KR102328259B1 - A carbon -surfur complex, manufacturing method thereof and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is a porous carbon material; And in the sulfur-carbon composite in which sulfur is coated on at least a portion of the inside and the surface of the porous carbon material, the pore volume of the sulfur-carbon composite is 0.250 to 0.400 cm ³ /g, and the specific surface area of the sulfur-carbon composite is 18.5 to 30 m ² /g It relates to a sulfur-carbon composite and a method for producing the same.

Description

Sulfur-carbon composite, manufacturing method thereof, and lithium secondary battery comprising same

The present invention relates to a sulfur-carbon composite, a manufacturing method thereof, and a lithium secondary battery comprising the same.

Recently, interest in energy storage technology is increasing. Efforts for research and development of electrochemical devices are becoming more and more concrete as the field of application is expanded to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles.

Electrochemical devices are the field receiving the most attention in this respect, and among them, the development of rechargeable batteries capable of charging and discharging is the focus of interest. Research and development for the design of new electrodes and batteries is in progress.

Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s have a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. is gaining popularity as

In particular, a lithium-sulfur (Li-S) battery is a secondary battery in which a sulfur-based material having an SS bond (Sulfur-Sulfur bond) is used as a positive electrode active material and lithium metal is used as a negative electrode active material. Sulfur, the main material of the cathode active material, has the advantage of being very abundant in resources, non-toxic, and having a low weight per atom. In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1675 mAh/g-sulfur, and the theoretical energy density is 2,600 Wh/kg. FeS battery: 480 Wh/kg, Li-MnO ₂ battery: 1,000 Wh/kg, Na-S battery: 800 Wh/kg), it is the most promising battery among the batteries being developed so far.

During the discharging reaction of a lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode, and a reduction reaction of sulfur occurs at the cathode. Sulfur before discharging has a cyclic S ₈ structure. During the reduction reaction (discharge), the oxidation number of S decreases as the SS bond is broken, and during the oxidation reaction (charge), the oxidation number of S increases as the SS bond is re-formed. Reduction reactions are used to store and generate electrical energy. During this reaction, sulfur _{is converted from cyclic S 8} to lithium polysulfide having a linear structure (Lithium polysulfide, Li ₂ S _x , x = 8, 6, 4, 2) by a reduction reaction, and eventually this lithium polysulfide is completely When reduced, lithium sulfide (Li ₂ S) is finally produced. Unlike lithium ion batteries, the discharge behavior of lithium-sulfur batteries by the process of reduction to each lithium polysulfide is characterized in that the discharge voltage is displayed in stages.

This lithium-sulfur battery has a problem that the capacity does not reach the theoretical value and the cycle life is short due to the insulating properties of sulfur as the positive electrode active material and lithium sulfide (LiS) as the discharge product, and the dissolution of polysulfide, which is a charge/discharge intermediate product. there is Therefore, in order to improve the performance of the lithium-sulfur battery, various studies are being conducted to improve the reactivity and cycle stability of the sulfur anode.

The sulfur/carbon composite, which is a lithium-sulfur battery positive electrode active material, has a great influence on the reactivity and cycle stability of the positive electrode according to its shape, structure, specific surface area, pore volume, and the like. As the contact range between sulfur and carbon is maximized, and the specific surface area and pore volume are large, electrical conductivity and lithium ion conductivity are secured, so that high-performance lithium-sulfur battery operation can be expected.

Therefore, while satisfying the above conditions, there is a need to develop a process for manufacturing a sulfur/carbon composite that is inexpensive and can be mass-produced.

In this regard, the existing sulfur/carbon composite manufacturing process is followed by dry mixing of sulfur and carbon powder, followed by a liquid phase impregnation process of sulfur through heating. The particle size of each sulfur and carbon powder is tens to hundreds of micrometers, During manufacturing through simple mixing and heating, sulfur/carbon is non-uniformly distributed, and the specific surface area and pore volume are low, so there is room for improvement.

Korean Patent Publication No. 2015-0043407 "Composite material for lithium-sulfur batteries"

After conducting various studies, the present inventors have mixed sulfur pulverized to a nanometer size with carbon and then impregnated the sulfur with a liquid phase using microwaves, so that sulfur/carbon is uniformly distributed throughout the composite, and sulfur is carbon The present invention was completed by confirming the fact that the surface was evenly coated with a thin thickness.

Accordingly, an object of the present invention is to impregnate sulfur in a liquid phase using microwaves, to coat the sulfur evenly on the carbon surface with a thin thickness, and when used as an electrode, sulfur-carbon exhibiting improved initial discharge capacity and high rate capacity compared to the prior art To provide a composite and a method for preparing the same.

In order to achieve the above object, the present invention

In the sulfur-carbon composite in which sulfur is coated on at least a portion of the interior and surface of the porous carbon material, the pore volume of the sulfur-carbon composite is 0.250 to 0.400 cm ³ /g, and the specific surface area of the sulfur-carbon composite is 18.5 to 30 m ² /g, a sulfur-carbon complex.

In addition, the present invention comprises the steps of (a) mixing sulfur and a porous carbon material having a particle diameter of 1 nm to 1 μm;

(b) drying the mixed sulfur and porous carbon material; and

(c) applying microwaves to the dried sulfur and porous carbon material mixture; provides a method for producing a sulfur-carbon composite comprising a.

In addition, the present invention provides a positive electrode comprising the sulfur-carbon composite.

In addition, the present invention is the positive electrode; cathode; and an electrolyte; provides a lithium secondary battery comprising.

According to the present invention, sulfur is impregnated in liquid phase using microwaves, sulfur is uniformly coated on the carbon surface with a thin thickness to maintain the specific surface area of the composite, and while it is possible to suppress the elution of lithium polysulfide, It has the effect of being able to express improved initial discharge capacity and high rate capacity compared to the existing ones.

1 is a SEM photograph of a sulfur-carbon composite according to Examples and Comparative Examples of the present invention.
2 is a graph showing the results of measuring the pore sizes of sulfur-carbon composites according to Examples and Comparative Examples of the present invention.
3 is a graph showing the discharge capacity of the lithium secondary battery prepared with the sulfur-carbon composite of Examples and Comparative Examples of the present invention.
4 is a graph showing the lifespan characteristics of the lithium secondary battery prepared with the sulfur-carbon composite of Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms, and is not limited thereto.

In the drawings, in order to clearly explain the present invention, parts irrelevant to the description are omitted, and similar reference numerals are used for similar parts throughout the specification. In addition, sizes and relative sizes of components shown in the drawings are independent of actual scale, and may be reduced or exaggerated for clarity of description.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

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

A lithium-sulfur battery, one of the types of lithium secondary batteries, uses sulfur as a positive electrode active material and lithium metal as a negative electrode active material. During discharging of a lithium-sulfur battery, an oxidation reaction of lithium occurs at the negative electrode and a reduction reaction of sulfur occurs at the positive electrode. At this time, the reduced sulfur is combined with lithium ions moved from the negative electrode to be converted into lithium polysulfide and finally accompanied by a reaction to form lithium sulfide.

Lithium-sulfur batteries have a significantly higher theoretical energy density than conventional lithium secondary batteries, and sulfur used as a positive electrode active material is abundant in resources and is inexpensive, so it is in the spotlight as a next-generation battery due to the advantage of lowering the manufacturing cost of the battery. have.

Despite these advantages, it is difficult to realize all of the theoretical energy density in actual operation due to the low electrical conductivity and lithium ion conductivity of sulfur, which is a positive electrode active material.

In order to improve the electrical conductivity of sulfur, methods such as composite formation with conductive materials such as carbon and polymer, and coating are used. Among various methods, the sulfur-carbon composite is most used as a positive electrode active material because it is effective in improving the electrical conductivity of the positive electrode, but it is not yet sufficient in terms of charge/discharge capacity and efficiency. The capacity and efficiency of a lithium-sulfur battery may vary depending on the amount of lithium ions delivered to the positive electrode. Therefore, facilitating the transfer of lithium ions into the sulfur-carbon composite is important for high capacity and high efficiency of the battery.

Sulfur-Carbon Complex

Accordingly, the present invention provides a sulfur-carbon composite in which sulfur is thinly and evenly coated inside and on the surface of a porous carbon material in order to secure the effect of improving the reactivity between the sulfur-carbon composite and the electrolyte and the capacity and efficiency characteristics of a lithium secondary battery. The inside of the porous carbon material is meant to include the inside of the pores of the porous carbon material.

The sulfur-carbon composite of the present invention includes a porous carbon material; And at least a portion of the interior and surface of the porous carbon material is coated with sulfur.

The porous carbon material of the sulfur-carbon composite of the present invention provides a skeleton in which sulfur, which is a cathode active material, can be uniformly and stably immobilized, and supplements the electrical conductivity of sulfur so that the electrochemical reaction can proceed smoothly.

The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped or bulk-type, as long as it is conventionally used for lithium-sulfur batteries.

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

The porous carbon material particles may have a diameter of 100 nm to 50 μm.

The sulfur of the sulfur-carbon composite of the present invention is inorganic sulfur (S ₈ ), Li ₂ S _n (n ≥ 1), an organic sulfur compound, and a carbon-sulfur polymer [(C ₂ S _x ) _n , x=2.5 to 50, n ≥ 2] may be at least one selected from the group consisting of. Preferably, inorganic sulfur (S ₈ ) may be used.

In addition, the sulfur is located on the surface as well as inside the pores of the porous carbon material, and at this time, less than 100%, preferably 1 to 95%, more preferably 60 to 90% of the entire outer surface of the porous carbon material. can When the sulfur is within the above range on the surface of the porous carbon material, the maximum effect may be exhibited in terms of electron transport area and wettability of the electrolyte. Specifically, since sulfur is thinly and evenly impregnated on the surface of the porous carbon material in the above range, the electron transport contact area may be increased in the charge/discharge process. If the sulfur is located in 100% of the surface of the porous carbon material, the porous carbon material is completely covered with sulfur, so the wettability of the electrolyte is poor and the contact with the conductive material included in the electrode is poor, so it cannot receive electron transfer and participate in the reaction. it won't be possible

The sulfur-carbon composite may support a high content of sulfur due to pores of various sizes and three-dimensionally interconnected and regularly arranged pores in the structure. Due to this, even if soluble polysulfide is generated by the electrochemical reaction, if it can be located inside the sulfur-carbon composite, the three-dimensional entangled structure is maintained even during polysulfide elution, thereby suppressing the collapse of the anode structure. have. As a result, the lithium-sulfur battery including the sulfur-carbon composite has an advantage that high capacity can be implemented even at high loading. The sulfur loading of the sulfur-carbon composite according to the present invention may be 1 to 20 mg/cm ² .

The sulfur-carbon composite of the present invention may be coated on the surface or pores of the porous carbon material to a thickness of 1 to 10 nm by using sulfur particles having a particle diameter of 1 nm to 1 μm during manufacturing.

In the sulfur-carbon composite according to the present invention, the weight ratio of sulfur to the porous carbon material may be 7.5:2.5 to 4:6, preferably 7.5:2.5 to 6:4. If the content of sulfur is less than the weight ratio range, the amount of binder required for preparing the positive electrode slurry increases as the content of the porous carbon material increases. An increase in the amount of the binder added may eventually increase the sheet resistance of the electrode and act as an insulator to prevent electron pass, thereby degrading cell performance. Conversely, when the content of sulfur exceeds the above weight ratio range, sulfur aggregates with each other, and it is difficult to receive electrons, so it may be difficult to directly participate in the electrode reaction. do.

In general, the porous carbon material may be prepared by carbonizing precursors of various carbon materials, and the porous carbon material has pores having an average diameter in the range of about 100 nm to 50 μm therein.

However, in the sulfur-carbon composite of the present invention, sulfur is coated on some of the inner and outer surfaces of the porous carbon material, and specifically, since sulfur is coated inside the pores of the porous carbon material, the size of the pores of the porous carbon material changes will arise

In the case of the sulfur-carbon composite prepared by the conventional method, since the size of the sulfur particles used for manufacturing are large at the level of several tens of micrometers, even if these sulfur particles are coated inside the pores of the porous carbon material, the There was a problem that the sulfur particles could not easily enter the pores, and the sulfur particles blocked the entrance of the pores. Therefore, when measuring the specific surface area, pore size, and pore volume of the sulfur-carbon composite, there was a problem in that it became rather small.

However, when the sulfur-carbon composite is manufactured by the manufacturing method of the present invention, sulfur having a particle size of less than 1 micrometer is used to thinly and evenly coat the sulfur inside the pores of the porous carbon material. In addition, by applying microwaves to the mixture of sulfur and porous carbon material, it is possible to remove the sulfur particles blocking the entrance of the pores, and to enter into the pores to coat them thinly and evenly.

Therefore, in the sulfur-carbon composite of the present invention, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the pore volume of the sulfur-carbon composite may be 0.250 to 0.400 cm ³ /g, preferably 0.300 to 0.350 cm ³ /g.

In addition, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the specific surface area of the sulfur-carbon composite may be 18.5 to 30 m ² /g, preferably 19.5 to 30 m ² /g .

In addition, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the average pore size of the sulfur-carbon composite may be 55 to 100 nm.

When the sulfur-carbon composite of the present invention satisfies the above ranges of pore volume, specific surface area and average pore size, sulfur is thinly and evenly coated inside the pores of the porous carbon material, and when applied to an electrode, excellent discharge capacity and lifespan characteristics will have If the above range is not satisfied, the sulfur is hardly coated in the pores, or the sulfur has blocked the entrance of the pores.

Manufacturing method of sulfur-carbon complex

The sulfur-carbon composite of the present invention comprises the steps of (a) mixing sulfur and a porous carbon material having a particle diameter of 1 nm to 1 μm; (b) drying the mixed sulfur and porous carbon material; And (c) applying a microwave to the mixture of the dried sulfur and the porous carbon material; is prepared through.

First, the method for producing a sulfur-carbon composite of the present invention includes (a) mixing sulfur having a particle diameter of 1 nm to 1 μm with a porous carbon material.

In step (a), when sulfur and the porous carbon material are mixed, the weight ratio of sulfur and the porous carbon material may be 7.5:2.5 to 4:6, preferably 7.5:2.5 to 6:4. If the content of sulfur is less than the weight ratio range, the amount of binder required for preparing the positive electrode slurry increases as the content of the porous carbon material increases. An increase in the amount of the binder added may eventually increase the sheet resistance of the electrode and act as an insulator to prevent electron pass, thereby degrading cell performance. Conversely, when the content of sulfur exceeds the above weight ratio range, sulfur aggregates with each other, and it is difficult to receive electrons, so it may be difficult to directly participate in the electrode reaction. do.

The sulfur used in step (a) is sulfur having a particle diameter of 1 nm to 1 μm, and other features are the same as described above. In addition, the characteristics of the porous carbon material are the same as those discussed above.

Next, the method for producing the sulfur-carbon composite of the present invention includes (b) drying the mixed sulfur and the porous carbon material.

The drying method may be dried in an oven at 60 to 100° C. for 12 to 36 hours, and before drying, a process of removing a solvent or a ball for a ball mill used in mixing in step (a) may be performed.

Next, the method for producing the sulfur-carbon composite of the present invention includes the step (c) of applying microwaves to the mixture of the dried sulfur and the porous carbon material.

The microwave application in step (c) may be applied with an output of 500 to 2000 W, and the microwave application may be performed 2 to 10 times with a frequency of 2 to 10 seconds.

The method for producing the sulfur-carbon composite of the present invention, through the application of microwaves as described above, removes the sulfur particles blocking the pore inlets of the porous carbon material among the sulfur-carbon composites so that the sulfur is coated thinly and evenly throughout. have.

Therefore, in the sulfur-carbon composite prepared by the method for producing a sulfur-carbon composite of the present invention, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the pore volume of the sulfur-carbon composite is 0.250 to 0.400 cm ³ /g may be, preferably 0.300 to 0.350 cm ³ /g.

In addition, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the specific surface area of the sulfur-carbon composite may be 18.5 to 30 m ² /g, preferably 19.5 to 30 m ² /g .

In addition, as sulfur is thinly and evenly coated inside the pores of the porous carbon material, the average pore size of the sulfur-carbon composite may be 55 to 100 nm.

anode

The sulfur-carbon composite presented in the present invention can be preferably used as a cathode active material for a lithium secondary battery, particularly, a lithium-sulfur battery.

The positive electrode is manufactured by coating and drying a composition for forming a positive electrode active material layer on a positive electrode current collector.

Specifically, in order to impart additional conductivity to the prepared sulfur-carbon composite, a conductive material may be added to the positive electrode composition. The conductive material serves to allow electrons to smoothly move within the positive electrode, and there is no particular limitation as long as it has excellent conductivity and can provide a large surface area without causing chemical change in the battery, but is preferably carbon-based. use material.

As the carbon-based material, natural graphite, artificial graphite, expanded graphite, graphite such as graphene, active carbon, channel black, furnace black, thermal Carbon black such as black (Thermal black), contact black (Contact black), lamp black (Lamp black), acetylene black (Acetylene black); One selected from the group consisting of carbon nanostructures such as carbon fiber, carbon nanotube (CNT), fullerene, and combinations thereof may be used.

In addition to the carbon-based material, metallic fibers such as metal mesh according to the purpose; metallic powders such as copper (Cu), silver (Ag), nickel (Ni), and aluminum (Al); Alternatively, an organic conductive material such as a polyphenylene derivative can also be used. The conductive materials may be used alone or in combination.

In addition, in order to provide the positive electrode active material with adhesion to the current collector, a binder may be additionally included in the positive electrode composition. The binder should be well soluble in a solvent, and should not only form a conductive network between the positive electrode active material and the conductive material, but also have adequate impregnation property of the electrolyte.

The binder applicable to the present invention may be all binders known in the art, and specifically, a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE). ; a rubber-based binder including a styrene-butadiene rubber, an acrylonitrile-butydiene rubber, and a styrene-isoprene rubber; Cellulose binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; It may be one selected from the group consisting of a polyimide-based binder, a polyester-based binder, and a silane-based binder, or a mixture of two or more, or a copolymer, but is not limited thereto.

The content of the binder resin may be 0.5 to 30% by weight based on the total weight of the positive electrode for a lithium secondary battery, but is not limited thereto. If the content of the binder resin is less than 0.5% by weight, the physical properties of the positive electrode may be lowered, and the positive electrode active material and the conductive material may fall off, and if it exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced The battery capacity may be reduced.

The solvent for preparing the cathode composition for a lithium secondary battery in a slurry state must be easy to dry and can dissolve the binder well, but the cathode active material and the conductive material are most preferably maintained in a dispersed state without dissolving them. When the solvent dissolves the positive active material, the sulfur in the slurry has a high specific gravity (D = 2.07), so sulfur sinks in the slurry, causing sulfur to collect on the current collector during coating, causing problems in the conductive network and causing problems in battery operation. have.

The solvent according to the present invention may be water or an organic solvent, and the organic solvent is an organic solvent including at least one selected from the group consisting of dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol, and tetrahydrofuran. possible.

The positive electrode composition may be mixed in a conventional manner using a conventional mixer, such as a rate mixer, a high-speed shear mixer, a homo mixer, or the like.

The positive electrode composition may be applied to a current collector and vacuum dried to form a positive electrode for a lithium secondary battery. The slurry may be coated on the current collector to an appropriate thickness depending on the viscosity of the slurry and the thickness of the positive electrode to be formed, and preferably may be appropriately selected within the range of 10 to 300 μm.

At this time, the method of coating the slurry is not limited thereto, and for example, doctor blade coating, dip coating, gravure coating, slit die coating, spin coating ( spin coating), comma coating, bar coating, reverse roll coating, screen coating, cap coating, and the like.

The positive electrode current collector may be generally made to have a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium may be used, and preferably an aluminum current collector may be used. The positive electrode current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, or a non-woven body.

lithium secondary battery

As an embodiment of the present invention, the lithium secondary battery includes the above-described positive electrode; a negative electrode comprising lithium metal or a lithium alloy as an anode active material; a separator interposed between the anode and the cathode; and an electrolyte impregnated in the negative electrode, the positive electrode and the separator, and containing a lithium salt and an organic solvent. In addition, the lithium secondary battery may be a lithium-sulfur battery including a sulfur compound in the positive electrode active material in the positive electrode.

The negative electrode is a material capable ^{of reversibly intercalating or deintercalating lithium ions (Li +} ) as an anode active material, and a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions , lithium metal or lithium alloy may be used. The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy may be, for example, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn.

In addition, in the process of charging and discharging a lithium-sulfur battery, sulfur used as a positive electrode active material may be changed to an inactive material and may be attached to the surface of the lithium negative electrode. As such, inactive sulfur refers to sulfur in a state in which sulfur can no longer participate in the electrochemical reaction of the positive electrode through various electrochemical or chemical reactions. There is also the advantage of acting as a layer). Accordingly, it is also possible to use lithium metal and an inert sulfur formed on the lithium metal, for example lithium sulfide, as the negative electrode.

The negative electrode of the present invention may further include a pretreatment layer made of a lithium ion conductive material and a lithium metal protective layer formed on the pretreatment layer in addition to the negative electrode active material.

The separator interposed between the positive electrode and the negative electrode separates or insulates the positive electrode and the negative electrode from each other, and enables the transport of lithium ions between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. The separator may be an independent member such as a thin film or film as an insulator having high ion permeability and mechanical strength, or may be a coating layer added to the anode and/or cathode. In addition, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally preferably 5 to 300 μm, and as such a separator, a glass electrolyte, a polymer electrolyte, or a ceramic electrolyte may be used. For example, a sheet, nonwoven fabric, kraft paper, etc. made of an olefin-based polymer such as chemical-resistant and hydrophobic polypropylene, glass fiber, or polyethylene is used. Representative examples currently on the market include Celgard series (Celgard ^R 2400, 2300 manufactured by Hoechest Celanese Corp.), polypropylene separator (manufactured by Ube Industries Ltd. or Pall RAI), and polyethylene series (Tonen or Entek).

The solid electrolyte separator may contain less than about 20% by weight of the non-aqueous organic solvent, and in this case, an appropriate gelling agent may be further included to reduce the fluidity of the organic solvent. Representative examples of such a gel-forming compound include polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and the like.

The electrolyte impregnated in the negative electrode, the positive electrode and the separator is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and an electrolyte. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte are used.

The lithium salt of the present invention is a material readily soluble in a non-aqueous organic solvent, for example, LiSCN, LiCl, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiClO ₄ , LiAlCl ₄ , Li(Ph) ₄ , LiC(CF ₃ SO ₂ ) ₃ , LiN(FSO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C _{2 )} F ₅ SO ₂ ) ₂ , LiN(SFO ₂ ) ₂ , LiN(CF ₃ CF ₂ SO ₂ ) ₂ , lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, lithium imide, and combinations thereof One or more of them may be included.

The concentration of the lithium salt varies from 0.2 to 2 M, depending on several factors such as the exact composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the operating temperature and other factors known in the art of lithium batteries, Specifically, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. If the amount is less than 0.2 M, the conductivity of the electrolyte may be lowered and the electrolyte performance may be deteriorated, and if used in excess of 2 M, the viscosity of the electrolyte may increase and ^{the mobility of lithium ions (Li +} ) may be reduced.

The non-aqueous organic solvent should dissolve lithium salt well, and the non-aqueous organic solvent of the present invention includes, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di ethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trime Aprotic, such as oxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate An organic solvent may be used, and the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ionic dissociation. A polymer comprising a group and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ Nitrides, halides, sulfates, etc. of Li such as SiO ₄ -LiI-LiOH, Li ₃ PO4-Li ₂ S-SiS _{2 may be used.}

In the electrolyte of the present invention, for the purpose of improving charge/discharge characteristics and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-ethylene) carbonate), propene sultone (PRS), fluoro-propylene carbonate (FPC), etc. can be further included.

The electrolyte may be used as a liquid electrolyte or in the form of a solid electrolyte separator. When used as a liquid electrolyte, a separator made of porous glass, plastic, ceramic, polymer, or the like is further included as a physical separator having a function of physically separating the electrodes.

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

[Example]

Preparation of Sulfur-Carbon Complex

[Example 1]

In a 125 mL container, _{200 g of 5 mm diameter ZrO 2} balls, 7.8 g of sulfur, and 30 g of ethanol were put, and ball milled at 200 rpm for 3 days to grind into nano-sized sulfur particles. Thereafter, 3 g of carbon nanotubes were added to a container containing the pulverized sulfur particles, ZrO ₂ balls, and ethanol, and ball milled at 200 rpm for 3 hours to mix sulfur and carbon. The mixture of sulfur and carbon was filtered _{to remove ethanol and ZrO 2} balls, and then dried in an oven at 80° C. for 24 hours. Thereafter, 1000W microwave (BP-110, Microwave Research and Applications) was applied to the dried mixture of sulfur and carbon three times for 3 seconds to prepare a sulfur-carbon composite.

[Comparative Example 1]

In a 1L container, _{270 g of ZrO 2} balls with a diameter of 5 mm, 23.4 g of sulfur, and 7 g of carbon nanotubes were put and ball milled at 200 rpm for 3 hours to mix sulfur and carbon. Thereafter, the mixture was heated in an oven at 155° C. for 30 minutes to prepare a sulfur-carbon composite.

Experimental Example 1: Evaluation of composite properties

(SEM analysis result)

The sulfur-carbon composites prepared in Example 1 and Comparative Example 1 were photographed with a scanning electron microscope (SEM, S-4800, HITACHI), which is shown in FIG. 1 .

As shown in FIG. 1 , the sulfur-carbon composites of Examples 1 and 2 were thinly and uniformly coated with sulfur at a level of several nm on the surface of the carbon nanotubes, whereas the sulfur-carbon composites of Comparative Examples 1 and 2 were carbon nanotubes. It was found that 30 to 40 nm or more of sulfur was coated on the surface of the tube.

(Comparison of pore structure)

The pore size, specific surface area and pore volume of the sulfur-carbon composites prepared in Example 1 and Comparative Example 1 were measured using nitrogen adsorption equipment (BELSorp, BEL), and are shown in Table 1 and FIG. 2 .

Specific surface area (m ² /g) Pore volume (cm ³ /g) mean pore (nm) Comparative Example 1 18.01 0.235 52.3 Example 1 19.71 0.310 62.8

Through the analysis of Table 1 and FIG. 2, it was found that the specific surface area, pore volume, and average pore volume of the sulfur-carbon composite prepared in Example 1 all increased.

Experimental Example 2: Battery physical property evaluation

(Manufacture of battery)

The sulfur-carbon composite prepared in Example 1 and Comparative Example 1: Binder (LiPAA/PVA mixed at 6.5:0.5): Conductive material (VGCF) was mixed in a weight ratio of 88:7:5 to prepare a slurry, An electrode was prepared by coating the current collector of 20 μm thick aluminum foil.

A coin cell was manufactured using the prepared electrode as a positive electrode and lithium metal as a negative electrode. In this case, as the coin cell, an electrolyte prepared with 2-Me-THF/DOL/DME (1:1:1), LiN(CF ₃ SO ₂ ) ₂ (LiTFSI) 1M, and LiNO _{3 0.1M was used.} For the 2-Me-THF/DOL/DME, 2-methyl tetrahydrofuran, dioxolane and dimethyl ether were used as solvents, respectively.

For the prepared coin cell, capacitances from 1.5 to 2.8 V were measured and shown in FIG. 3 and Table 2.

division Discharge capacity [mAh/g] Example 1 1,209 Comparative Example 1 1,144

3 and Table 2, in the case of Comparative Example 1 and Example 1 having the same sulfur:carbon ratio, it was found that the initial discharge capacity of Example 1 was improved. In addition, the prepared coin cell is charged at 0.1C rate CC, discharged at 0.1C rate CC 2.5 times, and then 0.2C charge/0.2C discharge is repeated 3 times, and then 0.3C charge/0.5C discharge is performed. The cycle was repeated 30 times to measure the charge/discharge efficiency. (CC: Constant Current)

The result can be confirmed through FIG. 4, and it can be seen that the lifespan characteristic of Example 1 is improved compared to Comparative Example 1.

Claims (17)

porous carbon material; and
In the sulfur-carbon composite in which sulfur is coated on at least a portion of the inside and the surface of the porous carbon material,
The sulfur-carbon composite has a pore volume of 0.250 to 0.400 cm ³ /g,
The specific surface area of the sulfur-carbon composite is 18.5 to 30 m ² /g, the sulfur-carbon composite. According to claim 1,
The sulfur-carbon composite has a pore volume of 0.300 to 0.350 cm ³ /g,
The sulfur-carbon composite has a specific surface area of 19.5 to 30 m ² /g. According to claim 1,
The pore size of the sulfur-carbon composite has an average pore in the range of 55nm to 100nm, sulfur-carbon composite. According to claim 1,
The sulfur is coated to a thickness of 1 to 10 nm, sulfur-carbon composite. According to claim 1,
The diameter of the porous carbon material is 100nm to 50㎛, sulfur-carbon composite. According to claim 1,
In the sulfur-carbon composite, sulfur and the porous carbon material are included in a weight ratio of 7.5:2.5 to 4:6, the sulfur-carbon composite. According to claim 1,
The porous carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotubes, carbon fibers and activated carbon, sulfur-carbon composite. A positive electrode comprising the sulfur-carbon composite of any one of claims 1 to 7. (a) mixing sulfur and a porous carbon material having a particle diameter of 1 nm to 1 μm;
(b) drying the mixed sulfur and porous carbon material; and
(c) applying a microwave to a mixture of the dried sulfur and porous carbon material;
The method for producing the sulfur-carbon composite of claim 1, wherein the microwave application of step (c) is applied 2 to 10 times at a frequency of 2 to 10 seconds with an output of 500 to 2000W. 10. The method of claim 9,
The porous carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotubes, carbon fibers, and activated carbon, a method for producing a sulfur-carbon composite. 10. The method of claim 9,
The drying of step (b) is drying in an oven at 60 to 100° C. for 12 to 36 hours, a method for producing a sulfur-carbon composite. delete delete 10. The method of claim 9,
The sulfur-carbon composite has a pore volume of 0.250 to 0.400 cm ³ /g,
The specific surface area of the sulfur-carbon composite is 18.5 to 30 m ² /g,
The pore size of the sulfur-carbon composite has an average pore size in the range of 55 to 100 nm, the method for producing a sulfur-carbon composite. 10. The method of claim 9,
In the sulfur-carbon composite, sulfur and the porous carbon material are included in a weight ratio of 7.5:2.5 to 4:6, a method for producing a sulfur-carbon composite. The positive electrode of claim 8; cathode; and an electrolyte; and a lithium secondary battery. 17. The method of claim 16,
The positive electrode active material in the positive electrode includes a sulfur compound, a lithium secondary battery.

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