Crosslinked polythiophene compound, sulfur-carbon composite, lithium-sulfur battery, and method for producing sulfur-carbon composite

Abstract

A sulfur-carbon composite is provided, which includes: a crosslinked polythiophene compound having a crosslinked structure and containing a cationic functional group; a porous carbon material; a coating layer located on at least one surface of the porous carbon material and containing the crosslinked polythiophene compound; and a sulfur compound located on at least a portion of the surface of the porous carbon material, in the pores of the porous carbon material, and on the surface of the coating layer; and a lithium-sulfur battery including the sulfur-carbon composite.

Description

[Technical Field]

[0001] The present invention relates to a crosslinked polythiophene compound capable of capturing polysulfides leached from a positive electrode to improve the life of the battery, and a battery containing the compound.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0118937, filed on September 20, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] As technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium secondary batteries have become common and are widely used due to their high energy density, working potential, long cycle life, and low self-discharge rate.

[0004] In addition, in recent years, with growing interest in environmental issues, active research has been conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles that use fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. Lithium secondary batteries, which have high energy density, high discharge voltage, and output stability, have been mainly researched and used as power sources for such electric vehicles and hybrid electric vehicles.

[0005] A lithium secondary battery has a structure in which a porous separator is interposed between an electrode assembly including a positive electrode and a negative electrode, each of which has an active material coated on a current collector, and a non-aqueous electrolyte containing a lithium salt is impregnated in the electrode assembly.

[0006] Currently, the lithium secondary battery market is dominated by technology based on the pairing of a lithium cobalt oxide (LiCoO2) cathode and a graphite anode. While most other types of batteries (Ni-CD, Ni-MH, etc.) have a rated voltage of 1.5V, lithium secondary batteries have a rated voltage of approximately 3.6V. Their volumetric and mass energy densities are approximately 300-500Wh / l and 160-200Wh / kg, respectively, which are among the highest levels of any commercially available battery. Lithium secondary batteries also have low self-discharge and long lifespans (500 or 1,000 cycles). Despite these impressive performances, all lithium-ion batteries have reached a plateau in performance, with limited prospects for improvement.

[0007] Therefore, lithium-sulfur (Li-S) batteries are gaining attention as an alternative to lithium-ion batteries.

[0008] Like conventional lithium-ion secondary batteries, lithium-sulfur batteries operate by lithium ions moving within an electrolyte between a positive electrode and a negative electrode. However, because lithium-sulfur batteries use only simple sulfur, they operate based on a redox reaction between sulfur and lithium ions, unlike conventional lithium-ion secondary batteries, in which lithium ions enter the gaps between the molecules of the electrode active material, transforming the electrode structure to store energy. Therefore, lithium-sulfur batteries are not limited in electrode structure compared to conventional lithium-ion secondary batteries, and theoretically can have a larger capacity for the same volume. Due to these characteristics, in a lithium-sulfur battery consisting of a sulfur cathode and a lithium metal anode, assuming that the ring-structured monomeric sulfur (S8) reacts completely to form lithium polysulfide (Li2S), the theoretical capacity is 1,675mAh / g and the theoretical energy density is 2,600Wh / kg, which is three to six times higher than other conventional battery systems (Ni / MH battery: 450Wh / kg, Li / FeS: 480Wh / kg, Li / MnO2: 1,000Wh / kg, Na / S: 800Wh / kg).

[0009] On the other hand, conventional transition metal oxide-based lithium-ion secondary batteries are considered to contain heavy metal pollutants because their cathodes use oxides of nickel (Ni), cobalt (Co), and manganese (Mn), which have densities higher than those of heavy metals (metals of 5 g / mL or more). However, lithium-sulfur batteries are environmentally friendly because they eliminate these pollutants and use non-toxic materials. Furthermore, sulfur, the cathode material, has the advantage of being abundant and inexpensive.

[0010] Meanwhile, in lithium-sulfur batteries, sulfur reduction and lithium metal oxidation occur during discharge. During this process, sulfur converts from a ring-shaped S8 to a linear lithium polysulfide (LiPS). These batteries exhibit a gradual discharge voltage until the lithium polysulfide is completely reduced to Li2S. However, during the charge / discharge process, lithium-sulfur batteries experience reduced charge / discharge efficiency, resulting in a shortened battery life. This shortened life of lithium-sulfur batteries can be attributed to a variety of factors, including electrolyte side reactions, lithium metal instability, and the accumulation of by-products on the cathode (e.g., lithium polysulfide leaching from the cathode).

[0011] Lithium-sulfur batteries, which use sulfur-based compounds as the positive electrode active material and alkali metals such as lithium as the negative electrode active material, suffer from the problem of lithium polysulfide leaching during charging and discharging. The lithium polysulfide leached from the positive electrode is transferred to the negative electrode, reducing the capacity of the lithium-sulfur battery and shortening its lifespan. Because lithium polysulfide leached from the positive electrode has high solubility in the electrolyte, it passes through the separator membrane in the electrolyte and unintentionally migrates to the negative electrode, resulting in a decrease in capacity due to irreversible loss of the positive electrode active material and a decrease in battery life due to the deposition of sulfur particles on the lithium metal surface due to side reactions.

[0012] To solve the problem of reduced battery life due to lithium polysulfides, the industry has been conducting research into adding reaction-reducing substances to the negative electrode to prevent side reactions on the surface of lithium metal, but no meaningful results have been achieved. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide a crosslinked polythiophene compound capable of capturing lithium polysulfides leached from a positive electrode to improve the life of a lithium-sulfur battery.

[0014] Another problem to be solved by the present invention is to provide a sulfur-carbon composite that can capture lithium polysulfides leached from a positive electrode and improve the life of a lithium-sulfur battery.

[0015] Another problem to be solved by another aspect of the present invention is to provide a lithium-sulfur battery including the sulfur-carbon composite.

[0016] Another object of the present invention is to provide a method for producing the sulfur-carbon composite. [Means for solving the problem]

[0017] To achieve the objects of the present invention, there are provided a crosslinked polythiophene compound, a sulfur-carbon composite, a lithium-sulfur battery, and a method for manufacturing the sulfur-carbon composite according to the following embodiments.

[0018] According to the first embodiment, A crosslinked polythiophene compound is provided that has a crosslinked structure and includes a cationic functional group.

[0019] According to the second embodiment, in the first embodiment, The cationic functional group may include a nitrogen cation, an oxygen cation, a sulfur cation, or two or more thereof.

[0020] According to the third embodiment, in the second embodiment, The cationic functional group can be a quaternary ammonium functional group.

[0021] According to the fourth embodiment, in the third embodiment, The quaternary ammonium functional group may comprise a dialkylamine group.

[0022] According to the fifth embodiment, in the first embodiment, The cationic functional group may further include a halogen anion as a counterion to the cation included in the cationic functional group.

[0023] According to the sixth embodiment, in the first embodiment, The crosslinked polythiophene compound may be represented by the following Chemical Formula 1. [ka] In Chemical Formula 1, R 1 , R 3 , R 5 , R 7 and R 9 are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R 2 and R 6 are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a -COO- group, and R 4 and R 8 is a divalent cationic linker group, A is F, Cl, Br, or I, and n and m are each independently 1 to 1,000,000.

[0024] According to the seventh embodiment, in the sixth embodiment, The divalent cationic linker group is —NR 10 R 11 and R 10 and R11 may each independently be hydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0025] According to the eighth embodiment, in the sixth embodiment, The crosslinked polythiophene compound can be represented by the following Chemical Formula 2. [ka] In Chemical Formula 2, n and m are each independently an integer of 1 to 1,000,000.

[0026] According to the ninth embodiment, a porous carbon material; a coating layer located on at least one surface of the porous carbon material, the coating layer including the crosslinked polythiophene compound according to any one of the first to eighth embodiments; a sulfur compound located on at least a portion of the surface of the porous carbon material, in the pores of the porous carbon material, and on the surface of the coating layer.

[0027] According to the tenth embodiment, in the ninth embodiment, The weight ratio of the porous carbon material to the crosslinked polythiophene compound may be 99:1 to 85:15.

[0028] According to the eleventh embodiment, in the ninth embodiment, The weight ratio of the porous carbon material coated with the coating layer to the sulfur compound may be 3:7 to 4:6.

[0029] According to the twelfth embodiment, The battery includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, The positive electrode may include the sulfur-carbon composite according to any one of the ninth to eleventh embodiments.

[0030] According to a thirteenth embodiment, the method for producing the sulfur-carbon composite according to any one of the ninth to eleventh embodiments includes: Injecting a polythiophene compound into a solution in which a porous carbon material is dispersed to coat at least one surface of the porous carbon material with the polythiophene compound; crosslinking the polythiophene compound coated on the porous carbon material to form a crosslinked polythiophene compound; and supporting a sulfur compound on the porous carbon material coated with the crosslinked polythiophene compound.

[0031] According to the fourteenth embodiment, in the thirteenth embodiment, The crosslinked polythiophene compound may be formed by injecting a crosslinking agent into the porous carbon material coated with the polythiophene compound, followed by heat treatment.

[0032] According to the fifteenth embodiment, in the fourteenth embodiment, The cross-linking agent may include a dihalogenated alkane compound.

[0033] According to the sixteenth embodiment, in the thirteenth embodiment, The polythiophene compound can be represented by the following Chemical Formula 3. [ka] In Chemical Formula 3, R 1 and R 3 are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R 2 is a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a -COO- group, and R 12 Ha-NR 10 R 11 and R 10 and R 11are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and n is 1 to 1,000,000.

[0034] According to the seventeenth embodiment, in the sixteenth embodiment, The method for producing the polythiophene compound includes the steps of: preparing a thiophene monomer having a thiophene group and a cationic functional group; injecting the thiophene monomer into the solution in which the porous carbon material is dispersed; and polymerizing the thiophene monomer.

[0035] According to the eighteenth embodiment, in the seventeenth embodiment, The thiophene monomer may be polymerized in situ on the surface of the porous carbon material.

[0036] According to the 19th embodiment, in the 17th embodiment, The step of preparing the thiophene monomer comprises: providing a thiophene compound having an anionic functional group; reacting the thiophene compound with a chloride; and reacting the thiophene compound reacted with the chloride with the alcohol compound having a cationic functional group to prepare the thiophene monomer.

[0037] According to a twentieth embodiment, the method for producing a sulfur-carbon composite according to any one of the ninth to eleventh embodiments includes: crosslinking the polythiophene compound to form a crosslinked polythiophene compound; supporting a sulfur compound on a porous carbon material; and coating the crosslinked polythiophene compound on at least one surface of the porous carbon material on which the sulfur compound is supported. [Effects of the Invention]

[0038] A sulfur-carbon composite according to one embodiment of the present invention includes a crosslinked polythiophene compound having a cationic functional group. By coating the sulfur-carbon composite with the crosslinked polythiophene compound having a cationic functional group, the cationic functional group inhibits the leaching of lithium polysulfide from the positive electrode of a lithium-sulfur battery. Furthermore, the crosslinked structure of the crosslinked polythiophene compound reduces the volumetric expansion of the positive electrode during battery charge and discharge. Therefore, the deposition of sulfur particles on the surface of the lithium metal anode is prevented, thereby maintaining the charge and discharge capacity of the lithium-sulfur battery and improving its lifespan.

[0039] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, and the present invention should not be interpreted as being limited only to the matters described in the drawings. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a diagram illustrating a method for producing a sulfur-carbon composite according to Example 1. [Figure 2] FIG. 1 is a diagram illustrating a method for producing a sulfur-carbon composite according to Example 1. [Figure 3] 1 is a graph showing the results of TGA analysis of the sulfur-carbon composite of Example 1. [Figure 4] 1 is a graph showing XRD analysis results for the sulfur-carbon composites of Example 1 and Comparative Example 1. [Figure 5] 1 is a graph showing the results of FT-IR analysis of the sulfur-carbon composites of Example 1 and Comparative Example 1. [Figure 6] 1 is a graph showing TEM analysis results for the sulfur-carbon composites of Example 1 and Comparative Example 1. [Figure 7] 1 is a graph showing SEM analysis results of the sulfur-carbon composites of Example 1 and Comparative Example 1. [Figure 8] 1 is a graph showing the results of evaluating the discharge capacity of lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. [Figure 9] 1 is a graph showing the results of evaluating the discharge capacity of lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. [Figure 10] 1 is a graph showing the results of evaluating the discharge capacity of lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. [Figure 11] 1 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Comparative Example 1 and Examples 2 to 4, which were charged and discharged at 25° C. [Figure 12] 1 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Example 5 and Comparative Example 1, which were charged and discharged at 25° C. [Figure 13] 1 is a Nyquist plot showing the resistance before and after cell testing for lithium-sulfur batteries according to Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be described in more detail below.

[0042] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary and dictionary meanings, but should be interpreted in a way that corresponds to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to explain the invention in the best way.

[0043] Throughout this specification, when a part is described as "comprising" or "having" a certain component, it does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0044] The present invention relates to a crosslinked polythiophene compound, a sulfur-carbon composite containing the crosslinked polythiophene compound, a lithium-sulfur battery containing the sulfur-carbon composite, a method for producing the sulfur-carbon composite, an electrochemical battery containing the same, and a method for producing the same.

[0045] In the present invention, the electrochemical battery may include any battery that performs an electrochemical reaction. Specific examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, and capacitors such as supercapacitors. In particular, the electrochemical battery may be a secondary battery, and the secondary battery may be a lithium-ion secondary battery. Examples of the lithium-ion secondary battery include a lithium-metal battery, a lithium-sulfur battery, an all-solid-state battery, and a lithium polymer battery. Of these, a lithium-sulfur battery is preferred.

[0046] Lithium-sulfur batteries have attracted attention as next-generation secondary batteries due to their high discharge capacity and theoretical energy density, as well as the advantages of reducing battery manufacturing costs and being environmentally friendly, as sulfur, which is used as a cathode active material, is abundant and inexpensive.

[0047] In the present invention, the positive electrode active material includes a carbon-sulfur composite, and the carbon-sulfur composite includes a porous carbon material. In lithium-sulfur batteries, sulfur, which is a positive electrode active material, is a non-conductor, so to compensate for its low electrical conductivity, a sulfur-carbon composite is generally used, which is composited with a conductive carbon material.

[0048] According to one aspect of the present invention, A crosslinked polythiophene compound is provided that has a crosslinked structure and includes a cationic functional group.

[0049] According to one embodiment of the present invention, the cationic functional group may include various cationic functional groups that impart conductivity to the crosslinked polythiophene compound. In one embodiment, the cationic functional group may include a nitrogen cation, an oxygen cation, a sulfur cation, or two or more thereof. For example, the cationic functional group may include a nitrogen cation. Specifically, the cationic functional group may be a quaternary ammonium functional group, and the crosslinked polythiophene compound may include a dialkylamine group having the quaternary ammonium functional group. In particular, when the cationic functional group is a quaternary ammonium functional group, lithium polysulfide adsorption is easier than with functional groups such as ethylene glycol, which support lithium migration.

[0050] Furthermore, according to one embodiment of the present invention, the crosslinked polythiophene compound can have improved rigidity due to its crosslinked structure. Generally, when a battery is charged and discharged, excessive volume expansion and swelling occur. However, the compound according to one embodiment of the present invention has high rigidity, making it possible to obtain a material that is resistant to volume expansion and swelling.

[0051] According to one embodiment of the present invention, the crosslinked polythiophene compound may further include a counterion to the cation contained in the cationic functional group, for example, the counterion may be a halogen anion (e.g., F - , Cl - , Br - , I - In one embodiment of the present invention, the counter ion may be derived from a crosslinking agent for crosslinking the crosslinked polythiophene compound.

[0052] According to one embodiment of the present invention, the crosslinked polythiophene compound may be represented by the following Formula 4: [ka] In Chemical Formula 4, R 1 , R 3 , R 5 , R 7 and R 9are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R 2 and R 6 are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a -COO- group, and R 4 and R 8 is a divalent cationic linker group, A is a halogen element (F, Cl, Br, I, etc.), and n and m can each independently be 1 to 1,000,000.

[0053] According to one embodiment of the present invention, the divalent cationic linker group is -NR 10 R 11 and R 10 and R 11 may each independently be hydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0054] According to one embodiment of the present invention, R 1 , R 3 , R 5 , R 7 and R 9 By adjusting the bond length, the polarity of the crosslinked polythiophene compound can be adjusted, thereby adjusting the crystallinity and thermal properties of the crosslinked polythiophene compound.

[0055] According to one embodiment of the present invention, the crosslinked polythiophene compound may be represented by the following Chemical Formula 5: [ka] In Chemical Formula 5, n and m can each independently be 1 to 1,000,000.

[0056] According to another aspect of the present invention, a porous carbon material; a coating layer located on at least one surface of the porous carbon material, the coating layer including the crosslinked polythiophene compound; a sulfur compound located on at least a portion of the surface of the porous carbon material, in the pores of the porous carbon material, and on the surface of the coating layer.

[0057] According to one embodiment of the present invention, the weight ratio of the porous carbon material to the crosslinked polythiophene compound may be 99:1 to 85:15 or 99:1 to 90:10.

[0058] The porous carbon material includes a plate-shaped carbon material, and the specific surface area of ​​the porous carbon material is 1,000 m 2 / g or more, and the pore volume of the porous carbon material is 4 cm 3 / g or more.

[0059] The porous carbon material may have a large specific surface area to increase the number of active sites where sulfur can participate in oxidation / reduction reactions, and may have a large pore volume to facilitate sulfur loading and ensure ion diffusion paths.

[0060] The sulfur-carbon composite includes a porous carbon material as a support for supporting a sulfur-containing compound. Specifically, the sulfur-carbon composite may include a plate-like porous carbon material as the porous carbon material. The plate-like porous carbon material may include, for example, graphene, graphene oxide, reduced graphene oxide (rGO), or a mixture of two or more thereof.

[0061] In an embodiment of the present invention, the plate-shaped porous carbon material may include reduced graphene oxide alone.

[0062] The porous carbon material is 1,000 m 2Specifically, the upper limit of the BET specific surface area of ​​the porous carbon material is not particularly limited, but it may be, for example, 1,000 m 2 / g or more 1,500m 2 / g or less, 1,300m 2 / g or less, 1,200m 2 / g or less, 1,100m 2 / g or less, 1,050m 2 The sulfur-carbon composite according to one embodiment of the present invention has a large number of micropores on the outer surface and / or inside thereof, and thus has an advantage of a very large specific surface area.

[0063] The BET specific surface area is measured by the BET method and may be a value measured by a known method for measuring a BET specific surface area. For example, the BET specific surface area may be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-max manufactured by BEL Japan Co., Ltd.

[0064] The porous carbon material is 4 cm 3 Specifically, the upper limit of the pore volume of the porous carbon material is not particularly limited, but it may be, for example, 4 cm 3 / g or more 15cm 3 / g or less, 6cm 3 / g or more 10cm 3 / g or less, 6cm 3 / g or more 8cm 3 / g or less, or 6.5cm 3 / g or more 7.5cm 3 The pore volume may be a value calculated and measured through, for example, N adsorption isotherm analysis obtained based on the adsorption of liquid nitrogen.

[0065] As described above, the porous carbon material in the sulfur-carbon composite according to one embodiment of the present invention may contain a large number of micropores for supporting the sulfur-containing compound.

[0066] In one embodiment of the present invention, the porous carbon material may include a plurality of micropores on the outer surface and inside thereof, and the micropores may include mesopores having a diameter of 1 nm or more and less than 50 nm, and macropores having a diameter of 50 nm or more and 200 nm or less. In one embodiment of the present invention, the mesopores and macropores may be uniformly distributed in the porous carbon material.

[0067] The diameter of the micropores can be measured by any known method in the art for measuring the diameter of pores in porous materials, and the measurement method is not particularly limited. For example, the average diameter of the micropores can be measured using a scanning electron microscope (SEM), a field emission electron microscope, or a laser diffraction method. Measurement using the laser diffraction method can be performed using, for example, a commercially available laser diffraction particle sizer (e.g., Microtrac MT3000).

[0068] In another embodiment of the present invention, the average diameter (D50) of all pores of the porous carbon material may be, but is not limited to, 20 nm to 25 nm, and the average diameter (D50) refers to the diameter at the 50% point of the cumulative number distribution according to the diameter.

[0069] In the present invention, the porous carbon material having the above-mentioned properties contains a sulfur compound on the outer surface and at least part of the interior of the pores.

[0070] The sulfur compound may be used without limitation as long as it can be used as a positive electrode active material in a lithium-sulfur secondary battery. For example, the sulfur compound may be inorganic sulfur (S), lithium polysulfide (LiS), or the like. n , 1≦n≦8), carbon-sulfur polymer (C2S x ) m , 2.5≦x≦50, 2≦m), or mixtures thereof.

[0071] The sulfur compound may be contained in the sulfur-carbon composite by physical adsorption onto the porous carbon material or by chemical bonding, such as covalent bonding or van der Waals bonding, between the sulfur element and carbon in the porous carbon material.

[0072] In one embodiment of the present invention, the porous carbon material and the sulfur compound in the sulfur-carbon composite may be present in a weight ratio of, for example, 1:9 to 9:1, specifically, 1:9 to 5:5, 1:9 to 4:6, 1:9 to 3:7, or 1:9 to 1.5:8.5. When the weight ratio of the porous carbon material to the sulfur compound in the sulfur-carbon composite is within the above range, the high content of the sulfur compound enhances the dynamic activity of the sulfur-carbon composite, while also improving the electrical conductivity of the porous carbon material. However, the present invention is not limited thereto.

[0073] In another embodiment of the present invention, the content of the sulfur compound in the sulfur-carbon composite may be, for example, 10 wt% or more, specifically 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 85 wt% or more, based on the total weight of the sulfur-carbon composite. Furthermore, within the above-mentioned range, the content may be 50 wt% to 90 wt%, specifically 60 wt% to 90 wt%, 70 wt% to 90 wt%, or 85 wt% to 90 wt% based on the total weight of the sulfur-carbon composite. When the content of the sulfur compound in the sulfur-carbon composite is within the above-mentioned range, the high content of the sulfur compound is advantageous in terms of enhancing the dynamic activity of the sulfur-carbon composite and improving the electrical conductivity of the porous carbon material, but the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the average particle size (D50) of the sulfur-carbon composite may be, for example, 0.5 μm to 200 μm, 0.5 μm to 200 μm, 1 μm to 150 μm, or 10 μm to 150 μm. The particle size of the sulfur-carbon composite may be measured using a scanning electron microscope (SEM), a field emission electron microscope, or a laser diffraction method. The measurement using the laser diffraction method may be performed using, for example, a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000). The average particle size (D50) refers to the particle size at the 50% point of the cumulative number distribution according to particle size.

[0075] In one embodiment of the present invention, the sulfur-carbon composite has a Raman peak intensity ratio (I G / I D The ratio of I to I may be 1 or less. G / I D If the ratio is 1 or less, it is possible to prevent the problem of the efficiency of the composite with the sulfur-containing compound or the lithium polysulfide conversion reaction decreasing due to excessively high crystallinity of the surface of the sulfur-carbon composite.

[0076] The Raman peak intensity ratio is calculated from the spectrum of the carbon composite obtained by Raman spectroscopy. G and I D In the resulting spectrum, I G means the peak of the crystalline part (G-peak, 1573 / cm), and I D means the peak of the amorphous part (D-peak, 1309 / cm). Therefore, in this case, I G / I D The smaller the ratio, the lower the crystallinity.

[0077] In one embodiment of the present invention, the sulfur-carbon composite may be formed by mixing the porous carbon material and a sulfur compound and then heat-treating the mixture; however, the manufacturing method of the present invention is not limited thereto.

[0078] The sulfur-carbon composite of the present invention includes a plate-like carbon material having a large specific surface area and pore volume, which not only increases the sulfur loading but also provides a large number of active sites for the sulfur oxidation / reduction reaction. Therefore, when used in the positive electrode of a lithium-sulfur battery, the battery efficiency and energy density can be improved. However, the mechanism of the present invention is not limited to this.

[0079] In one embodiment of the present invention, the coating layer contains the crosslinked polythiophene compound. For example, the weight ratio of the porous carbon material to the crosslinked polythiophene compound may be 99:1 to 85:15 or 99:1 to 90:10. The weight ratio of the porous carbon material coated with the coating layer to the sulfur compound may be 3:7 to 4:6.

[0080] According to yet another aspect of the present invention, Injecting a polythiophene compound into a solution in which a porous carbon material is dispersed to coat at least one surface of the porous carbon material with the polythiophene compound; crosslinking the polythiophene compound coated on the porous carbon material to form a crosslinked polythiophene compound; and supporting a sulfur compound on the porous carbon material coated with the crosslinked polythiophene compound.

[0081] According to yet another aspect of the present invention, crosslinking the polythiophene compound to form a crosslinked polythiophene compound; supporting a sulfur compound on a porous carbon material; and coating the crosslinked polythiophene compound on at least one surface of the porous carbon material on which the sulfur compound is supported.

[0082] The sulfur-carbon composite according to one embodiment of the present invention can be prepared by the two methods described above. For example, in the former method, the polythiophene compound can be in situ polymerized in the porous carbon material to form the cross-linked polythiophene compound, and the sulfur compound can be supported on the porous carbon material coated with the cross-linked polythiophene compound.

[0083] Alternatively, as in the latter manufacturing method, the polythiophene compound may be ex-situ polymerized to form the crosslinked polythiophene compound, and the crosslinked polythiophene compound may be coated on the porous carbon material carrying the sulfur compound.

[0084] According to an embodiment of the present invention, the crosslinked polythiophene compound may be formed by injecting a crosslinking agent into the porous carbon material coated with the polythiophene compound, followed by heat treatment.

[0085] According to one embodiment of the present invention, the polythiophene compound may be represented by the following Chemical Formula 6: [ka] In Chemical Formula 6, R 1 and R 3 are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R 2 is a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a -COO- group, and R 12 Ha-NR 10 R 11 and R 10 and R 11 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and n can be 1 to 1,000,000.

[0086] According to one embodiment of the present invention, the method for preparing the polythiophene compound includes the steps of: preparing a thiophene monomer having a thiophene group and a cationic functional group; injecting the thiophene monomer into the solution in which the porous carbon material is dispersed; and polymerizing the thiophene monomer.

[0087] The step of preparing the thiophene monomer comprises: providing a thiophene compound having an anionic functional group; reacting the thiophene compound with a chloride; and reacting the thiophene compound reacted with the chloride with the alcohol compound having a cationic functional group to prepare the thiophene monomer.

[0088] According to one embodiment of the present invention, the thiophene compound may be represented by the following Chemical Formula 7: [ka] In Chemical Formula 7, R 1 can be an anionic functional group, for example, the anionic functional group can include —COOH, —SO 3 H, —PhOH, —ArSO 3 H, or two or more thereof.

[0089] According to one embodiment of the present invention, the chloride may be a variety of chlorides including -Cl, and the R 1 is —COOH and the chloride is SOCl 2 , the thiophene compound reacted with the chloride may include the following formula 8: [ka] According to one embodiment of the present invention, the thiophene compound (e.g., the compound represented by Formula 8) reacted with the chloride may be reacted with the alcohol compound having the cationic functional group to prepare the thiophene monomer.

[0090] For example, the alcohol compound is 2-dimethylaminoethanol, and the thiophene monomer can be represented by the following Chemical Formula 9. [ka] The crosslinked polythiophene compound having the cationic functional group is coated on the porous carbon material, and the cationic functional group prevents lithium polysulfide leached from the positive electrode of the lithium-sulfur battery from being transferred to the negative electrode. This prevents sulfur particles from accumulating on the surface of the lithium metal in the negative electrode, thereby maintaining the charge / discharge capacity of the lithium-sulfur battery and improving its lifespan.

[0091] A method for producing a sulfur-carbon composite according to one embodiment of the present invention is as follows.

[0092] First, as described above, a thiophene compound having an anionic functional group (e.g., —COOH) is prepared, and the thiophene compound is reacted with a chloride (e.g., SOCl2) in a solvent at high temperature (e.g., 80°C to 100°C).

[0093] Here, the solvent is not particularly limited as long as it is a solvent capable of dissolving or dispersing the compound, and examples thereof include chlorine-based solvents such as chloroform, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, and o-dichlorobenzene; ether-based solvents such as tetrahydrofuran and dioxane; aromatic hydrocarbon-based solvents such as toluene, xylene, trimethylbenzene, and mesitylene; aliphatic hydrocarbon-based solvents such as cyclohexane, methylcyclohexane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane; ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone; ester-based solvents such as ethyl acetate, butyl acetate, and ethyl cellosolve; The solvent may be a polyhydric alcohol or a derivative thereof such as ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, dimethoxyethane, propylene glycol, diethoxymethane, triethylene glycol monoethyl ether, glycerin, or 1,2-hexanediol; an alcohol-based solvent such as methanol, ethanol, propanol, isopropanol, or cyclohexanol; a sulfoxide-based solvent such as dimethyl sulfoxide; an amide-based solvent such as N-methyl-2-pyrrolidone or N,N-dimethylformamide; a benzoate-based solvent such as butyl benzoate or methyl-2-methoxybenzoate; tetralin; or a solvent such as 3-phenoxytoluene.

[0094] The thiophene compound reacted with the chloride may be reacted with a solvent, such as 2-dimethylaminoethanol and triethyleneamine (TEA), to produce the thiophene monomer. The thiophene monomer may then be dissolved in a solvent and injected into a solution in which a porous carbon material (e.g., Ketjen Black (KB)) is dispersed together with a chloride (e.g., FeCl3), whereby the thiophene monomer is polymerized in situ on the surface of the porous carbon material to form the polythiophene compound.

[0095] The crosslinked polythiophene compound can be formed by injecting a crosslinker into a solution in which the porous carbon material coated with the polythiophene compound is dispersed, followed by heat treatment. For example, the crosslinker can be a dihalogenated alkane compound (e.g., 1,4-dibromobutane, 1,4-dichlorobutane, diiodobutane, dichlorobutane, and mixtures thereof), such as diiodobutane, as shown in FIG. 1.

[0096] The present invention will be described in detail below with reference to examples to aid in understanding the present invention. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0097] Example 1 Fabrication of sulfur-carbon composites and cathodes A thiophene compound having -COOH as an anionic functional group was prepared and reacted with a chloride, SOCl2, in a solvent at 90°C. Benzene was used as the solvent.

[0098] The thiophene compound reacted with the chloride was dissolved in methylene chloride, and then 2-dimethylaminoethanol and triethyleneamine (TEA) were added to prepare the thiophene monomer. The thiophene monomer was dissolved in chloroform, and then added to a chloroform solution containing Ketjen Black (KB) as a porous carbon material and FeCl3 as a chloride, and then ultrasonically treated for 3 hours. The thiophene monomer was polymerized in situ on the surface of the Ketjen Black to form the polythiophene compound (see Figure 1).

[0099] Diiodobutane was added as a cross-linking agent to the solution in which the polythiophene compound-coated porous carbon material was dispersed, and the cross-linking agent activated the dialkylamine groups, which were cationic functional groups of the polythiophene compound, cross-linking the polythiophene compound to form the cross-linked polythiophene compound.

[0100] The sulfur-carbon composite (CPTqD10-KB-S) prepared by loading a sulfur compound onto the crosslinked polythiophene compound-coated ketjen black (CPTqD10-KB) was used as the cathode active material. The weight ratio of the ketjen black to the crosslinked polythiophene compound was 90:10. The sulfur-carbon composite, polyacrylic acid (PAA, weight-average molecular weight 450,000) as a binder, and Super P as a carbon conductive material were mixed in a weight ratio of 85:10:5, and 0.5 wt% polyvinyl alcohol (PVA, weight-average molecular weight 9,500) was added as a dispersant. A cathode slurry was then prepared with a solid concentration of 18 wt%. The cathode slurry was uniformly coated on aluminum foil to a thickness of 400 μm and dried at 50°C to fabricate a cathode (see Figure 2).

[0101] Lithium-sulfur battery manufacturing A polyethylene porous film (Celgard separator) was used as the separator, lithium metal was used as the anode, and 1.0M LiNO3 was added to a mixed solvent of 1,3-dioxolane (DOL) and 1,2-dimethyl ether in a volume ratio (v / v) of 50:50 to prepare an electrolyte for a lithium-sulfur secondary battery.

[0102] A separator was interposed between the cathode and anode prepared as above to prepare an electrode assembly, which was then housed in a coin cell case and injected with the prepared electrolyte to prepare a coin cell-type lithium-sulfur battery.

[0103] <Example 2> Fabrication of sulfur-carbon composites and cathodes The sulfur compound was first supported on the Ketjen black, and then the crosslinked polythiophene compound was coated on the sulfur compound-supported Ketjen black. That is, the polythiophene compound was polymerized ex-situ to prepare the crosslinked polythiophene compound, which was then coated. The weight ratio of the Ketjen black to the crosslinked polythiophene compound was 99:1.

[0104] Lithium-sulfur battery manufacturing A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured in Example 2 was used.

[0105] Example 3 Fabrication of sulfur-carbon composites and cathodes A sulfur-carbon composite and a positive electrode were produced in the same manner as in Example 2, except that the weight ratio of the Ketjen black to the crosslinked polythiophene compound was 93:7.

[0106] Lithium-sulfur battery manufacturing A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured in Example 3 was used.

[0107] Example 4 Fabrication of sulfur-carbon composites and cathodes A sulfur-carbon composite and a positive electrode were produced in the same manner as in Example 2, except that the weight ratio of the Ketjen black to the crosslinked polythiophene compound was 95:5.

[0108] Lithium-sulfur battery manufacturing A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured in Example 4 was used.

[0109] <Example 5> Fabrication of sulfur-carbon composites and cathodes A sulfur-carbon composite and a positive electrode were produced in the same manner as in Example 1, except that the weight ratio of the ketjen black to the crosslinked polythiophene compound was 95:5.

[0110] Lithium-sulfur battery manufacturing A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured in Example 5 was used.

[0111] <Comparative Example 1> Fabrication of sulfur-carbon composites and cathodes A sulfur-carbon composite and a positive electrode were prepared in the same manner as in Example 1, except that a sulfur-carbon composite prepared by mixing Ketjen black and a sulfur compound in a weight ratio of 3:7 was used as the positive electrode active material.

[0112] Lithium-sulfur battery manufacturing A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured in Comparative Example 1 was used.

[0113] <Analysis results> TGA analysis results Figure 3 shows the TGA analysis results for the sulfur-carbon composite of Example 1. As a result of the TGA analysis, the content of the supported sulfur compound in the sulfur-carbon composite composed of Ketjen black coated with a crosslinked polythiophene compound and a sulfur compound was measured to be 61 wt%.

[0114] XRD analysis results 4 shows the results of XRD analysis of the sulfur-carbon composites of Example 1 and Comparative Example 1. As a result of the XRD analysis, a peak of the crosslinked polythiophene compound of Example 1 was observed at 2θ=25±5.

[0115] FT-IR analysis results Figure 5 shows the FT-IR analysis results for the sulfur-carbon composites of Example 1 and Comparative Example 1. As a result of the FT-IR analysis, characteristic peaks of the crosslinked polythiophene compound of Example 1 and the quaternary ammonium functional group contained therein were confirmed.

[0116] TEM analysis results 6 shows the TEM analysis results for the sulfur-carbon composites of Example 1 and Comparative Example 1. The TEM analysis results confirmed that the Ketjen black of Example 1 was coated with a crosslinked polythiophene compound.

[0117] SEM analysis results (surface observation) Figure 7 shows the SEM analysis results for the sulfur-carbon composites of Example 1 and Comparative Example 1. The SEM analysis results confirmed that the Ketjenblack of Example 1 was coated with a crosslinked polythiophene compound.

[0118] Charge / discharge evaluation FIG. 8 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. under the following conditions:

[0119] Evaluation equipment: WBSC3000 battery cycler (manufactured by WonA Tech) Current density: 0.2C rate Referring to FIG. 8, the lithium-sulfur battery according to Example 1 exhibited a higher discharge capacity than the lithium-sulfur battery according to Comparative Example 1 during the 1st to 120th cycles.

[0120] FIG. 9 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. under the following conditions:

[0121] Evaluation equipment: WBSC3000 battery cycler (manufactured by WonA Tech) Current density: 0.5C rate Referring to FIG. 9, the lithium-sulfur battery according to Example 1 exhibited a higher discharge capacity than the lithium-sulfur battery according to Comparative Example 1 during the 1st to 200th cycles.

[0122] FIG. 10 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Example 1 and Comparative Example 1, which were charged and discharged at 25° C. under the following conditions:

[0123] Evaluation equipment: WBSC3000 battery cycler (manufactured by WonA Tech) Current density: 1C rate Referring to FIG. 10, the lithium-sulfur battery according to Example 1 exhibited a higher discharge capacity than the lithium-sulfur battery according to Comparative Example 1 between 40 and 160 cycles.

[0124] FIG. 11 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Comparative Example 1 and Examples 2 to 4, which were charged and discharged at 25° C. under the following conditions:

[0125] Evaluation equipment: WBSC3000 battery cycler (manufactured by WonA Tech) Current density: 0.2C rate Referring to FIG. 11, the lithium-sulfur batteries according to Examples 2 to 4 exhibited higher discharge capacities than the lithium-sulfur battery according to Comparative Example 1 during the 1st to 70th cycles.

[0126] FIG. 12 is a graph showing the results of evaluating the discharge capacity of the lithium-sulfur batteries according to Example 5 and Comparative Example 1, which were charged and discharged at 25° C. under the following conditions:

[0127] Evaluation equipment: WBSC3000 battery cycler (manufactured by WonA Tech) Current density: 0.2C rate Referring to FIG. 12, the lithium-sulfur battery according to Example 5 exhibited a higher discharge capacity than the lithium-sulfur battery according to Comparative Example 1 during the 1st to 120th cycles.

[0128] 13 is a Nyquist plot showing the resistance before and after a 200-cycle cell test at a 0.5 C rate for the lithium-sulfur batteries of Example 1 and Comparative Example 1. Referring to FIG. 13, it was confirmed that the lithium-sulfur battery of Example 1 had improved resistance values ​​compared to the lithium-sulfur battery of Comparative Example 1 before and after the cell test.

Claims

1. A crosslinked polythiophene compound having a crosslinked structure and containing a cationic functional group.

2. 2. The crosslinked polythiophene compound of claim 1, wherein the cationic functional group comprises a nitrogen cation, an oxygen cation, a sulfur cation, or two or more thereof.

3. 3. The crosslinked polythiophene compound of claim 2, wherein the cationic functional group is a quaternary ammonium functional group.

4. 4. The crosslinked polythiophene compound of claim 3 comprising a dialkylamine group with said quaternary ammonium functional group.

5. 2. The crosslinked polythiophene compound according to claim 1, further comprising a halogen anion as a counterion to the cation contained in the cationic functional group.

6. The following chemical formula 1: 【Chemical 1】 is expressed as In Chemical Formula 1, R １ , R ３ , R ５ , R ７ and R ９ are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R ２ and R ６ are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a —COO— group; R ４ and R ８ is a divalent cationic linker group; A is F, Cl, Br, or I; and n and m are each independently 1 to 1,000,000.

7. The divalent cationic linker group is —NR １０ R １１ and R １０ and R １１ and each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

8. The following chemical formula 2: 【Chemistry 2】 is expressed as 7. The crosslinked polythiophene compound according to claim 6, wherein in Chemical Formula 2, n and m each independently represent an integer of 1 to 1,000,000.

9. a porous carbon material; a coating layer located on at least one surface of the porous carbon material, the coating layer comprising the crosslinked polythiophene compound according to any one of claims 1 to 8; a sulfur compound located on at least a portion of the surface of the porous carbon material, in the pores of the porous carbon material, and on the surface of the coating layer.

10. 10. The sulfur-carbon composite according to claim 9, wherein a weight ratio of the porous carbon material to the crosslinked polythiophene compound is 99:1 to 85:

15.

11. 10. The sulfur-carbon composite according to claim 9, wherein a weight ratio of the porous carbon material coated with the coating layer to the sulfur compound is 3:7 to 4:

6.

12. The battery includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, A lithium-sulfur battery, wherein the positive electrode comprises the sulfur-carbon composite of claim 9.

13. The method for producing a sulfur-carbon composite according to claim 9, Injecting a polythiophene compound into a solution in which a porous carbon material is dispersed to coat at least one surface of the porous carbon material with the polythiophene compound; crosslinking the polythiophene compound coated on the porous carbon material to form a crosslinked polythiophene compound; and supporting a sulfur compound on the porous carbon material coated with the crosslinked polythiophene compound.

14. 14. The method for producing a sulfur-carbon composite according to claim 13, wherein the crosslinked polythiophene compound is formed by injecting a crosslinking agent into the porous carbon material coated with the polythiophene compound, followed by heat treatment.

15. 15. The method for producing a sulfur-carbon composite according to claim 14, wherein the cross-linking agent comprises a dihalogenated alkane compound.

16. The polythiophene compound is represented by the following formula 3: 【Chemistry 3】 is expressed as In Chemical Formula 3, R １ and R ３ are each independently a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, or an arylene group having 6 to 20 carbon atoms; R ２ is a linker group, an alkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a —COO— group; R １２ Ha-NR １０ R １１ and R １０ and R １１ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and n is 1 to 1,000,000.

17. The method for producing the polythiophene compound includes the steps of: preparing a thiophene monomer having a thiophene group and a cationic functional group; injecting the thiophene monomer into the solution in which the porous carbon material is dispersed; and polymerizing the thiophene monomer.

18. 18. The method for producing a sulfur-carbon composite according to claim 17, wherein the thiophene monomer is polymerized in situ on the surface of the porous carbon material.

19. The step of preparing the thiophene monomer comprises: providing a thiophene compound having an anionic functional group; reacting the thiophene compound with a chloride; and reacting the thiophene compound reacted with the chloride with the alcohol compound having a cationic functional group to produce the thiophene monomer.

20. The method for producing a sulfur-carbon composite according to claim 9, crosslinking the polythiophene compound to form a crosslinked polythiophene compound; supporting a sulfur compound on a porous carbon material; and coating the crosslinked polythiophene compound on at least one surface of the porous carbon material on which the sulfur compound is supported.

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