Carbon nanotube dispersion liquid, slurry for electrode production, and secondary battery

Abstract

The present invention relates to a carbon nanotube dispersion liquid, a slurry for manufacturing an electrode containing a carbon nanotube, and a secondary battery, which can improve the performance of a secondary battery containing the carbon nanotube by controlling the particle size and content of the carbon nanotube.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube dispersion, a slurry for manufacturing an electrode containing carbon nanotubes, and a secondary battery. Background Art

[0002] With the rapid development of the electronics, communication, and computer industries, electric vehicles, mobile phones, laptop computers, etc. are continuously achieving remarkable development. As a power source for driving portable electronic devices, batteries need to have a higher energy density and stable output. In particular, lithium secondary batteries, as high-performance batteries with the highest energy density among currently commercialized secondary batteries, are the most actively developed.

[0003] A conductive material is a material used to promote the electron movement between electrode active materials - electrode active materials or electrode active materials - current collectors, and is mainly developed centered on carbon-based materials. A conductive material slurry is a solution in which the above-mentioned conductive material is dispersed in a solvent, and it becomes a material that constitutes an electrode slurry together with an electrode active material and a binder. In recent years, with the application of secondary batteries in medium and large battery markets such as electric vehicles or energy storage systems (ESS), its importance has been increasing day by day, and research on improving the theoretical capacity has also been continuously carried out.

[0004] Carbon nanotubes (CNTs) used as conductive materials can improve the energy density and lifespan compared with existing powdered carbon, and can reduce the battery size. In particular, these advantages are more prominent in batteries for electric vehicles that require high capacity and fast charge and discharge, etc. However, despite such prominent advantages of carbon nanotubes, carbon nanotubes have strong hydrophobicity and a coiled tube structure. In order to fully utilize its various advantages, a dispersion method or processing method of carbon nanotubes must be developed in advance. In addition, for secondary battery conductive material dispersions, many battery manufacturing companies require low-viscosity and high-content conductive material dispersions. However, as the carbon nanotube content increases, the dispersibility of the dispersion decreases, and this decrease in dispersibility will cause problems such as uneven coating and high viscosity, resulting in poor electrode coating.

[0005] Therefore, there is an urgent need for a method that can achieve a low-viscosity and high-content carbon nanotube dispersion. Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a carbon nanotube dispersion, a slurry for manufacturing an electrode containing the above carbon nanotubes, an electrode and a secondary battery manufactured from the above slurry, which can provide excellent electrical properties such as electrical conductivity for the electrode while maintaining low viscosity by controlling the amount of fine powder during the carbon nanotube processing.

[0008] Means for solving the problem

[0009] In the present invention, it has been confirmed that in a dispersion liquid containing carbon nanotubes, as the size of the carbon nanotube micropowder decreases and its quantity increases, the battery performance will deteriorate when the electrode is fabricated. To solve this problem, through in-depth research, it has been found that there is a direct correlation between the size and quantity of the micropowder corresponding to D5 in the overall particle size distribution of carbon nanotubes and the battery performance. Therefore, in the present invention, by controlling the particle size distribution D5 to be 7 μm or more, the battery performance can be improved when fabricating the electrode into an electrode.

[0010] Accordingly, according to one aspect of the present invention, there is provided a carbon nanotube dispersion liquid in which the particle size distribution D5 of the carbon nanotubes is 7 μm or more.

[0011] According to one embodiment, the above-mentioned particle size distribution D5 may specifically be 7 μm or more and 14 μm or less, 7 μm or more and 9 μm or less, 7.5 μm or more and 14 μm or less, or 7.5 μm or more and 9 μm or less. The above D5 can be measured by a particle size distribution analyzer, which represents the particle size value corresponding to when the cumulative volume distribution (volume density) reaches 5 volume density % starting from the sample with the smallest particle size. According to the present invention, by controlling the particle size to be 7 μm or more in the particle size distribution D5 of the carbon nanotubes, not only can the electrical properties such as the powder conductivity of the carbon nanotubes be achieved, but also the battery performance can be improved when fabricating the electrode.

[0012] In addition, according to another embodiment of the present invention, the particle size distribution D50 of the above-mentioned carbon nanotubes may be 15 μm to 50 μm, 20 μm to 45 μm, 20 μm to 40 μm, or 25 μm to 35 μm. According to still another embodiment of the present invention, the particle size distribution D90 of the above-mentioned carbon nanotubes may be 45 μm to 200 μm, specifically 45 μm to 100 μm, 45 μm to 95 μm, 45 μm to 90 μm, 45 μm to 85 μm, or 50 μm to 80 μm. Within the adjusted range, although the average particle size (D50) and the large particle size (D90) themselves have no direct correlation with the battery performance, under the condition of satisfying the above D5, if the average particle size and the large particle size are simultaneously controlled, good quality of the carbon nanotube powder can be obtained.

[0013] According to an embodiment of the present invention, in the above carbon nanotubes, based on the total volume of the carbon nanotubes, the content of carbon nanotubes with a particle size of 17.4 μm or less may be 30% by volume or less. According to the present invention, by controlling the content of carbon nanotubes with a particle size of 17.4 μm or less to 30% by volume or less, not only can the electrical properties such as the powder conductivity of the carbon nanotubes be improved, but it can also contribute to improving the battery performance when manufacturing electrodes. For example, the content of carbon nanotubes with a particle size of 17.4 μm or less may be 6% to 30% by volume, 7% to 30% by volume, or 7% to 27% by volume. When the above range is satisfied, a carbon nanotube dispersion liquid with both low viscosity and high conductivity can be provided.

[0014] The above carbon nanotubes may be at least one selected from the group consisting of single-wall carbon nanotubes, double-wall carbon nanotubes, triple-wall carbon nanotubes, and multi-wall carbon nanotubes. The type of the above carbon nanotubes can be appropriately selected according to needs. Since the above carbon nanotubes can be used as a conductive material in secondary batteries, from the perspective of conductivity, single-wall carbon nanotubes have more advantages. However, compared with multi-wall carbon nanotubes, single-wall carbon nanotubes require a high-temperature synthesis process, resulting in high process adjustment difficulty and a significant increase in the cost of removing metal impurities, which is a major drawback. Accordingly, according to an embodiment of the present invention, the above carbon nanotubes may be in a form of mixing single-wall carbon nanotubes with the above double-wall carbon nanotubes, triple-wall carbon nanotubes, or multi-wall carbon nanotubes, or may be double-wall carbon nanotubes, triple-wall carbon nanotubes, or multi-wall carbon nanotubes.

[0015] According to an embodiment, the above multi-wall carbon nanotubes may be carbon nanotubes with 30 walls or less, 20 walls or less, 10 walls or less, or having 4 to 30 walls. The above walls can be confirmed through TEM images, and the number of walls can be obtained by directly counting in the TEM images. In terms of conductivity, carbon nanotubes in a state where the number of walls is small, there are no breaks in the middle of the walls, and they are not connected to each other to form a complex path are more preferred.

[0016] According to an embodiment of the present invention, the central diameter of the above carbon nanotubes may be 4 nm to 50 nm, specifically 4 nm to 30 nm. For example, the above carbon nanotubes may be triple-walled or multi-walled carbon nanotubes with a central diameter of 4 nm to 20 nm. When using the above carbon nanotubes, electrodes with excellent electrical properties can be provided. The above central diameter is the total value of the core diameter and the number of walls of the carbon nanotubes. Among them, since the number of walls may vary at different positions, the above central diameter refers to the majority diameter. The above central diameter can be directly measured in the TEM image. However, since the measurement results may deviate due to different measurement positions in the sample, the above central diameter may be the value obtained by statistical analysis of the values measured at multiple measurement positions in the sample. In addition, the above central diameter can also be estimated by measuring the core diameter, counting the number of walls, and measuring the wall spacing. For example, in the case of a carbon nanotube with an actually measured central diameter of 30.5 nm in the TEM image, the above central diameter of 30.5 nm can be calculated from the conditions of a core diameter of 10 nm, 30 walls, and a wall spacing of The condition is calculated as follows.

[0017] According to an embodiment of the present invention, the above carbon nanotubes may be in a tangled or bundled form. The bundled form means that the carbon nanotube units are arranged neatly and form a bundle, which is beneficial to achieving dispersion into single fibers. Therefore, according to an embodiment, the above carbon nanotubes can be in a bundled form. The above bundled carbon nanotubes in the dispersion liquid of the present invention may exist in a form in which some relatively long carbon nanotube chains are unraveled during the dispersion process.

[0018] According to an embodiment of the present invention, metal catalysts for carbon nanotube synthesis, such as iron (Fe), cobalt (Co), aluminum (Al), or nickel (Ni), etc., may be mixed in the above carbon nanotubes, and the metal catalyst content in the above carbon nanotubes is as low as possible. For example, it can be 2.5 wt% or less, specifically 2.1 wt% or less. The above metal content can be measured by ICP after dissolving the metal by dispersing the carbon nanotubes in an acid solution and using high-temperature microwave treatment, etc.

[0019] The above carbon nanotube dispersion liquid may further contain a dispersion medium. The above dispersion medium may be one or more selected from N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), methanol, ethanol, propanol, isopropanol, butanol, isobutanol, acetone, tetrahydrofuran (THF), and water, etc., but is not necessarily limited thereto.

[0020] According to an embodiment of the present invention, the solid content of the carbon nanotube dispersion of the present invention may be 5% or more. In addition, according to another embodiment, the viscosity of the dispersion containing the above carbon nanotubes of the present invention under the condition that the shear rate is 50 / s may be 2000 cp or less, or 1000 cp or less. According to still another embodiment, the powder conductivity of the above carbon nanotubes may be 50 S / cm or more. According to the present invention, by controlling the particle size distribution D5, a high-content dispersion with a solid content of 5% or more can have both low viscosity and high powder conductivity, so that the electrode prepared from the carbon nanotubes, its dispersion or its slurry of the present invention and the secondary battery containing the electrode can exhibit excellent electrical properties.

[0021] The carbon nanotubes that meet the particle size distribution D5 conditions required by the present invention can be prepared by controlling the processing device and processing conditions for crushing the carbon nanotubes, etc. There is no particular limitation on the type of processing device that can be used to crush the carbon nanotubes, as long as the carbon nanotubes of the present invention can be manufactured by controlling the processing conditions. For example, various processing devices as shown in Figure 1 can be used. According to an embodiment, the carbon nanotubes of the present invention can be prepared using a low-speed bead mill. Specifically, a rotary bead mill rotating at a speed of 20 rpm to 200 rpm, 20 rpm to 100 rpm, or 20 rpm to 50 rpm can be used. According to an embodiment of the present invention, the above carbon nanotubes of the present invention can be prepared using a rotary bead mill without an internal stirrer, and preferably a rotary bead mill with low-speed rotation and without an internal stirrer. The above low-speed bead mill can be replaced by an improved rotor-type bead mill (which can be divided into pin type, disk type, etc. according to the rotor type) and a vibration ball mill. However, the above rotor-type bead mill is of a type in which the rotor rotates in the cylinder and the beads between the rotors move at high speed, and there is a disadvantage that it is difficult to adjust the generation of fine powder.

[0022] According to an embodiment of the present invention, the above carbon nanotubes can be micronized by a dry method.

[0023] On the other hand, the processing conditions for crushing the above carbon nanotubes, specifically, such as the bead filling rate, crushing strength, crushing time, bead size, etc. can be appropriately adjusted by those skilled in the art according to needs.

[0024] Specifically, when using a bead mill to process the above carbon nanotubes, the filling rate varies according to the bead size, container volume, etc., but it can be carried out at a filling rate of 30% to 90%, or 60% to 90%. Within the above filling rate range, the number of beads is sufficient and the movement of the beads is not restricted, so excellent processing effects can be obtained.

[0025] In addition, the processing of the above carbon nanotubes can be carried out at a rotational speed of 10 rpm to 100 rpm, or 20 rpm to 50 rpm. Within the above rpm range, excellent processing effects can be obtained.

[0026] In addition, the processing of the above carbon nanotubes can be carried out using one kind of bead, or two or more kinds of beads can be used in combination. If one kind of bead is used, the diameter of the bead can be greater than 2 mm, or 2 mm to 5 mm. According to an embodiment, the processing can be carried out in a bead mill using beads with a diameter of 5 mm. When the diameter of the above one kind of bead used is 2 mm to 5 mm, good pulverization effects can be obtained. If two or more kinds of mixed beads are used, the pulverization effect can be further improved. An example of two or more kinds of mixed beads can be the case of using beads with a diameter of 5 mm and beads with a diameter of 2 mm in combination. In the above mixed beads, the proportion of beads with different diameters can be appropriately adjusted by those skilled in the art considering factors such as pulverization intensity. For example, when mild pulverization is carried out in a low-speed bead mill, the usage amount of beads with a diameter of 5 mm can be higher than that of beads with a diameter of 2 mm.

[0027] The above pulverization time can be 20 hours or less, for example, 14 hours or less, but is not limited thereto, and can be appropriately adjusted according to the type of beads used, the state of the carbon nanotube raw material, etc.

[0028] According to another aspect of the present invention, there is provided a slurry for manufacturing an electrode containing carbon nanotubes with a particle size distribution D5 of 7 μm or more. For a detailed description of the carbon nanotubes including the above D5, reference can be made to the foregoing content.

[0029] In the above slurry for manufacturing an electrode, in addition to the above carbon nanotubes, at least one selected from a conductive material, an electrode active material, and a binder can be further included.

[0030] The above conductive material refers to a conductive material additionally added in addition to the carbon nanotubes. The above conductive material can be one or more selected from non-linear carbon conductive materials, for example, dot-like carbon black, low-structure dot-like carbon material (LSCB), medium-structure dot-like carbon material (MSCB), metal powder, metal fiber, Denka Black, polyaniline, polythiophene, polypyrrole, acetylene, etc., and is not limited thereto, and can also be any conductive material well known in the art used together with the above carbon nanotubes for electrode manufacturing.

[0031] The above-mentioned binder can be one or more selected from polyvinylpyrrolidone, polyvinylidene fluoride (PVdF), polyvinylidene fluoride copolymer, chlorotrifluoroethylene (CTFE), polyvinyl alcohol, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, starch, styrene-butadiene rubber, nitrile rubber, etc., but is not necessarily limited thereto, and any binder known in the art can also be used. Among them, polyvinylidene fluoride (PVdF) is widely used as a binder for electrode manufacturing because of its many kinds of soluble solvents, high electrochemical stability and low expansion rate. The molecular weight range of the above-mentioned binder can be from 500000 g / mol to 1200000 g / mol.

[0032] The above-mentioned electrode active material can be a positive electrode active material. The above-mentioned positive electrode active material can be lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiCoO2), lithium manganese oxide (LiMnO2, LiMnO3, LiMn2O3), lithium vanadate (LiV3O4, LiV3O8, V2O5, etc.), lithium copper oxide (Li2CuO2), lithium manganese composite oxide, lithium sulfide, etc., but is not necessarily limited thereto, and any active material known in the technical field can also be used. For example, the above-mentioned electrode active material can be a positive electrode active material selected from the group consisting of Li x1 NiO2 (0.5 < x1 < 1.3), Li x2 (Ni a1 Co b1 Mn c1 )O2 (0.5 < x2 < 1.3, 0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, a1 + b1 + c1 = 1), Li x3 Ni 1-y1 Co y1 O2 (0.5 < x3 < 1.3, 0 < y1 < 1), Li x4 Ni 1-y2 Mn y2 O2 (0.5 < x4 < 1.3, 0 ≤ y2 < 1), Li x5 (Ni a2 Co b2 Mn c2 )O4 (0.5 < x5 < 1.3, 0 < a2 < 2, 0 < b2 < 2, 0 < c2 < 2, a2 + b2 + c2 = 2) and Li x6 Mn 2-z1 Ni z1 O4 (0.5 < x6 < 1.3, 0 < z1 < 2).

[0033] According to another aspect of the present invention, there is provided a secondary battery including the above-mentioned slurry for electrode manufacturing. Here, the secondary battery including the slurry for electrode manufacturing means that it is made by using the slurry for electrode manufacturing, and thus includes the components in the above-mentioned slurry.

[0034] The secondary battery described above includes a positive electrode, a negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode can be prepared from an electrode manufacturing paste containing the above carbon nanotubes. The secondary battery can be a lithium secondary battery. In addition, the secondary battery can be a cylindrical, square, or pouch-type secondary battery, but as long as it is a type equivalent to a charge-discharge device, there is no particular limitation.

[0035] The DCIR (direct current internal resistance value) of the secondary battery described above can be 10 Ω or less, and the DCIR value can be a value measured in an electrode made by mixing a lithium manganese composite oxide active material, carbon nanotubes according to the present invention, and an adhesive used in the following examples of the present invention.

[0036] According to another aspect of the present invention, a battery module including the above secondary battery as a unit cell and a battery pack including the same can also be provided. For example, the battery pack can be used as a power source for at least one medium or large-sized device selected from the group consisting of power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); or energy storage systems.

[0037] Advantages of the Invention

[0038] According to the present invention, a carbon nanotube dispersion can be provided. The carbon nanotube dispersion has a low viscosity by controlling the fine powder content during the carbon nanotube processing process and can provide an electrode with excellent electrical properties such as high conductivity.

[0039] According to the present invention, the control of the fine powder size and content of the above carbon nanotubes can be achieved by a low-speed dry powder processing method in carbon nanotube powder processing technology. According to this low-speed dry powder processing method, not only can the fine powder size and content be effectively controlled as described above, but also the damage to carbon nanotubes during the processing can be reduced, and a slurry with a high content and low viscosity can be provided. Description of the Drawings

[0040] Figure 1 Schematic diagrams or photographs showing various processing apparatuses that can be used for processing carbon nanotubes.

[0041] Figure 2It is a graph showing the change in powder conductivity or slurry surface resistance based on the fine powder particle size D5 and the amount of fine powder (below 17.4 μm) according to Experimental Example 3, and is also a graph showing the change in the internal resistance DCIR value based on the above-mentioned slurry surface resistance obtained.

[0042] Figure 3 A graph showing the change in powder conductivity based on the fine powder particle sizes D50 and D90 according to Experimental Example 4. Detailed implementation mode

[0043] Hereinafter, in order to help understand the present invention, the present invention will be described in more detail with reference to preferred embodiments. The following embodiments are examples presented for the purpose of illustrating the invention, and thus the scope of protection of the present invention should not be limited thereto.

[0044] [Examples and Comparative Examples]

[0045] 1. Processing of carbon nanotubes

[0046] The multi-walled carbon nanotubes (10 walls, bundled, with a central diameter of 10 nm) are subjected to dry processing under different conditions according to the processing device used. The types of the above-mentioned processing devices (low-speed bead mill, cutting mill, rotor-type bead mill) and processing conditions (time, rpm, bead size, etc.) used in each comparative example and example are shown in Table 1. In addition, the schematic diagrams and photos of the low-speed bead mill used in the examples of the present invention and various processing devices available as comparative examples are shown in Figure 1 in.

[0047] 2. Preparation of carbon nanotube dispersion

[0048] The above-mentioned micronized carbon nanotubes are mixed by content in a solution of polyvinylpyrrolidone (PVP, with a molecular weight of 40,000 g / mol to 80,000 g / mol) dissolved in N-methylpyrrolidone, and a dispersion composition is prepared by a homogenizer.

[0049] 3. Manufacture of positive electrode

[0050] The positive electrode active material NCM811 is mixed in the ratio of [layered compound represented by the chemical formula Li1(Ni 0.8 Co 0.1 Mn 0.1 )O2]: conductive material [the above-mentioned prepared carbon nanotubes]: binder [PVDF, with a molecular weight of 60,000 Da] = 98:1:1, made into a slurry, and then coated on an aluminum foil current collector by a coater and dried to obtain a positive electrode.

[0051] 4. Manufacture of secondary battery

[0052] A solution prepared by mixing ethylene carbonate and dimethyl carbonate in a ratio of 3:7 and adding LiPF6 at a concentration of about 1.2 M was used as the electrolyte. The positive electrode used the positive electrode prepared above, and the counter electrode used a lithium electrode to assemble a coin cell.

[0053] [Analysis conditions]

[0054] The following analyses were performed on the carbon nanotubes obtained by the above-mentioned processing, i.e., micronization, the dispersion liquid containing the above-mentioned carbon nanotubes, or the secondary battery.

[0055] 1. Viscosity

[0056] For the above-prepared dispersion liquid, measurements were carried out at 23 °C and 50 s -1 conditions using a Haake viscometer (Φ35 mm plate).

[0057] 2. Powder conductivity

[0058] The powder conductivity of the carbon nanotubes processed dry by a processing device such as a low-speed bead mill was measured. The above powder conductivity was measured using a Han tech company (HPRM model) device in the applied pressure range of 200 kgf / cm 2 to 2000 kgf / cm 2 and the resistance value was obtained by comparing with a density of 0.8 g / cc.

[0059] 3. Particle size distribution

[0060] After diluting the above carbon nanotube dispersion liquid processed dry, the particle size distribution was measured using a particle size analyzer (Mastersizer 2000 of Malvern company).

[0061] 4. Surface resistance

[0062] The dispersion liquid containing the above carbon nanotubes was coated on a PET film using a bar coater, then dried at 120 °C, and then measured by the four-probe method (4-point probe) using a Mitsubishi Chemical Corporation's MCP-T610 device.

[0063] 5. DCIR

[0064] Under coin cell conditions, the secondary battery was charged and discharged under a certain C-rate condition, and its DCIR value was measured.

[0065] [Experimental example 1] Comparison according to the carbon nanotube processing method

[0066] As described above, for multi-walled carbon nanotubes, after dry processing under different conditions using a processing device, the properties of the obtained carbon nanotubes and their dispersions were measured, and the results are listed in Table 1 below.

[0067] Table 1

[0068]

[0069]

[0070] It can be confirmed from Table 1 above that Comparative Examples 1 to 7 with a particle size distribution D5 of less than 7 μm have a lower powder conductivity than Example 1 with a particle size distribution D5 of 7 μm or more, which means a reduction in their electrical properties. In particular, in Example 1, since the particle size distribution D5 satisfies the range of 7 μm or more and 14 μm or less, it not only exhibits a high powder conductivity but also a low viscosity, thus enabling uniform coating properties during the electrode manufacturing process.

[0071] [Experimental Example 2] Comparison according to bead mill conditions

[0072] Based on the conditions of Example 1, the powder conductivity of the powder processed under different bead mill conditions (time, filling rate, RPM, bead mixture) and the particle size and viscosity of the dispersion prepared using the powder were compared, and the results are shown in Table 2 below.

[0073] Table 2

[0074]

[0075]

[0076] It can be seen from Table 2 above that the particle size distribution D5 conditions according to the present invention can be controlled by the grinding time. In the cases of Comparative Examples 11 and 12, although milder conditions were used compared to Comparative Example 8, resulting in a decrease in the content of fine powder, since D5 still did not reach 7 μm or more, the powder conductivity was low, and thus the powder processing state also showed non-uniformity. In the case of Example 5, by using a mixture of two types of beads, the particle size distribution D5 conditions can be satisfied by changing other conditions (bead conditions) without changing the grinding time. In addition, as shown in Example 6, by repeating the experiment of Example 1, it can be confirmed that the present invention has good repeatability.

[0077] [Experimental Example 3] Confirming the relationship between the fine powder size and content and battery performance

[0078] Confirm the battery performance based on the fine powder particle size D5 and the fine powder content. For this purpose, as described above, a positive electrode is prepared using carbon nanotubes and a positive electrode active material, etc., and a secondary battery is assembled using the above positive electrode. The powder conductivity, the surface resistance of the dispersion liquid, and the DCIR were measured, and the results are shown in Table 3 below and Figure 2 as shown.

[0079] Table 3

[0080]

[0081]

[0082] From the above Table 3 and Figure 2 it can be confirmed that the particle size distribution D5 and the fine powder content (the fine powder content with a particle size of 17.4 μm or less) affect the powder conductivity, and further the above powder conductivity affects the surface resistance of the dispersion liquid, resulting in differences in the final battery performance. In other words, the particle size distribution D5 and the fine powder content (the fine powder content with a particle size of 17.4 μm or less) have a direct correlation with the battery performance. In particular, when the particle size distribution D5 reaches 7 μm or more and the carbon nanotube content with a particle size of 17.4 μm or less satisfies 30 vol% or less, a lower surface resistance of the dispersion liquid and a lower DCIR value can be exhibited.

[0083] [Experimental Example 4] Confirm the relationship between the fine powder size and content and the battery performance

[0084] Confirm the relationship between the average particle size (D50) and the large particle size (D90) in the particle size distribution and the powder conductivity in the same manner as in Experimental Example 3, and the results are shown in Table 4, Table 5 below and Figure 3 as shown.

[0085] Table 4

[0086]

[0087] Table 5

[0088]

[0089]

[0090] From the above Table 4, Table 5 below and Figure 3 it can be confirmed that the average particle size (D50) and the large particle size (D90) have no effect on the powder conductivity. In addition, as shown in Comparative Example 2-1 and Comparative Example 1-1, even if the pulverization conditions are changed, if D5 does not reach 7 μm or more, a high conductivity performance cannot be achieved.

[0091] Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art can understand that the present invention can be variously modified and changed without departing from the spirit and scope of the present invention described in the appended claims.

Claims

1. A carbon nanotube dispersion, characterized in that the D5 of the above-mentioned carbon nanotubes has a particle size distribution of 7 μm or more.

2. The carbon nanotube dispersion according to claim 1, characterized in that in the above-mentioned carbon nanotubes, based on the total volume of the carbon nanotubes, the content of carbon nanotubes with a particle size of 17.4 μm or less is 30% by volume or less.

3. The carbon nanotube dispersion according to claim 1, characterized in that the solid content is 5% or more.

4. The carbon nanotube dispersion according to claim 1, characterized in that the viscosity under the condition of a shear rate of 50 / s is 2000 cp or less.

5. The carbon nanotube dispersion according to claim 1, characterized in that the above-mentioned particle size distribution D5 is 7 μm or more and 14 μm or less.

6. The carbon nanotube dispersion according to claim 5, characterized in that the above-mentioned particle size distribution D5 is 7 μm or more and 9 μm or less.

7. The carbon nanotube dispersion according to claim 1, characterized in that the D50 of the above-mentioned carbon nanotubes has a particle size distribution of 15 μm to 50 μm.

8. The carbon nanotube dispersion according to claim 1, characterized in that the D90 of the above-mentioned carbon nanotubes has a particle size distribution of 45 μm to 200 μm.

9. The carbon nanotube dispersion according to claim 1, characterized in that the powder conductivity of the above-mentioned carbon nanotubes is 50 S / cm or more.

10. The carbon nanotube dispersion according to claim 1, characterized in that the above-mentioned carbon nanotubes are at least one selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, triple-walled carbon nanotubes, and multi-walled carbon nanotubes.

11. The carbon nanotube dispersion according to claim 1, characterized in that the central diameter of the above-mentioned carbon nanotubes is 4 nm to 50 nm.

12. A slurry for manufacturing an electrode, characterized in that it includes: carbon nanotubes with a D5 of the particle size distribution of 7 μm or more.

13. The slurry for manufacturing an electrode according to claim 12, characterized in that it further includes: at least one selected from conductive materials, electrode active materials, and binders other than carbon nanotubes.

14. A secondary battery, characterized in that it includes: the slurry for manufacturing an electrode according to claim 13.

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