Negative electrode for lithium metal battery and lithium metal battery comprising the same

Abstract

The present invention relates to a negative electrode for a lithium metal battery and a lithium metal battery comprising the same, the negative electrode comprising: a porous substrate; a carbon coating formed on the surface of the porous substrate; and a lithium metal layer located on the carbon coating, wherein the carbon coating comprises carbon particles having a plate-like structure.

Description

[0001] This application is a divisional application of Chinese invention patent application filed on May 2, 2022, with application number 202280007241.1 and invention title "Negative electrode for lithium metal battery and lithium metal battery including the same". Technical Field

[0002] This invention relates to a negative electrode for lithium metal batteries and a lithium metal battery comprising the same.

[0003] This application claims priority based on Korean Patent Application No. 10-2021-0057409, filed on May 3, 2021, and Korean Patent Application No. 10-2022-0053302, filed on April 29, 2022, the entire contents of which are incorporated herein by reference. Background Technology

[0004] With the continued increase in interest in energy storage technology, and its applications expanding from powering mobile phones, tablets, laptops, and cameras to powering electric vehicles (EVs) and hybrid electric vehicles (HEVs), research and development of electrochemical devices are gradually increasing. The field of electrochemical devices is the most closely watched area in this field. Among these, the development of secondary batteries, such as rechargeable / dischargeable lithium-sulfur batteries and lithium metal batteries, has become a focus of attention. In recent years, in developing these batteries, novel electrode and battery designs have been researched and developed to improve capacity density and specific energy.

[0005] Lithium, used as the anode in lithium-metal batteries, has an advantage in improving battery energy density due to its low density. However, it has been pointed out that lithium has disadvantages in the manufacturing process, as its relatively low mechanical strength and high ductility make it prone to dimensional changes. In addition, copper foil is often used as a current collector to support lithium, but although copper foil is thinner, it suffers from a significant loss of energy density per unit weight because copper's density is about 16.8 times that of lithium.

[0006] To compensate for the mechanical strength issues and manufacturing problems of anodes for lithium metal batteries, researchers have studied various anode structures. However, the limitation of improving the anode structure is that even by introducing new substrates to compensate for mechanical strength, it is difficult to reduce the loss of battery energy density, and the battery operation remains unstable.

[0007] [Existing Technical Documents]

[0008] [Patent Literature]

[0009] (Patent Document 1) Korean Patent Publication No. 10-2014-0146071 (December 24, 2014), "Reinforced Metal Foil Electrode" Summary of the Invention

[0010] Technical issues

[0011] The objective of this invention is to provide a lightweight negative electrode for lithium metal batteries and a lithium metal battery comprising the negative electrode, wherein by including a porous substrate, a carbon coating containing carbon particles with a plate-like structure, and a lithium metal layer in the negative electrode for lithium metal batteries, the energy density loss of the battery is minimized while compensating for the mechanical properties of lithium, and the operational stability and manufacturability of the battery are increased.

[0012] Technical solution

[0013] According to a first aspect of the present invention, a negative electrode for a lithium metal battery is provided, comprising a porous substrate; a carbon coating formed on the surface of the porous substrate; and a lithium metal layer located on the carbon coating, wherein the carbon coating comprises carbon particles having a plate-like structure.

[0014] In one embodiment of the present invention, the porous substrate may comprise, selected from polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyacetal, polycarbonate, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylenebenzobismuth subcarbonate) It is one of the groups consisting of azoles, polyarylates and combinations thereof.

[0015] In one embodiment of the present invention, the porosity of the porous substrate may be 40% to 90%.

[0016] In one embodiment of the present invention, the thickness of the porous substrate may be from 0.5 μm to 30 μm.

[0017] In one embodiment of the invention, the carbon coating may comprise graphene or graphene derivatives having a plate-like structure.

[0018] In one embodiment of the present invention, the weight of carbon particles coated per unit area of ​​the porous substrate may be 0.1 g / m². 2 Up to 5 g / m 2 .

[0019] In one embodiment of the present invention, the negative electrode for the lithium metal battery may have the following structure, wherein a carbon coating is formed on one surface of the porous substrate, and a lithium metal layer is stacked on one surface of the carbon coating facing the opposite direction to the porous substrate.

[0020] In one embodiment of the present invention, the negative electrode for the lithium metal battery may have a multilayer structure, wherein a porous substrate is located in the center, a carbon coating is formed on two surfaces of the porous substrate, and a lithium metal layer is stacked on each surface of the carbon coating facing the opposite direction to the porous substrate.

[0021] In one embodiment of the present invention, the tensile strength of the negative electrode for the lithium metal battery can be from 1 MPa to 300 MPa.

[0022] According to a second aspect of the present invention, a lithium metal battery comprising the negative electrode is provided.

[0023] Beneficial effects

[0024] The negative electrode for lithium metal batteries according to the present invention has the following effects: the manufacturability of the battery is improved by including a lightweight porous substrate in its structure that can compensate for the low mechanical properties of lithium; the affinity between lithium and the support is improved by including a carbon coating containing carbon particles with a plate-like structure, and a stable structure is formed during lithium plating, thereby improving lithium efficiency.

[0025] Furthermore, the lithium metal battery containing the negative electrode according to the present invention increases the electrolyte retention of the negative electrode due to the porous substrate, thereby improving battery life characteristics. Attached Figure Description

[0026] Figure 1 and Figure 2 This is a schematic diagram of one embodiment of the negative electrode for a lithium metal battery according to the present invention.

[0027] Figure 3 These are photographs of negative electrodes for lithium metal batteries manufactured according to manufacturing examples 2, 4 and 5 of the present invention.

[0028] Figure 4 The figure shows the measurement results of the tensile strength of the negative electrode for a lithium metal battery according to Manufacturing Example 4 of the present invention.

[0029] Figure 5 The figure shows the measurement results of the tensile strength of the negative electrode for a lithium metal battery according to Manufacturing Example 5 of the present invention.

[0030] Figure 6 An SEM image of the negative electrode for a lithium metal battery according to Manufacturing Example 2 of the present invention is shown.

[0031] Figure 7 An SEM image of the negative electrode for a lithium metal battery according to manufacturing example 5 of the present invention is shown.

[0032] Figure 8 The cycle life evaluation results of a lithium-lithium symmetric cell type battery containing a lithium metal battery negative electrode according to Embodiment 3 of the present invention are shown.

[0033] Figure 9 The cycle life evaluation results of a lithium-lithium symmetric battery containing a lithium metal battery negative electrode according to Comparative Example 4 of the present invention are shown.

[0034] Figure 10 The results of the evaluation of the discharge capacity of lithium metal batteries according to Examples 1 and 2 and Comparative Examples 1 and 2 are shown.

[0035] Figure 11 The results of the evaluation of the discharge capacity of lithium metal batteries according to Comparative Examples 1 and 3 of the present invention are shown. Detailed Implementation

[0036] The embodiments provided by the present invention can all be implemented through the following description. It should be understood that the following description describes preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0037] Negative electrode for lithium metal batteries

[0038] The negative electrode for a lithium metal battery according to the present invention comprises a porous substrate; a carbon coating formed on the surface of the porous substrate; and a lithium metal layer located on the carbon coating, wherein the carbon coating comprises carbon particles having a plate-like structure.

[0039] In this specification, a lithium metal battery can be defined as a battery that uses lithium metal as the negative electrode.

[0040] The negative electrode for lithium metal batteries according to the present invention comprises a porous substrate.

[0041] The porous substrate can be a porous polymer substrate that does not cause lithiation. When a porous substrate acting as a lithium support causes lithiation, the tensile strength and elongation of the negative electrode will decrease significantly. Therefore, it is preferable to use a substrate that does not cause lithiation as the porous substrate.

[0042] For example, the porous substrate may comprise a variety of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyetheretherketones, polyethersulfones, polyphenylene ethers, polyphenylene sulfides, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, and poly(p-phenylenebenzobismuth submersible) Polyimide is a polymer that is part of the group consisting of azoles, polyarylates, and combinations thereof, and is preferably polyethylene terephthalate, but is not particularly limited thereto. However, polyimide is a polymer that may cause lithiation and may not be suitable as a porous substrate.

[0043] The porosity of the porous substrate can be above 40%, above 45%, or above 50%, and can be below 90%, below 85%, below 80%, below 75%, below 70%, below 65%, or below 60%. Porosity refers to the volume ratio of pores in the porous substrate, and can be measured using, for example, the Brunol-Emmett-Teller (BET) measurement method or an Hg porosimeter, but is not limited to these methods. As another example, the porosity can be calculated using other parameters such as size, thickness, and density. Specifically, after measuring the particle layer thickness using a material thickness measuring device (TESA, u-hite), the porosity can be calculated using the true density of the particle layer measured using a material true density measuring device (Microtrac, BELPycno). If the porosity is less than 40%, the lithium migration path is restricted, and therefore the resistance may increase significantly during charging and discharging. On the other hand, if the porosity exceeds 90%, there is a problem with improving assembly processability because the physical properties of the negative electrode are not improved.

[0044] The thickness of the porous substrate can be 0.5 μm or more, 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or 10 μm or more, and can be less than 30 μm, less than 29 μm, less than 28 μm, less than 27 μm, less than 26 μm, less than 25 μm, less than 24 μm, less than 23 μm, less than 22 μm, less than 21 μm, or less than 20 μm. If the thickness is less than 0.5 μm, the porous substrate is too thin, and therefore its mechanical properties, such as tensile strength, may deteriorate when used as a negative electrode support. On the other hand, if the thickness exceeds 30 μm, there are problems such as an increased lithium migration path length, a potentially significant increase in resistance during charging and discharging, and a decrease in energy density per unit weight and volume.

[0045] The negative electrode for lithium metal batteries according to the present invention comprises a carbon coating formed on the surface of a porous substrate, the carbon coating comprising carbon particles having a plate-like structure.

[0046] The carbon coating formed on the surface of a porous substrate can contain conductive carbon particles. Because the carbon coating contains conductive carbon particles, the affinity between the porous substrate, which serves as the negative electrode support, and metallic lithium is improved. This allows for the formation of a stable structure during lithium plating, thereby improving lithium efficiency and the manufacturability of the lithium negative electrode.

[0047] The carbon coating may comprise carbon particles with a plate-like structure; for example, the carbon coating may comprise graphene or graphene derivatives with a plate-like structure. The carbon coating may preferably comprise one selected from the group consisting of graphene, reduced graphene oxide (RGO), graphene oxide (GO), and combinations thereof, and more preferably graphene. If carbon particles with a plate-like structure are included in the carbon coating, the pores on the surface of the porous substrate can be reduced, and the lithium plating effect can be controlled regardless of the relative distance to the positive electrode.

[0048] The weight of carbon particles coated per unit area of ​​the porous substrate can be 0.1 g / m². 2 Above, 0.2 g / m 2 Above, 0.3 g / m 2 Above, 0.4 g / m 2 Above, 0.5 g / m 2 Above, 0.6 g / m 2 Above, and can be 5.0 g / m 2 Below, 4.5 g / m 2 Below, 4.0 g / m 2 Below, 3.5 g / m 2 Below, 3.0 g / m 2 Below, 2.5 g / m 2 Below, 2.0 g / m 2 Below, 1.5 g / m 2 Below, 1.4 g / m 2 Below, 1.3 g / m 2 Below, 1.2 g / m 2 Below, 1.1 g / m 2 Below, 1.0 g / m 2 The following applies if the weight of the carbon particles is less than 0.1 g / m³. 2 The effect of improving battery performance, such as discharge capacity, by including carbon particles with a plate-like structure in the carbon coating may be weakened. On the other hand, if the weight of the carbon particles exceeds 5.0 g / m³... 2This increases the battery's resistance by hindering the movement of lithium ions, which may lead to deterioration in battery performance and lower energy density per unit weight and volume than required.

[0049] The negative electrode for a lithium metal battery according to the present invention comprises a lithium metal layer.

[0050] The lithium metal layer refers to a metal layer containing lithium metal. The material of the lithium metal layer can be a lithium alloy, lithium metal, lithium alloy oxide, or lithium oxide. As a non-limiting example, the negative electrode can be a lithium metal thin film, and can be an alloy of lithium and at least one metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. In this case, the surface oxide layer or a portion of the lithium metal layer may be altered by oxygen or moisture, or may contain impurities.

[0051] The lithium metal layer can be laminated onto a carbon coating formed on a porous substrate, and then subjected to a calendering process to achieve close contact with the porous substrate and carbon coating structure. Furthermore, during calendering, a release film that does not adhere to lithium can be used on the surface in direct contact with the rolls. Additionally, to stabilize the interface between the porous substrate and the lithium metal layer, an aging treatment process can be performed, blocking oxygen and moisture and storing the material in a sealed bag for several hours to several days.

[0052] The thickness of the lithium metal layer can be greater than 0.1 μm, greater than 0.5 μm, greater than 1.0 μm, greater than 3 μm, greater than 5 μm, greater than 7 μm, greater than 10 μm, greater than 13 μm, greater than 15 μm, greater than 20 μm, greater than 25 μm, greater than 30 μm, greater than 35 μm, greater than 40 μm, greater than 45 μm, greater than 50 μm, and greater than 55 μm, and can also be less than 100 μm, less than 95 μm, less than 90 μm, less than 85 μm, less than 80 μm, less than 75 μm, less than 70 μm, and less than 65 μm. If the thickness is less than 0.1 μm, the battery will struggle to perform well due to insufficient lithium efficiency. If the thickness exceeds 100 μm, the energy density may decrease due to the increased lithium thickness.

[0053] The negative electrode for the lithium metal battery can be manufactured by preparing a porous substrate, coating the surface of the porous substrate with a dispersion containing carbon particles having a plate-like structure, then vacuum drying to form a carbon coating, stacking lithium metal foil on it, and then calendering them. The coating method is preferably dip coating, but is not particularly limited thereto. Furthermore, the calendering method is not particularly limited, and methods commonly used in the art can be used.

[0054] refer to Figure 1 The negative electrode for the lithium metal battery comprises a carbon coating 200 formed on one surface of a porous substrate 100, and may have a structure in which a lithium metal layer 300 is stacked on one surface of the carbon coating 200 facing the opposite direction to the porous substrate 100. A negative electrode having a structure in which a lithium metal layer is stacked on one surface of the carbon coating is preferably used for single-cell or coin-operated batteries.

[0055] refer to Figure 2 The negative electrode for the lithium metal battery can have a multilayer structure, wherein a porous substrate 100 is located in the center, carbon coatings are formed on both sides of the porous substrate, and lithium metal layers are stacked on a surface of the carbon coating facing the opposite direction to the porous substrate. In the case of this multilayer negative electrode structure, it can be used in various types of batteries forming a multilayer structure.

[0056] The tensile strength of the negative electrode for the lithium metal battery can be above 1 MPa, above 2 MPa, above 3 MPa, above 4 MPa, above 5 MPa, above 6 MPa, above 7 MPa, above 8 MPa, above 9 MPa, above 10 MPa, above 11 MPa, above 12 MPa, above 13 MPa, above 14 MPa, above 15 MPa, above 16 MPa, above 17 MPa, above 17.5 MPa, or above 18 MPa, and can be below 300 MPa, below 280 MPa, below 260 MPa, below 240 MPa, below 220 MPa, below 200 MPa, below 180 MPa, below 160 MPa, below 140 MPa, below 120 MPa, below 100 MPa, below 80 MPa, below 60 MPa, below 40 MPa, below 35 MPa, below 30 MPa, below 29 MPa, below 28 MPa, or below 27 MPa. Below 20 MPa, 26 MPa, 25 MPa, 24 MPa, 23 MPa, 22 MPa, 21 MPa, and 20 MPa. If the tensile strength falls within the above range, the mechanical strength of the lithium metal can be compensated by introducing a porous substrate, thus enabling the fabrication of a lithium composite anode with a reinforced support.

[0057] Lithium metal batteries

[0058] The lithium metal battery according to the present invention includes the above-described negative electrode.

[0059] Specifically, the lithium metal battery includes a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the negative electrode comprises a negative electrode for a lithium metal battery according to the present invention.

[0060] The negative electrode is as described above in this specification.

[0061] The positive electrode may include a positive electrode current collector and a layer of positive electrode active material coated on one or both surfaces of the positive electrode current collector.

[0062] The positive electrode current collector supports the positive electrode active material and is not particularly limited, as long as it has high conductivity and will not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, sintered carbon; copper or stainless steel with surface treatments of carbon, nickel, silver, etc.; aluminum-cadmium alloys, etc., can be used as positive electrode current collectors.

[0063] The positive current collector can enhance its adhesion to the positive active material by having fine irregularities on its surface, and can be formed in various forms such as film, plate, foil, mesh, net, porous body, foam or non-woven fabric.

[0064] The positive electrode active material layer may include a positive electrode active material, a binder, and a conductive material.

[0065] The positive electrode active material can be, but is not limited to, layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds replaced by one or more transition metals; lithium manganese oxide, such as Li... 1+x Mn 2-x O4 (where x is 0~0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiFe3O4, V2O5 and Cu2V2O7; and LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01~0.3); LiMn 2-x M x Lithium-manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01~0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); and LiNi x Mn 2-x O4 represents a spinel-structured lithium manganese composite oxide; LiMn2O4 in which a portion of the Li is replaced by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3.

[0066] The positive electrode active material may contain sulfur. Sulfur alone is not conductive, therefore it is used in combination with conductive materials such as carbon materials. If the positive electrode active material contains sulfur, it can be contained in the form of a sulfur-carbon composite. The carbon contained in the sulfur-carbon composite is a porous carbon material, providing a framework for the sulfur to be uniformly and stably fixed and compensating for the low conductivity of sulfur, thus allowing the electrochemical reaction to proceed smoothly.

[0067] The porous carbon material is typically produced by carbonizing various carbon precursors. This porous carbon material may contain non-uniform pores with an average diameter ranging from 1 to 200 nm and a porosity ranging from 10% to 90% of the total volume of the porous carbon material. If the average pore diameter is smaller than this range, the pore size is only at the molecular level and impregnation with sulfur is impossible. Conversely, if the average pore diameter exceeds this range, the mechanical strength of the porous carbon material is weakened, which is undesirable for application in electrode manufacturing processes.

[0068] The porous carbon material can be in the form of spheres, rods, needles, plates, tubes or blocks, and can be used without restriction, as long as it is commonly used.

[0069] The porous carbon material may have a porous structure or a high specific surface area, and may be any of those conventionally 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 black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking 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 graphite such as natural graphite, artificial graphite, expanded graphite, etc., and activated carbon, preferably carbon nanotubes (CNTs).

[0070] The conductive material is a material that acts as a pathway for electrons to transfer from the current collector to the positive electrode active material by electrically connecting the electrolyte and the positive electrode active material. The conductive material can be used without restriction, as long as it is conductive.

[0071] For example, the conductive materials described can be used alone or in combination: graphite such as natural or artificial graphite; carbon black such as Super-P, Danka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, and thermal cracking 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.

[0072] The adhesive holds the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active material to increase the adhesion between them. Any adhesive known in the art can be used.

[0073] For example, the adhesive may be selected from any of the following: fluoropolymer adhesives, including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); rubber adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber and styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose and regenerated cellulose; polyol adhesives; polyolefin adhesives, including polyethylene and polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, or mixtures or copolymers of two or more of these.

[0074] The method for manufacturing the positive electrode is not particularly limited in this invention, and methods commonly used in the art can be used. For example, the positive electrode can be prepared by preparing a slurry composition for the positive electrode and then applying the slurry composition to at least one surface of the positive electrode current collector.

[0075] The positive electrode slurry composition comprises the above-mentioned positive electrode active material, conductive material and binder, and may also contain solvents other than those mentioned above.

[0076] As the solvent, a solvent capable of uniformly dispersing the positive electrode active material, conductive material, and binder is used. Such a solvent is an aqueous solvent, with water being the most preferred; in this case, the water can be distilled water or deionized water. However, the solvent is not necessarily limited to this; if necessary, lower alcohols that readily mix with water can be used. Examples of such lower alcohols include methanol, ethanol, propanol, isopropanol, and butanol, which can preferably be used in combination with water.

[0077] There are no particular limitations on the electrolyte, as long as it is a non-aqueous solvent that allows ions participating in the electrochemical reactions of the battery to move through. For example, the solvent can be a carbonate solvent, ester solvent, ether solvent, ketone solvent, alcohol solvent, or aprotic solvent. Specific examples of carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butyl carbonate (BC). Specific examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, mevalonate lactone, or caprolactone. Specific examples of the ether solvents may include diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, or polyethylene glycol dimethyl ether, etc. Specific examples of the ketone solvents may include cyclohexanone, etc. Specific examples of the alcohol solvents may include ethanol or isopropanol, etc. Specific examples of the aprotic solvents may include nitrile solvents such as acetonitrile; amide solvents such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane (DOL); or sulfolane, etc. The non-aqueous organic solvents may be used alone or in combination of one or more. The mixing ratio when using one or more in combination may be appropriately adjusted depending on the desired battery performance.

[0078] Electrolyte injection can be performed at an appropriate stage of the lithium metal battery manufacturing process, depending on the final product manufacturing steps and desired performance. That is, the injection can be performed before assembling the lithium metal battery or in the final stage of assembly.

[0079] A conventional diaphragm can be inserted between the positive and negative electrodes. The diaphragm is a physical diaphragm that functions to physically separate the electrodes and can be used without particular restriction, as long as it is used as a conventional diaphragm. In particular, a diaphragm with low resistance to ion migration in the electrolyte and excellent impregnation ability with the electrolyte is preferred.

[0080] Furthermore, the separator can be made of a porous, non-conductive, or insulating material that separates or insulates the positive and negative electrodes from each other, allowing lithium ions to transport between the positive and negative electrodes. The separator can be used without particular limitation, as long as it serves as a separator in a conventional lithium metal battery. The separator can be a stand-alone component, such as a membrane, or it can comprise a coating added to the positive and / or negative electrodes.

[0081] The separator can be made of a porous substrate, which can be any porous substrate commonly used in lithium metal batteries. It can be used alone or by stacking them. For example, it can be a non-woven fabric or a polyolefin porous membrane made of glass fiber, polyethylene terephthalate fiber, etc. with a high melting point, but is not limited to these.

[0082] The material of the porous substrate is not particularly limited in this invention; any material can be used, as long as it is a porous substrate commonly used in lithium metal batteries. For example, the porous substrate may comprise materials selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, polyimides, polyetheretherketones, polyethersulfones, polyphenylene ethers, polyphenylene sulfides, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, and poly(p-phenylenebenzobismuth subcarbonate). At least one material comprising the group consisting of azoles and polyarylates.

[0083] The thickness of the porous substrate is not particularly limited, but can be from 1 to 100 μm, preferably from 5 to 50 μm. Although the thickness range of the porous substrate is not particularly limited to the above range, if the thickness is much thinner than the lower limit mentioned above, the mechanical properties will deteriorate, and therefore the separator may be easily damaged during battery use.

[0084] There are no particular limitations on the average diameter and porosity of the pores present in the porous substrate, but they can be from 0.1 μm to 50 μm and from 10% to 95%, respectively.

[0085] The shape of the lithium metal battery according to the present invention is not particularly limited and can be of various shapes, such as cylindrical, stacked and coin-shaped.

[0086] Modes for implementing inventions

[0087] Preferred embodiments will be provided below to aid in understanding the invention. However, the following embodiments are provided to better understand the invention, and the invention is not limited thereto.

[0088] Example: Manufacturing of lithium metal batteries

[0089] Manufacturing of negative electrodes for lithium metal batteries: Manufacturing Examples 1 to 7

[0090] [Manufacturing Example 1]

[0091] After preparing a 50% porosity, 14 μm thick polyethylene terephthalate (PET) nonwoven fabric (manufacturer: FTENE Corporation (Korea)) as a porous substrate, a graphene dispersion (manufacturer: Cnano Corporation) was applied to the surface of the nonwoven fabric via dip coating, followed by vacuum drying to form a carbon coating. In this case, the weight of graphene particles coated per unit area of ​​the nonwoven fabric in the carbon coating is 0.3 g / m². 2 .

[0092] A 60 μm thick lithium metal foil is laminated onto a carbon coating formed on a nonwoven fabric, and then rolled to manufacture a negative electrode for lithium metal batteries.

[0093] [Manufacturing Example 2]

[0094] The negative electrode for lithium metal batteries was manufactured in the same manner as in Manufacturing Example 1, but the weight of graphene particles coated on the nonwoven fabric per unit area in the carbon coating was 0.6 g / m². 2 .

[0095] [Manufacturing Example 3]

[0096] The negative electrode for lithium metal batteries was manufactured in the same manner as in Manufacturing Example 1, but a 35 μm thick lithium metal foil was used.

[0097] [Manufacturing Example 4]

[0098] A 60 μm thick lithium metal foil was used as the negative electrode.

[0099] [Manufacturing Example 5]

[0100] After preparing the same nonwoven fabric as in Manufacturing Example 1 as a porous substrate, the same lithium metal foil as in Manufacturing Example 1 is laminated but without forming a carbon coating, and then rolled to manufacture a negative electrode for lithium metal batteries.

[0101] [Manufacturing Example 6]

[0102] After preparing a polyimide (PI) nonwoven fabric (manufacturer: Kolon Corporation) with a porosity of 71% and a thickness of 8 μm as a porous substrate, lithium metal foil, the same as in Example 1, was laminated without forming a carbon coating, and then calendered to manufacture a negative electrode for lithium metal batteries.

[0103] [Manufacturing Example 7]

[0104] The negative electrode for lithium metal batteries was manufactured in the same manner as in Manufacturing Example 5, but a 35 μm thick lithium metal foil was used.

[0105] Manufacturing of lithium metal batteries: Examples 1 to 3 and Comparative Examples 1 to 4

[0106] [Example 1]

[0107] Along with the negative electrode prepared by manufacturing Example 1, a positive electrode, a separator, and an electrolyte as described below are manufactured, and then a lithium metal battery is assembled.

[0108] (1) Positive electrode: Using water as a solvent, a sulfur-carbon composite (S:C=75:25), conductive material, and binder are mixed at a ratio of 90:5:5 to prepare a slurry for the positive electrode active material. At this time, Danka Black is used as the conductive material, and styrene-butadiene rubber / carboxymethyl cellulose (SBR:CMC=7:3) is used as the binder.

[0109] The positive electrode active material is applied to one surface of an aluminum current collector using a slurry and then dried to manufacture the positive electrode.

[0110] (2) Membrane: A polyethylene membrane with a thickness of 16 μm and a porosity of 45% is used.

[0111] (3) Electrolyte: As an organic solvent, 1 M LiTFSI was mixed with dimethoxyethane (DME) and dioxolane (DOL) in a 1:1 volume ratio, and LiNO3 was added at 1% by weight relative to the electrolyte to prepare the electrolyte.

[0112] [Example 2]

[0113] The lithium metal battery was manufactured in the same manner as in Example 1, but the negative electrode of the lithium metal battery in Manufacturing Example 2 was used.

[0114] [Example 3]

[0115] The lithium metal anode manufactured in Example 3 was used as both the anode and cathode (the 'porous substrate with carbon coating' contained in the anode and cathode were placed opposite each other), and the same separator as in Example 1 was placed between the anode and cathode. The same electrolyte as in Example 1 was injected and sealed to manufacture a lithium metal battery, which is a coin battery type lithium-lithium symmetric battery.

[0116] [Comparative Examples 1 to 3]

[0117] In Comparative Examples 1 to 3, lithium metal batteries were manufactured in the same manner as in Example 1, but the negative electrodes for lithium metal batteries from Manufacturing Examples 4 to 6 were used.

[0118] [Comparative Example 4]

[0119] A lithium metal battery (a lithium-lithium symmetric battery) was manufactured in the same manner as in Example 3, except that the lithium metal anode prepared in Manufacturing Example 7 was used as the anode and cathode, respectively (the porous substrates were placed opposite each other).

[0120] Experimental Example 1: Evaluation of the Physical Properties of the Negative Electrode

[0121] The physical properties of the negative electrodes for lithium metal batteries manufactured in Examples 1 to 7 were evaluated.

[0122] Specifically, thickness and mass per unit area were measured, and the results are shown in Table 1 below. Furthermore, tensile strength was measured based on ASTM E8 / E8M, and the results are shown in Table 1 below. The results for Manufacturing Example 4 and Manufacturing Example 5 are illustrated in the figures below. Figure 4 and Figure 5 middle.

[0123] Table 1:

[0124] As a result of the tensile strength measurement, it was found that in the case of manufacturing Example 4, where lithium metal was used alone when manufacturing the negative electrode, the tensile strength was less than 1 MPa and the mechanical strength of the negative electrode was low, so it was difficult to expect the battery to operate stably.

[0125] On the other hand, it was confirmed that in the case of manufacturing example 5 containing PET nonwoven fabric, the tensile strength of the negative electrode is 17 MPa or more, and the mechanical strength of the negative electrode is improved when a porous substrate is included as the support of the negative electrode.

[0126] Furthermore, it was confirmed that in Manufacturing Examples 1 and 2, which included PET nonwoven fabric and carbon coating, the tensile strength of the negative electrode was 18 MPa or higher, and the mechanical strength of the negative electrode was further improved compared with the case containing only PET nonwoven fabric.

[0127] Experimental Example 2: Surface Shape of the Negative Electrode (SEM)

[0128] The surfaces of the lithium metal battery negative electrodes prepared in Manufacturing Example 2 and Manufacturing Example 5 were photographed using a scanning electron microscope (SEM), and the results are shown below. Figure 6 and Figure 7 middle.

[0129] SEM images revealed that in Manufacturing Example 2, where a negative electrode was manufactured by forming a carbon coating containing carbon particles with a plate-like structure on a porous substrate, the number of pores in the porous substrate was relatively reduced due to the presence of graphene as carbon particles with a plate-like structure. On the other hand, in Manufacturing Example 5, where a negative electrode was manufactured by directly rolling lithium foil onto a porous substrate without forming a carbon coating, a large number of pores were found, unlike in Manufacturing Example 2.

[0130] Experimental Example 3: Lifetime Evaluation of Lithium-Lithium Symmetric Battery

[0131] The cycle life of the lithium metal batteries (which are lithium-lithium symmetric batteries) manufactured in Example 3 and Comparative Example 4 was evaluated at 25°C.

[0132] Specifically, at 0.5 mA / cm2 After a single discharge and charge cycle at a current density up to 10 mAh, the current density was 1.5 mA / cm². 2 The current density was repeatedly cycled to measure lifetime until a voltage range of -1.0 V or 1.0 V was reached. The results are shown in Table 2 below. Figure 8 and Figure 9 middle.

[0133] Table 2:

[0134] Refer to Table 2 above and the following... Figure 8 and Figure 9 It was confirmed that in Example 3, where a negative electrode was manufactured by forming a carbon coating containing carbon particles with a plate-like structure on a porous substrate, a longer lifespan was observed compared to Comparative Example 4, which used only a porous substrate without forming a carbon coating.

[0135] Thus, it was confirmed that although the porous substrate is located between the separator and the lithium surface and acts as a resistive layer, the lifetime is improved by forming a carbon coating containing carbon particles with plate-like structures, such as graphene, due to the effect of mitigating overvoltage.

[0136] Experimental Example 4: Evaluation of the discharge capacity of lithium metal batteries

[0137] The discharge capacity of the lithium metal batteries manufactured in Examples 1 and 2, and Comparative Examples 1 to 3, was evaluated.

[0138] Specifically, the battery's discharge capacity was measured by performing three cycles of 0.1 C discharge / 0.1 C charge and three cycles of 0.2 C discharge / 0.2 C charge within a voltage range of 1.8 V to 2.5 V, followed by three cycles of 0.5 C discharge / 0.3 C charge. The relative ratios of discharge capacities based on the discharge capacity (100%) of Comparative Example 1 are shown in Table 3 below. Furthermore, the aforementioned cycles were repeated to evaluate the discharge capacity, and the results are shown in... Figure 10 and Figure 11 middle.

[0139] Table 3:

[0140] Based on Table 3 above and Figure 10 and Figure 11The discharge capacity evaluation results confirmed that Examples 1 and 2, which contained a carbon coating with carbon particles having a plate-like structure and a porous substrate, exhibited relatively better discharge capacity as cycling progressed compared to Comparative Examples 1 to 3, which did not contain these. Furthermore, it was confirmed that in Comparative Example 3, which used polyimide (PI) as a porous substrate, the initial discharge capacity decreased rapidly due to the reactivity of lithium metal with polyimide.

[0141] It has been confirmed that, in the cases of Examples 1 and 2, the surface of the porous substrate, which serves as a support, has a higher affinity for lithium metal by using a carbon coating containing carbon particles with a plate-like structure. The pores of the porous substrate are reduced due to the carbon particles with a plate-like structure, such as graphene, forming a stable structure during lithium plating that is not affected by the relative distance to the positive electrode, thus improving lithium efficiency and discharge capacity.

[0142] Simple modifications and alterations to this invention fall within the scope of this invention, and the specific scope of protection of this invention will be apparent from the appended claims.

[0143] [Symbol Explanation]

[0144] 100: Porous substrate

[0145] 200: Carbon coating

[0146] 300: Lithium metal layer

Claims

1. A negative electrode for a lithium metal battery, wherein the lithium metal battery uses lithium metal as the negative electrode. The negative electrode comprises: Porous substrate; A carbon coating formed on the surface of the porous substrate; and The lithium metal layer located on the carbon coating, The carbon coating comprises carbon particles having a plate-like structure.

2. The negative electrode for a lithium metal battery according to claim 1, wherein the porous substrate comprises, selected from polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyacetal, polycarbonate, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon, poly(p-phenylenebenzobismuth subcarbonate) It is one of the groups consisting of azoles, polyarylates and combinations thereof.

3. The negative electrode for lithium metal batteries according to claim 1, wherein the porosity of the porous substrate is 40% to 90%.

4. The negative electrode for a lithium metal battery according to claim 1, wherein the thickness of the porous substrate is from 0.5 μm to 30 μm.

5. The negative electrode for a lithium metal battery according to claim 1, wherein the carbon coating comprises graphene or a graphene derivative having a plate-like structure.

6. The negative electrode for a lithium metal battery according to claim 1, wherein the weight of carbon particles coated per unit area of ​​the porous substrate is 0.1 g / m². 2 Up to 5 g / m 2 .

7. The negative electrode for a lithium metal battery according to claim 1, wherein the negative electrode has the following structure, wherein a carbon coating is formed on one surface of the porous substrate, and a lithium metal layer is stacked on one surface of the carbon coating facing the opposite direction to the porous substrate.

8. The negative electrode for a lithium metal battery according to claim 1, wherein the negative electrode has a multilayer structure, wherein a porous substrate is located in the center, a carbon coating is formed on two surfaces of the porous substrate, and a lithium metal layer is stacked on each surface of the carbon coating facing in the opposite direction to the porous substrate.

9. The negative electrode for a lithium metal battery according to claim 1, wherein the tensile strength of the negative electrode for a lithium metal battery is from 1 MPa to 300 MPa.

10. A lithium metal battery comprising a negative electrode according to any one of claims 1 to 9.

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