Electrolyte for lithium-sulfur batteries

Abstract

The present invention relates to an electrolyte for lithium-sulfur batteries, which comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the non-aqueous solvent includes an acyclic ether and a conjugated heterocyclic compound, and the additive includes P2S5 and a lithium- and fluorine-containing compound.

Description

Electrolyte for lithium-sulfur batteries

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

[0002] This application claims priority based on Korean application No. 10-2025-0007523 filed on January 17, 2025, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] As the application range of lithium secondary batteries expands to include not only portable electronic devices but also electric vehicles (EVs) and electric storage systems (ESS), there is a growing demand for high-capacity, high-energy-density, and long-life lithium secondary batteries.

[0004] Among various lithium secondary batteries, the lithium-sulfur battery is a battery system that uses a sulfur-based material containing a sulfur-sulfur bond as the positive electrode active material, and uses lithium metal, a carbon-based material in which lithium ion insertion / extraction occurs, or silicon or tin that forms an alloy with lithium as the negative electrode active material.

[0005] A lithium-sulfur battery is formed by the conversion reaction of lithium ions and sulfur (S8+16Li) at the positive electrode. + +16e - → The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the anode, it exhibits a theoretical energy density of 2,600 Wh / kg. Since this is a very high value compared to the theoretical energy densities of other battery systems currently under study (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480 Wh / kg, Li-MnO2 battery: 1,000 Wh / kg, Na-S battery: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg), it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries currently being developed.

[0006] However, in lithium-sulfur batteries, lithium ions can be reduced to lithium metal on the surface of the solid electrolyte interface (SEI) on the anode during the charging process, which leads to the formation of a non-uniform structure on the anode surface and causes a problem of non-uniform resistance distribution. Consequently, as lithium accumulates unevenly due to repeated charging and discharging, structures such as some lithium dendrites and inactive lithium appear.

[0007] Among these, lithium dendrites are a major cause of separator destruction and short circuits, so research is continuing to make the desorption of lithium ions and the electrodeposition of lithium uniform on the negative electrode surface of lithium-sulfur batteries.

[0008] To solve the aforementioned problem, the present invention aims to provide an electrolyte of a novel composition capable of suppressing and preventing the growth of lithium dendrites on the cathode.

[0009] Specifically, the present invention aims to provide an electrolyte of a novel composition advantageous for forming a solid electrolyte interface to suppress and prevent dendritic lithium growth on the cathode surface.

[0010] Through this, the present invention aims to provide a lithium-sulfur battery with improved energy density, battery life, and Coulomb efficiency.

[0011] The present invention provides an electrolyte for a lithium-sulfur battery or a lithium-sulfur battery of the following embodiments.

[0012] The electrolyte for a lithium-sulfur battery according to the first embodiment is,

[0013] It includes a non-aqueous solvent, a lithium salt, and additives,

[0014] The above-mentioned non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound, and

[0015] The above additive includes P2S5 and a lithium fluorine-containing compound.

[0016] The second embodiment is, in the first embodiment,

[0017] With respect to a total of 100 wt% of the above electrolyte, the above additive may be included in an amount of 5 wt% or less.

[0018] The third embodiment is, in the first embodiment or the second embodiment,

[0019] The above P2S5 and the above lithium fluorine-containing compound may be included in a weight ratio of 1:0.5 to 1:5.

[0020] The fourth embodiment is, in any one of the first to third embodiments,

[0021] With respect to a total of 100 wt% of the above electrolyte, the above P2S5 may be included in an amount of 4.0 wt% or less.

[0022] The fifth embodiment is, in any one of the first to fourth embodiments,

[0023] With respect to a total of 100 wt% of the above electrolyte, the lithium fluorine-containing compound may be included in an amount of 4.5 wt% or less.

[0024] The sixth embodiment may contain 60 volume% or more of the acyclic ether with respect to the total volume of the non-aqueous solvent in any one of the first to fifth embodiments.

[0025] The seventh embodiment is, in any one of the first to sixth embodiments,

[0026] The above-mentioned acyclic ether may include dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethylmethyl ether, ethylpropyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethylmethyl ether, diethylene glycol isopropylmethyl ether, diethylene glycol butylmethyl ether, diethylene glycol tert-butyl ethyl ether, ethylene glycol ethylmethyl ether, or a mixture of two or more of these.

[0027] The eighth embodiment is, in any one of the first to seventh embodiments,

[0028] The above-mentioned conjugated heterocyclic compound is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, 2H-pyran, 4H-pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, It may include 2-(2-Nitrovinyl)furan, thiphene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, benzothiophene, or a mixture of two or more of these.

[0029] The ninth embodiment is, in any one of the first to eighth embodiments,

[0030] The above lithium fluorine-containing compound may include LiF, LiBF4, LiPF6, LiAsF6, LiSbF6, LiN(SO2F)2, LiCF3SO3, LiCF3CO2, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2F)2, LiC(SO2CF3)3, or a mixture of two or more of these.

[0031] The 10th embodiment is, in any one of the 1st to 9th embodiments,

[0032] The molar concentration of the lithium salt in the above-mentioned non-aqueous solvent and lithium salt may be 1.0 M or less.

[0033] A lithium-sulfur battery according to the 11th embodiment is,

[0034] It includes an anode, a cathode, a separator interposed between the cathode and the anode, an electrolyte, and a battery case, and

[0035] The above anode comprises a sulfur-based compound containing sulfur(S)-sulfur(S) bonds as an active material, and

[0036] The above cathode includes a lithium metal layer, and

[0037] The above electrolyte may be an electrolyte for a lithium-sulfur battery according to any one of the first to ten embodiments.

[0038] The 12th embodiment is, in the 11th embodiment,

[0039] The active material of the above anode may include a sulfur-carbon composite in which the sulfur-based compound is supported on at least one of the outer surface and the inside of the pores of the porous carbon material.

[0040] The 13th embodiment is, in the 11th embodiment or the 12th embodiment,

[0041] The above lithium metal layer may include a lithium metal (Li) foil or a lithium alloy foil.

[0042] The 14th embodiment is, in any one of the 11th to 13th embodiments,

[0043] The above lithium-sulfur battery may be a coin type, pouch type, or cylindrical type battery.

[0044] According to one aspect of the present invention, the electrolyte of the present invention can form a lithium-fluorine-based protective layer on the surface of the negative electrode. Through this, the electrolyte of the present invention can exhibit the effect of suppressing and preventing the growth of lithium dendrites on the surface of the negative electrode during charging and discharging of a lithium-sulfur battery.

[0045] Through this, by using the electrolyte of the present invention, a lithium-sulfur battery with improved energy density, cycle life, and Coulomb efficiency can be provided.

[0046] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the description of the invention; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0047] FIG. 1 is a graph showing the performance evaluation of a battery according to one embodiment and a comparative example of the present invention.

[0048] FIG. 2 is a graph showing the performance evaluation of a battery according to one embodiment and a comparative example of the present invention.

[0049] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0050] Therefore, the embodiments described in this specification and the configurations described in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0051] Furthermore, throughout the specification, when a part is described as "include, comprise," "have," or "possess" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0052] Additionally, terms such as 'about,' 'substantially,' etc., used throughout this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding this invention.

[0053] Throughout this specification, the description of 'A and / or B' means 'A or B or both.'

[0054] Throughout the entire specification, unless otherwise specifically stated, temperature refers to Celsius temperature, and the unit is °C.

[0055] As used in this specification, the term "composite" refers to a material in which two or more materials are combined to form physically and chemically different phases, thereby exhibiting more effective functions.

[0056] The term "(poly)sulfide" as used in this specification refers to "(poly)sulfide ion (S x 2- , 1≤x≤8” and "lithium (poly)sulfide (Li2S x or Li2S x- It is a concept that includes all of 1≤x≤8”.

[0057] The term "polysulfide" as used in this specification refers to "polysulfide ions (S x 2- , 1 <x≤8)" 및 "리튬폴리설파이드(Li2S x or Li2S x - , 1 <x≤8)"를 모두 포함하는 개념이다.

[0058] Lithium secondary batteries have the characteristic that lithium ions are reduced on the surface of the negative electrode during charging and discharging, and lithium metal accumulates on the negative electrode through repeated charging and discharging.

[0059]

[0060] The first aspect of the present invention is an electrolyte for a lithium-sulfur battery.

[0061] The above electrolyte for a lithium-sulfur battery can improve the lifespan and Coulomb efficiency of a lithium-sulfur battery by suppressing and preventing the formation of lithium dendrites on the surface of a negative electrode containing a lithium metal layer.

[0062]

[0063] An electrolyte according to one aspect of the present invention comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound, and the additive comprises P2S5 and a lithium fluorine-containing compound.

[0064] The above-mentioned non-aqueous solvent is not limited to this role, but, for example, can dissolve lithium salts and additives and be included as an ion transfer medium within the battery.

[0065] The above lithium salt may be included as a medium for the transfer of lithium ions and electrons between the anode and cathode, although its role is not limited thereto.

[0066] The above additive may be included, although its role is not limited thereto, to prevent the decomposition and loss of the lithium salt or to facilitate the formation of a protective layer on the surface of the negative electrode, thereby preventing the degradation of the negative electrode and improving the lifespan of the battery.

[0067]

[0068] In one embodiment of the present invention, the electrolyte may contain the additive in an amount of 5 wt% or less with respect to a total of 100 wt%. Specifically, with respect to a total of 100 wt% of the electrolyte, the additive may be contained in an amount of 5 wt% or less, 4.5 wt% or less, 4 wt% or less, 0.1 wt% or more, 0.5 wt% or more, or 1 wt% or more.

[0069] In addition, the above P2S5 and the above lithium fluorine-containing compound may be included in a weight ratio of 1:0.5 to 1:5, 1:1 to 1:4, or 1:1 to 1:3.

[0070] When the above additive is included in the above range of content, the growth of lithium dendrites on the surface of the cathode can be sufficiently suppressed.

[0071]

[0072] In one embodiment of the present invention, although the mechanism of action of the P2S5 is not limited thereto, the P2S5 may react with lithium in an environment where polysulfide is present to form a protective layer containing a solid electrolyte such as Li3PS4 on the surface of a lithium-containing negative electrode.

[0073] To this end, the electrolyte may contain the P2S5 in an amount of 4.0 wt% or less, 3.5 wt% or less, 3.33 wt% or less, 3.0 wt% or less, 2.5 wt% or less, 2.0 wt% or less, 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 0.83 wt% or more, based on a total of 100 wt%.

[0074]

[0075] In one embodiment of the present invention, although the mechanism of action of the lithium fluorine-containing compound is not limited thereto, a fluorine-rich protective layer can be formed on a lithium-containing cathode. The surface of the fluorine-rich protective layer is hard, so it can suppress the formation of lithium dendrites.

[0076] To this end, the electrolyte may contain a lithium fluorine compound in an amount of 4.5 wt% or less, 4.16 wt% or less, 4.0 wt% or less, 3.5 wt% or less, 3.0 wt% or less, 2.5 wt% or less, 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 1 wt% or more, 1.5 wt% or more, or 1.66 wt% or more, based on a total of 100 wt%.

[0077]

[0078] In one embodiment of the present invention, the electrolyte for the lithium-sulfur battery may be a non-aqueous electrolyte, and the additive component may be uniformly distributed within the electrolyte.

[0079] When the above electrolyte is in a liquid phase, interfacial wettability can be provided to the surface of the negative electrode. In particular, even if the surface of the negative electrode becomes rough or undergoes a shape change due to the charging and discharging of the battery, interfacial wettability can be provided because the electrolyte is a liquid.

[0080] The above additive can be present at a uniform concentration across the entire surface of the cathode. Therefore, by preventing localized concentration of lithium ion flow and forming a uniform protective layer across the entire surface of the cathode, the nucleation of lithium dendrites can be fundamentally suppressed.

[0081]

[0082] In one embodiment of the present invention, the non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound.

[0083]

[0084] In one embodiment of the present invention, it may be preferable that the acyclic ether be included in an amount of 60 volume% or more based on the total volume of the non-aqueous solvent in order to improve the solubility of lithium polysulfide eluted from the anode and the solubility of the lithium salt and nitrate.

[0085] For example, the acyclic ether may be included in an amount of 60 to 95 volume%, 70 to 90 volume%, 75 to 85 volume%, or 80 volume% based on the total volume of the non-aqueous solvent.

[0086]

[0087] In one embodiment of the present invention, the acyclic ether comprises, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethylmethyl ether, ethylpropyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethylmethyl ether, diethylene glycol isopropylmethyl ether, diethylene glycol butylmethyl ether, diethylene glycol tert-butylethyl ether, ethylene glycol ethylmethyl ether, or a mixture of two or more of these. It may include one or more selected from the group consisting of dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. More preferably, it may include dimethoxyethane.

[0088] In one embodiment of the present invention, the acyclic ether may consist solely of dimethoxyethane (DME).

[0089]

[0090] In one embodiment of the present invention, the conjugated heterocyclic compound is a general term for a compound having a structure in which the p orbitals of three or more neighboring atoms constituting the compound can overlap with other p orbitals of adjacent atoms connected by sigma bonds, and containing atoms other than carbon as ring atoms within the structure.

[0091]

[0092] In one embodiment of the present invention, by including a conjugated heterocyclic compound as the non-aqueous solvent, the heterocyclic compound forms a stable solid electrolyte interface (SEI, also referred to as the 'electrode-electrolyte interface') on the surface of a lithium-based metal (negative electrode) through a ring-opening polymerization reaction during the initial discharge stage of the battery, thereby exhibiting an effect of suppressing the formation of lithium dendrites. Furthermore, by reducing electrolyte decomposition and the resulting side reactions on the surface of the lithium-based metal, it can exhibit an effect of improving the lifespan characteristics of the lithium-sulfur battery. In addition, because the conjugated structure has the characteristic of making it difficult to dissolve salt due to the delocalization of lone pair electrons of heteroatoms, typically sulfur atoms, it can play a role in reducing the amount of polysulfide leached from the electrolyte.

[0093]

[0094] In one embodiment of the present invention, the conjugated heterocyclic compound may be a heterocyclic compound having 4 to 15 groups, preferably 4 to 7 groups, and more preferably 5 to 6 groups. In addition, such a conjugated 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 addition, the conjugated heterocyclic compound may be a polycyclic compound of a heterocyclic compound with one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0095] When the above-mentioned conjugated heterocyclic compound is substituted with an alkyl group having 1 to 4 carbon atoms, the radical is stabilized, which is desirable as it can suppress side reactions between the electrolytes. In addition, when it is substituted with a halogen group or a nitro group, it is desirable as it can form a functional protective film on the surface of a lithium-based metal. In this case, the formed functional protective film is stable as a compact protective film, and has the advantage of enabling uniform deposition of the lithium-based metal and suppressing side reactions between the polysulfide and the lithium-based metal.

[0096]

[0097] In one embodiment of the present invention, the conjugated heterocyclic compound may comprise one or more of a conjugated cyclic ether compound and a thiophene-based compound.

[0098] In one embodiment of the present invention, the conjugated cyclic ether compound may be, for example, a furan-based compound and a pyran-based compound, and more specifically, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, 2H-pyran, 4H-pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, It may include benzofuran, 2-(2-nitrovinyl)furan, or a mixture of two or more selected from these, but is not limited thereto.

[0099] In one embodiment of the present invention, the thiophene-based compound may include, for example, thiophene, 2-methylthiophene, 2-ethylthiphene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, benzothiophene, or a mixture of two or more of these, but is not limited thereto.

[0100]

[0101] In one embodiment of the present invention, the non-aqueous solvent may further include a non-conjugated cyclic ether in addition to the acyclic ether and the conjugated heterocyclic compound. The above-mentioned non-conjugated cyclic ether is, for example, 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxybenzene, It may include one or more selected from the group consisting of 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and isosorbide dimethyl ether. Preferably, it may include one or more selected from the group consisting of 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran, but is not limited thereto.

[0102] In one embodiment of the present invention, the non-aqueous solvent may include 1,2-dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0103] In addition, the above-mentioned non-aqueous solvent may contain acyclic ether and a conjugated heterocyclic compound in a volume ratio of 95:5 to 5:95, preferably 95:5 to 50:50, most preferably 90:10 to 70:30 or 80:20. The above volume ratio corresponds to the ratio of "volume% of acyclic ether" to "volume% of conjugated heterocyclic compound" in the non-aqueous solvent.

[0104]

[0105] In one embodiment of the present invention, the non-aqueous solvent may be any organic solvent other than the aforementioned acyclic ether, conjugated heterocyclic compound, and non-conjugated cyclic ether compound, provided that it is capable of dissolving the lithium salt and the additive. For example, organic solvents used in the electrolyte of a conventional lithium-sulfur battery may include esters, amides, acyclic carbonates, and cyclic carbonates. In one embodiment of the present invention, the non-aqueous solvent may further include the aforementioned non-aqueous solvent used in the electrolyte of a conventional lithium-sulfur battery in addition to the aforementioned ether-based solvent.

[0106]

[0107] In one embodiment of the present invention, the ester may be, 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 of two or more of these, but is not limited thereto.

[0108]

[0109] In one embodiment of the present invention, the acyclic carbonate may be, for example, any one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate, or a mixture of two or more of these, but is not limited thereto.

[0110]

[0111] In one embodiment of the present invention, the cyclic carbonate is, for example, any one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more of these. Examples of their halides include, but are not limited to, fluoroethylene carbonate.

[0112] In another embodiment of the present invention, since the carbonate-based solvent does not dissolve the nitrate or exhibits low solubility, the non-aqueous solvent may not contain the carbonate-based solvent.

[0113] In one embodiment of the present invention, the non-aqueous solvent may contain a very small amount of carbonate-based solvent such that the carbonate-based solvent does not affect the solubility of the nitrate, and for example, when the non-aqueous solvent contains the carbonate-based solvent, the content of the carbonate-based solvent may be 3 weight% or less, 2 weight% or less, 1 weight% or less, 0.5 weight% or less, or 0 weight% (i.e., not included at all) based on the total weight of the electrolyte for the lithium-sulfur battery.

[0114]

[0115] In one embodiment of the present invention, the lithium fluorine-containing compound comprises a compound containing one or more fluorine (F) atoms as anions, specifically a fluorine-containing inorganic compound, a fluorine-containing organic compound, or a mixture of two or more of these.

[0116] In one embodiment of the present invention, the fluorine-containing inorganic compound may include, for example, LiF, LiBF4, LiPF6, LiAsF6, LiSbF6, LiN(SO2F)2, or a mixture of two or more of these, and preferably may be LiF, but the present invention is not limited thereto.

[0117] In one embodiment of the present invention, the fluorine-containing organic compound may include, for example, LiCF3SO3, LiCF3CO2, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2F)2, LiC(SO2CF3)3, or a mixture of two or more of these, but the present invention is not limited thereto.

[0118]

[0119] In one embodiment of the present invention, the electrolyte for a lithium-sulfur battery may further include two or more salt compounds. For example, it may further include a lithium salt and a nitrate.

[0120] In the present invention, the lithium salt is a lithium ion (Li) as a cation. + It collectively refers to all salt compounds containing ), and the nitrate is nitrate (-NO3) as an anion. - It is a collective term for all salt compounds containing ). In this case, compounds such as lithium nitrate (LiNO3) may correspond to both lithium salts and nitrates since they contain lithium ions as cations and nitrate ions as anions; regardless of which category they fall under, the electrolyte of the present invention may additionally include one type of lithium salt or nitrate in addition to lithium nitrate.

[0121]

[0122] In one embodiment of the present invention, the lithium salt may further include, in addition to the lithium fluorine-containing compound, a lithium salt that can be used as a lithium salt in the electrolyte of a lithium-sulfur battery, to the extent that it does not impede the purpose of the present invention. For example, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 It may further include , LiC4BO8, LiAlCl4, LiSO3CH3, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide, or two or more of these.

[0123]

[0124] In one embodiment of the present invention, the molar concentration of the lithium salt in the mixture of the non-aqueous solvent and the lithium salt may be limited to, for example, 1.0 M or less. When the concentration of the lithium salt is within the range described above, it may exhibit an advantageous effect on the solubility of the lithium salt in the electrolyte and the improvement of battery performance by the additive, but the present invention is not limited thereto.

[0125] In one embodiment of the present invention, the molar concentration of the lithium salt in the mixture of the non-aqueous solvent and the lithium salt may specifically be 0.3 M to 1.0 M, 0.5 M to 1.0 M, 0.5 M to 0.8 M, for example, 0.75 M.

[0126]

[0127] In one embodiment of the present invention, the nitrate is added to stabilize a cathode containing a lithium metal layer and to form a solid electrolyte interface on the cathode surface, wherein one or more nitrate ions (-NO3) are anions. - If it contains ), it may be used without limitation. For example, the nitrate may be an inorganic nitrate, an organic nitrate, or a mixture of two or more of these.

[0128] In one embodiment of the present invention, the inorganic nitrate may include, for example, lithium nitrate (LiNO3).

[0129]

[0130] In one embodiment of the present invention, regarding the solubility of the nitrate, it may be included in an amount of 0.1 to 5 parts by weight, specifically 0.5 to 5 parts by weight, 1 to 5 parts by weight, 2 to 5 parts by weight, or 3 to 5 parts by weight, based on 100 parts by weight of the sum of the non-aqueous solvent and the lithium salt. When the nitrate is included in the above-described range, it may exhibit an advantageous effect in terms of improving battery life due to the nitrate, but the present invention is not limited thereto.

[0131] As described above, according to one aspect of the present invention, an electrolyte of a novel composition is provided that is used in a lithium-sulfur battery and has excellent effects in preventing and controlling the degradation of the negative electrode.

[0132]

[0133] A second aspect of the present invention relates to a lithium-sulfur battery.

[0134] A lithium-sulfur battery according to the present invention comprises a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, an electrolyte, and a battery case, wherein the positive electrode comprises a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as an active material, the negative electrode comprises a lithium metal layer, and the electrolyte comprises an electrolyte for a lithium-sulfur battery according to one aspect of the present invention.

[0135]

[0136] In one embodiment of the present invention, the lithium metal layer may be a thin film layer composed solely of lithium metal (Li).

[0137] In another embodiment of the present invention, the lithium metal layer may be a thin film layer composed of lithium and a material that forms an alloy with lithium, such as silicon, tin, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, aluminum, or a lithium alloy alloyed with two or more of these materials.

[0138]

[0139] In one embodiment of the present invention, the cathode may be provided as a free-standing film comprising a lithium metal layer and a protective layer without a separate support.

[0140] In another embodiment of the present invention, the cathode may be provided in a form including a lithium metal layer and a protective layer on a support.

[0141] At this time, the support may be a polyolefin porous support used as a current collector or separator in conventional lithium secondary battery electrodes, but is not limited thereto.

[0142] In one embodiment of the present invention, the current collector supports the lithium metal layer and is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery using it. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, a surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used.

[0143]

[0144] In one embodiment of the present invention, the current collector may be a copper foil having, for example, a thickness of 10 to 30 μm, for example, 10 μm.

[0145] In addition, the cathode according to one embodiment of the present invention may further include conventional configurations that can be used as a cathode for a lithium secondary battery, particularly a lithium-sulfur battery, and is not particularly limited to the configurations further included as long as they do not impede the purpose of the present invention.

[0146]

[0147] In one embodiment of the present invention, the anode may be used without limitation as long as it comprises a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as an active material.

[0148] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector.

[0149] The above positive current collector supports the positive active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., and aluminum-cadmium alloy may be used.

[0150] The above positive current collector can strengthen the bonding force with the positive active material by forming fine irregularities on its surface, and can be used in various forms such as film, sheet, foil, mesh, net, porous body, foam, nonwoven fabric, etc.

[0151] The above positive active material layer includes a positive active material and may further include a conductive material, a binder, and additives.

[0152] In one embodiment of the present invention, the positive active material may include a sulfur-carbon composite.

[0153] In one embodiment of the present invention, the sulfur-carbon composite may comprise a porous carbon material; and a sulfur-based compound supported on at least one of the outer surface and the interior of the pores of the porous carbon material. Since sulfur acting as the positive electrode active material does not have electrical conductivity on its own, it is used in a composite with a conductive material such as a carbon material, and a porous carbon material may be used to support the sulfur. In addition, the sulfur-based compound is, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 <x≤8), 디설파이드 화합물, 탄소-황 폴리머((C2S y ) n , y=2.5 to 50, n≥2), lithium sulfide (Li2S), or may include two or more of these. Preferably, the sulfur compound may be inorganic sulfur (S8).

[0154] In one embodiment of the present invention, the porous carbon material supports a sulfur-based compound as an anode active material and provides a framework in which the sulfur-based compound can be uniformly and stably fixed, thereby improving the conductivity of the anode; any porous carbon material can be used without being particularly limited in type.

[0155] The above porous carbon material may be used in any form—spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk—as long as it is commonly used in lithium-sulfur batteries, without limitation. Any porous carbon material that has a porous structure or a high specific surface area and is commonly used in the industry may be acceptable.

[0156] For example, the porous carbon material may be one or more selected from the group consisting of graphite; graphene; carbon black such as Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermo Black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); graphite such as natural graphite, artificial graphite, and expanded graphite, and activated carbon, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0157]

[0158] In one embodiment of the present invention, the sulfur-carbon composite may contain the sulfur-based compound in an amount of 65% by weight or more, for example, 65% to 90% by weight, 65% to 85% by weight, 70% to 80% by weight, or 70% to 75% by weight, based on the total weight of the sulfur-based compound and the porous carbon material.

[0159] When the content of sulfur-based compounds in the sulfur-carbon composite is within the range described above, it may be desirable in terms of the electron transfer surface area of ​​the sulfur-carbon composite and the wettability with the electrolyte of the anode; for example, it may be desirable to suppress the leaching of sulfur from the anode by increasing the usable surface area of ​​the sulfur-carbon composite, but the present invention is not limited thereto.

[0160] The method for manufacturing the above sulfur-carbon composite is not specifically limited in the present invention, and methods commonly used in the industry may be used. For example, a method of simply mixing the sulfur and porous carbon material and then heat-treating them to form a composite may be used.

[0161] In addition to the composition described above, the positive electrode active material may comprise one or more selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

[0162] The above transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, the above Group IIIA elements include Al, Ga, In, Ti, etc., and the above Group IVA elements may include Ge, Sn, Pb, etc.

[0163] In one embodiment of the present invention, the conductive material, binder, and other components that can be used in the positive active material layer may utilize conventional technology and are not particularly limited to the present invention.

[0164]

[0165] In one embodiment of the present invention, the separator separates or insulates the anode and the cathode from each other and enables lithium ion transport between the anode and the cathode, and may be made of a porous non-conductive or insulating material, and may be used without special limitations as long as it is typically used as a separator in a lithium-sulfur battery. Such a separator may be an independent member such as a film, or may be a coating layer added to the anode and / or cathode.

[0166]

[0167] In one embodiment of the present invention, the lithium-sulfur battery may have various shapes, for example, coin-type, pouch-type, or cylindrical shapes, but is not limited thereto.

[0168]

[0169] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0170]

[0171] Example 1

[0172] A solution was prepared by adding P2S5 (Sigma-Aldrich) and LiF in a weight ratio of 1:1 to a mixed non-aqueous solvent in which 1,2-dimethoxyethane (DME) and 2-methylfuran (2-MeF) were mixed in a volume ratio of 8:2 (v / v) at room temperature (23℃).

[0173] Subsequently, a non-aqueous solvent comprising 1,2-dimethoxyethane (DME) and 2-methylfuran (2-MeF) mixed in an 8:2 (v / v) ratio was added to the prepared solution, and lithium nitrate (LiNO3) was dissolved to prepare an electrolyte.

[0174] In the prepared electrolyte, for a total of 100 wt% of the electrolyte, P2S5 was 0.7 wt%, LiF was 0.7 wt%, and LiNO3 was 6 wt%.

[0175]

[0176] Example 2

[0177] An electrolyte was prepared in the same manner as in Example 1, except that P2S5 (Sigma-Aldrich) and LiF were added to a non-aqueous solvent in a weight ratio of 1:2, and in the prepared electrolyte, P2S5 was included at 0.7 wt% and LiF at 1.4 wt% with respect to a total of 100 wt% of the electrolyte.

[0178]

[0179] Example 3

[0180] An electrolyte was prepared in the same manner as in Example 1, except that P2S5 (Sigma-Aldrich) and LiF were added to a non-aqueous solvent in a weight ratio of 1:3, and in the prepared electrolyte, P2S5 was included at 0.7 wt% and LiF at 2.1 wt% with respect to a total of 100 wt% of the electrolyte.

[0181]

[0182] Comparative Example 1

[0183] An electrolyte was prepared in the same manner as in Example 1, except that P2S5 (Sigma-Aldrich) and LiF were not added.

[0184]

[0185] Comparative Example 2

[0186] An electrolyte was prepared in the same manner as in Example 1, except that P2S5 (Sigma-Aldrich) and LiF were added to a non-aqueous solvent in a weight ratio of 1:5.5, and in the prepared electrolyte, P2S5 was included at 0.7 wt% and LiF at 3.85 wt% with respect to a total of 100 wt% of the electrolyte.

[0187]

[0188] Comparative Example 3

[0189] An electrolyte was prepared in the same manner as in Example 1, except that a non-aqueous solvent was used in which 1,2-dimethoxyethane and 1,3-dioxolane were mixed in a volume ratio of 1:1 (v / v).

[0190]

[0191] The composition of the electrolytes prepared in the above examples and comparative examples is summarized and shown in Table 1.

[0192] Weight ratio of non-aqueous solvent P2S5 and LiF Example 1:DME:2-MeF (8:2 v / v) 1:1 Example 2:1:2 Example 3:1:3 Comparative Example 1:Comparative Example 2:1:5.5 Comparative Example 3:DME:1-3-dioxolane (1:1 v / v) 1:1

[0193] [Manufacturing of Lithium-Sulfur Batteries]

[0194] A pouch-type lithium-sulfur battery was manufactured using each of the electrolytes of the examples and comparative examples prepared above in the following manner.

[0195] First, a negative electrode was prepared by laminating a lithium foil with a thickness of 50㎛.

[0196] Next, a sulfur-carbon composite (S870 wt%) was prepared by mixing inorganic sulfur (S8) and carbon nanotubes (CNT) as positive active materials, and a positive slurry composition was prepared by mixing 96 wt% of the prepared sulfur-carbon composite and 4 wt% of polyacrylate (PAA) as a binder. The positive slurry composition was coated onto an aluminum current collector and dried to produce a positive electrode having a loading amount of 3.3 mAh / cm2.

[0197] After preparing a polyethylene separator with a thickness of 11 μm and a porosity of 46 vol% as a separator, it was interposed between the anode and cathode prepared above.

[0198] After placing the anode / separator / cathode assembly into a pouch-type case, the electrolyte prepared above was injected, and the lid was closed and sealed (El / S ratio = 2.4 g / g).

[0199]

[0200] [Performance Evaluation of Lithium-Sulfur Batteries]

[0201] After aging the lithium-sulfur battery prepared as described above at room temperature (23℃) for 24 hours, the battery was subjected to 0.1C discharge and 0.1C charge twice, followed by a cycle of 0.3C discharge and 0.2C charge, and the battery's performance was evaluated as follows while repeating the charge and discharge cycle.

[0202]

[0203] energy density

[0204] In the charge-discharge cycle, the energy density was calculated according to the following equation, and the result is shown in Fig. 1.

[0205] Energy Density (Wh / kg) = [(Discharge Capacity × Driving Voltage)] / (Battery Weight)

[0206]

[0207] Coulomb efficiency

[0208] In a charge-discharge cycle, the ratio of discharge capacity to charge capacity within one cycle was evaluated according to the following equation to measure the Coulomb efficiency, and the results were shown in Figure 2.

[0209] Coulomb Efficiency (%) = (Discharge Capacity / Charge Capacity) × 100

[0210]

[0211] Referring to Fig. 1, it was confirmed that the energy density of the lithium-sulfur batteries using the electrolytes of Examples 1 to 3 was excellent. In particular, when the electrolyte of Comparative Example 2 was used, the energy density decreased rapidly after about 50 cycles because the LiF content was excessively high compared to P2S5. In addition, when the electrolyte of Comparative Example 3 was used, it was confirmed that the energy density was significantly lower. This is believed to be because it did not contain a heterocyclic compound conjugated with a non-aqueous solvent.

[0212]

[0213] Referring to Fig. 2, it was confirmed that the Coulomb efficiency of the lithium-sulfur battery using the electrolytes of Examples 1 to 3 was excellent. In particular, when the electrolyte of Comparative Example 2 was used, the content of LiF was excessively high compared to P2S5, so it was observed that the Coulomb efficiency decreased sharply after about 50 cycles. In addition, when the electrolyte of Comparative Example 3 was used, it was observed that the Coulomb efficiency decreased sharply after about 20 cycles. This is believed to be because it did not contain a heterocyclic compound conjugated with a non-aqueous solvent.

[0214]

[0215] As described above, although the present invention has been explained by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. As an electrolyte for a lithium-sulfur battery comprising a non-aqueous solvent, a lithium salt, and an additive, The above-mentioned non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound, and The above additive is an electrolyte for a lithium-sulfur battery comprising P2S5 and a lithium fluorine-containing compound.

2. In Paragraph 1, An electrolyte for a lithium-sulfur battery characterized by containing the additive in an amount of 5 wt% or less with respect to a total of 100 wt% of the electrolyte.

3. In Paragraph 1, Electrolyte for a lithium-sulfur battery characterized by comprising the above P2S5 and the above lithium fluorine-containing compound in a weight ratio of 1:0.5 to 1:

5.

4. In Paragraph 1, An electrolyte for a lithium-sulfur battery characterized by containing the P2S5 in an amount of 4.0 wt% or less with respect to a total of 100 wt% of the electrolyte.

5. In Paragraph 1, An electrolyte for a lithium-sulfur battery characterized by containing the lithium fluorine-containing compound in an amount of 4.5 wt% or less with respect to a total of 100 wt% of the electrolyte.

6. In Paragraph 1, An electrolyte for a lithium-sulfur battery characterized by containing 60 volume% or more of the acyclic ether with respect to the total volume of the above-mentioned non-aqueous solvent.

7. In Paragraph 1, The above-mentioned acyclic ether is characterized by comprising dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethylmethyl ether, ethylpropyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethylmethyl ether, diethylene glycol isopropylmethyl ether, diethylene glycol butylmethyl ether, diethylene glycol tert-butylethyl ether, ethylene glycol ethylmethyl ether, or a mixture of two or more of these, for a lithium-sulfur battery. Electrolytes.

8. In Paragraph 1, The above-mentioned conjugated heterocyclic compound is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, 2H-pyran, 4H-pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, An electrolyte for a lithium-sulfur battery characterized by comprising 2-(2-Nitrovinyl)furan, thiphene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, benzothiophene, or a mixture of two or more of these.

9. In Paragraph 1, The above lithium fluorine-containing compound comprises LiF, LiBF4, LiPF6, LiAsF6, LiSbF6, LiN(SO2F)2, LiCF3SO3, LiCF3CO2, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2F)2, LiC(SO2CF3)3, or a mixture of two or more of these, for an electrolyte for a lithium-sulfur battery.

10. In Paragraph 1, Electrolyte for a lithium-sulfur battery characterized in that the molar concentration of the lithium salt in the mixture of the above-mentioned non-aqueous solvent and the lithium salt is 1.0 M or less.

11. A positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, an electrolyte, and a battery case, comprising, The above anode comprises a sulfur-based compound containing sulfur(S)-sulfur(S) bonds as an active material, and The above cathode includes a lithium metal layer, and A lithium-sulfur battery, wherein the above electrolyte is an electrolyte for a lithium-sulfur battery according to any one of claims 1 to 10.

12. In Paragraph 11, A lithium-sulfur battery characterized in that the active material of the above-mentioned positive electrode comprises a sulfur-carbon composite in which the sulfur-based compound is supported on at least one of the outer surface and the inside of the pores of a porous carbon material.

13. In Paragraph 11, A lithium-sulfur battery characterized in that the lithium metal layer comprises a lithium metal (Li) foil or a lithium alloy foil.

14. In Paragraph 11, A lithium-sulfur battery characterized in that the above lithium-sulfur battery is a coin-type, pouch-type, or cylindrical battery.

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