Carbon nanotube dispersion composition, mixture slurry, electrode film, and secondary battery

Abstract

The carbon nanotube dispersion composition contains carbon nanotubes (A), a dispersant (B), and a solvent (C) and is characterized in that the particle diameter D50 at 50% cumulative volume by laser diffraction particle size distribution measurement is 0.3-7 μm and satisfies (1) and (2).　(1) The dispersant (B) is a polymer having a weight-average molecular weight of 5,000-360,000 and having a carboxyl group-containing structural unit derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and the content of the carboxyl group-containing structural unit is 80 mass% or more based on the mass of the polymer.　(2) When the particle diameter D50 at 50% cumulative volume by laser diffraction particle size distribution measurement of the carbon nanotube dispersion composition is taken to be X [μm] and the pH is taken to be Y, X and Y satisfy (formula a) and (formula b).　(Formula a): Y ≥ -0.149X + 4.545. (Formula b): Y ≤ -0.134X + 5.140

Description

Carbon nanotube dispersion composition, composite slurry, electrode film, and secondary battery

[0001] The present disclosure relates to a carbon nanotube dispersion composition. More specifically, the present disclosure relates to a carbon nanotube dispersion composition, a composite slurry containing the carbon nanotube dispersion composition and an active material, an electrode film formed from the composite slurry, and a secondary battery including the electrode film.

[0002] With the spread of electric vehicles and the trend toward smaller, lighter, and more powerful portable devices, secondary batteries with high energy density and higher capacity are required. Against this background, secondary batteries using non-aqueous electrolytes, particularly lithium-ion secondary batteries, are being used in many devices due to their high energy density and high voltage characteristics.

[0003] Because the capacity of lithium-ion secondary batteries is highly dependent on the cathode and anode active materials, various materials for these electrode active materials have been actively researched. However, the charge capacities achieved using commercially available electrode active materials are all close to the theoretical value, and improvements in electrode active materials are nearing their limits. Under these circumstances, silicon-based active materials, which can reversibly dope more lithium ions than current graphite powder, are expected to be the anode active material. However, when silicon-based active materials are used, volume changes during the absorption and desorption of lithium ions during charging and discharging tend to cause cracking or particle isolation, resulting in a decrease in capacity with repeated charging and discharging.

[0004] In addition, technology using carbon nanotubes as a conductive material is being investigated to improve the conductivity of electrodes. The use of carbon nanotubes is expected to reduce electrode resistance. In particular, when carbon nanotubes are used in the negative electrode, they are expected to prevent the electrically isolated silicon-based active material, which has low conductivity, from becoming electrically isolated due to volume changes that occur when lithium ions are absorbed and released during charging and discharging, thereby improving the battery's lifespan.

[0005] In recent years, the use of carbon nanotube dispersions has become the mainstream method for adding carbon nanotubes to composite slurries for secondary batteries. By adjusting the dispersed particle size of such carbon nanotube dispersions to an appropriate range, conductive paths can be established between the active materials that store lithium ions.

[0006] For example, Patent Document 1 discloses a method for improving the cycle characteristics of a secondary battery by stabilizing the dispersion of multi-walled carbon nanotubes in sodium carboxymethyl cellulose, the dispersion being an aqueous dispersion of multi-walled carbon nanotubes having an average fiber outer diameter in the range of 50 to 110 nm, and improving the conductivity of the carbon nanotube dispersion by using specific particle size distribution characteristics. ２ / g of carbon nanotube powder in a dispersion containing 2 to 15 wt %. －１ The document discloses a method for providing a carbon nanotube dispersion liquid with excellent cycle characteristics by adjusting the viscosity at 2 to 110 mPa·s and the dispersed particle diameter d50 to 100 to 600 nm.

[0007] JP 2016-028109 A JP 2015-195143 A

[0008] These methods can suppress the localization of the conductive material in the electrode due to entanglement of carbon nanotubes, maintain the conductive path, and improve cycle characteristics. However, carbon nanotubes usually form aggregates in which carbon fibers with nano-sized outer diameters are entangled. Because it is extremely difficult to defibrate and disperse these aggregates, it is difficult to obtain a carbon nanotube dispersion composition that has high initial fluidity and excellent dispersion stability. Furthermore, when a carbon nanotube dispersion composition with poor fluidity is used, the conductive material does not diffuse sufficiently in the composite slurry obtained by adding an active material. When a coating film is formed, the internal resistance at high rates increases, causing problems with rate characteristics.

[0009] Therefore, the present invention provides a carbon nanotube dispersion composition that achieves both fluidity and storage stability within a particle size range that results in a dispersion state of carbon nanotubes that exhibits good cycle characteristics when made into a secondary battery, i.e., excellent life performance. Furthermore, by using the carbon nanotube dispersion composition, a secondary battery that achieves both good cycle characteristics and rate characteristics is provided.

[0010] Furthermore, even when graphite powder and a silicon-based active material are used as the negative electrode active material, a secondary battery having excellent rate characteristics is provided.

[0011] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. One embodiment is a dispersion medium containing carbon nanotubes (A), a dispersant (B), and a solvent (C), and having a particle size D at 50% cumulative volume measured by laser diffraction particle size distribution measurement. ５０ The present invention relates to a carbon nanotube dispersion composition having a particle size D of 0.3 to 7 μm and satisfying the following (1) and (2): (1) the dispersant (B) is a polymer having a weight-average molecular weight of 5,000 or more and 360,000 or less, and having a carboxyl group-containing structural unit derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and the content of the carboxyl group-containing structural unit is 80 mass % or more based on the mass of the polymer; (2) the particle size D of the carbon nanotube dispersion composition at 50% cumulative volume as measured by laser diffraction particle size distribution measurement ５０ When X [μm] and pH is Y, X and Y satisfy the following (formula a) and (formula b): (formula a) Y≧−0.149X+4.545 (formula b) Y≦−0.134X+5.140 In the above embodiment, it is preferable that the carbon nanotube dispersion composition further contains a basic compound (D).

[0012] Another embodiment relates to a composite slurry containing the carbon nanotube dispersion composition of the above embodiment and an active material.

[0013] Another embodiment relates to an electrode film formed from the composite slurry of the above embodiment.

[0014] Another embodiment relates to a secondary battery including a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode has the electrode film of the above embodiment.

[0015] According to an embodiment of the present invention, it is possible to provide excellent fluidity and storage stability in a carbon nanotube dispersion composition having a particle size distribution range that is particularly expected to improve the life performance of secondary batteries, etc. Furthermore, by using this carbon nanotube dispersion composition, it is possible to provide a secondary battery that achieves both excellent cycle characteristics and excellent rate characteristics.

[0016] Furthermore, when graphite powder and a silicon-based active material are used as the negative electrode active material, even if the active material expands and contracts during charging and discharging, the carbon nanotubes are uniformly dispersed in the composite slurry, sufficiently maintaining the conductive path. This prevents an increase in internal resistance within the electrode, suppresses a decrease in charge and discharge capacity, and makes it possible to provide a secondary battery with excellent rate characteristics.

[0017] The dispersion composition, composite slurry, electrode film, and secondary battery according to the embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and also includes embodiments that are implemented within the scope of the present invention without departing from the spirit and scope of the present invention. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the range of the lower and upper limits.

[0018] In this specification, "carbon nanotubes" refers to "CNTs," "carbon nanotube dispersion composition" refers to "dispersion composition" or "CNT dispersion composition," and "particle size D at 50% cumulative volume measured by laser diffraction particle size distribution measurement." ５０ " to "particle size D ５０In this specification, unless otherwise specified, when the terms "(meth)acrylic", "(meth)acryloyl", "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyloxy" are used, they respectively mean "acrylic or methacrylic", "acryloyl or methacryloyl", "acrylic acid or methacrylic acid", "acrylate or methacrylate", and "acryloyloxy or methacryloyloxy".

[0019] Unless otherwise noted, the various components described herein may be used independently as a single type or as a mixture of two or more types. Numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0020] <1> Carbon nanotube dispersion composition The carbon nanotube dispersion composition of this embodiment contains carbon nanotubes (A), a dispersant (B), and a solvent (C), and has a particle size D at 50% cumulative volume measured by laser diffraction particle size distribution measurement. ５０ The particle size D of the carbon nanotube dispersion composition at 50% cumulative volume measured by laser diffraction particle size distribution measurement is 0.3 to 7 μm, and the following (1) and (2) are satisfied. (1) The dispersant (B) is a polymer having a weight average molecular weight of 5,000 or more and 360,000 or less, and having a carboxyl group-containing structural unit derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and the content of the carboxyl group-containing structural unit is 80 mass % or more based on the mass of the polymer. (2) The particle size D of the carbon nanotube dispersion composition at 50% cumulative volume measured by laser diffraction particle size distribution measurement is 0.3 to 7 μm, and the following (1) and (2) are satisfied. (1) The dispersant (B) is a polymer having a weight average molecular weight of 5,000 to 360,000, and having a carboxyl group-containing structural unit derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and the content of the carboxyl group-containing structural unit is 80 mass % or more based on the mass of the polymer. ５０ When X [μm] and pH is Y, X and Y satisfy the following (formula a) and (formula b). (Formula a) Y≧−0.149X+4.545 (Formula b) Y≦−0.134X+5.140

[0021] As described above, the present inventors have determined that the preferred pH range of the carbon nanotube dispersion composition is ５０ For example, it has been found that the particle size D ５０ The larger the value, the lower the pH can be adjusted to improve storage stability and fluidity.

[0022] In the carbon nanotube dispersion composition of this embodiment, the particle size at 50% cumulative volume measured by laser diffraction particle size distribution measurement is the particle size D ５０ The particle size D is 0.3 to 7 μm. A carbon nanotube dispersion composition having such a particle size distribution range tends to easily provide a secondary battery having excellent cycle characteristics. ５０ is preferably 0.35 μm or more, and more preferably 0.4 μm or more. ５０ is preferably 6 μm or less, more preferably 5.5 μm or less, and even more preferably 5 μm or less.

[0023] Particle size D ５０ is correlated with the length of the carbon nanotubes in the dispersion composition, and the particle size D ５０ In a carbon nanotube dispersion composition (hereinafter also referred to as a dispersion composition) in which the particle diameter D is within the above range, the carbon nanotubes are well dispersed in the dispersion composition, the cycle characteristics are excellent, and the battery life can be easily extended. ５０ If the particle diameter D exceeds the above range, the carbon nanotubes are in an aggregated state. ５０ If the particle size D is below the above range, a large number of finely cut conductive materials are generated, which tends to make it difficult to form an efficient conductive network. ５０ can be determined using a general laser diffraction particle size distribution analyzer that employs a dynamic light scattering method, but more specifically, can be measured by the method described in the Examples.

[0024] The pH of the carbon nanotube dispersion composition of this embodiment is in the range of "Y" defined by the above (Formula a) and (Formula b). The pH may be a value measured at 25°C using, for example, a pH meter. In some embodiments, the pH of the carbon nanotube dispersion composition, when measured using a pH meter at 25°C, is preferably in the range of 3.5 to 5.1, and more preferably in the range of 3.8 to 5.0. When the pH is within the above range, the dispersibility of the dispersant (B) can be easily improved, which tends to easily improve the fluidity and dispersion stability of the dispersion composition.

[0025] As described above, the carbon nanotube dispersion composition of this embodiment is a dispersion composition adjusted to a particle size distribution range that can be expected to produce a secondary battery with excellent cycle characteristics, and by using a dispersant (B) having sufficient carboxyl groups and adjusting the pH of the dispersion composition to a specific range, it achieves both excellent fluidity and storage stability. Furthermore, even when an active material is added to the dispersion composition to form a composite slurry, the carbon nanotubes are uniformly distributed relative to the active material, thereby suppressing a decrease in capacity retention.

[0026] To obtain the carbon nanotube dispersion composition of this embodiment, it is preferable to adjust the pH so that the range of "Y" defined by the above formulas (a) and (b) is satisfied. The pH adjustment method is not particularly limited. Examples include adding a basic compound to the dispersion composition and adjusting the amount added, or using carbon nanotubes that exhibit acidic or basic properties. Acidic carbon nanotubes can be obtained, for example, by introducing acidic functional groups into the carbon nanotubes through acid treatment or the like. Basic carbon nanotubes can be obtained, for example, by adjusting the amount of catalyst-derived metal remaining in the carbon nanotubes, or by pretreating the carbon nanotubes with a basic compound (e.g., a compound containing an alkali metal or alkaline earth metal, an amine compound, etc.). In some embodiments, from the perspective of ease of pH adjustment, the method of using a basic compound is preferred, and the method of adding a basic compound to the dispersion composition is more preferred. The desired pH value can be easily obtained by adjusting the amount of basic compound added. Details of the basic compound will be described later as "basic compound (D)."

[0027] In the dispersion composition of this embodiment, the dispersant (B) contains 80% by mass or more of a carboxyl group-containing structural unit. Therefore, the pH of a solution obtained by dissolving the dispersant (B) in a solvent (e.g., water) capable of dissolving the dispersant (B) is acidic. More specifically, the pH value of the solution containing the dispersant (B) can be 2 or more and less than 7. The pH of the solution containing the dispersant (B) can be adjusted to reduce COO. － By generating a group (carboxylate anion), the particles can be dispersed and stabilized by the charge repulsion. Based on this, the present inventors have determined that the particle size D at 50% cumulative volume as determined by laser diffraction particle size distribution measurement is the dispersed particle size in the carbon nanotube dispersion composition. ５０ and pH, the initial viscosity of the dispersion composition can be reduced, and both the fluidity and dispersion stability of the dispersion composition can be achieved.

[0028] Without being bound by theory, the particle size D ５０The reason why there are suitable ranges defined by the above formulas (formula a) and (formula b) in the relationship between COO and pH is considered to be as follows. First, the smaller the dispersed particle size, the faster the collision speed between particles due to Brownian motion. Therefore, in order to stabilize the dispersion, it is necessary to add more COO. － It is presumed that a repulsive force due to the charge repulsion of the COO groups is necessary. In other words, for example, when a basic compound is used to adjust the pH, the smaller the dispersed particle size, the more the basic compound needs to be added, and as a result, the pH tends to become higher. In addition, for dispersion stabilization, even when the dispersed particle size is large, the COO － A certain level of charge repulsion by the groups is necessary. On the other hand, since carboxyl groups have a high affinity for carbon nanotubes (CNTs), dispersants containing a large number of carboxyl groups are more likely to be adsorbed by CNTs. For example, if the pH becomes too high by adding an excessive amount of a basic compound to the dispersion composition, the amount of carboxyl groups will decrease relatively, and the dispersant may detach from the CNTs. In particular, when the dispersed particle size is large, the mass of the CNT particles in the dispersion composition increases, so it is preferable to set the pH low. In this way, by appropriately adjusting the pH according to the size of the dispersed particle size and increasing the adsorption force of the dispersant to the carbon nanotubes, it is possible to utilize the particle repulsion force due to the osmotic effect, which is thought to result in improved storage stability and fluidity.

[0029] The carbon nanotube dispersion composition of this embodiment does not contain an active material. In this specification, when the carbon nanotube dispersion composition further contains an active material, it is defined as a composite slurry. In other words, the dispersion composition of this embodiment refers to the state before the active material is added to the dispersion composition. In this respect, the dispersion composition is distinguished from a composite slurry containing an active material. That is, the dispersion composition is substantially free of an active material. The term "substantially free" excludes a state in which an active material is intentionally added to the dispersion composition. Specifically, the content of the active material may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, relative to the total mass of the dispersion composition, or may be 0% by mass. Details of the active material will be described later.

[0030] The dispersion composition of this embodiment can be suitably used to form an electrode for a secondary battery. However, the dispersion composition of this embodiment is not limited to the use in a secondary battery, and can also be used in other storage devices than a secondary battery, such as an electrode for an electric double layer capacitor, an electrode for a non-aqueous electrolyte capacitor, etc. In addition, it can also be used for applications such as IC trays for plastic and rubber products, antistatic materials for molded bodies of electronic component materials, electronic components, a transparent electrode (ITO film) replacement, electromagnetic wave shielding, etc.

[0031] The components of the carbon nanotube dispersion composition of this embodiment will be described below. <Carbon nanotubes (A)> The carbon nanotubes may be single-walled carbon nanotubes alone, multi-walled carbon nanotubes alone, or a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is wrapped around them, and multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wrapped around them.

[0032] The average outer diameter of the carbon nanotubes used as the raw material is preferably 1 nm to 50 nm, more preferably 1 nm to 40 nm, or even more preferably 1 nm to 20 nm. Within these ranges, the packing density of the active material in the electrode film can be further increased. By using carbon nanotubes within this range, bundles consisting of several CNTs can be formed in the dispersion composition, and a dispersion composition with the above-mentioned preferred average outer diameter can be obtained after dispersion.

[0033] The average outer diameter of the carbon nanotubes used as raw material is calculated by the following method. First, carbon nanotubes are dispersed in toluene using an ultrasonic homogenizer, and then the carbon nanotubes are placed on a collodion film and dried. The carbon nanotubes are observed and photographed using a transmission electron microscope (TEM). Next, 100 carbon nanotubes are randomly selected from the photograph, and the outer diameter of each is measured. Next, the average outer diameter (nm) of the raw material carbon nanotubes is calculated as the number average of the outer diameters.

[0034] The average fiber length of the carbon nanotubes used as the raw material is preferably 1 to 50 μm, and more preferably 1 to 20 μm. If it is within this range, it is easy to adjust the fiber length to a preferred length after dispersion.

[0035] The fiber length of the carbon nanotubes used as raw material can be measured by dispersing the carbon nanotubes in toluene using an ultrasonic homogenizer, then depositing the carbon nanotubes on a mica substrate, observing them with an SEM, and analyzing the images. The SEM image is analyzed using the image analysis software "WinROOF2015" (manufactured by Mitani Shoji), and the skeletal length of each carbon nanotube is calculated as the fiber length. The average fiber length of the carbon nanotubes used as raw material is calculated by counting the fiber lengths of 1,000 to 3,000 carbon nanotubes.

[0036] The BET specific surface area of ​​the carbon nanotubes used as raw materials measured by nitrogen adsorption is 100 m ２ / g or more 1200m ２When the BET specific surface area of ​​the carbon nanotubes is within the above range, the carbon nanotubes are easily distributed in the composite slurry when controlled to an appropriate dispersion state, and the cycle performance can be further improved.

[0037] The carbon nanotubes used as raw materials have a Raman spectrum of 1560 to 1600 cm －１ The maximum peak intensity in the range of 1310 to 1350 cm －１ When the maximum peak intensity within this range is D, the G / D ratio is preferably 0.5 or more and 100 or less, more preferably 0.8 or more and 50 or less, and even more preferably 1 or more and 45 or less.

[0038] Among them, the specific surface area is 100m ２ / g or more 700m ２ When the specific surface area is less than 700 m / g, the G / D ratio is preferably 0.8 or more and 8 or less, and more preferably 0.8 or more and 5 or less. ２ / g or more 1200m ２ / g or less, the G / D ratio is preferably 30 or more and 100 or less, and more preferably 40 or more and 50 or less. When the G / D ratio of the carbon nanotube is within the above range, it is preferable because it has high crystallinity and is easy to obtain good conductivity. The preferable range differs depending on the specific surface area because when the specific surface area is small, multi-walled CNTs are mainly used, and the D band becomes strong due to the influence of terminal sp3 hybridized carbon and interlayers, so the G / D ratio range for good conductivity is smaller than that of high-specific surface area carbon nanotubes. When the specific surface area is high, single-walled CNTs are mainly used, and sp2 carbon defects can be inferred from the G / D ratio, and when it is within the above range, defects are small and good conductivity can be exhibited.

[0039] The volume resistivity of the carbon nanotubes used as raw materials is 1.0 × 10 －３ Ω・cm or more 3.0×10 －２ It is preferably Ω cm or less, and 1.0 × 10 －３ Ω・cm or more 1.0×10 －２It is more preferable that the volume resistivity of the carbon nanotubes is Ω cm or less. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). When the volume resistivity of the carbon nanotubes is in the above range, it is possible to reduce the electron transfer resistance between the carbon nanotubes and the active material.

[0040] The carbon purity of the carbon nanotubes used as raw materials is expressed as the carbon atom content (%) in the carbon nanotubes. The carbon purity is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the carbon nanotubes. When the carbon purity of the carbon nanotubes is within the above range, problems such as short circuits caused by the formation of dendrites due to impurities such as metal catalysts can be prevented.

[0041] The amount of metal contained in the carbon nanotubes used as raw materials is preferably less than 20% by mass, more preferably less than 10% by mass, and even more preferably less than 5% by mass, based on 100% by mass of the carbon nanotubes. Examples of metals contained in the carbon nanotubes include metals and metal oxides used as catalysts when synthesizing carbon nanotubes, and metal powders mixed in due to wear of equipment, etc. Specific examples include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, alloys of these metals, metal oxides, and composite oxides thereof.

[0042] The carbon purity and metal content in the carbon nanotubes can be determined by ICP emission spectroscopy.

[0043] The carbon nanotubes used as raw materials may be surface-treated carbon nanotubes, or may be carbon nanotube derivatives to which functional groups such as carboxyl groups have been added. Carbon nanotubes containing organic compounds, metal atoms, or other substances may also be used.

[0044] The carbon nanotubes used as raw material may be pulverized carbon nanotubes. Pulverization is a process in which carbon nanotubes are pulverized using a mill containing milling media such as beads or steel balls, without the presence of any liquid material. This process is also called dry milling. Pulverization is carried out by utilizing the crushing and destructive force generated by the collision of the milling media. Pulverization primarily reduces the size of secondary particles of carbon nanotubes, thereby improving the dispersibility of carbon nanotubes. Known dry milling methods, such as dry attritors, ball mills, vibration mills, and bead mills, can be used, and the milling time can be set as desired depending on the device.

[0045] The carbon nanotubes used as the raw material may be produced by any method, including but not limited to laser ablation, arc discharge, thermal CVD, plasma CVD, and combustion.

[0046] <Dispersant (B)> The carbon nanotube dispersion composition of this embodiment contains a dispersant (B). The dispersant has the function of stabilizing the dispersion of CNTs in the dispersion composition, and other dispersants may be used in combination as long as the effect is not impaired. The dispersant (B) is a polymer having a weight-average molecular weight of 5,000 or more and 360,000 or less and having a carboxyl group-containing structural unit, and the content of the carboxyl group-containing structural unit is 80 mass% or more based on the mass of the polymer. By using such a dispersant (B) to disperse carbon nanotubes, it is possible to obtain a carbon nanotube having a specific particle size D ５０ It is possible to easily obtain a carbon nanotube dispersion composition that satisfies the above requirements and has excellent fluidity and storage stability.

[0047] The weight average molecular weight of the dispersant (B) is 5,000 or more and 360,000 or less. The weight average molecular weight of the dispersant (B) is preferably 6,000 or more, more preferably 8,000 or more. Also, it is preferably 260,000 or less, more preferably 100,000 or less. In some embodiments, the weight average molecular weight of the dispersant (B) may be preferably 9,000 or more, more preferably 10,000 or more, and even more preferably 50,000 or more. Also, the weight average molecular weight of the dispersant (B) may be preferably 90,000 or less, more preferably 80,000 or less, and more preferably 70,000. By having the weight average molecular weight in this range, the adsorption to carbon nanotubes is improved, and the stability of the dispersion can be further improved.

[0048] The dispersant (B) is a polymer having a carboxyl group-containing structural unit, and the content of the carboxyl group-containing structural unit is 80% by mass or more based on the mass of the polymer. Having sufficient carboxyl groups in the molecule provides strong ionicity. This enhances the adsorption of carbon nanotubes and affinity for the medium, allowing the carbon nanotubes to be stably present in the medium. In some embodiments, the dispersant (B) is preferably a polymer of at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group. That is, the dispersant (B) is preferably a polymer containing structural units derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and more preferably a polymer containing structural units derived from (meth)acrylic acid. When used as the dispersant (B), the dispersant (B) exhibits excellent carbon nanotube dispersibility and facilitates improved rate and cycle performance as a battery material. The dispersant (B) is preferably a polymer having an alkylene structure in its main chain.

[0049] In this specification, the content of each structural unit of the dispersant can be determined based on the mass % of the precursor (monomer) used during polymerization. Therefore, the content of the carboxyl group-containing structural unit described below means the content of (meth)acrylic acid and / or (meth)acrylate having a carboxyl group based on the total amount of monomers used to produce the dispersant (polymer).

[0050] From the viewpoint of providing a suitable affinity with the solvent described below, the content of the carboxyl group-containing structural unit is preferably 90% by mass or more, and more preferably 95% by mass or more, when the mass of the polymer (excluding the initiator and chain transfer agent) is taken as 100% by mass. On the other hand, the content may be 98% by mass or less. In one embodiment, the content may be 100% by mass. By having the content be 90% by mass or more, better dispersion stabilization of the CNTs due to the charge repulsion force of the carboxyl groups can be expected.

[0051] In one embodiment, the dispersant (B) may further contain, in addition to the carboxyl group-containing structural unit, one or more structural units selected from the group consisting of a nitrile group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocycle-containing structural unit. In this way, when the dispersant (B) further contains, in addition to the carboxyl group-containing structural unit, one or more structural units described above, it is preferable because polarization becomes stronger and the affinity between the carbon nanotubes and the medium becomes higher.

[0052] [Carboxyl Group-Containing Structural Unit] The carboxyl group-containing structural unit is a structural unit having a carboxyl group, and may be a structural unit having an alkylene structure substituted with a carboxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The number of carboxyl groups in the carboxyl group-containing structural unit is preferably one or two, more preferably one. The method for introducing the carboxyl group-containing structural unit into a polymer is not particularly limited. For example, a method of preparing a polymer by polymerization of a monomer having a carboxyl group, more specifically (meth)acrylic acid or a (meth)acrylate having a carboxyl group, etc., can be mentioned. Another method is a method of preparing a polymer by polymerization of a monomer containing a functional group other than a carboxyl group, and then modifying the functional group to a carboxyl group. In particular, a method of preparing a polymer by polymerization of a monomer having a carboxyl group can be preferably used.

[0053] Examples of monomers having a carboxyl group include unsaturated fatty acids such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and (meth)acrylates having a carboxyl group such as 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, ethylene oxide-modified succinic acid (meth)acrylate, and β-carboxyethyl (meth)acrylate. Further examples include polymers of the above-mentioned monomers having a carboxyl group, such as monomers having an acid anhydride group, such as maleic anhydride, itaconic anhydride, and citraconic anhydride, and monofunctional alcohol adducts thereof.

[0054] A "-C(=O)-O-C(=O)-" (herein referred to as an "acid anhydride group"), which is a group having a structure formed by dehydration condensation of two carboxyl groups, also forms a carboxyl group upon hydrolysis. Therefore, in this specification, it is included in the concept of a carboxyl group. Furthermore, a carboxyl group-containing structural unit may be obtained by hydrolyzing the carbamoyl group of a polymer obtained by polymerization of a monomer having a carbamoyl group, such as (meth)acrylamide.

[0055] As the carboxyl group-containing monomer, which is a precursor of the carboxyl group-containing structural unit, from the viewpoint of electrochemical stability, an unsaturated fatty acid is preferred, (meth)acrylic acid is more preferred, and acrylic acid is even more preferred. Acrylic acid is preferred because it has excellent solubility in water and dispersibility of carbon nanotubes, and can further improve the rate characteristics and cycle characteristics as a battery material.

[0056] [Nitrile group-containing structural unit] The nitrile group-containing structural unit is a structural unit having a nitrile group, and may be a structural unit having an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one or two, more preferably one. The method for introducing the nitrile group-containing structural unit into the dispersant is not particularly limited. In one embodiment, for example, a polymer can be prepared by polymerization of a monomer having a nitrile group.

[0057] Examples of monomers having a nitrile group include acrylonitrile, methacrylonitrile, and fumaronitrile. These can be used alone or in combination of two or more. When the nitrile group-containing monomer is acrylonitrile, the copolymer is less bent, and adjacent cyano groups are oriented to form a partial structure with strong polarization. This increases the intermolecular force between polymers or between the polymer and the carbon-based conductive material. From the viewpoints of increasing the intermolecular force as described above, ease of raw material availability, and reactivity, the nitrile group-containing monomer is preferably acrylonitrile. From the viewpoint of increasing the intermolecular force, the content of the nitrile group-containing structural unit is preferably 3% by mass or more, and more preferably 5% by mass or more, based on the mass of the polymer as 100% by mass. On the other hand, it is preferably 20% by mass or less, and more preferably 10% by mass or less. By adjusting the content of the nitrile group-containing structural unit within the above range, the carbon nanotubes can be more stably present in the medium. Furthermore, when such a polymer is used in a secondary battery, it is possible to prevent problems such as the dissolution of the dispersant in the electrolyte solution in the battery, which increases the resistance of the electrolyte solution, and this is preferable.

[0058] [Hydroxyl Group-Containing Structural Unit] The hydroxyl group-containing structural unit is a structural unit having a hydroxyl group, and may be a structural unit having an alkylene structure substituted with a hydroxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The number of hydroxyl groups contained in the hydroxyl group-containing structural unit is preferably one or two, more preferably one. The method for introducing the hydroxyl group-containing structural unit into a polymer is not particularly limited. For example, a method of preparing a polymer by the polymerization reaction of a monomer having a hydroxyl group, or a method of preparing a polymer by the polymerization reaction of a monomer having a functional group other than a hydroxyl group and modifying it to a hydroxyl group can be mentioned. A reasonable method can be selected from the viewpoints of reactivity and raw material cost.

[0059] Examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 2-hydroxy-3-phenoxypropyl acrylate, and caprolactone adducts of these monomers (the number of moles added is 1 to 5). The monomer containing a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably 2-hydroxyethyl (meth)acrylate, and even more preferably 2-hydroxyethyl acrylate.

[0060] One method for preparing a polymer by polymerization of a monomer having a functional group other than a hydroxyl group and modifying it to a hydroxyl group is to saponify the acetyl groups of polyvinyl acetate obtained by polymerizing vinyl acetate with an alkali such as sodium hydroxide to convert them to hydroxyl groups (saponification reaction).The saponification reaction rate (saponification degree) can be controlled as desired by changing the concentration of sodium hydroxide and the treatment time.

[0061] Furthermore, for the purpose of increasing the affinity between the carbon nanotubes and the medium, at least a part of the hydroxyl groups in the polymer may be reacted with an aldehyde compound to be modified into acetal groups (acetalization).

[0062] The aldehyde compound used in the acetalization reaction may be, for example, a linear, branched, cyclic saturated, unsaturated, or aromatic aldehyde compound having 1 to 15 carbon atoms, but is not limited thereto. Specific examples include formaldehyde, acetaldehyde, propionyl aldehyde, n-butyraldehyde, isobutyraldehyde, tert-butyraldehyde, benzaldehyde, and cyclohexyl aldehyde. These aldehyde compounds may be used alone or in combination of two or more. Furthermore, with the exception of formaldehyde, these aldehyde compounds may have one or more hydrogen atoms substituted with a halogen or the like. From the viewpoint of versatility, linear, branched, cyclic saturated, unsaturated, or aromatic aldehyde compounds having 1 to 10 carbon atoms are preferred, and linear aldehyde compounds having 1 to 4 carbon atoms are more preferred. By changing the aldehyde compound used and the treatment time, the reaction rate of acetalization (degree of acetalization) can be controlled as desired.

[0063] From the viewpoints of enhancing polarization, increasing affinity to carbon nanotubes and a medium, and resistance to an electrolyte, the content of the hydroxyl group-containing structural unit is preferably 3% by mass or more, more preferably 5% by mass or more, and is preferably 20% by mass or less, more preferably 10% by mass or less, based on 100% by mass of the polymer.

[0064] When the hydroxyl group-containing structural unit is acetalized to have an acetal group, the content of the acetal group-containing structural unit is, for the same reason as above, preferably 3% by mass or more, more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, based on 100% by mass of the polymer.

[0065] Furthermore, when one or more selected from the group consisting of nitrile group-containing structural units and heterocyclic ring-containing structural units are contained, the content of hydroxyl group-containing structural units is preferably 1% by mass or more, more preferably 3% by mass or more. On the other hand, it is preferably 10% by mass or less, more preferably 5% by mass or less. By adjusting it to the above range, polarization can be strengthened and affinity to carbon nanotubes and the medium can be increased. It is also preferable from the viewpoint of resistance to the electrolyte. It is particularly preferable to further contain one or more selected from the group consisting of nitrile group-containing structural units and heterocyclic ring-containing structural units, as this further strengthens polarization.

[0066] [Heterocycle-Containing Structural Unit] The heterocycle-containing structural unit is a structural unit having a heterocycle, and may be a structural unit having an alkylene structure substituted with a heterocycle-containing substituent. The alkylene structure is preferably a linear or branched alkylene structure. The heterocycle contained in the heterocycle-containing structural unit may be a monocyclic structure or a fused ring structure, but is preferably a monocyclic structure. The number of heterocycles contained in the heterocycle-containing structural unit is preferably one or two, more preferably one. The heterocycle contains atoms other than carbon in the ring-constituting atoms, such as one or more nitrogen atoms, oxygen atoms, sulfur atoms, etc. The atoms other than carbon in the ring are preferably nitrogen atoms or oxygen atoms, and more preferably nitrogen atoms. The inclusion of atoms other than carbon in the ring-constituting atoms generates polarization within the heterocycle, allowing it to strongly affect the carbon nanotube. The method for introducing the heterocycle into the polymer is not particularly limited. For example, a method for preparing a polymer by polymerization of a monomer having a heterocycle can be used.

[0067] As the monomer having a heterocycle, an N-vinyl cyclic amide structural unit is preferred, and examples thereof include N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, and N-vinyl-3,5-morpholinedione. In particular, N-vinyl-2-pyrrolidone is preferred from the viewpoint of improving battery characteristics. These may be used alone or in combination of two or more.

[0068] The content of the heterocycle-containing structural unit is preferably 3% by mass or more, more preferably 5% by mass or more, when the mass of the polymer is taken as 100% by mass, from the viewpoint of strengthening polarization and enhancing the effect on carbon nanotubes as described above. On the other hand, it is preferably 20% by mass or less, more preferably 15% by mass or less. However, when at least one of a nitrile group-containing structural unit and a hydroxyl group-containing structural unit is further contained, the content of the heterocycle-containing structural unit is preferably 1% by mass or more, more preferably 3% by mass or more, based on the mass of the polymer. On the other hand, it is preferably 20% by mass or less, more preferably 15% by mass or less. When at least one of a nitrile group-containing structural unit and a hydroxyl group-containing structural unit is further contained, the polarity is increased and the resistance to the electrolyte can be improved, which is more preferable.

[0069] [Other structural units] The polymer may further have, as other structural units, one or more structural units selected from the group consisting of active hydrogen group-containing structural units (excluding carboxyl groups and hydroxyl groups), basic group-containing structural units, and ester group-containing structural units. By selecting and incorporating the above structural units in accordance with the properties such as hydrophilicity, hydrophobicity, acidity, and basicity of the substrate to which the carbon nanotube dispersion composition of the present embodiment is applied or the material to be mixed, the carbon nanotube dispersion composition of the present embodiment can be easily applied to various uses.

[0070] The content of the other structural units is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of not impairing the polarization of the dispersant, when the mass of the polymer is taken as 100% by mass.

[0071] The active hydrogen group-containing structural unit is a structural unit having an active hydrogen group such as a primary amino group, a secondary amino group, or a mercapto group. ２ (amino group), and "secondary amino group" means a group in which one hydrogen atom on a primary amino group is substituted with an organic residue such as an alkyl group. However, in this specification, the primary amino group and secondary amino group in an acid amide are not included in the active hydrogen group.

[0072] The basic group-containing structural unit is a structural unit having a basic group.The basic group can be, for example, a tertiary amino group, an amide group, etc.In addition, the structural unit having a primary amino group and the structural unit having a secondary amino group are also included in the basic group-containing structural unit.However, in the present disclosure, they are treated as the active hydrogen group-containing structural unit, and are not included in the basic group-containing structural unit.

[0073] The ester group-containing structural unit is (R １ ) ２ C=C-CO-OR ２ In the above formula, R １ is a hydrogen atom or a methyl group, and at least one of them is a hydrogen atom. ２ is an alkyl group which may have a substituent. An alkyl group which contains the active hydrogen group or basic group as a substituent is treated as the active hydrogen group-containing structural unit or basic group-containing structural unit, and is not included in the ester group-containing structural unit.

[0074] In one embodiment, the combination of structural units contained in the polymer is preferably one or more selected from the group consisting of carboxyl group-containing structural units alone, and carboxyl group-containing structural units / nitrile group-containing structural units, hydroxyl group-containing structural units, and heterocyclic ring-containing structural units, and is preferably one selected from the group consisting of carboxyl group-containing structural units alone, carboxyl group-containing structural units / nitrile group-containing structural units, and carboxyl group-containing structural units / nitrile group-containing structural units / hydroxyl group-containing structural units. Among these, it is preferable to have only carboxyl group-containing structural units or a combination of carboxyl group-containing structural units / nitrile group-containing structural units.

[0075] The method for producing the polymer is not particularly limited. Examples include solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, and precipitation polymerization. Of these, solution polymerization or precipitation polymerization is preferred. Examples of the polymerization reaction system include addition polymerization such as ionic polymerization, free radical polymerization, and living radical polymerization. Of these, free radical polymerization or living radical polymerization is preferred. Examples of the radical polymerization initiator include peroxides and azo-based initiators.

[0076] When radical polymerization is carried out, examples of the polymerization initiator include, but are not limited to, the following: Organic peroxides such as di-t-butyl peroxide, lauroyl peroxide, stearyl peroxide, benzoyl peroxide, t-butyl peroxyneodecanate, t-butyl peroxypivalate, dilauroyl peroxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclohexane, and common azo-based radical polymerization initiators such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis(1-cyclohexanecarbonitrile), 2,2'-azobis-4-methoxy-2,4-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-2-methylbutyronitrile. These may be used alone or in combination of two or more. These radical polymerization initiators may be used in combination with an appropriate reducing agent as a redox initiator.

[0077] These polymerization initiators are generally used in an amount of 1 part by mass or less per 100 parts by mass of the total mass of all monomers used. The amount of the polymerization initiator can be appropriately selected taking into consideration the temperature at which the polymerization is carried out and the half-life of the polymerization initiator.

[0078] In the polymer production process, the molecular weight of the polymer to be produced can be controlled using a chain transfer agent or the like, within the scope of the present invention. Examples of chain transfer agents include alkyl mercaptans such as octyl mercaptan, nonyl mercaptan, decyl mercaptan, dodecyl mercaptan, and 3-mercapto-1,2-propanediol, thioglycolic acid esters such as octyl thioglycolate, nonyl thioglycolate, and 2-ethylhexyl thioglycolate, 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, and β-pinene. From the viewpoints of ease of handling and stability, 3-mercapto-1,2-propanediol, thioglycolic acid esters, 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, β-pinene, and the like are particularly preferred. The use of these compounds is also preferred in that the resulting polymer has a low odor. In one embodiment, it is preferable to use one of the above compounds alone or two or more of them in combination as the chain transfer agent. The chain transfer agent can be added appropriately depending on the required molecular weight. Generally, it is preferable to use it in a range of 0.001 to 4 parts by mass per 100 parts by mass of the total mass of all monomers used. In one embodiment, the amount of the chain transfer agent is preferably 0.01 to 4 parts by mass, more preferably 0.1 to 2 parts by mass. By setting the amount of the chain transfer agent within the above range, the molecular weight of the polymer used as a dispersant in this embodiment can be easily adjusted to a suitable range.

[0079] Other molecular weight control methods include changing the polymerization method, adjusting the amount of polymerization initiator, and changing the polymerization temperature, etc. These molecular weight control methods may be used alone or in combination of two or more methods.

[0080] Molecular weight can be measured, for example, by gel permeation chromatography (GPC) equipped with an RI detector and a UV detector (210 nm) using the following method. A specific example of an apparatus that can be used for measurement is the HLC-8320GPC (manufactured by Tosoh Corporation), and measurement can be performed as follows: Separation columns: The following are arranged in series, in this order: TSKgel Guard column PWXL (6.0 mm I.D. x 4 cm) Two TSKgel GMPXL (7.8 mm I.D. x 30 cm) Column temperature: 40°C Eluent: 0.2 M phosphate buffer (pH 7.0) Flow rate: 1.0 mL / min A sample is prepared at a concentration of 0.1% by mass in a mixture of the above eluent, and 0.1 mL is injected. The molecular weight is determined as a converted value using a standard PEO / PEG (Aglient Technologies).

[0081] In some embodiments, the acid value of the dispersant containing a carboxyl group-containing structural unit may be preferably 400 mgKOH / g to 800 mgKOH / g, more preferably 500 mgKOH / g to 800 mgKOH / g, and even more preferably 600 mgKOH / g to 800 mgKOH / g. When the acid value of the dispersant is within the above range, the adsorption to CNTs can be easily increased, and good solubility in the solvent that serves as the dispersion medium can be easily obtained, which tends to make it easier to maintain a good dispersion state. The dispersion medium (solvent) contains water and may further contain another medium that has affinity with water, as necessary. When the acid value of the dispersant is less than 400 mgKOH / g, COO － This reduces the number of electrically repulsive sites, which can lead to poor dispersion stability. On the other hand, if the acid value of the dispersant exceeds 900 mg KOH / g, it may cause corrosion of the equipment used during the dispersion process. The acid value is a value measured in accordance with the Japanese Industrial Standards "K0070:1992. Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponifiable matter of chemical products," and refers to the amount (mg) of potassium hydroxide required to completely neutralize 1 g of resin component.

[0082] In the carbon nanotube dispersion composition, the polymer functions as a dispersant. From this perspective, the content of the dispersant (B) in the carbon nanotube dispersion composition is preferably determined based on the specific surface area and wettability of the carbon nanotubes. In one embodiment, the content of the dispersant (B) is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, per 100 parts by mass of the carbon nanotubes. On the other hand, the content is preferably 160 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 90 parts by mass or less. A content equal to or greater than the lower limit ensures an appropriate amount of dispersant, thereby further suppressing the occurrence of carbon nanotube aggregation. A content equal to or less than the upper limit is preferable because it prevents a decrease in fluidity due to an increase in viscosity of the dispersion composition caused by an excess amount of polymer components and suppresses deterioration of storage stability. The content of the dispersant (B) has an appropriate amount depending on the specific surface area of ​​the carbon nanotubes, and it is preferable to increase the amount of dispersant within a preferred range as the specific surface area increases. For example, when the BET specific surface area of ​​the carbon nanotubes used as a raw material is 100 m2, as measured by nitrogen adsorption, the dispersant content is preferably 15 parts by mass or more, more preferably 20 parts by mass or more. On the other hand, the content is preferably 160 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 90 parts by mass or less. A content equal to or greater than the lower limit ensures an appropriate amount of dispersant, thereby further suppressing the occurrence of carbon nanotube aggregation. A content equal to or less than the upper limit is preferable because it prevents a decrease in fluidity due to an increase in viscosity of the dispersion composition caused by an excess amount of polymer components and suppresses deterioration of storage stability. The content of the dispersant (B) has an appropriate amount depending on the specific surface area of ​​the carbon nanotubes, and it is preferable to increase the amount ２ / g or more 1200m ２ / g or less, the content of the dispersant (B) is preferably 15 to 160 parts by mass relative to 100 parts by mass of the carbon nanotubes.

[0083] <Solvent (C)> The dispersion composition of this embodiment contains a solvent. The solvent is not particularly limited, but may contain water, and if necessary, may further contain another medium that is compatible with water. Examples of other mediums that are compatible with water include ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, acetylene alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, acetylene glycol, polyoxyalkylene glycol, propylene glycol, and other glycols.

[0084] <Basic Compound (D)> The dispersion composition of this embodiment can be applied with any method to obtain the desired pH value, but a basic compound can be preferably used. Therefore, in one embodiment, the dispersion composition contains a basic compound (D). By containing the basic compound (D), the dispersion composition interacts with the carboxyl group of the dispersant (B) through strong polarization, generating an electrochemical repulsion force, and easily improving the fluidity and storage stability of the dispersion composition. Examples of the basic compound (D) to be added include inorganic bases, inorganic metal salts, organic bases, and organic base salts. Among these, inorganic bases or inorganic metal salts with greater polarization are preferred because they can be effective even with a small amount added.

[0085] The basic compound may be added during dispersion, or may be added immediately after completion of dispersion and thoroughly mixed and stirred before use. Among these, adding the basic compound during dispersion is preferred because it can increase the dispersion speed of the dispersant (B).

[0086] Examples of inorganic bases and inorganic metal salts include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates of alkali metals or alkaline earth metals; and ammonium hydroxide, etc. Among these, hydroxides, carbonates, and alkoxides of alkali metals or alkaline earth metals are preferred from the viewpoint of easy supply of cations.

[0087] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkali metal carbonates include sodium carbonate and potassium carbonate. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate. The metal contained in the inorganic base may be a transition metal.

[0088] Examples of alkali metal alkoxides include lithium methoxide, lithium ethoxide, lithium n-butoxide, lithium t-butoxide, potassium methoxide, potassium ethoxide, potassium n-butoxide, potassium t-butoxide, sodium methoxide, sodium ethoxide, sodium n-butoxide, and sodium t-butoxide. The alkoxide may have 5 or more carbon atoms. Sodium t-butoxide is particularly preferred.

[0089] Examples of the alkoxide of alkaline earth metal include magnesium methoxide, magnesium ethoxide, magnesium n-butoxide, magnesium t-butoxide, etc. The alkoxide may have 5 or more carbon atoms.

[0090] Among these, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, lithium t-butoxide, potassium t-butoxide, and sodium t-butoxide are more preferred, sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate are even more preferred, and sodium hydroxide and sodium carbonate are most preferred. Note that, in the present embodiment, the metal contained in the inorganic base and the inorganic metal salt may be a transition metal.

[0091] Examples of the organic base include primary, secondary and tertiary amine compounds (such as alkylamines and amino alcohols) having 1 to 40 carbon atoms, which may have a substituent, organic hydroxides, and organic metal salts.

[0092] Examples of the organic base include primary, secondary, and tertiary alkylamines having 1 to 40 carbon atoms and an optionally substituted alkyl group, and compounds containing the basic nitrogen atom thereof.

[0093] Examples of primary alkylamines having 1 to 40 carbon atoms and an optionally substituted alkyl group include propylamine, butylamine, isobutylamine, octylamine, 2-ethylhexylamine, laurylamine, stearylamine, oleylamine, 2-aminoethanol, 3-aminopropanol, 3-ethoxypropylamine, and 3-lauryloxypropylamine.

[0094] Examples of secondary alkylamines having 1 to 40 carbon atoms and an optionally substituted alkyl group include dibutylamine, diisobutylamine, N-methylhexylamine, dioctylamine, distearylamine, and 2-methylaminoethanol.

[0095] Examples of tertiary alkylamines having 1 to 40 carbon atoms and an optionally substituted alkyl group include triethylamine, tributylamine, N,N-dimethylbutylamine, N,N-diisopropylethylamine, dimethyloctylamine, tri-n-butylamine, dimethylbenzylamine, trioctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine, triethanolamine, and 2-(dimethylamino)ethanol.

[0096] Among these, primary, secondary, or tertiary alkylamines having 1 to 30 carbon atoms and an optionally substituted alkyl group are preferred, and primary, secondary, or tertiary alkylamines having 1 to 20 carbon atoms and an optionally substituted alkyl group are more preferred. The optionally substituted alkyl group means that a hydrogen atom may be substituted, and examples of the substituent include a hydroxy group.

[0097] Examples of other compounds containing a basic nitrogen atom include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), imidazole, and 1-methylimidazole.

[0098] The content of the basic compound (D) is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, based on the mass of the dispersion composition. It is also preferably 0.40% by mass or less, more preferably 0.20% by mass or less, and even more preferably 0.15% by mass or less. When the content of the basic compound (D) is 0.01% by mass or more, the effect of storage stability tends to be easily obtained. Furthermore, when the content of the basic compound is 0.40% by mass or less, the dispersant is prevented from being detached from the carbon nanotubes, and further, corrosion of the dispersion device and / or the inside of the battery can be prevented, which is preferable.

[0099] <Other Optional Components> The carbon nanotube dispersion composition of the present embodiment may contain, as necessary, other carbon-based conductive materials such as carbon black other than the carbon nanotubes (A), dispersants other than the dispersant (B), binders, surfactants, other additives, and the like, as appropriate, within a range that does not impair the object of the present invention. These may be added at any timing, such as before, during, or after dispersing the dispersion composition, or when preparing a composite slurry.

[0100] The carbon nanotube dispersion composition of this embodiment is not particularly limited as long as it can stably disperse the carbon nanotubes, and when dispersing the carbon nanotubes, in addition to the dispersant (B), a surfactant or other dispersant can be further used.

[0101] [Surfactants] Surfactants are mainly classified as anionic, cationic, nonionic, and amphoteric. A suitable type of dispersant can be used in a suitable amount depending on the properties required for dispersing carbon nanotubes. When selecting an anionic surfactant, the type is not particularly limited. Specific examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfonates, alkylnaphthalenesulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalenesulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. Further specific examples include, but are not limited to, sodium dodecylbenzenesulfonate, sodium laurate sulfate, polyoxyethylene lauryl ether sodium sulfate, polyoxyethylene nonylphenyl ether sulfate, and the sodium salt of β-naphthalenesulfonic acid formalin condensates.

[0102] Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyl triethyl ammonium chloride. Amphoteric surfactants include, but are not limited to, aminocarboxylic acid salts.

[0103] Nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers, and more specifically, include, but are not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

[0104] The surfactant to be selected is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. In this case, it is preferable to blend an appropriate amount for each surfactant component. A combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0105] [Other Dispersants] In addition to the dispersant (B), other dispersants such as resin-type dispersants can also be used as dispersants for dispersing carbon nanotubes. Specific examples of resin-type dispersants include fluorine-based resins, polyvinyl alcohol, polyvinyl butyral, and polyvinyl pyrrolidone. Polyvinyl alcohol and polyvinyl pyrrolidone are particularly preferred. The molecular weight of the resin-type dispersant is preferably 10,000 to 300,000.

[0106] [Binder] The binder is a resin capable of bonding substances such as carbon-based conductive materials and other particles, and is further added to the dispersion liquid after dispersing the carbon nanotubes. In other words, it has a different role from the dispersant described in this specification. The binder may be the same as the dispersant described above. When the carbon nanotube dispersion composition is used in a secondary battery, the binder is not particularly limited as long as it is one that is usually used in secondary batteries, and can be selected appropriately depending on the purpose. Examples of binders used in secondary batteries include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as constituent units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; cellulose resins (e.g., carboxymethyl cellulose (CMC)); elastomers such as styrene butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms, mixtures, and copolymers of these resins may also be used. Among these, when used as a binder for the positive electrode, polymers or copolymers having fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene, are preferred from the perspective of durability. When used as a binder for the negative electrode, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, and the like, which have good adhesiveness, are preferred.

[0107] <Method of Manufacturing Dispersion Composition> The method of manufacturing the dispersion composition is to disperse a mixture of carbon nanotubes (A), a dispersant (B), a solvent (C), and, if necessary, a basic compound (D), and measure a particle size D at 50% cumulative volume by laser diffraction particle size distribution measurement. ５０and Step II, adjusting the pH of the mixture to the range of the following formulas (a) and (b): In the following formulas (a) and (b), X represents the particle diameter D at 50% cumulative volume measured by laser diffraction particle size distribution measurement after the dispersion treatment. ５０ [μm], and Y is pH. (Formula a) Y≧−0.149X+4.545 (Formula b) Y≦−0.134X+5.140 In the above production method, step I and step II may be carried out consecutively as independent steps, or may be carried out simultaneously without distinction. For example, when a basic compound (D) is used as a method for adjusting the pH, step I and step II can be carried out simultaneously.

[0108] Hereinafter, as an example of a method for producing a dispersion composition, a method for dispersing carbon nanotubes in a solvent will be described. The dispersion composition is preferably produced, for example, by finely dispersing carbon nanotubes (A), a dispersant (B), a solvent (C), and, if necessary, a basic compound (D) through a dispersion treatment using a dispersion device. Note that the dispersion treatment can be performed in two or more stages by arbitrarily adjusting the timing of addition of the materials used.

[0109] Examples of dispersing devices include kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, annular bead mills, attritors, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers. Among these, a high-shear mixer, a high-pressure homogenizer, an ultrasonic homogenizer, or a combination thereof is preferably used to finely disperse carbon nanotubes in the dispersion composition and obtain favorable dispersibility. In particular, a high-shear mixer is preferably used in the initial dispersion step to promote wetting of the carbon nanotubes and disintegrate coarse particles, followed by a high-pressure homogenizer to disperse the carbon nanotubes while maintaining their aspect ratio. The pressure when using a high-pressure homogenizer is preferably 40 to 150 MPa, more preferably 70 to 150 MPa.

[0110] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, and circulation dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device itself, without using piping or the like. Because it is easy to handle, it is preferred for small-scale production. Pass dispersion is a dispersion method in which the dispersing device itself is equipped with a tank that supplies the dispersion liquid (a mixture containing dispersoid and dispersion medium, a precursor to the dispersion composition) via piping, and a tank that receives the dispersion liquid, and the dispersion liquid passes through the dispersing device itself. Circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device itself is returned to the tank that supplies the dispersion liquid, and dispersion is performed while circulating. In both methods, the longer the processing time, the more the dispersion progresses; therefore, the pass or circulation can be repeated until the desired dispersion state is achieved, and the processing volume can be increased by changing the tank size or processing time. Pass dispersion is preferred over circulation dispersion because it is easier to homogenize the dispersion state. Circulation dispersion is preferred over pass dispersion because it requires simpler operations and manufacturing equipment. In the dispersion process, the disintegration of agglomerated particles, the loosening, wetting, stabilization, etc. of carbon nanotubes proceed sequentially or simultaneously, and the final dispersion state differs depending on how the processes proceed. Therefore, it is preferable to manage the dispersion state in each dispersion process using various evaluation methods.

[0111] In the dispersion composition of this embodiment, the carbon nanotube content is preferably 0.3% by mass or more, more preferably 0.4% by mass or more, and even more preferably 0.5% by mass or more, based on 100% by mass of the dispersion composition. It is also preferably 6.0% by mass or less, and more preferably 5.0% by mass or less. A content of at least the lower limit suppresses compression by the carbon nanotube dispersion composition in the formulation design of the composite slurry, while a content of at most the upper limit ensures the fluidity and handleability of the dispersion composition, which is preferable.

[0112] The average outer diameter of the carbon nanotubes in the carbon nanotube dispersion composition of this embodiment is preferably 1 nm or more and 100 nm or less, more preferably 1.5 nm or more and 70 nm or less, and even more preferably 2 nm or more and 50 nm or less. A value equal to or greater than the lower limit is preferred because it prevents the fibers from breaking and allows the active material to follow the volume change associated with the absorption and desorption of lithium ions. A value equal to or less than the upper limit is preferred because it ensures a sufficient number of fibers relative to the amount added to the electrode.

[0113] The average fiber length of the carbon nanotubes in the carbon nanotube dispersion composition of this embodiment is preferably 0.3 μm or more and 50 μm or less, and more preferably 0.5 μm or more and 20 μm or less. A length equal to or greater than the lower limit is preferred because a conductive path between active materials can be sufficiently formed. A length equal to or less than the upper limit is preferred because it can prevent entanglement of carbon nanotubes with each other in the electrode, resulting in localization and preventing deterioration of battery performance.

[0114] The average outer diameter and fiber length of the carbon nanotubes in the dispersion composition are measured by diluting the CNT dispersion composition with a solvent to a CNT concentration of 0.048% by mass, spraying a few μL of the diluted dispersion composition onto a mica substrate, and then drying on a hot plate at 100°C to prepare a substrate for observing the CNT fiber length. The solvent used is the same as that used to prepare the CNT dispersion composition. The mica substrate is observed under an SEM and image analysis is performed to measure the average value. The average value can be calculated by measuring the lengths of the minor and major axes of 300 nanotubes.

[0115] The dispersibility of carbon nanotubes in a dispersion composition can be evaluated by the complex modulus and phase angle measured by dynamic viscoelasticity measurement. The complex modulus indicates the hardness of the dispersion composition, and tends to decrease as the dispersibility of carbon nanotubes improves and the viscosity decreases. However, when the carbon nanotubes have a large fiber length, even if the carbon nanotubes are uniformly and stably dissolved in the medium, the structural viscosity of the carbon nanotubes themselves may result in a high complex modulus. In one embodiment, the complex modulus of the dispersion composition is preferably 5 Pa or more, more preferably 10 Pa or more, at 25°C and 1 Hz. It is also preferably less than 300 Pa, more preferably less than 60 Pa. By setting the complex modulus of the dispersion composition within the above range, even carbon-based conductive materials with long fiber lengths, such as carbon nanotubes, can be uniformly and well-dispersed in a dispersion composition of the carbonaceous conductive material while maintaining a certain length or more.

[0116] The phase angle refers to the phase shift of the stress wave when the strain applied to the dispersion composition is a sine wave. In a purely elastic body, the sine wave is in phase with the applied strain, resulting in a phase angle of 0°. On the other hand, in a purely viscous body, the stress wave is advanced by 90°. In a typical viscoelasticity measurement sample, the phase angle is a sine wave greater than 0° and less than 90°. If the carbon nanotubes in the dispersion composition are well dispersed, the phase angle approaches 90°, which is the phase angle for a purely viscous body. However, as with the complex modulus, if the carbon nanotubes themselves have structural viscosity, the phase angle may be low even if the carbon nanotubes are uniformly and stably dissolved in the medium. From this perspective, in one embodiment, the phase angle at 25°C and 1 Hz in dynamic viscoelasticity measurement of the dispersion composition is preferably 3° or more, more preferably 5° or more, and even more preferably 10° or more. Furthermore, it is preferably less than 60°, and more preferably 50° or less. By setting the phase angle of the dispersion composition within the above range, even carbon-based conductive materials with long fiber lengths, such as carbon nanotubes, can be made into a dispersion composition in which the carbon-based conductive material is uniformly and well dispersed while maintaining the length at a certain level or more.

[0117] By uniformly and effectively dispersing long carbon nanotubes while maintaining their length at a certain level, a well-developed conductive network is formed. Therefore, it is not enough for the carbon nanotube dispersion composition to simply have low viscosity and good (apparent) dispersibility; it is important to determine the dispersion state by combining either or both of the complex modulus and phase angle with conventional indicators such as viscosity. In particular, it is important to give priority to the phase angle. From this perspective, by setting the complex modulus and phase angle within the above ranges, a carbon nanotube dispersion composition with good conductivity and electrode strength can be easily obtained. The complex modulus and phase angle of the carbon nanotube dispersion composition can be measured by the method described in the Examples.

[0118] The viscosity of the dispersion composition of this embodiment is measured using a rheometer at a shear rate of 1 (s －１ When measured at a shear rate of 10 (s), the viscosity is preferably 5 Pa·s or more, more preferably 10 Pa·s or more, and even more preferably 20 Pa·s or more, and is preferably less than 60 Pa·s, and more preferably less than 40 Pa·s. －１ ), the viscosity is preferably 1 Pa s or more and less than 10 Pa. By setting the viscosity at each shear rate within the above range, the dispersed particle size and dispersed state of the carbon nanotubes can be improved, and the electrode strength and conductivity can be improved.

[0119] The dispersion composition of the present embodiment can be converted into a composite slurry by further adding an active material, and can be used to form an electrode film. In addition, a film formed using the dispersion composition can improve the adhesion between the electrode film and a current collector or improve the conductivity of the electrode film, and therefore can also be used as a base layer in an electrode.

[0120] <2> Composite Slurry The composite slurry of this embodiment can be obtained by adding an active material to the dispersion composition, and can be preferably used for secondary battery electrodes. Because the dispersion composition of this embodiment has excellent fluidity and dispersion stability, a composite slurry in which carbon nanotubes are uniformly dispersed can be obtained, and the conductive paths can be sufficiently maintained in the formed electrode.

[0121] The active material may be a positive electrode active material or a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material." An active material is a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on electromotive force, and a positive electrode composite slurry can be prepared by using a positive electrode active material, and a negative electrode composite slurry can be prepared by using a negative electrode active material. The composite slurry is preferably in a slurry form to improve uniformity and processability.

[0122] If necessary, other optional components may be appropriately contained as needed for the purposes of a binder, wetting, surface activity, pH adjustment, wetting promotion, leveling, conductivity assistance, etc., within a range that does not impair the object of the present invention. The optional components can be added at any timing, such as before preparing the composite slurry, during mixing, after mixing, or a combination thereof.

[0123] A binder may be added to the dispersion composition for the purpose of better binding the active material and the like.

[0124] The binder used in producing the composite slurry is not particularly limited as long as it is a polymer component typically used as a binder for batteries, and can be appropriately selected depending on the purpose. The aforementioned polyvinylidene fluoride resin, which may have a substituent, may be used. Other polymer components include, for example, polymers or copolymers having ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, etc. as constituent components; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified products, mixtures, and copolymers of these resins may also be used, and they may be used alone or in combination of two or more. These resins can also be used as thickeners.

[0125] The content of CNTs in the composite slurry is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the active material. Also, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. If it is below the upper limit, it is possible to prevent a decrease in the amount of active material filled in the electrode and suppress a decrease in the battery capacity. Also, if it is above the lower limit, it is preferable because the conductivity of the electrode and the battery is sufficient.

[0126] The content of the binder in the composite slurry is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, per 100 parts by mass of the active material. By setting the content at or above the lower limit, the adhesion of the conductive film can be further improved. Also, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. By setting the content at or below the upper limit, the active material concentration in the conductive film can be increased, thereby achieving a higher capacity.

[0127] <Positive Electrode Active Material> The positive electrode active material is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, lithium manganese composite oxides (e.g., Li ｘ Mn ２ O ４ or Li ｘ MnO ２ ), lithium nickel composite oxide (e.g., Li ｘ NiO ２ ), lithium cobalt composite oxide (Li ｘ CoO ２ ), lithium nickel cobalt composite oxide (e.g., Li ｘ Ni １－ｙ Co ｙ O ２ ), lithium manganese cobalt composite oxide (e.g., Li ｘ Mn ｙ Co １－ｙ O ２ ), lithium nickel manganese cobalt composite oxide (e.g., Li ｘ Ni ｙ Co ｚ Mn １－ｙ－ｚ O ２ ), spinel-type lithium manganese nickel composite oxide (e.g., Li ｘ Mn ２－ｙ Ni ｙ O ４ ), lithium phosphate powder having an olivine structure (e.g., Li ｘ FePO ４ , Li ｘ Fe １－ｙ Mn ｙ P.O. ４ , Li ｘ CoPO ４ etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V ２ O ５ , V ６ O １３ ), transition metal oxide powder such as titanium oxide, iron sulfate (Fe ２ (SO ４ ) ３ ), TiS２ and transition metal sulfide powders such as FeS, etc., where x, y, and z are numbers, and 0<x<1, 0<y<1, 0<z<1, 0<y+z<1. These positive electrode active materials can be used alone or in combination.

[0128] <Negative Electrode Active Material> The negative electrode active material is not particularly limited, but examples thereof include metal Li, or its alloy, tin alloy, silicon alloy negative electrode, Li ｘ TiO ２ , Li ｘ Fe ２ O ３ , Li ｘ Fe ３ O ４ , Li ｘ WO ２ Examples of materials that can be used include metal oxides such as those listed above, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and resin-baked carbon materials. Here, x is a number, 0<x<1. These negative electrode active materials can be used alone or in combination. In particular, when a silicon alloy negative electrode is used, the theoretical capacity is large, but the volume expansion is extremely large. Therefore, it is preferable to use it in combination with artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, resin-baked carbon materials, or the like.

[0129] Furthermore, silicon-based active materials undergo large volume changes due to the absorption and release of lithium ions, and unless a conductive path is secured by carbon nanotubes adjusted to an appropriate particle size, it is difficult to perform good repeated charging and discharging. However, because the dispersion composition of this embodiment has excellent fluidity and dispersion stability, even when graphite powder and a silicon-based active material are used as the negative electrode active material, it is possible to suppress an increase in internal resistance within the electrode and a decrease in charge and discharge capacity.

[0130] <Method for Producing Composite Slurry> When a binder is added to a dispersion composition in a method for producing a composite slurry, the order in which the binder and active material are added is not particularly limited. Examples include a method in which a binder is added to a dispersion composition and then an active material is added; a method in which an active material is added to a dispersion composition and then a binder is added; and a method in which a binder and an active material are added to a dispersion composition all at once. The binder may also be dissolved in advance before addition. A preferred method for producing a composite slurry is to add a binder to a dispersion composition, then add an active material, and then perform a stirring process. The stirring device used for stirring is not particularly limited. A disperser, a homogenizer, or the like can be used as the stirring device.

[0131] The nonvolatile content of the composite slurry is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the composite slurry (100% by mass), and is preferably 90% by mass or less, more preferably 85% by mass or less.

[0132] <3> Electrode Film The electrode film is formed by forming a composite slurry into a film shape, and contains at least carbon nanotubes (A), a dispersant (B), and optionally a basic compound (D), and an active material. The electrode film may further contain optional components such as a binder. For example, the electrode film can be obtained by adding an active material and, optionally, a binder, etc. to the carbon nanotube dispersion composition described above to prepare a composite slurry, and then applying or coating the composite slurry. For example, the electrode film can be formed by applying the composite slurry to a current collector and removing volatile components.

[0133] <4> Secondary Battery A secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and preferably includes at least one selected from the group consisting of the positive electrode and the negative electrode having an electrode film formed from the composite slurry according to this embodiment. The positive electrode and the negative electrode may further include a current collector. Note that when one of the electrode films of the positive electrode or the negative electrode is an electrode film using the dispersion composition according to this embodiment, the electrode film of the other electrode is not particularly limited and may be a conventionally known electrode film.

[0134] In this embodiment, the structure of the secondary battery is not particularly limited. The secondary battery may typically include a positive electrode, a negative electrode, an electrolyte, and a separator, if necessary. The secondary battery may have various shapes, such as a paper type, a cylindrical type, a button type, or a laminated type, depending on the intended use.

[0135] <Positive electrode or negative electrode> The positive electrode or negative electrode has an electrode film formed from a composite slurry using the dispersion composition of this embodiment, and a current collector. The electrode film can be formed, for example, by applying the dispersion composition to a current collector and drying it. The electrode film formed using the positive electrode composite slurry can be used as a positive electrode. The electrode film formed using the negative electrode composite slurry can be used as a negative electrode. In this specification, a film formed using a dispersion composition containing an active material may be referred to as an "electrode composite layer."

[0136] The material and shape of the current collector used to form the electrode film are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. Examples of current collector materials include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while flat foils are generally used, current collectors with roughened surfaces, perforated foil current collectors, and mesh current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0137] The method for applying the dispersion composition to the current collector is not particularly limited, and known methods can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic coating. Drying methods include, but are not limited to, leaving the composition to dry, or drying using a blower dryer, a hot air dryer, an infrared heater, a far-infrared heater, or the like.

[0138] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0139] <Electrolyte> As the electrolyte, various known electrolytes in which ions can move can be used. For example, LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (wherein Ph is a phenyl group) and the like. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0140] The non-aqueous solvent is not particularly limited, but examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

[0141] The secondary battery preferably has a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, or any of these nonwoven fabrics that have been subjected to a hydrophilic treatment.

[0142] The present invention includes the following embodiments. However, the present invention is not limited to the following embodiments and includes various forms. [1] A dispersion medium containing carbon nanotubes (A), a dispersant (B), a solvent (C), and a basic compound (D), and having a particle size D at 50% cumulative volume as measured by laser diffraction particle size distribution measurement. ５０ A carbon nanotube dispersion composition characterized by having a particle size D of 0.3 to 7 μm and satisfying the following (1) and (2): (1) the dispersant (B) is a polymer having a weight-average molecular weight of 5,000 or more and 360,000 or less and having a carboxyl group-containing structural unit, and the content of the carboxyl group-containing structural unit is 80 mass % or more based on the mass of the polymer; (2) the particle size D of the carbon nanotube dispersion composition at 50% cumulative volume as measured by laser diffraction particle size distribution measurement ５０where X [μm] and pH is Y, X and Y satisfy the following (formula a) and (formula b). (Formula a) Y≧−0.149X+4.545 (Formula b) Y≦−0.134X+5.140 [2] The carbon nanotube dispersion composition according to the above item [1], wherein the phase angle at 1 Hz at 25°C measured by dynamic viscoelasticity measurement is 3° or more and less than 60°. [3] The carbon nanotube dispersion composition according to item [1] or [2], wherein the complex modulus at 1 Hz at 25°C measured by dynamic viscoelasticity measurement is 5 Pa or more and less than 300 Pa. [4] The carbon nanotube dispersion composition according to any one of items [1] to [3], wherein the content of the dispersant (B) is 15 to 90 parts by mass per 100 parts by mass of the carbon nanotubes (A). [5] The carbon nanotube dispersion composition according to any one of [1] to [4] above, wherein the carboxyl group-containing structural unit is a structural unit derived from (meth)acrylic acid. [6] A composite slurry comprising the carbon nanotube dispersion composition according to any one of [1] to [5] above and an active material. [7] An electrode film formed from the composite slurry according to [6] above. [8] A secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode has the electrode film according to [7] above. The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2023-142456, filed on September 1, 2023, the entire disclosure of which is incorporated herein by reference.

[0143] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0144] <Average outer diameter of carbon nanotubes> Measurement method: Carbon nanotubes were dispersed in toluene using an ultrasonic homogenizer, and then placed on a collodion film and dried. The carbon nanotubes were observed and photographed using a transmission electron microscope (TEM). Next, 100 carbon nanotubes were randomly selected from the photograph and their outer diameters were measured. Next, the average outer diameter (nm) of the raw carbon nanotubes was calculated as the number average of the outer diameters.

[0145] <Measurement of Specific Surface Area of ​​Carbon Nanotubes> 0.03 g of CNTs was weighed using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried for 15 minutes at 110° C. while degassing. Thereafter, the BET specific surface area of ​​the CNTs was measured using a fully automatic specific surface area measuring device (HM-model 1208, manufactured by MOUNTECH).

[0146] Details of the materials used in the present examples and comparative examples are as follows: <Carbon nanotubes (A)> TUBALL: Single-wall carbon nanotubes (OCSiAl, average outer diameter 1.6 nm, specific surface area 980 m ２ / g) ・10B: JENOTUBE10B (manufactured by JEIO, multilayer CNT, average outer diameter 10 nm, specific surface area 233 m ２ / g) ・6A: JENOTUBE6A (manufactured by JEIO, multilayer CNT, average outer diameter 6 nm, specific surface area 680 m ２ / g) TNSAR: Single-wall carbon nanotube (manufactured by Timesnano, average outer diameter 1.5 nm, specific surface area 950 m ２ / g) ・BT1001М: (Made by LGC, multilayer CNT, average outer diameter 10 nm, specific surface area 260 m ２ / g)

[0147] <Basic Compound (D)> D-1: Na ２ CO ３ (Sodium carbonate, manufactured by Tokyo Chemical Industry Co., Ltd., purity > 99.0%) D-2: NaOH (Sodium hydroxide, manufactured by Tokyo Chemical Industry Co., Ltd., purity > 98.0%, granular) D-3: KOH (Potassium hydroxide, manufactured by Tokyo Chemical Industry Co., Ltd., purity > 86.0%) D-4: CH ３ COONa (sodium acetate, manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.5%) D-5:K ２ CO ３ (Potassium carbonate, manufactured by Tokyo Chemical Industry Co., Ltd., purity >99.0%) D-6: BtONa (sodium t-butoxide, manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.0%)

[0148] <Production of Dispersant (B) and the like> (Dispersant (B-1)) 137 parts of ion-exchanged water, 100 parts of acrylic acid, 0.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added to a reaction vessel equipped with a thermometer, a condenser, and a stirrer, and the mixture was heated to 70°C and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disperser, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B-1)).

[0149] (Dispersant (B-2)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 95 parts of acrylic acid, 5 parts of acrylonitrile, 2.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B-2)).

[0150] (Dispersant (B-3)) A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 137 parts of ion-exchanged water, 95 parts of acrylic acid, 5 parts of 2-hydroxyethyl acrylate, 0.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, heated to 70°C, and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the reaction was terminated by cooling. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B-3)).

[0151] (Dispersant (B-4)) A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 100 parts of methanol, 0.1 parts of diethanolamine, and 5 parts of sodium hypophosphite, and the atmosphere was replaced with nitrogen gas. The reaction vessel was heated to 70°C, and 90 parts of acrylic acid and 10 parts of N-vinyl-2-pyrrolidone were added dropwise over 2 hours. Subsequently, an aqueous initiator solution consisting of 2 parts of 2,2'-azobis-2-amidinopropane dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.: V-50) and 18 parts of ion-exchanged water was added dropwise over 1.5 hours. After the dropwise addition was completed and the mixture was allowed to react for 3.5 hours, an aqueous solution consisting of 0.1 parts of V-50 and 0.9 parts of ion-exchanged water was added, and after a further 30 minutes, an aqueous solution consisting of 0.1 parts of V-50 and 0.9 parts of ion-exchanged water was again added. After 4.5 hours from the start of polymerization, it was confirmed that the conversion rate had reached 95%, and 0.5 parts of a 10% aqueous solution of malonic acid was added as a pH adjuster to obtain an aqueous dispersion of the polymer. Subsequently, the polymer was filtered off under reduced pressure, washed with methanol, and dried under reduced pressure to completely remove the solvent, thereby obtaining a polymer (dispersant (B-4)).

[0152] (Dispersant (B-5)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 100 parts of methacrylic acid, 0.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B-5)).

[0153] (Dispersant (B-6)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 90 parts of acrylic acid, 5 parts of acrylonitrile, 5 parts of 2-hydroxyethyl acrylate, 2.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B-6)).

[0154] (Dispersant (B-7)) A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 137 parts of ion-exchanged water, 95 parts of acrylic acid, 5 parts of methyl acrylate, 0.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, heated to 70°C, and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the reaction was terminated by cooling. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B-7)).

[0155] (Dispersant (B-8)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 100 parts of acrylic acid, 6.9 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 250 parts of methyl ethyl ketone and 250 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B-8)).

[0156] (Dispersant (B-9)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 100 parts of acrylic acid, 1.25 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 250 parts of methyl ethyl ketone and 250 parts of methanol, and the flask was rotated at 1,000 revolutions in a disperser, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B-9)).

[0157] (Dispersant (B-10)) A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 137 parts of ion-exchanged water, 80 parts of acrylic acid, 20 parts of acrylamide, 0.55 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and the mixture was heated to 70°C and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B-10)).

[0158] (Dispersant (B'-1)) A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 137 parts of ion-exchanged water, 70 parts of acrylic acid, 30 parts of acrylonitrile, 2.8 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and the mixture was heated to 70°C and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B'-1)).

[0159] (Dispersant (B'-2)) Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 137 parts of ion-exchanged water, 100 parts of acrylic acid, 9.3 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added, and the mixture was heated to 70°C and stirred at a temperature of 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 250 parts of methyl ethyl ketone and 250 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was removed by filtration and dried under reduced pressure to obtain a polymer (dispersant (B'-2)).

[0160] (Dispersant (B'-3)) A reaction vessel equipped with a thermometer, a condenser, and a stirrer was charged with 137 parts of ion-exchanged water, 100 parts of acrylic acid, 0.03 parts of 3-mercapto-1,2-propanediol, and 0.5 parts of V-50 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and the mixture was heated to 70°C and stirred at 70°C for 300 minutes (5 hours). When the conversion rate reached 90% or more, the mixture was cooled to terminate the reaction. Thereafter, unreacted raw materials were reduced by heating and distillation under reduced pressure to obtain an aqueous solution of a polymer. A four-neck separable flask was charged with 250 parts of methyl ethyl ketone and 250 parts of methanol, and the flask was rotated at 1,000 revolutions in a disper, to which the aqueous solution of the polymer was added dropwise over 1 hour. The resulting white precipitate was filtered out and dried under reduced pressure to obtain a polymer (dispersant (B'-3)).

[0161] The molecular weight of dispersant (B) was measured by gel permeation chromatography (GPC) equipped with an RI detector and a UV detector (210 nm). Specifically, the following was used: Apparatus: HLC-8320GPC (manufactured by Tosoh Corporation) Separation columns: The following were arranged in series in this order: TSKgel Guard column PWXL (6.0 mm I.D. x 4 cm) TSKgel GMPXL (7.8 mm I.D. x 30 cm) x 2 Column temperature: 40°C Eluent: 0.2 M phosphate buffer (pH 7.0) Flow rate: 1.0 mL / min The sample was prepared at a concentration of 0.1% by mass in a mixture of the above eluent, and 0.1 mL was injected. The molecular weight was determined as a converted value using standard PEO / PEG (Aglient Technologies).

[0162]

[0163] <Preparation of Dispersion Composition> (Example 1-1) According to the materials and composition shown in Table 2, the materials were added sequentially, and a CNT dispersion composition was prepared according to the following method. 1960.8 parts of ion-exchanged water, 18 parts of dispersant (B-1), and 1.2 parts of basic compound (D) were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, 20 parts of CNT (TUBALL) were added while stirring with a disperser, and a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON). Batch dispersion was performed at a speed of 8,000 rpm until the entire mixture became uniform and the dispersion particle size was 250 μm or less as measured with a grind gauge. At this time, the dispersion particle size confirmed with a grind gauge was 180 μm. Subsequently, the liquid to be dispersed was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and the particle size D ５０ The pass-type dispersion treatment was carried out until the particle size D was 0.3 to 7 μm. ５０ The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.20 mm and a pressure of 150 MPa, and the carbon nanotubes (A) contained 1.0 mass % of TUBALL, the dispersant (B) contained 0.90 mass % of dispersant (B-1), and the basic compound (D-1) (Na ２ CO ３ As a result, a carbon nanotube dispersion composition 1 having a carbon nanotube content of 0.06 mass % was obtained.

[0164] (Examples 1-2 to 1-28, 1-31 to 1-33, Comparative Examples 1-1 to 1-5) Using the materials and compositions shown in Table 2, the particle size D ５０ The pass-type dispersion treatment was continued until the particle size D reached 0.3 to 7 μm, and each dispersion composition (Dispersion Compositions 2 to 28, 31 to 33, Comparative Dispersion Compositions 1 to 5) was obtained. The dispersion conditions were as follows: ５０ If the particle size is 7 μm or more, the dispersion treatment is additionally performed twice and the particle size D ５０ Repeat until the particle size D is 7 μm or less, and control the number of passes. ５０ was adjusted to be 0.3 to 7 μm.

[0165] (Examples 1-29) According to the composition shown in Table 2, a dispersant (B-1), a basic compound (D-1), and ion-exchanged water were charged into a glass bottle (M-225, manufactured by Kakuyo Glass Co., Ltd.), and after thorough mixing and dissolving or mixing, CNTs were added, and the mixture was dispersed using zirconia beads (bead diameter 0.5 mmφ) as a medium in a paint conditioner for a total of 8 hours while cooling the glass bottle every 2 hours, to obtain carbon nanotube dispersion composition 29. Particle size D ５０ was 3.8 μm.

[0166] (Examples 1-30) According to the composition shown in Table 2, a dispersant (B-1), a conductive material, and a small amount of ion-exchanged water were charged into a Laboplastomill (manufactured by Toyo Seiki Seisakusho, Ltd.) and dispersed for 3 hours, and then transferred to a stainless steel container. The remaining ion-exchanged water and basic compound (D-1) were added, and a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a square-hole high-shear screen was used. Batch dispersion was performed at a speed of 8,000 rpm until the entire mixture became uniform and the dispersion particle size measured by a grind gauge was 250 μm or less, yielding carbon nanotube dispersion composition 30. At this time, the dispersion particle size measured by a grind gauge was 80 μm, and the particle size D ５０ was 6.0 μm.

[0167] Examples 1-34 to 1-36 Carbon nanotube dispersion compositions 34 to 36 were obtained according to the compositions shown in Table 2 and in the same manner as in Example 1-1.

[0168] <Measurement and Evaluation of Physical Properties of Dispersion Composition> The physical properties of the dispersion composition were measured and the storage stability was evaluated by the following methods. The results are shown in Table 2.

[0169] (Particle size D of the dispersion composition ５０ Measurement method) Particle size D at 50% cumulative volume ５０was measured using a laser diffraction particle size distribution analyzer (Partial LA-960V2, manufactured by HORIBA). The circulation / ultrasonic operating conditions were circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, and stirring mode: continuous. During air evacuation, ultrasonic operation was performed with an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds. The particle refractive index of the carbon-based conductive material was 1.9, and the shape was aspherical. The refractive index of the solvent was 1.333. During measurement, the concentration of the CNT dispersion composition was diluted so that the transmittance value was in the range of 50 to 85%. The particle size was measured by volume.

[0170] (Method for Measuring pH of Dispersion Composition) The pH of the sample for measurement was measured at a temperature of 25°C using a tabletop pH meter (Seven Compact S200 Expert Pro, manufactured by Mettler Toledo).

[0171] (Complex modulus and phase angle of dispersion composition) The complex modulus and phase angle of the dispersion composition were determined by dynamic viscoelasticity measurement using a rheometer (RheoStress1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a diameter of 35 mm and a 2° cone at 25 ° C., a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%. The complex modulus is preferably 5 Pa or more and less than 300 Pa, and more preferably 10 Pa or more or less than 60 Pa. The phase angle is preferably 3 ° or more and less than 60 °, and more preferably 10 ° or more. The lower the complex modulus of the dispersion composition, and the closer the phase angle of the dispersion composition is to 90 °, the better the fluidity. Evaluation criteria for complex elastic modulus 1: 300 Pa or more or less than 5 Pa 2: 60 Pa or more and less than 300 Pa 3: 10 Pa or more and less than 60 Pa 4: 5 Pa or more and less than 10 Pa Evaluation criteria for phase angle 1: 10° or more and less than 60° 2: 3° or more and less than 10° 3: Less than 3°

[0172] (Method for Evaluating Storage Stability of Dispersion Composition) Storage stability was evaluated by determining whether or not the dispersion composition had fluidity after being left to stand and stored at 40°C. The evaluation method is as follows. Using a rheometer (RheoStress1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a 35 mm diameter and 2° cone, the complex modulus was evaluated by performing dynamic viscoelasticity measurement at 25°C, a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%. Evaluation criteria ◎ to △ indicate that the composition is practical. Evaluation criteria ◎: Less than 300 Pa after 1 month (excellent) ○: Reaches 300 Pa after 1 month (good) △: Reaches 300 Pa after 1 week (fair) ×: Reaches 300 Pa after 1 day

[0173]

[0174]

[0175] <Preparation and Evaluation of Secondary Battery> <Preparation of Negative Electrode Composite Slurry and Negative Electrode> (Example 2-1) A dispersion composition (dispersion composition 1), a thickener, and water were added to a plastic container, and then the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Thereafter, artificial graphite and silicon (artificial graphite: silicon = 9:1 (mass ratio)) were added as negative electrode active materials, and the mixture was stirred at 2,000 rpm for 150 seconds using the centrifugal mixer. Further, SBR (styrene butadiene rubber) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using the centrifugal mixer to obtain a negative electrode composite slurry. The active material, CNT, dispersant, thickener, and SBR in the negative electrode composite slurry were blended in the amounts (% by mass) shown in Table 3, assuming their total to be 100% by mass, and the amount of water was adjusted so that the non-volatile content of the negative electrode composite slurry was 45%. The blending amounts in Table 3 represent the net content (% by mass of non-volatile content) of each component in the negative electrode composite slurry.

[0176] The obtained negative electrode composite slurry was applied to a copper foil having a thickness of 20 μm using an applicator, and the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a negative electrode (Negative Electrode 1). The weight per unit area of ​​the composite layer was 10 mg / cm. ２ The density of the composite layer after rolling was 1.6 g / cm ３ It was.

[0177] The raw materials used are as follows: Artificial graphite: CGB-20 (manufactured by Nippon Graphite Industries Co., Ltd.), non-volatile content 100% Silicon: silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5 μm, non-volatile content 100%) Thickener: CMC (carboxymethyl cellulose, #1190 (manufactured by Daicel FineChem Co., Ltd.), non-volatile content 100%) Binder: SBR (styrene butadiene rubber, TRD2001 (manufactured by JSR Corporation), non-volatile content 48%)

[0178] (Examples 2-2 to 2-36) Negative electrode composite slurries were produced in the same manner as in Example 2-1, except that the dispersion composition was changed to each dispersion composition (dispersion compositions 2 to 36) shown in Table 3 and the composition ratio was changed to that shown in Table 3. Negative electrodes 2 to 36 were obtained in the same manner.

[0179] Comparative Examples 2-1 to 2-5 Comparative negative electrode composite slurries were produced in the same manner as in Example 2-1, except that the dispersion composition was changed to each dispersion composition (comparative dispersion compositions 1 to 5) shown in Table 3, and comparative negative electrodes 1 to 5 were obtained in the same manner.

[0180] (Reference Example 2-1: Preparation of standard negative electrode) 0.5% by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka Co., Ltd.), 1% by mass of MAC500LC (carboxymethyl cellulose sodium salt Sunrose special type MAC500LC, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%), and 98.4% by mass of water were added to a plastic container with a capacity of 150 ml, and then stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Further, 97% by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) was added as an active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Subsequently, 3.1% by mass of SBR (styrene butadiene rubber, TRD2001, non-volatile content 48%, manufactured by JSR) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain a standard negative electrode composite slurry. The non-volatile content of the standard negative electrode composite slurry was set to 50% by mass.

[0181] The above-mentioned standard negative electrode composite slurry was applied to a copper foil having a thickness of 20 μm as a current collector using an applicator, and then dried in an electric oven at 80° C.±5° C. for 25 minutes to obtain an electrode with a coating weight per unit area of ​​10 mg / cm. ２ Further, a rolling treatment was carried out using a roll press (a 3-ton hydraulic roll press manufactured by Thank Metal Co., Ltd.) to adjust the density of the electrode mixture layer to 1.6 g / cm. ３ A standard negative electrode was fabricated.

[0182]

[0183] <Preparation of Positive Electrode Composite Slurry and Positive Electrode> (Example 3-1) A dispersion composition (dispersion composition 1), a thickener, and water were added to a plastic container, and then the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). LFP was then added as the positive electrode active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). PTFE was then added as a binder, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). A positive electrode composite slurry was obtained. The active material, CNT, dispersant, thickener, and binder (PTFE) in the positive electrode mixture slurry were blended in the amounts (% by mass) shown in Table 4, assuming the total nonvolatile content of these components to be 100% by mass, and the amount of water was adjusted so that the nonvolatile content of the positive electrode mixture slurry was 65%. The blending amounts in Table 4 represent the net content (% by mass of nonvolatile content) of each component in the positive electrode mixture slurry.

[0184] The positive electrode composite slurry was applied to a 20 μm-thick aluminum foil using an applicator and then dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain a positive electrode (positive electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 2.1 g / cc.

[0185] The raw materials used are as follows: LFP: lithium iron phosphate HED (registered trademark) LFP-400 (manufactured by BASF, non-volatile content 100%) Binder: PTFE (polytetrafluoroethylene, Polyflon PTFE D-210C (manufactured by Daikin Industries, Ltd., non-volatile content 60%) Thickener: CMC (carboxymethyl cellulose #1190 (manufactured by Daicel FineChem, non-volatile content 100%)

[0186] Examples 3-2 to 3-36 Positive electrodes 2 to 36 were obtained in the same manner as in Example 3-1, except that the conductive material dispersion was changed to each dispersion composition shown in Table 4 (dispersion compositions 2 to 36).

[0187] Comparative Examples 3-1 to 3-5 Comparative positive electrodes 1 to 5 were obtained in the same manner as in Example 3-1, except that the conductive material dispersion was changed to each dispersion composition shown in Table 4 (comparative dispersion compositions 1 to 5).

[0188] (Reference Example 3-1: Preparation of Standard Positive Electrode) As the positive electrode active material, 92% by mass of LFP (HED (trademark) LFP-400, manufactured by BASF, non-volatile content 100%), 4% by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka Co., Ltd., non-volatile content 100%), and 1.6% by mass of thickener (carboxymethyl cellulose #1190, manufactured by Daicel FineChem Co., Ltd., non-volatile content 100%) were added to a plastic container and mixed until uniform using a spatula. Thereafter, 20.5% by mass of water was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Thinky Corporation, Awatori Rentaro, ARE-310). The mixture in the plastic container was then mixed with a spatula until uniform, and 4% by mass of PTFE (manufactured by Daikin Industries, Ltd., non-volatile content 60% by mass) was added using a planetary centrifugal mixer. The mixture was then stirred at 2,000 rpm for 30 seconds. 11.2% by mass of water was then added, and the mixture was stirred at 2,000 rpm for 30 seconds using the planetary centrifugal mixer. Finally, the mixture was stirred at 3,000 rpm for 10 minutes using a high-speed mixer to obtain a standard positive electrode composite slurry.

[0189] The standard positive electrode composite slurry was applied to a 20 μm-thick aluminum foil using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain a standard positive electrode. The weight per unit area of ​​the electrode composite layer was 20 mg / cm. ２ The density of the electrode mixture layer after the rolling treatment was 2.1 g / cc.

[0190]

[0191] (Preparation of Secondary Battery) Using a standard positive electrode and a negative electrode or a comparative negative electrode listed in Table 5, or a positive electrode or a comparative positive electrode and a standard negative electrode listed in Table 6, samples of 50 mm x 45 mm and 45 mm x 40 mm were punched out, respectively. The punched positive electrode and negative electrode, along with a separator (porous polypropylene film) inserted therebetween, were inserted into an aluminum laminate bag and dried in an electric oven at 70°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolyte (a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1 was prepared, and vinylene carbonate was further added as an additive at 1% by mass relative to 100% by mass), and LiPF ６ After 2 mL of a non-aqueous electrolyte solution prepared by dissolving 1M of PEG-14 in the aluminum laminate was poured into each battery, the aluminum laminate was sealed to prepare a secondary battery.

[0192] <Evaluation of Secondary Battery> The obtained secondary battery was evaluated by the following method. The results are shown in Tables 5 and 6. (Method for evaluating rate characteristics of secondary battery) This was carried out in the same manner as in paragraph 0178 of Japanese Patent No. 7107413. Evaluation criteria: ◎ to △ indicate practical use. Evaluation criteria for rate characteristics: ◎: 90% or more (excellent) ○: 85% or more and less than 90% (good) △: 80% or more and less than 85% (acceptable) ×: less than 80%

[0193] (Method for evaluating cycle characteristics of secondary battery) The method was carried out in the same manner as in paragraph 0179 of Japanese Patent No. 7107413. If the evaluation criteria are ◎ to △, the battery is usable. Evaluation criteria for cycle characteristics ◎: 90% or more (excellent) ○: 80% or more but less than 90% (good) △: 70% or more but less than 80% (acceptable) ×: Less than 70%

[0194]

[0195]

[0196] As can be seen from Tables 2, 5, and 6, the polymer containing 80% by mass or more of a carboxyl group-containing structural unit and a basic compound was used, and the particle size D ５０ It was confirmed that the dispersion composition adjusted to an appropriate pH for the particle size D of the carbon nanotube dispersion composition was able to achieve both fluidity, storage stability, and battery performance.５０ When the particle size was adjusted to 0.3 to 7.0 μm, dispersion with a dispersant (B) that was a polymer having a weight-average molecular weight of 5,000 to 360,000 and containing carboxyl group-containing structural units could be applied by adjusting the pH, regardless of the type of carbon nanotube or the type of basic compound. When the pH was low or a polymer with a low content of carboxyl group-containing structural units was used, as in the comparative example, poor fluidity was observed due to insufficient electrochemical repulsion of the carboxyl groups, while high pH resulted in decreased affinity between the polymer and the carbon nanotubes and thickening due to aggregation of the carbon nanotubes. When the dispersant was a polymer with a low molecular weight, poor fluidity was observed due to insufficient steric repulsion, while when the dispersant was a polymer with a high molecular weight, thickening occurred due to the viscosity of the polymer itself.

[0197] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

Claims

1. A dispersion containing carbon nanotubes (A), a dispersant (B), and a solvent (C), and having a particle size D at 50% cumulative volume measured by laser diffraction particle size distribution measurement. ５０ A carbon nanotube dispersion composition having a particle diameter D of 0.3 to 7 μm and satisfying the following (1) and (2): (1) the dispersant (B) is a polymer having a weight average molecular weight of 5,000 or more and 360,000 or less, and having a carboxyl group-containing structural unit derived from at least one of (meth)acrylic acid and a (meth)acrylate having a carboxyl group, and the content of the carboxyl group-containing structural unit is 80 mass % or more based on the mass of the polymer. (2) The particle diameter D of the carbon nanotube dispersion composition at a cumulative volume of 50% as measured by laser diffraction particle size distribution measurement is 0.3 to 7 μm, and the following (1) and (2) are satisfied. ５０ When the particle diameter is X [μm] and the pH is Y, X and Y satisfy the following (formula a) and (formula b). (Formula a) Y≧−0.149X+4.545 (Formula b) Y≦−0.134X+5.140 2. The carbon nanotube dispersion composition according to claim 1, further comprising a basic compound (D).

3. The carbon nanotube dispersion composition according to claim 1 or 2, wherein the phase angle at 1 Hz at 25° C. as determined by dynamic viscoelastic measurement is 3° or more and less than 60°.

4. The carbon nanotube dispersion composition according to any one of claims 1 to 3, wherein the complex modulus of elasticity at 1 Hz at 25°C as determined by dynamic viscoelasticity measurement is 5 Pa or more and less than 300 Pa.

5. A carbon nanotube dispersion composition according to any one of claims 1 to 4, wherein the content of the dispersant (B) is 15 to 160 parts by mass per 100 parts by mass of the carbon nanotubes (A).

6. A carbon nanotube dispersion composition according to any one of claims 1 to 5, wherein the content of the dispersant (B) is 15 to 90 parts by mass per 100 parts by mass of the carbon nanotubes (A).

7. The BET specific surface area of ​​the carbon nanotube (A) measured by nitrogen adsorption is 100 m ２ / g or more 1200m ２ The carbon nanotube dispersion composition according to any one of claims 1 to 6, wherein the average molecular weight of the carbon nanotube dispersion composition is 100% or less.

8. The carbon nanotube dispersion composition according to any one of claims 1 to 7, wherein the carboxyl group-containing structural unit is a structural unit derived from (meth)acrylic acid.

9. A composite slurry comprising the carbon nanotube dispersion composition according to any one of claims 1 to 8 and an active material.

10. An electrode film formed from the composite slurry according to claim 9.

11. A secondary battery comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode has the electrode film according to claim 10.

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