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

Abstract

The present invention relates to an electrolyte for a lithium-sulfur secondary battery and a lithium-sulfur secondary battery including the same, and provides an electrolyte for a lithium-sulfur secondary battery including a lithium salt, a non-aqueous solvent, and a cyclic anhydrous compound.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0050433 dated April 19, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated as part of this specification.

[0002] The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery containing the same. [Background technology]

[0003] As the application area of ​​secondary batteries expands to electric vehicles (EVs) and energy storage systems (ESSs), lithium-ion secondary batteries, which have a relatively low energy storage density relative to weight (~250Wh / kg), have limitations in their application to such products. In contrast, lithium-sulfur secondary batteries are theoretically capable of realizing a high energy storage density relative to weight (~2,600Wh / kg), and are therefore in the spotlight as a next-generation secondary battery technology. Lithium-sulfur secondary batteries refer to battery systems that use sulfur-based materials with S-S bonds as positive electrode active materials and lithium metal as negative electrode active materials. Sulfur, the main material of the positive electrode active material, is an abundant resource worldwide, has no toxicity, and has a low atomic weight.

[0004] During discharge, lithium, the negative electrode active material, removes electrons and is oxidized while being ionized, while the positive electrode active material, the sulfur-based material, receives electrons and is reduced. Here, the lithium oxidation reaction is the process in which lithium metal removes electrons and is converted into lithium cations. Meanwhile, the sulfur reduction reaction is the process in which the S-S bond receives two electrons and is converted into sulfur anions. The lithium cations produced by the lithium oxidation reaction are transferred to the positive electrode through the electrolyte and combine with the sulfur anions produced by the sulfur reduction reaction to form a salt. Specifically, sulfur before discharge has a cyclic S8 structure, which is converted into lithium polysulfide (LiS) by a reduction reaction. x If the lithium polysulfides are completely reduced, lithium sulfide (Li2S) will be produced.

[0005] Sulfur, which is a positive electrode active material, has low electrical conductivity, so it is difficult to ensure reactivity with electrons and lithium ions in the solid state. In order to improve the reactivity of sulfur, existing lithium-sulfur secondary batteries use Li2S x In this case, an ether solvent such as dioxolane or dimethoxyethane, which has high solubility in lithium polysulfide, is used as the electrolyte solvent.

[0006] However, when such an ether-based solvent is used, there is a problem that the life characteristics of the lithium-sulfur secondary battery are deteriorated due to various reasons, such as the elution of lithium polysulfide from the positive electrode, the occurrence of shorts due to the growth of dendrites on the lithium negative electrode, and the accumulation of by-products due to the decomposition of the electrolyte, which may deteriorate the life characteristics of the lithium-sulfur secondary battery.

[0007] In particular, when such an ether-based solvent is used, a large amount of lithium polysulfide can be dissolved and the reactivity is high. However, the reactivity and life characteristics of sulfur are affected depending on the content of the electrolyte due to the characteristics of the lithium polysulfide dissolved in the electrolyte.

[0008] In recent years, in order to develop lithium-sulfur secondary batteries with high energy density of over 500Wh / kg, which is required for aircraft and next-generation electric vehicles, there is a demand for a large sulfur loading in the electrodes and a minimized electrolyte content.

[0009] However, due to the characteristics of the ether-based solvent, the lower the content of the electrolyte, the more rapidly the viscosity increases during charging and discharging, which can cause overvoltage and degradation.

[0010] Therefore, research is being continuously conducted on the addition of additives to prevent the decomposition of the electrolyte and ensure excellent life characteristics. However, the components and composition of the electrolyte that can prevent the decomposition of the electrolyte and improve the life characteristics have not been clearly disclosed. In particular, the components and composition of the electrolyte suitable for pouch cells and the like that have an extremely small electrolyte content have not been specifically known. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2007-0027512 (2007.03.09) "Electrolyte for Lithium-Sulfur Electrochemical Battery" Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, in order to prevent decomposition of the electrolyte of the lithium-sulfur secondary battery and improve the life characteristics, the present invention has confirmed that the above problems can be solved and the performance of the lithium-sulfur secondary battery can be improved by adding a cyclic anhydrous compound as an additive to an electrolyte for the lithium-sulfur secondary battery containing a lithium salt and a non-aqueous solvent, thereby completing the present invention.

[0013] It is therefore an object of the present invention to provide an electrolyte for a lithium-sulfur secondary battery that can prevent decomposition of the electrolyte and improve the life characteristics, and to provide a lithium-sulfur secondary battery having improved battery performance by including the electrolyte. [Means for solving the problem]

[0014] To achieve the above object, the present invention provides an electrolyte solution for a lithium-sulfur secondary battery, which includes a lithium salt and a non-aqueous solvent, and further includes a cyclic anhydride compound as an additive.

[0015] The present invention also provides an electrolyte solution for a lithium-sulfur secondary battery, wherein the cyclic anhydrous compound is an anhydrous compound having a five-membered or six-membered ring.

[0016] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the 2- and 3-position carbons in the 5- or 6-membered ring of the cyclic anhydride compound are linked by a single bond or a double bond, or the 2- and 3-position carbons of the 5-membered ring are part of a substituted or unsubstituted aryl group.

[0017] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the cyclic anhydride compound is represented by any one of the following Chemical Formulas 1 to 3:

[0018] [ka]

[0019] In the above Chemical Formula 1 to Chemical Formula 3, The R's may be the same or different and are each a hydrogen atom; a substituted or unsubstituted alkyl group; a substituted or unsubstituted cycloalkyl group; a substituted or unsubstituted aryl group; or a substituted or unsubstituted heteroaryl group.

[0020] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the cyclic anhydride compound is represented by any one of the following Chemical Formulas 1-1 to 3-1.

[0021] [ka]

[0022] The present invention also relates to a method for producing a lithium salt, the method comprising the steps of: 10 Cl 10 The present invention provides an electrolyte for a lithium-sulfur secondary battery, which is one or more selected from the group consisting of LiB(Ph)4, LiC4BO8, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiSO3CH3, LiSO3CF3, LiSCN, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, and lower aliphatic lithium carbonate.

[0023] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the non-aqueous solvent contains a linear ether and a cyclic ether.

[0024] The present invention also provides an electrolyte solution for a lithium-sulfur secondary battery, wherein the linear ether is selected from the group consisting of 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 dimethyl 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, and ethylene glycol ethyl methyl ether.

[0025] The present invention also provides an electrolyte solution for a lithium-sulfur secondary battery, wherein the cyclic ether is selected from the group consisting of dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and 2-methylfuran.

[0026] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the content of the cyclic anhydride compound is 0.1 to 10% by weight based on the total weight of the electrolyte.

[0027] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, further comprising a nitric acid compound.

[0028] The present invention also provides an electrolyte for a lithium-sulfur secondary battery, wherein the nitric acid compound is at least one selected from the group consisting of lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, and pyridinium nitrate.

[0029] The present invention also provides a lithium-sulfur secondary battery comprising the electrolyte, a positive electrode, a negative electrode, and a separator. Effect of the Invention

[0030] The electrolyte for a lithium-sulfur secondary battery according to the present invention includes a lithium salt and a non-aqueous solvent, and further includes a cyclic anhydride compound as an additive, thereby preventing decomposition of the electrolyte during operation of the lithium-sulfur secondary battery and improving the life characteristics. [Brief description of the drawings]

[0031] [Figure 1] 1 is a graph showing life characteristics of lithium-sulfur secondary batteries according to Examples 1 to 3 of the present invention and Comparative Examples 1 and 2. [Diagram 2] 1 is a graph showing the life characteristics of lithium-sulfur secondary batteries according to Example 1 of the present invention and Comparative Example 3. [Diagram 3] 1 is a graph showing life characteristics of lithium-sulfur secondary batteries according to Examples 1, 4, and 5 of the present invention and Comparative Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The embodiments provided by the present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0033] The present invention provides an electrolyte solution for a lithium-sulfur secondary battery, comprising a lithium salt and a non-aqueous solvent, the electrolyte solution further comprising a cyclic anhydride compound as an additive.

[0034] The cyclic anhydride compound according to the present invention may be an anhydride compound consisting of a 5-membered or 6-membered ring. Specific examples include substituted or unsubstituted succinic anhydride, maleic anhydride, glutaric anhydride, glutaconic anhydride, etc. Substituents that can be substituted on the cyclic anhydride compound include hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted heteroaryl groups.

[0035] In addition, the cyclic anhydride compound may be part of an aryl group in which the carbons at the 2nd and 3rd positions of the 5-membered or 6-membered ring are connected by a single bond or a double bond, or the carbons at the 2nd and 3rd positions of the 5-membered ring are substituted or unsubstituted.

[0036] The cyclic anhydride compound according to the present invention may be a compound represented by any one of the following formulas 1 to 3:

[0037] [ka]

[0038] In the above Chemical Formula 1 to Chemical Formula 3, The R's may be the same or different and are each a hydrogen atom; a substituted or unsubstituted alkyl group; a substituted or unsubstituted cycloalkyl group; a substituted or unsubstituted aryl group; or a substituted or unsubstituted heteroaryl group.

[0039] The cyclic anhydride compound may be a compound represented by any one of the following formulas 1-1 to 3-1.

[0040] [ka]

[0041] The content of the cyclic anhydride compound according to the present invention may be 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, and more preferably 0.1 wt% to 3 wt% based on the total weight of the electrolyte. If the content of the cyclic anhydride compound is less than this range, the effect of forming a film (Solid Electrolyte Interphase, SEI) on the electrode surface is weak, and the effect of improving life characteristics is insufficient. If the content of the cyclic anhydride compound is more than this range, a problem of increased resistance due to excess additives may occur. Therefore, it is preferable that the content of the cyclic anhydride compound satisfies the above range.

[0042] Meanwhile, the electrolyte for the lithium-sulfur secondary battery of the present invention may contain a lithium salt and a non-aqueous solvent. The lithium salt is a material that is easily dissolved in a non-aqueous organic solvent, and is, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiB(Ph)4, LiC4BO8, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiSO3CH3, LiSO3CF3, LiSCN, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2 and lower aliphatic lithium carbonates, and preferably LiN(CF3SO2)2.

[0043] The concentration of the lithium salt may be 0.2-2M, specifically 0.5-1.8M, more specifically 0.6-1.7M, depending on various factors such as the exact composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charge and discharge conditions of the battery, the operating temperature, and other factors known in the lithium battery field. If the lithium salt is used at a concentration below this range, the conductivity of the electrolyte may be low, and the electrolyte performance may be deteriorated, and if the lithium salt is used at a concentration above this range, the viscosity of the electrolyte may increase, and the lithium ions (Li + ) mobility can be reduced.

[0044] The non-aqueous solvent according to the present invention may include an ether-based solvent and a non-solvent, and the ether-based solvent may include a linear ether and a cyclic ether.

[0045] The linear ether may be selected from the group consisting of 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 dimethyl 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, and ethylene glycol ethyl methyl ether, and is preferably dimethoxyethane.

[0046] The cyclic ether may be selected from the group consisting of dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan and 2-methylfuran, and preferably 2-methylfuran.

[0047] The volume ratio of the linear ether to the cyclic ether may be 9:1 to 1:9, preferably 8:2 to 2:8, and more preferably 7:3 to 3:7.

[0048] If the volume ratio of the linear ether to the cyclic ether is outside the above range, the effect of improving the battery life characteristics will be insufficient and the desired effect will not be obtained, so it is preferable that the volume ratio of the linear ether to the non-solvent falls within the above range.

[0049] The electrolyte for a lithium-sulfur secondary battery of the present invention may further include a nitric acid or nitrite compound as an additive, which forms a stable film on the lithium electrode and improves charge / discharge efficiency. Such nitric acid or nitrite compounds are not particularly limited, but may be one selected from the group consisting of inorganic nitric acid or nitrite compounds such as lithium nitrate (LiNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), barium nitrate (Ba(NO3)2), ammonium nitrate (NH4NO3), lithium nitrite (LiNO2), potassium nitrite (KNO2), cesium nitrite (CsNO2), and ammonium nitrite (NH4NO2); 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; and organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, and dinitrotoluene, and combinations thereof, and preferably lithium nitrate (LiNO3).

[0050] The electrolyte for a lithium-sulfur secondary battery of the present invention may further contain other additives for the purpose of improving charge / discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate (VC), etc.

[0051] The method for preparing the electrolyte for the lithium-sulfur secondary battery of the present invention is not particularly limited in the present invention, and the electrolyte can be prepared by a conventional method known in the art.

[0052] The present invention also provides a lithium-sulfur secondary battery including an electrolyte for a lithium-sulfur secondary battery.

[0053] The lithium-sulfur secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the electrolyte may include the electrolyte for a lithium-sulfur secondary battery according to the present invention.

[0054] The positive electrode may include a positive electrode current collector and a positive electrode active material coated on one or both sides of the positive electrode current collector.

[0055] The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not induce 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, etc., aluminum-cadmium alloy, etc. can be used.

[0056] The positive electrode current collector can have fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and can be in various forms such as a film, sheet, foil, mesh, net, porous body, foam, nonwoven fabric, etc.

[0057] The positive electrode active material may include a positive electrode active material, and optionally a conductive material and a binder.

[0058] The positive electrode active material is elemental sulfur (S8); Li2Sn (n≧1), an organic sulfur compound, or a carbon-sulfur polymer (C2S x ) n: x = 2.5 to 50, n ≥ 2) Preferably, inorganic sulfur (S8) can be used.

[0059] The positive electrode contains, in addition to the positive electrode active material, a transition metal element, 2 The composition may further comprise one or more additives selected from Group 1 elements, Group 2 elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0060] The transition metal element may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, and the like. 2 Group elements may include Al, Ga, In, Ti, etc., and the Group 3 elements include Ge, Sn, Pb, etc.

[0061] The conductive material is for improving electrical conductivity and is not particularly limited as long as it is an electronically conductive material that does not undergo chemical changes in the lithium secondary battery, and generally carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxide, organic conductive material, etc. can be used, and currently commercially available conductive materials include acetylene black (Chevron Chemical Company or Gulf Oil Company products, etc.), Ketjen Black EC (Armak Company product), Vulcan XC-72 (Cabot Company product), and Super P (MMM product), etc. Examples include acetylene black, carbon black, graphite, etc.

[0062] In addition, the positive electrode active material may further include a binder having a function of maintaining the positive electrode active material on the positive electrode current collector and binding the active material together. As the binder, various types of binders can be used, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC).

[0063] The positive electrode may be a positive electrode having a high sulfur loading. 2 More preferably, 4.0 mAh / cm 2 More preferably, it is 5.0 mAh / cm 2 It may be more than that.

[0064] The negative electrode may include a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector, or the negative electrode may be a lithium metal plate.

[0065] The negative electrode current collector is for supporting the negative electrode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage region of the lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, or the like, aluminum-cadmium alloy, or the like can be used.

[0066] The negative electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and may be in various forms such as a film, sheet, foil, mesh, net, porous body, foam, or nonwoven fabric.

[0067] The negative electrode active material is lithium (Li + The lithium ion (Li) may be reversibly inserted or removed, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy. + The material capable of reversibly absorbing and releasing lithium ions (Li) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + The material capable of reacting with lithium-containing compound to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitride, 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). Preferably, the negative electrode active material is lithium metal, and may be in the form of a lithium metal thin film or lithium metal powder.

[0068] The method for forming the negative electrode active material is not particularly limited, and a method for forming a layer or film commonly used in the art can be used, such as compression bonding, coating, deposition, etc. In addition, the negative electrode of the present invention also includes a case where a thin metallic lithium film is formed on a metal plate by initial charging after assembling a battery without a thin lithium film on a current collector.

[0069] The separator is for physically separating the positive electrode and the negative electrode in the lithium-sulfur secondary battery of the present invention, and may be any separator that is generally used in lithium-sulfur secondary batteries without any particular limitation. In particular, a separator that has low resistance to the ion transfer of the electrolyte and excellent electrolyte humidification capacity is preferred.

[0070] The separator may be made of a porous substrate. The porous substrate may be any porous substrate typically used in electrochemical devices, such as, but not limited to, a polyolefin-based porous membrane or nonwoven fabric.

[0071] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high density polyethylene, linear low density polyethylene, low density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in the form of a mixture of these polymers.

[0072] Examples of the nonwoven fabric include, in addition to polyolefin-based nonwoven fabric, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, each of which is used alone or as a mixture of polymers. The structure of the nonwoven fabric may be a spunbonded nonwoven fabric or a meltblown nonwoven fabric made of long fibers.

[0073] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

[0074] The pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

[0075] The electrolyte contains lithium ions and serves to induce electrochemical oxidation or reduction reactions at the positive and negative electrodes through the lithium ions, as described above.

[0076] The electrolyte may be injected at a suitable stage during the manufacturing process of the electrochemical device depending on the manufacturing process and required properties of the final product, i.e., before assembly of the electrochemical device or at the final stage of assembly of the electrochemical device.

[0077] The lithium-sulfur secondary battery according to the present invention can be manufactured by laminating (stack) and folding processes of the separator and the electrodes in addition to the general winding process.

[0078] The shape of the lithium-sulfur secondary battery is not particularly limited, and may be various shapes such as a cylindrical type, a laminated type, or a coin type.

[0079] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are provided only to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0080] Working Example : Manufacturing of electrolyte for lithium-sulfur secondary batteries Manufacturing Example 1 Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was dissolved in a non-aqueous solvent in which 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) were mixed in a volume ratio of 1:1 to a concentration of 1.0M (mol / L), lithium nitrate (LiNO3) was added in an amount of 1.0 wt % based on the total weight of the electrolyte, and then a cyclic anhydride compound represented by the following chemical formula 1-1 was added in an amount of 1 wt % based on the total weight of the electrolyte to prepare an electrolyte for a lithium-sulfur secondary battery.

[0081] [ka]

[0082] Manufacturing Example 2 An electrolyte solution for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was added in an amount of 0.1 wt %.

[0083] Production Example 3 An electrolyte solution for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was added in an amount of 3.0 wt %.

[0084] Production Example 4 An electrolyte for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was replaced with a cyclic anhydride compound represented by Chemical Formula 1-2 below.

[0085] [ka]

[0086] Production Example 5 An electrolyte for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was replaced with a cyclic anhydride compound represented by Chemical Formula 1-3 below.

[0087] [ka]

[0088] Comparative Manufacturing Example 1 An electrolyte solution for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Formula 1-1 was not added.

[0089] Comparative Manufacturing Example 2 An electrolyte solution for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was added in an amount of 10 wt %.

[0090] Comparative Manufacturing Example 3 An electrolyte for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the non-aqueous solvent obtained by mixing 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) in a volume ratio of 1:1 was replaced with a non-aqueous solvent obtained by mixing propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 4:3:3.

[0091] Comparative Example 4 An electrolyte for a lithium-sulfur secondary battery was prepared in the same manner as in Preparation Example 1, except that the cyclic anhydride compound represented by Chemical Formula 1-1 was replaced with Comparative Compound A below.

[0092] [ka]

[0093] The contents of the non-aqueous solvent and the cyclic anhydride compound in the electrolyte solutions for lithium-sulfur secondary batteries of Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 4 are shown in Table 1 below.

[0094] [Table 1]

[0095] Experimental Example Evaluation of life characteristics of lithium-sulfur secondary batteries Sulfur was mixed with a conductive material and a binder in acetonitrile using a ball mill to prepare a positive electrode active material slurry. Carbon black was used as the conductive material, and a binder in the form of a mixture of SBR and CMC was used as the binder, with the mixture ratio of sulfur:conductive material:binder being 72:24:4 by weight. The positive electrode active material slurry was loaded onto an aluminum current collector at a loading amount of 5.0 mAh / cm. 2 After coating, the mixture was dried to produce a positive electrode with a porosity of 68%. Lithium metal with a thickness of 45 μm was used as the negative electrode.

[0096] The positive and negative electrodes prepared as described above were positioned to face each other, and a polyethylene separator having a thickness of 20 μm and a porosity of 45% was interposed between the positive and negative electrodes.

[0097] Thereafter, the electrolyte solutions for lithium-sulfur secondary batteries according to Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 4 were charged into the case to fabricate the lithium-sulfur secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4.

[0098] The lithium-sulfur secondary battery manufactured by the above method was charged and discharged 2.5 times at a current density of 0.1 C, then charged and discharged 3 times at a current density of 0.2 C, and then subjected to 110 cycles at a current density of 0.5 C. The life cycle at which the capacity retention rate of the lithium-sulfur secondary battery reached 80% was measured to confirm the life characteristics of the battery. The results are shown in Table 1 and FIG. 1.

[0099] [Table 2]

[0100] As shown in Table 2, the lithium-sulfur secondary batteries using the electrolyte solutions for lithium-sulfur secondary batteries according to Examples 1 to 5 were found to have superior battery life characteristics compared to the lithium-sulfur secondary batteries using the electrolyte solutions for lithium-sulfur secondary batteries according to Comparative Examples 1 to 4.

[0101] Specifically, the lithium-sulfur secondary battery according to the present invention uses the electrolyte for lithium-sulfur secondary battery according to Examples 1 to 5, in which the content of the cyclic anhydride compound represented by any one of Chemical Formulas 1 to 3 in a non-aqueous solvent is 0.1 wt % to 3 wt %, and it has been confirmed that the lithium-sulfur secondary battery forms a stable SEI (Solid-Electrolyte Interphase) film on the lithium negative electrode, suppresses the reaction between lithium and polysulfide and the decomposition of the electrolyte, and improves the life characteristics of the battery.

[0102] On the other hand, when no cyclic anhydride compound was included (Comparative Example 1) or when an excessively large amount of the cyclic anhydride compound was included (Comparative Example 2), no improvement in life characteristics was observed. Also, when a carbonate-based solvent was used as the non-aqueous solvent (Comparative Example 3) and when a carbonate-based additive was used as the additive (Comparative Example 4), it was confirmed that the life characteristics were significantly decreased.

[0103] Considering these points, when an electrolyte for a lithium-sulfur secondary battery containing the cyclic anhydride compound according to the present invention is used, the life characteristics of the battery are improved compared to conventional lithium-sulfur secondary batteries.

[0104] Any mere variations or modifications of the present invention should belong to the scope of the present invention, and the specific scope of protection of the present invention will be defined by the appended claims.

Claims

1. A lithium salt, a non-aqueous solvent and a cyclic anhydrous compound are included, The non-aqueous solvent includes an ether solvent, The content of the cyclic anhydride compound is 0.1% by weight to 5% by weight based on the total weight of the electrolyte; The cyclic anhydride compound is represented by any one of the following Chemical Formulas 1-1 to 3-1. 【Chemistry 1】

2. The lithium salt is LiCl, LiBr, LiI, LiClO ４ , LiBF ４ , LiB １０ C １０ , LiB(Ph) ４ , LiC ４ B.O. ８ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , LiSO ３ CH ３ , LiSO ３ CF ３ , LiSCN, LiC(CF ３ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN (C ２ F ５ SO ２ ) ２ , LiN(SO ２ F) ２ and lower aliphatic carbonate lithium salts.

3. The electrolyte for a lithium-sulfur secondary battery according to any one of claims 1 to 2, wherein the ether-based solvent comprises a linear ether and a cyclic ether.

4. The linear ether is selected from the group consisting of 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 dimethyl 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, and ethylene glycol ethyl methyl ether. The electrolyte for a lithium-sulfur secondary battery according to claim 3.

5. The cyclic ether is selected from the group consisting of dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, oxane, dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and 2-methylfuran. The electrolyte for a lithium-sulfur secondary battery according to claim 3.

6. 6. The electrolyte for a lithium-sulfur secondary battery according to claim 1, wherein the content of the cyclic anhydride compound is 1% by weight to 3% by weight based on the total weight of the electrolyte.

7. The electrolyte for a lithium-sulfur secondary battery according to any one of claims 1 to 6, further comprising a nitric acid compound.

8. 8. The electrolyte for a lithium-sulfur secondary battery according to claim 7, wherein the nitric acid compound is at least one selected from the group consisting of lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, and pyridinium nitrate.

9. The electrolyte solution according to any one of claims 1 to 8; Positive electrode; A negative electrode; and A lithium-sulfur secondary battery comprising:

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