spectroscopy.

[0031] The fluorine-containing copolymer may further contain a non-fluorinated monomer unit. Examples of the non-fluorinated monomer include non-fluorinated monomers not having a polar group such as ethylene and propylene, and non-fluorinated monomers having a polar group (hereinafter, such monomers may be referred to as "polar group-containing monomers").

[0032] When a non-fluorinated monomer having a polar group is used, a polar group is introduced into the fluorine-containing copolymer, so stronger adhesion between the electrode mixture layer and the current collector can be achieved. As the polar group that can be introduced into the fluorine-containing copolymer, at least one selected from the group consisting of a carbonyl-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, an amino group, an amido group, and an alkoxy group is preferable. More preferred is at least one group selected from the group consisting of a carbonyl-containing group, an epoxy group and a hydroxy group, and even more preferred is a carbonyl-containing group. The hydroxy group is different from the hydroxy group constituting the carbonyl-containing group. The amino group is a monovalent functional group formed by the separation of hydrogen from ammonia or from a primary or secondary amine.

[0033] The carbonyl-containing group is a functional group including carbonyl (-C(=O)-). In order to achieve stronger adhesion between the electrode mixture layer and the current collector, it is preferable that the carbonyl-containing group be a group represented by the formula -COOR, where R is a hydrogen atom, an alkyl group or a hydroxyalkyl group or a carboxylic acid anhydride group. More preferred is the group represented by the formula -COOR. The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the formula -COOR include -COOCH ₂ CH ₂ OH, - COOCH ₂ CH(CH ₃ )OH, -COOCH(CH ₃ )CH ₂ OH, -COOH, -COOCH ₃ and -COOC ₂ H ₅ . When the group represented by the formula -COOR is or contains -COOH, the -COOH group may be a carboxylic acid salt group such as a metal carboxylic acid salt group or an ammonium carboxylic acid salt group.

[0034] As the amido group, a group represented by the formula -CO-NRR', where R and R' independently of each other are a hydrogen atom or a substituted or unsubstituted alkyl group, or a bond represented by the formula -CO-NR''-, where R'' represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group.

[0035] Examples of the monomer containing a polar group include: hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropylacrylate; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid and citraconic anhydride; malonic acid alkylidene esters such as dimethylmethylidenemalonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; esters of (meth)acryloyloxyalkyldicarboxylic acid such as acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate and methacryloyloxyethyl phthalate; and unsaturated dibasic acid monoesters such as monomethyl maleate, monoethyl maleate, monomethyl citraconate and monoethyl citraconate; and monomer (2) represented by the following formula (2):

[Formula 1]

,

,

where: R ¹ - R ³ independently of each other are a hydrogen atom, a chlorine atom or a hydrocarbon group having from 1 to 8 carbon atoms, R ⁴ is a connected single bond, a hydrocarbon group having from 1 to 8 carbon atoms, a heteroatom or an atomic a group with a molecular weight of 500 or less, and this atomic group contains at least one heteroatom selected from the group consisting of an oxygen atom, a sulfur atom, a nitrogen atom and a phosphorus atom, and contains a main chain having from 1 to 20 atoms; and Y ¹ means an inorganic cation and/or an organic cation. As used herein, "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid. The prefix "(meth)" used in the names of other compounds should be interpreted in the same way. The number of atoms in the backbone of an atomic group refers to the number of atoms in the linear skeleton and does not include oxygen atoms forming a carbonyl group or hydrogen atoms forming a methylene group. For example, when monomer (2) is acryloyloxyethyl phthalate, the linear skeleton is -C-OCCO-C-CC-, which has 8 atoms.

[0036] It is preferable that the fluorine-containing copolymer contains, as a unit derived from a monomer containing a polar group, a unit derived from the monomer (2) represented by the formula (2), to enable the formation of an electrode mixture layer with more excellent adhesion to the current collector and flexibility and more resistant to elastic return.

[0037] In formula (2), Y ¹ means an inorganic cation and/or an organic cation. Examples of the inorganic cation include cations such as H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of the organic cation include cations such as NH ₄ , NH ₃ R ⁵ , NH ₂ R ⁵ ₂ , NHR ⁵ ₃ , and NR ⁵ ₄ , wherein R ⁵ is independently an alkyl group having 1 to 4 carbon atoms. Preferred as Y ¹ are H, Li, Na, K, Mg, Ca, Al and NH ₄ . H, Li, Na, K, Mg, Al and NH ₄ are more preferred, H, Li, Al and NH ₄ are even more preferred, and H is particularly preferred. It should be noted that specific examples of the inorganic cation and the organic cation are presented for convenience. without indication of sign and valency.

[0038] In the formula (2), R ¹ - R ³ independently of each other are a hydrogen atom, a chlorine atom, or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a monovalent hydrocarbon group. It is preferred that the number of carbon atoms in the hydrocarbon group is 4 or less. Examples of the hydrocarbon group include alkyl, alkenyl and alkynyl groups with the indicated number of carbon atoms, and preferably a methyl or ethyl group. It is preferred that R ¹ and R ² are each independently a hydrogen atom, a methyl group or an ethyl group, and it is preferred that R ³ is a hydrogen atom or a methyl group.

[0039] In the formula (2), R ⁴ is a single bond, a hydrocarbon group having 1 to 8 carbon atoms, a heteroatom, or an atomic group with a molecular weight of 500 or less, and this atomic group contains at least one heteroatom selected from the group , consisting of an oxygen atom, a sulfur atom, a nitrogen atom and a phosphorus atom, and contains a main chain having from 1 to 20 atoms.

[0040] The hydrocarbon group is a divalent hydrocarbon group. It is preferred that the number of carbon atoms in the hydrocarbon group is 4 or less. Examples of the hydrocarbon group include an alkylene or alkenylene group with the indicated number of carbon atoms, of which at least one selected from the group consisting of a methylene group, an ethylene group, an ethyleneidene group, a propylene group, and an isopropylidene group is preferred, and more preferred is at least at least one selected from the group consisting of a methylene group and an ethylene group.

[0041] When R ⁴ is a heteroatom, it is preferred that the heteroatom is at least one selected from the group consisting of an oxygen atom, a sulfur atom, a nitrogen atom, and a phosphorus atom, of which an oxygen atom is more preferred.

[0042] When R ⁴ is an atomic group, it is preferred that the heteroatom in the atomic group is an oxygen atom.

[0043] When R ⁴ is an atomic group, it is preferable that the side chain represented by the formula -R ⁴ -CO ₂ Y ¹ in the formula (2) is any of the following side chains.

A side chain represented by the formula -CO-R ⁶ -CO ₂ Y ¹ where R ⁶ is an atomic group with a molecular weight of 472 or less and a backbone having 1 to 19 atoms, and where Y ¹ is the same as defined above.

A side chain represented by the formula -OR ⁷ -CO ₂ Y ¹ where R ⁷ is an atomic group with a molecular weight of 484 or less and a backbone having 1 to 19 atoms, and where Y ¹ is the same as defined above.

A side chain represented by the formula -COO-R ⁸ -CO ₂ Y ¹ , where R ⁸ is an atomic group with a molecular weight of 456 or less and a backbone having 1 to 18 atoms, and where Y ¹ is the same as defined above.

[0044] When R ⁴ is an atomic group, examples of monomer (2) include: (meth)acrylamide compounds such as N-carboxyethyl(meth)acrylamide; thio(meth)acrylate compounds such as carboxyethylthio(meth)acrylate; vinylcarboxyalkyl ethers such as vinylcarboxymethyl ether and vinylcarboxyethyl ether; and other compounds such as 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxypropyl succinate, acryloyloxyethyl phthalate, and methacryloyloxyethyl phthalate. When R ⁴ is an atomic group, monomer (2) is preferably 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxypropyl succinate or methacryloyloxypropyl succinate.

[0045] In order to be able to form an electrode mixture layer with more excellent adhesion to the current collector and flexibility and more resistant to elastic return, it is preferable that the monomer (2) is the monomer (2) represented by the formula (2) in which R ⁴ is a single bond or a hydrocarbon group having 1 to 8 carbon atoms.

In order to be able to form an electrode mixture layer with more excellent current collector adhesion and flexibility and more resistant to elastic return, it is more preferable that the monomer (2) is at least one monomer selected from the group consisting of (meth)acrylic acid, its salts, vinylacetic acid (3-butenoic acid), its salts, 3-pentenoic acid, its salts, 4-pentenoic acid, its salts, 3-hexenoic acid, its salts, 4-heptenoic acid, its salts, 5-hexenoic acid and its salts, and even more preferably at least one monomer selected from the group consisting of 3-butenoic acid, its salts, 4-pentenoic acid and its salts.

[0046] In order to be able to further reduce the increase in the viscosity of the electrode mixture and to be able to form an electrode mixture layer having a lower resistance, with better adhesion to the current collector and flexibility, and more resistant to springback, the unit content of the polar group-containing monomer in the fluorine-containing copolymer is preferably 0.05 to 2.0 mol%, more preferably 0.10 mol% or more, even more preferably 0.25 mol% or more, and particularly preferably 0.40 mol% or more, and more preferably is 1.5 mol.% or less, relative to the total number of monomer units.

[0047] As used herein, the unit content of a polar group-containing monomer in a fluorine-containing copolymer, for example, when the polar group is an acid group, for example, a carboxylic acid derivative, can be measured by acid-base titration of the acid group.

[0048] Examples of the fluorine-containing copolymer include VDF/TFE copolymer, VDF/HFP copolymer, VDF/TFE/HFP copolymer, VDF/TFE/(meth)acrylic acid copolymer, VDF/HFP/(meth)acrylic acid copolymer, VDF/CTFE copolymer , VDF/TFE/4-pentenoic acid copolymer, VDF/TFE/3-butenoic acid copolymer, VDF/TFE/HFP/(meth)acrylic acid copolymer, VDF/TFE/HFP/4-pentenoic acid copolymer, VDF/TFE copolymer /HFP/3-butenoic acid, VDF/PAVE copolymer, VDF/PAVE/(meth)acrylic acid copolymer, VDF/PAVE/carboxyalkyl(meth)acrylate copolymer and VDF/HFP/carboxyalkyl(meth)acrylate copolymer.

[0049] It is preferred that the fluorine-containing copolymer is at least one selected from the group consisting of a copolymer containing a VDF unit and a TFE unit, a copolymer containing a VDF unit and an HFP unit, and a copolymer containing a VDF unit and a PAVE unit.

[0050] Of these, the preferred fluorine-containing copolymer is a fluorine-containing copolymer consisting of a VDF unit, a TFE unit, and any non-fluorinated monomer unit, and having a molar ratio between the VDF unit and the TFE unit (VDF unit/TFE unit) of 50/50 to 90/10. That is, it is preferable that the fluorine-containing copolymer is a binary copolymer consisting of a VDF unit and a TFE unit, or a ternary or multicomponent copolymer consisting of a VDF unit, a TFE unit and one or more non-fluorinated monomer units, and does not contain other fluorinated monomer units. links than the VDF link and the TFE link. The inclusion of such a fluorine-containing copolymer in the electrochemical device composition of the present invention makes it possible to further reduce the increase in viscosity of the electrode mixture and form an electrode mixture layer having lower resistance, superior current collector adhesion and flexibility, and more resistant to springback.

[0051] When the fluorine-containing copolymer contains a VDF unit and a TFE unit, the molar ratio between the VDF unit and the TFE unit (VDF unit/TFE unit) is preferably 50/50 to 90/10, more preferably 55/45 to 89/11, and even more preferably from 60/40 to 88/12.

[0052] When the fluorine-containing copolymer contains a VDF unit and a TFE unit, the content of the non-fluorinated monomer unit is preferably 0 to 2.0 mol% relative to the total amount of monomer units in the fluorine-containing copolymer.

[0053] In particular, as the non-fluorinated monomer, a monomer containing a polar group is preferred, a monomer (2) is more preferred, at least one monomer selected from the group consisting of (meth)acrylic acid, its salts, vinylacetic acid ( 3-butenoic acid), its salts, 3-pentenoic acid, its salts, 4-pentenoic acid, its salts, 3-hexenoic acid, its salts, 4-heptenoic acid, its salts, 5-hexenoic acid and its salts, and particularly preferred is at least one monomer selected from the group consisting of 3-butenoic acid, its salts, 4-pentenoic acid and its salts.

[0054] It is preferred that the fluorine-containing copolymer consisting of a VDF unit, a TFE unit and any non-fluorinated monomer unit is VDF/TFE copolymer, VDF/TFE/HFP copolymer, VDF/TFE/(meth)acrylic acid copolymer, VDF copolymer /TFE/4-pentenoic acid, VDF/TFE/3-butenoic acid copolymer, VDF/TFE/HFP/(meth)acrylic acid copolymer, VDF/TFE/HFP/4-pentenoic acid copolymer and VDF/TFE/HFP copolymer/ 3-butenoic acid.

[0055] The fluorine-containing copolymer may be a VDF/HFP copolymer. The VDF/HFP copolymer contains a VDF unit and an HFP unit. The content of the VDF unit is preferably 55.0 mol% or more, more preferably 60.0 mol% or more, even more preferably 80.0 mol% or more, particularly preferably 90.0 mol% or more, and preferably is 99.0 mol.% or less, more preferably 97.0 mol.% or less, relative to the total number of monomer units of the VDF/HFP copolymer. The content of the HFP unit is preferably 1.0 mol% or more, more preferably 3.0 mol% or more, and preferably 45.0 mol% or less, more preferably 40.0 mol% or less, even more preferably 20.0 mol% or less, and particularly preferably 10.0 mol% or less, relative to the total amount of monomer units of the VDF/HFP copolymer.

[0056] In addition to the VDF unit and the HFP unit, the VDF/HFP copolymer may contain a unit derived from a monomer copolymerizable with VDF and HFP (excluding VDF and HFP). The content of the unit derived from the monomer copolymerizable with VDF and HFP is preferably 0 to 2.0 mol%, more preferably 0.05 to 2.0 mol%, relative to the total amount of monomer units of the VDF/HFP copolymer.

[0057] Examples of the monomer copolymerizable with VDF and HFP include the fluorinated monomer described above and the non-fluorinated monomer. In particular, as the monomer copolymerizable with VDF and HFP, at least one monomer selected from the group consisting of a fluorinated monomer and a polar group-containing monomer is preferred, at least one monomer selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene and monomer (2), monomer (2) is even more preferred.

[0058] The fluorine-containing copolymer may be a VDF/PAVE copolymer. The VDF/PAVE copolymer contains a VDF unit and a PAVE unit. The content of the VDF unit is preferably 55.0 mol% or more, more preferably 70.0 mol% or more, even more preferably 90.0 mol% or more, particularly preferably 95.0 mol% or more, and preferably is 99.0 mol.% or less, and more preferably 98.5 mol.% or less, relative to the total number of monomer units of the VDF/PAVE copolymer. The content of the PAVE unit is preferably 1.0 mol% or more, more preferably 1.5 mol% or more, and preferably 45.0 mol% or less, more preferably 30.0 mol% or less, even more preferably 10.0 mol% or less, and particularly preferably 5.0 mol% or less, relative to the total amount of monomer units of the VDF/PAVE copolymer.

[0059] As the surfactant, perfluoro(methyl vinyl ether) (PFMVE), perfluoro(ethyl vinyl ether) (PFEVE), perfluoro(propyl vinyl ether) (PFPVE) are preferred.

[0060] In addition to the VDF unit and the PAVE unit, the VDF/PAVE copolymer may contain a unit derived from a monomer copolymerizable with VDF and PAVE (excluding VDF and PAVE). The content of the unit derived from the monomer copolymerizable with VDF and PAVE is preferably from 0 to 2.0 mol.%, more preferably from 0.05 to 2.0 mol.%, relative to the total amount of monomer units of the VDF/PAVE copolymer.

[0061] Examples of the monomer copolymerizable with VDF and PAVE include the fluorinated monomer described above and the non-fluorinated monomer. In particular, as the monomer copolymerizable with VDF and PAVE, at least one monomer selected from the group consisting of a fluorinated monomer and a polar group-containing monomer is preferred, a polar group-containing monomer is more preferred, at least one monomer is even more preferred, selected from the group consisting of (meth)acrylic acid, its salts, carboxyalkyl (meth)acrylate and its salts.

[0062] The weight average molecular weight (polystyrene equivalent) of the fluorocopolymer is preferably 160,000 to 2,760,000, more preferably 200,000 to 2,530,000, and even more preferably 300,000 to 2,000,000. The weight average molecular weight can be measured by Gel Permeation Chromatography (GPC) using dimethylformamide as a solvent.

[0063] The number average molecular weight (polystyrene equivalent) of the fluorine-containing copolymer is preferably 70,000 to 1200,000, and more preferably 140,000 to 1100,000. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0064] The melting point of the fluorine-containing copolymer is preferably 100 to 200°C. The melting point can be measured using a differential scanning calorimetry (DSC) instrument and is defined as the temperature at which the heat of fusion curve obtained by heating at a rate of 10° C./min has a maximum.

[0065] The average particle size of the fluorine-containing copolymer is preferably 1000 µm or less, and more preferably 50 to 350 µm, in order to facilitate the dissolution or dispersion of the fluorine-containing copolymer in a solvent.

[0066] The fluorine-containing copolymer preferably has an elastic modulus (E') at 30°C of 100 to 1200 MPa and a dynamic elastic modulus (E') at 60°C of 50 to 600 MPa.

The storage modulus (E') at 30° C. of the fluorine-containing copolymer is more preferably 150 MPa or more, even more preferably 200 MPa or more, more preferably 800 MPa or less, even more preferably 600 MPa or less.

The elastic modulus (E') at 60° C. of the fluorine-containing copolymer is more preferably 80 MPa or more, even more preferably 130 MPa or more, more preferably 450 MPa or less, even more preferably 350 MPa or less.

When the dynamic modulus (E') of the fluorine-containing copolymer is in the above range, an electrode mixture layer can be formed that is even more excellent in flexibility.

[0067] The dynamic modulus of elasticity (E') is a value determined by dynamic analysis of the viscoelasticity of a sample 30 mm long, 5 mm wide and 50-100 μm thick at 30°C and 60°C using a DVA 220 dynamic viscoelasticity analyzer manufactured by the company IT keisoku seigyo sya in stretch mode using 20mm distance between supports at 2°C/min temperature increase rate from -30°C to 160°C at 1Hz.

[0068] It is preferable that the composition for the electrochemical device of the present invention further contains polyvinylidene fluoride (PVDF) to enable the formation of an electrode mixture layer with superior current collector adhesion and flexibility and more resistant to springback. In particular, when the electrochemical device composition of the present invention further contains PVDF, a lower resistance electrode mixture layer can be formed.

[0069] Polyvinylidene fluoride (PVDF) is a polymer containing a unit derived from vinylidene fluoride (VDF) (hereinafter, this unit will be referred to as a VDF unit), and may be a VDF homopolymer consisting of VDF units, or a polymer containing a VDF unit and a unit derived from from the monomer copolymerizable with VDF.

[0070] For PVDF, it is preferred that the VDF copolymerizable monomer is a monomer other than tetrafluoroethylene (TFE). That is, it is preferable that PVDF should not contain a TFE unit.

[0071] For PVDF, examples of the monomer copolymerizable with VDF include a fluorinated monomer and a non-fluorinated monomer, with the fluorinated monomer being preferred. Examples of the fluorinated monomer include vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene. Examples of the non-fluorinated monomer include ethylene and propylene.

[0072] For PVDF, it is preferred that the VDF copolymerizable monomer is at least one fluorinated monomer selected from the group consisting of CTFE, fluoroalkyl vinyl ether, HFP, and 2,3,3,3-tetrafluoropropene, and more preferably at least one fluorinated monomer selected from the group consisting of CTFE, HFP and fluoroalkyl vinyl ether.

[0073] In PVDF, the content of the unit derived from the monomer copolymerizable with VDF is preferably 0.10 to 8.0 mol%, more preferably 0.50 mol% or more and less than 5.0 mol%, and even more preferably from 0.50 to 3.0 mol.%, relative to the total number of monomer units. The content of the fluorinated monomer unit is preferably 0.10 to 8.0 mol%, more preferably 0.50 mol% or more and less than 5.0 mol%, relative to the total number of monomer units. In addition, the content of the unit derived from the monomer copolymerizable with VDF may be less than 1.0 mol.% relative to the total number of monomer units.

[0074] As used herein, compositional features of PVDF can be measured, for example, by ¹⁹ F-NMR spectroscopy.

[0075] PVDF may have a polar group, in which case stronger adhesion between the electrode mixture layer and the current collector can be achieved. The polar group is not limited and may be any functional group having polarity. In order to achieve stronger adhesion between the electrode mixture layer and the current collector, it is preferable that the polar group is at least one group selected from the group consisting of a carbonyl-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, an amino group. , amido groups and alkoxy groups. More preferably a group selected from the group consisting of a carbonyl-containing group, an epoxy group and a hydroxy group, and a carbonyl-containing group is even more preferred. The hydroxy group is different from the hydroxy group constituting the carbonyl-containing group. The amino group is a monovalent functional group formed by the separation of hydrogen from ammonia or from a primary or secondary amine.

[0076] The carbonyl-containing group is a functional group including carbonyl (-C(=O)-). In order to achieve stronger adhesion between the electrode mixture layer and the current collector, it is preferable that the carbonyl-containing group is a group represented by the formula -COOR, where R is a hydrogen atom, an alkyl group, or a hydroxyalkyl group or a carboxylic acid anhydride group. More preferred is the group represented by the formula -COOR. The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the formula -COOR include -COOCH ₂ CH ₂ OH, - COOCH ₂ CH(CH ₃ )OH, -COOCH(CH ₃ )CH ₂ OH, -COOH, -COOCH ₃ and -COOC ₂ H ₅ . When the group represented by the formula -COOR is or contains -COOH, the -COOH group may be derived from a carboxylic acid salt such as a metal carboxylate or ammonium carboxylate.

[0077] As the amido group, a group represented by the formula -CO-NRR', where R and R' independently of each other are a hydrogen atom or a substituted or unsubstituted alkyl group, or a bond represented by the formula -CO-NR''-, where R'' represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group.

[0078] A polar group may be introduced into PVDF by polymerization of VDF and a monomer having a polar group (this monomer is hereinafter referred to as "polar group-containing monomer"), or may be introduced into PVDF by reaction between PVDF and a compound having a polar group. From the point of view of productivity, it is preferable to carry out the polymerization of VDF and a monomer containing a polar group.

[0079] Polymerization of VDF and a polar group-containing monomer produces PVDF having a VDF unit and a polar group-containing monomer unit. That is, it is preferable that PVDF includes a monomer containing a polar group to achieve stronger adhesion between the electrode mixture layer and the current collector. The unit content of the polar group-containing monomer is preferably 0.001 to 8.0 mol%, more preferably 0.01 to 5.0 mol%, even more preferably 0.10 to 3.0 mol%, particularly preferably from 0.15 to 3.0 mole %, and most preferably 0.30 to 1.5 mole %, based on total monomer units. In addition, the content of the unit containing the polar group of the monomer may be less than 1.0 mol.% relative to the total number of monomer units.

[0080] As used herein, the unit content of a polar group-containing monomer in PVDF, for example, when the polar group is an acid group, for example, a carboxylic acid derivative, can be measured by acid-base titration of the acid group.

[0081] Examples of the monomer containing a polar group include: hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropylacrylate; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid and citraconic anhydride; malonic acid alkylidene esters such as dimethylmethylidenemalonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; esters of (meth)acryloyloxyalkyldicarboxylic acid such as acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate and methacryloyloxyethyl phthalate; and unsaturated dibasic acid monoesters such as monomethyl maleate, monoethyl maleate, monomethyl citraconate and monoethyl citraconate; and monomer (2) represented by the following formula (2):

[Formula 2]

where: R ¹ - R ³ independently of each other are a hydrogen atom, a chlorine atom or a hydrocarbon group having from 1 to 8 carbon atoms, R ⁴ is a single bond, a hydrocarbon group having from 1 to 8 carbon atoms, a heteroatom or an atomic group with a molecular weight of 500 or less, and this atomic group contains at least one heteroatom selected from the group consisting of an oxygen atom, a sulfur atom, a nitrogen atom and a phosphorus atom, and contains a main chain having from 1 to 20 atoms; and Y ¹ means an inorganic cation and/or an organic cation.

[0082] The monomer (2) is as described above with respect to the monomer (2) to obtain a fluorine-containing copolymer. Hydroxyethyl acrylate, 2-hydroxypropylacrylate, acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxypropyl succinate, and methacryloyloxypropyl succinate are preferred as the polar group-containing monomer for producing PVDF.

[0083] When a reaction is carried out between PVDF and a compound having a polar group to introduce a polar group into PVDF, the above polar group-containing monomer or a silane or titanate crosslinker having a PVDF-reactive group can be used as the polar group-containing compound, and hydrolysable group. The hydrolysable group is preferably an alkoxy group. When a crosslinker is used, it can be added to the PVDF through a reaction between the crosslinker and PVDF dissolved or swollen in a solvent.

[0084] The PVDF used can be obtained by partially dehydrogenating PVDF with a base and then reacting the partially dehydrogenated PVDF with an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide, hypochlorous acid salts, palladium halide, chromium halide, alkali metal permanganates, peroxyacid compounds, alkyl peroxides and alkyl persulfates.

[0085] In order to achieve higher adhesion between the electrode mixture layer and the current collector, the content of the VDF unit in PVDF is preferably from 84.0 to 99.999 mol.%, more preferably 90.0 mol.% or more, even more preferably 92.0 mol. % or more, particularly preferably 95.0 mol.% or more, and most preferably 97.0 mol.% or more, relative to the total number of monomer units. As for the upper limit, its content may preferably be 99.99 mol% or less, more preferably 99.909 mol% or less, even more preferably 99.899 mol% or less, even more preferably 99.70 mol% or less. , even more preferably 99.50 mol% or less, even more preferably 99.49 mol% or less, and most preferably 99.20 mol% or less.

[0086] The weight average molecular weight (polystyrene equivalent) of PVDF is preferably 160,000 to 2,760,000, more preferably 200,000 or more, even more preferably 300,000 or more, and more preferably 2,530,000 or less, and even more preferably 2,000,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as solvent.

[0087] The number average molecular weight (polystyrene equivalent) of PVDF is preferably 70,000 to 1,200,000, and more preferably 140,000 or more, and more preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as solvent.

[0088] The melting point of PVDF is preferably 100 to 240°C, more preferably 130 to 200°C, particularly preferably 140 to 180°C. The melting point can be measured using a differential scanning calorimetry (DSC) instrument and is defined as the temperature at which the heat of fusion curve obtained by heating at a rate of 10°C/min has a maximum.

[0089] The average particle size of PVDF is preferably 1000 µm or less, more preferably 750 µm or less, and even more preferably 350 µm or less, and preferably 0.1 µm or more, and more preferably 0.2 µm or more, for facilitating the dissolution or dispersion of PVDF in the solvent.

[0090] PVDF can be produced by a publicly known method such as mixing VDF, the aforementioned polar group-containing monomer, and additives such as a polymerization initiator and a polymerization emulsifier in the prescribed manner to carry out solution polymerization, suspension polymerization, or emulsion polymerization.

[0091] In order to be able to further reduce the increase in the viscosity of the electrode mixture and to be able to form an electrode mixture layer with more excellent adhesion to the current collector and flexibility and more resistant to elastic return, the weight ratio between the fluorine-containing copolymer and PVDF (fluorine-containing copolymer/PVDF) in the composition for electrochemical device of the present invention is preferably 99/1 to 1/99, more preferably 95/5 to 3/97, even more preferably 90/10 to 5/95, particularly preferably 70/30 to 7/93, and most preferably 50/50 to 10/90.

[0092] The composition for an electrochemical device of the present invention, in addition to the fluorine-containing copolymer and PVDF, may contain another polymer as a binder. Examples of the other polymer include polymethacrylate, polymethylmethacrylate, polyacrylonitrile, polyimide, polyamide, polyamideimide, polycarbonate, styrene rubber, and butadiene rubber.

[0093] The binder content of the electrochemical device composition of the present invention is preferably 0.01 to 10% by mass, more preferably 0.2 to 5.0% by mass, even more preferably 0.5 to 3.0 wt.%, and especially preferably from 0.8 to 2.5 wt.%, relative to the weight of the composition, so that the composition for an electrochemical device has the ability to maintain its viscosity at an appropriate level, and to achieve a strong binding effect when forming an electrode mixture layer . When the binder content is in the above range, the electrochemical device composition has an appropriate level of viscosity, and an electrode mixture with well-dispersed components can be prepared without applying too much shear. Therefore, a three-dimensional network of single-walled carbon nanotubes is properly formed in the resulting electrode mixture layer, and, in addition, stronger adhesion between the electrode mixture layer and the current collector and higher flexibility of the electrode design can be achieved.

[0094] The optical concentration (optical density) of the electrochemical device composition of the present invention is preferably 0.3 to 0.7 optical units, more preferably 0.40 to 0.65 optical units, and even more preferably 0.42 up to 0.62 optical units. The optical concentration can be determined by measuring the light absorption at a wavelength of 500 nm of a solution containing 0.001 wt.% single-walled carbon nanotubes, using a spectrophotometer cuvette with a path length of 10 mm and using the NMP solution as a reference.

When the absorption of light at a wavelength of 500 nm of a solution obtained by appropriately diluting or concentrating the electrochemical device composition of the present invention and thereby bringing the concentration of single-walled carbon nanotubes to 0.001 mass% is in the above range, the dispersibility of the electrode mixture is high, and the electrode mixture can be prepared without applying too much shear. Therefore, a three-dimensional network of single-walled carbon nanotubes is correctly formed in the resulting electrode mixture layer, and, in addition, both the adhesion between the electrode mixture layer and the current collector and the flexibility of the electrode design can be guaranteed.

[0095] Solvent

The electrochemical device composition of the present invention further comprises a solvent. As the solvent, an organic solvent is preferred, examples of which include the following commonly used low boiling point organic solvents: nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; β-alkoxypropionamides such as β-methoxy-N,N-dimethylpropionamide, β-n-butoxy-N,N-dimethylpropionamide and β-n-hexyloxy-N,N-dimethylpropionamide; and mixtures of these solvents. The preferred solvent is at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and β-alkoxypropionamides in terms of ease of application , and more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylacetamide.

[0096] The viscosity of the electrochemical device composition of the present invention is preferably 5 to 8000 mPa·s, more preferably 100 to 5000 mPa·s, and even more preferably 100 to 2000 mPa·s. Viscosity is measured using a type B viscometer (LV-DV2T manufactured by Brookfield) with rotor No. SC4-21 at 25° C. and 20 rpm. When the viscosity of the electrochemical device composition of the present invention is in the above range, an electrode mixture with well-dispersed components can be prepared without applying too much shear. Therefore, a three-dimensional network of single-walled carbon nanotubes is correctly formed in the resulting electrode mixture layer, and, in addition, both stronger adhesion between the electrode mixture layer and the current collector and higher flexibility of the electrode design can be achieved.

[0097] The composition for an electrochemical device of the present invention is a composition for use in forming a constituent element of an electrochemical device. The electrochemical device is not limited to any device that converts between electrical energy and chemical energy, and examples of such a device include a lithium ion battery, a lithium ion capacitor, a hybrid capacitor, an electrical double layer capacitor, and an aluminum oxide electrolytic capacitor. . The preferred electrochemical device is a lithium ion battery or a lithium ion capacitor. Examples of a constituent element of an electrochemical device include an electrode and a separator. In particular, it is preferable that the electrochemical device composition of the present invention is used in forming an electrode of a lithium ion battery or a lithium ion capacitor. For example, the electrochemical device composition of the present invention can be used in forming a positive electrode mixture layer, a negative electrode mixture layer, a conductive layer or adhesive layer (sublayer) formed between the positive electrode mixture layer and a current collector, and an electrically conductive layer or adhesive layer (sublayer). ) formed between the mixture layer of the negative electrode and the current collector. In addition, since the use of the electrochemical device composition of the present invention makes it possible to obtain a positive electrode mixture resistant to viscosity increase even after a long time after preparation, and also makes it possible to form a positive electrode mixture layer with low resistance, and to form a positive electrode mixture layer with excellent adhesion to current collector and flexibility and resistant to elastic return, it is more preferable to use this composition in forming the positive electrode of a lithium ion battery, it is even more preferable to use this composition in forming the mixture layer of the positive electrode of a lithium ion battery. It is preferable that the electrochemical device composition of the present invention does not contain a positive electrode active material, and this composition can be distinguished from the positive electrode mixture described below in that the composition does not contain a positive electrode active material.

[0098] The composition for the electrochemical device of the present invention can be prepared by mixing the components. The order of mixing components is not limited. For example, a composition for an electrochemical device can be prepared by a method in which single-walled carbon nanotubes and a solvent are mixed, and then the resulting dispersion and binder are mixed.

For mixing, a known mixing device can be used. Using a homogenizer, a composition for an electrochemical device containing single-walled carbon nanotubes and a binder uniformly dispersed in a solvent can be easily obtained.

As a homogenizer, for example, a rotary homogenizer, an ultrasonic homogenizer or a high pressure homogenizer can be used. The useful power of the ultrasonic homogenizer can be from 5 to 50 kW. The amount of energy transmitted by the ultrasonic homogenizer of the dispersion or composition for an electrochemical device may be from 0.1 to 1 kWh per kg of dispersion or composition for an electrochemical device. The pressure applied by the high pressure homogenizer during mixing can be between 100 and 2000 bar. The dispersion or composition for the electrochemical device may be passed through the high pressure homogenizer multiple times, and may be passed through the high pressure homogenizer 2 to 20 times.

The composition for the electrochemical device of the present invention can be prepared, for example, by a method in which single-walled carbon nanotubes and a solvent are mixed with an ultrasonic homogenizer, and then the obtained dispersion and a binder are mixed with a high pressure homogenizer. Single wall carbon nanotubes and the solvent can be mixed using an ultrasonic homogenizer while stirring with a stirrer.

[0099] Positive electrode mixture

The positive electrode mixture of the present invention includes the above-described composition for an electrochemical device and a positive electrode active material. Thus, the positive electrode mixture of the present invention includes single-wall carbon nanotubes, a binder and a solvent contained in an electrochemical device composition, and a positive electrode active material. The positive electrode mixture of the present invention is resistant to viscosity increase even after a long time after preparation, and can be formed into a positive electrode mixture layer with low resistance, as well as a positive electrode mixture layer with excellent current collector adhesion and flexibility, and resistant to elastic return.

[0100] The content of single-walled carbon nanotubes in the positive electrode mixture of the present invention may be 0.001 to 10 parts by mass, and preferably 0.001 to 2 mass parts, more preferably 0.005 mass parts or more, even more preferably 0.01 mass parts or more. more, and particularly preferably 0.05 mass parts or more, and more preferably 1.0 mass parts or less, more preferably 0.2 mass parts or less, and particularly preferably 0.1 mass parts or less, per 100 mass parts the active material of the positive electrode.

[0101] The binder content of the positive electrode mixture of the present invention is preferably 0.1 to 5.0 mass parts, more preferably 0.3 mass parts or more, and even more preferably 0.5 mass parts or more, and more preferably is 3.0 mass parts or less, and even more preferably 2.0 mass parts or less, per 100 mass parts of the positive electrode active material. The binder in the positive electrode mixture of the present invention may be any binder containing a fluorine-containing copolymer, and may be composed of a fluorine-containing copolymer and contain not only a fluorine-containing copolymer, but also PVDF. When the binder contains the fluorine-containing copolymer and PVDF, the weight ratio between the fluorine-containing copolymer and PVDF (fluorine-containing copolymer/PVDF) is preferably 99/1 to 1/99, more preferably 95/5 to 3/97, even more preferably 90/10 up to 5/95, particularly preferably from 70/30 to 7/93, and most preferably from 50/50 to 10/90, to allow further reduction in the increase in the viscosity of the positive electrode mixture and to be able to form a positive electrode mixture layer with more excellent adhesion to current collector and flexibility and more resistant to elastic return.

[0102] Positive electrode active material

The positive electrode active material is not limited, and may be any positive electrode active material capable of electrochemically intercalating and deintercalating lithium ions. As the active material of the positive electrode, a material containing lithium and at least one transition metal is preferable, and examples of such a material include a lithium transition metal complex oxide and a lithium-containing transition metal phosphate compound.

[0103] As the transition metal in the lithium transition metal composite oxide, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferred, and specific examples of the lithium transition metal composite oxide include: lithium composite oxides -cobalt, such as LiCoO ₂ ; complex oxides of lithium-nickel, such as LiNiO ₂ ; complex lithium-manganese oxides such as LiMnO ₂ , LiMn ₂ O ₄ and Li ₂ MnO ₃ ; and complex oxides resulting from the substitution of a part of the atoms of the base transition metal in these lithium transition metal complex oxides with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr and Si. Examples of substituted complex oxides include lithium-nickel-manganese complex oxides, lithium-nickel-cobalt-aluminum complex oxides, lithium-nickel-cobalt-manganese complex oxides, lithium-manganese-aluminum complex oxides, and lithium-titanium complex oxides. Specific examples of substituted complex oxides include LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.82 Co _0.15 Al _0.03 O ₂ , LiNi _{0, 80} Co _0.15 Al _0.05 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O ₄ and Li ₄ Ti ₅ O ₁₂ .

[0104] As the transition metal in the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferable. Specific examples of the lithium-containing transition metal phosphate compound include: iron phosphates such as LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ) ₃ and LiFeP ₂ O ₇ ; cobalt phosphates such as LiCoPO ₄ ; and transition metal phosphate compounds obtained by replacing a portion of the base transition metal atoms in these lithium-containing transition metal phosphate compounds with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg , Ga, Zr, Nb and Si.

[0105] Preferred positive electrode active materials are at least one selected from the group consisting of lithium-cobalt complex oxides, lithium-nickel complex oxides, lithium-manganese complex oxides, iron phosphates, lithium-nickel-manganese complex oxides, complex oxides of lithium-nickel-cobalt-manganese; and composite oxides of lithium-nickel-cobalt-aluminum, to enable the formation of a battery with excellent output performance, cycle performance and storage performance at 60°C. More preferred is at least one selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _0.33 Mn _0.33 Co _0.33 O ₂ , LiNi _0.5 Mn _{0, 3} Co _0.2 O ₂ , LiNi _0.82 Co _0.15 Al _0.03 O ₂ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ and LiNi _0.90 Mn _0.05 Co _0.05 O ₂ .

[0106] Positive electrode active materials that are composite oxides may be lithium nickel composite oxides, and may be lithium nickel composite oxides represented by the formula (1): Li _y Ni _1-x M _x O ₂ , where x satisfies the condition 0.01≤x≤0.5, y satisfies the condition 0.9≤y≤1.2, and M is a metal atom other than Ni. The positive electrode active material containing Ni in such a large proportion is advantageous in terms of increasing the battery capacity. Even when the positive electrode mixture of the present invention contains a positive electrode active material containing Ni in a large proportion, it is resistant to viscosity increase and can be formed into a positive electrode mixture layer with low resistance as well as a positive electrode mixture layer with excellent adhesion to the current collector. and flexibility and resistant to springback.

[0107] In the formula (1), x is a number satisfying the condition 0.01≤x≤0.5. To make it possible to obtain a battery with a larger capacity, x preferably satisfies the condition 0.05≤x≤0.4, and more preferably satisfies the condition 0.10≤x≤0.3.

[0108] Examples of the metal atom M in formula (1) include V, Ti, Cr, Mn, Fe, Co, Cu, Al, Zn, Mg, Ga, Zr, and Si. Preferred as the metal atom M are transition metals such as V, Ti, Cr, Mn, Fe, Co and Cu, or combinations of any of these transition metals with any other metal such as Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr or Si.

[0109] As lithium nickel composite oxides represented by formula (1), at least one selected from the group consisting of LiNi _0.82 Co _0.15 Al _0.03 O ₂ , LiNi _0.6 Mn _{0 ,2} Co _0.2 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ and LiNi _0.90 Mn _0.05 Co _0.05 O ₂ , and more preferably at least one selected from the group , consisting of LiNi _0.82 Co _0.15 Al _0.03 O ₂ and LiNi _0.8 Mn _0.1 Co _0.1 O ₂ .

[0110] The lithium nickel composite oxide represented by the formula (1) can be used in combination with other positive electrode active material. Specific examples of other positive electrode active material include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiMn _1.8 Al _0.2 O ₄ , Li ₄ Ti ₅ O ₁₂ , LiFePO ₄ , Li ₃ Fe ₂ ( PO ₄ ) ₃ , LiFeP ₂ O ₇ , LiCoPO ₄ , Li _1.2 Fe _0.4 Mn _0.4 O ₂ , LiNiO ₂ and LiNi _0.5 Mn _0.3 Co _0.2 O ₂ .

[0111] The positive electrode active material used may be a material formed from the positive electrode active material as a substrate and another material different in composition from the positive electrode active material and deposited on the surface of the positive electrode active material. Examples of the surface applied material include: oxides such as alumina, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfuric acid salts such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate and aluminum sulfate; and carbonic acid salts such as lithium carbonate, calcium carbonate and magnesium carbonate.

[0112] Such a surface applied material can be applied to the surface of the positive electrode active material by any method, such as: dissolving or suspending the material to be applied in a solvent, impregnating the positive electrode active material with the resulting solution or suspension, and drying the impregnated positive electrode active material; dissolving or suspending the surface coating material precursor in a solvent, impregnating the positive electrode active material with the resulting solution or suspension, and then causing a reaction by a method such as heating; and adding the material to be applied to the positive electrode active material precursor and calcining the material to be applied and the positive electrode active material precursor together.

[0113] The mass amount applied to the surface of the material relative to the active material of the positive electrode is preferably 0.1 ppm ( ^ppm ) or more, more preferably 1 ^ppm or more, and even more preferably 10 ^ppm or more, and preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The presence of the surface applied material can inhibit the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material and increase battery life. If the amount of deposited material is too small, a sufficient effect of its presence cannot be obtained, while if the amount of applied material is too large, the material may interfere with the entry and exit of lithium ions, causing an increase in resistance.

[0114] The shape of the particles used as the positive electrode active material may be the shape of commonly used particles, such as lumpy shape, polygonal shape, spherical shape, ellipsoidal shape, plate shape, needle shape, or columnar shape. Especially preferred are particles composed of secondary particles formed by aggregation of primary particles, wherein the secondary particles are spherical or ellipsoidal. An electrochemical cell generally undergoes swelling and shrinkage of the active material in the electrode during charging and discharging, and therefore, due to the stresses caused by swelling and shrinkage, defects such as breaking of the active material and breaking of a conductive path are likely to occur. Therefore, an active material composed of secondary particles formed by aggregation of primary particles is more preferable than an active material composed of individual primary particles in order to reduce swelling and shrinkage-induced stresses and prevent defects. In addition, spherical or ellipsoidal particles are preferred because the formation of these particles into the electrode leads to a lower degree of orientation of the electrode, and hence less swelling and shrinkage of the electrode during charge and discharge, than the formation of axially oriented particles, such as lamellar ones, into the electrode. particles, and because spherical or ellipsoidal particles are more uniformly mixed with the electrically conductive additive in the manufacture of the electrode.

[0115] The bulk density of the positive electrode active material is usually 1.3 g/cm ³ or more, preferably 1.5 g/cm ³ or more, more preferably 1.6 g/cm ³ or more, and most preferably 1.7 g/cm ³ or more. If the bulk density of the positive electrode active material is less than the lower limit, then the amount of the dispersing medium required to form the positive electrode mixture layer increases, and the necessary amounts of the electrically conductive additive and the binder also increase, which can lead to a limited filling degree of the positive electrode mixture layer with the positive electrode active material. , and hence the limited capacity of the battery. The use of a positive electrode active material with a high bulk density allows the formation of a high-density layer of the positive electrode mixture. A higher bulk density is generally preferred, so an upper limit on bulk density is not specifically indicated. However, if the bulk density is too large, the diffusion rate of lithium ions in the positive electrode mixture layer can be limited by the non-aqueous electrolyte solution, so that the load performance is likely to deteriorate. Thus, the bulk density is usually 2.5 g/cm ³ or less, and preferably 2.4 g/cm ³ or less.

[0116] The bulk density of the positive electrode active material is determined as follows: the sample is passed through a sieve with a mesh size of 300 μm and poured into a 20 cm ³ bulk cell, filling its volume, then using a powder density meter (for example, Tap Denser manufactured by Seishin Enterprise Co., Ltd.) to perform 1000 shakes at a stroke length of 10 mm and determine the density of the sample from the volume and weight of the sample, and the density value thus determined is taken as the bulk density.

[0117] The median particle diameter d50 of the positive electrode active material particles (secondary particle size when the particles are secondary particles formed by aggregation of primary particles) is usually 0.1 µm or more, preferably 0.5 µm or more, more preferably 1 µm or more, and most preferably 3 µm or more, and is usually 20 µm or less, preferably 18 µm or less, more preferably 16 µm or less, and most preferably 15 µm or less. If the median diameter d50 is less than the lower limit, a high bulk density product cannot be obtained. If the median diameter d50 is larger than the upper limit, the following problems may occur: it takes a long time for lithium to diffuse into particles, and therefore battery performance deteriorates; and in the manufacture of a battery positive electrode, namely, when the positive electrode active material, the conductive additive and the binder are mixed in a solvent and the resulting suspension is applied in a thin film, the suspension is viscous. Two or more different positive electrode active materials with different median diameter d50 can be mixed in order to further increase the degree of filling of the positive electrode produced.

[0118] The median diameter d50 in the present invention can be measured using a known instrument for measuring particle size distribution by laser diffraction/scattering. When LA-920 manufactured by HORIBA, LTD. is used as the particle size distribution analyzer, 0.1 wt% aqueous solution of sodium hexametaphosphate is used as the dispersion medium for measurement, the particles are dispersed in this solution by ultrasonic treatment for 5 minutes, followed by measurement with the refractive index set to 1.24.

[0119] When the positive electrode active material particles are secondary particles formed by aggregating the primary particles, the average size of the primary particles is usually 0.01 µm or more, preferably 0.05 µm or more, more preferably 0.08 µm or more, and most preferably 0.1 µm or more, and usually 3 µm or less, preferably 2 µm or less, more preferably 1 µm or less, and most preferably 0.6 µm or less. If the average size of the primary particles exceeds the upper limit, formation of spherical secondary particles is difficult, the powder filling degree may be deteriorated, or the specific surface area may be greatly reduced, so that deterioration in battery performance such as deterioration in output performance is likely. If the average size of the primary particles is less than the lower limit, crystal growth is generally insufficient, so problems such as poor reversibility of charge and discharge may occur. The size of the primary particles is measured by observation with a scanning electron microscope (SEM). Namely, in a photograph taken at a magnification of 10,000 times, 50 primary particles are randomly selected, the length of the longest of the horizontal straight line segments between the side boundaries of each primary particle is determined, and the average value of the lengths thus determined is taken as the average size of the primary particles.

[0120] The BET specific surface area of the positive electrode active material is usually 0.2 m ² /g or more, preferably 0.3 m ² /g or more, and more preferably 0.4 m ² /g or more, and usually is 4.0 m ² /g or less, preferably 2.5 m ² /g or less, and more preferably 1.5 m ² /g or less. If the BET specific surface area is less than the above range, performance of the battery is likely to deteriorate, while if the BET specific surface area is larger than the above range, it is difficult to increase the bulk density and problems with the ease of application of the positive electrode mixture are likely to occur.

[0121] The BET specific surface area is determined as follows using a surface area meter (for example, a fully automatic meter manufactured by Okura Riken Co., Ltd.): the sample is pre-dried in a stream of nitrogen at 150°C for 30 minutes, then the dried sample is measured by a BET nitrogen adsorption gas flow measurement method using a gaseous mixture of nitrogen and helium with the obligatory reduction of the nitrogen pressure to a value of 0.3 relative to atmospheric pressure, and the value thus measured is taken as the BET specific surface area.

[0122] The method used to produce the positive electrode active material is a conventional method for producing an inorganic compound. In particular, various methods for making a spherical or ellipsoidal active material are possible, and examples of these methods include: a method in which a transition metal starting material such as a nitric acid salt or a transition metal salt of sulfuric acid, and optionally another starting material based on another element is dissolved or crushed and dispersed in a solvent such as water, the pH of the solution or dispersion is adjusted with stirring to form and collect a spherical precursor, the collected precursor is dried as needed, then a source of Li such as LiOH, Li ₂ CO ₃ is added to the precursor or LiNO ₃ and the precursor is calcined at high temperature to obtain an active material; a method in which a transition metal starting material such as a nitric acid salt, a sulfuric acid salt, a transition metal hydroxide or oxide, and optionally another starting material based on another element is dissolved or pulverized and dispersed in a solvent such as water, a solution or a dispersion subjected to molding by drying into a spherical or ellipsoidal precursor by, for example, a spray dryer, then a Li source such as LiOH, Li ₂ CO ₃ or LiNO ₃ is added to the precursor, and the precursor is calcined at a high temperature to obtain an active material; and a method in which a transition metal raw material such as a nitric acid salt, a sulfuric acid salt, a transition metal hydroxide or oxide, a Li source such as LiOH, Li ₂ CO ₃ or LiNO ₃ , and optionally another raw material based on another element is dissolved or pulverized and dispersed in a solvent such as water, the solution or dispersion is shaped by drying into a spherical or ellipsoidal precursor by, for example, a spray dryer, and the precursor is calcined at a high temperature to obtain an active material.

[0123] A single positive electrode active material may be used alone, or two or more positive electrode active materials with different compositions or different powder properties may be used in any combination and any proportion.

[0124] Conductive additive

Preferably, the positive electrode mixture of the present invention should not contain any electrical conductive additive other than single-walled carbon nanotubes in order to be able to form a positive electrode with which an electrochemical device exhibiting a higher specific energy can be provided.

In order to be able to form a positive electrode with which an electrochemical device with improved output and cycle performance can be provided, it is preferable that the positive electrode mixture of the present invention further contains an electrical conductive additive other than single wall carbon nanotubes. Examples of the electrical conductive additive include: carbon blacks (carbon black) such as acetylene black and KETJENBLACK; carbon materials such as graphite and graphene; other carbon materials such as carbon fibers, multi-walled carbon nanotubes and carbon nanohorns.

[0125] The content of the electrical conductive additive (excluding single wall carbon nanotubes) in the positive electrode mixture of the present invention is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 up to 1.0 mass parts, per 100 mass parts of the active material of the positive electrode.

[0126] Additive

The positive electrode mixture may also include an additive such as an organic acid or a carboxylic acid to reduce the increase in viscosity of the positive electrode mixture. In particular, it is preferred that the positive electrode mixture contains an organic acid.

[0127] Examples of the organic acid are acrylic acid, formic acid, citric acid, acetic acid, oxalic acid, lactic acid, pyruvic acid, malonic acid, propionic acid, maleic acid, citraconic acid, and butyric acid.

[0128] The additive content of the positive electrode mixture is preferably 0.001 to 5 mass%, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more, and more preferably 3 mass% or less, and even more preferably 2 wt.% or less, relative to the total weight of the binder and the active material of the positive electrode. When the additive content is in the above range, the viscosity increase of the positive electrode mixture can be further reduced.

[0129] The positive electrode mixture may contain anionic surfactants (surfactants), cationic surfactants, nonionic surfactants, methyl cellulose, carboxymethyl cellulose, hydroxypropyl methylcellulose, polyacrylic acid, polymethyl methacrylate, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylonitrile to improve the viscosity stability of the positive electrode mixture.

[0130] The viscosity of the positive electrode mixture is preferably 1,000 to 80,000 mPa s, more preferably 2,000 to 70,000 mPa s, and even more preferably 3,000 to 60,000 mPa s, for easy application of the electrode mixture and easy preparation of the positive mixture layer. electrode of a given thickness. Viscosity is measured using a type B viscometer (LV-DV2T manufactured by Brookfield) with rotor No. LV-4 at 25° C. and 6 rpm.

[0131] The contents of single-wall carbon nanotubes, binder, positive electrode active material, solvent, and optionally contained electrically conductive additive in the positive electrode mixture are selected taking into account the ease of application to the current collector and the quality of thin film formation after drying. The total content of single-walled carbon nanotubes, binder, positive electrode active material and optionally contained electrically conductive additive in the positive electrode mixture is preferably 50 to 90 wt.%, and more preferably 60 to 80 wt.%.

[0132] The positive electrode mixture of the present invention can be prepared by mixing the components. The order of mixing components is not limited. For example, when the electrochemical device composition of the present invention does not contain PVDF, the electrochemical device composition of the present invention and PVDF may be mixed first, after which other components such as the positive electrode active material may be added, or the composition for of the electrochemical device of the present invention and the positive electrode active material, after which other components such as PVDF can be added.

[0133] Positive electrode design

The positive electrode structure of the present invention includes a current collector and a positive electrode mixture layer. The positive electrode mixture layer is formed using the positive electrode mixture described above. The positive electrode mixture layer may be provided on one or both sides of the positive electrode current collector.

[0134] The density of the positive electrode mixture layer is preferably 3.0 to 5.0 g/cm ² , more preferably 3.2 to 5.0 g/cm ² , and even more preferably 3.5 to 5.0 g/cm2 ^. Conventional high-density positive electrode mixture layers may exhibit a thickening (rebound) phenomenon upon heat treatment. Since, in the positive electrode structure of the present invention, the positive electrode mixture layer is formed using the above-described positive electrode mixture, the positive electrode mixture layer is resistant to springback and has excellent flexibility even in the presence of high density.

[0135] The density of the positive electrode mixture layer can be calculated from the mass and volume of the positive electrode mixture layer.

[0136] The thickness of the positive electrode mixture layer is preferably 20 µm or more, more preferably 45 µm or more, even more preferably 70 µm or more, particularly preferably 75 µm or more, and most preferably 80 µm or more, and preferably 170 µm or less, and more preferably 150 µm or less. The positive electrode mixture layer formed using the positive electrode mixture of the present invention is excellent in flexibility even when it is relatively thick.

[0137] The thickness of the positive electrode mixture layer can be measured with a micrometer. In the present invention, when the positive electrode mixture layer is provided on both sides of the positive electrode current collector, the thickness of the positive electrode mixture layer refers to the thickness of the positive electrode mixture layer on each side of the positive electrode current collector.

[0138] The content of positive electrode active material in the positive electrode mixture layer is preferably 96.0 to 99 mass%, more preferably 96.5 to 98.9 mass%, and even more preferably 97.0 to 98, 8 wt.%, relative to the weight of the positive electrode mixture layer, to enable further reduction in the increase in the viscosity of the positive electrode mixture and the possibility of forming a positive electrode mixture layer with lower resistance, more excellent adhesion to the current collector and flexibility, and more resistant to elastic return.

[0139] Conductor

The positive electrode design of the present invention includes a current collector. Examples of the current collector constituting the positive electrode of the present invention are a foil or mesh made of metals such as iron, stainless steel, copper, aluminium, nickel and titanium, of which aluminum foil is preferred.

[0140] Method for manufacturing a positive electrode structure

The positive electrode structure of the present invention can be suitably produced by a manufacturing method comprising the following steps: preparing a positive electrode mixture containing at least single-walled carbon nanotubes, a binder, a solvent, and a positive electrode active material; and apply the resulting positive electrode mixture to the current collector. After applying the positive electrode mixture, the coating of the applied positive electrode mixture can be dried and the dried coating can be pressed.

[0141] The amount of the positive electrode mixture applied to the current collector is preferably 20 mg/cm ² or more, more preferably 22 mg/cm ² or more, even more preferably 25 mg/cm ² or more, particularly preferably 28 mg/cm ² or more so as to be able to achieve an increased capacity of the lithium ion battery, and preferably 60 mg/cm ² or less, more preferably 50 mg/cm ² or less to prevent cracking of the positive electrode mixture layer. The applied amount of the positive electrode mixture corresponds to the dry weight of the positive electrode mixture per unit area. Even when a relatively thick positive electrode mixture layer is formed by applying a relatively large amount of the positive electrode mixture of the present invention to the current collector, the resulting positive electrode mixture layer has great flexibility. Even when a high-density positive electrode mixture layer is formed by depositing a relatively large amount of the positive electrode mixture of the present invention on the current collector and subjecting it to subsequent high-pressure pressing, the resulting positive electrode mixture layer is resistant to springback.

[0142] Battery

The present invention also provides a battery including the positive electrode structure described above. It is preferable that the battery of the present invention, in addition to the positive electrode structure described above, further includes a negative electrode structure and a non-aqueous electrolyte solution. With the above-described positive electrode structure, the battery of the present invention is excellent in output performance, cycle performance, and storage performance at 60°C.

[0143] The non-aqueous electrolyte solution is not limited, and one or more known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used. The electrolyte used may also be any of the commonly known electrolytes, and electrolytes such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and cesium carbonate can be used.

[0144] The positive electrode structure of the present invention has excellent flexibility and sufficient adhesion between the positive electrode mixture layer and the current collector, thus being suitable for use as a positive electrode structure for a coiled battery. The battery of the present invention may be a coiled battery.

[0145] The positive electrode structure of the present invention is suitable for use in batteries with a non-aqueous electrolyte solution, in particular, not only in the above-described lithium-ion batteries that use liquid electrolytes, but also in lithium polymer electrolyte batteries. The positive electrode design is also suitable for electrical double layer capacitor applications.

[0146] While various embodiments of the invention have been described above, it should be understood that various changes in form and detail are possible without departing from the spirit and scope of the invention as claimed herein or hereinafter.

EXAMPLES

[0147] Hereinafter, embodiments of the present invention will be described by way of example. The present invention is not limited to these examples only.

[0148] Various parameters regarding the examples were measured by the methods described below.

[0149] <Features of the composition of the fluorine-containing copolymer>

(Ratio between VDF unit and TFE unit)

The ratio between the VDF unit and the TFE unit was measured by ¹⁹ F-NMR spectroscopy using a solution of a fluorine-containing copolymer in DMF-d ₇ and an NMR analyzer (VNS400MHz manufactured by Agilent Technologies Inc.).

[0150] The area of the following peaks (A, B, C and D) was determined by ¹⁹ F-NMR spectroscopy and the ratio between the VDF unit and the TFE unit was calculated.

A: peak area from -86 ppm to -98 ppm

B: peak area from -105 ppm to -118 ppm

C: peak area -119 ppm to -122 ppm

D: peak area -122ppm to -126ppm

VDF Unit Proportion: (4A+2B)/(4A+3B+2C+2D) × 100 [mole%]

TFE unit proportion: (B+2C+2D)/(4A+3B+2C+2D) × 100 [mole%]

[0151] (Ratio between VDF unit and HFP unit and ratio between VDF unit and PFMVE unit)

The ratio between the VDF unit and the HFP unit and the ratio between the VDF unit and the PFMVE unit were measured by ¹⁹ F-NMR spectroscopy of a solution of the fluorine-containing copolymer in DMF-d ₇ using an NMR analyzer (VNS400MHz manufactured by Agilent Technologies Inc.).

[0152] (Unit content of polar group-containing monomer)

The unit content of the polar group-containing monomer (including the 4-pentenoic acid unit, the 3-butenoic acid unit, and the acrylic acid unit) in the fluorine-containing copolymer was measured by acid-base titration of the carboxyl group. About 0.5 g of the fluorine-containing copolymer was dissolved in acetone at a temperature of 70-80°C. 5 ml of water was added to prevent the fluorine-containing copolymer from solidifying. The titration was carried out with an aqueous solution of NaOH with a concentration of 0.1 N until neutral acidity was reached, passing through neutrality at about -270 mV. Based on the measured acid equivalent, the molar amount of the unit of the polar group-containing monomer contained in 1 g of the fluorine-containing copolymer was determined to calculate the unit content of the polar group-containing monomer.

[0153] <PVDF composition features>

(Unit content of polar group-containing monomer)

The unit content of a polar group-containing monomer (including an acrylic acid unit, a maleic acid unit, and a 3-butenoic acid unit) in PVDF was measured by acid-base titration of the carboxylic acid group. Approximately 0.5 g of PVDF was dissolved in acetone at a temperature of 70-80°C. 5 ml of water was added to prevent the PVDF from solidifying. The titration was carried out with an aqueous solution of NaOH with a concentration of 0.1 N until neutral acidity was reached, passing through neutrality at about -270 mV. Based on the measurement result, namely the measured acid equivalent, the molar amount of the unit of the polar group-containing monomer contained in 1 g of PVDF was determined to calculate the unit content of the polar group-containing monomer.

[0154] <Weight Average Molecular Weight>

The measurement was carried out by gel permeation chromatography (GPC). The weight average molecular weight was calculated from measurements obtained using AS-8010, CO-8020 and columns (three GMHHR-H in series) manufactured by Tosoh Corporation and RID-10A manufactured by Shimadzu Corporation, feeding dimethylformamide (DMF) as a solvent with flow rate of 1.0 ml/min (reference: polystyrene).

[0155] <Melting Point>

Using a differential scanning calorimetry (DSC) instrument, the melting point was determined to be the temperature at which the heat of fusion curve obtained by raising the temperature from 30°C to 220°C at a rate of 10°C/min and then lowering to 30°C With at a rate of 10°C/min and rising again to 220°C at a rate of 10°C/min, there is a maximum.

[0156] <Dynamic Modulus (E')>

The dynamic elastic modulus (E') is a value determined by analyzing the dynamic viscoelasticity at 30°C or 60°C, which was measured using the dynamic viscoelasticity analyzer DVA 220 manufactured by IT keisoku seigyo sya and a sample 30 mm long, 5 mm wide and 50-100 µm thick in tension mode using a distance between supports of 20 mm at a temperature increase rate of 2°C/min from -30°C to 160°C at 1 Hz.

A solution of a fluorine-containing copolymer obtained by dissolving a fluorine-containing copolymer in N-methyl-2-pyrrolidone (NMP) so that the concentration is 10-20 mass% was poured onto a glass dish, dried at 100°C for 12 hours, then dried in vacuum at 100°C for 12 hours, and the resulting film with a thickness of 50-100 μm was cut into samples of a length of 30 mm and a width of 5 mm in order to prepare samples used for measurements.

[0157] <Viscosity>

The viscosity of the composition was measured using a type B viscometer (LV-DV2T manufactured by Brookfield) with a rotor No. SC4-21 at a temperature of 25°C and a rotation speed of 20 rpm, and the viscosity was taken as the value measured 10 minutes after the start of the measurement. The viscosity of the positive electrode mixture was measured using a type B viscometer (LV-DV2T manufactured by Brookfield) with rotor No. LV-4 at a temperature of 25°C and a rotation speed of 6 rpm, and the viscosity was taken as the value measured 10 minutes after the start of the measurement. .

[0158] <Positive electrode mixture stability>

The viscosity (ƞ0) of the freshly prepared mixture and the viscosity (ƞn) of the mixture 24 hours after preparation were measured and the quantitative change in viscosity (Xn) was determined by the following equation:

Xn=ƞn/ƞ0 × 100 [%].

[0159] Based on the obtained quantitative change in viscosity (Xn), evaluation was carried out in accordance with the following criteria.

Good: Xn is 200% or less.

Moderate: Xn is greater than 200% and less than or equal to 300%.

Bad: Xn is greater than 300%.

By using a positive electrode mixture exhibiting a quantitative change in viscosity (Xn) of 200% or less, a positive electrode with good performance can be produced. By using a positive electrode mixture exhibiting a quantitative change in viscosity (Xn) greater than 200% and less than or equal to 300%, there is such a disadvantage that a positive electrode mixture layer with a smooth surface cannot be formed. A positive electrode mixture exhibiting a quantitative change in viscosity (Xn) of more than 300% is difficult to apply.

[0160] <Density of positive electrode mixture layer>

The double-sided coated positive electrode structure obtained by pressing using a roller press machine was cut to prepare a test sample, and the weight and area of the test sample were measured. The density of the positive electrode mixture layer was calculated from the masses of the test sample and the positive electrode current collector, the area of the test sample, and the thickness of the positive electrode mixture layer, which was measured with a micrometer.

[0161] <Coating resistance>

The positive electrode mixture was applied to the PET film with a squeegee and then dried. The surface resistance of the resulting coating was measured. A Loresta-GP instrument (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used for measurement (measurement was carried out in accordance with JIS K 7194).

[0162] <Adhesion between positive electrode mixture layer and current collector>

The single-sided coated positive electrode structure obtained by pressing using a roller press machine was cut to prepare a test specimen of 1.2 cm × 7.0 cm. current collector of the positive electrode. The tape was pulled at a 90 degree angle at a speed of 100 mm/minute and the force (N/cm) was measured using an Autograph. The torque element used in the Autograph was characterized by a maximum load of 50 N.

[0163] <Positive Electrode Flexibility>

The double-sided coated positive electrode structure obtained by pressing using a roller press machine was cut to prepare a 2 cm × 20 cm test specimen.

A cylindrical mandrel bending tester (manufactured by Allgood Co., Ltd.) was used. A mandrel with a diameter of ∅3 mm was installed in the device, to which the test sample was attached, clamping it between the brackets of the device body. After that, the roller was moved closer to the test sample and the handle was turned 180° at a uniform speed in 1-2 seconds. Then, the positive electrode mixture layer was visually examined and evaluated according to the following criteria.

Good: no cracking detected.

Moderate: Cracking detected, but positive electrode mixture layer fracture not detected.

Bad: The positive electrode mixture layer has broken.

[0164] <Spring Return>

A double-sided coated positive electrode structure obtained by pressing using a roller press machine was punched with a hand punch with a diameter size of 13 mm to prepare a test sample, and the weight and area of the test sample were measured. The density of the positive electrode mixture layer was calculated from the masses of the test sample and the positive electrode current collector, the area of the test sample, and the thickness of the positive electrode mixture layer, which was measured with a micrometer, and the calculated density was taken as the density (D ₀ ). The same test sample was dried in a vacuum dryer at 120° C. for 12 hours, after which the density of the positive electrode mixture layer was calculated in the same manner as described above. The calculated density was designated (D _n ). From the obtained values, the springback coefficient (Y _n ) was determined using the following equation. A higher springback ratio is preferable because it means that the positive electrode mixture layer undergoes less decrease in density during heat treatment.

Y _n \u003d D _n / D ₀ × 100 (%)

[0165] The following polymers were used in the examples and comparative examples.

[0166] <Fluorine-containing copolymer (A)>

(A-1): fluorine-containing copolymer containing a VDF unit and a TFE unit

VDF/TFE=81/19 (mole%)

Weight average molecular weight: 1230000

Melting point: 128°C

Dynamic modulus of elasticity at 30°C: 510 MPa

Dynamic modulus of elasticity at 60°C: 270 MPa

(A-2): a fluorine-containing copolymer containing a VDF unit, a TFE unit, and a 4-pentenoic acid unit

VDF/TFE=62/38 (mole%)

Content of 4-pentenoic acid unit: 0.5 mol.%

Weight average molecular weight: 930000

Melting point: 148°C

Dynamic modulus of elasticity at 30°C: 450 MPa

Dynamic modulus of elasticity at 60°С: 190 MPa

(A-3): a fluorine-containing copolymer containing a VDF unit and an HFP unit

VDF/HFP=95/5 (mole%)

Weight average molecular weight: 700000

Melting point: 135°C

Dynamic modulus of elasticity at 30°C: 320 MPa

Dynamic modulus of elasticity at 60°С: 155 MPa

(A-4): a fluorine-containing copolymer containing a VDF unit, a PFMVE unit, and an acrylic acid unit

VDF/PFMVE/acrylic acid=97.1/1.9/1.0 (mole%)

Weight average molecular weight: 1070000

Melting point: 147°C

[0167] <PVDF(B)>

(B-1): VDF homopolymer

Weight average molecular weight: 780000

Melting point: 162°C

(B-2): PVDF containing an acrylic acid unit

Acrylic acid unit content: 1.0 mol%

Weight average molecular weight: 1100000

Melting point: 161°C

(B-3): VDF homopolymer

Weight average molecular weight: 1820000

Melting point: 167°C

[0168] In the Examples and Comparative Examples, the following positive electrode active materials were used.

NMC811: LiNi _0.8 Mn _0.1 Co _0.1 O ₂

NCA: LiNi _0.82 Co _0.15 Al _0.03 O ₂

NMC622: LiNi _0.6 Mn _0.2 Co _0.2 O ₂

LCO: LiCoO ₂

[0169] In the Examples and Comparative Examples, the following single wall carbon nanotubes were used.

Single wall carbon nanotubes (trade name: "TUBALL BATT SWCNT" manufactured by OCSiAl)

Average outer diameter: 1.6±0.4 nm

Length: 5 µm or more

Average G/D ratio: 86.5±7.1

[0170] In the examples and comparative examples, the following multi-walled carbon nanotubes were used.

Average outside diameter: 11nm±4nm

Length: 5 µm or more

Average G/D ratio: 1.3

[0171] Example 1

(Preparation of composition)

0.4 kg of single-walled carbon nanotubes, 98.6 kg of N-methyl-2-pyrrolidone (NMP) and 1 kg of fluorocopolymer (A-1) were mixed in a 100-liter tank using an overhead stirrer with a rotation speed of 75 rpm and a homogenizer with an output power of 30 kW. The amount of energy supplied for homogeneous mixing was 0.2 kWh per kilogram of mixture. The resulting mixture was processed in a high pressure homogenizer (the mixture was passed through the homogenizer 10 times at a pressure of 700 bar). After homogenization, the slurry was collected and filtered through a 50 µm filter to obtain 100 kg of a composition containing 0.4 wt.% of single-walled carbon nanotubes. The optical density (light absorption of the composition containing 0.001 wt.% single-walled carbon nanotubes at a wavelength of 500 nm) was 0.51 optical units, and the viscosity was 750 mPa s, and these parameters indicated that the required quality of the composition for electrochemical device has been reached.

[0172] (Positive electrode mixture preparation)

The resulting composition was placed in a vessel with a volume of 1 l so that the content of single-walled carbon nanotubes corresponded to that shown in table 1. After that, the fluorine-containing copolymer (A-1) dissolved in NMP and PVDF (B-1) dissolved in NMP were added, and mixed with the composition so that the weight ratio of the fluorine-containing copolymer (A)/PVDF (B-1) and the binder content were as given in Table 2. Thus, a solution was obtained. The resulting solution, NMC811, and acetylene black were mixed with a stirrer to obtain a liquid mixture. Added NMP and mixed with the resulting liquid mixture to prepare a mixture of positive electrode with a solids concentration of 71 wt.%. Signs of the composition of the prepared positive electrode mixture are shown in Table 1.

[0173] (Production of the positive electrode structure)

The resulting positive electrode mixture was evenly applied to one side of the positive electrode current collector (aluminum foil 20 μm thick) and dried at 120° C. for 60 minutes until the NMP completely evaporated. Thereafter, pressing was carried out by applying a pressure of 10 tons using a roller pressing machine, and thus a positive electrode structure was made. The amount of positive electrode mixture deposited was 22.5 mg/cm ² and the density of the positive electrode mixture layer was 3.6 g/cm ³ .

In addition, the resulting positive electrode mixture was evenly applied to both sides of the positive electrode current collector (aluminum foil 20 μm thick) and dried at 120° C. for 60 minutes until the NMP completely evaporated. Thereafter, pressing was carried out by applying a pressure of 10 tons using a roller pressing machine, and thus a positive electrode structure was made. The amount of positive electrode mixture deposited on each side was 28.5 mg/cm ² and the density of the positive electrode mixture layer was 3.6 g/cm ³ .

The resulting positive electrode design was evaluated by the methods described above. The results are shown in table 1.

[0174] (Manufacture of the negative electrode structure)

Using artificial graphite powder as the negative electrode active material, sodium carboxymethyl cellulose aqueous emulsion (sodium carboxymethyl cellulose concentration 1 wt.%) as a thickener, and styrene-butadiene rubber aqueous dispersion (styrene-butadiene rubber concentration 50 wt.%) as a binder , the active material, the thickener and the binder were mixed in a solids content ratio of 97.6/1.2/1.2 (wt %) in an aqueous solvent as a slurry to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was evenly applied to a 20 µm thick copper foil. After it was dried, compression molding was performed with a pressing machine, and thus a negative electrode was produced.

[0175] (Manufacture of a lithium-ion battery)

The positive electrode (positive electrode structure) and the negative electrode prepared in the above manner and the polyethylene separator were stacked on top of each other in the order of the negative electrode, the separator and the positive electrode to form a battery cell.

This battery cell was inserted into a bag made of a laminated film coated on both sides with an aluminum sheet (40 µm thick) with a resin layer, with the positive electrode and negative electrode terminals protruding. Then, the bag was filled with an electrolytic solution (prepared by dissolving LiPF ₆ at a concentration of 1 mol/liter in a solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate in a 3/7 volume ratio) in an amount of 1.2 g, and sealed under vacuum to obtain a sheet-shaped lithium ion battery.

[0176] <Output characteristic>

The storage battery prepared as described above was subjected to constant current and constant voltage charge (hereinafter referred to as CC/CV charge) (shutdown at 0.1C) to 4.2V at a current corresponding to 0.2C at 25°C, then discharged to 3 V at a constant current of 0.2C. This process was considered as one cycle. The initial discharge capacity was determined from the discharge capacity of the third cycle. In this case, 1.0C means the amount of current required to discharge the reference battery capacity in one hour. For example, 0.2C indicates the amount of current in 1/5 of the capacitance. After assessing the initial discharge capacity, the battery was charged at 25°C and a constant current of 0.2C, then discharged to 3 V at a constant current of 5.0C. The ratio of the discharge capacity at 5.0C to the initial discharge capacity was determined, which was considered as the ratio of the discharge capacity at 5.0C (%).

(discharge capacity at 5.0C)/(initial discharge capacity at 0.2C)×100 = Discharge capacity ratio at 5.0C (%)

The results calculated by taking the value in Comparative Example 1 as 1 are shown in Table 1 and Table 3.

[0177] <Cyclic response>

The storage battery prepared as described above was subjected to a CC/CV charge (shutdown at 0.1C) to 4.2V at a current corresponding to 1.0C at 25°C, then discharged to 3V at a constant current of 1.0C. This process was considered as one cycle. According to the discharge capacity, the initial discharge capacity was determined. This cycle was repeated again and the discharge capacity was measured after 300 cycles. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity was determined, which was considered as the capacity retention ratio (%).

(Discharge capacity after 300 cycles)/(Initial discharge capacity at 1.0C)×100 = Capacity retention ratio (%)

The results calculated by taking the value in Comparative Example 1 as 1 are shown in Table 1 and Table 3.

[0178] <Storage specification at 60°C>

The battery prepared as described above was subjected to a CC/CV charge (shutdown at 0.1C) again to 4.2V, then stored at a temperature such as 60°C for 7 days. The battery was then discharged to 3 V at 0.2°C and 25°C, and the remaining capacity was measured after high temperature storage. Thereby, the ratio of the remaining capacity to the initial discharge capacity was determined, which was considered as the storage capacity retention ratio (%).

(Remaining capacity)/(Initial discharge capacity)×100 = Storage capacity retention ratio (%)

The results calculated by taking the value in Comparative Example 1 as 1 are shown in Table 1 and Table 3.

[0179] Examples 2-11

The positive electrode mixture was prepared in the same manner as in Example 1, except that the types of fluorine-containing copolymer (A) and PVDF (B), composition characteristics of the binder, and composition characteristics of the positive electrode mixture were changed as shown in Table 1. the positive electrode mixture was used and applied in the same amount as in Example 1 to prepare a positive electrode structure comprising a positive electrode mixture layer of the same density as in Example 1. The positive electrode structure was evaluated in the same manner as in Example 1. 1. The results are shown in table 1.

[0180] Comparative Example 1

(Preparation of positive electrode mixture)

The fluorine-containing copolymer (A-1) and PVDF (B-1) were dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a solution containing binders in a mass ratio of (fluorine-containing copolymer (A-1)/PVDF (B-1 )) shown in Table 1. The resulting solution, NMC811, and acetylene black were mixed with a stirrer to obtain a liquid mixture. More NMP was added and mixed with the resulting liquid mixture to prepare a positive electrode mixture with a solids concentration of 71% by weight. Signs of the composition of the resulting positive electrode mixture are shown in Table 1.

[0181] (Production of the positive electrode structure)

The positive electrode structure was made in the same manner as in Example 1, except that the positive electrode mixture obtained above was used. The positive electrode design was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0182] Comparative Example 2

A positive electrode mixture was prepared and a positive electrode structure was made in the same manner as in Comparative Example 1, except that PVDF (B-1) was used alone instead of the combination of fluorine-containing copolymer (A-1) and PVDF (B-1). The positive electrode design was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0183] Table 1

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Compar. example 1 Compar. example 2 Signs of the composition of the composition Fluorine-containing copolymer (A) A-1 A-1 A-1 A-2 A-3 A-1 A-1 A-2 A-2 A-1 A-1 n/a n/a The content of fluorine-containing copolymer (A) wt% 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 n/a n/a Content of single-walled carbon nanotubes wt% 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 n/a n/a Composition viscosity mPa s 750 750 750 930 710 750 750 930 930 750 750 n/a n/a Signs of the composition of the binder in the positive electrode mixture Fluorine-containing copolymer (A) A-1 A-1 A-1 A-2 A-3 A-1 A-1 A-2 A-2 A-1 A-1 A-1 n/a PVDF (B) IN 1 IN 1 IN 2 IN 2 IN 1 IN 1 n/a n/a IN 1 IN 3 IN 1 IN 1 IN 1 Mass ratio (fluorine-containing copolymer (A)/PVDF (B)) wt% 20/80 15/85 20/80 20/80 10/90 20/80 100/0 100/0 20/80 35/65 20/80 20/80 0/100 Signs of positive electrode mixture composition Positive electrode active material NMS 811 NMC 811 NMC 811 NMS 811 NMC 811 NMC 811 NMS 811 NMS 811 NMC 811 NMC 811 NMS 811 NMC 811 NMC 811 Positive electrode active material content parts one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred Acetylene black content parts 1.40 1.45 1.40 1.45 1.45 1.45 1.40 1.40 0.41 0.41 0 1.50 1.50 Content of single-walled carbon nanotubes parts 0.10 0.05 0.10 0.05 0.05 0.05 0.10 0.10 0.08 0.08 0.08 0 0 Binder content parts 1.5 1.5 1.0 1.5 1.5 0.8 1.5 1.5 1.0 1.0 1.0 1.5 1.5 Positive Electrode Design Properties Coating resistance ohm cm 2.5 4.6 3.3 4.6 4.0 3.6 9.8 10.3 2.2 3.3 3.0 43.0 40.5 Adhesion between positive electrode mixture layer and current collector N/cm 0.36 0.15 0.58 0.30 0.10 0.13 0.14 0.49 0.25 0.14 0.21 0.04 0.12 Flexibility of the positive electrode ∅3 mm Good Good Good Good Good Good Good Good Good Good Good Good bad Spring return % 98.9 98.4 98.9 98.9 98.6 98.4 98.5 98.9 98.7 98.5 98.5 94.6 94.3 Battery specifications Output characteristic: Discharge capacity ratio (5.0C/0.2C) % 3.67 2.79 3.50 2.76 2.78 2.72 3.33 3.44 3.19 3.22 2.67 1.00 0.97 Cyclic characteristic: capacity retention ratio (300 cycles) % 1.44 1.41 1.46 1.40 1.37 1.36 1.41 1.41 1.44 1.44 1.39 1.00 0.97 Storage characteristic at 60°C: storage capacity retention ratio (7 days) % 1.19 1.14 1.20 1.12 1.14 1.14 1.20 1.21 1.20 1.21 1.18 1.00 0.96

n/a - not applicable.

[0184] The results presented in Table 1 for examples demonstrated that the use of single-walled carbon nanotubes and a special binder allows us to offer a positive electrode design that exhibits sufficiently low coating resistance, excellent flexibility and resistance to springback, while guaranteeing sufficient adhesion between the mixture layer positive electrode and current lead.

[0185] For example, in Example 2, where single-wall carbon nanotubes were used in relatively small amounts, the use of single-wall carbon nanotubes in combination with a specific binder gave a sufficiently low coating resistance and, at the same time, provided both strong adhesion between the mixture layer of the positive electrode and the current collector and the high flexibility of the positive electrode design and sufficiently prevented the elastic return of the mixture layer of the positive electrode.

In Example 6, although the amount of binder used was less than in Comparative Example 2, the use of single-wall carbon nanotubes in combination with a specific binder gave a sufficiently low coating resistance and, at the same time, provided both strong adhesion between the positive electrode mixture layer and the current collector, and high flexibility of the design of the positive electrode and sufficiently prevented the elastic return of the mixture layer of the positive electrode.

As the results of Comparative Example 2 show, when single-walled carbon nanotubes and a specific binder are not used, the resulting positive electrode structure exhibits high coating resistance, has poor flexibility, and exhibits significant rebound, although adhesion between the positive electrode mixture layer and the current collector may be sufficient.

[0186] In addition, the results presented in Table 1 for examples demonstrated that a lithium-ion battery including a positive electrode structure obtained using a composition containing single-walled carbon nanotubes and a specific binder has excellent output performance, cycling performance, and storage characteristics at 60°C.

[0187] As the results of Comparative Example 1 show, when a specific binder is used but single-walled carbon nanotubes are not used, not only is the coating resistance high, but strong adhesion between the positive electrode mixture layer and the current collector and high design flexibility cannot be achieved at the same time. positive electrode, resulting in the design of the positive electrode is characterized by a significant elastic return. In addition, a lithium ion battery including such a positive electrode structure did not have sufficient output performance, cycle performance, and storage performance at 60°C.

[0188] Example 12

The composition prepared in Example 1 (composition containing 0.4 wt.% single wall carbon nanotubes) was placed in a vessel with a volume of 1 l, so that the content of single walled carbon nanotubes corresponded to that shown in table 2. After that, a fluorine-containing copolymer (A-1) was added, dissolved in NMP, and PVDF (B-1) dissolved in NMP, and mixed with the composition so that the mass ratio of the fluorine-containing copolymer (A)/PVDF (B) and the content of the binder were as shown in Table 2. Thus, a solution was obtained. The resulting solution, NCA and acetylene black were mixed with a stirrer to obtain a liquid mixture. Added NMP and mixed with the resulting liquid mixture, obtaining a positive electrode mixture with a solids concentration of 71 wt.%. The characteristics of the composition of the obtained positive electrode mixture are shown in Table 2. The stability of the obtained positive electrode mixture was evaluated by the method described above. The result is shown in table 2.

[0189] Example 13

The positive electrode mixture was prepared in the same manner as in Example 12, except that the composition prepared in Example 4 (a composition containing 0.4 mass% of single-walled carbon nanotubes) was used, and that the types of fluorine-containing copolymer (A) and PVDF (B) and the characteristics of the composition of the positive electrode mixture were changed as shown in Table 2. The characteristics of the composition of the obtained mixture of the positive electrode are shown in Table 2. The stability of the obtained mixture of the positive electrode was evaluated by the method described above. The result is shown in table 2.

[0190] Comparative Example 3

The positive electrode mixture was prepared in the same manner as in Comparative Example 2, except that the positive electrode active material was changed to NCA. The characteristics of the composition of the obtained positive electrode mixture are shown in Table 2. The stability of the obtained positive electrode mixture was evaluated by the method described above. The result is shown in table 2.

[0191] Table 2

Example 12 Example 13 Compar. example 3 Signs of the composition of the composition Fluorine-containing copolymer (A) A-1 A-2 - The content of fluorine-containing copolymer (A) wt% 1.0 1.0 - Content of single-walled carbon nanotubes wt% 0.4 0.4 - Composition viscosity mPa s 750 930 - Signs of the composition of the binder in the positive electrode mixture Fluorine-containing copolymer (A) A-1 A-2 n/a PVDF(B) IN 1 IN 1 IN 1 Mass ratio (fluorine-containing copolymer (A)/PVDF (B)) wt% 20/80 30/70 0/100 Signs of positive electrode mixture composition Positive electrode active material NSA NCA NCA Positive electrode active material content parts one hundred one hundred one hundred Acetylene black content parts 1.40 1.40 1.40 Content of single-walled carbon nanotubes parts 0.10 0.10 0.10 Binder content parts 1.5 1.5 1.5 Positive electrode mixture properties Viscosity of freshly mixed positive electrode mPa s 12200 14200 18000 Positive electrode mixture stability % Good Good bad

[0192] Examples 14-21

The positive electrode mixture was prepared in the same manner as in Example 1, except that the types of fluorine-containing copolymer (A) and PVDF (B), types of positive electrode active material, characteristics of the binder composition, characteristics of the composition of the positive electrode mixture, and viscosity were changed as as shown in Table 3. The obtained positive electrode mixture was used, and the positive electrode mixture was applied in the same amount as in Example 1, in order to manufacture a positive electrode structure including a positive electrode mixture layer of the same density, and evaluation was carried out in the same manner, as in example 1. The results are presented in table 3.

[0193] Comparative Examples 4-7

The positive electrode mixture was prepared and the positive electrode structure was fabricated in the same manner as in Comparative Example 1, except that the types of positive electrode active material, characteristics of the binder composition, characteristics of the composition of the positive electrode mixture, and viscosity were changed as shown in Table 3 The positive electrode design was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0194] Table 3

Table 3

Example 14 Example 15 Example 16 Example 17 Example 18 Example 19 Example 20 Example 21 Compar. example 4 Compar. example 5 Compar. example 7 Compar. example 7 Signs of the composition of the composition Fluorine-containing copolymer (A) A-4 A-1 A-1 A-1 A-1 A-1 A-1 A-1 - - - - The content of fluorine-containing copolymer (A) wt% 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.00 - - - - PVDF (B) - - - - - - - IN 3 - - - - PVDF content (B) wt% - - - - - - - 4.00 - - - - Content of single-walled carbon nanotubes wt% 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.4 - - - - Composition viscosity mPa s 1320 1440 1440 1440 1440 1440 1440 1980 - - - - Signs of the composition of the binder in the positive electrode mixture Fluorine-containing copolymer (A) A-4 A-1 A-1 A-1 A-1 A-1 A-1 A-1 A-1 A-1 A-1 A-1 PVDF (B) IN 3 IN 3 IN 3 IN 3 IN 3 IN 3 IN 3 IN 3 IN 1 IN 1 IN 1 IN 1 Mass ratio (fluorine-containing copolymer (A)/PVDF (B)) % 30/70 28/72 22/78 20/80 22/78 28/72 28/72 20/80 20/80 20/80 20/80 20/80 Signs of positive electrode mixture composition Positive electrode active material NMC622 NMC622 NMC622 NMC622 NMC622 LCO LCO NMC622 NMC622 LCO NMC622 NMC622 Positive electrode active material content parts one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred one hundred Acetylene black content parts 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 1.50 1.50 0.41 0.41 Content of single-walled carbon nanotubes parts 0.04 0.08 0.06 0.04 0.02 0.08 0.04 0.08 0 0 0 0 Content of multi-walled carbon nanotubes parts 0 0 0 0 0.41 0 0 0 0 0 0.08 0.41 Binder content parts 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.5 1.5 1.0 1.0 Positive Electrode Construction Properties Coating resistance ohm cm 3.8 3.2 3.3 8.8 4.6 3.8 9.1 3.0 43.0 40.5 120.0 15.0 Adhesion between positive electrode mixture layer and current collector N/cm 0.22 0.20 0.18 0.15 0.14 0.18 0.14 0.20 0.04 0.09 0.08 0.14 Flexibility of the positive electrode ∅3 mm Good Good Good Good Good Good Good Good Good Good Good Good Spring return % 98.2 98.9 98.7 98.6 98.8 98.6 98.4 98.8 94.6 94.3 98.5 98.5 Battery specifications Output characteristic: Discharge capacity ratio (5.0C/0.2C) % 3.00 3.42 3.34 3.11 2.89 3.11 2.67 3.56 1.11 1.11 1.11 1.78 Cyclic characteristic: capacity retention ratio (300 cycles) % 1.41 1.46 1.46 1.46 1.41 1.47 1.44 1.47 1.02 0.10 1.05 1.27 Storage characteristic at 60°C: storage capacity retention ratio (7 days) % 1.12 1.19 1.18 1.17 1.16 1.16 1.16 1.19 1.10 1.01 1.07 1.11

[0195] The results shown in Table 3 for examples demonstrated that by changing the type of positive electrode active material, a positive electrode structure having sufficiently low coating resistance, excellent flexibility and springback resistance can be obtained, while ensuring sufficient adhesion between the layer. mixture of positive electrode and current collector. In addition, it has been demonstrated that the lithium ion battery including the obtained positive electrode structure is excellent in output performance, cycle performance, and storage performance at 60°C.

Moreover, the results presented in Table 1 and Table 3 for examples demonstrated that by using single-walled carbon nanotubes and a specific binder, even when the number of single-walled carbon nanotubes is small, the desired effects can be sufficiently achieved, while using multi-walled carbon nanotubes. of nanotubes, sufficient adhesion and sufficiently low coating resistance cannot be obtained, and a lithium-ion battery including such a positive electrode design is unable to exhibit sufficient output performance, cycle performance, and storage performance at 60°C (Comparative Example 6). In addition, when the number of multi-walled carbon nanotubes is increased, a sufficiently low coating resistance could not be obtained, and a lithium ion battery having a sufficient output characteristic could not be produced (Comparative Example 7).

Claims (15)

1. A composition for an electrochemical device, including single-walled carbon nanotubes, a binder and a solvent, wherein the binder contains a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit other than the vinylidene fluoride unit, and the content of the vinylidene fluoride unit in the fluorine-containing copolymer is 50.0 mol.% or more relative to the total number of monomeric units, and wherein the solvent is at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and β-alkoxypropionamides. 2. The electrochemical device composition of claim 1, wherein the average outer diameter of the single-wall carbon nanotubes is 2.5 nm or less. 3. An electrochemical device composition according to claim 1 or 2, wherein the average G/D ratio of single walled carbon nanotubes is 2 or more. 4. Composition for an electrochemical device according to any one of paragraphs. 1-3, in which the content of the fluorinated monomer unit in the fluorine-containing copolymer is 1.0 mol.% or more relative to the total number of monomer units. 5. Composition for an electrochemical device according to any one of paragraphs. 1-4, wherein the fluorinated monomer unit is at least one selected from the group consisting of a tetrafluoroethylene unit, a chlorotrifluoroethylene unit, a fluoroalkyl vinyl ether unit, and a hexafluoropropylene unit. 6. Composition for an electrochemical device according to any one of paragraphs. 1-5, wherein the fluorinated monomer unit is at least one selected from the group consisting of a tetrafluoroethylene unit and a hexafluoropropylene unit. 7. Composition for an electrochemical device according to any one of paragraphs. 1-6, in which the dynamic elastic modulus (E') determined by analyzing the viscoelasticity of the fluorine-containing copolymer at 30°C is 100-1200 MPa, and the dynamic elastic modulus (E') determined by analyzing the viscoelasticity of the fluorine-containing copolymer at 60°C , is 50-600 MPa. 8. Composition for an electrochemical device according to any one of paragraphs. 1-7, in which the binder additionally contains polyvinylidene fluoride. 9. Composition for an electrochemical device according to any one of paragraphs. 1-8 for use in forming the electrode or separator of an electrochemical device. 10. A positive electrode mixture comprising an electrochemical device composition according to any one of paragraphs. 1-9 and the positive electrode active material. 11. The positive electrode mixture according to claim 10, wherein the content of single-walled carbon nanotubes in the positive electrode mixture is 0.001-10 mass parts per 100 mass parts of positive electrode active material. 12. The positive electrode mixture according to claim 10 or 11, wherein the content of the binder in the positive electrode mixture is 0.1 to 5.0 mass parts per 100 mass parts of the positive electrode active material. 13. A positive electrode structure including a current collector and a positive electrode mixture layer provided on one or both sides of the current collector, wherein the positive electrode mixture layer is made from the positive electrode mixture according to any one of paragraphs. 10-12. 14. A battery including the positive electrode structure of claim 13.