KR20230096854A - 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 provides a carbon nanotube dispersion, a method for preparing the same, an electrode slurry composition comprising the same, an electrode comprising the same, and a lithium secondary battery comprising the same, wherein the carbon nanotube dispersion includes single-walled carbon nanotubes (SWCNT) with a purity of 95 % or more and a cellulose-based dispersant, and the cellulose-based dispersant has a value, calculated by equation 1, of 7 to 13. The carbon nanotube dispersion according to the present invention has improved dispersion stability.

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 application claims the benefit of the filing date for No. 10-2021-0185214 filed with the Korean Intellectual Property Office on December 22, 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 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

On the other hand, silicon-based anode materials are emerging as high-capacity materials are required to overcome the limitations of graphite (low theoretical capacity). However, when silicon reacts with lithium, it not only generates a large initial irreversible capacity due to volume expansion at the level of 100 to 400%, but also loses electrical contact due to active material structure collapse and separation from the current collector during charging and discharging, resulting in a loss of electrode life characteristics. cause a decrease in

Therefore, it is urgent to introduce linear carbon nanotubes (single-wall or multi-wall carbon nanotubes) to buffer the volume expansion of silicon and maintain electrical contact.

However, carbon nanotubes have problems in that, due to the nature of the material itself, which grows in a bundle type or entangle type, its dispersibility in the slurry is poor, resulting in poor coating properties and processability, and is not evenly distributed in the electrode active material layer. In order to improve this problem, a method of preparing a carbon nanotube dispersion by first mixing carbon nanotubes with a dispersant and a solvent and then applying the carbon nanotube dispersion to an electrode slurry composition has been applied.

In addition, battery efficiency may be affected depending on the type of dispersant, the purity of SWCNT, and the degree of water dispersion.

JP 2010-251293 A

It relates to a carbon nanotube dispersion with improved dispersion stability, 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 single-walled carbon nanotube (SWCNT) having a purity of 95% or more; and

Including a cellulose-based dispersant,

The cellulose-based dispersant provides a carbon nanotube dispersion having a value calculated by Equation 1 below of 7 or more and 13 or less.

[Equation 1]

Degree of substitution (DS)/(weight average molecular weight of cellulosic dispersant) * 10 ⁶

In addition, an exemplary embodiment of the present invention is a single-walled carbon nanotube (SWCNT) having a purity of 95% or more; and mixing a cellulose-based dispersing agent.

In addition, another embodiment of the present invention provides an electrode slurry composition including the above-described carbon nanotube dispersion, a silicon-based 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 an effect of improving dispersion stability.

Hereinafter, the present invention will be described in detail.

In the present specification, 'carbon nanotube dispersion' means a dispersion containing carbon nanotubes. Specifically, it means that the carbon nanotubes are dispersed in the dispersion and do not aggregate with each other.

In this specification, 'carbon nanotube' means 'single-wall carbon nanotube' unless otherwise specified.

In the present specification, a single-walled carbon nanotube refers to a carbon nanotube having a single number of bonds constituting the wall.

In the present specification, the carbon nanotubes may have a secondary shape in which a plurality of carbon nanotubes are aggregated or arranged, and for example, 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 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.

An exemplary embodiment of the present invention is a single-walled carbon nanotube (SWCNT) having a purity of 95% or more; and

Including a cellulose-based dispersant,

The cellulose-based dispersant provides a carbon nanotube dispersion having a value calculated by Equation 1 below of 7 or more and 13 or less.

[Equation 1]

Degree of substitution (DS)/(weight average molecular weight of cellulosic dispersant) * 10 ⁶

The carbon nanotube dispersion according to an exemplary embodiment of the present invention includes single-walled carbon nanotubes having excellent conductivity, and has improved dispersibility of the carbon nanotubes, thereby minimizing mutual phenomena between the carbon nanotubes. This characteristic can be confirmed from the remarkably low viscosity of the dispersion.

A carbon nanotube dispersion according to an exemplary embodiment of the present invention includes a cellulose-based dispersant. The cellulose-based dispersant has characteristics of high dispersibility and high lithium ion conductivity. That is, when manufacturing a lithium ion battery using the carbon nanotube dispersion containing the cellulose-based dispersant, it is possible to manufacture a lithium ion battery with high performance.

In one embodiment of the present invention, the cellulose-based dispersant is characterized in that the value calculated by Equation 1 is 7 or more and 13 or less. Preferably, the value calculated by Equation 1 may be 8 or more and 10 or less, or 9 or more and 11 or less. When the numerical range is satisfied, the structural stability of the dispersant is improved, the dispersibility of the dispersion is improved, the viscosity of the dispersion is stabilized, and the carbon nanotubes included in the dispersion can be evenly distributed. When the dispersion liquid having the above characteristics is applied to a battery, there is an effect of improving the efficiency and capacity of the battery.

In one embodiment of the present invention, the degree of substitution of the cellulose-based dispersant may be 0.3 or more and 2 or less. Preferably, it may be 0.5 or more and 1.2 or less or 0.7 or more and 1 or less. When the above numerical range is satisfied, the solubility of the dispersant in the dispersion is excellent, and the dispersibility of the carbon nanotubes can be improved.

In one embodiment of the present invention, the degree of substitution of the cellulose-based dispersant means the average number of substituent groups substituted on cellulose per cellulose repeating unit. In this case, the substituent group may be a methyl group, an ethyl group, a hydroxyl group, a benzyl group, a trityl group, a cyano group, a carboxymethyl group, a carboxyethyl group, a hydroxyethyl group, an aminoethyl group, a nitro group, and the like.

In one embodiment of the present invention, the weight average molecular weight of the cellulose-based dispersant may be 30,000 to 1,000,000. Preferably, it may be 50,000 to 800,000 or 60,000 to 200,000. When the above numerical range is satisfied, the solubility of the dispersant in the dispersion is excellent, the dispersibility of the carbon nanotubes can be improved, and the dispersion stability can be improved. A unit of the weight average molecular weight may be g/mol.

In one embodiment of the present invention, the cellulose-based dispersant is methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, trityl cellulose, cyanoethyl cellulose, carboxymethyl cellulose (CMC), carboxyethyl It may be cellulose, aminoethyl cellulose, nitrocellulose, cellulose ether, carboxymethylcellulose sodium salt (CMCNa), or a combination thereof.

In one embodiment of the present invention, the cellulose-based dispersant may be carboxymethyl cellulose (CMC), carboxymethyl cellulose sodium salt (CMCNa), or a combination thereof. These materials have good solubility in water, high thickening properties, and excellent coating properties. Battery performance can be improved when a dispersion containing the material is applied to a battery.

In one embodiment of the present invention, the specific surface area (BET) of the single-walled carbon nanotubes may be 750 m ² /g or more. Preferably, it may be 900 m ² /g or more or 1,000 m ² /g or more. The upper limit is not particularly limited, but may be 2,000 m ² /g or less, 1,800 m ² /g or less, or 1,500 m ² /g or less. Within the above numerical range, it is possible to control aggregation of single-walled carbon nanotubes and improve electrical conductivity.

In one embodiment of the present invention, the carbon nanotube dispersion includes single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more.

In one embodiment of the present invention, the purity of the single-walled carbon nanotubes (SWCNTs) may be 96% or more, 97% or more, preferably 99% or more. The purity may refer to the weight ratio of the carbon element (C) in the mass of the carbon nanotubes. When the above numerical range is satisfied, there is an effect of improving the electrical conductivity of the carbon nanotubes.

In one embodiment of the present invention, the content of the single-walled carbon nanotubes may be 0.1 wt% to 5 wt% based on the total weight of the carbon nanotube dispersion. In addition, it may be 0.4wt% to 4wt% or 1wt% to 2wt%. When the above numerical range is exceeded, the loading amount decreases during electrode manufacturing, increasing process cost, and binder migration occurs during electrode drying, resulting in reduced adhesive strength or increased viscosity of the carbon nanotube dispersion. this can happen That is, when the above numerical range is satisfied, the initial efficiency and high-rate retention capacity of the manufactured electrode can be improved.

In one embodiment of the present invention, the single-walled 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 10 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 can be improved. In one embodiment of the present invention, the specific surface area (BET) of the carbon nanotubes is 10 to 5,000 m ² /g, preferably may be 30 m ² /g to 3,000 m ² /g, more preferably 500 m ² /g to 2000 m ² /g. When the specific surface area of the carbon nanotubes satisfies the above numerical range, there is an excellent effect of improving conductivity.

In one embodiment of the present invention, the average particle diameter (D10) of the single-walled carbon nanotubes may be 0.1 um or more and 10 um or less. Preferably, it may be 0.3um or more and 8um or less, or 0.5um or more and 5um or less.

In one embodiment of the present invention, the average particle diameter (D90) of the single-walled carbon nanotubes may be 0.1 um or more and 20 um or less. Preferably, it may be 1um or more and 20um or less or 5um or more and 20um or less.

In the particle diameter distribution curve of carbon nanotubes, the average particle diameter (D10) means a particle diameter corresponding to 10% of the cumulative number, and the average particle diameter (D50) means a particle diameter corresponding to 50% of the cumulative number, and the average The particle diameter (D90) means a particle diameter corresponding to 90% of the number accumulation amount.

When any one or more of the average particle diameter conditions are satisfied, carbon nanotubes do not aggregate with each other and dispersibility may be improved.

In one embodiment of the present invention, the carbon nanotube dispersion may further include multi-wall carbon nanotubes in addition to the above-described single-wall carbon nanotubes.

In one embodiment of the present invention, an aqueous solvent may be included.

In one embodiment of the present invention, the aqueous solvent may use at least one selected from the group consisting of water, alcohol and ether.

In one embodiment of the present invention, the aqueous solvent is ethers (dioxane, tetrahydrofuran, methyl cellosolve, etc.), ether alcohols (ethoxy ethanol, methoxy ethoxy ethanol, etc.), esters (methyl acetate , ethyl acetate, etc.), ketones (cyclohexanone, methylethyl ketone, etc.), alcohols (ethanol, isopropanol, phenol, etc.), lower carboxylic acids (acetic acid, etc.), amines (triethylamine, new methanol amine, etc.), nitrogen Containing polar solvents (N, N-dimethylformamide, nitromethane, N-methylpyrrolidone, acetonitrile, etc.), sulfur compounds (dimethyl sulfoxide, etc.), etc. can be used.

In one embodiment of the present invention, the carbon nanotube dispersion may have a viscosity of 10,000 cPs or less at 25° C. and a shear rate of 15 sec ⁻¹ . Preferably, it may be 5,000 cPs or less, 3,000 cPs or less, or 2,000 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, using Brookfield's DV NextCP Rheometer, it may be measured at a measurement temperature of 25 °C and a shear rate of 15 sec ^-1 . For more accurate measurement, the prepared carbon nanotube dispersion may be measured after being stored at 25° C. for one week.

An exemplary embodiment of the present invention is a single-walled carbon nanotube (SWCNT) having a purity of 95% or more; and mixing a cellulose-based dispersing agent.

In one embodiment of the present invention, the purity is 95% or more single-walled carbon nanotube (SWCNT); And mixing the cellulose-based dispersant 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 preparation method of the carbon nanotube dispersion may include dispersing the single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more.

In one embodiment of the present invention, the step of dispersing the single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more is a ball mill, a bead mill, a disc mill, or a basket. It may be performed by a method such as a basket mill or a high pressure homogenizer, and more specifically, it may be performed by a milling method using a disk 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.

In one embodiment of the present invention, the step of dispersing the single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more is 10 to 120 minutes, more specifically 20 minutes, so that the carbon nanotubes can be sufficiently dispersed. to 90 minutes.

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 ion movement, and can be used without particular limitation as long as it is normally used as a separator in a secondary battery. 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.

<Example 1>

Single-walled carbon nanotubes with a purity of 99% (TUBALL 01RW03, specific surface area: 1,160 m ² /g manufactured by OCSiAl), carboxymethyl cellulose as a cellulosic dispersant {degree of substitution (DS) 0.87, manufactured by sigma aldrich , product number 419273, weight average molecular weight 90,000}, a mixture of 1 kg was prepared by mixing water as a solvent, and then mixed using a high-shear force in-line mixer (IM001 K&S Co.), and then mixed using a high-pressure homogenizer under high pressure. treatment to prepare a carbon nanotube dispersion. At this time, D10 of the single-walled carbon nanotubes was 0.88um, D50 was 4.72um, and D90 was 18.5um.

At this time, the value calculated by Equation 1 below of the carboxymethyl cellulose was 9.67.

[Equation 1]

Degree of substitution (DS)/(weight average molecular weight of cellulosic dispersant) * 10 ⁶

<Comparative Example 1>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 80% pure single-walled carbon nanotubes (TUBALL 01RW02, manufactured by OCSiAl) were used instead of 99% pure single-walled carbon nanotubes.

<Comparative Example 2>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that single-walled carbon nanotubes (TUBALL 01RW01, manufactured by OCSiAl) having a purity of 75% were used instead of single-walled carbon nanotubes having a purity of 99%.

<Comparative Example 3>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone and tannic acid were used instead of carboxymethyl cellulose as a dispersant, and single-walled carbon nanotubes having particle size characteristics in Table 1 below were used. did

<Comparative Example 4>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone and HP20 (Sokalan HP20, manufactured by BASF) were used instead of carboxymethyl cellulose as a dispersing agent.

<Comparative Example 5>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that polyvinylpyrrolidone was used as a dispersant instead of carboxymethyl cellulose.

<Comparative Example 6>

A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that carboxymethyl cellulose {degree of substitution (DS) 1.2}, weight average molecular weight 90,000} was used instead of the carboxymethyl cellulose used in Example 1. did At this time, the value calculated by Equation 1 below of the carboxymethyl cellulose was 13.33.

<Comparative Example 7>

The same method as in Example 1 except that carboxymethyl cellulose {degree of substitution (DS) 0.6, 332601000, manufactured by Thermo Scientific}, weight average molecular weight 90,000} was used instead of the carboxymethyl cellulose used in Example 1. A carbon nanotube dispersion was prepared. At this time, the value calculated by Equation 1 below of the carboxymethyl cellulose was 6.67.

<Comparative Example 8>

Carboxymethyl cellulose {degree of substitution (DS) 0.87, 419303, manufactured by Sigma-Aldrich}, weight average molecular weight 250,000} was used instead of the carboxymethyl cellulose used in Example 1. A carbon nanotube dispersion was prepared by the method. At this time, the value calculated by Equation 1 below of the carboxymethyl cellulose was 3.48.

<Evaluation of physical properties>

Purity measurement of single-walled carbon nanotubes

Purity was measured and calculated by the method of the following formula.

[formula]

Purity = 100 * (Test vessel and ash content - Test vessel mass) / (Test vessel and dried sample mass - Test vessel mass)

Specifically, the content of impurities that may be incorporated during the electrode manufacturing process was analyzed using an electric furnace. According to the test procedure KS L 3412, the sample was dried and cooled to room temperature in a desiccator.

Measure the mass of the dried test vessel (A) by using a scale to ±0.002 g, and as soon as the temperature of the sample in the desiccator comes down to room temperature, put 25 to 50 g of sample (B) into the crucible and measure the mass did Reweigh the sample and test vessel to the nearest ±0.002 g.

After the test vessel containing the sample was placed in the electric furnace, air was injected into the furnace at a slow speed, and the electric furnace was operated so that the temperature of the sample reached 500 ° C. within 1 hour or 750 ° C. within 2 hours.

In order to help the oxidation of the sample, the sample was periodically mixed, and at the time of completion of ashing (black stain disappeared), the temperature of the electric furnace was raised to 950 ° C and maintained for 1 hour. After taking out the test vessel containing the ash from the electric furnace and cooling it to room temperature in a desiccator, the mass of the test vessel including the ash was measured. The sample was put into an electric furnace at 950 °C again and heated for 30 minutes, and then the mass (C) was measured to ±0.002 g.

Measurement of degree of substitution of cellulose-based dispersant

4 g of the cellulosic dispersant sample used in Examples and Comparative Examples, 75 ml of a 95% ethanol solution, and phenolphthalein (1% ethanol solution) were placed in a 250 ml beaker, and sodium hydroxide standard solution (0.4 mol/L) was added while stirring.

Thereafter, the mixture was stirred using a magnetic heating stirrer and titrated with a hydrochloric acid standard solution (0.4 mol/L).

The titration was terminated when the color changed from dark red to transparent.

The degree of substitution of the cellulose-based dispersant was calculated using Equation 1 below.

[Equation 1]

DS = (0.162 * A) / (1- 0.058 * A)

The A is the number of millimoles (mmol/g) of sodium hydroxide used to neutralize 1 g of the cellulosic dispersant, and the units of the coefficients of A of 0.162 and 0.058 are g/mmol.

The A was calculated using Equation 2 below.

[Equation 2]

A = (B*C - D*E)/F

In Equation 2,

B is the volume (mL) of sodium hydroxide standard solution added;

C is the concentration of sodium hydroxide standard solution added (mol/L),

D is the volume (mL) of hydrochloric acid standard solution used during titration,

E is the concentration (mol/L) of the hydrochloric acid standard solution used during titration,

F is the weight (g) of the cellulosic dispersant sample.

Weight average molecular weight measurement of cellulose-based dispersant

Detector: RI-detector; Column: Agilent PL aquagel-OH30 8um; eluent: 0.2M NaNO3+0.01M NaH2PO4 (pH 7); Standard material: Measured using Gel permeation chromatography (GPC) method using PEF/PEO.

Method for measuring the particle size of single-walled carbon nanotubes

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 by the measuring device. On the other hand, D10 and D90 mean particle sizes at 10% and 90% of the particle size distribution, respectively.

How to measure the viscosity of a dispersion

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

Cell initial efficiency measurement

A coin cell was manufactured in the following manner.

An electrode active material (including silicon microparticle and graphite at a weight ratio of 7:93) was mixed with water in the carbon nanotube dispersions of each Example and Comparative Example, and mixed for 30 minutes by a ball-mill method to prepare an electrode slurry.

The electrode slurry was applied to a Cu foil current collector and dried for 4 hours at 60° C. under vacuum conditions.

After punching the dried electrode to a diameter of 11 mm, a coin half cell was manufactured by using Li metal as a counter electrode. At this time, the separator was prepared with the composition of Celgard 2450 and the electrolyte was LiPF6 (1.3 M) in ethylene carbonate (EC): diethylene carbonate (DEC) in 30:70 volume ratio with 10 wt% of fluoroethylene carbonate (FEC) and injected.

The initial charge/discharge characteristics of the coin cell were evaluated at room temperature and 0.1 A/g in the voltage range of 0.01 to 1.5V.

Cell high-rate retention capacity measurement

For the coin cell prepared above, the late charge and discharge characteristics of the coin cell were evaluated at 2 A/g and 4 A/g, respectively.

division Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 SWCNT purity 99% 80% 75% 99% 99% 99% 99% 99% 99% Degree of substitution of cellulose-based dispersant 0.87 0.87 0.87 not included not included not included 1.2 0.6 0.87 Weight average molecular weight of cellulosic dispersant 90,000 90,000 90,000 not included not included not included 90,000 90,000 250,000 Equation 1 9.67 9.67 9.67 - - - 13.33 6.67 3.48 D10(um) 0.88 0.89 0.89 0.45 0.88 0.88 1.51 2.22 2.05 D50(um) 4.72 4.73 4.74 1.59 4.72 4.72 5.1 8.11 22 D90(um) 18.5 21.75 23.74 9.74 18.5 18.5 30 32.1 90.3 Viscosity (cps) 1,411 4,500 7,196 79.8 Over 15,000 Over 15,000 4,060 5,044 Over 15,000 Initial efficiency (%) 78.5 71.4 70.6 71.5 71.1 63.4 72.5 72.3 72 High-rate retention capacity (mAh/g, @2A/g) 300 100 100 100 80 not measurable 150 140 110 High-rate retention capacity (mAh/g, @4A/g) 200 50 50 60 40 not measurable 90 80 60

From the above results, the carbon nanotube dispersion containing the single-walled carbon nanotubes having a purity of 99% and the cellulose-based dispersing agent having a value calculated by Equation 1 of 7 or more and 13 or less showed low viscosity, maintaining initial efficiency and high rate It was confirmed that the capacity was high (Example 1). On the other hand, when the purity of the single-walled carbon tube was less than 95%, the viscosity was high, and the initial efficiency and high rate retention capacity were low (Comparative Examples 1 and 2).

In addition, even if the purity of the single-walled carbon tube was 95% or more, it was confirmed that the initial efficiency and high rate retention capacity were low when the cellulose-based dispersant was not included (Comparative Examples 3 to 5).

On the other hand, even if the purity of the single-walled carbon tube is 95% or more, when the value calculated by Equation 1 is less than 7 (Comparative Examples 7 and 8) or the value calculated by Equation 1 exceeds 13 (Comparative Example 6 ) it was confirmed that the initial efficiency and high rate retention capacity were low.

Claims (16)

Single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more; and
Including a cellulose-based dispersant,
The cellulose-based dispersant is a carbon nanotube dispersion having a value calculated by Equation 1 below of 7 or more and 13 or less.
[Equation 1]
Degree of substitution (DS)/(weight average molecular weight of cellulosic dispersant) * 10 ⁶ The method of claim 1,
The degree of substitution of the cellulose-based dispersant is 0.3 or more and 2 or less of the carbon nanotube dispersion. The method of claim 1,
A carbon nanotube dispersion of which the weight average molecular weight of the cellulose-based dispersant is 30,000 to 1,000,000. The method of claim 1,
The cellulosic dispersant is methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, trityl cellulose, cyanoethyl cellulose, carboxymethyl cellulose (CMC), carboxyethyl cellulose, aminoethyl cellulose, nitrocellulose, Cellulose ether, carboxymethylcellulose sodium salt (CMCNa), or a carbon nanotube dispersion that is a combination thereof. The method of claim 1,
The carbon nanotube dispersion of which the specific surface area (BET) of the single-walled carbon nanotubes is 750 m ² /g or more. The method of claim 1,
A carbon nanotube dispersion in which the content of the single-walled carbon nanotubes is 0.1 wt% to 5 wt% based on the total weight of the carbon nanotube dispersion. The method of claim 1,
The carbon nanotube dispersion of which the average particle diameter (D10) of the single-walled carbon nanotubes is 0.1 um or more and 10 um or less. The method of claim 1,
A carbon nanotube dispersion containing an aqueous solvent. The method of claim 1,
The carbon nanotube dispersion of which the average particle diameter (D10) of the single-walled carbon nanotubes is 0.1 um or more and 10 um or less. The method of claim 1,
A carbon nanotube dispersion having a viscosity of 10,000 cPs or less at a shear rate of 25 ° C and 15 sec ^-1 Single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more; and mixing a cellulose-based dispersant. The method for preparing a carbon nanotube dispersion according to any one of claims 1 to 10. The method of claim 11,
A method for producing a carbon nanotube dispersion comprising the step of dispersing single-walled carbon nanotubes (SWCNTs) having a purity of 95% or more. An electrode slurry composition comprising the carbon nanotube dispersion according to any one of claims 1 to 10, an electrode active material, and a binder. An electrode comprising an electrode active material layer formed by the electrode slurry composition according to claim 13. The method of claim 14,
The electrode is a negative electrode. A lithium secondary battery comprising the electrode according to claim 15.