Conductive material, electrode comprising same, and lithium secondary battery comprising same

Abstract

The present invention relates to an electrically conductive material satisfying a conductivity index (PC) of 0.03 to 8.10, in which the conductivity index is defined by the aspect ratio, the powder resistance, and the bulk density, BET specific surface area, and volume cumulative average particle size D50 when the powder resistance is measured as factors, and according to the present invention, the conductivity index of the electrically conductive material is less than or equal to 0.03 and less than or equal to 8.10, and according to the present invention, the conductivity index of the electrically conductive material is less than or equal to 0.03 and less than or equal to 8.10. By using physical properties that may relate to resistance characteristics and lifespan characteristics of an electrode, thereby clarifying and defining a relationship between the physical properties, it is possible to provide a conductive material capable of improving performance of an electrode when a specific range is satisfied. A conductive material, such as a conductive material disposed in the aperture and disposed on a surface of the active material, forms conductive network connection paths between and within the active material particles in the electrode.

Description

Technical Field

[0001] The present invention relates to a conductive material having excellent conductive properties, an electrode comprising the conductive material, and a lithium secondary battery comprising the electrode. Background Art

[0002] Due to the rapid increase in the use of fossil fuels, the demand for using alternative energy or clean energy is increasing, and as part of this trend, the most actively researched field is the field of power generation and storage using electrochemical reactions.

[0003] At present, a typical example of an electrochemical device that uses such electrochemical energy is a secondary battery, and the application fields of secondary batteries are constantly increasing. In recent years, with the technological development and increase in demand for portable devices such as portable computers, mobile phones and cameras, the demand for secondary batteries as energy sources has increased significantly. Among such secondary batteries, lithium secondary batteries with high energy density, that is, lithium secondary batteries with high capacity, have undergone considerable research and have also been commercialized and widely used.

[0004] At the same time, in order to manufacture a battery with high energy density, it is important to use a positive electrode active material with high capacity characteristics, but the material contained in the positive electrode together with the positive electrode active material can also play an important role. To this end, research has been conducted in the direction of maximizing the proportion of active material and minimizing the content of conductive material and binder. However, when the amount of active material used is increased, there is a problem in that the unit price of the battery cell increases significantly compared to the degree of performance improvement, which makes it difficult to apply the research to actual mass production.

[0005] Therefore, recent research trends have focused on improving price competitiveness while meeting certain energy densities or higher. Various approaches are applicable to producing batteries with high energy densities, but the presence of auxiliary materials such as conductive materials and binders, rather than the primary active material, can also play an important role. In particular, the performance of conductive materials varies greatly depending on the inherent characteristics of the material, such as conductivity, the form of the conductive material included in the electrode, and linear dispersion.

[0006] In particular, the electrical conductivity of carbon black, multi-walled carbon nanotubes (MWCNTs), and single-walled carbon nanotubes (SWCNTs), widely used as conductive materials, varies greatly even when the material is identical, due to differences in quantity, size, specific surface area, dispersion form, and shape. Therefore, before actual experiments are conducted, it is difficult to determine what properties each conductive material should possess in order to achieve high-performance electrodes. Furthermore, since conductivity can vary significantly even for materials with the same physical properties due to other differences, in-depth research is needed on this issue. Summary of the Invention

[0007] Technical issues

[0008] In order to solve the above problems, the present invention provides a conductive material with excellent electrical conductivity, and for this material, based on the conductive performance index reflecting the number characteristics, size characteristics, electrical conductivity characteristics, shape characteristics, etc. of carbon-based particles, it is possible to confirm the extent to which the conductive material forms a conductive path on the electrode and the extent to which the conductive material helps to reduce resistance.

[0009] In addition, even if each type of conductive material has different characteristics, the present invention provides a high-performance conductive material by reflecting the conductivity characteristics and shape characteristics in the conductive performance index, so that regardless of the type and shape of the conductive material, they can compensate each other to confirm the conductive performance index, and a high energy density electrode can be achieved through this confirmation.

[0010] Technical Solution

[0011] [1] According to an embodiment of the present invention, a conductivity performance index (P C ) satisfies a conductive material of 0.03 to 8.10, which is defined by the following Equation 1.

[0012] [Equation 1]

[0013] P C =[(AR x R P xρ P ) / (BET x D 50 )]x10 4

[0014] In Equation 1 above, AR is the aspect ratio, which is the ratio of the major axis to the minor axis of the conductive material, and R P and ρ P are powder resistance (Ωcm) and bulk density (g / cc), respectively. For conductive materials, when the bulk density is ρ P The powder resistance measured when P , BET is the specific surface area of the conductive material (m 2 / g), and D 50 is the volume cumulative 50% average particle size (μm) of the conductive material in the powder state, where in the above equation 1, R P , ρ P , BET and D 50 is a unitless number in which the above units are excluded.

[0015] [2] In the conductive material of the above [1], 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.

[0016] [3] In the conductive material of [1] and / or [2] above, the conductivity index may be 0.10 to 7.00.

[0017] [4] In at least one of the conductive materials of [1] to [3] above, the conductivity index may be 0.30 to 5.00.

[0018] [5] In at least one of the conductive materials of [1] to [4] above, the bulk density ρ P It can be 0.4 g / cc to 0.6 g / cc.

[0019] [6] In at least one of the conductive materials of [1] to [5] above, the conductive material may include carbon black, and the conductivity index may be 1.00 to 8.10.

[0020] [7] In at least one of the conductive materials of [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.

[0021] [8] In at least one of the conductive materials of [1] to [7] above, the conductive material may include multi-walled carbon nanotubes, and the conductivity performance index may be 0.30 to 3.90.

[0022] [9] In at least one of the conductive materials of [1] to [8] above, the conductive material may include single-walled carbon nanotubes, and the conductivity performance index may be 0.03 to 1.50.

[0023]

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

[0024]

[11] In the electrode of the above

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

[0025]

[12] In the electrode of the above

[11] , the positive electrode active material may be of a single particle type and may have a single particle degree D of 1 to 10. 50 / D 平均 , which is the volume cumulative average particle size D 50The average particle size D of the nodules 平均 ratio.

[0026]

[13] In the electrode of

[11] and / or

[12] above, the single particle type lithium nickel-based oxide may have a composition represented by the following formula 1, and the lithium metal phosphate-based compound may have a composition represented by the following formula 2.

[0027] [Formula 1]

[0028] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0029] In the above formula 1, M 1 including one or more selected from Mn and Al, M 2 The invention includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta and Nb, X includes one or more selected from the group consisting of N, P, S, F and Cl, and 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.

[0030] [Formula 2]

[0031] Li 1+x [Fe 1-y M y ]PO4

[0032] In the above Formula 2, M includes one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, and 0≤y<1.

[0033]

[14] In the electrode of the above-mentioned

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

[0034]

[15] According to yet another embodiment of the present invention, there is provided a lithium secondary battery including a structure in which electrodes and separators are alternately stacked, wherein the electrodes are the same as the above-described electrodes.

[0035] Beneficial effects

[0036] For the conductive material according to the present invention, the extent to which the conductive material forms a conductive path on the electrode and the extent to which the conductive material helps to reduce resistance can be confirmed by the conductive performance index reflecting the quantity characteristics, size characteristics, conductivity characteristics, shape characteristics, etc. of the carbon-based particles, and by applying a conductive material having such a defined conductive performance index that satisfies a specific range, an electrode with excellent conductivity and thus excellent resistance characteristics can be provided.

[0037] In addition, even if each type of conductive material has different characteristics, it is possible to confirm whether it is a high-performance conductive material by reflecting the conductivity characteristics and shape characteristics in the conductive performance index, thereby being able to compensate for each other to confirm the conductive performance index, regardless of the type and shape of the conductive material, through which a high-energy density electrode can be achieved. DETAILED DESCRIPTION

[0038] It should be understood that the words or terms used in the description and claims of the present invention should not be interpreted as limited to having the meanings defined in commonly used dictionaries. It will be further understood that based on the inventors' ability to appropriately define the meanings of words or terms to best explain the principles of the present invention, words or terms should be interpreted as having a meaning consistent with their meanings in the context of the relevant art and the technical concept of the present invention.

[0039] In this specification, the terms "comprises", "comprising" or "having" are intended to specify the presence of stated features, numbers, steps, elements or their combination, and do not preclude the presence or addition of one or more other features, numbers, steps, elements or their combination.

[0040] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the adsorption amount of nitrogen at liquid nitrogen temperature (77K) using Belsorp-mino II of BEL Japan Co.

[0041] In the present invention, "single particle type" refers to particles composed of 30 or fewer nodules, and single particle type particles are a concept including single particles composed of one nodule and quasi-single particles that are composites of 2 to 30 nodules.

[0042] A "nodule" is a sub-grain unit constituting a single grain or a quasi-single grain, and when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times, may be a single crystal without a crystalline grain boundary or a polycrystal without an apparent grain boundary.

[0043] In the present invention, "secondary particles" refer to particles formed by agglomeration of a plurality of tens to hundreds of primary particles. More specifically, the secondary particles are agglomerates of 50 or more primary particles.

[0044] The term "particle" used in the present invention may include any or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle.

[0045] In the present invention, the average particle size D of the nodules 平均 The diameter of each nodule of about 30 particles including one or more nodules is calculated by photographing the positive electrode active material particles with a scanning electron microscope (SEM), and then the average value is used to obtain the diameter.

[0046] In this specification, “50% cumulative volume average particle size D 50 " can be defined as the particle size corresponding to 50% of the maximum value of the volume cumulative sum of particle sizes in the particle size distribution curve of the particles. D can be measured by, for example, a laser diffraction method. 50 The laser diffraction method is generally capable of measuring particle sizes from the submicron region to several millimeters, thereby enabling the acquisition of highly reproducible and high-resolution results. Hereinafter, in this specification, “the volume cumulative 50% average particle size D 50 ” can be called 'volume cumulative average particle size', 'D 50 'wait.

[0047] In this specification, “aspect ratio” may mean the ratio of the longest line to the shortest line among lines passing through the center of a particle and extending to the periphery, regardless of the shape of the particle, i.e., whether the particle is linear, dot-shaped, or plate-shaped.

[0048] Hereinafter, the present invention will be described in detail.

[0049] The conductive material, the electrode, and the lithium secondary battery according to the present invention include at least one of the following configurations, and may include any combination of technically possible configurations among the following configurations.

[0050] Conductive materials

[0051] The conductive material according to the embodiment of the present invention has a conductivity performance index (P C ), which is defined by the following Equation 1.

[0052] [Equation 1]

[0053] P C=[(AR x R P xρ P ) / (BET x D 50 )]x 10 4

[0054] In Equation 1 above, AR is the aspect ratio, which is the ratio of the major axis to the minor axis of the conductive material, and R P and ρ P are powder resistance (Ωcm) and bulk density (g / cc), respectively. For conductive materials, when the bulk density is ρ P The powder resistance measured when P , BET is the specific surface area of the conductive material (m 2 / g), and D 50 is the volume cumulative 50% average particle size (μm) of the conductive material in the powder state, where in the above equation 1, R P , ρ P , BET and D 50 It is a unitless number that does not include the above units.

[0055] The volume cumulative 50% average particle size according to an embodiment of the present invention is not measured in a dispersed state in an organic solvent, but is measured in a dry powder state under air (aero) conditions, and is different from the value measured in a dispersed state, but can be confirmed to be basically the same as the shape and size distributed and existing in the active material layer of the electrode.

[0056] The conductive performance index according to the embodiment of the present invention includes powder resistance, packing density, BET specific surface area, D 50 and aspect ratio as factors, as defined in Equation 1 above.

[0057] As mentioned above, the performance of conductive materials is determined by various factors, and these factors can include the dispersion environment / conditions, the shape or particle size of the active material on the electrode, and porosity. However, factors due to the inherent characteristics of the conductive material can include shape characteristics, conductivity characteristics, quantity characteristics, and length characteristics. However, since the differences in these characteristics are very large for each type of conductive material, and the performance also varies greatly depending on how each characteristic is combined, it is not easy to achieve high performance when applying conductive materials.

[0058] However, in the present invention, by establishing a specific relationship using the above-mentioned characteristics as factors and parameterizing the relationship as a conductive performance index, it can be expected that there will be not only the following advantages: regardless of the type of conductive material, the conductive performance of the conductive material can be evaluated and the conductive performance between different conductive materials can be compared, but also the following advantages: an electrode with excellent conductivity can be provided by a conductive material controlled to have a conductive performance index within a specific numerical range.

[0059] The conductivity index is based on the product of powder resistance and bulk density, specific surface area and D 50 The specific surface area can reflect the quantity characteristics of the conductive material, D 50 It can partially reflect the length characteristics of the conductive material, and the powder resistance and bulk density can reflect the conductivity characteristics of the conductive material, so that in terms of powder resistance and bulk density, it is a factor of the numerator, the smaller the product value, the better the conductivity, and in terms of specific surface area and D 50 In terms of , it is a factor of the denominator, and the larger the product value, the smoother the conductive path that can be formed in the electrode, and the more optimal the conductive path that can be arranged in the hole in the electrode, so that it can be evaluated that the smaller the conductive performance index, the higher the performance of the conductive material.

[0060] However, powder resistance and bulk density, as molecular factors, require a paired relationship because the powder resistance value is measured at the bulk density. That is, when measuring powder resistance, the conductive material is measured at a specific bulk density, and the bulk density, which serves as a reference for the measurement, and the powder resistance, the measurement result, are reflected in the conductive performance index. The powder resistance based on the packing density is used to simulate the state in an electrode, and the powder resistance is measured after the conductive material is compressed to a certain pressure. This is because the conductive material is typically present under pressure in a rolled electrode. Therefore, when measuring powder resistance, the powder resistance is typically measured by compressing the conductive material to a density approximately 50% of its true density.

[0061] However, according to embodiments of the present invention, the powder resistance of the Conductive Performance Index may be a value measured when the bulk density is 0.4 g / cc to 0.6 g / cc. The conductive material is typically a carbon material and may have a true density of approximately 1.95 g / cc, so the measured bulk density may be approximately 1 g / cc. However, the Conductive Performance Index according to embodiments of the present invention utilizes the powder resistance value measured after further compressing the conductive material to have a bulk density of approximately 0.4 g / cc to 0.6 g / cc, and thus can more accurately reflect the conductive path formation and conductivity characteristics in the rolled electrode.

[0062] That is, the portion of the electrode where resistance initially increases is likely due to pores created by volume changes in the active material particles caused by the insertion and extraction of lithium. These pores have the problem of disconnecting the conductive path due to the lack, absence, or breakage of the conductive material, which may ultimately lead to an increase in battery resistance. However, if the conductivity is evaluated after adjusting the bulk density to the above range, the performance of the conductive material can be more accurately assessed, as the disconnection of the conductive path due to the generation of pores as described above can be partially reflected, and the presence of these pores can provide the advantages of a high energy density electrode.

[0063] Furthermore, the value of powder resistance varies depending on the bulk density at which the powder resistance is measured. Even if the powder resistance measured at a high bulk density has the same value, if the powder resistance is measured by lowering the bulk density according to the various characteristics of the conductive material, there is a high probability that the value will vary. Therefore, it may be necessary to relatively strictly control the value of powder resistance according to the bulk density.

[0064] The conductivity performance index also includes the aspect ratio of the conductive material as a factor. The aspect ratio of the conductive material can be understood as a correction factor that effectively corrects for the inherent conductivity exhibited by each type of conductive material. For example, in the case of carbon black and carbon nanotubes, the inherent powder resistance values of the respective conductive materials differ due to differences in the materials themselves, making it difficult to evaluate conductive materials on the same line. However, if the aspect ratio is also reflected as a factor, it can play a role in compensating for differences in inherent conductivity and reflecting length characteristics.

[0065] Therefore, the conductivity performance index according to the embodiment of the present invention can be used as a parameter that allows understanding that the smaller the conductivity performance index is, the better the performance of the conductive material is, and for the realization of a high-performance electrode, the conductivity performance index satisfies the range of 0.03 to 8.10 or less. If the conductivity performance index is less than 0.03, it can be considered that the evaluation based on the conductivity performance index is not reflected in the performance of the electrode, and due to the specific surface area and D 50 A conductive material with a surface area significantly greater than the powder resistance can be considered to have excellent performance, but may also have unexpected secondary issues. For example, an excessively large specific surface area may lead to aggregation between conductive material particles, making uniform dispersion in the dispersion and distribution in the electrode quite difficult, making the thus-estimated conductivity performance index difficult to reflect in the electrode performance evaluation. Furthermore, if the conductivity performance index exceeds 8.10, the conductivity itself may be reduced, as the conductivity characteristic is less supportive than the quantity or length characteristics, or the quantity or length may make it difficult to perform the functions of positioning the electrode holes and arranging them, potentially failing to promote the formation of conductive paths.

[0066] Therefore, the conductive performance index may preferably be 0.05 or greater, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, or 0.50 or greater, and 7.50 or less, 7.00 or less, 6.50 or less, 6.00 or less, 5.50 or less, 5.00 or less, or 4.50 or less.

[0067] In other words, the conductivity performance index reflects the inherent properties of the conductive material, such as shape characteristics, conductivity characteristics, quantity characteristics, and length characteristics, and these characteristics can play an important role in performing the function of distributing the conductive material in the electrode, such as connecting between active material particles, connecting between primary particles in the secondary particles if the active material is a secondary particle, and being arranged in the pores between the active material particles, thereby eliminating the factor that increases the resistance caused by the presence of empty spaces. In particular, in electrodes with increased rolling density, even when carbon nanotubes excellent in length characteristics are applied, there are many problems such as damage to the active material, disconnection of the conductive path between particles, etc., but as described above, the conductive material considering the conductivity performance index can have the function of being maximized in high rolling density electrodes (i.e., electrodes intended to maximize energy density).

[0068] According to an 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.

[0069] Specifically, according to an embodiment of the present invention, the conductive material may include carbon black, in which case the preferred conductivity index may be 1.00 to 8.10. Carbon black is most commonly used as a point-shaped conductive material, but due to the presence of carbon nanotubes, carbon black having a large specific surface area is not used, and is not used as a conductive material for electrodes that need to have a high energy density. However, even if carbon black is used, if D having a large specific surface area and an appropriate size is used, 50 And carbon black having a conductivity performance index satisfying 1.00 to 8.10 can realize an electrode with high energy density and excellent resistance characteristics.

[0070] Therefore, if carbon black is included as a conductive material, the conductive performance index may preferably be 1.20 or greater, 1.30 or greater, 1.40 or greater, 1.50 or greater, or 1.60 or greater, and 7.00 or less, 6.70 or less, 6.50 or less, 6.00 or less, 5.50 or less, 5.00 or less, or 4.50 or less.

[0071] In addition, the carbon black used at this time may have a 2 / g to 1,200m 2 / g specific surface area. The specific surface area can be preferably 285m 2 / g or greater, 290m 2 / g or greater, or 295m 2 / g or greater, 1,100m 2 / g or less, 1,050m 2 / g or less, 1000m 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 / g or less.

[0072] In addition, the carbon black may have a D 50 Preferably, D 50 It may be 0.7 μm or more, 0.8 μm or more, or 0.9 μm or more, and 1.4 μm or less, 1.3 μm or less, or 1.2 μm or less.

[0073] As mentioned above, if a D having a relatively high specific surface area and a suitable size is applied 50 Carbon black with excellent unit price competitiveness can easily meet the conductivity performance index, so that high-performance electrodes can be achieved even if carbon black with excellent unit price competitiveness is used.

[0074] In this case, the carbon black may have a powder resistance of 0.1 Ωcm to 0.3 Ωcm, 0.12 Ωcm or more, 0.13 Ωcm or more, or 0.14 Ωcm or more, and 0.26 Ωcm or less, 0.24 Ωcm or less, or 0.22 Ωcm or less, as measured at a bulk density of 0.4 g / cc to 0.6 g / cc.

[0075] According to an 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.

[0076] Specifically, according to an embodiment of the present invention, the conductive material may include multi-walled carbon nanotubes, in which case the conductivity performance index may be 0.30 to 3.90. Due to dispersion, multi-walled carbon nanotubes undergo relatively large changes in physical properties or particle size, so that if long multi-walled carbon nanotubes having a large specific surface area are used, there is a high possibility of encountering the above-mentioned problem. However, in the present invention, as a means of solving the above-mentioned problem, the aspect ratio, specific surface area, and D in the powder state are selected. 50, and the relationship between them is clarified in order to achieve high energy density electrodes through optimal uniform distribution in the electrode, thereby introducing a conductive performance index in its relationship with powder resistance.

[0077] Therefore, multi-walled carbon nanotubes can have a diameter of 150 m 2 / g to 300m 2 The specific surface area can be preferably 160m 2 / g or greater, 165m 2 / g or greater, or 170m 2 / g or greater, and 295m 2 / g or less, 290m 2 / g or less, 285m 2 / g or less, 280m 2 / g or less, 27 5m 2 / g or less, or 270m 2 / g or less.

[0078] In addition, the multi-walled carbon nanotubes can have a D of 2.0 μm to 4.0 μm in a powder state. 50 Preferably, D 50 It may be 2.2 μm or more, 2.3 μm or more, or 2.5 μm or more, and 3.8 μm or less, 3.7 μm or less, 3.6 μm or less, or 3.5 μm or less.

[0079] Furthermore, the multi-walled carbon nanotubes may have an aspect ratio of 3 to 8, preferably 3.5 or greater, or 4.5 or greater, and 7 or less, 6.5 or less, 6 or less, or 5.5 or less.

[0080] As described above, the specific surface area, the D 50 and aspect ratio to induce uniform distribution in the electrode and minimize the disconnection of the conductive path even in the pores generated by the electrochemical reaction of the battery.

[0081] In this case, the multi-walled carbon nanotubes may have a powder resistance of 0.02 Ωcm to 0.06 Ωcm, 0.022 Ωcm or greater, 0.023 Ωcm or greater, or 0.025 Ωcm or greater, and 0.055 Ωcm or less, 0.053 Ωcm or less, or 0.05 Ωcm or less, as measured at a bulk density of 0.4 g / cc to 0.6 g / cc.

[0082] Specifically, according to an embodiment of the present invention, the conductive material may include single-walled carbon nanotubes, in which case the conductivity performance index may be 0.03 to 1.50. Single-walled carbon nanotubes are conductive materials that are very difficult to disperse, and are known to be conductive materials that can only be used in small amounts to ensure conductivity due to their high specific surface area, but in practice, it is difficult to fully express the length characteristics of single-walled carbon nanotubes in the electrode, and it is not easy to evenly distribute single-walled carbon nanotubes. In addition, even if uniform distribution is achieved, the active material may be damaged or the carbon nanotubes may be damaged during rolling, thereby causing problems in the formation of conductive paths, which is also a problem that cannot be ruled out. However, in the present invention, as a means to overcome the above-mentioned problems, the aspect ratio, specific surface area and D in the powder state are selected. 50 , and elucidate the relationship between them in order to achieve high energy density electrodes through optimal uniform distribution in the electrode, so that the conductive performance index is introduced in its relationship with the powder resistance.

[0083] Therefore, a single-walled carbon nanotube can have a diameter of 500 m 2 / g to 1,300m 2 The specific surface area can be preferably 530m 2 / g or greater, 550m 2 / g or greater, or 570m 2 / g or greater, and 1,200m 2 / g or less, 1,100m 2 / g or less, 1,000m 2 / g or less, 900m 2 / g or less, 850m 2 / g or less, or 800m 2 / g or less.

[0084] In addition, single-walled carbon nanotubes can have a D of 2.0 μm to 7.0 μm in a powder state. 50 Preferably, D 50 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 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.

[0085] In addition, 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 90 or less, 85 or less, 80 or less, or 75 or less.

[0086] As described above, the specific surface area, the D 50and aspect ratio to induce uniform distribution in the electrode and minimize the disconnection of the conductive path even in the pores generated by the electrochemical reaction of the battery.

[0087] In this case, the single-walled carbon nanotubes may have a powder resistance of 0.001 Ωcm to 0.006 Ωcm, 0.0015 Ωcm or greater, 0.0017 Ωcm or greater, or 0.002 Ωcm or greater, and 0.0055 Ωcm or less, 0.0053 Ωcm or less, or 0.005 Ωcm or less, as measured at a bulk density of 0.4 g / cc to 0.6 g / cc.

[0088] According to an 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. In this case, as the conductivity index, a value obtained by calculating a weight average value using the conductivity index of each conductive material and the weight fraction of the mixed conductive material can be used, and calculation can be performed as shown in the following equation 2.

[0089] [Equation 2]

[0090] P C总 =(P C1 x w1)+(P C2 x w2)+...+(P Cn xw n )

[0091] In the above equation 2, P C总 is the conductivity index of the mixed conductive material, P C1 、P C2 …Pcn Cn is the conductivity performance index of each conductive material in the mixed conductive material, and w1, w2, ... w n is the weight fraction of each conductive material.

[0092] 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 and have conductive performance indices of 2.00 and 0.50, respectively, the conductive performance index of the mixed conductive material is calculated as "(2.00 x 0.3) + (0.50 x 0.7)" and may have a value of 0.95.

[0093] electrode

[0094] 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 above-described conductive material.

[0095] In this case, the conductive material is the above-mentioned conductive material according to the present invention. The description of the conductive material is the same as above, and therefore, a detailed description thereof will be omitted, and only the remaining components will be described hereinafter.

[0096] According to an embodiment of the present invention, the electrode active material may be a positive electrode active material, and the electrode may be a positive electrode, wherein 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 including the positive electrode active material.

[0097] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. Moreover, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and microscopic irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0098] The positive electrode active material may include, for example, one or more selected from the group consisting of lithium nickel-based oxides, high lithium manganese-based oxides, lithium metal phosphate-based compounds, lithium nickel oxides, lithium cobalt oxides, and lithium manganese oxides.

[0099] Preferably, the positive electrode active material may be of a single particle type and may include a lithium nickel-based oxide and / or a lithium metal phosphate-based compound, and the single particle type positive electrode active material may have a single particle degree D of 1 to 10. 50 / D 平均 The single-particle-type positive electrode active material has a higher particle strength than a typical single-particle-type positive electrode active material in the form of secondary particles in which tens to hundreds of primary particles are aggregated, and therefore there is less particle breakage during rolling. In addition, the single-particle-type positive electrode active material according to the present invention has a small number of subcomponents (i.e., nodules) constituting the particles, so that changes caused by volume expansion and contraction of the primary particles during charge and discharge are less, and thus the occurrence of intra-particle cracks is significantly reduced.

[0100] The smaller the degree of single particle formation, the more the single particle type positive electrode active material particles have single-particle characteristics. Therefore, the degree of single particle formation may preferably be 1 to 8, 1 to 7, 1 to 6, or 1 to 5. If the above range is satisfied, the degree of particle breakage can be reduced and the rolling density can be increased, which can be expected to improve life performance and energy density.

[0101] According to an embodiment of the present invention, the single particle type positive active material may have a D of 1.0 μm to 10.0 μm.50 .

[0102] The single-particle positive electrode active material may have an average particle diameter at 50% cumulative volume of 1.0 μm to 10.0 μm, 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 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. If the volume-average particle diameter D of the single-particle positive electrode active material 50 satisfies the above range, then there is an advantage that the rolling density can be increased without damaging the positive electrode active material particles.

[0103] According to an embodiment of the present disclosure, the average particle diameter D of the nodules of the single-particle positive electrode active material 平均 may be 0.2 μm to 3.0 μm, and the average particle diameter of the nodules may preferably be 0.5 μm or more, 0.7 μm or more, or 1.0 μm or more, and 2.8 μm or less, 2.5 μm or less, or 2.0 μm or less, and if the above range is satisfied, then the above range of the degree of single-particle formation can also be satisfied, such that the resulting effects can be expected.

[0104] The single-particle positive electrode active material according to the present invention may include a lithium nickel-based oxide and may have a composition represented by, for example, the following Formula 1.

[0105] [Formula 1]

[0106] Li 1+x Ni a Co b M 1 c M s 2 d O 2-e X e

[0107] In Formula 1 above, M 1 includes one or more selected from Mn and Al, M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X includes one or more selected from the group consisting of N, P, S, F, and Cl, and 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.

[0108] In Formula 1 above, M 1is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, M 2 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. M 2 element is not necessarily included, but when included in an appropriate amount, M 1 element can be used to promote particle growth during firing or improve crystal structure stability. In addition, X is an anion substituted at the oxygen site and can include N, P, S, F, or Cl.

[0109] 1 + x represents the molar ratio of lithium in the single-particle type lithium nickel-based oxide and can satisfy 0 ≤ x ≤ 0.1, 0 ≤ x ≤ 0.08, 0 ≤ x ≤ 0.05, 0 ≤ x ≤ 0.03, or 0 ≤ x ≤ 0.02.

[0110] a represents the molar ratio of nickel among all metals other than lithium in the single-particle type lithium nickel-based oxide and can satisfy 0.50 ≤ a ≤ 1, 0.60 ≤ a ≤ 0.99, 0.70 ≤ a ≤ 0.99, or 0.75 ≤ a ≤ 0.99, and 0.80 ≤ a ≤ 0.99, 0.82 ≤ a ≤ 0.99, 0.84 ≤ a ≤ 0.99, or 0.86 ≤ a ≤ 0.99.

[0111] b represents the molar ratio of cobalt among all metals other than lithium in the single-particle type lithium nickel-based oxide and can satisfy 0 < b ≤ 0.35, 0.01 ≤ b ≤ 0.34, 0.01 ≤ b ≤ 0.30, 0.01 ≤ b ≤ 0.25, 0.01 ≤ b ≤ 0.20, or 0.01 ≤ b ≤ 0.15.

[0112] c represents the molar ratio of M 1 among all metals other than lithium in the single-particle type lithium nickel-based oxide and can satisfy 0 < c ≤ 0.35, 0.01 ≤ c ≤ 0.34, 0.01 ≤ c ≤ 0.30, 0.01 ≤ c ≤ 0.25, 0.01 ≤ c ≤ 0.20, or 0.01 ≤ c ≤ 0.15.

[0113] d represents the molar ratio of the M 2 element among all metals other than lithium in the single-particle type lithium nickel-based oxide and can satisfy 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02, or 0 ≤ d ≤ 0.01.

[0114] e represents the molar ratio of the X element among all non-metals other than oxygen in the single-particle type lithium nickel-based oxide and can satisfy 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02, or 0 ≤ e ≤ 0.01.

[0115] In addition, the lithium metal phosphate-based compound may have a composition represented by Formula 2 below.

[0116] [Formula 2]

[0117] Li 1+x [Fe 1-y M y ]PO4

[0118] In the above Formula 2, M includes one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, and 0≤y≤1.

[0119] The lithium metal phosphate-based compound may be doped with M. In this case, the lattice structure and distance in the olivine crystal structure (which is a crystal structure) are changed so that the diffusion rate of lithium ions increases, and thus the electrochemical characteristics of a battery including the positive active material may be improved.

[0120] x may be -0.5 to 0.5, preferably -0.3 or greater, -0.1 or greater, or 0 or greater, and 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0121] y may be 0 or greater, and may be 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.

[0122] For example, the lithium metal phosphate-based compound may be, for example, LiFePO 4 .

[0123] The lithium metal phosphate-based 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 irregular secondary particles consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate-based compound may include an olivine structure, and specifically, may be formed solely of an olivine structure. The coating according to the present invention may be formed not only on secondary particles, but also on primary particles. In other words, the coating according to the present invention may be uniformly present on the surface of primary particles located within the secondary particles.

[0124] The coating layer may include a carbon coating layer having a graphite structure, and the coating layer may have a thickness of 0.5 nm to 5 nm. If the thickness of the coating layer is within the above range, the advantage is that the electrical conductivity is improved while not interfering with the entry and exit of lithium ions. Specifically, the thickness of the coating layer may be 0.5 nm or greater, 1.0 nm or greater, 1.5 nm or greater, 2.0 nm or greater, 2.5 nm or greater, or 3.0 nm or greater, and 5.0 nm or less.

[0125] The coating layer can be uniformly applied to the surface of the lithium metal phosphate-based compound. That is, the coating layer can be in the form of a thin film. The coating layer can improve ionic and electronic conductivity during charging and discharging of a battery including the positive electrode active material. In addition to carbon, the coating layer can include trace amounts of impurities such as nitrogen, oxygen, and hydrogen.

[0126] The coating layer may be included in an amount of 0.5 wt % to 3 wt % based on the total weight of the lithium metal phosphate-based compound in order to improve electrical conductivity while not interfering with entry and exit of lithium ions.

[0127] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder as well as the positive electrode active material.

[0128] The above-mentioned conductive material dispersion can be used as a positive electrode conductive material, and in addition to the conductive material dispersion, a conductive material may be further included to impart conductivity to the electrode, and any conductive material may be used without particular limitation as long as it has electronic conductivity without causing chemical changes in the battery to be constructed.

[0129] Specific examples of additional conductive materials may 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-based fibers or metal-based 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, and any one of them or a mixture of two or more thereof may be used.

[0130] In addition, the positive electrode binder is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0131] According to an embodiment of the present invention, the electrode active material may be a negative electrode active material, and the electrode may be a negative electrode, wherein 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 including the negative electrode active material.

[0132] The negative electrode 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 copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0133] The negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and microscopic irregularities may be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. In addition, the negative electrode current collector may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens.

[0134] As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used, and for example, a carbonaceous material such as artificial graphite, natural graphite, Kish graphite, pyrolytic carbon, meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch derived cokes, mesophase pitch-based carbon fiber, graphitized carbon fiber, amorphous carbon, soft carbon or hard carbon; a (semi-)metal material alloyable with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; a (semi-)metal oxide material capable of doping and dedoping lithium such as SiO b(0 < b ≤ 2), SnO2, vanadium oxide, and lithium vanadium oxide; heterogeneous composites such as Si-C composites or Sn-C composites; thin films of metallic lithium, etc., and any one of them or a mixture of two or more of them can be used.

[0135] Preferably, the negative electrode active material may include one or more selected from the group consisting of silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials, and more preferably, the carbon-based active material may include one or more selected from the group consisting of artificial graphite, natural graphite, soft carbon, and hard carbon, and the silicon-based active material may include pure Si particles and / or SiO b (0 < b ≤ 2), and the silicon-carbon composite active material may include Si-C composites. In addition, as the negative electrode active material, a mixed active material in which two or more of the above materials are mixed can be used.

[0136] Based on the total weight of the negative electrode mixture layer, the negative electrode active material may be included in an amount of 60 wt% to 99 wt%, preferably 70 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, and 98 wt% or less, 97 wt% or less, or 95 wt% or less.

[0137] The binder is a component for helping the bonding between the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode mixture layer, and may be included in an amount of 0.2 wt% or more, 0.3 wt% or more, or 0.5 wt% or more, and 8 wt% or less, or 5 wt% or less. Examples of the binder may 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, poly(ethylene 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. Among the above, the binder may include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylated amylose, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, and cyanoethylated sucrose. Preferably, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, or a mixture thereof may be preferably applied.

[0138] The binder is a component used to help the bonding between the conductive material, the active material and the current collector, and is generally added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of binders can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like.

[0139] The conductive material is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount 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, and 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. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, 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-based fibers or metal-based fibers; fluorocarbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0140] Meanwhile, if necessary, the electrode slurry may further include a solvent to control viscosity, etc. At this time, the solvent may be water, an organic solvent, or a mixture thereof. The organic solvent may be, for example, an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,3-propanediol ... -Butanediol, 1,5-pentanediol and hexanediol; polyols such as glycerol, trimethylolpropane, pentaerythritol and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone and ε-propiolactone. Any one thereof and a mixture of two or more thereof may be used, but the organic solvent is not limited thereto.

[0141] The content of the solvent can be such that the solid content in the electrode slurry is 60 wt % to 85 wt %, preferably 65 wt % to 80 wt %. When the above range is met, the binder migration can be suppressed, thereby improving the electrode adhesion, the drying temperature can be reduced, thereby improving the coatability, and the coating speed can be increased, thereby improving the productivity.

[0142] The electrode according to the present invention can be manufactured by applying and then drying an electrode slurry including the above-mentioned components, thereby forming an electrode active material layer on the current collector. Specifically, the electrode active material layer can be formed by applying the electrode slurry to the electrode current collector and then drying it, or by applying the electrode slurry to a separate carrier and then laminating the film obtained by peeling off the carrier on the electrode current collector. If necessary, after the electrode active material layer is formed by the above method, a process of rolling the electrode active material layer can be additionally performed. At this time, taking into account the physical properties of the electrode finally manufactured, drying and rolling can be performed under appropriate conditions and are not particularly limited.

[0143] lithium secondary batteries

[0144] According to another embodiment of the present invention, a lithium secondary battery has a structure in which a positive electrode, a separator and a negative electrode are stacked in sequence, and one or more of the positive electrode and the negative electrode are the above-mentioned electrodes. 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, and in this case, the positive electrode and the negative electrode are the same as described above.

[0145] Hereinafter, only the remaining components will be described.

[0146] According to an embodiment of the present invention, a separator is used to separate the negative electrode and the positive electrode and provide a mobile path for lithium ions, and any separator can be used without particular limitation, as long as it is a separator commonly used for lithium secondary batteries. Specifically, as a separator, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof. In addition, a typical porous non-woven fabric can be used, for example, a non-woven fabric made of glass fiber with a high melting point, polyethylene terephthalate fiber, etc. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single layer or multilayer structure.

[0147] According to an embodiment of the present invention, examples of the electrolyte may include 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, etc., but are not limited thereto.

[0148] Specifically, the electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0149] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxane, formamide, dimethylformamide, dioxane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate and ethyl propionate can be used.

[0150] In particular, among the carbonic acid-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be preferably used because they are high-viscosity organic solvents and have a high dielectric constant to dissociate lithium salts well. Such cyclic carbonates can be more preferably used because when they are mixed with low-viscosity and low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high conductivity is prepared.

[0151] As the metal salt, a lithium salt can be used, and the lithium salt is a material that is easily dissolved in a non-aqueous electrolyte solution, and as an anion of the lithium salt, for example, a material selected from F - 、Cl - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - One or more of the groups.

[0152] In the electrolyte, in order to improve the life characteristics of the battery, suppress the reduction of the battery capacity and improve the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, one or more additives may be included, for example, compounds based on halogenated alkylene carbonates, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride, etc.

[0153] Example

[0154] Hereinafter, the embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention can be embodied in many different forms and is not limited to the embodiments set forth herein.

[0155] Examples and Comparative Examples

[0156] For Examples 1a-5a and Comparative Examples 1a-3a, carbon black having the properties described in Table 1 below was prepared, for Examples 1b-4b and Comparative Examples 1b-3b, multi-walled carbon nanotubes having the properties described in Table 2 below were prepared, and for Examples 1c-5c and Comparative Examples 1c-2c, single-walled carbon nanotubes having the properties described in Table 3 below were prepared.

[0157] Volume average particle size D of the conductive material 50 (μm) was obtained by introducing a laser diffraction particle size measuring device (Malvern Co., Mastersizer 3000) to measure the difference in diffraction patterns according to the particle size when the particles pass through a laser beam, thereby calculating the particle size distribution. The particle size D was measured by determining the particle size at the 50% point in the volume cumulative distribution based on the particle size. 50 .

[0158] The powder resistance (Ωcm) of the conductive material was measured by introducing 0.1 g of the conductive material into a cylindrical geometry and then measuring the surface resistance while increasing the pressure in the press in which the pressure was measured, and also measuring the volume reduction as the pressure increased, thereby measuring the powder resistance when the bulk density was 0.4 g / cc to 0.6 g / cc.

[0159] The specific surface area (m2) of the conductive material was measured by the BET method. 2 / g) and calculated from the adsorption amount of nitrogen at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan Co.

[0160] More than 50 images of the conductive material are captured by a scanning electron microscope (SEM), and then the obtained images are analyzed by an image analysis program to obtain the ratio of the major axis to the minor axis of each conductive material particle, and then the average of these values is used to obtain the aspect ratio of the conductive material.

[0161] Experimental Example 1: Battery Performance Evaluation 1 (Resistance Characteristics)

[0162] Applications with LiNi 0.6 Co 0.1 Mn 0.3 A single particle type lithium nickel-based oxide having a composition of O 2 was used as a positive electrode active material, and the conductive material of each of the examples and comparative examples was applied to manufacture a positive electrode.

[0163] The positive electrode was manufactured by mixing lithium nickel-based oxide, a conductive material, and a PVDF binder in a weight ratio of 97.0:1.2:1.8. N-methylpyrrolidone solvent was then introduced to a solids content of 72%. The mixture was mixed using a homogenizer at 2,500 rpm for one hour to prepare a positive electrode slurry. The slurry was then applied to one side of an aluminum current collector, dried at 130°C, and then rolled twice using a roll-to-roll press at a linear pressure of 2,000 kgf / cm to produce the positive electrode.

[0164] The average particle size D 50 Graphite particles with a diameter of 50 μm were used as negative electrode active materials. A negative electrode including a negative electrode active material layer was manufactured. The negative electrode active material layer contained a 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 negative electrode active material layer had a capacity of 10 mAh / cm 2 The loading amount and thickness of 75 μm.

[0165] The positive electrode, negative electrode and porous polyethylene separator were assembled using a winding method, and an electrolyte solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio)) and lithium hexafluorophosphate (1 mol LiPF6) were injected into the assembled battery to manufacture a lithium secondary battery.

[0166] The lithium secondary battery was charged to 4.2 V at a 0.1 CC rate and then discharged to 2.5 V for an activation process.

[0167] After the lithium secondary battery was charged and discharged, the lithium secondary battery was fully charged and discharged again to measure the diffusion resistance (0.1 to 30 second resistance), and the results are shown in Tables 4 to 6.

[0168] Experimental Example 2: Battery Performance Evaluation 2 (Life Characteristics)

[0169] Each of the lithium secondary batteries manufactured in Experimental Example 3 above was charged in CCCV mode at 0.2C (terminal current 1 / 20C) to 4.25V. Thereafter, at 45°C, each lithium secondary battery was charged to 4.25V at a constant current of 0.33°C, and then discharged to 2.5V at a constant current of 0.33°C. The entire process was set as 1 cycle, and 100 cycles of charge and discharge were performed to measure the capacity retention. The measurement results are shown in Tables 4 to 6 below.

[0170] In this case, the capacity retention ratio was calculated as follows.

[0171] Capacity retention (%) = (discharge capacity after 100 cycles) / (discharge capacity after 1 cycle) x 100

[0172] Evaluation results

[0173] (1) Carbon black

[0174] The physical properties of the carbon black conductive materials of Examples 1a to 5a and Comparative Examples 1a to 3a are shown in Table 1 below, and the evaluation results of Experimental Examples 2 and 3 are shown in Table 2 below.

[0175] [Table 1]

[0176]

[0177] [Table 2]

[0178] Diffusion resistance (mΩ) Capacity retention rate (%) Example 1a 1.2704 85.4 Example 2a 1.2484 84.9 Example 3a 1.3586 85.6 Example 4a 1.2946 86.0 Example 5a 1.3224 85.7 Comparative Example 1a 1.5307 80.1 Comparative Example 2a 1.4821 81.1 Comparative Example 3a 1.5968 80.5

[0179] Referring to Tables 1 and 2 above, in the case of Examples 1a to 5a, which satisfy the conductivity performance index, it can be confirmed that the diffusion resistance is low and the lifespan is improved compared to Comparative Examples 1a to 3a. In particular, in Comparative Examples 1a to 3a, although the powder resistance is high relative to the bulk density and the average particle size of the conductive material is small, the specific surface area is even smaller, thereby preventing the quantitative characteristics from being properly implemented, resulting in the conductivity being evaluated as low, and thus the resistance and lifespan characteristics being determined to be poor.

[0180] (2) Multi-walled carbon nanotubes

[0181] 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 evaluation results of Experimental Examples 2 and 3 are shown in Table 4 below.

[0182] [Table 3]

[0183]

[0184] [Table 4]

[0185] Conductivity Index Diffusion resistance (mΩ) Capacity retention rate (%) Example 1b 2.08 1.2175 90.1 Example 2b 2.60 1.2170 89.7 Example 3b 2.16 1.3057 89.5 Example 4b 1.55 1.2572 89.0 Comparative Example 1b 10.38 1.3542 84.9 Comparative Example 2b 8.33 1.4116 85.2 Comparative Example 3b 8.17 1.4424 84.1

[0186] Referring to Tables 3 and 4 above, Examples 1b to 4b, which meet the conductivity performance index, can be confirmed to have lower diffusion resistance and improved lifespan compared to Comparative Examples 1b to 3b. In particular, in Comparative Examples 1b and 2b, there is a difference in conductivity due to high powder resistance relative to bulk density, even though the conductive material content is the same. In Comparative Example 3b, there is a difference in conductivity due to a problem with uniform distribution caused by an excessively large specific surface area, as evidenced by the data in the above table.

[0187] (3) Single-walled carbon nanotubes

[0188] The physical properties of the single-walled carbon nanotube conductive materials of Examples 1c-5c and Comparative Examples 1c and 2c are shown in Table 5 below, and the evaluation results of Experimental Examples 2 and 3 are shown in Table 6 below.

[0189] [Table 5]

[0190]

[0191] [Table 6]

[0192] Conductivity Index Diffusion resistance (mΩ) Capacity retention rate (%) Example 1c 0.09 1.1866 92.3 Example 2c 0.19 1.1690 93.3 Example 3c 1.28 1.2704 92.7 Example 4c 1.19 1.1994 92.1 Example 5c 0.22 1.2057 93.0 Comparative Example 1c 9.64 1.3322 88.4 Comparative Example 2c 8.89 1.3763 87.9

[0193] Referring to Tables 5 and 6 above, in the case of Examples 1c to 5c satisfying the conductivity performance index, it can be confirmed that the results show that the diffusion resistance is low and the life is improved compared to Comparative Examples 1c and 2c. In particular, it can be seen that the above results are derivative because single-walled carbon nanotubes are conductive materials that are greatly affected by length characteristics, and in the case of Comparative Examples 1c and 2c, the small aspect ratio is not affected by BET or D 50 Compensation is achieved, and the powder resistance is high relative to the bulk density.

Claims

1. A conductive material having a conductivity performance index (P C ), the conductivity performance index is defined by the following equation 1: [Equation 1] P C =[(AR x R P xρ P ) / (BET x D 50 )]x10 4 Wherein in the above equation 1, AR is the aspect ratio, which is the ratio of the major axis to the minor axis of the conductive material, R P and ρ P are powder resistance (Ωcm) and bulk density (g / cc), respectively. For the conductive material, when the bulk density is ρ P The powder resistance measured at P , BET is the specific surface area of the conductive material (m 2 / g), and D 50 is the volume cumulative 50% average particle size (μm) of the conductive material in powder state, Where in the above equation 1, R P , ρ P , BET and D 50 It is a unitless number that does not include the above units. 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. The conductive material according to claim 1 , wherein the conductive performance index is 0.10 to 7.

00. The conductive material according to claim 1 , wherein the conductive performance index is 0.30 to 5.

00.

5. The conductive material according to claim 1, wherein the packing density p P 0.4g / cc to 0.6g / cc. The conductive material according to claim 1 , wherein the conductive material comprises carbon black, and the conductive performance index is 1.00 to 8.

10. 7 . The conductive material according to claim 1 , wherein the conductive material comprises one or more selected from the group consisting of multi-walled carbon nanotubes and single-walled carbon nanotubes, and the conductivity performance index is 0.03 to 4.

00.

8. The conductive material of claim 1, wherein the conductive material comprises multi-walled carbon nanotubes, and the conductivity performance index is 0.30 to 3.

90.

9. The conductive material of claim 1, wherein the conductive material comprises single-walled carbon nanotubes, and the conductivity performance index is 0.03 to 1.

50.

10. An electrode comprising: electrode current collector; and An electrode active material layer is provided on the electrode current collector, wherein the electrode active material layer comprises the conductive material according to claim 1. 11 . The electrode according to claim 10 , wherein the electrode active material layer further comprises a positive electrode active material, wherein the positive electrode active material comprises one or more selected from the group consisting of lithium nickel-based oxides and lithium metal phosphate-based compounds.

12. The electrode according to claim 11, wherein the lithium nickel-based oxide is a single particle type and has a single particle degree D of 1 to 10. 50 / D 平均 , which is the volume cumulative average particle size D 50 The average particle size D of the nodules 平均 ratio.

13. The electrode according to claim 11, wherein: The lithium nickel-based oxide has a composition represented by the following Formula 1; and The lithium metal phosphate-based compound has a composition represented by the following Formula 2: [Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e Wherein in the above formula 1, M 1 comprises one or more selected from Mn and Al, M 2 comprises one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb, X comprises one or more selected from the group consisting of N, P, S, F, and Cl, and 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; [Formula 2] Li 1+x [Fe 1-y M y ]PO4 Wherein, in the above formula 2, M includes one or more 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 according to claim 10 , wherein the electrode active material layer further comprises a negative electrode active material, wherein the negative electrode active material comprises silicon-based particles. 15 . A lithium secondary battery comprising a structure in which electrodes and separators are alternately stacked, wherein the electrodes are the electrode according to claim 10 .

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