KR20210000503A - Electrolyte for lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery capable of improving the performance of a battery by suppressing the elution of lithium polysulfide and improving reactivity, and to a lithium secondary battery comprising the same. The electrolyte for a lithium secondary battery comprises: a glyme-based compound; and a nitrile-based compound.

Description

Electrolyte for lithium secondary battery and lithium secondary battery including the same

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, an electrolyte for a lithium secondary battery capable of improving the performance of a battery by suppressing the elution of lithium polysulfide and improving the reactivity, and including the same It relates to a lithium secondary battery.

As the interest in energy storage technology increases, the field of application of mobile phones, tablets, laptops, camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs) is expanded. Research and development of chemical devices are gradually increasing. Electrochemical devices are the field that is receiving the most attention in this respect, and among them, the development of secondary batteries such as lithium-sulfur batteries capable of charging and discharging has become the focus of interest, and in recent years, capacity density and In order to improve the specific energy, research and development on the design of new electrodes and batteries are being conducted.

Such an electrochemical device, among which a Li-S battery, has a high energy density (theoretical capacity), and is in the spotlight as a next-generation secondary battery that can replace a lithium ion battery. In such a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge, and at this time, sulfur forms lithium polysulfide (LiPS) of a linear structure from S ₈ having a ring structure. The lithium-sulfur battery is characterized by a stepwise discharge voltage until the polysulfide is completely reduced to Li ₂ S.

However, the biggest obstacle in the commercialization of lithium-sulfur batteries is the elution of lithium polysulfide (which occurs during charging and discharging in batteries that use sulfur-based compounds as positive electrode active materials and alkali metals such as lithium as negative electrode active materials). And a shuttle phenomenon, and lithium polysulfide is transferred to the negative electrode, thereby reducing the capacity of the lithium-sulfur battery, and thus the lithium-sulfur battery has a major problem in that the lifespan is reduced and the reactivity is reduced. That is, since the polysulfide eluted from the positive electrode has high solubility in the organic electrolyte, unwanted movement (PS shuttling) toward the negative electrode may occur through the electrolyte, and as a result, the capacity decrease due to irreversible loss of the positive electrode active material and The battery life is reduced due to the deposition of sulfur particles on the surface of the lithium metal by side reactions.

On the other hand, the behavior of such a lithium-sulfur battery can vary greatly depending on the electrolyte, and the electrolyte when sulfur of the positive electrode is eluted into the electrolyte in the form of lithium polysulfide (LiPS) is called Catholye, and sulfur is The electrolyte in the case of hardly eluting out in the form of lithium polysulfide is referred to as SSE (Sparingly Soluble or Solvating Electrolyte). That is, in the art, various studies on lithium-sulfur batteries in which sulfur, which is a positive electrode active material, does not elute out of the electrolyte solution (studies such as adding LiPS adsorption material to the positive electrode composite or modifying a separator made of existing PE, etc.) are conducted. In particular, studies are being conducted on an electrolyte solution capable of performing a solid-to-solid reaction with Li ₂ S, which is a final discharge product of sulfur, but it has not yet produced such results. Accordingly, there is a need for a more fundamental method of reducing the lifespan of the lithium-sulfur battery by moving lithium-polysulfide to the negative electrode, and suppressing the phenomenon that the reactivity decreases due to a large amount of lithium-polysulfide.

Accordingly, an object of the present invention is to provide an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same, which can improve the reactivity by suppressing the elution of lithium polysulfide, thereby improving battery performance.

In order to achieve the above object, the present invention, a glyme-based compound; It provides an electrolyte for a lithium secondary battery comprising; and a nitrile-based compound.

In addition, the present invention, the anode; cathode; A separator interposed between the anode and the cathode; And it provides a lithium secondary battery comprising the electrolyte for the lithium secondary battery.

According to the electrolyte for a lithium secondary battery and a lithium secondary battery including the same according to the present invention, it has the advantage of improving the performance of the battery by improving the reactivity by suppressing the elution of lithium polysulfide.

1 to 3 are graphs comparing and contrasting discharge capacities of lithium secondary batteries manufactured according to an embodiment and a comparative example of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The electrolyte for a lithium secondary battery according to the present invention contains a glyme-based compound and a nitrile-based compound.

That is, the present invention has a configuration in which a glyme-based compound and a nitrile-based compound are simultaneously applied as an electrolyte for a lithium secondary battery, thereby suppressing the elution of lithium polysulfide and improving the reactivity of the battery, thereby improving the performance of the battery. The object of the present invention can be achieved.

The electrolyte for a lithium secondary battery according to the present invention is an electrolyte that enables a solid-to-solid reaction to proceed with Li ₂ S, which is a final discharge product of sulfur, especially in a lithium-sulfur battery, and as described above, a glyme type ) Compound and nitrile type compound. The glyme compound has the effect of improving the initial reactivity of the battery compared to the existing electrolyte and increasing the discharge capacity, and the nitrile compound has the effect of reducing the overvoltage of the battery and improving the life characteristics compared to the existing electrolyte. The present applicant used a mixture of a glyme-based compound and a nitrile-based compound, which can take all of these advantages, and applied it as an electrolyte for a lithium secondary battery.

로 표시되는 화학식에 해당하는 모든 화합물일 수 있으며, 이때, 상기 화학식에서 R은 메틸기, 에틸기 또는 부틸기일 수 있고, n은 1 내지 4일 수 있다. 따라서, 상기 글라임계 화합물의 구체적인 예로는, 모노글라임(R=ME, n=1), 디글라임(R=ME, n=2), 트리글라임(R=ME, n=3), 테트라글라임(R=ME, n=4), 에틸글라임(R=Et, n=1), 에틸디글라임(R=Et, n=2), 부틸글라임(R=Bu, n=1), 부틸디글라임(R=Bu, n=2), 폴리글라임(R=ME) 및 이들 중 2종 이상을 포함한 혼합물 등일 수 있으며, 이에 제한되지는 않는다. 다만, 리튬 이차전지의 방전용량 등을 고려하였을 때 디글라임이 바람직할 수 있다.The glyme compound is, for example

It may be any compound corresponding to the formula represented by, in this case, in the above formula, R may be a methyl group, an ethyl group, or a butyl group, and n may be 1 to 4. Therefore, specific examples of the glyme-based compound include monoglyme (R=ME, n=1), diglyme (R=ME, n=2), triglyme (R=ME, n=3), tetra Glyme (R=ME, n=4), ethylglyme (R=Et, n=1), ethyldiglyme (R=Et, n=2), butylglyme (R=Bu, n=1) , Butyl diglyme (R=Bu, n=2), polyglyme (R=ME), and a mixture including two or more of them, but are not limited thereto. However, in consideration of the discharge capacity of the lithium secondary battery, diglyme may be preferable.

In addition, as the nitrile-based compound, acetonitrile, propionitrile, butyronitrile, isobutyronitrile, 3-hydroxypropionitrile, and acrylic Acrylonitrile, Adiponitrile, Malononitrile, Benzonitrile, and a mixture including two or more of these may be exemplified, but are not limited thereto, and acetonitrile is preferred. can do.

The content ratio of the glyme-based compound and the nitrile-based compound may be 1: 1 to 5: 1, preferably 1: 1 to 4: 1, more preferably 1: 1 to 2: 1 as a mass ratio. If the mass ratio of the glyme-based compound and the nitrile-based compound is out of the above range, the effects that can be obtained by mixing the two types of compounds may be insignificant.

Lithium salt (Li-Salt) may be additionally included in the electrolyte solution of the present invention including the above compounds. Lithium salts that can be included in the electrolyte include LiFSI, LiTFSI, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB(Ph) ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} LiSO 3 CH 3, LiSO 3 CF 3, LiSCN, LiC (CF 3 SO 2) 3, LiN (CF 3 SO 2) 2, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4- Lithium phenylborate, lithium imide, and a mixture including two or more of them may be exemplified, and among them, it may be preferable to use LiFSI in consideration of discharge capacity. When the lithium salt is included in the electrolyte, the content may be, for example, 20 to 50% by weight, preferably 25 to 40% by weight, based on the total weight of the electrolyte.

On the other hand, the electrolyte for a lithium secondary battery according to the present invention may further include a hydrofluoroether-based (HFE type) compound, if necessary. The hydrofluoroether-based compound is a component that can be added for the purpose of improving lithium ion conductivity by lowering the viscosity of the electrolyte, and is 1,1,2,2-tetrafluoroethyl-2,2,3,3 -Tetrafluoropropyl ether (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether), HFE-based compounds having similar properties, and mixtures thereof can be exemplified.

When the hydrofluoroether-based compound is included in the electrolyte for a lithium secondary battery of the present invention, the content may be 100 to 400 parts by weight, preferably 100 to 300 parts by weight, based on 100 parts by weight of the total weight of the glyme compound. And, if the content of the hydrofluoroether-based compound is out of the above range, the effect obtained by including the hydrofluoroether-based compound may be insignificant.

Next, a lithium secondary battery according to the present invention will be described. The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte for the lithium secondary battery. As described above, the electrolyte solution for a lithium secondary battery contains a glyme-based compound and a nitrile-based compound, and specific details are applied mutatis mutandis to the foregoing. In addition, the lithium secondary battery may be any lithium secondary battery commonly used in the art, of which a lithium-sulfur battery may be most preferred.

Hereinafter, in the lithium secondary battery according to the present invention, a more detailed description will be given of a positive electrode, a negative electrode, and a separator.

As described above, the positive electrode included in the lithium secondary battery of the present invention includes a positive electrode active material, a binder, and a conductive material. The positive electrode active material may be applied to a conventional lithium secondary battery, and may include, for example, elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof, and the sulfur-based compound is specifically As such, it may be Li ₂ S _n (n≥1), an organosulfur compound or a carbon-sulfur complex ((C ₂ S _x ) _n : x=2.5 to 50, n≥2). In addition, the positive electrode active material may include a sulfur-carbon composite, and since the sulfur material alone does not have electrical conductivity, it may be used in combination with a conductive material. The carbon material (or carbon source) constituting the sulfur-carbon composite may have a porous structure or a high specific surface area, so long as it is commonly used in the art. For example, as the porous carbon material, graphite; Graphene; Carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); Carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); And it may be one or more selected from the group consisting of activated carbon, but is not limited thereto, and the shape is spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped, or bulk-shaped, and may be used without limitation as long as they are commonly used for lithium secondary batteries.

In addition, pores are formed in the carbon material, and the porosity of the pores is 40 to 90%, preferably 60 to 80%, and if the porosity of the pores is less than 40%, lithium ions are not normally transferred and thus resistance components It may act as a problem, and if it exceeds 90%, a problem of lowering the mechanical strength may occur. In addition, the pore size of the carbon material is 10 nm to 5 μm, preferably 50 nm to 5 μm, and if the pore size is less than 10 nm, there may be a problem in which lithium ion penetration is impossible, and the pore size exceeding 5 μm In this case, a battery short circuit and safety problems may occur due to contact between electrodes.

The binder is a component that aids in bonding of a positive electrode active material and a conductive material and bonding to a current collector, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF/ HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE) ), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene -One or more selected from the group consisting of butylene rubber, fluorine rubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof may be used, but must be It is not limited thereto.

The binder is typically added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the binder is less than 1 part by weight, adhesion between the positive electrode active material and the current collector may be insufficient, and if it exceeds 50 parts by weight, the adhesion is improved, but the amount of the positive electrode active material decreases so that the battery capacity may be lowered.

The conductive material included in the positive electrode is not particularly limited as long as it does not induce side reactions in the internal environment of the lithium secondary battery, does not cause chemical changes in the battery, and has excellent electrical conductivity. Typically, graphite or conductive carbon may be used. Examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, and thermal black; A carbon-based material whose crystal structure is graphene or graphite; Conductive fibers such as carbon fibers and metal fibers; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And a conductive polymer such as a polyphenylene derivative, but may be used alone or in combination of two or more, but is not limited thereto.

The conductive material is typically added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is too small, such as less than 0.5 parts by weight, it is difficult to expect the effect of improving the electrical conductivity or the electrochemical properties of the battery may be deteriorated.If the content of the conductive material exceeds 50 parts by weight, the amount of the positive electrode active material is It becomes less, and the capacity and energy density may decrease. The method of including the conductive material in the positive electrode is not particularly limited, and a conventional method known in the art such as coating on a positive electrode active material may be used. In addition, if necessary, since the second conductive coating layer is added to the positive electrode active material, the addition of the conductive material as described above may be substituted.

In addition, a filler may be optionally added to the positive electrode of the present invention as a component that suppresses its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and examples thereof include olivine polymers such as polyethylene and polypropylene; Fibrous substances such as glass fibers and carbon fibers; Etc. can be used.

The positive electrode may be prepared by dispersing and mixing a positive electrode active material, a binder, and a conductive material in a dispersion medium (solvent) to form a slurry, and then coating the positive electrode current collector and drying and rolling the slurry. As the dispersion medium, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof may be used, but are not limited thereto.

The positive electrode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al ), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) surface-treated on the surface of aluminum (Al) or stainless steel may be used, but the present invention is not limited thereto. The shape of the positive electrode current collector may be in the form of a foil, film, sheet, punched, porous body, foam, or the like.

The negative electrode may be manufactured according to a conventional method known in the art. For example, a negative electrode active material, a conductive material, a binder, and if necessary, a filler, etc., are dispersed and mixed in a dispersion medium (solvent) to make a slurry, which is coated on the negative electrode current collector, and then dried and rolled to prepare a negative electrode. . As the negative active material, lithium metal or a lithium alloy (eg, an alloy of lithium and a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium) may be used. The anode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu). ), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Copper (Cu) or stainless steel may be surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not limited thereto. The negative electrode current collector may be in the form of a foil, a film, a sheet, a punched one, a porous body, or a foam.

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and serves to provide a passage for lithium ions to move. As the separator, olefin-based polymers such as polyethylene and polypropylene, glass fibers, etc. may be used in the form of sheets, multi-membrane, microporous films, woven fabrics and non-woven fabrics, but are not limited thereto. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The separator may have a pore diameter of generally 0.01 to 10 μm, and a thickness of 5 to 300 μm.

The lithium secondary battery of the present invention comprising the positive electrode, the negative electrode, the separator and the electrolyte as described above, after facing the positive electrode with the negative electrode and interposing a separator therebetween, comprising a glyme-based compound and a nitrile-based compound according to the present invention. It can be manufactured through a process of injecting an electrolyte solution. Meanwhile, any one or more of a lithium salt and a hydrofluoroether-based (HFE type) compound may be further mixed in the electrolyte solution, and the description thereof is also replaced with the foregoing.

On the other hand, the lithium secondary battery according to the present invention is not only applied to a battery cell used as a power source for a small device, but also can be particularly suitably used as a unit cell of a battery module that is a power source for a medium or large device. In this respect, the present invention also provides a battery module including two or more lithium secondary batteries electrically connected (series or parallel). It goes without saying that the number of lithium secondary batteries included in the battery module may be variously adjusted in consideration of the use and capacity of the battery module. Furthermore, the present invention provides a battery pack in which the battery modules are electrically connected according to conventional techniques in the art. The battery module and the battery pack may include a power tool; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric truck; Electric commercial vehicles; Alternatively, it can be used as a power supply for any one or more medium and large devices among the power storage systems, but is not limited thereto.

Hereinafter, preferred embodiments are presented to aid in the understanding of 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 spirit of the present invention, It is natural that such changes and modifications fall within the scope of the appended claims.

[Example 1] Manufacture of lithium secondary battery

First, carbon black (ECP600JD, Lion Specialty Chemicals) with a specific surface area of 800-1,500 m ² /g and a particle size of 1 to 10 µm and sulfur are mixed in a weight ratio of 3: 7 and then heat treated at 155°C to obtain sulfur-carbon. A composite was prepared, and a positive electrode was prepared by using the prepared sulfur-carbon composite, a conductive material (CNF) and a binder (PVDF) in a weight ratio of 90:5:5. Subsequently, after facing the prepared positive electrode with a lithium metal (Li-Metal) negative electrode and interposing a polyethylene (PE) separator therebetween, diethylene glycol dimethyl ether (glyme-based compound) 2.0 g, acetonitrile (nitrile-based compound) ) 0.5 g, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE-based compound) 6.0 g and LiFSI (lithium salt, 30% by weight based on the total weight of the electrolyte) ) Was injected to prepare a lithium secondary battery.

[Example 2] Preparation of lithium secondary battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of acetonitrile (nitrile compound) in the electrolyte was changed from 0.5 g to 1.0 g.

[Comparative Example 1] Manufacture of lithium secondary battery

Lithium secondary lithium secondary by performing the same as in Example 1, except that 0.75M LiFSI and 3wt% LiNO ₃ (above, lithium salt) and Catholyte (DOL:DME=1:1 (v/v)) were applied as an electrolyte solution. The battery was prepared.

[Comparative Example 2] Manufacture of lithium secondary battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that acetonitrile (nitrile-based compound) was not used in the electrolyte.

[Comparative Example 3] Manufacture of lithium secondary battery

Lithium secondary battery was carried out in the same manner as in Example 1, except that acetonitrile (nitrile-based compound) was not used in the electrolyte, and diethylene glycol dimethyl ether (glyme-based compound) was changed to triethylene glycol dimethyl ether. Was prepared.

[Comparative Example 4] Manufacture of lithium secondary battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiFSI (lithium salt) in the electrolyte was changed to LiTFSI.

The compositions of the electrolyte solutions used in Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1 below.

Electrolyte Glime system
compound Nitrile
compound HFE system
compound Lithium salt Catholyte Example 1 Diglyme
2.0 g 0.5 g of acetonitrile HFE
6.0 g LiFSI
30 wt% - Example 2 Diglyme
2.0 g 1.0 g of acetonitrile HFE
6.0 g LiFSI
30 wt% - Comparative Example 1 - - - 0.75 M LiFSI
3 wt% LiNO ₃ DOL:DME=
1:1(v/v) Comparative Example 2 Diglyme
2.0 g - HFE
6.0 g LiFSI
30 wt% - Comparative Example 3 Triglyme
2.0 g - HFE
6.0 g LiFSI
30 wt% - Comparative Example 4 Diglyme
2.0 g - HFE
6.0 g LiTFSI
30 wt% -

(* In Table 1, the exact name of the HFE-based compound is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether)

[Experimental Example 1] Evaluation of discharge capacity of lithium secondary battery

The lithium secondary batteries (precisely, lithium-sulfur batteries) prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were discharged to 0.1 C to evaluate the discharge capacity. 1 to 3 are graphs comparing and contrasting discharge capacities of lithium secondary batteries manufactured according to an embodiment and a comparative example of the present invention.

First, FIG. 1 is a graph comparing the discharging capacity of lithium secondary batteries prepared in Examples 1 and 2 and Comparative Example 2, and Examples 1 or 2 in which a glyme-based compound and a nitrile-based compound were applied together as an electrolyte. As shown in FIG. 1 and Table 2 below, both the discharge capacity and the nominal voltage (Vn) were increased compared to Comparative Example 2 in which only the glyme compound was applied as an electrolyte, and lithium-sulfur in which lithium polysulfide was not eluted. The discharge profile of the cell was observed. Through this, it was found that when a nitrile compound in addition to the glyme compound is applied as an electrolyte, the reactivity of the battery is improved by the nitrile compound. In addition, through Examples 1 and 2, it was confirmed that as the content of the nitrile-based compound increased, the discharge capacity and the nominal voltage also increased.

Discharge capacity (mAh/gS) Nominal voltage (V) Example 1 1,545 1,779 Example 2 1,553 1,812 Comparative Example 1 1,052 2,114 Comparative Example 2 1,360 1,774 Comparative Example 3 1,388 1,748 Comparative Example 4 973 1,721

In addition, Figure 2 is a graph comparing the discharge capacity of the lithium secondary batteries prepared in Comparative Examples 1 to 3, the battery of Comparative Example 2 using diglyme as a glyme-based compound, triglyme as a glyme-based compound Compared to the battery of Comparative Example 3 used, the charge overvoltage was small and the amount of charge was high compared to discharge, and through this, it was found that the glyme-based compound is more suitable for diglyme than triglyme. On the other hand, in the case of Comparative Example 1 in which the glyme-based compound or the nitrile-based compound was not added, it was confirmed that the discharge capacity was very low compared to Comparative Examples 2 and 3 using only the glyme-based compound.

In addition, Figure 3 is a graph comparing the discharge capacity of the lithium secondary batteries prepared in Comparative Examples 2 and 4, the battery of Comparative Example 4 using LiTFSI as a lithium salt, Comparative Example 2 using LiFSI as a lithium salt. Compared to the battery, it was confirmed that the discharge proceeded unstable and the discharge capacity was also low. Through this, it was found that LiFSI is more suitable for the lithium salt than LiTFSI.

Claims (12)

Glyme compounds; And
A lithium secondary battery electrolyte containing a nitrile-based compound. The method of claim 1, wherein the glyme-based compound is monoglyme, diglyme, triglyme, tetraglyme, ethylglyme, ethyl diglyme, butylglyme, butyl diglyme, polyglyme, and two or more of them An electrolyte for a lithium secondary battery, characterized in that selected from the group consisting of a mixture comprising a. The method of claim 1, wherein the nitrile compound is acetonitrile, propionitrile, butyronitrile, isobutyronitrile, 3-hydroxypropionitrile, acrylonitrile, adiponitrile, malononitrile, benzonitrile, and these An electrolyte for a lithium secondary battery, characterized in that selected from the group consisting of a mixture containing two or more of them. The electrolyte solution for lithium secondary batteries according to claim 1, wherein the glyme-based compound is diglyme, and the nitrile-based compound is acetonitrile. The electrolyte solution for lithium secondary batteries according to claim 1, wherein the content ratio of the glyme-based compound and the nitrile-based compound is 1:1 to 5:1 as a mass ratio. The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte for a lithium secondary battery further comprises a hydrofluoroether-based (HFE type) compound. The electrolyte solution for lithium secondary batteries according to claim 6, wherein the hydrofluoroether-based compound is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The electrolyte solution for a lithium secondary battery according to claim 6, wherein the content of the hydrofluoroether compound is 100 to 400 parts by weight based on 100 parts by weight of the total weight of the glyme compound. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the electrolyte solution for a lithium secondary battery further contains a lithium salt. The electrolyte for a lithium secondary battery according to claim 9, wherein the lithium salt is LiFSI. anode; cathode; A separator interposed between the anode and the cathode; And A lithium secondary battery comprising the electrolyte for a lithium secondary battery of claim 1. The lithium secondary battery according to claim 11, wherein the lithium secondary battery is a lithium-sulfur battery.

Images