Expandable carbon nanotube powder and dry electrode and lithium secondary battery including the same

Abstract

The present invention relates to an expandable carbon nanotube powder including carbon nanotube units, wherein, when electrical conductivity (S / cm) and compaction density (g / cc) are plotted on y-axis and x-axis, respectively, the expandable carbon nanotube powder has a slope equal to or greater than 95, and the electrical conductivity (S / cm) and the compaction density (g / cc) are measured when a pressure ranging from 50 MPa to 420 MPa is applied to the expandable carbon nanotube powder.

Description

Technical Field

[0001] Intersection of related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0079211, filed on June 18, 2024, and Korean Patent Application No. 10-2024-0079212, filed on June 18, 2024, the disclosures of which are incorporated herein by reference. Technical Field

[0003] This invention relates to expandable carbon nanotube powder and dry electrodes and lithium secondary batteries comprising expandable carbon nanotube powder. Background Technology

[0004] Secondary batteries are used in a wide range of products, including small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable gaming devices, power tools, and electric bicycles, as well as large products that require high power, such as electric vehicles and hybrid vehicles, power storage devices for storing surplus or renewable energy, and backup power storage devices.

[0005] Secondary batteries are typically manufactured as follows: an electrode active material slurry is applied to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, which is then dried and rolled to prepare a positive electrode and a negative electrode, and the positive and negative electrodes are stacked on both sides of a separator to form an electrode assembly with a predetermined shape, and then the electrode assembly is housed in a battery case, an electrolyte is injected, and the battery case is sealed.

[0006] Meanwhile, because the solvent contained in the slurry evaporates during the drying process of the electrode active material slurry, defects such as pinholes or cracks may occur in the electrode active material layer formed on the current collector. Furthermore, during the drying process, the electrode active material slurry dries unevenly between its internal and external portions, and therefore, powder floating may occur due to differences in solvent evaporation rates. That is, powder present in the earlier dried portions may float and form gaps with the relatively later dried portions, leading to a deterioration in electrode quality.

[0007] Therefore, in order to overcome the above limitations, drying devices that can control the evaporation rate of the solvent while allowing uniform drying of the electrode active material slurry inside and outside have been considered. However, these drying devices are very expensive and require considerable cost and operating time, and therefore have poor manufacturability.

[0008] Meanwhile, the solvent contained in typical electrode active material slurries is N-methyl-2-pyrrolidone (NMP), which has a high boiling point and therefore requires high heat energy and a very long drying oven, making it very unsuitable for large-scale production. In addition, N-methyl-2-pyrrolidone (NMP) is a toxic substance and harmful to organisms, and therefore not environmentally friendly.

[0009] Therefore, there has recently been a trend of active research into dry electrodes, which are prepared without the use of solvents. Dry electrodes are typically prepared by laminating a self-supporting electrode material mixture film, comprising an electrode active material, a binder, and a conductive material, in sheet form, onto a current collector. The electrode material mixture film involves the following process: first, the electrode active material, a carbon material as a conductive material, and a fibrillable binder are mixed together using a mixer or the like; the binder is fibrillated by applying shear force through processes such as jet milling or kneading; and then the resulting mixture is calendered into a film shape to prepare a self-supporting film.

[0010] However, unlike wet electrodes where the electrode active material, conductive material, and fibrillable binder are mixed in a solvent, the components are mixed in a solvent-free state during the preparation of dry electrodes, resulting in poor dispersibility of the conductive material. In this case, a method has been proposed to first disperse the conductive material to improve its dispersibility before mixing the electrode active material, conductive material, and fibrillable binder. However, conventional pre-dispersed conductive materials cannot meet specific physical properties and therefore exhibit poor resistivity characteristics.

[0011] Therefore, there is still a need for an expandable carbon nanotube powder that meets specific physical properties in order to achieve excellent dispersibility of conductive materials. Summary of the Invention

[0012] Technical issues

[0013] The present invention was designed to overcome the above-mentioned limitations, and therefore, one aspect of the present invention provides an expandable carbon nanotube powder with excellent conductivity when used as a conductive material by controlling the physical properties of the expandable carbon nanotube powder such that when the conductivity (S / cm) and compaction density (g / cc) measured within a specific pressure range are plotted on the y-axis and x-axis, the slope is greater than or equal to 95.

[0014] In order to overcome the above limitations, another aspect of the present invention provides a dry electrode and a lithium secondary battery comprising the expandable carbon nanotube powder, which have improved resistivity and lifetime characteristics due to their excellent conductivity and mechanical properties.

[0015] Technical solution

[0016] [1] According to one aspect of the present invention, an expandable carbon nanotube powder is provided, the expandable carbon nanotube powder comprising carbon nanotube units, wherein when the electrical conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis respectively, the slope is greater than or equal to 95, and the electrical conductivity (S / cm) and compaction density (g / cc) are measured when a pressure ranging from 50 MPa to 420 MPa is applied to the expandable carbon nanotube powder.

[0017] [2] The present invention provides expandable carbon nanotube powder according to [1] above, wherein the slope can be in the range of 100 to 125.

[0018] [3] The present invention provides expandable carbon nanotube powder according to [1] or [2] above, wherein the expandable carbon nanotube powder may have a bulk density of less than or equal to 0.022 g / cc.

[0019] [4] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [3] above, wherein the electrical conductivity can be greater than or equal to 70 S / cm when the compaction density of the expandable carbon nanotube powder is 1.0 g / cc.

[0020] [5] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [4] above, wherein the ratio of the true density (TD) to the bulk density (BD) of the expandable carbon nanotube powder (TD / BD) can be from 91 to 673.

[0021] [6] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [5] above, wherein the expandable carbon nanotube powder may have a true density (TD) of 1.850 g / cc to 2.500 g / cc.

[0022] [7] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [6] above, wherein the expandable carbon nanotube powder may have a 200 μm 2 / g to 1000 m 2 / g BET specific surface area.

[0023] [8] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [7] above, wherein the carbon nanotube unit can be a multi-walled carbon nanotube unit.

[0024] [9] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [8] above, wherein the multi-walled carbon nanotube units may have an aspect ratio of 30 to 10,000.

[0025]

[10] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to [9] above, wherein the multi-walled carbon nanotube units may have an average length of 0.1 μm to 100 μm.

[0026]

[11] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to

[10] above, wherein the multi-walled carbon nanotube units may have an average diameter of 5 nm to 200 nm.

[0027]

[12] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to

[11] above, wherein the multi-walled carbon nanotube units can have a thickness of 50 m. 2 / g to 500 m 2 / g BET specific surface area.

[0028]

[13] The present invention provides an expandable carbon nanotube powder according to at least one of [1] to

[12] above, wherein the multi-walled carbon nanotube unit may have three or more graphene layers arranged parallel to the axis of the multi-walled carbon nanotube unit.

[0029]

[14] According to another aspect of the invention, a dry electrode is provided comprising expandable carbon nanotube powder of at least one of [1] to

[13] above.

[0030]

[15] According to another aspect of the invention, a lithium secondary battery is provided, which includes the dry electrode of

[14] above.

[0031] Beneficial effects

[0032] The expandable carbon nanotube powder according to the present invention forms a properly expanded, expanded form without excessive cutting of carbon nanotubes. This is achieved by controlling the slope to be greater than or equal to 95 when the electrical conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis, respectively.

[0033] Furthermore, dry electrodes and lithium secondary batteries incorporating expandable carbon nanotube powder according to the present invention can achieve excellent resistance and lifetime characteristics. This is attributed to the aforementioned features, which enable the formation of a highly conductive network with excellent dispersion within the dry electrode, and increase the contact area with the electrode active material. Attached Figure Description

[0034] The accompanying drawings, which illustrate preferred embodiments of the invention by way of example, are provided together with the following detailed description of the invention to enable a further understanding of the technical concept of the invention, and therefore the invention should not be interpreted solely by the contents of these drawings. Furthermore, for clarity, the shapes, dimensions, scales, or proportions of the elements in the drawings may be exaggerated.

[0035] Figure 1 The graphs plot the electrical conductivity (S / cm) and compaction density (g / cc) on the y-axis and x-axis, respectively, where these values ​​are obtained by adding expandable carbon nanotube powder prepared in Example 1 and Comparative Examples 1 to 3 to a surface area of ​​0.38 cm². 2 The measurements were taken after applying forces ranging from 200 kgf to 1600 kgf in a circular mold.

[0036] Figure 2 and Figure 4 These are SEM images of carbon nanotube aggregates; and

[0037] Figure 3 and Figure 5 This is a SEM image of expandable carbon nanotube powder. Detailed Implementation

[0038] It will be understood that the words or terms used herein and in the claims of this invention should not be construed as having the meanings defined in commonly used dictionaries. It will be further understood that, based on the principle that the inventors may appropriately define the meanings of words or terms to best illustrate the invention, the words or terms should be interpreted as having meanings consistent with their meanings in the relevant technical context and the technical concept of the invention.

[0039] In this specification, the term "cumulative average particle diameter D" is used. 50 "" indicates the particle diameter when the cumulative volume in the particle size distribution curve is 50%. D 50 For example, this can be measured using laser diffraction. Laser diffraction typically allows for measurements ranging from submicron to millimeter particle sizes and can produce highly repeatable and high-resolution results.

[0040] In this specification, the term "average particle diameter" refers to the arithmetic mean of the particle diameters calculated after measuring the particle diameters of at least 30 particles observed in a scanning electron microscope image at a field of view of 5,000 to 20,000x. In this case, the particle diameter represents the diameter of the longest axis of the particle. Although "volume cumulative average particle diameter D" 50The methods for measuring “average particle diameter” and “volume-cumulative average particle diameter” are different, but their values ​​may be similar, and the volume-cumulative average particle diameter D measured in the powder state is... 50 It may have a value similar to the average particle diameter observed in scanning electron microscope images of the electrode after the powder has been prepared into an electrode, within the error range.

[0041] In this specification, the term "material mixture composition" refers to a mixture comprising electrode active materials, a binder, and optionally a conductive material, which is physically mixed to form a homogeneous dispersed phase. This mixture may be a powder mixture as a product of the mixing process according to this specification, and may be a mixture in which a solvent is substantially absent. The fact that a solvent is substantially absent herein means that no solvent is added or only trace amounts of solvent are added when mixing the material mixture composition.

[0042] In this specification, the term "mixed aggregate" means a mixed aggregate in which the powder mixture is transformed into a dough-like aggregate by combining or joining together, while the binder is fibrillated by applying shear force to the material mixture composition, wherein it is the product of the kneading process according to this specification, may have a solids content substantially close to 100%, and in some cases may contain a small amount of solvent.

[0043] In this specification, the term "electrode powder" refers to a material in which a mixture of aggregates is ground to form a powder by reducing the particle size, wherein it can refer to an electrode material in powder form comprising an electrode active material as well as a binder and optional conductive material.

[0044] In this specification, "electrode material mixture film" can refer to an electrode material mixture film prepared as a self-supporting single sheet using an "electrode material mixture" comprising an electrode active material, a conductive material, and a binder, without the involvement of solvents, or it can refer to an electrode material mixture layer laminated on a current collector. In this specification, the term "self-supporting" means that it can independently maintain its form without dependence on other components and can be moved or handled independently. Electrode material mixture films can be formed by compressing electrode powder, as described below. For example, electrode powder can be integrated by compression to form a layered structure.

[0045] In this specification, the term "powder-pressed film" refers to a film formed into a sheet form by a powder pressing process in which electrode powder is first passed through rollers in a roll-to-roll process (e.g., calendering), and before passing through the last roller in the roll-to-roll process. This film can be a self-supporting sheet, but may have relatively weak self-supporting capabilities. In this document, the term "powder-pressed" can refer to the formation of a self-supporting sheet form from electrode powder by rollers in a roll-to-roll process, while the term "pressing" is a process performed during the preparation of an electrode material mixture film from the powder-pressed film, where it can refer to the process of rolling the powder-pressed film.

[0046] In this specification, the term "three-dimensional fiber network structure" can refer to a structure that may be formed during the process of forming a sheet from a material mixture composition including an electrode active material and a binder, thus becoming an electrode material mixture film, through the fibrillation of the binder. Specifically, a three-dimensional fiber network structure can refer to various structures in which microfibers formed by the fibrillation of the binder form a skeleton and thereby serve as supports, making the electrode material mixture film a self-supporting film. In this case, the electrode active material and optionally a conductive material can be accommodated in the pores formed in the three-dimensional fiber network structure.

[0047] In this specification, porosity can be calculated using the following equation A.

[0048] [Equation A] Porosity (%) = {1 - (electrode density / true density)} × 100

[0049] In Equation A above, the true density is the density calculated from the density and mass ratio of each component material constituting the electrode material mixture film, assuming no pores are present, while the electrode density is the measured density of the electrode material mixture film obtained by cutting a portion of the electrode material mixture film to a certain size.

[0050] In this article, the term "specific surface area (m²)" is used. 2 The amount of nitrogen adsorbed by BELSORP-mino II from BEL JAPAN, INC. at liquid nitrogen temperature (77 K) is measured by the BET method and, more specifically, can be calculated by the amount of nitrogen adsorbed by BELSORP-mino II from BEL JAPAN, INC.

[0051] Unlike wet electrodes, where the electrode active material, fibrillable binder, and / or conductive material are mixed in a solvent, dry electrodes are prepared by mixing the components in a solvent-free state, resulting in poor dispersibility of the conductive material. In this case, a method has been proposed to first disperse the conductive material to improve its dispersibility, and then mix the electrode active material, conductive material, and fibrillable binder. However, with conventional pre-dispersion of the conductive material, excessive shear forces in a solvent-free state can lead to over-cutting of the conductive material or failure to achieve the desired degree of dispersion, resulting in poor resistance and lifetime characteristics.

[0052] Through continuous research aimed at solving the aforementioned problems, the inventors of this invention discovered that excellent electrical resistance and lifetime characteristics can be achieved by using expandable carbon nanotube powder that meets specific physical properties, thus completing this invention.

[0053] Expandable carbon nanotube powder

[0054] The expandable carbon nanotube powder according to the present invention comprises carbon nanotube units, wherein when the electrical conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis, respectively, the slope is greater than or equal to 95, and the electrical conductivity (S / cm) and compaction density (g / cc) are measured when a pressure ranging from 50 MPa to 420 MPa is applied to the expandable carbon nanotube powder.

[0055] Unlike wet electrodes, which are dispersed and / or mixed in a solvent, dry electrodes involve dispersing and / or mixing conductive materials (e.g., carbon nanotubes) in a solvent-free state during fabrication. This solvent-free dispersion and / or mixing process prevents the buffering and dispersing effects of the solvent, resulting in excessive shear forces that can cause over-cutting of the conductive material or prevent it from reaching the desired degree of expansion. In particular, when dry electrodes are fabricated using over-cut or undispersed conductive materials, the formation of conductive pathways within the electrode is limited, and the contact area with the electrode active material is reduced, leading to decreased battery performance.

[0056] Therefore, the present invention provides an expandable carbon nanotube powder with excellent dispersibility, which is achieved by controlling the specific properties of the carbon nanotube powder to exhibit maximum efficiency in a dry electrode, thereby forming an expandable structure without over-cutting.

[0057] Specifically, expandable carbon nanotube powder differs from high-density aggregated carbon nanotubes or high-density carbon nanotube aggregates typically used in large-scale industrial applications, and involves forming a pop-type structure with an expandable structure without over-cutting of the carbon nanotubes. Desiredly, unlike carbon nanotubes dispersed using aqueous dispersions, expandable carbon nanotube powder involves forming a pop-type structure with expandable carbon nanotubes in a dry, solvent-free state without over-cutting.

[0058] Expanded structures refer to a form in which high-density aggregates of carbon nanotubes are deaggregated and visually separated in a loose manner, resulting in increased space between the carbon nanotubes and looser connections between them, leading to an increase in overall volume. For example, expandable structures can form a honeycomb structure with reduced density between carbon nanotubes, thereby exposing more of the carbon nanotube surface.

[0059] Therefore, in the subsequent fabrication of dry electrodes, the inclusion of expandable carbon nanotubes according to the invention in the conductive material is desirable in terms of forming a well-dispersed conductive network while maintaining the continuity of the conductive network, thereby achieving excellent mechanical strength and electrical properties. For example, expandable carbon nanotubes with an expandable structure, appropriate dispersion, and minimal cutting can maintain excellent dispersibility while minimizing cutting during the subsequent dry electrode fabrication process, thereby forming an excellent conductive network between and / or within the electrode active materials in the electrode material mixture film, and sufficiently preventing the aggregation of conductive materials that reduce conductivity, thus resulting in excellent electrical and lifetime properties.

[0060] In this context, expandable carbon nanotube powders can be achieved through various methods, but ideally by controlling the properties of the carbon nanotubes, such as shape, diameter, length and / or number of walls, or by controlling the conditions used to depolymerize the carbon nanotubes.

[0061] In particular, the expandable carbon nanotube powders described above can have a low packing density by forming an expanded structure, and therefore, it is difficult to measure the conductivity based on the compaction density without applying high forces to ensure sufficient electrical contact between the powders.

[0062] In the expandable carbon nanotube powder according to the present invention, when the conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis, respectively, the slope is greater than or equal to 95. This slope represents the inherent conductivity because it allows for indirect inference of the resistivity of the conductive path itself when the expandable carbon nanotube powder forms a conductive path within the electrode. When the slope is less than 95, it indicates that over-cutting of the carbon nanotubes has occurred, resulting in problems in the formation of conductive paths, or that the carbon nanotubes have failed to form a properly expanded structure, thus preventing the formation of expandable carbon nanotube powder. That is, when the slope is less than 95, over-cutting or failure to form expandable carbon nanotube powder with an expanded structure has occurred, and therefore, excellent conductive paths may not be formed when subsequently used as a conductive material, and the contact area between the electrode active materials is reduced, resulting in poor resistance and lifetime characteristics.

[0063] According to embodiments of the present invention, expandable carbon nanotube powder has a slope greater than or equal to 95 when its conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis, respectively. Desiredly, the slope can be greater than or equal to 96, greater than or equal to 97, greater than or equal to 98, greater than or equal to 99, or greater than or equal to 100, less than or equal to 150, less than or equal to 140, less than or equal to 130, less than or equal to 129, less than or equal to 128, less than or equal to 127, less than or equal to 126, or less than or equal to 125, and more preferably, between 100 and 125. When the above ranges are satisfied, expandable carbon nanotube powder with an expanded structure can be formed with minimal cutting, which can achieve excellent resistivity and lifetime characteristics when subsequently used as a conductive material. In particular, this slope is a parameter measured in the powder state of expandable carbon nanotubes, which is extremely difficult to measure in the pre-dispersion of conventional conductive materials prepared by wet processes.

[0064] In the expandable carbon nanotube powder according to the invention, the electrical conductivity (S / cm) and compaction density (g / cc) are measured when a pressure ranging from 50 MPa to 420 MPa is applied to the expandable carbon nanotube powder. Desiredly, the measurements can be performed at pressures ranging from 60 MPa to 420 MPa, and more preferably at pressures ranging from 70 MPa to 420 MPa. The expandable carbon nanotube powder can form an expanded structure and has a low packing density; therefore, applying low pressure may result in insufficient electrical contact between the powder particles, making it difficult to accurately measure the inherent electrical conductivity of the powder. That is, when low pressure is applied, it may be difficult to measure the slope expected by the invention. Furthermore, the electrical conductivity of the expandable carbon nanotube powder is measured at a high pressure range actually applied during electrode preparation, and therefore, the electrical conductivity in the electrode state can be determined more clearly. Therefore, when measuring conductivity and compaction density by applying pressure within the above range, conductivity and compaction density can be measured with sufficient electrical contact between the powders, and thus a slope that can clearly represent the inherent electrical conductivity of the powder can be measured.

[0065] According to embodiments of the present invention, expandable carbon nanotube powder can have a packing density of less than or equal to 0.022 g / cc, preferably less than or equal to 0.020 g / cc, less than or equal to 0.018 g / cc, less than or equal to 0.016 g / cc, less than or equal to 0.014 g / cc, less than or equal to 0.012 g / cc, less than or equal to 0.010 g / cc, or less than or equal to 0.009 g / cc, and can have a packing density greater than or equal to 0.001 g / cc or greater than or equal to 0.002 g / cc, and more preferably a packing density from 0.001 g / cc to 0.009 g / cc. When the above ranges are met, a suitably expanded structure can be formed without over-cutting, thereby achieving excellent electrical resistance and lifetime characteristics.

[0066] According to embodiments of the present invention, when the expandable carbon nanotube powder has a compaction density of 1.0 g / cc, its electrical conductivity can be greater than or equal to 70 S / cm, preferably greater than or equal to 70 S / cm, greater than or equal to 71 S / cm, greater than or equal to 72 S / cm, greater than or equal to 73 S / cm, greater than or equal to 74 S / cm, or greater than or equal to 75 S / cm, and can be less than or equal to 125 S / cm, less than or equal to 123 S / cm, less than or equal to 120 S / cm, less than or equal to 117 S / cm, or less than or equal to 115 S / cm. More preferably, the electrical conductivity can be between 75 S / cm and 115 S / cm. When the above ranges are satisfied, it is expected that the expandable carbon nanotube powder can have a suitable expansion form, thereby forming an excellent expandable structure.

[0067] According to embodiments of the present invention, the ratio of true density (TD) to bulk density (BD) of the expandable carbon nanotube powder (TD / BD) can be from 91 to 673, preferably from 134 to 505, and more preferably from 200 to 405. When the above ranges are met, it is expected that the expandable carbon nanotube powder can expand appropriately while also achieving excellent dispersibility.

[0068] Bulk density (BD) can be measured by filling expandable carbon nanotube powder into a container of known specific volume, measuring the weight, and then converting the result into density.

[0069] The difference between true density (TD) and bulk density lies in the fact that true density (TD) is the density based on the volume of the material itself within a porous material, excluding pores. Devices used to measure true density (TD) can be, for example, dry automatic densitometers (Accupic II 1340 series, Shimadzu Corporation). Using this device, true density can be automatically measured by adding a small amount of expandable carbon nanotube powder. In addition to the measurement methods and / or devices described above, true density can also be obtained using other measurement methods and / or devices.

[0070] According to embodiments of the present invention, the true density (TD) of the expandable carbon nanotube powder can be from 1.850 g / cc to 2.500 g / cc, preferably from 1.900 g / cc to 2.300 g / cc, and more preferably from 1.950 g / cc to 2.150 g / cc. When the above range is satisfied, it is expected that this density can form sufficient conductive paths within the electrode and can easily form expandable structures.

[0071] According to an embodiment of the present invention, expandable carbon nanotube powder can have a diameter of 200 μm. 2 / g to 1000 m 2 / g, expected 250 m 2 / g to 950 m 2 / g, and more preferably 300 m 2 / g to 900 m 2 / g BET specific surface area. When the above range is met, it is expected that a properly expanded structure can be formed while achieving excellent dispersibility.

[0072] According to embodiments of the present invention, expandable carbon nanotube powder may comprise carbon nanotube units. The graphite sheets of carbon nanotubes have a cylindrical shape with a diameter at the nanometer scale and exhibit sp... 2Bonded structure. In this case, depending on the curl angle and structure of the graphite sheet, it may exhibit conductive or semiconductor properties. Carbon nanotubes can be classified into single-walled carbon nanotube (SWCNT) units, double-walled carbon nanotube (DWCNT) units, and multi-walled carbon nanotube (MWCNT) units based on the number of bonds forming the walls.

[0073] According to embodiments of the present invention, the carbon nanotube unit can be a multi-walled carbon nanotube unit. When the carbon nanotube unit is a single-walled or double-walled carbon nanotube unit, the battery manufacturing cost may be too high, which may reduce processability, and the carbon nanotube units may exist in an over-aggregated state, which may make it difficult to form expandable carbon nanotube powder with an expandable structure. Conversely, when the carbon nanotube unit is a multi-walled carbon nanotube unit, the manufacturing cost is relatively low, and the aggregation is not excessive, which makes it possible to form a suitable expandable structure.

[0074] According to embodiments of the present invention, multi-walled carbon nanotube units can have an aspect ratio of 30 to 10,000, preferably 60 to 2,000, and more preferably 100 to 1,000. When the above ranges are met, the dispersibility of the multi-walled carbon nanotube units can be excellent, and when the multi-walled carbon nanotube units are subsequently used as conductive materials, the contact area between electrode active materials can be increased. The aspect ratio can be defined as the ratio of the length to the diameter of the multi-walled carbon nanotube unit.

[0075] According to embodiments of the present invention, multi-walled carbon nanotube units can have an average length of 0.1 μm to 100 μm, preferably 0.1 μm to 50 μm, and more preferably 0.1 μm to 3 μm. When the above ranges are met, appropriate dispersion of the multi-walled carbon nanotube units can be achieved, and when the multi-walled carbon nanotube units are subsequently used as conductive materials, the formation of a conductive network can be maximized. The average length corresponds to the average diameter of the 100 longest and 100 shortest single-walled carbon nanotube units observed by SEM or TEM.

[0076] According to embodiments of the present invention, multi-walled carbon nanotube units can have an average diameter of 5 nm to 200 nm, preferably ≥5 nm, ≥6 nm, ≥7 nm, ≥8 nm, ≥9 nm, or ≥10 nm, and ≤200 nm, ≤180 nm, ≤160 nm, ≤140 nm, ≤120 nm, ≤100 nm, ≤80 nm, ≤60 nm, or ≤50 nm, and more preferably ≤10 nm to 50 nm. When the above ranges are met, dispersion is easy, and therefore conductivity can be improved when multi-walled carbon nanotube units are subsequently used as conductive materials. The average diameter corresponds to the average diameter of the 100 largest and 100 smallest single-walled carbon nanotube units observed by SEM or TEM.

[0077] According to an embodiment of the present invention, the multi-walled carbon nanotube unit can have a diameter of 50 m. 2 / g to 500 m 2 / g, 100 m 2 / g to 400 m 2 / g, more desirable 150 m 2 / g to 350 m 2 The BET specific surface area is measured in g. When the above specific surface area range is met, proper dispersion of multi-walled carbon nanotube units can be achieved, thus maintaining manufacturability. The BET specific surface area can be measured using the nitrogen adsorption BET method.

[0078] According to embodiments of the present invention, a multi-walled carbon nanotube unit may have three or more graphene layers arranged parallel to the axis of the multi-walled carbon nanotube unit. Desiredly, the multi-walled carbon nanotube unit may have 3 to 20 graphene layers, more preferably 3 to 10 graphene layers, and even more preferably 3 to 5 graphene layers. When the above ranges are satisfied, it is expected that the multi-walled carbon nanotube units are appropriately dispersed, thereby improving the conductivity of the expandable carbon nanotube powder while achieving the preparation of expandable carbon nanotube powder with an expandable structure.

[0079] Preparation method of expandable carbon nanotube powder

[0080] The preparation method of the expandable carbon nanotube powder according to the present invention will be described below.

[0081] The method for preparing expandable carbon nanotube powder according to the present invention includes depolymerizing carbon nanotube aggregates in a solvent-free state via mutual collision in a depolymerization device, wherein depolymerization is carried out by the rotation of two or more rotors disposed in the depolymerization device and by high-pressure gas ejected from nozzles disposed in the depolymerization device, the rotors having a rotational speed of at least 3000 rpm and the nozzles ejecting high-pressure gas at a pressure of at least 3.5 bar.

[0082] Unlike wet electrodes, which involve dispersion and / or mixing in a solvent, dry electrodes are fabricated by dispersing and / or mixing conductive materials (e.g., carbon nanotubes) in a solvent-free state. Dispersion and / or mixing in a solvent-free state prevents the buffering and dispersing effects of the solvent, resulting in excessive shear forces that can cause over-shearing of the conductive material or prevent the desired degree of depolymerization from being achieved. In particular, when attempting to depolymerize carbon nanotubes in a solvent-free state, van der Waals forces cause the nanotubes to aggregate, making depolymerization even more difficult. Furthermore, because carbon nanotubes have a linear shape, excessive shear forces during dispersion and / or mixing in a solvent-free state can easily lead to the fragmentation of the carbon nanotubes.

[0083] Therefore, the present invention provides a method for preparing expandable carbon nanotube powder with excellent dispersibility: by depolymerizing carbon nanotube aggregates through mutual collision in a solvent-free state, while controlling the depolymerization conditions to meet specific conditions, thereby forming an expandable structure that is not over-cut.

[0084] Specifically, devices such as jaw crushers and hammer crushers, which apply strong shearing forces in a solvent-free state, can damage carbon nanotubes, making it difficult to generate carbon nanotubes with expandable structures. However, in this invention, carbon nanotubes with expandable structures can be prepared by depolymerizing them with appropriate force through mutual collision in a solvent-free state, thereby achieving excellent resistivity and lifetime characteristics in the subsequent preparation of electrode powders and dry electrodes containing them.

[0085] Expandable carbon nanotube powder is as described above, and therefore a detailed description of expandable carbon nanotube powder is not provided hereafter.

[0086] According to embodiments of the present invention, the carbon nanotube aggregate can be an aggregate of carbon nanotubes in high density, such as bundled carbon nanotubes or entangled carbon nanotubes.

[0087] The method for preparing expandable carbon nanotubes according to the present invention includes depolymerizing carbon nanotube aggregates in a solvent-free state via mutual collision in a depolymerization apparatus, wherein depolymerization is carried out by the rotation of two or more rotors disposed in the depolymerization apparatus and by high-pressure gas ejected from nozzles disposed in the depolymerization apparatus. Desirably, depolymerization can be carried out by a swirling airflow generated by the rotation of the two or more rotors disposed in the depolymerization apparatus and by high-pressure gas ejected from nozzles disposed in the depolymerization apparatus; and more preferably, depolymerization can be carried out by a swirling airflow and impact force generated by the rotation of the two or more rotors disposed in the depolymerization apparatus and by high-pressure gas ejected from nozzles disposed in the depolymerization apparatus.

[0088] Unlike pulverizing methods such as ball milling that apply excessive and concentrated impact, this preparation method involves depolymerizing carbon nanotube aggregates via mutual collisions. Therefore, excessive cutting and aggregation of the carbon nanotube aggregates are prevented, thereby allowing… Figure 2 and Figure 4 The carbon nanotube aggregates are transformed into expandable carbon nanotube powder with an expandable structure, such as Figure 3 and Figure 5 As shown above, expandable carbon nanotube powder with an expandable structure is formed. In the subsequent preparation of electrode powders and / or dry electrodes, the carbon nanotubes can be appropriately connected to the electrode active material particles to form an excellent conductive network, and exhibit excellent dispersibility even in a solvent-free state, thereby achieving excellent resistivity and lifetime characteristics.

[0089] When the above conditions are met, the following can be expected: the degree of deagglomeration can be increased by enhancing the collision between carbon nanotube aggregates due to the swirling airflow and high-pressure gas, and by causing the carbon nanotube aggregates to collide with the rotor due to the impact force of the rotor and / or the pressure injected from the nozzle.

[0090] Meanwhile, the carbon nanotube aggregates are depolymerized by high-pressure gas ejected from nozzles in the depolymerization device through mutual collisions, without rotor rotation. Since there is no swirling airflow or impact force generated by rotor rotation, the depolymerization efficiency is low, and effective energy cannot be provided to depolymerize the high-density aggregates of carbon nanotubes caused by van der Waals forces, either between or within the aggregates, thus failing to form expandable carbon nanotube powder.

[0091] In the method for preparing expandable carbon nanotube powder according to the present invention, the rotor has a rotational speed of greater than or equal to 3000 rpm. Ideally, the rotor can have speeds greater than or equal to 3100 rpm, 3200 rpm, 3300 rpm, 3400 rpm, 3500 rpm, 3600 rpm, 3700 rpm, 3800 rpm, 3900 rpm, 4000 rpm, 4100 rpm, 4200 rpm, 4300 rpm, 4400 rpm, 4500 rpm, 4600 rpm, 4700 rpm, 4800 rpm, 4900 rpm, or 5000 rpm, and have speeds less than or equal to 7000 rpm, 6900 rpm, 6800 rpm, 6700 rpm, 6600 rpm, or 6500 rpm. Rotational speeds of 6400 rpm or less, 6300 rpm or less, and 6200 rpm or less are preferred. Rotational speeds can be 6100 rpm or less, 5900 rpm or less, 5800 rpm or less, 5700 rpm or less, 5600 rpm or less, 5500 rpm or less, or 5400 rpm or less, with a preferred range of 5000 rpm to 5400 rpm. When the rotor speed is below 3000 rpm, the van der Waals forces of the carbon nanotube aggregates may not be overcome, leading to aggregation and preventing the preparation of expandable carbon nanotube powder with an expandable structure. Therefore, when the above ranges are met, excessive cutting of the carbon nanotube aggregates is avoided, and fully deagglomerated expandable carbon nanotube powder with an expandable structure can be prepared, thereby achieving excellent electrical resistance and lifetime characteristics.

[0092] In the method for preparing expandable carbon nanotube powder according to the present invention, a nozzle injects high-pressure gas at a pressure of 3.5 bar or higher. The nozzle may desirably inject high-pressure gas at pressures of 3.6 bar or higher, 3.7 bar or higher, 3.8 bar or higher, 3.9 bar or higher, 4.0 bar or higher, 4.1 bar or higher, 4.2 bar or higher, 4.3 bar or higher, 4.4 bar or higher, 4.5 bar or higher, 4.6 bar or higher, 4.7 bar or higher, 4.8 bar or higher, 4.9 bar or higher, or 5.0 bar or higher, and may inject high-pressure gas at pressures of less than or equal to 7.5 bar. More desirably, the nozzle injects high-pressure gas at pressures between 5.0 bar and 7.5 bar. The nozzle is a nozzle that injects gases and / or fluids capable of generating pressure, such as water vapor, air, steam, nitrogen, and / or argon, and the carbon nanotube aggregates may be depolymerized via collisions between carbon nanotube aggregates or between carbon nanotube aggregates and a rotor. When the nozzle injects high-pressure gas at a pressure less than 3.5 bar, the carbon nanotube aggregates do not experience sufficient pressure to overcome van der Waals forces, preventing the formation of expandable carbon nanotubes with expandable structures. Therefore, when the above range is met, over-cutting of the carbon nanotube aggregates does not occur, and fully depolymerized expandable carbon nanotube powder with expandable structures can be prepared, thereby achieving excellent electrical resistance and lifetime characteristics.

[0093] According to an embodiment of the present invention, the depolymerization device is not particularly limited as long as it can apply an appropriate amount of force, but the depolymerization device can be, for example, Galaxy jet mill (JEM Corporation).

[0094] The carbon nanotube aggregates used in the preparation method according to the present invention will be described in more detail below.

[0095] In carbon nanotube aggregates, bundled carbon nanotubes refer to the form in which carbon nanotubes are aggregated into bundles due to the interaction between carbon nanotube units, rather than the form in which carbon nanotubes exist as single-chain units, and can be expected to represent the form in which carbon nanotube units are attached or entangled due to their interaction.

[0096] According to embodiments of the present invention, carbon nanotube aggregates can have a density of 0.011 g / cm³. 3 Up to 0.900 g / cm 3 With a packing density of 0.020 g / cm³, carbon nanotube aggregates can be expected to have a packing density of 0.020 g / cm³. 3 Up to 0.500 g / cm 3The packing density is high, and carbon nanotube aggregates can more desirablely have a density of 0.030 g / cm³. 3 Up to 0.150 g / cm 3 The packing density. When the above range is met, the carbon nanotube aggregates can be suitably deagglomerated to achieve the degree of deagglomeration according to the preparation method of the present invention.

[0097] Bulk density can be measured by filling expandable carbon nanotube powder into a container of known specific volume, measuring the weight, and then converting the result into density.

[0098] According to embodiments of the present invention, carbon nanotube aggregates can have a volume-cumulative average particle diameter of 100 μm to 600 μm, preferably 200 μm to 580 μm, and more preferably 300 μm to 560 μm. When the above ranges are met, an appropriate number of carbon nanotube units aggregate together, and therefore the carbon nanotube aggregates can be adapted to achieve the degree of deagglomeration according to the preparation method of the present invention. The volume-cumulative average particle diameter is not limited, as long as it can be measured by conventional methods, such as by using scanning electron microscopy or laser diffraction, but it is desirable to use laser diffraction to measure it by the volume-cumulative particle diameter distribution.

[0099] Carbon nanotube aggregates can comprise carbon nanotube units. Graphite sheets of carbon nanotubes have a cylindrical shape with a diameter at the nanometer scale and exhibit sp... 2 Bonded structure. In this case, depending on the curl angle and structure of the graphite sheet, it may exhibit conductive or semiconductor properties. Carbon nanotubes can be classified into single-walled carbon nanotube (SWCNT) units, double-walled carbon nanotube (DWCNT) units, and multi-walled carbon nanotube (MWCNT) units based on the number of bonds forming the walls.

[0100] According to embodiments of the present invention, carbon nanotube aggregates may include multi-walled carbon nanotube units. When the carbon nanotube units are single-walled or double-walled carbon nanotube units, the battery manufacturing cost may be too high, which may reduce processability, and the carbon nanotube units may exist in an over-aggregated state, which may make deaggregation difficult. Conversely, when the carbon nanotube units are multi-walled carbon nanotube units, the manufacturing cost is relatively low, and they do not aggregate excessively, which allows for proper deaggregation and results in excellent processability.

[0101] In particular, multi-walled carbon nanotube units are structurally highly defective due to their nodal growth mechanism (having nodes due to defects generated during the growth process, rather than being smooth and linear). Therefore, multi-walled carbon nanotube units are more easily cleaved during the depolymerization process, and due to the carbon surface bonding structure (sp... 2The shortened multi-walled carbon nanotube units, after being cut, are likely to aggregate together under π-π stacking. However, the deagglomeration performed by the preparation method according to the present invention can prevent the aggregation of multi-walled carbon nanotube units and also prevent the reduction in conductivity due to the shortening of carbon nanotube units caused by excessive cutting, thereby maximizing the effect of the present invention.

[0102] The above description of multi-walled carbon nanotube units also applies when the carbon nanotube aggregates include multi-walled carbon nanotube units.

[0103] dry electrode

[0104] The dry electrode according to the invention comprises expandable carbon nanotube powder according to the invention. Desiredly, the dry electrode according to the invention may comprise a current collector, an electrode material mixture film formed on the current collector, wherein the electrode material mixture film may comprise an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, and the conductive material may comprise expandable carbon nanotube powder according to the invention.

[0105] The expandable carbon nanotube powder according to the present invention exhibits excellent effects when used as a conductive material in an electrode material mixture film contained in a dry electrode. For example, properly dispersed expandable carbon nanotubes with a expandable structure and minimal cutting can maintain excellent dispersibility while minimizing cutting during the subsequent dry electrode preparation process, thereby forming an excellent conductive network between and / or within the electrode active materials in the electrode material mixture film, and sufficiently preventing the aggregation of conductive materials that reduce conductivity, thus resulting in excellent resistance and lifetime characteristics.

[0106] In particular, the expandable carbon nanotube powder of the present invention satisfies the above-mentioned relationship between conductivity and packing density in a solvent-free state, and therefore, when the expandable carbon nanotube powder is included in a dry electrode, environmental friendliness, processability, resistance and lifetime characteristics can be further maximized.

[0107] In addition, the dry electrode according to the present invention can be prepared by stacking a film of electrode material mixture on one or both sides of the current collector and laminating the resulting product.

[0108] Lamination can involve attaching a film of electrode material mixture to a current collector by roll pressing. Lamination can be performed by a roll pressing method using laminating rollers, in which case the laminating rollers can be maintained at a temperature between 20°C and 200°C.

[0109] The expandable carbon nanotube powder according to the present invention is as described above and will not be repeated hereafter, but the mixture film of current collector and electrode material will be described in detail.

[0110] (current collector)

[0111] When the dry electrode is the positive electrode, the current collector is not particularly restricted, as long as it is conductive and will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the current collector.

[0112] The current collector can have a thickness ranging from 8 μm to 500 μm, but the thickness of the current collector is not limited to this. In addition, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the electrode material mixture film.

[0113] When the dry electrode is the negative electrode, the current collector is not particularly restricted, as long as it has high conductivity and will not cause changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel, aluminum-cadmium alloys with surface treatment of one of carbon, nickel, titanium, silver, etc. can be used.

[0114] Current collectors can typically have a thickness of 3 μm to 500 μm, and when a dry electrode is used as the positive electrode, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the electrode material mixture film.

[0115] The current collector may be wholly or partially coated with a conductive primer to reduce surface resistance and improve adhesion. In this case, the conductive primer may include conductive materials and binders, and the conductive materials are not particularly limited, as long as they are conductive, but may be, for example, carbon-based materials. The binders may include solvent-soluble fluorine-based binders (including PVDF and PVDF copolymers), acrylic-based binders, and water-based binders.

[0116] (Electrode material mixture film)

[0117] The electrode material mixture film according to the present invention comprises an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, wherein the conductive material comprises expandable carbon nanotube powder according to the present invention.

[0118] 1) Electrode active materials

[0119] Electrode material mixture membranes include electrode active materials.

[0120] There are no particular restrictions on the electrode active material, as long as it is a commonly used electrode active material. For example, the electrode active material can be a positive electrode active material or a negative electrode active material.

[0121] The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium. Specifically, the positive electrode active material may include a lithium metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. More preferably, the lithium metal oxide may be a lithium manganese-based oxide (e.g., LiMnO₂, LiMn₂O₄, etc.), a lithium cobalt-based oxide (e.g., LiCoO₂, etc.), a lithium nickel-based oxide (e.g., LiNiO₂, etc.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O₂ (where 0 < Y < 1), LiMn 2- Z Ni Z O₄ (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O₂ (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O₂ (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O₄ (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O₂ (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O₄ (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc.), or a lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O₂ (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, and -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), etc., and may include any one of them or a compound of two or more of them.

[0122] Among these materials, lithium metal oxides that can improve battery capacity characteristics and stability include LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni)O2). 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 O2), lithium nickel cobalt aluminum oxide (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc.), lithium nickel cobalt manganese aluminum oxides (e.g., Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 The electrode active material can be lithium nickel cobalt manganese aluminum oxide (LiFePO4) or lithium iron phosphate (LiFePO4), and either or a mixture of two or more thereof can be used. More specifically, in order to prepare a mixture of electrode materials in the form of a uniform and stable film, the electrode active material can include lithium nickel cobalt manganese aluminum oxide.

[0123] More preferably, the electrode active material may include a phosphorus oxide represented by Formula 1 below.

[0124] [Formula 1] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0125] In Equation 1 above, M 1 It contains at least one element selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Mo, Nb, W, Zr, Ce, In, Zn, and Y, and x, a, and b satisfy -0.5 ≤ x ≤ 0.5, 0 ≤ a ≤ 0.8, and 0 ≤ b ≤ 0.1. Under these conditions, excellent economic efficiency and stability can be expected.

[0126] The negative electrode active material may include at least one of the following: lithium metal, carbon material capable of reversibly inserting / deintercalating lithium ions, metal or an alloy of lithium and the metal, metal composite oxide, material that can be doped with or undoped with lithium, and transition metal oxide.

[0127] As a carbon material capable of reversibly inserting / deintercalating lithium ions, carbon-based anode active materials commonly used in lithium-ion secondary batteries can be used without particular limitation, and as typical examples, crystalline carbon, amorphous carbon, or both can be used. Examples of crystalline carbon can be graphite, such as irregular, planar, flake-like, spherical, or fibrous natural or artificial graphite, and examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbides, and calcined coke.

[0128] As a metal or an alloy of lithium with that metal, a metal selected from the group consisting of Cu, Ni, sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), Mg, calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), In, Zn, barium (Ba), radium (Ra), germanium (Ge), Al, and tin (Sn), or an alloy of lithium with that metal, can be used.

[0129] As a metal composite oxide, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, and Li can be used. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1) and Sn x Me 1-x Me' y O z One of the groups consisting of (Me: Mn, Fe, Pb or Ge; Me′: Al, Boron (B), P, Si, Group I, II and III elements of the periodic table or halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8).

[0130] Materials that can be doped or undoped with lithium include Si and SiO2. xwhere \(0 \lt x \leq 2\), a 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 is not Si), Sn, \(SnO_2\), and Sn-Y (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 is not Sn), and a mixture of \(SiO_2\) and at least one of them may also be used. The element Y may be selected from the group consisting of: Mg, Ca, Sr, Ba, Ra, scandium (Sc), Y, Ti, Zr, hafnium (Hf), rutherfordium (Rf), V, Nb, Ta, dubnium (Db), Cr, Mo, W, seaborgium (Sg), technetium (Tc), rhenium (Re), bohrium (Bh), Fe, Pb, ruthenium (Ru), osmium (Os), hassium (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, Ga, Sn, In, Ge, P, arsenic (As), Sb, bismuth (Bi), S, selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0131] The transition metal oxide may include a lithium-containing titanium composite oxide (LTO), a vanadium oxide, and a lithium vanadium oxide.

[0132] According to an embodiment of the present invention, the content of the electrode active material may be 80 to 99 parts by weight, and desirably 90 to 99 parts by weight, relative to the total weight of the electrode material mixture film. When the above range is satisfied, it is possible to expect an increase in the electrode capacity and energy density.

[0133] 2) Conductive material

[0134] The electrode material mixture film includes a conductive material, and the conductive material includes the expandable carbon nanotube powder according to the present invention.

[0135] According to an embodiment of the present invention, the content of the conductive material may be 0.1 to 10 parts by weight, and desirably 0.1 to 5.0 parts by weight, relative to the total weight of the electrode material mixture film. When the above range is satisfied, it is possible to expect to form an excellent conduction path while achieving an excellent capacity density.

[0136] 3) Binder

[0137] The electrode material mixture film includes a binder having a three-dimensional fiber network structure.

[0138] The binder is used to form a three-dimensional fibrous network structure that allows the electrode material mixture film to be self-supporting. The binder is not particularly limited, as long as it is a fibrillable material, which is a material that can be fibrillated to form a three-dimensional fibrous network structure within the electrode material mixture film and provide pores capable of accommodating electrode active materials and optional conductive materials.

[0139] The fibrillation of an adhesive refers to the process of finely dividing the polymer used as an adhesive, which can be done, for example, by applying mechanical shear force, and thus the surface becomes loose and fibrillated, forming a large number of microfibers, thereby containing a three-dimensional fiber network structure.

[0140] Fibrillatable adhesives are not particularly limited, as long as they can be fibrillated, and fibrillation refers to a process of finely dividing the polymer. For example, fibrillation can be performed using mechanical shear forces, and thus the surface of the fibrillated polymer fibers becomes loose, producing a large number of microfibrils (fibrils). Fibrillatable adhesives may preferably include at least one selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefins, more preferably including PTFE, and even more preferably being PTFE. When the above conditions are met, excellent conductive dispersion can be achieved with appropriate reduction in resistance.

[0141] Meanwhile, the content of polytetrafluoroethylene (PTFE) relative to the total weight of the adhesive can be greater than or equal to 60% by weight. In this case, the adhesive may further include one or more of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polyolefin-based adhesives.

[0142] According to embodiments of the present invention, the content of the fibrillable binder can be from 0.1 to 10 parts by weight, and preferably from 0.1 to 5.0 parts by weight, relative to the total weight of the electrode material mixture film. When the above range is satisfied, it is expected that a degree of fibrillation suitable for the preparation of self-supporting sheets can be achieved with excellent resistive characteristics.

[0143] Meanwhile, the dry electrode according to the present invention can be prepared by including the following steps: step S1, mixing electrode active material, conductive material and fibrillable binder to obtain a material mixture composition; step S2, kneading the material mixture composition while applying shear force to form a mixed aggregate; step S3, crushing the mixed aggregate to prepare electrode powder; and step S4, pressing the electrode powder into an electrode material mixture film by rolling.

[0144] (Step S1)

[0145] This is the step of mixing electrode active materials, conductive materials, and binders to form a material mixture composition. The electrode active materials, conductive materials, and binders are as described above, and therefore their specific descriptions will not be provided again. In this case, mixing is performed to ensure that the electrode active materials, conductive materials, and binders are uniformly distributed, and the components are mixed in powder form. Therefore, mixing is not limited and can be carried out by various methods, as long as simple mixing is permitted. However, in this invention, a dry electrode is prepared without the use of solvents, and therefore mixing can be performed by dry mixing, and the aforementioned materials can be added to a device such as a mixer or blender and mixed.

[0146] In this case, mixing can be carried out in a mixer at 100 rpm to 5000 rpm for 1 minute to 60 minutes. Ideally, mixing can be carried out in a mixer at 500 rpm to 4000 rpm for 3 minutes to 45 minutes, and more preferably at 100 rpm to 3000 rpm for 5 minutes to 30 minutes. When mixing is carried out within these ranges, the materials can be uniformly mixed, thereby improving battery performance.

[0147] The control conditions of the mixing process can determine the uniformity and quality of the fibrillation of the binder during the kneading process in the subsequent step S2. When the mixing is uneven, even if the fibrillation is uniform, there may be uneven parts on the entire side of the membrane. Therefore, it is desirable to carry out the mixing process under the above conditions.

[0148] (Step S2)

[0149] Next, a fibrillation process of the binder can be performed on the material mixture composition obtained by mixing, using a binder capable of forming a three-dimensional fibrous network structure, thereby preparing a hybrid aggregate. Ideally, the material mixture composition can be kneaded while shear force is applied to form the hybrid aggregate.

[0150] The fibrillation process can be carried out, for example, by mechanical grinding or kneading, and is not particularly limited, as long as the process is a commonly performed process. However, it is desirable to carry out the process by high-temperature low-shear kneading, and it can be carried out, for example, by kneading machines such as kneaders. Through this kneading, the binder capable of forming a three-dimensional fiber network structure is fibrillated, and accordingly, the electrode active material and conductive material powder are combined or linked to form a mixed aggregate with 100% solids content.

[0151] Kneading can be performed at a rate of 10 rpm to 100 rpm, and more specifically at a rate of 20 rpm to 70 rpm. Furthermore, kneading can be carried out for 1 minute to 120 minutes, preferably 2 minutes to 60 minutes. When the above ranges are met, appropriate fibrillation can be achieved, thereby allowing the binder to be uniformly fibrillated throughout and forming a structurally stable three-dimensional fiber network structure.

[0152] In addition, kneading can be carried out at high temperatures and pressures greater than or equal to atmospheric pressure, and specifically, at pressures higher than atmospheric pressure.

[0153] More specifically, kneading can be performed at temperatures ranging from 50°C to 230°C, preferably from 90°C to 200°C. When kneading is performed at high temperatures within the above range, the fibrillation of the adhesive and the agglomeration through kneading can be well achieved, and the breakage of the adhesive undergoing fibrillation can be appropriately prevented.

[0154] In addition, kneading can be performed at pressures greater than or equal to atmospheric pressure, specifically between 1 atm and 3 atm. Kneading within this range can appropriately prevent the breakage of the fibrillated binder and prevent the aggregates from having excessively high density.

[0155] In other words, according to the present invention, when high-temperature-low-shear mixing is performed at high temperature and at pressure greater than or equal to atmospheric pressure instead of high-shear mixing, the desired effect of the present invention can be achieved.

[0156] (Step S3)

[0157] Next, the mixed aggregates prepared by kneading can be pulverized to obtain electrode powder. Ideally, the mixed aggregates can be pulverized to prepare electrode powder.

[0158] The mixed aggregates prepared by kneading can be directly pressed and molded into sheets (e.g., by calendering). However, in this case, the mixed aggregates may be pressed under high pressure and high temperature to form a film, and consequently, the film may have excessively high density or be unattainable uniformity. Therefore, the mixed aggregates prepared as above are pulverized to prepare powders for electrodes.

[0159] There are no particular restrictions on the equipment used for pulverization, but it is desirable to use equipment such as a mixer or a grinder for pulverization.

[0160] The grinding can be carried out at a rate of 1000 rpm to 15000 rpm for 1 minute to 30 minutes, and preferably at a rate of 3000 rpm to 10000 rpm for 5 minutes to 20 minutes. When grinding is carried out within the above range, sufficient grinding can be achieved to prepare powder of appropriate size for film formation, and a large amount of fine powder can be avoided in the mixed aggregates.

[0161] The average particle diameter of the electrode powder can range from 10 μm to 3,000 μm, specifically from 50 μm to 1,500 μm, and more specifically from 100 μm to 700 μm. When these ranges are met, an electrode material mixture film with uniform thickness and density can be formed, and excellent physical properties of the electrode material mixture film can be obtained.

[0162] Meanwhile, the electrode powder may further include fillers to suppress electrode expansion, although this is not necessary. The fillers are not particularly limited, as long as they are fibrous materials that do not cause chemical changes in the battery, and can be, for example, at least one selected from olefin-based polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0163] (Step S4)

[0164] Next, the electrode powder is pressed into an electrode material mixture film by rolling. Desiredly, step S4 can be a process of preparing a self-supporting sheet-like electrode material mixture film by using pressure rollers to thermally compress the electrode powder in a roll-to-roll process comprising two or more pairs of pressure rollers.

[0165] The roll-to-roll process may include a roll pressing unit for performing roll pressing, and the roll pressing unit may be a roll pressing unit in which a pair of pressure rollers facing each other are arranged, or a roll pressing unit in which multiple pressure rollers are arranged continuously, and multiple pressure rollers may be arranged continuously in the roll pressing unit. When multiple pressure rollers are arranged continuously, the temperature and tip speed ratio (rotational speed ratio of a pair of rollers) of each roller may be the same or different.

[0166] According to embodiments of the present invention, the temperature of the pressure roll can be from 50°C to 200°C, preferably from 50°C to 180°C, and more preferably from 60°C to 150°C. When the above ranges are met, an electrode material mixture film with excellent processability and uniformity can be obtained.

[0167] The rotational speed ratio of the pressure rollers provided during the roller-to-roll process in step S4 can be independently and appropriately adjusted within the range of 1:1 to 1:10. Additionally, the prepared electrode material mixture film can be returned to the roller pressing unit and subjected to 1 to 10 cycles of hot compression to adjust it to an appropriate thickness.

[0168] According to an embodiment of the present invention, step S4 may include: step S4a, pre-pressing the electrode powder to obtain a powder-pressed film; and step S4b, pressing the powder-pressed film two or more times to prepare an electrode material mixture film. That is, after converting the powder into a sheet in step S4a, step S4b can be performed to roll the sheet to enhance its strength and meet the porosity and loading requirements of the electrode.

[0169] Furthermore, according to embodiments of the present invention, the process may further include: stacking an electrode material mixture film on one or both sides of a current collector, and then inserting the resulting product into a lamination unit for lamination. In this manner, the electrode material mixture film is rolled onto the current collector, thereby preparing a dry electrode in which the electrode material mixture film is disposed on the current collector.

[0170] Lamination can involve attaching a film of electrode material mixture to a current collector by roll forming. Lamination can be performed using a roll forming method that includes a lamination unit comprising a lamination roller.

[0171] According to an embodiment of the invention, the laminating roller can be maintained at a temperature of 20°C to 200°C.

[0172] Lamination can ideally be performed after at least one or two hot-pressing operations, and then one or more additional hot-pressing operations can be performed to achieve the desired porosity. When lamination is performed during the aforementioned calendering process, the electrode appearance and calendering processability can be improved compared to reducing the porosity of the film state of the material mixture before lamination. Porosity control through additional hot pressing can be achieved by controlling the compression ratio using roll gap adjustment, which can be derived using the following relationship 2.

[0173] [Relation 2] Compression ratio (%) = [(electrode thickness) - (roller gap)] / [(electrode thickness) - (current collector thickness)]

[0174] Lithium secondary batteries

[0175] The lithium secondary battery according to the present invention will be described below.

[0176] The lithium secondary battery according to the present invention may include the dry electrode according to the present invention. For example, the lithium secondary battery may include a secondary battery containing a liquid electrolyte and an all-solid-state battery containing a solid electrolyte.

[0177] Specifically, the lithium secondary battery according to the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode can be a dry electrode, and specifically, the lithium secondary battery according to the present invention can be a lithium secondary battery comprising a dry electrode, a negative electrode, a separator, and an electrolyte according to the present invention. In the case where only one of the positive or negative electrodes is a dry electrode according to the present invention, the other electrode can be an electrode prepared by a conventional wet preparation method.

[0178] In the case of a lithium secondary battery according to an embodiment of the invention that includes a liquid electrolyte, a separator may be included between multiple electrodes. The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is generally used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer are desirable. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin-based polymers, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates having two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed from glass fibers or polyethylene terephthalate fibers with high melting points. Furthermore, coated separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be optionally used.

[0179] In addition, when the lithium secondary battery is an all-solid-state battery, a solid electrolyte membrane can be fabricated to perform the function of a separator.

[0180] The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer are desirable. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin-based polymers, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates having two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be optionally used.

[0181] In addition, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. All of these electrolytes can be used to prepare lithium secondary batteries, but are not limited thereto.

[0182] Specifically, electrolytes may include organic solvents and lithium salts.

[0183] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate-based solvents are desirable, and even more desirable are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant with linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity, which can improve the charge / discharge performance of the battery.

[0184] Lithium salts can be used without particular restriction, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one of the following: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3- CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - Furthermore, as lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. The lithium salts can be used in concentration ranges from 0.1 M to 4.0 M, preferably from 0.5 M to 3.0 M, and more preferably from 1.0 M to 2.0 M. When the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0185] To enhance battery life characteristics, suppress battery capacity decline, and increase battery discharge capacity, in addition to the electrolyte components mentioned above, at least one additive may be further included in the electrolyte, such as a haloalkylene carbonate compound of difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether, hexaphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additive relative to the total weight of the electrolyte can be from 0.1 wt% to 10.0 wt%.

[0186] Furthermore, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention, and is therefore useful for portable devices such as mobile phones, laptops and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0187] Therefore, according to another embodiment of the present invention, a battery module including a lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0188] Battery modules or battery packs can be used as a power source for at least one medium or large device in power tools, electric vehicles (including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs)), or energy storage systems.

[0189] In the following description, embodiments of the invention will be described in detail in a manner that enables those skilled in the art to readily practice the invention. However, the invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0190] Examples and Comparison Examples

[0191] Example 1: Preparation of expandable carbon nanotube powder

[0192] Bundles of carbon nanotubes (BET specific surface area: 256 m²) comprising multi-walled carbon nanotube units (average diameter: 10 nm) 2 The carbon nanotube powder was prepared by adding carbon nanotubes (g, bulk density: 0.110 g / cc) to a depolymerization device (Galaxy Jet Mill, JEM Co.) and depolymerizing them in a solvent-free state.

[0193] In this case, the jet nozzles included in the depolymerization device have a jet pressure of 5 bar.

[0194] Comparative Example 1: Preparation of Expandable Carbon Nanotube Powder

[0195] Expandable carbon nanotube powder was prepared in the same manner as in Example 1, except that: the multi-walled carbon nanotube units had an average diameter of 6 nm, and the bundled carbon nanotubes had an average diameter of 380 nm. 2 BET specific surface area of ​​0.080 g / cc and bulk density of 0.080 g / cc.

[0196] Comparative Example 2: Preparation of Expandable Carbon Nanotube Powder

[0197] Expandable carbon nanotube powder was prepared in the same manner as in Example 1, except that: the multi-walled carbon nanotube units had an average diameter of 8 nm, and the bundled carbon nanotubes had an average diameter of 300 nm. 2 BET specific surface area of ​​0.080 g / cc and bulk density of 0.080 g / cc.

[0198] Comparative Example 3: Preparation of Expandable Carbon Nanotube Powder

[0199] Expandable carbon nanotube powder was prepared in the same manner as in Example 1, except that: the multi-walled carbon nanotube units had an average diameter of 8 nm, and the bundled carbon nanotubes had an average diameter of 260 nm. 2 BET specific surface area of ​​0.12 g / cc and bulk density of 0.12 g / cc.

[0200] Experimental Example 1: Measurement of electrical conductivity, compaction density, slope, and bulk density of expandable carbon nanotube powder

[0201] 1) Measurement of electrical conductivity (S / cm) and compaction density (g / cc) of expandable carbon nanotube powder: 3.0 g of expandable carbon nanotube powder prepared in Example 1 and Comparative Examples 1 to 3 were added to a cylindrical die fixture (diameter: 6.38 mm, width: 0.38 cm). 2 In the process, the force is increased from 200 kgf to 1600 kgf in a force measuring device, the conductivity is measured every 200 kgf, and the volume decreases with increasing force is measured to determine the compaction density.

[0202] The measurement results are shown in Table 1.

[0203] 2) Measurement of the slope and bulk density of expandable carbon nanotube powder when conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis respectively:

[0204] For the expandable carbon nanotube powders prepared in Example 1 and Comparative Examples 1 to 3, the conductivity (S / cm) and compaction density (g / cc) measured under a specific force (kgf) in step 1) are plotted on the y-axis and x-axis respectively to obtain the slopes. In this case, the slopes of Example 1 and Comparative Examples 1 to 3 are... Figure 1 As shown in the image.

[0205] Alternatively, bulk density can be measured by filling expandable carbon nanotube powder into a 25 mL container, measuring the weight, and then converting the result into density.

[0206] The measurement results are shown in Table 2.

[0207] [Table 1]

[0208]

[0209] [Table 2]

[0210]

[0211] Experimental Example 2: Measurement of Electrode Layer Resistance (Ωcm)

[0212] 1) Preparation of dry electrode: The expandable carbon nanotube powder prepared in Example 1 and Comparative Examples 1 to 3 was prepared as a conductive material. Subsequently, lithium nickel cobalt manganese aluminum oxide (LNF) as the electrode active material, each of the above conductive materials, and polytetrafluoroethylene (PTFE) as a fibrillable binder were added to a mixer and mixed at 1500 rpm for 10 minutes to prepare a mixture composition of the materials.

[0213] Subsequently, the material mixture composition was added to a kneader and kneaded at 1.1 atm and 150°C at 50 rpm for 10 minutes to prepare a mixed aggregate. The mixed aggregate was then added to a blender and pulverized at 5000 rpm for 10 minutes. The aggregate was then sorted through a sieve with a 1 mm aperture to prepare electrode powders for Example 1 and Comparative Examples 1 to 3.

[0214] Electrode powder was pressed onto calendering rolls (roll diameter: 88 mm, roll temperature: 100°C) in a roll-to-roll process to prepare an electrode material mixture film. Subsequently, one sheet of the electrode material mixture film was placed on one side of an aluminum foil (thickness: 15 μm) with a conductive primer layer formed, and laminated using a roll press maintained at 100°C to prepare a dry electrode. In this case, the electrode material mixture film has a porosity of 23.5%.

[0215] 2) Measurement of electrode layer resistance: The prepared dry electrode was cut into 30 mm × 50 mm pieces, and a current of 100 μA was applied to the electrode using the MP resistance measurement method. Based on the potential difference measured between 46 probes, the resistivity (Ωcm) at any point in the electrode material mixture film was measured six times, and the average value was calculated.

[0216] The measurement results are shown in Table 3.

[0217] [Table 3]

[0218]

[0219] Referring to Table 3 above, it can be seen that, compared with Comparative Examples 1 to 3, Example 1, which satisfies the above slope range, has superior electrode layer resistance.

Claims

1. An expandable carbon nanotube powder, comprising carbon nanotube units, in, When electrical conductivity (S / cm) and compaction density (g / cc) are plotted on the y-axis and x-axis respectively, the slope is greater than or equal to 95, and The electrical conductivity (S / cm) and the compaction density (g / cc) were measured when a pressure ranging from 50 MPa to 420 MPa was applied to the expandable carbon nanotube powder.

2. The expandable carbon nanotube powder according to claim 1, wherein, The slope ranges from 100 to 125.

3. The expandable carbon nanotube powder according to claim 1 has a bulk density of less than or equal to 0.022 g / cc.

4. The expandable carbon nanotube powder according to claim 1, wherein, When the compaction density of the expandable carbon nanotube powder is 1.0 g / cc, the electrical conductivity is greater than or equal to 70 S / cm.

5. The expandable carbon nanotube powder according to claim 1, wherein, The ratio of the true density (TD) to the bulk density (BD) of the expandable carbon nanotube powder (TD / BD) is between 91 and 673.

6. The expandable carbon nanotube powder according to claim 1 has a true density (TD) of 1.850 g / cc to 2.500 g / cc.

7. The expandable carbon nanotube powder according to claim 1, having a thickness of 200 μm 2 / g to 1000 m 2 / g BET specific surface area.

8. The expandable carbon nanotube powder according to claim 1, wherein, The carbon nanotube unit is a multi-walled carbon nanotube unit.

9. The expandable carbon nanotube powder according to claim 8, wherein, The multi-walled carbon nanotube units have an aspect ratio of 30 to 10,000.

10. The expandable carbon nanotube powder according to claim 8, wherein, The multi-walled carbon nanotube units have an average length of 0.1 μm to 100 μm.

11. The expandable carbon nanotube powder according to claim 8, wherein, The multi-walled carbon nanotube units have an average diameter of 5 nm to 200 nm.

12. The expandable carbon nanotube powder according to claim 8, wherein, The multi-walled carbon nanotube unit has a diameter of 50m. 2 / g to 500 m 2 / g BET specific surface area.

13. The expandable carbon nanotube powder according to claim 8, wherein, The multi-walled carbon nanotube unit has three or more graphene layers arranged parallel to the axis of the multi-walled carbon nanotube unit.

14. A dry electrode comprising the expandable carbon nanotube powder according to claim 1.

15. A lithium secondary battery comprising a dry electrode according to claim 14.

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