Carbon nanotube dispersed composition, carbon nanotube resin composition, mixture slurry, electrode film, and nonaqueous electrolyte secondary battery

Abstract

The present invention provides a carbon nanotube dispersed composition with which it is possible to improve battery performance. Provided is a carbon nanotube dispersed composition which contains carbon nanotubes, a dispersant, and a solvent, and which satisfies the following requirements (1) and (2).　(1) The average outer diameter of the carbon nanotubes is 15 nm to 50 nm inclusive as calculated from an SEM image for the observation of carbon nanotubes contained in the carbon nanotube dispersed composition.　(2) When an object pixel group in an SEM image for the observation of carbon nanotubes contained in the carbon nanotube dispersed composition is taken as a carbon nanotube, and a value obtained by dividing the distance (absolute maximum length) between the most distant two points by the length (skeleton length) of a free curve is defined as a linearity, the proportion of the number of the carbon nanotubes each having a linearity of 0.9 or more among the carbon nanotubes each having a skeleton length of 1 μm or more is 40% to 90% inclusive.

Description

Carbon nanotube dispersion composition, carbon nanotube resin composition, composite slurry, electrode film, and non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a carbon nanotube dispersion composition, a carbon nanotube resin composition, a composite slurry, an electrode film, and a non-aqueous electrolyte secondary battery.

[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. Under these circumstances, non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, which use a non-aqueous electrolyte solution, are being used in many devices due to their high energy density and high voltage characteristics.

[0003] Carbon materials, such as graphite, are used as negative electrode materials for these lithium-ion secondary batteries. Carbon materials have a lower potential close to that of lithium (Li) and a large charge / discharge capacity per unit mass. However, the charge / discharge capacity per mass of these electrode materials has reached a level close to the theoretical value, and the energy density per mass of the battery is approaching its limit. Therefore, in order to increase the electrode utilization rate, attempts have been made to reduce the conductive additives and binders that do not contribute to the discharge capacity.

[0004] Examples of conductive additives include carbon black, ketjen black, fullerene, graphene, and fine carbon fibers such as carbon nanotubes and carbon nanofibers. Carbon nanotubes, a type of fine carbon fiber, are particularly widely used. For example, adding carbon nanotubes to a negative electrode containing graphite and silicon reduces electrode resistance, improves battery load resistance, improves electrode strength, and improves electrode expansion and contraction properties, thereby improving the cycle life of lithium-ion secondary batteries (see, for example, Patent Documents 1, 2, and 3). Adding carbon nanotubes to a positive electrode to reduce electrode resistance has also been studied (see, for example, Patent Document 4).

[0005] Patent Document 5 discloses that carbon nanotubes are specified by the pH, BET specific surface area, and average fiber length of a carbon nanotube aqueous dispersion in order to obtain an electrode film with excellent conductivity and adhesion. Patent Document 6 discloses that carbon nanotube dispersions are specified by the average outer diameter, BET specific surface area, fiber length, complex modulus, and phase angle of carbon nanotubes in order to obtain an electrode film with excellent conductivity and adhesion. Patent Document 7 discloses that multi-walled carbon nanotubes are specified by the average aspect ratio, tortuosity, secondary particle size, secondary particle size, and bulk density of inorganic oxide fine particles in order to obtain an aggregate of multi-walled carbon nanotubes with good dispersibility in resins, solvents, etc.

[0006] Japanese Patent Application Laid-Open No. 4-155776 Japanese Patent Application Laid-Open No. 4-237971 Japanese Patent Application Laid-Open No. 2004-178922 Japanese Patent Application Laid-Open No. 2011-70908 Japanese Patent No. 6961152 Japanese Patent No. 6801806 Japanese Patent Application Laid-Open No. 2012-082077

[0007] Patent Documents 5 and 6 disclose that a nonaqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics can be provided by obtaining an electrode film with excellent conductivity and adhesion. On the other hand, it is expected that battery performance can be further improved by specifying a more microscopic dispersion state of carbon nanotubes in the electrode film.

[0008] According to the technology disclosed in Patent Document 7, multi-walled carbon nanotubes having a certain degree of bending are preferable to those having a high degree of linearity, since agglomeration is prevented when the multi-walled carbon nanotubes are added to resins, etc. On the other hand, in order to secure conductive paths between multiple particles of active material in an electrode film and improve battery performance, investigations from other perspectives are also expected.

[0009] An object of the present disclosure is to provide a carbon nanotube dispersion composition, a carbon nanotube resin composition, and a composite slurry that can improve battery performance, as well as an electrode film and a nonaqueous electrolyte secondary battery obtained using these.

[0010] Some of the embodiments of the present disclosure relate to the following: However, the present invention is not limited to the following and may include various embodiments.

[0011] [1] A carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and a solvent, and satisfying the following (1) and (2): (1) The average outer diameter of the carbon nanotubes calculated from an SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is 15 nm or more and 50 nm or less; (2) When the target pixel group of the SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is defined as a carbon nanotube, and the distance between the two most distant points (absolute maximum length) divided by the length of the free curve (skeleton length) is defined as linearity, the proportion of carbon nanotubes with a skeleton length of 1 μm or more that have a linearity of 0.9 or more is 40% or more and 90% or less.

[0012] [2] (3) In the Raman spectrum of the coating film of the carbon nanotube dispersion composition, －１ The maximum peak intensity in the range of 1310 to 1350 cm －１ [1] The carbon nanotube dispersion composition according to [1], wherein the G / D ratio is 1.0 to 20.0, where D is the maximum peak intensity within the range.

[0013] [3] (4) After freeze-drying the carbon nanotube dispersion composition, the powder passed through a 60 μm mesh has a BET specific surface area relative to the mass of carbon nanotubes of 50 to 130 m ２ / g. [4] (5) The carbon nanotube dispersion composition according to any one of [1] to [3], wherein the complex modulus at 25°C and a frequency of 10 Hz, as measured by dynamic viscoelasticity measurement, is 0.1 Pa or more and 200 Pa or less. [5] (6) The carbon nanotube dispersion composition according to any one of [1] to [4], wherein the phase angle at 25°C and a frequency of 10 Hz, as measured by dynamic viscoelasticity measurement, is 3° or more and 60° or less.

[0014] [6] A carbon nanotube resin composition comprising the carbon nanotube dispersion composition according to any one of [1] to [5] and a binder. [7] A composite slurry comprising the carbon nanotube dispersion composition according to any one of [1] to [5], a binder, and an active material.

[0015] [8] An electrode film, which is a coating film of a composite slurry, the composite slurry containing the carbon nanotube dispersion composition according to any one of [1] to [5], a binder, and an active material. [9] A non-aqueous electrolyte secondary battery containing a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode contains the electrode film according to [8].

[0016] According to one embodiment of the present disclosure, it is possible to provide a carbon nanotube dispersion composition, a carbon nanotube resin composition, and a composite slurry that can improve battery performance, as well as an electrode film and a nonaqueous electrolyte secondary battery obtained using these.

[0017] Hereinafter, the carbon nanotube dispersion composition, and the resin composition, composite slurry, electrode film, and nonaqueous electrolyte secondary battery containing the same will be described in detail using several embodiments of the present disclosure. However, the present disclosure is not limited to these embodiments and various modifications are possible.

[0018] In this disclosure, carbon nanotubes may be abbreviated as "CNT," and a carbon nanotube dispersion composition may be abbreviated as "CNT dispersion composition." In addition, in this disclosure, an SEM image refers to an image captured by a scanning electron microscope. A scanning electron microscope may also be simply referred to as "SEM."

[0019] The present inventors have found that when the average outer diameter and linearity index of carbon nanotubes contained in a carbon nanotube dispersion composition satisfy predetermined ranges, each (i.e., individual) carbon nanotube comes into contact with multiple particles of active material (at a higher rate) in the electrode film, improving the conductivity between the particles of active material, thereby providing a secondary battery with excellent rate and cycle characteristics. Based on this finding, the present inventors have completed the present invention.

[0020] As an electrode material, whether it is a negative electrode or a positive electrode, electrical conductivity can be increased by electrically connecting multiple particles of active material with a single carbon nanotube. When the carbon nanotube has linearity, a single carbon nanotube can contact a larger number of particles of active material, contributing to electrical conductivity. This means that a small amount of carbon nanotubes can be expected to significantly contribute to electrical conductivity.

[0021] For example, the packing density of the active material in the electrode film can be increased by reducing the volume of dispersants, binders, etc., but the packing density of the active material can be further increased by further reducing the amount of carbon nanotubes used and thereby reducing the volume.

[0022] When a carbon-based active material is used in a negative electrode, multiple particles of the carbon-based active material can be electrically connected by a single carbon nanotube, thereby increasing conductivity. However, when a silicon-based active material is used in a negative electrode, volume changes tend to occur easily during charging and discharging. When volume changes occur in the negative electrode, the electrical connections between the active material particles are interrupted, and some active material particles may become electrically isolated. Because of their linearity, linear carbon nanotubes can relatively easily maintain contact with multiple active material particles, even if volume changes occur in the active material particles, preventing the interruption of the conductive path and suppressing a decrease in battery capacity.

[0023] Similarly, in the positive electrode, a single carbon nanotube can electrically connect multiple particles of active material to ensure a conductive path, so even a small amount of carbon nanotubes can be expected to make a significant contribution to conductivity.

[0024] <Carbon nanotube dispersion composition> One embodiment relates to a carbon nanotube dispersion composition. The carbon nanotube dispersion composition contains at least carbon nanotubes, a dispersant, and a solvent.

[0025] The carbon nanotube dispersion composition is characterized by satisfying the following (1) and (2): (1) the average outer diameter of the carbon nanotubes calculated from an SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is 15 nm or more and 50 nm or less; (2) when the target pixel group of the SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is taken as the carbon nanotube (i.e., based on the pixelated carbon nanotubes in the SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition, or in other words, using the pixel group corresponding to the carbon nanotubes as a proxy), and when the linearity is the value obtained by dividing the distance between the two most distant points (absolute maximum length) by the length of the free curve (skeleton length), the proportion of carbon nanotubes with a skeleton length of 1 μm or more that have a linearity of 0.9 or more is 40% or more and 90% or less.

[0026] Hereinafter, the index specified in (2) above will also be referred to as the linearity index.

[0027] When the carbon nanotubes are contained in a carbon nanotube dispersion composition, the average outer diameter of the carbon nanotubes falls within a predetermined range and the linearity index is specified, thereby making it possible to provide excellent battery performance in a secondary battery using the carbon nanotube dispersion composition.

[0028] Although the reason for this is not bound by theory, it is believed that by satisfying conditions (1) and (2), the linearity of the carbon nanotubes in the electrode film is maintained, and each carbon nanotube comes into contact with multiple particles of the active material at a higher rate, thereby improving conductivity. The number of particles of the active material that one carbon nanotube comes into contact with may be two or more, and preferably three or more. Note that it is not necessary for all carbon nanotubes to come into contact with multiple particles of the active material; it is sufficient that only some of the carbon nanotubes come into contact with multiple particles of the active material.

[0029] In condition (1), the average outer diameter of the carbon nanotubes is preferably 15 nm or more, even better if it exceeds 17 nm, more preferably 19 nm or more, and even more preferably 21 nm or more. Within these ranges, the carbon nanotubes are resistant to stress and can maintain a conductive path between the active materials, which change in volume with the absorption and desorption of lithium ions. Furthermore, carbon nanotubes with an average outer diameter of less than 15 nm are difficult to obtain from their manufacturing method in a manner that satisfies the appropriate range of physical properties described herein. For example, in a carbon nanotube dispersion composition, it is difficult to synthesize and obtain a carbon nanotube raw material that has an average outer diameter of less than 15 nm and that satisfies the linearity index of condition (2). Furthermore, when using a carbon nanotube raw material with an average outer diameter of 15 nm or more, a method for producing a carbon nanotube dispersion composition that satisfies the linearity index of condition (2) has not been known.

[0030] In condition (1), the average outer diameter of the carbon nanotubes is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. Within these ranges, the number of fibers per mass of carbon nanotubes can be increased, increasing the number of active materials into which the carbon nanotubes are distributed, thereby further improving battery performance. Furthermore, when the average outer diameter of the carbon nanotubes is 50 nm or less, the carbon nanotubes themselves have low resistance, thereby further increasing conductivity. This can further improve the rate characteristics of secondary batteries. Furthermore, because the carbon nanotubes of this embodiment are linear, they have high conductivity while also contacting multiple particles of active material in the electrode film to ensure conductive paths, which can contribute to improved conductivity. For example, the average outer diameter of the carbon nanotubes may be 15 to 50 nm, 15 to 40 nm, or 15 to 30 nm. Alternatively, they may be 17 to 40 nm, 19 to 30 nm, or 21 to 30 nm.

[0031] In the condition (2), the linearity index of the carbon nanotubes is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. Carbon nanotubes with a high linearity index can contact multiple particles of the active material at a higher rate in the electrode film, and can contribute to high conductivity in the secondary battery.

[0032] In condition (2), the linearity index of the carbon nanotubes is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. As the linearity index of the carbon nanotubes increases, the carbon nanotubes themselves tend to become stiffer, potentially resulting in breakage of the carbon nanotube fibers during dispersion processing to prepare an electrode film from the carbon nanotube dispersion composition. In this case, the number of active material particles that a single carbon nanotube can contact in the electrode film decreases, potentially resulting in insufficient conductivity in the secondary battery. For example, the linearity index of the carbon nanotubes may be 40 to 90%, 50 to 90%, 60 to 90%, 50 to 80%, 50 to 70%, or 60 to 70%.

[0033] In the present disclosure, the average outer diameter of the carbon nanotubes in the carbon nanotube dispersion composition is a value measured by the following procedure.

[0034] A sample is prepared using a carbon nanotube dispersion composition so that individual carbon nanotubes can be observed using an SEM. 300 carbon nanotubes are randomly selected from the SEM image of this sample, and the number-average average outer diameter is determined. Specifically, the following procedure is followed.

[0035] Sample preparation: The CNT dispersion composition is diluted with a solvent to a CNT concentration of 0.048% by mass. The solvent used is the same as that used to prepare the CNT dispersion composition. A few μL of the diluted dispersion composition is spray-coated onto a mica substrate and then dried on a hot plate at 100°C to prepare a substrate for observing the average outer diameter of the CNTs.

[0036] Measurement method: Carbon nanotubes are observed and photographed using a scanning electron microscope. Next, 300 carbon nanotubes are randomly selected from the photograph and their outer diameters are measured. Next, the average outer diameter (nm) of the carbon nanotubes is calculated as the number average of the outer diameters. Specifically, the method for measuring the average outer diameter follows the measurement method in the examples.

[0037] In the present disclosure, the linearity index of carbon nanotubes in a carbon nanotube dispersion composition is a value measured by the following procedure.

[0038] A sample is prepared using a carbon nanotube dispersion composition, allowing individual carbon nanotubes to be observed using an SEM. From the SEM image of this sample, a total of 1,000 to 3,000 carbon nanotubes are selected, and the absolute maximum length and skeletal length of each carbon nanotube are measured. The number of carbon nanotubes with a skeletal length of 1 μm or more is counted, and the linearity and linearity index are calculated. Specifically, the following procedure is followed.

[0039] Sample preparation: The CNT dispersion composition is diluted with a solvent to a CNT concentration of 0.048% by mass. The solvent used for preparing the CNT dispersion composition is used. A few μL of the diluted dispersion composition is spray-coated onto a mica substrate and then dried on a hot plate at 100°C to prepare a substrate for observing the CNT linearity index.

[0040] Measurement method: SEM images of the sample substrate are acquired. At this time, the field of view is set so that the shapes of 50 to 200 carbon nanotubes can be observed. SEM images are taken under conditions of 4.63 nm per pixel. Note that an error range of 4.63 nm ± 10% is allowed in the imaging conditions. The field of view is moved to acquire SEM images until a total of 1,000 to 3,000 carbon nanotubes can be observed.

[0041] Software: SEM images are analyzed using image analysis software such as "WinROOF2015" (Mitani Shoji), and the absolute maximum length and skeletal length of each carbon nanotube are calculated. Linearity is calculated using the following formula: Linearity = Absolute maximum length / Skeleton length The absolute maximum length is the distance between the two most distant points among the target pixel group (i.e., the pixel group derived from that single carbon nanotube). The skeletal length is the length of the free curve made up of the target pixel group.

[0042] Next, for each field of view of the SEM image, the number a of carbon nanotubes with a skeleton length of 1 μm or more is calculated, and the number b of carbon nanotubes with a skeleton length of 1 μm or more and a linearity of 0.9 or more is calculated. The linearity index is calculated using the following formula: Linearity index (%) = (b / a) × 100. Specifically, the linearity index is measured according to the method described in the Examples.

[0043] It is more preferable that the carbon nanotube dispersion composition satisfies the following (3): (3) A Raman spectrum of a coating film of the carbon nanotube dispersion composition has a peak intensity 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 defined as D, the G / D ratio is 1.0 to 20.0.

[0044] The G / D ratio of the coating film of the carbon nanotube dispersion composition is preferably 1.0 or more, preferably 1.1 or more, more preferably 1.3 or more, and even more preferably 1.7 or more. A high G / D ratio indicates high crystallinity of the carbon nanotubes. Highly crystalline carbon nanotubes have the advantage of contributing to conductivity in secondary batteries. Highly crystalline carbon nanotubes tend to maintain the linearity index in the carbon nanotube dispersion composition, further increasing linearity and enabling the effects described above to be more fully achieved.

[0045] The G / D ratio of the coating film of the carbon nanotube dispersion composition is preferably 20 or less, more preferably 10 or less, even more preferably 8.0 or less, and may be 7.0 or less, 5.0 or less, or 2.0 or less. When the G / D ratio of the coating film of the carbon nanotube dispersion composition is within this range, the contact area of ​​one carbon nanotube per one particle of active material in the electrode film tends to be large, thereby further improving the conductivity of the secondary battery. Furthermore, as the crystallinity of the carbon nanotubes increases, the carbon nanotubes themselves become harder, and the fiber length of the carbon nanotubes in the carbon nanotube dispersion composition decreases due to breakage, making it difficult to maintain the linearity index. Furthermore, preventing breakage of the carbon nanotubes can complicate the management of the dispersion process. From the viewpoint of providing the carbon nanotubes with appropriate flexibility, the G / D ratio of the coating film of the carbon nanotube dispersion composition is particularly preferably 8.0 or less. For example, the G / D ratio of the coating film of the carbon nanotube dispersion composition may be 1.0 or more and 20 or less, 1.1 or more and 10 or less, or 1.3 or more and 8.0 or less, or 1.0 or more and 7.0 or less, 1.0 or more and 5.0 or less, or 1.0 or more and 2.0 or less.

[0046] In the present disclosure, the G / D ratio of the coating film of the carbon nanotube dispersion composition is a value measured by the following procedure.

[0047] First, the carbon nanotube dispersion composition is applied to a substrate and dried to obtain a coating film. Drying may be carried out at a temperature sufficient to remove volatile components, which may be adjusted appropriately depending on the type of solvent, and may be, for example, 100°C to 200°C. The thickness of the coating film may be sufficient to allow measurement of the Raman spectrum, and may be, for example, 1 to 10 μm. The Raman spectrum of the obtained coating film is measured, and the G / D ratio is calculated. Specifically, the method for measuring the G / D ratio of the coating film of the carbon nanotube dispersion composition follows the measurement method in the Examples.

[0048] It is more preferable that the carbon nanotube dispersion composition satisfies the following (4): (4) After freeze-drying the carbon nanotube dispersion composition, the powder that has passed through a 60 μm mesh has a BET specific surface area relative to the mass of carbon nanotubes of 50 to 130 m ２ / g.

[0049] The BET specific surface area relative to the mass of carbon nanotubes of the carbon nanotube powder derived from the carbon nanotube dispersion composition is 50 m ２ / g or more is preferable, and 60m ２ / g or more is more preferable, and 65m ２ / g or more is more preferable. In these ranges, the carbon nanotubes in the carbon nanotube dispersion composition are expected to have a small average outer diameter, resulting in increased conductivity, and battery performance can be further improved. Furthermore, the fiber length of the carbon nanotubes per volume is expected to be long, resulting in increased linearity, and battery performance can be further improved with a small amount of carbon nanotubes in the electrode film.

[0050] The BET specific surface area relative to the mass of carbon nanotubes of the carbon nanotube powder derived from the carbon nanotube dispersion composition is 130 m ２ / g or less is preferable, and 125m ２ / g or less is more preferable, and 120m ２ / g or less is even more preferable. Within these ranges, aggregation of carbon nanotubes in the carbon nanotube dispersion composition is suppressed, the linearity of the carbon nanotubes is maintained in the electrode film, and battery performance can be further improved. Furthermore, even if the number of carbon nanotubes per volume is reduced, since the carbon nanotubes retain their linearity, a single carbon nanotube can contact multiple particles of the active material in the electrode film to maintain a conductive path, thereby contributing more to battery performance.

[0051] When the BET specific surface area relative to the mass of the carbon nanotubes in the carbon nanotube powder is within these ranges, the workability of dispersing the carbon nanotube raw material in a solvent is improved, and a carbon nanotube dispersion composition with good dispersibility can be obtained. By using a carbon nanotube dispersion composition with good dispersibility, the distribution of carbon nanotubes in the electrode film becomes more uniform, and each carbon nanotube comes into contact with a plurality of particles of a larger number of active materials, ensuring conductive paths and contributing to improved battery performance.

[0052] For example, the BET specific surface area relative to the mass of carbon nanotubes of the carbon nanotube powder derived from the carbon nanotube dispersion composition is 50 m ２ / g or more 130m ２ / g or less, 60m ２ / g or more 125m ２ / g or less, or 65m ２ / g or more 120m ２ / g or less. These ranges are preferred because they do not cause deterioration in battery performance due to excessive aggregation or over-dispersion.

[0053] In the present disclosure, the BET specific surface area of ​​the carbon nanotube powder derived from the carbon nanotube dispersion composition is a value measured by the following procedure.

[0054] 100 mL of the carbon nanotube dispersion composition is frozen in a -95°C ethanol bath for 5 hours using a freeze dryer (for example, FDU-1200 / UT-4000 manufactured by Tokyo Rikakikai Co., Ltd.), and then dried under reduced pressure at 10 to 30 Pa for 20 hours to obtain carbon nanotube powder. The obtained carbon nanotube powder is passed through a 60 μm mesh and then the BET specific surface area is measured. Specifically, the BET specific surface area of ​​the carbon nanotube powder derived from the carbon nanotube dispersion composition is measured according to the measurement method in the Examples.

[0055] (Carbon Nanotubes) It is more preferable that the carbon nanotubes contained in the carbon nanotube dispersion composition are specified by the following characteristics. The carbon nanotubes have a cylindrical shape formed by rolling planar graphite. The carbon nanotubes may be either single-walled carbon nanotubes or multi-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is rolled. Multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are rolled. The side walls of the carbon nanotubes do not have to have a graphite structure. For example, carbon nanotubes having side walls with an amorphous structure can also be used as carbon nanotubes. Multi-walled carbon nanotubes are preferably used from the viewpoint of suitability for industrial mass production. Multi-walled carbon nanotubes are also preferable from the viewpoint of dispersing the carbon nanotubes so that the average outer diameter and linearity index satisfy the desired ranges. When multi-walled carbon nanotubes are used, the carbon nanotubes may be mixed with single-walled carbon nanotubes.

[0056] The number of walls of the multi-walled carbon nanotube is preferably 3 to 30, more preferably 3 to 20, and even more preferably 3 to 10.

[0057] The shape of the carbon nanotubes is not particularly limited as long as the average outer diameter and linearity index satisfy the desired ranges. Examples of such shapes include various shapes including needle-like, cylindrical tube-like, fishbone-like (fishbone or cup-stacked), and coil-like. Among these, from the viewpoint of linearity, the shape of the carbon nanotubes is preferably needle-like or cylindrical tube-like. The carbon nanotubes may have a single shape or a combination of two or more shapes. When highly flexible carbon nanotubes such as fishbone-like and coil-like are included, it is sufficient that the average outer diameter and linearity index of the carbon nanotubes contained in the carbon nanotube dispersion composition as a whole satisfy the requirements.

[0058] Examples of carbon nanotube forms include, but are not limited to, graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes may have any of these forms alone or in combination.

[0059] The average fiber length of the carbon nanotubes contained in the carbon nanotube dispersion composition is preferably 1 to 5 μm, and more preferably 1 to 3.5 μm. To measure the fiber length of the carbon nanotubes, the CNT dispersion composition is diluted with a solvent so that the CNT concentration is 0.048 mass%, and then several μL of the diluted dispersion composition is spray-coated onto a mica substrate and dried 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 when preparing the CNT dispersion composition.

[0060] The SEM image is analyzed using image analysis software such as "WinROOF2015" (manufactured by Mitani Shoji Co., Ltd.), and the skeletal length of one carbon nanotube is calculated as the fiber length. The average fiber length is calculated by counting the fiber lengths of 1,000 to 3,000 carbon nanotubes.

[0061] The maximum fiber length of the carbon nanotubes contained in the carbon nanotube dispersion composition is preferably 20 μm or less, and more preferably 10 μm or less. The maximum fiber length of the carbon nanotubes can be measured by image analysis using the same method as for evaluating the average fiber length.

[0062] (Carbon nanotube raw material) The carbon nanotube dispersion composition can be obtained using a carbon nanotube raw material. Below, several examples of carbon nanotube raw materials that can be used in the method for producing a carbon nanotube dispersion composition will be described. The carbon nanotube dispersion composition according to the embodiment can achieve its effects using carbon nanotubes obtained from various sources. In the following description, carbon nanotube raw material refers to carbon nanotubes in a raw material state before being added to the carbon nanotube dispersion composition.

[0063] The average outer diameter of the carbon nanotube raw material is preferably 50 nm or less, more preferably 40 nm or less, or even more preferably 20 nm or less. Within these ranges, the amount of dispersant relative to the carbon nanotube raw material can be reduced, thereby further increasing the packing density of the active material in the electrode film. For example, the average outer diameter of the carbon nanotube raw material may be 1 to 50 nm, 5 to 40 nm, or 7 to 20 nm. By using a carbon nanotube raw material within these ranges, a carbon nanotube dispersion composition having an average outer diameter and linearity index within a more suitable range can be obtained.

[0064] The standard deviation of the outer diameter of the carbon nanotube raw material is preferably 1 to 5 nm, and more preferably 1 to 4 nm.

[0065] To measure the average outer diameter of the carbon nanotube raw material, first, carbon nanotubes are observed and photographed using a scanning electron microscope. Next, 300 carbon nanotubes are randomly selected from the photograph and their outer diameters are measured. Next, the average outer diameter (nm) of the carbon nanotube raw material is calculated as the number average of the outer diameters.

[0066] The linearity index of the carbon nanotube raw material may be 40 to 90%, 50 to 90%, 60 to 90%, 50 to 80%, or 60 to 70%. By using a carbon nanotube raw material in this range, a carbon nanotube dispersion composition containing carbon nanotubes exhibiting an average outer diameter and linearity index in a more suitable range can be obtained.

[0067] The linearity index of the carbon nanotube raw material is a value determined as described above using the same procedure as for the sample taken out from the carbon nanotube dispersion composition.

[0068] The carbon nanotube raw material has 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 defined as D, the G / D ratio may be 0.8 to 100, 1.1 to 10, or 1.7 to 7. By using a carbon nanotube raw material within these ranges, it is possible to obtain a carbon nanotube dispersion composition containing carbon nanotubes exhibiting a G / D ratio within a more suitable range.

[0069] The G / D ratio of the carbon nanotube raw material is a value determined by the same procedure as for the coating film of the carbon nanotube dispersion composition described above.

[0070] The BET specific surface area of ​​the carbon nanotube raw material is 100 to 1000 m ２ / g, 150-800m ２ / g, or 200 to 500 m ２ By using a carbon nanotube raw material in these ranges, it is possible to obtain a carbon nanotube dispersion composition containing carbon nanotubes exhibiting a BET specific surface area in a more suitable range. The BET specific surface area of ​​the carbon nanotube raw material may be 1000 m ２ / g or less, 800m ２ / g or less, or 500m ２ / g or less is preferable, and 100m ２ / g or more, 120m ２ / g or more, or 150m ２ Within these ranges, the dispersion treatment can be simplified when dispersing the carbon nanotube raw material in a solvent, and dispersibility can be obtained with a small amount of dispersant, so that the packing density of the active material in the electrode film can be increased.

[0071] The BET specific surface area of ​​the carbon nanotube raw material is a value determined by the same procedure as for the carbon nanotube powder derived from the carbon nanotube dispersion composition described above.

[0072] The carbon nanotube raw materials may be used alone or in combination of two or more. When two or more carbon nanotube raw materials are used, it is preferable that at least some of the two or more carbon nanotube raw materials have a BET specific surface area within the above-mentioned range, but it is even more preferable that all of the two or more carbon nanotube raw materials have a BET specific surface area within the above-mentioned range. Furthermore, when a mixed powder of all of the two or more carbon nanotube raw materials is used, it is even more preferable that the mixed powder has a BET specific surface area within the above-mentioned range.

[0073] The average fiber length of the carbon nanotube raw material is preferably 1 to 5 μm, and more preferably 1 to 3.5 μm. The fiber length of the carbon nanotube raw material can be measured by dispersing the carbon nanotube raw material 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 image analysis software such as "WinROOF2015" (manufactured by Mitani Shoji), and the skeletal length of each carbon nanotube is calculated as the fiber length. The average fiber length is calculated by counting the fiber lengths of 1,000 to 3,000 carbon nanotubes.

[0074] The maximum fiber length of the carbon nanotube raw material is preferably 20 μm or less, more preferably 10 μm or less. The maximum fiber length of the carbon nanotube raw material can be measured by dispersing the carbon nanotube raw material in toluene using an ultrasonic homogenizer, then depositing the carbon nanotubes on a mica substrate, and then subjecting the resulting carbon nanotubes to SEM observation and image analysis.

[0075] The volume resistivity of the carbon nanotube raw material is 1.0 × 10 －２ ~3.0 x 10 －２ Preferably, the resistance is Ω cm, and 1.0×10 －２ ~2.0 x 10 －２It is more preferable that the volume resistivity of the carbon nanotubes is Ω cm. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (for example, Loresta GP Powder Resistivity Measuring System "MCP-PD-51" manufactured by Mitsubishi Chemical Analytech Co., Ltd.). It is even more preferable that the volume resistivity of the carbon nanotubes contained in the carbon nanotube dispersion composition satisfies the above range, similar to that of the carbon nanotube raw material.

[0076] The carbon purity of the carbon nanotube raw material is expressed as the carbon atom content (%) in the carbon nanotube raw material. The carbon purity is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, relative to 100% by mass of the carbon nanotube raw material. It is even more preferable that the carbon purity of the carbon nanotubes contained in the carbon nanotube dispersion composition satisfies the above range, similar to that of the carbon nanotube raw material.

[0077] The amount of metal contained in the carbon nanotube raw material is preferably less than 10% by mass, more preferably less than 5% by mass, even more preferably less than 2% by mass, and even more preferably less than 1% by mass, relative to 100% by mass of the carbon nanotube raw material. Examples of metals contained in the carbon nanotube raw material include metals or metal oxides used as catalysts during the synthesis of the carbon nanotube raw material. Specific examples include at least one metal selected from the group consisting of cobalt, nickel, aluminum, magnesium, silica, manganese, molybdenum, etc., its metal oxide, and composite oxides thereof. It is even more desirable if the amount of metal in the carbon nanotubes contained in the carbon nanotube dispersion composition satisfies the above range, similar to the carbon nanotube raw material.

[0078] Carbon nanotubes usually exist as secondary particles. In the carbon nanotube raw material, the shape of the secondary particles of carbon nanotubes may be, for example, a state in which general primary carbon nanotubes are intricately entangled, or may be an aggregate of linearly arranged carbon nanotubes.

[0079] The shape of the secondary particles of the carbon nanotubes contained in the carbon nanotube dispersion composition may maintain the shape of the carbon nanotube raw material. For example, if the shape of the secondary particles of the carbon nanotubes contained in the carbon nanotube dispersion composition is a linear aggregate, the average outer diameter and linearity index of the carbon nanotubes can be more appropriately controlled within predetermined ranges.

[0080] The carbon nanotube raw material may be a surface-treated carbon nanotube, a carbon nanotube derivative to which a functional group such as a carboxyl group has been added, or a carbon nanotube raw material encapsulating an organic compound, a metal atom, or a substance such as fullerene.

[0081] The carbon nanotube raw material may be carbon nanotubes produced by any method. The carbon nanotube raw material can generally be produced by, but is not limited to, laser ablation, arc discharge, thermal CVD, plasma CVD, and combustion. For example, the carbon nanotube raw material can be produced by catalytically reacting a carbon source with a catalyst at 500 to 1000°C in an atmosphere with an oxygen concentration of 1% by volume or less. The carbon source may be at least one of a hydrocarbon and an alcohol.

[0082] Any conventionally known raw material can be used as the raw material gas serving as the carbon source for the carbon nanotube raw material. For example, hydrocarbons typified by methane, ethylene, propane, butane, and acetylene, carbon monoxide, and alcohols can be used as the carbon-containing raw material gas, but they are not limited to these. In particular, from the viewpoint of ease of use, it is desirable to use at least one of hydrocarbons and alcohols as the raw material gas.

[0083] Depending on the manufacturing method of the carbon nanotube raw material, when the heat treatment temperature is increased, the crystallinity of the carbon nanotubes tends to increase and the carbon nanotubes tend to become hard. In order to make the hardness of the carbon nanotubes appropriate and to prevent the carbon nanotubes from breaking during the dispersion treatment in the manufacturing of the carbon nanotube dispersion composition, the heat treatment temperature in the manufacturing of the carbon nanotubes may be relatively low, for example, 1000°C or lower.

[0084] A certain fiber length is required to obtain linear carbon nanotubes. However, if the crystallinity of carbon nanotubes is further increased by high-temperature heat treatment, the tendency of the carbon nanotubes to break increases. From this perspective, it is preferable to use a relatively low heat treatment temperature in the production of carbon nanotubes. In this case, the resulting carbon nanotube raw material may contain single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both. From the viewpoint of controlling the crystallinity and fiber length of carbon nanotubes, producing multi-walled carbon nanotubes is easier and more industrially advantageous.

[0085] (Dispersant) The dispersant can be used without any particular limitation as long as it can disperse and stabilize the carbon nanotubes. For example, at least one of surfactants and resin-type dispersants can be used. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric. Depending on the properties required for dispersing the carbon nanotubes, a suitable type of dispersant can be used in a suitable amount. In one embodiment, it is preferable to use a resin-type dispersant.

[0086] When an anionic surfactant is selected, its type is not particularly limited. Specific examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfonates, alkylnaphthalenesulfonates, dialkylsulfonates, dialkylsulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalenesulfonate-formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. 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-naphthalenesulfonate-formalin condensates.

[0087] Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts, and 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.

[0088] Amphoteric surfactants include, but are not limited to, aminocarboxylates.

[0089] 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, particularly, but not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

[0090] The surfactant to be selected is not limited to a single surfactant. Two or more surfactants can also be used in combination. 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 use an appropriate amount for each surfactant component. A combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant preferably contains a polycarboxylate. The nonionic surfactant preferably contains polyoxyethylene phenyl ether.

[0091] Specific examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose, and salts thereof), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, polyacrylonitrile polymers (copolymers of polyacrylonitrile and acrylic acid, and the like), poly(meth)acrylic acid or salts thereof, poly(meth)acrylate, and nitrile rubbers (acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, copolymers of hydrogenated nitrile rubber and hydrogenated butadiene acrylonitrile, and the like). Polymers in which other substituents have been introduced into a portion of these polymers, modified polymers, and the like may also be used. Particularly preferred are methyl cellulose, ethyl cellulose, carboxymethyl cellulose, or salts thereof, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyacrylonitrile polymers, copolymers of acrylonitrile and acrylic acid, (meth)acrylic acid, or salts thereof, hydrogenated acrylonitrile butadiene rubber, and copolymers of hydrogenated nitrile rubber and hydrogenated butadiene acrylonitrile. Resin-type dispersants may be used alone or in combination of two or more. The weight-average molecular weight (Mw) of the resin-type dispersant is preferably 5,000 to 250,000, and more preferably 10,000 to 150,000.

[0092] In some embodiments, the carbon nanotube dispersion composition may further include a basic compound. The basic compound may be either an organic compound or an inorganic compound, but a basic inorganic compound is preferred because it simplifies the control of the stability of the dispersion system. Examples of basic inorganic compounds include inorganic bases and inorganic metal salts.

[0093] As inorganic bases and inorganic metal salts, compounds containing at least one of alkali metals and alkaline earth metals are preferred. Specific examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates, which contain at least one of alkali metals and alkaline earth metals. Among these, chlorides, hydroxides, and carbonates containing at least one of alkali metals and alkaline earth metals are preferred because they can easily supply cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate is more preferred.

[0094] In some embodiments, the carbon nanotube dispersion composition may further contain other optional components, such as an amine compound, a wetting agent, an antifoaming agent, a surfactant, a pH adjuster, a wetting and penetrating agent, an antioxidant, a preservative, an antifungal agent, a leveling agent, or a thickener, as needed. The carbon nanotube dispersion composition may also contain conductive materials and polymeric components other than carbon nanotubes, as long as the object of the present invention is not impaired. These optional components can be added at any timing, such as before, during, or after the dispersion treatment of the carbon nanotube dispersion composition.

[0095] In some embodiments, the carbon nanotube dispersion composition may further include a defoaming agent. Any component having a defoaming effect, such as a commercially available defoaming agent, a wetting agent, a hydrophilic organic solvent, or a water-soluble organic solvent, may be used as the defoaming agent. One type of defoaming agent may be used, or two or more types may be used in combination.

[0096] Examples of the defoaming agent include alcohol-based agents such as 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; fatty acid ester-based agents such as diethylene glycol laurate, glycerin monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trilaurate, and the like. oleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural waxes, etc., amide-based; polyoxyalkylene amide, acrylate polyamine, etc., phosphate ester-based; tributyl phosphate, sodium octyl phosphate, etc., metal soap-based; aluminum stearate, calcium oleate, etc., oil-based; animal and vegetable oils, sesame oil, castor oil, etc., mineral oil-based; kerosene, paraffin, etc., silicone-based; dimethyl silicone oil, silicone paste, silicone emulsion, organically modified polysiloxane, fluorosilicone oil, etc.

[0097] In some embodiments, the carbon nanotube dispersion composition may further contain a thickener. Examples of thickeners include polysaccharides such as carboxymethyl cellulose or salts thereof, polyvinylidene fluoride, and derivatives thereof. Examples of commercially available thickeners include carboxymethyl cellulose #1190 (manufactured by Daicel FineChem Co., Ltd.). One type of thickener may be used, or two or more types may be used in combination.

[0098] (Solvent) In some embodiments, the solvent is not particularly limited as long as it is capable of dispersing carbon nanotubes. The solvent may be, for example, a mixed solvent containing one or more of water and a water-soluble organic solvent. The solvent preferably contains at least water. When the solvent contains water, the water content may be 50 parts by mass or more, 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 98 parts by mass or more relative to the total solvent (100 parts by mass), with the remainder being a water-soluble organic solvent. Alternatively, the total solvent (100 parts by mass) may be water. In one embodiment, it is preferable that the solvent contains an amide organic solvent from the viewpoint of affinity for carbon nanotubes. When the solvent contains an amide organic solvent, the content of the amide organic solvent may be 50 parts by mass or more, 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 98 parts by mass or more relative to the total solvent (100 parts by mass). Alternatively, the total solvent (100 parts by mass) may be an amide organic solvent.

[0099] Examples of the water-soluble organic solvent include alcohols (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.), polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene ...propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,Examples of suitable water-soluble organic solvents include amide-based organic solvents (e.g., 3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide-based solvents (e.g., dimethyl sulfoxide), sulfone-based solvents (e.g., hexamethylphosphorotriamide, sulfolane, etc.), lower ketone-based solvents (e.g., acetone, methyl ethyl ketone, etc.), and others, such as tetrahydrofuran, urea, and acetonitrile. In particular, when used in a positive electrode composite slurry, it is preferable to use an amide-based organic solvent as the water-soluble organic solvent. Among these, from the viewpoints of affinity for carbon nanotubes and solubility of the fluororesin binder resin, it is preferable to use at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP). The water-soluble organic solvent may be used alone or in combination of two or more.

[0100] (Characteristics of Carbon Nanotube Dispersed Composition) The carbon nanotube dispersed composition may be characterized by the complex modulus, phase angle, or a combination thereof at 25° C. and a frequency of 10 Hz, as determined by dynamic viscoelasticity measurement.

[0101] The carbon nanotube dispersion composition has a complex modulus of elasticity measured by dynamic viscoelasticity measurement at 25°C and a frequency of 10 Hz of preferably 4 Pa ​​or more, more preferably 10 Pa or more, even more preferably 20 Pa or more, and even more preferably 30 Pa or more. It is also preferably 250 Pa or less, more preferably 200 Pa or less, even more preferably 100 Pa or less, even more preferably 80 Pa or less, and particularly preferably 47 Pa or less. The carbon nanotube dispersion composition has a complex modulus of elasticity measured by dynamic viscoelasticity measurement at 25°C and a frequency of 10 Hz of preferably 4 Pa ​​or more and 250 Pa or less, 4 Pa ​​or more and 200 Pa or less, 10 Pa or more and 100 Pa or less, 20 Pa or more and 80 Pa or less, or 20 Pa or more and 47 Pa or less.

[0102] The carbon nanotube dispersion composition preferably has a phase angle of 3° or more, more preferably 8° or more, even more preferably 12° or more, and even more preferably 16° or more, as measured by dynamic viscoelasticity measurement at 25°C and a frequency of 10 Hz. It is also preferably 60° or less, more preferably 45° or less, even more preferably 35° or less, and even more preferably 31° or less. The carbon nanotube dispersion composition preferably has a phase angle of 3° or more and 60° or less, 8° or more and 60° or less, 16° or more and 60° or less, or 16° or more and 35° or less, as measured by dynamic viscoelasticity measurement at 25°C and a frequency of 10 Hz.

[0103] The carbon nanotube dispersion composition may have a complex modulus and a phase angle that satisfy the above ranges at 25° C. and a frequency of 10 Hz as determined by dynamic viscoelasticity measurement.

[0104] The complex modulus and phase angle can be evaluated by dynamic viscoelasticity measurement. The better the dispersibility of carbon nanotubes and the lower the viscosity of the carbon nanotube dispersion composition, the smaller the complex modulus of the carbon nanotube dispersion composition tends to be. Furthermore, the phase angle refers to the phase shift of the stress wave when the strain applied to the carbon nanotube dispersion composition is a sine wave. In a purely elastic body, the sine wave will be 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 will be advanced by 90°. In a typical viscoelasticity measurement sample, the phase angle will be a sine wave greater than 0° and less than 90°. If the dispersibility of carbon nanotubes in the carbon nanotube dispersion composition is good, the phase angle will approach 90°, which is the phase angle of a purely viscous body.

[0105] When the fiber length of the carbon nanotubes in the carbon nanotube dispersion composition is long, even if the dispersion is good, the carbon nanotubes themselves have structural viscosity, which may result in a high complex modulus. However, a carbon nanotube dispersion composition having complex modulus and phase angle values ​​within the above ranges has good dispersed particle size and dispersibility of the carbon nanotubes. Therefore, the carbon nanotube dispersion composition can be suitably used as a carbon nanotube dispersion composition for non-aqueous electrolyte secondary batteries.

[0106] The complex modulus and phase angle of the carbon nanotube dispersion composition at 25° C. and a frequency of 10 Hz obtained by dynamic viscoelasticity measurement are determined according to the measurement methods used in the examples.

[0107] The cumulative particle size D50 of the carbon nanotube dispersion composition is preferably 300 to 7000 nm, and more preferably 700 to 3000 nm. The cumulative particle size D50 of the carbon nanotube dispersion composition can be measured on a volume basis using a particle size distribution analyzer (for example, Partial LA-960V2, manufactured by Horiba, Ltd.).

[0108] The pH of the carbon nanotube dispersion composition may be 3 to 6. The pH of the carbon nanotube dispersion composition is preferably 4 to 6, and more preferably 4 to 5. The pH of the carbon nanotube dispersion composition can be measured using a pH meter (for example, pH METER F-52, manufactured by Horiba, Ltd.).

[0109] The viscosity of the carbon nanotube dispersion composition, measured at 25°C using a Brookfield viscometer at 60 rpm, is preferably 10 mPa·s or more and less than 10,000 mPa·s, and more preferably 10 mPa·s or more and less than 2,000 mPa·s.

[0110] In one embodiment, the content of carbon nanotubes in the carbon nanotube dispersion composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the carbon nanotube dispersion composition. Within these ranges, when preparing a composite slurry, the carbon nanotube dispersion composition can be more appropriately mixed and dispersed with the active material at a ratio that results in multiple particles of the active material per one carbon nanotube.

[0111] The content of carbon nanotubes in the carbon nanotube dispersion composition is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and may be 3 parts by mass or less, relative to 100 parts by mass of the carbon nanotube dispersion composition. Within these ranges, the dispersibility of the carbon nanotube dispersion composition can be maintained better. Furthermore, because the dispersibility is maintained in the carbon nanotube dispersion composition, when an electrode film is provided using the composite slurry, the carbon nanotubes maintain linearity in the electrode film, increasing the number of active material particles with which one carbon nanotube comes into contact, and further improving the performance of the secondary battery.

[0112] For example, the content of carbon nanotubes in the carbon nanotube dispersion composition is preferably 0.2 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the carbon nanotube dispersion composition.

[0113] In one embodiment, the amount of dispersant in the carbon nanotube dispersion composition is, from the viewpoint of dispersion stability, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 40 parts by mass or more, and may be 60 parts by mass or more, relative to 100 parts by mass of carbon nanotubes. From the viewpoint of dispersion stability, the amount of dispersant in the carbon nanotube dispersion composition is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 120 parts by mass or less, and may be 100 parts by mass or less, relative to 100 parts by mass of carbon nanotubes. For example, the amount of dispersant in the carbon nanotube dispersion composition is preferably 10 to 300 parts by mass, more preferably 40 to 200 parts by mass, even more preferably 60 to 120 parts by mass, and may be 70 to 100 parts by mass, relative to 100 parts by mass of carbon nanotubes.

[0114] In one embodiment, the nonvolatile content of the carbon nanotube dispersion composition may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more, relative to 100% by mass of the carbon nanotubes, with the remainder being solvent. Here, the nonvolatile content is the mass of a dried coating film of the carbon nanotube dispersion composition.

[0115] When the carbon nanotube dispersion composition contains components other than the carbon nanotubes, dispersant, and solvent, the amount of the other components in the carbon nanotube dispersion composition may be 0.1 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 3 parts by mass relative to 100 parts by mass of the carbon nanotube dispersion composition.

[0116] When the carbon nanotube dispersion composition contains a basic compound, the amount of the basic compound in the carbon nanotube dispersion composition may be 0.01 to 1 part by mass, 0.02 to 0.5 parts by mass, or 0.04 to 0.1 parts by mass, relative to 100 parts by mass of the carbon nanotube dispersion composition. When the carbon nanotube dispersion composition contains a basic compound, the amount of the basic compound in the carbon nanotube dispersion composition may be 1 to 20 parts by mass, 2 to 10 parts by mass, or 4 to 8 parts by mass, relative to 100 parts by mass of the dispersant.

[0117] When the carbon nanotube dispersion composition contains an antifoaming agent, the amount of the antifoaming agent in the carbon nanotube dispersion composition may be 0.01 to 1 part by mass, 0.02 to 0.5 parts by mass, or 0.04 to 0.1 parts by mass relative to 100 parts by mass of the carbon nanotube dispersion composition.

[0118] (Method for producing carbon nanotube dispersion composition) The method for producing the carbon nanotube dispersion composition is not particularly limited, and can be carried out by mixing the carbon nanotube raw material, dispersant, and solvent all at once or in portions. The carbon nanotube raw material can be one described above. Furthermore, when a dispersion treatment is carried out after mixing, it is preferable to carry out the dispersion treatment so that the carbon nanotubes in the resulting carbon nanotube dispersion composition have a predetermined average outer diameter and linearity index. The dispersing device used for the dispersion treatment is not particularly limited.

[0119] As the dispersing device, a dispersing machine that is commonly used for dispersing pigments, etc., can be used. For example, mixers such as a Disper, a Homomixer, and a Planetary Mixer; homogenizers (such as "Advanced Digital Sonifer (registered trademark)" Model 1 manufactured by BRANSON); 450DA, M Technique's "Clearmix", PRIMIX's "Filmix", etc., Silverson's "Abramix", etc.); paint conditioner (manufactured by Red Devil); colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"); cone mills (IKA's "Cone Mill MKO", etc.); media-type dispersers including ball mills, sand mills (Shinmaru Enterprises' "Dynomill", etc.), attritors, pearl mills (Eirich's "DCP Mill", etc.), and Coball mills; wet jet mills (Jenus's "Jenus PY", Sugino Machine's "Starburst", Nanomizer's "Nanomizer", etc.), M Technique's "Clear SS-5", Nara Kikai's "MICROS", etc.; and other roll mills, etc., but are not limited thereto.

[0120] In some embodiments, the dispersion treatment for preparing the carbon nanotube dispersion composition is preferably carried out using a homogenizer, a media-type disperser, a media-less disperser, or a combination thereof. The dispersion treatment using a homogenizer is preferably carried out under a high pressure of, for example, 60 to 150 MPa. When the dispersion treatment is carried out using a media-type disperser, beads such as zirconia beads are preferably used. The diameter of the beads used is preferably smaller than 1.25 mm, and more preferably 1.0 mm or less.

[0121] In the dispersion treatment, a homogenizer is preferably used, and the homogenizer may be used alone or in combination with at least one of a media-type disperser and a media-less disperser. In the dispersion treatment, the dispersion treatment may be performed without using a media-type disperser so that the carbon nanotubes are not broken by collision between the media and the carbon nanotubes. In this case, the dispersion treatment may be performed using a homogenizer alone or a combination of a homogenizer and a media-less disperser. For example, by performing wet kneading using a media-less disperser before and after the dispersion treatment using the homogenizer, the fiber length of the carbon nanotubes is maintained, and carbon nanotubes having a linearity index within a more appropriate range can be included in the dispersion composition.

[0122] Examples of commercially available homogenizers include, but are not limited to, "R-MODEL such as R5, G-MODEL such as G5" manufactured by MST Corporation, "STARBURST" manufactured by Sugino Machine Ltd., and "OMEGA" manufactured by Ashizawa Finetech Co., Ltd. Examples of commercially available media-less dispersers include, but are not limited to, "3L Kneader" manufactured by Inoue Manufacturing Co., Ltd., "Planetary Mixer" manufactured by Inoue Manufacturing Co., Ltd., "Plastomill" manufactured by Toyo Seiki Seisakusho Co., Ltd., "Twin-screw Kneading Extruder PCM30" manufactured by Ikegai Corporation, and "MIXING ROLL MILL" manufactured by Inoue Manufacturing Co., Ltd.

[0123] <Carbon nanotube resin composition> According to some embodiments, a carbon nanotube resin composition is provided. The carbon nanotube resin composition includes carbon nanotubes, a dispersant, a solvent, and a binder. The carbon nanotube resin composition may include a carbon nanotube dispersion composition and a binder. The binder will be described below.

[0124] (Binder) The binder is a resin that binds substances such as carbon nanotubes together.

[0125] Examples of binders 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, or the like as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Examples of fluororesins include polytetrafluoroethylene. The binder may be a modified product, mixture, or copolymer of the above resins. Among these, it is preferable that the binder contains at least one selected from the group consisting of carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0126] The carboxymethyl cellulose used as a binder preferably has a high viscosity. For example, the viscosity of a 1% aqueous solution of carboxymethyl cellulose is preferably 500 to 6,000 mPa·s, and more preferably 1,000 to 3,000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethyl cellulose can be measured using a Brookfield viscometer rotor at 25°C and a rotation speed of 60 rpm.

[0127] The carboxymethyl cellulose used as the binder preferably has a high degree of etherification, for example, a degree of etherification of preferably 0.6 to 1.5, and more preferably 0.8 to 1.2.

[0128] The styrene-butadiene rubber used as the binder resin may be any styrene-butadiene rubber commonly used as a binder for electrodes, as long as it is an oil-in-water emulsion. In one embodiment, the binder preferably contains an emulsion of styrene-butadiene rubber. For example, "TRD2001" manufactured by JSR Corporation can be suitably used.

[0129] The type and amount of the binder are appropriately selected according to the properties of the carbon nanotubes and the coexisting substances such as the active material, etc. In the carbon nanotube resin composition, the content of the binder may be 1 to 100 parts by mass, 5 to 500 parts by mass, or 10 to 30 parts by mass per part by mass of the carbon nanotubes.

[0130] The carbon nanotube resin composition contains carbon nanotubes, a dispersant, a solvent, and a binder, and can be obtained by mixing these together or in portions. In another example, the carbon nanotube resin composition contains a carbon nanotube dispersion composition and a binder, and can be obtained by mixing the binder with the carbon nanotube dispersion composition. In either method, it is preferable that the average outer diameter and linearity index of the carbon nanotubes in the obtained carbon nanotube resin composition satisfy the ranges described for the carbon nanotube dispersion composition.

[0131] For example, when mixing the carbon nanotube dispersion composition with the binder, it is advisable to use the dispersing device described for the carbon nanotube dispersion composition to prevent breakage of the carbon nanotubes during mixing, which allows the average outer diameter and linearity index of the carbon nanotubes in the carbon nanotube resin composition to be maintained within the predetermined ranges.

[0132] The carbon nanotube resin composition may further include additional optional components, which may be those described above in relation to the carbon nanotube dispersion composition.

[0133] <Assemble Slurry> According to some embodiments, a composite slurry is provided. The composite slurry includes carbon nanotubes, a dispersant, a solvent, a binder, and an active material. The composite slurry may include a carbon nanotube resin composition and an active material, or may include a carbon nanotube dispersion composition, a binder, and an active material. The active material will be described below.

[0134] (Active Material) Active materials are materials that are the basis of battery reactions. From the viewpoint of electromotive force, active materials are divided into positive electrode active materials and negative electrode active materials.

[0135] The positive electrode active material is not particularly limited, but may be metal compounds such as metal oxides and metal sulfides, and conductive polymers that can be doped or intercalated with lithium ions.

[0136] Examples of the oxide include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. ２ O ５ , V ６ O １３ , and TiO ２ transition metal oxide powders such as lithium nickel oxide, lithium cobalt oxide, and lithium manganate with a layered structure, lithium manganate with a spinel structure, and other composite oxide powders of lithium and transition metals; lithium iron phosphate-based materials which are phosphate compounds with an olivine structure; TiS ２ and transition metal sulfide powders such as FeS.

[0137] The positive electrode active material may be an organic compound. For example, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene may be used. The positive electrode active material may be a mixture of the inorganic and organic compounds.

[0138] The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, its alloys such as tin alloys, silicon alloys, and lead alloys, Li Ｘ Fe ２ O ３ , Li Ｘ Fe ３ O ４ , Li Ｘ WO ２(x is a number satisfying 0<x<1), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, graphite materials such as artificial graphite and natural graphite, including highly graphitized carbon materials, carbon materials such as carbon black, mesophase carbon black, resin-baked carbon materials, vapor-grown carbon fiber, and carbon fiber. These negative electrode active materials can be used singly or in combination.

[0139] In one embodiment, the negative electrode active material is preferably a silicon-based negative electrode active material, which is a negative electrode active material containing silicon such as a silicon alloy or lithium silicate.

[0140] Examples of silicon-based negative electrode active materials include so-called metallurgical grade silicon produced by reducing silicon dioxide with carbon; industrial grade silicon obtained by reducing impurities by treating metallurgical grade silicon with an acid or unidirectional solidification; high-purity silicon produced from silane obtained by reacting silicon and having different crystalline states such as high-purity single crystal, polycrystalline, and amorphous; and silicon obtained by highly purifying industrial grade silicon by a sputtering method, an EB vapor deposition (electron beam vapor deposition) method, or the like, and simultaneously adjusting the crystalline state and precipitation state.

[0141] Other examples include silicon oxide, which is a compound of silicon and oxygen, various alloys with silicon, and silicon compounds prepared by quenching the crystalline state of these by a method such as quenching, etc. Among these, a silicon-based negative electrode active material is preferred, which is a mixture of silicon oxide and silicon nanoparticles having a structure in which silicon nanoparticles are dispersed in silicon oxide, and the outside of the mixture is coated with a carbon film.

[0142] In one embodiment, the negative electrode active material may include, in addition to the silicon-based negative electrode active material, a carbon material such as a carbonaceous material, a graphitic carbonaceous material, or a graphitic material. Examples of the carbonaceous material include amorphous carbonaceous materials such as soft carbon and hard carbon. Examples of the graphitic material include artificial graphite and natural graphite, such as highly graphitized carbon materials. It is particularly preferable to use powders of graphitic materials such as artificial graphite and natural graphite.

[0143] The amount of the silicon-based negative electrode active material is preferably 3 to 50% by mass, and more preferably 5 to 25% by mass, when the amount of the carbon material such as artificial graphite or natural graphite is taken as 100% by mass.

[0144] In one embodiment, the BET specific surface area of ​​the active material is 0.1 to 10 m ２ / g is preferred, and 0.2 to 5m ２ / g is more preferable, and 0.3 to 3m ２ / g is more preferred.

[0145] In one embodiment, the average particle size of the active material is preferably in the range of 0.5 to 50 μm, and more preferably in the range of 2 to 20 μm. The "average particle size of the active material" described in this disclosure refers to the average value of particle diameters (major axes) of the active material measured using an electron microscope.

[0146] (Method for producing composite slurry) The composite slurry can be produced by various conventionally known methods. For example, a method of mixing an active material with a carbon nanotube resin composition, a method of mixing a binder and an active material with a carbon nanotube dispersion composition all at once or in separate portions, etc. The composite slurry may be obtained by mixing carbon nanotubes, a dispersant, a solvent, a binder, and an active material all at once or in separate portions.

[0147] Preferably, the composite slurry can be obtained by mixing the active material and binder with the carbon nanotube dispersion composition all at once or in portions. This method makes it possible to appropriately adjust the average outer diameter and linearity index of the carbon nanotubes in the carbon nanotube dispersion composition to fall within predetermined ranges, making it easier to control the dispersion conditions in the subsequent preparation of the composite slurry.

[0148] In one embodiment, to obtain a composite slurry, it is preferable to further perform a dispersion treatment after adding an active material to the carbon nanotube dispersion composition or the carbon nanotube resin composition. The dispersion device used for the dispersion treatment is not particularly limited. The composite slurry can be prepared using the dispersion device described above for the carbon nanotube dispersion composition.

[0149] In one embodiment, the amount of the active material in the composite slurry is preferably 20 to 90 parts by mass, more preferably 30 to 80 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of the composite slurry.

[0150] In one embodiment, the amount of carbon nanotubes in the composite slurry is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, even more preferably 0.1 to 1 part by mass, and even more preferably 0.15 to 0.5 parts by mass, relative to 100 parts by mass of the active material.

[0151] In one embodiment, the amount of binder in the composite slurry is preferably 0.1 to 30 mass %, more preferably 0.5 to 20 mass %, even more preferably 1 to 10 mass %, and even more preferably 1.5 to 5 mass %, relative to 100 parts by mass of the active material.

[0152] The amount of binder in the composite slurry may be more appropriately controlled depending on the type of binder. For example, the amount of carboxymethyl cellulose used as the binder is preferably 0.5 to 3.0% by mass, and more preferably 1.0 to 2.0% by mass, based on 100 parts by mass of the active material. The amount of styrene butadiene rubber used as the binder is preferably 0.5 to 3.0% by mass, and more preferably 1.0 to 2.0% by mass, based on 100% by mass of the active material. The amount of polyacrylic acid used as the binder is preferably 1 to 25% by mass, and more preferably 5 to 20% by mass, based on 100% by mass of the active material.

[0153] The composite slurry may further contain other additives. The other additives may be those described in the carbon nanotube dispersion composition above. For example, from the viewpoint of coatability onto a substrate, the composite slurry may additionally contain a thickener.

[0154] In one embodiment, the amount of solids in the composite slurry is preferably 30 to 90% by mass, more preferably 30 to 80% by mass, and more preferably 40 to 70% by mass, based on 100% by mass of the composite slurry. Here, the solids in the composite slurry are components that can form a coating film without volatilizing in the solvent removal step.

[0155] <Electrode Film> According to some embodiments, an electrode film is provided. The electrode film can be used in a secondary battery, such as a lithium-ion secondary battery. For example, the electrode film can be provided as an electrode mixture layer provided on a current collector in a secondary battery. The electrode film can be obtained by forming a mixture slurry into a film. For example, the electrode film may be a coated film obtained by applying the mixture slurry to a current collector and drying it.

[0156] The current collector on which the electrode film is provided is not particularly limited. It may be of a material and shape suitable for various secondary batteries and can be appropriately selected. For example, the current collector material may be metals such as aluminum, copper, nickel, titanium, and stainless steel, as well as alloys thereof. The current collector generally may be in the form of a flat foil, but current collectors with a roughened surface, perforated foils, and meshes may also be used.

[0157] The method for applying the composite slurry 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 painting. Drying methods that can be used include, but are not limited to, standing to dry, blowing dryers, hot air dryers, infrared heaters, and far-infrared heaters.

[0158] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the electrode film is generally 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0159] <Non-aqueous electrolyte secondary battery> According to some embodiments, a non-aqueous electrolyte secondary battery is provided. The non-aqueous electrolyte secondary battery may specifically be a lithium ion secondary battery. The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte. In the secondary battery, at least one of the positive electrode and the negative electrode includes an electrode film, and the electrode film may be an electrode film according to an embodiment. The electrode film according to an embodiment may be a coated film of a composite slurry according to an embodiment, or may be an electrode film obtained using the carbon nanotube dispersion composition or carbon nanotube resin composition according to an embodiment.

[0160] One or both of the positive electrode and the negative electrode may include an electrode film according to an embodiment. Furthermore, the inclusion of an electrode film according to an embodiment in the negative electrode can contribute to improvements in rate characteristics and cycle characteristics. For example, when a silicon-based active material is included in the negative electrode, cycle characteristics tend to deteriorate due to volume changes caused by charge and discharge. However, by using an electrode film according to an embodiment, the conductivity between particles of the active material can be maintained even before and after the volume changes, and deterioration in cycle characteristics can be suppressed.

[0161] The positive electrode may be prepared by coating a composite slurry containing a positive electrode active material on a current collector and drying the coated composite slurry.

[0162] The negative electrode may be prepared by coating a current collector with a composite slurry containing a negative electrode active material and drying the coated slurry to form an electrode film.

[0163] As the electrolyte, various conventionally known compounds capable of transferring ions can be used. Examples of compounds that can be used as the electrolyte include LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO３ , 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). However, the electrolyte is not limited to these, and compounds containing sodium salts and calcium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0164] The non-aqueous solvent is not particularly limited. Examples 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.

[0165] In one embodiment, the secondary battery preferably includes a separator. The separator may be made of, for example, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, or a material obtained by subjecting these to a hydrophilic treatment, but is not limited to these.

[0166] The secondary battery may have various shapes such as a paper type, a cylindrical type, a button type, and a laminated type depending on the purpose of use.

[0167] <Other Embodiments> According to some embodiments, a method for producing a carbon nanotube dispersion composition using carbon nanotubes can be provided. More specifically, a method for producing a carbon nanotube dispersion composition for use as an electrode material for a secondary battery using carbon nanotubes can be provided. For example, a method for producing a carbon nanotube dispersion composition for use in a nonaqueous electrolyte secondary battery, more specifically, a negative electrode of a lithium-ion secondary battery, more specifically, a negative electrode containing a silicon-based active material, can be provided. The carbon nanotubes used in this production method may be the carbon nanotube raw material described for the carbon nanotube dispersion composition. For example, the carbon nanotubes may at least satisfy the average outer diameter and linearity index within the ranges described for the carbon nanotube raw material above, and may optionally further satisfy one or both of the BET specific surface area and the G / D ratio, and may further optionally satisfy other physical property values.

[0168] According to some embodiments, it is possible to provide a method for producing a carbon nanotube resin composition using carbon nanotubes, a method for producing a composite slurry using carbon nanotubes, a method for producing an electrode film using carbon nanotubes, and a method for producing a secondary battery using carbon nanotubes. The carbon nanotubes are as described above.

[0169] Furthermore, according to some embodiments, there are provided a carbon nanotube dispersion composition, a carbon nanotube resin composition, a composite slurry, an electrode film, and a use of carbon nanotubes for a secondary battery. The carbon nanotubes are as described above. These may be various uses of carbon nanotubes for a non-aqueous electrolyte secondary battery, more specifically, for a negative electrode of a lithium-ion secondary battery, more specifically, for a negative electrode containing a silicon-based active material.

[0170] According to these embodiments, it is possible to include carbon nanotubes having an average outer diameter and a linearity index that satisfy predetermined ranges in the electrode film of one or both of the positive electrode and the negative electrode, thereby improving the rate characteristics and cycle characteristics of the secondary battery.

[0171] 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. In the examples, "carbon nanotubes" may be abbreviated as "CNT." Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0172] Table 1 shows the formulations and evaluation results of CNT dispersion compositions. Table 2 shows the formulations of composite slurries for negative electrodes. Table 3 shows the formulations of composite slurries for positive electrodes. Tables 4 and 5 show the rate characteristics and cycle characteristics of secondary batteries using the negative electrodes and positive electrodes produced in Examples and Comparative Examples, respectively. Tables 2 and 3 show the mass % of each component per 100 mass % of nonvolatile content, as well as the mass % of the total amount of nonvolatile content per 100 mass % of composite slurry.

[0173] <1> Methods for Measuring Physical Properties The methods for measuring physical properties used in the examples are described below.

[0174] (1) Average Outer Diameter of CNTs The average outer diameter of the CNT dispersion composition was measured by preparing a sample as follows using the CNT dispersion composition shown in Table 1, and using this sample, the average outer diameter was measured as follows.

[0175] Sample preparation: The CNT dispersion composition was diluted with a solvent to a CNT concentration of 0.048% by mass. A few μL of the diluted dispersion composition was spray-coated onto a mica substrate and then dried on a hot plate at 100°C to prepare a substrate for observing the average outer diameter of the CNTs. The surface of the prepared substrate was then sputtered with platinum. The solvent used was the same as that used to prepare the CNT dispersion composition.

[0176] Measurement method: Carbon nanotubes were observed and photographed using a scanning electron microscope (manufactured by JEOL Ltd.). Next, observations were conducted at a magnification of 50,000 times. 300 carbon nanotubes were randomly selected from multiple photographs, and their outer diameters were measured. The average outer diameter (nm) of the carbon nanotubes was calculated as the number average of the outer diameters.

[0177] (2) Linearity Index The linearity index of the CNT dispersion composition was measured by preparing a sample as follows using the CNT dispersion composition shown in Table 1, and using this sample, the linearity index was measured as follows.

[0178] Sample preparation: The CNT dispersion composition was diluted with a solvent to a CNT concentration of 0.048% by mass. A few μL of the diluted dispersion composition was spray-coated onto a mica substrate and then dried on a hot plate at 100°C to prepare a substrate for observing CNT fiber length. The surface of the prepared substrate was then sputtered with platinum. The solvent used was the same as that used to prepare the CNT dispersion composition.

[0179] Measurement method: SEM images of the sample piece were obtained using a scanning electron microscope (manufactured by JEOL Ltd.). At this time, the microscope was set so that the shapes of 50 to 200 carbon nanotubes could be observed in one field of view. The SEM images were taken under conditions of 4.63 nm per pixel. Note that an error range of 4.63 nm ± 10% was allowed in the photographing conditions. SEM images were taken by moving the field of view until a total of 1,000 to 3,000 carbon nanotubes could be observed.

[0180] Software: SEM images were analyzed using the image analysis software "WinROOF2015" (Mitani Shoji), and the absolute maximum length and skeletal length of a single carbon nanotube were calculated. Linearity was calculated using the following formula: Linearity = absolute maximum length / skeletal length The absolute maximum length is the distance between the two most distant points in the target pixel group. The skeletal length is the length of the free curve formed by the target pixel group.

[0181] Next, for each field of view of the SEM image, the number a of carbon nanotubes having a skeleton length of 1 μm or more was calculated, and the number b of carbon nanotubes having a skeleton length of 1 μm or more and a linearity of 0.9 or more was calculated. The linearity index was calculated using the following formula: Linearity index (%) = (b / a) × 100

[0182] (3) G / D Ratio The G / D ratio of the CNT dispersion composition was measured by preparing a sample as follows using the CNT dispersion composition shown in Table 1, and using this sample, the G / D ratio was measured as follows.

[0183] Sample preparation: The carbon nanotube dispersion composition was applied to a glass substrate (thickness 2 mm) using a KR PRINTCOAT K CONTROL COATER (No. 150) and dried to obtain a coating film. The drying was carried out by leaving the substrate to stand for 5 minutes in an oven (ESPEC CORP. SPHH-201) at 120°C.

[0184] Measurement method: CNTs were placed in a Raman microscope (XploRA, manufactured by Horiba, Ltd.), and measurements were performed using a 532 nm laser wavelength. The measurement conditions were: acquisition time 60 seconds, number of integrations 2, neutral density filter 10%, objective lens magnification 20x, confocus hole 500, slit width 100 μm, and measurement wavelength 100 to 3000 cm －１ In the obtained peak, the spectrum was 1560 to 1600 cm －１ The maximum peak intensity is G within the range of 1310 to 1350 cm －１ The maximum peak intensity within this range was defined as D, and the G / D ratio was calculated to be the G / D ratio of the CNT.

[0185] (4) BET Specific Surface Area The BET specific surface area of ​​the CNT dispersion composition was measured using a sample prepared as follows using the CNT dispersion composition shown in Table 1. Sample preparation: 100 mL of the carbon nanotube dispersion composition was measured into a 500 mL recovery flask and frozen in a -95°C ethanol bath for 5 hours using a freeze dryer (Tokyo Rikakikai Co., Ltd., FDU-1200 / UT-4000), followed by drying under reduced pressure at 10 to 30 Pa for 20 hours to obtain a carbon nanotube powder. The obtained carbon nanotube powder was then passed through a 60 μm mesh.

[0186] Measurement method: 0.03 g of CNT was weighed using an electronic balance (MSA225S100DI, manufactured by Sartorius) and then dried at 110°C for 15 minutes while degassing. The BET specific surface area of ​​the carbon nanotube powder was then measured using a fully automatic specific surface area measuring device (HM-model 1208, manufactured by MOUNTECH). The mass used as the denominator for calculating the specific surface area was the mass of the carbon nanotubes.

[0187] (5) Complex Elastic Modulus The complex elastic modulus of the CNT dispersion composition was evaluated by performing dynamic viscoelasticity measurements using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a cone diameter of 35 mm and an angle of 2° at 25°C, a frequency of 10 Hz, and a strain rate range of 0.01% to 5%.

[0188] (6) Phase Angle The phase angle of the CNT dispersion composition was evaluated by performing dynamic viscoelasticity measurements using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a cone diameter of 35 mm and an angle of 2° at 25°C, a frequency of 10 Hz, and a strain rate range of 0.01% to 5%.

[0189] <Preparation of Standard Positive Electrode> The standard positive electrode used in the examples and comparative examples described below was prepared by the following method.

[0190] First, 68.8 parts by mass of a positive electrode active material (manufactured by BASF Toda Battery Materials LLC, HED (registered trademark) NCM-111 1100), 3.0 parts by mass of acetylene black (manufactured by Denka Co., Ltd., Denka Black (registered trademark) HS100), and 2.2 parts by mass of PVdF (polyvinylidene fluoride, manufactured by Kureha Battery Materials Japan Co., Ltd., Kureha KF Polymer W#1300) were added to a 150 cm ３After adding the mixture to a plastic container, the powder was mixed using a spatula until it became uniform. Thereafter, 15.2 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, ARE-310). Thereafter, the mixture in the plastic container was mixed using a spatula until it became uniform, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Thereafter, 10.8 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Finally, the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer to obtain a positive electrode composite slurry.

[0191] Next, the positive electrode composite slurry was applied to a 20 μm thick aluminum foil as a current collector using an applicator to form a coating film. The coating film was then dried in an electric oven at 120°C ± 5°C for 25 minutes, resulting in an electrode with a coating weight per unit area of ​​20 mg / cm. ２ Further, a rolling treatment was carried out using a roll press (3 ton hydraulic roll press manufactured by Thank Metal Co., Ltd.) to adjust the density of the electrode film (dried coating film) to 3.1 g / cm. ３ A standard positive electrode was fabricated.

[0192] <Preparation of Standard Negative Electrode> The standard negative electrode used in the examples and comparative examples described below was prepared by the following method.

[0193] To a 150 ml plastic container were added 0.3 parts by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka Company Ltd.), 0.5% by mass of CMC (carboxymethyl cellulose #1190, manufactured by Daicel FineChem Co., Ltd., non-volatile content 100%), and 47.9 parts by mass of water, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Mixer, ARE-310). Further, 44.6 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd., non-volatile content 100%) and 5.1 parts by mass of silicon (silicon monoxide, manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5μm, non-volatile content 100%) were added as active materials, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation / revolution mixer (Thinky Corporation's Awatori Rentaro, ARE-310). Subsequently, 1.6 parts by mass of SBR (TRD2001, manufactured by JSR) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation / revolution mixer (Thinky Corporation's Awatori Rentaro, ARE-310), to obtain a standard negative electrode composite composition. The non-volatile content of the standard negative electrode composite composition was 50% by mass.

[0194] <2> Components Details of the components used in the examples and comparative examples are shown below. MIRALON: Multi-walled CNT manufactured by HUNTSMAN CNT (A): CNT (A), multi-walled CNT synthesized by the following synthesis method JENOTUBE 10B: JENOTUBE 10B (manufactured by JEIO, multi-walled CNT) NTF01: NTF01 (manufactured by Hamamatsu Carbonix Co., Ltd., multi-walled CNT)

[0195] Dispersant 1: A dispersant synthesized by the following synthesis method. Dispersant 2: A dispersant prepared by the following preparation method. Na ２ CO ３: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. NaOH: manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.0% CMC: carboxymethyl cellulose #1190 (manufactured by Daicel FineChem Co., Ltd.) Styrene butadiene rubber: TRD2001 (manufactured by JSR Corporation) HNBR: Therban 3406 (hydrogenated nitrile rubber manufactured by Arlanxeo) PVdF: Solef 5130 (polyvinylidene fluoride resin manufactured by Solvay) Polytetrafluoroethylene: Polyflon PTFE D-210C (manufactured by Daikin Industries, Ltd.)

[0196] <Synthesis of CNT(A)> The synthesis method of CNT(A) is described below. A catalyst composed of iron nitrate was vapor-deposited on a silicon wafer (substrate), forming a catalyst layer composed of a metal catalyst on the surface of the substrate. The catalyst-supported silicon wafer was then placed in the center of a horizontal reactor tube with an internal volume of 10 L, which could be pressurized and heated with an external heater. The reactor tube was evacuated while nitrogen gas was injected, and the air inside the reactor tube was replaced with nitrogen gas, resulting in an atmosphere with an oxygen concentration of 1% by volume or less. The reactor tube was then heated with an external heater until the central temperature reached 680°C. After reaching 680°C, acetylene gas was introduced into the reactor tube as a carbon source at a flow rate of 2 L per minute, and a catalytic reaction was carried out for 15 hours. After the reaction was completed, the gas inside the reactor tube was replaced with nitrogen gas, and the reactor tube was cooled to 100°C or less and removed, yielding CNT(A).

[0197] <Synthesis of Dispersant 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). The reaction was terminated by cooling when the conversion rate reached 90% or more. Thereafter, unreacted raw materials were reduced by heated, reduced-pressure distillation to obtain an aqueous polymer solution. A four-neck separable flask was charged with 500 parts of methyl ethyl ketone and 500 parts of methanol, and the aqueous polymer solution was added dropwise over 1 hour while the flask was rotated at 1,000 revolutions in a disperser. The resulting white precipitate was filtered out and dried under reduced pressure to obtain Dispersant 1.

[0198] <Preparation of Dispersant 2 Solution> Volume: 1000 cm ３ 475 parts by mass of NMP and 25 parts by mass of NaOH (Tosoh Corporation, Toso Pearl) were added to a plastic container, and the mixture was dispersed at a speed of 9000 rpm using a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a fine emulsion screen until the entire mixture was uniform. The mixture was then passed through a nylon filter with a mesh size of 150 μm using a filter bell to prepare a NaOH dispersion. 780 parts by mass of NMP was charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the atmosphere was replaced with nitrogen gas. The reaction vessel was then heated to 80°C, and 200 parts by mass of HNBR (Therban 3406) was added and stirred until the HNBR was completely dissolved. 20 parts by mass of the NaOH dispersion was then added, and the mixture was stirred while adding air. The reaction vessel was heated at 80°C for 12 hours, and a dispersant 2 solution (solids concentration 20.1% by mass) was obtained.

[0199] <4> CNT Dispersion Composition (Example 1-1) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of Dispersant 1 were added to a stainless steel container and stirred with a Dispersant until uniform. Thereafter, while stirring with a Dispersant, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to the Dispersant and a high-shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm, at a pressure of 100 MPa, and 25 passes were performed to obtain Dispersion Composition 1.

[0200] Example 1-2 The carbon nanotubes were changed to CNT(A), and dispersion was carried out in the same manner as in Example 1 to obtain a dispersion composition 2.

[0201] (Example 1-3) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high-shear mixer (L5M-A, manufactured by SILVERSON) and stirred at a speed of 7,000 rpm until uniform. 80 g of the dispersion liquid and 120 g of zirconia beads (bead diameter 1 mmΦ) were placed in a glass bottle (M-225, manufactured by Kashiwayo Glass Co., Ltd.), and a dispersion treatment was carried out for 5 hours using a paint conditioner manufactured by Red Devil. Thereafter, the dispersion liquid from which the zirconia beads had been separated was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a circulation dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, with 20 passes to obtain Dispersion Composition 3.

[0202] (Example 1-4) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, for 20 passes. Next, 80 g of the liquid to be dispersed and 120 g of zirconia beads (bead diameter 1 mmΦ) were placed in a glass bottle (M-225, manufactured by Kashiwa Glass Co., Ltd.), and a dispersion treatment was carried out for 5 hours using a paint conditioner manufactured by Red Devil Co., Ltd., after which the zirconia beads were separated to obtain Dispersion Composition 4.

[0203] (Examples 1-5) Laboplastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was charged with 14.4 parts by weight of dispersant 1, 16 parts by weight of MIRALON, and 69.6 parts by weight of ion-exchanged water, and dispersed for 3 hours. The mixture was then transferred to a stainless steel container, and 2565.6 parts by weight of ion-exchanged water and 1.07 parts by weight of sodium carbonate were added. A high-shear mixer (L5M-A, manufactured by SILVERSON) was fitted with a standard square-hole head and stirred at a speed of 7,000 rpm until uniform. From the stainless steel container, the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm, and 25 passes were performed at a pressure of 100 MPa to obtain dispersion composition 5.

[0204] (Examples 1-6) Laboplastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was charged with 14.4 parts by mass of dispersant 1, 16 parts by mass of MIRALON, and 69.6 parts by mass of ion-exchanged water, and dispersed for 3 hours. The mixture was then transferred to a stainless steel container, and 2565.6 parts by mass of ion-exchanged water and 1.07 parts by mass of sodium carbonate were added. A high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a standard square-hole head was added, and the mixture was stirred at a speed of 7,000 rpm until uniform. From the stainless steel container, the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation-type dispersion treatment was carried out. The dispersion treatment used a single nozzle chamber, with a nozzle diameter of 0.25 mm and 20 passes at a pressure of 100 MPa. Next, 80 g of the liquid to be dispersed and 120 g of zirconia beads (bead diameter 1 mmΦ) were placed in a glass bottle (M-225, manufactured by Kashiwa Glass Co., Ltd.), and a dispersion treatment was carried out for 5 hours using a paint conditioner manufactured by Red Devil Co., Ltd., after which the zirconia beads were separated to obtain Dispersion Composition 6.

[0205] (Examples 1-7) 14.4 parts by mass of Dispersant 1, 16 parts by mass of MIRALON, and 69.6 parts by mass of ion-exchanged water were charged into a Laboplastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) and dispersed for 3 hours, then transferred to a stainless steel container, 2565.6 parts by mass of ion-exchanged water and 1.07 parts by mass of sodium carbonate were added, and a high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a standard square-hole head was used, and the mixture was stirred at a speed of 7,000 rpm until uniform. Next, 80 g of the dispersion liquid and 120 g of zirconia beads (bead diameter 1 mmΦ) were charged into a glass bottle (M-225, manufactured by Kashiwa Glass Co., Ltd.), and the mixture was dispersed for 5 hours using a paint conditioner manufactured by Red Devil Co., Ltd., and the zirconia beads were then separated. The dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) and subjected to a circulation type dispersion treatment. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, with 20 passes to obtain Dispersion Composition 7.

[0206] (Examples 1-8) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of CNT (A) and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole type head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. From the stainless steel container, the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation type dispersion treatment was carried out. The dispersion treatment used a single nozzle chamber, and 40 passes were performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain dispersion composition 8.

[0207] (Examples 1-9) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 20 passes to obtain dispersion composition 9.

[0208] (Examples 1-10) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 40 passes to obtain dispersion composition 10.

[0209] (Examples 1-11) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment used a single nozzle chamber, and 15 passes were performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain dispersion composition 11.

[0210] (Examples 1-12) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 55 passes to obtain dispersion composition 12.

[0211] Comparative Example 1-1: The carbon nanotubes were changed to JENOTUBE 10B, and dispersion was carried out in the same manner as in Example 1 to obtain a comparative dispersion composition 1. However, the material ratio was 2.5 parts by mass of JENOTUBE 10B, 96.3 parts by mass of ion-exchanged water, 1.0 part by mass of dispersant 1, and 0.13 part by mass of sodium carbonate.

[0212] Comparative Example 1-2 The carbon nanotubes were changed to NTF01, and dispersion was carried out in the same manner as in Example 1, to obtain a comparative dispersion composition 2.

[0213] (Comparative Example 1-3) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 5 passes to obtain a comparative dispersion composition 3.

[0214] (Comparative Example 1-4) 98.82 parts by mass of ion-exchanged water and 0.54 parts by mass of dispersant 1 were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.6 parts by mass of MIRALON and 0.04 parts by mass of sodium carbonate were added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 80 passes to obtain a comparative dispersion composition 4.

[0215] (Example 1-101) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution (0.60 parts by mass of HNBR, 0.03 parts by mass of NaOH, 2.37 parts by mass of NMP) were added to a stainless steel container and stirred until uniform with a disperser. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON was added, and a standard square-hole type head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm, and 25 passes at a pressure of 100 MPa to obtain dispersion composition 101.

[0216] (Example 1-102) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of CNT (A) was added, and a standard square-hole head was attached to a disperser and high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment used a single nozzle chamber, and 25 passes were performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain dispersion composition 102.

[0217] (Example 1-103) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON was added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 15 passes to obtain dispersion composition 103.

[0218] (Example 1-104) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON was added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm, at a pressure of 100 MPa, and 55 passes were performed to obtain dispersion composition 104.

[0219] (Comparative Example 1-101) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution (0.60 parts by mass of HNBR, 0.03 parts by mass of NaOH, 2.37 parts by mass of NMP) were added to a stainless steel container and stirred until uniform with a disperser. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON was added, and a standard square-hole type head was attached to a disperser and high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa for 5 passes to obtain comparative dispersion composition 101.

[0220] (Comparative Example 1-102) 96.40 parts by mass of N-methyl-2-pyrrolidone (NMP) and 3.0 parts by mass of dispersant 2 solution were added to a stainless steel container and stirred with a disperser until uniform. Thereafter, while stirring with a disperser, 0.60 parts by mass of MIRALON was added, and a standard square-hole head was attached to a disperser and a high shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was stirred at a speed of 7,000 rpm until uniform. 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 a circulation-type dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm, at a pressure of 100 MPa for 80 passes to obtain a comparative dispersion composition 102.

[0221] <5> Preparation of CNT resin composition and composite slurry (negative electrode composite slurry 1) Capacity 150 cm ３5.7 parts by mass of Dispersion Composition 1, 11.4 parts by mass of an aqueous solution containing 2% by mass of carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190, referred to as CMC in the tables (the same applies hereinafter)), and 10.7 parts by mass of ion-exchanged water were weighed into a plastic container. These were then stirred for 30 seconds at 2000 rpm using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Next, 2.2 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) were added, and the mixture was stirred for 5 minutes at 2000 rpm using the planetary centrifugal mixer. Furthermore, 19.9 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added, and the mixture was stirred for 10 minutes at 2000 rpm using the rotation / revolution mixer. Then, 0.7 parts by mass of styrene-butadiene rubber (manufactured by JSR Corporation, TRD2001, non-volatile content 48%, referred to as SBR in the table (hereinafter the same)) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the rotation / revolution mixer to obtain a negative electrode composite slurry 1 having the non-volatile content (mass%) shown in Table 2.

[0222] (Negative Electrode Composite Slurries 2 to 7) Negative electrode composite slurries 2 to 7 were obtained in the same manner as for negative electrode composite slurry 1, except that dispersion composition 1 was changed to dispersion compositions 2 to 7, respectively.

[0223] (Comparative Negative Electrode Composite Slurry 1) The material ratio was the same as in the negative electrode composite slurry 1, except that the comparative dispersion composition 1 was 4.5 parts by mass, carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190) was dissolved in 11.3 parts by mass of an aqueous solution of 2% by mass of carboxymethyl cellulose, ion-exchanged water was 11.8 parts by mass, silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) was 2.2 parts by mass, artificial graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was 19.6 parts by mass, and styrene butadiene rubber (manufactured by JSR Corporation, TRD2001) was changed to 0.7 parts by mass to obtain a comparative negative electrode composite slurry 1.

[0224] (Comparative Negative Electrode Composite Slurry 2) The material ratio was the same as in the negative electrode composite slurry 1, except that the comparative dispersion composition 2 was 11.4 parts by mass, carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190) was dissolved in an aqueous solution of 2% by mass of 11.4 parts by mass, ion-exchanged water was 11.8 parts by mass, silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) was 2.2 parts by mass, artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) was 19.9 parts by mass, and styrene butadiene rubber (manufactured by JSR Corporation, TRD2001) was changed to 0.7 parts by mass to obtain a comparative negative electrode composite slurry 2.

[0225] (Negative Electrode Composite Slurries 8 to 12) Negative electrode composite slurries 8 to 12 were obtained in the same manner as for negative electrode composite slurry 1, except that dispersion composition 1 was changed to dispersion compositions 8 to 12, respectively.

[0226] (Comparative Negative Electrode Composite Slurries 3 to 4) Comparative dispersion composition 1 was changed to comparative dispersion compositions 3 to 4, and comparative negative electrode composite slurries 3 to 4 were obtained in the same manner as for comparative negative electrode composite slurry 1, respectively.

[0227] (Positive electrode composite slurry 1) Capacity 150 cm ３ 8.2 parts by mass of Dispersion Composition 1, 0.3 parts by mass of carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190), and 9.3 parts by mass of ion-exchanged water were weighed into a plastic container, and the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Thereafter, 32.0 parts by mass of LFP (LFP-400 (manufactured by BASF, non-volatile content 100%)) was added as a positive electrode active material, and the mixture was stirred at 2,000 rpm for 5 minutes using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro, ARE-310). Further, thereafter, 0.8 parts by mass of polytetrafluoroethylene (Daikin Industries, Ltd., Polyflon PTFE D-210C, non-volatile content 60%, referred to as PTFE in the table (the same applies hereinafter)) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro, ARE-310). This gave positive electrode composite slurry 1 having the non-volatile content by mass shown in Table 3.

[0228] (Positive Electrode Composite Slurries 2 to 7) Positive electrode composite slurries 2 to 7 were obtained in the same manner as in the positive electrode composite slurry 1, except that the dispersion composition was changed to 2 to 7.

[0229] (Comparative positive electrode composite slurry 1) The same procedure as for the positive electrode composite slurry 1 was used, but the material ratios were changed to 6.5 parts by mass of the comparative dispersion composition 1, 0.3 parts by mass of carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190), 11.0 parts by mass of ion-exchanged water, 31.4 parts by mass of LFP (LFP-400 (manufactured by BASF, non-volatile content 100%), and 0.8 parts by mass of polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., Polyflon PTFE D-210C, non-volatile content 60%) to obtain a comparative positive electrode composite slurry 1.

[0230] (Comparative positive electrode composite slurry 2) The same procedure as for the positive electrode composite slurry 1 was used, but the material ratios were changed to 16.5 parts by mass of the comparative dispersion composition 2, 0.3 parts by mass of carboxymethyl cellulose (manufactured by Daicel FineChem Co., Ltd., #1190), 1.1 parts by mass of ion-exchanged water, 31.9 parts by mass of LFP (LFP-400 (manufactured by BASF, non-volatile content 100%), and 0.8 parts by mass of polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., Polyflon PTFE D-210C, non-volatile content 60%) to obtain a comparative positive electrode composite slurry 2.

[0231] (Positive electrode composite slurry 101) Capacity 150 cm ３ Into a plastic container, 31.1 parts by mass of an NMP solution in which 8% by mass of PVdF (polyvinylidene fluoride, Solvey, Solef #5130) was dissolved, and 0.4 parts by mass of NMP were weighed. Thereafter, 24.9 parts by mass of the dispersion composition 101 was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Thinner Mixer, ARE-310). Further, 96.7 parts by mass of the positive electrode active material NCM1 was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotation / revolution mixer (Thinner Mixer, ARE-310), to obtain a positive electrode composite slurry 101.

[0232] (Positive electrode composite slurries 102 to 104, comparative positive electrode composite slurries 101 to 102) Dispersion composition 101 was changed to dispersion compositions 102 to 104 and comparative dispersion compositions 101 to 102, and positive electrode composite slurries 102 to 104 and comparative positive electrode composite slurries 101 to 102 were obtained in the same manner as for positive electrode composite slurry 101, respectively.

[0233] <6> Preparation and Evaluation of Electrode Film <6-1> Electrode Film for Negative Electrode (Example 2-1: Negative Electrode 1) The obtained negative electrode composite slurry 1 was applied to a copper foil having a thickness of 20 μm using an applicator, and the coating was then dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. Thereafter, the electrode film was subjected to a rolling treatment using a roll press (Thank Metal, 3 t 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.

[0234] Examples 2-2 to 2-12: Negative Electrodes 2 to 12 Negative electrodes 2 to 12 were obtained in the same manner as for negative electrode 1, except that negative electrode composite slurry 1 was changed to negative electrode composite slurry 2 to 12, respectively.

[0235] Comparative Examples 2-1 to 2-4: Comparative Negative Electrodes 1 to 4 Comparative negative electrodes 1 to 4 were obtained in the same manner as for negative electrode 1, except that negative electrode composite slurry 1 was changed to comparative negative electrode composite slurries 1 to 4, respectively.

[0236] <6-2> Electrode Film for Positive Electrode (Example 3-1: Positive Electrode 1) The obtained positive electrode composite slurry 1 was applied to an aluminum foil having a thickness of 20 μm 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.

[0237] (Examples 3-2 to 3-7, Comparative Examples 3-1 to 3-2: Positive Electrodes 2 to 7, Comparative Positive Electrodes 1 and 2) Positive electrode composite slurry 1 was changed to positive electrode composite slurries 2 to 7 and comparative positive electrode composite slurries 1 and 2, and positive electrodes 2 to 7 and comparative positive electrodes 1 and 2 were obtained, respectively, by the same procedure as for positive electrode 1.

[0238] (Examples 3-101 to 3-104, Comparative Examples 3-101 to 3-102: Positive Electrodes 101 to 104, Comparative Positive Electrodes 101 to 102) Positive electrode composite slurry 1 was changed to positive electrode composite slurries 101 to 104 and comparative positive electrode composite slurries 101 to 102, and positive electrodes 101 to 104 and comparative positive electrodes 101 to 102 were obtained in the same manner as for positive electrode 1, respectively.

[0239] <8> Laminated Lithium-Ion Secondary Battery (Example 4-1: Battery 1 for Negative Electrode Evaluation) The negative electrode 1 and the standard positive electrode were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively. The punched negative electrode and standard positive 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. Next, a nonaqueous electrolyte solution was prepared in a glove box filled with argon gas. Specifically, first, a mixed solvent was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 1:1:1 (volume ratio). Next, 1 part by mass each of VC (vinylene carbonate) and FEC (fluoroethylene carbonate) was added as additives to 100 parts by mass of the mixed solvent, and LiPF ６ A non-aqueous electrolyte solution was obtained by dissolving the above-mentioned compound in a solution of 1 M. Next, 2 mL of the non-aqueous electrolyte solution was poured into the aluminum laminate bag, and the aluminum laminate was sealed to prepare a laminate-type lithium ion secondary battery (battery 1 for negative electrode evaluation).

[0240] Examples 4-2 to 4-12 and Comparative Examples 4-1 to 4-4 Laminated lithium ion secondary batteries (batteries for negative electrode evaluation) 2 to 12 and comparative negative electrode evaluation batteries 1 to 4 were fabricated in the same manner as in Example 4-1, except that the negative electrode 1 in Example 4-1 was changed to negative electrodes 2 to 12 and comparative negative electrodes 1 to 4.

[0241] (Examples 5-1 to 5-7, 5-101 to 5-104, and Comparative Examples 5-1 to 5-2, 5-101 to 5-102) Laminated lithium ion secondary batteries using a positive electrode and a standard negative electrode were produced in the same manner as in Example 4-1, except that the negative electrode in Example 4-1 was changed to a standard negative electrode, and the positive electrode was changed to positive electrodes 1 to 7, positive electrodes 101 to 104, comparative positive electrodes 1 to 2, and comparative positive electrodes 101 to 102, to obtain positive electrode evaluation batteries 1 to 7, positive electrode evaluation batteries 101 to 104, comparative positive electrode evaluation batteries 1 to 2, and comparative positive electrode evaluation batteries 101 to 102, respectively.

[0242] The rate characteristics and cycle characteristics of the laminated lithium ion secondary battery were evaluated according to the following criteria. The evaluation results are shown in Tables 4 and 5.

[0243] (Method for evaluating rate characteristics of secondary batteries) The obtained negative electrode evaluation secondary battery and positive electrode evaluation secondary battery were placed in a thermostatic chamber at 25 ° C., and charge / discharge measurements were performed using a charge / discharge device (Hokuto Denko Corporation, SM-8). After performing constant current / constant voltage charging (cut-off current 1 mA (0.02 C)) at a charge current of 10 mA (0.2 C) and a charge end voltage of 4.3 V, a constant current discharge was performed at a discharge current of 10 mA (0.2 C) and a discharge end voltage of 3 V. This operation was repeated three times, and then a constant current / constant voltage charging (cut-off current (1 mA 0.02 C)) was performed at a charge current of 10 mA (0.2 C) and a charge end voltage of 4.3 V, and a constant current discharge was performed at discharge currents of 0.2 C and 3 C until the discharge end voltage reached 3.0 V, and the discharge capacity was determined. The rate characteristics can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, as shown in the following formula 1. (Formula 1) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%)

[0244] <Evaluation criteria> ◎: Rate characteristics are 80% or more (excellent) ○: Rate characteristics are 70% or more and less than 80% (good) △: Rate characteristics are 60% or more and less than 70% (poor)

[0245] (Method for Evaluating Cycle Characteristics of Secondary Battery) The obtained secondary battery for negative electrode evaluation and secondary battery for positive electrode evaluation were placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current 2.5mA (0.05C)) was performed at a charge current of 25mA (0.5C) and a charge cut-off voltage of 4.3V, followed by constant-current discharging at a discharge current of 25mA (0.5C) and a discharge cut-off voltage of 3V. This operation was repeated 200 times. The cycle characteristics can be expressed as the ratio of the third 0.5C discharge capacity to the 200th 0.5C discharge capacity at 25°C, using the following formula 2: (Formula 2) Cycle characteristics = 200th 0.5C discharge capacity / third 0.5C discharge capacity × 100 (%)

[0246] <Evaluation criteria> ◎◎: 90% or more (best) ◎: 85% or more (excellent) ○: 80% or more but less than 85% (good) ×: Less than 80% (poor)

[0247]

[0248]

[0249]

[0250]

[0251]

[0252] As shown in the table, examples in which the physical property values ​​of the CNTs observed in the CNT dispersion composition fall within the predetermined ranges can provide secondary batteries that exhibit good rate characteristics and cycle characteristics.

[0253] For example, in Comparative Example 4-1, the linearity index of the CNTs in the CNT dispersion composition is low, so it is expected that the number of active material particles that one CNT contacts in the secondary battery is small. In such a case, repeated charge and discharge in the secondary battery is likely to result in a decrease in the proportion of active material particles connected to each other by CNTs due to volume changes in the active material, and therefore a decrease in cycle performance. Furthermore, in Comparative Example 4-2, the average outer diameter of the CNTs in the CNT dispersion composition is large, so it is likely that the conductivity of the CNTs in the secondary battery is reduced, resulting in a decrease in rate performance. Similar trends were observed in Comparative Examples 5-1 and 5-2, as well as other Comparative Examples.

Claims

1. A carbon nanotube dispersion composition comprising carbon nanotubes, a dispersant, and a solvent, and satisfying the following (1) and (2): (1) the average outer diameter of the carbon nanotubes calculated from an SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is 15 nm or more and 50 nm or less; (2) when the target pixel group of the SEM image of the carbon nanotubes contained in the carbon nanotube dispersion composition is defined as a carbon nanotube, and the linearity is the value obtained by dividing the distance between the two most distant points (absolute maximum length) by the length of the free curve (skeleton length), the number ratio of carbon nanotubes having a linearity of 0.9 or more for a skeleton length of 1 μm or more is 40% or more and 90% or less.

2. (3) In the Raman spectrum of the coating film of the carbon nanotube dispersion composition, －１ The maximum peak intensity in the range of G, 1310 to 1350 cm －１ 2. The carbon nanotube dispersion composition according to claim 1, wherein the G / D ratio is 1.0 to 20.0, where D is the maximum peak intensity within the range.

3. (4) After freeze-drying the carbon nanotube dispersion composition, the powder passed through a 60 μm mesh has a BET specific surface area relative to the mass of carbon nanotubes of 50 to 130 m ２ The carbon nanotube dispersion composition according to claim 1, wherein the carbon nanotube dispersion composition has a molecular weight of 1000 or more.

4. (5) A carbon nanotube dispersion composition according to claim 1, which has a complex modulus of elasticity of 4 Pa ​​or more and 200 Pa or less at 25° C. and a frequency of 10 Hz as determined by dynamic viscoelasticity measurement.

5. (6) A carbon nanotube dispersion composition according to claim 1, which has a phase angle of 3° or more and 60° or less at 25° C. and a frequency of 10 Hz as determined by dynamic viscoelasticity measurement.

6. A carbon nanotube resin composition comprising the carbon nanotube dispersion composition according to any one of claims 1 to 5 and a binder.

7. A composite slurry comprising the carbon nanotube dispersion composition according to any one of claims 1 to 5, a binder, and an active material.

8. An electrode film, which is a coating film of a composite slurry, the composite slurry containing the carbon nanotube dispersion composition according to any one of claims 1 to 5, a binder, and an active material.

9. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises the electrode film according to claim 8.

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