Conductive material, electrode containing the same, and lithium secondary battery containing the electrode

Abstract

This invention relates to the aspect ratio of a conductive material, powder resistance, the packing density when measuring that powder resistance, the BET specific surface area, and the volume cumulative average particle size D. 50 Conductivity Performance Index (P) defined as a factor C The present invention relates to a conductive material satisfying a value of 0.03 to 8.10. According to the present invention, by using physical properties that can relate to the resistance characteristics and lifetime characteristics of an electrode, such as the conductive material forming conductive network connecting paths between active material particles and within active material particles within the electrode, being placed in voids, and being placed on the surface of the active material, and by investigating and defining the relationships between these physical properties, it is possible to provide a conductive material that can improve the performance of an electrode when it satisfies a specific range.

Description

[Technical Field]

[0001] The present invention relates to a conductive material with excellent conductive properties, an electrode containing the same, and a lithium secondary battery containing the electrode. [Background technology]

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

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

[0004] On the other hand, while applying a positive electrode active material with high capacity characteristics is important for manufacturing batteries with high energy density, the materials contained in the positive electrode can also play a crucial role. For this reason, research is being conducted to maximize the proportion of active material and minimize the content of conductive material and binder. However, when the amount of active material used increases, the increase in the unit cost of the cell is very large compared to the degree of performance improvement, making it difficult to actually apply this to mass production.

[0005] Therefore, the recent research trend is to satisfy a certain energy density requirement while also increasing price competitiveness. While various approaches are possible for manufacturing high-energy-density batteries, the presence of auxiliary materials such as conductive materials and binders, rather than just the main material like the active material, plays a crucial role. In particular, conductive materials exhibit many performance differences depending on their inherent properties such as conductivity, their morphology within the electrodes, and their pre-dispersion.

[0006] In particular, carbon black, multi-walled carbon nanotubes (MWCNTs), and single-walled carbon nanotubes (SWCNTs), which are widely used as conductive materials, exhibit significant differences in conductivity even when they are the same material, depending on their number characteristics, dimensional characteristics, specific surface area, dispersion morphology, and shape characteristics. Therefore, it is difficult to determine what characteristics are necessary to achieve high-performance electrodes with each conductive material before conducting actual experiments. Even with identical physical properties, significant differences in conductivity can occur due to some other differences, and in-depth research is needed on this matter. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] To solve the above-mentioned problems, the present invention aims to provide a conductive material with excellent conductivity, which allows for an understanding of how well conductive paths are formed on electrodes and how much they help reduce resistance, based on a conductivity performance index that reflects the number characteristics, dimensional characteristics, conductivity characteristics, and shape characteristics of carbon-based particles.

[0008] Furthermore, although the properties differ depending on the type of conductive material, the present invention adjusts the conductivity performance index to reflect the conductivity characteristics and shape characteristics, allowing for mutual correction. This enables the provision of high-performance conductive materials by understanding the conductivity performance index regardless of the type or shape of the conductive material, thereby realizing electrodes with high energy density. [Means for solving the problem]

[0009] [1] According to an embodiment of the present invention, a conductivity performance index (Conductivity Performance Index, P , P ,

[0011] ,

[0013] , , 4 , P , P , , 50 , , C , P , , P , , P , , 50 , , , P ,

[0010] , 50 , , P , , 2 ,

[0012] ) of 0.03 to 8.10 is provided for the conductive material. [Formula 1] P C = [(AR × R P × ρ P ) / (BET × D 50 )] × 10 4 In Formula 1 above, AR is the aspect ratio, which is the ratio of the long axis to the short axis of the conductive material, and R P and ρ P are the powder resistance (Ωcm) and the packing density (g / cc), respectively. The powder resistance measured when the packing density ρ P of the conductive material is R P . BET is the specific surface area (m 2 / g) of the conductive material, and D 50 is the volume cumulative 50% average particle size (μm) of the conductive material in powder form. In the above formula, R P , ρ P , BET, and D 50 are dimensionless numbers excluding the above units.

[0010] [2] In the conductive material of [1] above, the conductive material can include one or more selected from the group consisting of carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes.

[0011] [3] In the conductive material of [1] and / or [2] above, the conductivity performance index may be 0.10 to 7.00.

[0012] [4] In at least one of the conductive materials of [1] to [3] above, the conductivity performance index may be 0.30 to 5.00.

[0013] [5] In at least one of the conductive materials of [1] to [4] above, the packing density (ρP The concentration may be 0.4g / cc to 0.6g / cc.

[0014] [6] In at least one of the conductive materials from [1] to [5] above, the conductive material may contain carbon black, and the conductivity performance index may be 1.00 to 8.10.

[0015] [7] In at least one of the conductive materials from [1] to [6] above, the conductive material may include one or more selected from the group consisting of multi-walled carbon nanotubes and single-walled carbon nanotubes, and the conductivity performance index may be 0.03 to 4.00.

[0016] [8] In at least one of the conductive materials from [1] to [7] above, the conductive material may contain multi-walled carbon nanotubes, and the conductivity figure may be 0.30 to 3.90.

[0017] [9] In at least one of the conductive materials from [1] to [8] above, the conductive material may contain single-wall carbon nanotubes, and the conductivity figure may be 0.03 to 1.50.

[0018]

[10] According to another embodiment of the present invention, an electrode is provided comprising an electrode current collector and an electrode active material layer disposed on the electrode current collector, wherein the electrode active material layer comprises the conductive material described above.

[0019]

[11] In the electrode of

[10] , the electrode active material layer further comprises a positive electrode active material, the positive electrode active material may include one or more selected from the group consisting of lithium nickel oxides and lithium metal phosphate compounds.

[0020]

[12] In the electrode described in

[11] , the positive electrode active material is of the single-particle type, and the average particle size of the nodule (D mean ) relative to volume cumulative average particle size (D 50 The ratio of single-particle ratios (D 50 / D mean ) may be between 1 and 10.

[0021]

[13] In the electrodes of

[11] and / or

[12] , the single-particle lithium nickel oxide may have a composition represented by the following chemical formula 1, and the lithium metal phosphate compound may have a composition represented by the following chemical formula 2. [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e In the above chemical formula 1, M 1 It includes one or more selected from Mn and Al, and M 2 x contains one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X contains one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 <b≦0.35、0<c≦0.35、0≦d≦0.05および0≦e≦0.05である。 [Chemical formula 2] Li 1+x [Fe 1-y M y ]PO4 In the above chemical formula 2, M comprises one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

[0022]

[14] In the electrode of

[10] , the electrode active material layer may further contain silicon-based particles.

[0023]

[15] According to another embodiment of the present invention, a lithium secondary battery is provided which includes a structure in which electrodes and separators are alternately stacked, wherein the electrodes are the electrodes described above. [Effects of the Invention]

[0024] The conductive material according to the present invention allows for an understanding of how well it can form conductive paths on electrodes and how much it can help reduce resistance, based on a conductivity performance index that reflects the number characteristics, dimensional characteristics, conductivity characteristics, and shape characteristics of carbon-based particles. By applying a conductive material whose thus defined conductivity performance index satisfies a specific range, it is possible to provide electrodes with excellent conductivity and excellent resistance characteristics.

[0025] Furthermore, although the properties differ depending on the type of conductive material, by adjusting the conductivity performance index to reflect the conductivity characteristics and shape characteristics, it is possible to determine whether a conductive material is high-performance by understanding its conductivity performance index, regardless of its type or shape. This makes it possible to realize electrodes with high energy density. [Modes for carrying out the invention]

[0026] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0027] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of an implemented feature, figure, step, component, or combination thereof, but do not exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0028] In this specification, "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mini II manufactured by BEL Japan.

[0029] In this invention, "single-particle type" refers to a particle consisting of 30 or fewer nodules, and the concept of single-particle type particles includes single particles consisting of one nodule and pseudo-single particles which are composites of 2 to 30 nodules.

[0030] The aforementioned "nodule" is a lower particle unit that constitutes a single particle or a pseudo-single particle, and may be a single crystal without crystalline grain boundaries, or a polycrystalline material in which no grain boundaries appear to exist when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times magnification.

[0031] In this invention, "secondary particle" refers to a particle formed by the aggregation of several tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0032] The term "particle" as used in this invention may include one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0033] In this invention, "average particle size of nodules (D mean This method involves imaging the positive electrode active material particles with a scanning electron microscope (SEM), determining the particle size of each nodule for approximately 30 particles containing one or more nodules, and then using the average value.

[0034] In this specification, "Volume cumulative 50% average particle size D" 50 " can be defined as the particle size corresponding to 50% of the cumulative volume and the maximum particle size in the particle size distribution curve, respectively. 50 This can be measured, for example, using the laser diffraction method. The laser diffraction method generally allows for the measurement of particle sizes ranging from the submicron region to several millimeters, and can yield highly reproducible and high-resolution results. Hereinafter, in this specification, "50% volume-cumulative average particle size D" refers to the particle size D. 50" is "Volume Cumulative Average Particle Size" or "D 50 It can be referred to as such.

[0035] In this specification, "aspect ratio" may mean the ratio of the longest to the shortest line passing through the center of a particle and connecting to its outer edge, regardless of the particle's shape, whether linear, point-like, or plate-like.

[0036] The present invention will be described in detail below.

[0037] The conductive material, electrode, and lithium secondary battery according to the present invention include at least one of the configurations described below, and may include any combination of technically possible configurations from the following.

[0038] conductive material A conductive material according to one embodiment of the present invention has a Conductivity Performance Index (P) defined by the following formula 1. C ) satisfies 0.03 to 8.10.

[0039] [Formula 1] P C =[(AR×R P ×ρ P ) / (BET×D 50 )] × 10 4

[0040] In the above formula 1, AR is the aspect ratio, which is the ratio of the long axis to the short axis of the conductive material, and R P and ρ P These are the powder resistance (Ωcm) and packing density (g / cc), respectively, and the packing density ρ is relative to the conductive material. P The powder resistance measured at this time is R P Therefore, BET is the specific surface area (m²) of the conductive material. 2 / g) and D 50 R is the 50% average particle size (μm) of the conductive material in powder form, and in the above formula, P ρ P , BET and D 50This is a unitless number from which all of the aforementioned units have been removed.

[0041] The 50% volume-cumulative average particle size according to one embodiment of the present invention was measured in a dry powder state under aero conditions, not in a dispersed state in an organic solvent. Although this differs from the value measured in a dispersion state, it can be understood to be substantially identical to the form and size of particles distributed within the active material layer of the electrode.

[0042] The conductivity performance index according to one embodiment of the present invention is defined by formula 1, and the factors are powder resistance, packing density, BET specific surface area, and D 50 and aspect ratio.

[0043] As mentioned above, the performance of conductive materials is determined by various factors, including the dispersion environment / conditions, the morphology and particle size of the active material on the electrode, and the porosity. Factors inherent to the conductive material include shape characteristics, conductivity characteristics, number characteristics, and length characteristics. However, the differences in these characteristics are very large for each type of conductive material, and the performance also differs greatly depending on how these characteristics are combined. Therefore, achieving high performance when applying conductive materials is not easy.

[0044] However, in the present invention, by constructing a specific relationship using the aforementioned characteristics as factors and parameterizing it into a conductivity performance index, it is possible to evaluate the conductivity performance of a conductive material regardless of its type. This offers the advantage of being able to compare the conductivity performance between different types of conductive materials, as well as the advantage of being able to provide electrodes with superior conductivity by using a conductive material whose conductivity performance index is controlled to have a specific numerical range.

[0045] The aforementioned conductivity performance index is calculated by the specific surface area and D 50 This is a relationship based on the ratio of the product of powder resistance and packing density to the product of the two factors, and the specific surface area can reflect the number characteristics of the conductive material, D 50The length characteristics of the conductive material can be partially reflected, and the powder resistance and packing density can reflect the conductive properties of the conductive material. In the case of powder resistance and packing density, which are factors in the numerator, it can be seen that the smaller the product value, the better the conductivity. The specific surface area and D, which are factors in the denominator, can be seen. 50 The larger the coefficient of conductivity, the smoother the conductive path can be formed within the electrode and the more optimally it can be positioned in the void within the electrode. The smaller the coefficient of conductivity, the higher the performance of the conductive material.

[0046] However, the powder resistance and packing density, which are factors in the numerator, must be in a paired relationship, with the powder resistance value being measured at that packing density. That is, when measuring the powder resistance of a conductive material, it is measured under a specific packing density, and the packing density, which is the measurement reference value, and the powder resistance, which is the measurement result, are reflected in the conductivity performance index. The powder resistance due to packing density is used to simulate the state inside the electrode, and the powder resistance is measured after compressing the conductive material at a predetermined pressure, because normally, the conductive material exists under pressure inside a rolled electrode. For this reason, when measuring powder resistance, it is generally measured after compressing it to a density of approximately 50% of its true density.

[0047] However, according to one embodiment of the present invention, the powder resistance of the conductivity performance index can be a value measured when the packing density is 0.4 g / cc to 0.6 g / cc. Since the conductive material is usually a carbon material, its true density may be about 1.95 g / cc, which allows the measured packing density to be about 1 g / cc. However, the conductivity performance index according to one embodiment of the present invention can more accurately reflect the formation of conductive paths and conductivity characteristics in the rolled electrode by utilizing the powder resistance value measured after further compressing the conductive material to have a packing density of 0.4 g / cc to 0.6 g / cc.

[0048] In other words, the part of the electrode where resistance increases first may be the voids created by the volume change of active material particles due to the insertion and removal of lithium. Such voids have the problem of disrupting the conductivity path due to a shortage of conductive material, component failure, or damage, which can ultimately lead to an increase in cell resistance. However, if conductivity is evaluated by adjusting the packing density to the range described above, it is possible to partially reflect the case of disruption of the conductivity path due to the occurrence of such voids, allowing for a more accurate evaluation of the performance of the conductive material, which has the advantage of providing electrodes with high energy density.

[0049] Furthermore, it goes without saying that the powder resistance changes depending on the packing density being measured. Even if the powder resistance measured at a high packing density is the same, there is a very high probability that the value will change when the packing density is reduced and the powder resistance is measured according to the various characteristics of the conductive material. Therefore, the powder resistance based on the packing density needs to be derived relatively strictly.

[0050] Furthermore, the conductivity performance index is characterized by including the aspect ratio of the conductive material as a factor. The aspect ratio of the conductive material can be understood as a correction coefficient that substantially corrects for the intrinsic conductivity that appears depending on the type of conductive material. For example, in the case of carbon black and carbon nanotubes, the intrinsic powder resistance values ​​of the conductive materials differ, which is due to the difference in the substances themselves and may be difficult to evaluate on the same line. However, by reflecting the aspect ratio as a factor in both cases, it can play a role in compensating for the difference due to intrinsic conductivity, along with reflecting the length characteristics.

[0051] Therefore, the conductivity performance index according to one embodiment of the present invention can be used as a parameter in which a smaller value indicates a conductive material with superior performance, and in order to realize a high-performance electrode, it is characterized by satisfying a range of 0.03 to 8.10 or less. If the conductivity performance index is less than 0.03, it is considered that the evaluation by the conductivity performance index deviates from the range in which the performance of the electrode is reflected, but the specific surface area and D 50This means that the specific surface area is considerably larger than that of powder, and at first glance, it may seem like a conductive material with excellent performance, but further unforeseen problems may arise. For example, an excessively large specific surface area causes aggregation between conductive material particles, making uniform dispersion in the dispersion liquid and uniform distribution within the electrode considerably difficult, so the conductivity performance index evaluated in this way is not easily reflected in the performance evaluation of the electrode. Also, if the conductivity performance index is greater than 8.10, the conductivity characteristics cannot be supported as much as the number and length characteristics, and the conductivity itself is inferior, or the number or length is such that it is difficult to find and place in the voids of the electrode, making it difficult to smoothly form conductive paths.

[0052] Therefore, the conductivity performance index may preferably be 0.05 or higher, 0.10 or higher, 0.20 or higher, 0.30 or higher, 0.40 or higher, or 0.50 or higher, and may also be 7.50 or lower, 7.00 or lower, 6.50 or lower, 6.00 or lower, 5.50 or lower, 5.00 or lower, or 4.50 or lower.

[0053] In other words, the aforementioned conductivity performance index reflects the inherent characteristics of the conductive material, name, number, and length. These characteristics play an important role in the distribution of the conductive material in an electrode, connecting active material particles, connecting primary particles within secondary active material particles, and arranging in the gaps between active material particles to eliminate resistance increases caused by the presence of empty spaces. In particular, in electrodes with high rolling density, even when carbon nanotubes with good dispersion and excellent length characteristics are applied, many problems occur, such as damage to the active material and disruption of conductive paths between particles. However, conductive materials that take the conductivity performance index into consideration, as described above, can maximize their function in electrodes with high rolling density, i.e., electrodes that aim to maximize energy density.

[0054] According to one embodiment of the present invention, the conductive material may include one or more selected from the group consisting of carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes.

[0055] Specifically, according to one embodiment of the present invention, the conductive material may contain carbon black, in which case the preferred conductivity figure may be 1.00 to 8.10. In the case of carbon black, it is most commonly used as a point-type conductive material, but due to the presence of carbon nanotubes, materials with a large specific surface area are not utilized, and therefore it is not used as a conductive material for electrodes where high energy density is required. However, even if carbon black is used, if the specific surface area is high and the appropriate size D 50 By utilizing materials that possess these properties and applying materials with a conductivity index of 1.00 to 8.10, it is possible to realize electrodes with high energy density and excellent resistance characteristics.

[0056] Therefore, when the conductive material includes carbon black, the conductivity performance index may preferably be 1.20 or higher, 1.30 or higher, 1.40 or higher, 1.50 or higher, or 1.60 or higher, and may also be 7.00 or lower, 6.70 or lower, 6.50 or lower, 6.00 or lower, 5.50 or lower, 5.00 or lower, or 4.50 or lower.

[0057] Furthermore, the carbon black used here has a specific surface area of ​​280 m². 2 / g~1,200m 2 It may also be / g. The specific surface area is preferably 285m². 2 / g or more, 290m 2 / g or more, or 295m 2 It may be more than / g, and 1,100m 2 / g or less, 1,050m 2 / g or less, 1,000m 2 / g or less, 950m 2 / g or less, 900m 2 / g or less, 800m 2 / g or less, 700m 2 / g or less, or 600m 2 It may be less than / g.

[0058] Furthermore, the carbon black is D 50The particle size may be 0.6 μm to 1.5 μm. Preferably, it may be 0.7 μm or more, 0.8 μm or more, or 0.9 μm or more, and may also be 1.4 μm or less, 1.3 μm or less, or 1.2 μm or less.

[0059] As mentioned above, it has a relatively high specific surface area and an appropriate size D 50 When using carbon black with these properties, it is possible to achieve high-performance electrodes even when using carbon black that easily meets the conductivity performance index and is highly competitive in terms of unit price.

[0060] Here, the carbon black may have a powder resistance of 0.1 Ωcm to 0.3 Ωcm when measured at a packing density of 0.4 g / cc to 0.6 g / cc, and may be 0.12 Ωcm or more, 0.13 Ωcm or more, or 0.14 Ωcm or more, or it may be 0.26 Ωcm or less, 0.24 Ωcm or less, or 0.22 Ωcm or less.

[0061] According to one embodiment of the present invention, the conductive material may include one or more selected from the group consisting of multi-walled carbon nanotubes and single-walled carbon nanotubes, and the conductivity performance index may be 0.03 to 4.00.

[0062] Specifically, according to one embodiment of the present invention, the conductive material may include multi-walled carbon nanotubes, in which case the conductivity index may be 0.30 to 3.90. The multi-walled carbon nanotubes are prone to relatively large changes in physical properties and particle size due to dispersion, and when attempting to use those with a large specific surface area and long length, the above-mentioned problems are likely to occur. However, in the present invention, as a means to solve the above problems, the aspect ratio and specific surface area, as well as the D in powder form, are optimized to ensure uniform distribution in the electrode and to realize an electrode with high energy density. 50 A key feature of this approach is the introduction of a conductivity performance index in relation to powder resistance, achieved by selecting specific components and investigating their relationships.

[0063] As a result, the multi-walled carbon nanotube has a specific surface area of ​​150 m². 2 / g~300m 2 The specific surface area may be / g. Preferably, it is 160m². 2 / g or more, 165m 2 / g or more, or 170m 2 It may be more than / g, 295m 2 / g or less, 290m 2 / g or less, 285m 2 / g or less, 280m 2 / g or less, 275m 2 / g or less or 270m 2 It may be less than / g.

[0064] Furthermore, the multi-walled carbon nanotubes are in a powder state. 50 However, it may be 2.0 μm to 4.0 μm. Preferably, it may be 2.2 μm or more, 2.3 μm or more, or 2.5 μm or more, and may also be 3.8 μm or less, 3.7 μm or less, 3.6 μm or less, or 3.5 μm or less.

[0065] Furthermore, the multi-walled carbon nanotube may have an aspect ratio of 3 to 8, preferably 3.5 or more, 4.5 or more, or 7 or less, 6.5 or less, 6 or less, or 5.5 or less.

[0066] As mentioned above, the appropriate level of specific surface area and D in powder form 50 By appropriately adjusting the aspect ratio, a uniform distribution can be induced within the electrode, and the disruption of the conductive path can be minimized even in voids generated by the electrochemical reaction of the cell.

[0067] Here, the multi-wall carbon nanotube may have a powder resistance measured at a packing density of 0.4 g / cc to 0.6 g / cc of 0.02 Ωcm to 0.06 Ωcm, may be 0.022 Ωcm or more, 0.023 Ωcm or more, or 0.025 Ωcm or more, and may also be 0.055 Ωcm or less, 0.053 Ωcm or less, or 0.05 Ωcm or less.

[0068] Specifically, according to one embodiment of the present invention, the conductive material may include single-wall carbon nanotubes, and in this case, the conductive performance index may be 0.03 to 1.50. The single-wall carbon nanotube is a conductive material with a very high degree of difficulty in dispersion, and is known as a conductive material that can ensure conductivity with only a small amount of use due to its high specific surface area. However, in practice, it is difficult to fully exhibit its length characteristics in the electrode, and it is not easy to distribute uniformly. Also, even if it is uniformly distributed, it cannot be excluded that damage may be caused to the active material or the carbon nanotube during rolling, resulting in problems in the formation of the conductive path. However, in the present invention, as a means for solving the above problems, in order to optimally and uniformly distribute in the electrode and realize an electrode with a high energy density, the aspect ratio, specific surface area, and D in the powder state 50 are selected, and by investigating the relationship, it can be said that the conductive performance index is introduced in relation to the powder resistance.

[0069] Thereby, the single-wall carbon nanotube may have a specific surface area of 500 m 2 / g to 1,300 m 2 / g. The specific surface area is preferably 530 m 2 / g or more, 550 m 2 / g or more, or 570 m 2 / g or more, and may be 1,200 m 2 / g or less, 1,100 m 2 / g or less, 1,000 m 2 / g or less, 900 m 2 / g or less, 850 m 2 / g or less, or 800 m2 It may be less than / g.

[0070] Furthermore, the single-walled carbon nanotubes are in a powder state. 50 However, it may be between 2.0 μm and 7.0 μm. Preferably, it may be 2.3 μm or more, 2.5 μm or more, 2.7 μm or more, or 3.0 μm or more, and may also be 6.8 μm or less, 6.6 μm or less, 6.4 μm or less, 6.2 μm or less, or 6.0 μm or less.

[0071] Furthermore, the single-walled carbon nanotube may have an aspect ratio of 40 to 100, preferably 45 or more, 50 or more, or 55 or more, and may also have an aspect ratio of 90 or less, 85 or less, 80 or less, or 75 or less.

[0072] As mentioned above, the appropriate level of specific surface area and D in powder form 50 By appropriately adjusting the aspect ratio, a uniform distribution can be induced within the electrode, and the disruption of the conductive path can be minimized even in voids generated by the electrochemical reaction of the cell.

[0073] Here, the single-walled carbon nanotube may have a powder resistance measured at a packing density of 0.4 g / cc to 0.6 g / cc of 0.001 Ωcm to 0.006 Ωcm, or it may be 0.0015 Ωcm or more, 0.0017 Ωcm or more, or 0.002 Ωcm or more, or it may be 0.0055 Ωcm or less, 0.0053 Ωcm or less, or 0.005 Ωcm or less.

[0074] According to one embodiment of the present invention, the conductive material may include two or more selected from the group consisting of carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes. Here, the conductivity index can be calculated by using the conductivity index of each conductive material and the weight fraction of the mixed conductive material to obtain a weight average, and can be calculated as shown in Equation 2 below.

[0075] [Formula 2] P CTotal =(P C1 ×w1)+(P C2 ×w²)+…+(P Cn ×w n )

[0076] In the above equation 2, P CTotal P is the conductivity performance index of a mixed conductive material, C1 , P C2 ...P Cn w1, w2, ...w are the conductivity performance indices of each conductive material in the mixed conductive material. n This represents the weight fraction of each conductive material.

[0077] For example, in the case of a conductive material in which carbon black and multi-walled carbon nanotubes are mixed in a weight ratio of 3:7, if the conductivity index of performance is 2.00 and 0.50 respectively, the conductivity index of performance of the mixed conductive material can be calculated as "(2.00 × 0.3) + (0.50 × 0.7)" and may have a value of 0.95.

[0078] electrode An electrode according to another embodiment of the present invention includes an electrode current collector and an electrode active material layer disposed on the electrode current collector, wherein the electrode active material layer includes the conductive material described above.

[0079] Here, the conductive material is the conductive material according to the present invention described above. Since the details regarding the conductive material are as described above, a detailed explanation will be omitted, and the remaining components will be described below.

[0080] According to one embodiment of the present invention, the electrode active material may be a positive electrode active material, the electrode may be a positive electrode, and the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0081] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0082] The positive electrode active material may include, for example, one or more selected from the group consisting of lithium nickel oxide, perlithium manganese oxide, lithium metal phosphate compound, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide.

[0083] Preferably, the positive electrode active material may be of the single-particle type and may contain lithium nickel oxide and / or lithium metal phosphate compounds, and the single-particle type positive electrode active material has a degree of single-particle formation (D 50 / D mean ) may be 1 to 10. Single-particle positive electrode active materials have higher particle strength compared to conventional single-particle positive electrode active materials with a secondary particle form in which tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling. Furthermore, in the case of the single-particle positive electrode active material according to the present invention, since the number of lower-component elements (i.e., nodules) that make up the particle is small, there is less change due to volume expansion and contraction of the primary particles during charging and discharging, and as a result, the occurrence of cracks inside the particle is also significantly reduced.

[0084] The smaller the degree of single-particle formation, the more the single-particle type positive electrode active material particles can possess single-particle type particle characteristics. Therefore, the degree of single-particle formation may preferably be 1 to 8, but may also be 1 to 7, 1 to 6, or 1 to 5. When this range is met, the degree of particle fracture can be reduced, the rolling density can be improved, and improvements in both lifetime characteristics and energy density can be expected.

[0085] According to one embodiment of the present invention, the D of the single-particle type cathode active material 50 The particle size may be between 1.0 μm and 10.0 μm.

[0086] The single-particle type positive electrode active material has an average particle size of 1.0 μm to 10.0 μm at 50% of its volume cumulative amount, preferably 1.5 μm or more, 1.7 μm or more, 2.0 μm or more, 2.5 μm or more, or 3.0 μm or more, and may also be 9.0 μm or less, 8.0 μm or less, 7.5 μm or less, 7.0 μm or less, 6.5 μm or less, 6.0 μm or less, 5.5 μm or less, or 5.0 μm or less. The volume cumulative average particle size D of the single-particle type positive electrode active material 50 If the above range is met, there is the advantage that the rolling density can be increased without damaging the positive electrode active material particles.

[0087] According to one embodiment of the present invention, the average particle size (D) of the nodules of the single-particle type positive electrode active material. mean The particle size may be 0.2 μm to 3.0 μm, and the average particle size of the nodule may preferably be 0.5 μm or more, 0.7 μm or more, or 1.0 μm or more, and may also be 2.8 μm or less, 2.5 μm or less, or 2.0 μm or less. When the above range is satisfied, the range of single-particle degree can be satisfied, and the effects thereon can be expected.

[0088] The single-particle positive electrode active material according to the present invention may contain a lithium nickel-based oxide and may have a composition such as that shown in the following chemical formula 1.

[0089] [Chemical formula 1] Li 1+x Nia Co b M 1 c M 2 d O 2-e X e

[0090] In the above chemical formula 1, M 1 It includes one or more selected from Mn and Al, and M 2 x contains one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X contains one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 <b≦0.35、0<c≦0.35、0≦d≦0.05および0≦e≦0.05である。

[0091] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, M 2 This is 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 While elements are not essential, if present in appropriate amounts, they can promote grain growth during calcination or improve crystal structure stability. Furthermore, X is an anion substituted at the oxygen site and can include N, P, S, F, or Cl.

[0092] The aforementioned 1+x represents the molar ratio of lithium in the single-particle lithium nickel 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.

[0093] The above a represents the molar ratio of nickel among the total metals other than lithium in the single-particle lithium nickel oxide, and may be 0.50≦a<1.00, 0.60≦a≦0.99, 0.70≦a≦0.99, 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.

[0094] The above b represents the molar ratio of cobalt among the total metals other than lithium in the single-particle lithium nickel oxide, and 0 <b≦0.35、0.01≦b≦0.34、0.01≦b≦0.30、0.01≦b≦0.25、0.01≦b≦0.20、または0.01≦b≦0.15であってもよい。

[0095] The aforementioned c is M, which is the total metal other than lithium in the single-particle lithium nickel oxide. 1 The molar ratio is shown, 0 <c≦0.35、0.01≦c≦0.34、0.01≦c≦0.30、0.01≦c≦0.25、0.01≦c≦0.20、または0.01≦c≦0.15であってもよい。

[0096] The above d is M, which is the total metal other than lithium in the single-particle lithium nickel oxide. 2 This indicates the molar ratio of the elements, and may be 0≦d≦0.05, 0≦d≦0.02, or 0≦d≦0.01.

[0097] The aforementioned e represents the molar ratio of element X among the total nonmetals other than oxygen in the single-particle lithium nickel oxide, and may be 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02, or 0 ≤ e ≤ 0.01.

[0098] Furthermore, the lithium metal phosphate compound may have a composition represented by the following chemical formula 2.

[0099] [Chemical formula 2] Li 1+x [Fe 1-y M y ]PO4

[0100] In the above chemical formula 2, M comprises one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

[0101] The lithium metal phosphate compound can be doped with M. In this case, the lattice structure and distance within the olivine crystal structure, which is the crystalline structure, change, increasing the diffusivity of lithium ions, and as a result, the electrochemical properties of the battery containing the positive electrode active material can be improved.

[0102] The aforementioned x may be -0.5 to 0.5, preferably -0.3 or greater, -0.1 or greater, or 0 or greater, and may also be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0103] The aforementioned y may be 0 or greater, less than 1, and may be 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.

[0104] The lithium metal phosphate compound may be, for example, LiFePO4.

[0105] The lithium metal phosphate compound according to the present invention may be in the form of a single particle consisting of only one primary particle, or in the form of amorphous secondary particles consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate compound may contain an olivine structure, and more 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 can be uniformly present on the surface of primary particles that exist inside the secondary particles.

[0106] The coating layer may include a carbon coating layer with a graphite structure, and the thickness of the coating layer may be 0.5 nm to 5 nm. When the thickness of the coating layer is within the above range, there is an advantage in that electrical conductivity is improved and the movement of lithium ions is not hindered. Specifically, the thickness of the coating layer may be 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, or 3.0 nm or more, and may be 5.0 nm or less.

[0107] The coating layer may be uniformly coated on the surface of the lithium metal phosphate compound. That is, the coating layer may be in the form of a thin film. The coating layer can improve the ionic conductivity and electronic conductivity during charging and discharging of the battery containing the positive electrode active material. In addition to carbon, the coating layer may contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen.

[0108] The coating layer may be present in an amount of 0.5% to 3% by weight relative to the total weight of the lithium metal phosphate compound, in order to improve electrical conductivity and not hinder the movement of lithium ions.

[0109] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0110] The positive electrode conductive material can be the conductive material dispersion described above, and may also contain other materials to provide conductivity to the electrode. In the battery it is used in, it is not particularly limited as long as it does not cause a chemical change and has electronic conductivity.

[0111] Specific examples of the aforementioned additional conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal-linked fibers; metal powders such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used individually or in mixtures of two or more.

[0112] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more can be used.

[0113] According to one embodiment of the present invention, the electrode active material may be a negative electrode active material, the electrode may be a negative electrode, and the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing the negative electrode active material.

[0114] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used.

[0115] The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. Further, the negative electrode current collector can be used in various forms such as, for example, a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0116] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. For example, carbon materials such as artificial graphite, natural graphite, Kish graphite, pyrolytic carbon, meso-carbon microbeads, mesophase pitches, petroleum / coal tar pitch derived cokes, mesophase pitch based carbon fiber, graphitized carbon fiber, amorphous carbon, softened carbon, or cured carbon; (semi) metallic materials capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; SiO b (0 < b ≤ 2), (semi) metallic oxide materials capable of doping and undoping lithium such as SnO2, vanadium oxides, lithium vanadium oxides; heterogeneous composite materials such as Si-C composites or Sn-C composites; or a thin film of metallic lithium, etc. can be mentioned, and any one or a mixture of two or more of these can be used.

[0117] Preferably, the negative electrode active material can include one or more selected from the group consisting of a silicon-based active material, a carbon-based active material, and a silicon-carbon composite-based active material. More preferably, the carbon-based active material can include one or more selected from the group consisting of artificial graphite, natural graphite, softened carbon, and cured carbon, and the silicon-based active material is pure Si particles and / or SiO b(0 < b ≤ 2) can be included, and the silicon-carbon composite active material can include a Si-C composite. Further, as the negative electrode active material, a mixed active material in which two or more of the above substances are mixed may be applied.

[0118] The negative electrode active material can be contained at 60% to 99% by weight based on the total weight of the negative electrode binder layer, preferably 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, and can also be contained at 98% by weight or less, 97% by weight or less, 95% by weight or less.

[0119] The binder is a component that helps to bond the conductive material, active material, and current collector, and can usually be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode composite layer, and can be present in amounts of 0.2% or more by weight, 0.3% or more by weight, or 0.5% or more by weight, and can also be present in amounts of 8% or less by weight, or 5% or less by weight. Examples of such binders include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, and polyvinyl alcohol. In particular, it may contain one or more selected from the group consisting of styrene-butadiene copolymer, acrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, diacetylcellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylfuran, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, and cyanoethylsucrose. Preferably, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, or mixtures thereof are used.

[0120] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0121] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in amounts of 10% by weight or less, preferably 5% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less, relative to the total weight of the negative electrode composite layer. It can also be included in amounts of 0.01% by weight or more, 0.05% by weight or more, 0.08% by weight or more, 0.1% by weight or more, or 0.3% by weight or more. Such conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive. Examples of usable conductive materials include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0122] On the other hand, the electrode slurry may further contain a solvent as needed to adjust viscosity, etc. Here, the solvent may be water, an organic solvent, or a mixture thereof. Examples of the aforementioned organic solvents include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; and polyvalent solvents such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include alcohols; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. Any one or more of these mixtures may be used, but are not limited to these.

[0123] The solvent can be included in such a concentration that the solid content in the electrode slurry is 60% to 85% by weight, preferably 65% ​​to 80% by weight. When this range is met, binder migration can be suppressed, electrode adhesion can be improved, the drying temperature can be lowered, coating properties can be improved, the coating speed can be increased, and productivity can be improved.

[0124] The electrode according to the present invention can be manufactured by applying an electrode slurry containing the above-mentioned components, drying it, and forming an electrode active material layer on a current collector. Specifically, the electrode active material layer can be formed by applying the electrode slurry onto the electrode current collector and then drying it, or by applying the electrode slurry onto another support, peeling it off this support, and laminating the resulting film onto the electrode current collector. If necessary, after the electrode active material layer is formed by the above-mentioned method, a rolling step may be further performed. Here, drying and rolling can be carried out under appropriate conditions considering the physical properties of the electrode to be ultimately manufactured, and are not particularly limited.

[0125] Lithium-ion battery A lithium secondary battery according to yet another embodiment of the present invention has a structure in which a positive electrode, a separator, and a negative electrode are stacked in order, and one or more of the positive electrode and the negative electrode are the electrodes described above. Specifically, the lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, where the positive electrode and the negative electrode are as described above.

[0126] Below, we will only explain the remaining components.

[0127] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator that is normally used in secondary batteries. Specifically, as the separator, a porous polymer film can be used, for example, a porous polymer film made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0128] According to one embodiment of the present invention, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or any other such electrolyte that can be used in the manufacture of lithium secondary batteries, and is not limited to these.

[0129] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0130] Examples of non-aqueous organic solvents that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0131] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferable to use because they have high dielectric constants as high-viscosity organic solvents and readily dissociate lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more preferable to use.

[0132] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3- (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following.

[0133] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds including difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0134] Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0135] Examples and Comparative Examples For Examples 1a to 5a and Comparative Examples 1a to 3a, carbon black having the properties described in Table 1 below was prepared. For Examples 1b to 4b and Comparative Examples 1b to 3b, multi-wall carbon nanotubes having the properties described in Table 2 below were prepared. For Examples 1c to 5c and Comparative Examples 1c to 2c, single-wall carbon nanotubes having the properties described in Table 3 below were prepared.

[0136] Volume average particle size D of conductive material 50 The particle size (μm) was measured using a laser diffraction particle size analyzer (Malvern, Mastersizer 3000), and the difference in diffraction patterns due to particle size was measured as the particle passed through the laser beam to calculate the particle size distribution. The particle size at the point where the cumulative volume distribution by particle size reached 50% was confirmed, and D 50 We measured it.

[0137] The powder resistance (Ωcm) of the conductive material was determined by placing 0.1g of the conductive material into a cylindrical geometry, then increasing the pressure in a pressure-measuring press while measuring the sheet resistance. The decrease in volume as the pressure increased was also measured, and the powder resistance was determined when the packing density was between 0.4g / cc and 0.6g / cc.

[0138] Specific surface area (m²) of conductive material 2 The value ( / g) was measured using the BET method and calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using a BELSORP-mino II manufactured by BEL Japan.

[0139] The aspect ratio of the conductive material was determined by first capturing an image containing 50 or more conductive material particles using a scanning electron microscope (SEM). Then, an image analysis program was used to determine the ratio of the long axis to the short axis of each conductive material particle, and the average value of these values ​​was used.

[0140] Experimental Example 1: Battery Performance Evaluation 1 (Resistive Characteristics) LiRe 0.6 Co 0.1 Mn 0.3A material having an O2 composition was used as the positive electrode active material, and the positive electrode was manufactured by applying the conductive materials of the above examples and comparative examples.

[0141] The positive electrode was prepared by mixing the lithium nickel oxide, conductive material, and PVDF binder in a weight ratio of 97.0:1.2:1.8, adding N-methylpyrrolidone solvent to achieve a solid content of 72%, and mixing in a homogenizer at 2,500 rpm for 1 hour to produce a positive electrode slurry. Subsequently, the slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled twice using a roll-to-roll rolling mill at a linear pressure of 2,000 kgf / cm to produce the positive electrode slurry.

[0142] As the negative electrode active material, the average particle size D 50 Graphite particles with a diameter of 5 μm were used. A negative electrode was prepared containing a negative electrode active material layer comprising the negative electrode active material, CMC as a negative electrode binder, and carbon nanotubes as a negative electrode conductive material in a weight ratio of 80:10:10. The loading amount of the negative electrode active material layer was 10 mAh / cm². 2 The thickness was 75 μm.

[0143] The positive electrode, the negative electrode, and the porous polyethylene separator were assembled using a winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio) and lithium hexafluorophosphate (LiPF 61 moles)) was injected into the assembled battery to manufacture a lithium secondary battery.

[0144] The lithium secondary battery was charged at 4.2V with a 0.1C C-rate, and then discharged to 2.5V to perform an activation process.

[0145] After charging and discharging the lithium secondary battery, and after fully charging, while discharging, a 2.5C pulse current was applied for a specific time according to the change in SOC, and the diffusion resistance (resistance for 0.1 to 30 seconds) was measured. The results are shown in Tables 4 to 6.

[0146] Experimental Example 2: Battery Performance Evaluation 2 (Lifespan Characteristics) Each lithium secondary battery produced in Experimental Example 3 was charged in CCCV mode to 0.2C and 4.25V (termination current 1 / 20C). Subsequently, the battery was charged to 4.25V at 45°C with a constant current of 0.33C and discharged to 2.5V at a constant current of 0.33C, with each cycle being performed. The capacity retention rate was measured while performing 100 charge-discharge cycles. The measurement results are shown in Tables 4-6 below.

[0147] The capacity retention rate was calculated as follows:

[0148] Capacity retention rate (%) = (Discharge capacity after 100 cycles) / (Discharge capacity after 1 cycle) × 100

[0149] Evaluation results (1) Carbon Black The physical properties of the carbon black conductive materials in Examples 1a to 5a and Comparative Examples 1a to 3a are shown in Table 1 below, and the results of the evaluations in Experimental Examples 2 and 3 are shown in Table 2 below.

[0150] [Table 1]

[0151] [Table 2]

[0152] Referring to Tables 1 and 2, it can be confirmed that in Examples 1a to 5a, which satisfy the conductivity performance index, the diffusion resistance is lower and the lifespan is improved compared to Comparative Examples 1a to 3a. In particular, Comparative Examples 1a to 3a have high powder resistance relative to the packing density and a small average particle size of the conductive material, but the specific surface area is even smaller in comparison, so the number characteristics are not properly realized, the conductivity is evaluated as low, and as a result, the resistance and lifespan characteristics are judged to be inferior.

[0153] (2) Multi-walled carbon nanotubes The physical properties of the multi-walled carbon nanotube conductive materials of Examples 1b to 4b and Comparative Examples 1b to 3b are shown in Table 3 below, and the results of the evaluations in Experimental Examples 2 and 3 are shown in Table 4 below.

[0154] [Table 3]

[0155] [Table 4]

[0156] Referring to Tables 3 and 4, it can be confirmed that Examples 1b to 4b, which satisfy the conductivity performance index, exhibit lower diffusion resistance and improved lifespan compared to Comparative Examples 1b to 3b. In particular, Comparative Examples 1b and 2b, despite having the same conductive material content, exhibited high powder resistance to packing density, resulting in a difference in conductivity. In the case of Comparative Example 3b, the excessive specific surface area led to problems with uniform distribution, resulting in a difference in conductivity, which can be supported by the data in the aforementioned tables.

[0157] (3) Single-walled carbon nanotubes The physical properties of the single-wall carbon nanotube conductive materials of Examples 1c to 5c and Comparative Examples 1c and 2c are shown in Table 5 below, and the results of the evaluations in Experimental Examples 2 and 3 are shown in Table 6 below.

[0158] [Table 5]

[0159] [Table 6]

[0160] Referring to Tables 5 and 6, it can be confirmed that in Examples 1c to 5c, which satisfy the conductivity performance index, the diffusion resistance is lower and the lifespan is improved compared to Comparative Examples 1c and 2c. In particular, single-wall carbon nanotubes are conductive materials that are greatly affected by length characteristics, and in the case of Comparative Examples 1c and 2c, the aspect ratio is small, while BET and D 50 The above result is thought to have been derived from the fact that it is not compensated for by the formula and the powder resistance to packing density is high.

Claims

1. The conductivity performance index (P) is defined by the following formula 1. Ｃ A conductive material whose coefficient of permutation (%) is between 0.03 and 8.

10. [Formula 1] P Ｃ =[(AR×R Ｐ ×ρ Ｐ ) / (BET×D ５０ )]×10 ４ In the above formula 1, AR is the aspect ratio, which is the ratio of the long axis to the short axis of the conductive material. R Ｐ and ρ Ｐ are the powder resistance (Ωcm) and the packing density (g / cc), respectively, and the powder resistance measured when the packing density ρ Ｐ is R Ｐ and BET is the specific surface area (m²) of the conductive material. ２ / g) and D ５０ This is the 50% average particle size (μm) of the conductive material in powder form, In the above formula, R Ｐ ρ Ｐ , BET and D ５０ This is a unitless number from which all of the aforementioned units have been removed.

2. The conductive material according to claim 1, wherein the conductive material comprises one or more selected from the group consisting of carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes.

3. The conductive material according to claim 1, wherein the conductivity performance index is 0.10 or more and 7.00 or less.

4. The conductive material according to claim 1, wherein the conductivity performance index is 0.30 or more and 5.00 or less.

5. The packing density (ρ Ｐ The conductive material according to claim 1, wherein the amount is 0.4 g / cc or more and 0.6 g / cc or less.

6. The conductive material contains carbon black, The conductive material according to claim 1, wherein the conductivity performance index is 1.00 or more and 8.10 or less.

7. The conductive material comprises one or more selected from the group consisting of multi-walled carbon nanotubes and single-walled carbon nanotubes. The conductive material according to claim 1, wherein the conductivity performance index is 0.03 or more and 4.00 or less.

8. The conductive material includes multi-walled carbon nanotubes, The conductive material according to claim 1, wherein the conductivity performance index is 0.30 or more and 3.90 or less.

9. The conductive material includes single-wall carbon nanotubes, The conductive material according to claim 1, wherein the conductivity performance index is 0.03 or more and 1.50 or less.

10. It includes an electrode current collector and an electrode active material layer disposed on the electrode current collector, The electrode comprises an electrode, wherein the electrode active material layer includes the conductive material described in any one of claims 1 to 9.

11. The electrode active material layer further contains a positive electrode active material, The electrode according to claim 10, wherein the positive electrode active material comprises one or more selected from the group consisting of lithium nickel oxides and lithium metal phosphate compounds.

12. The lithium nickel oxide is of the single-particle type, and the average particle size of the nodule (D ｍｅａｎ ) for volume cumulative average particle size (D ５０ The ratio of single-particle particles (D ５０ / D ｍｅａｎ The electrode according to claim 11, wherein the value of ) is 1 to 10.

13. The lithium nickel oxide has the composition represented by the following chemical formula 1, The electrode according to claim 11, wherein the lithium metal phosphate compound has a composition represented by the following chemical formula 2. [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２－ｅ X ｅ In the above chemical formula 1, M １ It includes one or more selected from Mn and Al, M ２ X includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, and X includes one or more elements selected from the group consisting of N, P, S, F, and Cl, with 0 ≤ x ≤ 0.1, 0.5 ≤ a < 1, 0 < b ≤ 0.35, 0 < c ≤ 0.35, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.

05. [Chemical formula 2] Li １＋ｘ [Fe １－ｙ M ｙ ]PO ４ In the above chemical formula 2, M comprises one or more elements selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5 ≤ x ≤ 0.5 and 0 ≤ y < 1.

14. The electrode active material layer further contains a negative electrode active material, The electrode according to claim 10, wherein the negative electrode active material includes silicon-based particles.

15. It includes a structure in which electrodes and separators are stacked alternately, A lithium secondary battery wherein the electrode is the electrode described in claim 10.

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