Conductive material dispersion, slurry for secondary battery positive electrode, positive electrode for secondary battery, and secondary battery

Abstract

The present invention aims to provide a conductive material dispersion liquid that can reduce the internal resistance of a secondary battery and ensure good high-temperature storage characteristics of the secondary battery. The conductive material dispersion liquid of the present invention comprises a carbon material, a dispersant, and a dispersion medium. The Hansen Solubility Parameter (HSP) of the carbon material is c ) and the Hansen Solubility Parameters (HSP) of the above dispersants d ) of the HSP distance (R d ) is 10.0MPa 1 / 2 the following.

Description

Technical Field

[0001] The present invention relates to a conductive material dispersion, a slurry for a secondary battery positive electrode, a secondary battery positive electrode, and a secondary battery. Background Art

[0002] Secondary batteries such as lithium-ion secondary batteries have the characteristics of being small, lightweight, having high energy density, and being able to be repeatedly charged and discharged, and are used in a wide range of applications. Here, for example, an electrode for a lithium-ion secondary battery generally comprises a current collector and an electrode composite material layer formed on the current collector. Moreover, an electrode composite material layer, such as a positive electrode composite material layer, is generally formed by applying a positive electrode slurry formed by including a positive electrode active material in a dispersion medium, a conductive material for improving conductivity, and a binding material for bonding these components on the current collector and drying the slurry.

[0003] To achieve improved electrochemical device performance, attempts have been made to improve electrode slurries, such as positive electrode slurries. For example, carbon materials, which can be used as conductive materials, are prone to agglomeration. Therefore, the following technology has been proposed: in order to fully disperse the carbon material and achieve excellent battery characteristics for secondary batteries, the carbon material and a dispersant are pre-mixed in a dispersion medium to form a conductive material dispersion, and the resulting conductive material dispersion is combined with an electrode active material to prepare an electrode slurry (see, for example, Patent Documents 1 to 5).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2016 / 103730;

[0007] Patent Document 2: International Publication No. 2019 / 181869;

[0008] Patent Document 3: Japanese Patent Application No. 2018-522803;

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 2015-13302;

[0010] Patent Document 5: Japanese Patent Application Publication No. 2018-45820. Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, in the above-mentioned prior art, there is a demand for further improvement in the battery characteristics of secondary batteries. Specifically, there is a demand for further reduction in the internal resistance of secondary batteries and sufficient suppression of gas generation during high-temperature storage of secondary batteries (ie, improvement in high-temperature storage characteristics).

[0013] Therefore, an object of the present invention is to provide a conductive material dispersion, a slurry for a secondary battery positive electrode, and a secondary battery positive electrode that can reduce the internal resistance of a secondary battery and ensure good high-temperature storage characteristics of the secondary battery.

[0014] Another object of the present invention is to provide a secondary battery having reduced internal resistance and excellent high-temperature storage characteristics.

[0015] Solutions for solving problems

[0016] The present inventors have conducted intensive research to solve the above problems. Furthermore, the present inventors have found that if the Hansen Solubility Parameter (HSP) of the carbon material formed by using the carbon material and the dispersant contained in the dispersion medium is c ) and the Hansen Solubility Parameter (HSP) of the dispersant d ) of the HSP distance (R d ) is below a specified value to produce an electrode, the internal resistance of the secondary battery can be reduced and the high-temperature storage characteristics of the secondary battery can be improved, thus completing the present invention.

[0017] That is, the object of the present invention is to advantageously solve the above-mentioned problems. The conductive material dispersion of the present invention is characterized by comprising a carbon material, a dispersant, and a dispersion medium, wherein the Hansen Solubility Parameter (HSP) of the carbon material is c ) and the Hansen Solubility Parameters (HSP) of the above dispersants d ) of the HSP distance (R d ) is 10.0MPa 1 / 2 As follows. If the HSP distance (R d ) is less than the above-mentioned value and a conductive material dispersion formed by a dispersant to produce an electrode, the internal resistance of a secondary battery having the electrode can be reduced and good high-temperature storage characteristics can be ensured.

[0018] In addition, in the present invention, the "Hansen Solubility Parameter (HSP) of carbon materials c )” is determined by the polar term δ p1 , dispersion term δ d1 , and the hydrogen bond term δ h1 The Hansen Solubility Parameters (HSP) of the dispersant d )” is determined by the polar term δ p2 , dispersion term δ d2 , and the hydrogen bond term δ h2 constitute.

[0019] Here, in the present invention, “δ p1 ”, “δ d1 ” and “δ h1 ”, and “δ p2”, “δ d2 ” and “δ h2 " can be determined using the method described in the Examples.

[0020] Moreover, in the present invention, “HSP distance (R d )" can be calculated using the following formula (1):

[0021] HSP distance (R d )={(δ p1 -δ p2 ) 2 +4×(δ d1 -δ d2 ) 2 +(δ h1 -δ h2 ) 2} 1 / 2 …(1)

[0022] Here, the conductive material dispersion of the present invention preferably has a Hansen Solubility Parameter (HSP) of the carbon material. c ) in the hydrogen bond term δ h1 12.0MPa 1 / 2 Below. If the hydrogen bond term δ h1 When the viscosity is not more than the above value, the viscosity stability of the conductive material dispersion can be improved, the internal resistance of the secondary battery can be further reduced, and the high-temperature storage characteristics can be further improved.

[0023] Furthermore, in the conductive material dispersion of the present invention, it is preferable that the carbon material includes a fibrous carbon material. If a fibrous carbon material is used as the carbon material, the capacity of the secondary battery can be increased.

[0024] In the present invention, the aspect ratio (major diameter / minor diameter) of the "fibrous carbon material" is 5 or greater. Furthermore, the aspect ratio of the fibrous carbon material is preferably greater than 10. The "aspect ratio" can be determined by measuring the maximum diameter (major diameter) and the fiber diameter (minor diameter) in a direction perpendicular to the maximum diameter of any fibrous carbon material using a scanning electron microscope (SEM), and calculating the ratio of the major diameter to the minor diameter (major diameter / minor diameter).

[0025] Furthermore, the present invention aims to advantageously address the aforementioned issues. The secondary battery positive electrode slurry of the present invention is characterized by comprising a positive electrode active material and any of the aforementioned conductive material dispersions. Using the positive electrode slurry comprising the positive electrode active material and any of the aforementioned conductive material dispersions to produce a positive electrode can reduce the internal resistance of a secondary battery having the positive electrode and ensure excellent high-temperature storage characteristics.

[0026] The secondary battery positive electrode slurry of the present invention preferably further contains a binder. If the positive electrode slurry contains a binder, precipitation of the positive electrode active material can be suppressed and the positive electrode composite material layer formed using the positive electrode slurry can be well adhered to the current collector.

[0027] Furthermore, the slurry for the secondary battery positive electrode of the present invention preferably has a Hansen Solubility Parameter (HSP) of the carbon material. c ) and the Hansen Solubility Parameter (HSP) of the above-mentioned bonding materials b ) of the HSP distance (R b ) is greater than the above HSP distance (R d ). If the HSP distance (R b ) is greater than the HSP distance (R d ), the internal resistance of the secondary battery can be further reduced.

[0028] In addition, in the present invention, "Hansen Solubility Parameter (HSP) of the bonding material b )” is determined by the polar term δ p3 , dispersion term δ d3 and the hydrogen bond term δ h3 constitute.

[0029] Here, in the present invention, “δ p3 ”, “δ d3 ” and “δ h3 " can be determined using the method described in the Examples.

[0030] Moreover, in the present invention, “HSP distance (R b )" can be calculated using the following formula (2):

[0031] HSP distance (R b )={(δ p1 -δ p3 ) 2 +4×(δ d1 -δ d3 ) 2 +(δ h1 -δ h3 ) 2} 1 / 2 …(2)

[0032] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The secondary battery positive electrode of the present invention is characterized by comprising a positive electrode composite material layer formed using any of the above-mentioned secondary battery positive electrode slurries. According to the positive electrode comprising a positive electrode composite material layer formed using any of the above-mentioned secondary battery positive electrode slurries, the internal resistance of the secondary battery can be reduced while ensuring good high-temperature storage characteristics.

[0033] The present invention aims to advantageously solve the above-mentioned problems. The secondary battery of the present invention is characterized by comprising the above-mentioned positive electrode for a secondary battery. The secondary battery comprising the above-mentioned positive electrode for a secondary battery has reduced internal resistance and excellent high-temperature storage characteristics.

[0034] Effects of the Invention

[0035] According to the present invention, a conductive material dispersion, a secondary battery positive electrode slurry, and a secondary battery positive electrode can be provided, which can reduce the internal resistance of a secondary battery and ensure good high-temperature storage characteristics of the secondary battery.

[0036] Furthermore, according to the present invention, a secondary battery having reduced internal resistance and excellent high-temperature storage characteristics can be provided. DETAILED DESCRIPTION

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

[0038] Here, the conductive material dispersion of the present invention can be used as a material when manufacturing a slurry for a secondary battery electrode, preferably as a material when manufacturing a slurry for a secondary battery positive electrode. Moreover, the slurry for the secondary battery positive electrode of the present invention is prepared using the conductive material dispersion of the present invention. In addition, the secondary battery positive electrode of the present invention is characterized in that it has a positive electrode composite material layer formed using the slurry for the secondary battery positive electrode of the present invention. In addition, the secondary battery of the present invention is characterized in that it has a secondary battery positive electrode of the present invention.

[0039] (Conductive material dispersion)

[0040] The conductive material dispersion of the present invention comprises a carbon material, a dispersant, and a dispersion medium, and optionally contains other components. Furthermore, the conductive material dispersion generally does not contain an electrode active material (positive electrode active material, negative electrode active material).

[0041] Here, the conductive material dispersion of the present invention is characterized by the Hansen Solubility Parameter (HSP) of the carbon material. c ) and the Hansen Solubility Parameter (HSP) of the dispersant d ) of the HSP distance (R d ) is 10.0MPa 1 / 2 Furthermore, if the electrode composite material layer of an electrode is formed using the electrode slurry containing the conductive material dispersion of the present invention, the internal resistance of a secondary battery having the electrode can be reduced and the high-temperature storage characteristics can be improved.

[0042] Like this, by HSP distance (R d ) is 10.0MPa 1 / 2 The reason why the conductive material dispersion of the present invention can obtain the above-mentioned effects is not clear, but is presumed to be as follows.

[0043] That is, since the HSP distance (R d ) is 10.0MPa 1 / 2 Hereinafter, the affinity of the carbon material and the dispersant is extremely high, and the dispersant can be well coated on the surface of the carbon material in the dispersion medium, so that the carbon material is fully dispersed. Therefore, the carbon material as the conductive material is evenly arranged in the electrode composite material layer, forming a good conductive path, which can reduce the internal resistance of the secondary battery. In addition, as mentioned above, since the dispersant is well coated on the surface of the carbon material, the decomposition of the electrolyte on the surface of the carbon material can be suppressed inside the secondary battery. Thus, the gas generation when the secondary battery is stored at high temperature can be fully suppressed.

[0044] <Carbon Materials>

[0045] As a carbon material, as long as it functions as a conductive material that can ensure electrical contact between electrode active materials in the electrode composite material layer, it is not particularly limited. As such a carbon material, there can be mentioned: carbon black (such as acetylene black, Ketjen black (registered trademark), furnace black, etc.); graphite; carbon sheet; carbon nanofibers, carbon nanotubes (hereinafter sometimes abbreviated as "CNT") and fibrous carbon materials such as vapor-phase grown carbon fibers. These can be used alone or in combination with two or more. Moreover, among these, from the viewpoint of being able to form a good conductive path in the electrode composite material layer even in a small amount, so that the secondary battery has a high capacity, preferably a fibrous carbon material, more preferably carbon nanofibers, carbon nanotubes, and further preferably carbon nanotubes.

[0046] The above-mentioned carbon materials can be produced by known methods. For example, CNTs can be produced by a supergrowth method (see International Publication No. 2006 / 011655).

[0047] Alternatively, the carbon material may be subjected to a surface treatment. Surface treatment can be performed by, for example, contacting the carbon material with a treatment liquid such as an acid solution, an alkaline solution, and / or ozone water, or a gas containing ozone, followed by plasma treatment. The method for contacting the treatment liquid with the carbon material is not particularly limited, but preferably, the carbon material is immersed in the treatment liquid.

[0048] Hansen Solubility Parameters (HSP) c )》

[0049] As mentioned above, HSP c By the polar term δ p1 , dispersion term δ d1 and the hydrogen bond term δ h1 These three constitute.

[0050] Here, the polar term δ p1 Not particularly limited, but preferably 3.0 MPa 1 / 2More than 5.0 MPa 1 / 2 Above, preferably 13.0 MPa 1 / 2 Below, more preferably 11.0 MPa 1 / 2 the following.

[0051] In addition, the dispersion term δ d1 Preferably 13.0 MPa 1 / 2 More than 16.0 MPa 1 / 2 Above, preferably 22.0 MPa 1 / 2 Below, more preferably 20.0 MPa 1 / 2 the following.

[0052] Moreover, the hydrogen bond term δ h1 Preferably 12.0 MPa 1 / 2 Below, more preferably 10.0 MPa 1 / 2 Below, more preferably 7.0 MPa 1 / 2 Below, particularly preferably 5.0 MPa 1 / 2 Below. If the hydrogen bond term δ h1 12.0MPa 1 / 2 The following is speculated to be due to the improved affinity between the carbon material and the dispersant and (contributing to the hydrogen bonding term δ h1 The reduction of functional groups can inhibit the decomposition of the electrolyte on the surface of the carbon material, further improving the high temperature storage characteristics. In addition, the carbon materials will not excessively interact with each other, and the viscosity stability of the conductive material dispersion can be fully ensured.

[0053] In addition, the hydrogen bond term δ h1 The lower limit of is not particularly limited and can be, for example, 1.5 MPa 1 / 2 above.

[0054] In addition, the Hansen Solubility Parameter (HSP) of the carbon material is estimated c ) is affected by the amount of defects and functional groups on the surface of the carbon material, and can be adjusted by, for example, changing the type of carbon material, the manufacturing conditions of the carbon material, the surface treatment conditions of the carbon material, etc.

[0055] The content of the carbon material in the conductive material dispersion is not particularly limited. With the mass of the conductive material dispersion as a whole as 100 mass%, it is preferably 1.0 mass % or more, more preferably 2.0 mass % or more, further preferably 3.0 mass % or more, preferably 30.0 mass % or less, more preferably 25.0 mass % or less, and further preferably 20.0 mass % or less. If the content of the carbon material in the conductive material dispersion is within the above range, the carbon material can be well dispersed in the conductive material dispersion and the viscosity stability of the conductive material dispersion can be ensured. In addition, the internal resistance of the secondary battery can be further reduced, and the high temperature storage characteristics can be further improved.

[0056] <Dispersant>

[0057] The dispersant is not particularly limited as long as it is a polymer capable of dispersing the carbon material in the dispersion medium. Such a polymer preferably comprises at least a nitrile group-containing monomer unit and an alkylene structural unit, and optionally other repeating units.

[0058] In the present invention, “containing a monomer unit” means “a polymer obtained using the monomer contains a repeating unit derived from the monomer”.

[0059] Furthermore, in the present invention, “comprising alkylene structural units” means “a polymer comprising only alkylene structural units of the general formula -C n H 2n -[wherein n is an integer of 2 or more]"

[0060] Furthermore, in the present invention, the content ratio of the monomer unit and the structural unit in the polymer can be used 1 H-NMR and 13 The determination was performed using nuclear magnetic resonance (NMR) methods such as C-NMR.

[0061] 《Nitrile-containing monomer unit》

[0062] Examples of nitrile-containing monomers that can form nitrile-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group. Examples include acrylonitrile; α-halogenated acrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkyl acrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Furthermore, the nitrile-containing monomers may be used alone or in combination of two or more at any ratio. Among these, acrylonitrile is preferred.

[0063] With all repeating units in dispersant as 100 mass %, the containing ratio of the nitrile group monomeric unit in dispersant is preferably more than 3 mass %, more preferably more than 5 mass %, more preferably more than 7 mass %, preferably less than 50 mass %, more preferably less than 40 mass %, more preferably less than 30 mass %, particularly preferably less than 28 mass %. If the containing ratio of the nitrile group monomeric unit in dispersant is within the above range, it is possible to fully ensure the solubility of dispersant in dispersion medium (such as N- methyl -2- pyrrolidone), in addition, it is possible to make the obtained electrode composite material layer and current collector well fit. Therefore, it is possible to make carbon material well dispersed in conductive material dispersion liquid, and ensure the viscosity stability of the conductive material dispersion liquid. In addition, it is possible to further reduce the internal resistance of secondary battery, and further improve high temperature storage characteristics.

[0064] Alkylene structural unit

[0065] The alkylene structural unit may be linear or branched. From the viewpoint of further reducing the internal resistance of the secondary battery and further improving the high-temperature storage characteristics, the alkylene structural unit is preferably linear, ie, a straight-chain alkylene structural unit.

[0066] The method for introducing the alkylene structural unit into the polymeric dispersant is not particularly limited, and examples thereof include the following methods (1) and (2):

[0067] (1) A method of preparing a polymer from a monomer composition containing a conjugated diene monomer and hydrogenating the polymer to convert the conjugated diene monomer units into alkylene structural units;

[0068] (2) A method for producing a polymer from a monomer composition comprising a 1-olefin monomer.

[0069] Among them, method (1) is preferred because the dispersant can be easily produced.

[0070] Examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. Specifically, the alkylene structural unit is preferably a structural unit obtained by hydrogenating a conjugated diene monomer unit (a conjugated diene hydride unit), and more preferably a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (a 1,3-butadiene hydride unit).

[0071] Examples of the 1-olefin monomer include ethylene, propylene, and 1-butene.

[0072] These conjugated diene monomers and 1-olefin monomers may be used alone or in combination of two or more at any ratio.

[0073] Here, in the 1,3-butadiene hydrogenate unit, the following two types can exist depending on the bonding mode when the 1,3-butadiene unit is formed before hydrogenation.

[0074] (A) Structural unit formed by hydrogenation of 1,3-butadiene units formed by 1,4-bonding of 1,3-butadiene (-CH2-CH2-CH2-; hereinafter referred to as "1,4-bonded butadiene hydride unit")

[0075] (B) A structural unit formed by hydrogenating a 1,3-butadiene unit produced by 1,2-bonding of 1,3-butadiene (-CH2-CH(C2H5)-, hereinafter referred to as a "1,2-bond butadiene hydride unit").

[0076] Moreover, in the case where the dispersant includes a 1,3-butadiene hydride unit, the total 1,3-butadiene hydride unit (i.e., the total of the 1,4-key butadiene hydride unit and the 1,2-key butadiene hydride unit) in the dispersant is 100% by mass, and the 1,2-key butadiene hydride unit is preferably 15% by mass or less, more preferably 10% by mass or less. If the proportion of the 1,2-key butadiene hydride unit in the total 1,3-butadiene hydride unit is 15% by mass or less, the number of side chain ethyl groups (-C2H5) of the dispersant can be reduced, so that the dispersant is well dissolved in the dispersion medium (e.g., N-methyl-2-pyrrolidone). Therefore, the carbon material can be well dispersed in the conductive material dispersion, and the viscosity stability of the conductive material dispersion can be ensured. In addition, the internal resistance of the secondary battery can be further reduced, and the high temperature storage characteristics can be further improved.

[0077] The lower limit of the ratio of the 1,2-bond butadiene hydrogenated units to the total 1,3-butadiene hydrogenated units is not particularly limited, but is 0% by mass or more, and can be, for example, 4.0% by mass or more.

[0078] The ratio of the 1,2-bonded butadiene hydrogenate unit to the total 1,3-butadiene hydrogenate units can be adjusted by changing the method for preparing the dispersant (eg, the type of polymerization initiator).

[0079] Furthermore, based on the total repeating units in the dispersant being 100 mass%, the content of alkylene structural units in the dispersant is preferably 20 mass% or more, more preferably 25 mass% or more, and preferably 80 mass% or less, and more preferably 75 mass% or less. If the content of alkylene structural units in the dispersant is within the above range, it is inferred that due to the improved affinity between the carbon material and the dispersant, the carbon material can be well dispersed in the conductive material dispersion, and the viscosity stability of the conductive material dispersion can be ensured. Furthermore, by ensuring that the dispersant is well coated on the carbon material surface, electrolyte decomposition on the carbon material surface can be suppressed, further improving high-temperature storage characteristics.

[0080] Other repeating units

[0081] The other repeating units that may be contained in the dispersant are not particularly limited, and examples thereof include aromatic vinyl monomer units, acidic group-containing monomer units, and (meth)acrylate monomer units. The dispersant may contain one or more other repeating units.

[0082] In the present invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0083] [Aromatic vinyl monomer unit]

[0084] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. The aromatic vinyl monomers may be used alone or in combination of two or more at any ratio. Among these, styrene is preferred.

[0085] When the dispersant contains aromatic vinyl monomer units, from the viewpoint of further reducing the internal resistance of the secondary battery and further improving the high-temperature storage characteristics, the content ratio of the aromatic vinyl monomer units in the dispersant is preferably 10% by mass or more, more preferably 20% by mass or more, preferably 40% by mass or less, further preferably 35% by mass or less, and particularly preferably 31% by mass or less, based on all repeating units in the dispersant as 100% by mass.

[0086] [Acidic group-containing monomer unit]

[0087] Examples of acidic group-containing monomers that can form acidic group-containing monomer units include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Acidic group-containing monomers may be used alone or in combination of two or more at any ratio.

[0088] Examples of the carboxylic acid group-containing monomer include monocarboxylic acids and derivatives thereof, dicarboxylic acids and anhydrides thereof, and derivatives thereof.

[0089] Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

[0090] Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0091] Examples of the dicarboxylic acid include maleic acid, fumaric acid, and itaconic acid.

[0092] Examples of the dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0093] Examples of the anhydride of the dicarboxylic acid include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0094] Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group by hydrolysis can also be used. Among them, acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer.

[0095] Examples of the sulfonic acid group-containing monomer include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, 2-sulfoethyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0096] In the present invention, "(meth)allyl group" means an allyl group and / or a methallyl group.

[0097] Examples of the phosphoric acid group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0098] In the present invention, "(meth)acryloyl" means an acryloyl group and / or a methacryloyl group.

[0099] When the dispersant contains an acidic group-containing monomer unit, from the viewpoint of further reducing the internal resistance of the secondary battery and further improving the high-temperature storage characteristics, the content ratio of the acidic group-containing monomer unit in the dispersant is preferably 1 mass % or more, more preferably 3 mass % or more, and preferably 10 mass % or less, more preferably 7 mass % or less, based on all repeating units in the dispersant being 100 mass %.

[0100] [(Meth)acrylate monomer unit]

[0101] Examples of the (meth)acrylate monomers that can form the (meth)acrylate monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. The (meth)acrylate monomers may be used alone or in combination of two or more at any ratio.

[0102] Here, as described above, the dispersant may contain (meth)acrylate monomer units. However, from the perspective of further reducing the internal resistance of the secondary battery and further improving the high-temperature storage characteristics, the content of the (meth)acrylate monomer units in the dispersant is preferably 30% by mass or less, more preferably 15% by mass or less, further preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 1% by mass or less, and most preferably 0% by mass (i.e., the dispersant does not contain (meth)acrylate monomer units), based on the total repeating units in the dispersant being 100% by mass.

[0103] Preparation Method

[0104] The preparation method of dispersant is not particularly limited. Dispersant can for example polymerize a monomer composition comprising one or more monomers in an aqueous medium, arbitrarily hydrogenate, and thereby manufacture. In addition, the ratio of each monomer in the monomer composition can be determined according to the ratio of the desired repeating unit (monomeric unit and / or structural unit) in the polymer.

[0105] In addition, the polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used. In addition, as the polymerization reaction, any reaction such as ionic polymerization, free radical polymerization, living free radical polymerization, various condensation polymerizations, and addition polymerization can be used. Moreover, during the polymerization, known emulsifiers and polymerization initiators can be used as needed. In addition, hydrogenation can be carried out by known methods.

[0106] Hansen Solubility Parameters (HSP)d )》

[0107] As mentioned above, HSP d By the polar term δ p2 , dispersion term δ d2 and the hydrogen bond term δ h2 These three constitute.

[0108] Here, the polar term δ p2 Not particularly limited, but preferably 6.0 MPa 1 / 2 More than 7.0 MPa 1 / 2 Above, preferably 15.0 MPa 1 / 2 Below, more preferably 10.0 MPa 1 / 2 the following.

[0109] In addition, the dispersion term δ d2 Not particularly limited, but preferably 10.0 MPa 1 / 2 More than 15.0 MPa 1 / 2 Above, preferably 25.0 MPa 1 / 2 Below, more preferably 20.0 MPa 1 / 2 the following.

[0110] Moreover, the hydrogen bond term δ h2 Not particularly limited, but preferably 1.0 MPa 1 / 2 More than 2.0 MPa 1 / 2 , more preferably 4.0MPa 1 / 2 Above, preferably 15.0 MPa 1 / 2 Below, more preferably 10.0 MPa 1 / 2 Below, more preferably 8.0 MPa 1 / 2 the following.

[0111] In addition, the Hansen Solubility Parameter (HSP) of the dispersant c ) can be adjusted by changing the types and ratios of monomers used to prepare the dispersant, the ratio of 1,2-bonded butadiene hydride units to all 1,3-butadiene hydride units, and the preparation conditions of the dispersant.

[0112] "content"

[0113] The content of the dispersant in the conductive material dispersion is not particularly limited. It is preferably 1 part by mass or more, more preferably 5 parts by mass or more, further preferably 10 parts by mass or more, preferably 100 parts by mass or less, more preferably 70 parts by mass or less, further preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less, relative to 100 parts by mass of carbon material. If the content of the dispersant is within the above range, the carbon material can be well dispersed in the conductive material dispersion and the viscosity stability of the conductive material dispersion can be ensured. Furthermore, the internal resistance of the secondary battery can be further reduced, and the high temperature storage characteristics can be further improved.

[0114] HSP c With HSP d HSP distance (R d )》

[0115] Furthermore, in the conductive material dispersion of the present invention, HSP c With HSP d HSP distance (R d ) needs to be 10.0MPa 1 / 2 Below, preferably 8.0 MPa 1 / 2 Below, more preferably 6.0 MPa 1 / 2 Below, more preferably 4.0 MPa 1 / 2 Below, particularly preferably 3.8 MPa 1 / 2 When the HSP distance (R d ) greater than 10.0MPa 1 / 2 When the amount of the conductive material is too low, the internal resistance of the secondary battery increases and the high temperature storage characteristics are impaired. Furthermore, the carbon material cannot be well dispersed in the conductive material dispersion, and the viscosity stability of the conductive material dispersion is impaired.

[0116] In addition, the HSP distance (R d ) is not particularly limited, but is 0 MPa 1 / 2 Above, it can be, for example, 1.0 MPa 1 / 2 above.

[0117] <Dispersion Medium>

[0118] As the dispersion medium, any of water and organic solvents can be used, and organic solvents are preferred. The organic solvent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; diethyl ether, diethyl ether, and diethyl ether. Examples of the dispersion medium include ethers such as alkane and tetrahydrofuran; amide-based organic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene. The dispersion medium may be used alone or in combination of two or more at any ratio. From the perspective of ensuring good dispersion of the carbon material in the conductive material dispersion, the dispersion medium is preferably an organic solvent, with NMP being more preferred.

[0119] <Other ingredients>

[0120] The other components that may be contained in the conductive material dispersion are not particularly limited, and examples thereof include components other than the positive electrode active material described later in the “slurry for secondary battery positive electrode”.

[0121] <Method for Preparing Conductive Material Dispersion>

[0122] When the above components are mixed to obtain a conductive material dispersion, the mixing method is not particularly limited, and a common mixing device such as a disperser, a mill, or a kneader can be used.

[0123] (Slurry for secondary battery positive electrode)

[0124] The positive electrode slurry of the present invention comprises the above-mentioned conductive material dispersion and positive electrode active material, and optionally comprises optional components such as a binder. In other words, the positive electrode slurry of the present invention comprises a carbon material, a dispersant, and a dispersion medium, and optionally comprises optional components such as a binder.

[0125] Thus, a positive electrode having a positive electrode material layer formed from a positive electrode slurry containing the conductive material dispersion can reduce the internal resistance of a secondary battery and ensure good high-temperature storage characteristics of the secondary battery.

[0126] <Positive Electrode Active Material>

[0127] The positive electrode active material to be blended in the positive electrode slurry is not particularly limited, and a known positive electrode active material can be used.

[0128] As the positive electrode active material that can be used, for example, in a lithium ion secondary battery, there is no particular limitation, and metal oxides containing lithium (Li) can be cited. Moreover, as the positive electrode active material, a positive electrode active material containing at least one selected from cobalt (Co), nickel (Ni), and manganese (Mn) in addition to lithium (Li) is preferred. As such a positive electrode active material, lithium cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium manganese phosphate (LiMnPO4), Li 1+x Mn 2-x O4 (0 < X < 2) spinel compounds with excessive lithium, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4, etc. can be cited. In addition, the positive electrode active material can be used alone or two or more kinds can be used in any ratio.

[0129] Moreover, from the viewpoint of further increasing the capacity of the lithium ion secondary battery, it is preferable to use a positive electrode active material in which the proportion of nickel is 50.0 mol% or more and 100.0 mol% or less when the total amount of the contained transition metals is 100.0 mol%.

[0130] In addition, the particle size of the positive electrode active material is not particularly limited and can be the same as the positive electrode active material that has been used.

[0131] Furthermore, the amount of the positive electrode active material in the positive electrode slurry is not particularly limited and can be within the range that has been used.

[0132] <Any component>

[0133] As the any component that can be contained in the positive electrode slurry, for example, a binder material, a viscosity regulator, a reinforcing material, an antioxidant, and an electrolyte additive having a function of suppressing the decomposition of the electrolyte can be cited. These any components can be used alone or two or more kinds can be used in any ratio.

[0134] Among the above-mentioned any components, from the viewpoint of suppressing the precipitation of the positive electrode active material and making the obtained positive electrode composite material layer well adhered to the current collector, the positive electrode slurry preferably contains a binder material.

[0135] 《Binder material》

[0136] The binder is not particularly limited, but is preferably a fluorine-containing resin such as polyvinylidene fluoride, polyacrylonitrile (PAN), or polyvinyl alcohol (PVOH), and more preferably a fluorine-containing resin or PAN.

[0137] [Hansen Solubility Parameters (HSP) b )]

[0138] As mentioned above, HSP b By the polar term δ p3 , dispersion term δ d3 and the hydrogen bond term δ h3 These three constitute.

[0139] Here, the polar term δ p3 Not particularly limited, but preferably 5.0 MPa 1 / 2 More than 10.0 MPa 1 / 2 Above, preferably 25.0 MPa 1 / 2 Below, more preferably 20.0 MPa 1 / 2 the following.

[0140] In addition, the dispersion term δ d3 Not particularly limited, but preferably 10.0 MPa 1 / 2 More than 15.0 MPa 1 / 2 Above, preferably 30.0 MPa 1 / 2 Below, more preferably 20.0 MPa 1 / 2 the following.

[0141] Moreover, the hydrogen bond term δ h3 Not particularly limited, but preferably 5.0 MPa 1 / 2 More than 10.0 MPa 1 / 2 Above, preferably 25.0 MPa 1 / 2 Below, more preferably 20.0 MPa 1 / 2 the following.

[0142] In addition, the Hansen Solubility Parameter (HSP) of the bonding material b ) can be adjusted by changing the types and proportions of monomers used to prepare the adhesive material, as well as the manufacturing conditions of the adhesive material.

[0143] [HSP c With HSP b HSP distance (R b )]

[0144] Furthermore, in the positive electrode slurry of the present invention, the HSP of the carbon material is preferably c HSP with bonding materials b HSP distance (R b ) is greater than the HSP of carbon materialsc HSP with dispersant d HSP distance (R d ). If the HSP distance (R d ) is greater than the HSP distance (R d ), in the positive electrode slurry, the binding material does not excessively hinder the interaction between the dispersant and the carbon material, and these components can maintain a good dispersion state. Therefore, by using this positive electrode slurry, the internal resistance of the secondary battery can be further reduced.

[0145] Specifically, from the viewpoint of further reducing the internal resistance of the secondary battery, the HSP distance (R b ) is preferably greater than 4.0 MPa 1 / 2 , more preferably greater than 6.0 MPa 1 / 2 , more preferably greater than 8.0 MPa 1 / 2 , especially preferably greater than 10.0 MPa 1 / 2 In addition, the HSP distance (R b ) is not particularly limited and can be, for example, 40.0 MPa 1 / 2 the following.

[0146] <Method for Preparing Positive Electrode Slurry>

[0147] When the above components are mixed to obtain the positive electrode slurry, the mixing method is not particularly limited, and a common mixing device such as a disperser, a mill, or a kneader can be used.

[0148] (Positive electrode for secondary batteries)

[0149] The positive electrode of the present invention includes a positive electrode composite material layer obtained using the above-mentioned positive electrode slurry of the present invention.

[0150] More specifically, the positive electrode of the present invention generally has the above-mentioned positive electrode composite material layer on the current collector. Moreover, the positive electrode composite material layer comprises a positive electrode active material, a conductive material, and a dispersant, and optionally comprises a binding material, etc. In addition, the positive electrode active material, conductive material, dispersant, and binding material, etc. contained in the positive electrode composite material layer are those contained in the conductive material dispersion and the positive electrode slurry of the present invention, and the preferred presence ratio of these components is the same as the preferred presence ratio of the components in the conductive material dispersion and the positive electrode slurry of the present invention.

[0151] Furthermore, the positive electrode of the present invention includes a positive electrode composite material layer formed using the positive electrode slurry of the present invention, and thus can reduce the internal resistance of the secondary battery and ensure good high-temperature storage characteristics of the secondary battery.

[0152] <Current collector>

[0153] The current collector is conductive and made of a material with electrochemical durability. Specifically, aluminum or an aluminum alloy can be used as the current collector. Aluminum and aluminum alloys can be used in combination, or different types of aluminum alloys can be used in combination. Aluminum and aluminum alloys are excellent current collector materials due to their heat resistance and electrochemical stability.

[0154] <Method for Manufacturing Positive Electrode>

[0155] The method for manufacturing the positive electrode of the present invention is not particularly limited. For example, the positive electrode of the present invention can be manufactured by applying the positive electrode slurry of the present invention to at least one side of the current collector and drying it to form a positive electrode composite material layer. In more detail, the manufacturing method includes: a process of applying the positive electrode slurry to at least one side of the current collector (coating process); and a process of drying the positive electrode slurry applied to at least one side of the current collector to form a positive electrode composite material layer on the current collector (drying process).

[0156] 《Coating process》

[0157] As a method for applying the positive electrode slurry to the current collector, there is no particular limitation and known methods can be used. Specifically, as a coating method, a doctor blade method, an immersion method, a reverse roller method, a direct roller method, a gravure printing method, an extrusion method, a brush coating method, etc. can be used. At this time, the positive electrode slurry can be applied only to a single side of the current collector or to both sides. The thickness of the slurry film on the current collector before drying after coating can be appropriately set according to the thickness of the positive electrode composite material layer obtained by drying.

[0158] Drying process

[0159] The method for drying the positive electrode slurry on the current collector is not particularly limited, and known methods can be used, including drying using warm air, hot air, or low-humidity air; vacuum drying; and drying using irradiation with infrared rays, electron beams, etc. By drying the positive electrode slurry on the current collector in this manner, a positive electrode composite material layer can be formed on the current collector, resulting in a positive electrode having the current collector and the positive electrode composite material layer.

[0160] Alternatively, after the drying step, the positive electrode material layer may be subjected to a press treatment using a die press or a roll press, etc. The press treatment can ensure good adhesion of the positive electrode material layer to the current collector.

[0161] Furthermore, when the positive electrode material layer contains a curable polymer, the polymer may be cured after the positive electrode material layer is formed.

[0162] (Secondary Battery)

[0163] The secondary battery of the present invention comprises the aforementioned positive electrode of the present invention. Furthermore, due to the inclusion of the positive electrode of the present invention, the secondary battery of the present invention has reduced internal resistance and excellent high-temperature storage characteristics. Furthermore, the secondary battery of the present invention is, for example, a non-aqueous secondary battery, preferably a lithium-ion secondary battery.

[0164] Here, the structure of a lithium-ion secondary battery, an example of a secondary battery according to the present invention, is described below. This lithium-ion secondary battery typically includes, in addition to the positive electrode according to the present invention, a negative electrode, an electrolyte, and a separator. Each of these structures is described below.

[0165] <Negative electrode>

[0166] As the negative electrode of the lithium ion secondary battery, a known negative electrode that can be used as a negative electrode for lithium ion secondary batteries can be used. Specifically, as the negative electrode, for example, a negative electrode formed of a thin plate of metallic lithium or a negative electrode composite material layer formed on a current collector can be used.

[0167] In addition, as the current collector, a current collector formed of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. In addition, as the negative electrode composite material layer, a layer containing a negative electrode active material and a binding material can be used. Furthermore, the binding material is not particularly limited, and any known material can be used.

[0168] <Electrolyte>

[0169] As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent can generally be used. As the supporting electrolyte, for example, a lithium salt can be used. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, etc. Among them, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, due to their high solubility in solvents and their high degree of dissociation. In addition, one electrolyte can be used alone, or two or more electrolytes can be used in combination at any ratio. Generally, there is a tendency that the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted according to the type of supporting electrolyte.

[0170] As the organic solvent used in the electrolyte, there is no particular limitation 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) can be preferably used; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. In addition, a mixture of these solvents can also be used. Among them, due to the high dielectric constant and wide stable potential region, carbonates are preferably used, and a mixture of ethylene carbonate and ethyl methyl carbonate is more preferably used.

[0171] The concentration of the electrolyte in the electrolyte solution can be adjusted appropriately, and is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass. Furthermore, known additives such as fluoroethylene carbonate and ethyl methanesulfonate may be added to the electrolyte solution.

[0172] <Spacer>

[0173] The separator is not particularly limited, and for example, the separators described in Japanese Patent Application Laid-Open No. 2012-204303 can be used. Among these, a microporous membrane formed of a polyolefin resin (polyethylene, polypropylene, polybutylene, polyvinyl chloride) is preferred because the overall thickness of the separator can be reduced, thereby increasing the ratio of the electrode active material in the lithium-ion secondary battery and increasing the capacity per unit volume.

[0174] <Method for Manufacturing Lithium-Ion Secondary Battery>

[0175] The lithium-ion secondary battery of the present invention can be manufactured by, for example, the following method: overlapping the positive electrode and the negative electrode with a separator, winding or folding the battery according to the shape of the battery as needed, placing the battery container, injecting an electrolyte into the battery container, and sealing the battery. In order to prevent the internal pressure rise of the secondary battery, overcharge and discharge, etc., a fuse, a PTC element or other anti-overcurrent element, a porous metal mesh, a guide plate, etc. can be provided as needed. The shape of the secondary battery can be, for example, any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, etc.

[0176] Example

[0177] Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "parts" indicating amounts are based on mass unless otherwise specified.

[0178] Furthermore, unless otherwise specified, in a polymer produced by copolymerizing a plurality of monomers, the proportion of monomer units formed by polymerizing a certain monomer in the polymer generally corresponds to the ratio (charge ratio) of the certain monomer in all monomers used for polymerization of the polymer.

[0179] In addition, in the examples and comparative examples, the Hansen solubility parameters of the carbon material, dispersant, and binder, the ratio of 1,2-bonded butadiene hydride units in the dispersant to all 1,3-butadiene hydride units, the dispersion state and viscosity stability of the conductive material dispersion, and the internal resistance reduction and high-temperature storage characteristics of the secondary battery were evaluated using the following methods.

[0180] <Hansen Solubility Parameters>

[0181] HSP of Carbon Materials c 》

[0182] 0.1 g of carbon material was added to 10 ml of each of the 16 solvents shown in Table 1 below, and ultrasonic dispersion was performed at 20 kHz, 200 W, and 10 minutes to prepare a test solution. Pulse NMR measurement was performed on the above 16 solvents (pure solvents) and the test solution. Based on the obtained results, R was calculated as a function of the relaxation time T1 of the pure solvent and the relaxation time T2 of the solvent in the test solution using the following formula: sp .

[0183] R sp =(T1 / T2)-1

[0184] Based on the obtained R sp The affinity of each solvent to the carbon material was scored as follows.

[0185] ·R sp ≤0.2(poor solvent):0

[0186] 0.2<R sp ≤0.5(poor solvent):2

[0187] 0.5<R sp (Good solvent): 1

[0188] The HSP was calculated using the computer software "Hansen Solubility Parameters in Practice (HSPiP ver.5.2.05)" according to the obtained scores. c The polar term δ p1 , dispersion term δ d1 and the hydrogen bond term δ h1 .

[0189] HSP of Dispersantsd 》

[0190] 0.5 g of a dispersant was added to 10 ml of each of the 15 solvents shown in Table 2 described below, and the mixture was allowed to stand at 25° C. for 24 hours to prepare an evaluation solution. The evaluation solution was visually observed and scored as follows.

[0191] Insoluble (poor solvent): 0

[0192] Turbidity and / or fluctuation (poor solvent): 2

[0193] Completely dissolved (good solvent): 1

[0194] According to the obtained scores, use the above HSPiP to find HSP d The polar term δ p2 , dispersion term δ d2 and the hydrogen bond term δ h2 .

[0195] HSP of Adhesive Materials b 》

[0196] Able to be used with the above-mentioned "dispersant HSP d ” is obtained in the same way, but in this application the values of the above-mentioned HSPiP database are used.

[0197] <Ratio of 1,2-bonded butadiene hydrogenated units in all 1,3-butadiene hydrogenated units in the dispersant>

[0198] After the polymer aqueous dispersion was vacuum dried at 60°C for 24 hours, 1 The amount of 1,3-butadiene units having 1,4 bonds (1,4 bond amount) and 1,3-butadiene units having 1,2 bonds (1,2 bond amount) were quantitatively determined by H-NMR and calculated according to the following formula.

[0199] The ratio of 1,2-bond butadiene hydrogenated units to all 1,3-butadiene hydrogenated units in the dispersant = (1,2-bond amount) / (1,2-bond amount + 1,4-bond amount) × 100 (mass %)

[0200] <Dispersed State>

[0201] The shear rate dependency of the viscosity of the conductive material dispersion at a temperature of 25° C. was evaluated using a rheometer (manufactured by Anton Paar, product name “MCR302”).

[0202] At this time, the shear rate is 10s -1 Viscosity η 10 Viscosity η is an indicator and is evaluated according to the following criteria. 10The lower the value, the better the dispersion state of the conductive material dispersion.

[0203] A:η 10 5Pa·s or less

[0204] B:η 10 Greater than 5Pa·s and less than 10Pa·s

[0205] C:η 10 Greater than 10Pa·s and less than 20Pa·s

[0206] D: Viscosity is too high, and η cannot be measured 10

[0207] <Viscosity Stability>

[0208] The initial viscosity η of the conductive material dispersion just prepared was measured using a B-type viscometer at a temperature of 25°C, a rotation speed of 60 rpm, and a rotation time of 60 seconds. ini Then, with η ini The viscosity η of the conductive material dispersion after storage at room temperature for 7 days from the preparation was measured under the same conditions. 7d The viscosity ratio was calculated using the following formula.

[0209] Viscosity ratio = η 7d / η ini ×100(%)

[0210] The obtained viscosity ratio was used to evaluate according to the following criteria: A viscosity ratio value closer to 100% indicates a smaller change in viscosity of the conductive material dispersion due to long-term storage, and the conductive material dispersion has better viscosity stability.

[0211] A: Viscosity ratio is 70% or more and 130% or less

[0212] B: Viscosity ratio is 50% or more and less than 70% or more than 130% and less than 150%

[0213] C: Viscosity ratio is 0% or more and less than 50% or greater than 150% and less than 200%

[0214] <Reduction of internal resistance>

[0215] After the lithium-ion secondary battery is charged with a constant current of 0.2CmA until the battery voltage reaches 4.2V, it is charged with a constant voltage of 4.2V until the charging current reaches 0.02CmA. Next, after the battery voltage is discharged with a constant current of 0.2CmA until the battery voltage reaches 3.87V (state of charge (SOC) : 50%), the voltage change after discharging for 30 seconds at 0.2CmA, 0.5CmA, 1.0CmA, 2.0CmA, 2.5CmA, and 3.0CmA is measured. Moreover, each discharge current and the measured voltage change are plotted, and the slope thereof is used as the resistance value (Ω). The calculated resistance value is evaluated using the following benchmark. The lower the resistance value, the lower the internal resistance of the lithium-ion secondary battery.

[0216] A: Resistance value is less than 2Ω

[0217] B: Resistance value is 2Ω or more and less than 4Ω

[0218] C: Resistance value is 4Ω or more and less than 6Ω

[0219] D: Resistance value is 6Ω or more

[0220] <High-temperature storage characteristics>

[0221] The volume (V) of lithium-ion secondary batteries was calculated using the Archimedean method. ini ) was measured. Next, the lithium ion secondary battery was charged at a constant current of 0.2 CmA at 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the charging current reached 0.02 CmA. The battery was removed from the charging device and stored at 60°C for 7 days, then cooled to 25°C, and the volume (V 7d Then, the volume change was calculated using the following formula.

[0222] Volume change = V 7d -V ini (ml)

[0223] The obtained volume change was used to perform evaluation according to the following criteria: A smaller volume change value indicates better high-temperature storage characteristics of the lithium ion secondary battery.

[0224] A: Volume change is less than 2ml

[0225] B: Volume change is greater than 2ml and less than 3ml

[0226] C: Volume change is 3 ml or more and less than 4 ml

[0227] D: Volume change is 4 ml or more

[0228] (Example 1)

[0229] <Preparation of Carbon Material>

[0230] Preparation of substrate for carbon nanotube production

[0231] As a substrate, a Fe—Cr alloy SUS430 substrate (manufactured by JIFI Steel Corporation, 50 cm×50 cm, thickness: 0.3 mm, Cr: 18%, arithmetic mean roughness Ra≈0.59 μm) was prepared.

[0232] Separately, 1.9 g of tri-sec-butoxyaluminum as an aluminum compound was dissolved in 100 ml of 2-propanol as an organic solvent, and 0.9 g of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid A.

[0233] Furthermore, 174 mg of ferric acetate as an iron compound was dissolved in 100 ml of 2-propanol as an organic solvent, and 190 mg of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid B.

[0234] Next, the prepared substrate was coated with the aforementioned coating liquid A by dip coating at room temperature (25°C) and relative humidity (50%). Specifically, the substrate was immersed in coating liquid A, held for 20 seconds, and then lifted at a rate of 10 mm / second. The substrate was then air-dried for 5 minutes, heated in air at 300°C for 30 minutes, and cooled to room temperature. This formed a 14 nm thick aluminum oxide thin film on the substrate.

[0235] Next, the aforementioned coating liquid B was applied to the aluminum oxide thin film provided on the substrate by dip coating at room temperature of 25°C and relative humidity of 50%. Specifically, the substrate with the aluminum oxide thin film was immersed in coating liquid B, held for 20 seconds, and then lifted at a rate of 3 mm / second. The substrate was then air-dried for 5 minutes (drying temperature of 45°C), thereby forming a 1 nm thick iron thin film and a 15 nm thick catalyst layer composed of the aluminum oxide-iron thin film, thereby obtaining a substrate for carbon nanotube production.

[0236] Synthesis of CNTs

[0237] Next, a CVD device was used to form an aligned CNT aggregate on the carbon nanotube production substrate. Specifically, the prepared carbon nanotube production substrate was placed in a furnace maintained at a temperature of 750°C and a pressure of 1.02×10 5In the reaction chamber of the CVD device at Pa, He: 100 sccm and H2: 900 sccm were introduced into the reaction chamber for 6 minutes. This reduced the CNT synthesis catalyst (iron), promoted its micronization, and brought it into a state suitable for CNT growth (a state in which a plurality of nanometer-sized catalyst particles were formed) (forming step). In addition, the density of the catalyst particles at this time was adjusted to 1×10 12 ~1×10 14 pieces / cm 2 Then, the furnace temperature was kept at 750°C and the pressure at 1.02×10 5 In the Pa state, He (850 sccm), C₂H₄ (59 sccm), and H₂O (300 ppm) were supplied to the reaction chamber for 5 minutes. This allowed CNTs to grow from the catalyst particles (CNT growth process). After the CNT growth process was completed, only He (1000 sccm) was supplied to the reaction chamber, and the remaining feedstock gases and catalyst activating material were removed. This resulted in a substrate with an aligned aggregate of carbon nanotubes formed on the surface of the catalyst layer.

[0238] Then, the CNT-A, which is a carbon material, was obtained by peeling off the CNT-A grown on the catalyst layer from the surface of the obtained substrate. The affinity of the CNT-A with each solvent was scored using the above-mentioned method. The results are shown in Table 1. Then, the HSP was calculated. c The polar term δ p1 , dispersion term δ d1 and the hydrogen bond term δ h1 The results are shown in Table 3.

[0239] <Preparation of Dispersant>

[0240] 180 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate as an emulsifier, 28 parts of acrylonitrile as a nitrile-containing monomer, and 0.8 parts of tert-dodecylmercaptan as a molecular weight modifier were sequentially added to the reactor. After the atmosphere inside the reactor was replaced with nitrogen three times, 72 parts of 1,3-butadiene as a conjugated diene monomer was added. 0.1 parts of cumene hydroperoxide as a polymerization initiator was added to the reactor maintained at 10°C to initiate polymerization, and the polymerization reaction continued while stirring.

[0241] When the polymerization conversion reached 90%, 0.2 parts of hydroxylamine sulfate was added per 100 parts of monomer to terminate the polymerization. The mixture was then heated and steam distilled under reduced pressure at approximately 70°C to recover the residual monomers. Two parts of alkylated phenol were then added as an antioxidant to obtain an aqueous dispersion of the polymer. This aqueous dispersion of the polymer was used to determine the ratio of 1,2-butadiene hydride units to the total 1,3-butadiene hydride units in the dispersant. The results are shown in Table 3.

[0242] Next, 400 mL (total solid content: 48 g) of the resulting aqueous dispersion of the polymer was placed in a 1-liter autoclave equipped with a stirrer, and nitrogen was circulated for 10 minutes to remove dissolved oxygen in the aqueous dispersion. Then, as a hydrogenation catalyst, 50 mg of palladium acetate was dissolved in 180 mL of water to which nitric acid, 4 times the molar amount relative to Pd, was added. After the system was purged with hydrogen twice, the contents of the autoclave were heated to 50° C. while pressurized with hydrogen to 3 MPa, and a hydrogenation reaction was carried out for 6 hours.

[0243] Then, the contents were returned to room temperature, the system was placed in a nitrogen atmosphere, and then concentrated using an evaporator to a solid content concentration of 40%, thereby obtaining hydrogenated nitrile rubber A as a dispersant.

[0244] Next, NMP was added to a 40% solids concentration aqueous solution of hydrogenated nitrile rubber A as a dispersant, and then water and excess NMP were removed by vacuum distillation to obtain an NMP solution of hydrogenated nitrile rubber A with a solids concentration of 8%.

[0245] The affinity of the obtained hydrogenated nitrile rubber A to each solvent was scored using the above method. The results are shown in Table 2. Then, HSP was calculated. d The polar term δ p2 , dispersion term δ d2 and the hydrogen bond term δ h2 The results are shown in Table 3.

[0246] Furthermore, using the above formula (1), HSP is calculated c With HSP d HSP distance (R d The results are shown in Table 3.

[0247] <Preparation of Conductive Material Dispersion>

[0248] 5.0 parts of the CNT-A conductive material, 1.0 part (solids content equivalent) of the hydrogenated nitrile rubber A dispersant, and 94.0 parts of NMP as a dispersion medium were stirred using a disperser (3000 rpm, 10 minutes). The mixture was then dispersed using a bead mill with 1 mm diameter zirconia beads at a peripheral speed of 8 m / s for 1 hour to prepare a conductive material dispersion having a solids concentration of 6.0%. The dispersion state and storage stability of the resulting conductive material dispersion were evaluated. The results are shown in Table 3.

[0249] <Preparation of positive electrode slurry>

[0250] 98.0 parts of a ternary active material (LiNi 0.5 Co 0.2 Mn 0.3 A positive electrode slurry was prepared by mixing 1.0 part of polyvinylidene fluoride (PVDF) as a binder, 1.0 part (based on solid content) of the conductive material dispersion, and NMP using a planetary mixer (60 rpm, 30 minutes) to prepare the positive electrode slurry. The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry composition (measured using a single cylindrical rotational viscometer according to JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa·s.

[0251] <Production of positive electrode>

[0252] A 20 μm thick aluminum foil was prepared as a current collector. The positive electrode slurry was coated with a notch wheel coater to a weight per unit area of 20 mg / cm after drying. 2 The positive electrode raw material was coated on aluminum foil in the form of , dried at 90℃ for 20 minutes, dried at 120℃ for 20 minutes, and then heated at 60℃ for 10 hours to obtain a positive electrode raw material. The positive electrode raw material was rolled using a roller press to produce a material with a density of 3.2g / cm 3 A sheet-shaped positive electrode was formed of a positive electrode composite material layer and aluminum foil. The thickness of the sheet-shaped positive electrode was 70 μm. The sheet-shaped positive electrode was cut into pieces with a width of 4.8 mm and a length of 50 cm to serve as a positive electrode for a lithium-ion secondary battery.

[0253] <Production of negative electrode>

[0254] 90 parts of spherical artificial graphite (volume average particle size: 12 μm) as the negative electrode active material and 10 parts of SiO xA negative electrode slurry was prepared by mixing a mixture of 1 part of styrene-butadiene polymer (volume average particle size: 10 μm), 1 part of styrene-butadiene polymer as a binder, 1 part of carboxymethyl cellulose as a thickener, and an appropriate amount of water as a dispersion medium.

[0255] Next, a copper foil with a thickness of 15 μm was prepared as a current collector. The negative electrode slurry composition was applied in an amount of 10 mg / cm after drying. 2 The negative electrode material was coated on both sides of the copper foil, dried at 60°C for 20 minutes and at 120°C for 20 minutes. Then, it was heated at 150°C for 2 hours to obtain the negative electrode material. The negative electrode material was rolled using a roller press to produce a material with a density of 1.8 g / cm 3 The negative electrode sheet was formed by combining the negative electrode composite material layer (on both sides) and copper foil. The negative electrode sheet was then cut into pieces with a width of 5.0 mm and a length of 52 cm to serve as a negative electrode for a lithium ion secondary battery.

[0256] <Preparation of spacers>

[0257] A single-layer polypropylene separator (manufactured by Celgard, product name "Celgard 2500", thickness: 15 μm) was cut into a size of 120 cm×5.5 cm.

[0258] <Manufacturing of Secondary Batteries>

[0259] The positive electrode and negative electrode were wound around a core with a diameter of 20 mm, with a separator interposed therebetween, to form a wound body. The resulting wound body was compressed in one direction at a speed of 10 mm / s to a thickness of 4.5 mm. The compressed wound body had an elliptical shape when viewed from above, with a major diameter to minor diameter ratio (major diameter / minor diameter) of 7.7.

[0260] In addition, an electrolyte solution (composition: LiPF6 solution with a concentration of 1.0 M (the solvent is a mixed solution of 5 mass% of fluoroethylene carbonate added to a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3 / 7 (mass ratio) and 2 volume% of vinylene carbonate added as an additive)) is prepared.

[0261] The compressed wound body was then placed in an aluminum laminate housing along with 3.2 g of a non-aqueous electrolyte. A nickel lead was then connected to the designated position of the negative electrode, and an aluminum lead was connected to the designated position of the positive electrode. The opening of the housing was then sealed using heat to obtain a lithium-ion secondary battery. The lithium-ion secondary battery was in the form of a bag with a width of 35 mm, a height of 48 mm, and a thickness of 5 mm, and had a nominal capacity of 700 mAh. The resulting lithium-ion secondary battery was evaluated for internal resistance reduction and high-temperature storage characteristics. The results are shown in Table 3.

[0262] (Example 2)

[0263] When preparing the positive electrode slurry, the same procedures as in Example 1 were followed, except that polyacrylonitrile was used as the binder instead of polyvinylidene fluoride. The carbon material, dispersant, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared. Various evaluations were then performed. The results are shown in Table 3.

[0264] (Example 3)

[0265] To prepare the conductive material dispersion, CNT-B prepared as follows was used as the carbon material. The same procedures as in Example 1 were followed, except that the following procedures were followed: a dispersant, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared. Various evaluations were then performed. The results are shown in Tables 1 and 3.

[0266] <Preparation of Carbon Material (CNT-B)>

[0267] 10 g of CNT-A prepared in the same manner as in Example 1 was added to 1 L of ozone water with a dissolved ozone concentration of 5 mg / l and stirred at 20°C for 5 hours. The solid content (CNT) was then recovered by filtration and dried under reduced pressure at 100°C to obtain CNT-B.

[0268] (Example 4)

[0269] To prepare the conductive material dispersion, CNT-C prepared as follows was used as the carbon material. The same procedures as in Example 1 were followed, except that the following procedures were followed: a dispersant, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared. Various evaluations were then performed. The results are shown in Tables 1 and 3.

[0270] <Preparation of Carbon Material (CNT-C)>

[0271] 10 g of CNT-A prepared in the same manner as in Example 1 was added to 1 L of ozone water with a dissolved ozone concentration of 5 mg / l and stirred at 20°C for 10 hours. The solid content (CNT) was then recovered by filtration and dried under reduced pressure at 100°C to obtain CNT-C.

[0272] (Example 5)

[0273] When preparing the conductive material dispersion, hydrogenated nitrile rubber B prepared as follows was used as the dispersant. The carbon material, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared in the same manner as in Example 1, except that the following procedure was used. Various evaluations were then performed. The results are shown in Tables 2 and 3.

[0274] <Preparation of Dispersant (Hydrogenated Nitrile Rubber B)>

[0275] 180 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate as an emulsifier, 28 parts of acrylonitrile as a nitrile-containing monomer, and 0.8 parts of tert-dodecylmercaptan as a molecular weight regulator were sequentially added to the reactor. After the atmosphere inside the reactor was replaced with nitrogen three times, 72 parts of 1,3-butadiene as a conjugated diene monomer was added. 0.1 parts of potassium persulfate as a polymerization initiator was added to the reactor maintained at 30°C to initiate polymerization, and the polymerization reaction continued while stirring.

[0276] When the polymerization conversion rate reached 90%, 0.2 parts of hydroxylamine sulfate was added per 100 parts of monomer to terminate the polymerization. The mixture was then heated and steam distilled under reduced pressure at approximately 70°C to recover the residual monomers. Two parts of an alkylated phenol was then added as an antioxidant to obtain an aqueous dispersion of the polymer.

[0277] The subsequent operations were carried out in the same manner as in Example 1 to obtain an NMP solution of hydrogenated nitrile rubber B having a solid content concentration of 8%.

[0278] (Example 6)

[0279] A conductive material dispersion and a positive electrode slurry were prepared as follows. The same procedures as in Example 1 were followed to prepare the dispersant, positive electrode, negative electrode, separator, and secondary battery. Various evaluations were then performed. The results are shown in Tables 1 and 3.

[0280] <Preparation of Conductive Material Dispersion>

[0281] 18.0 parts of carbon black (manufactured by Temeco, product name "Super-T", hereinafter referred to as "CB-A") as a conductive material, 1.8 parts (solid content conversion) of hydrogenated nitrile rubber A obtained in the same manner as in Example 1 as a dispersant, and 80.2 parts of NMP were stirred (3000 rpm, 10 minutes) using a disperser. Then, the mixture was dispersed at a peripheral speed of 8 m / s for 1 hour using a bead mill using zirconia beads with a diameter of 1 mm to prepare a conductive material dispersion having a solid content concentration of 19.8%.

[0282] <Preparation of positive electrode slurry>

[0283] 96.0 parts of a ternary active material (LiNi 0.5 Co 0.2 Mn 0.3A positive electrode slurry was prepared by mixing 1.0 parts of polyvinylidene fluoride (PVDF) as a binder, 3.0 parts (based on solid content) of the conductive material dispersion, and NMP using a planetary mixer (60 rpm, 30 minutes) to prepare the positive electrode slurry. The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry composition (measured using a single cylindrical rotational viscometer according to JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa·s.

[0284] (Example 7)

[0285] When preparing the conductive material dispersion, CB-B prepared as follows was used as the carbon material. The same procedures as in Example 6 were followed, except that the following method was used: dispersant, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared. Various evaluations were then performed. The results are shown in Tables 1 and 4.

[0286] <Preparation of Carbon Material (CB-B)>

[0287] 10 g of CB-A was added to 1 L of ozone water with a dissolved ozone concentration of 5 mg / l and stirred at 20° C. for 5 hours. The solid content (carbon black) was recovered by filtration and dried under reduced pressure at 100° C. to prepare CB-B.

[0288] (Example 8)

[0289] When preparing the conductive material dispersion, hydrogenated styrene-butadiene-nitrile rubber prepared as follows was used as the dispersant. The carbon material, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared in the same manner as in Example 1. Various evaluations were then performed. The results are shown in Tables 2 and 4.

[0290] <Preparation of Dispersant (Hydrogenated Styrene-Butadiene-Nitrile Rubber)>

[0291] Into the reactor were sequentially added 180 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate as an emulsifier, 31 parts of styrene as an aromatic vinyl monomer, 7 parts of acrylonitrile as a nitrile-containing monomer, 7 parts of methacrylic acid as an acidic-group-containing monomer, and 2.0 parts of tert-dodecylmercaptan as a molecular weight modifier. After the atmosphere inside the reactor was replaced with nitrogen three times, 55 parts of 1,3-butadiene as a conjugated diene monomer was added.

[0292] The subsequent operations were carried out in the same manner as in Example 1 to obtain an NMP solution of a hydrogenated styrene-butadiene-nitrile rubber having a solid content concentration of 8%.

[0293] (Comparative Examples 1, 2, and 3)

[0294] When preparing the conductive material dispersion, polyvinyl pyrrolidone was used as the dispersant instead of hydrogenated nitrile rubber A. The same procedures as in Examples 1, 3, and 6 were followed to prepare the carbon material, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery. Various evaluations were then performed. The results are shown in Table 4.

[0295] (Comparative Example 4)

[0296] The carbon material, conductive material dispersion, positive electrode slurry, positive electrode, negative electrode, separator, and secondary battery were prepared in the same manner as in Example 1, except that polyvinyl butyral was used as the dispersant instead of hydrogenated nitrile rubber A. Various evaluations were then performed. The results are shown in Table 4.

[0297] In addition, in Tables 2 to 4,

[0298] "HNBR-A" means hydrogenated nitrile rubber A,

[0299] "HNBR-B" means hydrogenated nitrile rubber B,

[0300] "HSNBR" means hydrogenated styrene-butadiene-nitrile rubber,

[0301] "AN unit" means an acrylonitrile unit,

[0302] "ST unit" means a styrene unit,

[0303] "H-BD unit" means 1,3-butadiene hydride unit,

[0304] "MAA unit" means a methacrylic acid unit,

[0305] "1,2 bond H-BD unit" means a 1,2 bond butadiene hydride unit.

[0306] "PVP" stands for polyvinylpyrrolidone,

[0307] "PVB" stands for polyvinyl butyral,

[0308] "PVdF" stands for polyvinylidene fluoride,

[0309] "PAN" stands for polyacrylonitrile,

[0310] "NCM" means LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0311] [Table 1]

[0312]

[0313] [Table 2]

[0314]

[0315] [Table 3]

[0316]

[0317] [Table 4]

[0318]

[0319] As shown in Tables 3 and 4, when using a carbon material, a dispersant, a dispersion medium, and a carbon material, the Hansen solubility parameter (HSP c ) and the Hansen Solubility Parameter (HSP) of the dispersant d ) of the HSP distance (R d In Examples 1 to 8, in which positive electrodes were produced using conductive material dispersions having a ) value below a predetermined value, secondary batteries with reduced internal resistance and excellent high-temperature storage characteristics were produced. Furthermore, it was found that the conductive material dispersions of Examples 1 to 8 had a good dispersion state and excellent viscosity stability.

[0320] On the other hand, it can be seen from Table 4 that when using the HSP distance (R d In Comparative Examples 1 to 4, in which the positive electrodes were produced using a conductive material dispersion having a concentration greater than the specified value, the internal resistance of the secondary battery was not sufficiently reduced, and the high-temperature storage characteristics were degraded. Furthermore, it was found that the dispersion state of the conductive material dispersion was deteriorated in Comparative Examples 1 to 4.

[0321] Industrial applicability

[0322] According to the present invention, a conductive material dispersion, a secondary battery positive electrode slurry, and a secondary battery positive electrode can be provided, which can reduce the internal resistance of a secondary battery and ensure good high-temperature storage characteristics of the secondary battery.

[0323] Furthermore, according to the present invention, a secondary battery having reduced internal resistance and excellent high-temperature storage characteristics can be provided.

Claims

1. A conductive material dispersion comprising a carbon material, a dispersant, and a dispersion medium, The Hansen solubility parameter (HSP) of the carbon material c ) and the Hansen Solubility Parameter (HSP) of the dispersant d ) of the HSP distance (R d ) is 10.0MPa 1 / 2 the following, The dispersant comprises 1,3-butadiene hydride units, When all 1,3-butadiene hydrogenated units in the dispersant are taken as 100% by mass, the 1,2-bonded butadiene hydrogenated units account for 4.0% by mass or more and 15% by mass or less, The total 1,3-butadiene hydride units are the sum of the 1,4-bond butadiene hydride units and the 1,2-bond butadiene hydride units. The structure of the 1,4-bond butadiene hydride unit is -CH2-CH2-CH2-CH2-, The structure of the 1,2-bond butadiene hydride unit is -CH2-CH(C2H5)-.

2. The conductive material dispersion according to claim 1, wherein The Hansen solubility parameter (HSP) of the carbon material c ) in the hydrogen bond term δ h1 12.0MPa 1 / 2 the following.

3. The conductive material dispersion according to claim 1 or 2, wherein The carbon material includes a fibrous carbon material. 4 . A slurry for a secondary battery positive electrode, comprising a positive electrode active material and the conductive material dispersion according to claim 1 .

5. The secondary battery positive electrode slurry according to claim 4, wherein The secondary battery positive electrode slurry further includes a binder.

6. The secondary battery positive electrode slurry according to claim 5, wherein The Hansen solubility parameter (HSP) of the carbon material c ) and the Hansen Solubility Parameter (HSP) of the bonding material b ) of the HSP distance (R b ) is greater than the HSP distance (R d ). 7 . A secondary battery positive electrode comprising a positive electrode composite material layer formed using the slurry for a secondary battery positive electrode according to claim 4 . 8 . A secondary battery comprising the positive electrode for a secondary battery according to claim 7 .

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