KR20190087864A - A manufacturing method of sulfur-selenium-carbon complex, a cathode for lithium secondary battery comprising the sulfur-selenium-carbon complex manufactured by the same, and lithium sulfur-selenium battery comprising the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a sulfur-selenium-carbon complex. The method comprises steps of: (1) mixing selenium and carbon material and heat treating the same with microwave to form a selenium-carbon complex; and (2) mixing sulfur with the formed selenium-carbon complex and heat-treating the same with microwave to form the sulfur-selenium-carbon complex, wherein a heat treatment of the step (1) is performed at a higher temperature than a heat treatment of the step (2). The sulfur-selenium-carbon complex according to the present invention has an effect of improving electrical conductivity of a battery and alleviating overvoltage during a discharge process.

Description

TECHNICAL FIELD The present invention relates to a method for producing a sulfur-selenium-carbon composite material, a lithium-sulfur-selenium-carbon composite material containing the sulfur-selenium-carbon composite material and a lithium sulfur- CARBON COMPLEX, A CATHODE FOR LITHIUM SECONDARY BATTERY COMPRISING THE SULFUR-SELENIUM-CARBON COMPLEX MANUFACTURED BY THE SAME, AND LITHIUM SULFUR-SELENIUM BATTERY COMPRISING THE SAME}

The present invention relates to a process for producing a sulfur-selenium-carbon composite material, a cathode for a lithium secondary battery comprising the sulfur-selenium-carbon composite material produced by the method, and a lithium sulfur-selenium battery including the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified.

Electrochemical devices have attracted the greatest attention in this respect. Among them, the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve capacity density and energy efficiency in developing such batteries, Research and development on the design of new electrodes and batteries are underway.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution .

In particular, a lithium-sulfur (Li-S) battery is a secondary battery in which a sulfur-based material having a sulfur-sulfur bond is used as a cathode active material and lithium metal is used as an anode active material. Sulfur, the main material of the cathode active material, is very rich in resources, has no toxicity, and has a low atomic weight. The theoretical energy density of the lithium-sulfur battery is 1,675 mAh / g-sulfur and the theoretical energy density is 2,600 Wh / kg. The theoretical energy density (Ni-MH battery: 450 Wh / kg, , Which is the most promising battery ever developed because it is much higher than that of Li-FeS battery: 480Wh / kg, Li-MnO ₂ battery: 1,000Wh / kg, Na-S battery: 800Wh / kg.

During the discharge reaction of the lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode and a sulfur reduction reaction occurs at the cathode. Sulfur before discharging has an annular S ₈ structure. When the SS bond is cut off during the reduction reaction (discharging), the oxidation number of S is decreased, and the SS bond is formed again in the oxidation reaction (charging) The reduction reaction is used to store and generate electrical energy. During this reaction, the sulfur is converted to a linear polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) by the reduction reaction at the cyclic S ₈ , When it is reduced, lithium sulfide (Li ₂ S) is finally produced. The discharge behavior of the lithium-sulfur battery due to the reduction process with each lithium polysulfide characterizes the discharge voltage stepwise unlike the lithium ion battery.

However, during the discharge of the lithium-sulfur battery, lithium polysulfide (Li ₂ S _x , x = 2 to 8) dissolves in the electrolyte and diffuses into the negative electrode to cause various side reactions and to decrease the capacity of sulfur participating in the electrochemical reaction . In addition, during the charging process, the lithium polysulfide causes a shuttle reaction, thereby significantly reducing charge and discharge efficiency.

In addition, sulfur has an electric conductivity of 5 × 10 ^-30 S / cm, which is close to non-conducting, and therefore there is a problem that electrons generated by the electrochemical reaction are difficult to migrate. Therefore, it has been necessary to use an electrically conductive material such as carbon that can provide a smooth electrochemical reaction site. In this case, when the conductive material and sulfur are used in a simple mixture, the sulfur is leaked out to the electrolyte in the oxidation-reduction reaction and the battery life is deteriorated. Also, when the appropriate electrolyte is not selected, lithium polysulfide There is a problem that they are no longer able to participate in the electrochemical reaction.

Therefore, in order to solve the above problem, a method of adding an additive having a property of adsorbing sulfur has been proposed, but this has caused a deterioration problem, and a side reaction of an additional battery has newly occurred. Further, a method of adding metal chalcogenide, alumina or the like or coating the surface with oxycarbonate or the like has been proposed to retard the outflow of the cathode active material, that is, sulfur, There is a problem that the amount of sulfur (i.e., the amount of loading) is limited.

Thus, new techniques are needed to reduce the flux of sulfur to the electrolyte and to increase the electrical conductivity of the electrode containing sulfur.

Korean Patent Laid-Open No. 10-2015-0048544 (May 2015.05.07), "Cathode active material, a method for producing the same, and a lithium secondary battery comprising the same" Japanese Patent Laid-Open No. 1996-250119 (Sep. 28, 1996), "Lithium secondary battery"

In the present invention, after conducting various studies, a new structure of a cathode active material, which is obtained by adding selenium (Se) to a sulfur-carbon composite instead of an electrically non-conductive sulfur, is applied to a lithium secondary battery. As a result, And that the overvoltage is improved during the discharge process, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a method for producing a sulfur-selenium-carbon composite for a lithium sulfur-selenium battery improved in electric conductivity.

It is another object of the present invention to provide a lithium sulfur-selenium battery having a positive electrode including the composite and having improved battery performance.

In order to achieve the above object,

In a method for producing a sulfur-selenium-carbon composite,

The above-

(1) mixing selenium and carbon materials, and heat-treating the selenium and carbon materials by microwaves to form a selenium-carbon composite; And

(2) mixing the sulfur-containing selenium-carbon composite with the sulfur and heat-treating the selenium-carbon composite by microwave to form a sulfur-selenium-carbon composite;

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Wherein the heat treatment in the step (1) is performed at a temperature higher than the heat treatment in the step (2).

One embodiment of the present invention is that the heat treatment of step (1) is carried out at a temperature of 250 to 500 ° C.

In one embodiment of the present invention, the heat treatment in the step (2) is carried out at a temperature of 200 to 400 ° C.

One embodiment of the present invention is that the mixing in step (1) is carried out at a weight ratio of selenium and carbonaceous material of 1: 1 to 1: 5.

One embodiment of the present invention is that the mixing in step (2) is carried out in a weight ratio of sulfur and selenium-carbon composite of 6: 4 to 8: 2.

One embodiment of the present invention is that the heat treatment in the step (1) is performed for 5 to 20 seconds.

One embodiment of the present invention is that the heat treatment is performed for 3 to 10 seconds in the step (2).

In one embodiment of the present invention, the output of the microwave is 700 to 1000 W.

In one embodiment of the present invention, the frequency of the microwave is 2.44 to 2.46 GHz.

In one embodiment of the present invention, the sulfur-selenium-carbon composite comprises 1 to 10 parts by weight of selenium relative to 100 parts by weight of the total sulfur-selenium-carbon composite.

In one embodiment of the present invention, the carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotube, carbon fiber, and activated carbon.

The present invention also provides a positive electrode for a lithium sulfur-selenium battery comprising a sulfur-selenium-carbon composite produced by the above-described production method.

The sulfur-selenium-carbon composite according to the present invention further includes selenium which is superior in electric conductivity to the sulfur-carbon composite used as a cathode active material for a conventional lithium-sulfur battery, thereby improving the electric conductivity of the battery, There is an effect to improve.

The lithium sulfur-selenium battery having the anode containing the sulfur-selenium-carbon composite has improved electrical conductivity, enabling a high-capacity battery to be realized, and sulfur can be stably applied by high loading, and the charging and discharging efficiency of the battery is high The life characteristic is improved.

1 is a SEM photograph of a selenium-carbon composite and a sulfur-selenium-carbon composite according to an embodiment of the present invention.
FIG. 2 is a schematic view of a process for producing a sulfur-selenium-carbon composite according to an embodiment of the present invention.
3 is a graph showing a discharge capacity of a lithium sulfur-selenium battery according to Examples and Comparative Examples of the present invention.
4 is a graph showing lifetime characteristics of a lithium sulfur-selenium battery according to Examples and Comparative Examples of the present invention.
5 is a graph showing a discharge capacity of a lithium sulfur-selenium battery according to 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 skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the same reference numerals are used for similar parts throughout the specification. In addition, the size and relative size of the components shown in the figures are independent of the actual scale and may be reduced or exaggerated for clarity of description.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As used herein, the term " composite " refers to a material that combines two or more materials to form a physically and chemically distinct phase while exhibiting a more effective function.

The lithium-sulfur battery uses sulfur as the cathode active material and lithium metal as the anode active material.

At the discharge of the lithium-sulfur battery, the oxidation reaction of lithium occurs at the cathode and the reduction reaction of sulfur occurs at the anode. At this time, the reduced sulfur is converted to lithium polysulfide by binding with lithium ions that have been moved from the cathode, and finally involves a reaction to form lithium sulfide.

The lithium-sulfur battery has a much higher theoretical energy density than the conventional lithium secondary battery, and the sulfur used as the cathode active material is inexpensive because of its abundant resources, so it can be used as a next-generation battery have.

Despite these advantages, it is difficult to realize all the theoretical energy densities in actual operation due to the low electric conductivity and the lithium ion conductivity of the cathode active material sulfur.

In order to improve the electrical conductivity of sulfur, a method of forming a composite with a conductive material such as carbon, a polymer, and coating is used. Among the various methods, the sulfur-carbon composite is most widely used as a cathode active material because it is effective in improving the electric conductivity of the anode, but it is still insufficient in charge, discharge capacity and efficiency. Therefore, it is important to improve the electric conductivity of the battery to increase the capacity and high efficiency of the battery.

Method for producing sulfur-selenium-carbon composites

The sulfur-selenium-carbon composites of the present invention

(1) mixing selenium and carbon materials, and heat-treating the selenium and carbon materials by microwaves to form a selenium-carbon composite; And

(2) mixing the sulfur-containing selenium-carbon composite with the sulfur and heat-treating the selenium-carbon composite by microwave to form a sulfur-selenium-carbon composite;

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Wherein the heat treatment of step (1) is carried out at a temperature higher than the heat treatment of step (2).

First, the method for producing a sulfur-selenium-carbon composite of the present invention includes a step (1) of mixing selenium and a carbonaceous material.

The mixing of the selenium and the carbonaceous material can be carried out through a general ball mill process or the like in which the powders are mixed, but the present invention is not limited thereto.

When mixing the selenium and the carbonaceous material in the step (1), the weight ratio of selenium to carbonaceous material may be 1: 1 to 1: 5, preferably 15:30 to 7:30. If the content of selenium is less than the above range, the improvement of the electrical conductivity of the battery may be insignificant. If the content of selenium exceeds the above range, the unit weight of selenium is higher than that of sulfur, Adjust accordingly.

According to one embodiment of the present invention, selenium may be contained in an amount of 1 to 10 parts by weight, preferably 7 to 10 parts by weight, relative to 100 parts by weight of the sulfur-selenium-carbon composite as a whole.

In the case of a sulfur-carbon composite used as a cathode active material of a conventional lithium-sulfur battery, the electric conductivity of sulfur is 5 × 10 ^-30 S / cm, which is close to that of an insulator, , It has been necessary to use an electrically conductive material such as carbon which can provide a smooth electrochemical reaction site.

The carbon material mixed in this step provides a skeleton capable of uniformly and stably immobilizing sulfur, which is a cathode active material, and improves the electrical conductivity of sulfur, so that the electrochemical reaction proceeds smoothly.

The carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulky, and may be porous or have a high specific surface area, as long as it is commonly used in the art. For example, the 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 wall carbon nanotubes (SWCNTs) and multiwall carbon nanotubes (MWCNTs); Carbon fibers such as graphite nanofiber (GNF), carbon nanofiber (CNF), and activated carbon fiber (ACF); And activated carbon, but is not limited thereto. The carbon material particles having a diameter of 100 nm to 50 탆 may be used.

The selenium (Se) according to the present invention belongs to the group 16 on the periodic table in which oxygen and sulfur belong, but the electron conductivity is higher than that of sulfur because it has electrons in the d orbitals. Therefore, when the selenium is added to the conventional sulfur-carbon composite material used as the cathode active material, the electric conductivity is improved and the battery can be driven even when the content of the carbonaceous material in the cathode active material is decreased. Further, there is an effect that the discharge capacity of the battery including the same is increased and the overvoltage of the battery is improved even in the high-rate discharge period, so that the battery can be driven.

Thereafter, a mixture of selenium and carbonaceous material can be irradiated with microwaves and subjected to heat treatment to form a selenium-carbon composite.

At this time, since the melting point of selenium is 220 ° C, the heat treatment may be performed at a temperature of 250 to 500 ° C higher than the melting point of selenium so that the selenium is uniformly carried on the carbonaceous material. If the selenium is not melted and can not be uniformly supported on the carbon material, the effect of improving the electrical conductivity to be obtained by introducing selenium may be insufficient. Since selenium itself may be difficult to vaporize and form a complex with a carbonaceous agent, it is appropriately controlled within the above range.

According to one embodiment of the present invention, the microwave has a frequency of 2.44 to 2.46 GHz, preferably 2.45 GHz, and can have an output of 700 to 1000 W. [

If the frequency of the microwave is less than 2.44 GHz or the output is less than 700 W, the heating effect may be insufficient and the heat treatment may not be performed properly. If the frequency exceeds 2.46 GHz or the output exceeds 1000 W, The rate is excessively excessive and the heat treatment may occur excessively to cause a structural change or side reaction of the cathode active material, so that it is appropriately adjusted in the above range. Since the heat treatment using the microwave is proportional to the output of the microwave and the irradiation time, the irradiation time can be appropriately selected according to the output of the microwave.

According to one embodiment of the present invention, the irradiation of the microwave of step (1) may be performed for a time of 5 to 20 seconds.

And then mixing the sulfur and the selenium-carbon composite prepared in step (1).

The mixing of the sulfur and the selenium-carbon composite may be performed through a general ball mill process or the like in which the powders are mixed, but the present invention is not limited thereto.

At this time, the weight ratio of the sulfur and the selenium-carbon composite may be 6: 4 to 8: 2, preferably 6.3: 3.7 to 7: 3. If the content of sulfur is less than the above-mentioned weight ratio range, the energy density is lowered, and as the content of the carbonaceous material is increased, the amount of the binder required for preparing the cathode slurry is increased. Such an increase in the amount of the binder may increase the sheet resistance of the electrode and may act as an insulator to prevent electron transfer, thereby deteriorating the cell performance. On the contrary, when the content of sulfur exceeds the above-mentioned weight ratio range, overvoltage may occur and battery operation may be difficult, and sulfur may cause self-agglomeration phenomenon and it may be difficult to directly participate in electrode reaction due to difficulty in receiving electrons. .

The mixed selenium-carbon composite material and the sulfur mixture may be subjected to a heat treatment by irradiation with microwaves to form a sulfur-selenium-carbon composite material.

The heat treatment in step (2) may be carried out at a temperature of 200 to 400 ° C higher than the melting point of sulfur so that sulfur can be well supported on the selenium-carbon composite. If the heat treatment is performed at a temperature lower than the above temperature, the sulfur can not be melted and can not be uniformly supported on the selenium-carbon composite. When the heat treatment is performed in excess of the above temperature, the sulfur vaporizes and the selenium-carbon composite and the sulfur- It may be difficult to form it, so it is appropriately adjusted in the above range.

However, the heat treatment according to the present invention is characterized in that the temperature is higher in step (1) than in step (2). If step (2) is subjected to a heat treatment at a temperature higher than that of step (1), sulfur having a melting point lower than that of selenium can not vaporize to form a sulfur-selenium-carbon composite.

In addition, since the sulfur on the conventional sulfur-carbon composite material is evaporated and disappears when the sulfur-carbon composite is first formed as the step (1) to carry selenium and the selenium is mixed and heat-treated, The selenium-carbon composite may be formed first using an overbased material, and then the sulfur may be mixed to form a sulfur-selenium-carbon composite.

The heat treatment in the step (2) may use a microwave having the above-mentioned frequency and power range, and according to an embodiment of the present invention, the examination of the microwave in the step (2) is performed for a time of 3 to 10 seconds .

Sulfur of the sulfur-selenium-carbon composite of the present invention is a mixture of inorganic sulfur (S ₈ ), Li ₂ S _n (n ≥ 1), organic sulfur compound and carbon-sulfur polymer [(C ₂ S _x ) _n , x = , n > = 2]. Preferably, inorganic sulfur (S ₈ ) can be used.

Anode for lithium sulfur-selenium battery

The present invention provides a cathode for a lithium sulfur-selenium battery comprising a sulfur-selenium-carbon composite produced by the above-described method as a cathode active material. Specifically, the cathode for a lithium sulfur-selenium battery according to the present invention may include a sulfur-selenium-carbon composite as a cathode active material for a lithium sulfur-selenium battery, a binder, and a conductive material.

The anode may be prepared by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a cathode active material, and then coating (coating) the mixture on a current collector of a metal material, have.

Specifically, in order to impart additional conductivity to the prepared cathode active material, a conductive material may be added to the cathode active material. The conductive material plays a role in allowing electrons to move smoothly in the anode. The conductive material is not particularly limited as long as the conductive material does not cause a chemical change in the battery and can provide a large surface area. Materials are used.

Examples of the carbon-based material include natural graphite, artificial graphite, expanded graphite, graphite such as Graphene, active carbon, channel black, furnace black, Carbon black such as black, thermal black, contact black, lamp black, and acetylene black; A carbon nano structure such as a carbon fiber, a carbon nanotube (CNT), and a fullerene, and a combination thereof may be used.

In addition to the carbon-based materials, metallic fibers such as metal mesh may be used depending on the purpose. Metallic powder such as copper (Cu), silver (Ag), nickel (Ni) and aluminum (Al); Or 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 an adhesive force to the collector, a binder may be further included in the positive electrode composition. The binder must be well dissolved in a solvent, and it should not only constitute a conductive network between the cathode active material and the conductive material, but also have an ability to impregnate the electrolyte appropriately.

The binder applicable to the present invention may be any binder known in the art and specifically includes a fluororesin binder containing polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) ; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulosic binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Polyalcohol-based binders; Polyolefin binders including polyethylene and polypropylene; But are not limited to, polyimide-based binders, polyester-based binders, and silane-based binders, or a mixture or copolymer of two or more thereof.

The content of the binder resin may be 0.5-30 wt% based on the total weight of the cathode for lithium-sulfur 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 deteriorate and the positive electrode active material and the conductive material may fall off. When the amount of the binder resin is more than 30% by weight, the ratio of the active material and the conductive material is relatively decreased The battery capacity can be reduced.

It is most preferable that the solvent for preparing the cathode composition for a lithium sulfur-selenium battery in a slurry state should be easy to dry and can dissolve the binder well, while maintaining the cathode active material and the conductive material in a dispersed state without dissolving. When the solvent dissolves the cathode active material, the specific gravity (D = 2.07) of the sulfur in the slurry is high, so that the sulfur is submerged in the slurry, which causes sulfur in the current collector in the coating, have.

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

The mixing of the cathode composition may be carried out by a conventional method using a conventional mixer such as a latex mixer, a high-speed shear mixer, a homomixer, and the like.

The positive electrode composition may be applied to a current collector and vacuum dried to form a positive electrode for a lithium sulfur-selenium battery. The slurry may be coated on the current collector with an appropriate thickness according to the viscosity of the slurry and the thickness of the anode to be formed, and may be suitably selected within the range of 10 to 300 mu m.

The slurry may be coated by a method such as 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 cathode current collector generally has a thickness of 3 to 500 탆, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and an aluminum current collector can be preferably used. Such a positive electrode current collector may have various forms such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

Lithium sulfur-selenium battery

In one embodiment of the present invention, the lithium sulfur-selenium battery includes the positive electrode for the lithium sulfur-selenium battery described above; A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material; A separator interposed between the anode and the cathode; And an electrolyte impregnated with the negative electrode, the positive electrode and the separator, and including a lithium salt and an organic solvent.

The negative electrode is a negative active material that can reversibly intercalate or deintercalate lithium ions (Li ⁺ ), a material capable of reversibly reacting with lithium ions to form a lithium-containing compound , A lithium metal or a lithium alloy can 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 reacting with the lithium ion to form a lithium-containing compound reversibly 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.

Further, in the course of charging / discharging the lithium sulfur-selenium battery, the sulfur used as the cathode active material is changed to an inactive material and can be attached to the surface of the lithium anode. Inactive sulfur is sulfur in which sulfur can not participate in the electrochemical reaction of the anode after various electrochemical or chemical reactions. Inactive sulfur formed on the surface of the lithium anode is a protective film of the lithium anode layer as well. Therefore, a lithium metal and an inert sulfur formed on the lithium metal, such as lithium sulfide, may be used as the cathode.

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

The separator interposed between the anode and the cathode separates or insulates the anode and the cathode from each other and allows transport of lithium ions between the anode and the cathode, and may be made of a porous nonconductive or insulating material. Such a separator may be an independent member such as a thin film or a film as an insulator having high ion permeability and mechanical strength, or may be a coating layer added to the anode and / or the cathode. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separation membrane.

The separator preferably has a pore diameter of 0.01 to 10 mu m and a thickness of 5 to 300 mu m. The separator may be a glass electrolyte, a polymer electrolyte, a ceramic electrolyte, or the like. For example, olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity, sheets or non-woven fabrics made of glass fibers or polyethylene, kraft paper, or the like are used. Representative examples currently on the market include the Celgard ^R 2400 (2300 Hoechest Celanese Corp.), polypropylene separator (Ube Industries Ltd. or Pall RAI), and polyethylene (Tonen or Entek).

The solid electrolyte separation membrane may contain less than about 20% by weight of a non-aqueous organic solvent, in which case it may further comprise a suitable gelling agent to reduce the fluidity of the organic solvent. Representative examples of such gel-forming compounds include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

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

The lithium salt of the present invention can be dissolved 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 , chloroborane lithium, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide and combinations thereof One or more of the groups may be included.

The concentration of the lithium salt may be in the range of 0.2 to 2 M, preferably 1 to 2 M, depending on various factors such as the precise composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, Specifically, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. If it is used at less than 0.2 M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If it is used in excess of 2 M, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li ⁺ ) may be reduced.

Examples of the non-aqueous organic solvent of the present invention include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di Ethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 3-dioxolane, diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethylene Ethers such as ethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate Organic solvent And the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include organic polymers such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluoride, A polymer including a group 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 and the like of Li such as SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The electrolyte of the present invention may contain at least one selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexa-phosphoric triamide, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate) and the like.

The electrolyte may be used as a liquid electrolyte or as a solid electrolyte separator. When used as a liquid electrolyte, the separator further includes a separation membrane made of porous glass, plastic, ceramic, or polymer as a physical separation membrane having a function of physically separating the electrode.

The shape of the lithium sulfur-selenium battery described above is not particularly limited and may be, for example, a jelly-roll type, a stack type, a stack-folding type (including a stack-Z-folding type), or a lamination- May be of the stack-folding type.

The electrode assembly having the positive electrode, the separator, and the negative electrode sequentially laminated was prepared, and the electrode assembly was inserted into the battery case. Then, an electrolyte solution was injected into the upper part of the case and sealed with a cap plate and a gasket to assemble the lithium- .

The lithium sulfur-selenium battery may be classified into a cylindrical type, a square type, a coin type, a pouch type, and the like depending on the type, and may be divided into a bulk type and a thin type depending on the size. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the scope and content of the present invention can not be construed to be limited or limited by the following Examples. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the present invention as set forth in the following claims. It is natural that it belongs to the claims.

[Example]

Preparation of sulfur-selenium-carbon composites

[Example 1]

As shown in FIG. 2, 7 g of powdered selenium (Sigma-Aldrich, purity 99.99 or more) and 30 g of carbon nanotubes as carbon materials were mixed with ZrO ₂ balls and ethanol at 200 rpm for 3 hours to prepare a selenium- Selenium and carbon materials were mixed by ball milling. The mixture of selenium and carbonaceous material was filtered to remove ethanol and ZrO ₂ balls, followed by drying in an oven at 80 ° C for 24 hours. Thereafter, a selenium-carbon composite was prepared by irradiating a mixture of dried selenium and carbonaceous material with a microwave (BP-110, Microwave Research and Applications) having a frequency of 2.45 GHz and a power of 1000 W for 10 seconds. One))

Next, 37 g of the selenium-carbon composite prepared above and 63 g of powdery sulfur (Sigma-Aldrich, purity 99.99 or more) were ball-milled with a ZrO ₂ ball and ethanol at 200 rpm for 3 hours to mix the selenium- . The mixture of selenium-carbon composite and sulfur was filtered to remove ethanol and ZrO ₂ balls, followed by drying in an oven at 80 ° C for 24 hours. Thereafter, a sulfur-selenium-carbon composite was prepared by irradiating a mixture of the dried selenium-carbon composite material and sulfur to a microwave (BP-110, Microwave Research and Applications) having a frequency of 2.45 GHz and a power of 1000 W for 5 seconds. (Step (2)).

[Example 2]

10 g of selenium and 20 g of carbon nanotubes were used in step (1), and in step (2), 30 g of the selenium-carbon composite produced in step (1) and 70 g of sulfur were used. Respectively.

[Comparative Example 1]

As shown in FIG. 2, 7 g of powdered selenium (Sigma-Aldrich, purity 99.99 or more), 30 g of carbon nanotubes as carbon materials, sulfur in powder form (Sigma-Aldrich, Purity: 99.99 or more) were ball milled together with ZrO ₂ balls and ethanol at 200 rpm for 3 hours. The mixture was filtered to remove ethanol and ZrO ₂ balls, and then dried in an oven at 80 ° C for 24 hours.

And then heat-treated in an oven at 250 캜 for 3 hours to prepare a sulfur-selenium-carbon composite.

[Comparative Example 2]

30 g of carbon nanotubes as a carbon material instead of selenium, carbon nanotubes and sulfur, and 70 g of powdery sulfur (Sigma-Aldrich, purity 99.99 or more) were mixed in a weight ratio of 30:70. The same procedure as in Comparative Example 1 was conducted except that the heat treatment was performed for 30 minutes.

[Comparative Example 3]

20 g of carbon nanotubes as a carbon material instead of selenium, carbon nanotubes and sulfur and 80 g of powdery sulfur (Sigma-Aldrich, purity of 99.99 or more) were mixed at a weight ratio of 30:70, and the mixture was heat- The same procedure as in Comparative Example 1 was conducted except that the heat treatment was performed for 30 minutes.

[Experimental Example 1] SEM analysis results

Sulfur-selenium-carbon composites prepared in Example 1 were photographed with a scanning electron microscope (SEM, S-4800, HITACHI) and are shown in FIG.

As shown in FIG. 1, when the selenium-carbon composite was prepared by first heat-treating selenium and carbon nanotubes as a result of step (1), it was confirmed that selenium-carbon composites were formed without selenium aggregation.

In addition, as a result of step (2), it was confirmed that even in the case of the sulfur-selenium-carbon composite prepared by heat-treating the selenium-carbon composite and sulfur, the sulfur was not aggregated and a sulfur-selenium-carbon composite was formed.

[Experimental Example 2] Evaluation of battery physical properties

(VGCF) was mixed at a weight ratio of 88: 7: 5 to prepare a slurry. The slurry was prepared in the same manner as in Example 1, except that the sulfur-carbon composite material: binder (LiPAA / PVA mixed at 6.5: 0.5) And then coated on a collector of an aluminum foil having a thickness of 20 탆 to prepare an electrode.

The prepared electrode was used as an anode and lithium metal was used as a cathode to prepare a coin cell. In this case, the coin cell used was an electrolytic solution prepared from 2M MeTHF / DOL / DME (1: 1: 1), LiN (CF ₃ SO ₂ ) ₂ (LiTFSI) 1M and LiNO ₃ 0.1M. The 2-Me-THF / DOL / DME used 2-methyl tetrahydrofuran, dioxolane, and dimethyl ether as solvents, respectively.

Capacitance from 1.8 to 2.5 V was measured for the manufactured coin cell and is shown in FIG. 3 and FIG.

As shown in FIG. 3, the initial discharge capacity was improved in Example 1 in which selenium and sulfur were heat-treated by microwave in two stages, compared with Comparative Example 1 which was heat-treated in an oven.

The produced coin cell was charged at 0.1 C rate CC and discharged at 0.1 C rate CC three times, then repeated at 0.2 C charge / 0.2 C discharge three times, then at 0.3 C charge / 0.5 C discharge The cycle was repeated 20 times to measure charge and discharge efficiency (CC: Constant Current)

The results are shown in FIG. 4. In the case of Example 1, it was confirmed that stable charge and discharge were possible when the C-rate was increased. As a result, it was confirmed that the lifetime characteristics were improved as compared with Comparative Example 1.

The initial discharge capacity was measured in terms of the content of selenium and carbonaceous material in the composite and is shown in FIG. 5 and Table 1.

division Discharge capacity [mAh / g] Example 1 1,108 Example 2 1,009 Comparative Example 1 1,021 Comparative Example 2 1,088 Comparative Example 3 410

As a result, the initial discharge of the composite body (Example 1 and Comparative Example 2) in which the weight ratio of the carbon nanotubes was 30 (Comparative Example 2) and the composite body in which the weight ratio of the carbon nanotubes was 20 (Example 2 and Comparative Example 3) It can be seen from FIG. 5 that the overvoltage is improved and the discharge capacity is increased in the case of Examples 1 and 2 including 7 or 10 parts by weight in the interior of the composite.

Claims (13)

In a method for producing a sulfur-selenium-carbon composite,
The above-
(1) mixing selenium and carbon materials, and heat-treating the selenium and carbon materials by microwaves to form a selenium-carbon composite; And
(2) mixing the sulfur-containing selenium-carbon composite with the sulfur and heat-treating the selenium-carbon composite by microwave to form a sulfur-selenium-carbon composite;
Lt; / RTI >
Wherein the heat treatment of step (1) is performed at a temperature higher than the heat treatment of step (2). The method according to claim 1,
Wherein the heat treatment in step (1) is performed at a temperature of 250 to 500 ° C. The method according to claim 1,
Wherein the heat treatment in step (2) is performed at a temperature of 200 to 400 ° C. The method according to claim 1,
Wherein the mixing in step (1) is performed at a weight ratio of selenium and carbonaceous material of 1: 1 to 1: 5. The method according to claim 1,
Wherein the mixing in step (2) is performed in a weight ratio of sulfur to selenium-carbon composite of from 6: 4 to 8: 2. The method according to claim 1,
Wherein the heat treatment in the step (1) is performed for 5 to 20 seconds. The method according to claim 1,
Wherein the heat treatment in step (2) is performed for 3 to 10 seconds. The method according to claim 1,
Wherein the output of the microwave is in the range of 700 to 1000 W. A method of producing a sulfur-selenium-carbon composite material, The method according to claim 1,
Wherein the microwave has a frequency of 2.44 to 2.46 GHz. The method according to claim 1,
Wherein the sulfur-selenium-carbon composite comprises 1 to 10 parts by weight of selenium relative to 100 parts by weight of the total sulfur-selenium-carbon composite. The method according to claim 1,
Wherein the carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotube, carbon fiber, and activated carbon. A positive electrode for a lithium sulfur-selenium battery comprising a sulfur-selenium-carbon composite produced by the method of any one of claims 1 to 11. A positive electrode according to claim 12;
cathode; And
A lithium sulfur-selenium battery comprising an electrolyte.

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