WO2020060084A1 - Sulfur-carbon composite, preparation method thereof, positive electrode for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Sulfur-carbon composite, preparation method thereof, positive electrode for lithium secondary battery and lithium secondary battery comprising same Download PDF

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Publication number
WO2020060084A1
WO2020060084A1 PCT/KR2019/011540 KR2019011540W WO2020060084A1 WO 2020060084 A1 WO2020060084 A1 WO 2020060084A1 KR 2019011540 W KR2019011540 W KR 2019011540W WO 2020060084 A1 WO2020060084 A1 WO 2020060084A1
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Prior art keywords
sulfur
porous carbon
carbon material
carbon
functional group
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PCT/KR2019/011540
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French (fr)
Korean (ko)
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김민수
조은경
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주식회사 엘지화학
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Priority claimed from KR1020190109637A external-priority patent/KR20200033736A/en
Application filed by 주식회사 엘지화학 filed Critical 주식회사 엘지화학
Priority to CN201980030242.6A priority Critical patent/CN112088453B/en
Priority to US17/043,877 priority patent/US20210036306A1/en
Priority to EP19863294.5A priority patent/EP3767715B1/en
Priority to JP2021502687A priority patent/JP7167299B2/en
Publication of WO2020060084A1 publication Critical patent/WO2020060084A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a sulfur-carbon composite, a method for manufacturing the same, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery.
  • lithium-sulfur batteries use sulfur-sulfur compounds having a sulfur-sulfur bond as a positive electrode active material, and an alkali metal such as lithium or a carbon-based material in which metal ions such as lithium ions are inserted and de-inserted occurs or alloys with lithium. It is a secondary battery that uses silicon or tin to form as a negative electrode active material. Specifically, the sulfur-oxidation number of sulfur decreases as the sulfur-sulfur bond is cut off during the reduction reaction discharge, and the electrical energy is stored using an oxidation-reduction reaction in which the sulfur-sulfur bond is formed again as the oxidation number of sulfur increases during charging as the oxidation reaction And create.
  • sulfur used as a positive electrode active material in a lithium-sulfur battery has a theoretical energy density of 1.675 mAh / g, and has a theoretical energy density about 5 times higher than a positive electrode active material used in a conventional lithium secondary battery, resulting in high power and high energy density. It is a battery capable of expression.
  • sulfur is attracting attention as an energy source for medium and large-sized devices such as electric vehicles as well as portable electronic devices because of its low cost, rich reserves, and easy supply and demand.
  • sulfur has a problem in that it is difficult to move electrons generated by an electrochemical reaction because sulfur has an electrical conductivity of 5X10 -30 S / cm and has no electrical conductivity. Accordingly, it is used as a sulfur-carbon composite by being combined with an electrically conductive material such as carbon that can provide an electrochemical reaction site.
  • the carbon material whose surface is modified with a functional group having a hydrophilic group has excellent electrical conductivity. Accordingly, it was expected that if the sulfur-carbon composite was prepared using the carbon material, an improvement in reactivity due to efficient electron transfer could be expected.
  • the functional group having hydrophilicity of the carbon material has poor affinity with sulfur having hydrophobicity, so that the carbon material cannot be impregnated evenly, and accordingly, a problem of poor reactivity and life characteristics of the battery has occurred.
  • the present invention is to heat the porous carbon material surface-modified with a functional group to prepare a sulfur-carbon composite by combining sulfur with a porous carbon material from which the functional group has been removed, and thus to produce a high sulfur-carbon composite. It can be seen that sulfur is evenly supported on the inside and the surface of the porous carbon material due to the specific surface area and pore volume, and the present invention was completed by confirming that it exhibits excellent electrical conductivity, discharge effect, and life characteristic effect when used as a positive electrode active material.
  • the present invention aims to provide a sulfur-carbon complex.
  • an object of the present invention is to provide a method for producing the sulfur-carbon composite.
  • an object of the present invention is to provide a positive electrode for a lithium secondary battery including the sulfur-carbon composite, and a lithium secondary battery comprising the same.
  • the present invention is a porous carbon material
  • the sulfur-carbon composite has a specific surface area of 7 to 20 m 2 / g, and a pore volume of 0.1 to 0.3 cm 3 / g, thereby providing a sulfur-carbon composite.
  • the present invention comprises the steps of (a) heat-treating a porous carbon material modified with a functional group to remove the functional group;
  • the present invention provides a positive electrode for a lithium secondary battery comprising the sulfur-carbon composite of the present invention.
  • the present invention is an anode; cathode; A separator interposed between the anode and the cathode; And lithium secondary battery comprising an electrolyte,
  • the positive electrode provides a lithium secondary battery, characterized in that the positive electrode of the present invention.
  • the sulfur-carbon composite of the present invention is evenly supported on the inside and the surface of the porous carbon material, when used as a positive electrode active material of a lithium secondary battery, it is possible to improve the overvoltage of the battery and improve the discharge capacity and lifespan characteristics.
  • the sulfur-carbon composite manufacturing method of the present invention can remove the functional groups of the surface-modified porous carbon material as a functional group, and not only facilitates the support of sulfur, but can evenly support the pores and the surface of the porous carbon material. have.
  • Example 5 is a TGA graph of the porous carbon material of Example 1 and Comparative Example 1.
  • Example 6 is a TGA graph of the porous carbon material of Example 2 and Comparative Example 2.
  • Example 7 is a Raman measurement graph of the porous carbon material of Example 2.
  • Example 10 is a graph of electrical conductivity of the sulfur-carbon composites of Example 1 and Comparative Example 1.
  • Example 11 is a graph of electrical conductivity of the sulfur-carbon composites of Example 2 and Comparative Example 2.
  • Example 12 is a charge-discharge graph of a battery prepared using the sulfur-carbon composite of Example 1 and Comparative Example 1 as a positive electrode active material.
  • Example 13 is a charge-discharge graph of a battery prepared using the sulfur-carbon composite of Example 2 and Comparative Example 2 as a positive electrode active material.
  • Example 14 is a graph measuring the life characteristics of the battery prepared by using the sulfur-carbon composite of Example 1 and Comparative Example 1 as a positive electrode active material.
  • Example 15 is a graph measuring the life characteristics of the battery prepared by using the sulfur-carbon composite of Example 2 and Comparative Example 2 as a positive electrode active material.
  • the present invention is a porous carbon material
  • the sulfur-carbon composite has a specific surface area of 7 to 20 m 2 / g, and a pore volume of 0.1 to 0.3 cm 3 / g, which relates to a sulfur-carbon composite.
  • the specific surface area of the sulfur-carbon composite of the present invention is 7 to 20 m 2 / g, preferably 8 to 15 m 2 / g. If the specific surface area of the sulfur-carbon composite is less than 7 m 2 / g, it means that the surface of the porous carbon material is sulfur, and that the sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite decreases. If it exceeds 20m 2 / g, it means that the sulfur is not properly supported inside the porous carbon material.
  • the pore volume of the sulfur-carbon composite of the present invention is 0.1 to 0.3 cm 3 / g, preferably 0.1 to 0.15 cm 3 / g.
  • the pore volume of the sulfur-carbon composite is less than 0.1 cm 3 / g, the surface of the porous carbon material is covered with sulfur, which means that sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite is reduced. If it exceeds 0.3cm 3 / g, it means that sulfur is not properly supported inside the porous carbon material.
  • the sulfur-carbon composite of the present invention has sulfur evenly supported on at least a part of the surface and inside of the porous carbon material due to the specific surface area, and sulfur is evenly supported inside the porous carbon material due to the pore volume. have.
  • sulfur is evenly supported on at least a part of the inside and the surface of the porous carbon material, so that the electrical conductivity of the sulfur-carbon composite can be improved, and driving of a battery including the same as an electrode active material Characteristics, preferably discharge capacity and life characteristics.
  • the specific surface area and pore volume of the sulfur-carbon composite of the present invention can be obtained by heat-treating a porous carbon material surface-modified with a hydrophilic functional group, removing the functional group, and supporting sulfur.
  • the porous carbon material of the sulfur-carbon composite of the present invention is a porous carbon material with functional groups removed by heat-treating the porous carbon material modified with a hydrophilic functional group.
  • the porous carbon material surface-modified with a hydrophilic functional group may generally be prepared by treating the porous carbon material with an acid, and the hydrophilic functional group may be a hydroxy group or a carboxy group.
  • the porous carbon material surface-modified with the hydrophilic functional group may exhibit excellent electrical conductivity due to the hydrophilic functional group.
  • the hydrophilic functional group of the porous carbon material does not have excellent affinity with sulfur, which exhibits hydrophobicity, and thus does not evenly support sulfur.
  • sulfur When sulfur is supported, the sulfur covers the surface of the porous carbon material, thereby significantly reducing the electrical conductivity of the sulfur-carbon composite. You can. Therefore, even if the electrical conductivity of the porous carbon material surface-modified with the hydrophilic functional group does not evenly support sulfur, when the sulfur-carbon composite including it is used as an electrode active material, the battery may not be normally operated.
  • a porous carbon material having a functional group removed by heat-treating a porous carbon material modified with a hydrophilic functional group was used, and the sulfur-carbon composite of the present invention containing the porous carbon material has a specific surface area in the above-mentioned range and It has a pore volume, which means that sulfur is evenly supported on the porous carbon material, from which it can exhibit excellent electrical conductivity.
  • the porous carbon material from which the functional group of the sulfur-carbon composite of the present invention is removed can solve the problem of not evenly supporting the sulfur generated due to the hydrophilic functional group as described above, thereby providing a sulfur-carbon composite having excellent electrical conductivity. You can.
  • a sulfur-carbon composite prepared by heat-treating the same amount of sulfur on a porous carbon material surface-modified with a hydrophilic functional group and a porous carbon material surface-modified with a hydrophilic functional group on a porous carbon material having a functional group removed is the same. Even if a positive amount of sulfur is supported, the porous carbon material surface-modified with a hydrophilic functional group does not evenly support sulfur due to the hydrophilic functional group, and thus, the operation of the battery cannot be normally operated. Since it can be supported evenly, it has excellent electrical conductivity and can improve the discharge capacity and life characteristics of the battery.
  • thermogravimetric analysis Thermogravimetric Analyzer, TGA
  • TGA Thermogravimetric Analyzer
  • the porous carbon material from which the functional groups are removed by the heat treatment has a D / G peak ratio of 0.8 to 1.5 when measuring Raman. If the ratio is less than 0.8, the conductivity is greatly reduced, and if it exceeds 1.5, it means that the heat treatment is performed at a high temperature of 2000 ° C. or higher, and a graphitization reaction occurs due to the high temperature, and damage to the porous carbon material occurs.
  • the porous carbon material that can be used in the sulfur-carbon composite of the present invention is capable of imparting conductivity to sulfur, which is an insulator, and is capable of surface modification with a hydrophilic functional group.
  • the porous carbon material may be at least one selected from the group consisting of carbon nanotubes, graphene, graphite, amorphous carbon, carbon black and activated carbon.
  • carbon nanotubes, graphite, and carbon black are preferred from the viewpoint of excellent electrical conductivity, specific surface area, and sulfur loading.
  • the carbon nanotube (CNT) may be a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT).
  • the diameter of the carbon nanotube is preferably 1 to 200 nm, more preferably 1 to 100 nm, and most preferably 1 to 50 nm. When the diameter of the carbon nanotube exceeds 200 nm, there is a problem in that the specific surface area becomes small and the reaction area with the electrolyte decreases.
  • Natural graphite includes flake graphite, high crystalline graphite, microcrystalline or cryptocrystalline graphite, and artificial graphite is primary or electrographite, secondary.
  • Graphite, graphite fiber, and the like may be used alone or in combination of two or more of the above-described types of graphite.
  • the crystal structure is not particularly limited.
  • the graphite particles may have a surface spacing of 0.335 nm or more and less than 0.337 nm, for example, 0.335 nm or more and less than 0.337 nm by X-ray wide-angle diffraction.
  • the size of the graphite particles is preferably equal to or smaller than the size of the silicon-based particles from the viewpoint of improving mixing uniformity and mixture density.
  • the average particle diameter of the graphite particles may be 20 ⁇ m or less, specifically, for example, 0.1 to 20 ⁇ m, or more specifically, 0.1 to 10 ⁇ m, 1 to 10 ⁇ m, or 1 to 5 ⁇ m have.
  • the carbon black may be, for example, one or more selected from the group consisting of acetylene black, Ketjen black, furnace black, oil-furnace black, Columbia carbon, channel black, lamp black, and summer black.
  • the particle size of the carbon black is not limited, but an average particle diameter of 0.01 to 0.5 ⁇ m is preferable in terms of securing a reaction area with the electrolyte.
  • the sulfur is preferably inorganic sulfur or elemental sulfur (S 8 ).
  • the porous carbon material and sulfur are preferably mixed in a weight ratio of 1: 1 to 1: 9. If the content of the porous carbon material exceeds the above range, the content of sulfur as an active material is lowered, which causes problems in securing battery capacity, and if it is less than the above range, the content of the porous carbon material is insufficient to impart electrical conductivity, so within the above range Adjust accordingly.
  • the method for complexing the sulfur-carbon composite of the present invention is not particularly limited in the present invention, and a method commonly used in the art may be used. As an example, a method of simply mixing a porous carbon material having a specific surface area in the above range and sulfur and then heat-treating the compound may be used.
  • the sulfur is supported on at least a part of the inside and the surface of the porous carbon material, and a larger amount of sulfur is supported on the inside than on the surface.
  • the inside of the porous carbon material means pores of the porous carbon material.
  • the diameter of the sulfur-carbon composite of the present invention is not particularly limited in the present invention, and may vary, but may preferably be 0.1 to 20 ⁇ m, more preferably 1 to 10 ⁇ m. When the above range is satisfied, a high loading electrode can be manufactured.
  • the present invention relates to a sulfur-carbon composite manufacturing method
  • the step (a) is a step of removing the functional group of the porous carbon material by heat-treating the porous carbon material modified with the functional group.
  • the functional group is a hydrophilic functional group, and may be preferably a hydroxy group or a carboxy group.
  • the porous carbon material surface-modified with the functional group may be prepared by treatment with an acid.
  • the acid may be one or more selected from nitric acid, sulfuric acid, and mixed solutions thereof.
  • the surface-modified porous carbon material can be produced by a simple process of ultrasonic treatment or heat treatment.
  • the ultrasonic treatment may be performed by an ultrasonic processor commonly used in the art, and the treatment temperature is not particularly limited, but is preferably 15 to 35 ° C, preferably room temperature.
  • the heating temperature is preferably 90 to 120 ° C.
  • the mixed solution treatment is performed for 30 minutes to 4 hours, and preferably for 1 to 3 hours.
  • ultrasonic treatment and heat treatment may be performed at the same time, or they may be sequentially performed, such as heat treatment after ultrasonic treatment.
  • the functionalized surface of the porous carbon material is heat-treated to remove the functional group of the porous carbon material.
  • the heat treatment may be performed at a rate of 5 to 20 ° C / min to 500 to 1000 ° C, and then performed at the temperature for 1 to 5 hours.
  • the heating rate is less than 5 ° C / min, side reactions other than the functional group removal reaction may occur, and if it exceeds 20 ° C / min, the reaction may proceed to the excess temperature, which is not suitable.
  • the temperature is less than 500 ° C, functional groups may not be sufficiently removed, and if it exceeds 1000 ° C, graphitization of the porous carbon material may proceed.
  • the functional groups may not be sufficiently removed, and if it exceeds 5 hours, side reactions other than the functional group removal reaction may occur.
  • a porous carbon material having a functional group of a porous carbon material modified with a functional group may be prepared.
  • the heat treatment temperature is about 1500 ° C or higher. At this temperature, the porous carbon material not only removes functional groups but also causes a graphitization reaction.
  • a functional group can be removed without performing a graphitization reaction of the porous carbon material by heat treatment at a temperature of 500 to 1000 ° C. Therefore, even after the heat treatment, the properties of the porous carbon material before the heat treatment can be maintained as it is, and thus can exhibit high electrical conductivity, such as a porous carbon material modified with a hydrophilic functional group.
  • thermogravimetric analysis Thermogravimetric Analyzer, TGA
  • TGA Thermogravimetric Analyzer
  • the porous carbon material from which the functional groups are removed by the heat treatment has a D / G peak ratio of 0.8 to 1.5 when measuring Raman. If the ratio is less than 0.8, the conductivity is greatly reduced, and if it exceeds 1.5, it means that the heat treatment is performed at a high temperature of 2000 ° C. or higher, and a graphitization reaction occurs due to the high temperature, and damage to the porous carbon material occurs.
  • the step (b) is a step of preparing a sulfur-carbon composite by complexing the porous carbon material from which the functional group prepared in step (a) is removed with sulfur powder.
  • the porous carbon material and sulfur from which the functional group is removed are compounded in a weight ratio of 1: 1 to 1: 9. If the sulfur content is less than the above range, the amount of the active material is insufficient to be used as the positive electrode active material, and if the porous carbon material is less than the above range, the electrical conductivity of the sulfur-carbon composite becomes insufficient, so it is appropriately adjusted within the above range.
  • the complexing method is not particularly limited, and a method commonly used in the art, such as dry compounding or wet complexing such as spray coating, may be used. More specifically, after the sulfur powder and the porous carbon material from which the functional group has been removed are pulverized by ball milling, placed in an oven at 120 to 160 ° C. for 20 minutes to 1 hour, molten sulfur is placed on the inside and the surface of the porous carbon material from which the functional group has been removed. Any method can be used to ensure even loading.
  • the specific surface area of the sulfur-carbon composite is 7 to 20 m 2 / g, preferably 8 to 15 m 2 / g. If the specific surface area of the sulfur-carbon composite is less than 7 m 2 / g, it means that the surface of the porous carbon material is sulfur, and that the sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite decreases. If it exceeds 20m 2 / g, it means that the sulfur is not properly supported inside the porous carbon material.
  • the pore volume of the sulfur-carbon composite of the present invention is 0.1 to 0.3 cm 3 / g, preferably 0.1 to 0.15 cm 3 / g.
  • the pore volume of the sulfur-carbon composite is less than 0.1 cm 3 / g, the surface of the porous carbon material is covered with sulfur, which means that sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite is reduced. If it exceeds 0.3cm 3 / g, it means that sulfur is not properly supported inside the porous carbon material.
  • the present invention relates to a positive electrode for a lithium secondary battery comprising the sulfur-carbon composite of the present invention described above.
  • the sulfur-carbon composite is used as a positive electrode active material for a positive electrode for a lithium secondary battery, and the positive electrode for a lithium secondary battery may be preferably a positive electrode for a lithium-sulfur battery.
  • the positive electrode may be formed by applying a positive electrode composition to a current collector and vacuum drying.
  • the positive electrode current collector may be generally made to a thickness of 3 to 500 ⁇ m, and is not particularly limited as long as it has high conductivity without causing a chemical change in the battery.
  • a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and preferably, an aluminum current collector can be used.
  • the positive electrode current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.
  • the positive electrode composition includes the above-described sulfur-carbon composite of the present invention as a positive electrode active material, and may further include a conductive material and a binder.
  • the conductive material imparts additional conductivity to the positive electrode active material, and serves to move electrons smoothly within the positive electrode. If the conductive material is excellent in conductivity and can provide a large surface area without causing chemical changes, although not limited, carbon-based materials are preferably used.
  • the carbon-based material includes natural graphite, artificial graphite, expanded graphite, graphite-based graphite, active carbon-based, channel black, furnace black, and thermal.
  • Carbon black, carbon fiber, carbon nanotubes such as thermal black, contact black, lamp black, and acetylene black : CNT), carbon nanostructures such as fullerene, and one or more selected from the group consisting of combinations thereof.
  • metallic fibers such as a metal mesh depending on the purpose;
  • Metallic powders such as copper (Cu), silver (Ag), nickel (Ni), and aluminum (Al);
  • organic conductive materials such as polyphenylene derivatives can also be used. The conductive materials may be used alone or in combination.
  • the binder provides adhesion to the current collector to the positive electrode active material
  • the binder must be well soluble in a solvent, must not only properly constitute a conductive network between the positive electrode active material and the conductive material, but also have proper impregnation properties of the electrolyte. .
  • the binder applicable to the present invention may be all binders known in the art, and specifically, a fluorine resin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) ; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Poly alcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; Polyimide-based binders; Polyester-based binders; Silane-based binder; may be a mixture or copolymer of one or more selected from the group consisting of, but is not limited thereto.
  • PVdF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • the content of the binder resin may be 0.5 to 30% by weight based on the total weight of the positive electrode composition, but is not limited thereto.
  • 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 drop off, and when it exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced. Battery capacity can be reduced.
  • the positive electrode composition is prepared in a slurry state and applied to the positive electrode current collector, and the solvent for preparing in the slurry state should be easy to dry, and can dissolve the binder well, but do not dissolve the positive electrode active material and the conductive material, but in a dispersed state. It is most desirable to be able to maintain.
  • the solvent according to the present invention can be water or an organic solvent, and the organic solvent includes one or more selected from the group consisting of dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol, and tetrahydrofuran. Solvents are applicable.
  • the positive electrode composition may be mixed by a conventional method using a conventional mixer, such as a rate mixer, a high-speed shear mixer, or a homo mixer.
  • a conventional mixer such as a rate mixer, a high-speed shear mixer, or a homo mixer.
  • 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 anode to be formed, and preferably, it may be appropriately selected within a range of 10 to 300 ⁇ m.
  • a method of coating the slurry 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, and cap coating may be performed.
  • the present invention is an anode; cathode; A separator interposed between the anode and the cathode; And it relates to a lithium secondary battery comprising an electrolyte, the positive electrode is a positive electrode for a lithium secondary battery of the present invention described above.
  • the lithium secondary battery of the present invention may be preferably a lithium-sulfur battery.
  • the negative electrode may be composed of a current collector and a negative electrode active material layer formed on one or both surfaces thereof.
  • the negative electrode may be a lithium metal plate.
  • the current collector is for supporting the negative electrode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery.
  • copper, stainless steel, aluminum, nickel, titanium, and palladium Surface-treated with carbon, nickel, silver, etc. on the surface of calcined carbon, copper or stainless steel, aluminum-cadmium alloy, and the like can be used.
  • the negative electrode current collector can form a fine concavo-convex on its surface to enhance the bonding strength with the negative electrode active material, and various forms such as a film, sheet, foil, mesh, net, porous body, foam, and non-woven fabric can be used.
  • the negative active material is a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly reacting with lithium ions to form a lithium-containing compound, lithium metal or lithium alloy Can be used.
  • the material capable of reversibly intercalating or deintercalating the lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.
  • a material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion 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), and tin (Sn).
  • a separator may be additionally included between the aforementioned positive electrode and negative electrode.
  • the separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport 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 film, or may be a coating layer added to the anode and / or cathode.
  • the material constituting the separator includes, for example, polyolefin such as polyethylene and polypropylene, glass fiber filter paper, and ceramic materials, but is not limited thereto, and the thickness is about 5 to about 50 ⁇ m, preferably about 5 to about 25 ⁇ m.
  • the electrolyte is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and an electrolyte, and a non-aqueous organic solvent, an organic solid electrolyte and an inorganic solid electrolyte are used as the electrolyte.
  • the lithium salt may be used without limitation as long as it is commonly used in the electrolyte solution for lithium-sulfur batteries.
  • LiAsF 6, LiSbF 6, LiAlCl 4 may be included are one or more from LiFSI, chloro group consisting of borane lithium, lower aliphatic carboxylic acid lithium or the like.
  • the concentration of the lithium salt in the electrolyte may be 0.2 to 2 M, specifically 0.6 to 2 M, and more specifically 0.7 to 1.7 M.
  • concentration of the lithium salt is used less than 0.2 M, the conductivity of the electrolyte may be lowered to degrade the performance of the electrolyte, and when it is used above 2 M, the viscosity of the electrolyte may increase to decrease the mobility of lithium ions.
  • the non-aqueous organic solvent must dissolve a lithium salt well, and as the non-aqueous organic solvent of the present invention, 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, tetrahydroxyfran, franchyl 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 Non-proton such as methoxymethane, dioxolane derivatives, sulfolane, methyl
  • organic solid electrolyte examples include, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and 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 Li nitrides such as SiO 4 -LiI-LiOH and Li 3 PO 4 -Li 2 S-SiS 2 , halides, sulfates, and the like can be used.
  • the electrolyte of the present invention is for the purpose of improving charge / discharge characteristics, flame retardance, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. .
  • a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-ethylene) carbonate), PRS (Propene sultone), FPC (Fluoro-propylene carbonate), and the like.
  • the electrolyte may be used as a liquid electrolyte, or may be used in the form of a solid electrolyte separator.
  • a physical separator having a function of physically separating electrodes further includes a separator made of porous glass, plastic, ceramic, or polymer.
  • a sulfur-carbon composite in which sulfur is supported on the inside (pore) and the surface of the carbon nanotube was prepared in the same manner as in Comparative Example 1, except that the surface-modified carbon nanotube (SUSN, HCNTS10) was used as a hydrophilic functional group. .
  • Thermogravimetric analysis (Thermogravimetric Analyzer, TGA) of the carbon nanotubes of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 was performed. The temperature was raised from 0 ° C to 900 ° C, and the weight reduction rate at this time was measured to confirm whether the carbon nanotubes had functional groups removed.
  • the carbon nanotubes of Comparative Examples 1 and 2 showed a weight loss of 2% or more, respectively, as the temperature increased, and it was found that the carbon nanotubes contained functional groups.
  • the carbon nanotubes of Examples 1 and 2 showed a weight reduction rate of about 1% or less even when the temperature increased, and showed a result of maintaining the weight. Accordingly, it was found that the functional groups of the carbon nanotubes were removed through the heat treatment processes of Examples 1 and 2, and it was confirmed that about 2 to 4% by weight of the functional groups were removed.
  • the carbon nanotube of Example 2 in which the functional group was removed by heat treatment of Comparative Example 2 at a temperature of 500 to 1000 ° C., had a D / G ratio of 1.03.
  • the carbon nanotubes of Comparative Example 3 in which Comparative Example 2 was heat-treated at a high temperature of 2000 ° C. had a D / G ratio of 0.51. This can be seen as a result of graphitization of the carbon nanotubes at the above temperature and an increase in the G peak.
  • the heat treatment process for removing the functional group of the present invention selectively removes only the functional group without significantly changing the degree of graphitization of the porous carbon material.
  • Example 1 The specific surface area and pore volume of the sulfur-carbon composites prepared in Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were measured using a nitrogen adsorption equipment of Belsorp, and the results are shown in Table 1 below.
  • Example 1 Example 2 Comparative Example 1 Comparative Example 2 Specific surface area 8.359m 2 / g 13.726m 2 / g 5.863m 2 / g 6.864m 2 / g Pore volume 0.106cm 3 / g 0.13cm 3 / g 0.08cm 3 / g 0.08cm 3 / g
  • the sulfur-carbon composite including the functional group-removed carbon nanotube has a high specific surface area and pore volume, and evenly supports sulfur on the pores and surface of the carbon nanotube.
  • Example 1 The electrical conductivity of the sulfur-carbon composites prepared in Example 1, Example 2, and Comparative Example 1 and Comparative Example 2 was measured using a powder resistance meter manufactured by HANTECH.
  • the sulfur-carbon composite including the functional group-removed carbon nanotubes may exhibit high electrical conductivity since sulfur is evenly supported on the pores and surfaces of the carbon nanotubes.
  • the sulfur-carbon composite containing a carbon nanotube containing a functional group does not exhibit high electrical conductivity because the surface of the porous carbon material is covered with sulfur.
  • Each of the lithium-sulfur batteries (coin cells) was prepared using the sulfur-carbon composites prepared in Example 1, Example 2, and Comparative Example 1 and Comparative Example 2 as positive electrode active materials.
  • conductive material Denka black
  • CMC carboxymethylcellulose
  • SBR styrene-butadiene rubber
  • the prepared slurry was poured onto an aluminum foil, coated with a 200 ⁇ m thickness with a blade coater, and then dried in a 50 ° C. oven to prepare a positive electrode for a lithium-sulfur battery.
  • a positive electrode, a separator, a lithium negative electrode, a gasket, a stainless steel coin, a spring, and a stainless steel top plate were sequentially placed on a stainless steel lower plate, and pressure was applied to assemble the coin cell.
  • DEGDME diethylene glycol dimethyl ether
  • the lithium-sulfur batteries of Examples 1 to 2 and Comparative Examples 1 to 2 were tested for charge / discharge characteristic changes using a charge / discharge measurement device.
  • the obtained battery was examined for initial capacity under 0.1C / 0.1C charge / discharge conditions, and the results are shown in FIGS. 12 and 13.
  • lithium-sulfur batteries including the sulfur-carbon composites of Examples 1 and 2 had improved discharge capacity and overvoltage compared to the lithium-sulfur batteries including the sulfur-carbon composites of Comparative Examples 1 and 2.
  • the sulfur-carbon composites of Examples 1 and 2 support sulfur evenly.
  • the reactivity of the sulfur reduction reaction (S 8 + 16Li ⁇ 8Li 2 S) was improved by the evenly supported sulfur, and thus it was confirmed that the discharge capacity increased and the overvoltage was improved.
  • the sulfur-carbon composite containing a carbon nanotube containing a functional group is sulfur-covering the surface of the porous carbon material, and the reactivity of the sulfur reduction reaction is not improved, thus showing lower results than Examples 1 and 2.
  • the lithium-sulfur cells including the sulfur-carbon composites of Examples 1 and 2 showed a result of maintaining the capacity for 100 cycles.
  • the lithium-sulfur cells including the sulfur-carbon composites of Comparative Examples 1 and 2 showed a result of not maintaining the capacity for 100 cycles.
  • lithium-sulfur batteries including the sulfur-carbon composites of Examples 1 and 2 had improved life characteristics compared to the lithium-sulfur batteries including the sulfur-carbon composites of Comparative Examples 1 and 2.

Abstract

The present invention relates to a sulfur-carbon composite comprising a porous carbon material and sulfur in at least a portion of the inside and the surface of the porous carbon material, a preparation method thereof, and a positive electrode for a lithium secondary battery and a lithium secondary battery comprising same.

Description

황-탄소 복합체, 이의 제조방법, 이를 포함하는 리튬 이차전지용 양극 및 리튬 이차전지Sulfur-carbon composite, manufacturing method thereof, positive electrode for lithium secondary battery and lithium secondary battery including the same
본 출원은 2018년 9월 20일자 한국 특허출원 제10-2018-0112639호 및 2019년 9월 4일자 한국 특허출원 제10-2019-0109637호에 기초한 우선권의 이익을 주장하며, 해당 한국 특허 출원의 문헌에 개시된 모든 내용을 본 명세서의 일부로서 포함한다.This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0112639 on September 20, 2018 and Korean Patent Application No. 10-2019-0109637 on September 4, 2019. All content disclosed in the literature is included as part of this specification.
본 발명은 황-탄소 복합체, 이의 제조방법, 이를 포함하는 리튬 이차전지용 양극 및 리튬 이차전지에 관한 것이다.The present invention relates to a sulfur-carbon composite, a method for manufacturing the same, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery.
최근 전자기기 분야와 전기 자동차 분야의 급속한 발전에 따라 이차 전지의 수요가 증가하고 있다. 특히, 휴대용 전자기기의 소형화 및 경량화 추세에 따라 그에 부응할 수 있는 고에너지 밀도를 갖는 이차 전지에 대한 요구가 커지고 있다.2. Description of the Related Art Recently, with the rapid development of the electronics field and the electric vehicle field, demand for secondary batteries is increasing. Particularly, according to the trend of miniaturization and weight reduction of portable electronic devices, there is an increasing demand for secondary batteries having high energy densities that can respond thereto.
이차 전지 중 리튬-황 전지는 황-황 결합을 갖는 황계 화합물을 양극 활물질로 사용하고, 리튬과 같은 알칼리 금속 또는 리튬 이온과 같은 금속 이온의 삽입 및 탈삽입이 일어나는 탄소계 물질 또는 리튬과 합금을 형성하는 실리콘이나 주석 등을 음극 활물질로 사용하는 이차전지이다. 구체적으로, 환원 반응인 방전시 황-황 결합이 끊어지면서 황의 산화수가 감소하고, 산화 반응인 충전시 황의 산화수가 증가하면서 황-황 결합이 다시 형성되는 산화-환원 반응을 이용하여 전기적 에너지를 저장하고 생성한다.Among the secondary batteries, lithium-sulfur batteries use sulfur-sulfur compounds having a sulfur-sulfur bond as a positive electrode active material, and an alkali metal such as lithium or a carbon-based material in which metal ions such as lithium ions are inserted and de-inserted occurs or alloys with lithium. It is a secondary battery that uses silicon or tin to form as a negative electrode active material. Specifically, the sulfur-oxidation number of sulfur decreases as the sulfur-sulfur bond is cut off during the reduction reaction discharge, and the electrical energy is stored using an oxidation-reduction reaction in which the sulfur-sulfur bond is formed again as the oxidation number of sulfur increases during charging as the oxidation reaction And create.
특히, 리튬-황 전지에 양극 활물질로 사용되는 황은 이론 에너지 밀도가 1.675 mAh/g으로, 기존의 리튬 이차 전지에 사용되는 양극 활물질에 비해 5배 정도 높은 이론 에너지 밀도를 가지고 있어 고출력, 고에너지 밀도의 발현이 가능한 전지이다. 이에 더해서 황은 값이 저렴하고 매장량이 풍부해 수급이 용이하며 환경친화적이라는 이점 때문에 휴대용 전자기기뿐만 아니라 전기 자동차와 같은 중대형 장치의 에너지원으로 주목받고 있다.Particularly, sulfur used as a positive electrode active material in a lithium-sulfur battery has a theoretical energy density of 1.675 mAh / g, and has a theoretical energy density about 5 times higher than a positive electrode active material used in a conventional lithium secondary battery, resulting in high power and high energy density. It is a battery capable of expression. In addition, sulfur is attracting attention as an energy source for medium and large-sized devices such as electric vehicles as well as portable electronic devices because of its low cost, rich reserves, and easy supply and demand.
그러나, 황은 전기 전도도가 5X10-30S/cm로 전기 전도성이 없는 부도체이므로 전기화학 반응으로 생성된 전자의 이동이 어려운 문제가 있다. 이에 전기화학적 반응 사이트를 제공할 수 있는 탄소와 같은 전기적 도전재와 함께 복합화되어 황-탄소 복합체로 사용되고 있다.However, sulfur has a problem in that it is difficult to move electrons generated by an electrochemical reaction because sulfur has an electrical conductivity of 5X10 -30 S / cm and has no electrical conductivity. Accordingly, it is used as a sulfur-carbon composite by being combined with an electrically conductive material such as carbon that can provide an electrochemical reaction site.
표면이 친수성기를 갖는 작용기로 표면이 개질된 탄소재는 전기 전도도가 우수하다. 그에 따라 상기 탄소재를 사용하여 황-탄소 복합체를 제조하면 효율적인 전자 전달에 의한 반응성 향상을 기대할 수 있을 것이라 예상하였다.The carbon material whose surface is modified with a functional group having a hydrophilic group has excellent electrical conductivity. Accordingly, it was expected that if the sulfur-carbon composite was prepared using the carbon material, an improvement in reactivity due to efficient electron transfer could be expected.
그러나, 탄소재의 친수성을 갖는 작용기는 소수성을 갖는 황과 친화력이 불량하므로 탄소재에 황이 고르게 함침되지 못하며, 그에 따라 전지의 반응성 및 수명 특성이 불량한 문제가 발생하였다.However, the functional group having hydrophilicity of the carbon material has poor affinity with sulfur having hydrophobicity, so that the carbon material cannot be impregnated evenly, and accordingly, a problem of poor reactivity and life characteristics of the battery has occurred.
[선행기술문헌][Advanced technical literature]
[특허문헌][Patent Document]
대한민국 공개특허 제10-2014-0082994호Republic of Korea Patent Publication No. 10-2014-0082994
상기 문제를 해결하기 위하여, 본 발명은 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기가 제거된 다공성 탄소재와 황을 복합화하여 황-탄소 복합체를 제조하였고, 이렇게 제조된 황-탄소 복합체의 높은 비표면적 및 기공 부피로 인하여 다공성 탄소재의 내부 및 표면에 황이 고르게 담지된 것을 알 수 있으며, 이를 양극 활물질로 사용시 우수한 전기 전도성, 방전 효과 및 수명 특성 효과를 나타내는 것을 확인하여 본 발명을 완성하였다.In order to solve the above problem, the present invention is to heat the porous carbon material surface-modified with a functional group to prepare a sulfur-carbon composite by combining sulfur with a porous carbon material from which the functional group has been removed, and thus to produce a high sulfur-carbon composite. It can be seen that sulfur is evenly supported on the inside and the surface of the porous carbon material due to the specific surface area and pore volume, and the present invention was completed by confirming that it exhibits excellent electrical conductivity, discharge effect, and life characteristic effect when used as a positive electrode active material.
따라서, 본 발명은 황-탄소 복합체를 제공하는 것을 목적으로 한다.Accordingly, the present invention aims to provide a sulfur-carbon complex.
또한, 본 발명은 상기 황-탄소 복합체의 제조방법을 제공하는 것을 목적으로 한다.In addition, an object of the present invention is to provide a method for producing the sulfur-carbon composite.
또한, 본 발명은 상기 황-탄소 복합체를 포함하는 리튬 이차전지용 양극, 이를 포함하는 리튬 이차전지를 제공하는 것을 목적으로 한다.In addition, an object of the present invention is to provide a positive electrode for a lithium secondary battery including the sulfur-carbon composite, and a lithium secondary battery comprising the same.
상기 목적을 달성하기 위하여,In order to achieve the above object,
본 발명은 다공성 탄소재; 및The present invention is a porous carbon material; And
상기 다공성 탄소재의 내부 및 표면 중 적어도 일부에 황;을 포함하는 황-탄소 복합체로,A sulfur-carbon composite containing sulfur; at least a part of the inside and the surface of the porous carbon material,
상기 황-탄소 복합체의 비표면적은 7 내지 20m2/g이고, 기공부피는 0.1 내지 0.3cm3/g인, 황-탄소 복합체를 제공한다.The sulfur-carbon composite has a specific surface area of 7 to 20 m 2 / g, and a pore volume of 0.1 to 0.3 cm 3 / g, thereby providing a sulfur-carbon composite.
또한, 본 발명은 (a)작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기를 제거하는 단계;In addition, the present invention comprises the steps of (a) heat-treating a porous carbon material modified with a functional group to remove the functional group;
(b)상기 작용기가 제거된 다공성 탄소재를 황 분말과 복합화하여 황-탄소 복합체를 제조하는 단계;를 포함하는 황-탄소 복합체 제조방법을 제공한다.(b) preparing a sulfur-carbon composite by complexing the porous carbon material from which the functional group has been removed with sulfur powder;
또한, 본 발명은 상기 본 발명의 황-탄소 복합체를 포함하는 리튬 이차전지용 양극을 제공한다.In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the sulfur-carbon composite of the present invention.
또한, 본 발명은 양극; 음극; 상기 양극과 음극 사이에 개재되는 분리막; 및 전해액을 포함하는 리튬 이차전지로,In addition, the present invention is an anode; cathode; A separator interposed between the anode and the cathode; And lithium secondary battery comprising an electrolyte,
상기 양극은 상기 본 발명의 양극인 것을 특징으로 하는 리튬 이차전지를 제공한다.The positive electrode provides a lithium secondary battery, characterized in that the positive electrode of the present invention.
본 발명의 황-탄소 복합체는 다공성 탄소재의 내부 및 표면에 황이 고르게 담지됨에 따라, 리튬 이차전지의 양극 활물질로 사용시 전지의 과전압을 개선시키고, 방전 용량 및 수명 특성을 향상시킬 수 있다.As the sulfur-carbon composite of the present invention is evenly supported on the inside and the surface of the porous carbon material, when used as a positive electrode active material of a lithium secondary battery, it is possible to improve the overvoltage of the battery and improve the discharge capacity and lifespan characteristics.
또한, 본 발명의 황-탄소 복합체 제조방법은 작용기로 표면 개질된 다공성 탄소재의 작용기를 제거할 수 있어, 황의 담지를 용이하게 할 뿐만 아니라 다공성 탄소재의 기공 및 표면에 황을 고르게 담지시킬 수 있다.In addition, the sulfur-carbon composite manufacturing method of the present invention can remove the functional groups of the surface-modified porous carbon material as a functional group, and not only facilitates the support of sulfur, but can evenly support the pores and the surface of the porous carbon material. have.
도 1 및 2는 실시예 1에서 제조한 황-탄소 복합체의 SEM 사진이다.1 and 2 are SEM pictures of the sulfur-carbon composite prepared in Example 1.
도 3 및 4는 실시예 2에서 제조한 황-탄소 복합체의 SEM 사진이다.3 and 4 are SEM pictures of the sulfur-carbon composite prepared in Example 2.
도 5는 실시예 1 및 비교예 1의 다공성 탄소재의 TGA 그래프이다.5 is a TGA graph of the porous carbon material of Example 1 and Comparative Example 1.
도 6은 실시예 2 및 비교예 2의 다공성 탄소재의 TGA 그래프이다.6 is a TGA graph of the porous carbon material of Example 2 and Comparative Example 2.
도 7은 실시예 2의 다공성 탄소재의 라만(raman) 측정 그래프이다.7 is a Raman measurement graph of the porous carbon material of Example 2.
도 8은 비교예 2의 다공성 탄소재의 라만(raman) 측정 그래프이다.8 is a Raman measurement graph of the porous carbon material of Comparative Example 2.
도 9는 비교예 3의 다공성 탄소재의 라만(raman) 측정 그래프이다.9 is a Raman measurement graph of the porous carbon material of Comparative Example 3.
도 10은 실시예 1 및 비교예 1의 황-탄소 복합체의 전기 전도도 그래프이다.10 is a graph of electrical conductivity of the sulfur-carbon composites of Example 1 and Comparative Example 1.
도 11은 실시예 2 및 비교예 2의 황-탄소 복합체의 전기 전도도 그래프이다.11 is a graph of electrical conductivity of the sulfur-carbon composites of Example 2 and Comparative Example 2.
도 12는 실시예 1 및 비교예 1의 황-탄소 복합체를 양극 활물질로 하여 제조된 전지의 충·방전 그래프이다.12 is a charge-discharge graph of a battery prepared using the sulfur-carbon composite of Example 1 and Comparative Example 1 as a positive electrode active material.
도 13은 실시예 2 및 비교예 2의 황-탄소 복합체를 양극 활물질로 하여 제조된 전지의 충·방전 그래프이다.13 is a charge-discharge graph of a battery prepared using the sulfur-carbon composite of Example 2 and Comparative Example 2 as a positive electrode active material.
도 14는 실시예 1 및 비교예 1의 황-탄소 복합체를 양극 활물질로 하여 제조된 전지의 수명특성을 측정한 그래프이다.14 is a graph measuring the life characteristics of the battery prepared by using the sulfur-carbon composite of Example 1 and Comparative Example 1 as a positive electrode active material.
도 15는 실시예 2 및 비교예 2의 황-탄소 복합체를 양극 활물질로 하여 제조된 전지의 수명특성을 측정한 그래프이다.15 is a graph measuring the life characteristics of the battery prepared by using the sulfur-carbon composite of Example 2 and Comparative Example 2 as a positive electrode active material.
이하, 본 발명을 보다 자세히 설명한다.Hereinafter, the present invention will be described in more detail.
황-탄소 복합체Sulfur-carbon complex
본 발명은 다공성 탄소재; 및The present invention is a porous carbon material; And
상기 다공성 탄소재의 내부 및 표면 중 적어도 일부에 황;을 포함하는 황-탄소 복합체로,A sulfur-carbon composite containing sulfur; at least a part of the inside and the surface of the porous carbon material,
상기 황-탄소 복합체의 비표면적은 7 내지 20m2/g이고, 기공부피는 0.1 내지 0.3cm3/g인, 황-탄소 복합체에 관한 것이다.The sulfur-carbon composite has a specific surface area of 7 to 20 m 2 / g, and a pore volume of 0.1 to 0.3 cm 3 / g, which relates to a sulfur-carbon composite.
본 발명의 황-탄소 복합체의 비표면적은 7 내지 20m2/g, 바람직하게는 8 내지 15m2/g이다. 상기 황-탄소 복합체의 비표면적이 7m2/g 미만이면 다공성 탄소재의 표면을 황이 덮고 있는 것으로 황이 다공성 탄소재에 고르게 담지되지 않은 것을 의미하며, 이로부터 황-탄소 복합체의 전기 전도도가 감소할 수 있으며, 20m2/g을 초과하면 다공성 탄소재의 내부에 황이 제대로 담지되지 않은 것을 의미한다.The specific surface area of the sulfur-carbon composite of the present invention is 7 to 20 m 2 / g, preferably 8 to 15 m 2 / g. If the specific surface area of the sulfur-carbon composite is less than 7 m 2 / g, it means that the surface of the porous carbon material is sulfur, and that the sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite decreases. If it exceeds 20m 2 / g, it means that the sulfur is not properly supported inside the porous carbon material.
또한, 본 발명의 황-탄소 복합체의 기공 부피는 0.1 내지 0.3cm3/g, 바람직하게는 0.1 내지 0.15cm3/g이다. 상기 황-탄소 복합체의 기공 부피가 0.1cm3/g 미만이면 다공성 탄소재의 표면을 황이 덮고 있는 것으로 황이 다공성 탄소재에 고르게 담지되지 않은 것을 의미하며, 이로부터 황-탄소 복합체의 전기 전도도가 감소할 수 있으며, 0.3cm3/g을 초과하면 다공성 탄소재의 내부에 황이 제대로 담지되지 않은 것을 의미한다.Further, the pore volume of the sulfur-carbon composite of the present invention is 0.1 to 0.3 cm 3 / g, preferably 0.1 to 0.15 cm 3 / g. When the pore volume of the sulfur-carbon composite is less than 0.1 cm 3 / g, the surface of the porous carbon material is covered with sulfur, which means that sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite is reduced. If it exceeds 0.3cm 3 / g, it means that sulfur is not properly supported inside the porous carbon material.
본 발명의 황-탄소 복합체는 상기의 비표면적으로 인하여 다공성 탄소재의 표면 및 내부 중 적어도 일부에 황이 고르게 담지되어 있으며, 상기의 기공부피로 인하여 다공성 탄소재의 내부에 황이 고르게 담지된 것을 확인할 수 있다. It can be seen that the sulfur-carbon composite of the present invention has sulfur evenly supported on at least a part of the surface and inside of the porous carbon material due to the specific surface area, and sulfur is evenly supported inside the porous carbon material due to the pore volume. have.
따라서, 본 발명의 황-탄소 복합체는 다공성 탄소재의 내부 및 표면 중 적어도 일부에 황이 고르게 담지되어 있어, 상기 황-탄소 복합체의 전기 전도도를 향상시킬 수 있고, 이를 전극 활물질로 포함하는 전지의 구동특성, 바람직하게는 방전용량 및 수명특성 등을 향상시킬 수 있다.Therefore, in the sulfur-carbon composite of the present invention, sulfur is evenly supported on at least a part of the inside and the surface of the porous carbon material, so that the electrical conductivity of the sulfur-carbon composite can be improved, and driving of a battery including the same as an electrode active material Characteristics, preferably discharge capacity and life characteristics.
본 발명의 황-탄소 복합체의 비표면적 및 기공 부피는 친수성 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기를 제거한 후, 황을 담지함으로써 얻을 수 있다.The specific surface area and pore volume of the sulfur-carbon composite of the present invention can be obtained by heat-treating a porous carbon material surface-modified with a hydrophilic functional group, removing the functional group, and supporting sulfur.
즉, 본 발명의 황-탄소 복합체의 다공성 탄소재는 친수성 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기가 제거된 다공성 탄소재이다.That is, the porous carbon material of the sulfur-carbon composite of the present invention is a porous carbon material with functional groups removed by heat-treating the porous carbon material modified with a hydrophilic functional group.
친수성 작용기로 표면 개질된 다공성 탄소재는 일반적으로 다공성 탄소재를 산으로 처리하여 제조된 것일 수 있으며, 상기 친수성 작용기는 히드록시기 또는 카르복시기일 수 있다.The porous carbon material surface-modified with a hydrophilic functional group may generally be prepared by treating the porous carbon material with an acid, and the hydrophilic functional group may be a hydroxy group or a carboxy group.
상기 친수성 작용기로 표면 개질된 다공성 탄소재는 친수성 작용기로 인하여 우수한 전기 전도도를 나타낼 수 있다. 그러나 다공성 탄소재의 친수성 작용기는 소수성을 나타내는 황과의 친화력이 우수하지 못하여 황을 고르게 담지시키지 못할 뿐만 아니라, 황 담지시 황이 다공성 탄소재의 표면을 덮어 황-탄소 복합체의 전기 전도도가 크게 감소될 수 있다. 따라서, 상기 친수성 작용기로 표면 개질된 다공성 탄소재의 전기 전도도가 우수하더라도 황을 고르게 담지시키지 못하기 때문에 이를 포함한 황-탄소 복합체를 전극 활물질로 사용할 경우 전지의 구동이 정상적으로 이루어지지 않을 수 있다.The porous carbon material surface-modified with the hydrophilic functional group may exhibit excellent electrical conductivity due to the hydrophilic functional group. However, the hydrophilic functional group of the porous carbon material does not have excellent affinity with sulfur, which exhibits hydrophobicity, and thus does not evenly support sulfur. When sulfur is supported, the sulfur covers the surface of the porous carbon material, thereby significantly reducing the electrical conductivity of the sulfur-carbon composite. You can. Therefore, even if the electrical conductivity of the porous carbon material surface-modified with the hydrophilic functional group does not evenly support sulfur, when the sulfur-carbon composite including it is used as an electrode active material, the battery may not be normally operated.
이에, 본 발명에서는 친수성 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기가 제거된 다공성 탄소재를 사용하였으며, 상기 다공성 탄소재를 포함하는 본 발명의 황-탄소 복합체는 상술한 범위의 비표면적 및 기공 부피를 가져 황이 다공성 탄소재에 고르게 담지된 것을 의미하며, 그로부터 우수한 전기 전도도를 나타낼 수 있다.Accordingly, in the present invention, a porous carbon material having a functional group removed by heat-treating a porous carbon material modified with a hydrophilic functional group was used, and the sulfur-carbon composite of the present invention containing the porous carbon material has a specific surface area in the above-mentioned range and It has a pore volume, which means that sulfur is evenly supported on the porous carbon material, from which it can exhibit excellent electrical conductivity.
따라서, 본 발명의 황-탄소 복합체의 상기 작용기가 제거된 다공성 탄소재는 상술한 바와 같이 친수성 작용기로 인하여 발생하는 황의 담지를 고르게 하지 못하는 문제점을 해결할 수 있어 전기 전도도가 우수한 황-탄소 복합체를 제공할 수 있다.Accordingly, the porous carbon material from which the functional group of the sulfur-carbon composite of the present invention is removed can solve the problem of not evenly supporting the sulfur generated due to the hydrophilic functional group as described above, thereby providing a sulfur-carbon composite having excellent electrical conductivity. You can.
일례로, 같은 양의 황을 친수성 작용기로 표면 개질된 다공성 탄소재 및 친수성 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기가 제거된 다공성 탄소재에 각각 담지시켜 제조된 황-탄소 복합체는, 같은 양의 황이 담지되었다 하더라도 친수성 작용기로 표면 개질된 다공성 탄소재는 친수성 작용기로 인하여 황을 고르게 담지시키지 못하여 전지의 구동을 정상적으로 작동시키지 못하나, 열처리하여 작용기가 제거된 다공성 탄소재는 작용기가 존재하지 않으므로 황을 고르게 담지시킬 수 있어 전기 전도도가 우수하며, 전지의 방전 용량 및 수명 특성 등을 향상시킬 수 있다.For example, a sulfur-carbon composite prepared by heat-treating the same amount of sulfur on a porous carbon material surface-modified with a hydrophilic functional group and a porous carbon material surface-modified with a hydrophilic functional group on a porous carbon material having a functional group removed is the same. Even if a positive amount of sulfur is supported, the porous carbon material surface-modified with a hydrophilic functional group does not evenly support sulfur due to the hydrophilic functional group, and thus, the operation of the battery cannot be normally operated. Since it can be supported evenly, it has excellent electrical conductivity and can improve the discharge capacity and life characteristics of the battery.
보다 구체적으로, 상기 열처리하여 작용기가 제거된 다공성 탄소재의 열중량 분석(Thermogravimetric Analyzer, TGA) 결과, 0℃에서 900℃까지 승온하였을 때 중량 감소율이 1% 이하이다. 열처리를 통해 작용기의 제거가 이루어졌으므로 열중량 분석시 중량 감소가 매우 미미하게 나타난다. 그러나 친수성 작용기로 표면 개질된 다공성 탄소재는 작용기를 포함하고 있으므로 2% 이상의 중량 감소를 보인다.More specifically, as a result of thermogravimetric analysis (Thermogravimetric Analyzer, TGA) of the porous carbon material from which the functional groups are removed by the heat treatment, the weight reduction rate is 1% or less when the temperature is raised from 0 ° C to 900 ° C. Since the functional groups were removed through heat treatment, the weight reduction is very small when thermogravimetric analysis. However, since the porous carbon material surface-modified with a hydrophilic functional group contains a functional group, it shows a weight loss of 2% or more.
또한, 상기 열처리하여 작용기가 제거된 다공성 탄소재는 라만(Raman) 측정시 D/G 피크(peak) 비율(ratio)이 0.8 내지 1.5이다. 상기 비율이 0.8 미만이면 전도성이 크게 감소하고, 1.5를 초과하면 2000℃ 이상의 고온에서 열처리가 진행되었다는 것을 의미하며, 상기 고온의 온도로 인하여 흑연화 반응이 일어나며, 다공성 탄소재의 손상이 발생한다.In addition, the porous carbon material from which the functional groups are removed by the heat treatment has a D / G peak ratio of 0.8 to 1.5 when measuring Raman. If the ratio is less than 0.8, the conductivity is greatly reduced, and if it exceeds 1.5, it means that the heat treatment is performed at a high temperature of 2000 ° C. or higher, and a graphitization reaction occurs due to the high temperature, and damage to the porous carbon material occurs.
본 발명의 황-탄소 복합체에 이용될 수 있는 다공성 탄소재는 절연체인 황에 도전성을 부여할 수 있고, 친수성 작용기로 표면 개질이 가능한 것을 사용한다.The porous carbon material that can be used in the sulfur-carbon composite of the present invention is capable of imparting conductivity to sulfur, which is an insulator, and is capable of surface modification with a hydrophilic functional group.
구체적으로, 상기 다공성 탄소재는 탄소나노튜브, 그래핀, 흑연, 비정질 탄소, 카본 블랙 및 활성탄으로 이루어진 군으로부터 선택되는 1종 이상일 수 있다. 이 중 전기 전도도, 비표면적 및 황 담지량이 우수한 점에서 탄소나노튜브, 흑연 및 카본 블랙이 바람직하다.Specifically, the porous carbon material may be at least one selected from the group consisting of carbon nanotubes, graphene, graphite, amorphous carbon, carbon black and activated carbon. Of these, carbon nanotubes, graphite, and carbon black are preferred from the viewpoint of excellent electrical conductivity, specific surface area, and sulfur loading.
상기 탄소나노튜브(CNT)는 단일벽 탄소나노튜브(SWCNT) 또는 다중벽 탄소나노튜브(MWCNT)일 수 있다. 상기 탄소사노튜브의 직경은 1 내지 200nm인 것이 바람직하고, 1 내지 100nm인 것이 더욱 바람직하며, 1 내지 50nm인 것이 가장 바람직하다. 상기 탄소나노튜브의 직경이 200nm를 초과하는 경우 비표면적이 작아져 전해액과의 반응 면적이 줄어드는 문제점이 있다.The carbon nanotube (CNT) may be a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT). The diameter of the carbon nanotube is preferably 1 to 200 nm, more preferably 1 to 100 nm, and most preferably 1 to 50 nm. When the diameter of the carbon nanotube exceeds 200 nm, there is a problem in that the specific surface area becomes small and the reaction area with the electrolyte decreases.
상기 흑연은 인조 흑연 및 천연 흑연 중 하나 이상이 사용될 수 있다. 천연흑연으로는 인상(flake) 흑연, 고결정질(high crystalline) 흑연, 미정질(microcrystalline or cryptocrystalline; amorphous)흑연 등이 있고, 인조 흑연으로는 일차(primary) 혹은 전기흑연(electrographite), 이차(secondary) 흑연, 흑연섬유(graphite fiber) 등이 있다. 상기 흑연 입자는 상술한 흑연 종류를 1종 단독으로 또는 2종 이상 조합하여 사용할 수 있다.As the graphite, one or more of artificial graphite and natural graphite may be used. Natural graphite includes flake graphite, high crystalline graphite, microcrystalline or cryptocrystalline graphite, and artificial graphite is primary or electrographite, secondary. ) Graphite, graphite fiber, and the like. The graphite particles may be used alone or in combination of two or more of the above-described types of graphite.
상기 흑연 입자는 충·방전시에 리튬 이온을 가역적으로 흡장 방출(intercalation)할 수 있는 것이라면 결정구조가 특별히 제한되지 않는다. 예를 들어, 상기 흑연 입자는 X선 광각회절에 의한 면의 면간격이 0.335 nm 이상 0.337nm 미만, 예를 들어 0.335 nm 이상 0.337 nm 미만일 수 있다.If the graphite particles are capable of reversibly intercalating lithium ions during charging and discharging, the crystal structure is not particularly limited. For example, the graphite particles may have a surface spacing of 0.335 nm or more and less than 0.337 nm, for example, 0.335 nm or more and less than 0.337 nm by X-ray wide-angle diffraction.
또한, 상기 흑연 입자의 크기는 실리콘계 입자의 크기와 동등하거나 작은 형태인 것이 혼합 균일 및 합제 밀도 향상 측면에서 바람직하다. 예를 들어, 상기 흑연 입자의 평균 입경은 20 μm 이하일 수 있으며, 구체적으로 예를 들어 0.1 내지 20 μm 이하일 수 있고, 보다 구체적으로 0.1 내지 10 μm, 1 내지 10 μm, 또는 1 내지 5 μm 일 수 있다.In addition, the size of the graphite particles is preferably equal to or smaller than the size of the silicon-based particles from the viewpoint of improving mixing uniformity and mixture density. For example, the average particle diameter of the graphite particles may be 20 μm or less, specifically, for example, 0.1 to 20 μm, or more specifically, 0.1 to 10 μm, 1 to 10 μm, or 1 to 5 μm have.
상기 카본블랙은 예를 들어 아세틸렌 블랙, 케첸 블랙, 퍼니스 블랙, 오일-퍼니스 블랙, 콜럼비아 탄소, 채널 블랙, 램프 블랙, 서머 블랙으로 이루어진 군에서 선택된 하나 이상일 수 있다. 이러한 카본블랙의 입도는 제한되지 않으나, 평균 입경이 0.01 내지 0.5 μm인 것이 전해액과의 반응 면적 확보 측면에서 바람직하다.The carbon black may be, for example, one or more selected from the group consisting of acetylene black, Ketjen black, furnace black, oil-furnace black, Columbia carbon, channel black, lamp black, and summer black. The particle size of the carbon black is not limited, but an average particle diameter of 0.01 to 0.5 μm is preferable in terms of securing a reaction area with the electrolyte.
상기 황은 무기 황 또는 원소 황(elemental sulfur, S8)이 바람직하다.The sulfur is preferably inorganic sulfur or elemental sulfur (S 8 ).
본 발명에 따른 황-탄소 복합체에서 다공성 탄소재와 황은 1:1 내지 1:9의 중량비로 혼합되는 것이 바람직하다. 다공성 탄소재의 함량이 상기 범위를 초과하면 활물질인 황의 함량이 낮아져 전지 용량 확보에 있어서 문제가 발생하고, 상기 범위 미만이면 다공성 탄소재의 함량이 전기 전도도를 부여하기에 부족하게 되므로, 상기 범위 내에서 적절히 조절한다.In the sulfur-carbon composite according to the present invention, the porous carbon material and sulfur are preferably mixed in a weight ratio of 1: 1 to 1: 9. If the content of the porous carbon material exceeds the above range, the content of sulfur as an active material is lowered, which causes problems in securing battery capacity, and if it is less than the above range, the content of the porous carbon material is insufficient to impart electrical conductivity, so within the above range Adjust accordingly.
본 발명의 황-탄소 복합체의 복합화 방법은 본 발명에서 특별히 한정하지 않으며 당 업계에서 통상적으로 사용되는 방법이 사용될 수 있다. 일례로, 상기 범위의 비표면적을 갖는 다공성 탄소재와 황을 단순 혼합한 다음 열처리하여 복합화 하는 방법이 사용될 수 있다.The method for complexing the sulfur-carbon composite of the present invention is not particularly limited in the present invention, and a method commonly used in the art may be used. As an example, a method of simply mixing a porous carbon material having a specific surface area in the above range and sulfur and then heat-treating the compound may be used.
상기 황은 다공성 탄소재의 내부 및 표면 중 적어도 일부에 담지되어 있으며, 표면 보다는 내부에 보다 많은 양의 황이 담지되어 있다.The sulfur is supported on at least a part of the inside and the surface of the porous carbon material, and a larger amount of sulfur is supported on the inside than on the surface.
본 발명에서 다공성 탄소재의 내부는 다공성 탄소재의 기공을 의미한다.In the present invention, the inside of the porous carbon material means pores of the porous carbon material.
본 발명의 황-탄소 복합체의 직경은 본 발명에서 특별히 한정하지 않으며, 다양할 수 있으나, 바람직하게는 0.1 내지 20μm, 보다 바람직하게는 1 내지 10 μm 일 수 있다. 상기 범위를 만족할 때, 고로딩의 전극을 제조할 수 있다.The diameter of the sulfur-carbon composite of the present invention is not particularly limited in the present invention, and may vary, but may preferably be 0.1 to 20 μm, more preferably 1 to 10 μm. When the above range is satisfied, a high loading electrode can be manufactured.
황-탄소 복합체 제조방법Sulfur-carbon composite manufacturing method
본 발명은 황-탄소 복합체 제조방법에 관한 것으로,The present invention relates to a sulfur-carbon composite manufacturing method,
(a)작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기를 제거하는 단계;(a) removing the functional group by heat-treating the porous carbon material whose surface has been modified with the functional group;
(b)상기 작용기가 제거된 다공성 탄소재를 황 분말과 복합화하여 황-탄소 복합체를 제조하는 단계;를 포함한다.(b) preparing a sulfur-carbon composite by complexing the porous carbon material from which the functional group is removed with sulfur powder.
상기 (a)단계는 작용기로 표면 개질된 다공성 탄소재를 열처리하여 다공성 탄소재의 작용기를 제거하는 단계이다.The step (a) is a step of removing the functional group of the porous carbon material by heat-treating the porous carbon material modified with the functional group.
상기 작용기는 친수성 작용기이며, 바람직하게는 히드록시기 또는 카르복시기일 수 있다.The functional group is a hydrophilic functional group, and may be preferably a hydroxy group or a carboxy group.
탄소 분말 등 탄소계 물질을 산성 용액으로 처리하여 산화시키면 표면에 산소를 포함하는 작용기, 즉 히드록시기 또는 카르복시기 등의 작용기가 생성되는 것으로 알려져 있다. 상기 작용기를 포함하면 전기 전도도가 우수한 효과를 나타낼 수 있다.It is known that when a carbon-based material such as carbon powder is treated with an acidic solution and oxidized, a functional group containing oxygen on the surface, that is, a functional group such as a hydroxy group or a carboxy group is produced. When the functional group is included, an electric conductivity may be excellent.
따라서, 상기 작용기로 표면 개질된 다공성 탄소재는 산으로 처리하여 제조된 것일 수 있다. 상기 산은 질산, 황산 및 이들의 혼합 용액으로부터 선택되는 1종 이상인 것일 수 있다.Therefore, the porous carbon material surface-modified with the functional group may be prepared by treatment with an acid. The acid may be one or more selected from nitric acid, sulfuric acid, and mixed solutions thereof.
구체적으로 산에 다공성 탄소재를 담지한 후 초음파 처리 또는 가열 처리의 간단한 공정으로 작용기로 표면 개질된 다공성 탄소재를 제조할 수 있다.Specifically, after the porous carbon material is supported on the acid, the surface-modified porous carbon material can be produced by a simple process of ultrasonic treatment or heat treatment.
상기 초음파 처리는 당 업계에서 통상 사용되는 초음파 처리기에 의해 이루어질 수 있으며, 처리 온도는 특별히 제한되지 않으나 바람직하기로 15 내지 35℃, 바람직하기로 상온이다.The ultrasonic treatment may be performed by an ultrasonic processor commonly used in the art, and the treatment temperature is not particularly limited, but is preferably 15 to 35 ° C, preferably room temperature.
또한, 가열 처리에 의할 경우는 오토클레이브(Autoclave)와 같은 내열내압성 용기 내에서 이루어질 수 있으며, 가열 온도는 바람직하기로 90 내지 120℃이다. 이러한 혼합용액 처리는 30분 내지 4시간 동안 수행되며, 바람직하기로 1 내지 3시간 동안 수행된다.Further, when subjected to heat treatment, it may be made in a heat-resistant pressure-resistant container such as an autoclave, and the heating temperature is preferably 90 to 120 ° C. The mixed solution treatment is performed for 30 minutes to 4 hours, and preferably for 1 to 3 hours.
또한, 초음파 처리와 가열 처리를 동시에 수행하거나 초음파 처리 후 가열처리와 같이 이들을 순차적으로 수행할 수 있다.In addition, ultrasonic treatment and heat treatment may be performed at the same time, or they may be sequentially performed, such as heat treatment after ultrasonic treatment.
상기 작용기로 표면 개질된 다공성 탄소재를 열처리하여 다공성 탄소재의 작용기를 제거한다.The functionalized surface of the porous carbon material is heat-treated to remove the functional group of the porous carbon material.
상기 열처리는 5 내지 20℃/min의 속도로 500 내지 1000℃까지 승온시킨 후, 상기 온도로 1 내지 5시간 동안 수행하는 것일 수 있다.The heat treatment may be performed at a rate of 5 to 20 ° C / min to 500 to 1000 ° C, and then performed at the temperature for 1 to 5 hours.
상기 승온 속도가 5℃/min미만이면 작용기 제거 반응 이외의 부반응이 일어날 수 있고, 20℃/min을 초과하면 초과된 온도로 반응이 진행될 수 있어 적절하지 않다.If the heating rate is less than 5 ° C / min, side reactions other than the functional group removal reaction may occur, and if it exceeds 20 ° C / min, the reaction may proceed to the excess temperature, which is not suitable.
또한, 상기 온도가 500℃미만이면 작용기가 충분히 제거되지 않을 수 있고, 1000℃를 초과하면 다공성 탄소재의 흑연화가 진행될 수 있다.In addition, if the temperature is less than 500 ° C, functional groups may not be sufficiently removed, and if it exceeds 1000 ° C, graphitization of the porous carbon material may proceed.
또한, 승온 후 열처리 시간이 1시간 미만이면 작용기가 충분히 제거되지 않을 수 있고, 5시간을 초과하면 작용기 제거 반응 이외의 부반응이 일어날 수 있다.In addition, if the heat treatment time after heating is less than 1 hour, the functional groups may not be sufficiently removed, and if it exceeds 5 hours, side reactions other than the functional group removal reaction may occur.
상기 열처리를 통하여 작용기로 표면 개질된 다공성 탄소재의 작용기가 제거된 다공성 탄소재를 제조할 수 있다.Through the heat treatment, a porous carbon material having a functional group of a porous carbon material modified with a functional group may be prepared.
일반적으로 열처리하여 제조된 다공성 탄소재의 경우, 열처리 온도가 약 1500℃이상이다. 상기 온도에서 다공성 탄소재는 작용기 제거뿐만 아니라 흑연화(graphitization) 반응까지 일어나게 된다.In general, in the case of a porous carbon material produced by heat treatment, the heat treatment temperature is about 1500 ° C or higher. At this temperature, the porous carbon material not only removes functional groups but also causes a graphitization reaction.
그러나, 본 발명에서는 500 내지 1000℃의 온도로 열처리함으로써 다공성 탄소재의 흑연화 반응이 일어나지 않으면서도 작용기만을 제거할 수 있다. 따라서, 열처리 후에도 열처리 전의 다공성 탄소재의 성질은 그대로 유지할 수 있어, 친수성 작용기로 표면 개질된 다공성 탄소재와 같이 높은 전기 전도도를 나타낼 수 있다.However, in the present invention, only a functional group can be removed without performing a graphitization reaction of the porous carbon material by heat treatment at a temperature of 500 to 1000 ° C. Therefore, even after the heat treatment, the properties of the porous carbon material before the heat treatment can be maintained as it is, and thus can exhibit high electrical conductivity, such as a porous carbon material modified with a hydrophilic functional group.
상기 열처리하여 작용기가 제거된 다공성 탄소재의 열중량 분석(Thermogravimetric Analyzer, TGA) 결과, 0℃에서 900℃까지 승온하였을 때 중량 감소율이 1% 이하이다. 열처리를 통해 작용기의 제거가 이루어졌으므로 열중량 분석시 중량 감소가 매우 미미하게 나타난다. 그러나 친수성 작용기로 표면 개질된 다공성 탄소재는 작용기를 포함하고 있으므로 2% 이상의 중량 감소를 보인다.As a result of thermogravimetric analysis (Thermogravimetric Analyzer, TGA) of the porous carbon material from which the functional groups are removed by the heat treatment, the weight reduction rate is 1% or less when the temperature is raised from 0 ° C to 900 ° C. Since the functional groups were removed through heat treatment, the weight reduction is very small when thermogravimetric analysis. However, since the porous carbon material surface-modified with a hydrophilic functional group contains a functional group, it shows a weight loss of 2% or more.
또한, 상기 열처리하여 작용기가 제거된 다공성 탄소재는 라만(Raman) 측정시 D/G 피크(peak) 비율(ratio)이 0.8 내지 1.5이다. 상기 비율이 0.8 미만이면 전도성이 크게 감소하고, 1.5를 초과하면 2000℃ 이상의 고온에서 열처리가 진행되었다는 것을 의미하며, 상기 고온의 온도로 인하여 흑연화 반응이 일어나며, 다공성 탄소재의 손상이 발생한다.In addition, the porous carbon material from which the functional groups are removed by the heat treatment has a D / G peak ratio of 0.8 to 1.5 when measuring Raman. If the ratio is less than 0.8, the conductivity is greatly reduced, and if it exceeds 1.5, it means that the heat treatment is performed at a high temperature of 2000 ° C. or higher, and a graphitization reaction occurs due to the high temperature, and damage to the porous carbon material occurs.
상기 (b)단계는 상기 (a)단계에서 제조한 작용기가 제거된 다공성 탄소재를 황 분말과 복합화하여 황-탄소 복합체를 제조하는 단계이다.The step (b) is a step of preparing a sulfur-carbon composite by complexing the porous carbon material from which the functional group prepared in step (a) is removed with sulfur powder.
상기 작용기가 제거된 다공성 탄소재 및 황은 1:1 내지 1:9 중량비로 복합화되는 것이 바람직하다. 만일 황의 함량이 상기 범위 미만이면 양극 활물질로 사용되기에 활물질 양이 부족하게 되고, 다공성 탄소재가 상기 범위 미만이면 황-탄소 복합체의 전기 전도도가 충분하지 않게 되므로 상기 범위 내에서 적절히 조절한다.It is preferable that the porous carbon material and sulfur from which the functional group is removed are compounded in a weight ratio of 1: 1 to 1: 9. If the sulfur content is less than the above range, the amount of the active material is insufficient to be used as the positive electrode active material, and if the porous carbon material is less than the above range, the electrical conductivity of the sulfur-carbon composite becomes insufficient, so it is appropriately adjusted within the above range.
상기 복합화 방법은 특별히 제한되지 않으며, 건식 복합화 또는 스프레이 코팅 등과 같은 습식 복합화 등 당 업계에서 통상적으로 이용되는 방법을 이용할 수 있다. 보다 구체적으로, 황 분말과 작용기가 제거된 다공성 탄소재를 볼 밀링하여 분쇄한 후 120 내지 160℃의 오븐에 20분 내지 1시간 동안 두어 용융된 황이 작용기가 제거된 다공성 탄소재의 내부 및 표면에 고루 담지될 수 있도록 하는 방법이 사용될 수 있다.The complexing method is not particularly limited, and a method commonly used in the art, such as dry compounding or wet complexing such as spray coating, may be used. More specifically, after the sulfur powder and the porous carbon material from which the functional group has been removed are pulverized by ball milling, placed in an oven at 120 to 160 ° C. for 20 minutes to 1 hour, molten sulfur is placed on the inside and the surface of the porous carbon material from which the functional group has been removed. Any method can be used to ensure even loading.
상기 황-탄소 복합체의 비표면적은 7 내지 20m2/g, 바람직하게는 8 내지 15m2/g이다. 상기 황-탄소 복합체의 비표면적이 7m2/g 미만이면 다공성 탄소재의 표면을 황이 덮고 있는 것으로 황이 다공성 탄소재에 고르게 담지되지 않은 것을 의미하며, 이로부터 황-탄소 복합체의 전기 전도도가 감소할 수 있으며, 20m2/g을 초과하면 다공성 탄소재의 내부에 황이 제대로 담지되지 않은 것을 의미한다.The specific surface area of the sulfur-carbon composite is 7 to 20 m 2 / g, preferably 8 to 15 m 2 / g. If the specific surface area of the sulfur-carbon composite is less than 7 m 2 / g, it means that the surface of the porous carbon material is sulfur, and that the sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite decreases. If it exceeds 20m 2 / g, it means that the sulfur is not properly supported inside the porous carbon material.
또한, 본 발명의 황-탄소 복합체의 기공 부피는 0.1 내지 0.3cm3/g, 바람직하게는 0.1 내지 0.15cm3/g이다. 상기 황-탄소 복합체의 기공 부피가 0.1cm3/g 미만이면 다공성 탄소재의 표면을 황이 덮고 있는 것으로 황이 다공성 탄소재에 고르게 담지되지 않은 것을 의미하며, 이로부터 황-탄소 복합체의 전기 전도도가 감소할 수 있으며, 0.3cm3/g을 초과하면 다공성 탄소재의 내부에 황이 제대로 담지되지 않은 것을 의미한다.Further, the pore volume of the sulfur-carbon composite of the present invention is 0.1 to 0.3 cm 3 / g, preferably 0.1 to 0.15 cm 3 / g. When the pore volume of the sulfur-carbon composite is less than 0.1 cm 3 / g, the surface of the porous carbon material is covered with sulfur, which means that sulfur is not evenly supported on the porous carbon material, from which the electrical conductivity of the sulfur-carbon composite is reduced. If it exceeds 0.3cm 3 / g, it means that sulfur is not properly supported inside the porous carbon material.
리튬 이차전지용 양극Anode for lithium secondary battery
또한, 본 발명은 상술한 본 발명의 황-탄소 복합체를 포함하는 리튬 이차전지용 양극에 관한 것이다.In addition, the present invention relates to a positive electrode for a lithium secondary battery comprising the sulfur-carbon composite of the present invention described above.
상기 황-탄소 복합체는 리튬 이차전지용 양극의 양극 활물질로 사용되는 것이며, 상기 리튬 이차전지용 양극은 바람직하게는 리튬-황 전지용 양극일 수 있다.The sulfur-carbon composite is used as a positive electrode active material for a positive electrode for a lithium secondary battery, and the positive electrode for a lithium secondary battery may be preferably a positive electrode for a lithium-sulfur battery.
상기 양극은 집전체에 양극 조성물을 도포하고, 진공 건조하여 형성될 수 있다. The positive electrode may be formed by applying a positive electrode composition to a current collector and vacuum drying.
상기 양극 집전체는 일반적으로 3 내지 500㎛의 두께로 만들 수 있고, 전지에 화학적 변화를 유발하지 않으면서 높은 도전성을 가지는 것이라면 특히 제한하지 않는다. 예컨대 스테인레스 스틸, 알루미늄, 구리, 티타늄 등의 전도성 금속을 사용할 수 있고, 바람직하게는 알루미늄 집전체를 사용할 수 있다. 이러한 양극 집전체는 필름, 시트, 호일, 네트, 다공질체, 발포체 또는 부직포체 등 다양한 형태가 가능하다.The positive electrode current collector may be generally made to a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and preferably, an aluminum current collector can be used. The positive electrode current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.
상기 양극 조성물은 상술한 본 발명의 황-탄소 복합체를 양극 활물질로 포함하며, 추가로 도전재 및 바인더를 포함할 수 있다.The positive electrode composition includes the above-described sulfur-carbon composite of the present invention as a positive electrode active material, and may further include a conductive material and a binder.
상기 도전재는 양극 활물질에 추가적인 도전성을 부여하고, 전자가 양극 내에서 원활하게 이동하도록 하기 위한 역할을 하는 것으로, 전지에 화학적 변화를 유발하지 않으면서 도전성이 우수하고 넓은 표면적을 제공할 수 있는 것이면 특별히 제한하지는 않으나, 바람직하게는 탄소계 물질을 사용한다.The conductive material imparts additional conductivity to the positive electrode active material, and serves to move electrons smoothly within the positive electrode. If the conductive material is excellent in conductivity and can provide a large surface area without causing chemical changes, Although not limited, carbon-based materials are preferably used.
상기 탄소계 물질로는 천연 흑연, 인조 흑연, 팽창 흑연, 그래핀(Graphene)과 같은 흑연(Graphite)계, 활성탄(Active carbon)계, 채널 블랙(Channel black), 퍼니스 블랙(Furnace black), 써말 블랙(Thermal black), 컨택트 블랙(Contact black), 램프 블랙(Lamp black), 아세틸렌 블랙(Acetylene black)과 같은 카본 블랙(Carbon black)계, 탄소 섬유(Carbon fiber)계, 탄소나노튜브(Carbon nanotube:CNT), 풀러렌(Fullerene)과 같은 탄소 나노 구조체 및 이들의 조합으로 이루어진 군으로부터 선택되는 1종 이상을 사용할 수 있다.The carbon-based material includes natural graphite, artificial graphite, expanded graphite, graphite-based graphite, active carbon-based, channel black, furnace black, and thermal. Carbon black, carbon fiber, carbon nanotubes such as thermal black, contact black, lamp black, and acetylene black : CNT), carbon nanostructures such as fullerene, and one or more selected from the group consisting of combinations thereof.
상기 탄소계 물질 이외에도, 목적에 따라 금속 메쉬 등의 금속성 섬유; 구리(Cu), 은(Ag), 니켈(Ni), 알루미늄(Al) 등의 금속성 분말; 또는 폴리페닐렌 유도체 등의 유기 도전성 재료도 사용할 수 있다. 상기 도전성 재료들은 단독 또는 혼합하여 사용될 수 있다.In addition to the carbon-based material, metallic fibers such as a metal mesh depending on the purpose; Metallic powders such as copper (Cu), silver (Ag), nickel (Ni), and aluminum (Al); Alternatively, organic conductive materials such as polyphenylene derivatives can also be used. The conductive materials may be used alone or in combination.
또한, 상기 바인더는 양극 활물질에 집전체에 대한 부착력을 제공하며, 상기 바인더는 용매에 잘 용해되어야 하며, 양극 활물질과 도전재와의 도전 네트워크를 잘 구성해주어야 할 뿐만 아니라 전해액의 함침성도 적당히 가져야 한다.In addition, the binder provides adhesion to the current collector to the positive electrode active material, the binder must be well soluble in a solvent, must not only properly constitute a conductive network between the positive electrode active material and the conductive material, but also have proper impregnation properties of the electrolyte. .
본 발명에 적용 가능한 바인더는 당해 업계에서 공지된 모든 바인더들일 수 있고, 구체적으로는, 폴리비닐리덴 플루오라이드(Polyvinylidene fluoride, PVdF) 또는 폴리테트라플루오로에틸렌(Polytetrafluoroethylene, PTFE)을 포함하는 불소수지계 바인더; 스티렌-부타디엔 고무, 아크릴로니트릴-부티디엔 고무, 스티렌-이소프렌 고무를 포함하는 고무계 바인더; 카르복시메틸셀룰로우즈(CMC), 전분, 히드록시프로필셀룰로우즈, 재생 셀룰로우즈를 포함하는 셀룰로오스계 바인더; 폴리 알코올계 바인더; 폴리에틸렌, 폴리프로필렌를 포함하는 폴리 올레핀계 바인더; 폴리 이미드계 바인더; 폴리 에스테르계 바인더; 실란계 바인더;로 이루어진 군에서 선택된 1종 또는 2종 이상의 혼합물이거나 공중합체일 수 있으나, 이에 제한되지 않음은 물론이다.The binder applicable to the present invention may be all binders known in the art, and specifically, a fluorine resin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) ; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Poly alcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; Polyimide-based binders; Polyester-based binders; Silane-based binder; may be a mixture or copolymer of one or more selected from the group consisting of, but is not limited thereto.
상기 바인더 수지의 함량은 상기 양극 조성물 총 중량을 기준으로 0.5 내지 30 중량%일 수 있으나, 이에만 한정되는 것은 아니다. 상기 바인더 수지의 함량이 0.5 중량% 미만인 경우에는, 양극의 물리적 성질이 저하되어 양극 활물질과 도전재가 탈락할 수 있고, 30 중량%를 초과하는 경우에는 양극에서 활물질과 도전재의 비율이 상대적으로 감소되어 전지 용량이 감소될 수 있다.The content of the binder resin may be 0.5 to 30% by weight based on the total weight of the positive electrode composition, but is not limited thereto. When 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 drop off, and when it exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced. Battery capacity can be reduced.
상기 양극 조성물은 슬러리 상태로 제조되어 양극 집전체 상에 도포되며, 슬러리 상태로 제조하기 위한 용매는 건조가 용이해야하며, 바인더를 잘 용해시킬 수 있되, 양극 활물질 및 도전재는 용해시키지 않고 분산 상태로 유지시킬 수 있는 것이 가장 바람직하다. 용매가 양극 활물질을 용해시킬 경우에는 슬러리에서 황의 비중(D = 2.07)이 높기 때문에 황이 슬러리에서 가라앉게 되어 코팅시 집전체에 황이 몰려 도전 네트워크에 문제가 생겨 전지의 작동에 문제가 발생하는 경향이 있다.The positive electrode composition is prepared in a slurry state and applied to the positive electrode current collector, and the solvent for preparing in the slurry state should be easy to dry, and can dissolve the binder well, but do not dissolve the positive electrode active material and the conductive material, but in a dispersed state. It is most desirable to be able to maintain. When the solvent dissolves the positive electrode active material, the specific gravity of sulfur in the slurry (D = 2.07) is high, so the sulfur sinks in the slurry, and when it is coated, sulfur collects in the current collector, causing problems in the conductive network, which tends to cause problems in battery operation. have.
본 발명에 따른 용매는 물 또는 유기 용매가 가능하며, 상기 유기 용매는 디메틸포름아미드, 이소프로필알콜, 아세토니트릴, 메탄올, 에탄올, 및 테트라하이드로퓨란으로 이루어진 군으로부터 선택되는 1종 이상을 포함하는 유기 용매가 적용 가능하다.The solvent according to the present invention can be water or an organic solvent, and the organic solvent includes one or more selected from the group consisting of dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol, and tetrahydrofuran. Solvents are applicable.
상기 양극 조성물의 혼합은 통상의 혼합기, 예컨대 레이트스 믹서, 고속 전단 믹서, 호모 믹서 등을 이용하여 통상의 방법으로 교반할 수 있다.The positive electrode composition may be mixed by a conventional method using a conventional mixer, such as a rate mixer, a high-speed shear mixer, or a homo mixer.
상기 슬러리는 슬러리의 점도 및 형성하고자 하는 양극의 두께에 따라 적절한 두께로 집전체에 코팅할 수 있으며, 바람직하게는 10 내지 300㎛ 범위 내에서 적절히 선택할 수 있다.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 anode to be formed, and preferably, it may be appropriately selected within a range of 10 to 300 μm.
이때 상기 슬러리를 코팅하는 방법으로 그 제한은 없으며, 예컨대, 닥터 블레이드 코팅(Doctor blade coating), 딥 코팅(Dip coating), 그라비어 코팅(Gravure coating), 슬릿 다이 코팅(Slit die coating), 스핀 코팅(Spin coating), 콤마 코팅(Comma coating), 바 코팅(Bar coating), 리버스 롤 코팅(Reverse roll coating), 스크린 코팅(Screen coating), 캡 코팅(Cap coating)방법 등을 수행하여 제조할 수 있다.At this time, there is no limitation as a method of coating the slurry, 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, and cap coating may be performed.
리튬 이차전지Lithium secondary battery
또한, 본 발명은 양극; 음극; 상기 양극과 음극 사이에 개재되는 분리막; 및 전해액을 포함하는 리튬 이차전지에 관한 것으로, 상기 양극은 상술한 본 발명의 리튬 이차 전지용 양극이다.In addition, the present invention is an anode; cathode; A separator interposed between the anode and the cathode; And it relates to a lithium secondary battery comprising an electrolyte, the positive electrode is a positive electrode for a lithium secondary battery of the present invention described above.
또한, 본 발명의 리튬 이차전지는 바람직하게는 리튬-황 전지일 수 있다.Further, the lithium secondary battery of the present invention may be preferably a lithium-sulfur battery.
상기 음극은 집전체와 그의 일면 또는 양면에 형성된 음극 활물질층으로 구성될 수 있다. 또는 상기 음극은 리튬 금속판일 수 있다.The negative electrode may be composed of a current collector and a negative electrode active material layer formed on one or both surfaces thereof. Alternatively, the negative electrode may be a lithium metal plate.
상기 집전체는 음극 활물질의 지지를 위한 것으로, 우수한 도전성을 가지고 리튬 이차전지의 전압영역에서 전기화학적으로 안정한 것이라면 특별히 제한되는 것은 아니며, 예를 들어, 구리, 스테인리스 스틸, 알루미늄, 니켈, 티타늄, 팔라듐, 소성 탄소, 구리나 스테인리스 스틸 표면에 카본, 니켈, 은 등으로 표면 처리한 것, 알루미늄-카드뮴 합금 등이 사용될 수 있다.The current collector is for supporting the negative electrode active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, and palladium , Surface-treated with carbon, nickel, silver, etc. on the surface of calcined carbon, copper or stainless steel, aluminum-cadmium alloy, and the like can be used.
상기 음극 집전체는 그것의 표면에 미세한 요철을 형성하여 음극 활물질과의 결합력을 강화시킬 수 있으며, 필름, 시트, 호일, 메쉬, 네트, 다공질체, 발포체, 부직포체 등 다양한 형태를 사용할 수 있다.The negative electrode current collector can form a fine concavo-convex on its surface to enhance the bonding strength with the negative electrode active material, and various forms such as a film, sheet, foil, mesh, net, porous body, foam, and non-woven fabric can be used.
상기 음극 활물질은 리튬 이온을 가역적으로 인터칼레이션(Intercalation) 또는 디인터칼레이션(Deintercalation)할 수 있는 물질, 리튬 이온과 반응하여 가역적으로 리튬 함유 화합물을 형성할 수 있는 물질, 리튬 금속 또는 리튬 합금을 사용할 수 있다.The negative active material is a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly reacting with lithium ions to form a lithium-containing compound, lithium metal or lithium alloy Can be used.
상기 리튬 이온을 가역적으로 인터칼레이션 또는 디인터칼레이션할 수 있는 물질은 예를 들어, 결정질 탄소, 비정질 탄소 또는 이들의 혼합물일 수 있다.The material capable of reversibly intercalating or deintercalating the lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.
상기 리튬 이온과 반응하여 가역적으로 리튬 함유 화합물을 형성할 수 있는 물질은 예를 들어, 산화주석, 티타늄나이트레이트, 또는 실리콘일 수 있다.A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion may be, for example, tin oxide, titanium nitrate, or silicon.
상기 리튬 합금은 예를 들어, 리튬(Li)과 나트륨(Na), 칼륨(K), 루비듐(Rb), 세슘(Cs), 프랑슘(Fr), 베릴륨(Be), 마그네슘(Mg), 칼슘(Ca), 스트론튬(Sr), 바륨(Ba), 라듐(Ra), 알루미늄(Al) 및 주석(Sn)으로 이루어지는 군에서 선택되는 금속의 합금일 수 있다.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), and tin (Sn).
전술한 양극과 음극 사이에는 추가적으로 분리막이 포함될 수 있다. 상기 분리막은 상기 양극과 음극을 서로 분리 또는 절연시키고, 양극과 음극 사이에 리튬 이온 수송을 가능하게 하는 것으로 다공성 비전도성 또는 절연성 물질로 이루어질 수 있다. 이러한 분리막은 필름과 같은 독립적인 부재일 수도 있고, 양극 및/또는 음극에 부가된 코팅층일 수 있다.A separator may be additionally included between the aforementioned positive electrode and negative electrode. The separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport 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 film, or may be a coating layer added to the anode and / or cathode.
상기 분리막을 이루는 물질은 예를 들어 폴리에틸렌 및 폴리프로필렌 등의 폴리올레핀, 유리 섬유 여과지 및 세라믹 물질이 포함되나, 이에 한정되지 않고, 그 두께는 약 5 내지 약 50 ㎛, 바람직하게는 약 5 내지 약 25 ㎛일 수 있다.The material constituting the separator includes, for example, polyolefin such as polyethylene and polypropylene, glass fiber filter paper, and ceramic materials, but is not limited thereto, and the thickness is about 5 to about 50 μm, preferably about 5 to about 25 Μm.
상기 전해액은 리튬염을 함유하는 비수계 전해질로서 리튬염과 전해액으로 구성되어 있으며, 전해액으로는 비수계 유기 용매, 유기 고체 전해질 및 무기 고체 전해질 등이 사용된다.The electrolyte is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and an electrolyte, and a non-aqueous organic solvent, an organic solid electrolyte and an inorganic solid electrolyte are used as the electrolyte.
상기 리튬염은 리튬-황 전지용 전해액에 통상적으로 사용되는 것이라면 제한없이 사용될 수 있다. 예를 들어, LiSCN, LiBr, LiI, LiPF6, LiBF4, LiB10Cl10, LiSO3CF3, LiCl, LiClO4, LiSO3CH3, LiB(Ph)4, LiC(SO2CF3)3, LiN(SO2CF3)2, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, LiFSI, 클로로 보란 리튬, 저급 지방족 카르본산 리튬 등으로 이루어진 군으로부터 1종 이상이 포함될 수 있다.The lithium salt may be used without limitation as long as it is commonly used in the electrolyte solution for lithium-sulfur batteries. For example, LiSCN, LiBr, LiI, LiPF 6 , LiBF 4 , LiB 10 Cl 10 , LiSO 3 CF 3 , LiCl, LiClO 4 , LiSO 3 CH 3 , LiB (Ph) 4 , LiC (SO 2 CF 3 ) 3 , LiN (SO 2 CF 3) 2, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, may be included are one or more from LiFSI, chloro group consisting of borane lithium, lower aliphatic carboxylic acid lithium or the like.
또한, 상기 전해액에서 리튬염의 농도는 0.2 내지 2 M, 구체적으로 0.6 내지 2 M, 더욱 구체적으로 0.7 내지 1.7 M일 수 있다. 상기 리튬염의 농도가 0.2 M 미만으로 사용하면 전해액의 전도도가 낮아져서 전해액 성능이 저하될 수 있고, 2 M을 초과하여 사용하면 전해액의 점도가 증가하여 리튬 이온의 이동성이 감소될 수 있다.In addition, the concentration of the lithium salt in the electrolyte may be 0.2 to 2 M, specifically 0.6 to 2 M, and more specifically 0.7 to 1.7 M. When the concentration of the lithium salt is used less than 0.2 M, the conductivity of the electrolyte may be lowered to degrade the performance of the electrolyte, and when it is used above 2 M, the viscosity of the electrolyte may increase to decrease the mobility of lithium ions.
상기 비수계 유기용매는 리튬염을 잘 용해시켜야 하며, 본 발명의 비수계 유기용매로는, 예컨대, N-메틸-2-피롤리디논, 프로필렌 카보네이트, 에틸렌 카보네이트, 부틸렌 카보네이트, 디메틸 카보네이트, 디에틸 카보네이트, 에틸메틸 카보네이트, 감마-부티로락톤, 1,2-디메톡시 에탄, 1,2-디에톡시 에탄, 테트라히드록시프랑(franc), 2-메틸 테트라하이드로푸란, 디메틸술폭시드, 1,3-디옥소란, 4-메틸-1,3-디옥센, 디에틸에테르, 포름아미드, 디메틸포름아미드, 디옥소란, 아세토니트릴, 니트로메탄, 포름산 메틸, 초산메틸, 인산 트리에스테르, 트리메톡시 메탄, 디옥소란 유도체, 설포란, 메틸 설포란, 1,3-디메틸-2-이미다졸리디논, 프로필렌 카보네이트 유도체, 테트라하이드로푸란 유도체, 에테르, 피로피온산 메틸, 프로피온산 에틸 등의 비양자성 유기용매가 사용될 수 있으며, 상기 유기 용매는 하나 또는 둘 이상의 유기용매들의 혼합물일 수 있다.The non-aqueous organic solvent must dissolve a lithium salt well, and as the non-aqueous organic solvent of the present invention, 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, tetrahydroxyfran, franchyl 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 Non-proton such as methoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, ethyl propionate Organic solvent It may be used, and the organic solvent may be a mixture of one or more organic solvents.
상기 유기 고체 전해질로는, 예컨대, 폴리에틸렌 유도체, 폴리에틸렌 옥사이드 유도체, 폴리프로필렌 옥사이드 유도체, 인산 에스테르 폴리머, 폴리 에지테이션 리신(Agitation lysine), 폴리에스테르 설파이드, 폴리비닐 알코올, 폴리 불화비닐리덴, 이온성 해리기를 포함하는 중합체 등이 사용될 수 있다.Examples of the organic solid electrolyte include, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and ionic dissociation. Polymers containing groups and the like can be used.
상기 무기 고체 전해질로는, 예컨대, Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2 등의 Li의 질화물, 할로겐화물, 황산염 등이 사용될 수 있다.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 Li nitrides such as SiO 4 -LiI-LiOH and Li 3 PO 4 -Li 2 S-SiS 2 , halides, sulfates, and the like can be used.
본 발명의 전해질에는 충·방전 특성, 난연성 등의 개선을 목적으로, 예컨대, 피리딘, 트리에틸포스파이트, 트리에탄올아민, 환상 에테르, 에틸렌 디아민, n-글라임(glyme), 헥사 인산 트리 아미드, 니트로벤젠 유도체, 유황, 퀴논 이민 염료, N-치환 옥사졸리디논, N,N-치환 이미다졸리딘, 에틸렌 글리콜 디알킬 에테르, 암모늄염, 피롤, 2-메톡시 에탄올, 삼염화 알루미늄 등이 첨가될 수도 있다. 경우에 따라서는, 불연성을 부여하기 위하여, 사염화탄소, 삼불화에틸렌 등의 할로겐 함유 용매를 더 포함시킬 수도 있고, 고온 보존 특성을 향상시키기 위하여 이산화탄산 가스를 더 포함시킬 수도 있으며, FEC(Fluoro-ethylene carbonate), PRS(Propene sultone), FPC(Fluoro-propylene carbonate) 등을 더 포함시킬 수 있다.The electrolyte of the present invention is for the purpose of improving charge / discharge characteristics, flame retardance, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-ethylene) carbonate), PRS (Propene sultone), FPC (Fluoro-propylene carbonate), and the like.
상기 전해질은 액상 전해질로 사용할 수도 있고, 고체 상태의 전해질 세퍼레이터 형태로도 사용할 수 있다. 액상 전해질로 사용할 경우에는 전극을 물리적으로 분리하는 기능을 갖는 물리적인 분리막으로서 다공성 유리, 플라스틱, 세라믹 또는 고분자 등으로 이루어진 분리막을 더 포함한다.The electrolyte may be used as a liquid electrolyte, or may be used in the form of a solid electrolyte separator. When used as a liquid electrolyte, a physical separator having a function of physically separating electrodes further includes a separator made of porous glass, plastic, ceramic, or polymer.
이하, 본 발명을 구체적으로 설명하기 위해 실시예를 들어 상세하게 설명하기로 한다. 그러나 본 발명에 따른 실시예는 여러 가지 다른 형태로 변형될 수 있 으며, 본 발명의 범위가 아래에서 상술하는 실시예에 한정되는 것으로 해석되어서는 아니 된다. 본 발명의 실시예는 당업계에서 평균적인 지식을 가진 자에게 본 발명을 보다 완전하게 설명하기 위해서 제공되는 것이다.Hereinafter, examples will be described in detail to specifically describe the present invention. However, the embodiment according to the present invention may be modified in various other forms, and the scope of the present invention should not be interpreted as being limited to the above-described embodiment. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.
<황-탄소 복합체 제조><Preparation of sulfur-carbon composite>
실시예 1.Example 1.
산으로 처리된 탄소나노튜브(CNano, FT6120) 10g을 아르곤 분위기에서 1시간 동안 퍼징(purging)하였다. 그 후, 10℃/min의 승온 속도로 850℃까지 승온시킨 뒤 3시간 동안 열처리하여 작용기가 제거된 탄소나노튜브를 제조하였다.10 g of acid treated carbon nanotubes (CNano, FT6120) were purged in an argon atmosphere for 1 hour. Thereafter, the temperature was raised to 850 ° C at a heating rate of 10 ° C / min, and then heat-treated for 3 hours to prepare a carbon nanotube with functional groups removed.
상기 작용기가 제거된 탄소나노튜브 및 황을 25:75의 중량비로 혼합한 후, 155℃의 온도에서 35분 동안 반응시켜 탄소나노튜브의 내부(기공) 및 표면에 황이 담지된 황-탄소 복합체를 제조하였다(도 1 및 도 2).After mixing the functional group is removed carbon nanotubes and sulfur in a weight ratio of 25:75, and reacted at a temperature of 155 ℃ for 35 minutes to the sulfur (carbon) complex with sulfur on the inside (pores) and the surface of the carbon nanotubes It was prepared (Fig. 1 and Fig. 2).
실시예 2.Example 2.
탄소나노튜브(SUSN, HCNTS10)를 사용한 것을 제외하고는 상기 실시예 1과 동일하게 실시하여 탄소나노튜브의 내부(기공) 및 표면에 황이 담지된 황-탄소 복합체를 제조하였다(도 3 및 도 4).Except for using carbon nanotubes (SUSN, HCNTS10), sulfur-carbon composites in which sulfur was supported on the inside (pores) and surfaces of the carbon nanotubes were prepared in the same manner as in Example 1 (FIGS. 3 and 4). ).
비교예 1.Comparative Example 1.
친수성 작용기로 표면 개질된 탄소나노튜브(CNano, FT6120) 및 황을 25:75의 중량비로 혼합한 후, 155℃의 온도에서 35분 동안 반응시켜 탄소나노튜브의 내부(기공) 및 표면에 황이 담지된 황-탄소 복합체를 제조하였다.After mixing the surface-modified carbon nanotubes (CNano, FT6120) and sulfur at a weight ratio of 25:75 with hydrophilic functional groups, sulfur is supported on the inside (pores) and the surface of the carbon nanotubes by reacting at a temperature of 155 ° C for 35 minutes. A sulfur-carbon composite was prepared.
비교예 2.Comparative Example 2.
친수성 작용기로 표면 개질된 탄소나노튜브(SUSN, HCNTS10)를 사용한 것을 제외하고는 상기 비교예 1과 동일하게 실시하여 탄소나노튜브의 내부(기공) 및 표면에 황이 담지된 황-탄소 복합체를 제조하였다.A sulfur-carbon composite in which sulfur is supported on the inside (pore) and the surface of the carbon nanotube was prepared in the same manner as in Comparative Example 1, except that the surface-modified carbon nanotube (SUSN, HCNTS10) was used as a hydrophilic functional group. .
비교예 3.Comparative Example 3.
산으로 처리된 탄소나노튜브(SUSN, HCNTS10) 10g을 아르곤 분위기에서 1시간 동안 퍼징(purging)하였다. 그 후, 10℃/min의 승온 속도로 2000℃까지 승온시킨 뒤 3시간 동안 열처리하여 작용기가 제거된 탄소나노튜브를 제조하였다.10 g of acid treated carbon nanotubes (SUSN, HCNTS10) were purged in an argon atmosphere for 1 hour. Thereafter, the temperature was raised to 2000 ° C at a heating rate of 10 ° C / min, and then heat-treated for 3 hours to prepare a carbon nanotube with functional groups removed.
상기 작용기가 제거된 탄소나노튜브 및 황을 25:75의 중량비로 혼합한 후, 155℃의 온도에서 35분 동안 반응시켜 탄소나노튜브의 내부(기공) 및 표면에 황이 담지된 황-탄소 복합체를 제조하였다.After mixing the functional group is removed carbon nanotubes and sulfur in a weight ratio of 25:75, and reacted at a temperature of 155 ℃ for 35 minutes to the sulfur (carbon) complex with sulfur on the inside (pores) and the surface of the carbon nanotubes It was prepared.
실험예 1. 탄소나노튜브의 열중량 분석 측정Experimental Example 1. Measurement of thermogravimetric analysis of carbon nanotubes
상기 실시예 1, 실시예 2, 비교예 1 및 비교예 2의 탄소나노튜브의 열중량 분석(Thermogravimetric Analyzer, TGA)을 실시하였다. 0℃에서 900℃까지 승온하였으며, 이 때의 중량 감소율을 측정하여 탄소나노튜브의 작용기 제거 여부를 확인하였다.Thermogravimetric analysis (Thermogravimetric Analyzer, TGA) of the carbon nanotubes of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 was performed. The temperature was raised from 0 ° C to 900 ° C, and the weight reduction rate at this time was measured to confirm whether the carbon nanotubes had functional groups removed.
그 결과를 도 5 및 도 6에 나타내었다.The results are shown in FIGS. 5 and 6.
비교예 1 및 2의 탄소나노튜브는 온도가 증가함에 따라 각각 2% 이상의 중량 손실을 보여 탄소나노튜브가 작용기를 포함하고 있다는 것을 알 수 있었다.The carbon nanotubes of Comparative Examples 1 and 2 showed a weight loss of 2% or more, respectively, as the temperature increased, and it was found that the carbon nanotubes contained functional groups.
그러나, 실시예 1 및 2의 탄소나노튜브는 온도가 증가하여도 약 1% 이하의 중량 감소율을 보여, 중량을 유지하는 결과를 보였다. 그에 따라 실시예 1 및 2의 열처리 과정을 통하여 탄소나노튜브의 작용기가 제거되었음을 알 수 있었으며, 약 2 내지 4 중량%의 작용기가 제거된 것을 확인할 수 있었다.However, the carbon nanotubes of Examples 1 and 2 showed a weight reduction rate of about 1% or less even when the temperature increased, and showed a result of maintaining the weight. Accordingly, it was found that the functional groups of the carbon nanotubes were removed through the heat treatment processes of Examples 1 and 2, and it was confirmed that about 2 to 4% by weight of the functional groups were removed.
실험예 2. 탄소나노튜브의 라만 측정Experimental Example 2. Raman measurement of carbon nanotubes
상기 실시예 2, 비교예 2 및 비교예 3의 탄소나노튜브의 라만(Raman) 분석을 실시하여 상기 탄소나노튜브의 D/G ratio를 측정하였다.Raman analysis of the carbon nanotubes of Example 2, Comparative Example 2 and Comparative Example 3 was performed to measure the D / G ratio of the carbon nanotube.
그 결과를 도 7 내지 9에 나타내었다.The results are shown in FIGS. 7 to 9.
비교예 2를 500 내지 1000℃의 온도로 저온 열처리하여 작용기가 제거된 실시예 2의 탄소나노튜브는 D/G ratio가 1.03으로 나타났다. 열처리 전의 비교예 2의 탄소나노튜브는 D/G ratio가 0.94로, 열처리 전과 후의 D/G ratio가 크게 달라지지 않은 것을 확인할 수 있었다. 이로부터 작용기 제거 과정 중 탄소나노튜브의 흑연화정도가 크게 달라지지 않은 것을 알 수 있다.The carbon nanotube of Example 2, in which the functional group was removed by heat treatment of Comparative Example 2 at a temperature of 500 to 1000 ° C., had a D / G ratio of 1.03. The carbon nanotube of Comparative Example 2 before the heat treatment had a D / G ratio of 0.94, and it was confirmed that the D / G ratio before and after the heat treatment was not significantly changed. From this, it can be seen that the degree of graphitization of the carbon nanotubes does not change significantly during the functional group removal process.
반면, 비교예 2를 2000℃의 온도로 고온 열처리한 비교예 3의 탄소나노튜브는 D/G ratio가 0.51로 나타났다. 이는 상기 온도에서 탄소나노튜브의 흑연화가 진행되어 G peak가 증가한 결과로 볼 수 있다.On the other hand, the carbon nanotubes of Comparative Example 3 in which Comparative Example 2 was heat-treated at a high temperature of 2000 ° C. had a D / G ratio of 0.51. This can be seen as a result of graphitization of the carbon nanotubes at the above temperature and an increase in the G peak.
이로부터 본원 발명의 작용기를 제거하는 열처리 과정은 다공성 탄소재의 흑연화 정도를 크게 바꾸지 않으면서 작용기만을 선택적으로 제거하는 것을 알 수 있었다.From this, it was found that the heat treatment process for removing the functional group of the present invention selectively removes only the functional group without significantly changing the degree of graphitization of the porous carbon material.
실험예 3. 황-탄소 복합체의 비표면적 및 기공 부피 측정Experimental Example 3. Measurement of specific surface area and pore volume of sulfur-carbon composite
상기 실시예 1, 실시예 2 및 비교예 1, 비교예 2에서 제조한 황-탄소 복합체의 비표면적 및 기공 부피를 Belsorp사의 질소흡착장비를 이용하여 측정하였으며, 결과를 하기 표 1에 나타내었다.The specific surface area and pore volume of the sulfur-carbon composites prepared in Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were measured using a nitrogen adsorption equipment of Belsorp, and the results are shown in Table 1 below.
실시예 1Example 1 실시예 2Example 2 비교예 1Comparative Example 1 비교예 2Comparative Example 2
비표면적Specific surface area 8.359m2/g8.359m 2 / g 13.726m2/g13.726m 2 / g 5.863m2/g5.863m 2 / g 6.864m2/g6.864m 2 / g
기공 부피Pore volume 0.106cm3/g0.106cm 3 / g 0.13cm3/g0.13cm 3 / g 0.08cm3/g0.08cm 3 / g 0.08cm3/g0.08cm 3 / g
상기 표 1의 결과에서, 작용기가 제거된 탄소나노튜브로 제조된 실시예 1 및 2의 황-탄소 복합체는 작용기를 포함하는 탄소나노튜브로 제조된 비교예 1 및 2의 황-탄소 복합체 보다 비표면적 및 기공 부피가 큰 것을 확인하였다.In the results of Table 1, the sulfur-carbon composites of Examples 1 and 2 made of carbon nanotubes with functional groups removed were more than the sulfur-carbon composites of Comparative Examples 1 and 2 made of carbon nanotubes containing functional groups. It was confirmed that the surface area and pore volume were large.
따라서, 작용기가 제거된 탄소나노튜브를 포함하는 황-탄소 복합체는 높은 비표면적 및 기공 부피를 가짐에 따라 상기 탄소나노튜브의 기공 및 표면에 황을 고르게 담지하고 있다는 것을 알 수 있다.Therefore, it can be seen that the sulfur-carbon composite including the functional group-removed carbon nanotube has a high specific surface area and pore volume, and evenly supports sulfur on the pores and surface of the carbon nanotube.
실험예 4. 황-탄소 복합체의 전기 전도도 측정Experimental Example 4. Measurement of electrical conductivity of sulfur-carbon composite
HANTECH사의 분체저항측정기를 이용하여 상기 실시예 1, 실시예 2 및 비교예 1, 비교예 2에서 제조한 황-탄소 복합체의 전기 전도도를 측정하였다.The electrical conductivity of the sulfur-carbon composites prepared in Example 1, Example 2, and Comparative Example 1 and Comparative Example 2 was measured using a powder resistance meter manufactured by HANTECH.
그 결과를 도 10 및 도 11에 나타내었다.The results are shown in FIGS. 10 and 11.
작용기가 제거된 탄소나노튜브로 제조된 실시예 1 및 2의 황-탄소 복합체는 작용기를 포함하는 탄소나노튜브로 제조된 비교예 1 및 2의 황-탄소 복합체 보다 높은 전기 전도도를 나타내는 것을 확인하였다.It was confirmed that the sulfur-carbon composites of Examples 1 and 2 made of carbon nanotubes with functional groups removed showed higher electrical conductivity than the sulfur-carbon composites of Comparative Examples 1 and 2 made of carbon nanotubes containing functional groups. .
이는 상기 실험예 2에서 확인한 바와 같이, 작용기가 제거된 탄소나노튜브를 포함하는 황-탄소 복합체는 상기 탄소나노튜브의 기공 및 표면에 황이 고르게 담지되어 있어 높은 전기 전도도를 나타낼 수 있다.As shown in Experimental Example 2, the sulfur-carbon composite including the functional group-removed carbon nanotubes may exhibit high electrical conductivity since sulfur is evenly supported on the pores and surfaces of the carbon nanotubes.
반면, 작용기를 포함하는 탄소나노튜브를 포함하는 황-탄소 복합체는 다공성 탄소재의 표면을 황이 덮고 있어, 높은 전기 전도도를 나타내지 못하였다.On the other hand, the sulfur-carbon composite containing a carbon nanotube containing a functional group does not exhibit high electrical conductivity because the surface of the porous carbon material is covered with sulfur.
실험예 5. 리튬-황 전지의 충·방전 및 수명특성 평가Experimental Example 5. Evaluation of charge / discharge and life characteristics of lithium-sulfur batteries
상기 실시예 1, 실시예 2 및 비교예 1, 비교예 2에서 제조한 황-탄소 복합체를 양극 활물질로 하여 각각의 리튬-황 전지(코인셀)를 제조하였다.Each of the lithium-sulfur batteries (coin cells) was prepared using the sulfur-carbon composites prepared in Example 1, Example 2, and Comparative Example 1 and Comparative Example 2 as positive electrode active materials.
도전재(Denka black) 0.2g과 카르복시메틸셀룰로오스(CMC) 5g을 넣고 지르코니아 볼과 함께 혼합하였다. 그런 다음, 황-탄소 복합체 3.6g과 물을 일정량 넣고 다시 혼합하였다. 마지막으로 스티렌-부타디엔 고무(SBR)를 0.35g 넣고 다시 혼합하여 슬러리를 제조하였다.0.2g of conductive material (Denka black) and 5g of carboxymethylcellulose (CMC) were added and mixed with zirconia balls. Then, a certain amount of sulfur-carbon composite and water were added and mixed again. Finally, 0.35 g of styrene-butadiene rubber (SBR) was added and mixed again to prepare a slurry.
상기 제조된 슬러리를 알루미늄 호일 위에 슬러리를 붓고 블레이드 코터로 200μm 두께로 코팅한 뒤 50℃오븐에서 건조하여 리튬-황 전지용 양극을 제조하였다.The prepared slurry was poured onto an aluminum foil, coated with a 200 μm thickness with a blade coater, and then dried in a 50 ° C. oven to prepare a positive electrode for a lithium-sulfur battery.
아르곤 분위기의 글러브박스에서 스테인레스스틸 하판에 양극, 분리막(polyethylene), 리튬 음극, 가스킷, 스테인레스스틸 코인, 스프링, 스테인레스스틸 상판을 차례로 올려놓고 압력을 가해 코인셀을 조립하였다.In a glove box with an argon atmosphere, a positive electrode, a separator, a lithium negative electrode, a gasket, a stainless steel coin, a spring, and a stainless steel top plate were sequentially placed on a stainless steel lower plate, and pressure was applied to assemble the coin cell.
전해액은 1M LiFSI 1wt%의 LiNO3가 용해된 DOL(1,3-dioxolane):DEGDME(diethylene glycol dimethyl ether)=4:6 (v/v) 혼합액을 타발된 양극 위에 주액하여 사용하였다.The electrolyte solution was used by pouring a mixed solution of DOL (1,3-dioxolane): DEGDME (diethylene glycol dimethyl ether) = 4: 6 (v / v) in which 1% LiFSI 1% LiNO 3 was dissolved by pouring onto the punched anode.
4-1. 충·방전 평가4-1. Charge / discharge evaluation
상기 실시예 1 내지 2 및 비교예 1 내지 2의 리튬-황 전지에 대해, 충·방전 측정장치를 사용하여 충·방전 특성 변화를 시험하였다. 얻어진 전지는 0.1C/0.1C 충전/방전 조건에서 초기 용량을 살펴보았으며, 그 결과를 도 12 및 13에 나타내었다.The lithium-sulfur batteries of Examples 1 to 2 and Comparative Examples 1 to 2 were tested for charge / discharge characteristic changes using a charge / discharge measurement device. The obtained battery was examined for initial capacity under 0.1C / 0.1C charge / discharge conditions, and the results are shown in FIGS. 12 and 13.
실시예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지는 비교예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지 대비 방전 용량 및 과전압이 개선된 것을 확인할 수 있었다.It was confirmed that the lithium-sulfur batteries including the sulfur-carbon composites of Examples 1 and 2 had improved discharge capacity and overvoltage compared to the lithium-sulfur batteries including the sulfur-carbon composites of Comparative Examples 1 and 2.
실시예 1 및 2의 황-탄소 복합체는 황을 고르게 담지하고 있다. 상기 고르게 담지된 황에 의해 황 환원 반응(S8 + 16Li → 8Li2S)의 반응성이 향상되었으며, 그에 따라 방전 용량이 증가하고, 과전압이 개선된 것을 확인할 수 있었다.The sulfur-carbon composites of Examples 1 and 2 support sulfur evenly. The reactivity of the sulfur reduction reaction (S 8 + 16Li → 8Li 2 S) was improved by the evenly supported sulfur, and thus it was confirmed that the discharge capacity increased and the overvoltage was improved.
반면, 작용기를 포함하는 탄소나노튜브를 포함하는 황-탄소 복합체는 다공성 탄소재의 표면을 황이 덮고 있어, 황 환원 반응의 반응성이 개선되지 않아 실시예 1 및 2 보다 낮은 결과를 보였다.On the other hand, the sulfur-carbon composite containing a carbon nanotube containing a functional group is sulfur-covering the surface of the porous carbon material, and the reactivity of the sulfur reduction reaction is not improved, thus showing lower results than Examples 1 and 2.
4-2. 수명특성 평가4-2. Life characteristics evaluation
상기 실시예 1 내지 2 및 비교예 1 내지 2의 리튬-황 전지의 수명 특성 평가를 실시하였다.The life characteristics of the lithium-sulfur batteries of Examples 1 to 2 and Comparative Examples 1 to 2 were evaluated.
충·방전 측정장치를 사용하여 초기 3 cycle 동안 0.1C/0.1C 충전/방전, 그 이후 3 cycle 동안 0.2C/0.2C 충전/방전하고, 이후 0.5C/0.5C로 충전/방전하여 100 cycle의 충·방전을 반복하여 수명특성을 측정하였고, 그 결과를 도 14 및 도 15에 나타내었다.Charge / discharge 0.1C / 0.1C during the initial 3 cycles using the charge / discharge measuring device, then charge / discharge 0.2C / 0.2C for 3 cycles, then charge / discharge at 0.5C / 0.5C to 100 cycles Charging and discharging were repeated to measure the life characteristics, and the results are shown in FIGS. 14 and 15.
실시예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지는 100 cycle 동안 용량을 유지하는 결과를 보였다. 그러나, 비교예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지는 100 cycle 동안 용량을 유지하지 못하는 결과를 보였다.The lithium-sulfur cells including the sulfur-carbon composites of Examples 1 and 2 showed a result of maintaining the capacity for 100 cycles. However, the lithium-sulfur cells including the sulfur-carbon composites of Comparative Examples 1 and 2 showed a result of not maintaining the capacity for 100 cycles.
따라서, 실시예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지는 비교예 1 및 2의 황-탄소 복합체를 포함하는 리튬-황 전지 대비 수명 특성이 개선된 것을 확인할 수 있었다.Therefore, it was confirmed that the lithium-sulfur batteries including the sulfur-carbon composites of Examples 1 and 2 had improved life characteristics compared to the lithium-sulfur batteries including the sulfur-carbon composites of Comparative Examples 1 and 2.
실시예 1 및 2의 황-탄소 복합체의 탄소나노튜브는 작용기가 제거됨에 따라, 황을 고르게 담지하고 있어 그에 따라 이를 포함하는 전지의 수명 특성이 향상되는 것을 알 수 있다.As the carbon nanotubes of the sulfur-carbon composites of Examples 1 and 2 remove the functional groups, it can be seen that the life characteristics of the battery including them are improved accordingly because sulfur is evenly supported.

Claims (18)

  1. 다공성 탄소재; 및Porous carbon materials; And
    상기 다공성 탄소재의 내부 및 표면 중 적어도 일부에 황;을 포함하는 황-탄소 복합체로,A sulfur-carbon composite containing sulfur; at least a part of the inside and the surface of the porous carbon material,
    상기 황-탄소 복합체의 비표면적은 7 내지 20m2/g이고, 기공부피는 0.1 내지 0.3cm3/g인, 황-탄소 복합체.The sulfur-carbon composite has a specific surface area of 7 to 20 m 2 / g, and a pore volume of 0.1 to 0.3 cm 3 / g, sulfur-carbon composite.
  2. 제1항에 있어서, 상기 다공성 탄소재는 친수성 작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기가 제거된 다공성 탄소재인 것을 특징으로 하는 황-탄소 복합체.The sulfur-carbon composite according to claim 1, wherein the porous carbon material is a porous carbon material having functional groups removed by heat-treating the porous carbon material modified with a hydrophilic functional group.
  3. 제2항에 있어서, 상기 작용기가 제거된 다공성 탄소재의 열중량 분석 결과, 0℃에서 900℃까지 승온하였을 때 중량 감소율이 1% 이하이며, 라만 측정시 D/G 비율이 0.8 내지 1.5인 것을 특징으로 하는 황-탄소 복합체.According to claim 2, As a result of thermogravimetric analysis of the porous carbon material from which the functional group has been removed, when the temperature is increased from 0 ° C to 900 ° C, the weight reduction rate is 1% or less, and the D / G ratio is 0.8 to 1.5 when measuring Raman. Characterized by sulfur-carbon complex.
  4. 제2항에 있어서, 상기 다공성 탄소재는 탄소나노튜브, 그래핀, 흑연, 비정질 탄소, 카본블랙 및 활성탄으로 이루어진 군으로부터 선택되는 1종 이상인 것을 특징으로 하는 황-탄소 복합체.The sulfur-carbon composite according to claim 2, wherein the porous carbon material is at least one selected from the group consisting of carbon nanotubes, graphene, graphite, amorphous carbon, carbon black, and activated carbon.
  5. 제1항에 있어서, 상기 황-탄소 복합체는 다공성 탄소재 및 황을 1:1 내지 1:9의 중량비로 포함하고 있는 것을 특징으로 하는 황-탄소 복합체.The sulfur-carbon composite of claim 1, wherein the sulfur-carbon composite comprises a porous carbon material and sulfur in a weight ratio of 1: 1 to 1: 9.
  6. 제1항에 있어서, 상기 황-탄소 복합체의 직경은 0.1 내지 20μm인 것을 특징으로 하는 황-탄소 복합체.The sulfur-carbon composite of claim 1, wherein the sulfur-carbon composite has a diameter of 0.1 to 20 μm.
  7. (a)작용기로 표면 개질된 다공성 탄소재를 열처리하여 작용기를 제거하는 단계;(a) removing the functional group by heat-treating the porous carbon material whose surface has been modified with the functional group;
    (b)상기 작용기가 제거된 다공성 탄소재를 황 분말과 복합화하여 황-탄소 복합체를 제조하는 단계;를 포함하는 황-탄소 복합체 제조방법.(b) preparing a sulfur-carbon composite by complexing the porous carbon material from which the functional group has been removed with sulfur powder;
  8. 제7항에 있어서, 상기 (a)단계의 열처리는 5 내지 20℃/min의 속도로 500 내지 1000℃까지 승온시킨 후 1 내지 5시간 동안 수행는 것을 특징으로 하는 황-탄소 복합체 제조방법.The method according to claim 7, wherein the heat treatment of step (a) is performed for 1 to 5 hours after heating up to 500 to 1000 ° C at a rate of 5 to 20 ° C / min.
  9. 제7항에 있어서, 상기 (a)단계의 작용기는 히드록시기 또는 카르복시기인 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 7, wherein the functional group in step (a) is a hydroxy group or a carboxy group.
  10. 제7항에 있어서, 상기 작용기로 표면 개질된 다공성 탄소재는 다공성 탄소재를 산으로 처리하여 제조된 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 7, wherein the porous carbon material surface-modified with the functional group is prepared by treating a porous carbon material with an acid.
  11. 제10항에 있어서, 상기 산은 질산, 황산 및 이들의 혼합용액으로부터 선택되는 1종 이상인 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 10, wherein the acid is sulfuric acid, characterized in that at least one selected from nitric acid, sulfuric acid, and mixed solutions thereof.
  12. 제7항에 있어서, 상기 작용기가 제거된 다공성 탄소재의 열중량 분석 결과, 0℃에서 900℃까지 승온하였을 때 중량 감소율이 1% 이하이며, 라만 측정시 D/G 비율이 0.8 내지 1.5인 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 7, wherein the result of the thermogravimetric analysis of the porous carbon material from which the functional group is removed, when the temperature is increased from 0 ° C to 900 ° C, the weight reduction rate is 1% or less, and the D / G ratio is 0.8 to 1.5 when measuring Raman. Characteristic sulfur-carbon composite manufacturing method.
  13. 제7항에 있어서, 상기 작용기가 제거된 다공성 탄소재의 비표면적은 7 내지 20m2/g인 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 7, wherein the specific surface area of the porous carbon material from which the functional group is removed is 7 to 20 m 2 / g.
  14. 제7항에 있어서, 상기 작용기가 제거된 다공성 탄소재의 기공 부피는 0.1 내지 0.3cm3/g인 것을 특징으로 하는 황-탄소 복합체 제조방법.The method of claim 7, wherein the pore volume of the porous carbon material from which the functional group is removed is 0.1 to 0.3 cm 3 / g.
  15. 제1항 내지 제6항 중 어느 한 항의 황-탄소 복합체를 포함하는 리튬 이차 전지용 양극.A positive electrode for a lithium secondary battery comprising the sulfur-carbon composite of any one of claims 1 to 6.
  16. 제15항에 있어서, 상기 리튬-이차전지용 양극은 리튬-황 전지용 양극인 것을 특징으로 하는 리튬 이차전지용 양극.The positive electrode for a lithium secondary battery according to claim 15, wherein the positive electrode for a lithium-secondary battery is a positive electrode for a lithium-sulfur battery.
  17. 양극; 음극; 상기 양극과 음극 사이에 개재되는 분리막; 및 전해액을 포함하는 리튬 이차전지로,anode; cathode; A separator interposed between the anode and the cathode; And lithium secondary battery comprising an electrolyte,
    상기 양극은 제15항 또는 제 16항의 양극인 것을 특징으로 하는 리튬 이차전지.The positive electrode is a lithium secondary battery, characterized in that the positive electrode of claim 15 or claim 16.
  18. 제17항에 있어서, 상기 리튬 이차전지는 리튬-황 전지인 것을 특징으로 하는 리튬 이차전지.The lithium secondary battery according to claim 17, wherein the lithium secondary battery is a lithium-sulfur battery.
PCT/KR2019/011540 2018-09-20 2019-09-06 Sulfur-carbon composite, preparation method thereof, positive electrode for lithium secondary battery and lithium secondary battery comprising same WO2020060084A1 (en)

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