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

Abstract

The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including same. The electrolyte for a lithium-sulfur battery may include a non-aqueous solvent, a lithium salt, a nitrate, and an aryl derivative, wherein the non-aqueous solvent comprises: a heterocyclic compound containing one oxygen atom (O) or sulfur atom (S) in the ring structure; and glycol ether, and the aryl derivative contains at least one of compounds represented by any one of chemical formulas 1 to 4.

Description

Electrolyte for lithium-sulfur batteries and lithium-sulfur batteries containing the same

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

[0002] This application claims priority to Korean Patent Application No. 10-2024-0012695, filed with the Korean Intellectual Property Office on January 26, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the primary ingredient in the positive electrode active material, is abundant worldwide, is non-toxic, and has the advantages of a low per-atom weight.

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

[0005] In a lithium-sulfur battery, when discharging, the negative active material lithium is oxidized by donating electrons and ionizing into lithium cations, and the positive active material sulfur-based material is reduced by accepting electrons. Here, through the reduction reaction of the sulfur-based material, the S-S bond accepts two electrons and is converted into a sulfur anion. The lithium cation produced by the oxidation reaction of lithium is transferred to the positive electrode through the electrolyte, and this combines with the sulfur anion produced by the reduction reaction of the sulfur-based compound to form a salt. Specifically, before discharge, sulfur has a cyclic S8 structure, which is converted into lithium polysulfide (LiSx) through the reduction reaction, and is completely reduced to produce lithium sulfide (Li2S).

[0006] At this time, due to the low electrical conductivity of sulfur in the sulfur-based compound, which is the positive electrode active material, it is difficult to secure reactivity with electrons and lithium ions in the solid state. Therefore, in order to improve the reactivity of sulfur in a lithium-sulfur battery, Li2S x A technology has been developed to generate intermediate polysulfides in the form of sulfides, thereby inducing liquid-phase reactions and improving reactivity. This technology utilizes ether-based solvents, such as dioxolane and dimethoxyethane (DME), which have high solubility in lithium polysulfides, as electrolyte solvents. Consequently, the reactivity of sulfur and the lifespan of the battery are affected by the electrolyte content.

[0007] Additionally, during the discharge process of a lithium-sulfur battery, polysulfide (PS) generated from the positive electrode is dissolved into the electrolyte and reacts. This polysulfide causes side reactions within the battery, leading to battery degradation. Reducing the amount of electrolyte is crucial for achieving a high-energy-density cell. However, as the electrolyte amount decreases, the concentration of polysulfide increases, accelerating side reactions and reducing battery life. Therefore, the development of technology that can achieve high energy density while securing a certain amount of electrolyte is urgently needed.

[0008] Therefore, the problem that the present invention seeks to solve is to solve the above-described problem,

[0009] According to one aspect, it is intended to provide a lithium-sulfur battery with improved discharge capacity.

[0010] To this end, the present invention aims to provide an electrolyte for a lithium-sulfur battery that controls the elution characteristics of polysulfide (PS) by changing the reaction path of sulfur (S) and thereby improves problems caused by the elution of polysulfide, such as resistance characteristics.

[0011] Accordingly, it is intended to provide a lithium-sulfur battery having high energy density and lifespan characteristics by applying an appropriate amount of electrolyte.

[0012] To solve the above problem,

[0013] According to one aspect of the present invention, an electrolyte for a lithium-sulfur battery of the following embodiments is provided.

[0014] An electrolyte for a lithium-sulfur battery according to the first embodiment is

[0015] Containing non-aqueous solvents, lithium salts, nitrates and aryl derivatives,

[0016] The above non-aqueous solvent comprises a heterocyclic compound containing one oxygen atom (O) or sulfur atom (S) in the ring structure; and a glycol ether;

[0017] The above lithium salt includes an inorganic lithium salt,

[0018] The above aryl derivative comprises at least one of the compounds represented by any one of the following chemical formulae 1 to 4,

[0019] The content of the above aryl derivative is 3 wt% or more based on the total weight of the non-aqueous solvent, lithium salt, nitrate, and aryl derivative.

[0020] [Chemical Formula 1]

[0021] R 1 -Te-Li

[0022] [Chemical Formula 2]

[0023] R 2 -Te-Te-R 3

[0024] [Chemical Formula 3]

[0025] R 4 -Te-Sx-Li

[0026] [Chemical Formula 4]

[0027] R 5 -Te-Sx-Te-R 6

[0028] In the above chemical formulas 1 to 4,

[0029] R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently C6 to C 20 is an aryl group,

[0030] x is a number from 1 to 8.

[0031] According to the second embodiment, in the first embodiment,

[0032] The above aryl derivative may include diphenyl ditelluride (DPDTe).

[0033] According to the third embodiment, in the first embodiment or the second embodiment,

[0034] The content of the above nitrate and aryl derivative may be 6 wt% to 10 wt% based on the total weight of the non-aqueous solvent, lithium salt, nitrate and aryl derivative.

[0035] According to the fourth embodiment, in any one of the first to third embodiments,

[0036] The above nitrate may include lithium nitrate (LiNO3).

[0037] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0038] The weight of the above aryl derivative may be equal to or less than the weight of the above nitrate.

[0039] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0040] The concentration of the lithium salt may be 0.3 M to 0.75 M.

[0041] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0042] The above inorganic lithium salts are LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiAsF6, LiSbF6, LiAlCl4, (SO2F)2NLi, lithium chloroborane, lithium imide, or two or more thereof.

[0043] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0044] The above inorganic lithium salt may include (SO2F)2NLi.

[0045]

[0046] According to another aspect of the present invention, lithium-sulfur batteries of the following embodiments are provided.

[0047] A lithium-sulfur battery according to the ninth embodiment,

[0048] An electrolyte for a lithium-sulfur battery according to any one of the first to eighth embodiments, comprising: a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material; wherein the positive electrode active material includes elemental sulfur, a sulfur compound, or a mixture thereof.

[0049] According to the tenth embodiment, in the ninth embodiment,

[0050] The specific capacity can be greater than 1,400 mAh / gs.

[0051] An electrolyte for a lithium-sulfur battery according to one embodiment of the present invention has the effect of changing the discharge mechanism of a lithium-sulfur battery by changing the reduction reaction path of lithium sulfide.

[0052] Accordingly, a lithium-sulfur battery using this has the effect of increasing the discharge capacity of the lithium-sulfur battery and realizing high energy density by expressing additional capacity.

[0053] Figure 1 is a graph showing the results of evaluating the charge / discharge characteristics of a lithium-sulfur battery using Example 1, Comparative Example 1, and Comparative Example 2 in the present specification.

[0054] The present invention will be described in detail below. However, the present invention is not limited to the following description, and each component may be modified or selectively combined as needed. Therefore, it should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

[0055] In this specification, when a configuration is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0056] In this specification, the term "(poly)sulfide (PS)" means "(poly)sulfide ion (S x 2- , 1≤x≤8))" and "lithium (poly)sulfide (Li2S) x or LiS x - , is a concept that includes all integers (1≤x≤8).

[0057] In this specification, the term “lithium sulfide” refers to a material of Li2S.

[0058] An electrolyte for a lithium-sulfur battery according to one aspect of the present invention,

[0059] A non-aqueous solvent comprising a lithium salt, a nitrate, and an aryl derivative, wherein the non-aqueous solvent comprises a heterocyclic compound containing one oxygen atom (O) or one sulfur atom (S) in a ring structure; and a glycol ether; wherein the lithium salt comprises an inorganic lithium salt, and the aryl derivative comprises at least one compound represented by any one of the following chemical formulae 1 to 4.

[0060] [Chemical Formula 1]

[0061] R 1 -Te-Li

[0062] [Chemical Formula 2]

[0063] R 2 -Te-Te-R 3

[0064] [Chemical Formula 3]

[0065] R 4 -Te-Sx-Li

[0066] [Chemical Formula 4]

[0067] R 5 -Te-Sx-Te-R 6

[0068] In the above chemical formulas 1 to 4,

[0069] R 1 , R 2 , R3 , R 4 , R 5 and R 6 are each independently C6 to C 20 is an aryl group.

[0070] Also, x is a number from 1 to 8.

[0071] In one embodiment of the present invention, the non-aqueous solvent is included as a medium in an electrolyte for a lithium-sulfur battery. The lithium salt is included as an electrolyte salt in the electrolyte for a lithium-sulfur battery. The nitrate is included as an additive for forming a stable film on a negative electrode made of a material such as lithium metal and for improving charge-discharge efficiency. In addition, the aryl derivative is included as an additive for changing the path of the reduction reaction of lithium sulfide and for providing additional discharge capacity.

[0072] In the present invention, by including the aryl derivative in the electrolyte for a lithium-sulfur battery, the aryl derivative can play a role in chain-extending lithium sulfide (Li2S) present in the positive electrode or the electrolyte, thereby changing the path of the reduction reaction of lithium sulfide.

[0073] Specifically, when the aryl derivative comprises a compound represented by the chemical formula 1, the electrolyte for a lithium-sulfur battery comprising the same comprises -Te-R in lithium sulfide. 1 It can have the effect of extending the chain in the form of .

[0074] In addition, when the aryl derivative includes a compound represented by the chemical formula 2, the Te-Te bond is decomposed, and accordingly, in the electrolyte for a lithium-sulfur battery including it, -Te-R is formed in lithium sulfide. 2 or -Te-R 3 It can have the effect of extending the chain in the form of .

[0075] In addition, when the aryl derivative includes a compound represented by the chemical formula 3, in the electrolyte for a lithium-sulfur battery including it, -Sx-Te-R is added to lithium sulfide.4 It can have the effect of extending the chain in the form of .

[0076] Also, when the aryl derivative comprises a compound represented by the chemical formula 4, lithium sulfide-Sx-Te-R 5 and / or -Sx-Te-R 6 It can have the effect of extending the chain in the form of .

[0077] In one embodiment of the present invention, in the chemical formulas 1 to 4, R 1 , R 2 , R 3 , R 4 , R 5 and R 6 It could be a phenyl group.

[0078] In one embodiment of the present invention, the aryl derivative may include diphenyl ditelluride (DPDTe).

[0079] According to one aspect of the present invention, the aryl derivative is included in an amount of 3 wt% or more based on the total weight of the non-aqueous solvent, lithium salt, nitrate, and aryl derivative.

[0080] Specifically, the aryl derivative may be included in an amount of 3 wt% or more based on the total weight of the electrolyte for the lithium-sulfur battery, for example, 3 wt% to 10 wt%, specifically 3 wt% to 8 wt%, 3 wt% to 7 wt%, 3 wt% to 6 wt%, or 3 wt% to 5 wt%, but the present invention is not limited thereto.

[0081] In the present invention, the electrolyte for a lithium-sulfur battery contains a nitrate. Specifically, the nitrate refers to a nitric acid compound or a nitrite compound that can be used as an additive in an electrolyte for a lithium-sulfur battery. The nitric acid or nitrite compound can form a stable film on a negative electrode made of a material such as lithium metal and exhibit the effect of improving charge-discharge efficiency, but the mechanism of the present invention is not limited thereto.

[0082] In one embodiment of the present invention, the nitrate is not limited thereto, but includes, for example, inorganic nitric or nitrous 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 or nitrous compounds such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite; It may be an organic nitro compound such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, or a mixture of two or more thereof.

[0083] In one embodiment of the present invention, the cation of the nitrate may be selected from, but is not limited to, alkali metals such as lithium, sodium, potassium, rubidium and cesium.

[0084] In another embodiment of the present invention, the nitrate may include lithium nitrate (LiNO3).

[0085] In one embodiment of the present invention, the sum of the weights of the nitrate and the aryl derivative may be 4 wt% or more based on the total weight of the electrolyte for a lithium-sulfur battery. Specifically, the sum of the weights of the nitrate and the aryl derivative may be 4 wt% or more and 15 wt% or less, 4 wt% or more and 13 wt% or less, 4 wt% or more and 12 wt% or less, 4 wt% or more and 10 wt% or less, 6 wt% or more and 10 wt% or less, or 6 wt% or more and 8 wt% or less based on the total weight of the electrolyte for a lithium-sulfur battery. When the sum of the weights of the nitrate and the aryl derivative is within the above-described range, a lithium-sulfur battery using the same may exhibit advantageous effects in terms of increasing discharge capacity and improving lifespan characteristics, but the present invention is not limited thereto.

[0086] In another embodiment of the present invention, the weight of the aryl derivative may be equal to or less than the weight of the nitrate. Specifically, the weight of the aryl derivative may be less than the weight of the nitrate. When the weight ratio of the nitrate and the aryl derivative is within the above-described range, a lithium-sulfur battery using the same may exhibit advantageous effects in terms of increased discharge capacity and improved lifespan characteristics, but the present invention is not limited thereto.

[0087] In another embodiment of the present invention, based on the total weight of the electrolyte for the lithium-sulfur battery, the sum of the weights of the nitrate and the aryl derivative is 4 wt% or more, the weight of the aryl derivative is equal to or less than the weight of the nitrate, and the molar ratio of the aryl derivative to the nitrate (aryl derivative: nitrate) may be 1:1 to 1:4, 1:1 to 1:3, or 1:1 to 1:2, but the present invention is not limited thereto.

[0088] According to the present invention, the non-aqueous solvent comprises a combination of a heterocyclic compound and a glycol ether.

[0089] The above glycol ether is an acyclic ether containing two oxygen atoms and can be used without limitation as long as it can be used as an electrolyte for a lithium-sulfur battery.

[0090] In one embodiment of the present invention, the glycol ether may be represented by the following chemical formula:

[0091] R 7 -O-(CH2CH2O) x -R 8

[0092] (In the above chemical formula,

[0093] R 7 and R 8 are the same or different from each other, and each independently represents an unsubstituted or substituted alkyl group of C1 to C6, C6 to C 12 An unsubstituted or substituted aryl group, or C7 to C 13 is an unsubstituted or substituted arylalkyl group, and x is an integer from 0 to 4.)

[0094] The glycol ether may include, but is not limited to, for example, dimethoxy ethane, diethoxy ethane, 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, or two or more thereof.

[0095] According to one embodiment of the present invention, the non-aqueous solvent may include dimethoxy ethane as a glycol ether.

[0096] The above heterocyclic compound may be used without limitation as long as it is an ether that includes one oxygen atom (O) or sulfur atom (S) in the ring structure and one -COC- structure or -CSC- structure in the ring structure and can be used as an electrolyte for a lithium-sulfur battery.

[0097] In one embodiment of the present invention, the heterocyclic compound contains two or more double bonds and at the same time, either an oxygen atom or a sulfur atom, thereby forming a solid electrolyte interface (SEI layer) on the surface of the negative electrode (lithium-based metal) by a ring opening reaction of the heterocyclic compound in the initial discharge stage of the battery, thereby suppressing the formation of lithium dendrites. Furthermore, by reducing electrolyte decomposition and resulting side reactions on the surface of the lithium-based metal, the life characteristics of the lithium-sulfur battery can be improved. In addition, since it has a characteristic of having difficulty dissolving salt due to the delocalization of lone pair electrons of the heteroatom (oxygen atom or sulfur atom), it can play a role in reducing the amount of electrolyte elution of polysulfide, but the present invention is not limited thereto.

[0098] In one embodiment of the present invention, the heterocyclic compound must include two or more double bonds to form an SEI layer on the surface of the negative electrode (lithium-based metal), and must also include a heteroatom (oxygen atom or sulfur atom) to exhibit effects such as increasing affinity with other solvents in the electrolyte by imparting polarity.

[0099] In one embodiment of the present invention, the heterocyclic compound may be a 4 to 15-membered, specifically 4 to 7-membered, and more specifically 5 to 6-membered heterocyclic compound. In addition, the heterocyclic compound may be a heterocyclic compound substituted or unsubstituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO2), an amine group (-NH2), and a sulfonyl group (-SO2). In one embodiment of the present invention, when the heterocyclic compound is substituted as described above, it may exhibit an advantageous effect in terms of stabilizing radicals and suppressing side reactions between electrolytes, but the present invention is not limited thereto.

[0100] The heterocyclic compound may include, but is not limited to, for example, furan, 2-methyl furan, 3-methyl furan, 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 two or more thereof.

[0101] In one embodiment of the present invention, the non-aqueous solvent may include 2-methyl furan as a heterocyclic compound.

[0102] In one embodiment of the present invention, based on the total volume of the non-aqueous solvent, the glycol ether may be included in a volume of, for example, 60 wt% or more, for example, 65 wt% or more, 70 wt% or more, 75 wt% or more, 80 wt% or more, or 85 wt% or less, but is not limited thereto. When the volume of the glycol ether is in the above-described range, it may have the effect of providing appropriate solubility for lithium salts, nitrates, aryl derivatives, and lithium polysulfides eluted from the positive electrode during operation of the battery, but the present invention is not limited thereto.

[0103] In one embodiment of the present invention, based on the total volume of the non-aqueous solvent, the heterocyclic compound may constitute, for example, a volume other than the glycol ether. For example, based on the total volume of the non-aqueous solvent, the heterocyclic compound may be included in a volume of, for example, 15 wt% or more, for example, 20 wt% or more, 40 wt% or less, 35 wt% or less, 30 wt% or less, or 25 wt% or less, but is not limited thereto. When the volume of the heterocyclic compound is in the above-described range, there may be an effect of providing appropriate solubility for lithium salts, nitrates, aryl derivatives, and lithium polysulfides eluted from the positive electrode during operation of the battery, but the present invention is not limited thereto.

[0104] In another embodiment of the present invention, the ratio of the total volume of the glycol ether to the total volume of the heterocyclic compound may be 3:1 or more (glycol ether:heterocyclic compound). Specifically, the ratio of the total volume of the glycol ether to the total volume of the heterocyclic compound may be 3:1 to 5:1, 3:1 to 4:1, or 3.5:1 to 4:1. When the volume ratio of the heterocyclic compound and the glycol ether is within the above-described range, there may be an advantageous effect in terms of improving the operating stability of the battery, but the present invention is not limited thereto.

[0105] In one embodiment of the present invention, the non-aqueous solvent may further include an acyclic ether containing one oxygen atom in addition to the above-described heterocyclic compound and glycol ether. By further including the acyclic ether in the non-aqueous solvent, it may exhibit a beneficial effect in terms of improving the overvoltage at SOC70 during battery operation, but the present invention is not limited thereto.

[0106] In one embodiment of the present invention, the acyclic ether containing one oxygen atom may be represented by the following chemical formula.

[0107] R 9 -OR 10

[0108] In the above chemical formula, R 9 and R 10 are each independently unsubstituted or substituted C1 to C 20 is an alkyl group.

[0109] In one embodiment of the present invention, the substituted C1 to C 20In the alkyl group of, the above 'substitution' includes, for example, a halogen atom, a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, an acetamino group, a hydrazine, a hydrazone, a carboxyl group, a sulfonyl group, a sulfamoyl group, a sulfonic acid group, a phosphoric acid, a C1 to C5 alkyl group, a C1 to C5 alkoxy group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a C4 to C 10 Cycloalkyl group, C6 to C 10 Aryl group of C6 to C 10 Heteroaryl group, C6 to C 20 Arylalkyl group of C6 to C 20 It may be a heteroarylalkyl group, or a combination thereof.

[0110] In another embodiment of the present invention, in terms of suppressing side reactions with polysulfide or lithium during operation of the battery, the R 9 and R 10 are each independently unsubstituted C1 to C 20 It may be an alkyl group.

[0111] In another embodiment of the present invention, the R 9 and R 10are each independently, for example, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-amyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-eicosanyl group, an iso-propyl group, a sec-butyl group, an iso-butyl group, a tert-butyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a 2-methylbutyl group, an iso-amyl group, a neopentyl group, a 1,2-dimethylpropyl group, a 1,1-dimethylpropyl group, a tert-amyl group, a 1,3-dimethylbutyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, 2-ethyl-2-methylpropyl group, straight-chain or branched heptyl group, 1-methylheptyl group, 2-ethylhexyl group, 1,5-dimethylhexyl group, tert-octyl group, branched nonyl group, branched decyl group, branched undecyl group, branched dodecyl group, branched tridecyl group, branched tetradecyl group, branched pentadecyl group, branched hexadecyl group, branched heptadecyl group, branched octadecyl group, straight-chain or branched nonadecyl group, straight-chain or branched eicosanyl group, cyclopropyl group, cyclopropylmethyl group, cyclobutyl group, cyclobutylmethyl group, cyclopentyl group, cyclohexyl group, cyclohexylmethyl group, cycloheptyl group, cyclooctyl group, It may be a cyclohexylpropyl group, a cyclododecyl group, a norbornyl group, a bornyl group, a cyclopentylethyl group, or a bicyclooctyl group.

[0112] In another embodiment of the present invention, the present invention is not limited thereto, but for example, R in terms of suppressing side reactions with polysulfide or lithium during operation of the battery. 9 It may be preferable that it is an unsubstituted alkyl group.

[0113] In one embodiment of the present invention, the acyclic ether may include, for example, bis(2,2,2-trifluoroethyl) ether, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl t-butyl ether, methyl hexyl ether, ethyl t-butyl ether, ethyl hexyl ether, or two or more thereof.

[0114] In one embodiment of the present invention, the above-described type of acyclic ether can exhibit an advantageous effect in terms of suppressing the elution of polysulfide from the anode by acting as a nonsolvent for polysulfide eluting from the anode.

[0115] In another embodiment of the present invention, the acyclic ether may be included in an amount of, for example, 10% by volume or less based on the total volume of the non-aqueous solvent, but is not limited thereto. Specifically, the amount of the acyclic ether may be 1% by volume or more and 10% by volume or less, or 5% by volume or more and 10% by volume or less, based on the total volume of the non-aqueous solvent. When the amount of the acyclic ether is within the above-described range, it may exhibit a beneficial effect in terms of improving the operating stability of the battery, but the present invention is not limited thereto.

[0116] In another embodiment of the present invention, the acyclic ether is included in an amount of 10% by volume or less based on the total volume of the non-aqueous solvent, and the ratio of the total volume of the glycol ether to the total volume of the acyclic ether is not limited thereto, but may be, for example, 6:1 or more, such as 6:1 to 7.5:1 or 6.5:1 to 7:1.

[0117] In one embodiment of the present invention, when the content of the above-described solvent in the total volume of the non-aqueous solvent is within the above-described range, it may exhibit advantageous effects in terms of suppressing the dissolution of polysulfide and the operating stability of the battery, but the present invention is not limited thereto.

[0118] An electrolyte for a lithium-sulfur battery according to one aspect of the present invention comprises an inorganic lithium salt as a lithium salt. The inorganic lithium salt does not contain carbon (C) in its structure and can be used without limitation as long as it is commonly used in the electrolyte of a lithium-sulfur battery. For example, the inorganic lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiAsF6, LiSbF6, LiAlCl4, (SO2F)2NLi, lithium chloroborane, lithium imide, or two or more thereof, and specifically, (SO2F)2NLi(LiFSI), but the present invention is not limited thereto. When the lithium salt includes an inorganic lithium salt, it has a smaller structure and can exist at a higher density in the electrolyte compared to a typical organic lithium salt, so it can exhibit an advantageous effect in terms of ion conductivity, and further, it can exhibit an advantageous effect in implementing a lithium-sulfur battery having a high electrolyte ratio (E / S), but the present invention is not limited thereto.

[0119] In one embodiment of the present invention, the inorganic lithium salt may not include lithium nitrate salt. The lithium nitrate salt may be included as an example of the nitrate salt described above.

[0120] In one embodiment of the present invention, the lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0121] According to one embodiment of the present invention, the lithium salt may further include a typical organic lithium salt in addition to an inorganic lithium salt. The organic lithium salt that may further be included is a lithium salt containing carbon (C) in its structure, and the organic lithium salt may also be used without limitation as long as it can be used in a lithium-sulfur battery. For example, the organic lithium salt may include, but is not limited to, LiCF3SO3, LiCF3CO2, LiC4BO8, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (CF3SO2)3CLi, lower aliphatic lithium carboxylate, lithium 4-phenylborate, or two or more thereof.

[0122] In one embodiment of the present invention, the concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, etc., and may be, for example, 0.1 to 4.0 M, 0.3 to 2.0 M, 0.3 to 1.0 M, or 0.3 to 0.75 M. When the concentration of the lithium salt is within the above-described range, it may exhibit advantageous effects in terms of ionic conductivity and viscosity of the electrolyte, but is not limited thereto.

[0123] In another embodiment of the present invention, the electrolyte for the lithium-sulfur battery may further include other additives in addition to the composition described above for the purpose of improving charge-discharge characteristics, flame retardancy, etc. The additives are not particularly limited in the present invention, but examples thereof include pyridine, triethylphosphite, triethanolamine, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate (VC), etc.

[0124] The electrolyte for the lithium-sulfur battery according to one aspect of the present invention can be manufactured by a conventional method known in the art, and is not particularly limited in the present invention.

[0125]

[0126] According to another aspect of the present invention, a lithium-sulfur battery comprises the electrolyte for a lithium-sulfur battery as described above, and comprises a positive electrode comprising a positive electrode active material and a negative electrode comprising a negative electrode active material. Specifically, the positive electrode active material comprises elemental sulfur, a sulfur compound, or a mixture thereof.

[0127] The above positive electrode, positive electrode active material, negative electrode, and negative electrode active material may be used without particular limitation as long as they can be used in a lithium-sulfur battery within a range that does not impede the purpose of the present invention.

[0128] For example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both sides of the positive electrode current collector, and the negative electrode may include a negative electrode current collector and a negative electrode active material layer applied to one or both sides of the negative electrode current collector.

[0129] At this time, the positive electrode current collector supports the positive electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and the negative electrode current collector supports the negative electrode active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery.

[0130] In one embodiment of the present invention, the positive electrode active material comprises elemental sulfur, a sulfur compound, or a mixture thereof. Specifically, the positive electrode active material comprises inorganic sulfur (S8), Li2S. n (n≥1), disulfide compounds, organosulfur compounds, carbon-sulfur polymers (C2S) x ) n , x=2.5 to 50, n≥2) or may include two or more of these.

[0131] In one embodiment of the present invention, the negative active material is lithium (Li + ) can be used without particular limitation as long as it is a material that can reversibly intercalate or deintercalate lithium ions, or a material that can reversibly form a lithium-containing compound by reacting with lithium ions. For example, the negative electrode active material may include lithium metal, a lithium alloy, or a mixture thereof. The lithium alloy may be, for example, an alloy of lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), tin (Sn), or two or more of these metals.

[0132] In addition, each of the positive electrode active material layer and the negative electrode active material layer may further include a conductive material, a binder, and an additive in addition to the active material, and the specific types thereof are commonly used, so a description thereof is omitted.

[0133] In one embodiment of the present invention, the external shape of the lithium-sulfur battery may be, for example, a coin shape, a cylinder shape, a pouch shape, or a square shape, and the external shape of the battery is not particularly limited. In addition, the lithium-sulfur battery may be used not only as a battery cell used as a power source for a small device, but may also be used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells, and there is no particular limitation on the form of use thereof.

[0134] In one embodiment of the present invention, a lithium-sulfur battery using a positive electrode including the carbon composite is not only excellent in terms of initial capacity and cycle stability, but also exhibits excellent effects in terms of the energy density of the battery, but the effects of the present invention are not limited thereto.

[0135] In one embodiment of the present invention, the lithium-sulfur battery can exhibit the effect of securing the amount of electrolyte to improve side reactions caused by polysulfides in the electrolyte while increasing energy density.

[0136] In one embodiment of the present invention, the lithium-sulfur battery may have an electrolyte / sulfur (E / S) ratio, which represents the weight ratio of the sulfur, which is the positive electrode active material, and the electrolyte, of, for example, 2 g / g or more. Specifically, the electrolyte / sulfur (E / S) ratio may be 2.3 g / g or more. For example, the electrolyte / sulfur (E / S) ratio may be 2 g / g to 3 g / g, 2.1 g / g to 2.7 g / g, or 2.3 g / g to 2.5 g / g. In order to solve the problem that side reactions were caused by the high concentration of polysulfide in the electrolyte when the E / S ratio was lowered in the past to increase the energy density, the present invention has the effect of stabilizing the E / S ratio while increasing the energy density of the battery, and therefore, the E / S ratio of the lithium-sulfur battery may have a value greater than the above-described range, and it will be apparent to those skilled in the art that the upper limit thereof is not limited, and the present invention is not limited thereto.

[0137] In another embodiment of the present invention, the lithium-sulfur battery may have an energy density of 400 Wh / kg to 500 Wh / kg. Specifically, the lithium-sulfur battery may have an energy density of 430 Wh / kg or more, 450 Wh / kg or more, or 460 Wh / kg or more, but the present invention is not limited thereto.

[0138] In one embodiment of the present invention, the lithium-sulfur battery may exhibit a specific capacity of 1,400 mAh / gs or more. Specifically, the specific capacity may be 1,400 mAh / gs or more when discharged at a rate of 0.1 C.

[0139]

[0140] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0141] First, a lithium-sulfur battery in the form of a pouch cell was manufactured using the following method, and the performance of the manufactured battery was evaluated.

[0142] [Battery manufacturing]

[0143] Example 1

[0144] Preparation of electrolyte for lithium-sulfur batteries

[0145] 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI), 5.0 wt% lithium nitrate (LiNO) in a mixture (v / v=4:1) of dimethoxyethane (DME) and 2-methylfuran (2-MeF) 3, An electrolyte solution was prepared by adding 3 wt% of diphenyl ditelluride (DPDTe, 409 g / mol) (molar mass 69 g / mol) and stirring for 12 hours.

[0146]

[0147] Preparation of electrodes

[0148] A cathode slurry was prepared by mixing a sulfur-carbon complex (S:C = 70:30 (weight ratio)) as a cathode active material and polyacrylic acid (PAA) as a binder in a weight ratio of 97:3 using distilled water as a solvent.

[0149] The prepared positive electrode slurry composition was applied to both sides of a 12 ㎛ thick aluminum current collector, dried at 80°C, and rolled using a roll press to prepare a positive electrode. At this time, the loading amount of the positive electrode active material was 3.45 mAh / cm2.

[0150] Lithium metal with a thickness of 30 μm was prepared as a cathode.

[0151]

[0152] Manufacturing of lithium-sulfur batteries

[0153] The positive and negative electrodes manufactured above were positioned so as to face each other, and a polyethylene separator having a thickness of 16 ㎛ and a porosity of 68% was inserted between them, stacked, and assembled into a pouch cell. Then, 1 g of the electrolyte manufactured above was injected and sealed so that the E / S (Electrolyte / S loading amount) ratio was 2.15 g / g, thereby manufacturing a lithium-sulfur battery in the form of a pouch.

[0154]

[0155] Example 2

[0156] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that 8 wt% of DPDTe was added when preparing the electrolyte.

[0157]

[0158] Comparative Example 1

[0159] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that DPDTe was not added when preparing the electrolyte.

[0160]

[0161] Comparative Example 2

[0162] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that 1 wt% of DPDTe was added when preparing the electrolyte.

[0163]

[0164] Comparative Example 3

[0165] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that the non-aqueous solvent was changed to a mixture (v / v=4:1) of dioxolane (DOL) and 2-methylfuran (2-MeF) when preparing the electrolyte.

[0166]

[0167] Comparative Example 4

[0168] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI) was changed to 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt when preparing the electrolyte.

[0169]

[0170] Comparative Example 5

[0171] A lithium-sulfur battery was manufactured according to the same method as Example 1, except that the non-aqueous solvent was changed to a mixture (v / v=4:1) of dioxolane (DOL) and 2-methylfuran (2-MeF) when preparing the electrolyte, and the lithium salt was changed to 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0172]

[0173] [Battery Performance Evaluation and Results]

[0174] The performance of the battery was evaluated in the following manner, and the results are shown in Table 1 below.

[0175] The manufactured battery was operated three times at 30°C for 0.1C charge / 0.1C discharge (2.5 V upper limit / 1.8 V lower limit each) to measure the initial discharge capacity and evaluate the specific capacity. The capacity additionally developed by the aryl derivative was evaluated and is shown in Table 1 below.

[0176] Discharge capacity @ 0.1C (mAh / gs) Aryl derivative expression capacity (mAh / gs) Example 114269.5 Example 2137625.3 Comparative example 11214-Comparative example 212493.2 Comparative example 310929.5 Comparative example 411879.5 Comparative example 510999.5

[0177] As shown in the results in Table 1, it was confirmed that a high discharge capacity of a lithium-sulfur battery can be achieved by including an aryl derivative in an amount of 3 wt% or more in an electrolyte for a lithium-sulfur battery, including an inorganic lithium salt, and including a combination of a heterocyclic compound and a glycol ether as a non-aqueous solvent.

Claims

1. Containing non-aqueous solvents, lithium salts, nitrates and aryl derivatives, The above non-aqueous solvent comprises a heterocyclic compound containing one oxygen atom (O) or sulfur atom (S) in the ring structure; and a glycol ether; The above lithium salt includes an inorganic lithium salt, The above aryl derivative comprises at least one of the compounds represented by any one of the following chemical formulae 1 to 4, An electrolyte for a lithium-sulfur battery, wherein the content of the aryl derivative is 3 wt% or more based on the total weight of the non-aqueous solvent, lithium salt, nitrate, and aryl derivative: [Chemical Formula 1] R 1 -Te-Li [Chemical Formula 2] R 2 -Te-Te-R 3 [Chemical Formula 3] R 4 -Te-Sx-Li [Chemical Formula 4] R 5 -Te-Sx-Te-R 6 In the above chemical formulas 1 to 4, R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently C6 to C 20 is an aryl group, x is a number from 1 to 8.

2. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the above aryl derivative comprises diphenyl ditelluride (DPDTe).

3. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the content of the nitrate and aryl derivative is 6 wt% to 10 wt% based on the total weight of the non-aqueous solvent, lithium salt, nitrate and aryl derivative.

4. In claim 1, The above nitrate is an electrolyte for a lithium-sulfur battery containing lithium nitrate (LiNO3).

5. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the weight of the aryl derivative is equal to or less than the weight of the nitrate.

6. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the concentration of the lithium salt is 0.3 M to 0.75 M.

7. In claim 1, The above inorganic lithium salts are LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiAsF6, LiSbF6, LiAlCl4, (SO2F)2NLi, lithium chloroborane, lithium imide or two or more thereof, an electrolyte for a lithium-sulfur battery.

8. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the above inorganic lithium salt comprises (SO2F)2NLi.

9. An electrolyte for a lithium-sulfur battery according to any one of claims 1 to 8; a cathode comprising a cathode active material; and A negative electrode including a negative active material; A lithium-sulfur battery wherein the positive electrode active material comprises elemental sulfur, a sulfur compound, or a mixture thereof.

10. In claim 9, A lithium-sulfur battery having a specific capacity of 1,400 mAh / gs or more.

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