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

Abstract

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, wherein the polymer has a tan δ (loss tangent) of greater than 1 at 0.01-10% strain in dynamic viscoelasticity measurement at a temperature of 100°C and a frequency of 10 Hz.

Description

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

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

[0002] Lithium-ion secondary batteries, which are representative electrochemical devices, are characterized by their small size, light weight, high energy density, and ability to be repeatedly charged and discharged. These characteristics have led to their widespread use. In the field of secondary batteries, the use of highly conductive fine carbon nanotubes or well-structured carbon black as conductive materials in electrodes, particularly in the positive electrode, which has poor electrical conductivity, in a well-dispersed state facilitates the exploitation of electrode properties. Therefore, efforts have been made to improve the performance of secondary batteries by dispersing conductive materials using dispersible polymers.

[0003] As a technique for satisfactorily dispersing a conductive material in a binder composition for a secondary battery electrode, Patent Document 1 discloses the use of a copolymer (e.g., hydrogenated nitrile rubber) having an alkylene structural unit and a nitrile group-containing monomer unit and having a Mooney viscosity (ML1+4, 100°C) of 40 or less as the binder composition for a secondary battery electrode.

[0004] International Publication No. 2017 / 010093

[0005] The technology disclosed in Patent Document 1 aims to improve the dispersibility of the conductive material by making the Mooney viscosity of the copolymer in the binder composition 40 or less, thereby facilitating adsorption of the copolymer to the surface of the conductive material, suppressing aggregation of the conductive material, and improving the dispersibility of the conductive material. On the other hand, the technology disclosed in Patent Document 1 aims to make the Mooney viscosity of the copolymer in the binder composition 5 or more in order to obtain adsorption stability of the copolymer to the conductive material and maintain dispersion stability of the conductive material.

[0006] However, in order to further improve the dispersibility of the conductive material, the development of a new polymer composition is desired from the viewpoint of more microscopic observation. Furthermore, if the conductive material is broken during dispersion treatment using the polymer composition, small pieces of the conductive material will be included in the electrode film, which may result in insufficient formation of a conductive network and lead to a deterioration in the battery characteristics of the secondary battery.

[0007] An object of the present disclosure is to provide a polymer composition for electrochemical elements 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.

[0008] As a result of extensive research, the present inventors have found that dispersibility of a conductive material in a dispersion can be achieved by using a polymer composition for electrochemical devices that contains an aliphatic hydrocarbon unit and a nitrile group-containing unit, and that has a tan δ (loss tangent) of greater than 1 within a strain range of 0.01% to 10% in dynamic viscoelasticity measurements performed at a temperature of 100°C and a frequency of 10 Hz, and an amide-based liquid medium. Furthermore, they have found that the use of this polymer composition for electrochemical devices can achieve both dispersibility of a conductive material in a dispersion and conductivity in an electrode film. Specifically, the wetting-promoting effect of the conductive material in the dispersion is enhanced, thereby suppressing viscosity increases during dispersion treatment and improving the initial dispersibility of the conductive material. Furthermore, the conductive material can be concentrated in the dispersion. Furthermore, when a conductive material is dispersed using the polymer composition, the tan δ of the polymer appropriately controls the viscoelasticity of the dispersion, preventing breakage of the conductive material during dispersion treatment. As a result, not only is it possible to form a well-developed conductive network in an electrode film obtained using this dispersion, but also the margin for formulation design can be increased. This allows the conductive material to be uniformly distributed in the electrode film, and the shape of the conductive material is maintained, making it possible to provide an electrochemical element with high output, high capacity, and long life.

[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 electrochemical elements, 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 loss tangent tanδ (tan δ) of greater than 1 in a strain range of 0.01% to 10% in dynamic viscoelasticity measurement performed at a temperature of 100°C and a frequency of 10 Hz.

[0011] [2] The polymer composition for electrochemical elements according to [1], wherein the polymer has a measurement temperature of 80°C or lower at which tanδ (loss tangent) = 1 when the polymer is heated at a temperature range of 30°C to 110°C at a rate of 10°C / min in a viscoelasticity measurement performed at a frequency of 10 Hz and a strain of 0.1%.

[0012] [3] The polymer composition for electrochemical elements according to [1] or [2], wherein a solution containing the polymer and N-methyl-2-pyrrolidone and having a solids concentration of 20% by mass has a viscosity of less than 3,000 mPa s at 25°C and 60 rpm when measured with a Brookfield viscometer. [4] The polymer composition for electrochemical elements according to any 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 electrochemical elements according to any 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 comprising the polymer composition for electrochemical elements according to any one of [1] to [5] above and a conductive material. [7] A slurry composition comprising the polymer composition for electrochemical elements according to any one of [1] to [5] above, a conductive material, and an active material. [8] An electrode film formed using a slurry composition comprising the polymer composition for electrochemical elements according to any one of [1] to [5] above, 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 a slurry composition comprising the polymer composition for electrochemical elements according to any one of [1] to [5] above, a conductive material, and an active material.

[0014] According to the embodiments of the present disclosure, it is possible to provide a polymer composition for electrochemical devices 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.

[0015] Figure 1 shows a chart of tan δ (loss tangent) for evaluating the strain dependency of a polymer composition. Figure 2 shows a chart of tan δ (loss tangent) for evaluating the temperature dependency of a polymer composition.

[0016] Hereinafter, as embodiments of the present disclosure, a polymer composition for electrochemical devices, 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 that are implemented within the scope of the present disclosure.

[0017] In the present disclosure, carbon nanotubes may be referred to as "CNT" and carbon black as "CB." Acrylonitrile butadiene rubber may be referred to as "NBR" and hydrogenated acrylonitrile butadiene rubber may be referred to as "HNBR." In the present disclosure, the polymer composition for electrochemical elements may be referred to simply as the 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 be referred to as a nitrile polymer.

[0019] The aliphatic hydrocarbon unit is a unit containing an aliphatic hydrocarbon structure, and preferably a unit consisting solely 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 the aliphatic hydrocarbon unit include an alkylene unit, an alkenylene unit, an alkyl unit, an alkanetriyl unit, an alkanetetrayl unit, etc. The aliphatic hydrocarbon unit preferably contains at least an alkylene unit.

[0021] The alkylene unit is a unit containing an alkylene structure, and is preferably a unit consisting of only 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)

[0024] In general formula (1A), n represents 0 or an integer of 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, and more preferably an integer of 3 or more. n is preferably an integer of 5 or less, and 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)

[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 a polymer is not particularly limited, but examples thereof include the following method (1a) or (1b).

[0029] In method (1a), a polymer is produced by polymerization using a monomer composition containing a conjugated diene monomer. The produced polymer contains monomer units derived from the conjugated diene monomer. In the present disclosure, "monomer units derived from a conjugated diene monomer" may be referred to as "conjugated diene monomer units," and the same may be abbreviated for monomer units derived from other monomers. Next, the conjugated diene monomer units are hydrogenated to convert at least a portion of the conjugated diene monomer units into alkylene units. In the present disclosure, "hydrogenation" may be referred to as "hydrogenation." The finally obtained polymer contains units obtained by hydrogenating the conjugated diene monomer units as alkylene units.

[0030] The conjugated diene monomer unit includes 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, includes 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 include two or more types of monomer units. The conjugated diene monomer unit may further include a monomer unit that does not have a carbon-carbon double bond and includes a branch point. In the present disclosure, the "branch point" refers to a branch point in a branched polymer, and when the conjugated diene monomer unit includes a monomer unit including a branch point, the polymer prepared above is a branched polymer.

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

[0032] Among these, method (1a) is preferred because it allows for easy production of the polymer. The number of carbon atoms in the conjugated diene monomer is 4 or more, preferably 4 to 6. Examples of conjugated diene monomers include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Of these, 1,3-butadiene is preferred. The alkylene unit preferably contains a unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably contains a unit obtained by hydrogenating a 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer may be used alone or in combination of two or more.

[0033] The hydrogenation is preferably carried out by a method capable of selectively hydrogenating the conjugated diene monomer units. Examples of the hydrogenation method include known methods such as oil phase hydrogenation and aqueous phase hydrogenation.

[0034] The hydrogenation can be carried out by a conventional method. For example, the hydrogenation can be carried out by treating a polymer having conjugated diene monomer units dissolved in a suitable solvent with hydrogen gas in the presence of a hydrogenation catalyst. Examples of the hydrogenation catalyst include iron, nickel, palladium, rhodium, platinum, copper, alloys and compounds thereof, etc.

[0035] In the method (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more carbon atoms, and more preferably 4 or more carbon atoms. The α-olefin monomer has preferably 6 or less carbon atoms, and more preferably 5 or less carbon atoms. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomers 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 units containing a linear alkylene structure and units containing a branched alkylene structure, more preferably contains at least one selected from the group consisting of units consisting only of linear alkylene structures and units consisting only of branched alkylene structures, and further preferably contains at least one selected from the group consisting of units represented by the above formula (1B) and units represented by the above formula (1C).

[0037] In the aliphatic hydrocarbon units, the content of alkylene units 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 (i.e., when the mass of the aliphatic hydrocarbon units is 100% by mass). The content of alkylene units is, based on the total mass of the aliphatic hydrocarbon units (i.e., when the mass of the aliphatic hydrocarbon units is 100% by mass), for example, less than 100% by mass, and may be 99.5% by mass or less, 99% by mass or less, or 98% by mass or less. The content of alkylene units may be 100% by mass.

[0038] The content of the aliphatic hydrocarbon units 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 (i.e., when the mass of the polymer is 100% by mass). The content of the aliphatic hydrocarbon units 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 (i.e., 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 with a nitrile group, more preferably a unit consisting solely of an alkylene structure substituted with 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 with a nitrile group, or a unit consisting solely of an alkyl structure substituted with 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)

[0042] In 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)

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

[0046] The method for introducing the nitrile group-containing unit into the polymer is not particularly limited, but a method (method (2a)) in which a polymer is produced by polymerization using a monomer composition containing a nitrile group-containing monomer is preferably used. The final polymer contains units derived from the nitrile group-containing monomer as nitrile group-containing units. Examples of nitrile group-containing monomers that can form nitrile group-containing units include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. Examples include α,β-ethylenically unsaturated group-containing compounds having a nitrile group, and specific examples include acrylonitrile and methacrylonitrile. In particular, from the viewpoint of increasing the intermolecular forces between polymers and / or between a polymer and a dispersed substance (adsorbate), it is preferable that the nitrile group-containing monomer contains acrylonitrile. The nitrile group-containing monomers can be used alone or in combination of two or more.

[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 even 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, it is possible to control the adsorption to the dispersed substance and the affinity to the liquid medium, and the dispersed substance can be stably present in the liquid medium. In addition, the affinity of the polymer to the electrolyte can be controlled, and problems such as the polymer dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented. For example, the content of the nitrile group-containing units 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 units and the methacrylonitrile group-containing units satisfy these ranges, and it is more preferable that the acrylonitrile group-containing units satisfy these ranges.

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

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

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

[0051] The alkenylene unit preferably includes at least one selected from the group consisting of a unit having a linear alkenylene structure and a unit having a branched alkenylene structure, and more preferably includes 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 a polymer is obtained through the above method (1a), a conjugated diene monomer unit having a carbon-carbon double bond therein may remain in the molecule of the polymer without being hydrogenated. The finally obtained polymer may contain a conjugated diene monomer unit having a carbon-carbon double bond therein as an alkenylene unit.

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

[0054] The alkyl unit preferably includes at least one selected from the group consisting of units having a linear alkyl structure and units having a branched alkyl structure, and more preferably includes at least one selected from the group consisting of units consisting only of linear alkyl structures and units consisting only of branched alkyl structures. The number of carbon atoms in the alkyl unit may be 1 to 20, 2 to 10, 3 to 8, or 4 to 6. Examples of the alkyl unit include 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, and an isohexyl group.

[0055] For example, when a polymer is obtained via the above method (1a) or (1b), it is preferable that at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit is introduced into the polymer 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 of only an alkanetriyl structure. The alkanetetrayl unit is a unit containing an alkanetetrayl structure, and preferably a unit consisting of only an alkanetetrayl structure.

[0057] For example, when a polymer is obtained via the above method (1a), the conjugated diene monomer unit may be introduced into the molecule of the polymer as a monomer unit containing a branch point, which is a monomer unit not containing a carbon-carbon double bond within the unit. In this case, the finally obtained polymer is a branched polymer, and may contain the conjugated diene monomer unit as an aliphatic hydrocarbon unit containing a branch point, such as an alkanetriyl unit or an alkanetetrayl unit. When the aliphatic hydrocarbon unit contains a unit containing a branch point, the polymer is a branched polymer. The branched polymer may be a network polymer. A polymer containing a unit containing a branch point can be three-dimensionally adsorbed to the dispersed material, thereby further improving dispersibility and stability.

[0058] The polymer may contain any unit, such as an amide group-containing unit or a carboxyl group-containing unit.

[0059] The amide group-containing unit is a unit containing an amide group, preferably a unit containing an alkylene structure substituted with an amide group, more preferably a unit consisting solely of an alkylene structure substituted with an amide group. The alkylene structure is preferably a linear or branched alkylene structure. The amide group-containing unit may further contain a unit containing an alkyl structure substituted with an amide group, or a unit consisting solely of an alkyl structure substituted with 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 the amount of monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurement.

[0061] The polymer in an embodiment of the present disclosure is characterized by a tan δ (loss tangent) of greater than 1 in a strain range of 0.01% to 10% in dynamic viscoelasticity measurements performed at a temperature of 100° C. and a frequency of 10 Hz.

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

[0063] While improving dispersion efficiency increases the dispersibility of the conductive material, excessive dispersion may cause breakage of the conductive material. It has been discovered that when tan δ is 1 or less within the strain range of 0.01% to 10%, excessive dispersion during the dispersion treatment of the conductive material using a polymer composition is likely to cause breakage of the conductive material. When tan δ is greater than 1, the dispersion treatment can be controlled to prevent breakage of the conductive material by using appropriate viscoelasticity of the dispersion. This is thought to ensure sufficient shape retention of the conductive material in the electrode film and improve battery performance. For example, when a long conductive material such as carbon nanotubes is used as the dispersoid, breakage can be suppressed, resulting in a dispersion with good dispersibility while maintaining its long shape. Furthermore, a conductive material composition in which carbon nanotubes or the like are dispersed using such a polymer can maintain its shape in the electrode film, thereby exhibiting high conductivity.

[0064] Furthermore, when tan δ is greater than 1 in the strain range of 0.01% to 10%, the polymer becomes viscous or fluid. A polymer to which viscosity or fluidity has been imparted can suppress an increase in the viscosity of the polymer solution. From this perspective, the initial dispersibility of the conductive material can be improved. Furthermore, long-term storage stability can be achieved while maintaining the initial dispersibility. It is more preferable that the polymer exhibits viscosity or fluidity at 40°C. The polymer may be in a liquid state at 40°C. After the polymer composition is heated at 140°C for 1 hour to remove the solvent, the polymer preferably exhibits viscosity or fluidity at 40°C, and may be in a liquid state.

[0065] In dynamic viscoelasticity measurements performed at a temperature of 100°C and a frequency of 10 Hz, the polymer preferably has a tan δ (loss tangent) greater than 1 in a strain range of 0.01% to 10%, but may have a value of 1 to 100, 1 to 50, 1 to 10, or 1 to 5. The present disclosure has discovered that the strain range of 0.01% to 10% in this tan δ (loss tangent) measurement is a factor that affects the copolymer's adsorption to a conductive material, the copolymer's solubility, the copolymer's viscosity, and the like in a polymer composition. Controlling the tan δ (loss tangent) of the copolymer to be greater than 1 over the entire strain range of 0.01% to 10% can contribute to improving the dispersibility of the conductive material in the polymer composition and improving the shape retention of the conductive material. Due to these properties, the polymer can be used as a dispersant in a conductive material composition.

[0066] When using the polymer composition according to an embodiment of the present disclosure, the effects can be achieved in both media dispersion and media-less dispersion. In media dispersion, the tan δ (loss tangent) of the polymer is appropriately controlled, so that during the dispersion process of adding a conductive material to the polymer composition, the collision efficiency of the dispersion media is improved, and the appropriate viscoelasticity of the dispersion can prevent breakage of the conductive material. In media-less dispersion, the tan δ (loss tangent) of the polymer is appropriately controlled, so that during the dispersion process of adding a conductive material to the polymer composition, shear stress can be applied uniformly and sufficiently to the dispersion, improving dispersion efficiency, and the appropriate viscoelasticity of the dispersion can prevent breakage of the conductive material.

[0067] In an embodiment of the present disclosure, the polymer preferably has a measurement temperature at which tan δ (loss tangent) = 1 is 80°C or lower when the temperature is increased at 10°C / min from 30°C to 110°C in a viscoelasticity measurement performed at a frequency of 10 Hz and a strain of 0.1%. Hereinafter, the measurement temperature at which tan δ (loss tangent) = 1 is also referred to as the measurement temperature (tan δ = 1). The polymer may have a measurement temperature (tan δ = 1) lower than 110°C or 100°C or lower, preferably 80°C or lower, and may also have a measurement temperature (tan δ = 1) of 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, or 30°C or lower. This measurement temperature (tan δ = 1) may be such that tan δ is greater than 1 throughout the entire temperature range from 30 to 110°C.

[0068] By setting the measurement temperature (tan δ = 1) to 80°C or lower, the initial dispersibility can be further improved under normal temperature conditions in an environment in which a conductive material is dispersed as a dispersoid in the polymer composition. Furthermore, since the polymer's adsorption to the conductive material can be maintained in the polymer composition, long-term storage stability can be further improved. Furthermore, during the dispersion treatment of the conductive material using the polymer composition, breakage of the conductive material can be suppressed even if excessive dispersion is performed due to improved dispersion efficiency, and a conductive material composition can be obtained in which the shape of the conductive material is maintained. From this viewpoint, the measurement temperature (tan δ = 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 tan δ of a polymer is calculated by the following formula 1 and is measured by dynamic viscoelasticity measurement: tan δ = loss modulus (G'') / storage modulus (G') Formula 1

[0070] Regarding the strain dependency of a polymer, tan δ can be measured using a viscoelasticity measuring device (for example, MCR302e (Anton Paar)). Specifically, parallel plates with a diameter of 25 mm are used, the gap is set to the thickness of the sample, and measurements are performed under conditions of a temperature of 100°C, a frequency of 10 Hz, and a strain range of 0.01 to 10%. Whether tan δ is greater than 1 or not is determined within the strain range of 0.01 to 10%.

[0071] Regarding the temperature dependence of a polymer, tan δ can be measured using a viscoelasticity measuring device (for example, MCR302e (Anton Paar)). Specifically, using parallel plates with a diameter of 25 mm, measurements are performed under the following conditions: 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 heating rate of 10°C / min. The temperature at which tan δ = 1 is determined within the temperature range of 30°C to 110°C.

[0072] The polymer sample used for dynamic viscoelasticity measurement is obtained by dropping a polymer solution onto a fluororesin mold and drying to remove the solvent. In the case of a viscous polymer, it is cooled with liquid nitrogen and solidified before being removed from the fluororesin mold. More specifically, tan δ in the strain range of 0.01 to 10% and the measurement temperature (tan δ = 1) can be measured according to the method described in the Examples.

[0073] The method for controlling the tan δ of a nitrile polymer is not particularly limited. For example, tan δ 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 modifier, etc.) of the nitrile polymer. For example, the tan δ of a nitrile polymer can be controlled by the following method.

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

[0075] In control method b, a base may be added when preparing a polymer containing aliphatic hydrocarbon units and nitrile group-containing units. Alternatively, a polymer containing aliphatic hydrocarbon units and nitrile group-containing units that has already been prepared may be dissolved in a solvent capable of dissolving the polymer, and then a base may be added to prepare the polymer. The base to be added may be at least one selected from the group consisting of inorganic bases and organic hydroxides (organic bases). When preparing the polymer by adding a base, applying heat to an extent that does not cause the solvent to ignite or boil can increase tan δ in a shorter time.

[0076] Examples of inorganic bases include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates, or alkoxides of alkali metals or alkaline earth metals; and ammonium hydroxide. Among these, hydroxides or alkoxides of alkali metals or alkaline earth metals are preferred from the viewpoint of easy supply of cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkali metal alkoxides 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, and potassium n-butoxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. 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, with sodium hydroxide being more preferable. 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, and benzyltrimethylammonium hydroxide. 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] The base may be an alkanolamine, such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, methylethanolamine, or methyldiethanolamine.

[0079] The amount of the base used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the mass of the nitrile polymer. The amount of the base used is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the mass of the nitrile polymer. These ranges are preferred to control the tan δ of the nitrile polymer.

[0080] In control method b, the increase in tan δ can be achieved by mixing a polymer containing an aliphatic hydrocarbon unit and a nitrile group-containing unit with a base and a liquid medium. Any other component may be mixed. The order in which the polymer, base, and liquid medium are added to the container and the mixing method are not limited. They may be added simultaneously to the container; the polymer, base, and liquid medium may be added separately to the container; or one or both of the polymer and base may be mixed with the liquid medium to prepare a polymer-containing liquid and / or a base-containing liquid, which may then be added to the container. In particular, a method in which a base dispersion in a liquid medium is added to a polymer solution in which a polymer is dissolved in a liquid medium while stirring is preferred, since this method can efficiently modify nitrile groups. A disperser or homogenizer can be used for stirring. The liquid medium may be any liquid medium that can be used for the polymer composition described below.

[0081] Although there is no limitation on the temperature during mixing, heating to 30°C or higher can accelerate the denaturation. Furthermore, to promote the denaturation of the nitrile polymer, a small amount of water and / or alcohol may be added to the container. The water and / or alcohol may be added to the container while mixing the polymer and the base, before adding the nitrile polymer and the base to the container, or simultaneously with or subsequent to the nitrile polymer and the base. Furthermore, when the nitrile polymer, the base, and any optional components used as needed are highly hygroscopic, water may be contained as 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 polymer.

[0082] Examples of alcohols 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, and thiodiglycol. The alcohols can be used alone or in combination of two or more. 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 is particularly preferably carried out in the presence of water.

[0083] In the control method c, the tan δ may be adjusted by applying a mechanical shear stress when preparing a polymer containing aliphatic hydrocarbon units and nitrile group-containing units, or by dissolving an already prepared polymer containing aliphatic hydrocarbon units and nitrile group-containing units in a liquid medium that can dissolve the polymer and then applying a mechanical shear stress. Tan δ can also be controlled by applying a mechanical shear stress to the polymer before dissolution using a roll or kneader, but it is more efficient to use a nitrile polymer as a dispersant in a liquid medium that can dissolve the polymer, so it is more preferable to apply a shear stress to the polymer solution.

[0084] Examples of methods for applying shear stress to a polymer solution include methods using dispersing means such as a homogenizer or a Silverson mixer. Although shear stress can be applied using a disperser or the like, it is preferable to use dispersing means capable of applying higher shear stress, such as a homogenizer or a Silverson mixer. Examples of methods for applying mechanical shear stress to a polymer before dissolution include methods using dispersing means such as a kneader or a two-roll mill.

[0085] The polymer according to an embodiment of the present disclosure preferably contains a polymer and N-methyl-2-pyrrolidone, and when a solution having a solids concentration of 20% by mass is measured with a Brookfield viscometer, the viscosity at 25°C and 60 rpm is less than 3000 mPa·s. The polymer according to one embodiment has a tan δ greater than 1 in the strain range of 0.01 to 10%, thereby improving initial dispersibility, and therefore a low viscosity can be achieved in the polymer solution. The viscosity of the polymer solution can be reduced even when the polymer content is high. By using a polymer with such viscosity properties, the viscosity of the polymer composition and the conductive material composition can be reduced. When measured with a Brookfield 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 the polymer solution may be from 10 mPa·s to 3000 mPa·s, or from 100 mPa·s to 1000 mPa·s.

[0086] The viscosity of the polymer solution is a value measured using a Brookfield viscometer at a rotor rotation speed of 60 rpm after leaving the polymer solution to stand in a thermostatic bath at 25° C. for at least 1 hour. More specifically, the viscosity can be measured according to the method described in the Examples.

[0087] The polymer in an embodiment of the present disclosure preferably has a Z-average molecular weight of 10,000 or more and 250,000 or less. A polymer specified by a 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 high molecular weight molecules in the distribution decreases, and the polymer becomes viscous and fluid. When a conductive material is used as a dispersoid, this improves the wettability of the conductive material and further enhances initial dispersibility. This is particularly effective in improving the wettability of conductive materials that are carbon materials. A Z-average molecular weight of 100,000 or less is particularly preferred. Furthermore, when the Z-average molecular weight is 10,000 or more, adsorption to the conductive material in the conductive material composition can be maintained, maintaining dispersibility. 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. When the Z-average molecular weight is within the above range, both initial dispersibility and storage stability can be achieved when a conductive material composition is prepared using the polymer.

[0088] The polymer in the embodiment of the present disclosure 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, the effects of improving the wettability of the conductive material, particularly the carbon material, and suppressing aggregation can be obtained, and the storage stability of the polymer composition can be further improved.

[0089] In this 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. Specifically, they can be measured according to the method in the Examples. The Z-average molecular weight and the weight-average molecular weight are each polystyrene equivalent values.

[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, a measurement sample can be prepared according to the method in the Examples, and the molecular weight can be measured.

[0091] The wettability of a polymer to a conductive material can be evaluated by preparing a dispersion of a polymer, a conductive material, and a liquid medium, and leaving it to stand for 24 hours, based on the ratio of the solid content of the supernatant to the solid content of the bottom. Specifically, a polymer solution in N-methyl-2-pyrrolidone (NMP) containing 8% by mass of polymer is prepared. A conductive material is added to this polymer solution to prepare a polymer dispersion containing 2% by mass of conductive material. This polymer dispersion is left to stand for 1 hour without stirring, and after standing for 1 hour, measurement samples are collected from the supernatant and the bottom. The wettability of a polymer to a conductive material can be evaluated based on the mass ratio (solid content in the supernatant) / (solid content 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 is determined by using carbon nanotubes JENOTUBE 10B (average outer diameter 10 nm, BET specific surface area 230 m) as the conductive material. ２ / g, multi-walled CNT) can be used to relatively evaluate the wettability of a polymer. More specifically, it can be evaluated according to the method in 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 mass% or less. The insoluble content can be calculated by filtering the remaining polymer from the solution, recovering the remaining polymer, drying the recovered polymer with hot air, and measuring the mass. The liquid medium is preferably capable of dissolving the polymer, and more preferably a high-dielectric solvent capable of dissolving the polymer. In the present disclosure, "capable of dissolving 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 clear and transparent. When a liquid medium capable of dissolving 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 contains a solvent consisting of any one of high-dielectric-constant solvents or a mixed solvent consisting of two or more of them. Furthermore, the high-dielectric-constant solvent may be mixed with one or more other solvents. In the present disclosure, a "high-dielectric-constant solvent" preferably has a relative dielectric constant value at 20°C of 2.5 or more, more preferably 25 or more, as described in a solvent handbook or the like. 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 polymer solubility, the relative dielectric constant of the high-dielectric-constant solvent is preferably 60 or less, more preferably 50 or less, at 20°C. 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. Therefore, it is preferable that the liquid medium is substantially free of water. "Substantially free" means that water is not intentionally added in an amount exceeding the amount that would be contained due to 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 viewpoint, the liquid medium is preferably an organic solvent, and more preferably a polar organic solvent that does not donate protons.

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

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

[0097] Further examples of the liquid medium include polar organic solvents that do not donate protons, such as heterocyclic, sulfoxide, sulfone, lower ketone, and carbonate liquid media. More specifically, the following can be mentioned:

[0098] Heterocyclic: cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc. Sulfoxide: dimethyl sulfoxide, etc. Sulfone: hexamethylphosphorotriamide, 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> A polymer composition for electrochemical devices according to one embodiment of the present disclosure includes a polymer and an amide-based liquid medium. The polymer includes an aliphatic hydrocarbon unit and a nitrile group-containing unit, and details of the polymer are as described above. Details of the amide-based liquid medium are as described above.

[0100] In the polymer composition, the nitrile polymer may be present in an amount of 1 to 50, 2 to 40, or 5 to 30% by mass, relative to the total mass of the polymer composition. Even when the polymer composition is present in a high concentration of 20% by mass or more, the tan δ in the strain range of 0.01% to 10% is greater than 1, thereby providing a dispersion that maintains the shape of the conductive material while maintaining the dispersibility of the conductive material and suppressing breakage of the conductive material during dispersion treatment. In the polymer composition, the nitrile polymer may be present in an amount of 50 to 100% by mass, 75 to 100% by mass, or 80 to 99.8% by mass, relative to the total mass of the solid content. The polymer composition may contain other polymers in addition to the nitrile polymer. In the polymer composition, the other polymer may be present in an amount of 0 to 100 parts by mass, 0.1 to 50 parts by mass, or 1 to 10 parts by mass, relative to 100 parts by mass of the nitrile 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, relative to the total mass of the polymer composition. The polymer composition may contain another liquid medium 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, relative to 100 parts by mass of the amide-based liquid medium. The polymer composition does not necessarily contain another liquid medium. When a conductive material is dispersed using the polymer composition, by using a nitrile-based polymer as the main component, or more preferably by using only a nitrile-based polymer, the viscoelasticity of the polymer composition can be appropriately controlled, and breakage of the conductive material during the dispersion process can be further suppressed.

[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 depending on the molecular structure of the polymer, properties such as the type of liquid medium, the application of the polymer composition, the type of conductive material to be dispersed, and the like. In the present disclosure, the solid content is the total amount of components excluding the liquid medium. Specifically, the polymer composition is thoroughly dried in an oven set at a temperature at or above which the liquid medium can evaporate, leaving only the solid content, and the solid content of the polymer composition is measured and divided by the total mass of the polymer composition.

[0103] The polymer composition may contain additional optional components as needed. For example, the polymer composition may contain a base. The base may be a component that can be contained in the raw materials for the nitrile polymer, a component that is mixed in from the raw materials for synthesizing the nitrile polymer, or the like, and details are as described above.

[0104] The polymer composition refers to a composition that does not contain a conductive material or 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 be substantially absent. 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 be substantially absent.

[0105] <Conductive Material Composition> The conductive material composition according to one embodiment of the present disclosure comprises a polymer composition for electrochemical devices and a conductive material. Details of the polymer composition for electrochemical devices 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 conductive carbon materials include graphite, carbon black, graphene, multilayer graphene, fullerene; and 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, flake graphite, lump graphite; and natural graphite such as amorphous graphite.

[0107] The carbon material plays a role in forming a conductive path inside the electrode, and from the viewpoint of being required to be less susceptible to breakage due to expansion and contraction of the electrode film, it preferably contains a fibrous carbon material, and more preferably is a fibrous carbon material. From the viewpoints of conductivity, ease of availability, and cost, the use of carbon black and / or carbon nanotubes is preferred. Furthermore, from the viewpoints of reducing raw material costs and efficiently forming a conductive network, two or more types of the same type of carbon material with different physical properties may be combined and used. Examples of the same type of carbon material with different physical properties include two or more types of carbon nanotubes with different average outer diameters or average fiber diameters, or two or more types of carbon black with different specific surface areas.

[0108] The carbon purity of a carbon material is expressed as the content (% by mass) of carbon atoms in the carbon material. The higher the carbon purity, the better, and it is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the carbon material. By keeping the carbon purity within the above range, problems such as short circuits caused by the formation of dendrites due to impurities such as metals can be prevented.

[0109] <Carbon Nanotubes> Carbon nanotubes have a cylindrical shape formed by rolling up planar graphite, and include single-walled carbon nanotubes and multi-walled carbon nanotubes, or a mixture of these. Single-walled carbon nanotubes have a structure in which one layer of graphite is rolled up. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are rolled up. Furthermore, the sidewalls of carbon nanotubes do not have to have a graphite structure. For example, the carbon nanotubes may be carbon nanotubes with sidewalls having an amorphous structure.

[0110] The shape of the carbon nanotubes is not limited. Examples of the shape of the carbon nanotubes include various shapes, including needle-like, cylindrical, fishbone-like (fishbone or cup-stacked), trump-like (platelet), and coil-like. Among these, the shape of the carbon nanotubes in this embodiment is preferably needle-like or cylindrical. The carbon nanotubes may have a single shape or a combination of two or more shapes.

[0111] Examples of the form of carbon nanotubes include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes may have any of these forms alone or in combination of two or more.

[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. 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, a good conductive network is easily formed within the electrode, and the active material inside the secondary battery can be utilized evenly during charging and discharging, thereby suppressing deterioration of the active material and further improving the cycle characteristics of the secondary battery. The average outer diameter of the carbon nanotubes can be calculated by observing and photographing the carbon nanotubes with a transmission electron microscope, then randomly selecting 300 carbon nanotubes from the obtained photograph and measuring the outer diameter of each.

[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. The fiber length of the carbon nanotubes is preferably 100 μm or less, and more preferably 20 μm or less. The average fiber length of the carbon nanotubes can be calculated by observing and photographing the carbon nanotubes with a scanning electron microscope, then randomly selecting 300 carbon nanotubes from the photograph, and measuring the fiber length of each. The average fiber length of the carbon nanotubes in the conductor dispersion is also preferably within the above range.

[0114] The aspect ratio is the fiber length of a carbon nanotube divided by its outer diameter. A typical aspect ratio can be calculated using the average fiber length and the average outer diameter. A conductive material with a higher aspect ratio can provide higher conductivity when used to form an electrode. The aspect ratio of carbon nanotubes is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. The aspect ratio of carbon nanotubes is also 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 ​​carbon nanotubes is 100 m ２ / g or more, and ２ / g or more is more preferable, and 200m ２ The specific surface area of ​​the carbon nanotube is more preferably 1200 m / g or more. ２ / g or less, and ２ / g or less is more preferable, and 700m ２ The BET specific surface area of ​​the carbon nanotubes can be measured by the BET method using nitrogen adsorption measurement in accordance with JIS Z 8830.

[0116] The carbon purity of carbon nanotubes is expressed as the carbon atom content (mass%) in the carbon nanotubes. The carbon purity is preferably 80 mass% relative to 100 mass% of the carbon nanotubes, more preferably 90 mass% or more, even more preferably 95 mass% or more, even more preferably 98 mass% or more, and even better 99 mass% or more or 99.5 mass% or more. By keeping the carbon purity within the above range, problems such as the formation of dendrites due to impurities, which can cause short circuits, can be prevented. The carbon purity of carbon nanotubes can be determined using an ICP optical emission spectrometer according to the method described in the Examples.

[0117] <Carbon Black> Carbon black is a fine particle primarily composed of carbon. It is produced by incomplete combustion of oil or gas, with various properties controlled. Carbon black has a secondary structure (aggregate) in which primary particles are linked together like beads, and a tertiary structure (agglomerate) in which the secondary structures further aggregate. These secondary and tertiary structures are collectively referred to as "structure." Although primary particles appear spherical under an electron microscope, they are not chemically independent. Instead, they are chemically bonded to adjacent primary particles within the aggregate to form the secondary structure. Meanwhile, secondary structures are chemically independent, agglomerating through intermolecular forces to form the tertiary structure. Therefore, the conductivity within the secondary structures is higher than the conductivity between them, including the contact resistance. Therefore, deagglomerating the tertiary structure while maintaining the structure of the secondary structures as much as possible is effective in producing electrodes with excellent conductivity. The secondary structure is sometimes simply referred to as "structure."

[0118] As the carbon black, various types can be used, such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, Ketjen black, etc. Carbon black that has been subjected to a conventional oxidation treatment or graphitization treatment can also be used.

[0119] Oxidation treatment of carbon black is a treatment in which oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups are directly introduced (covalently bonded) to the surface of the carbon black by treating the carbon black at high temperatures in air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, or the like. This treatment is commonly carried out to improve the dispersibility of carbon black.

[0120] Examples of commercially available carbon black include Super P-Li (manufactured by TIMCAL Corporation), Ketjen Black EC-300J, EC-600JD (manufactured by Lion Corporation), Denka Black, Denka Black Li-400, Li-335 (manufactured by Denka Company, acetylene black), and the like, but are not limited thereto, and two or more types may be used in combination.

[0121] The average primary particle diameter of carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and more preferably 25 nm to 100 nm. The average primary particle diameter of carbon black can be calculated by first observing and photographing the carbon black using a transmission electron microscope, randomly selecting 100 spherical-like carbon black primary particles from the photograph, and measuring the outer diameter of each.

[0122] The BET specific surface area of ​​carbon black is 10 m ２ / g or more 1500m ２ / g or less, and ２ / g or more 1000m ２ / g or less is more preferable, and 100m ２ / g or more 850m ２ / g or less is even more preferable. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount of carbon black, allowing the amount of conductive material in the electrode to be reduced. This increases the degree of freedom in battery design, such as by increasing the amount of active material or binder resin. Furthermore, when preparing an electrode slurry, the active material and carbon black are more likely to be combined, making it easier to obtain an electrode film having a homogeneous conductive network in which the active material surface is coated with carbon black, thereby 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 ​​carbon black can be measured by the BET method described in JIS Z 8830.

[0123] In the conductive material composition, the conductive material may be present in an amount of 0.1 to 30 mass %, 1 to 25 mass %, or 3 to 20 mass % relative to the total mass of the conductive material composition, from the viewpoints of dispersibility and storage stability.

[0124] When carbon nanotubes are used as the conductive material in the conductive material composition, the content of the carbon nanotubes is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 1% by mass or more, and even more preferably 3% by mass or more, relative to the total mass of the conductive material composition. The carbon nanotube content is preferably 20% by mass or less, more preferably 10% by mass or less. By setting the carbon nanotube content within the above range, the carbon nanotubes can be maintained in a good and stable state without sedimentation or gelation. The carbon nanotube content is preferably adjusted appropriately depending on the BET specific surface area of ​​the carbon nanotubes, their affinity for the liquid medium, the dispersibility of the dispersant, and the like, so as to obtain a conductive material composition with appropriate fluidity or viscosity. According to one embodiment, the use of a nitrile-based polymer provides good initial dispersibility and shape retention of the carbon nanotubes, and allows for a higher concentration of carbon nanotubes to be contained. For example, the content of the carbon nanotubes is preferably in the range of 0.1 to 20 mass % relative to the total mass of the conductive material composition, but may also be 1 to 20 mass %, 3 to 20 mass %, 4 to 20 mass %, 5% or more mass %, or 8 to 20 mass %.

[0125] When carbon black is used as the conductive material in the conductive material composition, the content of carbon black is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to the total mass of the conductive material composition. The carbon black content is preferably 30% by mass or less, more preferably 20% by mass or less. By setting the carbon black content within the above range, the carbon black can be maintained in a good and stable state without causing sedimentation or gelation. The carbon black content is preferably adjusted appropriately depending on the BET specific surface area of ​​the carbon black, its affinity for the liquid medium, the dispersibility of the dispersant, and the like, so as to obtain a conductive material composition having appropriate fluidity or viscosity. According to one embodiment, the use of a nitrile-based polymer provides good initial dispersibility and shape retention of the carbon black, and allows for a higher concentration of carbon black to be included. For example, the content of carbon black is preferably in the range of 0.1 to 30 mass % relative to the total mass of the conductive material composition, but may also be 1 to 20 mass %, 5 to 20 mass %, 10 to 20 mass %, 12 to 10 mass %, or 15 to 20 mass %.

[0126] In the conductive material composition, the nitrile polymer may be present in an amount of 0.05 to 5 parts by mass, 0.1 to 1 part by mass, or 0.2 to 0.5 parts by mass relative to 100 parts by mass of the conductive material. According to one embodiment, the use of a nitrile polymer results in good initial dispersibility and shape retention of the conductive material. Furthermore, the nitrile polymer can exert its effect even in a small amount relative to the conductive material. For example, the nitrile polymer may be present in an amount of 0.05 to 5 parts by mass relative to 100 parts by mass of the conductive material, but may also be present in an amount of 0.05 to 0.5 parts by mass, or 0.05 to 0.2 parts by mass.

[0127] The conductive material composition may have a solids content of 0.1 to 30 mass %, 1 to 25 mass %, or 3 to 20 mass %.

[0128] When a conductive material is dispersed using a disperser that uses collision with media, such as a bead mill, or when the material is repeatedly passed through a disperser over a long period of time, the conductive material may break, resulting in the formation of short-sided carbonaceous material. When short-sided carbonaceous material is formed, 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. Judging from these evaluation results alone, however, short-sided carbonaceous material has high contact resistance and is difficult to form a conductive network, which may worsen the resistance of the electrode. According to one embodiment, the use of a nitrile-based polymer results in good initial dispersibility and good shape retention of the conductive material. Therefore, a conductive network is easily formed in the electrode film, improving the rate characteristics and cycle characteristics of secondary batteries.

[0129] In one embodiment, the conductive material composition may contain additional optional components as needed. For example, the conductive material composition may contain, as optional components, dispersants, wetting agents, surfactants, pH adjusters, wetting and penetrating agents, leveling agents, polymer components, and the like, as appropriate, to the extent that the object of the present invention is not impaired. These optional components can be added at any timing, such as before preparation of the conductive material composition, during dispersion, or after dispersion. These optional components may also be added at any timing during preparation of the polymer composition. These optional components may also be added at any timing during preparation of the slurry composition. These timings may also be combined and added in stages.

[0130] As the dispersant and polymer component, known materials other than nitrile polymers can be used. Among these, at least one selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, and polyvinyl acetal is particularly preferred. Polymers in which other substituents have been introduced into a portion of the above polymers, or modified polymers, may also be used. When a dispersant or polymer component is used, the weight-average molecular weight is preferably 30,000 or less, more preferably 20,000 or less, and preferably 3,000 or more. Outside the above range, there is a concern that the adsorption of the nitrile polymer and the conductive material may be hindered.

[0131] The dispersibility of the conductive material in the conductive material composition can also be evaluated by the median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer. The median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer allows the particle size of the conductive material agglomerated particles to be estimated from the scattered light intensity distribution by the particles. The median diameter (μm) is preferably 0.4 or more. 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 appropriately dispersed state can be obtained. If the median diameter (μm) is below the above range, the conductive material will be 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.

[0132] The dispersibility of the conductive material in the conductive material composition can also be evaluated by measuring the gloss at 60° (i.e., the intensity of reflected light at an angle of 60° relative to the incident angle) of a coating film obtained by coating the conductive material on a smooth glass substrate, baking and drying it. The better the dispersibility of light incident on the coating film, the smoother the coating film surface will be, and therefore the gloss will be higher. Conversely, the worse the dispersibility, the more light will be scattered by the unevenness of the coating film surface, and therefore the gloss will be lower.

[0133] The gloss of the 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. The gloss of the coating film at 60° is preferably 120 or less, more preferably 110 or less, and even more preferably 100 or less. By setting the gloss within the above range, a conductive material composition in an appropriately dispersed state can be obtained. If the gloss is below the above range, the conductive material will be in an aggregated state, and if the gloss is above the above range, a large amount of finely cut conductive material will be produced, making it difficult to form an efficient conductive network.

[0134] The TI value of the conductive material composition can be calculated by dividing the viscosity (mPa s) at 60 rpm measured with a Brookfield 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 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 entanglement of the conductive material, polymer, and other resin components, or their intermolecular forces, etc., 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 entanglement of the conductive material, polymer, and other resin components while allowing these intermolecular forces to act appropriately.

[0135] <Dispersion Method> The conductive material composition can be produced, for example, by finely dispersing the polymer composition and the conductive material using a dispersing device. The dispersion treatment can be a multi-stage treatment of two or more steps by arbitrarily adjusting the addition timing of the materials to be used.

[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, and an ultrasonic homogenizer.

[0137] From the viewpoint of promoting wetting of the conductive material and disintegrating coarse particles, it is more preferable to use a high-shear mixer in the initial dispersion step, followed by a high-pressure homogenizer from the viewpoint of dispersing the conductive material while maintaining its aspect ratio. Furthermore, by further dispersing the conductive material using a high-pressure homogenizer after dispersing it using a bead mill, it is possible to achieve a uniform dispersion state while maintaining fiber length. Alternatively, since the use of a polymer composition containing the nitrile polymer of the present disclosure allows the pre-dispersion mixture to be prepared with a lower viscosity, a uniform dispersion state can also be achieved by first dispersing the conductive material using a bead mill to disintegrate it to a certain level and then dispersing it using a high-pressure homogenizer while maintaining fiber length. The pressure when using a high-pressure homogenizer is preferably 60 to 150 MPa, more preferably 60 to 120 MPa.

[0138] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, and circulation dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device itself, without using piping or the like. Because handling is simple, it is preferred for small-scale production. Pass dispersion is a dispersion method in which the dispersing device itself is equipped with a tank that supplies the dispersion liquid via piping and a tank that receives the dispersion liquid, and the dispersion passes through the dispersing device itself. Furthermore, circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device itself is returned to the tank that supplies the dispersion liquid, and dispersion is performed while circulating. In both methods, the longer the processing time, the more the dispersion progresses; therefore, the pass or circulation can be repeated until the desired dispersion state is achieved, and the processing volume can be increased by changing the tank size or processing time. Pass dispersion is preferred over circulation dispersion because it is easier to achieve a uniform dispersion state. Circulation dispersion is preferred over pass dispersion because the operation and production equipment are simpler. In the dispersion step, the processes of crushing agglomerated particles, loosening, wetting, stabilization, etc., proceed sequentially or simultaneously, and the final dispersion state varies depending on how these processes proceed. Therefore, it is preferable to control the dispersion state in each dispersion step by using various evaluation methods. For example, the dispersion state can be controlled by the method described in the examples.

[0139] <Slurry Composition> The slurry composition according to one embodiment of the present disclosure contains a polymer composition for electrochemical devices, a conductive material, and an active material. Details of the polymer composition for electrochemical devices and the conductive material are as described above. The active material will now be described.

[0140] The slurry composition can contain a positive electrode active material or a negative electrode active material. In this disclosure, the positive electrode active material and the negative electrode active material may be simply referred to as "active material." An active material is a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on electromotive force. In this 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 to improve uniformity and processability.

[0141] <Positive Electrode Active Material> The positive electrode active material is not particularly limited, but 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 polymers can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium and sodium, inorganic compounds such as transition metal sulfides, polyanion compounds, and Prussian blues. Specific examples include MnO, V ２ O ５ , V ６Ｏ 1 ３ , TiO ２ transition metal oxide powders such as lithium nickel oxide, lithium cobalt oxide, lithium manganate, and lithium manganate having a spinel structure; lithium iron phosphate-based materials, which are phosphate compounds having an olivine structure; TiS ２ Examples of suitable materials include transition metal sulfide powders such as FeS, sodium ferrate, sodium manganate, sodium chromate, and sodium nickelate, which have a layered structure, and sodium iron phosphate-based materials, which are phosphate compounds with an olivine structure. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Mixtures of the above inorganic and organic compounds may also be used.

[0142] The positive electrode active material is preferably a composite oxide of lithium containing a transition metal such as Al, Fe, Co, Ni, or Mn, more preferably a composite oxide of lithium containing any of Al, Co, Ni, or Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. Active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metals is 50 mol% or more) tend to become more basic due to the elution of raw material-derived components or metal ions, which can easily cause binder gelation or deterioration of the dispersion state, thereby making the problems of the present disclosure more pronounced. Therefore, embodiments of the present disclosure are particularly effective in batteries containing active materials containing Ni and / or Mn.

[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, metallic Li or its alloys, alloys such as tin alloys, silicon alloys, and lead alloys, Li Ｘ TiO ２ , Li Ｘ Fe ２ O ３ , Li Ｘ Fe ３ O ４ , Li Ｘ WO ２ Examples of materials that can be used include metal oxides such as those listed above, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and resin-baked carbon materials, where x is a number in the range of 0<x<1.

[0144] These negative electrode active materials can be used alone or in combination of two or more. In particular, when a silicon alloy negative electrode is used, the theoretical capacity is large but the volume expansion is extremely large, so it is preferable to use it in combination with artificial graphite such as a highly graphitized carbon material, carbonaceous powder such as natural graphite, resin-baked carbon material, or the like.

[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 (the mass of the active material being 100% by mass). It is also 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 (the mass of the active material being 100% by mass). It is also preferably 20% by mass or less, and even more preferably 10% by mass or less. The conductive material may be a combination of carbon nanotubes and carbon black, or two or more of each may be used, but the total amount of each added is preferably within the above range. If the content exceeds the above range, the loading amount of the active material in the electrode decreases, resulting in a lower battery capacity. If the content is below the above range, the conductivity of the electrode and battery may be insufficient.

[0146] The content of the nitrile 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 (the mass of the active material being 100% by mass), and 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 together substances such as active materials and conductive materials. The binder resin is not particularly limited as long as it is typically used as a binder resin for paints, and can be appropriately selected depending on the purpose. That is, in addition to the nitrile polymer, the slurry composition may contain a resin capable of binding together substances such as active materials and conductive materials.

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

[0149] Among these, the binder resin used in the positive electrode composition is preferably a polymer or copolymer having a fluorine atom in the molecule in terms of durability. For example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. are preferred. Furthermore, the binder resin used in the negative electrode composition is preferably carboxymethyl cellulose (CMC), styrene butadiene rubber, polyacrylic acid, etc., because of their 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, of the nonvolatile 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 (the mass of the active material being 100% by mass), and 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 of 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 (the mass of the slurry composition being 100% by mass), and is preferably 90% by mass or less, more preferably 80% by mass or less.

[0153] The slurry composition can be prepared by various conventional methods. Examples include a method of adding an active material to a conductive material composition; a method of adding an active material to a conductive material composition and then adding a binder resin; a method of adding a binder resin to a conductive material composition and then adding an active material; and a method of first mixing an active material, a binder resin, and optionally a liquid medium, and then adding the conductive material composition. A preferred method for preparing a slurry composition containing carbon nanotubes as a conductive material is to add a binder resin to the conductive material composition, then add an active material and disperse the mixture. This method allows the slurry composition to be prepared without disrupting the dispersion state of the carbon nanotubes. The dispersing device used for dispersion is not particularly limited. The slurry composition can be obtained using the dispersing means mentioned in the description of the conductive material composition.

[0154] <Electrode Film> An 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. In addition, 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 applying a slurry composition to 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 mixture layer."

[0156] The material and shape of the current collector used to form the electrode film are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. Examples of current collector materials include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while flat foils are generally used, current collectors with roughened surfaces, perforated foil current collectors, and mesh current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0157] The method for applying the slurry composition to the current collector is not particularly limited, and any known method can be used. Specific examples of the application method include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic coating. Examples of the drying method include, but are not limited to, drying by standing, or drying using a blower dryer, a warm air dryer, an infrared heater, or a far-infrared heater.

[0158] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0159] The electrode film formed using the slurry composition can also be used as an underlayer for the electrode mixture layer. By providing such an underlayer, it is possible to improve the adhesion between the electrode mixture layer and the current collector or to improve the conductivity of the electrode film.

[0160] <Electrochemical element> According to one embodiment of the present disclosure, an electrochemical element can be provided. Suitable electrochemical elements include secondary batteries and capacitors. At least one electrode body of the electrochemical element may include an electrode film formed using the slurry composition. Details of the slurry composition and the electrode film are as described above. Examples of secondary batteries include lithium ion secondary batteries, alkaline secondary batteries, lead-acid batteries, sodium-sulfur secondary batteries, and lithium-air secondary batteries. The secondary battery is preferably a nonaqueous secondary battery. Examples of capacitors include electric double layer capacitors, lithium ion capacitors, hybrid capacitors, and redox capacitors.

[0161] 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 capable of ion migration can be used. For example, the electrolyte is LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (wherein Ph is a phenyl group) and the like. 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, but examples thereof include 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, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

[0165] The structure of the nonaqueous electrolyte secondary battery of this embodiment is not particularly limited. In one embodiment, the nonaqueous electrolyte secondary battery may generally include a positive electrode, a negative electrode, and a separator that is provided as needed. The nonaqueous electrolyte secondary battery may be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0166] The present invention will be explained in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". The blending amounts in the tables are parts by mass, and amounts other than the solvent are calculated as non-volatile contents. Blank spaces in the tables indicate that no ingredients are blended.

[0167] The materials used in the examples and comparative examples are as follows. Hydrogenated nitrile butadiene rubber (liquid hydrogenated nitrile butadiene rubber, manufactured by Zannan Scitech, weight average molecular weight 30,000, alkylene structural units 66% by mass, content of nitrile group-containing structural units 34% by mass), hereinafter referred to as HNBR2. Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural units 66% by mass, content of nitrile group-containing structural units 34% by mass), hereinafter referred to as HNBR4. Li-335: Denka Black Li-335 (acetylene black, manufactured by Denka Company, 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 Kinwa, non-volatile content 100%), hereinafter referred to as NCM2. NAT-7050 (LiNi0.8Co0.15Al0.05O2, manufactured by 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> JENOTUBE 10B (manufactured by JEIO, average outer diameter 10 nm, BET specific surface area 230 m) was placed in a 120 L heat-resistant container. ２10 kg of JENOTUBE10B (100% CO₂ / g) was weighed out, and a heat-resistant container containing JENOTUBE10B was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was evacuated while maintaining positive pressure. After the oxygen concentration in 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. Nitrogen gas was then introduced at 50 L / min, and the mixture was cooled while maintaining positive pressure, yielding purified JENOTUBE10B. The carbon purity was 99.9%. The purified JENOTUBE10B was then placed in a dynamic mill (manufactured by Nippon Coke & Co., Ltd.) with 8 mm diameter zirconia beads as milling media, fed 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 subjected to acid decomposition using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon material. Analysis was performed using a multi-type ICP optical emission spectrometer (720-ES, manufactured by Agilent), and the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, and chromium) contained in the extract was calculated. The carbon purity of CNT1 was calculated as follows and was found to be 99.9%: Carbon purity (%) = ((mass of carbon material - amount of metal) ÷ ​​mass of carbon material) × 100

[0170] <CNT2> JENOTUBE6A (manufactured by JEIO, average outer diameter 6 nm, BET specific surface area 650 m) was placed in a 120 L heat-resistant container. ２ 10 kg of JENOTUBE6A (CNT2) was weighed out, and the heat-resistant container containing the JENOTUBE6A was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, the furnace 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. Nitrogen gas was then introduced at 50 L / min, and the furnace was cooled while maintaining positive pressure, yielding purified JENOTUBE6A (CNT2).

[0171] CNT2 was subjected to acid decomposition using a microwave sample pretreatment device (Milestone General, ETHOS1) to extract the metals contained in the carbon material. Analysis was then performed using a multi-type ICP optical emission spectrometer (Agilent, 720-ES) to calculate the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, and chromium) contained in the extract. 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 mmol of lithium hydroxide monohydrate is added. 120 mmol of phosphoric acid is further added to the resulting solution using an 85 wt % aqueous phosphoric acid solution, and 96 mmol of manganese (II) sulfate monohydrate and 24 mmol of iron (II) sulfate heptahydrate are further added. The resulting solution is transferred to an autoclave and heated to maintain the temperature inside the container at 150°C for 4 hours. After heating, the supernatant of the solution is discarded, and lithium iron manganese phosphate LiMn is collected as a precipitate. ０．８ Fe ０．２ P.O. ４ The obtained manganese iron lithium phosphate was washed with pure water, and the supernatant was removed by centrifugation five times. Finally, pure water was added again to obtain a dispersion. Next, glucose was added to the dispersion in an amount equal to 15% by weight of the manganese iron lithium phosphate in the dispersion and dissolved, and then pure water was added to adjust the solids concentration of the dispersion to 20% by weight, thereby obtaining an LFMP dispersion. The obtained LFMP dispersion was dried with hot air at 200°C using a spray dryer (Fujisaki Electric Co., Ltd., MDL-050B) to obtain secondary particles. The obtained secondary particles were heated in a rotary kiln at 700°C under a nitrogen atmosphere for 4 hours to obtain carbon-coated LFMP particles (hereinafter referred to as LFMP).

[0173] <Polymer Composition> [Synthesis of HNBR1] HNBR1 is synthesized by the following synthesis 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: nitrile group-containing unit content 34%, Mooney viscosity 32) finely chopped with a rubber chopper is added and dissolved. After the nitrile rubber is completely dissolved, 4 phr of 1-hexene is added to the vessel, and the solution is stirred for 2 hours. At this time, a catalyst, 1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(tricyclohexylphosphine)-ruthenium(phenyl-methylene) dichloride, dissolved in 20 mL of monochlorobenzene, is added to the vessel. The reaction mixture is allowed to react for 12 hours with 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 with hydrogen to 85 bar. The reaction mixture is reacted at 135°C for 4 hours with stirring (500 rpm), to obtain a polymer solution. After concentrating to a certain extent using a rotary evaporator, the solution is poured into a stainless steel tray and dried in an exhaust-type heating oven heated to 140°C until the odor of monochlorobenzene disappears, to obtain HNBR1. １ The content of structural units derived from acrylonitrile was determined to be 34% from the H-NMR quantitative spectrum.

[0174] [Preparation of HNBR3] 92 parts by mass of NMP was placed in a stainless steel container and stirred with a disperser while heating so that the liquid temperature reached 80°C. 8 parts by mass of HNBR2, which had been heated to 80°C in a separate container, was added to the NMP and stirred for 1 hour to prepare a polymer solution. 1000 parts by mass of methanol was placed in another stainless steel container, and while stirring at room temperature (25°C), the polymer solution prepared previously was added dropwise to coagulate, followed by decantation and drying in an exhaust-type heating oven heated to 140°C. The above steps (preparation of polymer solution, coagulation with methanol, decantation, drying) were repeated three times to obtain HNBR3. １ The content of structural units derived from acrylonitrile was determined to be 34% from the H-NMR quantitative spectrum.

[0175] [Preparation of HNBR5] 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate as an emulsifier, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 0.85 parts of t-dodecyl mercaptan as a chain transfer agent were placed in this order in an autoclave equipped with a stirrer, and after the inside was purged with nitrogen, 65 parts of 1,3-butadiene as a conjugated diene monomer was injected, and 0.25 parts of ammonium persulfate as a polymerization initiator was added, and a polymerization reaction was carried out at a reaction temperature of 40°C. 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 with a total solids concentration adjusted to 12% by mass. 400 mL of the obtained solution (total solids: 48 g) was placed in a 1 L autoclave equipped with a stirrer, and nitrogen gas was passed through for 10 minutes to remove dissolved oxygen in the solution. 75 mg of palladium acetate as a hydrogenation catalyst was dissolved in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to palladium (Pd) and added. The system was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50 ° C. under pressure of 3 MPa with hydrogen gas, and the hydrogenation reaction was carried out for 6 hours.

[0177] Next, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate as a hydrogenation catalyst was dissolved in 60 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to Pd, and the solution was added. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and the hydrogenation reaction was carried out for 6 hours. Thereafter, the contents were returned to room temperature, and the system was substituted with a nitrogen atmosphere. The contents were then concentrated using an evaporator to a solids concentration of 40%, yielding an aqueous dispersion of the polymer.

[0178] Furthermore, an aqueous dispersion of the polymer was dropped into methanol to coagulate the polymer, and the coagulated product was then vacuum dried at 60° C. for 12 hours to obtain HNBR5. １ The content of structural units derived from acrylonitrile as 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) A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 800 parts by mass of NMP and purged with nitrogen gas. Thereafter, the reaction vessel was heated to 80°C, and 200 parts of HNBR1 were added and stirred until HNBR1 was completely dissolved, thereby obtaining Polymer Composition 1 (solid content concentration 20% by mass).

[0180] (Polymer Compositions 2 and 3) Polymer compositions 2 and 3 were obtained in the same manner as in the preparation of polymer composition 1, except that the polymer to be dissolved was changed to one shown in Table 1.

[0181] (Polymer composition 4) Capacity 1000cm ３ 475 parts by mass of NMP and 25 parts by mass of NaOH (Tosoh Pearl, manufactured by Tosoh Corporation) were added to a plastic container, and the mixture was dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by Silverson) equipped with a fine emulsion screen until the mixture was uniform.The mixture was then passed through a nylon filter with 150 μm openings using a filter bell, to prepare a NaOH dispersion (NaOH concentration 5% by mass).

[0182] A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 780 parts by mass of NMP and purged with nitrogen gas. The reaction vessel was then heated to 80°C, and 200 parts of HNBR2 was added, followed by stirring until the hydrogenated nitrile-butadiene rubber was completely dissolved. Then, 20 parts by mass of a NaOH dispersion (NaOH concentration 5% by mass) was added, and the mixture was stirred while adding air. The reaction vessel was heated at 80°C for 12 hours, yielding a polymer composition 4 (solid concentration 20.1% by mass).

[0183] (Polymer Compositions 5, 8 to 9) Polymer compositions 5, 8 to 9 were obtained in the same manner as for polymer composition 4, except that the type and amount of base added were changed as shown in Table 1.

[0184] (Polymer composition 6) Capacity 1000cm ３425 parts by mass of NMP and 75 parts by mass of NaOH (Tosoh Pearl, manufactured by Tosoh Corporation) were added to a plastic container, and the mixture was dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by Silverson) equipped with a fine emulsion screen until the mixture was uniform.The mixture was then passed through a nylon filter with 150 μm openings using a filter bell, to prepare a NaOH dispersion (NaOH concentration 15% by mass).

[0185] A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 773.3 parts by mass of NMP and purged with nitrogen gas. The reaction vessel was then heated to 80°C, and 200 parts of HNBR2 was added, followed by stirring until the hydrogenated nitrile-butadiene rubber was completely dissolved. Then, 26.7 parts by mass of NaOH dispersion was added, and the mixture was stirred while adding air. The reaction vessel was heated at 80°C for 12 hours, yielding a polymer composition 6 (solid concentration 20.4% by mass).

[0186] (Polymer composition 7) Polymer composition 7 was obtained in the same manner as polymer composition 6, except that the solid content concentration of the polymer was kept constant, the type and amount of base added were changed to those shown in Table 1, and the amount of NMP was adjusted.

[0187] (Comparative Polymer Composition 1) A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 800 parts by mass of NMP and purged with nitrogen gas. Thereafter, the reaction vessel was heated to 80°C, and 200 parts of HNBR4 was added and stirred until the hydrogenated nitrile-butadiene rubber was completely dissolved, thereby obtaining a comparative polymer composition 1 (solid content concentration 20% by mass).

[0188] (Comparative polymer composition 2) Capacity 1000cm ３ 475 parts by mass of NMP and 25 parts by mass of NaOH (Tosoh Pearl, manufactured by Tosoh Corporation) were added to a plastic container, and the mixture was dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by Silverson) equipped with a fine emulsion screen until the mixture was uniform.The mixture was then passed through a nylon filter with 150 μm openings using a filter bell to prepare a NaOH dispersion.

[0189] A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 780 parts by mass of NMP and purged with nitrogen gas. The reaction vessel was then heated to 80°C, and 200 parts of HNBR4 was added, followed by stirring until the hydrogenated nitrile-butadiene rubber was completely dissolved. 20 parts by mass of NaOH dispersion was then added, and the mixture was stirred while adding air. The reaction vessel was heated at 80°C for 12 hours, yielding a comparative polymer composition 2 (solid content concentration 20.1% by mass).

[0190] (Comparative Polymer Composition 3) A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 800 parts by mass of NMP and purged with nitrogen gas. Thereafter, the reaction vessel was heated to 80°C, and 200 parts of HNBR5 was added, followed by stirring until the hydrogenated nitrile-butadiene rubber was completely dissolved, thereby obtaining Comparative Polymer Composition 3 (solid content concentration 20% by mass).

[0191] (Comparative polymer composition 4) Capacity 1000cm ３ 425 parts by mass of NMP and 75 parts by mass of NaOH (Tosoh Corporation, Toso Pearl) were added to a plastic container, and the mixture was dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, Silverson) equipped with a fine emulsion screen until the mixture was uniform. The mixture was then passed through a 150 μm nylon filter using a filter bell to prepare a NaOH dispersion (NaOH concentration 15% by mass). 940 parts by mass of NMP was charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the atmosphere was purged with nitrogen gas. The reaction vessel was then heated to 80°C, 30 parts of HNBR4 was added, and the mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. 30 parts by mass of NaOH dispersion (NaOH concentration 15% by mass) was then added, and the mixture was stirred while adding air. The reaction vessel was heated at 80°C for 12 hours, and comparative polymer composition 4 (solids concentration 3.5% by mass) was obtained.

[0192] For Examples 1-3 and 1-6 and Comparative Examples 1-1 and 1-4, a chart of tan δ (loss tangent) for evaluating the strain dependency of the polymer compositions is shown in Figure 1. For Examples 1-3, 1-6, 1-7 and Comparative Example 1-1, a chart of tan δ (loss tangent) for evaluating the temperature dependency of the polymer compositions is shown in Figure 2. Note that HNBR 1 to 3 used in Polymer Compositions 1 to 9 exhibited viscosity or fluidity at 25°C.

[0193] <<Methods for Measuring and Evaluating Physical Properties>> The methods for measuring and evaluating the physical properties of the polymer compositions, conductive material compositions, electrode films, and secondary batteries used in the examples and comparative examples described below are as follows.

[0194] <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 using a Buchner funnel. The precipitate was rinsed directly on the Buchner funnel with purified water and then dissolved in tetrahydrofuran (THF) to obtain a solution. The obtained solution was dropped again into purified water, and the filtration and washing steps using purified water were repeated. The precipitate was redissolved in THF to obtain a molecular weight measurement sample.

[0195] <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 a molecular weight measurement sample. An HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, and three separation columns were connected in series. The packings used were, in order, Tosoh Corporation's "TSK-GEL SUPER AW-4000," "AW-3000," and "AW-2500." The oven temperature was 40°C, and the eluent was an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr. The measurement was performed at a flow rate of 0.6 mL / min. The concentration of the measurement sample was adjusted to 1% using a solvent consisting of the eluent, and 20 microliters was injected. The weight-average molecular weight and Z-average molecular weight are values ​​in terms of polystyrene. The weight average molecular weight (Mw) was evaluated as follows: A for 70,000 or less, B for more than 70,000 and 100,000 or less, and C for more than 100,000.

[0196] <Preparation of a solution with a solid content of 20% by mass> 80 parts by mass of NMP was placed in a stainless steel container and stirred with a disper while heating to a liquid temperature of 80° C. A polymer heated to 80° C. in a separate container was added to NMP so that the polymer concentration was 20% by mass, and after stirring for 1 hour, it was confirmed with a spoon or the like that no undissolved polymer remained on the liquid surface, container wall, or bottom. Then, the solid content was measured and corrected with NMP so that the solid content was 20% by mass, thereby preparing a polymer solution.

[0197] <Viscosity Measurement of Solution with Solid Content of 20% by Mass> The prepared polymer solution was left to stand in a thermostatic bath at 25°C for at least 1 hour, and then immediately measured using a B-type viscometer at a rotor rotation speed of 60 rpm. The viscosity was evaluated as follows: less than 500 mPa s: A; 500 mPa s or more but less than 1000 mPa s: B; 1000 mPa s or more but less than 3000 mPa s: C; and more than 3000 mPa s: D. Note that in Comparative Example 1-4, the solid content concentration was less than 20% by mass, so measurement was not performed.

[0198] <Measurement of Viscoelasticity of Polymer Composition> (Preparation of Sample Piece) A fluororesin mold was cut out to fit a measurement 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, producing a sample piece. The polymer compositions of the examples were viscous and could not be separated from the fluororesin mold as they were, so they were cooled with liquid nitrogen and solidified before being removed from the fluororesin mold. A plate was heated to 80°C to ensure a constant sample thickness, and the sample piece was placed on it, and the thickness was corrected using the measurement jig. It was also confirmed that the produced sample piece did not contain any bubbles.

[0199] (Dynamic Viscoelasticity Test: Evaluation of Strain Dependence) The dynamic viscoelasticity (strain dependency) of the polymer was measured using a viscoelasticity measuring device: MCR302e (Anton Paar). Specifically, using parallel plates with a diameter of 25 mm, the GAP was set to the thickness of the sample, and measurements were performed under conditions of a temperature of 100°C, a frequency of 10 Hz, and a strain of 0.01 to 10%. The strain dependency of the polymer was evaluated using a chart with strain on the horizontal axis and tan δ (loss tangent) on the vertical axis. Here, tan δ (loss tangent) is obtained by the formula: loss modulus (G") / storage modulus (G'). When tan δ is greater than 1 within the strain range of 0.01 to 10%, it is marked as ◯, and when it is 1 or less, it is marked as x.

[0200] (Dynamic Viscoelasticity Test: Evaluation of Temperature Dependence) The dynamic viscoelasticity (temperature dependency) of the polymer was measured using a viscoelasticity measuring device: MCR302e (Anton Paar). Specifically, using parallel plates with a diameter of 25 mm, the measurement was 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 of 30°C to 110°C, and a temperature decrease rate of 10°C / min. The temperature dependency of the polymer can be evaluated by reading the temperature at which tanδ (loss tangent) = 1 from a chart with temperature on the horizontal axis and tanδ (loss tangent) on the vertical axis. A was assigned to 40°C or higher and 80°C or lower, B to 30°C or higher and lower than 40°C or higher and lower than 80°C and 110°C or lower, C to lower than 30°C, and D to higher than 110°C.

[0201] (Method for measuring Mooney viscosity (ML1+4, 100°C) of polymer) Purified water was added dropwise to a polymer composition to coagulate the polymer. The coagulated product was recovered, washed with methanol, transferred to a petri dish, and vacuum-dried at 60°C for 12 hours to obtain 40 g of a flat plate sample for measurement. The Mooney viscosity (ML1+4, 100°C) was measured at a temperature of 100°C using an L-shaped rotor in accordance with Japanese Industrial Standard JIS K6300-1. It was not possible to measure the Mooney viscosity of HNBR1 to 3 used in Polymer Compositions 1 to 9 according to this measurement method.

[0202] <Evaluation of Dispersibility of Polymer Composition> 80 parts by mass of NMP was placed in a stainless steel container and stirred with a disperser while heating to a liquid temperature of 80° C. A polymer heated to 80° C. in a separate container was added to NMP so that the polymer concentration was 8% by mass, and after stirring for 1 hour, it was confirmed with a spoon or the like that no undissolved polymer remained on the liquid surface, container wall, or bottom. Then, the solid content was measured and corrected with NMP so that the solid content was 8% by mass, thereby preparing polymer solution X.

[0203] 98 parts by mass of the prepared polymer solution X was placed in a glass container, and carbon nanotubes JENOTUBE10B (average outer diameter 10 nm, BET specific surface area 230 m) were added. ２ 2 parts by mass of 100 ml of cellulose acetate (10% by mass of cellulose acetate / g, multi-walled CNT) was added to the glass container and allowed to stand for 1 hour without stirring. After that, samples were collected from the supernatant (10% height from the top of the glass container) and the bottom (10% height from the bottom of the glass container). Next, the amount dropped onto the tared aluminum dish (W1) was measured using a precision balance. The measured mass was designated as W2. After that, the aluminum dish was dried in an oven at 140°C for 1 hour, and the mass of the aluminum dish was measured again using the precision balance (W3). The solid content of the supernatant and the bottom was calculated using the following formula 2: Solid content = (W3 - W1) / W2 Formula 2

[0204] The dispersibility of the polymer composition was then evaluated from the dispersion degree of the carbon nanotubes, calculated by dividing the solid content of the supernatant by the solid content of the bottom. A value of 0.75 or more but less than 1.25 was rated A, 0.5 or more but less than 0.75 or 1.25 or more but less than 1.50 was rated B, and less than 0.5 or 1.50 or more was rated C.

[0205] <Initial Viscosity of Conductive Material Composition> After leaving the conductive material composition to stand in a thermostatic bath at 25° C. for at least 1 hour, the initial viscosity was immediately measured using a Brookfield viscometer at a rotor rotation speed of 100 rpm. The initial viscosity was evaluated as follows: A for 100 mPa·s or more and less than 500 mPa·s, B for 500 mPa·s or more and less than 1000 mPa·s, C for 1000 mPa·s or more and 2000 mPa·s or less, and D for more than 2000 mPa·s.

[0206] <Evaluation of Dispersibility of Conductive Material Composition> The dispersibility of the conductive material composition was evaluated by measuring the cumulative particle diameter D50. The cumulative particle diameter D50 was measured based on particle size distribution using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd.; Partial LA-960V2). The laser light wavelength of this analyzer was 650 nm, and the detectors included one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. The measurement unit used a flow-type cell (sample cell) made of synthetic quartz. First, NMP, the same solvent as the dispersion, was introduced into a sample bath containing the sample cell, and circulation / ultrasonic cleaning was performed. The operating modes were: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, and stirring mode: continuous. Next, ultrasonic operation was performed at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds to remove air, and then a blank (background) measurement was performed. The particle size was determined by volume, and the particle refractive index was set to 1.920-0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). Sample preparation was performed by adding the dispersion liquid dropwise so that the laser light transmittance during measurement was 60%±1%. The measurement was performed in the following operating modes: circulation speed: 3, stirring speed: 7, and stirring mode: continuous. The dispersibility of the conductive material composition was evaluated as follows: A if the cumulative particle diameter D50 value was less than 3 μm, B if it was 3 μm or more but less than 10 μm, and C if it was 10 μm or more.

[0207] <Evaluation of storage stability of conductive material composition> The conductive material composition was left to stand in a thermostatic chamber at 40°C for one week, and then cooled to 25°C. The viscosity over time was immediately measured using a B-type viscometer at a rotor rotation speed of 100 rpm. The storage stability was evaluated as the viscosity over time (after one week at 40°C) divided by the initial viscosity, with A being rated for 0.8 or more and less than 3.0, B being rated for 3.0 or more and less than 5.0, and C being rated for less than 0.8 or 5.0 or more.

[0208] <Evaluation of Adhesion of Electrode Film> The adhesion of the electrode film was evaluated by measuring the peel strength. The composite slurry was applied to the electrode using an applicator so that the coating weight per unit area of ​​the electrode was 20 mg / cm ２After coating on aluminum foil so that the coating was formed, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Two 90mm x 20mm rectangles were then cut with the coating direction as the long axis. Peel strength was measured using a tabletop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and evaluated using a 180-degree peel test method. Specifically, a 100mm x 30mm double-sided tape (No. 5000NS, manufactured by Nitoms Inc.) 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. The layer was peeled off while being pulled from below to above at a constant speed (50mm / min). The average stress value at this time was taken as the peel strength. The adhesion of the electrode film was evaluated as follows: A for a peel strength of 1.0 N / cm or more, B for a peel strength of 0.7 N / cm or more but less than 1.0 N / cm, C for a peel strength of 0.5 N / cm or more but less than 0.7 N / cm, and D for a peel strength less than 0.5 N / cm.

[0209] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery> A laminated lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). A constant-current, constant-voltage charge (cutoff current 1.0 mA (0.02 C)) was performed at a charge current of 10 mA (0.2 C) and a charge cut-off voltage of 4.2 V, followed by a constant-current discharge at a discharge current of 10 mA (0.2 C) and a discharge cut-off voltage of 2.5 V. This operation was repeated three times, and then a constant-current, constant-voltage charge (cut-off current 1.0 mA (0.02 C)) was performed at a charge current of 10 mA (0.2 C) and a charge cut-off voltage of 4.2 V, followed by constant-current discharge at discharge currents of 0.2 C and 3 C until the discharge cut-off voltage of 2.5 V was reached, and the discharge capacity was calculated for each. The rate characteristics can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, as shown in Equation 3 below. Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%) Equation 3 Rate characteristic was evaluated as follows: A if the rate characteristic was 80% or more, B if it was 70% or more but less than 80%, C if it was 60% or more but less than 70%, and D if it was less than 60%.

[0210] <Evaluation of High-Temperature Cycle Characteristics of Lithium-Ion Secondary Battery> A laminated lithium-ion secondary battery was placed in a thermostatic chamber at 45°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). A constant-current, constant-voltage charge (cutoff current 1.25 mA (0.025 C)) was performed at a charge current of 50 mA (1 C) with a charge cutoff voltage of 4.2 V, followed by a constant-current discharge at a discharge current of 50 mA (1 C) with a discharge cutoff voltage of 2.5 V. This operation was repeated 200 times. 1 C was the current value required to discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the 100th 1 C discharge capacity to the third 1 C discharge capacity at 45°C, as shown in Equation 4 below. The high-temperature cycle characteristics were evaluated as follows: A for 90% or more, B for 85% to less than 90%, C for 80% to less than 85%, and D for less than 80%. High temperature cycle characteristic = 100th 1C discharge capacity / 3rd 1C discharge capacity × 100 (%) Formula 4

[0211] Example 2-1 84.0 parts of N-methyl-2-pyrrolidone (NMP) and 8.0 parts of a polymer composition (solid content concentration 20% by mass) were placed in a stainless steel container and stirred using a disperser. Thereafter, 8 parts of CNT1 were taken and added while stirring with the disperser. A fine emulsion screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON) and batch-dispersed at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size measured with a grind gauge was 200 μm or less. The mixture was then passed through a high-magnetic force mag filter (manufactured by Eishin, surface magnetic flux density 17000 gauss) to prepare a carbon material pre-dispersion composition. Thereafter, the carbon material pre-dispersion composition was sent to a bead mill (Mugen Flow (registered trademark), manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mm, and a circulation dispersion treatment (bead filling rate 80%, peripheral speed 13 m / s) was carried out for a residence time of 15 minutes. The number of circulations was 30. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Co., Ltd.), and a 24-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, and then the liquid to be dispersed was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, electromagnet equipped with 31 grid screens, each 10 cm in diameter and 1.3 cm in thickness) and subjected to a three-pass treatment. After that, 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 produce conductive material composition 1.

[0212] Examples 2-2 to 2-12, Comparative Examples 2-1 to 2-4 Conductive compositions were prepared in the same manner as in Example 1 according to the formulations in Table 2, and conductive compositions 2 to 12 and comparative conductive compositions 1 to 4 were prepared.

[0213] (Example 3-1) Capacity 150 cm ３Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVdF (polyvinylidene fluoride, Solvay, Solef #5130) was dissolved, and 14.5 parts by mass of NMP were weighed. Thereafter, 18.8 parts by mass of a conductive material composition (Conductive material composition 1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro, ARE-310). Further, 96.7 parts by mass of a positive electrode active material NCM1 was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotation / revolution mixer (Awatori Rentaro, ARE-310) to obtain a composite slurry.

[0214] Next, the composite slurry was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm ２ After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (electrode film 1). The electrode film (electrode film 1) was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a positive electrode (positive electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.1 g / cc.

[0215] Examples 3-2 to 3-16, Comparative Examples 3-1 to 3-4 Positive electrodes (positive electrode 2) to (comparative positive electrode 4) were produced by the same method as for producing the positive electrode (positive electrode 1), except that the positive electrode active material and conductive material composition were changed to those shown in Table 3.

[0216] (Example 4-1) A positive electrode (positive electrode 1) and a standard negative electrode were punched out to 45 mm x 40 mm and 50 mm x 45 mm, respectively, and the 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 electrolyte solution (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) was prepared, and 2 parts by mass of VC (vinylene carbonate) was added as an additive to 100 parts by mass of the mixed solvent, and then LiPF ６After 2 mL of a non-aqueous electrolyte solution prepared by dissolving 1M of ethylenediaminetetraacetic acid in the aluminum laminated bag was poured into the bag, the bag was sealed to prepare a laminated lithium ion secondary battery (Battery 1).

[0217] Examples 4-2 to 4-16, Comparative Examples 4-1 to 4-4 Laminated lithium ion secondary batteries (Battery 2) to (Comparative Battery 4) were produced by the same method as for producing the laminated lithium ion secondary battery (Secondary Battery 1), except that the positive electrode was changed as shown in Table 4.

[0218]

[0219]

[0220]

[0221]

[0222] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0223] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-222006, filed on December 27, 2023, the entire disclosure of which is incorporated herein by reference.

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) greater than 1 in the range of 0.01% to 10% strain 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 when a solution having a solid content concentration of 20% by mass is measured with a B-type viscometer, the viscosity at 25 °C and 60 rpm is less than 3000 mPa·s.

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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