Conductive material dispersion, electrodes, and lithium secondary batteries

Abstract

The present invention relates to a conductive material dispersion containing single-walled carbon nanotube (SWCNT) clusters, wherein the SWCNT clusters have a number average length of 0.8 μm to 8.0 μm, with less than 15% of the total number of SWCNT clusters having a length greater than 10 μm, a number average diameter of 5 nm to 30 nm, with less than 15% of the total number of SWCNT clusters having a diameter greater than 30 nm, and the length and diameter of the SWCNT clusters being measured using atomic force microscopy (AFM). The invention also relates to an electrode containing the SWCNT clusters, and has the advantage of being able to form a conductive network well due to its excellent dispersibility, ensuring excellent conductivity even in small amounts, having excellent processability due to the low viscosity of the dispersion, and being useful in improving battery performance when the conductive material dispersion is applied to an electrode.

Description

[Technical Field]

[0001] The present invention relates to a conductive material dispersion containing SWCNT clusters with restricted length and diameter characteristics, and to electrodes and lithium secondary batteries to which this dispersion is applied. [Background technology]

[0002] With the rapid increase in the use of fossil fuels, the need for alternative and clean energy sources is growing, and one of the most actively researched areas in this field is power generation and energy storage using electrochemical reactions.

[0003] Currently, a typical example of an electrochemical element that uses electrochemical energy is the secondary battery, and its range of applications is gradually expanding. Recently, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly. Among such secondary batteries, various studies are being conducted on high-energy-density, i.e., high-capacity lithium secondary batteries, and these have been commercialized and are widely used.

[0004] The electrodes of a secondary battery include an electrode active material, a conductive material, and a binder. To improve the conductivity of the electrodes, carbon nanotubes can be used as the conductive material, and in particular, when using those with a large specific surface area, even a small amount can have an excellent effect on improving conductivity.

[0005] When single-walled carbon nanotubes (SWCNTs) are used as carbon nanotubes, the resistance of the electrodes can be further reduced, and because their specific surface area is relatively large, conductivity can be easily ensured with only a small amount. In order to ensure that the single-walled carbon nanotubes are uniformly distributed within the electrode, a conductive material dispersion containing the single-walled carbon nanotubes is first formed during the manufacture of the electrode, and then the electrode slurry is manufactured using this conductive material dispersion.

[0006] However, single-walled carbon nanotubes have a problem that the degree of improvement in battery performance varies significantly depending on their dispersibility and inherent physical properties. There is also a problem that the dispersibility measured in the conductive material dispersion liquid is not directly related to the degree of distribution in the electrode, resulting in a deviation in evaluation.

[0007] Therefore, when applying single-walled carbon nanotubes as a conductive material for electrodes, research on a conductive material dispersion liquid is necessary, which has excellent properties in the dispersion liquid state, whose properties are directly reflected in the electrode, and whose performance can be intuitively predicted by evaluating the dispersion liquid.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] One problem according to the present invention is to apply a single-walled carbon nanotube (SWCNT) cluster, which is an aggregate of single-walled carbon nanotubes with a relatively short length and a small diameter. At this time, the ratio of SWCNT clusters with a long length and a large diameter is minimized, and an SWCNT cluster having a characteristic that the number average length distribution and the number average diameter distribution are widely distributed among SWCNT clusters with a relatively short length and a small diameter is applied, thereby providing a conductive material dispersion liquid having excellent dispersibility, low viscosity, and excellent processability. <​​​​​​​​​​​​​[1] According to an embodiment of the present invention, a single-walled carbon nanotube (SWCNT) cluster is included, and the SWCNT cluster has a number average length of 0.8 μm to 8.0 μm, the number of SWCNT clusters with a length exceeding 10 μm is 15% or less of the total number, a number average diameter of 5 nm to 25 nm, and the number of SWCNT clusters with a diameter exceeding 30 nm is 15% or less of the total number. The length and diameter of the SWCNT cluster are measured using an atomic force microscope (AFM) to provide a conductive material dispersion liquid.

[0012] [2] In [1] above, the SWCNT cluster may have a number average length of 1.0 μm to 6.0 μm.

[0013] [3] In [1] and / or [2] above, the SWCNT cluster may have the number of single-walled carbon nanotubes with a length exceeding 10 μm being 10% or less of the total number. [[ID=X]]

[0014] [[ID=Y]] [4] In at least one of [1] to [3] above, the SWCNT cluster may have a number average diameter of 7 nm to 20 nm.

[0015] [5] In at least one of [1] to [4] above, the SWCNT cluster may have the number of SWCNT clusters with a diameter exceeding 30 nm being 10% or less of the total number.

[0016] [6] In at least one of [1] to [5] above, the conductive material dispersion further comprises a dispersant, the dispersant may include one or more selected from the group consisting of polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol (Polyvinylalchol), polyacrylamide, polyethylene oxide, carboxymethyl cellulose (CMC), and diisopropylamine (DIPA).

[0017] [7] In the above [6], the conductive material dispersion may contain 0.2 to 3.5 parts by weight of SWCNT clusters and 0.2 to 7.0 parts by weight of a dispersant per 100 parts by weight of the conductive material dispersion.

[0018] [8]According to another embodiment of the present invention, an electrode is provided in which an electrode active material layer comprising an electrode active material, single-walled carbon nanotube (SWCNT) clusters and a binder is arranged on a current collector, wherein the SWCNT clusters have a number average length of 0.8 μm to 8.0 μm, less than 15% of the total number of SWCNT clusters have a length greater than 10 μm, a number average diameter of 5 nm to 30 nm, less than 15% of the total number of SWCNT clusters have a diameter greater than 30 nm, and the length and diameter of the SWCNT clusters are measured using atomic force microscopy (AFM).

[0019] [9] In the above [8], the electrode active material is a positive electrode active material, and the positive electrode active material may include one or more selected from the group consisting of lithium nickel-ternary oxide, perlithium manganese oxide, lithium iron phosphorus oxide, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide.

[0020]

[10] In the above [8] and / or [9], the electrode active material is a negative electrode active material, and the negative electrode active material may include one or more selected from the group consisting of carbon-based particles, silicon-based particles and carbon-silicon composite particles.

[0021]

[11] In at least one of the above [8] to

[10] , the electrode further comprises a point conductive material, the point conductive material may include carbon black.

[0022]

[12] According to another embodiment of the present invention, a lithium secondary battery is provided having a structure in which a positive electrode, a separator and a negative electrode are stacked in order, wherein one or more of the positive electrode and the negative electrode are the electrodes described above. [Effects of the Invention]

[0023] The conductive material dispersion according to the present invention contains SWCNT clusters having unique length and diameter characteristics, resulting in excellent dispersibility, low viscosity, and minimal change in viscosity over time, thus providing excellent storage stability and improving processability.

[0024] As a result, applying SWCNT clusters having the aforementioned characteristics to the electrode slurry can contribute to the phase stability of the slurry, and because of their excellent dispersibility, sufficient conductivity can be ensured even with a small amount, enabling the realization of electrodes with excellent resistance characteristics. Furthermore, by applying electrodes with excellent resistance characteristics as described above, the output of lithium secondary batteries can be improved, and not only is a well-formed conductive network formed, but its retention capacity is also outstanding, which can contribute to improving the lifespan of lithium secondary batteries. [Modes for carrying out the invention]

[0025] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0026] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of an implemented feature, figure, step, component, or combination thereof, but do not exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0027] In this specification, volume cumulative average particle size D 50 and D 90 These can be defined as particle sizes corresponding to 50% and 90% of the cumulative volume, respectively, in the particle size distribution curve. 50 and D 90 This can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can obtain highly reproducible and high-resolution results.

[0028] In this specification, the number-average length and diameter of carbon nanotubes, as well as the ratio of nanotubes with a length greater than 10 μm and a diameter greater than 30 nm, can be derived by measuring the length and diameter of 400 or more carbon nanotubes using an atomic force microscope (AFM) (Asylum Research, Cypher ES AFM System) in AC Air Topography mode (Tapping mode) under the conditions of a set point of 0.4 V and a scan rate of 1.5 Hz, at magnifications of 20 μm × 20 μm, 15 μm × 15 and / or 10 μm × 10 μm, and obtaining the cumulative length and diameter distribution of the number of nanotubes.

[0029] In this specification, "cluster" may mean a form in which multiple units are bonded together to form a single aggregate, and a single-wall carbon nanotube (SWCNT) cluster may mean an aggregate or collection in which multiple SWCNT units are bonded together to form a single fiber.

[0030] The present invention will be described in detail below.

[0031] In this specification, each of the conductive material dispersion, electrode, and lithium secondary battery includes one or more of the technical features and / or technical configurations described below, and these technical features and / or technical configurations can be combined in various ways.

[0032] <Conductive material dispersion> A conductive material dispersion according to one embodiment of the present invention contains single-walled carbon nanotube (SWCNT) clusters, wherein the SWCNT clusters have a number average length of 0.8 μm to 8.0 μm, with SWCNT clusters having a length greater than 10 μm accounting for 15% or less of the total number of clusters, a number average diameter of 5 nm to 25 nm, and SWCNT clusters having a diameter greater than 30 nm accounting for 15% or less of the total number of clusters, and the length and diameter of the SWCNT clusters were measured using an atomic force microscope (AFM).

[0033] <(1) Single-walled carbon nanotubes> Carbon nanotubes have a graphite sheet that has the form of a cylinder with a nanoscale diameter and possesses an sp2 bonding structure. Depending on the angle and structure in which the graphite sheet is wound, they exhibit conductive or semiconductor properties. Carbon nanotubes are classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) according to the number of bonds forming the walls.

[0034] According to one embodiment of the present invention, the conductive material dispersion contains SWCNT clusters, which are aggregates of single-walled carbon nanotubes (SWCNTs). Because single-walled carbon nanotubes have a larger specific surface area than multi-walled carbon nanotubes, even if only a small amount is added, sufficient conductivity can be ensured, and the reduction in electrode resistance can be significantly increased. However, in the case of single-walled carbon nanotubes, in order to maximize the advantage of easily ensuring conductivity even when used in small amounts, excellent length characteristics are necessary. However, these length characteristics are not easy to measure accurately, and the expected degree of improvement in conductivity is often not reflected. Furthermore, even if the length characteristics are good, if they are excessive, there is a problem that they can affect the viscosity of the dispersion and even the viscosity of the slurry.

[0035] Therefore, the present inventors aim to provide a conductive material dispersion containing SWCNT clusters with limited length and diameter characteristics and unique features, which ensures excellent dispersibility without increasing the viscosity of the dispersion, and allows for intuitive prediction of the ability to form conductive paths within the electrode based on such measurements.

[0036] SWCNT clusters contained in a conductive material dispersion according to one embodiment of the present invention are characterized by having a number-average length of 0.8 μm to 8.0 μm, with SWCNT clusters having a length exceeding 10 μm accounting for 15% or less of the total number of clusters. The ratio of the number-average length of the SWCNT clusters to the number of SWCNT clusters having a length exceeding 10 μm can be derived from the number distribution obtained by the atomic force microscope measurement described above.

[0037] The SWCNT clusters are characterized by having an appropriate length that satisfies a number-average length of 0.8 μm to 8.0 μm, and by the exclusion of SWCNT clusters with lengths exceeding 10 μm. Furthermore, within the range that satisfies the number-average length, the formed conductive network is well maintained despite the volume expansion of the electrodes that occurs during the charge-discharge cycle process.

[0038] According to one embodiment of the present invention, the SWCNT clusters have a number average length of 0.8 μm to 8.0 μm, preferably 0.9 μm or more, 1.0 μm or more, 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm or more, or 1.5 μm or more, and may be 7.8 μm or less, 7.5 μm or less, 7.0 μm or less, 6.5 μm or less, 6.0 μm or less, 5.5 μm or less, 5.0 μm or less, 4.5 μm or less, or 4.0 μm or less. If the number average length is less than 0.8 μm, the length may be too short, making it difficult to maintain the conductive network connection path due to volume changes in the electrode caused by charging and discharging. Also, if the number average length exceeds 8.0 μm, the number of SWCNT clusters per unit weight decreases, while the viscosity of the dispersion increases, which can lead to problems in achieving a uniform distribution within the electrode.

[0039] Furthermore, according to one embodiment of the present invention, the SWCNT cluster is characterized in that SWCNT clusters with a length exceeding 10 μm account for 15% or less of the total number of SWCNT clusters, preferably 13% or less, 11% or less, 10% or less, or 9% or less. If the number of SWCNT clusters with a length exceeding 10 μm exceeds 15%, it becomes impossible to control the viscosity of the dispersion, and even if the dispersion conditions are adjusted to achieve uniform dispersion, the possibility of a rapid and drastic change in viscosity over time can increase sharply. In addition, the more long SWCNT clusters there are in number, the more difficult it becomes to achieve a uniform distribution within the electrode, and the greater the possibility that the prediction for ensuring conductivity measured in the dispersion will not be intuitively reflected in the state of the electrode. Therefore, the control of the number of SWCNT clusters with a length exceeding 10 μm needs to be precise.

[0040] SWCNT clusters contained in a conductive material dispersion according to one embodiment of the present invention are characterized by having a number-average diameter of 7 nm to 20 nm, with SWCNT clusters having a diameter exceeding 30 nm accounting for 10% or less of the total number. The ratio of the number-average diameter of the SWCNT clusters to the number of SWCNT clusters with a diameter exceeding 30 nm can be derived from the number distribution obtained by the atomic force microscope measurement described above.

[0041] The SWCNT clusters are characterized by having a diameter at an appropriate level that satisfies a number-average diameter of 7 nm to 20 nm, and by the exclusion of an excessive amount of SWCNT clusters with a diameter exceeding 30 nm. Furthermore, within the range that satisfies the number-average diameter, the formed conductive network can be well maintained despite the volume expansion of the electrodes that occurs during the charge-discharge cycle process.

[0042] According to one embodiment of the present invention, the SWCNT cluster has a number-average diameter of 7 nm to 20 nm, preferably 8 nm or more, 9 nm or more, 10 nm or more, 11 nm or more, or 12 μm or more, and may also be 19 nm or less, 18 nm or less, 17 nm or less, 16 nm or less, or 15 nm or less. If the number-average diameter is less than 7 nm, the diameter is too small, making the SWCNT cluster easily damaged during charging and discharging, and problems such as disconnection due to volume expansion may occur, making it difficult to maintain the conductive network connection path. Furthermore, if the number-average diameter exceeds 20 nm, the number of SWCNT clusters per unit weight decreases, while the viscosity of the dispersion increases, resulting in inadequate dispersion and problems where the distribution within the electrode cannot be uniform. If it adheres to the surface of the active material, it may act as a factor that hinders the mobility of lithium ions.

[0043] According to one embodiment of the present invention, the SWCNT cluster is characterized in that SWCNT clusters with a length exceeding 30 nm account for 10% or less of the total number of SWCNT clusters, preferably 9% or less, 8% or less, or 7% or less. If the number of SWCNT clusters with a diameter exceeding 30 nm exceeds 10%, it becomes impossible to control the viscosity of the dispersion, and even if the dispersion conditions are adjusted to achieve uniform dispersion, the possibility of a rapid and drastic change in viscosity over time can increase sharply. Furthermore, the more SWCNT clusters with a large diameter there are in number, the more difficult it becomes to achieve a uniform distribution within the electrode, and as mentioned above, they are likely to act as a factor that hinders the mobility of lithium ions. Therefore, the number of SWCNT clusters with a diameter exceeding 30 nm needs to be precisely controlled.

[0044] Typically, in the case of conductive material dispersions containing carbon nanotubes, the volume-cumulative average particle size (D) is used to predict the formation of conductive paths and uniform distribution at the electrodes. 50 and / or D 90 While it is common to utilize ) in such dispersions, the particle size distribution in such dispersions does not accurately reflect the length and diameter of carbon nanotubes or their aggregates, and even when applying materials with the same particle size distribution, the performance of the electrodes differs. However, the length and diameter characteristics obtained from the cumulative length and diameter distribution obtained from atomic force microscope images according to one embodiment of the present invention show substantially the same degree of formation of conductive networks in the dispersion state and within the electrode, and can therefore act more effectively and intuitively to improve the performance of the electrodes.

[0045] According to one embodiment of the present invention, the SWCNT cluster can be included in an amount of 0.2 to 3.5 parts by weight per 100 parts by weight of the conductive material dispersion, specifically 0.2 to 3.0 parts by weight. When this range is met, high productivity is maintained, and the transfer and input of the electrode slurry is easy. Furthermore, since the solid content of the manufactured electrode slurry is not excessively low, the occurrence of binder migration during electrode drying can be suppressed. This improves the adhesion of the electrode, allows for effective packing of the electrode active material layer, and enables the manufacture of electrodes with a small thickness.

[0046] (2) Dispersant A conductive material dispersion according to one embodiment of the present invention may further contain a dispersant, the dispersant of which one or more are selected from the group consisting of polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol (Polyvinylalchol), polyacrylamide, polyethylene oxide, hydrogenated nitrile copolymer, cellulosic compound, and diisopropylamine (DIPA). Here, the hydrogenated nitrile copolymer may be hydrogenated acrylonitrile-butadiene rubber, and the cellulosic compound may be carboxymethyl cellulose (CMC) or hydroxyethyl cellulose (HEC).

[0047] Furthermore, the dispersant in the conductive material dispersion can be present in an amount of 0.2 to 7.0 parts by weight, specifically 0.2 to 6.0 parts by weight, or more specifically 0.3 to 5.0 parts by weight, per 100 parts by weight of the conductive material dispersion. When this range is met, the carbon-based conductive material can be smoothly dispersed in the conductive material dispersion, improving the energy density of the manufactured electrode and reducing its resistance.

[0048] <(3) Solvent> According to one embodiment of the present invention, the conductive material dispersion may further contain a solvent, the solvent of which includes water or an organic solvent, and the organic solvent may contain one or more heteroatoms selected from the group consisting of nitrogen atoms (N) and oxygen atoms (O) having lone pairs of electrons.

[0049] Specifically, the organic solvents 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; and glycerin, trimethylolpropane, pentaerythritol, or sorbitanol. Examples include polyhydric alcohols such as thor; 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; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. One or more of these mixtures can be used. N-methylpyrrolidone (NMP) is particularly preferred considering its miscibility with the electrode slurry.

[0050] (4) Others According to one embodiment of the present invention, the solid content of the conductive material dispersion may be 0.3% to 7.0% by weight, more specifically 0.4% to 5.0% by weight, and more specifically 0.5% to 3.5% by weight. When this range is satisfied, the viscosity of the conductive material dispersion can be kept at a low level, and the dispersion of the conductive material can be effectively carried out. Here, the solid content may refer to SWCNT clusters and dispersants contained in the conductive material dispersion.

[0051] The conductive material dispersion of the present invention, containing the components described above, can be produced by mixing SWCNT clusters, a dispersant, and a solvent. Here, the mixing can be carried out using a conventional mixing method, specifically using a mixing device such as a homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer, clear mixer, spike mill, or TK mixer, and the mixing order of each component is not particularly limited. That is, the conductive material dispersion of the present invention may be produced by adding single-wall carbon nanotubes (e.g., in a large bundle state of micro units) to the solvent, followed by adding and mixing the dispersant; or by first adding the dispersant to the solvent, followed by mixing the single-wall carbon nanotube bundles; or by adding both the single-wall carbon nanotube bundles and the dispersant to the solvent, followed by mixing.

[0052] On the other hand, in the mixing process, cavitation dispersion treatment may be performed to improve the dispersibility of the single-wall carbon nanotube bundles. This cavitation dispersion treatment is a dispersion method that uses shock waves generated when vacuum bubbles formed in water burst when high energy is applied to the liquid, and this method allows for dispersion in SWCNT clusters without damaging the properties of the single-wall carbon nanotubes. Specifically, this cavitation dispersion treatment can be performed by ultrasound, jet milling, or shear dispersion treatment.

[0053] According to one embodiment of the present invention, the conductive material dispersion may further contain point-like conductive materials. The further conductive materials may have different properties from the SWCNT clusters having the above-described properties, and it is preferable that their shape characteristics are different. If conductive materials with similar shape characteristics, such as linear conductive materials like multi-walled carbon nanotubes or carbon nanofibers, are included, it may affect the formation of the conductive network due to the characteristics of the SWCNT clusters described above.

[0054] For example, the dot-shaped conductive material may contain carbon black, and the carbon black may include one or more selected from the group consisting of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.

[0055] <Electrode> In another embodiment of the present invention, an electrode comprising an electrode active material layer containing an electrode active material, single-walled carbon nanotube (SWCNT) clusters, and a binder is arranged on a current collector, wherein the SWCNT clusters have a number average length of 0.8 μm to 8.0 μm, with SWCNT clusters having a length greater than 10 μm accounting for 15% or less of the total number, and a number average diameter of 5 nm to 30 nm, with SWCNT clusters having a diameter greater than 30 nm accounting for 15% or less of the total number, and the length and diameter of the SWCNT clusters were measured using an atomic force microscope (AFM).

[0056] Here, the SWCNT cluster is an SWCNT cluster contained in the conductive material dispersion according to the present invention described above. The details regarding this are as described above, so a detailed explanation will be omitted, and the remaining components will be described below.

[0057] According to one embodiment of the present invention, the electrode active material may be a positive electrode active material, the electrode may be a positive electrode, and the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0058] In the positive electrode, the positive electrode current collector may be any material that does not cause a chemical change in the battery and has conductivity, and is not particularly limited. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0059] The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, preferably 300 μm or less, 200 μm or less, 100 μm or less, or 8 μm or less. Fine irregularities can also be formed on the surface of the current collector to strengthen the bonding force with the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0060] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganate such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3) represented by Ni-site type lithium nickel oxide or lithium nickel - ternary system oxide; chemical formula LiMn 2-c3 M c3Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li metal.

[0061] Preferably, the positive electrode active material may include one or more selected from the group consisting of lithium nickel-ternary oxide, perlithium manganese oxide, lithium iron phosphorus oxide, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide.

[0062] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0063] Here, the positive electrode conductive material can be the conductive material dispersion described above, and may also be further included in addition to the conductive material dispersion to impart conductivity to the electrode. In the battery that is constructed, it can be used without particular limitations as long as it does not cause a chemical change and has electronic conductivity.

[0064] Specific examples include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; fibrous carbon materials such as carbon nanotubes, carbon nanofibers, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone or in mixtures of two or more.

[0065] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used.

[0066] According to one embodiment of the present invention, the electrode active material may be a negative electrode active material, the electrode may be a negative electrode, and the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing the negative electrode active material.

[0067] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used.

[0068] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm, preferably 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities can be formed on the surface of the current collector to strengthen the bonding force with the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0069] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; (quasi) 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; SiO v (0 < v ≤ 2), (quasi) metal oxides such as SnO2, vanadium oxides, and lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material, such as Si-C composites or Sn-C composites. Any one or a mixture of two or more of these can be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0070] For example, the negative electrode active material can include one or more selected from the group consisting of carbon-based particles, silicon-based particles, and carbon-silicon-based composite particles. Further, preferably, the negative electrode active material can include a silicon-based active material. For example, it can include Si particles, SiO v (0 < v ≤ 2), or a Si-C composite.

[0071] The negative electrode active material may be present in an amount of 70% to 99% by weight relative to the total solid content in the negative electrode slurry, and may be present in an amount of 75% or more by weight, 80% or more by weight, 85% or more by weight, 90% or more by weight, or 95% or more by weight, or 99.0% or less by weight, 98.5% or less by weight, 98.0% or less by weight, or 97.5% or less by weight. When the content of the negative electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0072] The binder is for ensuring adhesion between electrode active materials or between electrode active materials and current collectors, and any common binder used in the art can be used, and its type is not particularly limited. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more can be used.

[0073] The binder may be present in an amount of 10.0% by weight or less relative to the total solid content in the negative electrode slurry, preferably 0.5% by weight or more, 1.0% by weight or more, 1.5% by weight or more, or 2.0% by weight or more, or 9.0% by weight or less, 8.0% by weight or less, 7.0% by weight or less, or 5.0% by weight or less. When the binder content satisfies the above range, the increase in electrode resistance can be minimized and excellent electrode adhesion can be achieved.

[0074] Here, the negative electrode conductive material can be the conductive material dispersion described above, and may also be further included in addition to the conductive material dispersion to impart conductivity to the electrode. In the battery that is constructed, it can be used without particular limitations as long as it does not cause a chemical change and has electronic conductivity.

[0075] Specific examples include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; fibrous carbon materials such as carbon nanotubes, carbon nanofibers, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone or in mixtures of two or more.

[0076] On the other hand, the electrode active material layer can be formed by coating a current collector with an electrode slurry obtained by dispersing a conductive material dispersion containing the electrode active material, binder, and SWCNT clusters in a solvent, followed by drying and rolling processes.

[0077] Specifically, the electrode active material layer can be formed by applying an electrode slurry onto an electrode current collector and then drying it, or by applying an electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the electrode current collector. If necessary, after forming the electrode active material layer by the above methods, a rolling step may be further performed. Here, drying and rolling can be carried out under appropriate conditions considering the physical properties of the electrode to be ultimately manufactured, and are not particularly limited.

[0078] The electrode slurry may further contain a solvent as needed to adjust viscosity, etc. Here, the solvent may be water, an organic solvent, or a mixture thereof. Examples of the aforementioned organic solvents 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; and polyvalent solvents such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include 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, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. Any one or more of these mixtures may be used, but are not limited to these.

[0079] The solvent can be included in such a concentration that the solid content in the electrode slurry is 40% to 85% by weight, preferably 50% to 80% by weight. When this range is met, binder migration can be suppressed, electrode adhesion can be improved, the drying temperature can be lowered, coating properties can be improved, the coating speed can be increased, and productivity can be improved.

[0080] <Lithium-ion secondary battery> A lithium secondary battery according to yet another embodiment of the present invention has a structure in which a positive electrode, a separator, and a negative electrode are stacked in order, and one or more of the positive electrode and the negative electrode are the electrodes described above. Specifically, the lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, where the positive electrode and the negative electrode are as described above.

[0081] Below, we will only explain the remaining components.

[0082] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator that is normally used in secondary batteries. Specifically, as the separator, a porous polymer film can be used, for example, a porous polymer film made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0083] According to one embodiment of the present invention, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or any other such electrolyte that can be used in the manufacture of lithium secondary batteries, and is not limited to these.

[0084] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0085] Examples of non-aqueous organic solvents that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0086] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferable to use because they have high dielectric constants as high-viscosity organic solvents and readily dissociate lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more preferable to use.

[0087] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 - You may use one or more selected from the group consisting of the following.

[0088] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds including difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0089] Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0090] <Examples 1a-4a and Comparative Examples 1a-9a: Conductive Material Dispersions> One part by weight of a single-wall carbon nanotube bundle, one part by weight of polyvinylpyrrolidone (PVP, K15, manufactured by Zhangzhou Huafu) as a dispersant, and 200 parts by weight of N-methylpyrrolidone were mixed. The mixture was then primary-mixed for 180 minutes using a mixer (BTM-50, disper 1000 rpm / anchor 100 rpm). The resulting mixture was then subjected to secondary mixing of conductive material dispersions obtained by varying the number of circulation cycles using a high-pressure homogenizer (NG-20K, manufactured by Genizer) at different mixing ratios (weight ratios) as shown in Table 1 below. Dispersions containing SWCNT clusters with a solid content of 1% by weight were obtained.

[0091] [Table 1]

[0092] <Experimental Example 1: Measurement of Length and Particle Size> After diluting the conductive material dispersions of the above examples and comparative examples with water, 50 μl of the diluted solution was dropped onto the surface of freshly cleaved mica, and then vacuum-dried to prepare the samples.

[0093] The manufactured samples were imaged using an atomic force microscope (AFM) (Asylum Research, Cypher ES AFM System) under the following conditions.

[0094] -Measurement mode: AC Air Topography mode (Tapping mode) -Measurement conditions: Set point 0.4V, Scan rate 1.5 Hz - Measurement image size: Measured at magnifications of 20μm×20μm, 15μm×15, and 10μm×10μm. -Probe:AC160TS(n-type doped Si, reflective Al coating, f0300 kHz, k 26 N / m)

[0095] Using the AFM images obtained under the aforementioned conditions, the lengths and diameters of 100 or more SWCNT clusters were measured (using an image processing program). After obtaining the length distribution, the number-average lengths and diameters, the number ratio of SWCNT clusters with a length exceeding 10 μm, and the number ratio of SWCNT clusters with a diameter exceeding 30 nm were derived.

[0096] Volume cumulative average particle diameter D 50 (μm) and D 90 The particle size (μm) was determined by introducing the conductive material dispersion into a laser diffraction particle size analyzer (Mastersizer2000, Malvern), irradiating it with ultrasound at approximately 28 kHz at an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume-cumulative amount.

[0097] [Table 2]

[0098] Referring to Table 2 above, the volume cumulative average particle size D in the dispersion 50 and D 90 Despite similar values, it can be observed that the lengths of the SWCNT clusters contained in the electrodes are substantially different.

[0099] Examples 1b-4b and Comparative Examples 1b-9b As the negative electrode active material, the average particle size (D 50A negative electrode slurry with a solid content of 30% was prepared by mixing pure Si particles (5 μm in diameter), particulate conductive material (SFG6L), the conductive material dispersions (based on solid content weight) produced in Examples 1a to 4a and Comparative Examples 1a to 9a, and an aqueous binder in a weight ratio of 80:9.6:0.8:9.6, and using water as the solvent. Here, the aqueous binder is a polymer obtained by polymerization using acrylamide, acrylic acid, and acrylonitrile in a weight ratio of 60:30:10 (polymerization reaction using ammonium persulfate polymerization initiator at 75°C for 8 hours).

[0100] The anode slurry was coated onto one side of an 18 μm thick copper foil to create an active material layer with a thickness of 50 μm, and then dried to produce the anode.

[0101] <Experimental Example 2: Evaluation of Coating Processability and Lifetime Characteristics> An electrode assembly was manufactured by interposing a porous polyethylene separator between the negative electrode and the positive electrode of Examples 1b to 4b and Comparative Examples 1b to 9b. After positioning this assembly inside a case, an electrolyte solution was injected to manufacture a lithium secondary battery.

[0102] Here, the electrolyte was prepared by dissolving 1M LiPF6 in an organic solvent of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate in a volume ratio of 3:4:4, and the positive electrode was prepared as follows.

[0103] The positive electrode is LiNi 0.6 Co 0.1 Mn 0.3 O2, polyvinylidene fluoride, and carbon black were added in a weight ratio of 95:3:2 to produce a positive electrode slurry with a solid content of 70.1% by weight. This slurry was then coated onto a 20 μm thick Al thin film current collector, dried at 130°C, and rolled to produce the product.

[0104] The lithium secondary battery was charged at a rate of 0.1 CC to 4.2 V, and then discharged to 2.5 V to perform an activation process.

[0105] The capacity retention rate was calculated for each lithium secondary battery by first charging it in CCCV mode at 0.2C until it reached 4.25V (termination current 1 / 20C), then charging it to 4.25V at a constant current of 0.33C at 45°C, and finally discharging it to 2.5V at a constant current of 0.33C. One cycle was defined as performing 100 charge-discharge cycles while measuring the charge-discharge capacity, and the capacity retention rate was calculated as follows.

[0106] Capacity retention rate (%) = (Discharge capacity after 100 cycles) / (Discharge capacity after 1 cycle) × 100

[0107] The coating processability was assessed by observing whether stains occurred on the electrode surface, whether pinholes occurred, and whether the filter in the slurry circulation pump became clogged when coating the copper foil with the negative electrode slurry. If any of these problems occurred, it was evaluated as ×, and if no problems occurred, it was evaluated as ○.

[0108] [Table 3]

[0109] Referring to Table 3 above, it can be confirmed that when the negative electrodes of Examples 1b to 4b were applied, no problems occurred in the coating process and the capacity retention rate was at an excellent level. However, when the negative electrodes of Comparative Examples 1b and 2b were applied, the capacity retention rate was about 20% lower than that of the examples, which can be said to be a difference in performance that cannot be distinguished by the particle size distribution of the conductive material dispersion.

[0110] Specifically, the results of Comparative Examples 1b and 2b indicate that, even if the particle size in the dispersion is considered to be of an appropriate size, the actual length of the SWCNT clusters was too short to properly form conductive paths. This suggests that performance can be improved when the conductive material dispersion has the characteristics of the present invention.

[0111] Furthermore, when the negative electrode of Comparative Example 3b is applied, an excessive amount of long SWCNT clusters are present, the number-average length is also long, and it can be confirmed that problems occur in the coating process.

[0112] Furthermore, when the negative electrode of Comparative Example 4b was applied, the length characteristics were satisfied, but the particle size characteristics in the dispersion did not differ significantly from those of the example, as the SWCNT clusters had a large number-average diameter relative to their length. Therefore, it is thought that no problems occurred during dispersion. However, because the diameter was relatively large relative to the length, a good conductive network could not be formed overall within the electrode, resulting in a low capacity retention rate. Comparative Examples 5b and 6b showed similar results to Comparative Example 4b because they contained a relatively excessive amount of SWCNT clusters with large diameters.

[0113] Furthermore, when the negative electrode of Comparative Example 7b is applied, although the number of long SWCNT clusters is small, it is expected that the difference in number-average length will increase the likelihood of dispersion problems compared to when the negative electrode of Example 4b is applied, and the capacity retention rate will also be about 10% lower.

[0114] Comparative Example 8b, similar to the case where the negative electrode of Comparative Example 3b was applied, shows that the presence of an excessive number of long SWCNT clusters causes dispersion problems and leads to issues with the coating processability. When the negative electrode of Comparative Example 9b was applied, the capacity retention rate was very poor, suggesting that the clusters were short in length and diameter, and that the conductive network was not formed properly.

Claims

1. Contains single-walled carbon nanotube (SWCNT) clusters, The SWCNT clusters have a number-average length of 0.8 μm to 8.0 μm. SWCNT clusters with a length exceeding 10 μm account for less than 15% of the total number. The number-average diameter is 5 nm to 25 nm. SWCNT clusters with a diameter exceeding 30 nm account for less than 15% of the total number. The length and diameter of the SWCNT cluster are measured using an atomic force microscope in a conductive material dispersion.

2. The conductive material dispersion according to claim 1, wherein the SWCNT clusters have a number-average length of 1.0 μm to 6.0 μm.

3. The conductive material dispersion according to claim 1, wherein the SWCNT clusters consist of SWCNT clusters with a length exceeding 10 μm, accounting for 10% or less of the total number of SWCNT clusters.

4. The conductive material dispersion according to claim 1, wherein the SWCNT cluster has a number mean diameter of 7 nm to 20 nm.

5. The conductive material dispersion according to claim 1, wherein the SWCNT clusters consist of SWCNT clusters with a diameter greater than 30 nm, accounting for 10% or less of the total number of SWCNT clusters.

6. The conductive material dispersion further comprises a dispersant, The conductive material dispersion according to claim 1, wherein the dispersant comprises one or more selected from the group consisting of polyacrylate, polyvinylidene fluoride, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylamide, polyethylene oxide, carboxymethylcellulose, and diisopropylamine.

7. With respect to 100 parts by weight of the conductive material dispersion, SWCNT cluster 0.2 parts by weight to 3.5 parts by weight, A conductive material dispersion according to claim 6, comprising 0.2 to 7.0 parts by weight of a dispersant.

8. An electrode active material layer containing electrode active material, single-wall carbon nanotube (SWCNT) clusters, and a binder is arranged on a current collector. The SWCNT cluster is The number-average length is 0.8 μm to 8.0 μm. SWCNT clusters with a length exceeding 10 μm account for less than 15% of the total number. The number-average diameter is 5 nm to 30 nm. SWCNT clusters with a diameter exceeding 30 nm account for less than 15% of the total number. The length and diameter of the SWCNT cluster are measured using an atomic force microscope, and the electrodes.

9. The electrode active material is a positive electrode active material, The electrode according to claim 8, wherein the positive electrode active material comprises one or more selected from the group consisting of lithium nickel-ternary oxide, perlithium manganese oxide, lithium iron phosphorus oxide, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide.

10. The electrode active material is a negative electrode active material, The electrode according to claim 8, wherein the negative electrode active material comprises one or more selected from the group consisting of carbon-based particles, silicon-based particles, and carbon-silicon composite particles.

11. The electrode further comprises a point-shaped conductive material, The electrode according to claim 8, wherein the point-shaped conductive material includes carbon black.

12. It has a structure in which the positive electrode, separator, and negative electrode are stacked in order. A lithium secondary battery in which one or more of the positive electrode and the negative electrode are electrodes according to any one of claims 8 to 11.

Images