KR102532085B1 - 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 is a carbon nanotube; A first dispersing agent having an amide group; A carbon nanotube dispersion comprising a second dispersant having an aromatic ring and having a viscosity of 2,000 cPs or less at 25° C. and a shear rate of 15 sec ^-1 , a method for preparing the same, an electrode slurry composition comprising the same, It relates to an electrode including the same and a lithium secondary battery including the same.

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}

This specification claims the benefit of the filing date for No. 10-2021-0139170 filed with the Korean Intellectual Property Office on October 19, 2021, the contents of which are incorporated herein.

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.

KR No. 10-2011-0118460

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

The present specification provides 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.

An exemplary embodiment of the present invention is a carbon nanotube;

A first dispersing agent having an amide group; and

Including a second dispersing agent having an aromatic ring,

25 ℃ and 15 sec ^-1 It provides a carbon nanotube dispersion that has a viscosity of 1,000 cPs or less at a shear rate (shear rate).

Another embodiment of the present invention is a carbon nanotube;

A first dispersing agent having an amide group; and

Comprising the step of mixing a second dispersing agent having an aromatic ring

A method for preparing the above-described carbon nanotube dispersion is provided.

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.

Another embodiment of the present invention provides an electrode including an electrode active material layer formed by the electrode slurry composition described above.

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.

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; A first dispersing agent having an amide group; and a second dispersing agent having an aromatic ring, and a viscosity of 2,000 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ .

The carbon nanotube dispersion may lower the viscosity of the dispersion by including a first dispersant having an amide group and a second dispersant having an aromatic ring. In particular, the complex structure of the second dispersant having an aromatic ring can effectively reduce the viscosity of the dispersion.

In particular, when the second dispersant includes a functional group (hydroxyl group or carboxy group), 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 to reduce the viscosity of the dispersion. has a contributing effect. However, there is a problem that insolubles or complexes are formed because the above hydrogen bonds are 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.

The inventors of the present invention have developed a dispersion in which the phenomenon of aggregation of the above-described first and second dispersants is improved, even though the dispersion includes the above-described first and second dispersants, and completed the invention. The improvement in aggregation can be confirmed by visually observing whether or not aggregation occurs after preparing a carbon nanotube dispersion containing the above materials and leaving it for a certain period of time.

The carbon nanotube dispersion according to an exemplary embodiment of the present invention includes carbon nanotubes having excellent conductivity, but has improved dispersibility of the carbon nanotubes, thereby minimizing aggregation of the carbon nanotubes. This characteristic can be confirmed from the remarkably low viscosity of the dispersion.

In one embodiment of the present invention, the carbon nanotube dispersion has a viscosity of 2,000 cPs or less, 1,000 cPs or less, 800 cPs or less, 700 cPs or less, 500 cPs or less at 25 ° C and a shear rate of 15 sec ^-1 It may be 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 10 cPs or more, 30 cPs or more, or 50 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.

The viscosity of the carbon nanotube dispersion may be adjusted by adjusting the contents of the first dispersant and the second dispersant or adding an alkali metal salt to the dispersion, which will be described later.

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, At least one selected from the group consisting of thioamido amine and water soluble nylon may be included. 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, when the first dispersing agent and the second dispersing agent are simultaneously used, the dispersing effect may be improved compared to when each dispersing agent is used alone.

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 carbon nanotube dispersion includes the first dispersant; and a second dispersant in a weight ratio of 1:10 to 10:1. Preferably, it may be 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 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).

In one embodiment of the present invention, the specific surface area (BET) of the carbon nanotubes is 10 m ² /g to 5,000 m ² /g, preferably 30 m ² /g to 3,000 m ² /g, more preferably may be 50 m ² /g to 2,000 m ² /g. When the above numerical range is satisfied, there is an excellent effect of improving conductivity. The specific surface area (BET) of the carbon nanotubes may vary depending on the type of carbon nanotubes.

In one embodiment of the present invention, the specific surface area (BET) of the single-walled carbon nanotubes is 800 m ² /g to 5,000 m ² /g, preferably 800 m ² /g to 3,000 m ² /g, more preferably Preferably, it may be 900 m ² /g to 2,000 m ² /g. When the above numerical range is satisfied, there is an excellent effect of improving conductivity.

In one embodiment of the present invention, the average particle diameter (D50) of the carbon nanotubes may be 0.1 μm to 20 μm. Preferably, it may be 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 20 wt% based on the total weight of the carbon nanotube dispersion. Preferably, it may be 0.1 wt% to 10 wt% or 0.1 wt% to 8 wt%. The content of the carbon nanotubes may be appropriately adjusted according to the specific surface area of the carbon nanotubes used. For example, in the case of using carbon nanotubes having a specific surface area of 800 m ² /g or more, the content of the carbon nanotubes is 0.01 wt% to 5 wt%, preferably 0.01 wt% to 5 wt%, based on the total weight of the carbon nanotube dispersion. 3wt%, more preferably about 0.01 wt% to 2wt%. When the specific surface area and content of the carbon nanotubes are out of the above ranges, the loading amount decreases during electrode manufacturing, increasing process cost, and binder migration occurs during electrode drying, resulting in a decrease in adhesive strength, or the carbon nanotube dispersion. Problems such as increased viscosity may occur.

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 carbon nanotube dispersion may include an alkali metal element. As the carbon nanotube dispersion of the present invention includes the alkali metal element, the dispersibility of materials included in the dispersion may be improved. Specifically, the first dispersant and the second dispersant included in the dispersion may form a complex with each other, and such a complex has a problem in that the viscosity of the dispersion increases due to low solubility in a solvent such as water. However, the above problem can be solved by disintegrating the complex with the alkali metal included in the carbon nanotube dispersion of the present invention.

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 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 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 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 resin. , 60 mol or less. Preferably, it may be 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, 1 mol or more, or 2 mol or more. When the above range is satisfied, the viscosity of the carbon nanotube dispersion may be adjusted to 2,000 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 3 below.

[Equation 3]

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 0.6 wt% and 0.01 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 7.7 mol based on 100 mol of the vinylpyrrolidone unit [7.7={(0.01)/(24)}/{(0.6)/(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 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, there is an effect that 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. Preferably it 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.

In one embodiment of the present invention, the value expressed by the following formula 1 of the carbon nanotube dispersion may be 2 to 10. Preferably, it may be 2 to 6.5 or 3 to 6. The value represented by Equation 1 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 1]

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

In the above formula 1,

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 2 below of the carbon nanotube dispersion may be 1 to 5. Preferably, it may be 1 to 3 or 1.1 to 2. The value calculated by Equation 2 below shows the relationship between the above-described shear thinning index (STI) characteristics of the dispersion and the average particle diameter of the carbon nanotubes included in the dispersion.

In general, if the carbon nanotube particle diameter (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 2]

In the above formula 2,

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

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

An exemplary embodiment of the present invention is a carbon nanotube;

A first dispersing agent having an amide group; and

Provided is a method for preparing the above-described carbon nanotube dispersion including the step of mixing a second dispersing agent having an aromatic ring.

In one embodiment of the present invention, the carbon nanotube;

A first dispersing agent having an amide group; and

The mixing of the second dispersing agent 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 in a dispersion may be further included.

In one embodiment of the present invention, the step of dispersing the carbon nanotubes in the dispersion is a ball mill, bead mill, disc mill or basket mill, high pressure homogenization It may be performed by a method such as a high pressure homogenizer, and more specifically, it may be performed by a milling method using a disc mill or a 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 in the dispersion 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.

<How to measure physical properties>

Physical properties of the dispersions of Examples and Comparative Examples were measured through the following methods.

viscosity measurement

Brookfield's DVNextCP Rheometer was used, and the shear rate at 25 °C was changed to 15 sec ^-1 and 150 sec ^-1 , respectively.

Average particle size measurement

A laser diffraction method was used and a commercially available laser diffraction particle size measuring device (Malvern Mastersizer 3000) was used. The average particle diameter (D50) at 50% of the particle diameter distribution was calculated in the measuring device. On the other hand, D10 and D90 mean particle sizes at 10% and 90% of the particle size distribution, respectively.

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, and then waited for 30 seconds until the signal was stabilized, and then the pH was measured.

solids determination

It was measured using OHAUS's MB95 moisture analyzer. After putting about 3g of the sample on an aluminum sample dish, 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%

Shear thinning index (STI) measurement

It was calculated according to Equation 1 below.

[Equation 1]

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

In Equation 1, V _low is the viscosity of the dispersion measured at a shear rate of 25°C and 15 sec ^-1 , and V _high is measured at a shear rate of 25°C and 150 sec ^-1 is the viscosity of a dispersion.

Calculate the value calculated by Equation 2

The physical property values represented by Equation 2 below were calculated. At this time, STI is the shear thinning index (STI) of the dispersion, and D50 is the average particle diameter (D50) of the carbon nanotubes.

[Equation 2]

<Preparation of dispersion>

Example 1

Single-walled carbon nanotube (TUBALL 01RW03, manufactured by OCSiAl) 0.4wt%, polyvinyl pyrrolidone (K15, Sigma-Aldrich) 0.45wt% as a first dispersant, tannic acid (Aldrich) 0.15wt% as a second dispersant , water as a solvent was mixed to prepare a dispersion of 1 kg of carbon nanotubes.

At this time, the molar ratio of the alkali metal salt was 7.7 mol [={(0.0075)/(24)}/{(0.45)/(111.14)}*100] based on 100 mol of the vinylpyrrolidone unit, according to Equation 3 below.

[Equation 3]

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.

division Example One 2 3 4 5 CNT Single wall carbon nanotube content (wt%) 0.4 0.4 0.4 0.4 0.4 1st dispersant Polyvinylidone-based resin content (wt%) 0.45 0.45 0.45 0.6 0.3 Types of polyvinylidone-based resins K15 K15 K15 K15 K15 2nd dispersing agent Tannic acid compound content (wt%) 0.15 0.15 0.15 0.2 0.1 - Content ratio of polyvinylidone-based resin and tannic acid compound 3:1 3:1 3:1 3:1 3:1 alkali
metal salt LiOHweight 0.0075% - - 0.010% 0.005% NaOHWeight - 0.0125% - - - KOH weight - - 0.0175% - - Alkali metal element content in dispersion (ppm) 22 68 124 24 18 Number of moles of alkali salt per 100 moles of N-vinylpyrrolidone 7.7 7.7 7.7 7.7 7.7 Properties Viscosity (15/s) 333.3 366.7 425.2 79.6 476 Viscosity (150/s) 59 73.8 79 24.6 72 D50 (μm) 4.17 4.56 4.78 1.59 4.97 pH 5.43 6.7 6.6 7.08 5.64 Actual solid content (%) 1.01 1.02 1.03 1.24 0.81 Equation 1 5.65 4.97 5.38 3.24 6.61 Equation 2 1.35 1.09 1.13 2.04 1.33

division Example comparative example 6 7 One 2 3 CNT Single wall carbon nanotube content (wt%) 0.4 0.4 0.4 0.4 0.4 1st dispersant Polyvinylidone-based resin content (wt%) 0.45 0.45 0.45 0.45 0.6 Types of polyvinylidone-based resins K12 K17 K15 K15 K15 2nd dispersing agent Tannic acid compound content (wt%) 0.15 0.15 0.15 0.15 0 - Content ratio of polyvinylidone-based resin and tannic acid compound 3:1 3:1 3:1 3:1 - alkali
metal salt LiOHweight 0.0075% 0.0075% - 0.030% - NaOHWeight - - - - - KOH weight - - - - - Alkali metal element content in dispersion (ppm) 22 22 0 85 0 Number of moles of alkali salt per 100 moles of N-vinylpyrrolidone 7.7 7.7 0 31 0 Properties Viscosity (15/s) 140.6 328.8 2069 2303 5550 Viscosity (150/s) 32.5 65.9 384 438 762 D50 (μm) 1.8 1.94 10.9 9.7 21 pH 6.96 7.06 4.01 7.89 4.75 Actual solid content (%) 1.11 1.1 1.05 1.08 1.1 Equation 1 4.33 4.99 5.38 5.25 7.28 Equation 2 2.40 2.57 0.49 0.54 0.35

In Tables 1 and 2, K12, K15, and K17 refer to Aldrich products.

From the above results, it was confirmed that the viscosity of the dispersions of Examples at 25° C. and a shear rate of 15 sec ⁻¹ was 2,000 cPs or less.

From the above results, when the dispersion did not contain a tannic acid compound (Comparative Example 3), it was confirmed that the viscosity at 25° C. and a shear rate of 15 sec ⁻¹ exceeded 5,000 cPs. In the case of having the above viscosity characteristics, the coating property of the dispersion is significantly lowered, making it difficult to apply to the process.

In addition, when the dispersion did not contain an alkali metal salt (Comparative Example 1), it was confirmed that the viscosity at 25° C. and a shear rate of 15 sec ⁻¹ exceeded 2,000 cPs. In the case of having the above viscosity characteristics, the coating property of the dispersion is significantly lowered, making it difficult to apply to the process.

On the other hand, even when the dispersion solution contains an excessive amount of an alkali metal salt, it was confirmed that the viscosity at 25° C. and a shear rate of 15 sec ⁻¹ exceeded 2,000 cPs (Comparative Example 1).

Claims (17)

carbon nanotubes;
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 2,000 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 and water-soluble A carbon nanotube dispersion comprising at least one selected from the group consisting of nylon compounds (water soluble nylon). 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. The method of claim 1,
The carbon nanotubes are single-walled carbon nanotubes (SWCNTs). 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. 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 9,
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,
A carbon nanotube dispersion having a value of 2 to 10 represented by Equation 1 below:
[Equation 1]
Shear thinning index (STI) = V _low /V _high
In the above formula 1,
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 . The method of claim 1,
A carbon nanotube dispersion having a value calculated from Equation 2 below of 1 to 5:
[Equation 2]

In the above formula 2,
STI is the shear thinning index (STI) of the dispersion,
D50 is the average particle diameter (D50) of the carbon nanotubes. carbon nanotubes;
A first dispersing agent having an amide group; and
Comprising the step of 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 7 and 9 to 12. An electrode slurry composition comprising the carbon nanotube dispersion according to any one of claims 1 to 7 and 9 to 12, an electrode active material, and a binder. An electrode comprising an electrode active material layer formed of the electrode slurry composition according to claim 14. The method of claim 15
The electrode is a negative electrode. A lithium secondary battery comprising the electrode according to claim 16.