Lithium electrode and lithium secondary battery containing the same

Abstract

The present invention relates to a lithium electrode and a lithium secondary battery comprising the lithium electrode. More specifically, it suppresses the formation of dendrites and improves the transmission characteristics of lithium ions by arranging a protective layer comprising a two-dimensional material and an intrinsic microporous polymer on the surface of a lithium metal layer, thereby extending the life of the lithium secondary battery.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0071605 filed on June 2, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a lithium electrode and a lithium secondary battery comprising the lithium electrode. Background Art

[0003] As the use of lithium secondary batteries is expanded not only to portable electronic devices and communication devices but also to electric vehicles (EVs) and energy storage systems (ESSs), there is an increasing demand for higher capacity and higher energy density of lithium secondary batteries used as their power sources.

[0004] Conventional lithium secondary batteries have an energy density of 700Wh / kg by using graphite as the negative electrode and lithium cobalt oxide (LCO) as the positive electrode. However, as mentioned above, in recent years, the field of lithium secondary batteries requiring high energy density is expanding, so there is a continuous need to increase the energy density of lithium secondary batteries. For example, even in order to increase the driving range of electric vehicles on a single charge to more than 500 kilometers, it is necessary to increase the energy density.

[0005] In order to increase the energy density of lithium secondary batteries, the use of lithium electrodes containing lithium metal is increasing. Specifically, the advantage is that lithium metal not only has a very high theoretical specific capacity of 3860mAh / g, but also has a very low standard hydrogen electrode (SHE) of -3.045V, so it is possible to achieve a battery with high capacity and high energy density.

[0006] However, due to the high reactivity of lithium metal and the difficulty in handling, there is a problem of being difficult to handle in the process. In addition, when the lithium electrode is used as the negative electrode of a lithium secondary battery, the lithium metal easily reacts with electrolytes, water, or impurities or lithium salts in the battery, thereby forming a solid electrolyte interface layer (SEI layer) on the surface, which is a passivation layer. Such a passivation layer causes local current density differences, thereby promoting the formation of dendrites caused by lithium metal during charging, and the dendrites gradually grow during charge / discharge, causing an internal short circuit between the positive and negative electrodes. In addition, the dendrites have a mechanically weak part (bottleneck), thereby forming inert lithium (dead lithium), which loses electrical contact with the collector during discharge, thereby reducing the battery capacity, shortening the cycle life, and adversely affecting the stability of the battery.

[0007] In order to improve the problems of the lithium electrode as described above, a lithium electrode in which a protective layer having various compositions or shapes is formed is being studied.

[0008] For example, Korean Patent Publication No. 2018-0041086 relates to a protective layer formed by applying a slurry containing carbon fluoride or metal fluoride and a PVdF-based resin to a lithium metal negative electrode. The lithium metal negative electrode on which the protective layer containing the above components is formed can prevent the formation of dendrites. However, there is a problem that the uniform distribution of lithium ions on the negative electrode surface and the formation of an effective solid electrolyte interface layer that enables uniform plating and stripping of lithium metal during charge / discharge to improve battery performance are not smooth.

[0009] In addition, Korean Patent Publication No. 2016-0052351 discloses that by incorporating a lithium dendrite absorbing material into a polymer protective film formed on the surface of a lithium metal electrode, the growth of lithium dendrites can be suppressed, thereby improving the stability and life characteristics of a lithium secondary battery. However, due to the polymer protective film, it is difficult to evenly distribute lithium ions on the electrode surface and it is difficult to apply it to a lithium-sulfur battery.

[0010] In addition, Qiuli Yang et al. and Gi Hyeon Moon et al. disclosed that the formation of dendrites can be suppressed by forming a protective film on a lithium metal negative electrode using an intrinsic microporous polymer (PIM) having inherent pores in the polymer structure, thereby uniformly distributing lithium ions on the surface of the lithium metal negative electrode. However, when the protective film formed on the lithium metal negative electrode contains only a polymer having intrinsic microporosity, since lithium ions can only move through the pores contained in the polymer having intrinsic microporosity, there is a problem of reduced conductivity of lithium ions, and a large overvoltage occurs during charge / discharge.

[0011] As described above, to date, some research has been conducted on the development of a protective layer to prevent the growth of dendrites of lithium metal in a battery using a lithium electrode as a negative electrode. However, the research results on a protective layer capable of improving the overall performance of the battery are not sufficient. Therefore, there is still a need to develop a lithium electrode that can achieve a lithium secondary battery with high capacity, high energy density and long life by preventing the formation of dendrites on the lithium electrode.

[0012] [Prior art literature]

[0013] [Patent Document]

[0014] (Patent Document 1) Korean Patent Publication No. 2018-0041086 (April 23, 2018), Negative electrode for lithium ion secondary battery and method for manufacturing the same

[0015] (Patent Document 2) Korean Patent Publication No. 2016-0052351 (May 12, 2016), Lithium metal electrode for lithium secondary battery with safety protection layer and lithium secondary battery including the same

[0016] [Non-patent literature]

[0017] (Non-patent document 1) Qiuli Yang et al., PIM-1 as an artificial solid electrolyte interphase forstable lithium metal anode in high-performance batteries, Journal of Energy Chemistry, 2020, 42, 83-90

[0018] (Non-patent document 2) Gi Hyeon Moon et al., An artificial solid interphase with polymers of intrinsic microporosity for highly stable Li metal anodes, Chemical Communications, 2019, 55, 6313-6316. Summary of the invention

[0019] Technical issues

[0020] Therefore, as a result of various studies conducted to solve the above-mentioned problems, the inventors of the present invention have confirmed that when a protective layer containing a two-dimensional material and an intrinsic microporous polymer is formed on a lithium electrode, dendrite formation can be prevented and excellent lithium ion transport performance can be exhibited, thereby improving the performance of a battery containing it, and the inventors of the present invention have thus completed the present invention.

[0021] Therefore, an object of the present invention is to provide a lithium electrode having a protective layer, wherein the protective layer can suppress the formation of dendrites and has lithium ion transport properties, thereby improving the life characteristics of a lithium secondary battery.

[0022] Furthermore, another object of the present invention is to provide a lithium secondary battery comprising the above lithium electrode.

[0023] Technical Solution

[0024] In order to achieve the above objectives,

[0025] The present invention provides a lithium electrode, comprising:

[0026] a lithium metal layer; and a protective layer formed on at least one surface of the lithium metal layer,

[0027] The protective layer comprises a two-dimensional material and an intrinsically microporous polymer.

[0028] In addition, the present invention provides a method for manufacturing a lithium electrode, comprising the following steps:

[0029] (a) dispersing a two-dimensional material in a first solvent to prepare a first solution;

[0030] (b) dissolving an intrinsically microporous polymer in a second solvent to prepare a second solution;

[0031] (c) mixing the first solution and the second solution to prepare a coating solution; and

[0032] (d) applying the coating solution onto at least one surface of the lithium metal layer.

[0033] In addition, the present invention provides a lithium secondary battery including the lithium electrode.

[0034] Beneficial Effects

[0035] The protective layer according to the present invention includes a two-dimensional material and an intrinsically microporous polymer and is therefore effective against dendrite formation and can also exhibit excellent lithium ion transport properties, thereby improving the life of a lithium secondary battery including the protective layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 These are photographs showing the surfaces of lithium electrodes used in Examples 1 to 4 and Comparative Example 1 ((a): Example 1, (b): Example 2, (c): Example 3, (d): Example 4, (e): Comparative Example 1).

[0037] Figure 2 Photographs of the surfaces of the lithium electrodes according to Examples 1 to 4 taken with a scanning electron microscope are shown.

[0038] Figure 3 3 is a graph showing the evaluation results of the life characteristics of the lithium-sulfur battery according to Experimental Example 2.

[0039] Figure 4 3 is a graph showing the evaluation results of the capacity retention rate of the lithium-sulfur battery according to Experimental Example 2. DETAILED DESCRIPTION

[0040] Hereinafter, the present invention will be described in more detail.

[0041] The terms and words used in this specification and claims should not be construed as limited to common or dictionary terms, but should be interpreted according to the meaning and concept consistent with the technical concept of the present invention based on the principle that the inventor can appropriately define the concept of the term to describe his invention in the best possible way.

[0042] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It should be understood that the terms "including" or "having" as used in this specification are intended to specify the presence of the features, quantities, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts or combinations thereof.

[0043] When a lithium electrode including lithium metal is used as a negative electrode of a lithium secondary battery, the following problems may occur.

[0044] First, lithium metal is difficult to handle because it is highly reactive and mechanically weak.

[0045] Secondly, lithium metal reacts with electrolytes, water, or impurities or lithium salts in the battery to form a solid electrolyte interface layer (SEI layer) as a passivation layer on the surface of lithium metal. Such a solid electrolyte interface layer causes local current density differences, thereby forming dendrites. In addition, the growth of the dendrites formed thereby causes an internal short circuit in the battery and forms inert lithium, which leads to battery performance degradation or explosion.

[0046] Thirdly, when the positive electrode contains sulfur-based materials, there is lithium polysulfide (Li 2 S x , x = 8, 6, 4, 2) and lithium metal have side reactions. Therefore, with the lithium sulfide (Li 2 S) adheres to the surface of lithium metal, thereby passivating the lithium electrode and reducing the electrochemical reactivity of the lithium electrode.

[0047] In order to solve these problems, various materials are used to form a protective layer on lithium metal in the prior art. However, the problem of dendrite generation has not been effectively improved, and there is a problem of deterioration in the capacity and life characteristics of the battery and the operating stability.

[0048] Therefore, the present invention provides a lithium electrode that can realize a lithium secondary battery with excellent capacity, life and operational stability by forming a protective layer comprising a two-dimensional material and an intrinsic microporous polymer (PIM) on the surface of lithium metal, thereby preventing the formation of dendrites and improving the transport characteristics of lithium ions.

[0049] Specifically, the lithium electrode according to the present invention includes a lithium metal layer; and a protective layer formed on at least one surface of the lithium metal layer, wherein the protective layer includes a two-dimensional material and an intrinsic microporous polymer.

[0050] In particular, the protective layer according to the present invention can suppress the generation of dendrites and ensure that the conductivity of lithium ions is higher than a certain level by including an intrinsic microporous polymer and a two-dimensional material together. Such an intrinsic microporous polymer contains micropores, so it is possible to provide a uniform channel for lithium ions. Therefore, it is known in the prior art to use it as a protective layer for lithium electrodes to suppress the growth of dendrites. However, in the case of the prior art, a satisfactory prevention effect on the generation of dendrites cannot be ensured, and if the protective layer of the lithium electrode only contains an intrinsic microporous polymer, then since only lithium ions may move through the micropores contained in the intrinsic microporous polymer, there is a problem that the lithium ion conductivity of the lithium electrode itself is reduced, so a large overvoltage occurs during the charge / discharge process, thereby adversely affecting the overall performance of the battery. On the other hand, as described above, in the present invention, by introducing a protective layer containing both an intrinsic microporous polymer and a two-dimensional material on the lithium metal layer, so that lithium ions are uniformly distributed on the lithium metal layer, the formation of dendrites can be suppressed, excellent lithium ion transport characteristics are obtained, and the capacity and life characteristics of the lithium secondary battery containing it are improved.

[0051] In the present invention, the lithium metal layer comprises lithium metal, and the lithium metal may comprise a lithium metal film in the form of a foil or sheet, or a lithium metal powder in which the lithium metal is aggregated in the form of particles. In addition, the lithium metal layer may be in the form of a lithium metal plate, wherein the lithium metal film is formed on at least one surface of the current collector.

[0052] The current collector is used to support the lithium metal layer and is not particularly limited as long as it has high conductivity and does not cause chemical changes in the lithium secondary battery. As the current collector, for example, copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon; copper or stainless steel surface-treated with carbon, nickel, silver, etc.; aluminum-cadmium alloy, etc. can be used.

[0053] The current collector may have fine concavities and convexities on its surface to improve the bonding force with lithium metal, and may be formed in various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, or a nonwoven fabric.

[0054] There is no particular limitation on the method for forming the lithium metal thin film on the current collector, and a method for forming a layer or film commonly used in the art can be used. For example, a method such as pressing, coating or vapor deposition can be used.

[0055] As described above, when a lithium metal thin film as a lithium metal layer is formed on one surface of a current collector, a protective layer to be described later may be formed on the entire surface of the lithium metal thin film except for a surface of the lithium metal thin film in contact with the current collector.

[0056] In addition, when the current collector is a porous current collector, lithium metal may be contained in the pores of the porous current collector. In this case, a protective layer described later may be provided on the entire surface of the porous current collector except for a terminal connected to the porous current collector and extending to the outside.

[0057] The thickness of the lithium metal layer may be 20 to 200 μm, preferably 25 to 100 μm, and more preferably 30 to 80 μm. If the thickness of the lithium metal layer is less than the above range, the capacity and life characteristics of the battery may be reduced. On the contrary, if the thickness of the lithium metal layer exceeds the above range, the thickness of the lithium electrode may become thicker, which may be detrimental to commercialization.

[0058] In the present invention, the protective layer comprises a two-dimensional material and an intrinsically microporous polymer.

[0059] The two-dimensional material is a substance in which atoms have a single atomic thickness and form a crystal structure in a two-dimensional plane. It has a plate-like, thin-sheet, or sheet-like shape of a certain thickness, and can be divided into conductors, semiconductors, and insulators according to electrical properties. The two-dimensional material maximizes the number of lithium ion transfers of the protective layer formed on the lithium metal, thereby not only improving the lithium ion transfer properties of the protective layer, but also improving the mechanical strength of the protective layer.

[0060] The two-dimensional material may include at least one selected from the group consisting of graphene, graphene oxide (GO), transition metal dichalcogenide, hexagonal boron nitride (h-BN) and graphite carbon nitride (g-C3N4). The transition metal chalcogenide is a compound having a two-dimensional layered structure composed of a transition metal element such as tungsten (W) or molybdenum (Mo) and a chalcogenide element such as sulfur (S), and specifically may be molybdenum disulfide (MoS 2 ), tungsten disulfide (WS 2 ) etc. Preferably, the two-dimensional material may include at least one selected from the group consisting of graphene oxide and graphite-phase carbon nitride.

[0061] The intrinsically microporous polymer (PIM) is a polymer with a very rigid but distorted structural backbone, thereby disturbing the arrangement of polymer chains through strong intermolecular interactions and forming a free volume formed by connecting functional groups, resulting in micropores in the structure. Therefore, the intrinsically microporous polymer contains micropores smaller than 2 nm and has a diameter of 300 nm formed by these micropores. 2 / g or more very high specific surface area.

[0062] As described above, since the intrinsic microporous polymer has a microporous structure, when used as a protective layer for a lithium electrode, it forms uniform lithium ion channels on the surface of the lithium metal layer, making the current density distribution uniform, thereby suppressing the formation of dendrites.

[0063] Specifically, the intrinsic microporous polymer may be a polymer (PIM-1) comprising a repeating structure represented by the following Formula 1:

[0064] [Formula 1]

[0065]

[0066] The polymer (PIM-1) including the repeating structure represented by Formula 1 may have a weight average molecular weight (Mw) of 1,000 to 100,000 g / mol, preferably 3,000 to 60,000 g / mol, and more preferably 5,000 to 50,000 g / mol.

[0067] In the protective layer, the two-dimensional material and the intrinsic microporous polymer may be contained in a weight ratio of 1:1 to 1:20, preferably 1:5 to 1:18, and more preferably 1:7 to 1:12. In the present invention, the weight ratio corresponds to the ratio of "weight % of two-dimensional material": "weight % of intrinsic microporous polymer". If the weight ratio of the two-dimensional material to the intrinsic microporous polymer is within the above range, it can exhibit excellent lithium ion conductivity while having an excellent effect of inhibiting dendrite formation. If the weight ratio of the two-dimensional material to the intrinsic microporous polymer is less than the above range, coating imbalance may occur and battery performance may be reduced. On the contrary, if the weight ratio exceeds the above range, the problem of increased resistance may occur.

[0068] The thickness of the protective layer may be 0.1 to less than 5 μm, preferably 0.2 to 3 μm, and more preferably 0.5 to 1.5 μm. Considering the desired performance of the battery, the protective layer may be formed to have an appropriate thickness. If the thickness of the protective layer is less than the above range, there is a concern that the intended function as a protective layer may not be performed. On the contrary, if the thickness exceeds the above range, the capacity of the battery will be reduced due to overvoltage, and there may be a problem that the battery cannot operate at a high rate.

[0069] The lithium ion conductivity of the protective layer according to the present invention comprising the above components can be 10 -20 Up to 10 -4 S / cm, preferably 10 -10 Up to 10 -5Compared with a lithium electrode including a conventional protective layer made of only an intrinsic microporous polymer, the lithium electrode according to the present invention can exhibit excellent lithium ion conductive properties by including a protective layer containing a two-dimensional material and an intrinsic microporous polymer.

[0070] In addition, the surface resistance of the lithium electrode with the protective layer according to the present invention in the electrolyte is 50 to 300Ω, preferably 100 to 200Ω, more preferably 120 to 150Ω, and there is no resistance change for 1 to 72 hours, preferably 24 to 65 hours, more preferably 36 to 60 hours. This means that the protective layer comprising the two-dimensional material and the intrinsic microporous polymer does not react with the electrolyte and remains in a stable state.

[0071] In the present invention, there is no particular limitation on the method for producing the lithium electrode, and a method known to those skilled in the art or various methods modified therefrom can be used.

[0072] As an example, a method for manufacturing a lithium electrode includes the following steps:

[0073] (a) dispersing a two-dimensional material in a first solvent to prepare a first solution;

[0074] (b) dissolving an intrinsically microporous polymer in a second solvent to prepare a second solution;

[0075] (c) mixing the first solution and the second solution to prepare a coating solution; and

[0076] (d) applying the coating solution onto at least one surface of the lithium metal layer.

[0077] Specific examples of the two-dimensional material and the intrinsic microporosity polymer are as described above.

[0078] The first solvent and the second solvent for preparing the coating solution may be at least one selected from the group consisting of tetrahydrofuran (THF), toluene, cyclohexane, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), tetramethylurea, dimethyl sulfoxide (DMSO) and triethyl phosphate. Since the two-dimensional material and the intrinsic microporous polymer have high solubility and are conducive to forming a protective layer through a coating process, tetrahydrofuran is preferably used as the first solvent and the second solvent.

[0079] The content of the first solvent and the second solvent may be a level having a concentration sufficient to promote coating, and the specific content varies depending on the coating method and equipment.

[0080] When preparing the first solution and the second solution, the respective contents of the two-dimensional material and the intrinsic microporous polymer are appropriately adjusted in consideration of their weight ratio in the above-mentioned protective layer.

[0081] The coating method of the coating solution for forming the protective layer may be, but is not limited to, a method selected from the group consisting of dip coating, spray coating, spin coating, die coating, roller coating, slot die coating, rod coating, gravure coating, comma coating, curtain coating and micro gravure coating, as well as various coating methods available in the art for forming a coating layer.

[0082] After coating, a drying process for removing the solvent may be performed. The drying process is performed at a temperature and time sufficient to fully remove the solvent, and the conditions may vary depending on the type of solvent, and therefore are not particularly limited in the present invention. As an example, a drying method using warm air, hot air or low-humidity air, a vacuum drying method, or a drying method using (far) infrared rays and electron beams is mentioned. The drying speed is usually adjusted so that the solvent is removed as quickly as possible within a speed range that does not cause the protective layer to rupture or the lithium metal layer to be peeled off from the collector due to stress concentration.

[0083] The thickness of the protective layer formed by the above manufacturing method can be 0.1 to less than 5 μm, preferably 0.2 to 3 μm, more preferably 0.5 to 1.5 μm. The protective layer can inhibit the formation of dendrites and improve the transport characteristics of lithium ions, thereby increasing the life characteristics of the lithium secondary battery containing the protective layer.

[0084] Furthermore, the present invention provides a lithium secondary battery including the lithium electrode.

[0085] The lithium secondary battery comprises a positive electrode; a negative electrode; and an electrolyte interposed therebetween, wherein the negative electrode comprises the lithium electrode according to the present invention.

[0086] The positive electrode may include a positive electrode collector and a positive electrode active material layer formed on one or both surfaces of the positive electrode collector.

[0087] As described above, the positive electrode current collector is used to support the positive electrode active material.

[0088] The positive electrode active material layer includes a positive electrode active material, and may further include a conductive material, a binder, or an additive.

[0089] There is no particular limitation on the positive electrode active material in terms of its material, as long as the positive electrode active material can be applied to a lithium secondary battery to reduce lithium ions during discharge and oxidize lithium ions during charge. For example, the positive electrode active material may be a transition metal oxide or a sulfur (S)-based compound. Specifically, the positive electrode active material may include at least one of the following: a layered compound, such as lithium cobalt oxide (LiCoO2 ), lithium nickel oxide (LiNiO 2 ), or compounds replaced by one or more transition metals; lithium manganese oxides, such as Li 1+x Mn 2-x O 4 (0≤x≤0.33), LiMnO 3 、LiMn 2 O 3 and LiMnO 2 ; Lithium copper oxide (Li 2 CuO 2 ); Vanadium oxides, such as LiV 3 O 8 、V 2 O 5 and Cu 2 V 2 O 7 ; LiNi 1- x M x O 2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga; 0.01≤x≤0.3) represented by Ni-site lithium nickel oxide; represented by the formula LiMn 2-x M x O 2 (wherein M = Co, Ni, Fe, Cr, Zn or Ta; 0.01≤x≤0.1) or Li 2 Mn 3 MO 8 (wherein M = Fe, Co, Ni, Cu or Zn) represented by a lithium manganese composite oxide; LiNi x Mn 2-x O 4 The spinel structure of lithium-manganese composite oxide represented by LiCoPO 4 ;LiFePO 4 Elemental sulfur (S 8 ); sulfur compounds, such as Li 2 Sn (n ≥ 1), organic sulfur compounds or carbon-sulfur polymers ((C 2 S x ) n :x=2.5~50,n≥2).

[0090] If the positive electrode active material is a sulfur-containing compound, the lithium secondary battery may be a lithium-sulfur battery.

[0091] In addition, if the positive electrode active material is elemental sulfur, it is used in combination with a conductive material such as a porous carbon material because it alone does not have conductivity. In this case, the positive electrode active material may be a sulfur-carbon composite.

[0092] The porous carbon material provides a framework capable of uniformly and stably fixing sulfur as a positive electrode active material, and supplements the low conductivity of sulfur, allowing the electrochemical reaction to proceed smoothly.

[0093] The porous carbon material may have a porous structure or a high specific surface area, and may be any material commonly used in the art. For example, the porous carbon material may be, but is not limited to, at least one selected from the group consisting of: graphite; graphene; carbon blacks such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; carbon nanotubes (CNTs), such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); and graphites such as natural graphite, artificial graphite, expanded graphite, and activated carbon.

[0094] Based on 100 parts by weight of the sulfur-carbon composite, the sulfur-carbon composite may contain 60 to 90 parts by weight, preferably 65 to 85 parts by weight, and more preferably 70 to 80 parts by weight of sulfur. If the sulfur content is lower than the above range, the content of the porous carbon material in the sulfur-carbon composite increases relatively, the specific surface area increases, and the content of the binder increases in the manufacture of the positive electrode. The increase in the amount of such binders may eventually increase the sheet resistance of the positive electrode and act as an insulator to block the passage of electrons, thereby reducing the performance of the battery. On the contrary, if the sulfur content exceeds the above range, the sulfur that is not combined with the porous carbon material agglomerates with each other or re-leaches to the surface of the porous carbon material, and therefore may be difficult to receive electrons and cannot participate in the electrochemical reaction, resulting in a loss of battery capacity.

[0095] In addition, the sulfur in the sulfur-carbon composite is located on at least one of the inner surface and the outer surface of the porous carbon material. In this case, the area in which it exists can account for less than 100% of the entire inner and outer surfaces of the porous carbon material, preferably 1% to 95%, and more preferably 60% to 90%. If the above sulfur exists on the inner and outer surfaces of the porous carbon material within the above range, the maximum effect can be exhibited in terms of electron transfer area and wettability to the electrolyte. Specifically, since the sulfur is thinly and uniformly impregnated on the inner and outer surfaces of the porous carbon material within the above range, it is possible to increase the electron transfer contact area during the charge / discharge process. If the sulfur is located in 100% of the area of ​​the entire inner and outer surfaces of the porous carbon material, since the carbon material is completely covered with sulfur, the wettability to the electrolyte is reduced, and the contact with the conductive material contained in the electrode is reduced, so that it cannot accept electron transfer and therefore cannot participate in the electrochemical reaction.

[0096] In the present invention, there is no particular limitation on the method for preparing the sulfur-carbon composite, and a method commonly used in the art can be used. As an example, a method of simply mixing sulfur and a porous carbon material and then heat-treating them to form a composite can be used.

[0097] Based on the total weight of 100 weight percent of the positive electrode active material layer constituting the positive electrode, the content of the positive electrode active material may be 40 to 95 weight percent, preferably 50 to 90 weight percent, and more preferably 60 to 85 weight percent. If the content of the positive electrode active material is lower than the above range, it is difficult for the electrode to fully perform an electrochemical reaction. On the contrary, if the content of the positive electrode active material exceeds the above range, there is a problem that the content of the conductive material and the binder to be described later is relatively insufficient, thereby increasing the resistance of the positive electrode and deteriorating the physical properties of the positive electrode.

[0098] The positive electrode active material layer may optionally further include a conductive material for smoothly moving electrons in the positive electrode and a binder for well adhering the positive electrode active material to the current collector.

[0099] The conductive material is a material that electrically connects the electrolyte and the positive electrode active material to serve as a path for electrons to move from the current collector to the positive electrode active material, and any conductive material may be used without limitation as long as it has conductivity.

[0100] For example, as the conductive material, the following can be used alone or in combination: graphite, such as natural graphite and artificial graphite; carbon black, such as Super-P, Danka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon black; carbon derivatives, such as carbon nanotubes and fullerenes; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; or conductive polymers, such as polyaniline, polythiophene, polyacetylene and polypyrrole.

[0101] Based on the total weight of the positive electrode active material layer 100 weight %, the content of the conductive material can be 0.01 to 30 weight %. If the content of the conductive material is lower than the above range, it is difficult to transfer electrons between the positive electrode active material and the current collector, thereby reducing the voltage and capacity. On the contrary, if the content of the conductive material exceeds the above range, the proportion of the positive electrode active material may be reduced, thereby reducing the total energy (charge) of the battery. Therefore, it is preferred that the content of the conductive material is determined to be an appropriate content within the above range.

[0102] The binder holds the positive electrode active material in the positive electrode current collector and organically connects the positive electrode active materials to further increase the binding force therebetween. Any binder known in the art may be used as the binder.

[0103] For example, the adhesive can be a fluororesin-based adhesive, including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); a rubber-based adhesive, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber and styrene-isoprene rubber; a cellulose-based adhesive, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose and regenerated cellulose; a polyol-based adhesive; a polyolefin-based adhesive, including polyethylene and polypropylene; a polyimide-based adhesive; a polyester-based adhesive; and a silane-based adhesive, or a mixture or copolymer of two or more thereof.

[0104] Based on the total weight of the positive electrode active material layer 100 weight %, the content of the binder can be 0.5 to 30 parts by weight. If the content of the binder is lower than the above range, the physical properties of the positive electrode may deteriorate, so the positive electrode active material, additives and conductive materials in the positive electrode may fall off. If the content exceeds the above range, the capacity of the battery may be reduced due to the relative decrease in the ratio of the positive electrode active material to the conductive material in the positive electrode. Therefore, it is preferred to appropriately determine the content within the above range.

[0105] In the present invention, there is no particular limitation on the method for producing the positive electrode for a lithium-sulfur battery, and a method known to those skilled in the art or various modified methods thereof may be used.

[0106] For example, the positive electrode for a lithium-sulfur battery may be manufactured by preparing a positive electrode slurry composition including the above components and then applying it onto at least one surface of a positive electrode collector to form a positive electrode active material layer.

[0107] The slurry composition for a positive electrode includes the positive electrode active material, a conductive material, a binder, and an additive as described above, and further, may include a solvent.

[0108] As a solvent, a solvent that can evenly disperse the positive electrode active material, additives, conductive materials and binder is used. As such a solvent, water is the most preferred as an aqueous solvent. At this time, water can be distilled water or deionized water, but it is not necessarily limited thereto. If necessary, a lower alcohol that can be easily mixed with water can be used. Examples of the lower alcohol can include methanol, ethanol, propanol, isopropanol and butanol. Preferably, they can be mixed with water for use.

[0109] The solvent may be present at such concentration levels to facilitate coating, with the specific amount varying depending on the coating method and equipment.

[0110] If necessary, the slurry composition for positive electrode may further contain materials commonly used in the related technical field in order to improve its function. For example, a viscosity modifier, a fluidizer, a filler, etc. may be mentioned.

[0111] In the present invention, there is no particular limitation on the coating method of the positive electrode slurry composition, and for example, methods such as doctor blade, die casting, comma coating, and screen printing can be mentioned. In addition, after forming on a separate substrate, the positive electrode slurry composition can be coated on the positive electrode collector by pressing or laminating.

[0112] After coating, a drying process for removing the solvent may be performed. The drying process is performed at a temperature and time at a level at which the solvent can be fully removed, and the conditions may vary depending on the type of solvent, and therefore are not particularly limited in the present invention. As examples, drying methods using warm air, hot air or low-humidity air, vacuum drying methods, and drying methods using (far) infrared irradiation or electron beams may be mentioned. The drying speed is adjusted so that the solvent can be removed as quickly as possible within a speed range that does not cause the positive electrode active material layer to rupture due to normal stress concentration or within a speed range that causes the positive electrode active material layer to be peeled off from the positive electrode collector.

[0113] In addition, after drying, the density of the positive electrode active material in the positive electrode can be increased by pressing the current collector. As a pressing method, methods such as mold pressing and roll pressing can be mentioned.

[0114] The positive electrode prepared by the components and manufacturing methods as described above, specifically the porosity of the positive electrode active material layer, may be 50% to 80%, preferably 60% to 75%. If the porosity of the positive electrode is less than 50%, there is a problem that the filling degree of the positive electrode slurry composition containing the positive electrode active material, the conductive material and the binder is too high, and therefore, it is not possible to maintain enough electrolytes capable of exhibiting ion conduction and / or electrical conduction between the positive electrode active materials, so that the output characteristics or cycle characteristics of the battery may deteriorate and the overvoltage and discharge capacity of the battery may decrease. On the contrary, if the porosity of the positive electrode exceeds 80%, thereby having an excessively high porosity, there is a problem that the physical connection and electrical connection with the collector are reduced, the adhesion is reduced and the reaction becomes difficult, and the increased porosity is filled with the electrolyte, which may reduce the energy density of the battery. Therefore, the porosity of the positive electrode is appropriately adjusted within the above range.

[0115] In addition, the sulfur loading in the positive electrode according to the present invention, that is, the mass of sulfur per unit area in the positive electrode active material layer in the positive electrode, may be 0.5 to 15 mg / cm 2 , preferably 1 to 10 mg / cm 2 .

[0116] The negative electrode is as described above.

[0117] The electrolyte is located between the positive electrode and the negative electrode as described above to cause an electrochemical oxidation or reduction reaction therethrough at the positive electrode and the negative electrode, and contains a lithium salt and a nonaqueous organic solvent.

[0118] The lithium salt may be used without limitation as long as it can be generally used in lithium secondary batteries.

[0119] The specific example of the lithium salt may be at least one selected from the group consisting of: LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 、LiPF 6 、LiCF 3 SO 3 、LiCF 3 CO 2 ,LiC 4 BO 8 、LiAsF 6 、LiSbF 6 、LiAlCl 4 、LiSO 3 CH 3 、LiSO 3 CF 3 、LiSCN、LiC(CF 3 SO 2 ) 3 、LiN(CF 3 SO 2 ) 2 (Lithium bis(trifluoromethanesulfonyl)imide; LiTFSI), LiN(C 2 F 5 SO 2 ) 2 、LiN(SO 2 F) 2 (lithium bis(fluorosulfonyl)imide; LiFSI), lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, and lithium imide.

[0120] Depending on various factors, such as the composition of the electrolyte, the solubility of the lithium salt, the conductivity of the dissolved lithium salt, the charge / discharge conditions of the battery, the operating temperature, and other factors known in the field of lithium secondary batteries, the concentration of the lithium salt may be 0.2 to 4M, specifically 0.6 to 2M, and more specifically 0.7 to 1.7M. If the concentration of the lithium salt is less than 0.2M, the conductivity of the electrolyte may be reduced, and thus the performance of the electrolyte may be deteriorated. If the concentration of the lithium salt exceeds 4M, the viscosity of the electrolyte may increase, and thus the mobility of the lithium ions may decrease.

[0121] As the non-aqueous organic solvent, those commonly used in lithium secondary battery electrolytes can be used without limitation. For example, as the non-aqueous organic solvent, ethers, esters, amides, linear carbonates, cyclic carbonates, etc. can be used alone, or a combination of two or more thereof can be used. Among them, ether compounds can generally be used.

[0122] The ether-based compound may include acyclic ethers and cyclic ethers.

[0123] For example, the non-cyclic ether can be, but is not limited to, at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, ethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether and polyethylene glycol methyl ethyl ether.

[0124] For example, the cyclic ether may be, but is not limited to, at least one selected from the group consisting of 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran, 1,4-dioxolane, 1,4-dioxolane, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran ... alkanes, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene and dimethyl isosorbide.

[0125] The ester compound may be, but is not limited to, at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone, and a mixture of two or more thereof.

[0126] Specific examples of the linear carbonate compound may representatively include, but are not limited to, at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, or a mixture of two or more thereof.

[0127] In addition, specific examples of the cyclic carbonate compound may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate and halides thereof, or mixtures of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

[0128] In addition, in addition to the above-mentioned non-aqueous organic solvent, it can also contain at least one selected from the group consisting of: N-methylpyrrolidone, dimethyl sulfoxide, cyclopentanefuran, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene and 2,5-dimethylthiophene.

[0129] In addition to the above components, the electrolyte may also contain nitric acid compounds commonly used in the related field. Examples thereof may include lithium nitrate (LiNO 3 ), potassium nitrate (KNO 3 ), cesium nitrate (CsNO 3 ), magnesium nitrate (Mg(NO 3 ) 2 ), barium nitrate (Ba(NO 3 ) 2 ), lithium nitrite (LiNO 2 ), potassium nitrite (KNO 2 ), cesium nitrite (CsNO 2 )wait.

[0130] Depending on the manufacturing process and the required performance of the final product, the injection of the electrolyte can be carried out at an appropriate stage during the battery manufacturing process. That is, it can be injected before the battery assembly or at the final stage of the battery assembly.

[0131] A separator may be further included between the positive electrode and the negative electrode.

[0132] The separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ions to be transmitted between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. The separator may be used without particular limitation as long as it is used as a separator in a typical lithium secondary battery. The separator may be an independent member, such as a film or coating added to the positive electrode and / or the negative electrode.

[0133] The separator is preferably one that has excellent impregnation ability with the electrolyte and low resistance to ion migration in the electrolyte.

[0134] The separator may be made of a porous substrate. Any porous substrate may be used as long as it is a porous substrate commonly used in secondary batteries. A porous polymer film may be used alone or in the form of a laminate. For example, a nonwoven fabric or a polyolefin-based porous film made of high melting point glass fiber or polyethylene terephthalate fiber may be used, but is not limited thereto.

[0135] In the present invention, there is no particular limitation on the material of the porous substrate, and any material can be used as long as it is a porous substrate commonly used in electrochemical devices. For example, the porous substrate may include at least one material selected from the group consisting of polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyamides; polyacetals; polycarbonates; polyimides; polyetheretherketones, polyethersulfones; polyphenylene oxides; polyphenylene sulfides; polyethylene naphthalate; polytetrafluoroethylene; polyvinylidene fluoride; polyvinyl chloride; polyacrylonitrile; cellulose; nylon; poly(p-phenylene benzophenone); ... azoles) and polyarylates.

[0136] The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the porous substrate is not particularly limited to the above range, if the thickness is excessively thinner than the above lower limit, the mechanical properties may deteriorate, and thus the separator may be easily damaged during battery use.

[0137] The average diameter and porosity of pores present in the porous substrate are also not particularly limited, but may be 0.001 μm to 50 μm and 10% to 95%, respectively.

[0138] The lithium secondary battery of the present invention can be classified into cylindrical, rectangular, coin-shaped, pouch-shaped, etc. according to shape, and can be classified into block type and film type according to size. The structure and preparation method of these batteries are well known in the art, so their detailed description is omitted.

[0139] Furthermore, the present invention provides a battery module including the above-mentioned lithium secondary battery as a unit battery.

[0140] The battery module can be used as a power source for medium or large-sized devices requiring high temperature stability, long cycle characteristics, high capacity characteristics, and the like.

[0141] Examples of the medium and large devices may include, but are not limited to, power tools powered by a battery-powered motor; electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems.

[0142] Modes for carrying out the invention

[0143] Hereinafter, preferred embodiments of the present invention will be described to facilitate understanding of the present invention. However, it will be apparent to those skilled in the art that the following embodiments are examples of the present invention, and various changes and modifications may be made within the scope and spirit of the present invention. Such changes and modifications are within the scope of the appended claims.

[0144] Examples and Comparative Examples

[0145] [Example 1]

[0146] (1) Manufacturing of lithium electrodes

[0147] In one reactor, 0.1 g of hexagonal boron nitride was dispersed in 100 mL of tetrahydrofuran using an ultrasonic dispersion device to prepare a first solution.

[0148] In another reactor, 1.0 g of PIM-1 (Mw: 10,000 g / mol) was dissolved in 50 mL of tetrahydrofuran to prepare a second solution.

[0149] The first solution and the second solution prepared by the above method are mixed to prepare a protective layer-forming coating solution.

[0150] The coating solution was coated on the surface of the lithium metal layer with a thickness of 30 μm using a bar coating process, and then dried in a vacuum oven at 80°C for 12 hours to prepare a lithium electrode including a protective layer with a thickness of 0.5 μm. At this time, the weight ratio of hexagonal boron nitride to PIM-1 contained in the protective layer was 1:10.

[0151] (2) Manufacturing of lithium-sulfur batteries

[0152] 90 wt % of sulfur-carbon composite (S:C=75:25 (weight ratio)) as a positive electrode active material, 5.0 wt % of Dancar black as a conductive material, and 5.0 wt % of styrene-butadiene rubber / carboxymethyl cellulose (SBR:CMC=70:30 (weight ratio)) as a binder were mixed to prepare a positive electrode slurry composition.

[0153] The prepared positive electrode slurry composition was coated on an aluminum current collector with a thickness of 20 μm, dried at 50° C. for 12 hours, and pressed with a roller press to prepare a positive electrode. At this time, the loading amount of the positive electrode active material was 5.4 mAh / cm 2 Below, the porosity of the positive electrode is 68%.

[0154] The prepared positive electrode was positioned to face the lithium electrode (negative electrode) prepared in (1) above, a polyethylene separator having a thickness of 20 μm and a porosity of 68% was inserted therebetween, and then 0.1 ml of electrolyte was injected to prepare a lithium-sulfur battery.

[0155] At this time, the electrolyte used was a mixed solution of 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt % lithium nitrate (LiNO 3 ) was dissolved in an organic solvent consisting of 1,3-dioxolane and dimethyl ether (DOL:DME=1:1 (volume ratio)) to obtain a mixed solution.

[0156] [Example 2]

[0157] A lithium-sulfur battery was prepared in the same manner as in Example 1, except that 0.1 g of molybdenum disulfide was used instead of 0.1 g of hexagonal boron nitride when preparing the first solution, so that the weight ratio of molybdenum disulfide to PIM-1 contained in the protective layer was 1:10.

[0158] [Example 3]

[0159] A lithium-sulfur battery was prepared in the same manner as in Example 1, except that 0.1 g of graphene oxide was used instead of 0.1 g of hexagonal boron nitride when preparing the first solution, so that the weight ratio of graphene oxide to PIM-1 contained in the protective layer was 1:10.

[0160] [Example 4]

[0161] A lithium-sulfur battery was prepared in the same manner as in Example 1, except that 0.1 g of graphite carbon nitride was used instead of 0.1 g of hexagonal boron nitride when preparing the first solution, so that the weight ratio of graphite carbon nitride to PIM-1 contained in the protective layer was 1:10.

[0162] [Comparative Example 1]

[0163] A lithium-sulfur battery was prepared in the same manner as in Example 1 above, except that a lithium metal thin film having a thickness of 30 μm without a protective layer was used as the negative electrode.

[0164] [Comparative Example 2]

[0165] A lithium-sulfur battery was prepared in the same manner as in Example 1, except that a solution prepared by dissolving 1.0 g of PIM-1 (Mw: 10,000 g / mol) in 50 mL of tetrahydrofuran was used as a coating solution for forming a protective layer, thereby using a lithium electrode having a protective layer containing only PIM-1.

[0166] [Comparative Example 3]

[0167] A lithium-sulfur battery was prepared in the same manner as in Example 1, except that a solution prepared by dissolving 0.1 g of hexagonal boron nitride and 1.0 g of a polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) polymer in 150 mL of tetrahydrofuran was used as a coating solution for forming a protective layer, thereby using a lithium electrode having a protective layer formed by using such a solution.

[0168] Experimental Example 1 Lithium Electrode Surface Evaluation

[0169] The surfaces of the lithium electrodes prepared in Examples 1 to 4 and the lithium metal thin film in Comparative Example 1 were observed with naked eyes and a scanning electron microscope (SEM). In this case, S-4800 manufactured by Hitachi Corporation was used as a scanning electron microscope, and the results obtained are shown in FIG. Figure 1 and Figure 2 middle.

[0170] like Figure 1 As shown in , in the case of the lithium electrodes according to Examples 1 to 4, compared with Comparative Example 1, it can be confirmed that a pale yellow coating layer is formed by including the intrinsic microporous polymer.

[0171] In addition, refer to Figure 2 , it can be confirmed that the two-dimensional material and the intrinsic microporous polymer coated in the form of a film are located on the surface of the lithium metal layer.

[0172] Experimental Example 2 Evaluation of Battery Performance

[0173] The batteries manufactured by the examples and comparative examples were subjected to performance evaluation using a charge / discharge measuring device (model name: LAND CT-2001A, manufacturer: product of Wuhan Company).

[0174] Specifically, the process of discharging to 1.8V at 0.1C current density and charging to 2.5V at 0.1C current density was repeated for 3 cycles at 25°C, and then charging and discharging were performed for 3 cycles at 0.2C current density in the same voltage range, and the capacity and life characteristics of the battery were evaluated while discharging at 0.5C current density and charging at 0.3C current density. The results obtained at this time are shown in Table 1 and Figure 3 and Figure 4 middle.

[0175] Table 1:

[0176] Capacity retention rate (%@70 cycles) Example 1 85 Example 2 84 Example 3 95 Example 4 87 Comparative Example 1 80 Comparative Example 2 81 Comparative Example 3 79

[0177] like Figure 3 and Figure 4 As shown in Table 1, it can be seen that the life characteristics in the case of the battery according to the embodiment are superior to those of the comparative example.

[0178] Depend on Figure 3 and Figure 4 It can be seen that, compared with the batteries according to Examples 1 to 4, in the case of the batteries according to Comparative Examples 1 to 3, the discharge capacity was relatively low and the capacity retention ratio (ie, life characteristics) was also poor.

[0179] In particular, refer to Figure 4 As can be seen from Table 1, Comparative Example 2 is a case where only the intrinsic microporous polymer PIM-1 is used to form a protective layer on the lithium metal layer, and its discharge capacity is lower than that of Comparative Example 1 without a protective layer, and its capacity retention rate is also similar to that of Comparative Example 1. It can be seen from this that in order to improve the capacity and life characteristics of the battery, the protective layer of the lithium electrode should contain both the intrinsic microporous polymer and the two-dimensional material. In addition, it can be confirmed that in the case of Examples 3 and 4, since the capacity retention rate is better than that of Examples 1 and 2, graphene oxide and graphite phase carbon nitride as two-dimensional materials are effective in improving the life characteristics of the battery.

Claims

1. A lithium electrode comprising: a lithium metal layer; and a protective layer formed on at least one surface of the lithium metal layer, wherein the protective layer comprises a two-dimensional material and an intrinsically microporous polymer, The intrinsic microporous polymer comprises a repeating structure represented by the following formula 1: [Formula 1] and The two-dimensional material comprises at least one selected from the group consisting of graphene, graphene oxide, molybdenum disulfide and graphitic carbon nitride. 2 . The lithium electrode according to claim 1 , wherein the two-dimensional material comprises at least one selected from the group consisting of graphene oxide and graphitic carbon nitride.

3. The lithium electrode according to claim 1, wherein the weight ratio of the two-dimensional material to the intrinsic microporous polymer is 1:1 to 1:

20. The lithium electrode according to claim 1 , wherein the protective layer has a thickness of 0.1 to less than 5 μm. 5 . The lithium electrode according to claim 1 , wherein the lithium metal layer has a thickness of 20 to 200 μm.

6. A method for manufacturing the lithium electrode according to claim 1, the method comprising: (a) dispersing the two-dimensional material in a first solvent to prepare a first solution; (b) dissolving the intrinsically microporous polymer in a second solvent to prepare a second solution; (c) mixing the first solution and the second solution to prepare a coating solution; and (d) applying the coating solution onto at least one surface of the lithium metal layer.

7. The method for manufacturing a lithium electrode according to claim 6, wherein the first solvent and the second solvent are the same or different and contain at least one selected from the group consisting of tetrahydrofuran, toluene, cyclohexane, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, tetramethylurea, dimethyl sulfoxide and triethyl phosphate.

8. A lithium secondary battery comprising: A positive electrode comprising a positive electrode active material; a negative electrode comprising the lithium electrode according to claim 1; and an electrolyte interposed between the positive electrode and the negative electrode. 9 . The lithium secondary battery according to claim 8 , wherein the positive electrode active material comprises a sulfur-containing compound. 10 . The lithium secondary battery according to claim 8 , wherein the lithium secondary battery is a lithium-sulfur battery.

Images