Carbon nanotube dispersion, its manufacturing method, electrode slurry composition containing the same, electrode containing the same, and secondary battery containing the same

Abstract

The present disclosure relates to a carbon nanotube dispersion containing carbon nanotubes, a first dispersant having an amide group, a second dispersant having at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group, and sulfur. The present disclosure also relates to a method for producing the dispersion, an electrode slurry composition containing the dispersion, an electrode containing the electrode slurry composition, and a secondary battery containing the electrode.

Description

[Technical Field]

[0001] This application claims priority to Korean Patent Application No. 10-2022-0112212, filed on September 5, 2022, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a carbon nanotube dispersion, a method for producing the same, an electrode slurry composition containing the same, an electrode containing the same, and a secondary battery containing the same. [Background technology]

[0003] A secondary battery can be repeatedly used through a discharge process, which converts chemical energy into electrical energy, and a charge process, which is the reverse of the discharge process. A secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Generally, the positive electrode and the negative electrode each comprise an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is formed by applying an electrode slurry composition containing an electrode active material, a conductive material, and a binder onto the electrode current collector, followed by drying and rolling.

[0004] Conductive materials are used to improve the conductivity of electrode active materials. Conventionally, spherical conductive materials such as carbon black have been used. However, because spherical conductive materials do not show a significant effect in improving electrical conductivity, excessive amounts of conductive materials are used to achieve sufficient effects. This reduces the amount of electrode active material in the electrode, resulting in a problem of reduced battery capacity.

[0005] To overcome these problems, active efforts are being made to use highly conductive carbon nanotubes (CNTs) as a conductive material. Even a small amount of carbon nanotubes can provide good conductivity, and the use of carbon nanotubes significantly reduces the amount of conductive material used in battery electrodes compared to using carbon black, thereby increasing the electrical capacity of the battery.

[0006] In order to use carbon nanotubes as a negative electrode conductive material, it is necessary to prepare an aqueous dispersion with low viscosity from the viewpoint of processability.

[0007] Polyvinylpyrrolidone (PVP), a dispersant containing an amide group, is a polymer surfactant. PVP is used as a dispersant, emulsifier, thickener, etc. in various dispersion systems and is known to be effective in dispersing carbon nanotubes (Patent Document 1).

[0008] In addition, polyacrylic acid and tannic acid, which contain carboxyl groups, are also known to be effective in dispersing carbon nanotubes.

[0009] Summarizing the above known information, it is assumed that the combined use of polyvinylpyrrolidone and polyacid would result in better CNT dispersion effects. However, in reality, mixing these materials usually results in excessively strong bonds between the two materials, which leads to the formation of insoluble matter or agglomerates, reducing the dispersibility of the dispersion. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Application No. 10-2011-0118460 [Non-patent literature]

[0011] [Non-Patent Document 1] Toxicol. Res., 2015.4, 160-168 Summary of the Invention [Problem to be solved by the invention]

[0012] The present disclosure relates to a carbon nanotube dispersion liquid with improved dispersibility, a method for producing the same, an electrode slurry composition containing the same, an electrode containing the same, and a secondary battery containing the same. [Means for solving the problem]

[0013] One embodiment of the present disclosure provides a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant containing an amide group; a second dispersant comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group; and sulfur.

[0014] Another embodiment of the present disclosure provides a method for producing the above-mentioned carbon nanotube dispersion, the method comprising mixing carbon nanotubes, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group.

[0015] A further embodiment of the present disclosure provides an electrode slurry composition comprising the above-described carbon nanotube dispersion, a silicon-based electrode active material, and a binder.

[0016] A further embodiment of the present disclosure provides an electrode comprising an electrode active material layer made from the above-described electrode slurry composition.

[0017] A further embodiment of the present disclosure provides a secondary battery including the above-described electrode. [Effects of the Invention]

[0018] A carbon nanotube dispersion according to one embodiment of the present disclosure has significantly lower viscosity and improved carbon nanotube dispersibility.

[0019] The carbon nanotube dispersion according to an embodiment of the present disclosure has excellent coating properties and processability when used in electrode manufacturing. [Brief explanation of the drawings]

[0020] [Figure 1] Figure 1 shows the experimental results of Experimental Example 1; [Figure 2-4]2 to 4 show the results of checking whether sulfur is present in the first dispersants used in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure will be described in detail below.

[0022] A carbon nanotube dispersion according to an embodiment of the present disclosure is a dispersion containing carbon nanotubes. Specifically, the carbon nanotube dispersion refers to a system in which carbon nanotubes are dispersed in a dispersant and do not aggregate.

[0023] One embodiment of the present disclosure provides a carbon nanotube dispersion comprising: carbon nanotubes; a first dispersant comprising an amide group; a second dispersant comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group; and sulfur.

[0024] It has been known that a first dispersant containing an amide group is effective in dispersing carbon nanotubes (Patent Document 1), and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group has the effect of reducing the viscosity of the dispersion due to the influence of the functional group (Non-Patent Document 1).

[0025] Furthermore, the oxygen of the amide group in the first dispersant and the functional group (hydroxyl or carboxyl group) in the second dispersant form hydrogen bonds with each other, which contributes to reducing the viscosity of the dispersion. However, strong hydrogen bonds can lead to the formation of insoluble matter or aggregates (complexes). In this case, there are many constraints on the selection of dispersant. For example, it is necessary to control the content of each of the first and second dispersants, or to use only specific types of dispersants as the first and / or second dispersants.

[0026] The inventors discovered that the aggregation problem between the first dispersant and the second dispersant is alleviated when the dispersion contains elemental sulfur, leading to the completion of the present disclosure. In such a case, even if the dispersion contains carbon nanotubes with a large specific surface area, the viscosity of the dispersion is low. The effect of alleviating aggregation can be confirmed by visually observing the carbon nanotube dispersion after storing it for a certain period of time.

[0027] The carbon nanotube dispersion according to one embodiment of the present disclosure contains carbon nanotubes with excellent conductivity and dispersibility, such that carbon nanotube aggregation is minimized, as evidenced by the dispersion's significantly lower viscosity.

[0028] The carbon nanotube dispersion according to one embodiment of the present disclosure is characterized by containing sulfur. The sulfur may be present in the dispersion in the form of a compound, an element, or an ion. For example, the sulfur may be derived from sulfur-containing compounds, which are described below. The presence and content of sulfur can be confirmed by elemental analysis.

[0029] In one embodiment of the present disclosure, the sulfur content in the carbon nanotube dispersion may be 0.01 to 10 wt %, 0.05 to 8 wt %, or 0.1 to 5 wt % based on the solid content. The sulfur content range can be satisfied by controlling the content of sulfur-containing compounds. The sulfur content can be measured and calculated using an elemental analyzer (EA), the details of which will be described later.

[0030] In one embodiment of the present disclosure, the sulfur content may be 0.01 to 20%, 0.1 to 10%, or 1 to 5% of the total content of oxygen (O) and nitrogen (N) on a solids basis. When the above numerical ranges are satisfied, the ratio of the total content of oxygen and nitrogen elements involved in hydrogen bonding to the sulfur content is controlled, dispersants do not aggregate, and the dispersibility of carbon nanotubes is improved. The content of each element can be measured and calculated using an elemental analyzer (EA), the details of which will be described later.

[0031] In one embodiment of the present disclosure, the first dispersant may be partially or completely sulfur-substituted. If a portion of the first dispersant is sulfur-substituted, the remainder of the first dispersant may be composed of non-sulfur-substituted materials. For example, the first dispersant may be composed of a sulfur-substituted portion and a non-sulfur-substituted portion.

[0032] In one embodiment of the present disclosure, the sulfur substitution ratio of the first dispersant may comprise 10 to 100 mol %, 20 to 80 mol %, or 40 to 60 mol %.

[0033] In one embodiment of the present disclosure, the first dispersant has a Fourier transform infrared (FTIR) spectrum of 1,110 cm -1 ~1,050cm -1 The first peak, 1,140 cm -1 ~1,180cm -1 and the second peak at 1,180 cm -1 ~1,220cm -1 and a third peak. The first through third peaks indicate the presence of S=O bonds in the dispersant, and the presence of these peaks confirms that the first dispersant is sulfur substituted.

[0034] In one embodiment of the present disclosure, the first dispersant has an amide group, so that the first dispersant can form a hydrogen bond with a hydroxyl group or a carboxyl group of the second dispersant described below.

[0035] In one embodiment of the present disclosure, the first dispersant may be polyvinylpyrrolidone, polyesteramide, polycarboxylamide, polyamidoamine, thioamidoamine, water-soluble nylon, or a combination thereof. Because the first dispersant has an amide group, the first dispersant improves viscosity and suppresses changes in viscosity over time.

[0036] In one embodiment of the present disclosure, the first dispersant may have a weight-average molecular weight of 1,000 to 100,000 g / mol, preferably 2,000 to 80,000 g / mol, more preferably 2,000 to 30,000 g / mol, and even more preferably 2,000 to 15,000 g / mol. If the weight-average molecular weight of the first dispersant is less than 1,000 g / mol, the dispersibility of carbon nanotubes may decrease, potentially resulting in the problem of the first dispersant leaching out during electrode production. On the other hand, if the weight-average molecular weight exceeds 100,000 g / mol, the viscosity of the carbon nanotube dispersion may increase, potentially resulting in poor coatability and processability. Therefore, it is preferable that the weight-average molecular weight of the first dispersant be within the above-mentioned range.

[0037] In one embodiment of the present disclosure, the second dispersant has a hydroxyl group or a carboxyl group, so that the second dispersant can form hydrogen bonds with the amide group of the first dispersant described above.

[0038] In one embodiment of the present disclosure, the second dispersant may contain an aromatic ring, in which case the viscosity of the dispersion can be effectively reduced due to the complex structure of the second dispersant.

[0039] In one embodiment of the present disclosure, the second dispersing agent may contain two or more aromatic rings. For example, the second dispersing agent may be one or more types selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatenol, and tannic acid. Preferably, the second dispersing agent may be tannic acid, quercetin, epigallocatechin gallate, or a combination thereof.

[0040] In one embodiment of the present disclosure, the second dispersant may be a phenolic compound. In the phenolic compound, one or more aromatic rings may have one or more structures selected from the group consisting of a phenol structure, a catechol structure, a gallol structure, and a naphthol structure. The phenolic structure is a structure in which one hydroxyl group is bonded to a benzene ring, the catechol structure is a structure in which two hydroxyl groups are bonded to a benzene ring, the gallol structure is a structure in which three hydroxyl groups are bonded to a benzene ring, and the naphthol structure is a structure in which one hydroxyl group is bonded to a naphthalene.

[0041] In one embodiment of the present disclosure, the second dispersant may be a polyacrylic acid compound, which is an acrylic acid compound containing two or more acidic hydrogen atoms.

[0042] In one embodiment of the present disclosure, the polyacrylic acid compound may be polyacrylic acid (PAA) or a polyacrylic acid derivative, which may be polyacrylic acid-co-maleic acid (PAAMA).

[0043] In one embodiment of the present disclosure, the second dispersant may comprise a compound containing an aromatic ring, a polyacrylic acid compound, or a combination thereof, as described above for the compound containing an aromatic ring and the polyacrylic acid compound.

[0044] In one embodiment of the present disclosure, the weight ratio of the first dispersant to the second dispersant may be 1:10 to 10:1, 1:5 to 5:1, or 1:1 to 1:5. When the above range is satisfied, the effect of dispersing the carbon nanotubes is improved and the viscosity of the dispersion is maintained at a low level.

[0045] In one embodiment of the present disclosure, the content of the first dispersant may be in the range of 0.01 to 10 wt %, 0.01 to 5 wt %, or 0.1 to 3 wt %, based on the total weight of the dispersion.

[0046] In one embodiment of the present disclosure, the content of the second dispersant may be in the range of 0.01 to 10 wt %, 0.01 to 5 wt %, or 0.1 to 3 wt %, based on the total weight of the dispersion.

[0047] In one embodiment of the present disclosure, carbon nanotubes are used to improve the electrical conductivity of electrodes. Carbon nanotubes are formed by forming graphite sheets into cylindrical shapes with nanoscale diameters. Carbon nanotubes are sp 2 Carbon nanotubes have a bonding structure. Depending on the angle at which the graphite sheet is rolled and the structure of the graphite sheet, they can be conductive or semiconductive. Depending on the number of bonds that form the walls, carbon nanotubes can be classified as single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). These carbon nanotubes can be appropriately selected depending on the purpose of the dispersion. Furthermore, carbon nanotubes can form two-dimensional shapes in which carbon nanotubes are aggregated or arranged two-dimensionally. For example, carbon nanotubes can be regularly arranged in a specific direction to form bundles or ropes. Alternatively, carbon nanotubes can be irregularly arranged in many directions and entangled to form spheres or potato shapes.

[0048] In one embodiment of the present disclosure, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs).

[0049] In one embodiment of the present disclosure, the BET specific surface area of ​​the carbon nanotubes is 10 to 5,000 m 2 / g, preferably 30 to 3,000m 2 / g, more preferably 50 to 2,000m 2 / g. When the above numerical range is satisfied, the effect of increasing the conductivity is excellent. The BET specific surface area of ​​carbon nanotubes may vary depending on the type of carbon nanotube.

[0050] In one embodiment of the present disclosure, the BET specific surface area of ​​the single-walled carbon nanotubes is 800 to 5,000 m 2 / g, preferably 800 to 3,000 m 2 / g, more preferably 900 to 2,000 m 2 When the above numerical range is satisfied, an excellent effect of increasing the electrical conductivity is obtained.

[0051] In one embodiment of the present disclosure, the BET specific surface area of ​​the multi-walled carbon nanotubes is 10 to 1,200 m 2 / g, preferably 30 to 1,000m 2 / g, more preferably 50 to 800m 2 When the above numerical range is satisfied, an excellent effect of increasing the electrical conductivity is obtained.

[0052] In one embodiment of the present disclosure, the content of carbon nanotubes may be in the range of 0.01 to 10 wt %, preferably 0.1 to 8 wt %, based on the total weight of the carbon nanotube dispersion. The content of carbon nanotubes can be appropriately adjusted depending on the specific surface area of ​​the carbon nanotubes used. For example, 2 When using carbon nanotubes with a specific surface area of ​​1 / g or more, the content of the carbon nanotubes may be in the range of 0.01 to 5 wt %, preferably 0.01 to 3 wt %, and more preferably 0.01 to 2 wt %, based on the total weight of the carbon nanotube dispersion. If the specific surface area and content of the carbon nanotubes are outside the above ranges, problems such as increased process costs due to a reduced load during electrode production, decreased adhesive strength due to binder migration during electrode drying, and increased viscosity of the carbon nanotube dispersion may occur.

[0053] In one embodiment of the present disclosure, the carbon nanotube may be composed of two or more carbon nanotube units, which are formed by forming a graphite sheet into a cylindrical shape with a nanoscale diameter, and sp 2 It may have a bond structure.

[0054] In an embodiment of the present disclosure, the diameter of the carbon nanotube unit may be in the range of 1 to 200 nm, 1 to 150 nm, or 1 to 100 nm. When the above numerical range is satisfied, the dispersibility of the carbon nanotubes is improved, and when the carbon nanotubes are applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0055] In an embodiment of the present disclosure, the length of the carbon nanotube unit may be in the range of 0.1 to 200 μm, 0.1 to 150 μm, or 0.5 to 100 μm. When the above numerical range is satisfied, the dispersibility of the carbon nanotubes is improved, and when the carbon nanotubes are applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0056] In one embodiment of the present disclosure, the aspect ratio (i.e., the ratio of length to diameter) of the carbon nanotubes may be in the range of 5 to 50,000 or 10 to 15,000. When the above numerical range is satisfied, the dispersibility of the carbon nanotubes is improved, and when the carbon nanotubes are applied to an electrode, an increase in the resistance of the electrode can be prevented.

[0057] In one embodiment of the present disclosure, the average particle size (D50) of the carbon nanotubes may be in the range of 0.1 to 20 μm, 0.5 to 1 μm, 1 to 5 μm, or 2 to 4 μm. The average particle size (D50) refers to the particle size value at 50% of the cumulative particle size distribution of the carbon nanotubes. The average particle size (D50) can be measured using, for example, a laser diffraction method. When the above range is satisfied, the carbon nanotubes do not aggregate with each other, and the dispersibility of the carbon nanotubes can be improved.

[0058] In one embodiment of the present disclosure, the temperature is 25°C, the shear rate is 15 sec -1The viscosity of the carbon nanotube dispersion at this temperature may be 4,000 cPs or less, 3,000 cPs or less, 1,000 cPs or less, or 600 cPs or less. There is no particular limit to the lower limit of the viscosity range, but the lower the viscosity, the better the dispersibility. However, considering the objectives of the present disclosure, the viscosity may be 10 cPs or more, 30 cPs or more, or 50 cPs or more. When the above viscosity range is satisfied, the carbon nanotubes in the carbon nanotube dispersion do not aggregate, improving the processability when the carbon nanotube dispersion is used to manufacture electrodes.

[0059] The viscosity of the carbon nanotube dispersion can be measured by a method commonly used in the technical field to which this technology belongs. For example, the viscosity can be measured at 25°C and a shear rate of 15 sec. -1 The rheological properties of carbon nanotubes can be measured using a Brookfield DVNextCP Rheometer at 25°C. For more accurate measurements, the prepared carbon nanotube dispersion can be stored at 25°C for one week before measurement.

[0060] In one embodiment of the present disclosure, the value of the carbon nanotube dispersion calculated according to the following formula 1 may be in the range of 2 to 10, 2 to 6.5, or 3 to 6. The calculated value of the following formula 1 is the shear thinning index of the dispersion. This index refers to the ratio of viscosities measured at different shear rates. When the above range is satisfied, the fluidity of the dispersion is prevented from decreasing due to an excessive increase in viscosity that occurs under static conditions, enabling uniform mixing during electrode fabrication. In addition, sedimentation of carbon nanotube particles is prevented, thereby improving the storage stability of the carbon nanotube dispersion.

[0061] [Formula 1] Shear Thinning Index (STI) = V low / V high In the above formula 1, V low is at a temperature of 25°C and a shear rate of 15 sec -1 is the viscosity of the dispersion at V high is at a temperature of 25°C and a shear rate of 150 sec -1is the viscosity of the dispersion at

[0062] In one embodiment of the present disclosure, the value calculated by the following formula 2 for a carbon nanotube dispersion may be in the range of 1 to 5, 1 to 3, or 1.1 to 2. The calculated value of the following formula 2 indicates the relationship between the shear thinning index (STI) characteristics of the dispersion and the average particle size of the carbon nanotubes contained in the dispersion. Generally, when the particle size (D50) of the carbon nanotubes is excessively small, the carbon nanotubes tend to aggregate, thereby increasing the shear thinning index (STI) of the dispersion. Furthermore, when the particle size (D50) of the carbon nanotubes is excessively large, the carbon nanotubes are not sufficiently dispersed and form a network structure, thereby increasing the overall viscosity and shear thinning index (STI) of the carbon nanotubes.

[0063] However, in the carbon nanotube dispersion according to an embodiment of the present disclosure, when the calculated value of Equation 2 is within the above numerical range, the viscosity stability over time is improved even if the particle size of the carbon nanotubes is small.

[0064] [Formula 2] JPEG2025529298000001.jpg16160In the above formula 2, STI is the shear thinning index of the dispersion, D50 is the average particle size of the carbon nanotubes.

[0065] In one embodiment of the present disclosure, the carbon nanotube dispersion may contain an alkali metal element. Because the carbon nanotubes of the present disclosure contain an alkali metal element, the dispersibility of the material contained in the dispersion may be improved. Specifically, the first dispersant and the second dispersant contained in the dispersion may form a complex. These complexes have low solubility in solvents such as water, which increases the viscosity of the dispersion. However, the alkali metal element contained in the carbon nanotube dispersion of the present disclosure solves this problem by dissolving the complex.

[0066] In one embodiment of the present disclosure, the form of the alkali metal is not particularly limited, and the alkali metal may be present in the form of its alkali metal salt.

[0067] In one embodiment of the present disclosure, the concentration of the alkali metal element in the carbon nanotube dispersion may be in the range of 1 to 300 ppm, 5 to 200 ppm, or 5 to 150 ppm.

[0068] In one embodiment of the present disclosure, the carbon nanotube dispersion liquid may contain at least one alkali metal salt selected from the group consisting of KOH, NaOH, K2CO3, Na2CO3, or LiCo3.

[0069] In one embodiment of the present disclosure, when the first dispersant is a polyvinylpyrrolidone resin, the molar ratio of the alkali metal salt may be 60 moles or less, 30 moles or less, or 25 moles or less per 100 moles of vinylpyrrolidone monomer. While the lower limit of the molar ratio is not particularly limited, the molar ratio may be 0.1 moles or more, 1 mole or more, or 2 moles or more. When the above range is satisfied, the viscosity of the carbon nanotube dispersion is adjusted to 25°C and a shear rate of 15 sec. -1 It can be controlled to a range of 1,300 cPs or less.

[0070] The molar ratio of the alkali metal salt can be calculated from the molecular weights of the alkali metal salt and vinylidone monomer, and the contents (wt%) of the alkali metal salt and polyvinylidone. Specifically, the value can be calculated using the following equation 3.

[0071] [Formula 3] Molar ratio of alkali metal salt = {(weight % of alkali metal salt) / (molecular weight of alkali metal salt)} / {(weight % of polyvinylidone) / (molecular weight of vinylidone monomer)}*100

[0072] For example, if the respective contents of polyvinylpyrrolidone and alkali metal salt (LiOH) are in the range of 0.6 wt % and 0.01 wt %, based on the total weight of the dispersion, and if the molecular weight of the alkali metal salt (LiOH) is 24 g / mol and the molecular weight of the vinylidone monomer is 111.14 g / mol, the molar ratio of the alkali metal salt is calculated to be 7.7 moles per 100 moles of vinylpyrrolidone monomer [7.7 = {(0.01) / (24)} / {(0.6) / (111.14)}*100].

[0073] The vinylpyrrolidone monomer refers to a five-membered lactam ring bonded to a vinyl group, and is a unit that constitutes a polyvinylpyrrolidone resin. Specifically, the vinylpyrrolidone monomer may be a monomer represented by Chemical Formula 2 in polyvinylpyrrolidone represented by Chemical Formula 1.

[0074] [ka]

[0075] [ka]

[0076] In one embodiment of the present disclosure, the carbon nanotube dispersion may further contain a solvent, which is used to pre-disperse the carbon nanotubes and supply them as a carbon nanotube dispersion in order to prevent aggregation of the carbon nanotubes, which may occur when the carbon nanotubes are directly mixed with the electrode active material to prepare the electrode slurry composition.

[0077] In one embodiment of the present disclosure, the solvent may be an aqueous solvent. For example, the aqueous solvent may be water. When water is used as the solvent, it is easy to control the viscosity of the dispersion liquid and there are advantages in that toxic substances are not produced.

[0078] Another embodiment of the present disclosure relates to a method for producing a carbon nanotube dispersion, comprising mixing carbon nanotubes, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group.

[0079] In one embodiment of the present disclosure, the step of mixing the carbon nanotubes, the first dispersant containing an amide group, and the second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group may be performed under temperature conditions that do not change the physical properties. For example, this step may be performed at a temperature of 50°C or less, more specifically, in the range of 5°C to 50°C.

[0080] In one embodiment of the present disclosure, the step of dispersing carbon nanotubes in a dispersion liquid may be carried out by a milling method using a ball mill, a bead mill, a disc mill, a basket mill, or a high-pressure homogenizer, more specifically, a milling method using a disc mill or a high-pressure homogenizer.

[0081] When using a disk mill, the bead size can be determined appropriately depending on the type and amount of carbon nanotubes and the type of dispersant. Specifically, the bead diameter may be in the range of 0.1 to 5 mm, more specifically 0.5 to 4 mm. Furthermore, bead milling may be performed at a speed of 2,000 to 10,000 rpm, more specifically 5,000 to 9,000 rpm.

[0082] When milling using a high-pressure homogenizer, the plunger pump pushes the mixture through the gap in the homogenizing valve, and the mixture is subjected to cavitation, shear, impact, explosion, etc. as it passes through the gap.

[0083] In one embodiment of the present disclosure, the step of dispersing the carbon nanotubes in the dispersion liquid may be carried out for 10 to 120 minutes, more specifically 20 to 90 minutes, so that the carbon nanotubes are sufficiently dispersed.

[0084] A further embodiment of the present disclosure relates to an electrode slurry composition comprising the above carbon nanotube dispersion, electrode active material, and binder.

[0085] In one embodiment of the present disclosure, the electrode active material includes a silicon-based electrode active material. The silicon-based electrode active material may include at least one selected from the group consisting of metallic silicon (Si), silicon oxide (SiOx, where 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but does not include Si in the examples of silicon-based electrode active materials). The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0086] The silicon-based electrode active material exhibits higher capacity characteristics than the carbon-based electrode active material. Therefore, when such a silicon-based electrode active material is used, better capacity characteristics can be obtained. However, since the silicon-based electrode active material exhibits a large volume change during charge and discharge, the battery characteristics deteriorate rapidly as the battery is repeatedly charged and discharged. This deteriorates the cycle characteristics and hinders the commercialization of the battery using this material. However, when carbon nanotubes are used as a conductive material as in the present disclosure, the cycle characteristics can be improved even when a silicon-based electrode active material is used. Therefore, by using the electrode slurry composition of the present disclosure including the carbon nanotube dispersion of the present disclosure and the silicon-based electrode active material, a secondary battery having excellent cycle characteristics and capacity characteristics can be realized.

[0087] In one embodiment of the present disclosure, the electrode slurry composition may further contain other types of electrode active materials in addition to the silicon-based electrode active material. Examples of additional electrode active materials include carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, and Al alloys; metal oxides capable of doping and dedoping with lithium, such as SnO, vanadium oxide, and lithium vanadium oxide; and composite materials, such as Sn-C composites, containing metal compounds and carbon materials. Among these, carbon materials are particularly preferred.

[0088] In one embodiment of the present disclosure, the total amount of the electrode active material, which is a combination of the silicon-based electrode active material and another type of electrode active material, may be in the range of 70 to 99 wt %, preferably 80 to 98 wt %, based on the total solid content of the electrode slurry composition. When the content of the electrode active material satisfies the above range, excellent capacity characteristics can be obtained.

[0089] In one embodiment of the present disclosure, a binder is used to ensure adhesion between active materials or between an active material and a current collector. A binder commonly used in this field can be used, and the type of binder is not particularly limited. For example, the binder may be polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorinated rubber, or any of various copolymers thereof, or a mixture of two or more of these.

[0090] In one embodiment of the present disclosure, the binder may be contained in an amount of 5 wt % or less, preferably 1 to 3 wt %, based on the total solid content of the electrode slurry composition. When the binder content satisfies the above range, an increase in electrode resistance is minimized, and excellent electrode adhesion can be obtained.

[0091] In an embodiment of the present disclosure, the electrode slurry composition may further contain a solvent for viscosity control, if necessary. In this case, the solvent may be water, an organic solvent, or a mixture thereof. Examples of the organic solvent include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; and glycerin and trimethylolpropane. Examples of suitable solvents include polyhydric alcohols such as PEG, pentaerythritol, and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and β-propiolactone. Examples of suitable solvents include polyhydric alcohols such as PEG, pentaerythritol, and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and β-propiolactone. Examples of suitable solvents include, but are not limited to, those listed above.

[0092] In an embodiment of the present disclosure, the electrode slurry composition may further contain additives such as a viscosity modifier and a filler, if necessary.

[0093] In one embodiment of the present disclosure, an electrode is provided that includes an electrode active material layer formed from the above-described electrode slurry composition. Specifically, the electrode can be manufactured by applying the above-described electrode slurry composition of the present disclosure and drying it to form an electrode active material layer. More specifically, the electrode active material layer can be formed by applying the electrode slurry composition to an electrode current collector and then drying it. Alternatively, the electrode active material layer can be formed by applying the electrode slurry composition to a support, peeling the resulting film from the support, and laminating the film on an electrode current collector. After the electrode active material layer is formed in this manner, an additional rolling process can be performed, if necessary. In this case, the drying and rolling processes can be performed under appropriate conditions taking into account the physical properties of the final electrode.

[0094] In one embodiment of the present disclosure, the material of the electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery cell. For example, any material selected from copper, stainless steel, aluminum, nickel, titanium, or alloys thereof can be used. Alternatively, a member surface-treated with carbon, nickel, titanium, or silver, or calcined carbon can be used.

[0095] In one embodiment of the present disclosure, the electrode current collector may have a thickness of 3 to 500 μm, and forming fine irregularities on the surface of the electrode current collector can strengthen the bond between the electrode active material layer and the electrode current collector. The electrode current collector can be provided in any form. For example, the electrode current collector can be in the form of a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0096] In one embodiment of the present disclosure, the electrode may be a negative electrode.

[0097] One embodiment of the present disclosure provides a secondary battery including the above-described electrode.

[0098] One embodiment of the present disclosure provides a secondary battery including a positive electrode; a negative electrode; and a separator and an electrolyte interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the above-described electrode.

[0099] In one embodiment of the present disclosure, the secondary battery may be a lithium secondary battery.

[0100] In one embodiment of the present disclosure, the separator separates the negative electrode and the positive electrode from each other and provides a path for the movement of lithium ions. Separators that can be used in secondary batteries are not particularly limited. Specifically, a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, can be used as the separator. Alternatively, a laminate of two or more layers made of the above-mentioned exemplary materials can be used as the separator. Furthermore, conventional porous nonwoven fabric members made of high-melting-point glass fibers or polyethylene terephthalate fibers can also be used as the separator. Furthermore, to obtain good heat resistance and mechanical strength, coated separators containing ceramic components or polymer materials can be used, and these separators may have a single-layer or multi-layer structure.

[0101] In one embodiment of the present disclosure, the electrolyte can be selected from organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, inorganic solid electrolytes, and inorganic molten electrolytes that can be used in secondary batteries, but the type of electrolyte is not limited thereto. [Example]

[0102] The present disclosure will be described in more detail below with reference to examples of the present disclosure.

[0103] <Preparation of carbon nanotubes> The following carbon nanotubes are prepared.

[0104] - CNT-1 (single-walled carbon nanotubes; manufactured by OCSiA; product name 01RW03; specific surface area > 800m 2 / g; average diameter of each unit = 2 nm) - CNT-2 (multi-walled carbon nanotubes; manufactured by JEIO; product name 6A; specific surface area = 643 m 2 / g; average diameter of each unit = 9-10 nm) - CNT-3 (multi-walled carbon nanotubes; manufactured by LG CHEM; product name BT1003M; specific surface area = 186 m 2 / g; average diameter of each unit = 13 nm)

[0105] <Preparation of First Dispersant> Ar gas was added to the reactor to stabilize the atmosphere. A mixed solution was prepared by dissolving the monomer N-vinylpyrrolidone and potassium sulfite in water. The mixed solution was stirred under an Ar atmosphere at 40°C for 24 hours to react, and then slowly cooled to room temperature. A certain amount of water was evaporated from the mixed solution to prepare a concentrated solution. The concentrated solution was precipitated with acetone, filtered, and dried to produce sulfur (S)-containing PVP-1.

[0106] PVP-2 purchased from Aldrich and PVP-3 purchased from Ashland were prepared as sulfur-free dispersants.

[0107] Attenuated total reflectance (ATR) was used to confirm the presence of sulfur in the primary dispersant. PVP-1 exhibited a peak at 1,030 cm -1 , 1,160cm -1 , and 1,200 cm -1 The first dispersant, PVP-1, showed a peak at the same position (Fig. 2), whereas PVP-2 (Fig. 3) and PVP-3 (Fig. 4) did not show a peak at the same position. These results confirmed that PVP-1, the primary dispersant, contained sulfur.

[0108] <Preparation of Second Dispersant> Tannic acid (TA) purchased from Aldrich and polyacrylic acid (PAA, weight average molecular weight 2,000) purchased from Thermo Scientific were prepared.

[0109] <Preparation of Dispersion> Example 1 A carbon nanotube dispersion was prepared by mixing 0.4 wt% CNT-1 as carbon nanotubes, 0.48 wt% PVP-1 as a first dispersant, 0.12 wt% TA as a second dispersant, and 99 wt% distilled water as a solvent using a high-pressure homogenizer.

[0110] Examples and Comparative Examples In other examples and comparative examples, dispersions were prepared with varying weights and types of each material as shown in Table 1 below. The physical properties of each dispersion were analyzed.

[0111] The compositions of the dispersions prepared in the Examples and Comparative Examples and the results of each experimental example are summarized in the following Table 1. The content of each component is based on the total weight of the dispersion.

[0112] Experimental Example 1: Observation of dispersant aggregation Test solutions were prepared in the same manner as in the above examples and comparative examples, except that carbon nanotubes were not added. Each test solution was mixed at room temperature using a vortex mixer and allowed to stand for 6 hours to observe aggregation and precipitation.

[0113] The test solutions of Examples 4 and 1 did not exhibit aggregation and precipitation, but the test solution of Comparative Example 1 exhibited aggregation and precipitation (FIG. 1).

[0114] Experimental Example 2: Viscosity measurement Using a Brookfield DVNextCP Rheometer, the test was performed at 25°C and a shear rate of 2.5 sec. -1 and 15 seconds -1 The viscosity was measured at 1000 kJ / min.

[0115] Experimental Example 3: Calculation of average particle size A commercially available laser diffraction particle sizer (Malvern Mastersizer 3000) was used for laser diffraction. The instrument was used to calculate the mean particle size at 50% of the particle size distribution (D50). D10 and D90 are the particle sizes at 10% and 90% of the particle size distribution, respectively.

[0116] Experimental Example 4: Measurement of sulfur content - Sample preparation The dispersions prepared in the Examples and Comparative Examples were dried in a convection oven at 90°C for 3 days, and then powder samples were prepared using a mixer grinder.

[0117] -- Determination of sulfur content An elemental analyzer (EA) was used for the measurement.

[0118] Organic samples were oxidized to CO2, H2O, NO2, and SO2 using a catalyst at high temperature (approximately 1,000°C), and the resulting gases were separated using a GC column (packed column). Detection was performed using a thermal conductivity detector (TCD), and calibration curves were prepared in advance using standard substances for C, H, N, and S. The content of each element was quantified in % from the GC chromatogram.

[0119] [Table 1] JPEG2025529298000005.jpg230155JPEG2025529298000006.jpg149161

[0120] The above results confirmed that when sulfur was not contained (Comparative Examples 1 to 4), the viscosity of each dispersion increased significantly. In other words, the first and second dispersants aggregated, increasing the viscosity of the dispersion.

[0121] The dispersant in Example 1 contains a first dispersant and a second dispersant that can form hydrogen bonds with each other. However, the first dispersant is substituted with sulfur, which inhibits hydrogen bonding between the first and second dispersants, resulting in less aggregation between the first and second dispersants. Meanwhile, the dispersions in Comparative Examples 1 and 2 were identical to the dispersion in Example 1, except that non-sulfur-substituted PVP was used as the first dispersant. A problem occurred in which numerous hydrogen bonds were formed between the first and second dispersants, causing the viscosity of the dispersion to increase by more than 10 times.

[0122] The dispersion of Comparative Example 3 was the same as that of Example 5, except that PVP-2 was used as the first dispersant. Because many hydrogen bonds were formed between the first and second dispersants, the viscosity of the dispersion increased by more than 20 times (at 2.5 s).

[0123] The dispersion of Comparative Example 4 was the same as that of Example 6, except that PVP-2 was used as the first dispersant. In this case, many hydrogen bonds were formed between the first and second dispersants, which caused a problem in that the viscosity of the dispersion increased by more than 20 times (at 2.5 / s).

[0124] Elemental sulfur can be added to the dispersion by using sulfur-substituted PVP (Examples 1 to 6) or by adding a sulfide salt (Example 7). Both methods significantly reduced the viscosity of the dispersion. Among these, the method using sulfur-substituted PVP was found to reduce the viscosity more significantly.

[0125] From the above results, it can be concluded that adding sulfur to the carbon nanotube dispersion significantly reduces the viscosity of the dispersion.

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a first dispersant containing an amide group, a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group, and sulfur.

2. 2. The dispersion according to claim 1, wherein the elemental sulfur is contained in an amount of 0.01 to 10% by weight based on the total weight of the solid content of the dispersion.

3. 2. The dispersion according to claim 1, wherein the content of the sulfur element is 0.01% to 20% relative to the total content of oxygen (O) and nitrogen (N), based on the total weight of the solid content of the dispersion.

4. 10. The dispersion of claim 1, wherein the first dispersant is partially or fully sulfur substituted.

5. 10. The dispersion of claim 1, wherein the proportion of sulfur-substituted first dispersant in the first dispersant is 10 to 100 mole percent.

6. The first dispersant has a Fourier transform infrared (FTIR) spectrum of 1,110 to 1,050 cm －１ The first peak, 1,140-1,180 cm －１ and a second peak at 1,180-1,220 cm －１ 2. The dispersion of claim 1, wherein the dispersion has at least one peak selected from the group consisting of:

7. 10. The dispersion of claim 1, wherein the first dispersing agent is polyvinylpyrrolidone, polyesteramide, polycarboxylamide, polyamidoamine, thioamidoamine, water-soluble nylon, or a combination thereof.

8. The dispersion of claim 1 , wherein the second dispersant comprises an aromatic ring.

9. 10. The dispersion of claim 1, wherein the first dispersant and the second dispersant are included in a weight ratio of 1:10 to 10:

1.

10. The carbon nanotubes have a BET specific surface area of ​​10 to 5,000 m ２ 10. The dispersion of claim 1 having a molecular weight of 1000 or more.

11. 2. The dispersion according to claim 1, wherein the carbon nanotubes have an average particle size (D50) of 0.1 to 20 μm.

12. 12. A method for producing a carbon nanotube dispersion liquid according to claim 1, comprising mixing carbon nanotubes, a first dispersant containing an amide group, and a second dispersant containing at least one functional group selected from the group consisting of a hydroxyl group and a carboxyl group.

13. An electrode slurry composition comprising an electrode active material, a binder, and the carbon nanotube dispersion liquid according to any one of claims 1 to 11.

14. An electrode comprising an electrode active material layer formed from the electrode slurry composition of claim 13.

15. 15. The electrode of claim 14, wherein the electrode is a negative electrode.

16. A secondary battery comprising the electrode according to claim 14.

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