Electrode and secondary battery including electrode

Abstract

To provide an electrode having improved electrode adhesion, electrical conductivity, and life characteristics by including a carbon nanotube structure having a relatively uniform size and capable of minimizing surface defects.SOLUTION: The present invention relates to an electrode including an electrode active material layer, the electrode active material layer including an electrode active material, a conductive material, and a sodium dodecyl sulfate (SDS), the conductive material including a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, and a weight ratio of the carbon nanotube structure and the SDS is 1:3 to 1:30. The present invention also relates to a secondary battery including the electrode.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0036124 filed on Mar. 19, 2020, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to an electrode and a secondary battery including the same, and includes an electrode active material layer, and the electrode active material layer includes an electrode active material, a conductive material, and SDS (Sodium dodecyl sulfate). The conductive material includes a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, and the weight ratio of the carbon nanotube structure and the SDS can be 1:3 to 1:30.

Background Art

[0003] As a typical example of an electrochemical device using electrochemical energy, a secondary battery is mentioned, and its usage area is gradually expanding. Recently, with the development of technologies related to portable devices such as portable computers, mobile phones, and cameras and the increasing demand, the demand for secondary batteries as an energy source has increased rapidly. Among such secondary batteries, many studies have been conducted on lithium secondary batteries with high energy density, that is, high capacity, and they have also been commercialized and widely used.

[0004] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode and the negative electrode generally consist of an electrode current collector and an electrode active material layer formed on the electrode current collector, and the electrode active material layer is manufactured by applying an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc. on the electrode current collector, drying it, and then rolling it.

[0005] On the one hand, conventionally, as a conductive material for secondary batteries, dot-shaped conductive materials such as carbon black have been mainly used. However, in the case of such dot-shaped conductive materials, there has been a problem that the effect of improving electrical conductivity is not sufficient. In order to improve such problems, research on methods of applying linear conductive materials such as carbon nanotubes (Carbon NanoTube, CNT) and carbon nanofibers (Carbon NanoFiber, CNF) and sheet-shaped conductive materials such as graphene has been actively conducted.

[0006] However, sheet-shaped conductive materials such as graphene are excellent in electrical conductivity. However, single-layer graphene with a thin thickness has a problem that it is difficult to manufacture. When using thick graphene, there is a problem that battery efficiency decreases. In addition, in the case of sheet-shaped conductive materials, there is a problem that the mobility of the electrolyte is restricted inside the battery due to wide sheet-like contact.

[0007] On the other hand, in the case of linear conductive materials such as carbon nanotubes and carbon nanofibers, although they are excellent in electrical conductivity, due to the characteristics of the material itself that grows in a bundle type or intertwined type, the dispersibility in the slurry is poor, resulting in a decrease in coating properties and processability, and there is a problem that they are not uniformly distributed in the electrode active material layer. In order to improve such problems, there have been attempts to introduce functional groups or the like into the linear conductive material to improve the dispersibility. However, in this case, there is a problem that surface side reactions occur due to the presence of the functional group, resulting in a decrease in electrochemical characteristics.

[0008] In addition, in order to use carbon nanotubes, it is common to use a conductive material dispersion liquid in which bundle-type carbon nanotubes are dispersed using a dispersant. However, in the dispersion process, many surface defects of carbon nanotubes occur due to external forces, resulting in a decrease in the mechanical strength and electrical conductivity of carbon nanotubes, an increase in electrode resistance, and a decrease in battery life. In addition, the size of the dispersed carbon nanotubes is not uniform, and there is also a problem of a decrease in electrode adhesion and electrode life.

[0009] Therefore, there is a need to develop an electrode that can minimize surface defects and includes carbon nanotubes having a relatively constant size. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] One problem to be solved by the present invention is to provide an electrode with improved electrode adhesion, conductivity, and lifespan characteristics by minimizing surface defects and including a carbon nanotube structure having a relatively constant size.

[0011] Another problem to be solved by the present invention is to provide a secondary battery including the electrode. MEANS FOR SOLVING THE PROBLEMS

[0012] According to an embodiment of the present invention, there is provided an electrode including an electrode active material layer, the electrode active material layer including an electrode active material, a conductive material, and SDS (Sodium dodecyl sulfate), the conductive material including a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units are bonded to each other, and the weight ratio of the carbon nanotube structure and the SDS being 1:3 to 1:30.

[0013] According to another embodiment of the present invention, there is provided a secondary battery including the electrode. EFFECTS OF THE INVENTION

[0014] The electrode according to the present invention includes a network structure in which rope-shaped carbon nanotube structures (long fibrous) are connected to each other, so that a conductive path can be effectively formed within the electrode. Thereby, even with a very small content of the conductive material, the electrical conductivity within the electrode can be greatly improved. Further, the electrode active material layer is firmly fixed by the carbon nanotube structure forming the network structure, and the electrode adhesion is improved. Further, SDS (Sodium dodecyl sulfate) is included in the electrode, and the SDS minimizes the occurrence of defects on the surface of the carbon nanotube structure during the formation of the carbon nanotube structure, so that the resistance of the electrode is reduced and the battery life can be improved. Furthermore, the diameter of the carbon nanotube structure is formed at a predetermined level, and the electrode adhesion and the battery life characteristics can be further improved.

Brief Description of Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0017] The terms used in this specification are used merely for the purpose of describing exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless they have clearly different meanings in the context.

[0018] In this specification, terms such as "including", "comprising", or "having" are intended to affirm the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0019] In this specification, "%", unless otherwise explicitly indicated, means weight %.

[0020] In this specification, the "specific surface area" 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-mini II manufactured by BEL Japan, Inc.

[0021] Hereinafter, the present invention will be specifically described.

[0022] Electrode The electrode according to the present invention includes an electrode active material layer, and the electrode active material layer includes an electrode active material, a conductive material, and SDS (Sodium dodecyl sulfate). The conductive material includes a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units are bonded to each other, and the weight ratio of the carbon nanotube structure to the SDS can be 1:3 to 1:30.

[0023] The electrode can include an electrode active material layer. The electrode can further include a current collector, and in such a case, the electrode active material layer can be disposed on one or both sides of the current collector.

[0024] The current collector is not particularly limited as long as it is a material that does not cause chemical changes in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, those surface-treated with carbon, nickel, titanium, silver, etc. on their surfaces, or fired carbon, etc. can be used.

[0025] The current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. Further, the electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0026] The electrode active material layer can contain an electrode active material, a conductive material, and SDS.

[0027] The electrode active material can be a positive electrode active material or a negative electrode active material generally used in the art, and its type is not particularly limited.

[0028] For example, as the positive electrode active material, lithium oxides containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium can be used. More specifically, the lithium oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O, LiMnO3, 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-Y1 Mn Y1 O2 (where 0 < Y1 < 1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y2 Co Y2 O2 (where 0 < Y2 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y3 Mn Y3O2 (where 0 < Y3 < 1), LiMn 2-Z2 Co Z2 O4 (where 0 < Z2 < 2), etc.), lithium-nickel-cobalt-manganese-based oxides (e.g., Li(Ni P1 Co Q1 Mn R1 )O2 (where 0 < P1 < 1, 0 < Q1 < 1, 0 < R1 < 1, P1 + Q1 + R1 = 1) or Li(Ni P2 Co Q2 Mn R2 )O4 (where 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, P2 + Q2 + R2 = 2), etc.), or lithium-nickel-cobalt-manganese-other metal (M) oxides (e.g., Li(Ni P3 Co Q3 Mn R3 M 1 S )O2 (where M 1 is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W, and Mo, and P3, Q3, R3, and S are, as atomic fractions of independent elements, 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, and P3 + Q3 + R3 + S = 1), etc.), etc. may be mentioned, and any one or two or more of these compounds can be included.

[0029] On the other hand, as the negative electrode active material, for example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides such as SiO v (0 < v < 2), SnO2, vanadium oxides, and metal oxides capable of doping and dedoping lithium such as lithium vanadium oxides; or composites containing the metallic compounds and carbonaceous materials such as Si-C composites, Ag-C composites, or SN-C composites, etc. may be mentioned, and any one or two or more of these mixtures can be used. Also, a thin film of metallic lithium can be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used.

[0030] The electrode active material as described above can be contained in an amount of 70% to 99.5% by weight, preferably 80% to 99% by weight, based on the total weight of the electrode active material layer. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0031] The conductive material can include a carbon nanotube structure.

[0032] The carbon nanotube structure can include a plurality of single-walled carbon nanotube units. Specifically, the carbon nanotube structure can be a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other. More specifically, the carbon nanotube structure can be a carbon nanotube structure in which 2 to 4,500 single-walled carbon nanotube units are bonded to each other. Even more specifically, in consideration of the dispersibility of the carbon nanotube structure and the durability of the electrode, it is most preferable that the carbon nanotube structure is a carbon nanotube structure in which 2 to 50 single-walled carbon nanotube units are bonded to each other.

[0033] In the carbon nanotube structure, the single-walled carbon nanotube units can be arranged in parallel and bonded to each other (a cylindrical structure having flexibility with the major axes of the units bonded in parallel to each other), thereby forming the carbon nanotube structure. In the electrode, the carbon nanotube structures can be connected to each other to exhibit a network structure.

[0034] Conventional electrodes containing carbon nanotubes generally involve manufacturing a conductive material dispersion liquid by dispersing bundle type or entangled type carbon nanotubes (single-wall carbon nanotube units or multi-wall carbon nanotube units that are stuck together or entangled with each other) in a dispersion medium, and then manufacturing using the said conductive material dispersion liquid. Here, within the conventional conductive material dispersion liquid, the carbon nanotubes are completely dispersed and exist as a conductive material dispersion liquid in which single-stranded carbon nanotube units are dispersed. The said conventional conductive material dispersion liquid has the carbon nanotube units easily cut by an excessive dispersion process and has a shorter length compared to the initial stage. Also, during the rolling process of the negative electrode, the carbon nanotube units can be easily cut, and during the driving of the battery, there is further a problem that the carbon nanotube units are cut according to the volume change of the electrode active material. Therefore, there is a problem that the conductivity of the electrode decreases and the input characteristics, output characteristics, and life characteristics of the battery deteriorate. Furthermore, in the case of multi-wall carbon nanotube units, the defect rate of the structure is high due to the mechanism of nodular growth (there are nodules due to defects generated during the growth process rather than smooth linear). Therefore, during the dispersion process, the multi-wall carbon nanotube units are more easily cut, and the multi-wall carbon nanotube units cut short by π-π stacking due to the carbon surface structure of the units are likely to aggregate with each other. Therefore, it is difficult to exist more uniformly dispersed within the electrode slurry.

[0035] In contrast, in the case of the carbon nanotube structure included in the electrode of the present invention, since 2 to 5,000 single-wall carbon nanotube units that maintain high crystallinity with relatively few structural defects are bonded in parallel to each other, they are not cut even during the driving of the battery, and the length can be smoothly maintained, and the conductivity of the electrode can be maintained. In addition, due to the high conductivity of the single-wall carbon nanotube units having high crystallinity, the conductivity of the electrode can be increased, and the input characteristics, output characteristics, and life characteristics of the battery can be greatly improved. Further, in the electrode, the carbon nanotube structures can be connected to each other to have a network structure, suppressing excessive volume changes of the electrode active material, securing a strong conductive path, suppressing the detachment of the electrode active material, and greatly improving the electrode adhesion force.

[0036] In the carbon nanotube structure, the average diameter of the single-wall carbon nanotube units can be 0.5 nm to 10 nm, specifically 1 nm to 9 nm, and more specifically 1 nm to 6 nm. When the average diameter is satisfied, there is an effect that the conductivity in the electrode can be maximized even with a very small content of the conductive material. The average diameter corresponds to the average value of the 100 single-wall carbon nanotubes with the largest average diameter and the 100 single-wall carbon nanotubes with the smallest average diameter when the manufactured electrode is observed by TEM.

[0037] In the carbon nanotube structure, the average length of the single-walled carbon nanotube unit can be 1 μm to 100 μm, specifically 5 μm to 50 μm. When the average length is satisfied, a long conductive path for the conductive connection between the electrode active materials can be formed, a unique network structure can be formed, and even with a very small content of the conductive material, the conductivity in the electrode can be maximized. The average length corresponds to the average value of the top 100 single-walled carbon nanotubes with a large average length and the bottom 100 single-walled carbon nanotubes when the manufactured electrode is observed by TEM.

[0038] The specific surface area of the single-walled carbon nanotube unit can be 500 m 2 / g to 1,000 m 2 / g, specifically 600 m 2 / g to 800 m 2 / g. When the above range is satisfied, due to the large specific surface area, the conductive path in the electrode can be ensured smoothly, and even with a very small content of the conductive material, the conductivity in the electrode can be maximized. The specific surface area of the single-walled carbon nanotube unit can be specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan.

[0039] The average diameter of the carbon nanotube structure can be 2 nm to 200 nm, specifically 5 nm to 150 nm, specifically 5 nm to 50 nm, for example, 7 nm to 20 nm. When the above range is satisfied, it is effective for the formation of a conductive network structure, is advantageous for the connection between the active materials, and excellent electrical conductivity can be realized. The average length corresponds to the average value of the diameters of the top 100 carbon nanotube structures with a large average length and the bottom 100 carbon nanotube structures when the manufactured electrode is observed by SEM.

[0040] The average length of the carbon nanotube structure can be from 1 μm to 500 μm, specifically from 5 μm to 300 μm, and specifically from 5 μm to 150 μm. When the above range is satisfied, it is effective for the formation of the conductive network structure, advantageous for the connection between the active materials, and excellent electrical conductivity can be realized. The average length corresponds to the average value of the lengths of the top 100 carbon nanotube structures with large average length and the bottom 100 carbon nanotube structures when the manufactured electrode is observed by SEM.

[0041] The carbon nanotube structure can be contained in the electrode active material layer at 0.01% by weight to 0.5% by weight, specifically at 0.01% by weight to 0.3% by weight. When the above range is satisfied, the conductive path of the electrode is ensured, the electrode resistance is maintained at a low level, and the life characteristics of the battery can be improved. When manufacturing the conductive material dispersion liquid, when the bundled carbon nanotubes are completely dispersed (as a general dispersion method, the single-chain carbon nanotube units are dispersed as far apart as possible), the carbon nanotube structure does not occur, or even if it occurs contrary to intention, it occurs in a very small amount (for example, 0.0005% by weight). That is, the above content range cannot be achieved by general methods.

[0042] In the case of the prior art where the electrode contains multi-walled carbon nanotube units, in order to complement the low conductivity of the multi-walled carbon nanotube units, a high content (for example, more than 0.5% by weight) of multi-walled carbon nanotube units had to be used. Also, when manufacturing the electrode through a conductive material dispersion liquid in which single-walled carbon nanotube units are completely dispersed, due to the problem of the single-walled carbon nanotube units being cut, the single-walled carbon nanotube units could not be used at a low content.

[0043] On the one hand, the carbon nanotube structure included in the electrode of the present invention has a form in which 2 to 5,000 single-walled carbon nanotube units are bonded in parallel to each other. Therefore, even during the driving of the battery, it is not cut and the length can be smoothly maintained, the conductivity of the electrode can be maintained, and the high conductivity of the single-walled carbon nanotube unit can ensure the smooth conductivity of the electrode. Thereby, even when the content of the carbon nanotube structure in the electrode is at a low level, the battery can be excellent in input characteristics, output characteristics, and life characteristics.

[0044] On the other hand, although not essential, the single-walled carbon nanotube unit may be surface-treated by oxidation treatment, nitridation treatment, etc. to improve the affinity of polyvinylidene fluoride.

[0045] The SDS can be disposed on the carbon nanotube structure. Specifically, the SDS is disposed on the single-walled carbon nanotube units included in the carbon nano-structure. The SDS serves as a kind of "surface protection agent" that minimizes the occurrence of surface defects of the carbon nanotube structure on the carbon nano-structure. Further, during the formation of the carbon nanotube structure, the SDS serves as a kind of "dispersion stabilizer" to enable the smooth dispersion of the carbon nanotube structure and to make the diameter of the carbon nanotube structure reach a certain level.

[0046] Figure 1 is a graph of the XPS analysis results for the carbon nanotube structures of Samples 1 to 5 (Samples 1 to 5 correspond to (a) to (e) in order). Sample 1 has no surface defect prevention substance arranged on the surface of the carbon nanotube structure, and Samples 2 to 5 have PBA (Pyrene Butyric Acid), PSA (Pyrene Sulfonic Acid), PMA (Pyrene Methyl - Amine), and SDS (Sodium Dodecyl - Sulfate) arranged on the surface of the carbon nanotube structure, respectively. Referring to Figure 1, it can be seen that except for Sample 5 using SDS, defects occur on the surface of the carbon nanotubes due to the dispersion process by mechanical external force, and fine peaks (the parts indicated by circles in Figure 1) appearing due to the bond between carbon and oxygen appear. That is, when using SDS containing a sulfonate anion functional group (SO3 - ) at the end of the linear straight - chain molecular structure, SDS can wrap the surface of the carbon nanotube structure linearly and minimize the defects of the carbon nanotube structure even during the dispersion process. When using SDS, no bond between carbon and oxygen was observed from the results of the XPS surface analysis in Figure 1. Also, due to the repulsive force of the sulfonate anion functional group (SO3 - ) at the end of SDS, the dispersion uniformity of the carbon nanotube structure can be improved.

[0047] The weight ratio of the carbon nanotube structure and the SDS can be 1:3 to 1:30, specifically 1:3 to 1:20, and more specifically 1:5 to 1:10. When the weight ratio of the carbon nanotube structure and the SDS deviates from 1:3 to 1:30 and the content of the SDS becomes less, there is a problem that the effect of minimizing the surface defects of the carbon nanotube structure by the SDS becomes insufficient. Conversely, when the content of the SDS deviates from 1:3 to 1:30 and is more, there is a problem that side reactions occur violently at the electrode and the electrical conductivity decreases.

[0048] On the one hand, most preferably, the weight ratio of the carbon nanotube structure and the SDS can be 1:5 to 1:10. When the range of 1:5 to 1:10 is satisfied, the surface defects of the carbon nanotube structure can be minimized, and the excessive dispersion (debundling) of the raw material, bundled carbon nanotubes, can be effectively suppressed, and carbon nanotube structures with preferable diameter and length can be derived.

[0049] The SDS can be contained in the electrode active material layer at 0.1 wt% to 5 wt%, specifically can be contained at 0.1 wt% to 3 wt%, more specifically can be contained at 0.1 wt% to 1.5 wt%, for example, 0.4 wt% to 1.0 wt%. When the above range is satisfied, the SDS can effectively prevent the surface defects of the carbon nanotube structure. Also, this range is a low level of content, because the SDS is not arranged on the completely dispersed single-wall carbon nanotube unit, but is arranged on the carbon nanotube structure in which single-wall carbon nanotube units are combined in parallel. Specifically, when a carbon nanotube structure is formed in which single-wall carbon nanotube units are combined in parallel instead of a completely dispersed single-wall carbon nanotube unit, the degree of separation of the bundled carbon nanotubes is small, so the single-wall carbon nanotube units inside the carbon nanotube structure are not directly subjected to shear force, and thus the possibility of surface defects occurring is relatively small. Therefore, even with a small content of SDS (0.1 wt% to 5 wt%), the surface defects of the carbon nanotube structure can be minimized.

[0050] The electrode active material layer may further contain polyvinylidene fluoride. The polyvinylidene fluoride can be a substance that begins to be included in the electrode from the conductive material dispersion liquid required for the production of the electrode slurry (optionally, it can be further added to reinforce the role of the binder during the production of the electrode slurry). The polyvinylidene fluoride serves to facilitate the smooth dispersion of the bundle-type carbon nanotubes in the conductive material dispersion liquid.

[0051] The weight average molecular weight of the polyvinylidene fluoride can be from 10,000 g / mol to 1,000,000 g / mol, and specifically can be from 100,000 g / mol to 900,000 g / mol. When the above range is satisfied, since the polyvinylidene fluoride can easily penetrate between the single-wall carbon nanotube units in the bundle-type carbon nanotubes, appropriate dispersion of the bundle-type carbon nanotubes is possible, and the stability on the conductive material dispersion liquid can be improved.

[0052] The polyvinylidene fluoride can be contained in the electrode active material layer at 0.1% by weight to 10.0% by weight, specifically at 0.2% by weight to 5.0% by weight, and more specifically at 0.2% by weight to 2.5% by weight. When the above range is satisfied, the carbon nanotube structure can be uniformly dispersed, the energy density of the electrode can be high, and the electrode adhesion can be excellent.

[0053] The polyvinylidene fluoride can contain a modified polyvinylidene fluoride modified with a hydrophilic functional group in order to improve the affinity with the single-wall carbon nanotube unit. Specifically, the polyvinylidene fluoride can contain a modified polyvinylidene fluoride containing at least one functional group among acid functional groups and ester functional groups. The functional group of the modified polyvinylidene fluoride can interact with the single-wall carbon nanotube unit to improve the dispersibility of the carbon nanotube structure and further improve the electrode adhesion.

[0054] The functional group can be contained in the modified polyvinylidene fluoride in an amount of 0.1% to 5% by weight, specifically, it can be contained in an amount of 0.3% to 3% by weight. When the above range is satisfied, the dispersibility of the carbon nanotube structure can be further improved, and the electrode adhesion can be further enhanced.

[0055] The modified polyvinylidene fluoride can be contained in an amount of 1% to 100% by weight based on the total weight of the polyvinylidene fluoride, specifically, it can be contained in an amount of 1% to 50% by weight, and more specifically, it can be 1% to 20% by weight. When the above range is satisfied, the dispersibility of the carbon nanotube structure becomes higher, and the electrode adhesion can be further improved.

[0056] The electrode active material layer can further contain a binder. The binder is for ensuring the adhesion between the electrode active materials or between the electrode active material and the current collector, and a general binder used in the technical field can be used, and its type is not particularly limited. Examples of the binder include vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds can be used.

[0057] The binder can be contained in an amount of 10% by weight or less, preferably 0.1% to 5% by weight, based on the total weight of the electrode active material layer. When the content of the binder satisfies the above range, an increase in electrode resistance can be minimized and excellent electrode adhesion can be achieved.

[0058] Method for manufacturing electrode Next, a method for manufacturing the electrode of the present invention will be described.

[0059] The method for manufacturing the electrode of the present invention includes: (1) a step of introducing bundle-type single-walled carbon nanotubes and SDS into a dispersion medium and performing a first treatment by ultrasonic crushing to prepare a mixture; (2) adding polyvinylidene fluoride to the mixture and performing a second treatment by ultrasonic crushing to produce a conductive material dispersion liquid containing a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and (3) a step of forming an electrode slurry containing the conductive material dispersion liquid and an electrode active material, and the weight ratio of the carbon nanotube structure and the SDS can be 1:3 to 1:30. By the above method, the electrode of the above-described embodiment can be manufactured. Since the SDS and the carbon nanotube structure are the same as those in the above-described embodiment, the description thereof will be omitted.

[0060] (1) Step of preparing a mixture The mixture can be manufactured by introducing bundle-type carbon nanotubes and SDS into a dispersion medium and then performing a first treatment by ultrasonic crushing. The bundle-type carbon nanotubes are those in which the above-described single-walled carbon nanotube units are bonded and exist in a bundle shape, and generally contain 2 or more, substantially 500 or more, for example, 5,000 or more single-walled carbon nanotube units.

[0061] The bundled single-walled carbon nanotubes can be contained in the mixture at 0.1% to 1.0% by weight, specifically, can be contained at 0.2% to 0.5% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes can be dispersed at an appropriate level, an appropriate level of carbon nanotube structure can be formed, and the dispersion stability can be improved.

[0062] The SDS can be contained in the mixture at 0.1% to 20% by weight, specifically, can be contained at 1% to 10% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes can be dispersed at an appropriate level, and finally a carbon nanotube structure can be formed, and the SDS can be disposed on the carbon nanotube structure to play a role as a surface protecting agent. Thereby, the surface defects of the carbon nanotube structure can be minimized.

[0063] Examples of the dispersion medium include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. Any one or a mixture of two or more of these can be used, but it is not limited thereto. More specifically, the dispersion medium can be N-methylpyrrolidone (NMP).

[0064] In the mixture, the solid content can be from 0.1 wt% to 20 wt%, specifically it can be from 1 wt% to 10 wt%. When the above range is satisfied, the bundled single-walled carbon nanotubes can be dispersed at an appropriate level, an appropriate level of carbon nanotube structure can be formed, and the dispersion stability can be improved. Also, the electrode slurry can have a viscosity and elasticity suitable for the electrode manufacturing process, which also helps to increase the solid content of the electrode slurry.

[0065] The first treatment step for dispersing the bundled carbon nanotubes in the mixture can be carried out using a mixing device such as sonification, homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer, clear mixer, spike mill or TK mixer. Among them, the sonification method is preferred. When strong-intensity ultrasonic waves are emitted into the solution during the sonification method, a large amount of vacuum bubbles are generated by extreme vibration. Such bubbles instantaneously entangle or grow with each other, but are violently and continuously fragmented by the subsequent vibration. When such continuous fragmentation of bubbles occurs, a strong shock wave is generated by the violent flow or vortex phenomenon of the solution, and the energy of such a shock wave can disperse (Debundling) the bundled carbon nanotubes. The sonification method enables nano-level fine dispersion without cutting the length direction of the single-walled carbon nanotubes in the bundled carbon nanotubes. For this reason, the sonification method is preferred.

[0066] The sonification method is as follows. Ultrasonic waves can be applied to the mixture to disperse the solid content in the mixture.

[0067] Here, the conditions under which the sonification method is carried out are as follows.

[0068] The ultrasonic crushing can be carried out at an output of 800 W to 1,500 W, specifically, it can be carried out at an output of 800 W to 1,200 W. The ultrasonic crushing can be carried out for 0.5 hour to 5 hours, specifically, it can be carried out for 1 hour to 3 hours. When the above range is satisfied, the bundled carbon nanotubes can be separated at an appropriate level, and the carbon nanotube structure can be formed. The implementation time means the total time to which ultrasonic crushing is applied. For example, when ultrasonic crushing is carried out several times, it means the total time over those several times.

[0069] (2) Step of manufacturing the conductive material dispersion The polyvinylidene fluoride can be added to the mixture, and the second treatment can be carried out by the ultrasonic crushing method.

[0070] The polyvinylidene fluoride can be contained in the mixture at 0.1 wt% to 20 wt%, specifically, it can be contained at 1 wt% to 10 wt%. When the above range is satisfied, the bundled single-walled carbon nanotubes can be dispersed at an appropriate level, an appropriate level of carbon nanotube structure can be formed, and the dispersion stability can be improved.

[0071] Since the polyvinylidene fluoride is the same as the polyvinylidene fluoride in the above-described embodiment, the description thereof is omitted.

[0072] In the conductive material dispersion, the weight ratio of the bundled carbon nanotubes to the polyvinylidene fluoride can be 1:0.1 to 1:10, specifically, it can be 1:1 to 1:10. When the above range is satisfied, the bundled single-walled carbon nanotubes can be dispersed at an appropriate level, an appropriate level of carbon nanotube structure can be formed, and the dispersion stability can be improved.

[0073] The conditions of the ultrasonic crushing method used in the second treatment are as follows.

[0074] The ultrasonic crushing can be carried out at an output of 800 W to 1,500 W, specifically, it can be carried out at an output of 800 W to 1,200 W. The ultrasonic crushing can be carried out for 0.5 hour to 5 hours, specifically, it can be carried out for 1 hour to 3 hours. When the above range is satisfied, the bundled carbon nanotubes can be separated at an appropriate level, and the carbon nanotube structure can be formed. The implementation time means the total time when ultrasonic crushing is applied. For example, when ultrasonic crushing is carried out several times, it means the total time over those several times.

[0075] The above conditions are for the bundled carbon nanotubes to be dispersed at an appropriate level and form a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units are joined in parallel with each other in the produced conductive material dispersion liquid. This can be achieved only when the composition of the mixture, ultrasonic crushing conditions, etc. are strictly adjusted.

[0076] Also, the SDS can be present on the carbon nanotube structure.

[0077] (3) Electrode Slurry Formation Step When the conductive material dispersion liquid is produced by the above process, an electrode active material is mixed with the conductive material dispersion liquid to form an electrode slurry. Here, as the electrode active material, the above-mentioned electrode active material can be used.

[0078] Also, the electrode slurry may further contain a binder and a solvent, if necessary. Here, as the binder, the binders of the above-described embodiments can be used. As the solvent, for example, amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone, etc. Any one or a mixture of two or more of these can be used, but it is not limited thereto. The solvent may be the same as or different from the dispersion medium previously used in the dispersion liquid, and preferably, it can be N-methylpyrrolidone (NMP).

[0079] On the one hand, here, the electrode active material can be contained in an amount of 70% to 99.5% by weight, preferably 80% to 99% by weight, based on the total solid content in the electrode slurry. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0080] Also, when a binder is further contained, the binder can be contained in an amount of 10% by weight or less, specifically 0.1% to 5% by weight, based on the total solid content in the electrode slurry.

[0081] The solid content in the electrode slurry can be 60% to 80% by weight, specifically 65% to 75% by weight. When the above range is satisfied, during drying after applying the electrode slurry, migration of the conductive material and the binder due to evaporation of the solvent can be suppressed, and an electrode with excellent electrode adhesion and electrical conductivity can be manufactured. Furthermore, during rolling, a high-quality electrode with less deformation of the electrode can be manufactured.

[0082] The carbon nanotube structure can be contained in an amount of 0.01% to 0.5% by weight, specifically 0.02% to 0.2% by weight, in the solid content of the electrode slurry. When the above range is satisfied, a conductive path of the electrode is ensured, the electrode resistance is maintained at a low level, and the life characteristics of the battery can be improved.

[0083] Next, the electrode slurry manufactured as described above is applied and dried to form an electrode active material layer. Specifically, the electrode active material layer can be formed by a method of applying the electrode slurry on an electrode current collector and then drying, or by a method of applying the electrode slurry on another support, peeling the film obtained from this support, and laminating it on the electrode current collector. If necessary, after the electrode active material layer is formed by the above method, a rolling process can be further implemented.

[0084] Here, drying and rolling can be performed under appropriate conditions in consideration of the physical properties of the electrode to be finally manufactured, and are not particularly limited.

[0085] Secondary battery Next, the secondary battery according to the present invention will be described.

[0086] The secondary battery according to the present invention includes the electrode of the present invention described above. Here, the electrode can be at least one of a positive electrode and a negative electrode. Specifically, the secondary battery according to the present invention can include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Here, at least one or more of the positive electrode and the negative electrode can be the electrode of the present invention described above, that is, an electrode including an electrode active material layer including an electrode active material and a carbon nanotube structure. Preferably, the electrode of the present invention can be a positive electrode. Since the electrode according to the present invention has been described above, specific description is omitted, and only the remaining components will be described below.

[0087] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used as a separator in a secondary battery can be used without particular limitation. Specifically, as the separator, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. can also be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and optionally, it can be used as a single-layer or multi-layer structure.

[0088] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0089] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt.

[0090] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate.

[0091] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used because they have a high dielectric constant as high-viscosity organic solvents and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte having high electrical conductivity can be manufactured and can be more preferably used.

[0092] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, as the anion of the lithium salt, F - , Cl - , I- , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One selected from the group consisting of can be used.

[0093] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride in order to improve the life characteristics of the battery, suppress the capacity reduction of the battery, improve the discharge capacity of the battery, and the like.

[0094] The secondary battery according to the present invention as described above has excellent electrode adhesion and excellent life characteristics at high temperatures as compared with conventional secondary batteries.

[0095] Hereinafter, the present invention will be described in more detail with reference to specific examples.

[0096] Production Example 1: Production of Conductive Material Dispersion 0.4 parts by weight of a bundle-type carbon nanotube composed of single-wall carbon nanotube units having an average diameter of 1.5 nm and an average length of 5 μm (specific surface area: 650 m 2 / g), 2.0 parts by weight of SDS (Sodium dodecyl sulfate), and 2.0 parts by weight of polyvinylidene fluoride (weight average molecular weight: 685,000 g / mol, Standard Homo-polymer) were prepared.

[0097] The bundle-type carbon nanotubes and SDS were added to N-methylpyrrolidone (NMP), a dispersion medium, and then the first ultrasonic crushing method was performed to produce a mixture in which the bundle-type carbon nanotubes were dispersed. The ultrasonic crushing was performed at an output of 1,000 W for 30 minutes.

[0098] After adding polyvinylidene fluoride to the mixture, ultrasonic crushing was performed (at an output of 1,000 W for 30 minutes) to produce a conductive material dispersion (solid content: 4.4% by weight) containing a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units were joined in parallel.

[0099] In the conductive material dispersion, the carbon nanotube structure was 0.4% by weight, the SDS was 2.0% by weight, and the polyvinylidene fluoride was 2.0% by weight.

[0100] Production Example 2: Production of Conductive Material Dispersion A conductive material dispersion was produced in the same manner as in Production Example 1, except that the polyvinylidene fluoride was a modified polyvinylidene fluoride containing 2.1% by weight of acid functional groups (weight average molecular weight: 880,000 g / mol).

[0101] Production Example 3: Production of Conductive Material Dispersion Liquid A bundle-type carbon nanotube composed of single-wall carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm (specific surface area of 650 m 2 / g) 0.4 parts by weight and polyvinylidene fluoride (weight average molecular weight: 685,000 g / mol, (Standard Homo-polymer)) 2.0 parts by weight were mixed in N-methylpyrrolidone (NMP) as a dispersion medium, and a mixture was produced so that the solid content became 2.2% by weight.

[0102] The mixture was stirred by an ultrasonic crushing method to disperse the bundle-type carbon nanotubes in the dispersion medium to produce a conductive material dispersion liquid. Here, the ultrasonic crushing was performed at an output of 1,000 W for 1.5 hours. The conductive material dispersion liquid contains a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units are bonded in parallel. In the conductive material dispersion liquid, the carbon nanotube structure was 0.4% by weight and the polyvinylidene fluoride was 2.0% by weight.

[0103] Production Example 4: Production of Conductive Material Dispersion Liquid A bundle-type carbon nanotube composed of multi-wall carbon nanotube units with an average diameter of 10 nm and an average length of 1 μm (specific surface area of 185 m 2 / g) 4.0 parts by weight, SDS (sodium dodecyl sulfate) 1.0 part by weight, and 0.8 part by weight of modified polyvinylidene fluoride containing 2.1% by weight of acid functional groups (weight average molecular weight 880,000 g / mol) were prepared.

[0104] After adding the bundle-type carbon nanotubes composed of the multi-wall carbon nanotube units and SDS to N-methylpyrrolidone (NMP) as the dispersion medium, the first ultrasonic crushing method was performed to produce a mixture in which the bundle-type carbon nanotubes were dispersed. The ultrasonic crushing was performed at an output of 1,000 W for 30 minutes.

[0105] After adding polyvinylidene fluoride to the mixture, ultrasonic crushing was performed (at an output of 1,000 W for 30 minutes) to produce a conductive material dispersion (solid content: 5.8% by weight).

[0106] In the conductive material dispersion, the multi-wall carbon nanotubes were 4.0% by weight, the SDS was 2.0% by weight, and the polyvinylidene fluoride was 0.8% by weight.

[0107] Production Example 5: Production of Conductive Material Dispersion 0.4 part by weight of bundle-type carbon nanotubes (specific surface area: 650 m 2 / g) composed of single-wall carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm, 0.5 part by weight of SDS (Sodium dodecyl sulfate), and 2.0 parts by weight of polyvinylidene fluoride (weight average molecular weight: 685,000 g / mol, standard homo-polymer) were prepared.

[0108] After adding the bundle-type carbon nanotubes and SDS to N-methylpyrrolidone (NMP) as the dispersion medium, the first ultrasonic crushing method was performed to produce a mixture in which the bundle-type carbon nanotubes were dispersed. The ultrasonic crushing was performed at an output of 1,000 W for 30 minutes.

[0109] After adding polyvinylidene fluoride to the mixture, ultrasonic crushing was performed (at an output of 1,000 W for 30 minutes) to produce a conductive material dispersion (solid content 4.4% by weight) containing a carbon nanotube structure in which 2 to 5,000 single-wall carbon nanotube units were joined in parallel.

[0110] In the conductive material dispersion, the carbon nanotube structure was 0.4% by weight, the SDS was 0.5% by weight, and the polyvinylidene fluoride was 2.0% by weight.

[0111] Referring to Figure 2, it can be seen that in the conductive material dispersion of Production Example 1, the carbon nanotube structure is formed with a relatively uniform diameter. On the other hand, referring to Figure 3, it can be seen that in the conductive material dispersion of Production Example 3, the diameter of the carbon nanotube structure is not uniform.

[0112] Examples and Comparative Examples Example 1: Production of the positive electrode LiNi was added to the conductive material dispersion of Production Example 1 0.6 Co 0.2 Mn 0.2 O2 (NCM622) and modified polyvinylidene fluoride (modified PVDF, KF9700, weight average molecular weight: 880,000 g / mol, containing 2.1% by weight of acid functional groups) were added, and further N-methylpyrrolidone (NMP) was added to produce a positive electrode slurry with a solid content of 70.1% by weight. After coating the positive electrode slurry on an Al thin film current collector with a thickness of 20 μm, it was dried at 130 °C and rolled to produce a positive electrode containing a positive electrode active material layer.

[0113] In the positive electrode active material layer, the LiNi 0.6 Co 0.2 Mn 0.2O2 (NCM622) is contained at 97.9% by weight, the polyvinylidene fluoride is contained at 1.8% by weight, the SDS is contained at 0.25% by weight, and the carbon nanotube structure is contained at 0.05% by weight. The content of the modified polyvinylidene fluoride was 1.55% by weight based on the total weight of the polyvinylidene fluoride.

[0114] Example 2: Production of the positive electrode In the positive electrode active material layer, the LiNi 0.6 Co 0.2 Mn 0.2 A positive electrode was produced in the same manner as in Example 1, except that O2 (NCM622) was contained at 97.6% by weight, the polyvinylidene fluoride was contained at 1.8% by weight, the SDS was contained at 0.5% by weight, the carbon nanotube structure was contained at 0.1% by weight, and the content of the modified polyvinylidene fluoride was 1.30% by weight based on the total weight of the polyvinylidene fluoride.

[0115] Example 3: Production of the positive electrode A positive electrode was produced in the same manner as in Example 1, except that the conductive material dispersion liquid of Production Example 2 was used instead of the conductive material dispersion liquid of Production Example 1.

[0116] Comparative Example 1: Production of the positive electrode A positive electrode was produced in the same manner as in Example 1, except that the conductive material dispersion liquid of Production Example 5 was used instead of the conductive material dispersion liquid of Production Example 1.

[0117] In the positive electrode active material layer, the LiNi 0.6 Co 0.2 Mn 0.2 A positive electrode was produced in the same manner as in Example 1, except that O2 (NCM622) was contained at 98.0875% by weight, the polyvinylidene fluoride was contained at 1.8% by weight, the SDS was contained at 0.0625% by weight, the carbon nanotube structure was contained at 0.05% by weight, and the content of the modified polyvinylidene fluoride was 1.55% by weight based on the total weight of the polyvinylidene fluoride.

[0118] Comparative Example 2: Production of the positive electrode A positive electrode was produced in the same manner as in Example 1, except that the conductive material dispersion of Production Example 3 was used instead of the conductive material dispersion of Production Example 1.

[0119] Comparative Example 3: Production of Positive Electrode A positive electrode was produced in the same manner as in Example 2, except that the conductive material dispersion of Production Example 3 was used instead of the conductive material dispersion of Production Example 1.

[0120] Comparative Example 4: Production of Positive Electrode A positive electrode was produced in the same manner as in Example 1, except that the conductive material dispersion of Production Example 4 was used instead of the conductive material dispersion of Production Example 1. In the positive electrode active material layer, except that the content of the modified polyvinylidene fluoride is 1.68% by weight based on the total weight of the polyvinylidene fluoride, the LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) contains 97.3% by weight, the polyvinylidene fluoride contains 1.8% by weight, the SDS contains 0.3% by weight, and the multi-walled carbon nanotube contains 0.6% by weight, a positive electrode was produced in the same manner as in Example 1.

[0121] Experimental Example 1: Analysis of XPS surface defects Bundle-type carbon nanotubes (specific surface area: 650 m 2 / g) composed of single-wall carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm, PBA, PSA, PMA, and SDS were each prepared. The bundle-type carbon nanotubes and any one of the additives PBA, PSA, PMA, and SDS were put into NMP as a dispersion medium, and ultrasonic crushing was performed at an output of 1,000 W for 30 minutes, and then dried in a vacuum oven at 150 °C for 24 hours to produce a surface-treated powder.

[0122] Sample 1: Without using an additive Sample 2: Using PBA Sample 3: Using PSA Sample 4: Using PMA Sample 5: Using SDS

[0123] Next, using a tabletop ball-mill device (SungHo SIGMA), after mixing 500 g of each sample with zirconia balls, the ball-mill treatment was performed at 1,000 RPM for 30 minutes, and then the surface defects were analyzed using an XPS (JPS-9000MC, JEOL, JAPAN) device. As can be seen from the XPS spectra in Figure 1, in all samples other than sample 5 using SDS, peaks corresponding to oxygen functional groups generated by surface defects of bundled carbon nanotubes were observed in the 288 eV - 290 eV region. On the other hand, in sample 5, since such peaks were not observed, it can be seen that the generation of surface defects was suppressed.

[0124] Experimental Example 2: Observation of positive electrode The active material layers of the positive electrodes manufactured according to Example 1 (Figure 4) and Comparative Example 1 (Figure 5) were observed via a scanning electron microscope.

[0125] Looking at the positive electrode in Figure 4, a carbon nanotube structure in which 2 to 10 single-wall carbon nanotube units are combined in parallel has a rope-like shape, the average diameter of the carbon nanotube structure is at the 10 nm level, and the average length is at the 5.8 μm level, and it can be seen that it generally has a uniform diameter.

[0126] On the other hand, looking at the positive electrode in Figure 5, a carbon nanotube structure having an average diameter at the 100 nm level and a generally relatively non-uniform diameter was observed.

[0127] Experimental Example 3: Measurement of powder resistance of positive electrode slurry The positive electrode slurries used in the manufacture of the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 4 were vacuum dried at a temperature of 130°C for 3 hours and then pulverized to produce powders. Next, using a Loresta GP device manufactured by Mitsubishi Chem Analytic, pellets were manufactured under the condition of a load of 9.8 MPa in an atmosphere of 25°C and a relative humidity of 50%. Next, the powder resistance was measured by the four-probe method. The measurement results are shown in Table 1 below.

[0128] Experimental Example 4: Measurement of positive electrode adhesion The adhesion of the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 4 was measured by the 90° peel test method.

[0129] Specifically, a double-sided tape was attached to a slide glass, and an electrode with a size of 20 mm × 180 mm and having holes was placed thereon and adhered by reciprocating 10 times with a 2 kg roller. Then, using a UTM (manufactured by TA Instruments) device, it was pulled at 200 mm / min, and the force of peeling from the slide glass was measured. Here, the measurement angle between the slide glass and the electrode was 90°. The measurement results are shown in Table 1 below.

[0130] Experimental Example 5: Evaluation of battery life characteristics Monocells were manufactured by combining the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 4 with a negative electrode and a polyethylene-based separator having a thickness of 15 μm. Here, the negative electrode was manufactured by mixing graphite, SBR / CMC, and a conductive material at a weight ratio of 96.5:2.5:1 to produce a negative electrode slurry, coating this on a 10-μm copper foil, and drying at 100°C. Then, an electrolytic solution in which 1 M of LiPF6 was dissolved in a mixed solvent of dimethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 1:1) was injected to fabricate a lithium secondary battery.

[0131] The lithium secondary battery manufactured as described above was charged and discharged 60 times at 45°C under the conditions of 0.33C / 0.33C, and then the life characteristics were measured with the measured charge-discharge efficiency. The measurement results are shown in Table 1 below.

[0132]

Table 1

Claims

1. comprising an electrode active material layer, wherein the electrode active material layer comprises an electrode active material, a conductive material, and SDS (sodium dodecyl sulfate), wherein the conductive material comprises a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, and the weight ratio of the carbon nanotube structure to the SDS is 1:3 to 1:

30. An electrode.

2. The electrode according to claim 1, wherein the SDS is contained in the electrode active material layer at 0.1% by weight to 5% by weight.

3. The electrode according to claim 1 or 2, wherein the carbon nanotube structure is contained in the electrode active material layer at 0.01% by weight to 0.5% by weight.

4. The electrode according to any one of claims 1 to 3, wherein in the electrode, the carbon nanotube structures are connected to each other to form a network structure.

5. Within the carbon nanotube structure, the single-walled carbon nanotube units are arranged in parallel and bonded together. The electrode according to any one of claims 1 to 4.

6. The electrode according to any one of claims 1 to 5, wherein the average diameter of the carbon nanotube structure is 2 nm to 200 nm.

7. The electrode according to any one of claims 1 to 6, wherein the electrode active material layer further comprises polyvinylidene fluoride.

8. The electrode according to claim 7, wherein the weight average molecular weight of the polyvinylidene fluoride is 10,000 g / mol to 1,000,000 g / mol.

9. The electrode according to claim 7 or 8, wherein the polyvinylidene fluoride comprises a modified polyvinylidene fluoride containing at least one of an acid functional group and an ester functional group.

10. The electrode according to claim 9, wherein the functional group is contained in the modified polyvinylidene fluoride at 0.1% by weight to 5% by weight.

11. The electrode according to any one of claims 1 to 10, wherein the electrode is a positive electrode.

12. A secondary battery comprising the electrode according to any one of claims 1 to 11.

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