KR20160037084A - Surfur-carbonnanotube complex, method of preparing the same, cathode active material for lithium-sulfur battery including the same and lithium-sulfur battery including the same - Google Patents

Abstract

The present invention relates to a sulfur-carbon nanotube composite, a production method thereof, a cathode active material for a lithium-sulfur battery comprising the same, and a lithium-sulfur battery comprising the same. According to the present invention, the lithium-sulfur battery ensures high capacity even under a high loading condition.

Description

TECHNICAL FIELD The present invention relates to a sulfur-carbon nanotube composite, a method for producing the same, a cathode active material for a lithium-sulfur battery including the same, and a lithium-sulfur battery including the same. BACKGROUND ART AND LITHIUM-SULFUR BATTERY INCLUDING THE SAME}

The present invention relates to a sulfur-carbon nanotube composite, a method for producing the same, a cathode active material for a lithium-sulfur battery including the same, and a lithium-sulfur battery including the same.

The lithium-sulfur battery is a secondary battery using a sulfur-based compound having a sulfur-sulfur bond as a cathode active material and an alkali metal such as lithium as an anode active material. The reduction of the sulfur-sulfur bond during the reduction reaction leads to a decrease in the oxidation number of sulfur and an oxidation-reduction reaction in which the sulfur-sulfur bond is regenerated while the oxidation number of the sulfuric acid is increased .

The lithium-sulfur battery has an energy density of 3,830 mAh / g when lithium metal is used as an anode active material and 1,675 mAh / g of sulfur (S ₈ ) used as a cathode active material. Battery. In addition, the sulfur oxide used as the cathode active material is advantageous in that it is a cheap and environmentally friendly material.

However, sulfur has an electrical conductivity of 5 × 10 ^-30 S / cm, which is close to that of insulators. Therefore, it is difficult to transfer electrons generated by an electrochemical reaction. To solve this problem, an electrically conductive material such as carbon, which can provide a smooth electrochemical reaction site, has been used.

Sulfur is used as a cathode active material in lithium-sulfur batteries. These active materials are mixed with a binder and a conductive material and slurried. When the slurry is coated on an aluminum current collector having a conductive structure, the cathode becomes a cathode. In this case, when sulfur and the conductive material are used in a simple mixture, not only the life of the battery is deteriorated due to the leakage of sulfur into the electrolyte during the oxidation-reduction reaction, but also the lithium polysulfide which is a reducing substance of sulfur is eluted, There is a problem that it can not be done. In addition, there is a problem that capacity is reduced during sulfur loading in the electrode.

Korean Patent Publication No. 10-2007-0083384

The present invention provides a sulfur-carbon nanotube composite, a method for producing the same, a cathode active material for a lithium-sulfur battery including the same, and a lithium-sulfur battery including the same.

One embodiment of the present disclosure relates to a three-dimensional carbon nanotube aggregate;

A sulfur or sulfur compound provided on at least a part of the inner surface and the outer surface of the aggregate of carbon nanotubes; And

Carbon nanotube composite comprising graphene provided on at least a part of an inner surface and an outer surface of a carbon nanotube aggregate having the sulfur or sulfur compound.

One embodiment of the present disclosure also provides a method of making the sulfur-carbon nanotube composite.

An embodiment of the present disclosure also provides a cathode active material for a lithium-sulfur battery including the sulfur-carbon nanotube composite.

An embodiment of the present disclosure also provides a cathode for a lithium-sulfur battery including the cathode active material for the lithium-sulfur battery.

In addition, one embodiment of the present invention provides a method of manufacturing the cathode for a lithium-sulfur battery.

In addition, one embodiment of the present disclosure relates to an anode;

A cathode including the cathode active material;

A separation membrane positioned between the cathode and the anode; And

And an electrolyte positioned between the cathode and the anode.

The present disclosure also provides a battery module comprising the lithium-sulfur battery as a unit cell.

The sulfur-carbon nanotube composite according to one embodiment of the present invention suppresses the collapse of the cathode structure during the discharge of sulfur into the polysulfide during the charge and discharge of the battery through the three-dimensional structure of the carbon nanotube aggregate, Pin coating can increase polysulfide inhibition and conductivity of the sulfur-carbon nanotube complex.

Furthermore, a lithium-sulfur battery including the sulfur-carbon nanotube composite according to the present invention can realize a high capacity even at high loading.

FIG. 1 (a) is an image taken by a scanning electron microscope (SEM) of a carbon nanotube-based composite having a three-dimensional structure before sulfur impregnation.
FIG. 1 (b) is an image obtained by scanning electron microscopy (SEM) of a carbon nanotube-based composite having a three-dimensional structure after sulfur impregnation.
2 is an SEM image of a sulfur-carbon nanotube composite according to an embodiment of the present invention.
FIGS. 3 to 5 are schematic views showing a state in which polysulfide is eluted into an electrolytic solution in a conventional lithium-sulfur battery. FIG.
6 is a cell capacity graph of Examples and Comparative Examples.
FIG. 7 is a graph showing the charge-discharge efficiency of the examples and comparative examples.

Hereinafter, the present invention will be described in more detail.

Brief Description of the Drawings The advantages and features of the present disclosure and how to accomplish them will become apparent with reference to the embodiments described below in detail with reference to the accompanying drawings. It should be understood, however, that the intention is not to limit the present disclosure to the specific embodiments disclosed hereinafter but that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, To fully disclose the scope of the invention to those skilled in the art, and this specification is only defined by the scope of the claims. Unless defined otherwise, all terms, including technical and scientific terms used herein, may be used in a manner that is commonly understood by one of ordinary skill in the art to which this application belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

According to one embodiment of the present invention, a sulfur-carbon nanotube composite includes a three-dimensional structure of carbon nanotube aggregates; A sulfur or sulfur compound provided on at least a part of the inner surface and the outer surface of the aggregate of carbon nanotubes; And a graphene provided on at least a part of an inner surface and an outer surface of the carbon nanotube aggregate having the sulfur or sulfur compound.

FIG. 2 shows the appearance of a sulfur-carbon nanotube composite according to an embodiment of the present invention. Specifically, graphene was coated on the outer surface of a carbon nanotube aggregate having a three-dimensional structure equipped with sulfur. However, the shape of the sulfur-carbon nanotube composite according to the present invention is not limited to the structure of FIG.

In the conventional lithium-sulfur battery, a state in which polysulfide is eluted into the electrolytic solution is schematically shown in FIG. 3 to FIG. 5. More specifically, FIG. 3 shows that at the time of discharging of the lithium-sulfur battery, the lithium ions at the cathode react with sulfur, and the sulfur changes into lithium polysulfide form as the ring is opened. 4 shows a state in which lithium polysulfide is dissolved in an electrolytic solution to float in an electrolyte or to move to an anode. 5 shows a state in which lithium polysulfide is completely dissolved in the electrolytic solution and exposed to the surface of the cathode.

As described above, in the conventional lithium-sulfur battery, when sulfur is discharged to the electrolyte during the oxidation-reduction reaction, the life of the battery deteriorates. In addition, when an appropriate electrolyte is not selected, lithium polysulfide, which is a reducing material of sulfur, There is a problem that it can not participate in the electrochemical reaction.

Sulfur changes to polysulfide during electrochemical reaction and initially produces a soluble phase. As a result, sulfur converted to polysulfide is dissolved in the electrolytic solution and is no longer able to participate in the electrochemical reaction, which is a major cause of capacity loss of the cell. Also, there is a risk that the cathode structure may collapse as the electrolyte is eluted.

The sulfur-carbon nanotube composite according to one embodiment of the present invention has sulfur in the three-dimensional structure of the carbon nanotube, so that even if a polysulfide having solubility is generated by an electrochemical reaction, , It is possible to suppress the phenomenon that the structure of the cathode structure is collapsed due to the structure entangled in three dimensions in the release of polysulfide. As a result, the lithium-sulfur battery including the sulfur-carbon nanotube composite has an advantage that a high capacity can be realized even at high loading.

According to one embodiment of the present invention, the sulfur or sulfur compound may be included in the inner pores of the carbon nanotube aggregate.

Furthermore, the sulfur-carbon nanotube composite according to one embodiment of the present invention further comprises a graphene layer in a carbon nanotube aggregate having a sulfur or sulfur compound. The graphene serves to inhibit the elution of polysulfide and to improve the conductivity of the sulfur-carbon nanotube composite.

In the present specification, a three-dimensional structure may mean that intersections where two or more strands intersect are distributed in three dimensions.

In this specification, the term " three-dimensional structure " may mean that each basic unit entangled in two dimensions is entangled again in three dimensions and finally has a three-dimensional structure. The " tangled " may mean that more than two strands cross each other through physical contact.

In this specification, the carbon nanotube aggregates of the three-dimensional structure may be expressed in terms of cage-type carbon nanotubes or the like, in which carbon nanotubes are crosslinked or entangled with each other to form a net structure.

In this specification, the carbon nanotube aggregates have a structure in which a plurality of carbon nanotube strands are intertwined, and the cross-sectional diameter of each carbon nanotube may be 1 nanometer or more and 100 nanometers or less.

The three-dimensional carbon nanotube aggregate used as the material of the sulfur-carbon nanotube composite according to one embodiment of the present invention may be a cage-type carbon nanotube as described above, and the carbon nanotube may take the form of a cage There is an advantage in that it does not require a complicated process separately. Specifically, since the carbon nanotubes are not separately separated after their manufacture, a complicated process for taking a cage shape is not required. This is because the complex is produced by using the aggregate form at the initial stage of CNT production as it is.

The carbon nanotube refers to a linear conductive carbon. Specifically, carbon nanotube (CNT), graphite nanofiber (GNF), carbon nanofiber (CNF), or activated carbon fiber (ACF) Both tube (SWCNT) and multiwall carbon nanotubes (MWCNT) are available.

According to one embodiment of the present disclosure, the sulfur-carbon nanotube composite has a cage shape.

1 (a) shows an image of a three-dimensional carbon nanotube aggregate included in a sulfur-carbon nanotube composite according to an embodiment of the present invention, and FIG. 1 (b) is an image after sulfur impregnation .

According to one embodiment of the present disclosure, the thickness of the graphene layer is less than 100 sheets of graphene sheet. The thickness of the graphene sheet and / or the number of graphene sheets can be confirmed by SEM images taken with a scanning electron microscope or TEM images taken with a transmission electron microscope.

According to an embodiment of the present invention, the tap density of the carbon nanotube aggregate may be 0.01 g / cc or more and 1 g / cc or less. If the tap density of the carbon nanotube agglomerate is 0.01 g / cc or more, the addition amount of the binder and the solvent per unit volume is decreased, thereby increasing the content of sulfur and increasing the capacity of the battery. If the tap density of the carbon nanotube agglomerate is 1 g / cc or less, the porosity between the carbon nanotube agglomerates in the electrode is drastically reduced, so that the sulfur impregnated with the impregnated carbon nanotube aggregates to reduce the wettability of the electrolyte solution, have. Furthermore, since sulfur reacts to generate Li ₂ S, the volume increases. Therefore, when the tap density is 1 g / cc or less, the porosity is further reduced, and the problems of durability of the electrode and capacity are also reduced.

According to one embodiment of the present invention, the carbon nanotube aggregates have one or more shapes selected from the group consisting of a spherical type, an entangled type, and a bundle type, depending on the manufacturing method.

The shape and tap denity of the carbon nanotube aggregates may vary depending on the content of the catalyst added in the production of the carbon nanotubes. By this property, the tap density of the carbon nanotube aggregates and the carbon nanotube particles The spacing of the gaps also changes. In the case of varying the tap density by using the amount of the catalyst, the larger the amount of the catalyst, the larger the tap density, the more closely tangled each other, and the greater the twist of the carbon nanotubes. On the other hand, the tap density is low and the carbon nanotubes aggregate in a linearly less twisted state. The entangled carbon nanotube aggregates have different porosity.

In the present specification, the tap density can be measured by a method commonly used in the art as a method for measuring the degree of filling of a sample per unit volume. For example, the apparent density may be obtained by tapping the measuring container into which the sample is placed until the volume change amount is mechanically within 2%.

In one embodiment of the present invention, the tap density can be adjusted by varying the catalyst amount when growing the carbon nanotubes in the step of preparing the carbon nanotubes.

The method for growing the carbon nanotubes is not limited, and the methods used in the art can be used. The type of the catalyst is not particularly limited, and a common catalyst used in the art can be used.

The catalyst may be a metal catalyst or a metal oxide catalyst.

The metal catalyst may be Fe, Ni, Co, Cr, Ni / Ti, Co / Ti and Fe / Ti.

The metal oxide catalyst may be Fe ₂ O ₃ , Al ₂ O ₃ And CuO.

As described above, the porosity of the carbon nanotube aggregates and the length and shape of the carbon nanotubes can be controlled by controlling the kind and content of the metal catalyst or the metal oxide catalyst. The smaller the amount of the catalyst, the larger the density of the carbon nanotube agglomerate is, and the shape of the particles may be a shape of the thread. When the amount of the catalyst is larger, the particles in the carbon nanotube agglomerate are linear, The density can be made small. Therefore, the tap density of the carbon nanotube agglomerate can be controlled by adjusting the amount of catalyst in the production of the carbon nanotube agglomerate as described above.

The carbon nanotube-sulfur composite according to the present invention can be produced by dispersing conventional carbon nanotube particles using a carbon nanotube aggregate to produce a larger amount of sulfur than carbon nanotube- The nanotubes can be uniformly impregnated. Accordingly, the loading of sulfur per unit volume can be increased to increase the capacity of the electrode.

In the carbon nanotube-sulfur composite, the carbon nanotube aggregates may have a diameter of 1 to 500 micrometers, specifically 1 to 100 micrometers, more specifically 1 to 50 micrometers, More specifically, not less than 1 micrometer and not more than 10 micrometers. The diameter of the aggregate of carbon nanotubes means the largest diameter of the cross-section of the agglomerate.

If the diameter of the carbon nanotube agglomerate exceeds 500 micrometers, the uniformity of the electrode is lowered, the inter-particle voids are increased, the sulfur content is decreased, and the contact area with the current collector is decreased. Therefore, it is preferable that the diameter of the carbon nanotube agglomerate is 500 micrometers or less in order to provide proper air gap and electrode uniformity.

According to an embodiment of the present invention, the carbon nanotube aggregate has a diameter of 10 to 20 占 퐉.

In this specification, the sulfur-carbon nanotube composite refers to a sulfur-carbon nanotube composite having sulfur or a sulfur-carbon nanotube composite having a sulfur compound. In other words, sulfur of a sulfur-carbon nanotube composite means sulfur contained in a sulfur element or a sulfur compound.

According to one embodiment of the present disclosure, the sulfur may have a particulate form.

Specifically, the sulfur may be located in an area of less than 100%, specifically 1% to 80%, more specifically 50% to 80% of the entire outer surface of the carbon nanotube aggregate. When the sulfur is within the above range in the entire outer surface area of the carbon nanotube aggregates, it can exhibit the maximum effect in terms of the electron transfer area and the wettability of the electrolyte solution. In this region, sulfur is impregnated thinly in the carbon nano-vieve agglomerates by capillary force, thereby increasing the electron transfer contact area in the charging and discharging process.

When the sulfur is located in a 100% region of the entire outer surface of the carbon nanotube aggregate, the carbon nanotube aggregate is completely covered with sulfur, thereby deteriorating the wettability of the electrolyte, It can not contribute to the reaction. That is, when the sulfur is located on the entire outer surface of the carbon nanotube agglomerates, the electron transferring role of the carbon nanotubes is undesirably reduced.

The composite is impregnated with carbon nanotubes. When the sulfur is impregnated into the carbon nanotube aggregates, there is little change in the particle size. The impregnation may be such that sulfur is uniformly mixed with carbon nanotube agglomerate and sulfur, and sulfur is coated by capillary action along carbon nanotube agglomerates at a temperature above the melting point of sulfur.

According to another embodiment, the sulfur-carbon nanotube composite is surface-treated with an amphipathic substance.

By coating the sulfur-carbon nanotube composite with an amphipathic substance, the role of trapping polysulfide can be enhanced. As a result, the dissolution of the polysulfide into the electrolytic solution is inhibited, leading to improvement in the life of the battery.

The amphipathic substance is a substance having a hydrophilicity portion and a hydrophobicity portion at the same time. Examples of the amphipathic substance include polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), polyvinyl alcohol (PVA), gelatin, and copolymers thereof , But is not limited thereto.

The method of surface-treating the sulfur-carbon nanotube composite with an amphipathic substance may be carried out by adding a carbon nanotube aggregate to a surfactant solution in which the amphipathic substance is dissolved, stirring the mixture at a temperature lower than 50 ° C for about 24 hours , And filtering and drying the carbon nanotube aggregates. However, any method may be used as long as it is a method known in the art.

According to one embodiment of the present disclosure, the amphipathic substance may be located on at least a portion of the surface of the sulfur-carbon nanotube complex. In addition, the amphipathic substance may be located in the entire area of the surface of the sulfur-carbon nanotube.

According to one embodiment of the present disclosure, the amphipathic substance may be contained in an amount of more than 0 wt% to less than 35 wt% based on the total weight of the cathode active material. Specifically, it may be contained in an amount of 0.1% by weight to 33% by weight, more specifically 1% by weight to 33% by weight, based on the total weight of the cathode active material.

One embodiment of the present invention provides a cathode active material for a lithium-sulfur battery including the sulfur-carbon nanotube composite.

The present specification also provides a cathode for a lithium-sulfur battery including the cathode active material for the lithium-sulfur battery.

According to one embodiment of the present invention, the cathode for the lithium-sulfur battery has an initial discharge capacity of 1100 mAh / g or more when the electrode loading amount is 3 mAh / cm ² .

According to one embodiment of the present invention, the cathode for the lithium-sulfur battery has an initial discharge capacity of 900 mAh / g or more when the electrode loading amount is 3 mAh / cm ² .

According to one embodiment of the present invention, the cathode for the lithium-sulfur battery has an initial discharge capacity of 800 mAh / g or more when the electrode loading amount is 3 mAh / cm ² .

According to one embodiment of the present invention, the cathode for the lithium-sulfur battery has an initial discharge capacity of 700 mAh / g or more when the electrode loading amount is 3 mAh / cm ² .

According to an embodiment of the present invention, the cathode for a lithium-sulfur battery may further include at least one of a conductive material and a binder resin.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, but may be a graphite based material such as KS6; Super P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Funace Black, Lamp Black, Summer Black, Carbon Black; Carbon derivatives such as carbon nanotubes and fullerene; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The conductive material may be added in an amount of 0.5 wt% to 30 wt% based on the total weight of the mixture including the cathode active material.

Examples of the binder include poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate) (Trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polystyrene, polyvinylidene fluoride, polyvinylidene fluoride, Derivatives thereof, blends, copolymers and the like can be used.

The content of the binder may be from 0.5% by weight to 30% by weight based on the total weight of the composition for the cathode material.

The disclosure also includes an anode; A cathode including the cathode active material; A separation membrane located between the cathode and the anode; And an electrolyte positioned between the cathode and the anode.

When the battery is discharged, the anode oxidizes to generate metal ions while discharging electrons, and may function as a cathode (reductive electrode) when charging the battery.

The cathode receives the positive ions transferred from the anode when the battery is discharged, and performs a reduction reaction. The cathode can act as an anode (oxidizing electrode) when the battery is charged.

According to one embodiment of the present disclosure, the anode comprises lithium metal or a lithium alloy.

The lithium alloy as the anode active material is an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, .

The separation membrane located between the cathode and the anode may be made of a porous nonconductive or insulating material which separates or insulates the cathode from the anode and enables lithium ion transport between the cathode and the anode. Such a separation membrane may be an independent member such as a film, or may be a coating layer added to the cathode and / or the anode.

The material forming the separation membrane includes, for example, a polyolefin such as polyethylene and polypropylene, a glass fiber filter paper, and a ceramic material, but is not limited thereto. The thickness of the separation membrane is about 5 탆 to about 50 탆, Can be about 25 [mu] m

According to one embodiment of the present disclosure, the electrolyte located between the cathode and the anode comprises a lithium salt and an organic solvent.

The concentration of the lithium salt may be in the range of about 0.2M to about 10M, depending on various factors such as the precise composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, 2.0M. Lithium salt for example for use in the present application, LiSCN, LiBr, LiI, LiPF 6, LiBF 4, LiSO 3 CF 3, LiClO 4, LiSO 3 CH 3, LiB (Ph) 4, LiC (SO 2 CF 3) 3 and LiN (SO ₂ CF ₃₎ may include one or more from the group consisting of _2.

The organic solvent may be a single solvent or two or more mixed organic solvents. When two or more mixed organic solvents are used, it is preferable to use at least one solvent selected from two or more of the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

A weakly polar solvent is defined as a solvent having a dielectric constant of less than 15 which is capable of dissolving a sulfur element among aryl compounds, bicyclic ethers and acyclic carbonates, and the strong polar solvent includes bicyclic carbonates, sulfoxide compounds, lactone compounds, Ketone compounds, ester compounds, sulfate compounds, and sulfite compounds, wherein the lithium metal protective solvent is a saturated ether compound, an unsaturated ether compound, N, O , S or a heterocyclic compound containing a combination of these, is defined as a solvent having a charge / discharge cycle efficiency of 50% or more to form a stable SEI (Solid Electrolyte Interface) on a lithium metal.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme and tetraglyme.

Specific examples of the strong polar solvent include hexamethyl phosphoric triamide,? -Butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethylformamide, sulfolane, dimethylacetamide, dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, or ethylene glycol sulfite.

Specific examples of the lithium-protecting solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane and 4-methyldioxolane.

The present invention provides a battery module including the lithium-sulfur battery as a unit battery.

The battery module may be specifically used as a power source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.

Further, the present specification discloses a method of manufacturing a carbon nanotube aggregate, comprising: introducing a sulfur or sulfur compound into at least a part of an inner surface and an outer surface of a three-dimensional carbon nanotube aggregate; And a graphene layer on at least a part of an inner surface and an outer surface of the carbon nanotube aggregate having the sulfur or sulfur compound.

According to one embodiment of the present invention, the step of providing the graphene may include spray coating of graphene or graphene oxide, or a method of dissolving graphene oxide in water and reducing at a high temperature.

The method for producing a cathode active material for a lithium-sulfur battery according to the present invention is a method for manufacturing a cathode active material for a lithium-sulfur battery, wherein the coagulated carbon nanotubes are dried by a dry method such as a jet mill or a dyno mill, And then impregnating the carbon nanotube aggregates with a sulfur or sulfur compound.

In one embodiment of the present disclosure, the sulfur or sulfur compound is impregnated with molten carbon nanobut aggregates under pressure. A method of dissolving a sulfur or a sulfur compound in a solvent and then adding a carbon nanotube aggregate to regenerate sulfur in the interior of the carbon nanotube aggregate; And a ball mill method. The carbon nanotube aggregates may be introduced into the carbon nanotube aggregates by one or more methods.

After impregnating the raw material of carbon nanotubes with sulfur, the particles can be controlled to a few micrometers by using a jet mill, a dyno mill, a ball mill, etc. However, after the carbon nanotube agglomerates are adjusted to a few micrometers, .

The carbon nanotube agglomerates of the three-dimensional structure used in this specification can be used directly without any special process as a product for dispersing carbon nanotubes, and there is no limitation in the shape, which is advantageous in the process.

Conventionally, the surfaces of carbon nanotubes are subjected to an acid treatment or a pitch oxide treatment to disperse the carbon nanotubes into individual carbon nanotube particles, and then sulfur is grown on the inside or the surface of the carbon nanotube particles, To prepare a carbon nanotube-sulfur complex. Alternatively, hollow carbon or porous carbon was produced by artificially forming pores in carbon to prepare a carbon-sulfur complex. It is not easy to perform surface treatment or artificial pore formation on carbon nanotubes, and it is difficult to produce composite particles of uniform size, and it is difficult to mass-produce carbon nanotubes.

However, the sulfur-carbon nanotube composite according to the present invention has an advantage that the carbon nanotube improves the electron conductivity because the carbon nanotube acts as an electron transfer path, and the capacity of the electrode can be improved. At the same time, the carbon nanotube can serve as a contact site of sulfur, so that even if sulfur is swelled by the electrolyte solution, the separation of carbon and sulfur does not occur so that sulfur can be prevented from flowing out to the electrolyte, There is an advantage that it can be improved.

Further, a method of manufacturing a cathode for a lithium-sulfur battery according to another embodiment of the present invention includes the steps of: 1) preparing a slurry containing the cathode active material according to one embodiment of the present specification; and 2) Applying the coating liquid to the current collector, and drying the coating liquid.

According to one embodiment of the present disclosure, the drying is vacuum drying.

In the method for manufacturing a cathode for a lithium-sulfur battery according to the present invention, the content of the cathode active material is the same as that described above, and thus a detailed description thereof will be omitted.

In one embodiment of the present invention, the slurry may further include an organic solvent. More specifically, the organic solvent is not particularly limited as long as it is an organic solvent capable of uniformly dispersing the cathode active material and the conductive material and easily evaporated. Specific examples of the solvent include ethanol, toluene, benzene, N-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), acetone, chloroform, dimethylformamide, cyclohexane, tetrahydrofuran, Methylene chloride, and mixtures thereof.

The slurry is applied to a current collector and vacuum dried to form a cathode for a lithium-sulfur battery. The slurry can be coated on the current collector to have an appropriate thickness according to the viscosity of the slurry and the thickness of the cathode to be formed.

The current collector generally has a thickness of 3 탆 to 500 탆 and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. More specifically, a conductive material such as stainless steel, aluminum, copper, or titanium may be used. More specifically, a carbon-coated aluminum current collector may be used. The use of a carbon-coated aluminum substrate is advantageous in that it has an excellent adhesion to an active material, has a low contact resistance, and can prevent corrosion caused by aluminum polysulfide, as compared with a carbon-coated aluminum substrate. The current collector may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam or a nonwoven fabric.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the examples and comparative examples according to the present specification can be modified in various other forms, and the scope of the present specification is not construed as being limited to the above-described embodiments and comparative examples. The examples and comparative examples provided herein are provided to more fully describe the present specification to those skilled in the art.

[Example]

(tap density: 0.02 g / cc, diameter: 100 μm or less) at 150 ° C., graphene oxide was impregnated with sulfur-impregnated carbon nanotube agglomerates Lt; 0 > C for 3 hours to prepare a composite. The weight ratio of S: Carbon in the prepared composite was 7: 3. At this time, Carbon contains the weight of graphene oxide and carbon nanotube agglomerates.

The prepared composite was used to prepare a slurry at a weight ratio of composite: conductive black (Denka black): SBR / CMC = 75: 20: 5 (2.5 / 2.5) Electrode.

Styrene-butadiene rubber and Carboxymethyl cellulose were used as SBR / CMC as binders, respectively.

[Comparative Example]

In Examples, electrodes were prepared in the same manner except that super-C was used instead of carbon nanotube aggregates.

[Experimental Example 1]

The electrodes prepared in Examples and Comparative Examples were respectively used as cathodes, and lithium metal was used as an anode to prepare coin cells. At this time, the coin cell used was an electrolytic solution prepared from TEGDME / DOL / DME (1: 1: 1), LiN (CF ₃ SO ₂ ) ₂ (LiTFSI) 1M and LiNO ₃ 0.1M.

TEGDME / DOL / DME was prepared by using triethylene glycol dimethyl ether, dioxolane, and dimethyl ether as solvents.

The prepared coin cell was measured for capacities from 1.5 to 2.8V.

The charge / discharge efficiency was measured by repeating a cycle of charging 0.1C rate CC / CV and discharging 0.1C rate CC 50 times. (CC: Constant Current, CV: Constant Voltage)

The results are shown in Fig. 6 and Fig.

FIG. 6 shows that the initial discharge capacity of the embodiment is improved compared to the comparative example. FIG. 7 shows that the life characteristics of the embodiment are improved as compared with the comparative example.

[Experimental Example 2]

In preparing the sulfur-carbon nanotube composite in the examples, a composite having a three-dimensional carbon nanotube aggregate, a sulfur-impregnated carbon nanotube aggregate, and a graphene oxide before the sulfur impregnation was observed with a scanning electron microscope.

FIG. 1 (a) is an image obtained by scanning electron microscopy (SEM) of a carbon nanotube aggregate before sulfur impregnation in the production of a composite using a three-dimensional carbon nanotube.

FIG. 1 (b) is an image obtained by scanning electron microscopy (SEM) of a carbon nanotube-based composite having a three-dimensional structure after sulfur impregnation.

FIG. 2 is an SEM photograph of the sulfur-carbon nanotube composite prepared in Example. FIG.

Claims (19)

A three-dimensional carbon nanotube aggregate;
A sulfur or sulfur compound provided on at least a part of the inner surface and the outer surface of the aggregate of carbon nanotubes; And
And a graphene layer provided on at least a part of an inner surface and an outer surface of the carbon nanotube aggregate having the sulfur or sulfur compound. The sulfur-carbon nanotube composite according to claim 1, wherein the thickness of the graphene layer is not less than one sheet of graphene and not more than 100 sheets. The sulfur-carbon nanotube composite according to claim 1, wherein the carbon nanotube aggregate has a tap density of 0.01 g / cc to 1 g / cc. The sulfur-carbon nanotube composite according to claim 1, wherein the aggregate of carbon nanotubes has a diameter of 500 mu m or less. The sulfur-carbon nanotube composite according to claim 1, wherein the carbon nanotube aggregate has a diameter of 10 mu m to 20 mu m. The sulfur-carbon nanotube composite according to claim 1, wherein the sulfur has a particle shape. The sulfur-carbon nanotube composite according to claim 1, wherein the sulfur content is more than 1 wt% and less than 80 wt% based on the total weight of the cathode active material for a lithium-sulfur battery. The sulfur-carbon nanotube composite according to claim 1, wherein the sulfur-carbon nanotube composite has a cage shape. The sulfur-carbon nanotube composite according to claim 1, wherein the sulfur-carbon nanotube composite is surface-treated with an amphipathic substance. The method of claim 9, wherein the amphipathic substance comprises at least one selected from the group consisting of polyvinylpyrrolidone (PVP), polyethylene oxide, polyvinyl alcohol, gelatin, and copolymers thereof. Tube composite. A cathode active material for a lithium-sulfur battery comprising the sulfur-carbon nanotube composite according to any one of claims 1 to 10. A cathode for a lithium-sulfur battery comprising the cathode active material for a lithium-sulfur battery according to claim 11. 13. The cathode of claim 12, wherein the cathode for lithium-sulfur batteries further comprises at least one of a conductive material and a binder resin. Anode;
A cathode comprising the cathode active material of claim 11;
A separation membrane located between the cathode and the anode; And
And an electrolyte positioned between the cathode and the anode. A battery module comprising the lithium-sulfur battery according to claim 14 as a unit cell. Introducing a sulfur or sulfur compound into at least a part of the inner surface and the outer surface of the carbon nanotube aggregate of the three-dimensional structure; Carbon nanotube composite according to any one of claims 1 to 10, comprising a step of providing a graphene layer on at least a part of an inner surface and an outer surface of the carbon nanotube aggregate into which the sulfur or sulfur compound is introduced Gt; [16] The method of claim 16, wherein the step of introducing the sulfur or sulfur compound comprises: impregnating the sulfur or sulfur compound into molten carbon nanotube agglomerates under pressure in a molten state; A method of dissolving a sulfur or a sulfur compound in a solvent and then adding a three-dimensional carbon nanotube agglomerate to regenerate a sulfur or a sulfur compound inside the carbon nanotube; Wherein the sulfur or sulfur compound is introduced into a three-dimensional carbon nanotube aggregate by at least one method selected from the group consisting of a ball mill method and a ball mill method. [16] The method of claim 16, wherein the step of providing the graphene comprises spray coating a graphene or graphene oxide or a method of melting graphene oxide in water and reducing at a high temperature. Gt; 1) preparing a slurry comprising the cathode active material according to claim 11, and
2) applying the slurry to a current collector, and drying the slurry.

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