Carbon nanotube dispersion, and anode slurry, anode and lithium secondary battery including the same

Abstract

The present invention relates to a carbon nanotube dispersion comprising a carbon nanotube (CNT) having a Brunauer-Emmet-Teller (BET) specific surface area of 800 m2 / g or more, a dispersant, and a water-based solvent, in which the dispersant comprises a polymeric dispersant comprising an amine and a phenolic compound comprising two or more aromatic rings.

Description

[0001] This application is a divisional application of an invention patent application with an application date of August 21, 2020, application number 202080022453.8, and invention name “Carbon nanotube dispersion and negative electrode slurry, negative electrode and lithium secondary battery comprising the carbon nanotube dispersion”. Technical Field

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of Korean Patent Application No. 10-2019-0102591, filed on August 21, 2019, the disclosure of which is incorporated herein by reference. Technical Field

[0005] The present invention relates to a carbon nanotube dispersion, a negative electrode slurry, a negative electrode and a lithium secondary battery including the carbon nanotube dispersion, and more particularly to a carbon nanotube dispersion having low viscosity and little change in viscosity over time, a negative electrode slurry including the carbon nanotube dispersion, and a negative electrode and a lithium secondary battery prepared by using the negative electrode slurry. Background Art

[0006] With the increase of technology development and demand for mobile devices, the demand for secondary batteries as energy sources has greatly increased. Among these secondary batteries, lithium secondary batteries with high energy density, high voltage, long cycle life and low self-discharge rate have been commercialized and widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, a method for preparing an electrode with higher energy density per unit volume by increasing electrode density has been actively studied.

[0007] Generally, high-density electrodes are formed by molding electrode active material particles having a diameter of several μm to several tens of μm using a high-pressure press, wherein the permeability of the electrolyte solution is easily reduced because the particles may be deformed and the space between the particles may be reduced during the molding process.

[0008] In order to solve such limitations, a conductive agent with excellent conductivity and strength is used in the preparation process of the electrode. Since the conductive agent is arranged between the electrode active material particles to maintain the pores between the electrode active material particles, the electrolyte solution can be easily penetrated even when the electrode active material particles are subjected to the molding process, and the excellent conductivity can reduce the resistance in the electrode. Among these conductive agents, the use of carbon nanotubes is increasing as a fiber-type carbon-based conductive agent that can further reduce the electrode resistance by forming a conductive path in the electrode.

[0009] As one of the fine carbon fibers, carbon nanotubes are tubular carbon fibers having a diameter of 1 μm or less, and are expected to be used and applied in various fields due to their high conductivity, tensile strength, and heat resistance caused by their specific structure. However, carbon nanotubes have the following problems: due to their high specific surface area, carbon nanotubes have strong van der Waals attraction, so their dispersibility is low and agglomeration may occur.

[0010] In order to solve this problem, a method of dispersing carbon nanotubes in a dispersion medium by mechanical dispersion treatment such as ultrasonic treatment has been proposed. However, with the mechanical dispersion treatment method, carbon nanotubes may aggregate at the same time as the ultrasonic irradiation is terminated.

[0011] In addition, with the recent increase in demand for high-capacity batteries, attempts have been actively made to use silicon-based active materials with excellent theoretical capacity as negative electrode active materials. However, silicon-based negative electrode active materials have limitations in that they have poor cycle characteristics due to large volume changes during charge and discharge.

[0012] Therefore, there is a need to develop a carbon nanotube dispersion having low viscosity and suppressing an increase in viscosity over time while being able to improve the dispersibility of the carbon nanotubes, and a negative electrode material that can improve cycle characteristics when used for a silicon-based negative electrode active material. Summary of the invention

[0013] Technical issues

[0014] An aspect of the present invention provides a carbon nanotube dispersion, a negative electrode slurry composition including the carbon nanotube dispersion, an electrode prepared by using the negative electrode slurry composition, and a lithium secondary battery including the electrode. The carbon nanotube dispersion has low viscosity and low rate of change of viscosity over time and can improve cycle characteristics when used with a silicon-based negative electrode active material.

[0015] Technical Solution

[0016] According to one aspect of the present invention, there is provided a carbon nanotube dispersion comprising a Brunauer-Emmett-Teller (BET) specific surface area of ​​800 m 2 / g or more carbon nanotubes (CNTs), a dispersant, and a water-based solvent, wherein the dispersant includes an amine-containing polymer dispersant and a phenolic compound containing two or more aromatic rings.

[0017] According to another aspect of the present invention, a negative electrode slurry composition is provided, comprising the carbon nanotube dispersion, a silicon-based negative electrode active material, and a binder.

[0018] According to another aspect of the present invention, provided are a negative electrode including a negative electrode active material layer formed of the negative electrode slurry composition, and a lithium secondary battery including the negative electrode.

[0019] Beneficial Effects

[0020] The carbon nanotube dispersion of the present invention is characterized in that it comprises a Brunauer-Emmett-Teller (BET) specific surface area of ​​800 m 2 / g or more of carbon nanotubes (CNTs), and in the case of using carbon nanotubes having a large BET specific surface area as described above, when a silicon-based negative electrode active material is used together therewith, an effect of improving cycle characteristics can be obtained.

[0021] However, in the case of using carbon nanotubes having a large BET specific surface area, the viscosity increases rapidly due to the decrease in dispersibility of the carbon nanotubes, and the viscosity changes over time due to the formation of a carbon nanotube network, so the storage property and stability of the conductive agent dispersion may be reduced, and the processability of the electrode may be reduced. However, since the carbon nanotube dispersion according to the present invention uses a polymer dispersant containing an amine and a phenolic compound having a specific structure together, the viscosity changes less over time and a relatively low viscosity is obtained despite the use of carbon nanotubes having a large specific surface area.

[0022] Therefore, if the negative electrode slurry composition including the carbon nanotube dispersion of the present invention and a silicon-based negative electrode active material having excellent capacity characteristics is used, a negative electrode and a secondary battery having excellent capacity characteristics and cycle characteristics can be prepared. DETAILED DESCRIPTION

[0023] It will be understood that the words or terms used in the specification and claims should not be interpreted as the meanings defined in commonly used dictionaries, and it will be further understood that, based on the principle that the inventor can appropriately define the meanings of words or terms in order to best explain the present invention, the words or terms should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and the technical concept of the present invention.

[0024] The terms used herein are for the purpose of describing particular exemplary embodiments only and are not intended to limit the present invention.In the specification, unless otherwise indicated, a term in the singular form may include a plural form.

[0025] It will be further understood that when used in this specification, the terms "comprises", "comprising" or "having" specify the presence of stated features, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0026] In the present specification, unless otherwise specifically stated, the expression "%" means % by weight.

[0027] In this specification, the expression "average particle size D 50 " indicates the particle size when the cumulative volume is 50%. For example, D 50 This can be measured using a laser diffraction method, which can generally measure particle sizes ranging from submicron to several millimeters, and can obtain highly reproducible and high-resolution results.

[0028] In this specification, the expression "specific surface area" is measured by the Brunauer-Emmett-Teller (BET) method, wherein, specifically, the specific surface area can be calculated from the nitrogen adsorption at liquid nitrogen temperature (77K) using BELSORP-mini II of Bell Japan.

[0029] Hereinafter, the present invention will be described in detail.

[0030] Carbon Nanotube Dispersion

[0031] First, the carbon nanotube dispersion according to the present invention will be described.

[0032] The carbon nanotube dispersion according to the present invention comprises: (1) a Brunauer-Emmett-Teller (BET) specific surface area of ​​800 m 2 / g or more of carbon nanotubes (CNTs); (2) a dispersant; and (3) a water-based solvent, wherein the dispersant comprises an amine-containing polymer dispersant and a phenolic compound containing two or more aromatic rings.

[0033] (1) Carbon nanotubes

[0034] Carbon nanotubes are used to improve the conductivity of electrodes, wherein graphite sheets have a cylindrical shape with a nanometer-scale diameter, and include carbon allotropes having an sp2 bonding structure and aggregates thereof. Carbon nanotube aggregates refer to secondary structures formed by arranging or aggregating a plurality of carbon nanotubes. For example, carbon nanotube aggregates may be bundle-type carbon nanotubes in a bundle or rope shape, in which a plurality of carbon nanotubes are arranged or arranged side by side in a predetermined direction, or may be spherical or potato-shaped entangled type carbon nanotubes, in which a plurality of carbon nanotubes are entangled together without a predetermined direction.

[0035] The carbon nanotube dispersion of the present invention comprises a BET specific surface area of ​​800 m 2 / g or more, preferably 800m 2 / g to 5,000m 2 / g, more preferably 900m 2 / g to 2,000m 2 If the carbon nanotubes having a high BET specific surface area as described above are used, since the formation of a conductive network between silicon-based negative electrode active materials is excellent, the effect of improving the cycle characteristics of the secondary battery can be obtained.

[0036] Regarding the carbon nanotubes with a high BET specific surface area used in the present invention, due to the very high cohesive force between the carbon nanotubes, the viscosity of the carbon nanotube dispersion is high, so not only the stability of the dispersion is poor, but also an excessive amount of carbon nanotubes must be used to fully form a conductive path, so the amount of active material in the active material layer is reduced, which may lead to a decrease in electrode performance. Therefore, it is difficult to commercialize carbon nanotubes with a high specific surface area as a conductive agent.

[0037] However, according to the research of the present inventors, when a polymer dispersant containing an amine to be described later and a phenolic compound containing two or more aromatic rings are used together in a carbon nanotube dispersion, it is found that although carbon nanotubes having a large specific surface area as described above are used, the initial viscosity is low and the change in viscosity over time is suppressed due to the excellent dispersibility of the carbon nanotubes.

[0038] Therefore, in the case where the carbon nanotube dispersion of the present invention is used to prepare an electrode slurry, since the carbon nanotubes are uniformly arranged between the active materials, even during the preparation of the electrode by coating and drying the electrode slurry and then rolling, a good space between the electrode active materials can be always maintained. In addition, since the carbon nanotubes are not aggregated and are uniformly distributed, a conductive path can be fully formed even with a small amount of carbon nanotubes.

[0039] The carbon nanotube used in the present invention may be a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), or a combination thereof, but the carbon nanotube is not limited thereto. The single-walled carbon nanotube or the double-walled carbon nanotube has a higher specific surface area than the multi-walled carbon nanotube, and therefore, the single-walled carbon nanotube or the double-walled carbon nanotube is more effective in improving the cycle characteristics of a battery in which a silicon-based negative electrode active material is used.

[0040] The average diameter of the carbon nanotubes may be 0.6 nm to 10 nm, preferably 0.8 nm to 5 nm, and more preferably 0.8 nm to 3 nm. In addition, the average length of the carbon nanotubes may be 0.5 μm to 20 μm, preferably 0.5 μm to 10 μm, and more preferably 0.5 μm to 5 μm. When the average diameter and average length of the carbon nanotubes satisfy the above range, it is effective to reduce the viscosity of the dispersion and improve the storage stability, and even when a silicon-based negative electrode active material is used, excellent cycle characteristics can be obtained.

[0041] In this case, the average diameter of the carbon nanotubes can be measured by photographing the carbon nanotube powder using a scanning electron microscope, and the average length of the carbon nanotubes can be measured by photographing the carbon nanotube dispersion using a scanning electron microscope.

[0042] The carbon nanotubes may be included in an amount of 0.01 wt % to 5 wt %, preferably 0.01 wt % to 3 wt %, more preferably 0.1 wt % to 2 wt %, and most preferably 0.1 wt % to 1 wt %, based on the total weight of the carbon nanotube dispersion. When the amount of the carbon nanotubes satisfies the above range, the effect of improving the viscosity of the dispersion and the effect of improving the cycle characteristics of the secondary battery are excellent.

[0043] (2) Dispersant

[0044] The dispersant is used to make the carbon nanotubes uniformly dispersed in the carbon nanotube dispersion without aggregation, wherein the carbon nanotube dispersion of the present invention uses a polymer dispersant containing an amine and a phenolic compound containing two or more aromatic rings as a dispersant. According to the research of the present inventors, it is found that when two specific dispersants are used together, the change in viscosity of the carbon nanotube dispersion over time is significantly reduced.

[0045] In the present invention, the dispersant may be included in an amount of 10 to 2,000 parts by weight, preferably 50 to 1,000 parts by weight, and more preferably 70 to 500 parts by weight, based on 100 parts by weight of the carbon nanotubes. If the amount of the dispersant is too small, the viscosity of the carbon nanotube dispersion may increase, and if the amount of the dispersant is too large, the physical properties of the secondary battery may be deteriorated because the dispersant acts as an impurity after preparing the electrode.

[0046] The amine-containing polymer dispersant may include, for example, at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethylenimine.

[0047] In the case of using a specific polymer dispersant containing an amine in the polymer structure as described above, further improved viscosity increasing effect and effect of suppressing the change in viscosity over time can be exhibited.

[0048] Next, compared with the conventional case, due to the bulky structure generated by two or more aromatic rings and the influence of the hydroxyl group included in the phenol group, the phenolic compound containing two or more aromatic rings can reduce the viscosity of the carbon nanotube dispersion, especially the water-based carbon nanotube dispersion, and can significantly improve the increase in viscosity over time. In the case of using a phenolic compound containing only one aromatic ring (such as dopamine, gallic acid, pyrogallol, catechol, etc.), the effect of increasing the viscosity of the dispersion and the effect of suppressing the change in viscosity over time are not sufficient.

[0049] Preferably, the phenolic compound may include at least one structure selected from the group consisting of a phenol structure, a catechol structure, a gallol structure, and a naphthol structure in at least one aromatic ring, and specifically may include at least one structure selected from the group consisting of a catechol structure and a gallol structure in at least one aromatic ring. The phenol structure is a structure in which two hydroxyl groups are bonded to a benzene ring, the catechol structure is a structure in which two hydroxyl groups are bonded to a benzene ring, the gallol structure is a structure in which three hydroxyl groups are bonded to a benzene ring, and the naphthol structure is a structure in which one hydroxyl group is bonded to naphthalene.

[0050] In the case where the phenolic compound containing two or more aromatic rings includes the above structure, since in the carbon nanotube dispersion, the interaction between the aromatic rings and the carbon nanotubes and the hydrogen bond interaction between the -OH of the phenolic compound and the polymer dispersant are properly balanced, the effect of reducing the viscosity of the carbon nanotube dispersion and suppressing the increase in viscosity over time can be exhibited.

[0051] Specific examples of the phenolic compound containing two or more aromatic rings may be at least one selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatannol, and tannic acid, and preferably may be tannic acid, quercetin, or a combination thereof.

[0052] In one example of the present invention, the aromatic rings contained in the phenolic compound containing two or more aromatic rings may have a structure in which one aromatic ring is not fused with another aromatic ring, or a structure in which two aromatic rings are fused to each other, and may not include a structure in which three or more aromatic rings are fused to each other.

[0053] That is, a structure in which three or more aromatic rings are condensed in the molecular structure may be excluded from the scope of the phenolic compound containing two or more aromatic rings.

[0054] In the case where the phenolic compound containing two or more aromatic rings includes a structure in which three or more aromatic rings are fused in the molecular structure, since the structure in which the three or more aromatic rings are fused may cause agglomeration between carbon nanotubes by applying a more than sufficiently strong binding force with the carbon nanotubes in the carbon nanotube dispersion, it may not be suitable for improving the dispersibility of the carbon nanotubes. In addition, since the balance between the interaction between the aromatic rings in the carbon nanotube dispersion and the carbon nanotubes and the hydrogen bonding interaction between -OH of the phenolic compound and the polymer dispersant is destroyed, it may be difficult to appropriately exhibit the effect of reducing the viscosity of the carbon nanotube dispersion and the effect of suppressing the increase in viscosity over time.

[0055] The phenolic compound may be included in an amount of 1 to 100 parts by weight, preferably 5 to 100 parts by weight, and more preferably 10 to 100 parts by weight, based on 100 parts by weight of the amine-containing polymer dispersant. When the amounts of the amine-containing polymer dispersant and the phenolic compound satisfy the above ranges, the effects of reducing the viscosity of the dispersion and improving the storage stability are more excellent.

[0056] (3) Water-based solvents

[0057] The solvent is a dispersion medium for dispersing carbon nanotubes, a polymer dispersant, and a phenolic compound containing two or more aromatic rings, wherein the solvent is used to pre-disperse the carbon nanotubes and provide them as a carbon nanotube dispersion in order to prevent agglomeration when the electrode slurry composition is used by directly mixing the carbon nanotubes with a negative electrode active material.

[0058] The solvent can dissolve or disperse the carbon nanotubes, the polymer dispersant, and the phenolic compound containing two or more aromatic rings to above a certain level. For example, the water-based solvent can be water, and considering the coatability of the electrode slurry composition subsequently prepared by using the carbon nanotube dispersion, the water-based solvent can be included in an amount such that the electrode slurry composition has an appropriate viscosity.

[0059] Since the carbon nanotube dispersion of the present invention including the above components has excellent dispersibility, the viscosity of the dispersion is low and the viscosity increases less over time.

[0060] The initial viscosity of the carbon nanotube dispersion is measured using a viscometer (manufactured by TOKI SANGYO CO., LTD., viscometer TV-22) at 25° C. and 1 rpm, and the initial viscosity may be 0.1 Pa·s to 12 Pa·s, specifically 0.1 Pa·s to 10 Pa·s, more specifically 0.1 Pa·s to 5 Pa·s, and especially 0.1 Pa·s to 3 Pa·s. In the case where the carbon nanotube dispersion has an initial viscosity within the above range, an electrode slurry may be more smoothly prepared by using the carbon nanotube dispersion, and the electrode slurry including the carbon nanotube dispersion may have an appropriate viscosity for forming an electrode.

[0061] Furthermore, when the carbon nanotube dispersion is left standing at 25° C. for 1 week, the viscosity increase rate calculated by the following equation (1) may be 80% or less, specifically 50% or less, and more specifically 20% or less.

[0062] Equation (1): Viscosity increase rate (%) = {(viscosity measured after standing at 25°C for 1 week - initial viscosity) / initial viscosity} × 100

[0063] In this case, the initial viscosity and the viscosity after standing for 1 week were measured at 25°C and 1 rpm.

[0064] The carbon nanotube dispersion of the present invention as described above can be prepared by a preparation method comprising the following steps: (1) preparing a mixture by mixing carbon nanotubes, a polymer dispersant, a phenolic compound containing two or more aromatic rings, and a water-based solvent; and (2) grinding the mixture.

[0065] In step (1), carbon nanotubes, a polymer dispersant, a phenolic compound containing two or more aromatic rings, and a water-based solvent are mixed to prepare a mixture.

[0066] Preparation of the mixture can be carried out under temperature conditions in which physical properties including viscosity of the mixture do not change due to evaporation of the water-based solvent. For example, preparation of the mixture can be carried out at a temperature of 50°C or lower, for example, 5°C to 50°C.

[0067] In step (2), the mixture is subjected to a dispersion treatment to prepare a carbon nanotube dispersion.

[0068] The grinding can be performed by a method using a ball mill, a bead mill, a disc mill, a basket mill or a high pressure homogenizer, and more specifically can be performed by a grinding method using a disc mill or a high pressure homogenizer.

[0069] When grinding by a disc mill, the size of the beads can be appropriately determined according to the type and amount of the carbon nanotubes and the type of the dispersant, and specifically, the diameter of the beads can be 0.1 mm to 5 mm, for example, 0.5 mm to 4 mm. In addition, the bead milling process can be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, can be performed at a speed of 5,000 rpm to 9,000 rpm.

[0070] For example, when the mixture is pressurized by a plunger pump of the high pressure homogenizer and pushed through the gap of the homogenizing valve so as to pass through the gap, the high pressure homogenizer performs grinding by forces such as cavitation, shear, impact, and explosion.

[0071] The grinding process may be performed according to the dispersion degree of the carbon nanotube dispersion, and specifically may be performed for 30 minutes to 120 minutes, for example, 60 minutes to 90 minutes.

[0072] Negative electrode slurry composition

[0073] Next, the negative electrode slurry composition according to the present invention will be described.

[0074] The negative electrode paste composition according to the present invention includes the carbon nanotube dispersion according to the present invention, a negative electrode active material, and a binder, and may further include a solvent and / or other additives if necessary. Since the carbon nanotube dispersion is the same as described above, its detailed description will be omitted.

[0075] The negative electrode active material includes a silicon-based negative electrode active material. The silicon-based negative electrode active material may include at least one selected from the group consisting of: metallic silicon (Si), silicon oxide (SiO x , where 0 < x < 2), silicon carbide (SiC), and Si-Y alloy (where Y is an element selected from the group consisting of: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and Y is not Si). The element Y may be selected from the group consisting of: magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), (Rf), vanadium (V), niobium (Nb), tantalum (Ta), (Db), chromium (Cr), molybdenum (Mo), tungsten (W), (Sg), technetium (Tc), rhenium (Re), (Bh), iron (Fe), lead (Pb), ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B), aluminum (Al), gallium (Ga), tin (Sn), indium (In), germanium (Ge), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0076] Since the silicon-based negative electrode active material has higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained when the silicon-based negative electrode active material is further included. However, since the silicon-based negative electrode active material has a large volume change during charging and discharging, when charging and discharging are repeated, the battery characteristics decrease sharply and the cycle characteristics are insufficient, so commercialization is difficult.

[0077] However, in the case of using carbon nanotubes having a large specific surface area as a conductive agent as in the present invention, when a silicon-based negative electrode active material is used, the effect of improving the cycle characteristics can be obtained. Therefore, when using the negative electrode paste composition of the present invention including the carbon nanotube dispersion and the silicon-based negative electrode active material of the present invention, a secondary battery having excellent capacity characteristics and cycle characteristics can be obtained.

[0078] The negative electrode active material may further include other types of negative electrode active materials and silicon-based negative electrode active materials. As other types of negative electrode active materials, for example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers and amorphous carbon can be used; metal compounds that can be alloyed with lithium, such as aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy, or Al alloy; metal oxides that can be doped and undoped with lithium, such as SnO2, vanadium oxide and lithium vanadium oxide; or composites including metal compounds and carbonaceous materials, such as Sn-C composites, and carbonaceous materials are particularly preferred.

[0079] Based on the total solid content in the negative electrode slurry composition, the total amount of the negative electrode active material combined with the silicon-based negative electrode active material and other types of negative electrode active materials can be in the range of 70 wt % to 99 wt %, for example, 80 wt % to 98 wt %. When the amount of the negative electrode active material satisfies the above range, excellent capacity characteristics can be obtained.

[0080] In the entire negative electrode active material, the silicon-based negative electrode active material may be included in an amount of 3 wt % or more, preferably 3 wt % to 70 wt %, and more preferably 3 wt % to 50 wt %. When the amount of the silicon-based negative electrode active material in the total negative electrode active material satisfies the above range, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0081] Next, the binder is used to ensure the adhesion between the active materials or the adhesion of the active materials to the collector, wherein the common binder used in the art can be used, and its type is not particularly limited. The binder may include, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or their copolymers, and any one of them or a mixture of two or more of them can be used.

[0082] The binder may be included in an amount of 5 wt % or less, for example, 1 wt % to 3 wt %, based on the total solid content in the negative electrode slurry composition. When the amount of the binder satisfies the above range, excellent electrode adhesion can be achieved while minimizing the increase in resistance of the electrode.

[0083] If necessary, the negative electrode slurry composition may further include a solvent for viscosity control. In this case, the solvent may be water, an organic solvent, or a mixture thereof. Examples of organic solvents may be: amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc) and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,5-pentanediol or hexanediol ; polyols such as glycerol, trimethylolpropane, pentaerythritol or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl acetone or cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone and ε-propiolactone, and any one of them and a mixture of two or more of them may be used, but the present invention is not limited thereto.

[0084] The solvent may be included so that the solid content in the negative electrode slurry composition is in the range of 30 wt % to 70 wt %, for example, 30 wt % to 50 wt %. In the case where the solid content in the negative electrode slurry is less than 30 wt %, the processing cost may increase due to the reduction in electrode loading, the electrode adhesion may decrease due to the occurrence of binder migration, and coating defects may occur. In the case where the solid content in the negative electrode slurry is greater than 70 wt %, the processability may decrease and coating defects may occur due to the excessive increase in the viscosity of the negative electrode slurry.

[0085] In addition, if necessary, the negative electrode slurry may further include additives such as a viscosity adjuster and a filler.

[0086] The viscosity modifier may be carboxymethyl cellulose or polyacrylic acid, and may be added to adjust the viscosity of the negative electrode slurry to facilitate the preparation of the negative electrode slurry and the coating process on the negative electrode collector.

[0087] The filler as a component for suppressing electrode expansion is selectively used but is not particularly limited as long as it is a fiber material and does not cause chemical changes in the battery, and, for example, olefin-based polymers such as polyethylene and polypropylene; and fiber materials such as glass fiber and carbon fiber can be used.

[0088] negative electrode

[0089] Next, the negative electrode according to the present invention will be described.

[0090] The negative electrode of the present invention includes a negative electrode active material layer formed of the negative electrode slurry composition according to the present invention, that is, a negative electrode slurry composition including a carbon nanotube dispersion, a silicon-based negative electrode active material, and a binder.

[0091] Specifically, the negative electrode can be prepared by applying the negative electrode slurry composition of the present invention described above and drying to form a negative electrode active material layer. More specifically, the negative electrode active material layer can be formed by coating the negative electrode slurry composition on the negative electrode collector and drying the coated negative electrode collector, or can be formed by coating the negative electrode slurry composition on a separate support, and then laminating the film separated from the support on the negative electrode collector. If necessary, the negative electrode active material layer can be formed by the above method, and then the rolling process can be further performed. In this case, taking into account the physical properties of the electrode finally prepared, drying and rolling can be performed under appropriate conditions, and there is no particular restriction.

[0092] The negative electrode current collector is not particularly limited as long as it is a material that has conductivity and does not cause adverse chemical changes in the battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, these materials surface-treated with one of carbon, nickel, titanium, silver or the like, or calcined carbon can be used.

[0093] The negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. In addition, the negative electrode current collector may be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

[0094] Lithium secondary battery

[0095] Next, a secondary battery according to the present invention will be described.

[0096] The secondary battery according to the present invention includes the above-mentioned negative electrode of the present invention. Specifically, the secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and, in this case, the negative electrode is the above-mentioned negative electrode of the present invention. Since the negative electrode has been described above, its detailed description will be omitted, and hereinafter, only other components will be described.

[0097] The positive electrode can be one commonly used in the art and is not particularly limited. For example, the positive electrode can be prepared by applying a positive electrode paste composition and drying it to form a positive electrode active material layer. Specifically, the positive electrode active material layer can be formed by coating the positive electrode paste composition on a positive electrode current collector and drying the coated positive electrode current collector, or can be formed by coating the positive electrode paste composition on a separate support and then laminating the film separated from the support on the positive electrode current collector. If necessary, the positive electrode active material layer can be formed by the above method, and then a rolling process can be further performed. In this case, considering the physical properties of the finally prepared electrode, drying and rolling can be carried out under appropriate conditions and are not particularly limited.

[0098] The positive electrode current collector is not particularly limited as long as it is a material having conductivity and not causing adverse chemical changes, and, for example, copper, stainless steel, aluminum, nickel, titanium, their alloys, these materials surface-treated with one of carbon, nickel, titanium, silver or the like, or calcined carbon can be used.

[0099] The positive electrode current collector generally can have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. In addition, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies and the like.

[0100] The positive electrode paste composition includes a positive electrode active material, a binder, and a solvent, and if necessary, a conductive agent and an additive can be further included.

[0101] As the positive electrode active material, positive electrode active materials known in the art can be used without limitation. For example, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium iron phosphate, lithium nickel manganese cobalt-based oxides, or combinations thereof can be used. Specifically, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi a Mn b Co c aMnbCocO2 (where 0 < a, b, c < 1) can be used as the positive electrode active material, but the present invention is not limited thereto.

[0102] The binder is used to ensure the adhesion between active materials or the adhesion of active materials to the collector, wherein the commonly used binders used in the art can be used, and the type thereof is not particularly limited. The binder may include, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or copolymers thereof, and any one of them or a mixture of two or more of them may be used.

[0103] The binder may be included in an amount of 5 wt % or less, for example, 1 wt % to 3 wt %, based on the total solid content in the positive electrode slurry composition. When the amount of the binder satisfies the above range, excellent electrode adhesion can be achieved while minimizing the increase in resistance of the electrode.

[0104] The solvent is used to mix each component in the positive electrode slurry composition and adjust the viscosity, wherein, for example, water, an organic solvent, or a mixture thereof can be used. Examples of organic solvents can be: amide-based polar organic solvents, such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc) and N-methylpyrrolidone (NMP); alcohols, such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; diols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,5-pentanediol or hexanediol ; polyols such as glycerol, trimethylolpropane, pentaerythritol or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl acetone or cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone and ε-propiolactone, and any one of them and a mixture of two or more of them may be used, but the present invention is not limited thereto.

[0105] The solvent may be included so that the solid content in the positive electrode slurry composition is in the range of 30 wt % to 85 wt %, for example, 30 wt % to 80 wt %. In the case where the solid content in the positive electrode slurry composition is less than 30 wt %, the processing cost may increase due to the reduction in electrode loading, the electrode adhesion may decrease due to the occurrence of binder migration, and coating defects may occur. In the case where the solid content in the positive electrode slurry is greater than 85 wt %, the processability may decrease and coating defects may occur due to the excessive increase in the viscosity of the positive electrode slurry composition.

[0106] The conductive agent is a component for further improving the conductivity, wherein conductive agents for secondary batteries known in the art can be used without restriction, for example, conductive materials such as: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0107] The conductive agent may be included in an amount of 10 wt % or less, preferably 0.1 wt % to 10 wt %, and more preferably 0.1 wt % to 5 wt %, based on the total solid content in the positive electrode slurry composition.

[0108] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used. In addition, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and may have a surface with a fine roughness to improve adhesion to the positive electrode material. The positive electrode current collector may be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, and the like.

[0109] Next, the separator separates the negative electrode and the positive electrode and provides a transmission path for lithium ions, wherein any separator can be used as a separator without particular limitation, as long as it is commonly used for secondary batteries. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof can be used as a separator. In addition, a typical porous non-woven fabric can be used, for example, a non-woven fabric formed of a high melting point glass fiber or a polyethylene terephthalate fiber. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single layer or a multilayer structure can be selectively used.

[0110] Next, the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the preparation of a lithium secondary battery, but the present invention is not limited thereto.

[0111] Specifically, the electrolyte may include a nonaqueous organic solvent and a metal salt.

[0112] Examples of the non-aqueous organic solvent may be aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0113] In particular, cyclic carbonates (ethylene carbonate and propylene carbonate) in carbonate-based organic solvents are well dissociated into lithium salts as high-viscosity organic solvents due to their high dielectric constant, so cyclic carbonates can be preferably used. Since when the cyclic carbonates are mixed with low-viscosity, low-dielectric-constant straight-chain carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high conductivity can be prepared, so the cyclic carbonates can be more preferably used.

[0114] As the metal salt, a lithium salt can be used, and the lithium salt is a material that is easily soluble in a non-aqueous electrolyte solution, wherein, as an anion of the lithium salt, for example, any one selected from the group consisting of the following can be used: - , Cl - ,I- 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - .

[0115] In order to improve the life characteristics of the battery, prevent the reduction of the battery capacity, and improve the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, at least one additive may be further included in the electrolyte, for example, a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum chloride.

[0116] As described above, the lithium secondary battery including the negative electrode prepared by using the negative electrode slurry composition of the present invention including the silicon-based negative electrode active material having a large theoretical capacity and the carbon nanotube having a large specific surface area has excellent capacity characteristics and cycle characteristics. As a result, the lithium secondary battery can be suitably used in portable devices such as mobile phones, notebook computers and digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

[0117] Hereinafter, the present invention will be described in more detail according to specific examples.

[0118] Example 1

[0119] By adding 0.4 wt% of 2 / g of single-walled carbon nanotubes (TUBALL, OCSiAl), 0.45 wt% of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant, 0.15 wt% of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings, and water as a solvent were mixed to prepare 1 kg of the mixture, and the mixture was treated using a high shear in-line mixer Verso (Silverson) at 10,000 rpm for 30 minutes, and then treated four times using a PICOMAX device (high-pressure homogenizer) from Micronox at a pressure of 1,500 bar to prepare a carbon nanotube dispersion.

[0120] Example 2

[0121] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.375 wt % of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant and 0.125 wt % of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0122] Example 3

[0123] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.54 wt % of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant and 0.06 wt % of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0124] Example 4

[0125] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.4 wt % of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant and 0.1 wt % of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0126] Example 5

[0127] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.1 wt % of the carbon nanotube with a specific surface area of ​​920 m 2 / g of single-walled carbon nanotubes (ZEON CORPORATION), 0.1125 wt% of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant, and 0.0375 wt% of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0128] Example 6

[0129] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.45 wt % of polyethyleneimine (Sigma-Aldrich Co., Mw=2,000 g / mol) as a polymer dispersant and 0.15 wt % of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0130] Example 7

[0131] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.45 wt % of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant and 0.15 wt % of epigallocatechin gallate (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings were mixed.

[0132] Example 8

[0133] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.8 wt % of a carbon nanotube having a specific surface area of ​​1,160 m 2 / g of single-walled carbon nanotubes (TUBALL, OCSiAl), 0.9 wt% of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.) as a polymer dispersant, 0.3 wt% of tannic acid (Sigma-Aldrich Co.) as a phenolic compound containing two or more aromatic rings, and water as a solvent were mixed to prepare 1 kg of a mixture.

[0134] Comparative Example 1

[0135] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that tannic acid was not used in Example 1 and 0.6 wt % of polyvinyl pyrrolidone was mixed.

[0136] Comparative Example 2

[0137] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that polyvinyl pyrrolidone was not used in Example 1 and 0.6 wt % of tannic acid was mixed.

[0138] Comparative Example 3

[0139] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.6 wt % of carboxymethyl cellulose (CMC, Daicel Corporation) was mixed instead of polyvinyl pyrrolidone and tannic acid in Example 1.

[0140] Comparative Example 4

[0141] A carbon nanotube dispersion was prepared in the same manner as in Example 1, except that 0.45 wt % of carboxymethyl cellulose (CMC, Daicel Corporation) was used instead of polyvinyl pyrrolidone in Example 1.

[0142] Comparative Example 5

[0143] By adding 4 wt% of 2 / g of multi-walled carbon nanotubes, 0.8 wt% of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.), and water as a solvent were mixed to prepare 1 kg of the mixture, and the mixture was treated using a high shear in-line mixer Verso (Silverson) at 10,000 rpm for 30 minutes, and then treated four times using a PICOMAX device (high-pressure homogenizer) from Micronox at a pressure of 1,500 bar to prepare a carbon nanotube dispersion.

[0144] Comparative Example 6

[0145] By adding 2 wt% of 2 / g of multi-walled carbon nanotubes, 0.4 wt% of polyvinyl pyrrolidone (K15, Zhangzhou Huafu Chemical Co., Ltd.), and water as a solvent were mixed to prepare 1 kg of the mixture, and the mixture was treated using a high shear in-line mixer Verso (Silverson) at 10,000 rpm for 30 minutes, and then treated four times using a PICOMAX device (high-pressure homogenizer) from Micronox at a pressure of 1,500 bar to prepare a carbon nanotube dispersion.

[0146] Test Example 1: Viscosity Evaluation of Carbon Nanotube Dispersion

[0147] The initial viscosity of the carbon nanotube dispersions of Examples 1 to 8 and Comparative Examples 1 to 6 was measured, and the viscosity after the carbon nanotube dispersions were left to stand for 1 week at 25° C. was measured again to measure the viscosity increase rate. The viscosity increase rate was calculated by the following equation (1).

[0148] Equation (1): Viscosity increase rate (%) = {(viscosity after standing for 1 week - initial viscosity) / initial viscosity} × 100

[0149] The measurement results are shown in Table 1 below.

[0150] The viscosity was measured using a viscometer (Viscometer TV-22, manufactured by TOKI SANGYO CO., LTD.) at 25° C. and 1 rpm.

[0151] [Table 1]

[0152]

[0153]

[0154] As shown in Table 1, the carbon nanotube dispersions of Examples 1 to 8 according to the present invention exhibited excellent storage stability due to a low viscosity increase rate even after storage for one week, and also exhibited a low initial viscosity. In contrast, for the carbon nanotube dispersions of Comparative Examples 1 and 3 to 6, since the viscosity increase rate after storage for one week was relatively high at 80% or more, the storage stability was low.

[0155] Since agglomeration occurred in the carbon nanotube dispersion of Comparative Example 2, viscosity measurement could not be performed.

[0156] Embodiment 11

[0157] The negative electrode active material (graphite: SiO weight ratio = 85:15), styrene butadiene rubber (SBR) binder, carboxymethyl cellulose (CMC), and the carbon nanotube dispersion prepared in Example 1 were mixed in water so that the weight ratio of negative electrode active material: carbon nanotube: PVP: tannic acid: CMC: SBR binder was 98: 0.05: 0.05625: 0.01875: 0.925: 0.95. A 15 μm thick negative electrode current collector (Cu film) was coated with the negative electrode slurry composition, dried and rolled to prepare a negative electrode.

[0158] (Positive electrode preparation)

[0159] The positive electrode active material (NCM 811), the conductive agent (carbon black) and the binder (polyvinylidene fluoride, PVDF) were mixed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.08:1.6:1.32 to prepare a positive electrode slurry composition (solid content 70 wt%). A 25 μm thick positive electrode collector (Al film) was coated with the positive electrode active material slurry, dried and rolled to prepare a positive electrode.

[0160] (Secondary Battery Preparation)

[0161] After preparing an electrode assembly by sequentially stacking a polyethylene porous film with the positive electrode and the negative electrode prepared as described above by a conventional method, the electrode assembly is placed in a pouch type secondary battery case, and the nonaqueous electrolyte prepared as described above is injected therein to prepare a lithium secondary battery.

[0162] Example 12

[0163] A positive electrode, a negative electrode, and a lithium secondary battery were prepared in the same manner as in Example 11, except that the carbon nanotube dispersion prepared in Example 5 was used instead of the carbon nanotube dispersion prepared in Example 1.

[0164] Comparative Example 7

[0165] A positive electrode, a negative electrode, and a lithium secondary battery were prepared in the same manner as in Example 11, except that the carbon nanotube dispersion prepared in Comparative Example 5 was used instead of the carbon nanotube dispersion prepared in Example 1.

[0166] Comparative Example 8

[0167] A positive electrode, a negative electrode, and a lithium secondary battery were prepared in the same manner as in Example 11, except that the carbon nanotube dispersion prepared in Comparative Example 6 was used instead of the carbon nanotube dispersion prepared in Example 1.

[0168] Test Example 2

[0169] Each lithium secondary battery prepared in Examples 11 and 12 and Comparative Examples 7 and 8 was charged to 4.2 V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, and then each lithium secondary battery was discharged to 2.0 V at a constant current (CC) of 1C, and the above charging and discharging was set as 1 cycle, and 100 charging and discharging cycles were performed to measure the capacity retention rate.

[0170] In this case, the capacity retention ratio was calculated according to the following equation (1), and the measurement results are shown in the following [Table 2].

[0171] Equation (1): Capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity after one cycle) × 100

[0172] [Table 2]

[0173] Capacity retention rate (%) Embodiment 11 91.7 Example 12 89.4 Comparative Example 7 79.7 Comparative Example 8 81.1

[0174] As shown in Table 2, the lithium secondary batteries of Examples 11 and 12, respectively using the carbon nanotube dispersions of Examples 1 and 5 of the present invention, have significantly better cycle characteristics than the lithium secondary batteries of Comparative Examples 7 and 8, respectively using the carbon nanotube dispersions of Comparative Examples 5 and 6 containing multi-walled carbon nanotubes having a low specific surface area.

Claims

1. A carbon nanotube dispersion comprising: Brunauer-Emmett-Teller (BET) specific surface area is 800m 2 / g or more carbon nanotubes (CNTs), a dispersant, and a water-based solvent, The dispersant comprises an amine-containing polymer dispersant and a phenolic compound containing two or more aromatic rings, wherein the polymer dispersant comprises at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkylpolyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethylenimine, and The phenolic compound containing two or more aromatic rings includes at least one selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatannol, and tannic acid. 2 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotubes are single-walled carbon nanotubes, double-walled carbon nanotubes, or a combination thereof. 3 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotubes are included in an amount of 0.01 wt % to 5 wt % based on the total weight of the carbon nanotube dispersion. 4 . The carbon nanotube dispersion according to claim 1 , wherein the dispersant is included in an amount of 10 parts by weight to 2,000 parts by weight based on 100 parts by weight of the carbon nanotubes. 5 . The carbon nanotube dispersion according to claim 1 , wherein the phenol compound is included in an amount of 1 part by weight to 100 parts by weight based on 100 parts by weight of the amine-containing polymer dispersant. 6 . The carbon nanotube dispersion according to claim 1 , wherein the phenolic compound includes at least one structure selected from the group consisting of a phenol structure, a catechol structure, a gallol structure, and a naphthol structure in at least one aromatic ring. 7 . The carbon nanotube dispersion according to claim 1 , wherein the phenolic compound does not include a structure in which three or more aromatic rings are fused in a molecular structure.

8. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube dispersion has a viscosity increase rate represented by equation (1) of 80% or less: Equation (1): Viscosity increase rate (%) = {(viscosity measured after standing at 25° C. for 1 week - initial viscosity) / initial viscosity}×100. 9 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube dispersion has an initial viscosity measured at 25° C. and 1 rpm of 0.1 Pa·s to 12 Pa·s.

10. A negative electrode slurry composition, comprising: The carbon nanotube dispersion, silicon-based negative electrode active material, and binder as claimed in claim 1. 11 . A negative electrode comprising a negative electrode active material layer formed from the negative electrode slurry composition according to claim 10 . 12 . A lithium secondary battery comprising the negative electrode according to claim 11 .

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