Electrolyte for lithium-sulfur battery

Abstract

The present invention relates to an electrolyte for use in a lithium-sulfur battery, the electrolyte comprising a non-aqueous solvent, a first lithium salt, a second lithium salt, an inorganic nitrate, and an organic nitrate, wherein the non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound, thereby achieving the improvement in coulombic efficiency and lifespan of the lithium-sulfur battery.

Description

Electrolyte for lithium-sulfur batteries

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

[0002] This application claims priority to Korean Patent Application No. 2024-0030251, filed with the Korean Intellectual Property Office on February 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] As the scope of application of lithium secondary batteries expands beyond portable electronic devices to include electric vehicles (EVs) and electric storage systems (ESS), the demand for lithium secondary batteries with high capacity, high energy density, and long lifespan is increasing.

[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 a positive electrode active material, and lithium metal, a carbon-based material in which lithium ions can be inserted / deinserted, or silicon or tin that forms an alloy with lithium as a negative electrode active material.

[0005] Lithium-sulfur batteries are based on the conversion reaction of lithium ions and sulfur (S8+16Li) at the cathode. + +16e - → The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the negative electrode, it shows a theoretical energy density of 2,600 Wh / kg. This is a very high figure compared to the theoretical energy density of other battery systems currently being studied (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), and therefore, it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries being developed so far.

[0006] However, lithium-sulfur batteries have a problem in that lithium ions can be reduced to lithium metal on the surface of the solid electrolyte interface (SEI) on the anode during the charging process, forming an uneven structure on the anode surface and causing uneven resistance distribution. Consequently, repeated charging and discharging eventually causes lithium to accumulate unevenly, resulting in the appearance of structures such as some dendrites and inactive lithium.

[0007] Among these, dendrites are the main cause of separator destruction and short circuits, so research is ongoing to ensure uniform desorption of lithium ions and deposition of lithium on the negative electrode surface of lithium-sulfur batteries.

[0008] In addition, during the charge / discharge process of lithium-sulfur batteries, polysulfides that are eluted from the cathode during the first discharge (~2.3 V) are deposited on the cathode during the second discharge (~2.1 V), which causes a deterioration in the coulombic efficiency and lifespan of the battery. Accordingly, research is ongoing to improve the lifespan of lithium-sulfur batteries by controlling the amount of polysulfide eluted into the electrolyte using a non-solvent for polysulfide.

[0009] In order to solve the above-described problem, the present invention aims to provide an electrolyte having a novel composition capable of suppressing and preventing the growth of lithium dendrites on a negative electrode and controlling the solubility of polysulfide.

[0010] Specifically, the present invention seeks to provide an electrolyte having a novel composition that is advantageous for forming a solid electrolyte interface, thereby suppressing and preventing lithium dendritic growth on the surface of the cathode. Furthermore, the present invention seeks to provide an electrolyte that enables long-term operation of a lithium-sulfur battery by controlling the amount of polysulfide released from the cathode into the electrolyte.

[0011] Through this, the present invention aims to provide a lithium-sulfur battery with improved battery life and coulombic efficiency.

[0012] To achieve the above purpose,

[0013] According to one aspect of the present invention, electrolytes for lithium-sulfur batteries of the following embodiments are provided.

[0014] The electrolyte according to the first embodiment is

[0015] A non-aqueous solvent comprising a first lithium salt, a second lithium salt, an inorganic nitrate and an organic nitrate, wherein the non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound.

[0016] According to the second embodiment, in the first embodiment,

[0017] The above inorganic nitrate may include a monovalent nitrate, and the above organic nitrate may include a divalent nitrate.

[0018] According to the third embodiment, in the first embodiment or the second embodiment,

[0019] The organic nitrate may include isosorbide dinitrate, 2,2,3,3-tetrafluorobutane-1,4-diol dinitrate, triethylene glycol dinitrate, or a mixture of two or more thereof.

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

[0021] The above inorganic nitrate may include lithium nitrate (LiNO3).

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

[0023] The organic nitrate may be included in an amount equal to or less than the weight of the inorganic nitrate.

[0024] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0025] The non-cyclic ether may be included in an amount of 70% by volume or more based on the total volume of the non-aqueous solvent.

[0026] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0027] The first lithium salt may include a fluorine-containing inorganic lithium salt, and the second lithium salt may include a fluorine-containing organic lithium salt.

[0028] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0029] The combined concentration of the first lithium salt and the second lithium salt may be 0.50 M or less.

[0030] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0031] The ratio of the molar concentrations of the first lithium salt and the second lithium salt may be 1:1 to 2:1.

[0032]

[0033] According to another aspect of the present invention, lithium-sulfur batteries of the following embodiments are provided.

[0034] A lithium-sulfur battery according to the 10th embodiment,

[0035] A lithium-sulfur battery comprising an electrolyte, a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and a battery case according to any one of the first to ninth embodiments, wherein the positive electrode comprises a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material, and the negative electrode comprises a lithium metal layer.

[0036] According to the 11th embodiment, in the 10th embodiment,

[0037] The active material of the positive electrode may include a sulfur-carbon complex in which the sulfur-based compound is supported on at least one of the outer surface and the interior of the pores of the porous carbon material.

[0038] According to the 12th embodiment, in the 10th embodiment or the 11th embodiment,

[0039] The above lithium metal layer may include a lithium metal (Li) foil or a lithium alloy foil.

[0040] According to the 13th embodiment, in any one of the 10th to 12th embodiments,

[0041] The above negative electrode includes the lithium metal layer and a solid electrolyte interface (SEI) formed on the surface of the lithium metal layer, and the solid electrolyte interface may contain nitrogen element (N).

[0042] According to the 14th embodiment, in any one of the 10th to 13th embodiments,

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

[0044] According to one aspect, the electrolyte of the present invention can exhibit a beneficial effect in forming a solid electrolyte interface, specifically a single-ion conductive thin film based on an inorganic all-solid-state material, on the surface of the negative electrode. Accordingly, the electrolyte of the present invention can exhibit an effect in suppressing and preventing lithium dendrite growth on the surface of the negative electrode during charge and discharge of a lithium-sulfur battery.

[0045] Furthermore, the electrolyte of the present invention can exhibit an effect of suppressing the elution of polysulfide itself from the anode into the electrolyte.

[0046] Through this, a lithium-sulfur battery with improved lifespan and coulombic efficiency can be provided using the electrolyte of the present invention.

[0047] Figure 1 shows the results of evaluating the specific capacity according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolyte of Comparative Manufacturing Example 1 and Manufacturing Example 1 in this specification.

[0048] Figure 2 shows the results of evaluating the columbic efficiency according to repeated charge / discharge cycles of a lithium-sulfur battery manufactured using the electrolyte of Comparative Manufacturing Example 1 and Manufacturing Example 1 in this specification.

[0049] Figure 3 shows the results of evaluating the first discharge capacity during the activation process of a lithium-sulfur battery manufactured using the electrolyte of Comparative Manufacturing Example 1 and Manufacturing Example 1 in the present specification.

[0050] Figure 4 shows the results of evaluating the discharge capacity at the first 0.3C discharge after the activation process of a lithium-sulfur battery manufactured using the electrolyte of Comparative Manufacturing Example 1 and Manufacturing Example 1 in the present specification.

[0051] Figure 5 shows the results of evaluating the specific capacity according to repeated charge / discharge cycles of lithium-sulfur batteries manufactured using the electrolytes of Comparative Example 1, Example 1, Example 2, and Example 3 in the present specification.

[0052] Figure 6 shows the results of evaluating the energy density according to repeated charge and discharge cycles of lithium-sulfur batteries manufactured using the electrolytes of Comparative Example 1, Example 1, Example 2, and Example 3 in the present specification.

[0053] Figure 7 shows the results of evaluating the energy density according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolytes of Comparative Example 2, Example 4, and Example 5 in the present specification.

[0054] Figure 8 shows the results of evaluating the specific capacity according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolytes of Comparative Example 2, Example 4, and Example 5 in the present specification.

[0055] Figure 9 shows the results of evaluating the columbic efficiency according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolytes of Comparative Example 2, Example 4, and Example 5 in the present specification.

[0056] Figure 10 shows the results of evaluating the specific capacity according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolytes of Examples 1, 6, and 7 in the present specification.

[0057] Figure 11 shows the results of evaluating the columbic efficiency according to repeated charge and discharge cycles of a lithium-sulfur battery manufactured using the electrolytes of Examples 1, 6, and 7 of the present specification.

[0058] Hereinafter, the present invention will be described in more detail.

[0059] The term "composite" used in this specification refers to a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions.

[0060] The term "(poly)sulfide" as used herein means "(poly)sulfide ion (S x 2- , 1≤x≤8)" and "lithium (poly)sulfide (Li2Sx or Li2S x - It is a concept that includes all of "1≤x≤8".

[0061] The term "polysulfide" as used herein means "polysulfide ion (S x 2- , 1 <x≤8)" 및 "리튬폴리설파이드(Li2S x or Li2S x - 1 <x≤8)"를 모두 포함하는 개념이다.

[0062] 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.

[0063] According to one aspect of the present invention, an electrolyte for a lithium secondary battery is provided, which improves the lifespan and coulombic efficiency of a lithium-sulfur battery using the electrolyte by suppressing and preventing the formation of lithium ion dendrites on the surface of a negative electrode including a lithium metal layer. In particular, according to one aspect of the present invention, an electrolyte for use in a lithium-sulfur battery is provided.

[0064] In addition, according to one aspect of the present invention, an electrolyte is provided that suppresses the dissolution of polysulfide from the positive electrode into the electrolyte, thereby reducing the amount of active material lost on the electrolyte and negative electrode, and improving the lifespan of a lithium-sulfur battery by suppressing degradation of the negative electrode.

[0065]

[0066] An electrolyte according to one aspect of the present invention comprises a non-aqueous solvent, a first lithium salt, a second lithium salt, an inorganic nitrate, and an organic nitrate.

[0067] The above non-aqueous solvent may, but is not limited to, dissolve additives such as lithium salts and nitrates and may be included as an ion transfer medium within the battery.

[0068] As described above, the electrolyte according to one aspect of the present invention comprises two or more salt compounds. Specifically, the electrolyte comprises a lithium salt and a nitrate, the lithium salt comprises a first lithium salt and a second lithium salt, and the nitrate comprises an inorganic nitrate and an organic nitrate.

[0069] In the present invention, the lithium salt is a lithium ion (Li) as a cation. + ) is a general term for all salt compounds containing nitrate, and the nitrate is an anion of nitrate (-NO3 - ) is a general term for all salt compounds containing nitrate. At this time, as described below, lithium nitrate (LiNO3) may be included as a type of the inorganic nitrate, and since lithium nitrate contains lithium ions as cations and nitrate ions as anions, it may correspond to both lithium salts and nitrates. In one example, when lithium nitrate is included as the inorganic nitrate, the electrolyte includes first and second lithium salts and organic nitrates in addition to lithium nitrate. In another example, when lithium nitrate is included as a type of the lithium salt, the electrolyte includes other types of lithium salts, inorganic nitrates and organic nitrates in addition to lithium nitrate.

[0070] In the present invention, the first lithium salt and the second lithium salt may be included as a medium for transferring lithium ions and electrons between the positive and negative electrodes, although their roles are not limited thereto.

[0071] In the present invention, the roles of the inorganic nitrate and organic nitrate are not limited thereto, but may be to suppress the dissolution of polysulfide from the positive electrode into the electrolyte phase, to prevent lithium salts from being decomposed and lost, or to have a beneficial effect on the formation of a protective layer on the negative electrode surface, thereby preventing deterioration of the negative electrode and improving the lifespan of the battery.

[0072] In the present invention, -NO3 in the nitrate -The role of ions is not limited to this, but they can play a role in improving the life of a lithium-sulfur battery by forming LiNxOy material in the protective layer formed on the negative electrode (also called solid electrolyte interface (SEI)) and stabilizing the negative electrode through this. In particular, the inventors of the present invention have found that -NO3 in the electrolyte of a lithium-sulfur battery - It was found that when inorganic nitrate and organic nitrate are included together as nitrates providing ions, there is a beneficial effect on improving the lifespan of lithium-sulfur batteries through stabilization of the negative electrode and suppression of polysulfide in the positive electrode.

[0073] In one embodiment of the present invention, the inorganic nitrate may include, for example, a monovalent nitrate, and may typically include lithium nitrate (LiNO3), but the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the organic nitrate may include, for example, monovalent nitrate, divalent nitrate, trivalent nitrate, or a mixture thereof.

[0075] For example, the organic nitrate may include a divalent nitrate, and representative examples thereof include isosorbide dinitrate (ISDN), 2,2,3,3-tetrafluorobutane-1,4-diol dinitrate, triethylene glycol dinitrate, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0076] In one embodiment of the present invention, the organic nitrate may include isosorbide dinitrate (ISDN).

[0077] The above dinitrate isosorbide (ISDN) is a substance having a structure represented by the following chemical formula 1. As shown in the following chemical formula 1, the ISDN has two -NO3 groups in its organic skeleton structure. - A substance in which ions are bonded, with one molecule of conjugated -NO3 - It is a substance that can provide two ions.

[0078] [Chemical Formula 1]

[0079]

[0080] In one embodiment of the present invention, the electrolyte may exhibit advantageous effects in terms of stabilization of the negative electrode and suppression of dissolution of polysulfide by including the organic nitrate together with the conjugated heterocyclic compound as a non-aqueous solvent.

[0081] In one embodiment of the present invention, the inorganic nitrate may be included in an amount of 0.1 to 8 parts by weight, specifically 0.5 to 6 parts by weight, 1 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, the first lithium salt, and the second lithium salt, in terms of solubility in the electrolyte. When the inorganic nitrate is included in an amount within the above-described range, it may exhibit a beneficial effect in terms of improving the lifespan of the battery due to the inorganic nitrate, but the present invention is not limited thereto.

[0082] According to one embodiment of the present invention, it may be preferable that the organic nitrate be included in an amount equal to or less than the weight of the inorganic nitrate. The organic nitrate may be included in a greater amount than the inorganic nitrate, but in terms of the efficiency of providing nitrate ions relative to the weight, it may be preferable that the organic nitrate be included in an amount equal to or less than the weight of the inorganic nitrate.

[0083] In this respect, the organic nitrate may be included in an amount of, for example, 0.1 to 5 parts by weight, 0.5 to 5 parts by weight, 0.5 to 4 parts by weight, 0.5 to 3.5 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2.5 parts by weight, 0.5 to 2 parts by weight, 0.5 to 1.5 parts by weight, or 0.5 to 1 part by weight, based on 100 parts by weight of the sum of the non-aqueous solvent, the first lithium salt, and the second lithium salt, but the present invention is not limited thereto.

[0084] In one embodiment of the present invention, the inorganic nitrate and the organic nitrate may be included in a weight ratio of, for example, 10:1 to 1:1, 5:1 to 1:1, 5:1 to 3:1, 7:1 to 3:1, 7:1 to 4:1, 6:1 to 4:1, or 6:1 to 5:1, but the present invention is not limited thereto. For example, when the inorganic nitrate and the organic nitrate are included in the above-described weight ratio, it may be more preferable in terms of a synergistic effect on battery performance due to the combined use of the inorganic nitrate and the organic nitrate, but the present invention is not limited thereto.

[0085] In one embodiment of the present invention, the electrolyte may include 3 to 6 parts by weight of inorganic nitrate and 0.5 to 3 parts by weight of organic nitrate based on 100 parts by weight of the sum of the non-aqueous solvent, the first lithium salt, and the second lithium salt.

[0086] According to one aspect of the present invention, the non-aqueous solvent comprises an acyclic ether and a conjugated heterocyclic compound.

[0087] In one embodiment of the present invention, it may be preferable that the non-cyclic ether is included in an amount of 70% by volume or more based on the total volume of the non-aqueous solvent in terms of improving the solubility of lithium polysulfide eluted from the positive electrode and the solubility of the lithium salt and nitrate.

[0088] For example, the acyclic ether may be included in an amount of 70% to 95% by volume, 75% to 90% by volume, 75% to 85% by volume, or 80% by volume based on the total volume of the non-aqueous solvent.

[0089] In one embodiment of the present invention, the acyclic ether is, for example, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethylpropyl ether, ethyl tertbutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tertbutyl ethyl ether, ethylene glycol ethyl methyl ether, or two or more thereof. It may contain a mixture. Preferably, it may contain at least one 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 contain dimethoxyethane.

[0090] In one embodiment of the present invention, the acyclic ether may consist solely of dimethoxyethane (DME).

[0091] In one embodiment of the present invention, the conjugated heterocyclic compound is a general term for a compound having a structure in which 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 including atoms other than carbon as ring atoms in the structure.

[0092] In one embodiment of the present invention, by including a conjugated heterocyclic compound as the non-aqueous solvent, the heterocyclic compound can form a stable solid electrolyte interface (SEI, also referred to as 'electrode-electrolyte interface') on the surface of the lithium-based metal (negative electrode) through a ring opening reaction 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 heteroatoms, typically sulfur atoms, due to the conjugate structure, it can play a role in reducing the amount of polysulfide dissolved from the electrolyte.

[0093] In the present invention, the conjugation action between the nitrate and the conjugated heterocyclic compound in the non-aqueous solvent can exhibit more advantageous effects in terms of stabilizing the negative electrode and suppressing the dissolution of polysulfides in the electrolyte. In particular, the organic nitrate contains a carbon skeleton structure in its structure, which is more advantageous in terms of forming a conjugate structure with the conjugated heterocyclic compound, and therefore, can exhibit a synergistic effect between the organic nitrate and the conjugated heterocyclic compound in terms of stabilizing the negative electrode and suppressing the dissolution of polysulfides.

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

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

[0096] In one embodiment of the present invention, the conjugated heterocyclic compound may include at least one of a conjugated cyclic ether compound and a thiophene compound.

[0097] In one embodiment of the present invention, the conjugated cyclic ether compound may be, for example, a furan compound and a pyran 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, but is not limited to, benzofuran, 2-(2-nitrovinyl)furan, or a mixture of two or more thereof.

[0098] In one embodiment of the present invention, the thiophene-based compound may include, but is not limited to, 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 thereof.

[0099] In one embodiment of the present invention, the non-aqueous solvent may further include a non-conjugated cyclic ether in addition to the non-cyclic ether and the conjugated heterocyclic compound. The above non-conjugated cyclic ethers are, 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-dimethoxy It may include at least one selected from the group consisting of benzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and isosorbide dimethyl ether. Preferably, it may include at least one selected from the group consisting of 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran, but is not limited thereto.

[0100] In one embodiment of the present invention, the non-aqueous solvent may include 1,2-dimethoxyethane (DME) and 2-methylfuran (2-MeF).

[0101] Additionally, the non-aqueous solvent may contain a non-cyclic 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 volume ratio corresponds to the ratio of "volume % of non-cyclic ether" to "volume % of conjugated heterocyclic compound" in the non-aqueous solvent.

[0102] In one embodiment of the present invention, the non-aqueous solvent may further include other organic solvents in addition to the acyclic ether, conjugated heterocyclic compound and non-conjugated cyclic ether compound described above, as long as they can dissolve the lithium salt and the additive. For example, organic solvents used in conventional electrolytes of lithium secondary batteries may include esters, amides, acyclic carbonates and cyclic carbonates, and in one embodiment of the present invention, the non-aqueous solvent may further include, in addition to the ether solvent, the non-aqueous solvent used in conventional electrolytes of lithium secondary batteries described above. However, preferably, in terms of the solubility of the lithium salt, nitrate and aryl derivative, the lithium secondary battery electrolyte may preferably not include the carbonate solvent as the non-aqueous solvent.

[0103] In one embodiment of the present invention, the ester may be, for example, 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 thereof, but is not limited thereto.

[0104] In one embodiment of the present invention, the acyclic carbonate may be, for example, 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 thereof, but is not limited thereto.

[0105] In one embodiment of the present invention, the cyclic carbonate is, for example, 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 halogenides thereof, or a mixture of two or more thereof. Examples of the halogenides thereof include, but are not limited to, fluoroethylene carbonate.

[0106] In another embodiment of the present invention, since the carbonate solvent does not dissolve the nitrate or exhibits low solubility, the non-aqueous solvent may not contain the carbonate solvent.

[0107] In one embodiment of the present invention, the non-aqueous solvent may include a very small amount of carbonate solvent such that the carbonate solvent does not affect the solubility of the nitrate, and for example, when the non-aqueous solvent includes the carbonate solvent, the content of the carbonate solvent may be 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0 wt% (i.e., not included at all) based on the total weight of the electrolyte for the lithium-sulfur battery.

[0108]

[0109] In particular, according to one embodiment of the present invention, the first lithium salt and the second lithium salt each include a fluorine-containing compound. The first lithium salt and the second lithium salt include a compound containing one or more fluorine (F) atoms as an anion, and may specifically include a fluorine-containing inorganic lithium salt, a fluorine-containing organic lithium salt, or a mixture of two or more thereof.

[0110] In one embodiment of the present invention, the fluorine-containing inorganic lithium salt may include, for example, LiBF4, LiPF6, LiAsF6, LiSbF6, LiN(SO2F)2, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0111] In one embodiment of the present invention, the fluorine-containing organic lithium salt may include, for example, LiCF3SO3, LiCF3CO2, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0112] In one embodiment of the present invention, the first lithium salt may include a fluorine-containing inorganic lithium salt, and the second lithium salt may include a fluorine-containing organic lithium salt.

[0113] In another embodiment of the present invention, the first lithium salt may be composed of a fluorine-containing inorganic lithium salt, and the second lithium salt may be composed of a fluorine-containing organic lithium salt.

[0114] In one embodiment of the present invention, the first lithium salt may comprise LiN(SO2F)2 alone.

[0115] In another embodiment of the present invention, the second lithium salt may comprise LiN(SO2C2F5)2 alone.

[0116] In one embodiment of the present invention, the lithium salt may further include a third lithium salt in addition to the first lithium salt and the second lithium salt, as long as it does not hinder the purpose of the present invention. The third lithium salt is not limited as long as it is a lithium salt other than a lithium salt containing fluorine and can be used as a lithium salt in the electrolyte of a lithium-sulfur battery. For example, the third lithium salt may be LiCl, LiBr, LiI, LiClO4, LiB. 10 Cl10 , LiC4BO8, LiAlCl4, LiSO3CH3, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4-phenylborate, lithium imide, or two or more thereof may be further included, but the present invention is not limited thereto.

[0117] In one embodiment of the present invention, the combined molar concentration of the first lithium salt and the second lithium salt in the mixture of the non-aqueous solvent and the first lithium salt and the second lithium salt may be limited to, for example, 1.0 M or less, specifically 0.75 M or less. More specifically, it may be limited to 0.50 M or less. When the concentration of the lithium salt is in the above-described range, it may exhibit a beneficial effect on the solubility of the lithium salt in the electrolyte and the effect of improving battery performance by the additive, but the present invention is not limited thereto.

[0118] In one embodiment of the present invention, the combined molar concentration of the first and second lithium salts in the mixture of the non-aqueous solvent and the first and second lithium salts may be specifically 0.3 M to 1.0 M, 0.33 M to 0.8 M, 0.33 M to 0.75 M, 0.40 M to 0.70 M, 0.40 M to 0.60 M, for example, 0.50 M.

[0119] In one embodiment of the present invention, the first lithium salt and the second lithium salt may be included in the same molar ratio, but considering the mobility of the lithium salt in the electrolyte, it may be preferable for the first lithium salt to be included in a greater molar concentration than the second lithium salt. For example, the molar concentration ratio of the first lithium salt and the second lithium salt may be 5:1 to 1:1, 3:1 to 1:1, or 2:1 to 1:1, but the present invention is not limited thereto.

[0120] As described above, according to one aspect of the present invention, a novel composition of electrolyte is provided that is excellent in preventing and suppressing degeneration of a negative electrode when used in a lithium-sulfur battery.

[0121]

[0122] According to another aspect of the present invention, a lithium-sulfur battery comprising an electrolyte for a lithium-sulfur battery having the composition described above is provided.

[0123] The lithium-sulfur battery includes an electrolyte, a cathode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and a battery case.

[0124] According to one aspect of the present invention, the lithium-sulfur battery may mean a battery including a sulfur series compound containing a sulfur (S)-sulfur (S) bond as a positive electrode active material and including a lithium metal layer as a negative electrode.

[0125] In one embodiment of the present invention, the lithium metal layer may be a thin film layer composed only of lithium metal (Li).

[0126] In another embodiment of the present invention, the lithium metal layer may be a thin film layer made 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.

[0127] In one embodiment of the present invention, the negative electrode may be provided as a free-standing film including a lithium metal layer and a protective layer without a separate support.

[0128] In another embodiment of the present invention, the negative electrode may be provided in a form including a lithium metal layer and a protective layer (also called a solid electrolyte interface (SEI)) on a support.

[0129] In one embodiment of the present invention, the negative electrode may include the lithium metal layer and a solid electrolyte interface (SEI) formed on the surface of the lithium metal layer.

[0130] At this time, the solid electrolyte interface (SEI) may contain nitrogen element (N) as a constituent component. More specifically, the solid electrolyte interface may contain nitrogen element (N) derived from the inorganic nitrate and organic nitrate.

[0131] In one embodiment of the present invention, when ISDN is included as an organic nitrate in the electrolyte for the lithium-sulfur battery, the content of nitrogen element (N) in the solid electrolyte interface (SEI) within the negative electrode can be the most excellent. This can exhibit the most excellent effect in slowing down battery deterioration due to repeated charge and discharge of the lithium-sulfur battery, but the present invention is not limited thereto.

[0132] At this time, the support may be a polyolefin porous support used as a current collector or a separator used in a conventional lithium secondary battery electrode, but is not limited thereto.

[0133] 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 the current collector. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0134] In one embodiment of the present invention, the current collector may be a copper foil having a thickness of, for example, 10 to 30 μm, for example, 10 μm.

[0135] In addition, the negative electrode according to one embodiment of the present invention may further include a conventional configuration that can be used for the negative electrode of a lithium secondary battery, particularly a lithium-sulfur battery, and is not particularly limited to the configuration further included as long as it does not impede the purpose of the present invention.

[0136] In one embodiment of the present invention, the positive electrode can be used without limitation as long as it includes a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material.

[0137] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both surfaces of the positive electrode current collector.

[0138] The above-mentioned 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. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0139] The above positive electrode current collector can form fine irregularities on its surface to strengthen the bonding strength with the positive electrode active material, and can be used in various forms such as a film, sheet, foil, mesh, net, porous body, foam, and non-woven fabric.

[0140] The above positive electrode active material layer includes a positive electrode active material and may further include a conductive material, a binder, and additives.

[0141] In one embodiment of the present invention, the positive electrode active material may include a sulfur-carbon complex.

[0142] In one embodiment of the present invention, the sulfur-carbon composite may include 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. In the case of sulfur acting as the positive electrode active material, since sulfur alone does not have electrical conductivity, 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 sulfur. In addition, the sulfur-based compound may include, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≤ 8), a disulfide compound, a carbon-sulfur polymer ((C2S) y ) n , y = 2.5 to 50, n≥2), lithium sulfide (Li2S) or two or more thereof. Preferably, the sulfur compound may be inorganic sulfur (S8).

[0143] In one embodiment of the present invention, the porous carbon material is used to support a sulfur-based compound as a positive electrode active material, and to provide a framework in which the sulfur-based compound can be uniformly and stably fixed, while improving the conductivity of the positive electrode. Any porous carbon material can be used without particular limitation in its type.

[0144] The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped, and may be any shape commonly used in lithium-sulfur batteries. The porous carbon material may be any shape commonly used in the art, as long as it has a porous structure or a high specific surface area.

[0145] For example, the porous carbon material may be at least one 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 summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); and graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0146] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNTs).

[0147] In one embodiment of the present invention, the sulfur-carbon composite may contain the sulfur-based compound in an amount of 65 wt% or more, for example, 65 wt% to 90 wt%, 65 wt% to 85 wt%, 70 wt% to 80 wt%, or 70 wt% to 75 wt%, based on the total weight of the sulfur-based compound and the porous carbon material.

[0148] When the content of the sulfur series compound in the above sulfur-carbon complex is within the above-described range, it may be preferable in terms of the electron transfer area of ​​the sulfur-carbon complex and wettability with the electrolyte of the positive electrode, and for example, the available surface of the sulfur-carbon complex increases, which may be preferable in suppressing the elution of sulfur from the positive electrode, but the present invention is not limited thereto.

[0149] The method for manufacturing the above sulfur-carbon composite is not particularly limited in the present invention, and any method commonly used in the art may be used. For example, a method may be used in which the sulfur and porous carbon material are simply mixed and then heat-treated to form a composite.

[0150] In addition to the composition described above, the positive electrode active material may include at least one selected from among a transition metal element, a group Ⅲ element, a group ⅣA element, a sulfur compound of these elements, and an alloy of these elements and sulfur.

[0151] 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, etc., the above group Ⅲ elements include Al, Ga, In, Ti, etc., and the above group ⅣA elements may include Ge, Sn, Pb, etc.

[0152] In one embodiment of the present invention, the conductive material, binder, and other components that can be used in the positive electrode active material layer can utilize conventional techniques and are not particularly limited to the present invention.

[0153] In one embodiment of the present invention, the binder may be, for example, a mixture of three types of binder resins. Specifically, in one embodiment of the present invention, the binder may include a first binder resin, a second binder resin, and a third binder resin, wherein the first binder resin may be a lithium-substituted polyacrylic acid, the second binder resin may be a lithium-substituted carboxymethylcellulose, and the third binder resin may be a colloidal particle-type aqueous binder resin.

[0154] According to one embodiment of the present invention, the binder in the positive electrode active material layer includes a specific combination of a first binder resin and a second binder resin that can contribute to improving processability and a third binder resin that can contribute to improving adhesive strength, thereby maintaining high levels of productivity and output performance and exhibiting excellent adhesive strength, but the present invention is not limited thereto.

[0155] In one embodiment of the present invention, the first binder resin is a lithium-substituted polyacrylic acid. The lithium-substituted polyacrylic acid is a form in which the hydrogen of a carboxyl group (COOH) in polyacrylic acid is substituted with lithium. The lithium-substituted polyacrylic acid can be formed through a neutralization reaction by adding a base containing lithium to polyacrylic acid. It may be preferable that the lithium-substituted polyacrylic acid is formed by completely neutralizing the polyacrylic acid by adding the base so that the amount of carboxyl groups and lithium of the polyacrylic acid is 1:1 molar ratio. For example, the lithium-substituted polyacrylic acid of the present invention may be formed by neutralizing the polyacrylic acid using LiOH so that the pH is in the range of 6 to 9, or in the range of 6.5 to 8.

[0156] In one embodiment of the present invention, the second binder resin is lithium-substituted carboxymethyl cellulose. The lithium-substituted carboxymethyl cellulose can provide excellent adhesion not only to the electrode active material but also to the surface of the electrode current collector. Furthermore, it can function as a dispersant within the binder composition, and particularly, when mixed with the positive electrode active material, it can enhance the dispersibility of the positive electrode active material. Furthermore, its high viscosity can improve the stability of the slurry.

[0157] The lithium-substituted carboxymethyl cellulose may be formed by adding a base containing lithium to carboxymethyl cellulose through a neutralization reaction and then washing, or by directly binding lithium ions to carboxymethyl cellulose. For example, when formed through a neutralization reaction, it may be preferable that the lithium-substituted carboxymethyl cellulose be formed by adding a base such that the amount of carboxymethyl cellulose and lithium is in a 1:1 molar ratio, thereby completely neutralizing the carboxymethyl cellulose. For example, the lithium-substituted carboxymethyl cellulose of the present invention may be formed by neutralizing the pH using LiOH to a range of 6 to 9, or 6.5 to 8.

[0158] In one embodiment of the present invention, the third binder resin is a colloidal particle-type aqueous binder resin. The colloidal particle-type aqueous binder resin can suppress an increase in viscosity of the dissolved polymer and the binder composition by existing in an undissolved particle state within the aqueous binder composition, and can serve as a binder that increases the adhesive strength between electrode active materials and / or between the electrode active material and the electrode current collector.

[0159] The above colloidal particle-type aqueous binder resin exists in a state of being dispersed in an aqueous solvent, and is stably dispersed in a particle state having a shape close to a spherical shape without being dissolved and having an average particle diameter (D50) of 50 to 500 nm. The above average particle diameter (D50) may refer to the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter.

[0160] The colloidal particle-type aqueous binder resin may be styrene butadiene rubber, an acrylic polymer containing repeating units derived from at least one acrylic monomer, or a mixture of two or more thereof.

[0161] The above acrylic polymer may be applied without limitation as long as it contains a repeating unit derived from at least one acrylic monomer, and may be, for example, an acrylic polymer derived from one acrylic monomer or a copolymer containing repeating units derived from at least two or more acrylic monomers. Examples of the acrylic monomer include acrylic acid, alkyl acrylate, alkyl methacrylate, isoalkyl (meth)acrylate, and the like, and in this case, “alkyl” may be an alkyl group having 1 to 10 carbon atoms, and more specifically, an alkyl group having 1 to 5 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, and the like. Preferably, the acrylic monomer may include an acrylic copolymer containing repeating units derived from acrylic acid and butyl (meth)acrylate.

[0162] In one embodiment of the present invention, the separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode. The separator may be made of a porous non-conductive or insulating material, and any material commonly used as a separator in a lithium secondary battery may be used without special limitation. The separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and / or the negative electrode.

[0163] In one embodiment of the present invention, the electrolyte may include a non-aqueous solvent and a lithium salt as a medium through which ions involved in the electrochemical reaction of a lithium secondary battery, for example, a lithium-sulfur battery, can move.

[0164] The above electrolyte is not particularly limited as long as it has a composition that can be used in a lithium secondary battery, specifically a lithium-sulfur battery.

[0165] In one embodiment of the present invention, the lithium-sulfur battery may have various shapes, for example, a coin shape, a pouch shape, or a cylindrical shape, but is not limited thereto.

[0166]

[0167] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0168]

[0169] Experimental Example 1. Performance verification of organic nitrates

[0170] [Electrolyte production]

[0171] Comparative Manufacturing Example 1

[0172] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2) and 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours to dissolve the lithium salt. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0173]

[0174] Manufacturing Example 1

[0175] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2) and 5 wt% isosorbide dinitrate (ISDN) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0176]

[0177] [Manufacturing of lithium-sulfur batteries]

[0178] A pouch-type lithium-sulfur battery was manufactured using each of the electrolytes of Comparative Manufacturing Example 1 and Manufacturing Example 1 manufactured above, using the following method.

[0179] As a cathode, a 60 μm thick lithium film (Ganfeng lithium group) was prepared.

[0180] As a positive electrode, a sulfur-carbon composite (S8 75 wt%) was prepared by mixing inorganic sulfur (S8) and carbon nanotubes (CNT) as a positive electrode active material, and 95 wt% of the prepared sulfur-carbon composite and 5 wt% of PAA (polyacrylate) as a binder were mixed to prepare a positive electrode slurry composition. The positive electrode slurry composition was applied to both sides of an aluminum current collector, dried at 80°C, and rolled with a roll press to obtain a positive electrode having a capacity of 3.0 mAh / cm 2 An electrode having a loading amount of was prepared.

[0181] A polyethylene separator having a thickness of 12 ㎛ and a porosity of 46 vol% was prepared as a separator and then interposed between the positive and negative electrodes prepared above.

[0182] After placing the above positive electrode / separator / negative electrode assembly in a pouch-type case, the electrolyte manufactured above was injected, and the lid was covered and sealed to manufacture a pouch-type lithium-sulfur battery.

[0183]

[0184] [Performance Evaluation of Lithium-Sulfur Battery]

[0185] The lithium-sulfur battery manufactured as described above was activated by performing 0.1C discharge three times at 25°C, and then charge and discharge (CC mode, 1.8 V to 2.5 V) was repeated with 0.2C charge and 0.3C discharge as one cycle. The results of evaluating the performance of the battery during the charge and discharge process are shown in FIGS. 1 to 4.

[0186] Figure 1 shows the results of evaluating the specific capacity according to repeated charge / discharge cycles, and Figure 2 shows the results of evaluating the columbic efficiency according to repeated charge / discharge cycles. Referring to the results of Figures 1 and 2, it was confirmed that the lifespan of a lithium-sulfur battery can be dramatically improved by adding ISDN to the electrolyte.

[0187] In addition, Fig. 3 shows the results of evaluating the first discharge capacity during the activation process, and Fig. 4 shows the results of evaluating the discharge capacity at the first 0.3C discharge after the activation process. Referring to the results of Fig. 3, when ISDN was added to the electrolyte, the reduction voltage of ISDN was observed during the activation of the lithium-sulfur battery. Thereafter, referring to the results of Fig. 4, when ISDN was added to the electrolyte, it was confirmed that the discharge was performed stably during the discharge after the activation process, whereas when ISDN was not added, it was confirmed that the battery was operated unstably in the first charge / discharge cycle.

[0188] Through this, it was confirmed that by adding ISDN to the electrolyte of a lithium-sulfur battery, the charge-discharge characteristics of the lithium-sulfur battery can be stabilized and the life characteristics of the battery can be improved.

[0189]

[0190] Experimental Example 2. Performance Evaluation of Combined Use of Inorganic and Organic Nitrates 1

[0191] [Electrolyte production]

[0192] Comparative Example 1

[0193] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2) and 5 wt% lithium nitrate (LiNO3) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0194]

[0195] Example 1

[0196] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2), 5 wt% lithium nitrate (LiNO3), and 1 wt% isosorbide dinitrate (ISDN) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0197]

[0198] Example 2

[0199] An electrolyte was prepared in the same manner as in Example 1, except that 3 wt% of isosorbide dinitrate (ISDN) was added.

[0200]

[0201] Example 3

[0202] An electrolyte was prepared in the same manner as in Example 1, except that 5 wt% of isosorbide dinitrate (ISDN) was added.

[0203]

[0204] The electrolyte compositions of Comparative Example 1 and Examples 1 to 3 prepared above are summarized in Table 1 below.

[0205] Non-aqueous solvent 1 Lithium salt 2 Lithium salt Inorganic nitrate Organic nitrate Comparative example 1 DME:2-MeF (8:2 v / v) LiFSI, 0.33 MLiBETI, 0.17 MLiNO3, 5 wt% - Example 1 ISDN, 1 wt% Example 2 ISDN, 3 wt% Example 3 ISDN, 5 wt%

[0206] [Performance Evaluation of Lithium-Sulfur Battery]

[0207] A pouch-type lithium-sulfur battery was manufactured using each of the electrolytes of Comparative Example 1 and Examples 1 to 3 manufactured above, using the following method.

[0208] As a cathode, a 60 μm thick lithium film (Ganfeng lithium group) was prepared.

[0209] As a cathode, a sulfur-carbon composite (S8 75 wt%) was prepared by mixing inorganic sulfur (S8) and carbon nanotubes (CNT) as cathode active materials, and 96 wt% of the prepared sulfur-carbon composite, a three-component mixed binder of lithium-substituted carboxymethyl cellulose (GL Chem Co.): lithium-substituted polyacrylic acid (Chemtros Co.): acrylic colloid (acrylic acid ester copolymer, LG Chem, ADB84) in a weight ratio of 1.5:0.5:2.0 was mixed to prepare a cathode slurry composition. The cathode slurry composition was applied to both sides of an aluminum current collector, dried at 80°C, and rolled with a roll press to obtain a cathode having a capacity of 2.95 mAh / cm 2 An electrode having a loading amount of was prepared.

[0210] A polyethylene separator having a thickness of 12 ㎛ and a porosity of 46 vol% was prepared as a separator and then interposed between the positive and negative electrodes prepared above.

[0211] After placing the above positive electrode / separator / negative electrode assembly in a pouch-type case, the electrolyte manufactured above was injected, and the lid was covered and sealed to manufacture a pouch-type lithium-sulfur battery.

[0212] After manufacturing a lithium-sulfur battery as described above, charging and discharging were performed in the same manner as in Experimental Example 1, and the results are shown in Figures 5 and 6 below.

[0213] Referring to the results of FIGS. 5 and 6, it was confirmed that the lifespan of the battery using the electrolytes of Examples 1 to 3 used together with ISDN was superior to that of Comparative Example 1 using LiNO3 alone as a nitrate in the electrolyte. In particular, it was confirmed that the performance of the lithium-sulfur battery using the electrolyte of Example 1 containing 1 wt% ISDN was the best in terms of improved capacity decrease in the early stage of the cycle.

[0214]

[0215] Experimental Example 3. Performance Evaluation of Combined Use of Inorganic and Organic Nitrates 2

[0216] [Electrolyte production]

[0217] Comparative Example 2

[0218] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2) and 6 wt% lithium nitrate (LiNO3) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0219]

[0220] Example 4

[0221] 0.33 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2), 0.17 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2), 6 wt% lithium nitrate (LiNO3), and 0.5 wt% isosorbide dinitrate (ISDN) were added to 1,2-dimethoxyethane (DME) and stirred for 12 hours. Then, 2-methylfuran (2-MeF) as a conjugated heterocyclic compound was added and stirred to prepare an electrolyte (DME:2-MeF=8:2 v / v).

[0222]

[0223] Example 5

[0224] An electrolyte was prepared in the same manner as in Example 1, except that 1 wt% of isosorbide dinitrate (ISDN) was added.

[0225]

[0226] The electrolyte compositions of Comparative Example 2, Examples 4 and 5 manufactured above are summarized and shown in Table 2 below.

[0227] Non-aqueous solvent 1 Lithium salt 2 Lithium salt Inorganic nitrate Organic nitrate Comparative example 2 DME:2-MeF (8:2 v / v) LiFSI, 0.33 MLiBETI, 0.17 MLiNO3, 6 wt% - Example 4 ISDN, 0.5 wt% Example 5 ISDN, 1 wt%

[0228] [Performance Evaluation of Lithium-Sulfur Battery]

[0229] Each of the electrolytes of Comparative Example 2, Examples 4 and 5 manufactured above was used, and the loading amount of the positive electrode was 2.7 mAh / cm 2 After manufacturing a lithium-sulfur battery in the same manner as described in Experimental Example 2, except that the thickness of the cathode was changed to 50 ㎛, charge and discharge were performed in the same manner as in Experimental Example 1, and the results are shown in Figures 7 to 9 below.

[0230] Referring to the results of FIGS. 7 to 9, it was confirmed that the battery using the electrolyte of Examples 4 and 5, which included 0.5 wt% and 1.0 wt% of ISDN, respectively, was superior in terms of lifespan compared to Comparative Example 2, which used LiNO3 alone as a nitrate in the electrolyte.

[0231]

[0232] Experimental Example 4. Performance Evaluation of Electrolyte Composition

[0233] Example 6

[0234] An electrolyte was prepared in the same manner as in Example 1, except that the composition of the lithium salt was changed to 0.66 M lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2) and 0.34 M lithium bis(pentafluoroethanesulfonyl)imide (LiBETI, LiN(SO2C2F5)2).

[0235]

[0236] Example 7

[0237] An electrolyte was prepared in the same manner as in Example 1, except that the non-aqueous solvent composition was changed to a ratio of DME:2-MeF=2:1 v / v.

[0238]

[0239] The electrolyte compositions of Examples 6 and 7 prepared above are summarized in Table 3 below.

[0240] Non-aqueous solvent 1 Lithium salt 2 Lithium salt Inorganic nitrate Organic nitrate Example 1 DME:2-MeF(8:2 v / v)LiFSI, 0.33 MLiBETI, 0.17 MLiNO3, 5 wt% ISDN, 1 wt% Example 6 DME:2-MeF(8:2 v / v)LiFSI, 0.66 MLiBETI, 0.34 M Example 7 DME:2-MeF(2:1 v / v)LiFSI, 0.33 MLiBETI, 0.17 M

[0241] [Performance Evaluation of Lithium-Sulfur Battery]

[0242] Using the electrolytes of Examples 1, 6 and 7 manufactured above, the loading amount of the positive electrode was 2.7 mAh / cm 2 After manufacturing a lithium-sulfur battery in the same manner as described in Experimental Example 1, except that the thickness of the cathode was changed to 50 ㎛, charge and discharge were performed in the same manner as in Experimental Example 1, and the results are shown in Figures 10 and 11 below.

[0243] Referring to the results of FIGS. 10 and 11, it was confirmed that when inorganic nitrate and organic nitrate were used in combination as nitrates, the performance improvement of the battery using them decreased as the combined concentration of the first lithium salt and the second lithium salt increased (Example 1 vs. Example 6). In addition, when inorganic nitrate and organic nitrate were used in combination as nitrates, it was confirmed that when the ratio of the conjugated heterocyclic compound in the non-aqueous solvent composition increased, the performance improvement of the battery using them decreased (Example 1 vs. Example 7).

[0244] Through the above experiments, it was confirmed that a lithium secondary battery, particularly a lithium-sulfur battery, using an electrolyte according to one embodiment of the present invention can exhibit a significant lifespan improvement effect and a Coulomb improvement effect.

Claims

1. Containing a non-aqueous solvent, a first lithium salt, a second lithium salt, an inorganic nitrate and an organic nitrate, The above non-aqueous solvent is an electrolyte for a lithium-sulfur battery comprising an acyclic ether and a conjugated heterocyclic compound.

2. In claim 1, The above inorganic nitrate includes monovalent nitrate, The above organic nitrate is an electrolyte for a lithium-sulfur battery containing divalent nitrate.

3. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the organic nitrate comprises isosorbide dinitrate, 2,2,3,3-tetrafluorobutane-1,4-diol dinitrate, triethylene glycol dinitrate, or a mixture of two or more thereof.

4. In claim 1, The above inorganic 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 organic nitrate is contained in an amount equal to or less than the weight of the inorganic nitrate.

6. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the non-cyclic ether is contained in an amount of 70% by volume or more based on the total volume of the non-aqueous solvent.

7. In claim 1, The above first lithium salt comprises a fluorine-containing inorganic lithium salt, The second lithium salt is an electrolyte for a lithium-sulfur battery comprising an organic lithium salt containing fluorine.

8. In claim 1, An electrolyte for a lithium-sulfur battery, wherein the combined concentration of the first lithium salt and the second lithium salt is 0.50 M or less.

9. In claim 8, An electrolyte for a lithium-sulfur battery, wherein the molar concentration ratio of the first lithium salt and the second lithium salt is 1:1 to 2:

1.

10. A lithium-sulfur battery comprising an electrolyte, a cathode, an anode, a separator interposed between the cathode and the anode, and a battery case according to any one of claims 1 to 9, The above positive electrode includes a sulfur series compound containing a sulfur (S)-sulfur (S) bond as an active material, A lithium-sulfur battery, wherein the negative electrode comprises a lithium metal layer.

11. In claim 10, A lithium-sulfur battery, wherein the active material of the positive electrode comprises a sulfur-carbon complex in which the sulfur-based compound is supported on at least one of the outer surface and the interior of the pores of the porous carbon material.

12. In claim 10, A lithium-sulfur battery, wherein the lithium metal layer comprises a lithium metal (Li) foil or a lithium alloy foil.

13. In claim 10, The cathode includes the lithium metal layer and a solid electrolyte interface (SEI) formed on the surface of the lithium metal layer, A lithium-sulfur battery, wherein the solid electrolyte interface contains nitrogen element (N).

14. In claim 10, The above lithium-sulfur battery is a lithium-sulfur battery that is a coin-shaped, pouch-shaped or cylindrical battery.

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