Positive electrode material for lithium-sulfur battery and lithium-sulfur battery comprising same

Abstract

The present invention discloses a novel form of positive electrode active material for use in a positive electrode of a lithium-sulfur battery.SOLUTION: A cathode active material of the present invention includes a) particles (A) including a first porous carbon material of which at least a part is crystalline and catalyst particles deposited on the first porous carbon material, and b) particles (B) including a second porous carbon material of which at least a part is crystalline and sulfur supported on the second porous carbon material, wherein the particles (A) and the particles (B) have different morphologies.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cathode material for a lithium-sulfur battery and a lithium-sulfur battery including the same.

[0002] This application claims priority from Korean Patent Application Nos. 10-2022-0110413 and 10-2022-0110385, filed on August 31, 2022, 10-2022-0187899, filed on December 28, 2022, 10-2023-0025408, filed on February 24, 2023, and 10-2023-0042283, filed on March 30, 2023, and the contents disclosed in the specifications and drawings of those applications are incorporated herein in their entirety. [Background technology]

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond (SS bond) as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the positive electrode active material, has the advantages of being abundant worldwide, non-toxic, and having a low atomic weight.

[0004] As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESSs), lithium-sulfur battery technology is gaining attention because it can theoretically achieve a relatively high energy storage density (up to 2,600Wh / kg) relative to its weight, compared to lithium-ion secondary batteries, which have a relatively low energy storage density (up to 250Wh / kg) relative to their weight.

[0005] During discharge, lithium, the negative electrode active material, is oxidized by giving up electrons and being ionized into lithium cations, while the positive electrode active material, the sulfur-based material, is reduced by accepting electrons. The S-S bond accepts two electrons through the reduction reaction of the sulfur-based material, converting it into a sulfur anion. The lithium cations generated by the oxidation reaction of lithium are transferred to the positive electrode via the electrolyte, where they combine with sulfur anions generated by the reduction reaction of the sulfur-based compound to form a salt. Specifically, sulfur before discharge has a cyclic S8 structure, which is converted into lithium polysulfide (Li2S) through a reduction reaction. x ), and the lithium polysulfides are completely reduced to form lithium sulfide (LiS).

[0006] As described above, sulfur used as a positive electrode active material is a non-conductor, so electrons generated by electrochemical reactions are difficult to move, which causes problems such as the elution of lithium polysulfide (LiSx) during the charge / discharge process, and the slow kinetic activity of the electrochemical reaction due to the low electrical conductivity of sulfur and lithium sulfide, resulting in reduced battery life and speed characteristics.

[0007] In this regard, research efforts have been underway to improve the performance of lithium-sulfur secondary batteries by using platinum (Pt), which has been widely used as an electrochemical catalyst, to improve the kinetic activity of the sulfur redox reaction during the charge and discharge process of the lithium-sulfur secondary battery. However, precious metal catalysts such as platinum are not only difficult to commercialize due to their high cost, but also have the problem of being difficult to use as positive electrode materials for lithium-sulfur secondary batteries due to the possibility of poisoning by the sulfur redox reaction during the charge and discharge process.

[0008] For these reasons, there is a continuing need to develop technology for positive electrode materials that can improve the kinetic activity of electrochemical reactions during charging and discharging of lithium-sulfur secondary batteries and that are advantageous for commercialization from a cost perspective. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the problem to be solved by the present invention is to provide a novel form of positive electrode active material for use in the positive electrode of a lithium-sulfur battery. [Means for solving the problem]

[0010] In order to solve the above problems, according to one aspect of the present invention, there is provided a positive electrode active material having the following embodiment.

[0011] A carbon composite according to a first aspect includes: a) particles A including a first porous carbon material, at least a portion of which is crystalline, and catalyst particles deposited on the first porous carbon material; and b) particles B including a second porous carbon material, at least a portion of which is crystalline, and sulfur supported on the second porous carbon material; and the particles A and B have different morphologies.

[0012] According to the second aspect, in the first aspect, the sphericity of the particles B may be greater than the sphericity of the particles A, and the sphericity may be defined according to the following formula 1:

[0013]

number

[0014] According to the third embodiment, in the first or second embodiment, the particle A may have a structure in which 50% or more of the particle A is dispersed on the surface of the particle B.

[0015] According to the fourth aspect, in any one of the first to third aspects, at least a portion of the surface of the particle B is covered by the particle A, and the coverage area of ​​the particle B by the particle A can be 20% to 50% based on the total external area of ​​the particle B.

[0016] According to a fifth aspect, in any one of the first to fourth aspects, the porosity of the particles A may be greater than the porosity of the particles B.

[0017] According to a sixth aspect, in any one of the first to fifth aspects, the specific surface area of ​​the particles A may be greater than the specific surface area of ​​the particles B.

[0018] According to the seventh aspect, in any one of the first to sixth aspects, the particle A and the particle B may be in contact with each other at at least one position where the catalyst particle contained in the particle A is present.

[0019] According to an eighth aspect, in any one of the first to seventh aspects, the weight of the sulfur (S8) can be 60 wt % to 90 wt % based on the total weight of the first porous carbon material and the second porous carbon material.

[0020] According to a ninth aspect, in any one of the first to eighth aspects, the first porous carbon material and the second porous carbon material may be different materials from each other.

[0021] According to a tenth aspect, in any one of the first to ninth aspects, the first porous carbon material and the second porous carbon material may be the same material.

[0022] According to an eleventh aspect, in any one of the first to tenth aspects, the first porous carbon material and the second porous carbon material may each independently contain at least one of bundled CNTs, entangled CNTs, and reduced graphene oxide (rGO).

[0023] According to a twelfth aspect, in any one of the first to eleventh aspects, the catalyst particles may contain vanadium nitride.

[0024] According to a thirteenth aspect, in any one of the first to twelfth aspects, the catalyst particles may contain at least one element of cobalt (Co) and iron (Fe).

[0025] According to a fourteenth aspect, in any one of the first to thirteenth aspects, the elasticity of each of the first porous carbon material and the second porous carbon material may be even greater than the elasticity of an amorphous carbon material.

[0026] According to the 15th aspect, in any one of the 1st to 14th aspects, the electrical conductivity of each of the first porous carbon material and the second porous carbon material may be greater than the elasticity of the amorphous carbon material.

[0027] According to a sixteenth aspect, in any one of the first to fifteenth aspects, the I of the positive electrode active material D / I G The value may be 2.0 or less.

[0028] According to another aspect of the present invention, there is provided a lithium-sulfur battery having the following configuration.

[0029] A lithium-sulfur battery according to a seventeenth aspect includes the positive electrode active material according to any one of the first to sixteenth aspects. [Effects of the Invention]

[0030] A positive electrode active material according to one aspect of the present invention has a novel form for use in secondary batteries, particularly lithium-sulfur batteries.

[0031] Specifically, the cathode active material according to one embodiment of the present invention has a novel form that can significantly improve the sulfur loading amount, catalytic activity, and the like, and can thereby exhibit the effect of improving the performance of secondary batteries, particularly lithium-sulfur batteries, using the cathode active material, but the effects of the present invention are not limited thereto.

[0032] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical concepts of the present invention as well as the content of the invention, and therefore the present invention should not be interpreted as being limited to only the matters described in the drawings. [Brief explanation of the drawings]

[0033] [Figure 1] 1 shows an SEM image of a positive electrode active material according to one embodiment of the present invention. In Fig. 1, the region indicated by "A" represents particle A, and the region indicated by "B" represents particle B. The SEM image in Fig. 1 was obtained at a magnification of 2,000 times over an area of ​​10 μm × 10 μm. [Figure 2] 2 shows an SEM image of a positive electrode active material in which vanadium nitride is supported as catalyst particles on particles A according to one embodiment of the present invention. The SEM image in FIG. 2 was obtained at a magnification of 15,000 times over an area of ​​10 μm × 10 μm. [Figure 3] 3 shows an SEM image of the bundled CNTs used in one embodiment of the present invention, the image being obtained at a magnification of 500 times over an area of ​​10 μm×10 μm. [Figure 4] 4 shows an SEM image of the entangled CNTs used in one embodiment of the present invention. The image in Fig. 4 was obtained at a magnification of 500 times over an area of ​​10 μm x 10 μm. [Figure 5] 5 shows an SEM image of the reduced graphene oxide (rGO) used in one embodiment of the present invention. The image in FIG. 5 was obtained at 1,000x magnification over an area of ​​10 μm × 10 μm. [Figure 6] 6 shows an SEM image of a positive electrode active material in which iron particles are supported as catalyst particles on particles A according to one embodiment of the present invention. The SEM image in FIG. 6 was obtained at a magnification of 2,000 times over an area of ​​10 μm × 10 μm. [Figure 7] 1 is a graph showing the capacity-voltage curves obtained by evaluating the performance of batteries using the positive electrode active materials of Example 1 and Comparative Example 1 according to an embodiment of the present invention. [Figure 8] 1 is a graph showing the capacity-voltage curves obtained by evaluating the performance of batteries using the positive electrode active materials of Comparative Examples 1 and 2 according to an embodiment of the present invention. [Figure 9] 1 is a graph showing the results of performance evaluation of batteries using the positive electrode active materials of Example 1 and Comparative Example 1 according to one embodiment of the present invention, illustrating curves of discharge capacity vs. cycle vs. coulomb efficiency. [Figure 10] 1 is a graph showing the results of evaluating the performance of batteries using the positive electrode active materials of Comparative Example 1 and Comparative Example 2 according to an embodiment of the present invention, illustrating curves of discharge capacity vs. cycle vs. coulomb efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will be described in detail below. However, the present invention is not limited to the following content, and each component may be variously modified or selectively combined as necessary. Therefore, it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0035] Throughout this specification, when a certain component is referred to as "comprising" another component, this does not mean that it may further include other components, unless otherwise specified.

[0036] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0037] Certain terms used in this specification are for ease of description only and are not limiting. For example, positional terms such as "upper," "lower," "left," "right," "front," "rear," "inner," and "outer" are used to describe relative positions and orientations of components relative to one another or in the drawings to which reference is made, rather than absolute positions. The terms used herein encompass not only the terms themselves, but also words containing them, their derivatives, and words of similar import.

[0038] In this specification, the term "composite" refers to a combination of two or more substances that have physically and / or chemically distinct phases and exhibit effective functions.

[0039] In this specification, the term "polysulfide" means "polysulfide ions (Sx 2- , x=8, 6, 4, 2) and "Lithium polysulfide (Li2S x or LiS x ,x=8, 6, 4, 2).

[0040] Unless the measurement conditions and measurement methods are specifically described for the properties described in this specification, the properties are measured by the measurement conditions and methods commonly used by those of ordinary skill in the art.

[0041] According to one aspect of the present invention, there is provided a positive electrode active material that can be used in secondary batteries, specifically lithium-sulfur batteries.

[0042] The positive electrode active material includes a porous carbon material, catalyst particles, and sulfur (S). Specifically, the positive electrode active material includes two types of porous carbon materials, catalyst particles, and sulfur (S).

[0043] The positive electrode active material includes: a) particles A including a first porous carbon material, at least a portion of which is crystalline, and catalyst particles deposited on the first porous carbon material; and b) particles B including a second porous carbon material, at least a portion of which is crystalline, and sulfur supported on the second porous carbon material, wherein particles A and particles B have different morphologies.

[0044] In one embodiment of the present invention, the sulfur (S) may be provided without being infiltrated into the pores of the first porous carbon material. According to one embodiment of the present invention, the first porous carbon material and / or particles A may be provided substantially free of sulfur (S), i.e., sulfur-free. Here, the term "free of" does not exclude impurities. However, sulfur may be included as an impurity, provided that the purpose of the present invention is not impaired.

[0045] In one embodiment of the present invention, the catalyst particles may not be located on the second porous carbon material. According to one embodiment of the present invention, the second porous carbon material and / or particles B may be provided in a state that is substantially free of catalyst particles, i.e., free of the catalyst particles. Here, the term "free of" does not exclude impurities. However, impurities may be included as long as it does not detract from the objective of the present invention.

[0046] In one embodiment of the present invention, the porous carbon material is a material containing a large number of micropores, and contains the catalyst particles and / or sulfur on either the outer surface of the porous carbon material or the inner surface of the pores.

[0047] In one embodiment of the present invention, the first porous carbon material and the second porous carbon material may be the same or different. In one embodiment of the present invention, the first porous carbon material is a material containing micropores and includes the catalyst particles located on at least one of the outer surface and / or the inner surface of the micropores of the first porous carbon material. In one embodiment of the present invention, the second porous carbon material is a material containing micropores and includes sulfur (S) on at least one of the outer surface and / or the inner surface of the micropores of the second porous carbon material.

[0048] In one embodiment of the present invention, the catalyst particles may be chemically and / or physically bound to one or more of the outer surface and the inner surface of the pores of the first porous carbon material, and the pores may be micropores.

[0049] In one embodiment of the present invention, the catalyst particles may be physically adsorbed on the outer surface and / or the inner surface of the pores of the first porous carbon material. Alternatively, the catalyst particles may be chemically bonded to the outer surface and / or the inner surface of the pores of the first porous carbon material by C-C covalent bonds and / or pi-pi interactions between elements present in the catalyst particles and carbon of the first porous carbon material. Furthermore, the above-mentioned physical adsorption and chemical bonding may simultaneously exist between the catalyst particles and the first porous carbon material.

[0050] In one embodiment of the present invention, the catalyst particles may be physically adsorbed on the outer surface of the first porous carbon material.

[0051] In one embodiment of the invention, the sulfur (S, such as S) may be chemically and / or physically bound to one or more of the exterior surface and the interior surface of the pores of the second porous carbon material.

[0052] In one embodiment of the present invention, the weight ratio of the second porous carbon material to the sulfur may be 10:90 to 90:10, 10:90 to 50:50, or 25:75.

[0053] In one embodiment of the present invention, the sulfur contained in the particles B is derived from a sulfur-based compound, e.g., S8, mixed with a porous carbon material during preparation of a positive electrode active material, and may be contained at one or more of the outer surface and the inner surface of the pores of the second porous carbon material. Examples of the sulfur-containing compound include, but are not limited to, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 2≦x≦8), a disulfide compound, or a mixture of two or more thereof.

[0054] In this specification, the "morphology" of a particle refers to the form, shape, and physicochemical or biochemical structure of the particle. For example, particle A and particle B may have different shapes and therefore different morphologies. For example, particle A may have an uneven or rough surface, such as a broccoli shape, curry flower shape, or spike shape, while particle B may have a relatively soft shape, such as a potato shape, sphere, or oval shape, with a somewhat smooth surface, although some uneven shapes are not excluded. Particle morphology can be confirmed, for example, using scanning electron microscope images.

[0055] Therefore, the fact that particle A and particle B have different morphologies means that particle A and particle B are different from each other in at least one aspect of the particle form, shape, physiochemical structure, and biochemical structure.

[0056] In one embodiment of the present invention, whether the particles A and the particles B have different morphologies can be confirmed by measuring their respective specific surface areas, porosities, particle diameters, particle shapes observed using an optical microscope, or two or more of these physical properties.

[0057] In one embodiment of the present invention, the particle A may contain, but is not limited to, catalyst particles, thereby promoting the kinetic activity of the electrochemical reaction of the cathode active material. Furthermore, the particle B may contain, but is not limited to, sulfur (S), thereby providing sites for the electrochemical reaction of the cathode active material. Therefore, the cathode active material may exhibit improved performance when the particle A, particularly the catalyst particles present in particle A, has a morphology adjacent to the sulfur present in particle B, particularly the sulfur contained in particle B.

[0058] In this context, according to one embodiment of the present invention, the sphericity of the particles B is preferably greater than that of the particles A. By configuring the sphericity of the particles B to be greater than that of the particles A, a cathode active material can be provided in which the particles B are enveloped by the particles A. This allows the sulfur (S)-supporting particles B to be electrically connected to each other (without direct surface contact) without contacting each other due to the physicochemical adhesion between the porous carbon material of the particles B and the porous carbon material of the particles A, thereby providing an excellent cathode active material. Here, it is obvious to those skilled in the art that two or more particles B may be present in contact with each other or may not be present in contact with each other within the cathode active material, and the above mechanism does not limit the form in which the particles B are not in contact with each other.

[0059] In one embodiment of the present invention, the "sphericity" may be defined according to the following formula 1:

[0060]

number

[0061] In one embodiment of the present invention, the V p may indicate the apparent volume of the particle. The apparent volume of the particle may be measured according to a common method for measuring apparent volume. In one embodiment of the present invention, the apparent volume may be measured using the value of (mass / apparent density) of the particle, and the apparent density may be measured using the value of [dry weight / (dry weight-weight in water)] of the particle, but the method for measuring the volume of the particle is not limited thereto. In addition, the apparent volume may be measured according to a method for measuring the particle volume of the porous material.

[0062] In one embodiment of the present invention, the A p can represent the apparent area of ​​a particle. The apparent area of ​​the particle can be, for example, 1 / 3 (6V p ) 2 / 3 Alternatively, it can be measured according to a method for measuring the apparent area of ​​the porous material.

[0063] In one embodiment of the present invention, the positive electrode active material may have a morphology in which the particles A are dispersed on the surfaces of the particles B. Specifically, the positive electrode active material may have a morphology in which the particles A, which have a smaller sphericity, cover at least a portion of the surfaces of the particles B, which have a larger sphericity.

[0064] An SEM image of a positive electrode active material according to one embodiment of the present invention is shown in Fig. 1. In Fig. 1, the region indicated by "A" represents particles A, and the region indicated by "B" represents particles B.

[0065] Referring to FIG. 1, it can be seen that the positive electrode active material includes particles B having a higher sphericity and particles A having a lower sphericity, and the particles A are dispersed on the surfaces of the particles B, specifically, the particles A are wrapped around and cover at least a portion of the surfaces of the particles B.

[0066] In one embodiment of the present invention, the particles A may have a particle size of, for example, 10 to 100 μm, 15 to 50 μm, or 20 to 40 μm, for example, 35 μm.

[0067] In one embodiment of the present invention, the particles B may have a particle size of, for example, 10 to 100 μm or 20 to 80 μm.

[0068] The particle size of the particles is D 50 It can mean the particle size of D 50The particle size of the particles can be measured by a conventional method, and the method is not particularly limited. For example, the particle size of the particles, for example, D 50 The particle size can be measured by a scanning electron microscope (SEM), a laser diffraction method, or a field emission scanning electron microscope. For measuring the particle size according to the laser diffraction method, a commercially available laser diffraction particle size analyzer, such as Microtrac Mt 3000, can be used, but is not limited thereto. In addition, the particle size D 50 can be measured according to a method of measuring the diameter of particles at 50% points in a cumulative distribution according to particle size.

[0069] In one embodiment of the present invention, particles A contained in the positive electrode active material may be present without being dispersed on the surface of particles B. However, it is advantageous for the above-described effect to be exhibited when 50% or more of the total number of particles A contained in the positive electrode active material are present in a dispersed form on the surface of particles B. Thus, 50% or more of the particles A may be dispersed on the surface of particles B. That is, 50% or more of the particles A may be in direct contact with the surface of at least one particle B. Specifically, based on the total number of particles A contained in the positive electrode active material, the number of particles A dispersed on the surface of particle B may be 50% to 100%, for example, 55% to 90%, 60% to 85%, or 70% to 80%, but is not limited thereto.

[0070] In this specification, the form in which particle A is dispersed on the surface of particle B may refer to, for example, a form in which the surface area of ​​particle B encapsulated by particle A accounts for 20% or more of the total area of ​​the outer surface of particle B. Here, the surface area of ​​particle B encapsulated by particle A can be measured, for example, by analyzing an SEM image of the positive electrode active material. Specifically, it can be measured at a magnification of 2,000 times for an area of ​​10 μm × 10 μm.

[0071] In one embodiment of the present invention, the positive electrode active material may have a form in which at least a part of the surface of the particle B is enveloped by the particle A, that is, a coated form.

[0072] Specifically, since the particles B are particles in which sulfur (S) is supported on a porous carbon material, they may have an outer surface and a specific surface area, which are characteristics of a porous carbon material. The particles B may have a specific surface area and / or an outer surface that matches that of a second porous carbon material. In this case, the outer surface area of ​​the particles B may be measured by analyzing an SEM image as described above, and the specific surface area of ​​the particles B may have substantially the same value as the inner area, and may be measured, for example, according to a BET specific surface area measurement method known in the art, such as a method conforming to ISO 9277:2010.

[0073] According to one embodiment of the present invention, the coverage area of ​​particle B with particle A may be, for example, 20% or more, specifically 20% to 90%, preferably 20% to 80%, 30% to 70%, or 40% to 50% of the total external area of ​​particle B. In one embodiment of the present invention, if the entire external area of ​​particle B is covered by particle A, for example, if the coverage area of ​​particle B with particle A is 100%, assembling a battery using the same may hinder the inflow and outflow of electrolyte into and out of the cathode active material, resulting in a decrease in the activity of the electrochemical reaction during battery operation. In one aspect, when the coverage area of ​​particle B with particle A is within the above-mentioned range, a novel cathode active material can be provided that can significantly improve the sulfur loading amount, catalytic activity, and the like, but the present invention is not limited thereto.

[0074] According to one embodiment of the present invention, the weight ratio of the particles A to the particles B contained in the positive electrode active material may be, for example, but is not limited to, 50:50 to 1:99, 40:60 to 2.5:95, 30:70 to 5:95, 20:80 to 5:95, or 7.5:92.5. When the weight ratio of the particles A to the particles B is within the above-mentioned range, the coverage area of ​​the particles B by the particles A satisfies the above-mentioned range, and advantageous effects can be shown in improving the activity of the positive electrode active material and the performance of a battery using the same, but the present invention is not limited thereto.

[0075] In one embodiment of the present invention, the porosity of particle A may be greater than the porosity of particle B. In other words, the total pore volume of particle A may be greater than the total pore volume of particle B. Since both particle A and particle B include a porous carbon material having external pores and internal pores, a predetermined porosity is ensured. As described above, the pores of particle B are surrounded by and / or support sulfur (S), whereas particle A may have open pores, and thus the porosity of particle A may be greater than the porosity of particle B. The porosity and / or pore volume of particle A and / or particle B may be measured by a method in accordance with ISO 15901:2019, which is well known in the art, but the measurement method is not limited thereto.

[0076] In one embodiment of the present invention, the specific surface area of ​​the particle A may be larger than that of the particle B. As described above, at least a portion of the outer surface of the particle B is covered by the particle A, and the pores of the particle B are surrounded by and / or support sulfur (S), whereas the particle A may have open pores. This allows the particle A to have a larger specific surface area than that of the particle B. Because the specific surface area of ​​the particle A surrounding the particle B is larger than that of the particle B, lithium polysulfide that may be eluted from the particle B can be adsorbed onto the particle A, which can be advantageous in terms of promoting reactivity due to the large specific surface area of ​​the particle A.

[0077] In this specification, the specific surface area can be measured, for example, by the BET method, and specifically, it can be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan, but the measurement method is not limited to this in any way.

[0078] In one embodiment of the present invention, as described above, the particles A include catalyst particles located on at least one of the outer surface and the inner surface of the pores of the first porous carbon material. Specifically, the catalyst particles may be adsorbed on the outer surface of the particles A.

[0079] At this time, according to one embodiment of the present invention, particle A and particle B may be in contact with each other at at least one position where the catalyst particle contained in particle A is present. In other words, particle A and particle B may be anchored to each other by the catalyst particle. Alternatively, particle A may be anchored to the surface of particle B by the catalyst particle. That is, the connection between particle A and particle B may be formed by the catalyst particle. At least one particle A and at least one particle B may be anchored to each other by at least one catalyst particle.

[0080] In one embodiment of the present invention, the positive electrode active material may have a morphology in which the particles A are fused with the particles B. For example, as described above, the positive electrode active material may have a morphology in which the particles A are fused with the particles B while covering at least a portion of the surface of the particles B. In one embodiment of the present invention, the particles A may be fused with the particles B, and thus the particles A may be at least partially aligned between the particles B.

[0081] In one embodiment of the present invention, the positive electrode active material may have a morphology in which the particles A fill the gaps between the particles B. For example, the positive electrode active material may have a morphology in which the particles A envelop the surfaces of at least two particles B that are separated by a predetermined distance, filling the space between the particles B. In one embodiment of the present invention, the space may represent a distance of at least 10% of the diameter of the smaller particle B, and the distance may represent, for example, the shortest distance between two opposite surfaces of the particle B.

[0082] The cathode active material having the above-described structure can increase the content of supported sulfur and improve the catalytic activity of the supported catalyst particles, thereby improving the performance of a battery, particularly a lithium-sulfur battery, using the cathode active material.

[0083] In one embodiment of the present invention, the positive electrode active material may be in a fully charged state. In this specification, the term "fully charged state" refers to a charging state of at least 90%, for example, at least 99% or 100%. Specifically, a lithium-sulfur battery using the positive electrode active material involves a sulfur oxidation / reduction reaction depending on the charging / discharging state, and as the battery is repeatedly charged and discharged, the sulfur content decreases relative to the initial sulfur content. Therefore, the positive electrode active material according to one embodiment of the present invention may have the above-described morphology when the positive electrode active material is in a fully charged state. The fully charged state of the positive electrode active material may refer to a state in which the positive electrode active material contains at least 90%, for example, at least 99% or 100%, of the initial sulfur content or at least the reversible sulfur content, but the present invention is not limited thereto.

[0084] In one embodiment of the present invention, the positive electrode active material may include sulfur (S8) in an amount of, for example, 60 wt% to 90 wt% based on the total weight of the first porous carbon material and the second porous carbon material. Specifically, the weight of the sulfur (S8) may be 65 wt% to 90 wt%, 70 wt% to 85 wt%, 75 wt% to 80 wt%, or 65 wt% to 75 wt% based on the total weight of the first porous carbon material and the second porous carbon material.

[0085] In one embodiment of the present invention, the first at least partially crystalline porous carbon material and the second at least partially crystalline porous carbon material may be different from each other.

[0086] In one embodiment of the present invention, the first at least partially crystalline porous carbon material and the second at least partially crystalline porous carbon material may be identical to each other.

[0087] In one embodiment of the present invention, the first porous carbon material and the second porous carbon material may each independently include, for example, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofibers (GNFs), carbon nanofibers (CNFs), activated carbon fibers (ACFs), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or a material selected from the group consisting of two or more of these materials.

[0088] In one embodiment of the present invention, the first porous carbon material and the second porous carbon material may be independently selected from carbon nanotubes and reduced graphene oxide. In one embodiment of the present invention, the first porous carbon material may be independently selected from carbon nanotubes and reduced graphene oxide, and the second porous carbon material may be carbon nanotubes.

[0089] In one embodiment of the present invention, the carbon nanotubes can be classified as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) depending on the number of carbon atom layers (also referred to as "carbon walls") that constitute them. In one embodiment of the present invention, when the first porous carbon material and the second porous carbon material each selectively contain carbon nanotubes, the carbon nanotubes can include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or both.

[0090] In another embodiment of the present invention, the carbon nanotubes may be present in a form in which two or more carbon nanotubes are closely entangled with each other due to the cohesive force between them. In particular, in one embodiment of the present invention, the carbon nanotubes may be provided in the form of a carbon nanotube dispersion in which the carbon nanotubes are dispersed as single nanotubes in a dispersion medium or the like, or in the form of secondary structures in which primary structure carbon nanotubes are aggregated with each other.

[0091] In view of this, when the first porous carbon material and the second porous carbon material each selectively contain carbon nanotubes, the carbon nanotubes may have a bundled secondary structure, an entangled secondary structure, or both. In one embodiment of the present invention, the first porous carbon material may be selected from bundled carbon nanotubes and reduced graphene oxide, and the second porous carbon material may be entangled carbon nanotubes.

[0092] The bundled secondary structure of carbon nanotubes is a structure in which a single carbon nanotube is used as a primary structure, and multiple primary structures are aligned in the longitudinal direction of the carbon nanotube due to cohesive forces between carbons, etc., and are aggregated together to form a mass, and is sometimes called a bundled CNT.

[0093] FIG. 3 shows an SEM image of an example of a bundle of CNTs.

[0094] The entangled secondary structure of carbon nanotubes is a structure in which a single carbon nanotube is used as a primary structure, and multiple primary structures are randomly entangled to form a spherical mass overall, and is sometimes referred to as entangled CNTs. The entangled CNTs may be characterized by improved porosity compared to primary carbon nanotubes due to the interstitial volume formed by the entanglement of primary carbon nanotubes.

[0095] Figure 4 shows an SEM image of an example of intertangled CNTs.

[0096] 3 and 4, comparing the morphologies of an example of bundled CNTs and an example of intertangled CNTs, it can be seen that the bundled CNTs are close to plate-like, whereas the intertangled CNTs are close to spherical, resulting in a higher degree of spheroidization of the example of intertangled CNTs than the example of bundled CNTs.

[0097] In one embodiment of the present invention, the first porous carbon material supporting catalyst particles may contain a plate-like carbon material in order to increase the specific surface area of ​​particles A. For example, when the first porous carbon material contains carbon nanotubes, it may preferably contain bundled carbon nanotubes, but the present invention is not limited thereto. Furthermore, when the first porous carbon material contains a graphene-based material, it may preferably contain reduced graphene oxide, but the present invention is not limited thereto.

[0098] In one embodiment of the present invention, the second porous carbon material supporting sulfur may include carbon nanotubes to improve the sulfur content in the positive electrode active material. For example, when the second porous carbon material includes carbon nanotubes, the second porous carbon material may include bundled CNTs, entangled CNTs, or both. More specifically, the second porous carbon material may include entangled CNTs to increase the coverage area of ​​particles A, but the present invention is not limited thereto.

[0099] In one embodiment of the present invention, each of the first porous carbon material and the second porous carbon material contains a large number of micropores on the outer surface and inside thereof, and the average diameter of the micropores may be, for example, in the range of 1 nm to 200 nm, for example, 1 to 100 nm, 10 to 80 nm, or 20 to 50 nm. The average diameter of the pores may be measured in accordance with ISO 15901:2019, which is known in the art, but is not limited thereto. The average diameter is D 50 The diameter of the D 50 The diameter of refers to the diameter at the 50% point in the cumulative distribution according to diameter.

[0100] In one embodiment of the present invention, the porosity (also referred to as void ratio) of each of the first and second porous carbon materials may be in the range of 10 to 90% of the total volume of each of the porous carbon materials. The porosity of the porous carbon material may be measured according to a method conforming to ISO 15901:2019, which is well known in the art, but the measurement method is not limited thereto.

[0101] In one embodiment of the present invention, the pore volume of the porous carbon material is, for example, 1 cm 3 / g~20cm 3 / g or 1cm 3 / g~10cm 3 The pore volume may be a value calculated and measured using, for example, an N2 isotherm analysis obtained based on the adsorption of liquid nitrogen.

[0102] In one embodiment of the present invention, each of the first porous carbon material and the second porous carbon material has a thickness of, for example, 100 to 2000 m. 2 / g, 300-2000m 2 / g, 400-1800m 2 / g, 450-1500m 2 / g or 500~1200m 2 The specific surface area may be measured according to the BET method in accordance with ISO 15901:2019, which is well known in the art, but is not limited thereto.

[0103] In one embodiment of the present invention, the catalyst particles can be used without any particular limitation as long as they promote the dynamic activity of the lithium-sulfur battery.

[0104] In one embodiment of the present invention, the catalyst particles may have catalytic activity for oxidation and reduction reactions of sulfur (S) contained in the particles B and lithium sulfide (LiS), lithium polysulfide (LiS, 2≦x≦8), disulfide compounds, or mixtures of two or more thereof, which are generated by oxidation / reduction of sulfur during operation of a lithium-sulfur battery.

[0105] In another embodiment of the present invention, the catalyst particles may comprise vanadium nitride.

[0106] In one embodiment of the present invention, the catalyst particles may include cobalt (Co) or iron (Fe).

[0107] In one embodiment of the present invention, the catalyst particles in the particle A may be present in an amount of 10 to 30 wt %, for example, 20 wt %, based on the total weight of the particle A. The amount of the catalyst particles may be measured using a thermogravimetric analyzer (TGA).

[0108] In one embodiment of the present invention, the catalyst particles may be metal composite particles. The metal composite particles may include a core portion containing a metal and a carbon coating layer covering at least a portion of the surface of the core portion, and the carbon coating layer may be, for example, a crystalline carbon coating layer. The catalyst particles may have an average particle diameter D of the core portion. 50 The carbon coating layer may have a thickness of 10 to 20%, for example 15%, compared to the thickness of the substrate, but the present invention is not limited thereto.

[0109] In one embodiment of the present invention, the particle A may be doped with a hetero element. Specifically, the first porous carbon material and / or the carbon coating layer may be doped with the hetero element. The hetero element may be independently one or more elements selected from nitrogen, sulfur, and oxygen, and may include, for example, a "nitrogen" element. Specifically, the doped hetero element may be derived from, for example, a precursor used when the carbon coating layer is incorporated, but the present invention is not limited thereto.

[0110] In one embodiment of the present invention, the catalyst particles have an average particle size (D 50 ), but the present invention is not limited thereto. In this specification, the particle size of the particles can be measured according to a known method for measuring the particle size, and there is no particular limitation on the measurement method. For example, the particle size of the particles can be measured according to a scanning electron microscope (SEM), a field emission electron microscope (laser diffraction method), or a laser diffraction method. Measurement using the laser diffraction method can be performed, for example, using a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000). The average particle size (D 50 ) means the particle size at the 50% point of the cumulative distribution of volume according to particle size.

[0111] In one embodiment of the present invention, each of the first porous carbon material and the second porous carbon material may be at least partially crystalline due to a heat treatment process during the preparation of the positive electrode active material. Specifically, each of the first porous carbon material and the second porous carbon material may be entirely crystalline.

[0112] As used herein, when any material, such as the porous carbon material, is said to be at least partially crystalline, this may be confirmed by at least one peak in the X-ray diffraction (XRD) spectrum of the material. For example, a material is said to be at least partially crystalline when the signal to noise ratio in the XRD spectrum for that material is greater than 1, e.g., 1.5:1, 2:1, 5:1, or 10:1.

[0113] Therefore, in one embodiment of the present invention, the elasticity of each of the first and second porous carbon materials may be higher than the elasticity of an amorphous carbon material.

[0114] In addition, in one embodiment of the present invention, the electrical conductivity of each of the first and second porous carbon materials may be higher than the electrical conductivity of the amorphous carbon material.

[0115] In this specification, the amorphous carbon material may be, for example, the carbon material disclosed in Liu at al. Nanoscale, 2018, 10 5246-5253.

[0116] In this specification, the crystallinity of the porous carbon material can be measured, for example, by X-ray diffraction (XRD) analysis. XRD analyzes diffraction (Brugh's condition: 2d sin θ = nλ, where d is the distance between two planes, θ is the angle between the X-ray and the plane, n is an arbitrary integer, and λ is the wavelength of the X-ray) that occurs when a sample is irradiated with X-rays and the X-rays are scattered and interfered with by electrons around the atoms. This analysis enables identification and quantification of constituent components, as well as determination of crystal size and crystallinity. For example, the presence of at least one independent peak in the XRD spectrum indicates that the material is at least partially crystalline. In this case, the signal of the independent peak is measured to be at least 1, 1.5, 2, 5, or 10 times greater than the noise.

[0117] In one embodiment of the present invention, I of the positive electrode active material D / I G For example, the intensity ratio of the Raman peaks (I D / I G )<2.0.

[0118] The Raman peak intensity ratio is calculated by the Raman peak intensity ratio I obtained from the spectrum of the positive electrode active material obtained by Raman spectroscopy. G and I D In the resulting spectrum, I G means the peak of the crystalline part (G-peak, 1573 / cm), and I D means the peak of the amorphous part (D-peak, 1309 / cm). Therefore, in this case, I G / I D A smaller ratio indicates lower crystallinity.

[0119] In one embodiment of the present invention, the positive electrode active material may be formed by sequentially or simultaneously mixing the first porous carbon material, the second porous carbon material, the catalyst particles, and the sulfur-based compound, followed by heat treatment. The positive electrode active material produced by the heat treatment may include the first and second porous carbon materials, at least a portion of which is crystalline, as described above, but the present invention is not limited thereto.

[0120] According to another aspect of the present invention, there is provided a positive electrode for a lithium-sulfur battery, to which the positive electrode active material is applied.

[0121] The positive electrode for the lithium-sulfur battery may further include a binder in addition to the positive electrode active material. The binder may be any binder that can be used in a positive electrode for a lithium-sulfur battery without any particular limitation.

[0122] The binder is a component that aids in bonding the positive electrode active material to the conductive material and the current collector, and may be, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, or two or more thereof. However, the binder is not necessarily limited to these.

[0123] In one embodiment of the present invention, the binder may include, for example, PVDF (polyvinylidene fluoride), and specifically, PVDF dispersed in NMP (N-methyl-2-pyrrolidone).

[0124] In another embodiment of the present invention, the binder may include, for example, an aqueous binder such as SBR (styrene butadiene rubber), and specifically, an aqueous binder dispersed in an aqueous solvent such as water.

[0125] In one embodiment of the present invention, the positive electrode for the lithium-sulfur battery may include a positive electrode current collector and a positive electrode active material layer in which the positive electrode active material and a binder are coated on one or both sides of the current collector. In this case, the positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery.

[0126] In another embodiment of the present invention, the positive electrode for the lithium-sulfur battery may further include, in addition to the positive electrode active material and the binder, a conductive material, an additive, etc. Specific types of the binder, conductive material, and additive may be conventional ones, and therefore, description thereof will be omitted.

[0127] According to yet another aspect of the present invention, there is provided a lithium-sulfur battery including the above-described positive electrode active material.

[0128] The lithium-sulfur battery includes, for example, a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, and the positive electrode includes the above-mentioned positive electrode active material.

[0129] In one embodiment of the present invention, the negative electrode and separator may be any material that can be used in a lithium-sulfur battery without any particular limitation, as long as the material does not impair the object of the present invention. For example, lithium metal may be used as the negative electrode.

[0130] In one embodiment of the present invention, the separator may be any separator that can be used as a separator for a lithium-sulfur battery without any particular limitations.

[0131] In one embodiment of the present invention, the separator may include a porous polyolefin substrate, and optionally, may further include inorganic particles on at least one surface of the porous polyolefin substrate. The separator may also optionally include a binder to bind the inorganic particles.

[0132] In another embodiment of the present invention, the separator may be a film-like electrolyte membrane containing a solid electrolyte, and may further contain a binder to bind the solid electrolyte, as needed. The solid electrolyte may be a polymer-based solid electrolyte, an inorganic-based solid electrolyte, or a mixture thereof, and may be any solid electrolyte that can be used in lithium-sulfur batteries without any particular limitation.

[0133] In one embodiment of the present invention, the electrolyte solution includes those typically used in lithium-sulfur batteries. The electrolyte solution may include a lithium salt and a non-aqueous solvent.

[0134] The lithium salt can be any lithium salt that can be used in an electrolyte solution for a lithium-sulfur battery without any particular limitation. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, or two or more thereof, but are not limited thereto.

[0135] The non-aqueous solvent may be any solvent that can be used in an electrolyte solution for a lithium-sulfur battery, and may include, but is not limited to, a cyclic carbonate solvent, a linear carbonate solvent, an ester solvent, a ketone solvent, or a mixture of two or more thereof.

[0136] In one embodiment of the present invention, the electrolyte may include (CF3SO2)2NLi as a lithium salt and a dioxolane (DOL) / dimethoxyethane (DME) binary system as a non-aqueous solvent. For example, the electrolyte may further include a common additive such as LiNO3.

[0137] In one embodiment of the present invention, the lithium-sulfur battery may have a shape such as a coin, a cylinder, a pouch, or a square, but the shape of the battery is not particularly limited. The lithium-sulfur battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells, and the usage form is not particularly limited.

[0138] Hereinafter, a method for preparing a cathode active material according to one embodiment of the present invention will be described in more detail with reference to examples. However, the following examples are merely for illustrative purposes and are not intended to limit the scope of the present invention.

[0139] [Production of positive electrode active material] According to the following method, a positive electrode active material was prepared, which includes: a) particles A including a first porous carbon material, at least a portion of which is crystalline, and catalyst particles deposited on the first porous carbon material; and b) particles B including a second porous carbon material, at least a portion of which is crystalline, and sulfur supported on the second porous carbon material, wherein particles A and particles B have different morphologies.

[0140] FIG. 3 shows an SEM image of the bundled CNTs used as the source material.

[0141] FIG. 4 shows an SEM image of the entangled CNTs used as the source material.

[0142] Figure 5 shows an SEM image of the reduced graphene oxide (rGO) used as the source material.

[0143] Example 1 142 mg of iron hydrochloride hydrate (FeCl2·6H2O) and 100 mg of dopamine hydrochloride (98 wt%) were added to 500 mL of distilled water in a 1:1 molar ratio and stirred at 230 rpm for 30 minutes at room temperature (23 °C). 300 mg of bundled CNTs (Figure 3) were added and stirred at room temperature for 30 minutes to produce a dispersion. 960 ppm of Trizma® base (Tris(hydroxymethyl)aminomethane, TRIS) was then added to the dispersion to maintain a pH of 8.5. The resulting dispersion was stirred at room temperature for 24 hours, filtered, washed three times with distilled water, then once with ethanol, and dried at 60 °C. The reaction product was then placed in a tube electric furnace under an argon atmosphere and heat-treated at 800 °C for 2 hours (heating rate: 1 °C / min) to obtain a granular material with an average particle size (D 50 ) was 35 μm.

[0144] The obtained particles A include bundled CNTs as a porous carbon substrate, transition metal composite particles located on at least one of the outer surface of the bundled CNTs and the inner surface of the pores, the core portion including iron particles, and a crystalline carbon coating layer covering at least a part of the surface of the core portion, and doped nitrogen element. At this time, the average particle size (D 50 The ratio of the thickness of the carbon coating layer to the total thickness was 15%.

[0145] Next, entangled carbon nanotubes (CNTs, Figure 4) and sulfur (S8) were mixed in a weight ratio of 25:75, and then heat-treated at 155°C for 1 hour using the melt-diffusion method to prepare sulfur-carbon composites (particles B).

[0146] The particles A and the particles B were mixed in a weight ratio of 7.5:92.5, dispersed in water, and then dried to obtain a positive electrode active material having a structure in which particles A and particles B, which have different morphologies, are in contact with each other.

[0147] Example 2 1.6 g of reduced graphene oxide (rGO, Figure 5) was mixed with 24 g of dicyanodiamide, 0.8 g of ammonium metavanadate, and 0.2 g of glucose in 500 mL of a 1:1 volumetric mixture of ethanol and water. The mixture was dissolved and dispersed by ultrasonication and magnetic stirring. The solvent, excluding the vanadium nitride precursor adsorbed on the carbon nanotube surface, was then removed by vacuum filtration. The mixture was then dried in an oven at 80 °C for 12 hours. This was followed by heat treatment in an inert atmosphere tube furnace at 600 °C for 3 hours and then at 800 °C for 2 hours to obtain a carbon composite (particle A) in which vanadium nitride particles were positioned as catalyst particles on the surface of the reduced graphene oxide. Figure 2 shows an SEM image of the resulting particle A. The vanadium nitride particles were present in 20 parts by weight per 100 parts by weight of the resulting particle A. The content of the vanadium nitride particles was measured using a thermogravimetric analyzer (TGA).

[0148] Next, entangled carbon nanotubes (CNTs, Figure 4) and sulfur (S8) were mixed in a weight ratio of 25:75 to prepare a sulfur-carbon composite (particle B).

[0149] The particles A and the particles B were mixed in a weight ratio of 7.5:92.5, dispersed in water, and then dried to obtain a positive electrode active material having a structure in which particles A and particles B, which have different morphologies, are in contact with each other.

[0150] An SEM image of the obtained positive electrode active material is shown in FIG. 1, in which the regions where particles A and B are located are distinguished and labeled using an image analysis method based on energy dispersive X-ray spectroscopy (EDS).

[0151] Example 3 Instead of using reduced graphene oxide, the same amount of bundled carbon nanotubes (bundeled carbon nanotubes, Figure 3) was used to produce particles A. Figure 6 shows an SEM image of the resulting particles A.

[0152] Thereafter, a positive electrode active material was obtained in the same manner as in Example 2.

[0153] Comparative Example 1 A positive electrode active material was produced in the same manner as in Example 1, except that the particles A were replaced with the same amount of bundled CNTs (FIG. 3).

[0154] Specifically, entangled CNTs (FIG. 4) and sulfur (S8) were mixed in a weight ratio of 25:75 to prepare a sulfur-carbon composite (particle B).

[0155] Next, the bundled CNTs and the particles B were mixed in a weight ratio of 7.5:92.5, dispersed in water, and then dried to obtain a positive electrode active material having a structure in which the bundled CNTs and particles B were in contact with each other.

[0156] Comparative Example 2 Particles A were prepared in the same manner as in Example 1 above.

[0157] The prepared particles A, entangled CNTs, and sulfur (S8) were mixed in a weight ratio of 5:20:75, and the mixture was subjected to a thermal diffusion method in which heat treatment was carried out at 155°C for 1 hour to obtain a positive electrode active material in which sulfur was supported on particles A and entangled CNTs.

[0158] [Battery performance evaluation] In order to evaluate the performance of lithium-sulfur batteries using the positive electrode active materials produced in Example 1, Comparative Example 1, and Comparative Example 2, lithium-sulfur coin-shaped batteries were prepared as follows.

[0159] Battery manufacturing First, to prepare the working electrode, each of the cathode active materials prepared above was mixed with PVDF (polyvinylidene fluoride) as a binder in a weight ratio of 9:1 using NMP (N-methyl-2-pyrrolidone) solvent to prepare a cathode slurry. The prepared cathode slurry was coated on a carbon-coated Al foil and dried at 60°C for 8 hours. Then, the electrode was pressed against the foil and cut into coins to prepare cathodes.

[0160] Next, a battery was fabricated by placing a positive electrode, a negative electrode, and a separator between the positive and negative electrodes in a case together with an electrolyte. The positive electrode fabricated above was used as the positive electrode, and a porous polypropylene membrane (Celgard® 2400, manufactured by WELCOS CO., LTD.) was used as the separator. Lithium metal (200 μm thick) was used as the reference electrode and counter electrode. The electrolyte solution used was a solution containing 1.0 M LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) as an electrolyte and 2.0 wt% LiNO3 (99.99% metal basis, manufactured by Sigma-Aldrich) as an additive in a solvent (manufactured by PANAX E-TEC Co., LTD., Korea) containing 1,3-dioxolane and dimethoxymethane (DOL / DME) in a 1:1 volume ratio.

[0161] The sulfur loading in the positive electrode was 2.25 mg / cm 2 and the El / S ratio of the battery was 10 μL / mg.

[0162] Discharge capacity and life evaluation Each battery manufactured as described above was repeatedly charged / discharged three times at a current density of 0.1 C and a voltage of 1.8 V to 2.5 V, then three times at a current density of 0.2 C, and then up to 20 times at a current density of 0.5 C. The evaluation was all carried out in a thermostatic chamber at 25°C using a PESCO5-0.1 device manufactured by PNE Solution Co., Ltd.

[0163] The graphs showing the results of measuring the capacity-voltage after three charge / discharge cycles at a current density of 0.1 C (FIGS. 7 and 8) and the results of measuring the discharge capacity after 20 charge / discharge cycles (FIGS. 9 and 10) are shown in the drawings.

[0164] First, referring to the graphs of FIGS. 7 and 9, it was confirmed that the battery using the cathode active material according to Example 1 was superior in both discharge capacity and lifespan characteristics to the battery using the cathode active material according to Comparative Example 1, which did not support Fe catalyst particles.

[0165] In contrast, referring to the graphs of FIGS. 8 and 10, it was confirmed that the battery using the cathode active material of Comparative Example 2, in which sulfur was also loaded on Particle A carrying Fe catalyst particles, was inferior in 0.1C charge / discharge, 0.2C charge / discharge, and 0.5C charge / discharge performance to the battery using the cathode active material of Comparative Example 1, which did not carry catalyst particles, despite containing catalyst particles.

[0166] From this, it was confirmed that the performance of lithium-sulfur batteries can be improved by using a positive electrode active material containing particles A and particles B having different morphologies according to the present invention.

Claims

1. a) particles (A) comprising a first porous carbon material, at least a portion of which is crystalline, and catalyst particles deposited on the first porous carbon material; b) particles (B) comprising a second porous carbon material, at least a portion of which is crystalline, and sulfur supported on the second porous carbon material; Including, The positive electrode active material, wherein the particles (A) and the particles (B) have different morphologies.

2. the sphericity of the particles (B) is greater than the sphericity of the particles (A); The positive electrode active material according to claim 1 , wherein the sphericity is defined according to the following formula 1: [Equation 1] In the above formula 1, Ψ indicates the spheroidization degree, V ｐ denotes the volume of the particle, A ｐ indicates the surface area of ​​the particle.

3. 2. The positive electrode active material according to claim 1, wherein 50% or more of the particles (A) are dispersed on the surfaces of the particles (B).

4. At least a part of the surface of the particles (B) is coated with the particles (A), 2. The positive electrode active material according to claim 1, wherein the coverage area of ​​the particles (B) with the particles (A) is 20% to 50% based on the total external area of ​​the particles (B).

5. The positive electrode active material according to claim 1 , wherein the porosity of the particles (A) is greater than the porosity of the particles (B).

6. The positive electrode active material according to claim 1 , wherein the specific surface area of ​​the particles (A) is larger than the specific surface area of ​​the particles (B).

7. 2. The positive electrode active material according to claim 1, wherein the particles (A) and the particles (B) are in contact with each other at least at one position where the catalyst particles contained in the particles (A) are present.

8. The sulfur (S ８ 2. The positive electrode active material according to claim 1, wherein a weight of the first porous carbon material and the second porous carbon material is 60% by weight to 90% by weight based on a total weight of the first porous carbon material and the second porous carbon material.

9. The positive electrode active material according to claim 1 , wherein the first porous carbon material and the second porous carbon material are different materials from each other.

10. The positive electrode active material according to claim 1 , wherein the first porous carbon material and the second porous carbon material are the same material.

11. 2. The cathode active material of claim 1, wherein the first porous carbon material and the second porous carbon material each independently include at least one of bundled CNTs, entangled CNTs, and reduced graphene oxide (rGO).

12. The positive electrode active material of claim 1 , wherein the catalyst particles comprise vanadium nitride.

13. The positive electrode active material according to claim 1 , wherein the catalyst particles contain at least one element selected from the group consisting of cobalt (Co) and iron (Fe).

14. The positive electrode active material according to claim 1 , wherein the elasticity of each of the first porous carbon material and the second porous carbon material is greater than the elasticity of an amorphous carbon material.

15. The positive electrode active material according to claim 1 , wherein the electrical conductivity of each of the first porous carbon material and the second porous carbon material is higher than the elasticity of the amorphous carbon material.

16. I of the positive electrode active material Ｄ / I Ｇ The positive electrode active material according to claim 1 , wherein the value is 2.0 or less.

17. a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte solution; A lithium-sulfur battery, wherein the positive electrode contains the positive electrode active material according to any one of claims 1 to 16 as a positive electrode active material.

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