KR102532086B1 - Carbon nanotube despersion, manufacturing method for same, slurry composition for electrode comprising same, eletrode comprising same and lithum secondary battery comprising same - Google Patents

Abstract

The present specification relates to carbon nanotube dispersion, which contains carbon nanotubes having a specific surface area (BET) of 250 to 750 m^2/g; a first dispersant having an amide group; and a second dispersant having an aromatic ring, and a viscosity of 1,300 cPs or less at a temperature of 25℃ and a shear rate of 15 sec^-1, a manufacturing method thereof, a slurry composition for an electrode comprising the same, an electrode comprising the same and a lithium secondary battery comprising the same. According to the present specification, the carbon nanotube dispersion shows improved dispersibility of the carbon nanotubes.

Description

Carbon nanotube dispersion, method for preparing the same, electrode slurry composition including the same, electrode including the same, and lithium secondary battery including the same BATTERY COMPRISING SAME}

The present specification relates to a carbon nanotube dispersion, a method for preparing the same, an electrode slurry composition including the same, an electrode including the same, and a lithium secondary battery including the same.

A secondary battery is a battery that can be used repeatedly through a charging process in the opposite direction to a discharging process in which chemical energy is converted into electrical energy. A secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode and the negative electrode generally consist of an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is prepared by applying an electrode slurry composition including an electrode active material, a conductive material, a binder, and the like on an electrode current collector, drying it, and then rolling it.

The conductive material is to improve the conductivity of the electrode active material, and conventionally, a point-shaped conductive material such as carbon black has been mainly used. However, since the dotted conductive material does not have a high electrical conductivity improvement effect, it must be used in an excessive amount to obtain a sufficient effect, thereby reducing the content of the electrode active material and lowering the battery capacity.

In order to improve this problem, attempts to apply highly conductive carbon nanotubes (Carbon NanoTubes, CNTs) as a conductive material have been actively made. Since carbon nanotubes can achieve high conductivity with a small amount, the use of carbon nanotubes can significantly reduce the amount of conductive material compared to the case of using carbon black, thereby increasing the electrical capacity. there is

In order for carbon nanotubes to be used as an anode conductive material, it is necessary to prepare a low-viscosity aqueous dispersion in terms of processability.

Polyvinylpyrrolidone (PVP), a dispersing agent having an amide group, is a polymer surfactant and is used as a dispersing agent, emulsifying agent, thickening agent, etc. in various dispersion systems, and is known to be effective even when dispersing carbon nanotubes (Patent Document 1). .

In addition, it is known that polyacrylic acid or tannic acid, which are polyacids containing a carboxyl group, is also effective in dispersing carbon nanotubes.

From the above information, it can be assumed that a better CNT dispersion effect can be obtained when polyvinylpyrrolidone and polyacid are mixed. It is generated to form insoluble matter or aggregates, and there is a problem that the dispersibility of the dispersion is rather poor.

KR No. 10-2011-0118460

Toxicol. Res., 2015, 4, 160-168

The present invention relates to a carbon nanotube dispersion with improved dispersibility of carbon nanotubes, a method for preparing the same, an electrode slurry composition including the same, an electrode including the same, and a lithium secondary battery including the same.

An exemplary embodiment of the present invention is a carbon nanotube having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; and a second dispersant having an aromatic ring, and a viscosity of 1,300 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ .

In addition, another embodiment of the present invention is a carbon nanotube having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; and mixing a second dispersing agent having an aromatic ring.

In addition, another embodiment of the present invention provides an electrode slurry composition including the above-described carbon nanotube dispersion, an electrode active material, and a binder.

In addition, another embodiment of the present invention provides an electrode including an electrode active material layer formed by the electrode slurry composition described above.

In addition, another embodiment of the present invention provides a lithium secondary battery including the electrode described above.

The carbon nanotube dispersion according to an exemplary embodiment of the present invention has a remarkably low viscosity and improved dispersibility of the carbon nanotubes in the dispersion.

The carbon nanotube dispersion according to an exemplary embodiment of the present invention has excellent coating properties and processability when used in electrode production.

1 to 3 show the results of Experimental Example 1.

Hereinafter, the present invention will be described in detail.

A carbon nanotube dispersion according to an exemplary embodiment of the present invention refers to a dispersion containing carbon nanotubes. Specifically, it means that the carbon nanotubes are dispersed in the dispersion and do not aggregate with each other.

An exemplary embodiment of the present invention is a carbon nanotube having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; and a second dispersant having an aromatic ring, and a viscosity of 1,300 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ .

In one embodiment of the present invention, the carbon nanotube dispersion is characterized by a viscosity of 1,300 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ . The viscosity may be 1,200 cPs or less, 1,000 cPs or less, 900 cPs or less, 800 cPs or less, or 600 cPs or less. Considering the object of the present invention, the lower the viscosity, the better, so the lower limit is not particularly limited, but may be 1 cPs or more, 3 cPs or more, or 5 cPs or more. When the above viscosity range is satisfied, the carbon nanotubes of the carbon nanotube dispersion do not agglomerate with each other, and the processability is improved when used in electrode manufacturing.

The viscosity of the carbon nanotube dispersion may be measured by a method commonly used in the field to which this technology belongs. For example, it may be measured at a measurement temperature of 25° C. and a shear rate of 15 sec ^-1 using Brookfield's DVNextCP Rheometer. For more accurate measurement, the prepared carbon nanotube dispersion may be measured after being stored at 25° C. for one week.

In one embodiment of the present invention, the carbon nanotube dispersion is characterized in that it includes carbon nanotubes having a specific surface area (BET) of 250 m ² /g to 750 m ² /g. The specific surface area (BET) of the carbon nanotubes may be 300 m ² /g to 700 m ² /g or 350 m ² /g to 650 m ² /g. Within the above numerical range, the electrical conductivity of the carbon nanotubes is excellent and the aggregation phenomenon can be controlled.

In general, carbon nanotubes are easily agglomerated due to mutual van der Waals forces, and a dispersion technique capable of well dispersing the agglomerated carbon nanotubes when dispersed in a solvent is required. When the carbon nanotubes are aggregated with each other, there is a problem in that the viscosity of the dispersion is increased. The high viscosity of the dispersion may increase the viscosity of the slurry during the manufacture of secondary battery electrodes, thereby creating dispersion non-uniformity between the anode material, which is an electrode material, and the binder.

Various types of carbon nanotubes can be selected for each purpose/performance. For example, single-walled carbon nanotubes (SWCNTs) are expensive due to high difficulty in manufacturing, and have a high specific surface area (>800 m ² /g), which limits the increase in solid content due to high viscosity of the dispersion. Multi-walled carbon nanotubes (MWCNTs) with a low specific surface area (<250 m ² /g) have the advantage of being easily expandable and having low viscosity, but the aggregation phenomenon inherent in the material is so large that it cannot suppress the volume expansion that occurs during charging and discharging of the electrode. Performance is limited.

The present inventors have developed a dispersion liquid with improved dispersibility and economical electrode production using carbon nanotubes having a specific surface area (BET) of 250 m ² /g to 750 m ² /g.

In one embodiment of the present invention, the carbon nanotube dispersion includes a first dispersant having an amide group; and a second dispersant having an aromatic ring. The first dispersant having an amide group is effective in dispersing carbon nanotubes, and the complex structure of the second dispersant having an aromatic ring can effectively reduce the viscosity of the dispersion. In addition, the oxygen of the amide group included in the first dispersant and the functional group (hydroxyl group or carboxy group) of the second dispersant form a hydrogen bond with each other, thereby contributing to reducing the viscosity of the dispersion.

In one embodiment of the present invention, the first dispersant may form a hydrogen bond with a hydroxyl group or a carboxy group of the second dispersant to be described later by having an amide group.

In one embodiment of the present invention, the first dispersant is polyvinylpyrrolidone, polyester amide, polycarboxylic amide, polyamido amine, It may be thioamido amine, water soluble nylon, or a combination thereof. By having an amide group, the first dispersing agent may exhibit a more improved effect of improving viscosity and an effect of inhibiting change in viscosity with time.

In one embodiment of the present invention, the weight average molecular weight of the first dispersant is 1,000 g/mol to 100,000 g/mol, preferably 2,000 g/mol to 80,000 g/mol, more preferably 2,000 g/mol to 30,000 g/mol, even more preferably 2,000 g/mol to 15,000 g/mol. When the weight average molecular weight of the first dispersant is less than 1,000 g/mol, carbon nanotube dispersing performance is deteriorated, and a problem in that the first dispersant is eluted during electrode preparation may occur, and when it exceeds 100,000 g/mol, carbon Since the viscosity of the nanotube dispersion may increase and the coating property and processability may deteriorate, it is preferable to adjust the viscosity within the above range.

In one embodiment of the present invention, the second dispersant is a hydroxyl group; or a carboxyl group. The second dispersant is a hydroxyl group; Alternatively, by having a carboxyl group, a hydrogen bond may be formed with the amide group of the first dispersant described above.

In one embodiment of the present invention, the second dispersant may include two or more aromatic rings. For example, the second dispersant is selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatenol and tannic acid It may be one or more, preferably tannic acid, quercetin, epigallocatechin gallate, or a combination thereof.

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

In one embodiment of the present invention, the weight ratio of the first dispersant and 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 dispersing effect of the carbon nanotubes is improved so that the viscosity of the dispersion may be maintained low.

In one embodiment of the present invention, the content of the first dispersant may be 0.01 wt% to 10 wt%, 0.01 wt% to 5 wt%, or 0.1 wt% to 3 wt% based on the total weight of the dispersion. .

In one embodiment of the present invention, the content of the second dispersant may be 0.01 wt% to 10 wt%, 0.01 wt% to 5 wt%, or 0.1 wt% to 3 wt% based on the total weight of the dispersion. .

In one embodiment of the present invention, the carbon nanotube dispersion is characterized in that it contains an alkali metal element. As the carbon nanotube dispersion includes the alkali metal element, dispersibility of materials included in the dispersion may be improved.

The first dispersant and the second dispersant may form a hydrogen bond to contribute to a decrease in the viscosity of the dispersion, but there is a problem in that insolubles or complexes are formed because the above hydrogen bond is too strong. In this case, many restrictions are imposed on the selection of the dispersing agent, such as adjusting the contents of the first dispersing agent and the second dispersing agent or using only a specific type of the first dispersing agent and/or the second dispersing agent. However, when the carbon nanotube dispersion includes an alkali metal element, the viscosity of the dispersion may be maintained low by suppressing the aggregation of the first dispersant and the second dispersant with the alkali metal element. The improvement of the aggregation phenomenon can be confirmed by visually observing whether or not aggregation occurs after preparing a carbon nanotube dispersion containing the materials and leaving it for a certain period of time.

In one embodiment of the present invention, the form of the alkali metal is not particularly limited, but may exist in the form of an alkali metal salt containing an alkali metal.

In one embodiment of the present invention, the carbon nanotube dispersion is selected from the group consisting of KOH, NaOH, LiOH, KOHH ₂ O, NaOHH ₂ O, LiOHH ₂ O, K ₂ CO ₃ , Na ₂ CO ₃ and LiCO ₃ One or more alkali metal salts may be included.

In one embodiment of the present invention, the content of the alkali metal element may be 1 ppm or more and 300 ppm or less, 5 ppm or more and 200 ppm or less, 5 ppm or more and 150 ppm or less, based on the entire carbon nanotube dispersion.

In one embodiment of the present invention, the content of the alkali metal element may be adjusted in consideration of the type and content of the first dispersant.

In one embodiment of the present invention, the first dispersant includes a polyvinylpyrrolidone-based resin, and the molar ratio of the alkali metal salt is based on 100 mol of vinylpyrrolidone units included in the polyvinylpyrrolidone-based resin. , 60 mol or less, 30 mol or less, or 25 mol or less. The lower limit of the content is not particularly limited, but may be 0.1 mol or more, 0.2 mol or more, or 0.5 mol or more. When the above range is satisfied, the viscosity of the carbon nanotube dispersion may be adjusted to 1,300 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ .

The molar ratio of the alkali metal salt can be calculated using the molecular weight of the alkali metal salt and vinylidone unit and the weight % of the alkali metal salt and polyvinylidone. Specifically, it can be calculated through Equation 1 below.

[Equation 1]

Molar ratio of alkali metal salt = {(wt% of alkali metal salt)/(molecular weight of alkali metal salt)}/{(wt% of polyvinylidone)/(molecular weight of vinylidone unit)}*100

For example, based on the total weight of the dispersion, the contents of polyvinylpyrrolidone and alkali metal salt (LiOH) are 0.9 wt% and 0.003 wt%, respectively, the molecular weight of alkali metal salt (LiOH) is 24 g / mol, and vinylidone When the molecular weight of the monomer is 111.14 g/mol, the molar ratio of the alkali metal salt is calculated as 1.5 mol based on 100 mol of the vinylpyrrolidone unit [1.5 = {(0.003)/(24)}/{(0.9)/(111.14 )}*100]

The vinylpyrrolidone unit means a unit composed of a 5-membered lactam linked to a vinyl group, and refers to a unit constituting the polyvinylpyrrolidone-based resin. Specifically, it may be a unit represented by Chemical Formula 2 below among polyvinylpyrrolidone represented by Chemical Formula 1 below.

[Formula 1]

[Formula 2]

In one embodiment of the present invention, the carbon nanotube is to improve the conductivity of the electrode, the graphite sheet has a cylindrical shape with a nano-sized diameter, and has an sp ² bonding structure. At this time, the characteristics of a conductor or a semiconductor are exhibited according to the angle and structure at which the graphite surface is rolled. Carbon nanotubes are single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs), depending on the number of bonds constituting the wall. carbon nanotube), and these carbon nanotubes may be appropriately selected according to the use of the dispersion. In addition, the carbon nanotubes may have a secondary shape formed by aggregating or arranging a plurality of carbon nanotubes, for example, a bundle in which a plurality of carbon nanotubes are arranged or aligned side by side in a certain direction ( It may be a bundle type carbon nanotube in the form of a bundle or a rope, or an entangled type carbon nanotube in the form of a sphere or potato in which a plurality of carbon nanotubes are entangled without a certain direction.

In one embodiment of the present invention, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or a combination thereof.

In one embodiment of the present invention, the carbon nanotubes may include two or more carbon nanotube units. The carbon nanotube unit may have a cylindrical shape in which a graphite sheet has a nano-sized diameter, and has an sp ² bonding structure.

In one embodiment of the present invention, the diameter of the carbon nanotube unit may be 1 nm or more and 200 nm or less, 1 nm or more and 150 nm or less, or 1 nm or more and 100 nm or less.

It is possible to improve the dispersibility of carbon nanotubes within the above numerical range and to prevent an increase in resistance when applied to an electrode.

In one embodiment of the present invention, the length of the carbon nanotube unit may be 0.1 μm or more and 200 μm or less, 0.1 μm or more and 150 μm or less, or 0.5 μm or more and 100 μm or less. It is possible to improve the dispersibility of carbon nanotubes within the above numerical range and to prevent an increase in resistance when applied to an electrode.

In one embodiment of the present invention, the aspect ratio (length/diameter) of the carbon nanotubes may be 5 to 50,000 or 10 to 15,000. It is possible to improve the dispersibility of carbon nanotubes within the above numerical range and to prevent an increase in resistance when applied to an electrode.

In one embodiment of the present invention, the average particle diameter (D50) of the carbon nanotubes may be 0.1 μm to 20 μm, 0.5 μm to 1 μm, 1 μm to 5 μm, or 2 μm to 4 μm. The average particle diameter (D50) means a particle diameter corresponding to 50% of the cumulative number in the particle diameter distribution curve of carbon nanotubes. The average particle diameter (D50) can be measured using, for example, a laser diffraction method. Within this range, carbon nanotubes do not aggregate with each other, and dispersibility may be improved.

In one embodiment of the present invention, the content of the carbon nanotubes may be 0.01 wt% to 10 wt%, preferably 0.1 wt% to 8 wt%, based on the total weight of the carbon nanotubes and dispersion. In the above numerical range, it is possible to prevent an increase in process cost due to a decrease in the loading amount during electrode manufacturing, and to solve problems such as decrease in adhesive strength due to binder migration when drying the electrode or increase in viscosity of the carbon nanotube dispersion. It can be prevented.

In an exemplary embodiment of the present invention, the value expressed by Equation 2 below of the carbon nanotube dispersion may be 2 to 10, 2 to 6.5, or 3 to 6. The value represented by Equation 2 below is the shear thinning index of the dispersion, and means the ratio of the viscosities measured at different shear rates. When the above range is satisfied, uniform mixing is possible during manufacture of the electrode by preventing the fluidity from deteriorating due to too high viscosity in a stationary state. In addition, it is possible to improve storage stability by preventing sedimentation of carbon nanotube particles.

[Equation 2]

Shear thinning index (STI) = V _low /V _high

In the above formula 2,

V _low is the viscosity of the dispersion measured at 25 ° C and a shear rate of 15 sec ^-1 ,

V _high is the viscosity of the dispersion measured at 25° C. and a shear rate of 150 sec ⁻¹ .

In one embodiment of the present invention, the value calculated from Equation 3 below of the carbon nanotube dispersion may be 1 to 5, 1 to 3, or 1.1 to 2. The value calculated by Equation 3 below shows the relationship between the shear thinning index (STI) characteristics of the above-described dispersion and the average particle diameter of the carbon nanotubes included in the dispersion. In general, if the carbon nanotube particle size (D50) is too small, the shear thinning index (STI) of the dispersion tends to increase as the carbon nanotubes aggregate with each other. In addition, if the particle diameter (D50) of the carbon nanotubes is too large, the carbon nanotubes are not sufficiently dispersed, so the carbon nanotubes form a network structure, and the overall viscosity and shear thinning index (STI) of the dispersion tend to increase.

However, in the carbon nanotube dispersion according to an exemplary embodiment of the present invention, by adjusting the value calculated by Equation 2 below to the above numerical range, even if the particle diameter of the carbon nanotube is small, the stability of the overall viscosity of the dispersion over time is improved. .

[Equation 3]

In the above formula 3,

STI is the shear thinning index (STI) of the dispersion,

D50 is the average particle diameter (D50) of the carbon nanotubes.

In one embodiment of the present invention, the carbon nanotube dispersion may further include a solvent. The solvent is used to pre-disperse carbon nanotubes and supply them as a carbon nanotube dispersion in order to prevent aggregation when the carbon nanotubes are directly mixed with an electrode active material and used as an electrode slurry composition.

In one embodiment of the present invention, the solvent may be an aqueous solvent. For example, the water-based solvent may be water. In this case, it is easy to control the viscosity of the dispersion.

In one embodiment of the present invention, the pH of the carbon nanotube dispersion may be 3 to 10. The pH may be 4 to 9 or 5 to 8. Within the above numerical range, it is possible to further suppress the phenomenon of aggregation of the above-described first dispersant and the second dispersant. Specifically, when the pH of the dispersion is out of the above range, the surface charge of the first and second dispersants becomes too strong or too weak, so hydrogen bonds become too strong and aggregation may occur. At this time, by adjusting the pH of the dispersion to the above numerical range, it is possible to further suppress the phenomenon of aggregation of the first dispersant and the second dispersant. The pH can be measured at 25°C.

An exemplary embodiment of the present invention is a carbon nanotube having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; and mixing a second dispersing agent having an aromatic ring.

In one embodiment of the present invention, a carbon nanotube having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; and the mixing of the second dispersant having an aromatic ring may be performed under a temperature condition in which physical properties do not change. For example, it may be carried out at a temperature of 50 ° C or less, more specifically 5 ° C to 50 ° C.

In one embodiment of the present invention, the step of dispersing the carbon nanotubes is a ball mill, a bead mill, a disc mill or a basket mill, a high pressure homogenizer ( high pressure homogenizer), etc., and more specifically, it may be performed by a milling method using a disc mill or high pressure homogenizer.

When milling by the disk mill, the size of the beads may be appropriately determined according to the type and amount of carbon nanotubes and the type of dispersant, specifically, the diameter of the beads is 0.1 mm to 5 mm, more specifically 0.5 mm. mm to 4 mm. In addition, the bead milling process may be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, at a speed of 5,000 rpm to 9,000 rpm.

The milling by the high-pressure homogenizer, for example, by pressurizing the mixture with a plunger pump of the high-pressure homogenizer and pushing it through the gap of the homogenization valve, cavitation, shear, It is made by forces such as impact and explosion.

Milling by the high-pressure homogenizer may be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, at a speed of 2,000 rpm to 5,000 rpm.

Milling by the high-pressure homogenizer may be performed under pressure conditions of 500 bar to 3,000 bar, and more specifically, pressure conditions of 1,000 bar to 2,000 bar.

In one embodiment of the present invention, the step of dispersing the carbon nanotubes may be performed for 10 minutes to 120 minutes, more specifically, 20 minutes to 90 minutes so that the carbon nanotubes can be sufficiently dispersed.

An exemplary embodiment of the present invention provides an electrode slurry composition including the above-described carbon nanotube dispersion, an electrode active material, and a binder.

In one embodiment of the present invention, the electrode active material includes a silicon-based electrode active material. The silicon-based electrode active material includes metal silicon (Si), silicon oxide (SiOx, where 0<x<2), silicon carbide (SiC), and a Si—Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13 element, or a Group 14 element). It is an element selected from the group consisting of elements, transition metals, rare earth elements, and combinations thereof, and may include at least one selected from the group consisting of Si). The element Y is 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, It may be selected from the group consisting of Se, Te, Po, and combinations thereof.

In one embodiment of the present invention, since the silicon-based electrode active material exhibits higher capacitance characteristics than the carbon-based electrode active material, when the silicon-based electrode active material is additionally included, better capacitance characteristics can be obtained. However, the silicon-based electrode active material has a large volume change during charging and discharging, and when charging and discharging are repeated, battery characteristics rapidly deteriorate and cycle characteristics are not sufficient, which makes commercialization difficult. However, when carbon nanotubes are used as a conductive material as in the present invention, an effect of improving cycle characteristics can be obtained when a silicon-based electrode active material is applied. Therefore, when the electrode slurry composition of the present invention including the carbon nanotube dispersion and the silicon-based electrode active material of the present invention is used, a secondary battery having excellent capacity characteristics and cycle characteristics can be implemented.

In one embodiment of the present invention, the electrode active material may further include another type of electrode active material together with the silicon-based electrode active material. Examples of the other types of electrode active materials include, for example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material may be used, such as a Sn-C composite, and among these, a carbonaceous material is particularly preferable.

In one embodiment of the present invention, the total amount of the electrode active material, which is a combination of the silicon-based electrode active material and other types of electrode active materials, is 70 to 99 wt%, preferably 80 to 99 wt% based on the total solid content in the electrode slurry composition It may be 98wt%. When the content of the electrode active material satisfies the above range, excellent capacity characteristics can be implemented.

In one embodiment of the present invention, the binder is for securing adhesion between active materials or between the active material and the current collector, and general binders used in the art may be used, and the type is not particularly limited. . Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxylate. Methylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated - EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used.

In one embodiment of the present invention, the binder may be included in an amount of 5 wt% or less, preferably 1 to 3 wt%, based on the total solid content in the electrode slurry composition. When the content of the binder satisfies the above range, excellent electrode adhesion may be implemented while minimizing an increase in electrode resistance.

In one embodiment of the present invention, the electrode slurry composition may further include a solvent, if necessary, for viscosity control. 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), diethyl formamide, dimethyl acetamide (DMAc), and N-methyl pyrrolidone (NMP); Methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl alcohols such as -2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; 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 glycol ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and the like, and any one or a mixture of two or more of these may be used, but is not limited thereto.

In one embodiment of the present invention, the electrode slurry composition may further include additives such as a viscosity modifier and a filler, if necessary.

One embodiment of the present invention provides an electrode including an electrode active material layer formed by the electrode slurry composition described above. Specifically, the electrode may be prepared by applying the electrode slurry composition of the present invention described above and drying it to form an electrode active material layer. More specifically, the electrode active material layer is obtained by applying the electrode slurry composition on the electrode current collector and then drying it, or applying the electrode slurry composition on a separate support body and then peeling it from the support body. It can be formed through a method of lamination on the entire surface. If necessary, after forming the electrode active material layer through the above method, a rolling process may be additionally performed. At this time, drying and rolling may be performed under appropriate conditions in consideration of the physical properties of the electrode to be finally manufactured, and are not particularly limited.

In one embodiment of the present invention, the electrode current collector is not particularly limited as long as it is a material that has conductivity without causing chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof. , surface treatment with carbon, nickel, titanium, silver, etc., or calcined carbon may be used.

In one embodiment of the present invention, the electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the electrode active material. In addition, the electrode current collector may be used in various forms such as, for example, a film, sheet, foil, net, porous material, foam, or non-woven fabric.

In one embodiment of the present invention, the electrode may be a negative electrode.

One embodiment of the present invention provides a lithium secondary battery including the electrode described above.

An exemplary embodiment of the present invention is an anode; cathode; and a separator and an electrolyte provided between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the above-described lithium secondary battery.

In one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and any separator used as a separator in a secondary battery can be used without particular limitation. Specifically, a porous polymer film as the separator, for example, a porous film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer A polymer film or a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

In one embodiment of the present invention, the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery, It is not limited to these.

Hereinafter, the present invention will be described in more detail through examples.

<Preparation of carbon nanotubes>

The following carbon nanotubes were prepared.

CNT-1 (multi-walled carbon nanotube, manufactured by JEIO, product name 6A, specific surface area 643 m ² /g, average unit diameter 5-7 nm)

CNT-2 (specific surface area 375 m ² /g, average diameter of monomers 9-10 nm)

CNT-3 (specific surface area 385 m ² /g, average diameter of monomers 5-9 nm)

CNT-4 (specific surface area 1,131 m ² /g, average diameter of monomers 1-2 nm)

CNT-5 (specific surface area 221 m ² /g, average diameter of monomers 7-12 nm)

CNT-6 (specific surface area 186 m ² /g, average diameter of monomers 13 nm)

<Preparation of the first dispersing agent>

A polyvinyl pyrrolidone (K15) compound obtained from MERK was prepared.

<Preparation of the second dispersing agent>

Tannic acid (TA) obtained from MERK was prepared.

<Preparation of dispersion>

Example 1

Carbon nanotube (6A, manufactured by JEIO) 1.5wt%, polyvinyl pyrrolidone (K15, MERK) 0.9wt% as a first dispersant, tannic acid (MERK) 0.3wt% as a second dispersant, water as a solvent After mixing to prepare a mixture of 1 kg, it was treated for 30 minutes at 3,000 rpm using a high-shear force in-line mixer (IM001 K&S Co.), and treated 7 times at a pressure of 1,500 bar using a high-pressure homogenizer to make carbon A nanotube dispersion was prepared.

At this time, the molar ratio of the alkali metal salt was 1.5 mol [={(0.003)/(24)}/{(0.9)/(111.14)}*100] based on 100 mol of the vinylpyrrolidone unit, according to Equation 1 below.

[Equation 1]

Molar ratio of alkali metal salt = {(wt% of alkali metal salt)/(molecular weight of alkali metal salt)}/{(wt% of polyvinylidone)/(molecular weight of vinylidone unit)}*100

Examples and Comparative Examples

For the remaining examples and comparative examples, dispersions were prepared by changing the weight and type of each material as shown in Tables 1 and 2 below, and physical properties were tested.

Experimental Example 1: Confirmation of dispersant aggregation

After sufficiently diluting the carbon nanotube dispersions of Example 1 and Comparative Example with diwater, coat them on Si wafers, dry them sufficiently at 60 ° C. for 30 minutes or more using a hot plate, and then apply COXEM's SPT-20 Ion sputter coater. was coated with Pt. Then, the surface was observed using COXEM's EM-30 SEM (15 kV), and the results are shown in FIGS. 1 to 3.

The test solution of Example 4 did not show aggregation and precipitation (FIG. 1), but the test solutions of Comparative Examples 4 and 5 confirmed that the dispersants aggregated with each other and even precipitated (FIG. 2: Comparative Example 4 , Figure 3: Comparative Example 5).

Experimental Example 2: Viscosity measurement

Brookfield's DVNextCP Rheometer was used and measured at a temperature of 25 °C and a shear rate of 15 sec ^-1 .

Experimental Example 3: Measurement of average particle diameter

A laser diffraction method was used and a commercially available laser diffraction particle size measuring device (Malvern Mastersizer 3000) was used. Before the measurement, the carbon nanotube dispersions of Examples and Comparative Examples were diluted sufficiently to have a concentration of 0.05 wt% or less, stabilized for 10 minutes, and then measured. The average particle diameter (D50) at 50% of the particle diameter distribution was calculated in the measuring device.

Experimental Example 4: pH measurement

It was measured using OHAUS ST3100 pH meter, and after calibrating the electrode with a buffer solution at 25 ° C, the electrode was put into the sample, stirred for 5 seconds, waited for 30 seconds until the signal was stable, and then the pH was measured.

Experimental Example 5: Solid content measurement

Solid content was measured using OHAUS's MB95 moisture analyzer. After putting about 3g of the sample on an aluminum sample plate, measure the starting weight, heat it up to 150℃ and measure the weight. If the weight changes less than 1mg for 60 seconds at 150℃, set it as dry weight and The solid content is calculated by the formula of

%DC (solid content) = dry weight/start weight x 100%

Experimental Example 6: Evaluation of Battery Charge/Discharge Characteristics

coin cell manufacturing

An electrode active material (including silicon microparticle and graphite at a weight ratio of 30:70) was mixed with water in the carbon nanotube dispersions of each Example and Comparative Example, and mixed for 30 minutes with a paste mixer to prepare an electrode slurry.

The electrode slurry was applied to a Cu foil current collector and dried for 4 hours at 75° C. under vacuum conditions.

After punching the dried electrode to a diameter of 14 mm, a counter electrode was made of Li metal (diameter of 15 mm) to manufacture a coin half cell 2032. At this time, the separator was prepared with a composition of Celgard 2450 and the electrolyte was LiPF6 (1 M) in ethylene carbonate (EC): diethylene carbonate (DEC) in 1: 1 volume ratio, and 100 uL was injected.

Evaluation of charge and discharge characteristics

The charge and discharge characteristics of the coin cell were evaluated at room temperature in the voltage range of 0.005 to 1.5V.

Initial efficiency (0.1C) = delithiation capacity (mAh/g) / lithiation capacity (mAh/g)

Charge/discharge life (0.5C) = number of cycles at the point of reaching 80% retention

division Example One 2 3 4 5 6 CNT type CNT-1 CNT-1 CNT-2 CNT-3 CNT-1 CNT-1 Specific surface area [m2/g] 643 643 375 385 643 643 Diameter [nm] 5 to 7 5 to 7 9-10 5 to 9 5 to 7 5 to 7 Content in dispersion [wt%] 1.5 1.5 1.5 1.5 15 1.5 dispersant First dispersant [wt%] 0.9 0.9 0.9 0.9 0.9 0.9 Second dispersant [wt%] 0.3 0.3 0.3 0.3 0.3 0.3 1st dispersant/2nd dispersant 3 3 3 3 3 3 alkali
metal salt LiOHweight 0.003 0.009 0.003 0.003 NaOHWeight 0.003 KOH weight 0.003 Alkali metal element content in dispersion (ppm) 7.5 22.5 7.5 7.5 16.5 20.9 Number of moles of alkali salt per 100 moles of N-vinylpyrrolidone 1.5 4.6 1.5 1.5 0.9 0.7 Properties Viscosity (15/s) 364 678 12 22 408 434 D50 (μm) 1.5 1.3 1.1 1.5 1.4 1.5 pH 6.7 7.2 5.6 7.5 6.6 6.7 Solid content (%) 2.76 2.69 2.77 2.75 2.81 2.74 Initial Efficiency (%) 85.9 85.9 85.7 85.7 85.8 85.8 charge/discharge life 29 29 13 14 27 25

division comparative example One 2 3 4 5 6 CNT type CNT-1 CNT-1 CNT-1 CNT-4 CNT-5 CNT-6 Specific surface area [m2/g] 643 643 643 1,131 221 186 Diameter [nm] 5 to 7 5 to 7 5 to 7 1~2 7 to 12 13 Content in dispersion [wt%] 1.5 1.5 1.5 1.5 3 3 dispersant First dispersant [wt%] 0.9 not included 1.2 2.25 0.675 0.675 Second dispersant [wt%] 0.3 1.2 not included 0.75 0.225 0.225 1st dispersant/2nd dispersant 3 - - 3 3 3 alkali
metal salt LiOHweight - 0.012 - 0.0075 0.00225 0.00225 NaOHWeight - - KOH weight - - Alkali metal element content in dispersion (ppm) - 83.4 - 52.1 15.6 15.6 Number of moles of alkali salt per 100 moles of N-vinylpyrrolidone - - - 0.7 0.7 0.7 Properties Viscosity (15/s) 1,720 Over 3,000 Over 3,000 1,457 76 26 D50 (μm) 1.9 4.3 4.6 0.9 1.1 0.9 pH 6.4 6.8 7.3 4.5 6.4 6.4 Solid content (%) 2.77 2.76 2.71 4.6 3.94 3.94 Initial Efficiency (%) Impossible to make slurry due to high viscosity (exceeding 1,300) 85.6 85.6 charge and discharge life 10 10

From the above results, when the carbon nanotubes having a specific surface area (BET) of 250 m ² /g to 750 m ² /g are included, and the first dispersing agent having an amide group and the second dispersing agent having an aromatic ring are included (Example 1 to 6), it was confirmed that the viscosity of the dispersion was as low as 1,300 cPs or less, and the battery characteristics were excellent.

When the dispersion did not contain an alkali element (Comparative Example 1), it was confirmed that the viscosity of the dispersion exceeded 1,300 cps.

In addition, when the first dispersant or part of the second dispersant was not included, it was confirmed that the viscosity of the dispersion liquid exceeded 1,300 cps (Comparative Examples 2 and 3).

On the other hand, when the specific surface area exceeds 750 m ² /g (Comparative Example 4), when the viscosity of the dispersion exceeds 1,300 cps and the specific surface area (BET) is less than 250 m ² /g (Comparative Example 5 and 6), it was confirmed that the battery characteristics were remarkably deteriorated.

Claims (15)

carbon nanotubes having a specific surface area (BET) of 250 m ² /g to 750 m ² /g;
A first dispersing agent having an amide group;
a second dispersing agent having an aromatic ring; and
Contains an alkali metal salt,
A carbon nanotube dispersion having a viscosity of 1,300 cPs or less at a shear rate of 25° C. and 15 sec ^-1 . The method of claim 1,
The first dispersant is polyvinylpyrrolidone, polyester amide, polycarboxylic amide, polyamido amine, thioamido amine, water-soluble A carbon nanotube dispersion that is a water soluble nylon or a combination thereof. The method of claim 1,
The second dispersant is a hydroxyl group; Or a carbon nanotube dispersion containing a carboxyl group. The method of claim 1,
the first dispersant; and a second dispersant in a weight ratio of 1:10 to 10:1. delete The method of claim 1,
The alkali metal salt is KOH, NaOH, LiOH, KOHH ₂ O, NaOHH ₂ O, LiOHH ₂ O, K ₂ CO ₃ , Na ₂ CO ₃ and LiCO ₃ Carbon nanotubes containing one or more selected from the group consisting of dispersion. The method of claim 6,
The first dispersant includes a polyvinylpyrrolidone-based resin,
The molar ratio of the alkali metal salt is 60 mol or less based on 100 mol of the vinylpyrrolidone unit contained in the polyvinylpyrrolidone-based resin. The method of claim 1,
The carbon nanotube dispersion of which the average particle diameter (D50) of the carbon nanotubes is 0.1 μm to 20 μm. The method of claim 1,
The content of the carbon nanotubes is 0.01 wt% to 10 wt% based on the total weight of the carbon nanotube dispersion. The method of claim 1,
A carbon nanotube dispersion that has a pH of 3 to 10. carbon nanotubes having a specific surface area (BET) of 250 m ² /g to 750 m ² /g; A first dispersing agent having an amide group; And mixing a second dispersing agent having an aromatic ring.
A method for preparing a carbon nanotube dispersion according to any one of claims 1 to 4 and 6 to 10. An electrode slurry composition comprising the carbon nanotube dispersion according to any one of claims 1 to 4 and 6 to 10, an electrode active material, and a binder. An electrode comprising an electrode active material layer formed of the electrode slurry composition according to claim 12. The method of claim 13,
The electrode is a negative electrode. A lithium secondary battery comprising the electrode according to claim 14.

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