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

Abstract

The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including the same. The electrolyte for a lithium-sulfur battery includes a non-aqueous solvent, a lithium salt, a nitrate salt, and trioxane. The non-aqueous solvent includes an ether-based solvent, and the ether-based solvent includes a cyclic ether and an acyclic ether.

Description

[Technical Field]

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

[0002] This application claims priority based on Korean Patent Application No. 2022-0186449 filed with the Korean Intellectual Property Office on December 27, 2022, and the entire contents disclosed in the specification of that application are incorporated herein by reference. [Background technology]

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond (SS bond) as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the positive electrode active material, has the advantages of being abundant worldwide, non-toxic, and having a low atomic weight.

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

[0005] During discharge, lithium, the negative electrode active material, releases electrons and ionizes into lithium cations, while the positive electrode active material, the sulfur-based material, receives electrons and is reduced. The sulfur-based material undergoes a reduction reaction, converting the S-S bond into a sulfur anion by receiving two electrons. The lithium cations generated by the oxidation of lithium are transported to the positive electrode via the electrolyte, where they combine with sulfur anions generated by the reduction of sulfur-based compounds to form salts. Specifically, sulfur, which has a cyclic S8 structure before discharge, is converted to lithium polysulfide (LiSx) through a reduction reaction, and then completely reduced to form lithium sulfide (Li2S).

[0006] In this case, sulfur in sulfur-based compounds, which is the positive electrode active material, has low electrical conductivity, making it difficult to ensure reactivity with electrons and lithium ions in the solid phase. Therefore, in lithium-sulfur batteries, Li2S( x A technology has been developed to improve reactivity by generating intermediate polysulfides in the form of sulfur dioxide (SO2) to induce a liquid-phase reaction. In this technology, ether solvents such as dioxolane and dimethoxyethane (DME), which have high solubility in lithium polysulfides, are used as electrolyte solvents. Therefore, the sulfur content in the electrolyte affects the reactivity of the sulfur and the battery life.

[0007] Meanwhile, in recent years, active research and development efforts have been made on lithium-sulfur secondary batteries capable of low-temperature operation, which is required for aircraft and next-generation electric vehicles, etc. However, in lithium-sulfur secondary batteries, the material resistance of the electrolyte increases when polysulfide (PS) elutes from the positive electrode, making it difficult to operate at low temperatures.

[0008] In short, lithium-sulfur (Li-S) batteries operate by undergoing a solid-to-liquid reaction during the first discharge (up to 2.3 V), in which the active material dissolves from the positive electrode in the form of polysulfide (PS), and then undergoing a liquid-to-solid reaction during the second discharge (up to 2.1 V), in which the dissolved PS is re-deposited on the positive electrode. The reaction efficiency at which the PS dissolved from the positive electrode is re-deposited on the positive electrode acts as a factor that determines the degradation of lithium-sulfur secondary batteries.

[0009] Therefore, in order to improve the lifespan of lithium-sulfur batteries, it is necessary to develop technologies to improve the conversion efficiency of polysulfide (PS) and to control the amount of PS leaching from the positive electrode into the electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, the problem to be solved by the present invention is: The present invention provides an electrolyte for lithium-sulfur batteries that has improved life characteristics by controlling the elution characteristics of polysulfide (PS) from the positive electrode, and a lithium-sulfur battery using the same.

[0011] In particular, the object is to provide a lithium-sulfur battery that can be operated for a long period of time by suppressing the elution of polysulfides from the positive electrode, thereby improving the deterioration of the electrolyte properties and the deterioration characteristics of the negative electrode. [Means for solving the problem]

[0012] In order to solve the above problems, According to one aspect of the present invention, there is provided an electrolyte for a lithium-sulfur battery having the following embodiment.

[0013] The electrolyte for a lithium-sulfur battery according to the first aspect comprises: a non-aqueous solvent, a lithium salt, a nitrate salt, and trioxane; the non-aqueous solvent includes an ether-based solvent, The ether solvent is characterized by containing a cyclic ether and an acyclic ether.

[0014] According to the second aspect, in the first aspect, Based on the total volume of the non-aqueous solvent, The content of the cyclic ether may be 30% by volume or less.

[0015] According to the third aspect, in the first or second aspect, Based on the total volume of the non-aqueous solvent, The content of the cyclic ether may be 20% by volume or less.

[0016] According to a fourth aspect, in any one of the first to third aspects, Based on the total volume of the non-aqueous solvent, The content of the cyclic ether is 20% by volume or less, The content of the acyclic ether may be 80% by volume or more.

[0017] According to the fifth aspect, in any one of the first to fourth aspects, The non-aqueous solvent may not include a carbonate-based solvent.

[0018] According to the sixth aspect, in any one of the first to fifth aspects, The cyclic ether may comprise 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, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbide dimethyl ether, or a mixture of two or more thereof.

[0019] According to the seventh aspect, in any one of the first to sixth aspects, The acyclic ether may include dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl 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 tert-butyl ethyl ether, ethylene glycol ethyl methyl ether, or a mixture of two or more thereof.

[0020] According to the eighth aspect, in any one of the first to seventh aspects, Based on the total weight of the lithium-sulfur battery electrolyte, The content of the trioxane may be 5% by weight to 45% by weight.

[0021] According to the ninth aspect, in any one of the first to eighth aspects, Based on the total weight of the lithium-sulfur battery electrolyte, The content of the trioxane may be 10% by weight to 20% by weight.

[0022] According to the tenth aspect, in any one of the first to ninth aspects, The weight ratio of the trioxane to the nitrate may be 2-15.

[0023] According to another aspect of the present invention, there is provided a lithium-sulfur battery having the following configuration.

[0024] The lithium-sulfur battery according to the eleventh aspect comprises: a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; The electrolyte is an electrolyte according to any one of the first to tenth aspects; The positive electrode may include a sulfur-containing compound as a positive electrode active material.

[0025] According to the 12th aspect, in the 11th aspect, The sulfur-containing compounds include inorganic sulfur (S), LiSn (n≧1), disulfide compounds, organic sulfur compounds, carbon-sulfur polymers (C2S x ) n , x=an integer of 2.5 to 50, and n≧2), or a mixture of two or more of these.

[0026] According to the thirteenth aspect, in the eleventh or twelfth aspect, The negative electrode may include lithium metal, a lithium alloy, or a mixture thereof as a negative electrode active material.

[0027] According to the 14th aspect, in any one of the 11th to 13th aspects, The lithium-sulfur battery can be a coin cell or a pouch cell. [Effects of the Invention]

[0028] The lithium-sulfur battery electrolyte according to one embodiment of the present invention has the effect of suppressing the elution of polysulfide (PS) from the positive electrode.

[0029] As a result, the battery for a lithium-sulfur battery according to one aspect of the present invention has the effect of improving the life characteristics of the battery by preventing deterioration of the positive electrode, electrolyte, and negative electrode due to repeated charge-discharge cycles of the lithium-sulfur battery.

[0030] The electrolyte for a lithium-sulfur battery according to one aspect of the present invention can have an advantageous effect on realizing a high-energy density lithium-sulfur battery.

[0031] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention to be given later, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters depicted in these drawings. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graph showing the evaluation results of Experimental Example 1 in the present specification. [Figure 2] 1 is a graph showing the evaluation results of Experimental Example 1 in the present specification. [Figure 3] 1 is a graph showing the evaluation results of Experimental Example 2 in the present specification. [Figure 4] 1 is a graph showing the evaluation results of Experimental Example 2 in the present specification. [Figure 5] 1 is a graph showing the evaluation results of Experimental Example 3 in the present specification. [Figure 6] 1 is a graph showing the evaluation results of Experimental Example 3 in the present specification. [Figure 7]It is a graph of the evaluation results of Experimental Example 4 in this specification. [Figure 8] It is a graph of the evaluation results of Experimental Example 4 in this specification. [Figure 9] It is a graph of the evaluation results of Experimental Example 4 in this specification.

Mode for Carrying Out the Invention

[0033] Hereinafter, the present invention will be described in detail. However, the present invention is not limited only by the following contents, and each component may be variously modified or selectively mixed as necessary. Therefore, it should be understood that the present invention includes all changes, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0034] In this specification, when a certain configuration "includes" a certain component, this means that, unless otherwise specified, it does not exclude certain other components, and may further include other components.

[0035] In this specification, the term "polysulfide (PS)" includes both "polysulfide ions (S x 2- , 1 < x ≦ 8))" and "lithium (poly) sulfide (Li2S x or LiS x - , 1 < x ≦ 8)".

[0036] During the operation of a lithium-sulfur battery, polysulfide (PS, LiSx) formed by the reduction of sulfur (S8) from the positive electrode elutes into the electrolyte. At this time, in an electrolyte with a high ratio of solvent to polysulfide, the concentration of polysulfide in the solvent becomes high, and there is a problem of induced overvoltage. Thus, lithium-sulfur batteries have the problem that the battery capacity rapidly deteriorates in response to repeated charge-discharge cycles due to the shuttle phenomenon peculiar to lithium polysulfide released from the positive electrode to the electrolyte during charge and discharge. Therefore, the lithium-sulfur battery electrolyte according to one aspect of the present invention aims to solve the above-mentioned problems by suppressing the elution of polysulfide into the electrolyte by using a combination of a solvent and an additive that have non-solvent properties for polysulfide.

[0037] Electrolytes for lithium secondary batteries According to one aspect of the present invention, an electrolyte for a lithium-sulfur battery comprises: a non-aqueous solvent, a lithium salt, a nitrate salt, and trioxane; the non-aqueous solvent includes an ether-based solvent, The ether solvent is characterized by containing a cyclic ether and an acyclic ether.

[0038] In this specification, trioxane is a general term for an organic compound having a six-membered ring with three carbon atoms and three oxygen atoms, and is represented by the molecular formula C3H6O3. Trioxane may have three isomers, specifically, 1,2,3-trioxane, 1,2,4-trioxane, 1,3,5-trioxane, or a mixture of two or more of these.

[0039] In one embodiment of the invention, the trioxane may include 1,3,5-trioxane.

[0040] According to one embodiment of the present invention, when trioxane is added to the lithium-sulfur battery electrolyte, the solubility of the polysulfide in the non-aqueous solvent, particularly in an ether-based solvent among non-aqueous solvents, is reduced, thereby suppressing the leaching of the polysulfide from the positive electrode; however, the mechanism of the present invention is not limited thereto.

[0041] According to one aspect of the present invention, the non-aqueous solvent is a medium in which ions involved in the electrochemical reaction of a lithium secondary battery (LIB: Lithium Ion Battery) can move, and this is for dissolving the lithium salt, the nitrate, and / or trioxane.

[0042] According to one aspect of the present invention, the lithium-sulfur battery electrolyte contains an ether-based solvent as a non-aqueous solvent, and in particular, the ether-based solvent contains two types of ether-based solvents, such as a cyclic ether and an acyclic ether.

[0043] In one embodiment of the present invention, the non-aqueous solvent may contain the ethereal solvent in an amount of 80% by volume or more, for example, 85% to 100% by volume, 90% to 100% by volume, 95% to 100% by volume, 98% to 100% by volume, 90% to 98% by volume, or 90% to 95% by volume, based on the total volume of the non-aqueous solvent. When the amount of the ethereal solvent is within this range based on the total volume of the non-aqueous solvent, advantageous effects can be exhibited in terms of the solubility of the lithium salt, nitrate, and trioxane, but the present invention is not limited thereto.

[0044] In one embodiment of the present invention, the cyclic ether may function as a non-solvent for polysulfides eluted from the positive electrode, thereby suppressing the elution of polysulfides. In one embodiment of the present invention, the cyclic ether may be contained in an amount of, for example, 30% by volume or less, 25% by volume or less, 20% by volume or less, or 15% by volume or less, specifically 1% by volume to 20% by volume, or 5% by volume to 20% by volume, based on the total volume of the non-aqueous solvent. When the content of the cyclic ether is within the above range, advantageous effects can be exhibited in terms of suppressing the elution of polysulfides and improving the solubility of lithium salts, nitrates, and trioxane, but the present invention is not limited thereto.

[0045] In another embodiment of the present invention, the non-aqueous solvent may have a cyclic ether content of 20% by volume or less and an acyclic ether content of 80% by volume or more, for example, 85% by volume or more, 80% by volume to 99% by volume, or 80% by volume to 90% by volume, based on the total volume.

[0046] In one embodiment of the present invention, the cyclic ether may include, 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, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbide dimethyl ether, or a mixture of two or more thereof. Preferably, the cyclic ether may include one or more selected from the group consisting of 2-methylfuran, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran. More preferably, the cyclic ether may include 2-methylfuran.

[0047] In one embodiment of the present invention, the cyclic ether may preferably include a conjugated heterocyclic compound. For example, the conjugated heterocyclic compound may include a heterocyclic compound containing two or more double bonds and one of an oxygen atom and a sulfur atom. During the initial discharge step of the battery, the ring-opening polymerization reaction of the heterocyclic compound forms a polymer protective film (solid electrolyte interface, SEI layer) on the surface of the lithium-based metal (anode). This can suppress the formation of lithium dendrites and further reduce electrolyte decomposition and associated side reactions on the lithium-based metal surface, thereby improving the lifespan of the lithium-sulfur battery. Furthermore, the delocalization of lone pair electrons of the heteroatom (oxygen atom or sulfur atom) makes it difficult for salt to dissolve, thereby reducing the amount of polysulfide electrolyte leaching. Such conjugated heterocyclic compounds may be heterocyclic compounds substituted or unsubstituted with one or more groups selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO2), an amine group (-NH2), and a sulfonyl group (-SO2).Furthermore, the conjugated heterocyclic compounds may be polycyclic compounds containing one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0048] In one embodiment of the present invention, the conjugated heterocyclic compound may be, for example, one or more selected from the group consisting of 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, but is not limited thereto. Of these, 2-methylfuran may be most preferred.

[0049] Therefore, in one embodiment of the present invention, the cyclic ether may consist solely of 2-methylfuran (2-MeF), but the present invention is not limited thereto.

[0050] In one embodiment of the present invention, the acyclic ether may include, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl 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 tert-butyl ethyl ether, ethylene glycol ethyl methyl ether, or a mixture of two or more thereof.

[0051] Preferably, the solvent may contain one or more selected from the group consisting of dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, and more preferably, dimethoxyethane.

[0052] In one embodiment of the present invention, the acyclic ether may consist solely of dimethoxyethane (DME).

[0053] In one embodiment of the present invention, the non-aqueous solvent may include 2-methylfuran and dimethoxyethane.

[0054] The non-aqueous solvent may contain a cyclic ether and an acyclic ether in a volume ratio of 5:95 to 95:5, preferably 5:95 to 50:50, 10:90 to 30:70, and most preferably 15:85 to 25:75 or 20:80. The volume ratio corresponds to the ratio of "volume % of cyclic ether" to "volume % of acyclic ether" in the non-aqueous solvent.

[0055] In one embodiment of the present invention, the non-aqueous solvent may further include organic solvents other than ether-based solvents, as long as they can dissolve the lithium salt, nitrate, and trioxane. For example, organic solvents used in conventional lithium secondary battery electrolytes include esters, amides, linear carbonates, and cyclic carbonates in addition to the ether-based solvents. In one embodiment of the present invention, the non-aqueous solvent may further include the non-aqueous solvents used in conventional lithium secondary battery electrolytes in addition to the ether-based solvents. However, in terms of the solubility of the lithium salt, nitrate, and trioxane, it is preferable that the lithium-sulfur battery electrolyte does not include the carbonate-based solvent as the non-aqueous solvent.

[0056] In one embodiment of the present invention, the ester may be, for example, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0057] In one embodiment of the present invention, the carbonate that the lithium-sulfur battery electrolyte does not contain includes a chain carbonate, a cyclic carbonate, or a mixture thereof.

[0058] Representative examples of the chain carbonate include, but are not limited to, any one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more of these.

[0059] Representative examples of the cyclic carbonate include, but are not limited to, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or mixtures of two or more thereof. Examples of the halides thereof include, but are not limited to, fluoroethylene carbonate.

[0060] In another embodiment of the present invention, the non-aqueous solvent may not include a carbonate-based solvent because the carbonate-based solvent cannot dissolve the nitrate salt and / or oxane or has low solubility in the carbonate-based solvent.

[0061] In another embodiment of the present invention, the non-aqueous solvent may contain a small amount of carbonate-based solvent to the extent that the carbonate-based solvent does not affect the solubility of the nitrate and / or trioxane. For example, when the non-aqueous solvent contains the carbonate-based solvent, the content of the carbonate-based 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., none) based on the total weight of the lithium secondary battery electrolyte.

[0062] In one embodiment of the present invention, the lithium-sulfur battery electrolyte may have a trioxane content of, for example, 5% to 45% by weight, specifically 10% to 40% by weight, 10% to 30% by weight, 10% to 25% by weight, or 10% to 20% by weight, based on the total weight of the lithium-sulfur battery electrolyte. When the trioxane content is within this range, advantageous effects can be achieved in terms of suppressing the elution of polysulfides due to the addition of trioxane and improving the life characteristics of lithium-sulfur batteries using the same, but the present invention is not limited thereto.

[0063] In one embodiment of the present invention, the lithium salt is contained as an electrolyte salt in the electrolyte for a lithium-sulfur battery, and any lithium salt that can be commonly used in the electrolyte for a lithium-sulfur battery can be used without any particular limitation. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, or two or more thereof.

[0064] In one embodiment of the present invention, the lithium salt may not include lithium nitrate salts, which may be included as examples of the nitrate salt.

[0065] In one embodiment of the present invention, the lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0066] In one embodiment of the present invention, the lithium salt may consist solely of lithium bis(fluorosulfonyl)imide (LiFSI).

[0067] In one embodiment of the present invention, the concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, etc., and may be, for example, 0.1 to 4.0 M, 0.5 to 2.0 M, 0.5 to 1.0 M, or 0.5 M. When the concentration of the lithium salt is within the above range, advantageous effects can be exhibited in terms of ionic conductivity and electrolyte viscosity, but the concentration is not limited thereto.

[0068] In one embodiment of the present invention, the nitrate, in addition to the lithium salt, dissolves in the electrolyte of the lithium secondary battery to provide ions, thereby improving the electrical conductivity of the lithium secondary battery and, when the electrolyte for a lithium secondary battery is used in a lithium-sulfur battery, improving the battery's life characteristics. Specifically, the nitrate may, for example, but is not limited to, inhibit the reduction reaction of lithium polysulfide that occurs during the charge and discharge process of the lithium-sulfur battery, thereby preventing irreversible consumption of lithium polysulfide, thereby improving the performance of the lithium-sulfur battery.

[0069] In one embodiment of the present invention, the nitrate may be any nitrate that can form a stable coating on a lithium metal electrode, which is the negative electrode of a lithium secondary battery, specifically a lithium-sulfur battery, and improve charge-discharge efficiency. For example, the nitrate may be a nitric acid compound, a nitrite compound, or a mixture thereof.

[0070] In one embodiment of the present invention, the nitrate may be selected from the group consisting of, but is not limited to, inorganic nitric acid or nitrite compounds such as lithium nitrate (LiNO), potassium nitrate (KNO), cesium nitrate (CsNO), barium nitrate (Ba(NO)), ammonium nitrate (NHNO), lithium nitrite (LiNO), potassium nitrite (KNO), cesium nitrite (CsNO), and ammonium nitrite (NHNO); organic nitric acid or nitrite compounds such as methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrate, propyl nitrate, butyl nitrate, pentyl nitrate, and octyl nitrate; organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, and dinitrotoluene; and combinations thereof.

[0071] In one embodiment of the present invention, the cation of the nitrate may be selected from alkali metals, such as, but not limited to, lithium, sodium, potassium, rubidium, and cesium.

[0072] In other embodiments of the present invention, the nitrate may include lithium nitrate (LiNO3).

[0073] In one embodiment of the present invention, the nitrate may be present in an amount of, for example, 1 wt % to 10 wt %, 2 wt % to 10 wt %, or 3 wt % to 10 wt %, specifically 3 wt % to 8 wt %, 3 wt % to 6 wt %, or 3 wt % to 5 wt %, based on the total weight of the electrolyte for lithium secondary batteries, but is not limited thereto. When the nitrate is present in the amount described above, the nitrate can exhibit more advantageous effects in terms of improving the electrical conductivity of the electrolyte and suppressing polysulfide elution when used in a lithium-sulfur battery, but the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the weight ratio of the trioxane to the nitrate may be, for example, 2 to 15, specifically 3 to 10, 3 to 8, or 3.3 to 7, but the present invention is not limited thereto.

[0075] In another embodiment of the present invention, the lithium-sulfur battery electrolyte may further contain, in addition to the above-described composition, other additives for the purpose of improving charge / discharge characteristics, flame retardancy, etc. The additives are not particularly limited in the present invention, but examples thereof include pyridine, triethyl phosphite, triethanolamine, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propane sultone (PRS), and vinylene carbonate (VC).

[0076] The lithium-sulfur battery electrolyte according to one aspect of the present invention can be prepared by a conventional method known in the art, and is not particularly limited in the present invention.

[0077] Lithium-sulfur battery A lithium-sulfur battery according to another aspect of the present invention includes the above-described lithium-sulfur battery electrolyte, a positive electrode including a positive electrode active material, and a negative electrode including a negative electrode active material. Specifically, the battery includes the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0078] [Positive electrode] The positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector.

[0079] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not cause chemical changes in the battery, and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, silver, or the like, aluminum-cadmium alloy, etc. may be used.

[0080] The positive electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and may be used in various forms such as a film, sheet, foil, mesh, net, porous body, foam, or nonwoven fabric.

[0081] The positive electrode active material layer includes a positive electrode active material, and may further include a conductive material, a binder, an additive, and the like.

[0082] The positive electrode active material may include a porous carbon material and a sulfur-carbon composite containing sulfur on at least a portion of the inner and outer surfaces of the porous carbon material. Since sulfur contained in the positive electrode active material does not have electrical conductivity by itself, it is used in a composite with a conductive material such as a carbon material. Therefore, the sulfur is contained in the form of a sulfur-carbon composite.

[0083] In one embodiment of the present invention, the positive electrode active material may include elemental sulfur, a sulfur compound, or a mixture thereof. Specifically, the positive electrode active material may include inorganic sulfur (S), LiS, or a mixture thereof. n (n≧1), disulfide compounds, organic sulfur compounds, carbon-sulfur polymers (C2S x ) n , x=2.5 to 50, n≧2), or a mixture of two or more thereof. Preferably, the sulfur may be inorganic sulfur.

[0084] The sulfur-carbon composite includes a porous carbon material that not only provides a framework for uniformly and stably immobilizing sulfur but also complements the low electrical conductivity of sulfur to facilitate smooth electrochemical reactions.

[0085] The porous carbon material can generally be prepared by carbonizing various carbon precursors. The porous carbon material contains non-uniform pores, with an average pore diameter ranging from 1 to 200 nm and a porosity ranging from 10 to 90 vol% of the total volume of the porous carbon material. If the average pore diameter is below this range, the pore size is merely at the molecular level, making sulfur impregnation impossible. Conversely, if the average pore diameter exceeds this range, the mechanical strength of the porous carbon material is weakened, making it unsuitable for use in electrode manufacturing processes.

[0086] In one embodiment of the present invention, the "average pore diameter" can be measured according to a method known in the art for measuring the pore diameter of a porous material, and the measurement method is not particularly limited. For example, the pore diameter can be measured using a scanning electron microscope (SEM), a field emission electron microscope (laser diffraction method), or a laser diffraction method. Measurement using the laser diffraction method can be performed, for example, using a commercially available laser diffraction particle sizer (e.g., Microtrac MT 3000).

[0087] In one embodiment of the present invention, the term "porosity" refers to the ratio of the volume of pores to the total volume of a structure, and is expressed in units of vol%. It can be used interchangeably with terms such as void ratio, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and according to one embodiment of the present invention, it can be measured, for example, by the Brunauer-Emmett-Teller (BET) measurement method using nitrogen gas or a mercury penetration method (Hg porosimeter) and ASTM D2873.

[0088] The shape of the porous carbon material may be spherical, rod-like, needle-like, plate-like, tubular or bulk, and any shape commonly used in lithium-sulfur batteries may be used without limitation.

[0089] The porous carbon material may be any material that has a porous structure or a large surface area and is commonly used in the art. For example, the porous carbon material may be: Examples of the porous carbon material include, but are not limited to, one or more selected from the group consisting of graphite, graphene, carbon black such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black, carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs), graphite such as natural graphite, artificial graphite, and expanded graphite, and activated carbon. Preferably, the porous carbon material is carbon nanotubes.

[0090] In the sulfur-carbon composite according to the present invention, the sulfur is located on at least one of the inner and outer surfaces of the porous carbon material. For example, the sulfur may be present on less than 100%, preferably 1 to 95%, and more preferably 40 to 96% of the total inner and outer surfaces of the porous carbon material. When the sulfur is present on the inner and outer surfaces of the porous carbon material within the above range, it can maximize the electron transfer area and wettability with the electrolyte. Specifically, the sulfur is impregnated thinly and uniformly on the inner and outer surfaces of the porous carbon material within the above range, thereby increasing the electron transfer contact area during charge and discharge. If the sulfur is located on 100% of the total inner and outer surfaces of the porous carbon material, the porous carbon material will be completely covered with sulfur, reducing its wettability and contact with the electrolyte, preventing electron transfer and preventing it from participating in the electrochemical reaction.

[0091] The sulfur-carbon composite may contain, for example, 65 wt % or more of sulfur, specifically 65 to 90 wt %, 70 to 85 wt %, or 72 to 80 wt % of sulfur, based on 100 wt % of the sulfur-carbon composite. When the sulfur content is within the above range, advantageous effects can be exhibited in terms of improving battery performance and ensuring battery capacity, but the present invention is not limited thereto.

[0092] The method for producing the sulfur-carbon composite of the present invention is not particularly limited, and any method commonly used in the art may be used. For example, a method in which sulfur and a porous carbon material are simply mixed together and then heat-treated to form a composite may be used.

[0093] In one embodiment of the present invention, the positive electrode active material may further include, in addition to the above-described composition, one or more additives selected from a transition metal element, a Group IIIA element, a Group IVA element, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0094] Examples of 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, and Hg. Examples of the IIIA group elements include Al, Ga, In, and Ti. Examples of the IVA group elements include Ge, Sn, and Pb.

[0095] In the positive electrode for a lithium secondary battery according to the present invention, the positive electrode active material may be present in an amount of, for example, 80 wt % or more, specifically 80 wt % to 100 wt %, more specifically 85 wt % to 98 wt %, or 80 wt % to 95 wt %, based on the total weight of the positive electrode active material layer. The content of the positive electrode active material may be, based on 100 wt % of the total weight of the positive electrode active material layer, a lower limit of 70 wt % or more or 85 wt % or more, and an upper limit of 99 wt % or less or 90 wt % or less. The content of the positive electrode active material may be determined by combining the lower and upper limits. If the content of the positive electrode active material is below the above ranges, the relative contents of auxiliary materials such as conductive materials and binders increase, while the content of the positive electrode active material decreases, making it difficult to achieve a battery with a high capacity and high energy density. Conversely, if the content exceeds the above ranges, the content of the conductive materials or binders described below is relatively insufficient, resulting in poor physical properties of the electrode.

[0096] The conductive material is a material that electrically connects the electrolyte and the positive electrode active material and serves as a path for electrons to move from a current collector to the positive electrode active material. Any conductive material that is physically distinct from the carbon contained in the sulfur-carbon composite and has electrical conductivity can be used without limitation.

[0097] 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, or Summer Black; carbon derivatives such as carbon nanotubes or fullerenes; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole, which may be used alone or in combination.

[0098] The content of the conductive material may be 1 to 10 wt % based on the total weight of the positive electrode active material. If the content of the conductive material is below this range, electron transfer between the positive electrode active material and the current collector is difficult, resulting in a decrease in voltage and capacity. Conversely, if the content exceeds this range, the proportion of the positive electrode active material decreases relatively, which may result in a decrease in the total energy (charge amount) of the battery. Therefore, it is preferable to determine an appropriate content within this range.

[0099] The binder supports the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further enhance the binding strength therebetween, and any binder known in the art may be used.

[0100] For example, the binder may be one or a mixture or copolymer of two or more selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-based polymers containing at least one vinylidene fluoride repeating unit, polytetrafluoroethylene (PTFE), or a fluororesin-based binder including a mixture of two or more of these; rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, and styrene-isoprene rubber; acrylic-based binders; cellulose-based binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0101] The content of the binder may be 1 to 10 wt % based on the total weight of the positive electrode active material layer. If the content of the binder is within this range, the physical properties of the positive electrode may be deteriorated, and the positive electrode active material and the conductive material may fall off. If the content of the binder exceeds this range, the ratio of the positive electrode active material to the conductive material in the positive electrode may be relatively reduced, and the battery capacity may be reduced. Therefore, it is desirable to determine an appropriate content within the above range.

[0102] In the present invention, the method for manufacturing the positive electrode for the lithium secondary battery is not particularly limited, and any method known to those skilled in the art or various modified methods thereof can be used.

[0103] For example, the positive electrode for a lithium secondary battery may be manufactured by preparing a positive electrode slurry composition including the above-described composition, and then applying the same to at least one surface of the positive electrode current collector to form the positive electrode active material layer.

[0104] The positive electrode slurry composition may include the positive electrode active material described above, and may further include a binder, a conductive material, and a solvent.

[0105] The solvent used can uniformly disperse the positive electrode active material. Water is the most preferred aqueous solvent, and the water may be distilled water or deionized water. However, the solvent is not limited thereto, and a lower alcohol that is easily miscible with water can be used as needed. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and these can be preferably mixed with water.

[0106] The content of the solvent may be any concentration that allows easy coating, and the specific content varies depending on the coating method and device.

[0107] The positive electrode slurry composition may further contain, as needed, substances commonly used in the art for the purpose of improving its performance, etc. Examples thereof include a viscosity modifier, a fluidizing agent, and a filler.

[0108] The method for applying the positive electrode slurry composition is not particularly limited in the present invention, and examples thereof include a doctor blade, die casting, comma coating, screen printing, etc. Alternatively, the positive electrode slurry may be applied to a positive electrode current collector by molding the positive electrode slurry on a separate substrate and then pressing or laminating the same.

[0109] After the coating, a drying process may be performed to remove the solvent. The drying process is performed at a temperature and time sufficient to remove the solvent. The conditions vary depending on the type of solvent, and are not particularly limited in the present invention. Examples of drying methods include drying with warm air, hot air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying rate is usually adjusted so that the solvent can be removed as quickly as possible, within a range that does not cause cracks in the positive electrode active material layer due to stress concentration or peeling of the positive electrode active material layer from the positive electrode current collector.

[0110] Furthermore, the density of the positive electrode active material in the positive electrode can be increased by pressing the current collector after the drying, using methods such as die pressing and roll pressing.

[0111] The positive electrode manufactured using the above-described composition and manufacturing method, specifically the porosity of the positive electrode active material layer, may be 50 to 80 vol%, specifically 60 to 75 vol%. If the porosity of the positive electrode is less than 50 vol%, the filling level of the positive electrode slurry composition containing the positive electrode active material, conductive material, and binder may be too high, resulting in insufficient electrolyte for ionic and / or electrical conduction between the positive electrode active material, potentially resulting in reduced battery output and cycle characteristics, and significant reductions in battery overvoltage and discharge capacity. Conversely, if the porosity of the negative electrode is too high, exceeding 80 vol%, the physical and electrical connection with the current collector may be weakened, resulting in reduced adhesion and poor reactivity. Furthermore, the increased porosity may result in electrolyte filling, resulting in reduced battery energy density. Therefore, the porosity should be appropriately adjusted within the above range.

[0112] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector, or may be a lithium metal plate.

[0113] The negative electrode current collector is for supporting the negative electrode active material layer, and is the same as that described for the positive electrode current collector.

[0114] The negative electrode active material layer may include, in addition to the negative electrode active material, a conductive material, a binder, etc. In this case, the conductive material and the binder are as described above.

[0115] The negative electrode active material is lithium (Li + The material may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing material, lithium metal, or a lithium alloy.

[0116] The lithium ion (Li + The material capable of reversibly inserting or de-inserting lithium ions (Li) can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + The material capable of reversibly forming a lithium-containing material by reacting with lithium (Li) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy may be, for example, an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

[0117] Preferably, the negative electrode active material may be lithium metal, specifically in the form of a lithium metal thin film or lithium metal powder.

[0118] In one embodiment of the present invention, the positive electrode may be a lithium metal thin film or a lithium-containing thin film.

[0119] In one embodiment of the present invention, the negative electrode can be thin, for example, 20 μm to 120 μm, specifically 20 μm to 100 μm, 30 μm to 80 μm, 40 μm to 70 μm, or 50 μm to 60 μm, in order to improve the energy density of the lithium-sulfur battery. The thickness of the negative electrode can be measured using a known thickness gauge manufactured by Mitutoyo Corporation or confirmed in an SEM image of the cross section of the negative electrode, and the measurement method is not particularly limited.

[0120] [Separator (separation membrane)] The separator separates or insulates the positive electrode and the negative electrode from each other and allows lithium ions to be transported between the positive electrode and the negative electrode. The separator may be made of a porous non-conductive or insulating material, and any separator commonly used in lithium ion batteries (LIBs) may be used without any particular limitation. The separator may be an independent member such as a film, or may be a coating layer attached to the positive electrode and / or the negative electrode.

[0121] The separator preferably has low resistance to ion migration of the electrolyte and has excellent moisture-absorbing ability for the electrolyte.

[0122] The separator may be made of a porous substrate. Any porous substrate typically used in secondary batteries may be used as the porous substrate. A porous polymer film may be used alone or in combination. For example, a nonwoven fabric or polyolefin-based porous film made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

[0123] The material of the porous substrate is not particularly limited in the present invention, and any porous substrate generally used in electrochemical devices can be used. For example, the porous substrate can be made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene oxides, polyphenylene sulfides, polyethylene naphthalates, polytetrafluoroethylenes, polyvinylidene fluorides, polyvinyl chlorides, and the like. The material may include one or more materials selected from the group consisting of poly(p-phenylene benzobisoxazole), polyacrylonitrile, cellulose, nylon, poly(p-phenylene benzobisoxazole), and polyarylate.

[0124] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. The thickness of the porous substrate is not limited to the above range, but if the thickness is smaller than the lower limit, the mechanical properties may be reduced, and the separator may be easily damaged during use of the battery.

[0125] The average diameter and porosity of the pores present in the porous substrate are not particularly limited, but may be 0.001 to 50 μm and 10 to 95 vol%, respectively.

[0126] The lithium-sulfur battery according to the present invention can be manufactured by laminating (stacking) and folding the separator and electrode in addition to the general winding process.

[0127] The shape of the lithium-sulfur battery is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, a coin shape, and a pouch shape can be used.

[0128] The present invention will be described in more detail below with reference to examples. However, the following examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not limited to these examples.

[0129] [Lithium-sulfur battery manufacturing] Example 1 Preparation of electrolyte for lithium-sulfur batteries A mixture of 2-methylfuran (2MeF) and 1,2-dimethoxyethane (DME) (2:8 v / v) was added with 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI), 3 wt% lithium nitrate (LiNO3, molar mass 69 g / mol), and 10 wt% 1,3,5-trioxane (TOX). , The mixture was stirred at room temperature (23°C) for 12 hours to prepare an electrolyte.

[0130] Electrode preparation A positive electrode slurry was prepared by mixing a sulfur-carbon composite (S8:CNT = 75:25 (weight ratio)) as a positive electrode active material and polyacrylic acid (PAA) as a binder in a weight ratio of 95:5 using distilled water as a solvent.

[0131] The positive electrode slurry composition was applied to both sides of a 12 μm thick aluminum current collector, dried at 80° C., and rolled using a roll press to prepare a positive electrode. At this time, the loading of the positive electrode active material was 2.9 mAh / cm. 2 It was.

[0132] A lithium metal thin film with a thickness of 50 μm was prepared as the negative electrode.

[0133] Lithium-sulfur battery manufacturing The prepared positive and negative electrodes were positioned facing each other, and a polyethylene separator with a thickness of 16 μm and a porosity of 68 vol% was inserted between them. Then, the electrodes were stacked to assemble a pouch cell. 1 g of the prepared electrolyte was then injected and sealed to prepare a pouch-type lithium-sulfur battery.

[0134] Example 2 A lithium-sulfur battery was produced in the same manner as in Example 1, except that 20 wt % of 1,3,5-trioxane (TOX) was added.

[0135] Example 3 A lithium-sulfur battery was produced in the same manner as in Example 1, except that 30 wt % of 1,3,5-trioxane (TOX) was added.

[0136] Example 4 A lithium-sulfur battery was produced in the same manner as in Example 1, except that 40 wt % of 1,3,5-trioxane (TOX) was added.

[0137] Example 5 Preparation of electrolyte for lithium-sulfur batteries An electrolyte was prepared by adding 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI), 3 wt% lithium nitrate (LiNO3, molar mass 69 g / mol), and 10 wt% 1,3,5-trioxane (TOX, molar mass 90.08 g / mol) to a mixture of 2-methylfuran (2MeF) and 1,2-dimethoxyethane (DME) (2:8 v / v), and stirring at room temperature (23 °C) for 12 h.

[0138] Electrode preparation Distilled water was used as a solvent, and the cathode active material was sulfur-carbon composite (S8:CNT = 75:25 (weight ratio)) and the binder was a mixture of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene butyl rubber (SBR) (0 . A mixture of 1.5:1.5:2.0 by weight of ammonium hydroxide and ammonium hydroxide was mixed in a weight ratio of 96:4 to prepare a positive electrode slurry.

[0139] The positive electrode slurry composition was applied to both sides of a 12 μm thick aluminum current collector, dried at 80° C., and rolled using a roll press to prepare a positive electrode. At this time, the loading of the positive electrode active material was 3.0 mAh / cm. 2 It was.

[0140] A lithium metal thin film with a thickness of 50 μm was prepared as the negative electrode.

[0141] Lithium-sulfur battery manufacturing The prepared positive and negative electrodes were positioned facing each other, and a polyethylene separator with a thickness of 16 μm and a porosity of 68 vol% was inserted between them. Then, the electrodes were stacked to assemble a pouch cell. 1 g of the prepared electrolyte was then injected and sealed to prepare a pouch-type lithium-sulfur battery.

[0142] Example 6 A lithium-sulfur battery was produced in the same manner as in Example 5, except that 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added as the lithium salt instead of 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI).

[0143] Example 7 A lithium-sulfur battery was produced in the same manner as in Example 6, except that 1,3-dioxolane (DOL) was used instead of 2-MeF as the non-aqueous solvent, and DOL:DME (2:8 v / v) was used.

[0144] Comparative Example 1 A lithium-sulfur battery was produced in the same manner as in Example 1, except that 1,3,5-trioxane (TOX) was not added.

[0145] Comparative Example 2 A lithium-sulfur battery was fabricated in the same manner as in Example 1, except that 1,3-dioxolane and 1,2-dimethoxyethane (1:1 v / v) were used as the non-aqueous solvent instead of 2-MeF:DME (2:8 v / v), and 1,3,5-trioxane (TOX) was not added.

[0146] Comparative Example 3 A lithium-sulfur battery was produced in the same manner as in Example 1, using 1,3-dioxolane and monofluoroethylene carbonate as the nonaqueous solvent, and adding 1,3,5-trioxane to the solution so that the volume ratio of 1,3,5-trioxane:1,3-dioxolane:monofluoroethylene carbonate was 10:80:10. 0.5 M LiFSI and 3 wt % LiNO were added.

[0147] Experimental Example 1: Evaluation of battery performance with and without TOX addition and the results The performance of the batteries of Example 1 and Comparative Example 1 manufactured above was evaluated by the following method.

[0148] The battery was activated by six cycles of 0.5C charge / 0.5C discharge at 25°C under 1.8V to 2.5V cut-off conditions, and then the battery performance was evaluated by repeating a CC mode cycle of 0.3C charge / 1C discharge. The results are shown in Figures 1 and 2 below.

[0149] 1 and 2, it was confirmed that when TOX was contained in the lithium-sulfur battery electrolyte, the capacity degradation characteristics of the battery due to repeated charge-discharge cycles were significantly improved compared to Comparative Example 1, which did not contain TOX.

[0150] Experimental Example 2: Evaluation of battery performance depending on TOX content and results The performance of the batteries of Examples 1 to 4 manufactured above was evaluated in the same manner as in Experimental Example 1, and the results are shown in FIGS.

[0151] 3 and 4, it was confirmed that the addition of TOX improved all battery life characteristics, and in particular, the order of the lifespan increase was excellent in Example 4 (40 wt% added) < Example 3 (30 wt% added) < Example 1 (10 wt% added) < Example 2 (20 wt% added).

[0152] Experimental Example 3. Evaluation of battery performance depending on electrolyte composition and results The performance of the batteries of Example 2, Comparative Example 2, and Comparative Example 3 manufactured above was evaluated in the same manner as in Experimental Example 1, and the results are shown in FIGS.

[0153] 5 and 6, the battery of Example 2 containing TOX exhibited significantly better capacity retention over repeated charge-discharge cycles than the battery of Comparative Example 2, which contained no TOX and a nonaqueous solvent consisting of 1,3-dioxolane and 1,2-dimethoxyethane (1 / 1 v / v). In particular, the battery of Comparative Example 3 contained TOX, but the nonaqueous solvent did not contain a combination of cyclic ether and chain ether, but instead contained a composition consisting of 1,3-dioxolane and a carbonate-based solvent. This was presumably due to a side reaction between the carbonate-based solvent and polysulfide, which resulted in a significant deterioration in battery performance.

[0154] Experimental Example 4. Evaluation of battery performance depending on electrolyte composition and results The batteries of Examples 5, 6, and 7 prepared above were activated by repeating 0.1 C discharge and 0.1 C charge twice in CC mode at 25°C in the range of 1.8 V to 2.5 V, followed by 0.1 C discharge. The battery performance was then evaluated by repeating 0.2 C charge and 0.3 C discharge cycles in CC mode at 25°C in the range of 1.8 V to 2.5 V. The charge and discharge were performed while the battery was pressurized at 7 atm using a pressure jig. The evaluation results are shown in Figures 7, 8, and 9.

[0155] 7, 8, and 9, the discharge protocols of Examples 5, 6, and 7, in which TOX was added to the electrolyte, did not show any significant changes. However, it was confirmed that the battery life of Example 5 was significantly improved compared to Example 6, in which the lithium salt was changed to LiTFSI, and Example 7, in which the cyclic ether in the non-aqueous solvent was changed to DOL instead of 2-MeF.

[0156] Therefore, when TOX was used as the electrolyte, it was confirmed that there was an excellent synergistic effect between LiFSI as the lithium salt and the mixed solvent of 2-MeF and DME as the non-aqueous solvent.

Claims

1. a non-aqueous solvent, a lithium salt, a nitrate salt, and trioxane; the non-aqueous solvent includes an ether-based solvent, The ether-based solvent includes a cyclic ether and an acyclic ether.

2. Based on the total volume of the non-aqueous solvent, 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the content of the cyclic ether is 30% by volume or less.

3. Based on the total volume of the non-aqueous solvent, 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the content of the cyclic ether is 20% by volume or less.

4. Based on the total volume of the non-aqueous solvent, the content of the cyclic ether is 20% by volume or less, 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the content of the acyclic ether is 80% by volume or more.

5. 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the non-aqueous solvent does not contain a carbonate-based solvent.

6. 2. The lithium-sulfur battery electrolyte of claim 1, wherein the cyclic ether comprises 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, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbide dimethyl ether, or a mixture of two or more thereof.

7. 2. The lithium-sulfur battery electrolyte of claim 1, wherein the acyclic ether comprises dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl 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 tert-butyl ethyl ether, ethylene glycol ethyl methyl ether, or a mixture of two or more thereof.

8. Based on the total weight of the lithium-sulfur battery electrolyte, 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the content of trioxane is 5% by weight or more and 45% by weight or less.

9. Based on the total weight of the lithium-sulfur battery electrolyte, 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the content of trioxane is 10% by weight or more and 20% by weight or less.

10. 2. The lithium-sulfur battery electrolyte according to claim 1, wherein the weight ratio of the trioxane to the nitrate is 2 or more and 15 or less.

11. a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; The electrolyte is the electrolyte according to any one of claims 1 to 10, The positive electrode of the lithium-sulfur battery comprises a sulfur-containing compound as a positive electrode active material.

12. The sulfur-containing compound is inorganic sulfur (S ８ ), Li ２ Sn (n≧1), disulfide compounds, organic sulfur compounds, carbon-sulfur polymers ((C ２ S ｘ ) ｎ , x=an integer from 2.5 to 50, and n≧2), or a mixture of two or more thereof.

13. 12. The lithium-sulfur battery of claim 11, wherein the negative electrode comprises lithium metal, a lithium alloy, or a mixture thereof as a negative electrode active material.

14. 12. The lithium-sulfur battery of claim 11, wherein the lithium-sulfur battery is a coin cell or a pouch cell.

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