Expandable carbon nanotube powder, and dry electrode and lithium secondary battery comprising same

Abstract

The present invention relates to an expandable carbon nanotube powder including carbon nanotube units, wherein when electrical conductivity (S / cm) and packing density (g / cc) are plotted on the y-axis and the x-axis, respectively, the expandable carbon nanotube powder has a slope of 95 or more, and the electrical conductivity (S / cm) and the packing density (g / cc) are measured while applying a pressure of 50 to 420 MPa to the expandable carbon nanotube powder.

Description

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

[0001] Cross-citation with related applications

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

[0003]

[0004] Technology field

[0005] The present invention relates to an expandable carbon nanotube powder, a dry electrode comprising the same, and a lithium secondary battery.

[0006]

[0007] Secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices that store surplus generated power or renewable energy and power storage devices for backup purposes.

[0008] Typically, secondary batteries are manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, then manufacturing a positive electrode and a negative electrode through a drying and rolling process, and then laminating these on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting electrolyte, and sealing the electrode assembly.

[0009] Meanwhile, during the drying process of the electrode active material slurry, the solvent contained in the slurry may evaporate, causing defects such as pinholes or cracks in the electrode active material layer formed on the current collector. In addition, since the inside and outside of the electrode active material slurry are not uniformly dried during the drying process, there is a concern that the powder floating phenomenon due to the difference in solvent evaporation rate may occur, i.e., the powder in the area that dries first may rise and form a gap with the area that dries relatively later, which may deteriorate the electrode quality.

[0010] To solve the above problem, a drying device capable of controlling the evaporation rate of the solvent so that the inside and outside of the electrode active material slurry can be dried evenly is being considered, but such drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing process.

[0011] On the other hand, the solvent typically used in electrode active material slurries is N-methyl-2-pyrrolidone (NMP). Its high boiling point necessitates high heat energy and a very long drying process for drying, making it highly unsuitable for mass production. Furthermore, NMP is toxic and harmful to living organisms, making it unfriendly to the environment.

[0012] Accordingly, there has been a recent trend of active research on dry electrodes that manufacture electrodes without using solvents. The dry electrode is generally manufactured by laminating a free-standing electrode composite film manufactured in the form of a sheet containing an electrode active material, a binder, a conductive material, etc., onto a current collector. This electrode composite film includes a process of first mixing an electrode active material, a carbon material as a conductive material, and a fiberizable binder together using a blender, etc., and then applying a shear force through a process such as jet milling or kneading to fiberize the binder, and then calendering the obtained mixture into a film form to manufacture a free-standing film.

[0013] However, when manufacturing the above dry electrode, unlike the wet electrode where the electrode active material, conductive material, and fiberizable binder are mixed in a solvent, there is a problem in that the dispersibility of the conductive material is poor because they are mixed in a solvent-free state. At this time, a method of first dispersing the conductive material and then mixing it with the electrode active material, conductive material, and fiberizable binder to increase the dispersibility of the conductive material has been proposed. However, in the case of the conventional conductive material that is first dispersed, it does not satisfy specific physical properties and exhibits poor resistance characteristics.

[0014] Therefore, there is a need for an expandable carbon nanotube powder that can satisfy specific properties and achieve excellent dispersibility of a conductive material.

[0015]

[0016] One object of the present invention is to solve the above-described problem, and to provide an expanded carbon nanotube powder having excellent electrical conductivity when used as a conductive material by controlling the properties of the expanded carbon nanotube powder so that when the electrical conductivity (S / cm) and packing density (g / cc) measured under a specific pressure range are plotted on the y-axis and the x-axis, respectively, the slope is 95 or more.

[0017]

[0018] In addition, another object of the present invention is to solve the above-mentioned problems, and to provide a dry electrode and a lithium secondary battery including the expandable carbon nanotube powder, which have improved resistance characteristics and lifespan characteristics due to excellent electrical conductivity and mechanical properties.

[0019]

[0020] [1] The present invention provides an expanded carbon nanotube powder comprising carbon nanotube units, wherein when the electrical conductivity (S / cm) and the packing density (g / cc) are plotted on the y-axis and the x-axis, respectively, the slope is 95 or more, and the electrical conductivity (S / cm) and the packing density (g / cc) are measured while applying a pressure of 50 MPa to 420 MPa to the expanded carbon nanotube powder.

[0021] [2] In the present invention, in the above [1], the slope may be 100 to 125.

[0022] [3] In the present invention, in the above [1] or [2], the bulk density of the expanded carbon nanotube powder may be 0.022 g / cc or less.

[0023] [4] In at least one of the above [1] to [3], when the filling density of the expandable carbon nanotube powder is 1.0 g / cc, the electrical conductivity may be 70 S / cm or more.

[0024] [5] In at least one of the above [1] to [4], the ratio of true density (TD) to bulk density (BD) of the expanded carbon nanotube powder (TD / BD) may be 91 to 673.

[0025] [6] In at least one of the above [1] to [5], the true density (TD) of the expanded carbon nanotube powder may be 1.850 g / cc to 2.500 g / cc.

[0026] [7] The present invention is characterized in that, in at least one of the above [1] to [6], the BET specific surface area of ​​the expanded carbon nanotube powder is 200 m 2 / g to 1000m 2 / g may be.

[0027] [8] In at least one of the above [1] to [7], the carbon nanotube unit may be a multi-walled carbon nanotube unit.

[0028] [9] In at least one of the above [1] to [8], the aspect ratio of the multi-walled carbon nanotube unit may be 30 to 10000.

[0029]

[0010] In at least one of the above [1] to [9], the average length of the multi-walled carbon nanotube unit may be 0.1 μm to 100 μm.

[0030]

[0011] In at least one of the above [1] to

[0010] , the average diameter of the multi-walled carbon nanotube unit may be 5 nm to 200 nm.

[0031]

[0012] The present invention is characterized in that in at least one of the above [1] to

[0011] , the BET specific surface area of ​​the multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g may be.

[0032]

[0013] In at least one of the above [1] to

[0012] , the multi-walled carbon nanotube unit may have three or more graphene layers arranged in parallel with respect to the axis of the multi-walled carbon nanotube unit.

[0033]

[0014] The present invention provides a dry electrode comprising at least one expandable carbon nanotube powder among the above [1] to

[0013] .

[0034]

[0015] The present invention provides a lithium secondary battery including the dry electrode of

[0014] above.

[0035]

[0036] The expandable carbon nanotube powder according to the present invention is characterized in that, when the electrical conductivity (S / cm) and the filling density (g / cc) are plotted on the y-axis and the x-axis, respectively, the slope is controlled to be 95 or more, thereby preventing excessive cutting of the carbon nanotubes and forming an appropriately expanded pop-type.

[0037]

[0038] In addition, the dry electrode and lithium secondary battery including the expandable carbon nanotube powder according to the present invention can form an excellent conductive network with excellent dispersibility within the dry electrode due to the above-mentioned characteristics, and at the same time, increase the contact area with the electrode active material, thereby realizing excellent resistance characteristics and life characteristics.

[0039]

[0040] The drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further enhance the understanding of the technical spirit of the present invention. Therefore, the present invention is not limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0041] Figure 1 shows the expanded carbon nanotube powders manufactured in Example 1 and Comparative Examples 1 to 3 with an area of ​​0.38 cm. 2 This is a graph showing the electrical conductivity (S / cm) and filling density (g / cc) measured while applying a force from 200 kgf to 1600 kgf after being injected into a circular mold, plotted on the y-axis and x-axis, respectively.

[0042] Figures 2 and 4 are SEM images of carbon nanotube aggregates.

[0043] Figures 3 and 5 are SEM photographs of expanded carbon nanotube powder.

[0044]

[0045] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0046] In this specification, "volume cumulative average particle diameter D 50 "In the particle size distribution curve of silver particles, it means the particle size corresponding to 50% of the volume accumulation amount. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0047] In this specification, "average particle diameter" means the arithmetic average value calculated by measuring the particle diameters of at least 30 particles observed in a scanning electron microscope image when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope. In this case, the particle diameter means the longest axis diameter of the particle. The above "volume cumulative average particle diameter D 50 " and "average particle size" have different measurement methods, but their values ​​can be derived similarly, and the volume cumulative average particle size D measured in the powder state 50 The powder may have a similar value to the average particle size observed in the scanning electron microscope image of the electrode after it is manufactured into an electrode, within the error range.

[0048] In this specification, the term "composite composition" means a mixture including an electrode active material and a binder and optionally a conductive material, which is physically mixed to form a uniform dispersion phase, and may be a powder mixture as a product of the mixing process (mixing process) according to this specification, and may be substantially solvent-free. Here, substantially solvent-free means that no solvent is added or only a very small amount of solvent is added during mixing of the composite composition.

[0049] In this specification, the “mixed aggregate” refers to a mixture of powders that are converted into a dough-like aggregate by binding or connecting each other when the binder is fiberized by applying a shear force to the composite composition, and is a product of the kneading process (kneading process) according to this specification, which may have a solid content substantially close to 100% and may contain a small amount of solvent in some cases.

[0050] In this specification, “electrode powder” may mean a powder-type electrode material that is a material in which the above mixed aggregate is pulverized to form smaller particles and is in a powder form, and includes an electrode active material, a binder, and optionally a conductive material.

[0051] In this specification, the "electrode composite film" may mean an electrode composite layer manufactured in the form of a free-standing single sheet using an "electrode composite" including an electrode active material, a conductive material, and a binder without involving a solvent, or in a state of being laminated on a current collector. The term "free-standing" in this specification means that it can maintain a single shape without relying on other members and can be moved or handled by itself. The electrode composite film may be formed by compressing the electrode powder as described below. For example, the electrode powder may have a shape in which a layered structure is formed by being accumulated by compressing.

[0052] In this specification, “powder-sheeting film” means a film formed in a sheet form through a powder-sheeting process in which the electrode powder first passes through a rolling roll in a roll-to-roll process (e.g., a calendaring process) and before passing through the last rolling roll in the roll-to-roll process. It may be a self-supporting sheet, but may be a sheet with relatively weak self-supporting force. Here, the “powder-sheeting” means that the electrode powder is formed into a self-supporting sheet form by a rolling roll in the roll-to-roll process, and “sheeting” is a process performed in the process in which the powder-sheeting film is manufactured into an electrode composite film, and may mean a process of roll-rolling the powder-sheeting film.

[0053] In this specification, the term "three-dimensional fiber network structure" may refer to a structure that can be formed by fiberization of a binder during the process of forming a sheet into an electrode composite film from a composite composition including an electrode active material and a binder. Specifically, the three-dimensional fiber network structure may refer to various structures in which fine fibers formed by fiberization of the binder form a skeleton, thereby functioning as a support that enables the electrode composite film to be a self-supporting film. In this case, the electrode active material and, optionally, a conductive material may be accommodated within the pores formed in the three-dimensional fiber network structure.

[0054] In this specification, the porosity can be calculated using the following mathematical formula A.

[0055] [Mathematical Formula A]

[0056] Porosity (%) = {1-(electrode density / true density)} x 100

[0057] In the above mathematical formula A, the true density is a calculated density derived from the density and mass ratio of each component material forming the electrode composite film under the assumption that no pores are included, and the electrode density is a measured density of the electrode composite film measured by sampling the electrode composite film to a certain size.

[0058] In the present invention, “specific surface area (m 2 / g)” is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0059]

[0060] When manufacturing a dry electrode, unlike a wet electrode where the electrode active material, fiberizable binder, and / or conductive agent are mixed in a solvent, there is a problem of poor conductive agent dispersibility because they are mixed in a solvent-free state. At this time, a method has been proposed to improve the conductive agent dispersibility by first dispersing the conductive agent and then mixing it with the electrode active material, conductive agent, and fiberizable binder. However, in the case of conventional conductive agent pre-dispersion, there is a problem that excessive cutting of the conductive agent occurs due to excessive shear force in a solvent-free state, or the desired degree of dispersion cannot be achieved, resulting in poor resistance and life characteristics.

[0061] The inventors of the present invention have conducted continuous research to solve such problems and have discovered that excellent resistance and lifespan characteristics can be achieved when using expandable carbon nanotube powder that satisfies specific properties, thereby completing the present invention.

[0062]

[0063] Expandable carbon nanotube powder

[0064] The expandable carbon nanotube powder according to the present invention is an expandable carbon nanotube powder including carbon nanotube units, and when the electrical conductivity (S / cm) and the packing density (g / cc) are plotted on the y-axis and the x-axis, respectively, the slope is 95 or more, and the electrical conductivity (S / cm) and the packing density (g / cc) are measured while applying a pressure of 50 MPa to 420 MPa to the expandable carbon nanotube powder.

[0065]

[0066] Unlike wet electrodes, which undergo a process of dispersing and / or mixing in a solvent, in the manufacture of dry electrodes, conductive materials (e.g., carbon nanotubes) are dispersed and / or mixed in a solvent-free state. When dispersing and / or mixing in a solvent-free state, the buffering and dispersing effects of the solvent cannot occur, so there is a problem that excessive cutting of the conductive material occurs due to excessive shear force, or it is difficult to achieve the desired degree of swelling. In particular, when a dry electrode is manufactured using a conductive material that undergoes excessive cutting or is not dispersed, the formation of conductive paths within the electrode is limited, and the contact area with the electrode active material is reduced, which causes the cell performance to deteriorate.

[0067] Accordingly, the present invention aims to provide an expandable carbon nanotube powder having excellent dispersibility by forming an expandable structure without excessive cutting by controlling specific properties of the carbon nanotube powder so as to exhibit the best efficiency in a dry electrode.

[0068] Specifically, the expanded carbon nanotube powder is characterized by forming a kind of pop-type having an expanded structure without excessive breakage of carbon nanotubes, which is different from high-density aggregated carbon nanotubes or high-density carbon nanotube aggregates generally used in large-scale industries. Preferably, unlike carbon nanotubes dispersed using an aqueous dispersion, the expanded carbon nanotube powder is characterized by forming a pop-type having an expanded structure without excessive breakage of carbon nanotubes in a dry, solvent-free state.

[0069] The above-mentioned pop-type refers to a form in which densely packed carbon nanotube aggregates are disassembled, visually loosely separated, the space between carbon nanotubes increases, and the connections between carbon nanotubes become loose, increasing the overall volume. For example, the expanded structure may form a honeycomb structure with a reduced density between carbon nanotubes, thereby exposing more of the carbon nanotube surfaces to the outside.

[0070] Therefore, when the conductive material comprises the expandable carbon nanotubes according to the present invention during subsequent dry electrode manufacturing, it is preferable in that it can form a well-dispersed conductive network while maintaining the continuity of the conductive network, thereby realizing excellent mechanical strength and resistance characteristics. For example, in the case of expandable carbon nanotubes having an expandable structure that is appropriately dispersed while minimizing cutting, excellent dispersibility can be maintained while minimizing cutting during the subsequent dry electrode manufacturing process, thereby forming an excellent conductive network between and / or within the electrode active materials in the electrode composite film, and sufficiently preventing agglomeration of the conductive material that reduces the conductive effect, thereby realizing excellent resistance characteristics and lifespan characteristics.

[0071] At this time, expanded carbon nanotube powder having a pop-type shape can be achieved by various methods, but preferably, it can be achieved by controlling the characteristics of the carbon nanotube, such as shape, diameter, length and / or number of walls, or the conditions for disintegrating the carbon nanotube.

[0072] In particular, since the expanded carbon nanotube powder as described above can have a low bulk density by forming an expanded structure, it is difficult to measure the electrical conductivity according to the packing density unless a high force is applied to achieve sufficient electrical contact between the powders.

[0073]

[0074] The expandable carbon nanotube powder according to the present invention has a slope of 95 or higher when the electrical conductivity (S / cm) and packing density (g / cc) are plotted on the y-axis and the x-axis, respectively. The slope represents the inherent conductive properties in that the resistivity of the conductive path itself can be indirectly inferred when the expandable carbon nanotube powder forms a conductive path inside the electrode. If the slope is less than 95, this may indicate that excessive cutting of the carbon nanotubes has occurred, causing a problem in forming the conductive path, or that the carbon nanotubes have not formed an appropriately expanded structure, resulting in the failure of the expandable carbon nanotube powder to be constructed. That is, if the slope is less than 95, excessive cutting has occurred or the expandable carbon nanotube powder with an expanded structure has not been formed, so that an excellent conductive path cannot be formed when used as a conductive material in the future, and the contact area between electrode active materials is reduced, resulting in inferior resistance characteristics and life characteristics.

[0075]

[0076] According to one embodiment of the present invention, when the electrical conductivity (S / cm) and the packing density (g / cc) of the expanded carbon nanotube powder are plotted on the y-axis and the x-axis, respectively, the slope may be 95 or more, preferably, the slope may be 96 or more, 97 or more, 98 or more, 99 or more, or 100 or more, and may be 150 or less, 140 or less, 130 or less, 129 or less, 128 or less, 127 or less, 126 or less, or 125 or less, and more preferably, the slope may be 100 to 125. When the above range is satisfied, the occurrence of cutting is minimized, and the expanded carbon nanotube powder having an expanded structure can be formed, thereby realizing excellent resistance characteristics and life characteristics when used as a conductive material in the future. In particular, since the above slope is measured in the powder state of the expanded carbon nanotube, it is a parameter that is very difficult to measure in a conductive dispersion liquid manufactured under general wet conditions.

[0077]

[0078] In the case of the expandable carbon nanotube powder according to the present invention, the electrical conductivity (S / cm) and the packing density (g / cc) are measured while applying a pressure of 50 MPa to 420 MPa to the expandable carbon nanotube powder. Preferably, the measurement can be performed while applying a pressure of 60 MPa to 420 MPa, and more preferably, the measurement can be performed while applying a pressure of 70 MPa to 420 MPa. Since the expandable carbon nanotube powder may have a low bulk density while forming an expanded structure, when a low pressure is applied, sufficient electrical contact between the powders may not be achieved, making it difficult to clearly measure the conductive properties inherent in the powder. That is, when a low pressure is applied, it may be difficult to measure the slope intended by the present invention. In addition, since the conductivity of the expandable carbon nanotube powder is measured under a high pressure range that is applied when actually manufacturing an electrode, one of the characteristics of the present invention is that the conductivity in the electrode state can be more clearly determined. Therefore, when measuring the electrical conductivity and packing density by applying a pressure within the above range, the electrical conductivity and packing density can be measured with sufficient electrical contact between the powders, and thus a slope that can clearly represent the conductive properties inherent in the powder can be measured.

[0079]

[0080] According to one embodiment of the present invention, the bulk density of the expanded carbon nanotube powder may be 0.022 g / cc or less, preferably 0.020 g / cc or less, 0.018 g / cc or less, 0.016 g / cc or less, 0.014 g / cc or less, 0.012 g / cc or less, 0.010 g / cc or less, or 0.009 g / cc or less, and may be 0.001 g / cc or more or 0.002 g / cc or more, and more preferably 0.001 g / cc to 0.009 g / cc. When the above range is satisfied, an appropriately expanded structure can be formed while excessive cutting can be prevented, so that excellent resistance characteristics and life characteristics can be implemented.

[0081]

[0082] According to one embodiment of the present invention, when the packing density of the expandable carbon nanotube powder is 1.0 g / cc, the electrical conductivity may be 70 S / cm or more, preferably 70 S / cm or more, 71 S / cm or more, 72 S / cm or more, 73 S / cm or more, 74 S / cm or more, or 75 S / cm or more, and may be 125 S / cm or less, 123 S / cm or less, 120 S / cm or less, 117 S / cm or less, or 115 S / cm or less. More preferably, it may be 75 S / cm to 115 S / cm. When the above range is satisfied, it may be preferable in that the expandable carbon nanotube powder has an appropriate expanded form and can form an excellent expandable structure.

[0083]

[0084] According to one embodiment of the present invention, the ratio of true density (TD) to bulk density (BD) of the expanded carbon nanotube powder (TD / BD) may be 91 to 673, preferably 134 to 505, and more preferably 200 to 405. When the above range is satisfied, the expanded carbon nanotube powder may be preferable in that it can appropriately expand and simultaneously implement excellent dispersibility.

[0085] The above bulk density (BD) can be measured by filling an expanded carbon nanotube powder into a container of known volume, measuring the weight, and then converting the weight to density.

[0086] The above true density (TD) differs from bulk density in that it is the density of the volume of the material itself, excluding the pores within the porous material. A device for measuring the above true density (TD) may be, for example, a dry automatic density meter (Accupick II 1340 series, Shimadzu Corporation). Using the above device, the true density can be automatically measured by adding a small amount of expanded carbon nanotube powder. The above true density can also be obtained using other measuring methods and / or devices in addition to the above-described measuring methods and / or devices.

[0087]

[0088] According to one embodiment of the present invention, the true density (TD) of the expanded carbon nanotube powder may be 1.850 g / cc to 2.500 g / cc, preferably 1.900 g / cc to 2.300 g / cc, and more preferably 1.950 g / cc to 2.150 g / cc. When the above range is satisfied, the density may be such that a sufficient conductive path can be formed within the electrode, and may be preferable in that an expanded structure can be easily formed.

[0089]

[0090] According to one embodiment of the present invention, the BET specific surface area of ​​the expanded carbon nanotube powder is 200 m 2 / g to 1000m 2 / g can be, preferably 250m 2 / g to 950m 2 / g can be, more preferably 300m 2 / g to 900m 2 / g may be. If the above range is satisfied, it may be desirable in that an appropriately expanded structure can be formed while also implementing excellent dispersibility.

[0091]

[0092] According to one embodiment of the present invention, the expanded carbon nanotube powder comprises carbon nanotube units. The graphite sheet of the carbon nanotube has a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT) unit, a double-walled carbon nanotube (DWCNT) unit, and a multi-walled carbon nanotube (MWCNT) unit, depending on the number of bonds forming the wall.

[0093]

[0094] According to one embodiment of the present invention, the carbon nanotube unit may be a multi-walled carbon nanotube unit. If the carbon nanotube unit is a single-walled carbon nanotube or a double-walled carbon nanotube, the battery manufacturing cost may be excessively high, which may lower the processability, and the carbon nanotube unit may exist in an excessively aggregated state, making it difficult to form an expandable carbon nanotube powder having an expandable structure. On the other hand, if the carbon nanotube unit is a multi-walled carbon nanotube unit, the manufacturing cost is relatively low, and the cohesion between them is not excessive, so that the formation of an appropriate expandable structure may be possible.

[0095]

[0096] According to one embodiment of the present invention, the aspect ratio of the multi-walled carbon nanotube unit may be 30 to 10,000, preferably 60 to 2,000, and more preferably 100 to 1,000. When the above range is satisfied, the dispersibility of the multi-walled carbon nanotube unit may be excellent, and when used as a conductive material in the future, the contact area between electrode active materials may be increased. The aspect ratio may be defined as the ratio of the length and diameter of the multi-walled carbon nanotube unit.

[0097]

[0098] According to one embodiment of the present invention, the average length of the multi-walled carbon nanotube units may be 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 range is satisfied, appropriate dispersion of the multi-walled carbon nanotube units may be possible, and when used as a conductive material in the future, the formation of a conductive network may be maximized. The above average length corresponds to the average value of the top 100 multi-walled carbon nanotube units with the longest lengths and the bottom 100 multi-walled carbon nanotube units observed through SEM or TEM.

[0099]

[0100] According to one embodiment of the present invention, the average diameter of the multi-walled carbon nanotube units may be 5 nm to 200 nm, preferably 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, or 10 nm or more, 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, 80 nm or less, 60 nm or less, or 50 nm or less, and more preferably 10 nm to 50 nm. When the above range is satisfied, dispersion is easy, so that conductivity can be improved when used as a conductive material in the future. The above average diameter corresponds to the average value of the top 100 multi-walled carbon nanotube units with large diameters and the bottom 100 multi-walled carbon nanotube units observed through SEM or TEM.

[0101]

[0102] According to one embodiment of the present invention, the BET specific surface area of ​​the multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g can be, preferably 100m 2 / g to 400m 2 / g can be, more preferably 150m 2 / g to 350m 2 / g. When the above specific surface area range is satisfied, appropriate dispersion between the multi-walled carbon nanotube units is possible, thereby maintaining the manufacturing processability. The BET specific surface area can be measured through the nitrogen adsorption BET method.

[0103]

[0104] According to one embodiment of the present invention, the multi-walled carbon nanotube unit may have three or more graphene layers arranged in parallel with respect to the axis of the multi-walled carbon nanotube unit. Preferably, it may have three to twenty graphene layers, more preferably, it may have three to ten graphene layers, and even more preferably, it may have three to five graphene layers. When the above range is satisfied, it is preferable in that the multi-walled carbon nanotube unit is appropriately dispersed, enabling the production of an expandable carbon nanotube powder having an expandable structure, while improving the conductivity of the expandable carbon nanotube powder.

[0105]

[0106] Method for producing expandable carbon nanotube powder

[0107] Hereinafter, a method for manufacturing an expandable carbon nanotube powder according to the present invention will be described.

[0108]

[0109] A method for producing an expandable carbon nanotube powder according to the present invention comprises the step of colliding carbon nanotube aggregates with each other in a disintegrating device in a solvent-free state to disintegrate them, wherein the disintegration is performed by the rotation of two or more rotors provided in the disintegrating device and high-pressure gas injected from an injection port provided in the disintegrating device, the rotation speed of the rotor is 3000 rpm or more, and the injection port injects high-pressure gas at a pressure of 3.5 bar or more.

[0110]

[0111] Unlike wet electrodes that undergo a process of dispersing and / or mixing in a solvent, in the production of dry electrodes, conductive materials (e.g., carbon nanotubes) are dispersed and / or mixed in a solvent-free state. When dispersing and / or mixing in a solvent-free state, the buffering and dispersing effects of the solvent cannot be achieved, so there is a problem that excessive cutting of the conductive material occurs due to excessive shear force, or it is difficult to achieve the desired degree of disintegration. In particular, when attempting to disintegrate carbon nanotubes in a solvent-free state, aggregation of carbon nanotubes occurs due to van der Waals forces, making disintegration even more difficult. In addition, since carbon nanotubes have a linear shape, there is a problem that the carbon nanotubes are easily pulverized due to excessive shear force when dispersion and / or mixing are performed in a solvent-free state.

[0112] Accordingly, the present invention provides a method for manufacturing an expanded carbon nanotube powder having excellent dispersibility by colliding carbon nanotube aggregates with each other in a solvent-free state and controlling the disintegration conditions to satisfy specific conditions, thereby forming an expanded structure without excessive cutting and thereby disintegrating carbon nanotube aggregates.

[0113] Specifically, devices such as jaw crushers and hammer crushers that can apply a strong shear force in a solvent-free state perform crushing that causes damage to carbon nanotubes, which makes it difficult to produce carbon nanotubes with an expanded structure. However, in the present invention, carbon nanotubes can be crushed with an appropriate force while minimizing cutting by colliding with each other in a solvent-free state, thereby producing carbon nanotubes with an expanded structure, thereby realizing excellent resistance characteristics and life characteristics when manufacturing electrode powders and dry electrodes containing the same thereafter.

[0114] Since the above-mentioned expandable carbon nanotube powder has been described above, detailed information about the above-mentioned expandable carbon nanotube powder is omitted.

[0115]

[0116] According to one embodiment of the present invention, the carbon nanotube aggregate may be an aggregate in which carbon nanotubes are densely assembled, and may be, for example, a bundled carbon nanotube or an entangled carbon nanotube.

[0117]

[0118] A method for manufacturing carbon nanotubes according to the present invention comprises the step of disintegrating carbon nanotube aggregates by colliding them with each other in a disintegrator in a solvent-free state, wherein the disintegration is performed by the rotation of two or more rotors provided in the disintegrator and by high-pressure gas sprayed from an injection port provided in the disintegrator. Preferably, the disintegration can be performed by a swirling airflow generated by the rotation of two or more rotors provided in the disintegrator and a high-pressure gas sprayed from an injection port provided in the disintegrator, and more preferably, the disintegration can be performed by a swirling airflow and impact force generated by the rotation of two or more rotors provided in the disintegrator and a high-pressure gas sprayed from an injection port provided in the disintegrator.

[0119] The above manufacturing method is characterized by colliding carbon nanotube aggregates with each other to break them apart, unlike pulverizing methods such as ball milling that apply excessive aggregated impact. Accordingly, excessive cutting and agglomeration of carbon nanotube aggregates can be prevented, and the carbon nanotube aggregates of FIGS. 2 and 4 can be formed into expanded carbon nanotube powders having an expanded structure as shown in FIGS. 3 and 5. When the expanded carbon nanotube powders having an expanded structure are formed as described above, when manufacturing electrode powders and / or dry electrodes thereafter, the carbon nanotubes can form an excellent conductive network while appropriately connecting electrode active material particles, and can exhibit excellent dispersibility even in a solvent-free state, so that excellent resistance characteristics and life characteristics can be realized.

[0120] When the above conditions are satisfied, it may be desirable in that the degree of disintegration can be increased by strengthening the collision between carbon nanotube aggregates due to the swirling airflow and the high-pressure gas, and it may be desirable in that the degree of disintegration can be increased by causing the carbon nanotube aggregates to collide with the rotor due to the impact force by the rotor and / or the pressure injected from the nozzle.

[0121] Meanwhile, when carbon nanotube aggregates are crushed by colliding with each other using only high-pressure gas injected from a nozzle provided in a crushing device without rotor rotation, the crushing efficiency is low because there is no swirling airflow or impact force due to rotor rotation, and there is no energy provided to effectively break up the agglomeration due to the van der Waals force between or within densely aggregated carbon nanotube aggregates, so there is a problem in that an expandable carbon nanotube powder cannot be formed.

[0122]

[0123] In the method for manufacturing an expandable carbon nanotube powder according to the present invention, the rotation speed of the rotor is 3000 rpm or more. Preferably, the rotation speed of the rotor may be 3100 rpm or more, 3200 rpm or more, 3300 rpm or more, 3400 rpm or more, 3500 rpm or more, 3600 rpm or more, 3700 rpm or more, 3800 rpm or more, 3900 rpm or more, 4000 rpm or more, 4100 rpm or more, 4200 rpm or more, 4300 rpm or more, 4400 rpm or more, 4500 rpm or more, 4600 rpm or more, 4700 rpm or more, 4800 rpm or more, 4900 rpm or more or 5000 rpm or more, and 7000 rpm or less, 6900 rpm or less, 6800 rpm or less, 6700 rpm or less, 6600 rpm or less, 6500 rpm or less, 6400 rpm or less, 6300 rpm or less, 6200 rpm Below, it may 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, and more preferably, it may be 5000 rpm to 5400 rpm. When the rotation speed of the rotor is less than 3000 rpm, the van der Waals force of the carbon nanotube aggregates cannot be overcome, so there is a problem that the carbon nanotube aggregates aggregate and the expanded carbon nanotube powder of the expanded structure cannot be manufactured. Therefore, when the above range is satisfied, excessive cutting of the carbon nanotube aggregates may not occur, and the expanded carbon nanotube powder of the expanded structure in which sufficient disintegration has been performed can be manufactured, thereby realizing excellent resistance characteristics and life characteristics.

[0124]

[0125] In the method for manufacturing an expandable carbon nanotube powder according to the present invention, the injection port injects high-pressure gas at a pressure of 3.5 bar or more. Preferably, the injection port can inject high-pressure gas at a pressure of 3.6 bar or more, 3.7 bar or more, 3.8 bar or more, 3.9 bar or more, 4.0 bar or more, 4.1 bar or more, 4.2 bar or more, 4.3 bar or more, 4.4 bar or more, 4.5 bar or more, 4.6 bar or more, 4.7 bar or more, 4.8 bar or more, 4.9 bar or more, or 5.0 bar or more, and can inject high-pressure gas at a pressure of 7.5 bar or less. More preferably, the high-pressure gas can be injected at a pressure of 5.0 bar to 7.5 bar. The above nozzle is a nozzle that injects a gas and / or fluid that can generate pressure, such as water vapor, air, steam, nitrogen, and / or argon gas, and can disintegrate carbon nanotube aggregates through collisions between carbon nanotube aggregates or between carbon nanotube aggregates and the rotor. When the nozzle injects high-pressure gas at a pressure of less than 3.5 bar, it is difficult to form carbon nanotubes of an expanded structure because the carbon nanotube aggregates cannot apply enough pressure to overcome the van der Waals force. Therefore, when the above range is satisfied, excessive cutting of the carbon nanotube aggregates may not occur, and an expanded carbon nanotube powder of an expanded structure in which disintegration has progressed sufficiently may be manufactured, thereby realizing excellent resistance characteristics and life characteristics.

[0126]

[0127] According to one embodiment of the present invention, the crushing device is not particularly limited as long as it is a crushing device that can apply a non-excessive force, but may be, for example, a Galaxy jet mill (JEM Corporation).

[0128]

[0129] Hereinafter, the carbon nanotube aggregate used in the manufacturing method according to the present invention will be described in more detail.

[0130]

[0131] Among carbon nanotube aggregates, bundle-type carbon nanotubes refer to a form in which carbon nanotubes are aggregated into a bundle due to interactions between carbon nanotube units, rather than a form in which carbon nanotubes exist in the form of single strands. Preferably, it can refer to a form in which carbon nanotube units are attached or entangled with each other due to interactions between each other.

[0132]

[0133] According to one embodiment of the present invention, the bulk density of the carbon nanotube aggregate is 0.011 g / cm 3 0.900g / cm 3 It may be, and preferably, the bulk density of the carbon nanotube aggregates is 0.020 / cm 3 0.500g / cm 3 It may be, and more preferably, the bulk density of the carbon nanotube aggregate is 0.030 g / cm 3 0.150g / cm 3 If the above range is satisfied, it may be a carbon nanotube aggregate suitable for implementing the degree of disintegration according to the manufacturing method of the present invention.

[0134] The above bulk density can be measured by filling an expanded carbon nanotube powder into a container of known weight, measuring the weight, and then converting the density.

[0135]

[0136] According to one embodiment of the present invention, the volume cumulative average particle diameter of the carbon nanotube aggregate may be 100 ㎛ to 600 ㎛, preferably 200 ㎛ to 580 ㎛, and more preferably 300 ㎛ to 560 ㎛. When the above range is satisfied, an appropriate number of carbon nanotube units are aggregated, so that the carbon nanotube aggregate may be suitable for implementing the degree of disintegration according to the manufacturing method of the present invention. The volume cumulative average particle diameter is not limited as long as it is measured by a conventional method, such as measuring using a scanning electron microscope or measuring using laser diffraction, but preferably, it may be measured through the volume cumulative particle diameter distribution using laser diffraction.

[0137]

[0138] The above carbon nanotube aggregate may include carbon nanotube units. The graphite sheet of the carbon nanotube has a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT) unit, a double-walled carbon nanotube (DWCNT) unit, and a multi-walled carbon nanotube (MWCNT) unit, depending on the number of bonds forming the wall.

[0139] According to one embodiment of the present invention, the carbon nanotube aggregate may include a multi-walled carbon nanotube unit. When the carbon nanotube unit is a single-walled carbon nanotube unit or a double-walled carbon nanotube unit, the manufacturing cost of the battery may be excessively high, which may lower the processability, and the carbon nanotube unit may exist in an excessively aggregated state, which may make it difficult to disintegrate. On the other hand, when the carbon nanotube unit is a multi-walled carbon nanotube unit, the manufacturing cost is relatively low, and the cohesion between the carbon nanotube units is not excessive, which allows for appropriate disintegration, and thus the processability may be excellent.

[0140] In particular, in the case of multi-walled carbon nanotube units, the structural defects are high due to the mechanism of node growth (nodes exist due to defects that occur during the growth process, not in a smooth linear manner). Therefore, during the disintegration process, the multi-walled carbon nanotube units can be more easily cut, and the short-cut multi-walled carbon nanotube units are prone to aggregation due to π-π stacking caused by the carbon surface bonding structure (sp2) of the units. However, when disintegration is performed through the manufacturing method according to the present invention, the multi-walled carbon nanotube units may not be agglomerated, and the effect of the present invention can be maximized in that the length of the carbon nanotube units may not be shortened due to excessive cutting, thereby preventing the electrical conductivity from being deteriorated.

[0141] When the above carbon nanotube aggregate includes a multi-walled carbon nanotube unit, the same applies as described above with respect to the multi-walled carbon nanotube unit.

[0142]

[0143] dry electrode

[0144] A dry electrode according to the present invention comprises an expandable carbon nanotube powder according to the present invention. Preferably, the dry electrode according to the present invention may comprise a current collector; an electrode composite film formed on the current collector; wherein the electrode composite film comprises an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure; and the conductive material may comprise an expandable carbon nanotube powder according to the present invention.

[0145]

[0146] The expandable carbon nanotube powder according to the present invention can exhibit excellent effects when used as a conductive material within an electrode composite film included in a dry electrode. For example, in the case of expandable carbon nanotube powder having an expandable structure that is appropriately dispersed while minimizing cutting, excellent dispersibility is maintained while minimizing cutting during the subsequent dry electrode manufacturing process, thereby forming an excellent conductive network between and / or within electrode active materials within the electrode composite film, and sufficiently preventing agglomeration of conductive materials that reduces the conductive effect, thereby realizing excellent resistance characteristics and life characteristics.

[0147] In particular, in the case of the expandable carbon nanotube powder of the present invention, since the relationship between the electrical conductivity and bulk density already described above is satisfied in a solvent-free state, when the expandable carbon nanotube powder is included in a dry electrode, the environmental friendliness, processability, resistance, and lifespan characteristics can be further maximized.

[0148]

[0149] In addition, the dry electrode according to the present invention can be manufactured by laminating the electrode composite film on one or both sides of a current collector and laminating the resultant product.

[0150] The above lamination may be a step of rolling and attaching the electrode composite film onto a current collector. The above lamination may be performed by a roll press method using a lamination roller, and at this time, the lamination roller may be maintained at a temperature of 20°C to 200°C.

[0151]

[0152] The expanded carbon nanotube powder according to the present invention is described above and is omitted, and the current collector and electrode composite film are described in detail.

[0153]

[0154] (entire house)

[0155] When the above dry electrode is a positive electrode, the current collector may be any conductive material that does not cause chemical changes in the battery, and is not particularly limited. For example, the current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0156] The thickness of the above current collector may be from 8 μm to 500 μm, but is not limited thereto. In addition, fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the electrode composite film.

[0157]

[0158] When the above dry electrode is a negative electrode, the current collector is not particularly limited as long as it has high conductivity without causing changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0159] The above current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and, as in the case where the dry electrode is used as a positive electrode, fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the electrode composite film.

[0160]

[0161] The above-mentioned collector may be used with a conductive primer coated entirely or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder, and the conductive material is not limited to any conductive material, but may be, for example, a carbon-based material. The binder may include a fluorine-based binder (including PVDF and PVDF copolymer), an acrylic-based binder, and an aqueous binder that can be dissolved in a solvent.

[0162]

[0163] (electrode composite film)

[0164] An electrode composite 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 an expandable carbon nanotube powder according to the present invention.

[0165]

[0166] 1) Electrode active material

[0167] The above electrode composite film includes an electrode active material.

[0168] There is no particular limitation on the above electrode active material as long as it is a commonly used electrode active material. For example, the above electrode active material may be a positive electrode active material or a negative electrode active material.

[0169] The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0170] Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 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, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium nickel cobalt manganese aluminum oxide (e.g. Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02)O2), lithium iron phosphate (e.g., LiFePO4), etc., and any one or a mixture of two or more of these may be used. More specifically, the electrode active material may include lithium nickel cobalt manganese aluminum oxide in terms of being able to produce a uniform and stable film-shaped electrode composite film.

[0171] More preferably, the electrode active material may include a phosphorus oxide represented by the following chemical formula 1.

[0172] [Chemical Formula 1]

[0173] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0174] In the above chemical formula 1, M 1 It contains one or more elements selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Mo, Nb, W, Zr, Ce, In, Zn and Y, and -0.5≤x≤0.5, 0≤a≤0.8, 0≤b≤0.1. When the above conditions are satisfied, it may be desirable in terms of being able to implement excellent economic efficiency and stability.

[0175] The above negative active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0176] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0177] As the above metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals with lithium may be used.

[0178] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0179] Materials capable of doping and dedoping the above lithium include Si, SiO x(0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0180] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0181]

[0182] According to one embodiment of the present invention, the electrode active material may be included in an amount of 80 to 99 parts by weight, and preferably 90 to 99 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in terms of increasing the capacity and energy density of the electrode.

[0183]

[0184] 2) Challenge

[0185] The above electrode composite film includes a conductive material, and the conductive material includes an expandable carbon nanotube powder according to the present invention.

[0186]

[0187] According to one embodiment of the present invention, the conductive material may be included in an amount of 0.1 to 10 parts by weight, and preferably 0.1 to 5.0 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in that an excellent conductive path can be formed while also implementing an excellent capacity density.

[0188]

[0189] 3) Binder

[0190] The above electrode composite film includes a binder having a three-dimensional fiber network structure.

[0191] The above binder has the function of forming a three-dimensional fiber network structure so that the electrode composite film can be self-supporting. The binder is not specified as a specific one as long as it is fiberizable, that is, can form a three-dimensional fiber network structure in the electrode composite film through fiberization and provide pores that can accommodate an electrode active material and optionally a conductive material.

[0192] The fiberization of the above binder refers to a process of dividing and finely dividing the polymer applied as the binder, and can be performed, for example, by applying a mechanical shear force, etc., and as a result, the surface is loosened and fiberized, thereby forming a plurality of fine fibers, and thereby including a three-dimensional fiber network structure.

[0193] The above-mentioned fiberizable binder is not specifically defined as long as it is fibrillizable, and the fibrillation refers to a process of dividing a polymer into small pieces. For example, it can be performed using a mechanical shear force, etc., and the surface of the fibrillated polymer fiber is loosened to generate a large number of fine fibers (fibrils). The fiberizable binder may preferably include at least one selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefin, more preferably polytetrafluoroethylene (PTFE), and even more preferably polytetrafluoroethylene (PTFE). When the above conditions are satisfied, excellent conductive material dispersibility can be realized, while appropriately reducing resistance.

[0194]

[0195] Meanwhile, the polytetrafluoroethylene (PTFE) may be included in an amount of 60 wt% or more based on the total binder weight. At this time, the binder may additionally include at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-cohexafluoropropylene (PVdF-HFP), and a polyolefin-based binder.

[0196]

[0197] According to one embodiment of the present invention, the fiberizable binder may be included in an amount of 0.1 to 10 parts by weight, and preferably 0.1 to 5.0 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in that it is possible to realize a degree of fiberization appropriate for producing a self-supporting sheet, while also exhibiting excellent resistance characteristics.

[0198]

[0199] Meanwhile, a dry electrode according to the present invention can be manufactured by including a step S1 of obtaining a composite composition by mixing an electrode active material, a conductive material, and a fiberizable binder; a step S2 of kneading the composite composition while applying a shear force to form a mixed aggregate; a step S3 of pulverizing the mixed aggregate to manufacture an electrode powder; and a step S4 of sheet-forming the electrode powder into an electrode composite film by roll-rolling.

[0200]

[0201] (Stage S1)

[0202] This is a step of forming a composite composition by mixing an electrode active material, a conductive material, and a binder. A detailed description of the electrode active material, the conductive material, and the binder is omitted as described above, and at this time, the mixing is performed so that the electrode active material, the conductive material, and the binder can be uniformly distributed. Since they are mixed in a powder form, they can be mixed by various methods without limitation as long as they enable simple mixing thereof. However, since the present invention is manufactured as a dry electrode that does not use a solvent, the mixing can be performed by dry mixing, and the materials can be mixed by putting them into a device such as a mixer or blender.

[0203]

[0204] At this time, the mixing can be performed in a mixer at 100 rpm to 5,000 rpm for 1 to 60 minutes. Preferably, it can be performed at 500 rpm to 4,000 rpm for 3 to 45 minutes, and more preferably, it can be performed at 100 rpm to 3,000 rpm for 5 to 30 minutes. When performed within the above range, the materials can be uniformly mixed, thereby improving battery performance.

[0205]

[0206] The control conditions of the above mixing process can determine how uniformly the binder is fiberized in the subsequent mixing process of step S2. If the mixing is not uniform, even if fiberization occurs uniformly, non-uniform parts may occur on the entire side of the film. Therefore, it may be desirable to perform the mixing process under the conditions described above.

[0207]

[0208] (S2 stage)

[0209] Next, a fiberization process using a binder capable of forming a three-dimensional fiber network structure can be performed on the composite material composition obtained from the above mixing to produce a mixed aggregate. Preferably, a step of kneading the composite material composition while applying a shear force to form a mixed aggregate can be performed.

[0210] The above fiberization process can be performed, for example, through mechanical milling or kneading, and there are no particular limitations as long as it is generally performed, but preferably, it can be performed through high-temperature, low-shear kneading, and can be performed, for example, through a kneader. By such kneading, the binder capable of forming the three-dimensional fiber network structure is fiberized, thereby combining or linking the electrode active material and conductive powders, so that a mixed aggregate with a solid content of 100% can be formed.

[0211] The above mixing can be performed at a speed of 10 rpm to 100 rpm, and more specifically, at a speed of 20 rpm to 70 rpm. In addition, the mixing can be performed for 1 minute to 120 minutes, and more specifically, for 2 minutes to 60 minutes. When the above range is satisfied, appropriate fiberization can proceed, and a three-dimensional fiber network structure that is uniformly fiberized overall and structurally stable can be formed.

[0212] In addition, the above mixing can be performed under conditions of high temperature and pressure higher than atmospheric pressure, and more specifically, under conditions of pressure higher than atmospheric pressure.

[0213] More specifically, the mixing can be performed at a temperature of 50°C to 230°C, preferably 90°C to 200°C. When mixing is performed at a high temperature such as the above range, the fiberization and lump formation of the binder through mixing can be effectively achieved, and the problem of breakage of the fiberized binder can be appropriately prevented.

[0214] Additionally, the process can be performed under a pressure higher than atmospheric pressure, specifically, a pressure of 1 to 3 atm. When performed within the above range, the problem of breakage of the binder undergoing fiberization can be appropriately prevented, and the problem of the density of the aggregates becoming excessively high can be prevented.

[0215] That is, according to the present invention, when a high-temperature-low-shear mixing process is performed under high-temperature and higher-than-normal pressure conditions instead of high-shear mixing, the intended effect of the present invention can be achieved.

[0216]

[0217] (S3 stage)

[0218] Next, a step of pulverizing the mixed aggregate produced through the above mixing step to obtain powder for electrodes may be performed. Preferably, a step of pulverizing the mixed aggregate to produce powder for electrodes may be performed.

[0219] The mixed aggregates produced through the above mixing process can be directly pressed into a sheet shape (sheeting, for example, using a calendaring process). However, in this case, the mixed aggregates may need to be pressed under strong pressure and high temperature to produce a thin film, which may result in problems such as the film density becoming too high or the inability to obtain a uniform film. Therefore, the mixed aggregates produced as described above are pulverized to produce a powder for electrodes.

[0220] The device used for the above crushing is not particularly limited, but it can preferably be performed by a device such as a blender or grinder.

[0221] The above grinding can be performed at a speed of 1000 rpm to 15000 rpm for 1 to 30 minutes, preferably at a speed of 3000 rpm to 10000 rpm for 5 to 20 minutes. When performed within the above range, sufficient grinding can be achieved to produce powder of a size suitable for film formation, and a large amount of fine powder can be prevented from being generated in the mixed aggregate.

[0222] The average particle size of the above electrode powder may be 10 µm to 3,000 µm, specifically 50 µm to 1,500 µm, and more specifically 100 µm to 700 µm. When the above range is satisfied, an electrode composite film having a uniform thickness and density can be formed, and excellent electrode composite film properties can be secured.

[0223]

[0224] Meanwhile, the electrode powder may additionally include fillers, although not essential, to suppress electrode expansion. The fillers are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery, and examples thereof include at least one selected from olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0225]

[0226] (Stage S4)

[0227] Next, the electrode powder is rolled into a sheet and formed into an electrode composite film. Preferably, this may be a process of manufacturing an electrode composite film in the form of a self-supporting sheet by heating and pressing the electrode powder using a rolling roll in a roll-to-roll process including two or more pairs of rolling rolls.

[0228] The above roll-to-roll process may include a roll press section in which roll rolling is performed, and the roll press section may have rolling rolls arranged in pairs facing each other, and may have a plurality of rolling rolls arranged continuously, and such rolling rolls may be arranged continuously in the roll press section. When a plurality of rolling rolls are arranged continuously, the temperature and main speed ratio (rotation speed ratio of a pair of rolls) of each roll may be the same or different.

[0229]

[0230] According to one embodiment of the present invention, the temperature of the rolling roll may be 50°C to 200°C, preferably the temperature of the calendar roll may be 50°C to 180°C, and more preferably the temperature of the calendar roll may be 60°C to 150°C. When the above range is satisfied, an electrode composite film having excellent processability and uniformity can be obtained.

[0231]

[0232] The rotation speed ratio of the rolling rolls provided in the roll-to-roll process of the above step S4 can be appropriately adjusted independently within a range of 1:1 to 1:10. In addition, the manufactured electrode composite film can be put back into the roll press section and subjected to heat pressing 1 to 10 times to adjust it to an appropriate thickness.

[0233]

[0234] According to one embodiment of the present invention, the step S4 may include a step (S4a) of pre-sheeting the electrode powder to obtain a powder-sheeting film; and a step (S4b) of sheeting the powder-sheeting film two or more times to produce an electrode composite film. That is, after the powder is converted into a sheet in step S4a, the sheet may be rolled in step S4b to improve strength and satisfy the porosity and loading required for the electrode.

[0235]

[0236] Meanwhile, according to one embodiment of the present invention, a step of laminating the electrode composite film on one or both sides of a current collector and then inserting it into a lamination unit for lamination may be further included. Through this, the electrode composite film is rolled onto the current collector, thereby manufacturing a dry electrode in which the electrode composite film is arranged on the current collector.

[0237] The above lamination may be performed by rolling and attaching the electrode composite film onto a current collector. The above lamination may be performed by a roll press method using a lamination unit including a lamination roll.

[0238]

[0239] According to one embodiment of the present invention, the lamination roll can be maintained at a temperature of 20°C to 200°C.

[0240]

[0241] The above lamination may preferably be performed after one or more, or two or more, heat pressings, and then one or more additional heat pressings may be performed to achieve the desired porosity. When lamination is performed in the middle of calendering in this manner, the appearance of the electrode and the calendering processability may be superior to lowering the porosity in the composite film state before lamination. Control of the porosity through additional heat pressing can be achieved by controlling the compression ratio by adjusting the roll gap, and the compression ratio can be derived by the following equation 2.

[0242] [Relationship 2]

[0243] Compression ratio (%) = [(electrode thickness) - (roll gap)] / [(electrode thickness) - (current collector thickness)]

[0244]

[0245] lithium secondary battery

[0246] Hereinafter, a lithium secondary battery according to the present invention will be described.

[0247]

[0248] A lithium secondary battery according to the present invention may include a dry electrode according to the present invention. For example, the lithium secondary battery may include a secondary battery including a liquid electrolyte and an all-solid-state battery including a solid electrolyte.

[0249] Specifically, it includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and / or the negative electrode may be a dry electrode, and specifically, it may be a lithium secondary battery including the dry electrode, negative electrode, separator, and electrolyte according to the present invention. When only one of the positive electrode or the negative electrode is a dry electrode according to the present invention, the other electrode may be an electrode manufactured through a conventional wet manufacturing method.

[0250]

[0251] In the case where the lithium secondary battery according to one embodiment of the present invention is a secondary battery including a liquid electrolyte, a separator may be included between a plurality of electrodes. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used without particular limitation, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may also be used. Additionally, a coated separator containing ceramic components or polymeric materials may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0252] Additionally, if the lithium secondary battery is an all-solid-state battery, the solid electrolyte membrane can be manufactured to perform the function of the separator.

[0253]

[0254] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0255]

[0256] In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

[0257] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0258] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include 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 dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0259]

[0260] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is 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 - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0261]

[0262] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10.0 wt% based on the total weight of the electrolyte.

[0263]

[0264] In addition, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0265] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0266] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0267]

[0268] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0269]

[0270] Examples and Comparative Examples

[0271] Example 1: Preparation of expandable carbon nanotube powder

[0272] Bundled carbon nanotubes (BET surface area: 256 m) containing multi-walled carbon nanotube units (average diameter: 10 nm) 2 / g, bulk density: 0.110 g / cc) was introduced into a disintegrator (Galaxy Jet Mill, JEM Co.) and disintegrated in a solvent-free state to produce expanded carbon nanotube powder.

[0273] At this time, the injection pressure of the jet nozzle included in the crushing device was 5 bar.

[0274]

[0275] Comparative Example 1: Preparation of expandable carbon nanotube powder

[0276] The average diameter of the multi-walled carbon nanotube unit is 6 nm, and the BET specific surface area of ​​the bundled carbon nanotube is 380 m 2 / g and the bulk density was 0.080 g / cc, and an expanded carbon nanotube powder was manufactured in the same manner as in Example 1.

[0277]

[0278] Comparative Example 2: Preparation of expandable carbon nanotube powder

[0279] The average diameter of the multi-walled carbon nanotube unit is 8 nm, and the BET specific surface area of ​​the bundled carbon nanotube is 300 m 2 / g and the bulk density was 0.080 g / cc, and an expanded carbon nanotube powder was manufactured in the same manner as in Example 1.

[0280]

[0281] Comparative Example 3: Preparation of expandable carbon nanotube powder

[0282] The average diameter of the multi-walled carbon nanotube unit is 8 nm, and the BET specific surface area of ​​the bundled carbon nanotube is 260 m 2 / g and the bulk density was 0.12 g / cc, and an expanded carbon nanotube powder was manufactured in the same manner as in Example 1.

[0283]

[0284] Experimental Example 1: Measurement of electrical conductivity, packing density, slope, and bulk density of expanded carbon nanotube powders.

[0285] 1) Measurement of electrical conductivity (S / cm) and packing density (g / cc) of expanded carbon nanotube powder: The expanded carbon nanotube powder manufactured in Example 1 and Comparative Examples 1 to 3 was placed in a cylindrical punch-die jig (diameter: 6.38 mm, width: 0.38 cm). 2 ) was injected into the press machine, and the force was increased from 200 kgf to 1600 kgf, and the electrical conductivity was measured at every 200 kgf unit, and the volume decreased as the force increased was also measured to determine the filling density.

[0286] The measurement results are shown in Table 1 below.

[0287]

[0288] 2) Measurement of bulk density of inclined and expanded carbon nanotube powders when electrical conductivity (S / cm) and packing density (g / cc) are plotted on the y-axis and x-axis, respectively:

[0289] For the expandable carbon nanotube powders manufactured in Example 1 and Comparative Examples 1 to 3, the electrical conductivity (S / cm) and packing density (g / cc) at the specific force (kgf) measured in 1) were plotted on the y-axis and x-axis, respectively, to obtain the slope. At this time, the slopes of Example 1 and Comparative Examples 1 to 3 are shown in Fig. 1.

[0290] Additionally, bulk density was measured by filling the expanded carbon nanotube powder into a 25 mL container of known weight, measuring the weight, and then converting the density.

[0291] The measurement results are shown in Table 2 below.

[0292]

[0293] Force (kgf) 200 400 600 800 1000 1200 1400 1600 Pressure (MPa) 51.6 10 3 15 5 20 6 25 8 30 9 36 14 13 Example 1 Filling density (g / cc) 0.43 5 0.57 7 0.69 20.79 9 0.90 5 1.01 8 1.13 4 1.26 7 Electrical conductivity (S / cm) 25.7 5 3 9.8 5 1.7 16 2.86 7 4.0 8 5.5 19 8 11 2 Comparative example 1 Filling density (g / cc) 0.37 20.49 50.59 0.67 50.75 40.83 40.91 50.99 9 Electrical conductivity (S / cm) Conductivity (S / cm) 16.25 25.17 32.54 39.36 45.75 52.35 9.04 65.93 Comparative Example 2 Filling Density (g / cc) 0.41 20.53 10.62 90.71 70.79 70.87 40.95 61.039 Electrical Conductivity (S / cm) 11.1 42 0.64 27.78 34.33 40.48 46.59 53.17 59.53 Comparative Example 3 Filling Density (g / cc) 0.40 9 0.54 60.65 60.75 90.86 0.96 71.07 81.20 2 Electrical Conductivity (S / cm) 17.66 29.30 39.42 48.99 58.43 68.22 78.88 90.4

[0294] When the electrical conductivity (S / cm) and packing density (g / cc) are plotted on the y-axis and x-axis, respectively, the slope Bulk density (g / cc) Example 11040.009 Comparative Example 1800.008 Comparative Example 2770.034 Comparative Example 3920.019

[0295] Experimental Example 2: Measurement of electrode layer resistance (Ωcm)

[0296] 1) Preparation of dry electrode: The expandable carbon nanotube powders prepared in Example 1 and Comparative Examples 1 to 3 were prepared as conductive materials. Thereafter, lithium nickel cobalt manganese aluminum oxide (LNF) as an electrode active material, each of the aforementioned conductive materials, and polytetrafluoroethylene (PTFE) as a fiberizable binder were placed in a blender and mixed at 1500 rpm for 10 minutes to prepare each composite composition.

[0297] Thereafter, the above composite composition was put into a kneader and kneaded at a rotation speed of 50 rpm at a temperature of 150°C and a pressure of 1.1 atm for 10 minutes to produce a mixed aggregate, and the mixed aggregate was put into a blender, ground at 5000 rpm for 10 minutes, and classified through a sieve having pores of 1 mm in size to produce powder for electrodes of Example 1 and Comparative Examples 1 to 3.

[0298] The above electrode powder was sheeted onto a calendaring roll (roll diameter: 88 mm, roll temperature: 100°C) in a roll-to-roll process to produce an electrode composite film. Thereafter, one sheet of the electrode composite film was placed on one side of an aluminum foil (thickness: 15 μm) having a conductive primer layer formed thereon, and laminated using a roll press maintained at 100°C to produce a dry electrode. At this time, the porosity of the electrode composite film was 23.5%.

[0299]

[0300] 2) Measurement of electrode layer resistance: For the dry electrode manufactured above, after cutting it into 30 mm x 50 mm, a current of 100 μA was applied to the electrode using the MP resistance measurement method, and the resistivity (Ωcm) value for an arbitrary point inside the electrode composite film was measured 6 times using the potential difference measured between 46 probes, and the average value was calculated.

[0301] The measurement results are shown in Table 3 below.

[0302]

[0303] Electrode layer resistance (Ωcm) Example 112.8 Comparative example 137.9 Comparative example 234.2 Comparative example 323.1

[0304] Referring to Table 3 above, it can be seen that in the case of Example 1, which satisfies the above-mentioned slope range, the electrode layer resistance is superior to that of Comparative Examples 1 to 3.

Claims

1. An expanded carbon nanotube powder containing carbon nanotube units, When the electrical conductivity (S / cm) and filling density (g / cc) are plotted on the y-axis and x-axis, respectively, the slope is 95 or more, The above-mentioned electrical conductivity (S / cm) and the above-mentioned packing density (g / cc) are measured while applying a pressure of 50 MPa to 420 MPa to the above-mentioned expanded carbon nanotube powder.

2. In claim 1, Expandable carbon nanotube powder having a slope of 100 to 125.

3. In claim 1, Expanded carbon nanotube powder having a bulk density of 0.022 g / cc or less.

4. In claim 1, Expandable carbon nanotube powder having an electrical conductivity of 70 S / cm or more when the filling density of the above expandable carbon nanotube powder is 1.0 g / cc.

5. In claim 1, The expanded carbon nanotube powder has a ratio of true density (TD) to bulk density (BD) (TD / BD) of 91 to 673.

6. In claim 1, Expanded carbon nanotube powder having a true density (TD) of 1.850 g / cc to 2.500 g / cc.

7. In claim 1, The BET specific surface area of ​​the above expanded carbon nanotube powder is 200 m 2 / g to 1000m 2 / g, expandable carbon nanotube powder.

8. In claim 1, The above carbon nanotube unit is an expanded carbon nanotube powder, which is a multi-walled carbon nanotube unit.

9. In claim 8, Expandable carbon nanotube powder, wherein the aspect ratio of the multi-walled carbon nanotube unit is 30 to 10000.

10. In claim 8, Expandable carbon nanotube powder, wherein the average length of the multi-walled carbon nanotube units is 0.1 μm to 100 μm.

11. In claim 8, Expandable carbon nanotube powder, wherein the average diameter of the multi-walled carbon nanotube units is 5 nm to 200 nm.

12. In claim 8, The BET surface area of ​​the above multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g, expandable carbon nanotube powder.

13. In claim 8, The above multi-walled carbon nanotube unit is an expanded carbon nanotube powder having three or more graphene layers arranged in parallel with respect to the axis of the above multi-walled carbon nanotube unit.

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

15. A lithium secondary battery comprising the dry electrode of claim 14.

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