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

Abstract

The present disclosure relates to an electrolyte for a lithium-sulfur battery comprising a Lewis acidic additive comprising cations having a higher Lewis acidity than lithium ions. The composition inhibits the dissolution of polysulfide into the electrolyte, improves the ionic conductivity of the electrolyte, and improves the sulfur utilization rate, thereby providing the beneficial effect of stable operation of the lithium-sulfur battery with poor electrolyte and high capacity.

Description

Technical Field

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

[0002] This application claims priority to Korean Patent Application No. 2023-0046347 filed in Korea on April 7, 2023, the disclosure of which is incorporated herein by reference. Background Art

[0003] Lithium-sulfur battery is a battery system that uses a sulfur-sulfur (SS) bonded sulfur-based material as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main component of the positive electrode active material, is abundant in nature, can be found worldwide, is non-toxic, and has a low atomic weight.

[0004] As secondary batteries are used in a wide range of applications including electric vehicles (EVs) and energy storage systems (ESSs), lithium-sulfur battery technology, which can theoretically achieve a higher gravimetric energy storage density (~2,600Wh / kg) than lithium-ion secondary batteries with a lower gravimetric energy storage density (~250Wh / kg), has attracted attention.

[0005] During the discharge process, the lithium-sulfur battery is oxidized at the lithium as the negative electrode active material, and becomes a lithium cation by releasing electrons, and is reduced at the sulfur-based material as the positive electrode active material to accept electrons. Through the reduction reaction, the sulfur-based material accepts two electrons from the SS bond and is converted into a sulfur anion. The lithium cation generated by the oxidation reaction of lithium migrates to the positive electrode through the electrolyte and combines with the sulfur anion generated by the reduction reaction of the sulfur-based compound to form a salt. Specifically, the sulfur before discharge has a cyclic S8 structure and is converted into lithium polysulfide (LiS) by the reduction reaction. x ) and is completely reduced to lithium sulfide (Li2S).

[0006] In this case, the discharge capacity of the lithium-sulfur battery is lower than the theoretical capacity due to the accumulation of lithium sulfide on the electrode surface of the lithium-sulfur battery. In particular, in order to commercialize the lithium-sulfur battery, when the content of lithium salt in the electrolyte or the content of the electrolyte used in the battery is reduced, the side reaction of lithium polysulfide continues to occur on the lithium negative electrode, resulting in corrosion of the negative electrode and a decrease in life performance.

[0007] Specifically, as the content of the electrolyte used in the battery decreases, the concentration of lithium polysulfide dissolved in the electrolyte rises sharply and reaches a saturation concentration. In this case, due to the high concentration of lithium polysulfide in the electrolyte, the lithium negative electrode continues to undergo side reactions that intensify corrosion. In addition, as a smaller amount of electrolyte is used, the shuttle effect, one of the chronic diseases of lithium-sulfur batteries, occurs more seriously, resulting in loss of active materials and decreased battery performance.

[0008] To solve this problem, many studies have been conducted on high-concentration lithium salts. When the lithium salt concentration is high, most of the solvent molecules participate in the solvation shell, resulting in low activity of the solvent and low solubility of polysulfides. It is reported that when the concentration of lithium salt increases, the volatility of the electrolyte decreases and the transport of lithium ions improves, resulting in good battery performance under poor electrolyte conditions. However, it has been reported that the high price and low ionic conductivity make it difficult to commercialize and operate at high currents.

[0009] Therefore, there is a continuing need for lithium-sulfur batteries that suppress the dissolution of polysulfides, improve the ionic conductivity of the electrolyte, maintain sulfur utilization at the cathode, and operate stably under lean electrolyte and high sulfur loading conditions. Summary of the invention

[0010] Technical issues

[0011] The present disclosure is directed to overcoming the passivation caused by lithium sulfide accumulation on electrodes used in lithium-sulfur batteries.

[0012] To this end, one aspect of the present disclosure is to provide an electrolyte for a lithium-sulfur battery, which is used to inhibit the dissolution of lithium polysulfide in the electrolyte.

[0013] Furthermore, one aspect of the present disclosure is to provide an electrolyte for a lithium-sulfur battery having a lower lithium salt concentration and a higher ion conductivity.

[0014] Furthermore, another aspect of the present disclosure is to provide a lithium-sulfur battery with lower electrolyte content and higher sulfur loading.

[0015] Technical Solution

[0016] In order to solve the above problems, according to one aspect of the present disclosure, an electrolyte for a lithium-sulfur battery according to the following embodiments is provided.

[0017] The electrolyte for a lithium-sulfur battery according to the first embodiment includes a lithium salt, a nitric acid compound, a nonaqueous solvent, and a Lewis acidic additive, wherein the Lewis acidic additive includes a Lewis acidity greater than that of lithium ions (Li + ) a salt of a high cation, and wherein the total concentration of the lithium salt, the nitric acid compound and the Lewis acidic additive is 2M or less.

[0018] According to the second embodiment, in the first embodiment, the total concentration of the lithium salt, the nitric acid compound, and the Lewis acidic additive may be 1.5 M or less.

[0019] According to a third embodiment, in the first or second embodiment, the Lewis acidic additive may include aluminum (Al) ions, magnesium (Mg) ions, calcium (Ca) ions, strontium (Sr) ions, barium (Ba) ions, or two or more thereof as the cations.

[0020] According to a fourth embodiment, in any one of the first to third embodiments, the Lewis acidic additive may include a calcium salt.

[0021] According to a fifth embodiment, in any one of the first to fourth embodiments, the Lewis acidic additive may include a fluorine-containing anion.

[0022] According to a sixth embodiment, in any one of the first to fifth embodiments, the Lewis acidic additive may include F - 、BF4 - PF6 - CF3SO3 - 、[(CF3SO2)2N] - 、[(FSO2)2N] - or two or more thereof as anions.

[0023] According to a seventh embodiment, in any one of the first to sixth embodiments, the concentration of the lithium salt in the lithium-sulfur battery electrolyte may be 2 M or less.

[0024] According to an eighth embodiment, in any one of the first to seventh embodiments, the concentration of the Lewis acidic additive in the lithium-sulfur battery electrolyte may be 0.3 M or less.

[0025] According to a ninth embodiment, in any one of the first to eighth embodiments, the concentration of the Lewis acidic additive in the lithium-sulfur battery electrolyte may be 0.01M to 0.1M.

[0026] According to a tenth embodiment, in any one of the first to ninth embodiments, the nonaqueous solvent may include an ether-based solvent.

[0027] According to an eleventh embodiment, in any one of the first to tenth embodiments, the nonaqueous solvent may include an ether solvent, and the volume of the ether solvent may be 60 volume % or more of the total volume of the nonaqueous solvent.

[0028] According to a twelfth embodiment, in any one of the first to eleventh embodiments, the nonaqueous solvent may consist of one type of ether-based solvent.

[0029] According to a thirteenth embodiment, in any one of the first to twelfth embodiments, the nonaqueous solvent may include a cyclic ether and an acyclic ether.

[0030] According to another aspect of the present disclosure, a lithium-sulfur battery of the following embodiment is provided.

[0031] A lithium-sulfur battery according to a fourteenth embodiment includes the electrolyte according to any one of the first to thirteenth embodiments, a positive electrode including inorganic sulfur (S8), a negative electrode, and a separator between the positive electrode and the negative electrode.

[0032] According to a fifteenth embodiment, in the fourteenth embodiment, the lithium-sulfur battery may have a solid electrolyte interface (SEI) layer including LiF on the negative electrode.

[0033] According to the sixteenth embodiment, in the fourteenth or fifteenth embodiment, the electrolyte / sulfur (El / S) ratio may be 7 μL / mg or less.

[0034] Beneficial Effects

[0035] The electrolyte for a lithium-sulfur battery according to one embodiment of the present disclosure can overcome the passivation caused by the accumulation of lithium sulfide on the negative electrode of the lithium-sulfur battery, thereby improving the operation stability of the lithium-sulfur battery.

[0036] In addition, the high-fluorine-content stable interface on the negative electrode of the lithium-sulfur battery can induce uniform lithium deposition and inhibit the decomposition of the electrolyte, thereby achieving higher coulombic efficiency and longer life of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the foregoing description, serve to provide a further understanding of the technical aspects of the present disclosure, and thus the present disclosure should not be construed as being limited to the accompanying drawings.

[0038] Figure 1 The life characteristics evaluation results of lithium-sulfur batteries using the electrolyte solutions of Comparative Example 1, Example 1, and Example 2 in this specification are shown.

[0039] Figure 2 The results of rate performance evaluation according to charge and discharge cycles in lithium-sulfur batteries using the electrolyte solutions of Comparative Examples 1 to 4, Example 1, and Example 2 in this specification are shown.

[0040] Figure 3 The elemental analysis results of the SEI layer on the negative electrode of the lithium-sulfur battery using the electrolyte solutions of Comparative Example 1 (without Ca(OTF)2) and Example 1 (with Ca(OTF)2) in this specification are shown.

[0041] Figure 4The elemental analysis results of the SEI layer on the negative electrode of the lithium-sulfur battery using the electrolyte solutions of Comparative Example 1 and Example 1 in this specification are shown.

[0042] Figure 5 The results of current measurement due to the shuttle effect using the electrolytes of Comparative Example 1 and Example 1 in this specification are shown.

[0043] Figure 6 In this specification, the results of electrolyte decomposition analysis and evaluation using the electrolytic solutions of Comparative Example 1 and Example 1 are shown.

[0044] Figure 7 The life characteristics evaluation results of lithium-sulfur batteries using the electrolyte solutions of Comparative Examples 1, 5, 6, and Examples 1 to 3 in this specification are shown.

[0045] Figure 8 The results of specific capacity evaluation according to charge and discharge cycles in lithium-sulfur batteries using the electrolyte solutions of Example 4 and Comparative Example 7 in this specification are shown.

[0046] Fig. 9 The charge and discharge curves of the first charge and discharge cycle in the lithium-sulfur battery using the electrolyte of Comparative Example 8 in this specification are shown.

[0047] Fig.10 The results of specific capacity evaluation according to charge and discharge cycles in the lithium-sulfur battery using the electrolyte solution of Example 5 in this specification are shown. DETAILED DESCRIPTION

[0048] Hereinafter, the present disclosure will be described in more detail.

[0049] It should be understood that the terms or words used in this specification and the appended claims should not be interpreted as limited to their usual and dictionary meanings, but should be interpreted with meanings and concepts consistent with the technical spirit of the present disclosure based on the principle of allowing the inventor to appropriately define the terms so as to be best interpreted.

[0050] The term "comprising" used in the present specification indicates the presence of the elements stated, but does not exclude the presence or addition of one or more other elements, unless the context clearly indicates otherwise.

[0051] Additionally, the terms "about" and "substantially" as used herein mean "equal to" or "substantially equal to" when taking into account manufacturing and material tolerances inherent in the circumstances being described, and are used to prevent unscrupulous infringers from taking unfair advantage of the present disclosure, where precise or absolute numbers are expressed to aid in understanding the present disclosure.

[0052] Throughout the specification, "A and / or B" means A or B or both A and B.

[0053] The term "polysulfide" as used herein encompasses "polysulfide ions (S x 2- , 1 < x ≤ 8)" and "lithium polysulfide (Li2S x or LiS x - , 1 < x ≤ 8)".

[0054] The present disclosure relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including the same.

[0055] An electrolyte for a lithium-sulfur battery according to one aspect of the present disclosure includes a lithium salt, a nitrate compound, a non-aqueous solvent, and a Lewis acidic additive. In particular, the total concentration of the lithium salt, the nitrate compound, and the Lewis acidic additive is 2 M or less.

[0056] The term "Lewis acidic additive" as used herein is defined as a salt containing a cation having a higher Lewis acidity than lithium ions (Li + ).

[0057] The definitions of acids and bases proposed by Gilbert Newton Lewis are known. According to the definitions, substances can be classified as Lewis acids or Lewis bases. Specifically, a "Lewis base" can be defined as a substance that provides a lone pair of electrons to a Lewis acid, and a "Lewis acid" can be defined as a substance that accepts a lone pair of electrons from a Lewis base.

[0058] More specifically, Lewis acids are a general term for chemical substances containing empty orbitals capable of accepting an electron pair from a Lewis base to form a Lewis adduct, and Lewis bases are a general term for chemical substances having filled orbitals containing an electron pair that can form a chemical bond with a Lewis acid to form a Lewis adduct.

[0059] In this specification, "Lewis acidity" is a quantitative index of the acceptance degree of a lone pair of electrons and can be measured by known methods for measuring Lewis acidity. Accordingly, "higher Lewis acidity" means a higher ability to accept a lone pair of electrons, for example, it can be represented by a lower energy level of the empty orbital capable of accepting a lone pair of electrons.

[0060] According to one embodiment of the present disclosure, since the Lewis acidic additive is a salt containing a cation having a higher Lewis acidity than lithium ions (Li + ), when the electrolyte for a lithium-sulfur battery includes a Lewis acidic additive, decomposition of the lithium salt caused by electrons (e - ) present in the electrolyte during the operation of the lithium-sulfur battery can be suppressed. Accordingly, an electrolyte with a low lithium salt content and high ionic conductivity during the operation of the lithium-sulfur battery can be provided, but the mechanism of the present disclosure is not limited thereto.

[0061] In one embodiment of the present disclosure, the cation of the Lewis acidic additive is in contact with the lithium ion (Li + ) can be determined, for example, by comparing the acid dissociation constants (Ka) of the conjugate bases of the cation and the lithium ion. The method of comparing acidity by comparing the acid dissociation constants is well known, and the smaller the pKa (-logKa), the stronger the acidity.

[0062] In one embodiment of the present disclosure, when the cation is represented by “M + ", the Lewis acidity between the cation and the lithium ion can be determined by the pKa value of the conjugate base MH of the cation and the lithium ion (Li + ) by comparing the pKa values ​​of its conjugate base (LiH).

[0063] Specifically, in one embodiment of the present disclosure, the Lewis acidic additive may include a cation whose conjugate base has a pKa value greater than the pKa value of the conjugate base of the lithium ion, LiH.

[0064] In one embodiment of the present disclosure, the Lewis acidic additive may include aluminum (Al) ions, magnesium (Mg) ions, calcium (Ca) ions, strontium (Sr) ions, barium (Ba) ions, or two or more thereof as cations.

[0065] In one embodiment of the present disclosure, the Lewis acidic additive may include calcium ions as cations. Specifically, the Lewis acidic additive may include a calcium salt.

[0066] In another embodiment of the present disclosure, the Lewis acidic additive may be a salt containing a known anion for the cation. The anion is not particularly limited and may include anions that do not hinder the purpose of the present disclosure when included in the electrolyte.

[0067] In one embodiment of the present disclosure, the anion of the Lewis acidic additive may include, for example, a halide, an alkyl, an alkoxide, an aryl, an aryloxide, an alkylate, a cyclopentadienyl, an acetylacetonate, an amide, a sulfonate, a sulfate, a borate, aluminate, an aluminoxide, a phosphate, an arsenide, an imide, or two or more thereof, but is not limited thereto.

[0068] In one embodiment of the present disclosure, the anion of the Lewis acidic additive may include a - , Cl - Br - ,I - , R- ,RO - , cyclopentadienyl (Cp), pentamethylcyclopentadienyl, R2N - , acetylacetonate (acac), hexafluoroacetylacetonate (hfac), CF3SO2O - (-OTf), RSO2O - ROSO2O - 、BF4 - BR4 - 、AlCl4 - PF6 - PR3F3 - 、AsF6 - 、NO3 - and SO4 - At least one of the group consisting of, but not limited to. Wherein, R represents an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, an aryloxy group, a halogenated alkyl group, a halogenated alkoxy group or a polymer.

[0069] In another embodiment of the present disclosure, the anion of the Lewis acidic additive may contain elemental fluorine. When the Lewis acidic additive contains anions containing elemental fluorine as anions, a solid electrolyte interface (SEI) layer may be quickly formed on the surface of the negative electrode. Specifically, when the Lewis acidic additive contains anions containing elemental fluorine as anions, elemental fluorine is present in the electrolyte containing the Lewis acidic additive, and during the operation of a lithium-sulfur battery using the electrolyte, an SEI layer containing elemental fluorine may be formed on the surface of the negative electrode. When the SEI layer containing elemental fluorine is formed on the surface of the negative electrode of the lithium-sulfur battery, it may induce uniform deposition of lithium on the negative electrode and mitigate degradation of the negative electrode during the operation of the lithium-sulfur battery, but the present disclosure is not limited thereto.

[0070] According to another embodiment of the present disclosure, the Lewis acidic additive may include the following as anions: - ), or an anion containing at least elemental fluorine and also containing a heterogeneous element, or both thereof.

[0071] In another embodiment of the present disclosure, the Lewis acidic additive may include, for example, F - 、BF4 - PF6 - CF3SO3 - (OTF - )、[(CF3SO2)2N] - (TFSI - )、[(FSO2)2N] - (FSI -) or two or more thereof as anions, but the present disclosure is not limited thereto.

[0072] In another embodiment of the present disclosure, the Lewis acidic additive may include, for example, AlF3, Al(BF4)3, Al(PF6)3, Al(CF3SO3)3, Al[(CF3SO2)2N]3, Al[(FSO2)2N]3, MgF2, Mg(BF4)2, Mg(PF6)2, Mg(CF3SO3)2, Mg[(CF3SO2)2N]2, Mg[(FSO2)2N]2, CaF2, Ca(BF4)2, Ca(PF6)2, Ca(CF3SO3)2, Ca[(CF3SO2)2N]2, Ca[(FSO2)2N]2, SrF2, Sr(BF4)2, Sr(PF6)2, Sr(CF3SO3)2, Sr[(CF3SO2)2N]2, Sr[(FSO2)2N]2, or two or more thereof, but are not limited thereto.

[0073] In another embodiment of the present disclosure, the Lewis acidic additive may include Ca(CF3SO3)2.

[0074] In one embodiment of the present disclosure, the lithium salt is not particularly limited and may include a lithium salt used as an electrolyte in an electrolyte of a lithium-sulfur battery. The lithium salt may include, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide or two or more thereof, but not limited to these.

[0075] In one embodiment of the present disclosure, the lithium salt may include (CF3SO2)2NLi (LiFSI).

[0076] In one embodiment of the present disclosure, the nitric acid compound is a general term for a nitric acid compound or a nitrous acid compound that can be used as an additive in an electrolyte for a lithium-sulfur battery. The nitric acid compound or the nitrous acid compound can form a stable thin film on a negative electrode made of, for example, lithium metal and improve charge and discharge efficiency, but the mechanism of the present disclosure is not limited thereto.

[0077] In one embodiment of the present disclosure, the nitric acid compound may include, for example, but not limited to, inorganic nitric acid or nitrous acid 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), ammonium nitrite (NH4NO2); organic nitric acid or nitrous acid compounds, such as methyl nitrate, dialkylimidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, amyl nitrite, octyl nitrite; organic nitro compounds, such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, or a mixture thereof.

[0078] In one embodiment of the present disclosure, the cation of the nitric acid compound may be selected from alkali metals such as lithium, sodium, potassium, rubidium, and cesium, but is not limited thereto.

[0079] In another embodiment of the present disclosure, the nitric acid compound may include lithium nitrate (LiNO 3 ).

[0080] As described above, according to the embodiments of the present disclosure, the total salt content in the electrolyte may be reduced and ion conductivity may be improved by the Lewis acidic additive.

[0081] According to one aspect of the present disclosure, the electrolyte for a lithium-sulfur battery includes the lithium salt, the nitric acid compound, and the Lewis acidic additive as salts.

[0082] Accordingly, according to one aspect of the present disclosure, the total concentration of the lithium salt, the nitric acid compound, and the Lewis acidic additive in the lithium-sulfur battery electrolyte is 2 M or less.

[0083] Specifically, according to one embodiment of the present disclosure, the total concentration of the lithium salt, the nitric acid compound and the Lewis acidic additive in the lithium-sulfur battery electrolyte may be, for example, 1.8 M or less, 1.75 M or less, 1.70 M or less, 1.65 M or less, 1.60 M or less, 1.55 M or less, 1.50 M or less, 1.45 M or less, 1.40 M or less, 1.35 M or less, 1.30 M or less, 1.25 M or less, or 1.20 M or less. More specifically, the total concentration of the lithium salt, the nitric acid compound and the Lewis acidic additive in the lithium-sulfur battery electrolyte may be, for example, 0.5 M or more, 0.8 M or more, or 1 M or more.

[0084] In one embodiment of the present disclosure, the total concentration of the lithium salt, the nitric acid compound, and the Lewis acidic additive in the electrolyte for the lithium-sulfur battery may be, for example, 0.5 M to 2 M, specifically 0.8 M to 1.8 M, 1 M to 1.5 M, 1 M to 1.3 M, 1 M to 1.25 M, or 1.20 M to 1.25 M. According to one aspect of the present disclosure, when the lithium salt, the nitric acid compound, and the Lewis acidic additive are included at the above concentrations, there may be a beneficial effect on low electrolyte in the electrolyte and long life of the lithium-sulfur battery, but the present disclosure is not limited thereto.

[0085] In one embodiment of the present disclosure, the electrolyte for a lithium-sulfur battery may further include a salt compound in addition to the lithium salt, the nitric acid compound, and the Lewis acidic additive without hindering the purpose of the present disclosure.

[0086] In one embodiment of the present disclosure, when the lithium-sulfur battery electrolyte further comprises a salt compound in addition to the lithium salt, the nitric acid compound and the Lewis acidic additive, the total salt concentration of the lithium-sulfur battery electrolyte may preferably be 2.5 M or less, specifically 2 M or less.

[0087] In another embodiment of the present disclosure, the electrolyte for lithium-sulfur battery may not contain any salt compound other than the lithium salt, the nitric acid compound and the Lewis acidic additive. Accordingly, in this case, the total salt concentration in the electrolyte for lithium-sulfur battery may be the sum of the concentrations of the lithium salt, the nitric acid compound and the Lewis acidic additive.

[0088] Specifically, according to one embodiment of the present disclosure, the total salt concentration in the electrolyte for the lithium-sulfur battery may be, for example, 2 M or less or 1.5 M or less. More specifically, the salt concentration in the electrolyte for the lithium-sulfur battery may be, for example, 0.1 M to 2.5 M, 0.5 M to 2 M, 0.5 M to 1.5 M, 1 M to 1.25 M, 1 M to 1.20 M, or 1.20 M to 1.25 M. According to one embodiment of the present disclosure, when the salt concentration is within the above range, the decomposition of the lithium salt during battery operation may be suppressed, thereby improving ion conductivity and battery life, but the present disclosure is not limited thereto.

[0089] In one embodiment of the present disclosure, the concentration of the lithium salt in the electrolyte for lithium-sulfur batteries may be, for example, 2 M or less. Specifically, the concentration of the lithium salt in the electrolyte for lithium-sulfur batteries may be, for example, 1.8 M or less, 1.5 M or less, or 1 M or less. Specifically, within the above range, the concentration of the lithium salt in the electrolyte for lithium-sulfur batteries may be, for example, 0.05 M or more, 0.1 M or more, 0.5 M or more, or 0.6 M or more. More specifically, the concentration of the lithium salt in the electrolyte for lithium-sulfur batteries may be, for example, 0.05 M to 2 M, 0.1 M to 1.75 M, 0.5 M to 1.5 M, 0.5 M to 1.25 M, 0.5 M to 1.0 M, 0.5 M to 0.8 M, 0.5 M to 0.75 M, 0.6 M to 0.8 M, or 0.75 M to 1.0 M.

[0090] In one embodiment of the present disclosure, the concentration of the Lewis acidic additive in the lithium-sulfur battery electrolyte may be, for example, 0.3 M or less, 0.2 M or less, or 0.1 M or less. Specifically, the concentration of the Lewis acidic additive in the lithium-sulfur battery electrolyte may be 0.01 M to 0.3 M, 0.01 M to 0.2 M, 0.01 M to 0.1 M, 0.03 M to 0.2 M, 0.04 M to 0.1 M, 0.04 M to 0.075 M, or 0.05 M to 0.075 M.

[0091] In one embodiment of the present disclosure, the concentration of the nitric acid compound in the lithium-sulfur battery electrolyte may be, for example, 1 M or less or 0.5 M or less. Specifically, the concentration of the nitric acid compound in the lithium-sulfur battery electrolyte may be 0.05 M to 1 M, 0.1 M to 0.8 M, 0.2 M to 0.6 M, 0.3 M to 0.5 M, or 0.4 M to 0.5 M.

[0092] In one embodiment of the present disclosure, the non-aqueous solvent may include, but is not limited to, a non-aqueous solvent used in an electrolyte of a lithium-sulfur battery. For example, the non-aqueous solvent may include an ether solvent, an ester solvent, an amide solvent, a carbonate solvent, or a mixture thereof.

[0093] In one embodiment of the present disclosure, the ether solvent may include, but is not limited to, an ether solvent used in an electrolyte of a lithium-sulfur battery.

[0094] In another embodiment of the present disclosure, the ether-based solvent may be divided into cyclic ethers and acyclic ethers, for example, according to the structure.

[0095] In one embodiment of the present disclosure, the acyclic ether may include, for example, dimethoxyethane, diethoxyethane, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, polyethylene glycol methyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl tert-butyl ether, methyl hexyl ether, ethyl tert-butyl ether, ethyl hexyl ether, or a mixture thereof.

[0096] In one embodiment of the present disclosure, the cyclic ether may include, for example, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene or a mixture thereof.

[0097] In one embodiment of the present disclosure, the ester solvent may include, for example, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture thereof, but is not limited thereto.

[0098] In one embodiment of the present disclosure, the carbonate solvent may include, for example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate and halides thereof, or mixtures thereof. The halides may include, for example, fluoroethylene carbonate, but are not limited thereto.

[0099] In another embodiment of the present disclosure, since the carbonate-based solvent does not dissolve the nitric acid compound or has low solubility, the nonaqueous solvent may not substantially contain the carbonate-based solvent.

[0100] In one embodiment of the present disclosure, the non-aqueous solvent may contain the carbonate-based solvent in an amount so small that the solubility of the nitric acid compound is not affected, and when the non-aqueous solvent contains, for example, the carbonate-based solvent, the content of the carbonate-based solvent may be 3 wt % or less, 2 wt % or less, 1 wt % or less, 0.5 wt % or less, or 0 wt % (i.e., none) based on the total weight of the lithium-sulfur battery electrolyte.

[0101] In one embodiment of the present disclosure, as described above, the Lewis acidic additive can suppress the dissolution of lithium polysulfide, thereby realizing an excellent lithium-sulfur battery without using a non-solvent for lithium polysulfide. From this perspective, the non-aqueous solvent may include the ether-based solvent.

[0102] In one embodiment of the present disclosure, the non-aqueous solvent may contain more than half of the total volume of the ether solvent. Specifically, based on the total volume of the non-aqueous solvent, the volume of the ether solvent may be more than 50% by volume, specifically more than 60% by volume, more specifically 70% to 100% by volume, 80% to 100% by volume, 85% to 100% by volume, 90% to 100% by volume, or 95% to 100% by volume.

[0103] In another embodiment of the present disclosure, the non-aqueous solvent may consist of one type of ether-based solvent.

[0104] According to one embodiment of the present disclosure, the non-aqueous solvent may consist of the acyclic ether. For example, the non-aqueous solvent may contain 100% by volume of the acyclic ether based on the total volume.

[0105] More specifically, in one embodiment of the present disclosure, the non-aqueous solvent may include dimethoxyethane (DME) as an ether solvent, and the volume of DME may be 60 volume % or more, based on the total volume of the non-aqueous solvent, more specifically 70 volume % to 100 volume %, 80 volume % to 100 volume %, 85 volume % to 100 volume %, 90 volume % to 100 volume % or 95 volume % to 100 volume %.

[0106] In another embodiment of the present disclosure, the non-aqueous solvent may include the cyclic ether and the acyclic ether. For example, the non-aqueous solvent may include a mixture of 2-methylfuran (2-MeF) as a cyclic ether and dimethoxyethane (DME) as an acyclic ether.

[0107] According to one embodiment of the present disclosure, when the nonaqueous solvent includes the cyclic ether and the acyclic ether, the cyclic ether and the acyclic ether may be included, for example, in a volume ratio of 5:1 to 1:5, 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, or 1:1, but the present disclosure is not limited thereto.

[0108] Using the composition of the lithium-sulfur battery electrolyte according to one aspect of the present disclosure can inhibit the dissolution of lithium polysulfide and passivation caused by the deposition of lithium sulfide on the negative electrode, thereby improving the operating stability of the lithium-sulfur battery, but the present disclosure is not limited thereto.

[0109] According to another aspect of the present disclosure, a lithium-sulfur battery comprising the above-mentioned electrolyte for a lithium-sulfur battery is provided.

[0110] The lithium-sulfur battery comprises the lithium-sulfur battery electrolyte of the above composition, a positive electrode, a negative electrode and a separator located between the positive electrode and the negative electrode.

[0111] Here, the positive electrode may include inorganic sulfur (S8) as a positive electrode active material. Specifically, in addition to the inorganic sulfur, the positive electrode may also include a sulfur-containing compound as a positive electrode active material. In this case, the sulfur-containing compound may include a compound selected from Li2Sn (n≥1), a disulfide compound, an organic sulfur compound, and a carbon-sulfur polymer (C2S x ) n , x=2.5 to 50, n≥2) is selected from the group consisting of at least one.

[0112] In one embodiment of the present disclosure, the positive electrode, the negative electrode and the separator may include a positive electrode, a negative electrode and a separator that can be used in the lithium-sulfur battery without limitation, and descriptions of the corresponding components are omitted in this specification. In addition, the lithium-sulfur battery is not limited to a specific shape and may have a variety of shapes, such as a cylindrical shape, a stacked type, a coin type, etc.

[0113] As described above, the lithium-sulfur battery includes the electrolyte containing the Lewis acidic additive. According to one embodiment of the present disclosure, the Lewis acidic additive may include elemental fluorine as an anion. During the initial charging process of the lithium-sulfur battery, an SEI layer may be formed on the negative electrode. According to one embodiment of the present disclosure, when elemental fluorine is included as an anion of the Lewis acidic additive, the lithium-sulfur battery may have an SEI layer formed on the negative electrode during the initial charging process and including elemental fluorine.

[0114] Specifically, according to one embodiment of the present disclosure, the lithium-sulfur battery may have a SEI layer disposed on the negative electrode during an initial charge process and including LiF.

[0115] According to one embodiment of the present disclosure, when the lithium-sulfur battery includes the above-mentioned electrolyte, a lithium-sulfur battery with low electrolyte and high capacity can be realized.

[0116] For example, the lithium-sulfur battery can stably operate at an electrolyte / sulfur (El / S) ratio of, for example, 7 μL / mg or less, specifically 5 μL / mg or less, but the present disclosure is not limited thereto. In particular, since the lithium-sulfur battery is intended to achieve low electrolyte and high capacity, when the above-mentioned electrolyte is used, a battery having an El / S ratio higher than the above-mentioned El / S ratio can operate and exhibit high performance at the above-mentioned El / S ratio, and the El / S ratio is not limited thereto.

[0117] According to one embodiment of the present disclosure, the El / S ratio of the lithium-sulfur battery may be, for example, 2 μL / mg to 7 μL / mg, 3 μL / mg to 5 μL / mg, 4 μL / mg to 5 μL / mg, 2 μL / mg to 5 μL / mg, 2 μL / mg to 3 μL / mg, or 2 μL / mg to 2.5 μL / mg, but the present disclosure is not limited thereto.

[0118] Hereinafter, embodiments will be described in detail to help understanding of the present disclosure.

[0119] Experimental Example 1

[0120] [Preparation of electrolyte for lithium-sulfur batteries]

[0121] In order to confirm the improvement in performance of a lithium-sulfur battery when the electrolyte for a lithium-sulfur battery contains a Lewis acidic additive, an electrolyte having the composition of Table 1 was prepared.

[0122] Specifically, in order to evaluate the performance of an electrolyte solution containing 2-methylfuran (2-MeF), bis(2,2,2-trifluoroethyl) ether (BTFE) or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as a non-solvent for lithium polysulfide, electrolyte solutions of Comparative Examples 2 to 4 were prepared.

[0123]

[0124] Evaluation Example 1. Evaluation of the solubility of lithium polysulfide

[0125] In order to evaluate the inhibitory effect of Lewis acidic additives on the dissolution of lithium polysulfide, the following experiment was conducted.

[0126] The electrolytes of Comparative Example 1 and Example 1 were added dropwise at room temperature of 23°C until an equal amount of lithium polysulfide (Li2S8) was completely dissolved. The concentration of the experimental solution was measured when the initial solid lithium polysulfide was no longer observed, and the results are shown in Table 2 below.

[0127]

[0128] As can be seen from Table 2 above, it is confirmed that to dissolve the same amount of lithium polysulfide, the amount of the electrolyte used in Example 1 is larger than that of the electrolyte used in Comparative Example 1, and accordingly the final concentration of the experimental solution is lower.

[0129] This confirmed that the Lewis acidic additive suppressed the dissolution of lithium polysulfide in the electrolyte solution, thereby suppressing the elution of lithium polysulfide into the electrolyte solution.

[0130] [Manufacturing of lithium-sulfur batteries]

[0131] The prepared electrolyte was used to manufacture a lithium-sulfur battery.

[0132] A positive electrode slurry was applied on an aluminum foil using a sulfur-carbon composite (S / C 70 / 30) and an acrylic acid (PAA) adhesive and dried to prepare a positive electrode (sulfur content was 45 wt % based on the total weight of the positive electrode). A 35 μm thick lithium metal foil was used as a negative electrode. A porous polyethylene was used as a separator. The separator was placed between the prepared positive electrode and the negative electrode, and the prepared electrolyte was injected to manufacture a soft pack battery.

[0133] As the electrolyte solution, the electrolyte solutions of Comparative Examples 1 to 6 and Examples 1 to 3 were used, and were injected according to the target El / S ratio (unit: μL / mg).

[0134] Evaluation Example 2. Battery Life Evaluation

[0135] Using the electrolyte solutions of Comparative Example 1, Example 1, and Example 2, batteries were manufactured at an El / S ratio of 5 μL / mg.

[0136] Subsequently, the prepared lithium-sulfur batteries were discharged at 0.3C to 1.8V in CC mode at 25°C and charged at 0.3C constant current to 2.7V, and the discharge capacities were measured / compared. The discharge capacities were measured based on the sulfur content (mAh / g (sulfur weight)).

[0137] The measurement results are as follows Figure 1 shown.

[0138] according to Figure 1 The results of the experiment confirmed that the electrolyte containing the Lewis acidic additive ensured the operation stability of the battery in a lean electrolyte and high sulfur loading (El / S 5 μL / mg) environment. In particular, it was confirmed that the electrolyte of Example 1 ensured the operation stability up to 100 cycles.

[0139] Evaluation Example 3. Battery Rate Evaluation

[0140] Using the electrolyte solutions of Comparative Examples 1 to 4 and Examples 1 and 2, batteries were manufactured at an El / S ratio of 4 μL / mg.

[0141] The charge and discharge characteristics were evaluated by the same method as in Evaluation Example 2. Figure 2 shown.

[0142] It is expected that the electrolyte containing the non-solvent for lithium polysulfide (Comparative Examples 2 to 4) will reduce the amount of lithium polysulfide dissolved in the electrolyte by introducing the non-solvent, but according to Figure 2 The results confirmed that the result was 800mAh / g s The maximum current density of the above discharge capacity is lower than that of Examples 1 and 2. In particular, it was confirmed that the maximum current density was about half that of Example 2. In contrast, in the case of Examples 1 and 2, it was confirmed that the introduction of the Lewis acidic additive could suppress the dissolution of lithium polysulfide and improve the mobility of lithium ions.

[0143] Evaluation Example 4: Element Evaluation of Negative Electrode SEI Layer

[0144] The lithium-sulfur batteries of Comparative Example 1 and Example 1 prepared in Evaluation Example 2 were used. After 5 cycles, the negative electrode was separated, and the SEI layer on the negative electrode was subjected to elemental analysis by molecular dynamics (MD) and X-ray photoelectron spectroscopy (XPS) analysis.

[0145] The elemental analysis results are as follows Figure 3 and 4 shown.

[0146] according to Figure 3 The results confirmed that when the Lewis acid additive was introduced, lithium ions (Li + ) and FSI - The coordination number of - The LiF in the SEI layer produced by decomposition reduces the loss of bulk lithium and electrolyte, thereby improving the battery life performance. - When the coordination number increases, according to Figure 4 The result is FSI - The decomposition of is reduced, which means that the introduction of Lewis acidic additives induces the formation of a stable SEI layer and prevents the excessive decomposition of the electrolyte, thereby improving the performance of the battery.

[0147] Evaluation Example 5. Evaluation of decomposition current of electrolyte solution

[0148] For each of the electrolytic solutions of Comparative Example 1 and Example 1, the decomposition current was evaluated by the following method.

[0149] First, during the charging process of the lithium-sulfur battery of Comparative Example 1 and Example 1 prepared in Evaluation Example 2, the voltage was fixed to 2.3 V, and the current generated by the shuttling of lithium polysulfide to the negative electrode was measured. The results are as follows: Figure 5 shown.

[0150] Subsequently, a lithium nickel battery was prepared using the electrolyte solutions prepared in each of Comparative Example 1 and Example 1, and 1.6 M lithium polysulfide (LiPS) was injected into the electrolyte solutions to create conditions similar to those of the electrolyte solution during discharge of a lithium sulfur battery. Figure 6 The voltage-current graph obtained by linear sweep voltammetry (LSV) in the voltage range between OCV and 0.05 V at a scan rate of 1 mV / s using the prepared lithium nickel battery is shown.

[0151] according to Figure 5 and Figure 6 The results showed that the shuttle current of Example 1 was much lower than that of Comparative Example 1 due to the Lewis acidic additive. In addition, it was confirmed that in the case of Example 1 containing the Lewis acidic additive, the reduction reaction of LiPS to Li2S was greatly suppressed.

[0152] Thus, it is confirmed that Lewis acid additives can reduce the loss of positive electrode active materials due to the shuttle effect during the operation of lithium-sulfur batteries and prevent the electrolyte decomposition problem under low electrolyte conditions, thereby achieving a longer lithium-sulfur battery life.

[0153] Evaluation Example 6. Battery Life Evaluation

[0154] In order to evaluate the effect of different concentrations of lithium salt on battery life when the amount of Lewis acidic additive is kept constant, the electrolytes of Comparative Example 1, Comparative Example 5, Comparative Example 6 and Examples 1 to 3 were used to evaluate the battery life in the same manner as Evaluation Example 2. The results are shown in FIG. Figure 7 shown.

[0155] Reference Figure 7 , it was confirmed that Examples 1 to 3 using the Lewis acidic additive according to an embodiment of the present disclosure and having a total concentration of the lithium salt, the nitric acid compound and the acidic additive of 2 M or less exhibited higher performance than Comparative Example 1 containing no acidic additive, while Comparative Examples 5 and 6 containing the Lewis acidic additive but having a total concentration of the lithium salt, the nitric acid compound and the acidic additive of 2 M or more had a shorter life than Comparative Example 1 containing no acidic additive.

[0156] Thus, it was confirmed that the acidic additive was effective in improving the life of the lithium-sulfur battery under the condition that the total concentration of the lithium salt, the nitric acid compound and the acidic additive was 2 M or less.

[0157] Experimental Example 2

[0158] [Preparation of electrolyte for lithium-sulfur batteries]

[0159] In order to determine the improvement in lithium-sulfur battery performance caused by the composition when the electrolyte for a lithium-sulfur battery contains a Lewis acidic additive, an electrolyte was prepared according to the composition of Table 3 below.

[0160]

[0161] [Preparation of lithium-sulfur batteries]

[0162] A lithium-sulfur battery was produced using an electrolyte having the composition shown in Table 3 as follows.

[0163] A positive electrode slurry was applied on an aluminum foil using a sulfur-carbon composite (S / C 70 / 30) and an acrylic acid (PAA) adhesive and dried to prepare a positive electrode (sulfur content was 45 wt % based on the total weight of the positive electrode). A 35 μm thick lithium metal foil was used as a negative electrode. A porous polyethylene was used as a separator. The separator was placed between the prepared positive electrode and the negative electrode, and the prepared electrolyte was injected to manufacture a soft pack battery.

[0164] As the electrolyte solution, the electrolyte solution of Example 4, Example 5, Comparative Example 7 or Comparative Example 8 was used, and injected at an El / S ratio (unit: μL / mg) of 2.4.

[0165] Subsequently, the lithium-sulfur battery was discharged to 1.8 V at 0.3 C in CC mode at 25 °C and charged to 2.7 V at 0.3 C constant current to evaluate the charge and discharge characteristics. Figures 8 to 10 Each capacity is measured based on the sulfur content (mAh / g (sulfur weight)).

[0166] Figure 8 The results of the specific capacity evaluation according to the charge and discharge cycles are shown. As with the previous results, it was confirmed that the contained Lewis acidic additive significantly suppressed the capacity decay after repeated charge and discharge cycles.

[0167] Fig. 9 The charge-discharge curve of the first charge-discharge cycle in the lithium-sulfur battery using the electrolyte of Comparative Example 8 is shown. Fig. 9 , confirming that when the electrolyte composition contains a Lewis acidic additive but does not contain a nitric acid compound additive, subsequent cycles cannot be performed normally due to charging delay.

[0168] Fig.10 The results of the specific capacity evaluation according to the charge and discharge cycles in the lithium-sulfur battery using the electrolyte of Example 5 are shown. Fig.10 , confirming that when the Lewis acid additive is used in excess, subsequent cycles cannot be performed due to the rapid increase in discharge overvoltage at the initial stage of the cycle.

Claims

1. An electrolyte for a lithium-sulfur battery, comprising: Lithium salt, nitric acid compound, non-aqueous solvent and Lewis acid additive, The Lewis acidic additive comprises a Lewis acidity greater than that of lithium ions (Li + ) high cation salt, and The total concentration of the lithium salt, the nitric acid compound and the Lewis acidic additive is 2 M or less. 2 . The electrolyte for a lithium-sulfur battery according to claim 1 , wherein the total concentration of the lithium salt, the nitric acid compound and the Lewis acidic additive is 1.5 M or less.

3. The electrolyte for a lithium-sulfur battery according to claim 1, wherein the Lewis acidic additive comprises aluminum (Al) ions, magnesium (Mg) ions, calcium (Ca) ions, strontium (Sr) ions, barium (Ba) ions, or two or more thereof as the cations. 4 . The electrolyte for lithium-sulfur batteries according to claim 1 , wherein the Lewis acidic additive comprises a calcium salt. 5 . The electrolyte for lithium-sulfur batteries according to claim 1 , wherein the Lewis acidic additive comprises a fluorine-containing anion.

6. The electrolyte for lithium-sulfur batteries according to claim 1, wherein the Lewis acidic additive comprises F - 、BF4 - PF6 - CF3SO3 - 、[(CF3SO2)2N] - 、[(FSO2)2N] - or two or more thereof as anions. 7 . The electrolyte for a lithium-sulfur battery according to claim 1 , wherein the concentration of the lithium salt in the electrolyte for a lithium-sulfur battery is 2 M or less. 8 . The electrolyte for lithium-sulfur batteries according to claim 1 , wherein the concentration of the Lewis acidic additive in the electrolyte for lithium-sulfur batteries is 0.3 M or less. 9 . The electrolyte for lithium-sulfur batteries according to claim 1 , wherein the concentration of the Lewis acidic additive in the electrolyte for lithium-sulfur batteries is 0.01 M to 0.1 M. 10 . The electrolyte for a lithium-sulfur battery according to claim 1 , wherein the nonaqueous solvent comprises an ether solvent.

11. The electrolyte for lithium-sulfur batteries according to claim 1, wherein the non-aqueous solvent comprises an ether solvent, and The volume of the ether solvent is greater than 60 volume % of the total volume of the non-aqueous solvent.

12. The electrolyte for lithium-sulfur batteries according to claim 1, wherein the nonaqueous solvent consists of one type of ether-based solvent. 13 . The electrolyte for lithium-sulfur batteries according to claim 1 , wherein the nonaqueous solvent comprises a cyclic ether and an acyclic ether.

14. A lithium-sulfur battery comprising: The electrolyte according to any one of claims 1 to 13; a positive electrode comprising inorganic sulfur (S8); negative electrode; and A separator is provided between the positive electrode and the negative electrode. 15 . The lithium-sulfur battery according to claim 14 , wherein the lithium-sulfur battery has a solid electrolyte interface (SEI) layer comprising LiF on the negative electrode.

16. The lithium-sulfur battery according to claim 14, wherein the electrolyte / sulfur (El / S) ratio is less than 7 μL / mg.

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