Silica-coated sulfur-carbon composite and lithium-sulfur battery comprising same

Abstract

To provide a lithium sulfur battery having improved performance and uniform quality, and to provide an electrode having improved performance, uniform quality and few defects for use in the lithium sulfur battery, thereby increasing production yield.SOLUTION: The present invention relates to a silica-coated sulfur-carbon composite, and the silica-coated sulfur-carbon composite includes a sulfur-carbon composite and silica particles coated on at least a part of the surface of the sulfur-carbon composite. The silica-coated sulfur-carbon composite according to the present invention may be used as a positive electrode active material of a lithium sulfur secondary battery as a non-limiting example.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sulfur-carbon composite and a lithium-sulfur battery including the same.

[0002] This application claims priority from Korean Patent Application No. 2022-0065671 filed on May 27, 2022, and Korean Patent Application No. 2022-0135073 filed on October 19, 2022, the entire contents of which are incorporated herein by reference in their entirety in their specification and drawings. [Background technology]

[0003] Secondary batteries are used as large-capacity energy storage batteries and as high-performance energy sources for portable electronic devices such as mobile phones, video cameras, and laptop computers.

[0004] Lithium ion secondary batteries as secondary batteries have advantages such as higher energy density and larger capacity per area than nickel-manganese batteries or nickel-cadmium batteries, but have disadvantages such as reduced stability due to overheating and low output characteristics.

[0005] 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.

[0006] 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.

[0007] The sulfur used in lithium-sulfur batteries has an electrical conductivity of 5×10 -30 Because sulfur-containing materials are non-conductors with a conductivity of 0.5 S / cm, electrons generated during electrochemical reactions are difficult to move. Therefore, sulfur-containing materials are combined with conductive materials such as carbon, which can provide chemical reaction sites, to form sulfur-carbon composites, which are then used as cathode active materials.

[0008] Despite the above advantages, when a sulfur-containing material is used as an active material, the utilization rate of sulfur involved in the electrochemical oxidation-reduction reaction in the battery is low compared to the total amount of sulfur added as a raw material, resulting in a problem that the actual battery capacity is lower than the theoretical capacity.

[0009] Therefore, when considering the theoretical capacity of a lithium-sulfur battery containing a sulfur-containing material, the current situation is that the full potential has not yet been realized.

[0010] This problem can be caused by a variety of factors, such as the presence of sulfur aggregates due to uneven sulfur incorporation in the sulfur-carbon composite, or the sulfur-carbon composite itself being aggregated during electrode fabrication, resulting in inconsistent feeding.

[0011] For example, when manufacturing a lithium-sulfur battery using a dry electrode, a powdered sulfur-carbon composite is uniformly fed, thinly spread, and flattened with a blade to fabricate an electrode. However, if the sulfur-carbon composite has low fluidity, uniform feeding is difficult, resulting in significant variations in electrode loading and consequent electrode defects.

[0012] Therefore, in order to commercialize lithium-sulfur batteries with the above-mentioned excellent properties, it is necessary to improve the fluidity of the sulfur-carbon composite to solve the above-mentioned problems.

[0013] Therefore, when fabricating dry electrodes for lithium-sulfur batteries, it is necessary to uniformly stretch and flatten the sulfur-carbon composite to achieve uniform electrode loading and minimize electrode defects, for example, by using a blade. To achieve this, it is necessary to reduce the formation of agglomerates of the sulfur-carbon composite. Summary of the Invention [Problem to be solved by the invention]

[0014] Therefore, the problem to be solved by the present invention is to provide a lithium-sulfur battery that solves the above-mentioned problems and has improved performance and uniform quality, and an electrode for use therein that has improved performance, uniform quality, and fewer defects, thereby enabling an increase in production yield.

[0015] For this reason, efforts are being made to provide an electrode, for example, a positive electrode, which can be produced efficiently, can be loaded uniformly, and can minimize electrode defects.

[0016] To commercialize lithium-sulfur batteries with the above-mentioned excellent properties, it may be necessary to improve the fluidity of the sulfur-carbon composite to solve the above problems.

[0017] Therefore, one aspect of the present invention provides a sulfur-carbon composite with improved fluidity and a method for producing the same.

[0018] According to one aspect, the present invention provides a silica-coated sulfur-carbon composite having improved cohesion, and a method for producing the same.

[0019] In another aspect, the present invention seeks to provide a method for improving the surface roughness of a sulfur–carbon composite to improve the flowability of the silica-coated sulfur–carbon composite. [Means for solving the problem]

[0020] To solve the above problems, according to one aspect of the present invention, a silica-coated sulfur-carbon composite in the following embodiments is provided.

[0021] The silica-coated sulfur-carbon composite according to the first embodiment includes a sulfur-carbon composite and silica particles coated on at least a part of the surface of the sulfur-carbon composite.

[0022] According to the second embodiment, it can be the silica-coated sulfur-carbon composite according to the first embodiment, in which the angle of repose of the silica-coated sulfur-carbon composite is 32° or less.

[0023] According to the third embodiment, it can be the silica-coated sulfur-carbon composite according to the first or second embodiment, in which the average particle diameter (D 50 ) of the silica particles is 10 to 50 nm.

[0024] According to the fourth embodiment, it can be the silica-coated sulfur-carbon composite according to any one of the first to third embodiments, in which the silica particles are nanoparticles represented by the following formula 1.

[0025] [Formula 1] [SiO2] p [SiO(OH)2] 1-p In the above formula 1, p is a number such that 0 < p ≤ 1.

[0026] According to the fifth embodiment, it can be the silica-coated sulfur-carbon composite according to any one of the first to fourth embodiments, in which the thickness of the silica particles coated on at least a part of the surface of the silica-coated sulfur-carbon composite is 20 nm to 5 μm.

[0027] According to the sixth embodiment, it can be the silica-coated sulfur-carbon composite according to any one of the first to fifth embodiments, which has the characteristics of the following formula 2.

[0028]

number

[0029] In Equation 2, Mp is the mass of the silica particles; Mc is the mass of the sulfur-carbon complex; So is the area of ​​the region coated with the silica particles; St is the surface area of ​​the silica-coated sulfur-carbon composite.

[0030] According to a seventh aspect, the silica-coated sulfur-carbon composite may be the silica-coated sulfur-carbon composite according to any one of the first to sixth aspects, comprising the sulfur-carbon composite and the silica particles in a weight ratio of 99.9:0.1 to 80:20.

[0031] According to an eighth aspect, the average particle diameter (D 50 ) may be the silica-coated sulfur-carbon composite according to any one of the first to seventh embodiments, having a particle size of 20 μm to 50 μm.

[0032] According to a ninth aspect, the sulfur-carbon composite may be the silica-coated sulfur-carbon composite according to any one of the first to eighth aspects, comprising a porous carbon material and a sulfur-containing compound supported on at least a part of the internal and external surfaces of the pores of the porous carbon material.

[0033] According to a tenth aspect, the silica-coated sulfur-carbon composite according to any one of the first to ninth aspects may have an average diameter of pores present in the porous carbon material of 1 to 200 nm.

[0034] According to an eleventh aspect, the sulfur-containing compound is inorganic sulfur (S), lithium polysulfide (LiS, 1≦n≦8), carbon-sulfur polymer (CS), x) m (2.5≦x≦50, 2≦m) or a mixture thereof.

[0035] According to a twelfth aspect, the sulfur-carbon composite may be the silica-coated sulfur-carbon composite according to any one of the ninth to eleventh aspects, wherein the porous carbon material and the sulfur-containing compound are contained in a weight ratio of 1:9 to 5:5.

[0036] According to a thirteenth aspect, the maximum average particle size (D) of the sulfur-carbon composite with respect to the maximum thickness of the coating layer formed by the silica particles is 50 ) is 100:1 to 1000:1.

[0037] According to a fourteenth aspect, the silica-coated sulfur-carbon composite according to any one of the first to thirteenth aspects may comprise 0.01 to 20 wt % of the silica particles and 80 to 99.99 wt % of the sulfur-carbon composite, based on the total weight of the silica-coated sulfur-carbon composite.

[0038] According to a fifteenth aspect, the sulfur-carbon composite may be a silica-coated sulfur-carbon composite according to any one of the first to fourteenth aspects, in which 60% to 100% of the surface area of ​​the sulfur-carbon composite is coated with the silica particles.

[0039] According to another aspect of the present invention, there is provided a method for producing a silica-coated sulfur-carbon composite having the following embodiment:

[0040] A method for producing a silica-coated sulfur-carbon composite according to a sixteenth aspect includes a step of coating silica particles on at least a part of the surface of the sulfur-carbon composite.

[0041] According to a seventeenth aspect, the method for producing the silica-coated sulfur-carbon composites according to the sixteenth aspect may further include, before the coating step, a step of preparing the sulfur-carbon composites, wherein the step of preparing the sulfur-carbon composites includes a step of mixing a sulfur-containing compound and a porous carbon material.

[0042] According to an eighteenth aspect, the method for producing a silica-coated sulfur-carbon composite according to the sixteenth or seventeenth aspect may further include, after the coating step, separating the silica-coated sulfur-carbon composite.

[0043] According to a 19th aspect, the coating step may be the method for producing a silica-coated sulfur-carbon composite according to any one of the 16th to 18th aspects, which includes mixing the sulfur-carbon composite and the silica particles in a solid state.

[0044] According to a twentieth aspect, the coating step may be the method for producing a silica-coated sulfur-carbon composite according to any one of the sixteenth to nineteenth aspects, wherein the weight ratio of the sulfur-carbon composite to the silica particles is 99.9:0.1 to 80:20.

[0045] According to still another aspect of the present invention, there are provided a positive electrode active material, an electrode, and a lithium-sulfur battery having the following embodiments.

[0046] According to a twenty-first aspect, there is provided a positive electrode active material comprising the silica-coated sulfur-carbon composite according to any one of the first to fifteenth aspects.

[0047] According to a twenty-second aspect, there is provided an electrode comprising the silica-coated sulfur-carbon composite according to any one of the first to fifteenth aspects.

[0048] According to a twenty-third aspect, there is provided a lithium-sulfur battery including a positive electrode comprising the silica-coated sulfur-carbon composite according to any one of the first to fifteenth aspects, a negative electrode comprising a negative electrode active material, and an electrolyte. [Effects of the Invention]

[0049] The silica-coated sulfur-carbon composite according to one embodiment of the present invention has an improved surface fluidity. The increased fluidity of the sulfur-carbon composite reduces the aggregation of the silica-coated sulfur-carbon composite. As a result, the silica-coated sulfur-carbon composite can be uniformly coated on the electrode support, improving the battery performance.

[0050] Specifically, compared with conventional sulfur-carbon composites, which have a high surface roughness, the silica-coated sulfur-carbon composite according to one embodiment of the present invention includes silica particles coated on at least a portion of the surface of the sulfur-carbon composite. As a result, the silica particles are inserted into the surface of the sulfur-carbon composite, reducing the surface roughness of the sulfur-carbon composite, thereby providing the sulfur-carbon composite with excellent particle flowability. Therefore, the silica-coated sulfur-carbon composite according to one embodiment of the present invention reduces agglomeration and can be uniformly applied to an electrode support to produce an electrode with uniform loading.

[0051] In addition, an electrode, e.g., a positive electrode, manufactured using the silica-coated sulfur-carbon composite can be manufactured more efficiently due to the improved fluidity of the silica-coated sulfur-carbon composite, thereby improving the productivity of lithium-sulfur batteries.

[0052] 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]

[0053] [Figure 1] 1 shows scanning electron microscope (SEM) images of the sulfur–carbon composite according to Comparative Example 1 and the silica-coated sulfur–carbon composites according to Examples 1 and 2. The upper SEM image is an image with a magnification of 15,000, and the lower SEM image is an image with a magnification of 2,000. [Figure 2] FIG. 1 shows the measurement results of the angle of repose of the sulfur-carbon composite of Comparative Example 1 and the silica-coated sulfur-carbon composites of Examples 1 and 2 in the present specification. [Figure 3] 1 shows photographs confirming the flowability of the sulfur-carbon composite according to Comparative Example 1 and the silica-coated sulfur-carbon composites according to Examples 1 and 2. [Figure 4] FIG. 1 shows SEM images of the sulfur–carbon composite of Comparative Example 2, and the zinc oxide (ZnO)-coated sulfur–carbon composites of Comparative Examples 3 and 4. The upper SEM image is an image with a magnification of 10,000, and the lower SEM image is an image with a magnification of 2,000. [Figure 5] 1 shows the results of measuring the angle of repose of the sulfur-carbon composite according to Comparative Example 2, and the zinc oxide (ZnO)-coated sulfur-carbon composites according to Comparative Examples 3 and 4 in the present specification. DETAILED DESCRIPTION OF THE INVENTION

[0054] 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 mixed as necessary. Therefore, it should be understood that the present invention includes all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention.

[0055] Throughout this specification, when a certain component is described as "comprising" another component, this does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0056] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0057] As used herein, the term "composite" refers to a material in which two or more materials are combined to form physically and chemically different phases, thereby exhibiting more effective functions.

[0058] One aspect of the present invention provides a silica-coated sulfur-carbon composite that can be used as a support for a cathode active material in a cathode of a lithium-sulfur battery, as a cathode active material itself, or as a conductive material, although the use of the silica-coated sulfur-carbon composite according to one aspect of the present invention is not limited thereto.

[0059] Silica-coated sulfur-carbon composite A silica-coated sulfur-carbon composite according to one aspect of the present invention comprises a sulfur-carbon composite and silica particles coated on at least a portion of the surface of the sulfur-carbon composite.

[0060] According to one embodiment of the present invention, the sulfur–carbon composite may include a sulfur–carbon composite having an outer surface at least partially coated with the silica particles. Preferably, the entire outer surface of the sulfur–carbon composite may be coated with the silica particles.

[0061] In one aspect of the present invention, if the sulfur-carbon composite is coated with silica particles, the silica particles may not be distinguishable as particles by themselves, but a coating layer can be formed on the surface of the sulfur-carbon composite. At this time, the particle size of the sulfur-carbon composite is preferably larger than the particle size of one silica particle. Here, the particle size may mean the average particle size (D 50 ) in accordance with ISO 13320:2020 well-known in the art, but the method for measuring the particle size is not limited thereto.

[0062] In one aspect of the present invention, the silica particles can be nanoparticles having a chemical formula according to the following Chemical Formula 1.

[0063] [Formula 1] [SiO2] p [SiO(OH)2] 1-p In the above Formula 1, p is a number where 0 < p ≤ 1.

[0064] In one aspect of the present invention, p can be 0.3 ≤ p ≤ 1.

[0065] In one aspect of the present invention, p can be 0.5 ≤ p ≤ 1.

[0066] In one aspect of the present invention, p can be 0.6 ≤ p ≤ 1.

[0067] In one aspect of the present invention, p can be 0.7 ≤ p ≤ 1.

[0068] In one aspect of the present invention, p can be 0.8 ≤ p ≤ 1.

[0069] In one aspect of the present invention, p can be 0.9 ≤ p ≤ 1.

[0070] In another aspect of the present invention, p can be 1.

[0071] A silica-coated sulfur-carbon composite according to one embodiment of the present invention comprises a sulfur-carbon composite and silica particles coated on at least a portion of the surface of the sulfur-carbon composite.

[0072] In one embodiment of the present invention, the silica particles coated on at least a portion of the surface of the sulfur-carbon composite can react with surrounding moisture (HO) to provide hydroxyl groups (-OH) on the surface of the sulfur-carbon composite. That is, the above formula (1) can vary depending on the amount of surrounding moisture. Therefore, the sulfur-carbon composite, at least partially coated on the surface with silica particles, exhibits reduced roughness and improved fluidity due to the intercalation of silica particles, but the mechanism of the present invention is not limited thereto.

[0073] In this specification, the fluidity can be measured by the angle of repose as described later. The roughness of the silica-coated sulfur-carbon composite can be measured in accordance with ISO-25718:2016, which is well known in the art, but the method for measuring roughness is not limited thereto.

[0074] In one aspect of the present invention, the silica-coated sulfur-carbon composite may have improved fluidity compared to a sulfur-carbon composite in which silica particles are not coated, resulting in a smaller angle of repose.

[0075] In one embodiment of the present invention, the angle of repose of the silica-coated sulfur-carbon composite may be at least 5% smaller than that of the sulfur-carbon composite before the silica particles are coated. More specifically, the angle of repose of the silica-coated sulfur-carbon composite may be at least 6%, 6.5%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, or 30% smaller than that of the sulfur-carbon composite before the silica particles are coated. The fact that the angle of repose of the silica-coated sulfur-carbon composite is smaller than that of the sulfur-carbon composite before the silica particles are coated may reflect improved fluidity of the sulfur-carbon composite. In one embodiment of the present invention, the angle of repose may vary depending on the specific sulfur-carbon composite used.

[0076] In this specification, the angle of repose being reduced can be calculated according to the following formula 3.

[0077] [Formula 3] Angle of repose increase / decrease rate (%) = [(Ra-Rb) / Rb] x 100 Rb is the angle of repose of the sulfur-carbon composite before coating, Ra is the angle of repose of the silica-coated sulfur-carbon composite.

[0078] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may exhibit an angle of repose of 32° or less due to the improved fluidity as described above.

[0079] As used herein, the "angle of repose" may refer to a value measured according to a method commonly used in the art for measuring the angle of repose of a sample. Examples of methods for measuring the angle of repose include the Angle of Repose Method described in U.S. Pharmacopoeia 1174 and EP Pharmacopoeia 2.9.76. In one embodiment of the present invention, the angle of repose may be measured, for example, according to the following method. First, a funnel was positioned 7.5 cm above the ground and centered using a level. The bottom of the funnel was then closed to prevent the sample from draining downward. 100 g of the sample to be measured was placed on the funnel, and the bottom was opened to allow the sample to fall freely and pile up on a circular plate (13 cm in diameter) located at the bottom. The angle of repose (θ) of the piled sample was then measured.

[0080] In one aspect of the present invention, the angle of repose may be, for example, 5° to 32°, 5° to 31.5°, 5° to 31°, 10° to 31°, 5° to 30.5°, 5° to 30°, 10° to 30°, 15° to 28°, 15.5° to 27°, 20° to 26.5°, or 23° to 26°, or 5° to 30.3°, or 5° to 25.5°, or 5° to 23°, or 23° to 30.3°, or 23° to 25.5°, or 25.5° to 30.3°.

[0081] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may satisfy the following formula 4:

[0082]

number

[0083] In Equation 4,

[0084]

number

[0085] Mp = mass of silica particles Mc = mass of sulfur-carbon complex θ = angle of repose of silica-coated sulfur-carbon composite (US Pharmacopoeia 36 "Particle Flowability" <1174> (measured in accordance with

[0086] As shown in Equation 4, the angle of repose can be determined depending on the content of silica particles used for a specific content of sulfur-carbon composite to obtain a silica-coated sulfur-carbon composite. A silica-coated sulfur-carbon composite satisfying Equation 4 ideally exhibits excellent fluidity and low density. Furthermore, a silica-coated sulfur-carbon composite satisfying Equation 4 is advantageous in improving the capacity and / or performance of an electrode, e.g., a cathode, using the composite, and the performance of a lithium-sulfur battery using the composite.

[0087] In another embodiment of the present invention, the silica-coated sulfur-carbon composite may satisfy the following formula 5A:

[0088]

number

[0089] In Equation 5A,

[0090]

number

[0091] Mp = mass of silica particles Mc = mass of sulfur-carbon complex Sspec = specific surface area of ​​porous carbon material

[0092] As shown in Equation 5A, the weight of silica particles based on the weight of the silica-coated sulfur-carbon composite can be determined according to the specific surface area of ​​the porous carbon material. A large specific surface area of ​​the porous carbon material can mean a large external surface area of ​​the porous carbon material, and therefore, a large external surface area of ​​the sulfur-carbon composite. Coating the large external surface of the sulfur-carbon composite can mean that a large amount of silica particles can be used. Therefore, the larger the specific surface area of ​​the porous carbon material, the more silica particles can be used. Furthermore, when the silica-coated sulfur-carbon composite satisfies Equation 5A, advantageous effects are achieved in terms of the flowability and low density of the silica-coated sulfur-carbon composite. The specific surface area of ​​the porous carbon material can be measured by the BET measurement method in accordance with ISO 9277:2010, which is well known in the art. When measured by this method, little, preferably no, sulfur-containing compounds remain in the silica-coated sulfur-carbon composite. Therefore, most preferably, the specific surface area of ​​the porous carbon material in the silica-coated sulfur–carbon composites can be nearly similar, preferably the same, as that of the porous carbon material that may not have been used to form the sulfur–carbon composites and / or silica-coated sulfur–carbon composites.

[0093] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may satisfy the following formula 5B:

[0094]

number

[0095] In Equation 5B,

[0096]

number

[0097] Mp = mass of silica particles Mc = mass of sulfur-carbon complex Sspec = specific surface area of ​​porous carbon material

[0098] As shown in Equation 5B, the weight of silica particles based on the weight of the silica-coated sulfur-carbon composite can be determined depending on the specific surface area of ​​the porous carbon material. Therefore, the amount of silica particles may have a lower limit for silica-coated sulfur-carbon composites containing porous carbon materials with higher specific surface areas to provide silica-coated sulfur-carbon composites with improved flowability. Here, the specific surface area can be measured by BET in accordance with ISO 9277:2010, as is well known to those skilled in the art. Silica-coated sulfur-carbon composites satisfying Equation 5B exhibit advantageous effects in terms of excellent flowability and low density.

[0099] In one embodiment of the present invention, the average particle diameter (D 50 The average particle diameter (D) of the silica particles may be, for example, 10 to 50 nm, 10 to 40 nm, 15 to 40 nm, or 10 to 15 nm. 50 ) satisfies such a range, it may be advantageous in terms of improving the uniformity of the silica particle coating and the cohesion of the sulfur-carbon composite.

[0100] In this specification, the average particle diameter (D 50 ) means the particle size at the 50% point of the cumulative distribution of the number of particles according to the particle size. The particle size may be measured using a particle size analyzer (PSA) for a silica-coated sulfur-carbon composite coated with silica particles, but the method for measuring the particle size is not limited thereto. The average particle size (D 50 A particle size distribution measuring device for measuring the particle size distribution may be used in accordance with ISO 13320:2020, which is known in the art, but the measuring method is not limited thereto.

[0101] In one embodiment of the present invention, the thickness of the silica particles coated on at least a portion of the surface of the silica-coated sulfur-carbon composite may be, for example, 20 nm to 5 μm, 40 nm to 5 μm, or 40 nm to 1 μm. When the silica particle coating thickness is within the above range, the silica-coated sulfur-carbon composite can achieve low density while improving fluidity, but the present invention is not limited thereto. In other words, when the silica-coated sulfur-carbon composite has the above coating thickness, it can have an optimal balance between excellent fluidity and low density. The thickness of the silica particle coating can be measured using a scanning electron microscope (SEM), but the measurement method is not limited thereto.

[0102] In one embodiment of the present invention, the maximum average particle size (D 50 ) may be, for example, 100:1 to 1000:1. A silica-coated sulfur-carbon composite satisfying this ratio exhibits advantageous effects in terms of excellent fluidity and low density, but the present invention is not limited thereto. The average particle size of the silica-coated sulfur-carbon composite may be measured according to the above-mentioned method, and the thickness of the coating layer may also be measured according to the above-mentioned method, and the ratio may be a unitless value.

[0103] In one embodiment of the present invention, 60% to 100% of the surface area of ​​the sulfur-carbon composite may be coated with the silica particles. Specifically, the surface area of ​​the sulfur-carbon composite coated with the silica particles may be 65% to 100%, 70% to 100%, 75% to 100%, 80% to 100%, 85% to 100%, 90% to 100%, 95% to 100%, or 95% to 99%, but the present invention is not limited thereto.

[0104] Specifically, the sulfur-carbon composite may have an outer surface and a specific surface area, and the surface area of ​​the sulfur-carbon composite coated with the silica particles may be measured based on 100% of the entire outer surface of the sulfur-carbon composite.

[0105] More specifically, the silica particles may cover 60% to 100%, 65% to 100%, 70% to 100%, 75% to 100%, 80% to 100%, 85% to 100%, 90% to 100%, 95% to 100%, or 95% to 99% of the outer surface of the sulfur-carbon composite. The area of ​​the outer surface of the silica-coated sulfur-carbon composite can be measured, for example, by SEM image analysis of the surface of the silica-coated sulfur-carbon composite. Specifically, it can be measured at a magnification of 15,000 times for an area of ​​10 μm × 10 μm. The specific surface area may have a similar value to the internal area, and can be measured by the BET method in accordance with ISO 9277:2010, which is well known in the art, but is not limited thereto.

[0106] In one embodiment of the present invention, the thickness of the silica particles coated on the silica-coated sulfur-carbon composite can be estimated from the correlation between the weight ratio of the silica particles based on the total weight of the silica-coated sulfur-carbon composite and the area ratio of the silica particles to the total surface area of ​​the silica-coated sulfur-carbon composite.

[0107] For example, in one embodiment of the present invention, the silica-coated sulfur-carbon composite may have the properties of Formula 2 below.

[0108]

number

[0109] In Equation 2, Mp is the mass of the silica particles; Mc is the mass of the sulfur-carbon complex; So is the area of ​​the region coated with the silica particles; St is the surface area of ​​the silica-coated sulfur-carbon composite.

[0110] In this specification, the "area of ​​the region coated with silica particles" can be measured according to a method for measuring the area of ​​the silica particles coated on the surface of a sulfur-carbon composite, for example, using a scanning electron microscope (SEM).

[0111] In this specification, the "surface area of ​​the silica-coated sulfur-carbon composite" may be, for example, the value of the specific surface area measured by the BET method. For example, it may be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mini II (manufactured by BEL Japan). The specific surface area may be measured according to ISO 9277:2010, which is well known in the art, but the measurement method is not limited thereto.

[0112] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may contain 0.01 to 20 wt %, specifically 0.01 to 10 wt %, more specifically 1 to 10 wt %, 1 to 5 wt %, or 1 to 3 wt % of the silica particles based on the total weight. The silica-coated sulfur-carbon composite may also contain 80 to 99.99 wt %, specifically 90 to 99.99 wt %, more specifically 90 to 99 wt %, 95 to 99 wt %, or 97 to 99 wt % of the sulfur-carbon composite based on the total weight. When the contents of the silica particles and sulfur-carbon composite are within the above-mentioned ranges, respectively, excellent fluidity and improved density can be advantageously exhibited. Therefore, electrodes and lithium-sulfur batteries using the same may be advantageously exhibiting improved performance, particularly capacity and / or lifespan.

[0113] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may contain the sulfur-carbon composite and the silica particles in a weight ratio of 99.9:0.1 to 80:20. That is, the weight ratio of the sulfur-carbon composite to the silica particles may be, for example, within the range of 99.9:0.1 to 80:20. For example, the weight ratio of the sulfur-carbon composite to the silica particles may be 99.9:0.1 to 90:10, 99:1 to 90:10, 99:1 to 95:5, 97:3 to 90:10, or 99:1 to 97:3. When the weight ratio of the sulfur-carbon composite to the silica particles is within the above range, the silica-coated sulfur-carbon composite exhibits low density and improved flowability, but the present invention is not limited thereto.

[0114] In one aspect of the present invention, the silica-coated sulfur-carbon composite has a technical significance in that silica particles are inserted into the surface of a sulfur-carbon composite commonly used in the positive electrode of a lithium-sulfur battery, thereby reducing the roughness. Therefore, the specific type and shape of the sulfur-carbon composite are not particularly limited. The roughness can be measured according to the above-mentioned method.

[0115] In one embodiment of the present invention, the average particle diameter (D 50 The average particle diameter (D) may be 20 μm to 50 μm, but the present invention is not limited thereto. 50 The method for measuring the average particle size of silica particles is the same as that described in the section on the average particle size of silica particles.

[0116] In one aspect of the present invention, the sulfur-carbon composite may refer to a composite containing a sulfur-containing compound supported on at least a portion of the inner and outer surfaces of the pores of a porous carbon material.

[0117] In one aspect of the present invention, the sulfur-containing compound may be located on at least a portion of the interior surfaces of the pores of the porous carbon material. The interior surfaces of the pores of the porous carbon material may be non-surfaces of the porous carbon material. In another aspect of the present invention, the sulfur-containing compound may be located on at least a portion of the exterior surfaces of the porous carbon material.

[0118] In one aspect of the present invention, the porous carbon material provides a framework to which a sulfur-containing compound, a positive electrode active material, can be uniformly and stably immobilized, thereby enhancing the electrical conductivity of the sulfur-containing compound and facilitating the electrochemical reaction. Therefore, the sulfur-containing compound can be in direct contact with the surface of the porous carbon material, i.e., the surface outside the pores of the porous carbon material, such as the surface inside the pores of the porous carbon material, and / or a non-surface of the porous carbon material. The sulfur-containing compound in direct contact with the porous carbon material can have the technical effect of allowing an electrochemical reaction to occur, making the silica-coated sulfur-carbon composite suitable for use in electrodes, such as cathodes, and further for use in lithium-sulfur batteries.

[0119] In one aspect of the present invention, the porous carbon material may be generally prepared by carbonizing a variety of carbon precursors. The porous carbon material may contain pores with varying internal sizes, and the average pore diameter may be in the range of 1 to 200 nm, for example, 1 to 100 nm, 10 to 80 nm, or 20 to 50 nm. The average pore diameter may be measured in accordance with ISO 15901:2019, which is well known in the art, but is not limited thereto.

[0120] In one embodiment of the present invention, the porosity (also referred to as void ratio) of the porous carbon material may be in the range of 10 to 90% of the total volume of the porous carbon material. 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.

[0121] When the average pore diameter and porosity of the porous carbon material are within the above-mentioned ranges, impregnation with a sulfur-containing compound is possible and the mechanical strength of the sulfur-carbon composite is ensured, making it suitable for use in an electrode manufacturing process. However, the present invention is not limited thereto.

[0122] In one aspect of the present invention, the shape of the porous carbon material may be any shape that can be commonly used for a positive electrode of a lithium-sulfur battery, such as a sphere, a rod, a needle, a plate, a tube, or a bulk.

[0123] In one embodiment of the present invention, the porous carbon material may be any porous carbon material commonly used in the art, as long as it has a porous structure. For example, the porous carbon material may be, but is not limited to, graphene; carbon black such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite such as natural graphite, artificial graphite, and expanded graphite; activated carbon, or two or more of these.

[0124] In one embodiment of the present invention, the porous carbon material has a thickness of, for example, 300 to 2000 m 2 / g, 400-1800m 2 / g, 450-1500m 2 / g or 500~1200m 2The specific surface area may be measured by the BET method in accordance with ISO 15901:2019, which is well known in the art, but is not limited thereto. Porous carbon materials with a higher specific surface area can reduce the density of silica-coated sulfur-carbon composites and improve the electrochemical reaction of sulfur-containing compounds. However, porous carbon materials with a specific surface area exceeding this range may have poor mechanical properties and may be unsuitable for use in electrodes or lithium-sulfur batteries, but the present invention is not limited thereto.

[0125] In one aspect of the present invention, the sulfur-containing compound supported on the porous carbon material is not particularly limited in type as long as it can be used as a positive electrode active material for a lithium-sulfur battery. For example, the sulfur-containing compound can be inorganic sulfur (S), lithium polysulfide (LiS), or the like. n ,1 ≦ n≦8), carbon-sulfur polymer (C2S x ) m (2.5≦x≦50, 2≦m) or a mixture of two or more of these, but is not limited thereto.

[0126] In another embodiment of the present invention, the sulfur-containing compound can be inorganic sulfur (S8).

[0127] In one embodiment of the present invention, the sulfur-carbon composite may contain the porous carbon material and the sulfur-containing compound in a weight ratio of 1:9 to 1:1. For example, the weight ratio of the porous carbon material to the sulfur-containing compound in the sulfur-carbon composite may be 1:1.5 to 1:7, 1:2 to 1:5, 1:2.5 to 1:4, 1:2.7 to 1:3.5, 1:2.8 to 1:3.5, or 1:3. When the weight ratio of the porous carbon material to the sulfur-containing compound is within the above range, advantageous effects are achieved in terms of reducing the resistance of the positive electrode active material layer and improving the battery performance, but the present invention is not limited thereto.

[0128] In the silica-coated sulfur-carbon composite according to one embodiment of the present invention, the concentration of silica may be higher at the outer surface than at the non-surface of the porous carbon material.

[0129] Specifically, the inner surfaces of the pores of the porous carbon material are mostly supported by the sulfur-containing compound. As a result, the concentration of silica that can penetrate into the inner surfaces (non-surfaces) of the pores of the porous carbon material may be lower than the concentration of silica present on the outer surfaces of the silica-coated sulfur-carbon composite. When most, preferably all, of the silica particles coat the outer surfaces of the porous carbon material, the silica-coated sulfur-carbon composite exhibits advantageous effects in terms of excellent flowability and density.

[0130] The silica concentration can be determined by the weight of the silica particles divided by their respective surface areas. Thus, the concentration of silica particles on the interior surface of the pores of the porous carbon material can be determined by dividing the weight of the silica particles by the specific surface area of ​​the porous carbon material. On the exterior surface of the porous carbon material, the concentration of silica particles can be determined by dividing the weight of the silica particles by the exterior surface area of ​​the porous carbon material.

[0131] In one embodiment of the present invention, the surface area of ​​the porous carbon material of the silica-coated sulfur-carbon composite can be estimated by subtracting the amount of sulfur-containing compounds from the silica-coated sulfur-carbon composite. The specific surface area can be determined by BET in accordance with ISO 9277:2010, as is well known to those skilled in the art. However, the method for measuring the specific surface area is not limited thereto.

[0132] Method for producing silica-coated sulfur-carbon composites According to another aspect of the present invention, there is provided a method for producing the above-mentioned silica-coated sulfur-carbon composite.

[0133] The method for producing the silica-coated sulfur-carbon composite includes coating silica particles on at least a portion of the surface of the sulfur-carbon composite.

[0134] In one embodiment of the present invention, the coating step may be performed by uniformly mixing the sulfur-carbon composite and silica particles.

[0135] In one embodiment of the present invention, the sulfur-carbon composite and the silica particles may be mixed in a weight ratio of 99.9:0.1 to 80:20 for coating. For example, the sulfur-carbon composite and the silica particles may be mixed in a weight ratio of 99.9:0.1 to 90:10, 99:1 to 90:10, 99:1 to 95:5, 97:3 to 90:10, or 99:1 to 97:3. When the weight ratio of the sulfur-carbon composite and the silica particles is within the above range, the silica-coated sulfur-carbon composite has low density and improved flowability, but the present invention is not limited thereto.

[0136] In one embodiment of the present invention, the mixing for the coating may be performed so that the sulfur-carbon composite and silica particles are uniformly distributed.

[0137] In one embodiment of the present invention, the coating step may include mixing the sulfur-carbon composite and the silica particles in a solid state. For example, the sulfur-carbon composite and the silica particles may be in powder form and mixed in a solid state by introducing the sulfur-carbon composite and the silica particles into a powder mixer.

[0138] In one embodiment of the present invention, the mixing is performed by a variety of methods that allow simple mixing of the sulfur-carbon composite and the silica particles, since the sulfur-carbon composite and the silica particles are in solid forms.

[0139] In one embodiment of the present invention, the mixing for the coating may be performed by putting the materials into a mixer such as a bead mill or an acoustic mixer.

[0140] In one embodiment of the present invention, the mixing for coating may be performed for 60 seconds to 60 minutes while stirring in the mixer at 1,000 rpm to 2,000 rpm, specifically, 1,300 rpm to 2,000 rpm, 1,400 rpm to 2,000 rpm, 1,500 rpm to 2,000 rpm, or 1,000 rpm to 1,500 rpm, for 15 minutes to 60 minutes, 15 minutes to 30 minutes, 60 seconds to 30 minutes, or 30 minutes to 60 minutes, in order to ensure uniformity of the silica coating. However, the mixing time may vary depending on the content of the substance, and the present invention is not limited thereto.

[0141] In one embodiment of the present invention, the mixing for coating may be carried out for, for example, 60 seconds to 60 minutes, specifically 15 minutes to 60 minutes, more specifically 15 minutes to 30 minutes. In another embodiment of the present invention, the mixing for coating may be carried out for, for example, 60 seconds to 30 minutes, or 30 minutes to 60 minutes, but is not limited thereto.

[0142] In one embodiment of the present invention, the mixing for coating may be performed in a mixer at, for example, 1,000 rpm to 2,000 rpm, specifically 1,400 rpm to 2,000 rpm, 1,500 rpm to 2,000 rpm, or 1,000 rpm to 1,500 rpm, in order to achieve uniform mixing, but is not limited thereto.

[0143] In one embodiment of the present invention, the mixing for coating may be performed at room temperature (25±1°C) to minimize deformation of the shape of the sulfur-carbon composite and to uniformly coat the silica particles, but the present invention is not limited thereto.

[0144] In one embodiment of the present invention, the matters described above regarding the silica-coated sulfur-carbon composite are incorporated with respect to the sulfur-carbon composite and the silica particles.

[0145] In one embodiment of the present invention, the method for preparing the silica-coated sulfur-carbon composite may further include preparing the sulfur-carbon composite before coating the silica particles.

[0146] In one embodiment of the present invention, the step of preparing the sulfur-carbon composite may include mixing the porous carbon material and the sulfur-containing compound.

[0147] In one embodiment of the present invention, the step of preparing the sulfur-carbon composite may include mixing and molding the porous carbon material and the sulfur-containing compound.

[0148] In one embodiment of the present invention, the porous carbon material and the sulfur-containing compound may be mixed using a commonly used mixer, and the mixing time, temperature, speed, and the contents and conditions of the raw materials may be selectively adjusted.

[0149] In one aspect of the present invention, the step of molding the porous carbon material and the sulfur-containing compound mixed as described above may include heating the mixture. The heating temperature is not particularly limited as long as the sulfur-containing compound is melted, and may be, for example, 110°C to 180°C, specifically 115°C to 180°C.

[0150] In one embodiment of the present invention, the method may further include, after the coating step, separating the sulfur-carbon composite coated with the silica particles.

[0151] The silica-coated sulfur-carbon composite thus prepared contains sulfur-carbon composites with improved cohesion due to silica coating on at least a portion of the surface, and therefore exhibits improved fluidity.

[0152] According to yet another aspect of the present invention, there is provided a method for improving the flowability of the above-mentioned silica-coated sulfur-carbon composite.

[0153] The method for improving the flowability of the silica-coated sulfur–carbon composite includes coating silica particles on at least a portion of the surface of the sulfur–carbon composite.

[0154] With regard to the step of coating at least a portion of the surface of the sulfur-carbon composite with silica particles, the above-mentioned method for producing the silica-coated sulfur-carbon composite is applicable.

[0155] Positive electrode active material and electrode According to yet another aspect of the present invention, there is provided a positive electrode active material comprising the silica-coated sulfur-carbon composite.

[0156] In one embodiment of the present invention, the silica-coated sulfur carbon composite itself can be used as a positive electrode active material.

[0157] In another embodiment of the present invention, the silica-coated sulfur carbon composite may be used as a positive electrode active material, optionally together with a sulfur-containing compound.

[0158] According to yet another aspect of the present invention, there is provided an electrode comprising the silica-coated sulfur-carbon composite.

[0159] Specifically, the electrodes may include porous carbon materials, each of which may be coated with silica particles, and the porous carbon materials may be derived from the silica-coated sulfur-carbon composite.

[0160] In one embodiment of the present invention, the electrode may include a silica-coated sulfur-carbon composite, which may include a porous carbon material coated with silica particles. The silica particles may form a silica coating layer between the porous carbon material and / or the sulfur-carbon composite. The presence of the sulfur-carbon composite or the porous carbon material in the silica-coated sulfur-carbon composite may vary depending on whether the electrode is in a charged or discharged state when used in a lithium-sulfur battery. In one embodiment of the present invention, the electrode may include a current collector and an electrode active material layer comprising a plurality of silica-coated sulfur-carbon composites on at least one surface of the current collector.

[0161] In one aspect of the present invention, the electrode may be used as at least one of an anode and a cathode for a lithium secondary battery. For example, the electrode may be used as a cathode for a lithium-sulfur battery, but the use of the present invention is not limited thereto.

[0162] According to yet another aspect of the present invention, there is provided a lithium-sulfur battery comprising the silica-coated sulfur-carbon composite.

[0163] The lithium-sulfur battery includes a positive electrode including the silica-coated sulfur-carbon composite, a negative electrode including a negative electrode active material, and an electrolyte.

[0164] In one embodiment of the present invention, the silica-coated sulfur-carbon composite may be included in a positive electrode as a support for supporting a positive electrode active material, as the positive electrode active material itself, or as a conductive material.

[0165] In one aspect of the present invention, a lithium-sulfur battery including the silica-coated sulfur-carbon composite may have improved performance. A lithium-sulfur battery including the silica-coated sulfur composite according to the present invention may have improved capacity. Therefore, the lithium-sulfur battery according to the present invention may have improved performance and capacity. Without being bound by any theory, the silica-coated sulfur-carbon composite may improve the dispersibility of the silica-coated sulfur-carbon composite in an electrode, e.g., a positive electrode, thereby providing lithium-sulfur batteries with improved performance and capacity. Furthermore, the formation of aggregates of the silica-coated sulfur-carbon composite on an electrode, e.g., a positive electrode, is minimized, thereby providing the above-mentioned effects.

[0166] The performance improvement of a lithium-sulfur battery containing the silica-coated sulfur-carbon composite as described above can be measured by comparing it with a lithium-sulfur battery containing a sulfur-carbon composite that is not coated with silica particles.

[0167] In one aspect of the present invention, the positive electrode, negative electrode, positive electrode active material, negative electrode active material, and electrolyte solution can be used without any particular limitation as long as they are usable in a lithium-sulfur battery within a range that does not impair the object of the present invention.

[0168] For example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, and the negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector.

[0169] In this case, the positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not cause chemical changes in the battery, and has high conductivity, and the negative electrode current collector is not particularly limited as long as it supports the negative electrode active material, does not cause chemical changes in the battery, and has high conductivity.

[0170] In one embodiment of the present invention, the negative electrode active material is lithium (Li + Any material capable of reversibly intercalating or deintercalating lithium ions or capable of reacting with lithium ions to reversibly form a lithium-containing compound may be used without particular limitation. For example, the negative electrode active material may include lithium metal, a lithium alloy, or a mixture thereof. The lithium alloy may be, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), tin (Sn), or an alloy of two or more of these metals.

[0171] In one aspect of the present invention, the electrolyte solution may be any suitable electrolyte solution for lithium-sulfur batteries, and may include, for example, a lithium salt and a solvent. The solvent may be, for example, an ether-based compound, a carbonate-based compound, or a mixture thereof, but is not limited thereto. The lithium salt may be any suitable electrolyte solution for lithium-sulfur batteries, and may include, for example, LiSCN, LiBr, LiI, LiPF, LiBF, LiB, etc. 10 Cl 10 , LiSO3CF3, LiCl, LiClO4, LiSO3CH3, LiB(Ph)4, LiC(SO2CF3)3, LiN(SO2CF3)2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiFSI, lithium chloroborane, lithium lower aliphatic carboxylate, or a mixture of two or more of these, but are not limited thereto.

[0172] In one embodiment of the present invention, the lithium-sulfur battery may further include a separator interposed between the positive electrode and the negative electrode. The separator separates or insulates the positive electrode and the negative electrode from each other and allows lithium ions to be transported between the positive electrode and the negative electrode. The separator may be made of a porous, non-conductive or insulating material. The separator may be an independent member such as a film, or may be a coating layer applied to the positive electrode and / or the negative electrode.

[0173] In one embodiment of the present invention, the material constituting the separator may include, for example, polyolefins such as polyethylene and polypropylene, glass fiber filter paper, silica materials, or two or more of these, but is not limited thereto.

[0174] In one embodiment of the present invention, the shape of the lithium-sulfur battery is not particularly limited, and may be a variety of shapes such as a cylindrical shape, a laminated shape, or a coin shape.

[0175] In one aspect of the present invention, the method for manufacturing the lithium-sulfur battery may include, but is not limited to, winding, which is a common process for manufacturing a battery, lamination of a separator and an electrode, stacking, or folding.

[0176] The present invention will be described in more detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not limited to these examples in any way.

[0177] Experimental Example 1. Preparation of silica-coated sulfur-carbon composite Example 1 Sulfur (S8)-carbon (CNT) composite (sulfur (S8) raw material: H SULPHUR CORP, Korea, carbon (CNT) raw material: Nano C corp, S8 70 wt%, CNT 30 wt%) 99 parts by weight and silica particles ([SiO2] x[SiO(OH)2] 1-x ,0.5≦x≦1,D 50 1 part by weight of the sulfur-carbon composite (15 nm) was added to a mixer (Henschel mixer) and mixed uniformly at 1,500 rpm for 30 minutes at room temperature to prepare a silica-coated sulfur-carbon composite in which at least a portion of the surface of the sulfur-carbon composite was coated with silica particles.

[0178] At this time, the thickness of the silica particles coated was 40 nm to 5 μm (average 2.5 μm).

[0179] Example 2 97 parts by weight of the sulfur-carbon composite and silica particles ([SiO x [SiO(OH)2] 1-x ,0.5≦x≦1,D 50 A silica-coated sulfur-carbon composite was produced in the same manner as in Example 1, except that 3 parts by weight of 15 nm (1500 kJ / g) was mixed.

[0180] Example 3 90 parts by weight of the sulfur-carbon composite and silica particles ([SiO x [SiO(OH)2] 1-x ,0.5≦x≦1,D 50 A silica-coated sulfur-carbon composite was produced in the same manner as in Example 1, except that 10 parts by weight of silica-coated sulfur-carbon composite (15 nm) was mixed.

[0181] Comparative Example 1 The sulfur–carbon composite used in Example 1 was prepared as Comparative Example 1, without the step of mixing silica particles with the sulfur–carbon composite to coat at least a portion of the surface of the sulfur–carbon composite with silica particles.

[0182] [Average particle size of silica particles (D 50 ) Measurement The average particle diameter (D 50) was measured using a particle size analyzer (PSA) based on the particle diameter at 50% of the cumulative distribution of particles according to particle diameter.

[0183] [Measuring the thickness of silica particle coating] The thickness of the coating on the silica particles was confirmed using a scanning electron microscope (SEM).

[0184] [Confirmation of the structure of silica-coated sulfur-carbon composites] To confirm the structures of the silica-coated sulfur-carbon composites prepared in Examples 1 and 2 and Comparative Example 1, we observed them using a scanning electron microscope (SEM) (manufactured by JEOL Ltd.). The results are shown in Figure 1.

[0185] In FIG. 1, an image at 15k magnification is shown on the top, and an image at 2k magnification is shown on the bottom.

[0186] 1, the sulfur-carbon composite of Comparative Example 1, which is not coated with silica particles, has a rough surface due to the porosity of the sulfur-carbon composite, whereas the sulfur-carbon composites of Examples 1 and 2 have smooth surfaces due to the silica particle coating. Among the silica-coated sulfur-carbon composites of Examples 1 and 2, the surface of Example 2, which has a larger amount of silica particle coating, is even smoother.

[0187] [Confirmation of flowability of silica-coated sulfur-carbon composite] To confirm the flowability of the silica-coated sulfur-carbon composites prepared in Examples 1, 2, 3, and Comparative Example 1, the angles of repose were measured according to the angle of repose test described below. The results are shown in Table 1, Figures 2, and 3. First, a funnel was positioned 7.5 cm above the ground, centered using a level, and fixed. The bottom of the funnel was then closed to prevent the sample from spilling out. 100 g of the sample to be measured was placed on the funnel, and the bottom was opened to allow the sample to fall freely and pile up on a circular plate (13 cm in diameter) located at the bottom. The angle of repose (θ) of the piled sample was then measured.

[0188] The results also include those for the sulfur-carbon composite of Comparative Example 1, in which the silica particles were not coated.

[0189] Repose angle increase / decrease rate (%) = [(Ra-Rb) / Rb] x 100 Rb is the angle of repose of the sulfur-carbon composite before coating, Ra is the angle of repose of the silica-coated sulfur-carbon composite.

[0190] [Table 1]

[0191] As shown in Table 1, FIGS. 2 and 3, the angles of repose of the silica-coated sulfur-carbon composites of Examples 1 to 3 were reduced compared to Comparative Example 1, confirming that the flowability was improved.

[0192] In particular, the results in Table 1 confirm that the angle of repose is further improved in Examples 2 and 3, which have a higher content of silica particles.

[0193] Experimental Example 2: Preparation of zinc oxide (ZnO) coated sulfur-carbon composite To compare and evaluate whether coating the sulfur–carbon composite with other ceramic particles besides silica particles can suppress the aggregation phenomenon of the sulfur–carbon composite and improve its flowability, the following experiment was conducted using zinc oxide (ZnO).

[0194] Comparative Example 2 To carry out Experimental Example 2, a sulfur (S8)-carbon (CNT) composite (sulfur (S8) raw material: H sulfur corp., carbon (CNT) raw material: Nano C corp, S8 75 wt%, CNT 25 wt%) was prepared.

[0195] Comparative Example 3 99 parts by weight of the sulfur-carbon composite prepared in Comparative Example 2 and 1 part by weight of zinc oxide (ZnO) (Sigma-Aldrich) were added to a mixer (Henschel mixer) and mixed uniformly at 1,500 rpm for 30 minutes at room temperature to prepare a sulfur-carbon composite at least partially coated with zinc oxide.

[0196] Comparative Example 4 A zinc oxide-coated sulfur-carbon composite was prepared in the same manner as in Comparative Example 3, except that 95 parts by weight of the sulfur-carbon composite and 5 parts by weight of ZnO were mixed.

[0197] [Confirmation of the structure of zinc oxide-coated sulfur-carbon composite] In order to confirm the structures of the sulfur-carbon composites according to Comparative Examples 2 to 4 prepared above, observation was performed using a scanning electron microscope (SEM) (manufactured by JEOL Ltd.) and the results are shown in FIG.

[0198] In FIG. 4, an image at 10k magnification is shown on the top, and an image at 2k magnification is shown on the bottom.

[0199] As shown in Figure 4, the sulfur-carbon composite of Comparative Example 2, which was not coated with zinc oxide, had a rough surface due to the porosity of the sulfur-carbon composite. In Comparative Examples 3 and 4, it was confirmed that some zinc oxide was inserted into the surface of the sulfur-carbon composite by mixing with zinc oxide. However, in many cases, the zinc oxide was not uniformly coated on the surface but clumped together.

[0200] It was observed that the surface roughness of Comparative Examples 3 and 4 was partially reduced compared to Comparative Example 2, but the degree of reduction in surface roughness compared to Comparative Example 2 was not significant.

[0201] [Confirmation of flowability of zinc oxide coated sulfur-carbon composite] In order to confirm the flowability of the sulfur-carbon composites prepared in Comparative Examples 2 to 4, the angles of repose were measured in the same manner as in Experimental Example 1, and the results are shown in Table 2 below and FIG. 5.

[0202] [Table 2]

[0203] According to the results in Table 2 and Figure 5, unlike silica particles, zinc oxide suppresses the aggregation phenomenon on the surface of the sulfur-carbon composite, thereby failing to improve the flowability of the composite. Instead, it further agglomerates the sulfur-carbon composite. Furthermore, varying the zinc oxide content did not affect the improvement of the aggregation of the sulfur-carbon composite.

Claims

1. Sulfur-carbon composites, Silica particles coating at least a portion of the surface of the sulfur-carbon composite, A silica-coated sulfur-carbon composite comprising, The angle of repose of the silica-coated sulfur-carbon composite is 32° or less. The silica-coated sulfur-carbon composite has an average particle size (D 50) of 20 μm to 50 μm.

2. The silica-coated sulfur-carbon composite according to claim 1, except that the sulfur-carbon composite contains silica.

3. The silica-coated sulfur-carbon composite according to claim 1, wherein the sulfur-carbon composite comprises sulfur and carbon.

4. The silica-coated sulfur-carbon composite according to claim 1, wherein the ratio of the average particle size (D 50) of the sulfur-carbon composite to the maximum thickness of the coating layer formed by the silica particles is 100:1 to 1000:

1.

5. The silica-coated sulfur-carbon composite according to claim 1, wherein 60% to 100% of the surface area of ​​the sulfur-carbon composite is coated with the silica particles.

Images