KR20210067608A - An electrode for secondary battery having a high sulfur loading and the method for producing the same - Google Patents

Abstract

According to the present specification, provided is an electrode material for a secondary battery which includes a carbon structure and sulfur supported on the carbon structure, and has a sulfur loading amount of 1.0 mg cm^2 or more per unit electrode area of the electrode material. The electrode material for a secondary battery can have a high sulfur loading amount.

Description

Electrode material for secondary battery carrying high-capacity sulfur and manufacturing method therefor {AN ELECTRODE FOR SECONDARY BATTERY HAVING A HIGH SULFUR LOADING AND THE METHOD FOR PRODUCING THE SAME}

Disclosed herein is a high-efficiency electrode material through high energy density of an electrode material for a secondary battery using sulfur as an active material.

Recently, research and development of high-capacity and high-stability secondary batteries that can be used for large-capacity energy storage or electric vehicles are being actively conducted. Among the electrode materials for such high-capacity secondary batteries, sulfur has a high theoretical capacity (1,687 mA hg ^{- 1} ), and thus is being used as an active material for secondary batteries such as lithium-sulfur batteries and magnesium-sulfur batteries. However, sulfur is an electrical insulator (1 x 10 ^-16 S m ^{- 1} ) and in the form of metal polysulfide combined with metal ions, there is a problem of eluting into an organic solvent, which in turn leads to a decrease in the capacity of the battery.

In order to solve this problem, a conductive carbon material is manufactured in a shape such as a porous powder, a hollow carbon sphere, and a hollow carbon fiber, and then sulfur is supported in such a structure, whereby the amount of sulfur supported Studies to increase the polysulfide and solve the dissolution problem of polysulfide are being actively conducted.

By supporting sulfur in these carbon nanotubes and hollow fiber carbon fibers, a high-capacity sulfur electrode material development technology that provides a solution to the problem of low electrical conductivity and elution of sulfur is disclosed.

Patent Document 1 is a stack of nano-short fibers including a core part containing at least one selected from elemental sulfur, a sulfur-based compound, and a mixture thereof, and a shell part including a conductive material and a polymer for fiber formation, coating the core part A positive electrode for a lithium-sulfur battery in the form of a nanofiber network, a method for manufacturing the positive electrode, and a lithium-sulfur battery including the positive electrode are provided.

In addition, Patent Document 2 relates to a carbon-tin oxide-sulfur composite, a manufacturing method thereof, and a cathode material for a lithium-sulfur battery comprising the same, and more particularly, a carbon-tin oxide-sulfur composite having a ladder-type structure by strong chemical bonding. provides a lithium-sulfur battery manufacturing technology with excellent lifespan characteristics and electrochemical performance due to smooth electron movement as well as suppression of polysulfide elution and volume expansion of sulfur during charging/discharging. .

In addition, Non-Patent Document 1 provides a lithium-sulfur positive electrode manufacturing technology that enhances electrical properties by increasing the amount of sulfur supported and manufacturing a bendable electrode using graphene made by one of the carbon elements and carbon manufacturing methods are doing

In addition, Non-Patent Document 2 provides a method for manufacturing a lithium-sulfur positive electrode including a three-dimensional aluminum support for increasing the amount of sulfur supported by using carbon nanotubes and a three-dimensional aluminum support.

However, these techniques are not suitable for manufacturing an electrode having a high content of active material by manufacturing the electrode in a state of mixing sulfur or a sulfur compound in a solvent such as an organic solvent or water. In addition, in the case of the technique of simply melt-impregnating sulfur and injecting it into carbon nanotubes, there is a problem in that sulfur is adsorbed and supported only on the surface of the carbon structure, so that the sulfur loading amount is very low.

Accordingly, there is a growing need for a technology for manufacturing an electrode having a high content of sulfur supported thereon and a technology for manufacturing a secondary battery using the sulfur electrode.

KR 10-2016-0087511 A KR 10-1794317 B1 KR 10-2042108 B1 KR 10-2039211 B1 KR 10-2019-0118732 A

G Zhou, L Li, C Ma, S Wang, Y Shi, N Koratkar, W ren 11 January 2015, Pages 356-365 XB Cheng, HJ Peng, JQ Huang, L Zhu, SH Yang J. Power Sources

Embodiments of the present invention relate to the development of a new sulfur injection technique that overcomes the disadvantages of the existing sulfur injection techniques that do not utilize 100% of the space in the porous carbon structure material, and provides a porous carbon structure electrode material having a high sulfur content per unit area there is a purpose to

When the conventional sulfur-supporting methods such as a vaporization method, a hydrothermal synthesis method, and a solvent impregnation method are used, sulfur is supported only in some pores and surfaces of a porous carbon structure, for example, a hollow fiber carbon structure. In addition, when the melt impregnation method is used, the molten sulfur exists in a long chain form due to its polymeric properties, making it difficult to inject into the pores of the micro- and nano-sized porous carbon structures. Due to this, the space in the carbon structure cannot be used properly, so that the amount of sulfur supported per unit area of the electrode is very small, and thus there is a limit in increasing the battery capacity.

Therefore, in the present invention, a sulfur loading method that can utilize 100% of the internal space of a porous carbon structure is developed, a carbon electrode material having a high sulfur loading content is manufactured, and using this, a high-capacity lithium-sulfur battery or a magnesium-sulfur battery and An object of the present invention is to provide a technology for manufacturing a positive electrode of the same secondary battery.

One embodiment of the present invention provides an electrode material for a secondary battery, comprising: a carbon structure; and sulfur supported on the carbon structure, ^{and having a sulfur loading amount of 1.0 mg cm -2} or more per unit electrode area of the electrode material, providing an electrode material for a secondary battery.

In an exemplary embodiment, the electrode material for a secondary battery may have a sulfur loading amount of ^{10 mg cm -2 or more per unit electrode area of the electrode material.}

In an exemplary embodiment, the carbon structure may be a porous carbon structure.

In an exemplary embodiment, the porous carbon structure is a group consisting of porous carbon powder, carbon hollow fibers, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, porous carbon sheets, porous carbon cloth, and porous carbon felt. It may include one or more carbon materials selected from.

In an exemplary embodiment, the carbon structure may be a carbon hollow fiber including a hollow having an inner diameter of 100 μm or less.

In an exemplary embodiment, the carbon hollow fiber may include a plurality of pores with a diameter of 10 μm or less located on the wall surface.

In an exemplary embodiment, a secondary battery comprising the above-described electrode material for a secondary battery is provided.

In an exemplary embodiment, the secondary battery may have a capacity per unit area ^{of 1 mA h cm - 2 or more under a condition of 0.1 C-rate.}

Another embodiment of the present invention comprises the steps of forming a sulfur active site in the carbon structure; and injecting sulfur into the carbon structure to bond and grow the sulfur active site; It includes, and provides a method of manufacturing an electrode material for a secondary battery, having a sulfur loading amount of ^{1.0 mg cm - 2} or more per unit electrode area of the electrode material.

In an exemplary embodiment, the step of forming the sulfur active point may be to disperse sulfur particles in the carbon structure.

In an exemplary embodiment, the step of forming the sulfur active point may be performed by a solvent impregnation method, a vaporization impregnation method, or a hydrothermal impregnation method.

In an exemplary embodiment, the sulfur injection may be injection of molten sulfur into the carbon structure.

In an exemplary embodiment, the melting temperature of the sulfur may range from 120 to 250 °C.

In an exemplary embodiment, the melting temperature of the sulfur may range from 150 to 160 °C.

The electrode material for a secondary battery according to embodiments of the present invention can be manufactured using a hollow fiber type carbon structure having a high sulfur content, and when it is used as a positive electrode of a secondary battery, a high battery capacity per unit area can be realized. In addition, by effectively suppressing the dissolution of polysulfide, it is possible to manufacture a secondary battery such as a lithium-sulfur battery or a magnesium-sulfur battery having a high capacity/high efficiency.

The electrode material for a secondary battery according to embodiments of the present invention creates a sulfur active site in which sulfur can stably grow inside a hollow carbon nanofiber (HCNF) type carbon structure through a pretreatment process, and then carries out a sulfur loading process By allowing sulfur to be supported inside the carbon structure through the effective sulfur loading, it can have a high sulfur content per unit area.

In addition, the electrode material for a secondary battery according to embodiments of the present invention injects a pure sulfur material, not a sulfur compound or a twilight compound, into the hollow fiber-shaped porous carbon structure, so that a high-capacity sulfur-supported electrode manufacturing technology and the sulfur electrode To provide a secondary battery manufacturing technology using

1 is an electrode material for a secondary battery according to an embodiment of the present invention, schematically showing a manufacturing process of a sulfur-injected nano-carbon hollow fiber.
2 shows the molecular structure and viscosity of sulfur as a function of temperature.
3 shows a scanning electron microscope image of the carbon structure (carbon hollow fiber) according to Example 1.
Figure 4a shows a scanning electron micrograph in which an active site capable of stably growing sulfur in a carbon hollow fiber is generated through a primary pretreatment process as a sulfur loading process according to an embodiment of the present invention.
Figure 4b is a sulfur loading process according to an embodiment of the present invention, by injecting and growing sulfur in the carbon hollow fiber through the secondary process shows a scanning electron micrograph showing that the inside of the hollow fiber is completely filled with sulfur 100%. .
Figure 5a shows a scanning electron microscope photograph of a sulfur-supported hollow fiber carbon structure prepared through a conventional vaporization impregnation method.
Figure 5b shows a scanning electron microscope photograph of the sulfur-supported hollow fiber carbon structure prepared through the conventional solvent impregnation method.
Figure 5c shows a scanning electron micrograph of the sulfur-supported hollow fiber carbon structure prepared only through the post-treatment sulfur injection method (the same as the conventional melt impregnation method) without going through the first pre-treatment process.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention disclosed in the text are illustrated for the purpose of explanation only, and the embodiments of the present invention may be embodied in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention can make various changes and can have various forms, and the embodiments are not intended to limit the present invention to a specific disclosed form, and all changes, equivalents or substitutes included in the spirit and scope of the present invention should be understood as including

The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

As used herein, the term “porous carbon structure” refers to a carbon structure having micro- and nano-sized spaces capable of supporting sulfur.

As used herein, the term “carbon hollow fiber” refers to a hollow fiber having pores formed in the interior of the carbon fiber in the fiber length direction.

Electrode material for secondary battery

One embodiment of the present invention provides an electrode material for a secondary battery, comprising: a carbon structure; and sulfur supported on the carbon structure; and including, 1 mg cm per unit area of the electrode material ^{- having a sulfur loading amount of 2} or more, providing an electrode material for a secondary battery. The electrode material for a secondary battery is a carbon electrode material having a high sulfur loading content, and has the advantage of realizing a high-capacity battery when employed as a positive electrode of a secondary battery.

Specifically, the electrode material for the secondary battery ^{may have a sulfur loading amount of 5 mg cm - 2} or more, 10 mg cm ^{- 2} or more, 15 mg cm ^{- 2} or more, 20 mg cm ^{- 2} or more, for example, 1 to 100 mg cm ^{- 2} range or 10 to 100 mg cm ^- can have a sulfur loading in the ^second range. When the sulfur loading has the above-mentioned range, a high content of sulfur, for example, 10 mg cm ^{- 2} or more sulfur per unit area of the electrode material, is supported in the carbon structure, and a high capacity per unit area can be realized, and polysulfide generated during the battery reaction By effectively suppressing the elution, it can be applied to a secondary battery such as a lithium-sulfur battery or a magnesium-sulfur battery having a high capacity/high efficiency.

In one embodiment, the carbon structure may be a porous carbon structure. The porous carbon structure may have pores and/or hollows, and sulfur may be supported in the pores and/or hollows. In this case, crystals of sulfur may not be formed outside the structure, and polysulfide elution problems may not occur in battery driving.

In one embodiment, the carbon structure is selected from the group consisting of porous carbon powder, carbon hollow fibers, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, porous carbon sheets, porous carbon cloth, and porous carbon felt. It may include one or more carbon materials.

That is, the carbon structure may be an empty space in which sulfur can be supported, for example, a carbon structure having hollows or pores. When sulfur is efficiently supported in the internal space of the carbon structure, it can be expected to improve the reversible capacity of the battery, prevent the dissolution of polysulfide, and improve the rate capability.

In one embodiment, the carbon structure may be a carbon hollow fiber including a hollow having an inner diameter of 100 μm or less. Specifically, the carbon hollow fiber may have pores formed in the fiber length direction, and the inner diameter of the pores may be 100 μm or less. The cross section and/or pores of the carbon hollow fiber may have various shapes other than a circular shape.

In one embodiment, the carbon hollow fiber may include a plurality of pores with a diameter of 10 μm or less positioned on the wall surface. Lithium-sulfide, which is a lithium ion or sulfur-lithium combination, may pass through the pores during the battery reaction, and preferably only lithium ions may pass through the pores. In addition, sulfur particles and/or sulfur molecules may enter the inside of the carbon hollow fiber through the pores.

In one embodiment of the present invention, a secondary battery comprising the above-described electrode material for secondary batteries is provided.

In one embodiment, the secondary battery may have a capacity per unit area ^{of 1 mA h cm - 2 or more under the condition of 0.1C-rate.} Specifically, 5 mA h cm ^{- 2} or more, 7 mA h cm ^{- 2} or more, 9 mA h cm ^{- 2} or more, 10 mA h cm ^{- 2} or more, 11 mA h cm ^-2 , 12 mA h cm ^-2 , 13 mA h cm ^-2 , 14 mA h cm ^-2 , 15 mA h cm ^-2 , 16 mA h cm ^-2 , 17 mA h cm ^-2 , 18 mA h cm ^-2 , 19 mA h cm ^-2 , 20 mA h cm ^-2 , 21 mA h cm ^-2 , 22 mA h cm ^-2 , or 23 mA h cm ^-2 or more. This capacity value per unit area is due to the configuration including the carbon structure on which sulfur is supported in a high content according to the embodiment of the present invention, and it can be confirmed that it has an excellent capacity per unit area.

In one embodiment, the secondary battery may be applied to an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, a portable power source, or a power storage device.

Method of manufacturing electrode material for secondary battery

Hereinafter, a method of manufacturing an electrode material for a secondary battery will be described with reference to FIG. 1 .

One embodiment of the present invention comprises the steps of forming a sulfur active point in the carbon structure; and injecting sulfur into the carbon structure to bond and grow the sulfur active site; It includes, and provides a method of manufacturing an electrode material for a secondary battery, having a sulfur loading amount of ^{10 mg cm - 2} or more per unit electrode area.

First, a sulfur active site may be formed in the carbon structure. For example, by evenly dispersing sulfur particles in the carbon structure to induce sulfur loading in the porous carbon structure, it may be to form a seed for additional sulfur growth.

_{In general, sulfur exists as a ring-crown S 8} in the solid state, and when it rises above about 120˚C, it begins to melt, and at 150˚C or higher, it separates into small cyclic sulfur with mobility, and becomes 155˚C or higher. In this case, the ring shape is broken and it starts to become a chain shape. Thereafter, when the temperature is increased to 160° C. or higher, the chain forms start to be connected to each other, and thus exist as long-chain macromolecules having polymer properties (see FIG. 2).

Due to these characteristics of sulfur, it is very difficult to inject macromolecular sulfur into a porous structure having micro- and nano-sized pores in a molten state using the conventional melt impregnation method. As another method, there exist a method using vaporization and a hydrothermal synthesis method, but in these cases, the sulfur particles are inserted in the form of very small particles in the micropores of the wall surface of the carbon structure, and thereafter, no further loading and growth of sulfur occurs. As a result, there is a problem in that it is difficult to inject additional sulfur even if the process time is increased after a certain amount of sulfur particles are supported.

In order to overcome this limitation of the amount of sulfur supported, one embodiment of the present invention includes the step of forming a sulfur active point, and specifically, after dispersing the sulfur particles in the carbon structure first, the carbon structure is brought into contact with molten sulfur. As a result, sulfur molecules in a molten state can be induced to flow into the carbon structure.

That is, the method for manufacturing an electrode material for a secondary battery according to an embodiment of the present invention may include two or more active material loading steps, for example, a process including a first pre-treatment step and a second post-treatment step.

In one embodiment, the first pretreatment step, that is, the sulfur active point formation step may be to form sulfur active points by dispersing sulfur particles in the carbon structure. Here, the sulfur particles dispersed in the carbon structure act as a seed or an active point, and then the sulfur introduced into the carbon structure in the second post-treatment step is induced to grow into macromolecules. Through this process, sulfur molecules in the molten state continue to flow into the carbon structure to fill the entire void, and a carbon structure with high sulfur content is formed. When such a high-content sulfur-supported carbon structure is used as an electrode material, a high-capacity battery can be realized by high battery capacity expression per unit area.

In one embodiment, the step of forming the sulfur active point may be performed by a solvent impregnation method, a vaporization impregnation method, or a hydrothermal impregnation method. The step of forming the sulfur active point may be a primary pretreatment method for generating sulfur particles in the carbon structure.

The solvent impregnation method may be to impregnate the carbon structure in a solution in which sulfur is dissolved in a solvent. Specifically, as a method of dissolving sulfur in a suitable solvent and supporting it on a carbon structure, for example, 10 g of sulfur powder is put in 100 ml of toluene solution, and then heated to 95° C. for 1 hour with continuous stirring. do. Then, the porous carbon structure can be immersed in the prepared solution for 1 hour and then taken out and washed/dried to form a sulfur active site. As the usable solvent, toluene, xylene, fluorobenzene, cyclohexane, or benzene having solubility in sulfur may be used.

In addition, the vaporization impregnation method may be to heat sulfur to vaporize it, and then to support it on the carbon structure. For example, a sulfur particle active point in the carbon structure may be formed by placing the porous carbon structure on top of the container containing the sulfur powder and then heating the container, for example, heating to about 200° C. to vaporize the sulfur.

In addition, the hydrothermal impregnation method may be to induce the movement of sulfur particles into the carbon structure by treating a compound containing sulfur under a high temperature and high pressure condition. For example, the solution used for the hydrothermal impregnation method is used by dissolving sodium thiosulfate pentahydrate (Na ₂ S ₂ O ₃ ·5H ₂ O) in non-ionized water that can be dissolved in an aqueous solution. The sample to be used may be sulfur or any compound containing sulfur. Additionally, 5 wt% of hexadecyltrimethylammonium bromide (hereafter, CTAB) was added and stirred for 2 hours to make a uniformly mixed aqueous solution, and then the porous carbon structure was placed in the aqueous solution and 0.2 M hydrochloric acid (HCl) was added to 1 After slowly adding and mixing at a rate of mL min ^-1 , heat treatment at 150°C in a hydrothermal synthesizer for 12 hours. Heat treated samples can be washed and dried to form sulfur active sites.

Next, in the secondary post-treatment step, sulfur may be further injected into the carbon structure to bond and grow with the sulfur active point. For example, by immersing a carbon structure in which sulfur seeds (active points) are evenly dispersed in molten sulfur, sulfur flows into the carbon structure, grows from the sulfur seeds, and finally fills the pores of the carbon structure with sulfur. .

In one embodiment, the sulfur injection may be to inject molten sulfur into the carbon structure. Specifically, when the carbon structure in which the sulfur particles are dispersed is immersed in a sulfur solution in a molten state, the molten sulfur can be introduced into the carbon structure, and the introduced sulfur can grow through the active point (sulfur particles dispersed in the carbon structure), Accordingly, the inside of the carbon structure may be filled with sulfur.

On the other hand, since the physical properties of sulfur vary greatly depending on the temperature, the melting temperature must be appropriately controlled in order to inject sulfur into the porous structure having micro- and nano-sized pores.

Therefore, in one embodiment of the present invention, when the sulfur melting temperature is controlled in a specific temperature range when sulfur is injected into the carbon structure, a hollow fiber-type carbon structure having a high sulfur content can be manufactured.

Specifically, the melting temperature of the sulfur may have a range of 120 to 250 ℃. Preferably, the melting temperature of the sulfur may have a range of 150 to 160 ℃. Meanwhile, Table 1 below shows the viscosity according to the melting temperature of sulfur.

Viscosity of sulfur as a function of melting temperature (cp) 120.0 ℃ 17 140.0 ℃ 8 158.0℃ 6.4 160.0 ℃ 5952

As can be seen in Table 1, sulfur has the smallest molecular weight at a melting temperature of about 158° C. and the viscosity is also very low, so that it is easily introduced into the carbon nanotube. On the other hand, when sulfur rises above 160 ˚C, sulfur reacts with oxygen to show a high viscosity, thus making it difficult for sulfur to move into the carbon structure. This result is also consistent with the result of the sulfur loading in the carbon structure according to the melting temperature to be described later (Experimental Example 1). Therefore, it is possible to manufacture an electrode material having a high sulfur content in the above-described melting temperature range of sulfur.

Example

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not to be construed as being limited by these examples.

Example 1: Preparation of porous carbon structure (carbon hollow fiber)

Electrospinning technology was used to prepare carbon nanotubes, which are porous carbon structures. A double nozzle was used to prepare a tube shape, and at this time, a shell and a core solution were required respectively. The shell solution was prepared by dissolving 1.3 wt% of poly-acrylonitrile (PAN), a crystalline polymer, in dimethylformamide (DMF). It was prepared by dissolving 2.5 wt% of acrylate (Poly-methyl methacrylate, PMMA) in a DMF solvent.

The two solutions prepared for the preparation of a uniform solvent were stirred at 60 °C for 24 hours, and then cooled to room temperature before use.

For the electrospinning conditions, the shell solvent was set to 1.5 ml h ^-1 and the core solvent was set to 1.0 ml h ^-1 , the electrospinning potential was set to 1.3 kV, and the discharge area was 200 mm wide and 300 mm long for 2 hours. During the electrospinning was performed.

Thereafter, the electrospun sample is dried in an oven at 60° C. for 12 hours, and then subjected to a two-step heat treatment process in a heating furnace. The primary heat treatment condition is a stabilization step performed in an oxygen atmosphere, and a heat treatment process is performed at 250° C. for 1 hour. Finally, after the first heat treatment process, the second heat treatment process is carried out in an inert gas atmosphere such as nitrogen and argon, and the second heat treatment process is heat treated at 800 °C for 1 hour under the temperature increase condition ^{of 10 °C min -1,} As shown in FIG. 3 , carbon nanotubes or nano-carbon hollow fibers (HCNFs), which are porous carbon structures having an inner diameter of about 200 nm and a shell portion having a thickness of about 20 nm, were prepared.

Comparative Example 1: Preparation of electrode material using conventional sulfur loading method

The porous carbon structure (carbon hollow fiber) prepared in Example 1 was used, and sulfur was supported by using the vaporization impregnation method and the solvent impregnation method, which are conventional sulfur loading methods.

5a shows a photograph of the sulfur-supported hollow fiber carbon structure prepared through the vaporization impregnation method, and FIG. 5b shows a photograph of the sulfur-supported hollow fiber carbon structure prepared through the solvent impregnation method.

When sulfur is supported through the conventional sulfur loading technology, it can be confirmed that crystals of sulfur are formed outside the structure or only a very small amount of sulfur particles are formed on the wall surface of the carbon structure because it is difficult to inject sulfur into the carbon structure. In particular, in the case of sulfur formed on the outer wall of the carbon structure, it causes a problem of polysulfide elution in battery driving, and is not suitable for manufacturing a high-capacity battery due to a low sulfur loading as a whole.

Example 2: Formation of sulfur active sites inside the porous carbon structure (manufacture of sulfur dispersed carbon structure)

In order to support the sulfur particles more efficiently in the inner space of the carbon structure (carbon hollow fiber) prepared in Example 1, first, 0.1 M Na ₂ S ₂ O ₃ ·5H ₂ O and 0.5 wt of 100 mL of non-ionized water. % of Hexadecyltrimethylammonium bromide (CTAB) was stirred for 2 hours to prepare a uniformly mixed aqueous solution. Then, 0.1 mg of the nano-carbon hollow fiber (HCNF) sample (10 mm x 10 mm) prepared in Example 1 was placed in the aqueous solution prepared above, and 0.2 M hydrochloric acid (HCl) was slowly added at a rate ^{of 1 mL min -1} Add and mix. The resulting mixture of carbon structure and sulfur compound is put into a hydrothermal synthesizer, and then heat-treated at 150°C for 12 hours. The heat-treated HCNF sample is washed and dried, thereby forming an active site in which sulfur can be supported in the carbon structure as shown in FIG. 4a.

Example 3: Sulfur injection into the porous carbon structure

The sulfur powder was heated to 158° C. to prepare a molten state. By immersing the sulfur-dispersed carbon structure of Example 2 in sulfur in a molten state so that the molten sulfur flows into the internal space of the carbon structure, sulfur grows inside the carbon structure after a certain period of time, and the pores of the carbon structure are filled with sulfur.

A schematic diagram for this is shown in FIG. 1 , and FIG. 4b is a photograph of the sulfur-supported hollow fiber carbon structure prepared in this embodiment.

Comparative Example 2: Sulfur injection into the porous carbon structure without the step of forming a sulfur active point

Sulfur was injected into the porous carbon structure in the same manner as in Example 3, except that the porous carbon structure of Example 1 was used instead of the sulfur-dispersed carbon structure of Example 2. That is, sulfur was supported on the carbon structure by using the conventional melt impregnation method without a pretreatment process of forming an active point inside the carbon structure.

FIG. 5c is a photograph of a hollow fiber carbon structure supported with sulfur prepared through the conventional melt impregnation using only the post-treatment sulfur injection method. It is very different from FIG. 4b, and it can be seen that sulfur does not enter the inside of the nano-sized carbon hollow fiber structure, and sulfur is formed only on the outer wall. When this type of sulfur-supported carbon body is used, non-conductive sulfur surrounds the outside, making it difficult to move electrons in the electrode, thereby greatly reducing the efficiency of the battery.

Test Example 1: Measurement of sulfur loading in carbon structure according to sulfur melting temperature

In Example 3, sulfur was supported in the pores of the carbon structure by varying the melting temperature of the sulfur powder, and the amount of sulfur supported in the carbon structure according to the sulfur melting temperature (mg cm ^{- 2} ) is shown in Table 2 below.

division Sulfur loading (mg cm ^-2 ) Example 3 (120° C.) ~ 0 Example 3 (140° C.) < 0.1 Example 3 (158° C.) 23.9 Example 3 (160°C) < 0.1 Comparative Example 1 1.0 Comparative Example 2 < 0.1

Table 2 compares the amount of sulfur supported in the carbon structure under various conditions. In order to present the optimum sulfur melting temperature presented in Example 3, the amount of sulfur supported in the carbon structure according to the melting temperature was compared. Below 140° C., since sulfur exists in a ring state, the mobility of sulfur molecules is very low and, accordingly, the viscosity is also high as shown in Table 1, so it is difficult to carry it into the carbon structure. As a result, very trace amounts of sulfur were supported. However, when the sulfur melting temperature is increased to about 158° C., the cyclic sulfur molecules start to break, and the mobility increases, and accordingly, it has a very low viscosity, so that it is induced to grow as an active point inside the carbon structure. As a result, it shows a very high loading of 23.9 mg cm- ^2. Thereafter, at a temperature of 160° C. or higher, the broken sulfur molecules are connected to each other to form a large chain like polymer molecules, and thus have a very high viscosity. Therefore, since it is difficult to introduce sulfur into the carbon structure with small pores, it shows a very low loading amount.

Test Example 2: Capacity per unit area evaluation for lithium-sulfur batteries

The battery capacity per unit area of a lithium-sulfur battery using the sulfur-supported hollow fiber carbon structure prepared according to Comparative Examples 1, 2 and 3 as a sulfur positive electrode was evaluated.

The battery evaluation voltage range was 2.7 - 1.7V, and it was performed under 0.1C-rate current density conditions, and the results are shown in Table 3 below.

The lithium-sulfur battery employing Comparative Example 1 has a capacity per unit area of about 4 mA h cm ^-2 under the condition of 0.1 C-rate, and the lithium-sulfur battery employing Comparative Example 2 has a unit area under the condition of 0.1 C-rate. The capacity per area was about 0.5 mA h cm ^-2, and the lithium-sulfur battery according to Example 3 had a capacity per unit area of about 17 mA h cm ^-2 under the condition of 0.1 C-rate.

Capacity per unit area for lithium-sulfur batteries (mA h cm ^-2 ) Comparative Example 1 4 Comparative Example 2 0.5 Example 3 17

As shown in Table 3, in the case of the sulfur-supported carbon structure electrode prepared in Comparative Example 1, ^{the performance of 4 mA h cm -2} per unit area was exhibited due to the small amount of sulfur loaded, and the sulfur-supported carbon by Comparative Example 2 In the case of the structure, the amount of supported sulfur was very low, and the performance of ^{0.5 mA h cm -2 was very low.} Exemplary case of a sulfur-carbon electrode structure prepared in the Example 3 meurosseo per unit area of the high loading capacity of 17 mA h cm ^- was increased by ^2.

The embodiments of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can improve and change the technical idea of the present invention in various forms. Accordingly, such improvements and modifications will fall within the protection scope of the present invention as long as they are apparent to those of ordinary skill in the art.

Claims (14)

As an electrode material for a secondary battery,
carbon structure; and sulfur supported on the carbon structure, wherein the electrode material has a sulfur loading amount of ^{1.0 mg cm -2 or more per unit electrode area of the electrode material.} According to claim 1,
The electrode material for a secondary battery is an electrode material for a secondary battery, characterized in that it has a sulfur loading amount of ^{10 mg cm - 2} or more per unit electrode area of the electrode material. According to claim 1,
The carbon structure is a porous carbon structure, characterized in that the secondary battery electrode material. 4. The method of claim 3,
The porous carbon structure is at least one carbon selected from the group consisting of porous carbon powder, carbon hollow fibers, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, porous carbon sheets, porous carbon cloth, and porous carbon felt. An electrode material for a secondary battery, characterized in that it contains a material. According to claim 1,
The carbon structure is an electrode material for a secondary battery, characterized in that it is a carbon hollow fiber including a hollow having an inner diameter of 100 μm or less. 6. The method of claim 5,
The carbon hollow fiber is an electrode material for a secondary battery, characterized in that it includes a plurality of pores with a diameter of 10 μm or less located on the wall surface. A secondary battery comprising the electrode material for a secondary battery of any one of claims 1 to 6. 8. The method of claim 7,
The secondary battery, characterized in that it has a capacity per unit area ^{of 1 mA h cm - 2} or more under the condition of 0.1C-rate, the secondary battery. forming a sulfur active site in the carbon structure; and
injecting sulfur into the carbon structure to bond and grow the sulfur active site; ^{Including, 1.0 mg cm - 2} or more sulfur loading per unit electrode area of the electrode material, the secondary battery electrode material manufacturing method. 10. The method of claim 9,
The active point forming step is characterized in that the sulfur particles are dispersed in the carbon structure, a method for manufacturing an electrode material for a secondary battery. 10. The method of claim 9,
The active point forming step is a method for manufacturing an electrode material for a secondary battery, characterized in that it is performed by a solvent impregnation method, a vaporization impregnation method, or a hydrothermal synthesis impregnation method. 10. The method of claim 9,
The sulfur injection is a method of manufacturing an electrode material for a secondary battery, characterized in that by injecting molten sulfur into the carbon structure. 13. The method of claim 9 or 12,
The melting temperature of the sulfur is characterized in that it has a range of 120 to 250 ℃, secondary battery electrode material manufacturing method. 13. The method of claim 9 or 12,
The melting temperature of the sulfur is characterized in that it has a range of 150 to 160 ℃, secondary battery electrode material manufacturing method.

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