Electrode for lithium-sulfur battery comprising metal oxide nanoparticle layer, manufacturing method thereof, and lithium-sulfur battery using same

Abstract

In an electrode for a lithium-sulfur battery according to a preferred embodiment of the present invention, a metal oxide nanoparticle layer can be formed on the surface of a carbon substrate by performing a carbothermal reduction reaction on a metal oxide shell, formed on the surface of the carbon substrate, by an atomic layer deposition process. A metal oxide nanoparticle layer formed by dry-etching at least a portion of the metal oxide shell through reductive sublimation is chemically anchored to the carbon substrate and induces the growth of lithium sulfide (Li2S) having a low film density in the form of three-dimensional particles on the surface thereof, and thus a high discharge capacity and a fast conversion rate can be exhibited even under high sulfur loading and lean electrolyte conditions.

Description

Electrode for lithium-sulfur battery including metal oxide nanoparticle layer, method for manufacturing same, and lithium-sulfur battery using same

[0001] The present invention relates to a lithium-sulfur battery, and more particularly, to a lithium-sulfur battery including an electrode using an ultra-high-density nanoparticle layer.

[0002] This study was conducted with the support of the following National Research and Development Program of the Republic of Korea.

[0003] <1>

[0004] [Project ID] 1711191403

[0005] [Assignment Number] 2022R1A2C2005228

[0006] [Ministry Name] Ministry of Science and ICT

[0007] [Name of Project Management (Specialist) Institution] National Research Foundation of Korea

[0008] [Research Project Name] Individual Basic Research (Ministry of Science and ICT)

[0009] [Research Project Title] Formation of Polymer-Derived Carbon Nanostructures by Controlling Compressive Stress-Adhesion and Their Application to Energy Devices

[0010] [Name of Project Performing Organization] Korea University

[0011] [Research Period] March 1, 2022 - February 28, 2025

[0012] <2>

[0013] [Project ID] 2710079320

[0014] [Assignment Number] RS202500559443

[0015] [Ministry Name] Ministry of Science and ICT

[0016] [Name of Project Management (Specialist) Institution] National Research Foundation of Korea

[0017] [Research Project Name] Individual Basic Research (Ministry of Science and ICT) (R&D)

[0018] [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.

[0019] [Name of Project Performing Organization] Korea University

[0020] [Research Period] March 1, 2025 - February 29, 2028

[0021] 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 electrodes with high sulfur loading to develop batteries with higher energy density.

[0022] The present invention has been conceived to solve the above-described problem, and can include a lithium-sulfur battery in which battery performance is maintained even in an electrode having a high sulfur loading.

[0023] In order to achieve the above technical task, a method for manufacturing an electrode for a lithium-sulfur battery using ultra-high-density nanoparticle formation according to a preferred example of the present invention is provided.

[0024] A step (S01) of forming a metal oxide shell on the surface of the carbon substrate by positioning a carbon substrate inside a chamber and performing an atomic layer deposition process by injecting two or more precursors; and

[0025] It may include a step (S02) of performing a carbon thermal reduction reaction on a carbon substrate on which the metal oxide shell is formed, thereby forming a metal oxide nanoparticle layer on the surface of the carbon substrate.

[0026] The above metal oxide nanoparticle layer may be formed by dry etching at least a portion of the metal oxide shell through reductive sublimation.

[0027] The dry etching of the metal oxide shell through the above carbon thermal reduction reaction may be performed by a reaction represented by the following reaction formula 1:

[0028] [Reaction Formula 1]

[0029] yC + M x O y → xM(g) + yCO(g)

[0030] In the above reaction formula 1, M includes any one selected from Zn, Fe, Ni, Cu, W, Ti, Mn, Al, Ti, Co, and combinations thereof, and x and y are independent arbitrary integers.

[0031] As the carbon thermal reduction reaction time increases, the thickness of the metal oxide nanoparticle layer may decrease, and the film density of the metal oxide nanoparticle layer may decrease.

[0032] The metal oxide nanoparticle layer formed through the above carbon thermal reduction reaction may be chemically fixed to the carbon substrate.

[0033] The metal oxide content of the electrode for the above lithium-sulfur battery may be 5 to 25 wt% relative to the total weight.

[0034] The sulfur loading of the above lithium-sulfur battery electrode is 5 to 20 mg cm -2 It could be.

[0035] The above carbon thermal reduction reaction is performed by performing a first heat treatment in a first temperature range and a second heat treatment in a second temperature range, wherein the second temperature range is higher than the first temperature range, and the second temperature range may be 300°C or higher.

[0036] The above carbon substrate may include any one selected from carbon nanotubes, carbon fibers, graphene fibers, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, graphite, activated carbon, carbon nanoribbons, carbon nanobelts, carbon nanorods, mesoporous carbon, Super P, derivatives thereof, and combinations thereof.

[0037] In order to achieve the above technical task, a lithium-sulfur battery electrode using ultra-high-density nanoparticle formation according to a preferred example of the present invention comprises: a carbon substrate; and a metal compound nanoparticle layer formed on the surface of the carbon substrate; wherein the metal compound nanoparticle layer is chemically fixed to the surface of the carbon substrate.

[0038] The above-mentioned lithium-sulfur battery electrode can induce the growth of lithium sulfide in a three-dimensional (3D) particle form during the charge / discharge process of the battery.

[0039] The above metal compound nanoparticle layer may be formed by dry etching at least a portion of a metal oxide shell formed on the surface of the carbon substrate by an atomic layer deposition method through reductive sublimation.

[0040] The metal oxide content of the electrode for the above lithium-sulfur battery may be 5 to 25 wt% relative to the total weight.

[0041] The sulfur loading of the above lithium-sulfur battery electrode is 5 to 20 mg cm -2 It could be.

[0042] In order to achieve the above technical task, a lithium-sulfur battery using ultra-high density nanoparticle formation according to a preferred example of the present invention is provided.

[0043] An anode including an electrode as described above, which includes a carbon substrate and a metal compound nanoparticle layer formed on the surface of the carbon substrate, wherein the metal compound nanoparticle layer is chemically fixed to the surface of the carbon substrate;

[0044] A cathode disposed opposite to the positive electrode and comprising lithium metal or a lithium alloy;

[0045] A separator disposed between the anode and the cathode to suppress the movement of solid polysulfide; and

[0046] It may include an electrolyte that is interposed between the positive electrode and the negative electrode, contains lithium ions and sulfur ions, and serves as a passage for the ions.

[0047] The above positive electrode can induce the growth of lithium sulfide (Li2S) in the form of three-dimensional (3D) particles during the charge / discharge process of the battery.

[0048] The above metal compound nanoparticle layer may be formed by dry etching at least a portion of a metal oxide shell formed on the surface of the carbon substrate by an atomic layer deposition method through reductive sublimation.

[0049] The content of the metal oxide in the anode may be 5 to 25 wt% relative to the total weight of the anode.

[0050] The sulfur loading of the above anode is 5 to 20 mg cm -2 It could be.

[0051] According to the present invention as described above, the electrode for a lithium-sulfur battery according to a preferred embodiment of the present invention can form a metal oxide nanoparticle layer on the surface of a carbon substrate by performing a carbothermal reduction reaction on a metal oxide shell formed on the surface of the carbon substrate by an atomic layer deposition process. The metal oxide nanoparticle layer formed by dry etching at least a portion of the metal oxide shell through reductive sublimation is chemically fixed to the carbon substrate, and induces three-dimensional lithium polysulfide growth on the surface thereof during the charge / discharge process of the battery, thereby exhibiting a high sulfur loading amount, a high discharge capacity, and a fast conversion rate.

[0052] 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.

[0053] Figure 1 is a schematic diagram showing a method for manufacturing a metal compound nanoparticle layer using a carbon thermal reduction method according to one embodiment of the present invention.

[0054] FIG. 2 is a scanning electron microscope (SEM) image of (a) a carbon nanotube (CNT), (b) a carbon nanotube having a zinc oxide shell (ZnO shell) formed, and (c) a carbon nanotube electrode having a zinc oxide nanoparticle layer formed according to an embodiment of the present invention, and a transmission electron microscope (TEM) image (inset: high-contrast TEM) (scale bar: 25 nm) of carbon nanotubes having a zinc oxide shell (ZnO shell) formed with a thickness of (d) 6 nm, (e) 12 nm, and (f) 18 nm.

[0055] Figure 3 is a scanning electron microscope (SEM) photograph of a carbon nanotube electrode formed with a zinc oxide nanoparticle layer according to an embodiment of the present invention, as a function of heat treatment (carbon thermal reduction reaction) time. (Scale bar: 50 nm)

[0056] FIG. 4 is a graph showing (a) thermogravimetric analysis (TGA) and (b) the content of zinc oxide (ZnO) nanoparticles for carbon nanotubes formed with a layer of zinc oxide (ZnO) nanoparticles through a carbon thermal reduction reaction according to Manufacturing Examples 1 to 3 of the present invention.

[0057] FIG. 5 is a graph comparing (a) the specific surface area and (b) the BET (Brunauer Emmett Teller) adsorption isotherm results for carbon nanotube electrodes in which a zinc oxide (ZnO) nanoparticle layer is formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0058] FIG. 6 shows the UV-vis spectrum of a lithium polysulfide (LiPS) electrolyte solution (2 mM Li2S6) after 3 hours of immersion in a carbon nanotube electrode having a zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention (a) (inset: photograph of an electrode immersed in a lithium polysulfide (LiPS) electrolyte), (b) a graph showing the amount of LiPS (Li2S4) adsorption, (c) the result of calculating the adsorption binding energy of lithium polysulfide (LiPS) on ZnO and CNT substrates (replaced with graphene) through DFT calculation (inset: optimized atomic image of LiPS molecules), (d) S 2p XPS result after LiPS adsorption, (e) symmetric cyclic voltammetry (CV) curve, (f) asymmetric cyclic voltammetry (CV) curve, and (g) electrochemical This is the result of the impedance spectrum (EIS, Electrochemical Impedance Spectroscopy).

[0059] Figure 7 is a Tafel plot for a carbon nanotube electrode in which a zinc oxide (ZnO) nanoparticle layer is formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0060] FIG. 8 shows (a to d) potentiostatic current-time (it) curves of LiPS-Li2S conversion, (e to h) normalized current-time (it) curves (solid lines) and profiles (dotted lines) based on 2D and 3D electrodeposition models, and (i to l) ex-situ scanning electron microscope (SEM) images after precipitation discharge (scale bar: 500 nm) for carbon nanotube electrodes having a zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0061] FIG. 9 is a schematic diagram illustrating a mechanism for explaining the growth of Li2S through LiPS adsorption and conversion in an electrode (anode) of a lithium-sulfur electrode according to an embodiment of the present invention, wherein (a) an ultra-high-density zinc oxide (ZnO) nanoparticle layer (Preparation Example 1), (b) a low-density zinc oxide (ZnO) nanoparticle layer (Preparation Example 2), and (c) a thick zinc oxide (ZnO) nanoparticle layer (Preparation Example 3) are formed.

[0062] Figure 10 shows (a) galvanostatic charge / discharge profiles of lithium-sulfur batteries using carbon nanotube electrodes having zinc oxide (ZnO) nanoparticle layers formed in Comparative Example 2 and Examples 1 to 3 of the present invention as cathodes, (b) comparison of voltage polarization at 0.03 C current density, (c) comparison of specific capacity at various C-rates, (d) charge / discharge cycle results at 2 C, (e) results of 300 charge / discharge cycles at 10 C, (f) results of 500 charge / discharge cycles at 2 C, (g) 10 to 12 mg cm -2 (E / S: 7 μL mg -1 ) Capacity comparison in electrodes with very high sulfur (S) loading (12 nm-ZnO NPs, Example 1) (Inset: 10 mg cm -2(h) Capacity comparison with other studies at high sulfur (S) loading, (i) charge-discharge profile and (j) cycle performance graph when applying 12 nm-ZnO NP electrode (Example 1) under full-cell conditions.

[0063] FIG. 11 is (a) a scanning electron microscope image (scale bar: 100 nm) and (c) a TGA result of a carbon nanotube electrode having an ultra-high-density zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Manufacturing Example 1 of the present invention, and (b) a scanning electron microscope image (scale bar: 100 nm) and (d) a TGA result of a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles through a solution-based nanoparticle synthesis method according to Comparative Example 3.

[0064] Figure 12 is an absorbance spectrum for a carbon nanotube electrode having an ultra-high density zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Manufacturing Example 1 of the present invention and a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles through a solution-based nanoparticle synthesis method according to Comparative Example 3.

[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] Method for manufacturing an electrode for a lithium-sulfur battery comprising a carbon substrate having a metal compound nanoparticle layer formed thereon using a carbothermal reduction method

[0070] Figure 1 is a schematic diagram showing a method for manufacturing a metal compound nanoparticle layer using a carbon thermal reduction method according to one embodiment of the present invention.

[0071] Referring to FIG. 1, a method for manufacturing an electrode for a lithium-sulfur battery may include a step (S01) of positioning a carbon substrate inside a chamber, injecting two or more precursors to perform an atomic layer deposition process, and forming a metal oxide shell on the surface of the carbon substrate.

[0072] The carbon substrate may include any one selected from carbon nanotubes, carbon fibers, graphene fibers, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, graphite, activated carbon, carbon nanoribbons, carbon nanobelts, carbon nanorods, mesoporous carbon, Super P, derivatives thereof, and combinations thereof, and specifically, the carbon substrate may be a carbon nanotube, but is not limited thereto.

[0073] Through the above-described atomic layer deposition (ALD) process, a metal oxide shell can be formed on the surface of a carbon substrate. The metal oxide shell is a metal oxide film thicker than the thickness of a metal oxide nanoparticle layer described later, and can be partially etched through the carbon thermal reduction reaction described later to form metal oxide particles in the form of nanoparticles.

[0074] Next, a step (S02) of performing a carbon thermal reduction reaction on a carbon substrate on which the metal oxide shell is formed to form a metal oxide nanoparticle layer on the surface of the carbon substrate may be included.

[0075] Carbothermal reduction is a method in which at least a portion of a metal oxide shell is etched through reductive sublimation to form a metal oxide nanoparticle layer. The dry etching process of the metal oxide shell through reductive sublimation can be represented by the reaction of the following reaction formula 1.

[0076] [Reaction Formula 1]

[0077] yC + M x O y → xM(g) + yCO(g)

[0078] In the above reaction formula 1, M includes any one selected from Zn, Fe, Ni, Cu, W, Ti, Mn, Al, Ti, Co, and combinations thereof, and x and y are independent arbitrary integers.

[0079] In one specific example, M may be, but is not limited to, Zn.

[0080] Above M x O y It may be a metal oxide shell formed through the above-described atomic layer deposition process.

[0081] At least a portion of the metal oxide shell may be removed in the gas phase through reductive sublimation, and the remaining portion may remain in the form of particles to form a metal oxide nanoparticle layer. Accordingly, as the time for performing the step of chemical formula 1 of etching the thick metal oxide shell increases, the thickness of the metal oxide nanoparticle layer, i.e., the size of the metal oxide nanoparticles, may decrease.

[0082] The heat treatment applied to the above-mentioned carbon-thermal reduction reaction may be to perform a first heat treatment in a first temperature range and a second heat treatment in a second temperature range. Specifically, the second temperature range may be higher than the first temperature range, and the second temperature range may be 300°C or higher. The first heat treatment may be performed at a temperature within a range in which stabilization treatment of the metal oxide crystal is possible. Meanwhile, the second heat treatment is performed at a temperature in a range for performing the carbon-thermal reduction reaction, and in particular, the second heat treatment may be performed at a relatively low temperature or a similar temperature compared to a high temperature used in a conventional general method, for example, a heat treatment temperature of about 800 to 900°C, and in one specific example, may be performed at 300°C or higher. When the temperature range in which the second heat treatment is performed is less than 300°C, the carbon-thermal reduction reaction may not be performed.

[0083] The size of metal oxide nanoparticles decreases as the carbon thermal reduction reaction (heat treatment) time increases, and the film density of the metal oxide nanoparticle layer may decrease as the carbon thermal reduction reaction (heat treatment) time increases.

[0084] The method for manufacturing a carbon substrate including a metal oxide nanoparticle layer manufactured through such a carbon thermal reduction reaction can be formed with much stronger and more solid binding because the final structure appears to be formed by simply physical attraction of the metal oxide nanoparticles to the surface of the carbon substrate, but is chemically fixed to the carbon substrate compared to the process of subsequently coating nanoparticles manufactured in advance by solvent-based synthesis methods such as sol-gel and solvothermal synthesis methods, which are generally used to synthesize nanoparticles, onto the carbon substrate.

[0085] In particular, a dry nanoparticle layer manufacturing method in which a metal oxide thin film formed by an atomic layer deposition process is reduced to form nanoparticles through a dry process can produce a film that is densely packed on a carbon substrate, has ultra-high density properties, and is chemically fixed to the carbon substrate, which are difficult to achieve with conventional solution synthesis and / or solution processes. The metal oxide nanoparticle layer manufactured by this method exhibits excellent performance in the sulfur (S) conversion rate and can act as an active site that promotes sulfur (S) conversion at the interface between carbon and metal oxide nanoparticles.

[0086] The solution-based method of pre-synthesizing and then coating nanoparticles, which is generally known, has difficulty forming a thin and uniform nanoparticle layer due to the aggregation characteristics of the nanoparticles. On the other hand, the nanoparticle layer formed by the carbon thermal reduction reaction according to a preferred embodiment of the present invention can produce a coating layer in which the nanoparticles are not agglomerated but are homogeneously dispersed in a nano-thick layer. However, such a homogeneously dispersed coating layer can produce lithium sulfide nanoparticles in the form of three-dimensional particles with an uneven surface rather than a smooth film-like shape.

[0087]

[0088] Electrode for lithium-sulfur battery comprising carbon substrate having metal compound nanoparticle layer formed thereon and lithium-sulfur battery comprising same

[0089] An electrode for a lithium-sulfur battery according to one embodiment of the present invention may include a carbon substrate; and a metal compound nanoparticle layer formed on the surface of the carbon substrate; and in particular, the metal compound nanoparticle layer may be chemically fixed to the surface of the carbon substrate.

[0090] When a carbon substrate having a metal oxide nanoparticle layer formed on the surface is applied as an electrode for a lithium-sulfur battery, lithium polysulfide (LiPS) dissolved in the electrolyte is adsorbed on the metal oxide nanoparticle layer and diffuses to the surface of the carbon substrate, and can induce the growth of lithium sulfide (Li2S) in the form of three-dimensional (3D) particles during the charge and discharge process of the battery. At this time, compared to the process of subsequently coating nanoparticles prepared in advance by a solvent-based synthesis method such as sol-gel or solvothermal synthesis, which are generally used to synthesize nanoparticles, onto a carbon substrate, a film having the characteristics of being densely packed on the carbon substrate, having ultra-high density properties, and being chemically fixed to the carbon substrate is formed, so that the growth of lithium sulfide (Li2S) in the form of three-dimensional (3D) particles is induced, and a very high discharge capacity and a fast conversion rate can be exhibited. Specifically, the lithium sulfide growth in the form of three-dimensional clustered particles is promoted by the high concentration of S4 2- It is mainly a solution-phase disproportionation reaction (2S4) 2- → S 2- + S7 2- ) to derive S 2- This may mean that Li2S growth is promoted in the form of clustered particles in three-dimensional (3D) particle form through bulk diffusion.

[0091] On the other hand, on carbon electrodes with thick shells and / or low-density metal oxide nanoparticle layers, the LiPS adsorption rate is fast, but the exposure of the metal oxide nanoparticle / carbon interface is limited, which induces a slowdown in the LiPS adsorption / conversion rate, resulting in abundant S4 2- Since the environment cannot be created, Li2S growth can be induced mainly in the form of a two-dimensional (2D) film.

[0092]

[0093] Additionally, the metal compound nanoparticle layer can be chemically fixed to the surface of the carbon substrate.

[0094] The metal oxide content of the electrode for the lithium-sulfur battery may be 5 to 25 wt% relative to the total weight, and specifically, may be 6 to 21 wt%, but is not limited thereto.

[0095] The sulfur loading of the above lithium-sulfur battery electrode is 5 to 20 mg cm -2 may be, specifically, 7 to 15 mg cm -2 may be, more specifically, 9 to 13 mg cm -2 may be, but is not limited to, 5 mg cm -2 Unlike the case where the internal and external sulfur loading is present, the electrode having a metal oxide nanoparticle layer formed through a carbon thermal reduction process induces three-dimensional lithium sulfide (Li2S) growth on the surface of the electrode during the charge and discharge process of the battery, thereby exhibiting high sulfur loading, high discharge capacity, fast conversion speed, and excellent cycle capacity retention.

[0096]

[0097] 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.

[0098]

[0099] Manufacturing Example 1: Carbon nanotube (ZnO nanoparticle coated CNT) electrode formed with a zinc oxide (ZnO) nanoparticle layer using a carbothermal reduction method using a 12 nm thick zinc oxide shell (ZnO shell)

[0100] First, carbon nanotubes (CNTs) were prepared as carbon substrates. Diethylzinc ((C2H5)2Zn) and water vapor were used as precursors, and the atomic layer deposition process temperature was set to 80°C. The carbon substrate was placed in an atomic layer deposition (ALD) chamber to synthesize a zinc oxide shell (ZnO shell). One ALD process cycle involved exposure to diethylzinc ((C2H5)2Zn) for 20 seconds, purging with nitrogen (N2) gas for 10 seconds, exposure to water vapor (H2O) for 20 seconds, and purging with nitrogen (N2) gas again for 10 seconds, which was performed 120 times. The growth rate of the zinc oxide shell (ZnO shell) per ALD cycle was approximately 0.1 nm / cycle. At this time, the thickness of the zinc oxide shell (ZnO shell) manufactured through the ALD process was approximately 12 nm. Afterwards, the nanoparticle crystals were stabilized at 200°C for 2 hours, and a heat treatment (carbothermal reduction) step was performed at 350°C for 2 hours under an argon atmosphere. At this time, a portion of the zinc oxide shell (ZnO shell) was dry etched through reductive sublimation to produce a nanoparticle layer. Thus, a carbon nanotube (ZnO nanoparticle coated CNT) electrode with a zinc oxide (ZnO) nanoparticle layer formed on the surface was produced. At this time, the thickness of the zinc oxide (ZnO) nanoparticle layer is approximately 10 nm.

[0101] Adsorption of LiPS was performed by immersing 20 mg of the cathode substrate in a 2 mM Li2S6 solution for 3 h.

[0102]

[0103] Manufacturing Example 2: Carbon nanotube (ZnO nanoparticle coated CNT) electrode formed with a zinc oxide (ZnO) nanoparticle layer using a carbothermal reduction method using a 6 nm thick zinc oxide shell (ZnO shell)

[0104] A carbon nanotube (ZnO nanoparticle coated CNT) electrode formed with zinc oxide nanoparticles was manufactured in the same manner as in Manufacturing Example 1, except that the ALD cycle was performed 60 times. At this time, the thickness of the zinc oxide shell (ZnO shell) manufactured through the ALD process was approximately 6 nm, and the thickness of the zinc oxide (ZnO) nanoparticle layer after dry etching was approximately 5 nm.

[0105]

[0106] Manufacturing Example 3: Carbon nanotube (ZnO nanoparticle coated CNT) electrode formed with a zinc oxide (ZnO) nanoparticle layer using a carbothermal reduction method using a zinc oxide shell (ZnO shell) with a thickness of 18 nm.

[0107] A carbon nanotube (ZnO nanoparticle coated CNT) electrode formed with zinc oxide nanoparticles was manufactured in the same manner as in Manufacturing Example 1, except that the ALD cycle was performed 180 times. At this time, the thickness of the zinc oxide shell (ZnO shell) manufactured through the ALD process was 18 nm, and the thickness of the zinc oxide (ZnO) nanoparticle layer after dry etching was approximately 15 to 17 nm.

[0108]

[0109] Comparative Example 1: Carbon nanotube (ZnO nanoparticle coated CNT) electrode without zinc oxide (ZnO) nanoparticle layer formed

[0110] Untreated carbon nanotubes (CNTs) were used as the carbon substrate.

[0111]

[0112] FIG. 2 is a scanning electron microscope (SEM) image of (a) a carbon nanotube (CNT), (b) a carbon nanotube having a zinc oxide shell (ZnO shell) formed, and (c) a carbon nanotube electrode having a zinc oxide nanoparticle layer formed according to an embodiment of the present invention, and a transmission electron microscope (TEM) image (inset: high-contrast TEM) (scale bar: 25 nm) of carbon nanotubes having a zinc oxide shell (ZnO shell) formed with a thickness of (d) 6 nm, (e) 12 nm, and (f) 18 nm.

[0113] Referring to FIGS. 2(a) to 2(c), it can be confirmed that the average size of each zinc oxide nanoparticle is about 5 nm to 10 nm, and as a result of observing the surface of a carbon nanotube (CNT), a carbon nanotube having a zinc oxide shell (ZnO shell) formed, and a carbon nanotube electrode having a zinc oxide nanoparticle layer formed, it can be confirmed that the zinc oxide shell (ZnO shell) coated on the surface of the carbon nanotube through the atomic layer deposition method is a thick zinc oxide (ZnO) film, and it can be confirmed that the film form of the zinc oxide shell (ZnO shell) is partially etched to form a nanoparticle layer remaining in the form of a nanoparticle.

[0114] Referring to FIGS. 2(d) to 2(f), it can be seen that the thinner the zinc oxide shell formed with a thickness of 6 nm, 12 nm, and 18 nm, the more the nanoparticle layer is formed in a loose manner with a low density, and the thicker the zinc oxide shell, the more the nanoparticle layer is formed with a high density and appears rather aggregated. In addition, it can be seen that the zinc oxide (ZnO) nanoparticles are well dispersed and form a homogeneous film without aggregation in the electrode formed with the nanoparticle layer formed from the zinc oxide shell with a thickness of 12 nm.

[0115]

[0116] Figure 3 is a scanning electron microscope (SEM) photograph of a carbon nanotube electrode formed with a zinc oxide nanoparticle layer according to an embodiment of the present invention, as a function of heat treatment (carbon thermal reduction reaction) time. (Scale bar: 50 nm)

[0117] Referring to FIG. 3, as the carbon thermal reduction reaction time increases (in the order of a, b, and c), the dry etching process of the zinc oxide shell (ZnO) is performed more frequently, and thus the size of the zinc oxide nanoparticles, the thickness of the zinc oxide nanoparticle layer, and / or the film density of the zinc oxide nanoparticle layer are confirmed to decrease.

[0118]

[0119] FIG. 4 is a graph showing (a) thermogravimetric analysis (TGA) and (b) the content of zinc oxide (ZnO) nanoparticles for carbon nanotubes formed with a layer of zinc oxide (ZnO) nanoparticles through a carbon thermal reduction reaction according to Manufacturing Examples 1 to 3 of the present invention.

[0120] Referring to FIG. 4, it can be deduced through thermogravimetric analysis (TGA) that the contents of zinc oxide (ZnO) in the electrodes including nanoparticle layers manufactured from zinc oxide shells formed with thicknesses of 6 nm (Manufacturing Example 2), 12 nm (Manufacturing Example 1), and 18 nm (Manufacturing Example 3) are 6.2 wt%, 12.2 wt%, and 19.4 wt%, respectively, based on the total weight.

[0121]

[0122] FIG. 5 is a graph comparing (a) the specific surface area and (b) the BET (Brunauer Emmett Teller) adsorption isotherm results for carbon nanotube electrodes in which a zinc oxide (ZnO) nanoparticle layer is formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0123] Referring to Figure 5, the BET area (specific surface area of ​​the sample surface) of the carbon nanotube (Comparative Example 1) without any treatment is about 30 m2 Considering that / g, the BET area of ​​carbon nanotubes (Manufacturing Examples 1 to 3) in which a zinc oxide (ZnO) nanoparticle layer is formed through a carbon thermal reduction reaction is about 45 to 60 m 2 / g, it can be confirmed that the BET area of ​​the carbon nanotube (manufacturing example 1) formed with a nanoparticle layer manufactured from a zinc oxide (ZnO) shell having a thickness of 12 nm is about 60 m 2 / g can be confirmed as the largest. Therefore, it can be confirmed that the specific surface area increased due to the formation of a zinc oxide (ZnO) nanoparticle layer, and it can also be seen that the nanoparticle layer manufactured from a 12 nm thick zinc oxide shell has a high specific surface area.

[0124]

[0125] FIG. 6 shows (a) UV-vis spectrum of an electrolyte solution (2 mM Li2S6) after 3 hours of immersion in an electrolyte solution (2 mM Li2S6) for a carbon nanotube electrode having a zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention (inset: photograph of an electrode immersed in an electrolyte), (b) graph showing the amount of LiPS (Li2S4) adsorption, (c) calculation results of lithium polysulfide (LiPS) adsorption binding energy on ZnO and CNT substrates (replaced with graphene) through DFT calculation (inset: optimized atomic image of LiPS molecule), (d) S 2p XPS results after LiPS adsorption, (e) symmetric cyclic voltammetry (CV) curve, (f) asymmetric cyclic voltammetry (CV) curve, and (g) electrochemical impedance spectrum (EIS). This is the result.

[0126] Referring to Fig. 6(a) and Fig. 6(b), the electrode for a lithium-sulfur battery is immersed in a lithium polysulfide (LiPS) electrolyte, and the degree of LiPS adsorption can be confirmed by the color change of the electrolyte. Compared to the untreated carbon nanotube electrode (indicated as Bare), the carbon nanotube electrode formed with a ZnO nanoparticle layer adsorbed the LiPS electrolyte regardless of the thickness, resulting in a light color of the electrolyte, and the UV-Vis absorption spectrum showed S4 2- As a result of measuring and comparing the absorbance at a wavelength of 420 nm, which indicates absorption, the carbon nanotube electrode (denoted as 12 nm-ZnO NP) formed with a nanoparticle layer manufactured from a ZnO shell having a thickness of 12 nm showed the lowest absorbance, confirming that the adsorption of LiPS (Li2S4) was performed the most. In particular, it was confirmed that the electrode of 6 nm-ZnO NP (Manufacturing Example 1) showed an adsorption amount that was about 2.03 times higher than that of Bare (CNT, Comparative Example 1) and about 1.3 times higher than that of 6 nm-ZnO NP (Manufacturing Example 2).

[0127] Referring to Fig. 6(c), the binding energies for LiPS adsorption on ZnO and CNT substrates can be compared using DFT calculations. The CNT substrate was replaced with a graphene sheet substrate for the convenience of calculation. Modeling the (100) plane of the ZnO substrate and the CNT substrate using graphene sheets shows that the ZnO substrate exhibits a binding energy for Li2S4 that is about 6 times higher than that of the CNT substrate, which may indicate that the ZnO surface has chemically friendly properties toward polysulfides (LiPS). It can also be confirmed that the LiPS binding energies on the ZnO substrate are about 5 to 16 times higher than those on carbon-based substrates (graphene, CNT) for other types of LiPS molecules, such as Li2S8, Li2S6, and more specifically, Li2S, Li2S2, Li2S4, Li2S6, Li2S8, and S8.

[0128] Referring to Fig. 6(d), the S 2p XPS spectrum of the ZnO NP substrate on which polysulfide (LiPS) is adsorbed can be compared with the spectrum of the bare CNT substrate (Comparative Example 1) to analyze the chemical interaction with the polysulfide (LiPS) molecules. The spectrum of the bare CNT substrate (Comparative Example 1) shows a strong intensity peak at 160 to 167 eV, which is the terminal S (S) indicating the physical adsorption of Li2S4. T -1 ; 161.38 eV, 162.34 eV) and bridging S (S B 0 ; can be deconvoluted into peaks corresponding to 163.57 eV, 164.61 eV). In contrast, the spectrum of the ZnO NP substrate is characterized by relatively strong peaks at 165–172 eV, which can be separated into peaks of polythionate (polythionate complex; 169.70 eV, 170.51 eV) and thiosulfate (thiosulphate, thiosulfate; 167.39 eV, 168.65 eV). This may indicate the chemical immobilization of polysulfide (LiPS) mediated by the thiosulfate-polythionate conversion on the zinc oxide (ZnO) surface. Therefore, the peaks appearing through the thiosulfate-polythionate conversion on the zinc oxide (ZnO) surface may indicate the formation of chemical bonds with polysulfide (LiPS) on ZnO. A zinc oxide nanoparticle layer chemically fixed to a carbon substrate may have higher adhesion compared to a nanoparticle coating layer formed by coating ZnO nanoparticles formed by a solution synthesis method described below.

[0129] Referring to Fig. 6(e) and Fig. 6(f), comparing the Li diffusivities analyzed by the Randles-Sevcik equation for each redox peak, it can be confirmed that the 12 nm-ZnO NP electrode has a higher diffusivity than the 6 nm-ZnO NP and 18 nm-ZnO NP electrodes. The Randles-Sevcik equation can be expressed by the following Equation 1.

[0130] [Formula 1]

[0131]

[0132] In the above equation 1, I p is the peak current of the CV curve, n is the number of electrons participating in the reaction, ν is the scan rate, D is the diffusion coefficient, A is the area of ​​the working electrode, and C is the electrolyte concentration.

[0133] Referring to Fig. 6(g), the charge transfer resistance between the substrate and electrode can be compared through the semicircle size of the electrochemical impedance spectrum results. Manufacturing Example 1 (denoted as 12 nm-ZnO NP) exhibits the smallest semicircle size, confirming that it has the smallest charge transfer resistance between the substrate and electrode.

[0134]

[0135] Figure 7 is a Tafel plot for a carbon nanotube electrode in which a zinc oxide (ZnO) nanoparticle layer is formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0136] Referring to Fig. 7, the kinetics of LiPS-Li2S conversion can be compared through the slope of the Tafel plot, and it can be confirmed that Manufacturing Example 1 (denoted as 12 nm-ZnO NP) shows the lowest slope and thus the fastest kinetics.

[0137]

[0138] FIG. 8 shows (a to d) potentiostatic current-time (it) curves of LiPS-Li2S conversion, (e to h) normalized current-time (it) curves (solid lines) and profiles (dotted lines) based on 2D and 3D electrodeposition models, and (i to l) ex-situ scanning electron microscope (SEM) images after precipitation discharge (scale bar: 500 nm) for carbon nanotube electrodes having a zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Comparative Example 1 and Manufacturing Examples 1 to 3 of the present invention.

[0139] Referring to Figs. 8(a-d) and 8(e-h), the current-time (it) curves were obtained using chronoamperometry, and under potentiostatic discharge conditions, the conversion step from LiPS to Li2S at the electrode in a lithium-sulfur battery cell accounts for 75% of the total discharge capacity, and is a diffusion-limited process involving electrode deposition from LiPS dissolved in the electrolyte solution to insoluble Li2S. The current-time (it) curves show a pattern in which the current initially rapidly decreases, reaches a peak current, and then gradually decreases. The section before reaching the peak current is the section in which Li2S nucleation saturates, and the subsequent current decrease is the section in which passivation of the electrode surface progresses during the coalescence of Li2S nuclei. The area under the current-time (it) curves (shaded portion) corresponds to the capacity of the lithium sulfide (Li2S) precipitation process. Comparative Example 1 (bare CNT) electrode showed low peak current and fast current decay, resulting in a low 254 mAh g -1 While the electrode of Preparation Example 1 (12 nm-ZnO NP) showed a slow current decay and the highest peak current of 517 mAh g -1It can be confirmed that the highest deposition capacity corresponding to Preparation Example 1 (12 nm-ZnO NP) is shown. This means that the capacity of Preparation Example 1 (12 nm-ZnO NP) is about 38% and about 45% higher than that of Preparation Example 2 (6 nm-ZnO NP) and Preparation Example 3 (18 nm-ZnO NP), respectively. This difference in capacity can be explained by the relatively low conversion rate observed in 18 nm-ZnO NP and the growth of Li2S in the form of three-dimensional (3D) particles on the electrode of Preparation Example 1 (12 nm-ZnO NP).

[0140] Referring to Fig. 8(i to l), it can be seen that a Li2S film is formed on the surface of the carbon nanotube electrodes (Preparation Examples 1 to 3, j to l) on which a zinc oxide (ZnO) nanoparticle layer is formed through a carbothermal reduction reaction after discharge. Growth exhibiting a 2D profile (2D growth) means that a uniform film is produced, characterized by growth by multiple nuclei generation and surface diffusion. In the Preparation Example 2 (6 nm-ZnO NP) electrode, the Li2S layer appeared as a mixed 2D and 3D profile and was formed so as not to completely cover the surface of the substrate. In addition, the Preparation Example 3 (18 nm-ZnO NP) electrode exhibited 2D growth similar to the growth observed in the Comparative Example 1 (bare CNT) electrode, and it could be confirmed that almost no ZnO nanoparticle layer was formed on the surface. Meanwhile, in the electrode of Manufacturing Example 1 (12 nm-ZnO NP), a 3D sulfide growth profile is observed, and it can be confirmed that Li2S nanoparticles on the surface of the substrate exhibit a 3D morphology on the electrode surface. Therefore, the electrode of Manufacturing Example 1 (12 nm-ZnO NP) can provide a very high discharge capacity and a fast conversion rate by inducing Li2S growth in a 3D morphology.

[0141]

[0142] FIG. 9 is a schematic diagram illustrating a mechanism for explaining the growth of Li2S through LiPS adsorption and conversion in an electrode (anode) of a lithium-sulfur electrode according to an embodiment of the present invention, wherein (a) an ultra-high-density zinc oxide (ZnO) nanoparticle layer (Preparation Example 1), (b) a low-density zinc oxide (ZnO) nanoparticle layer (Preparation Example 2), and (c) a thick zinc oxide (ZnO) nanoparticle layer (Preparation Example 3) are formed.

[0143] Referring to Figure 9, the carbon nanotube electrode coated with ultra-high-density zinc oxide (ZnO) nanoparticles (Figure 9(a), Preparation Example 1) exhibits abundant S4 due to rapid LiPS adsorption and conversion. 2- Li2S electrodeposition occurs in a diffuse three-dimensional (specifically, cluster-like particle) form, where a high concentration of S4 2- is mainly a solution-phase disproportionation reaction (2S4) 2- → S 2- + S7 2- ) and induces S 2- This bulk diffusion promotes the growth of Li2S in the form of three-dimensional clustered particles. On the other hand, in the carbon nanotube electrode coated with low-density zinc oxide (ZnO) nanoparticles (Fig. 9(b), Preparation Example 2), the adsorption rate of LiPS is relatively slow despite the rapid LiPS conversion, resulting in S4 2-As the concentration decreases, it does not drive the solution-phase reaction, resulting in the electrodeposition of 2D Li2S. In addition, in the carbon nanotube electrode formed with a thick zinc oxide (ZnO) nanoparticle layer (Fig. 9(c), Fabrication Example 3), sufficient etching is not performed due to the thick ZnO shell thickness, resulting in a high film density of the zinc oxide (ZnO) nanoparticle layer, so the LiPS adsorption rate is fast, but the exposure of the zinc oxide (ZnO) nanoparticle / carbon (CNT) interface is limited, leading to a slowdown in the LiPS adsorption and conversion rate, resulting in abundant S4 2- Since the environment cannot be created, the growth of Li2S is mainly induced in the form of a two-dimensional (2D) film.

[0144]

[0145] Example 1: Lithium-sulfur battery using a carbon nanotube electrode formed with a nanoparticle layer manufactured from a zinc oxide (ZnO) shell with a thickness of 12 nm as a cathode of a lithium-sulfur battery.

[0146] The carbon nanotubes formed with the zinc oxide (ZnO) nanoparticle layer of Manufacturing Example 1 were used as the cathode of a lithium-sulfur battery, and this was immersed in a lithium polysulfide (LiPS) electrolyte solution to adsorb the electrolyte to the electrode. The lithium polysulfide (LiPS) electrolyte solution was prepared by dissolving lithium sulfide (Li2S) and sulfur (S8) in a mixed organic solvent of 1,3-dioxolane (DOL) and dimethoxyethane (DME) (1:1 v / v%) at a molar ratio of 8:5 to prepare a polysulfide electrolyte with a concentration of 2 mM. Then, a 1 mm lithium foil (Li foil) was used as the anode, and the lithium-sulfur battery was manufactured by assembling it with a separator (Celgard 2400), and the battery performance was measured in a battery test system (Maccor 4300).

[0147]

[0148] Example 2: Lithium-sulfur battery using a carbon nanotube electrode formed with a nanoparticle layer manufactured from a 6 nm thick zinc oxide (ZnO) shell as a cathode of a lithium-sulfur battery.

[0149] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the carbon nanotubes having a zinc oxide (ZnO) nanoparticle layer formed in Manufacturing Example 2 were used as the cathode of the lithium-sulfur battery.

[0150]

[0151] Example 3: Lithium-sulfur battery using a carbon nanotube electrode formed with a nanoparticle layer manufactured from a zinc oxide (ZnO) shell with a thickness of 12 nm as a cathode of a lithium-sulfur battery.

[0152] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the carbon nanotubes having a zinc oxide (ZnO) nanoparticle layer formed in Manufacturing Example 3 were used as the cathode of the lithium-sulfur battery.

[0153]

[0154] Comparative Example 2: Lithium-sulfur battery using an untreated carbon nanotube electrode as the cathode of a lithium-sulfur battery.

[0155] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the carbon nanotubes of Comparative Example 1 were used as the cathode of the lithium-sulfur battery.

[0156]

[0157] Figure 10 shows (a) galvanostatic charge / discharge profiles of lithium-sulfur batteries using carbon nanotube electrodes having zinc oxide (ZnO) nanoparticle layers formed in Comparative Example 2 and Examples 1 to 3 of the present invention as cathodes, (b) comparison of voltage polarization at 0.03 C current density, (c) comparison of specific capacity at various C-rates, (d) charge / discharge cycle results at 2 C, (e) results of 300 charge / discharge cycles at 10 C, (f) results of 500 charge / discharge cycles at 2 C, (g) 10 to 12 mg cm -2 (E / S: 7 μL mg -1 ) Capacity comparison in electrodes with very high sulfur (S) loading (12 nm-ZnO NPs, Example 1) (Inset: 10 mg cm -2 (h) Capacity comparison with other studies at high sulfur (S) loading, (i) charge-discharge profile and (j) cycle performance graph when applying 12 nm-ZnO NP electrode (Example 1) under full-cell conditions.

[0158] Referring to FIGS. 10(a) to 10(c), the battery characteristics were compared between a lithium-sulfur battery using a carbon nanotube electrode having a zinc oxide (ZnO) nanoparticle layer formed thereon as a cathode and a lithium-sulfur battery using an untreated carbon nanotube electrode as a cathode. As a result of measuring the capacity for various C-rates from 0.2 C to 10 C, the cell applying the 12 nm-ZnO NP (Example 1) positive electrode showed a capacity retention rate of about 60% even after the C-rate increased 50-fold (10 C), and compared to the capacity retention rates of the cells applying the 6 nm-ZnO NP (Example 2), 18 nm-ZnO NP (Example 3), and untreated CNT (Comparative Example 2) positive electrodes, which were 52.2%, 50.4%, and 41.6%, respectively, it can be confirmed that the cell applying the 12 nm-ZnO NP (Example 1) positive electrode showed the highest capacity retention rate. In addition, the initial capacity at 10 C was 753 mAh g. -1 It can be confirmed that it exhibits stability with a capacity retention rate of 85% for 300 cycles.

[0159] Referring to FIGS. 10(d) to 10(f), the cycle performance at 2 C of a lithium-sulfur battery using a carbon nanotube electrode having a zinc oxide (ZnO) nanoparticle layer formed thereon as a cathode was confirmed, and the capacity decay rates per cycle of the 6 nm-ZnO NP (Example 2), 12 nm-ZnO NP (Example 1), and 18 nm-ZnO NP (Example 3) cells were 0.0902%, 0.0594%, and 0.0756%, respectively. Therefore, it can be confirmed that the 12 nm-ZnO NP (Example 1) cell exhibits the highest cycle stability. In addition, it was confirmed that the 12 nm-ZnO NP (Example 1) cell maintained a low capacity decay rate of 0.0381% even after 500 cycles of operation, and exhibited stable cycle operation up to 300 times even under high rate conditions of 10 C.

[0160] Referring to Figures 10(g) to 10(j), the battery performance was measured by increasing the sulfur loading amount to increase the energy density of the lithium-sulfur battery. The sulfur (S) loading amount (5 mg cm) that is commonly used -2 ) with a sulfur (S) loading higher than 10 mg cm -2 , 11 mg cm -2 and 12 mg cm -2 ) for the battery capacity evaluation, the initial capacity was 10.7 mAh cm for each loading condition at 0.1 C. -2 , 9.8 mAh cm -2 and 9.1 mAh cm -2 It can be confirmed that the sulfur loading per unit area (areal sulfur loading) is 7 mg cm -2 , E / S ratio (Electrolyte-to-sulfur ratio) is 4.5 μl mg -1 , when the N / P ratio is 1.76, the capacity per unit area of ​​the lithium-sulfur battery (full-cell) is 7.51 mAh cm -2 , reaching 6.82 mAh cm after 50 cycles. -2 It can be confirmed that the ultra-high density zinc oxide electrocatalytic nanoparticle layer coating of the 12 nm-ZnO NP anode can promote sulfur (S) conversion even in a high viscosity electrolyte.

[0161]

[0162] Comparative Example 3: Fabrication of a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles synthesized using a solution-based synthesis method (Solution process coating of ZnO)

[0163] Zinc oxide nanoparticles were synthesized by hydrothermal synthesis at 100°C for 2 hours using zinc nitrate hexahydrate (Zn(NO3)2·6H2O) as a precursor without using the carbothermal reduction method. Carbon nanotubes (CNTs) were immersed in a solution containing the synthesized zinc oxide nanoparticles and annealed at 500°C for 5 hours. Thus, a carbon nanotube electrode coated with zinc oxide nanoparticles synthesized by a solution-based method was manufactured.

[0164]

[0165] FIG. 11 is (a) a scanning electron microscope image (scale bar: 100 nm) and (c) a TGA result of a carbon nanotube electrode having an ultra-high-density zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Manufacturing Example 1 of the present invention, and (b) a scanning electron microscope image (scale bar: 100 nm) and (d) a TGA result of a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles through a solution-based nanoparticle synthesis method according to Comparative Example 3.

[0166] Referring to FIG. 11, the microstructure and film density of a carbon nanotube electrode formed with an ultra-high-density zinc oxide (ZnO) nanoparticle layer of Example 1 and a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles using a solution-based nanoparticle synthesis method of Comparative Example 3 can be compared. As a result, it can be confirmed that the method using carbothermal reduction (Example 1) has a nanoparticle layer with much smaller zinc oxide (ZnO) particles and a higher density than the method first synthesized using a solution-based method and then coated (Comparative Example 3). The particle size of the ultra-high-density zinc oxide (ZnO) nanoparticle layer formed by the carbothermal reduction reaction of Example 1 was found to be about 10 to 20 nm, which is about 4 to 10 times smaller than the size of zinc oxide (ZnO) particles synthesized using a solution-based synthesis method.

[0167]

[0168]

[0169] *Figure 12 is an absorbance spectrum for a carbon nanotube electrode having an ultra-high density zinc oxide (ZnO) nanoparticle layer formed through a carbon thermal reduction reaction according to Manufacturing Example 1 of the present invention and a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles through a solution-based nanoparticle synthesis method according to Comparative Example 3.

[0170] Referring to FIG. 12, the lithium polysulfide (LiPS) adsorption capacity and LiPS-Li2S potentiostatic conversion of a carbon nanotube electrode having an ultra-high-density zinc oxide (ZnO) nanoparticle layer formed in Example 1 and a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles using a solution-based nanoparticle synthesis method in Comparative Example 3 can be compared. As a result, the electrode prepared by carbothermal reduction (Example 1) exhibits about twice the lithium polysulfide (LiPS) adsorption capacity compared to the electrode first synthesized and coated using a solution-based method (Comparative Example 3), and although the materials and compositions constituting the nanoparticle coating layer are similar, the electrode prepared by carbothermal reduction (Example 1) has a much smaller particle size and thus has a higher lithium polysulfide (LiPS) adsorption capacity.

[0171]

[0172] FIG. 13 shows (a) a potentiostatic current-time (it) curve, (b) a normalized current-time (it) curve (solid line) and a profile based on 2D and 3D electrodeposition models (dotted line), and (c) an ex-situ scanning electron microscope (SEM) image after discharge (scale bar: 100 nm) for a carbon nanotube electrode on which a layer of ultra-high-density zinc oxide (ZnO) nanoparticles is formed through a carbon thermal reduction reaction according to Manufacturing Example 1 of the present invention, and (a) a potentiostatic current-time (it) curve, (b) a normalized current-time (it) curve (solid line) and a profile based on 2D and 3D electrodeposition models (dotted line), and (c) an ex-situ scanning electron microscope (SEM) image after discharge (scale bar: 100 nm) for a carbon nanotube electrode coated with zinc oxide (ZnO) nanoparticles through a solution-based nanoparticle synthesis method according to Comparative Example 3.

[0173] Referring to Fig. 13, the electrode of Comparative Example 3 (solution coating) showed a low peak current and a fast current decay, resulting in a low 330 mAh g -1 While the electrode of Manufacturing Example 1 (Dry coating) showed a slow current decay and the highest peak current of 517 mAh g -1 It can be confirmed that the electrode of Manufacturing Example 1 (Dry coating) exhibits the highest deposition capacity. In addition, a 3D sulfide growth profile is observed in the electrode of Manufacturing Example 1 (Dry coating), and it can be confirmed that Li2S nanoparticles on the surface of the substrate exhibit a 3D shape on the electrode surface. Therefore, the electrode of Manufacturing Example 1 (Dry coating) can provide a very high discharge capacity and a fast conversion rate because it induces Li2S growth in a 3D shape.

[0174]

[0175] 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 step (S01) of positioning a carbon substrate inside a chamber and injecting two or more precursors to form a metal oxide shell on the surface of the carbon substrate; and A step (S02) of performing a carbon thermal reduction reaction on a carbon substrate on which a metal oxide shell is formed to form a metal oxide nanoparticle layer on the surface of the carbon substrate; A method for manufacturing an electrode for a lithium-sulfur battery, characterized in that the metal oxide nanoparticle layer is formed by dry etching at least a portion of the metal oxide shell through reductive sublimation.

2. In paragraph 1, A method for manufacturing an electrode for a lithium-sulfur battery, wherein dry etching of the metal oxide shell through the above carbon thermal reduction reaction is performed by a reaction represented by the following reaction formula 1: [Reaction Formula 1] yC + M x O y → xM(g) + yCO(g) In the above reaction formula 1, M includes any one selected from Zn, Fe, Ni, Cu, W, Ti, Mn, Al, Ti, Co, and combinations thereof, and x and y are independent arbitrary integers.

3. In paragraph 1, A method for manufacturing an electrode for a lithium-sulfur battery, wherein as the carbon thermal reduction reaction time increases, the thickness of the metal oxide nanoparticle layer decreases and the film density of the metal oxide nanoparticle layer decreases.

4. In paragraph 1, A method for manufacturing an electrode for a lithium-sulfur battery, wherein a metal oxide nanoparticle layer formed through the above carbon thermal reduction reaction is chemically fixed to the carbon substrate.

5. In paragraph 1, A method for manufacturing an electrode for a lithium-sulfur battery, wherein the metal oxide content of the electrode for the lithium-sulfur battery is 5 to 25 wt% based on the total weight.

6. In paragraph 1, The sulfur loading of the above lithium-sulfur battery electrode is 5 to 20 mg cm -2 A method for manufacturing an electrode for a lithium-sulfur battery.

7. In paragraph 1, The above carbon thermal reduction reaction is performed by performing a first heat treatment in a first temperature range and a second heat treatment in a second temperature range, The second temperature range is higher than the first temperature range, A method for manufacturing an electrode for a lithium-sulfur battery, wherein the second temperature range is 300°C or higher.

8. Carbon substrate; and A metal compound nanoparticle layer formed on the surface of the carbon substrate; An electrode for a lithium-sulfur battery, characterized in that the metal compound nanoparticle layer is chemically fixed to the surface of the carbon substrate.

9. In paragraph 8, The above lithium-sulfur battery electrode is an electrode for a lithium-sulfur battery that induces the growth of lithium sulfide in a three-dimensional (3D) particle form during the charge / discharge process of the battery.

10. In paragraph 8, An electrode for a lithium-sulfur battery, wherein the metal compound nanoparticle layer is formed by dry etching at least a portion of a metal oxide shell formed on the surface of the carbon substrate by an atomic layer deposition method through reductive sublimation.

11. In paragraph 8, An electrode for a lithium-sulfur battery, wherein the metal oxide content of the electrode for the lithium-sulfur battery is 5 to 25 wt% based on the total weight.

12. In paragraph 8, The sulfur loading of the above lithium-sulfur battery electrode is 5 to 20 mg cm -2 Electrode for lithium-sulfur batteries.

13. A positive electrode including an electrode for a lithium-sulfur battery, comprising: a carbon substrate; and a metal compound nanoparticle layer formed on the surface of the carbon substrate; wherein the metal compound nanoparticle layer is chemically fixed to the surface of the carbon substrate; A cathode disposed opposite to the positive electrode and comprising lithium metal or a lithium alloy; A separator disposed between the positive electrode and the negative electrode and suppressing polysulfide movement but for the transfer of lithium ions; and A lithium-sulfur battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

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