Carbon composite for the positive electrode of a lithium-sulfur battery and method for manufacturing the same

Abstract

The present invention relates to a carbon composite for use in a positive electrode of a lithium-sulfur battery and a method for producing the same, the carbon composite comprising a porous carbon material and vanadium nitride particles located on a surface of the porous carbon material. The lithium-sulfur battery using the carbon composite can rapidly convert lithium polysulfide into lithium sulfide, thereby improving the stability of the lithium-sulfur battery.

Description

[Technical Field]

[0001] This invention relates to a carbon composite used in the positive electrode of a lithium-sulfur battery and a method for producing the same.

[0002] This application claims priority based on Korean Patent Application No. 2022-0110385 filed on 31 August 2022 and Korean Patent Application No. 2022-0187899 filed on 28 December 2022, and all content disclosed in the specifications and drawings of said applications is incorporated into this application. [Background technology]

[0003] A lithium-sulfur battery refers to a battery system that uses a sulfur-based material with SS bonds (sulfur-sulfur bonds) 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 weight per atom.

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

[0005] In a lithium-sulfur battery, during discharge, lithium, which is the negative electrode active material, is oxidized while giving off electrons and being ionized into lithium cations, and a sulfur-based material, which is the positive electrode active material, accepts electrons and is reduced. Here, by utilizing the reduction reaction of the sulfur-based material, the S-S bond accepts two electrons and is converted into the form of sulfur anions. The lithium cations generated by the oxidation reaction of lithium are transmitted to the positive electrode through the electrolyte, and this combines with the sulfur anions generated by the reduction reaction of the sulfur-based compound to form a salt. Specifically, sulfur before discharge has a cyclic S8 structure, but this is converted into lithium polysulfide (Lithium polysulfide, Li2S x , where x = 8, 6, 4, 2, and the lithium polysulfide is completely reduced to generate lithium sulfide (Li2S).

[0006] However, the lithium polysulfide generated during the charge-discharge process is easily eluted into the electrolyte, causing a decrease in the battery capacity and degradation of the cell. In order to solve the problem regarding the elution of such lithium polysulfide, various attempts have been made to support sulfur in the pores of various porous carbon materials and utilize them for the positive electrode. In particular, since there are problems with production costs in synthesizing and applying carbon with a large specific surface area, mainly attempts have been made to physically and chemically modify carbon materials having a low specific surface area and utilize them for the positive electrode.

[0007] However, although such attempts have been able to solve the problem of lithium polysulfide elution to some extent, there is a problem that the reaction of converting lithium polysulfide to lithium sulfide (Li2S) cannot be promoted.

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a carbon composite for a positive electrode of a lithium-sulfur battery and a method for manufacturing the same, which can promote the conversion of lithium polysulfide to lithium sulfide.

Means for Solving the Problem

[0009] According to one aspect of the present invention, in order to achieve the above object, a carbon composite of the following aspect is provided.

[0010] The carbon composite according to the first aspect includes a porous carbon material and vanadium nitride particles located on the surface of the porous carbon material.

[0011] According to the second aspect, it can be the carbon composite according to the first aspect in which the specific surface area of the carbon composite is 250 m 2 / g or more.

[0012] According to the third aspect, it can be the carbon composite according to the first aspect or the second aspect in which the pore volume of the carbon composite is 1.0 cm 3 / g or more.

[0013] According to the fourth aspect, it can be the carbon composite according to any one of the first to third aspects in which the average pore diameter of the carbon composite is 10 nm or more.

[0014] According to the fifth aspect, it can be the carbon composite according to any one of the first to fourth aspects in which the average particle diameter of the vanadium nitride particles is 200 nm or less.

[0015] According to the sixth aspect, it can be the carbon composite according to any one of the first to fifth aspects in which the vanadium nitride particles are contained in an amount of 3 to 50 parts by weight with respect to 100 parts by weight of the carbon composite.

[0016] According to the seventh aspect, it can be the carbon composite according to any one of the first to sixth aspects in which the porous carbon material includes carbon nanotubes (CNT), reduced graphene oxide (rGO), or a mixture thereof.

[0017] According to another aspect of the present invention, positive electrode active material, positive electrode and battery in the following embodiments are provided.

[0018] The positive electrode active material according to the eighth aspect comprises a carbon composite according to any one of the first to seventh aspects, and a sulfur-containing compound supported in the pores of the carbon composite.

[0019] According to the ninth aspect, the positive electrode active material may be the one described in the eighth aspect, wherein the weight ratio of the sulfur-containing compound to the carbon composite is 1:1 to 9:1.

[0020] The positive electrode according to the tenth embodiment comprises a current collector and a positive electrode active material layer located on at least one side of the current collector, which includes the positive electrode active material and binder according to the eighth or ninth embodiment.

[0021] The battery according to the 11th embodiment includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the 10th embodiment.

[0022] The positive electrode according to the twelfth embodiment comprises a current collector and a positive electrode active material layer located on at least one side of the current collector, comprising a positive electrode active material, a binder, and a positive electrode additive, wherein the positive electrode active material comprises a sulfur-containing compound, and the positive electrode additive comprises a carbon composite according to any one of the first to seventh embodiments.

[0023] According to the 13th aspect, the positive electrode additive may be the positive electrode described in the 12th aspect, comprising 0.01 to 30 parts by weight per 100 parts by weight of the total positive electrode active material layer.

[0024] The battery according to the 14th embodiment includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the 12th or 13th embodiment.

[0025] According to yet another aspect of the present invention, a method for producing a carbon composite is provided in the following embodiments.

[0026] A method for producing a carbon composite according to the 15th embodiment includes: a first step of introducing and dispersing a porous carbon material, vanadium nitride or its precursor, and a reducing agent in a solvent; a second step of filtering the result of the first step to remove the solvent and drying it; and a third step of heat-treating the result of the second step in an inert atmosphere, wherein the third step includes a first process of heat treatment at 350 to 650°C and a second process of heat treatment at 650 to 1400°C. [Effects of the Invention]

[0027] The carbon composite according to the present invention can be used as a positive electrode additive in a lithium-sulfur battery or as a support for a sulfur-containing compound in a lithium-sulfur battery, thereby enabling rapid conversion of lithium polysulfide to lithium sulfide.

[0028] Furthermore, the method for producing carbon composites according to the present invention allows for the uniform deposition of a catalyst onto a porous carbon support without the use of harmful gases such as NH3 and strong acids such as hydrogen fluoride (HF).

[0029] The following drawings accompanying this specification illustrate preferred embodiments of the present invention and are intended to further illustrate the technical idea of ​​the invention along with the content of the invention; therefore, the present invention shall not be construed as being limited only to what is shown in the drawings. [Brief explanation of the drawing]

[0030] [Figure 1] This graph shows the specific surface area of ​​a carbon composite according to one embodiment of the present invention. [Figure 2] This is a scanning electron microscope (SEM) image of a carbon composite according to one embodiment of the present invention. [Figure 3] This is an SEM image of a carbon composite according to one embodiment of the present invention. [Figure 4] This is an SEM image of a carbon composite according to a comparative example of the present invention. [Figure 5] This is an evaluation graph of the charge and discharge performance of a lithium-sulfur battery according to one embodiment of the present invention. [Figure 6] This is an evaluation graph of the charge and discharge performance of a lithium-sulfur battery according to a comparative example of the present invention. [Figure 7] This is an evaluation graph of the charge and discharge performance of a lithium-sulfur battery according to a comparative example of the present invention. [Figure 8] This is a performance evaluation graph of a lithium-sulfur battery according to one embodiment of the present invention. [Figure 9] This is a performance evaluation graph of a lithium-sulfur battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0031] The present invention will be described in detail below. However, the present invention is not limited to the following, and each component may be modified or selectively mixed as needed. Therefore, it should be understood that this includes all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0032] Throughout this specification, when a configuration is described as "including" a component, unless otherwise specified, this does not exclude any other component, but rather means that it may further include other components.

[0033] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0034] If the measurement conditions and methods for any physical properties described in this specification are not specifically described, such physical properties shall be measured in accordance with the measurement conditions and methods commonly used by ordinary articulators in the art.

[0035] As used in this specification, the term "polysulfide" means "polysulfide ion (S x 2- ,x=8,6,4,2) and "Lithium polysulfide (Li2S x or LiS x This concept includes both x = 8, 6, 4, and 2.

[0036] As used in this specification, the term "composite" refers to a substance in which two or more materials are combined to form physically and chemically distinct phases while simultaneously exhibiting effective functions.

[0037] This invention provides a carbon composite that can be used in lithium-sulfur batteries.

[0038] According to one aspect of the present invention, the carbon composite can be used as the positive electrode of a lithium-sulfur battery.

[0039] In one embodiment of the present invention, the carbon composite can be used as a positive electrode additive added separately from the positive electrode active material in the positive electrode of a lithium sulfur battery.

[0040] In another embodiment of the present invention, the carbon composite may be used as a porous carbon support for supporting a positive electrode active material, specifically a sulfur-containing compound, in the positive electrode of a lithium-sulfur battery.

[0041] In yet another embodiment of the present invention, the carbon composite can be used as the above-described cathode additive and cathode active material in the cathode of a lithium-sulfur battery.

[0042] A carbon composite according to one aspect of the present invention comprises a porous carbon material and vanadium nitride particles located on the surface of the porous carbon material.

[0043] In the charging and discharging process of a conventional lithium-sulfur battery, lithium polysulfide is leached from the positive electrode. However, when a carbon composite according to one aspect of the present invention is applied to one or more of the positive electrode additive and sulfur-containing compound supports of a lithium-sulfur battery, the vanadium nitride particles contained in the carbon composite act as a catalyst to rapidly convert lithium polysulfide to lithium sulfide, thereby preventing the leaching of lithium polysulfide into the electrolyte.

[0044] In one embodiment of the present invention, the "porous carbon material" may function as a support for supporting vanadium nitride particles as a catalyst.

[0045] In one embodiment of the present invention, the porous carbon material may be at least partially or entirely crystalline in order to improve the catalytic activity of vanadium nitride particles. For example, when an amorphous porous carbon material is used as at least part of a positive electrode additive and / or positive electrode active material, the amorphous carbon portion may act as a resistor in the electrochemical reaction of the battery, potentially causing a decrease in battery performance. Therefore, if the porous carbon material is at least partially or entirely crystalline, it can reduce resistance in the electrode using it and improve the catalytic activity of vanadium nitride particles, but the mechanism of the present invention is not limited to this.

[0046] In one embodiment of the present invention, the crystallinity of the porous carbon material can be measured by X-ray diffraction (XRD) analysis. "XRD" analyzes diffraction (Black condition: 2dsinθ=nλ: where d is the distance between two planes, θ is the angle between the X-ray and the plane, n is an arbitrary integer, and λ is the wavelength of the X-ray) that occurs when X-rays are irradiated onto a sample and the X-rays are scattered and interfered with by electrons around the atoms. This makes it possible to identify and quantify the constituent components, determine the crystal size and degree of crystallinity, etc.

[0047] For example, when at least one independent peak occurs in the XRD spectrum, it can be seen that it is at least partially crystalline. At this time, for the independent peak, a signal of 1 time or more, 1.5 times or more, 2 times or more, 5 times or more, or 10 times or more compared to the noise is measured.

[0048] In one aspect of the present invention, when the porous carbon material is at least partially crystalline, it may have even higher elasticity compared to the amorphous carbon material. Here, for example, the amorphous carbon material can be the carbon material disclosed in Liuatal Nanoscale, 2018, 105246 - 5253.

[0049] In one aspect of the present invention, when the whole of the porous carbon material is crystalline, it becomes possible to have even higher elasticity compared to the amorphous carbon material.

[0050] In one aspect of the present invention, the porous carbon material includes a large number of micropores on the external surface and inside, and the average diameter of the micropores can be, for example, in the range of 1 nm to 200 nm, for example, 1 to 100 nm, 10 to 80 nm, or 20 to 50 nm. The average diameter of the pores can be measured according to the well - known ISO 15901:2019 in the industry, but is not limited thereto.

[0051] Also, in one aspect of the present invention, the porosity (or also referred to as the attack rate) of the porous carbon material can be in the range of 10 to 90 vol% of the total volume of the porous carbon material. The porosity of the porous carbon material can be measured according to the method compliant with ISO 15901:2019, which is known in the industry, but the measuring method is not limited thereto.

[0052] In one aspect of the present invention, the pore volume of the porous carbon material is, for example, 1 cm 3 / g to 20 cm 3 / g or 1 cm 3 / g to 10 cm 3It may be / g. The pore volume may be a value calculated and measured, for example, using N2 isotherm analysis based on the adsorption of liquid nitrogen. If the pore volume of the porous carbon material falls within the above range, it may be advantageous in terms of adequately positioning the vanadium nitride particles acting as a catalyst on the surface of the porous carbon material, but the present invention is not limited thereto.

[0053] The pore volume can be measured using the AUTOSORB iQ series (manufactured by Quantachrome) based on ASTMD 4641, and the pore volume may be a value calculated and measured using N2 isotherm analysis based on the adsorption of liquid nitrogen.

[0054] In one embodiment of the present invention, the average particle size (D) of the porous carbon material 50 The particle size (D) can be 10 to 80 μm. For example, multiple porous carbon materials can be used as primary particles to form a porous carbon material in the form of secondary particles, in which case the average particle size (D) of the porous carbon material as primary particles is 10 to 80 μm. 50 ) can fall within the aforementioned numerical range.

[0055] The average particle size (D 50 ) refers to the particle size at the point where the cumulative distribution of particle volume according to particle size reaches 50%. The particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the particle is placed in a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution. By calculating the diameter of the particles at the point where the cumulative distribution of particle volume according to particle size reaches 50% in the measuring device, D 50 It can be measured.

[0056] In one embodiment of the present invention, the porous carbon material is, for example, 100 to 2000 m 2 / g, 300~2000m 2 / g, 400~1800m 2 / g, 450~1500m 2 / g or 500-1200m 2 It may have a specific surface area of ​​ / g. The specific surface area can be measured according to the BET method of ISO 15901:2019, which is well known in the industry, but is not limited thereto. When the specific surface area of ​​the porous carbon material is within the range described above, the effect of being able to adequately support the vanadium nitride particles is achieved, but the present invention is not limited thereto.

[0057] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofiber (GNF), carbon nanofiber (CNF), activated carbon fiber (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more materials selected from these.

[0058] In one embodiment of the present invention, the porous carbon material may contain one or more selected from carbon nanotubes and reduced graphene oxide.

[0059] In one embodiment of the present invention, the porous carbon material may be doped with at least one element selected from nitrogen, oxygen, and phosphorus.

[0060] In another embodiment of the present invention, the porous carbon material may include carbon nanotubes doped with at least one element among nitrogen, oxygen, and phosphorus, reduced graphene oxide doped with at least one element among nitrogen, oxygen, and phosphorus, or a mixture thereof.

[0061] The carbon nanotube described above is characterized by carbon atoms connected in a hexagonal shape, forming a tube. According to one aspect of the present invention, the carbon nanotube may be a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), or a combination thereof, depending on the number of carbon atom layers (also referred to as "carbon walls") that constitute it. Here, the length of the individual carbon nanotubes is not particularly limited.

[0062] In another embodiment of the present invention, the carbon nanotubes may exist in a form in which two or more carbon nanotubes are tightly intertwined with each other due to cohesive forces between them.

[0063] Specifically, in one embodiment of the present invention, the carbon nanotubes may be provided in the form of a carbon nanotube dispersion liquid in which they exist as single nanotubes in a dispersion medium or the like, or they may be provided in the form of a secondary structure in which the primary carbon nanotubes aggregate with each other. From this perspective, when the porous carbon material contains carbon nanotubes, the carbon nanotubes may be bundle-shaped secondary structures, entangled secondary structures, or a combination of both. The bundle-shaped secondary structure of carbon nanotubes is one in which a single carbon nanotube is used as the primary structure, and the multiple primary structures are oriented in the longitudinal direction of the carbon nanotube by cohesive forces between carbons, etc., and are aggregated with each other to form a mass, and is sometimes called bundled CNTs (bundled CNTs).

[0064] Thus, the carbon nanotubes contained in the carbon composite are formed by the twisting and entanglement of one or more carbon nanotubes, which allows the carbon composite to have a porous structure in which spaces are formed between the carbon nanotubes.

[0065] The reduced graphene oxide may be formed as a single bent structure, or as multiple bent and intertwined structures. Alternatively, multiple reduced graphene oxides may be formed in a crumpled shape. In this way, the reduced graphene oxide contained in the carbon composite is formed by the intertwining or crumpling of one or more reduced graphene oxides, allowing the carbon composite to have a porous structure in which spaces are formed between the reduced graphene oxides.

[0066] The carbon composite comprises vanadium nitride particles located on the surface of the porous carbon material described above.

[0067] The vanadium nitride (VN) refers to a compound of nitrogen and vanadium. The vanadium nitride particles are located on the surface of the porous carbon material.

[0068] In one embodiment of the present invention, the "vanadium nitride particles" may have catalytic activity for oxidation and reduction reactions of sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 2≦x≦8), disulfide compounds, or mixtures of two or more of these.

[0069] In one embodiment of the present invention, the vanadium nitride particles may be located on at least one of the outer surface and the inner surface of the pores of the porous carbon material. Specifically, the vanadium nitride particles may be adsorbed and present on the outer surface of the porous carbon material.

[0070] In one aspect of the present invention, since the carbon nanotube is formed by carbon atoms connected in a hexagonal shape, the carbon composite may have a structure in which the vanadium nitride particles are located on the inner and / or outer surfaces of the carbon nanotube that exhibits a tubular shape. In particular, the vanadium nitride particles may be located on the outer surface of the carbon nanotube. Here, the method for positioning the vanadium nitride on the surface of the porous carbon material is not particularly limited, but for example, it may be done by bonding or depositing the vanadium nitride onto the surface of the porous carbon material.

[0071] In one embodiment of the present invention, the average particle size (D) of the vanadium nitride particles. 50 ) can be less than 200 nm, specifically, the average particle size (D 50 The average particle size (D) of the vanadium nitride particles may be 190 nm or less, 180 nm or less, 170 nm or less, 160 nm or less, or 20 nm or less. 50 The average particle size (D) of the vanadium nitride particles may be 1 nm or more, or 2 nm or more. When the average particle size of the vanadium nitride particles falls within the above range, the specific surface area of ​​the vanadium nitride particles that act as a catalyst is increased, allowing them to react more effectively with lithium polysulfide. This prevents the lithium sulfide generated during discharge from completely covering the surface, enabling a reversible reaction and allowing even more catalyst to be positioned on the surface of the porous carbon material. The average particle size (D) of the vanadium nitride particles 50 ) can be measured in the same manner as the method for measuring the particle size of porous carbon materials.

[0072] In one embodiment of the present invention, the vanadium nitride particles may be included in a content of, for example, 3 to 50 parts by weight per 100 parts by weight of the carbon composite, specifically, in a content of 3 to 40 parts by weight, 3 to 30 parts by weight, 40 to 50 parts by weight, 35 to 50 parts by weight, 10 to 40 parts by weight, or 20 to 30 parts by weight per 100 parts by weight of the carbon composite. When the vanadium nitride particles are included in a content within the above range, the vanadium nitride particles can rapidly convert lithium polysulfide to lithium sulfide, prevent lithium polysulfide from dissolving into the electrolyte, and maintain appropriate resistance and weight.

[0073] In one embodiment of the present invention, at least a portion of the surface of the vanadium nitride may be coated with a carbon layer. Alternatively, the entire surface of the vanadium nitride may be coated with a carbon layer. Specifically, when the carbon layer is present, the thickness of the carbon layer may be 5 nm or less. The thickness of the carbon layer can be measured by a transmission electron microscope (TEM). By keeping the thickness of the carbon layer within the above range, it is advantageous in that the stability of the catalyst is enhanced while maintaining the effect of the vanadium nitride catalyst.

[0074] In one embodiment of the present invention, the carbon layer coated on vanadium nitride may be formed from 1 to 3 or 1 to 5 layers. In this case, the total thickness of the carbon layer may be 5 nm or less.

[0075] In one embodiment of the present invention, the specific surface area of ​​the carbon composite is, for example, 250 m². 2 It can be more than / g, specifically 260m 2 / g or more, 270m 2 / g or more, 280m 2 / g or more, 290m 2 / g or more or 300ml 2 It may be more than / g, 400m 2 / g or less or 500m 2It may be less than or equal to / g. When the specific surface area of ​​the carbon composite falls within the above range, the vanadium nitride present on the surface can fully exhibit its ability to convert lithium polysulfide to lithium sulfide, and since the surface of the carbon composite is not completely covered by the lithium polysulfide or lithium sulfide generated during discharge, the reaction can be carried out reversibly.

[0076] The specific surface area was measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan.

[0077] In one embodiment of the present invention, the pore volume of the carbon composite is, for example, 1.0 cm³. 3 It may be 1.1 cm² or more. Specifically, the pore volume of the carbon composite is 1.1 cm². 3 / g or more, 1.2cm 3 / g or more, 1.3cm 3 / g or more or 1.4cm 3 It may be more than / g, and 2.5cm 3 / g or less, 2.7cm 3 / g or less, 3.0cm 3 It may be less than or equal to / g. When the pore volume of the carbon composite is within the range described above, the electrolyte of a battery using it as the positive electrode can be sufficiently impregnated into the pores, improving ionic conductivity. In addition, it has advantageous effects in improving the sulfur (S8) loading efficiency and improving the electrical conductivity of the positive electrode by using the pores of the carbon composite, but the present invention is not limited in any way to this.

[0078] In one embodiment of the present invention, the average pore size of the carbon composite may be 10 nm or more. Specifically, the average pore size of the carbon composite may be 15 nm or more, or 50 nm or less, 70 nm or less, or 100 nm or less. When the average pore size of the carbon composite satisfies such a range, lithium polysulfide can be effectively adsorbed, and it is advantageous in terms of improving reactivity by allowing the electrolyte to approach the pores and appropriately maintaining ionic conductivity.

[0079] The average pore diameter can be a value measured by being calculated through, for example, N2 isotherm analysis obtained based on the adsorption of liquid nitrogen.

[0080] In one aspect of the present invention, the carbon composite contains V formed as a by-product during the formation of vanadium nitride particles x O y (0 < x < 2.0 < y < 5) in trace amounts. However, V x O y (0 < x < 2.0 < y < 5) can be less than 1% by weight based on the total weight of the vanadium nitride particles contained in the carbon composite. At this time, the content can be measured by calculating the residual mass at 950 °C using thermogravimetric analysis (TGA: Thermo Gravimetric Analysis).

[0081] In one aspect of the present invention, the carbon composite is characterized in that an XRD (X-Ray Diffraction) peak occurs at 2θ.

[0082] In one aspect of the present invention, the intensity ratio (I D / I G ratio) of the Raman spectrum peak of the carbon composite can be 2.0 or less. Specifically, the I D / I G ratio can be 0.5 or more and 2.0 or less. The intensity ratio (I D / I G ratio) can be measured using the peak intensities I G and I D obtained from the spectrum of the carbon composite obtained using Raman spectroscopy. The I G means the peak (G-peak, 1573 / cm) of the crystalline part, and I D means the peak (D-peak, 1309 / cm) of the amorphous part. Therefore, at this time, I D / I GA smaller ratio indicates higher crystallinity. When the ratio satisfies the above range, electrical conductivity and mechanical strength can be appropriately maintained.

[0083] In one embodiment of the present invention, the crystallinity of the carbon composite may be, for example, 70% or more. The crystallinity is characterized by being measured using at least one of Raman spectroscopy and XRD analysis. Having the crystallinity within the above range is advantageous in that it prevents a decrease in catalyst performance and keeps the resistance below a certain level while maintaining appropriate electrical conductivity.

[0084] According to another aspect of the present invention, a positive electrode active material comprising the carbon composite described above is provided.

[0085] Specifically, the positive electrode active material may be intended for use in lithium-sulfur batteries.

[0086] A positive electrode active material according to one aspect of the present invention may include the above-mentioned carbon composite as a support, and may include a sulfur-containing compound supported within the pores of the carbon composite.

[0087] In one embodiment of the present invention, the sulfur-containing sulfide supported in the pores of the carbon composite is inorganic sulfur (S8), Li2S n (n≧1), may contain one or more compounds selected from the group consisting of disulfide compounds such as 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid, and organic sulfur compounds. Preferably, it may contain inorganic sulfur (S8).

[0088] In one embodiment of the present invention, the weight ratio of the sulfur-containing compound to the carbon composite may be, for example, 1:1 to 9:1. Specifically, the weight ratio of the sulfur-containing compound to the carbon composite may be 2:1 to 8:1, 5:1 to 9:1, or 8:1 to 9:1. When the weight ratio satisfies such a range, the clumping phenomenon between the sulfur-containing compounds is prevented, making them more receptive to electrons. This allows them to directly contribute to the electrode reaction, enabling appropriate control of the amount of binder required in the production of the positive electrode slurry, thereby preventing problems such as increased electrode surface resistance and decreased cell performance.

[0089] According to another aspect of the present invention, a positive electrode comprising the positive electrode active material described above is provided.

[0090] The positive electrode is located on a current collector and at least one side of the current collector and comprises a positive electrode active material layer containing the positive electrode active material and binder described above. Optionally, the positive electrode active material layer may further contain a conductive material.

[0091] In one embodiment of the present invention, the binder holds the positive electrode active material to the positive electrode current collector and organically connects the positive electrode active materials to each other, further enhancing the bonding force between them, and any binder known in the art can be used. For example, the binder can be one, a mixture of two or more, or a copolymer selected from the group consisting of: a fluororesin-based binder containing polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); a rubber-based binder containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; a cellulose-based binder containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol-based binder; a polyolefin-based binder containing polyethylene or polypropylene; a polyimide-based binder; a polyester-based binder; a polyacrylic-based binder; or a silane-based binder.

[0092] In one embodiment of the present invention, the content of the binder can be added in an amount of, for example, 0.5 to 30 parts by weight, when the total weight of the positive electrode active material layer is 100 parts by weight. When the content of the binder is within this range, the physical properties of the positive electrode are improved, preventing the phenomenon of the active material and conductive material falling out of the positive electrode, and the ratio of active material to conductive material in the positive electrode is appropriately controlled, thereby ensuring the capacity of the battery.

[0093] In one embodiment of the present invention, the conductive material is a substance that electrically connects the electrolyte and the positive electrode active material, serving as a path for electrons to move from the current collector to the positive electrode active material, and can be used without limitation as long as it is conductive. In one embodiment, the conductive material can be carbon black such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Thermal Black, and Carbon Black; carbon derivatives such as carbon nanotubes, graphene, and fullerene; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, which can be used alone or in mixtures. It is also possible to use the carbon composite according to the present invention as the conductive material.

[0094] In one embodiment of the present invention, if the conductive material is included, the content of the conductive material may be 0.01 to 30 parts by weight based on 100 parts by weight of the total positive electrode active material layer.

[0095] In one embodiment of the present invention, the current collector is not particularly limited as long as it supports the positive electrode active material layer, does not cause chemical changes in the battery, and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, silver, etc., and aluminum-cadmium alloys can be used.

[0096] In one aspect of the present invention, the current collector can have minute irregularities formed on its surface to strengthen the bonding force with the positive electrode active material, and can be used in a wide variety of forms such as films, sheets, foils, meshes, nets, porous materials, foams, and nonwoven fabrics.

[0097] In one embodiment of the present invention, the thickness of the current collector is not particularly limited, but may be, for example, 3 to 500 μm.

[0098] According to another aspect of the present invention, a battery using the above-described positive electrode can be provided, in particular a battery for lithium secondary batteries, specifically a lithium-sulfur battery.

[0099] The battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0100] The positive electrode is provided for by the above-mentioned matters.

[0101] In one embodiment of the present invention, the negative electrode and separator can be used without particular limitations, as long as they are suitable for use in a lithium-sulfur battery, as long as they do not impair the purpose of the present invention. For example, the negative electrode can be made of lithium metal.

[0102] In one embodiment of the present invention, the separator can be used without limitation as long as it is one that is normally usable as a separator for lithium-sulfur batteries.

[0103] In one embodiment of the present invention, the separator may include a porous polyolefin substrate, and optionally further include inorganic particles on at least one side of the porous polyolefin substrate. The separator may also optionally further include a binder for binding the inorganic particles.

[0104] In another embodiment of the present invention, the separator may be a film-like electrolyte membrane containing a solid electrolyte, and may further include a binder for binding the solid electrolyte as needed. The solid electrolyte can be any type that is typically usable in lithium-sulfur batteries, such as a polymer-based solid electrolyte, an inorganic solid electrolyte, or a mixture thereof.

[0105] In one embodiment of the present invention, the electrolyte typically includes one that can be used in lithium-sulfur batteries. The electrolyte may include a lithium salt and a non-aqueous solvent.

[0106] The lithium salt can be used without restriction as long as it is normally usable as an electrolyte for lithium-sulfur batteries. Examples of lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 This may include, but is not limited to, LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3Cli, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide, or two or more of these.

[0107] The non-aqueous solvent can be used without limitation as long as it is suitable for use as an electrolyte in lithium-sulfur batteries. The non-aqueous solvent may include, but is not limited to, cyclic carbonate solvents, linear carbonate solvents, ester solvents, ketone solvents, or mixtures of two or more of these.

[0108] In one embodiment of the present invention, the electrolyte may contain (CF3SO2)2NLi as a lithium salt and a two-component system of dioxolane (DOL) / dimethoxyethane (DME) as a non-aqueous solvent. For example, the electrolyte may further contain common additives such as LiNO3.

[0109] In one embodiment of the present invention, the external shape of the lithium-sulfur battery may be, for example, coin-shaped, cylindrical, pouch-shaped, or rectangular, and the external shape of the battery is not particularly limited. Furthermore, the lithium-sulfur battery can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in medium- and large-sized battery modules containing a large number of battery cells, and its usage is not particularly limited.

[0110] According to yet another aspect of the present invention, a cathode is provided to which the above-described carbon composite is added as a cathode additive.

[0111] In one embodiment of the present invention, the positive electrode comprises a current collector and a positive electrode active material layer located on at least one side of the current collector, the positive electrode active material comprising a binder and a positive electrode additive, wherein the positive electrode active material comprises a sulfur-containing compound and the positive electrode additive comprises the carbon composite described above.

[0112] In one embodiment of the present invention, when the positive electrode additive is the carbon composite described above, the positive electrode additive may be present in an amount of, for example, 0.1 to 30 parts by weight per 100 parts by weight of the total positive electrode active material layer. Specifically, the positive electrode additive may be present in an amount of 0.5 to 20 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight per 100 parts by weight of the total positive electrode active material layer. When the positive electrode additive is present in the above range, it has the effect of improving the electrical conductivity between active material particles or between the active material and the current collector, and reducing the resistance within the electrode. Furthermore, by dispersing the positive electrode additive between the compressed active material particles, micropores are maintained between the active material particles, making it easier for the electrolyte to penetrate.

[0113] According to yet another aspect of the present invention, a battery is provided which includes a positive electrode using the above-described carbon composite as a positive electrode additive.

[0114] The battery comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode contains the carbon composite described above as a positive electrode additive.

[0115] In this case, the above-mentioned matters shall apply to the negative electrode, separator, and electrolyte.

[0116] According to yet another aspect of the present invention, a method for producing the carbon composite described above is provided.

[0117] As described above, the carbon composite comprises a porous carbon material and vanadium nitride particles located on the surface of the porous carbon material.

[0118] The method for producing the carbon composite includes a first step of introducing and dispersing a porous carbon material, vanadium nitride or its precursor, and a reducing agent in a solvent; a second step of filtering the result of the first step to remove the solvent and drying it; and a third step of heat-treating the result of the second step in an inert atmosphere.

[0119] In one embodiment of the present invention, the vanadium nitride precursor may include one or more selected from dicyandiamide, ammonium metavanadate (NH4VO3), vanadium oxide, ammonia (NH3), and ammonium chloride.

[0120] For example, the vanadium nitride may be produced by a synthesis reaction between dicyandiamide and ammonium metavanadate.

[0121] In one embodiment of the present invention, the reducing agent may comprise one or more selected from glucose, sucrose, lactose, fructose, starch, polydopamine, and tannic acid.

[0122] In one embodiment of the present invention, the solvent used in the first step may be one or more organic solvents selected from the group consisting of dimethyl carbonate, dimethylformamide, N-methylformamide, sulfolane (tetrahydrothiophene-1,1-dioxide), 3-methylsulfolane, N-butylsulfone, dimethyl sulfoxide, pyrrolidinone (HEP), dimethylpiperidone (DMPD), N-methylpyrrolidinone (NMP), N-methylacetamide, dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), diethylacetamide (DEAc), dipropylacetamide (DPAc), ethanol, propanol, butanol, hexanol, ethylene glycol, tetrachloroethylene, propylene glycol, toluene, terpentin, methyl acetate, ethyl acetate, petroleum ether, acetone, cresol, and glycerol.

[0123] In one embodiment of the present invention, based on 100 parts by weight of porous carbon material introduced in the first step, the content of vanadium nitride or its precursor may be 1 to 100 parts by weight or 5 to 40 parts by weight, and the content of the reducing agent may be 10 to 100 parts by weight or 20 to 80 parts by weight. By satisfying the above ranges for vanadium nitride or its precursor and the reducing agent, it becomes possible to uniformly form vanadium nitride catalyst particles at an appropriate level on the surface of the porous carbon material. Furthermore, by minimizing amorphous carbon with low electrical conductivity and maximizing the exposure of the catalyst surface while maintaining a large specific surface area, it is advantageous to maximize the reactivity of lithium polysulfide and prevent it from dissolving into the electrolyte, but the present invention is not limited thereto.

[0124] In one embodiment of the present invention, in the first step, dispersion may be carried out by ultrasonic treatment and / or magnetic stirring.

[0125] In one embodiment of the present invention, in the second step, the removal of the solvent may be carried out by vacuum filtration. The drying may be carried out under temperature conditions of 50°C to 150°C. The drying may be carried out for, for example, 1 to 48 hours.

[0126] In one embodiment of the present invention, the third step includes a first step of heat treatment at a low temperature and a second step of heat treatment at a high temperature. Specifically, the first step may be carried out such that a vanadium nitride precursor is thermally decomposed and reduced to produce vanadium nitride, and the second step may be carried out such that a carbonization reaction is carried out so that vanadium nitride particles are bonded to the surface of a porous carbon material.

[0127] In one embodiment of the present invention, the third step may include a first step of heat treatment at 350 to 650°C and a second step of heat treatment at 650 to 1400°C.

[0128] In one embodiment of the present invention, the first process may be carried out at 350-650°C, 500-650°C, or 550-650°C.

[0129] In one embodiment of the present invention, the second process may be carried out at a temperature of 650 to 1400°C, 700 to 900°C, or 750 to 850°C.

[0130] In one embodiment of the present invention, the third step may be carried out in an inert atmosphere, which may be formed using one or more gases selected from helium, neon, argon, carbon dioxide, and nitrogen.

[0131] In one embodiment of the present invention, the method for producing the carbon composite described above may be characterized by not using NH3, HF, and an acid having an acid dissociation constant (pKa) of 4.0 or less.

[0132] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and the scope of the present invention is not limited in any way to them.

[0133] [Manufacturing of carbon composites] Example 1 1.6 g of carbon nanotubes, 24 g of dicyanodiamide, 0.8 g of ammonium metavanadate, and 0.2 g of glucose were mixed in 500 mL of solvent containing ethanol and water in a 1:1 volume ratio, and then dissolved and dispersed by sonication and magnetic stirring.

[0134] Subsequently, the solvent was removed by vacuum filtration, which removed the vanadium nitride precursor adsorbed on the surface of the carbon nanotubes.

[0135] After this, it was dried in an 80°C oven for 12 hours.

[0136] Subsequently, the carbon nanotubes were heat-treated in an inert atmosphere tube furnace at 600°C for 3 hours and then at 800°C for 2 hours to obtain a carbon composite in which vanadium nitride particles were located on the surface of the carbon nanotubes. At this time, the content of vanadium nitride particles was 20 parts by weight per 100 parts by weight of the obtained carbon composite. The content of vanadium nitride particles was measured using a thermogravimetric analyzer (TGA).

[0137] Example 2 A carbon composite in which vanadium nitride particles are located on the surface of reduced graphene oxide was obtained in the same manner as in Example 1, except that reduced graphene oxide was used instead of carbon nanotubes. At this time, the content of vanadium nitride particles was 20 parts by weight per 100 parts by weight of the obtained carbon composite. The content of vanadium nitride particles was measured using a thermogravimetric analyzer (TGA).

[0138] Comparative Example 1 24 g of dicyanodiamide, 0.8 g of ammonium metavanadate, and 0.8 g of glucose were mixed in 500 mL of solvent containing ethanol and water in a 1:1 volume ratio, and then dissolved and dispersed by sonication and magnetic stirring.

[0139] Subsequently, the solvent, excluding dicyanodiamide and ammonium metavanadate, was removed by vacuum filtration.

[0140] After this, it was dried in an 80°C oven for 12 hours.

[0141] Subsequently, the material was heat-treated in an inert atmosphere tube furnace at 600°C for 3 hours and then at 800°C for 2 hours to obtain a carbon composite in which vanadium nitride particles are located on the surface of amorphous carbon formed from glucose through a carbonization process.

[0142] At this time, the vanadium nitride particle content was 20 parts by weight per 100 parts by weight of the obtained carbon composite. The vanadium nitride particle content was measured using a thermogravimetric analyzer (TGA).

[0143] Evaluation of the physical properties of carbon composites In the carbon composites produced by Example 1, Example 2, and Comparative Example 1, the specific surface area, pore volume, and average pore diameter were measured using a BELSORP-mino II manufactured by BEL Japan, according to a method calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K).

[0144] Furthermore, the degree of crystallinity of carbon in the carbon composite prepared above was measured using Raman spectroscopy, and the spectrum obtained as a result of the measurement was used to determine the degree of carbon crystallization. D / I G The ratio was derived.

[0145] The physical properties evaluated according to the method described above are shown in Table 1 below.

[0146] [Table 1]

[0147] Figure 1 shows the results of measuring the 77K N2 isotherm of the carbon composites from Example 1, Example 2, and Comparative Example 1.

[0148] Figure 2 is an SEM image of the carbon composite of Example 1, in which vanadium nitride particles are located on the surface of carbon nanotubes. The SEM image in Figure 2 was obtained at a magnification of 2,000 times for an area of ​​10 μm x 10 μm.

[0149] Figure 3 is an SEM image of the carbon composite of Example 2, in which vanadium nitride particles are located on the surface of reduced graphene oxide. The SEM image in Figure 3 was obtained at a magnification of 2,000 times for an area of ​​10 μm x 10 μm.

[0150] Figure 4 is an SEM image of Comparative Example 1, a carbon composite in which vanadium nitride particles are located on the surface of amorphous carbon nanotubes. The SEM image in Figure 4 was obtained at a magnification of 2,000 times for an area of ​​10 μm x 10 μm.

[0151] Referring to Figures 2 to 4, it was confirmed that vanadium nitride particles were uniformly formed on the surfaces of carbon nanotubes, reduced graphene oxide, and amorphous carbon, respectively. The average particle size (D) of the vanadium nitride particles formed on the surface of amorphous carbon. 50 The particle size is 1 μm, and it can be confirmed that the vanadium nitride particles are quite solidified into clumps. In contrast, the vanadium nitride particles formed on the surface of reduced graphene oxide or carbon nanotubes have an average particle size (D 50 It can be confirmed that the size is 0.1 μm or less.

[0152] [Manufacturing of lithium-sulfur batteries] Example 3 <Manufacturing of positive electrodes> As the cathode active material, a porous carbon support in which sulfur was supported on carbon nanotubes was prepared. At this time, the weight ratio of the carbon composite to sulfur (S8) was set to 1:3. The carbon composite from Example 1 was used as the cathode additive, and polyacrylic acid (PAA) was mixed as a binder to produce a cathode slurry.

[0153] At this time, the weight ratio of the positive electrode active material, positive electrode additive, and binder was 88:5:7.

[0154] The slurry was coated onto aluminum foil using a Mathis coating apparatus, dried at 50°C for 24 hours, and then rolled to produce the cathode.

[0155] <Manufacturing of lithium-sulfur batteries> A lithium metal thin film with a thickness of 45 μm was prepared as the negative electrode, and a mixture was prepared by dissolving 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% lithium nitrate (LiNO3) in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME = 1:1 (volume ratio)) as the electrolyte.

[0156] The manufactured and prepared positive and negative electrodes were positioned facing each other, a polyethylene separator with a thickness of 16 μm and a porosity of 46% was interposed between them, and then 70 μl of the electrolyte was injected to manufacture a lithium sulfur battery.

[0157] Example 4 A lithium-sulfur battery was manufactured in the same manner as in Example 3, except that the carbon composite of Example 2 was used as the positive electrode additive instead of the carbon composite of Example 1.

[0158] Example 5 <Manufacturing of positive electrodes> As the positive electrode active material, a carbon composite prepared in Example 1 was prepared by supporting sulfur using a melt-loading method. Specifically, the carbon composite was mixed uniformly with sulfur (S8). After this, it was heat-treated in an oven at 150°C for 30 minutes to impregnate the inside of the carbon composite with sulfur. At this time, the weight ratio of the carbon composite to the sulfur was 1:3.

[0159] Here, a positive electrode slurry was prepared by mixing a polyacrylic acid (PAA) binder with a carbon fiber conductive material. In this slurry, the weight ratio of the positive electrode active material, conductive material, and binder was 88:5:7.

[0160] The slurry was coated onto aluminum foil using a Matisse coating apparatus, dried at a temperature of 50°C for 24 hours, and then rolled to produce the positive electrode.

[0161] <Manufacturing of lithium-sulfur batteries> A lithium metal thin film with a thickness of 45 μm was prepared as the negative electrode, and a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1% by weight lithium nitrate (LiNO3) was dissolved in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME = 1:1 (volume ratio)) as the electrolyte.

[0162] The manufactured and prepared positive and negative electrodes were positioned facing each other, a polyethylene separator with a thickness of 16 μm and a porosity of 46% was interposed between them, and then 70 μl of the electrolyte was injected to manufacture a lithium sulfur battery.

[0163] Comparative Example 2 A lithium-sulfur battery was manufactured in the same manner as in Example 3, except that carbon nanotubes (CNTs) were used as the cathode additive instead of the carbon composite in Example 1.

[0164] Comparative Example 3 A lithium-sulfur battery was manufactured in the same manner as in Example 3, except that the carbon composite of Comparative Example 1 was used as the positive electrode additive instead of the carbon composite of Example 1.

[0165] Comparative Example 4 The cathode and lithium-sulfur battery were manufactured in the same manner as in Example 5, except that carbon nanotubes (CNTs) were used as the cathode additive instead of the carbon composite manufactured in Example 1.

[0166] Comparative Example 5 <Manufacturing of positive electrodes> As the positive electrode active material, a material was prepared in which sulfur was supported on carbon nanotubes (CNTs) using a melt-loading method. Specifically, the carbon composite was mixed uniformly with sulfur (S8). After this, it was heat-treated in an oven at 150°C for 30 minutes to impregnate the inside of the carbon composite with sulfur. At this time, the weight ratio of the carbon composite to the sulfur was 1:3.

[0167] A positive electrode slurry was then prepared by adding and mixing a polyacrylic acid (PAA) binder, polyvinyl alcohol, PVA (polyvinyl alcohol) thickener, and carbon nanotube conductive material. In the slurry, the weight ratio of the positive electrode active material, binder, thickener, and conductive material was 88:6.5:0.5:5.

[0168] The slurry was coated onto aluminum foil using a Matisse coating apparatus, dried at a temperature of 50°C for 24 hours, and then rolled to produce the positive electrode.

[0169] <Manufacturing of lithium-sulfur batteries> A lithium metal thin film with a thickness of 45 μm was prepared as the negative electrode, and a mixture was prepared by dissolving 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt% lithium nitrate (LiNO3) in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME = 1:1 (volume ratio)) as the electrolyte.

[0170] The manufactured and prepared positive and negative electrodes were positioned facing each other, a polyethylene separator with a thickness of 16 μm and a porosity of 46% was interposed between them, and then 70 μl of the electrolyte was injected to manufacture a lithium sulfur battery.

[0171] [Evaluation of lithium-sulfur battery performance] The lithium-sulfur batteries of Examples 3 to 5 and Comparative Examples 2 to 5, manufactured as described above, were evaluated for performance using the circulating current-voltage method (CV), and the results are shown in Figures 5 to 9.

[0172] Specifically, for the battery being evaluated, 1.7V~2.8V (vs Li / Li + Within the voltage range, the first three charge-discharge cycles were performed at a current density of 0.1C, the next three at 0.3C, and subsequent charge-discharge cycles at 0.5C. The capacity-voltage curve (Figures 5, 7, and 8), voltage-current density curve (Figure 6), and cycle-specific capacity curve (Figure 9) for the first cycle are shown.

[0173] Referring to Figure 5, it was confirmed that the batteries of Examples 3 and 4, which used a carbon composite containing vanadium nitride particles on a porous carbon material as a positive electrode additive, showed improved battery performance compared to the battery of Comparative Example 5 due to the catalytic activity of the vanadium nitride particles. From this, it was confirmed that vanadium nitride particles can improve the overvoltage of lithium-sulfur batteries and improve the rate at which lithium polysulfide is converted to lithium sulfide. In particular, it was confirmed that Example 3, which used carbon nanotubes, showed even more outstanding performance than Example 4, which used reduced graphene oxide.

[0174] Furthermore, referring to Figures 6 and 7, it was confirmed that the battery of Comparative Example 3, which uses the carbon composite of Comparative Example 1 as a positive electrode additive, having a small specific surface area, small pores, and vanadium nitride particles located on the surface of amorphous carbon, exhibits increased resistance due to the low electrical conductivity of amorphous carbon. As a result, it is actually inferior in performance to Comparative Example 5, which uses a positive electrode without vanadium nitride particles.

[0175] Referring to Figures 8 and 9, we were able to confirm that the lithium-sulfur battery of Example 5 had improved performance due to the reduction of overvoltage and the acceleration of the conversion reaction. From this, we confirmed that the performance of a lithium-sulfur battery can be improved by supporting sulfur (S8) on a carbon composite containing vanadium nitride particles on a porous carbon material and using this as the positive electrode active material.

[0176] Although the present invention has been described above with reference to limited embodiments and drawings, it goes without saying that the present invention is not limited thereto, and that various modifications and variations can be made by persons with ordinary skill in the art to which the present invention pertains, within the equivalent scope of the technical idea and claims of the present invention.

Claims

1. Current collector and, A positive electrode active material layer located on at least one side of the current collector, comprising a positive electrode active material, a binder, and a positive electrode additive, Equipped with, The positive electrode active material contains a sulfur-containing compound, The positive electrode additive is a positive electrode containing a carbon composite, The carbon composite is A porous carbon material that is at least partially crystalline, Vanadium nitride particles located on the surface of the porous carbon material, Includes, A positive electrode having a specific surface area of ​​250 m² / g or more of the carbon composite.

2. The specific surface area of ​​the carbon composite is 250 m². ２ The positive electrode according to claim 1, wherein the concentration is 1 / g or more and 400 m² / g or less.

3. The pore volume of the carbon composite is 1.0 cm ３ The positive electrode according to claim 1, wherein the amount is 1g or more.

4. The positive electrode according to claim 1, wherein the average pore size of the carbon composite is 10 nm or more.

5. The positive electrode according to claim 1, wherein the average particle diameter of the vanadium nitride particles is 200 nm or less.

6. The positive electrode according to claim 1, wherein the vanadium nitride particles are contained in an amount of 3 to 50 parts by weight per 100 parts by weight of the carbon composite.

7. The cathode according to claim 1, wherein the porous carbon material comprises carbon nanotubes (CNTs), reduced graphene oxide (rGO), or a mixture thereof.

8. The positive electrode according to any one of claims 1 to 7, wherein the positive electrode additive is contained in an amount of 0.01 to 30 parts by weight per 100 parts by weight of the total positive electrode active material layer.

9. The system includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. A battery wherein the positive electrode is the positive electrode described in any one of claims 1 to 7.

10. A first step involves adding and dispersing a porous carbon material, vanadium nitride or its precursor, and a reducing agent in a solvent. A second step involves filtering the result of the first step to remove the solvent and drying it, A third step involves heat-treating the result of the second step in an inert atmosphere, Includes, Step 3 above is, A first step involves heat treatment at 350°C to 650°C, A second process involves heat treatment at 650°C to 1400°C, A method for producing carbon composites, including [the specified element].

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