Electrode and secondary battery including said 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 March 19, 2020, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrode and a secondary battery including the same, and includes 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-walled carbon nanotube units are bonded to each other, and a weight ratio of the carbon nanotube structure to the SDS may be 1:3 to 1:30. [Background technology]

[0003] A typical example of an electrochemical element that uses electrochemical energy is a secondary battery, and its range of use is gradually expanding. Recently, with the development of technology and increasing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as energy sources has rapidly increased. Among such secondary batteries, much research has been conducted on high-energy density, i.e., high-capacity lithium secondary batteries, which have 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 comprise an electrode current collector and an electrode active material layer formed on the electrode current collector. The electrode active material layer is manufactured by coating an electrode current collector with an electrode slurry composition containing an electrode active material, a conductive material, a binder, etc., drying the composition, and then rolling the composition.

[0005] Meanwhile, conventionally, dot-type conductive materials such as carbon black have been mainly used as conductive materials for secondary batteries, but these dot-type conductive materials have the problem of insufficient improvement in electrical conductivity. To address this issue, active research is being conducted into methods of applying linear conductive materials such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) and sheet-type conductive materials such as graphene.

[0006] However, while sheet-type conductive materials such as graphene have excellent electrical conductivity, they have the problem that it is difficult to manufacture thin single-layer graphene, and the use of thick graphene results in reduced battery efficiency.In addition, sheet-type conductive materials have the problem that the mobility of the electrolyte within the battery is restricted due to the wide sheet contact.

[0007] On the other hand, linear conductive materials such as carbon nanotubes and carbon nanofibers have excellent electrical conductivity, but due to the characteristics of the material itself, which grows in a bundled or entangled form, they have poor dispersibility in the slurry, which reduces coating and processability, and they are not uniformly distributed in the electrode active material layer. To address these issues, attempts have been made to improve dispersibility by introducing functional groups into the linear conductive materials, but in this case, the presence of the functional groups causes surface side reactions, which leads to problems with reduced electrochemical properties.

[0008] In addition, to use carbon nanotubes, a conductive material dispersion in which bundled carbon nanotubes are dispersed using a dispersant is generally used. However, during the dispersion process, external forces can cause numerous surface defects on the carbon nanotubes, reducing their mechanical strength and electrical conductivity, resulting in increased electrode resistance and reduced battery life. Furthermore, the size of the dispersed carbon nanotubes is not uniform, resulting in reduced electrode adhesion and electrode life.

[0009] Therefore, there is a need to develop electrodes containing carbon nanotubes that have relatively uniform sizes and can minimize surface defects. Summary of the Invention [Problem to be solved by the invention]

[0010] One problem to be solved by the present invention is to provide an electrode that includes a carbon nanotube structure having a relatively uniform size and that can minimize surface defects, thereby improving electrode adhesion, conductivity, and life characteristics.

[0011] Another problem to be solved by the present invention is to provide a secondary battery including the electrode. [Means for solving the problem]

[0012] According to one embodiment of the present invention, there is provided an electrode comprising an electrode active material layer, the electrode active material layer comprising an electrode active material, a conductive material, and SDS (sodium dodecyl sulfate), the conductive material comprising 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 to the SDS is 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-like carbon nanotube structures (long fiber structures) are connected to each other, thereby effectively forming conductive paths within the electrode. This significantly improves the electrical conductivity within the electrode even with a small amount of conductive material. Furthermore, the network-structured carbon nanotube structure firmly fixes the electrode active material layer, thereby improving electrode adhesion. Furthermore, the electrode contains sodium dodecyl sulfate (SDS), which minimizes surface defects on the carbon nanotube structure during its formation, thereby reducing electrode resistance and improving battery life. Furthermore, the diameter of the carbon nanotube structure is formed to a predetermined level, further improving electrode adhesion and battery life. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an XPS analysis graph of the carbon nanotube structures of Samples 1 to 5. [Figure 2] 1 is a SEM photograph of a carbon nanotube structure dispersion liquid of Production Example 1. [Figure 3] 1 is a SEM photograph of a carbon nanotube structure dispersion liquid of Production Example 3. [Figure 4] 1 is a SEM photograph of the electrode of Example 1. [Figure 5] 1 is a SEM photograph of the electrode of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0017] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0018] In this specification, the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

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

[0020] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan.

[0021] The present invention will be specifically described below.

[0022] electrode The electrode according to the present invention includes 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-walled carbon nanotube units are bonded to each other, and the weight ratio of the carbon nanotube structure to the SDS may be 1:3 to 1:30.

[0023] The electrode may include an electrode active material layer. The electrode may further include a current collector, and in such a case, the electrode active material layer may 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 a chemical change 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 also 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 a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0026] The electrode active material layer can include 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 technical field, and its type is not particularly limited.

[0028] For example, as the positive electrode active material, a lithium oxide 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 < , 0 < S < 1, and P3 + Q3 + R3 + S = 1), etc.), etc. are included, 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 alloy, Sn alloy, or Al alloy; metal oxides such as SiO v (0 < v < 2), SnO2, vanadium oxides, and metal oxides capable of doping and undoping 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. are included, and any one or two or more of these mixtures can be used. Also, as the negative electrode active material, a thin film of metallic lithium can also be used. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used.

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

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

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

[0033] The carbon nanotube structure may be formed by arranging the single-walled carbon nanotube units in parallel and connecting them (the long axes of the units are connected in parallel to each other to form a flexible cylindrical structure). The carbon nanotube structures may be connected to each other in the electrode to form a network structure.

[0034] Conventional electrodes containing carbon nanotubes are generally fabricated using a conductive material dispersion prepared by dispersing bundle-type or entangled-type carbon nanotubes (single-walled carbon nanotube units or multi-walled carbon nanotube units attached or entangled with each other) in a dispersion medium. The carbon nanotubes are completely dispersed in the conventional conductive material dispersion, resulting in a conductive material dispersion containing single-stranded carbon nanotube units. Excessive dispersion in the conventional conductive material dispersion can easily cause the carbon nanotube units to break, resulting in shorter lengths than the initial size. Furthermore, the carbon nanotube units can easily break during the rolling process of the negative electrode, further increasing the risk of breakage of the carbon nanotube units due to volumetric changes in the electrode active material during battery operation. This reduces the conductivity of the electrode and reduces the input, output, and life characteristics of the battery. Furthermore, multi-walled carbon nanotube units have a high structural defect rate due to the mechanism of nodal growth (i.e., nodes exist due to defects generated during the growth process, rather than smooth lines). Therefore, during the dispersion process, the multi-walled carbon nanotube units are more easily cut, and the cut multi-walled carbon nanotube units are more likely to aggregate due to π-π stacking due to the carbon surface structure of the units, making it difficult for them to be more uniformly dispersed in the electrode slurry.

[0035] In contrast, the carbon nanotube structure included in the electrode of the present invention has a configuration in which 2 to 5,000 single-walled carbon nanotube units, which maintain high crystallinity and are relatively free of structural defects, are bonded in parallel to each other, and therefore is not broken even during battery operation, smoothly maintaining its length and maintaining the conductivity of the electrode. Furthermore, the high conductivity of the single-walled carbon nanotube units with high crystallinity enhances the conductivity of the electrode, significantly improving the input, output, and life characteristics of the battery. Furthermore, the carbon nanotube structures within the electrode can be interconnected to form a network structure, which can suppress excessive volumetric changes in the electrode active material and ensure strong conductive paths, thereby suppressing detachment of the electrode active material and significantly improving electrode adhesion.

[0036] In the carbon nanotube structure, the average diameter of the single-walled carbon nanotube units may 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, even a very small amount of conductive material can be contained, thereby maximizing the conductivity within the electrode. The average diameter corresponds to the average value of the top 100 single-walled carbon nanotubes and the bottom 100 single-walled carbon nanotubes with the largest 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 units may be 1 μm to 100 μm, specifically 5 μm to 50 μm. When this average length is satisfied, a long conductive path for conductive connection between the electrode active materials can be formed, a unique network structure can be formed, and even a small amount of conductive material can be used to maximize the conductivity within the electrode. The average length corresponds to the average value of the top 100 single-walled carbon nanotubes and the bottom 100 single-walled carbon nanotubes with the longest average lengths when the fabricated electrode is observed using a TEM.

[0038] The specific surface area of ​​the single-walled carbon nanotube unit is 500 m 2 / g~1,000m 2 / g, specifically 600m 2 / g~800m 2 / g. When this range is satisfied, the large specific surface area ensures smooth conductive paths within the electrode, thereby maximizing the conductivity within the electrode even with a very small amount of conductive material. Specifically, the specific surface area of ​​the single-walled carbon nanotube unit can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan.

[0039] The average diameter of the carbon nanotube structures may be 2 nm to 200 nm, specifically 5 nm to 150 nm, more specifically 5 nm to 50 nm, for example 7 nm to 20 nm. When the diameter satisfies this range, it is effective for forming a conductive network, favorable for connecting active materials, and excellent electrical conductivity can be achieved. The average length corresponds to the average value of the diameters of the top 100 carbon nanotube structures and the bottom 100 carbon nanotube structures with the longest average length when the fabricated electrode is observed by SEM.

[0040] The average length of the carbon nanotube structures may be 1 μm to 500 μm, specifically 5 μm to 300 μm, specifically 5 μm to 150 μm. When the average length satisfies this range, it is effective for forming a conductive network, favorable for connecting active materials, and excellent electrical conductivity can be achieved. The average length corresponds to the average length of the top 100 and bottom 100 carbon nanotube structures when the fabricated electrode is observed using a SEM.

[0041] The carbon nanotube structure may be included in the electrode active material layer at 0.01 wt % to 0.5 wt %, specifically 0.01 wt % to 0.3 wt %. When this range is satisfied, the conductive path of the electrode is secured, the electrode resistance is maintained at a low level, and the battery life characteristics can be improved. When the bundled carbon nanotubes are completely dispersed during the preparation of the conductive material dispersion (a typical dispersion method is to disperse single-stranded carbon nanotube units as far apart as possible), the carbon nanotube structure does not form, or if it does form, it forms in a very small amount (e.g., 0.0005 wt %). In other words, this content range cannot be achieved by a typical method.

[0042] In the case of conventional electrodes containing multi-walled carbon nanotube units, a high content (e.g., more than 0.5 wt%) of multi-walled carbon nanotube units had to be used to compensate for the low conductivity of the multi-walled carbon nanotube units. Also, even when an electrode was fabricated using a conductive material dispersion in which single-walled carbon nanotube units were completely dispersed, the single-walled carbon nanotube units could not be used at a low content due to the problem of the single-walled carbon nanotube units being cut.

[0043] Meanwhile, the carbon nanotube structure included in the electrode of the present invention has a configuration in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other in parallel. Therefore, even when the battery is operated, the carbon nanotube structure can smoothly maintain its length without being broken, thereby maintaining the conductivity of the electrode. The high conductivity of the single-walled carbon nanotube units can smoothly ensure the conductivity of the electrode. As a result, even if the content of the carbon nanotube structure in the electrode is low, the input, output, and life characteristics of the battery can be excellent.

[0044] Meanwhile, although not essential, the single-walled carbon nanotube unit may be surface-treated by oxidation or nitridation to improve the affinity of the single-walled carbon nanotube unit with polyvinylidene fluoride.

[0045] The SDS may be disposed on the carbon nanotube structure. Specifically, the SDS may be disposed on a single-walled carbon nanotube unit included in the carbon nanotube structure. The SDS acts as a surface protectant that minimizes surface defects on the carbon nanotube structure. During the formation of the carbon nanotube structure, the SDS acts as a dispersion stabilizer that allows the carbon nanotube structure to be smoothly dispersed and maintain a consistent diameter.

[0046] Figure 1 shows the XPS analysis results for carbon nanotube structures of Samples 1 to 5 (Samples 1 to 5 correspond to (a) to (e) respectively). Sample 1 does not have any surface defect prevention material disposed on the surface of the carbon nanotube structure, while Samples 2 to 5 have PBA (pyrene butyric acid), PSA (pyrene sulfonic acid), PMA (pyrene methylamine), and SDS (sodium dodecyl sulfate) disposed on the surface of the carbon nanotube structure, respectively. Referring to Figure 1, it can be seen that, except for Sample 5, which used SDS, defects occur on the carbon nanotube surface due to the dispersion process using mechanical external force, and fine peaks (circled in Figure 1) appear due to carbon-oxygen bonds. That is, sulfonate anion functional groups (SO3) are attached to the ends of the linear, straight-chain molecular structure. - When SDS containing ) is used, SDS wraps the surface of the carbon nanotube structure in a linear fashion, and the defects of the carbon nanotube structure can be minimized even during the dispersion process. When SDS is used, no carbon-oxygen bonds were observed from the results of the XPS surface analysis shown in Figure 1. In addition, the sulfonate anion functional group (SO3 - ) can improve the uniformity of dispersion of the carbon nanotube structures.

[0047] The weight ratio of the carbon nanotube structure to the SDS may be 1:3 to 1:30, specifically 1:3 to 1:20, and more specifically 1:5 to 1:10. If the weight ratio of the carbon nanotube structure to the SDS deviates from 1:3 to 1:30 and the SDS content is reduced, the SDS may not be effective in minimizing surface defects of the carbon nanotube structure. Conversely, if the SDS content is higher than 1:3 to 1:30, side reactions may occur more severely at the electrode, resulting in reduced electrical conductivity.

[0048] On the other hand, most preferably, the weight ratio of the carbon nanotube structure to the SDS is 1:5 to 1:10. When the weight ratio is in the range of 1:5 to 1:10, surface defects of the carbon nanotube structure can be minimized, and excessive debundling of the raw material bundled carbon nanotubes can be effectively suppressed, resulting in a carbon nanotube structure with a desired diameter and length.

[0049] The SDS may be included in the electrode active material layer at 0.1 wt % to 5 wt %, specifically 0.1 wt % to 3 wt %, more specifically 0.1 wt % to 1.5 wt %, for example 0.4 wt % to 1.0 wt %. When the SDS content is within this range, surface defects of the carbon nanotube structure can be effectively prevented. Furthermore, this range is a low content because the SDS is not disposed on completely dispersed single-walled carbon nanotube units but on a carbon nanotube structure in which single-walled carbon nanotube units are bonded in parallel. Specifically, when a carbon nanotube structure in which single-walled carbon nanotube units are bonded in parallel is formed rather than on completely dispersed single-walled carbon nanotube units, the degree of separation of bundled carbon nanotubes is low. As a result, the single-walled carbon nanotube units inside the carbon nanotube structure are not directly subjected to shear stress, and the likelihood of surface defects is relatively low. Therefore, even a small amount of SDS (0.1% by weight to 5% by weight) can minimize surface defects in the carbon nanotube structure.

[0050] The electrode active material layer may further include polyvinylidene fluoride. The polyvinylidene fluoride may be a material that is initially contained in the electrode from the conductive material dispersion liquid required for preparing the electrode slurry (in some cases, it may be further added to reinforce the role of a binder during the preparation of the electrode slurry). The polyvinylidene fluoride facilitates smooth dispersion of the bundled carbon nanotubes in the conductive material dispersion liquid.

[0051] The weight-average molecular weight of the polyvinylidene fluoride may be 10,000 g / mol to 1,000,000 g / mol, specifically 100,000 g / mol to 900,000 g / mol. When the weight-average molecular weight satisfies this range, the polyvinylidene fluoride can easily penetrate between the single-walled carbon nanotube units in the bundled carbon nanotubes, thereby enabling the bundled carbon nanotubes to be properly dispersed and improving the stability of the conductive material dispersion liquid.

[0052] The polyvinylidene fluoride may be contained in the electrode active material layer in an amount of 0.1 wt % to 10.0 wt %, specifically 0.2 wt % to 5.0 wt %, more specifically 0.2 wt % to 2.5 wt %. When the amount is within this range, the carbon nanotube structures are uniformly dispersed, resulting in high electrode energy density and excellent electrode adhesion.

[0053] The polyvinylidene fluoride may include a modified polyvinylidene fluoride modified with a hydrophilic functional group to improve affinity with the single-walled carbon nanotube units. Specifically, the polyvinylidene fluoride may include a modified polyvinylidene fluoride having at least one functional group selected from an acid functional group and an ester functional group. The functional group of the modified polyvinylidene fluoride may interact with the single-walled carbon nanotube units to improve the dispersibility of the carbon nanotube structure and further enhance electrode adhesion.

[0054] The functional group may be contained in the modified polyvinylidene fluoride in an amount of 0.1 to 5 wt %, specifically 0.3 to 3 wt %. When the amount is within this range, the dispersibility of the carbon nanotube structure can be further improved, and the electrode adhesive strength can be further improved.

[0055] The modified polyvinylidene fluoride may be contained in an amount of 1 wt % to 100 wt %, specifically 1 wt % to 50 wt %, and more specifically 1 wt % to 20 wt %, based on the total weight of the polyvinylidene fluoride. When the amount is within this range, the dispersibility of the carbon nanotube structure is improved, and the electrode adhesive strength can be further improved.

[0056] The electrode active material layer may further include a binder. The binder ensures adhesion between the electrode active materials or between the electrode active material and the current collector. A binder commonly used in the art may be used, and the type of binder is not particularly limited. Examples of binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination.

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

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

[0059] The method for manufacturing an electrode of the present invention includes the steps of: (1) adding bundled single-walled carbon nanotubes and SDS to a dispersion medium and subjecting the mixture to a first ultrasonic treatment to prepare a mixture; (2) adding polyvinylidene fluoride to the mixture and subjecting the mixture to a second ultrasonic treatment to prepare a conductive material dispersion containing a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and (3) forming an electrode slurry containing the conductive material dispersion and an electrode active material, wherein the weight ratio of the carbon nanotube structure to the SDS may be 1:3 to 1:30. The electrode of the above-described embodiment can be manufactured by this method. The SDS and carbon nanotube structure are the same as those in the above-described embodiment, and therefore further description is omitted.

[0060] (1) Preparing a mixture The mixture can be prepared by adding bundled carbon nanotubes and SDS to a dispersion medium and then subjecting the mixture to a first ultrasonic treatment. The bundled carbon nanotubes are composed of the above-mentioned single-walled carbon nanotube units bound together in a bundle, and typically contain two or more, substantially 500 or more, e.g., 5,000 or more, single-walled carbon nanotube units.

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

[0062] The SDS may be included in the mixture at 0.1 wt % to 20 wt %, specifically 1 wt % to 10 wt %. When the SDS content is within this range, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, ultimately forming a carbon nanotube structure. The SDS is disposed on the carbon nanotube structure and serves as a surface protectant, thereby minimizing surface defects of the carbon nanotube structure.

[0063] Examples of the dispersion medium include amide 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, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; and polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, and sorbitol. Examples of suitable dispersion media include, but are not limited to, alcohols; 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, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. These may be used singly or in combination. More specifically, the dispersion medium may be N-methylpyrrolidone (NMP).

[0064] The solid content of the mixture may be 0.1 wt% to 20 wt%, specifically 1 wt% to 10 wt%. When this range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, a carbon nanotube structure of an appropriate level is formed, and dispersion stability is improved. Furthermore, the electrode slurry may have 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 performed using a mixer such as an ultrasonicator, homogenizer, bead mill, ball mill, basket mill, attrition mill, universal mixer, clear mixer, spike mill, or TK mixer. Among these, ultrasonic disruption is preferred. In ultrasonic disruption, when high-intensity ultrasound is emitted into a solution, a large number of vacuum-state bubbles are generated by extreme vibration. These bubbles momentarily entangle or grow larger, but are violently broken in a chain reaction by subsequent vibrations. When the bubbles are broken down in this manner, powerful shock waves are generated by the violent flow or vortex phenomenon of the solution, and the energy of these shock waves can debundle the bundled carbon nanotubes. The ultrasonic disruption method enables fine dispersion at the nano level without longitudinally breaking the single-walled carbon nanotubes within the bundled carbon nanotubes. For these reasons, ultrasonic disruption is preferred.

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

[0067] The conditions for performing the ultrasonic disruption method are as follows:

[0068] The ultrasonic disruption may be performed at an output of 800W to 1,500W, specifically 800W to 1,200W. The ultrasonic disruption may be performed for 0.5 to 5 hours, specifically 1 to 3 hours. When this range is satisfied, the bundled carbon nanotubes can be separated at an appropriate level to form the carbon nanotube structure. The implementation time refers to the total time for ultrasonic disruption; for example, if ultrasonic disruption is performed several times, it refers to the total time for all the times.

[0069] (2) Step of producing a conductive material dispersion The polyvinylidene fluoride may be added to the mixture, and a second treatment may be performed using an ultrasonic disruption method.

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

[0071] The polyvinylidene fluoride is the same as the polyvinylidene fluoride in the above-described embodiment, and therefore a description thereof will be omitted.

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

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

[0074] The ultrasonic disruption may be performed at an output of 800W to 1,500W, specifically 800W to 1,200W. The ultrasonic disruption may be performed for 0.5 to 5 hours, specifically 1 to 3 hours. When this range is satisfied, the bundled carbon nanotubes can be separated at an appropriate level to form the carbon nanotube structure. The implementation time refers to the total time for ultrasonic disruption; for example, if ultrasonic disruption is performed several times, it refers to the total time for all the times.

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

[0076] The SDS may also be present on the carbon nanotube structure.

[0077] (3) Electrode slurry formation step After the conductive material dispersion liquid is prepared by the above process, an electrode active material is mixed with the conductive material dispersion liquid to form an electrode slurry. Here, the electrode active material may be any of the above-described electrode active materials.

[0078] The electrode slurry may further include a binder and a solvent, if necessary. The binder may be the same as that described in the above embodiment. Examples of the solvent include amide 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, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; and polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, and sorbitol. Examples of suitable solvents include, but are not limited to, glycols 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, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. These solvents may be used singly or in combination. The solvent may be the same as or different from the dispersion medium used in the previous dispersion, and is preferably N-methylpyrrolidone (NMP).

[0079] The electrode active material may be contained in an amount of 70 to 99.5 wt %, preferably 80 to 99 wt %, based on the total solid content of the electrode slurry. When the content of the electrode active material satisfies this range, excellent energy density, electrode adhesive strength, and electrical conductivity can be achieved.

[0080] In addition, when a binder is further included, the binder may be included in an amount of 10 wt % or less, specifically 0.1 wt % to 5 wt %, based on the total solid content in the electrode slurry.

[0081] The solid content of the electrode slurry may be 60 wt% to 80 wt%, specifically 65 wt% to 75 wt%. When this range is satisfied, migration of the conductive material and binder due to evaporation of the solvent can be suppressed when the electrode slurry is applied and dried, and an electrode with excellent electrode adhesion and electrical conductivity can be manufactured. Furthermore, a high-quality electrode with minimal deformation during rolling can be manufactured.

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

[0083] Next, the electrode slurry prepared as described above is applied and dried to form an electrode active material layer. Specifically, the electrode active material layer can be formed by applying the electrode slurry to an electrode current collector and then drying it, or by applying the electrode slurry to a separate support and then peeling it off from the support to obtain a film, which is then laminated 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 performed.

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

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

[0086] A secondary battery according to the present invention includes the electrode according to the present invention. Here, the electrode may be at least one of a positive electrode and a negative electrode. Specifically, the secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode may be the electrode according to the present invention, i.e., an electrode including an electrode active material layer including an electrode active material and a carbon nanotube structure. Preferably, the electrode according to the present invention may be a positive electrode. Since the electrode according to the present invention has been described above, a detailed description thereof will be omitted, and only the remaining components will be described below.

[0087] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. Specifically, the separator can be a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in 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-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0089] Specifically, the electrolyte may 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, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

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

[0092] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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:

[0093] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in the capacity of the battery, and improve the discharge capacity of the battery.

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

[0095] The present invention will be described in more detail below with reference to specific examples.

[0096] Production Example 1: Production of conductive material dispersion A bundled carbon nanotube (specific surface area: 650 m) consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm. 2 0.4 parts by weight of PEG-400 / 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 homopolymer) were prepared.

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

[0098] Polyvinylidene fluoride was added to the mixture, and then ultrasonically crushed (at 1,000 W for 30 minutes) to prepare a conductive material dispersion (solid content 4.4 wt%) containing carbon nanotube structures in which 2 to 5,000 single-walled carbon nanotube units are connected in parallel.

[0099] In the conductive material dispersion liquid, 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 prepared in the same manner as in Preparation Example 1, except that the polyvinylidene fluoride was modified polyvinylidene fluoride (weight average molecular weight: 880,000 g / mol) containing 2.1 wt % of acid functional groups.

[0101] Production Example 3: Production of conductive material dispersion A bundled carbon nanotube (specific surface area: 650 m) consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm. 2 0.4 parts by weight of ethylenediaminetetraacetic acid (ethylenediaminetetraacetic acid / g) and 2.0 parts by weight of polyvinylidene fluoride (weight average molecular weight: 685,000 g / mol, (standard homopolymer)) were mixed with N-methylpyrrolidone (NMP) as a dispersion medium to prepare a mixture with a solid content of 2.2% by weight.

[0102] The mixture was stirred using an ultrasonic disruption method to disperse the bundled carbon nanotubes in the dispersion medium, producing a conductive material dispersion. The ultrasonic disruption was performed for 1.5 hours at an output of 1,000 W. The conductive material dispersion contained a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units were bound in parallel. The carbon nanotube structure and polyvinylidene fluoride were present in the conductive material dispersion at 0.4 wt % and 2.0 wt %, respectively.

[0103] Production Example 4: Production of conductive material dispersion The bundled carbon nanotubes (specific surface area: 185 m) consist of multi-walled carbon nanotube units with an average diameter of 10 nm and an average length of 1 μm. 2 4.0 parts by weight of PEG-100 / g), 1.0 part by weight of SDS (sodium dodecyl sulfate), and 0.8 parts by weight of modified polyvinylidene fluoride (weight average molecular weight 880,000 g / mol) containing 2.1% by weight of acid functional groups were prepared.

[0104] The bundled carbon nanotubes composed of multi-walled carbon nanotube units and SDS were added to a dispersion medium, N-methylpyrrolidone (NMP), and then subjected to a first ultrasonic disruption method to prepare a mixture in which the bundled carbon nanotubes were dispersed. The ultrasonic disruption was performed at an output of 1,000 W for 30 minutes.

[0105] Polyvinylidene fluoride was added to the mixture, and then ultrasonic disruption was performed (at an output of 1,000 W for 30 minutes) to prepare a conductive material dispersion (solid content 5.8 wt %).

[0106] In the conductive material dispersion, the multi-walled 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 A bundled carbon nanotube (specific surface area: 650 m) consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm. 2 0.4 parts by weight of PEG-100 / g), 0.5 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 homopolymer) were prepared.

[0108] The bundled carbon nanotubes and SDS were added to a dispersion medium, N-methylpyrrolidone (NMP), and then subjected to a first ultrasonic disruption method to prepare a mixture in which the bundled carbon nanotubes were dispersed. The ultrasonic disruption was performed at an output of 1,000 W for 30 minutes.

[0109] Polyvinylidene fluoride was added to the mixture, and then ultrasonically crushed (at 1,000 W for 30 minutes) to prepare a conductive material dispersion (solid content 4.4 wt%) containing carbon nanotube structures in which 2 to 5,000 single-walled carbon nanotube units are connected in parallel.

[0110] In the conductive material dispersion liquid, 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] 2, it can be seen that the carbon nanotube structures formed in the conductive material dispersion liquid of Preparation Example 1 have a relatively uniform diameter, while FIG. 3 shows that the carbon nanotube structures formed in the conductive material dispersion liquid of Preparation Example 3 do not have a uniform diameter.

[0112] Examples and Comparative Examples Example 1: Preparation of the positive electrode The conductive material dispersion liquid of Production Example 1 was 0.6 Co 0.2 Mn 0.2 A positive electrode slurry with a solid content of 70.1 wt% was prepared by adding O2 (NCM622), modified polyvinylidene fluoride (modified PVDF, KF9700, weight average molecular weight: 880,000 g / mol, containing 2.1 wt% acid functional groups), and N-methylpyrrolidone (NMP). The positive electrode slurry was applied to a 20 μm-thick Al thin film current collector, dried at 130°C, and rolled to prepare a positive electrode including a positive electrode active material layer.

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

[0114] Example 2: Preparation 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 prepared in the same manner as in Example 1, except that the O2 (NCM622) was contained in an amount of 97.6 wt%, the polyvinylidene fluoride in an amount of 1.8 wt%, the SDS in an amount of 0.5 wt%, and the carbon nanotube structure in an amount of 0.1 wt%, and the content of the modified polyvinylidene fluoride relative to the total weight of the polyvinylidene fluoride was 1.30 wt%.

[0115] Example 3: Preparation of 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 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 prepared in the same manner as in Example 1, except that the O2 (NCM622) was contained in an amount of 98.0875 wt %, the polyvinylidene fluoride was contained in an amount of 1.8 wt %, the SDS was contained in an amount of 0.0625 wt %, and the carbon nanotube structure was contained in an amount of 0.05 wt %, and the content of the modified polyvinylidene fluoride relative to the total weight of the polyvinylidene fluoride was 1.55 wt %.

[0118] Comparative Example 2: Production of 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 3 was used instead of the conductive material dispersion liquid 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 liquid of Production Example 3 was used instead of the conductive material dispersion liquid 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 liquid of Production Example 4 was used instead of the conductive material dispersion liquid of Production Example 1. 0.6 Co 0.2 Mn 0.2 A positive electrode was prepared in the same manner as in Example 1, except that the O2 (NCM622) was contained in an amount of 97.3 wt%, the polyvinylidene fluoride in an amount of 1.8 wt%, the SDS in an amount of 0.3 wt%, and the multi-walled carbon nanotubes in an amount of 0.6 wt%, and the content of the modified polyvinylidene fluoride relative to the total weight of the polyvinylidene fluoride was 1.68 wt%.

[0121] Experimental Example 1: XPS Surface Defect Analysis A bundled carbon nanotube (specific surface area: 650 m) consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm. 2 The bundled carbon nanotubes and one of the additives PBA, PSA, PMA, and SDS were added to NMP, a dispersion medium, and subjected to ultrasonic disruption at 1,000 W for 30 minutes. The surface-treated powder was then dried in a vacuum oven at 150°C for 24 hours.

[0122] Sample 1: No additives used Sample 2: Using PBA Sample 3: Using PSA Sample 4: Using PMA Sample 5: SDS used

[0123] Next, 500 g of each sample was mixed with zirconia balls using a benchtop ball mill (SungHo SIGMA), and then ball-milled at 1,000 RPM for 30 minutes. Surface defects were then analyzed using an XPS (JPS-9000MC, JEOL, JAPAN) device. As can be seen from the XPS spectra in Figure 1, in all samples except for Sample 5, which used SDS, a peak corresponding to oxygen functional groups generated by surface defects in the bundled carbon nanotubes was observed in the 288 eV to 290 eV region. In contrast, no such peak was observed in Sample 5, indicating that the generation of surface defects was suppressed.

[0124] Experimental Example 2: Observation of the positive electrode The active material layers of the positive electrodes prepared in Example 1 (FIG. 4) and Comparative Example 1 (FIG. 5) were observed using a scanning electron microscope.

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

[0126] On the other hand, in the positive electrode of FIG. 5, carbon nanotube structures having an average diameter of about 100 nm and having relatively non-uniform diameters were observed.

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

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

[0129] Specifically, double-sided tape was attached to a glass slide, and an electrode with a 20mm x 180mm hole was placed on top of it and rolled back and forth with a 2kg roller 10 times to adhere it.Then, using a UTM (manufactured by TA Co.) device, the electrode was pulled at 200mm / min and the peel force from the glass slide was measured.The measurement angle between the glass slide 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 fabricated by combining the positive electrodes of Examples 1 to 3 and Comparative Examples 1 to 4 with negative electrodes and 15 μm-thick polyethylene separators. The negative electrodes were fabricated by mixing graphite, SBR / CMC, and a conductive material in a weight ratio of 96.5:2.5:1 to fabricate negative electrode slurry, which was then coated onto 10 μm-thick copper foil and dried at 100°C. Lithium secondary batteries were then fabricated by injecting an electrolyte solution prepared by dissolving 1M LIPF6 in a mixed solvent of dimethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 1:1).

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

[0132] [Table 1]

Claims

1. an electrode active material layer; The electrode active material layer is an electrode active material; A conductive material; 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, A method for manufacturing an electrode, wherein the weight ratio of the carbon nanotube structure to the SDS is 1:3 to 1:30, (1) adding bundled single-walled carbon nanotubes and SDS to a dispersion medium, and performing a first process using a mixer to prepare a mixture; (2) adding polyvinylidene fluoride to the mixture and performing a second process using a mixer to prepare a conductive material dispersion including the carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; (3) forming an electrode slurry containing the conductive material dispersion and the electrode active material.

2. A method for manufacturing an electrode as described in claim 1, wherein the first treatment is performed by ultrasonic crushing.

3. A method for manufacturing an electrode as described in claim 1, wherein the second treatment is performed by ultrasonic crushing.

4. The method for manufacturing an electrode according to claim 1 , wherein the SDS is contained in the electrode active material layer in an amount of 0.1% by weight to 5% by weight.

5. 5. The method for manufacturing an electrode according to claim 1, wherein the carbon nanotube structure is contained in the electrode active material layer in an amount of 0.01% by weight to 0.5% by weight.

6. The method for manufacturing an electrode according to claim 1 , wherein the carbon nanotube structures are interconnected to form a network structure within the electrode.

7. In the carbon nanotube structure, The method for manufacturing an electrode according to claim 1 , wherein the single-walled carbon nanotube units are arranged in parallel and bonded together.

8. 8. The method for manufacturing an electrode according to claim 1, wherein the carbon nanotube structure has an average diameter of 2 nm to 200 nm.

9. The method for manufacturing an electrode according to claim 1 , wherein the electrode active material layer further contains polyvinylidene fluoride.

10. The method for manufacturing an electrode according to claim 9, wherein the weight average molecular weight of the polyvinylidene fluoride is 10,000 g / mol to 1,000,000 g / mol.

11. The method for manufacturing an electrode according to claim 9 or 10, wherein the polyvinylidene fluoride includes a modified polyvinylidene fluoride containing at least one functional group selected from the group consisting of an acid functional group and an ester functional group.

12. The method for manufacturing an electrode according to claim 11, wherein the functional group is contained in the modified polyvinylidene fluoride in an amount of 0.1% by weight to 5% by weight.

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