WO2018004103A1 - Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising same - Google Patents

Abstract

The present invention relates to an electrolyte for a three component-based lithium-sulfur battery, and a lithium-sulfur battery comprising same. The electrolyte for a lithium-sulfur battery, according to the present invention, exhibits a high use rate of sulfur and excellent stability when applied to a lithium-sulfur battery. As a result, the electrolyte for a lithium-sulfur battery, according to the present invention, can secure capacity characteristics as well as improve life characteristics of the lithium-sulfur battery.

Description

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

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0080630 dated June 28, 2016 and Korean Patent Application No. 10-2017-0019514 dated February 13, 2017. All content disclosed in the literature is included as part of this specification.

The present invention relates to a three-component lithium-sulfur battery electrolyte and a lithium-sulfur battery comprising the same.

Recently, with the development of portable electronic devices, electric vehicles and large-capacity power storage systems, the need for a large-capacity battery is emerging. Lithium-sulfur battery is a secondary battery that uses a sulfur-based material having an SS bond (Sulfur-sulfur bond) as a positive electrode active material and a lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, is very rich in resources and toxic. This has the advantage of having a low weight per atom.

In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1672mAh / g-sulfur, and the theoretical energy density is 2,600 Wh / kg, and the theoretical energy density of other battery systems currently being studied (Ni-MH battery: 450 Wh / kg, Li- FeS cells: 480 Wh / kg, Li-MnO ₂ batteries: 1,000 Wh / kg, Na-S cells: 800 Wh / kg) is very high compared to the attention has been attracting attention as a battery having a high energy density characteristics.

However, the lithium-sulfur battery has not been commercialized yet. This is because, when sulfur is used as an active material, the ratio (sulfur utilization rate) used for the electrochemical reaction is low, so that a sufficient capacity as the theoretical capacity is not obtained. In order to overcome this problem, development of an anode material having an increased sulfur impregnation amount and an electrolyte solution capable of increasing sulfur utilization rate has been made.

Currently, 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME), which show excellent sulfur utilization, are used as electrolyte solvents of lithium-sulfur batteries. These are used alone or in combination, and Korean Patent Laid-Open Publication No. 10-2009-0086575 uses a polymer to separate 1,3-dioxolane in an anode and 1,2-dimethoxyethane in an unbalanced manner in a positive electrode. Lithium-sulfur batteries are disclosed.

However, the solvent has a disadvantage in that it is easy to decompose during battery operation. When the solvent is decomposed, gases such as hydrogen, methane, and ethene are generated, which causes swelling and eventually shortens the life of the battery.

Therefore, in order to obtain stable life characteristics in a lithium-sulfur battery, it is necessary to develop a stable electrolyte solution that does not cause decomposition during battery cell operation.

[Preceding technical literature]

Republic of Korea Patent Publication No. 10-2009-0086575, separation of the electrolyte

The present inventors studied the electrolyte solvent composition of the lithium-sulfur battery to solve the above problems, and as a result, the present invention was completed.

Accordingly, an object of the present invention is to provide an electrolyte solution for lithium-sulfur batteries with excellent stability.

In addition, another object of the present invention to provide a lithium-sulfur battery comprising the electrolyte.

In order to solve the above problems, the present invention

Including lithium salts and non-aqueous solvents,

The non-aqueous solvent is

i) a cyclic ether comprising one oxygen in the ring structure;

ii) glycol ethers represented by the following formula (1); And

iii) a linear ether represented by the following formula (2); It provides an electrolyte for a lithium-sulfur battery, comprising:

[Formula 1]

R ¹ -O- (CH ₂ CH ₂ O) _x -R ²

[Formula 2]

R ³ -O- (CH ₂ CH ₂ O) _y -R ⁴

(In Chemical Formulas 1 and 2, R ¹ to R ⁴ , x, and y are as described in the specification)

In this case, the cyclic ether may be a 5 to 7 membered cyclic ether unsubstituted or substituted with a C1 to C4 alkyl or alkoxy group.

In this case, the cyclic ether may be tetrahydrofuran or tetrahydropyran unsubstituted or substituted with an alkyl or alkoxy group of C1 to C4.

In this case, the cyclic ether is tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, 2,4-dimethyltetrahydrofuran, 2,5-dimethyltetrahydro Furan, 2-methoxytetrahydrofuran, 3-methoxytetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 3-ethoxytetrahydrofuran, tetrahydropyran, 2- It may be one selected from the group consisting of methyltetrahydropyran, 3-methyltetrahydropyran, and 4-methyltetrahydropyran.

In this case, the glycol ether may be one selected from the group consisting of 1,2-dimethoxyethane, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

In this case, the linear ether may be one selected from the group consisting of ethylene glycol ethyl methyl ether, ethylene glycol diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and diisobutyl ether.

In this case, the cyclic ether may be included in 10 to 50% by volume of the total weight of the non-aqueous solvent.

In this case, the glycol ether and the linear ether may be included in a volume ratio of 1: 3 to 3: 1.

At this time, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, Chloro It may be one selected from the group consisting of lithium borane, lower aliphatic lithium carbonate, lithium 4-phenyl borate, lithium imide, and combinations thereof.

In this case, the lithium salt may be included in a concentration of 0.1 to 4.0 M.

In this case, the electrolyte may further include an additive having an intramolecular N-O bond.

At this time, the additive is lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imida Zolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitro pyridine, dinitro It may be at least one selected from the group consisting of pyridine, nitrotoluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl.

In this case, the additive may be included in 0.01 to 10% by weight relative to 100% by weight of the electrolyte.

The present invention also provides a lithium-sulfur battery comprising the electrolyte solution.

The electrolyte according to the present invention exhibits excellent sulfur utilization when applied to lithium-sulfur batteries and shows excellent stability. Therefore, the electrolyte solution for a lithium-sulfur battery according to the present invention can ensure the capacity characteristics of the lithium-sulfur battery and at the same time improve the life characteristics.

1 is a graph showing specific discharge capacities of batteries of Examples 1 to 2 and 1 to 2 in comparison.

2 is a graph showing specific discharge capacities of batteries of Examples 3 to 6 and Comparative Example 3. FIG.

Hereinafter, the present invention will be described in detail so that those skilled in the art can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Electrolyte for Lithium Sulfur Battery

At present, the most commonly used solvent for the electrolyte of lithium-sulfur batteries is a mixed solvent of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME). The use of a mixed solvent of DOL and DME improves the sulfur utilization resulting in excellent results in terms of battery capacity.

However, when the combination of the above is applied to a large battery having a high energy density, there is a problem in that the service life characteristics are significantly decreased. As a result of the experiments of the present inventors, it was confirmed that the capacity retention rate dropped very quickly in the case of a large capacity battery using a mixed solvent of DOL and DME. In addition, the battery decomposes the solvent during operation and generates a significant amount of gas. Such solvent decomposition causes electrolyte depletion, swells the battery and causes electrode desorption, resulting in deformation of the battery, which in turn shortens the battery life.

The electrolyte according to the present invention exhibits excellent solvent stability compared to conventional electrolytes, including cyclic ethers, glycol ethers, and linear ethers, and exhibits improved life characteristics.

Specifically, the present invention includes a lithium salt and a non-aqueous solvent in order to improve the battery life degradation due to decomposition of the electrolyte generated when driving the lithium-sulfur battery, the non-aqueous solvent is

i) a cyclic ether comprising one oxygen in the ring structure;

ii) glycol ethers represented by the following formula (1); And

iii) a linear ether represented by the following formula (2); It provides an electrolyte for a lithium-sulfur battery, comprising:

 [Formula 1]

R ¹ -O- (CH ₂ CH ₂ O) _x -R ²

[Formula 2]

R ³ -O- (CH ₂ CH ₂ O) _y -R ⁴

(In Chemical Formulas 1 and 2,

R ¹ to R ⁴ are the same as or different from each other, and each independently an alkyl group of C1 to C6, an aryl group of C6 to C12, or an arylalkyl group of C7 to C13,

x is an integer from 1 to 4,

y is an integer from 0 to 4,

The ether of Formula 1 is different from the ether of Formula 2)

The alkyl group of C1 to C6 referred to herein is a linear or branched alkyl group, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, t-butyl group, pen Tyl group, hexyl group, etc. can be mentioned, It is not limited to these.

In addition, the C6 to C12 aryl group referred to herein may be, for example, a phenyl group unsubstituted or substituted with a C1 to C6 alkyl group, or a naphthyl group.

In addition, the C7 to C13 arylalkyl group mentioned herein may be, for example, a benzyl group, a phenylethyl group, a phenylpropyl group, or a phenylbutyl group unsubstituted or substituted with a C1 to C6 alkyl group.

In Formula 1, R ¹ and R ² may be the same as or different from each other, and preferably may be a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group, and more preferably, a methyl group, an ethyl group, or a propyl group.

In Chemical Formula 2, R ³ and R ⁴ may be the same as or different from each other, preferably, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a pentyl group, a hexyl group, a phenyl group, or a benzyl group, y may preferably be 0, 1 or 2.

The electrolyte according to the present invention contains a cyclic ether containing one oxygen in the ring structure as the first solvent. The cyclic ether is a 5- or more-membered cyclic ether unsubstituted or substituted with an alkyl group, preferably a 5- to 7-membered cyclic ether unsubstituted or substituted with an alkyl group or an alkoxy group of C1 to C4, and more preferably C1. Tetrahydrofuran or tetrahydropyran unsubstituted or substituted with an alkyl group or an alkoxy group of from C4.

Non-limiting examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, 2,4-dimethyltetrahydrofuran, 2,5 -Dimethyltetrahydrofuran, 2-methoxytetrahydrofuran, 3-methoxytetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 3-ethoxytetrahydrofuran, tetrahydro Pyran, 2-methyltetrahydropyran, 3-methyltetrahydropyran, 4-methyltetrahydropyran, etc. are mentioned.

The cyclic ether has a low viscosity, good ion mobility, and high reduction stability, thus showing high stability even for long-term operation of the battery.

The first solvent is preferably included in 10 to less than 50% by volume, more preferably 10 to 40% by volume based on the total weight of the non-aqueous solvent. If the above range is exceeded, there may be a problem in that electrolyte stability is lowered, thereby making it difficult to secure an effect of improving battery life characteristics.

The electrolyte according to the present invention includes a glycol ether represented by Chemical Formula 1 as the second solvent.

The glycol ether is, for example, 1,2-dimethoxyethane, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, ethylene glycol dipropyl ether, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl Ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether and the like, and preferably, 1,2-dimethoxyethane, ethylene glycol ethyl methyl ether, Diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether can be used. Such glycol ethers may have high solubility of sulfur-based materials to increase sulfur utilization.

The third solvent of the electrolyte according to the present invention may be a linear ether represented by Chemical Formula 2, and the linear ether may be a glycol ether or an ether including one oxygen in a molecule. Provided that the third solvent is a glycol ether, this is a different compound from the second solvent.

Non-limiting examples of ethers containing one oxygen in the molecular structure include dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dipentyl ether, dihexyl ether, ethyl methyl ether, methyl Propyl ether, butyl methyl ether, ethyl propyl ether, butyl propyl ether, phenyl methyl ether, diphenyl ether, dibenzyl ether and the like.

The third solvent may be preferably ethylene glycol ethyl methyl ether, ethylene glycol diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, or diisobutyl ether. Such linear ethers exhibit dissolution and solvent degradation inhibitory effects of polysulfides, contributing to electrolyte stability.

The 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like are excellent in solubility of sulfur-based materials and contribute to improving capacity characteristics of the battery by increasing sulfur utilization. On the other hand, ethylene glycol ethyl methyl ether, ethylene glycol diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether and the like are excellent in stability and do not easily decompose during battery operation. Therefore, when the solvent is used in a suitable mixture, there is an advantage in that the sulfur utilization and the stability of the electrolyte can be secured at the same time.

The second solvent and the third solvent is preferably contained at least 50% by volume based on the total weight of the non-aqueous solvent. At this time, the relative ratio of the second solvent and the third solvent may be appropriately adjusted according to the type of the electrode used, the battery capacity, etc., each of which is at least 10% by volume based on the total weight of the non-aqueous solvent, It is preferable in terms of stability. Specifically, the second solvent and the third solvent are preferably mixed in a volume ratio of 1: 3 to 3: 1, and more preferably in a volume ratio of 1: 2 to 2: 1.

According to one preferred embodiment of the lithium-sulfur battery electrolyte according to the present invention, the non-aqueous solvent of the electrolyte is tetrahydrofuran as the first solvent, 1,2-dimethoxyethane as the second solvent, ethylene glycol ethyl as the third solvent. Methyl ether or dipropyl ether, and the volume ratio thereof may be 1: 1: 1 to 1: 2: 2. In this case, the sulfur utilization rate of the lithium-sulfur battery can be increased, thereby ensuring the capacity characteristics of the battery and improving the battery life. Therefore, it is advantageous for a battery including a high capacity, high loading electrode.

Another preferred embodiment includes tetrahydrofuran as the first solvent, ethylene glycol ethylmethyl ether as the second solvent, ethylene glycol diethyl ether, dipropyl ether, or diisobutyl ether as the third solvent, and these The volume ratio of may be 1: 1: 1 to 1: 2: 2. In this case, electrolyte stability is greatly improved, and the life characteristics of the battery can be significantly improved. Thus, the electrolyte may be suitably used in high temperature operating batteries requiring high electrolyte stability.

As such, the electrolyte solution of the present invention may be prepared to meet various characteristics required in a battery by appropriately selecting a solvent combination.

The electrolyte solution for lithium-sulfur batteries of the present invention includes a lithium salt added to the electrolyte to increase the ionic conductivity. The lithium salt is not particularly limited in the present invention, and may be used without limitation as long as it is commonly used in a lithium secondary battery. Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, One selected from the group consisting of chloroborane lithium, lower aliphatic lithium carbonate, lithium phenyl borate, lithium imide and combinations thereof is preferred, and preferably (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi and the like can be used.

The concentration of the lithium salt may be determined in consideration of ionic conductivity and the like, and preferably, 0.1 to 4.0 M, or 0.5 to 2.0 M. If the concentration of the lithium salt is less than the above range it is difficult to secure the ionic conductivity suitable for driving the battery, if it exceeds the above range, the viscosity of the electrolyte may be increased to reduce the mobility of lithium ions and the decomposition reaction of the lithium salt itself increases to increase the battery Since the performance of may be degraded, it is appropriately adjusted within the above range.

The non-aqueous electrolyte solution for lithium-sulfur batteries of the present invention may further include an additive having an intramolecular NO bond. The additive has an effect of forming a stable film on the lithium electrode and greatly improves the charge and discharge efficiency. Such additives may be nitric acid or nitrous acid compounds, nitro compounds and the like. Examples include lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate , Pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitro One or more selected from the group consisting of toluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl can be used. According to one embodiment of the present invention, lithium nitrate (LiNO ₃ ) may be used.

The additive is used in the range of 0.01 to 10% by weight, preferably 0.1 to 5% by weight based on 100% by weight of the total electrolyte composition. If the content is less than the above range, the above-described effects cannot be secured. On the contrary, if the content exceeds the above range, the resistance may be increased by the film, so that the above-mentioned range is appropriately adjusted.

As described above, the lithium-sulfur battery electrolyte according to the present invention uses a mixed solvent of a cyclic ether and a linear ether as a solvent in order to secure electrolyte stability, thereby suppressing gas generation in the battery during charging and discharging of the battery. The swelling phenomenon can be improved.

The preparation method of the electrolyte according to the present invention is not particularly limited in the present invention, and may be prepared by conventional methods known in the art.

Lithium-sulfur battery

The lithium-sulfur battery according to the present invention includes a positive electrode and a negative electrode and a separator and an electrolyte interposed therebetween, and use the electrolyte solution for a lithium-sulfur battery according to the present invention as an electrolyte.

The lithium-sulfur battery according to the present invention has improved electrolyte stability and shows excellent life characteristics.

The structure of the positive electrode, the negative electrode, and the separator of the lithium-sulfur battery is not particularly limited in the present invention, and is known in the art.

anode

The positive electrode according to the present invention includes a positive electrode active material formed on a positive electrode current collector.

As the cathode current collector, any one that can be used as a current collector in the technical field is possible, and specifically, it may be preferable to use foamed aluminum, foamed nickel, and the like having excellent conductivity.

The cathode active material may include elemental sulfur (S8), a sulfur-based compound, or a mixture thereof. Specifically, the sulfur-based compound may be Li ₂ S _n (n ≧ 1), an organic sulfur compound, or a carbon-sulfur polymer ((C ₂ S _x ) _n : x = 2.5 to 50, n ≧ 2). They can be applied in combination with a conductive material because the sulfur material alone is not electrically conductive.

The conductive material may be porous. Therefore, the conductive material may be used without limitation as long as it has porosity and conductivity, and for example, a carbon-based material having porosity may be used. As such a carbon-based material, carbon black, graphite, graphene, activated carbon, carbon fiber, or the like can be used. Moreover, metallic fibers, such as a metal mesh; Metallic powders such as copper, silver, nickel and aluminum; Or organic conductive materials, such as a polyphenylene derivative, can also be used. The conductive materials may be used alone or in combination.

The positive electrode may further include a binder for coupling the positive electrode active material and the conductive material and the current collector. The binder may include a thermoplastic resin or a thermosetting resin. For example, polyethylene, polyethylene oxide, polypropylene, polytetrafluoro ethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoro alkylvinyl ether copolymer, vinyl fluoride Liden-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoro propylene copolymer, propylene Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetra fluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoro ethylene aerial Copolymers, ethylene-acrylic acid copolymers, and the like may be used alone or in combination. It is not limited as long as they can both be used as binders in the art.

The positive electrode as described above may be manufactured according to a conventional method. Specifically, a positive electrode active material layer-forming composition prepared by mixing a positive electrode active material, a conductive material, and a binder on an organic solvent is applied and dried on a current collector, and optionally In order to improve the electrode density, the current collector may be manufactured by compression molding. In this case, the organic solvent may uniformly disperse the positive electrode active material, the binder, and the conductive material, and preferably evaporates easily. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, etc. are mentioned.

cathode

The negative electrode according to the present invention includes a negative electrode active material formed on the negative electrode current collector.

The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a nonconductive polymer surface-treated with a conductive material, or a conductive polymer may be used.

As the negative active material, a material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ), a material capable of reacting with lithium ions to form a reversibly lithium-containing compound, a lithium metal or a lithium alloy Can be used. The material capable of reversibly occluding or releasing the lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon or a mixture thereof. The material capable of reacting with the lithium ions (Li ⁺ ) to form a lithium-containing compound reversibly may be, for example, tin oxide, titanium nitrate or silicon. The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al) and tin (Sn).

The negative electrode may further include a binder for coupling the negative electrode active material and the conductive material and the current collector. Specifically, the binder is the same as described above for the binder of the positive electrode.

Separator

A conventional separator may be interposed between the positive electrode and the negative electrode. The separator is a physical separator having a function of physically separating the electrode, and can be used without particular limitation as long as it is used as a conventional separator, and in particular, it is preferable that the separator has a low resistance to electrolyte migration and excellent electrolyte-moisture capability.

In addition, the separator enables the transport of lithium ions between the positive electrode and the negative electrode while separating or insulating the positive electrode and the negative electrode from each other. Such a separator may be made of a porous and nonconductive or insulating material. The separator may be an independent member such as a film or a coating layer added to the anode and / or the cathode.

Specifically, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer may be used alone. It may be used as a lamination or or a conventional porous non-woven fabric, for example, a non-woven fabric made of glass fibers, polyethylene terephthalate fibers of high melting point, etc. may be used, but is not limited thereto.

The positive electrode, the negative electrode, and the separator included in the lithium-sulfur battery may be prepared according to conventional components and manufacturing methods, respectively, and the appearance of the lithium-sulfur battery is not particularly limited, but may be cylindrical, rectangular, or pouch using a can. It may be a pouch type or a coin type.

Hereinafter, preferred examples are provided to help the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art. It goes without saying that changes and modifications belong to the appended claims.

EXAMPLE

Examples 1-2 and Comparative Examples 1-2

(1) Preparation of Electrolyte

LiTFSI ((CF ₃ SO ₂ ) ₂ NLi) was added to the mixed solvent having the composition shown in Table 1 at a concentration of 1.0 M, and 1% by weight of LiNO ₃ was added based on 100% by weight of the electrolyte. The non-aqueous electrolyte solution of Examples 1-2 was produced. The solvent used at this time is as follows.

THF: Tetrahydrofuran

DOL: 1,3-dioxolane (1,3-Dioxolane)

DME: 1,2-dimethoxyethane

EGEME: Ethyleneglycol ethylmethyl ether

DPE: Dipropyl ether

	Solvent (Volume Ratio)	Lithium salt	additive
Example 1	THF: DME: EGEME (1: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Example 2	THF: DME: DPE (1: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Comparative Example 1	DOL: DME (1: 1)	1.0M LiTFSI	1wt% LiNO 3
Comparative Example 2	THF: DME (1: 1)	1.0M LiTFSI	1wt% LiNO 3

(2) Preparation of lithium-sulfur battery

A positive electrode active material slurry was prepared by mixing 65 wt% sulfur, 25 wt% carbon black, and 10 wt% polyethylene oxide with acetonitrile. The positive electrode active material slurry was coated on an aluminum current collector and dried to prepare a positive electrode having a loading amount of 5 mAh / cm ² having a size of 30 × 50 mm ² . In addition, a lithium metal having a thickness of 150 µm was used as the negative electrode.

The positive electrode and the negative electrode prepared above were disposed to face each other, and a polyethylene separator having a thickness of 20 μm was interposed therebetween, followed by filling with the electrolyte solutions of Examples and Comparative Examples.

Experimental Example 1: Battery Performance Evaluation

Specific Discharge Capacity was measured for each of the lithium-sulfur batteries of Examples 1 to 2 and Comparative Examples 1 and 2 under 20 conditions under the following conditions, and the results are shown in FIG. 1.

Charge: 0.1C at rate, 2.8V, CC / CV (5% current cut at 0.1C)

Discharge: Rate 0.1C, Voltage 1.5V, CC

As shown in Figure 1, it can be seen that the batteries of Comparative Examples 1 and 2 start to drop the discharge capacity after 10 cycles. However, it can be seen that the batteries of Examples 1 and 2 were stably maintained in the discharge capacity even up to 20 cycles. In addition, in the batteries of Comparative Examples 1 and 2, a swelling phenomenon was observed due to gas generation as the battery was driven, but the swelling phenomenon was not observed in the batteries of Examples 1 and 2.

Examples 3 to 6 and Comparative Example 3

(1) Preparation of Electrolyte

To LiTFSI ((CF ₃ SO ₂ ) ₂ NLi) at a concentration of 1.0 M to a mixed solvent having the composition of Table 2, and compared with Examples 3 to 6 by adding 1% by weight of LiNO ₃ based on 100% by weight of the electrolyte A non-aqueous electrolyte solution of Example 3 was prepared. The solvent used at this time is as follows.

THF: Tetrahydrofuran

DOL: 1,3-dioxolane (1,3-Dioxolane)

DME: 1,2-dimethoxyethane

EGEME: Ethyleneglycol ethylmethyl ether

EGDEE: Ethyleneglycol diethyl ether

DPE: Dipropyl ether

DIBE: Diisobutyl ether

	Solvent (Volume Ratio)	Lithium salt	additive
Example 3	THF: EGEME: EGDEE (1: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Example 4	THF: EGEME: DPE (1: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Example 5	THF: EGEME: DIBE (1: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Example 6	THF: EGEME: DPE (2: 1: 1)	1.0M LiTFSI	1wt% LiNO 3
Comparative Example 3	DOL: DME (1: 1)	1.0M LiTFSI	1wt% LiNO 3

(2) Preparation of lithium-sulfur battery

A positive electrode active material slurry was prepared by mixing 60 wt% sulfur, 30 wt% carbon black, and 10 wt% polyethylene oxide with acetonitrile. The positive electrode active material slurry was coated on an aluminum current collector and dried to prepare a positive electrode having a loading amount of 5 mAh / cm ² having a size of 30 × 50 mm ² . In addition, a lithium metal having a thickness of 150 µm was used as the negative electrode.

The positive electrode and the negative electrode prepared above were disposed to face each other, and a polyethylene separator having a thickness of 20 μm was interposed therebetween, followed by filling with the electrolyte solutions of Examples and Comparative Examples.

Experimental Example 2: Battery Performance Evaluation

Examples The specific discharge capacity was measured for each lithium-sulfur battery of Examples 3 to 6 and Comparative Example 3 while repeating the charging and discharging under the following conditions, and the results are shown in FIG. 2.

Charge: 0.1C at rate, 2.8V, CC / CV (5% current cut at 0.1C)

Discharge: Rate 0.1C, Voltage 1.5V, CC

As shown in FIG. 2, in the case of a lithium-sulfur battery using the electrolyte solution of the present invention, it can be seen that a high initial charge / discharge capacity is maintained during several dozen cycles. On the other hand, the battery of Example 6 in which the cyclic ether occupies 50% of the total volume of the solvent was found to have a slightly lower effect of improving the battery life characteristics compared to the other Example batteries.

In comparison, the battery of Comparative Example 3 showed a tendency that the initial capacity greatly decreased after about 15 charge / discharge cycles. This result is considered to be due to the decomposition of the electrolyte during battery operation due to the low stability of the solvent itself.

From the above results, it can be seen that the electrolyte composition of the three-component combination of the present invention increases the retention rate of the initial charge and discharge capacity of the battery, and also improves the life characteristics of the battery compared to the electrolyte of the existing combination. In addition, it can be seen that the electrolyte of the present invention exhibits a better battery life improving effect when the content of the cyclic ether is less than 50% of the total volume of the solvent.

Claims (14)

1. Including lithium salts and non-aqueous solvents,

   The non-aqueous solvent is

   i) a cyclic ether comprising one oxygen in the ring structure;

   ii) glycol ethers represented by the following formula (1); And

   iii) a linear ether represented by the following formula (2); Lithium-sulfur battery electrolyte, characterized in that it comprises a.

   [Formula 1]

   R ¹ -O- (CH ₂ CH ₂ O) _x -R ²

   [Formula 2]

   R ³ -O- (CH ₂ CH ₂ O) _y -R ⁴

   (In Chemical Formulas 1 and 2,

   R ¹ to R ⁴ are the same as or different from each other, and each independently an alkyl group of C1 to C6, an aryl group of C6 to C12, or an arylalkyl group of C7 to C13,

   x is an integer from 1 to 4,

   y is an integer from 0 to 4,

   The ether of Formula 1 is different from the ether of Formula 2)
2. The method of claim 1,

   The cyclic ether is a 5-7 membered cyclic ether unsubstituted or substituted with an alkyl or alkoxy group of C1 to C4.
3. The method of claim 1,

   The cyclic ether is a tetrahydrofuran or tetrahydropyran unsubstituted or substituted with an alkyl group or an alkoxy group of C1 to C4 electrolyte for lithium-sulfur battery.
4. The method of claim 1,

   The cyclic ether may be tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, 2,4-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-methoxytetrahydrofuran, 3-methoxytetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 3-ethoxytetrahydrofuran, tetrahydropyran, 2-methyltetra An electrolyte solution for a lithium-sulfur battery, characterized in that it is one kind selected from the group consisting of hydropyran, 3-methyltetrahydropyran, and 4-methyltetrahydropyran.
5. The method of claim 1,

   The glycol ether is lithium-, characterized in that one selected from the group consisting of 1,2-dimethoxyethane, ethylene glycol ethylmethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Electrolyte for Sulfur Battery.
6. The method of claim 1,

   The linear ether is one type selected from the group consisting of ethylene glycol ethyl methyl ether, ethylene glycol diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and diisobutyl ether. Electrolyte solution.
7. The method of claim 1,

   The cyclic ether is a lithium-sulfur battery electrolyte, characterized in that it comprises 10 to 50% by volume of the total weight of the non-aqueous solvent.
8. The method of claim 1,

   The glycol ether and linear ether is an electrolyte solution for a lithium-sulfur battery, characterized in that it is included in a volume ratio of 1: 3 to 3: 1.
9. The method of claim 1,

   The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, chloroborane lithium An electrolyte solution for a lithium-sulfur battery, comprising one selected from the group consisting of lower aliphatic lithium carbonate, lithium phenyl borate, lithium imide, and combinations thereof.
10. The method of claim 1,

    The lithium salt is a lithium-sulfur battery electrolyte, characterized in that it is included in a concentration of 0.1 to 4.0 M.
11. The method of claim 1,

    The electrolyte solution further comprises an additive having an intramolecular N-O bond.
12. The method of claim 11,

    The additives include lithium nitrate, potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, lithium nitrite, potassium nitrite, cesium nitrite, ammonium nitrite, methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate Latex, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitro pyridine, dinitropyridine, An electrolyte solution for lithium-sulfur batteries, which is at least one member selected from the group consisting of nitrotoluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl.
13. The method of claim 11,

    The additive is an electrolyte solution for a lithium-sulfur battery, characterized in that contained in 0.01 to 10% by weight relative to 100% by weight of the electrolyte.
14. A lithium-sulfur battery comprising the electrolyte solution of any one of claims 1 to 13.

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