KR102081774B1 - Sulfur-carbon composite and lithium-sulfur battery including the same - Google Patents

Abstract

The present invention relates to a sulfur-carbon composite and a lithium-sulfur battery including the same, more specifically a porous carbon material; And it relates to a sulfur-carbon composite having an organic solvent of 5% by weight or less in the sulfur-carbon composite containing sulfur in the pores or on the surface thereof and a lithium-sulfur battery comprising the same.
According to the present invention, sulfur is evenly filled without pores in the pores of the porous carbon material and is evenly distributed on the surface of the porous carbon material, thereby improving the performance of the electrode as well as improving the capacity, stability, and life characteristics of the lithium-sulfur battery including the same. You can.

Description

Sulfur-Carbon Composites and Lithium-Sulfur Batteries Containing the Same {SULFUR-CARBON COMPOSITE AND LITHIUM-SULFUR BATTERY INCLUDING THE SAME}

The present invention relates to a sulfur-carbon composite having improved sulfur distribution characteristics and a lithium-sulfur battery including the same.

Recently, with the rapid development of the electronic device field and the electric vehicle field, the demand for secondary batteries is increasing. In particular, with the trend toward miniaturization and light weight of portable electronic devices, there is an increasing demand for secondary batteries having a high energy density that can cope with them.

The lithium-sulfur battery of the secondary battery uses a sulfur-based compound having a sulfur-sulfur bond as a positive electrode active material, and a carbon-based material or an alloy with lithium, in which insertion and deintercalation of alkali metals such as lithium or metal ions such as lithium ions occur. It is a secondary battery using silicon, tin, etc. to form as a negative electrode active material. Specifically, the electrical energy is stored by using an oxidation-reduction reaction in which the sulfur-sulfur bond is broken when the sulfur-sulfur bond is broken during the reduction reaction, and the sulfur-sulfur bond is formed again when the sulfur-oxide bond is increased when the oxidation-charging charge is increased. And generate

In particular, sulfur used as a positive electrode active material in a lithium-sulfur battery has a theoretical energy density of 1675 mAh / g, and has a theoretical energy density of about five times higher than that of a conventional positive electrode active material used in a lithium secondary battery. Is a battery capable of expression. In addition, sulfur is attracting attention as an energy source for medium and large devices such as electric vehicles as well as portable electronic devices due to its low cost, rich reserves, and easy supply and environmental friendliness.

However, since sulfur has an electrical conductivity of 5Х10 ^-30 S / cm, since sulfur is an insulator that does not have electrical conductivity, it is difficult to move electrons generated by an electrochemical reaction. It is therefore used in conjunction with an electrically conductive material, such as carbon, which can provide an electrochemical reaction site.

In this case, when the conductive material and sulfur are simply mixed and used, sulfur is leaked into the electrolyte during the oxidation-reduction reaction, thereby deteriorating the battery life, and lithium polysulfide, which is a reducing material of sulfur, is eluted and no longer participates in the electrochemical reaction. There was a problem. In addition, there is a problem in that the capacity decreases when sulfur in the electrode is excessively loaded. Accordingly, various techniques have been proposed to improve the mixing quality of the conductive material and sulfur.

For example, Korean Patent Laid-Open Publication No. 2014-0086811 proposes a technique for increasing the sulfur content by pulverizing a sulfur-porous conductive material composite impregnated with a large amount of sulfur through mechanical milling.

In addition, the Republic of Korea Patent Publication No. 2015-0026098 relates to a positive electrode for a lithium-sulfur battery in which molten sulfur is supported on a porous carbon foam having a network structure, and does not include a binder resin, thereby increasing sulfur loading and battery capacity. Doing.

In addition, the Republic of Korea Patent Publication No. 2016-0037084 discloses that by coating the graphene on the carbon nanotube aggregate containing sulfur can increase the conductivity and sulfur loading of the sulfur-carbon nanotube composite.

The sulfur-carbon composites proposed in these patents improve the sulfur content to some extent by changing the manufacturing method or composition, but the effect is not sufficient. Therefore, there is a need for further research on sulfur-carbon composites that exhibit excellent reactivity and quality by improving mixing uniformity.

Republic of Korea Patent Publication No. 2014-0086811 (2014.07.08), Method of manufacturing sulfur-porous conductive material nanocomposite for lithium sulfur secondary battery positive electrode Republic of Korea Patent Publication No. 2015-0026098 (2015.03.11), a positive electrode for a lithium-sulfur battery and a manufacturing method thereof Republic of Korea Patent Publication No. 2016-0037084 (2016.04.05), sulfur-carbon nanotube composite, a manufacturing method thereof, a cathode active material for a lithium-sulfur battery including the same and a lithium-sulfur battery including the same

Accordingly, the present inventors conducted various studies to solve the above problems, and confirmed that sulfur is more uniformly distributed by filling a specific organic solvent in the sulfur-carbon composite and filled sufficiently in the pores of the carbon material. It was.

Accordingly, an object of the present invention is to provide a sulfur-carbon composite in which sulfur is uniformly distributed due to a small amount of organic solvent remaining therein.

Another object of the present invention is to provide a positive electrode including the sulfur-carbon composite and a lithium-sulfur battery including the same.

In order to achieve the above object, the present invention provides a sulfur-carbon composite, characterized in that the organic solvent remaining in 5% by weight or less.

Residual amount of the organic solvent is characterized in that 0.001 to 5% by weight or less.

At this time, the organic solvent is characterized in that the boiling point of 155 to 300 ℃.

The sulfur-carbon composite is a porous carbon material; And sulfur in or on the surface of the pores.

In addition, the present invention is sulfur-carbon, characterized in that at least two organic solvents selected from the group consisting of diethylene glycol dimethyl ether, dioxolane, dimethoxyethane, xylene and sulfolane remain at 5% by weight or less. To provide a complex.

In addition, the present invention provides a positive electrode for a lithium-sulfur battery including the sulfur-carbon composite.

In addition, the present invention is a positive electrode comprising the sulfur-carbon composite; cathode; And it provides a lithium-sulfur battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

The sulfur-carbon composite according to the present invention has a small amount of a specific organic solvent remaining therein so that sulfur can be sufficiently filled without voids in the pores of the porous carbon material, and the dispersion property of sulfur is improved to distribute evenly on the surface of the porous carbon material. Can be.

Accordingly, the positive electrode and the lithium-sulfur battery including the sulfur-carbon composite may have improved stability, cycle characteristics, and capacity characteristics.

1 is a SEM photograph of a sulfur-carbon composite prepared according to Example 1 of the present invention.
2 is a SEM photograph of a sulfur-carbon composite prepared according to Comparative Example 1 of the present invention.
Figure 3 is a graph showing the thermal properties of the sulfur-carbon composite prepared according to Example 1 of the present invention.
4 is a graph showing charge and discharge characteristics of the lithium-sulfur battery coin cell manufactured by applying Example 1 and Comparative Example 1 of the present invention.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concepts of terms in order to best describe their invention. There is

Based on the principle, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

As used herein, the term “composite” refers to a substance in which two or more materials are combined to form physically and chemically different phases and express more effective functions.

Lithium-sulfur batteries have a much higher theoretical energy density than conventional lithium secondary batteries, and sulfur, which is used as a positive electrode active material, has been spotlighted as a next-generation battery because of its rich resources and low price. have.

In order to solve the low electrical conductivity of sulfur in the lithium-sulfur battery, a conductive material such as carbon or a polymer is coated or a composite is prepared. In the case of the composite, since other conductive materials are included instead of sulfur in the positive electrode, it may affect the reactivity of the positive electrode active material and lower the energy density of the battery. Therefore, it is important to maximize the content of sulfur in the sulfur-carbon composite and to uniform the distribution. In this case, it is possible to increase the content of sulfur by using a porous carbon material, molten sulfur, or through a mechanical milling process. However, even when introducing a method of mixing and heat-treating sulfur and porous carbon material or impregnating liquid sulfur, it is difficult to uniformly fill sulfur in the pores without voids.

Therefore, in the present invention, sulfur-carbon containing a certain amount of organic solvent to improve the distribution and filling uniformity of sulfur in the sulfur-carbon composite to secure the reactivity of the sulfur-carbon composite and the charge and discharge characteristics in the lithium-sulfur battery. To provide a complex.

Specifically, the sulfur-carbon composite according to the embodiment of the present invention includes sulfur in the porous carbon material and its pores or the surface thereof, and at this time, the organic solvent remains within 5% by weight or less of the porous carbon material.

The organic solvent increases sulfur dispersibility in the sulfur-carbon composite so that sulfur may be more evenly distributed in or on the surface of the pores of the porous carbon material. In particular, sulfur is sufficiently filled without voids in the pores of the porous carbon material to improve the capacity and life characteristics of the lithium-sulfur battery as well as improving reactivity as a cathode active material.

In the sulfur-carbon composite according to one embodiment of the present invention, the organic solvent may remain in an amount of 0.001 to 5 wt%, preferably 0.005 to 1 wt%. When the organic solvent remains below the above range, the effect of improving the distribution and filling characteristics of sulfur is insignificant, and on the contrary, when the organic solvent remains above the above range, it may adversely affect the function and battery performance as the positive electrode active material.

The organic solvent has a boiling point of 155 to 300 ° C., and does not volatilize even during a melt-diffusion process for filling sulfur into pores of the porous carbon material when the sulfur-carbon composite is manufactured. Allow sulfur to be uniformly filled in the pores.

In addition, the organic solvent is not particularly limited to the above-mentioned boiling point, but because it is included in the final manufactured sulfur-carbon composite does not affect other components of the battery, in particular does not react with the electrolyte or the electrolyte It may be selected from constituent solvents. Organic solvents usable in the present invention are selected from the group consisting of ketones, ethers, esters, alcohols, sulfoxides and amides. It may include one or more. For example, the type of the organic solvent and its boiling point are as shown in Table 1 below, but the present invention is not limited to the following examples.

Organic solvent Boiling Point (℃) Isoamyl Propionate 156 Ethyl ethoxy acetate 156 2-ethoxyethyl acetate 156 2-methyl-3-heptanone 159 Ethyl-3-methoxypropionate 158 2-methoxy ethyl ether 162 3-methoxy butyl acetate 170 2-ethoxyethyl ether 185 2-butoxyethanol 171 3-ethoxy-propanol 161 Diethylene glycol dodecyl ether 169 Dipropylene glycol methyl ether 188 2,6-dimethyl-4-heptanone 169 2-octanone 173 3-octanone 168 3-nonnanon 188 5-nonnanon 187 4-hydroxy-4-methyl-2-pentanone 166 2-methylcyclohexanone 163 3-methylcyclohexanone 170 4-methylcyclohexanone 170 2,6-dimethylcyclohexanone 175 2,2,6-trimethylcyclohexanone 179 Cyclohaptanone 179 Hexyl acetate 169 Amyl butyrate 185 Isopropyl lactate 167 Butyl lactate 186 Ethyl-3-hydroxybutyrate 170 Ethyl-3-ethoxypropionate 170 Ethyl-3-hydroxy butyrate 180 Propyl-2-hydroxypropionate 169 Propylene Glycol Diacetate 186 Propylene Glycol Butyl Ether 170 Propylene Glycol Methyl Ether Propionate 160 Diethylene glycol dimethyl ether 162 Diethylene Glycol Dimethyl Ether Acetate 165 Dipropylene Glycol Methyl Ether 188 Dipropylene Glycol Dimethyl Ether 171 Ethylene Glycol Butyl Ether 171 Diethylene glycol methylethyl ether 176 Diethylene Glycol Methyl Isopropyl Ether 179 Ethylene Glycol Diethyl Ether 189 Butyl butyrate 165 Diethylene glycol monomethyl ether 194 4-ethylcyclohexanone 193 2-butoxyethyl acetate 192 Diethylene glycol monoethyl ether 202 γ-butyrolactone 204 Hexylbutyrate 205 Diethylene Glycol Methyl Ether Acetate 209 Diethylene glycol butyl methyl ether 212 N-methyl-2-pyrrolidone 212 Tripropylglycol dimethyl ether 215 Triethylene glycol dimethyl ether 216 Diethylene glycol ethyl ether acetate 217 Diethylene Glycol Butyl Ether Acetate 245 3-epoxy-1,2-propanediol 222 Ethyl-4-acetylbutyrate 222 Diethylene glycol monobutyl ether 231 Tripropylglycol methyl ether 242 Diethylene glycol 245 2- (2-butoxyethoxy) ethyl acetate 245 Catechol 245 Triethylene glycol methyl ether 249 Diethylene glycol dibutyl ether 256 Triethylene glycol ethyl ether 256 Diethylene glycol monohexyl ether 260 Triethylene glycol butyl methyl ether 261 Triethylene Glycol Butyl Ether 271 Tripropylene glycol 273 Tetraethylene Glycol Dimethyl Ether 276 Ethylene carbonate 248 Propylene carbonate 204 Sulfolane 285

Preferably, the solvent may include at least one selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, γ-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane. have.

On the other hand, the present invention is methanol, ethanol, isopropanol, 1-propanol, butanol, tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene, acetonitrile, heptane, cyclohexane, diethylene glycol dimethyl ether, dioxolane, And sulfur-carbon complexes in which at least two organic solvents selected from the group consisting of dimethoxyethane, xylene and sulfolane remain at most 5% by weight. At this time, the sulfur-carbon composite is preferable in terms of performance and stability when introduced into the battery as an electrode because it contains a solvent constituting the electrolyte while achieving a uniform distribution of sulfur.

The porous carbon material provides a framework in which sulfur can be uniformly and stably immobilized, and complements low electrical conductivity of sulfur to allow the electrochemical reaction to proceed smoothly.

The porous carbon material may generally be prepared by carbonizing precursors of various carbon materials. The porous carbon material may include non-uniform pores therein, and the average diameter of the pores may be in the range of 1 to 200 nm and porosity or porosity may range from 10 to 90% of the volume. If the average diameter of the pores is less than 1 nm, the pore size is only molecular level, so impregnation of sulfur is impossible, and conversely, if the average pore size exceeds 200 nm, the size of the sulfur-carbon composite is large, which is not preferable.

In addition, the spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk type may be used as the form of the porous carbon material.

The porous carbon material may be any one as long as it has a porous structure or a high specific surface area. Specifically, the porous carbon material is graphite (graphite); Graphene; Carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black and summer black; Carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); Carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); And may be one or more selected from the group consisting of mesoporous carbon, such as CMK-3, CMK-8, MSU-F-C, but is not limited thereto.

The sulfur is from the group consisting of inorganic sulfur (S ₈ ), Li ₂ S _n (n ≧ 1), organic sulfur compound and carbon-sulfur polymer [(C ₂ S _x ) _n , x = 2.5 to 50, n ≧ 2] It may be one or more selected. Preferably inorganic sulfur (S ₈ ) can be used.

In the sulfur-carbon composite according to the present invention, the weight ratio of the aforementioned porous carbon material and sulfur may be 1: 9 to 5: 5, preferably 2: 9 to 3: 7. If less than the weight ratio range, as the content of the porous carbonaceous material is increased, the amount of binder required for preparing the positive electrode slurry increases. Increasing the amount of binder added may eventually increase the sheet resistance of the electrode and serve as an insulator that prevents electron pass, thereby degrading cell performance. On the contrary, when the weight ratio exceeds the range, sulfur may be agglomerated among them, and it may be difficult to directly participate in the electrode reaction because it is difficult to receive electrons.

In addition, the sulfur is located on the surface as well as inside the pores of the porous carbon material, wherein the sulfur is present in less than 100%, preferably 1 to 80%, more preferably 50 to 80% region of the entire outer surface of the porous carbon material. Can be. When the sulfur is in the above range on the surface of the porous carbon material may exhibit the maximum effect in terms of the electron transfer area and the wettability of the electrolyte. Specifically, since the sulfur is thinly and evenly impregnated on the surface of the porous carbon material in the above range region, the electron transfer contact area may be increased during the charge and discharge process. If the sulfur is located at 100% of the surface of the porous carbon material, the porous carbon material is completely covered with sulfur, so that the wettability of the electrolyte is inferior and the contact with the conductive material included in the electrode is poor, and thus the electrons cannot be transferred to participate in the reaction. It becomes impossible.

The present invention also provides a method for producing the sulfur-carbon composite.

The method for producing the sulfur-carbon composite according to the present invention is not particularly limited and may be prepared by methods commonly known in the art.

For example, the method of manufacturing the sulfur-carbon composite may include mixing sulfur, a porous conductive material and an organic solvent, and heating the mixture to melt and mix sulfur to form a sulfur-carbon composite.

The heating temperature may be any temperature at which sulfur is melted, and may be specifically 120 to 180 ° C., preferably 150 to 180 ° C. If the heating temperature is less than 120 ℃ sulfur may not be sufficiently melted structure of the sulfur-carbon composite is not properly formed, if it exceeds 180 ℃ organic solvent does not remain difficult to obtain the desired effect. In addition, the heating time may be adjusted according to the content of sulfur.

The mixing method is to increase the degree of mixing of the raw material sulfur, the porous conductive material and the organic solvent can be performed using a stirring device commonly used in the art, but is not limited thereto. In this case, the mixing time and speed may also be selectively adjusted according to the content and conditions of the raw materials.

The sulfur-carbon composite formed through the above-described manufacturing method may be dried to have an organic solvent of 5% by weight or less remaining therein, and finally, may be manufactured as a sulfur-carbon composite powder.

In addition, the present invention provides a positive electrode for a lithium-sulfur battery including the sulfur-carbon composite. The sulfur-carbon composite may be included as a cathode active material in a cathode.

The positive electrode may further include at least one additive selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur in addition to the positive electrode active material.

The transition metal element may be 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, the Group IIIA element may include Al, Ga, In, Ti, and the like, and the Group IVA element may include Ge, Sn, Pb and the like.

The positive electrode may further include a positive electrode active material or, optionally, an additive, an electrically conductive conductive material for allowing electrons to move smoothly in the positive electrode, and a binder for attaching the positive electrode active material to the current collector.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes to the battery, but may include graphite-based materials such as KS6; Carbon blacks such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, Summer Black, Carbon Black; Carbon derivatives such as carbon nanotubes and fullerenes; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The conductive material may be added in an amount of 0.01 to 30 wt% based on the total weight of the mixture including the cathode active material.

The binder includes poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), polyvinylidene Copolymers of fluoride, polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylenepolyvinylchloride, polyacrylonitrile, polyvinylpyridine, polystyrene, Derivatives, blends, copolymers and the like thereof can be used.

The binder may be added in an amount of 0.5 to 30 wt% based on the total weight of the mixture including the cathode active material. If the content of the binder is less than 0.5% by weight, the physical properties of the positive electrode may be deteriorated, so that the active material and the conductive material may be dropped in the positive electrode. If the content is more than 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively decreased, thereby reducing battery capacity. can do.

Looking at the method of manufacturing the positive electrode of the present invention in detail, first, the binder is dissolved in a solvent for preparing a slurry, and then the conductive material is dispersed. The solvent for preparing the slurry can uniformly disperse the positive electrode active material, the binder, and the conductive material, and it is preferable to use one that is easily evaporated. Typically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, iso Propyl alcohol and the like. Next, the positive electrode active material, or optionally together with an additive, is uniformly dispersed again in a solvent in which the conductive material is dispersed to prepare a positive electrode slurry. The amount of the solvent, the positive electrode active material, or optionally the additive included in the slurry does not have a particularly important meaning in the present application, and it is sufficient only to have an appropriate viscosity to facilitate the coating of the slurry.

The slurry thus prepared is applied to a current collector and vacuum dried to form a positive electrode. The slurry may be coated on the current collector in an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed.

The current collector can be generally made to a thickness of 3 to 500 ㎛, and is not particularly limited as long as it has a high conductivity without causing chemical changes in the battery. Specifically, conductive materials such as stainless steel, aluminum, copper, and titanium may be used, and more specifically, a carbon-coated aluminum current collector may be used. The use of an aluminum substrate coated with carbon has an advantage in that the adhesion to the active material is excellent, the contact resistance is low, and the corrosion of polysulfide of aluminum is prevented, compared with the non-carbon coated aluminum substrate. In addition, the current collector may be in various forms such as a film, sheet, foil, net, porous body, foam or nonwoven fabric.

In addition, the present invention is a positive electrode comprising a sulfur-carbon composite described above; cathode; And it provides a lithium-sulfur battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

The anode is according to the invention and according to the foregoing.

The negative electrode may include a current collector and a negative electrode active material layer formed on one or both surfaces thereof. The negative electrode active material may be a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal or a lithium alloy.

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

The material capable of reacting with the lithium ions to reversibly form a lithium-containing compound may be, for example, tin oxide, titanium nitrate, or silicon.

The lithium alloy may be, for example, an alloy of lithium with a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn.

A separator may be additionally included between the positive electrode and the negative electrode. The separator may be made of a porous non-conductive or insulating material to isolate or insulate the positive electrode and the negative electrode from each other, and to enable lithium ion transport between the positive electrode and the negative electrode. The separator may be an independent member such as a film, or may be a coating layer added to the anode and / or the cathode.

Materials forming the separator include, but are not limited to, for example, polyolefins such as polyethylene and polypropylene, glass fiber filter paper, and ceramic materials, and the thickness thereof is about 5 to about 50 μm, preferably about 5 to about 25 May be μm.

The electrolyte is located between the positive electrode and the negative electrode and includes a lithium salt and an electrolyte solvent.

The concentration of the lithium salt is 0.2 to 2 M, depending on several factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and preconditioning of the cell, the operating temperature and other factors known in the lithium battery art, Specifically, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. When the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte may be lowered, and thus the performance of the electrolyte may be lowered. When the lithium salt is used in excess of 2 M, the viscosity of the electrolyte may be increased, thereby reducing the mobility of lithium ions.

Examples of the lithium salt include LiSCN, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , LiClO ₄ , LiSO ₃ CH ₃ , LiB (Ph) ₄ , LiC (SO ₂ CF ₃ ) ₃ and LiN (SO ₂ CF ₃ ) ₂ or more may be included from the group consisting of.

The electrolyte solvent is a non-aqueous organic solvent, a single solvent may be used, or two or more mixed organic solvents may be used. When using two or more mixed organic solvents, it is preferable to use one or more solvents selected from two or more groups among the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

The weak polar solvent is defined as a solvent having a dielectric constant of less than 15 which is capable of dissolving elemental sulfur among aryl compounds, bicyclic ethers, and acyclic carbonates, and strong polar solvents include acyclic carbonates, sulfoxide compounds, and lactone compounds. In the ketone compound, ester compound, sulfate compound, and sulfite compound, a dielectric constant capable of dissolving lithium polysulfide is defined as greater than 15, and the lithium metal protective solvent is a saturated ether compound, unsaturated ether compound, N, It is defined as a solvent having a charge / discharge cycle efficiency of 50% or more to form a stable solid interface (SEI) on a lithium metal such as a heterocyclic compound including O, S, or a combination thereof.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme or tetraglyme. .

Specific examples of the strong polar solvent include hexamethyl phosphoric triamide, γ-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazoli Don, dimethyl formamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, or ethylene glycol sulfite.

Specific examples of the lithium protective solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane or 4-methyldioxolane.

The electrolyte may include one or more selected from the group consisting of a liquid electrolyte, a gel polymer electrolyte and a solid polymer electrolyte. It may be preferably an electrolyte in a liquid state.

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

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

Examples of the medium-to-large device include a power tool that is driven by an electric motor; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric motorcycles including electric bicycles (E-bikes) and electric scooters (Escooters); Electric golf carts; Power storage systems, etc., but is not limited thereto.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely to illustrate the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art, It is natural that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

Example 1

4.2 g of sulfur, 1.8 g of carbon nanotubes, and 2 ml of tetraethylene glycol dimethyl ether (TEGDME) were evenly mixed in a reactor, and then heat-treated at 155 ° C. for 30 minutes to prepare a sulfur-carbon composite.

The slurry was prepared in a weight ratio of sulfur-carbon composite: conductor: binder = 90: 5: 5 using the prepared sulfur-carbon composite, and then coated on a current collector of 20 μm thick aluminum foil to prepare an electrode. In this case, carbon black was used as the conductive material, and styrene-butadiene rubber and carboxymethyl cellulose were used as the binders.

Example 2

The electrode was prepared in the same manner as in Example 1, except that dioxolane / diethylene glycol dimethylether / sulforan / dimethoxyethane (5: 2: 1: 2) was used as an organic solvent instead of TEGDME. Prepared.

Comparative Example 1

An electrode was manufactured in the same manner as in Example 1, except that TEGDME, which is an organic solvent, was not used to prepare a sulfur-carbon composite.

Experimental Example 1. Scanning electron microscope analysis

The sulfur-carbon composites prepared in Example 1 and Comparative Example 1 were observed with a scanning electron microscope (S-4800, HITACHI). The results obtained at this time are shown in FIGS. 1 and 2.

1 and 2, it can be seen that the sulfur-carbon composite obtained in Example 1 has more evenly distributed sulfur in the composite containing sulfur of the same content as compared to the conventional sulfur-carbon composite. In particular, in the case of the sulfur-carbon composite prepared by the conventional process it can be seen that sulfur is also present in the space between the carbon nanotubes and carbon nanotubes having an aggregated shape.

Experimental Example 2 Thermal Properties Analysis

Thermogravimetric Analysis (TGA) was performed on the sulfur-carbon composite prepared in Example 1 above. The TGA measurement was carried out under nitrogen conditions, and the temperature change was measured by steadily raising the temperature without stopping the heating by 10 ℃ per minute at a rate of 10 ℃ / min. The results obtained at this time are shown in FIG. 3.

As shown in FIG. 3, two weight loss temperatures were confirmed during thermal property analysis. The first weight loss temperature is 110 to 180 ℃, the second weight loss temperature was confirmed to appear at 200 to 300 ℃. At this time, it can be seen that the first weight loss temperature contains a small amount of the organic solvent in the sulfur-carbon composite, and the second weight loss temperature was found to decrease the mass as the sulfur contained in the sulfur-carbon composite melts.

Experimental Example 3. Evaluation of charge and discharge characteristics

A lithium-sulfur battery coin cell was prepared using the electrodes prepared in Example 1 and Comparative Example 1 as a positive electrode and using a 150 μm thick lithium foil as a negative electrode. At this time, the coin cell used an electrolyte consisting of TEGDME / DOL (dioxolane) / DME (Dimethyl ether) (1: 1: 1), LiN (CF ₃ SO ₂ ) ₂ (LiTFSI) 1M, LiNO ₃ 0.1M.

The manufactured coin cell was measured for a capacity from 1.5 to 2.8V using a charge / discharge measuring device. Specifically, charging and discharging efficiency was measured by repeating 50 cycles of charging at 0.1 C rate CC / CV and discharging at 0.1 C rate CC (CC: Constant Current, CV: Constant Voltage). The results obtained at this time are shown in FIG. 4.

4, when the sulfur-carbon composite of Example 1 was used as the cathode active material compared to Comparative Example 1, it was confirmed that the initial discharge capacity was improved.

In the sulfur-carbon composite of the present invention, sulfur is evenly filled without pores in the pores of the porous carbon material and is evenly distributed on the surface of the porous carbon material, thereby improving the performance of the electrode and increasing the capacity of the lithium-sulfur battery including the same. It enables stabilization and long life.

Claims (11)

Organic solvent remains at 0.005 to 5% by weight,
The organic solvent is at least one selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, γ-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane Sulfur-carbon composite. The method of claim 1,
Sulfur-carbon composite, characterized in that the organic solvent has a boiling point of 155 to 300 ℃. delete The method of claim 1,
The sulfur-carbon composite is
Porous carbon material; And
Sulfur-carbon composite, characterized in that containing sulfur in or on its surface. The method of claim 4, wherein
The porous carbon material is sulfur-carbon composite, characterized in that the porous carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotubes, carbon fibers and mesoporous carbon. The method of claim 4, wherein
Sulfur-carbon composite, characterized in that the average diameter of the pores of the porous carbon material is 1 to 200 nm. The method of claim 4, wherein
The porosity of the porous carbon material is sulfur-carbon composite, characterized in that 10 to 90% of the total volume of the porous carbon material. The method of claim 4, wherein
The sulfur is from the group consisting of inorganic sulfur (S ₈ ), Li ₂ S _n (n ≧ 1), organic sulfur compound and carbon-sulfur polymer [(C ₂ S _x ) _n , x = 2.5 to 50, n ≧ 2] Sulfur-carbon composite, characterized in that at least one selected. The method of claim 4, wherein
Sulfur-carbon composite, characterized in that the weight ratio of the porous carbon material and sulfur is 1: 9 to 5: 5. A cathode for a lithium-sulfur battery comprising the sulfur-carbon composite according to claim 1. A positive electrode comprising a sulfur-carbon composite according to claim 1;
cathode; And
Lithium-sulfur battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

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