Positive electrode containing a sulfur-carbon composite and lithium ion 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 as a positive electrode active material. The sulfur-carbon composite comprises a porous carbon material having a high specific surface area and a specific range of particle diameter, and the lithium-sulfur battery using the sulfur-carbon composite has a reduced initial irreversible capacity and improved output characteristics and life characteristics.

Description

Technical Field

[0001] The present invention relates to a lithium-ion secondary battery having a high energy density, suppressing elution of polysulfide, and improving low initial irreversible characteristics, and a positive electrode for the battery.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0147385 filed on October 29, 2021, and all of the contents disclosed in the specification and drawings of the application are incorporated into this application.

Background Art

[0003] Conventional lithium-sulfur (Li-S) batteries utilizing a catholyte system depend on a catholyte type reaction through the generation of polysulfide, which is an intermediate product in the form of Li2S. Therefore, the high theoretical discharge capacity of sulfur (1,675 mAh / g) cannot be fully utilized, and there is a problem that the life characteristics of the battery deteriorate due to elution of polysulfide. X In recent years, an SSE (sparingly solvating electrolyte) system for suppressing elution of polysulfide has been proposed. When a carbon material with a high specific surface area having a BET specific surface area of 1,500 (m

[0004] / g) or more is applied, it has been confirmed that more than 90% of the theoretical capacity can be utilized. However, it is necessary to improve low life characteristics and output characteristics. 2 As a result, in order to construct a battery system having a high energy density of 400 Wh / kg or more and 600 Wh / L or more, an electrolyte and a positive electrode active material system that can be driven even with a porosity of 4.0 mAh / cm

[0005] or more and 60 vol% or less are required. 2

Summary of the Invention

Problems to be Solved by the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a positive electrode active material for a battery system having a high energy density of 400 Wh / kg or more and 600 Wh / L or more.

[0007] Another object of the present invention is to provide a lithium-ion secondary battery including the positive electrode active material.

[0008] It will be easily understood that other objects and advantages of the present invention can be achieved by the means or methods and combinations thereof described in the claims.

Means for Solving the Problems

[0009] A first aspect of the present invention relates to a positive electrode for a lithium-sulfur battery. The positive electrode includes a positive electrode active material including a sulfur-carbon composite. The sulfur-carbon composite includes a porous carbon material and sulfur. The carbon material has a BET specific surface area exceeding 1,600 m 2 / g, and the particle size (D 50 ) of the primary particles is 500 nm or more and less than 8 μm.

[0010] In a second aspect of the present invention, in the first aspect, the carbon material has a particle size (D 50 ) of the primary particles of 1 μm or more and less than 8 μm.

[0011] In a third aspect of the present invention, in the first or second aspect, the carbon material has a BET specific surface area of 2,000 m 2 / g or more of the primary particles.

[0012] In a fourth aspect of the present invention, in any one of the first to third aspects, the carbon material has pores having a pore diameter of less than 3 nm accounting for 40 vol% or more with respect to 100 vol% of the total pores.

[0013] In a fifth aspect of the present invention, in any one of the first to fifth aspects, the carbon material has a Span value of 2.0 or less in the following formula 1.

[0014] [Formula 1] Span = (Particle size of primary particle (D 90 )) - Particle size of primary particle (D 10 )) / Particle size of primary particle (D 50 )

[0015] In the sixth aspect of the present invention, in any one of the first to fifth aspects, the sulfur-carbon composite has an SCP value of more than 0.85 in the following formula 2.

[0016] [Formula 2] SCP = Ratio of sulfur content (A) ÷ Ratio of pore volume of carbon material (B)

[0017] In formula 2, A is the ratio of the mass of sulfur to the mass of the carbon-sulfur composite, and B is the ratio of the pore volume in the carbon material to the total volume (apparent volume) of the carbon material.

[0018] In the seventh aspect of the present invention, in any one of the first to sixth aspects, the carbon material contains 95 wt% or more of activated carbon with respect to 100 wt% of the carbon material.

[0019] In the eighth aspect of the present invention, in any one of the first to seventh aspects, the positive electrode active material contains 70 wt% or more of the sulfur-carbon composite with respect to 100 wt% of the positive electrode active material.

[0020] In the ninth aspect of the present invention, in any one of the first to eighth aspects, the sulfur-carbon composite has any one or more of a state in which sulfur and a carbon material are simply mixed and compounded, a state having a coating form of a core-shell structure, and a state in which sulfur is filled in internal pores of the carbon material.

[0021] In the tenth aspect of the present invention, in any one of the first to ninth aspects, the positive electrode active material further contains a binder resin and a conductive material.

[0022] The 11th aspect of the present invention relates to a lithium-sulfur battery, which includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The electrolyte contains one or more of a cyclic ether, a linear ether, and a fluorinated ether, and the positive electrode is the positive electrode for a lithium-sulfur battery according to any one of the 1st to 10th aspects.

Effect of the Invention

[0023] The lithium-sulfur battery applying the sulfur-carbon composite according to the present invention can reduce the initial irreversible capacity and improve the output characteristics and life characteristics.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, the present invention will be described more specifically.

[0025] In this specification and the claims, the terms and words used are not to be construed as being limited to the ordinary and dictionary meanings. The inventors interpret them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that they can appropriately define the concept of the terms in order to explain the invention in the best way.

[0026] Throughout this specification, when a certain part "includes" or "comprises" other components, this means that, unless otherwise specified, it does not exclude other components, but may further include other components.

[0027] Also, throughout this specification, terms such as "about" and "substantially" are used to mean the numerical value or a value close to it when manufacturing and material tolerances inherent in the mentioned meaning are presented, and are used to prevent unscrupulous infringers from improperly using the disclosed content where exact or absolute numerical values are mentioned to assist in the understanding of the present application.

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

[0029] In the present invention, the "specific surface area" is measured by the BET method. Specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc.

[0030] As used herein, the term "polysulfide" includes both "polysulfide ion (S x 2- , x = 8, 6, 4, 2))" and "lithium polysulfide (Li2S X or LiS x - , 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 while exhibiting 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 % is used as its unit, and it can be used interchangeably with terms such as void fraction and porosity.

[0033] In the present invention, " n D n (n = 10, 50 or 90)" means the particle size based on n% (n = 10, 50 or 90) of the volume cumulative particle size distribution of the particles. The particle size D

[0034] The present invention relates to a positive electrode active material for an electrochemical element and a positive electrode containing the same. In the present invention, the electrochemical element may include any element that undergoes an electrochemical reaction. Specific examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In particular, the electrochemical element may be a secondary battery, and the secondary battery may be a lithium-ion secondary battery. Examples of the lithium-ion secondary battery include a lithium-metal battery, a lithium-sulfur battery, an all-solid-state battery, and a lithium polymer battery, and among them, a lithium-sulfur battery is desirable.

[0035] The positive electrode active material according to the present invention contains a sulfur-carbon composite, the sulfur-carbon composite contains a porous carbon material, and the porous carbon material has a BET specific surface area and particle size within a specific range.

[0036] Among many secondary batteries, the lithium-sulfur battery not only has a high discharge capacity and theoretical energy density, but also, since sulfur used as a positive electrode active material is abundant in reserves and inexpensive, the manufacturing cost of the battery can be reduced, and it is attracting attention as a next-generation secondary battery because of its environmental friendliness.

[0037] Since sulfur, which is a positive electrode active material in a lithium-sulfur battery, is an insulator, a sulfur-carbon composite in which sulfur is combined with a carbon material, which is a conductive substance, is generally used to compensate for its low electrical conductivity.

[0038] However, in the case of conventional sulfur-carbon composites, lithium polysulfide formed during the electrochemical oxidation-reduction reaction of lithium-sulfur batteries leaks into the electrolyte, resulting in sulfur loss. As a result, the amount of sulfur involved in the electrochemical reaction decreases rapidly, and it is impossible to achieve both the theoretical discharge capacity and the theoretical energy density during actual operation. In addition, sulfur changes to lithium sulfide (Li2S) during full discharge, accompanied by a volume expansion of about 80%, which leads to a reduction in the void volume inside the positive electrode and makes it difficult to contact the electrolyte. Furthermore, lithium polysulfide undergoes a circulation reaction that consumes electrons without being fully reduced due to the shuttle phenomenon that occurs between the positive and negative electrodes, resulting in problems such as reduced charge-discharge efficiency and lifespan.

[0039] Therefore, in the prior art, methods such as increasing the sulfur loading amount, changing the type or mixing method of the carbon material, or introducing a coating layer for suppressing the elution of lithium polysulfide have been proposed. However, these methods do not effectively improve the performance of lithium-sulfur batteries, and furthermore, they have drawbacks such as causing serious problems in battery stability or being inefficient in terms of the process.

[0040] Therefore, the present invention provides a positive electrode including a sulfur-carbon composite in which the BET specific surface area and the particle size are controlled within a specific range to improve the electrochemical reactivity, stability, and electrical conductivity of the sulfur-carbon composite and ensure the improvement effect of the capacity and lifespan characteristics of a lithium-sulfur battery including the same.

[0041] Specifically, the positive electrode active material according to the present invention includes a sulfur-carbon composite. The sulfur-carbon composite includes a porous carbon material and sulfur, and the sulfur is supported in the pores of the porous carbon material. The carbon material has a BET specific surface area exceeding 1,600 m 2 / g, the particle size (D 50 ) of the primary particles is 500 nm or more, desirably 1 μm or more, and less than 8 μm.

[0042] The carbon material serves as a carrier that provides a framework in which sulfur can be uniformly and stably immobilized, compensating for the low electrical conductivity of sulfur to enable smooth electrochemical reactions. In particular, the sulfur-carbon composite has a large BET specific surface area of the carbon material serving as the sulfur carrier and an appropriate particle size (D 50 ). Therefore, although the sulfur loading amount is large, the irreversible capacity is small and the energy density is high. That is, it has a structure that can increase the utilization rate of sulfur during the electrochemical reaction.

[0043] In conventional sulfur-carbon composites, in order to increase the sulfur loading amount and improve the reactivity, the use of carbon materials with a high specific surface area has been proposed. However, since the relationship between the particle size of the carbon material and the sulfur utilization rate has not been clearly understood, it is difficult to realize a high-capacity lithium-sulfur battery.

[0044] Therefore, in the present invention, by controlling the BET specific surface area and the particle size (D 50 ) of the carbon material serving as the sulfur carrier within a specific range, sulfur can be uniformly dispersed on the internal and external surfaces of the carbon material, while reducing the irreversible capacity and increasing the electrochemical reactivity of sulfur. In addition, by using the carbon material, the electrochemical reactivity, stability, and electrical conductivity of the sulfur-carbon composite are improved, thereby not only improving the capacity and life characteristics of the lithium-sulfur battery, but also exhibiting optimal charge-discharge performance even when sulfur loss or volume change occurs during charge and discharge.

[0045] In the sulfur-carbon composite of the present invention, the carbon material used as the sulfur carrier can generally be produced by carbonizing various carbon material precursors.

[0046] The carbon material may contain a large number of non-uniform pores on the surface and inside. The carbon material has a BET specific surface area exceeding 1,600 m 2 / g. Desirably, it may be 2,000 m 2 / g or more, or 2500 m 2 / g or more. On the other hand, the carbon material has a particle size (D 50) is 500 nm or more and less than 8 μm, preferably 1 μm or more and less than 8 μm. When the particle size (D 50 ) exceeds 8 μm, it is difficult for lithium ions to move due to the restriction on mass transfer, and it is difficult to efficiently use sulfur located at the carbon center. When the particle size of the primary particles is less than 500 nm, fine impurities are likely to adsorb, and a large amount of solvent is required in the process of manufacturing the electrode slurry, so it is difficult to increase the solid content, and there is a problem that the ratio of the irreversible capacity after battery driving increases.

[0047] 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 10 nm based on the longest diameter. On the other hand, from the viewpoint of effectively using the non-conductive sulfur by finely and uniformly dispersing and supporting it, it is desirable that the pores having a pore diameter of less than 3 nm among the pores of the carbon material be 40 vol% or more with respect to 100 vol% of the total pores of the carbon material.

[0048] The carbon material can be used without limitation as long as it is spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped or bulk-shaped and is commonly used in lithium-sulfur secondary batteries.

[0049] As the carbon material, any carbon-based material having porosity and conductivity and commonly used in the art can be used without limitation. For example, graphite; graphene; carbon black such as Denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); graphite such as natural graphite, artificial graphite, and expanded graphite; carbon nanoribbons; carbon nanobelts, carbon nanorods; and activated carbon, and may include one or more selected from the group consisting of them. Preferably, the carbon material may include activated carbon.

[0050] In one embodiment of the present invention, the carbon material may include those having a particle size distribution of primary particles with a Span value of 2.0 or less. The Span is the width of the particle size distribution calculated from the values of particle size D 10 , D 50 , D 90 , and is calculated by the following formula 1.

[0051] [Formula 1] Span = (particle size of primary particles (D 90 ) - particle size of primary particles (D 10 )) / particle size of primary particles (D 50 )

[0052] When the particle size distribution is wide, the Span value is calculated to be large, and when the particle size distribution is narrow, the Span value is calculated to be small. Therefore, the state of the particle size distribution can be grasped through the Span value. When the particle size distribution satisfies a Span value of 2.0 or less, the particle size distribution is uniform, so that the mixing of excessively large or small particles can be suppressed. Furthermore, this can ensure the stability of the battery and improve the battery performance, such as suppressing the phenomenon that the electrode material is destroyed or the electrode expands during the charge and discharge process.

[0053] In one embodiment of the present invention, the carbon material may contain 95 wt% or more, preferably 99 wt% or more of activated carbon based on 100 wt% of the carbon material. For example, the carbon material may be composed of only activated carbon.

[0054] As described above, the carbon material has a BET specific surface area exceeding 1,600 m 2 / g, and it is desirable that the particle size (D 50 ) is 500 nm or more and less than 8 μm or 1 μm or more and less than 8 μm. If the above range is not satisfied, there may be a problem when forming a structure for increasing the utilization rate of sulfur in the electrode.

[0055] In the present invention, the sulfur-carbon composite contains sulfur. Since sulfur alone does not have electrical conductivity, it is used in combination with the above-described carbon material.

[0056] The sulfur may be one or more selected from the group consisting of 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 sulfur compounds, and carbon-sulfur polymers ((C2S x ), where x = 2.5 to 50 and n≧2). Desirably, it may contain inorganic sulfur (S8). n

[0057] In one embodiment of the present invention, the positive electrode active material may be 50 wt% or more, 70 wt% or more, 90 wt% or more, or 95 wt% or more of the sulfur-carbon composite having the above-described characteristics with respect to 100 wt% of the positive electrode active material. In one embodiment of the present invention, the positive electrode active material may consist only of the sulfur-carbon composite.

[0058] In the present invention, the sulfur content in the sulfur-carbon composite is such that the SCP value according to the following formula 2 exceeds 0.85.

[0059] [Formula 2] SCP = Ratio of sulfur content (A) ÷ Ratio of pore volume of carbon material (B)

[0060] In formula 2, A is the ratio of the mass of sulfur to the mass of the carbon-sulfur composite (mass of sulfur / mass of sulfur-carbon composite), B is the ratio of the pore volume in the carbon material to the total volume of the carbon material (apparent volume, volume of carbon only + pore volume) (pore volume in carbon material / apparent volume of carbon material), and the unit of SCP is none.

[0061] In one embodiment of the present invention, the true density of carbon is 2.0 g / cm 3 (excluding the pore volume in the carbon material), and the unit volume of carbon can be 0.5 cm 3 / g.

[0062] The SCP value means the content of sulfur that can be reversibly utilized inside a carbon material having a specific pore structure.

[0063] In the sulfur-carbon composite, when the SCP value satisfies the above range, it is advantageous from the viewpoint of efficiently using sulfur. Specifically, when the sulfur-carbon composite in the lithium-sulfur battery containing the sulfur-carbon composite satisfies the range of the SCP value, the cell of the lithium-sulfur battery can have a high energy density.

[0064] When the content of the sulfur exceeds the above range, sulfur or sulfur compounds that cannot be bonded to the carbon material may aggregate or redissolve on the surface of the porous carbon material, making it difficult to receive electrons and unable to participate in the electrochemical reaction, which may cause capacity loss of the battery.

[0065] In the sulfur-carbon composite according to the present invention, the sulfur is located on at least one of the inner pores and the outer surface of the carbon material. At this time, it may exist in an area of less than 100%, preferably 1 to 95%, more preferably 60 to 90% of the entire inner and outer surfaces of the carbon material. When the sulfur exists on the surface of the carbon material within the above range, the maximum effect can be achieved in terms of the electron transfer area and the wettability of the electrolyte. Specifically, since the sulfur is thinly and uniformly impregnated on the surface of the carbon material in the area of the above range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur is located in an area of 100% of the entire surface of the carbon material, the carbon material is completely covered with sulfur, so the wettability of the electrolyte decreases, and the contact with the conductive material contained in the electrode decreases, and the carbon material cannot receive electron transfer and cannot participate in the reaction.

[0066] The sulfur-carbon composite may be formed by simply mixing the sulfur and the carbon material, or may have a coating form or a supported form with a core-shell structure. The coating form of the core-shell structure is one in which either sulfur or the carbon material coats the other. For example, the surface of the carbon material may be covered with sulfur, or vice versa. Also, the supported form may be a form in which sulfur is filled inside the carbon material, particularly inside the internal pores. The form of the sulfur-carbon composite can be any form as long as it satisfies the content ratio of the sulfur-based compound and the carbon material described above, and is not limited in the present invention.

[0067] The present invention also provides a method for producing the sulfur-carbon composite.

[0068] The method for producing the sulfur-carbon composite according to the present invention is not particularly limited, and as a usual method well-known in the art, a method comprising (S1) a step of mixing a carbon material and sulfur, and then (S2) a step of forming a composite can be adopted.

[0069] The mixing in the step (S1) is for increasing the mixing degree of sulfur and the carbon material, and can be carried out using a stirring device usually used in the art. At this time, the mixing time and speed can also be selectively adjusted according to the content and conditions of the raw materials.

[0070] The composite formation in the step (S2) is not particularly limited in the present invention, and can be carried out by a method usually used in the art. As an example, a method usually used in the art such as dry composite formation or wet composite formation such as spray coating can be adopted. For example, after the mixture of sulfur and the carbon material obtained after mixing is ball-milled and pulverized, it may be left in an oven at 120°C to 160°C for 20 minutes to 1 hour so that the molten sulfur is uniformly coated on the inside and the outer surface of the carbon material.

[0071] The sulfur-carbon composite produced by the above-described manufacturing method has a structure with a high specific surface area, a large sulfur loading amount, and an improved sulfur utilization rate. Therefore, not only can the electrochemical reactivity of sulfur be improved, but also the capacity and life characteristics of the lithium-sulfur battery can be improved by enhancing the accessibility and contact of the electrolyte.

[0072] Another aspect of the present invention relates to a positive electrode including the sulfur-carbon composite. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material may be contained in an amount of 70 wt% or more, preferably 85 wt% or more, based on 100 wt% of the positive electrode active material layer.

[0073] In the present invention, the positive electrode active material includes the sulfur-carbon composite described above. In one embodiment of the present invention, the positive electrode active material may contain the sulfur-carbon composite in an amount of 70 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, based on 100 wt% of the positive electrode active material. In one embodiment of the present invention, the positive electrode active material may be composed only of the sulfur-carbon composite. 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 and sulfur may further be included.

[0074] In a specific embodiment of the present invention, the positive electrode active material layer may include a lithium transition metal composite oxide represented by the following Chemical Formula 1.

[0075] [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0076] In Chemical Formula 1, M 1can be Mn, Al, or a combination thereof, and desirably can be Mn, or Mn and Al.

[0077] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and desirably can be one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more desirably can be Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0078] On the other hand, as the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesive force of the positive electrode active material. The positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0079] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; 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. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can usually be contained in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, more preferably 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0080] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM) rubber, sulfonated EPDM, styrene - butadiene rubber (SBR), fluorine rubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds can be used. The binder can be contained in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, more preferably 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0081] The positive electrode can be manufactured by a conventional method well - known in the art.

[0082] For example, the method for manufacturing the positive electrode of the present invention will be specifically described. First, after dissolving the binder in a solvent for manufacturing a slurry, a conductive material is dispersed. As the solvent for manufacturing the slurry, it is desirable to use a solvent that can uniformly disperse the positive electrode active material, the binder, and the conductive material and can be easily evaporated. Typically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, etc. can be used. Next, the positive electrode active material is selectively added together with an additive and uniformly dispersed again in the solvent in which the conductive material is dispersed to manufacture a positive electrode slurry. The amount of the solvent, the positive electrode active material, or the additive selectively contained in the slurry does not have a particularly important meaning in the present application, and it is sufficient if it has an appropriate viscosity for facilitating the coating of the slurry.

[0083] The slurry thus manufactured is applied to a current collector and vacuum dried to form a positive electrode. Depending on the viscosity of the slurry and the thickness of the positive electrode to be formed, the slurry can be coated on the current collector with an appropriate thickness.

[0084] The application can be performed by a conventional method known in the art. For example, after distributing the positive electrode active material slurry on one surface of the positive electrode current collector, it can be uniformly dispersed using a doctor blade or the like. In addition, it can be performed by methods such as die casting, comma coating, screen printing, etc.

[0085] The drying is not particularly limited, but it can be performed within one day in a vacuum oven at 50°C to 200°C.

[0086] Further, the present invention provides an electrode assembly including a positive electrode having the sulfur-carbon composite described above, and a lithium-sulfur battery including an electrolytic solution. The electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0087] The electrode assembly may, for example, be laminated in a state where a separation membrane is interposed between the negative electrode and the positive electrode to form a stack-type or stack / folding-type structure, or may be wound to form a jelly roll-type structure. Further, when forming a jelly roll-type structure, a separation membrane may be further disposed on the outside to prevent contact between the negative electrode and the positive electrode.

[0088] 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, and the negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder.

[0089] Hereinafter, the negative electrode will be described in more detail.

[0090] The negative electrode has a structure in which a negative electrode active material layer is formed on one or both surfaces 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.

[0091] Specifically, the negative electrode can be manufactured by applying a negative electrode slurry, which is 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, water, etc., on one or both surfaces of a long sheet-like negative electrode current collector, removing the solvent of the negative electrode slurry through a drying process, and then rolling. On the other hand, when applying the negative electrode slurry, a negative electrode without a coated portion can be manufactured by a method of not applying the negative electrode slurry to a partial region of the negative electrode current collector, for example, one end portion of the negative electrode current collector.

[0092] The negative electrode active material is lithium ion (Li +It may contain a substance capable of reversibly intercalating or deintercalating [[ID=]], a substance capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal or a lithium alloy. The substance capable of reversibly inserting or desorbing the lithium ions may be, for example, crystalline carbon, amorphous carbon or a mixture thereof, and specifically, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc. may be mentioned, but it is not limited thereto. The substance capable of reacting with the lithium ions to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate or a silicon-based compound. The lithium alloy may be, for example, an alloy of lithium (Li) and a metal selected from the group consisting of 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 may be lithium metal, and specifically, it may be in the form of a lithium metal thin film or lithium metal powder. The silicon-based negative electrode active material may be Si, a 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, SiO y (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when a silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0093] As the negative electrode current collector, a negative electrode current collector generally used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0094] The conductive material is used to impart conductivity to the negative electrode. In the battery to be configured, any material having electron conductivity without causing a chemical change can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can usually be contained in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, more preferably 1 to 10 wt% based on the total weight of the negative electrode active material layer.

[0095] The binder serves to improve the adhesion between negative electrode active material particles and the adhesive force between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. One of these alone or a mixture of two or more can be used. The binder can be contained in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, more preferably 1 to 10 wt% based on the total weight of the negative electrode active material layer.

[0096] On the other hand, the electrode assembly further includes a separator, and the separator is disposed in the electrode assembly intervening between the negative electrode and the positive electrode. The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions, and can be used without particular limitation as long as it is usually used as a separator for a lithium secondary battery. Specifically, as the separator, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers 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 can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, a coated separator containing a ceramic component or a polymer substance may be used to ensure heat resistance or mechanical strength.

[0097] Still another aspect of the present invention relates to an electrochemical element including the electrode assembly. In the electrochemical element, the electrode assembly and the electrolyte are both housed in a battery case. As the battery case, any suitable one can be selected without particular limitation as long as it is commonly used in the art, such as a pouch type or a metal can type.

[0098] As the electrolyte used in the present invention, various electrolytes that can be used in lithium secondary batteries can be used, for example, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., and the type thereof is not particularly limited.

[0099] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0100] As the organic solvent, any one can be used without particular limitation as long as it can function as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specifically, as the organic solvent, 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; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to C 20 which may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. can be used.

[0101] On the one hand, in one embodiment of the present invention, from the perspective of enhancing the charge and discharge performance of the battery, it is desirable that the non-aqueous solvent of the electrolyte solution contains an ether-based solvent. Such ether-based solvents include cyclic ethers (e.g., 1,3-dioxolane, tetrahydrofuran, tetrahydropyran, etc.), linear ether compounds (e.g., 1,2-dimethoxyethane, etc.), and low-viscosity fluorinated ethers (e.g., 1H,1H,2’H,3H-decafluorodipropyl ether, difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl trifluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, 1H,1H,2’H,3H-decafluorodipropyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether, 1H,1H,2’H-perfluorodipropyl ether). It may contain a mixture of one or more of these as the non-aqueous solvent.

[0102] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used 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, etc. The concentration of the lithium salt can be in the range of 0.1 to 5.0 M, desirably in the range of 0.1 to 3.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it exhibits excellent electrolyte performance and lithium ions can move effectively.

[0103] In addition to the constituent components of the electrolyte described above, the electrolyte may further contain additives for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, and the like. For example, as the additive, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride may be used alone or in combination, but is not limited thereto. The additive may be contained in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0104] The shape of the lithium-sulfur battery is not particularly limited and may be various shapes such as cylindrical, laminated, coin type, and the like.

[0105] The present invention also provides a battery module including 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.

[0106] Examples of the medium and large-sized devices include power tools powered by an electric motor; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; electric two-wheel vehicles including electric bicycles (E-bike) and electric scooters (E-scooter); electric golf carts; power storage systems, etc., but are not limited thereto.

[0107] The following presents preferred embodiments for assisting in the understanding of the present invention. However, the following embodiments are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the scope of its technical concept. It is natural that such variations and modifications belong to the scope of the appended claims.

[0108] <Production Example> [Production of Sulfur-Carbon Composite] Activated carbon and sulfur (S8) were uniformly mixed at the weight ratios shown in Table 1 below, pulverized with a ball mill, and then left in an oven at 155 °C for 30 minutes to produce a sulfur-carbon composite.

[0109] In Table 1, SCP is the value calculated based on the above-described formula 2.

[0110] [Production of Battery] 90% by weight of the produced sulfur-carbon composite as the positive electrode active material, 5% by weight of Denka black as the conductive material, and 5% by weight of styrene-butadiene rubber / carboxymethyl cellulose (SBR:CMC = 7:3 weight ratio) as the binder were put into a solvent and mixed to produce a positive electrode slurry composition.

[0111] The positive electrode slurry composition produced on an aluminum current collector with a thickness of 20 μm was coated at a thickness of 350 μm, dried at 50 °C for 12 hours, and crimped with a roll press to produce a positive electrode.

[0112] Together with the positive electrode, a lithium metal thin film with a thickness of 35 μm was used as the negative electrode, and a mixed solution in which 1 M concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1% by weight of lithium nitrate (LiNO3) were dissolved in an organic solvent composed of 1,3-dioxolane and dimethyl ether (DOL:DME = 1:1 (volume ratio)) was used as the electrolyte.

[0113] Specifically, the manufactured positive electrode and negative electrode were arranged facing each other, and after interposing polyethylene with a thickness of 20 μm and a porosity of 45% as a separator therebetween, 70 μl of the manufactured electrolyte was injected to manufacture a lithium-sulfur battery.

[0114]

Table 1

[0115] As can be confirmed from Table 1, in Examples 1 to 3, the BET of the carbon material was 3,000 m 2 / g, and the particle size of the primary particles was less than 8 μm. As a result, the ratio of the irreversible capacity showed a very low value of less than 4%. On the other hand, in Comparative Example 1 and Comparative Example 2, although the BET value was high, the particle size of the primary particles was large (8 μm), and the ratio of the irreversible capacity was higher than that in the examples. On the other hand, when using a carbon material having a low specific surface area of 1,600 m 2 / g or less, it was confirmed that the irreversible capacity increased compared to the examples when the particle size was small (Comparative Examples 3, 4, 5) or too large (Comparative Example 6). Also, as can be confirmed from Table 1, in Examples 1 to 3, the Span value of the primary particles of the carbon material was 2 or less. As a result, the irreversible capacity showed a very low value of less than 4%. On the other hand, in Comparative Examples 1 to 7, the Span value of the primary particles of the carbon material exceeded 2, and it was confirmed that the irreversible capacity was higher than that in Examples 1 to 3. In particular, in Comparative Examples 4, 5, and 7 where the SCP value was 0.85 or less, it was confirmed that the irreversible capacity further increased.

[0116] <Experimental Example 1. Physical Property Evaluation of Carbon Material> The specific surface area, total pore volume, and average pore diameter of the carbon material used in the production example were measured. Specifically, for each carbon material used in the production example, the adsorption and desorption amounts of nitrogen were measured under vacuum using a specific surface area measuring instrument (model name: BELSORP-MINI, manufacturer: BEL Japan Inc.). From this, an isothermal adsorption-desorption curve was obtained, and the specific surface area was calculated using the BET (Brunaure-Emmett-Teller) method.

[0117] <Experimental Example 2. Method for Measuring Particle Size> Using a particle size analyzer (model name: Bluewave, manufacturer: Microtrac), the particle size corresponding to D was measured by the dry method. 50 When the carbon material was secondary-particleized due to aggregation, the primary particle size was observed and measured using a scanning electron microscope (model name: SEM, manufacturer: JEOL).

[0118] <Experimental Example 3. Method for Measuring Irreversible Capacity> Using a battery charger (manufacturer: PNE), charging and discharging were performed at a rate of 0.1C / 0.1C in the range of 1.0 to 3.6V under a constant temperature condition of 25°C, and the irreversible capacity was calculated using the following formula 3.

[0119] [Formula 3] Irreversible capacity = [Discharge capacity of the first cycle (0.1C rate) - Discharge capacity of the second cycle (0.1C rate)] ÷ Discharge capacity of the first cycle (0.1C rate) × 100 (%)

Claims

1. comprising a positive electrode active material containing a sulfur-carbon composite, said sulfur-carbon composite containing a porous carbon material and sulfur, said porous carbon material having a BET specific surface area of 2000 m ２ / g or more, said porous carbon material having a primary particle size (D ５０ ) of 500 nm or more and less than 8 μm, said porous carbon material having a Span value of 2.0 or less according to the following formula 1, said sulfur-carbon composite being a positive electrode for a lithium-sulfur battery having an SCP value according to the following formula 2 exceeding 0.9, In formula 2, A is the ratio of the mass of sulfur to the mass of the carbon-sulfur composite, and B is the ratio of the pore volume in the carbon material to the total volume (apparent volume) of the carbon material, a positive electrode for a lithium-sulfur battery. [Formula 1] Span = (primary particle size (D90) - primary particle size (D10)) / primary particle size (D50) [Formula 2] SCP = ratio of sulfur content (A) ÷ ratio of pore volume of carbon material (B)

2. said porous carbon material having a primary particle size (D ５０ ) of 1 μm or more and less than 8 μm, the positive electrode for a lithium-sulfur battery according to claim 1.

3. said porous carbon material having a BET specific surface area of the primary particles of 2500 m ２ / g or more, the positive electrode for a lithium-sulfur battery according to claim 1.

4. said porous carbon material having pores with a pore diameter of less than 3 nm accounting for 40 vol% or more with respect to 100 vol% of the total pores, the positive electrode for a lithium-sulfur battery according to claim 1.

5. said porous carbon material having a Span value of 1.9 or less, the positive electrode for a lithium-sulfur battery according to claim 1.

6. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the porous carbon material contains 95 wt% or more of activated carbon with respect to 100 wt% of the carbon material.

7. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the positive electrode active material contains 70 wt% or more of the sulfur-carbon composite with respect to 100 wt% of the positive electrode active material.

8. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the sulfur-carbon composite has at least one of a state in which sulfur and a carbon material are simply mixed and complexed, a coating form having a core-shell structure, and a state in which sulfur is filled in internal pores of the carbon material.

9. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the positive electrode active material layer further contains a binder resin and a conductive material.

10. A lithium-sulfur battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, wherein the electrolytic solution contains one or more of a cyclic ether, a linear ether, and a fluorinated ether, and the positive electrode is the positive electrode for a lithium-sulfur battery according to any one of claims 1 to 9.

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