KR102448075B1 - Method for preparing positive electrode active material for lithium sulfur battery, positive electrode active material for lithium sulfur battery prepared thereby and lithium sulfur battery including the same - Google Patents

Abstract

A method of manufacturing a positive electrode active material for a lithium-sulfur battery, which can improve the initial discharge capacity of a battery by forming pores on the surface of a carbon structure used to conduct a positive electrode, a positive electrode active material for a lithium-sulfur battery prepared thereby, and the same A lithium-sulfur battery comprising is disclosed. The method for preparing a cathode active material for a lithium-sulfur battery includes: a) forming a carbon structure including a carbon-based compound; and b) supplying a CO ₂ /O ₂ mixed gas to the formed carbon structure and performing heat treatment to form pores on the surface of the carbon structure; including, wherein the specific surface area of the carbon structure in which the pores are formed is 10 to 2,000 m ² /g is characterized.

Description

A method for preparing a cathode active material for a lithium-sulfur battery, a cathode active material for a lithium-sulfur battery prepared thereby, and a lithium-sulfur battery comprising the same thereby and lithium sulfur battery including the same}

The present invention relates to a positive active material for a lithium-sulfur battery, and more particularly, to a lithium-sulfur battery, which can improve the initial discharge capacity of the battery by forming pores on the surface of a carbon structure used to make the positive electrode conductive A method of manufacturing a positive electrode active material, a positive electrode active material for a lithium-sulfur battery prepared thereby, and a lithium-sulfur battery including the same.

As interest in energy storage technology increases, the field of application expands to energy of mobile phones, tablets, laptops and camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs). Research and development of chemical devices is gradually increasing. Electrochemical devices are the field receiving the most attention in this aspect, and among them, the development of secondary batteries such as lithium-sulfur batteries capable of charging/discharging is the focus of interest, and in recent years, capacity density in developing such batteries And in order to improve specific energy, it leads to research and development for design of new electrodes and batteries.

Among these electrochemical devices, a lithium-sulfur (Li-S) battery has a high energy density and is spotlighted as a next-generation secondary battery 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 is converted from S ₈ of a ring structure to lithium polysulfide (Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ ) is formed. This lithium-sulfur battery is characterized by exhibiting a step-by-step discharge voltage until polysulfide (PS) is completely reduced to Li ₂ S.

However, since the sulfur positive electrode of the lithium-sulfur battery is non-conductive, the use of the lithium-sulfur battery, which is a composite of conductive carbon and polymer, which constitutes the positive electrode active material, is gradually increasing. However, in a lithium-sulfur battery, the final reaction product, Li ₂ S, changes the electrode structure as its volume increases compared to S, and polysulfide, an intermediate product, is easily dissolved in the electrolyte. quantity decreases. As a result, battery degradation is accelerated and long-term stability of the battery cannot be ensured. In order to solve this problem, the sulfur-carbon composite is used as the anode, and when sulfur is supported inside the pores of the carbon structure in the cathode, the structure of the pores is increased to increase the supported content of sulfur, and the elution of polysulfide is trapped into the pores. research is in progress.

On the other hand, pore size control such as increasing the carbon structure pore structure of the sulfur-carbon composite anode is possible by locally oxidizing carbon by giving a defect to an amorphous layer on the carbon surface. As a method for this, heat treatment is performed after adding potassium hydroxide solution (KOH solution) (specifically, K is reduced by heat treatment in an inert gas atmosphere mixed with KOH to partially oxidize carbon, and then wash K to create pores) , there is a method of heat treatment while flowing carbon dioxide (CO ₂ ) gas. However, since the process using the potassium hydroxide solution is a wet process, there is a disadvantage in that mass synthesis is difficult because a drying process is added after washing. Therefore, it is necessary to find a method for improving the initial discharge capacity of the battery by using carbon dioxide gas to control the size of the pores of the carbon structure, but by further increasing the specific surface area and the volume of the pores.

Therefore, an object of the present invention is to increase the specific surface area and pore volume of the carbon structure by flowing a CO ₂ /O ₂ mixed gas to the carbon structure used to conduct the positive electrode, thereby improving the initial discharge capacity of the battery. It is to provide a method for producing a cathode active material for a lithium-sulfur battery, a cathode active material for a lithium-sulfur battery prepared thereby, and a lithium-sulfur battery including the same.

In order to achieve the above object, the present invention, a) forming a carbon structure comprising a carbon-based compound; and b) supplying a CO ₂ /O ₂ mixed gas to the formed carbon structure and performing heat treatment to form pores on the surface of the carbon structure; including, wherein the specific surface area of the carbon structure in which the pores are formed is 10 to 2,000 m ² /g, it provides a method for producing a positive active material for a lithium-sulfur battery.

In addition, the present invention, as produced by the method for producing a cathode active material for a lithium-sulfur battery, includes a carbon structure in which pores are formed on the surface to support sulfur, and the specific surface area of the carbon structure is 10 to 2,000 m ² /g It provides a cathode active material for a lithium-sulfur battery, characterized in that.

In addition, the present invention provides a lithium-sulfur battery including a positive electrode including the positive electrode active material for a lithium-sulfur battery, a negative electrode, an electrolyte interposed between the positive electrode and the negative electrode, and a separator.

According to the method for manufacturing a positive electrode active material for a lithium-sulfur battery according to the present invention, a positive electrode active material for a lithium-sulfur battery prepared thereby, and a lithium-sulfur battery comprising the same, CO ₂ /O in the carbon structure used to make the positive electrode conductive ₂ By flowing the mixed gas, the initial discharge capacity of the battery can be improved by increasing the specific surface area and pore volume of the carbon structure. In addition, the method for manufacturing a cathode active material for a lithium-sulfur battery according to the present invention has an advantage that the process is simple and mass synthesis is possible.

1 is an SEM image (a) of an LD-CNT prepared according to an embodiment of the present invention and an SEM image (b) of an LD-CNT prepared according to a comparative example.
2 is a graph showing the discharge capacity retention rate of lithium-sulfur batteries prepared according to an embodiment and a comparative example of the present invention.
3 is a graph showing the degree of adsorption of lithium polysulfide in lithium-sulfur batteries prepared according to Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail.

The method for manufacturing a cathode active material for a lithium-sulfur battery according to the present invention comprises the steps of: a) forming a carbon structure including _a carbon _- based compound; and forming pores on the surface of the carbon structure, wherein the specific surface area of the carbon structure in which the pores are formed is 10 to 2,000 m ² /g.

The carbon structure constitutes a sulfur-carbon composite positive electrode applied to a lithium-sulfur battery, carbon nanotube (CNT), graphene and graphene oxide (GO), etc., CO ₂ /O ₂ Any carbon-based compound in which pores are formed on the surface during the supply and heat treatment of the mixed gas may be applied without particular limitation. In addition, the carbon structure is not particularly limited in its form as long as it can be applied to a lithium-sulfur battery. In addition, the carbon structure may further include additives such as an inorganic metal compound and an organic polymer material in addition to the carbon-based compound, if necessary. On the other hand, in the formation of the carbon structure, a conventional method for producing a carbon-based compound such as carbon nanotube, graphene, or graphene oxide may be applied mutatis mutandis.

When the carbon structure is formed in this way, a process for forming pores on the surface of the carbon structure is performed. To this end, first, a mixed gas containing CO ₂ and O ₂ must be flowed (or supplied) to the carbon structure. Here, the mixing ratio of CO ₂ and O ₂ may be 7 to 9: 1 to 3, preferably 7.5 to 8.5: 1.5 to 2.5, more preferably about 8: 2 as a volume ratio, and the CO ₂ and O ₂ If the mixing ratio is out of the above range, there is a fear that the specific surface area of the surface of the carbon structure or the volume of pores targeted by the present invention may not be reached.

By flowing the mixed gas as described above to the carbon structure and performing heat treatment at the same time, the cathode active material for a lithium-sulfur battery according to the present invention is manufactured. The heat treatment is performed at a temperature of 600 to 850 °C, preferably 650 to 800 °C, more preferably 700 to 750 °C, for 10 minutes to 3 hours, preferably 20 minutes to 2.5 hours, more preferably 30 minutes to It can be carried out for 2 hours.

When the above CO ₂ /O ₂ mixed gas is supplied and heat treatment is performed, a defect is applied to the surface of the carbon structure, and the oxidized carbon is blown away to form pores on the surface of the carbon structure. This is a method of forming pores on the surface of a carbon structure using only CO ₂ gas, a method of producing a cathode active material unique to the present invention in which the pore volume and specific surface area of the surface of the carbon structure are increased.

That is, in other words, the present invention adds a mechanism such as the following Reaction Scheme 2 or 3 for burning carbon to a mechanism such as the following Reaction Scheme 1 for locally oxidizing carbon using the oxidizing power of CO ₂ , the carbon structure surface Since it is possible to uniformly and stably support sulfur (S) inside the pores formed in the , it is possible to ultimately increase the initial discharge capacity of the lithium-sulfur battery.

[Scheme 1]

C + CO ₂ → 2CO

[Scheme 2]

2C + O ₂ → 2CO

[Scheme 3]

C + O ₂ → CO ₂

In addition, the present invention has the advantage that mass synthesis is possible because there is no drying process after washing, unlike the existing process using potassium hydroxide solution (KOH solution), and it is a single process of heat treatment while flowing gas. On the other hand, the diameter of the pores is 20 to 2,000 Å. In addition, due to the pores, the specific surface area of the (pore-formed) carbon structure may be 10 to 2,000 m ² /g, preferably 50 to 1,000 m ² /g.

Next, a cathode active material for a lithium-sulfur battery prepared by the method for preparing a cathode active material for a lithium-sulfur battery will be described. The cathode active material for a lithium-sulfur battery includes a carbon structure in which pores are formed on the surface to support sulfur, and the carbon structure has a specific surface area of 10 to 2,000 m ² /g. Here, the description of the carbon structure and the pores is applied mutatis mutandis as described above.

Finally, when describing the lithium-sulfur battery including the positive electrode active material for the lithium-sulfur battery, the lithium-sulfur battery includes a positive electrode and a negative electrode including the positive electrode active material for a lithium-sulfur battery, and between the positive electrode and the negative electrode. It includes an electrolyte and a separator interposed therebetween. The content of the positive electrode active material may be 50 to 90 parts by weight, preferably 60 to 80 parts by weight, based on 100 parts by weight of the positive electrode (positive electrode material). If the content of the positive active material is less than 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode, the electrochemical properties of the battery due to the positive active material are lowered, and when it exceeds 90 parts by weight, additional components such as binders and conductive materials are included in a small amount. Therefore, it may be difficult to manufacture an efficient battery.

On the other hand, the general configuration of the positive electrode, except for the positive electrode active material, the negative electrode, the electrolyte, and the separator may be conventional ones used in the art, and a detailed description thereof will be given below.

[anode]

The positive electrode included in the lithium-sulfur battery of the present invention further includes a binder and a conductive material in addition to the above-described positive electrode active material. The binder is a component that assists in bonding between the positive electrode active material and the conductive material and 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 - At least one selected from the group consisting of butylene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof may be used, but must be The present invention is not limited thereto.

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

The conductive material included in the positive electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the lithium secondary battery and has excellent electrical conductivity without causing chemical changes in the battery. Typically, graphite or conductive carbon may be used. and, 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 summer black; a carbon-based material having a crystal structure of graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; Conductive whiskey, such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; may be used alone or in mixture of two or more, but is not necessarily limited thereto.

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

In addition, a filler may be selectively added to the positive electrode of the present invention as a component for suppressing its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and for example, an olipine-based polymer such as polyethylene or polypropylene; fibrous materials such as glass fiber and carbon fiber; etc. can be used.

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

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

[cathode]

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

[Separator]

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and serves to provide a passage for lithium ions to move. As the separator, an olefin-based polymer such as polyethylene or polypropylene, glass fiber, or the like may be used in the form of a sheet, a multi-membrane, a microporous film, a woven fabric, or a non-woven fabric, but is not necessarily limited thereto. On the other hand, when a solid electrolyte such as a polymer (eg, an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally in the range of 0.01 to 10 μm, and the thickness is generally in the range of 5 to 300 μm.

[electrolyte]

As the electrolyte or electrolyte, carbonate, ester, ether, or ketone as a non-aqueous electrolyte (non-aqueous organic solvent) may be used alone or in combination of two or more, but is not necessarily limited thereto. For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n- such as ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3 -Dimethyl-2-imidazolidinone, methyl propionate, an aprotic organic solvent such as ethyl propionate may be used, but is not necessarily limited thereto.

A lithium salt may be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and as the lithium salt, a known lithium salt that is well soluble in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, imide, and the like, but is not necessarily limited thereto. In the (non-aqueous) electrolyte, for the purpose of improving charge/discharge characteristics and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, trihexaphosphate Amide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. are added. it might be If necessary, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart incombustibility, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

The lithium-sulfur battery of the present invention may be manufactured according to a conventional method in the art. For example, it can be prepared by putting a porous separator between the positive electrode and the negative electrode and introducing a non-aqueous electrolyte. The lithium-sulfur battery according to the present invention is not only applied to a battery cell used as a power source for a small device, but can be particularly suitably used as a unit cell for a battery module, which is a power source for a medium or large device. In this aspect, the present invention also provides a battery module including two or more of the lithium-sulfur batteries are electrically connected (series or parallel). Of course, the quantity of lithium-sulfur batteries included in the battery module may be variously adjusted in consideration of the use and capacity of the battery module.

Furthermore, the present invention provides a battery pack electrically connected to the battery module according to a conventional technique in the art. The battery module and the battery pack is a power tool (Power Tool); electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric truck; electric commercial vehicle; Alternatively, it may be used as a power source for any one or more medium or large devices among power storage systems, but is not limited thereto.

Hereinafter, preferred embodiments are presented to aid the understanding of the present invention, but these are merely illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, such changes and It goes without saying that the modifications fall within the scope of the appended claims.

[Example 1] Preparation of positive electrode active material using LD-CNT

First, a large-diameter carbon nanotube (LD-CNT, carbon structure) having a diameter of about 100 nm is supplied to the kiln, and then a CO ₂ /O ₂ mixed gas in which the mixing ratio of CO ₂ and O ₂ is 8: 2 by volume. (World Energies) was flowed at a rate of 100 cc/min and heat-treated at 700° C. for 30 minutes to prepare a cathode active material for a lithium-sulfur battery in which pores were formed on the surface of the LD-CNT.

[Example 2] Preparation of positive electrode active material using LD-CNT

A cathode active material for a lithium-sulfur battery in which pores were formed on the surface of the LD-CNT was prepared in the same manner as in Example 1, except that the heat treatment temperature was increased from 700 °C to 750 °C.

[Example 3] Preparation of a cathode active material using CNTs

In the same manner as in Example 1, except that a general carbon nanotube (CNT) having a diameter of about 20 nm was applied instead of a large-diameter carbon nanotube (LD-CNT) and heat-treated for 2 hours, the surface of the CNT A cathode active material for a lithium-sulfur battery in which pores were formed was prepared.

[Example 4] Preparation of a cathode active material using CNTs

In the same manner as in Example 1, except that a general carbon nanotube (CNT) having a diameter of about 20 nm was applied instead of a large-diameter carbon nanotube (LD-CNT) and heat-treated at a temperature of 750 ° C. A cathode active material for a lithium-sulfur battery in which pores were formed on the surface of was prepared.

[Comparative Example 1] Preparation of positive active material using LD-CNT

A cathode active material for a lithium-sulfur battery including a large-diameter carbon nanotube (LD-CNT) having a diameter of about 100 nm was prepared without supplying a CO ₂ /O ₂ mixed gas and heat treatment.

[Comparative Example 2] Preparation of a cathode active material using CNTs

A cathode active material for a lithium-sulfur battery including a general carbon nanotube (CNT) having a diameter of about 20 nm was prepared without supply of a CO ₂ /O ₂ mixed gas and heat treatment.

[Experimental Example 1] Evaluation of specific surface area and pore volume of positive active material

The specific surface area (BET surface area) and pore volume of the positive active materials prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were respectively measured, and the results are shown in Table 1 below.

BET surface area (m ² /g) Total pore volume(cm ³ /g) Example 1 29.5 0.20 Example 2 27.6 0.19 Example 3 217 1.56 Example 4 264 1.45 Comparative Example 1 17.9 0.1 Comparative Example 2 181 1.37

As shown in Table 1, in the case of a positive electrode active material using LD-CNT, Examples 1 and 2 in which the CO ₂ /O ₂ mixed gas supply and heat treatment process were performed, compared to Comparative Example 1 where the specific surface area and It was confirmed that all of the total pore volume increased. In addition, even in the case of a cathode active material using CNT, it was confirmed that Examples 3 and 4, in which the supply of the CO ₂ /O ₂ mixed gas and the heat treatment process were performed, increased both the specific surface area and the total pore volume compared to Comparative Example 2, which is not. could

1 is an SEM image (a) of an LD-CNT prepared according to an embodiment of the present invention and an SEM image (b) of an LD-CNT prepared according to a comparative example, wherein a of FIG. 1 corresponds to Example 1. and, b of FIG. 1 corresponds to Comparative Example 1. As shown in FIG. 1, the LD-CNT positive active material prepared according to the present invention (FIG. 1 a) is a LD-CNT positive active material (FIG. 1) without supply of a CO ₂ /O ₂ mixed gas and heat treatment. Unlike b), it was observed that pores were formed on the wall surface of the carbon nanotubes. In addition, the same result was shown even when the CNT positive electrode active material was used.

[Examples 5 to 8, Comparative Examples 3 to 4] Preparation of positive electrode for lithium-sulfur battery

The cathode active material (carbon structure) prepared in Examples 1 to 4 and Comparative Examples 1 and 2, respectively, and sulfur were mixed in a weight ratio of 7:3, and then a sulfur-carbon composite was prepared by a melt-diffusion method at 155°C. Then, the prepared sulfur-carbon composite, super-P as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 88:5:7 and dispersed in an NMP solvent to prepare a slurry, This was coated on an aluminum current collector (Al foil) to a thickness of 500 μm, and then dried in a vacuum oven at 120° C. for 13 hours to prepare a cathode for a lithium-sulfur battery.

[Examples 9 to 12, Comparative Examples 5 to 6] Preparation of lithium-sulfur batteries

After placing the prepared positive electrode to face the negative electrode (Li metal foil), a polyethylene separator was interposed therebetween, and then, an electrolyte solution in which LiFSI was dissolved at a concentration of 4 M in dimethyl ether solvent was injected to form a lithium-sulfur battery. prepared.

[Experimental Example 2] Evaluation of battery discharge capacity retention rate

The lithium-sulfur battery prepared in Example 12 (battery including the positive active material of Example 4) and Comparative Example 6 was repeatedly charged/discharged (charge: 0.1 C, discharge: 0.1 C) to increase the battery's discharge capacity retention rate was measured (discharged to 1.5 V), and the results are shown in Table 2 and FIG. 2 below (Mg content was analyzed by ICP).

1st discharge capacity (mAh/g) 2nd Discharge capacity (mAh/g) Retention (%) Example 12 1132 1052 93 Comparative Example 6 1080 975 90.2

2 is a graph showing the discharge capacity retention rate of lithium-sulfur batteries prepared according to an embodiment (Example 12) and Comparative Example (Comparative Example 6) of the present invention, as shown in FIG. 2, and Table 2 Likewise, it was confirmed that the lithium-sulfur battery of the present invention had a primary discharge capacity of about 50 mAh/g higher than that of the other lithium-sulfur battery.

[Experimental Example 3] Evaluation of Lithium Polysulfide Adsorption Degree of Battery

3 is a graph showing the degree of adsorption of lithium polysulfide in lithium-sulfur batteries prepared according to an embodiment (Example 12) and a comparative example (Comparative Example 6) of the present invention. The lower the intensity, the lower the concentration. do. As shown in FIG. 3 , the lithium-sulfur battery prepared according to the present invention had a higher degree of adsorption of lithium polysulfide than the non-lithium-sulfur battery.

Judging from the results of Experimental Examples 2 and 3 as described above, when the CO ₂ /O ₂ mixed gas is supplied and the heat treatment process is performed according to the present invention, the specific surface area and pore volume of the positive electrode active material are increased, It can be seen that the discharge capacity retention rate is improved by reducing the leakage of lithium polysulfide due to this effect.

Claims (9)

a) forming a carbon structure including a carbon-based compound; and
b) supplying a CO ₂ /O ₂ mixed gas to the formed carbon structure and performing heat treatment to form pores on the surface of the carbon structure; including,
The mixing ratio of the CO ₂ and O ₂ is 7 to 9: 1 to 3 as a volume ratio,
The carbon structure is a carbon nanotube,
When the specific surface area of the carbon nanotube having the pores is 27.6 to 29.5 m ² /g or 217 to 264 m ² /g, the specific surface area of the carbon nanotube having the pores is 27.6 to 29.5 m ² /g ^{Li- _ _} A method for producing a cathode active material for a sulfur battery. The method according to claim 1, wherein the pores have a diameter of 20 to 2,000 Å. delete delete The method according to claim 1, wherein the heat treatment is performed at a temperature of 600 to 850 °C for 10 minutes to 3 hours. As prepared by the method for producing a cathode active material for a lithium-sulfur battery of claim 1,
It includes a carbon structure in which pores are formed on the surface so that sulfur is supported,
The carbon structure in which the pores are formed is a carbon nanotube,
When the specific surface area of the carbon nanotube having the pores is 27.6 to 29.5 m ² /g or 217 to 264 m ² /g, the specific surface area of the carbon nanotube having the pores is 27.6 to 29.5 m ² /g ^{Li- _ _} A cathode active material for sulfur batteries. The positive active material for a lithium-sulfur battery according to claim 6, wherein the pores have a diameter of 20 to 2,000 Å. delete A lithium-sulfur battery comprising a positive electrode comprising the positive electrode active material for a lithium-sulfur battery of claim 6, a negative electrode, an electrolyte interposed between the positive electrode and the negative electrode, and a separator.

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