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

Abstract

Provided is a polymer composition for an electrochemical element, which contains an amide-based liquid medium and a polymer that contains an aliphatic hydrocarbon unit and a nitrile group-containing unit, and which is characterized in that the tan [delta] (loss tangent) in the strain range of 0.01-10% is greater than 1 in a dynamic viscoelasticity measurement at a temperature of 100 DEG C and a frequency of 10 Hz.

Description

Technical Field

[0001] Embodiments of this disclosure relate to a polymer composition for electrochemical elements, a conductive material composition, a slurry composition, an electrode film, and a secondary battery. Background Technology

[0002] Lithium-ion batteries, as a representative type of electrochemical element, are characterized by their small size, light weight, high energy density, and ability to be repeatedly charged and discharged. Due to these characteristics, they are used in a wide range of applications. In the field of rechargeable batteries, the electrode, especially the positive electrode which lacks conductivity, readily exhibits electrode characteristics when using highly conductive micro-carbon nanotubes or structurally well-developed carbon materials such as carbon black in a well-dispersed state. Therefore, research is underway to use polymers with dispersibility to disperse conductive materials, thereby improving the characteristics of rechargeable batteries.

[0003] As a technique for effectively dispersing conductive materials in an adhesive composition for secondary battery electrodes, Patent Document 1 discloses the following: using a copolymer (e.g., hydrogenated nitrile rubber) having alkylene structural units and nitrile-containing monopolymer units, and a Mooney viscosity (ML1+4, 100°C) of 40 or less as an adhesive composition for secondary battery electrodes.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2017 / 010093 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In the technology disclosed in Patent Document 1, the Mooney viscosity of the copolymer in the adhesive composition is set to 40 or less to facilitate adsorption of the copolymer onto the surface of the conductive material, suppress agglomeration of the conductive material, and improve the dispersibility of the conductive material. On the other hand, in the technology disclosed in Patent Document 1, the Mooney viscosity of the copolymer in the adhesive composition is 5 or more to obtain the adsorption stability of the copolymer on the conductive material and maintain the dispersion stability of the conductive material.

[0009] However, to further improve the dispersibility of the conductive material, it is desirable to develop new polymer compositions for more microscopic observation. Furthermore, when the conductive material breaks during dispersion treatment using polymer compositions, small fragments of the conductive material are contained within the electrode film, resulting in insufficient formation of the conductive network and potentially degrading the battery characteristics of the secondary battery.

[0010] One of the objectives of this disclosure is to provide a polymeric composition for electrochemical elements that provides a conductive material composition with good dispersibility, a conductive material composition comprising the polymeric composition for electrochemical elements, a slurry composition, an electrode film formed using the slurry composition, and a secondary battery.

[0011] Technical means to solve the problem

[0012] Through diligent research, the inventors discovered that, as a polymeric composition for electrochemical elements, using a polymer and an amide-based liquid medium, a conductive material can be dispersed in a dispersion. This polymer, measured at 100°C and 10 Hz, exhibits a tanδ (loss tangent) greater than 1 within a strain range of 0.01% to 10% and contains aliphatic hydrocarbon units and nitrile-containing units. Furthermore, it was found that by using this polymeric composition for electrochemical elements, both the dispersibility of the conductive material in the dispersion and the conductivity in the electrode film can be achieved. Specifically, since the wetting-promoting effect of the conductive material is enhanced in the dispersion, the viscosity increase during dispersion treatment can be suppressed, improving the initial dispersibility of the conductive material. Furthermore, a high concentration of the conductive material can be achieved in the dispersion. Additionally, when using the polymeric composition to disperse the conductive material, the viscoelasticity of the dispersion can be appropriately controlled according to the tanδ of the polymer, preventing breakage of the conductive material during dispersion treatment. As a result, not only can a well-developed conductive network be formed in the electrode film obtained using the dispersion, but also the margin for formulation design can be increased. Thus, the conductive material is uniformly distributed in the electrode film, and the shape of the conductive material is maintained, enabling the provision of electrochemical devices with high output, high capacity, and long lifetime.

[0013] That is, this disclosure relates to the following implementation methods. However, the implementation methods of this disclosure are not limited to the following.

[0014] [1] A polymer composition for an electrochemical element comprising a polymer containing aliphatic hydrocarbon units and nitrile units and an amide liquid medium, wherein the polymer has a tanδ (loss tangent) greater than 1 in a dynamic viscoelasticity test at a temperature of 100°C and a frequency of 10 Hz, within a strain range of 0.01% to 10%.

[0015] [2] According to the polymer composition for electrochemical elements described in [1], the polymer is measured at a frequency of 10 Hz and a strain of 0.1% at a temperature of 80°C or below when the temperature is increased at 10°C / min within a temperature range of 30°C to 110°C to achieve a tanδ (loss tangent) = 1.

[0016] [3] The polymer composition for electrochemical elements according to [1] or [2], wherein when the viscosity of a solution containing the polymer and N-methyl-2-pyrrolidone and having a solid content of 20% by mass is measured using a type B viscometer, the viscosity at 25°C and 60 rpm is less than 3000 mPa·s.

[0017] [4] The polymer composition for electrochemical elements according to any one of [1] to [3], 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-containing unit is 25% by mass or more and 50% by mass or less.

[0018] [5] The polymer composition for electrochemical elements according to any one of [1] to [4], wherein the Z-average molecular weight of the polymer is 10,000 or more and 250,000 or less.

[0019] [6] A conductive material composition comprising a polymeric composition for an electrochemical element according to any one of [1] to [5] and a conductive material.

[0020] [7] A slurry composition comprising a polymer composition for an electrochemical element according to any one of [1] to [5], a conductive material, and an active substance.

[0021] [8] An electrode membrane is formed using a slurry composition comprising a polymeric composition for an electrochemical element according to any one of [1] to [5], a conductive material, and an active substance.

[0022] [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 an electrochemical element polymer composition according to any one of [1] to [5], a conductive material, and an active substance.

[0023] The effects of the invention

[0024] The embodiments of this disclosure provide a polymer composition for electrochemical elements capable of providing a conductive material composition with good dispersibility, a conductive material composition comprising the polymer composition for electrochemical elements, a slurry composition, an electrode film formed using the slurry composition, and a secondary battery. Attached Figure Description

[0025] [ Figure 1 ] Figure 1 A graph representing the tanδ (loss tangent) of the strain dependence evaluation of the polymer composition.

[0026] [ Figure 2 ] Figure 2 A graph showing the tanδ (loss tangent) of the temperature dependence evaluation of polymer compositions. Detailed Implementation

[0027] The following describes in detail, as embodiments of the present disclosure, polymer compositions for electrochemical elements, conductive material compositions, slurry compositions, electrode films, and secondary batteries. However, the present invention is not limited to the following embodiments, and also includes embodiments implemented within the scope of the present invention without altering the spirit of the invention.

[0028] In this disclosure, carbon nanotubes are sometimes referred to as "CNT" and carbon black as "CB". Acrylonitrile butadiene rubber is sometimes referred to as "NBR" and hydrogenated acrylonitrile butadiene rubber as "HNBR". Furthermore, in this disclosure, polymeric compositions of electrochemical elements are sometimes simply referred to as polymeric compositions.

[0029] <Aggregate>

[0030] In one embodiment of this disclosure, the polymer is a polymer comprising at least an aliphatic hydrocarbon unit and a nitrile-containing unit. Hereinafter, the polymer will sometimes be referred to as a nitrile polymer.

[0031] An aliphatic hydrocarbon unit is a unit containing an aliphatic hydrocarbon structure, preferably a unit containing only an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure can be saturated or unsaturated, substituted or unsubstituted, chain-like or cyclic. Preferably, the aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure, and may also contain unsaturated aliphatic hydrocarbon structures. The aliphatic hydrocarbon structure preferably contains at least a straight-chain aliphatic hydrocarbon structure, and may also contain branched aliphatic hydrocarbon structures.

[0032] Examples of aliphatic hydrocarbon units include: alkylene units, alkenyl units, alkyl units, alkane trimethyl units, alkane tetramethyl units, etc. Aliphatic hydrocarbon units preferably contain at least an alkylene unit.

[0033] An alkylene unit is a unit containing an alkylene structure, preferably a unit containing only an alkylene structure. The alkylene structure is preferably a straight-chain alkylene structure or a branched alkylene structure.

[0034] The alkylene unit is preferably a unit represented by the following general formula (1A).

[0035] General formula (1A)

[0036] [Chemistry 1]

[0037]

[0038] In general formula (1A), n represents an integer of 0 or 1 or higher. n can be 1 to 20, 2 to 10, or 3 to 5. n is preferably an integer of 2 or higher, more preferably an integer of 3 or higher. n is preferably an integer of 5 or lower, more preferably an integer of 4 or lower. Particularly preferred is n = 3.

[0039] The alkylene unit is preferably a unit represented by the following general formula (1B).

[0040] General formula (1B)

[0041] [Chemistry 2]

[0042]

[0043] In general formula (1B), n represents an integer greater than or equal to 1. n can 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. Particularly preferred is n = 2.

[0044] There are no particular limitations on the method of introducing alkylene units into the polymer, for example, the following methods (1a) or (1b) can be listed.

[0045] In the method of (1a), a polymer is prepared by using a monomeric composition containing a conjugated diene monomer and by a polymerization reaction. The prepared polymer comprises monomeric units derived from the conjugated diene monomer. In this disclosure, "monomer units derived from the conjugated diene monomer" are sometimes referred to as "conjugated diene monomer units," and monomeric units derived from other monomers are sometimes similarly omitted. Subsequently, at least a portion of the conjugated diene monomer units is converted into alkylene units by hydrogenation. In this disclosure, "hydrogenation" is sometimes referred to as "hydrogenation." The finally obtained polymer comprises units obtained by hydrogenation of the conjugated diene monomer units as alkylene units.

[0046] Furthermore, the conjugated diene monomeric unit comprises at least one monomeric unit having a carbon-carbon double bond. For example, the 1,3-butadiene monomeric unit as a conjugated diene monomeric unit comprises at least one monomeric unit selected from the group consisting of monomeric units having a cis-1,4 structure, monomeric units having a trans-1,4 structure, and monomeric units having a 1,2 structure, and may also comprise two or more monomeric units. Additionally, the conjugated diene monomeric unit may also comprise a monomeric unit that does not have a carbon-carbon double bond and contains a branch point. In this disclosure, a "branch point" refers to a branch point in a branched polymer; when the conjugated diene monomeric unit comprises a monomeric unit containing a branch point, the polymer produced is a branched polymer.

[0047] In the method of (1b), a polymer is prepared by using a monomeric composition containing α-olefin monomers and by a polymerization reaction. The prepared polymer contains α-olefin monomer units. The final polymer contains α-olefin monomer units as alkylene units.

[0048] Of these methods, method (1a) is preferred in terms of ease of polymer production. The conjugated diene monomer has 4 or more carbon atoms, preferably 4 or more and 6 or less. Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. The alkylene unit preferably includes a unit obtained by hydrogenating the conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), more preferably a unit obtained by hydrogenating the 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer can be used alone or in combination of two or more.

[0049] Hydrogenation is preferably carried out by selectively hydrogenating conjugated diene monomer units. Examples of known hydrogenation methods include oil layer hydrogenation and aqueous layer hydrogenation.

[0050] Hydrogenation can be carried out using conventional methods. For example, hydrogenation can be performed by treating a polymer having conjugated diene monomer units with hydrogen in the presence of a hydrogenation catalyst while the polymer is dissolved in a suitable solvent. Examples of hydrogenation catalysts include: iron, nickel, palladium, rhodium, platinum, copper, their alloys, and compounds.

[0051] In the method of (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more, and more preferably 4 or more. The α-olefin monomer preferably has 6 or fewer carbon atoms, more preferably 5 or fewer. Examples of α-olefin monomers include ethylene, propylene, 1-butene, and 1-hexene. One α-olefin monomer may be used alone, or two or more may be used in combination.

[0052] The alkylene unit is preferably at least one selected from the group consisting of units containing a straight-chain alkylene structure and units containing a branched alkylene structure, more preferably at least one selected from the group consisting of units containing only a straight-chain alkylene structure and units containing only a branched alkylene structure, and even more preferably at least one selected from the group consisting of units represented by formula (1B) and units represented by formula (1C).

[0053] In the aliphatic hydrocarbon unit, based on the total mass of the aliphatic hydrocarbon units (i.e., when the mass of the aliphatic hydrocarbon units is set to 100% by mass), the content of the alkylene unit is preferably 60% by mass or more, more preferably 70% by mass or more, further 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 set to 100% by mass), the content of the alkylene unit may be, for example, less than 100% by mass, 99.5% by mass or less, 99% by mass or less, or 98% by mass or less. The content of the alkylene unit may be 100% by mass.

[0054] Based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of 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 set to 100% by mass), the content of 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.

[0055] The nitrile-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 containing only an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a straight-chain or branched alkylene structure. The nitrile-containing unit may also contain a unit containing an alkyl structure substituted with a nitrile group, or a unit containing only an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile-containing unit is preferably one.

[0056] The nitrile-containing unit is preferably a unit represented by the following general formula (2A).

[0057] General formula (2A)

[0058] [Chemistry 3]

[0059]

[0060] In general formula (2A), n represents an integer of 2 or more. n can 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. Particularly preferred is n = 2.

[0061] The nitrile-containing unit is preferably a unit represented by the following general formula (2B).

[0062] General formula (2B)

[0063] [Chemistry 4]

[0064]

[0065] In general formula (2B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

[0066] The method of introducing nitrile-containing units into the polymer is not particularly limited, but a method of producing the polymer by means of a monomeric composition containing nitrile-containing monomers and a polymerization reaction is preferred (method (2a)). The polymer obtained at the end contains units derived from nitrile-containing monomers as nitrile-containing units. Examples of nitrile-containing monomers that can form nitrile-containing units include monomers containing polymerizable carbon-carbon double bonds and nitrile groups. For example, compounds containing α,β-vinyl unsaturated groups with nitrile groups can be listed, specifically acrylonitrile, methacrylonitrile, etc. In particular, from the viewpoint of improving the intermolecular forces between polymers and / or between polymers and the dispersed material (adsorbate), nitrile-containing monomers are preferably those containing acrylonitrile. One nitrile-containing monomer can be used alone, or two or more can be used in combination.

[0067] Based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of the nitrile-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 set to 100% by mass), the content of the nitrile-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 also be 40% by mass or less. By setting the content of the nitrile-containing unit within the aforementioned range, the adsorption of the dispersed material and its affinity for the liquid medium can be controlled, allowing the dispersed material to exist stably in the liquid medium. In addition, the affinity of the polymer for the electrolyte can also be controlled, thereby preventing adverse conditions such as the polymer dissolving in the electrolyte within the battery and increasing the electrolyte resistance. For example, based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of the nitrile-containing unit can be 10% to 80% by mass, 20% to 60% by mass, or 30% to 40% by mass. Preferably, the total amount of the acrylonitrile-containing unit and the methacrylonitrile-containing unit satisfies these ranges, and more preferably, the acrylonitrile-containing unit satisfies these ranges.

[0068] As a preferred embodiment, the polymer may have the following composition: based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of aliphatic hydrocarbon units is 50% by mass or more and 75% by mass or less, and the content of nitrile-containing units is 25% by mass or more and 50% by mass or less. As a more preferred embodiment, the polymer comprises alkylene units and nitrile-containing units. More preferably, the polymer has the following composition: based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of alkylene units is 50% by mass or more and 75% by mass or less, and the content of nitrile-containing units is 25% by mass or more and 50% by mass or less.

[0069] The polymer may also contain alkenyl units; alkyl units; alkane trimethyl units, alkane tetramethyl units, and other units containing branching points as aliphatic hydrocarbon units. Units containing branching points are different from units containing branched alkylene structures and units containing branched alkyl structures.

[0070] An alkenyl unit is a unit containing an alkenyl structure, preferably a unit containing only an alkenyl structure. The alkenyl structure is preferably a linear alkenyl structure or a branched alkenyl structure.

[0071] The subalkenyl unit is preferably at least one selected from the group consisting of units comprising a linear subalkenyl structure and units comprising a branched subalkenyl structure, and more preferably at least one selected from the group consisting of units comprising only a linear subalkenyl structure and units comprising only a branched subalkenyl structure.

[0072] For example, when a polymer is obtained by the method described in (1a), sometimes the conjugated diene monomer unit having a carbon-carbon double bond within the unit remains in the molecule without hydrogenation. The resulting polymer may contain the conjugated diene monomer unit having a carbon-carbon double bond within the unit as an alkenyl unit.

[0073] The alkyl unit is a unit containing an alkyl structure (wherein, it is a unit that is not equivalent to other aliphatic hydrocarbon units such as branched alkylene units, units containing nitrile groups, units containing amide groups, and units containing carboxyl groups), and preferably a unit containing only an alkyl structure. The alkyl structure is preferably a straight-chain alkyl structure or a branched alkyl structure.

[0074] The alkyl unit is preferably composed of at least one selected from the group consisting of units comprising a straight-chain alkyl structure and units comprising a branched alkyl structure, more preferably comprising at least one selected from the group consisting of units comprising only a straight-chain alkyl structure and units comprising only a branched alkyl structure. The number of carbon atoms in the alkyl unit can be 1 to 20, 2 to 10, 3 to 8, or 4 to 6. Examples of alkyl units include: n-butyl, sec-butyl, tert-butyl, isobutyl, n-pentyl, isopentyl, neopentyl, n-hexyl, isohexyl, etc.

[0075] For example, when a polymer is obtained by the method described in (1a) or (1b), it is preferable to introduce at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit in the polymer, preferably in the form of a terminal group of the polymer. The resulting polymer may contain these monomer units as alkyl units.

[0076] An alkane trimethyl unit is a unit containing an alkane trimethyl structure, preferably a unit containing only an alkane trimethyl structure. An alkane tetramethyl unit is a unit containing an alkane tetramethyl structure, preferably a unit containing only an alkane tetramethyl structure.

[0077] For example, when a polymer is obtained by the method described in (1a), the conjugated diene monomer unit in the polymer is a monomer unit without a carbon-carbon double bond within the unit, and sometimes it is introduced into the molecule in the form of a monomer unit containing branch points. In this case, the final polymer obtained is a branched polymer, which may contain aliphatic hydrocarbon units containing branch points, such as alkane tri-units or alkane tetra-units. When the aliphatic hydrocarbon units contain units containing branch points, the polymer is a branched polymer. The branched polymer may be a mesh polymer. The polymer containing units containing branch points can be three-dimensionally adsorbed onto the dispersed material, thus further improving dispersibility and stability.

[0078] Polymers can contain any type of unit. Examples of arbitrary units include those containing amide groups and those containing carboxyl groups.

[0079] The amide-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 containing only an alkylene structure substituted with an amide group. The alkylene structure is preferably a linear or branched alkylene structure. The amide-containing unit may also contain a unit containing an alkyl structure substituted with an amide group, or a unit containing only an alkyl structure substituted with an amide group. The amide-containing unit preferably contains one amide group.

[0080] In this disclosure, the content of the unit can be determined by the amount of unit used, nuclear magnetic resonance (NMR) and / or infrared spectroscopy (IR).

[0081] The polymer in the embodiments of this disclosure is characterized in that, in a dynamic viscoelasticity measurement at a temperature of 100°C and a frequency of 10 Hz, the tanδ (loss tangent) is greater than 1 in the range of strain from 0.01% to 10%.

[0082] The following insights were obtained: when the strain range is 0.01% to 10% and the tanδ is below 1, the wettability of the polymer composition to the conductive material decreases. It is believed that by having a tanδ greater than 1, sufficient wettability of the polymer composition to the conductive material can be obtained, thus improving initial dispersion.

[0083] While improved dispersion efficiency leads to increased dispersibility of the conductive material, excessive dispersion can potentially cause breakage. It has been observed that when tanδ is below 1 within a strain range of 0.01% to 10%, excessive dispersion during the dispersion process using a polymer composition can easily lead to conductor breakage. When tanδ is greater than 1, appropriate viscoelasticity of the dispersion can be used to control the dispersion process and prevent breakage. Therefore, it is believed that adequate shape retention of the conductive material in the electrode film can improve battery performance. For example, when using elongated conductive materials such as carbon nanotubes as the dispersant, breakage can be suppressed, resulting in a well-dispersible dispersion while maintaining the elongated shape. Furthermore, conductive material compositions formed by using such polymers and dispersing carbon nanotubes can maintain their shape in the electrode film, thus exhibiting high conductivity.

[0084] Furthermore, if tanδ is greater than 1 within the strain range of 0.01% to 10%, the polymer exhibits viscosity or fluidity. Polymers possessing viscosity or fluidity can suppress the increase in viscosity of the polymer solution. From this perspective, the initial dispersibility of the conductive material can also be improved. Additionally, initial dispersibility can be maintained, resulting in long-term storage stability. The polymer is more preferably exhibiting viscosity or fluidity at 40°C. The polymer may also be liquid at 40°C. After removing the solvent by heating the polymer composition at 140°C for 1 hour, the polymer preferably exhibits viscosity or fluidity at 40°C, but may also be liquid.

[0085] The polymer is preferably a polymer with a tanδ (loss tangent) greater than 1 in the dynamic viscoelasticity test at a temperature of 100°C and a frequency of 10 Hz, within the range of strain from 0.01% to 10%, but it can be 1 to 100, 1 to 50, 1 to 10, or 1 to 5.

[0086] In this disclosure, it is observed that the strain range of 0.01% to 10% in the tanδ (loss tangent) measurement is a factor affecting the adsorption of the copolymer to the conductive material, the solubility of the copolymer, the viscosity of the copolymer, and its stickiness in the polymer composition. By controlling the tanδ (loss tangent) of the copolymer to be greater than 1 in all ranges of 0.01% to 10% of the strain, it is beneficial to improve the dispersibility of the conductive material and the shape retention of the conductive material in the polymer composition. Based on this characteristic, the polymer can be used as a dispersant in conductive material compositions.

[0087] When using the polymer composition in the embodiments of this disclosure, its effects can be achieved in both medium dispersion and medium-free dispersion. In medium dispersion, the tanδ (loss tangent) of the polymer is appropriately controlled, thus improving the collision efficiency of the dispersion medium during the dispersion treatment with the addition of a conductive material to the polymer composition, and the appropriate viscoelasticity of the dispersion can be used to suppress the breakage of the conductive material. In medium-free dispersion, the tanδ (loss tangent) of the polymer is appropriately controlled, thus applying shear stress uniformly and sufficiently to the dispersion during the dispersion treatment with the addition of a conductive material to the polymer composition, improving dispersion efficiency, and the appropriate viscoelasticity of the dispersion can be used to suppress the breakage of the conductive material.

[0088] In the embodiments of this disclosure, the polymer is preferably measured at a frequency of 10 Hz and a strain of 0.1%, and the measurement temperature at which tanδ (loss tangent) = 1 is 80°C or below when the temperature is increased at a rate of 10°C / min within a temperature range of 30°C to 110°C. Hereinafter, the measurement temperature at which tanδ (loss tangent) = 1 is also referred to as the measurement temperature (tanδ = 1).

[0089] The measurement temperature (tanδ=1) in the polymer may be less than 110°C or below 100°C, preferably below 80°C, but may also be below 70°C, below 60°C, below 50°C, below 40°C, or below 30°C. Regarding the measurement temperature (tanδ=1), tanδ may be greater than 1 in the entire temperature range of 30°C to 110°C.

[0090] By setting the measurement temperature (tanδ=1) to 80°C or below, the initial dispersibility can be further improved under normal temperature conditions when the conductive material, as the dispersing phase, is dispersed in the polymer composition. Furthermore, the adsorption of the polymer to the conductive material can be maintained within the polymer composition, thus further improving long-term storage stability. Additionally, even if excessive dispersion occurs due to increased dispersion efficiency during the dispersion treatment of the conductive material using the polymer composition, breakage of the conductive material can be suppressed, resulting in a conductive material composition that maintains the shape of the conductive material. From this perspective, the measurement temperature (tanδ=1) is preferably 30°C or higher and 110°C or lower, more preferably 30°C or higher and 80°C or lower, and even more preferably 40°C or higher and 80°C or lower.

[0091] The tanδ of the polymer is calculated using Equation 1 below and is measured in a dynamic viscoelasticity test.

[0092] tanδ = Loss elasticity coefficient (G'') / Storage elasticity coefficient (G') Equation 1

[0093] The strain dependence of polymers can be measured using a viscoelastic measuring device (e.g., MCR302e, Anton Paar). Specifically, a parallel plate with a diameter of 25 mm is used, with the GAP set to the sample thickness, and the measurement is performed at a temperature of 100°C, a frequency of 10 Hz, and a strain range of 0.01%–10%. The result is determined whether tanδ is greater than 1 within the strain range of 0.01%–10%.

[0094] The temperature dependence of polymers can be measured using a viscoelastic measuring apparatus (e.g., MCR302e, Anton Paar). Specifically, the measurement is performed using a parallel plate with a diameter of 25 mm 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. Within the temperature range of 30°C to 110°C, the temperature at which tanδ = 1 is determined.

[0095] The polymer sample for dynamic viscoelasticity testing is obtained by adding a polymer solution dropwise into a fluoropolymer mold, followed by drying to remove the solvent. In the case of a viscous polymer, it is removed from the fluoropolymer mold and used after being cooled and solidified by liquid nitrogen. Specifically, the tanδ of the strain range of 0.01% to 10% and the measurement temperature (tanδ=1) can be measured according to the method described in the examples.

[0096] There are no particular limitations on the methods for controlling the tanδ of nitrile polymers. For example, tanδ can be controlled by changing the composition (type and content of structural units, hydrogenation rate, etc.), structure (linear chain ratio, etc.), molecular weight, and production conditions (polymerization temperature, molecular weight adjustment dosage, etc.) of the nitrile polymer. For example, the following methods can be used to control the tanδ of nitrile polymers.

[0097] In control method a, tanδ is increased by increasing the amount of molecular weight modifier used in the production of the polymer.

[0098] In control method b, the polymer's tanδ is increased by adding an alkali to hydrolyze the nitrile groups in the nitrile-containing structural units, thereby increasing the polymer's tanδ.

[0099] In control method c, tanδ is increased by applying mechanical shear stress to the polymer.

[0100] Regarding control method b, when preparing a polymer containing aliphatic hydrocarbon units and nitrile-containing units, an alkali can be added for adjustment. Alternatively, the prepared polymer containing aliphatic hydrocarbon units and nitrile-containing units can be dissolved in a solvent capable of dissolving it, and then an alkali can be added for adjustment. The added alkali can be at least one selected from the group consisting of inorganic bases and organic hydroxides (organic bases). When adjusting with alkali, tanδ can be increased in a shorter time when the added solvent is heated to a degree that does not ignite or boil.

[0101] 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, etc. Among these, alkali metal or alkaline earth metal hydroxides or alkoxides are preferred from the viewpoint that they can readily provide cations.

[0102] 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 tert-butoxide, lithium n-butoxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium tert-butoxide, sodium n-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium tert-butoxide, and potassium n-butoxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Preferably, at least one of the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, and sodium tert-butoxide is used, and more preferably, sodium hydroxide. Furthermore, the metal contained in the inorganic base may be a transition metal.

[0103] Organic hydroxides are salts comprising an organic cation and a hydroxide ion. Examples of organic hydroxides include: trimethyl-2-hydroxyethyl ammonium hydroxide, tetramethyl ammonium hydroxide, cetyltrimethyl ammonium hydroxide, hexadecyltrimethyl ammonium hydroxide, trimethylphenyl ammonium hydroxide, 3-trifluoromethyl-phenyltrimethyl ammonium hydroxide, benzyltrimethyl ammonium hydroxide, etc. Among these, at least one selected from the group consisting of trimethyl-2-hydroxyethyl ammonium hydroxide and tetramethyl ammonium hydroxide is particularly preferred.

[0104] Alkanolamines can also be used as bases. Examples of alkanolamines include: monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, methylethanolamine, and methyldiethanolamine.

[0105] Based on the mass of the nitrile polymer, the amount of alkali 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 alkali 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. These ranges are preferred when controlling the tanδ of the nitrile polymer.

[0106] In control method b, the increase in tanδ can be achieved by mixing a polymer containing aliphatic hydrocarbon units and nitrile-containing units, an alkali, and a liquid medium. Any components can be further mixed. There are no restrictions on the order in which the polymer, alkali, and liquid medium are added to the container or the method of mixing them; they can be added to the container simultaneously; or the polymer, alkali, and liquid medium can be added to the container separately; or either or both of the polymer and alkali can be mixed with the liquid medium to prepare a polymer-containing liquid and / or an alkali-containing liquid, and then the polymer-containing liquid and / or alkali-containing liquid can be added to the container. Particularly for efficient modification of the nitrile groups, the following method is preferred: while stirring, an alkali dispersion is added to a polymer solution in which the polymer is dissolved in the liquid medium. A disperser (dispersant) or homogenizer can be used for stirring. As the liquid medium, any liquid medium suitable for the polymer composition described later can be used.

[0107] There are no restrictions on the mixing temperature, but heating to above 30°C can accelerate the modification. Additionally, to promote the modification of the nitrile polymer, trace amounts of water and / or alcohol may be added to the container. Water and / or alcohol may be added to the container simultaneously with the polymer and alkali, or before adding the nitrile polymer and alkali, or simultaneously with or after the nitrile polymer and alkali. Furthermore, if the nitrile polymer, alkali, or any other component used as needed has high hygroscopicity, water may be included in the form of hygroscopic water. Based on the mass of the nitrile polymer, 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.

[0108] Examples of alcohols include: methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, hexanediol, pentanediol, glycerol, glycerol, thiodiglycol, etc. 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 particularly preferably in the presence of water.

[0109] Regarding method c, adjustment can be made by applying mechanical shear stress during the production of the polymer containing aliphatic hydrocarbon units and nitrile-containing units. Alternatively, adjustment can be made by applying mechanical shear stress after dissolving the produced polymer containing aliphatic hydrocarbon units and nitrile-containing units in a liquid medium in which it can be dissolved. Tanδ can also be controlled by applying mechanical shear stress to the polymer before dissolution using rollers or kneaders, but it is more efficient to use nitrile polymers as dispersants in a liquid medium in which they can be dissolved. Therefore, applying shear stress in the polymer solution state is more preferable.

[0110] Methods for applying shear stress to a polymer in solution include using dispersion components such as homogenizers and Silverson mixers. While shear stress can also be applied using dispersers, methods using dispersion components such as homogenizers and Silverson mixers, which can apply higher shear stress, are preferred. Methods for applying mechanical shear stress to a polymer before dissolution include using dispersion components such as kneaders and two-roll mills.

[0111] The polymer in the embodiments of this disclosure is preferably such that, when a solution containing the polymer and N-methyl-2-pyrrolidone with a solid content of 20% by mass is measured using a type B viscometer, the viscosity at 25°C and 60 rpm is less than 3000 mPa·s.

[0112] In one embodiment, the polymer exhibits improved initial dispersibility due to a tanδ greater than 1 within a strain range of 0.01% to 10%, thus achieving low viscosity in the polymer solution. Low viscosity of the polymer solution can be achieved even with a high polymer content. By using polymers with these viscosity properties, low viscosity can be achieved in polymer compositions and conductive material compositions.

[0113] When measured using a type B 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 between 10 mPa·s and 3000 mPa·s, or between 100 mPa·s and 1000 mPa·s.

[0114] The viscosity of the polymer solution is measured using a type B viscometer at a rotor speed of 60 rpm after the polymer solution has been allowed to stand in a constant temperature bath at 25°C for more than 1 hour. Specifically, the measurement can be performed according to the method described in the examples.

[0115] In embodiments of this disclosure, the polymer is preferably of average molecular weight of 10,000 or more and 250,000 or less.

[0116] The molecular distribution of the polymer, determined by the Z-average molecular weight, is controlled on the high molecular weight side. When the Z-average molecular weight is 250,000 or less, the proportion of high molecular weight molecules decreases, and the polymer exhibits viscosity and flowability. When a conductive material is used as a dispersant, the wettability of the conductive material is improved, further enhancing the initial dispersion. 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 especially preferred. Furthermore, when the Z-average molecular weight is 10,000 or more, adsorption of the conductive material can be maintained in the conductive material composition, thus maintaining dispersion.

[0117] For example, the Z-average molecular weight of the polymer can be 10,000–250,000, 10,000–200,000, 20,000–150,000, 30,000–100,000, 30,000–60,000, or 30,000–50,000. By using the polymer within these ranges, both initial dispersibility and storage stability can be achieved when preparing conductive material compositions.

[0118] The weight-average molecular weight (Mw) of the polymer in the embodiments of this disclosure can be 5,000 to 100,000, 10,000 to 70,000, or 20,000 to 50,000. Within these ranges, the wettability of the conductive material, wherein the carbon material, and the effect of inhibiting agglomeration can be obtained, and the storage stability of the polymer composition can be further improved.

[0119] In this disclosure, the Z-mean molecular weight and weight-average molecular weight are determined using a molecular weight determination sample via gel permeation chromatography (GPC) equipped with a refractive index (RI) detector. Specifically, the determination can be performed according to the methods described in the examples. The Z-mean molecular weight and weight-average molecular weight are converted values ​​for polystyrene.

[0120] The following method is used to prepare a test sample for determining the molecular weight of the polymer contained in a polymeric composition. The polymeric composition is added dropwise to purified water to precipitate the polymer, and the precipitate is recovered. The precipitate is dissolved in tetrahydrofuran (THF) to obtain a solution. The solution is washed with purified water, and the purified precipitate is redissolved in THF to obtain the test sample. Specifically, the test sample can be prepared according to the method described in the examples for determining the molecular weight.

[0121] Regarding the wettability of the polymer to the conductive material, a dispersion of the polymer, the conductive material, and the liquid medium can be prepared, and the evaluation is based on the ratio of the amount of solid component in the supernatant to that in the bottom after standing for 24 hours. Specifically, a polymer solution containing 8% by mass of N-methyl-2-pyrrolidone (NMP) is prepared. The conductive material is added to the polymer solution to prepare a polymer dispersion containing 2% by mass of the conductive material. The polymer dispersion is allowed to stand without stirring for 1 hour, and after standing for 1 hour, samples are collected from the supernatant and the bottom for testing. The wettability of the polymer to the conductive material can be evaluated based on the mass ratio of (amount of solid component in the supernatant) / (amount of solid component in the bottom). This mass ratio is preferably 0.5 or more and less than 1.5, more preferably 0.75 or more and less than 1.25. Regarding the aforementioned mass ratio, JENOTUBE 10B carbon nanotubes (average outer diameter 10 nm, Brunauer-Emmett-Teller, BET specific surface area 230 m²) can be used as the conductive material. 2 The wettability of the polymer ( / g, multilayer CNT) is evaluated relatively. Specifically, the evaluation can be performed according to the methods described in the examples.

[0122] <Liquid Medium>

[0123] In polymer compositions, the liquid medium is not particularly limited as long as it is mixed with the polymer. In this disclosure, "mixed with the polymer" means that when 0.5 g of the polymer is dissolved in 100 g of a liquid medium at 25°C, the insoluble component is less than 10% by mass. The insoluble component can be recovered by filtering the dissolved residual polymer from the solution, then hot-air drying the recovered polymer, and measuring its mass.

[0124] The liquid medium is preferably a soluble polymer, and more preferably a solvent with a high dielectric constant of a soluble polymer. In this disclosure, "soluble polymer" refers to a solution in which, at 25°C, 0.5 g of the polymer is dissolved in 100 g of a liquid medium, and no insoluble components are visually identifiable, and the solution becomes transparent without becoming turbid. When using a liquid medium containing a soluble polymer, good dispersion can be easily obtained when a conductive material is added.

[0125] In one embodiment, the liquid medium is preferably a solvent containing any one of the high dielectric constant solvents, or a mixture of two or more solvents. Alternatively, one or more other solvents may be mixed with the high dielectric constant solvent. In this disclosure, a "high dielectric constant solvent" is defined as having a relative permittivity of 2.5 or more, more preferably 25 or more, as recorded in solvent handbooks, etc., at 20°C. When using a high dielectric constant solvent as the liquid medium to prepare a conductive material composition, the interaction between the nitrile group, the conductive material, and the liquid medium in the polymer of the described embodiment can be improved. From the viewpoint of the polymer's solubility, the relative permittivity of the high dielectric constant solvent is preferably 60 or less, more preferably 50 or less, at 20°C. In one embodiment, the relative permittivity of the high dielectric constant solvent is preferably 30 to 50.

[0126] In one embodiment, the liquid medium is preferably a non-aqueous liquid medium. The polymer of the 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 the desired good dispersion. Therefore, the liquid medium is preferably substantially free of water. "Substantially free of water" means that water is not intentionally added in an amount exceeding the level contained by moisture absorption, etc. 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 made without adding water, the conductive material composition sometimes contains about 0.1% by mass of water due to moisture absorption, etc. From this point of view, the liquid medium is preferably an organic solvent, more preferably a polar organic solvent that does not provide protons.

[0127] In polymer compositions using polymers comprising aliphatic hydrocarbon units and nitrile-containing units, amide-based liquid media are preferred. Amide-based liquid media exhibit excellent solubility in the polymer. Furthermore, as high dielectric constant solvents, amide-based liquid media enhance interaction with the polymer, contributing to improved initial dispersion. Additionally, as non-proton-donating polar organic solvents, amide-based liquid media contribute to the long-term stability of the polymer, as well as conductive materials and adhesive resins.

[0128] 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, and N-methylcaprolactam. From the viewpoint of superior polymer solubility and high dielectric constant, it is preferable to use at least one of N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), more preferably using N-methyl-2-pyrrolidone (NMP) alone, and also preferably using N-methyl-2-pyrrolidone (NMP) in combination with other liquid media.

[0129] Furthermore, examples of other polar organic solvents that do not provide protons as liquid media include: heterocyclic, sulfoxide, sulfone, lower ketone, and carbonate liquid media. More specifically, the following can be listed.

[0130] Heterocyclic systems: cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolone, γ-butyrolactone, etc.

[0131] Sulfoxides: such as dimethyl sulfoxide.

[0132] Sulfones: hexamethylphosphoric acid triamine, sulfolane, etc.

[0133] Lower ketones: acetone, methyl ethyl ketone, etc.

[0134] Carbonate series: diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, etc.

[0135] Others: tetrahydrofuran, acetonitrile, etc.

[0136] <Polymer Composition>

[0137] The polymer composition for an electrochemical element, as one embodiment of this disclosure, comprises a polymer and an amide-based liquid medium. The polymer comprises aliphatic hydrocarbon units and nitrile-containing units, as detailed in the description. The amide-based liquid medium is also detailed in the description.

[0138] In the polymer composition, the nitrile polymer can be 1% to 50% by mass, 2% to 40% by mass, or 5% to 30% by mass relative to the total mass of the polymer composition. Even when the polymer composition contains a high concentration of 20% by mass or more, a dispersion that provides the dispersibility of a conductive material while suppressing the breakage of the conductive material and maintaining the shape of the conductive material during dispersion processing can be provided by having a tanδ greater than 1 within the strain range of 0.01% to 10%.

[0139] In the polymer composition, the nitrile polymer may be 50% to 100% by mass, 75% to 100% by mass, or 80% to 99.8% by mass relative to the total mass of solid components.

[0140] In addition to nitrile polymers, other polymers may be included in the polymer composition. In the polymer composition, relative to 100 parts by weight of the nitrile polymer, the other polymers may be 0 to 100 parts by weight, 0.1 to 50 parts by weight, or 1 to 10 parts by weight. The polymer composition may also not contain other polymers.

[0141] In the polymer composition, the amide 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.

[0142] In addition to the amide-based liquid medium, the polymer composition may also contain other liquid media. The amount of other liquid media 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 may also not contain other liquid media. When using the polymer composition to disperse conductive materials, using a nitrile polymer as the main component, and more preferably using only a nitrile polymer, allows for appropriate control of the viscoelasticity of the polymer composition, further suppressing the breakage of the conductive material during dispersion.

[0143] The solid content of the polymer composition can be 1% to 60% by mass, 2% to 50% by mass, or 5% to 35% by mass. The solid content of the polymer composition can be appropriately set according to the molecular structure of the polymer, the type of liquid medium, the intended use of the polymer composition, and the type of conductive material to which it is dispersed. In this disclosure, the solid content is the total amount of components excluding the liquid medium. Specifically, the polymer composition is thoroughly dried in an oven at a temperature above which the liquid medium can evaporate; this is defined as the solid content only. The mass of the solid content of the polymer composition is measured, and the substance obtained by dividing the solid content by the total mass of the polymer composition is defined as the solid content.

[0144] The polymer composition may contain any additional 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 of the nitrile polymer, a component mixed in from the synthetic raw materials of the nitrile polymer, etc., as detailed in the description below.

[0145] Furthermore, a polymeric composition refers to a composition that does not contain conductive materials or active substances. In a polymeric composition, the conductive component may be less than 5% by mass, less than 1% by mass, or less than 0.1% by mass, and it may substantially contain no conductive component. Similarly, in a polymeric composition, the active substance may be less than 5% by mass, less than 1% by mass, or less than 0.1% by mass, and it may substantially contain no active substance.

[0146] <Conductive Material Composition>

[0147] The conductive material composition according to one embodiment of this disclosure comprises a polymer composition for electrochemical elements and a conductive material. Details of the polymer composition for electrochemical elements are as described above. The conductive material will be described below.

[0148] <Conductive Materials>

[0149] There are no particular limitations on the conductive material, but carbon materials are preferred. Examples of conductive carbon materials include: graphite, carbon black, graphene, multilayer graphene, fullerene; fibrous carbon materials such as carbon nanotubes and carbon nanofibers. They can be used alone or in combination of two or more. Examples of graphite include: artificial graphite, flake graphite, block graphite; and natural graphite such as amorphous graphite.

[0150] Carbon materials serve to form conductive paths within the electrode. From the viewpoint of minimizing the risk of interruption due to the expansion and contraction of the electrode film, fibrous carbon materials are preferred, and more preferably fibrous carbon materials. In terms of conductivity, ease of acquisition, and cost, carbon black and / or carbon nanotubes are preferred. Furthermore, from the viewpoint of reducing raw material costs or forming an efficient conductive network, it is also possible to use a combination of two or more materials of the same type with different physical properties. Examples of materials of the same type with different physical properties include, for example, 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.

[0151] The carbon purity of a carbon material is expressed as the percentage (by mass%) of carbon atoms in the carbon material. Higher carbon purity is preferred; preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the carbon material. By setting the carbon purity within this range, it is possible to prevent the formation of dendrites due to impurities such as metals, which could lead to adverse conditions such as short circuits.

[0152] <Carbon nanotubes>

[0153] Carbon nanotubes are formed by winding planar graphite into a cylindrical shape, and can include single-layer carbon nanotubes, multi-layer carbon nanotubes, and combinations thereof. Single-layer carbon nanotubes have a structure consisting of a single layer of graphite. Multi-layer carbon nanotubes have a structure consisting of two or more layers of graphite. Furthermore, the sidewalls of carbon nanotubes may not be graphite. For example, carbon nanotubes may also include sidewalls with an amorphous structure.

[0154] The shape of carbon nanotubes is not limited. Various shapes can be listed, including needle-like, cylindrical, fishbone-like (or cup-like), playing card-like (small thin sheets), and coil-like. In this embodiment, the shape of the carbon nanotubes is preferably needle-like or cylindrical. Carbon nanotubes can be a single shape or a combination of two or more shapes.

[0155] Examples of carbon nanotube forms include: graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon nanotubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes can exist in a single form or in a combination of two or more of these forms.

[0156] 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. Furthermore, 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 aforementioned range, a good conductive network can be easily formed within the electrode when applied to a secondary battery. During charging and discharging, the active material inside the secondary battery can be utilized uniformly and effectively, thereby suppressing the degradation of the active material and further improving the cycle characteristics of the secondary battery. In addition, the average outer diameter of the carbon nanotubes can be calculated by observing and photographing the carbon nanotubes using a transmission electron microscope, and then selecting any 300 carbon nanotubes from the obtained photographs and measuring their respective outer diameters.

[0157] 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. Furthermore, the fiber length of the carbon nanotubes is preferably 100 μm or less, more preferably 20 μm or less. The average fiber length of the carbon nanotubes can be calculated by observing and photographing the carbon nanotubes using a scanning electron microscope, and then selecting any 300 carbon nanotubes from the obtained photographs and measuring the fiber length of each. The average fiber length of the carbon nanotubes in the conductive dispersion is also preferably within the aforementioned range.

[0158] The aspect ratio is the value obtained by dividing the fiber length of a carbon nanotube by its outer diameter. A representative aspect ratio can be determined using the average fiber length and average outer diameter. Conductive materials with higher aspect ratios exhibit higher conductivity when forming electrodes. The aspect ratio of carbon nanotubes is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. Furthermore, the aspect ratio of carbon nanotubes is preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

[0159] The preferred BET specific surface area of ​​carbon nanotubes is 100 m². 2 / g or more, preferably 150 m 2 / g or more, and preferably 200 m 2 / g or more. Furthermore, the specific surface area of ​​carbon nanotubes is preferably 1200 m². 2 / g or less, more preferably 1000 m 2 / g or less, and preferably 700 m 2 / g or less. The BET specific surface area of ​​carbon nanotubes can be determined according to Japanese Industrial Standards (JIS) Z 8830 by the BET method based on nitrogen adsorption.

[0160] The carbon purity of carbon nanotubes is expressed as the percentage (mass%) of carbon atoms contained in the carbon nanotubes. Relative to 100% mass of carbon nanotubes, the carbon purity is preferably 80% mass, more preferably 90% mass or more, even more preferably 95% mass or more, and further preferably 98% mass or more, and can be 99% mass or more or 99.5% mass or more. By setting the carbon purity within this range, it is possible to prevent dendrite formation due to impurities, which could lead to adverse conditions such as short circuits. Furthermore, the carbon purity of carbon nanotubes can be determined using an ICP-based spectral analyzer, employing the method described in the examples.

[0161] <Carbon Black>

[0162] Carbon black is manufactured from carbon-based microparticles through the incomplete combustion of oil or gas, controlling various properties. Carbon black possesses a secondary structure (aggregate) where primary particles are linked together in a bead-like pattern, and a tertiary structure (agglomerate) formed by further aggregation of these secondary structures. Both secondary and tertiary structures are collectively referred to as the "structure." When observed using an electron microscope, primary particles appear spherical, but these particles are not chemically independent entities; they are linked to adjacent primary particles within the aggregate through chemical bonds, forming the secondary structure. Conversely, secondary structures are chemically independent entities that aggregate through intermolecular forces to form the tertiary structure. Therefore, the conductivity within a secondary structure is higher than the conductivity between secondary structures containing contact resistance. It can be said that for obtaining electrodes with excellent conductivity, it is effective to deagglomerate the tertiary structure while preserving the secondary structure as much as possible. Furthermore, the secondary structure is sometimes simply referred to as the "structure."

[0163] As carbon black, various types of carbon black can be used, such as acetylene black, furnace black, hollow carbon black, channel black, thermal cracking black, and Ketjen black. Alternatively, carbon black that has undergone conventional oxidation treatment or graphitization treatment can also be used.

[0164] The oxidation treatment of carbon black involves subjecting it to high-temperature treatment in air or secondary treatment using nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenolic, quinone, carboxyl, and carbonyl groups onto the surface of the carbon black. This process is generally carried out to improve the dispersibility of the carbon black.

[0165] Commercially available carbon blacks include, for example, Super P-Li (manufactured by TIMCAL), Ketjen Black EC-300J and EC-600JD (manufactured by Lion), Denka Black, Denka Black Li-400, and Li-335 (manufactured by DENKA, acetylene black), but are not limited to these, and two or more can be used in combination.

[0166] The average primary particle size of carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and even more preferably 25 nm to 100 nm.

[0167] The average primary particle diameter of carbon black can be calculated as follows: First, observe and photograph the carbon black using a transmission electron microscope. Then, select any 100 spherical carbon black primary particles from the photographs and measure their outer diameters.

[0168] The preferred BET specific surface area for carbon black is 10 m².2 / g or more and 1500 m 2 / g or less, more preferably 40 m 2 / g or more and 1000 m 2 / g or less, and preferably 100 m 2 / g or more and 850 m 2 / g or less. When the BET specific surface area is within the specified range, a small amount of efficient conductive network can be formed, reducing the amount of conductive material in the electrode. This increases the freedom of battery design, such as increasing the amount of active material or binder resin. Furthermore, during electrode slurry preparation, the composite of active material and carbon black becomes easier to achieve, thus easily obtaining an electrode film with a homogeneous conductive network of carbon black coated on the surface of the active material. This suppresses electrolyte decomposition reactions at the interface between the electrolyte and the active material, improving the battery's cycle characteristics. The BET specific surface area of ​​carbon black can be determined by the BET method described in JIS Z 8830.

[0169] In the conductive material composition, from the viewpoint of dispersibility and storage stability, the conductive material can be 0.1% to 30% by mass, 1% to 25% by mass, or 3% to 20% by mass relative to the total mass of the conductive material composition.

[0170] When carbon nanotubes are used as the conductive material in a conductive material composition, the content of carbon nanotubes relative to the total mass of the conductive material composition is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more. Furthermore, the content of carbon nanotubes is preferably 20% by mass or less, more preferably 10% by mass or less. By setting the content of carbon nanotubes within the aforementioned range, the carbon nanotubes can be present well and stably without causing sedimentation or gelation. Additionally, the content of carbon nanotubes is preferably appropriately adjusted based on the BET specific surface area of ​​the carbon nanotubes, their affinity for the liquid medium, the dispersing ability of the dispersant, etc., to obtain a conductive material composition with appropriate flowability or viscosity. According to one embodiment, since a nitrile polymer is used, the initial dispersibility and shape maintenance of the carbon nanotubes are good, and carbon nanotubes can be included at a higher concentration. For example, the carbon nanotube content relative to the total mass of the conductive material composition can be in the range of 0.1% to 20% by mass, but can also be 1% to 20% by mass, 3% to 20% by mass, 4% to 20% by mass, 5% to 20% by mass, or 8% to 20% by mass.

[0171] When carbon black is used as the conductive material in a conductive material composition, the carbon black content relative to the total mass of the conductive material composition is preferably 0.1% by mass or more, more preferably 1% by mass or more, further preferably 5% by mass or more, and even more preferably 10% by mass or more. Furthermore, 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 aforementioned range, the carbon black can be present well and stably without causing sedimentation or gelation. Additionally, the carbon black content is preferably appropriately adjusted based on the BET specific surface area of ​​the carbon black, its affinity for liquid media, the dispersing ability of the dispersant, etc., to obtain a conductive material composition with appropriate flowability or viscosity. According to one embodiment, since a nitrile polymer is used, the initial dispersibility and shape retention of the carbon black are good, allowing for the inclusion of carbon black at a higher concentration. For example, the carbon black content relative to the total mass of the conductive material composition can be in the range of 0.1% to 30% by mass, but can also be 1% to 20% by mass, 5% to 20% by mass, 10% to 20% by mass, 12% to 20% by mass, or 15% to 20% by mass.

[0172] In the conductive material composition, the nitrile polymer can be 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, since a nitrile polymer is used, the initial dispersibility and shape retention of the conductive material are good. In addition, the nitrile polymer can function even in small amounts relative to the conductive material. For example, the nitrile polymer can be 0.05 to 5 parts by mass relative to 100 parts by mass of the conductive material, but it can be 0.05 to 0.5 parts by mass, or 0.05 to 0.2 parts by mass.

[0173] In the conductive material composition, the solid component may be 0.1% to 30% by mass, 1% to 25% by mass, or 3% to 20% by mass.

[0174] When conductive materials are dispersed using a disperser based on collision with the medium, such as a bead mill, or when the process of repeatedly passing the disperser through the medium for an extended period of time is required, the conductive material sometimes breaks, resulting in short-sided carbon material. If short-sided carbon material is produced, the viscosity of the conductive material composition decreases, and the gloss of the coating obtained by applying and drying the conductive material composition increases; therefore, based solely on these evaluation results, the dispersion is considered good. However, the short-sided carbon material has high contact resistance, making it difficult to form a conductive network, which can sometimes degrade the resistance of the electrode. According to one embodiment, since a nitrile polymer is used, the initial dispersibility and the shape retention of the conductive material are good. Therefore, a conductive network is easily formed in the electrode film, which can improve rate characteristics and cycle characteristics in secondary batteries.

[0175] In one embodiment, the conductive material composition may also include any additional components as needed. For example, the conductive material composition may suitably include dispersants, wetting agents, surfactants, pH adjusters, wetting and penetrating agents, leveling agents, polymer components, etc., as optional components, without hindering the purpose of the present invention. These optional components may be added at any time before, during, or after the preparation of the conductive material composition. Additionally, these optional components may be added at any time during the preparation of the polymer composition. Furthermore, these optional components may be added at any time during the preparation of the slurry composition. These timings can be combined and the components added in stages.

[0176] As a dispersant and polymeric component, known substances other than nitrile polymers can be used. Particularly preferred are at least one selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, and polyvinyl acetal. Polymers in which other substituents have been introduced into a portion of the polymer, or modified polymers, can be used. When using a dispersant or polymeric component, the weight-average molecular weight is preferably 30,000 or less, more preferably 20,000 or less, and most preferably 3,000 or more. Deviations from these ranges may hinder the adsorption of the nitrile polymer onto the conductive material.

[0177] The dispersibility of the conductive material in the conductive material composition can also be evaluated by the median particle size (μm) determined using a laser diffraction / scattering particle size analyzer. When the median particle size (μm) is determined using a laser diffraction / scattering particle size analyzer, the particle size of the aggregated conductive material particles can be estimated based on the particle-based scattered light intensity distribution. The median particle size (μm) is preferably 0.4 or more. Furthermore, the median particle size (μm) is preferably 5.0 or less, more preferably 2.0 or less. By setting the median particle size (μm) to the aforementioned range, a conductive material composition with an appropriate dispersion state can be obtained. If the median particle size (μm) is below the aforementioned range, there is an aggregated state of conductive material; conversely, if it is above the aforementioned range, a large number of finely cut conductive materials are generated, making it difficult to form an efficient conductive network.

[0178] The dispersibility of the conductive material in the conductive material composition can also be evaluated by measuring the gloss (i.e., the intensity of reflected light at 60° relative to the angle of incidence) of a coating obtained by applying it to a smooth glass substrate and then sintering and drying it. Regarding light incident on the coating, the better the dispersibility, the smoother the coating surface, and therefore the higher the gloss. Conversely, the worse the dispersibility, the more light scattering occurs due to the unevenness of the coating surface, and therefore the lower the gloss.

[0179] The coating film preferably has a gloss level of 5 or higher at 60°, more preferably 20 or higher, even more preferably 30 or higher, and particularly preferably 40 or higher. Furthermore, the coating film preferably has a gloss level of 120 or lower at 60°, more preferably 110 or lower, and even more preferably 100 or lower. By setting these ranges, a conductive material composition with an appropriate dispersion state can be obtained. If the gloss level is below these ranges, a condensed conductive material exists; if the gloss level is above these ranges, a large amount of finely chopped conductive material is produced, making it difficult to form an efficient conductive network.

[0180] The thixotropic index (TI) of the conductive material composition can be calculated by dividing the viscosity (mPa·s) measured at 60 rpm using a type B viscometer by the viscosity (mPa·s) at 6 rpm. The TI value is preferably 1.5 or higher and 5.0 or lower. In one embodiment, the TI value is more preferably 1.5 or higher and less than 3.0. A higher TI value indicates greater structural viscosity due to the entanglement of the conductive material, polymer, or other resin components, or the intermolecular forces thereof; a lower TI value indicates less structural viscosity. By setting the TI value within the aforementioned range, the intermolecular forces of the conductive material, polymer, or other resin components can be appropriately utilized while suppressing entanglement.

[0181] <Dispersion Methods>

[0182] Conductive material compositions can be manufactured, for example, by using a dispersion device to disperse and finely disperse the polymer composition and the conductive material. Furthermore, the dispersion process can be performed in multiple stages, with the timing of material addition arbitrarily adjusted.

[0183] Dispersion devices include, for example, kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, ring bead mills, grinding mills, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers.

[0184] From the viewpoint of promoting the wetting of the conductive material and dispersing coarse particles, it is more preferable to use a high-shear mixer in the initial dispersion process, and then disperse the conductive material while maintaining its aspect ratio. From this viewpoint, it is more preferable to use a high-pressure homogenizer. Furthermore, by dispersing using a high-pressure homogenizer followed by dispersion using a bead mill, the dispersion state can be homogenized while maintaining the fiber length. Alternatively, by using the polymer composition containing a nitrile polymer disclosed herein, a lower viscosity mixture can be prepared before dispersion. Therefore, by first dispersing using a bead mill to disperse the conductive material to a certain level and then dispersing it using a high-pressure homogenizer, a uniform dispersion state can also be achieved while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 60 MPa to 150 MPa, more preferably 60 MPa to 120 MPa.

[0185] Dispersion methods using dispersion devices include batch dispersion, through-flow dispersion, and circulating dispersion. Any one of these methods can be used, or a combination of two or more. Batch dispersion is a method that disperses the liquid without piping, performing the dispersion solely within the dispersion device itself. It is preferred for small-scale production due to its ease of operation. Through-flow dispersion includes a tank for supplying the liquid to be dispersed and a tank for receiving the liquid, both connected to the dispersion device, and the liquid passes through the dispersion device. Circulating dispersion involves returning the liquid to be dispersed in the tank after passing through the dispersion device, dispersing it while it circulates. All of these methods advance dispersion more with longer processing times; therefore, simply repeating the through-flow or circulating process until the target dispersion state is achieved is sufficient. Changing the tank size or processing time can increase the throughput. Through-flow dispersion is preferred because it more easily homogenizes the dispersion state compared to circulating dispersion. Circulating dispersion is also preferred because it simplifies the operation or manufacturing equipment compared to through-flow dispersion. In the dispersion process, the fragmentation of agglomerated particles, the dispersion of conductive materials, wetting, and stabilization are carried out sequentially or simultaneously. Depending on the method of execution, the final dispersion state varies. Therefore, it is preferable to manage the dispersion state in each dispersion process using various evaluation methods. For example, the methods described in the embodiments can be used for management.

[0186] <Slurry Composition>

[0187] The slurry composition according to one embodiment of this disclosure includes a polymer composition for electrochemical devices, a conductive material, and an active substance. Details regarding the polymer composition for electrochemical devices and the conductive material are as described above. The active substance will be described below.

[0188] The slurry composition may contain either 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 are sometimes simply referred to as "active material." Active material is the material fundamental to the battery reaction. Active material is classified into positive electrode active material and negative electrode active material according to its electromotive force. In this disclosure, the slurry composition containing either positive electrode active material or negative electrode active material is sometimes referred to as a "positive electrode slurry composition," a "negative electrode slurry composition," or simply a "slurry composition," respectively. To improve uniformity and processability, the slurry composition is preferably in slurry form.

[0189] <Positive Electrode Active Material>

[0190] There are no particular limitations on the positive electrode active material. For example, in secondary battery applications, metal oxides, metal sulfides, and other metal compounds that can reversibly dope or intercalate lithium ions, sodium ions, etc., as well as conductive polymers, can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn; composite oxides with lithium or sodium; inorganic compounds such as transition metal sulfides; polyanionic compounds; and Prussian blue compounds. Specifically, examples include MnO, V₂O₅, and V₆O. 13 The materials include transition metal oxide powders such as TiO2, layered lithium nickelate, lithium cobalt oxide, lithium manganese oxide, and lithium manganese oxide composite oxide powders with spinel structure, olivine-structured phosphoric acid compounds (i.e., lithium iron phosphate materials), transition metal sulfide powders such as TiS2 and FeS, layered sodium ferrite, sodium manganate, sodium chromate, sodium nickelate, and olivine-structured phosphoric acid compounds (i.e., sodium iron phosphate materials), etc. Additionally, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the aforementioned inorganic or organic compounds can be mixed and used.

[0191] The positive electrode active material is preferably a lithium composite oxide containing transition metals such as Al, Fe, Co, Ni, and Mn, more preferably a lithium composite oxide containing any one of Al, Co, Ni, and Mn, and particularly preferably a lithium composite oxide 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 alkaline due to the composition of the raw materials or the dissolution of metal ions. This can easily lead to gelation of the binder or deterioration of the dispersion state, thus sometimes significantly contributing to the problems of this disclosure. Therefore, the embodiments of this disclosure are particularly effective in the case of batteries containing active materials containing Ni and / or Mn.

[0192] <Negative Electrode Active Material>

[0193] There are no particular limitations on the negative electrode active material, as long as it can be doped or intercalated with lithium ions, sodium ions, etc. For example, metallic Li, its alloys, tin alloys, silicon alloys, lead alloys, and other alloy systems can be used. X TiO2, Li X Fe2O3, Li X Fe3O4, Li X Metal oxides such as WO2, conductive polymers such as polyacetylene and poly(p-phenylene oxide), highly graphitized carbon materials such as artificial graphite or natural graphite, and carbonaceous powders and resin-calcined carbon materials. Where x represents the quantity, and 0 < x < 1.

[0194] These negative electrode active materials can be used individually or in combination. Especially when using silicon alloy negative electrodes, the theoretical capacity is large, but conversely, the volume expansion is extremely large. Therefore, it is preferable to use them in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, or resin-calcined carbon materials.

[0195] When carbon nanotubes are used as the conductive material in the slurry composition, 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 (where the mass of the active material is set to 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, based on the mass of the active material (where the mass of the active material is set to 100% by mass). When carbon black is used as the conductive material, 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. It is also preferably 20% by mass or less, and even more preferably 10% by mass or less. Furthermore, carbon nanotubes and carbon black can be used together as the conductive material, or two or more can be used separately, but the total amount added is preferably within the range described above. If the amount is higher than the range, the amount of active material in the electrode decreases, resulting in a low battery capacity. Conversely, if the amount is lower than the range, the conductivity of the electrode and the battery may be insufficient.

[0196] Based on the mass of the active substance (with the mass of the active substance set as 100% by mass), the content of acrylonitrile polymer in the slurry composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more. Furthermore, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0197] <Adhesive Resin>

[0198] The slurry composition may also include a binder resin. The binder resin used in the slurry composition is a resin that can bond active substances, conductive materials, and other substances together. There are no particular restrictions on the binder resin, as long as it is a resin commonly used as a binder resin in coatings; it can be selected appropriately according to the purpose. That is, in addition to containing nitrile polymers, it may also contain resins that can bond active substances, conductive materials, and other substances together.

[0199] Examples of adhesive resins used in slurry compositions include: polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc., as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins such as carboxymethyl cellulose (CMC); elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Additionally, modified forms or mixtures of these resins, and copolymers, may also be used.

[0200] Of these, the adhesive resin used in the positive electrode composition is preferably a polymer or copolymer having fluorine atoms within its molecule, in terms of durability. Examples include polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene. Furthermore, the adhesive resin used in the negative electrode composition is preferably carboxymethyl cellulose (CMC), styrene-butadiene rubber, and polyacrylic acid, in terms of good adhesion.

[0201] In the non-volatile components of the slurry composition, the content of the adhesive resin used in the slurry composition is preferably 0.5% to 30% by mass, more preferably 0.5% to 25% by mass.

[0202] 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 substance (where the mass of the active substance is set to 100% by mass). Furthermore, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0203] Based on the mass of the slurry composition (with the mass of the slurry composition set as 100% by mass), the amount of solids in the slurry composition is preferably 30% by mass or more, more preferably 40% by mass or more. Furthermore, it is preferably 90% by mass or less, more preferably 80% by mass or less.

[0204] The slurry composition can be prepared using various methods known previously. Examples include: methods involving adding an active substance to a conductive material composition; methods involving adding an active substance to a conductive material composition followed by adding a binder resin; methods involving adding a binder resin to a conductive material composition followed by adding an active substance; and methods involving mixing the active substance with a binder resin and, if desired, a liquid medium before adding the conductive material composition. As a method for preparing a slurry composition containing carbon nanotubes as a conductive material, a preferred method is to add a binder resin to the conductive material composition, then add the active substance and disperse it. By using this method, the slurry composition can be prepared without disrupting the dispersion of the carbon nanotubes. The dispersion apparatus used for dispersion is not particularly limited. The dispersion components listed in the description of the conductive material composition can be used to obtain the slurry composition.

[0205] <Electrode film>

[0206] The electrode film, as one embodiment of this disclosure, is formed using a slurry composition. Details regarding the slurry composition are as described above. Alternatively, an electrode may be provided comprising a current collector and an electrode film formed on the current collector.

[0207] Electrode films can be obtained, for example, by coating a current collector with a slurry composition and allowing it to dry. Electrode films formed using a positive electrode slurry composition can be used as positive electrodes. Electrode films formed using a negative electrode slurry composition can be used as negative electrodes. In this disclosure, films formed using slurry compositions containing active substances are sometimes referred to as "electrode composite layers."

[0208] The material and shape of the current collector used in the formation of the electrode film are not particularly limited, and materials and shapes suitable for various secondary batteries can be selected. Examples of materials for the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Regarding the shape, a planar foil is generally used, but a current collector with a roughened surface, a perforated foil, or a mesh-like current collector can also be used. The thickness of the current collector is preferably around 0.5 μm to 30 μm.

[0209] There are no particular limitations on the method of applying the paste composition to the current collector, and known methods can be used. Specifically, examples of coating methods include: mold coating, dip coating, roller coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating. Examples of drying methods include, but are not particularly limited to, drying by means of a forced-air dryer, a warm-air dryer, an infrared heater, or a far-infrared heater.

[0210] Alternatively, after coating, the film can be rolled using a flatbed press, calendering roller, or similar method. The resulting film thickness is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0211] Electrode films formed using slurry compositions can also be used as a base layer for electrode composite layers. By providing such a base layer, the adhesion between the electrode composite layer and the current collector can be improved, or the conductivity of the electrode film can be increased.

[0212] <Electrochemical Components>

[0213] An electrochemical element can be provided through one embodiment of this disclosure. Suitable electrochemical elements include secondary batteries and capacitors. At least one electrode body of the electrochemical element may include an electrode film formed using a slurry composition. Details regarding the slurry composition and 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. Non-aqueous secondary batteries are preferred. Examples of capacitors include double-layer capacitors, lithium-ion capacitors, hybrid capacitors, and redox capacitors.

[0214] Secondary batteries

[0215] One embodiment of the secondary battery disclosed herein is a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive and negative electrodes comprises an electrode film formed using a slurry composition. Details regarding the slurry composition and the electrode film are as described above.

[0216] As the electrolyte, various previously known electrolytes capable of ion movement can be used. For example, the electrolyte may contain lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is phenyl), but is not limited to these. The electrolyte is preferably used in the form of an electrolyte solution dissolved in a non-aqueous solvent.

[0217] There are no particular limitations on non-aqueous solvents. Examples include: carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octyl lactone; ethylene glycol dimethyl ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxacyclopentane, 4-methyl-1,3-dioxacyclopentane, 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 can be used individually or in mixtures of two or more.

[0218] Non-aqueous electrolyte secondary batteries preferably include a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have undergone hydrophilic treatment, but are not particularly limited to these.

[0219] The structure of the non-aqueous electrolyte secondary battery in this embodiment is not particularly limited. In one embodiment, the non-aqueous electrolyte secondary battery typically includes a positive electrode and a negative electrode, as well as a separator as needed. The non-aqueous electrolyte secondary battery can be formed into various shapes, such as paper type, cylindrical type, button type, and stacked type, depending on the intended use.

[0220] Example

[0221] The following examples illustrate the invention in more detail. The invention is not limited to these examples unless it departs from its spirit. Furthermore, unless otherwise specified, "parts" means "parts by mass," and "%" means "% by mass." Additionally, the mixing amounts in the table are parts by mass, and values ​​other than solvents are converted values ​​for non-volatile components. Furthermore, empty columns in the table indicate no mixing.

[0222] The materials used in the embodiments and comparative examples are shown below.

[0223] • Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, liquid hydrogenated nitrile butadiene rubber, weight average molecular weight 30,000, alkylene structural units 66% by mass, nitrile-containing structural units 34% by mass), hereinafter referred to as HNBR2.

[0224] • Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural units 66% by mass, nitrile structural units 34% by mass), hereinafter referred to as HNBR4.

[0225] • Li-335: Denka Black (manufactured by Denka Corporation), acetylene black, average primary particle diameter 23 nm, BET specific surface area 141 m² 2 / g, carbon purity 99.9%), hereinafter referred to as CB1.

[0226] Cellseed NMC (LiNi) 0.6 Co 0.2 Mn 0.2 O2 (manufactured by Japan Chemical Industry, 100% non-volatile components), hereinafter referred to as NCM1.

[0227] S800 (LiNi) 0.8 Mn 0.1 Co 0.1 O2, gold and manufacturing, 100% non-volatile components), hereinafter referred to as NCM2.

[0228] NAT-7050 (LiNi) 0.8 Co 0.15 Al 0.05 O2 (manufactured by BASF Toda Battery Materials), hereinafter referred to as NCA.

[0229] • HED (trademark) LFP-400 (lithium iron phosphate, manufactured by BASF), hereinafter referred to as LFP.

[0230] <CNT1>

[0231] JENOTUBE 10B (manufactured by JEIO, with an average outer diameter of 10 nm and a BET specific surface area of ​​230 m²) was metered in a 120 L heat-resistant container. 2 10 kg of JENOTUBE 10B was placed in a heat-resistant container inside a furnace. Nitrogen gas was then introduced into the furnace, and air was purged while maintaining positive pressure. Once the oxygen concentration inside the furnace reached below 0.1%, the furnace was heated to 1600°C over 30 hours. Chlorine gas was then introduced at a rate of 50 L / min for 50 hours while maintaining the furnace temperature at 1600°C. Nitrogen gas was then introduced at a rate of 50 L / min, and the furnace was cooled while maintaining positive pressure to obtain purified JENOTUBE 10B. The carbon purity was 99.9%.

[0232] Then, the purified JENOTUBE 10B was processed using a dynamic mill (manufactured by Nippon Cokes Industries), with 8 mm diameter zirconia beads as the grinding medium, fed at an operating condition of 10.0 kg / h and processed at a circumferential speed of 5.0 m / s to obtain CNT1.

[0233] CNT1 was acid-decomposed using a microwave sample pretreatment system (Milestone-general, ETHOS 1) to extract the metals contained in the carbon material. The extract was analyzed using a multi-type ICP-ELISA system (Agilent 720-ES) to calculate the total amount of metals (iron, cobalt, nickel, copper, nickel, and chromium). The carbon purity of CNT1 was calculated to be 99.9%.

[0234] Carbon purity (%) = ((mass of carbon material - metal content) ÷ mass of carbon material) × 100

[0235] <CNT2>

[0236] JENOTUBE6A (manufactured by JEIO, with an average outer diameter of 6 nm and a BET specific surface area of ​​650 m²) was metered in a 120 L heat-resistant container. 2 10 kg of JENOTUBE6A was placed in a heat-resistant container inside a furnace. Nitrogen gas was then introduced into the furnace, and air was purged while maintaining positive pressure. Once the oxygen concentration in the furnace reached below 0.1%, the furnace was heated to 1600°C over 30 hours. Chlorine gas was then introduced at a rate of 50 L / min for 50 hours while maintaining the furnace temperature at 1600°C. Nitrogen gas was then introduced at a rate of 50 L / min, and the furnace was cooled while maintaining positive pressure to obtain purified JENOTUBE6A (CNT2).

[0237] CNT2 was acid-decomposed using a microwave sample pretreatment system (Milestone-general, ETHOS 1) to extract the metals contained in the carbon material. Subsequently, the extract was analyzed using a multi-mode ICP-ELISA system (Agilent 720-ES) to calculate the total amount of metals (iron, cobalt, nickel, copper, nickel, and chromium). The carbon purity of CNT2 was 99.9%.

[0238] <LFMP>

[0239] LFMP was synthesized via the following procedure: 200 g of dimethyl sulfoxide and 360 mmol of lithium hydroxide monohydrate were added to 150 g of pure water. To the resulting solution, 120 mmol of phosphoric acid was added using an 85% (w / w) aqueous solution, followed by 96 mmol of manganese(II) sulfate monohydrate and 24 mmol of ferric(II) sulfate heptahydrate. The resulting solution was transferred to an autoclave and heated for 4 hours at 150°C. After heating, the supernatant was discarded, yielding lithium manganese iron phosphate (LiMn) phosphate as a precipitate. 0.8 Fe 0.2 PO4. After washing the obtained lithium manganese iron phosphate with pure water, the supernatant was removed by centrifugation. This operation was repeated five times, and finally, pure water was added again to form a dispersion. Then, glucose, in the same weight as 15% of the lithium manganese iron phosphate in the dispersion, was added to the dispersion and dissolved. Pure water was then added to adjust the solid content concentration of the dispersion to 20% by weight, obtaining an LFMP dispersion. The obtained LFMP dispersion was dried using a spray dryer (manufactured by Fujisaki Electric Co., Ltd., MDL-050B) with hot air at 200°C to obtain secondary particles. The obtained secondary particles were heated in a rotary kiln at 700°C under nitrogen atmosphere for 4 hours to obtain carbon-coated LFMP particles (hereinafter referred to as LFMP).

[0240] <Polymer Composition>

[0241] [Synthesis of HNBR1]

[0242] HNBR1 was synthesized using the following procedure: 500 g of monochlorobenzene was added to a 1 L autoclave equipped with a stirrer and stirred. Simultaneously, 75 g of finely chopped nitrile rubber (Perbunan (registered trademark) 3430: 34% nitrile unit content, Mooney viscosity 32) was added using a rubber chopper and dissolved. After the nitrile rubber was completely dissolved, 4 phr of 1-hexene was added to the container, and the solution was stirred for 2 hours. At this point, 1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinedimethyl(tricyclohexylphosphine)-ruthenium(phenyl-methylene)dichloride, acting as a catalyst, was dissolved in 20 mL of monochlorobenzene and added to the container. The reaction mixture was stirred at 22 °C for 12 hours. After the reaction, a solution of tris-(triphenylphosphine)rhodium chloride (0.06 phr) in monochlorobenzene was added to the reactor, and the reactor was pressurized to 85 bar using hydrogen. The reaction mixture was stirred (500 rpm) and reacted at 135°C for 4 hours to obtain a polymer solution. After concentration to a certain extent using a rotary evaporator, the solution was injected into a stainless steel ball rod and dried in a vented heating oven heated to 140°C until the odor of monochlorobenzene disappeared, thus obtaining HNBR1. 1 The structural unit from which acrylonitrile originated, determined by H-NMR quantitative spectroscopy, is 34.

[0243] [Preparation of HNBR3]

[0244] 92 parts by mass of NMP were placed in a stainless steel container and heated to 80°C while stirring with a disperser. In another container, 8 parts by mass of HNBR2, heated to 80°C, were added to the NMP and stirred for 1 hour to prepare a polymer solution. 1000 parts by mass of methanol were placed in another stainless steel container and, while stirring at room temperature (25°C), the previously prepared polymer solution was added dropwise and allowed to solidify. The solution was then decanted and dried using a vented oven heated to 140°C. This process (preparation of the polymer solution, solidification with methanol, decantation, and drying) was repeated three times to obtain HNBR3. 1 The structural unit from which acrylonitrile originated, determined by H-NMR quantitative spectroscopy, is 34.

[0245] [Preparation of HNBR5]

[0246] 240 parts of deionized water, 2.5 parts of sodium alkylbenzene sulfonate as an emulsifier, 35 parts of acrylonitrile as a nitrile-containing monomer, and 0.85 parts of tert-dodecyl mercaptan as a chain transfer agent were sequentially added to a high-pressure reactor equipped with a stirrer. After nitrogen replacement of the interior, 65 parts of 1,3-butadiene as a conjugated diene monomer were introduced, and 0.25 parts of ammonium persulfate as a polymerization initiator were added. The polymerization reaction was carried out at a reaction temperature of 40°C. A polymer of acrylonitrile and 1,3-butadiene was then obtained. The polymerization conversion rate was 85%.

[0247] The obtained copolymer was treated with ion-exchanged water 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 added to a 1 L autoclave equipped with a stirrer. Nitrogen gas was purged for 10 minutes to remove dissolved oxygen from the solution. Then, 75 mg of palladium acetate, used as a catalyst for the hydrogenation reaction, was dissolved and added to 180 mL of ion-exchanged water containing 4 moles of nitric acid relative to palladium (Pd). After two purgings of the system with hydrogen, the contents of the autoclave were pressurized to 3 MPa with hydrogen and heated to 50 °C for 6 hours for hydrogenation.

[0248] Subsequently, the autoclave was restored to atmospheric pressure, and 25 mg of palladium acetate, used as a catalyst for the hydrogenation reaction, was dissolved and added to 60 mL of ion-exchanged water containing 4 moles of nitric acid relative to Pd. After two purgings of the system with hydrogen, the contents of the autoclave were heated to 50°C under a hydrogen pressure of 3 MPa for 6 hours for the hydrogenation reaction.

[0249] Afterward, the contents were brought back to room temperature, the system was set to a nitrogen environment, and then concentrated using an evaporator until the solid content was 40% to obtain an aqueous dispersion of the polymer.

[0250] Alternatively, an aqueous dispersion of the polymer was added dropwise to methanol to solidify the polymer, and the solidified material was then vacuum-dried at 60°C for 12 hours to obtain HNBR5. According to... 1 The structural units derived from acrylonitrile by H-NMR quantitative spectroscopy were 35%, and the Mooney viscosity (ML1+4, 100℃) was 10.

[0251] [Preparation of polymeric compositions]

[0252] (Polymer composition 1)

[0253] 800 parts by mass of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR1 were added. The mixture was stirred until HNBR1 was completely dissolved, thus obtaining polymer composition 1 (solid component concentration 20% by mass).

[0254] (Polymer composition 2 to polymer composition 3)

[0255] The dissolved polymer was changed to the polymer shown in Table 1, and polymer compositions 2 to 3 were obtained using the same method as polymer composition 1.

[0256] (Polymer composition 4)

[0257] 1000 cm³ 3 475 parts by weight of NMP and 25 parts by weight of NaOH (manufactured by Tosoh Corporation, Tosohpearl) were added to a plastic container. The mixture was dispersed at 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsor screen until the mixture became homogeneous. Then, the mixture was filtered through a nylon filter with a mesh size of 150 μm to prepare a NaOH dispersion (NaOH concentration 5% by weight).

[0258] 780 parts by weight of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by weight of HNBR2 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. Next, 20 parts by weight of NaOH dispersion (5% by weight) was added, and the mixture was stirred while adding air. The reaction vessel was maintained at 80°C for 12 hours under heating to obtain polymer composition 4 (20.1% by weight of solids).

[0259] (Polymer composition 5, polymer composition 8 to polymer composition 9)

[0260] The types and amounts of alkali added are changed to those shown in Table 1. Otherwise, polymer compositions 5, 8 to 9 are obtained using the same method as polymer composition 4.

[0261] (Polymer composition 6)

[0262] 1000 cm³ 3425 parts by weight of NMP and 75 parts by weight of NaOH (manufactured by Tosoh Corporation, Tosohpearl) were added to a plastic container. The mixture was dispersed at 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsifying screen until the mixture became homogeneous. The solution was then filtered through a nylon filter with a mesh size of 150 μm to prepare a NaOH dispersion (NaOH concentration 15% by weight).

[0263] 773.3 parts by mass of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR2 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. Next, 26.7 parts by mass of NaOH dispersion was added, and the mixture was stirred while adding air. The reaction vessel was maintained at 80°C for 12 hours, with simultaneous heating, to obtain polymer composition 6 (solid content concentration 20.4% by mass).

[0264] (Polymer composition 7)

[0265] The concentration of the solid components of the polymer was set to a certain value. The type and amount of alkali added were changed to those shown in Table 1. The amount of NMP was adjusted. Otherwise, the polymer composition 7 was obtained using the same method as polymer composition 6.

[0266] (Comparative polymer composition 1)

[0267] 800 parts by mass of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR4 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved, thus obtaining comparative polymer composition 1 (solids concentration 20% by mass).

[0268] (Comparative polymer composition 2)

[0269] 1000 cm³ 3 475 parts by weight of NMP and 25 parts by weight of NaOH (manufactured by Tosoh Corporation, Tosohpearl) were added to a plastic container. The mixture was dispersed at 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsifying screen until the mixture became homogeneous. The solution was then filtered through a nylon filter with a mesh size of 150 μm to prepare a NaOH dispersion.

[0270] 780 parts by mass of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR4 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. Next, 20 parts by mass of NaOH dispersion was added, and the mixture was stirred while adding air. The reaction vessel was maintained at 80°C for 12 hours while being heated, thus obtaining comparative polymer composition 2 (solid content concentration 20.1% by mass).

[0271] (Comparative polymer composition 3)

[0272] 800 parts by mass of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR5 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved, yielding comparative polymer composition 3 (solid component concentration 20% by mass).

[0273] (Comparative polymer composition 4)

[0274] 1000 cm³ 3 425 parts by weight of NMP and 75 parts by weight of NaOH (manufactured by Tosoh Corporation, Tosohpearl) were added to a plastic container. The mixture was dispersed at 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsifying screen until the mixture became homogeneous. The solution was then filtered through a nylon filter with a mesh size of 150 μm to prepare a NaOH dispersion (NaOH concentration 15% by weight).

[0275] 940 parts by weight of NMP were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen. The reaction vessel was then heated to 80°C, and 30 parts by weight of HNBR4 were added. The mixture was stirred until the hydrogenated nitrile butadiene rubber was completely dissolved. Next, 30 parts by weight of NaOH dispersion (15% by weight) was added, and the mixture was stirred while adding air. The reaction vessel was maintained at 80°C for 12 hours while being heated, thus obtaining comparative polymer composition 4 (3.5% by weight of solids).

[0276] For Examples 1-3, 1-6, Comparative Examples 1-1, and 1-4, the tanδ (loss tangent) graphs for evaluating the strain dependence of the polymer compositions are shown below. Figure 1For Examples 1-3, 1-6, 1-7, and Comparative Example 1-1, the tanδ (loss tangent) graphs for evaluating the temperature dependence of the polymer compositions are shown below. Figure 2 Furthermore, the HNBR1 to HNBR3 used in polymer compositions 1 to 9 exhibit viscous or fluid properties at 25°C.

[0277] <<Methods for Determination and Evaluation of Physical Properties>>

[0278] The methods for measuring and evaluating the physical properties of the polymer compositions, conductive material compositions, electrode films, and secondary batteries used in the embodiments and comparative examples described below are as follows.

[0279] <Sample Preparation for Molecular Weight Determination>

[0280] The polymer composition was added dropwise to purified water to precipitate the polymer. The precipitate was then recovered by filtration using a Buchner funnel. The precipitate was rinsed directly with purified water onto the Buchner funnel and then dissolved in tetrahydrofuran (THF) to obtain a solution. This solution was then added dropwise to purified water again, and the filtration and rinsing processes with purified water were repeated to redissolve the precipitate in THF, thus preparing a sample for molecular weight determination.

[0281] <Determination of weight-average molecular weight (Mw) and Z-average molecular weight (Mz)>

[0282] The weight-average molecular weight (Mw) and Z-average molecular weight (Mz) of the polymer composition were determined using gel permeation chromatography (GPC) with an RI detector, based on the molecular weight determination sample. An HLC-8320 GPC (manufactured by Tosoh Corporation) was used, with three separation columns connected in series. The packing materials were successively "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" (manufactured by Tosoh Corporation). The determination was performed at an oven temperature of 40°C using a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide as the eluent, at a flow rate of 0.6 mL / min. For the sample, the concentration was adjusted to 1% using a solvent containing the eluent, and 20 μL was injected. The weight-average molecular weight and Z-average molecular weight are converted from polystyrene values.

[0283] Regarding the evaluation of weight-average molecular weight (Mw), those below 70,000 are designated as A, those above 70,000 but below 100,000 are designated as B, and those above 100,000 are designated as C.

[0284] <Preparation of a 20% by mass solution of solid components>

[0285] 80 parts by mass of NMP were placed in a stainless steel container and heated to 80°C while stirring with a disperser. In another container, the polymer heated to 80°C was added to the NMP at a polymer concentration of 20% by mass. The mixture was stirred for 1 hour. After confirming with a spoon that there was no dissolved polymer residue on the surface, walls, or bottom of the container, the solid content was measured and corrected using NMP to achieve a solid content of 20% by mass. This process was used to prepare the polymer solution.

[0286] <Viscosity determination of a 20% by mass solution containing solid components>

[0287] Regarding viscosity measurement, after the prepared polymer solution has been left to stand in a constant temperature bath at 25°C for more than 1 hour, it is immediately measured using a type B viscometer at a rotor rotation speed of 60 rpm.

[0288] Regarding viscosity evaluation, less than 500 mPa·s was designated as A, 500 mPa·s or more but less than 1000 mPa·s as B, 1000 mPa·s or more but less than 3000 mPa·s as C, and more than 3000 mPa·s as D. Furthermore, the solid content concentration in Comparative Examples 1-4 was less than 20% by mass, therefore no measurement was performed.

[0289] <Determination of Viscoelasticity of Polymer Compositions>

[0290] (Preparation of sample pieces)

[0291] A fluoropolymer mold was cut out in a manner consistent with the measuring fixture (parallel plate diameter 25 mm). The polymer composition was dripped into the fluoropolymer mold, and the mold was dried in an oven at 140°C for 1 hour to remove the solvent, thereby preparing a sample sheet. The polymer composition in this example was viscous and could not be separated from the fluoropolymer mold in this state; therefore, it was removed from the mold after being cooled and solidified with liquid nitrogen. The plate was heated to 80°C to maintain a constant sample thickness, and the sample sheet was placed on it and the thickness was corrected using the measuring fixture. Furthermore, it was confirmed that the prepared sample sheet did not contain air bubbles.

[0292] (Dynamic viscoelasticity test: Strain dependence evaluation)

[0293] The dynamic viscoelasticity (strain dependence) of the polymer was determined using a viscoelasticity measuring apparatus: MCR302e (Anton Paar). Specifically, a parallel plate with a diameter of 25 mm was used, with GAP set to the sample thickness, and measurements were performed at a temperature of 100°C, a frequency of 10 Hz, and a strain of 0.01%–10%. The strain dependence of the polymer was evaluated using a graph of strain on the horizontal axis versus tanδ (loss tangent) on the vertical axis. Here, tanδ (loss tangent) is obtained by calculating the loss elastic coefficient (G'') / storage elastic coefficient (G'). Cases with tanδ greater than 1 within the strain range of 0.01%–10% are marked as ○, and cases with tanδ less than 1 are marked as ×.

[0294] (Dynamic viscoelasticity test: temperature dependence evaluation)

[0295] The dynamic viscoelasticity (temperature dependence) of polymers was determined using a viscoelasticity measuring apparatus: MCR302e (Anton Paar). Specifically, the measurement was conducted using a parallel plate with a diameter of 25 mm 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 cooling rate of 10°C / min. The temperature dependence of the polymer was evaluated by reading the temperature on the horizontal axis and the tanδ (loss tangent) on the vertical axis, and determining the temperature at which tanδ (loss tangent) = 1. A was defined as above 40°C and below 80°C; B was defined as above 30°C but below 40°C or above 80°C but below 110°C; C was defined as below 30°C; and D was defined as above 110°C.

[0296] (Method for determining the Mooney viscosity (ML1+4, 100℃) of polymers)

[0297] Purified water was added dropwise to the polymer composition to allow the polymer to solidify. The solidified material was recovered and washed with methanol, transferred to a petri dish, and vacuum dried at 60°C for 12 hours to obtain a 40 g plate sample for testing. Mooney viscosity (ML1+4, 100°C) was determined using an L-shaped rotor at 100°C according to Japanese Industrial Standard JIS K6300-1. Furthermore, the HNBR1 to HNBR3 used in polymer compositions 1 to 9 could not have their Mooney viscosity determined using the aforementioned method.

[0298] <Evaluation of the dispersibility of polymer compositions>

[0299] 80 parts by mass of NMP were placed in a stainless steel container and heated to 80°C while stirring with a disperser. In another container, the polymer heated to 80°C was added to the NMP at a polymer concentration of 8% by mass. The mixture was stirred for 1 hour. After confirming with a spoon that there was no dissolved polymer residue on the surface, walls, or bottom of the container, the solid content was measured and corrected using NMP to achieve a solid content of 8% by mass. This yielded polymer solution X.

[0300] 98 parts by mass of the prepared polymer solution were placed in a glass container, and then JENOTUBE10B carbon nanotubes (average outer diameter 10 nm, BET specific surface area 230 m²) were added. 2 Two parts by weight (g, multilayer CNTs) were collected and allowed to stand for 1 hour without stirring. Then, samples were collected from the supernatant (10% of the height from the top of the glass container) and the bottom (10% of the height from the bottom of the glass container). The amount added to the aluminum pan after tare weight determination (W1) was then measured using a precision balance. The measured mass was designated as W2. The aluminum pan was then dried in a 140°C oven for 1 hour, and its mass was measured again using a precision balance (W3). The solid content of the supernatant and the bottom was calculated using Equation 2 below.

[0301] Solid composition = (W3 - W1) / W2 (Equation 2)

[0302] Then, the dispersibility of the polymer composition can be evaluated based on the dispersion of carbon nanotubes, using the values ​​obtained from the solid components of the supernatant and the bottom. Values ​​of 0.75 or higher but less than 1.25 are designated as A, values ​​of 0.5 or higher but less than 0.75 or 1.25 or higher but less than 1.50 are designated as B, and values ​​of less than 0.5 or 1.50 or higher are designated as C.

[0303] <Initial viscosity of the conductive material composition>

[0304] After the conductive material composition was allowed to stand in a constant temperature bath at 25°C for more than 1 hour, it was immediately tested using a Type B viscometer at a rotor speed of 100 rpm. Regarding the evaluation of the initial viscosity, A was defined as 100 mPa·s or more but less than 500 mPa·s, B as 500 mPa·s or more but less than 1000 mPa·s, C as 1000 mPa·s or more but less than 2000 mPa·s, and D as more than 2000 mPa·s.

[0305] <Evaluation of the dispersibility of conductive material compositions>

[0306] The dispersibility of conductive material compositions was evaluated by measuring the cumulative particle size (D50). The cumulative particle size (D50) based on particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba Corporation; Partica LA-960V2). This measuring device used a laser wavelength of 650 nm and included one annular 64-segment silicon photodiode, five four-channel (4ch) array detectors, and three silicon photodetectors as detectors. Furthermore, the measurement section used a flow cell (sample cell) based on synthetic quartz.

[0307] First, NMP, the same solvent as the dispersion, was added to a sample bath containing the sample cell, and a circulating / ultrasonic cleaning process was performed. The operating mode was set as follows: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, stirring mode: continuous. Next, to remove air, ultrasonic cleaning was performed at ultrasonic intensity: 7 and ultrasonic time: 5 seconds, followed by a blank (background) measurement. The particle size reference was set to volume, the particle refractive index was set to 1.920-0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The dispersion was added dropwise to adjust the sample so that the laser light transmittance during measurement was 60% ± 1%. The measurement was performed using the following operating mode: circulation speed: 3, stirring speed: 7, stirring mode: continuous.

[0308] Regarding the evaluation of the dispersibility of conductive material compositions, a cumulative particle diameter D50 value of less than 3 μm is designated as A, 3 μm or more but less than 10 μm is designated as B, and 10 μm or more is designated as C.

[0309] <Evaluation of the storage stability of conductive material compositions>

[0310] After the conductive material composition was left to stand in a constant temperature bath at 40°C for one week, it was cooled to 25°C, and then the viscosity over time was measured immediately using a Type B viscometer at a rotor speed of 100 rpm. The storage stability was evaluated by dividing the viscosity over time (at 40°C and after one week) by the initial viscosity. A value of 0.8 or higher but less than 3.0 was designated as A, 3.0 or higher but less than 5.0 as B, and less than 0.8 or higher than 5.0 as C.

[0311] <Evaluation of Electrode Film Adhesion>

[0312] Peel strength was measured to evaluate the adhesion of the electrode membrane. A dressing applicator was used, with the weight per unit area of ​​the electrode calculated as 20 mg / cm². 2After the composite slurry was applied to aluminum foil, it was dried in an electric oven at 120℃±5℃ for 25 minutes. Then, the coating was cut into two 90 mm × 20 mm rectangles, with the coating direction as the long axis. The peel strength was determined using a benchtop tensile testing machine (Toyo Seiki Co., Ltd., Strograph E3) using the 180-degree peel test method. Specifically, a 100 mm × 30 mm double-sided tape (No. 5000NS, Nitoms Co., Ltd.) was attached to a stainless steel plate, with the battery electrode composite layer in close contact with the other side of the tape. The tape was then stretched and peeled from bottom to top at a certain speed (50 mm / min), and the average stress at this point was taken as the peel strength. Regarding the evaluation of the adhesion of the electrode film, a peel strength of 1.0 N / cm or more is designated as A, a peel strength of 0.7 N / cm or more but less than 1.0 N / cm is designated as B, a peel strength of 0.5 N / cm or more but less than 0.7 N / cm is designated as C, and a peel strength of less than 0.5 N / cm is designated as D.

[0313] <Evaluation of the rate characteristics of lithium-ion secondary batteries>

[0314] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). Constant current and constant voltage charging (cutoff current 1.0 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) with a charging termination voltage of 4.2 V, followed by constant current discharging at a discharging current of 10 mA (0.2 C) with a discharging termination voltage of 2.5 V. This operation was repeated three times. Then, constant current and constant voltage charging (cutoff current 1.0 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) with a charging termination voltage of 4.2 V, followed by constant current discharging at discharging currents of 0.2 C and 3 C until the discharging termination voltage of 2.5 V was reached. The discharge capacity was calculated for each discharge. The rate characteristic can be expressed by the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, as shown in Equation 3 below.

[0315] Rate characteristic = 3 C discharge capacity / third 0.2 C discharge capacity × 100 (%) Equation 3

[0316] Regarding the evaluation of rate characteristics, a rate characteristic of 80% or higher is designated as A, 70% or higher but less than 80% is designated as B, 60% or higher but less than 70% is designated as C, and less than 60% is designated as D.

[0317] <Evaluation of High-Temperature Cycling Characteristics of Lithium-ion Secondary Batteries>

[0318] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 45°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). Constant current and constant voltage charging was performed at a charging current of 50 mA (1 C) with a charging termination voltage of 4.2 V (cutoff current 1.25 mA (0.025 C)). Then, constant current discharging was performed at a discharging current of 50 mA (1 C) with a discharging termination voltage of 2.5 V. This operation was repeated 200 times. 1 C is defined as the current value at which the theoretical capacity of the positive electrode is discharged within 1 hour. The cycle characteristics can be expressed by the ratio of the 1 C discharge capacity of the 100th cycle to the 1 C discharge capacity of the third cycle at 45°C, as shown in Equation 4 below. Regarding the evaluation of high-temperature cycle characteristics, a cycle characteristic of 90% or more was designated as A, 85% or more but less than 90% as B, 80% or more but less than 85% as C, and less than 80% as D.

[0319] High-temperature cycling characteristics = (1C discharge capacity at the 100th cycle / 1C discharge capacity at the 3rd cycle) × 100 (%) Equation 4

[0320] (Example 2-1)

[0321] 84.0 parts of N-methyl-2-pyrrolidone (NMP) and 8.0 parts of polymer composition (solid content concentration 20% by mass) were added to a stainless steel container and stirred using a disperser. Then, 8 parts of CNT1 were added while stirring using a disperser, and batch-dispersed at 9000 rpm on a high-shear mixer (L5M-A, manufactured by SILVERSON) with a fine emulsifying screen until the mixture became homogeneous and the particle size was reduced to below 200 μm using a grinding tester. The resulting carbon material pre-dispersed composition was then passed through a high-magnetic-force amplification filter (magFilter) (manufactured by Eishin, surface magnetic flux density 17000 Gauss). Next, the carbon material pre-dispersed composition is fed and subjected to a circulating dispersion process with a residence time of 15 minutes (80% bead filling rate, circumferential speed 13 m / s) through a bead mill filled with 1.0 mm diameter zirconia beads. The number of cycles is 30. Subsequently, the dispersed liquid is supplied to a high-pressure homogenizer (manufactured by Sugino Machine, Star Burst Labo) for 24 pass-through dispersion processes. The dispersion process is carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersed liquid is then supplied to an electromagnet (manufactured by Daebo Magnetic, EMF-100S, consisting of 31 electromagnets with a magnetic flux density of 16,000 Gauss, a volume of 1.7 L, a diameter of 10 cm, and a thickness of 1.3 cm). After a three-pass process, the liquid passes through two series-connected depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy of 40 μm) to produce conductive material composition 1.

[0322] (Examples 2-2 to 2-12, Comparative Examples 2-1 to 2-4)

[0323] Conductive material compositions were prepared in the same manner as in Example 1, according to the composition in Table 2, thereby producing conductive material compositions 2 to 12, and comparative conductive material compositions 1 to 4.

[0324] (Example 3-1)

[0325] 150 cm 3In a plastic container, 18.8 parts by mass of an NMP solution containing 8% by mass PVdF (polyvinylidene fluoride, manufactured by Solvay, Solef #5130) and 14.5 parts by mass of NMP were dissolved. Then, 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 rotary mixer (defoaming Rentaro, ARE-310). Next, 96.7 parts by mass of the positive electrode active material NCM1 was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotary mixer (defoaming Rentaro, ARE-310) to obtain a composite slurry.

[0326] Subsequently, using a dressing applicator, the weight per unit area of ​​the electrode was set at 20 mg / cm². 2 The composite slurry was coated onto aluminum foil and then dried in an electric oven at 120℃±5℃ for 25 minutes to obtain an electrode film (electrode film 1). The electrode film (electrode film 1) was then rolled using a roller press (manufactured by Thank-Metal, a 3t hydraulic roller press) to obtain a positive electrode (positive electrode 1). Furthermore, the weight per unit area of ​​the composite layer was 20 mg / cm³. 2 The density of the composite layer after rolling was set to 3.1 g / cc.

[0327] (Examples 3-2 to 3-16, Comparative Examples 3-1 to 3-4)

[0328] The positive electrode active material and conductive material composition are changed to those shown in Table 3. Otherwise, the positive electrode (positive electrode 2 to comparative positive electrode 4) is manufactured using the same method as the positive electrode (positive electrode 1).

[0329] (Example 4-1)

[0330] The positive electrode (positive electrode 1) and the standard negative electrode were punched into 45 mm × 40 mm and 50 mm × 45 mm respectively, and inserted into an aluminum laminated bag together with the separator (porous polypropylene membrane) inserted between them. The bags were then dried in an electric oven at 60°C for 1 hour. Afterward, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a 1:1:1 (volume ratio) mixture, and then adding 2 parts by mass of vinylene carbonate (VC) as an additive to 100 parts by mass of the mixture, and then dissolving LiPF6 at a concentration of 1 M) was injected into an argon-filled glove box. The aluminum laminated bag was then sealed to produce a laminated lithium-ion secondary battery (battery 1).

[0331] (Examples 4-2 to 4-16, Comparative Examples 4-1 to 4-4)

[0332] The positive electrode is changed to that shown in Table 4. Otherwise, the laminated lithium-ion secondary battery (battery 2 to comparative battery 4) is manufactured using the same method as that used in manufacturing the laminated lithium-ion secondary battery (secondary battery 1).

[0333] [Table 1]

[0334]

[0335]

[0336] [Table 3]

[0337]

[0338] [Table 4]

[0339]

[0340] The present invention has been described with reference to several embodiments, but the present invention is not limited to these embodiments. Various modifications can be made to the structure or details of the present invention within the scope of the present invention.

[0341] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-222006, filed on December 27, 2023, and all of its disclosure is incorporated herein by reference.

Claims

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

2. The polymer composition for electrochemical devices according to claim 1, wherein the polymer, in a viscoelasticity test at a frequency of 10 Hz and a strain of 0.1%, reaches a temperature of 80°C or below when heated at a rate of 10°C / min within a temperature range of 30°C to 110°C to achieve tanδ (loss tangent) = 1.

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

4. The polymer composition for electrochemical elements 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-containing unit is 25% by mass or more and 50% by mass or less.

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

6. A conductive material composition comprising the polymeric composition for electrochemical elements as described in claim 1 or 2 and a conductive material.

7. A slurry composition comprising the polymeric composition for electrochemical elements as described in claim 1 or 2, a conductive material, and an active substance.

8. An electrode membrane formed using a slurry composition comprising a polymeric composition for electrochemical elements as described in claim 1 or 2, a conductive material, and an active substance.

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 membrane. The electrode membrane is formed using a slurry composition comprising a polymeric composition for electrochemical elements as described in claim 1 or 2, a conductive material, and an active substance.

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