KR20230089021A - Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including the same. The electrolyte for a lithium-sulfur battery includes: lithium salt; an organic solvent; and an additive. The organic solvent is a three-component solvent mixture including a cyclic ether compound, a linear ether compound, and a heterocyclic compound. The present invention increases the stability of an electrolyte to suppress the formation of a lithium dendrite and to improve the lifespan of a battery.

Description

Electrolyte for lithium-sulfur battery and lithium-sulfur battery containing the same

The present invention relates to an electrolyte solution for a lithium-sulfur battery and a lithium-sulfur battery including the same.

As the range of utilization of secondary batteries has expanded from small portable electronic devices to mid-to-large sized electric vehicles (EV), energy storage systems (ESS), and electric ships, high capacity, high energy density and long Demand for a lithium secondary battery having a lifespan is rapidly increasing.

Lithium metal has theoretically a very high specific capacity of 3,860 mAh/g, has a low potential as an anode material, and has a very low density, so various attempts have been made to use it as a negative electrode of a battery.

Among them, the lithium-sulfur secondary battery refers to a battery system that uses a sulfur-based material having a 'S-S 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, has characteristics in that it has a low weight per atom, is abundant in resources, is easy to supply and demand is cheap, can lower the manufacturing cost of a battery, and is environmentally friendly because it is non-toxic.

In particular, since the lithium-sulfur secondary battery has a theoretical discharge capacity of 1,675 mAh/g-sulfur and can theoretically realize a high energy storage density of 2,600 Wh/kg compared to its weight, other battery systems currently being researched (Ni-MH cell: 450 Wh/kg, Li-FeS cell: 480 Wh/kg, Li-MnO ₂ cell: 1,000 Wh/kg, Na-S cell: 800 Wh/kg) and Li-ion cell (250 Wh/kg) theory Since it has a very high value compared to the energy density, it is receiving great attention in the medium and large-sized secondary battery market that is currently being developed.

Deterioration of the lithium negative electrode may be mentioned as a factor affecting the lifespan of the lithium-sulfur secondary battery, which may occur due to a reaction with a positive electrode active material or a reaction with an electrolyte. It has been pointed out that the deterioration of the negative electrode results in the formation of dendrites and a decrease in Coulombic Efficiency (C.E). In particular, when dendrites are formed in a one-dimensional form, an internal short circuit may occur through a separator including pores, which may cause problems in safety or lifespan reduction due to combustion of the electrolyte.

Therefore, in order to improve the problem of the lithium-sulfur battery due to the dendrite phenomenon, research is needed to suppress the formation of dendrites by uniformly depositing and stripping lithium on the surface of the negative electrode.

Korean Patent Publication No. 10-2019-0119963 "Electrolyte additive, electrolyte including the same, positive electrode including the electrolyte, lithium-air battery including the positive electrode"

In a lithium-sulfur battery using a lithium-based metal as an anode, lithium dendrites are formed on the surface of the anode, and electrolyte decomposition continuously occurs, resulting in deterioration in performance of the lithium-sulfur battery. Accordingly, the inventors of the present invention completed the present invention by finding that it can be solved through the use of an electrolyte solution containing a three-component solvent mixture as a result of conducting research on forming a protective layer on a lithium electrode in a new way.

Accordingly, an object of the present invention is to provide an electrolyte solution for a lithium-sulfur battery.

In addition, an object of the present invention is to provide a lithium-sulfur battery including the electrolyte solution.

In order to achieve the above object, the present invention provides an electrolyte solution for a lithium-sulfur battery comprising a lithium salt, an organic solvent and an additive, wherein the organic solvent is a three-component solvent comprising a cyclic ether compound, a linear ether compound and a heterocyclic compound. An electrolyte solution for a lithium-sulfur battery, which is a mixture, is provided.

In addition, the present invention is a positive electrode; cathode; a separator interposed between the anode and the cathode; and an electrolyte solution, wherein the negative electrode is a lithium-based metal, and the electrolyte solution is an electrolyte solution according to the present invention.

The lithium-sulfur battery according to the present invention includes a three-component solvent mixture in the electrolyte to form a protective film through ring opening polymerization on the surface of a lithium-based metal anode, enhances the stability of the electrolyte, and It can have the effect of suppressing generation and improving the lifespan of a battery.

1 is a graph measuring lifespan characteristics of a lithium-sulfur battery according to an embodiment of the present invention.
2 is a graph measuring lifespan characteristics of a lithium-sulfur battery according to an embodiment of the present invention.

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

A major cause of early deterioration of a lithium secondary battery is a decrease in efficiency of a lithium-based negative electrode. When a lithium-based metal is used as an anode, not only the reaction is non-uniform due to the non-uniform native oxide layer, but also dendrites grow during charging (Li plating) and dead Li is easily generated, and the reaction Lithium that can participate in is consumed, and the efficiency of the lithium-based negative electrode is lowered.

Methods of forming a protective film, a conductive host matrix, and the like on a lithium-based metal layer have been attempted to ensure uniform reactivity of the surface of the lithium-based metal and suppress growth of lithium-based metal. In the case of the protective film, high mechanical strength for suppressing lithium dendrites and high ionic conductivity for lithium ion transfer are required at the same time, but the mechanical strength and ionic conductivity are in a trade-off relationship with each other, so mechanical strength and ion It is difficult to simultaneously improve the conductivity.

In the present invention, by using an electrolyte solution for a lithium-sulfur battery containing a three-component solvent mixture, ring-opening polymerization of a cyclic ether compound included in the electrolyte solution in the initial discharge step without forming a separate protective film on the surface of a lithium-based metal, which is an anode. It is intended to provide an electrolyte solution for a lithium-sulfur battery capable of forming a polymer protective film on the surface of the lithium-based metal due to the reaction to increase the reaction uniformity of the lithium-based metal, suppress the generation of lithium dendrites, and improve the lifespan characteristics of the battery.

Electrolyte for lithium-sulfur batteries

The present invention is a lithium salt; An electrolyte solution for a lithium-sulfur battery including an organic solvent and an additive, wherein the organic solvent is a three-component solvent mixture including a cyclic ether compound, a linear ether compound, and a heterocyclic compound.

In one embodiment of the present invention, the cyclic ether compound is 1,3-dioxolane, 2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-ethyl-2 -Methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane and 4,5-di It may include at least one selected from the group consisting of ethyl-1,3-dioxolane.

In another embodiment of the present invention, the cyclic ether compound may include 2-methyl-1,3-dioxolane.

In one embodiment of the present invention, the linear ether compound is dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol Dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethyl ether, butylene glycol ether, diethylene glycol ethylmethyl ether, diethylene It may include at least one selected from the group consisting of glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tert-butyl ethyl ether, and ethylene glycol ethyl methyl ether.

In another embodiment of the present invention, the linear ether compound is one selected from the group consisting of dimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol ethylmethyl ether and ethylene glycol ethylmethyl ether may contain more than

In one embodiment of the present invention, the heterocyclic compound is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 3-ethylfuran, 2-propylfuran, 3-propylfuran, 2-butylfuran , 3-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran and benzofuran One or more selected species may be included.

In another embodiment of the present invention, the heterocyclic compound is selected from the group consisting of 2-methylfuran, 3-methylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran and 2,5-dimethylfuran One or more may be included.

In one embodiment of the present invention, the organic solvent may be a three-component solvent mixture including a cyclic ether compound, a linear ether compound, and a heterocyclic compound.

In another embodiment of the present invention, the solvent mixture may include a cyclic ether compound and a heterocyclic compound in an amount of 10 to 40% by volume based on 100% by volume of the organic solvent.

In another embodiment of the present invention, the solvent mixture may include a cyclic ether compound and a heterocyclic compound in an amount of 20 to 30% by volume based on 100% by volume of the organic solvent.

When the solvent mixture contains a cyclic ether compound and a heterocyclic compound in a volume ratio of less than 10, the content of the linear ether compound is relatively high, so that the solubility of polysulfide increases, causing problems such as increased side reactions and reduced battery life. can In addition, when the solvent mixture includes the cyclic ether compound and the heterocyclic compound in a volume ratio of more than 40, the viscosity of the organic solvent increases, thereby reducing battery life.

In another embodiment of the present invention, the solvent mixture may include a cyclic ether compound in an amount of 10 to 20 and a heterocyclic compound in an amount of 20 to 10 by volume, based on 100% by volume of the organic solvent.

If the solvent mixture contains the cyclic ether compound or the heterocyclic compound in an amount of less than 10% by volume, the protective film may not be formed on the surface of the lithium-based metal, and the solvent mixture contains the cyclic ether compound or the heterocyclic compound in an amount of 20% by volume. If it is included in excess, the viscosity of the organic solvent may increase, resulting in a decrease in the lifespan of the battery.

In one embodiment of the present invention, when the electrolyte solution for a lithium-sulfur battery containing the solvent mixture is used, in the initial discharge stage of the battery, a ring opening polymerization of a cyclic ether compound is used to form a lithium-based metal. Formation of a solid electrolyte interface (SEI layer) on the surface can suppress the generation of lithium dendrites, and furthermore, by reducing electrolyte decomposition and subsequent side reactions on the surface of lithium-based metals, the lifespan of lithium-sulfur batteries is improved. can improve

The electrolyte solution for a lithium-sulfur battery of the present invention may include a lithium salt as an electrolyte salt to increase ionic conductivity. The lithium salt is not particularly limited in the present invention, and can be used without limitation as long as it is commonly available in the art.

In one embodiment of the present invention, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl 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(C ₂ F ₅ SO ₂ ) ₂ and LiN(SO ₂ F) ₂ may include one or more selected from the group consisting of.

In another embodiment of the present invention, the lithium salt may be LiN(SO ₂ F) ₂ (LiFSI).

The concentration of the lithium salt depends on several factors, such as the precise composition of the mixture in the electrolyte, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the operating temperature and other factors known in the lithium battery art, ranging from 0.1 to 0.1 5.0 M, preferably 0.2 to 3.0 M, more specifically 0.5 to 2.5 M. If less than 0.1 M is used, the conductivity of the electrolyte may be lowered, resulting in deterioration in electrolyte performance, and if more than 5.0 M is used, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li+) may be reduced.

The electrolyte solution for a lithium-sulfur battery of the present invention may include additives commonly used in the art in addition to the above-described composition.

In one embodiment of the present invention, the additive is lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), magnesium nitrate (MgNO ₃ ), barium nitrate (BaNO ₃ ), lithium nitrite ( LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), and may include one selected from the group consisting of combinations thereof.

The method for preparing the electrolyte for a lithium-sulfur battery according to the present invention is not particularly limited in the present invention, and may be prepared by a conventional method known in the art.

lithium-sulfur battery

A lithium-sulfur battery according to the present invention includes a positive electrode; cathode; a separator interposed between the anode and the cathode; and an electrolyte solution, wherein the negative electrode is a lithium-based metal, and the electrolyte solution relates to the above-described electrolyte solution for a lithium-sulfur battery according to the present invention.

The electrolyte solution for a lithium-sulfur battery of the present invention is the above-described electrolyte solution for a lithium-sulfur battery of the present invention.

The polymer protective film is formed on the surface of the lithium-based metal by ring opening polymerization of the cyclic ether compound contained in the above-described electrolyte solution in the initial discharge stage of the battery.

Due to the formed polymer protective film, it is possible to suppress generation of lithium dendrites on the surface of a lithium-based metal, which is an anode, and to prevent decomposition of an electrolyte solution, thereby improving lifespan characteristics of a lithium-sulfur battery.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

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

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

The cathode active material layer may include a cathode active material, a binder, and a conductive material.

1) 및 탄소-황 폴리머((C₂S_x)_n: x=2.5 ~ 50, n

2) 이루어진 군으로부터 선택된 1종 이상일 수 있다. 바람직하게는 무기 황(S₈)을 사용할 수 있다.The cathode active material is elemental sulfur (S ₈ ), an organosulfur compound Li ₂ S _n (n

1) and carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n

2) may be one or more selected from the group consisting of Preferably, inorganic sulfur (S ₈ ) may be used.

Since sulfur included in the cathode active material does not have electrical conductivity alone, it is used in combination with a conductive material such as a carbon material. Accordingly, the sulfur is included in the form of a sulfur-carbon complex, and preferably, the cathode active material may be a sulfur-carbon complex.

The carbon included in the sulfur-carbon composite is a porous carbon material and provides a skeleton to which the sulfur can be uniformly and stably fixed, and complements the low electrical conductivity of sulfur so that the electrochemical reaction can proceed smoothly.

The porous carbon material may be generally prepared by carbonizing various carbon precursors. The porous carbon material includes irregular pores therein, the average diameter of the pores is in the range of 1 to 200 nm, and the porosity or porosity may be in the range of 10 to 90% of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level, and sulfur impregnation is impossible. Not desirable.

The shape of the porous carbon material is spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk, and may be used without limitation as long as it is commonly used in lithium-sulfur batteries.

The porous carbon material may have a porous structure or a high specific surface area and may be any one commonly used in the art. For example, the porous carbon material includes graphite; graphene; Carbon black, such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); It may be at least one selected from the group consisting of natural graphite, artificial graphite, graphite such as expanded graphite, and activated carbon, but is not limited thereto.

The manufacturing method of the sulfur-carbon composite is not particularly limited in the present invention, and a method commonly used in the art may be used.

The positive electrode may further include one or more additives selected from a transition metal element, a group ²A element, a group ₃A element, a sulfur compound of these elements, and an alloy of these elements and sulfur, in addition to the positive electrode active material.

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 and the like are included, the ²A group elements include Al, Ga, In, Ti, and the like, and the ₃A group elements may include Ge, Sn, Pb, and the like.

The binder maintains the positive electrode active material in the positive electrode current collector and organically connects the positive electrode active materials to further increase the bonding strength between them, and all binders known in the art may be used.

For example, the binder may be a fluororesin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulosic binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; A polyalcohol-based binder including polyvinyl alcohol (PVA); A polyacrylic binder containing polyacrylic acid (PAA); polyolefin binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binder; And a silane-based binder; one selected from the group consisting of, two or more mixtures or copolymers may be used.

The conductive material serves as a path for electrons to move from a current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material, and any conductive material may be used without limitation.

For example, the conductive material may include graphite such as natural graphite and artificial graphite; carbon blacks such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Summer Black; carbon derivatives such as carbon nanotubes and fullerenes; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon; A metal powder such as aluminum or nickel powder or a conductive polymer such as polyaniline, polythiophene, polyacetylene, or polypyrrole may be used alone or in combination.

The manufacturing method of the positive electrode is not particularly limited in the present invention, and a method commonly used in the art may be used. For example, the positive electrode may be manufactured by preparing a positive electrode slurry composition and then applying the positive electrode slurry composition to at least one surface of the positive electrode current collector.

The positive electrode slurry composition includes the above-described positive electrode active material, conductive material, and binder, and may further include a solvent other than that.

As the solvent, one capable of uniformly dispersing the cathode active material, the conductive material, and the binder is used. As such a solvent, water is most preferable as an aqueous solvent, and in this case, the water may be distilled water or deionized water. However, it is not necessarily limited to this, and if necessary, a lower alcohol that can be easily mixed with water may be used. The lower alcohol includes methanol, ethanol, propanol, isopropanol, and butanol, and the like, preferably mixed with water.

The loading amount of sulfur in the positive electrode may be 1 to 10 mAh/cm ² , preferably 1 to 6 mAh/cm ² .

The positive electrode as described above may be prepared according to a conventional method, and specifically, a composition for forming a positive electrode active material layer in a slurry state prepared by mixing a positive electrode active material, a conductive material, and a binder in an organic solvent is coated on a current collector and dried. , Optionally, it may be manufactured by compression molding the current collector to improve the electrode density. At this time, as the organic solvent, it is preferable to use an organic solvent capable of uniformly dispersing the cathode active material, the binder, and the conductive material and easily evaporating. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, etc. are mentioned.

The composition for forming the positive electrode active material layer may be coated on the positive electrode current collector using a conventional method known in the art, for example, a dipping method, a spray method, or a roll court method. , A gravure printing method, a bar coat method, a die coating method, a comma coating method, or a combination thereof may be used.

The positive electrode active material layer that has undergone such a coating process is then evaporated through a drying process to improve the density of the coating film, the adhesion between the coating film and the current collector, and the like. At this time, drying is carried out according to a conventional method, and this is not particularly limited.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector.

The negative electrode is a lithium-based metal, and may further include a current collector on one side of the lithium-based metal. An anode current collector may be used as the current collector.

The anode current collector is for supporting the anode active material layer, and is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. Copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, It may be selected from the group consisting of iron, chromium, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy, and in addition, calcined carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer can also be used.

The negative electrode current collector may be formed in various forms such as a film, sheet, foil, net, porous material, foam, non-woven fabric, etc. having fine irregularities/unformed on its surface.

In addition, the anode current collector is applied that has a thickness range of 3 to 500 ㎛. If the thickness of the anode current collector is less than 3 μm, the current collecting effect is deteriorated, whereas if the thickness exceeds 500 μm, workability is deteriorated when the cell is assembled by folding.

The lithium-based metal may be lithium or a lithium alloy. At this time, the lithium alloy includes elements capable of alloying with lithium, and specifically, lithium and Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, It may be an alloy with at least one selected from the group consisting of Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, and Al.

The lithium-based metal may be in the form of a sheet or foil, and in some cases, lithium or a lithium alloy is deposited or coated on a current collector by a dry process, or metal and alloy on particles are deposited or coated by a wet process. may be in the form of

The anode active material layer may include a binder, a conductive material, and the like in addition to the anode active material. At this time, the binder and the conductive material are as described above.

The anode active material includes a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy. can include

The material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, 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).

Preferably, the negative electrode active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder.

The method of forming the negative electrode active material is not particularly limited, and a method of forming a layer or film commonly used in the art may be used. For example, methods such as compression, coating, and deposition may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery in a state in which the lithium thin film is not present on the current collector is also included in the negative electrode of the present invention.

The electrolyte solution is used to cause an electrochemical oxidation or reduction reaction at the anode and the cathode through this, and follows the above description.

Injection of the electrolyte solution may be performed at an appropriate stage during the manufacturing process of the lithium-sulfur battery according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling a lithium-sulfur battery or at a final stage of assembly.

A conventional separator may be interposed between the anode and the cathode. The separator is a physical separator having a function of physically separating electrodes, and can be used without particular limitation as long as it is used as a normal separator, and in particular, it is preferable to have low resistance to ion movement of the electrolyte and excellent ability to wet the electrolyte.

In addition, the separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode. This separator is porous and may be made of a non-conductive or insulating material. The separator may be used without particular limitation as long as it is commonly used as a separator in a lithium-sulfur battery. The separator may be an independent member such as a film or may be a coating layer added to an anode and/or a cathode.

The separator may be made of a porous substrate. As for the porous substrate, any porous substrate commonly used in a lithium-sulfur battery may be used, and a porous polymer film may be used alone or in a laminated manner. Non-woven fabrics or polyolefin-based porous membranes made of melting glass fibers, polyethylene terephthalate fibers, etc. may be used, but are not limited thereto.

The material of the porous substrate is not particularly limited in the present invention, and any porous substrate commonly used in a lithium-sulfur battery can be used. For example, the porous substrate may be a polyolefin such as polyethylene or polypropylene, polyester such as polyethyleneterephthalate or polybutyleneterephthalate, or polyamide. (polyamide), polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylene sulfide ( polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon (nylon), poly(p-phenylene benzobisoxazole), and polyarylate.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the porous substrate is not limited to the aforementioned range, if the thickness is too thin than the aforementioned lower limit, mechanical properties may deteriorate and the separator may be easily damaged during use of the battery.

The average diameter and porosity of pores present in the porous substrate are also not particularly limited, but may be 0.1 to 50 μm and 10 to 95%, respectively. If the pore size of the separator is less than 0.1 μm or the porosity is less than 10%, the separator acts as a resistance layer, and if the pore size exceeds 50 μm or the porosity exceeds 95%, mechanical properties cannot be maintained. .

In the lithium-sulfur battery according to the present invention, in addition to winding, which is a general process, lamination and stacking and folding processes of a separator and an electrode are possible.

The shape of the lithium-sulfur battery is not particularly limited and may be of various shapes such as a cylindrical shape, a prismatic shape, a pouch shape, a stacked shape, and a coin shape.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are provided to more easily understand the present invention, but the present invention is not limited thereto.

Preparation Example: Preparation of Electrolyte for Lithium-Sulfur Batteries

[Production Example 1]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed in a volume ratio of 20:10:70. (v/v) and stirred, and 0.75M of lithium bis(fluorosulfonyl)imide (LiFSi) and 5 wt% of LiNO ₃ as electrolyte salts and additives were dissolved to obtain lithium -An electrolyte solution for a sulfur battery was prepared.

[Production Example 2]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed in a volume ratio of 10:10:80. An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the mixture was mixed and stirred at (v/v).

[Production Example 3]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed in a volume ratio of 10:20:70. An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the mixture was mixed and stirred at (v/v).

[Production Example 4]

Lithium in the same manner as in Preparation Example 1, except that the organic solvents 2-methyl furan and dimethoxyethane were mixed at a volume ratio (v/v) of 20:80 and stirred. -An electrolyte solution for a sulfur battery was prepared.

[Production Example 5]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed in a volume ratio of 20:20:60. An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the mixture was mixed and stirred at (v/v).

[Production Example 6]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed in a volume ratio of 10:30:60. An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the mixture was mixed and stirred at (v/v).

[Production Example 7]

The organic solvents 2-methyl furan, 2-methyl-1,3-dioxolane and dimethoxyethane were mixed at a volume ratio of 20:5:75. An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the mixture was mixed and stirred at (v/v).

The electrolyte composition in Preparation Examples 1 to 7 is shown in Table 1 below.

electrolyte composition Preparation Example 1 2Me-furan: Me-DOL: DME = 20:10:70 (v/v) 0.75M LiFSI 5wt% _LiN03 Preparation Example 2 2Me-furan: Me-DOL: DME = 10:10:80 (v/v) 0.75M LiFSI 5wt% _LiN03 Preparation Example 3 2Me-furan: Me-DOL: DME = 10:20:70 (v/v) 0.75M LiFSI 5wt% _LiN03 Production Example 4 2Me-furan: DME = 20:80 (v/v) 0.75M LiFSI 5wt% _LiN03 Preparation Example 5 2Me-furan: Me-DOL: DME = 20:20:60 (v/v) 0.75M LiFSI 5wt% _LiN03 Preparation Example 6 2Me-furan: Me-DOL: DME = 10:30:60 (v/v) 0.75M LiFSI 5wt% _LiN03 Preparation Example 7 2Me-furan: Me-DOL: DME = 20:5:75 (v/v) 0.75M LiFSI 5wt% _LiN03

Example: Preparation of a lithium-sulfur battery

[Example 1]

A cathode active material slurry was prepared by mixing a sulfur-carbon composite and a binder in a ratio of 95:5 as a cathode active material. At this time, the sulfur-carbon composite was prepared by mixing sulfur and carbon nanotubes (CNT) at a weight ratio of 75:25. In addition, a positive electrode active material slurry composition was prepared by mixing lithium polyacrylate (LiPAA) as a binder.

The cathode active material slurry was applied to one surface of an aluminum current collector, dried at 100° C., and then rolled to prepare a cathode having a porosity of 68% and a loading amount of 4.5 mAh/cm ² .

Lithium metal (Honjo Co., Ltd.) having a thickness of 45 μm was used as the negative electrode.

After placing the prepared positive electrode and negative electrode to face each other, a polyethylene separator having a thickness of 16 μm and a porosity of 46% was interposed between the positive electrode and the negative electrode to prepare an electrode assembly. Thereafter, after placing the electrode assembly inside the case, a lithium-sulfur battery was prepared by injecting the electrolyte solution for a lithium-sulfur battery of Preparation Example 1 into the case.

[Examples 2 and 3]

A lithium-sulfur battery was prepared in the same manner as in Example 1, except that the electrolyte solutions of Preparation Examples 2 and 3 were used as the electrolyte for a lithium-sulfur battery.

[Comparative Examples 1 to 4]

A lithium-sulfur battery was prepared in the same manner as in Example 1, except that the electrolyte solutions of Preparation Examples 4 to 7 were used as the electrolyte for a lithium-sulfur battery.

Experimental Example 1: Measurement of Life Characteristics of Lithium-Sulfur Batteries

For the lithium-sulfur batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 4, life characteristics of the batteries were evaluated through repeated charge/discharge cycles. The evaluation results are shown in Table 2 below.

Specifically, for a lithium-sulfur battery, discharge to 1.8V at 0.1C and charge to 2.5V at 0.1C are repeated twice in constant current (CC) mode under the battery operating temperature condition of 25 ° C., then 0.2C Charging and discharging were repeated three times, and 0.3C charging / 0.5C discharging was repeated up to 500 cycles to evaluate the lifespan characteristics of the battery.

In the evaluation of battery life characteristics, the ratio (%) of the discharge capacity in the corresponding cycle to the discharge capacity in the cycle starting 0.3C charge / 0.5C discharge is defined as capacity retention, and also to evaluate the lifespan The number of cycles when the capacity retention rate reached 80% was shown in Table 2 below.

Number of cycles to reach 80% capacity retention Example 1 401 Example 2 407 Example 3 459 Comparative Example 1 328 Comparative Example 2 234 Comparative Example 3 225 Comparative Example 4 312

From the results of Table 2, the lithium-sulfur battery using the electrolyte solution for a lithium-sulfur battery including a three-component solvent mixture including a cyclic ether compound, a linear ether compound, and a heterocyclic compound maintains a high capacity retention rate even when cycles are repeated. It was confirmed that it had excellent battery life characteristics.

Specifically, the solvent mixture contains 20 to 30 volume ratio of 2-methyl-1,3-dioxolane as a cyclic ether compound and 2-methylfuran as a heterocyclic compound with respect to 100 volume ratio of the organic solvent, In the case of a solvent compound having a volume ratio of 2-methyl-1,3-dioxolane, which is an ether compound, at a volume ratio of 10 or more, a capacity retention rate of 80% or more was exhibited even after 300 cycles of charging and discharging, and it was confirmed that it had excellent lifespan characteristics. .

Claims (11)

lithium salt; In the electrolyte solution for a lithium-sulfur battery containing an organic solvent and an additive,
The organic solvent is a three-component solvent mixture containing a cyclic ether compound, a linear ether compound and a heterocyclic compound, characterized in that, the lithium-sulfur battery electrolyte. According to claim 1,
The cyclic ether compound is 1,3-dioxolane, 2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane Solan, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane and 4,5-diethyl-1,3-dioxolane Characterized in that it comprises at least one selected from the group consisting of, lithium-sulfur battery electrolyte. According to claim 1,
The linear ether compound is dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether. , ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethylmethyl ether, diethylene glycol isopropylmethyl ether, diethylene An electrolyte solution for a lithium-sulfur battery, characterized in that it comprises at least one selected from the group consisting of glycol butyl methyl ether, diethylene glycol tert-butyl ethyl ether and ethylene glycol ethyl methyl ether. According to claim 1,
The heterocyclic compound is furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 3-ethylfuran, 2-propylfuran, 3-propylfuran, 2-butylfuran, 3-butylfuran, 2,3 -Containing at least one selected from the group consisting of dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran and benzofuran Characterized in, an electrolyte solution for a lithium-sulfur battery. According to claim 1,
The solvent mixture is an electrolyte solution for a lithium-sulfur battery, characterized in that the cyclic ether compound and the heterocyclic compound are included in a volume ratio of 10 to 40 with respect to 100 volume ratio of the organic solvent. According to claim 1,
The solvent mixture is an electrolyte solution for a lithium-sulfur battery, characterized in that the cyclic ether compound is included in 10 to 20 volume ratio and the heterocyclic compound is included in 20 to 10 volume ratio with respect to 100 volume ratio of the organic solvent. According to claim 1,
The solvent mixture is an electrolyte solution for a lithium-sulfur battery, characterized in that to form a polymer protective film on the surface of the negative electrode by ring opening polymerization. According to claim 1,
The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl 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(C ₂ F ₅ SO ₂ ) ₂ and LiN(SO ₂ F ) ₂ , an electrolyte solution for a lithium-sulfur battery, characterized in that selected from the group consisting of. According to claim 1,
The additives are lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), magnesium nitrate (MgNO ₃ ), barium nitrate (BaNO ₃ ), lithium nitrite (LiNO ₂ ), and potassium nitrite (KNO _{2 )} . ), cesium nitrite (CsNO ₂ ), characterized in that selected from the group consisting of combinations thereof, lithium-sulfur battery electrolyte. anode; cathode; a separator interposed between the anode and the cathode; And a lithium-sulfur battery comprising an electrolyte solution,
The negative electrode is a lithium-based metal,
The electrolyte solution is the lithium-sulfur battery of any one of claims 1 to 9. According to claim 10,
A lithium-sulfur battery, characterized in that a polymer protective film is formed on the surface of a lithium-based metal by a ring-opening polymerization reaction of a solvent mixture contained in an electrolyte in an initial discharge step of the lithium-sulfur battery.

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