KR102663586B1 - Lithium-sulfur secondary battery - Google Patents

Abstract

The present invention applies a positive electrode active material layer containing a LiOH-containing sulfur-carbon composite and specifically adjusts the porosity (%) and the mass of sulfur per unit area (mg/cm2) of the positive electrode active material layer, thereby improving the initial reactivity and cycle of the battery. Provides a lithium-sulfur secondary battery that improves performance and can implement a lithium-sulfur secondary battery with high energy density.

Description

Lithium-sulfur secondary battery{LITHIUM-SULFUR SECONDARY BATTERY}

The present invention relates to lithium-sulfur secondary batteries.

As the application area of secondary batteries expands to electric vehicles (EV) and energy storage systems (ESS), lithium-ion batteries with a relatively low energy storage density to weight (~250 Wh/kg) Ion secondary batteries have limitations in their application to these products. In contrast, lithium-sulfur secondary batteries are in the spotlight as next-generation secondary battery technology because they can theoretically achieve high energy storage density relative to weight (~2,600 Wh/kg).

A lithium-sulfur secondary battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond as a positive electrode active material and lithium metal as a negative electrode active material. These lithium-sulfur secondary batteries have the advantage that sulfur, the main material of the positive electrode active material, is abundant in resources worldwide, is not toxic, and has a low weight per atom.

In a lithium-sulfur secondary battery, when discharging, lithium, the negative electrode active material, gives up electrons and is ionized and oxidized, and the sulfur-based material, which is the positive electrode active material, accepts electrons and is reduced. At this time, the oxidation reaction of lithium is a process in which lithium metal gives up electrons and is converted into lithium cation form. Additionally, the reduction reaction of sulfur is a process in which the sulfur-sulfur bond accepts two electrons and is converted to sulfur anion form. The lithium cation generated by the oxidation reaction of lithium is transferred to the anode through the electrolyte and combines with the sulfur anion generated by the reduction reaction of sulfur to form a salt. Specifically, sulfur before discharge has a cyclic S ₈ structure, which is converted to lithium polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) through a reduction reaction. When is completely reduced, lithium sulfide (Li ₂ S) is ultimately produced.

Sulfur, a positive electrode active material, has low electrical conductivity, making it difficult to secure reactivity with electrons and lithium ions in solid-state form. In order to improve the reactivity of sulfur, existing lithium-sulfur secondary batteries generate intermediate polysulfide in the form of Li ₂ S _x to induce a liquid-state reaction and improve reactivity. In this case, ether-based solvents such as dioxolane and dimethoxyethane, which are highly soluble in lithium polysulfide, are used as the solvent for the electrolyte solution. In addition, in order to improve the reactivity of existing lithium-sulfur secondary batteries, a catholyte type lithium-sulfur secondary battery system is constructed. In this case, due to the characteristics of lithium polysulfide that easily dissolves in the electrolyte, the amount of sulfur depends on the content of the electrolyte. Reactivity and lifetime characteristics are affected. In addition, in order to build a high energy density, a low content of electrolyte must be injected, but as the electrolyte content decreases, the concentration of lithium polysulfide in the electrolyte increases, resulting in a decrease in the fluidity of the active material and an increase in side reactions, preventing normal battery operation. difficult.

Since this elution of lithium polysulfide has a negative effect on the capacity and lifespan characteristics of the battery, various technologies have been proposed to suppress the elution of lithium polysulfide.

For example, Republic of Korea Patent Publication No. 2016-0037084 uses a three-dimensional carbon nanotube aggregate coated with graphene as a carbon material to block lithium polysulfide from melting and improve the conductivity of the sulfur-carbon nanotube composite. It is disclosed that it can be improved.

In addition, Republic of Korea Patent No. 1379716 uses a graphene composite containing sulfur produced by treating graphene with hydrofluoric acid to form pores on the graphene surface and growing sulfur particles in the pores as a positive electrode active material. It is disclosed that the reduction in battery capacity can be minimized by suppressing lithium polysulfide elution.

These patents have improved the performance degradation problem of lithium-sulfur secondary batteries to some extent by preventing the elution of lithium polysulfide by changing the structure or material of the sulfur-carbon composite used as the positive electrode active material, but the effect is not sufficient. Therefore, in order to construct a lithium-sulfur secondary battery with high energy density, a battery system capable of driving a high-loading, low-porosity electrode is required, and research on such a battery system is continuously conducted in the relevant technical field. .

Republic of Korea Patent Publication No. 2016-0037084 (2016.04.05), sulfur-carbon nanotube composite, manufacturing method thereof, cathode active material for lithium-sulfur battery containing the same, and lithium-sulfur battery containing the same Republic of Korea Patent No. 1379716 (2014.03.25), lithium-sulfur secondary battery including graphene composite anode containing sulfur and method for manufacturing the same

Abbas Fotouhi et al., Lithium-Sulfur Battery Technology Readiness and Applications—A Review, Energies 2017, 10, 1937.

Accordingly, the present inventors conducted various studies to solve the above problem, and as a result, applied a positive electrode active material layer containing a LiOH-containing sulfur-carbon complex, and determined the porosity (%) and mass of sulfur per unit area (mg/ The present invention was completed by confirming that when ㎠) is specifically adjusted, the initial reactivity and cycle performance of the battery can be improved and a lithium-sulfur secondary battery with high energy density can be implemented.

In addition, the present invention was completed by confirming that the above effect can be further enhanced by configuring the battery so that the electrolyte satisfies specific conditions along with the above configuration.

Therefore, the purpose of the present invention is to provide a lithium-sulfur secondary battery with excellent initial reactivity and cycle performance and excellent energy density.

In order to achieve the above object, the present invention

A lithium-sulfur secondary battery comprising an anode, a cathode, a separator, and an electrolyte,

The anode includes a LiOH-containing sulfur-carbon complex,

Provided is a lithium-sulfur secondary battery having an SC factor value of 0.45 or more, expressed by Equation 1 below:

[Equation 1]

(In Equation 1 above,

P is the porosity (%) of the positive electrode active material layer in the positive electrode,

L is the mass of sulfur (mg/cm2) per unit area of the positive electrode active material layer in the positive electrode,

α is 10 (constant).).

In one embodiment of the present invention,

The electrolyte solution includes a solvent and a lithium salt,

The solvent may have the characteristic of comprising a first solvent having a DV ² factor value of 1.75 or less as expressed by Equation 2 below, and a second solvent being a fluorinated ether-based solvent:

[Equation 2]

(In Equation 2 above,

DV is the dipole moment per unit volume (Dmol/L),

μ is the viscosity of the solvent (cP),

γ is 100 (constant)).

In one embodiment of the present invention, the lithium-sulfur secondary battery may have a NS factor value of 3.5 or less, expressed by Equation 3 below:

[Equation 3]

(In Equation 3 above,

SC factor is equal to the value defined by Equation 1 above,

DV ² factor is the same as the value defined by Equation 2 above.).

In one embodiment of the present invention, the lithium-sulfur secondary battery may have an ED factor value of 850 or more, expressed by Equation 4 below:

[Equation 4]

(In Equation 4 above,

V is the nominal discharge voltage (V) for Li/Li ⁺ ,

SC factor is the same as the value defined by Equation 1 above,

C is the discharge capacity (mAh/g) when discharging at a rate of 0.1C,

D is the density of the electrolyte (g/cm3).

The lithium-sulfur secondary battery according to the present invention applies a positive electrode active material layer containing a LiOH-containing sulfur-carbon composite, and specifically adjusts the porosity (%) and the mass of sulfur per unit area (mg/cm2) of the positive electrode active material layer. , improves the initial reactivity and cycle performance of the battery, and provides the effect of realizing a lithium-sulfur secondary battery with high energy density.

In addition, by configuring the battery so that the electrolyte satisfies specific conditions along with the above configuration, the effect is further enhanced.

Figure 1 is an SEM image of a conventional sulfur-carbon composite (a) (Comparative Preparation Example 1) and a LiOH-containing sulfur-carbon composite (b) of the present invention (Example 2).
Figure 2 is a graph showing the lifespan characteristics of the lithium-sulfur secondary battery conducted in Experimental Example 2 of the present invention.

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

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

The terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as 'include' or 'have' are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

As used herein, the term “composite” refers to a material that combines two or more materials to form physically and chemically different phases while exhibiting more effective functions.

The term “polysulfide” used in this specification means “polysulfide ion (S _x ^2- , x = 8, 6, 4, 2)” and “lithium polysulfide (Li ₂ S _x ^or _LiS It is a concept that includes “8, 6, 4, 2)”.

Lithium-sulfur secondary batteries have the highest discharge capacity and energy density among many secondary batteries. Sulfur, which is used as a positive electrode active material, has abundant reserves and is inexpensive, so it can lower the manufacturing cost of the battery, and has the advantage of being environmentally friendly, making it the next-generation secondary battery. It is attracting attention as a battery.

However, in the case of the existing lithium-sulfur secondary battery system, loss of sulfur occurs due to failure to suppress lithium polysulfide elution, and as a result, the amount of sulfur participating in the electrochemical reaction is drastically reduced, so that in actual operation, theoretical discharge capacity and theoretical energy density are reduced. Not everything can be implemented.

The present inventors have made diligent efforts to solve the above problem, and in a lithium-sulfur secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, by using a LiOH-containing sulfur-carbon composite as a positive electrode active material, the surface of the carbon material particles If sulfur is evenly supported and the porosity (%) of the positive electrode active material layer and the mass of sulfur per unit area (mg/cm2) are specifically adjusted, the initial reactivity and cycle performance of the battery can be improved, and the high energy density lithium-sulfur The present invention was completed by confirming that secondary batteries can also be implemented.

In addition, it was confirmed that the above effects can be further strengthened by adjusting the electrolyte solution to meet specific conditions with the above configuration.

This invention

A lithium-sulfur secondary battery comprising an anode, a cathode, a separator, and an electrolyte,

The anode includes a LiOH-containing sulfur-carbon complex,

It relates to a lithium-sulfur secondary battery with a SC factor value of 0.45 or more, expressed by Equation 1 below:

[Equation 1]

(In Equation 1 above,

P is the porosity (%) of the positive electrode active material layer in the positive electrode,

L is the mass of sulfur (mg/cm2) per unit area of the positive electrode active material layer in the positive electrode,

α is 10 (constant).).

The LiOH-containing sulfur-carbon composite preferably contains more than 0 to 15% by weight of LiOH, more preferably 0.12 to 10% by weight, and even more preferably 0.15 to 5% by weight, based on the total weight of the composite. may be included.

In the case where LiOH exceeds 15 parts by weight, the effect is no longer increased, but it results in a decrease in the active material content, which is not preferable.

In the LiOH-containing sulfur-carbon composite, LiOH may be impregnated or coated on the carbon material, but is not limited thereto, and LiOH may be included in a mixed form with the carbon material and sulfur or a sulfur compound.

In the above, the carbon material may be one or more selected from the group consisting of graphite, carbon nanotubes, graphene, graphite, amorphous carbon, carbon black, and activated carbon, but is not limited to these.

The carbon material is not particularly limited, but microporous carbon materials having micropores may be preferably used. Microporous carbon materials provide a framework in which sulfur can be fixed uniformly and stably, and allow the electrochemical reaction of sulfur to proceed smoothly.

Hereinafter, the microporous carbon material will be described as an example, but the present invention is not limited to the following content.

The microporous carbon material can generally be manufactured by carbonizing precursors of various carbon materials. The microporous carbon material includes a plurality of pores on the surface and inside, including micropores with an average diameter of 1 to 10 nm, and the porosity (or porosity) may be in the range of 10 to 90%.

If the average diameter of the micropores is less than the above range, the pore size is only at the molecular level, making sulfur impregnation impossible. Conversely, if it exceeds the above range, it is difficult for the carbon material to have a high specific surface area.

The microporous carbon material may have a specific surface area of 200 to 4500 m2/g, preferably 250 to 4000 m2/g. At this time, the specific surface area can be measured using the usual BET method. If the specific surface area of the microporous carbon material is less than the above range, there is a problem of reduced reactivity due to a decrease in the contact area with sulfur. Conversely, if the specific surface area of the microporous carbon material exceeds the above range, there is a problem of increased side reactions due to excessive specific surface area and when producing anode slurry. There may be a problem of increasing the amount of binder required.

The microporous carbon material may have a pore volume of 0.8 to 5 cm3/g, preferably 1 to 4.5 cm3/g. At this time, the pore volume can be measured using the conventional BET method. If the pore volume of the microporous carbon material is less than the above range, sulfur impregnation into the pore structure does not occur well, and on the contrary, if it exceeds the above range, the porosity of the electrode increases and the amount of electrolyte to fill the pores increases, resulting in high There may be issues where energy density may be difficult to achieve.

The microporous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, fiber-shaped, tube-shaped or bulk-shaped, and can be used without limitation as it is commonly used in lithium-sulfur secondary batteries.

In the LiOH-containing sulfur-carbon composite of the present invention, the carbon material may be included in an amount of 10 to 50% by weight, preferably 20 to 40% by weight, based on the total weight of the LiOH-containing sulfur-carbon composite.

The sulfur may be one or more selected from the group consisting of inorganic sulfur, Li ₂ S _n (n=1), disulfide compounds, organic sulfur compounds, and carbon-sulfur polymers.

The sulfur may be included in an amount of 10 to 90 wt%, more preferably 15 to 60 wt%, based on the total weight of the LiOH-containing sulfur-carbon complex. If the sulfur is contained in less than 10% by weight, it is difficult to meet the SC factor due to insufficient mass (mg/cm2) ( L ) of sulfur per unit area of the positive electrode active material layer, and if it exceeds 90% by weight, sulfur is a component of the carbon material. This is undesirable because the pores and surfaces are unevenly impregnated, causing sulfur to clump together, causing a significant decrease in the conductivity of the sulfur-carbon composite.

Additionally, the weight ratio of carbon material and sulfur in the LiOH-containing sulfur-carbon composite may be 1:1 to 1:9, preferably 1:1.5 to 1:4. If the weight ratio is less than the above range, as the content of the porous carbon material increases, the amount of binder added when producing the positive electrode slurry increases. This increase in the amount of binder added ultimately increases the sheet resistance of the electrode and acts as an insulator to prevent electrons from passing, which can reduce cell performance. Conversely, if the weight ratio exceeds the above range, the sulfur may clump together and have difficulty receiving electrons, making it difficult to directly participate in the electrode reaction.

In the present invention, the LiOH-containing sulfur-carbon composite preferably has a specific surface area of 3 to 20 m2/g, and more preferably 5.5 to 15 m2/g. If the specific surface area of the LiOH-containing sulfur-carbon composite is less than 3 m2/g, it is undesirable in that sulfur is not evenly impregnated on the surface of the carbon material, resulting in a decrease in cell performance, and if it exceeds 20 m2/g, the electrode This is undesirable because it increases the amount of binder added during manufacturing.

In the present invention, the LiOH-containing sulfur-carbon composite preferably has a pore volume of 0.075 to 1.000 cm3/g, and more preferably 0.080 to 1.000 cm3/g. If the pore volume of the LiOH-containing sulfur-carbon composite is less than 0.075 cm3/g, it is undesirable in that sulfur is not impregnated into the sulfur-carbon composite and exists separately on the surface or agglomeration occurs, and if it exceeds 1.000 cm3/g In this case, although there is a lot of space to be impregnated with sulfur, it is undesirable in that it is difficult to manufacture a high energy density electrode because the pores of the sulfur-complex are not utilized.

In the present invention, the LiOH-containing sulfur-carbon complex is

(a) impregnating or coating a carbon material with a LiOH solution and then drying it; and

(b) mixing the LiOH-impregnated or coated carbon material dried in step (a) with sulfur.

According to the above method, it is possible to improve the performance of a lithium sulfur battery by uniformly treating the sulfur content of the composite through surface treatment of carbon using an aqueous LiOH solution without undergoing heat treatment or complex chemical processes.

In addition, in the present invention, the positive electrode containing LiOH-containing sulfur-carbon complex is

(1) LiOH-containing sulfur-carbon complex: conducting agent; and a binder; preparing a slurry composition comprising; and

(2) applying the prepared slurry on a positive electrode current collector to form a positive electrode active material layer.

Impregnation and coating method in step (a); Components and composition ratio of the slurry composition in step (1); And regarding the method of applying the current collector and slurry in step (c), methods known in the field can be applied as is.

In step (a), water, an organic solvent, or a mixture thereof may be used as a solvent in the LiOH solution. However, it is more preferable to use water as the solvent because it can dissolve LiOH and facilitate impregnation. there is.

The type of organic solvent is not particularly limited as long as it can dissolve LiOH and vaporize without decomposing carbon.

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

The positive electrode current collector can strengthen the bonding force with the positive electrode active material by forming fine irregularities on its surface, and can be used in various forms such as film, sheet, foil, mesh, net, porous material, foam, and non-woven fabric.

The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 3 to 500 ㎛.

The positive electrode active material layer may include a positive electrode active material and optionally a conductive material and a binder.

The average diameter of the LiOH-containing sulfur-carbon composite according to the present invention is not particularly limited in the present invention and may vary, but may preferably be 0.1 to 100 ㎛, preferably 1 to 50 ㎛. There is an advantage in that a high loading electrode can be manufactured when the above range is satisfied.

In addition to the composition described above, the positive electrode active material may further include one or more additives selected from transition metal elements, Group IIIA elements, Group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

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

The conductive material is a material that electrically connects the electrolyte and the positive electrode active material and serves as a path for electrons to move from the current collector to the positive electrode active material. It can be used without limitation as long as it has conductivity.

For example, the conductive material includes carbon black such as Super-P, Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon black; Carbon derivatives such as carbon nanotubes and fullerenes; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Alternatively, conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole can be used alone or in combination.

The content of the conductive material may be 0.01 to 30% by weight based on the total weight of the mixture containing the positive electrode active material.

The binder maintains the positive electrode active material in the positive electrode current collector and organically connects the positive active materials to increase the binding force between them. All binders known in the art can be used.

For example, the binder may be a fluororesin binder containing polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; polyalcohol-based binder; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; and a silane-based binder; one, two or more types of mixtures or copolymers selected from the group consisting of may be used.

The binder may be added in an amount of 0.5 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. If the binder content is less than 0.5% by weight, the physical properties of the positive electrode may deteriorate, causing the active material and conductive material in the positive electrode to fall off. If the binder content exceeds 30% by weight, the ratio of the active material and conductive material in the positive electrode is relatively reduced, reducing battery capacity. can do.

The anode can be manufactured by the method described above, and can also be manufactured by a conventional method known in the art. More specifically, for example, a slurry is prepared by mixing and stirring the positive electrode active material with a solvent and, if necessary, additives such as binders, conductive materials, and fillers, and then applying (coating) to a current collector of a metal material, compressing, and drying. Thus, the anode can be manufactured.

Specifically, first, the binder is dissolved in a solvent for preparing a slurry, and then the conductive material is dispersed. It is preferable to use a solvent for preparing the slurry that can uniformly disperse the positive electrode active material, binder, and conductive material and that evaporates easily. Representative examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropanol. Propyl alcohol, etc. can be used. Next, a positive electrode slurry is prepared by uniformly dispersing the positive electrode active material, or optionally together with an additive, into the solvent in which the conductive material is dispersed. The amount of solvent, positive electrode active material, or optionally additives contained in the slurry is not particularly important in the present application, and it is sufficient that the slurry has an appropriate viscosity to facilitate application. The slurry prepared in this way is applied to a current collector and dried in vacuum to form a positive electrode. The slurry can be applied to the current collector at an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

The application may be performed by a method commonly known in the art, but for example, the positive electrode active material slurry may be distributed on one upper surface of the positive electrode current collector and then uniformly dispersed using a doctor blade or the like. You can. In addition, it can be performed through methods such as die casting, comma coating, and screen printing.

The drying is not particularly limited, but may be performed within 1 day in a vacuum oven at 50 to 200°C.

The positive electrode of the present invention manufactured using the above-described materials and methods is classified by the SC factor value expressed by Equation 1 below.

[Equation 1]

(In Equation 1 above,

P is the porosity (%) of the positive electrode active material layer in the positive electrode,

L is the mass of sulfur per unit area of the positive electrode active material layer in the positive electrode (mg/cm2),

α is 10 (constant).).

The lithium-sulfur secondary battery according to the present invention realizes high energy density by organic combination of not only the above-described positive electrode, but also the negative electrode, separator, and electrolyte. According to the present invention, the lithium-sulfur secondary battery realizes high energy density. To this end, the SC factor value may be 0.45 or more, preferably 0.5 or more. In the present invention, the upper limit of the SC factor value is not particularly limited, but considering the actual operation of a lithium-sulfur secondary battery, the SC factor value may be 4.5 or less. When the SC factor value is 0.45 or more, the performance of the existing lithium-sulfur secondary battery, such as energy density of the battery, deteriorates during actual operation, but in the case of the lithium-sulfur secondary battery according to the present invention, the performance of the battery is improved even during actual operation. This is maintained without deterioration.

The negative electrode according to the present invention may be composed of a negative electrode current collector and a negative electrode active material layer formed on one or both sides thereof. Alternatively, the negative electrode may be a lithium metal plate.

The negative electrode active material layer may include a negative electrode active material and optionally a conductive material and a binder.

The negative electrode active material is a material that can reversibly intercalate or deintercalate lithium ions, a material that can reversibly form a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy. can be used.

The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.

The material that can react with the lithium ion to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate, or silicon.

The lithium alloy includes, for example, lithium (Li), 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 composition of the current collector, conductive material, binder, etc., excluding the negative electrode active material, and the manufacturing method of the negative electrode may be the materials and methods used in the positive electrode described above.

The separator according to the present invention is a physical separator that has the function of physically separating the anode and the cathode, and can be used without particular restrictions as long as it is used as a normal separator. In particular, it has low resistance to ion movement in the electrolyte solution and has an electrolyte moisturizing ability. Excellent is desirable.

Additionally, the separator separates or insulates the positive and negative electrodes from each other and enables the transport of lithium ions between the positive and negative electrodes. This separator is porous with a porosity of 30 to 50% and may be made of a non-conductive or insulating material.

Specifically, porous polymer films, such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, can be used. and non-woven fabrics made of high melting point glass fibers, etc. can be used. Among these, a porous polymer film is preferably used.

If a polymer film is used for both the buffer layer and the separator, the electrolyte impregnation amount and ion conduction characteristics are reduced, and the effects of reducing overvoltage and improving capacity characteristics are minimal. Conversely, when all non-woven materials are used, mechanical rigidity cannot be secured, resulting in the problem of battery short circuit. However, if a film-type separator and a polymer non-woven buffer layer are used together, mechanical strength can be secured along with improved battery performance due to the adoption of the buffer layer.

Preferably, in the present invention, an ethylene homopolymer (polyethylene) polymer film is used as a separator and a polyimide nonwoven fabric is used as a buffer layer. At this time, the polyethylene polymer film preferably has a thickness of 10 to 25 μm and a porosity of 40 to 50%.

The electrolyte according to the present invention is a non-aqueous electrolyte containing lithium salt and is composed of lithium salt and a solvent. The electrolyte solution has a density of less than 1.5 g/cm3. When the electrolyte has a density of 1.5 g/cm3 or more, it is difficult to implement high energy density of a lithium-sulfur secondary battery due to an increase in the weight of the electrolyte.

The lithium salt is a material that can be easily dissolved in non-aqueous organic solvents, such as LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁ 0Cl ₁₀ , LiB(Ph) ₄ , LiC ₄ BO ₈ , 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 , LiN It may be one or more from the group consisting of (C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, and lithium imide. In one embodiment of the present invention, the lithium salt may preferably be lithium imide such as LiTFSI.

The concentration of the lithium salt is 0.1 to 8.0 M, depending on several factors such as the exact composition of the electrolyte mixture, solubility of the salt, conductivity of the dissolved salt, charging and discharging conditions of the battery, operating temperature, and other factors known in the field of lithium secondary batteries. , preferably 0.5 to 5.0 M, more preferably 1.0 to 3.0 M. If the concentration of lithium salt is less than the above range, the conductivity of the electrolyte may decrease and battery performance may deteriorate, and if it exceeds the above range, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li ⁺ ) may decrease, so within the above range It is desirable to select an appropriate concentration.

The solvent includes a first solvent and a second solvent. The first solvent is characterized by having a high dipole moment and low viscosity. When a solvent with a high dipole moment is used, it has the effect of improving the solid phase reactivity of sulfur, and this effect can be excellently expressed when the solvent itself has a low viscosity. In the present invention, the first solvent is classified by the DV ² factor expressed by Equation 2 below.

[Equation 2]

(In Equation 2 above,

DV is the dipole moment per unit volume (Dmol/L),

μ is the viscosity of the solvent (cP),

γ is 100 (constant)).

According to the present invention, the DV ² factor value may be 1.75 or less, preferably 1.5 or less. In the present invention, the lower limit of the DV ² factor value is not particularly limited, but considering the actual operation of a lithium-sulfur secondary battery, the DV ² factor value may be 0.1 or more. When mixing a solvent with a DV ² factor value of 1.75 or less like the first solvent, the functionality of the electrolyte can be maintained even when a positive electrode with low porosity and high loading of sulfur, which is the positive electrode active material, is applied to a lithium-sulfur battery. Therefore, the performance of the battery does not deteriorate.

In the present invention, the type of the first solvent is not particularly limited as long as it is within the range of the above-mentioned DV ² factor value, but includes propionitrile, dimethylacetamide, dimethylformamide, gamma- It may include one or more selected from the group consisting of butyrolactone (Gamma-Butyrolactone), triethylamine, and 1-iodopropane.

The first solvent may be included in an amount of 1 to 50% by weight, preferably 5 to 40% by weight, and more preferably 10 to 30% by weight, based on the total weight of the solvent constituting the electrolyte solution. When the solvent according to the present invention contains the first solvent within the above-mentioned weight percent range, it can have the effect of improving battery performance even when used with a positive electrode with low porosity and a high loading amount of sulfur, which is a positive electrode active material.

The lithium-sulfur secondary battery of the present invention can be further distinguished by the NS factor, which is a combination of the SC factor and the DV ² factor. The NS factor is expressed as Equation 3 below.

[Equation 3]

(In Equation 3 above,

SC factor is equal to the value defined by Equation 1 above,

DV ² factor is the same as the value defined by Equation 2 above.).

In the present invention, the NS factor value may be 3.5 or less, preferably 3.0 or less, and more preferably 2.7 or less. In the present invention, the lower limit of the NS factor value is not particularly limited, but considering the actual operation of a lithium-sulfur secondary battery, the NS factor value may be 0.1 or more. When the NS factor value is adjusted within the above range, the performance improvement effect of the lithium-sulfur secondary battery may be better.

In the present invention, the second solvent is a fluorinated ether-based solvent. Previously, in order to control the viscosity of the electrolyte, solvents such as dimethoxyethane and dimethylcarbonate were used as diluents. When such solvents are used as diluents, high loading as in the present invention is used. , a battery containing a low-porosity anode cannot be driven. Therefore, in the present invention, the second solvent is added together with the first solvent to drive the positive electrode according to the present invention. The type of the second solvent is not particularly limited as long as it is a fluorinated ether-based solvent commonly used in the relevant technical field, but may be 1H,1H,2′H,3H-decafluorodipropyl ether (1H,1H,2′) H,3H-Decafluorodipropyl ether), Difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl trifluoro Methyl ether (1,2,2,2-Tetrafluoroethyl trifluoromethyl ether), 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether (1,1,2,3,3,3- Hexafluoropropyl difluoromethyl ether), pentafluoroethyl 2,2,2-trifluoroethyl ether (Pentafluoroethyl 2,2,2-trifluoroethyl ether) and 1H,1H,2′H-perfluorodipropyl ether (1H,1H, 2′H-Perfluorodipropyl ether) may include one or more selected from the group consisting of

The second solvent may be included in an amount of 50 to 99% by weight, preferably 60 to 95% by weight, and more preferably 70 to 90% by weight, based on the total weight of the solvent constituting the electrolyte solution. When the solvent according to the present invention contains a second solvent within the above-mentioned weight % range, the effect of improving battery performance even when used with a positive electrode that has a low porosity like the first solvent and a high loading amount of sulfur, which is a positive electrode active material. You can have When mixing the first solvent and the second solvent, the second solvent may be included in the electrolyte solution in an amount equal to or greater than that of the first solvent, considering the effect of improving battery performance. According to the present invention, the solvent may include a first solvent and a second solvent in a weight ratio of 1:1 to 1:9, preferably 3:7 to 1:9 (first solvent:second solvent).

The non-aqueous electrolyte solution for lithium-sulfur batteries of the present invention may further include nitric acid or nitrous acid-based compounds as additives. The nitric acid or nitrous acid-based compound has the effect of forming a stable film on the lithium electrode and improving charge/discharge efficiency. Such nitric acid or nitrite-based compounds are not particularly limited in the present invention, but include lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), barium nitrate (Ba(NO ₃ ) ₂ ), and ammonium nitrate. Inorganic nitric acid or nitrite compounds such as (NH ₄ NO ₃ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), and ammonium nitrite (NH ₄ NO ₂ ); Organic nitric acids such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite. or nitrous acid compounds; One type selected from the group consisting of organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof is possible, preferably uses lithium nitrate.

In addition, the electrolyte solution may further include other additives for the purpose of improving charge/discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazoli. Dinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate ( VC), etc.

The lithium-sulfur secondary battery according to the present invention is classified by the ED factor value expressed by Equation 4 below.

[Equation 4]

(In Equation 4 above,

V is the nominal discharge voltage (V) for Li/Li ⁺ ,

SC factor is the same as the value defined by Equation 1 above,

C is the discharge capacity (mAh/g) when discharging at a rate of 0.1C,

D is the density of the electrolyte (g/cm3).

The higher the value of the ED factor, the higher energy density can be realized in an actual lithium-sulfur secondary battery. According to the present invention, the ED factor value may be 850 or more, preferably 870 or more, and more preferably 891 or more. In the present invention, the upper limit of the ED factor value is not particularly limited, but considering the actual operation of a lithium-sulfur secondary battery, the ED factor value may be 10,000 or less. The range of the ED factor value means that the lithium-sulfur secondary battery according to the present invention can implement more improved energy density than the existing lithium-sulfur secondary battery.

The lithium-sulfur secondary battery of the present invention can be manufactured by placing a separator between the positive electrode and the negative electrode to form an electrode assembly, and placing the electrode assembly in a cylindrical battery case or a square battery case and then injecting electrolyte. Alternatively, it may be manufactured by stacking the electrode assembly, impregnating it with an electrolyte, and sealing the resulting product in a battery case.

Additionally, the present invention provides a battery module including the lithium-sulfur secondary battery as a unit cell.

The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large devices include power tools that are powered by an omni-electric motor; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear 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 variations and modifications fall within the scope of the attached patent claims.

Preparation Example 1: Preparation of LiOH-impregnated sulfur-carbon composite active material

After dissolving 4 mg of LiOH in 50 g of water to prepare a LiOH aqueous solution, it was impregnated on 10 g of carbon nanotubes (CNTs) with a specific surface area of 300 m2/g and a pore volume of 1.9 cm3/g by the incipient wetness impregnation method. Impregnated. LiOH-impregnated CNTs were filtered, washed, and vacuum dried to prepare LiOH-impregnated CNTs.

7.5 g of the LiOH-impregnated CNTs were mixed with 22.5 g of sulfur (S), and a LiOH-impregnated sulfur-carbon composite was prepared by melt diffusion in a convection oven.

Preparation Example 2: Preparation of LiOH-impregnated sulfur-carbon composite active material

After preparing a LiOH aqueous solution by dissolving 20 mg of LiOH in 50 g of water, 10 g of carbon nanotubes (CNTs) with a specific surface area of 300 m2/g and a pore volume of 1.9 cm3/g were subjected to the incipient wetness impregnation method. impregnated by LiOH-impregnated CNTs were filtered, washed, and vacuum dried to prepare LiOH-impregnated CNTs.

7.5 g of the LiOH-impregnated CNTs were mixed with 22.5 g of sulfur (S), and a LiOH-impregnated sulfur-carbon composite was prepared by melt diffusion in a convection oven.

Preparation Example 3: Preparation of LiOH-impregnated sulfur-carbon composite active material

After preparing a LiOH aqueous solution by dissolving 0.5 g of LiOH in 50 g of water, it was applied to 10 g of carbon nanotubes (CNTs) with a specific surface area of 300 m2/g and a pore volume of 1.9 cm3/g using the incipient wetness impregnation method. impregnated by LiOH-impregnated CNTs were filtered, washed, and vacuum dried to prepare LiOH-impregnated CNTs.

7.5 g of the LiOH-impregnated CNTs were mixed with 22.5 g of sulfur (S), and a LiOH-impregnated sulfur-carbon composite was prepared by melt diffusion in a convection oven.

Comparative Preparation Example 1: Preparation of sulfur-carbon composite active material

7.5 g of carbon nanotubes (CNTs) with a specific surface area of 300 ㎡/g and a pore volume of 1.9 ㎤/g were mixed with 22.5 g of sulfur (S), and a sulfur-carbon composite was prepared by melt diffusion in a convection oven. did.

Preparation Examples 4 to 6 and Comparative Preparation Example 2: Preparation of anode for lithium-sulfur battery containing LiOH

88% by weight of the LiOH-impregnated sulfur-carbon composite prepared in Preparation Examples 1 to 3 or 88% by weight of the sulfur-carbon composite prepared in Comparative Preparation Example 1, 5% by weight of Denka Black as a conductive material, and SBR and CMC 7 as binders. A composition for forming an active material layer was prepared by mixing % by weight with distilled water.

The composition was coated on an aluminum current collector in an amount of 6 mg/cm ² to prepare a positive electrode, the porosity of the positive electrode active material layer and the mass of sulfur per unit area of the positive active material layer were measured, and the SC factor value was calculated based on this as follows. It is shown in Table 1.

LiOH-containing sulfur-carbon complex used Porosity of the positive electrode active material layer Mass of sulfur per unit area of the positive electrode active material layer SC factor Production example 4 Manufacturing Example 1 60% 4.2mg 0.7 Production example 5 Production example 2 60% 4.2mg 0.7 Production example 6 Production example 3 60% 4.2mg 0.7 Comparative Manufacturing Example 2 Comparative Manufacturing Example 1 60% 4.2mg 0.7

Comparative Manufacturing Example 3: Preparation of anode for lithium-sulfur battery

A composition for forming a positive electrode active material layer was prepared by using water as a solvent and mixing sulfur, Super-P (SP), a conductive material, and a binder using a ball mill. At this time, Denka Black was used as the conductive material, and a mixed binder of SBR and CMC was used as the binder, and the mixing ratio was 90:10:10 by weight of sulfur and SP (9:1 by weight):conductive material:binder. It was made possible. The prepared composition for forming a positive electrode active material layer was applied to an aluminum current collector and dried to prepare a positive electrode (energy density of the positive electrode: 6.18 mAh/cm2). In the manufactured positive electrode, the porosity of the positive electrode active material layer was 75%, the mass of sulfur per unit area of the positive active material layer was 3.1 mg/cm2, and the SC factor value calculated based on this was 0.41.

Examples 1 to 3: Preparation of lithium-sulfur secondary battery

Each of the positive electrodes prepared in Preparation Examples 4 to 6, lithium foil with a thickness of 150 ㎛ as the negative electrode, and polyethylene with a thickness of 20 ㎛ and 45% porosity as a separator were placed so that the positive and negative electrodes faced each other. Then, an electrode assembly was manufactured by interposing a separator between them.

Next, the electrode assembly was placed inside the case and an electrolyte solution was injected to manufacture a lithium-sulfur secondary battery.

At this time, the electrolyte solution was prepared by dissolving lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) at a concentration of 3M in an organic solvent, where the organic solvent was propionitrile (first solvent) and 1H, 1H, 2 A solvent mixed with ′H,3H-decafluorodipropyl ether (second solvent) at a weight ratio of 3:7 was used. In the first solvent, the dipole moment per unit volume was 97.1 D·mol/L, and the viscosity of the solvent was 0.38 cP. The DV ² factor value calculated based on this was 0.39.

Comparative Example 1: Manufacturing of lithium-sulfur secondary battery

A lithium-sulfur secondary battery was manufactured in the same manner as Example 2, except that the positive electrode prepared in Comparative Preparation Example 2 was used.

Comparative Example 2: Manufacturing of lithium-sulfur secondary battery

A lithium-sulfur secondary battery was manufactured in the same manner as Example 2, except that the positive electrode prepared in Comparative Preparation Example 3 was used.

Comparative Example 3: Manufacturing of lithium-sulfur secondary battery

The same method as Comparative Example 1 except that the preparation conditions of the electrolyte were changed and an electrolyte containing dimethoxyethane (DME) was used instead of 1H,1H,2′H,3H-decafluorodipropyl ether as the second solvent. A lithium-sulfur secondary battery was manufactured.

Comparative Example 4: Manufacturing of lithium-sulfur secondary battery

By changing the manufacturing conditions of the electrolyte, instead of propionitrile as the first solvent, propylene carbonate ( A lithium-sulfur secondary battery was manufactured in the same manner as Comparative Example 1, except that propylene carbonate) was used.

The conditions of Examples 1 to 3 and Comparative Examples 1 to 4 are summarized and shown in Table 2 below.

Electrolyte composition SC factor DV ² factor NS factor Example 1 First electrolyte composition ¹⁾ 0.7 0.39 0.557 Example 2 0.7 0.39 0.557 Example 3 0.7 0.39 0.557 Comparative Example 1 0.7 0.39 0.557 Comparative Example 2 0.41 0.39 0.951 Comparative Example 3 Second electrolyte composition ²⁾ 0.6 0.39 0.65 Comparative Example 4 Third electrolyte composition ³⁾ 0.6 1.77 2.95 ¹⁾ First electrolyte composition = Propionitrile:1H,1H,2'H,3H-Decafluorodipropyl ether (3:7, w/w) solvent, 3.0M LiTFSI
²⁾ Second electrolyte composition = Propionitrile:Dimethoxyethane (3:7, w/w) solvent, 3.0M LiTFSI
³⁾ Third electrolyte composition = Propylene carbonate:1H,1H,2'H,3H-Decafluorodipropyl ether(3:7, w/w) solvent, 3.0M LiTFSI

Experimental Example 1: Measurement of physical properties of sulfur-carbon complex

The BET of the sulfur-carbon composite prepared in Preparation Example 2 and Comparative Preparation Example 1 was measured using the BET 6 point method using the nitrogen gas adsorption flow method and is shown in Table 3 below, and the SEM image was taken and shown in FIG. 1.

Comparative Manufacturing Example 1
sulfur-carbon complex Production example 2
sulfur-carbon complex a _{s, BET} [m ² g ^-1 ] 5.2102 6.2175 Pore Volume [cm ³ g ^-1 ] 0.0705 0.8749 Mean pore diameter[nm] 54.125 65.981

As shown in Table 3, in the case of the sulfur-carbon composite of Preparation Example 2, the specific surface area and pore volume greatly increase after the sulfur loading process compared to the comparative example, and as confirmed from the SEM image in Figure 1, sulfur is inside the composite. It can be seen that it is evenly supported.

Experimental Example 2: Battery performance evaluation

The performance of the batteries manufactured in Example 2 and Comparative Example 1 was evaluated using a charge/discharge measurement device (LAND CT-2001A, Wuhan, China). The battery was initially discharged at a rate of 0.1C for 2.5 cycles of charge-discharge-discharge-charge-discharge, and after 3 cycles of charge-discharge at 0.2C, charging was performed at a rate of 0.3C and discharge at a rate of 0.5C, allowing the battery to last up to 50 cycles. Performance was evaluated. The evaluation results are shown in Figures 2 and 3.

As shown in Figure 2, the battery of Example 2 of the present invention showed a greatly improved cycle life compared to the battery of Comparative Example 1.

Experimental Example 3: Battery performance evaluation

The ED factor values of the lithium-sulfur secondary batteries according to Examples 1 to 3 and Comparative Examples 1 to 4 were measured under the same charging and discharging conditions as in Experimental Example 2, and are shown in Table 4 below.

Electrolyte composition SC factor ED factor Example 1 First electrolyte composition ¹⁾ 0.7 1399 Example 2 0.7 1410 Example 3 0.7 1419 Comparative Example 1 0.7 1350 Comparative Example 2 0.41 802 Comparative Example 3 Second electrolyte composition ²⁾ 0.6 1115 Comparative Example 4 Third electrolyte composition ³⁾ 0.6 1074 ¹⁾ First electrolyte composition = Propionitrile:1H,1H,2'H,3H-Decafluorodipropyl ether (3:7, w/w) solvent, 3.0M LiTFSI
²⁾ Second electrolyte composition = Propionitrile:Dimethoxyethane (3:7, w/w) solvent, 3.0M LiTFSI
³⁾ Third electrolyte composition = Propylene carbonate:1H,1H,2'H,3H-Decafluorodipropyl ether(3:7, w/w) solvent, 3.0M LiTFSI

According to Table 4, the lithium-sulfur secondary batteries according to Examples 1 to 3 have a relatively large ED factor value compared to the lithium-sulfur secondary batteries with the second electrolyte composition, the third electrolyte composition, or the SC factor of 0.41 or less. You can have it. This means that the lithium-sulfur secondary battery according to the present invention can achieve a higher energy density that could not be achieved in existing lithium-sulfur secondary batteries.

Claims (16)

A lithium-sulfur secondary battery comprising an anode, a cathode, a separator, and an electrolyte,
The anode includes a LiOH-containing sulfur-carbon complex,
The SC factor value expressed by Equation 1 below is 0.45 or more,
A lithium-sulfur secondary battery characterized in that the ED factor value expressed by the following equation 4 is 850 or more:
[Equation 1]

(In Equation 1 above,
P is the porosity (%) of the positive electrode active material layer in the positive electrode,
L is the mass of sulfur (mg/cm2) per unit area of the positive electrode active material layer in the positive electrode,
α is 10 (constant).)
[Equation 4]

(In Equation 4 above,
V is the nominal discharge voltage (V) for Li/Li ⁺ ,
SC factor is the same as the value defined by Equation 1 above,
C is the discharge capacity (mAh/g) when discharging at a rate of 0.1C,
D is the density of the electrolyte (g/cm3). According to paragraph 1,
The LiOH-containing sulfur-carbon composite is a lithium-sulfur secondary battery, characterized in that it contains more than 0 to 15% by weight of LiOH based on the total weight of the composite. According to paragraph 1,
A lithium-sulfur secondary battery, characterized in that the sulfur is contained in an amount of 10 to 90% by weight based on the total weight of the LiOH-containing sulfur-carbon composite. According to paragraph 1,
A lithium-sulfur secondary battery, wherein the LiOH-containing sulfur-carbon composite has a specific surface area of 3 to 20 m2/g. According to paragraph 1,
The LiOH-containing sulfur-carbon composite is a lithium-sulfur secondary battery, characterized in that the pore volume is 0.075 to 1.000 cm3/g. According to paragraph 1,
The LiOH-containing sulfur-carbon composite is a lithium-sulfur secondary battery, characterized in that the carbon material is impregnated or coated with LiOH. According to paragraph 1,
The sulfur is a lithium-sulfur secondary battery, characterized in that it contains at least one selected from the group consisting of inorganic sulfur, Li ₂ S _n (n=1), disulfide compounds, organic sulfur compounds, and carbon-sulfur polymers. According to paragraph 1,
The electrolyte solution includes a solvent and a lithium salt,
The solvent is a lithium-sulfur secondary battery, characterized in that it includes a first solvent having a DV ² factor value of 1.75 or less as expressed by Equation 2 below, and a second solvent that is a fluorinated ether-based solvent:
[Equation 2]

(In Equation 2 above,
DV is the dipole moment per unit volume (Dmol/L),
μ is the viscosity of the solvent (cP),
γ is 100 (constant)). According to clause 8,
The first solvent is a lithium-sulfur secondary battery, characterized in that the DV ² factor value is 1.5 or less. According to clause 8,
The lithium-sulfur secondary battery is characterized in that the NS factor value expressed by Equation 3 below is 3.5 or less:
[Equation 3]

(In Equation 3 above,
SC factor is equal to the value defined by Equation 1 above,
DV ² factor is the same as the value defined by Equation 2 above.). delete According to clause 8,
The first solvent is a lithium-containing solvent containing at least one selected from the group consisting of propionitrile, dimethylacetamide, dimethylformamide, gamma-butyrolactone, triethylamine, and 1-iodopropane. Sulfur secondary battery. According to clause 8,
The second solvent is 1H,1H,2′H,3H-decafluorodipropyl ether, difluoromethyl 2,2,2-trifluoroethyl ether, 1,2,2,2-tetrafluoroethyl tri. Fluoromethyl ether, 1,1,2,3,3,3-hexafluoropropyl difluoromethyl ether, pentafluoroethyl 2,2,2-trifluoroethyl ether and 1H,1H,2′H - A lithium-sulfur secondary battery comprising at least one selected from the group consisting of perfluorodipropyl ether. According to clause 8,
The solvent is a lithium-sulfur secondary battery, characterized in that it contains 1 to 50% by weight of the first solvent based on the total weight of the solvent. According to clause 8,
A lithium-sulfur secondary battery, wherein the solvent contains 50 to 99% by weight of a second solvent based on the total weight of the solvent. According to clause 8,
The solvent is a lithium-sulfur secondary battery, characterized in that it contains a first solvent and a second solvent in a weight ratio of 3:7 to 1:9.