Conductive material dispersion for electrochemical element, slurry for electrochemical element electrode, electrode for electrochemical element, and electrochemical element

Abstract

The object of the present invention is to provide a conductive material dispersion for an electrochemical element, which has excellent viscosity stability and can form an electrode that enables the electrochemical element to exhibit excellent rate characteristics. The conductive material dispersion of the present invention comprises a conductive material containing CNT, a dispersant, and a dispersion medium, and the thermal decomposition time of the CNT is 1.5 minutes / mg or more and less than 10 minutes / mg. In addition, the thermal decomposition time is calculated by preparing a thermogravimetric curve and a differential thermogravimetric curve by thermogravimetric analysis, and then using the following formula (I). Thermal decomposition time T = (T1-T0) / W0... (I) T0: The time (minutes) when the minimum value is taken just before the final peak of the differential thermogravimetric curve appears T1: The time (minutes) required for the mass M1 of the above-mentioned measurement sample when the elapsed time is T0 minutes obtained from the thermogravimetric curve to decrease to M1×0.10 W0: The weight (mg) of the measurement sample at the start of the above-mentioned heat treatment in an air atmosphere at 600°C.

Description

Technical Field

[0001] The present invention relates to a conductive material dispersion for an electrochemical element, a slurry for an electrochemical element electrode, an electrochemical element electrode, and an electrochemical element. Background Art

[0002] Electrochemical devices such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double-layer capacitors are compact, lightweight, have high energy density, and are capable of repeated charge and discharge, making them used in a wide range of applications. Electrodes for these electrochemical devices include, for example, a current collector and an electrode composite material layer formed by drying a slurry for the electrochemical device electrodes onto the current collector.

[0003] In recent years, carbon nanotubes (hereinafter sometimes referred to as "CNTs") have been used as conductive materials in the formation of electrode composite material layers. In order to obtain an electrode composite material layer in which the CNTs are well dispersed, a technique has been proposed in which the CNTs, as a conductive material, are premixed with a dispersant to form a conductive material dispersion for an electrochemical element, and the resulting conductive material dispersion is combined with an electrode active material to prepare an electrode slurry (see, for example, Patent Documents 1 to 3).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2018-533175;

[0007] Patent Document 2: International Publication No. 2017 / 010093;

[0008] Patent Document 3: Japanese Patent Application Publication No. 2018-127397. Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, in the above-mentioned prior art, it is required to improve the physical properties of the conductive material dispersion and further improve the device characteristics of the electrochemical element. Specifically, in the above-mentioned prior art, it is required to suppress the viscosity change of the conductive material dispersion during long-term storage (i.e., ensure viscosity stability) and enable the electrochemical element to exhibit excellent rate characteristics.

[0011] Therefore, an object of the present invention is to provide a conductive material dispersion for an electrochemical device that has excellent viscosity stability and can form an electrode that enables the electrochemical device to exhibit excellent rate characteristics.

[0012] Another object of the present invention is to provide a slurry for electrochemical device electrodes that can form an electrode that enables an electrochemical device to exhibit excellent rate characteristics.

[0013] Furthermore, an object of the present invention is to provide an electrode for an electrochemical device that enables the electrochemical device to exhibit excellent rate characteristics.

[0014] Furthermore, an object of the present invention is to provide an electrochemical device having excellent rate characteristics.

[0015] Solutions for solving problems

[0016] The present inventors conducted intensive research with the goal of solving the above-mentioned problems. The inventors discovered that a conductive material dispersion comprising a dispersant and CNTs (conductive material) in a dispersion medium, wherein the CNT thermal decomposition time measured by a prescribed method is within a prescribed range, exhibits excellent viscosity stability. Furthermore, when electrodes are fabricated using this conductive material dispersion, electrochemical devices exhibit excellent rate characteristics, leading to the completion of the present invention.

[0017] That is, the purpose of the present invention is to advantageously solve the above-mentioned problems. The conductive material dispersion for electrochemical elements of the present invention is characterized in that it contains a conductive material, a dispersant and a dispersion medium, the above-mentioned conductive material contains carbon nanotubes, and the thermal decomposition time of the above-mentioned carbon nanotubes is greater than 1.5 minutes / mg and less than 10 minutes / mg.

[0018] Here, the above-mentioned thermal decomposition time is the following value: the above-mentioned conductive material dispersion for electrochemical elements is dried at a temperature of 130°C for 2 hours, the above-mentioned dispersion medium is removed, and a residue is obtained, the above-mentioned residue is heated from 25°C to 600°C at a heating rate of 20°C / min in a nitrogen atmosphere, and then heated at 600°C for 10 minutes to prepare a measurement sample, and a thermogravimetric curve and a differential thermogravimetric curve are prepared based on the mass change and the elapsed time when the above-mentioned measurement sample is heat-treated in an air atmosphere at 600°C, and the value is calculated by the following formula (I).

[0019] Thermal decomposition time T = (T1-T0) / W0...(I)

[0020] In formula (I),

[0021] T0: The time (minutes) before the final peak of the differential thermogravimetric curve reaches its minimum value

[0022] T1: Time (minutes) required for the mass M1 of the measurement sample to decrease to M1×0.10 when the elapsed time is T0 minutes, as determined from the thermogravimetric curve.

[0023] W0: Weight (mg) of the measurement sample at the start of the above-mentioned heat treatment in an air atmosphere at 600° C. More specifically, the thermal decomposition time of CNT can be derived using the method described in Examples.

[0024] As described above, a conductive material dispersion containing a dispersant and a conductive material containing CNTs in a dispersion medium, wherein the thermal decomposition time of the CNTs is within the above-mentioned range, has excellent viscosity stability. Furthermore, when an electrode is fabricated using this conductive material dispersion, an electrochemical element can exhibit excellent rate characteristics.

[0025] Furthermore, the conductive material dispersion for electrochemical devices of the present invention preferably comprises a nitrile-containing monomer unit in the dispersant. Using a polymer comprising a nitrile-containing monomer unit as the dispersant can further improve the viscosity stability of the conductive material dispersion and the rate characteristics of the electrochemical device.

[0026] In the present invention, the statement that a polymer such as a dispersant "contains a monomer unit" means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer."

[0027] In the present invention, the content ratio of the repeating units (monomer units and structural units described below) in the polymer can be expressed as follows: 1 H-NMR and 13 The measurement is performed by nuclear magnetic resonance (NMR) methods such as C-NMR.

[0028] Furthermore, the present invention aims to advantageously solve the aforementioned problems. The present invention provides an electrochemical device electrode slurry comprising an electrode active material and any of the aforementioned conductive material dispersions for electrochemical devices. When an electrode is fabricated using the electrode slurry comprising the electrode active material and any of the aforementioned conductive material dispersions, the electrochemical device comprising the electrode can exhibit excellent rate characteristics.

[0029] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The present invention is characterized in that the electrode for an electrochemical element comprises an electrode composite material layer formed using the above-mentioned slurry for an electrochemical element electrode. The electrode comprising the electrode composite material layer formed using the above-mentioned slurry for an electrochemical element enables the electrochemical element to exhibit excellent rate characteristics.

[0030] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the electrochemical device of the present invention is characterized by comprising the above-mentioned electrode for an electrochemical device. The electrochemical device comprising the above-mentioned electrode has excellent device characteristics such as rate characteristics.

[0031] Effects of the Invention

[0032] According to the present invention, it is possible to provide a conductive material dispersion for an electrochemical device that has excellent viscosity stability and can form an electrode that enables an electrochemical device to exhibit excellent rate characteristics.

[0033] Furthermore, according to the present invention, it is possible to provide a slurry for electrochemical device electrodes capable of forming an electrode that enables an electrochemical device to exhibit excellent rate characteristics.

[0034] Furthermore, according to the present invention, it is possible to provide an electrode for an electrochemical device that enables the electrochemical device to exhibit excellent rate characteristics.

[0035] Furthermore, according to the present invention, an electrochemical device having excellent rate characteristics can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a graph showing the results of thermogravimetric analysis of a measurement sample prepared from the conductive material dispersion in Example 1. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described in detail.

[0038] Here, the electrochemical element conductive material dispersion of the present invention can be used as a material when manufacturing an electrochemical element electrode slurry. Furthermore, the electrochemical element electrode slurry of the present invention can be prepared using the electrochemical element conductive material dispersion of the present invention. In addition, the electrochemical element electrode of the present invention is characterized in that it has an electrode composite material layer formed using the electrochemical element electrode slurry of the present invention. In addition, the electrochemical element of the present invention is characterized in that it has an electrochemical element electrode of the present invention.

[0039] (Conductive material dispersion for electrochemical devices)

[0040] The conductive material dispersion of the present invention comprises a conductive material, a dispersant, and a dispersion medium, and optionally contains other components. At least CNTs are required as the conductive material. Furthermore, the conductive material dispersion typically does not contain an electrode active material (positive electrode active material or negative electrode active material).

[0041] Furthermore, the conductive material dispersion of the present invention is characterized in that the thermal decomposition time of CNTs, measured using a prescribed method, is 1.5 minutes / mg or greater and less than 10 minutes / mg. Such a conductive material dispersion exhibits excellent viscosity stability, and using this conductive material dispersion to fabricate electrodes can improve the rate characteristics of electrochemical devices.

[0042] The reason why the conductive material dispersion of the present invention, in which the thermal decomposition time of CNTs is within the above-mentioned range, achieves the above-mentioned effects is not clear, but the present inventors speculate as follows based on their studies.

[0043] First, the technical significance of thermal decomposition time will be explained. The degree of dispersion of conductive materials (e.g., acetylene black, a granular conductive material) in conductive material dispersions has traditionally been evaluated using average particle size and viscosity. On the other hand, CNTs, as cylindrical structures, are easily bundled due to van der Waals forces. By unbundling (defibration) and using them, various properties can be improved. However, according to the inventors' research, the above-mentioned conventional methods of evaluating average particle size and viscosity are sometimes inappropriate for evaluating the degree of defibration of CNTs in cylindrical structures. For example, it is conceivable that the decrease in average particle size is not due to defibration of the CNT bundle, but rather to the CNTs being cut and shortened during the dispersion process. Similarly, it is conceivable that the decrease in viscosity is not due to defibration of the CNT bundle, but rather to the CNTs being cut and shortened during the dispersion process, thereby reducing viscous resistance. Thus, average particle size and viscosity are sometimes inappropriate for properly evaluating the "maintained CNT length and defibrated state" required for effective use of CNT structures.

[0044] In contrast, the thermal decomposition time, which is of interest in this invention, is a parameter more suitable for evaluating the degree of CNT defibration in a conductive material dispersion. Specifically, based on the principle that as CNTs defibrate (unbundle more), their exposed surface area actually increases, leading to increased thermal decomposition (i.e., their mass decreases faster during heat treatment), the degree of CNT defibration is assessed by measuring the mass loss of the sample and the time required for this mass reduction. More specifically, a longer thermal decomposition time indicates less CNT defibration, while a shorter thermal decomposition time indicates more CNT defibration.

[0045] Therefore, it is speculated that if the thermal decomposition time of CNTs is below the upper limit, the CNT bundles will be well defibrated, and the CNTs will form a good conductive path in the electrode composite material layer, enabling the electrochemical device to achieve excellent rate characteristics. On the other hand, it is believed that if the thermal decomposition time of CNTs is above the lower limit, the CNTs will not be subjected to excessive defibration, and the CNTs will exist in a bundle to a certain extent, and their length will be maintained. Therefore, it is possible to suppress disadvantages such as insufficient conductive path formation and increased defects caused by CNT severance, the occurrence of side reactions caused by increased reactive sites, and reduced viscosity stability of the conductive material dispersion.

[0046] Furthermore, the BET specific surface area, which is generally shown as a physical property of CNTs, is often measured in a bundled state and is therefore not suitable for use in evaluating the defibrillated state (dispersed state) of CNTs.

[0047] <Conductive Materials>

[0048] As the conductive material, at least CNTs are used, but CNTs may be used in combination with a conductive material other than CNTs (other conductive materials).

[0049] <<Carbon Nanotubes>>

[0050] The CNTs may be single-walled carbon nanotubes or multi-walled carbon nanotubes. In addition, single-walled CNTs and multi-walled CNTs may be used in combination.

[0051] [Thermal decomposition temperature]

[0052] Furthermore, as described above, the thermal decomposition temperature of the CNTs in the conductive material dispersion of the present invention needs to be within a predetermined range.

[0053] Here, the method for measuring the thermal decomposition temperature is described in detail. The thermal decomposition temperature can be derived through the following steps [1] to [3].

[0054] [1] Drying the conductive material dispersion at 130° C. for 2 hours to remove the dispersion medium and obtain a residue;

[0055] [2] The residue obtained in [1] was heated from 25°C to 600°C at a heating rate of 20°C / min under a nitrogen atmosphere, and then heated at 600°C for 10 minutes to prepare a measurement sample; and

[0056] [3] A thermogravimetric curve and a differential thermogravimetric curve were prepared based on the mass change and the elapsed time of the measurement sample obtained in [2] when it was heat-treated at 600°C in an air atmosphere, and the thermal decomposition temperature was calculated using the above formula (I).

[0057] -Step [1]-

[0058] In step [1], the conductive material dispersion is dried at 130°C for 2 hours. This step [1] volatilizes and removes the dispersion medium contained in the conductive material dispersion, thereby obtaining a residue. The resulting residue does not need to completely remove the dispersion medium; a portion of the dispersion medium may remain. Drying of the conductive dispersion can be performed using any device, and is not particularly limited.

[0059] -Step [2]-

[0060] In step [2], the residue obtained in step [1] is heated from 25°C to 600°C at a heating rate of 20°C / minute under a nitrogen atmosphere, and then heated at 600°C for 10 minutes. This step [2] allows the polymer, such as the dispersant, to be decomposed and removed while maintaining the defibrillated state of the CNTs, which are the conductive material, to obtain a measurement sample. If any dispersion medium remains in step [1], it can be removed in step [2].

[0061] The heating of the residue in a nitrogen atmosphere can be performed using any apparatus without particular limitation, but is preferably performed using a thermogravimetric analyzer. This is because, if a thermogravimetric analyzer is used, step [3] can be performed continuously after step [2] in a single thermogravimetric analyzer, and the removal status of the polymer can be understood from the weight change data.

[0062] The measurement sample obtained in step [2] usually contains CNTs in a state substantially similar to that in the residue. Alternatively, the measurement sample may contain a polymer carbonized by heating or any component that can be contained in the conductive material dispersion.

[0063] -Step [3]-

[0064] In step [3], the measurement sample obtained in step [2] is subjected to thermogravimetric analysis. Specifically, the sample is heat treated at 600°C in an air atmosphere, and the change in mass (mass change) over time is measured. A thermogravimetric curve and a differential thermogravimetric curve are then generated based on the mass change and elapsed time, and the thermal decomposition time is calculated using formula (I).

[0065] The heat treatment of the measurement sample in an air atmosphere at 600° C. is preferably performed by performing step [2] using a thermogravimetric analyzer and then replacing the nitrogen atmosphere used with an air atmosphere in step [3].

[0066] Here, the measurement sample may contain components other than CNTs, such as the polymer carbonized in step [2]. Furthermore, if the measurement sample contains CNTs, the temporal change in the mass of the measurement sample during thermogravimetric analysis of the measurement sample also includes changes in the mass of the sample other than CNTs. Therefore, from the perspective of accurately evaluating the defibration state of CNTs, step [3] is performed as follows.

[0067] Specifically, the following operations are performed in step [3]: operation [3-1], obtaining a differential thermogravimetric curve based on the mass change and elapsed time of the measurement sample obtained in step [2]; operation [3-2], determining the elapsed time T0 at which the differential thermogravimetric curve reaches its minimum value just before the peak corresponding to the combustion of the CNT appears in the differential thermogravimetric curve; and operation [3-3], determining the time T1 required for the mass M1 of the measurement sample at time T0 to decrease to M1×0.10.

[0068] In a differential thermogravimetric curve, changes in the sample mass after time T0 correspond solely to changes in the mass of the CNTs. Therefore, by calculating the time T1 required for the sample mass M1 at time T0 to decrease to M1 × 0.10, and using this time to evaluate the CNT defibration state in the sample, the influence of components other than CNTs in the sample can be reduced, allowing for highly accurate evaluation of the CNT defibration state.

[0069] In addition, generally, in a differential thermogravimetric curve, the final peak of the differential thermogravimetric curve is a peak corresponding to combustion of CNTs.

[0070] Here, the differential thermogravimetric curve can be obtained by time-differentiating a thermogravimetric decrease curve of a measurement sample, which is obtained by, for example, fitting the mass change of the measurement sample to the elapsed time. Specifically, the differential thermogravimetric curve can be obtained, without particular limitation, by fitting the mass change of the measurement sample to the elapsed time using, for example, a Boltzmann (Double Boltzmann) function as shown below, and then time-differentiating the obtained thermogravimetric decrease curve of the measurement sample.

[0071] [Mathematical formula 1]

[0072]

[0073] The thermal decomposition time of CNTs was calculated using the values ​​of T0 (unit: minute) and T1 (unit: minute) obtained above and the mass W0 (unit: mg) of the measurement sample at the start of the heat treatment at 600°C in air atmosphere using the following formula (I).

[0074] Thermal decomposition time T = (T1-T0) / W0...(I)

[0075] Moreover, as mentioned above, the thermal decomposition time of CNT needs to be 1.5 minutes / mg or more and less than 10 minutes / mg, preferably 1.8 minutes / mg or more, more preferably 2.2 minutes / mg or more, preferably less than 8 minutes / mg, more preferably less than 5 minutes / mg. If the thermal decomposition time of CNT is less than 1.5 minutes / mg, the viscosity stability of the conductive material dispersion is reduced. On the other hand, if the thermal decomposition time of CNT is more than 10 minutes / mg, the rate characteristics of the electrochemical element are reduced. In addition, by making the thermal decomposition time within the above range, the cycle characteristics can be improved while suppressing the gas generation of the electrochemical element. In addition, even with the same solid content concentration, the viscosity of the conductive material dispersion can be suppressed to a low level.

[0076] The thermal decomposition time of CNTs in the conductive material dispersion can be adjusted by, for example, changing the type of dispersant used, or by changing the settings of various conditions in the conductive material dispersion preparation method described below.

[0077] Here, the BET specific surface area of ​​CNT is preferably 180 m 2 / g or more, 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 180m 2 / g or more, the rate characteristics of the electrochemical device can be further improved. In addition, the cycle characteristics can be improved while suppressing the gas generation of the electrochemical device. On the other hand, if the BET specific surface area of ​​CNT is 1500m 2 / g or less, the viscosity of the conductive material dispersion can be suppressed to be low even at the same solid content concentration.

[0078] In the present invention, the "BET specific surface area" refers to a nitrogen adsorption specific surface area measured using the BET method.

[0079] The CNTs are not particularly limited, and CNTs synthesized by a known CNT synthesis method such as an arc discharge method, a laser ablation method, or a chemical vapor deposition method (CVD method) can be used.

[0080] <<Other conductive materials>>

[0081] As other conductive materials, any other conductive materials that can function as conductive materials capable of ensuring electrical contact between electrode active materials in the electrode composite layer can be used without particular limitation. Examples of other conductive materials include carbon materials other than CNT. Moreover, as such carbon materials, the following can be cited: carbon black (e.g., acetylene black, Ketjen black (registered trademark), furnace black, etc.); graphite; carbon flakes; carbon nanofibers. These can be used alone or in combination of two or more.

[0082] In addition, as the conductive material, CNT can be used alone or CNT can be used in combination with other conductive materials as described above. However, in the present invention, from the viewpoint of achieving the desired effects well, taking the total mass of the conductive material as 100% by mass, the proportion of CNT 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 only of CNT).

[0083] <<Content of CNT>>

[0084] The content of CNT in the conductive material dispersion is not particularly limited. Taking the total mass of the conductive material dispersion as 100% by mass, the content of CNT in the conductive material dispersion is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, further preferably 3.0% by mass or more, preferably 30.0% by mass or less, more preferably 15.0% by mass or less, and further preferably 7.0% by mass or less. If the content of CNT in the conductive material dispersion is within the above range, the viscosity stability of the conductive material dispersion and the rate characteristics of the electrochemical element can be further improved. In addition, by making the content of CNT in the conductive material dispersion within the above range, the cycle characteristics can be improved while suppressing gas generation in the electrochemical element. In addition to this, the viscosity of the conductive material dispersion can be suppressed to be low.

[0085] <Dispersant>

[0086] As the dispersant, any polymer that can disperse the above-mentioned CNT-containing conductive material in the dispersion medium is not particularly limited. As such a polymer, a polymer containing a nitrile group monomer unit is preferably included.

[0087] <<Nitrile group monomer unit>>

[0088] Examples of nitrile-containing monomers that can form nitrile-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenated acrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkyl acrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Furthermore, the nitrile-containing monomers may be used alone or in combination of two or more at any ratio. Among these, acrylonitrile is preferred.

[0089] Using the whole repeating units in the polymer constituting the dispersant as 100 mass %, as the containing ratio of the nitrile group monomeric unit in the dispersant of polymer is preferably more than 10 mass %, more preferably more than 15 mass %, more preferably more than 20 mass %, preferably less than 50 mass %, more preferably less than 45 mass %, more preferably less than 40 mass %. If the containing ratio of the nitrile group monomeric unit in the dispersant is in the above-mentioned range, it is possible to fully ensure the solubility of the dispersant in the dispersion medium (such as N- methyl -2- pyrrolidone), and the electrode composite material layer obtained can be made to be well fitted in the current collector. Therefore, it is possible to make conductive material well dispersed in conductive material dispersion liquid, and it is possible to further improve the viscosity stability of the conductive material dispersion liquid. In addition, it is possible to further improve the rate characteristics of electrochemical device.

[0090] <<Examples of polymers containing nitrile group-containing monomer units>>

[0091] As the polymer containing a nitrile group-containing monomer unit, preferred examples include a polymer containing a nitrile group-containing monomer unit and an alkylene structural unit, and a polymer containing a nitrile group-containing monomer unit and a (meth)acrylate monomer unit. From the viewpoint of further improving the viscosity stability of the conductive material dispersion and the rate characteristics of the electrochemical element, and from the viewpoint of improving the cycle characteristics while suppressing gas generation of the electrochemical element, the polymer containing a nitrile group-containing monomer unit and an alkylene structural unit is preferred.

[0092] In the present invention, an "alkylene structural unit" is a unit consisting only of the general formula: -C n H 2n -[wherein n is an integer of 2 or more], a repeating unit consisting of an alkylene structure represented by.

[0093] Furthermore, in the present invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0094] [Polymer comprising a nitrile group-containing monomer unit and an alkylene structural unit]

[0095] This polymer contains at least an alkylene structural unit in addition to the above-mentioned nitrile group-containing monomer unit, and may optionally contain repeating units (other repeating units) other than the nitrile group-containing monomer unit and the alkylene structural unit.

[0096] -Alkylene structural unit-

[0097] The alkylene structural unit may be linear or branched. From the perspective of further improving the rate characteristics of the electrochemical device, the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. In addition, the number of carbon atoms in the alkylene structural unit is preferably 4 or more (i.e., n in the above general formula is an integer of 4 or more).

[0098] The method for introducing the alkylene structural unit into the dispersant as a polymer is not particularly limited, and examples thereof include the following methods (1) and (2):

[0099] (1) A method of preparing a polymer from a monomer composition containing a conjugated diene monomer and hydrogenating the polymer to convert the conjugated diene monomer units into alkylene structural units;

[0100] (2) Method for preparing a polymer from a monomer composition containing a 1-olefin monomer Among these methods, method (1) is preferred because it is easy to produce a dispersant.

[0101] Examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is 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).

[0102] Examples of the 1-olefin monomer include ethylene, propylene, and 1-butene.

[0103] These conjugated diene monomers and 1-olefin monomers may be used alone or in combination of two or more at any ratio.

[0104] Moreover, taking the whole repeating units in the polymer constituting the dispersant as 100 mass %, the containing ratio of the alkylene structural unit in the dispersant as the polymer is preferably more than 40 mass %, more preferably more than 45 mass %, more preferably more than 50 mass %, preferably below 90 mass %, more preferably below 85 mass %, more preferably below 80 mass %. If it is inferred that the containing ratio of the alkylene structural unit in the dispersant is in the above-mentioned range, the affinity of the conductive materials such as CNT and the dispersant is improved, therefore, the viscosity stability of the conductive material dispersion can be further improved. In addition, by coating the conductive materials such as CNT well with dispersant, the decomposition of the electrolyte on the conductive material surface can be suppressed, and the gas generation of the electrochemical element can be suppressed.

[0105] When the dispersant is a polymer obtained by the method (1) above, it is preferred that the content ratio of the alkylene structural unit and the total ratio of the conjugated diene monomer units in the dispersant satisfy the above range.

[0106] -Other repeating units-

[0107] The other repeating units in the polymer comprising nitrile group-containing monomer units and alkylene structural units are not particularly limited, and examples thereof include aromatic vinyl monomer units, acidic group-containing monomer units, and (meth)acrylate monomer units. Furthermore, the polymer comprising nitrile group-containing monomer units and alkylene structural units may contain one type of other repeating unit, or may contain two or more types of other repeating units.

[0108] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. The aromatic vinyl monomers may be used alone or in combination of two or more at any ratio. Among these, styrene is preferred.

[0109] Examples of acidic group-containing monomers capable of forming acidic group-containing monomer units include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Acidic group-containing monomers may be used alone or in combination of two or more at any ratio.

[0110] Examples of the carboxylic acid group-containing monomer include monocarboxylic acids and derivatives thereof, dicarboxylic acids and anhydrides thereof, and derivatives thereof.

[0111] Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

[0112] Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0113] Examples of the dicarboxylic acid include maleic acid, fumaric acid, and itaconic acid.

[0114] Examples of the dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0115] Examples of the anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0116] Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group by hydrolysis can also be used. Among them, acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer.

[0117] Examples of the sulfonic acid group-containing monomer include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, 2-sulfonic ethyl (meth)acrylate, 2-acrylamide-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0118] In the present invention, "(meth)allyl group" means an allyl group and / or a methallyl group.

[0119] Examples of the phosphoric acid group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0120] In addition, in the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0121] Examples of the (meth)acrylate monomers that can form the (meth)acrylate monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. The (meth)acrylate monomers may be used alone or in combination of two or more at any ratio.

[0122] In addition, taking all repeating units in the polymer comprising nitrile group-containing monomeric units and alkylene structural units as 100 mass%, the content ratio of other repeating units in the polymer comprising nitrile group-containing monomeric units and alkylene structural units is preferably 0 mass% or more and 30 mass% or less, more preferably 0 mass% or more and 20 mass% or less, further preferably 0 mass% or more and 10 mass% or less, and particularly preferably 0 mass% or more and 5 mass% or less.

[0123] [Polymer comprising a nitrile group-containing monomer unit and a (meth)acrylate monomer unit]

[0124] This polymer contains at least a (meth)acrylic acid ester monomer unit in addition to the above-mentioned nitrile group-containing monomer unit, and may optionally contain repeating units (other repeating units) other than the nitrile group-containing monomer unit and the (meth)acrylic acid ester monomer unit.

[0125] Examples of the (meth)acrylate monomers that can form the (meth)acrylate monomer units include the same (meth)acrylate monomers as described in the section "Polymer comprising a nitrile group-containing monomer unit and an alkylene structural unit." The (meth)acrylate monomers may be used alone or in combination of two or more at any ratio. Among these, 2-ethylhexyl acrylate is preferred.

[0126] Moreover, based on 100 mass% of all repeating units in the polymer constituting the dispersant, the content ratio of the (meth)acrylate monomer units in the dispersant as a polymer is preferably 10 mass% or more, more preferably 20 mass% or more, even more preferably 30 mass% or more, and preferably 70 mass% or less, more preferably 60 mass% or less, and even more preferably 50 mass% or less.

[0127] -Other repeating units-

[0128] The other repeating units in the polymer comprising nitrile group-containing monomer units and (meth)acrylate monomer units are not particularly limited, but preferably include aromatic vinyl monomer units and acidic group-containing monomer units. The polymer comprising nitrile group-containing monomer units and (meth)acrylate monomer units as a dispersant may contain one type of other repeating unit or two or more types of other repeating units.

[0129] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include the same aromatic vinyl monomers as those described in the section "Polymer comprising nitrile group-containing monomer units and alkylene structural units." The aromatic vinyl monomers may be used alone or in combination of two or more at any ratio. Among these, styrene is preferred.

[0130] Moreover, taking all repeating units in the polymer constituting the dispersant as 100 mass%, the content ratio of the aromatic vinyl monomer unit in the dispersant as a polymer is preferably 10 mass% or more, more preferably 20 mass% or more, further preferably 30 mass% or more, and preferably 70 mass% or less, more preferably 60 mass% or less, and further preferably 50 mass% or less.

[0131] Examples of acidic group-containing monomers capable of forming acidic group-containing monomer units include the same acidic group-containing monomers as those described in the section "Polymer comprising nitrile group-containing monomer units and alkylene structural units." The acidic group-containing monomers may be used alone or in combination of two or more at any ratio. Among these, methacrylic acid is preferred.

[0132] Moreover, based on 100 mass% of all repeating units in the polymer constituting the dispersant, the content of the acidic group-containing monomer unit in the dispersant as a polymer is preferably 0.5 mass% or more, more preferably 1 mass% or more, even more preferably 1.5 mass% or more, and preferably 10 mass% or less, more preferably 7 mass% or less, and even more preferably 4 mass% or less.

[0133] <<Weight Average Molecular Weight>>

[0134] In addition, the weight average molecular weight of the dispersant as a polymer is preferably more than 10,000, more preferably more than 15,000, further preferably more than 20,000, preferably less than 400,000, more preferably less than 300,000, and further preferably less than 200,000. It is inferred that if the weight average molecular weight of the dispersant is more than 10,000, the dispersant can be suppressed from dissolving into the electrolyte, and therefore, the cycle characteristics of the electrochemical element can be improved. On the other hand, if the weight average molecular weight of the dispersant is less than 400,000, the rate characteristics can be further improved while suppressing the gas generation of the electrochemical element. In addition, even if the solid content concentration is the same, the viscosity of the conductive material dispersion can be suppressed to a low level.

[0135] In the present invention, the "weight average molecular weight" can be measured using the method described in Examples.

[0136] <<Preparation Method of Dispersant>>

[0137] The preparation method of the dispersant is not particularly limited. The dispersant can be prepared by, for example, polymerizing a monomer composition comprising one or more monomers in an aqueous solvent, optionally hydrogenating the monomer composition, and thereby producing the dispersant. In addition, the proportion of each monomer in the monomer composition can be determined according to the proportion of the desired repeating unit (monomeric unit and / or structural unit) in the polymer.

[0138] In addition, the polymerization method is not particularly limited, and any method among solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. In addition, as the polymerization reaction, any reaction among ionic polymerization, free radical polymerization, living free radical polymerization, various polycondensations, addition polymerization, etc. can be used. Moreover, during the polymerization, known emulsifiers and polymerization initiators can be used as needed. In addition, hydrogenation can be carried out by known methods.

[0139] <<Dispersant Content>>

[0140] The content of the dispersant in the conductive material dispersion is not particularly limited. Taking the overall mass of the conductive material dispersion as 100 mass %, the content of the dispersant in the conductive material dispersion is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, further preferably 0.5 mass % or more, preferably 3.0 mass % or less, more preferably 2.5 mass % or less, further preferably 2.0 mass % or less. If the content of the dispersant is within the above-mentioned range, the viscosity stability of the conductive material dispersion and the rate characteristics of the electrochemical element can be further improved. In addition, by making the content of the dispersant within the above-mentioned range, the cycle characteristics can be improved while suppressing the gas generation of the electrochemical element. In addition, the viscosity of the conductive material dispersion can be suppressed to a low level.

[0141] <Dispersion Medium>

[0142] As the dispersion medium, any one of water and organic solvents can be used, and organic solvents are preferred. The organic solvent is not particularly limited, and examples thereof include: alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; diethyl ether, diethyl ether, and diethyl ether. Examples of the dispersion medium include ethers such as alkanes and tetrahydrofuran; 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. The dispersion medium may be used singly or in combination of two or more in any ratio. From the perspective of ensuring good dispersion of the conductive material, such as CNTs, in the conductive material dispersion, an organic solvent is preferred, with NMP being more preferred.

[0143] <Other ingredients>

[0144] The other components that may be included in the conductive material dispersion are not particularly limited, and include components other than the electrode active material described later in the "slurry for electrochemical element electrodes." The other components may be used alone or in combination of two or more in any ratio.

[0145] <Solid Content Concentration>

[0146] In addition, the conductive material dispersion of the present invention preferably has a solid content in the conductive material dispersion as a whole (i.e., solid content concentration) preferably 1.0% by mass or more, more preferably 3.0% by mass or more, further 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, further preferably 10.0% by mass or less, particularly preferably 7.0% by mass or less. If the solid content concentration of the conductive material dispersion is within the above-mentioned range, the viscosity and viscosity stability of the conductive material dispersion can be made into a state suitable for processes such as transfer in the slurry preparation process. In addition, the electrode slurry obtained can also be easily controlled to an appropriate solid content concentration, and an electrode well formed with a conductive path can be efficiently produced.

[0147] <Method for Preparing Conductive Material Dispersion>

[0148] Here, a conductive material dispersion in which CNTs have a thermal decomposition time within the aforementioned range can be produced, for example, by mixing the aforementioned conductive material, dispersant, and dispersion medium through at least two dispersion steps (a first dispersion step and a second dispersion step). In this method, the thermal decomposition time of the CNTs contained in the conductive material dispersion can be controlled by adjusting the dispersion conditions in the first and / or second dispersion steps (the type of dispersing device, the rotational speed and peripheral speed, the dispersion time and temperature, and the ratio of CNTs to dispersant during the dispersion).

[0149] Below, the preferred conditions for controlling the thermal decomposition time of CNTs in a conductive material dispersion liquid within a specified range via a two-stage dispersion process are described. In addition, in this method, different dispersion devices are usually used in the two-stage dispersion process. By using different dispersion devices in the two-stage dispersion process, different dispersion treatments can be applied to the dispersed body in the initial dispersion stage (coarse dispersion stage) and the later dispersion stage (main dispersion stage), making it easy to prepare a new conductive material dispersion liquid with a thermal decomposition time of CNTs within the above-mentioned range. In addition, in this method, processes other than the first dispersion process and the second dispersion process can also be implemented.

[0150] To control the dispersant's adsorption state to the conductive material, methods have traditionally been used, such as changing the dispersant addition method or the ratio of the conductive material to the dispersant. Indeed, when using carbon black as the conductive material, the adsorption state can be controlled using these methods. However, the conductive material dispersion of the present invention contains CNTs as the conductive material, making the control of multiple factors even more crucial in controlling the adsorption state.

[0151] In addition, the method for preparing the conductive material dispersion of the present invention is not necessarily limited to the method described below.

[0152] <<First Dispersion Step>>

[0153] In the first dispersion step, a composition containing at least CNTs, a dispersant, and a dispersion medium is dispersed to obtain a coarse dispersion. The first dispersion step is a step whose main purpose is to wet (fuse) the CNTs, which are dispersed, with the dispersant and dispersion medium.

[0154] Examples of the dispersing apparatus used in the first dispersing step include a disperser, a homogenizer, a planetary mixer, a kneader, and a ball mill. Furthermore, the dispersing apparatus used in the first dispersing step is preferably a disperser or a planetary mixer, and more preferably a disperser.

[0155] When a disperser is used as the dispersing device, the rotation speed is preferably 500 rpm or higher, more preferably 1000 rpm or higher, further preferably 2000 rpm or higher, and preferably 8000 rpm or lower, more preferably 7000 rpm or lower, further preferably 6000 rpm or lower.

[0156] When a planetary mixer is used as the dispersing device, the rotation speed is preferably 5 rpm or more, more preferably 10 rpm or more, further preferably 30 rpm or more, and preferably 150 rpm or less, more preferably 120 rpm or less, further preferably 100 rpm or less.

[0157] The time for the dispersion treatment in the first dispersion step is preferably 12 minutes or longer, more preferably 15 minutes or longer, and even more preferably 20 minutes or longer, and is preferably 60 minutes or shorter, more preferably 50 minutes or shorter, and even more preferably 40 minutes or shorter.

[0158] From the perspective of controlling the molecular mobility of the dispersant and / or dispersion medium, controlling the viscosity of the dispersion system, and controlling the degree of interaction between the CNTs, the dispersion medium, and the dispersant, the temperature of the dispersion treatment in the first dispersion step is preferably 5°C or higher, preferably 50°C or lower, more preferably 45°C or lower, even more preferably 35°C or lower, and particularly preferably 25°C or lower. If the temperature of the dispersion treatment in the first dispersion step is 5°C or higher, the dispersion medium easily penetrates into the gaps between CNT bundles. If the temperature of the dispersion treatment in the first dispersion step is 50°C or lower, deterioration of the dispersant is suppressed, and the dispersant easily adsorbs to the CNTs.

[0159] Regarding the ratio of CNTs to dispersant during the dispersion treatment in the first dispersion step, the content of the dispersant in the composition subjected to the dispersion treatment in the first dispersion step is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, per 100 parts by mass of CNTs. Furthermore, in the first dispersion step, the dispersant can be added all at once at the initial stage of the dispersion treatment, or it can be added in batches. The choice of adding all at once or in batches can be appropriately determined based on, for example, the adsorption capacity of the dispersant.

[0160] <<Second Dispersion Step>>

[0161] In the second dispersion step, the coarse dispersion obtained in the first dispersion step is further dispersed, optionally with the addition of additional dispersants, to obtain a conductive material dispersion. The second dispersion step primarily applies shear force and collision energy to disperse and defibrate the CNTs.

[0162] In the second dispersion step, as described above, a different dispersing device is generally used than that used in the first dispersion step. Examples of dispersing devices used in the second dispersion step include dispersers, homogenizers, planetary mixers, kneaders, and ball mills; and thin-film rotating high-speed mixers such as FILMIX (registered trademark). Furthermore, as a dispersing device used in the second dispersion step, one that does not use a medium (i.e., a medium-free) is preferred, with a thin-film rotating high-speed mixer being more preferred. In particular, when a dispersing device that uses a medium is used in the second dispersion step, which serves as the main dispersion, the CNTs, as cylindrical structures, may be damaged due to contact with the medium, resulting in a reduction in their length, which in turn reduces the viscosity stability of the conductive material dispersion and the rate characteristics of the electrochemical device. In contrast, using a medium-free dispersing device such as a thin-film rotating high-speed mixer allows for efficient defibration of the CNT bundles while suppressing CNT damage, further enhancing the desired effect.

[0163] When using a thin-film rotating high-speed stirrer as the dispersion device, the peripheral speed is preferably 10 m / s or higher, more preferably 20 m / s or higher, and even more preferably 25 m / s or higher, and preferably 45 m / s or lower, more preferably 40 m / s or lower, and even more preferably 35 m / s or lower. When the peripheral speed is within this range, the CNT bundle can be efficiently defibrated without compromising its length.

[0164] The dispersion treatment time in the second dispersion step is preferably 2 minutes or longer, more preferably 3 minutes or longer, and even more preferably 4 minutes or longer, and preferably 20 minutes or shorter, more preferably 10 minutes or shorter, and even more preferably 7 minutes or shorter. When the dispersion treatment time is within this range, homogenization of the conductive material dispersion can be promoted, viscosity can be reduced, and viscosity stability can be improved.

[0165] Furthermore, the ratio of CNTs to dispersant during the dispersion treatment in the second dispersion step is generally the same as that in the resulting conductive material dispersion. Furthermore, in the second dispersion step, the entire amount of dispersant can be added all at once during the initial dispersion treatment, or it can be added in batches to promote efficient adsorption of the dispersant to the newly formed interfaces created by the dispersion and defibration of the CNTs.

[0166] (Slurry for electrochemical device electrodes)

[0167] The electrode slurry of the present invention comprises the above-mentioned conductive material dispersion and electrode active material, and optionally contains optional components such as a binder. In other words, the electrode slurry of the present invention comprises a conductive material containing CNTs, a dispersant, and a dispersion medium, and optionally contains optional components such as a binder.

[0168] In this way, an electrochemical element can exhibit excellent rate characteristics by means of an electrode having an electrode composite layer formed from an electrode paste containing the above-described conductive material dispersion liquid.

[0169] <Electrode active material>

[0170] The electrode active material (positive electrode active material, negative electrode active material) incorporated in the electrode paste is not particularly limited, and known electrode active materials can be used.

[0171] The positive electrode active material used in, for example, a lithium ion secondary battery is not particularly limited, and metal oxides containing lithium (Li) can be cited. Further, as the positive electrode active material, a positive electrode active material containing at least one selected from cobalt (Co), nickel (Ni), manganese (Mn), and iron (Fe) in addition to lithium (Li) is preferred. Examples of such positive electrode active materials include: lithium cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium manganese phosphate (LiMnPO4), olivine-type lithium iron phosphate (LiFePO4), lithium-excess spinel compounds represented by Li 1+x Mn 2-x O4 (0 < X < 2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4, etc. In addition, the positive electrode active material can be used alone or in combination of two or more in any ratio.

[0172] Further, 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 conventionally.

[0173] In addition, the amount of the electrode active material in the electrode paste is not particularly limited and can be within the range used conventionally.

[0174] <Optional components>

[0175] Examples of the optional components that can be included in the electrode paste include, for example, a binder material, a viscosity regulator, a reinforcing material, an antioxidant, and an electrolyte additive having a function of suppressing the decomposition of the electrolyte. These optional components can be used alone or in combination of two or more in any ratio.

[0176] Among the above-mentioned optional components, the slurry for electrodes preferably contains a binder from the viewpoint of allowing the obtained electrode composite material layer to adhere well to the current collector.

[0177] <<Bonding Material>>

[0178] The binder is not particularly limited, but for example, fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyvinyl alcohol (PVOH) are preferred, and fluorine-containing resins and PAN are more preferred.

[0179] The amount of the binder in the electrode slurry is not particularly limited and can be within the range conventionally used.

[0180] <Method for Preparing Electrode Slurry>

[0181] When the above-mentioned components are mixed to obtain the electrode slurry, the mixing method is not particularly limited, and a common mixing device can be used.

[0182] (Electrodes for electrochemical devices)

[0183] The electrode of the present invention has an electrode composite material layer obtained using the above-mentioned electrode slurry of the present invention. More specifically, the electrode of the present invention generally has the above-mentioned electrode composite material layer on a current collector. Here, the electrode composite material layer contains an electrode active material, CNTs and a dispersant, and optionally contains a binder, etc. Moreover, the electrode of the present invention has an electrode composite material layer formed using the above-mentioned electrode slurry of the present invention, so it can enable the electrochemical element to exhibit excellent rate characteristics.

[0184] <Current collector>

[0185] The current collector is formed of a material having electrical conductivity and electrochemical durability. There are no particular limitations on the current collector, and known current collectors can be used. For example, as the current collector of the positive electrode of a lithium-ion secondary battery, a current collector made of aluminum or an aluminum alloy can be used. In this case, aluminum and an aluminum alloy can be used in combination, or different types of aluminum alloys can be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they are heat-resistant and electrochemically stable.

[0186] <Method for Manufacturing Electrode>

[0187] 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 above-mentioned electrode slurry of the present invention to the surface of at least one side of the current collector, drying it, and forming an electrode composite material layer. In more detail, the manufacturing method includes: a process of applying the electrode slurry to the surface of at least one side of the current collector (coating process); and a process of drying the electrode slurry applied to the surface of at least one side of the current collector to form an electrode composite material layer on the current collector (drying process).

[0188] <<Coating process>>

[0189] As the method for applying the electrode slurry to the current collector, it is not particularly limited and known methods can be used. Specifically, as a coating method, it is possible to use a blade coating method, an immersion method, a reverse roll coating method, a direct roll coating method, a gravure printing method, an extrusion method, a brush coating method, etc. At this time, the electrode slurry can be applied only to a single side of the current collector, or it can be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the electrode composite material layer obtained by drying.

[0190] <<Drying process>>

[0191] The method for drying the electrode slurry on the current collector is not particularly limited, and known methods can be used, including drying using warm air, hot air, or low-humidity air; vacuum drying; and drying using irradiation with infrared rays, electron beams, etc. By drying the electrode slurry on the current collector in this manner, an electrode composite material layer can be formed on the current collector, resulting in an electrode having the current collector and the electrode composite material layer.

[0192] Alternatively, after the drying step, the electrode material layer may be subjected to a press treatment using a die press or a roll press, etc. The press treatment can ensure good adhesion of the electrode material layer to the current collector.

[0193] Furthermore, when the electrode composite material layer contains a curable polymer, the polymer may be cured after the electrode composite material layer is formed.

[0194] (Electrochemical Components)

[0195] The electrochemical device of the present invention comprises the electrode of the present invention described above. Furthermore, the electrochemical device of the present invention exhibits excellent rate characteristics due to the electrode of the present invention. Furthermore, the electrochemical device of the present invention is, for example, a non-aqueous secondary battery, preferably a lithium-ion secondary battery.

[0196] Here, the structure of a lithium ion secondary battery as an example of an electrochemical element of the present invention is described below. The lithium ion secondary battery has a positive electrode, a negative electrode, an electrolyte, and a separator. Moreover, at least one of the positive electrode and the negative electrode is an electrode of the present invention. That is, in the lithium ion secondary battery, the positive electrode can be an electrode of the present invention, and the negative electrode can be an electrode other than the electrode of the present invention, or the positive electrode can be an electrode other than the electrode of the present invention, and the negative electrode can be an electrode of the present invention, or both the positive electrode and the negative electrode can be electrodes of the present invention.

[0197] <Electrodes Other Than the Electrode of the Present Invention>

[0198] The electrodes that do not belong to the electrodes of the present invention are not particularly limited, and known electrodes can be used.

[0199] <Electrolyte>

[0200] As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent can generally be used. As the supporting electrolyte, for example, a lithium salt can be used. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, etc. Among them, LiPF6, LiClO4, and CF3SO3Li are preferred because they are easy to dissolve in solvents and show a high degree of dissociation, and LiPF6 is particularly preferred. In addition, one electrolyte can be used alone, or two or more electrolytes can be used in combination in any ratio. Generally, there is a tendency that the higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0201] As the organic solvent used in the electrolyte, as long as it is an organic solvent that can dissolve the supporting electrolyte, there is no particular limitation, and preferably, for example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) can be used; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. In addition, a mixture of these solvents can also be used. Among them, carbonates with a high dielectric constant and a wide stable potential region are preferably used, and a mixture of ethylene carbonate and ethyl methyl carbonate is further preferably used.

[0202] The concentration of the electrolyte in the electrolyte solution can be adjusted appropriately, and is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass. Furthermore, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolyte solution.

[0203] <Spacer>

[0204] The separator is not particularly limited, and for example, the separators described in Japanese Patent Application Laid-Open No. 2012-204303 can be used. Among these, a microporous membrane formed of a polyolefin resin (polyethylene, polypropylene, polybutylene, polyvinyl chloride) is preferred because the overall thickness of the separator can be reduced, thereby increasing the ratio of the electrode active material in the lithium-ion secondary battery and increasing the capacity per unit volume.

[0205] <Method for Manufacturing Lithium-Ion Secondary Battery>

[0206] The lithium-ion secondary battery of the present invention is manufactured, for example, by overlapping the positive electrode and the negative electrode with a separator, winding or folding the battery according to the shape of the battery as needed, placing the battery container, injecting an electrolyte into the battery container, and sealing the battery. In order to prevent the internal pressure rise of the secondary battery, overcharge and discharge, etc., a fuse, a PTC element or other overcurrent protection element, a porous metal mesh, a guide plate, etc. can be provided as needed. The shape of the secondary battery can be, for example, any one of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, etc.

[0207] Example

[0208] Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "parts" indicating amounts are based on mass unless otherwise specified.

[0209] In addition, unless otherwise specified, in a polymer produced by copolymerizing multiple monomers, the proportion of monomer units formed by polymerizing a certain monomer in the above-mentioned polymer is generally consistent with the ratio (feed ratio) of the monomer to the total monomers used in the polymerization of the polymer. In addition, in the case of a hydrogenated polymer formed by hydrogenating a polymer containing conjugated diene monomer units, the total content ratio of the unhydrogenated conjugated diene monomer units and the alkylene structural units that are the hydrogenated conjugated diene monomer units in the hydrogenated polymer is consistent with the ratio (feed ratio) of the conjugated diene monomer to the total monomers used in the polymerization of the polymer.

[0210] In the Examples and Comparative Examples, the weight-average molecular weight of the dispersant, the thermal decomposition time of CNTs in the conductive material dispersion, the viscosity and viscosity stability of the conductive material dispersion, and the rate characteristics, cycle characteristics, and gas generation suppression of the lithium ion secondary battery were evaluated using the following methods.

[0211] <Weight Average Molecular Weight>

[0212] The weight average molecular weight (Mw) of the dispersant, which is a polymer, was measured by gel permeation chromatography (GPC) using a LiBr-dimethylformamide (DMF) solution having a concentration of 10 mM under the following measurement conditions.

[0213] Separation column: Shodex KD-806M (Showa Denko K.K.)

[0214] Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation)

[0215] Flow rate of sichuan elution solution: 0.3mL / min

[0216] Column temperature: 40℃

[0217] Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0218] <Thermal Decomposition Time>

[0219] The prepared conductive material dispersion was collected in an aluminum pan so as to have a solid content of 1 g, and dried at 130° C. for 2 hours to volatilize the dispersion medium, thereby obtaining a residue.

[0220] The obtained residue of about 3 mg was placed in a thermogravimetric analyzer (manufactured by Hitachi High-Technologies Corporation, product name "STA7200"), and then heated from 25°C to 600°C at a heating rate of 20°C / min under a nitrogen atmosphere, and maintained at 600°C for 10 minutes to obtain a measurement sample (mass: W0g).

[0221] While maintaining the temperature at 600°C, the atmosphere was switched from nitrogen to air and kept at 600°C for 30 minutes. Then, a thermogravimetric curve (thermogravimetric reduction curve) and a differential thermogravimetric curve were prepared based on the mass change and the elapsed time after switching to the air atmosphere. The prepared curves are shown in FIG. Figure 1 The thermogravimetric decrease curve was prepared by fitting the mass change and the elapsed time using the Double Boltzmann function, and the differential thermogravimetric curve was prepared by differentiating the thermogravimetric decrease curve with respect to time.

[0222] Next, the time T0, at which the minimum value is reached just before the final peak of the differential thermogravimetric curve, is determined from the differential thermogravimetric curve. The mass M1 of the measurement sample at time T0 is then determined from the thermogravimetric curve. The time T1 required for M1 to decrease to M1 × 0.10 (90% reduction time) is then determined. The thermal decomposition time of the CNT is calculated using the formula (I): Thermal decomposition time T = (T1 - T0) / W0.

[0223] <Viscosity>

[0224] A rheometer (manufactured by Anton Paar, product name "MCR302") was used to measure the flow rate at a temperature of 25°C and a shear rate of 10 -2 s -1 to 10 3 s -1 The viscosity of the prepared conductive material dispersion was measured in the range of 10s. -1 The viscosity value at 37°C was evaluated based on the following criteria.

[0225] A: Viscosity less than 5 Pa·s

[0226] B: Viscosity is 5 Pa·s or more and less than 20 Pa·s

[0227] C: Viscosity is 20 Pa·s or more and less than 100 Pa·s

[0228] D: Viscosity is 100 Pa·s or more

[0229] <Viscosity stability>

[0230] A rheometer (manufactured by Anton Paar, product name "MCR302") was used at a temperature of 25°C and a shear rate of 10 s -1 The viscosity of the prepared conductive material dispersion was measured for 120 seconds. The average of the measured values ​​from 61 seconds to 120 seconds was defined as η1. The conductive material dispersion was then stored at 25°C for 3 days and stirred for 1 hour using a planetary mixer (60 rpm). The viscosity of the stirred conductive material dispersion was measured in the same manner as for η1, and the average of the measured values ​​was defined as η2. The viscosity ratio was then calculated as η2 / η1 × 100 (%) and evaluated according to the following criteria. A smaller viscosity ratio indicates greater viscosity stability of the conductive material dispersion.

[0231] A: Viscosity ratio is 90% or more and 110% or less

[0232] B: Viscosity ratio is 80% or more and less than 90% or greater than 110% and less than 120%

[0233] C: Viscosity ratio is 70% or more and less than 80% or greater than 120% and less than 130%

[0234] D: Viscosity ratio is less than 70% or greater than 130%

[0235] <Rate Characteristics>

[0236] The prepared lithium-ion secondary battery was left to stand at a temperature of 25°C for 5 hours after the electrolyte was injected. Next, it was charged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.65V, and then aged at a temperature of 60°C for 12 hours. Then, it was discharged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.00V. After that, CC-CV charging was performed by a constant current method at 0.2C (the upper limit battery cell voltage was 4.20V), and CC discharge was performed by a constant current method at 0.2C to 3.00V. This charge and discharge at 0.2C was repeated 3 times.

[0237] Next, at a temperature of 25°C, the battery was charged to 4.2V by a constant current method at 0.1C, and then discharged to 3.0V at 0.1C to determine the 0.1C discharge capacity. Furthermore, the battery 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 manufactured lithium-ion secondary battery, and the average value of each measured value 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 based on the following criteria. The larger the capacitance ratio, the better the rate characteristics of the lithium-ion secondary battery.

[0238] A: The capacitance ratio is more than 90%

[0239] B: The capacitance ratio is 80% or more and less than 90%

[0240] C: The capacitance ratio is 70% or more and less than 80%

[0241] D: Capacitance ratio is less than 70%

[0242] <Cycling Characteristics>

[0243] The prepared lithium-ion secondary battery was left to stand at a temperature of 25°C for 5 hours after the electrolyte was injected. Next, it was charged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.65V, and then aged at a temperature of 60°C for 12 hours. Then, it was discharged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.00V. After that, CC-CV charging was performed by a constant current method at 0.2C (the upper limit battery cell voltage was 4.20V), and CC discharge was performed by a constant current method at 0.2C to 3.00V. This 0.2C charge and discharge was repeated 3 times.

[0244] Next, at a temperature of 45°C, 100 cycles of charge and discharge were performed at a cell voltage of 4.20-3.00V and a charge and discharge rate of 1.0C. The discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 100th cycle was defined as X2. Using the discharge capacities X1 and X2, the capacity retention rate was calculated as (X2 / X1) × 100 (%), and the battery was evaluated based on the following criteria. A higher capacity retention rate indicates better cycle characteristics for the lithium-ion secondary battery.

[0245] A: Capacity retention rate is above 93%

[0246] B: Capacity retention rate is 90% or more and less than 93%

[0247] C: Capacity retention rate is 87% or more and less than 90%

[0248] D: Capacity retention rate is less than 87%

[0249] <Gas Generation Suppression>

[0250] The prepared lithium-ion secondary battery was left to stand at a temperature of 25°C for 5 hours after the electrolyte was injected. Next, it was charged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.65V, and then aged at a temperature of 60°C for 12 hours. Then, it was discharged by a constant current method at a temperature of 25°C and 0.2C until the battery cell voltage reached 3.00V. After that, CC-CV charging was performed by a constant current method at 0.2C (the upper limit battery cell voltage was 4.20V), and CC discharge was performed by a constant current method at 0.2C to 3.00V. This 0.2C charge and discharge was repeated 3 times.

[0251] Next, the battery was charged to 4.20 V at 0.1 C and discharged to 3.00 V at 0.1 C in an environment of 25° C. Thereafter, the battery was immersed in liquid paraffin, and its volume V0 was measured.

[0252] Furthermore, an operation of charging to 4.20 V at 1 C and discharging to 3.00 V at 1 C as one cycle was repeated 200 times under an environment of 60° C. Thereafter, the battery was immersed in liquid paraffin, and its volume V1 was measured.

[0253] The volume change ΔV of the battery cell before and after 200 cycles of repeated charge and discharge was calculated using the formula "ΔV = (V1 - V0) / V0 × 100 (%)" and evaluated using the following criteria. A smaller volume change ΔV indicates a better ability of the lithium-ion secondary battery to suppress gas generation.

[0254] A: ΔV is less than 18%

[0255] B: ΔV is 18% or more and less than 22%

[0256] C: ΔV is 22% or more and less than 26%

[0257] D: ΔV is 26% or more

[0258] (Example 1)

[0259] <Preparation of Dispersant (HNBR-1)>

[0260] In a reactor having an internal volume of 10 liters, 100 parts of ion-exchanged water, 35 parts of acrylonitrile and 65 parts of 1,3-butadiene as monomers 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. Emulsion polymerization was carried out at 30° C. in the presence of 0.35 parts of potassium persulfate as a polymerization initiator to copolymerize 1,3-butadiene and acrylonitrile.

[0261] When the polymerization conversion rate reached 90%, 0.2 parts of hydroxylamine sulfate was added per 100 parts of monomer to terminate the polymerization. The mixture was then heated and steam distilled under reduced pressure at approximately 70°C to recover the residual monomers. Two parts of alkylated phenol was then added as an antioxidant to obtain an aqueous dispersion of the polymer.

[0262] Next, 400 mL of the obtained aqueous dispersion of the polymer (total solid content: 48 g) was placed in a 1-liter autoclave with a stirrer and nitrogen was circulated for 10 minutes to remove dissolved oxygen in the aqueous dispersion of the polymer. Afterwards, 50 mg of palladium acetate, a hydrogenation catalyst, was dissolved in 180 mL of water to which nitric acid, 4 times the molar equivalent of Pd, was added. After the system was purged twice with hydrogen, the contents of the autoclave were heated to 50° C. in a state pressurized with hydrogen to 3 MPa (gauge pressure) and a hydrogenation reaction was performed for 6 hours.

[0263] Thereafter, the contents were returned to room temperature, the system was placed in a nitrogen atmosphere, and then concentrated using an evaporator to a solid content concentration of 40% to obtain an aqueous dispersion of hydrogenated nitrile rubber (HNBR-1).

[0264] 200 parts of NMP were added to 100 parts of the aqueous dispersion, and all water and residual monomers were evaporated under reduced pressure. Then, NMP was evaporated to obtain an NMP solution of HNBR-1 (solid content concentration: 8%). The weight average molecular weight of the obtained HNBR-1 was measured. The results are shown in Table 1. In addition, the weight average molecular weight is "130000", and "×10 4 ”, recorded as “13”.

[0265] <Preparation of Conductive Material Dispersion (Preparation Method: A-1)>

[0266] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solids equivalent to 1 part) of an HNBR-1 NMP solution, and 82.5 parts of NMP were dispersed at 3000 rpm using a disperser while maintaining the temperature at 25°C or below for 30 minutes (first dispersion step). Subsequently, a thin film rotary high-speed stirrer (Primix, product name "FILMIX, Model 56-50") was used for 5 minutes at a peripheral speed of 30 m / s to prepare a conductive material dispersion (second dispersion step). The viscosity and viscosity stability of this conductive material dispersion were evaluated. The results are shown in Table 1.

[0267] <Preparation of positive electrode slurry>

[0268] 98.0 parts of a ternary active material (LiNi 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 (solid content conversion) of the above conductive material dispersion, and NMP were mixed using a planetary mixer (60 rpm, 30 minutes) to prepare a positive electrode slurry. In addition, the amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry (measured by a single cylinder rotational viscometer in accordance with JIS Z8803:1991. Temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa·s.

[0269] <Production of positive electrode>

[0270] A 20 μm thick aluminum foil was prepared as a current collector. The positive electrode slurry was coated with a notch wheel coater so that the weight per unit area after drying was 20 mg / cm 2 The positive electrode raw material was coated on aluminum foil in the form of , dried at 90°C for 20 minutes, dried at 120°C for 20 minutes, and then heated at 60°C for 10 hours to obtain a positive electrode raw material. The positive electrode raw material was rolled using a roller press to produce a material with a density of 3.2 g / cm 3 The positive electrode sheet was formed by a positive electrode composite material layer and aluminum foil. The positive electrode sheet was cut into pieces with a width of 48.0 mm and a length of 47 cm to serve as a positive electrode for a lithium ion secondary battery.

[0271] <Production of negative electrode>

[0272] In a 5 MPa pressure-resistant container 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 ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were added and stirred thoroughly. The mixture was then heated to 50°C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, resulting in a mixture containing a granular binder (styrene-butadiene copolymer). A 5% aqueous sodium hydroxide solution was added to the mixture to adjust the pH to 8, and then unreacted monomers were removed by heating and reduced pressure distillation. The mixture was then cooled to below 30°C to obtain an aqueous dispersion containing the negative electrode binder.

[0273] In a planetary mixer, 48.75 parts of artificial graphite and 48.75 parts of natural graphite as negative electrode active materials, and 1 part (solid content equivalent) of carboxymethyl cellulose as a thickener were added. Furthermore, the mixture was diluted with ion exchange water to a solid content concentration of 60%, and then kneaded at a rotation speed of 45 rpm for 60 minutes. Thereafter, 1.5 parts of the aqueous dispersion containing the negative electrode binder obtained as described above was added in terms of solid content equivalent, and kneaded at a rotation speed of 40 rpm for 40 minutes. Then, ion exchange water was added until the viscosity reached 3000±500 mPa·s (measured by a B-type viscometer at 25°C and 60 rpm), thereby preparing a negative electrode slurry.

[0274] The negative electrode slurry was coated with a notch wheel coater at a coating amount of 10 ± 0.5 mg / cm 2 The negative electrode slurry on the copper foil was dried by applying the negative electrode composite material layer composition to the surface of a 15 μm thick copper foil serving as a current collector. The copper foil coated with the negative electrode composite material layer slurry composition was then conveyed through an oven at 80°C for 2 minutes at a speed of 400 mm / min, and then through an oven at 110°C for 2 minutes. This dried the negative electrode slurry on the copper foil, yielding a negative electrode raw material having a negative electrode composite material layer formed on the current collector.

[0275] The negative electrode raw material was rolled using a roller press to produce a material having a density of 1.6 g / cm 3 The negative electrode sheet was formed by the negative electrode composite material layer and the aluminum foil. Then, the negative electrode sheet was cut into pieces with a width of 50.0 mm and a length of 52 cm to prepare a negative electrode for a lithium ion secondary battery.

[0276] <Production of Lithium-ion Secondary Batteries>

[0277] The positive electrode for the lithium ion secondary battery and the negative electrode for the lithium ion secondary battery were wound with a separator (microporous film made of polyethylene) having a thickness of 15 μm in a manner such that the electrode composite material layers faced each other, using a core with a diameter of 20 mm to obtain a wound body. The wound body was then compressed in one direction at a speed of 10 mm / second to a thickness of 4.5 mm. In addition, the compressed wound body was elliptical when viewed from above, and the ratio of its major diameter to minor diameter (major diameter / minor diameter) was 7.7.

[0278] In addition, a LiPF6 solution with a concentration of 1.0 M (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), containing an additive: 2% by volume of vinylene carbonate (solvent ratio)) was prepared as an electrolyte.

[0279] The compressed wound body was then placed in an aluminum laminate case along with 3.2g of electrolyte. A nickel lead was then connected to a designated location on the negative electrode, and an aluminum lead was connected to a designated location on the positive electrode. The opening of the case was then heat-sealed to produce a lithium-ion secondary battery. This lithium-ion secondary battery was in the form of a pouch, 35mm wide, 60mm high, and 5mm thick, with a nominal capacity of 700mAh.

[0280] The obtained lithium ion secondary battery was evaluated for rate characteristics, cycle characteristics, and gas generation suppression. The results are shown in Table 1.

[0281] (Example 2)

[0282] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0283] <Preparation of Conductive Material Dispersion (Preparation Method: B-2)>

[0284] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solid content equivalent to 1 part) of an HNBR-1 NMP solution, and 82.5 parts of NMP were dispersed for 30 minutes using a planetary mixer at 60 rpm while maintaining the temperature at 45°C (first dispersion step). Subsequently, a thin film rotary high-speed mixer (Primix, product name "FILMIX, 56-50") was used for 5 minutes at a peripheral speed of 30 m / s to prepare a conductive material dispersion (second dispersion step).

[0285] (Example 3)

[0286] A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the dispersant (HNBR-2) and conductive material dispersion prepared as follows were used, and various evaluations were performed. The results are shown in Table 1.

[0287] <Preparation of Dispersant (HNBR-2)>

[0288] Except that the amount of TDM used was changed to 0.4 parts, the same procedure as in HNBR-1 of Example 1 was carried out to obtain an NMP solution of HNBR-2 (solid content concentration: 8%).

[0289] <Preparation of Conductive Material Dispersion (Preparation Method: B-3)>

[0290] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 6.25 parts (0.5 parts solid content equivalent) of an HNBR-2 NMP solution, and 82.5 parts of NMP were mixed and dispersed at 60 rpm for 30 minutes using a planetary mixer while maintaining the temperature at 25°C or lower (first dispersion step). To the composition obtained after the first dispersion step, 6.25 parts (0.5 parts solid content equivalent) of an HNBR-2 NMP solution were further added, and a thin film rotary high-speed mixer (Primix, product name "FILMIX, 56-50") was used to disperse the mixture at a peripheral speed of 30 m / s for 5 minutes to prepare a conductive material dispersion (second dispersion step).

[0291] (Example 4)

[0292] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0293] <Preparation of Conductive Material Dispersion (Preparation Method: A-3)>

[0294] In the second dispersing step, a conductive material dispersion was prepared in the same manner as in Preparation Method A-1 of Example 1, except that the peripheral speed of the thin film rotary high-speed stirrer was changed to 20 m / s.

[0295] (Example 5)

[0296] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0297] <Preparation of Conductive Material Dispersion (Preparation Method: A-4)>

[0298] In the second dispersing step, a conductive material dispersion was prepared in the same manner as in Preparation Method A-1 of Example 1, except that the peripheral speed of the thin film rotary high-speed stirrer was changed to 40 m / s.

[0299] (Example 6)

[0300] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0301] <Preparation of Conductive Material Dispersion (Preparation Method: A-5)>

[0302] In the second dispersing step, a conductive material dispersion was prepared in the same manner as in Preparation Method A-1 of Example 1, except that the time for the dispersion treatment using the thin film rotating high-speed stirrer was changed to 3 minutes.

[0303] (Example 7)

[0304] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0305] <Preparation of Conductive Material Dispersion (Preparation Method: A-6)>

[0306] In the second dispersion step, a conductive material dispersion was prepared in the same manner as in Preparation Method A-1 of Example 1, except that the time for the dispersion treatment using the thin film rotating high-speed stirrer was changed to 10 minutes.

[0307] (Example 8)

[0308] A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that a dispersant (ACL) prepared as follows was used, and various evaluations were performed.

[0309] <Preparation of Dispersant (ACL)>

[0310] In an autoclave equipped with a stirrer, 164 parts of ion-exchanged 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 modifier were added and stirred thoroughly. The mixture was then heated at 70°C for 3 hours and then at 80°C for 2 hours to carry out polymerization, thereby obtaining an aqueous dispersion of an acrylic acid polymer (ACL). The solids concentration of the aqueous dispersion was 37.3%, and the polymerization conversion rate, determined from the solids concentration, was 96%.

[0311] 200 parts of NMP were added to 100 parts of the aqueous dispersion, and after all water and residual monomers were evaporated under reduced pressure, NMP was evaporated to obtain an NMP solution of ACL (solid content: 8%).

[0312] (Example 9)

[0313] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 1.

[0314] <Preparation of Conductive Material Dispersion (Preparation Method: C-2)>

[0315] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 6.25 parts (solid content equivalent to 0.5 parts) of an NMP solution of HNBR-1, and 82.5 parts of NMP were dispersed using a disperser at a rotation speed of 3000 rpm for 30 minutes while maintaining the temperature at 25°C or lower (first dispersion step).

[0316] Next, 6.25 parts (0.5 parts solids equivalent) of an HNBR-1 NMP solution were added to the composition obtained after the first dispersion step, and the mixture was mixed at a peripheral speed of 12 m / s for 20 minutes using a bead mill (manufactured by Ashizawa Finetech Ltd., product name "LMZ015") to achieve an apparent filling rate of 50% by volume for zirconia beads with a diameter of 1.5 mm. Next, mixing was performed at a peripheral speed of 8 m / s for 20 minutes to achieve an apparent filling rate of 50% by volume for zirconia beads with a diameter of 0.8 mm. Furthermore, mixing was performed at a peripheral speed of 12 m / s for 20 minutes to achieve an apparent filling rate of 80% by volume for zirconia beads with a diameter of 0.8 mm, thereby preparing a conductive material dispersion (second dispersion step).

[0317] (Comparative Example 1)

[0318] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 2.

[0319] <Preparation of Conductive Material Dispersion (Preparation Method: A-2)>

[0320] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 6.25 parts (0.5 parts solid content equivalent) of an HNBR-1 NMP solution, and 82.5 parts of NMP were mixed and dispersed at 3000 rpm for 30 minutes using a disperser while maintaining the temperature at 25°C or lower (first dispersion step). To the composition obtained after the first dispersion step, 6.25 parts (0.5 parts solid content equivalent) of an HNBR-1 NMP solution were further added, and dispersion was carried out at a peripheral speed of 30 m / s for 5 minutes using a thin film rotary high-speed stirrer (Primix, product name "FILMIX, 56-50") to prepare a conductive material dispersion (second dispersion step).

[0321] (Comparative Example 2)

[0322] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 2.

[0323] <Preparation of Conductive Material Dispersion (Preparation Method: B-1)>

[0324] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solid content equivalent to 1 part) of an HNBR-1 NMP solution, and 82.5 parts of NMP were dispersed for 30 minutes using a planetary mixer at a rotation speed of 60 rpm while maintaining the temperature at 25°C or below (first dispersion step). Subsequently, a thin film rotary high-speed mixer (Primix, product name "FILMIX, 56-50") was used to disperse the conductive material for 5 minutes at a peripheral speed of 30 m / s to prepare a conductive material dispersion (second dispersion step).

[0325] (Comparative Example 3)

[0326] A conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared in the same manner as in Comparative Example 2, except that HNBR-2, prepared in the same manner as in Example 3, was used instead of HNBR-1 when preparing the conductive material dispersion. Various evaluations were performed. The results are shown in Table 2.

[0327] (Comparative Example 4)

[0328] A conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, and lithium-ion secondary battery were prepared in the same manner as in Comparative Example 1, except that HNBR-2, prepared in the same manner as in Example 3, was used instead of HNBR-1 when preparing the conductive material dispersion. Various evaluations were performed. The results are shown in Table 2.

[0329] (Comparative Example 5)

[0330] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 2.

[0331] <Preparation of Conductive Material Dispersion (Preparation Method: C-1)>

[0332] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solid content equivalent to 1 part) of an NMP solution of HNBR-1 and 82.5 parts of NMP were dispersed using a disperser at a rotation speed of 3000 rpm for 30 minutes while maintaining the temperature at 25°C or lower (first dispersion step).

[0333] Next, after the first dispersion step, the obtained composition was mixed for 1 hour at a peripheral speed of 8 m / s using a bead mill (manufactured by Ashizawa Finetech Ltd., product name "LMZ015") so that the apparent filling rate of zirconia beads with a diameter of 1.25 mm became 80 volume %, thereby preparing a conductive material dispersion (second dispersion step).

[0334] (Comparative Example 6)

[0335] A dispersant (HNBR-2), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 3 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 2.

[0336] <Preparation of Conductive Material Dispersion (Preparation Method: C-3)>

[0337] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 6.25 parts (solid content equivalent to 0.5 parts) of an NMP solution of HNBR-2 and 82.5 parts of NMP were dispersed using a planetary mixer at a rotation speed of 60 rpm for 30 minutes while maintaining the temperature at 25°C or lower (first dispersion step).

[0338] Next, 6.25 parts (0.5 parts solid content equivalent) of an NMP solution of HNBR-2 was further added to the composition obtained after the first dispersion step, and the mixture was mixed at a peripheral speed of 8 m / s for 20 minutes using a bead mill (manufactured by Ashizawa Finetech Ltd., product name "LMZ015") so that the apparent filling rate of zirconia beads with a diameter of 1.25 mm became 80% by volume, thereby preparing a conductive material dispersion (second dispersion step).

[0339] (Comparative Example 7)

[0340] A positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed.

[0341] <Preparation of Conductive Material Dispersion (Preparation Method: A-7)>

[0342] A NMP solution (solid content concentration: 8%) of polyvinyl pyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd., product name "PVP K15") was prepared.

[0343] 4 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solid content equivalent to 1 part) of a PVP NMP solution, and 83.5 parts of NMP were dispersed using a disperser at a rotation speed of 3000 rpm for 30 minutes while maintaining the temperature at 25°C or below (first dispersion step). Subsequently, a thin film rotary high-speed stirrer (Primix, product name "FILMIX, 56-50") was used for dispersion at a peripheral speed of 40 m / s for 1 minute to prepare a conductive material dispersion (second dispersion step).

[0344] (Comparative Example 8)

[0345] A dispersant (HNBR-1), a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the conductive material dispersion prepared below was used, and various evaluations were performed. The results are shown in Table 2.

[0346] <Preparation of Conductive Material Dispersion (Preparation Method: A-8)>

[0347] 5 parts of multi-walled carbon nanotubes (BET specific surface area: 250 m 2 / g), 12.5 parts (solid content equivalent to 1 part) of a PVP NMP solution, and 82.5 parts of NMP were dispersed at 3000 rpm using a disperser for 30 minutes while maintaining the temperature at 45°C (first dispersion step). Subsequently, a thin film rotary high-speed stirrer (Primix, product name "FILMIX, 56-50") was used for 20 minutes at a peripheral speed of 50 m / s to prepare a conductive material dispersion (second dispersion step).

[0348] [Table 1]

[0349]

[0350] [Table 2]

[0351]

[0352] As shown in Tables 1 and 2, the conductive material dispersions of Examples 1 to 9, which comprise a conductive material containing CNTs, a dispersant, and a dispersion medium, and have CNT thermal decomposition times within the specified range, exhibit excellent viscosity stability. Furthermore, using these conductive material dispersions to form positive electrodes enables lithium-ion secondary batteries to exhibit excellent rate characteristics. Furthermore, Examples 1 to 9 demonstrate the ability to prepare low-viscosity conductive material dispersions, resulting in excellent cycle characteristics and suppressed gas generation in lithium-ion secondary batteries.

[0353] Industrial applicability

[0354] According to the present invention, it is possible to provide a conductive material dispersion for an electrochemical device that has excellent viscosity stability and can form an electrode that enables an electrochemical device to exhibit excellent rate characteristics.

[0355] Furthermore, according to the present invention, it is possible to provide a slurry for electrochemical device electrodes capable of forming an electrode that enables an electrochemical device to exhibit excellent rate characteristics.

[0356] Furthermore, according to the present invention, it is possible to provide an electrode for an electrochemical device that enables the electrochemical device to exhibit excellent rate characteristics.

[0357] Furthermore, according to the present invention, an electrochemical device having excellent rate characteristics can be provided.

Claims

1. A conductive material dispersion for an electrochemical element, comprising a conductive material, a dispersant and a dispersion medium, The conductive material contains carbon nanotubes, The weight average molecular weight of the dispersant is 10,000 or more and 400,000 or less, The thermal decomposition time of the carbon nanotubes is 1.9 minutes / mg or more and 9.0 minutes / mg or less. Here, the thermal decomposition time is the following value: The electrochemical device conductive material dispersion is dried at 130° C. for 2 hours to remove the dispersion medium and obtain a residue. The residue was heated from 25°C to 600°C at a heating rate of 20°C / min in a nitrogen atmosphere, and then heated at 600°C for 10 minutes to prepare a measurement sample. The value calculated by the following formula (I) is obtained by preparing a thermogravimetric curve and a differential thermogravimetric curve based on the mass change and the elapsed time when the measurement sample is heat-treated in an air atmosphere at 600°C. Thermal decomposition time T = (T1-T0) / W0...(I) In formula (I), T0: The time (minutes) when the differential thermogravimetric curve reaches its minimum value just before the final peak appears. T1: Time (minutes) required for the mass M1 of the measurement sample to decrease to M1×0.10 when the elapsed time is T0 minutes, as determined from the thermogravimetric curve W0: The weight (mg) of the measurement sample at the start of the heat treatment in an air atmosphere at 600°C.

2. The conductive material dispersion for electrochemical devices according to claim 1, wherein The dispersant comprises a nitrile group-containing monomer unit. 3 . A slurry for electrochemical device electrodes, comprising an electrode active material and the conductive material dispersion for electrochemical devices according to claim 1 . 4 . An electrochemical device electrode comprising an electrode composite material layer formed using the slurry for an electrochemical device electrode according to claim 3 . 5 . An electrochemical device comprising the electrode for an electrochemical device according to claim 4 .

Images