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

Abstract

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, and provides an electrolyte for a lithium secondary battery including a lithium salt, a non-aqueous solvent, and a benzo-dioxole-based compound or a benzo-dioxane-based compound in which hydrogen or an electron-donating group is substituted at the carbon position located between two oxygen atoms.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0064492 filed on May 20, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary 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.

[0004] 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.

[0005] 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.

[0006] 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 phase. 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] Therefore, in order to prevent the decomposition of the electrolyte and ensure excellent life characteristics, research is being continuously conducted on the addition of additives. 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 a pouch cell or the like with an extremely small electrolyte content have not been specifically known. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Korean Patent Publication No. 10-2017-0027512 (March 9, 2007), "Electrolyte for Lithium-Sulfur Electrochemical Battery" Summary of the Invention [Problem to be solved by the invention]

[0013] Therefore, in the present invention, in order to prevent the decomposition of the electrolyte of the lithium secondary battery and improve the life characteristics, a benzo-dioxole-based compound or a benzo-dioxane-based compound is added as an additive to an electrolyte for a lithium secondary battery containing a lithium salt and a non-aqueous solvent, and it has been confirmed that the above problems can be solved and the performance of the lithium secondary battery can be improved, thereby completing the present invention.

[0014] Therefore, an object of the present invention is to provide an electrolyte for a lithium secondary battery, which can prevent the decomposition of the electrolyte and form a stable coating on the negative electrode interface, thereby preventing the degradation of the electrolyte and the negative electrode, thereby improving the life characteristics. Another object of the present invention is to provide a lithium secondary battery having improved battery performance, comprising the electrolyte. [Means for solving the problem]

[0015] To achieve the above object, the present invention provides an electrolyte for a lithium secondary battery including a lithium salt and a non-aqueous solvent, further including a benzo-dioxole-based compound or a benzo-dioxane-based compound as an additive. In particular, the benzo-dioxole-based compound or the benzo-dioxane-based compound has hydrogen or an electron donating group at a carbon position between two oxygen atoms of the compound.

[0016] In addition, the present invention provides an electrolyte for a lithium secondary battery, wherein the benzo-dioxole-based compound or the benzo-dioxane-based compound is a compound represented by the following Chemical Formula 1:

[0017] [ka]

[0018] In the above Chemical Formula 1, R is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 10 carbon atoms, or a substituted or unsubstituted heteroaryl group having 5 to 10 carbon atoms, The multiple Ra's are the same or different and each independently represents hydrogen or an electron donating group; The n is an integer from 1 to 3.

[0019] In addition, the present invention provides an electrolyte for a lithium secondary battery, wherein the plurality of Ra in Formula 1 are the same or different, and each independently represents a substituent having a Hammett substituent constant of 0 or less.

[0020] The present invention also provides an electrolyte for a lithium secondary battery, wherein the plurality of Ra in Chemical Formula 1 are the same or different and are each independently selected from the group consisting of hydrogen, an amino group, an alkylamino group having 1 to 10 carbon atoms, a dialkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 10 carbon atoms, a diarylamino group having 12 to 20 carbon atoms, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an amide group having 1 to 10 carbon atoms, an ester group having 1 to 10 carbon atoms, an allyl group, an alkylaryl group having 1 to 10 carbon atoms, and a dialkylaryl group having 2 to 20 carbon atoms.

[0021] The present invention also provides an electrolyte for a lithium secondary battery, wherein the compound represented by Chemical Formula 1 is a compound represented by the following Chemical Formula 1-1 or 1-2:

[0022] [ka]

[0023] 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 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 carboxylates.

[0024] 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.

[0025] The present invention also provides an electrolyte for a lithium 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 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, and ethylene glycol ethyl methyl ether.

[0026] The present invention also provides an electrolyte solution for a lithium 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.

[0027] The present invention also provides an electrolyte for a lithium secondary battery, wherein the content of the benzo-dioxole-based compound or the benzo-dioxane-based compound is 0.1 to 10% by weight based on the total weight of the electrolyte.

[0028] The present invention also provides an electrolyte for a lithium secondary battery, further comprising a nitric acid compound.

[0029] The present invention also provides an electrolyte for a lithium 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.

[0030] The present invention also provides a lithium secondary battery comprising the electrolyte, a positive electrode, a negative electrode and a separator.

[0031] The lithium secondary battery is also provided as a lithium-sulfur secondary battery. Effect of the Invention

[0032] The electrolyte for a lithium secondary battery according to the present invention includes a lithium salt and a non-aqueous solvent, and further includes a benzo-dioxole-based compound or a benzo-dioxane-based compound as an additive, thereby preventing decomposition of the electrolyte during operation of the lithium secondary battery and forming a stable film on the negative electrode interface to prevent degradation of the electrolyte and the negative electrode, thereby improving the life characteristics. [Brief description of the drawings]

[0033] [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 the life characteristics of lithium-sulfur secondary batteries according to Examples 1 and 4 of the present invention and Comparative Examples 1 and 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] 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.

[0035] The present invention provides an electrolyte for lithium secondary batteries, comprising a lithium salt and a non-aqueous solvent, further comprising a benzo-dioxole-based compound or a benzo-dioxane-based compound as an additive, in which the benzo-dioxole-based compound or the benzo-dioxane-based compound has hydrogen or an electron donating group at a carbon position between two oxygen atoms.

[0036] The benzo-dioxole-based compound or benzo-dioxane-based compound according to the present invention has an electron-donating group substituted at a carbon position with low electron density located between two oxygen atoms, thereby increasing the electron density and reducing the reactivity with polysulfide, thereby suppressing the loss of the positive electrode active material and preventing a sudden decrease in the capacity of the battery, thereby improving the life characteristics of the lithium secondary battery.

[0037] In this regard, the conventional lithium-sulfur secondary battery has a problem that the lithium polysulfide dissolved in the electrolyte causes a chemical reaction with the electrolyte components, which causes a loss of the positive electrode active material, and the battery capacity is rapidly reduced. In particular, the polysulfide exhibits nucleophilicity and easily reacts with electrophilic substances with low electron density, but the carbon site located between two oxygen atoms of the benzo-dioxole-based compound or benzo-dioxane-based compound has low electron density due to the two oxygen atoms that withdraw electrons, and is highly reactive with polysulfides. In contrast, the benzo-dioxole-based compound or benzo-dioxane-based compound according to the present invention, in which hydrogen or an electron-donating group is substituted on the carbon atom located between the two oxygen atoms, has high electron density due to the electron-donating group, and is therefore less reactive with polysulfides. This makes it possible to prevent the loss of the positive electrode active material. On the other hand, when an electron-withdrawing group is substituted on the carbon atom located between the two oxygen atoms of a benzo-dioxole-based compound or a benzo-dioxane-based compound, the electron density becomes lower and the reactivity with polysulfide becomes higher, which causes a problem of increased loss of the positive electrode active material.

[0038] Therefore, it is more preferable that the carbon atom located between the two oxygen atoms of the benzo-dioxole-based compound or the benzo-dioxane-based compound is substituted with hydrogen or an electron-donating group.

[0039] The benzo-dioxole-based compound or benzo-dioxane-based compound according to the present invention may be a compound represented by the following Chemical Formula 1:

[0040] [ka]

[0041] In the above Chemical Formula 1, R is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 10 carbon atoms, or a substituted or unsubstituted heteroaryl group having 5 to 10 carbon atoms, The plurality of Ra are the same or different, and each independently represents hydrogen or an electron donating group; The n is an integer from 1 to 3.

[0042] In addition, in the compound represented by Chemical Formula 1 according to the present invention, the plurality of Ra may be the same or different, and each may be independently a substituent having a Hammett substituent constant of 0 or less. Specific examples thereof may be selected from the group consisting of hydrogen, an amino group, an alkylamino group having 1 to 10 carbon atoms, a dialkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 10 carbon atoms, a diarylamino group having 12 to 20 carbon atoms, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an amide group having 1 to 10 carbon atoms, an ester group having 1 to 10 carbon atoms, an allyl group, an alkylaryl group having 1 to 10 carbon atoms, and a dialkylaryl group having 2 to 20 carbon atoms, and preferably, hydrogen, an amino group, an alkylaryl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and a dialkylaryl group having 2 to 20 carbon atoms. It may be selected from the group consisting of a hydroxyl group, an alkylamino group having 1 to 6 carbon atoms, an alkylamino group having 1 to 6 carbon atoms, a dialkylamino group having 2 to 12 carbon atoms, an arylamino group having 6 to 10 carbon atoms, a diarylamino group having 12 to 20 carbon atoms, a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an amide group having 1 to 6 carbon atoms, an ester group having 1 to 6 carbon atoms, an allyl group, an alkylaryl group having 1 to 6 carbon atoms, and a dialkylaryl group having 2 to 12 carbon atoms, and more preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0043] In addition, the compound represented by Formula 1 according to the present invention may be a compound represented by Formula 1-1 or 1-2 below.

[0044] [ka]

[0045] The content of the benzo-dioxole-based compound or benzo-dioxane-based compound according to the present invention may be 0.1% to 10% by weight, preferably 0.1% to 5% by weight, more preferably 0.1% to 3% by weight, based on the total weight of the electrolyte. If the content of the benzo-dioxole-based compound or benzo-dioxane-based compound is less than the above range, the effect of forming a film (Solid Electrolyte Interphase, SEI) on the electrode surface is weak, and the effect of improving the life characteristics is insufficient. If the content of the benzo-dioxole-based compound or benzo-dioxane-based compound exceeds the above range, a problem of increased resistance due to excess additives may occur. Therefore, it is preferable that the content of the benzo-dioxole-based compound or benzo-dioxane-based compound satisfies the above range.

[0046] Meanwhile, the electrolyte for a lithium secondary battery according to the present invention may contain a lithium salt and a non-aqueous solvent. The lithium salt is a substance that is easily dissolved in a non-aqueous organic solvent, and may be 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 carboxylates, and preferably LiN(CF3SO2)2.

[0047] 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 art. If the lithium salt is used at a concentration below this range, the conductivity of the electrolyte may be reduced, resulting in a decrease in the performance of the electrolyte, and if the lithium salt is used at a concentration above this range, the viscosity of the electrolyte may increase, resulting in a decrease in the dissolution of lithium ions (Li + ) may have reduced mobility.

[0048] 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.

[0049] 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 t-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 t-butyl ethyl ether, and ethylene glycol ethyl methyl ether, and is preferably dimethoxyethane.

[0050] 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 is preferably 2-methylfuran.

[0051] The volume ratio of the linear ether to the cyclic ether may be from 9:1 to 1:9, preferably from 8:2 to 2:8, and more preferably from 7:3 to 5:5.

[0052] 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 cyclic ether falls within the above range.

[0053] The electrolyte for lithium secondary batteries 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).

[0054] The electrolyte for lithium secondary batteries 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.

[0055] The method for preparing the electrolyte for lithium secondary batteries 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.

[0056] The present invention also provides a lithium secondary battery including the electrolyte for lithium secondary batteries.

[0057] The lithium 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 secondary battery according to the present invention.

[0058] In an embodiment, the lithium secondary battery may be a lithium-sulfur secondary battery.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The positive electrode active material may include a positive electrode active material, and optionally a conductive material and a binder.

[0063] 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.

[0064] In addition to the positive electrode active material, the positive electrode may further include one or more additives selected from a transition metal element, a Group 2 element, a Group 3 element, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0065] 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 The group elements may include Al, Ga, In, Ti, etc., and the group 3 elements may include Ge, Sn, Pb, etc.

[0066] 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 cause 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.

[0067] 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).

[0068] The positive electrode may be a positive electrode having a high sulfur loading. 2 It can be equal to or greater than 4.0 mAh / cm 2 More preferably, it can be 5.0 mAh / cm or more. 2 It can be more than that.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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) can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + The material capable of reversibly forming a lithium-containing compound by reacting with lithium (Li) 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 may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

[0073] 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.

[0074] The separator is for physically separating the positive electrode and the negative electrode in the lithium secondary battery of the present invention, and any separator that is usually used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to the ion migration of the electrolyte and excellent moisture-absorbing ability for the electrolyte solution is preferable.

[0075] 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.

[0076] 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, and ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0077] 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.

[0078] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

[0079] The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

[0080] 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.

[0081] The electrolyte solution may be added at an appropriate 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.

[0082] The lithium secondary battery according to the present invention can be manufactured by lamination, stacking and folding processes of the separator and the electrodes in addition to the general winding process.

[0083] The shape of the lithium secondary battery is not particularly limited, and may be various shapes such as a cylindrical type, a laminated type, or a coin type.

[0084] 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.

[0085] Working Example : Manufacture of electrolyte for lithium secondary batteries Manufacturing Example 1 Lithium bis(fluoromethylsulfonyl)imide (LiFSI) was dissolved in a non-aqueous solvent of 2-methylfuran:1,2-dimethoxyethane (DME) mixed at a volume ratio of 3:7 to give a concentration of 0.75M (mol / L), lithium nitrate (LiNO3) was added to give a total weight of 3.0% of the electrolyte solution, and then a benzo-dioxole compound represented by the following chemical formula 1-1 was added to give a total weight of 1% of the electrolyte solution to produce an electrolyte solution for lithium secondary batteries.

[0086] [ka]

[0087] Manufacturing Example 2 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole compound represented by Formula 1-1 was added in an amount of 0.1 wt %.

[0088] Production Example 3 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole compound represented by Formula 1-1 was added in an amount of 3.0 wt %.

[0089] Production Example 4 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole-based compound represented by Chemical Formula 1-1 was replaced with a benzo-dioxane-based compound represented by Chemical Formula 1-2 below.

[0090] [ka]

[0091] Comparative Manufacturing Example 1 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole compound represented by Formula 1-1 was not added.

[0092] Comparative Manufacturing Example 2 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole compound represented by Formula 1-1 was added in an amount of 10 wt %.

[0093] Comparative Manufacturing Example 3 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the non-aqueous solvent in which 2-methylfuran:1,2-dimethoxyethane (DME) was mixed in a volume ratio of 3:7 was replaced with a non-aqueous solvent in which ethylene carbonate (EC):diethyl carbonate (DEC) was mixed in a volume ratio of 1:1.

[0094] Comparative Example 4 An electrolyte for a lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the benzo-dioxole compound represented by Chemical Formula 1-1 was replaced with the following Comparative Compound A (2,2-fluoro-1,3-benzodioxole).

[0095] [ka]

[0096] The contents of the non-aqueous solvent and the benzo-dioxole-based compound or benzo-dioxane-based compound in the lithium secondary battery electrolytes of Preparation Examples 1 to 4 and Comparative Examples 1 to 4 are as shown in Table 1 below.

[0097] [Table 1]

[0098] Life characteristic evaluation of experimental example 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 90:5:5 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.

[0099] The positive and negative electrodes prepared as described above were placed facing 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.

[0100] Thereafter, the electrolyte solutions for lithium secondary batteries according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 4 were charged into the case to manufacture coin cells according to Examples 1 to 4 and Comparative Examples 1 to 4.

[0101] The coin cell manufactured by the above method was discharged and charged twice at a current density of 0.1C at 25°C, and then the life cycle was measured at the point where the capacity retention rate was 80% while proceeding for 200 cycles at a current density of 0.3C / 0.5C to confirm the life characteristics of the battery. At this time, the discharge proceeded to an upper limit voltage of 1.8V (vs. Li / Li+), and the charge proceeded at an upper limit voltage of 2.5V (vs. Li / Li+). The results obtained are shown in Table 1 and Figure 1.

[0102] [Table 2]

[0103] As shown in Table 2, it was confirmed that the lithium-sulfur secondary batteries using the electrolytes for lithium secondary batteries according to Examples 1 to 4 had better battery life characteristics than the lithium-sulfur secondary batteries using the electrolytes for lithium secondary batteries according to Comparative Examples 1 to 4. Specifically, it was confirmed that the lithium-sulfur secondary battery according to the present invention uses the electrolytes for lithium-sulfur secondary batteries according to Examples 1 to 4, in which the content of the benzo-dioxole-based compound or benzo-dioxane-based compound represented by Chemical Formula 1-1 or Chemical Formula 1-2 in a non-aqueous solvent is 0.1 wt % to 3 wt %, forming a stable SEI (Solid-Electrolyte Interphase) film on the lithium anode and suppressing the reaction between lithium and polysulfide and decomposition of the electrolyte, thereby improving the battery life characteristics.

[0104] On the other hand, when no benzo-dioxole or benzo-dioxane compound was included (Comparative Example 1) or when an excessively large amount of the 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 benzo-dioxole-based compound (Comparative Compound A) having an electron withdrawing group was used as an additive (Comparative Example 4), it was confirmed that the life characteristics were significantly decreased.

[0105] Considering this, when the electrolyte for a lithium secondary battery containing the benzo-dioxole-based compound or benzo-dioxane-based compound according to the present invention is used, the life characteristics of the battery are improved compared to conventional lithium secondary batteries.

[0106] Any mere variations or modifications of the present invention belong to the scope of the present invention, and the specific protection scope of the present invention will be defined by the appended claims.

Claims

1. An electrolyte for a lithium-sulfur secondary battery comprising a lithium salt, a non-aqueous solvent, and an additive, The additive includes a benzo-dioxole-based compound or a benzo-dioxane-based compound, The benzo-dioxole-based compound or the benzo-dioxane-based compound has a hydrogen or an electron donating group at a carbon position between two oxygen atoms, The benzo-dioxole-based compound or benzo-dioxane-based compound is a compound represented by the following formula 1: 【Chemistry 1】 In the above Chemical Formula 1, R is hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 10 carbon atoms, or a substituted or unsubstituted heteroaryl group having 5 to 10 carbon atoms; the plurality of Ra's are the same or different and are each independently selected from the group consisting of hydrogen, an amino group, an alkylamino group having 1 to 10 carbon atoms, a dialkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 10 carbon atoms, a diarylamino group having 12 to 20 carbon atoms, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an amide group having 2 to 10 carbon atoms, and an ester group having 2 to 10 carbon atoms; wherein n is an integer from 1 to 3; the non-aqueous solvent comprises a linear ether and a cyclic ether; The electrolyte for a lithium-sulfur secondary battery is characterized in that the content of the benzo-dioxole-based compound or the benzo-dioxane-based compound is 0.1% by weight or more and less than 10% by weight based on the total weight of the electrolyte.

2. The electrolyte for a lithium-sulfur secondary battery according to claim 1, wherein the compound represented by Formula 1 is a compound represented by Formula 1-1 or 1-2: 【Chemistry 2】

3. 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 carboxylates.

4. 2. The electrolyte for a lithium-sulfur secondary battery according to claim 1, 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 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, and ethylene glycol ethyl methyl ether.

5. The electrolyte for a lithium-sulfur secondary battery according to claim 1, characterized in that 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.

6. The electrolyte for a lithium-sulfur secondary battery according to claim 1, further comprising a nitric acid compound.

7. 7. The electrolyte for a lithium-sulfur secondary battery according to claim 6, wherein the nitric acid compound is 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.

8. The electrolyte solution according to any one of claims 1 to 7; positive electrode; A negative electrode; and A lithium-sulfur secondary battery comprising a separator.

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