KR20230153299A - Lithium-sulfur battery with high energy density - Google Patents

Abstract

It is based on the SSE (sparingly solvating electrolyte) electrolyte system (discharge capacity: ~1,600 mAh/gs) rather than the existing catholyte electrolyte system (discharge capacity: ~1,600 mAh/gs), but does not use nitrile-based solvents, so it has a theoretical discharge capacity of 1,675 mAh. A lithium-sulfur battery with high energy density is disclosed, which can utilize more than 80% of /g) and can also achieve a high average discharge voltage by using a positive electrode carbon material with high porosity and specific surface area. The lithium-sulfur battery includes a first solvent containing a fluorine-based ether compound, a second solvent containing a glyme-based compound, and an electrolyte containing a lithium salt; and a positive electrode containing sulfur and carbon material as active materials, wherein the carbon material has a pore volume of more than 3 cm ³ /g and 10 cm ³ /g or less.

Description

Lithium-sulfur battery with high energy density}

The present invention relates to a high energy density lithium-sulfur battery that can utilize more than 80% of the theoretical discharge capacity of sulfur and can even realize a high average discharge voltage. More specifically, it relates to a lithium-sulfur battery with an existing catholyte electrolyte system (discharge capacity: ~1,200 mAh). /gs), but rather an SSE (sparingly solvating electrolyte) electrolyte system (discharge capacity ~1,600 mAh/gs), but no nitrile-based solvent is used, allowing more than 80% of sulfur's theoretical discharge capacity (1,675 mAh/g) to be utilized. In addition, it relates to a lithium-sulfur battery with high energy density that can achieve a high average discharge voltage by using a positive electrode carbon material with high porosity and specific surface area.

As interest in energy storage technology grows, its application areas expand to include energy from mobile phones, tablets, laptops and camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs). Research and development on chemical devices is gradually increasing. Electrochemical devices are the field that is receiving the most attention in this regard, and among them, the development of secondary batteries such as lithium-sulfur batteries that can be charged and discharged has become the focus of attention. Recently, capacity density and To improve specific energy, research and development is being conducted on the design of new electrodes and batteries.

Such electrochemical devices, including lithium-sulfur batteries (Li-S batteries), have high energy density (theoretical capacity) and are attracting attention as next-generation secondary batteries that can replace lithium ion batteries. In such a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge, and at this time, sulfur forms a linear structure of lithium polysulfide (LiPS) from the ring structure of S ₈ . Lithium-sulfur batteries are characterized by a gradual discharge voltage until polysulfide is completely reduced to Li ₂ S.

However, the biggest obstacle to commercialization of lithium-sulfur batteries is their lifespan. During the charging and discharging process, charging/discharging efficiency decreases and the lifespan of the batteries deteriorates. The causes of the deterioration of the lifespan of such lithium-sulfur batteries include side reactions of the electrolyte (deposition of by-products due to decomposition of the electrolyte), instability of lithium metal (short circuit caused by dendrites growing on the lithium cathode), and anode by-products. It varies from deposition (lithium polysulfide dissolution from the anode), etc.

That is, in a battery that uses a sulfur-based compound as the positive electrode active material and an alkali metal such as lithium as the negative electrode active material, lithium polysulfide elution and shuttle phenomenon occur during charging and discharging, and the lithium polysulfide is transferred to the negative electrode, producing lithium. -The capacity of the sulfur battery is reduced, and as a result, the lithium-sulfur battery has major problems such as reduced lifespan and reduced reactivity. In other words, since the polysulfide eluted from the positive electrode has high solubility in the organic electrolyte solution, unwanted movement (PS shuttling) toward the negative electrode through the electrolyte may occur, resulting in a decrease in capacity due to irreversible loss of the positive electrode active material and The battery life is reduced due to the deposition of sulfur particles on the surface of lithium metal due to side reactions.

On the other hand, the behavior of such lithium-sulfur batteries can greatly change depending on the electrolyte. When sulfur from the anode is eluted into the electrolyte in the form of lithium polysulfide (LiPS), the electrolyte is called Catholyte, and the sulfur is lithium. An electrolyte that rarely elutes in the form of polysulfide is called SSE (sparingly solvating electrolyte). Lithium-sulfur batteries utilizing the existing catholyte system rely on a liquid phase reaction through the creation of an intermediate polysulfide in the form of Li _{2 S} g) is not fully utilized, and rather, there is a problem in that the lifespan of the battery is drastically reduced due to battery deterioration due to the elution of polysulfide.

On the other hand, recently, an SSE (sparingly solvating electrolyte) electrolyte system that can suppress the elution of polysulfide has been developed, making it possible to utilize more than 90% of sulfur's theoretical discharge capacity, but it exhibits a low average discharge voltage of less than 2.0 V at room temperature. There is a problem. In addition, most SSE electrolyte systems rely on nitrile-based solvents, which have fatal drawbacks to the lifespan of the battery, such as deterioration of the lithium negative electrode due to reaction with the lithium negative electrode and gas generation inside the lithium-sulfur battery. there is.

Accordingly, in the industry, various studies are being conducted on lithium-sulfur batteries in which sulfur, which is the positive electrode active material, does not leach out into the electrolyte (research such as adding LiPS adsorption material to the positive electrode composite or modifying the existing separator made of PE, etc.). In particular, research is being conducted on an electrolyte that can perform a solid-to-solid reaction of sulfur into Li ₂ S, the final discharge product, but no significant results have been achieved yet. Therefore, there is a need to develop an innovative battery that uses the SSE electrolyte system and has a high average discharge voltage of 2.0 V or more at room temperature, does not degrade the lithium cathode or generate gas inside the battery, and has high energy density ( ※ High energy density means more than about 400 Wh/kg or more than 600 Wh/L, and to build it, an electrolyte and positive electrode active material system that can operate even at porosity of more than 4.0 mAh/cm ² and less than 60% is required).

Therefore, the purpose of the present invention is to use a SSE (sparingly solvating electrolyte) electrolyte system (discharge capacity: ~1,600 mAh/gs) rather than the existing catholyte electrolyte system (discharge capacity: ~1,200 mAh/gs), but without using a nitrile-based solvent. Therefore, it has a high energy density that can utilize more than 80% of sulfur's theoretical discharge capacity (1,675 mAh/g) and can even achieve a high average discharge voltage by using an anode carbon material with high porosity and specific surface area. To provide a lithium-sulfur battery.

In order to achieve the above object, the present invention includes a first solvent containing a fluorine-based ether compound, a second solvent containing a glyme-based compound, and an electrolyte containing a lithium salt; and a positive electrode containing sulfur and carbon material as active materials, wherein the carbon material has a pore volume of more than 3 cm ³ /g and 10 cm ³ /g or less.

According to the lithium-sulfur battery with high energy density according to the present invention, it is used in the SSE (sparingly solvating electrolyte) electrolyte system (discharge capacity: ~1,600 mAh/gs) rather than the existing catholyte electrolyte system (discharge capacity: ~1,200 mAh/gs). However, since nitrile-based solvents are not used, more than 80% of the theoretical discharge capacity of sulfur (1,675 mAh/g) can be utilized, and by using an anode carbon material with high porosity and specific surface area, a high average discharge voltage can be realized. It has the advantage of being able to In addition, the lithium-sulfur battery with high energy density according to the present invention has an electrolyte and positive electrode active material system that can be operated even at porosity of 4.0 mAh/cm ² or more and 60% or less, so that the energy density is about 400 Wh/ It has the advantage of being maintained high at more than kg or more than 600 Wh/L.

Figure 1 is a pore size distribution diagram of a carbon material in a sulfur-carbon composite used in an example and a comparative example of the present invention.
Figure 2 is a nitrogen adsorption/desorption isotherm of a carbon material in a sulfur-carbon composite used in an example and a comparative example of the present invention.
Figure 3 is a graph showing the discharge capacity and discharge voltage of a lithium-sulfur battery manufactured according to an embodiment of the present invention.
Figure 4 is a graph showing the discharge capacity and discharge voltage of a lithium-sulfur battery manufactured according to a comparative example.

Hereinafter, the present invention will be described in detail.

The lithium-sulfur battery according to the present invention includes a first solvent containing a fluorine-based ether compound, a second solvent containing a glyme-based compound, and an electrolyte containing a lithium salt; and a positive electrode containing sulfur and carbon material as active materials, wherein the carbon material has a pore volume of more than 3 cm ³ /g and 10 cm ³ /g or less.

Recently, an SSE (sparingly solvating electrolyte) electrolyte system that can suppress the elution of polysulfide has been developed, making it possible to utilize more than 90% of sulfur's theoretical discharge capacity, but the problem is that it shows a low average discharge voltage of less than 2.0 V at room temperature. There is. In addition, due to the nature of the SSE electrolyte system, which relies on nitrile-based solvents, the lithium negative electrode still deteriorates due to reaction with the lithium negative electrode, and gas is generated inside the lithium-sulfur battery, shortening the lifespan of the battery. Shiki's problem is not being solved.

Accordingly, the present applicant uses an SSE electrolyte system that can utilize a sulfur utilization rate of 80% or more, preferably 90 to 100%, and more preferably 94 to 100% of the theoretical discharge capacity, while maintaining a high average of 2.0 V or more at room temperature. It indicates the discharge voltage, excludes nitrile-based electrolyte solvents that are fatal to the lifespan of lithium-sulfur batteries, and uses stable ether-based electrolyte solvents, so the lithium negative electrode does not deteriorate or gas is not generated inside the battery (i.e. improved lifespan), a lithium-sulfur battery with a high energy density of about 400 Wh/kg or more or 600 Wh/L or more by providing an electrolyte and positive electrode active material system that can be operated even at porosity of 4.0 mAh/cm ² or more and 60% or less. developed it. Meanwhile, the 'sulfur utilization rate' is specifically the ratio of the discharge capacity (mAh) per weight (gram) of sulfur element contained in the positive electrode of the battery compared to the theoretical capacity of 1,675 mAh/g (sulfur) per weight of sulfur, for example. For example, when the discharge capacity per weight of elemental sulfur present in the positive electrode of a lithium-sulfur battery is 1,600 mAh/g (sulfur), the sulfur utilization rate is 95.5% (1,600/1,675).

In other words, the present applicant sought ways to complement the problems of the existing technology, which did not maximize the performance of the battery while using the SSE electrolyte system, and developed a first solvent containing a fluorine-based ether compound and a solvent containing a glyme-based compound. 2 The synergy effect between the electrolyte containing a solvent and lithium salt and the positive electrode containing sulfur and carbon material as active materials was confirmed, and through this, more than 80% of the theoretical discharge capacity of sulfur (i.e., the initial discharge capacity of the battery was about 1,340 mAh/g or more), preferably 90 to 100%, more preferably 94 to 100%, and exhibits a high average discharge voltage of 2.0 V or more at room temperature (i.e., up to the high average discharge voltage of sulfur), A lithium-sulfur battery with a high energy density of more than about 400 Wh/kg or more than 600 Wh/L was invented.

Hereinafter, each of A) the first solvent containing a fluorine-based ether compound, B) the second solvent containing a glyme-based compound, C) lithium salt, and D) the positive electrode included in the lithium-sulfur battery of the present invention will be described in detail. do.

A) first solvent

The first solvent is an electrolyte solvent containing a fluorine-based ether compound, and has the effect of suppressing the dissolution of polysulfide and solvent decomposition, thereby improving the coulombic efficiency (C.E.) of the battery, ultimately reducing the life of the battery. It plays a role in improving. More specifically, the first solvent containing the fluorine-based ether compound has excellent structural stability compared to a general organic solvent containing an alkane due to fluorine substitution, and thus has very high stability. Accordingly, if this is used in the electrolyte solution of a lithium-sulfur battery, the stability of the electrolyte solution can be greatly improved, thereby improving the lifespan performance of the lithium-sulfur battery.

Examples of the fluorine-based ether compound include 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (1,1,2,2-tetrafluoroethyl 2,2,3,3 -tetrafluoropropyl ether, TTE), bis(fluoromethyl) ether, 2-fluoromethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl Ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropyl At least one hydrofluoro ether (HFE type) selected from the group consisting of ethyl ether, 1H, 1H, 2'H, 3H-decafluorodipropyl ether, and 1H, 1H, 2'H-perfluorodipropyl ether Compounds may be mentioned.

B) secondary solvent

The second solvent is an electrolyte solvent containing a glyme-based compound (but not fluorine), which not only dissolves lithium salts to give the electrolyte lithium ion conductivity, but also elutes sulfur, which is the positive electrode active material, to form lithium and It plays a role in allowing electrochemical reactions to proceed smoothly.

Specific examples of the glyme-based compounds include dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, and trimethylene glycol. Ethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether and polyethylene glycol methyl ethyl ether. One or more types selected from the group consisting of, but not limited to, dimethoxyethane may be used.

C) lithium salt

The lithium salt is an electrolyte salt used to increase ionic conductivity, and can be used without limitation as long as it is commonly used in the art. Specific examples of the lithium salt include LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, chloro One or more types selected from the group consisting of lithium borane, lithium lower aliphatic carboxylate having 4 or less carbon atoms, lithium 4-phenyl borate, and lithium imide can be exemplified.

The concentration of the lithium salt may be determined considering ionic conductivity, etc., and may be, for example, 0.1 to 2 M, preferably 0.5 to 1 M, and more preferably 0.5 to 0.75 M. If the concentration of the lithium salt is less than the above range, it may be difficult to secure ionic conductivity suitable for battery operation, and if it exceeds the above range, the viscosity of the electrolyte increases and the mobility of lithium ions decreases, or the decomposition reaction of the lithium salt itself occurs. As this increases, battery performance may deteriorate.

In the electrolyte containing the first solvent, second solvent, and lithium salt as described above, the molar ratio of the lithium salt, second solvent, and first solvent may be 1:0.5 to 3:4.1 to 15. Additionally, in one embodiment of the present invention, the molar ratio of the lithium salt, the second solvent, and the first solvent may be 1:2:4 to 13 or 1:3:3 to 10 or 1:4:5 to 10. In the electrolyte included in the lithium-sulfur battery of the present invention, the first solvent containing a fluorine-based ether compound may be included in a higher content ratio than the second solvent containing a glyme-based compound. In this way, when the first solvent containing a fluorine-based ether compound is contained in a higher content ratio than the second solvent containing a glyme-based compound, the production of polysulfide is suppressed, making it possible to realize a battery capacity close to the theoretical capacity of sulfur. Since there is an advantage in terms of suppressing the decrease in battery capacity due to battery use, the first solvent containing a fluorine-based ether compound is set to be contained in a high content ratio compared to the second solvent containing a glyme-based compound as much as possible. It is desirable.

D) anode

The lithium-sulfur battery according to the present invention includes a positive electrode containing sulfur and carbon material as an active material, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and A) a first solvent containing a fluorine-based ether compound described above, B ) a second solvent containing a glyme-based compound, and C) an electrolyte containing a lithium salt. Hereinafter, the positive electrode will be described in detail.

The positive electrode included in the lithium-sulfur battery of the present invention includes a positive electrode active material, a binder, and a conductive material. The positive electrode active material may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof, and the sulfur-based compound is specifically Li ₂ S _n (n≥1), an organic sulfur compound, or It may be a sulfur-carbon complex ((C ₂ S _x ) _n : x=2.5 ~ 50, n≥2). However, since sulfur materials do not conduct electricity alone and must be used in combination with a conductive material, the positive electrode active material preferably contains a sulfur-carbon complex.

The sulfur-carbon composite may have a particle size of 1 to 100 ㎛. If the particle size of the sulfur-carbon composite is less than 1 ㎛, the inter-particle resistance increases, which may cause overvoltage in the electrode of the lithium-sulfur battery. If it exceeds 100 ㎛, the surface area per unit weight decreases and the electrolyte in the electrode The wetting area and reaction site with lithium ions decreases, and the amount of electron transfer decreases compared to the size of the composite, which slows down the reaction and reduces the discharge capacity of the battery.

The sulfur (S) may be included in an amount of 60 to 80% by weight, preferably 65 to 80% by weight, and more preferably 65 to 75% by weight, based on the total weight of the positive electrode. The content of sulfur in the positive electrode of a typical lithium-sulfur battery is about 40 to 60% by weight relative to the total weight of the positive electrode, and despite using sulfur in a significantly higher content than this, the present invention shows a high initial discharge capacity under the electrolyte conditions of the present invention. . If sulfur is used in an amount of less than 60% by weight relative to the total weight of the positive electrode, a problem may occur in which the energy density of the battery is reduced, and if it is used in an amount exceeding 80% by weight, the conductivity within the electrode decreases and the electrode Problems with reduced stability may occur.

The carbon material (or sulfur supporting material) constituting the sulfur-carbon composite has porosity, and in particular, the carbon material used as the positive electrode active material of the present invention has a high specific surface area (more than 1,000 m ² /g) and high porosity. Since it has the characteristics of (pore volume: more than 3 cm ³ /g to 10 cm ³ /g or less, preferably 4 to 5 cm ³ /g, average pore size: 4 to 100 nm), high capacity ( Not only is it possible to drive (approximately 1,340 ~ 1,675 mAh/g), but it is also possible to achieve a high average discharge voltage of 2.0 V or more, preferably 2.0 to 2.2 V, at room temperature.

The porous carbon material may include any carbon material that satisfies a pore volume of more than 3 cm ³ /g to 10 cm ³ /g or less, specifically, more than 3 cm ³ /g to 10 cm ³ /g. Graphite satisfying the following pore volume; graphene; reduced graphene oxide (rGO); Carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal 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) may be exemplified by one or more types selected from the group consisting of spherical, rod-shaped, needle-shaped, and plate-shaped. , it may be a tube type or a bulk type. And, among these, Ketjen Black that satisfies the above pore volume may be preferable.

The positive electrode active material containing the above sulfur and carbon material may be included in an amount of 80 to 99 parts by weight, preferably 90 to 95 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the positive electrode active material is less than 80 parts by weight based on 100 parts by weight of the total weight of the positive electrode, a problem may occur in which the energy density of the battery is reduced, and if it exceeds 99 parts by weight, the conductivity within the electrode decreases and the stability of the electrode decreases. Problems may arise.

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

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

The conductive material included in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the battery and without causing chemical changes in the battery. Representative examples include graphite or conductive carbon. , for example, graphite such as natural graphite and artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and thermal black; Carbon-based materials with a crystal structure of graphene or graphite; carbon nanotubes; Conductive fibers such as carbon fiber and metal fiber; fluorinated carbon; Metal powders such as aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; may be used alone or in a mixture of two or more types, but are not necessarily limited thereto.

The conductive material may typically be added in an amount of 0.5 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the total weight of the positive electrode, but may not be included in the positive electrode of the present invention. If the content of the conductive material is too large, exceeding 10 parts by weight, the amount of positive electrode active material may be relatively small, resulting in reduced capacity and energy density. The method of including the conductive material in the positive electrode is not greatly limited, and conventional methods known in the art, such as coating the positive electrode active material, can be used. Additionally, if necessary, a conductive second coating layer may be added to the positive electrode active material to replace the addition of the above-described conductive material.

Additionally, a filler may be selectively added to the positive electrode of the present invention as a component to suppress its expansion. These fillers are not particularly limited as long as they can suppress the expansion of the electrode without causing chemical changes in the battery, and include, for example, olipine polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber; etc. can be used.

The positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying it on a positive electrode current collector, and then drying and rolling it. The dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

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

The negative electrode is a lithium-based metal, and may further include a current collector on one side of the lithium-based metal. The current collector may be a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may include copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and these. It may be selected from the group consisting of a combination of. The stainless steel may be surface treated with carbon, nickel, titanium, or silver, and the alloy may be an aluminum-cadmium alloy, and in addition, calcined carbon, a non-conductive polymer or a conductive polymer surface-treated with a conductive material, etc. You can also use it. Generally, a thin copper plate is used as the negative electrode current collector.

In addition, various forms may be used, such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics with or without fine irregularities formed on the surface. In addition, the negative electrode current collector is used in a thickness range of 3 to 50 ㎛. If the thickness of the negative electrode current collector is less than 3 ㎛, the current collecting effect is reduced. On the other hand, if the thickness is more than 50 ㎛, there is a problem that processability is reduced when the cell is folded and assembled.

The lithium-based metal may be lithium or a lithium alloy. At this time, the lithium alloy includes elements that can be alloyed 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 one or more types 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 lithium alloy may be deposited or coated on a current collector by a dry process, or metals and alloys on particles may be deposited or coated by a wet process, etc. It may be in a given form.

A conventional separator may be interposed between the anode and the cathode. The separator is a physical separator that has the function of physically separating electrodes, and can be used without particular limitations as long as it is used as a normal separator. In particular, it is desirable to have low resistance to ion movement in the electrolyte solution and excellent electrolyte moisturizing ability.

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. These separators are porous and may be made of non-conductive or insulating materials. The separator may be an independent member such as a film, or may be a coating layer added to the anode and/or cathode.

Examples of polyolefin-based porous membranes that can be used as the separation membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, respectively, individually or together. Examples include membranes formed from mixed polymers. Examples of nonwoven fabrics that can be used as the separator include polyphenyleneoxide, polyimide, polyamide, polycarbonate, polyethyleneterephthalate, and polyethylenenaphthalate. , polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc., individually or Nonwoven fabrics made of polymers mixed with these are possible, and such nonwoven fabrics are in the form of fibers that form a porous web, and include spunbond or meltblown forms made of long fibers.

The thickness of the separator is not particularly limited, but is preferably in the range of 1 to 100 ㎛, and more preferably in the range of 5 to 50 ㎛. If the thickness of the separator is less than 1 ㎛, the mechanical properties cannot be maintained, and if it exceeds 100 ㎛, the separator acts as a resistance layer and battery performance deteriorates. The pore size and porosity of the separator are not particularly limited, but it is preferable that the pore size is 0.1 to 50 ㎛ and the porosity is 10 to 95%. If the pore size of the separator is less than 0.1 ㎛ or the porosity is less than 10%, the separator acts as a resistance layer, and if the pore size is greater than 50 ㎛ or the porosity is greater than 95%, the mechanical properties cannot be maintained. .

The lithium-sulfur battery of the present invention, which includes the electrolyte solution, positive electrode, negative electrode, and separator as described above, can be manufactured through a process of placing the positive electrode against the negative electrode, interposing a separator between them, and then injecting the electrolyte solution.

Meanwhile, the lithium-sulfur battery according to the present invention is not only applied to battery cells used as a power source for small devices, but can also be particularly suitably used as a unit cell of a battery module that is a power source for medium to large devices. In this aspect, the present invention also provides a battery module containing two or more lithium-sulfur batteries electrically connected (series or parallel). Of course, the quantity of lithium-sulfur batteries included in the battery module can be adjusted in various ways considering the use and capacity of the battery module. Furthermore, the present invention provides a battery pack in which the battery modules are electrically connected according to common techniques in the art. The battery module and battery pack include Power Tool; Electric vehicles, including Electric Vehicle (EV), Hybrid Electric Vehicle (HEV), and Plug-in Hybrid Electric Vehicle (PHEV); electric truck; electric commercial vehicles; Alternatively, it can be used as a power source for any one or more mid- to large-sized devices among power storage systems, but is not necessarily limited to this.

Preferred examples are presented below to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such changes and modifications fall within the scope of the attached patent claims.

[Example 1] Preparation of lithium-sulfur battery

electrolyte manufacturing

First, LiTFSI (concentration: 0.65 M), dimethoxyethane (second solvent), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE, first solvent) ) was mixed at room temperature at a molar ratio of 1:2:9 to prepare an electrolyte (SSE) for a lithium-sulfur battery.

anode manufacturing

As the positive electrode active material, 90 parts by weight of a sulfur-carbon composite (S:C = 70:30 weight ratio) (the content of sulfur alone was set to 63% by weight based on the total weight of the positive electrode, and the carbon material included in the sulfur-carbon composite was Ketjen) Black was used), 5 parts by weight of Denka Black as a conductive material, and 5 parts by weight of styrene butadiene rubber/carboxymethyl cellulose (SBR: CMC = 7:3) as a binder were mixed to prepare a positive electrode slurry composition, and then the prepared slurry The composition was coated on a current collector (Al Foil), dried at 50°C for 12 hours, and pressed with a roll press to prepare a positive electrode (at this time, the sulfur loading amount was 3.0 mAh/cm ² ).

Lithium-sulfur battery manufacturing

A coin cell type lithium-sulfur battery was manufactured by placing the prepared positive electrode face to face with a 150 ㎛ thick lithium metal negative electrode, interposing a polyethylene (PE) separator between them, and then injecting the prepared electrolyte. Meanwhile, in manufacturing the battery, the positive electrode was punched into a 14phi circular electrode, the polyethylene separator was punched into a 19phi, and the lithium metal was punched into a 16phi. Additionally, the battery was manufactured using a sparing solvating electrolyte (SSE) electrolyte system.

[Example 2] Preparation of lithium-sulfur battery

A coin cell type lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the S:C weight ratio of the sulfur-carbon composite was changed from 70:30 to 60:40.

[Comparative Example 1] Manufacturing of lithium-sulfur battery

A coin cell type lithium-sulfur battery was manufactured in the same manner as in Example 1, except that activated carbon was used instead of Ketjen black as the carbon material included in the sulfur-carbon composite.

[Comparative Example 2] Manufacturing of lithium-sulfur battery

A coin cell type lithium-sulfur battery was manufactured in the same manner as Comparative Example 1, except that the S:C weight ratio of the sulfur-carbon composite was changed from 70:30 to 60:40.

[Experimental Example 1] Evaluation of pore properties of carbon materials in sulfur-carbon composite

The pore volume, pore size, and specific surface area of the carbon materials in the sulfur-carbon composites used in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, were measured, and the results are shown in Table 1 below. In addition, Figure 1 is a pore size distribution chart of the carbon material in the sulfur-carbon composite used in an example and a comparative example of the present invention, and Figure 1 a is a pore size distribution chart of Ketjen Black used in Examples 1 and 2. , and b in FIG. 1 is a pore size distribution chart of activated carbon used in Comparative Examples 1 and 2. Meanwhile, the pore volume, pore size, and specific surface area were derived from the nitrogen adsorption/desorption isotherm at 77K using porosity analysis equipment (model name: Belsorp-max, manufacturer: Bel Japan).

Pore volume
( ^cm3 /g) Pore diameter
(nm) BET S.A.
( ^m2 /g) Examples 1 and 2 4.0 < 2, 10 ~ 140 1,500 Comparative Examples 1 and 2 1.7 < 3 3,000

In addition, in order to evaluate the pore properties according to the specific surface area of the carbon material among the sulfur-carbon composites used in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, the nitrogen adsorption and desorption isotherm is shown in FIG. 2. Here, a in Figure 2 is the nitrogen adsorption and desorption isotherm of Ketjen Black used in Examples 1 and 2, and b in Figure 2 is the nitrogen adsorption and desorption isotherm of activated carbon used in Comparative Examples 1 and 2. am.

As a result of evaluating the pore properties according to the specific surface area size of the carbon material among the sulfur-carbon composites used in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, in the case of Ketjen Black used in Examples 1 and 2, 3 While pores with a diameter of nanometers or more are mainly distributed (specifically, pores with a diameter of 10 to 140 nm are mainly distributed), the activated carbon used in Comparative Examples 1 and 2 has a diameter of less than 3 nanometers. Pores with large diameters were mainly distributed.

[Experimental Example 2] Evaluation of discharge capacity and discharge voltage of lithium-sulfur battery

The lithium-sulfur batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were charged and discharged at 0.1C, and the discharge capacity and discharge voltage of the batteries were evaluated. At this time, the voltage range used was 0.8 to 3.6 V and the evaluation temperature was 25°C. Figure 3 is a graph showing the discharge capacity and discharge voltage of a lithium-sulfur battery manufactured according to an embodiment of the present invention, and Figure 4 is a graph showing the discharge capacity and discharge voltage of a lithium-sulfur battery manufactured according to a comparative example. As, Figure 3 corresponds to Examples 1 and 2, and Figure 4 corresponds to Comparative Examples 1 and 2.

As a result of measuring the discharge capacity and discharge voltage of the lithium-sulfur batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2, it was found that the SSE electrolyte was applied and a carbon material with a pore volume exceeding 3 cm ³ /g was used. The batteries of Examples 1 and 2 included in the sulfur-carbon composite had a discharge capacity of more than 1,340 mAh/g (i.e., utilizing more than 80% of the theoretical discharge capacity of sulfur) and an average discharge voltage of more than 2.0 V at room temperature. I was able to confirm that it was implemented. On the other hand, although the SSE electrolyte was applied, it was confirmed that the average discharge voltage of the cells of Comparative Examples 1 and 2, which included a carbon material with a pore volume of less than 2 cm ³ /g in the sulfur-carbon composite, did not reach 2.0 V. .

In this way, the lithium-sulfur battery of the present invention utilizes more than 80% of the theoretical discharge capacity of sulfur and realizes an average discharge voltage of more than 2.0 V at room temperature, which is compared to a conventional lithium-sulfur battery using an SSE electrolyte system. It is a level that has not been shown before. Therefore, from the above, it can be seen that the performance of the lithium-sulfur battery using the SSE electrolyte system can be maximized only when the positive electrode active material contains a carbon material with a pore volume exceeding 3 cm ³ /g.

Claims (13)

A first solvent containing a fluorine-based ether compound, a second solvent containing a glyme-based compound, and an electrolyte containing a lithium salt; and
It includes a positive electrode containing sulfur and carbon material as active materials,
A lithium-sulfur battery, characterized in that the pore volume of the carbon material is greater than 3 cm ³ /g and less than 10 cm ³ /g. The lithium-sulfur battery according to claim 1, wherein the utilization rate of sulfur contained in the positive electrode is 80% or more of the theoretical discharge capacity. The lithium-sulfur battery according to claim 1, wherein the average discharge voltage of the lithium-sulfur battery is 2.0 V or more at room temperature. The lithium-sulfur battery according to claim 1, wherein the positive electrode active material included in the positive electrode includes a sulfur-carbon composite. The lithium-sulfur battery according to claim 1, wherein the electrolyte does not contain a nitrile-based solvent. The method according to claim 1, wherein the fluorine-based ether compound is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis (fluoromethyl) ether, 2-fluoro Romethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether A lithium-sulfur battery, characterized in that it is at least one hydrofluoro ether-based compound selected from the group consisting of 1H, 1H, 2'H-perfluorodipropyl ether. The method according to claim 1, wherein the glyme-based compound is dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, Triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether and polyethylene glycol methyl ethyl ether. A lithium-sulfur battery, characterized in that it is one or more types selected from the group consisting of. The method of claim 1, wherein the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiC ₄ BO ₈ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ F) ₂ NLi, (CF ₃ SO ₂ ) ₃ A lithium-sulfur battery, characterized in that it is at least one selected from the group consisting of CLi, lithium chloroborane, lithium lower aliphatic carboxylate having 4 or less carbon atoms, lithium 4-phenyl borate, and lithium imide. The lithium-sulfur battery according to claim 1, wherein the concentration of the lithium salt is 0.1 to 2 M. The lithium-sulfur battery according to claim 1, wherein the molar ratio of the lithium salt, the second solvent, and the first solvent is 1:0.5 to 3:4.1 to 15. The lithium-sulfur battery according to claim 1, wherein the sulfur is contained in an amount of 60 to 80% by weight based on the total weight of the positive electrode. The lithium-sulfur battery according to claim 1, wherein the utilization rate of sulfur contained in the positive electrode is 90 to 100% of the theoretical discharge capacity. The lithium-sulfur battery according to claim 1, wherein the lithium-sulfur battery has an energy density of 400 Wh/kg or more or 600 Wh/L or more.