Conductive material dispersion, electrode slurry comprising same, and secondary battery comprising electrode derived from electrode slurry

Abstract

Disclosed in the present specification is an invention relating to a conductive material dispersion comprising a carbon nanocable and a dispersant, wherein the carbon nanocable is formed by arranging a plurality of carbon nanotube units comprising single-walled carbon nanotubes and double-walled carbon nanotubes in the longitudinal direction and the radial direction and bonding same, the carbon nanotube units have an average diameter of 1.8 nm to 4.0 nm, and the carbon nanocable has a volume cumulative 90% average particle diameter D90 of 10 µm or less and a volume cumulative 99% average particle diameter D99 of 15 µm or less in dispersion. The conductive material dispersion can provide a secondary battery having improved resistance characteristics and lifespan characteristics by using the carbon nanocable having a high packing density and a long length as a conductive material.

Description

A secondary battery comprising a conductive material dispersion, an electrode slurry containing the same, and an electrode derived from the electrode slurry.

[0001] The present invention relates to a conductive material dispersion, an electrode slurry containing the same, an electrode derived from the conductive material dispersion, an electrode derived from the electrode slurry, and a secondary battery comprising the electrode.

[0002]

[0003] Rechargeable batteries are a representative example of electrochemical devices that utilize electrochemical energy, and their application areas are increasingly expanding. Recently, with the technological development and growing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for rechargeable batteries as an energy source has been rapidly increasing. Among these rechargeable batteries, much research has been conducted on high-energy-density, or high-capacity, rechargeable batteries, which have been commercialized and are widely used.

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

[0005] Meanwhile, point conductive materials such as carbon black have conventionally been primarily used as conductive materials for secondary batteries; however, these point conductive materials have the problem of not providing sufficient improvement in electrical conductivity. To address this issue, research is actively underway on methods to apply linear conductive materials such as carbon nanotubes (CNT) and carbon nanofibers (CNF), as well as planar conductive materials such as graphene.

[0006] However, in the case of linear conductive materials such as carbon nanotubes or carbon nanofibers, although electrical conductivity is excellent, there are problems such as poor dispersibility in the slurry due to the inherent characteristics of the material itself, which grows in a bundle or entangle type, resulting in poor coating and processability, and uneven distribution within the electrode composite layer. To address these issues, there have been attempts to improve dispersibility by introducing functional groups into the linear conductive materials; however, in this case, there is a problem in that the presence of functional groups causes surface side reactions, leading to a decrease in electrochemical properties.

[0007] Meanwhile, although planar conductive materials such as graphene exhibit excellent electrical conductivity, there is a problem in that manufacturing thin single-layer graphene is difficult, and using thick graphene leads to a decrease in cell efficiency. Additionally, planar conductive materials present a problem in that the mobility of the electrolyte within the battery is restricted due to the wide planar contact.

[0008] Therefore, there is a need to develop electrodes incorporating conductive materials that have excellent electrical conductivity and can be uniformly distributed within the electrode.

[0009]

[0010] In this specification, we aim to provide a conductive material dispersion comprising carbon nanocables that have excellent dispersibility, high solid content despite low viscosity, and excellent length characteristics despite having few defects, thereby providing excellent ability to form a conductive network within an electrode.

[0011] In this specification, we aim to provide an electrode comprising a carbon nanocable that, by including the conductive material, can maintain excellent electrical characteristics even with damage occurring during the dispersion process of the conductive material or slurry and damage caused by shrinkage and expansion of the electrode during the operation process of the battery, has few defects and excellent length characteristics, and substantially does not have long lengths that hinder the movement of lithium ions.

[0012] In this specification, we aim to provide a secondary battery with improved resistance characteristics and lifespan characteristics by including the electrode.

[0013]

[0014] [1] In one aspect, the carbon nanocable comprises a carbon nanocable and a dispersant, wherein the carbon nanocable comprises a plurality of carbon nanotube units, including single-walled carbon nanotubes and double-walled carbon nanotubes, arranged and bonded in the longitudinal and diametrical directions, and the carbon nanotube units have an average diameter of 1.8 nm to 4.0 nm, and the carbon nanocable has an average particle size D of 90% of the cumulative volume in the dispersion phase. 90 This is 10 µm or less, and the 99% volume-cumulative average particle size D 99 A conductive material dispersion with a thickness of 15 μm or less is provided.

[0015] [2] In the conductive material dispersion of [1] above, the carbon nanocable has an average particle size D of 50% of the cumulative volume of the dispersion phase. 50 This may be 5 μm or less.

[0016] [3] In the conductive material dispersion of [1] and / or [2] above, the carbon nanocable may have an oxygen atom content of 1.5 at% or more as measured by photoelectron spectroscopy (XPS).

[0017] [4] In at least one of the conductive material dispersions of [1] to [3] above, the carbon nanocable may have a chlorine atom content of 0.1 at% or less as measured by photoelectron spectroscopy.

[0018] [5] In at least one of the conductive material dispersions of [1] to [4] above, the carbon nanocable has a peak due to CO bonding and a peak due to C=O bonding in a graph obtained by photoelectron spectroscopy, and the intensity of the peak due to CO bonding may be stronger than the intensity of the peak due to C=O bonding.

[0019] [6] In at least one of the conductive material dispersions of [1] to [5] above, the carbon nanocable has a BET specific surface area of ​​500 m² 2 / g to 900 m 2 It could be / g.

[0020] [7] In at least one of the conductive material dispersions of [1] to [6] above, the carbon nanotube unit may have an average diameter of 2.0 nm to 3.8 nm and a standard deviation of diameter of 0.30 or more.

[0021] [8] In at least one of the conductive material dispersions of [1] to [7] above, the plurality of carbon nanotube units may contain at least 30% double-walled carbon nanotubes based on the number.

[0022] [9] In at least one of the conductive material dispersions of [1] to [8] above, the carbon nanocable contains four or fewer carbon nanotube units within a 5 nm x 5 nm grid defined on a cross-sectional diameter, and the number of carbon nanotube units may be such that the cross-sectional area within the region is at least 50%.

[0023]

[0010] In another aspect, an electrode slurry comprising an electrode active material, a binder, and the conductive material dispersion is provided.

[0024]

[0011] In the electrode slurry of

[0010] above, the electrode active material is a negative electrode active material, and the negative electrode active material may include a silicon-based active material.

[0025]

[0012] In another aspect, a secondary battery is provided comprising an electrode comprising an electrode active material, a binder, and a conductive material derived from at least one of [1] to [9].

[0026]

[0013] In the secondary battery of the above

[0012] , the electrode active material is a negative electrode active material, and the negative electrode active material may include a silicon-based active material.

[0027]

[0028] The conductive material dispersion described in this specification is a fibrous conductive material that contains a small amount of particles with a large volume-cumulative average particle size in the dispersion and a small volume-cumulative average particle size of 90%, thereby allowing the solid content to be increased while maintaining a low viscosity, resulting in excellent dispersibility and an increase in the solid content of the conductive material in the slurry. In addition, due to the excellent dispersibility, a smooth and seamless conductive network can be formed, and since there are no factors hindering the movement of lithium ions as well as the movement of electric charges, an electrode with excellent resistance characteristics can be manufactured.

[0029] The electrode described in this specification has a low content of large particles and a small size of the large particles present, thereby minimizing the presence of excessively long fiber-shaped conductive materials dispersed within the electrode, so that the region where the conductive material is aggregated is minimized and there are no factors hindering the movement of lithium ions, so that it can have excellent resistance characteristics.

[0030] In addition, the carbon nanocable, which is a fiber-shaped conductive material, comprises a carbon nanocable containing single-walled carbon nanotubes and double-walled carbon nanotubes as units. The carbon nanocable can form a carbon nanocable with excellent packing density, and because it includes double-walled carbon nanotubes, it can minimize the interruption of the conductive path even in the event of defects caused by external forces, thereby improving resistance characteristics and contributing to the improvement of the lifespan of the secondary battery due to its excellent ability to maintain the conductive path.

[0031] The secondary battery described in this specification has excellent resistance characteristics of the electrode and excellent durability against volume expansion due to the length characteristics and conductive path retention ability of the carbon nanocables included in the electrode, so output characteristics and lifespan characteristics can be improved.

[0032]

[0033] Figure 1 is a schematic diagram showing the shape of a carbon nanocable viewed from the side.

[0034] Figure 2 shows a cross-section perpendicular to the longitudinal direction of a carbon nanocable, and is a schematic cross-sectional diagram along the line A-A' of Figure 1.

[0035] Figure 3 is a schematic cross-sectional view showing a cross-section perpendicular to the longitudinal direction of a structure composed solely of single-walled carbon nanotubes.

[0036] Figure 4 is a transmission electron microscope (TEM) image of a cross- section of a carbon nanocable.

[0037] Figure 5 is a transmission electron microscope (TEM) image of a cross- section of a single-walled carbon nanotube structure.

[0038]

[0039] 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 in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0040] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0041] In this specification, "carbon nanocable" may refer to a specific type of structure formed by combining or aggregating multiple units (e.g., several to thousands) of "units," which represent a single strand of carbon nanotube. Here, the unit may consist of a mixture of single-walled carbon nanotubes with one wall and double-walled carbon nanotubes with two walls. Here, "specific type" may refer to a structure in which multiple unit units are arranged side by side and combined such that their major axes form a substantially parallel relationship, thereby forming a structure similar to an optical fiber while maintaining flexibility through the combination of multiple unit units in the longitudinal and diametric directions. Here, "substantial parallel relationship" does not refer to the relationship between two straight lines that never meet, as in the mathematical sense of parallelism, but rather refers to a relationship in which the major axes of the unit units do not meet within at least 50% of the total length of the individual carbon nanocable.

[0042] In this specification, the term "structure" may refer to a form in which a plurality of "units" (e.g., several to thousands) of which represent a single strand of carbon nanotube are combined / aggregated to form a cluster, and may include the meanings of "bundle" or "entangle" commonly used in this technical field; however, when used after a specific term, for example, in a term such as "single-walled carbon nanotube structure," the term "structure" refers to a form different from the "bundle" or "entangle," and may refer to a form similar to the carbon nanocable.

[0043] In this specification, "D 50 ", "D 90 " and "D 99 " refers to the particle size at the 50%, 90%, and 99% references of the volume-cumulative particle size distribution of the powder or dispersion. The above average particle size can be measured using the laser diffraction method. For example, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000, Malvern), obtaining a volume-cumulative particle size distribution graph, and then determining the particle sizes corresponding to 50%, 90%, and 99% of the volume-cumulative amount.

[0044] In this specification, "average particle size" refers to the arithmetic mean of the particle sizes of at least 30 particles observed in a scanning electron microscope image when observed at a field of view of 5,000 to 20,000x using a scanning electron microscope. In this case, particle size refers to the diameter of the longest axis of the particle. The above "volume cumulative average particle size D" 50 Although " and "average particle size" differ in their measurement methods, their values ​​can be derived similarly, and the volume-cumulative average particle size D measured in the powder state 50After the powder is manufactured into an electrode, it may have a value similar to the average particle size observed in the scanning electron microscope image of the electrode and the error range level.

[0045] In this specification, “specific surface area (m² 2 / g)” is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BEL Japan’s BELSORP-mino II.

[0046]

[0047] Each of the carbon nanocable, conductive material dispersion, electrode, and secondary battery according to the present specification comprises at least one of the configurations described below and may comprise any combination of technically feasible configurations among the following configurations.

[0048]

[0049] Dispersed conductive material

[0050] In one aspect, the apparatus comprises a carbon nanocable and a dispersant, wherein the carbon nanocable may consist of a plurality of carbon nanotube units, including single-walled carbon nanotubes and double-walled carbon nanotubes, arranged and bonded in the longitudinal and diametrical directions, and the carbon nanotube units may have an average diameter of 1.8 nm to 4.0 nm, and the carbon nanocable has an average particle size D of 90% of the cumulative volume in the dispersion phase. 90 This is 10 µm or less, and the 99% volume-cumulative average particle size D 99 It can be characterized as being 15 μm or less.

[0051] Generally, fibrous conductive materials have excellent length characteristics; for instance, their long length makes them advantageous for forming conductive networks, which gives them the advantage of high utility despite their high unit cost. However, long conductive materials present difficulties in dispersion, and due to these difficulties, various attempts are being made to reduce the use of long conductive materials or devise dispersion methods.

[0052] Meanwhile, in the case of long conductive materials, such as structures formed by the combination of multiple carbon nanotubes, it has been believed that there are no performance issues if the dispersion phase problem described above can be resolved. However, when fibers with excessively long lengths are present, there is inevitably some aggregation regions within the electrode due to the remaining dispersion phase problem. This can hinder the movement of lithium ions, which has the disadvantage of potentially causing problems with the rapid charging performance that is a recent trend. Furthermore, defects are bound to occur in some form in the materials contained within the electrode during the dispersion process of the conductive material, the dispersion process of the slurry, and the charge-discharge reaction process of the battery. In the case of relatively long fibers, the number of defects within a single conductive path may be high. When there are many defects within a single conductive path, there is a problem that the movement of electric charge may be obstructed.

[0053] The present invention aims to provide a conductive material dispersion that can maximize the solid content while controlling the viscosity to a low level by controlling the volume-cumulative average particle size in the conductive material dispersion state, thereby ensuring excellent dispersibility within the electrode and eliminating the presence of long fibers, which can minimize factors that may hinder the mobility of lithium ions or charge mobility.

[0054]

[0055] Cumulative average particle size of the dispersion phase

[0056] The above conductive material dispersion has a volume-cumulative average particle size D of carbon nanocables in the dispersion phase at 90%. 90 This is 10 µm or less, and the 99% volume-cumulative average particle size D 99 It can be characterized as being 15 μm or less.

[0057] The above carbon nanocable is in a dispersion state D 90 It is characterized by being 10 μm or less, preferably 9.5 μm or less, 9.0 μm or less, or 8.8 μm or less, and additionally may be 5.0 μm or more, 6.0 μm or more, or 7.0 μm or more. The above D 90 If this exceeds 10 μm, it means that about 10 volume percent of the particles have an average particle size of 10 μm or more, so the presence of long carbon nanocables may result in poor dispersibility. In other words, as the particles reaching 10 volume percent become larger, the viscosity characteristics of the dispersion may deteriorate, and it may also be difficult to increase the solid content.

[0058] The above carbon nanocable is in a dispersion state D 99 It is characterized by being 15 μm or less, preferably 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, 10 μm or less, or 9.5 μm or less, and additionally may be 7.0 μm or more, 7.5 μm or more, 8.0 μm or more, or 8.5 μm or more. D 99 In cases where the particle size is larger than 15 μm, the large particle size is too large, so long carbon nanocables exist within the electrode, which inevitably leads to the existence of factors that hinder the mobility or charge mobility of lithium ions.

[0059] In addition, the above carbon nanocable is in a dispersion state D 50 This may be 5 μm or less, preferably 4.8 μm or less, 4.7 μm or less, or 4.5 μm or less, and D 50The smaller the size, the more advantageous it may be for the dispersibility of carbon nanocables in the conductive material dispersion or the viscosity characteristics of the dispersion; however, if it is too small, it cannot have the advantages due to the length characteristics of the fiber-type conductive material, so it may be desirable to use at least 1.0 μm, 1.2 μm or more, or 1.5 μm or more.

[0060]

[0061] carbon nano cable

[0062] The above conductive material dispersion is characterized by comprising a carbon nanocable in which a plurality of carbon nanotube units, including single-walled carbon nanotubes and double-walled carbon nanotubes, are arranged and bonded in the longitudinal and diametrical directions.

[0063] The carbon nanocable described above is a single structure in which multiple carbon nanotube units are bonded together, and can be distinguished from bundled or entangled carbon nanotubes with a diameter of several hundred nanometers to micrometers. For example, the carbon nanocable may consist of several to several hundred carbon nanotube units bonded together, and bonding may occur in both the diameter direction and the length direction of the units. Additionally, by including single-walled carbon nanotubes and double-walled carbon nanotubes as units, a longer structure can be formed.

[0064] FIGS. 1 and 2 are schematic diagrams of a carbon nanocable described in the present specification. Referring to FIG. 1, carbon nanotube units (110) are combined with each other in the diameter direction (Y) and the length direction (X). A carbon nanocable of long length can be formed in such a structure that a single-walled carbon nanotube with a small diameter and a double-walled carbon nanotube with a large diameter are not packed together in a high-density manner, and are easily connected to each other in the length direction and inserted into the gaps.

[0065] Due to having the above-described structure, the carbon nanocable has superior length characteristics compared to a structure containing only single-walled carbon nanotubes, and thus can have an excellent ability to maintain a conductive path.

[0066] Meanwhile, FIG. 3 is a schematic diagram showing a cross-section perpendicular to the longitudinal direction of a carbon nanotube structure (10) composed of carbon nanotube units (110) of the same diameter. Since single-walled carbon nanotubes have only one wall, if they are damaged by an external force, such as during the process of dispersing a conductive material, the process of manufacturing a slurry, or the process of volume expansion of an active material during charging and discharging of a battery, the damaged area may act as a defect, and such a defect may cause a disconnection of the conductive path.

[0067] In other words, in the case of a structure composed of single-walled carbon nanotubes, it can be a conductive material capable of significantly improving battery performance due to the excellent electrical properties of single-walled carbon nanotubes. However, damage is inevitable during the dispersion process of the conductive material, the slurry preparation process, and the charging and discharging process of the battery, and consequently, it is very difficult to fully realize the expected performance.

[0068] However, since the carbon nanocables mentioned above exist not only with one wall but also with two, even if a defect occurs in the outer wall of a unit with two walls, there is a path that can be bypassed during charge transfer, thereby significantly reducing the interruption of the conductive path. Due to these structural characteristics of the carbon nanocables, when incorporated into an electrode, it becomes possible to realize a secondary battery with improved resistance characteristics, output characteristics, and lifespan characteristics.

[0069] In one aspect of the present specification, the plurality of carbon nanotube units included in the carbon nanocable may include single-walled carbon nanotubes and double-walled carbon nanotubes, and the double-walled carbon nanotubes may be included in an amount of 30% or more. That is, when the proportion of double-walled carbon nanotubes among the carbon nanotube units constituting the carbon nanocable is 30% or more in terms of number, the multimodalization of the units may have an excellent effect of preventing the interruption of the conductive path even when a defect occurs, and as the proportion of double-walled carbon nanotubes increases, the packing density may decrease, thereby allowing for the formation of a carbon nanocable of a longer length, and preferably, it may be 35% or more, 40% or more, 45% or more, or 50% or more. Additionally, it may be preferable for the proportion of double-walled carbon nanotubes to be 80% or less in terms of number, and may be 75% or less, 70% or less, or 65% or less.

[0070]

[0071] Raman spectral characteristics of carbon nanocables

[0072] In one aspect, the carbon nanocable may exhibit different characteristics in the Raman spectrum compared to structures or units composed of other multiwalled carbon nanotubes or singlewalled carbon nanotubes.

[0073] Raman spectroscopy is an analytical method capable of verifying various characteristics of carbon-based materials; for example, it can be analyzed using a Raman spectroscopic analyzer (NRS-2000B, Jasco) with an Ar-ion laser at a wavelength of 514.5 nm, and the resulting wavenumber is 60 cm⁻¹ -1 to 1800 cm -1 Characteristics such as crystallinity, length, and diameter of the carbon-based material can be derived through the peaks appearing between them.

[0074]

[0075] In one aspect, the carbon nanocable is I in the Raman spectrum. G / I D It may be characterized by the ratio being 55 to 100. In addition, the above I G / I D The ratio may preferably be 60 or more, 65 or more, or 70 or more, and may also be 98 or less, 95 or less, 92 or less, or 90 or less. Here, the above I G is 1560 cm -1 up to 1600 cm -1 It is the maximum peak intensity within the range of, and the above I D is 1350 cm -1 up to 1400 cm -1 It is the maximum peak intensity within the range.

[0076] As mentioned above, various characteristics of carbon-based materials can be analyzed through the results of Raman spectra, and the aforementioned wavenumber range can indicate the regularity of the arrangement of carbon nanotubes or the degree of defects. For example, a wavenumber range of 1560 cm⁻¹ -1 up to 1600 cm -1 The G peak appearing at [location] can indicate the regularity of the arrangement of the carbon nanocable under measurement, ultimately allowing verification of the length over which a regular structure is maintained, with a wavenumber range of 1350 cm⁻¹. -1 up to 1400 cm -1 The D peak appearing in may indicate the extent to which defects exist in the carbon nanocable being measured.

[0077] For example, multi-walled carbon nanotubes are I G / I D The ratio has a value close to 1, and single-walled carbon nanotubes are I G / I DThe ratio has a large value exceeding 100, which means that the method varies depending on how the number of walls is determined when manufacturing carbon nanotubes, and due to this difference in method, the I as described above G / I D The values ​​may appear differently.

[0078] Multiwalled carbon nanotubes can be manufactured by flowing a carbon source onto a porous catalyst supported with an active ingredient via chemical vapor deposition, allowing carbon nanotubes to grow from the catalyst as the carbon source decomposes. In this process, the catalyst absorbs the carbon source to grow a certain amount, and this absorption and growth process is repeated; consequently, nodes may form in the middle of the manufactured multiwalled carbon nanotubes. These nodes act as defects, which can result in a strong intensity of the D peak in the Raman spectrum. Furthermore, because the manufacturing method inevitably leads to the formation of nodes, cleavage can easily occur at each node, making it difficult to maintain the long length during the dispersion process.

[0079] In the case of single-walled carbon nanotubes, unlike multi-walled carbon nanotubes, controlling conditions during the manufacturing process can be critical. The size of catalyst particles must be controlled to the nanoscale, and the nanotubes can be manufactured by supplying a carbon source while suspended in the air via arc discharge, while maintaining the catalyst particles to prevent aggregation, thereby inducing bidirectional growth. Consequently, carbon nanotubes produced through bidirectional growth rather than nodal growth have almost no nodes, resulting in a very low frequency of defects. Furthermore, because they do not undergo nodal growth, they can be manufactured with longer lengths, which can be well maintained during the dispersion process.

[0080] In the case of the carbon nanocable above, it is obtained by dispersing bundles manufactured by applying a method that combines the manufacturing methods of the single-walled and multi-walled carbon nanotubes above. Although node growth occurs, the size of the catalyst particles is controlled very finely to minimize node formation while also allowing for the formation of a long length. Accordingly, the intensity ratio of the G peak and the D peak can have the range described above. Furthermore, even if the length cannot be maintained when manufacturing the bundle due to node growth, the length can be made longer by inducing de-bundling and re-bundling of the bundle through a dispersion process to recombine the single-walled and double-walled carbon nanotubes.

[0081] Although the above carbon nanocable has some defects compared to single-walled carbon nanotubes, its length is equivalent to that of single-walled carbon nanotubes, as stated in I above. G / I D This can be seen from the ratio, and since the existence of such defects is inevitable even in single-walled carbon nanotubes during the dispersion process or battery operation process, carbon nanocables that can maintain a conductive path even with the presence of defects may be able to exhibit superior electrical properties compared to single-walled carbon nanotubes.

[0082] The above I G / I D The meaning of the ratio may differ depending on whether the carbon nanotubes being measured are large structures such as bundles or entangles, whether they are stranded monomers, and whether they are formed into medium structures through debundling and rebundling from the appropriate dispersion of the large structures. That is, I G / I DEven if the ratios are similar, a simple comparison is not possible because the number or length of defects can have different meanings depending on the form of the material being measured. For example, when measuring large multi-walled carbon nanotube bundles at the micro-scale and single-walled carbon nanotubes cut to very short lengths, the multi-walled carbon nanotube bundles have a long length of regular arrangement but also many defects, so the G peak and D peak intensities may be similar. Similarly, even though the short-cut single-walled carbon nanotubes have fewer defects, their relatively short length means the length is short relative to the number of defects, so it cannot be ruled out that the intensities of the G peak and D peak will also appear similar. Therefore, for an appropriate comparison, it may be desirable to limit the comparison to cases where the scale of the carbon nanotubes is equivalent.

[0083] I of the above carbon nanocable G / I D If the ratio appears between 55 and 100, it may mean that there are few defects even if it is relatively short, or that the length is long, so it can be said to be a range where performance improvement can be expected.

[0084]

[0085] Average diameter of the unit, etc.

[0086] In one aspect, the carbon nanocable may be characterized in that the average diameter of the carbon nanotube unit constituting it is 1.8 nm to 4.0 nm. The average diameter of the carbon nanotube unit may preferably be 2.0 nm to 3.8 nm, 2.1 nm or more, 2.2 nm or more, or 2.3 nm or more, and may also be 3.7 nm or less, 3.6 nm or less, or 3.5 nm or less.

[0087] The average diameter of the carbon nanotube unit is the average value of the diameters of the single-walled and double-walled carbon nanotube units present in the cable. The above range can be interpreted to mean that a certain amount or more of double-walled carbon nanotube units are included, which implies that the packing density is lower compared to when only single-walled carbon nanotube units are present, and ultimately, it is possible to determine whether a long length CNC can be formed.

[0088] The carbon nanocable may be characterized by having a standard deviation of diameter of 0.30 or more. It is difficult to consider a smaller standard deviation of diameter as superior, and it may be desirable to have a slight deviation so that the packing density of the carbon nanocable is as low as possible. If the standard deviation is less than 0.30, the packing density is effectively at the level of a single-walled carbon nanotube, making it difficult to form a long-length structure; therefore, it is preferable to have a standard deviation of 0.30 or more, and more preferably 0.40 or more, 0.45 or more, or 0.50 or more. Additionally, the standard deviation of the diameter may be 0.90 or less, and preferably 0.85 or less, 0.80 or less, 0.75 or less, or 0.70 or less.

[0089] Since the above carbon nanotube unit comprises single-walled carbon nanotubes and multi-walled carbon nanotubes, the diameter can also vary, and the resulting effects are as described above.

[0090] The average diameter and standard deviation of the carbon nanotube monomers can be measured and calculated using a transmission electron microscope (TEM). For example, carbon nanocables extracted from an electrode or carbon nanocables in a dispersion can be diluted 1,000 to 30,000 times and then dried to obtain an image of the diameter cross-section of each carbon nanocable, and the diameters of the monomers present within a single carbon nanocable can be measured from the image to derive the average value and standard deviation.

[0091] Meanwhile, the average diameter of the carbon nanotube unit can be derived from the aforementioned Raman spectrum results, for example, through Radial Breathing Mode analysis, the Raman shift (cm²) in the Raman spectrum -1 ) is 100 cm -1 up to 300 cm -1 Raman shift value of the peak appearing in the range (W r A specific constant for ) 224 cm -1 By calculating the ratio of average diameter (d t , nm) can be calculated, and the following formula can be used.

[0092] [Equation 1]

[0093] d t (nm) = 224 (cm -1 ) / W r (cm -1 )

[0094]

[0095] In one aspect, the carbon nanocable may have a maximum value of 5 or fewer carbon nanotube units contained within a 5 nm x 5 nm grid defined on a cross-sectional diameter, and the number of carbon nanotube units may be such that at least 50% of the cross-sectional area within the region is contained.

[0096] The maximum number of units contained within the 5 nm x 5 nm lattice indicates how tightly or loosely the units within the carbon nanocable are bonded to form a structure; for example, in a structure containing only single-walled carbon nanotubes, seven or more units may be contained within the lattice. Accordingly, the inclusion of seven or more units suggests the possibility of forming a long conductive network and the effect of durability regarding bonding. Preferably, the number of units contained within the 5 nm x 5 nm lattice may be five or fewer, preferably four or fewer, or three or fewer, and at least one may be included.

[0097]

[0098] Method for preparing a conductive material dispersion

[0099] In one aspect, a method for manufacturing a conductive material dispersion containing the carbon nanocable is provided.

[0100] The method for manufacturing the above conductive material dispersion may include the step (S1) of mixing bundled carbon nanotubes and a dispersant with a dispersion medium and then applying a shear force to produce a primary dispersion; and the step (S2) of applying an external force to the primary dispersion to produce a conductive material dispersion comprising carbon nanocables in which single-walled carbon nanotubes and double-walled carbon nanotubes are bonded together in the diameter direction and the length direction.

[0101] The bundled carbon nanotubes are large aggregates having a micro-scale diameter, and through the S1 and S2 steps, the bundled carbon nanotubes can be debundled and rebundled and dispersed into carbon nanocables in a solvent.

[0102] The above S1 step may include a premixing step of mixing bundled carbon nanotubes, a dispersant, and a dispersion medium, and a step of applying shear force to the premixed mixture. The premixing and shear force application processes may be carried out in a single piece of equipment or may be carried out separately in two pieces of equipment. The equipment in which the premixing and / or shear force application processes are performed may be a mixing device such as a bead mill, ball mill, basket mill, attrition mill, spike mill, universal stirrer, high-pressure homogenizer, clear mixer, twin mixer, or TK mixer, and the mixing order of each component is not particularly limited. Preferably, the premixing may be performed in a clear mixer, twin mixer, or TK mixer, and the shear force application step may be performed using milling equipment, such as a bead mill, ball mill, basket mill, attrition mill, or spike mill.

[0103] The above S2 step may be a step of applying an external force to the primary dispersion of the S1 step, and the external force may include physical impact, shear force, and shock waves caused by cavitation, and by using this, bundle-shaped carbon nanotubes, which are large aggregates, can be dispersed into carbon nanocables by debundling and / or rebundling. The equipment that can be used in the above S2 step may be performed using a mixing device such as, for example, a bead mill, ball mill, basket mill, attrition mill, spike mill, universal stirrer, high-pressure homogenizer, clear mixer, twin mixer, TK mixer, ultrasonic crushing equipment, etc., and preferably, a high-pressure homogenizer may be used.

[0104] In the dispersion process of the above S2 step, a dispersion treatment may be performed by applying various types of external forces to form carbon nanocables and enhance dispersibility. For example, a physical impact may be applied first to the primary dispersion liquid, which may be applied by high-pressure spraying of the primary dispersion liquid so that solid particles within the dispersion liquid strike the outer wall of the equipment or collide with each other. Additionally, a shear force may be applied secondarily, which may be applied, for example, while passing through a nozzle equipped in the equipment, and thirdly, a shock wave caused by cavitation may be applied.

[0105] The shock wave applied in the third stage above is generated by cavitation, which occurs when vacuum bubbles formed in water burst when high energy is applied to the liquid, thereby enabling dispersion without damaging the intrinsic properties of carbon nanotubes. Dispersion treatments that induce cavitation may include ultrasonic fracturing, jet milling, or shear dispersion.

[0106] The above S2 step preferably utilizes a high-pressure homogenizer, and for example, the high-pressure homogenizer may include a primary nozzle and a secondary nozzle. As pressure is applied to the primary dispersion, the mixture passes sequentially through the primary nozzle and the secondary nozzle. Since the diameter of the secondary nozzle is smaller than the diameter of the primary nozzle, the dispersion can be subjected to shear force as it passes through the nozzles.

[0107] For example, the diameter of the first nozzle may be 100 mm to 500 mm, 150 mm to 300 mm, or 150 mm to 250 mm. The second nozzle may be 100 μm to 1000 μm, 200 μm to 800 μm, or 200 μm to 650 μm.

[0108] In addition, the pressure applied to the primary dispersion may be 100 bar to 1800 bar, preferably 200 bar or more, 300 bar or more, 400 bar or more, or 500 bar or more, and may also be 1600 bar or less, 1500 bar or less, 1400 bar or less, or 1300 bar or less.

[0109] The above S2 step is a step in which debundling and rebundling are appropriately performed so that the units are not completely dispersed and the aggregation is appropriately broken down, so that single-walled or double-walled carbon nanotube units are combined with a high packing density to form a carbon nanocable. Since the formation of the carbon nanocable as intended may not be realized if factors such as excessive external force are applied, for example, high pressure or a thin nozzle diameter, are present, it may be desirable to control this appropriately.

[0110] As another example, ultrasonic crushing equipment may be used in the above S2 step. The ultrasonic crushing may be performed with an output of 800W to 1,500W, specifically with an output of 800W to 1,200W. The ultrasonic crushing may be performed for 0.5 hours to 5 hours, or for 1 hour to 3 hours. Since the performance time refers to the total time during which ultrasonic crushing is applied, for example, if ultrasonic crushing is performed several times, it refers to the total time over those several times.

[0111] Through a series of dispersion processes such as the above-mentioned steps S1 and S2, bundled carbon nanotubes can be manufactured into carbon nanocables in which the monomers are aggregated into a specific shape, possessing long length, flexibility, and unbreakable properties. For example, if step S2, which involves applying various types of external forces, is performed immediately without performing the premixing process of step S1, problems may arise such as the equipment nozzle becoming clogged or significant damage to the carbon nanotubes during debundling. Furthermore, if various types of external forces are not applied as in step S2, proper debundling and rebundling may not occur, making it difficult to manufacture carbon nanocables to the desired level. Therefore, it may be desirable to perform both of the above-mentioned dispersion processes.

[0112]

[0113] Dispersant and dispersion medium

[0114] The above-mentioned dispersant may include one or more selected from the group consisting of polyacrylate, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl alcohol, polyacrylamide, polyethylene oxide, hydrogenated nitrile copolymer, cellulose-based compound, and diisopropylamine (DIPA). Here, the hydrogenated nitrile copolymer may be hydrogenated acrylonitrile-butadiene rubber, and the cellulose-based compound may be carboxymethyl cellulose (CMC) or hydroxyethyl cellulose (HEC).

[0115] In addition, the dispersant may be included in the carbon nanocable dispersion in an amount of 0.5 to 10 parts by weight, specifically 0.7 to 5 parts by weight, more specifically 1 to 3 parts by weight, per 100 parts by weight of the dispersion. When the above range is satisfied, the carbon nanocable can be smoothly dispersed within the dispersion, and the energy density of the manufactured electrode can be improved and the resistance reduced.

[0116]

[0117] The carbon nanocable dispersion may include an organic solvent or an aqueous solvent as a dispersion medium. For example, the aqueous solvent may include water, and the organic solvent may include one or more heteroatoms selected from the group consisting of nitrogen atoms (N) and oxygen atoms (O) having non-covalent electron pairs.

[0118] Specifically, the organic solvent is an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; and polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include 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, methylpropyl ketone, or cyclopentanone; esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone, and any one or a mixture of two or more of these may be used. N-methylpyrrolidone (NMP) is particularly preferred when considering miscibility with the electrode slurry.

[0119]

[0120] Electrode slurry and electrode

[0121] In one aspect, an electrode slurry comprising an electrode active material, a binder, and a dispersion of a conductive material such as that described above is provided.

[0122] The above-mentioned conductive material dispersion is identical to that described above, so its description is omitted.

[0123] Based on the total weight of the solids in the electrode slurry, the conductive material dispersion may have a content of solids (carbon nanocables) of 0.001 wt% to 1.0 wt%, preferably 0.005 wt% or more, 0.01 wt% or more, 0.015 wt% or more, 0.02 wt% or more, or 0.025 wt% or more, and may also have a content of 0.5 wt% or less, 0.4 wt% or less, 0.3 wt% or less, 0.2 wt% or less, 0.1 wt% or less, 0.08 wt% or less, 0.06 wt% or less, 0.05 wt% or less, or 0.04 wt% or less. As described above, the carbon nanocables can exhibit excellent electrical characteristics even when present in only a very small amount within the electrode, and their excellent durability can extend their lifespan. Furthermore, since the expected performance of the conductive material can be satisfied by including only a small amount, an improvement in energy density can also be expected.

[0124]

[0125] Electrode active material and binder

[0126] In one aspect, the electrode slurry comprises an electrode active material and a binder in addition to a conductive material dispersion containing carbon nanocables. The electrode active material may be a positive active material or a negative active material commonly used in the art, and its type is not particularly limited.

[0127] As the above-mentioned cathode active material, a lithium transition metal oxide or a lithium transition metal phosphate-based compound containing lithium and one or more transition metals such as cobalt, manganese, nickel, or aluminum may be used. More specifically, the lithium transition metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y1 Mn Y1O2(here, 0 <Y1<1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y2 Co Y2 O2(here, 0 <Y2<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y3 Mn Y3 O2(here, 0 <Y3<1), LiMn 2-Z2 Co Z2 O4 (where 0 < Z2 < 2), etc.), lithium-nickel-cobalt-manganese 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) oxide (e.g., Li(Ni P3 Co Q3 Mn R3 M 1S )O2(wherein M1 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 each atomic fractions of independent elements, such that 0<P3<1, 0<Q3<1, 0<R3<1, 0<S<1, P3+Q3+R3+S=1), etc.), any one or more of these compounds may be included.

[0128] In addition, the above lithium transition metal phosphate-based compound is an olivine-based lithium metal phosphate (e.g., Li 1+x [M3 1-q M4 q ]PO 4-r X r(Here, M3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, M4 is at least one selected from the group consisting of Al, Mg, and Ti, X is at least one selected from the group consisting of F, S, and N, and -0.5≤x≤0.5, 0≤q≤0.5, 0≤r≤0.1) etc.) may be included.

[0129] Preferably, the positive electrode active material may include a lithium-nickel-cobalt-manganese oxide or a lithium phosphate compound, and the lithium-nickel-cobalt-manganese oxide may be in the form of a single particle or a secondary particle, and if the chemical formula exemplified above is expressed more specifically, it may have a composition such as Chemical Formula 1 below.

[0130] [Chemical Formula 1]

[0131] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0132] In the above chemical formula 1, M 1 ... comprises one or more selected from Mn and Al, and M 2 comprises 1 or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X comprises 1 or more selected from the group consisting of N, P, S, F, and Cl, where 0≤x≤0.1, 0.5≤a<1, 0 <b≤0.35, 0<c≤0.35, 0≤d≤0.05 및 0≤e≤0.05 이다.

[0133] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, and M 2is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 The element is not necessarily included, but if included in an appropriate amount, it can play a role in promoting grain growth during sintering or improving crystal structure stability. In addition, the above X is an anion substituted at the oxygen site and may include N, P, S, F, or Cl.

[0134] The above 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0≤x≤0.1, 0≤x≤0.08, 0≤x≤0.05, 0≤x≤0.03, or 0≤x≤0.02.

[0135] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.50≤a<1.00, 0.60≤a≤0.99, 0.70≤a≤0.99 or 0.75≤a≤0.99, 0.80≤a≤0.99, 0.82≤a≤0.99, 0.84≤a≤0.99, or 0.86≤a≤0.99.

[0136] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b≤0.35, 0.01≤b≤0.34, 0.01≤b≤0.30, 0.01≤b≤0.25, 0.01≤b≤0.20, 또는 0.01≤b≤0.15일 수 있다.

[0137] The above c is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of, 0 <c≤0.35, 0.01≤c≤0.34, 0.01≤c≤0.30, 0.01≤c≤0.25, 0.01≤c≤0.20, 또는 0.01≤c≤0.15일 수 있다.

[0138] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements, which can be 0≤d≤0.05, 0≤d≤0.02, or 0≤d≤0.01.

[0139] The above e represents the molar ratio of element X among all nonmetals excluding oxygen in the lithium nickel-based oxide, and may be 0≤e≤0.05, 0≤e≤0.02, or 0≤e≤0.01.

[0140] Meanwhile, the lithium nickel-based oxide may further include a coating layer on the particle surface comprising one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0141] The above positive active material includes a lithium transition metal phosphate-based compound and may be represented by the following chemical formula 2.

[0142] [Chemical Formula 2]

[0143] Li 1+x [Fe 1-y M y ]PO4

[0144] In the above chemical formula 2, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0145] The above lithium transition metal phosphate-based compound can be doped with M. In this case, the lattice structure and distance within the olivine crystal structure, which is the crystal structure, are changed, thereby increasing the diffusivity of lithium ions, and consequently, the electrochemical properties of the battery containing the positive electrode active material can be improved.

[0146] The above x may be -0.5 to 0.5, preferably -0.3 or more, -0.1 or more, or 0 or more, and may be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0147] The above y may be 0 or greater, less than 1, or 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, 0.20 or less, 0.10 or less, or 0.05 or less.

[0148] The above lithium metal phosphate-based compound may be, for example, LiFePO4.

[0149] In one aspect, the lithium metal phosphate-based compound may be in the form of a single particle consisting of only one primary particle, or in the form of an irregular secondary particle consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate-based compound may include an olivine structure, and specifically, may consist solely of an olivine structure. The coating layer according to the present invention may be formed not only on the secondary particles but also on the primary particles. That is, the coating layer according to the present invention may be uniformly present on the surface of the primary particles existing inside the secondary particles.

[0150]

[0151] The above-mentioned negative electrode active material may be a material capable of reversibly intercalating / deintercalating lithium ions, and may include, for example, at least one selected from the group consisting of lithium metal; carbon-based active material; metalloid-based active material including Si or Sn; metal-based active material including a metal or an alloy of these metals and lithium; metal composite oxide; and transition metal oxide.

[0152] The above carbon-based active material may be used without particular limitation as long as it is commonly used in lithium-ion secondary batteries, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the above crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the above amorphous (or low-crystallinity) carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0153] The above metalloid active material may include silicon-based active materials and / or tin-based active materials, and silicon-based active materials include Si and SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)으로 이루어진 군에서 선택될 수 있다. 또한 주석계 활물질은, Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0154] As the above-mentioned metal-based active material, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals and lithium may be used.

[0155] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0156] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0157]

[0158] In one aspect, the positive active material may be 90% to 99% by weight, more specifically 93% or more, 95% or more, 96% or more, or 97% or more by weight, based on the total weight of the positive composite layer, and may be included in an amount of 98.5% or less, or 98% or less by weight, and excellent energy density, electrode adhesion, and electrical conductivity can be achieved when included within the above content range.

[0159] In addition, the above-mentioned cathode active material may be included in an amount of 70% to 99.5% by weight, preferably 80% to 99% by weight, based on the total weight of the cathode composite layer. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0160]

[0161] The above electrode slurry may include a binder. The binder serves to improve adhesion between electrode active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0162] The binder may be included in an amount of 0.1% to 10% by weight relative to the total weight of the solid content of the electrode slurry, preferably 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more by weight, and may also be 9.0% or less by weight, 8.5% or less by weight, 8.0% or less by weight, 7.5% or less by weight, 7.0% or less by weight, or 6.5% or less by weight.

[0163]

[0164] Conductive additive

[0165] The electrode slurry comprises a conductive dispersion containing carbon nanocables, and the electrode slurry and / or conductive dispersion may further include a conductive additive in addition to carbon nanocables. The conductive additive is a component for further enhancing the conductivity of the electrode active material, and such conductive additive is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery. For example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite or artificial graphite with a highly developed crystal structure; conductive fibers such as carbon-based fibers (e.g., carbon nanotubes, carbon nanofibers, carbon fibers) or metallic fibers; fluorinated carbon powder; metallic powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, etc. may be used.

[0166] The conductive material may be included in an amount of 0.1% to 10.0% by weight relative to the total weight of the solids of the electrode slurry. Preferably, it may be included in an amount of 0.2% or more, 0.3% or more, 0.5% or more, or 0.7% or more by weight, and may also be included in an amount of 8.0% or less, 6.0% or less, or 5.0% or less by weight.

[0167]

[0168] electrode

[0169] In one aspect, an electrode comprising a conductive material derived from the conductive material dispersion is provided. The electrode may include an electrode composite layer comprising an electrode active material, a binder, and the conductive material, and a current collector on which the electrode composite layer is disposed.

[0170]

[0171] Length and diameter of carbon nanocables

[0172] The above-mentioned conductive material dispersion contains carbon nanocables, and since this has been explained previously, a detailed explanation is omitted. Because the carbon nanocables have particle size characteristics as described above within the conductive material dispersion, the number of carbon nanocables with long lengths, for example, exceeding 10 μm in length, in the electrode composite layer within the electrode may be 10% or less of the total carbon nanocables, for example, and may not substantially exist.

[0173] As mentioned above, in the case of the carbon nanocable, there are many crystal defects compared to a structure composed of single-walled carbon nanotubes, I G / I D It can be characterized by small values, a large average diameter of the unit, and a large standard deviation. Through advantages in manufacturing methods, these characteristics allow the length to be realized at a level similar to that of single-walled carbon nanotube structures. Furthermore, even if some defects are present, it can maintain a long network without breaking during dispersion or charge / discharge processes, thereby ensuring cost competitiveness while improving lifespan and resistance characteristics.

[0174] In this regard, it may be desirable for the electrode to include carbon nanocables with a length exceeding 10 μm in a ratio of 10% or less relative to the total carbon nanocables.

[0175] More preferably, carbon nanocables with a length exceeding 10 μm can be controlled so that they do not exist. When controlled in this way, the area where the conductive material is clustered within the electrode is reduced, which can be expected to improve lithium ion mobility and thereby improve battery performance.

[0176] Preferably, the carbon nanocables having a length exceeding 10 μm may have a number ratio of 8% or less, 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, or 0.1% or less with respect to the total carbon nanocables, and most preferably may not be substantially included.

[0177] Here, the ratio of the number of carbon nanocables can be calculated by obtaining 20 scanning electron microscope images of size 20 μm x 20 μm for an electrode cross-section of size 5 mm x 5 mm, and then measuring the length of the linear conductive material using an image analysis program on these scanning electron microscope images to calculate the ratio of linear conductive materials exceeding 10 μm among the total linear conductive materials, and in this case, the case where there are no linear conductive materials exceeding 10 μm can be defined as “substantially not included.”

[0178] Alternatively, the carbon nanocable extracted from the electrode or from a dispersion containing it can be diluted in a solvent 1,000 to 30,000 times and then dried again. After photographing the sample using a scanning electron microscope so that it contains about 50 or more carbon nanocables, it can be analyzed in the same manner as above using an image analysis program.

[0179]

[0180] In addition, the carbon nanocable may have an average length of 1 μm to 20 μm, preferably 2 μm or more, or 3 μm or more, and may be 18 μm or less, 16 μm or less, 14 μm or less, 12 μm or less, or 10 μm or less. The above average length range is the length maintained when substantially applied to an electrode, and may maintain a longer length within the electrode compared to a structure formed by combining single-walled carbon nanotube units, thereby maximizing the electrical properties of the carbon nanotubes.

[0181] The average length of the carbon nanocable can be obtained by using a scanning electron microscope (SEM) to obtain an image of a sample that contains at least 50 carbon nanocables, after the carbon nanocable extracted from an electrode or from a dispersion is diluted in a solvent by 1,000 to 30,000 times and then dried, and then using the image to obtain the average value of the length of the carbon nanocable using an image analysis program.

[0182] In addition, the carbon nanocable may have an average diameter of 1.0 μm or less, 500 nm or less, 300 nm or less, or 200 nm or less. Furthermore, the carbon nanocable may have an average diameter of 4 nm to 120 nm, preferably 5 nm or more, 7 nm or more, or 10 nm or more, and 110 nm or less, 100 nm or less, or 90 nm or less. Moreover, as mentioned above, the carbon nanocable may have a high packing density, so the number of carbon nanotube units existing within the diameter range may be greater than that of a single-walled carbon nanotube structure, and thus may possess the property of not easily breaking due to external force. In addition, when having an average diameter within the above range, it has excellent dispersibility and an appropriate thickness when positioned on the surface of an active material, so it may not hinder the movement of lithium ions, thereby allowing for the expectation of an effect that improves not only electrical characteristics but also ion mobility.

[0183] The average diameter of the carbon nanocable can be obtained by using a scanning electron microscope (SEM) to obtain an image of a sample in which carbon nanocables extracted from an electrode or from a dispersion are diluted in a solvent by a factor of 1,000 to 30,000 and then dried, such that the sample contains at least 50 carbon nanocables, and using the image analysis program to obtain the average value of the diameter of the carbon nanocable. The ratio (L / D) of the average length (L) to the average diameter (D) of the carbon nanocable may be 50 to 1500, preferably 60 or more, 80 or more, 100 or more, and 1300 or less, 1100 or less, 1000 or less, 900 or less, or 850 or less. The length-to-diameter ratio may be a ratio that can be maintained even when subjected to a certain level of external force, similar to the average length, and may refer to the length-to-diameter ratio of carbon nanocables in a state where multiple units are combined rather than units dispersed as strands. If this range is satisfied, the resistance characteristics can be improved by fully exhibiting the length characteristics of the conductive material while maintaining its length even with the volume expansion of the active material within the electrode.

[0184]

[0185] Specific surface area of ​​carbon nanocables

[0186] The specific surface area of ​​the above carbon nanocable is 500 m² 2 / g to 900 m 2 It may be / g, preferably 600 m 2 / g to 800 m 2It can be / g. When the above range is satisfied, a conductive pathway within the electrode can be smoothly secured due to the large specific surface area, so there is an effect of maximizing conductivity within the electrode even with a very small amount of conductive material content. Specifically, the specific surface area of ​​the single-walled carbon nanotube unit can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan.

[0187]

[0188] electrode current collector

[0189] In one aspect, the electrode may include an electrode composite layer and an electrode current collector on which the electrode composite layer is disposed, and the electrode current collector may be a positive current collector or a negative current collector.

[0190] The above positive current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, the above positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0191] The above positive current collector can typically have a thickness of 3 μm to 500 μm, and preferably can have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities may be formed on the surface of the current collector to strengthen the bonding force with the positive active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0192] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used.

[0193] The above-mentioned negative current collector can typically have a thickness of 3 μm to 500 μm, and preferably can have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities may be formed on the surface of the current collector to strengthen the bonding force with the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0194]

[0195] The above electrode slurry can be manufactured according to a conventional electrode manufacturing method, except for using the above-described electrode active material powder. Specifically, it can be manufactured by dissolving or dispersing the above-described electrode active material powder and, optionally, a binder, a conductive material (here including carbon nanocables), and a dispersant in a solvent to produce an electrode slurry composition, applying it onto an electrode current collector, and then drying and rolling.

[0196] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for electrode manufacturing thereafter.

[0197] In addition, the electrode may also be manufactured by casting the electrode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an electrode current collector.

[0198]

[0199] secondary battery

[0200] In one aspect, a secondary battery is provided that includes an electrode comprising a conductive material derived from the conductive material dispersion.

[0201] As the conductive material dispersion included in the above electrode has been explained previously, a description thereof is omitted.

[0202] Specifically, the above secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a diaphragm interposed between the positive electrode and the negative electrode. Since the positive electrode and the negative electrode are identical to those previously described, a detailed description is omitted, and only the remaining components are described in detail below.

[0203] The above secondary battery may include, for example, a lithium secondary battery in which charging and discharging occur through the movement of lithium ions and electrons, or a sodium secondary battery in which charging and discharging occur through the movement of sodium ions and electrons; however, the following description uses a lithium secondary battery as an example. Additionally, the above secondary battery may be a non-aqueous electrolyte secondary battery, in which case the diaphragm may be a separator, and may further include a battery container housing an electrode assembly of a positive electrode, a negative electrode, and a separator, a liquid electrolyte injected into the battery container, and a sealing member sealing the battery container.

[0204] In the above secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as 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 polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0205]

[0206] In addition, the above electrolytes may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of secondary batteries, but are not limited to these.

[0207] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0208] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0209]

[0210] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0211]

[0212] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0213]

[0214]

[0215] In one aspect, when the secondary battery is an all-solid-state battery, the diaphragm may be a solid electrolyte, and the solid electrolyte may be, for example, a halide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, or a sulfide-based solid electrolyte, and in particular, a sulfide-based solid electrolyte may be preferably used.

[0216] The above sulfide-based solid electrolyte may include a solid electrolyte represented by the following chemical formula 1:

[0217] [Chemical Formula 1]

[0218] Li x M y P z S v A w

[0219] In the above chemical formula 1, x, y, z, v, and w are independently 0 to 7, and can be determined such that the total charge is neutral; M is one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and A is one or more of F, Cl, Br, or I.

[0220] The above sulfide-based solid electrolyte is a representative sulfide-based solid electrolyte having an argyrodite structure, and due to high Li+ mobility, the cubic phase at high temperatures has improved ionic conductivity and can be stabilized by replacing sulfur with halogen anions. As halogen elements are substituted, vacancies are formed in the Li-site portions inside the argyrodite unit cell, thereby improving Li ion conductivity, and due to this substitution of halogen ions, the cubic structure can be stabilized even at room temperature.

[0221] For example, the above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are positive, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2SSiS2-Li p MO q(p and q are positive, and M is one of P, Si, Ge, B, Al, Ga, or In), or a combination thereof may be included. The solid electrolyte may be composed of one material selected from such sulfide-based solid electrolyte materials, or may be composed of two or more materials. Preferably, a material comprising Li2S-P2S5 may be used. When a material comprising Li2S-P2S5 is used as a sulfide-based solid electrolyte material, the mixed molar ratio of Li2S and P2S5 may be selected in the range of, for example, Li2S:P2S5 = 50:50 to 90:10.

[0222]

[0223] battery box

[0224] In another aspect, a battery box comprising a plurality of the above secondary batteries may be provided. The battery box may include a plurality of secondary batteries and may include a packaging that accommodates the plurality of secondary batteries. Here, the battery box may be, for example, a battery module or a battery pack.

[0225] Since the above secondary battery stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it can be usefully applied in portable devices such as mobile phones, laptops, and digital cameras, or in the field of electric vehicles such as Full Electric Vehicles (FEVs) and Hybrid Electric Vehicles (HEVs).

[0226] The above battery box may be used as one or more power devices selected from the group consisting of a power tool; an electric vehicle including a full electric vehicle (FEV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0227] According to the present specification, in another aspect, an electric device or electronic device may be provided that includes the battery box, wherein the battery box is included as a power source.

[0228]

[0229] Examples

[0230] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0231]

[0232] Example 1

[0233] Bundled carbon nanotubes (specific surface area 700 m²) 2 / g, I G / I D 70. A mixture was prepared by mixing 0.6 parts by weight of (monomer diameter of 1.0–3.0 nm as measured by Raman spectrum) with 0.9 parts by weight of polyvinylidene carboxymethylcellulose (CMC) and 98.5 parts by weight of water as a dispersion medium, so that the solid content was 1.5% by weight.

[0234] The above mixture was fed into an inline mixer (Mixenmill, IM-02) and mixed at 2000 rpm for 3 hours to prepare a primary dispersion, and the primary dispersion was fed into a high-pressure homogenizer (Picomax, MN400HF) and mixed by repeating the process of passing through a nozzle with a diameter of 200 μm at a pressure of 1500 bar 10 times.

[0235] Through this, it has a multimodal diameter distribution, having various diameters between 1.0 nm and 3.0 nm, and I G / I D A dispersion was prepared in which carbon nanotube units comprising single-walled and double-walled carbon nanotubes having a dispersion particle size as described in Table 1 below and a value of 70 were dispersed, and carbon nanocables were dispersed.

[0236]

[0237] Example 2

[0238] I in Example 1 above G / I D A carbon nanocable dispersion having the dispersion particle size as described in Table 1 below was prepared using the same method, except that bundled carbon nanotubes with a particle size of 90 were applied.

[0239]

[0240] Example 3

[0241] A carbon nanocable dispersion was prepared in the same manner as in Example 1, except that the process of passing through a high-pressure homogenizer was repeated 12 times.

[0242]

[0243] Example 4

[0244] Mixing was performed by introducing the material into a high-pressure homogenizer and repeating the process of passing it through a nozzle with a diameter of 250 μm at a pressure of 1300 bar 10 times. A carbon nanocable dispersion was prepared using the same method as in Example 1.

[0245]

[0246] Comparative Example 1

[0247] Bundled carbon nanotubes composed of single-walled carbon nanotube monomers with an average diameter of 1.5 nm and an average length of 5 µm as measured by Raman spectrum (specific surface area of ​​1300 m² 2 0.8 parts by weight of (g) and 1.2 parts by weight of carboxymethylcellulose were mixed with 98.0 parts by weight of water, which is a dispersion medium, to prepare a mixture with a solid content of 2.0% by weight.

[0248] A dispersion of the above mixture was prepared in the same manner as in Example 1.

[0249]

[0250] Comparative Example 2

[0251] Bundled carbon nanotubes composed of multiwalled carbon nanotube monomers with an average diameter of 10 nm and an average length of 1 µm as measured by Raman spectrum (specific surface area of ​​185 m² 2 0.8 parts by weight of (g) and 1.2 parts by weight of carboxymethylcellulose were mixed with 98.0 parts by weight of water, which is a dispersion medium, to prepare a mixture with a solid content of 2.0% by weight.

[0252] A dispersion of the above mixture was prepared in the same manner as in Example 1.

[0253]

[0254] Comparative Example 3

[0255] The bundled carbon nanotubes of Example 1 were utilized in their bundled state as a conductive material without a separate dispersion process, and a conductive material dispersion was prepared by mixing carboxymethylcellulose, styrene-butadiene rubber, and water in the same manner as in Example 1.

[0256]

[0257] Comparative Example 4

[0258] The bundled carbon nanotubes of Comparative Example 1 above were utilized in their bundled state as a conductive material without a separate dispersion process, and a conductive material dispersion was prepared by mixing carboxymethylcellulose, styrene-butadiene rubber, and water in the same manner as in Example 1.

[0259]

[0260] Comparative Example 5

[0261] The bundled carbon nanotubes of Comparative Example 2 above were utilized in their bundled state as a conductive material without a separate dispersion process, and a conductive material dispersion was prepared by mixing carboxymethylcellulose, styrene-butadiene rubber, and water in the same manner as in Example 1.

[0262]

[0263] Comparative Example 6

[0264] A carbon nanocable dispersion was prepared in the same manner as in Example 1, except that the process of passing through a high-pressure homogenizer was repeated 6 times.

[0265]

[0266] Comparative Example 7

[0267] A carbon nanocable dispersion was prepared in the same manner as in Example 1, except that the process of mixing in an inline mixer for 1 hour and passing through a high-pressure homogenizer was repeated 4 times.

[0268]

[0269] Experimental Example 1: Evaluation of Physical Properties of Conductive Material

[0270] 1) Raman Spectrum: The dispersions prepared in the above examples and comparative examples were dried, and the Raman spectrum was analyzed using a Raman spectroscopic analyzer (NRS-2000B, Jasco) with an Ar-ion laser at a wavelength of 514.5 nm to obtain a wavenumber of 1300 cm⁻¹. -1 up to 1700 cm -1The intensities of the G and D peaks were derived from the peaks appearing within the range, and their ratios are shown in Table 1 below. In addition, the average diameter (nm) of the unit cell based on the Raman spectrum was determined through Radial Breathing Mode analysis, and the Raman shift (cm²) in the Raman spectrum was calculated. -1 ) is 100 cm -1 up to 300 cm -1 Raman shift value of the peak appearing in the range (W r A specific constant for ) 224 cm -1 By calculating the ratio of using Equation 1 below, the average diameter (d t , nm) was derived.

[0271] [Equation 1]

[0272] d t (nm) = 224 (cm -1 ) / W r (cm -1 )

[0273] 2) Average diameter (nm), standard deviation, and number of units within a 5 nm x 5 nm area of ​​the diameter cross-section of carbon nanotube (CNT) units within a carbon nanocable (or structure): For a sample of the CNC extracted from the dispersion of the above examples and comparative examples that was dried after diluting it 2,000 times, about 50 carbon nanocables were analyzed using images measured by a transmission electron microscope (TEM). The average and standard deviation of the diameter of the carbon nanotube units within a single carbon nanocable were calculated, and a 5 nm x 5 nm grid was positioned in an area where the maximum number of units containing more than 50% of the area could be included, and the number of units inside was counted.

[0274] 3) Volume-cumulative average particle size: D 50 , D 90 and D 99The dispersion was introduced into a laser diffraction particle size measuring device (Mastersizer 3000, Malvern) using the laser diffraction method, and after obtaining a volume cumulative particle size distribution graph, the particle sizes corresponding to 50%, 90%, and 99% of the volume cumulative amount were determined.

[0275] 4) Average diameter (nm) of carbon nanocables (CNC): About 50 carbon nanocables were analyzed using images measured by Transmission Electron Microscopy (TEM) on a sample dried after diluting the dispersion of the above examples and comparative examples 2,000 times, and the average diameter of the carbon nanocables (structures) or monomers (when completely dispersed into strands) was measured.

[0276] 5) Average length (㎛) of carbon nanocables (CNC) and ratio of the number of units with a length exceeding 10㎛: For samples dried after diluting the dispersions of the above examples and comparative examples 20,000 times, images captured using a scanning electron microscope (SEM) to include approximately 50 carbon nanocables were analyzed to measure and calculate the average length of the dispersed units, which are shown in Table 1 below. In addition, the number of carbon nanocables with a length exceeding 10㎛ was confirmed using the 50 images, and the results are shown in Table 1 below.

[0277] 6) Specific surface area (m² 2 / g): Using a BET measuring instrument (BEL-SORP-MAX, Nippon Bell), gas was degassed at 200°C for 8 hours, and N2 absorption / desorption was performed at 77 K.

[0278]

[0279] I G / I DAverage diameter of monomers within CNC (nm) Standard deviation of monomer diameter within CNC Number of monomers within a 5nm x 5nm area Cumulative average particle size of CNC (or CNT structure) Specific surface area (m²) 2 / g)D 50 (㎛)D 90 (㎛)D 99 (㎛) Average Diameter (nm) Average Length (nm) Number of Lengths Exceeding 10㎛ Example 1 70 2.6 0.6 34 3.8 38.7 9 9.2 040 3,5000 700 Example 2 90 2.3 0.5 64 4.6 47.9 9 9.1 050 4,0000 800 Example 3 70 2.8 0.7 134.7 18.8 59.9 660 6,0000 700 Example 4 90 2.5 0.6 44 4.9 58.5 19.7 970 8,0000 800 Comparative Example 1 1300 0.8 0.1 47 3.3 36.7 98.1 150 3,5000 1,300 Comparative Example 2123.05.0001.123.517.00503000185 Comparative Example 3702.60.633--->1,000--700 Comparative Example 41300.70.148--->1,000--1,300 Comparative Example 51225.000--->1,000--185 Comparative Example 6702.50.6134.989.9717.8706,0005700 Comparative Example 7902.30.4545.1415.221.2908,00010800

[0280] Referring to Table 1 above, Comparative Examples 3 to 5 were not debundled or rebundled into the form of cables or structures because no separate dispersion treatment was performed, and in the case of Comparative Examples 6 and 7, although the same TWCNT was used, D was not applied due to the failure to apply an appropriate dispersion method. 99 It was measured to be very large, which can be understood as indicating that dispersion was poor due to the presence of aggregated large particles.

[0281] That is, in the conductive material dispersion of Examples 1 to 4 above, bundled carbon nanotubes are appropriately dispersed, and as shown in the schematic diagram in FIG. 1, it can be confirmed that each of the plurality of units, each having single-walled carbon nanotubes and double-walled carbon nanotubes as units, is combined in the longitudinal and diametrical directions to form a carbon nanocable.

[0282] Figures 4 and 5 are transmission electron microscope images of the carbon nanocable and carbon nanotube structures of Example 1 and Comparative Example 1, respectively, which are the actual shapes shown in the schematic diagrams of Figures 2 and 3. Looking at this, it can be seen that within a 5 nm x 5 nm grid, the carbon nanocable of Example 1 has units that exist in a relatively loose form, whereas the carbon nanotube structure of Comparative Example 1 has a shape in which units of the same diameter are densely packed.

[0283]

[0284] Experimental Example 2: Battery Performance Evaluation

[0285] An electrode assembly was manufactured by introducing the conductive material dispersion of the above examples and comparative examples into a cathode composite layer, interposing a porous polyethylene separator between the cathode and the anode, and then placing the assembly inside a case and injecting an electrolyte to manufacture a secondary battery.

[0286] At this time, the electrolyte was prepared by dissolving 1 M concentration of LiPF6 in an organic solvent of ethylene carbonate / ethylmethyl carbonate / diethyl carbonate in a volume ratio of 3:4:4, and the cathode was prepared as follows.

[0287] The above cathode was prepared by mixing 98.1 parts by weight of a mixed active material of graphite and SiO2, 0.9 parts by weight of carboxymethylcellulose, and 0.9 parts by weight of styrene-butadiene rubber into a dispersion (0.1 parts by weight based on solid content), and additionally adding water to prepare a cathode slurry with a solid content of 48%. The cathode slurry was coated onto a copper thin film current collector with a thickness of 15 μm, dried at 110°C, and rolled to produce a cathode including a cathode composite layer.

[0288] The above anode is LiNi 0.6 Co 0.1 Mn 0.3 O2, polyvinylidene fluoride, and multi-walled carbon nanotubes were added in a weight ratio of 98:1:1, and N-methylpyrrolidone (NMP) was additionally added to prepare an anode slurry with a solid content of 70.1 wt%. The anode slurry was coated onto an Al thin film current collector with a thickness of 20 μm, dried at 130°C, and rolled to produce an anode including an anode composite layer.

[0289] The above secondary battery was charged to 4.2V at a 0.1C C-rate, and then discharged to 2.5V to proceed with the activation process.

[0290] After charging and discharging each secondary battery manufactured above, and then fully charging and discharging to 50% SOC, a 2.5C pulse current was applied to measure the cell resistance, and the results are shown in Table 2.

[0291] Each secondary battery manufactured above was charged in CCCV mode until it reached 4.25V at 0.2C (termination current 1 / 20C). Subsequently, the discharge capacity was measured while performing 100 cycles of charging and discharging, with 1 cycle consisting of charging to 4.25V at 45℃ with a constant current of 0.33C and discharging to 2.5V with a constant current of 0.33C, and the capacity retention rate was calculated as follows.

[0292] Capacity Retention Rate (%) = (Discharge Capacity after 100 cycles) / (Discharge Capacity after 1 cycle) × 100

[0293] Capacitance Retention Rate (%) Cell Resistance (mΩ) Example 1 90.21.702 Example 2 90.41.687 Example 3 89.91.699 Example 4 89.51.709 Comparative Example 1 88.11.710 Comparative Example 2 69.01.989 Comparative Example 3 50.02.210 Comparative Example 4 49.92.188 Comparative Example 5 49.92.146 Comparative Example 6 81.21.899 Comparative Example 7 71.01.974

[0294] Referring to Table 2 above, in the case of Examples 1 and 2, carbon nanocables were applied that include single-walled and double-walled carbon nanotube units satisfying the dispersion liquid particle size characteristics and the average diameter range of the units, and it can be confirmed that the lifespan and resistance characteristics are excellent. It can be anticipated that this is because there are various conduction paths, that is, conduction paths that can bypass defects even if they occur, and at the same time, the mobility of lithium ions is also improved due to the absence of large particles.

[0295] However, although the particle size characteristics are satisfied, the structure containing the single-walled carbon nanotube unit of Comparative Example 1, which does not include double-walled carbon nanotubes in the unit, has a small standard deviation of the unit diameter and a small unit diameter, resulting in a densely packed structure. Consequently, the length of the structure is relatively short compared to the examples, and in the event of a defect, the path is severed without any alternative path available for bypassing, which confirms that the lifespan and resistance are slightly inferior. However, due to the difficulty of the manufacturing process, the unit cost of a single-walled carbon nanotube structure like Comparative Example 1 is about twice that of a carbon nanocable manufactured with a mixture of double walls. When considering this unit cost competitiveness as well, the above-mentioned improvement in lifespan can be seen as a significant difference.

[0296] In addition, in the case of Comparative Example 2, although the structure containing multi-walled carbon nanotubes also satisfies the particle size characteristics, it can be seen that there is a performance difference that is difficult to overcome because the characteristics of the carbon nanotubes themselves are inferior. In the case of Comparative Examples 3 to 5, the bundle type was used as is, and it can be confirmed that even if single-walled and double-walled carbon nanotube units are included, performance improvement is impossible if they do not form a single structure shape through a process of debundling or rebundling, such as carbon nanocables.

[0297] Meanwhile, Comparative Examples 6 and 7 included double-walled carbon nanotubes as monomers, but carbon nanocables with a length exceeding 10 μm were present, and as these fibers eventually acted as aggregates, they became a factor hindering the mobility of lithium ions, resulting in inferior lifespan and resistance performance.

[0298]

[0299] [Explanation of the symbol]

[0300] 10: Carbon nanotube structure

[0301] 100: Carbon nanocable

[0302] 110: Carbon nanotube monomer

Claims

1. Includes carbon nanocables and a dispersant, The above carbon nanocable is composed of a plurality of carbon nanotube units, including single-walled carbon nanotubes and double-walled carbon nanotubes, arranged and combined in the longitudinal and diametrical directions. The carbon nanotube monomer has an average diameter of 1.8 nm to 4.0 nm, and The above carbon nanocable has an average particle size D at 90% of the volume accumulated in the dispersion phase. 90 This is 10 µm or less, and the 99% volume-cumulative average particle size D 99 A conductive dispersion having a g of 15 μm or less.

2. In Paragraph 1, The above carbon nanocable has an average particle size D at 50% of the cumulative volume of the dispersion phase. 50 A conductive material dispersion having a thickness of 5 μm or less.

3. In Paragraph 1, The above carbon nanocable is a conductive dispersion having an oxygen atom content of 1.5 at% or more as measured by photoelectron spectroscopy (XPS).

4. In Paragraph 1, The above carbon nanocable is a conductive dispersion having a chlorine atom content of 0.1 at% or less as determined by photoelectron spectroscopy.

5. In Paragraph 1, The above carbon nanocable has a peak due to CO bonds and a peak due to C=O bonds in the graph obtained by photoelectron spectroscopy, and A conductive dispersion in which the intensity of the peak due to the CO bond is stronger than the intensity of the peak due to the C=O bond.

6. In Paragraph 1, The above carbon nanocable has a BET specific surface area of ​​500 m² 2 / g to 900 m 2 / g, conductive material dispersion.

7. In Paragraph 1, The above carbon nanotube monomer has an average diameter of 2.0 nm to 3.8 nm and a standard deviation of diameter of 0.3 or more, in a conductive dispersion.

8. In Paragraph 1, The above plurality of carbon nanotube monomers is a conductive dispersion containing at least 30% double-walled carbon nanotubes by number.

9. In Paragraph 1, The above carbon nanocable has a maximum number of carbon nanotube units that can be included within a 5 nm x 5 nm lattice defined on a cross-sectional diameter, and A conductive dispersion in which the number of carbon nanotube units includes at least 50% of the cross-sectional area within the region.

10. An electrode slurry comprising an electrode active material, a binder, and a dispersion of the conductive material of claim 1.

11. In Paragraph 10, The above electrode active material is a negative electrode active material, and The above-mentioned negative electrode active material is an electrode slurry comprising a silicon-based active material.

12. A secondary battery comprising an electrode comprising an electrode active material, a binder, and a conductive material derived from the conductive material dispersion of claim 1.

13. In Paragraph 12, The above electrode active material is a negative electrode active material, and The above negative electrode active material comprises a silicon-based active material, in a secondary battery.

Images