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

Abstract

The present invention relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery comprising the same, the electrolyte comprising a lithium salt, a nonaqueous solvent, and a benzo-dimethan compound or a benzo-dioxolan compound substituted with hydrogen or an electron-donating group at a carbon position between two oxygen atoms.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0064492, filed on May 20, 2021, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the electrolyte. Background Technology

[0003] As the application of secondary batteries expands to electric vehicles (EVs) and energy storage devices (ESS), lithium-ion secondary batteries, with their relatively low energy storage density relative to weight (~250 Wh / kg), limit their application in these products. In contrast, lithium-sulfur secondary batteries are attracting attention as a next-generation secondary battery technology because they theoretically can achieve a high energy storage density relative to their weight (~2600 Wh / kg).

[0004] Lithium-sulfur secondary batteries are battery systems that use sulfur-sulfur materials with sulfur-sulfur bonds (SS bonds) as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, as the main material for the positive electrode active material, has the advantages of being abundant in resources worldwide, non-toxic, and having a low atomic weight.

[0005] In lithium-sulfur secondary batteries, during discharge, lithium, as the negative electrode active material, is oxidized while releasing electrons and thus becoming ionized, while sulfur, as the positive electrode active material, is reduced while accepting electrons. In this case, the lithium oxidation reaction is the process by which lithium metal releases electrons and transforms into lithium cations. Furthermore, the sulfur reduction reaction is the process by which the S-S bond accepts two electrons and transforms into sulfide anions. The lithium cations generated from the lithium oxidation reaction are transferred to the positive electrode via the electrolyte and combine with the sulfide anions generated through the sulfur reduction reaction to form a salt. Specifically, before discharge, sulfur has a cyclic S8 structure, which is converted into lithium polysulfide (LiS) through a reduction reaction. x When lithium polysulfides are completely reduced, lithium sulfide (Li₂S) is formed.

[0006] Sulfur, as a positive electrode active material, suffers from low conductivity, making it difficult to ensure reactivity with electrons and lithium ions in the solid state. In existing lithium-sulfur secondary batteries, Li₂S is generated to improve the reactivity of sulfur. x Intermediate polysulfides are used to induce liquid-phase reactions and improve reactivity. In this case, ether solvents with high solubility for lithium polysulfides, such as dioxolane and dimethoxyethane, are used as solvents for the electrolyte.

[0007] However, when using such ether solvents, the lifespan characteristics of lithium-sulfur batteries deteriorate due to various reasons. For example, the lifespan characteristics of lithium-sulfur batteries may deteriorate due to the following reasons: lithium polysulfides dissolving from the positive electrode, short circuits occurring due to dendrite growth on the lithium negative electrode, and accumulation of byproducts due to electrolyte decomposition.

[0008] In particular, when using such ether solvents, they can dissolve large amounts of lithium polysulfides, resulting in high reactivity. However, because lithium polysulfides are inherently soluble in electrolytes, the reactivity and lifetime characteristics of sulfur are affected by the electrolyte concentration.

[0009] Recently, in order to develop lithium-sulfur secondary batteries with energy densities of over 500 Wh / kg required for aircraft and next-generation electric vehicles, it is necessary to have a high sulfur loading in the electrodes and minimize the electrolyte content.

[0010] However, due to the characteristics of ether solvents, the following problems exist: as the electrolyte content decreases, the viscosity increases rapidly during charging / discharging, which may lead to increased overvoltage and battery degradation.

[0011] Therefore, research has been continuously conducted on the addition of additives to prevent electrolyte decomposition and ensure excellent lifespan characteristics. However, the components and composition of electrolytes that can prevent electrolyte decomposition and improve lifespan characteristics have not yet been clearly determined. In particular, the details of the components and composition of electrolytes suitable for pouch cells with very low electrolyte content are still unclear.

[0012] Existing technical documents

[0013] [Patent Literature]

[0014] (Patent Document 1) Korean Patent Publication No. 10-2007-0027512 (March 9, 2007), "Electrolyte for Lithium-Sulfur Electrochemical Batteries" Summary of the Invention

[0015] [Technical Issues]

[0016] Therefore, it has been confirmed in this invention that, in order to prevent electrolyte decomposition in lithium secondary batteries and improve lifespan characteristics, in the case of lithium secondary battery electrolytes containing lithium salts and non-aqueous solvents, benzo[a]bis(II) is introduced as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds solve the above-mentioned problems and can improve the performance of the lithium secondary battery, thus completing the present invention.

[0017] Therefore, one object of the present invention is to provide an electrolyte for lithium secondary batteries that prevents electrolyte decomposition and forms a stable film at the interface of the negative electrode, thereby preventing the degradation of the electrolyte and the negative electrode, and thus improving the lifespan characteristics of the electrolyte for lithium secondary batteries. Furthermore, another object of the present invention is to provide a lithium secondary battery that exhibits improved performance by providing the aforementioned electrolyte.

[0018] [Technical Solution]

[0019] To achieve the above objectives, the present invention provides an electrolyte for lithium secondary batteries, wherein the electrolyte contains lithium salt and a non-aqueous solvent, and further contains benzo[a]pyrene as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds. In particular, the present invention provides an electrolyte for lithium secondary batteries, wherein the electrolyte further comprises benzo[a]di[a] as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds, wherein the benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds have hydrogen or electron-donating groups at the carbon position between the two oxygen atoms.

[0020] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the benzo[a]bis(2,3-di ... Magnoliopsinoids or benzo[a]2 Alkane compounds are those represented by the following chemical formula 1:

[0021] [Chemical Formula 1]

[0022]

[0023] in,

[0024] The R group 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.

[0025] The multiple Ra groups in Formula 1 may be the same as or different from each other, and each independently represents hydrogen or an electron-donating group.

[0026] n is an integer from 1 to 3.

[0027] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the plurality of Ra groups in chemical formula 1 are the same or different from each other, and each is independently a substituent having a Hammet substituent constant of less than 0.

[0028] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the plurality of Ra groups in Formula 1 are identical or different from each other, and each is independently selected from the group consisting of: hydrogen, amino groups, alkylamino groups having 1 to 10 carbon atoms, dialkylamino groups having 2 to 20 carbon atoms, arylamino groups having 6 to 10 carbon atoms, diarylamino groups having 12 to 20 carbon atoms, hydroxyl groups, alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, amide groups having 1 to 10 carbon atoms, ester groups having 1 to 10 carbon atoms, allyl groups, alkylallyl groups having 1 to 10 carbon atoms, and dialkylallyl groups having 2 to 20 carbon atoms.

[0029] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the compound represented by chemical formula 1 is a compound represented by chemical formula 1-1 or chemical formula 1-2.

[0030] [Chemical Formula 1-1]

[0031]

[0032] [Chemical Formula 1-2]

[0033]

[0034] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the lithium salt is at least one selected from the group consisting of: 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 carboxylic acids lithium.

[0035] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the non-aqueous solvent comprises linear ethers and cyclic ethers.

[0036] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the linear ether is at least one 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, butanediol 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.

[0037] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the cyclic ether is selected from the group consisting of: dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, ... Alkane, di Alkane, trialkyl Alkane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and 2-methylfuran.

[0038] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein, based on the total weight of the electrolyte, the benzo[i]pyrene... Magnoliopsinoids or benzo[a]2 The content of alkane compounds is from 0.1% to 10% by weight.

[0039] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the electrolyte for lithium secondary batteries further contains nitrate compounds.

[0040] Furthermore, the present invention provides an electrolyte for lithium secondary batteries, wherein the nitrate compound is at least one selected from the group consisting of: lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, methyl nitrate, and dialkylimidazolium nitrate. guanidine nitrate, imidazole nitrate and pyridine nitrate

[0041] In addition, the present invention provides a lithium secondary battery, which includes the above-mentioned electrolyte, positive electrode, negative electrode and separator.

[0042] Furthermore, the present invention provides a lithium secondary battery, wherein the lithium secondary battery is a lithium-sulfur secondary battery.

[0043] Beneficial effects

[0044] The electrolyte for lithium secondary batteries according to the present invention comprises a lithium salt and a non-aqueous solvent, and further comprises benzo[a]pyrene as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds are used to prevent the electrolyte from decomposing during the operation of the lithium secondary battery and to form a stable film at the interface of the negative electrode to prevent the degradation of the electrolyte and the negative electrode, thereby exhibiting the effect of improving lifespan characteristics. Attached Figure Description

[0045] Figure 1 The graph shows the life characteristics of lithium secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention.

[0046] Figure 2 This is a graph showing the lifespan characteristics of the lithium secondary batteries of Embodiment 1 and Comparative Example 3 according to the present invention.

[0047] Figure 3 The graph shows the lifespan characteristics of lithium secondary batteries according to Embodiments 1 and 4 and Comparative Examples 1 and 4 of the present invention. Detailed Implementation

[0048] The embodiments provided by the present invention can all be implemented through the following description. It should be understood that the following description is intended to depict preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0049] This invention provides an electrolyte for lithium secondary batteries, the electrolyte containing lithium salt and a non-aqueous solvent, and further containing benzo[a]pyrene as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds. In particular, the present invention provides an electrolyte for lithium secondary batteries containing lithium salts and non-aqueous solvents, said electrolyte further comprising benzo[a]di[a] as an additive. Magnoliopsinoids or benzo[a]2 Alkane compounds, wherein the benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds have hydrogen or electron-donating groups at the carbon position between the two oxygen atoms.

[0050] According to the benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds increase electron density by replacing the low electron density carbon positions between two oxygen atoms with electron-donating groups, thereby reducing their reactivity with polysulfides. This suppresses the loss of positive electrode active material and prevents a sharp decline in battery capacity. As a result, the lifespan characteristics of lithium secondary batteries can be improved.

[0051] In this regard, a problem with conventional lithium-sulfur secondary batteries is that the dissolved lithium polysulfides react chemically with the electrolyte components, leading to the loss of the positive electrode active material and a sharp decrease in battery capacity. In particular, because these polysulfides are nucleophilic, they readily react with electrophilic materials with low electron density, thereby causing benzo[a]bismuth substituents to react with the electrolyte. Magnoliopsinoids or benzo[a]2 The carbon position between the two oxygen atoms in alkane compounds has a low electron density due to the two electron-attracting oxygen atoms, thus exhibiting high reactivity with polysulfides. Conversely, according to the invention, the benzo[a]di[a] is wherein the carbon atom between the two oxygen atoms is substituted with hydrogen or an electron-donating group. Magnolioplasminates or the benzo[a]di[a] Alkane compounds have increased electron density due to their electron-donating groups, resulting in low reactivity with polysulfides. This prevents the loss of the positive electrode active material. On the other hand, if the benzo[a]di[a]... Magnolioplasminates or the benzo[a]di[a] When an electron-withdrawing group is replaced at the carbon atom between two oxygen atoms in an alkane compound, the electron density decreases and the reactivity with polysulfides increases, resulting in increased loss of the positive electrode active material.

[0052] Therefore, in the benzo[a]di according to the present invention Magnoliopsinoids or benzo[a]2 In alkane compounds, more preferably, hydrogen or electron-donating groups are present in the benzo[a]di[a]benzene[b]ene ... Magnolioplasminates or the benzo[a]di[a] Substitution at the carbon atom between two oxygen atoms in alkane compounds.

[0053] According to the benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds can be compounds represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055]

[0056] in,

[0057] The R group 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.

[0058] The multiple Ra groups in Formula 1 may be the same as or different from each other, and each independently represents hydrogen or an electron-donating group.

[0059] n is an integer from 1 to 3.

[0060] Furthermore, in the compounds represented by Formula 1 according to the present invention, the plurality of Ra groups may be the same as or different from each other, and each may independently be a substituent having a Hammett substituent constant of less than 0. Specific examples may be selected from the group consisting of: hydrogen, amino groups, alkylamino groups having 1 to 10 carbon atoms, dialkylamino groups having 2 to 20 carbon atoms, arylamino groups having 6 to 10 carbon atoms, diarylamino groups having 12 to 20 carbon atoms, hydroxyl groups, alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, amide groups having 1 to 10 carbon atoms, ester groups having 1 to 10 carbon atoms, allyl groups, alkylallyl groups having 1 to 10 carbon atoms, and dialkylallyl groups having 2 to 20 carbon atoms, preferably selected from... The group consisting of: hydrogen, amino group, alkylamino group having 1 to 6 carbon atoms, dialkylamino group having 2 to 12 carbon atoms, arylamino group having 6 to 10 carbon atoms, diarylamino group having 12 to 20 carbon atoms, hydroxyl group, alkyl group having 1 to 6 carbon atoms, aryl group having 6 to 10 carbon atoms, alkoxy group having 1 to 6 carbon atoms, amide group having 1 to 6 carbon atoms, ester group having 1 to 6 carbon atoms, allyl group, alkylallyl group having 1 to 6 carbon atoms, and dialkylallyl group having 2 to 12 carbon atoms, more preferably hydrogen or alkyl group having 1 to 6 carbon atoms.

[0061] Furthermore, the compounds represented by chemical formula 1 according to the present invention can be compounds represented by chemical formula 1-1 or chemical formula 1-2.

[0062] [Chemical Formula 1-1]

[0063]

[0064] [Chemical Formula 1-2]

[0065]

[0066] Based on the total weight of the electrolyte, according to the present invention, benzo[a]bis[a] Magnoliopsinoids or benzo[a]2 The content of alkane compounds can be from 0.1% to 10% by weight, preferably from 0.1% to 5% by weight, more preferably from 0.1% to 3% by weight. If the benzo[a]di[a] is... Magnoliopsinoids or benzo[a]2 If the content of alkane compounds is below the above range, the effect of forming a film (solid electrolyte interface, SEI) on the electrode surface is not significant, thus the effect of improving lifetime characteristics is insufficient. If the benzo[a]di[a] is present... Magnoliopsinoids or benzo[a]2 If the content of alkane compounds exceeds the above range, there may be a problem of increased electrical resistance due to excessive additives. Therefore, it is preferable that the benzo[a]di[a] is [a]-[a]-[b]-[c ... Magnoliopsinoids or benzo[a]2 The content of alkane compounds preferably meets the above-mentioned range.

[0067] On the other hand, the electrolyte for lithium secondary batteries of the present invention may contain lithium salts and non-aqueous solvents, and the lithium salts are materials readily soluble in non-aqueous organic solvents, and may be selected from the group consisting of: 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 carboxylic acids, with LiN(CF3SO2)2 being preferred.

[0068] The concentration of the lithium salt can be from 0.2 to 2 M, specifically from 0.5 to 1.8 M, and more specifically from 0.6 to 1.7 M, 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 charging and discharging conditions of the battery, the operating temperature, and other factors known in the field of lithium batteries. If the concentration of the lithium salt is below the above range, the conductivity of the electrolyte may decrease, thereby potentially degrading the performance of the electrolyte. If the concentration of the lithium salt exceeds the above range, the viscosity of the electrolyte may increase, thereby potentially reducing the conductivity of lithium ions (Li). + The mobility of ) may decrease.

[0069] The non-aqueous solvents according to the present invention may include ether solvents and non-solvents, and the ether solvents may include linear ethers and cyclic ethers.

[0070] 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 dimethylene ether, butanediol 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. Preferably, dimethoxyethane may be used.

[0071] The cyclic ether may be selected from the group consisting of: dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, etc. Alkane, di Alkane, trialkyl Alkane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan and 2-methylfuran, preferably, 2-methylfuran can be used.

[0072] The volume ratio of the linear ether to the cyclic ether can be from 9:1 to 1:9, preferably from 8:2 to 2:8, and more preferably from 7:3 to 5:5.

[0073] If the volume ratio of linear ether to cyclic ether exceeds the above range, the effect of improving battery life characteristics will be insufficient, and the desired effect cannot be obtained. Therefore, it is preferable that the volume ratio of linear ether to cyclic ether satisfies the above range.

[0074] The electrolyte for lithium secondary batteries of the present invention may further contain nitric acid or nitrite compounds as additives. The nitric acid or nitrite compounds have the effect of forming a stable coating on the lithium electrode and improving charging / discharging efficiency. The nitric acid or nitrite compounds may be, but are not limited to, at least 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 and dialkylimidazolium nitrate. guanidine nitrate, imidazole nitrate Pyridine Nitrate Ethyl nitrite, propyl nitrite, butyl nitrite, amyl nitrite, octyl nitrite; organic nitro compounds such as nitromethane, nitrobenzene, nitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof. Preferably, lithium nitrate (LiNO3) may be used.

[0075] Furthermore, to improve charging / discharging characteristics, flame retardancy, etc., the electrolyte for lithium secondary batteries of the present invention may also contain other additives. Examples of such additives may include pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted... Zyzolidinediones, N,N-substituted imidazolidinedions, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propylene sulpholactone (PRS), vinylene carbonate (VC), etc.

[0076] The preparation method of the electrolyte for lithium secondary batteries of the present invention is not particularly limited in the present invention, and can be prepared by conventional methods known in the art.

[0077] The present invention provides a lithium secondary battery, wherein the lithium secondary battery comprises the above-mentioned electrolyte for lithium secondary batteries.

[0078] The lithium secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte inserted between the positive electrode and the negative electrode, and may include the electrolyte for lithium secondary batteries according to the present invention.

[0079] In one embodiment, the lithium secondary battery may be a lithium-sulfur secondary battery.

[0080] The positive electrode may include a positive electrode current collector and a positive electrode active material applied to one or both surfaces of the positive electrode current collector.

[0081] The positive electrode current collector is used to support the positive electrode active material, and there are no particular restrictions as long as it has high conductivity and does not cause chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon, copper or stainless steel with surface treatments of carbon, nickel, silver, etc., and aluminum-cadmium alloys can be used.

[0082] The positive current collector may have fine irregularities formed on its surface to enhance the bonding force with the positive active material, and may be formed in various forms, such as membrane, sheet, foil, mesh, net, porous body, foam, non-woven fabric, etc.

[0083] The positive electrode active material layer may include a positive electrode active material and optionally a conductive material and an adhesive.

[0084] The positive electrode active material may be at least one selected from the group consisting of: elemental sulfur (S8); Li2S n (n≥1), organic sulfur compounds or carbon-sulfur polymers (C2S) x ) n (x = 2.5–50, n ≥ 2). Preferably, inorganic sulfur (S8) can be used.

[0085] In addition to the positive electrode active material, the positive electrode may also contain at least one additive selected from the following: transition metal elements, group II elements, group III elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0086] The transition metal elements may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, Hg, etc.; the group II elements may include Al, Ga, In, Ti, etc.; and the group III elements may include Ge, Sn, Pb, etc.

[0087] The conductive material is intended to improve conductivity, and there are no particular limitations as long as it is a conductive material that does not cause chemical changes in the lithium secondary battery. Typically, carbon black, graphite, carbon fiber, carbon nanotubes, metal powders, conductive metal oxides, organic conductive materials, etc., can be used. Currently, commercially available conductive materials include acetylene black series (from Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (from Armak), Vulcan XC-72 (from Cabot Company), and Super P (from MMM). For example, acetylene black, carbon black, graphite, etc., can be used.

[0088] Furthermore, the positive electrode active material layer may also include an adhesive that functions to hold the positive electrode active material on the positive electrode current collector and to connect the active materials. As the adhesive, various types of adhesives can be used, such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc.

[0089] As the positive electrode, a positive electrode with a high sulfur loading can be used. The sulfur loading can be 3.0 mAh / cm³. 2 The preferred value is 4.0mAh / cm³. 2The above is preferred, with 5.0 mAh / cm³ being even better. 2 above.

[0090] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

[0091] The negative electrode current collector is used to support the negative electrode active material, and there are no particular restrictions as long as it has excellent conductivity and is electrochemically stable within the voltage range of the lithium secondary battery. For example, it can be made of copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon; or copper or stainless steel with surface treatment of carbon, nickel, silver, etc.; or aluminum-cadmium alloy, etc.

[0092] The negative electrode current collector can enhance its bonding force with the negative electrode active material by having fine irregularities on its surface, and can be formed in various forms such as film, sheet, foil, mesh, net, porous body, foam or non-woven fabric.

[0093] The negative electrode active material may include: materials capable of reversibly inserting or de-intercalating lithium ions (Li... + Materials capable of reacting with lithium ions to reversibly form lithium-containing compounds; lithium metal or lithium alloys. The reversibly intercalating or deintercalating lithium ions (Li...) + The material can be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reacting with lithium ions (Li...) + The material used to reversibly form a lithium-containing compound in the reaction can be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy can 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 can be lithium metal, and specifically in the form of a lithium metal film or lithium metal powder.

[0094] The method for forming the negative electrode active material layer is not particularly limited, and methods commonly used in the art for forming layers or films can be used. For example, methods such as compression, coating, or deposition can be used. Furthermore, the negative electrode of the present invention also includes cases in which a thin film of metallic lithium is formed on a metal plate by initial charging after assembling the battery in a state where there is no lithium film in the current collector.

[0095] The separator is used to physically separate the positive and negative electrodes in the lithium secondary battery of the present invention, and can be used without any particular limitation, as long as it is generally used as a separator in a lithium secondary battery. In particular, it is preferred as long as the separator has low resistance to ion migration in the electrolyte and excellent impregnation ability of the electrolyte.

[0096] The diaphragm can be made of a porous substrate. Any porous substrate can be used, as long as it is a porous substrate commonly used in electrochemical devices, such as polyolefin porous membranes or nonwoven fabrics, but is not particularly limited thereto.

[0097] Examples of the polyolefin porous membranes may be membranes formed from any polymer selected from the following, either alone or from mixtures thereof: polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene; and polyolefin polymers such as polypropylene, polybutene, and polypentene.

[0098] In addition to the aforementioned polyolefin nonwoven fabrics, the nonwoven fabric may be formed from any polymer selected alone or from mixtures thereof: polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, etc. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

[0099] The thickness of the porous substrate is not particularly limited, but can be 1 to 100 μm, preferably 5 to 50 μm.

[0100] There are no particular limitations on the size and porosity of the pores present in the porous substrate, but they can be from 0.001 μm to 50 μm and from 10% to 95%, respectively.

[0101] The electrolyte contains lithium ions and serves as a medium for inducing electrochemical oxidation or reduction reactions between the positive and negative electrodes, as described above.

[0102] The injection of the electrolyte can be performed at an appropriate stage of the manufacturing process of the electrochemical device, depending on the manufacturing method of the final product and the required performance. That is, it can be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

[0103] In the case of the lithium secondary battery according to the present invention, in addition to the winding process, which is a normal process, the lamination or stacking and folding processes of the separator and the electrode can also be performed.

[0104] The shape of the lithium secondary battery is not particularly limited, and it can have various shapes such as cylindrical, laminated, or coin-shaped.

[0105] Modes for implementing inventions

[0106] Preferred embodiments are provided below to aid in understanding the invention, but the following embodiments are provided to make the invention more readily understood, and the invention is not limited thereto.

[0107] Example

[0108] Preparation of electrolyte for lithium secondary batteries

[0109] Preparation Example 1

[0110] Lithium bis(fluoromethanesulfonyl)imide (LiFSI) was dissolved in a non-aqueous solvent obtained by mixing 2-methylfuran and 1,2-dimethoxyethane (DME) in a volume ratio of 3:7 to achieve a concentration of 0.75 M (mol / L). Lithium nitrate (LiNO3) was added at 3.0 wt% based on the total weight of the electrolyte, followed by benzo[a]pyrene, represented by the following chemical formula 1-1, at 1 wt% based on the total weight of the electrolyte. Magnoliopsin compounds are used to prepare electrolytes for lithium secondary batteries.

[0111] [Chemical Formula 1-1]

[0112]

[0113] Preparation Example 2

[0114] Except for the addition of benzo[a]2, represented by chemical formula 1-1, in an amount of 0.1% by weight. In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0115] Preparation Example 3

[0116] In addition to adding benzo[a]di, represented by chemical formula 1-1, in an amount of 3.0% by weight. In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0117] Preparation Example 4

[0118] Except for benzo[a]2 represented by the following chemical formulas 1-2 Alkane compounds replace benzo[a]di, represented by chemical formula 1-1. In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0119] [Chemical Formula 1-2]

[0120]

[0121] Comparative Preparation Example 1

[0122] Except for the absence of benzo[a]di, represented by chemical formula 1-1 In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0123] Comparative Preparation Example 2

[0124] In addition to adding benzo[a]di, represented by chemical formula 1-1, in an amount of 10% by weight. In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0125] Comparative Preparation Example 3

[0126] The electrolyte for lithium secondary batteries was prepared in the same manner as in Preparation Example 1, except that the non-aqueous solvent obtained by mixing ethylene carbonate (EC): diethyl carbonate (DEC) in a 1:1 volume ratio was used instead of the non-aqueous solvent obtained by mixing 2-methylfuran: 1,2-dimethoxyethane (DME) in a 3:7 volume ratio.

[0127] Comparative preparation example 4

[0128] In addition to comparing compound A (2,2-fluoro-1,3-benzodi) with the following compound... (Mao) replaces benzo[i] (represented by chemical formula 1-1) In addition to cyclohexene compounds, electrolytes for lithium secondary batteries were prepared in the same manner as in Preparation Example 1.

[0129] [Compare compound A]

[0130]

[0131] The non-aqueous solvent and benzo[a]di[a]ene[a]ene[b ... Magnoliopsinoids or benzo[a]2 The contents of alkane compounds are shown in Table 1 below.

[0132] Table 1:

[0133]

[0134] Experimental Example: Evaluation of Lifetime Characteristics

[0135] A slurry of the positive electrode active material was prepared by mixing sulfur with a conductive material and a binder in acetonitrile using a ball mill. Carbon black was used as the conductive material, and a mixture of SBR and CMC binder was used as the binder, with a mixing ratio of sulfur:conductive material:binder weight ratio of 90:5:5. The slurry of the positive electrode active material was then subjected to a process at 5.0 mAh / cm³. 2 The loading was applied to an aluminum current collector and then dried to prepare a positive electrode with a porosity of 68%. Additionally, a 45 μm thick layer of lithium metal was used as the negative electrode.

[0136] After placing the positive electrode and the negative electrode prepared by the above method facing each other, a polyethylene diaphragm with a thickness of 20 μm and a porosity of 45% is inserted between the positive electrode and the negative electrode.

[0137] Subsequently, the electrolytes for lithium secondary batteries prepared according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 4 were injected into the casing to manufacture the coin batteries of Examples 1 to 4 and Comparative Examples 1 to 4.

[0138] The coin cell battery prepared by the above method was repeatedly discharged and charged twice at a current density of 0.1C at 25°C, and then cycled 200 times at a current density of 0.3C / 0.5C. The battery's life cycle characteristics were confirmed by measuring the battery's capacity retention at 80%. At this point, it was discharged to 1.8V (relative to Li / Li). + The lower limit voltage is 2.5V (relative to Li / Li). + The device is charged to its upper limit voltage. The results obtained at this time are shown in Table 2 and... Figure 1 middle.

[0139] Table 2:

[0140]

[0141] As shown in Table 2 above, it has been confirmed that the lithium secondary battery using the electrolyte for lithium secondary batteries according to Examples 1 to 4 exhibits superior lifespan characteristics compared to the lithium secondary battery using the electrolyte for lithium secondary batteries according to Comparative Examples 1 to 4. Specifically, it can be confirmed that the use of benzo[a]bis(benzo[b])represented by chemical formula 1-1 or 1-2... Magnoliopsinoids or benzo[a]2 The lithium secondary battery electrolyte according to Examples 1 to 4 contains 0.1% to 3% by weight of alkane compounds in a non-aqueous solvent. The lithium secondary battery according to the present invention forms a stable SEI (solid electrolyte interface) film on the lithium anode, thereby suppressing the reaction between lithium and polysulfides and the decomposition of the electrolyte, thereby exhibiting the effect of improving the battery life characteristics.

[0142] On the other hand, if it does not contain benzo[a]2 Magnoliopsinoids or benzo[a]2 No improvement in lifetime characteristics was observed when alkane compounds were used (Comparative Example 1) or in excess (Comparative Example 2). Furthermore, it was confirmed that the use of carbonate solvents as non-aqueous solvents (Comparative Example 3) and the use of benzo[a]benzene with electron-withdrawing groups also resulted in improvements. When a cyclohexene compound (comparative compound A) is used as an additive (comparative example 4), the lifetime characteristics are significantly degraded.

[0143] When these points are taken into account, if the benzo[a]di-containing compound according to the present invention is used Magnoliopsinoids or benzo[a]2 Alkane-based electrolytes for lithium secondary batteries improve battery life characteristics compared to conventional lithium secondary batteries.

[0144] All simple modifications and variations of this invention fall within the scope of this invention, and the specific scope of protection of this invention will become apparent from the appended claims.

Claims

1. An electrolyte for lithium-sulfur secondary batteries, said electrolyte comprising a lithium salt, a non-aqueous solvent, and additives. The additive mentioned above contains benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds, The benzo[a]2 Magnoliopsinoids or benzo[a]2 Alkane compounds have a hydrogen atom or an electron-donating group at the carbon position between two oxygen atoms, and The non-aqueous solvents include linear ethers and cyclic ethers. Wherein, based on the total weight of the electrolyte, the benzo[a]di Magnoliopsinoids or benzo[a]2 The content of alkane compounds is from 0.1% to 5% by weight. The benzo[a]di Magnoliopsinoids or benzo[a]2 Alkane compounds are those represented by the following chemical formula 1: [Chemical Formula 1] in, The R group 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 groups in Formula 1 may be the same as or different from each other, and each independently represents hydrogen or an electron-donating group. n is an integer from 1 to 3. or The benzo[a]2 Magnoliopsinoids or benzo[a]2 Alkane compounds are compounds represented by the following chemical formulas 1-1 or 1-2: [Chemical Formula 1-1] [Chemical Formula 1-2] 。 2. The electrolyte for lithium-sulfur secondary batteries according to claim 1, wherein the plurality of Ra groups are the same or different from each other, and each is independently a substituent having a Hammett substituent constant of less than 0.

3. The electrolyte for lithium-sulfur secondary batteries according to claim 1, wherein the plurality of Ra groups are the same or different from each other, and each is independently selected from the group consisting of: hydrogen, amino groups, alkylamino groups having 1 to 10 carbon atoms, dialkylamino groups having 2 to 20 carbon atoms, arylamino groups having 6 to 10 carbon atoms, diarylamino groups having 12 to 20 carbon atoms, hydroxyl groups, alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, amide groups having 1 to 10 carbon atoms, ester groups having 1 to 10 carbon atoms, allyl groups, alkylallyl groups having 1 to 10 carbon atoms, and dialkylallyl groups having 2 to 20 carbon atoms.

4. The electrolyte for lithium-sulfur secondary batteries according to claim 1, wherein the lithium salt is at least one selected from the group consisting of: 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 carboxylic acids lithium.

5. The electrolyte for lithium-sulfur secondary batteries according to claim 4, 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, butanediol 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.

6. The electrolyte for lithium-sulfur secondary batteries according to claim 4, wherein the cyclic ether is selected from the group consisting of: dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, ... Alkane, di Alkane, trialkyl Alkane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, dihydropyran, tetrahydropyran, furan, and 2-methylfuran.

7. The electrolyte for lithium-sulfur secondary batteries according to claim 1 further comprises nitrate compounds.

8. The electrolyte for lithium-sulfur secondary batteries according to claim 7, wherein the nitrate compound is at least one selected from the group consisting of: lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, methyl nitrate, and dialkylimidazolium nitrate. guanidine nitrate, imidazole nitrate and pyridine nitrate .

9. A lithium-sulfur secondary battery, the lithium-sulfur secondary battery comprising: an electrolyte according to any one of claims 1 to 8; a positive electrode; a negative electrode; and a separator.

Images