Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising the same

Abstract

The present invention relates to an electrolyte for a lithium-sulfur battery comprising a non-aqueous organic solvent including specific three compounds and a lithium-sulfur battery comprising the same.

Description

Technical Field

[0001] The present invention provides an electrolyte for lithium-sulfur batteries and a lithium-sulfur battery containing the electrolyte.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0157907, filed on November 23, 2020, the entire contents of which are incorporated herein by reference. Background Technology

[0003] As the application of lithium-ion batteries expands not only to portable electronic devices and communication devices, but also to electric vehicles (EVs) and energy storage systems (ESS), the demand for higher-capacity lithium-ion batteries used as their power source has grown.

[0004] Among various lithium secondary batteries, lithium-sulfur batteries are battery systems that use sulfur-sulfur bonded sulfur-based materials as positive electrode active materials and lithium metal, carbon materials with lithium ion intercalation / deintercalation, or silicon, tin, etc., which are alloyed with lithium, as negative electrode active materials.

[0005] Sulfur, the main material for the positive electrode active material in lithium-sulfur batteries, has the advantages of low atomic weight, easy supply due to abundant resources, low price, non-toxicity, and environmental friendliness.

[0006] Furthermore, lithium-sulfur batteries exhibit a conversion reaction between lithium ions and sulfur in the positive electrode (S₈ + 16Li₂). + +16e - The theoretical discharge capacity of lithium-sulfur batteries (→8Li₂S) reaches as high as 1675 mAh / g, and the theoretical energy density is 2600 Wh / kg when lithium metal (theoretical capacity: 3860 mAh / g) is used as the negative electrode. This is a very high value compared with the theoretical energy density of other battery systems currently under study (Ni-MH battery: 450 Wh / kg; Li-FeS battery: 480 Wh / kg; Li-MnO₂ battery: 1000 Wh / kg; Na-S battery: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg). Therefore, among the secondary batteries developed to date, lithium-sulfur batteries have attracted attention as high-capacity, environmentally friendly and low-cost lithium secondary batteries, and various studies have been conducted on them as next-generation battery systems.

[0007] In this type of lithium-sulfur battery, sulfur accepts electrons during discharge to initiate a reduction reaction at the positive electrode. Specifically, sulfur, as the positive electrode active material, is ultimately reduced by lithium polysulfide (Li₂S₂). x (x = 8, 6, 4, 2) are reduced to lithium sulfide (Li2S).

[0008] However, lithium sulfide, the final product of the sulfur reduction reaction (discharge), is a material with low electrical conductivity. When deposited on the electrode, it passivates the electrode surface on which the electrochemical reaction takes place. As a result, the electrochemical reactivity of the electrode decreases, leading to the problem that the theoretical discharge capacity cannot be fully achieved in actual operation.

[0009] Furthermore, because the deposited lithium sulfide no longer participates in the electrochemical reaction, the positive electrode active material is lost, which accelerates the decline in the battery's discharge capacity.

[0010] Due to these issues, the capacity and charging and discharging efficiency of lithium-sulfur batteries decline rapidly with cycling, which also shortens their lifespan. Furthermore, they have not yet been successfully commercialized because it is difficult to ensure sufficient performance and operational stability.

[0011] Most research aimed at solving these problems has focused on modifying the cathode. Specifically, as one method to improve electrode conductivity, attempts have been made to minimize the decrease in conductivity of electrodes with lithium sulfide accumulation by adding conductive materials made of carbon, or by using sulfur supports with nanostructures to control the generation and accumulation of intermediate products and lithium sulfide.

[0012] However, most of these technologies are difficult to commercialize, and their effectiveness in improving capacity performance is insufficient. Therefore, there is still a need to develop a lithium-sulfur battery that can achieve excellent capacity performance by suppressing electrode passivation caused by lithium sulfide and the resulting reduction in electrode electrochemical reactivity. Summary of the Invention

[0013] [Technical Issues]

[0014] As a result of extensive research conducted in view of the above circumstances, the inventors of the present invention have discovered that when conjugated cyclic ether compounds, dimethoxyethane, and diol diether compounds are included as non-aqueous organic solvents in the electrolyte for lithium-sulfur batteries, the discharge capacity of the battery can be improved by preventing electrode passivation caused by lithium sulfide, thus completing the present invention.

[0015] Therefore, the present invention aims to provide an electrolyte for lithium-sulfur batteries that can exhibit excellent capacity performance.

[0016] Furthermore, the present invention also aims to provide a lithium-sulfur battery comprising the electrolyte.

[0017] [Technical Solution]

[0018] One embodiment of the present invention provides an electrolyte for lithium-sulfur batteries, the electrolyte comprising a lithium salt and a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises:

[0019] The first solvent includes conjugated cyclic ether compounds;

[0020] A second solvent, the second solvent comprising dimethoxyethane; and

[0021] The third solvent comprises diol diether compounds represented by the following chemical formula 1:

[0022] [Chemical Formula 1]

[0023] R1(CH2CH2O) n R2

[0024] In chemical formula 1, R1, R2, and n are as described in the specification.

[0025] In one embodiment of the invention, based on 100 vol% of a non-aqueous organic solvent comprising a first solvent, a second solvent, and a third solvent, the content of the first solvent is 20 vol% to 49 vol%, the content of the second solvent is 50 vol% to 79 vol%, and the content of the third solvent is greater than or equal to 1 vol% and less than 25 vol%.

[0026] In one embodiment of the invention, conjugated cyclic ether compounds include 4- to 15-membered heterocyclic compounds containing two or more double bonds while also containing oxygen or sulfur atoms.

[0027] In one embodiment of the present invention, the conjugated cyclic ether compound includes one or more selected from furan compounds and thiophene compounds.

[0028] In one embodiment of the invention, the furan compound includes one or more selected from the following: furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, and 2-(2-nitrovinyl)furan.

[0029] In one embodiment of the invention, the thiophene compound includes one or more selected from the following: thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene.

[0030] In one embodiment of the present invention, the diol diether compound includes one or more selected from the following: diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol methyl ethyl ether.

[0031] Another embodiment of the present invention provides a lithium-sulfur battery comprising an electrolyte for the lithium-sulfur battery.

[0032] [Beneficial Effects]

[0033] The electrolyte for lithium-sulfur batteries according to the present invention comprises a non-aqueous organic solvent including three specific compounds, and suppresses electrode passivation caused by lithium sulfide, thereby suppressing the reduction of electrochemical reactivity of the electrode. As a result, the capacity performance of the lithium-sulfur battery can be improved, and stable lifespan performance can be ensured. Detailed Implementation

[0034] The invention will be described in more detail below.

[0035] The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts corresponding to the technical ideas of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to describe the invention in the best possible way.

[0036] The terminology used in this invention is for describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein also include the plural forms. In this invention, terms such as “comprising” or “having” are used to indicate the presence of the features, numbers, steps, actions, ingredients, components, or combinations thereof described in the specification, but are not to be construed as precluding the possibility of the presence or addition of one or more other features, numbers, steps, actions, ingredients, components, or combinations thereof.

[0037] As used in this specification, the term "composite material" refers to a material that combines two or more materials and exhibits more effective functions while forming physically and chemically different phases.

[0038] The term "polysulfide" as used in this specification includes "polysulfide ions (S...)". x 2- "x = 8, 6, 4, 2)" and "lithium polysulfide (Li2S)" x or LiS x - The concept of "x = 8, 6, 4, 2".

[0039] Among various lithium-ion rechargeable batteries, lithium-sulfur batteries have high theoretical discharge capacity and energy density. They also have the advantages of abundant and inexpensive sulfur resources, which can be used as positive electrode active materials, thus reducing the manufacturing cost of batteries and being environmentally friendly. Therefore, they have attracted much attention as the next generation of rechargeable batteries.

[0040] As the lithium-sulfur battery discharges, sulfur, as the positive electrode active material, continuously reacts with lithium ions and is reduced to the final discharge product, lithium sulfide (Li2S).

[0041] However, as mentioned above, lithium sulfide is insoluble in electrolytes and has very low conductivity, thus it adheres to the electrode surface, leading to electrode passivation. As a result, the electrochemical reactivity of the electrode decreases, and the amount of sulfur participating in the electrochemical reaction is also reduced, making it impossible to obtain the theoretical discharge capacity. Furthermore, there is a problem of low battery life performance due to capacity degradation with cycling.

[0042] In view of the above, methods such as changing the composition of the positive electrode or electrolyte and using additives have been used in this field. However, these are not preferred for practical applications because they are not only ineffective in suppressing passivation caused by lithium sulfide, but also cause serious problems in battery performance and operational stability due to compatibility issues with other components forming the battery.

[0043] Therefore, the present invention provides an electrolyte for lithium-sulfur batteries, which can improve the solubility of lithium sulfide by specifying a three-component system in the electrolyte used in lithium-sulfur batteries, thereby delaying the decrease in passivation and electrochemical reactivity, and thus obtaining lithium-sulfur batteries with improved capacity and lifespan performance.

[0044] Specifically, the electrolyte for lithium-sulfur batteries according to the present invention comprises a lithium salt and a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises: a first solvent comprising a conjugated cyclic ether compound; a second solvent comprising dimethoxyethane; and a third solvent comprising a diol diether compound represented by the following chemical formula 1:

[0045] [Chemical Formula 1]

[0046] R1(CH2CH2O) n R2

[0047] In chemical formula 1,

[0048] R1 and R2 may be the same as or different from each other, and each is independently an alkyl or alkoxy group having 1 to 10 carbon atoms.

[0049] n is an integer from 2 to 4.

[0050] As used in this specification, the term "alkyl" refers to a straight-chain or branched saturated hydrocarbon group, although not particularly limited thereto, but preferably having 1 to 10 carbon atoms. Specific examples may include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl, hexyl, heptyl, etc.

[0051] As used in this specification, the term "alkoxy" refers to an alkyl group attached to an oxygen radical, although not particularly limited thereto, but preferably has 1 to 10 carbon atoms. Specific examples may include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentoxy, isopentoxy, hexoxy, etc.

[0052] One or more hydrogen atoms contained in an alkyl or alkoxy group may optionally be replaced by one or more substituents (e.g., alkyl, alkenyl, alkynyl, heterocyclic, aryl, heteroaryl, acyl, oxygen, imino, thiooxy, cyano, isocyano, amino, azide, nitro, hydroxyl, thiol, halogen, etc.). Halogens are a collective term for fluorine, chlorine, bromine, and iodine.

[0053] Lithium sulfide, a discharge product of the positive electrode in lithium-sulfur batteries, is a non-conductor and deposits on the electrode, particularly on the surface of electrodes containing carbon materials, thereby rapidly passivating the electrode surface and causing electrode passivation. However, the electrolyte according to the present invention comprises the following substances as a non-aqueous organic solvent: a first solvent comprising a conjugated cyclic ether compound; a second solvent comprising dimethoxyethane; and a third solvent comprising a diol diether compound represented by Formula 1, and can suppress electrode passivation by dissolving lithium sulfide present on the electrode surface. Therefore, the active surface area of ​​the electrode for electrochemical reactions can be maintained, and no loss of sulfur as the positive electrode active material occurs. As a result, lithium-sulfur batteries can exhibit excellent lifetime performance and achieve excellent capacity rate relative to the theoretical discharge capacity of lithium-sulfur batteries.

[0054] First solvent

[0055] In this invention, the first solvent comprising conjugated cyclic ether compounds includes 4- to 15-membered heterocyclic compounds containing two or more double bonds and also containing oxygen or sulfur atoms.

[0056] During the initial discharge phase of the battery, conjugated cyclic ether compounds form a polymer protective film (solid electrolyte interface, SEI layer) on the negative electrode surface containing lithium metal through the ring-opening reaction of heterocyclic compounds. This suppresses side reactions between lithium polysulfides generated and dissolved from the positive electrode and lithium metal, and prevents lithium sulfides from adhering to the lithium metal surface and thus preventing the loss of positive electrode active material. Furthermore, the delocalization of the lone pair electrons of heteroatoms (oxygen or sulfur atoms) makes the salt difficult to dissolve, which reduces the amount of lithium polysulfides dissolved.

[0057] In other words, the conjugated cyclic ether compound used as the first solvent of the present invention needs to contain more than two double bonds to form a polymer protective film on the negative electrode surface containing lithium metal, and needs to contain heteroatoms (oxygen or sulfur atoms) to be polar and have effects such as increasing affinity for other components in the electrolyte.

[0058] The conjugated cyclic ether compounds can be heterocyclic compounds with 4 to 15 membered cyclic groups, preferably 4 to 7 membered cyclic groups, and more preferably 5 to 6 membered cyclic groups.

[0059] Furthermore, the conjugated cyclic ether compounds can be: unsubstituted heterocyclic compounds, or heterocyclic compounds substituted by one or more of the following: alkyl groups having 1 to 4 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms, aryl groups having 6 to 10 carbon atoms, halogen groups, nitro (-NO2), amino (-NH2), and sulfonyl (-SO2); or said heterocyclic compounds and polycyclic compounds selected from one or more of the following: cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 10 carbon atoms.

[0060] Conjugated heterocyclic compounds substituted with alkyl groups having 1 to 4 carbon atoms are preferred because the free radicals are stable, thereby suppressing side reactions between the electrolyte and other components forming the battery. Furthermore, conjugated heterocyclic compounds substituted with halogen or nitro groups are preferred because a functional protective film can be formed on the negative electrode surface containing lithium metal, and in this document, the formed functional protective film has the advantage of being stably and uniformly deposited as a dense protective film.

[0061] Conjugated cyclic ether compounds may include one or more selected from furan compounds and thiophene compounds.

[0062] Specific examples of furan compounds may include one or more selected from the following: furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, and 2-(2-nitrovinyl)furan. Preferably, it may include one or more selected from 2-methylfuran and 2,5-dimethylfuran.

[0063] Specific examples of thiophene compounds may include one or more selected from the following: thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene.

[0064] Second solvent

[0065] In this invention, the second solvent, including dimethoxyethane (DME; (mono)glycol dimethyl ether), serves to ensure the ion transfer capability of the electrolyte by advantageously dissolving the lithium salt and maintaining the low viscosity of the electrolyte.

[0066] Third solvent

[0067] In this invention, the third solvent, comprising a glycol diether compound represented by Formula 1, serves to dissolve the lithium salt to impart lithium-ion conductivity to the electrolyte and also to dissolve lithium sulfide. The glycol diether compound of Formula 1 contains two or more -(CH2CH2O)- structures to lower the solvation energy of lithium sulfide, thus exhibiting higher lithium sulfide solubility compared to the second solvent, which includes dimethoxyethane (monoethylene glycol dimethyl ether). By dissolving the lithium sulfide generated during battery discharge, the glycol diether compound of Formula 1 prevents electrode passivation and maintains the electrochemical reactivity of the electrode, thereby improving the capacity and lifespan performance of the lithium-sulfur battery. Furthermore, since no sulfur loss occurs as the positive electrode active material, the obtained capacity of the positive electrode active material can be maximized.

[0068] In chemical formula 1, R1 and R2 may be the same as or different from each other, and preferably each is independently an alkyl or alkoxy group having 1 to 5 carbon atoms.

[0069] Specific examples of diethylene glycol diether compounds may include one or more selected from the following: diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol ethyl methyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol ethyl methyl ether. Preferably, it may include one or more selected from diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; more preferably, it may include one or more selected from diethylene glycol dimethyl ether and triethylene glycol dimethyl ether.

[0070] The electrolyte for lithium-sulfur batteries of the present invention comprises the first solvent, the second solvent, and the third solvent as described above, and for each of them, based on 100 vol% of a non-aqueous organic solvent comprising the first solvent, the second solvent, and the third solvent, the content of the first solvent is 20 vol% to 49 vol%, the content of the second solvent is 50 vol% to 79 vol%, and the content of the third solvent is greater than or equal to 1 vol% and less than 25 vol%.

[0071] The non-aqueous organic solvent contained in the electrolyte for lithium-sulfur batteries according to the present invention comprises 100% by volume, and the content of the first solvent is preferably 20% to 35% by volume. When the content of the first solvent is less than 20% by volume, a protective film may not be perfectly formed on the negative electrode surface, resulting in the inability to suppress the formation of lithium sulfide or a reduction in the effect of suppressing the dissolution of lithium polysulfides. Conversely, when the content of the first solvent is greater than 49% by volume, excessive prevention of lithium polysulfide dissolution may occur, and the electrochemical reaction may not proceed normally, which may lead to a reduction in battery discharge capacity.

[0072] The electrolyte for lithium-sulfur batteries according to the present invention contains 100% by volume of non-aqueous organic solvent, and the content of the second solvent is preferably 55% to 75% by volume. When the content of the second solvent is less than 50% by volume, the viscosity of the electrolyte increases, thereby reducing battery performance. Conversely, when the content of the second solvent is greater than 79% by volume, lithium polysulfide dissolution increases, thereby shortening the cycle life of the battery.

[0073] The lithium-sulfur battery electrolyte of the present invention contains 100% by volume of non-aqueous organic solvent, and the content of the third solvent is preferably 5% to 20% by volume. When the content of the third solvent is less than 1% by volume, the increase in lithium sulfide solubility is small, resulting in insignificant capacity improvement. Conversely, when the content of the third solvent is 25% by volume or more, the effect of improving capacity performance may be insignificant due to the increase in electrolyte viscosity.

[0074] lithium salts

[0075] The electrolyte for lithium-sulfur batteries according to the present invention comprises a lithium salt as the electrolyte salt. The lithium salt can be used without limitation, as long as it is commonly used in lithium secondary batteries.

[0076] Specific examples of lithium salts can be selected from one or more of the following: LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10The lithium salts include LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, LiSO3CH3, LiSO3CF3, LiSCN, LiC(CF3SO2)3, LiN(CF3SO2)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), LiN(C2F5SO2)2, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), lithium nitrate (LiNO3), lithium nitrite (LiNO2), lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, and lithium imide. Lithium salts preferably contain LiN(SO2F)2 (LiFSI) as an essential component, and more preferably contain lithium nitrate as needed.

[0077] The concentration of lithium salt can be appropriately determined by considering factors such as ionic conductivity and solubility. For example, the concentration can be from 0.1M to 4.0M, preferably from 0.2M to 2.0M, and more preferably from 0.5M to 2.0M. When the concentration of lithium salt is less than the above range, it is difficult to ensure suitable ionic conductivity for battery operation. Conversely, when the concentration of lithium salt is greater than the above range, the viscosity of the electrolyte increases, thereby reducing the mobility of lithium ions, and the battery performance may deteriorate due to the increased decomposition reaction of the lithium salt itself. Therefore, the concentration should be appropriately adjusted within the above range.

[0078] In addition to the above-described composition, the electrolyte for lithium-sulfur batteries according to the present invention may also contain additives commonly used in the art to enhance its function.

[0079] For example, the additive may be selected from one or more of the following: lanthanum nitrate (La(NO3)3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium nitrate (Mg(NO3)2), barium nitrate (Ba(NO3)2), potassium nitrite (KNO2), and cesium nitrite (CsNO2). Furthermore, based on 100% by weight of the electrolyte for lithium-sulfur batteries, the additive content may be from 1% by weight to 10% by weight, preferably from 2% by weight to 8% by weight, and more preferably from 2.5% by weight to 6% by weight. When the additive content is below the above range, the coulombic efficiency may decrease sharply, while when the content is above the above range, the viscosity of the electrolyte increases, leading to operational difficulties.

[0080] Furthermore, the present invention provides a lithium-sulfur battery comprising an electrolyte for the lithium-sulfur battery.

[0081] A lithium-sulfur battery comprises: a positive electrode; a negative electrode; and an electrolyte disposed between the positive and negative electrodes, and the electrolyte includes the electrolyte for lithium-sulfur batteries according to the present invention.

[0082] The positive electrode may include a positive current collector and a layer of positive active material coated on one or both surfaces of the positive current collector.

[0083] There are no particular restrictions on the positive electrode current collector, as long as it supports the positive electrode active material, has high conductivity, and does not cause chemical changes to the corresponding battery. For example, the following can be used: copper; stainless steel; aluminum; nickel; titanium; palladium; calcined carbon; copper or stainless steel with a surface treated with carbon, nickel, silver, etc.; aluminum-cadmium alloy, etc.

[0084] Positive current collectors can enhance their bonding strength with positive active materials by forming fine bumps and depressions on their surface, and can be used in a variety of forms such as membranes, sheets, foils, sieves, meshes, porous bodies, foams or nonwoven fabrics.

[0085] The positive electrode active material layer contains positive electrode active material, and may also contain conductive material, binder, additives, etc.

[0086] The positive electrode active material contains sulfur, specifically, it may contain one or more selected from: elemental sulfur (S₈) and sulfur compounds. The positive electrode active material may also include one or more selected from: inorganic sulfur, Li₂S… n (n≥1), disulfide compounds, organosulfur compounds, and carbon-sulfur polymers (C2S) x ) n (x = 2.5 to 50, n ≥ 2). Preferably, the positive electrode active material can be inorganic sulfur.

[0087] Sulfur contained in the positive electrode active material is not conductive on its own, and therefore it is combined with a conductive material such as carbon. Therefore, sulfur is contained in the form of a sulfur-carbon composite material, and preferably, the positive electrode active material can be a sulfur-carbon composite material.

[0088] The carbon contained in the sulfur-carbon composite is a porous carbon material, which provides a framework that can uniformly and stably fix sulfur, and allows electrochemical reactions to proceed smoothly by compensating for the low conductivity of sulfur.

[0089] Porous carbon materials are typically manufactured by carbonizing precursors made from various carbon materials. Porous carbon materials can contain non-uniform pores internally. The average diameter of these pores ranges from 1 nm to 200 nm, and the porosity can range from 10% to 90% of the total volume of the porous carbon material. When the average pore diameter is smaller than the above range, the pore size is only at the molecular level, making sulfur impregnation impossible. When the average pore diameter is larger than the above range, the mechanical strength of the porous carbon material weakens, which is undesirable for use in electrode fabrication processes.

[0090] Porous carbon materials can take the form of spheres, rods, needles, plates, tubes, or blocks, and can be used without restriction, as long as they are typically used in lithium-sulfur batteries.

[0091] As porous carbon materials, any material commonly used in the art can be used, provided it has a porous structure or a high specific surface area. For example, porous carbon materials can be selected from one or more of the following: graphite; graphene; carbon black, such as tandoor black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; carbon nanotubes (CNTs), such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs); carbon fibers, such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), or activated carbon fibers (ACFs); graphite, such as natural graphite, artificial graphite, or expanded graphite; and activated carbon, but not limited thereto. Preferably, the porous carbon material can be carbon nanotubes.

[0092] Based on 100 parts by weight of a sulfur-carbon composite material, the sulfur-carbon composite material may contain 60 to 90 parts by weight, preferably 65 to 85 parts by weight, and more preferably 70 to 80 parts by weight of sulfur. When the sulfur content is below the above range, the content of porous carbon material in the sulfur-carbon composite material relatively increases, which increases the specific surface area and increases the content of binder during the preparation of the cathode. This increase in the amount of binder ultimately increases the sheet resistance of the cathode, thereby acting as an insulator to prevent electron migration (electron passage), and battery performance may degrade. Conversely, when the sulfur content is above the above range, sulfur that is not bound to the porous carbon material aggregates itself or redissolves to the surface of the porous carbon material, making it difficult to accept electrons and thus unable to participate in electrochemical reactions, which may result in a loss of battery capacity.

[0093] Furthermore, in the sulfur-carbon composite material, sulfur is located on at least one of the inner and outer surfaces of the aforementioned porous carbon material, and herein, it can be present in less than 100%, preferably 1 to 95%, more preferably 60 to 90% of the entire inner and outer surfaces of the porous carbon material. When sulfur is present on the inner and outer surfaces of the porous carbon material within the aforementioned range, maximum effect can be achieved in terms of electron migration area and wettability with the electrolyte. Specifically, sulfur is thinly and uniformly impregnated on the inner and outer surfaces of the porous carbon material within the aforementioned range, thus increasing the electron migration contact area during charging and discharging. When sulfur is present in 100% of the entire inner and outer surfaces of the porous carbon material, the carbon material is completely covered by sulfur, thereby reducing the wettability of the electrolyte and reducing contact with the conductive material contained in the electrode. As a result, electrons cannot migrate and become unable to participate in the electrochemical reaction.

[0094] There are no particular limitations on the methods for preparing sulfur-carbon composite materials, and methods commonly used in the art can be employed. For example, a method can be used that involves simply mixing sulfur and porous carbon materials, followed by heat treatment of the mixture to achieve composite formation.

[0095] In addition to the components mentioned above, the positive electrode active material may also contain one or more additives selected from the following: transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0096] Transition metal elements can 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 can include Al, Ga, In, Tl, etc., and Group IVA elements can include Ge, Sn, Pb, etc.

[0097] Based on 100% by weight of the positive electrode active material layer forming the positive electrode, the content of the positive electrode active material can be from 40% by weight to 95% by weight, preferably from 45% by weight to 90% by weight, and more preferably from 60% by weight to 90% by weight. When the content of the positive electrode active material is lower than the above range, it is difficult to fully carry out the electrochemical reaction of the positive electrode. Conversely, when the content of the positive electrode active material is higher than the above range, the content of the conductive material and the binder, described later, is relatively insufficient, thereby increasing the resistance of the positive electrode and causing a decrease in the physical properties of the positive electrode.

[0098] The positive electrode active material layer may optionally also include a conductive material for facilitating the migration of electrons in the positive electrode (specifically, the positive electrode active material) and an adhesive for completely adhering the positive electrode active material to the current collector.

[0099] Conductive materials are materials that electrically connect electrolytes and positive electrode active materials to serve as pathways for electrons to migrate from the current collector to the positive electrode active material. Furthermore, conductive materials can be used without restriction, as long as they are conductive.

[0100] For example, as conductive materials, the following substances can be used alone or in mixtures: graphite, such as natural or artificial graphite; carbon black, such as Super-P, Danka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, or thermal cracking black; carbon derivatives, such as carbon nanotubes or fullerenes; conductive fibers, such as carbon fibers or metal fibers; fluorinated carbon; metal powders, such as aluminum powder or nickel powder; or conductive polymers, such as polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0101] Based on 100% by weight of the positive electrode active material layer forming the positive electrode, the content of conductive material can be from 1% by weight to 10% by weight, preferably from 4% by weight to 7% by weight. When the content of conductive material is below the above range, electron transfer between the positive electrode active material and the current collector is less likely to occur, thereby reducing voltage and capacity. Conversely, when the content of conductive material is above the above range, the proportion of positive electrode active material is relatively reduced, which may reduce the total energy (charge capacity) of the battery. Therefore, it is preferable to determine a suitable content within the above range.

[0102] Adhesives are used to hold positive electrode active materials on positive electrode current collectors and to organically connect positive electrode active materials to further increase the bonding force between them, and all adhesives known in the art can be used.

[0103] Examples of adhesives may include mixtures or copolymers of one or more of the following: fluoropolymer adhesives, including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); rubber adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives.

[0104] Based on 100% by weight of the positive electrode active material layer forming the positive electrode, the binder content can be from 1% by weight to 10% by weight. When the binder content is below the above range, the physical properties of the positive electrode decrease, and the positive electrode active material and conductive material may detach. When the binder content is above the above range, the proportion of positive electrode active material and conductive material in the positive electrode is relatively reduced, which may reduce the battery capacity. Therefore, it is preferable to determine an appropriate content within the above range.

[0105] In this invention, there are no particular limitations on the method for preparing the positive electrode, and various methods known to those skilled in the art or modified methods can be used.

[0106] For example, the positive electrode can be prepared by preparing a positive electrode slurry composition containing the above-mentioned components and coating the slurry composition on at least one surface of the positive electrode current collector.

[0107] The positive electrode slurry composition comprises the aforementioned positive electrode active material, conductive material, and binder, and may also contain a solvent.

[0108] As a solvent, a solvent capable of uniformly dispersing the positive electrode active material, conductive material, and binder is used. Water is most preferably used as an aqueous solvent, and the water used herein can be distilled water or deionized water. However, the solvent is not limited to this, and lower alcohols that are readily miscible with water can be used as needed. Examples of lower alcohols include methanol, ethanol, propanol, isopropanol, butanol, etc., and these substances are preferably mixed with water and used.

[0109] The solvent can be contained at a concentration that facilitates coating, and the specific content can vary depending on the coating method and apparatus.

[0110] For the purpose of enhancing functionality in the corresponding technical field, the positive electrode slurry composition may also include materials commonly used in the art, as needed. For example, it may include viscosity modifiers, fluidizing agents, fillers, etc.

[0111] In this invention, the method of coating the positive electrode slurry composition is not particularly limited, and may include, for example, methods such as doctor blade coating, die casting, comma coating, and screen printing. Furthermore, after being formed on a separate substrate, the positive electrode slurry can also be coated onto the positive electrode current collector using pressing or lamination methods.

[0112] After coating, a drying process can be performed to remove the solvent. This drying process is carried out at a temperature and time sufficient to remove the solvent, and the present invention does not impose particular limitations on the conditions, as they can vary depending on the type of solvent. For example, drying methods may include: drying with warm air, hot air, or low-humidity air; vacuum drying; and irradiation with (far)infrared rays, electron beams, etc. The drying rate is typically adjusted to remove the solvent as quickly as possible, within a speed range that does not cause the positive electrode active material layer to crack due to stress concentration or to prevent the positive electrode active material layer from peeling off from the positive electrode current collector.

[0113] Furthermore, the density of the positive electrode active material in the positive electrode can also be increased by pressing the current collector after drying. Pressing methods can include molding and rolling.

[0114] The positive electrode, specifically the positive electrode active material layer, prepared using the above composition and preparation method can have a porosity of 40% to 80%, preferably 60% to 75%. When the porosity of the positive electrode is less than 40%, the filling degree of the positive electrode slurry composition containing the positive electrode active material, conductive material, and binder is excessively increased. Therefore, it may not be possible to maintain sufficient electrolyte to achieve ion conduction and / or electrical conduction between the positive electrode active materials, thereby reducing the battery's output performance or cycle performance, and causing problems such as battery overvoltage and a sharp drop in discharge capacity. Conversely, when the positive electrode has a porosity greater than 80% and the porosity is too high, the physical and electrical connections with the current collector are reduced, resulting in decreased adhesion strength and difficulty in reaction. It may also cause a decrease in energy density due to the increased pores filled with electrolyte. Therefore, the porosity should be appropriately adjusted within the above range.

[0115] Furthermore, according to the present invention, the sulfur loading in the cathode, i.e., the mass of sulfur per unit area of ​​the cathode active material layer, can be 2 mg / cm³. 2 Up to 15 mg / cm 2 The preferred value is 2.5 mg / cm³. 2 Up to 5 mg / cm 2 .

[0116] The negative electrode may comprise a negative electrode current collector and a layer of negative electrode active material coated on one or both surfaces of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

[0117] The negative electrode current collector is used to support the negative electrode active material layer, and its description is the same as that of the positive electrode current collector.

[0118] In addition to the negative electrode active material, the negative electrode active material layer may also include conductive materials, binders, etc. In this paper, the descriptions of conductive materials and binders are the same as those provided above.

[0119] As a negative electrode active material, it can include: materials capable of reversibly inserting or de-intercalating lithium ions (Li... + Materials that can reversibly form lithium-containing compounds by reacting with lithium ions; lithium metal; or lithium alloys.

[0120] Capable of reversibly inserting or de-inserting lithium ions (Li) + Examples of materials that can be synthesized by reacting with lithium ions (Li) can include crystalline carbon, amorphous carbon, or mixtures thereof. +Examples of materials that reversibly form lithium-containing compounds through a reaction may include tin oxide, titanium nitrate, or silicon. Examples of lithium alloys may include lithium (Li) and alloys of metals selected from the following: 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).

[0121] Preferably, the negative electrode active material can be lithium metal, specifically, it can be in the form of a lithium metal thin film or lithium metal powder.

[0122] There are no particular limitations on the method for forming the negative electrode active material, and methods commonly used in the art for forming layers or films can be used. For example, methods such as pressing, coating, and deposition can be used. Furthermore, the negative electrode of the present invention also includes cases where the battery is assembled without a lithium film in the current collector, and then a lithium metal film is formed on a metal plate through initial charging.

[0123] The electrolyte is used to generate electrochemical oxidation or reduction reactions at the positive and negative electrodes, and the description provided above can be applied.

[0124] Depending on the manufacturing process and required performance of the final product, the electrolyte can be injected at an appropriate stage in the lithium-sulfur battery manufacturing process. That is, the electrolyte can be injected before assembling the lithium-sulfur battery or at the final stage of assembly.

[0125] A membrane can also be included between the positive and negative electrodes.

[0126] The separator separates or insulates the positive and negative electrodes from each other, and allows lithium ions to transfer between the positive and negative electrodes. It can be formed of a porous, non-conductive, or insulating material. The separator can be used without particular limitation, as long as it is typically used as a separator in a lithium-ion secondary battery. The separator can be a separate component, such as a membrane, or it can be a coating added to the positive and / or negative electrodes.

[0127] As a separator, a separator that has low resistance to the ion migration of electrolytes while having excellent moisturizing ability for electrolytes is preferred.

[0128] The separator can be formed from a porous substrate, and porous substrates commonly used in lithium-sulfur batteries can be used as such. The porous polymer membrane can be used alone or as a laminate. For example, nonwoven fabrics or polyolefin porous membranes made of high-melting-point glass fibers, polyethylene terephthalate, etc., can be used, but are not limited to these.

[0129] In this invention, the material of the porous substrate is not particularly limited, and porous substrates commonly used in lithium-sulfur batteries can be used. For example, the porous substrate may include one or more materials selected from: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene ethers, polyphenylene sulfides, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylenebenzobismuth subcarbonate) (azole) and polyarylate.

[0130] There is no particular limitation on the thickness of the porous substrate, but it can be from 1 μm to 100 μm, preferably from 5 μm to 50 μm. Although the thickness range of the porous substrate is not limited to the above range, when the thickness is much thinner than the lower limit mentioned above, the mechanical properties deteriorate, and the separator may be easily damaged during battery use.

[0131] There are no particular limitations on the average diameter and porosity of the pores present in the porous substrate, but they can be from 0.001 μm to 50 μm and from 10% to 95%, respectively.

[0132] In addition to the usual winding process, the lithium-sulfur battery according to the present invention can also undergo the lamination (stacking) and folding processes of the separator and electrodes.

[0133] There are no particular restrictions on the shape of lithium-sulfur batteries, and they can take various shapes such as cylindrical, laminated or coin-shaped.

[0134] Furthermore, the present invention provides a battery module comprising the lithium-sulfur battery as a unit cell.

[0135] The battery module can be used as a power source for medium to large-sized devices that require high-temperature stability, long cycle performance, and high capacity performance.

[0136] Examples of the medium to large-sized devices may include: power tools that operate by receiving power from an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheeled vehicles, including electric bicycles (E-bicycles) and electric scooters (E-scooters); electric golf carts; power storage systems, etc., but not limited to these.

[0137] Preferred implementation scheme

[0138] Preferred embodiments will be provided below to illustrate the invention; however, the following embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various modifications and variations can be made within the scope of the category and technical concept of the invention, and such modifications and variations also fall within the scope of the appended claims.

[0139] Examples and Comparative Examples

[0140] [Example 1]

[0141] (1) Preparation of electrolytes

[0142] LiFSI was dissolved in an organic solvent obtained by mixing 2-methylfuran (first solvent), dimethoxyethane (second solvent), and diethylene glycol dimethyl ether (third solvent) in a volume ratio of 20:75:5 to obtain a concentration of 0.75 M. Then, lithium nitrate was added to the solvent at a weight of 3% based on the total weight of the electrolyte to prepare an electrolyte for lithium-sulfur batteries.

[0143] (2) Manufacturing of lithium-sulfur batteries

[0144] Sulfur and carbon nanotubes were uniformly mixed at a weight ratio of 70:30 using a ball mill, and then heat-treated at 155°C for 30 minutes to prepare a sulfur-carbon composite material.

[0145] A positive electrode slurry composition was prepared by mixing 90% by weight of the prepared sulfur-carbon composite material, 5% by weight of Danka Black as a conductive material, and 5% by weight of styrene-butadiene rubber / carboxymethyl cellulose (SBR:CMC = 7:3, by weight) as a binder.

[0146] The positive electrode slurry composition prepared as described above was coated onto a current collector (aluminum foil) with a thickness of 20 μm, dried at 50°C for 12 hours, and then pressed using a roller press to prepare the positive electrode. Here, the energy density of the positive electrode is 5 mAh / cm³. 2 And its porosity is 65%.

[0147] The prepared positive electrode and a lithium metal negative electrode with a thickness of 150 μm were placed facing each other, and a separator was placed between them. Then, the electrolyte prepared in (1) was injected to manufacture a coin cell type lithium-sulfur battery. Here, polyethylene with a thickness of 20 μm and a porosity of 45% was used as a separator with a diameter of Φ19, and the positive electrode was stamped into a circular electrode with a diameter of Φ14 and the negative electrode was stamped into a circular electrode with a diameter of Φ16 for use.

[0148] [Example 2]

[0149] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the volume ratio of 2-methylfuran (first solvent), dimethoxyethane (second solvent), and diethylene glycol dimethyl ether (third solvent) was changed from 20:75:5 to 20:70:10 during electrolyte preparation.

[0150] [Example 3]

[0151] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the volume ratio of 2-methylfuran (first solvent), dimethoxyethane (second solvent), and diethylene glycol dimethyl ether (third solvent) was changed from 20:75:5 to 20:60:20 during electrolyte preparation.

[0152] [Example 4]

[0153] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the third solvent was changed from diethylene glycol dimethyl ether to triethylene glycol dimethyl ether during electrolyte preparation.

[0154] [Example 5]

[0155] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the third solvent was changed from diethylene glycol dimethyl ether to triethylene glycol dimethyl ether during electrolyte preparation, and the volume ratio of the first solvent, second solvent, and third solvent was changed from 20:75:5 to 20:70:10.

[0156] [Example 6]

[0157] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the third solvent was changed from diethylene glycol dimethyl ether to triethylene glycol dimethyl ether during electrolyte preparation, and the volume ratio of the first solvent, second solvent, and third solvent was changed from 20:75:5 to 20:60:20.

[0158] [Comparative Example 1]

[0159] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that a third solvent was not used when preparing the electrolyte, and an organic solvent obtained by mixing only 2-methylfuran (first solvent) and dimethoxyethane (second solvent) in a volume ratio of 20:80 was used.

[0160] [Comparative Example 2]

[0161] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the volume ratio of 2-methylfuran (first solvent), dimethoxyethane (second solvent), and diethylene glycol dimethyl ether (third solvent) was changed from 20:75:5 to 20:50:30 during electrolyte preparation.

[0162] [Comparative Example 3]

[0163] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the third solvent was changed from diethylene glycol dimethyl ether to triethylene glycol dimethyl ether during electrolyte preparation, and the volume ratio of the first, second, and third solvents was changed from 20:75:5 to 20:50:30.

[0164] [Comparative Example 4]

[0165] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the volume ratio of 2-methylfuran (first solvent), dimethoxyethane (second solvent), and diethylene glycol dimethyl ether (third solvent) was changed from 20:75:5 to 10:80:10 during electrolyte preparation.

[0166] [Comparative Example 5]

[0167] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the third solvent was changed from diethylene glycol dimethyl ether to triethylene glycol dimethyl ether during electrolyte preparation, and the volume ratio of the first, second, and third solvents was changed from 20:75:5 to 10:80:10.

[0168] [Comparative Example 6]

[0169] The lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the first solvent was changed from 2-methylfuran to 1,3-dioxolane during electrolyte preparation.

[0170] The composition of the electrolytes used in the examples and comparative examples is summarized and shown in Table 1 below.

[0171] [Table 1]

[0172]

[0173] Experimental Example 1. Evaluation of Battery Performance

[0174] Each battery manufactured in the examples and comparative examples was subjected to the first three charge-discharge cycles at 0.1C at 25°C, and the discharge capacity was measured. Subsequently, the cycle life was measured by repeating the charging at 0.2C and discharging at 0.3C. The voltage range used was 1.8V to 2.5V (i.e., discharging to 1.8V and charging to 2.5V), and the results are shown in Table 2.

[0175] [Table 2]

[0176]

[0177] Referring to Table 2, it was confirmed that the lithium-sulfur battery containing the electrolyte for lithium-sulfur batteries according to the present invention has excellent capacity and cycle life performance. Specifically, it was confirmed that, compared with Comparative Example 1 (not containing a third solvent), Comparative Examples 2 and 3 (the content of the third solvent is 25% or more by volume), Comparative Examples 4 and 5 (the content of the first solvent is less than 20% by volume), or Comparative Example 6 (containing a non-conjugated cyclic ether compound as the first solvent), Examples 1 to 6, containing a first solvent (2-methylfuran) in a content of 20% to 49% by volume, a second solvent (dimethoxyethane) in a content of 50% to 79% by volume, and a third solvent (diethylene glycol dimethyl ether or triethylene glycol dimethyl ether) in a content of greater than or equal to 1% by volume and less than 25% by volume, have improved battery discharge capacity and cycle life.

[0178] These results show that electrolytes for lithium-sulfur batteries containing the following organic solvents improve the capacity and lifespan performance of lithium-sulfur batteries. The organic solvents contain, within a specific content range, a first solvent including conjugated cyclic ether compounds, a second solvent including dimethoxyethane, and a third solvent including diol diether compounds represented by Formula 1. When any of the above components are not included or their content exceeds the content range specified in this invention, the capacity or lifespan performance decreases significantly.

Claims

1. An electrolyte for lithium-sulfur batteries, the electrolyte comprising: Lithium salts; and Non-aqueous organic solvents in, The non-aqueous organic solvent comprises: The first solvent includes conjugated cyclic ether compounds; A second solvent, the second solvent comprising dimethoxyethane; and The third solvent comprises diol diether compounds represented by the following chemical formula 1: [Chemical Formula 1] R1(CH2CH2O) n R2 In chemical formula 1, R1 and R2 may be the same as or different from each other, and each is independently an alkyl or alkoxy group having 1 to 10 carbon atoms. n is an integer from 2 to 4. Wherein, based on 100% by volume of the non-aqueous organic solvent comprising the first solvent, the second solvent, and the third solvent. The content of the first solvent is 20% to 49% by volume. The content of the second solvent is 50% to 79% by volume; and The content of the third solvent is greater than or equal to 1% by volume and less than 25% by volume.

2. The electrolyte for lithium-sulfur batteries according to claim 1, wherein, The conjugated cyclic ether compounds include 4- to 15-membered heterocyclic compounds containing two or more double bonds and also containing oxygen or sulfur atoms.

3. The electrolyte for lithium-sulfur batteries according to claim 1, wherein, The conjugated cyclic ether compounds include one or more selected from furan compounds and thiophene compounds.

4. The electrolyte for lithium-sulfur batteries according to claim 3, wherein, The furan compounds include one or more selected from the following: furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, and 2-(2-nitrovinyl)furan.

5. The electrolyte for lithium-sulfur batteries according to claim 3, wherein, The thiophene compounds include one or more selected from the following: thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene.

6. The electrolyte for lithium-sulfur batteries according to claim 1, wherein, The diol diether compounds include one or more selected from the following: diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol methyl ethyl ether.

7. The electrolyte for lithium-sulfur batteries according to claim 1, wherein, In chemical formula 1, R1 and R2 may be the same as or different from each other, and each is independently an alkyl or alkoxy group having 1 to 5 carbon atoms.

8. The electrolyte for lithium-sulfur batteries according to claim 1, wherein, The diol diether compounds include one or more selected from the following: diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

9. A lithium-sulfur battery, the lithium-sulfur battery comprising: Positive electrode, wherein the positive electrode comprises a positive electrode active material; Negative electrode, said negative electrode comprising a negative electrode active material; and The electrolyte according to claim 1.

10. The lithium-sulfur battery according to claim 9, wherein, The positive electrode active material includes one or more selected from the following: Inorganic sulfur, Li2S n (where n≥1), Disulfide compounds, Organic sulfur compounds, and Carbon-sulfur polymers (C2S) x ) n , where x = 2.5 to 50, n ≥ 2.

11. The lithium-sulfur battery according to claim 9, wherein, The negative electrode active material includes one or more selected from lithium metal and lithium alloys.

Images