Positive electrode for lithium-sulfur batteries containing different types of conductive materials and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode for a lithium-sulfur battery, the positive electrode comprising a sulfur-carbon composite containing a porous carbon material and sulfur (S) as a positive electrode active material, a first conductive material having a fibrous shape with an average particle size of 5 μm or less, and a second conductive material containing secondary particles formed by agglomeration of two or more CNT primary particles. The novel combination of conductive materials according to the present invention improves the output characteristics of the battery and increases the capacity.

Description

[Technical Field]

[0001] This invention relates to a lithium-sulfur battery with improved battery performance, such as output and capacity.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0036689, filed on March 24, 2022, and all content disclosed in the specification and drawings of said application is incorporated herein. [Background technology]

[0003] The positive electrode of a lithium-sulfur battery contains a conductive material in a content range of 0 to 10 wt% relative to 100 wt% of the positive electrode material to ensure electronic conductivity. Typically, activated carbon materials such as carbon black, denka black, and ketjenblack, as well as carbon fibers or carbon nanotubes (CNTs), are used as conductive materials.

[0004] When using carbon nanotubes (CNTs) or carbon fibers, they are typically pre-dispersed so that the fiber strands are completely dispersed, or they can be used as entangled powder particles. However, no techniques have yet been proposed to control such dispersion states and optimize the performance improvement of conductive materials. [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a novel combination of conductive material components and their content that can improve the output and capacity characteristics of a positive electrode for a lithium-sulfur battery. Another objective of the present invention is to provide a positive electrode for a lithium-sulfur battery containing the novel combination of conductive materials and a lithium secondary battery containing the positive electrode. [Means for solving the problem]

[0006] A first aspect of the present invention relates to a positive electrode material composition for a lithium-sulfur battery, wherein the composition comprises a positive electrode active material, a conductive material, and a binder material, the positive electrode active material comprises a porous carbon material and a sulfur-carbon composite containing sulfur (S), the conductive material comprises a first conductive material and a second conductive material, the first conductive material is fibrous with an average particle size of 5 μm or less, the second conductive material comprises secondary particles formed by the aggregation of two or more CNT primary particles, and the second conductive material exhibits an average particle size of 10 μm to 70 μm. The positive electrode active material, conductive material, and binder material are contained in amounts ranging from 80 wt% to 97 wt%, 2 wt% to 10 wt%, and 2 wt% to 10 wt%, respectively.

[0007] According to a second aspect of the present invention, in the first aspect, the first conductive material includes CNTs, and the CNTs have an average number of layers of 1 to 20.

[0008] A third aspect of the present invention is that, in the second aspect, the first conductive material contains CNTs, and is present in an amount of 0.1% to 0.5% of 100 wt% of the total weight of the positive electrode active material, binder material and conductive material.

[0009] According to a fourth aspect of the present invention, in any one of the first to third aspects, the first conductive material includes carbon fibers, and the carbon fibers have a diameter of 100 nm to 2 μm.

[0010] According to the fifth aspect of the present invention, in any one of the first to fourth aspects, the second conductive material, which is CNT, has an average number of layers of 1 to 20, and the average diameter of the primary CNT particles is 0.4 nm to 100 nm.

[0011] According to the sixth aspect of the present invention, in any one of the first to fifth aspects, the first conductive material is included in an amount of 0.1 wt% to 5 wt% and the second conductive material in an amount of 1 wt% to 5 wt% based on 100 wt% of the total weight of the positive electrode active material, binder material and conductive material.

[0012] According to the seventh aspect of the present invention, in any one of the first to sixth aspects, the porous carbon material has a BET specific surface area of primary particles of 100 m 2 / g to 3,000 m 2 / g.

[0013] According to the eighth aspect of the present invention, in any one of the first to seventh aspects, the porous carbon material contains one or more selected from the group consisting of activated carbon, carbon nanotubes (CNT), and graphene.

[0014] According to the ninth aspect of the present invention, in any one of the first to eighth aspects, the CNT has an average number of layers of 1 to 20.

[0015] According to the tenth aspect of the present invention, in any one of the first to ninth aspects, the sulfur-carbon composite contains 70 wt% or more with respect to 100 wt% of the positive electrode active material.

[0016] According to the eleventh aspect of the present invention, in any one of the first to tenth aspects, the sulfur-carbon composite contains 70 wt% or more of sulfur with respect to 100 wt% of the sulfur-carbon composite.

[0017] According to the twelfth aspect of the present invention, in any one of the first to eleventh aspects, the sulfur-carbon composite has any one or more of a state in which sulfur and a carbon material are simply mixed and complexed, a state having a coating form of a core-shell structure, and a state in which sulfur is filled in the internal pores of the carbon material.

[0018] In addition, the thirteenth aspect of the present invention relates to a positive electrode for an electrochemical element, and the positive electrode contains a positive electrode material composition according to any one of the first to twelfth aspects.

[0019] Furthermore, the fourteenth aspect of the present invention relates to a lithium secondary battery including the positive electrode for the electrochemical element.

[0020] The present invention also relates to a method for producing a slurry for forming a positive electrode. The fifteenth aspect of the present invention relates to the method, wherein a positive electrode material composition according to any one of the first to twelfth aspects is mixed with a second solvent, the first conductive material is added after being adjusted to have an average particle size of 5 μm or less, the second conductive material is added in powder form and contains secondary particles in which two or more primary CNT particles are aggregated, and the second conductive material containing the secondary particles has an average particle size of 10 μm to 70 μm.

[0021] According to the sixteenth aspect of the present invention, in the fifteenth aspect, the second solvent comprises one or more selected from water and organic solvents.

[0022] According to the 17th aspect of the present invention, in the 15th or 16th aspect, if the first conductive material contains CNTs, the CNTs are mixed with the first solvent and added to the slurry in the form of a mixed solution. [Effects of the Invention]

[0023] In lithium-sulfur secondary batteries, the inclusion of a novel combination of conductive materials according to the present invention improves the battery's output characteristics and increases its capacity. [Brief explanation of the drawing]

[0024] [Figure 1] The output and capacity characteristics of the batteries according to Examples 1 and 2 of the present invention are shown. [Figure 2] The measurement results of the electrode resistivity for Comparative Examples 1, 3, and 4 are shown. [Figure 3] The measurement results of the electrode resistivity for Comparative Examples 1, 6, 7, and 8 are shown. [Figure 4a] The measurement results of the battery discharge characteristics for Comparative Examples 1 to 4 are shown. [Figure 4b] The measurement results of the battery discharge characteristics for Comparative Examples 1 to 4 are shown. [Figure 5] The measurement results of the battery discharge characteristics for Comparative Examples 1, 5, and 6 are shown. [Figure 6] The measurement results of the battery discharge characteristics for Comparative Examples 1, 9, and 10 are shown. [Figure 7] The discharge characteristics of the batteries according to Example 1 and Comparative Examples 1 and 11 are shown. [Modes for carrying out the invention]

[0025] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Prior to this, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept that is in line with the technical idea of ​​the present invention, in accordance with the principle that the inventor himself may appropriately define the concepts of terms in order to best describe the invention.

[0026] When a part of the specification is described as "including" a certain component, unless otherwise specified, it means that it may include other components, rather than excluding them.

[0027] Terms used throughout this specification, such as “approximately” and “substantially,” are used to mean, when specific manufacturing and material tolerances are presented, the numerical values ​​or values ​​close to those values, and are used to prevent unscrupulous infringers from unfairly using disclosures that refer to precise or absolute numerical values ​​to aid in understanding this application.

[0028] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0029] In this invention, "specific surface area" refers to the amount measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan.

[0030] As used herein, the term "polysulfide" refers to "polysulfide ion (S x 2- , x=8, 6, 4, 2) and "Lithium polysulfide (Li2S x or LiSx - It is a concept that includes both "(x = 8, 6, 4, 2)".

[0031] As used herein, the term "composite" means a substance in which two or more materials are combined to form physically and chemically different phases and exhibit a more effective function.

[0032] As used herein, the term "porosity" means the ratio of the volume occupied by pores to the total volume in a certain structure, and the unit "%" is used, which can be used interchangeably with terms such as void fraction and porosity.

[0033] In the present invention, "particle size D 50 " means the size of the particles based on 50% of the volume cumulative particle size distribution. The particle size D 50 can be measured using the laser diffraction method. For example, after dispersing the particles in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60W, and after obtaining a volume cumulative particle size distribution graph, it can be measured by determining the size of the particles corresponding to 50% of the volume cumulative amount.

[0034] In the present invention, the "thickness of the fiber" means the average thickness of the fibrous carbon material when observed with a scanning electron microscope (SEM). When showing the distribution of the particle sizes measured by the laser diffraction method, if multiple peaks are observed, it is also possible to estimate the fiber thickness from the particle size at which the smallest peak is located.

[0035] Note that the sizes and thicknesses of each component shown in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not necessarily limited to such illustrations. In the drawings, the thicknesses are enlarged to clearly show multiple layers and regions. And in the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated.

[0036] Furthermore, when a specification as a whole states that a certain part "includes" a certain component, this means that, unless otherwise specified, it may include other components without excluding them.

[0037] The present invention relates to a positive electrode material composition for lithium-sulfur batteries. In one embodiment of the present invention, the positive electrode material composition comprises a positive electrode active material, a conductive material, and a binder material. In the positive electrode material composition, the positive electrode active material may be present in proportions of 80 wt% to 97 wt%, the conductive material in proportions of 2 wt% to 10 wt%, and the binder in proportions of 2 wt% to 10 wt%, based on the total weight of the positive electrode active material, conductive material, and binder material. On the other hand, the positive electrode material composition may further contain a solvent if necessary, and the solvent may further contain one or more of a first solvent and a second solvent as described later.

[0038] Next, we will explain each of the aforementioned components in more detail.

[0039] positive electrode active material The positive electrode active material according to the present invention contains a sulfur-carbon composite. Preferably, the positive electrode active material contains 80 wt% or more, preferably 90 wt% or more, of the sulfur-carbon composite per 100 wt% of the positive electrode active material, and more preferably, the positive electrode active material may consist solely of the sulfur-carbon composite. Furthermore, it is desirable that the sulfur content be 70 wt% or more per 100 wt% of the sulfur-carbon composite.

[0040] In one embodiment of the present invention, the sulfur-carbon composite may be formed by simply mixing the sulfur and carbon material, or it may be in the form of a coating or support in a core-shell structure. In the core-shell structure coating form, either the sulfur or the carbon material coats the other substance, for example, the surface of the carbon material may be surrounded by sulfur, or vice versa. In the support form, sulfur may be filled inside the carbon material, particularly in the internal pores. The form of the sulfur-carbon composite can be any form that satisfies the content ratio of the sulfur-based compound to the carbon material presented above, and is not limited to the present invention. On the other hand, in the present invention, it is desirable that the sulfur content be 70% by weight or more relative to the total weight of the positive electrode active material.

[0041] Since the aforementioned sulfur is not electrically conductive on its own, it is used in combination with a carbon material. See the description below for details on the carbon material. In one embodiment of the present invention, the sulfur is inorganic sulfur (S8), Li2S n (n≧1), disulfide compounds such as 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid, organic compounds and carbon-sulfur polymers ((C2S x ) n It can be one or more selected from the group consisting of x = 2.5 to 50, n ≥ 2). Preferably, it may contain inorganic sulfur (S8).

[0042] Lithium-sulfur batteries are attracting attention as a next-generation rechargeable battery not only because they have high discharge capacity and theoretical energy density among rechargeable batteries, but also because the sulfur used as the positive electrode active material is abundant and inexpensive, which allows for lower manufacturing costs and environmental friendliness.

[0043] In lithium-sulfur batteries, sulfur, the positive electrode active material, is an insulator. Therefore, to compensate for its low electrical conductivity, a sulfur-carbon composite, which is a compound of sulfur and a conductive material such as carbon, is commonly used.

[0044] The sulfur-carbon composite comprises a porous carbon material and sulfur. In one embodiment of the present invention, the sulfur-carbon composite may be in a form in which sulfur is supported in the pores of the porous carbon material.

[0045] The carbon material has a porous structure containing multiple non-uniform pores on its surface and inside, and acts as a support that provides a uniform and stably immobilizable framework for sulfur, compensating for the low electrical conductivity of sulfur and facilitating electrochemical reactions. In particular, in a sulfur-carbon composite, the carbon material that acts as a sulfur support has a large BET specific surface area and an appropriate particle size D 50 When it has a certain size, it can carry a high amount of sulfur while having a low irreversible capacity, which can increase the energy density and thus the utilization rate of sulfur during electrochemical reactions.

[0046] In one embodiment of the present invention, the BET specific surface area of ​​the carbon material is a minimum of 100 m². 2 It is 1 / g or more, and the maximum is 3,000m 2 It may be / g. Together with or independently of this, the carbon material has a primary particle size D 50 This can range from 1 μm to 50 μm.

[0047] BET specific surface area and particle size D of the carbon material 50 By satisfying the aforementioned range, sulfur can be uniformly dispersed on the internal and external surfaces of the carbon material, while reducing irreversible capacity and increasing the electrochemical reactivity of sulfur. Furthermore, the use of carbon material improves the electrochemical reactivity, stability, and electrical conductivity of the sulfur-carbon composite, thereby improving the capacity and lifespan characteristics of the lithium-sulfur battery, as well as ensuring optimal charge-discharge performance even when sulfur loss or volume change occurs during charging and discharging.

[0048] Particle size D of the primary particles 50 When the particle size exceeds 50 μm, the movement of lithium ions into the particle becomes difficult due to limitations on mass transfer, making it difficult to efficiently utilize the sulfur located at the carbon center. Primary particle size D 50When the particle size is less than 1 μm, it is difficult to increase the solid content because a large amount of solvent is required during the electrode slurry preparation process. This results in insufficient pores between particles, leading to a decrease in output.

[0049] In the sulfur-carbon composite of the present invention, the carbon material used as the sulfur support can typically be produced by carbonizing precursors of various carbon materials.

[0050] On the other hand, in one embodiment of the present invention, the pores of the carbon material may have a diameter in the range of 0.5 nm to 200 nm with respect to the longest diameter. The carbon material is not particularly limited, as it can be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped, and is suitable for use in lithium-sulfur batteries.

[0051] The carbon material may be any porous and conductive carbon-based material commonly used in the industry. For example, it may include graphite; graphene; carbon blacks such as Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermal Black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and 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; carbon nanoribbons; carbon nanobelts, carbon nanorods, and activated carbon.

[0052] In the sulfur-carbon composite according to the present invention, the sulfur is located on at least one surface, either inside or outside the pores of the carbon material, and may be present in a region of less than 100%, preferably 1% to 95%, and more preferably 60% to 90%, of the entire surface of the carbon material, both inside and outside. When the sulfur is present on the surface of the carbon material within this range, it can achieve the greatest effect in terms of electron transfer area and electrolyte wettability. Specifically, because the sulfur is thinly and uniformly impregnated into the surface of the carbon material within this range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur is located in a region of 100% of the entire surface of the carbon material, the carbon material is completely covered with sulfur, the wettability of the electrolyte is reduced, the contact with the conductive material contained in the electrode decreases, electrons are less likely to be transferred, and the sulfur cannot participate in the reaction.

[0053] Furthermore, in one embodiment of the present invention, the sulfur-carbon composite is obtained by the following manufacturing method.

[0054] The method for producing the sulfur-carbon composite according to the present invention is not particularly limited and is commonly known in the art, and can be produced by a composite method comprising the steps of (S1) mixing a carbon material and sulfur, followed by (S2) compounding.

[0055] The mixing in step (S1) is intended to increase the degree of mixing between the sulfur and the carbon material, and can be carried out using a stirring device commonly used in this industry. In this case, the mixing time and speed can also be selectively adjusted according to the content and conditions of the raw materials.

[0056] The compounding method in step (S2) is not particularly limited in the present invention, and methods commonly used in the industry may be used. For example, methods commonly used in the industry, such as dry compounding or wet compounding such as spray coating, may be used. For example, a method may be used in which the mixture of sulfur and carbon material obtained after mixing is heat-treated so that the molten sulfur is uniformly coated on the inside and outside surface of the carbon material. On the other hand, in one embodiment of the present invention, the mixture of sulfur and carbon material is ground by a method such as ball milling before the heat treatment. In one embodiment of the present invention, the heat treatment is carried out at a temperature of 120°C to 160°C for about 20 minutes to 24 hours, and a heating device such as an oven may be used.

[0057] The sulfur-carbon composite produced by the aforementioned manufacturing method has a high specific surface area, a high sulfur load capacity, and a structure that improves sulfur utilization. As a result, not only is the electrochemical reactivity of sulfur improved, but the accessibility and contactability of the electrolyte are also improved, thereby improving the capacity and lifespan characteristics of lithium-sulfur batteries.

[0058] conductive material The positive electrode material composition according to the present invention comprises a conductive material, wherein the conductive material comprises a first conductive material and a second conductive material.

[0059] The first conductive material is fibrous or needle-shaped, and its average particle size is 5 μm or less, as determined by PSD (particle size distribution) analysis. The PSD can be measured using a particle size distribution analyzer. For example, the first conductive material can be introduced into a commercially available laser diffraction particle size distribution analyzer (e.g., Microtrac S3500), and the particle size distribution can be calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam.

[0060] In one embodiment of the present invention, the average particle size may be a value confirmed by dry or wet analysis among PSD analyses. Dry analysis is a method of analyzing particle size by scattering the analyte particles in the atmosphere, for example, while wet analysis is a method of analyzing particle size by dispersing the analyte particles in a solvent (for example, water). On the other hand, the average particle size of the first conductive material can also be maintained in the positive electrode material composition, the slurry for forming the positive electrode, and the positive electrode obtained therefrom.

[0061] The first conductive material may include one or more selected from the group consisting of carbon nanotubes and carbon fibers. In one embodiment of the present invention, the carbon fibers may have a fiber diameter of 100 nm to 2 μm. The carbon nanotubes have an average number of layers of 1 to 20, and the average diameter (diameter) of the primary particles (single carbon nanotubes) may be 0.4 nm to 100 nm. Here, the diameters of the carbon fibers and carbon nanotube primary particles can be measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0062] The average diameter of the carbon nanotube primary particles can be calculated by averaging the diameters of multiple primary particles in a carbon nanotube image observed by TEM or SEM. In this case, the number of primary particles observed may be, for example, 10 to 50, but is not limited to this.

[0063] The fact that the diameter of the carbon fiber is 100 nm to 2 μm may mean that the diameters of several carbon fibers arbitrarily selected from a carbon fiber image observed by TEM or SEM fall within this range. For example, if an image of carbon fibers is taken with TEM, and 10 to 50 carbon fibers are arbitrarily selected from the image and their diameters are measured, and all the measured diameters are 100 nm to 2 μm, then the diameter of the carbon fiber can be considered to be 100 nm to 2 μm. However, the number of carbon fibers selected for diameter measurement is not limited to 10 to 50.

[0064] As described above, when the first conductive material includes one or more selected from the group consisting of carbon nanotubes and carbon fibers, a battery containing a positive electrode material composition including this material can have a lower resistivity and improve capacity.

[0065] On the other hand, if the first conductive material contains CNTs, it is desirable that the CNT content be in the range of 0.1 wt% to 0.5 wt% per 100 wt% of the total weight of the positive electrode active material, binder material, and conductive material. If the content is not within this range, the coupling effect of the conductive path is small and no effect of improving output is shown, and if it is higher, the CNTs form a film and block the pores, hindering a smooth battery reaction and reducing output.

[0066] On the other hand, if the first conductive material contains carbon fibers, it is desirable that the carbon fiber content be in the range of 1 wt% to 10 wt% of the total weight of the positive electrode active material, binder material, and conductive material. If the content is not within this range, the coupling effect of the conductive path is small and no effect of improving output is shown, and if it is higher, the carbon fibers form a film and block the pores, which hinders the smooth battery reaction and reduces output.

[0067] In one embodiment of the present invention, the first conductive material can be dispersed in water or a suitable organic solvent (NMP, acetone, etc.) to produce a mixed solution in order to maintain an average particle size of 5 μm or less and to improve dispersibility in the cathode material composition, and this mixed solution can be added to the cathode material composition. In particular, CNTs exist as undispersed secondary particles in a gas-phase synthesized state, and even if dispersion is performed, if the degree of dispersion is insufficient, they tend to aggregate and become secondary particles, and can become large particles with an average particle size exceeding 5 μm. Therefore, when producing the mixed solution described above, the average particle size of the CNTs can be controlled to 5 μm or less. On the other hand, when carbon fibers are used instead of CNTs as the first conductive material, the carbon fibers can be sufficiently dispersed during the production of the mixed solution (slurry) of the cathode composition without prior dispersion in the solvent, and may have an average particle size of 5 μm or less. Therefore, the first conductive material does not necessarily have to be added in the form of a mixed solution.

[0068] On the other hand, in one embodiment of the present invention, the second conductive material has an average particle size of 10 μm to 70 μm as determined by PSD measurement. The second conductive material may contain carbon nanotubes (CNTs). The CNTs have an average number of layers of 1 to 20, and the average diameter of the primary particles may be 0.4 nm to 100 nm. The second conductive material has an average particle size of 10 μm to 70 μm and contains secondary particles formed by the aggregation of two or more primary particles. The second conductive material is introduced into the cathode material composition in a state containing secondary particles of the average particle size, and maintains the average particle size even in the cathode material composition. Unlike the first conductive material, it is desirable that a process of preparing a mixed solution and pre-dispersing it before introducing it into the cathode material composition is not applied.

[0069] On the other hand, in one specific embodiment of the present invention, the first conductive material may be included in an amount of 0.1 wt% to 5 wt% and the second conductive material in an amount of 1 wt% to 5 wt% relative to 100 wt% of the total weight of the positive electrode active material, binder material and conductive material.

[0070] Binder material The binder material plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinyllidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used individually or in mixtures of two or more.

[0071] Other cathode materials In one embodiment of the present invention, the positive electrode active material may consist solely of the sulfur-carbon composite. On the other hand, in one embodiment of the present invention, the positive electrode active material may further include, in addition to the sulfur-carbon composite, one or more additives selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0072] In one specific embodiment of the present invention, the positive electrode active material layer may further contain a lithium transition metal composite oxide represented by the following chemical formula 1.

[0073] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 This is Mn, Al, or a combination thereof, and preferably Mn or Mn and Al.

[0074] Said M 2This is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 While elements are not essential, when present in appropriate amounts, they can play a role in promoting particle growth during firing or improving the stability of the crystal structure.

[0075] On the other hand, a cathode slurry and a cathode can be manufactured using the cathode material composition as described below.

[0076] The positive electrode slurry can be prepared by mixing the positive electrode material composition described above with a second solvent. The solid content in the positive electrode slurry may be in the range of 20 wt% to 50 wt%. The solid content in the positive electrode slurry does not include the second solvent, and if the first conductive material is pre-dispersed and added in a mixed solution, it refers only to the remaining components after excluding the first solvent from the pre-dispersed solution.

[0077] The first conductive material is adjusted to have an average particle size of 5 μm or less and is added to the slurry. On the other hand, the second conductive material is added in powder form containing CNT secondary particles, the average particle size of which is 10 μm to 70 μm.

[0078] In one embodiment of the present invention, the second solvent may include one or more selected from water and organic solvents (NMP or acetone).

[0079] On the other hand, as mentioned above, if the first conductive material contains CNTs, the CNTs can be pre-dispersed by mixing them with the first solvent so that the average particle size is 5 μm or less, and then added to the slurry in the form of such a mixed solution.

[0080] Once the positive electrode slurry is prepared in this manner, the positive electrode can be manufactured by coating it onto at least one surface of a thin metal film for a positive electrode current collector and drying it. In the manufacturing of the positive electrode, the specific steps for slurry coating, drying, and adjusting the thickness and porosity by pressurization can be replaced by known techniques in the art to which this invention belongs.

[0081] For example, a second solvent can be prepared, and the aforementioned cathode material composition can be added to prepare a cathode slurry. Alternatively, in one embodiment of the present invention, the binder material from the cathode material composition can be added to the second solvent first to produce a binder solution, and then the remaining materials can be added sequentially. As the second solvent for producing the cathode slurry, it is desirable to use one that can uniformly disperse the cathode material composition and evaporates easily. Typical examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

[0082] The slurry produced in this manner is applied to a current collector and dried to form a positive electrode. The slurry can be coated onto the current collector to an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

[0083] The coating can be carried out by methods known in the industry. For example, the positive electrode active material slurry can be distributed to one upper surface of the positive electrode current collector and then uniformly dispersed using a doctor blade or the like. Other methods include die casting, comma coating, and screen printing.

[0084] The drying process is not particularly limited, but can be carried out at a temperature of 50°C to 200°C for no more than one day. The drying may be carried out using an apparatus such as an oven, and may be carried out under vacuum conditions.

[0085] A further aspect of the present invention relates to a positive electrode comprising the sulfur-carbon composite. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a conductive material, and a binder material. The positive electrode active material layer is derived from the positive electrode material composition described above, and the specific contents of the positive electrode components are as described above. On the other hand, in one embodiment of the present invention, the positive electrode active material layer may, as described above, comprise a positive electrode active material, a conductive material, and a binder material, and may contain the positive electrode active material in a proportion of 80 wt% to 97 wt%, the conductive material in a proportion of 2 wt% to 10 wt%, and the binder in a proportion of 2 wt% to 10 wt%, based on the total weight of the positive electrode active material, conductive material, and binder material. Furthermore, the sulfur-carbon composite may be present in an amount of 70 wt% or more relative to the total weight of the positive electrode active material, and the sulfur content may be present in an amount of 70 wt% or more relative to the total weight of the sulfur-carbon composite. In one specific embodiment of the present invention, it is desirable that the sulfur content be 70 wt% or more relative to the total weight of the positive electrode active material.

[0086] On the other hand, a variety of positive electrode current collectors used in the art can be used as the positive electrode current collector. For example, the positive electrode current collector can be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and it is also possible to form fine irregularities on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. The positive electrode current collector can be used in a variety of forms, such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0087] Furthermore, the present invention provides a lithium-sulfur battery comprising an electrode assembly including a positive electrode containing the aforementioned sulfur-carbon composite and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode.

[0088] The electrode assemblies can be stacked, for example, with a separation membrane interposed between the negative and positive electrodes to form a stacked or stacked / folded structure, or they can be wound up to form a jelly roll structure. When a jelly roll structure is formed, an additional separation membrane may be placed on the outside to prevent contact between the negative and positive electrodes.

[0089] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive material, and a binder.

[0090] Next, the negative electrode will be explained in more detail.

[0091] The negative electrode has a structure in which a negative electrode active material is formed on one or both sides of a long sheet-like negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0092] Specifically, the negative electrode can be manufactured by applying a negative electrode slurry, prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, to one or both sides of a long, sheet-like negative electrode current collector; removing the solvent from the negative electrode slurry through a drying process; and then rolling the slurry. Alternatively, a negative electrode including an uncoated portion can be manufactured by not applying the negative electrode slurry to a portion of the negative electrode current collector, for example, one end of the negative electrode current collector.

[0093] The negative electrode active material is lithium (Li + This may include materials that can be reversibly intercalated or deintercalated, materials that can react with lithium ions to reversibly form lithium-containing compounds, lithium metals, lithium alloys, and the like.

[0094] In one embodiment of the present invention, when lithium metal and / or lithium alloy is used as the negative electrode active material for the negative electrode, a metal thin film obtained by thinning these metal materials can be used as the negative electrode, and in this case, it may not include another current collector. The thinned negative electrode may have a thickness of 30 μm to 200 μm. In one embodiment of the present invention, the negative electrode may be one in which a reinforcing material of 100 μm or less is bonded to or inserted into the metal thin film. The reinforcing material may be porous. On the other hand, the reinforcing material may be conductive or non-conductive.

[0095] The substance capable of reversibly inserting or desorbing the lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. Specifically, artificial graphite, natural graphite, graphite carbon fiber, amorphous carbon, soft carbon, hard carbon, etc. may be mentioned, but are not limited thereto. The substance capable of reacting with the lithium ions to form a lithium-containing compound reversibly may be, for example, tin oxide, titanium nitride, or a silicon-based compound. The lithium alloy may be, for example, an alloy of a metal selected from the group consisting of 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), and tin (Sn). Desirably, the negative electrode active material is lithium metal, and specifically, it may be in the form of a lithium metal thin film or lithium metal powder. The silicon negative electrode active material may be Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < y < 2), a Si-C composite, or a combination thereof, and desirably, it may be SiO y (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when the silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0096] As the negative electrode current collector, a negative electrode current collector commonly used in the art may be used. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0097] The conductive material is used to impart conductivity to the negative electrode and can be used without particular limitations as long as it is conductive in the battery without inducing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material is usually included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, relative to the total weight of the negative electrode active material layer.

[0098] The binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinyllidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, relative to the total weight of the negative electrode active material layer.

[0099] On the other hand, the electrode assembly further includes a separation membrane, which is arranged within the electrode assembly in such a manner that it is interposed between the negative electrode and the positive electrode. The separation membrane can be used without particular limitations as long as it is one that is commonly used as a separator in lithium secondary batteries, separating the negative electrode and the positive electrode and providing a passage for lithium ions to move. Specifically, the separation membrane can be a porous polymer film, for example, a porous polymer film made from a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, can be used. Furthermore, a separation membrane coated with a ceramic component or polymeric substance may be used to ensure heat resistance or mechanical strength.

[0100] A further aspect of the present invention relates to an electrochemical element including the electrode assembly. The electrochemical element comprises an electrode assembly and an electrolyte housed together in a battery case, and the battery case can be any suitable one that is commonly used in the art, such as a pouch type or a metal can type, without any particular limitations.

[0101] The electrolyte used in this invention can be a variety of electrolytes usable in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, and the type is not particularly limited.

[0102] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0103] The organic solvent can be used without particular limitations, as long as it can act as a medium that allows ions involved in the electrochemical reaction of the battery to move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used.

[0104] On the other hand, in one embodiment of the present invention, it is desirable that the non-aqueous solvent of the electrolyte include an ether-based solvent in order to improve the charge and discharge performance of the battery. Such ether-based solvents include linear ethers (e.g., methoxyethane, ethoxyethane, 1,2-dimethoxyethane, dimethoxymethane, dimethoxyethane), cyclic ethers (e.g., 1,3-dioxolane or tetrahydrofuran, tetrahydropyran, etc.), linear ether compounds (e.g., 1,2-dimethoxyethane, etc.), low viscosity fluoride ethers, for example, (1H,1H,2'H,3H-Decafluorodipropyl ether, Difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-Tetrafluoroethyl trifluoromethyl Examples include ether, 1,1,2,3,3,3-Hexafluoropropyl difluoromethyl ether, 1H,1H,2'H,3H-Decafluorodipropyl ether, Pentafluoroethyl 2,2,2-trifluoroethyl ether, and 1H,2H,2'H-Perfluorodipropyl ether), and a mixture of one or more of these may be included as a non-aqueous solvent.

[0105] The lithium salt can be used without particular limitation as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide), LiFSI (Lithium bis(fluorosulfonyl)imide), etc. The concentration of the lithium salt can be used in the range of 0.1M to 5.0M, preferably 0.1M to 3.0M. When the lithium salt concentration falls within the aforementioned range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and enabling effective movement of lithium ions.

[0106] The electrolyte may further contain additives in addition to the components of the electrolyte, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. For example, the additives may include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination. The additives may be present in an amount of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, relative to the total weight of the electrolyte.

[0107] The shape of the lithium-sulfur battery is not particularly limited and can be various shapes such as cylindrical, stacked, or coin-shaped.

[0108] Furthermore, the present invention provides a battery module that includes the lithium-sulfur battery as a unit cell. The battery module can be used as a power source for medium- and large-sized devices that require high-temperature stability, long cycle characteristics, and high capacity characteristics.

[0109] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, power tools powered by electric motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power systems.

[0110] The following describes desirable embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative examples of the present invention, and it will be obvious to those skilled in the art that various modifications and alterations are possible within the scope of the present invention and the technical concept, and such modifications and alterations are, of course, included in the claims of the appended patent.

[0111] Manufacturing example [Production of sulfur-carbon composites] A sulfur-carbon composite was produced by uniformly mixing CNT (average number of layers, 6) particles with sulfur and baking it in an oven at 155°C for 30 minutes. The sulfur content in 100 wt% of the sulfur-carbon composite was 75 wt%.

[0112] [Manufacturing of positive electrodes] Example 1 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, VGCF as the first conductive material, CNT particles (average number of layers: 9) as the second conductive material, and PAA (Polyacrylic acid) as a binder in water in a weight ratio of 92.0:2.5:2.5:3.0. The solid content concentration in the slurry was 25 wt%. The average particle size of the VGCF was 5 μm. The CNT, which is the second conductive material, contains aggregates of aggregated particles, has an average particle size of 35 μm, and was added to the positive electrode slurry in powder form. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a total thickness of 200 μm.

[0113] Example 2 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers 2) as a first conductive material, CNTs (average number of layers 9) as a second conductive material, and PAA as a binder in water in a weight ratio of 94.3:0.2:2.5:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs, which were the first conductive material, were added to the slurry in a mixed solution dispersed in water. In the mixed solution, the weight ratio of water:CNT:dispersant was 99:0.3:0.7. The average particle size of the CNTs in the mixed solution was 1 μm. The CNTs, which were the second conductive material, contained aggregates of particles and had an average particle size of 35 μm. They were added to the positive electrode slurry in powder form. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and then pressed together with a roll press to produce a positive electrode with a thickness of 200 μm.

[0114] Comparative Example 1 The sulfur-carbon composite prepared above and PAA as a binder were mixed with water in a weight ratio of 97:3 to produce a slurry for manufacturing a positive electrode. The solid content concentration in the slurry was 25 wt%. The prepared positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a thickness of 200 μm.

[0115] Comparative Example 2 A slurry for producing a positive electrode was prepared by mixing the aforementioned sulfur-carbon composite, VGCF as a conductive material, and PAA as a binder in water in a weight ratio of 94.5:2.5:3.0. The solid content concentration in the slurry was 25 wt%. The average particle size of the VGCF was 5 μm. The prepared positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a thickness of 200 μm.

[0116] Comparative Example 3 A slurry for manufacturing a positive electrode was prepared by mixing the aforementioned sulfur-carbon composite, VGCF as a conductive material, and PAA as a binder in water in a weight ratio of 92.0:5.0:3.0. The solid content concentration in the slurry was 25 wt%. The average particle size of the VGCF was 5 μm. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a thickness of 200 μm.

[0117] Comparative Example 4 A slurry for producing a positive electrode was prepared by mixing the aforementioned sulfur-carbon composite, VGCF as a conductive material, and PAA as a binder in water in a weight ratio of 87.0:10.0:3.0. The solid content concentration in the slurry was 25 wt%. The average particle size of the VGCF was 5 μm. The prepared positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a thickness of 200 μm.

[0118] Comparative Example 5 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 2) as a conductive material, and PAA as a binder in water in a weight ratio of 96.75:0.25:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs were added to the slurry in a mixed solution dispersed in water. In the mixed solution, the weight ratio of water:CNT:dispersant was 99:0.3:0.7. The average particle size of the CNTs in the mixed solution was approximately 1 μm. The manufactured positive electrode slurry composition was applied to a 20 μm thick aluminum current collector to a thickness of 350 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a 200 μm thick positive electrode.

[0119] Comparative Example 6 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 2) as a conductive material, and PAA as a binder in water in a weight ratio of 96.5:0.5:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs were added to the slurry in a mixed solution dispersed in water. In the mixed solution, the weight ratio of water:CNT:dispersant was 99:0.3:0.7. The average particle size of the CNTs in the mixed solution was approximately 1 μm. The manufactured positive electrode slurry composition was applied to a 20 μm thick aluminum current collector to a thickness of 350 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a 200 μm thick positive electrode.

[0120] Comparative Example 7 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 2) as a conductive material, and PAA as a binder in water in a weight ratio of 96.0:1.0:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs were added to the slurry in the form of a mixed solution dispersed in water. In the mixed solution, the weight ratio of water:CNT:dispersant was 99:0.3:0.7. The average particle size of the CNTs in the mixed solution was approximately 1 μm. The manufactured positive electrode slurry composition was applied to a 20 μm thick aluminum current collector to a thickness of 350 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a positive electrode with a thickness of 200 μm.

[0121] Comparative Example 8 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 2) as a conductive material, and PAA as a binder in water in a weight ratio of 94.0:3.0:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs were added to the slurry in a mixed solution dispersed in water. In the mixed solution, the weight ratio of water:CNT:dispersant was 99:0.3:0.7. The average particle size of the CNTs in the mixed solution was approximately 1 μm. The manufactured positive electrode slurry composition was applied to a 20 μm thick aluminum current collector to a thickness of 350 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a 200 μm thick positive electrode.

[0122] Comparative Example 9 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 9) as a conductive material, and PAA as a binder in water in a weight ratio of 94.5:2.5:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs included aggregates of aggregated particles, had an average particle size of 35 μm, and were added to the positive electrode slurry in powder form. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a positive electrode with a thickness of 200 μm.

[0123] Comparative Example 10 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, CNTs (average number of layers: 9) as a conductive material, and PAA as a binder in water in a weight ratio of 92.0:5.0:3.0. The solid content concentration in the slurry was 25 wt%. The CNTs included aggregates of aggregated particles, had an average particle size of 35 μm, and were added to the positive electrode slurry in powder form. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed with a roll press to produce a positive electrode with a thickness of 200 μm.

[0124] Comparative Example 11 A slurry for manufacturing a positive electrode was prepared by mixing the manufactured sulfur-carbon composite, VGCF as the first conductive material, Ketjenblack as the second conductive material, and PAA as a binder in water in a weight ratio of 92.0:2.5:2.5:3.0. The solid content concentration in the slurry was 25 wt%. The average particle size of the VGCF was 5 μm. The Ketjenblack, the second conductive material, contained aggregates of aggregated particles, had an average particle size of 35 μm, and was added to the positive electrode slurry in powder form. The manufactured positive electrode slurry composition was applied to both sides of a 20 μm thick aluminum current collector to a thickness of 250 μm, dried at 50°C for 12 hours, and pressed together with a roll press to produce a positive electrode with a total thickness of 200 μm.

[0125] [Battery manufacturing] Along with the positive electrode, a 35 μm thick lithium metal thin film was used as the negative electrode, and a mixture of 0.6 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 3 wt% lithium nitrate (LiNO3) was dissolved in an organic solvent in which 2-methylfuran and dimethoxyethane were mixed in a volume ratio of 33:77 as the electrolyte.

[0126] Specifically, the manufactured positive electrode and negative electrode were positioned opposite each other, a polyethylene film with a thickness of 20 μm and a porosity of 45% was interposed between them as a separation membrane, and then the manufactured electrolyte was injected to produce a lithium-sulfur battery. In the battery, the positive electrode and negative electrode were each constructed by stacking seven sheets.

[0127] [evaluation] Referring to Figure 1, when the first conductive material and the second conductive material according to the present invention are used as in Examples 1 and 2, it can be confirmed that the output and capacity in both the initial and late stages of discharge are improved.

[0128] On the other hand, as can be seen from Figures 2 and 3, when using only VCGF as the conductive material, as in Comparative Examples 2 and 3, or when using only dispersed CNTs, as in Comparative Examples 4 and 5, it was confirmed that an improvement effect was achieved in which the resistivity decreased in proportion to the amount added. Therefore, as in Comparative Example 2 in Figures 4a and 4b, when only 2.5% of VGCF is used, the output is improved. However, as in Comparative Example 4, when VGCF exceeds 5% and is included at 10%, it can be seen that there is almost no further improvement in output compared to when 5% is used.

[0129] Furthermore, when dispersed CNTs are used as shown in Figure 5, using 0.25% as in Comparative Example 5 improves the initial and late-stage output, but using 0.5% as in Comparative Example 6 actually decreases the mid- and late-stage output. Also, when undispersed CNT particles are used as shown in Figure 6, improvements in late-stage capacity and output are obtained, but there is no improvement in initial output.

[0130] On the other hand, as shown in Figure 7, in the case of Comparative Example 1, which does not use CNTs, and in the case of Comparative Example 11, which uses Ketjenblack as the second conductive material, it can be seen that there is almost no improvement in resistivity and capacitance compared to Example 1.

[0131] Experimental Example 1: Method for Measuring Particle Size Using a particle size analyzer (model: Bluewave, manufacturer: Microtrac), the dry method D 50 The resulting particle size was measured. When the carbon material was formed into secondary particles by aggregation, the particle size of the primary particles was observed and measured using an electron scanning microscope (model SEM, manufacturer: JEOL).

[0132] Experimental Example 2. Measurement of Discharge Characteristics For each example and comparative example, the batteries were discharged at 25°C in CC mode at 0.2C until the voltage reached 1.8V, and then charged to 2.5V at a constant current of 0.2C. The discharge capacity was measured and compared. The discharge capacity was measured based on the sulfur content (mAh / g(S)).

[0133] Experimental Example 3. Measurement of Electrode Resistivity The resistivity of the electrodes was measured using a Hioki RM2610 instrument. Specifically, the multi-electrode array of the instrument was brought into contact with the manufactured electrodes, and the resistivity was measured. The resistivity value of the electrode layer was obtained from the results displayed on the instrument.

Claims

1. It comprises a positive electrode active material, a conductive material, and a binder material, The positive electrode active material comprises a porous carbon material and a sulfur-carbon composite containing sulfur (S), The conductive material includes a first conductive material and a second conductive material. The first conductive material is fibrous with an average particle size of 5 μm or less, as determined by particle size distribution analysis using a laser diffraction particle size distribution analyzer. The second conductive material contains secondary particles formed by the aggregation of two or more primary CNT particles, and the second conductive material has an average particle size of 10 μm to 70 μm as determined by particle size distribution analysis using a laser diffraction particle size distribution analyzer. A lithium-sulfur battery positive electrode material composition wherein the positive electrode active material, conductive material, and binder material are contained in amounts ranging from 80 wt% to 97 wt%, 2 wt% to 10 wt%, and 2 wt% to 10 wt%, respectively.

2. The positive electrode material composition according to claim 1, wherein the first conductive material includes CNTs, and the CNTs have an average number of layers of 1 to 20.

3. The positive electrode material composition according to claim 2, wherein the first conductive material includes CNTs, and the amount of the first conductive material is 0.1 wt% to 0.5 wt% based on 100 wt% of the total weight of the positive electrode active material, binder material and conductive material.

4. The positive electrode material composition according to claim 1, wherein the first conductive material includes carbon fibers, and the carbon fibers have a diameter of 100 nm to 2 μm.

5. The positive electrode material composition according to claim 1, wherein the second conductive material, CNT, has an average number of layers of 1 to 20 and an average diameter of the primary CNT particles of 0.4 nm to 100 nm.

6. The positive electrode material composition according to claim 1, comprising 0.1 wt% to 5 wt% of the first conductive material and 1 wt% to 5 wt% of the second conductive material, based on 100 wt% of the total weight of the positive electrode active material, binder material and conductive material.

7. The porous carbon material has a primary particle BET specific surface area of ​​100 m². ２ / g to 3,000m ２ The positive electrode material composition according to claim 1, wherein the value is / g.

8. The cathode material composition according to claim 1, wherein the porous carbon material comprises one or more selected from the group consisting of activated carbon, carbon nanotubes (CNTs), and graphene.

9. The positive electrode material composition according to claim 8, wherein the CNT has an average number of layers of 1 to 20.

10. The positive electrode material composition according to claim 1, comprising 70 wt% or more of a sulfur-carbon composite with respect to 100 wt% of the positive electrode active material.

11. The positive electrode material composition according to claim 10, wherein the sulfur content is 70 wt% or more relative to 100 wt% of the sulfur-carbon composite.

12. The positive electrode material composition according to claim 1, wherein the sulfur-carbon composite has one or more of the following states: a state in which sulfur and carbon material are simply mixed and composited, a state having a coating form of a core-shell structure, and a state in which sulfur is filled into the internal pores of the carbon material.

13. A positive electrode for an electrochemical element comprising the positive electrode material composition according to any one of claims 1 to 12.

14. A lithium secondary battery comprising a positive electrode for an electrochemical element as described in claim 13.

15. The positive electrode material composition according to claim 1 is mixed with the second solvent, The first conductive material is added after being adjusted to a state where the average particle size is 5 μm or less, as determined by particle size distribution analysis using a laser diffraction particle size distribution analyzer. A method for manufacturing a slurry for forming a positive electrode, wherein the second conductive material is introduced in powder form and contains secondary particles formed by the aggregation of two or more primary CNT particles, and the second conductive material containing the secondary particles has an average particle size of 10 μm to 70 μm as determined by particle size distribution analysis using a laser diffraction particle size distribution analyzer.

16. The method for producing a slurry for forming a positive electrode according to claim 15, wherein the second solvent comprises one or more selected from water and organic solvents.

17. The method for producing a cathode forming slurry according to claim 15, wherein, if the first conductive material contains CNTs, the CNTs are mixed with the first solvent and added to the slurry in the form of a mixed solution.

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