Dispersant composition for electrochemical element, conductor dispersion for electrochemical element, slurry for electrochemical element electrode, electrode for electrochemical element, and electrochemical element

Abstract

A purpose of the present invention is to provide a dispersant composition for an electrochemical element, said composition being capable of forming an electrode for an electrochemical element that makes it possible to lower IV resistance of the electrochemical element. The dispersant composition for the electrochemical element according to the present invention contains a polymer A, and the polymer A contains a nitrile group-containing monomer unit and an alkylene structural unit that has 4 or more carbon atoms. A value (FA) that is calculated by FA = (ηA / MA) × 1000 is 0.1–9.0, where MA is the weight-average molecular weight of the polymer A, and ηA (mPa･s) is the viscosity measured at a temperature of 25°C of a polymer solution that is obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A is 10 mass%. When the lateral relaxation time measured at a temperature of 25°C of N-methyl-2-pyrrolidone is T2S (milliseconds) and the lateral relaxation time measured at a temperature of 25°C of the polymer solution that is obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A is 1 mass% is T2C (milliseconds), a T2 ratio calculated as T2 ratio = T2S / T2C is 1.1–1.8.

Description

Dispersant composition for electrochemical elements, conductive material dispersion for electrochemical elements, slurry for electrodes for electrochemical elements, electrodes for electrochemical elements, and electrochemical elements

[0001] The present invention relates to a dispersant composition for electrochemical devices, a conductive material dispersion for electrochemical devices, a slurry for electrochemical device electrodes, an electrode for electrochemical devices, and an electrochemical device.

[0002] Electrochemical devices such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications.

[0003] Here, an electrode used in an electrochemical element such as a lithium-ion secondary battery typically includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition (hereinafter referred to as "electrochemical element electrode slurry" or sometimes abbreviated as "electrode slurry"), which is obtained by dispersing an electrode active material, a conductive material such as CNT, and a polymer that functions as a dispersant in a solvent, onto the current collector and drying it.

[0004] Therefore, in recent years, in order to achieve further performance improvements in electrochemical elements, attempts have been made to improve dispersant compositions for electrochemical elements (hereinafter sometimes abbreviated as "dispersant compositions") and conductive material dispersions for electrochemical elements (hereinafter sometimes abbreviated as "conductive material dispersions") used in preparing electrode slurries. Specifically, Patent Document 1 discloses a conductive material dispersion containing carbon nanotubes having a specific surface area and a volume average particle diameter each within a predetermined range, a hydrogenated acrylonitrile-butadiene copolymer having a weight average molecular weight equal to or less than a predetermined value, and a solvent. According to Patent Document 1, the conductive material dispersion can provide secondary batteries with excellent output characteristics and cycle characteristics. Furthermore, Patent Document 2 discloses a conductive material dispersion containing bundled carbon nanotubes, a hydrogenated nitrile rubber, and a dispersion medium, and having a complex modulus within a predetermined range. According to Patent Document 2, the conductive material dispersion has excellent dispersibility and low powder resistivity, making it useful for producing high-power electrodes.

[0005] International Publication No. 2022 / 070736 Special Publication No. 2018-533175

[0006] However, the above-mentioned conventional conductive material dispersion liquids have room for further improvement in terms of reducing the IV resistance of electrochemical elements such as secondary batteries.

[0007] Therefore, an object of the present invention is to provide a dispersant composition for electrochemical devices, a conductive material dispersion for electrochemical devices, and a slurry for electrochemical device electrodes, which are capable of forming electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. Another object of the present invention is to provide electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. Another object of the present invention is to provide an electrochemical device having low IV resistance.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have found that the IV resistance of an electrochemical element can be reduced by using a dispersant composition containing a polymer A containing a nitrile group-containing monomer unit and an alkylene structural unit having 4 or more carbon atoms, wherein the weight-average molecular weight of the polymer A and the viscosity of an N-methyl-2-pyrrolidone (NMP) solution of the polymer A under specified conditions satisfy a specified relationship, and the ratio of the transverse relaxation time in NMP to the transverse relaxation time of the NMP solution of the polymer A under specified conditions is within a specified range, thereby completing the present invention.

[0009] That is, the present invention has an object to advantageously solve the above-mentioned problems, and provides the following dispersant compositions for electrochemical elements (1) to (5), conductive material dispersions for electrochemical elements (6) to (8), a slurry for electrochemical element electrodes (9), an electrode for electrochemical elements (10), and an electrochemical element (11).

[0010] [1] A dispersant composition for electrochemical elements containing a polymer A, wherein the polymer A contains a nitrile group-containing monomer unit and an alkylene structural unit having 4 or more carbon atoms, and the weight average molecular weight of the polymer A is M Ａ The viscosity of a polymer solution obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A becomes 10% by mass, measured at a temperature of 25°C, is defined as η Ａ (mPa·s) as the following formula (1): F Ａ =(η Ａ / M Ａ ) × 1000 (1) Ａ ) is 0.1 or more and 9.0 or less, and the transverse relaxation time T2 measured in N-methyl-2-pyrrolidone at a temperature of 25 ° C. Ｓ (milliseconds), and the transverse relaxation time measured at a temperature of 25°C of a polymer solution obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A becomes 1% by mass is T2 Ｃ (milliseconds) and the following formula (2): T2 ratio = T2 Ｓ / T2 Ｃ...(2) A dispersant composition for electrochemical elements, which has a T2 ratio calculated by the following formula: of 1.1 or more and 1.8 or less. Ａ By using a dispersant composition containing polymer A in which the values ​​of "T2 ratio" and "T3 ratio" are within the above-mentioned ranges, an electrochemical device with low IV resistance can be obtained.

[0011] In the present invention, the term "monomer unit" of a polymer means "a repeating unit derived from the monomer contained in a polymer obtained using the monomer." In addition, in the present invention, the term "transverse relaxation time" refers to １ H-nuclear magnetic resonance ( １ The term "weight average molecular weight (M)" refers to the transverse relaxation time (also called "spin-spin relaxation time") measured using a H-NMR method. Ａ )”, “Viscosity (η Ａ ) and "Transverse relaxation time (T2 Ｓ ") and "Transverse relaxation time (T2 Ｃ ) can be measured by the methods described in the Examples of the present specification. Ａ " and "T2 ratio" can be calculated more specifically using the method described in the Examples of this specification.

[0012] [2] The dispersant composition for electrochemical elements according to the above [1], wherein the nitrile group-containing monomer unit is an acrylonitrile unit and the alkylene structural unit is a 1,3-butadiene hydride unit. By using polymer A containing acrylonitrile units and 1,3-butadiene hydride units, the IV resistance of the electrochemical element can be further reduced.

[0013] [3] The dispersant composition for electrochemical elements according to the above [1] or [2], wherein the polymer A further comprises at least one of an aromatic vinyl monomer unit and an acid group-containing monomer unit. By using the polymer A further comprising at least one of an aromatic vinyl monomer unit and an acid group-containing monomer unit, the IV resistance of the electrochemical element can be further reduced.

[0014] [4] The iodine value of the polymer A is 5 mg / 100 mg or more and 60 mg / 100 mg or less, and the weight average molecular weight (M Ａ The dispersant composition for electrochemical elements according to any one of [1] to [3] above, wherein the iodine value and weight-average molecular weight of polymer A are each within the above-mentioned ranges, the dispersibility of carbon nanotubes (hereinafter sometimes abbreviated as "CNT") in the conductive material dispersion is improved, and the IV resistance of the electrochemical element can be further reduced while improving the rate characteristics. In addition, the oxidation resistance of polymer A can be well ensured, and elution of polymer A into the electrolyte can be suppressed.

[0015] In the present invention, the "iodine value" of polymer A can be measured by the method described in the examples of this specification.

[0016] [5] The dispersant composition for electrochemical devices according to any one of [1] to [4] above, further comprising a solvent.

[0017] [6] A conductive material dispersion for electrochemical elements, comprising the dispersant composition for electrochemical elements according to any one of [1] to [5] above, a conductive material, and a solvent, wherein the conductive material comprises carbon nanotubes. By using a conductive material dispersion comprising at least any one of the dispersant compositions described above, a conductive material containing CNTs, and a solvent, an electrochemical element having low IV resistance can be obtained.

[0018] [7] The conductive material dispersion for electrochemical elements according to [6] above, having a solid content concentration of 0.1 mass % or more and 15 mass % or less. When the solid content concentration of the conductive material dispersion is within the above range, the rate characteristics of the electrochemical element can be improved. In addition, the coatability of a slurry for electrodes prepared using the conductive material dispersion can be improved.

[0019] [8] The conductive material dispersion liquid for electrochemical elements according to [6] or [7] above, wherein the content of the carbon nanotubes is 0.05% by mass or more and 10% by mass or less, and the content of the polymer A is 0.02% by mass or more and 8% by mass or less. When the content ratios of the CNTs and the polymer A are each within the above-mentioned ranges, the dispersibility of the CNTs in the conductive material dispersion liquid is improved, and the IV resistance of the electrochemical element can be further reduced while the rate characteristics can be improved.

[0020] [9] A slurry for an electrochemical element electrode, comprising the conductive material dispersion for an electrochemical element according to any one of [6] to [8] above and an electrode active material. The electrode slurry prepared using any one of the conductive material dispersions described above makes it possible to obtain an electrochemical element having low IV resistance.

[0021]

[10] An electrode for an electrochemical element, comprising an electrode mixture layer formed using the slurry for an electrochemical element electrode according to [9] above. By using an electrode comprising an electrode mixture layer formed using the above-mentioned electrode slurry, an electrochemical element having low IV resistance can be obtained.

[0022]

[11] An electrochemical device comprising the electrode for electrochemical devices according to

[10] above. The electrochemical device comprising the electrode for electrochemical devices described above has reduced IV resistance.

[0023] According to the present invention, it is possible to provide a dispersant composition for electrochemical devices, a conductive material dispersion for electrochemical devices, and a slurry for electrochemical device electrodes, which are capable of forming electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. Furthermore, according to the present invention, it is possible to provide electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. And according to the present invention, it is possible to provide an electrochemical device with low IV resistance.

[0024] Hereinafter, embodiments of the present invention will be described in detail. Here, the dispersant composition for electrochemical devices of the present invention can be used when preparing the conductive material dispersion for electrochemical devices of the present invention. Furthermore, the conductive material dispersion for electrochemical devices of the present invention can be used when preparing the slurry for electrochemical device electrodes of the present invention. Then, the slurry for electrochemical device electrodes of the present invention prepared using the conductive material dispersion for electrochemical devices of the present invention can be used when forming electrodes for electrochemical devices such as lithium ion secondary batteries. Furthermore, the electrochemical device of the present invention includes an electrode for electrochemical devices formed using the slurry for electrochemical device electrodes of the present invention. Note that the dispersant composition for electrochemical devices, the conductive material dispersion for electrochemical devices, and the slurry for electrochemical device electrodes of the present invention can be particularly suitably used when producing a positive electrode for an electrochemical device.

[0025] (Dispersant composition for electrochemical elements) The dispersant composition of the present invention is used for preparing a conductive material dispersion liquid containing CNT, and contains at least a predetermined polymer A described in detail below, and optionally further contains a solvent. Components other than the polymer A and the solvent contained in the dispersant composition are not particularly limited, and examples thereof include other components described below. The dispersant composition of the present invention does not usually contain a conductive material or an electrode active material, and the proportion of polymer A in the total solid content contained in the dispersant composition can be, for example, 90% by mass or more, and can be 95% by mass or more. The solid content concentration of the dispersant composition can be, for example, 5% by mass or more and 20% by mass or less. The dispersant composition of the present invention has an F calculated by the following formula (1): Ａ and the T2 ratio calculated by the following formula (2) are each within a predetermined range. Ａ =(η Ａ / M Ａ )×1000...(1) [In formula (1), M Ａ is the weight average molecular weight of polymer A, and η Ａ is the viscosity (mPa·s) measured at 25°C of a polymer solution prepared by adding N-methyl-2-pyrrolidone to polymer A so that the concentration of polymer A becomes 10% by mass.] T2 ratio = T2 Ｓ / T2Ｃ ...(2) [In formula (2), T2 Ｓ is the transverse relaxation time (milliseconds) measured in N-methyl-2-pyrrolidone at 25°C, and T2 Ｃ is the transverse relaxation time (milliseconds) measured at 25°C of a polymer solution prepared by adding N-methyl-2-pyrrolidone to polymer A so that the concentration of polymer A becomes 1% by mass.

[0026] The dispersant composition of the present invention contains a polymer A containing a nitrile group-containing monomer unit and an alkylene structural unit having 4 or more carbon atoms, and is Ａ Since the "T2 ratio" and "T2 ratio" are within the above-mentioned ranges, the use of the dispersant composition can reduce the IV resistance of an electrochemical element. The reason why the above-mentioned effects are obtained by using the dispersant composition of the present invention is not clear, but is presumed to be as follows.

[0027] In the CNT mixture before dispersion treatment, CNTs are likely to form bundle-shaped aggregates (CNT aggregates) due to van der Waals forces. A conductive material dispersion in which CNTs are well dispersed can be produced, for example, by going through a step of infiltrating a polymer and a solvent acting as a dispersant into the CNT aggregates, a step of disintegrating the CNT aggregates, and a step of stabilizing the CNTs in a dispersed state in the solvent. The present inventors have focused on the first step of the above steps, i.e., the step of infiltrating a polymer and a solvent acting as a dispersant into the CNT aggregates. First, the dispersant composition of the present invention is prepared by F Ａ The value of is 0.1 or more and 9.0 or less. Ａ As shown in equation (1), η Ａ / M Ａ is the value obtained by multiplying by 1000, and η Ａ is the viscosity of an NMP solution of polymer A (concentration of polymer A is 10% by mass), and M Ａ is the weight average molecular weight of polymer A. That is, F Ａ can be regarded as a value correlated with the viscosity per weight average molecular weight of polymer A. The dispersant composition of the present invention has F Ａ When the value of F is 0.1 or more, it can be said that the weight average molecular weight of polymer A is not excessively large. ＡWhen the value of is 9.0 or less, the viscosity of the NMP solution of polymer A is not excessively high, that is, it can be said that the spreading of the molecular chains of polymer A is sufficiently suppressed. Polymer A, which does not have an excessively high weight-average molecular weight and has suppressed spreading of the molecular chains, can penetrate well into the gaps between CNT aggregates, thereby improving the dispersibility of CNTs in the resulting conductive material dispersion. Furthermore, the dispersant composition of the present invention has a T2 ratio of 1.1 or more and 1.8 or less. The T2 ratio is, as shown in formula (2), Ｓ T2 Ｃ is the value obtained by dividing by T2 Ｓ is the transverse relaxation time of NMP, while T2 Ｃ is the transverse relaxation time of the NMP solution of polymer A (concentration of polymer A is 1% by mass), and T2 Ｃ Specifically, T2 is composed of two components: the transverse relaxation time of the NMP molecules adsorbed on the surface of polymer A and the transverse relaxation time of the NMP molecules in the bulk liquid. Here, the mobility of the NMP molecules adsorbed on the surface of polymer A is restricted, and therefore the transverse relaxation time is shorter than that of the NMP molecules in the bulk liquid, which can move freely. Therefore, the lower the affinity between polymer A and NMP, the fewer the NMP molecules adsorbed on the surface of polymer A, and therefore, T2 Ｃ is considered to increase, and the T2 ratio is considered to decrease. Furthermore, since the dispersant composition of the present invention has a T2 ratio of 1.1 or more and 1.8 or less, it can be said that the affinity of polymer A for NMP is appropriately adjusted. Polymer A, whose affinity for the solvent (NMP) is appropriately adjusted in this manner, can penetrate well into the gaps between CNT aggregates with the solvent attached to its surface, thereby improving the dispersibility of CNTs in the resulting conductive material dispersion. Furthermore, it is considered that the use of a conductive material dispersion with such high CNT dispersibility can form a good conductive path in the electrode mixture layer, thereby reducing the IV resistance of the electrochemical element. Therefore, the use of the dispersant composition of the present invention can reduce the IV resistance of the electrochemical element.

[0028] <Polymer A> The polymer A contained in the dispersant composition of the present invention contains a nitrile group-containing monomer unit and an alkylene structural unit having 4 or more carbon atoms, and optionally further contains repeating units other than the nitrile group-containing monomer unit and the alkylene structural unit having 4 or more carbon atoms (hereinafter referred to as "other repeating units"). The polymer A is a component that can satisfactorily disperse CNTs as a conductive material in a conductive material dispersion. The polymer A is also a component that can exert a function of retaining components contained in the electrode mixture layer so that they do not detach from the electrode mixture layer.

[0029] <<Nitrile Group-Containing Monomer Unit>> The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Here, examples of nitrile group-containing monomers that can form the nitrile group-containing monomer unit include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. These may be used alone or in combination of two or more. Among these, acrylonitrile is preferred.

[0030] The content of the nitrile group-containing monomer units in polymer A is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, particularly preferably 28% by mass or more, preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 32% by mass or less, when the total amount of repeating units in polymer A is taken as 100% by mass. When the content of the nitrile group-containing monomer units in polymer A is 5% by mass or more, the solubility of polymer A in the dispersant composition can be well ensured. On the other hand, when the content of the nitrile group-containing monomer units in polymer A is 50% by mass or less, the dissolution of polymer A in the electrolyte solution can be suppressed, and the conductive path formed by the conductive material in the electrode mixture layer can be well maintained. Note that in the present invention, the content (mass%) of each monomer unit is １ It can be measured using a nuclear magnetic resonance (NMR) method such as H-NMR.

[0031] <<Alkylene structural unit having 4 or more carbon atoms>> The alkylene structural unit having 4 or more carbon atoms is represented by the general formula: —C ｎ H ２ｎ - [where n is an integer of 4 or more].

[0032] Here, the alkylene structural unit having 4 or more carbon atoms may be linear or branched, but the alkylene structural unit having 4 or more carbon atoms is preferably linear, i.e., a straight-chain alkylene structural unit. The method for introducing the alkylene structural unit having 4 or more carbon atoms into the polymer is not particularly limited, and examples include the following methods (1) and (2): (1) a method in which a polymer is prepared from a monomer composition containing a conjugated diene monomer and the polymer is hydrogenated to convert the conjugated diene monomer unit into an alkylene structural unit; and (2) a method in which a polymer is prepared from a monomer composition containing a 1-olefin monomer having 4 or more carbon atoms. Among these, method (1) is preferred because it allows for easy production of the polymer.

[0033] Here, examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred. That is, the alkylene structural unit having 4 or more carbon atoms is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, more preferably a structural unit (1,3-butadiene hydride unit) obtained by hydrogenating a 1,3-butadiene unit or a structural unit (isoprene hydride unit) obtained by hydrogenating an isoprene unit, and even more preferably a 1,3-butadiene hydride unit. Note that the selective hydrogenation of the conjugated diene monomer unit can be carried out using known methods such as oil phase hydrogenation and aqueous phase hydrogenation. Examples of the 1-olefin monomer having 4 or more carbon atoms include 1-butene, 1-hexene, etc. These conjugated diene monomers and 1-olefin monomers having 4 or more carbon atoms can be used alone or in combination of two or more.

[0034] The content of alkylene structural units having 4 or more carbon atoms in polymer A is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less, when all repeating units in polymer A are taken as 100% by mass. If the content of alkylene structural units having 4 or more carbon atoms in polymer A is 30% by mass or more, the dispersibility of the conductive material dispersion can be improved due to the interaction between polymer A and the conductive material surface. Furthermore, if the content of alkylene structural units having 4 or more carbon atoms in polymer A is 90% by mass or less, the solubility of polymer A in the dispersant composition can be well ensured.

[0035] <<Other Repeating Units>> The other repeating units that can be contained in the polymer A are not particularly limited, and examples thereof include aromatic vinyl monomer units, acid group-containing monomer units, etc. In particular, from the viewpoint of further reducing the IV resistance of the electrochemical device, it is preferable that the polymer A contains aromatic vinyl monomer units and / or acid group-containing monomer units as the other repeating units.

[0036] [Aromatic vinyl monomer unit] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, etc. These may be used alone or in combination of two or more. Among these, styrene is preferred.

[0037] When polymer A contains aromatic vinyl monomer units, the content of aromatic vinyl monomer units in polymer A is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of all repeating units in polymer A. When the content of aromatic vinyl monomer units in polymer A is 5% by mass or more, the adsorption of polymer A to conductive materials can be improved. When the content of aromatic vinyl monomer units in polymer A is 40% by mass or less, excessive adsorption of polymer A to conductive materials can be suppressed. Note that polymer A does not necessarily have to contain aromatic vinyl monomer units (the content of aromatic vinyl monomer units in polymer A may be 0% by mass).

[0038] [Acid group-containing monomer unit] Examples of acid group-containing monomers that can form acid group-containing monomer units include carboxyl group-containing monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, etc. The acid group in the acid group-containing monomer unit may form a salt with an alkali metal, ammonia, etc.

[0039] Here, examples of carboxyl group-containing monomers capable of forming carboxyl group-containing monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as monobutyl maleate, monononyl maleate, monodecyl maleate, monododecyl maleate, monooctadecyl maleate, and monofluoroalkyl maleate. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and citraconic anhydride. Furthermore, acid anhydrides that generate carboxyl groups upon hydrolysis can also be used as carboxyl group-containing monomers. Furthermore, examples of carboxyl group-containing monomers that can be used include ethylenically unsaturated polycarboxylic acids such as butenetricarboxylic acid, and partial esters of ethylenically unsaturated polycarboxylic acids such as monobutyl fumarate and mono-2-hydroxypropyl maleate.

[0040] Examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include styrenesulfonic acid, vinylsulfonic acid (ethylenesulfonic acid), methylvinylsulfonic acid, (meth)allyl sulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0041] Furthermore, examples of the phosphate group-containing monomer capable of forming the phosphate group-containing monomer unit include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0042] The above-mentioned monomers may be used singly or in combination of two or more. The acid group-containing monomer capable of forming the acid group-containing monomer unit is preferably a carboxyl group-containing monomer, more preferably methacrylic acid, itaconic acid, acrylic acid, or monobutyl maleate, and still more preferably methacrylic acid.

[0043] When polymer A contains acid group-containing monomer units, the content of the acid group-containing monomer units in polymer A is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 20% by mass or less, and more preferably 15% by mass or less, based on 100% by mass of all repeating units in polymer A. When the content of the acid group-containing monomer units in polymer A is 1% by mass or more, the dispersibility of CNTs in the conductive material dispersion is improved, and the rate characteristics can be improved while the IV resistance of the electrochemical device is further reduced. On the other hand, when the content of the acid group-containing monomer units in polymer A is 20% by mass or less, excessive adsorption of polymer A to the conductive material can be suppressed, and the IV resistance of the electrochemical device can be further reduced.

[0044] The content of the other repeating units in polymer A is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. The lower limit of the content of the other repeating units in polymer A is not particularly limited, and can be, for example, 1% by mass or more, or 5% by mass or more.

[0045] <<Properties>> [Weight average molecular weight (M Ａ ) )] Weight average molecular weight of polymer A (M Ａ) is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, even more preferably 20,000 or more, particularly preferably 25,000 or more, and is preferably 100,000 or less, more preferably 70,000 or less, even more preferably 55,000 or less, even more preferably less than 50,000, particularly preferably 45,000 or less. Ａ When M is 1,000 or more, the elution of polymer A into the electrolyte solution can be suppressed. Ａ If M is 100,000 or less, polymer A can easily penetrate into the CNT aggregates. Therefore, the dispersibility of CNTs in the conductive material dispersion liquid is improved, and the rate characteristics can be improved while the IV resistance of the electrochemical device is further reduced. Ａ can be adjusted, for example, by changing the type and amount of the polymerization initiator and / or chain transfer agent used in the preparation of polymer A. Specifically, by increasing the amount of the chain transfer agent used in the preparation of polymer A, M Ａ can be reduced, and by reducing Ａ can be increased.

[0046] [Viscosity (η Ａ ) )] The viscosity (η) of a polymer solution obtained by adding NMP to polymer A so that the concentration of polymer A becomes 10% by mass was measured at a temperature of 25°C. Ａ ) is preferably 400 mPa·s or less, more preferably 350 mPa·s or less, even more preferably 300 mPa·s or less, even more preferably 250 mPa·s or less, and particularly preferably 200 mPa·s or less. Ａ When the viscosity is 400 mPa s or less, the molecular chains of the polymer A are suppressed from spreading, and the polymer A easily penetrates into the CNT aggregates. Therefore, the dispersibility of the CNTs in the conductive material dispersion is improved, and the rate characteristics can be improved while the IV resistance of the electrochemical device is further reduced. In addition, the handleability of the dispersant composition can be ensured well. ＡThe lower limit of η is not particularly limited, and can be, for example, 10 mPa·s or more, 30 mPa·s or more, or 50 mPa·s or more. Ａ is determined by, for example, the composition of polymer A and the weight average molecular weight (M Ａ Specifically, the weight average molecular weight (M Ａ ) by increasing η Ａ can be increased, and by reducing η Ａ can be reduced.

[0047] [F Ａ ] where F Ａ The value of F must be 0.1 or more and 9.0 or less. Ａ The value of is preferably 0.5 or more, more preferably 1.0 or more, and even more preferably 1.5 or more, and is preferably 8.0 or less, more preferably 7.0 or less, even more preferably 6.0 or less, still more preferably 5.0 or less, and particularly preferably 4.0 or less. Ａ If the value of F is less than 0.1, the weight average molecular weight of polymer A increases, making it difficult for polymer A to penetrate into the CNT aggregates. As a result, the dispersibility of CNTs in the conductive material dispersion liquid decreases, and the IV resistance of the electrochemical device increases and the rate characteristics deteriorate. Ａ If the value of exceeds 9.0, the molecular chains of polymer A become more spread, making it difficult for polymer A to penetrate into CNT aggregates. As a result, the dispersibility of CNTs in the conductive material dispersion decreases, the IV resistance of the electrochemical device increases, and the rate characteristics decrease. In addition, the amount of CNT aggregates in the conductive material dispersion increases, increasing the volume resistivity of the coating obtained by applying the conductive material dispersion to a substrate.

[0048] [Transverse relaxation time (T2 Ｃ ) )]. The transverse relaxation time (T2 Ｃ) is preferably 1,850 milliseconds or more, more preferably 1,900 milliseconds or more, even more preferably 1,950 milliseconds or more, even more preferably 2,000 milliseconds or more, particularly preferably 2,200 milliseconds or more, and is preferably 2,500 milliseconds or less, more preferably 2,450 milliseconds or less, and even more preferably 2,400 milliseconds or less. Ｃ When T2 is 1,850 milliseconds or more, excessive adsorption of the solvent to the polymer A is suppressed, and the polymer A can easily penetrate into the CNT aggregates. Therefore, the dispersibility of the CNTs in the conductive material dispersion liquid is improved, and the rate characteristics can be improved while the IV resistance of the electrochemical device is further reduced. Ｃ When T2 is 2,500 milliseconds or less, the affinity of polymer A to the solvent is improved. Therefore, the dispersibility of CNTs in the conductive material dispersion is improved, and the rate characteristics can be improved while the IV resistance of the electrochemical device is further reduced. Ｃ can be adjusted by, for example, changing the composition or weight-average molecular weight of polymer A. Specifically, by increasing the weight-average molecular weight of polymer A, T2 Ｃ can be reduced, and by reducing Ｃ can be increased.

[0049] [T2 Ratio] The T2 ratio must be 1.1 or more and 1.8 or less, and is preferably 1.2 or more, more preferably 1.3 or more, even more preferably 1.4 or more, preferably 1.7 or less, more preferably 1.6 or less, and even more preferably 1.5 or less. If the T2 ratio is less than 1.1, the affinity of polymer A for the solvent decreases. As a result, the dispersibility of CNT in the conductive material dispersion decreases, the viscosity of the conductive material dispersion increases, the IV resistance of the electrochemical device increases, and the rate characteristics decrease. If the T2 ratio exceeds 1.8, the affinity of polymer A for the solvent increases, making it difficult for polymer A to penetrate into the CNT aggregates. As a result, the dispersibility of CNT in the conductive material dispersion decreases, the IV resistance of the electrochemical device increases, and the rate characteristics decrease.

[0050] [Iodine Value] Here, the iodine value of polymer A is preferably 5 mg / 100 mg or more, more preferably 10 mg / 100 mg or more, even more preferably 15 mg / 100 mg or more, particularly preferably 17 mg / 100 mg or more, and preferably 60 mg / 100 mg or less, more preferably 50 mg / 100 mg or less, even more preferably 40 mg / 100 mg or less, even more preferably 30 mg / 100 mg or less, and particularly preferably 20 mg / 100 mg or less. If the iodine value of polymer A is 60 mg / 100 mg or less, the oxidation resistance of polymer A can be well ensured. The iodine value of polymer A can be adjusted, for example, by changing the hydrogenation conditions during the production of polymer A.

[0051] <<Method for Preparing Polymer A>> The method for preparing the above-mentioned polymer A is not particularly limited, and for example, the polymer A can be prepared by polymerizing a monomer composition containing the above-mentioned monomers, optionally in the presence of a chain transfer agent, to obtain a polymer, and then hydrogenating (hydrogenating) the obtained polymer.

[0052] Here, the content ratio of each monomer in the monomer composition used to prepare polymer A can be determined in accordance with the content ratio of each repeating unit in polymer A. The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. Furthermore, any reaction such as ionic polymerization, radical polymerization, or living radical polymerization can be used as the polymerization reaction. Commonly used emulsifiers, dispersants, polymerization initiators, chain transfer agents, and the like can be used in common amounts. Among these, tert-dodecyl mercaptan is preferred as the chain transfer agent. The amount of the chain transfer agent added is preferably 0.5 parts by mass or more and 2.5 parts by mass or less, based on 100 parts by mass of the total amount of monomers in the monomer composition used in the polymerization reaction. Furthermore, the polymerization temperature is preferably 0°C or more and 50°C or less.

[0053] Furthermore, the method for hydrogenating the polymer is not particularly limited, and a general method using a catalyst (see, for example, WO 2012 / 165120, WO 2013 / 080989, and JP 2013-8485 A) can be used.

[0054] <Solvent> The solvent that may be contained in the dispersant composition of the present invention is not particularly limited, and examples thereof include water and organic solvents. Examples of organic solvents that can be used include acetonitrile, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, acetone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, dimethylbenzene (xylene), methylbenzene (toluene), cyclopentyl methyl ether, and isopropyl alcohol. These may be used alone or in combination of two or more. Among these, NMP is preferred from the viewpoint of further reducing the IV resistance of the electrochemical element. It should be noted that the dispersant composition of the present invention does not necessarily contain a solvent.

[0055] <Other Components> The dispersant composition of the present invention can contain components (other components) other than the above-described polymer A and solvent. For example, the dispersant composition may contain a known polymer component other than the above-described polymer A (such as a copolymer of polyethylene glycol and styrene, a styrene-maleic acid copolymer, or an acrylic acid copolymer). The dispersant composition may also contain a monomer (unreacted residual monomer) used in producing polymer A or a known additive. The proportion of other components in the total solid content contained in the dispersant composition is not particularly limited, but is usually 10 mass % or less.

[0056] Examples of such known additives include emulsifiers, viscosity modifiers, antioxidants, etc. These are not particularly limited as long as they do not affect the reaction of the electrochemical device, and known additives, such as those described in WO 2012 / 115096, can be used. Note that the other components may be used alone or in combination of two or more in any ratio.

[0057] <Preparation of Dispersant Composition for Electrochemical Devices> The dispersant composition of the present invention can be prepared by mixing the above-mentioned polymer A, solvent, and other components by a known method. Specifically, the dispersant composition can be prepared by mixing the above-mentioned components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0058] When the polymer A is polymerized in a solvent, the dispersion of the polymer A dispersed in the solvent may be used as the dispersant composition as it is. ２ SO ４ The pH of the dispersant composition can also be adjusted by adding an alkali (such as an aqueous solution of methyl methacrylate) or an alkali (such as an aqueous KOH solution), and for example, the pH can be adjusted to a range of 3.0 to 9.5. Furthermore, when a solvent different from the polymerization solvent used in the synthesis of polymer A is desired to be used as the solvent for the dispersant composition, polymer A may be prepared in the polymerization solvent, and then the pH may be adjusted as desired, followed by solvent substitution using a known method to prepare the dispersant composition.

[0059] (Conductive material dispersion for electrochemical element) The conductive material dispersion of the present invention contains at least the dispersant composition, a conductive material, and a solvent described above, and optionally further contains other components that can be incorporated into electrodes of electrochemical elements. That is, the conductive material dispersion contains at least polymer A, a conductive material, and a solvent, and optionally further contains other components. The conductive material dispersion of the present invention usually does not contain an electrode active material. The solvent contained in the conductive material dispersion may be only the solvent contained in the dispersant composition, or may be a mixture of the solvent contained in the dispersant composition and an additional solvent used in preparing the conductive material dispersion. Since the conductive material dispersion of the present invention contains the dispersant composition described above, the use of this conductive material dispersion can reduce the IV resistance of an electrochemical element.

[0060] <Dispersant Composition> As the dispersant composition used in the conductive material dispersion, the above-described dispersant composition of the present invention is used.

[0061] <<Content of Polymer A>> Here, the content of polymer A in the conductive material dispersion is preferably 0.02% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 8% by mass or less, more preferably 6% by mass or less, still more preferably 4% by mass or less, and particularly preferably 2% by mass or less, based on the total amount of the conductive material dispersion being 100% by mass. If the content of polymer A in the conductive material dispersion is 0.02% by mass or more, the dispersibility of CNTs in the conductive material dispersion can be improved due to intermolecular interactions. Furthermore, if the content of polymer A in the conductive material dispersion is 8% by mass or less, the viscosity of the conductive material dispersion can be reduced, thereby improving operability during electrode production.

[0062] The conductive material dispersion of the present invention preferably contains 5 parts by mass or more of polymer A per 100 parts by mass of the conductive material, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, and preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. If the conductive material dispersion contains 5 parts by mass or more of polymer A per 100 parts by mass of the conductive material, the dispersibility of CNTs in the conductive material dispersion can be improved. On the other hand, if the conductive material dispersion contains 35 parts by mass or less of polymer A per 100 parts by mass of the conductive material, the rate characteristics can be improved while further reducing the IV resistance of the electrochemical device.

[0063] <Conductive Material> The conductive material used in the conductive material dispersion of the present invention is not particularly limited as long as it contains CNT. For example, the conductive material dispersion of the present invention may contain only CNT as the conductive material, or may contain CNT and a conductive material other than CNT. Examples of CNT include single-walled and multi-walled CNT (multi-walled CNT includes cup-stacked CNT). Furthermore, conductive materials other than CNT may further include conductive carbon materials such as carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), carbon nanohorns, milled carbon fibers obtained by calcining and then crushing polymer fibers, single-walled or multi-walled graphene, and carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers; fibers or foils of various metals, etc. These may be used alone, or two or more may be used in combination in any ratio.

[0064] <<CNT Content>> Here, the CNT content in the conductive material dispersion is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 9% by mass or less, even more preferably 8% by mass or less, and particularly preferably 7% by mass or less, based on the total amount of the conductive material dispersion being 100% by mass. If the CNT content in the conductive material dispersion is 0.05% by mass or more, an excessive decrease in the solids concentration during preparation of the electrode slurry can be suppressed. Furthermore, if the CNT content in the conductive material dispersion is 10% by mass or less, the viscosity of the conductive material dispersion can be kept low, thereby improving operability.

[0065] <Solvent> The solvent can function as a dispersion medium in the conductive material dispersion of the present invention. The solvent used in the conductive material dispersion of the present invention is not particularly limited, and the same solvents as those that can be blended in the dispersant composition of the present invention can be used.

[0066] <Solid content concentration> The solid content concentration of the conductive material dispersion is preferably 0.1 mass% or more, more preferably 1 mass% or more, even more preferably 5 mass% or more, and is preferably 15 mass% or less, more preferably 12.5 mass% or less, and even more preferably 10 mass% or less. If the solid content concentration in the conductive material dispersion is 0.1 mass% or more, the rate characteristics of the electrochemical element can be improved. On the other hand, if the solid content concentration in the conductive material dispersion is 15 mass% or less, the coatability of the electrode slurry prepared using the conductive material dispersion is improved.

[0067] <Preparation of Conductive Material Dispersion for Electrochemical Devices> The conductive material dispersion of the present invention can be prepared, for example, by mixing the dispersant composition of the present invention described above, a conductive material, a solvent, and any other components to obtain a mixed liquid (wetting step), subjecting the resulting mixed liquid to a dispersion treatment to obtain a conductive material preliminary dispersion (primary dispersion step), and subjecting the resulting conductive material preliminary dispersion to a further dispersion treatment to obtain a conductive material dispersion (secondary dispersion step). The wetting step aims to penetrate polymer A and the solvent into the gaps between the CNT aggregates. The primary dispersion step aims to disintegrate the CNT aggregates contained in the mixed liquid by a relatively weak dispersion treatment. The secondary dispersion step aims to stabilize the dispersion of the CNTs by a stronger dispersion treatment. Examples of dispersion treatments used in the primary dispersion step include ultrasonic treatment, a homodisper, a homomixer, and the like, and examples of dispersion treatments used in the secondary dispersion step include a bead mill, a planetary mill, a high-pressure homogenizer, and the like.

[0068] (Slurry for Electrochemical Device Electrode) The electrode slurry of the present invention contains at least the conductive material dispersion liquid and an electrode active material described above, and optionally further contains other components. That is, the electrode slurry of the present invention contains at least polymer A, a conductive material, a solvent, and an electrode active material, and optionally further contains other components. Furthermore, since the electrode slurry of the present invention contains the dispersant composition of the present invention described above, use of the electrode slurry can reduce the IV resistance of an electrochemical device.

[0069] In the following, an example will be described in which the electrode slurry of the present invention is a slurry for a positive electrode of a lithium ion secondary battery, but the present invention is not limited to the following example.

[0070] <Conductive Material Dispersion> As the conductive material dispersion used in the electrode slurry, the conductive material dispersion of the present invention described above is used.

[0071] <Electrode Active Material> An electrode active material is a material that transfers electricity to and from the electrode of a secondary battery. As a positive electrode active material for a lithium ion secondary battery, a material that can absorb and release lithium is usually used.

[0072] Specifically, the positive electrode active material for a lithium ion secondary battery is not particularly limited, and may be a lithium-containing cobalt oxide (LiCoO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), Co—Ni—Mn lithium-containing composite oxide (Li(CoMnNi)O ２ ;LiNi ０．８ Co ０．１ Mn ０．１ O ２ ), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al (Li(CoNiAl)O ２ ), olivine-type lithium iron phosphate (LiFePO ４ ), olivine-type lithium manganese phosphate (LiMnPO ４ ), Li ２ MnO ３ -LiNiO ２ system solid solution, Li １＋ｘ Mn ２－ｘ O ４ (0<X<2) Lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ ]O ２ , LiNi ０．５ Mn １．５ O ４The amount of the positive electrode active material and the particle size thereof are not particularly limited, and may be the same as those of conventionally used electrode active materials.

[0073] The other components are not particularly limited, and examples thereof include known binders (for example, fluorine-containing polymers such as polyvinylidene fluoride) that are generally used in electrodes for electrochemical elements, and other components that can be blended into the dispersant composition of the present invention.

[0074] <Preparation of Slurry for Electrochemical Device Electrode> The electrode slurry of the present invention can be prepared by mixing the above-described dispersant composition, a conductive material, a solvent, an electrode active material, and any other components. Here, the mixing method is not particularly limited, and the same method as used for preparing the above-described dispersant composition of the present invention can be used. Furthermore, the order in which the above-described components are mixed is not particularly limited, and all of the components to be incorporated into the dispersant composition, the conductive material, the solvent, the electrode active material, and any other components may be mixed together, or, for example, the above-described conductive material dispersion may be prepared, and then the obtained conductive material dispersion may be mixed with the electrode active material and any other components.

[0075] (Electrode for electrochemical device) The electrode for electrochemical device of the present invention comprises, for example, an electrode mixture layer formed on a current collector using the above-mentioned electrode slurry. Specifically, the electrode mixture layer is usually made of a dried product of the above-mentioned electrode slurry, and the electrode mixture layer contains at least the above-mentioned polymer A, a conductive material, and an electrode active material, and optionally contains other components. Note that the components contained in the electrode mixture layer are the same as those contained in the above-mentioned electrode slurry, and the preferred abundance ratio of each of these components is the same as the preferred abundance ratio of each component in the electrode slurry.

[0076] Furthermore, in the electrode for an electrochemical element of the present invention, the electrode mixture layer is formed using the above-mentioned electrode slurry, and therefore the IV resistance of the electrochemical element can be reduced.

[0077] <Method for forming an electrode for an electrochemical element> Here, the electrode mixture layer of the electrode for an electrochemical element of the present invention can be formed on a current collector, for example, through a step of applying the above-mentioned electrode slurry onto a current collector (application step) and a step of drying the electrode slurry applied onto the current collector to form an electrode mixture layer on the current collector (drying step).

[0078] <<Coating Step>> The method for applying the electrode slurry onto the current collector is not particularly limited, and known methods can be used. Specifically, examples of the coating method that can be used include a comma coater method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the electrode slurry may be applied to only one surface of the current collector, or may be applied to both surfaces of the current collector. The thickness of the electrode slurry film on the current collector after application and before drying can be set appropriately depending on the thickness of the electrode mixture layer obtained by drying.

[0079] Here, the current collector to which the electrode slurry is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. Note that the above-mentioned materials may be used alone or in combination of two or more in any ratio.

[0080] <<Drying Step>> The method for drying the electrode slurry on the current collector is not particularly limited, and known methods can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams. By drying the electrode slurry on the current collector in this manner, an electrode mixture layer is formed on the current collector, and an electrode for an electrochemical device comprising the current collector and the electrode mixture layer can be obtained. After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a mold press or a roll press. The pressure treatment can further improve the adhesion between the electrode mixture layer and the current collector.

[0081] (Electrochemical element) The electrochemical element of the present invention is not particularly limited, and may be a lithium ion secondary battery or an electric double layer capacitor, and is preferably a lithium ion secondary battery. The electrochemical element of the present invention has a low IV resistance because it includes the electrode for an electrochemical element of the present invention.

[0082] Hereinafter, a case where the electrochemical element is a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example. A lithium ion secondary battery as the electrochemical element of the present invention usually comprises electrodes (positive and negative electrodes), an electrolyte, and a separator, and uses the electrochemical element electrode of the present invention for at least one of the positive and negative electrodes.

[0083] <Electrode> Here, the electrode other than the above-described electrode for an electrochemical element that can be used in the lithium ion secondary battery as the electrochemical element of the present invention is not particularly limited, and any known electrode can be used. Specifically, the electrode other than the above-described electrode for an electrochemical element can be an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method.

[0084] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte of a lithium ion secondary battery, for example, a lithium salt is used. As the lithium salt, for example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２Among them, LiPF is the most popular because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred, and LiPF ６ is particularly preferred. The electrolyte may be used alone or in combination of two or more kinds in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0085] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) are preferably used. Other suitable solvents include carbonates such as γ-butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran, and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range, and a mixture of ethylene carbonate and diethyl carbonate is even more preferred. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Known additives, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethyl methyl sulfone, may also be added to the electrolyte.

[0086] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the lithium ion secondary battery and increasing the capacity per volume.

[0087] <Method for Manufacturing Lithium-Ion Secondary Battery> The lithium-ion secondary battery as an electrochemical element of the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting assembly as necessary according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent internal pressure increases, overcharge and overdischarge, and the like, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the lithium-ion secondary battery may be any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type.

[0088] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by polymerizing a plurality of types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, "M Ａ ", "η Ａ "," "F Ａ "," "T2 Ｃ "," "T2 Ｓ The "T2 ratio", the iodine value of polymer A, the volume resistivity, the viscosity of the conductive material dispersion, and the IV resistance and rate characteristics of the secondary battery were evaluated by the following methods.

[0089] <Weight average molecular weight (M Ａ )> Weight average molecular weight (M Ａ) was measured by gel permeation chromatography (GPC) using a 10 mM LiBr-DMF (N,N-dimethylformamide) solution under the following measurement conditions. Separation column: Shodex KD-806M (Showa Denko K.K.) Detector: Differential refractometer detector RID-10A (Shimadzu Corporation) Eluent flow rate: 0.3 mL / min Column temperature: 40°C Standard polymer: TSK standard polystyrene (Tosoh Corporation) <Iodine value> 100 g of the aqueous dispersion of polymer A prepared in the examples and comparative examples was coagulated with 1 L of methanol and then vacuum-dried at a temperature of 60°C for 12 hours to obtain a dried polymer. The iodine value (mg / 100 mg) of the obtained dried polymer was then measured in accordance with JIS K6235 (2006). <Viscosity (η Ａ )> In the same manner as in the above-mentioned method for evaluating the iodine value, a dried polymer was obtained from the aqueous dispersion of polymer A prepared in each of the Examples and Comparative Examples. NMP was added to the obtained dried polymer so that the concentration of polymer A became 10%, to prepare a polymer solution. The viscosity (mPa s) of this polymer solution was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10", temperature: 25°C, rotation speed: 60 rpm), and this was expressed as η Ａ (mPa·s). Ａ > The "M Ａ " and "η Ａ (mPa·s)" to obtain "F" from the following formula (1). Ａ The value of " was calculated. Ａ =(η Ａ / M Ａ ) × 1000 (1) <Transverse relaxation time (T2 Ｓ NMP was poured into a 10 mm diameter NMR sample tube to a height of approximately 4 cm from the bottom of the tube. The NMR sample tube was set in a holder heated to 25°C and left to stand for 5 minutes or more until the temperature stabilized. Then, the transverse relaxation time (T2 Ｓ The measurement conditions were as follows: １H, a measurement frequency of 13 MHz, a pulse sequence of CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence, and a free induction decay (FID) curve were obtained with four accumulations. Using dedicated software provided with the instrument, the obtained FID curve was subjected to curve fitting with a single exponential function to determine the transverse relaxation time (T2 Ｓ ) was obtained. T2 Ｓ The transverse relaxation time (T2 Ｃ )> In the same manner as in the evaluation method of the iodine value described above, a dried polymer was obtained from the aqueous dispersion of polymer A prepared in each of the Examples and Comparative Examples. NMP was added to the obtained dried polymer so that the concentration of polymer A became 1%, to prepare a polymer solution. Measurement and curve fitting were carried out in the same manner as in the case of T2s, except that this polymer solution was used as the measurement sample, and the transverse relaxation time (T2c) was determined. <T2 ratio> The "T2 Ｃ (milliseconds)" and "T2 Ｓ The "T2 ratio" was calculated from the following formula (2) using the time (milliseconds) between the start of the pulse and the end of the pulse. T2 ratio = T2 Ｓ / T2 Ｃ... (2) <Volume Resistivity> The conductive material preliminary dispersions prepared in the examples and comparative examples were applied to a PET (polyethylene terephthalate) film using a doctor blade and a table coater, and then dried in an oven at 100°C for 1 hour to obtain coatings with a film thickness of 10 to 20 μm. The surface resistivity (Ω / sq.) of the resulting coatings was measured using a resistivity meter (manufactured by Mitsubishi Chemical Corporation, product name "Loresta GP") in accordance with JIS K7194:1994. Furthermore, the thickness (cm) of the coating at the measurement point excluding the thickness of the PET film was measured. The volume resistivity (Ω·cm) was then calculated by the formula: volume resistivity (Ω·cm) = surface resistivity (Ω / sq.) × thickness (cm). Similar measurements were performed at 10 points, and the average value was evaluated according to the following criteria. A smaller average volume resistivity indicates that the CNT aggregates in the conductive material dispersion have been disintegrated, i.e., the dispersant composition functions well as a dispersant. A: Average volume resistivity is 3 Ω cm or less B: Average volume resistivity is more than 3 Ω cm and 10 Ω cm or less C: Average volume resistivity is more than 10 Ω cm <Viscosity of Conductive Material Dispersion> The viscosity of the conductive material dispersions having a solid content of 7.2% prepared in the examples and comparative examples was measured. Specifically, the viscosity was measured using a rheometer (manufactured by Anton Paar, product name "MCR302") at a temperature of 25°C and a shear rate of 2.5 s －１The viscosity was measured under the above conditions and evaluated according to the following criteria. At the same solid content concentration, the lower the viscosity of the conductive material dispersion, the better the dispersion of CNTs in the conductive material dispersion, i.e., the better the dispersant composition functions as a dispersant. A: Viscosity of 20 mPa·s or less B: Viscosity of more than 20 mPa·s and less than 40 mPa·s C: Viscosity of 40 mPa·s or more <IV Resistance> The lithium ion secondary batteries produced in the Examples and Comparative Examples were allowed to stand at a temperature of 25°C for 5 hours after injection of the electrolyte. Next, the batteries were charged to a cell voltage of 4.2 V by a constant current method of 0.2 C and then discharged to a cell voltage of 3.0 V. This charge-discharge cycle was repeated three times, and the initial capacity was measured. Thereafter, the batteries were charged to a depth of charge (SOC) of 50%, and then charged for 20 seconds and discharged for 20 seconds at 0.5 C, 1.0 C, 1.5 C, and 2.0 C, centered around 50% SOC. The battery voltage after 20 seconds in each case (charge side and discharge side) was plotted against the current value, and the slope was calculated as the IV resistance (Ω) (IV resistance during charge and IV resistance during discharge). The obtained IV resistance values ​​(Ω) were evaluated according to the following criteria. A: IV resistance value less than 2.20 Ω B: IV resistance value 2.20 Ω or more but less than 2.35 Ω C: IV resistance value 2.35 Ω or more but less than 2.50 Ω D: IV resistance value 2.50 Ω or more <Rate Characteristics> The lithium ion secondary batteries fabricated in the examples and comparative examples were allowed to stand at a temperature of 25°C for 5 hours after injection of the electrolyte. Next, the battery was charged to a cell voltage of 3.65 V at a constant current of 0.2 C at 25 ° C, and then aged for 12 hours at 60 ° C. It was then discharged to a cell voltage of 3.0 V at a constant current of 0.2 C. It was then CC-CV charged at a constant current of 0.2 C (upper limit cell voltage 4.20 V), and CC discharged at a constant current of 0.2 C to a cell voltage of 3.00 V. This 0.2 C charge / discharge cycle was repeated three times. Next, in a 25 ° C environment, a 0.2 C constant current charge / discharge was performed between cell voltages of 4.20 and 3.00 V, and the discharge capacity at this time was defined as C0. It was then similarly CC-CV charged at a constant current of 0.2 C, and CC discharged at a constant current of 3.0 C to 3.00 V in a 25 ° C environment, and the discharge capacity at this time was defined as C1.The rate characteristics were calculated by calculating the ratio (percentage, capacity retention) of the discharge capacity (C1) at 3.0 C to the discharge capacity (C0) at 0.2 C, expressed as (C1 / C0) x 100 (%), and evaluated according to the following criteria. A larger capacity retention value indicates less decrease in discharge capacity at high current and lower internal resistance (i.e., better rate characteristics). A: Capacity retention value is 65% or more. B: Capacity retention value is 55% or more but less than 65%. C: Capacity retention value is less than 55%.

[0090] Example 1 Preparation of Dispersant Composition Synthesis of Polymer A A reactor was charged with 200 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate, 30 parts of acrylonitrile as nitrile group-containing monomer units, 10 parts of methacrylic acid as acid group-containing monomer units, and 1.80 parts of tert-dodecyl mercaptan as a chain transfer agent, in that order. The internal gas was then purged with nitrogen three times, and 60 parts of 1,3-butadiene as a conjugated diene monomer was then charged. The reactor was then maintained at 10°C, and 0.03 parts of cumene hydroperoxide as a polymerization initiator, a reducing agent, and an appropriate amount of a chelating agent were charged. The polymerization reaction was continued with stirring, and when the polymerization conversion rate reached 80%, the polymerization reaction was terminated by adding 0.1 parts of a 10% aqueous solution of hydroquinone as a polymerization terminator. The residual monomer was then removed at a water temperature of 80°C, yielding an aqueous dispersion of a precursor of Polymer A. A palladium catalyst (a solution obtained by mixing 1% palladium acetate acetone solution with an equal weight of ion-exchanged water) was added to the aqueous dispersion of the precursor of polymer A in an autoclave so that the palladium content relative to the weight of the solids contained in the obtained aqueous dispersion of the precursor of polymer A was 3,000 ppm, and ion-exchanged water was added to make the solids concentration 10%, and a hydrogenation reaction was carried out at a hydrogen pressure of 3 MPa and a temperature of 55°C for 3 hours to obtain an aqueous dispersion of polymer A. Thereafter, the contents were returned to room temperature, the system was conditioned under a nitrogen atmosphere, and then the system was concentrated using an evaporator until the solids concentration reached 20%. [pH adjustment] 2.5% H ２ SO ４An aqueous solution was added thereto, and the pH was adjusted to 3.0. 200 parts of NMP was added to 100 parts of the aqueous dispersion of polymer A after the pH adjustment, and all of the water and residual monomers were evaporated under reduced pressure, and then the NMP was evaporated to obtain a dispersant composition (an NMP solution of polymer A with a solid content of 10%). <Preparation of Conductive Material Dispersion> [Wetting Step] Multi-walled CNTs (specific surface area: 186 m) were used as the conductive material. ２ A mixed solution was obtained by mixing 6.0 parts of a polymer A (polymer A solution in NMP with a solids concentration of 10% (equivalent to the solids content)), 1.2 parts (solids content equivalent) of the dispersant composition prepared above (a solution of polymer A in NMP with a solids concentration of 10%), and an amount of NMP such that the total amount of the obtained conductive material pre-dispersion would be 100 parts. [Primary Dispersion Step] The mixed solution obtained was stirred for 300 seconds at a peripheral speed of 30 m / s using a thin film rotary high-speed mixer (manufactured by Primix Corporation, product name "FILMIX (registered trademark) 40-L type") to prepare a conductive material pre-dispersion with a solids concentration of 7.2 mass%. The volume resistivity was evaluated using this conductive material pre-dispersion. The results are shown in Table 1. [Secondary Dispersion Step] The conductive material pre-dispersion obtained above was mixed for 1 hour using a bead mill with zirconia beads with a diameter of 1 mm at a peripheral speed of 8 m / s to produce a conductive material dispersion with a solids concentration of 7.2%. The viscosity of this conductive material dispersion was evaluated. The results are shown in Table 1. <Preparation of Positive Electrode Slurry> A ternary active material (LiNi) was used as the positive electrode active material. ０．６ Co ０．２ Mn ０．２ O ２ 98.0 parts of PEG-1000 (average particle size: 6 μm), 1.0 part of polyvinylidene fluoride as a binder, 1.0 part of the conductive material dispersion liquid prepared above (solid content equivalent), and NMP as a solvent were mixed and mixed in a planetary mixer (60 rpm, 30 minutes) to prepare a positive electrode slurry. The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry (measured using a single cylindrical rotational viscometer in accordance with JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 3000 to 5000 mPa·s. <Preparation of Positive Electrode> A 15 μm thick aluminum foil was prepared as a current collector. The positive electrode slurry prepared above was coated on the aluminum foil using a comma coater to a basis weight of 19 mg / cm after drying. ２The positive electrode blank was then rolled with a roll press to a density of 3.5 g / cm. ３ A positive electrode was fabricated comprising a positive electrode mixture layer of the above and aluminum foil. <Fabrication of Negative Electrode> A planetary mixer equipped with a disperser was used to fabricate a negative electrode active material, artificial graphite (specific surface area: 4 m ２ 100 parts of a 1% aqueous solution of carboxymethyl cellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "BSH-12") as a viscosity modifier was added in solids equivalent to 1 part, and the solids concentration was adjusted to 55% with ion-exchanged water, followed by mixing at a temperature of 25°C for 60 minutes. Next, the solids concentration was adjusted to 52% with ion-exchanged water. Mixing was then continued for an additional 15 minutes to obtain a mixed solution. To the obtained mixed solution, 1.0 part in solids equivalent of a 40% aqueous dispersion of styrene-butadiene copolymer as a binder and ion-exchanged water were added, and the final solids concentration was adjusted to 50%, followed by mixing for an additional 10 minutes. The obtained mixture was degassed under reduced pressure to obtain a negative electrode slurry composition with good fluidity. The obtained negative electrode slurry composition was coated with a comma coater onto a 20 μm-thick copper foil current collector to a basis weight of 11 mg / cm after drying. ２ The negative electrode blank was then rolled with a roll press to a density of 1.5 g / cm. ３ A negative electrode of 1000 kJ / cm was obtained. <Production of Lithium-ion Secondary Battery> An aluminum packaging material was prepared as the packaging material for the lithium-ion secondary battery. The positive electrode was cut into a 4 cm x 4 cm square and placed so that the surface on the current collector side was in contact with the aluminum packaging material. Next, a 15 μm thick separator (a polyethylene microporous film) cut into a 5 cm x 5 cm square was interposed on the surface of the positive electrode composite layer of the positive electrode. Furthermore, the negative electrode was cut into a 4.2 cm x 4.2 cm square and placed on the separator so that the surface on the negative electrode composite layer side faced the separator. Thereafter, LiPF 5 with a concentration of 1.0 M was used as the electrolyte. ６A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume % vinylene carbonate (solvent ratio)) was filled. Furthermore, in order to seal the opening of the aluminum packaging material, the aluminum packaging exterior was closed by heat sealing at 150°C, and a laminate cell type lithium ion secondary battery was produced. The IV resistance and rate characteristics of the produced lithium ion secondary battery were evaluated. The results are shown in Table 1.

[0091] Example 2 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that monobutyl maleate was used instead of methacrylic acid as the acid group-containing monomer. [pH Adjustment] A 2.5% KOH aqueous solution was added to the aqueous dispersion of polymer A (solids concentration: 20%) obtained as described above, and the pH was adjusted to 9.0. 200 parts of NMP was added to 100 parts of the aqueous dispersion of polymer A after the pH adjustment, and all water and residual monomers were evaporated under reduced pressure. Then, the NMP was evaporated to a concentration of 10% to obtain an NMP solution of polymer A as a dispersant composition.

[0092] Example 3 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of Polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that the amount of acrylonitrile used as the nitrile group-containing monomer was changed from 30 parts to 25 parts, the amount of 1,3-butadiene used as the conjugated diene monomer was changed from 60 parts to 50 parts, the amount of methacrylic acid used as the acid group-containing monomer was changed from 10 parts to 3 parts, and 22 parts of styrene was used as the aromatic vinyl monomer. [pH Adjustment] A 2.5% KOH aqueous solution was added to the aqueous dispersion of Polymer A obtained as described above (solids concentration: 20%) to adjust the pH to 9.5. To 100 parts of the pH-adjusted aqueous dispersion of polymer A, 200 parts of NMP was added, and all of the water and residual monomers were evaporated under reduced pressure. Then, NMP was evaporated until the concentration reached 10%, thereby obtaining an NMP solution of polymer A as a dispersant composition.

[0093] Example 4 A dispersant composition, a conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a 2.5% KOH aqueous solution was added during the preparation of the dispersant composition to adjust the pH of the dispersant composition to 7.5. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0094] Example 5 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of Polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that the amount of acrylonitrile used as the nitrile group-containing monomer was changed from 30 parts to 37 parts, the amount of 1,3-butadiene used as the conjugated diene monomer was changed from 60 parts to 62 parts, and the amount of methacrylic acid used as the acid group-containing monomer was changed from 10 parts to 1 part. [pH Adjustment] A 2.5% KOH aqueous solution was added to the aqueous dispersion of Polymer A obtained as described above (solids concentration: 20%) to adjust the pH to 9.5. To 100 parts of the pH-adjusted aqueous dispersion of polymer A, 200 parts of NMP was added, and all of the water and residual monomers were evaporated under reduced pressure. Then, NMP was evaporated until the concentration reached 10%, thereby obtaining an NMP solution of polymer A as a dispersant composition.

[0095] Comparative Example 1 A dispersant composition, a conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a 2.5% KOH aqueous solution was added during the preparation of the dispersant composition to adjust the pH of the dispersant composition to 12. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0096] Comparative Example 2 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] A reactor was charged with 200 parts of ion-exchanged water and 0.2 parts of sodium carbonate. After dissolving the sodium carbonate, 2.25 parts of fatty acid potassium soap (potassium salt of fatty acid) was added to prepare an aqueous soap solution. Then, 35 parts of acrylonitrile as a nitrile group-containing monomer and 0.4 parts of tert-dodecyl mercaptan as a chain transfer agent were charged to the resulting aqueous soap solution, in this order. The internal gas was purged with nitrogen three times, and then 65 parts of 1,3-butadiene as a conjugated diene monomer was charged. Next, the reactor was kept at 10°C, and 0.1 parts of cumene hydroperoxide, 0.01 parts of ethylenediaminetetraacetic acid monosodium iron hydrate, 0.03 parts of sodium hydroxymethanesulfinate dihydrate, and 0.03 parts of EDTA.4Na.4H were added. ２ A redox polymerization initiator consisting of a combination of 0.02 parts of methyl methyl acrylate and 0.02 parts of methyl acrylate was added to initiate the polymerization reaction. When the polymerization conversion rate reached 85%, 0.1 parts of a 10% aqueous solution of hydroquinone (polymerization terminator) was added to terminate the polymerization reaction, and residual monomers were removed using a rotary evaporator at a water temperature of 60 ° C. to obtain a nitrile rubber latex. Next, a portion of the obtained latex was added to an aqueous solution of magnesium sulfate as a coagulant in an amount of 1.0% relative to the nitrile rubber content, and the mixture was stirred to coagulate the latex. The coagulated latex was then filtered while washing with water, and the obtained coagulated material was vacuum dried at 60 ° C. for 12 hours to obtain a precursor of polymer A. The obtained precursor of polymer A was dissolved in acetone to a concentration of 12%, which was then placed in an autoclave. 500 ppm by mass of palladium-silica catalyst was added relative to the precursor of polymer A, and a hydrogenation reaction was carried out at a hydrogen pressure of 3.0 MPa. After the hydrogenation reaction was completed, the mixture was poured into a large amount of water to coagulate, followed by filtration and drying to obtain polymer A. [pH Adjustment] NMP was added to the polymer A obtained as described above to a concentration of 10%, to obtain an NMP solution of polymer A as a dispersant composition.

[0097] Comparative Example 3 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium-ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that the amount of tert-dodecyl mercaptan used was changed from 1.80 parts to 2.50 parts. [pH Adjustment] A 2.5% KOH aqueous solution was added to the aqueous dispersion of polymer A (solids concentration: 20%) obtained as described above, and the pH was adjusted to 9.5. 200 parts of NMP was added to 100 parts of the aqueous dispersion of polymer A after pH adjustment, and all water and residual monomers were evaporated under reduced pressure. Then, the NMP was evaporated until the concentration reached 10%, thereby obtaining an NMP solution of polymer A as a dispersant composition.

[0098] Comparative Example 4 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that the amount of acrylonitrile used as the nitrile group-containing monomer was changed from 30 parts to 40 parts, the amount of 1,3-butadiene used as the conjugated diene monomer was changed from 60 parts to 55 parts, the amount of methacrylic acid used as the acid group-containing monomer was changed from 10 parts to 5 parts, and the amount of tert-dodecyl mercaptan used was changed from 1.80 parts to 0.90 parts. [pH Adjustment] A 2.5% H ２ SO ４ To 100 parts of the aqueous dispersion of polymer A after the pH adjustment, 200 parts of NMP was added, and all of the water and residual monomers were evaporated under reduced pressure. Then, NMP was evaporated until the concentration reached 10%, thereby obtaining an NMP solution of polymer A as a dispersant composition.

[0099] Comparative Example 5 A conductive material dispersion, a positive electrode slurry, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared or fabricated in the same manner as in Example 1, except that a dispersant composition prepared as follows was used. Evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. <Preparation of Dispersant Composition> [Synthesis of Polymer A] An aqueous dispersion of polymer A (solids concentration: 20%) was obtained in the same manner as in Example 1, except that the amount of acrylonitrile used as the nitrile group-containing monomer was changed from 30 parts to 38 parts, the amount of 1,3-butadiene used as the conjugated diene monomer was changed from 60 parts to 61.5 parts, and the amount of methacrylic acid used as the acid group-containing monomer was changed from 10 parts to 0.5 parts. [pH Adjustment] A 2.5% H ２ SO ４ To 100 parts of the aqueous dispersion of polymer A after the pH adjustment, 200 parts of NMP was added, and all of the water and residual monomers were evaporated under reduced pressure. Then, NMP was evaporated until the concentration reached 10%, thereby obtaining an NMP solution of polymer A as a dispersant composition.

[0100] In Table 1 shown below, "AN" represents an acrylonitrile unit, "HBD" represents a 1,3-butadiene hydride unit, "BD" represents a unit derived from a 1,3-butadiene monomer other than HBD, "ST" represents a styrene unit, "MAA" represents a methacrylic acid unit, "MBM" represents a monobutyl maleate unit, "CNT" represents a carbon nanotube, and "NMP" represents N-methyl-2-pyrrolidone. In Table 1, "F Ａ " is a value rounded to one decimal place, and "T2 ratio" is a value rounded to two decimal places.

[0101]

[0102] From Table 1, it can be seen that the copolymers containing the nitrile group-containing monomer unit and the alkylene structural unit having 4 or more carbon atoms and the copolymers containing the F ＡIt can be seen that in Examples 1 to 5, which used dispersant compositions containing polymer A in which the T2 ratio and T3 ratio were within the respective predetermined ranges, lithium ion secondary batteries with low IV resistance were produced. Ａ It can be seen that the IV resistance of the lithium ion secondary battery was increased in Comparative Examples 1 to 3, which used dispersant compositions containing polymer A whose T2 ratio was outside the specified range, and in Comparative Examples 4 and 5, which used dispersant compositions containing polymer A whose T2 ratio was outside the specified range, compared to Examples 1 to 5.

[0103] According to the present invention, it is possible to provide a dispersant composition for electrochemical devices, a conductive material dispersion for electrochemical devices, and a slurry for electrochemical device electrodes, which are capable of forming electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. Also, according to the present invention, it is possible to provide electrodes for electrochemical devices that can reduce the IV resistance of the electrochemical device. Furthermore, according to the present invention, it is possible to provide an electrochemical device having low IV resistance.

Claims

1. A dispersant composition for electrochemical elements comprising a polymer A, the polymer A comprising a nitrile group-containing monomer unit and an alkylene structural unit having 4 or more carbon atoms, and a weight average molecular weight of the polymer A being M Ａ The viscosity of the polymer solution obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A becomes 10% by mass, measured at a temperature of 25° C., is η Ａ (mPa·s) as shown in the following formula (1): Ａ = (η Ａ / M Ａ ) × 1000 ... (1) Ａ ) is 0.1 or more and 9.0 or less, and the transverse relaxation time T2 measured in N-methyl-2-pyrrolidone at a temperature of 25°C is Ｓ (milliseconds), and the transverse relaxation time measured at a temperature of 25° C. of a polymer solution obtained by adding N-methyl-2-pyrrolidone to the polymer A so that the concentration of the polymer A becomes 1% by mass is T2 Ｃ (milliseconds), the following formula (2): T2 ratio = T2 Ｓ / T2 Ｃ A dispersant composition for electrochemical elements, wherein the T2 ratio calculated by the above formula (2) is 1.1 or more and 1.8 or less.

2. The dispersant composition for electrochemical devices according to claim 1, wherein the nitrile group-containing monomer unit is an acrylonitrile unit, and the alkylene structural unit is a 1,3-butadiene hydride unit.

3. The dispersant composition for electrochemical devices according to claim 1 or 2, wherein the polymer A further contains at least one of an aromatic vinyl monomer unit and an acid group-containing monomer unit.

4. The iodine value of the polymer A is 5 mg / 100 mg or more and 60 mg / 100 mg or less, and the weight average molecular weight (M Ａ 4. The dispersant composition for electrochemical elements according to claim 1, wherein the molecular weight distribution (Mw) of the dispersant composition for electrochemical elements is 1,000 or more and 100,000 or less.

5. The dispersant composition for electrochemical devices according to any one of claims 1 to 4, further comprising a solvent.

6. A conductive material dispersion for electrochemical elements, comprising the dispersant composition for electrochemical elements according to any one of claims 1 to 5, a conductive material, and a solvent, wherein the conductive material comprises carbon nanotubes.

7. The conductive material dispersion liquid for electrochemical elements according to claim 6, having a solid content concentration of 0.1% by mass or more and 15% by mass or less.

8. The conductive material dispersion liquid for electrochemical elements according to claim 6 or 7, wherein the content of the carbon nanotubes is from 0.05% by mass to 10% by mass, and the content of the polymer A is from 0.02% by mass to 8% by mass.

9. A slurry for an electrochemical element electrode, comprising the electroconductive material dispersion for an electrochemical element according to any one of claims 6 to 8 and an electrode active material.

10. An electrode for an electrochemical element, comprising an electrode mixture layer formed using the slurry for an electrochemical element electrode according to claim 9.

11. An electrochemical element comprising the electrode for an electrochemical element according to claim 10.

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