Conductive material dispersion, electrode slurry containing the same, and lithium secondary battery containing the same

Abstract

To provide a conductive material dispersion with improved dispersibility, an electrode slurry containing the same, and a lithium secondary battery containing the same. [Solution] The conductive material dispersion according to the embodiment of the present disclosure comprises a conductive material containing carbon nanotubes, a first dispersant containing a cellulose polymer, and a second dispersant containing a polyethylene oxide polymer. By including both the first and second dispersants, the dispersibility of the conductive material dispersion can be improved, and the resistance characteristics of the secondary battery can be improved.

Description

[Technical Field]

[0001] This disclosure relates to a conductive material dispersion, an electrode slurry containing the same, and a secondary battery. [Background technology]

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged, and with the development of the information and communication and display industries, they are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. More recently, battery packs containing rechargeable batteries have also been developed and applied as power sources for environmentally friendly vehicles such as hybrid cars.

[0003] Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries are being actively researched and developed due to their high operating voltage and energy density per unit weight, as well as advantages in charging speed and weight reduction.

[0004] Electrodes for secondary batteries may contain conductive materials, which provide conductivity between electrode active material particles and reduce resistance within the electrodes. Examples of conductive materials include point-type conductive materials such as carbon black and / or linear conductive materials such as carbon nanotubes. For instance, electrode slurry can be produced by mixing electrode active material particles with a conductive material, and an electrode for a secondary battery (or the electrode active material layer of an electrode) can be manufactured from this slurry.

[0005] However, conductive materials that are not uniformly dispersed can exacerbate the aggregation phenomenon between electrode active material particles in the electrode slurry, potentially reducing the conductivity of the electrode. Furthermore, increased viscosity of the electrode slurry can lengthen the manufacturing time, potentially reducing process efficiency. Therefore, research and development are needed to improve the dispersibility of conductive materials. [Overview of the project] [Problems that the invention aims to solve]

[0006] One of the objectives of this disclosure is to provide a conductive material dispersion with improved dispersibility.

[0007] One of the objectives of this disclosure is to provide an electrode slurry with improved dispersibility.

[0008] One of the objectives of this disclosure is to provide a lithium secondary battery having improved electrochemical properties. [Means for solving the problem]

[0009] The conductive material dispersion according to the embodiment of this disclosure comprises a conductive material containing carbon nanotubes, a first dispersant containing a cellulose polymer, and a second dispersant containing a polyethylene oxide polymer.

[0010] According to exemplary embodiments, the content of the conductive material may be 0.2% to 8.0% by weight relative to the total weight of the conductive material dispersion.

[0011] According to an exemplary embodiment, the content of the first dispersant may be 50 to 400 parts by weight per 100 parts by weight of the conductive material.

[0012] According to an exemplary embodiment, the content of the second dispersant may be 10 to 100 parts by weight per 100 parts by weight of the conductive material.

[0013] According to exemplary embodiments, the weight ratio of the second dispersant to the first dispersant may be 0.05 to 0.5.

[0014] According to an exemplary embodiment, the weight-average molecular weight (MW) of the first dispersant may be between 75,000 and 400,000.

[0015] According to an exemplary embodiment, among the three hydroxy groups per glucose unit of the cellulose polymer of the first dispersant, the average value of the number of hydroxy groups substituted with an alkyl group or an acyl group may be 0.5 to 1.0.

[0016] According to an exemplary embodiment, the second dispersant may include polyethylene oxide or a copolymer of polyethylene oxide and polypropylene oxide.

[0017] According to an exemplary embodiment, the second dispersant may have an ethylene oxide repeating unit and a repeating unit represented by the following Chemical Formula 1.

[0018]

Chemical Formula

[0019] According to an exemplary embodiment, the second dispersant may include one or more polymers represented by the following Chemical Formula 2 to Chemical Formula 4.

[0020]

Chemical Formula

[0021]

Chemical Formula

[0022]

Chemical Formula

[0023] In Chemical Formula 2, a is an integer of 5 to 500. In Chemical Formula 3, R1 is an alkyl group or an alkenyl group having 1 to 5 carbon atoms, and b, c, and d are each an integer of 5 to 150. In Chemical Formula 4, R2 and R3 are each independently an alkyl group or an alkenyl group having 1 to 5 carbon atoms, and e, f, and g are each an integer of 5 to 150.

[0024] According to an exemplary embodiment, the weight-average molecular weight (MW) of the second dispersant may be 500 to 30,000.

[0025] According to an exemplary embodiment, the viscosity change rate of the conductive material dispersion may be 15% or less.

[0026] According to exemplary embodiments, the conductive material dispersion may further contain an aqueous solvent.

[0027] The electrode slurry according to the exemplary embodiment includes a conductive material dispersion according to the embodiment described above.

[0028] An exemplary lithium secondary battery includes an electrode for a lithium secondary battery containing an electrode active material layer formed from the electrode slurry according to the above-described embodiment, and a counter electrode facing the electrode for the lithium secondary battery. [Effects of the Invention]

[0029] According to embodiments of this disclosure, the conductive material dispersion includes a first dispersant containing a cellulose-based polymer and a second dispersant containing a polyethylene oxide-based polymer. The first and second dispersants improve the dispersibility of the conductive material dispersion, enabling the formation of electrodes with low surface resistance. Furthermore, the dispersants suppress aggregation of the conductive material, thereby improving storage stability.

[0030] According to exemplary embodiments, the contents of the first dispersant and the second dispersant can be adjusted within a predetermined range. This can further improve the dispersibility and storage stability of the conductive material dispersion. [Brief explanation of the drawing]

[0031] [Figure 1] Figure 1 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment. [Figure 2]Figure 2 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. [Modes for carrying out the invention]

[0032] According to embodiments of the present disclosure, a conductive material dispersion is provided, comprising a conductive material and a dispersant. According to embodiments of the present disclosure, an electrode slurry comprising the conductive material dispersion is provided. According to embodiments of the present disclosure, a lithium secondary battery is provided, comprising an electrode active material layer formed from the electrode slurry.

[0033] The lithium secondary battery according to the embodiments of this disclosure can be widely applied to electric vehicles, battery charging stations, and other green technologies such as solar and wind power generation using batteries. Furthermore, the lithium secondary battery according to the embodiments of this disclosure can be used in environmentally friendly electric vehicles, hybrid vehicles, etc., with the aim of suppressing air pollution and greenhouse gas emissions and preventing climate change.

[0034] The embodiments of this disclosure will be described in detail below.

[0035] If isomers exist for a compound represented by a chemical formula used in this disclosure, the compound represented by that chemical formula also includes those isomers.

[0036] As used in this disclosure, the term "X-based polymer" may mean a polymer comprising X compound and derivatives of X compound. For example, the X compound may be included as the main repeating unit. For example, the X compound may be included as part of a copolymer. For example, a cellulose-based polymer may represent a polymer containing cellulose.

[0037] As used in this disclosure, “derivative of compound X” means a compound synthesized or produced from compound X by a chemical reaction that alters the chemical structure of compound X. The alteration of chemical structure can occur in various ways, such as by adding, removing, or substituting specific atoms or functional groups within the compound X molecule. Derivatives of compound X retain the core molecular structure of compound X, while their chemical structure is altered, resulting in new physical, chemical, and / or biological properties.

[0038] The conductive material dispersion according to the present disclosure embodiment comprises a conductive material containing carbon nanotubes. The conductive material dispersion comprises a first dispersant containing a cellulose polymer and a second dispersant containing a polyethylene oxide polymer.

[0039] Carbon nanotubes can be defined as polymeric carbon allotropes formed by the interconnection of carbon atoms with sp2 bonds in a hexagonal honeycomb structure. Carbon nanotubes can have a cylindrical shape with a nanoscale diameter. The size and morphology of carbon nanotubes can be confirmed by scanning electron microscopy (SEM).

[0040] Carbon nanotubes possess high electrical conductivity and mechanical strength. They can be positioned between electrode active materials. This prevents blockage of micropores between electrode active materials during the pressurizing and molding processes for electrode formation. Therefore, the electrolyte can easily penetrate the electrode, reducing the internal resistance of the electrode active material layer.

[0041] In some embodiments, the carbon nanotube may include one or more single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0042] In one embodiment, the carbon nanotube may include a single-walled carbon nanotube.

[0043] In the case of single-walled carbon nanotubes, the surface area on which they can bond with the first dispersant containing a cellulose-based polymer and the second dispersant containing a polyethylene oxide-based polymer (described later) is large, which further improves the dispersibility of the conductive material dispersion.

[0044] In one embodiment, the average length of the carbon nanotubes may be 0.1 μm to 500 μm, 0.1 μm to 100 μm, or 1 μm to 10 μm. The length of the carbon nanotubes may also be the length along the long axis of the carbon nanotubes. That is, the length of the carbon nanotubes is the largest absolute value of the length that can be measured in the longitudinal direction of the carbon nanotubes. The average length can mean the average value of the lengths measured in the carbon nanotube powder. For example, the average length can be determined by summing the individual lengths along the long axes of a statistically sufficient number of carbon nanotubes (e.g., 50) and dividing the resulting value by the number of carbon nanotubes (e.g., 50). The resulting value is the average length of the carbon nanotubes.

[0045] In some embodiments, the outer diameter of the carbon nanotube may be 1 nm to 15 nm, 1 nm to 10 nm, 1 nm to 7 nm, 1.1 nm to 5 nm, 1.2 nm to 4 nm, 1.5 nm to 3 nm, 1.6 nm to 2.5 nm, or 1.8 nm to 2.1 nm.

[0046] In some embodiments, the inner diameter of the carbon nanotube may be 0.1 nm to 5 nm, 0.3 nm to 4 nm, 0.5 nm to 3 nm, 0.8 nm to 2.5 nm, 1.0 nm to 2.2 nm, 1.1 nm to 2.0 nm, or 1.2 nm to 1.5 nm.

[0047] The outer and inner diameters of carbon nanotubes represent the average values ​​of the outer and inner diameters measured in carbon nanotube powder, respectively. The outer and inner diameters of carbon nanotubes can be measured using a scanning electron microscope (SEM). The average outer diameter can be calculated, for example, by summing the outer diameters of a sufficient number of carbon nanotubes (e.g., 50) and then dividing that value by the number of carbon nanotubes (e.g., 50). The average inner diameter can be calculated using a similar method.

[0048] The bonding strength of carbon nanotubes having the aforementioned length and diameter range with the dispersant described later is increased, further improving the dispersibility of the conductive material dispersion.

[0049] According to exemplary embodiments, the content of the conductive material containing carbon nanotubes may be 0.20% by weight or more, 0.22% by weight or more, 0.24% by weight or more, 0.25% by weight or more, 0.27% by weight or more, 0.28% by weight or more, 0.29% by weight or more, or 0.30% by weight or more, based on the total weight of the conductive material dispersion.

[0050] According to exemplary embodiments, the content of the conductive material containing carbon nanotubes may be 8.0% by weight or less, 7.5% by weight or less, 7.2% by weight or less, 7.0% by weight or less, 6.8% by weight or less, 6.5% by weight or less, 6.2% by weight or less, 6.0% by weight or less, 5.5% by weight or less, or 5.0% by weight or less, based on the total weight of the conductive material dispersion.

[0051] For example, the content of the conductive material containing carbon nanotubes may be 0.2% to 8.0% by weight, 0.22% to 7.5% by weight, 0.24% to 7.2% by weight, 0.25% to 7.0% by weight, 0.28% to 6.0% by weight, 0.29% to 5.5% by weight, or 0.30% to 5.0% by weight, relative to the total weight of the conductive material dispersion. Furthermore, the content of the conductive material containing carbon nanotubes may be 0.30% to 4.0% by weight, 0.3% to 3.5% by weight, 0.30% to 3.0% by weight, 0.30% to 2.5% by weight, 0.30% to 2.0% by weight, 0.30% to 1.5% by weight, 0.30% to 1.0% by weight, 0.30% to 0.8% by weight, 0.30% to 0.5% by weight, or 0.30% to 0.45% by weight. The content of the conductive material containing carbon nanotubes may be 0.40% by weight relative to the total weight of the conductive material dispersion.

[0052] Within the aforementioned content range, the energy density of the secondary battery can be increased by increasing the content of the electrode active material, while maintaining improved electrical conductivity.

[0053] In one embodiment, the conductive material may be included in powder form.

[0054] Carbon nanotubes have a high specific surface area and a long aspect ratio, and can exhibit strong cohesive forces due to their surface bonding energy and strong van der Waals forces. Therefore, carbon nanotubes tend to aggregate with each other in solvents, and their low dispersibility can increase the viscosity of conductive material dispersions.

[0055] In contrast, according to the exemplary embodiment, the conductive material dispersion contains a cellulose-based polymer, which improves the dispersibility of carbon nanotubes.

[0056] According to an exemplary embodiment, the first dispersant comprises a cellulosic polymer.

[0057] The cellulosic polymer may contain units derived from cellulose. For example, the cellulosic polymer may include carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, diacetyl cellulose, carboxyethyl cellulose, and the like.

[0058] For example, the cellulose-based polymer can adsorb (absort) conductive materials containing carbon nanotubes as its main dispersant, and the electrostatic repulsion force mediated by the polar functional groups of the cellulose-based polymer reduces the cohesive force between the conductive materials, thereby dispersing them.

[0059] In one embodiment, the first dispersant may contain carboxymethylcellulose.

[0060] The polymer chain of the first dispersant containing carboxymethylcellulose can more efficiently adsorb carbon nanotubes through hydrophobic bonding.

[0061] According to exemplary embodiments, the weight-average molecular weight (MW) of the first dispersant may be 75,000 or more, 80,000 or more, 85,000 or more, 90,000 or more, 95,000 or more, or 100,000 or more.

[0062] According to exemplary embodiments, the weight-average molecular weight (MW) of the first dispersant may be 600,000 or less, 400,000 or less, 390,000 or less, 380,000 or less, 370,000 or less, 360,000 or less, 350,000 or less, 340,000 or less, or 330,000 or less.

[0063] According to exemplary embodiments, the weight-average molecular weight (MW) of the first dispersant may be 100,000 to 400,000, or 100,000 to 350,000, or 100,000 to 300,000, or 150,000 to 300,000, or 200,000 to 300,000. For example, the weight-average molecular weight of the first dispersant may be 200,000 to 300,000. For example, the average molecular weight of the first dispersant is approximately 250,000.

[0064] For example, the average molecular weight of the first dispersant may be between 100,000 and 250,000.

[0065] For example, the weight-average molecular weight may be a value calculated in polystyrene equivalent based on the measurement results of gel permeation chromatography (GPC). The weight-average molecular weight can be measured according to the ASTM D6474 standard.

[0066] According to exemplary embodiments, the viscosity of the first dispersant may be 100 cP or more, 200 cP or more, 300 cP or more, 400 cP or more, 500 cP or more, or 600 cP or more.

[0067] According to exemplary embodiments, the viscosity of the first dispersant may be 4,000 cP or less, 3,500 cP or less, 3,200 cP or less, 3,000 cP or less, 2,800 cP or less, or 2,500 cP or less.

[0068] For example, the viscosity of the first dispersant may be 100 cP to 4,000 cP, 200 cP to 3,500 cP, 300 cP to 3,200 cP, 400 cP to 3,000 cP, 500 cP to 2,800 cP, or 600 cP to 2,500 cP.

[0069] The viscosity mentioned above can represent the value measured in aqueous solution. For example, an aqueous solution containing 2 wt% of the first dispersant relative to the total weight of the aqueous solution at a shear rate of 96.2 s⁻¹. -1 The viscosity measured may fall within the aforementioned range.

[0070] Polymer chains of the first dispersant having a weight-average molecular weight and / or viscosity within the aforementioned range have high compatibility with the diameter and length of carbon nanotubes, and can improve adsorption efficiency.

[0071] According to exemplary embodiments, the degree of substitution of the first dispersant may be 0.4 or greater, 0.5 or greater, 0.55 or greater, 0.60 or greater, 0.65 or greater, 0.68 or greater, or 0.70 or greater.

[0072] According to an exemplary embodiment, the degree of substitution of the first dispersant may be 1.0 or less, 0.98 or less, 0.96 or less, 0.94 or less, 0.92 or less, or 0.90 or less.

[0073] For example, the degree of substitution of the first dispersant may be 0.4-1.0, 0.5-1.0, 0.55-0.98, 0.60-0.96, 0.65-0.94, 0.68-0.92, or 0.70-0.90.

[0074] The term "degree of substitution (DS)" can refer to the extent to which the hydroxyl groups of glucose units in cellulose are substituted by alkyl groups, acyl groups, etc. For example, the degree of substitution can be calculated as the average number of hydroxyl groups substituted by alkyl groups or acyl groups out of three hydroxyl groups per glucose unit. For example, the degree of substitution can be measured by methods known in the art.

[0075] According to exemplary embodiments, the content of the first dispersant may be 50 parts by weight or more, 60 parts by weight or more, 65 parts by weight or more, 70 parts by weight or more, 72 parts by weight or more, or 75 parts by weight or more, based on 100 parts by weight of the conductive material.

[0076] According to an exemplary embodiment, the content of the first dispersant may be 400 parts by weight or less, 380 parts by weight or less, 350 parts by weight or less, 330 parts by weight or less, 320 parts by weight or less, or 300 parts by weight or less, per 100 parts by weight of the conductive material.

[0077] For example, the content of the first dispersant may be 50 to 400 parts by weight, 60 to 380 parts by weight, 65 to 350 parts by weight, 70 to 330 parts by weight, or 75 to 300 parts by weight per 100 parts by weight of the conductive material.

[0078] Within the aforementioned range, the increase in viscosity can be suppressed, improving the fluidity of the conductive material dispersion and enhancing the dispersibility of the conductive material. This improves the penetration rate of the electrolyte by securing space between the electrode active materials, thereby improving the electrical conductivity characteristics of the secondary battery.

[0079] According to an exemplary embodiment, the second dispersant comprises a polyethylene oxide polymer.

[0080] The polyethylene oxide polymer may contain units derived from polyethylene oxide. For example, the polyethylene oxide polymer may include polymers and / or copolymers that contain ethylene oxide repeating units as part of their composition.

[0081] For example, the polyethylene oxide polymer can act as an auxiliary dispersant and form micelles on the surface of carbon nanotubes dispersed by a cellulose polymer. These micelles reduce intermolecular interactions involving the carbon nanotubes and increase steric hinderance. This allows for stable maintenance of the dispersed state.

[0082] According to exemplary embodiments, the second dispersant may include polyethylene oxide or a copolymer of polyethylene oxide and polypropylene oxide.

[0083] Polyethylene oxide can form hydrogen bonds with the solvent contained in the dispersion, thereby improving dispersion stability.

[0084] According to exemplary embodiments, the second dispersant may further have repeating units represented by the following chemical formula 1.

[0085] [ka]

[0086] For example, the repeating unit represented by chemical formula 1 can form block copolymers, random copolymers, alternating copolymers, graft copolymers, and the like, together with ethylene oxide repeating units.

[0087] According to exemplary embodiments, the repeating unit represented by chemical formula 1 can form a block copolymer with ethylene oxide repeating units. This block copolymer exhibits a certain interaction between the conductive material and the solvent, thereby demonstrating repeatability.

[0088] Copolymers of polyethylene oxide and polypropylene oxide, by containing both hydrophilic and hydrophobic moieties, can form hydrophobic interactions with conductive materials and hydrophilic interactions with solvents. This ensures that distances are maintained between conductive materials, allowing for stable dispersion.

[0089] According to an exemplary embodiment, the second dispersant may contain ethylene oxide repeating units at its terminal ends. This allows for bonding with the solvent and improves its stability in the solvent.

[0090] In one embodiment, the second dispersant may contain a polymer represented by the following chemical formula 2.

[0091] [ka]

[0092] In chemical formula 2, 'a' is an integer between 5 and 500.

[0093] In one embodiment, a may be 50-500, 80-450, or 100-400.

[0094] Within the aforementioned range, a certain chain length of the second dispersant can be ensured, thereby suppressing aggregation between conductive materials.

[0095] In some embodiments, the second dispersant may include a polymer represented by the following chemical formula 3.

[0096] [ka]

[0097] In chemical formula 3, R1 is an alkyl or alkenyl group having 1 to 5 carbon atoms, and b, c, and d are integers from 5 to 150.

[0098] In one embodiment, the second dispersant may contain a polymer represented by the following chemical formula 3-1.

[0099] [ka]

[0100] In chemical formula 3-1, b, c, and d are integers between 5 and 150.

[0101] In one embodiment, b and d may be 30-150, 50-140, or 60-130, respectively.

[0102] Within the aforementioned range, the length of the hydrophilic portion at the end of the second dispersant can be maintained within a predetermined range, thereby further improving dispersibility.

[0103] In one embodiment, c may be 20-150, 25-120, or 30-90. Within this range, the distance between the hydrophobic and hydrophilic portions is ensured, improving the dispersion stability of the conductive material dispersion.

[0104] In some embodiments, the second dispersant may include a polymer represented by the following chemical formula 4.

[0105] [ka]

[0106] In chemical formula 4, R2 and R3 are each independently an alkyl or alkenyl group having 1 to 5 carbon atoms, and e, f, and g are each integers from 5 to 150.

[0107] In one embodiment, the second dispersant may contain a polymer represented by the following chemical formula 4-1 or 4-2.

[0108] [ka]

[0109] In chemical formula 4-1, e, f, and g are integers between 5 and 150.

[0110] In one embodiment, in chemical formula 4-1, e and g may be 20-150, 25-120, or 30-90, respectively.

[0111] In one embodiment, in chemical formula 4-1, f may be 30-150, 50-140, or 60-130.

[0112] Within the aforementioned range, the distance between the hydrophobic and hydrophilic portions of the second dispersant is ensured, thereby improving the dispersion stability of the conductive material dispersion.

[0113] In some embodiments, the second dispersant may also include a polysorbate polymer.

[0114] For example, the polysorbate polymers include polysorbate 20 (sorbitan monolaurate), polysorbate 21 (PEG-4 sorbitan monolaurate), polysorbate 40 (PEG-20 sorbitan monopalmitate), polysorbate 60 (PEG-20 sorbitan monostearate), polysorbate 61 (PEG-4 sorbitan monosterate), polysorbate 65 (PEG-20 sorbitan tristearate), and polysorbate 80 (PEG-80 sorbitan monooleate).

[0115] According to exemplary embodiments, the weight-average molecular weight (MW) of the second dispersant may be 400 or more, 500 or more, 700 or more, 1,000 or more, 1,500 or more, 2,000 or more, 3,000 or more, or 5,000 or more.

[0116] According to exemplary embodiments, the weight-average molecular weight (MW) of the second dispersant may be 50,000 or less, 30,000 or less, 28,000 or less, 25,000 or less, 22,000 or less, or 20,000 or less, or 18,000 or less.

[0117] For example, the weight-average molecular weight (MW) of the second dispersant may be 400-50,000, 500-30,000, 700-28,000, 1,000-25,000, 1,500-22,000, 2,000-20,000, or 5,000-18,000.

[0118] For example, the weight-average molecular weight may be a value calculated in polystyrene equivalent based on the measurement results of gel permeation chromatography (GPC).

[0119] The second dispersant having a weight-average molecular weight within the aforementioned range can be distributed between the first dispersant and the carbon nanotubes to form steric hinderance, thereby further improving the dispersion stability of the conductive material dispersion.

[0120] According to exemplary embodiments, the content of the second dispersant may be 0.9 parts by weight or more, 10 parts by weight or more, 11 parts by weight or more, 11.5 parts by weight or more, 12 parts by weight or more, or 12.5 parts by weight or more, based on 100 parts by weight of the conductive material.

[0121] According to exemplary embodiments, the content of the second dispersant may be 100 parts by weight or less, 90 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, 72 parts by weight or less, or 70 parts by weight or less, per 100 parts by weight of the conductive material.

[0122] For example, the content of the second dispersant may be 0.9 to 100 parts by weight, 10 to 100 parts by weight, 11 to 90 parts by weight, 11.5 to 80 parts by weight, 12 to 75 parts by weight, or 12.5 to 70 parts by weight per 100 parts by weight of the conductive material.

[0123] Within the aforementioned range, the second dispersant can be uniformly distributed, thereby further improving dispersion stability due to steric hindrance. Consequently, the storage stability of the conductive material dispersion can be improved.

[0124] According to exemplary embodiments, the weight ratio of the second dispersant to the first dispersant may be 0.01 or more, 0.05 or more, 0.055 or more, 0.06 or more, 0.065 or more, 0.07 or more, 0.075 or more, or 0.08 or more.

[0125] According to exemplary embodiments, the weight ratio of the second dispersant to the first dispersant may be 0.50 or less, 0.45 or less, 0.42 or less, 0.40 or less, 0.38 or less, 0.37 or less, 0.36 or less, or 0.35 or less.

[0126] For example, the weight ratio of the second dispersant to the first dispersant may be 0.01-0.50, 0.05-0.50, 0.055-0.45, 0.06-0.42, 0.07-0.40, 0.075-0.37, or 0.08-0.35.

[0127] Within the aforementioned range, dispersibility can be improved while suppressing the viscosity increase caused by the first dispersant. The degree of dispersion of the conductive material can be further improved.

[0128] According to exemplary embodiments, the conductive material dispersion may contain a solvent. For example, the solvent may be an aqueous or non-aqueous solvent.

[0129] According to exemplary embodiments, the solvent may include an aqueous solvent. For example, the aqueous solvent may include a polar aqueous solvent such as water, an aqueous acid solution, or an aqueous base solution.

[0130] The aqueous solvent may contain water as its main component. For example, the water content in the aqueous solvent may be 80% by weight or more, 90% by weight or more, or 95% by weight or more. The aqueous solvent may be substantially composed of water.

[0131] The aqueous solvent can interact with the second dispersant by hydrogen bonding, thereby improving its stability in the solvent.

[0132] In exemplary embodiments, the conductive material dispersion can be produced by mixing the conductive material, the first dispersant, the second dispersant, and the solvent. For example, the mixture can be produced by adding the conductive material, the first dispersant, and the second dispersant to the solvent and performing rotation, vibration, sliding, rolling, lifting, ultrasonic treatment, etc.

[0133] In one embodiment, the dispersion step of the mixture can be further carried out. For example, it can be uniformly mixed and dispersed using a mixer, a disperser, a high-pressure disperser, a nano-high-pressure disperser, an ultrasonic disperser, etc.

[0134] In one embodiment, mixing and dispersion can be performed together. For example, a conductive material, a first dispersant, a second dispersant, and a solvent can be uniformly mixed and dispersed.

[0135] In one embodiment, the first dispersant and the second dispersant can be added sequentially.

[0136] After adsorbing carbon nanotubes with the first dispersant, steric hindrance can be formed by the second dispersant, thereby more efficiently improving dispersibility.

[0137] According to exemplary embodiments, the conductive material dispersion may include particles dispersed by the first and second dispersants described above.

[0138] According to an exemplary embodiment, the average particle size (D50) of the dispersed particles may be 10 μm to 120 μm, 10 μm to 100 μm, 20 μm to 80 μm, 30 μm to 70 μm, or 40 μm to 60 μm.

[0139] The average particle size (D50) of the dispersed particles can represent the average particle size of the particles contained in the conductive material dispersion during manufacturing. For example, if the material is manufactured in film form to evaluate electrodes or electrode resistance, the average particle size of the dispersed particles may be smaller than the average particle size.

[0140] According to an exemplary embodiment, the average particle size (D50) of the dispersed particles contained in the electrode may be 0.1 μm or more, 0.5 μm or more, 0.8 μm or more, 1.0 μm or more, 1.2 μm or more, or 1.5 μm or more.

[0141] According to an exemplary embodiment, the average particle size (D50) of the dispersed particles contained in the electrode may be 5 μm or less, 4.8 μm or less, 4.5 μm or less, 4.2 μm or less, 4.0 μm or less, 3.8 μm or less, 3.6 μm or less, or 3.5 μm or less.

[0142] For example, the average particle size (D50) of the dispersed particles contained in the electrode may be 0.1 μm to 5 μm, 0.5 μm to 4.8 μm, 0.8 μm to 4.5 μm, 1.0 μm to 3.8 μm, 1.2 μm to 3.6 μm, or 1.5 μm to 3.5 μm.

[0143] A conductive material dispersion containing particles having an average particle size within the aforementioned range can improve the permeability of the electrolyte by ensuring pores between the electrode active materials.

[0144] The average particle size of the dispersed particles contained in the electrode can be adjusted by the average particle size of the dispersed particles contained in the conductive material dispersion. For example, if the average particle size of the dispersed particles contained in the conductive material dispersion is 60 μm or less, the average particle size of the dispersed particles contained in the electrode may be 3 μm or less.

[0145] The average particle size (D50) can represent the particle size at the 50% and 99.9% points of the volume particle size distribution, based on the volume particle size distribution obtained by the laser diffraction method.

[0146] According to an exemplary embodiment, the viscosity of the conductive material dispersion may be 910 cP or less, 750 cP or less, 700 cP or less, 670 cP or less, 650 cP or less, 630 cP or less, 620 cP or less, or 600 cP or less.

[0147] The lower limit of the viscosity of the conductive material dispersion is not limited, but may be, for example, 10 cP or more, 50 cP or more, 100 cP or more, 150 cP or more, or 200 cP or more.

[0148] An electrode slurry containing a conductive material dispersion having the viscosity within the aforementioned range can be used to form an electrode with low surface resistance.

[0149] The viscosity can be measured by methods known in the art, and for example, it may represent a value measured using a viscometer.

[0150] According to an exemplary embodiment, the viscosity change rate of the conductive material dispersion may be 15% or less, 12% or less, 10% or less, 8% or less, 6% or less, or 5% or less.

[0151] The lower limit of the viscosity change rate of the conductive material dispersion is not limited, but may be, for example, 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, or 0.5% or more.

[0152] The viscosity change rate can be represented by the value calculated using the following formula 1.

[0153] [Formula 1] [(Viscosity of initial conductive material dispersion - Viscosity of conductive material dispersion after storage at high temperature (50°C) for one week) / Viscosity of initial conductive material dispersion] × 100

[0154] A conductive material dispersion having a viscosity change rate within the aforementioned range can ensure long-term storage.

[0155] The electrode slurry according to the embodiments of this disclosure may contain the conductive material dispersion described above.

[0156] For example, an electrode slurry can be manufactured by mixing and stirring an electrode active material in a solvent and then adding the aforementioned conductive material dispersion. Alternatively, an electrode slurry can be manufactured by adding and mixing an electrode active material into the conductive material dispersion. For example, the electrode slurry may contain 90% to 97% by weight of electrode active material, 0.1% to 1% by weight of the conductive material dispersion, and the remainder being a binder, based on the total weight. For example, the binder content may be 2.5% to 9% by weight.

[0157] The solvent in the electrode slurry may include aqueous solvents such as water, aqueous hydrochloric acid solution, or aqueous sodium hydroxide solution, or non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, or tetrahydrofuran.

[0158] The electrode active material may be either a positive electrode active material or a negative electrode active material.

[0159] Examples of the positive electrode active material include one or more compounds selected from lithium iron phosphate compounds, lithium cobalt oxides, lithium manganese oxides, lithium nickel oxides, or lithium composite oxides. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2VO7, or lithium iron phosphate oxides such as LiFePO4.

[0160] In one embodiment, the positive electrode active material may include a compound represented by the following chemical formula 5.

[0161] [ka]

[0162] In chemical formula 5, 0.95 ≤ a ≤ 1.08 and b ≥ 0.5, and M may be at least one element from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Sr.

[0163] In one embodiment, the positive electrode active material comprises nickel (Ni) and may further comprise at least one of cobalt (Co) or manganese (Mn). For example, nickel-cobalt-manganese (NCM) lithium oxide can be used as the positive electrode active material.

[0164] For example, nickel (Ni) can be supplied as a metal related to the capacity of lithium secondary batteries. A higher nickel content improves the capacity and output of the lithium secondary battery, but an excessive increase in nickel content can reduce lifespan and be detrimental in terms of mechanical and electrical stability.

[0165] In one embodiment, cobalt (Co) can be used to improve the conductivity or resistance of a lithium secondary battery, and manganese (Mn) can be used to improve the mechanical and electrical stability of a lithium secondary battery.

[0166] The chemical structure represented by chemical formula 5 shows the bonding relationships contained in the lattice or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M may be provided as the main active element of the positive electrode active material. Chemical formula 5 is provided to represent the bonding relationships of the said main active element and should be understood as a formula that includes the introduction and substitution of additional elements.

[0167] In one embodiment, in addition to the main active element, auxiliary elements may be further included to improve the chemical stability of the positive electrode active material or the crystal structure. It should be understood that these auxiliary elements can be incorporated together into the crystal structure to form bonds, and in this case too, they fall within the range of the chemical structure represented by chemical formula 5.

[0168] The negative electrode active material can be any material known in the art that can intercept and deintercept lithium ions, without any particular limitations. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon or tin can be used.

[0169] Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) fired at temperatures below 1500°C, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0170] In one embodiment, the electrode slurry may further include a binder.

[0171] Examples of the aforementioned binders include aqueous binders such as styrene-butadiene rubber (SBR); and non-aqueous binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and nitrile butadiene rubber.

[0172] In one embodiment, if the electrode slurry contains a positive electrode active material, the binder may include a PVDF-based binder. In another embodiment, if the electrode slurry contains a negative electrode active material, the binder may include, for example, an aqueous binder for compatibility with a carbon-based active material.

[0173] In one embodiment, the electrode slurry may further contain a thickening agent such as carboxymethylcellulose (CMC).

[0174] Figures 1 and 2 are schematic plan and cross-sectional views, respectively, of a lithium secondary battery according to an exemplary embodiment. However, this is illustrative only, and the disclosure is not limited to the specific embodiments described herein.

[0175] Referring to Figures 1 and 2, a lithium secondary battery may include a positive electrode 100 and a negative electrode 130 facing the positive electrode 100. Either the positive electrode 100 or the negative electrode 130 may be an electrode for a lithium secondary battery containing an electrode active material layer formed from the electrode slurry described above, while the other may be a counter electrode.

[0176] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one surface of the positive electrode current collector 105. For example, the positive electrode 100 can be manufactured by coating at least one surface of the positive electrode current collector 105 with a positive electrode slurry, then drying and rolling it.

[0177] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0178] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one surface of the negative electrode current collector 125.

[0179] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and may include, for example, copper or a copper alloy.

[0180] In one embodiment, the electrode for the lithium secondary battery may be the positive electrode and the counter electrode may be the negative electrode.

[0181] In one embodiment, the counter electrode may include, as a conductive material, carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, which are perovskite materials.

[0182] In some embodiments, a separation membrane 140 can be interposed between the positive electrode 100 and the negative electrode 130. The separation membrane 140 may include a porous polymer film made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The separation membrane may also include a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0183] According to exemplary embodiments, an electrode assembly 150 can be formed by repeatedly arranging a positive electrode 100, a negative electrode 130, and a separator membrane 140. In some embodiments, the electrode assembly 150 may be of the winding, stacking, Z-folding, or stack-folding type.

[0184] The electrode assembly 150 is housed in the case 160, thus defining a lithium secondary battery. The lithium secondary battery can be manufactured, for example, in the form of a cylindrical, rectangular, pouch, or coin-shaped container.

[0185] Electrode tabs (positive electrode tab and negative electrode tab) protrude from the positive electrode current collector 105 and negative electrode current collector 125 belonging to each electrode cell, and can extend to one side of the case 160. The electrode tabs can fuse together with the one side of the case 160 to form electrode leads (positive electrode lead 107 and negative electrode lead 127) that extend or are exposed outside the case 160.

[0186] According to an exemplary embodiment, an electrolytic solution can be housed together with an electrode assembly 150 in a case 160. As the electrolytic solution, a non-aqueous electrolytic solution can be used.

[0187] The non-aqueous electrolytic solution can contain a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented by, for example, Li + X - and the anion (X - ) of the lithium salt includes F - , Cl - , Br - , 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 - etc.

[0188] Examples of organic solvents that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These can be used individually or in combination of two or more.

[0189] The following are specific examples to aid in understanding the present invention, but these examples are merely illustrative and do not limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications can be made to these examples within the scope of the present invention and the technical concept, and it is also obvious that these variations and modifications fall within the scope of the appended claims.

[0190] Examples and Comparative Examples (1) Manufacturing of conductive material dispersion (Manufacturing Method A) Carbon nanotubes (SWCNT, length: 5-15 μm; outer diameter: 1 nm-15 nm; inner diameter: 0.1 nm-5 nm), carboxymethyl cellulose sodium salt (MW: 250,000 Da) as a first dispersant, and polyethylene oxide (PEO, MW: 6,000 Da) as a second dispersant were mixed in the amounts shown in Table 1 below. The mixture was then mixed at a speed of 8,000 rpm for 3 hours using a high-shear mixer to produce a lab-scale conductive material dispersion.

[0191] (Manufacturing Method B) A commercially available conductive material dispersion was manufactured using a dispersant composition that shows performance improvement effects in lab-scale conductive material dispersions. Specifically, carbon nanotubes (SWCNT, length: 5 μm to 15 μm), carboxymethyl cellulose sodium salt (MW: 250,000 Da) as the first dispersant, and polyethylene oxide (PEO, MW: 6,000 Da) as the second dispersant were mixed in distilled water (H2O) solvent in the amounts shown in Table 1 below. After mixing at a speed of 3,000 rpm for 20 hours using a reverse-scrapping mixer, the dispersion was produced by mixing at 60 Hz for 20 passes using a high-pressure homogenizer (bead mill).

[0192] Conductive material dispersions were prepared by changing the carbon nanotubes, first dispersant, and second dispersant as shown in Table 1 below. In Table 1 below, when the first dispersant contained A-2, the conductive material dispersion was prepared by mixing at a speed of 8,000 rpm for 3 hours.

[0193] The weight-average molecular weight (MW) of each compound was measured by GPC analysis under the following conditions. i) Equipment: Agilent 1260 Infinity II (RI-detector, Agilent software) ii) Developing solvent: DI Water with NaCl iii) Column: Agilent PL aquagel-OH+M+H iv) Temperature: 40℃, flow rate: 1.0mL / min, injection volume: 100mL v) Standard material: PEG / PEO

[0194] [Table 1]

[0195] The specific compounds listed in Table 1 are as follows: A-1: Carboxymethylcellulose, MW: 250,000, Degree of substitution: 0.7 A-2: Carboxymethyl cellulose, MW: 110,000, degree of substitution: 0.85 A-3: Carboxymethyl cellulose, MW: 600,000, degree of substitution: 0.7 A-4: Carboxymethyl cellulose, MW: 250,000, degree of substitution: 1.2 A-5: Carboxymethyl cellulose, MW: 250,000, degree of substitution: 0.4 B-1: Polyethylene oxide, MW: 6,000 B-2: Polyethylene oxide, MW: 400 B-3: Polyethylene oxide, MW: 50,000 B-4: Pluronic (registered trademark) F-127, MW: 12,500 B-5: Pluronic (registered trademark) 10R5, MW: 2,000 B-6: SDBS (Sodium dodecylbenzene sulfonate), MW: 348 B-7: CTAB (Cetrimonium bromide), MW: 365

[0196] (2) Manufacture of negative electrode slurry and manufacture of film for electrode resistance evaluation 96.3 parts by weight of negative electrode active material (SiOx, 0 < x < 2), 1.5 parts by weight of carboxymethyl cellulose as the first binder, and 2.0 parts by weight of styrene-butadiene rubber as the second binder were added to a water (H2O) solvent. Using a mixer (manufactured by Thinky, ARE-310), it was mixed at 1,000 rpm for 10 minutes. 0.25 parts by weight of the conductive material dispersion liquid manufactured in the examples and comparative examples was added to the slurry containing the negative electrode active material and the binder. Then, using a mixer, it was mixed at 1,000 rpm for 10 minutes to obtain a negative electrode active material slurry. The total solid content of the negative electrode active material slurry was 90 wt% - 98 wt%.

[0197] A slurry of the negative electrode active material was applied to a PET substrate (thickness: 50 μm) using an applicator. Then, it was dried in an electric oven at 100°C for 1 hour to obtain a negative electrode film for surface resistance measurement with an average thickness of 100 μm to 130 μm (excluding the thickness of the PET substrate).

[0198] Experimental example (1) Particle size analysis of particles in conductive material dispersion The particle size of the particles contained in the conductive material dispersions produced in the above examples and comparative examples was analyzed. Specifically, the conductive material dispersion was diluted 2,000 times using an aqueous solution (H2O). The particle size was calculated by measuring the difference in diffraction patterns due to the particle size of the diluted conductive material dispersion using a laser diffraction particle size analyzer (HORIBA, LA-950V2). The minimum particle size in the measured volume-based particle size distribution curve was defined as Dmin, and D50 was measured by calculating the particle size at the points where the volume fraction reached 50% and 99.9%. The particle size was evaluated according to the following criteria.

[0199] <Criteria for evaluating particle size> ◎: Less than 60 μm based on D50 ○: Based on D50, 60 μm or more and less than 80 μm △: Based on D50, 80 μm or more and less than 120 μm ×: 120 μm or larger based on D50.

[0200] (2) Measurement of the viscosity of the conductive material dispersion The viscosity of the conductive material dispersions produced in the above examples and comparative examples was measured. Viscosity was measured using a rheometer viscometer (Antonparr apparatus, equipped with a Standard measuring system CC27 / T200 / SS Cylinder type, 25.0°C). Shear rate: 96.2 s² -1 This was used as the basis for verification.

[0201] (3) Evaluation of electrode resistance Using the electrode resistance measuring films produced in the above examples and comparative examples, the electrode resistance of the negative electrode was measured according to the measuring device and conditions.

[0202] The surface resistance was measured at six points in the negative electrode film using a device (LORESTA-Gx, MCP-T700, manufactured by Nitto Seiko Analytech), and the average value was calculated. The electrode resistance was calculated by multiplying the measured surface resistance value by the film thickness.

[0203] (4) Evaluation of storage stability Storage stability was evaluated by calculating the change in rheometer viscosity during storage of conductive material dispersions prepared in the examples and comparative examples through high-temperature accelerated experiments.

[0204] The initial rheometer viscosity was measured within 3 days of preparation for the conductive material dispersions produced in the examples and comparative examples.

[0205] The conductive material dispersions prepared in the examples and comparative examples were stored at a high temperature (50°C) for one week, and their viscosity was measured using the same method as for measuring the initial viscosity. The degree of change (viscosity change rate) between the initial viscosity and the viscosity measured after one week of storage at a high temperature was calculated, and the storage stability was evaluated according to the following criteria.

[0206] The viscosity change rate was calculated using the following formula 1. [Formula 1] Viscosity change rate (%) = [(Initial viscosity of conductive material dispersion - Viscosity of conductive material dispersion after storage at high temperature for 1 week) / Initial viscosity of conductive material dispersion] × 100

[0207] <Evaluation Criteria for Storage Stability> ◎: Viscosity change rate of 5% or less ○: Viscosity change rate greater than 5% and 15% or less △: Viscosity change rate greater than 15% and less than or equal to 30% ×: Viscosity change rate exceeding 30%

[0208] The measurement results for particle size, viscosity, electrode resistance of the negative electrode, and storage stability of the conductive material dispersion in the aforementioned conductive material dispersion are shown in Table 2 below.

[0209] [Table 2]

[0210] [Table 3]

[0211] A comparison of the examples (Examples 1-17) and comparative examples (Comparative Examples 1-7) of the present disclosure shown in Table 2 revealed that the particle size and viscosity of the conductive material dispersions decreased in the examples, and the dispersibility improved. Furthermore, the viscosity change rate decreased, improving storage stability, and the negative electrode produced from the negative electrode slurry composition containing the conductive material dispersion exhibited reduced electrode resistance.

[0212] According to Table 2, in the comparative example, the particle size of the conductive material dispersion increased, the viscosity of the negative electrode slurry composition increased, and it was confirmed that the conductive material was agglomerating. Furthermore, the high viscosity change rate resulted in low storage stability, and the negative electrode produced from the negative electrode slurry composition containing the conductive material dispersion showed increased electrode resistance.

[0213] According to Table 3, the conductive material dispersion according to the example (Example 18) had low particle size, viscosity, and viscosity change rate, and the negative electrode produced from it showed reduced electrode resistance. In contrast, the conductive material dispersion according to the comparative example (Comparative Example 8) had high particle size, viscosity, and viscosity change rate, and the negative electrode produced from it showed increased electrode resistance. This confirms the commercial viability of the conductive material dispersion according to the example.

[0214] In Example 4, where the content of the second dispersant was relatively low, the particle size increased relatively, and the viscosity of the conductive material dispersion increased relatively.

[0215] In Example 6, where the molecular weight of the second dispersant was relatively high, the particle size increased relatively, and the electrode resistance increased.

[0216] In Example 9, where different types of secondary dispersants were used, and the content was relatively low, the particle size increased relatively. Furthermore, the viscosity of the conductive material dispersion increased relatively, and its storage stability decreased relatively.

[0217] In Example 15, where the molecular weight of the first dispersant was relatively high, the particle size increased relatively. In addition, the viscosity of the conductive material dispersion increased, and the electrode resistance increased.

[0218] In Example 16, which used a first dispersant with a relatively high degree of substitution, the storage stability of the conductive material dispersion was relatively reduced.

[0219] In Example 17, which used a first dispersant with a relatively low degree of substitution, the viscosity of the conductive material dispersion increased, and the storage stability decreased relatively. [Explanation of symbols]

[0220] 100: Positive electrode 105: Positive electrode current collector 107: Positive electrode lead 110: Positive electrode active material layer 120: Negative electrode active material layer 125: Negative electrode current collector 127: Negative electrode lead 130: Negative electrode 140: Separation membrane 150: Electrode assembly 160: Case

Claims

1. Conductive materials containing carbon nanotubes, A first dispersant containing a cellulose polymer, A conductive material dispersion comprising a second dispersant containing a polyethylene oxide polymer.

2. The conductive material dispersion according to claim 1, wherein the content of the conductive material is 0.2% by weight to 8.0% by weight based on the total weight of the conductive material dispersion.

3. The conductive material dispersion according to claim 1, wherein the content of the first dispersant is 50 to 400 parts by weight per 100 parts by weight of the conductive material.

4. The conductive material dispersion according to claim 1, wherein the content of the second dispersant is 10 to 100 parts by weight per 100 parts by weight of the conductive material.

5. The conductive material dispersion according to claim 1, wherein the weight ratio of the second dispersant to the first dispersant is 0.05 to 0.

5.

6. The conductive material dispersion according to claim 1, wherein the weight-average molecular weight (MW) of the first dispersant is 75,000 to 400,000.

7. The conductive material dispersion according to claim 1, wherein the average number of hydroxyl groups substituted with alkyl groups or acyl groups among the three hydroxyl groups per glucose unit of the cellulose polymer of the first dispersant is 0.5 to 1.

0.

8. The conductive material dispersion according to claim 1, wherein the second dispersant comprises polyethylene oxide or a copolymer of polyethylene oxide and polypropylene oxide.

9. The conductive material dispersion according to claim 1, wherein the second dispersant has ethylene oxide repeating units and repeating units represented by the following chemical formula 1. 【Chemistry 1】

10. The conductive material dispersion according to claim 1, wherein the second dispersant contains one or more polymers represented by the following chemical formulas 2 to 4. 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 (In chemical formula 2, a is an integer between 5 and 500, and in chemical formula 3, R １ is an alkyl or alkenyl group having 1 to 5 carbon atoms, and b, c, and d are integers from 5 to 150, in chemical formula 4, R ２ and R ３ Each of these is independently an alkyl or alkenyl group having 1 to 5 carbon atoms, and e, f, and g are integers from 5 to 150.

11. The conductive material dispersion according to claim 1, wherein the weight-average molecular weight (MW) of the second dispersant is 500 to 30,000.

12. The conductive material dispersion according to claim 1, wherein the viscosity change rate is 15% or less.

13. The conductive material dispersion according to claim 1, further comprising an aqueous solvent.

14. An electrode slurry comprising the conductive material dispersion described in claim 1.

15. An electrode for a lithium secondary battery comprising an electrode active material layer formed from the electrode slurry described in claim 14, A lithium secondary battery comprising a counter electrode facing the aforementioned lithium secondary battery electrode.

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