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

Abstract

Disclosed is a novel positive electrode active material for use in a lithium-sulfur battery positive electrode. The positive electrode active material of the invention comprises: a) particles A comprising a first porous carbon material that is at least partially crystalline and catalyst particles deposited on the first porous carbon material; and b) particles B comprising a second porous carbon material that is at least partially crystalline and sulfur supported in the second porous carbon material, wherein particles A and particles B have different morphologies.

Description

Technical Field

[0001] This invention relates to cathode materials for lithium-sulfur batteries and lithium-sulfur batteries containing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2022-0110413, filed August 31, 2022; Korean Patent Application No. 10-2022-0110385, filed August 31, 2022; Korean Patent Application No. 10-2022-0187899, filed December 28, 2022; Korean Patent Application No. 10-2023-0025408, filed February 24, 2023; and Korean Patent Application No. 10-2023-0042283, filed March 30, 2023, the disclosures of which are incorporated herein by reference. Background Technology

[0003] Lithium-sulfur batteries are battery systems that use sulfur-sulfur (SS) bonds in sulfur-based materials as the positive electrode active material and metallic lithium as the negative electrode active material. Sulfur, the main component of the positive electrode active material, is abundant in nature and widely available worldwide; it is non-toxic and has a low atomic weight.

[0004] Because secondary batteries are widely used in applications including electric vehicles (EVs) and energy storage systems (ESS), lithium-sulfur batteries, which theoretically have a higher energy density (~2600 Wh / kg) compared to lithium-ion secondary batteries, which have a lower energy density (~250 Wh / kg), are attracting attention.

[0005] During discharge, the lithium-sulfur battery undergoes oxidation at the negative electrode active material (lithium) by releasing electrons to lithium cations and reduction at the positive electrode active material (sulfur-based material) by accepting electrons. Through the reduction reaction, the sulfur-based material is converted into sulfide anions via SS bonds that accept two electrons. The lithium cations generated from the lithium oxidation reaction migrate via the electrolyte to the positive electrode and combine with the sulfide anions generated from the reduction reaction of the sulfur compounds to form a salt. Specifically, the sulfur before discharge has a cyclic S8 structure, and it is converted into lithium polysulfides (Li₂Sx) through the reduction reaction and then completely reduced to lithium sulfide (Li₂S).

[0006] Because sulfur used in the positive electrode active material is non-conductive, electrons generated by the electrochemical reaction cannot move, and polysulfides (LiSx) dissolve during charging and discharging. The low conductivity of sulfur and lithium sulfide slows down the kinetics of the electrochemical reaction, which reduces the battery's lifespan and rate performance.

[0007] In this context, recent years have seen research focusing on utilizing platinum (Pt), primarily used as an electrochemical catalyst, to improve the kinetics of sulfur oxidation and reduction reactions during the charge-discharge cycle of lithium-sulfur secondary batteries, thereby enhancing battery performance. However, the high cost of noble metal catalysts such as platinum hinders commercialization, and the risk of poisoning due to sulfur oxidation and reduction reactions during charge-discharge makes them unsuitable for use as cathode materials in lithium-sulfur secondary batteries.

[0008] Therefore, there is a need to develop technologies for cathode materials that improve the electrochemical reaction kinetics during the charge and discharge of lithium-sulfur secondary batteries and can be commercialized at a cost-effective level. Summary of the Invention

[0009] Technical issues

[0010] The present invention aims to provide a novel positive electrode active material for use in the positive electrode of lithium-sulfur batteries.

[0011] Technical solution

[0012] To address the aforementioned problems, according to one aspect of the present invention, a positive electrode active material with the following embodiment is provided.

[0013] The positive electrode active material according to the first embodiment comprises: a) particle A, said particle A comprising at least partially crystalline first porous carbon material and catalyst particles deposited on the first porous carbon material; and b) particle B, said particle B comprising at least partially crystalline second porous carbon material and sulfur supported in the second porous carbon material, wherein particle A and particle B have different morphologies.

[0014] According to the second implementation scheme, in the first implementation scheme, the sphericity of particle B can be greater than that of particle A, and the sphericity can be defined according to the following formula 1:

[0015] [Formula 1]

[0016]

[0017] Where Ψ represents sphericity, V p Let A represent the volume of the particle, and A... p This represents the surface area of ​​a particle.

[0018] According to the third embodiment, in the first or second embodiment, more than 50% of particle A can exist on the surface of particle B.

[0019] According to the fourth embodiment, in any one of the first to third embodiments, at least a portion of the surface of particle B may be covered by particle A, and the area of ​​particle B covered by particle A may be 20% to 50% of the total external area of ​​particle B.

[0020] According to the fifth implementation scheme, in any one of the first to fourth implementation schemes, the porosity of particle A can be greater than that of particle B.

[0021] According to the sixth implementation plan, in any one of the first to fifth implementation plans, the specific surface area of ​​particle A can be greater than that of particle B.

[0022] According to the seventh embodiment, in any of the first to sixth embodiments, particle A and particle B may be in contact with each other at at least one location where the catalyst particles contained in particle A are present.

[0023] According to the eighth embodiment, in any of the first to seventh embodiments, the weight of sulfur (S8) can be from 60% to 90% by weight based on the total weight of the first porous carbon material and the second porous carbon material.

[0024] According to the ninth implementation scheme, in any one of the first to eighth implementation schemes, the first porous carbon material and the second porous carbon material can be different materials.

[0025] According to the tenth implementation scheme, in any one of the first to ninth implementation schemes, the first porous carbon material and the second porous carbon material can be the same material.

[0026] According to the eleventh embodiment, in any one of the first to tenth embodiments, the first porous carbon material and the second porous carbon material may each independently include at least one of bundled carbon nanotubes (CNTs), entangled CNTs, or reduced graphene oxide (rGO).

[0027] According to the twelfth embodiment, in any of the first to eleventh embodiments, the catalyst particles may contain vanadium nitride.

[0028] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, the catalyst particles may contain at least one of cobalt (Co) or iron (Fe).

[0029] According to the fourteenth implementation plan, in any one of the first to thirteenth implementation plans, the elasticity of the first porous carbon material and the second porous carbon material can be greater than the elasticity of the amorphous carbon material.

[0030] According to the fifteenth implementation scheme, in any one of the first to fourteenth implementation schemes, the electrical conductivity of the first porous carbon material and the second porous carbon material can be greater than the electrical conductivity of the amorphous carbon material.

[0031] According to the sixteenth implementation plan, in any one of the first to fifteenth implementation plans, the positive electrode active material I D / I G The value can be equal to or less than 2.0.

[0032] According to another aspect of the present invention, a lithium-sulfur battery with the following embodiments is provided.

[0033] The lithium-sulfur battery according to the seventeenth embodiment includes a positive electrode active material according to any one of the first to sixteenth embodiments.

[0034] Beneficial effects

[0035] According to one embodiment of the present invention, the positive electrode active material is a novel positive electrode active material for use in secondary batteries, especially lithium-sulfur batteries.

[0036] Specifically, the positive electrode active material according to one embodiment of the present invention is a novel positive electrode active material suitable for significantly improving sulfur loading and catalytic activity. Therefore, the performance of secondary batteries using it, especially lithium-sulfur batteries, can be improved, but the effects of the present invention are not limited thereto. Attached Figure Description

[0037] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the foregoing description, serve to provide a further understanding of the technical aspects of the invention; therefore, the invention should not be construed as limited to the drawings.

[0038] Figure 1 A scanning electron microscope (SEM) image of a positive electrode active material according to one embodiment of the present invention is shown. Figure 1 In the diagram, "A" represents particle A, and "B" represents particle B. Figure 1 The SEM images were obtained by taking pictures of an area of ​​10 μm × 10 μm at a magnification of 2,000x.

[0039] Figure 2 The image shows a SEM image of a positive electrode active material in which vanadium nitride particles, serving as catalyst particles, are loaded into particle A according to one embodiment of the present invention. Figure 2 The SEM images were obtained by photographing an area of ​​10 μm × 10 μm at a magnification of 15,000x.

[0040] Figure 3The image shows a SEM image of a bundle-type CNT used in one embodiment of the present invention. Figure 3 The image was obtained by photographing an area of ​​10 μm × 10 μm at a magnification of 500x.

[0041] Figure 4 The image shows a SEM image of entangled CNTs used in one embodiment of the present invention. Figure 4 The image was obtained by photographing an area of ​​10 μm × 10 μm at a magnification of 500x.

[0042] Figure 5 The image shows a SEM image of reduced graphene oxide (rGO) used in one embodiment of the present invention. Figure 5 The image was obtained by photographing an area of ​​10 μm × 10 μm at a magnification of 1,000x.

[0043] Figure 6 The image shows a SEM image of a positive electrode active material, in which iron particles, serving as catalyst particles, are supported in particle A, according to one embodiment of the present invention. Figure 6 The SEM images were obtained by taking pictures of an area of ​​10 μm × 10 μm at a magnification of 2,000x.

[0044] Figure 7 The capacity-voltage graph is shown, which displays the performance evaluation results of batteries using the positive electrode active material of Example 1 and Comparative Example 1, respectively, according to one embodiment of the present invention.

[0045] Figure 8 The capacity-voltage graph is shown, which displays the performance evaluation results of batteries using the positive electrode active materials of Comparative Example 1 and Comparative Example 2, respectively, according to an embodiment of the present invention.

[0046] Figure 9 The graphs showing discharge capacity-cycle count-coulombic efficiency are displayed, illustrating the performance evaluation results of batteries using the positive electrode active material of Example 1 and Comparative Example 1, respectively, according to one embodiment of the present invention.

[0047] Figure 10 The graphs showing discharge capacity-cycle count-coulombic efficiency are displayed, illustrating the performance evaluation results of batteries using the positive electrode active materials of Comparative Example 1 and Comparative Example 2, respectively, according to an embodiment of the present invention. Detailed Implementation

[0048] The present invention will be described in detail below. However, the invention is not limited to the following description, and various modifications or selective use of the various elements may be made as necessary. Therefore, it should be understood that the invention includes all variations, equivalents, or substitutions included in the aspects and scope of the invention.

[0049] Unless the context clearly indicates otherwise, the term "comprising" as used in this specification explicitly states the presence of the stated element, but does not preclude the presence or addition of more than one other element.

[0050] When used in this specification, “A and / or B” means A or B or both.

[0051] The terminology used in this specification is for convenience and not intended to be limiting. For example, terms indicating position such as “up,” “down,” “left,” “right,” “front,” “back,” “inner,” and “outer” are not absolute and may refer to positions or directions used or referenced in the accompanying drawings to describe the relative positions or directions between elements. These terms include themselves as well as the words that include them and their derivatives and synonyms.

[0052] As used in this article, the term "composite material" refers to a combination of two or more materials that have physically and / or chemically different phases and perform more effective functions.

[0053] The term "polysulfide" as used in this article includes "polysulfide ions (S...)". x 2- (x=8, 6, 4, 2) and "lithium polysulfide (Li2S) x or LiS x The concept of "x=8, 6, 4, 2"

[0054] Regarding the properties described herein, without detailed description of the measurement conditions and methods, the properties are measured using the measurement conditions and methods commonly used by those skilled in the art.

[0055] According to one aspect of the present invention, a positive electrode active material for secondary batteries, specifically lithium-sulfur batteries, is provided.

[0056] The positive electrode active material comprises porous carbon material, catalyst particles, and sulfur (S). Specifically, the positive electrode active material may comprise two types of porous carbon material, catalyst particles, and sulfur (S).

[0057] The positive electrode active material includes:

[0058] a) Particle A, said particle A comprising at least partially crystalline first porous carbon material and catalyst particles deposited on the first porous carbon material; and

[0059] b) Particle B, said particle B comprising at least partially crystalline second porous carbon material and sulfur loaded in the second porous carbon material.

[0060] Among them, particle A and particle B have different shapes.

[0061] In one embodiment of the invention, sulfur can be provided without permeating into the pores of the first porous carbon material. According to one embodiment of the invention, a first porous carbon material and / or particle A that is substantially free of (or contains no) sulfur can be provided. In this respect, the term "free of" does not exclude impurities. Impurities may be included without hindering the achievement of the objectives of the invention.

[0062] In one embodiment of the invention, catalyst particles that do not deposit on the second porous carbon material can be provided. According to one embodiment of the invention, a second porous carbon material and / or particles B that are substantially free of (or contain no) catalyst particles can be provided. In this regard, the term "free of" does not exclude impurities. Impurities may be included without hindering the achievement of the objectives of the invention.

[0063] In one embodiment of the invention, the porous carbon material is a material containing micropores, and catalyst particles and / or sulfur are contained on at least one of the outer surface or the inner surface of the pores of the porous carbon material.

[0064] In one embodiment of the invention, the first porous carbon material and the second porous carbon material may be the same as or different from each other. In one embodiment of the invention, the first porous carbon material is a material containing micropores, and catalyst particles are contained on at least one of the outer surface of the porous carbon material or the inner surface of the micropores. In one embodiment of the invention, the second porous carbon material is a material containing micropores, and sulfur is contained on at least one of the outer surface of the porous carbon material or the inner surface of the micropores.

[0065] In one embodiment of the invention, catalyst particles may be chemically and / or physically bonded to at least one of the outer surface or the interior surface of the pores of the first porous carbon material. In one embodiment of the invention, the pores may be micropores.

[0066] In one embodiment of the invention, catalyst particles can be physically adsorbed onto the outer surface and / or the surface inside the pores of the first porous carbon material. Alternatively, catalyst particles can be chemically bonded to the outer surface and / or the surface inside the pores of the first porous carbon material through C-C covalent bonds and / or π-π interactions between elements present in the catalyst particles and the carbon in the first porous carbon material. Furthermore, physical adsorption and chemical bonding can coexist between the catalyst particles and the first porous carbon material.

[0067] In one embodiment of the present invention, catalyst particles can be physically adsorbed on the outer surface of the first porous carbon material.

[0068] In one embodiment of the invention, sulfur (S, such as S8) may be chemically and / or physically bonded to at least one of the outer surface or the inner surface of the pores of the second porous carbon material.

[0069] In one embodiment of the present invention, the weight ratio of the second porous carbon material to sulfur can be 10:90 to 90:10, 10:90 to 50:50, or 25:75.

[0070] In one embodiment of the invention, the sulfur contained in particle B originates from sulfur compounds, such as S8, mixed with porous carbon materials during the manufacture of the positive electrode active material, and the sulfur may be contained at at least one location on the outer surface or the surface inside the pores of the second porous carbon material. The sulfur-containing compounds may include, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfides (Li2Sx, 2≤x≤8), disulfide compounds, or mixtures thereof, but are not limited thereto.

[0071] In this invention, the "morphology" of a particle refers to its form, shape, and physicochemical or biochemical structure. For example, particle A and particle B can have different morphologies by having different shapes. For example, particle A can have a shape with an uneven or rough surface, such as a broccoli-shaped shape, a cauliflower-shaped shape, a spiky shape, etc., while particle B can have a shape with a relatively smooth surface or a smooth surface, such as a potato-shaped shape (generally elliptical or rectangular, with a slightly smooth surface that does not exclude minor bumps), a spherical shape, an elliptical shape, etc. The morphology of a particle can be determined, for example, by scanning electron microscopy (SEM) images.

[0072] Therefore, the fact that particles A and B have different morphologies means that particles A and B are different in at least one aspect of particle form, shape, physicochemical structure, or biochemical structure.

[0073] In one embodiment of the invention, particles A and B with different morphologies can be determined by measuring at least one of the following material properties: specific surface area, porosity, particle size, and particle shape observed by an optical microscope.

[0074] In one embodiment of the invention, because particle A contains catalyst particles, particle A can promote the electrochemical reaction kinetics of the positive electrode active material, but its function is not limited thereto. Furthermore, because particle B contains sulfur (S), particle B can provide sites for electrochemical reactions to occur in the positive electrode active material, but its function is not limited thereto. Therefore, when particle A, especially the catalyst particles present in or on particle A, has a similar morphology to the sulfur in particle B, especially the sulfur present in (infiltrated) particle B, the positive electrode active material can have improved performance.

[0075] In this context, according to one embodiment of the invention, the sphericity of particle B is preferably greater than that of particle A. When the sphericity of particle B is greater than that of particle A, a positive electrode active material can be provided such that particle B is surrounded by particle A. Thus, a positive electrode active material with excellent performance can be provided, wherein sulfur-loaded (S) particles B are electrically connected to each other without direct surface-to-surface contact through the physicochemical contact between the porous carbon material of particle B and the porous carbon material of particle A. Here, two or more particles B can exist in the positive electrode active material in a manner that allows them to contact each other or not, and it will be apparent to those skilled in the art that this mechanism is not intended to limit the non-contact between particles B.

[0076] In one embodiment of the present invention, "sphericity" can be defined according to the following formula 1.

[0077] [Formula 1]

[0078]

[0079] Where Ψ represents sphericity,

[0080] V p Represents the volume of the particle, and

[0081] A p This represents the surface area of ​​a particle.

[0082] In one embodiment of the invention, "V" p "The apparent volume of a particle can be represented. The apparent volume of a particle can be measured using conventional methods for measuring apparent volume. In one embodiment of the invention, the apparent volume can be measured by the particle's (mass / apparent density) value, and the apparent density can be measured by the particle's [dry weight / (dry weight - weight in water)] value, but the method for measuring particle volume is not limited to these. Furthermore, it can be measured using methods for measuring the particle volume of porous materials."

[0083] In one embodiment of the present invention, "A" p"This can represent the apparent area of ​​a particle. The apparent area of ​​a particle can be expressed according to, for example, π." 1 / 3 (6V p ) 2 / 3 It can be calculated, and it can also be measured by measuring the apparent area of ​​porous materials.

[0084] In one embodiment of the present invention, in the positive electrode active material, particle A may exist on the surface of particle B. Specifically, in the positive electrode active material, at least a portion of the surface of particle B with greater sphericity may be covered by particle A with less sphericity.

[0085] Figure 1 A scanning electron microscope (SEM) image of a positive electrode active material according to one embodiment of the present invention is shown. Figure 1 In the diagram, "A" represents particle A, and "B" represents particle B.

[0086] Reference Figure 1 It can be seen that the positive electrode active material contains particles B with larger sphericity and particles A with smaller sphericity, such that particles A exist on the surface of particles B, specifically, particles A cover at least a portion of the surface of particles B.

[0087] In one embodiment of the invention, the size of particle A can be, for example, 10 to 100 µm, 15 to 50 µm, or 20 to 40 µm, such as 35 µm.

[0088] In one embodiment of the invention, the size of particle B can be, for example, 10 to 100 µm or 20 to 80 µm.

[0089] The particle size can refer to the D50 size, and the D50 size can be measured using methods commonly used in the art without particular limitation. For example, the particle size, such as the D50 size, can be measured using scanning electron microscopy (SEM), laser diffraction, or field emission electron microscopy. Particle size measurements using laser diffraction can be performed using, for example, a commercially available laser diffraction particle size analyzer, such as the Microtrac MT 3000, but are not limited thereto. Particle size D50 refers to the particle diameter at 50% of the cumulative particle size distribution.

[0090] In one embodiment of the present invention, particles A contained in the positive electrode active material may not exist on the surface of particles B. However, the above-mentioned effect can be better achieved when more than 50% of the total number of particles A contained in the positive electrode active material exists on the surface of particles B. Therefore, more than 50% of particles A can exist on the surface of particles B. That is, more than 50% of particles A can be in direct contact with the surface of at least one particle B. Specifically, the number of particles A present on the surface of particles B can be 50% to 100% of the total number of particles A contained in the positive electrode active material, for example, 55% to 90%, 60% to 85%, or 70% to 80%, but is not limited thereto.

[0091] In this invention, particle A can exist on the surface of particle B, for example, such that the surface of particle B surrounded by particle A accounts for more than 20% of the total area of ​​the outer surface of particle B. Here, for example, the area of ​​the surface of particle B surrounded by particle A can be measured by SEM image analysis of the positive electrode active material. Specifically, the measurement can be performed on an area of ​​10 μm × 10 μm at a magnification of 2,000x.

[0092] In one embodiment of the present invention, in the positive electrode active material, at least a portion of the surface of particle B may be surrounded and / or covered by particle A.

[0093] Specifically, since particle B is a sulfur-loaded porous carbon material particle, particle B can possess one of the characteristics of porous carbon materials: external surface area and specific surface area. Particle B can have an external surface area and / or specific surface area corresponding to a second porous carbon material. In this case, the area of ​​the external surface of particle B can be measured by SEM image analysis as described above, and the specific surface area of ​​particle B can have a value similar to the internal area, for example, by a BET specific surface area measurement method known in the relevant technical field, such as the method according to ISO 9277:2010.

[0094] In this case, according to one embodiment of the invention, the area of ​​particle B covered by particle A relative to the entire external area of ​​particle B can be, for example, more than 20%, specifically 20% to 90%, preferably 20% to 80%, 30% to 70%, or 40% to 50%. In one embodiment of the invention, when the entire external area of ​​particle B is covered by particle A, for example, when the area of ​​particle B covered by particle A is 100%, the electrolyte cannot easily move in and out of the positive electrode active material during battery assembly, and it can slow down the kinetics of the electrochemical reaction during battery operation. In one aspect, when the area of ​​particle B covered by particle A is within the above-mentioned range, it is advantageous to provide a novel positive electrode active material with significantly improved sulfur loading and catalytic activity, but the invention is not limited thereto.

[0095] According to one embodiment of the present invention, the weight ratio of particle A to particle B in the positive electrode active material can be, for example, 50:50 to 1:99, 40:60 to 5:95, 30:70 to 5:95, 20:80 to 5:95, or 7.5:92.5, but is not limited thereto. When the weight ratio of particle A to particle B is within the above range, the coverage area of ​​particle A over particle B satisfies the above range, and can be beneficial to improving the activity of the positive electrode active material and the performance of the battery using it, but the present invention is not limited thereto.

[0096] In one embodiment of the invention, the porosity of particle A can be greater than that of particle B. In other words, the total pore volume of particle A can be greater than that of particle B. Because particles A and B comprise porous carbon material with external and internal pores, a predetermined porosity can be ensured. As described above, the pores of particle B can be surrounded by sulfur (S) and / or sulfur can be loaded into the pores of particle B, while particle A can have open pores, thereby allowing the porosity of particle A to be greater than that of particle B. The porosity and / or pore volume of particles A and / or particle B can be measured by methods known in the relevant art according to ISO 15901:2019, but the measurement methods are not limited thereto.

[0097] In one embodiment of the invention, the specific surface area of ​​particle A can be greater than that of particle B. As described above, at least a portion of the outer surface of particle B can be covered by particle A, and the pores of particle B can be surrounded by sulfur (S) and / or sulfur can be loaded into the pores of particle B, while particle A can have open pores, thereby allowing the specific surface area of ​​particle A to be greater than that of particle B. Because the specific surface area of ​​particle A surrounding particle B is greater than that of particle B, lithium polysulfides that can migrate from particle B can be adsorbed onto particle A, and the larger specific surface area of ​​particle A can facilitate reactivity.

[0098] In this invention, the specific surface area can be measured, for example, by the BET method, specifically by calculating the amount of nitrogen adsorbed by the BEL JapanBELSORP mini II at liquid nitrogen temperature (77K), but the measurement method is not limited to this.

[0099] In one embodiment of the invention, as described above, particle A is a catalyst particle contained in or on at least one of the outer surface of the first porous carbon material or the surface inside the pores of the first porous carbon material. Specifically, the catalyst particle can be adsorbed onto the outer surface of particle A.

[0100] In this case, according to one embodiment of the invention, particle A and particle B can contact each other at at least one location where the catalyst particles contained in particle A are present. In other words, particle A and particle B can be anchored to each other by the catalyst particles. Alternatively, particle A can be anchored to the surface of particle B by the catalyst particles. That is, the connection between particle A and particle B can be made via the catalyst particles. At least one particle A and at least one particle B can be anchored to each other by at least one catalyst particle.

[0101] In one embodiment of the invention, in the positive electrode active material, particle A can be fused with particle B. For example, as described above, in the positive electrode active material, particle A can be fused with particle B such that particle A covers at least a portion of the surface of particle B. In one embodiment of the invention, particle A can be fused with particle B such that particle A is at least partially disposed between particles B.

[0102] In one embodiment of the invention, in the positive electrode active material, particle A can fill the gap between particles B. For example, in the positive electrode active material, particle A can fill the gap between particles B while covering the surfaces of at least two particles B spaced at a predetermined distance. In one embodiment of the invention, the gap can refer to a distance of at least 10% of the diameter of the smaller particle B, and this distance can refer to, for example, the shortest distance between two opposing surfaces of particle B.

[0103] The above-mentioned types of positive electrode active materials can increase the sulfur loading and improve the catalytic activity of the supported catalyst particles, thereby improving the performance of batteries using them, especially lithium-sulfur batteries.

[0104] In one embodiment of the invention, the positive electrode active material can be in a fully charged state. In this invention, "fully charged state" means a state of charge of at least 90%, for example, at least 99% or 100%. Specifically, lithium-sulfur batteries containing positive electrode active materials involve sulfur oxidation / reduction reactions depending on the charge / discharge state, and experience sulfur content loss relative to the initial sulfur content during repeated charge / discharge cycles. Therefore, a positive electrode active material having the above-described form according to one embodiment of the invention can be seen in a fully charged state of the positive electrode active material, and the fully charged state of the positive electrode active material can, for example, refer to a state where the sulfur content, based on the initial amount of sulfur loaded in the positive electrode active material or the amount of sulfur in at least a reversible state, is at least 90%, for example, at least 99% or 100%, but the invention is not limited thereto.

[0105] In one embodiment of the invention, the positive electrode active material may contain sulfur (S8) in an amount of, for example, 60% to 90% by weight, based on the total weight of the first porous carbon material and the second porous carbon material. Specifically, the weight of sulfur (S8) may be 65% to 90% by weight, 70% to 85% by weight, 75% to 80% by weight, or 65% to 75% by weight, based on the total weight of the first porous carbon material and the second porous carbon material.

[0106] In one embodiment of the invention, the first porous carbon material, which is at least partially crystalline, and the second porous carbon material, which is at least partially crystalline, may be different from each other.

[0107] In one embodiment of the invention, the first porous carbon material, which is at least partially crystalline, and the second porous carbon material, which is at least partially crystalline, may be the same.

[0108] In one embodiment of the present invention, for example, the first porous carbon material and the second porous carbon material may each be independently selected from at least one of the following: carbon nanotubes (CNT), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, or fullerene.

[0109] In one embodiment of the present invention, the first porous carbon material and the second porous carbon material can each be independently selected from carbon nanotubes and reduced graphene oxide. In another embodiment of the present invention, the first porous carbon material can be independently selected from carbon nanotubes and reduced graphene oxide, and the second porous carbon material can be carbon nanotubes.

[0110] In one embodiment of the invention, carbon nanotubes can be classified as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) based on the number of carbon atom layers in their structure. In one embodiment of the invention, when the first porous carbon material and the second porous carbon material each optionally contain carbon nanotubes, the carbon nanotubes may contain at least one of single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs).

[0111] In another embodiment of the invention, carbon nanotubes can exist in such a manner that two or more carbon nanotubes are in close contact and entangled with each other by their adhesive strength. In particular, in one embodiment of the invention, carbon nanotubes can be provided in the form of a carbon nanotube dispersion in which carbon nanotubes are dispersed as single strands in a dispersion medium, and can be provided in the form of aggregates of carbon nanotubes with secondary or primary structures.

[0112] In this regard, when the first porous carbon material and the second porous carbon material each optionally comprise carbon nanotubes, the carbon nanotubes may each comprise at least one of bundled secondary structures or entangled secondary structures. In one embodiment of the 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.

[0113] The bundle-type secondary structure of carbon nanotubes is an aggregate of primary structures oriented along the length of the carbon nanotubes by the bonding strength between carbon atoms. Each primary structure is a single strand of carbon nanotube and can be called a bundle-type carbon nanotube (bundle-type CNT).

[0114] Figure 3 The image shown is an SEM image of an example of a bundle-type CNT.

[0115] The entangled secondary structure of carbon nanotubes is a random entanglement and aggregation of primary structures in a spherical shape. Each primary structure is a single strand of carbon nanotube, and can be called entangled carbon nanotubes (entangled CNTs). Compared with primary carbon nanotubes, entangled CNTs have improved porosity due to the interstitial volume formed by the entanglement of primary carbon nanotubes.

[0116] Figure 4 The image shown is a SEM image of an instance of tangled CNTs.

[0117] When reference Figure 3 and Figure 4 When comparing the morphologies of bundled CNT instances and tangled CNT instances, it can be seen that bundled CNTs are closer to a planar shape, while tangled CNTs are closer to a spherical shape. Therefore, the sphericity of tangled CNT instances can be higher than that of bundled CNT instances.

[0118] In one embodiment of the present invention, the first porous carbon material supporting the catalyst particles may comprise planar carbon material to improve the specific surface area of ​​particle A. For example, when the first porous carbon material comprises carbon nanotubes, it is preferable that the first porous carbon material comprises bundled carbon nanotubes, but the present invention is not limited thereto. Furthermore, when the first porous carbon material comprises graphene-like materials, it is preferable that the first porous carbon material comprises reduced graphene oxide, but the present invention is not limited thereto.

[0119] In one embodiment of the invention, the sulfur-loaded second porous carbon material may contain carbon nanotubes to improve the sulfur content in the positive electrode active material. For example, in the case where the second porous carbon material contains carbon nanotubes, specifically, the second porous carbon material may contain at least one of bundled CNTs or entangled CNTs, more specifically, it may contain entangled CNTs to improve the area covered by particle A, but the invention is not limited thereto.

[0120] In one embodiment of the invention, the first porous carbon material and the second porous carbon material may each contain micropores in their outer surface and interior, and the average diameter of the micropores may be in the range of, for example, 1 nm to 200 nm, such as 1 nm to 100 nm, 10 nm to 80 nm, or 20 nm to 50 nm. The average diameter of the pores can be measured according to ISO 15901:2019, as known in the relevant art, but is not limited thereto. This average diameter may be the D50 diameter, and the D50 diameter refers to the diameter at 50% of the particles in the cumulative particle size distribution.

[0121] Furthermore, in one embodiment of the invention, the porosity (or void ratio) of the first porous carbon material and the second porous carbon material can be in the range of 10% to 90% of the total volume of their respective porous carbon materials. The porosity of the porous carbon material can be measured by a method known in the relevant art according to ISO 15901:2019, but the measurement method is not limited thereto.

[0122] In one embodiment of the present invention, the pore volume of the porous carbon material can be, for example, 1 cm³. 3 / g to 20 cm 3 / g or 1 cm 3 / g to 10 cm 3 / g. For example, the pore volume can be a value calculated and measured by N2 isotherm analysis obtained based on liquid nitrogen adsorption.

[0123] In one embodiment of the present invention, for example, the specific surface area of ​​the first porous carbon material and the second porous carbon material can each be 100 to 2000 m². 2 / g, 300 to 2000 m 2 / g, 400 to 1800 m 2 / g, 450 to 1500 m 2 / g or 500 to 1200 m 2 / g. Specific surface area can be measured by the BET method according to ISO 15901:2019, which is known in the relevant technical field, but is not limited to this.

[0124] In one embodiment of the invention, the catalyst particles are not limited to a specific type and may include any catalyst particles that promote lithium-sulfur battery kinetics.

[0125] In one embodiment of the invention, the catalyst particles may be catalytically active for the oxidation and reduction reactions of at least one of the following: sulfur (S8) contained in particle B, and lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 2≤x≤8), or disulfide compounds generated by the oxidation / reduction of sulfur during lithium-sulfur battery operation.

[0126] In another embodiment of the invention, the catalyst particles may comprise vanadium nitride.

[0127] In one embodiment of the invention, the catalyst particles may contain cobalt (Co) or iron (Fe).

[0128] In one embodiment of the invention, the content of catalyst particles in particle A can be 10 to 30% by weight, for example, 20% by weight, based on the total weight of particle A. The amount of catalyst particles can be measured using a thermogravimetric analyzer (TGA).

[0129] In one embodiment of the invention, the catalyst particles may be metal composite particles. The metal composite particles may contain a core comprising a metal and a carbon coating coated on at least a portion of the surface of the core, the carbon coating being, for example, a crystalline carbon coating. In the catalyst particles, the thickness of the carbon coating is related to the average particle size D of the core. 50 The ratio can be 10% to 20%, for example 15%, but the present invention is not limited thereto.

[0130] In one embodiment of the invention, particle A may be doped with a heteroelement. Specifically, the first porous carbon material and / or carbon coating may be doped with a heteroelement. The heteroelement may independently include one or more elements selected from nitrogen, sulfur, and oxygen, and may include, for example, nitrogen. Specifically, the heteroelement used in the doping may be derived from the precursor used when introducing the carbon coating, but the invention is not limited thereto.

[0131] In one embodiment of the invention, the catalyst particles may, for example, have an average particle size (D) of 1 nm to 200 nm. 50 However, the present invention is not limited thereto. In this invention, particle size can be measured using known measurement methods, and the measurement methods are not limited to any particular method. For example, particle size can be measured using scanning electron microscopy (SEM), field emission scanning electron microscopy, or laser diffraction. Measurements using laser diffraction can be performed, for example, using a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000). Average particle size (D...) 50 () refers to the particle size at 50% of the particles in the cumulative volumetric particle size distribution.

[0132] In one embodiment of the present invention, when manufacturing the positive electrode active material, at least a portion of each of the first porous carbon material and the second porous carbon material can be crystallized due to a heat treatment process. Specifically, the first porous carbon material and the second porous carbon material can each be integrally crystallized.

[0133] In this invention, when a material such as a porous carbon material is at least partially crystallized, this can be observed by at least one peak in the material's XRD spectrum. In the material's XRD spectrum, for example, when the signal-to-noise ratio is greater than 1, such as 1.5:1, 2:1, 5:1, or 10:1, it can be said that the material is at least partially crystallized.

[0134] Therefore, in one embodiment of the present invention, the elasticity of the first porous carbon material and the second porous carbon material can be higher than that of the amorphous carbon material.

[0135] Furthermore, in one embodiment of the present invention, the electrical conductivity of the first porous carbon material and the second porous carbon material can be higher than that of the amorphous carbon material.

[0136] In this invention, the amorphous carbon material can be, for example, as described by Liu et al. Nanoscale Carbon materials disclosed in Volume 10, 2018, pp. 5246-5253.

[0137] In this invention, the degree of crystallinity of porous carbon materials can be measured, for example, by X-ray diffraction (XRD) analysis. "XRD" is the analysis of diffraction produced by the scattering and interference of X-rays caused by electrons surrounding atoms when a sample is irradiated with X-rays (Bragg condition: 2dsinθ = nλ: the distance between two planes is d, the angle between the formed plane and the X-ray is θ, an arbitrary integer is n, and the wavelength of the X-ray is λ), and is used to determine the phase, amount, crystal size, or crystallinity of the components. For example, when at least one independent peak appears in the XRD spectrum, it can be seen that at least a portion is crystalline. In this case, the measured signal is more than 1, 1.5, 2, 5, or 10 times stronger than the noise in the independent peak.

[0138] In one embodiment of the present invention, the positive electrode active material I D / I G The value can be equal to or less than 2.0. For example, the Raman peak intensity ratio (I0) D / I G <2.0.

[0139] The Raman peak intensity ratio can be obtained from the I in the spectrum of the positive electrode active material obtained by Raman spectroscopy. G and I D The value is used for measurement. In the obtained spectrum, I GThis refers to the peak in the crystalline region (G peak, 1573 / cm), and I D The peak is in the amorphous region (D peak, 1309 / cm). Therefore, in this case, I G / I D The smaller the ratio, the lower the crystallinity.

[0140] According to another aspect of the present invention, a positive electrode for a lithium-sulfur battery is provided, the positive electrode comprising a positive electrode active material.

[0141] In addition to the positive electrode active material, the positive electrode for lithium-sulfur batteries may further include a binder. The binder is not limited to a specific type and may include any binder that can be used in the positive electrode of a lithium-sulfur battery.

[0142] The adhesive is a component that helps to bond the positive electrode active material and the conductive material and helps to bind to the current collector, and may include at least one of the following: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(meth)acrylate, poly(ethyl)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, nitrile rubber, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butadiene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose, but is not necessarily limited thereto.

[0143] In one embodiment of the invention, the adhesive may comprise, for example, polyvinylidene fluoride (PVDF), specifically PVDF dispersed in N-methyl-2-pyrrolidone (NMP).

[0144] In another embodiment of the invention, the adhesive may comprise an aqueous adhesive, such as styrene-butadiene rubber (SBR), specifically an aqueous adhesive dispersed in an aqueous solvent such as water.

[0145] In one embodiment of the invention, the positive electrode for a lithium-sulfur battery may comprise a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the current collector and comprising a positive electrode active material and a binder. In this case, the positive electrode current collector is not limited to a specific type and may include a current collector with high conductivity that will not cause any chemical changes to the corresponding battery.

[0146] In another embodiment of the invention, in addition to the positive electrode active material and the binder, the positive electrode for lithium-sulfur batteries may further comprise conductive materials and additives. In this case, the binder, conductive material, and additives may comprise corresponding substances of conventional types, and their detailed description is omitted.

[0147] According to another aspect of the present invention, a lithium-sulfur battery is a lithium-sulfur battery comprising the above-mentioned positive electrode active material.

[0148] A lithium-sulfur battery includes, for example, a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte, wherein the positive electrode contains the aforementioned positive electrode active material.

[0149] In one embodiment of the invention, the negative electrode and separator are not limited to a particular type and can include negative electrodes and separators used in lithium-sulfur batteries without hindering the objectives achieved by the invention. The negative electrode may contain, for example, metallic lithium.

[0150] In one embodiment of the invention, the separator is not limited to a specific type and may include commonly used separators for lithium-sulfur batteries.

[0151] In one embodiment of the invention, the membrane may comprise a porous polyolefin substrate, and, if necessary, may further comprise inorganic particles on at least one surface of the porous polyolefin substrate. Furthermore, if necessary, the membrane may further comprise an adhesive to bind the inorganic particles.

[0152] In another embodiment of the invention, the separator may be a membrane-like electrolyte membrane containing a solid electrolyte, and may further include an adhesive, if necessary, to bind the solid electrolyte. The solid electrolyte is not limited to a specific type and may include at least one of the solid electrolytes commonly used in lithium-sulfur batteries, such as polymeric solid electrolytes or inorganic solid electrolytes.

[0153] In one embodiment of the invention, the electrolyte comprises an electrolyte commonly used in lithium-sulfur batteries. The electrolyte may contain lithium salts and non-aqueous solvents.

[0154] Lithium salts are not limited to a specific type and may include lithium salts commonly used in the electrolytes of lithium-sulfur batteries. Lithium salts may include at least one of the following, for example: LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, or lithium imide, but not limited to these.

[0155] The non-aqueous solvent is not limited to a specific type and may include non-aqueous solvents commonly used in the electrolytes of lithium-sulfur batteries. The non-aqueous solvent may include, but is not limited to, at least one of cyclic carbonate solvents, linear carbonate solvents, ester solvents, or ketone solvents.

[0156] In one embodiment of the invention, the electrolyte may comprise a two-component system of (CF3SO2)2NLi as a lithium salt and dioxolane (DOL) / dimethoxyethane (DME) as a non-aqueous solvent. For example, the electrolyte may further comprise conventional additives such as LiNO3.

[0157] In one embodiment of the invention, the shape of the lithium-sulfur battery is not limited to a specific shape and may include, for example, coin-shaped, cylindrical, pouch-shaped, or prismatic shapes. Furthermore, the lithium-sulfur battery can be used as a battery cell for powering small devices and as a unit battery in medium to large-sized battery modules comprising multiple battery cells, and its applications are not limited to specific application ranges.

[0158] The following will describe in detail, by way of examples, a method for manufacturing a positive electrode active material according to an embodiment of the present invention. However, the following embodiments are provided by way of illustration, and the scope of the invention is not limited thereto.

[0159] [Manufacturing of positive electrode active materials]

[0160] The positive electrode active material is manufactured by the following method, the positive electrode active material comprising: a) particle A, said particle A comprising at least partially crystalline first porous carbon material and catalyst particles deposited on the first porous carbon material; and b) particle B, said particle B comprising at least partially crystalline second porous carbon material and sulfur supported in the second porous carbon material, wherein particle A and particle B have different morphologies.

[0161] In one embodiment of the present invention, the positive electrode active material can be formed by sequentially or simultaneously mixing a first porous carbon material, a second porous carbon material, catalyst particles, and a sulfur compound, followed by heat treatment. The positive electrode active material manufactured by heat treatment may contain the first and second porous carbon materials, at least a portion of which are crystalline as described above, but the present invention is not limited thereto.

[0162] Figure 3 SEM images of bundled CNTs used as raw materials are shown.

[0163] Figure 4 SEM images of entangled CNTs used as raw materials are shown.

[0164] Figure 5 The image shows a SEM image of reduced graphene oxide (rGO) used as a raw material.

[0165] Example 1

[0166] 142 mg of ferric chloride hexahydrate (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 were then added. Figure 3 The mixture was stirred at room temperature for 30 minutes to prepare a dispersion. Subsequently, 960 ppm of Trizma base (tris(hydroxymethyl)aminomethane (TRIS)) was added to the prepared dispersion to maintain a pH of 8.5. The resulting dispersion was stirred at room temperature for 24 hours, then 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 furnace under an argon atmosphere and heat-treated at 800 °C for 2 hours (heating rate 1 °C / min) to obtain an average particle size (D). 50 Particle A is 35 μm in size.

[0167] The obtained particle A comprises: a bundled CNT as a porous carbon substrate; transition metal composite particles disposed in at least one of the outer surface or the interior surface of the pores of the bundled CNT, and containing a core containing iron particles and a crystalline carbon coating coated on at least a portion of the surface of the core; and nitrogen doping. In this case, the thickness of the carbon coating is related to the average particle size D of the transition metal composite particles. 50 The ratio is 15%.

[0168] Subsequently, entangled CNTs ( Figure 4 Sulfur (S8) and sulfur (S8) were mixed in a weight ratio of 25:75 and heat-treated at 155°C for 1 hour by melt diffusion to prepare sulfur-carbon composite material (particle B).

[0169] Particles A and B are mixed in a weight ratio of 7.5:92.5, dispersed in water, and dried to obtain a positive electrode active material having a structure in which particles A and B with different morphologies are in contact with each other.

[0170] Example 2

[0171] 1.6 g of reduced graphene oxide (rGO) Figure 524 g of dicyandiamide and 0.8 g of ammonium metavanadate, along with 0.2 g of glucose, were mixed in 500 mL of a solvent containing ethanol and water in a 1:1 volume ratio. The mixture was dissolved and dispersed by ultrasonic and magnetic stirring. Subsequently, the solvent, except for the vanadium nitride precursor, adsorbed on the surface of the carbon nanotubes was removed by vacuum filtration. The nanotubes were then dried in an oven at 80°C for 12 hours. Following this, they were heat-treated in a tube furnace under an inert atmosphere at 600°C for 3 hours and then at 800°C for 2 hours to obtain a carbon composite material (particle A), wherein vanadium nitride particles, acting as catalyst particles, were deposited on the surface of reduced graphene oxide. Figure 2 The SEM image of the obtained particle A is shown. In this case, based on 100 parts by weight of the obtained particle A, the content of vanadium nitride particles is 20 parts by weight. The amount of vanadium nitride particles was measured using a thermogravimetric analyzer (TGA).

[0172] Subsequently, entangled CNTs ( Figure 4 Sulfur (S8) and sulfur (S8) were mixed in a weight ratio of 25:75 to prepare sulfur-carbon composite material (particle B).

[0173] Particles A and B are mixed in a weight ratio of 7.5:92.5, dispersed in water, and dried to obtain a positive electrode active material having a structure in which particles A and B with different morphologies are in contact with each other.

[0174] Figure 1 The obtained SEM images of the positive electrode active material are shown, and... Figure 1 In the image analysis method based on energy-dispersive X-ray spectroscopy (EDS), the regions where particles A and B are set are represented.

[0175] Example 3

[0176] When manufacturing particle A, the same amount of beam-type CNTs ( Figure 3 Particle A is obtained by replacing reduced graphene oxide. Figure 6 The obtained SEM image of particle A is displayed.

[0177] Subsequently, the positive electrode active material was obtained using the same method as in Example 2.

[0178] Comparative Example 1

[0179] In addition to replacing particle A with the same amount of beam-type CNTs, Figure 3 In addition, the positive electrode active material is manufactured using the same method as in Example 1.

[0180] Specifically, entangled CNTs ( Figure 4 Sulfur (S8) and sulfur (S8) were mixed in a weight ratio of 25:75 to prepare sulfur-carbon composite material (particle B).

[0181] Subsequently, the bundled CNTs and particles B were mixed at a weight ratio of 7.5:92.5, dispersed in water, and dried to obtain a positive electrode active material having a structure in which the bundled CNTs and particles B are in contact with each other.

[0182] Comparative Example 2

[0183] Particle A was prepared using the same method as in Example 1.

[0184] The prepared particles A, entangled CNTs and sulfur (S8) were mixed in a weight ratio of 5:20:75 and heat-treated at 155°C for 1 hour by melt diffusion method to obtain a positive electrode active material in which sulfur is loaded in particles A and entangled CNTs.

[0185] [Battery Performance Evaluation]

[0186] To evaluate the performance of lithium-sulfur batteries using the positive electrode active materials manufactured in Example 1 and Comparative Examples 1 and 2, lithium-sulfur coin-type batteries were prepared as follows.

[0187] Manufacturing batteries

[0188] First, to fabricate the working electrode, the various positive electrode active materials prepared as described above were mixed with polyvinylidene fluoride (PVDF) as a binder at a weight ratio of 9:1 using N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was coated onto a carbon-coated Al foil and dried at 60°C for 8 hours. Subsequently, the electrode was rolled and cut into coin shapes to fabricate the positive electrode.

[0189] Subsequently, the positive and negative electrodes, along with the electrolyte, were placed together in a casing, and a separator was inserted between the positive and negative electrodes to manufacture the battery. For the positive electrode, the aforementioned positive electrode was prepared, and for the separator, a porous polypropylene membrane (Celgard 2400, Welcos Ltd.) was prepared. For each reference and counter electrode, lithium metal (200 μm thick) was prepared. The electrolyte consisted of a 1:1 volume ratio of 1,3-dioxolane and dimethoxymethane (DOL / DME) (PANAX E-TEC Co., Korea), 1.0 M of bis(trifluoromethane)sulfonamide lithium salt (LiTFSI) as the electrolyte, and 2.0 wt% LiNO3 (99.99%, metal-based, Sigma-Aldrich) as an additive.

[0190] The sulfur loading in each cathode was 2.25 mg / cm³. 2 Furthermore, the battery's El / S ratio is 10 μL / mg.

[0191] Discharge capacity and lifetime evaluation

[0192] Each battery manufactured as described above was subjected to three charge-discharge cycles at a current density of 0.1 C and a voltage range of 1.8 V to 2.5 V, three charge-discharge cycles at a current density of 0.2 C, and then 20 charge-discharge cycles at a current density of 0.5 C. All evaluations were conducted using a PESCO5-0.1 instrument from PNE Solution in a constant temperature chamber at 25°C.

[0193] In this case, the attached figure ( Figure 7 and Figure 8 The figure shows the results of capacity-voltage measurements after 3 charge / discharge cycles at a current density of 0.1C, and the figure itself is shown in the figure. Figure 9 and Figure 10 The results show the discharge capacity measured after 20 charge / discharge cycles.

[0194] First, refer to Figure 7 and Figure 9 The figures confirm that, compared with the battery using the positive electrode active material according to Example 1, which uses the positive electrode active material without Fe catalyst particles according to Comparative Example 1, the battery using the positive electrode active material according to Example 1 has better discharge capacity and lifespan characteristics.

[0195] Conversely, refer to Figure 8 and Figure 10 The figure confirms that, compared with the battery using the positive electrode active material according to Comparative Example 1 in which no catalyst particles are loaded, the battery using the positive electrode active material according to Comparative Example 2 in which sulfur is loaded into particle A loaded with Fe catalyst particles has lower performance at 0.1C charge / discharge, 0.2C charge / discharge and 0.5C charge / discharge.

[0196] It was thus discovered that the performance of lithium-sulfur batteries can be improved by using the positive electrode active material containing particles A and B with different morphologies according to the present invention.

Claims

1. A positive electrode active material, said positive electrode active material comprising: a) Particle A, said particle A comprising: a first porous carbon material, the first porous carbon material being at least partially crystalline; and catalyst particles deposited on the first porous carbon material; and b) Particle B, said particle B comprising: a second porous carbon material, the second porous carbon material being at least partially crystalline; and sulfur supported in the second porous carbon material. in, Particle A and particle B have different shapes. Wherein, the sphericity of particle B is greater than that of particle A; The sphericity is defined according to the following formula 1: [Formula 1] Where Ψ represents sphericity, V p Represents the volume of the particle, and A p This represents the surface area of ​​a particle.

2. The positive electrode active material according to claim 1, wherein, The first porous carbon material and / or particle A are substantially sulfur-free.

3. The positive electrode active material according to claim 1, wherein, The second porous carbon material and / or particle B are substantially free of catalyst particles.

4. The positive electrode active material according to claim 1, wherein, The catalyst particles are attached to at least one of the outer surface or the inner surface of the pores of the first porous carbon material.

5. The positive electrode active material according to claim 1, wherein, The weight ratio of the second porous carbon material to the sulfur is 10:90 to 90:

10.

6. The positive electrode active material according to claim 1, wherein, The sulfur is contained at at least one location on the outer surface or inside the pores of the second porous carbon material.

7. The positive electrode active material according to claim 1, wherein, The sulfur includes: inorganic sulfur S8; lithium sulfide Li2S; lithium polysulfide Li2Sx, wherein 2≤x≤8; disulfide compounds; or mixtures thereof.

8. The positive electrode active material according to claim 1, wherein, The particle A has a broccoli-like shape, a cauliflower-like shape, or a spiky shape. The particle B has a potato-shaped, spherical, or elliptical shape.

9. The positive electrode active material according to claim 1, wherein, The size of particle A is from 10 µm to 100 µm. The size of particle B is 10 µm to 100 µm.

10. The positive electrode active material according to claim 1, wherein, More than 50% of the particle A exists on the surface of the particle B.

11. The positive electrode active material according to claim 1, wherein, At least a portion of the surface of particle B is covered by particle A, and Wherein, the area of ​​particle B covered by particle A is 20% to 50% of the total external area of ​​particle B.

12. The positive electrode active material according to claim 1, wherein, At least a portion of the surface of particle B is covered by particle A, and Wherein, the area of ​​particle B covered by particle A is 20% to 90% of the total external area of ​​particle B.

13. The positive electrode active material according to claim 1, wherein, The weight ratio of particle A to particle B is from 50:50 to 1:

99.

14. The positive electrode active material according to claim 1, wherein, The porosity of particle A is greater than that of particle B.

15. The positive electrode active material according to claim 1, wherein, The specific surface area of ​​particle A is greater than that of particle B.

16. The positive electrode active material according to claim 1, wherein, Particle A and particle B are in contact with each other at at least one location where the catalyst particle contained in particle A is present.

17. The positive electrode active material according to claim 1, wherein, Particle A is anchored to the surface of particle B by the catalyst particle.

18. The positive electrode active material according to claim 1, wherein, Particle A and particle B are fused together.

19. The positive electrode active material according to claim 1, wherein, Particle A fills the gap between particles B.

20. The positive electrode active material according to claim 1, wherein, The positive electrode active material is in a fully charged state.

21. The positive electrode active material according to claim 1, wherein, Based on the total weight of the first porous carbon material and the second porous carbon material, the weight of sulfur is 60% to 90% by weight.

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

23. 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.

24. The positive electrode active material according to claim 1, wherein, The first porous carbon material and the second porous carbon material each independently comprise at least one of bundled carbon nanotubes (CNTs), entangled CNTs, or reduced graphene oxide (rGO).

25. The positive electrode active material according to claim 1, wherein, The first porous carbon material and the second porous carbon material are each independently selected from at least one of the following: carbon nanotubes (CNT), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, or fullerene.

26. The positive electrode active material according to claim 1, wherein, The first porous carbon material and the second porous carbon material each contain micropores in their outer surface and interior, and the average diameter of the micropores is in the range of 1 nm to 200 nm.

27. The positive electrode active material according to claim 1, wherein, The porosity of the first porous carbon material and the second porous carbon material is in the range of 10% to 90% of the total volume of their respective porous carbon materials.

28. The positive electrode active material according to claim 1, wherein, The pore volume of both the first porous carbon material and the second porous carbon material is 1 cm³. 3 / g to 20 cm 3 / g.

29. The positive electrode active material according to claim 1, wherein, The specific surface area of ​​the first porous carbon material and the second porous carbon material is 100 m². 2 / g to 2000 m 2 / g.

30. The positive electrode active material according to claim 1, wherein, The catalyst particles contain vanadium nitride.

31. The positive electrode active material according to claim 1, wherein, The catalyst particles contain at least one of cobalt (Co) or iron (Fe).

32. The positive electrode active material according to claim 1, wherein, The catalyst particles are catalytically active for the oxidation and reduction reactions of sulfur S8 contained in particles B and for at least one of lithium sulfide Li2S, lithium polysulfide Li2Sx, or disulfide compounds generated by the oxidation / reduction of sulfur during lithium-sulfur battery operation, wherein 2≤x≤8.

33. The positive electrode active material according to claim 1, wherein, Based on the total weight of particle A, the content of the catalyst particles in particle A is from 10% to 30% by weight.

34. The positive electrode active material according to claim 1, wherein, The catalyst particles are metal composite particles, which contain a metal core and a carbon coating on at least a portion of the surface of the core.

35. The positive electrode active material according to claim 34, wherein, In the catalyst particles, the thickness of the carbon coating is related to the average particle size D of the core. 50 The ratio is 10% to 20%.

36. The positive electrode active material according to claim 1, wherein, The particle A is doped with a heterogeneous element, which includes one or more elements selected from nitrogen, sulfur, and oxygen.

37. The positive electrode active material according to claim 1, wherein, The catalyst particles have an average particle size D of 1 nm to 200 nm. 50 .

38. The positive electrode active material according to claim 1, wherein, Both the first porous carbon material and the second porous carbon material are integrally crystalline.

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

40. The positive electrode active material according to claim 1, wherein, The electrical conductivity of the first porous carbon material and the second porous carbon material is greater than that of the amorphous carbon material.

41. The positive electrode active material according to claim 1, wherein, The positive electrode active material I D / I G The value is equal to or less than 2.

0.

42. A lithium-sulfur battery, the lithium-sulfur battery comprising: Positive electrode, negative electrode, a membrane between the positive and negative electrodes; and a non-aqueous electrolyte. in, The positive electrode comprises the positive electrode active material according to any one of claims 1 to 41.

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