Polymer composition for electrochemical element, conductive material composition, slurry composition, electrode membrane, and secondary battery

Abstract

To provide a polymer composition for an electrochemical element capable of providing a conductive material composition with good dispersibility.SOLUTION: Provided is a polymer composition for an electrochemical element, the polymer composition comprising: a polymer including an aliphatic hydrocarbon unit and a nitrile group-containing unit; and an amide-based liquid medium, where the polymer has a tan δ (loss tangent) of more than 1 in the strain range of 0.01-10% in dynamic viscoelasticity measurement at a temperature of 100°C and a frequency of 10 Hz.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a polymer composition for an electrochemical element, a conductive material composition, a slurry composition, an electrode film, and a secondary battery.

Background Art

[0002] As one representative of electrochemical elements, a lithium-ion secondary battery has characteristics such as being small and lightweight, having a high energy density, and being capable of repeated charge and discharge. Due to such characteristics, secondary batteries are used in a wide range of applications. In the field of secondary batteries, for an electrode, particularly a positive electrode with poor conductivity, when a carbon material such as fine carbon nanotubes with excellent conductivity or carbon black with a developed structure is used as a conductive material in a well-dispersed state, it becomes easy to draw out the characteristics of the electrode. Therefore, studies have been made to disperse the conductive material using a polymer or the like having dispersibility and improve the characteristics of secondary batteries.

[0003] As a technique for well-dispersing a conductive material in a binder composition for a secondary battery electrode, Patent Document 1 discloses using a copolymer (for example, a hydrogenated nitrile rubber) having an alkylene structural unit and a monomer unit containing a nitrile group and having a Mooney viscosity (ML 1+4 , 100 ° C) of 40 or less as a binder composition for a secondary battery electrode.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology disclosed in Patent Document 1, the Mooney viscosity of the copolymer in the binder composition is set to 40 or less to facilitate the adsorption of the copolymer on the surface of the conductive material, suppress the aggregation of the conductive material, and improve the dispersibility of the conductive material. On the other hand, in the technology disclosed in Patent Document 1, the Mooney viscosity of the copolymer in the binder composition is set to 5 or more in order to obtain the adsorption stability of the copolymer with respect to the conductive material and maintain the dispersion stability of the conductive material.

[0006] However, in order to further enhance the dispersibility of the conductive material, the development of a new polymer composition is desired from the aspect of more microscopic observation. Further, when the conductive material is broken during the dispersion treatment using the polymer composition, small pieces of the conductive material will be included in the electrode film, resulting in insufficient formation of the conductive network and possibly causing a deterioration in the battery characteristics of the secondary battery.

[0007] One of the objectives of the present disclosure is to provide a polymer composition for an electrochemical element, a conductive material composition containing the same, a slurry composition, an electrode film formed using the same, and a secondary battery, which can provide a conductive material composition having good dispersibility.

Means for Solving the Problems

[0008] As a result of intensive studies by the present inventors, as a polymer composition for an electrochemical element, in a dynamic viscoelasticity measurement measured at a temperature of 100° C. and a frequency of 10 Hz, a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit having a tan δ (loss tangent) in the range of 0.01% to 10% of strain greater than 1 and an amide-based liquid medium are used, and it has been found that dispersibility in a dispersion of a conductive material can be obtained. Furthermore, by using this polymer composition for an electrochemical element, it has been found that both dispersibility in a dispersion of a conductive material and conductivity in an electrode film can be achieved. Specifically, since the wetting promotion effect of the conductive material in the dispersion becomes stronger, an increase in viscosity during the dispersion treatment can be suppressed, and the initial dispersibility of the conductive material can be enhanced. Furthermore, the concentration of the conductive material can be increased in the dispersion. Also, when the conductive material is dispersed using the polymer composition, the viscoelasticity of the dispersion can be appropriately controlled by the tan δ of the polymer so as not to cause breakage of the conductive material during the dispersion treatment. As a result, not only can a developed conductive network be formed in the electrode film obtained using this dispersion, but the margin for formulation design can be increased. Thereby, the conductive material is uniformly distributed in the electrode film and the shape of the conductive material is maintained, making it possible to provide a high-output, high-capacity, and long-life electrochemical element.

[0009] That is, the present disclosure relates to the following embodiments. However, the embodiments of the present disclosure are not limited to the following.

[0010] [1] A polymer composition for an electrochemical element, comprising a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit, and an amide-based liquid medium, wherein the polymer has a tan δ (loss tangent) in the range of 0.01% to 10% of strain greater than 1 in a dynamic viscoelasticity measurement measured at a temperature of 100° C. and a frequency of 10 Hz.

[0011] [2] The polymer composition for an electrochemical element according to [1], wherein in a viscoelasticity measurement measured at a frequency of 10 Hz and a strain of 0.1%, when the temperature is increased from 30° C. to 110° C. at a rate of 10° C. / min, the measurement temperature at which tan δ (loss tangent)=1 is 80° C. or lower.

[0012] [3] The polymer composition for an electrochemical device according to [1] or [2], which contains the polymer and N-methyl-2-pyrrolidone and has a viscosity of less than 3000 mPa·s at 25°C and 60 rpm when a solution with a solid content concentration of 20% by mass is measured using a B-type viscometer. [4] The polymer composition for an electrochemical device according to any one of [1] to [3], wherein the content of the aliphatic hydrocarbon unit is 50% by mass or more and 75% by mass or less, and the content of the nitrile group-containing unit is 25% by mass or more and 50% by mass or less, based on the mass of the polymer. [5] The polymer composition for an electrochemical device according to any one of [1] to [4], wherein the Z-average molecular weight of the polymer is 10,000 or more and 250,000 or less.

[0013] [6] A conductive material composition containing the polymer composition for an electrochemical device according to any one of [1] to [5] and a conductive material. [7] A slurry composition containing the polymer composition for an electrochemical device according to any one of [1] to [5], a conductive material, and an active material. [8] An electrode film formed using a slurry composition containing the polymer composition for an electrochemical device according to any one of [1] to [5], a conductive material, and an active material. [9] A secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode includes an electrode film formed using a slurry composition containing the polymer composition for an electrochemical device according to any one of [1] to [5], a conductive material, and an active material. [Effect of the Invention]

[0014] According to the embodiments of the present disclosure, it is possible to provide a polymer composition for an electrochemical device that can provide a conductive material composition having good dispersibility, a conductive material composition containing the same, a slurry composition, an electrode film formed using the same, and a secondary battery. [Brief Description of the Drawings]

[0015]

Figure 1

Figure 2

[0016] Hereinafter, as embodiments of the present disclosure, a polymer composition for an electrochemical element, a conductive material composition, a slurry composition, an electrode film, and a secondary battery will be described in detail. However, the present invention is not limited to the following embodiments, and the present invention also includes embodiments implemented within a range not changing the gist of the present invention.

[0017] In the present disclosure, carbon nanotubes may be denoted as "CNT", and carbon black may be denoted as "CB". Acrylonitrile-butadiene rubber may be denoted as "NBR", and hydrogenated acrylonitrile-butadiene rubber may be denoted as "HNBR". In the present disclosure, the polymer composition for an electrochemical element may sometimes be simply denoted as a polymer composition.

[0018] <Polymer> In one embodiment of the present disclosure, the polymer is a polymer containing at least an aliphatic hydrocarbon unit and a nitrile group-containing unit. Hereinafter, this polymer may sometimes be denoted as a nitrile-based polymer.

[0019] The aliphatic hydrocarbon unit is a unit containing an aliphatic hydrocarbon structure, preferably a unit consisting only of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure may be a saturated or unsaturated, substituted or unsubstituted, chain or cyclic aliphatic hydrocarbon structure. Preferably, the aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure and may further contain an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably contains at least a linear aliphatic hydrocarbon structure and may further contain a branched aliphatic hydrocarbon structure.

[0020] Examples of aliphatic hydrocarbon units include alkylene units, alkenylene units, alkyl units, alkanetriyl units, alkanetetrayl units, and the like. The aliphatic hydrocarbon unit preferably contains at least an alkylene unit.

[0021] An alkylene unit is a unit containing an alkylene structure, preferably a unit consisting only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0022] The alkylene unit preferably contains a unit represented by the following general formula (1A).

[0023] General formula (1A)

Chemical formula

[0024] In general formula (1A), n represents an integer of 0 or 1 or more. n may be 1 to 20, 2 to 10, or 3 to 5. n is preferably an integer of 2 or more, more preferably an integer of 3 or more. n is preferably an integer of 5 or less, more preferably an integer of 4 or less. In particular, n is preferably 3.

[0025] The alkylene unit preferably contains a unit represented by the following general formula (1B).

[0026] General formula (1B)

Chemical formula

[0027] In general formula (1B), n represents an integer of 1 or more. n may be 1 to 20, 2 to 10, or 2 to 4. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, and even more preferably an integer of 2 or less. In particular, n is preferably 2.

[0028] The method for introducing alkylene units into the polymer is not particularly limited, and examples thereof include the following methods (1a) or (1b).

[0029] In the method of (1a), a polymer is prepared by a polymerization reaction using a monomer composition containing a conjugated diene monomer. The prepared polymer contains monomer units derived from the conjugated diene monomer. In the present disclosure, the "monomer unit derived from the conjugated diene monomer" may be referred to as the "conjugated diene monomer unit", and the same may be omitted for monomer units derived from other monomers. Next, by hydrogenating the conjugated diene monomer unit, at least a part of the conjugated diene monomer unit is converted into an alkylene unit. In the present disclosure, "hydrogenation" may be referred to as "hydrogenation". The finally obtained polymer contains, as alkylene units, units obtained by hydrogenating the conjugated diene monomer units.

[0030] Note that the conjugated diene monomer unit contains at least a monomer unit having one carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, contains at least one monomer unit selected from the group consisting of a monomer unit having a cis-1,4 structure, a monomer unit having a trans-1,4 structure, and a monomer unit having a 1,2 structure, and may contain two or more monomer units. Further, the conjugated diene monomer unit may be a monomer unit having no carbon-carbon double bond and further contain a monomer unit containing a branch point. In the present disclosure, the "branch point" refers to the branch point in the branched polymer. When the conjugated diene monomer unit contains a monomer unit containing a branch point, the prepared polymer is a branched polymer.

[0031] In the method of (1b), a polymer is prepared by a polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared polymer contains α-olefin monomer units. The finally obtained polymer contains, as alkylene units, α-olefin monomer units.

[0032] Among these, the method of (1a) is preferred because the polymer can be easily produced. The number of carbon atoms of the conjugated diene monomer is 4 or more, preferably 4 or more and 6 or less. Examples of the conjugated diene monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among them, 1,3-butadiene is preferred. The alkylene unit preferably includes a unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably includes a unit obtained by hydrogenating a 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer can be used alone or in combination of two or more.

[0033] The hydrogenation is preferably a method capable of selectively hydrogenating the conjugated diene monomer unit. Examples of the hydrogenation method include known methods such as an oil-phase hydrogenation method or an aqueous-phase hydrogenation method.

[0034] The hydrogenation can be carried out by a usual method. The hydrogenation can be carried out, for example, by treating a polymer having a conjugated diene monomer unit with hydrogen gas in the presence of a hydrogenation catalyst in a state where it is dissolved in an appropriate solvent. Examples of the hydrogenation catalyst include iron, nickel, palladium, rhodium, platinum, copper, and alloys and compounds thereof.

[0035] In the method of (1b), the number of carbon atoms of the α-olefin monomer is 2 or more, preferably 3 or more, and more preferably 4 or more. The number of carbon atoms of the α-olefin monomer is preferably 6 or less, and more preferably 5 or less. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomer can be used alone or in combination of two or more.

[0036] The alkylene unit preferably contains at least one selected from the group consisting of a unit having a linear alkylene structure and a unit having a branched alkylene structure, more preferably contains at least one selected from the group consisting of a unit composed only of a linear alkylene structure and a unit composed only of a branched alkylene structure, and even more preferably contains at least one selected from the group consisting of the unit represented by the above formula (1B) and the unit represented by the above formula (1C).

[0037] In the aliphatic hydrocarbon unit, the content of the alkylene unit is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total mass of the aliphatic hydrocarbon units (that is, when the mass of the aliphatic hydrocarbon units is 100% by mass). The content of the alkylene unit may be, for example, less than 100% by mass, 99.5% by mass or less, 99% by mass or less, or 98% by mass or less, based on the total mass of the aliphatic hydrocarbon units (that is, when the mass of the aliphatic hydrocarbon units is 100% by mass). The content of the alkylene unit may be 100% by mass.

[0038] The content of the aliphatic hydrocarbon unit is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). The content of the aliphatic hydrocarbon unit is preferably less than 85% by mass, more preferably 75% by mass or less, and even more preferably 70% by mass or less, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass).

[0039] The nitrile group-containing unit is a unit containing a nitrile group, preferably a unit containing an alkylene structure substituted by a nitrile group, more preferably a unit consisting only of an alkylene structure substituted by a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing unit may further contain a unit containing an alkyl structure substituted by a nitrile group, or a unit consisting only of an alkyl structure substituted by a nitrile group. The number of nitrile groups contained in the nitrile group-containing unit is preferably one.

[0040] The nitrile group-containing unit preferably contains a unit represented by the following general formula (2A).

[0041] General formula (2A)

Chemical formula

[0042] In the general formula (2A), n represents an integer of 2 or more. n may be 2 to 20, 2 to 10, or 2 to 6. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2.

[0043] The nitrile group-containing unit preferably contains a unit represented by the following general formula (2B).

[0044] General formula (2B)

Chemical formula

[0045] In the general formula (2B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

[0046] The method for introducing a nitrile group-containing unit into the polymer is not particularly limited, but a method of producing a polymer by a polymerization reaction using a monomer composition containing a nitrile group-containing monomer (the method of (2a)) can be preferably used. The finally obtained polymer contains units derived from the nitrile group-containing monomer as nitrile group-containing units. Examples of the nitrile group-containing monomer capable of forming a nitrile group-containing unit include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. For example, α,β-ethylenically unsaturated group-containing compounds having a nitrile group can be mentioned, and specifically, acrylonitrile, methacrylonitrile, etc. can be mentioned. In particular, from the viewpoint of enhancing the intermolecular force between polymers and / or between the polymer and the dispersed substance (adsorbed substance), the nitrile group-containing monomer preferably contains acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more kinds.

[0047] The content of the nitrile group-containing unit is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on the mass of the polymer (i.e., when the mass of the polymer is 100% by mass). The content of the nitrile group-containing unit is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and may be 40% by mass or less, based on the mass of the polymer (i.e., when the mass of the polymer is 100% by mass). By setting the content of the nitrile group-containing unit within the above range, the adsorptivity to the dispersed substance and the affinity to the liquid medium can be controlled, and the dispersed substance can be stably present in the liquid medium. In addition, the affinity of the polymer to the electrolytic solution can also be controlled, and problems such as the polymer dissolving in the electrolytic solution in the battery and increasing the resistance of the electrolytic solution can be prevented. For example, the content of the nitrile group-containing unit may be 10% by mass to 80% by mass, 20% by mass to 60% by mass, or 30% by mass to 40% by mass, based on the mass of the polymer (i.e., when the mass of the polymer is 100% by mass). It is preferable that the total amount of the acrylonitrile group-containing unit and the methacrylonitrile group-containing unit satisfies these ranges, and it is more preferable that the acrylonitrile group-containing unit satisfies these ranges.

[0048] In a preferred embodiment, based on the mass of the polymer (i.e., when the mass of the polymer is 100% by mass), the content of the aliphatic hydrocarbon unit is 50% by mass or more and 75% by mass or less, and the content of the nitrile group-containing unit is 25% by mass or more and 50% by mass or less. In a more preferred embodiment, the polymer contains an alkylene unit and a nitrile group-containing unit. Based on the mass of the polymer (i.e., when the mass of the polymer is 100% by mass), it is more preferable that the content of the alkylene unit is 50% by mass or more and 75% by mass or less, and the content of the nitrile group-containing unit is 25% by mass or more and 50% by mass or less.

[0049] The polymer may further contain, as aliphatic hydrocarbon units, alkenylene units; alkyl units; units containing branch points such as alkanetriyl units and alkanetetrayl units. The unit containing a branch point is a unit different from the unit containing a branched alkylene structure and the unit containing a branched alkyl structure.

[0050] An alkenylene unit is a unit containing an alkenylene structure, preferably a unit consisting only of an alkenylene structure. The alkenylene structure is preferably a linear alkenylene structure or a branched alkenylene structure.

[0051] The alkenylene unit preferably contains at least one selected from the group consisting of a unit containing a linear alkenylene structure and a unit containing a branched alkenylene structure, and more preferably contains at least one selected from the group consisting of a unit consisting only of a linear alkenylene structure and a unit consisting only of a branched alkenylene structure.

[0052] For example, when obtaining a polymer through the method of (1a) above, a conjugated diene monomer unit having a carbon-carbon double bond within the unit may remain in the molecule without being hydrogenated. The finally obtained polymer may contain a conjugated diene monomer unit having a carbon-carbon double bond within the unit as an alkenylene unit.

[0053] An alkyl unit is a unit containing an alkyl structure (however, it does not apply to other aliphatic hydrocarbon units such as branched alkylene units, nitrile group-containing units, amide group-containing units, and carboxyl group-containing units), and is preferably a unit consisting only of an alkyl structure. The alkyl structure is preferably a linear alkyl structure or a branched alkyl structure.

[0054] The alkyl unit preferably contains at least one selected from the group consisting of a unit having a linear alkyl structure and a unit having a branched alkyl structure, and more preferably contains at least one selected from the group consisting of a unit consisting only of a linear alkyl structure and a unit consisting only of a branched alkyl structure. The number of carbon atoms of the alkyl unit may be 1 to 20, 2 to 10, 3 to 8, or 4 to 6. For example, the alkyl unit includes an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an isohexyl group, and the like.

[0055] For example, when obtaining a polymer through the method of (1a) or (1b) above, it is preferable that at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit is introduced as a terminal group of the polymer. The finally obtained polymer may contain these monomer units as alkyl units.

[0056] The alkanetriyl unit is a unit containing an alkanetriyl structure, and preferably a unit consisting only of an alkanetriyl structure. The alkanetetrayl unit is a unit containing an alkanetetrayl structure, and preferably a unit consisting only of an alkanetetrayl structure.

[0057] For example, when obtaining a polymer through the method of (1a) above, a conjugated diene monomer unit may be introduced into the polymer as a monomer unit having no carbon-carbon double bond in the unit and containing a branching point. In this case, the finally obtained polymer is a branched polymer, and the conjugated diene monomer unit may be included as an aliphatic hydrocarbon unit containing a branching point such as an alkanetriyl unit or an alkanetetrayl unit. When the aliphatic hydrocarbon unit contains a unit having a branching point, the polymer is a branched polymer. The branched polymer may be a network polymer. Since the polymer containing a unit having a branching point can adsorb three-dimensionally to the dispersed material, the dispersibility and stability can be further improved.

[0058] The polymer may contain any unit. Examples of any unit include an amide group-containing unit; a carboxyl group-containing unit, etc.

[0059] The amide group-containing unit is a unit containing an amide group, preferably includes a unit containing an alkylene structure substituted by an amide group, and more preferably includes a unit consisting only of an alkylene structure substituted by an amide group. The alkylene structure is preferably a linear or branched alkylene structure. The amide group-containing unit may further include a unit containing an alkyl structure substituted by an amide group, or a unit consisting only of an alkyl structure substituted by an amide group. The number of amide groups contained in the amide group-containing unit is preferably one.

[0060] In the present disclosure, the content of the unit can be determined by using the amount of the monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurements.

[0061] The polymer in the embodiment of the present disclosure is characterized in that in the dynamic viscoelasticity measurement measured at a temperature of 100 °C and a frequency of 10 Hz, the tanδ (loss tangent) in the range of 0.01% to 10% of the strain is greater than 1.

[0062] When tanδ is in the range of 1 or less in the range of 0.01% to 10% of the strain, it has been found that the wettability of the polymer composition to the conductive material decreases. It is considered that when this tanδ is greater than 1, sufficient wettability of the polymer composition to the conductive material can be obtained, and the initial dispersibility can be improved.

[0063] As the dispersion efficiency increases, the dispersibility of the conductive material improves. However, excessive dispersion may cause the conductive material to break. When tanδ is in the range of 1 or less within the strain range of 0.01% to 10%, it was found that excessive dispersion is likely to cause the conductive material to break during the dispersion treatment of the conductive material using the polymer composition. In the range where tanδ is greater than 1, it can be controlled so that the appropriate viscoelasticity of the dispersion does not cause the conductive material to break during the dispersion treatment. Thus, it is considered that sufficient shape maintainability of the conductive material can be obtained in the electrode film, and the battery performance can be improved. For example, when using a long conductive material such as carbon nanotubes as the dispersoid, it is possible to suppress its breakage and obtain a dispersion with good dispersibility while maintaining the long shape. Further, since the conductive material composition in which carbon nanotubes or the like are dispersed using such a polymer can maintain its shape in the electrode film, it can exhibit high conductivity.

[0064] Also, when tanδ in the range of strain 0.01% to 10% is greater than 1, viscosity or fluidity is generated in the polymer. The polymer with imparted viscosity or fluidity can suppress the increase in the viscosity of the polymer solution. From this viewpoint as well, the initial dispersibility of the conductive material can be enhanced. Also, the initial dispersibility can be maintained to obtain long-term storage stability.

[0065] In the dynamic viscoelasticity measurement at a temperature of 100 °C and a frequency of 10 Hz, it is preferable that tanδ (loss tangent) in the range of strain 0.01% to 10% is greater than 1, but it may be 1 to 100, 1 to 50, 1 to 10, or 1 to 5. In the present disclosure, in the measurement of this tanδ (loss tangent), it has been found that the strain range of 0.01% to 10% is a factor affecting the adsorption of the copolymer to the conductive material, the solubility of the copolymer, the viscosity and stickiness of the copolymer, etc. in the polymer composition. By controlling the tanδ (loss tangent) of the copolymer to be greater than 1 in all ranges of this strain of 0.01% to 10%, it is possible to contribute to the improvement of the dispersibility of the conductive material and the improvement of the shape maintenance of the conductive material in the polymer composition. Due to such characteristics, the polymer can be used as a dispersant in the conductive material composition.

[0066] When using the polymer composition in an embodiment of the present disclosure, the effect can be exerted in both media dispersion and media - less dispersion. In media dispersion, since the tanδ (loss tangent) of the polymer is appropriately controlled, during the addition of the conductive material to the polymer composition for dispersion treatment, the collision efficiency of the dispersion medium is improved, and the generation of breakage of the conductive material can be suppressed by the appropriate viscoelasticity of the dispersion. In media - less dispersion, since the tanδ (loss tangent) of the polymer is appropriately controlled, during the addition of the conductive material to the polymer composition for dispersion treatment, a shear stress can be uniformly and sufficiently applied to the dispersion, the dispersion efficiency is improved, and the generation of breakage of the conductive material can be suppressed by the appropriate viscoelasticity of the dispersion.

[0067] The polymer in an embodiment of the present disclosure preferably has a measurement temperature at which tanδ (loss tangent) = 1 of 80°C or less when the temperature is raised from 30°C to 110°C at a rate of 10°C / min in a viscoelasticity measurement measured at a frequency of 10 Hz and a strain of 0.1%. Hereinafter, this measurement temperature at which tanδ (loss tangent) = 1 is also referred to as the measurement temperature (tanδ = 1). The polymer may have a measurement temperature (tanδ = 1) of less than 110°C, or 100°C or less, preferably 80°C or less, and may also be 70°C or less, 60°C or less, 50°C or less, 40°C or less, or 30°C or less. This measurement temperature (tanδ = 1) may have a tanδ greater than 1 in all ranges of the temperature range of 30 to 110°C.

[0068] Since this measured temperature (tanδ = 1) is 80°C or lower, the initial dispersibility can be further improved under normal temperature conditions in an environment where the conductive material is dispersed as a disperse phase in the polymer composition. Also, since the adsorptivity of the polymer to the conductive material can be maintained in the polymer composition, the long-term storage stability can be further improved. Further, during the dispersion treatment of the conductive material using the polymer composition, even if excessive dispersion occurs along with an improvement in the dispersion efficiency, breakage of the conductive material can be suppressed, and a conductive material composition maintaining the shape of the conductive material can be obtained. From this viewpoint, the measured temperature (tanδ = 1) is preferably 30°C or higher and 110°C or lower, more preferably 30°C or higher and 80°C or lower, and even more preferably 40°C or higher and 80°C or lower.

[0069] The tanδ of the polymer is determined by the following formula (1) and measured in dynamic viscoelasticity measurement. tanδ = loss modulus (G'') / storage modulus (G') Formula (1)

[0070] Regarding the strain dependence of the polymer, tanδ can be measured using a viscoelasticity measuring device (for example, MCR302e (Anton Paar)). Specifically, using a 25 mm diameter parallel plate, the GAP is set to the thickness of the sample, and measurement is performed under the conditions of a temperature of 100°C, a frequency of 10 Hz, and a strain range of 0.01 to 10%. It is determined whether tanδ is greater than 1 in the strain range of 0.01 to 10%.

[0071] Regarding the temperature dependence of the polymer, tanδ can be measured using a viscoelasticity measuring device (for example, MCR302e (Anton Paar)). Specifically, using a 25 mm diameter parallel plate, measurement is performed under the conditions of a constant normal force of 100 mN, a frequency of 10 Hz, a strain of 0.1%, a temperature range from 30°C to 110°C, and a heating rate of 10°C / min. The temperature at which tanδ = 1 is determined in the temperature range from 30°C to 110°C.

[0072] A sample of the polymer to be subjected to dynamic viscoelasticity measurement is obtained by dropping a polymer solution into a fluororesin mold and drying to remove the solvent. In the case of a viscous polymer, it is taken out of the fluororesin mold and used in a state of being cooled and solidified by liquid nitrogen. Specifically, according to the method described in the examples, tanδ in the strain range of 0.01 to 10% and the measurement temperature (tanδ = 1) can be measured.

[0073] The method for controlling tanδ of a nitrile-based polymer is not particularly limited. For example, tanδ can be controlled by changing the composition (structural unit type, content, hydrogenation rate, etc.), structure (linearity rate, etc.), molecular weight, production conditions (polymerization temperature, amount of molecular weight regulator, etc.) of the nitrile-based polymer. For example, the tanδ of a nitrile-based polymer can be controlled by the following methods.

[0074] In control method a, tanδ is increased by increasing the amount of the molecular weight regulator used in the production of the polymer. In control method b, tanδ of the polymer is increased by adding a base to modify it, such as by hydrolyzing the nitrile groups contained in the nitrile group-containing structural unit of the polymer. In control method c, tanδ is increased by applying mechanical shear stress to the polymer.

[0075] In control method b, when producing a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit, a base may be added for adjustment. Also, after dissolving a polymer already produced and containing an aliphatic hydrocarbon unit and a nitrile group-containing unit in a solvent capable of dissolving it, a base may be added for adjustment. As the base to be added, at least one selected from the group consisting of inorganic bases and organic hydroxides (organic bases) can be used. When adjusting by adding a base, when heat is applied to such an extent that the solvent does not catch fire or boil, tanδ can be increased in a shorter time.

[0076] Examples of the inorganic base include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates, or alkoxides of an alkali metal or an alkaline earth metal; and ammonium hydroxide and the like. Among these, from the viewpoint of easily supplying cations, hydroxides or alkoxides of an alkali metal or an alkaline earth metal are preferable. Examples of the hydroxide of an alkali metal include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the alkoxide of an alkali metal include lithium methoxide, lithium ethoxide, lithium propoxide, lithium t-butoxide, lithium n-butoxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium-t-butoxide, sodium-n-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium t-butoxide, potassium n-butoxide and the like. Examples of the hydroxide of an alkaline earth metal include calcium hydroxide, magnesium hydroxide and the like. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, and sodium-t-butoxide, and sodium hydroxide is more preferable. Note that the metal contained in the inorganic base may be a transition metal.

[0077] The organic hydroxide is a salt containing an organic cation and a hydroxide ion. Examples of the organic hydroxide include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide and the like. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide.

[0078] An alkanolamine may be used as the base. Examples of the alkanolamine include monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, methylethanolamine, methyldiethanolamine, and the like.

[0079] The amount of the base used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more, based on the mass of the nitrile-based polymer. The amount of the base used is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the mass of the nitrile-based polymer. In order to control the tanδ of the nitrile-based polymer, it is preferable that the amount is within these ranges.

[0080] In the control method b, the increase in tanδ can be achieved by mixing a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit, a base, and a liquid medium. Further, an arbitrary component may be mixed. There is no limitation on the order of addition of the polymer, the base, and the liquid medium to the container and the mixing method, and these may be added to the container simultaneously; the polymer, the base, and the liquid medium may be added to the container separately; or either one or both of the polymer and the base may be mixed with the liquid medium to prepare a polymer-containing liquid and / or a base-containing liquid, and the polymer-containing liquid and / or the base-containing liquid may be added to the container. In particular, since the nitrile group can be efficiently modified, a method of adding a base dispersion liquid in which the base is dispersed in the liquid medium to a polymer solution in which the polymer is dissolved in the liquid medium while stirring is preferable. For stirring, a disper (dispersion machine) or a homogenizer or the like can be used. As the liquid medium, a liquid medium that can be used for the polymer composition described later can be used.

[0081] There is no restriction on the temperature during mixing, but denaturation can be accelerated by heating to 30 °C or higher. Also, in order to promote the denaturation of the nitrile-based polymer, a small amount of water and / or alcohol may be added to the container. Water and / or alcohol may be added to the container while mixing the polymer and the base, may be added to the container before adding the nitrile-based polymer and the base to the container, or may be added to the container simultaneously with or subsequent to the nitrile-based polymer and the base. Further, when the nitrile-based polymer, the base, and any components used as necessary have high hygroscopicity, water may be contained as the absorbed water. The amount of water and / or alcohol is preferably 0.05 to 20% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.05 to 1% by mass based on the mass of the nitrile-based polymer.

[0082] Examples of the alcohol include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, and the like. The alcohol can be used alone or in combination of two or more. The hydrolysis is preferably carried out in the presence of at least one selected from the group consisting of methanol, ethanol, butanol, hexanol, and water, and particularly preferably in the presence of water.

[0083] The control method c may be adjusted by applying mechanical shear stress when producing a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit, or a polymer already produced and containing an aliphatic hydrocarbon unit and a nitrile group-containing unit may be dissolved in a liquid medium capable of dissolving it, and then adjusted by applying mechanical shear stress. Although tanδ can also be controlled by applying mechanical shear stress to the polymer before dissolution using a roll, kneader, etc., since it is efficient to use a nitrile-based polymer as a dispersant in a dissolved state in a liquid medium capable of dissolving it, it is more preferable to apply shear stress in the state of the polymer solution.

[0084] Examples of the method of applying shear stress in the polymer solution state include methods using dispersion means such as a homogenizer and a Silverson mixer. Although shear stress can also be applied using a disper, etc., it is preferable to use dispersion means such as a homogenizer and a Silverson mixer that can apply higher shear stress. Examples of the method of applying mechanical shear stress to the polymer before dissolution include methods using dispersion means such as a kneader and a two-roll mill.

[0085] The polymer in the embodiment of the present disclosure preferably contains a polymer and N-methyl-2-pyrrolidone, and when measuring a solution with a solid content concentration of 20% by mass using a B-type viscometer, the viscosity at 25°C and 60 rpm is less than 3000 mPa·s. According to one embodiment, the polymer has a tanδ in the strain range of 0.01 to 10% greater than 1, so that the initial dispersibility is improved, and thus the viscosity of the polymer solution can also be reduced. Even when the polymer content is high, the viscosity of the polymer solution can be reduced. By using such a polymer with viscosity physical properties, the viscosity of the polymer composition and the conductive material composition can be reduced. When measured with a B-type viscometer, at 25°C and 60 rpm, the viscosity of the polymer solution may be less than 3000 mPa·s, less than 1000 mPa·s, or less than 500 mPa·s. For example, the viscosity of this polymer solution may be from 10 mPa·s to 3000 mPa·s, or may be from 100 mPa·s to 1000 mPa·s.

[0086] The viscosity of the polymer solution is a value measured at a rotor rotation speed of 60 rpm using a B-type viscometer after allowing the polymer solution to stand in a constant temperature bath at 25°C for 1 hour or more. Specifically, it can be measured according to the method of the examples.

[0087] In the embodiment of the present disclosure, the polymer preferably has a Z-average molecular weight of 10,000 or more and 250,000 or less. The polymer specified by the Z-average molecular weight has a controlled molecular distribution on the high molecular weight side. When the Z-average molecular weight is 250,000 or less, the proportion of the high molecular weight molecular distribution decreases, and the polymer becomes viscous and fluid. When using a conductive material as a dispersoid, the wettability of the conductive material can be improved, and the initial dispersibility can be further enhanced. It is particularly effective in improving the wettability of a carbon material as the conductive material. Also, when the Z-average molecular weight is 10,000 or more, adsorption to the conductive material in the conductive material composition can be maintained, and the dispersibility can be maintained. For example, the Z-average molecular weight of the polymer may be 10,000 to 250,000, 10,000 to 200,000, 20,000 to 150,000, 30,000 to 100,000, 30,000 to 60,000, or 30,000 to 50,000. By being within the above range, when preparing a conductive material composition using the polymer, both initial dispersibility and storage stability can be achieved.

[0088] In the embodiment of the present disclosure, the polymer may have a weight average molecular weight (Mw) of 5,000 to 100,000, 10,000 to 70,000, or 20,000 to 50,000. Within these ranges, effects such as improving the wettability of the conductive material, especially the carbon material, and suppressing aggregation can be obtained, and the storage stability of the polymer composition can be further improved.

[0089] In the present disclosure, the Z-average molecular weight and the weight-average molecular weight are measured by gel permeation chromatography (GPC) equipped with an RI detector using a molecular weight measurement sample, respectively. Specifically, they can be measured according to the method of the examples. The Z-average molecular weight and the weight-average molecular weight are polystyrene-converted values, respectively.

[0090] A measurement sample for measuring the molecular weight of the polymer contained in the polymer composition is prepared by the following method. The polymer composition is dropped into purified water to precipitate the polymer, and the precipitate is collected. The precipitate is dissolved in tetrahydrofuran (THF) to obtain a solution. This solution is washed with purified water, and the purified precipitate is redissolved in THF to obtain a measurement sample. Specifically, the measurement sample can be prepared according to the method of the examples, and the molecular weight can be measured.

[0091] The wettability of the polymer to the conductive material can be evaluated from the ratio of the solid content in the supernatant and the bottom after standing for 24 hours by preparing a dispersion of the polymer, the conductive material, and the liquid medium. Specifically, a polymer solution of N-methyl-2-pyrrolidone (NMP) containing 8% by mass of the polymer is prepared. A conductive material is added to this polymer solution to prepare a polymer dispersion containing 2% by mass of the conductive material. This polymer dispersion is allowed to stand for 1 hour without stirring, and measurement samples are collected from the supernatant and the bottom after 1 hour of standing. The wettability of the polymer to the conductive material can be evaluated from the mass ratio of (solid content contained in the supernatant) / (solid content contained in the bottom). This mass ratio is preferably 0.5 or more and less than 1.5, and more preferably 0.75 or more and less than 1.25. This mass ratio can be used to relatively evaluate the wettability of the polymer using carbon nanotube JENOTUBE10B (average outer diameter 10 nm, BET specific surface area 230 m 2 / g, multi-walled CNT) as the conductive material. Specifically, it can be evaluated according to the method of the examples.

[0092] <Liquid medium> In the polymer composition, the liquid medium is not particularly limited as long as it is miscible with the polymer. In the present disclosure, "miscible with the polymer" means that when 0.5 g of the polymer is dissolved in 100 g of the liquid medium at 25°C, the insoluble content is 10% by mass or less. The insoluble content can be calculated by filtering off the undissolved polymer from the solution of the undissolved polymer and the solution, then recovering the undissolved polymer, and then drying the recovered polymer with hot air and measuring its mass. The liquid medium preferably can dissolve the polymer, and more preferably is a high-dielectric constant solvent that can dissolve the polymer. In the present disclosure, "can dissolve the polymer" means that when 0.5 g of the polymer is dissolved in 100 g of the liquid medium at 25°C, no insoluble content can be visually confirmed and the solution is transparent without turbidity. When a liquid medium that can dissolve the polymer is used, a good dispersion state can be easily obtained when a conductive material is added.

[0093] In one embodiment, the liquid medium preferably comprises a solvent consisting of any one of high-dielectric constant solvents or a mixed solvent consisting of two or more thereof. Further, one or two or more other solvents may be mixed with the high-dielectric constant solvent and used. In the present disclosure, the "high-dielectric constant solvent" preferably has a relative dielectric constant value described in a solvent handbook or the like of 2.5 or more at 20°C, and more preferably 25 or more. When a conductive material composition is prepared using a high-dielectric constant solvent as the liquid medium, the interaction between the nitrile group contained in the polymer of the above embodiment, the conductive material, and the liquid medium can be enhanced. From the viewpoint of the solubility of the polymer, the relative dielectric constant of the high-dielectric constant solvent is preferably 60 or less at 20°C, and more preferably 50 or less. In one embodiment, the relative dielectric constant of the high-dielectric constant solvent may preferably be 30 to 50.

[0094] In one embodiment, the liquid medium is preferably a non-aqueous liquid medium. The polymer of the above embodiment tends to have low solubility in water. Therefore, when water is present in the conductive material composition, it tends to be difficult to obtain a desired good dispersion state. Thus, the liquid medium preferably substantially does not contain water. "Substantially does not contain" means that water is not intentionally added beyond the amount contained by moisture absorption or the like. The water content based on the total mass of the liquid medium is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. Even when the conductive material composition is prepared without adding water, the conductive material composition may contain about 0.1% by mass of water due to moisture absorption or the like. From the above viewpoints, the liquid medium is preferably an organic solvent, and more preferably a polar organic solvent that does not donate protons.

[0095] In the polymer composition, when a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit is used, it is preferable to use an amide-based liquid medium. The amide-based liquid medium is excellent in the solubility of this polymer. Further, the amide-based liquid medium is a high dielectric constant solvent, can enhance the interaction with this polymer, and can contribute to the improvement of the initial dispersibility. Further, the amide-based liquid medium is a polar organic solvent that does not donate protons, and can contribute to the stability over time of this polymer, and further the conductive material and the binder resin.

[0096] Examples of the amide-based liquid medium include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, and the like. Among them, from the viewpoints of excellent solubility of the polymer, high dielectric constant, etc., it is preferable to use at least one of N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), more preferably to use N-methyl-2-pyrrolidone (NMP) alone, and it is also preferable to use N-methyl-2-pyrrolidone (NMP) in combination with other liquid media.

[0097] Examples of other liquid media include polar organic solvents that do not donate protons, such as heterocyclic, sulfoxide, sulfone, lower ketone, and carbonate liquid media. More specifically, the following are included.

[0098] Heterocyclic: cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc. Sulfoxide: dimethyl sulfoxide, etc. Sulfone: hexamethylphosphoramide, sulfolane, etc. Lower ketone: acetone, methyl ethyl ketone, etc. Carbonate: diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, etc. Others: tetrahydrofuran, acetonitrile, etc.

[0099] <Polymer Composition> The polymer composition for an electrochemical device, which is one embodiment of the present disclosure, contains a polymer and an amide-based liquid medium. The polymer contains an aliphatic hydrocarbon unit and a nitrile group-containing unit, and the details are as described above. The details of the amide-based liquid medium are as described above.

[0100] In the polymer composition, the nitrile-based polymer may be 1 to 50, 2 to 40, or 5 to 30% by mass based on the total mass of the polymer composition. Even when the polymer composition is contained at a high concentration of 20% by mass or more, the tanδ in the strain range of 0.01% to 10% is greater than 1, so that while having dispersibility of the conductive material, breakage of the conductive material in the dispersion treatment can be suppressed, and a dispersion maintaining the shape of the conductive material can be provided. In the polymer composition, the nitrile-based polymer may be 50 to 100, 75 to 100, or 80 to 99.8% by mass based on the total mass of the solid content. In the polymer composition, other polymers may be included in addition to the nitrile-based polymer. In the polymer composition, the other polymer may be 0 to 100 parts by mass, 0.1 to 50 parts by mass, or 1 to 10 parts by mass with respect to 100 parts by mass of the nitrile-based polymer. The polymer composition may not contain other polymers.

[0101] In the polymer composition, the amide-based liquid medium may be 50 to 99% by mass, 60 to 98% by mass, or 70 to 95% by mass with respect to the total mass of the polymer composition. In the polymer composition, other liquid media may be included in addition to the amide-based liquid medium. In the polymer composition, the other liquid medium may be 0 to 100 parts by mass, 0.1 to 50 parts by mass, or 1 to 10 parts by mass with respect to 100 parts by mass of the amide-based liquid medium. The polymer composition may not contain other liquid media. When dispersing a conductive material using the polymer composition, by using a nitrile-based polymer as the main component, more preferably using only the nitrile-based polymer, the viscoelasticity of the polymer composition can be appropriately controlled to more suppress the breakage of the conductive material in the dispersion treatment.

[0102] The solid content of the polymer composition may be 1 to 60% by mass, 2 to 50% by mass, or 5 to 35% by mass. The solid content of the polymer composition may be appropriately set according to the molecular structure of the polymer, characteristics such as the type of liquid medium, the use of the polymer composition, the type of conductive material to be dispersed, etc. In the present disclosure, the solid content is the total amount of components excluding the liquid medium. Specifically, the polymer composition is sufficiently dried in an oven set at a temperature at which the liquid medium can evaporate to obtain only the solid content, the solid content mass of the polymer composition is measured, and the value obtained by dividing it by the total mass of the polymer composition is defined as the solid content.

[0103] The polymer composition may contain additional optional components as necessary. For example, the polymer composition may contain a base. The base may be a component contained in the raw material of the nitrile-based polymer, a component mixed in from the synthesis raw material of the nitrile-based polymer, etc., and the details are as described above.

[0104] Note that the polymer composition means a composition in a state that does not contain a conductive material and an active material. In the polymer composition, the conductive component may be 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, and the conductive component may not be substantially contained. In the polymer composition, the active material may be 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, and the active material may not be substantially contained.

[0105] <Conductive material composition> The conductive material composition according to one embodiment of the present disclosure includes a polymer composition for an electrochemical element and a conductive material. Details of the polymer composition for an electrochemical element are as described above. The conductive material will be described below.

[0106] <Conductive material> The conductive material is not particularly limited, but is preferably a carbon material. Examples of the carbon material having conductivity include graphite, carbon black, graphene, multilayer graphene, fullerene; fibrous carbon materials such as carbon nanotubes and carbon nanofibers. These may be used alone or in combination of two or more. Examples of graphite include artificial graphite, flaky graphite, massive graphite; natural graphite such as earthy graphite.

[0107] The carbon material plays a role of forming a conductive path inside the electrode, and from the viewpoint that it is difficult to be cut due to the expansion and contraction of the electrode film, it is preferably included a fibrous carbon material, and more preferably a fibrous carbon material. From the viewpoints of conductivity, availability, and cost, the use of carbon black and / or carbon nanotubes is preferred. Also, from the viewpoint of reducing raw material costs and forming an efficient conductive network, two or more kinds of carbon materials having different physical properties of the same kind may be used in combination. Examples of carbon materials of the same kind having different physical properties include, for example, two or more kinds of carbon nanotubes having different average outer diameters or average fiber diameters, or two or more kinds of carbon black having different specific surface areas.

[0108] The carbon purity of the carbon material is represented by the content ratio (mass %) of carbon atoms in the carbon material. The higher the carbon purity, the more preferable it is. With respect to 100% by mass of the carbon material, 90% by mass or more is preferable, 95% by mass or more is more preferable, 98% by mass or more is still more preferable, and 99% by mass or more is particularly preferable. By setting the carbon purity within the above range, problems such as the formation of dendrites and short circuits due to impurities such as metals can be prevented.

[0109] <Carbon nanotube> A carbon nanotube has a shape in which planar graphite is wound into a cylindrical shape, and includes single-walled carbon nanotubes and multi-walled carbon nanotubes, and these may be mixed. A single-walled carbon nanotube has a structure in which one layer of graphite is wound. A multi-walled carbon nanotube has a structure in which two or more layers of graphite are wound. Further, the side wall of the carbon nanotube does not have to be a graphite structure. The carbon nanotube may be, for example, a carbon nanotube having a side wall with an amorphous structure.

[0110] The shape of the carbon nanotube is not limited. Examples of the shape of the carbon nanotube include various shapes such as needle-like, cylindrical tube-like, fishbone-like (fishbone or cup stacking type), trump-like (platelet), and coil-like. Among them, in the present embodiment, the shape of the carbon nanotube is preferably needle-like or cylindrical tube-like. The carbon nanotube may have a single shape or a combination of two or more shapes.

[0111] Examples of the form of the carbon nanotube include graphite whiskers, filamentous carbon, graphite fibers, ultra-fine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. The carbon nanotube may have these single forms or a form in which two or more of them are combined.

[0112] The average outer diameter of the carbon nanotubes is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. Also, the average outer diameter of the carbon nanotubes is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. When the average outer diameter is within the above range, when applied to a secondary battery, it is easy to form a good conductive network in the electrode, and during charge and discharge, the active material inside the secondary battery can be utilized evenly, suppressing the deterioration of the active material, and improving the cycle characteristics of the secondary battery. Incidentally, the average outer diameter of the carbon nanotubes can be calculated by observing and imaging the carbon nanotubes with a transmission electron microscope, and then selecting any 300 carbon nanotubes in the obtained observation photograph and measuring their respective outer diameters.

[0113] The average fiber length of the carbon nanotubes is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Also, the fiber length of the carbon nanotubes is preferably 100 μm or less, more preferably 20 μm or less. Incidentally, the average fiber length of the carbon nanotubes can be calculated by observing and imaging the carbon nanotubes with a scanning electron microscope, and then selecting any 300 carbon nanotubes in the obtained observation photograph and measuring their respective fiber lengths. It is also preferable that the average fiber length of the carbon nanotubes in the conductor dispersion liquid is within the above range.

[0114] The value obtained by dividing the fiber length of the carbon nanotube by the outer diameter is the aspect ratio. Using the values of the average fiber length and the average outer diameter, a representative aspect ratio can be determined. The higher the aspect ratio of the conductive material, the higher the conductivity can be obtained when forming the electrode. The aspect ratio of the carbon nanotube is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. Also, the aspect ratio of the carbon nanotube is preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

[0115] The BET specific surface area of the carbon nanotube is preferably 100 m 2 / g or more, more preferably 150 m 2 / g or more, and even more preferably 200 m 2 / g or more. Also, the specific surface area of the carbon nanotube is preferably 1200 m 2 / g or less, more preferably 1000 m 2 / g or less, and even more preferably 700 m 2 / g or less. The BET specific surface area of the carbon nanotube can be measured by the BET method based on nitrogen adsorption measurement in accordance with JIS Z 8830.

[0116] The carbon purity of the carbon nanotube is represented by the content rate (mass%) of carbon atoms in the carbon nanotube. The carbon purity is preferably 80 mass% with respect to 100 mass% of the carbon nanotube, more preferably 90 mass% or more, even more preferably 95 mass% or more, still more preferably 98 mass% or more, and even better 99 mass% or more or 99.5 mass% or more. By setting the carbon purity within the above range, problems such as dendrite formation and short circuit caused by impurities can be prevented. The carbon purity of the carbon nanotube can be determined by the method described in the examples using an ICP emission spectroscopic analyzer.

[0117] <Carbon black> Carbon black is fine particles mainly composed of carbon, and is produced by controlling various properties through the incomplete combustion of oil or gas. Carbon black has a secondary structure (aggregate) in which primary particles are connected in a bead-like manner, and a tertiary structure (agglomerate) in which secondary structures are further aggregated. The secondary and tertiary structures are collectively referred to as the structure. When observing primary particles with an electron microscope or the like, they appear spherical, but primary particles are not chemically independent individuals. They are connected by chemical bonds to adjacent primary particles within the aggregate to form a secondary structure. On the other hand, secondary structures are chemically independent individuals and aggregate by intermolecular forces to form a tertiary structure. Therefore, it can be said that the conductivity inside the secondary structure is higher than the conductivity between secondary structures including contact resistance, and it is effective to obtain an electrode with excellent conductivity by de-aggregating the tertiary structure while maintaining the structure of the secondary structure as much as possible. Note that the secondary structure is sometimes simply referred to as "structure".

[0118] As carbon black, various types such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, and ketjen black can be used. Also, commonly used oxidized carbon black or graphitized carbon black can be used.

[0119] The oxidation treatment of carbon black is a treatment in which carbon black is heat-treated in air or secondarily treated with nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenolic groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface. It is generally carried out to improve the dispersibility of carbon black.

[0120] Examples of commercially available carbon blacks include, but are not limited to, SuperP-Li (manufactured by TIMCAL), Ketjenblack EC-300J, EC-600JD (manufactured by Lion), Denka Black, Denka Black Li-400, Li-335 (manufactured by Denka, acetylene black), etc., and two or more of them may be used in combination.

[0121] The average primary particle diameter of the carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and even more preferably 25 nm to 100 nm. The average primary particle diameter of the carbon black can be calculated by first observing and imaging the carbon black with a transmission electron microscope, and then selecting any 100 spherical carbon black primary particles in the observation photograph and measuring their respective outer diameters.

[0122] The BET specific surface area of the carbon black is preferably 10 m 2 / g or more and 1500 m 2 / g or less, more preferably 40 m 2 / g or more and 1000 m 2 / g or less, and even more preferably 100 m 2 / g or more and 850 m 2 / g or less. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount, and the amount of conductive material in the electrode can be reduced. Thereby, the degree of freedom in battery design, such as increasing the amount of active material and binder resin, is increased. Furthermore, when preparing the electrode slurry, the composite of the active material and the carbon black tends to proceed, so it is easy to obtain an electrode film having a homogeneous conductive network in which the surface of the active material is covered with carbon black, suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material, and improving the cycle characteristics of the battery. The BET specific surface area of the carbon black can be measured by the BET method described in JIS Z 8830.

[0123] In the conductive material composition, from the viewpoints of dispersibility and storage stability, the conductive material may be 0.1 to 30% by mass, 1 to 25% by mass, or 3 to 20% by mass based on the total mass of the conductive material composition.

[0124] In the conductive material composition, when using carbon nanotubes as the conductive material, the content of the carbon nanotubes is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, further preferably 1% by mass or more, and still more preferably 3% by mass or more based on the total mass of the conductive material composition. Also, the content of the carbon nanotubes is preferably 20% by mass or less, and more preferably 10% by mass or less. By setting the content of the carbon nanotubes within the above range, the carbon nanotubes can be present well and stably without causing sedimentation or gelation. Further, the content of the carbon nanotubes is preferably adjusted appropriately so that a conductive material composition having appropriate fluidity or viscosity can be obtained depending on the BET specific surface area of the carbon nanotubes, the affinity for the liquid medium, the dispersing ability of the dispersant, etc. According to one embodiment, since a nitrile-based polymer is used, the initial dispersibility and the shape maintainability of the carbon nanotubes are good, and it is possible to contain carbon nanotubes at a higher concentration. For example, the content of the carbon nanotubes may be in the range of 0.1 to 20% by mass based on the total mass of the conductive material composition, but may also be 1 to 20% by mass, 3 to 20% by mass, 4 to 20% by mass, 5 to 20% by mass, or 8 to 20% by mass.

[0125] In a conductive material composition, when carbon black is used as the conductive material, the content of carbon black is preferably 0.1% by mass or more, more preferably 1% by mass or more, still more preferably 5% by mass or more, and even more preferably 10% by mass or more with respect to the total mass of the conductive material composition. Further, the content of this carbon black is preferably 30% by mass or less, and more preferably 20% by mass or less. By setting the content of carbon black within the above range, carbon black can be present well and stably without causing sedimentation or gelation. Further, the content of carbon black is preferably adjusted as appropriate so that a conductive material composition having appropriate fluidity or viscosity can be obtained depending on the BET specific surface area of carbon black, the affinity for the liquid medium, the dispersibility of the dispersant, etc. According to one embodiment, since a nitrile-based polymer is used, the initial dispersibility and the shape maintainability of carbon black are good, and it is possible to contain carbon black at a higher concentration. For example, the content of carbon black may be in the range of 0.1 to 30% by mass with respect to the total mass of the conductive material composition, but may also be 1 to 20% by mass, 5 to 20% by mass, 10 to 20% by mass, 12 to mass%, or 15 to 20% by mass.

[0126] In a conductive material composition, the nitrile-based polymer may be 0.05 to 5 parts by mass, 0.1 to 1 part by mass, or 0.2 to 0.5 parts by mass with respect to 100 parts by mass of the conductive material. According to one embodiment, since a nitrile-based polymer is used, the initial dispersibility and the shape maintainability of the conductive material are good. Further, even if the nitrile-based polymer is a small amount with respect to the conductive material, it is possible to exhibit its action. For example, the nitrile-based polymer may be 0.05 to 5 parts by mass with respect to 100 parts by mass of the conductive material, but may also be 0.05 to 0.5 parts by mass, or 0.05 to 0.2 parts by mass.

[0127] In a conductive material composition, the solid content may be 0.1 to 30% by mass, 1 to 25% by mass, or 3 to 20% by mass.

[0128] When the conductive material is dispersed by a disperser through collision with media such as a bead mill, or when a process of repeatedly passing the disperser over a long period of time is performed, etc., the conductive material may break and short-sided carbon materials may be generated. When short-sided carbon materials are generated, the viscosity of the conductive material composition decreases, and the gloss of the coating film obtained by coating and drying the conductive material composition increases. Therefore, judging only from these evaluation results, the dispersion state seems to be good. However, short-sided carbonaceous materials have a high contact resistance and it is difficult to form a conductive network, so the resistance of the electrode may deteriorate. According to one embodiment, since a nitrile-based polymer is used, the initial dispersibility and the shape maintainability of the conductive material are good. Therefore, a conductive network is likely to be formed in the electrode film, and the rate characteristics and cycle characteristics can be improved in the secondary battery.

[0129] In one embodiment, the conductive material composition may optionally contain additional optional components as necessary. For example, the conductive material composition may optionally contain a dispersant, a wetting agent, a surfactant, a pH adjuster, a wetting penetrant, a leveling agent, a polymer component, etc. within a range that does not inhibit the object of the present invention. These optional components can be added at any timing, such as before the preparation of the conductive material composition, during dispersion, after dispersion, etc. Also, these optional components may be added at any timing during the preparation of the polymer composition. Also, these optional components may be added at any timing during the preparation of the slurry composition. These timings may be combined and added step by step.

[0130] As the dispersant and the polymer component, known ones other than nitrile-based polymers can be used. Among them, in particular, it is preferably at least one selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, and polyvinyl acetal. A polymer in which other substituents are introduced into a part of the above polymer, or a modified polymer may be used. When using a dispersant or a polymer component, the weight average molecular weight is preferably 30,000 or less, more preferably 20,000 or less, and preferably 3,000 or more. If outside the above range, there is a concern of inhibiting the adsorption between the nitrile-based polymer and the conductive material.

[0131] The dispersibility of the conductive material in the conductive material composition can also be evaluated by the median diameter (μm) determined by a laser diffraction / scattering type particle size distribution analyzer. With the median diameter (μm) determined by a laser diffraction / scattering type particle size distribution analyzer, the particle diameter of the aggregated particles of the conductive material can be estimated from the scattered light intensity distribution by the particles. The median diameter (μm) is preferably 0.4 or more. Also, the median diameter (μm) is preferably 5.0 or less, and more preferably 2.0 or less. By setting the median diameter (μm) within the above range, a conductive material composition in an appropriate dispersed state can be obtained. If the median diameter (μm) is below the above range, there is a conductive material in an aggregated state, and if it exceeds the above range, a large number of finely cut conductive materials are generated, making it difficult to form an efficient conductive network.

[0132] The dispersibility of the conductive material in the conductive material composition can also be evaluated by the gloss (that is, the intensity of the reflected light at 60°) measured at 60° of the coating film obtained by coating on a smooth glass substrate and baking and drying. The light incident on the coating film is such that the smoother the coating film surface is due to better dispersibility, the higher the gloss. Conversely, the worse the dispersibility is, the more the light is scattered by the unevenness of the coating film surface, resulting in a lower gloss.

[0133] The gloss of the above coating film at 60° is preferably 5 or more, more preferably 20 or more, even more preferably 30 or more, and particularly preferably 40 or more. Also, the gloss of the above coating film at 60° is preferably 120 or less, more preferably 110 or less, and even more preferably 100 or less. By setting it within the above range, a conductive material composition with an appropriate dispersion state can be obtained. If it is below the above range, there will be a conductive material in an aggregated state, and if it exceeds the above range, a large number of finely cut conductive materials will be generated, making it difficult to form an efficient conductive network.

[0134] The TI value of the conductive material composition can be calculated from the value obtained by dividing the viscosity (mPa·s) at 60 rpm measured with a B-type viscometer by the viscosity (mPa·s) at 6 rpm. The TI value is preferably 1.5 or more and 5.0 or less. In one embodiment, the above TI value is more preferably 1.5 or more and less than 3.0. The higher the TI value, the greater the structural viscosity due to the entanglement of the conductive material, polymer, and other resin components, or the intermolecular forces between them, and the lower the TI value, the smaller the structural viscosity. By setting the TI value within the above range, it is possible to suppress the entanglement of the conductive material, polymer, and other resin components while allowing the intermolecular forces between them to act appropriately.

[0135] <Dispersion method> The conductive material composition can be produced, for example, by subjecting a polymer composition and a conductive material to a dispersion treatment using a dispersion device to finely disperse them. Note that the dispersion treatment can arbitrarily adjust the addition timing of the materials used and can be a multi-stage treatment of two or more times.

[0136] Examples of the dispersion device include a kneader, a two-roll mill, a three-roll mill, a planetary mixer, a ball mill, a horizontal sand mill, a vertical sand mill, an annular bead mill, an attritor, a high-shear mixer, a high-pressure homogenizer, an ultrasonic homogenizer, and the like.

[0137] From the viewpoint of promoting the wetting of the conductive material and dissociating coarse particles, it is more preferable to use a high-shear mixer in the initial stage of dispersion, and then use a high-pressure homogenizer from the viewpoint of dispersing while maintaining the aspect ratio of the conductive material. Further, after dispersing with a high-pressure homogenizer, by further dispersing with a bead mill, the dispersion state can be made uniform while maintaining the fiber length. Alternatively, since the mixed liquid before dispersion can be prepared to have a lower viscosity by using the polymer composition containing the nitrile-based polymer of the present disclosure, by first dispersing with a bead mill to dissociate the conductive material to a certain level and then dispersing with a high-pressure homogenizer, a uniform dispersion state can be realized while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 60 to 150 MPa, and more preferably 60 to 120 MPa.

[0138] The dispersion methods using a dispersion device include batch dispersion, pass dispersion, circulation dispersion, etc. Any method may be used, or two or more methods may be combined. Batch dispersion is a method of performing dispersion only with the dispersion device main body without using piping or the like. Since it is easy to handle, it is preferable when manufacturing a small amount. Pass dispersion is a dispersion method in which the dispersion device main body is provided with a tank for supplying the liquid to be dispersed via a pipe and a tank for receiving the liquid to be dispersed, and the liquid to be dispersed is passed through the dispersion device main body. Further, circulation dispersion is a method in which the liquid to be dispersed that has passed through the dispersion device main body is returned to the tank for supplying the liquid to be dispersed and dispersed while being circulated. In any case, the longer the processing time, the more the dispersion progresses. Therefore, pass or circulation can be repeated until the desired dispersion state is achieved, and the throughput can be increased by changing the size of the tank or the processing time. Pass dispersion is preferable in that it is easier to make the dispersion state uniform compared to circulation dispersion. Circulation dispersion is preferable in that the work and manufacturing equipment are simpler compared to pass dispersion. In the dispersion process, the disintegration of agglomerated particles, the dissociation of the conductive material, wetting, stabilization, etc. proceed sequentially or simultaneously, and the final dispersion state varies depending on the manner of progress. Therefore, it is preferable to manage the dispersion state in each dispersion process by using various evaluation methods. For example, it can be managed by the method described in the examples.

[0139] <Slurry Composition> A slurry composition according to an embodiment of the present disclosure includes a polymer composition for an electrochemical element, a conductive material, and an active material. Details of the polymer composition for an electrochemical element and the conductive material are as described above. Hereinafter, the active material will be described.

[0140] The slurry composition can contain a positive electrode active material or a negative electrode active material. In the present disclosure, the positive electrode active material and the negative electrode active material may be simply referred to as "active material". The active material is a material that serves as the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force. In the present disclosure, a slurry composition containing a positive electrode active material or a negative electrode active material may be referred to as a "positive electrode slurry composition", a "negative electrode slurry composition", or simply a "slurry composition", respectively. The slurry composition is preferably in a slurry state in order to improve uniformity and processability.

[0141] <Positive Electrode Active Material> The positive electrode active material is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions, sodium ions, etc., and conductive polymer materials can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium or sodium, inorganic compounds such as transition metal sulfides, polyanion compounds, Prussian blue compounds, and the like. Specifically, MnO, V2O5, V 6O13. Examples include transition metal oxide powders such as TiO2, lithium transition metal composite oxide powders such as layered lithium nickelate, lithium cobaltate, lithium manganate, and lithium manganese oxide having a spinel structure, lithium iron phosphate-based materials which are phosphate compounds having an olivine structure, transition metal sulfide powders such as TiS2 and FeS, sodium iron oxide, sodium manganate, sodium chromate, sodium nickelate having a layered structure, and sodium iron phosphate-based materials which are phosphate compounds having an olivine structure. Further, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0142] The positive electrode active material is preferably a composite oxide of lithium containing transition metals such as Al, Fe, Co, Ni, and Mn, more preferably a composite oxide of lithium containing any one of Al, Co, Ni, and Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When the active material contains Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metal is 50 mol% or more), the basicity tends to increase due to components derived from the raw materials or elution of metal ions, and as a result, gelation of the binder and deterioration of the dispersion state are likely to occur, and thus the problems of the present disclosure may become prominent. Therefore, in the case of a battery containing an active material containing Ni and / or Mn, the embodiments of the present disclosure are particularly effective.

[0143] <Negative electrode active material> The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions, sodium ions, etc. For example, metal Li, or its alloys, alloy systems such as tin alloys, silicon alloys, and lead alloys, Li X TiO2, Li X Fe2O3, Li X Fe3O4, Li XMetal oxide systems such as WO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number and 0 < x < 1.

[0144] These negative electrode active materials can be used alone or in combination of two or more. In particular, when using a silicon alloy negative electrode, although the theoretical capacity is large, the volume expansion is extremely large. Therefore, it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials.

[0145] When the conductive material in the slurry composition is carbon nanotubes, the content of carbon nanotubes is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. When the conductive material is carbon black, the content of carbon black is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 20% by mass or less, more preferably 10% by mass or less. The conductive material may be used in combination of carbon nanotubes and carbon black, or two or more of each may be used, but the total addition amount of each is preferably within the above range. If it exceeds the above range, the filling amount of the active material in the electrode will decrease, leading to a reduction in the battery's low-dose performance. If it is below the above range, the conductivity of the electrode and the battery may be insufficient.

[0146] The content of the nitrile-based polymer in the slurry composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Further, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0147] <Binder resin> The slurry composition may further contain a binder resin. The binder resin used in the slurry composition is a resin capable of binding substances such as active materials and conductive materials. The binder resin is usually not particularly limited as long as it is used as a binder resin for paints and can be appropriately selected according to the purpose. That is, it may contain a resin capable of binding substances such as active materials and conductive materials other than the nitrile-based polymer.

[0148] Examples of the binder resin used in the slurry composition include polymers or copolymers containing, as constituent units, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters, methacrylic acid, methacrylic esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluorine resins; cellulose resins such as carboxymethyl cellulose (CMC); elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Further, modified products, mixtures, and copolymers of these resins may also be used.

[0149] Among these, as the binder resin used in the positive electrode composition, a polymer or copolymer having a fluorine atom in the molecule is preferable from the viewpoint of resistance. For example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. are preferable. Further, as the binder resin used in the negative electrode composition, carboxymethyl cellulose (CMC), styrene-butadiene rubber, polyacrylic acid, etc. are preferable because of good adhesion.

[0150] The content of the binder resin used in the slurry composition is preferably 0.5 to 30% by mass, more preferably 0.5 to 25% by mass, based on the non-volatile content of the slurry composition.

[0151] When the slurry composition contains a binder resin, the content of the binder resin in the slurry composition is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Further, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0152] The solid content in the slurry composition is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the slurry composition (assuming the mass of the slurry composition is 100% by mass). Further, it is preferably 90% by mass or less, more preferably 80% by mass or less.

[0153] The slurry composition can be prepared by various conventionally known methods. For example, a method of preparing by adding an active material to a conductive material composition; a method of preparing by adding a binder resin after adding an active material to the conductive material composition; a method of preparing by adding an active material after adding a binder resin to the conductive material composition; a method of preparing by adding a conductive material composition after previously mixing an active material, a binder resin, and a liquid medium as necessary, etc. can be mentioned. As a method of preparing a slurry composition containing carbon nanotubes as a conductive material, a method of performing a process of adding an active material and dispersing it after adding a binder resin to the conductive material composition is preferable. By preparing in this way, a slurry composition can be prepared without disturbing the dispersion state of the carbon nanotubes. The dispersion device used for dispersion is not particularly limited. A slurry composition can be obtained using the dispersion means mentioned in the description of the conductive material composition.

[0154] <Electrode film> The electrode film according to one embodiment of the present disclosure is formed using a slurry composition. Details of the slurry composition are as described above. Also, an electrode including a current collector and an electrode film formed on the current collector can be provided.

[0155] The electrode film can be obtained, for example, by coating a slurry composition on a current collector and drying it. An electrode film formed using a positive electrode slurry composition can be used as a positive electrode. An electrode film formed using a negative electrode slurry composition can be used as a negative electrode. In the present disclosure, a film formed using a slurry composition containing an active material may be referred to as an "electrode composite layer".

[0156] The material and shape of the current collector used for forming the above electrode film are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. Examples of the material of the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Also, as the shape, generally a flat foil is used, but a current collector with a roughened surface, a perforated foil-shaped current collector, or a mesh-shaped current collector can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0157] As a method of coating the slurry composition on the current collector, there is no particular limitation, and known methods can be used. Specifically, as the coating method, a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, an electrostatic coating method, etc. can be mentioned. As the drying method, for example, natural drying, or drying using a blowing dryer, a hot air dryer, an infrared heater, a far infrared heater, etc. can be mentioned, but it is not particularly limited to these.

[0158] After coating, a rolling treatment may be performed using a lithographic press, a calendar roll, etc. The thickness of the formed film is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0159] The electrode film formed using the slurry composition can also be used as an underlayer of the electrode composite layer. By providing such an underlayer, the adhesion between the electrode composite layer and the current collector can be improved, or the conductivity of the electrode film can be improved.

[0160] <Electrochemical element> According to an embodiment of the present disclosure, an electrochemical element can be provided. As the electrochemical element, a secondary battery, a capacitor, etc. are suitable. In at least one of the electrode bodies of the electrochemical element, it is preferable to include an electrode film formed using the slurry composition. Details of the slurry composition and the electrode film are as described above. Examples of the secondary battery include a lithium ion secondary battery, an alkaline secondary battery, a lead storage battery, a sodium sulfur secondary battery, a lithium air secondary battery, etc. The secondary battery is preferably a non-aqueous secondary battery. Examples of the capacitor include an electric double layer capacitor, a lithium ion capacitor, a hybrid capacitor, a redox capacitor, etc.

[0161] <Secondary battery> A secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode includes an electrode film formed using a slurry composition. Details of the slurry composition and the electrode film are as described above.

[0162] As the electrolyte, various conventionally known materials in which ions can move can be used. For example, the electrolyte may include, but is not limited to, lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is a phenyl group). The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0163] The non-aqueous solvent is not particularly limited. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

[0164] The non-aqueous electrolyte secondary battery preferably includes a separator. Examples of the separator include, but are not particularly limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and non-woven fabrics obtained by subjecting these to hydrophilic treatment.

[0165] The structure of the non-aqueous electrolyte secondary battery of this embodiment is not particularly limited. In one embodiment, the non-aqueous electrolyte secondary battery may usually include a positive electrode, a negative electrode, and a separator provided as needed. The non-aqueous electrolyte secondary battery can have various shapes according to the purpose of use, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

Examples

[0166] Examples are given below to explain the present invention more specifically. The present invention is not limited to the following examples as long as it does not exceed the gist thereof. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass". Also, the compounding amounts in the table are in parts by mass, and except for the solvent, they are values in terms of non-volatile content. Note that the blanks in the table indicate that they are not compounded.

[0167] The materials used in the examples and comparative examples are shown below. · Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, liquid hydrogenated nitrile butadiene rubber, weight average molecular weight 30,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass), hereinafter referred to as HNBR2. · Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass), hereinafter referred to as HNBR4. · Li-335: Denka Black Li-335 (manufactured by Denka Co., Ltd., acetylene black, average primary particle diameter 23 nm, BET specific surface area 141 m 2 / g, carbon purity 99.9%), hereinafter referred to as CB1. · Cellseed NMC (LiNi0.6Co0.2Mn0.2O2, manufactured by Nippon Chemical Industry Co., Ltd., non-volatile content 100%), hereinafter referred to as NCM1. · S800 (LiNi0.8Mn0.1Co0.1O2, manufactured by Kanwa, non-volatile content 100%), hereinafter referred to as NCM2. · NAT-7050 (manufactured by LiNi0.8Co0.15Al0.05O2, BASF Toda Battery Materials), hereinafter referred to as NCA. · HED (trademark) LFP-400 (lithium iron phosphate, manufactured by BASF), hereinafter referred to as LFP.

[0168] <cnt1> 10 kg of JENOTUBE10B (manufactured by JEIO, average outer diameter 10 nm, BET specific surface area 230 m 2 / g) was weighed into a heat-resistant container with a capacity of 120 L, and the heat-resistant container containing JENOTUBE10B was placed in a furnace. Then, nitrogen gas was introduced into the furnace, and while maintaining a positive pressure, the air inside the furnace was discharged. After the oxygen concentration inside the furnace reached 0.1% or less, it was heated to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain purified JENOTUBE10B. The purity was 99.9%. Furthermore, the purified JENOTUBE10B was charged into a dynamic mill (manufactured by Nippon Coke Industry Co., Ltd.) using zirconia beads with a diameter of 8 mm as the grinding medium, supplied at an operating condition of 10.0 kg / h, and processed at a peripheral speed of 5.0 m / s to obtain CNT1.

[0169] CNT1 was acid-decomposed using a microwave sample pretreatment device (manufactured by Milestone General Co., Ltd., ETHOS1) to extract the metals contained in the carbon material. Analysis was performed using a multi-type ICP emission spectroscopic analyzer (manufactured by Agilent Technologies, 720-ES), and the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, chromium) contained in the extract was calculated. The carbon purity of CNT1 was calculated as follows and was 99.9%. Carbon purity (%) = ((carbon material mass - metal mass) ÷ carbon material mass) × 100

[0170] <cnt2> Weighed 10 kg of JENOTUBE6A (manufactured by JEIO, average outer diameter 6 nm, BET specific surface area 650 m 2 / g) into a heat-resistant container of 120 L, and installed the heat-resistant container containing JENOTUBE6A in the furnace. Then, introduced nitrogen gas into the furnace and discharged the air in the furnace while maintaining a positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, heated it to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, introduced chlorine gas at a rate of 50 L / min for 50 hours. Then, introduced nitrogen gas at 50 L / min and cooled it while maintaining a positive pressure to obtain purified JENOTUBE6A (CNT2).

[0171] CNT2 was subjected to acid decomposition using a microwave sample pretreatment device (manufactured by Milestone General, ETHOS1) to extract the metals contained in the carbon material. Then, analysis was performed using a multi-type ICP emission spectroscopic analyzer (manufactured by Agilent, 720-ES), and the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, chromium) contained in the extract was calculated. The carbon purity of CNT2 was 99.9%.

[0172] <lfmp> LFMP is synthesized by the following synthesis procedure. 200 g of dimethyl sulfoxide is added to 150 g of pure water, and 360 millimoles of lithium hydroxide monohydrate is added. To the resulting solution, 120 millimoles of phosphoric acid is further added using an 85 wt% aqueous phosphoric acid solution, and 96 millimoles of manganese(II) sulfate monohydrate and 24 millimoles of iron(II) sulfate heptahydrate are added. The resulting solution is transferred to an autoclave and heated and held for 4 hours so that the inside of the container maintains 150 °C. After heating, the supernatant of the solution is discarded, and lithium manganese iron phosphate LiMn 0.8 Fe 0.2 PO4 is obtained. After washing the obtained lithium manganese iron phosphate with pure water, the operation of removing the supernatant by centrifugation is repeated 5 times, and finally pure water is added again to form a dispersion. Subsequently, glucose having the same weight as 15 wt% of the lithium manganese iron phosphate in the dispersion is added to the dispersion and dissolved, and then pure water is added to adjust the solid content concentration of the dispersion to 20 wt%, obtaining an LFMP dispersion. The obtained LFMP dispersion is dried with hot air at 200 °C using a spray dryer (manufactured by Fujisaki Electric Co., Ltd., MDL-050B) to obtain secondary particles. The obtained secondary particles are heated at 700 °C for 4 hours in a nitrogen atmosphere using a rotary kiln to obtain carbon-coated LFMP particles (hereinafter referred to as LFMP).

[0173] <Polymer composition> [Synthesis of HNBR1] HNBR1 is synthesized by the following synthetic procedure. 500 g of monochlorobenzene is placed in a 1 L autoclave equipped with a stirrer, and while stirring, 75 g of nitrile rubber (Perbunan (registered trademark) 3430: content rate of nitrile group-containing units 34%, Mooney viscosity 32) finely cut with a rubber chopper is added and dissolved. After the nitrile rubber is completely dissolved, 4 phr of 1-hexene is added to the container, and the solution is stirred for 2 hours. At this time, 1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(tricyclohexylphosphine)-ruthenium(phenyl-methylene) dichloride, which is a catalyst, is dissolved in 20 mL of monochlorobenzene and added to the container. The reaction mixture is reacted for 12 hours while stirring at a temperature of 22 °C. After the reaction, a monochlorobenzene solution of tris-(triphenylphosphine) rhodium chloride (0.06 phr) is charged into the reactor, and the reactor is pressurized to 85 bar with hydrogen. The polymer solution is obtained by reacting the reaction mixture at a temperature of 135 °C for 4 hours while stirring (500 rpm). After concentrating to a certain extent with a rotary evaporator, the solution is poured into a stainless steel bath and dried in an evacuated heating oven heated to 140 °C until the odor of monochlorobenzene disappears to obtain HNBR1. 1 The structural unit derived from acrylonitrile determined from the H-NMR quantitative spectrum is 34%.

[0174] [Preparation of HNBR3] 92 parts by mass of NMP was placed in a stainless steel container, and while heating to a liquid temperature of 80 °C, it was stirred with a disper. 8 parts by mass of HNBR2 heated to 80 °C was added to NMP in another container and stirred for 1 hour to prepare a polymer solution. 1000 parts by mass of methanol was placed in another stainless steel container and stirred at room temperature (25 °C), and the previously prepared polymer solution was dropped and coagulated, decanted, and dried in an evacuated heating oven heated to 140 °C. The above steps (preparation of the polymer solution, coagulation with methanol, decantation, drying) were repeated 3 times to obtain HNBR3. 1 The structural unit derived from acrylonitrile determined from the H-NMR quantitative spectrum was 34%.

[0175] [Preparation of HNBR5] Into an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzene sulfonate as an emulsifier, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 0.85 part of t-dodecyl mercaptan as a chain transfer agent were added in this order. After purging the inside with nitrogen, 65 parts of 1,3-butadiene as a conjugated diene monomer was press-fitted, and 0.25 part of ammonium persulfate as a polymerization initiator was added, followed by a polymerization reaction at a reaction temperature of 40 °C. Thus, a polymer of acrylonitrile and 1,3-butadiene was obtained. The polymerization conversion rate was 85%.

[0176] Ion-exchanged water was added to the obtained copolymer to obtain a solution having a total solid content concentration adjusted to 12% by mass. 400 mL (48 g of total solid content) of the obtained solution was charged into an autoclave equipped with a stirrer having a volume of 1 L, and nitrogen gas was passed through for 10 minutes to remove dissolved oxygen in the solution. Then, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 mL of ion-exchanged water to which nitric acid at 4 times the molar amount of palladium (Pd) was added, and added. After replacing the inside of the system twice with hydrogen gas, the contents of the autoclave were heated to 50 °C under a pressure of hydrogen gas up to 3 MPa, and a hydrogenation reaction was carried out for 6 hours.

[0177] Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 60 mL of ion-exchanged water to which nitric acid at 4 times the molar amount of Pd was added, and added. After replacing the inside of the system twice with hydrogen gas, the contents of the autoclave were heated to 50 °C under a pressure of hydrogen gas up to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid content concentration reached 40% to obtain an aqueous dispersion of the polymer.

[0178] Also, the aqueous dispersion of the polymer was dropped into methanol to coagulate the polymer, and then the coagulated product was vacuum dried at a temperature of 60 °C for 12 hours to obtain HNBR5. 1 The structural unit derived from acrylonitrile determined from the H-NMR quantitative spectrum was 35%, and the Mooney viscosity (ML1+4, 100 °C) was 10.

[0179] [Preparation of Polymer Composition] (Polymer Composition 1) 800 parts by mass of NMP was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. Then, the inside of the reaction vessel was heated to 80 °C, 200 parts of HNBR1 was added, and stirring was carried out until HNBR1 was completely dissolved to obtain Polymer Composition 1 (solid content concentration: 20% by mass).

[0180] (Polymer Compositions 2 - 3) Polymer Compositions 2 - 3 were obtained in the same manner as Polymer Composition 1, except that the polymer to be dissolved was changed to those shown in Table 1.

[0181] (Polymer Composition 4) In a plastic container with a volume of 1000 cm 3 , 475 parts by mass of NMP and 25 parts by mass of NaOH (manufactured by Tosoh Corporation, Toso Pearl) were added. Using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsifier screen, dispersion was carried out at a speed of 9000 rpm until the whole became uniform. Then, it was passed through a nylon filter with an opening size of 150 μm using a filtering bell to prepare a NaOH dispersion (NaOH concentration: 5% by mass).

[0182] 780 parts by mass of NMP was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. Then, the inside of the reaction vessel was heated to 80 °C, 200 parts of HNBR2 was added, and stirring was carried out until the hydrogenated nitrile butadiene rubber was completely dissolved. Then, 20 parts by mass of the NaOH dispersion was added, and stirring was carried out while adding air. Heating was carried out while maintaining the reaction vessel at 80 °C for 12 hours to obtain Polymer Composition 4 (solid content concentration: 20.1% by mass).

[0183] (Polymer Compositions 5 - 9) Polymer compositions 5 to 9 were obtained in the same manner as polymer composition 4, except that the base species and the addition amount were changed as shown in Table 1.

[0184] (Comparative Polymer Composition 1) 800 parts by mass of NMP was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. Then, the inside of the reaction vessel was heated to 80°C, 200 parts of HNBR4 was added, and the mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved to obtain Comparative Polymer Composition 1 (solid content concentration: 20% by mass).

[0185] (Comparative Polymer Composition 2) 1000 cm 3 of a plastic container, 475 parts by mass of NMP and 25 parts by mass of NaOH (manufactured by Tosoh Corporation, Tosoh Pearl) were added, and dispersion was carried out at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsifier screen until the whole became uniform. Then, it was passed through a nylon filter with an opening of 150 μm using a filtration bell to prepare a NaOH dispersion.

[0186] 780 parts by mass of NMP was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. Then, the inside of the reaction vessel was heated to 80°C, 200 parts of HNBR4 was added, and the mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. Then, 20 parts by mass of the NaOH dispersion was added, and the mixture was stirred while adding air, and heated while maintaining the reaction vessel at 80°C for 12 hours to obtain Comparative Polymer Composition 2 (solid content concentration: 20.1% by mass).

[0187] (Comparative Polymer Composition 3) 800 parts by mass of NMP was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. Then, the inside of the reaction vessel was heated to 80°C, 200 parts of HNBR5 was added, and the mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved to obtain Comparative Polymer Composition 3 (solid content concentration: 20% by mass).

[0188] For Examples 1-3, 1-6, and Comparative Example 1-1, the chart of tanδ (loss tangent) for the strain dependence evaluation of the polymer composition is shown in FIG. 1. For Examples 1-3, 1-6, 1-7, and Comparative Example 1-1, the chart of tanδ (loss tangent) for the temperature dependence evaluation of the polymer composition is shown in FIG. 2.

[0189] <<Physical Property Measurement and Evaluation Methods>> The physical property measurement and evaluation methods for the polymer composition, conductive material composition, electrode film, and secondary battery used in each of the following Examples and Comparative Examples are as follows.

[0190] <Preparation of Molecular Weight Measurement Sample> The polymer composition was dropped into purified water to precipitate the polymer, and the precipitate was collected by filtration with a Buchner funnel. The precipitate was directly rinsed with purified water on the Buchner funnel and then dissolved in tetrahydrofuran (THF) to obtain a solution. The obtained solution was dropped into purified water again to perform the filtration and washing steps using purified water, and the precipitate was redissolved in THF to obtain a molecular weight measurement sample.

[0191] <Measurement of Weight-Average Molecular Weight (Mw) and Z-Average Molecular Weight (Mz)> The weight-average molecular weight (Mw) and Z-average molecular weight (Mz) of the polymer composition were measured by gel permeation chromatography (GPC) equipped with an RI detector using the molecular weight measurement sample. HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, three separation columns were connected in series, and "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" manufactured by Tosoh Corporation were used as the packing materials in order. The oven temperature was 40 °C, a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide was used as the eluent, and the measurement was performed at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% using the solvent consisting of the eluent and 20 microliters were injected. The weight-average molecular weight and Z-average molecular weight are values in terms of polystyrene. For the evaluation of the weight-average molecular weight (Mw), A was defined as 70,000 or less, B as greater than 70,000 and 100,000 or less, and C as exceeding 100,000.

[0192] <Preparation of 20 mass% solid content solution> 80 parts by mass of NMP was put into a stainless steel container and stirred with a disperser while heating to a liquid temperature of 80°C. The polymer heated to 80°C in another container was added to NMP so that the polymer concentration became 20 mass%, and stirred for 1 hour. After confirming with a spatula or the like that there was no undissolved polymer on the liquid surface, container wall, or bottom, the solid content was measured and corrected with NMP to a solid content of 20 mass%, thereby preparing a polymer solution.

[0193] <Viscosity measurement of 20 mass% solid content solution> For the viscosity measurement, the prepared polymer solution was allowed to stand in a thermostatic bath at 25°C for 1 hour or more, and then immediately measured using a B-type viscometer at a rotor rotation speed of 60 rpm. For the evaluation of viscosity, those less than 500 mPa·s were rated as A, those 500 mPa·s or more and less than 1000 mPa·s were rated as B, those 1000 mPa·s or more and 3000 mPa·s or less were rated as C, and those exceeding 3000 mPa·s were rated as D.

[0194] <Viscoelasticity measurement of polymer composition> (Preparation of sample piece) A fluororesin mold was cut out to fit the measuring jig (parallel plate diameter 25 mm), the polymer composition was dropped onto the fluororesin mold, and the fluororesin mold was dried in an oven at 140°C for 1 hour to remove the solvent, thereby preparing a sample piece. The polymer composition of the example was viscous and could not be separated from the fluororesin mold as it was, so it was taken out of the fluororesin mold in a state of being cooled and solidified with liquid nitrogen. The plate was heated to 80°C so that the thickness of the sample was constant, the sample piece was placed on it, and the thickness was corrected with the measuring jig. Also, it was confirmed that the prepared sample piece did not contain bubbles.

[0195] (Dynamic viscoelasticity test: Strain dependence evaluation) The dynamic viscoelasticity (strain-dependence) of the polymer was measured using a viscoelasticity measuring device: MCR302e (Anton Paar). Specifically, using a parallel plate with a diameter of 25 mm, the GAP was set to the thickness of the sample, and the measurement was carried out under the conditions of a temperature of 100 °C, a frequency of 10 Hz, and a strain of 0.01 to 10%. The strain-dependence of the polymer was evaluated by a chart with the strain on the horizontal axis and tanδ (loss tangent) on the vertical axis. Here, tanδ (loss tangent) = loss elastic modulus (G'') / storage elastic modulus (G').

[0196] (Dynamic Viscoelasticity Test: Temperature-Dependence Evaluation) The dynamic viscoelasticity (temperature-dependence) of the polymer was measured using a viscoelasticity measuring device: MCR302e (Anton Paar). Specifically, using a parallel plate with a diameter of 25 mm, the measurement was carried out under the conditions of a constant normal force of 100 mN, a frequency of 10 Hz, a strain of 0.1%, a temperature range of 30 °C to 110 °C, and a temperature decrease rate of 10 °C / min. The temperature-dependence of the polymer can be evaluated by reading the temperature at which tanδ (loss tangent) = 1 from a chart with the temperature on the horizontal axis and tanδ (loss tangent) on the vertical axis. A was defined as 40 °C or more and 80 °C or less, B as 30 °C or more and less than 40 °C or more than 80 °C and 110 °C or less, C as less than 30 °C, and D as more than 110 °C.

[0197] (Method for Measuring Mooney Viscosity (ML1+4, 100 °C) of Polymer) Purified water was dropped onto the polymer composition to coagulate the polymer. The coagulated product was collected, washed with methanol, transferred to a petri dish, and vacuum dried at 60 °C for 12 hours to obtain a 40 g flat plate sample for measurement. The Mooney viscosity (ML1+4, 100 °C) was measured using an L-shaped rotor at a temperature of 100 °C in accordance with Japanese Industrial Standard JIS K6300-1.

[0198] (Evaluation of Dispersibility of Polymer Composition) 80 parts by mass of NMP was placed in a stainless steel container, and while heating to a liquid temperature of 80 °C, it was stirred with a disperser. In another container, the polymer heated to 80 °C was added to NMP so that the polymer concentration became 8% by mass, and it was stirred for 1 hour. After confirming with a spatula or the like that there was no undissolved polymer on the liquid surface, container walls, or bottom, the solid content was measured and corrected with NMP to a solid content of 8% by mass to prepare a polymer solution X.

[0199] 98 parts by mass of the adjusted polymer solution X was placed in a glass container, and further 2 parts by mass of carbon nanotube JENOTUBE10B (average outer diameter 10 nm, BET specific surface area 230 m 2 / g, multi-walled CNT) was added, and it was allowed to stand for 1 hour without stirring. Then, samples were taken from the supernatant (10% height from the top of the glass container) and the bottom (10% height from the bottom of the glass container). Subsequently, the amounts dropped onto an aluminum dish whose tare had been measured (W1) were measured with an analytical balance, respectively. The measured mass was designated as W2. Then, after drying the aluminum dish in an oven at 140 °C for 1 hour, the mass of the aluminum dish was measured again with an analytical balance (W3). The solid contents of the supernatant and the bottom were calculated using Equation 2 below. Solid content = (W3 - W1) / W2 Equation 2

[0200] After that, the dispersibility of the polymer composition can be evaluated from the dispersion degree of the carbon nanotubes by the value obtained by dividing the solid content of the supernatant by the solid content of the bottom. A value of 0.75 or more and less than 1.25 was designated as A, a value of 0.5 or more and less than 0.75 or 1.25 or more and less than 1.50 was designated as B, and a value of less than 0.5 or 1.50 or more was designated as C.

[0201] <Initial viscosity of the conductive material composition> After allowing the conductive material composition to stand in a thermostatic bath at 25 °C for 1 hour or more, it was immediately measured using a B-type viscometer at a rotor rotation speed of 100 rpm. For the evaluation of the initial viscosity, a value of 100 mPa·s or more and less than 500 mPa·s was designated as A, a value of 500 mPa·s or more and less than 1000 mPa·s was designated as B, a value of 1000 mPa·s or more and 2000 mPa·s or less was designated as C, and a value exceeding 2000 mPa·s was designated as D.

[0202] <Evaluation of the dispersibility of the conductive material composition> The dispersibility of the conductive material composition was evaluated by measuring the cumulative particle size D50. The measurement of the cumulative particle size D50 by the particle size distribution was performed using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.; Partical LA-960V2). The laser light wavelength of this measuring device is 650 nm, and as detectors, it is equipped with one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. In addition, the measuring unit uses a flow cell (sample cell) made of synthetic quartz. First, NMP, which is the same solvent as the dispersion liquid, was introduced into the sample bath including the sample cell, and circulation / ultrasonic cleaning was performed. As the operation mode, the circulation rate: 3, the ultrasonic intensity: 7, the ultrasonic time: 1 minute, the stirring speed: 7, and the stirring mode: continuous were set. Subsequently, for degassing, after performing ultrasonic operation at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds, blank (background) measurement was performed. The particle size standard was volume, the particle refractive index was set to 1.920 - 0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The dispersion liquid was dropped so that the laser light transmittance during measurement was 60% ± 1%, and sample adjustment was performed. During the measurement, the operation mode was set as the circulation rate: 3, the stirring speed: 7, and the stirring mode: continuous, and the measurement was performed. Regarding the evaluation of the dispersibility of the conductive material composition, when the value of the cumulative particle size D50 is less than 3 μm, it is rated as A; when it is 3 μm or more and less than 10 μm, it is rated as B; when it is 10 μm or more, it is rated as C.

[0203] <Evaluation of the storage stability of the conductive material composition> After leaving the conductive material composition to stand in a constant temperature bath at 40 °C for one week, after cooling the conductive material composition to 25 °C, the viscosity over time was measured immediately at a rotor rotation speed of 100 rpm using a B-type viscometer. The evaluation of the storage stability was performed based on the value obtained by dividing the viscosity over time (after one week at 40 °C) by the initial viscosity. When the value is 0.8 or more and less than 3.0, it is rated as A; when it is 3.0 or more and less than 5.0, it is rated as B; when it is less than 0.8 or 5.0 or more, it is rated as C.

[0204] <Evaluation of the adhesion of the electrode film> The adhesion of the electrode film was evaluated by measuring the peel strength. The composite slurry was applied using an applicator so that the weight per unit area of the electrode was 20 mg / cm 2 After coating on the aluminum foil so as to achieve this, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes. Then, it was cut into two rectangles of 90 mm × 20 mm with the coating direction as the major axis. For the measurement of the peel strength, a tabletop tensile testing machine (manufactured by Toyo Seiki Seisakusho, Strograph E3) was used and evaluated by the 180-degree peel test method. Specifically, a double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) with a size of 100 mm × 30 mm was attached to a stainless steel plate, and the prepared battery electrode composite layer was adhered to the other side of the double-sided tape. While pulling it upward from below at a constant speed (50 mm / min), the average value of the stress at this time was taken as the peel strength. For the evaluation of the adhesion of the electrode film, a peel strength of 1.0 N / cm or more was rated as A, a peel strength of 0.7 N / cm or more and less than 1.0 N / cm was rated as B, a peel strength of 0.5 N / cm or more and less than 0.7 N / cm was rated as C, and a peel strength of less than 0.5 N / cm was rated as D.

[0205] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Batteries> The laminated lithium-ion secondary battery was placed in a thermostatic chamber at 25 °C, and charge and discharge measurements were performed using a charge and discharge device (manufactured by Hokuto Denko, SM-8). After performing constant current and constant voltage charging (cutoff current 1.0 mA (0.02C)) at a charging current of 10 mA (0.2C) and a charging termination voltage of 4.2V, constant current discharge was performed at a discharge current of 10 mA (0.2C) and a discharge termination voltage of 2.5V. After repeating this operation 3 times, constant current and constant voltage charging (cutoff current (1.0 mA 0.02C)) was performed at a charging current of 10 mA (0.2C) and a charging termination voltage of 4.2V, and constant current discharge was performed at discharge currents of 0.2C and 3C until the discharge termination voltage of 2.5V was reached, and the discharge capacities were obtained respectively. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in the following formula 3. Rate Characteristics = 3C Discharge Capacity / 0.2C Discharge Capacity of the Third Cycle × 100 (%) Formula 3 For the evaluation of the rate characteristics, a rate characteristic of 80% or more was rated as A, 70% or more and less than 80% was rated as B, 60% or more and less than 70% was rated as C, and less than 60% was rated as D.

[0206] <Evaluation of High-Temperature Cycle Characteristics of Lithium-Ion Secondary Batteries> A laminated lithium-ion secondary battery was installed in a thermostatic chamber at 45°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant-current constant-voltage charging (cutoff current: 1.25 mA (0.025C)) at a charging current of 50 mA (1C) and a charging termination voltage of 4.2V, constant-current discharging was performed at a discharging current of 50 mA (1C) and a discharging termination voltage of 2.5V. This operation was repeated 200 times. 1C was defined as the current value that discharges the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be represented by the ratio of the 100th 1C discharge capacity to the 3rd 1C discharge capacity at 45°C, as shown in Equation 4 below. For the high-temperature cycle characteristics evaluation, if the cycle characteristics were 90% or more, it was rated as A; if they were 85% or more and less than 90%, it was rated as B; if they were 80% or more and less than 85%, it was rated as C; and if they were less than 80%, it was rated as D. High-temperature cycle characteristics = 100th 1C discharge capacity / 3rd 1C discharge capacity × 100 (%) Equation 4

[0207] (Example 2-1) To a stainless steel container, 84.0 parts of N-methyl-2-pyrrolidone (NMP) and 8.0 parts of a polymer composition (solid content concentration: 20% by mass) were added, and the mixture was stirred using a disper. Thereafter, 8 parts of CNT1 were taken and added while stirring with a disper. A fine emulsifier screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 9000 rpm until the whole became uniform and the dispersed particle size became 200 μm or less as measured by a grind gauge. Thereafter, a carbon material preliminary dispersion composition was prepared through a high magnetic force magnetic filter (manufactured by Aisin, surface magnetic flux density: 17000 gauss). Subsequently, the carbon material preliminary dispersion composition was fed, and a circulation type dispersion treatment with a residence time of 15 minutes (bead filling rate: 80%, peripheral speed: 13 m / s) was performed using a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Mugen Flow (registered trademark)) filled with zirconia beads having a diameter of 1.0 mm. The number of circulation times was 30. Subsequently, the liquid to be dispersed was supplied to a high-pressure homogenizer (manufactured by Sugino Machine, Starburst Turbo), and a 24-pass type dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 Mpa. Thereafter, the liquid to be dispersed was supplied to an electromagnet (manufactured by Daiho Magnetic Co., Ltd., EMF-100S, magnetic flux density: 16000 gauss, spatial volume: 1.7 L, an electromagnet provided with 31 grid screens having a diameter of 10 cm and a thickness of 1.3 cm), and a 3-pass type treatment was performed. Then, the liquid was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy: 40 μm) installed in series to prepare Conductive Material Composition 1.

[0208] (Examples 2-2 to 2-12, Comparative Examples 2-1 to 2-3) According to the compositions in Table 2, conductive material compositions were prepared in the same manner as in Example 1 to prepare Conductive Material Compositions 2 to 12 and Comparative Conductive Material Compositions 1 to 3.

[0209] (Example 3-1) Volume: 150 cm 3 18.8 parts by mass of an NMP solution in which 8% by mass of PVdF (polyvinylidene fluoride, manufactured by Solvey, Solef#5130) was dissolved was weighed into a plastic container, and 14.5 parts by mass of NMP was also weighed. Then, 18.8 parts by mass of a conductive material composition (conductive material composition 1) was added, and using a rotation / revolution mixer (Avataro Rentaro, ARE-310), it was stirred at 2000 rpm for 30 seconds. Subsequently, 96.7 parts by mass of the positive electrode active material NCM1 was added, and using a rotation / revolution mixer (Avataro Rentaro, ARE-310), it was stirred at 2000 rpm for 2.5 minutes to obtain a composite slurry.

[0210] Subsequently, the composite slurry was applied onto an aluminum foil using an applicator so that the coating weight per unit of the electrode was 20 mg / cm 2 Then, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain an electrode film (electrode film 1). Subsequently, the electrode film (electrode film 1) was subjected to rolling treatment using a roll press (manufactured by Sanku Metal, 3t hydraulic roll press) to obtain a positive electrode (positive electrode 1). Note that the coating weight per unit of the composite layer was 20 mg / cm 2 and the density of the composite layer after the rolling treatment was 3.1 g / cc.

[0211] (Examples 3-2 to 3-16, Comparative Examples 3-1 to 3-3) Positive electrodes (positive electrode 2) to (comparative positive electrode 3) were produced in the same manner as the production of the positive electrode (positive electrode 1), except that the positive electrode active material and the conductive material composition shown in Table 3 were changed.

[0212] (Example 4-1) The positive electrode (positive electrode 1) and the standard negative electrode were each punched out to 45 mm × 40 mm and 50 mm × 45 mm, and a separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 60 °C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 1:1:1 (volume ratio), and further adding 2 parts by mass of VC (vinylene carbonate) to 100 parts by mass of the mixed solvent, and then dissolving LiPF6 at a concentration of 1 M) was injected in an amount of 2 mL, and then the aluminum laminate was sealed to fabricate a laminated lithium ion secondary battery (battery 1).

[0213] (Examples 4-2 to 4-16, Comparative Examples 4-1 to 4-3) Laminated lithium ion secondary batteries (batteries 2) to (comparative battery 3) were fabricated in the same manner as the fabrication of the laminated lithium ion secondary battery (secondary battery 1), except that the positive electrode was changed to the one shown in Table 4.

[0214]

Table 1

[0215]

Table 2

[0216]

Table 3

[0217]

Table 4

Claims

1. A polymer composition for an electrochemical element, comprising a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit, and an amide-based liquid medium, wherein the polymer has a tanδ (loss tangent) in the range of 0.01% to 10% of strain greater than 1 in a dynamic viscoelasticity measurement at a temperature of 100 ° C and a frequency of 10 Hz.

2. The polymer composition for an electrochemical element according to claim 1, wherein in a viscoelasticity measurement at a frequency of 10 Hz and a strain of 0.1%, when the temperature is increased from 30 ° C to 110 ° C at a rate of 10 ° C / min, the measurement temperature at which tanδ (loss tangent) = 1 is 80 ° C or lower.

3. The polymer composition for an electrochemical element according to claim 1 or 2, comprising the polymer and N-methyl-2-pyrrolidone, and having a viscosity of less than 3000 mPa·s at 25 ° C and 60 rpm when a solution having a solid content concentration of 20% by mass is measured with a B-type viscometer.

4. The polymer composition for an electrochemical element according to claim 1 or 2, wherein based on the mass of the polymer, the content of the aliphatic hydrocarbon unit is 50% by mass or more and 75% by mass or less, and the content of the nitrile group-containing unit is 25% by mass or more and 50% by mass or less.

5. The polymer composition for an electrochemical element according to claim 1 or 2, wherein the Z-average molecular weight of the polymer is 10,000 or more and 250,000 or less.

6. A conductive material composition, comprising the polymer composition for an electrochemical element according to claim 1 or 2 and a conductive material.

7. A slurry composition, comprising the polymer composition for an electrochemical element according to claim 1 or 2, a conductive material, and an active material.

8. An electrode film formed using the slurry composition comprising the polymer composition for an electrochemical element according to claim 1 or 2, a conductive material, and an active material.

9. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises an electrode film formed using the slurry composition comprising the polymer composition for an electrochemical element according to claim 1 or 2, a conductive material, and an active material.

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