KR102363965B1 - Lithium-sulfur battery comprising sulfurized polymer modified throuth over-discharge and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a lithium-sulfur battery including a sulfide polymer modified through overdischarge and a method for manufacturing the same. The polymer is polyacrylonitrile or polyvinyl chloride. The overdischarge is performed by discharging to 0.2 to 0.5V during initial discharging of the lithium-sulfur battery. The lithium-sulfur battery according to the present invention has an effect of improving some overvoltage and improving lifespan characteristics.

Description

Lithium-sulfur battery containing sulfide polymer modified through overdischarge and manufacturing method thereof

The present invention relates to a lithium-sulfur battery including a sulfide polymer modified through overdischarge and a method for manufacturing the same.

Recently, miniaturization and weight reduction of electronic products, electronic devices, communication devices, etc. is rapidly progressing, and as the need for electric vehicles is greatly raised in relation to environmental problems, the demand for performance improvement of batteries used as power sources for these products is also increasing. the current situation. Among them, a lithium battery has received considerable attention as a high-performance battery because of its high energy density and high standard electrode potential.

In particular, a lithium-sulfur (Li-S) battery uses a sulfur-based material having an SS bond as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode 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 discharge 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.

Among the technical problems to be solved in order to achieve commercialization of lithium-sulfur batteries, the biggest problem is the dissolution of polysulfide, which greatly contributes to the degradation of lithium-sulfur batteries. Specifically, among lithium polysulfides such as Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ , and Li ₂ S ₂ , lithium polysulfide with a high sulfur oxidation number (Li ₂ S _x , usually x > 4) is hydrophilic. It is easily soluble in the electrolyte of Lithium polysulfide dissolved in the electrolyte diffuses away from the anode where lithium polysulfide is generated due to the concentration difference. The lithium polysulfide eluted from the positive electrode is lost out of the positive electrode reaction region, so that the stepwise reduction to lithium sulfide (Li ₂ S) is impossible. That is, lithium polysulfide existing in a dissolved state beyond the positive electrode and negative electrode cannot participate in the charge and discharge reaction of the battery, so the amount of sulfur material participating in the electrochemical reaction in the positive electrode decreases, and eventually lithium-sulfur It is a major factor causing a decrease in the charge capacity of the battery and a decrease in energy.

When a sulfurized polyacrylonitrile (S-PAN) material obtained by heat-treating a mixture of sulfur and polyacrylonitrile is applied as a cathode material for a lithium-sulfur battery, sulfur generally applied to the cathode of a lithium-sulfur battery / Compared to the carbon composite, polysulfide is not generated due to the solid-liquid-solid charging and discharging process, so it shows improved lifespan characteristics. This is because sulfur atoms or short-chain sulfur compounds are intrinsically bound in a dispersed form in the carbonized polymer backbone. It is judged that this is because the charge/discharge process proceeds in the form of solid-solid as the production is suppressed.

However, since the sulfur content of the sulfided polyacrylonitrile material is usually 50% or less, the residual moisture content (~40,000ppm) is too large, and the rated voltage is 2V or less, this material is applied and practically used There are technical difficulties in realizing a battery having this possible energy density.

Accordingly, there is a need in the art for an improved cathode material capable of compensating for the disadvantages of sulfided polyacrylonitrile while maintaining the advantages of sulfided polyacrylonitrile.

US Registered Patent No. 7,939,198 International Publication No. WO2000-067339 International Publication No. WO2001-058805

In order to solve the above problems, the present invention provides a lithium-sulfur battery capable of improving some overvoltage of the battery and improving lifespan characteristics by transforming a sulfide polymer through a polymer and applying it to a lithium-sulfur battery as a cathode material want to

According to a first aspect of the present invention,

The present invention includes a sulfided polymer modified through overdischarge as a cathode material,

The polymer provides a lithium-sulfur battery of polyacrlonitrile or polyvinyl chloride.

In one embodiment of the present invention, the sulfided polymer is a carbon composite prepared by adding a carbon-based material during sulfiding.

In one embodiment of the present invention, the carbon-based material is added in an amount of 1 to 10% by weight relative to the polymer before sulfiding.

In one embodiment of the present invention, the overdischarge is performed by discharging to 0.2 to 0.5V during the initial discharge of the lithium-sulfur battery.

In one embodiment of the present invention, the overdischarge is performed in the presence of an ether-based electrolyte solution or a carbonate-based electrolyte solution.

According to a second aspect of the present invention,

As a method for manufacturing the above-described lithium-sulfur battery,

The manufacturing method, (1) mixing a polymer and sulfur to prepare a mixture; (2) heating the mixture under an inert gas; (3) mixing the heated mixture with a binder to prepare a slurry; (4) preparing a positive electrode by applying and drying the slurry on a positive electrode current collector; (5) preparing a battery by disposing a negative electrode, a separator, and an electrolyte solution on the prepared positive electrode; and (6) overdischarging the battery, wherein the polymer in step (1) is polyacrylonitrile or sulfided polyvinyl chloride.

In one embodiment of the present invention, the heating in step (2) is performed at 300 to 500 ℃.

By applying the sulfide polymer modified through overdischarge according to the present invention to a lithium-sulfur battery, there is an advantage in that it is possible to improve some overvoltages occurring in a lithium-sulfur battery and improve the lifespan of a lithium-sulfur battery.

1 is a graph showing a charging/discharging profile for overdischarging according to an embodiment of the present invention.
FIG. 2 is a graph showing the measurement of specific capacity and voltage during charging and discharging of the battery according to Example 1. FIG.
3 is a graph showing the measurement of specific capacity and voltage during charging and discharging of a battery according to Comparative Example 1.
4 is a graph showing the measurement of specific capacity and voltage during charging and discharging of a battery according to Comparative Example 2.
5 is a graph showing the measurement of specific capacity and voltage during charging and discharging of a battery according to Example 2;

The embodiments provided according to the present invention can all be achieved by the following description. It is to be understood that the following description is to be understood as describing preferred embodiments of the present invention, and the present invention is not necessarily limited thereto.

The present invention provides a lithium-sulfur battery comprising a sulfide polymer modified through overdischarge as a component of a cathode material. Here, the sulfurized polymer refers to a compound in which sulfur and a polymer are mixed and then heat-treated, and an S-S bond is formed in the molecule. The polymer mixed with sulfur is suitable for use as a material for the positive electrode, and if it is deformed through subsequent overdischarge to improve battery performance, the type is not particularly limited. According to one embodiment of the present invention, the polymer may be polyacrlonitrile or polyvinyl chloride, more preferably polyvinyl chloride. When polyacrylonitrile is sulfurized, it has a sulfur content of 30 to 50% and a moisture content of 40,000 ppm or less. When the sulfurized polyacrylonitrile is used as a cathode material, lifespan characteristics are improved due to the reaction conditions in which polysulfide is not generated, and stable C-rate characteristics are exhibited due to the improved discharge reaction rate. However, the sulfur content is 50% or less, the residual moisture content is too large, 40,000ppm or less, and the rated voltage is 2V or less. In addition, polyvinyl chloride has a sulfur content of 60% or more and a moisture content of 300 ppm or less when sulfided. When this sulfurized polyvinyl chloride is used as a cathode material, it exhibits a solid-solid charge and discharge process like sulfurized polyacrylonitrile, but has a disadvantage in that it has low battery performance due to a larger charge and discharge overvoltage. It is difficult to apply practically to a battery. Therefore, in order to apply the sulfurized polyacrylonitrile or sulfurized polyvinyl chloride as a cathode material, there is a need to improve the material.

An overdischarge method is used to improve the above-described sulfurized polymer material. The overdischarge method is performed by manufacturing a battery by applying the above-described sulfurized polymer as a cathode material, and then discharging to a voltage greater than or equal to the discharge capacity of the battery during initial discharge. According to one embodiment of the present invention, the overdischarge is performed by discharging to 0.2 to 0.5V, preferably 0.2 to 0.4V, more preferably 0.2 to 0.3V during initial discharge of the lithium-sulfur battery. 1 is a charge-discharge profile for over-discharge of a battery according to an embodiment of the present invention. As shown in FIG. 1 , in the case of overdischarging to less than 1.0V during the first discharge, the first charge/discharge capacity increases and the charge/discharge capacity is improved from the second discharge. When the overdischarge is performed to a voltage of less than 0.2V, it is difficult to secure the reversibility of the battery depending on the characteristics of the material. is insignificant Even when the overdischarge is performed more than once, there is no significant difference in the effect of improving the performance of the battery, and therefore it may be preferable in terms of efficiency to perform the overdischarge once.

In order to impart additional conductivity to the sulfided polymer, a conductive material may be added. 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 changes 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. According to one embodiment of the present invention, the conductive material is a carbon-based material, specifically, at least one carbon black selected from the group consisting of channel black, furnace black, thermal black, contact black, lamp black, and acetylene black, more specifically As such, acetylene black may be preferable. The carbon-based material may be added in an amount of 1 to 10 wt%, preferably 4 to 7 wt%, based on the polymer before sulfiding. When the carbon-based material is added in an amount of less than 1% by weight, conductivity may not be sufficient to the cathode material, and when the carbon-based material is added in an amount of more than 10% by weight, the effect of improving conductivity due to the addition of the conductive material is insignificant. increase is undesirable.

The electrolyte during overdischarge is not particularly limited as long as it is an electrolyte generally included in a lithium-sulfur battery. According to one embodiment of the present invention, the electrolyte during overdischarge may be preferably an ether-based electrolyte or a carbonate-based electrolyte. The ether-based electrolyte may be 1,3-dioxolane (DOL), dimethoxy methane (DME), or a combination thereof. The carbonate-based electrolyte may be ethylene carbonate (EC), dimethyl carbonate (DMC), or a combination thereof.

According to the present invention, a method for manufacturing a lithium-sulfur battery including a sulfide polymer modified through overdischarge is as follows.

The manufacturing method comprises the steps of preparing a mixture by mixing a polymer and sulfur; heating the mixture under an inert gas; mixing the heated mixture with a binder to prepare a slurry; preparing a positive electrode by applying and drying the slurry on a positive electrode current collector; manufacturing a battery by arranging a negative electrode, a separator, and an electrolyte solution on the prepared positive electrode; and overdischarging the battery. In the slurry preparation step, a carbon-based material as a conductive material may be additionally mixed. The specific content of each step is determined according to the contents disclosed herein, and the heating of the mixture may be performed at 300 to 500°C. At a temperature within the above range, the most appropriate amount of sulfur may be bound into the polymer. In addition, the inert gas is not particularly limited, but argon gas may be preferable.

Hereinafter, the overall configuration of the lithium-sulfur battery including the positive electrode material according to the above-described content will be described in detail.

The lithium-sulfur battery includes a positive electrode; cathode; a separator interposed between the anode and the cathode; and an electrolyte impregnated in contact with the positive electrode, the negative electrode and the separator, and including a lithium salt and an organic solvent. In the lithium-sulfur battery of the present invention, the specific configuration of the positive electrode, the negative electrode, the separator, and the electrolyte except for the above-described positive electrode material is as follows.

The positive electrode may be manufactured in the form of a positive electrode by forming a film of a positive electrode material including a positive electrode active material, a conductive material, and a binder on a positive electrode current collector. First, in the positive electrode material, the above-described material is used for the positive electrode active material and the conductive material.

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 dissolved 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-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 be deteriorated, 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-sulfur battery in a slurry state should be easy to dry and capable of dissolving 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. there is. 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, or a homo mixer. The positive electrode composition may be applied to a current collector and vacuum dried to form a positive electrode for a lithium-sulfur 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 may be appropriately selected within the range of preferably 10 to 300 μm. According to one embodiment of the present invention, the positive electrode may have a loading amount of 4 to 6 mAh/cm ² by coating the positive electrode composition.

At this time, the method for 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, etc. may be performed.

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 foamed body, or a non-woven body.

The negative electrode is a material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ) as an anode active material, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal or lithium alloys may be used. The material capable of reversibly occluding or releasing lithium ions (Li ⁺ ) 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 (Li ⁺ ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), silicon (Si), and may be an alloy of a metal selected from the group consisting of tin (Sn).

In the negative electrode, a conductive material and a binder may be used as needed. The conductive material and the binder may be selected without limitation within the applicable range in the relevant technical field based on the above-described conductive material and binder of the positive electrode.

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 means 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, and the inactive sulfur formed on the surface of the lithium negative electrode is a protective layer of the lithium negative electrode. ) also has the advantage of acting as a

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 a 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, an olefin-based polymer such as chemical-resistant and hydrophobic polypropylene, a sheet made of glass fiber or polyethylene, or a non-woven fabric, kraft paper, or the like 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 gel-forming compound (Gelling agent) may be further included in order 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 , LiFSI, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, lithium imide, and combinations thereof One or more may be included from the group consisting of.

The concentration of the lithium salt may vary from 0.2 to 2 M, specifically, 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. As 0.6 to 2M, more specifically, it may be 0.7 to 1.7M. If it is used less than 0.2M, the conductivity of the electrolyte may be lowered, and thus the electrolyte performance may be deteriorated. If used in excess of 2M, 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, phosphoric acid triester, trime Aprotic, such as oxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, 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. Polymers containing groups 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 Nitride, halide, sulfate, 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 help the understanding of the present invention, but the following examples are provided for easier understanding of the present invention, and the present invention is not limited thereto.

Example

Example One

1. Preparation of anode

Polyvinyl chloride powder (manufacturer: Sigma Aldrich, molecular weight (M _w ): 43,000) and sulfur were mortar mixed. The mixture was transferred to an alumina boat, and then heated to about 300° C. in a quartz tube under an argon atmosphere using a tube furnace. The heated product was mixed with Denka black, styrene-butadiene rubber (SBR) solution and carboxymethyl cellulose (CMC) solution to prepare a slurry. A positive electrode was prepared by coating the slurry on an aluminum current collector.

2. Preparation of lithium-sulfur batteries

A lithium-sulfur battery was assembled by preparing a negative electrode, a separator, and an electrolyte as follows, together with the positive electrode prepared by the above-described method.

(1) cathode

A lithium foil having a thickness of about 35 μm was used as the negative electrode.

(2) separator

A polyethylene membrane was used as the separator

(3) electrolyte

As the electrolyte, an electrolyte in which 0.4M LiFSI and 4% by weight of LiNO ₃ were added to a mixed solvent of ethylene carbonate and dimethyl carbonate (1:1, v/v) was used.

3. Over discharge

The lithium-sulfur battery prepared by the above method was discharged once to 0.2V.

comparative example One

A lithium-sulfur battery was assembled in the same manner as in Example 1, except that Denka Black was not used and a positive electrode was manufactured. After this, the overdischarge process was not performed.

comparative example 2

A lithium-sulfur battery was assembled in the same manner as in Example 1, and the overdischarge process was not performed.

Example 2

A lithium-sulfur battery was assembled in the same manner as in Example 1, except that a positive electrode was prepared using polyacrylonitrile powder (manufacturer: Sigma Aldrich, molecular weight (M _w ): 150,000) instead of polyvinyl chloride powder. . After that, overdischarge was performed in the same manner as in Example 1.

Experimental example

Experimental example One: Example Evaluation of the battery according to 1

The battery according to Example 1 was charged and discharged twice under 0.1C discharge/0.1C charging conditions. Specific capacity and voltage were measured during charging and discharging, and the results are shown in FIG. 2 . The experiment was repeated 3 times on the same battery, and in FIG. 2 , the color was displayed differently for each experiment.

According to FIG. 2 , as shown in FIG. 1 , it can be confirmed that the discharge voltage is improved during the second discharge after the overdischarge.

Experimental example 2: comparative example Evaluation of the battery according to 1

The battery according to Comparative Example 1 was charged and discharged under the following conditions. Specific capacity and voltage were measured during charging and discharging, and the results are shown in FIG. 3 .

Charge/discharge conditions: 0.1C discharge/0.1C charge (2.5 cycles) ⇒ 0.1C charge/0.5C, 1C, 2C, 5C, 10C discharge (each discharge condition is performed 3 times) ⇒ 0.1C charge/0.1C discharge ( recovery) ⇒ 0.2C charge/0.5C discharge (remaining cycle)

Referring to FIG. 3 , it can be seen that when Denka Black is not used and an overdischarge process is not performed, the discharge voltage and cycle performance are significantly lowered compared to the battery of Example 1 .

Experimental example 3: comparative example Evaluation of the battery according to 2

The battery according to Comparative Example 2 was charged and discharged under the same conditions as in Experimental Example 2. Specific capacity and voltage were measured during charging and discharging, and the results are shown in FIG. 4 .

According to FIG. 4 , when Denka Black is used, unlike the battery of Comparative Example 1, it can be confirmed that the discharge voltage and cycle performance are partially improved compared to the battery of Comparative Example 1, but the discharge voltage of the battery of Example 1 is The result was much lower than the result.

Experimental example 4: Example Evaluation of the battery according to 2

The battery according to Example 2 was charged and discharged under the same conditions as in Experimental Example 1. Specific capacity and voltage were measured during charging and discharging, and the results are shown in FIG. 5 .

According to FIG. 5 , it can be confirmed that the effect of improving the discharge voltage during the second discharge due to overdischarge occurs even when the sulfided polyacrylonitrile is used as the cathode material. However, it can be seen that there is no difference in the voltage improvement effect from that performed once even when the overdischarge step is performed 5 times.

All simple modifications and variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will become apparent from the appended claims.

Claims (10)

It contains a sulfided polymer modified through overdischarge as a cathode material,
The overdischarge is performed by discharging to 0.2 to 0.5V during initial discharging of the lithium-sulfur battery,
The polymer is polyacrlonitrile (polyacrlonitrile) or polyvinyl chloride (polyvinyl chloride) lithium-sulfur battery.
The method according to claim 1,
The sulfided polymer is a lithium-sulfur battery, characterized in that the carbon composite prepared by adding a carbon-based material during sulfiding.
3. The method according to claim 2,
The carbon-based material is a lithium-sulfur battery, characterized in that 1 to 10% by weight is added compared to the polymer before sulfiding.
3. The method according to claim 2,
The sulfided polymer is a lithium-sulfur battery, characterized in that sulfided polyvinyl chloride (polyvinyl chloride).
3. The method according to claim 2,
The carbon-based material is from the group consisting of channel black, furnace black, thermal black, contact black, lamp black and acetylene black. Lithium-sulfur battery, characterized in that at least one selected carbon black (Carbon black).
delete The method according to claim 1,
The overdischarge is a lithium-sulfur battery, characterized in that it is performed in the presence of an ether-based electrolyte or a carbonate-based electrolyte.
A method for manufacturing a lithium-sulfur battery according to claim 1, comprising:
The manufacturing method is
(1) mixing a polymer and sulfur to prepare a mixture;
(2) heating the mixture under an inert gas;
(3) mixing the heated mixture with a binder to prepare a slurry;
(4) preparing a positive electrode by applying and drying the slurry on a positive electrode current collector;
(5) preparing a battery by disposing a negative electrode, a separator, and an electrolyte solution on the prepared positive electrode; and
(6) over-discharging the battery;
In step (1), the polymer is polyacrylonitrile or polyvinyl chloride,
The method of manufacturing a lithium-sulfur battery in which the overdischarge in step (6) is performed by discharging to 0.2 to 0.5V during the initial discharge of the lithium-sulfur battery.
9. The method of claim 8,
A method of manufacturing a lithium-sulfur battery, characterized in that the slurry is prepared by further mixing the carbon-based material in step (3).
9. The method of claim 8,
The method of manufacturing a lithium-sulfur battery, characterized in that the heating in step (2) is performed at 300 to 500 ℃.

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