Positive electrode for lithium-sulfur batteries and lithium-sulfur batteries containing same

Abstract

A positive electrode for lithium-sulfur batteries according to the present invention includes predetermined contents of polyacrylic acid, polyacrylamide, carboxymethyl cellulose, and styrene-butadiene rubber as binder polymers. The positive electrode for lithium-sulfur batteries has excellent adhesion between a positive electrode active material layer and a positive electrode current collector, and can ensure sufficient output performance when applied to lithium-sulfur batteries.

Description

Anode for lithium-sulfur battery and lithium-sulfur battery containing same

[0001] The present invention relates to a positive electrode for a lithium-sulfur battery and a lithium-sulfur battery including the same.

[0002] This application claims priority to Korean Application No. 10-2024-0054905, filed April 24, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] As the scope of application of lithium secondary batteries expands from portable electronic devices to electric vehicles (EVs) and electric storage systems (ESSs), the demand for lithium secondary batteries with high capacity, high energy density, and long lifespan is increasing.

[0004] Among various lithium secondary batteries, the lithium-sulfur battery is a battery system that uses a sulfur-based material containing a sulfur-sulfur bond as a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions can be inserted / deinserted, or silicon or tin that forms an alloy with lithium as a negative electrode active material.

[0005] Sulfur, the main material of the cathode active material in lithium-sulfur batteries, has the advantages of being a low atomic weight, abundant in resources, easy to supply, inexpensive, non-toxic, and environmentally friendly material.

[0006] Conventionally, the cathodes of lithium-sulfur batteries have been manufactured using aqueous binder polymers. However, this method suffers from poor adhesion between the cathode active material layer and the cathode current collector. Attempts have been made to use high-adhesion binder polymers, but these methods have resulted in poor output performance.

[0007] The purpose of the present invention is to provide a cathode for a lithium-sulfur battery using a binder polymer that has excellent adhesion between a cathode active material layer and a cathode current collector while improving the output performance of the battery, and a lithium-sulfur battery including the same, by solving the above problems.

[0008] In one aspect of the present invention, a cathode for a lithium-sulfur battery and a lithium-sulfur battery of the following embodiments are provided.

[0009] The cathode for a lithium-sulfur battery according to the first embodiment is:

[0010] A cathode active material layer comprising a sulfur-carbon complex and a binder polymer;

[0011] The above binder polymer may include polyacrylic acid, polyacrylamide, carboxymethylcellulose, and styrene-butadiene rubber.

[0012] The second embodiment is, in the first embodiment,

[0013] The above binder polymer may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total positive electrode active material layer.

[0014] The third embodiment is, in the first embodiment or the second embodiment,

[0015] The above polyacrylic acid may be included in an amount of 5 to 30 parts by weight based on 100 parts by weight of the total binder polymer.

[0016] The fourth embodiment is, in any one of the first to third embodiments,

[0017] The above polyacrylic acid may be included in an amount of 5 to 25 parts by weight based on 100 parts by weight of the total binder polymer.

[0018] The fifth embodiment is, in any one of the first to fourth embodiments,

[0019] The above polyacrylamide may be included in an amount of 10 to 35 parts by weight based on 100 parts by weight of the total binder polymer.

[0020] The sixth embodiment is, in any one of the first to fifth embodiments,

[0021] The above polyacrylamide may be included in an amount of 10 to 31.25 parts by weight based on 100 parts by weight of the total binder polymer.

[0022] The seventh embodiment is, in any one of the first to sixth embodiments,

[0023] The above carboxymethyl cellulose may be included in an amount of 10 to 20 parts by weight based on 100 parts by weight of the total binder polymer.

[0024] The eighth embodiment is, in any one of the first to seventh embodiments,

[0025] The above carboxymethyl cellulose may be included in an amount of 12.5 to 20 parts by weight based on 100 parts by weight of the total binder polymer.

[0026] The ninth embodiment is, in any one of the first to eighth embodiments,

[0027] The above styrene-butadiene rubber may be included in an amount of 40 to 60 parts by weight based on 100 parts by weight of the total binder polymer.

[0028] The tenth embodiment is, in any one of the first to ninth embodiments,

[0029] The above styrene-butadiene rubber may be included in an amount of 45 to 60 parts by weight based on 100 parts by weight of the total binder polymer.

[0030] The eleventh embodiment is any one of the first to tenth embodiments,

[0031] The above-mentioned positive electrode for a lithium-sulfur battery has the positive electrode active material layer formed on at least one surface of the electrode current collector, and the adhesive force between the electrode current collector and the positive electrode active material layer may be 35 gf / 2 cm or more.

[0032] A lithium-sulfur battery according to the 12th embodiment,

[0033] Anode; cathode; comprising the anode and an electrolyte,

[0034] The above positive electrode may be a positive electrode for a lithium sulfur battery according to any one of the first to eleventh embodiments.

[0035] The 13th embodiment is, in the 12th embodiment,

[0036] The above lithium sulfur battery may have an output of 2.2 wh / kg or more.

[0037] The 14th embodiment may further include, in the 12th embodiment or the 13th embodiment, a separator positioned between the anode and the cathode.

[0038] The positive electrode for a lithium-sulfur battery according to the present invention contains four types of binder polymers in an optimal ratio, so that it has excellent adhesive performance between the positive electrode active material layer and the positive electrode current collector, while also ensuring sufficient output performance of the lithium-sulfur battery.

[0039] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept that conforms to the technical spirit of the present invention.

[0040] Accordingly, the embodiments described in this specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0041] Additionally, throughout the specification, whenever a part is said to "include," "comprise," "have," or "have" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0042] In addition, the terms 'about', 'substantially', etc. used throughout this specification are used in the sense of or near to the numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure where exact or absolute values ​​are mentioned to aid understanding of this specification.

[0043] Throughout this specification, references to 'A and / or B' mean 'A or B or both.'

[0044] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0045]

[0046] The first aspect of the present invention relates to a cathode for a lithium sulfur battery.

[0047] According to one aspect of the present invention, a cathode for a lithium sulfur battery is

[0048] A positive electrode current collector; and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector;

[0049] The above positive electrode active material layer comprises a sulfur-carbon complex; and a binder polymer,

[0050]

[0051] The above binder polymers include polyacrylic acid, polyacrylamide, carboxymethylcellulose and styrene-butadiene rubber.

[0052]

[0053] In the field of lithium-sulfur battery technology, cathodes are manufactured using aqueous binder polymers, but the problem has been the inability to ensure sufficient adhesion between the cathode active material layer and the cathode current collector. Therefore, attempts have been made to apply binder polymers with strong adhesion to the cathode current collector. However, to ensure sufficient cell performance while maintaining adhesion, it is necessary to use multiple binder polymers at optimal composition ratios.

[0054] Accordingly, in the present invention, the binder polymer included in the positive electrode active material layer of the positive electrode for a lithium-sulfur battery includes polyacrylic acid (PAA), polyacrylamide, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). The binder polymer can maintain the positive electrode active material on the positive electrode current collector and organically connect the positive electrode active materials to further enhance the bonding strength therebetween.

[0055]

[0056] In one embodiment of the present invention, the binder polymer may be included in an amount of 1 to 10 parts by weight, 2 to 8 parts by weight, or 3 to 5 parts by weight, based on 100 parts by weight of the total positive electrode active material layer. When the binder polymer is included in the above range, the lithium-sulfur battery can exhibit excellent cell performance while ensuring sufficient adhesiveness between the positive electrode active material layer and the positive electrode current collector.

[0057]

[0058] In one embodiment of the present invention, polyacrylic acid may be included in an amount of 5 to 30 parts by weight, 5 to 25 parts by weight, 6.25 to 25 parts by weight, or 12.5 to 25 parts by weight, based on 100 parts by weight of the total binder polymer. When polyacrylic acid is included in the above amount, the lithium-sulfur battery can secure appropriate output while ensuring adhesion between the positive electrode current collector and the positive electrode active material layer.

[0059]

[0060] In one embodiment of the present invention, the weight average molecular weight of the polyacrylic acid may be 50,000 to 1.5 million g / mol, 100,000 to 1.5 million g / mol, 200,000 to 1.5 million g / mol, 300,000 to 1.5 million g / mol, 400,000 to 1.5 million g / mol, 500,000 to 1.5 million g / mol, 100,000 to 1.4 million g / mol, 100,000 to 1.3 million g / mol, 200,000 to 1.4 million g / mol, 300,000 to 1.4 million g / mol, 400,000 to 1.4 million g / mol, or 500,000 to 1.3 million g / mol. When the weight average molecular weight of the polyacrylic acid falls within the above range, the lithium-sulfur battery can secure appropriate output while ensuring adhesive strength between the positive electrode current collector and the positive electrode active material layer.

[0061] The above weight average molecular weight can be measured under the following gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies) analysis conditions.

[0062] - Column: PL MiniMixed B x 2

[0063] - Solvent: THF

[0064] - Flow rate: 0.3 ml / min

[0065] - Sample concentration: 2.0 mg / ml

[0066] - Injection volume: 10 ㎕

[0067] - Column temperature: 40℃

[0068] - Detector: Agilent RI detector

[0069] - Standard: Polystyrene (corrected with a cubic function)

[0070] - Data processing: ChemStation

[0071]

[0072] In one embodiment of the present invention, the polyacrylamide may be included in an amount of 10 to 35 parts by weight, 10 to 31.25 parts by weight, 12.5 to 35 parts by weight, 12.5 to 31.25 parts by weight, or 12.5 to 25 parts by weight, based on 100 parts by weight of the total binder polymer. When the polyacrylamide is included in the above amount, sufficient adhesiveness can be secured between the positive electrode active material layer and the positive electrode current collector while maintaining an appropriate output of the battery. When the polyacrylamide is included in an excessive amount, the binder polymer increases at the interface of the positive electrode active material layer, which may increase the resistance and decrease the output of the battery.

[0073]

[0074] In one embodiment of the present invention, the weight average molecular weight of the polyacrylamide may be 50,000 to 1.5 million g / mol, 100,000 to 1.5 million g / mol, 200,000 to 1.5 million g / mol, 300,000 to 1.5 million g / mol, 400,000 to 1.5 million g / mol, 500,000 to 1.5 million g / mol, 100,000 to 1.4 million g / mol, 100,000 to 1.3 million g / mol, 200,000 to 1.4 million g / mol, 300,000 to 1.4 million g / mol, 400,000 to 1.4 million g / mol, or 500,000 to 1.3 million g / mol. When the weight average molecular weight of the polyacrylamide falls within the above range, sufficient adhesive strength can be secured between the positive electrode active material layer and the positive electrode current collector while maintaining an appropriate output of the battery.

[0075] The above weight average molecular weight can be measured using the same method as the method for measuring the weight average molecular weight of polyacrylic acid.

[0076]

[0077] In one embodiment of the present invention, carboxymethyl cellulose may be included in an amount of 10 to 20 parts by weight, 12.5 to 20 parts by weight, or 10 to 15 parts by weight, based on 100 parts by weight of the total binder polymer. When carboxymethyl cellulose is included in the above range, when the slurry for forming a positive electrode active material layer is applied on the current collector, the carboxymethyl cellulose acts as a thickener, thereby preventing the slurry from flowing down on the current collector and maintaining a viscous form, thereby allowing the positive electrode active material layer to be formed to an appropriate thickness.

[0078]

[0079] In one embodiment of the present invention, the carboxymethyl cellulose may have a viscosity of 200 to 5000 cps in a 1 wt% aqueous solution. When the viscosity of the carboxymethyl cellulose falls within the above range, a positive electrode active material layer can be formed to an appropriate thickness.

[0080] The above viscosity can be measured at room temperature at a speed of 12 rpm using a No. 4 spindle of a Brookfield viscometer (model name: LVDV2T) in water in which carboxymethyl cellulose is dissolved at a content of 1 wt%.

[0081]

[0082] In one embodiment of the present invention, the styrene-butadiene rubber may be included in an amount of 40 to 60 parts by weight, 45 to 60 parts by weight, 40 to 55 parts by weight, or 45 to 55 parts by weight based on 100 parts by weight of the total binder polymer. When the styrene-butadiene rubber is included in the above range, sufficient adhesive strength can be secured between the positive electrode active material layer and the positive electrode current collector.

[0083]

[0084] In one embodiment of the present invention, the gel content of the styrene-butadiene rubber may be 90 to 100%. When the gel content of the styrene-butadiene rubber falls within the above range, sufficient adhesive strength can be secured between the positive electrode active material layer and the positive electrode current collector.

[0085] The gel content of a binder polymer such as the above styrene-butadiene rubber can be measured by a method known in the art, and can be calculated, for example, by the following measuring method.

[0086] First, when measuring a binder polymer under electrolyte conditions, the binder polymer is added to the electrolyte and stored for approximately 48 hours at the desired temperature. The initial mass of the added binder polymer is measured, and after storage, the binder polymer is removed and its mass while immersed in the electrolyte is measured.

[0087] Afterwards, the binder polymer is immersed in ethanol for approximately 24 hours to remove the components of the electrolyte, and then dried at approximately 25°C for 24 hours, and the mass of the binder polymer is measured again.

[0088] The gel content (%) can be calculated by using the mass ratio of the binder after immersion in ethanol and drying it relative to the mass of the initial binder polymer.

[0089] Gel content (%) = (B / A) × 100

[0090] The above A is the mass of the binder polymer, and the above B is the mass of the binder polymer having the above mass A, which is stored in an electrolyte for 48 hours, immersed in ethanol for 24 hours, and then dried.

[0091]

[0092] In one embodiment of the present invention, the glass transition temperature (Tg) of the styrene-butadiene rubber may be -20 to 20°C. When the glass transition temperature of the styrene-butadiene rubber falls within the above range, sufficient adhesive strength can be secured between the positive electrode active material layer and the positive electrode current collector.

[0093]

[0094] In one embodiment of the present invention, the positive electrode active material layer may further include other binder polymers known in the art. For example, a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); a rubber binder including acrylonitrile-butidiene rubber, styrene-isoprene rubber; a cellulose binder including starch, hydroxypropyl cellulose, regenerated cellulose, etc.; a polyalcohol binder; a polyolefin binder including polyethylene, polypropylene, etc.; a polyimide binder; a polyester binder; and a silane binder; or a mixture thereof, or a copolymer including two or more of their repeating units may be used.

[0095]

[0096] In one embodiment of the present invention, the sulfur-carbon composite is a positive electrode active material, and a sulfur-based material is supported on a porous carbon material.

[0097] The above sulfur-based material may be sulfur and / or sulfide, specifically inorganic sulfur (S8), Li2S. n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole, 1,3,5-trithiocyanuic acid, etc., an organic sulfur compound, or two or more thereof may be included. Preferably, inorganic sulfur (S8) can be used as the sulfur-based material.

[0098] In addition, the positive electrode active material may further include 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. The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, Hg, etc., Group IIIA elements may include Al, Ga, In, Tl, etc., and Group IVA elements may include Ge, Sn, Pb, etc.

[0099] The porous carbon material may be a crystalline or amorphous carbon material, and may be a conductive carbon. The carbon material provides a framework capable of uniformly and stably fixing sulfur and / or sulfides, and compensates for the low electrical conductivity of sulfur and / or sulfides, thereby enabling the electrochemical reaction to proceed smoothly.

[0100] The above porous carbon material can be manufactured by carbonizing various carbon precursors, and can include irregularities and / or pores inside, and the average diameter of the pores of the porous carbon material can be 1 nm to 200 nm, and the porosity of the porous carbon material can be 10 vol% to 90 vol% of the total volume of the carbon material. When the average diameter of the porous carbon material satisfies the above range, the mechanical strength of the porous carbon material can be maintained.

[0101] The above porous carbon material can be used without limitation as long as it is commonly used in lithium sulfur batteries, such as spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped. In addition, the porous carbon material can have a high specific surface area. For example, the porous carbon material can be graphite, graphene, Super P, carbon black, Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, carbon nanofiber, carbon nanotube (SWCNT, MWCNT), carbon nanowire, carbon nanoring, carbon fabric, fullerene (C 60 ), or may include two or more of these.

[0102] The sulfur-carbon composite in which the sulfur-based substance is supported on the porous carbon material may contain 60 to 90 wt% of the sulfur-based substance based on 100 wt% of the total sulfur-carbon composite. Since the content of the sulfur-based substance is within the above range, the content of the sulfur-based substance and the content of the porous carbon material are appropriately balanced, so that only an appropriate amount of the binder polymer for binding the sulfur-based substance to the porous carbon material can be used. Accordingly, since only an appropriate amount of the binder polymer that may cause an increase in resistance can be used, the battery performance of the lithium-sulfur battery can be improved.

[0103] In the above sulfur-carbon composite, the sulfur-based material may be positioned externally in a manner that at least partially fills the internal space (e.g., pores) of the porous carbon material, or covers at least a portion of the surface of the porous carbon material, either together with or independently of the internal space. In a specific embodiment, the sulfur-based material may be positioned on less than 100%, 1 to 95%, or 60 to 90% of the surface of the porous carbon material. The presence of the sulfur-based material within the above range improves wettability with respect to an electrolyte and improves electrical conductivity.

[0104] The method for producing the above sulfur-carbon composite is not particularly limited and can be produced using methods commonly used in the art. For example, a sulfur-carbon composite can be produced by mixing a sulfur-based material, such as sulfur (S8), with a porous carbon material and heat-treating the mixture.

[0105] The above sulfur-carbon complex may be included in an amount of 50 to 95 parts by weight, 60 to 95 parts by weight, or 70 to 95 parts by weight based on 100 parts by weight of the total positive electrode active material layer. When the sulfur-carbon complex is included in an amount within the above range, the positive electrode can sufficiently cause an electrochemical reaction.

[0106]

[0107] In one embodiment of the present invention, the positive electrode active material layer may further include a conductive material.

[0108] The conductive material electrically connects the electrolyte and the positive electrode active material, acts as a path for electrons to move from the positive electrode current collector to the positive electrode active material, and improves electrical conductivity or ionic conductivity. Any conductive material can be used without limitation. For example, the conductive material may be carbon black such as Super-P, Denka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, summer black, carbon black; carbon derivatives such as carbon nanotubes, graphene, and fullerene; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, which can be used alone or in combination. The content of the conductive material may be included in an amount of 0.01 to 30 parts by weight based on 100 parts by weight of the entire positive electrode active material layer. The above-mentioned conductive material is included in the above range, so that electrons can move better from the current collector to the positive electrode active material, and the ionic conductivity or electrical conductivity of the positive electrode can be appropriately maintained.

[0109]

[0110] In one embodiment of the present invention, the positive electrode for a lithium-sulfur battery may be a current collector-free type that does not include a current collector and is composed only of a positive electrode active material layer, or may be a positive electrode active material layer formed on at least one surface of a positive electrode current collector.

[0111] The above-mentioned positive electrode current collector may be a current collector used in the technical fields of lithium secondary batteries and lithium-sulfur batteries, and is not particularly limited as long as it has high conductivity and does not cause side reactions in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used.

[0112] The thickness of the above-mentioned positive electrode collector may be 1 µm to 300 µm, but is not particularly limited, and may be set to an appropriate range considering the mechanical strength of the electrode, productivity, capacity of the battery, etc.

[0113] The thickness of the positive electrode active material layer may be 1 µm to 200 µm, 5 µm to 100 µm, 10 µm to 80 µm, or 20 µm to 50 µm. When the thickness of the positive electrode active material layer falls within the above range, the growth of lithium dendrites can be suppressed, and sufficient battery capacity can be secured.

[0114]

[0115] In one embodiment of the present invention, the positive electrode for a lithium-sulfur battery may have an adhesive strength of 30 gf / 2 cm or more, 35 gf / 2 cm or more, or 35 to 100 gf / 2 cm between the positive electrode current collector and the positive electrode active material layer. When the electrode adhesive strength of the positive electrode for a lithium-sulfur battery falls within the above range, sufficient adhesive strength may be provided during the manufacture of a lithium-sulfur battery, so that the lithium-sulfur battery may not be separated from the separator, and the lithium-sulfur battery may have a sufficient cycle life.

[0116] The above adhesive strength can be measured by using UTM equipment to measure the adhesive strength between the positive electrode active material layer of the positive electrode sample and the current collector (90° peeling experiment, Load Cell: 10N, Speed: 100 mm / min).

[0117]

[0118] The second aspect of the present invention relates to a lithium sulfur battery.

[0119] A lithium-sulfur battery according to one aspect of the present invention comprises a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode is a positive electrode for a lithium-sulfur battery according to one aspect of the present invention described above.

[0120]

[0121] In one embodiment of the present invention, the lithium sulfur battery may further include a separator positioned between the positive electrode and the negative electrode.

[0122]

[0123] In one embodiment of the present invention, the negative electrode may be a current collector-free type that does not include the entire negative electrode and is composed only of a negative electrode active material layer, or may be a type that 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.

[0124] The above negative electrode current collector is for supporting the negative electrode active material layer, as described in the positive electrode current collector.

[0125] The above-mentioned negative electrode active material layer may include a conductive material, a binder, etc. in addition to the negative electrode active material. In this case, the conductive material and the binder follow the above-mentioned.

[0126] The above negative active material is lithium (Li + ) can be reversibly intercalated or deintercalated, a material that can react with lithium ions to form a reversibly lithium-containing compound, or a lithium metal or a lithium alloy.

[0127] The above lithium ion (Li + ) can be reversibly inserted or de-inserted, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The lithium ion (Li + ) can be, for example, tin oxide, titanium nitrate or silicon. The lithium alloy can be, for example, an alloy of two or more metals 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).

[0128] According to one embodiment of the present invention, the negative active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

[0129]

[0130] In one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator commonly used in lithium-sulfur batteries, it can be used without any particular limitation, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity.

[0131] For example, the separator may be a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0132]

[0133] In one embodiment of the present invention, a separate separator may not be provided, and a solid electrolyte or gel electrolyte may serve as a separator.

[0134]

[0135] In one embodiment of the present invention, the electrolyte may include a lithium salt and a solvent, and optionally further include additives. The electrolyte is not particularly limited as long as it has a composition that can be used in a lithium secondary battery, specifically a lithium-sulfur battery.

[0136] The solvent of the above electrolyte may be a non-aqueous solvent, and the non-aqueous solvent may be used without particular limitation as long as it is of a type that can be used in a lithium-sulfur battery, and for example, ether solvents, esters, amides, linear carbonates, and cyclic carbonates may be used.

[0137] In one embodiment of the present invention, the ester may include, but is not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, or a mixture of two or more thereof.

[0138] In one embodiment of the present invention, the linear carbonate may include, but is not limited to, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, or a mixture of two or more thereof.

[0139] In one embodiment of the present invention, the cyclic carbonate may include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, halides thereof, or mixtures of two or more thereof. Examples of the halides thereof include, but are not limited to, fluoroethylene carbonate.

[0140] In one embodiment of the present invention, the non-aqueous solvent may include an ether solvent.

[0141] In one embodiment of the present invention, the ether solvent may be included in an amount of 80% by volume or more, for example, 85% by volume to 100% by volume, 90% by volume to 100% by volume, 95% by volume to 100% by volume, 98% by volume to 100% by volume, 90% by volume to 98% by volume, or 90% by volume to 95% by volume, based on the total volume of the non-aqueous solvent. When the amount of the ether solvent is in the above-described range based on the total volume of the non-aqueous solvent, an advantageous effect may be exhibited in terms of the solubility of the electrolyte composition such as a lithium salt, but the present invention is not limited thereto.

[0142] In one embodiment of the present invention, the ether solvent may include an acyclic ether, a cyclic ether, or a mixture thereof.

[0143] In one embodiment of the present invention, the acyclic ether is, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethylpropyl ether, ethyl tertbutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tertbutyl ethyl ether, ethylene glycol ethyl methyl ether, or two or more thereof. It may include a mixture. Preferably, it may include dimethyl ether, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a mixture of two or more thereof.

[0144] In one embodiment of the present invention, the cyclic ether is, for example, 2-methylfuran, 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran, 1,4-dioxane, It may include 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbide dimethyl ether, or a mixture of two or more thereof. Preferably, it may include 2-methylfuran, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, or a mixture of two or more thereof, and more preferably, it may include 2-methylfuran.

[0145] In one embodiment of the present invention, the non-aqueous solvent may include a mixture of an acyclic ether and a cyclic ether.

[0146] In one embodiment of the present invention, the non-aqueous solvent may include dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0147] In one embodiment of the present invention, the volume ratio of the acyclic ether and the cyclic ether may be 95:5 to 5:95 (v / v), specifically 95:5 to 50:50, more specifically 90:10 to 70:30, or 85:15 to 75:25, or 95:5 to 80:20, or 80:20 to 5:95, or 90:10 to 80:20, or 80:20. In the present invention, the volume ratio corresponds to the ratio of "volume % of acyclic ether": "volume % of cyclic ether" in the ether solvent.

[0148] In one embodiment of the present invention, the non-aqueous solvent may not contain a carbonate solvent in terms of the solubility of the electrolyte. Alternatively, the non-aqueous solvent may contain a very small amount of a carbonate solvent such that the carbonate solvent does not affect the solubility of the lithium salt. For example, when the non-aqueous solvent contains the carbonate solvent, the content of the carbonate solvent may be 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0 wt% (i.e., not contained at all) based on the total weight of the electrolyte for a lithium secondary battery.

[0149]

[0150] In one embodiment of the present invention, the lithium salt may be any compound capable of providing lithium ions, which is generally used in lithium-sulfur batteries, without particular limitation. For example, the lithium salt may be LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyyl)imide), LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0151]

[0152] In one embodiment of the present invention, the additive may include a nitric acid compound, and the nitric acid compound may be selected from lithium nitrate (LiNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium nitrate (MgNO3), barium nitrate (BaNO3), potassium nitrite (KNO2), and cesium nitrite (CsNO2). In this case, the additive may be included in an amount of 0.1 wt% to 10 wt%, or 0.1 wt% to 3 wt%, or 3 wt% to 10 wt% based on the total weight of the electrolyte.

[0153] In addition to the nitric acid compound, the additive may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0154]

[0155] In one embodiment of the present invention, the lithium sulfur battery may be a coin-type battery, a pouch-type battery, or a cylindrical battery, but is not limited thereto.

[0156]

[0157] In one embodiment of the present invention, the lithium sulfur battery may have an output of 2.2 Wh / kg or more, or 2.3 Wh / kg or more.

[0158] The above output can be calculated by performing a hybrid pulse power characterization (HPPC) test on a lithium-sulfur battery at 25°C. For example, if an HPPC test is performed at 25°C, a lithium-sulfur battery with a SOC of 75 is discharged at 5C for 10 seconds, and the output can be obtained by dividing the discharge by the weight of each lithium-sulfur battery.

[0159]

[0160] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0161]

[0162] Example 1

[0163] A sulfur-carbon composite was prepared as a cathode active material by mixing sulfur (S8) and carbon nanotubes in a weight ratio of 75:25, pulverizing them by ball milling, and then placing them in an oven at 155°C for 30 minutes.

[0164] The above sulfur-carbon complex and binder polymer were added to water at a weight ratio of 96:4 to prepare a cathode slurry. At this time, the binder polymer was a mixture of polyacrylic acid (weight average molecular weight: 1,250,000 g / mol), polyacrylamide (number average molecular weight: 780,000 g / mol), carboxymethyl cellulose (GLchem, GBLi1000), and styrene-butadiene rubber (Tg = 8°C) at a weight ratio of 12.5:25:12.5:50.

[0165] The above positive electrode slurry was applied to both sides of aluminum foil, dried at 80°C, and then rolled using a roll press to manufacture a positive electrode. At this time, the loading of the positive electrode was set to 2.6 mAh / cm2.

[0166]

[0167] Example 2

[0168] A positive electrode was manufactured in the same manner as in Example 1, except that a binder polymer consisting of polyacrylic acid, polyacrylamide, carboxymethyl cellulose, and styrene-butadiene rubber was used in a weight ratio of 25:12.5:12.5:50.

[0169]

[0170] Example 3

[0171] A positive electrode was manufactured in the same manner as in Example 1, except that a binder polymer consisting of polyacrylic acid, polyacrylamide, carboxymethyl cellulose, and styrene-butadiene rubber was used in a weight ratio of 18.75:18.75:12.5:50.

[0172]

[0173] Example 4

[0174] A positive electrode was manufactured in the same manner as in Example 1, except that a binder polymer consisting of polyacrylic acid, polyacrylamide, carboxymethyl cellulose, and styrene-butadiene rubber was used in a weight ratio of 6.25:31.25:12.5:50.

[0175]

[0176] Comparative Example 1

[0177] A positive electrode was manufactured in the same manner as in Example 1, except that the sulfur-carbon complex and the binder polymer were added to water at a weight ratio of 97:3 and only polyacrylamide was used as the binder polymer.

[0178]

[0179] Comparative Example 2

[0180] A positive electrode was manufactured in the same manner as in Example 1, except that a binder polymer consisting of polyacrylamide, carboxymethylcellulose, and styrene-butadiene rubber was used in a weight ratio of 37.5:12.5:50.

[0181]

[0182] Comparative Example 3

[0183] A positive electrode was manufactured in the same manner as in Example 1, except that the sulfur-carbon complex and the binder polymer were added to water at a weight ratio of 97:3 and only polyacrylic acid was used as the binder polymer.

[0184]

[0185] Comparative Example 4

[0186] A positive electrode was manufactured in the same manner as in Example 1, except that a binder polymer consisting of polyacrylic acid, carboxymethyl cellulose, and styrene-butadiene rubber was used in a weight ratio of 37.5:12.5:50.

[0187]

[0188] Comparative Example 5

[0189] The procedure of Example 1 was the same, except that a mixture of polyacrylic acid, polyacrylamide, and styrene-butadiene rubber in a weight ratio of 25:25:50 was used as the binder polymer. However, the positive electrode slurry failed to be applied to the current collector and flowed down, resulting in failure in the manufacture of the positive electrode.

[0190]

[0191] The types and contents of binders used in Examples 1 to 4 and Comparative Examples 1 to 5 are as shown in Table 1 below.

[0192] Weight of binder polymer relative to 100 parts by weight of the total positive electrode active material layer Weight of polyacrylic acid relative to 100 parts by weight of the total binder polymer Weight of polyacrylamide relative to 100 parts by weight of the total binder polymer Weight of carboxymethyl cellulose relative to 100 parts by weight of the total binder polymer Weight of styrene-butadiene rubber relative to 100 parts by weight of the total binder polymer Weight Example 1 4 12.5 25 12.550 Example 2 4 25 12.5 12.550 Example 3 4 18.75 18.75 12.550 Example 4 4 ​​6.25 31.25 12.550 Comparative Example 1 3 0 10 000 Comparative Example 2 4 0 37.5 12.550 Comparative Example 3 3 10 0000 Comparative Example 4 4 ​​37.5 12.550 Comparative Example 5 4 25 25 0 50

[0193] Experimental Example 1: Adhesion Measurement

[0194] The positive electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 4 were cut to a width of 20 mm and a length of 100 mm to prepare positive electrode samples.

[0195] A 55 mm long double-sided adhesive tape was attached on the slide glass, and the prepared positive electrode samples of Examples 1 to 4 and Comparative Examples 1 to 4 were laminated onto the slide glass using a laminator.

[0196] The adhesion between the positive electrode active material layer of the positive electrode sample and the current collector was measured using UTM equipment, and the results are shown in Table 2 below (90° peeling experiment, Load Cell: 10N, Speed: 100 mm / min).

[0197]

[0198] Adhesive strength (gf / 2cm) Example 1 45.3 Example 2 35.5 Example 3 37.7 Example 4 48.5 Comparative Example 1 17.3 Comparative Example 2 40.4 Comparative Example 39.9 Comparative Example 4 23.8

[0199] Referring to Table 2 above, the anodes according to Comparative Examples 1 and 3 were measured to have significantly lower adhesive strengths because they did not contain styrene-butadiene rubber. In addition, the anode according to Comparative Example 4 was measured to have lower adhesive strengths because it did not contain polyacrylamide.

[0200]

[0201] Example 5

[0202] The positive electrode manufactured in Example 1 was prepared, and lithium metal having a thickness of 60 μm was prepared as the negative electrode.

[0203] An electrode assembly was prepared by positioning the positive and negative electrodes so that they face each other and interposing a polyethylene separator having a thickness of 16 ㎛ and a porosity of 46 vol% between them.

[0204] The prepared electrode assembly was stored in a pouch-type case, and an electrolyte solution containing 0.75 M lithium salt (LiTFSI) and 3 wt% lithium nitrate (LiNO3) dissolved in a solvent mixed with dimethoxyethane:2-methyl furan (2-MeF) in a volume ratio of 8:2 was injected so that the E / S ratio was 3.0 g / g, thereby manufacturing a lithium-sulfur battery.

[0205]

[0206] Example 6

[0207] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Example 2 was used.

[0208]

[0209] Example 7

[0210] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Example 3 was used.

[0211]

[0212] Example 8

[0213] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Example 4 was used.

[0214]

[0215] Comparative Example 6

[0216] An attempt was made to manufacture a lithium-sulfur battery in the same manner as Example 5, except that the positive electrode manufactured in Comparative Example 1 was used, but the battery manufacturing failed due to the weak adhesive strength of the positive electrode.

[0217]

[0218] Comparative Example 7

[0219] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Comparative Example 2 was used.

[0220]

[0221] Comparative Example 8

[0222] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Comparative Example 3 was used.

[0223]

[0224] Comparative Example 9

[0225] A lithium-sulfur battery was manufactured in the same manner as in Example 5, except that the positive electrode manufactured in Comparative Example 4 was used.

[0226]

[0227] Experimental Example 2: Output Test

[0228] Lithium-sulfur batteries manufactured in Examples 5 to 8 and Comparative Examples 7 to 9 were prepared. Hybrid pulse power characterization (HPPC) tests were performed on each lithium-sulfur battery at 25°C. At this time, lithium-sulfur batteries with an SOC of 75 were discharged at 5C for 10 seconds, and the output was calculated by dividing the output by the weight of each lithium-sulfur battery.

[0229]

[0230] Output (Wh / kg) Example 52.51 Example 62.61 Example 72.55 Example 82.33 Comparative Example 72.11 Comparative Example 82.17 Comparative Example 92.61

[0231] Referring to Table 3 above, it was confirmed that the lithium-sulfur battery according to Comparative Example 7 contained too much polyacrylamide in the positive electrode active material layer, resulting in a low measured output. In the lithium-sulfur battery according to Comparative Example 8, although polyacrylamide was sufficiently used during the manufacture of the positive electrode, the positive electrode active material layer was not formed to an appropriate thickness because carboxymethyl cellulose was not used, resulting in a low measured output. In the lithium-sulfur battery according to Comparative Example 9, the output was measured high because polyacrylamide and carboxymethyl cellulose were used.

[0232] On the other hand, it was confirmed that the lithium sulfur batteries according to the embodiments of the present invention all measured excellent outputs.

[0233]

[0234] As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A positive electrode current collector; and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector; The above positive electrode active material layer comprises a sulfur-carbon complex; and a binder polymer, A cathode for a lithium-sulfur battery, characterized in that the binder polymer comprises polyacrylic acid, polyacrylamide, carboxymethylcellulose, and styrene-butadiene rubber.

2. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the binder polymer is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total positive electrode active material layer.

3. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the polyacrylic acid is contained in an amount of 5 to 30 parts by weight based on 100 parts by weight of the total binder polymer.

4. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the polyacrylic acid is contained in an amount of 5 to 25 parts by weight based on 100 parts by weight of the total binder polymer.

5. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the polyacrylamide is included in an amount of 10 to 35 parts by weight based on 100 parts by weight of the total binder polymer.

6. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the polyacrylamide is included in an amount of 10 to 31.25 parts by weight based on 100 parts by weight of the total binder polymer.

7. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the carboxymethyl cellulose is included in an amount of 10 to 20 parts by weight based on 100 parts by weight of the total binder polymer.

8. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the carboxymethyl cellulose is included in an amount of 12.5 to 20 parts by weight based on 100 parts by weight of the total binder polymer.

9. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the styrene-butadiene rubber is included in an amount of 40 to 60 parts by weight based on 100 parts by weight of the total binder polymer.

10. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the styrene-butadiene rubber is included in an amount of 45 to 60 parts by weight based on 100 parts by weight of the total binder polymer.

11. In paragraph 1, A positive electrode for a lithium-sulfur battery, characterized in that the adhesive strength between the positive electrode current collector and the positive electrode active material layer is 35 gf / 2 cm or more.

12. In a lithium-sulfur battery including a positive electrode, a negative electrode, and an electrolyte, A lithium-sulfur battery, characterized in that the positive electrode is a positive electrode for a lithium-sulfur battery according to any one of claims 1 to 11.

13. In paragraph 12, The above lithium-sulfur battery is a lithium-sulfur battery characterized in that the output is 2.2 Wh / kg or more.

14. In paragraph 12, A lithium-sulfur battery further comprising a separator positioned between the positive electrode and the negative electrode.