Carbon nanotube dispersion, slurry for nonaqueous secondary battery negative electrode, nonaqueous secondary battery negative electrode, and nonaqueous secondary battery

Abstract

The purpose of this invention is to provide a CNT dispersion with excellent dispersibility and storage stability. This invention is a carbon nanotube dispersion comprising carbon nanotubes, a water-soluble polymer with acidic functional groups, and water, wherein the Hansen solubility parameter (HSP) of the aforementioned carbon nanotubes is specified. c The Hansen solubility parameter (HSP) of the above water-soluble polymers d HSP distance (R) a ) is 7.0 MPa 1 / 2 the following.

Description

Technical Field

[0001] This invention relates to carbon nanotube dispersions, slurries for anodes of non-aqueous secondary batteries, anodes for non-aqueous secondary batteries, and non-aqueous secondary batteries. Background Technology

[0002] Carbon nanotubes (CNTs) possess excellent mechanical strength, optical properties, electrical properties, thermal properties, and molecular adsorption capabilities. Therefore, they are used in various electronic components, including logic circuits, DRAM (Dynamic Random Access Memory), SRAM (Static Random-Access Memory), NRAM (Nano Random Access Memory), semiconductor devices, interconnects, complementary MOS (Metal-Oxide-Semiconductor Field-Effect Transistors), bipolar transistors, chemical sensors such as detectors for trace gases, and biosensors such as analyzers for DNA and proteins.

[0003] Furthermore, in recent years, CNTs have also been used as conductive materials in the electrode composite layer formation of non-aqueous secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") such as lithium-ion secondary batteries, in the slurry for secondary battery electrodes. The electrodes of secondary batteries expand and contract significantly due to charging and discharging, thereby reducing electrode conductivity and the cycle characteristics of the secondary battery. As a result, when CNTs are used as the conductive material in the slurry for secondary battery electrodes, the decrease in conductivity can be suppressed, and secondary batteries with excellent cycle characteristics can be obtained.

[0004] In this regard, from the viewpoint of fully utilizing the properties of CNTs, it is necessary to disperse them in a solvent when using them, and dispersions containing CNTs have been proposed. For example, Patent Document 1 proposes a conductive dispersion, which is a conductive material dispersion containing CNTs, a dispersant, and an organic solvent as a dispersion medium, wherein the Hansen solubility parameter (HSP) distance between the CNTs and the dispersant is below a specified value.

[0005] On the other hand, from the perspectives of environmental impact and operability, it is desirable to use water instead of organic solvents to disperse CNTs. However, CNTs have a low affinity for water, making it very difficult to obtain a CNT dispersion in water.

[0006] Therefore, in recent years, there has been a focus on developing CNT dispersions with excellent dispersibility and storage stability, particularly for CNT dispersions containing water. For example, Patent Document 2 discloses a CNT dispersion containing CNTs, carboxymethyl cellulose or its salts, and water. The weight-average molecular weight of the carboxymethyl cellulose or its salts is 10,000 to 100,000, the degree of etherification is 0.5 to 0.9, and the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) of the CNT dispersion is 100 or more and 1500 or less.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2021 / 200126;

[0010] Patent Document 2: Japanese Patent No. 6860740. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Therefore, it is required to further improve the dispersibility and storage stability of carbon nanotubes in water-containing carbon nanotube dispersions.

[0013] Therefore, the purpose of this invention is to provide a carbon nanotube dispersion with excellent dispersibility and storage stability.

[0014] Furthermore, the present invention aims to provide a slurry for a non-aqueous secondary battery negative electrode containing the carbon nanotube dispersion.

[0015] Furthermore, the present invention aims to provide a negative electrode for a non-aqueous secondary battery that uses the non-aqueous secondary battery negative electrode slurry.

[0016] Furthermore, the present invention aims to provide a non-aqueous secondary battery having the negative electrode for a non-aqueous secondary battery.

[0017] Solution for solving the problem

[0018] The inventors conducted in-depth research with the aim of solving the above-mentioned problems. Then, the inventors made a new discovery: if the carbon nanotube dispersion comprises carbon nanotubes, a water-soluble polymer having acid functional groups (hereinafter sometimes simply referred to as "water-soluble polymer"), and water, and the Hansen solubility parameter (HSP) of the carbon nanotubes is... c The Hansen solubility parameter (HSP) of water-soluble polymers d HSP distance (R) aWhen the carbon nanotube dispersion is below a specified value, the carbon nanotubes exhibit excellent dispersibility and storage stability, thus completing this invention.

[0019] That is, the object of the present invention is to advantageously solve the above-mentioned problems. The present invention is a carbon nanotube dispersion comprising carbon nanotubes, a water-soluble polymer having acid functional groups, and water, wherein the Hansen solubility parameter (HSP) of the carbon nanotubes is... c The Hansen solubility parameter (HSP) of the above water-soluble polymers d HSP distance (R) a ) is 7.0 MPa 1 / 2 The following applies. If it is such a carbon nanotube dispersion, it can become a carbon nanotube dispersion with excellent dispersibility and storage stability.

[0020] In this specification, "Hansen solubility parameter (HSP) of carbon nanotubes" c ")" is derived from the polarity term δ p1 δ, the dispersion term d1 and the hydrogen bond term δ h1 Composition, "Hansen solubility parameter (HSP) of water-soluble polymers" d ")" is derived from the polarity term δ p2 δ, the dispersion term d2 and the hydrogen bond term δ h2 Composition. Herein, in this specification, "δ" p1 “δ” d1 "and "δ h1 ” and “δ” p2 “δ” d2 "and "δ h2 "It can be determined using the methods described in the embodiments. Furthermore, in this specification, 'HSP distance (R...')..." a The following formula (1) can be used to calculate:

[0021] .

[0022] In this specification, "water-soluble" means that when 0.5g of the polymer is dissolved in 100g of water at 25°C, the insoluble component is less than 1.0g by mass.

[0023] In this specification, the polarity term δ p δ, the dispersion term d and the hydrogen bond term δ h The unit is "MPa" 1 / 2 , which is sometimes omitted below.

[0024] In the carbon nanotube dispersion of the present invention, the Hansen solubility parameter (HSP) of the above-mentioned water-soluble polymer is... d ) and polarity term δp3 10.7 MPa 1 / 2 δ, the dispersion term d3 18.6 MPa 1 / 2 Hydrogen bond term δ h3 7.0 MPa 1 / 2 Hansen solubility parameter (HSP) of the material m HSP distance (R) b ) is 8.0 MPa 1 / 2 the following.

[0025] If the HSP distance (R) b If the value is below the aforementioned upper limit, then when using a non-aqueous secondary battery negative electrode slurry containing a carbon nanotube dispersion to manufacture a negative electrode for a non-aqueous secondary battery, the peel strength of the electrode composite layer from the current collector can be improved.

[0026] In this specification, “δ p3 “δ” d3 ” and “δ” h3 "is a value determined using the method described in the embodiments. Furthermore, in this specification, "HSP distance (R)" is used to indicate the distance. b The following formula (2) can be used to calculate:

[0027] .

[0028] The carbon nanotube dispersion of the present invention preferably has a pH of 6 or higher and 10 or lower.

[0029] If the pH is within the above range, the viscosity stability of the slurry for the negative electrode of a non-aqueous secondary battery containing carbon nanotube dispersion can be improved, and the cycle characteristics of a non-aqueous secondary battery with a negative electrode made using the slurry for the negative electrode of a non-aqueous secondary battery can be improved.

[0030] In the carbon nanotube dispersion of the present invention, preferably at least a portion of the acid functional groups of the above-mentioned water-soluble polymer are alkali metal salts or ammonium salts.

[0031] If at least a portion of the acid functional groups of the water-soluble polymer are alkali metal salts or ammonium salts, the dispersibility and storage stability of the carbon nanotube dispersion can be improved, and the viscosity stability of the slurry for the negative electrode of a non-aqueous secondary battery containing the carbon nanotube dispersion can be improved, thereby improving the cycle characteristics of a non-aqueous secondary battery with a negative electrode made using the slurry for the negative electrode of a non-aqueous secondary battery.

[0032] In the carbon nanotube dispersion of the present invention, the acid functional group is preferably a carboxylic acid group.

[0033] If the acid functional group is a carboxylic acid group, the dispersibility and storage stability of the carbon nanotube dispersion can be improved, and the viscosity stability of the slurry for non-aqueous secondary battery anodes containing carbon nanotube dispersions can be improved, thereby enhancing the cycle characteristics of non-aqueous secondary batteries with anodes made using non-aqueous secondary battery anode slurries. Furthermore, the dispersibility and storage stability of the carbon nanotube dispersion can be maintained regardless of the type of carbon nanotubes.

[0034] In the carbon nanotube dispersion of the present invention, the acid functional group is preferably a sulfonic acid group.

[0035] If the acid functional group is a sulfonic acid group, it can improve the dispersibility and storage stability of the carbon nanotube dispersion, and improve the viscosity stability of the slurry for the negative electrode of a non-aqueous secondary battery containing the carbon nanotube dispersion, thereby improving the cycle characteristics of the non-aqueous secondary battery with a negative electrode made using the slurry for the negative electrode of a non-aqueous secondary battery.

[0036] In the carbon nanotube dispersion of the present invention, the water-soluble polymer preferably contains an ether group.

[0037] If the water-soluble polymer contains an ether group, it can improve the dispersibility and storage stability of the carbon nanotube dispersion, and improve the viscosity stability of the slurry for the negative electrode of a non-aqueous secondary battery containing the carbon nanotube dispersion, thereby improving the cycle characteristics of the non-aqueous secondary battery with a negative electrode made using the non-aqueous secondary battery negative electrode slurry.

[0038] In the carbon nanotube dispersion of the present invention, the mass ratio of the carbon nanotubes to the water-soluble polymer is preferably 0.1 or more and 10 or less.

[0039] If the mass ratio of carbon nanotubes to water-soluble polymers is within the above range, the storage stability of the carbon nanotube dispersion can be improved.

[0040] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The present invention is a slurry for a non-aqueous secondary battery negative electrode, comprising a negative electrode active material and the aforementioned carbon nanotube dispersion. Such a non-aqueous secondary battery negative electrode slurry can achieve excellent viscosity stability and form a negative electrode capable of enabling the non-aqueous secondary battery to exhibit excellent cycle characteristics.

[0041] In the non-aqueous secondary battery negative electrode slurry of the present invention, the negative electrode active material preferably includes a silicon-based negative electrode active material.

[0042] If the negative electrode active material includes a silicon-based negative electrode active material (a negative electrode active material containing silicon), then a high-capacity non-aqueous secondary battery with a negative electrode made using a non-aqueous secondary battery negative electrode slurry can be achieved. Furthermore, silicon-based negative electrode active materials exhibit particularly large expansion and contraction during charging and discharging. However, since the negative electrode slurry of the present invention is prepared using the carbon nanotube dispersion of the present invention described above, even when using a silicon-based negative electrode active material, the decrease in conductivity of the electrode composite layer can be suppressed, enabling the formation of a negative electrode that allows the non-aqueous secondary battery to exhibit superior cycle characteristics.

[0043] The slurry for the negative electrode of the non-aqueous secondary battery of the present invention preferably further comprises a particulate polymer, wherein the particulate polymer comprises a carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a conjugated diene monomer unit.

[0044] If the above-mentioned non-aqueous secondary battery negative electrode slurry is used, the cycle characteristics of the non-aqueous secondary battery with a non-aqueous secondary battery negative electrode made using the non-aqueous secondary battery negative electrode slurry can be improved.

[0045] In this specification, a polymer "containing monomer units" means "a polymer obtained using the monomer contains repeating units derived from that monomer".

[0046] In the non-aqueous secondary battery negative electrode slurry of the present invention, all repeating units contained in the above-mentioned particulate polymer are taken as 100% by mass, and the content ratio of the above-mentioned carboxylic acid group-containing monomer units in the above-mentioned particulate polymer is preferably 3% by mass or more and 30% by mass or less.

[0047] If the proportion of carboxylic acid group monomer units in the particulate polymer is within the above range, the cycle characteristics of the non-aqueous secondary battery with a non-aqueous secondary battery negative electrode made using a non-aqueous secondary battery negative electrode slurry can be further improved.

[0048] In this specification, the content ratio of repeating units (monomer units) in the polymer can be used... 1 H-NMR and 13 It is determined by nuclear magnetic resonance (NMR) methods such as C-NMR.

[0049] In the non-aqueous secondary battery negative electrode slurry of the present invention, the Hansen solubility parameter (HSP) of the above-mentioned water-soluble polymer is preferred. d The Hansen solubility parameter (HSP) of the above-mentioned particulate polymers. b HSP distance (R) c ) is 7.0 MPa 1 / 2 the following.

[0050] If the HSP distance (R) c If the value is below the aforementioned upper limit, the cycle characteristics of a non-aqueous secondary battery with a non-aqueous secondary battery negative electrode made using a non-aqueous secondary battery negative electrode slurry can be improved.

[0051] In this specification, "Hansen solubility parameter (HSP) of particulate polymers" b ")" is derived from the polarity term δ p4 δ, the dispersion term d4 and the hydrogen bond term δ h4 Composition. Here, "δ" p4 “δ” d4 ” and “δ” h4 "It can be determined using the methods described in the embodiments. Furthermore, in this specification, 'HSP distance (R...')..." c The following formula (3) can be used to calculate:

[0052] .

[0053] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The present invention is a negative electrode for a non-aqueous secondary battery, which has a current collector and a negative electrode composite material layer formed by using the aforementioned non-aqueous secondary battery negative electrode slurry on the current collector. If such a negative electrode for a non-aqueous secondary battery is provided, it can become a negative electrode for a non-aqueous secondary battery that enables the non-aqueous secondary battery to exhibit excellent cycle characteristics.

[0054] In the negative electrode for a non-aqueous secondary battery of the present invention, the current collector is preferably an electrolytic copper foil.

[0055] If the current collector is electrolytic copper foil, the peel strength of the electrode composite layer from the current collector can be improved.

[0056] Furthermore, the object of the present invention is to advantageously solve the above-mentioned problems. The present invention is a non-aqueous secondary battery having the aforementioned negative electrode for non-aqueous secondary batteries. Such a non-aqueous secondary battery can become a non-aqueous secondary battery with excellent cycle characteristics.

[0057] Invention Effects

[0058] According to the present invention, a carbon nanotube dispersion with excellent dispersibility and storage stability can be provided.

[0059] Furthermore, according to the present invention, a non-aqueous secondary battery negative electrode slurry containing the carbon nanotube dispersion can be provided.

[0060] Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery negative electrode using the non-aqueous secondary battery negative electrode slurry.

[0061] Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery having the negative electrode for the non-aqueous secondary battery. Detailed Implementation

[0062] The embodiments of the present invention will now be described in detail.

[0063] Here, the CNT dispersion of the present invention is not particularly limited and can be used as a material in the manufacture of, for example, a slurry for a negative electrode of a non-aqueous secondary battery (hereinafter sometimes simply referred to as "negative electrode slurry"). Furthermore, the negative electrode slurry of the present invention can be prepared using the CNT dispersion of the present invention. In addition, the negative electrode for a non-aqueous secondary battery of the present invention (hereinafter sometimes simply referred to as "negative electrode") is characterized by having a negative electrode composite material layer formed using the negative electrode slurry of the present invention. Furthermore, the non-aqueous secondary battery of the present invention is characterized by having the negative electrode of the present invention. Additionally, the CNT dispersion of the present invention can be used as a raw material for composite materials containing resin and CNTs, and in the manufacture of electronic products, etc.

[0064] (CNT dispersion)

[0065] The CNT dispersion of the present invention comprises CNTs, a water-soluble polymer having acidic functional groups, and water, and optionally contains other components. Furthermore, the CNT dispersion typically does not contain electrode active materials (positive electrode active material, negative electrode active material).

[0066] Here, in the CNT dispersion of the present invention, the Hansen solubility parameter (HSP) of CNTs is... c The Hansen solubility parameter (HSP) of water-soluble polymers d HSP distance (R) a ) is 7.0 MPa 1 / 2 The following describes how such a CNT dispersion can achieve excellent dispersibility and storage stability. The reasons for this are not necessarily clear, but are speculated to be related to the affinity between CNTs and water-soluble polymers, the affinity between water-soluble polymers and water, and electrostatic repulsion caused by the presence of acidic functional groups in the water-soluble polymers. However, as can be seen from the examples and comparative examples described later, in a CNT dispersion, the Hansen solubility parameter (HSP) of CNTs is... c The Hansen solubility parameter (HSP) of water-soluble polymers d HSP distance (R) a ) is 7.0 MPa 1 / 2 The CNT dispersion exhibits excellent dispersibility and storage stability under the following conditions.

[0067] Furthermore, if it is the above-mentioned CNT dispersion, a negative electrode slurry with excellent viscosity stability can be obtained, which can form a negative electrode that enables the secondary battery to exhibit excellent cycle characteristics.

[0068] Additionally, the HSP distance (R) a It is possible to modify the HSP of CNT appropriately. c (polarity term δ) p1 δ, the dispersion term d1 and the hydrogen bond term δ h1 HSPs of water-soluble polymers d (polarity term δ) p2 δ, the dispersion term d2 and the hydrogen bond term δ h2 The HSP of the polymer can be adjusted by appropriately selecting and combining known monomers for polymerization. The HSP of the monomers can be referenced from databases such as "HSPiP ver. 5.3.04".

[0069] HSP distance (R) a The preferred pressure is 6.0 MPa. 1 / 2 Hereinafter, 5.0 MPa is more preferred. 1 / 2 Hereinafter, 4.5 MPa is further preferred. 1 / 2 the following.

[0070] If the HSP distance (R) a If the value is above the lower limit mentioned above, the dispersibility and storage stability of the CNT dispersion can be improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be improved, thereby improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0071] On the other hand, HSP distance (R a For example, 0.1 MPa 1 / 2 The above can be 1.0 MPa 1 / 2 above.

[0072] The CNT dispersion of the present invention preferably has the Hansen solubility parameter (HSP) of a water-soluble polymer. d ) and polarity term δ p3 10.7, dispersion term δ d3 18.6, hydrogen bond term δ h3 Hansen solubility parameter (HSP) of the material is 7.0 m HSP distance (R) b ) is 8.0 MPa 1 / 2 Hereinafter, 5.0 MPa is more preferred. 1 / 2 Hereinafter, 4.0 MPa is further preferred. 1 / 2 the following.

[0073] Materials used as current collectors for the negative electrode of secondary batteries typically employ Hansen solubility parameters close to the aforementioned Hansen solubility parameters (HSP).d The material, if the HSP distance (R) b If the value is below the aforementioned upper limit, then when using a negative electrode slurry containing CNT dispersion to make a negative electrode, the peel strength of the electrode composite layer from the current collector can be improved.

[0074] On the other hand, HSP distance (R b For example, 0.1 MPa 1 / 2 The above can also be 1.0 MPa. 1 / 2 above.

[0075] Additionally, the HSP distance (R) b It is possible to modify the HSP of water-soluble polymers appropriately. d (polarity term δ) p2 δ, the dispersion term d2 and the hydrogen bond term δ h2 ) to make adjustments.

[0076] In addition, δ is the polar term p3 10.7, dispersion term δ d3 18.6, hydrogen bond term δ h3 Materials rated 7.0 include, for example, electrolytic copper foil. Electrolytic copper foil refers to copper foil obtained by immersing a metal drum in an electrolyte solution containing dissolved copper ions, rotating the drum while passing an electric current through it, thereby depositing copper on the surface of the drum, and then peeling off the copper.

[0077] The CNT dispersion of the present invention preferably has a pH of 6 or higher, more preferably 7 or higher, even more preferably 7.5 or higher, preferably 10 or lower, more preferably 9 or lower, and even more preferably 8.5 or lower.

[0078] If the pH is within the above range, the viscosity stability of the negative electrode slurry containing the CNT dispersion can be improved, and the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry can be improved.

[0079] The CNT dispersion of the present invention preferably has a CNT to water-soluble polymer mass ratio (CNT / water-soluble polymer) of 0.1 or more, more preferably 0.5 or more, even more preferably 1.5 or more, preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less.

[0080] If the mass ratio of CNTs to the water-soluble polymer is within the above-mentioned range, the storage stability of the CNT dispersion can be improved. In particular, when the CNT dispersion contains multi-walled CNTs (described later), the storage stability of the CNT dispersion can be effectively improved if the mass ratio of CNTs to the water-soluble polymer is within the above-mentioned range.

[0081] On the other hand, when the CNT dispersion contains single-walled CNTs as described later, the mass ratio of CNTs to the water-soluble polymer (CNT / water-soluble polymer) is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, even more preferably 1 or less, and even more preferably 0.5 or less.

[0082] When a CNT dispersion contains single-walled CNTs (described later), if the mass ratio of CNTs to water-soluble polymers is within the range described above, the dispersibility and storage stability of the CNT dispersion can be improved.

[0083] <cnt>

[0084] CNTs can be either single-walled or multi-walled. Furthermore, single-walled and multi-walled CNTs can be used in combination as CNTs.

[0085] The average diameter of CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, even more preferably 2 nm or more, preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 20 nm or less.

[0086] If the average diameter of CNTs is within the above range, the dispersibility and storage stability of the CNT dispersion can be improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be improved, thereby improving the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry.

[0087] In this specification, the average diameter of CNTs can be obtained by observing CNTs with a transmission electron microscope (TEM), measuring the diameter (outer diameter) of 50 CNTs from the obtained TEM images, and using the arithmetic mean of these measurements.

[0088] The ratio of the intensity of the G band peak to the intensity of the D band peak in the Raman spectrum of CNT (G / D ratio) is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more.

[0089] If the G / D ratio of CNTs is above the lower limit mentioned above, the cycle characteristics of the secondary battery can be further improved. Furthermore, there is no particular upper limit to the G / D ratio of CNTs, which is, for example, below 200.

[0090] In this specification, the "G / D ratio" of CNTs can be calculated as follows: The Raman spectrum of the CNTs is measured using a microlaser Raman spectrophotometer (Nicolet Almega XR, Thermo Fisher Scientific). From the obtained Raman spectrum, the value at 1590 cm⁻¹ is determined. -1 The intensity of the G-band peak observed nearby and at 1340 cm⁻¹ -1 The intensity of the D-band peaks observed nearby is used to calculate the ratio between them.

[0091] With the total mass of the CNT dispersion as 100% by mass, the CNT content in the CNT dispersion is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.7% by mass or more.

[0092] If the proportion of CNTs in the CNT dispersion is above the lower limit mentioned above, the productivity of the product obtained using the CNT dispersion can be improved.

[0093] On the other hand, with the total mass of the CNT dispersion as 100% by mass, the proportion of CNTs in the CNT dispersion is, for example, 10.0% by mass or less, or 5.0% by mass or less, or 2.0% by mass or less.

[0094] CNTs are not particularly limited and can be synthesized using known CNT synthesis methods such as arc discharge, laser ablation, and chemical vapor deposition (CVD).

[0095] The polar term δ of CNT p1 For example, 5 or above can be 5.5 or above, or 6.0 or above; for example, 8.0 or below can be 7.5 or below, or 7.0 or below.

[0096] In addition, the dispersion term δ of CNT d1 For example, 15.0 or above can be 17.0 or above, or 18.5 or above; for example, 23.0 or below can be 21.0 or below, or 19.4 or below.

[0097] In addition, the hydrogen bond term δ of CNT h1 For example, a value of 3.0 or higher can be 4.0 or higher, or 4.5 or higher; for example, a value of 7.0 or lower can be 5.5 or lower, or 4.8 or lower.

[0098] Water-soluble polymers

[0099] In the CNT dispersion of the present invention, the water-soluble polymer has acidic functional groups and can function as a dispersant. Furthermore, the CNT dispersion of the present invention may also contain dispersants other than the aforementioned water-soluble polymer. For example, the CNT dispersion of the present invention may further contain HSP distance (R... a Greater than 7.0 MPa 1 / 2 Water-soluble polymers, HSP distance 7.0 MPa 1 / 2 The following water-soluble polymers that do not have acid functional groups are used as dispersants other than the water-soluble polymers mentioned above.

[0100] The polar term δ of water-soluble polymers p2 The polarity term δ of CNT p1 The smaller the difference, the better the choice. The polarity term δ of water-soluble polymers... p2 For example, 3.0 or above can be 3.5 or above, or 6.0 or above; for example, 10.0 or below can be 9.0 or below, or 8.0 or below.

[0101] In addition, the dispersion term δ of water-soluble polymers d2 The dispersion term δ of CNT d1 The smaller the difference, the better the selection. The dispersion term δ of water-soluble polymers... d2 For example, 15.0 or above can be 17.0 or above, or 18.0 or above; for example, 23.0 or below can be 21.0 or below, or 19.0 or below.

[0102] Hydrogen bond term δ of water-soluble polymers h2 Preferably, it is 5.0 or higher, more preferably 6.0 or higher, and even more preferably 6.5 or higher.

[0103] If the hydrogen bond term δ h2 If the concentration is above the lower limit mentioned above, the dispersibility and storage stability of the CNT dispersion can be improved. The reason for this is not necessarily clear, but it is speculated that it is due to the increased ability to form hydrogen bonds with water molecules, thus improving its affinity for water.

[0104] On the other hand, the hydrogen bond term δ of water-soluble polymers h2 For example, it can be below 12.0, below 10.0, or below 9.5.

[0105] Water-soluble polymers possess "acid functional groups" that include salts neutralized by bases. For example, in the case of carboxylic acid groups, the acid functional groups include not only -COOH but also lithium carboxylate groups (-COO). - Li + Neutralization type, etc. From the perspective of improving the dispersibility and storage stability of CNT dispersions, improving the viscosity stability of negative electrode slurries containing CNT dispersions, and further improving the cycle characteristics of secondary batteries with negative electrodes made using negative electrode slurries, the water-soluble polymer preferably has at least a portion of its acid functional groups being alkali metal salts or ammonium salts. Alternatively, all acid functional groups may be alkali metal salts or ammonium salts.

[0106] Examples of alkali metal bases include lithium, sodium, and potassium metal bases. These can also be combined in combinations of two or more.

[0107] Examples of acid functional groups in water-soluble polymers include carboxylic acid groups, sulfonic acid groups, and phosphate groups. Two or more of these can also be combined.

[0108] In one embodiment, the acid functional group of the water-soluble polymer is preferably a carboxylic acid group. If the acid functional group is a carboxylic acid group, the dispersibility and storage stability of the CNT dispersion can be improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be improved, thereby improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry. Furthermore, regardless of the type of CNT, the dispersibility and storage stability of the CNT dispersion can be maintained.

[0109] In another embodiment, the acid functional group of the water-soluble polymer is preferably a sulfonic acid group. If the acid functional group is a sulfonic acid group, the dispersibility and storage stability of the CNT dispersion can be improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be improved, thereby improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0110] The water-soluble polymer preferably contains an ether group. Here, "ether group" refers to the group represented by "-R'OR-". Furthermore, R and R' represent straight-chain or branched hydrocarbon groups with one or more but less than ten carbon atoms, preferably alkyl groups, and may be the same or different. R and R' preferably have two or more but less than five carbon atoms, more preferably two or three, and even more preferably two.

[0111] If the water-soluble polymer contains an ether group, it can improve the dispersibility and storage stability of the CNT dispersion, and improve the viscosity stability of the negative electrode slurry containing the CNT dispersion, thereby improving the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry.

[0112] Hereinafter, a first, second, and third embodiment of the water-soluble polymer contained in the CNT dispersion of the present invention will be described, but the water-soluble polymer is not limited to these embodiments.

[0113] [First-method water-soluble polymer]

[0114] The water-soluble polymer of the first embodiment comprises a carboxylic acid-containing monomer unit and a conjugated diene monomer unit. Alternatively, the water-soluble polymer of the first embodiment may also comprise repeating units other than the carboxylic acid-containing monomer unit and the conjugated diene monomer unit (other repeating units).

[0115] [Contains a carboxylic acid group monomer unit]

[0116] The carboxylic acid-containing monomer unit is a repeating unit containing a carboxylic acid group (-COOH). Furthermore, in the CNT dispersion, it is preferable that some or all of the carboxylic acid groups in the carboxylic acid-containing monomer unit are sodium carboxylate groups (-COOH). - Na + ), lithium carboxylate group (-COO) - Li + ), and carboxylic acid ammonium group (-COO) - NH4 + At least one of the states in ). By making the carboxylic acid group into at least one of the above-mentioned carboxylate groups, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0117] Examples of carboxylic acid-containing monomers that can form water-soluble polymers in the first manner include monocarboxylic acids and their derivatives, dicarboxylic acids and their anhydrides, and their derivatives.

[0118] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

[0119] 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.

[0120] Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0121] Examples of dicarboxylic acid derivatives include: methylmaleic acid; dimethylmaleic acid; phenylmaleic acid; chloromaleic acid; dichloromaleic acid; fluoromaleic acid; nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and other maleic acid monoesters.

[0122] Examples of anhydrides that are dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0123] In addition, as a monomer containing a carboxylic acid group, anhydrides that generate a carboxylic acid group through hydrolysis can also be used.

[0124] The carboxylic acid-containing monomer can be used alone or in combination with two or more. Furthermore, from the viewpoint of improving the cycle characteristics of secondary batteries, acrylic acid and methacrylic acid are preferred as the carboxylic acid-containing monomer. That is, the water-soluble polymer of the first embodiment preferably contains at least one of acrylic acid units and methacrylic acid units as the carboxylic acid-containing monomer unit.

[0125] The water-soluble polymer of the first embodiment contains 100% by mass of all repeating units. The proportion of carboxylic acid-containing monomer units in the water-soluble polymer of the first embodiment is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0126] Furthermore, the water-soluble polymer of the first embodiment contains 100 mol% of all repeating units, and the proportion of carboxylic acid group-containing monomer units in the water-soluble polymer of the first embodiment is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, preferably 90 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, and even more preferably 60 mol% or less.

[0127] If the proportion of carboxylic acid-containing monomer units in the water-soluble polymer of the first method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0128] [Conjugated diene monomer unit]

[0129] Examples of conjugated diene monomers that can form the water-soluble polymer of the first embodiment include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These can be used individually or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred, and isoprene is more preferred. That is, the water-soluble polymer of the first embodiment preferably contains at least one of a 1,3-butadiene unit and an isoprene unit as the conjugated diene monomer unit, and more preferably contains an isoprene unit as the conjugated diene monomer unit.

[0130] The water-soluble polymer of the first embodiment contains 100% by mass of all repeating units. The proportion of conjugated diene monomer units in the water-soluble polymer of the first embodiment 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 30% by mass or more, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0131] Furthermore, the water-soluble polymer of the first embodiment contains 100 mol% of all repeating units, and the proportion of conjugated diene monomer units in the water-soluble polymer of the first embodiment is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 40 mol% or more, preferably 70 mol% or less, more preferably 60 mol% or less, and even more preferably 50 mol% or less.

[0132] If the proportion of conjugated diene monomer units in the water-soluble polymer of the first method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0133] [Other repeating units]

[0134] The water-soluble polymer of the first type can contain repeating units other than the aforementioned carboxylic acid-containing monomer units and conjugated diene monomer units, without particular limitation. Examples include monomer units from known monomers (other monomers) capable of copolymerizing with the aforementioned carboxylic acid-containing monomers and conjugated diene monomers. Other monomers may be used alone or in combination of two or more.

[0135] However, from the viewpoint of further improving the cycle characteristics of the secondary battery, the water-soluble polymer of the first embodiment comprises 100% by mass of all repeating units, and the content of other repeating units in the water-soluble polymer of the first embodiment is preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass. Furthermore, the water-soluble polymer of the first embodiment comprises 100% by mol%, and the content of other repeating units in the water-soluble polymer of the first embodiment is preferably 20% by mol% or less, more preferably 10% by mol%, further preferably 5% by mol% or less, even more preferably 1% by mol% or less, and particularly preferably 0% by mol%.

[0136] In other words, the water-soluble polymer of the first embodiment comprises 100% by mass of all repeating units, and the total content ratio of carboxylic acid-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first embodiment is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass. Furthermore, the water-soluble polymer of the first embodiment comprises 100% by mol%, and the total content ratio of carboxylic acid-containing monomer units and conjugated diene monomer units in the water-soluble polymer of the first embodiment is preferably 80% by mol% or more, more preferably 90% by mol%, further preferably 95% by mol% or more, even more preferably 99% by mol% or more, and particularly preferably 100% by mol%.

[0137] [Second method: water-soluble polymer]

[0138] The second type of water-soluble polymer comprises sulfonic acid-containing monomer units and alkylene oxide-containing monomer units. Alternatively, the second type of water-soluble polymer may also comprise repeating units (other repeating units) other than sulfonic acid-containing monomer units and alkylene oxide-containing monomer units.

[0139] [Sulfonic acid group-containing monomer unit]

[0140] The sulfonic acid-containing monomer unit is a repeating unit containing a sulfonic acid group (-SO3H). Furthermore, in the CNT dispersion, it is preferable that some or all of the sulfonic acid groups in the sulfonic acid-containing monomer unit are sodium sulfonate groups (-SO3H). - Na + ), lithium sulfonate (-SO3) - Li + ), and ammonium sulfonate group (-SO3) - NH4 + At least one of the states in ). By making the sulfonic acid group into at least one of the above-mentioned sulfonate groups, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0141] Examples of sulfonic acid monomers that are sulfonic acid monomer units capable of forming water-soluble polymers in the second manner include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, ethyl (meth)acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and their salts.

[0142] Additionally, in this specification, "(methyl)allyl" refers to allyl and / or methylallyl.

[0143] The sulfonic acid-containing monomer can be used alone or in combination with two or more. Furthermore, from the viewpoint of improving the cycle characteristics of secondary batteries, styrene sulfonic acid is preferred as the sulfonic acid-containing monomer. That is, the water-soluble polymer of the second approach preferably contains a styrene sulfonic acid unit as the sulfonic acid-containing monomer unit.

[0144] The water-soluble polymer of the second manner comprises 100% by mass of all repeating units, and the content of sulfonic acid-containing monomer units in the water-soluble polymer of the second manner is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0145] Furthermore, the water-soluble polymer of the second manner comprises 100 mol% of all repeating units, and the content of sulfonic acid-containing monomer units in the water-soluble polymer of the second manner is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and even more preferably 70 mol% or less.

[0146] If the proportion of sulfonic acid-containing monomer units in the water-soluble polymer of the second method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0147] [Monomer units containing oxidized olefin structures]

[0148] The second type of water-soluble polymer has an oxidized olefin-containing monomer unit that contains a structure that can be represented by the following general formula (I).

[0149] [Chemical Formula 1]

[0150] .

[0151] [In formula (I), m is an integer greater than or equal to 1, and n is an integer greater than or equal to 1.]

[0152] By including olefin-containing monomer units in the water-soluble polymer of the second method, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry. In the above formula (I), the integer m is preferably 2 or more and 5 or less, more preferably 2 or 3, and even more preferably 2. When the integer m is 2, the monomer unit containing the structural unit represented by the general formula (I) is called an ethylene oxide-containing monomer unit. Furthermore, when the integer m is 3, the monomer unit containing the structural unit represented by the general formula (I) is called a propylene oxide-containing monomer unit. If the integer m is less than or equal to the above upper limit, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry. In particular, when m is an integer of 2, that is, when the water-soluble polymer of the second type contains monomer units containing ethylene oxide structures, it is possible to impart appropriate hydrophilicity to the water-soluble polymer of the second type, and to improve the affinity of the water-soluble polymer of the second type for water. As a result, especially when the water-soluble polymer of the second type contains monomer units containing ethylene oxide structures, the dispersibility and storage stability of the CNT dispersion can be particularly improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be particularly improved, thereby particularly improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0153] Furthermore, the water-soluble polymer of the second approach can also contain multiple monomer units containing olefin oxide structures. In other words, for example, the water-soluble polymer of the second approach can contain both monomer units containing ethylene oxide structures and monomer units containing propylene oxide structures.

[0154] The integer n, which specifies the number of repetitions of the monomer unit comprising the structure represented by formula (I) above, is preferably 10 or less, more preferably 5 or less, even more preferably 3 or less, and more preferably 2 or more. That is, the water-soluble polymer of the second type preferably comprises a polyoxyethylene structural unit formed by repeating the oxyethylene structural unit n times. Furthermore, some or all of the hydrogen atoms of the oxyethylene structural unit may be substituted with any substituent.

[0155] In the case where the water-soluble polymer of the second approach comprises multiple olefin-containing monomer units, the number of repetitions n for each olefin-containing monomer unit may be the same or different. In this case, it is preferable that the numerical average of all repetitions n is within the aforementioned preferred range, and more preferably that all repetitions n are within the aforementioned preferred range.

[0156] Examples of oxidized olefin monomers that can form water-soluble polymers in the second manner include monomers represented by the following general formula (II).

[0157] [Chemical Formula 2]

[0158] .

[0159] In general formula (II), R 1 It is (meth)acryloyl, R 2 This refers to a straight-chain or branched alkyl group having one or more hydrogen atoms and ten or fewer carbon atoms. The alkyl group preferably has two or more and five or fewer carbon atoms, more preferably two or three, and even more preferably two. Furthermore, in general formula (II), m and n are the same as in general formula (I).

[0160] Examples of straight-chain or branched alkyl groups having one or more but less than ten carbon atoms include methyl, ethyl, and propyl.

[0161] More specifically, the monomer represented by general formula (II) is not particularly limited, and examples include: methoxy polyethylene glycol (meth)acrylate, ethoxy diethylene glycol (meth)acrylate, etc., ethoxy polyethylene glycol (meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, etc. As the monomer represented by general formula (II), ethoxy polyethylene glycol (meth)acrylate is particularly preferred, ethoxy diethylene glycol (meth)acrylate is even more preferred, and ethoxy diethylene glycol acrylate is particularly especially preferred.

[0162] In addition, in this specification, "(meth)acrylate" refers to acrylate or methacrylate, and "(meth)acryloyl" refers to acryloyl or methacryloyl.

[0163] The water-soluble polymer of the second manner contains 100% by mass of all repeating units, and the content of the oxidized olefin-containing monomer unit in the water-soluble polymer of the second manner 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 30% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less.

[0164] Furthermore, the water-soluble polymer of the second manner comprises 100 mol% of all repeating units, and the content of the oxidized olefin-containing monomer unit in the water-soluble polymer of the second manner is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 20 mol% or more, even more preferably 30 mol% or more, preferably 60 mol% or less, more preferably 50 mol% or less, and even more preferably 45 mol% or less.

[0165] If the proportion of the oxidized olefin-containing monomer unit in the water-soluble polymer of the second method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry.

[0166] [Other repeating units]

[0167] The water-soluble polymer of the second type can contain repeating units other than the sulfonic acid-containing monomer units and oxidized olefin-containing monomer units mentioned above. Examples include monomer units from known monomers (other monomers) that can copolymerize with the sulfonic acid-containing monomers and oxidized olefin-containing monomers mentioned above. Other monomers can be used alone or in combination of two or more.

[0168] However, from the viewpoint of further improving the cycle characteristics of the secondary battery, the water-soluble polymer of the second type comprises 100% by mass of all repeating units, and the content of other repeating units in the water-soluble polymer of the second type is preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass. Furthermore, the water-soluble polymer of the second type comprises 100% by mol%, and the content of other repeating units in the water-soluble polymer of the second type is preferably 20% by mol% or less, more preferably 10% by mol%, further preferably 5% by mol% or less, even more preferably 1% by mol% or less, and particularly preferably 0% by mol%.

[0169] In other words, the water-soluble polymer of the second embodiment comprises 100% by mass of all repeating units, and the total content ratio of sulfonic acid-containing monomer units and oxidized olefin-containing monomer units in the water-soluble polymer of the second embodiment is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass. Furthermore, the water-soluble polymer of the second embodiment comprises 100% by mol%, and the total content ratio of sulfonic acid-containing monomer units and oxidized olefin-containing monomer units in the water-soluble polymer of the second embodiment is preferably 80% by mol% or more, more preferably 90% by mol%, further preferably 95% by mol% or more, even more preferably 99% by mol% or more, and particularly preferably 100% by mol%.

[0170] [Third-line water-soluble polymer]

[0171] The third type of water-soluble polymer comprises carboxylic acid-containing monomer units and (meth)acrylate alkyl monomer units. Alternatively, the third type of water-soluble polymer may also comprise repeating units other than carboxylic acid-containing monomer units and (meth)acrylate alkyl monomer units (other repeating units).

[0172] Additionally, in this specification, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0173] [Contains a carboxylic acid group monomer unit]

[0174] As a carboxylic acid-containing monomer unit capable of forming a water-soluble polymer of the third type, examples of carboxylic acid-containing monomers include the same type of monomer as that described in the item "Water-soluble polymer of the first type".

[0175] Monomers containing carboxylic acid groups can be used alone or in combination of two or more.

[0176] The water-soluble polymer of the third method contains 100% by mass of all repeating units, and the proportion of carboxylic acid group-containing monomer units in the water-soluble polymer of the third method is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0177] Furthermore, the water-soluble polymer of the third manner comprises 100 mol% of all repeating units, and the proportion of carboxylic acid group-containing monomer units in the water-soluble polymer of the third manner is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less.

[0178] If the proportion of carboxylic acid group-containing monomer units in the water-soluble polymer of the third method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry.

[0179] [(Meth)acrylate alkyl monomer unit]

[0180] Examples of alkyl methacrylate monomers that can form water-soluble polymers in a third manner include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, and other alkyl methacrylates; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and other alkyl methacrylates. Furthermore, one alkyl methacrylate monomer can be used alone, or two or more can be used in combination. Among these, ethyl acrylate is preferred. That is, the water-soluble polymer of the third approach preferably contains ethyl acrylate units as (meth)acrylate alkyl ester monomer units.

[0181] The water-soluble polymer of the third method contains 100% by mass of all repeating units, and the content of (meth)acrylate alkyl monomer units in the water-soluble polymer of the third method is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0182] Furthermore, the water-soluble polymer of the third manner comprises 100 mol% of all repeating units, and the content of (meth)acrylate alkyl monomer units in the water-soluble polymer of the third manner is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 65 mol% or more, preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less.

[0183] If the proportion of (meth)acrylate alkyl ester monomer units in the water-soluble polymer of the third method is within the above range, the dispersibility and storage stability of the CNT dispersion can be further improved, and the viscosity stability of the negative electrode slurry containing the CNT dispersion can be further improved, thereby further improving the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry.

[0184] [Other repeating units]

[0185] The water-soluble polymer of the third type can contain repeating units other than the carboxylic acid-containing monomer units and (meth)acrylate alkyl monomer units mentioned above. Examples include monomer units from known monomers (other monomers) that can copolymerize with the aforementioned carboxylic acid-containing monomers and (meth)acrylate alkyl monomers. Other monomers may be used alone or in combination of two or more.

[0186] However, from the viewpoint of further improving the cycle characteristics of the secondary battery, the water-soluble polymer of the third type comprises 100% by mass of all repeating units, and the content of other repeating units in the water-soluble polymer of the third type is preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass. Furthermore, the water-soluble polymer of the third type comprises 100% by mol%, and the content of other repeating units in the water-soluble polymer of the third type is preferably 20% by mol% or less, more preferably 10% by mol%, further preferably 5% by mol% or less, even more preferably 1% by mol% or less, and particularly preferably 0% by mol%.

[0187] In other words, the water-soluble polymer of the third type comprises 100% by mass of all repeating units, and the total content of the carboxylic acid-containing monomer units and (meth)acrylate alkyl monomer units in the water-soluble polymer of the third type is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass. Furthermore, the water-soluble polymer of the third type comprises 100% by mol%, and the total content of the carboxylic acid-containing monomer units and (meth)acrylate alkyl monomer units in the water-soluble polymer of the third type is preferably 80% by mol% or more, more preferably 90% by mol%, further preferably 95% by mol% or more, even more preferably 99% by mol% or more, and particularly preferably 100% by mol%.

[0188] [Preparation Method]

[0189] There are no particular limitations on the preparation method of water-soluble polymers. Water-soluble polymers can be obtained, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent. The polymer can be obtained by hydrogenation in any manner. Furthermore, the content ratio of each monomer in the monomer composition can be determined based on the content ratio of desired repeating units (monomer units) in the polymer.

[0190] There are no particular restrictions on the polymerization method; any of the following methods can be used: solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Furthermore, as the polymerization reaction, any of the following reactions can be used: ionic polymerization, free radical polymerization, living free radical polymerization, various condensation polymerizations, addition polymerization, etc. Moreover, known emulsifiers and polymerization initiators can be used as needed during polymerization. In addition, hydrogenation can be carried out using known methods.

[0191] In addition, after polymerization, the polymer can be neutralized as needed using sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, ammonia water, etc., to prepare water-soluble polymers with the above-mentioned neutralized acid functional groups.

[0192] [Contains percentage]

[0193] The proportion of water-soluble polymer in the CNT dispersion is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, more preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and even more preferably 0.8% by mass or less, with the total mass of the CNT dispersion being 100% by mass.

[0194] If the proportion of water-soluble polymer in the CNT dispersion is above the lower limit mentioned above, the dispersibility of the CNT dispersion can be improved. On the other hand, if the proportion of water-soluble polymer in the CNT dispersion is below the upper limit mentioned above, the storage stability of the CNT dispersion can be improved.

[0195] <Other Ingredients>

[0196] There are no particular limitations on the components that a CNT dispersion can contain, other than CNTs, water-soluble polymers, and water. Examples include conductive materials other than CNTs, dispersion media other than water, and components other than the negative electrode active material described in the section on "slurry for negative electrodes of non-aqueous secondary batteries".

[0197] As a conductive material other than CNT, there are no particular limitations, and materials such as carbon black (acetylene black, Ketjen black (registered trademark), furnace black, etc.), graphite, carbon sheets, and carbon nanofibers can be used.

[0198] As a dispersion medium other than water, known organic solvents that are miscible with water can be used.

[0199] In addition, one kind of other components can be used alone, or two or more kinds can be used in combination.

[0200] <Preparation method of CNT dispersion liquid>

[0201] The method for preparing the CNT dispersion liquid is not particularly limited. The CNT dispersion liquid can be prepared by mixing CNT, a specified water-soluble polymer, water, and other components used as needed. In addition, for mixing, known mixing devices such as a disperser, a homogenizer, a planetary mixer, a kneader, a ball mill, and a bead mill can be used.

[0202] (Slurry for negative electrode of non-aqueous secondary battery)

[0203] The slurry for the negative electrode of the present invention contains the above-mentioned CNT dispersion liquid and a negative electrode active material, and optionally contains any components such as a binder material as needed. In other words, the slurry for the negative electrode of the present invention contains CNT, a water-soluble polymer, and water, and optionally contains any components such as a binder material as needed.

[0204] Thus, the slurry for the negative electrode containing the above-mentioned CNT dispersion liquid has excellent viscosity stability and can form a negative electrode that enables the secondary battery to exhibit excellent cycle characteristics.

[0205] <Negative electrode active material>

[0206] The negative electrode active material incorporated in the slurry for the negative electrode is not particularly limited, and known negative electrode active materials can be used.

[0207] For example, as the negative electrode active material used in a lithium ion secondary battery, there is no particular limitation, and carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials combining them can be cited.

[0208] Here, the carbon-based negative electrode active material refers to an active material having a carbon-based main skeleton capable of embedding (also referred to as "doping") lithium. As the carbon-based negative electrode active material, for example, carbonaceous materials and graphitic materials can be cited.

[0209] Moreover, as the carbonaceous material, for example, easily graphitizable carbon, and difficult-to-graphitize carbon having a structure close to an amorphous structure represented by vitreous carbon can be cited.

[0210] Here, as the easily graphitizable carbon, for example, carbon materials using petroleum or tar pitch obtained from coal as raw materials can be cited. When specific examples are cited, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, pyrolytic vapor-grown carbon fiber, etc. can be cited.

[0211] In addition, examples of difficult-to-graphitize carbons include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0212] Furthermore, examples of graphitic materials include natural graphite and artificial graphite.

[0213] Here, examples of artificial graphite include, for instance, artificial graphite that is mainly heat-treated at temperatures above 2800°C to contain carbon that is easily graphitized, graphitic MCMB that is heat-treated at temperatures above 2000°C, and graphitic mesophase pitch-based carbon fibers that are heat-treated at temperatures above 2000°C.

[0214] Furthermore, metal-based anode active materials are active materials containing metals, generally referring to active materials that contain elements capable of lithium intercalation in their structure and have a theoretical capacity of 500 mAh / g or more per unit mass when lithium intercalation is achieved. Examples of metal-based active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, silicon-based anode active materials (anode active materials containing silicon) are preferred as metal-based anode active materials. This is because using silicon-based anode active materials enables the secondary battery to achieve higher capacity. Furthermore, silicon-based anode active materials expand and contract significantly during charging and discharging. However, since the anode slurry of the present invention is prepared using the CNT dispersion of the present invention described above, even when using silicon-based anode active materials as anode active materials, the decrease in conductivity of the electrode composite material layer can be suppressed, and an anode capable of forming a secondary battery with superior cycle characteristics can be formed.

[0215] Examples of silicon-based anode active materials include silicon (Si), silicon-containing alloys, SiO, and SiO2. x Composites of Si-containing materials and conductive carbon, formed by coating or compositing Si-containing materials with conductive carbon.

[0216] Furthermore, with the total negative electrode active material as 100% by mass, the proportion of silicon-based negative electrode active material in the negative electrode active material is preferably 1% by mass or more, more preferably 3% by mass or more, more preferably 20% by mass or less, and more preferably 15% by mass or less. If the proportion of silicon-based negative electrode active material is 1% by mass or more, the capacity of the secondary battery can be sufficiently improved; if the proportion of silicon-based negative electrode active material is 20% by mass or less, the cycle characteristics of the secondary battery can be further improved.

[0217] In addition, the particle size of the negative electrode active material is not particularly limited and can be the same as the negative electrode active material used in the past.

[0218] In addition, the amount of the negative electrode active material in the negative electrode paste is not particularly limited and can be within the range used in the past.

[0219] Moreover, the negative electrode active material can be used alone or in combination of two or more. From the viewpoint of making the secondary battery have a sufficiently high capacity and further improving the cycle characteristics, the negative electrode paste preferably contains both a carbon-based negative electrode active material formed of a graphite material and a silicon-based negative electrode active material.

[0220] <CNT dispersion liquid>

[0221] As the CNT dispersion liquid, the CNT dispersion liquid of the present invention described above can be used.

[0222] Here, when the content of the negative electrode active material is 100 parts by mass, the content of CNT in the negative electrode paste is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, further preferably 0.08 part by mass or more, preferably 0.5 part by mass or less, more preferably 0.3 part by mass or less, and further preferably 0.15 part by mass or less.

[0223] In addition, when the content of the negative electrode active material is 100 parts by mass, the content of the water-soluble polymer in the negative electrode paste is preferably 0.005 part by mass or more, more preferably 0.01 part by mass or more, further preferably 0.02 part by mass or more, preferably 0.2 part by mass or less, more preferably 0.1 part by mass or less, and more preferably 0.05 part by mass or less.

[0224] <Optional component>

[0225] Examples of the optional components that the negative electrode paste can contain include, for example, a binder material, a viscosity regulator, a reinforcing material, an antioxidant, and an electrolyte additive having a function of suppressing electrolyte decomposition. These optional components can be used alone or in combination of two or more.

[0226] Among the above optional components, from the viewpoint of improving the cycle characteristics of the secondary battery, the negative electrode paste preferably contains a binder material.

[0227] [Binder material]

[0228] As the binder material, there is no particular limitation, and any binder material that can be used as a binder for the negative electrode can be used.

[0229] Furthermore, in this invention, from the perspective of further improving the cycle characteristics of a secondary battery having a negative electrode made using a negative electrode slurry, it is preferable to use a particulate polymer containing at least a carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a conjugated diene monomer unit as a binder material.

[0230] In addition, particulate polymers that can be used as adhesive materials can be prepared using known methods.

[0231] Here, the negative electrode slurry of the present invention preferably has a Hansen solubility parameter (HSP) of a water-soluble polymer. d ) and the Hansen solubility parameter (HSP) of particulate polymers b HSP distance (R) c ) is 7.0 MPa 1 / 2 Hereinafter, 5.0 MPa is more preferred. 1 / 2 the following.

[0232] If the HSP distance (R) c If the value is below the aforementioned upper limit, the cycle characteristics of a secondary battery with a negative electrode made using a negative electrode slurry can be further improved.

[0233] On the other hand, HSP distance (R c For example, 0.1 MPa 1 / 2 The above can also be 1.0 MPa. 1 / 2 above.

[0234] Additionally, the HSP distance (R) c It is possible to modify the HSP of water-soluble polymers appropriately. d (polarity term δ) p2 δ, the dispersion term d2 Hydrogen bond term δ h2 HSP of ) and particulate polymers b (polarity term δ) p4 δ, the dispersion term d4 Hydrogen bond term δ h4 ) to make adjustments.

[0235] The polar term δ of particulate polymers p4 The polar term δ of water-soluble polymers p2 The smaller the difference, the better the preferred option. The polarity term δ of particulate polymers... p4 For example, it can be 5.0 or above, or 6.5 or above, or 8.0 or below, or 7.5 or below.

[0236] In addition, the dispersion term δ of particulate polymers d4 Dispersion term δ with water-soluble polymers d2 The smaller the difference, the better the selection. The dispersion term δ of particulate polymers. d4 For example, it can be 17.0 or above, or 18.5 or above, or 21.0 or below, or 19.5 or below.

[0237] In addition, the hydrogen bonding term δ of particulate polymers h4 Hydrogen bond term δ with water-soluble polymers h4 The smaller the difference, the better the selection. The hydrogen bonding term δ of particulate polymers... h4 For example, it can be 3.0 or above, or 4.0 or above, or 6.0 or below, or 5.0 or below.

[0238] [Contains a carboxylic acid group monomer unit]

[0239] As a carboxylic acid-containing monomer unit capable of forming particulate polymers, examples of carboxylic acid-containing monomers include the same carboxylic acid-containing monomers described in the item "Water-soluble polymers of the first type".

[0240] Monomers containing carboxylic acid groups can be used alone or in combination of two or more.

[0241] Here, taking all repeating units contained in the particulate polymer as 100% by mass, the proportion of carboxylic acid-containing monomer units in the particulate polymer is preferably 3% by mass or more, more preferably 5% by mass or more, more preferably 30% by mass or less, and more preferably 20% by mass or less.

[0242] If the proportion of carboxylic acid group monomer units in the particulate polymer is within the above range, the cycle characteristics of the secondary battery with a negative electrode made using a negative electrode slurry can be further improved.

[0243] [Aromatic vinyl monomer unit]

[0244] Examples of aromatic vinyl monomers that can form particulate polymers include styrene, styrene sulfonic acid and its salts, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Aromatic vinyl monomers can be used alone or in combination of two or more. Furthermore, styrene is preferred as an aromatic vinyl monomer from the perspective of further improving the cycle characteristics of a secondary battery having a negative electrode made using a negative electrode slurry. That is, the particulate polymer preferably contains styrene units as aromatic vinyl monomer units.

[0245] Here, taking all repeating units contained in the particulate polymer as 100% by mass, the content of aromatic vinyl monomer units in the particulate polymer is preferably 20% by mass or more, more preferably 25% by mass or more, more preferably 80% by mass or less, and more preferably 75% by mass or less. If the content of aromatic vinyl monomer units in the particulate polymer is within the above range, the cycle characteristics of the secondary battery having a negative electrode made using a negative electrode slurry can be further improved.

[0246] [Conjugated diene monomer unit]

[0247] As a conjugated diene monomer unit capable of forming particulate polymers, examples of conjugated diene monomers include those identical to those described in the section on "water-soluble polymers".

[0248] The conjugated diene monomer can be used alone or in combination of two or more. Furthermore, 1,3-butadiene is preferred as the conjugated diene monomer from the perspective of further improving the cycle characteristics of secondary batteries with a negative electrode made using a negative electrode slurry. That is, the particulate polymer preferably contains 1,3-butadiene units as conjugated diene monomer units.

[0249] Here, taking all repeating units contained in the particulate polymer as 100% by mass, the content ratio of conjugated diene monomer units in the particulate polymer is preferably 15% by mass or more, more preferably 20% by mass or more, more preferably 50% by mass or less, and more preferably 45% by mass or less. If the content ratio of conjugated diene monomer units in the particulate polymer is within the above range, the cycle characteristics of the secondary battery having a negative electrode made using a negative electrode slurry can be further improved.

[0250] [Other repeating units]

[0251] The repeating units that can be contained in the above-mentioned particulate polymer, other than carboxylic acid monomer units, aromatic vinyl monomer units, and conjugated diene monomer units, are not particularly limited. Examples include monomer units from known monomers (other monomers) that can copolymerize with the above-mentioned carboxylic acid monomers, aromatic vinyl monomers, and conjugated diene monomers. Other monomers may be used alone or in combination of two or more.

[0252] With all repeating units contained in the particulate polymer as 100% by mass, the proportion of other repeating units in the particulate polymer is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.

[0253] Furthermore, the content of the particulate polymer in the negative electrode slurry is preferably 100 parts by mass or more, more preferably 500 parts by mass or more, more preferably 5000 parts by mass or less, and more preferably 2000 parts by mass or less, relative to 100 parts by mass of CNT. If the content of the particulate polymer is within the above range, the cycle characteristics of the secondary battery having a negative electrode made using the negative electrode slurry can be further improved.

[0254] Characteristics of negative electrode pastes

[0255] The pH of the negative electrode slurry of the present invention is preferably 6 or higher, more preferably 7 or higher, more preferably 10 or lower, and more preferably 9 or lower.

[0256] If the pH is within the above range, the viscosity stability of the negative electrode slurry can be improved, and the cycle characteristics of the secondary battery with a negative electrode made using the negative electrode slurry can be improved.

[0257] <Preparation Method of Negative Electrode Slurry>

[0258] When mixing the above components to obtain a negative electrode slurry, there are no particular restrictions on the mixing method, and the known mixing apparatus described in the "Method for Preparing CNT Dispersion" can be used.

[0259] (Negative electrode for non-aqueous secondary batteries)

[0260] The negative electrode of the present invention has a current collector and a negative electrode composite material layer formed by using the aforementioned negative electrode slurry on the current collector. Here, the negative electrode composite material layer includes a negative electrode active material, CNTs, and a water-soluble polymer, and optionally includes a binder material. Furthermore, because the negative electrode of the present invention has a negative electrode composite material layer formed using the aforementioned negative electrode slurry, the secondary battery can exhibit excellent cycle characteristics.

[0261] <Current collector>

[0262] The current collector is formed of a material that is both conductive and electrochemically durable. Specifically, current collectors made of materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum can be used. From the viewpoint of improving the peel strength of the electrode composite layer from the current collector, copper foil, and especially electrolytic copper foil, is particularly preferred as a current collector used in the negative electrode of a lithium-ion secondary battery. Furthermore, the aforementioned materials constituting the current collector can be used alone or in combination of two or more.

[0263] Here, the polarity term δ of the electrolytic copper foil used in the current collector... p5 Preferably, the value is 9.0 or higher, more preferably 10.0 or higher, preferably 12.0 or lower, and more preferably 11.0 or lower. The polarity term δ of the electrolytic copper foil... p5 The preferred value is 10.7.

[0264] In addition, the dispersion term δ of the electrolytic copper foil used in the current collector d5 Preferably, it is 17.0 or higher, more preferably 18.0 or higher, preferably 20.0 or lower, and more preferably 19.0 or lower. The dispersion term δ of the electrolytic copper foil... d5 The preferred value is 18.6.

[0265] Furthermore, the hydrogen bond term δ of the electrolytic copper foil used in the current collector h5 Preferably, the value is 5.0 or higher, more preferably 6.0 or higher, more preferably 9.0 or lower, and even more preferably 8.0 or lower. The hydrogen bonding term δ of electrolytic copper foil... h5 7.0 is particularly preferred.

[0266] <Method for manufacturing the negative electrode>

[0267] The method for manufacturing the negative electrode of the present invention is not particularly limited. For example, the negative electrode of the present invention can be manufactured by coating the negative electrode slurry of the present invention onto at least one side of a current collector and drying it to form a negative electrode composite material layer. More specifically, the manufacturing method includes: a step of coating the negative electrode slurry onto at least one side of a current collector (coating step); and a step of drying the negative electrode slurry coated onto at least one side of the current collector to form a negative electrode composite material layer on the current collector (drying step).

[0268] [Coating Process]

[0269] There are no particular limitations on the method for applying the negative electrode slurry to the current collector, and known methods can be used. Specifically, the coating method can include doctor blade coating, dip coating, reverse roller coating, direct roller coating, gravure coating, extrusion coating, brush coating, etc. The negative electrode slurry can be applied to only one side of the current collector or to both sides. The thickness of the slurry film on the current collector before drying can be appropriately set according to the thickness of the negative electrode composite material layer obtained after drying.

[0270] [Drying Process]

[0271] There are no particular limitations on the method for drying the negative electrode slurry on the current collector; 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, electron beams, etc. By drying the negative electrode slurry on the current collector in this way, a negative electrode composite material layer can be formed on the current collector, resulting in a negative electrode having both a current collector and a negative electrode composite material layer.

[0272] In addition, after the drying process, a molding machine or roller press can be used to apply pressure to the negative electrode composite material layer. This pressure treatment ensures a good bond between the negative electrode composite material layer and the current collector.

[0273] Furthermore, if the negative electrode composite layer contains a curable polymer, the polymer can be cured after the negative electrode composite layer is formed.

[0274] (Non-aqueous secondary battery)

[0275] The secondary battery of the present invention has the negative electrode described above. Furthermore, the secondary battery of the present invention exhibits excellent cycle characteristics due to having the negative electrode described above. Additionally, the secondary battery of the present invention is preferably, for example, a lithium-ion secondary battery.

[0276] Hereinafter, the structure of a lithium-ion secondary battery, which is an example of a secondary battery according to the present invention, will be described. This lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a spacer. Furthermore, the negative electrode is the aforementioned negative electrode for a non-aqueous secondary battery of the present invention.

[0277] Positive electrode

[0278] As a positive electrode, there are no special restrictions, and any known positive electrode can be used.

[0279] Electrolyte

[0280] As the electrolyte, an organic electrolyte containing a supporting electrolyte dissolved in an organic solvent is typically used. Lithium salts, for example, can be used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. LiPF6, LiClO4, and CF3SO3Li are particularly preferred due to their high degree of dissociation and easy solubility in solvents, with LiPF6 being especially preferred. Furthermore, a single electrolyte can be used, or two or more can be used in any ratio. Generally, there is a tendency for higher lithium-ion conductivity to be achieved with a supporting electrolyte having a higher degree of dissociation; therefore, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0281] As for the organic solvent used in the electrolyte, there are no particular limitations as long as it can dissolve the supporting electrolyte. Preferred solvents include: carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), and methyl ethyl carbonate (EMC); esters 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 can also be used. Carbonates are particularly preferred due to their high dielectric constant and wide stable potential range, and mixtures of ethylene carbonate and methyl ethyl carbonate are even more preferred.

[0282] Furthermore, the concentration of the electrolyte in the electrolyte can be appropriately adjusted, for example, preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass. In addition, known additives such as fluoroethylene carbonate, methyl ethyl sulfone, etc., can also be added to the electrolyte.

[0283] <spacer>

[0284] There are no particular limitations on the spacer used; for example, the spacer described in Japanese Patent Application Publication No. 2012-204303 can be used. Among these, a microporous membrane formed of a polyolefin-based resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred from the perspective of reducing the overall film thickness of the spacer, thereby increasing the ratio of electrode active materials in the lithium-ion secondary battery and thus increasing the capacity per unit volume.

[0285] <Manufacturing Method of Lithium-ion Secondary Batteries>

[0286] The lithium-ion secondary battery of the present invention can be manufactured by, for example, overlapping the positive and negative electrodes with a spacer between them, winding or folding it according to the battery shape as needed, placing it in a battery container, injecting electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharging, or over-discharging of the secondary battery, overcurrent protection components such as fuses and PTC elements, porous metal mesh, and conductive plates can be provided as needed. The shape of the secondary battery can be any of, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0287] Example

[0288] The present invention will now be described in detail based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0289] Furthermore, unless otherwise specified, in polymers made by copolymerizing multiple monomers, the proportion of monomer units formed by polymerizing a particular monomer in the polymer is usually consistent with the proportion (feed ratio) of that particular monomer in all the monomers used to polymerize the polymer.

[0290] Furthermore, in the examples and comparative examples, the Hansen solubility parameter (HSP), HSP distance, dispersibility of CNT dispersion, storage stability of CNT dispersion, viscosity stability of negative electrode slurry, and cycle characteristics of secondary battery were evaluated using the following methods.

[0291] <Hansen Solubility Parameter (HSP)>

[0292] [CNT's HSP] c ]

[0293] 0.1 g of CNT was added to 10 ml of each of 12 solvents (acetone, toluene, ethanol, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, benzyl alcohol, γ-butyrolactone, nitrobenzene, N-methyl-2-pyrrolidone, salicylaldehyde, and methyl acetate), and the mixture was ultrasonically dispersed at 20 kHz, 200 W, and 10 minutes to prepare the assay solution. Pulse NMR was performed on both the 12 solvents (pure solvents) and the assay solution. Based on the results, R1, the relaxation time T1 of the pure solvent, and the relaxation time T2 of the solvent in the assay solution were calculated using the following formula. sp .

[0294] .

[0295] Based on the obtained R sp The values ​​are used to score the affinity of each solvent for CNT, as described below.

[0296] ·R sp ≤0.2 (poor solvent): 0

[0297] 0.2 < R sp ≤0.5 (poor solvent): 2

[0298] 0.5 < R sp (Good solvent): 1

[0299] Based on the obtained score, the HSP is calculated using the computer software "Hansen Solubility Parameters in Practice (HSPiP ver. 5.3.04)". c polarity term δ p1 δ, the dispersion term d1 and the hydrogen bond term δ h1 .

[0300] HSP of water-soluble polymers d ]

[0301] When the water-soluble polymer is a homopolymer, the HSP of the water-soluble polymer is... d The Y-MB method of HSPiP ver.5.3.04 was used to determine the result.

[0302] When the water-soluble polymer is a copolymer, the HSP of the water-soluble polymer d The following method is used to determine the HSP when each monomer unit constituting the copolymer is a homopolymer, using the Y-MB method of HSPP ver. 5.3.04. The polarity term δ of each homopolymer is then used to determine the HSP. p δ, the dispersion term d and the hydrogen bond term δ h The polarity term δ is determined by the molar ratio of each monomer unit in the copolymer. For example, a water-soluble polymer is a copolymer of monomer unit A and monomer unit B, where monomer unit A accounts for 60 mol% and monomer unit B accounts for 40 mol%. In the homopolymer of monomer unit A, the polarity term δ... p For A p δ, the dispersion term d For A d Hydrogen bond term δ h For A h In the homopolymer of monomer unit B, the polar term δ p For B p δ, the dispersion term d For B d Hydrogen bond term δ h For B h Under the above circumstances, the HSP of the water-soluble polymer d It is possible to use the polarity term δ p2 =0.4×A p +0.6×B p "、"Dispersion term δ d2 =0.4×A d +0.6×B d "Hydrogen bond term δ" h2 =0.4×A h +0.6×B h "To find out."

[0303] In addition, in this embodiment, the HSP of the water-soluble polymer d The above methods can be used to determine the composition of water-soluble polymers. However, when the detailed composition of the water-soluble polymer is unknown, it can be determined by methods such as the following.

[0304] First, 0.5 g of a water-soluble polymer (dried at 25°C for 7 days and then vacuum-dried at 60°C for 10 hours) was added to 10 ml of each of 12 solvents (acetone, toluene, ethanol, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, benzyl alcohol, γ-butyrolactone, nitrobenzene, N-methyl-2-pyrrolidone, salicylaldehyde, and methyl acetate). The mixture was then allowed to stand at 25°C for 24 hours to prepare an evaluation solution. The evaluation solution was visually observed and scored as described below.

[0305] • Insoluble (poor solvent): 0

[0306] • Turbid and / or unstable (poor solvent): 2

[0307] • Completely dissolved (good solvent): 1

[0308] Based on the obtained score, calculate the HSP using the HSP method described above. d polarity term δ p2 δ, the dispersion term d2 and the hydrogen bond term δ h2 .

[0309] HSP of electrolytic copper foil m ]

[0310] HSP on the surface of electrolytic copper foil m The following method is used to determine the result.

[0311] First, 2.0 μL of each of 12 solvents (aniline, benzyl benzoate, dimethyl sulfoxide, γ-butyrolactone, benzyl alcohol, N-methyl-2-pyrrolidone, methyl ethyl ketone, salicylaldehyde, ethyl acetate, ethanol, 1,1,2,2-tetrabromoethane, and formamide) was dropwise added to the surface of the electrolytic copper foil. The contact angle was recorded 30 seconds after the drop was added. Based on the contact angle value, γ-butyrolactone was calculated using the Young-Dupre formula and the Hata-Kitasaki and extended Hawkes formula. sL According to the relationship between Hansen solubility parameters and surface tension (Equation 1) (Hansen Solubility Parameters 50 th Anniversary conference, preprint 2017, pp. 14-21 (2017), focusing on "the HSP distance between the HSP of each solvent and the HSP of the electrolytic copper foil" and "(γ)". sL / (V L 1 / 3 )) 1 / 2 "The relevant methods are used to find it."

[0312] .

[0313] The HSP of the electrolytic copper foil (manufactured by Furukawa Electric Industry Co., Ltd., product name: HC-WS) used in the examples and comparative examples was determined using the method described above. m The result is that the polarity term δ p3 10.7, dispersion term δ d3 18.6, hydrogen bond term δ h3 It is 7.0.

[0314] In addition, the contact angle was measured using a simple contact angle meter, Dme-211.

[0315] HSP of particulate polymers (adhesive materials) b ]

[0316] Add 0.5 g of the granular polymer (dried at 25°C for 7 days and then vacuum-dried at 60°C for 10 hours) to 10 ml of each of 12 solvents (acetone, toluene, ethanol, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, benzyl alcohol, γ-butyrolactone, nitrobenzene, N-methyl-2-pyrrolidone, salicylaldehyde, and methyl acetate) to prepare the evaluation solution. Visually observe the evaluation solution and score it as described below.

[0317] • Insoluble (poor solvent): 0

[0318] • Turbid and / or unstable (poor solvent): 2

[0319] • Completely dissolved (good solvent): 1

[0320] Based on the obtained score, calculate the HSP using the HSP method described above. b polarity term δ p4 δ, the dispersion term d4 and the hydrogen bond term δ h4 .

[0321] <HSP Distance>

[0322] HSP distance (R) a )]

[0323] HSP using CNT c HSPs of water-soluble polymers d The HSP distance (R) is calculated using the following formula (1). a ).

[0324] .

[0325] HSP distance (R) b )]

[0326] HSP using water-soluble polymers d HSP of electrolytic copper foil m (Polar term δ p3 = 10.7, dispersion term δ d3 = 18.6, hydrogen bond term δ h3 = 7.0), the HSP distance (R b ) is calculated by the following formula (2).

[0327] .

[0328] [HSP distance (R c )]

[0329] Using the HSP of the water-soluble polymer d and the HSP of the particulate polymer b , the HSP distance (R c ) is calculated by the following formula (3).

[0330] .

[0331] <Dispersibility of CNT dispersion liquid>

[0332] For the CNT dispersion liquid, according to JIS Z8825:2013, using a laser diffraction scattering type particle size distribution measuring device (manufactured by MicrotracBEL Co., Ltd., Microtrac MT-3300EXII), the volume average particle diameter D50 is measured wet. The smaller the value of the volume average particle diameter D50, the better the dispersibility.

[0333] S: The volume average particle diameter D50 is less than 5 μm

[0334] A: The volume average particle diameter D50 is 5 μm or more and less than 15 μm

[0335] B: The volume average particle diameter D50 is 15 μm or more and less than 50 μm

[0336] C: The volume average particle diameter D50 is 50 μm or more

[0337] <Storage stability of CNT dispersion liquid>

[0338] Using a B-type viscometer, under the conditions of a temperature of 25 °C and a spindle rotation speed of 60 rpm, the viscosity η1 of the freshly prepared CNT dispersion liquid is measured 60 seconds after the spindle starts to rotate. The CNT dispersion liquid after measuring η1 is stored under the condition of standing at 25 °C for 10 days, and the viscosity η2 after storage is measured in the same manner as η1. The ratio of η2 to η1 (η2 / η1) is used as the viscosity ratio of the dispersion liquid, and the evaluation is carried out according to the following criteria. The closer the value of the viscosity ratio of the dispersion liquid is to 1.0, the more the increase in the viscosity of the CNT dispersion liquid is suppressed, and the better the storage stability.

[0339] A: The viscosity ratio of the dispersion is less than 1.15.

[0340] B: The viscosity ratio of the dispersion is greater than 1.15 and less than 1.6.

[0341] C: The viscosity ratio of the dispersion is 1.6 or higher.

[0342] <Viscosity stability of negative electrode slurry>

[0343] Using a Type B viscometer, the viscosity η3 of the freshly prepared negative electrode slurry was measured 60 seconds after the spindle started rotating, at a temperature of 25°C and a spindle rotation speed of 60 rpm. The negative electrode slurry after η3 measurement was then stored at 25°C for 3 days, and the viscosity η4 after storage was measured in the same manner as η3. The ratio of η4 to η3 (η4 / η3) was taken as the slurry viscosity ratio and evaluated according to the following criteria. The closer the slurry viscosity ratio is to 1.0, the better the viscosity increase of the negative electrode slurry is suppressed, and the better the viscosity stability.

[0344] A: The viscosity ratio of the slurry is less than 1.2.

[0345] B: The slurry viscosity ratio is above 1.2 and less than 1.4.

[0346] C: The slurry viscosity ratio is above 1.4 and less than 1.6.

[0347] D: Slurry viscosity ratio is 1.6 or higher.

[0348] <Cycle Characteristics of Secondary Batteries>

[0349] After electrolyte injection, the secondary battery was left to stand at 25°C for 24 hours. Next, a charge-discharge cycle was performed, charging at 0.2C constant current-constant voltage (cutoff current 0.02C) to a cell voltage of 4.35V and discharging at constant current to a cell voltage of 2.75V, and the initial capacity C0 was measured. Then, at 25°C, a repeatable charge-discharge cycle was performed, charging at 1.0C constant current-constant voltage (cutoff current 0.02C) to a cell voltage of 4.35V and discharging at constant current to a cell voltage of 2.75V, and the capacity C1 after 100 cycles was measured. The capacity retention rate (%) was then calculated as C1 / C0 × 100, and evaluated according to the following criteria. A higher capacity retention rate indicates better cycle characteristics of the secondary battery.

[0350] A: Capacity retention rate is above 90%.

[0351] B: Capacity retention rate is above 85% and below 90%.

[0352] C: Capacity retention rate is above 80% and below 85%.

[0353] D: Capacity retention rate less than 80%

[0354] (Example 1)

[0355] <Preparation of Water-Soluble Polymers (Dispersants)>

[0356] 473 parts of deionized water, 58 parts of methacrylic acid (containing carboxylic acid monomers), 0.6 parts of tert-dodecyl mercaptan, and 3.0 parts of sodium dodecylbenzenesulfonate diluted with deionized water to a solids concentration of 10% were added to the reactor. Next, the reactor was sealed, and two nitrogen replacements were performed while stirring with a stirring blade. After the nitrogen replacements were completed, 42 parts of nitrogen-replaced isoprene (conjugated diene monomer) were added to the reactor. The reactor temperature was then maintained at 5°C. After confirming that the reactor temperature was maintained at 5°C, 0.01 parts of dithionite were dissolved in deionized water and added to the reactor. Five minutes after adding dithionite, 0.1 parts of cumene hydroperoxide were added (first addition). Then, using another container, 0.04 parts of sodium formaldehyde sulfoxylate (first time) (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "SFS"), 0.003 parts of ferrous sulfate (first time) (manufactured by Chubu Chelest Co., Ltd., product name "Frost Fe"), and 0.03 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chelest Co., Ltd., product name "Chelest400G") were dissolved in 9.0 parts of ion-exchanged water and added to the reactor.

[0357] When the polymerization conversion reaches 40%, the reactor interior temperature is raised to 10°C. Then, after the polymerization conversion reaches 60%, the reactor interior temperature is raised to 18°C. Then, when the polymerization conversion reaches 70%, 0.09 parts of cumene hydroperoxide (second addition) are added to the reactor interior. Subsequently, using a separate container, 0.04 parts of sodium formaldehyde sulfoxylate (second addition) (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "SFS"), 0.003 parts of ferrous sulfate (second addition) (manufactured by Chubu Chelest Co., Ltd., product name "Frost Fe"), and 0.03 parts of ethylenediaminetetraacetic acid (manufactured by Chubu Chelest Co., Ltd., product name "Chelest 400G") are dissolved in 9.0 parts of ion-exchanged water and added to the reactor interior.

[0358] After the polymerization conversion reached 93%, 0.12 parts of 2,2,6,6-tetramethylpiperidine-1-oxyl was diluted with 10.35 parts of ion-exchanged water and added to the inside of the reactor to terminate the reaction. After the reaction termination, deodorization was carried out with an evaporator until the residual isoprene became less than 300 ppm. After the deodorization was completed, the pH was adjusted to 8 with a 5% aqueous lithium hydroxide solution while stirring to obtain an aqueous solution of a water-soluble polymer (dispersant).

[0359] The HSP was determined for the obtained water-soluble polymer d (polar term δ p2 , dispersive term δ d2 , hydrogen bond term δ h2 ).

[0360] <Preparation of CNT Dispersion>

[0361] 1 part of multi-walled CNT (average diameter: 10 nm, G / D ratio: 0.8, polar term δ p1 = 7.0, dispersive term δ d1 = 18.5, hydrogen bond term δ h1 = 4.8), 0.3 parts (equivalent amount of solid content) of the water-soluble polymer as a dispersant prepared above, and an appropriate amount of ion-exchanged water were stirred with a disperser (3000 rpm, 60 minutes). Next, a bead mill using zirconia beads with a diameter of 1 mm was used to mix at a circumferential speed of 8 m / s for 30 minutes. Then, the pH was adjusted to 8 with a 5% aqueous lithium hydroxide solution to produce a CNT dispersion (solid content concentration of CNT = 1%, solid content concentration of water-soluble polymer = 0.3%).

[0362] The HSP distance (R a ) and the HSP distance (R b ) were calculated for the obtained CNT dispersion. The results are shown in Table 1.

[0363] In addition, the dispersibility and storage stability of the obtained CNT dispersion were evaluated. The results are shown in Table 1.

[0364] <Preparation of Granular Polymer (Binder Material)>

[0365] 3.15 parts of styrene, 1.66 parts of 1,3-butadiene, 0.2 parts of sodium dodecyl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure-resistant container A equipped with a stirrer. After sufficient stirring, the mixture was heated to 60 °C to initiate polymerization and allowed to react for 6 hours to obtain seed particles.

[0366] After the above reaction, the mixture is heated to 75°C, and the mixture is added from another container B containing 53.85 parts of styrene, 31.34 parts of 1,3-butadiene, 10.0 parts of acrylic acid, 0.25 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.35 parts of sodium dodecyl sulfate as an emulsifier to pressure container A. At the same time, 1 part of potassium persulfate as a polymerization initiator is added to pressure container A, thereby initiating the second stage of polymerization.

[0367] That is, as a monomer composition as a whole, 57 parts of styrene, 33 parts of 1,3-butadiene, and 10 parts of acrylic acid are used.

[0368] Five and a half hours after the second-stage polymerization initiation, the entire amount of the mixture containing these monomer compositions was added, and then the mixture was further heated to 85°C and allowed to react for 6 hours. The reaction was terminated by cooling when the polymerization conversion reached 97%. A 5% aqueous sodium hydroxide solution was added to the mixture containing the polymer to adjust the pH to 8. Unreacted monomers were then removed by heated vacuum distillation. Further cooling yielded an aqueous dispersion of the insoluble particulate polymer.

[0369] The HSP was determined for the obtained particulate polymer. b The result is that the polarity term δ p4 The value is 6.8, and the dispersion term δ d4 19.0, hydrogen bond term δ h4 It is 4.6.

[0370] <Preparation of Negative Electrode Slurry>

[0371] 90 parts of artificial graphite (volume average particle size: 24.5 μm, specific surface area: 3.5 m²) as a carbon-based negative electrode active material were added to a planetary mixer equipped with a disperser. 2 / g), 10 parts of SiO2 as a silicon-based negative electrode active material X 2.0 parts (equivalent to solids) of an aqueous solution of carboxymethyl cellulose as a viscosity modifier were mixed at room temperature for 60 minutes with deionized water to adjust the solids concentration to 58%. After mixing, the CNT dispersion obtained as described above was added to a planetary mixer at a ratio of 0.1 parts (equivalent to solids) of multi-walled CNTs and mixed. Next, the solids concentration was adjusted to 50% with deionized water, and 1.0 part (equivalent to solids) of an aqueous dispersion of the particulate polymer (binder) obtained as described above was further added to obtain a mixture. The obtained mixture was degassed under reduced pressure to obtain a slurry for negative electrodes with good flowability.

[0372] The HSP distance (R) was calculated using the obtained negative electrode slurry. c The results are shown in Table 1.

[0373] In addition, the viscosity stability of the obtained negative electrode was evaluated using a slurry. The results are shown in Table 1.

[0374] <Manufacturing the Negative Electrode>

[0375] A notched roller coater was used to achieve a dried film thickness of 105 μm and a coating amount of 10 mg / cm³. 2 The negative electrode obtained as described above is coated with a slurry onto a 16μm thick electrolytic copper foil (manufactured by Furukawa Electric Industry Co., Ltd., product name: HC-WS, polarity term δ) serving as the current collector. p3 =10.7, Dispersion term δ d3 =18.6, hydrogen bond term δ h3 =7.0) or higher. The electrolytic copper foil coated with the negative electrode slurry was transported at a speed of 0.5 m / min in an oven at 100°C for 2 minutes, and then further transported in an oven at 120°C for 2 minutes, thereby drying the negative electrode slurry on the electrolytic copper foil to obtain the negative electrode raw material. The negative electrode raw material was calendered using a roller press to obtain a negative electrode with a negative electrode composite layer thickness of 80 μm.

[0376] <The Manufacturing of the Positive Electrode>

[0377] In a planetary mixer, 95 parts of LiCoO2 with a spinel structure, which serves as the positive electrode active material, 3 parts of PVDF (polyvinylidene fluoride) as a binder (based on solid content), 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent are added and mixed to obtain a slurry for the positive electrode.

[0378] The obtained cathode slurry was coated onto a 20 μm thick aluminum foil (current collector) using a corner-shaped coating machine to achieve a dried film thickness of approximately 100 μm. The aluminum foil coated with the cathode slurry was then transported at 0.5 m / min in an oven at 60°C for 2 minutes, followed by a further transport in an oven at 120°C for 2 minutes to dry the cathode slurry, thus obtaining the cathode raw material. This cathode raw material was then calendered using a roller press to obtain a cathode with a 70 μm thick composite layer.

[0379] <Preparation of spacers>

[0380] Prepare a single-layer polypropylene spacer (manufactured by dry process, 65mm wide, 500mm long, 25μm thick, with a porosity of 55%). Cut the spacer into 5cm × 5cm squares for use in the manufacture of secondary batteries.

[0381] Manufacturing of Secondary Batteries

[0382] An aluminum packaging material is prepared as the outer packaging for the battery. The positive electrode is cut into a 4cm × 4cm square and arranged so that the current collector side surface is in contact with the aluminum packaging material. Next, the square spacer is arranged on the surface of the positive electrode composite layer. Then, the negative electrode is cut into a 4.2cm × 4.2cm square and arranged on the spacer so that the negative electrode composite layer side surface is opposite to the spacer. Then, a 1.0M LiPF6 solution (a mixed solvent of ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio), containing 2% (volume ratio) each of fluoroethylene carbonate and vinylene carbonate as additives) is filled as the electrolyte. Then, to seal the opening of the aluminum packaging material, heat sealing at 150°C is performed to seal the outer packaging of the aluminum packaging material, thus manufacturing a laminated cell type lithium-ion secondary battery.

[0383] The obtained lithium-ion secondary batteries were used to evaluate their cycle characteristics. The results are shown in Table 1.

[0384] (Example 2)

[0385] In the preparation of the CNT dispersion, the amount of water-soluble polymer used was varied so that the concentration of the solid component of the water-soluble polymer in the CNT dispersion was 1%. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0386] (Example 3)

[0387] In the preparation of CNT dispersions, single-walled CNTs (average diameter: 3 nm, G / D ratio: 5, polarity term δ) were used. p1 =6.0, dispersion term δ d1 =19.4, hydrogen bond term δ h1 =4.5) instead of multi-walled CNTs, all other operations, measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0388] (Example 4)

[0389] In the preparation of the water-soluble polymer, 59 parts of sodium styrene sulfonate (containing sulfonic acid monomers) and 41 parts of ethoxydiethylene glycol acrylate (containing oxidized olefin monomers) were used instead of isoprene and methacrylic acid. In the preparation of the CNT dispersion, the pH of the CNT dispersion was adjusted to 7.7. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0390] (Example 5)

[0391] In the preparation of the CNT dispersion, single-walled CNTs (average diameter: 3 nm, G / D ratio: 5) were used instead of multi-walled CNTs. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 4. The results are shown in Table 1.

[0392] (Example 6)

[0393] In the preparation of the CNT dispersion, the pH of the CNT dispersion was adjusted to 4.0. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 4. The results are shown in Table 1.

[0394] (Example 7)

[0395] In the preparation of the CNT dispersion, the pH of the CNT dispersion was adjusted to 12.0. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 4. The results are shown in Table 1.

[0396] (Example 8)

[0397] In the preparation of the water-soluble polymer, the amount of sodium styrene sulfonate was changed to 77 parts and the amount of ethoxydiethylene glycol acrylate was changed to 23 parts. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 7. The results are shown in Table 1.

[0398] (Example 9)

[0399] In the preparation of the water-soluble polymer and the CNT dispersion, a 5% sodium hydroxide aqueous solution was used instead of a 5% lithium hydroxide aqueous solution. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0400] (Example 10)

[0401] In the preparation of the CNT dispersion, the amounts of CNT and water-soluble polymer were varied so that the solid content concentration of CNT in the CNT dispersion was 0.4% and the solid content concentration of the water-soluble polymer was 1%. Otherwise, various operations, measurements, and evaluations were performed in the same manner as in Example 3. The results are shown in Table 1.

[0402] (Example 11)

[0403] In the preparation of the water-soluble polymer, 70 parts of ethyl acrylate ((meth)acrylate alkyl ester monomer) and 30 parts of methacrylic acid were used instead of 42 parts of isoprene and 58 parts of methacrylic acid. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 9. The results are shown in Table 1.

[0404] (Example 12)

[0405] In the preparation of the CNT dispersion, 70 parts of ethyl acrylate ((meth)acrylate alkyl ester monomer) and 30 parts of methacrylic acid were used instead of 42 parts of isoprene and 58 parts of methacrylic acid. Furthermore, in the preparation of the water-soluble polymer and the CNT dispersion, a 5% sodium hydroxide aqueous solution was used instead of a 5% lithium hydroxide aqueous solution. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 10. The results are shown in Table 1.

[0406] (Comparative Example 1)

[0407] In the preparation of the water-soluble polymer, sodium styrene sulfonate was used instead of sodium styrene sulfonate and ethoxydiethylene glycol acrylate. In the preparation of the CNT dispersion, the pH of the CNT dispersion was adjusted to 8.5. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 8. The results are shown in Table 1.

[0408] (Comparative Example 2)

[0409] In the preparation of the water-soluble polymer, 25 parts of acrylic acid and 75 parts of acrylamide were used instead of isoprene and methacrylic acid. In the preparation of the CNT dispersion, the amounts of CNT and water-soluble polymer were varied so that the solid component concentrations of CNT and water-soluble polymer in the CNT dispersion were each 0.75%. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0410] (Comparative Example 3)

[0411] In the preparation of the water-soluble polymer, 49 parts of sodium styrene sulfonate, 24 parts of acrylic acid, and 27 parts of acrylamide were used instead of isoprene and methacrylic acid. In the preparation of the CNT dispersion, the amounts of CNT and water-soluble polymer were varied so that the solid component concentrations of CNT and water-soluble polymer in the CNT dispersion were each 0.75%. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0412] (Comparative Example 4)

[0413] As a CNT dispersion, a mixture containing multi-walled CNTs (average diameter: 10 nm, G / D ratio: 0.8, polarity term δ) was used. p1 =7.0, dispersion term δ d1 =18.5, hydrogen bond term δ h1 A negative electrode slurry was prepared using a CNT dispersion of carboxymethyl cellulose (CNT) in water (CNT solids concentration = 1%, sodium carboxymethyl cellulose solids concentration = 1%, pH = 8.0), sodium carboxymethyl cellulose (CNT) (dispersant), and sodium carboxymethyl cellulose (CNT) in water (CNT solids concentration = 1%, sodium carboxymethyl cellulose solids concentration = 1%, pH = 8.0). Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0414] (Comparative Example 5)

[0415] In the preparation of the CNT dispersion, single-walled CNTs (average diameter: 3 nm, G / D ratio: 5) were used instead of multi-walled CNTs. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Comparative Example 4. The results are shown in Table 1.

[0416] (Comparative Example 6)

[0417] Instead of preparing a water-soluble polymer, a non-water-soluble hydrogenated nitrile rubber prepared as described below was used in place of the water-soluble polymer, and the same procedure as in Example 1 was followed in an attempt to prepare a CNT dispersion. However, the multi-walled CNTs did not disperse, and it was impossible to prepare a CNT dispersion suitable for forming a negative electrode composite layer. Therefore, no evaluation was carried out.

[0418] <Preparation of Hydrogenated Nitrile Rubber>

[0419] In a reactor with an internal volume of 10 liters, 100 parts of deionized water, 23 parts of acrylonitrile, 30 parts of 1,3-butadiene, 4 parts of methacrylic acid, and 43 parts of styrene were added as monomers. 2 parts of potassium oleate as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and 0.5 parts of 2,2',4,6,6'-pentamethylheptane-4-thiol (TIBM) as a molecular weight regulator were added. Emulsion polymerization was carried out at 30°C in the presence of 0.35 parts of potassium persulfate as a polymerization initiator to copolymerize the above monomers.

[0420] At a polymerization conversion rate of 90%, 0.2 parts of hydroxylamine sulfate were added per 100 parts of monomer to terminate the polymerization. Next, the mixture was heated and steam distilled at approximately 70°C under reduced pressure to recover the residual monomer. Then, 2 parts of alkylated phenol were added as an antioxidant to obtain an aqueous dispersion of the polymer.

[0421] Next, 400 mL of the obtained polymer aqueous dispersion (total solids: 48 g) was added to a 1-liter autoclave equipped with a stirrer, and nitrogen gas was circulated for 10 minutes to remove dissolved oxygen from the aqueous dispersion. Then, 50 mg of palladium acetate was dissolved in 180 mL of water with nitric acid added at a molar equivalent to Pd as a hydrogenation catalyst. After purging the system twice with hydrogen, the contents of the autoclave were heated to 50 °C under hydrogen pressure (gauge pressure) for 6 hours. Subsequently, the contents were returned to room temperature, and the system was concentrated under a nitrogen atmosphere using an evaporator to a solids concentration of 40%, yielding hydrogenated nitrile rubber. The obtained hydrogenated nitrile rubber is non-water-soluble.

[0422] (Comparative Example 7)

[0423] In the preparation of the water-soluble polymer, only acrylic acid was used in place of isoprene and methacrylic acid. Otherwise, all operations, measurements, and evaluations were performed in the same manner as in Example 2. The results are shown in Table 1.

[0424] Additionally, in Table 1,

[0425] "MW" indicates multi-walled CNTs.

[0426] "SW" indicates single-walled CNTs.

[0427] "IP" stands for isoprene unit.

[0428] "MAA" represents methacrylic acid unit.

[0429] "SS" represents sodium styrene sulfonate unit.

[0430] "EC-A" indicates ethoxylated diethylene glycol acrylate unit.

[0431] "EA" represents the ethyl acrylate unit.

[0432] "AA" represents acrylic unit.

[0433] "AAm" represents an acrylamide unit.

[0434] "CMC" indicates the sodium salt of carboxymethyl cellulose.

[0435] "HNBR" indicates hydrogenated nitrile rubber.

[0436] "Li" indicates lithium salt group.

[0437] "Na" indicates sodium salt base.

[0438] "K" indicates potassium salt group.

[0439] "LIB" stands for Lithium-ion Rechargeable Battery.

[0440] [Table 1]

[0441] .

[0442] As shown in Table 1, the CNT dispersions of Examples 1-9 exhibit excellent dispersibility and storage stability of CNTs.

[0443] Industrial availability

[0444] According to the present invention, a CNT dispersion with excellent dispersibility and storage stability can be provided.

[0445] Furthermore, according to the present invention, a non-aqueous secondary battery negative electrode slurry containing the CNT dispersion can be provided.

[0446] Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery negative electrode using the non-aqueous secondary battery negative electrode slurry.

[0447] Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery having the negative electrode for the non-aqueous secondary battery.< / cnt>

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a water-soluble polymer having acidic functional groups, and water. The Hansen solubility parameter (HSP) of the carbon nanotubes c The Hansen solubility parameter (HSP) of the water-soluble polymer. d HSP distance (R) a ) is 7.0 MPa 1 / 2 the following.

2. The carbon nanotube dispersion according to claim 1, wherein, The Hansen solubility parameter (HSP) of the water-soluble polymer d ) and polarity term δ p3 10.7 MPa 1 / 2 δ, the dispersion term d3 18.6 MPa 1 / 2 Hydrogen bond term δ h3 7.0 MPa 1 / 2 Hansen solubility parameter (HSP) of the material m HSP distance (R) b ) is 8.0 MPa 1 / 2 the following.

3. The carbon nanotube dispersion according to claim 1 or 2, wherein, The pH of the carbon nanotube dispersion is above 6 and below 10.

4. The carbon nanotube dispersion according to claim 1 or 2, wherein, At least a portion of the acid functional groups of the water-soluble polymer are alkali metal salts or ammonium salts.

5. The carbon nanotube dispersion according to claim 1 or 2, wherein, The acid functional group is a carboxylic acid group.

6. The carbon nanotube dispersion according to claim 1 or 2, wherein, The acid functional group is a sulfonic acid group.

7. The carbon nanotube dispersion according to claim 1 or 2, wherein, The water-soluble polymer contains an ether group.

8. The carbon nanotube dispersion according to claim 1 or 2, wherein, The mass ratio of the carbon nanotubes to the water-soluble polymer is greater than 0.1 and less than 10.

9. A slurry for a non-aqueous secondary battery negative electrode, comprising a negative electrode active material and a carbon nanotube dispersion according to any one of claims 1 to 8.

10. The slurry for the negative electrode of a non-aqueous secondary battery according to claim 9, wherein, The negative electrode active material includes silicon-based negative electrode active material.

11. The slurry for the negative electrode of a non-aqueous secondary battery according to claim 9 or 10, wherein, The slurry for the negative electrode of the non-aqueous secondary battery further comprises a particulate polymer, wherein the particulate polymer comprises a carboxylic acid monomer unit, an aromatic vinyl monomer unit, and a conjugated diene monomer unit.

12. The slurry for the negative electrode of a non-aqueous secondary battery according to claim 11, wherein, The total number of repeating units contained in the particulate polymer is taken as 100% by mass, and the proportion of the carboxylic acid-containing monomer units in the particulate polymer is more than 3% by mass and less than 30% by mass.

13. The slurry for the negative electrode of a non-aqueous secondary battery according to claim 11, wherein, The Hansen solubility parameter (HSP) of the water-soluble polymer d The Hansen solubility parameter (HSP) of the particulate polymer. b HSP distance (R) c ) is 7.0 MPa 1 / 2 the following.

14. A negative electrode for a non-aqueous secondary battery, comprising a current collector and a negative electrode composite material layer formed by using the non-aqueous secondary battery negative electrode slurry according to any one of claims 9 to 13 on the current collector.

15. The negative electrode for a non-aqueous secondary battery according to claim 14, wherein, The current collector is an electrolytic copper foil.

16. A non-aqueous secondary battery having a negative electrode for a non-aqueous secondary battery as described in claim 14 or 15.