KR20210026290A - Homogenous porous carbon-sulfur complex, lithium-sulfur battery including the same, and preparing method thereof - Google Patents

Abstract

A porous carbon-sulfur complex has a hollow spherical shell, and includes porous carbon including a plurality of pores on the surface and inside of the shell, and sulfur positioned inside the plurality of pores. A method for preparing the porous carbon-sulfur complex includes the steps of: preparing porous carbon having a hollow spherical porous shell; and adding porous carbon and sulfur to a binary solution.

Description

Uniform porous carbon-sulfur composite, lithium-sulfur battery including the same, and a manufacturing method thereof {HOMOGENOUS POROUS CARBON-SULFUR COMPLEX, LITHIUM-SULFUR BATTERY INCLUDING THE SAME, AND PREPARING METHOD THEREOF}

A uniform porous carbon-sulfur composite, a lithium-sulfur battery including the same, and a method of manufacturing the same are provided.

Recently, small and light-weight reduction of electronic products, electronic devices, communication devices, etc. is rapidly progressing, and as the necessity of electric vehicles emerges greatly in relation to environmental issues, the demand for performance improvement of secondary batteries used as power sources of these products is also increasing. It is the actual situation. Among them, lithium secondary batteries are receiving considerable attention as high-performance batteries because of their high energy density and high standard electrode potential.

In particular, a lithium-sulfur (Li-S) battery is a secondary battery that uses a sulfur-based material having an S-S bond (Sulfur-Sulfur bond) as a positive electrode active material and a lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, is very rich in resources, non-toxic, and has a low weight per atom. In addition, the theoretical discharge capacity of the lithium-sulfur battery is about 1675 mAh/g, and the theoretical energy density is about 2,600 Wh/kg, and the theoretical energy density of other battery systems currently being studied (Ni-MH battery: about 450 Wh/kg , Li-FeS battery: about 480 Wh/kg, Li-MnO2 battery: about 1,000 Wh/kg, Na-S battery: about 800 Wh/kg). It is the most promising battery among batteries.

During the discharge reaction of a lithium-sulfur battery, an oxidation reaction of lithium occurs at the negative electrode and a reduction reaction of sulfur occurs at the positive electrode. Sulfur before discharge has a cyclic S8 structure, and the oxidation number of S decreases as the SS bond is broken during the reduction reaction (discharge), and the oxidation number of S increases as the SS bond is re-formed during the oxidation reaction (charging). Electrical energy is stored and generated using a reduction reaction. During this reaction, sulfur is converted from cyclic S8 to linear lithium polysulfide (Li ₂ S _x , x = 8, 6, 4, 2) by a reduction reaction. Eventually, when these lithium polysulfides are completely reduced, Finally, lithium sulfide (Li ₂ S) is produced. The discharge behavior of a lithium-sulfur battery by the process of being reduced to each lithium polysulfide shows a discharge voltage in stages, unlike a lithium ion battery.

However, in the case of such a lithium-sulfur battery, problems such as low electrical conductivity of sulfur, elution and volume expansion of lithium polysulfide during charging and discharging, low coulomb efficiency and rapid capacity reduction due to charging and discharging must be solved.

In order to solve this problem, research has been conducted to apply a cathode active material of a lithium-sulfur battery to various porous carbon materials such as carbon nanotubes and graphene. Such a porous carbon material can provide high electrical conductivity and physically prevent the elution of lithium polysulfide into the electrolyte, and thus the capacity and life of the lithium-sulfur battery can be improved.

For example, a melt diffusion method is being studied as a method of compounding sulfur into a porous carbon material, and a solution method through drying of carbon disulfide is being studied. However, the porous carbon-sulfur composite by this method has a limitation in uniformly compounding sulfur in the porous carbon. Furthermore, recently, a gas phase complexing method and a sulfur complexing method using a supercritical fluid have been studied for uniform sulfur complexation.

One embodiment provides a porous carbon-sulfur composite in which sulfur is uniformly compounded in the pores of porous carbon, thereby improving the electrochemical performance of a lithium-sulfur battery including the same, and expanding the capacity and life of the lithium-sulfur battery. For.

In addition to the above problems, embodiments according to the present invention may be used to achieve other tasks not specifically mentioned.

The porous carbon-sulfur composite according to an embodiment includes a hollow spherical shell, porous carbon including a plurality of pores on the surface and inside of the shell, and sulfur located inside the plurality of pores.

By EDS mapping for porous carbon and sulfur, sulfur located inside the shell may be uniformly distributed.

Sulfur remaining on the outside of the shell may be greater than 0% and less than 20% based on the surface area of the shell.

The electrode according to an embodiment includes a substrate, and a porous carbon-sulfur composite positioned on the substrate, wherein the porous carbon-sulfur composite has a hollow spherical shell, and a plurality of pores on the surface and inside of the shell Porous carbon containing the, and sulfur located inside the plurality of pores.

The lithium-sulfur battery according to an embodiment includes a porous carbon-sulfur composite, and is interposed between the positive electrode and the negative electrode, facing the positive electrode, the negative electrode where the oxidation reaction of lithium occurs, and the positive electrode in which a sulfur reduction reaction occurs, the positive electrode. And a porous carbon-sulfur composite, wherein the porous carbon-sulfur composite has a hollow spherical shell, porous carbon including a plurality of pores on the surface and inside of the shell, and sulfur located inside the plurality of pores do.

A method of manufacturing a porous carbon-sulfur composite according to an embodiment includes preparing porous carbon having a hollow spherical porous shell, and adding porous carbon and sulfur to a binary solution.

The binary solution can be prepared by mixing carbon disulfide and a polar solvent.

The polar solvent may be an alcohol-based solvent.

The step of preparing porous carbon may include mixing an organic solvent and a metal oxide precursor, adding and stirring the carbon precursor, sintering under an inert gas atmosphere, and etching with an etching solution.

Here, the metal oxide precursor may be a silica precursor.

Here, the carbon precursor may include a phenolic compound.

In addition, the carbon precursor may include an aldehyde-based compound.

The method of manufacturing a porous carbon-sulfur composite according to an embodiment includes the steps of preparing porous carbon having a hollow spherical porous shell, and adding porous carbon and sulfur to a solution in which carbon disulfide and isopropyl alcohol are mixed. Includes steps.

Here, the organic solvent may include ethanol, distilled water, and ammonia.

Here, the etching solution may be a sodium hydroxide solution.

By using a binary solution containing a solvent having a low surface tension or low interface (carbon surface/solvent) energy, the penetration of sulfur into the porous carbon is facilitated, so that a uniform porous carbon-sulfur composite can be prepared. Accordingly, the electrochemical properties of the lithium-sulfur battery can be improved, and the capacity and life of the lithium-sulfur battery can be extended.

1 is a schematic diagram of a homogeneous porous carbon-sulfur composite prepared according to sulfur complexation using a binary solution (hereinafter, Example).
2 is a schematic diagram of a conventional porous carbon-sulfur composite prepared according to sulfur complexation using a single solution (hereinafter, Comparative Example).
3 is a high magnification transmission electron microscope (TEM) image and EDS (Energy Dispersive Spectroscopy) mapping analysis results of Comparative Examples and Examples.
4 is a low magnification scanning electron microscope (SEM) image of Comparative Examples and Examples.
5 is a graph showing thermogravimetric analysis results of Comparative Examples and Examples.
6 is a graph showing galvanostatic charge/discharge results for each current density in Comparative Examples and Examples.
7 is a graph showing charging and discharging results under a constant current condition in 1 C-rate condition of Comparative Examples and Examples.

With reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and the same reference numerals are used for the same or similar components throughout the specification. In addition, in the case of a well-known technology, a detailed description thereof will be omitted.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

Then, a uniform porous carbon-sulfur composite according to an embodiment, a lithium-sulfur battery including the same, and a method of manufacturing the same will be described in detail.

1 is a schematic diagram of a uniform porous carbon-sulfur composite prepared by sulfur complexation using a binary solvent, and FIG. 2 is a schematic diagram of a conventional porous carbon-sulfur composite prepared by sulfur complexation using a single solvent.

The porous carbon 10 has a hollow spherical shell structure, and the spherical shell has a porosity including a plurality of pores. For example, porous carbon 10 having a spherical porous shell structure may be formed using a metal oxide precursor and a carbon precursor. For example, the metal oxide precursor includes a silica precursor, an alumina precursor, and the like. For example, carbon precursors include sugars, alcohol compounds, phenol compounds, olefin compounds, and aldehyde compounds. A carbon precursor is grown on a metal oxide core formed from the metal oxide precursor. For example, an organic solvent and a metal oxide precursor are mixed and stirred, and a carbon precursor is added and stirred again. Subsequently, a powder is obtained through a washing and drying process. Subsequently, the obtained powder is sintered under an inert gas atmosphere to produce carbon having a porous structure. Subsequently, carbon having a porous structure is etched with an etching solution, whereby the metal oxide core is removed to produce carbon having a hollow spherical porous shell structure.

When a silica precursor is used and a phenol-based compound and an aldehyde-based compound are mixed and used, the electrical conductivity of carbon having a spherical porous shell structure is excellent, and accordingly, the electrochemical performance of a lithium-sulfur battery can be improved. .

Furthermore, in the case of using tetrapropylorthosilicate, resorcinol, or formaldehyde, the electrical conductivity of carbon having a spherical porous shell structure is more excellent. The performance can be further improved.

Referring to FIG. 1, sulfur 20 is dispersed in a binary solution 30. For example, the binary solution is a mixture of carbon disulfide and a polar solvent. When a polar solvent is added to the carbon disulfide solution, the wettability of the carbon surface is improved due to the polar solvent having a low surface tension or low interfacial (carbon surface/solvent) energy. Therefore, it is easy to inject a solution into the porous carbon 10. After the solvent evaporates through the drying process, most of the sulfur is uniformly located in the plurality of pores located inside and on the surface of the shell of the porous carbon 10. Accordingly, the cross-sectional area of sulfur remaining on the surface of the shell is more than 0% and less than 20% based on the total surface area of the shell. Due to structural properties of sulfur composites, porous carbon-uniform porous carbon of this numerical value range the sulfur composite is lithium when used as an electrode of sulfur batteries, lithium ion (Li ⁺⁾ transfer assist electron (e ^-) of the transfer Both degrees are high, and accordingly, the elution of lithium polysulfide (LiPS) is small. Accordingly, the electrochemical performance of the lithium-sulfur battery can be improved, and the capacity and life of the lithium-sulfur battery can be extended.

In the case of using an alcohol-based solvent among the polar solvents, due to the polar solvent having a lower surface tension or lower interfacial (carbon surface/solvent) energy, the wettability of the carbon surface is better, and sulfur is the shell of the porous carbon (10). It can be more evenly located in a plurality of pores located on the surface and inside of the shell of the, the electrochemical performance of the lithium-sulfur battery can be further improved, and the capacity and life of the lithium-sulfur battery can be further extended. .

Furthermore, when isopropyl alcohol is used among alcohol-based solvents, the wettability of the carbon surface is further improved and the sulfur is porous due to the polar solvent having a lower surface tension or even lower interfacial (carbon surface/solvent) energy. The carbon 10 can be positioned more evenly in a plurality of pores located on the surface and inside of the shell, and the electrochemical performance of the lithium-sulfur battery can be further improved, and the capacity and lifespan of the lithium-sulfur battery This can be further magnified.

Meanwhile, referring to FIG. 2, sulfur 20 is dispersed in a single solution 40. For example, the single solution 40 is a solution containing only carbon disulfide. When sulfur is dissolved in the existing single solution 40 and injected into the porous carbon 10, it is difficult to inject the solution into the porous carbon 10 because the solution is not well wetted on the carbon surface. Accordingly, after the solvent evaporates through the drying process, sulfur is unevenly located outside the shell of the porous carbon 10. Due to the structure of the sulfur composite, the porous carbon - such a non-uniform porous carbon sulfur composite is a lithium-were all passed, as is low ^- when used as an electrode of the sulfur battery, transfer assist electron (e) of the lithium ion (Li ⁺⁾ Accordingly, the elution of lithium polysulfide (LiPS) is large. Thus, the capacity and life of the lithium-sulfur battery can be reduced.

The porous carbon-sulfur composite may be positioned on a substrate to constitute an electrode. For example, it can be used as a positive electrode for a lithium-sulfur battery.

The lithium-sulfur battery includes a porous carbon-sulfur composite and includes a positive electrode in which a sulfur reduction reaction occurs, a negative electrode in which an oxidation reaction of lithium occurs facing the positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode. Such a lithium-sulfur battery has excellent electrochemical performance, and thus the capacity and life of the battery can be extended.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are only examples of the present invention, and the present invention is not limited to the following examples.

Example

Preparation of carbon having a spherical porous shell structure

Tetrapropyl orthosilicate is used as a silica precursor. To a solution in which 70 mL of ethanol, 10 mL of distilled water, and 3 mL (25-28%) of ammonia are mixed, 3.5 mL of 12 mM tetrapropyl orthosilicate was added and stirred. After 15 minutes of stirring, 0.4 g of resorcinol and 0.56 mL of formaldehyde (37 wt%) were added, followed by stirring for 24 hours. After washing several times with distilled water, it is dried at 60 degrees Celsius for 12 hours or more to obtain a powder. The obtained powder was sintered in an argon atmosphere under conditions of a heating time of 2 hours and a holding time of 5 hours at 700 degrees Celsius. After sintering, it is etched in sodium hydroxide solution for 5 hours. After washing several times with distilled water, it was dried at 60 degrees Celsius for 12 hours or more to obtain a carbon powder having a spherical porous shell structure.

Preparation of porous carbon-sulfur composite

A solution of 7:3 mol% of carbon disulfide and isopropyl alcohol is prepared. Carbon powder and sulfur having a spherical porous shell structure are added to the mixed solution in a ratio of 1:3 wt%. Subsequently, it is dried at 45 degrees Celsius for 12 hours or more to obtain a porous carbon-sulfur composite.

Comparative example

In the above Example, a porous carbon-sulfur composite was obtained in the same manner as in Example, except that a 100% carbon disulfide solution was used instead of a mixed solution of carbon disulfide and isopropyl alcohol.

Analysis of properties of porous carbon-sulfur composites

TEM And EDS analysis

Transmission Electron Microscopy (TEM) analysis was performed to confirm the structure of the porous carbon-sulfur composite prepared in Examples and Comparative Examples. During TEM analysis, a TEM image is taken, and EDS mapping analysis for carbon and sulfur elements is performed through the EDS (Energy Dispersive Spectroscopy) analysis function at the corresponding location. The results of TEM and EDS analysis are shown in FIG. 3.

It can be seen that a porous carbon-sulfur composite structure having a spherical shell structure was formed. It can be seen that the examples are more uniformly located inside the shell of carbon than the comparative examples.

SEM analysis

In order to confirm the structure of the porous carbon-sulfur composite prepared in Examples and Comparative Examples, SEM (Scanning Electron Microscopy) analysis was performed, and the results are shown in FIG. 4.

In the case of the embodiment, since the solution penetration property in the pores is high, it can be seen that sulfur is uniformly compounded with the pores inside the porous carbon shell, and there is little sulfur remaining outside the shell.

On the other hand, in the case of the comparative example, since the affinity between sulfur and carbon is low and the penetration characteristics are low, it can be seen that the sulfur cannot be complexed into the pores inside the porous carbon shell, and remains outside the porous carbon shell upon drying.

TGA (Thermogravimetric analysis)

The porous carbon-sulfur composites prepared in Examples and Comparative Examples were subjected to thermogravimetric analysis, and the results are shown in FIG. 5. It can be seen that both Examples and Comparative Examples are complexed with sulfur at a high mass ratio of 75% by weight. However, it can be seen that the temperature at which the weight reduction of 75% by weight occurs in the Example is higher than that of the Comparative Example, and thus, sulfur is more uniformly compounded in the pores of the composite of the Example.

Of the positive electrode of a lithium-sulfur battery Rate And life characteristics evaluation

The porous carbon-sulfur composite prepared according to Examples and Comparative Examples was applied to a positive electrode of a lithium-sulfur battery. 1M LiTFSI (Lithium bis(trifluoromethanesulphonyl)imide), 0.2M LiNO ₃ , Dioxolane: dimethyl ether (5:5v/v%) was mixed with an electrolyte condition using a battery tester. Here, the weight of sulfur per electrode area is 1 mg/cm ² .

6 is a graph showing constant current charging and discharging evaluation under various C-rate current density conditions between 0.2C-2C ratio using the positive electrode made of the porous carbon-sulfur composite prepared in Examples and Comparative Examples. Referring to FIG. 6, the Example shows an improved specific capacity in all current density conditions compared to the Comparative Example. This is because sulfur is uniformly compounded into the porous carbon-sulfur composite, and it can be seen that the rate-limiting characteristics of the Example, that is, the electron transport and the ion transport, are higher than that of the Comparative Example.

7 is a graph showing the analysis of lifespan characteristics in 100 charge/discharge conditions under a 1 C-rate current density condition using a positive electrode made of a porous carbon-sulfur composite prepared in Examples and Comparative Examples. Referring to FIG. 7, it can be seen that the embodiment has higher lifespan characteristics than the comparative example. This is because, in the case of the embodiment, sulfur is uniformly compounded into the porous carbon-sulfur composite, and the elution of LiPS to the outside of the porous carbon shell decreases, thereby increasing the lifetime.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of rights of

1: porous carbon-sulfur composite
10: porous carbon
20: sulfur
30: binary solution
40: single solution

Claims (16)

Porous carbon having a hollow spherical shell and including a plurality of pores on the surface and inside of the shell, and
Sulfur located inside the plurality of pores
Porous carbon-sulfur composite comprising a. In claim 1,
By EDS (Energy Dispersive Spectroscopy) mapping of the porous carbon and the sulfur, the sulfur located inside the shell is uniformly distributed. In paragraph 2,
The porous carbon-sulfur composite in which the sulfur remaining on the outside of the shell is more than 0% and 20% or less based on the surface area of the shell. Substrate, and
Porous carbon-sulfur composite positioned on the substrate
Including,
The porous carbon-sulfur composite,
Porous carbon having a hollow spherical shell and including a plurality of pores on the surface and inside of the shell, and
Sulfur located inside the plurality of pores
Electrode comprising a. An anode comprising a porous carbon-sulfur composite, and in which a sulfur reduction reaction occurs,
Facing the positive electrode, a negative electrode in which an oxidation reaction of lithium occurs, and
Electrolyte interposed between the positive electrode and the negative electrode
Including,
The porous carbon-sulfur composite,
Porous carbon having a hollow spherical shell and including a plurality of pores on the surface and inside of the shell, and
Sulfur located inside the plurality of pores
Lithium-sulfur battery comprising a. Producing porous carbon having a hollow spherical porous shell, and
Adding the porous carbon and sulfur to the binary solution
A method for producing a porous carbon-sulfur composite comprising a. In paragraph 6,
The binary solution is a method for producing a porous carbon-sulfur composite prepared by mixing carbon disulfide and a polar solvent. In clause 7,
The polar solvent is an alcohol-based solvent, a method for producing a porous carbon-sulfur composite. In paragraph 6,
The step of preparing the porous carbon,
Mixing an organic solvent and a metal oxide precursor,
Stirring by adding a carbon precursor,
Sintering under an inert gas atmosphere, and
Etching with an etching solution
A method for producing a porous carbon-sulfur composite comprising a. In claim 9,
The metal oxide precursor is a silica precursor, a method of manufacturing a porous carbon-sulfur composite. In claim 10,
The carbon precursor is a method of manufacturing a porous carbon-sulfur composite containing a phenolic compound. In clause 11,
The carbon precursor is a method of producing a porous carbon-sulfur composite containing an aldehyde-based compound. Producing porous carbon having a hollow spherical porous shell, and
Adding the porous carbon and sulfur to a mixed solution of carbon disulfide and isopropyl alcohol
A method for producing a porous carbon-sulfur composite comprising a. In claim 13,
The step of preparing the porous carbon,
Mixing an organic solvent and tetrapropyl orthosilicate,
Adding and stirring resorcinol and formaldehyde,
Sintering under an inert gas atmosphere, and
Etching with an etching solution
A method for producing a porous carbon-sulfur composite comprising a. In clause 14,
The organic solvent is ethanol, distilled water, and a method for producing a porous carbon-sulfur composite containing ammonia. In paragraph 15,
The etching solution is a sodium hydroxide solution, a method for producing a porous carbon-sulfur composite.

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