Metal carbide-carbon composite having selectively coated bilayer structure, electrode comprising same, lithium-sulfur battery comprising same, and method for manufacturing same

Abstract

A metal carbide-carbon composite according to a preferred embodiment of the present invention comprises: a first carbon layer including a metal carbide coating layer; and a second carbon layer in contact with the first carbon layer and having no metal carbide coating layer, wherein the metal carbide-carbon composite can be used for a positive electrode and a negative electrode as an electrode of a lithium-sulfur battery. In particular, since the metal carbide coating layer (first carbon layer) is located on the side away from a separator of the lithium-sulfur battery, when an electrode including the metal carbide-carbon composite is used as a positive electrode, the elution of lithium polysulfides can be structurally suppressed and the sulfur content can be increased, and when the electrode is used as a negative electrode, there is an effect of suppressing lithium dendrite growth by suppressing electrodeposition caused by limiting the diffusion of lithium ions.

Description

A metal carbide-carbon composite having a double-layer structure with an optional coating, an electrode comprising the same, a lithium-sulfur battery comprising the same, and a method for manufacturing the same

[0001] The present invention relates to a lithium-sulfur battery, and more particularly, to an electrode comprising a metal carbide-carbon composite having a selectively coated double-layer structure, and a lithium-sulfur battery comprising the same.

[0002] This research was supported by the Samsung Future Technology Promotion Project (Project No. SRFC-MA2001-05) and the National Research and Development Program of the Republic of Korea.

[0003] [Project ID] 2710079320

[0004] [Assignment Number] RS202500559443

[0005] [Ministry Name] Ministry of Science and ICT

[0006] [Name of Project Management (Specialist) Institution] National Research Foundation of Korea

[0007] [Research Project Name] Individual Basic Research (Ministry of Science and ICT) (R&D)

[0008] [Research Project Title] Development of an electrochemical catalyst / carbon composite electrode and a polymer all-solid-state lithium-sulfur battery that resolves the adsorption-diffusion tradeoff.

[0009] [Name of Project Performing Organization] Korea University

[0010] [Research Period] March 1, 2025 - February 29, 2028

[0011] Lithium-sulfur batteries (Li-S batteries) theoretically have high energy density (about 2,600 Whkg) and high specific capacity (about 1,675 mAh g). -1) is a next-generation energy storage system. However, lithium polysulfide (LiPS), an intermediate formed during the charge / discharge cycle, has high solubility in the electrolyte and has slow reactivity due to a thermodynamically unfavorable multi-step reaction, which limits the performance of the battery as it cannot express the theoretical maximum capacity. In an effort to overcome these problems, methods have been studied to include metal compound electrocatalysts as active materials that promote the adsorption and electrochemical conversion of lithium polysulfide (LiPS) in carbon-based materials such as carbon nanotubes (CNTs), graphene, and mesoporous carbon. However, active attempts are being made to develop a cathode with a high sulfur loading to develop a battery with a higher energy density.

[0012] Meanwhile, research is being conducted to solve the problem of dendrite formation and cell short-circuiting due to uneven lithium ion mobility density caused by repeated desorption / deposition of lithium ions in the negative electrode for lithium-sulfur batteries.

[0013] The present invention has been conceived to solve the above-described problem, and an electrode for a lithium-sulfur battery comprising a metal carbide-carbon composite according to a preferred example of the present invention can provide a lithium-sulfur battery having a high sulfur loading by preventing the elution of lithium polysulfide into the electrolyte when applied as a positive electrode, and suppressing lithium dendrite growth when applied as a negative electrode.

[0014] In order to achieve the above technical task, a metal carbide-carbon composite having a selectively coated double-layer structure according to a preferred example of the present invention may be characterized in that it includes a first carbon layer including a metal carbide coating layer, and a second carbon layer in contact with the first carbon layer and not including a metal carbide coating layer, wherein the first and second carbon layers are carbon substrates including a plurality of pores.

[0015] The above metal carbide may be a carbide of a transition metal.

[0016] The above transition metal may be at least one selected from the group consisting of molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), vanadium (V), zinc (Zn), cobalt (Co), and copper (Cu).

[0017] The above carbon substrate may include at least one of carbon nanotubes, carbon fibers, graphene fibers, activated carbon, carbon black, and derivatives thereof.

[0018] The first and second carbon layers may each be formed by laminating independent carbon substrates.

[0019] The first and second carbon layers may be a single integrated carbon substrate.

[0020] The above metal carbide coating layer may be a metal carbide coated layer on the surface of all or part of the plurality of pores formed in the first carbon layer.

[0021] EDS (Energy Dispersive Spectroscopy) mapping can confirm that only the first carbon layer among the first and second carbon layers is asymmetrically coated with metal oxide.

[0022] In order to achieve the above technical task, an electrode for a lithium-sulfur battery according to a preferred example of the present invention may include the above-described metal carbide-carbon composite.

[0023] The above electrode further includes sulfur as a positive electrode active material, and can suppress the dissolution of lithium polysulfide by promoting chemical adsorption and conversion of lithium polysulfide.

[0024] In the above positive electrode, the first carbon layer may be located away from the separator of the lithium-sulfur battery.

[0025] The above electrode further includes lithium as an anode active material and is used in the anode, and can minimize dendritic growth by suppressing electrodeposition due to limited diffusion of lithium ions.

[0026] In the above negative electrode, the first carbon layer may be located away from the separator of the lithium-sulfur battery.

[0027] The capacity per unit area of ​​the above electrode is 16.75 to 33.50 mAh / cm 2 It could be.

[0028] In order to achieve the above technical task, a lithium-sulfur battery according to a preferred example of the present invention comprises an electrode including the above-described metal carbide-carbon composite, and a positive electrode in which a reduction reaction of sulfur occurs;

[0029] An anode comprising an electrode including the above-described metal carbide-carbon composite, and arranged to face the anode, in which a lithium oxidation reaction occurs;

[0030] A separator disposed between the positive electrode and the negative electrode to suppress the movement of lithium polysulfide but for the transfer of ions; and

[0031] It may include an electrolyte interposed between the positive and negative electrodes.

[0032] In the above positive and negative electrodes, the first carbon layer can be positioned farther away from the separator.

[0033] The sulfur content per anode area of ​​the lithium-sulfur battery is 5 to 10 mg / cm 2 It could be.

[0034] In order to achieve the above technical task, a method for manufacturing a metal carbide-carbon composite having a selectively coated double-layer structure according to a preferred example of the present invention is provided.

[0035] (a) a step of preparing a carbon substrate including a plurality of pores; and

[0036] (b) a step of adding a precursor solution containing a metal to the carbon substrate and then carbonizing the same to form a metal carbide coating layer;

[0037] (i) In step (b), a metal carbide coating layer may be formed only in a certain thickness region of the carbon substrate, or (ii) by laminating a separate uncoated carbon substrate after step (b), the metal carbide may be asymmetrically coated only in a certain thickness region or in one layer.

[0038] The step (a) above comprises: (a-1) preparing a dispersion in which carbon material powder including at least one of carbon nanotubes, carbon fibers, graphene fibers, activated carbon, carbon black, and derivatives thereof is dispersed in a solvent; and

[0039] (a-2) A step of separating the carbon material from the dispersion and drying it to produce a carbon substrate having a plurality of pores; may be included.

[0040] The step (b) above comprises: (b-1) a step of dropping a precursor solution containing a metal onto the carbon substrate and drying it to evaporate the solvent in the precursor solution; and

[0041] (b-2) A step of carbonizing the metal by heat treatment under an inert gas atmosphere may be included.

[0042] Before the above step (b-1), a pretreatment step of applying plasma to the carbon substrate to generate a functional group may be further included.

[0043] The heat treatment temperature in the above step (b-2) may be 800 to 1,000°C.

[0044] In the above step (b), the metal may be molybdenum and the metal carbide may be molybdenum carbide.

[0045] In the above step (b), the precursor may be ammonium heptamolybdate.

[0046] In the case of the above (ii), the carbon substrate coated with metal carbide and the uncoated carbon substrate may be laminated through a physical pressing process.

[0047] The above physical pressing process may be performed through a rolling press machine.

[0048] According to the present invention as described above, a metal carbide-carbon composite according to a preferred embodiment of the present invention includes a first carbon layer including a metal carbide coating layer, and a second carbon layer in contact with the first carbon layer and not having a metal carbide coating layer, and can be used as a positive electrode and a negative electrode as an electrode of a lithium-sulfur battery. In particular, since the metal carbide coating layer (the first carbon layer) is located far from the separator of the lithium-sulfur battery, when the electrode including the metal carbide-carbon composite is used as a positive electrode, it structurally suppresses the dissolution of lithium polysulfide and increases the sulfur content, and when it is used as a negative electrode, it has the effect of suppressing the growth of lithium dendrites by suppressing electrodeposition due to limited diffusion of lithium ions.

[0049] The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned, although they can be clearly understood by those skilled in the art from the description throughout the specification.

[0050] FIG. 1 is a schematic diagram of an electrode comprising a metal carbide-carbon composite having a selectively coated double-layer structure according to one embodiment of the present invention.

[0051] FIG. 2 shows the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) of the surface of a metal carbide-carbon composite electrode according to Example 1 of the present invention.

[0052] FIG. 3 shows scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) results for a cross-section of a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0053] FIG. 4 is an X-ray diffraction (XRD) result of a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0054] FIG. 5 shows the results of UV-vis spectroscopy of a metal carbide-carbon composite electrode according to one embodiment of the present invention and the change in solution color after electrolyte adsorption of the metal carbide-carbon composite electrode (inset).

[0055] Figure 6 shows the results of cyclic voltammetry of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0056] FIG. 7 is a result of XPS (X-ray photoelectron spectroscopy) analysis for evaluating the cathode discharge amount of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0057] Figure 8 shows the charge / discharge results for a lithium-sulfur battery symmetrical cell using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0058] Figure 9 shows the results of comparing lithium ion affinity and stability of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0059] Figure 10 shows the results of lithium electrodeposition on the negative electrode of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0060] Figure 11 shows the cycle operation results of a lithium-sulfur battery symmetrical cell using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0061] Figure 12 shows the results of analysis of the life characteristics at high active material content of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0062] Figure 13 shows the results of analysis of the life characteristics of a lithium-sulfur battery with a high active material content using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0063] Figure 14 shows the results of analyzing the battery capacity at high sulfur content of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0064] FIG. 15 is a graph showing the energy density according to various sulfur loading amounts and E / S ratios of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0065] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described in detail below together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

[0066] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise.

[0067] The terms "comprises" and / or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations and / or elements.

[0068]

[0069] A metal carbide-carbon composite having a double-layer structure with an optional coating, an electrode comprising the same, and a lithium-sulfur battery comprising the same

[0070] FIG. 1 is a schematic diagram of an electrode comprising a metal carbide-carbon composite having a selectively coated double-layer structure according to one embodiment of the present invention.

[0071] Referring to FIG. 1, a metal carbide-carbon composite having a selectively coated double-layer structure according to one embodiment of the present invention includes a first carbon layer including a metal carbide coating layer, and a second carbon layer in contact with the first carbon layer and not having a metal carbide coating layer, wherein the first and second carbon layers may be carbon substrates including a plurality of pores.

[0072] The metal carbide may be a transition metal carbide. Transition metal carbides may have high adsorption energy between transition metal cations and lithium polysulfide, and specifically, possess a metallic d-band state similar to Pt, resulting in high electronic conductivity and catalytic activity. Therefore, they may be applied to a cathode to exhibit sulfur-philic properties. Furthermore, the transition metal carbide may be applied to anodes to exhibit lithium ion diffusion-limiting properties, i.e., lithium-philic properties.

[0073] Specifically, the carbide of the transition metal may be a carbide of at least one transition metal selected from the group consisting of molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), vanadium (V), zinc (Zn), cobalt (Co), and copper (Cu). In one specific example, the metal carbide may be, but is not limited to, molybdenum carbide (Mo2C).

[0074] The above carbon substrate may be a carbon material having multiple pores in which porous pores are exposed on the surface. The carbon substrate having multiple pores provides high electrical conductivity to the electrode of a high cell, physically prevents lithium polysulfide from dissolving into the electrolyte, and has a three-dimensional (3D) pore structure to facilitate the desorption / deposition of lithium ions, thereby preventing cell short-circuiting due to lithium dendrite formation in the negative electrode. Specifically, the carbon substrate may include at least one or more of carbon nanotubes, carbon fibers, graphene fibers, activated carbon, carbon black, and derivatives thereof. Specifically, the carbon substrate may include, but is not limited to, carbon nanotubes.

[0075] At this time, when applying the carbon substrate as the positive electrode or negative electrode of the lithium-sulfur battery according to one embodiment of the present invention, a carbon substrate having the same detailed properties such as physical properties, thickness, and pore size may be used, or different carbon substrates may be used depending on the ease of manufacturing process and the required characteristics of the battery. For example, a carbon substrate having a relatively large pore size may be used for the negative electrode of the lithium-sulfur battery, and a carbon substrate having a relatively small pore size may be used for the positive electrode, but is not limited thereto.

[0076] The metal carbide coating layer may be formed by coating the metal carbide on all or part of the surfaces of the plurality of pores formed in the first carbon layer. Specifically, the metal carbide coating layer may be formed only on a certain thickness region of the carbon substrate, or may mean that the metal carbide coating layer is formed asymmetrically on a certain thickness region or only on one layer by laminating a separate carbon substrate that is not coated thereon. More specifically, an asymmetric metal oxide coating may be confirmed only on the first carbon layer among the first and second carbon layers by energy dispersive spectroscopy (EDS) mapping. Since the metal carbide coating layer is asymmetrically provided on only one layer of the electrode, when applying the electrode to a lithium-sulfur battery, a composite having properties imparted selectively and / or hierarchically can be formed within one electrode.

[0077] The above metal carbide-carbon composite may be a composite in which the first and second carbon layers are each independently laminated carbon substrates, or the first and second carbon layers may be provided within a single integrated carbon substrate.

[0078] The metal carbide-carbon composite with a double-layer structure selectively coated as described above can be applied as an electrode for a lithium-sulfur battery, such as a positive electrode or a negative electrode.

[0079]

[0080] A lithium-sulfur battery according to one embodiment of the present invention includes an electrode including the metal carbide-carbon composite having a double-layer structure selectively coated as described above, wherein the electrode may include a positive electrode in which a reduction reaction of sulfur occurs; and a negative electrode arranged to face the positive electrode in which an oxidation reaction of lithium occurs.

[0081] In addition, it may include a separator disposed between the anode and the cathode and suppressing polysulfide movement but allowing ion transfer; and an electrolyte interposed between the anode and the cathode.

[0082] In particular, the first carbon layer including a metal carbide coating layer in the electrodes, specifically the positive and negative electrodes, may be positioned farther from the separator. By including a metal carbide coating layer on the side farther from the separator and a carbon layer on the side closer to the separator, when applied as a positive electrode, the dissolution of lithium polysulfide can be structurally suppressed, and when applied as a negative electrode, the electrodeposition due to limited diffusion of lithium ions can be suppressed, thereby increasing the operating performance and stability of a lithium-sulfur battery.

[0083] The above electrode can be used as a positive electrode by further including sulfur as a positive electrode active material. When a metal carbide-carbon composite including a metal carbide coating layer is used as a positive electrode, the chemical adsorption reaction and conversion reaction of lithium polysulfide are promoted, and the elution of lithium polysulfide into the electrolyte can be suppressed.

[0084] The above electrode can be used as an anode by further including lithium as an anode active material. When a metal carbide-carbon composite including a metal carbide coating layer is used as an anode, the diffusion of lithium ions within the electrode can be restricted, the deposition of lithium can be suppressed, and dendritic growth can be minimized.

[0085] The capacity per unit area of ​​the above electrode is 16.75 to 33.50 mAh / cm 2It can be. Specifically, the capacity per area of ​​the electrode is 16.75 mAh / cm 2 In case of sulfur (S) loading of 5 mg / cm 2 Based on this, the theoretical capacity of the positive electrode is 8.375 mAh / cm 2 , and at this time, the cathode capacity / positive electrode capacity ratio (N / P ratio) is 2. The capacity per area is 33.5 mAh / cm 2 In case of sulfur (S) loading of 10 mg / cm 2 The theoretical capacity of the anode is 16.75 mAh / cm 2 , and at this time, the cathode capacity / anode capacity ratio (N / P ratio) is 2.

[0086] The sulfur content per area of ​​the lithium-sulfur battery is 5 to 10 mg / cm 2 The above sulfur content, i.e. sulfur (S) loading, may be 5 mg / cm 2 If it is less than 10 mg / cm, the cell energy density is lower than the energy density of a typical lithium-ion battery (300 Wh / kg, below the dotted line), and thus cannot have the required high capacity. On the other hand, if it is less than 10 mg / cm, the cell energy density is lower than the energy density of a typical lithium-ion battery (300 Wh / kg, below the dotted line), and thus cannot have the required high capacity. 2 In the case of excess, the efficiency of energy density increase obtained by increasing sulfur (S) loading may be reduced because a high E / S ratio must be maintained even if the active material content is increased. Therefore, the appropriate sulfur content per area to have a high energy density while having a low E / S ratio is 5 to 10 mg / cm 2 It may include, but is not limited to.

[0087] The electrolyte may include an organic electrolyte including a lithium salt. Specifically, the lithium salt may be a single type of lithium salt or a mixed lithium salt comprising a mixture of multiple types of lithium salts, and may be dissolved in an organic solvent for use. The organic solvent may be a single type of organic solvent or a mixed organic solvent comprising a mixture of multiple types of organic solvents. In one specific example, the electrolyte may be a lithium electrolyte in which a mixed lithium salt of 1 M LiTFSI (Lithium bis(trifluoromethanesulphonyl)imide) and 0.2 M LiNO3 is dissolved in a 5:5 v / v% mixed organic solvent of dioxolane and dimethyl ether, but is not limited thereto.

[0088]

[0089] Method for producing a metal carbide-carbon composite having a double-layer structure with an optional coating

[0090] A method for manufacturing a metal carbide-carbon composite having a selectively coated double-layer structure according to one embodiment of the present invention may first include the step of (a) preparing a carbon substrate including a plurality of pores.

[0091] The step (a) above may be performed by first preparing a dispersion in which a carbon material powder including at least one of carbon nanotubes, carbon fibers, and graphene fibers is dispersed in a solvent (a-1).

[0092] Thereafter, (a-2) a step of separating the carbon material from the dispersion and drying it to manufacture a carbon substrate in the form of a film having a plurality of pores can be performed.

[0093] In addition, (b) a step of adding a precursor solution containing a metal to the carbon-based film and then carbonizing the same to form a metal carbide coating layer may be included.

[0094] The step (b) above may include: (b-1) a step of dropping a precursor solution containing a metal onto the carbon-based film and drying it to evaporate a solvent in the precursor solution; and (b-2) a step of carbonizing the metal by heat treatment under an inert gas atmosphere.

[0095] Before the above step (b-1), a pretreatment step of applying plasma to the carbon-based film to generate a functional group may be further included.

[0096] The heat treatment temperature in the above step (b-2) may be 600 to 1,000°C. Specifically, the heat treatment temperature is a temperature for carbonizing a precursor containing a transition metal cation, and may be, for example, 800°C, but is not limited thereto.

[0097] In the above step (b), the metal may be a transition metal, and has a high adsorption energy between the transition metal cation and lithium polysulfide. Specifically, the transition metal is at least one selected from the group consisting of molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), vanadium (V), zinc (Zn), cobalt (Co), and copper (Cu), and in one specific example, may be molybdenum.

[0098] The metal carbide may be a carbide of the transition metal, for example, a carbide of at least one transition metal selected from the group consisting of molybdenum (Mo), tungsten (W), titanium (Ti), nickel (Ni), vanadium (V), zinc (Zn), cobalt (Co), and copper (Cu), and in one specific example, the metal carbide may be molybdenum carbide.

[0099] In the above step (b), the precursor may be used without limitation as long as it is a precursor that can be carbonized under a certain sintering temperature condition to form a transition metal carbide, but in one specific example, the precursor may be ammonium heptamolybdate.

[0100] (i) In step (b), a metal carbide coating layer is formed only in a certain thickness region of the carbon substrate film, or (ii) by laminating a separate uncoated carbon substrate film after step (b), the metal carbide can be asymmetrically coated only in a certain thickness region or in one layer. Since the metal carbide coating layer is asymmetrically provided only in one layer of the electrode, when applying the electrode to a lithium-sulfur battery, a composite having properties imparted selectively and / or hierarchically can be formed within one electrode.

[0101] In the case of (ii) above, the carbon substrate film coated with metal carbide and the uncoated carbon substrate film may be laminated through a physical pressing process. The physical pressing process is not particularly limited, but in one specific example, may be performed through a rolling press machine.

[0102] Meanwhile, in the case of (i) above, since metal carbide is formed only at a certain thickness within a single integrated carbon substrate, a metal carbide coating layer can be selectively and / or hierarchically formed on a single substrate without bonding additional materials.

[0103]

[0104] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the following examples and comparative examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0105]

[0106] Example 1: Fabrication of a metal carbide-carbon composite electrode with a selectively coated double-layer structure.

[0107] First, the solvent and carbon substrate were separated through a known process that can utilize a carbon nanotube dispersion, and the separated carbon substrate was dried to manufacture a carbon substrate in the form of a film. Two types of carbon substrate films were manufactured depending on the pore size of the carbon substrate used. Next, a pretreatment was performed to generate hydrophilic functional groups by applying oxygen plasma to the manufactured carbon substrate, and ammonium heptamolybdate ((NH4)6Mo7O) was added to the surface. 24 ) The precursor solution was dropped. The dropped precursor solution was dried to evaporate the solvent, and the carbon substrate coated with the precursor solution was sintered at 800°C in an argon gas atmosphere. By sintering to carbonize the precursor, a metal carbide-carbon composite was manufactured in which molybdenum carbide (Mo2C) was formed on the surface of the carbon substrate.

[0108] The manufactured metal carbide-carbon composite was physically pressed with a general carbon substrate using a rolling press machine to form a composite electrode in which molybdenum carbide (Mo2C) was formed asymmetrically on only one side of the film, and this was used as an electrode of a lithium-sulfur battery. At this time, the metal carbide-carbon composite manufactured using a carbon substrate with relatively large pores was used as a negative electrode, and the metal carbide-carbon composite manufactured using a carbon substrate with relatively small pores was used as a positive electrode.

[0109]

[0110] Example 2: Fabrication of a metal carbide-carbon composite electrode with a symmetrically coated double-layer structure.

[0111] Instead of using a metal carbide-carbon composite in one layer and a carbon substrate in the other layer in Example 1, both layers were attached by physical compression using the same metal carbide-carbon composite in the same manner as in Example 1, thereby fabricating a metal oxide-carbon composite electrode in which molybdenum carbide (Mo2C) was symmetrically formed in two layers of the electrode.

[0112]

[0113] Comparative Example 1: Using a carbon substrate as an electrode

[0114] First, a carbon substrate was manufactured using the same method as in Example 1 and used as an electrode for a lithium-sulfur battery.

[0115]

[0116] FIG. 2 shows the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) of the surface of a metal carbide-carbon composite electrode according to Example 1 of the present invention.

[0117] Referring to FIG. 2, it can be confirmed that the surface of the metal carbide-carbon composite electrode manufactured in Example 1 has metal carbide evenly formed on the surface of the tubular carbon nanotube carbon substrate.

[0118]

[0119] FIG. 3 shows scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) results for a cross-section of a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0120] Referring to FIG. 3(a) and FIG. 3(b), cross-sections of the metal carbide-carbon composite electrode manufactured in Example 1 can be confirmed. In both the positive electrode (a, b) of the metal carbide-carbon composite manufactured using a carbon substrate with relatively small pores and the negative electrode (c, d) of the metal carbide-carbon composite manufactured using a carbon substrate with relatively large pores, it can be confirmed that metal carbide is evenly formed on the surface of the tubular carbon nanotube carbon substrate.

[0121]

[0122] FIG. 4 is an X-ray diffraction (XRD) result of a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0123] Referring to FIG. 4, it can be confirmed that molybdenum metal carbide is well formed in the metal carbide-carbon composite having a selectively coated double-layer structure manufactured according to Example 1.

[0124]

[0125] FIG. 5 shows the results of UV-vis spectroscopy of a metal carbide-carbon composite electrode according to one embodiment of the present invention and the change in solution color after electrolyte adsorption of the metal carbide-carbon composite electrode (inset).

[0126] Referring to FIG. 5, the degree of adsorption of lithium polysulfide (Li2S6) for each electrode manufactured according to Example 1 and Comparative Example 1 can be compared. Judging from the fact that Example 1 has a more transparent color and much lower absorbance compared to Comparative Example 1 or the lithium polysulfide (Li2S6) solution, it can be seen that the molybdenum carbide-carbon composite of Example 1 chemically adsorbs more lithium polysulfide.

[0127]

[0128] Figure 6 shows the results of cyclic voltammetry of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0129] Referring to FIG. 6, it can be seen that Example 1, which includes a molybdenum carbide-carbon composite, exhibits better catalytic properties and is more reversible than Comparative Example 1, which includes only carbon. This confirms that using a carbon composite including molybdenum carbide leads to improved performance of a lithium-sulfur battery.

[0130]

[0131] FIG. 7 is a result of XPS (X-ray photoelectron spectroscopy) analysis for evaluating the cathode discharge amount of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0132] Referring to Fig. 7, lithium-sulfur batteries were manufactured using each of the positive electrodes manufactured according to Examples 1 and 2, and the corresponding negative electrodes were evaluated through XPS analysis after a specific number of cycles. In Example 2, the size of the peak indicating Li2S rapidly increases as the cycles pass, indicating that a side reaction occurs in which more active material is eluted into the negative electrode and Li2S is generated. On the other hand, in Example 1, the intensity of the peak indicating Li2S is weaker than in Example 2 even after 100 cycles, confirming that the elution of lithium polysulfide, which is an active material, into the negative electrode is suppressed.

[0133]

[0134] Figure 8 shows the charge / discharge results for a lithium-sulfur battery symmetrical cell using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0135] Referring to Fig. 8, the amount of precipitated Li2S, a discharge product, can be compared through potentiostatic discharge at 2.05 V of the positive electrodes manufactured through Examples 1 and 2. As the charge and discharge cycles pass, it can be confirmed that the area of ​​the graph indicating the amount of precipitated Li2S in Example 2 decreases rapidly, whereas the amount of decrease in the amount of precipitated Li2S in Example 1 is significantly less than that in Example 2. Through this, it can be confirmed that the positive electrode with a double-layer structure selectively coated with molybdenum carbide having a catalytic effect suppresses the dissolution of lithium polysulfide.

[0136]

[0137] Figure 9 shows the results of comparing lithium ion affinity and stability of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0138] Referring to Fig. 9, the results of electrically electrodepositing lithium on each negative electrode manufactured according to Examples 1, 2, and Comparative Example 1 are shown. Seeing that the overvoltage between lithium electrodepositions is greater in Comparative Example 1 than in Examples 1 and 2, it can be confirmed that the high lithium affinity of molybdenum carbide improves the lithium electrodeposition ability. In addition, when the Coulombic efficiency of lithium electrodeposition / desorption of Examples 1, 2, and Comparative Example 1 is compared, it can be confirmed that Example 1 shows a high Coulombic efficiency of 99.8% even after 100 cycles.

[0139]

[0140] Figure 10 shows the results of lithium electrodeposition on the negative electrode of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0141] Referring to Fig. 10, the results of electrically depositing lithium on each negative electrode manufactured according to Examples 1 and 2 can be confirmed. It can be confirmed that more lithium is deposited on the upper side of the two-layer metal carbide-carbon composite electrode manufactured according to Example 1 compared to Example 2.

[0142]

[0143] Figure 11 shows the cycle operation results of a lithium-sulfur battery symmetrical cell using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0144] Referring to Fig. 11, symmetrical cells were fabricated for each negative electrode manufactured according to Examples 1, 2, and Comparative Example 1 to evaluate the life of lithium desorption / deposition cycles. It can be confirmed that Example 1 has high life stability by showing a stable overvoltage compared to Comparative Examples 1 and 2. In particular, at a high current density of 10 mA / cm 2In Example 1, high operating stability was observed for about 250 hours and a high cathode capacity of 20 mAh / cm 2 Under these conditions, stable desorption / deposition behavior for more than 2,000 hours can be confirmed.

[0145]

[0146] Battery Example 1: Lithium-sulfur battery using a metal carbide-carbon composite with a selectively coated double-layer structure as the positive and negative electrodes.

[0147] The electrodes of Example 1 were used as the positive and negative electrodes, and a separator and electrolyte were injected between them to assemble a lithium-sulfur complete battery. At this time, the direction of the layer in which the metal carbide was formed on the positive and negative electrodes was positioned so that it faced away from the separator.

[0148]

[0149] Figure 12 shows the results of analysis of the life characteristics at high active material content of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0150] Referring to Figure 12, the evaluation results for a lithium-sulfur full battery (Battery Example 1) in which the electrode manufactured according to Example 1 was simultaneously applied to the positive and negative electrodes, a lithium-sulfur half-cell (Example 1 - indicated as positive electrode) in which the electrode of Example 1 was applied to the positive electrode, and a lithium-sulfur half-cell (Example 1 - indicated as negative electrode) in which the electrode of Example 1 was applied to the negative electrode and the electrode of Comparative Example 1 was applied to the positive electrode can be confirmed. Here, the sulfur content per electrode area is 1 mg / cm 2As a result of conducting a galvanostatic charge / discharge evaluation under various C-rate current density conditions between 0.2 C and 4 C ratios, it can be confirmed that Battery Example 1 exhibits a particularly high specific capacity of 1,380 mAh / g and a capacity retention rate of 75.2% even at a 20-fold rate increase. In addition, it shows an improved specific capacity under all current density conditions compared to a lithium-sulfur half-cell in which a molybdenum carbide-carbon composite is applied as a positive or negative electrode, and the capacity retention rates are 69.8% and 64.8%, respectively, which are lower than those of Battery Example 1.

[0151]

[0152] Figure 13 shows the results of analysis of the life characteristics of a lithium-sulfur battery with a high active material content using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0153] Referring to Fig. 13, a high active material content (6 mg / cm 2 ) can be confirmed in the life characteristics. It can be seen that Battery Example 1 has a high life stability with a capacity retention rate of 63% even after 200 cycles while having a specific capacity of 1,013 mAh / g compared to the Example 1-positive electrode and the Example 1-negative electrode. In particular, it can be seen that the lithium-sulfur half-cell using the Example 1-negative electrode experiences a cell short circuit due to severe dissolution of lithium polysulfide after 70 cycles, and the lithium-sulfur half-cell using the Example 1-positive electrode experiences a capacity decrease due to instability in the negative electrode after 100 cycles.

[0154]

[0155] Figure 14 shows the results of analyzing the battery capacity at high sulfur content of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0156] Referring to Figure 14, the completeness of battery example 1 is 7 mg / cm 2This is a graph analyzing the capacity per area at high sulfur content. Under these conditions, the full capacity of battery example 1 was 8.7 mAh / cm 2 It has a high capacity per unit area, which is more than twice that of currently commercialized lithium-ion batteries. This confirms the effectiveness of the double-layer structure electrode with selective coating.

[0157]

[0158] FIG. 15 is a graph showing the energy density according to various sulfur loading amounts and E / S ratios of a lithium-sulfur battery using a metal carbide-carbon composite electrode according to one embodiment of the present invention.

[0159] Referring to Figure 15, the sulfur content, i.e., sulfur (S) loading, is 5 mg / cm 2 If it is less than 10 mg / cm, the cell energy density is lower than the energy density of a typical lithium-ion battery (300 Wh / kg, below the dotted line), and thus cannot have the required high capacity. On the other hand, if it is less than 10 mg / cm, the cell energy density is lower than the energy density of a typical lithium-ion battery (300 Wh / kg, below the dotted line), and thus cannot have the required high capacity. 2 In the case of excess, the efficiency of energy density increase obtained by increasing sulfur (S) loading may be reduced because a high E / S ratio must be maintained even if the active material content is increased. Therefore, the appropriate sulfur content per area to have a high energy density while having a low E / S ratio is 5 to 10 mg / cm 2 It could be.

[0160]

[0161] Although embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. A first carbon layer including a metal carbide coating layer, and a second carbon layer in contact with the first carbon layer and having no metal carbide coating layer, A metal carbide-carbon composite having an optionally coated double-layer structure, characterized in that the first and second carbon layers are carbon substrates including a plurality of pores.

2. In paragraph 1, A metal carbide-carbon composite having a selectively coated double-layer structure, characterized in that the metal carbide is a carbide of a transition metal.

3. In paragraph 1, A metal carbide-carbon composite having a selectively coated double-layer structure, characterized in that the first and second carbon layers are each independently laminated carbon substrates.

4. In paragraph 1, A metal carbide-carbon composite having an optionally coated double-layer structure, characterized in that the first and second carbon layers are a single integrated carbon substrate.

5. In paragraph 1, A metal carbide-carbon composite having a selectively coated double-layer structure, characterized in that the metal carbide coating layer is coated with metal carbide on the surfaces of all or part of the plurality of pores formed in the first carbon layer.

6. In paragraph 1, A metal carbide-carbon composite having a selectively coated double-layer structure, characterized in that an asymmetric metal oxide coating is confirmed only on the first carbon layer among the first and second carbon layers by EDS (Energy Dispersive Spectroscopy) mapping.

7. An electrode for a lithium-sulfur battery, comprising a metal carbide-carbon composite having a selectively coated double-layer structure, comprising a first carbon layer including a metal carbide coating layer, and a second carbon layer in contact with the first carbon layer and not having a metal carbide coating layer, wherein the first and second carbon layers are carbon substrates including a plurality of pores.

8. In paragraph 7, An electrode for a lithium-sulfur battery, characterized in that the electrode further includes sulfur as a positive electrode active material, and is used in the positive electrode, and suppresses the dissolution of lithium polysulfide by promoting chemical adsorption and conversion of lithium polysulfide.

9. In paragraph 8, An electrode for a lithium-sulfur battery, characterized in that the first carbon layer in the electrode is located farther away from the separator of the lithium-sulfur battery.

10. In paragraph 7, The above electrode further includes lithium as an anode active material, and is used in a cathode, and is characterized by minimizing dendritic growth by suppressing electrodeposition due to limited diffusion of lithium ions, an electrode for a lithium-sulfur battery.

11. In paragraph 10, An electrode for a lithium-sulfur battery, characterized in that the first carbon layer in the electrode is located farther away from the separator of the lithium-sulfur battery.

12. In paragraph 10, The capacity per unit area of ​​the above electrode is 16.75 to 33.50 mAh / cm 2 An electrode for a lithium-sulfur battery, characterized by: 13.(a) a step of preparing a carbon substrate including a plurality of pores; and (b) a step of adding a precursor solution containing a metal to the carbon substrate and then carbonizing the same to form a metal carbide coating layer; (i) A method for manufacturing a metal carbide-carbon composite having a selectively coated double-layer structure, characterized in that the metal carbide is asymmetrically coated only in a certain thickness region or in one layer by forming a metal carbide coating layer only in a certain thickness region of the carbon substrate in step (b) above, or (ii) laminating a separate carbon substrate that is not coated after step (b).

14. In paragraph 13, Step (a) above, (a-1) a step of preparing a dispersion in which carbon material powder including at least one of carbon nanotubes, carbon fibers, graphene fibers, activated carbon, carbon black and derivatives thereof is dispersed in a solvent; and (a-2) A method for producing a metal carbide-carbon composite having an optionally coated double-layer structure, comprising the step of separating the carbon material from the dispersion and drying it to produce a carbon substrate having a plurality of pores.

15. In paragraph 13, Step (b) above, (b-1) a step of dropping a precursor solution containing a metal onto the carbon substrate and drying it to evaporate the solvent in the precursor solution; and (b-2) A method for producing a metal carbide-carbon composite having an optionally coated double-layer structure, comprising the step of carbonizing the metal by heat treatment under an inert gas atmosphere.

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