KR20210065857A - Electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

An electrolyte for a lithium secondary battery of the present invention contains 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in an amount of 5 to 10 wt% based on the total weight of an organic solvent, so that high stability of the electrolyte can be ensured and the lifespan characteristics of the lithium secondary battery including the same can be improved.

Description

Electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same {ELECTROLYTE FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

With the recent development of portable electronic devices, electric vehicles, and large-capacity power storage systems, the need for large-capacity batteries has emerged. Among lithium secondary batteries, a lithium-sulfur battery uses a sulfur-based material having an SS bond (Sulfur-sulfur bond) as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, is very resource-intensive. It has the advantage of being abundant, non-toxic, and having a low weight per atom.

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

However, lithium-sulfur batteries have not yet been commercialized. This is because, when sulfur is used as an active material, the ratio (sulfur utilization ratio) used in the electrochemical reaction is low, so that sufficient capacity is not secured as much as the theoretical capacity. In order to overcome this problem, the development of an anode material with an increased sulfur impregnation amount and an electrolyte capable of increasing the sulfur utilization rate is being developed.

Currently, as an electrolyte solvent for a lithium-sulfur battery, an ether-based solvent having excellent sulfur utilization is used as the electrolyte. However, as the driving time of the lithium-sulfur battery increases, the decomposition of the electrolyte according to the electrochemical reaction continuously occurs, and as a result, gases such as hydrogen, methane, and ethene are generated, which causes a swelling phenomenon and eventually lithium- Sulfur leads to shortening the battery life.

Therefore, in order to obtain stable lifespan characteristics in a lithium-sulfur battery, it is necessary to develop a stable electrolyte that does not cause decomposition while driving the battery.

Republic of Korea Patent Publication No. 10-2009-0086575

As a result of various studies conducted by the present inventors to solve the above problem, when an organic solvent that decomposes a lot among organic solvents used as an electrolyte for a lithium secondary battery is replaced with a high-stability organic solvent, the decomposition of the electrolyte is suppressed and lithium The present invention was completed by confirming that the stability and lifespan characteristics of the secondary battery were improved.

Accordingly, an object of the present invention is to provide an electrolyte for a lithium secondary battery capable of improving the lifespan characteristics of the lithium secondary battery.

Another object of the present invention is to provide a lithium secondary battery including the electrolyte solution for a lithium secondary battery.

In order to achieve the above object,

The present invention is an electrolyte for a lithium secondary battery comprising a lithium salt and an organic solvent,

The organic solvent includes an etheric solvent and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether,

The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is contained in an amount of 5 to 10% by weight based on the total weight of the organic solvent, and provides an electrolyte for a lithium secondary battery.

In addition, the present invention is a positive electrode; cathode; a separator interposed between the anode and the cathode; and an electrolyte; a lithium secondary battery comprising:

The electrolyte provides a lithium secondary battery, characterized in that the electrolyte of the present invention.

The electrolyte for a lithium secondary battery of the present invention contains 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, which is a high-stability organic solvent, in an amount of 5 to 10% by weight based on the total weight of the organic solvent. As it is included, it is possible to suppress the decomposition of the electrolyte generated during battery driving, thereby improving the lifespan characteristics of the lithium secondary battery.

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

Currently, the ether-based solvent, which is most often used as an electrolyte solvent for a lithium secondary battery, preferably a lithium-sulfur battery, improves the sulfur utilization rate and shows excellent results in terms of battery capacity.

However, the ether-based solvent decomposes the solvent during battery operation to cause depletion of the electrolyte, swells the battery, and causes battery deformation such as electrode detachment, which eventually shortens the lifespan of the battery.

Therefore, in the present invention, it was intended to provide an electrolyte for a lithium secondary battery with excellent stability by suppressing the decomposition of the electrolyte by replacing the solvent that causes a lot of decomposition of the electrolyte among the ether-based solvents with an organic solvent with excellent stability.

Electrolyte for lithium secondary battery

The present invention is an electrolyte for a lithium secondary battery comprising a lithium salt and an organic solvent,

The organic solvent includes an etheric solvent and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether,

The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is contained in an amount of 5 to 10% by weight based on the total weight of the organic solvent, and relates to an electrolyte for a lithium secondary battery.

The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, TTE) is As a fluorine-based ether containing fluorine (hydrofluoro ether), Due to the substitution of fluorine, the structural stability of the solvent is superior to that of a general organic solvent containing an alkane, and thus the stability is very high. Accordingly, when it is used in an electrolyte for a lithium secondary battery, the stability of the electrolyte can be greatly improved, and thereby, the lifespan characteristics of a lithium secondary battery including the electrolyte for a lithium secondary battery can be improved.

That is, by using the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether by replacing some or all of the unstable ether-based solvent that causes a lot of decomposition of the electrolyte, lithium By improving the stability of the electrolyte for a secondary battery, it is possible to increase the lifespan characteristics of a lithium secondary battery including the same.

The ether-based solvent causing a lot of decomposition of the electrolyte may include, but is not limited to, 2-methyl tetrahydrofuran, 1,2-dimethylethane, and 1,3-dioxolane.

The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is 5 to 10 wt%, preferably 5 to 9 wt%, more preferably 5 to 10 wt%, based on the total weight of the organic solvent Preferably 5 to 8% by weight, most preferably 5 to 7% by weight may be included.

When the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is included in an amount of less than 5% by weight, the effect of improving the stability of the electrolyte for a lithium secondary battery cannot be expected. Since the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether does not dissolve lithium polysulfide, if it is included in excess of 10 wt%, the density of the electrolyte increases and It is difficult to manufacture a lithium secondary battery having an energy density, and the viscosity of the electrolyte increases and the ionic conductivity of the electrolyte decreases, making it difficult to drive a lithium secondary battery including the same, preferably a lithium-sulfur battery.

The etheric solvent may include an acyclic ether and a cyclic ether.

The acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl It may include at least one selected from the group consisting of ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether, and preferably may include ethylene glycol ethyl methyl ether, but is limited thereto. it is not

In addition, the cyclic ether is 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl -1,3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, 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 benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene and i It may include one or more selected from the group consisting of sorbide dimethyl ether, and preferably include 2-methyl tetrahydrofuran, but is not limited thereto.

The cyclic ether and the acyclic ether may be mixed in a weight ratio of 1:9 to 9:1, preferably 2:8 to 5:5, but is not limited thereto.

In one embodiment, the organic solvent of the present invention comprises 2-methyltetrahydrofuran, ethylene glycol ethyl methyl ether and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. may include

At this time, based on the total weight of the organic solvent, 15 to 35 wt% of 2-methyltetrahydrofuran, 60 to 80 wt% of ethylene glycol ethyl methyl ether, and 1,1,2,2-tetrafluoroethyl 2,2, 3,3-tetrafluoropropyl ether may be included in an amount of 5 to 10% by weight. Also, preferably, 2-methyltetrahydrofuran is 15 to 30% by weight, ethylene glycol ethyl methyl ether is 60 to 70% by weight, and 1,1,2,2-tetrafluoroethyl 2,2,3,3- Tetrafluoropropyl ether may be included in an amount of 5 to 7% by weight.

The 2-methyltetrahydrofuran is rapidly decomposed and disappears during battery operation, which can be confirmed through analysis. Therefore, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is used to replace the 2-methyltetrahydrofuran. However, as described above, when the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is included in an amount in excess of 10% by weight based on the total weight of the organic solvent, the operation of the battery is impaired. There is a problem that does not work normally. Accordingly, in the present invention, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is contained in an amount of 5 to 10% by weight based on the total weight of the organic solvent in an amount of 2- It is preferable to replace part of the content of methyltetrahydrofuran.

In addition, the electrolyte solution for a lithium secondary battery of the present invention includes a lithium salt as an electrolyte salt to increase ion 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 the art. For example, 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 , lithium bis (oxalato) borate, lithium-oxalyl difluoroborate, lithium 4,5-dicyano-2- (trifluoromethyl) imidazole, lithium dicyanotriazolate, lithium thiocyanate, It may include at least one selected from the group consisting of lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, and lithium imide, preferably (SO ₂ F) ₂ NLi (lithium bis(fluorosulfonyl) imide, LiFSI).

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

In addition, in the electrolyte solution for a lithium secondary battery of the present invention, an additive may be additionally used to form a stable film on the lithium electrode and greatly improve charge/discharge efficiency. The additive may be nitric acid or a nitrite-based compound, a nitro compound, and the like.

For example, 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 Late, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, At least one selected from the group consisting of nitrotoluene, dinitrotoluene, pyridine N-oxide, alkylpyridine N-oxide, and tetramethyl piperidinyloxyl may be used, and lithium nitrate (LiNO ₃ ) is preferably used. can

The additive may be used in an amount of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the electrolyte for a lithium secondary battery. If the additive is included in less than 0.01% by weight, the above-described effect cannot be ensured, and when included in an amount exceeding 10% by weight, there is a risk that the resistance may be rather increased by the film, so it should be appropriately adjusted within the above range.

In addition, the electrolyte for a lithium secondary battery may preferably be an electrolyte for a lithium-sulfur battery.

The electrolyte for a lithium secondary battery of the present invention replaces an organic solvent in which electrolyte decomposition occurs a lot, and 1,1,2,2-tetrafluoroethyl 2,2,3,3 in an amount of 5 to 10% by weight based on the total weight of the electrolyte - By including tetrafluoropropyl ether, it is possible to suppress the decomposition of the electrolyte by increasing the stability of the electrolyte, thereby improving the lifespan characteristics of a lithium secondary battery including the same, preferably a lithium-sulfur battery.

lithium secondary battery

In addition, the present invention is a positive electrode; cathode; a separator interposed between the anode and the cathode; And a lithium secondary battery comprising an electrolyte, wherein the electrolyte may be the electrolyte of the present invention described above.

The positive electrode includes a positive electrode active material formed on a positive electrode current collector.

As the positive electrode current collector, any one that can be used as a current collector in the art may be used, and specifically, it may be preferable to use foamed aluminum, foamed nickel, etc. having excellent conductivity.

The positive active material may include a sulfur compound, and the sulfur compound may include elemental sulfur (S ₈ ), 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). Since the sulfur material alone has no electrical conductivity, it can be applied in combination with a conductive material.

As the positive active material includes a sulfur compound, the lithium secondary battery of the present invention may be a lithium-sulfur battery.

The conductive material may be porous. Accordingly, the conductive material may be used without limitation as long as it has porosity and conductivity, 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 may be used. Moreover, metallic fibers, such as a metal mesh; metallic powders such as copper, silver, nickel, and aluminum; Alternatively, an organic conductive material 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 bonding the positive electrode active material and the conductive material and bonding to the current collector. The binder may include a thermoplastic resin or a thermosetting resin. For example, polyethylene, polyethylene oxide, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinyl fluoride Leadene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene -Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer Copolymer, ethylene-acrylic acid copolymer, etc. may be used alone or in combination, but it is not necessarily limited thereto, and any one that can be used as a binder in the art may be used.

The positive electrode may be manufactured according to a conventional method, and specifically, a composition for forming a positive electrode active material layer prepared by mixing a positive electrode active material, a conductive material, and a binder in an organic solvent is applied on a current collector and dried, and optionally the electrode density It can be manufactured by compression molding on the current collector in order to improve the In this case, as the organic solvent, the positive electrode active material, the binder, and the conductive material can be uniformly dispersed, and it is preferable to use one that is easily evaporated. Specific examples thereof include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

The negative electrode may include a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

The negative electrode current collector is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of a lithium secondary battery, for supporting the negative electrode active material, for example, copper, stainless steel, aluminum, nickel, titanium, Palladium, fired carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., an aluminum-cadmium alloy, etc. may be used.

The negative electrode current collector may form fine irregularities on its surface to enhance bonding strength with the negative electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous materials, foams, and nonwovens may be used.

The negative active material includes ^{a material capable of reversibly intercalating or deintercalating lithium (Li +} ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or a lithium alloy. can do. The material capable of reversibly occluding or releasing lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions (Li ⁺ ) 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 ( Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and may be an alloy of a metal selected from the group consisting of tin (Sn). Preferably, the negative active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

A method of forming the negative active material is not particularly limited, and a method of forming a layer or a film commonly used in the art may be used. For example, a method such as pressing, coating, or vapor deposition may be used. In addition, a case in which a metallic lithium thin film is formed on a metal plate by initial charging after assembling a battery in a state in which there is no lithium thin film in the current collector is included in the negative electrode of the present invention.

The separator is for physically separating both electrodes in the lithium secondary battery of the present invention, and can be used without any particular limitation as long as it is normally used as a separator in a lithium secondary battery. It is preferable that the ability is excellent.

The separator may be made of a porous substrate. The porous substrate may be any porous substrate commonly used in electrochemical devices. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto. .

Examples of the polyolefin-based porous membrane include polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, and polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, individually or in a mixture thereof. One membrane is mentioned.

As the nonwoven fabric, in addition to the polyolefin-based nonwoven fabric, for example, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide and polyethylenenaphthalate alone Alternatively, a nonwoven fabric formed of a polymer obtained by mixing them may be mentioned. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a melt blown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The size and pore size of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

The electrolyte contains lithium ions, and is intended to cause an electrochemical oxidation or reduction reaction in the positive electrode and the negative electrode through this, according to the above description.

The injection of the electrolyte may be performed at an appropriate stage during the manufacturing process of the electrochemical device according to the manufacturing process of the final product and required properties. That is, it may be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

In the lithium secondary battery according to the present invention, in addition to the general process of winding, lamination, stack, and folding processes of a separator and an electrode are possible.

The shape of the lithium secondary battery is not particularly limited, and may be manufactured in various shapes such as a cylindrical shape, a stacked type, and a coin type.

The lithium secondary battery of the present invention, preferably a lithium-sulfur battery, may exhibit excellent lifespan characteristics by including the electrolyte solution for a lithium secondary battery having very excellent stability of the present invention.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

Experimental Example 1. Identification of an etheric organic solvent with poor stability

A cathode active material slurry was prepared by mixing sulfur in acetonitrile with a conductive material, a binder, and a ball mill. At this time, carbon black was used as a conductive material and polyethylene oxide (molecular weight 5,000,000 g/mol) was used as a binder, respectively, and the mixing ratio was sulfur: conductive material: binder 90:5:5 in a weight ratio. The positive electrode active material slurry was applied to an aluminum current collector and dried to prepare a positive electrode (in this case, the positive electrode loading amount was 3.8 mAh/cm ² ).

A lithium metal thin film having a thickness of 40 μm was used as the negative electrode.

A lithium-sulfur battery was prepared by placing the prepared positive electrode and the negative electrode to face each other, placing a polyethylene separator therebetween, and injecting an electrolyte.

The electrolyte solution was prepared by adding _{0.45 M LiFSI and 3 wt% LiNO 3} to ethylene glycol ethyl methyl ether (EGEME) and 2-methyltetrahydrofuran (2-Me-THF) (volume ratio of 2:1). .

Discharging and charging of the lithium-sulfur battery at a current density of 0.1 C were repeated 2.5 times, and then 40 and 65 cycles were performed at a current density of 0.2 C, respectively. After completion of the process, the lithium-sulfur battery was disassembled to extract the components of the remaining electrolyte, and the amount was measured, and the results are shown in Table 1 below.

electrolyte weight EGEME 2-Me-THF
40 cycle Injection volume (g) 0.622 0.615 Actual extraction electrolyte amount (g) 0.529 0.263 Extraction rate (%) 85 83.5
65 cycles (charge) Injection volume (g) 0.623 0.315 Actual extraction electrolyte amount (g) 0.522 0.249 Extraction rate (%) 83.8 79

From the results of Table 1, it was confirmed that 2-Me-THF was decomposed faster than EGEME. This means that 2-Me-THF is less stable than EGEME, and in the example, 2-Me-THF is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl It was attempted to measure the lifespan characteristics of lithium-sulfur batteries by partially replacing them with ether.

<Production of electrolyte for lithium-sulfur batteries>

Examples 1 to 3 and Comparative Examples 1 to 6

An electrolyte solution for a lithium-sulfur battery was prepared with the composition shown in Table 2 below.

Organic solvent (wt%) Additives (wt%) Lithium salt (M) 2-Me-THF EGEME EGDEE TTE LiNO ₃ LiFSI Example 1 28 67 - 5 3 0.45 Example 2 26 67 - 7 3 0.45 Example 3 23 67 - 10 3 0.45 Comparative Example 1 33 67 - - 3 0.45 Comparative Example 2 28 67 5 - 3 0.45 Comparative Example 3 23 67 10 - 3 0.45 Comparative Example 4 18 67 - 15 3 0.45 Comparative Example 5 13 67 - 20 3 0.45 Comparative Example 6 30 67 - 3 3 0.45 2-Me-THF: 2-Methyltetrahydrofuran
EGEME: Ethylene glycol ethyl methyl ether
EGDEE: Ethylene glycol diethyl ether
TTE: 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether
LiFSI: Lithium bis(fluorosulfonyl)imide

Experimental Example 2. Evaluation of lifetime characteristics of lithium-sulfur batteries

A cathode active material slurry was prepared by mixing sulfur in acetonitrile with a conductive material, a binder, and a ball mill. At this time, carbon black was used as a conductive material and polyethylene oxide (molecular weight 5,000,000 g/mol) was used as a binder, respectively, and the mixing ratio was sulfur: conductive material: binder 90:5:5 in a weight ratio. The positive electrode active material slurry was applied to an aluminum current collector and dried to prepare a positive electrode (in this case, the positive electrode loading amount was 3.8 mAh/cm ² ).

A lithium metal thin film having a thickness of 40 μm was used as the negative electrode.

A lithium-sulfur battery was prepared by placing the prepared positive electrode and the negative electrode to face each other, placing a polyethylene separator therebetween, and injecting an electrolyte.

In this case, each lithium-sulfur battery was prepared using the electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 6 as the electrolyte.

After repeating discharging and charging 2.5 times at a current density of 0.1 C for the battery prepared by the above method, discharging and charging at a current density of 0.2 C were repeated 3 times, and then 200 cycles at a current density of 0.5 C were performed. The lifespan characteristics were confirmed. The results obtained at this time are shown in Table 3 below.

life (cycles) Example 1 214 Example 2 220 Example 3 230 Comparative Example 1 137 Comparative Example 2 143 Comparative Example 3 146 Comparative Example 4 cannot be driven Comparative Example 5 cannot be driven Comparative Example 6 162

From the results of Table 3, Examples 1 to 3 including 5 wt%, 7 wt%, and 10 wt% of TTE based on the total weight of the organic solvent, respectively, showed that the capacity was maintained even when the cycle progressed. That is, the lifespan characteristics of the lithium-sulfur battery showed very good results. In addition, it was confirmed that as the content of TTE was increased, the battery life characteristics were also improved.

On the other hand, Comparative Example 1 not including TTE and Comparative Examples 2 and 3 including EGDEE instead of TTE showed the result that the capacity could not be maintained as the cycle progressed. That is, compared to Examples 1 to 3, the lifespan characteristics were very poor.

In addition, from the results of Table 3, it was confirmed that the capacity of Comparative Example 6 including 3% by weight of TTE based on the total weight of the organic solvent was rapidly decreased when about 4 cycles were performed.

On the other hand, in Comparative Example 4 and Comparative Example 5 containing 20% by weight of TTE with respect to the total weight of the organic solvent, the driving itself was impossible.

In addition, it was also confirmed that the continuous increase of the TTE content does not unconditionally improve the lifespan characteristics of the battery.

Therefore, when a part of 2-Me-THF, which is an unstable organic solvent, is replaced with TTE, and the TTE is included in an amount of 5 to 10% by weight based on the total weight of the organic solvent, the best lifespan characteristics of the lithium-sulfur battery result was found to be obtained. Therefore, the electrolyte solution for a lithium secondary battery of the present invention has very high stability, and may have an effect of improving the lifespan characteristics of a lithium secondary battery including the same.

Claims (10)

An electrolyte for a lithium secondary battery comprising a lithium salt and an organic solvent,
The organic solvent includes an etheric solvent and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether,
The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether is contained in an amount of 5 to 10% by weight based on the total weight of the organic solvent, an electrolyte for a lithium secondary battery. According to claim 1,
The ether-based solvent is an electrolyte for a lithium secondary battery, characterized in that it comprises an acyclic ether and a cyclic ether. 3. The method of claim 2,
The acyclic ether is dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl An electrolyte for a lithium secondary battery, comprising at least one selected from the group consisting of ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and ethylene glycol ethyl methyl ether. 3. The method of claim 2,
The cyclic ether is 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1 ,3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, 2,5-dimethoxy tetrahydrofuran, 2-ethoxy tetrahydrofuran, 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 benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene and isosorbide An electrolyte for a lithium secondary battery, comprising at least one selected from the group consisting of dimethyl ether. According to claim 1,
wherein the organic solvent comprises 2-methyltetrahydrofuran, ethylene glycol ethyl methyl ether and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. Electrolyte for secondary batteries. 6. The method of claim 5,
15 to 35% by weight of 2-methyltetrahydrofuran, 60 to 80% by weight of ethylene glycol ethyl methyl ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3- based on the total weight of the organic solvent An electrolyte for a lithium secondary battery, characterized in that it contains 5 to 10% by weight of tetrafluoropropyl ether. According to 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, lithium bis( Oxalato) borate, lithium-oxalyldifluoroborate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole, lithium dicyanotriazolate, lithium thiocyanate, chloroborane lithium, An electrolyte for a lithium secondary battery, comprising at least one selected from the group consisting of lower aliphatic lithium carboxylate, lithium tetraphenyl borate, and lithium imide. According to claim 1,
The electrolyte for a lithium secondary battery is an electrolyte for a lithium secondary battery, characterized in that it is an electrolyte for a lithium-sulfur battery. anode; cathode; a separator interposed between the anode and the cathode; and an electrolyte; a lithium secondary battery comprising:
The electrolyte is a lithium secondary battery, characterized in that the electrolyte of any one of claims 1 to 8. 10. The method of claim 9,
The lithium secondary battery is a lithium secondary battery, characterized in that the lithium-sulfur battery.