Lithium metal electrode for secondary battery, method for manufacturing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a lithium metal electrode for a secondary battery, a method for manufacturing the same, and a secondary battery including the same. According to one embodiment, a lithium metal electrode for a secondary battery can be provided, which includes a current collector and a metal layer including a lithium component and positioned on at least one surface of the current collector, and a protective layer including amorphous carbon and electronically insulating ceramic particles is formed on the metal side surface.

Description

[Technical Field]

[0001] The present embodiment relates to a lithium metal electrode for a secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. [Background technology]

[0002] In recent years, with the explosive demand for electric vehicles and the demand for increased driving distances, the development of secondary batteries with high capacity and high energy density to meet this demand has been actively pursued worldwide.

[0003] In order to reduce the cost of secondary batteries and improve their energy density, it has been proposed to use a lithium metal electrode as the negative electrode of lithium secondary batteries.

[0004] To form such a lithium metal anode, a lithium foil is typically rolled onto the current collector, but rolling it presents a problem in that it is difficult to achieve a lithium metal anode with a thickness of 20 μm or less.

[0005] On the other hand, in order to realize a secondary battery having a high energy density by substantially utilizing a lithium metal negative electrode, a thin-film lithium metal negative electrode having a thickness of 10 to 20 μmm is required.

[0006] However, when lithium metal is used as the anode in an all-solid-state battery, a high-resistance phase is generated due to the reaction between lithium and the all-solid-state electrolyte, and localized non-uniformity in current density during the charge / discharge process leads to the continuous generation of lithium dendrites or the generation of high-resistance lithium by-products, which can cause failures due to short circuits or overvoltage during charge / discharge, or a decrease in capacity.

[0007] To solve these problems, various methods have been proposed, such as forming a protective coating layer or a lithium alloy layer on the lithium metal to prevent reactions with the solid-state battery and the precipitation and growth of lithium dendrites, but they have yet to achieve sufficient lifespan characteristics for use in electric vehicles (EVs).

[0008] To meet these demands, active research is being conducted on secondary batteries that use a method in which lithium is deposited during the charge and discharge process using an anode-less coating layer made of a mixture of amorphous carbon and silver (Ag) nanoparticles.

[0009] However, during the charge and discharge process, materials with electronic conductivity, such as lithium-based alloys or lithium-containing compounds, are generated within the anode coating layer or at the interface, which can cause current concentration and lithium dendrites, resulting in a shortened lifespan.

[0010] In addition, the initial coulomb efficiency is low due to the irreversible reaction caused by amorphous carbon, which is the main material of the anode coating layer.

[0011] To solve these problems, a sacrificial cathode is used, and a large amount of noble metal nanoparticles is also used, which significantly reduces price competitiveness and makes commercialization difficult.

[0012] Therefore, there is a need to develop a technology that can produce electrodes with excellent initial efficiency and excellent charge-discharge characteristics. Summary of the Invention [Problem to be solved by the invention]

[0013] The present embodiment aims to provide a lithium metal electrode for a secondary battery that has excellent charge / discharge characteristics by preventing dendrite formation through a protective layer included in the electrode layer, a method for manufacturing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0014] According to an embodiment, a lithium metal electrode for a secondary battery includes a current collector, a metal layer including a lithium alloy and disposed on at least one surface of the current collector, and a protective layer disposed on the metal layer, the protective layer including amorphous carbon and electronically insulating ceramic particles. [Effects of the Invention]

[0015] According to this embodiment, the problem of a decrease in initial Coulomb efficiency can be solved by including electronically insulating ceramic particles in the electronically insulating protective layer and forming a lithium-containing metal layer between the electronically insulating protective layer and the current collector, and the charge-discharge characteristics can be significantly improved. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a lithium metal electrode fabricated according to an embodiment. [Figure 2] 10 is a schematic diagram of a lithium metal electrode according to another embodiment. [Figure 3] 1 is a schematic diagram illustrating a method for manufacturing a lithium metal electrode for a secondary battery according to an embodiment. [Figure 4] 1 is a SEM photograph showing a cross section of a current collector on which an alloy material coating layer is formed during the process of manufacturing a lithium metal electrode according to Example 1. [Figure 5] 1 is a SEM photograph showing a cross section of a current collector on which an alloy material coating layer and an electronic insulating protective layer are formed during the process of manufacturing a lithium metal electrode according to Example 1. [Figure 6A] 1 is an SEM photograph showing a cross section of a lithium metal electrode produced in Example 1. [Figure 6B] 1 is an SEM photograph showing a cross section of a lithium metal electrode produced according to Comparative Example 1. [Figure 6C] 1 is an SEM photograph showing a cross section of a lithium metal electrode produced in Comparative Example 2. [Figure 6D] 1 is an SEM photograph showing a cross section of a lithium metal electrode produced in Comparative Example 3. [Figure 7A] 1 is a photograph showing the surface microstructure of the lithium metal electrode prepared in Example 1. [Figure 7B] 1 is a photograph showing the results of component analysis of the lithium metal electrode produced in Example 1. [Figure 8A] 1 is a photograph showing the surface microstructure of a lithium metal electrode prepared according to Comparative Example 1. [Figure 8B] 1 is a photograph showing the results of component analysis of the lithium metal electrode produced in Comparative Example 1. [Figure 9A] 1 is a photograph showing the surface microstructure of a lithium metal electrode prepared according to Comparative Example 2. [Figure 9B] 1 is a photograph showing the results of component analysis of the lithium metal electrode produced in Comparative Example 2. [Figure 10A] 1 is a photograph showing the surface microstructure of a lithium metal electrode prepared according to Comparative Example 3. [Figure 10B] 1 is a photograph showing the results of component analysis of the lithium metal electrode produced in Comparative Example 3. [Figure 11] 1 is a diagram showing the results of evaluating the initial effects of secondary batteries manufactured according to Example 1 and Comparative Examples 1 to 3. [Figure 12] 1 is a diagram showing the results of evaluating the charge-discharge life of secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3. [Figure 13] 1 is a diagram showing the results of evaluating the charge-discharge life of secondary batteries manufactured in Examples 1 to 4 and Comparative Example 2. [Figure 14] 1 is a schematic diagram of a secondary battery to which a lithium metal electrode manufactured according to the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0017] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Thus, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention.

[0018] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0019] When a part is referred to as being "on" or "above" another part, this can be on or above the other part, with other parts in between. In contrast, when a part is referred to as being "directly on top of" another part, there are no other parts in between.

[0020] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0021] Hereinafter, embodiments of the present invention will be described in detail, but these are presented as examples and are not intended to limit the present invention, which is defined only by the scope of the claims set forth below.

[0022] FIG. 1 is a schematic diagram of a lithium metal electrode manufactured according to one embodiment, FIG. 2 is a schematic diagram of a lithium metal electrode according to another embodiment, and FIG. 3 is a schematic diagram of a method for manufacturing a lithium metal electrode for a secondary battery according to one embodiment.

[0023] Referring to FIG. 1, a lithium metal electrode 100 for a secondary battery according to one embodiment includes a current collector 11 and a metal layer 12 located on at least one surface of the current collector 11, and also includes a protective layer 30 located on the other surface of the metal layer 12 facing the current collector 11.

[0024] The current collector 11 is for electrical connection within the lithium secondary battery.

[0025] The current collector 11 may have the form of a thin film (foil), but is not limited thereto. For example, the current collector 11 may have the form of a mesh, a foam, a rod, a wire, or a sheet made by weaving wire (fiber).

[0026] A material having electrical conductivity and limited reactivity with lithium can be used as the material for the current collector 11. Examples of materials that can be used for the current collector 11 include copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, conductive polymers, and composite fibers in which a conductive layer is coated on a non-conductive polymer, or a combination thereof.

[0027] If the thickness of current collector 11 is too thick, the battery weight increases and the energy density of the battery decreases, whereas if the thickness of current collector 11 is too thin, there is a risk of overheating and damage during high current operation and there is a risk of damage due to tension during the battery manufacturing process. Therefore, the thickness of current collector 11 may be in the range of 1 μm to 50 μm.

[0028] The metal layer 12 includes a lithium alloy layer 21 disposed on the current collector 11 and containing a lithium alloy, and a lithium metal layer 41 disposed on the lithium alloy layer 21. The lithium alloy layer 21 may be a layer containing a lithium alloy formed by applying a current between the current collector 11 and a lithium supply source, resulting in an alloy of lithium-based elements contained in the coating layer of the current collector 11 and lithium deposited from the lithium supply source. When a high current is applied to form the metal layer, the electrodeposition process may result in a decrease in the performance of the lithium secondary battery. However, when the metal layer 12 is formed with a structure including a lithium alloy layer 21 containing a lithium element, applying a high current to the electrodeposition process may prevent excessive production of fine lithium particles or damage to the surface protective coating of the lithium metal layer already formed during the electrodeposition process.

[0029] More specifically, since the metal layer 12 of this embodiment includes a lithium alloy layer containing a lithium component, when a lithium metal layer is formed on the lithium alloy layer by applying a high current in the electrodeposition process, the initially generated lithium particles are induced to grow well, resulting in the formation of particles with a coarse structure, and the lithium metal layer, and consequently the metal layer 12, can have a uniform surface.

[0030] Therefore, the performance of the secondary battery using the lithium metal electrode of this embodiment, specifically the charge / discharge characteristics, can be significantly improved. Furthermore, since a high-performance lithium metal electrode for a secondary battery can be manufactured even when a high current is applied and an electrodeposition process is performed at a high speed, the productivity of the lithium metal electrode for a secondary battery can also be significantly improved.

[0031] The lithium alloy layer 21 may be an alloy of lithium and a lithium-loving metal, and the lithium-loving metal may be one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi, but is not limited thereto.

[0032] In this embodiment, the lithium alloy layer includes a lithium-phile metal, which has high electronic conductivity, and thus has the advantage of facilitating the electrodeposition of the lithium metal layer by smoothly supplying electrons from the current collector and reducing lithium ions.

[0033] The thickness of the metal layer 12 may be in the range of 1 μm to 100 μm, more specifically, 5 μm to 30 μm.

[0034] If the thickness of the metal layer 12 is too thick, when the lithium metal electrode of this embodiment is applied to a secondary battery, the weight and volume of the battery increase, resulting in a problem of a low energy density. In addition, when forming the metal layer 12, the time and cost of the electrodeposition process increase in proportion to the thickness, so the thickness of the metal layer 12 is preferably 100 μm or less.

[0035] Furthermore, if the thickness of the metal layer 12 is too thin, when the lithium metal electrode of this embodiment is applied to a secondary battery, the charge / discharge life of the battery may be reduced. Specifically, during charge / discharge of the battery, lithium in the battery is gradually consumed due to side reactions between the lithium contained in the negative electrode active material layer, i.e., the metal layer of the present invention, and the electrolyte, resulting in a decrease in battery capacity. However, if the thickness of the metal layer 12 is too thin, the amount of lithium available to replenish the lithium consumed during charge / discharge is reduced, thereby reducing the charge / discharge life of the battery. Therefore, it is preferable that the thickness of the metal layer 12 be 1 μm or more.

[0036] The protective layer 30 is located on the metal layer 12 and includes amorphous carbon and electronically insulating ceramic particles.

[0037] When lithium metal is used as the anode in an all-solid-state battery, high resistance is generated due to the reaction between the all-solid-state electrolyte and lithium, and localized non-uniformity in current density during the charge / discharge process can lead to the continuous generation of lithium dendrites or the generation of highly resistive lithium by-products, which can cause failures or a decrease in battery capacity due to short circuits or overvoltage during charge / discharge.

[0038] However, the protective layer containing amorphous carbon and electronically insulating ceramic particles as in this embodiment can improve not only the output characteristics and life characteristics of the lithium metal electrode, but also the structural stability.

[0039] More specifically, the lithium metal electrode of this embodiment includes a protective layer 30 containing amorphous carbon and electronically insulating ceramic particles, which can promote the movement of lithium ions on the electrode surface during charge and discharge, suppress the generation of electronically conductive materials at the interface, and reduce the electronic conductivity inside the protective layer 30.

[0040] Therefore, the performance of a secondary battery to which the lithium metal electrode according to this embodiment is applied, specifically the output characteristics and life characteristics of the battery, can be significantly improved.

[0041] The amorphous carbon may be at least one selected from the group consisting of acetylene black, super P black, carbon black, denka black, activated carbon, graphite, hard carbon, and soft carbon, but is not limited thereto.

[0042] The electronically insulating ceramic particles may be one or more selected from the group consisting of particles with low electronic conductivity, such as BN, AlN, C3N4, SiC, and Al2O3, but are not limited thereto.

[0043] In this embodiment, the electronically insulating ceramic particles may have an average particle size D(50) in the range of 100 nm to 1,000 nm. If the average particle size D(50) of the electronically insulating ceramic particles is less than 100 nm, aggregation between primary particles may cause uneven distribution of the ceramic particles in the coating layer. If the average particle size D(50) is greater than 1,000 nm, large particles may act as a resistance layer, reducing lithium ion conductivity.

[0044] The electronically insulating ceramic particles may be formed in a plate-like shape, but are not limited thereto. When the ceramic particles are in a plate-like shape, the wettability with the metal layer 12 is improved, thereby increasing the adhesive strength and strengthening the mechanical bond between the metal layer 12 and the protective layer 30, which is advantageous for improving the performance of the lithium metal electrode.

[0045] The electronically insulating protective layer may contain amorphous carbon and electronically insulating ceramic particles in a weight ratio of 99.5:0.5 to 40:60, specifically 98.5:1.5 to 50:50, and more specifically 97:3 to 70:30.

[0046] If the amount of electronically insulating ceramic particles mixed is too small, the effect of suppressing the generation of electronically conductive substances by mixing the electronically insulating ceramic particles cannot be fully obtained, and if the amount of electronically insulating ceramic particles mixed is too large, the resistance of the entire coating layer becomes too high, which causes a problem of impeding lithium ion conduction.

[0047] On the other hand, the protective layer of this embodiment may contain a binder.

[0048] In this case, the binder may be an aqueous binder, and the aqueous binder may be at least one selected from the group consisting of a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), and acrylic rubber, and a polymer resin such as hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylidene fluoride, but is not limited thereto.

[0049] Here, the binder may be added in an amount of 1 to 15 parts by weight, more specifically 3 to 10 parts by weight, based on the weight of the slurry formed by mixing the electronically insulating ceramic particles, amorphous carbon, and water.

[0050] When the amount of binder added satisfies the above range, the particles constituting the protective layer can be efficiently bound to form a protective layer with excellent performance without causing a decrease in battery energy density due to an increase in weight and volume, thereby further improving the life characteristics of the secondary battery. If the amount of binder added is too small, the bonding strength between the particles when forming the protective layer will be reduced, while if the amount of binder added is too large, not only will the energy density be reduced but the resistance of the protective layer will also be significantly increased, hindering lithium ion conduction.

[0051] The thickness of the protective layer containing amorphous carbon, electronically insulating ceramic particles, and a binder may be in the range of 0.01 μm to 50 μm, specifically 1 μm to 20 μm. When the thickness of the protective layer satisfies this range, the effect of containing amorphous carbon and electronically insulating ceramic particles is suppressed, which reduces the electronic conductivity within the protective layer. On the other hand, if the protective layer containing amorphous carbon and electronically insulating ceramic particles is too thin, it may not be able to fulfill its role as a protective layer. On the other hand, if the protective layer is too thick, the resistance of the protective layer may be too high, which may cause an increase in overvoltage during secondary battery operation. Furthermore, the increase in weight and volume may cause a decrease in battery energy density. However, the thickness of the protective layer can be variably adjusted depending on the design of the secondary battery structure.

[0052] Meanwhile, although not shown, the metal layer 12 of this embodiment may further include a coating layer (SEI, Solid-Electrolyte Interphase) located on the surface of the metal layer 12 .

[0053] The coating layer is formed by a reaction between the lithium metal of the electrodeposited lithium source and a plating solution during the manufacturing process of the metal layer 12. The thickness, composition, and properties of the coating layer can be controlled by adjusting the composition of the plating solution used and the conditions of the electrodeposition process.

[0054] The thickness of the coating layer may be, for example, in the range of 2 nm to 2 μm, more specifically, 10 nm to 500 nm.

[0055] If the coating layer located on the surface of the metal layer 12 is too thick, the lithium ion conductivity may decrease and the interfacial resistance may increase, which may result in a deterioration in charge / discharge characteristics when used in a battery. Also, if the coating layer is too thin, the coating layer may be easily washed away during the process of applying the lithium metal electrode of the present embodiment to a battery.

[0056] Therefore, it is preferable that the coating layer be formed uniformly and densely over the entire surface of the metal layer 12 with a small thickness that satisfies the above thickness range.

[0057] In this case, the coating layer may include at least one material selected from the group consisting of Li-NCHO-based ionic compounds, Li-PCHO-based ionic compounds, LiF, and Li3N.

[0058] FIG. 2 is a schematic diagram of a lithium metal electrode according to another embodiment.

[0059] 2, a lithium metal electrode 100 for a secondary battery according to another embodiment includes a current collector 11 and a metal layer 12 formed by mixing lithium and a lithium alloy and located on at least one surface of the current collector 11. Here, the lithium alloy may be formed by applying a current between the current collector 11 and a lithium supply source, and alloying a lithium-loving component contained in a coating layer formed on the current collector 11 with lithium deposited from the lithium supply source.

[0060] In this case, the metal layer 12 may include a lithium-philic metal, which may be, but is not limited to, one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

[0061] In this example, the metal layer 12 contains a lithium-philic metal. When the metal layer 12 containing the lithium-philic metal is formed in this manner, the nucleation free energy can be reduced at the initial stage of nucleation of lithium particles in the electrodeposition process, and therefore a lithium metal layer having a coarse particle structure can be formed even under high current and overvoltage conditions.

[0062] In this embodiment, the thickness of the metal layer 12 may be in the range of 1 μm to 100 μm, more specifically, 5 μm to 30 μm. In this embodiment, when the metal layer 12 satisfies this thickness range, it is possible to improve the charge / discharge life of the battery, maximize the energy density of the battery, and minimize the time and cost of the electrodeposition process when forming the metal layer 12. If the metal layer is too thin, initial irreversibility reduces the initial coulomb efficiency, resulting in a lack of surplus lithium, and charge / discharge performance deteriorates. On the other hand, if the metal layer is too thick, it not only reduces the energy density of the battery, but also increases the process time and the amount of metal raw material used when forming the metal layer.

[0063] Meanwhile, although not shown in FIG. 2, the metal layer of this embodiment may further include a coating layer located on the surface of the metal layer.

[0064] Such a coating layer is the same as that described in the lithium metal electrode for a secondary battery according to the embodiment described above, and therefore will not be described here.

[0065] According to one embodiment, a method for manufacturing a lithium metal electrode includes the steps of: forming a coating layer on at least one surface of a current collector using a coating composition including a lithium-phile component; forming a protective layer on the surface of the coating layer using a slurry including amorphous carbon and electronic insulating particles; positioning the current collector on which the coating layer and protective layer are formed in a plating solution, and then positioning a lithium supply source at a predetermined distance from the protective layer; and applying a current between the current collector and the lithium supply source to form a metal layer including a lithium alloy in which the lithium-phile component included in the coating layer and lithium deposited from the lithium supply source are alloyed.

[0066] In the step of forming a protective layer on the surface of the coating layer using the slurry containing amorphous carbon and electronically insulating particles, the electronically insulating protective layer may contain amorphous carbon and electronically insulating ceramic particles in a weight ratio of 99.5:0.5 to 40:60, specifically 98.5:1.5 to 50:50, and more specifically 97:3 to 70:30.

[0067] First, a coating composition containing a lithium-phile metal is used to form an alloy material coating layer on at least one surface of a current collector.

[0068] In this case, the lithium-loving metal may be, for example, one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi, but is not limited thereto.

[0069] The alloy material coating layer may be formed by at least one of electrolytic and electroless plating, sputtering, electron beam deposition, and thermal vapor deposition.

[0070] Meanwhile, in the step of forming the alloy material coating layer, the thickness of the alloy material coating layer formed on at least one surface of the current collector may be in the range of 0.001 μm to 10 μm, specifically 0.01 μm to 1 μm, and more specifically 100 nm to 500 nm.

[0071] If the thickness of the alloy material coating layer is too thin, it is insufficient to perform the function of forming a lithium alloy with lithium, and if the thickness is too thick, forming the alloy material coating layer requires a large amount of cost and time, resulting in reduced production efficiency and economic efficiency, and an increased weight of the battery, resulting in a reduced energy density.

[0072] After the alloy material coating layer forming step, a protective layer is applied to the surface of the formed alloy material coating layer.

[0073] In this case, the protective layer may be an electronically insulating protective layer, and may include amorphous carbon and electronically insulating ceramic particles.

[0074] In this case, the amorphous carbon may be at least one selected from the group consisting of acetylene black, Super P black, carbon black, Denka black, activated carbon, graphite, hard carbon, and soft carbon, but is not limited thereto.

[0075] The electronically insulating ceramic particles may be one or more selected from the group consisting of particles with low electronic conductivity, such as BN, AlN, C3N4, SiC, and Al2O3, but are not limited thereto.

[0076] Meanwhile, the electron insulating protective layer may contain a binder.

[0077] The binder may be an aqueous binder, and the aqueous binder may be at least one selected from the group consisting of a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), and acrylic rubber, and a polymer resin such as hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylidene fluoride, but is not limited thereto.

[0078] The electronic insulating protective layer may be formed by applying a slurry prepared by mixing the amorphous carbon, electronic insulating ceramic particles, and a binder in water using at least one of a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

[0079] Here, the electronically insulating protective layer may contain amorphous carbon and electronically insulating ceramic particles in a weight ratio of 99.5:0.5, specifically 98.5:1.5 to 50:50, and more specifically 97:3 to 70:30.

[0080] The binder may be added in an amount of 0.5 to 10 parts by weight, more specifically 1 to 3 parts by weight, based on the weight of the electronically insulating ceramic particles, amorphous carbon, and water mixed together.

[0081] Meanwhile, in the step of forming the electronic insulating protective layer, the thickness of the electronic insulating protective layer formed on the surface of the alloy material coating layer may be in the range of 0.01 μm to 50 μm, more specifically, 1 μm to 20 μm.

[0082] When the thicknesses of the alloy material coating layer and the electronic insulating protective layer satisfy the above ranges, a lithium metal electrode for a secondary battery according to an embodiment can be manufactured, more specifically, to have a lithium metal electrode structure as shown in FIG. 1 or FIG. 2.

[0083] After the step of forming the electronic insulating protective layer, the steps of positioning the current collector on which the alloy material coating layer and the electronic insulating protective layer are sequentially formed in a plating solution, positioning a lithium supply source at a predetermined distance from the current collector, and applying a current between the current collector and the lithium supply source to form a metal layer are performed.

[0084] The step of forming the metal layer will be described in more detail with reference to FIG.

[0085] First, the current collector 11 having the alloy material coating layer 20 and the electronic insulating protective layer 30 formed thereon is placed in the plating solution 50, and then the lithium supply source 40 is placed at a predetermined distance from the electronic insulating protective layer 30.

[0086] The lithium supply source 40 may be, for example, lithium metal, a lithium alloy, a foil of the lithium metal or lithium alloy pressed onto a current collector, or a plating solution in which a lithium salt is dissolved.

[0087] The current collector 11 is the same as that described above, and therefore will not be described here.

[0088] The plating solution 50 can be prepared by dissolving a lithium salt in a non-aqueous solvent.

[0089] More specifically, the lithium salt may be LiCl, LiBr, LiI, LiCO3, LiNO3, LiFSI, LiTFSI, LiBF4, LiPF6, LiAsF6, LiClO4, LiN(SO2CF3)2, LiBOB, or a combination thereof. The concentration of the lithium salt may be 0.1 to 3.0 M based on the total electrolyte solution.

[0090] More specifically, in this embodiment, the plating solution is characterized in that it contains a nitrogen-based compound in at least one of the lithium salt and the non-aqueous solvent.

[0091] The nitrogen-based compound may include, for example, one or more selected from the group consisting of lithium nitrate, lithium bis fluorosulfonyl imide, lithium bis trifluoromethane sulfonimide, caprolactam (e-caprolactam), methyl caprolactam (N-methyl-e-caprolactam), triethylamine, and tributylamine.

[0092] Among the nitrogen-based compounds, at least one of lithium nitrate, lithium bisfluorosulfonyl imide, and lithium bistrifluoromethane sulfonimide can be used as the lithium salt.

[0093] Among the nitrogen-based compounds, at least one of caprolactam (e-caprolactam), methylcaprolactam (N-methyl-e-caprolactam), triethylamine, and tributylamine can be used as the non-aqueous solvent.

[0094] Meanwhile, a typical non-aqueous solvent may be added to the plating solution depending on the viscosity of the plating solution. If the viscosity of the plating solution is too high, the mobility of lithium ions decreases, reducing the ionic conductivity of the plating solution, thereby increasing the time required for the electrodeposition process and reducing productivity.

[0095] The solvent can include, for example, one or more selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and 1,3,5-trioxane.

[0096] The current density of the current applied in the step of applying a current to form a lithium metal layer on at least one surface of the current collector is 0.1 mA / cm 2 ~100mA / cm 2 in the range of 0.2 mA / cm 2 ~50mA / cm 2 range, 5mA / cm 2 ~30mA / cm 2 range or 7mA / cm 2 ~25mA / cm 2 may be in the range of

[0097] The duration of application of the current may be in the range of 0.05 hours to 50 hours, more specifically in the range of 0.25 hours to 25 hours.

[0098] As described above, this embodiment can prevent excessive production of fine lithium particles even under high current conditions and encourage the initial production of lithium particles to grow well, thereby fabricating a lithium metal electrode having a metal layer including a lithium metal layer with a coarse particle structure. Furthermore, the metal layer fabricated in this manner also has excellent surface uniformity. Specifically, as shown in FIG. 1, a lithium metal electrode structure can be fabricated having a lithium alloy layer 21 containing a lithium component and a lithium metal layer 41 located on the lithium alloy layer 21, as shown in FIG. 1, or a lithium metal electrode structure can be fabricated having a metal layer 12 composed of a mixture of lithium and a lithium alloy, as shown in FIG. 2. The thickness of the metal layer 12 may be in the range of 1 μm to 100 μm, more specifically, 5 μm to 30 μm.

[0099] When the lithium metal electrode manufactured according to this embodiment is used, the charge and discharge characteristics of the secondary battery can be significantly improved.

[0100] A secondary battery according to one embodiment includes a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, where the negative electrode may be a lithium metal electrode according to the present invention.

[0101] FIG. 14 is a schematic diagram showing the structure of a secondary battery according to one embodiment.

[0102] Referring to FIG. 14, the secondary battery 200 of this embodiment may include an electrode assembly including a positive electrode 70, a negative electrode 100, and a separator 90 disposed between the positive electrode 70 and the negative electrode 100.

[0103] Such an electrode assembly is wound or folded and housed in a battery case 95 .

[0104] Then, the electrolyte 80 is injected into the battery case 95 and sealed to complete the secondary battery 200. The battery case 95 may have a cylindrical, square, pouch, coin, or other shape.

[0105] For convenience, FIG. 14 illustrates the negative electrode 100 according to one embodiment, but any of the lithium metal electrodes for secondary batteries according to the above-described embodiments can be used as the negative electrode.

[0106] The positive electrode 70 may include a positive electrode active material layer and a positive electrode current collector.

[0107] The positive electrode active material layer may contain, for example, a Li compound containing at least one metal selected from the group consisting of Ni, Co, Mn, Al, Cr, Fe, Mg, Sr, V, La, and Ce, and at least one nonmetallic element selected from the group consisting of O, F, S, P, and combinations thereof. The positive electrode active material layer may contain active material particles having an average particle size of approximately 0.01 μm to 200 μm, which may be appropriately selected depending on the required characteristics of the battery.

[0108] In some cases, a conductive agent may be added to the positive electrode active material layer.

[0109] The conductive agent may be, for example, fine carbon such as carbon black and ultrafine graphite particles, acetylene black, nano metal particle paste, etc., but is not limited thereto.

[0110] The positive electrode current collector serves to support the positive electrode active material layer, and may be, for example, an aluminum foil, a nickel foil, or a combination thereof, but is not limited thereto.

[0111] The electrolyte 80 filled in the lithium secondary battery 200 may be a non-aqueous electrolyte solution or a solid electrolyte.

[0112] The non-aqueous electrolyte may include, for example, a lithium salt such as lithium hexafluorophosphate or lithium perchlorate and a solvent such as ethylene carbonate, propylene carbonate, or butylene carbonate. The solid electrolyte may be, for example, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte, or an inorganic solid electrolyte such as LiI or LiN.

[0113] The separator 90 separates the positive and negative electrodes and provides a path for lithium ions to move. Any material commonly used in lithium secondary batteries can be used. That is, a material having low resistance to ion movement in the electrolyte and excellent electrolyte humidification ability can be used. Here, the separator may be made of, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven or woven fabric. Meanwhile, when a solid electrolyte is used as the electrolyte 80, the solid electrolyte may also serve as the separator 90.

[0114] [Mode for carrying out the invention] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined solely by the scope of the claims set forth below.

[0115] Example 1 A lithium metal electrode for a secondary battery according to Example 1 was manufactured by the process shown in FIG.

[0116] First, a coating layer 20 containing silver (Ag) was formed to a thickness of about 300 nm on one surface of a copper current collector 11 using an electroless plating method (see FIG. 4).

[0117] Next, a protective layer 30 was formed on the surface of the coating layer 20 by slurry coating using a comma coater to a thickness of about 5 μm, specifically, an electronic insulating protective layer (see FIG. 5).

[0118] Here, the protective layer 30 was made by mixing amorphous carbon using acetylene black and electronic insulating ceramic particles using hexagonal boron nitride (h-BN) in a weight ratio of 7:3 with water as a solvent. At this time, 1.5 wt% each of carboxymethyl cellulose and styrene-butadiene rubber binders were added based on the weight of the mixture of acetylene black, hexagonal boron nitride, and water to prepare a slurry.

[0119] The current collector 11 having the coating layer 20 and the protective layer 30 formed thereon is placed in the plating solution 50, and then the lithium supply source 40 is placed at a predetermined distance from the protective layer 30.

[0120] The plating solution 50 was prepared by adding 40 wt % and 10 wt % of nitrogen-based compounds, lithium bis(fluorosulfonyl)imide and lithium nitrate, respectively, based on 100 wt % of the plating solution, to a 1,2-dimethoxyethane solvent, and adding 10 wt % of fluoroethylene carbonate, a fluorine-based compound, based on 100 wt % of the plating solution.

[0121] As the lithium supply source 40, a lithium metal plate having a purity of 99.9% or more and a thickness of 500 μm was used by being pressed onto a copper current collector plate (Cu plate).

[0122] After laminating the lithium supply source 40 and the current collector 11 in an electrically insulated state in the plating solution 50, a current was applied using a power supply device with the lithium supply source 40 and the current collector 11 as the (+) electrode and (-) electrode, respectively, to deposit lithium between the current collector 11 and the electronic insulating protective layer 30, thereby forming a metal layer.

[0123] At this time, the average current density of the process is 4mA / cm 2 The process took about 15 minutes to produce a lithium metal electrode, i.e., a negative electrode, on which a metal layer of about 5 μm in thickness was formed.

[0124] <Examples 2, 3, 4 and Reference Example 1> A negative electrode was prepared in the same manner as in Example 1, except that the weight ratio of amorphous carbon and electronic insulating ceramic particles was adjusted as shown in Table 3 below when preparing the protective layer.

[0125] <Comparative Example 1> A negative electrode was prepared in the same manner as in Example 1, except that a coating layer was not formed on one side of the current collector, a protective layer was formed using 100% amorphous carbon, and no metal layer was formed between the current collector and the protective layer.

[0126] <Comparative Example 2> A negative electrode was prepared in the same manner as in Example 1, except that the protective layer was formed using 100% amorphous carbon.

[0127] <Comparative Example 3> A negative electrode was prepared in the same manner as in Example 1, except that no coating layer was formed on one surface of the current collector and no metal layer was formed between the current collector and the protective layer.

[0128] (Experimental Example 1) The cross-sectional structures of the negative electrodes prepared in Example 1 and Comparative Examples 1, 2, and 3 were analyzed and are shown in FIGS. 6A, 6B, 6C, and 6D, respectively.

[0129] 6A, 6B, 6C, and 6D are photographs showing cross sections of the negative electrodes prepared in Example 1 and Comparative Examples 1, 2, and 3 analyzed using a scanning electron microscope (SEM).

[0130] 6B and 6D, it can be seen that the negative electrodes prepared in Example 1 and Comparative Example 2 had a uniform metal layer formed between the protective layer and the current collector.

[0131] (Experimental Example 2) The surface microstructures of the negative electrodes prepared in Example 1 and Comparative Examples 1, 2, and 3 are shown in Figures 7A, 8A, 9A, and 10A, respectively. The surface components of the negative electrodes prepared in Example 1 and Comparative Examples 1, 2, and 3 were analyzed and are shown in Figures 7B, 8B, 9B, and 10B.

[0132] The surface microstructure of the negative electrode was analyzed using a scanning electron microscope (SEM), and the components of the negative electrode surface were analyzed using energy dispersive X-ray spectroscopy.

[0133] Comparing Figures 7A, 7B, 10A, and 10B with Figures 8A, 8B, 9A, and 9B, it can be seen that boron (B) and nitrogen (N) elements are observed on the surface of the anodes fabricated in Example 1 and Comparative Example 3, which contain electronically insulating ceramic particles. This is believed to be due to the use of hexagonal boron nitride as the electronically insulating ceramic particles. On the other hand, fluorine (F) and sulfur (S) are additionally observed on the surface of the anodes fabricated in Example 1 and Comparative Example 2, which used an electrodeposition plating process. This is believed to be due to a surface insulating layer (SEI) formed by the decomposition reaction of the plating solution during the electrodeposition process. This confirms that the surface of the anode contains a layer containing a Li-NCHO-based ionic compound and an ion-conductive material, such as LiF, formed by the fluorine-based compound in the plating solution.

[0134] (Experimental Example 3) All-solid-state batteries were fabricated using the negative electrodes, i.e., lithium metal electrodes, fabricated in Example 1 and Comparative Examples 1, 2, and 3, as shown in FIG. 14, and the initial coulombic efficiency was evaluated.

[0135] For evaluation of the initial coulombic efficiency of the all-solid-state battery cell, a pressurized dedicated evaluation cell capable of maintaining an inert atmosphere was used.

[0136] Specifically, the solid electrolyte was sulfide-based argyrodite (Li6PS5Cl), which was fabricated into pellets with a thickness of approximately 0.7 mm and compressed at a pressure of 370 MPa to increase its density.

[0137] Lithium having a thickness of 0.5 mm was placed on one side of the solid electrolyte, and the negative electrodes prepared in Example 1 and Comparative Examples 1, 2, and 3 were placed on the other side. The positive electrode and the negative electrode according to the present invention were attached to the solid electrolyte by applying a pressure of 50 MPa.

[0138] During the initial coulombic efficiency evaluation, the dedicated evaluation cell was pressurized to a pressure of 16 MPa.

[0139] Here, the initial coulombic efficiency is 1 mA / cm during the first charging process. 2 Charge for 3 hours at a constant current of 3mAh / cm 2 After charging, 1mA / cm 2 The discharge was stopped when the discharge voltage exceeded 1V, and the discharge capacity was measured and calculated.

[0140] The results of evaluating the initial coulombic efficiency of the secondary battery are shown in FIG. 11 and Table 1 below.

[0141] [Table 1]

[0142] 8A, 8B, 10A, 10B and Table 1, the all-solid-state batteries using the anodes manufactured according to Comparative Examples 1 and 3, in which no metal layer was formed between the current collector and the protective layer, exhibited low initial Coulombic efficiencies of 81.3% and 88.8%, respectively. This confirms that a considerable amount of lithium is consumed in an initial irreversible reaction during the charging process, which is believed to be mainly due to the irreversible reaction caused by amorphous carbon in the protective layer.

[0143] Meanwhile, the secondary batteries using the anodes manufactured in Example 1 and Comparative Example 2, in which a metal layer was formed between the current collector and the protective layer through an electrodeposition process, exhibited high initial Coulombic efficiency of 131.0% and 144.0%, respectively. This is believed to be because the initial discharge capacity was larger than the charge capacity due to the lithium contained in the metal layer and the excess lithium in the lithium alloy.

[0144] Therefore, it can be confirmed that when a negative electrode having a metal layer formed thereon is manufactured by the method of this example, the problem of a decrease in discharge capacity due to initial irreversibility does not occur.

[0145] (Experimental Example 4) (Experimental Example 4-1) All-solid-state batteries were fabricated using the negative electrodes, i.e., lithium metal electrodes, fabricated in Example 1 and Comparative Examples 1, 2, and 3, as shown in FIG. 14, and then the charge-discharge characteristics were evaluated.

[0146] The all-solid-state battery cell used in the charge / discharge evaluation was the pressurized dedicated evaluation cell used in Experimental Example 3.

[0147] The charge / discharge performance was evaluated as follows.

[0148] 1mA / cm 2 Charge for 1 hour at a constant current of 1mA / cm 2 One cycle was defined as one hour of discharge at a constant current of 1000 kJ / s.

[0149] In addition, the charge / discharge life was defined as the end of the life when a short circuit occurs between the positive electrode and the negative electrode prepared according to the present invention during the charge / discharge process or when the voltage between the two electrodes exceeds 2V.

[0150] The results of evaluating the charge / discharge performance are shown in FIG. 12 and Table 2 below.

[0151] [Table 2]

[0152] 12 and Table 2, the charge-discharge lifespans of the all-solid-state batteries employing the anodes manufactured according to Comparative Example 1 and Comparative Example 3, in which no metal layer was formed between the current collector and the protective layer, were 68 and 215 cycles, respectively, and the charge-discharge lifespans of the all-solid-state batteries employing the anodes manufactured according to Comparative Example 2 and Example 1, in which a metal layer was formed between the current collector and the protective layer, were 292 and 881 cycles, respectively. In other words, it can be seen that the all-solid-state battery employing the anode in which a metal layer was formed between the current collector and the protective layer had a significantly better charge-discharge lifespan than the all-solid-state battery employing the anode in which no metal layer was formed between the current collector and the protective layer.

[0153] Therefore, when a negative electrode having a metal layer formed between a current collector and a protective layer is used, it can be confirmed that the charge / discharge life of the secondary battery is significantly improved.

[0154] Furthermore, when Example 1 was compared with Comparative Example 2 in which a metal layer was formed between the current collector and the protective layer, the charge-discharge life of the all-solid-state battery employing the anode manufactured according to Example 1, which contained ceramic particles in the protective layer, was 881 cycles, which was significantly superior to the charge-discharge life of the all-solid-state battery employing the anode manufactured according to Comparative Example 2, which did not contain ceramic particles in the protective layer, which was 292 cycles.

[0155] Similarly, when comparing Comparative Example 1 and Comparative Example 3 in which no metal layer was formed between the current collector and the protective layer, the charge-discharge life of the all-solid-state battery using the anode manufactured according to Comparative Example 3, in which the protective layer contained ceramic particles, was 215 cycles, which was significantly superior to the charge-discharge life of the all-solid-state battery using the anode manufactured according to Comparative Example 1, in which the protective layer did not contain ceramic particles, which was 68 cycles.

[0156] Therefore, it can be confirmed that the charge / discharge life of the secondary battery containing ceramic particles in the protective layer is significantly improved.

[0157] In particular, the charge-discharge life of the all-solid-state battery using the anode manufactured according to Example 1, in which a metal layer was formed between the current collector and the protective layer and the protective layer contained ceramic particles, was 881 cycles, which was significantly superior to the charge-discharge life of the all-solid-state batteries using the anodes manufactured according to Comparative Examples 1, 2, and 3.

[0158] Therefore, it can be seen that when a negative electrode in which a metal layer is formed between a protective layer containing ceramic particles and a current collector according to the present invention is applied, the charge / discharge life of the secondary battery can be significantly improved.

[0159] (Experimental Example 4-2) The charge-discharge characteristics of all-solid-state batteries using anodes prepared according to Examples 2, 3, and 4 and Reference Example 1, in which the weight ratio of amorphous carbon to electronic insulating ceramic particles was changed when preparing the electronic insulating protective layer, were evaluated and are shown in FIG. 13 and Table 3 below.

[0160] [Table 3]

[0161] Referring to FIG. 13 and Table 3, as the amount of electronically insulating ceramic particles in the electronically insulating protective layer increases, the charge / discharge life of the all-solid-state battery tends to increase and then decrease again.

[0162] When the weight ratio of electronically insulating ceramic particles to amorphous carbon in the electronically insulating protective layer was 70:30, the charge / discharge life was found to be shorter than that of an all-solid-state battery containing a protective layer made of 100% amorphous carbon.

[0163] The present invention is not limited to the above-described embodiments, and may be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not limiting.

Claims

1. current collector; a metal layer including a lithium alloy and located on at least one surface of the current collector; and a protective layer overlying the metal layer; The protective layer comprises amorphous carbon and electronically insulating ceramic particles.

2. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the electronically insulating ceramic particles are plate-like particles having an average particle diameter D(50) in the range of 100 nm to 1,000 nm.

3. The electronic insulating ceramic particles are BN, AlN, C ３ N ４ , SiC and Al ２ O ３ 2. The lithium metal electrode for a secondary battery according to claim 1, comprising one or more of the following:

4. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the protective layer contains amorphous carbon and electronically insulating ceramic particles in a weight ratio of 99.5:0.5 to 40:

60.

5. The metal layer containing a lithium alloy is 2. The lithium metal electrode for a secondary battery according to claim 1, comprising a lithium alloy layer located on the current collector and a lithium metal layer located on the lithium alloy layer.

6. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the metal layer containing a lithium alloy is a composite layer containing lithium and a lithium alloy.

7. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the metal layer containing a lithium alloy is a composite layer containing at least one of In, Ag, Sn, Zn, Si, Al, and Bi.

8. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the average thickness of the metal layer is 1 μm to 100 μm.

9. 2. The lithium metal electrode for a secondary battery according to claim 1, wherein the protective layer has an average thickness of 1 μm to 20 μm.

10. The protective layer is further comprising a coating layer located on the surface of the protective layer; The coating layer is made of an ionic compound such as Li-N-C-H-O, Li-P-C-H-O, LiF, and Li ３ 2. The lithium metal electrode for a secondary battery according to claim 1, comprising one or more materials selected from the group consisting of N.

11. forming a coating layer on at least one surface of a current collector using a coating composition containing a lithium-philic component; forming a protective layer on the surface of the coating layer using a slurry containing amorphous carbon and electronically insulating ceramic particles; placing the current collector having the coating layer and the protective layer formed thereon in a plating solution, and then placing a lithium supply source at a predetermined distance from the protective layer; applying a current between the current collector and the lithium supply source to form a metal layer including a lithium alloy in which the lithium-loving component contained in the coating layer is alloyed with lithium deposited from the lithium supply source.

12. In the step of forming the coating layer, 12. The method for manufacturing a lithium metal electrode for a secondary battery according to claim 11, wherein the thickness of the coating layer formed on at least one surface of the current collector is in the range of 0.001 μm to 10 μm.

13. forming a protective layer on the surface of the coating layer using a slurry containing amorphous carbon and electronically insulating ceramic particles; 12. The method for manufacturing a lithium metal electrode for a secondary battery according to claim 11, wherein the weight ratio of the amorphous carbon to the electronic insulating ceramic particles is 99.5:0.5 to 40:

60.

14. In the step of forming the metal layer, The metal layer is a lithium alloy layer containing the lithium alloy; The method for producing a lithium metal electrode for a secondary battery according to claim 11, wherein the electrode has a multilayer structure including a lithium metal layer formed on the lithium alloy layer.

15. In the step of forming the metal layer, The metal layer is 12. The method for producing a lithium metal electrode for a secondary battery according to claim 11, wherein the electrode has a single layer structure containing the lithium alloy and lithium metal deposited from the lithium supply source.

16. In the step of forming the metal layer containing a lithium alloy, 12. The method for producing a lithium metal electrode for a secondary battery according to claim 11, wherein the thickness of the metal layer is 1 μm to 100 μm.

17. Negative electrode; a positive electrode; and Contains electrolytes, The negative electrode is a lithium metal electrode for a secondary battery according to any one of claims 1 to 10.

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