Electrode material dispersion liquid for electrochemical element, slurry for electrode of electrochemical element, electrode for electrochemical element, and electrochemical element

Abstract

The purpose of this invention is to provide a conductive material dispersion for electrochemical devices, which can form electrodes with excellent flexibility and smoothness, enabling the electrochemical devices to exhibit excellent cycling characteristics. The conductive material dispersion of this invention comprises a conductive material containing CNTs, a dispersant, and a dispersion medium. The Carson viscosity of the conductive material dispersion of this invention is 30 (Pa·s). 1 / 2 The following is a Carson yield value of 20 Pa. 1 / 2 The following conditions apply, and the hysteresis constant is 0.7 or less. Furthermore, the hysteresis constant is calculated using the following formula (I). Hysteresis constant C = (N1 - N2) / N1···(I) N1: The shear rate is reduced from 10... ‑2 s ‑1 Rise to 10 3 s ‑1 To measure viscosity (25℃), shear rate 10s ‑1 The viscosity (Pa·s) of the conductive material dispersion N2: This allows the shear rate to decrease from 10... 3 s ‑1 dropped to 10 ‑2 s ‑1 To measure viscosity (25℃), shear rate 10s ‑1 The viscosity (Pa·s) of the conductive material dispersion.

Description

Technical Field

[0001] This invention relates to conductive material dispersions for electrochemical elements, slurries for electrochemical element electrodes, electrodes for electrochemical elements, and electrochemical elements. Background Technology

[0002] Electrochemical components such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double-layer capacitors are widely used due to their small size, light weight, high energy density, and ability to be repeatedly charged and discharged. Here, the electrode for the electrochemical component has, for example, a current collector and an electrode composite material layer formed by drying an electrode slurry for the electrochemical component on the current collector.

[0003] In recent years, carbon nanotubes (hereinafter sometimes simply referred to as "CNTs") have been used as conductive materials when forming electrode composite layers. Here, in order to obtain an electrode composite layer with well-dispersed CNTs when using CNTs to form the electrode composite layer, the following technique is proposed: premixing CNTs (as a conductive material) with a dispersant to prepare a conductive material dispersion for electrochemical elements; combining the obtained conductive material dispersion with an electrode active material to prepare an electrode slurry (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2018-533175. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, in the aforementioned prior art, it is necessary to improve the physical properties of the electrodes formed using conductive material dispersions, and at the same time, it is also necessary to further improve the device characteristics of the electrochemical element. Specifically, in the aforementioned prior art, it is necessary to improve the flexibility and smoothness of the electrodes while enabling the electrochemical element to exhibit excellent cycling characteristics.

[0009] Therefore, the object of the present invention is to provide a conductive material dispersion for electrochemical elements and a slurry for electrochemical element electrodes that can form electrodes with excellent softness and smoothness, while also enabling electrochemical elements to exhibit excellent cycle characteristics.

[0010] Furthermore, the present invention aims to provide an electrode for an electrochemical element that exhibits excellent flexibility and smoothness, while also enabling the electrochemical element to perform excellent cycle characteristics.

[0011] Moreover, the purpose of this invention is to provide an electrochemical element with excellent cycle characteristics.

[0012] Solution for solving the problem

[0013] The inventors conducted in-depth research with the aim of solving the above-mentioned problems. They then discovered that, in a conductive material dispersion containing CNTs (conductive materials) and a dispersant in a dispersion medium, if a conductive material dispersion with a Carson viscosity, Carson yield value, and a hysteresis constant determined by a prescribed method, respectively, is used, an electrode exhibiting excellent softness and smoothness can be obtained. Furthermore, based on this electrode, an electrochemical element can exhibit excellent cycling characteristics, thus completing the present invention.

[0014] That is, the object of the present invention is to advantageously solve the above-mentioned problems. The conductive material dispersion for electrochemical devices of the present invention is characterized by comprising a conductive material, a dispersant, and a dispersion medium, wherein the conductive material contains carbon nanotubes, and the Casson viscosity of the conductive material dispersion for electrochemical devices is 30 (Pa·s). 1 / 2 The following is a Carson yield value of 20 Pa. 1 / 2 The following, and the lag constant is below 0.7.

[0015] In this invention, "Casson viscosity" and "Casson yield value" are respectively equivalent to the Casson equation: S 1 / 2 =A×D 1 / 2 The values ​​of A (slope) and B (intercept) in +B. Furthermore, in this invention, for the Carson viscosity A and Carson yield value B in the Carson formula, the square root (St) representing the shear stress S can be generated using the method described in the embodiments. 1 / 2 ) and shear rate D(D 1 / 2 The Carson curve is derived from the relationship between the square root of and .

[0016] Furthermore, in this invention, the "hysteresis constant" is a value calculated using the following formula (I).

[0017] The lag constant C = (N1 - N2) / N1…(I)

[0018] In formula (I),

[0019] N1: For the conductive material dispersion of the above electrochemical components, the shear rate was adjusted from 10 at 25°C using a rheometer. -2 s -1 Rise to 10 3 s -1 The shear rate during viscosity measurement was 10 s. -1 viscosity (Pa·s),

[0020] N2: For the conductive material dispersion of the above electrochemical element after N1 determination, the shear rate was adjusted from 10 at 25°C using a rheometer. 3 s-1 Reduced to 10 -2 s -1 The shear rate during viscosity measurement was 10 s. -1 The viscosity (Pa·s).

[0021] In this way, if a conductive material dispersion containing CNTs and a dispersant is used in the dispersion medium, and the Carson viscosity, Carson yield value, and hysteresis constant are all below the aforementioned values, an electrode with excellent softness and smoothness, and an electrochemical element with excellent cycling characteristics can be obtained.

[0022] Furthermore, the conductive material dispersion for the electrochemical element of the present invention preferably contains a dispersant comprising a nitrile-containing monomer unit. Using a polymer comprising a nitrile-containing monomer unit as the dispersant further improves the flexibility and smoothness of the electrode, as well as the cycling characteristics of the electrochemical element. In addition, it also improves the low-temperature output characteristics and rate performance of the electrochemical element.

[0023] Furthermore, in this invention, the term "contains monomer units" in polymers such as dispersants means "a polymer obtained using the monomer contains repeating units derived from that monomer".

[0024] Furthermore, in this invention, the content ratio of repeating units (monomer units and structural units described later) in the polymer can be used... 1 H-NMR and 13 It is determined by nuclear magnetic resonance (NMR) methods such as C-NMR.

[0025] Here, the conductive material dispersion for the electrochemical element of the present invention preferably contains carbon nanotubes at a content of 1.0% by mass or more and 30.0% by mass or less, and the dispersant at a content of 0.1% by mass or more and 3.0% by mass or less. If the proportions of CNTs and the dispersant in the conductive material dispersion are within the above-mentioned ranges, the flexibility and smoothness of the electrode, as well as the cycling characteristics of the electrochemical element, can be further improved. In addition, the low-temperature output characteristics and rate performance of the electrochemical element can also be improved.

[0026] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The slurry for the electrode of the electrochemical element of the present invention is characterized by comprising an electrode active material and a dispersion of any of the above-mentioned conductive materials for electrochemical elements. If an electrode slurry comprising an electrode active material and a dispersion of any of the above-mentioned conductive materials is used, an electrode with excellent softness and smoothness can be obtained, and the electrochemical element having the electrode can exhibit excellent cycling characteristics.

[0027] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The electrode for electrochemical devices of the present invention is characterized by having an electrode composite material layer formed using the aforementioned electrode slurry for electrochemical devices. The electrode having the electrode composite material layer formed using the aforementioned electrode slurry has excellent flexibility and smoothness. In addition, according to this electrode, the electrochemical device can exhibit excellent cycling characteristics.

[0028] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems, and the electrochemical element of the present invention is characterized by having the aforementioned electrode for electrochemical elements. Electrochemical elements having the aforementioned electrode exhibit excellent element characteristics such as cycle performance.

[0029] Invention Effects

[0030] According to the present invention, it is possible to provide a conductive material dispersion for electrochemical elements and a slurry for electrochemical element electrodes that can form electrodes with excellent softness and smoothness while also enabling electrochemical elements to exhibit excellent cycle characteristics.

[0031] Furthermore, according to the present invention, it is possible to provide an electrode for an electrochemical element that exhibits excellent flexibility and smoothness, while also enabling the electrochemical element to perform excellent cycle characteristics.

[0032] Moreover, according to the present invention, an electrochemical element with excellent cycle characteristics can be provided. Detailed Implementation

[0033] The embodiments of the present invention will now be described in detail.

[0034] Here, the conductive material dispersion for electrochemical elements of the present invention is used as a material in manufacturing the slurry for the electrode of the electrochemical element. Furthermore, the slurry for the electrode of the electrochemical element of the present invention is prepared using the conductive material dispersion for the electrochemical element of the present invention. Moreover, the electrode for the electrochemical element of the present invention is characterized by having an electrode composite material layer formed using the slurry for the electrode of the electrochemical element of the present invention. Furthermore, the electrochemical element of the present invention is characterized by having the electrode for the electrochemical element of the present invention.

[0035] (Dispersion of conductive material for electrochemical components)

[0036] The conductive material dispersion of the present invention comprises a conductive material, a dispersant, and a dispersion medium, and optionally includes other components. Here, at least CNTs are required as the conductive material. Furthermore, the conductive material dispersion typically does not contain electrode active materials (positive electrode active material, negative electrode active material).

[0037] Furthermore, the conductive material dispersion of the present invention is characterized in that the Carson viscosity, Carson yield value, and hysteresis constant, as determined by a prescribed method, are all below a prescribed value. Using such a conductive material dispersion, it is possible to produce electrodes with excellent softness and smoothness, and which enable electrochemical elements to exhibit excellent cycling characteristics.

[0038] <Conductive Materials>

[0039] As a conductive material, CNTs are used at least, and CNTs can also be used in combination with other conductive materials (other conductive materials).

[0040] <<Carbon Nanotubes>>

[0041] CNTs can be either single-walled carbon nanotubes or multi-walled carbon nanotubes. Furthermore, single-walled CNTs and multi-walled CNTs can also be used in combination as CNTs.

[0042] Here, the preferred BET specific surface area of ​​CNT is 180 m². 2 / g or more, preferably 200m 2 / g or more, preferably 1500m 2 / g or less, more preferably 1000m 2 / g or less. If the BET specific surface area of ​​CNT is 180m² 2 If the concentration is above / g, the cycling characteristics of the electrochemical element can be further improved, while also enhancing its low-temperature output and rate performance. On the other hand, if the BET specific surface area of ​​CNTs is 1500 m²... 2 With a concentration of less than 1 g, even at the same solid content, the viscosity of the conductive material dispersion can be kept low. Therefore, since the solid content of the conductive material dispersion can be increased, the density of the electrode composite layer obtained using the conductive material dispersion can be increased, resulting in further improvement in the flexibility of the electrode.

[0043] In addition, in this invention, "BET specific surface area" means the nitrogen adsorption specific surface area measured using the BET method.

[0044] CNTs are not particularly limited and can be synthesized using known CNT synthesis methods such as arc discharge, laser ablation, and chemical vapor deposition (CVD).

[0045] <<Other Conductive Materials>>

[0046] Other conductive materials can be used without particular limitation, as long as they function as conductive materials that ensure electrical contact between the active electrode materials in the electrode composite layer. Examples of other conductive materials include carbon materials other than CNTs. Moreover, examples of such carbon materials include carbon black (e.g., acetylene black, Ketjen black (registered trademark), furnace black, etc.), graphite, carbon sheets, and carbon nanofibers. These can be used alone or in combination of two or more.

[0047] Furthermore, CNTs can be used alone as a conductive material, or they can be used in combination with other conductive materials as described above. However, in this invention, from the viewpoint of achieving the desired effect, when the total mass of the conductive material is set to 100% by mass, the proportion of CNTs in the total conductive material is preferably 20% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, further preferably 80% by mass or more and 100% by mass or less, and particularly preferably 100% by mass (i.e., the conductive material is composed solely of CNTs).

[0048] <<CNT content>>

[0049] The CNT content in the conductive material dispersion is not particularly limited. When the total mass of the conductive material dispersion is set to 100% by mass, it is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, even more preferably 3.0% by mass or more, preferably 30.0% by mass or less, more preferably 15.0% by mass or less, and even more preferably 7.0% by mass or less. If the CNT content in the conductive material dispersion is within the above range, the flexibility and smoothness of the electrode, as well as the cycling characteristics of the electrochemical element, can be further improved. In addition, the low-temperature output characteristics and rate performance of the electrochemical element can also be improved.

[0050] <Dispersant>

[0051] As a dispersant, there is no particular limitation as long as it is a polymer capable of dispersing the aforementioned CNT-containing conductive material in a dispersion medium. Preferably, such a polymer comprises nitrile monomer units.

[0052] <<Nitrile-containing monomer units>>

[0053] Examples of nitrile-containing monomers capable of forming nitrile-containing monomer units include α,β-ene unsaturated nitrile monomers. Specifically, there is no particular limitation on α,β-ene unsaturated nitrile monomers, as long as they are α,β-ene unsaturated compounds having a nitrile group; examples include acrylonitrile; α-haloacrylonitrile such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile. Furthermore, a single nitrile-containing monomer can be used, or two or more can be used in any ratio. Among these, acrylonitrile is preferred.

[0054] Regarding the proportion of nitrile-containing monomer units in the dispersant used as the polymer, when all repeating units in the polymer constituting the dispersant are set to 100% by mass, it is preferably 10% by mass or more, more preferably 15% by mass or more, further preferably 20% by mass or more, preferably 50% by mass or less, more preferably 45% by mass or less, and further preferably 40% by mass or less. If the proportion of nitrile-containing monomer units in the dispersant is within the above range, the solubility of the dispersant in the dispersion medium (e.g., N-methyl-2-pyrrolidone) can be sufficiently ensured, and the resulting electrode composite material layer can also be well bonded to the current collector. Therefore, the conductive material can be well dispersed in the conductive material dispersion, and the flexibility and smoothness of the electrode, as well as the cycling characteristics of the electrochemical element, can be further improved. In addition, the low-temperature output characteristics and rate characteristics of the electrochemical element can also be improved.

[0055] <<Examples of polymers containing nitrile monomer units>>

[0056] Examples of polymers containing nitrile monomer units include polymers containing nitrile monomer units and alkylene structural units, and polymers containing nitrile monomer units and (meth)acrylate monomer units. From the viewpoint of improving the rate performance of electrochemical elements while further improving cycle performance, polymers containing nitrile monomer units and alkylene structural units are preferred.

[0057] Furthermore, in this invention, "alkylene structural unit" means only those units of the general formula: -C n H 2n -[where n is an integer greater than or equal to 2] represents a repeating unit composed of alkylene structures.

[0058] Furthermore, in this invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0059] [Polymers containing nitrile monomer units and alkylene structural units]

[0060] In addition to the aforementioned nitrile-containing monomer units, the polymer also contains at least alkylene structural units, and may arbitrarily contain repeating units (other repeating units) other than the nitrile-containing monomer units and alkylene structural units. Furthermore, the number of carbon atoms in the alkylene structural units is preferably 4 or more (i.e., n in the above general formula is an integer of 4 or more).

[0061] —alkylene structural unit—

[0062] The alkylene structural unit can be either linear or branched. From the perspective of improving the rate performance of electrochemical elements, it is preferred that the alkylene structural unit is linear, i.e., a linear alkylene structural unit.

[0063] Furthermore, there are no particular limitations on the method of introducing alkylene structural units into the dispersant used as a polymer, and methods such as (1) and (2) below can be cited as examples:

[0064] (1) A method for preparing a polymer from a monomer composition containing a conjugated diene monomer, and hydrogenating the polymer thereby converting the conjugated diene monomer unit into an alkylene structural unit;

[0065] (2) A method for preparing a polymer from a monomer composition containing a 1-olefin monomer.

[0066] Of these, method (1) is preferred because it is easy to produce dispersants.

[0067] Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 1,3-pentadiene, which are conjugated diene compounds with 4 or more carbon atoms. 1,3-butadiene is particularly preferred. Specifically, the alkylene structural unit is preferably a structural unit obtained by hydrogenating a conjugated diene monomer unit (a conjugated diene hydride unit), and more preferably a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (a 1,3-butadiene hydride unit).

[0068] In addition, examples of 1-olefin monomers include ethylene, propylene, and 1-butene.

[0069] These conjugated diene monomers and 1-olefin monomers can be used individually or in combination of two or more in any ratio.

[0070] Furthermore, regarding the proportion of alkylene structural units in the dispersant used as the polymer, when all repeating units in the polymer constituting the dispersant are set to 100% by mass, it is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. If the proportion of alkylene structural units in the dispersant is within the above range, it is presumed that due to the increased affinity between conductive materials such as CNTs and the dispersant, the flexibility and smoothness of the electrode, as well as the cycling characteristics of the electrochemical element, can be further improved. In addition, the low-temperature output characteristics and rate performance of the electrochemical element can also be improved.

[0071] In addition, when the dispersant is a polymer obtained by the method described above (1), it is preferable that the proportion of alkylene structural units and the total proportion of conjugated diene monomer units in the dispersant satisfy the above range.

[0072] —Other repeating units—

[0073] Other repeating units in polymers containing nitrile monomer units and alkylene structural units are not particularly limited, but examples include: aromatic vinyl monomer units, monomer units containing acidic groups, and (meth)acrylate monomer units. Furthermore, polymers containing nitrile monomer units and alkylene structural units may contain one or more other repeating units.

[0074] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Furthermore, an aromatic vinyl monomer can be used alone or in combination of two or more in any ratio. Styrene is preferred among these.

[0075] Examples of monomers containing acidic groups that can form monomer units containing acidic groups include: monomers containing carboxylic acid groups, monomers containing sulfonic acid groups, and monomers containing phosphate groups. Furthermore, monomers containing acidic groups can be used alone or in combination of two or more in any ratio.

[0076] Examples of monomers containing carboxylic acid groups include: monocarboxylic acids and their derivatives, dicarboxylic acids and their anhydrides, and their derivatives.

[0077] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

[0078] Examples of monocarboxylic acid derivatives include: 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0079] Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0080] Examples of dicarboxylic acid derivatives include: methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and other maleic acid monoesters.

[0081] Examples of anhydrides that are dicarboxylic acids include: maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0082] Furthermore, acid anhydrides that generate carboxylic acid groups through hydrolysis can also be used as monomers containing carboxylic acid groups. Acrylic acid and methacrylic acid are particularly preferred as monomers containing carboxylic acid groups.

[0083] Examples of monomers containing sulfonic acid groups include: vinyl sulfonic acid, methyl vinyl sulfonic acid, (methyl)allyl sulfonic acid, styrene sulfonic acid, ethyl (meth)acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0084] In addition, in this invention, "(methyl)allyl" means allyl and / or methylallyl.

[0085] Examples of phosphate-containing monomers include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0086] Additionally, in this invention, "(meth)acryl" means acrylamide and / or methacrylamide.

[0087] Examples of (meth)acrylate monomers capable of forming (meth)acrylate monomer units include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, and other alkyl acrylates; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and other alkyl methacrylates. Furthermore, a single (meth)acrylate monomer can be used alone, or two or more monomers can be used in any ratio.

[0088] Furthermore, regarding the proportion of other repeating units in a polymer containing nitrile monomer units and alkylene structural units, when all repeating units in the polymer are set to 100% by mass, it is preferably 0% or more and 30% or less by mass, more preferably 0% or more and 20% or less by mass, even more preferably 0% or more and 10% or less by mass, and particularly preferably 0% or more and 5% or less by mass.

[0089] [Polymers containing nitrile monomer units and (meth)acrylate monomer units]

[0090] In addition to the aforementioned nitrile-containing monomer units, the polymer also contains at least (meth)acrylate monomer units and may optionally contain repeating units (other repeating units) other than nitrile-containing monomer units and (meth)acrylate monomer units.

[0091] Examples of (meth)acrylate monomers capable of forming (meth)acrylate monomer units include monomers identical to those described in the section on "polymers comprising nitrile monomer units and alkylene structural units". Furthermore, a single (meth)acrylate monomer may be used, or two or more may be used in any ratio. Among these, 2-ethylhexyl acrylate is preferred.

[0092] Furthermore, regarding the content of (meth)acrylate monomer units in the dispersant of the polymer, when all repeating units in the polymer constituting the dispersant are set to 100% by mass, it is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0093] —Other repeating units—

[0094] Other repeating units in polymers containing nitrile monomer units and (meth)acrylate monomer units are not particularly limited, but aromatic vinyl monomer units and monomer units containing acidic groups are preferred examples. Polymers containing nitrile monomer units and (meth)acrylate monomer units as dispersants may contain one or more other repeating units.

[0095] As aromatic vinyl monomers capable of forming aromatic vinyl monomer units, examples include monomers identical to those described in the section "polymers comprising nitrile monomer units and alkylene structural units". Furthermore, aromatic vinyl monomers can be used alone or in combination of two or more in any ratio. Among these, styrene is preferred.

[0096] Furthermore, regarding the content of aromatic vinyl monomer units in the polymer dispersant, when all repeating units in the polymer constituting the dispersant are set to 100% by mass, it is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0097] As a monomer capable of forming a monomer unit containing an acidic group, examples of monomers containing acidic groups include those described in the section on "polymers comprising nitrile monomer units and alkylene structural units". Furthermore, a single monomer containing an acidic group may be used, or two or more may be used in any ratio. Among these, methacrylic acid is preferred.

[0098] Furthermore, regarding the proportion of the monomer units containing acidic groups in the polymer dispersant, when all repeating units in the polymer constituting the dispersant are set to 100% by mass, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 4% by mass or less.

[0099] <<Weight-average molecular weight>>

[0100] Furthermore, the weight-average molecular weight of the dispersant used as the polymer is preferably 10,000 or more, more preferably 15,000 or more, even more preferably 20,000 or more, preferably 400,000 or less, more preferably 300,000 or less, and even more preferably 200,000 or less. If the weight-average molecular weight of the dispersant is 10,000 or more, it is presumed that the dissolution of the dispersant into the electrolyte is suppressed, thereby further improving the cycling characteristics of the electrochemical element. On the other hand, if the weight-average molecular weight of the dispersant is 400,000 or less, the low-temperature output characteristics and rate performance can be improved. In addition, even with the same solid content concentration, the viscosity of the conductive material dispersion can be kept low. Therefore, since the solid content concentration of the conductive material dispersion can be increased, the density of the electrode composite layer obtained using the conductive material dispersion can be increased, resulting in further improvement in the flexibility of the electrode.

[0101] Furthermore, in this invention, the "weight-average molecular weight" can be determined using the method described in the examples.

[0102] <<Preparation Methods of Dispersants>>

[0103] There are no particular limitations on the preparation method of the dispersant. The dispersant can be manufactured, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent and then hydrogenating it. In addition, the content ratio of each monomer in the monomer composition can be determined according to the content ratio of the desired repeating units (monomer units and / or structural units) in the polymer.

[0104] Furthermore, there are no particular restrictions on the polymerization method; any method from solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc., can be used. In addition, as the polymerization reaction, any reaction from ionic polymerization, free radical polymerization, living free radical polymerization, various condensation polymerizations, addition polymerization, etc., can be used. Moreover, known emulsifiers and polymerization initiators can be used as needed during polymerization. Furthermore, hydrogenation can be carried out using known methods.

[0105] <<Dispersant Content>>

[0106] The content of dispersant in the conductive material dispersion is not particularly limited. When the total mass of the conductive material dispersion is set to 100% by mass, it is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. If the content of dispersant is within the above range, the flexibility and smoothness of the electrode, as well as the cycle characteristics of the electrochemical element, can be further improved. In addition, the low-temperature output characteristics and rate performance of the electrochemical element can also be improved.

[0107] <Dispersion Medium>

[0108] As a dispersion medium, water or an organic solvent can be used, with an organic solvent being preferred. The organic solvent is not particularly limited, but examples include: alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and pentanol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and diethyl ether, diethyl ester, etc. Ethers such as alkanes and tetrahydrofurans; amide-based organic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene. Furthermore, a single dispersion medium can be used, or two or more can be used in any ratio. Moreover, from the viewpoint of ensuring good dispersion of conductive materials such as CNTs in a conductive material dispersion, organic solvents are preferred, and NMP is more preferred.

[0109] <Other Ingredients>

[0110] Other components that can be included in the conductive material dispersion are not particularly limited, and examples include those other than the electrode active material described in "Slurry for Electrode of Electrochemical Components". Furthermore, other components may be used alone or in combination of two or more in any ratio.

[0111] <Carson viscosity>

[0112] Here, the Cassen viscosity of the conductive material dispersion of the present invention needs to be 30 (Pa·s) as described above. 1 / 2 The preferred value is 20 (Pa·s). 1 / 2 Hereinafter, 10 (Pa·s) is more preferred. 1 / 2 The following applies when the Carson viscosity is greater than 30 (Pa·s). 1 / 2 At this point, the conductive material dispersion will have excessive viscosity. Therefore, it is difficult to increase the solid content concentration of the conductive material dispersion, and consequently, the density of the electrode composite layer obtained using the conductive material dispersion cannot be increased, resulting in compromised electrode flexibility. Furthermore, the lower limit of the Carson viscosity only needs to be greater than 0 (Pa·s). 1 / 2 There is no specific limitation, for example, 0.01 (Pa·s). 1 / 2 above.

[0113] Here, a conductive material dispersion with a Carson viscosity below a specified value can be prepared by the method described in "Preparation Method of Conductive Material Dispersion". The Carson viscosity can also be controlled by changing the weight-average molecular weight and composition of the dispersant (e.g., the proportion of nitrile monomer units).

[0114] <Carson Yield Value>

[0115] Furthermore, the Cassen yield value of the conductive material dispersion of the present invention needs to be 20 Pa as described above. 1 / 2 The following is preferred: 15 Pa 1 / 2 The following is more preferably 10 Pa. 1 / 2 Hereinafter, 6 Pa is further preferred. 1 / 2 The following is a description of the Carson yield value, which is the shear stress equivalent to a shear rate of 0. When this value is high, the viscosity stability of the conductive material dispersion is compromised. Therefore, when an electrode slurry containing a conductive material dispersion with low viscosity stability is used to form an electrode composite layer on a current collector or similar surface, unevenness occurs on the surface of the composite layer, impairing the smoothness of the electrode. Furthermore, using an electrode with poor smoothness prevents the electrochemical element from exhibiting excellent element characteristics (especially low-temperature output characteristics). Additionally, the lower limit of the Carson yield value only needs to be greater than 0 Pa. 1 / 2 There are no specific limitations, for example, 0.01 Pa. 1 / 2 above.

[0116] <Lapse constant>

[0117] The hysteresis constant is determined by the following equation (I).

[0118] The lag constant C = (N1 - N2) / N1…(I)

[0119] Here, in equation (I),

[0120] N1: For conductive material dispersions used in electrochemical components, the shear rate was adjusted from 10 at 25°C using a rheometer. - 2 s -1 Rise to 10 3 s -1 The shear rate during viscosity measurement was 10 s. -1 viscosity (Pa·s);

[0121] N2: For the conductive material dispersion used in the electrochemical element after N1 determination, the shear rate was adjusted from 10 at 25°C using a rheometer. 3 s -1 Reduced to 10 -2 s -1 The shear rate during viscosity measurement was 10 s. -1 The viscosity (Pa·s).

[0122] In other words, the hysteresis constant can be obtained as follows: as described above, when the shear rate is reduced from the lower side (10... -2 s -1 ) To the higher side (10 3 s -1The shear rate during the upward process (first shear treatment) is 10s. -1 The viscosity N1 of the conductive material dispersion and the shear rate from the high side (10) after the first shear treatment. 3 s -1 ) to the lower side (10 -2 s -1 The shear rate during the reduction process (second shear treatment) is 10s. -1 The viscosity N2 of the conductive material dispersion is calculated, and the degree of decrease from viscosity N1 to viscosity N2 is calculated using equation (I).

[0123] According to the inventors' research, a small decrease in viscosity caused by shearing implies that the conductive material dispersion is resistant to shearing and is not prone to structural changes. Furthermore, it is speculated that because conductive material dispersions exhibiting such strong properties are less prone to thickening and poor dispersion of the conductive material, they can be used to form electrode composite layers, thus enabling the formation of conductive pathways based on the conductive material and allowing electrochemical elements to exhibit excellent cycling characteristics.

[0124] Furthermore, the hysteresis constant of the conductive material dispersion of the present invention needs to be 0.7 or less, preferably 0.6 or less, more preferably 0.5 or less, and even more preferably 0.3 or less, as described above. When the hysteresis constant is greater than 0.7, the cycling characteristics of the electrochemical element decrease. In addition, the lower limit of the hysteresis constant is not particularly limited as long as it is greater than 0, for example, it is 0.01 or more.

[0125] <Concentration of solid components>

[0126] Furthermore, in the conductive material dispersion of the present invention, the proportion of solid component to the total conductive material dispersion (i.e., the solid component concentration) is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, even more preferably 4.0% by mass or more, particularly preferably 5.0% by mass or more, preferably 30.0% by mass or less, more preferably 15.0% by mass or less, even more preferably 10.0% by mass or less, and particularly preferably 7.0% by mass or less. If the solid component concentration of the conductive material dispersion is 1.0% by mass or more, the hysteresis constant can be reduced, further improving the cycling characteristics of the electrochemical element. On the other hand, if the solid component concentration of the conductive material dispersion is 30.0% by mass or less, the Carson viscosity and Carson yield value can be reduced, further improving the flexibility and smoothness of the electrode, and improving the low-temperature output characteristics and rate performance of the electrochemical element.

[0127] <Preparation Method of Conductive Material Dispersion>

[0128] Here, a conductive material dispersion with a Carson viscosity, Carson yield value, and hysteresis constant below the aforementioned upper limits can be manufactured, for example, by mixing the aforementioned conductive material, dispersant, and dispersion medium through at least two stages of dispersion processes (a first dispersion process and a second dispersion process). In this method, the Carson viscosity, Carson yield value, and hysteresis constant of the conductive material dispersion can be controlled by adjusting the dispersion conditions in the first and / or second dispersion processes (type of dispersion device, rotational speed and circumferential speed, dispersion time and temperature, and the ratio of CNTs to dispersant during dispersion).

[0129] The preferred conditions for controlling the Carson viscosity, Carson yield value, and hysteresis constant of a conductive material dispersion to be below predetermined upper limits through a two-stage dispersion process are described below. Furthermore, in this method, different dispersion devices are typically used for the two-stage dispersion processes. By using different dispersion devices in the two-stage dispersion processes, different dispersion treatments can be applied to the dispersed material in the initial dispersion stage (coarse dispersion stage) and the later dispersion stage (main dispersion stage), making it easy to prepare novel conductive material dispersions with Carson viscosity, Carson yield value, and hysteresis constant below predetermined upper limits. Moreover, in this method, processes other than the first and second dispersion processes can also be performed.

[0130] To control the adsorption state of the dispersant on the conductive material, conventional methods have involved changing the method of adding the dispersant and changing the ratio of the conductive material to the dispersant. Indeed, when using carbon black as the conductive material, the adsorption state can be controlled by the above methods. However, since the conductive material dispersion of the present invention contains CNTs as the conductive material, the control of multiple factors becomes more important in controlling the adsorption state, as well as the Carson viscosity, Carson yield value, and hysteresis constant (especially the hysteresis constant).

[0131] Furthermore, the method for preparing the conductive material dispersion of the present invention is not necessarily limited to this method.

[0132] <<First Dispersion Process>>

[0133] In the first dispersion step, the composition comprising at least CNTs, a dispersant, and a dispersion medium is dispersed to obtain a coarse dispersion. The main purpose of the first dispersion step is to wet (fuse) the CNTs, which are the dispersed components, with the dispersant and the dispersion medium.

[0134] Examples of dispersion devices used in the first dispersion step include dispersers, homogenizers, planetary mixers, kneaders, and ball mills. Furthermore, dispersers and planetary mixers are preferred, and dispersers are more preferably used in the first dispersion step.

[0135] When using a disperser as the dispersing device, the rotation speed is preferably 500 rpm or more, more preferably 1000 rpm or more, even more preferably 2000 rpm or more, preferably 8000 ppm or less, more preferably 7000 rpm or less, and even more preferably 6000 rpm or less.

[0136] When using a planetary mixer as a dispersing device, the rotational speed is preferably 5 rpm or more, more preferably 10 rpm or more, even more preferably 30 rpm or more, preferably 150 rpm or less, more preferably 120 rpm or less, and even more preferably 100 rpm or less.

[0137] The dispersion process in the first dispersion step is preferably 12 minutes or more, more preferably 15 minutes or more, even more preferably 20 minutes or more, preferably 60 minutes or less, more preferably 50 minutes or less, and even more preferably 40 minutes or less.

[0138] From the viewpoint of controlling the molecular mobility of the dispersant and dispersion medium, controlling the viscosity of the dispersion system, and the degree of interaction between the CNTs, dispersion medium, and dispersant, the dispersion treatment temperature in the first dispersion step is preferably 5°C or higher, preferably 50°C or lower, more preferably 45°C or lower, further preferably 35°C or lower, and particularly preferably 25°C or lower. If the dispersion treatment temperature is 5°C or higher, the dispersion medium can easily enter the gaps between the CNT bundles; if it is 50°C or lower, the deterioration of the dispersant can be suppressed, and the dispersant can easily adsorb onto the CNTs. Furthermore, by keeping the dispersion treatment temperature within the above range, cross-linking of the dispersants can be suppressed, and the Carson yield value of the conductive material dispersion can be appropriately reduced.

[0139] Furthermore, regarding the ratio of CNTs to dispersant during the dispersion treatment in the first dispersion step, the content of dispersant in the composition subjected to dispersion treatment in the first dispersion step is preferably 5 parts by mass or more, more preferably 10 parts by mass, more preferably 100 parts by mass or less, and more preferably 50 parts by mass or less, relative to 100 parts by mass of CNTs. Additionally, in the first dispersion step, the dispersant can be added in its entirety at the initial stage of dispersion treatment, or it can be added in batches. The choice between adding it all at once or in batches can be appropriately determined based on factors such as the adsorption capacity of the dispersant. By employing a dispersant addition method corresponding to the adsorption capacity of the dispersant, the Carson yield value of the conductive material dispersion can be appropriately reduced.

[0140] <<Second Dispersion Process>>

[0141] In the second dispersion step, additional dispersants are added to the coarse dispersion obtained in the first dispersion step, and further dispersion treatment is carried out to obtain a conductive material dispersion. The main purpose of the second dispersion step is to apply shear force and collision energy to disperse and de-fibril the CNTs, which are the dispersed components.

[0142] In the second dispersion step, as described above, a dispersion device different from that used in the first dispersion step is typically used. Examples of dispersion devices used in the second dispersion step include dispersers, homogenizers, planetary mixers, kneaders, ball mills, and high-speed rotary film mixers such as Filmix (registered trademark). Furthermore, a media-free dispersion device is preferred, and a high-speed rotary film mixer is more preferable. In particular, when a media-using dispersion device is used in the second dispersion step, which is the main dispersion step, the contact between the CNTs and the media can cause damage to the cylindrical CNT structure, resulting in reduced length and sometimes a decrease in the rate capability, low-temperature output characteristics, and cycle characteristics of the electrochemical element. In contrast, if a media-free dispersion device, such as a high-speed rotary film mixer, is used, it is possible to effectively unbundle the CNTs while suppressing CNT damage, further improving the desired effect.

[0143] When using a thin-film rotary high-speed mixer as the dispersing device, the circumferential speed is preferably 10 m / s or more, more preferably 20 m / s or more, even more preferably 25 m / s or more, preferably 45 m / s or less, more preferably 40 m / s or less, and even more preferably 35 m / s or less. If the circumferential speed is within the above range, the bundle can be efficiently de-fired without damaging the length of the CNTs.

[0144] The dispersion time in the second dispersion step is preferably 2 minutes or more, more preferably 3 minutes or more, even more preferably 4 minutes or more, preferably 20 minutes or less, more preferably 10 minutes or less, and even more preferably 7 minutes or less. If the dispersion time is within the above range, it can promote the homogenization of the conductive material dispersion, reduce viscosity, and improve viscosity stability.

[0145] Furthermore, the ratio of CNTs to dispersant during the dispersion process in the second dispersion step is generally the same as that of the resulting conductive material dispersion. Additionally, in the second dispersion step, the dispersant can be added in its entirety at the initial stage of the dispersion process, or it can be added in batches to promote efficient adsorption of the newly formed interfaces created by the dispersion and defibrillation of CNTs.

[0146] (Slurry for electrodes of electrochemical components)

[0147] The electrode slurry of the present invention comprises the above-mentioned conductive material dispersion and electrode active material, and may include any components such as binder materials as needed. In other words, the electrode slurry of the present invention comprises a conductive material containing CNTs, a dispersant, and a dispersion medium, and may include any components such as binder materials as needed.

[0148] In this way, an electrode having an electrode composite material layer formed from an electrode slurry containing the above-mentioned conductive material dispersion has excellent softness and smoothness, and according to the electrode, the electrochemical element can exhibit excellent cycling characteristics.

[0149] <Electrode Active Materials>

[0150] There are no particular limitations on the electrode active materials (positive electrode active material and negative electrode active material) used in electrode slurries, and known electrode active materials can be used.

[0151] For example, the positive electrode active material used in lithium-ion secondary batteries is not particularly limited, and examples include metal oxides containing lithium (Li). Furthermore, as the positive electrode active material, it is preferable to include at least one of cobalt (Co), nickel (Ni), manganese (Mn), and iron (Fe) in addition to lithium (Li). Examples of such positive electrode active materials include lithium-containing cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium-containing nickel oxide (LiNiO2), Co-Ni-Mn lithium-containing composite oxides, Ni-Mn-Al lithium-containing composite oxides, Ni-Co-Al lithium-containing composite oxides, olivine-type lithium manganese phosphate (LiMnPO4), olivine-type lithium iron phosphate (LiFePO4), and Li... 1+x Mn 2-x O4 (0 < X ​​< 2) represents lithium-excess spinel compounds, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4, etc. In addition, a single positive electrode active material can be used alone, or two or more materials can be used in any ratio.

[0152] In addition, the particle size of the electrode active material is not particularly limited and can be the same as that of the electrode active materials used in the past.

[0153] Furthermore, there are no particular limitations on the amount of electrode active material in the electrode slurry, and it can be within the range that has been used in the past.

[0154] <Any ingredient>

[0155] Examples of components that can be included in electrode pastes include, for instance, binders, viscosity modifiers, reinforcing materials, antioxidants, and electrolyte additives that inhibit electrolyte decomposition. These components can be used individually or in combination of two or more in any ratio.

[0156] From the viewpoint of ensuring good adhesion between the resulting electrode composite layer and the current collector, the electrode slurry preferably contains a binder material.

[0157] <<Adhesive Materials>>

[0158] There are no particular limitations on the adhesive material, but preferred materials include fluorinated resins such as polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyvinyl alcohol (PVOH), with fluorinated resins and PAN being more preferred.

[0159] In addition, there is no particular limitation on the amount of binder material in the electrode paste, and it can be within the range of previous uses.

[0160] <Preparation Method of Electrode Slurry>

[0161] When mixing the above components to obtain the electrode slurry, there are no particular restrictions on the mixing method, and conventional mixing equipment can be used.

[0162] (Electrodes for electrochemical devices)

[0163] The electrode of the present invention has an electrode composite material layer obtained using the electrode slurry of the present invention described above. More specifically, the electrode of the present invention typically has the electrode composite material layer described above on a current collector. Here, the electrode composite material layer includes an electrode active material, CNTs, and a dispersant, and optionally includes a binder material, etc. Moreover, because the electrode of the present invention has an electrode composite material layer formed using the electrode slurry of the present invention described above, it exhibits excellent flexibility and smoothness, and enables the electrochemical element to perform excellent cycling characteristics.

[0164] <Current collector>

[0165] The current collector is made of a material that is both conductive and electrochemically durable. There are no particular limitations on the current collector; any known current collector can be used. For example, a current collector made of aluminum or an aluminum alloy can be used as the positive electrode of a lithium-ion secondary battery. In this case, aluminum and aluminum alloys can be used in combination, or different types of aluminum alloys can be combined. Aluminum and aluminum alloys are heat-resistant and electrochemically stable, making them excellent current collector materials.

[0166] <Methods for manufacturing electrodes>

[0167] The method for manufacturing the electrode of the present invention is not particularly limited. For example, the electrode of the present invention can be manufactured by applying the electrode slurry of the present invention described above to at least one side of the current collector and drying it to form an electrode composite material layer. More specifically, the manufacturing method includes: a step of applying the electrode slurry to at least one side of the current collector (coating step), and a step of drying the electrode slurry applied to at least one side of the current collector to form an electrode composite material layer on the current collector (drying step).

[0168] <<Coating Process>>

[0169] There are no particular limitations on the method for applying the electrode paste to the current collector, and any known method can be used. Specifically, the coating method can include doctor blade coating, dip coating, reverse roller coating, direct roller coating, gravure printing, extrusion coating, brush coating, etc. The electrode paste can be applied to only one side of the current collector or to both sides. The thickness of the paste film on the current collector after coating and before drying can be appropriately set according to the thickness of the electrode composite layer obtained after drying.

[0170] <<Drying Process>>

[0171] There are no particular limitations on the method for drying the electrode slurry on the current collector; known methods can be used, such as drying with warm air, hot air, low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams. By drying the electrode slurry on the current collector in this way, an electrode composite material layer can be formed on the current collector, resulting in an electrode having both a current collector and an electrode composite material layer.

[0172] Alternatively, after the drying process, a metal molding machine or roller press can be used to apply pressure to the electrode composite material layer. This pressure treatment ensures a good seal between the electrode composite material layer and the current collector.

[0173] Furthermore, if the electrode composite layer contains a curable polymer, the polymer can be cured after the electrode composite layer is formed.

[0174] (Electrochemical element)

[0175] The electrochemical element of the present invention has the electrodes described above. Furthermore, because the electrochemical element of the present invention has the electrodes described above, it exhibits excellent cycle characteristics. Additionally, the electrochemical element of the present invention is, for example, a non-aqueous secondary battery, preferably a lithium-ion secondary battery.

[0176] Here, the structure of a lithium-ion secondary battery, which is an example of an electrochemical element of the present invention, will be described. This lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a spacer. Furthermore, at least one of the positive and negative electrodes is an electrode of the present invention. That is, in this lithium-ion secondary battery, the positive electrode may be an electrode of the present invention, and the negative electrode may be an electrode other than the electrode of the present invention; the positive electrode may be an electrode other than the electrode of the present invention, and the negative electrode may be an electrode of the present invention; or both the positive and negative electrodes may be electrodes of the present invention.

[0177] <Electrodes other than those of the present invention>

[0178] There are no particular limitations on the electrodes that are not part of this invention, and known electrodes may be used.

[0179] Electrolyte

[0180] As the electrolyte, an organic electrolyte in which the supporting electrolyte is dissolved in an organic solvent is typically used. As the supporting electrolyte, lithium salts can be used, for example. Examples of lithium salts include: LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. LiPF6, LiClO4, and CF3SO3Li are particularly preferred due to their high degree of dissociation from their easy solubility in solvents, with LiPF6 being especially preferred. Furthermore, a single electrolyte can be used, or two or more can be used in any ratio. Generally, there is a tendency for higher dissociation degrees of supporting electrolytes to result in higher lithium-ion conductivity; therefore, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0181] As for the organic solvent used in the electrolyte, there are no particular limitations as long as it can dissolve the supporting electrolyte. Preferably, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), and methyl ethyl carbonate (EMC) can be used; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents can also be used. Carbonates are particularly preferred due to their high dielectric constant and wide stable potential range, and mixtures of ethylene carbonate and methyl ethyl carbonate are even more preferred.

[0182] Furthermore, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted, for example, preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass. In addition, known additives, such as ethylene fluorocarbonate, ethyl methyl sulfone, etc., can be added to the electrolyte solution.

[0183] <spacer>

[0184] There are no particular limitations on the spacer used; for example, spacers disclosed in Japanese Patent Application Publication No. 2012-204303 can be used. Among these, a microporous membrane made of a polyolefin-based resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred from the perspective of reducing the overall film thickness of the spacer, thereby increasing the ratio of electrode active materials in the lithium-ion secondary battery and thus increasing the capacity per unit volume.

[0185] <Manufacturing Method of Lithium-ion Secondary Batteries>

[0186] The lithium-ion secondary battery of the present invention can be manufactured, for example, by overlapping the positive and negative electrodes with a spacer between them, and then, as needed, winding, folding, or placing them into a battery container according to the battery shape. Electrolyte is then injected into the battery container, and the container is sealed. To prevent internal pressure rise and overcharging / discharging, overcurrent protection components such as fuses and PTC elements, porous metal mesh, and conductive plates can be provided as needed. The secondary battery can be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0187] Example

[0188] The present invention will now be specifically described based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0189] Furthermore, unless otherwise specified, in polymers manufactured by copolymerizing multiple monomers, the proportion of monomer units formed by polymerizing a particular monomer in the polymer is generally consistent with the proportion (feed ratio) of that particular monomer in all monomers used to polymerize the polymer. Additionally, in the case of a hydrogenated polymer, which is formed by hydrogenating a polymer containing conjugated diene monomer units, the total proportion of unhydrogenated conjugated diene monomer units and alkylene structural units that are hydrogenated conjugated diene monomer units in the hydrogenated polymer is consistent with the proportion (feed ratio) of the conjugated diene monomer in all monomers used to polymerize the polymer.

[0190] Furthermore, in the examples and comparative examples, the weight-average molecular weight of the dispersant, the Carson viscosity, Carson yield value and hysteresis constant of the conductive material dispersion, the smoothness and flexibility of the positive electrode, and the low-temperature output characteristics, rate characteristics and cycle characteristics of the lithium-ion secondary battery were evaluated using the following methods.

[0191] <Weight-average molecular weight>

[0192] The weight-average molecular weight (Mw) of the polymer dispersant was determined by gel permeation chromatography (GPC) under the following conditions using a 10 mM LiBr-dimethylformamide (DMF) solution.

[0193] • Separation column: Shodex KD-806M (manufactured by Showa Denko Co., Ltd.)

[0194] • Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation)

[0195] • Flow rate of eluent: 0.3 mL / min

[0196] Column temperature: 40℃

[0197] • Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0198] <Kassen viscosity, Kassen yield value, and hysteresis constant>

[0199] For the prepared conductive material dispersion, a rheometer (Anton Paar, product name "MCR302") was used at 25°C with a shear rate set at 10. -2 s -1 Up to 10 3 s -1 Within a certain range, the force generated to rotate the plate was measured, and then the complex modulus of elasticity for the first shear treatment was determined. Then, using the same rheometer as for the first shear treatment, the shear rate was set to 10 at a temperature of 25°C. 3 s -1 Up to 10 -2 s -1 The range is determined by measuring the force generated to rotate the plate, and then the complex modulus of elasticity is measured a second time (second shear treatment).

[0200] The shear stress (Pa) relative to the shear rate D (s) of the first obtained complex elastic modulus -1 The measured data are expressed as the square root of the shear rate D (D 1 / 2 (S) is the X-axis, and the square root of the shear stress S is (S) 1 / 2 Plot a Carson curve with the Y-axis as the axis. Then, at a shear rate D of 10... 2s -1 Up to 10 3 s -1 Within the range, S is obtained by performing a first-order linear regression on the curve. 1 / 2 =A×D 1 / 2 In +B, A (slope) is used as the Carson viscosity, and B is used as the Carson yield value.

[0201] Furthermore, based on the shearing rate of 10s during the first shearing process... -1 Viscosity N1 (Pa·s) and shear rate during the second shear treatment (10s) -1 The viscosity N2 (Pa·s) is used to calculate the hysteresis constant C using the following formula (I).

[0202] The lag constant C = (N1 - N2) / N1…(I)

[0203] <Smoothness>

[0204] To determine the surface roughness Ra of the cathode composite layer in the fabricated cathode, a cathode composite layer was mounted on a glass slide. The roughness was measured using a nanoscale hybrid microscope (Keyence, product name "VN-8010") at 100x magnification, at a temperature of 25°C, and evaluated according to the following criteria. A smaller surface roughness Ra indicates better smoothness of the cathode.

[0205] A: Surface roughness Ra is below 1μm

[0206] B: Surface roughness Ra is greater than 1μm and less than 3μm

[0207] C: Surface roughness Ra is greater than 3μm and less than 5μm

[0208] D: Surface roughness Ra is greater than 5μm

[0209] <Softness>

[0210] SUS cylindrical rods of different diameters were placed on the side of the positive electrode composite layer of the fabricated positive electrode. The positive electrode was then wound around the cylindrical rods, and the presence of cracks in the positive electrode composite layer was visually evaluated. The smaller the diameter, the better the flexibility of the positive electrode composite layer and the positive electrode.

[0211] A: The rod with a diameter of 2.0 mm will not break.

[0212] B: The rod with a diameter of 2.5mm will not break.

[0213] C: The rod with a diameter of 3.0 mm does not break.

[0214] D: The rod with a diameter of 3.5mm will not break.

[0215] <Low Temperature Output Characteristics>

[0216] After injecting the electrolyte into the fabricated lithium-ion secondary battery, it was left to stand at 25°C for 5 hours. Next, it was charged at 0.1C for 5 hours at 25°C, and the voltage V0 after the charging operation was measured.

[0217] Next, a discharge operation was performed at -10℃ with a discharge rate of 1C, and the voltage V1 was measured 15 seconds after the start of discharge. Then, the voltage change ΔV was calculated using the formula ΔV = V0 - V1. The smaller the value of this voltage change ΔV, the better the low-temperature output characteristics of the lithium-ion secondary battery.

[0218] A: Voltage change ΔV is less than 350mV

[0219] B: Voltage change ΔV is greater than 350mV and less than 450mV

[0220] C: Voltage change ΔV is greater than 450mV and less than 550mV

[0221] D: Voltage change ΔV is above 550mV

[0222] <Magnification Characteristics>

[0223] After injecting the electrolyte into the fabricated lithium-ion secondary battery, it was left to stand at 25°C for 5 hours. Next, it was charged at 25°C using a constant current method at 0.2C until the cell voltage reached 3.65V, followed by an aging treatment at 60°C for 12 hours. Then, it was discharged at 25°C using a constant current method at 0.2C until the cell voltage reached 3.00V. Finally, it underwent CC-CV charging (upper limit cell voltage 4.20V) using a constant current method at 0.2C, followed by CC discharging at 0.2C until 3.00V. This 0.2C charge-discharge cycle was repeated three times.

[0224] Next, at 25°C, the battery was charged to 4.2V using a constant current method at 0.1C, and then discharged to 3.0V at 0.1C to determine the 0.1C discharge capacity. Then, it was charged to 4.2V at 0.1C, and then discharged to 3.0V at 1C to determine the 1C discharge capacity. These measurements were performed on 10 battery cells of the fabricated lithium-ion secondary battery, and the average of the measured values ​​was taken as the 0.1C discharge capacity *a* and the 1C discharge capacity *b*. Then, the capacitance ratio = *b / a* × 100 (%) was calculated, and evaluated according to the following criteria. A higher capacitance ratio indicates better rate performance of the lithium-ion secondary battery.

[0225] A: The capacitance ratio is above 85%.

[0226] B: The capacitance ratio is above 75% and below 85%.

[0227] C: The capacitance ratio is above 60% and below 75%.

[0228] D: The capacitance ratio is less than 60%.

[0229] <Cyclic Characteristics>

[0230] After injecting the electrolyte into the fabricated lithium-ion secondary battery, it was left to stand at 25°C for 5 hours. Next, it was charged at 25°C using a constant current method at 0.2C to a cell voltage of 3.65V, followed by an aging treatment at 60°C for 12 hours. Then, it was discharged at 25°C using a constant current method at 0.2C to a cell voltage of 3.00V. Next, it underwent CC-CV charging (upper limit cell voltage 4.20V) using a constant current method at 0.2C, followed by CC discharging at 0.2C to 3.00V. This 0.2C charge-discharge cycle was repeated three times.

[0231] Next, at a temperature of 25°C, 100 charge-discharge cycles were performed with a battery cell voltage of 4.20-3.00V and a charge-discharge rate of 1.0C. The discharge capacity of the first cycle is defined as X1, and the discharge capacity of the 100th cycle is defined as X2. Using these discharge capacities X1 and X2, the capacity retention rate = (X2 / X1) × 100 (%) was calculated and evaluated according to the following criteria. A higher capacity retention rate indicates better cycle characteristics of the lithium-ion rechargeable battery.

[0232] A: Capacity retention rate is above 93%.

[0233] B: Capacity retention rate is above 88% and below 93%.

[0234] C: Capacity retention rate is above 83% and below 88%.

[0235] D: Capacity retention rate less than 83%

[0236] (Example 1)

[0237] <Preparation of Dispersant (HNBR-1)>

[0238] In a 10-liter reactor, 100 parts of deionized water, 35 parts of acrylonitrile as a monomer, and 65 parts of 1,3-butadiene as a monomer were added. 2 parts of potassium oleate as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and 0.7 parts of tert-dodecyl mercaptan (TDM) as a molecular weight regulator were also added. In the presence of 0.35 parts of potassium persulfate as a polymerization initiator, emulsion polymerization was carried out at 30°C to copolymerize 1,3-butadiene and acrylonitrile.

[0239] At the point where the polymerization conversion reaches 90%, 0.2 parts of hydroxylamine sulfate are added per 100 parts of monomer to terminate the polymerization. Next, the mixture is heated and steam distilled at approximately 70°C under reduced pressure to recover the residual monomer. Then, 2 parts of alkylated phenol are added as an anti-aging agent to obtain an aqueous dispersion of the polymer.

[0240] Next, 400 mL (total solids: 48 g) of the obtained polymer aqueous dispersion was added to a 1-liter autoclave equipped with a stirrer, and nitrogen gas was purged for 10 minutes to remove dissolved oxygen from the polymer aqueous dispersion. Then, as a hydrogenation catalyst, 50 mg of palladium acetate was dissolved in 180 mL of water with 4 molar equivalents of nitric acid added relative to Pd, and added. After purging the system twice with hydrogen gas, the contents of the autoclave were heated to 50 °C under hydrogen pressure to 3 MPa (gauge pressure) and the hydrogenation reaction was carried out for 6 hours.

[0241] Then, the contents were brought back to room temperature to create a nitrogen environment within the system. The mixture was then concentrated using an evaporator until the solid content reached 40%, resulting in an aqueous dispersion of hydrogenated nitrile rubber (HNBR-1).

[0242] 200 parts of NMP were added to 100 parts of the aqueous dispersion. After the water and residual monomers were completely evaporated under reduced pressure, the NMP was evaporated to obtain an NMP solution of HNBR-1 (solid concentration: 8%). The weight-average molecular weight of the obtained HNBR-1 was determined. The results are shown in Table 1. Additionally, although the weight-average molecular weight is "130,000", the "×10" symbol is omitted in Table 1. 4 And it is recorded as "13".

[0243] <Preparation of Conductive Material Dispersion (Preparation Method: A-1)>

[0244] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 A dispersion of HNBR-1 was prepared by dispersing 12.5 parts (equivalent to 1 part as solids) of NMP solution and 82.5 parts of NMP at 3000 rpm for 30 minutes while maintaining the temperature below 25°C (first dispersion step). Next, a conductive material dispersion was prepared by dispersing the material at 30 m / s for 5 minutes using a thin-film rotary high-speed mixer (Plutomix Machinery Co., Ltd., product name "Filmix, model 56-50"), with the dispersion occurring at a circumferential speed of 30 m / s (second dispersion step). The Carson viscosity, Carson yield value, and hysteresis constant of the conductive material dispersion were evaluated. The results are shown in Table 1.

[0245] <Preparation of Cathode Slurry>

[0246] Add 98.0 parts of a layered ternary active material (LiNi) as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 (average particle size: 10 μm), 1.0 part of polyvinylidene fluoride as a binder, 1.0 part (solids content converted) of the above-mentioned conductive material dispersion, and NMP were mixed using a planetary mixer (60 rpm, 30 minutes) to prepare a slurry for the positive electrode. The amount of NMP added was adjusted so that the viscosity of the obtained positive electrode slurry (measured according to JIS Z8803:1991 by a single-cylinder rotational viscometer, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000–5000 mPa·s.

[0247] <The Making of Positive Electrode>

[0248] As the current collector, prepare an aluminum foil with a thickness of 20 μm. Use a notched wheel coater to coat the above-mentioned positive electrode slurry to a dry weight of 20 mg / cm³. 2 The material was coated onto aluminum foil, dried at 90℃ for 20 minutes, then dried at 120℃ for 20 minutes, and finally heat-treated at 60℃ for 10 hours to obtain the positive electrode raw material. This positive electrode raw material was then calendered using a roller press to produce a product with a density of 3.2 g / cm³. 3 A sheet-like positive electrode was formed by combining a positive electrode composite layer and aluminum foil. This sheet-like positive electrode was cut into pieces 48.0 cm wide and 47 cm long for use as a positive electrode in lithium-ion secondary batteries. The flexibility and smoothness of this positive electrode were evaluated. The results are shown in Table 1.

[0249] <Making the Negative Electrode>

[0250] In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of deionized water, and 0.5 parts of potassium persulfate as a polymerization initiator were added. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. The polymerization reaction was terminated by cooling when the polymerization conversion reached 96%, yielding a mixture containing particulate binder material (styrene-butadiene copolymer). A 5% sodium hydroxide aqueous solution was added to the mixture to adjust the pH to 8, and unreacted monomers were removed by heated vacuum distillation. The mixture was then cooled to below 30°C to obtain an aqueous dispersion containing binder material for the negative electrode.

[0251] In a planetary mixer, 48.75 parts of artificial graphite and 48.75 parts of natural graphite, as the negative electrode active material, and 1 part (equivalent to the solid content) of carboxymethyl cellulose as a thickener were added. The mixture was then diluted with deionized water to a solid content concentration of 60%, and then kneaded at 45 rpm for 60 minutes. Next, 1.5 parts (equivalent to the solid content) of the aqueous dispersion containing the negative electrode binder material obtained above were added, and the mixture was kneaded at 40 rpm for 40 minutes. Then, deionized water was added to achieve a viscosity of 3000 ± 500 mPa·s (measured with a Type B viscometer at 25°C and 60 rpm), thereby preparing a negative electrode slurry.

[0252] The above-mentioned negative electrode slurry was applied using a corner-shaped coating machine at a coating amount of 10 ± 0.5 mg / cm². 2 The slurry composition for the negative electrode composite layer is applied to the surface of a 15 μm thick copper foil used as a current collector. Then, the copper foil coated with the slurry composition for the negative electrode composite layer is transported at a speed of 400 mm / min in an oven at 80°C for 2 minutes, and then in an oven at 110°C for 2 minutes, thereby drying the negative electrode slurry on the copper foil, and obtaining a negative electrode raw material with a negative electrode composite layer formed on the current collector.

[0253] The negative electrode raw material was calendered using a roller press to produce a material with a density of 1.6 g / cm³. 3 A sheet-shaped negative electrode is formed by a negative electrode composite material layer and aluminum foil. Then, the sheet-shaped negative electrode is cut into pieces with a width of 50.0 mm and a length of 52 cm to serve as the negative electrode for lithium-ion secondary batteries.

[0254] <The Manufacturing of Lithium-ion Secondary Batteries>

[0255] The positive and negative electrodes for lithium-ion secondary batteries described above are sandwiched between 15 μm thick spacers (microporous membranes made of polyethylene) in an electrode composite material layer configuration, and wound using a 20 mm diameter core to obtain a wound body. The wound body is then compressed in one direction at a speed of 10 mm / s until its thickness reaches 4.5 mm. Furthermore, the compressed wound body, viewed from above, is elliptical in shape, with a major-to-minor axis ratio (major axis / minor axis) of 7.7.

[0256] In addition, a 1.0 M LiPF6 solution (a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio) and containing an additive of 2% (volume ratio) of ethylene carbonate) was prepared as the electrolyte.

[0257] The compressed winding was then placed inside an aluminum laminated casing along with 3.2g of electrolyte. Nickel wires were then connected to the designated location on the negative electrode, and aluminum wires were connected to the designated location on the positive electrode. Finally, the opening of the casing was sealed using heat to obtain a lithium-ion secondary battery. This lithium-ion secondary battery is a pouch-shaped battery with a width of 35mm, a height of 60mm, and a thickness of 5mm, and has a nominal capacity of 700mAh.

[0258] The low-temperature output characteristics, rate performance, and cycle performance of the obtained lithium-ion secondary batteries were evaluated. The results are shown in Table 1.

[0259] (Example 2)

[0260] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0261] <Preparation of Conductive Material Dispersion (Preparation Method: B-2)>

[0262] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were mixed using a planetary mixer as the conductive material. 2 12.5 parts (equivalent to 1 part as solid component) of HNBR-1 NMP solution and 82.5 parts of NMP were dispersed at 60 rpm for 30 minutes while maintaining a temperature of 45°C (first dispersion step). Next, a conductive material dispersion was prepared by dispersing the solution at 30 m / s for 5 minutes using a thin-film rotary high-speed mixer (Plutomix Machinery Co., Ltd., product name "Filmix, model 56-50") to a circumferential speed of 30 m / s (second dispersion step).

[0263] (Example 3)

[0264] Using the dispersant (HNBR-2) and conductive material dispersion prepared as described below, except that, the same procedures as in Example 1 were followed to fabricate positive electrode slurries, positive electrodes, negative electrodes, and lithium-ion secondary batteries, and various evaluations were performed. The results are shown in Table 1.

[0265] <Preparation of Dispersant (HNBR-2)>

[0266] The amount of TDM used was changed to 0.4 parts, and otherwise the same procedure was performed as for HNBR-1 in Example 1 to obtain an NMP solution of HNBR-2 (solid component concentration: 8%).

[0267] <Preparation of Conductive Material Dispersion (Preparation Method: B-3)>

[0268] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were mixed using a planetary mixer as the conductive material. 2 The first dispersion step involves dispersing the composition obtained after the first dispersion step with 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-2 NMP solution and 82.5 parts of NMP at 60 rpm for 30 minutes while maintaining the temperature below 25°C. The second dispersion step involves further adding 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-2 NMP solution and dispersing the composition using a thin-film rotary high-speed mixer (Plutomix Machinery Co., Ltd., product name "Filmix, model 56-50") at a circumferential speed of 30 m / s for 5 minutes.

[0269] (Example 4)

[0270] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0271] <Preparation of Conductive Material Dispersion (Preparation Method: A-3)>

[0272] In the second dispersion step, the circumferential speed of the thin-film rotary high-speed mixer is changed to 20 m / s. Otherwise, the preparation method A-1 of Example 1 is carried out in the same manner to prepare the conductive material dispersion.

[0273] (Example 5)

[0274] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0275] <Preparation of Conductive Material Dispersion (Preparation Method: A-4)>

[0276] In the second dispersion step, the circumferential speed of the thin-film rotary high-speed mixer is changed to 40 m / s. Otherwise, the preparation method A-1 of Example 1 is carried out in the same manner to prepare the conductive material dispersion.

[0277] (Example 6)

[0278] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0279] <Preparation of Conductive Material Dispersion (Preparation Method: A-5)>

[0280] In the second dispersion step, the dispersion time using a thin-film rotary high-speed mixer is changed to 3 minutes. Otherwise, the process is carried out in the same manner as preparation method A-1 in Example 1 to prepare a conductive material dispersion.

[0281] (Example 7)

[0282] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0283] <Preparation of Conductive Material Dispersion (Preparation Method: A-6)>

[0284] In the second dispersion step, the dispersion time using a thin-film rotary high-speed mixer is changed to 10 minutes. Otherwise, the process is carried out in the same manner as preparation method A-1 in Example 1 to prepare a conductive material dispersion.

[0285] (Example 8)

[0286] Using the dispersant (ACL) prepared as described below, except as in Example 1, conductive material dispersions, positive electrode slurries, positive electrodes, negative electrodes, and lithium-ion secondary batteries were prepared and various evaluations were performed. The results are shown in Table 1.

[0287] <Preparation of Dispersant (ACL)>

[0288] In an autoclave equipped with a stirrer, 164 parts of deionized water, 35 parts of 2-ethylhexyl acrylate, 32 parts of styrene, 30 parts of acrylonitrile, 3 parts of methacrylic acid, 0.3 parts of potassium persulfate as a polymerization initiator, 1.2 parts of sodium polyoxyethylene alkyl ether sulfate as an emulsifier, and 0.6 parts of TDM as a molecular weight regulator were added. After thorough stirring, the mixture was heated at 70°C for 3 hours and then at 80°C for 2 hours to carry out polymerization, obtaining an aqueous dispersion of acrylic polymer (ACL). The solids concentration of this aqueous dispersion was 37.3%, and the polymerization conversion rate calculated based on the solids concentration was 96%.

[0289] Add 200 parts of NMP to 100 parts of the aqueous dispersion, and evaporate all water and residual monomers under reduced pressure, then evaporate NMP to obtain an NMP solution of ACL (solid component concentration: 8%).

[0290] (Example 9)

[0291] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 1.

[0292] <Preparation of Conductive Material Dispersion (Preparation Method: C-2)>

[0293] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 The first dispersion step involves dispersing 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-1 NMP solution and 82.5 parts of NMP at 3000 rpm for 30 minutes while maintaining the temperature below 25°C.

[0294] Next, 6.25 parts (equivalent to 0.5 parts as solids) of an NMP solution of HNBR-1 were added to the composition obtained after the first dispersion step, and 1.5 mm diameter zirconia beads were mixed at a circumferential speed of 12 m / s for 20 minutes with an apparent filling rate of 50 vol%. Next, 0.8 mm diameter zirconia beads were mixed at a circumferential speed of 8 m / s for 20 minutes with an apparent filling rate of 50 vol%. Further, 0.8 mm diameter zirconia beads were mixed at a circumferential speed of 12 m / s for 20 minutes with an apparent filling rate of 80 vol%, to prepare a conductive material dispersion (second dispersion step).

[0295] (Comparative Example 1)

[0296] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared and various evaluations were performed. The results are shown in Table 2.

[0297] <Preparation of Conductive Material Dispersion (Preparation Method: A-2)>

[0298] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2The first dispersion step involves dispersing the composition obtained after the first dispersion step with 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-1 NMP solution and 82.5 parts of NMP at 3000 rpm for 30 minutes while maintaining the temperature below 25°C. The second dispersion step involves further adding 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-1 NMP solution to the composition obtained after the first dispersion step and dispersing it for 5 minutes at a circumferential speed of 30 m / s using a thin-film rotary high-speed mixer (Plutomix Machinery Co., Ltd., product name "Filmix, model 56-50") to prepare a conductive material dispersion.

[0299] (Comparative Example 2)

[0300] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared and various evaluations were performed. The results are shown in Table 2.

[0301] <Preparation of Conductive Material Dispersion (Preparation Method: B-1)>

[0302] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were mixed using a planetary mixer as the conductive material. 2 The first dispersion step involves dispersing 12.5 parts (equivalent to 1 part as solid component) of HNBR-1 NMP solution and 82.5 parts of NMP at 60 rpm for 30 minutes while maintaining the temperature below 25°C. Next, a conductive material dispersion is prepared by dispersing the mixture using a thin-film rotary high-speed mixer (Plutomix Machinery Co., Ltd., product name "Filmix, model 56-50") at a circumferential speed of 30 m / s for 5 minutes.

[0303] (Comparative Example 3)

[0304] In preparing the conductive material dispersion, HNBR-2, prepared in the same manner as in Example 3, was used instead of HNBR-1. Otherwise, the process was the same as in Comparative Example 2. Conductive material dispersions, positive electrode slurries, positive electrodes, negative electrodes, and lithium-ion secondary batteries were prepared, and various evaluations were performed. The results are shown in Table 2.

[0305] (Comparative Example 4)

[0306] In preparing the conductive material dispersion, HNBR-2, prepared in the same manner as in Example 3, was used instead of HNBR-1. Otherwise, the process was the same as in Comparative Example 1. Conductive material dispersions, positive electrode slurries, positive electrodes, negative electrodes, and lithium-ion secondary batteries were prepared, and various evaluations were performed. The results are shown in Table 2.

[0307] (Comparative Example 5)

[0308] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared and various evaluations were performed. The results are shown in Table 2.

[0309] <Preparation of Conductive Material Dispersion (Preparation Method: C-1)>

[0310] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 The first dispersion step involves dispersing 12.5 parts (equivalent to 1 part as solid component) of HNBR-1 NMP solution and 82.5 parts of NMP at 3000 rpm for 30 minutes while keeping the temperature below 25°C.

[0311] Next, the composition obtained after the first dispersion step is mixed with zirconia beads with a diameter of 1.25 mm for 1 hour at a circumferential speed of 8 m / s using a bead mill (manufactured by Ashizawa Fine Technology Co., Ltd., product name "LMZ015") to prepare a conductive material dispersion (second dispersion step).

[0312] (Comparative Example 6)

[0313] Using the conductive material dispersion prepared as described below, except as in Example 3, dispersant (HNBR-2), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 2.

[0314] <Preparation of Conductive Material Dispersion (Preparation Method: C-3)>

[0315] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were mixed using a planetary mixer as the conductive material. 2 The first dispersion step involves dispersing 6.25 parts (equivalent to 0.5 parts as solids) of HNBR-2 NMP solution and 82.5 parts of NMP at 60 rpm for 30 minutes while maintaining the temperature below 25°C.

[0316] Next, 6.25 parts (equivalent to 0.5 parts as solids) of NMP solution of HNBR-2 were added to the composition obtained after the first dispersion step, and zirconia beads with a diameter of 1.25 mm were mixed at a circumferential speed of 8 m / s for 20 minutes with an apparent filling rate of 80% by volume using a bead mill (manufactured by Ashizawa Fine Technology Co., Ltd., product name "LMZ015") to prepare a conductive material dispersion (second dispersion step).

[0317] (Comparative Example 7)

[0318] Using the conductive material dispersion prepared as described below, except as in Example 1, positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated, and various evaluations were performed. The results are shown in Table 2.

[0319] <Preparation of Conductive Material Dispersion (Preparation Method: A-7)>

[0320] Prepare an NMP solution (solid component concentration: 8%) of polyvinylpyrrolidone (manufactured by Tokyo Chemical Co., Ltd., product name "PVP K15").

[0321] Four parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 A dispersion of PVP was prepared by dispersing 12.5 parts (equivalent to 1 part as solid component) of NMP solution and 83.5 parts of NMP at 3000 rpm for 30 minutes while maintaining the temperature below 25°C (first dispersion step). Next, a conductive material dispersion was prepared by dispersing the mixture at 40 m / s for 1 minute using a thin-film rotary high-speed mixer (Pulex Machinery Co., Ltd., product name "Filmix, model 56-50") to prepare the dispersion (second dispersion step).

[0322] (Comparative Example 8)

[0323] Using the conductive material dispersion prepared as described below, except as in Example 1, dispersant (HNBR-1), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared and various evaluations were performed. The results are shown in Table 2.

[0324] <Preparation of Conductive Material Dispersion (Preparation Method: A-8)>

[0325] Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 A dispersion of PVP was prepared by dispersing 12.5 parts (equivalent to 1 part as solid component) of NMP solution and 82.5 parts of NMP at 3000 rpm for 30 minutes while maintaining a temperature of 45°C (first dispersion step). Next, a conductive material dispersion was prepared by dispersing the PVP solution using a thin-film rotary high-speed mixer (Pulex Machinery Co., Ltd., product name "Filmix, model 56-50") at a circumferential speed of 50 m / s for 20 minutes (second dispersion step).

[0326] (Comparative Example 9)

[0327] Using the conductive material dispersion prepared as described below, except as in Example 3, dispersant (HNBR-2), positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were fabricated and various evaluations were performed. The results are shown in Table 2.

[0328] <Preparation of Conductive Material Dispersion (Preparation Method: C-1)>

[0329] Two parts of multi-walled carbon nanotubes (BET specific surface area: 250 m²) were dispersed using a disperser as the conductive material. 2 5 parts (equivalent to 0.4 parts as solid component) of HNBR-2 NMP solution and 93 parts of NMP were dispersed at 3000 rpm for 30 minutes while keeping the temperature below 25°C (first dispersion step).

[0330] Next, the composition obtained after the first dispersion step is mixed with zirconia beads with a diameter of 1.25 mm for 1 hour at a circumferential speed of 8 m / s using a bead mill (manufactured by Ashizawa Fine Technology Co., Ltd., product name "LMZ015") to prepare a conductive material dispersion (second dispersion step).

[0331] [Table 1]

[0332]

[0333] [Table 2]

[0334]

[0335] As shown in Tables 1 and 2, if the conductive material dispersions of Examples 1 to 9, which contain CNT-containing conductive materials, dispersants, and dispersion media, and whose Carson viscosity, Carson yield value, and hysteresis constant are all below specified values, are used, a positive electrode with excellent flexibility and smoothness can be produced. Furthermore, based on this positive electrode, lithium-ion secondary batteries can exhibit excellent cycle characteristics. It is also evident that in Examples 1 to 9, the low-temperature output characteristics and cycle characteristics of the lithium-ion secondary batteries are also excellent.

[0336] Industrial availability

[0337] According to the present invention, it is possible to provide a conductive material dispersion for electrochemical elements and a slurry for electrochemical element electrodes that can form electrodes with excellent softness and smoothness and enable electrochemical elements to exhibit excellent cycle characteristics.

[0338] Furthermore, according to the present invention, it is possible to provide an electrode for an electrochemical element that exhibits excellent flexibility and smoothness and enables the electrochemical element to perform excellent cycle characteristics.

[0339] Moreover, according to the present invention, an electrochemical element with excellent cycle characteristics can be provided.

Claims

1. A conductive material dispersion for electrochemical components, comprising a conductive material, a dispersant, and a dispersion medium. The conductive material contains carbon nanotubes. The Cassen viscosity of the conductive material dispersion for the electrochemical element is 30 (Pa·s). 1 / 2 The following is a Carson yield value of 20 Pa. 1 / 2 The following, and the lag constant is below 0.7, Here, the hysteresis constant is calculated using the following equation (I). The lag constant C = (N1 - N2) / N1…(I) In formula (I), N1: For the conductive material dispersion of the electrochemical element, the shear rate was adjusted from 10 at 25°C using a rheometer. - 2 s -1 Rise to 10 3 s -1 The shear rate during viscosity measurement was 10 s. -1 viscosity (Pa·s), N2: For the conductive material dispersion of the electrochemical element after N1 determination, the shear rate was adjusted from 10 at 25°C using a rheometer. 3 s -1 Reduced to 10 -2 s -1 The shear rate during viscosity measurement was 10 s. -1 The viscosity (Pa·s).

2. The conductive material dispersion for electrochemical elements according to claim 1, wherein, The dispersant contains nitrile-based monomer units.

3. The conductive material dispersion for electrochemical elements according to claim 1 or 2, wherein, The content of the carbon nanotubes is 1.0% by mass or more and 30.0% by mass or less, and the content of the dispersant is 0.1% by mass or more and 3.0% by mass or less.

4. A slurry for an electrochemical element electrode, comprising an electrode active material and a dispersion of a conductive material for an electrochemical element according to any one of claims 1 to 3.

5. An electrode for an electrochemical element having an electrode composite material layer formed using the slurry for an electrochemical element electrode as described in claim 4.

6. An electrochemical element having the electrode for an electrochemical element as described in claim 5.

Images