Lithium metal electrode for lithium secondary battery and method of manufacturing same

Abstract

The present invention relates to a lithium metal electrode and method of manufacturing same. The lithium metal electrode of the present invention comprises: a current collector; a metal layer positioned on at least one surface of the current collector and including a lithium alloy; and a protective layer positioned on the metal layer. The porosity of the protective layer is 30-60%, and the binder content is 5-15 wt % with reference to 100 wt % of the entire amorphous carbon in the protective layer.

Description

Lithium metal electrode for lithium secondary battery and method for manufacturing same

[0001] The present invention relates to a lithium secondary battery, and more particularly, to a lithium metal electrode for a lithium secondary battery and a method for manufacturing the same.

[0002] To reduce the cost and increase the energy density of secondary batteries, the use of lithium metal electrodes as cathodes in lithium secondary batteries is essential. Specifically, all-solid-state batteries are attracting attention as next-generation batteries for high-energy densities, such as those required for electric vehicles (EVs).

[0003] All-solid-state batteries offer numerous advantages, including superior stability and high-voltage operation due to the elimination of liquid electrolytes. Furthermore, they reduce the need for cooling and safety-related components, resulting in higher energy density within the battery pack. Furthermore, they operate over a wide temperature range. To achieve truly high energy densities in these all-solid-state batteries, the thick, low-capacity graphite-based anode materials must be replaced with thin, high-capacity lithium. Considering cost-effectiveness and energy density, a thin-film lithium metal electrode with a thickness of 10 to 20 μm is practically required.

[0004] Typically, lithium metal electrodes are formed by rolling copper foil as a current collector and lithium foil, or by depositing a lithium thin film on copper foil. However, rolling is difficult to produce wide and thin films, and deposition is uneconomical. To address these shortcomings, a method has been proposed to form an anode by electrochemically depositing lithium on copper foil.

[0005] However, when a lithium metal electrode is used as a cathode in an all-solid-state battery, a high-resistance phase is created by the reaction between lithium and the all-solid-state electrolyte, and lithium dendrites are continuously created or high-resistance lithium byproducts are created due to local unevenness in the current density during the charge and discharge process, which causes problems such as the battery not being able to perform its function due to a short circuit or overvoltage during charge and discharge, or a problem of reduced capacity.

[0006] In particular, when forming a protective layer, there is growing interest in improving the lifespan characteristics when applied to batteries by increasing the adhesive strength between the metal layer and the protective layer, enhancing the bonding strength, and preventing dendrite growth.

[0007] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery increases the adhesive strength between a metal layer and a protective layer, increases the bonding strength, and suppresses the growth of dendrites, thereby providing a lithium metal battery having improved life characteristics when applied to the battery.

[0008] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode for a lithium secondary battery provides a method for manufacturing a lithium metal electrode for a lithium secondary battery having the advantages described above.

[0009] According to one embodiment of the present invention, a lithium metal electrode includes a current collector, a metal layer positioned on at least one surface of the current collector and including a lithium alloy, and a protective layer positioned on the metal layer, wherein the porosity of the protective layer is 30 to 60%, and in one embodiment, the protective layer may include amorphous carbon and a binder. The content of the binder may be 5 to 15 wt% based on 100 wt% of the total amorphous carbon in the protective layer.

[0010] In one embodiment, the bonding strength of the entire body and the protective layer may be 30 to 80 mN / cm. In one embodiment, the metal layer may include a lithium alloy layer including an alloy composed of lithium and a lithium-friendly metal.

[0011] In one embodiment, the lithium-friendly metal may be at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi. In one embodiment, the metal layer may include a lithium metal layer positioned on a lithium alloy layer.

[0012] In one embodiment, the protective layer may further include ceramic particles. In one embodiment, the weight ratio of the amorphous carbon to the ceramic particles in the protective layer may be from 97:3 to 70:30.

[0013]

[0014] According to another embodiment of the present invention, a method for forming a coating layer on at least one surface of a current collector using a coating composition including a lithium-philic component, a step of forming a protective layer by applying slurry to the surface of the coating layer, a step of positioning the current collector on which the coating layer and the protective layer are formed in a plating solution and then positioning a lithium source at a predetermined distance from the protective layer, and a step of applying a current between the current collector and the lithium source to form a metal layer including a lithium alloy in which the lithium-philic component included in the coating layer and lithium precipitated from the lithium source are alloyed, may include a step of mixing a first solvent and a second solvent having different boiling points in the slurry in the step of forming the protective layer on the surface of the coating layer.

[0015] In one embodiment, the second solvent may have a higher boiling point than the first solvent. In one embodiment, the ratio of the first solvent to the second solvent may be 60:40 to 90:10.

[0016] In one embodiment, in the step of forming a protective layer on the surface of the coating layer, the protective layer may include amorphous carbon and a binder. The content of the binder may be 5 to 15 wt% based on 100 wt% of the total amorphous carbon in the protective layer. In the step of forming a protective layer on the surface of the coating layer, the difference in boiling points between the first solvent and the second solvent may be 50°C or more.

[0017] In one embodiment, the step of forming a protective layer on the surface of the coating layer includes a step of drying a solvent, and the step of drying the solvent may include a first drying step and a second drying step. In one embodiment, the drying step in the step of forming the protective layer may be performed at a temperature higher than the boiling point of the first solvent.

[0018] In one embodiment, the first drying step may be performed at a temperature range of 90° C. or higher. In one embodiment, the second drying step may be performed at a temperature range of 185° C. or higher.

[0019] According to one embodiment of the present invention, a lithium metal electrode controls the porosity within a protective layer to an appropriate range, thereby increasing the adhesive strength between a metal layer and a protective layer, enhancing the bonding strength, and inhibiting the growth of dendrites, thereby providing a lithium metal battery having improved life characteristics when applied to the battery.

[0020] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode is provided, wherein when a protective layer is applied as a slurry on a metal layer, a first solvent and a second solvent having different boiling points are mixed and added to the slurry, thereby reducing excessive use of a binder, increasing the adhesive strength between the metal layer and the protective layer, enhancing the bonding strength, and inhibiting the growth of dendrites, thereby providing a lithium metal battery having improved life characteristics when applied to the battery.

[0021] Figures 1a and 1b illustrate a lithium metal electrode manufactured according to one embodiment.

[0022] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode of the present invention.

[0023] FIG. 3 is a scanning electron microscope (SEM) photograph of a cross-section when an alloy material coating layer is formed on a current collector according to one embodiment of the present invention.

[0024] FIG. 4a is a scanning electron microscope (SEM) photograph of the surface when a protective layer of the present invention is formed on a current collector coated with an alloy material according to one embodiment of the present invention, and FIG. 4b is a scanning electron microscope (SEM) photograph of a cross-section.

[0025] Figures 5a to 5f represent the microstructure and pore image mapping of the cross-section of the protective layer of the embodiment and comparative example of the present invention.

[0026] Figure 6 shows the bonding strength of the protective layer measured using a peel strength measuring device in examples and comparative examples of the present invention.

[0027] FIGS. 7a and 7b are photographs comparing the appearance of electrodeposition between a current collector and an ion concentration protective layer when electrodeposited at the maximum current density according to one embodiment of the present invention.

[0028] FIG. 8 illustrates a cross-sectional structure in which lithium is deposited between a protective layer and a current collector by an electrodeposition process according to one embodiment of the present invention.

[0029] Figure 9 shows the charge / discharge life results of examples and comparative examples of the present invention.

[0030] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0034] FIG. 1a and FIG. 1b illustrate a lithium metal electrode (100) manufactured according to one embodiment.

[0035] Referring to FIG. 1a, a lithium metal electrode (100) according to one embodiment includes a current collector (11) and a metal layer (12) positioned on at least one surface of the current collector (11), and also includes a protective layer (30) positioned on the other surface of the metal layer (12) facing the current collector (11).

[0036] The current collector (11) may be a member for electrical connection within a lithium secondary battery. The current collector (11) may have a foil form, but is not limited thereto, and may have, for example, a mesh, foam, rod, wire, or sheet made by weaving wire (fiber).

[0037] The current collector (11) may be made of a material that is electrically conductive and has limited reaction with lithium. Specifically, the material of the current collector (11) may be any one or a combination of, for example, copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, conductive polymers, and composite fibers coated with a conductive layer on a non-conductive polymer.

[0038] In one embodiment, the thickness of the current collector (11) may be 1 μm to 50 μm. If the thickness of the current collector (11) is excessively thick, there is a problem that the battery weight increases and the energy density of the battery decreases. If the thickness of the current collector (11) is excessively thin, there is a risk of overheating damage during high current operation and damage due to tension during the battery manufacturing process.

[0039] The metal layer (12) is positioned on the current collector (11), and may include a lithium alloy layer (21) including a lithium alloy, and a lithium metal layer (41) positioned on the lithium alloy layer (21). The lithium alloy layer (21) may be a layer including a lithium alloy in which a lithium-friendly component included in the metal layer (12) and lithium precipitated from the lithium source (40) are alloyed by applying a current between the current collector (11) and a lithium source (40 in FIG. 2).

[0040] When the electrodeposition process is performed by applying a high current to increase the speed of electrodeposition during the formation of the metal layer (12), there is a problem that the performance of the lithium secondary battery is reduced. However, when the metal layer (12) is formed with a structure including a lithium alloy layer (21) containing a lithium component as in the present embodiment, even if the electrodeposition process is performed by applying a high current, it is possible to prevent excessive generation of fine lithium particles or destruction of the protective layer (30) located on the surface of the lithium metal layer (41) already formed in the electrodeposition process.

[0041] Specifically, since the metal layer (12) of one embodiment includes a lithium alloy layer (21) containing a lithium component, when a high current is applied in the electrodeposition process to form a lithium metal layer (41) on the lithium alloy layer (21), the initially generated lithium particles are induced to grow well, thereby forming particles with a coarse structure, and at the same time, the lithium metal layer (41), and consequently the metal layer (12), can have a uniform surface.

[0042] Therefore, the performance, specifically the charge / discharge characteristics, of a secondary battery using the lithium metal electrode according to the present embodiment 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 the electrodeposition process is performed at a high speed, the productivity of the lithium metal electrode for a secondary battery can also be significantly improved.

[0043] The lithium alloy layer (21) may be an alloy composed of lithium and a lithium-friendly metal, wherein the lithium-friendly metal may be at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi, but is not limited thereto.

[0044] In this embodiment, the lithium alloy layer (21) includes a lithium-friendly metal. In this way, when the lithium alloy layer (21) includes a lithium-friendly metal, since it includes a lithium-friendly metal with high electronic conductivity, there is an advantage in that electrons are smoothly supplied from the current collector, lithium ions are reduced, and thus electrodeposition of the lithium metal layer is easily performed. The metal layer (21) plays a role in helping lithium to be more effectively deposited under the protective layer (30) during the charging process of the battery.

[0045] In one 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. If the thickness of the metal layer (12) is excessively thick, when the lithium metal electrode of the present embodiment is applied to a secondary battery, there is a problem in that the weight and volume of the battery increase, resulting in a decrease in energy density. In addition, since the time and cost of the electrodeposition process increase in proportion to the thickness when forming the metal layer (12), the thickness of the metal layer (12) is preferably 100 μm or less.

[0046] When the thickness of the metal layer (12) is excessively thin, when the lithium metal electrode of the present embodiment is applied to a secondary battery, there is a problem that the charge / discharge life of the battery is 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 active material layer, i.e., the metal layer of the present invention, and the electrolyte, so that the battery capacity is reduced, and the amount of lithium that can replenish the lithium consumed during charge / discharge is reduced, so that the charge / discharge life of the battery is reduced. Therefore, the thickness of the metal layer (12) is preferably 1 ㎛ or more.

[0047] The protective layer (30) may have a porosity of 30 to 60%. Specifically, to measure the porosity of the cross-section of the protective layer (30), a mirror-finished surface was obtained using an llion 697 processing device from Gatan, and the microstructure was observed using a GEMINI-500 scanning electron microscope from ZEISS. Specifically, the porosity within the protective layer (30) was measured in a two-dimensional plane using an ImageJ image program developed by the National Institute of Health (NIH) based on a photograph observed with a scanning electron microscope. The pore area ratio was confirmed through the measured image value.

[0048] The porosity may be 35 to 60%, more specifically, 40 to 60%. By satisfying the above-mentioned porosity range, lithium is rapidly precipitated on the lower surface of the protective layer, which has the advantage of providing excellent characteristics when applied to a battery.

[0049] If the porosity exceeds the upper limit of the aforementioned range, the density of the protective layer becomes too low, causing problems such as dendrite growth during battery operation. If the porosity exceeds the lower limit of the aforementioned range, the density of the protective layer becomes too high, making it difficult to grow lithium on the underside of the protective layer through the electrodeposition process.

[0050] The protective layer (30) is positioned on the metal layer (12) and may include amorphous carbon. When lithium metal is used as an anode in an all-solid-state battery, high resistance is generated by the reaction between the all-solid-state electrolyte and lithium, and lithium dendrites are continuously generated or high-resistance lithium byproducts are generated due to local unevenness in the current density during the charge / discharge process, resulting in a failure or a decrease in battery capacity due to a short circuit or overvoltage during charge / discharge.

[0051] According to one embodiment, a lithium metal electrode can further improve structural safety as well as output characteristics and life characteristics of the lithium metal electrode by including a protective layer including amorphous carbon.

[0052] Specifically, the lithium metal electrode of the present embodiment includes a protective layer (30) containing amorphous carbon, thereby not only improving ion conductivity, but also improving the strength of the protective layer (30), and preventing short circuits between electrodes by physically blocking dendrites when they grow on the lithium electrode, thereby improving the charge / discharge life.

[0053] The above 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.

[0054] In one embodiment, the protective layer (30) may include a binder. The binder may be an aqueous binder, and the aqueous binder may be, but is not limited to, a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), and acrylic rubber, and at least one selected from the group consisting of polymer resins such as hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylidene fluoride.

[0055] In one embodiment, the binder may be included in a solid content of 5 to 15 wt% based on 100 wt% of amorphous carbon in the protective layer (30). Specifically, the content of the binder means that when the amorphous carbon is 100 wt%, the binder is additionally included in an amount of 5 to 15 wt%. Specifically, it may be included in an amount of 6 to 12 wt%, and more specifically, 6 to 10 wt%. Specifically, the content of the binder refers to the content of the solid content, and the same content range can be maintained in the final product, which is a lithium metal negative electrode.

[0056] When the content of the binder satisfies the above-mentioned range, the particles constituting the protective layer (30) are efficiently bound together to form a protective layer (30) 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. When the content of the binder is excessively less than the above-mentioned range, the porosity may be excellent, but there is a problem that the bonding strength of the protective layer (30) is excessively reduced. When the content of the binder is excessively more than the above-mentioned range, the bonding strength of the protective layer (30) may be high in hardness, but the porosity within the protective layer may be low, which is disadvantageous in electrodeposition.

[0057] In one embodiment, the thickness of the protective layer (30) may be 0.01 μm to 50 μm. Specifically, the thickness of the protective layer (30) may be in the range of 1 μm to 20 μm. When the thickness of the protective layer satisfies the above-described range, the effect obtained by including the amorphous carbon and the silicate clay mineral prevents the formation of lithium dendrites on the surface of the protective layer, and allows lithium ions to penetrate well inside the protective layer and conduct, thereby allowing lithium to be precipitated from the lower surface of the protective layer.

[0058] If the thickness of the protective layer is excessively thin, there is a problem in that it cannot function as a protective layer. If the thickness of the protective layer is excessively thick, the resistance of the protective layer may be excessively high, which may cause an increase in overvoltage during secondary battery operation, and there is a problem in that it causes a decrease in battery energy density due to an increase in weight and volume. However, the thickness of the protective layer can be variably adjusted depending on the design of the secondary battery structure.

[0059] In one embodiment, the protective layer (30) may include ceramic particles. Specifically, the ceramic particles may be Li2TiO3, LiNbO3, LiTaO3, LiZrO3, Li4Ti5O 12 , Li2CO3, Li3BO3, SrTiO3, etc., and may be at least one selected from a group consisting of particles having low electronic conductivity and high lithium ion conductivity, but is not limited thereto.

[0060] In one embodiment, the protective layer (30) may have a weight ratio of amorphous carbon to ceramic particles ranging from 97:3 to 70:30. Specifically, the weight ratio may range from 98.5:1.5 to 70:30. By satisfying the weight ratio within the aforementioned range, the ion conductivity of lithium is improved, thereby realizing a battery with improved charge / discharge characteristics.

[0061] In one embodiment, the bonding strength between the current collector (11) and the protective layer (30) may be 30 to 80 mN / cm. Specifically, the bonding strength may be 40 to 80 mN / cm, and more specifically, 48 to 75 mN / cm. The bonding strength was measured between the protective layer and the current collector using a peel strength meter.

[0062] The above bonding strength can improve the life characteristics of the battery by increasing the bonding strength between the current collector and the protective layer by satisfying the above-mentioned range, while at the same time smoothly performing lithium movement. If the bonding strength is outside the upper limit of the above-mentioned range, there is a problem that the bonding strength between the protective layer (30) and the current collector (11) is too strong, so that lithium is not easily electroplated on the lower surface of the protective layer (30). If the bonding strength is outside the lower limit of the above-mentioned range, peeling between the protective layer (30) and the current collector (11) may occur during the electroplating process or handling process, and there is a problem that the protective layer (30) itself is easily damaged.

[0063] In one embodiment, the lithium metal electrode may further include a film layer (not shown) on the protective layer (30). The film layer is formed during the manufacturing process of the metal layer (12) by a reaction between the lithium metal of the electrodeposited lithium source (40) and the plating solution, and the thickness, composition, and characteristics of the film can be controlled by adjusting the composition of the plating solution used and the conditions of the electrodeposition process.

[0064] In one embodiment, the film layer may include at least a portion of LiF. The LiF may be formed by including at least one solvent having a high dielectric constant among a plurality of solvents used in the electrodeposition process. Specifically, by increasing the salt decomposition dissociation degree of the solvent of the electrodeposition plating solution, the salt decomposition reaction may be suppressed and the solvent decomposition reaction may be promoted during electrodeposition, thereby allowing a sufficient LiF film to be formed within and / or on the surface of the protective layer. By including the film layer including at least a portion of LiF, the battery can have a high ionic conductivity, thereby improving the lifespan and preventing dendrite growth during battery operation.

[0065] In one embodiment, the thickness of the film layer may be 2 nm to 2 μm. Specifically, the thickness of the film layer may be specifically in the range of 10 nm to 500 nm. If the thickness of the film layer is excessively thick, there is a problem that the lithium ion conductivity decreases and the interfacial resistance increases, thereby deteriorating the charge / discharge characteristics when applied to a battery. If the thickness of the film layer is excessively thin, the film layer may be easily lost during the process of applying the lithium metal electrode according to the embodiment to a battery. Therefore, the film layer may have a thin thickness within the range satisfying the above thickness range and may be uniformly and densely formed on the surface of the metal layer (12) and the entire protective layer (30).

[0066] Referring to FIG. 1B, in one embodiment, a lithium metal electrode (100) includes a current collector (11) and a metal layer (12) positioned on at least one surface of the current collector (11) and composed of a mixture of lithium and a lithium alloy. Here, the lithium alloy may be formed by applying a current between the current collector (11) and a lithium source (40), thereby alloying a lithium-philic component included in the metal layer (30) formed on the current collector (11) with lithium precipitated from the lithium source (40).

[0067] The above metal layer (12) may include a lithium-friendly metal. Here, the lithium-friendly 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.

[0068] In one embodiment, the metal layer (12) is in a form that includes a lithium-philic metal. When the metal layer (12) including a lithium-philic metal is formed in this way, the free energy for nucleation of lithium particles can be lowered in the early stage of nucleation during the electrodeposition process, so that a lithium metal layer having a coarse particle structure can be formed even under high current and overvoltage conditions.

[0069] In one 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 one embodiment, when the metal layer (12) satisfies the above thickness range, it is possible to maximize the energy density of the battery while improving the charge / discharge life of the battery, and also has the advantage of minimizing the time and cost of the electrodeposition process when forming the metal layer (12).

[0070] If the metal layer is too thin, the initial coulombic efficiency decreases due to initial irreversibility, and the charge-discharge performance deteriorates due to insufficient excess lithium. If the metal layer is too thick, not only does the battery's energy density decrease, but the process time and amount of metal raw materials used during the metal layer formation also increase.

[0071] In one embodiment, the metal layer (12) includes a protective layer (30) positioned on the surface of the metal layer (12), and may include a film layer on the interior and / or surface of the protective layer (30). For a detailed description of the protective layer (30) and the film layer, reference may be made to the description given above in FIG. 1A.

[0072] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode of the present invention.

[0073] Referring to FIG. 2, a method for manufacturing a lithium metal electrode according to one embodiment includes a step of forming a coating layer (20) on at least one surface of a current collector (11) using a coating composition including a lithium-philic component, a step of forming a protective layer (30) on the surface of the coating layer (20) using a slurry including amorphous carbon, a step of positioning the current collector (11) on which the coating layer (20) and the protective layer (30) are formed in a plating solution (50) and then positioning a lithium source (40) at a predetermined distance from the protective layer (30), and a step of applying a current between the current collector and the lithium source (40) to form a metal layer including a lithium alloy in which the lithium-philic component included in the coating layer and lithium precipitated from the lithium source (40) are alloyed.

[0074] The step of forming a coating layer (20) on at least one surface of a current collector (11) using a coating composition containing a lithium-friendly component may include coating an alloy material on at least one surface of the current collector. The alloy material may be, for example, at least one selected from the group consisting of the lithium-friendly metal, for example, In, Ag, Sn, Zn, Si, Al, and Bi, but is not limited thereto.

[0075] In one embodiment, the step of forming the coating layer (20) may be performed using at least one of electrolytic and electroless plating, sputtering, electron beam, and thermal vapor deposition. For example, the step of forming the coating layer may be performed by an electroless plating method.

[0076] Meanwhile, in the step of forming the coating layer (20), the thickness of the coating layer (20) formed on at least one surface of the current collector may be 0.001 µm to 10 µm, specifically 0.01 µm to 1 µm, more specifically 150 to 400 nm, more specifically 200 to 400 nm, and more specifically 250 to 350 nm.

[0077] If the thickness of the coating layer (20) is excessively thin, it is insufficient to perform the role of forming lithium and a lithium alloy, and if the thickness is excessively thick, a large amount of cost and time are consumed in forming the coating layer (20), so production efficiency and economic feasibility are reduced, and the weight and weight of the battery increase, resulting in a problem of lowering the energy density.

[0078] A protective layer (30) can be formed on the surface of a coating layer (20) using a slurry containing amorphous carbon. The protective layer (30) can be formed by applying a slurry formed by mixing the amorphous carbon and a binder in a solvent using at least one of a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush application method.

[0079] In the step of forming a protective layer (30) on the surface of the coating layer (20), the solvent in the slurry may be formed by mixing a first solvent and a second solvent having different boiling points. Specifically, the solvent in the slurry may include a plurality of solvents, including a first solvent and a second solvent.

[0080] In one embodiment, the second solvent may be a solvent having a higher boiling point than the first solvent. Specifically, the solvent in the slurry may be formed by mixing solvents with different boiling points. When the solvent is a single solvent, there is a problem that the solvent in the slurry for forming the protective layer escapes and the solid content simultaneously settles, making it difficult to secure a structure of a protective layer with high porosity. In contrast, by including a plurality of solvents with different boiling points, the low-temperature solvent escapes first near the volatilization point of the low-temperature solvent, the high-temperature solvent remains, and then the high-temperature solvent escapes near the volatilization point of the high-temperature solvent, thereby forming a structure with high porosity.

[0081] In one embodiment, the content of the first solvent may be greater than the content of the second solvent. By having the content of the first solvent be greater than the content of the second solvent, the problem of excessive pore formation and reduced adhesive strength can be prevented.

[0082] In one embodiment, the ratio of the first solvent to the second solvent may be 60:40 to 90:10. Specifically, the ratio may be 70:30 to 80:20. By satisfying the above-described range, the porosity within the protective layer is formed within an appropriate range, which is advantageous in terms of the bonding strength of the protective layer, the maximum current that can be deposited, and the charge / discharge characteristics of the battery.

[0083] In the above ratio, if the first solvent is excessively large, there is a problem that most of the solvent simultaneously volatilizes at the boiling point of the first solvent, causing the solid content to precipitate, making it difficult to obtain a microstructure with high porosity. In the above ratio, if the second solvent is excessively large, not only is a high temperature required to completely volatilize the second solvent with a high boiling point, but in some cases, there is a problem that the second solvent remains even after drying the slurry.

[0084] In one embodiment, the difference in boiling points between the first solvent and the second solvent may be 50°C or greater. The boiling point difference may refer to a value obtained by subtracting the boiling point of the first solvent, which has a low boiling point, from the boiling point of the second solvent, which has a high boiling point. Specifically, the boiling point difference may be 50 to 150°C. More specifically, the boiling point difference may be 70 to 120°C.

[0085] When the boiling point difference satisfies the above-mentioned range, the porosity within the protective layer is formed within an appropriate range, so that the bonding strength, maximum electrodeposition current, and charge / discharge characteristics of the protective layer can be excellent. When the boiling point difference is excessively greater than the above-mentioned range, the slurry must be dried at two boiling points, so there is a problem with the length or configuration of the device when drying the slurry using a continuous device. When the boiling point difference is excessively smaller than the above-mentioned range, there is a problem that the first solvent and the second solvent volatilize simultaneously, making it difficult to obtain a microstructure with a high porosity.

[0086] In one embodiment, the binder may be added in an amount of 5 to 15 wt%, specifically 4 to 12 wt%, and more specifically 6 to 10 wt%, based on 100 wt% of the total amorphous carbon or amorphous carbon and ceramic particles in the slurry. Specifically, the content of the binder refers to the content of the solid content, and the same content range can be maintained in the final product, which is a lithium metal negative electrode.

[0087] When the content of the binder satisfies the above-mentioned range, the particles constituting the protective layer (30) are efficiently bound together to form a protective layer (30) 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. When the content of the binder is excessively less than the above-mentioned range, the porosity may be excellent, but there is a problem that the bonding strength of the protective layer (30) is excessively reduced. When the content of the binder is excessively more than the above-mentioned range, the bonding hardness of the protective layer (30) may be increased, but the porosity within the protective layer may be reduced, which is disadvantageous in electrodeposition.

[0088] In this way, when a second solvent with a high boiling point is used, the addition of a high binder is possible, and at the same time, the porosity of the protective layer being manufactured can be controlled to a high level, which has the advantage of facilitating electrodeposition.

[0089] In one embodiment, the step of forming a protective layer (30) may include a step of drying a solvent. In one embodiment, the drying step may be performed at a temperature higher than the boiling point of the first solvent. As the drying step is performed at a temperature higher than the boiling point of the first solvent, the solvent may be appropriately volatilized, thereby enabling the production of an electrode having the porosity of the present invention.

[0090] In one embodiment, the step of forming a protective layer (30) on the surface of the coating layer (20) may include a first drying step and a second drying step. Specifically, the step of forming a protective layer (30) on the surface of the coating layer (20) may include a step of drying the slurry at different temperatures.

[0091] In one embodiment, the first drying step may be performed at a temperature range of 90°C or higher. The first drying step may be a step in which a first solvent having a low boiling point is dried. By performing the first drying step within the aforementioned temperature range, only the first solvent evaporates and the second solvent remains, thereby preventing sedimentation of the solids. Thereafter, the high-temperature solvent escapes near the evaporation point of the second solvent, thereby advantageously forming a structure with high porosity.

[0092] If the above first drying step exceeds the upper limit of the aforementioned range, there is a problem in that the second solvent also evaporates simultaneously, making it difficult to obtain a microstructure with high porosity. If the above first drying step exceeds the lower limit of the aforementioned range, there is a problem in that the first solvent does not evaporate easily.

[0093] In one embodiment, the second drying step may be performed at a temperature range of 185°C or higher. The second drying step may be a step in which a second solvent having a high boiling point is dried. Specifically, the second drying step may be performed at a temperature range of 190 to 250°C, more specifically, 200 to 230°C. By performing the second drying step within the aforementioned temperature range, there is an advantage in that pores are formed within the protective layer as the remaining second solvent evaporates.

[0094] If the second drying step exceeds the upper limit of the aforementioned range, there is a problem that the binder contained within the protective layer decomposes. If the second drying step exceeds the lower limit of the aforementioned range, there is a problem that the second solvent remains even after the slurry is dried.

[0095] In one embodiment, in the step of forming the protective layer (30), the thickness of the protective layer that promotes lithium ion conductivity 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.

[0096] After the step of forming a protective layer (30), a step of positioning a current collector in which the coating layer (20) and the protective layer (30) are sequentially formed in a plating solution (50), a step of positioning a lithium supply source (40) at a predetermined distance from the current collector (11), and a step of applying current between the current collector (11) and the lithium supply source (40) to form a metal layer (12) are performed.

[0097] Specifically, after positioning a current collector (11) having a coating layer (20) and a protective layer (30) formed within a plating solution, a lithium supply source (40) is positioned at a predetermined distance from the protective layer (30). The lithium supply source (40) may be, for example, lithium metal, a lithium alloy, a foil obtained by pressing the lithium metal or lithium alloy onto a current collector, a plating solution in which a lithium salt is dissolved, etc.

[0098] The plating solution (50) can be prepared by dissolving a lithium salt in a plurality of solvents. Specifically, the lithium salt can 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 can be 1.0 to 3.0 M based on the total electrolyte.

[0099] Specifically, in the present embodiment, the plating solution (50) is characterized in that it includes a nitrogen-based compound as at least one of the lithium salt and a plurality of solvents. 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, e-caprolactam, N-methyl-e-caprolactam, triethylamine, and tributylamin.

[0100] Among the above nitrogen compounds, at least one of lithium nitrate, lithium bis fluorosulfonyl imide, and lithium bis trifluoromethane sulfonimide can be used as a lithium salt.

[0101] Among the above nitrogen compounds, at least one of caprolactam (e-caprolactam), methyl caprolactam (N-methyl-e-caprolactam), triethylamine, and tributylamin can be used as a non-aqueous solvent.

[0102] The above plating solution (50) may be manufactured using only the nitrogen-based compound, but may include a general non-aqueous solvent as an auxiliary solvent in consideration of the viscosity of the plating solution (50), etc.

[0103] The auxiliary solvent may include, for example, at least one 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.

[0104] In one embodiment, the auxiliary solvent may be included in an amount of 5 to 70 wt%, preferably 10 to 60 wt%, based on 100 wt% of the total plating solution (50), but is not limited thereto. However, when the auxiliary solvent is included within the above range, the viscosity of the plating solution (50) may be appropriate, thereby shortening the time required for the formation process of the lithium metal layer (12), but is not limited thereto.

[0105] In one embodiment, the plating solution (50) may further include a fluorine-based compound. When the plating solution (50) further includes the fluorine-based compound, there is an advantage in that the properties of the film layer (13) formed on the lithium metal layer (12) can be improved.

[0106] The fluorine-based compounds include, for example, lithium difluoro phosphate, lithium hexafluorophosphate, lithium difluoro bisoxalato phosphate, lithium tetrafluoro oxalato phosphate, lithium difluoro oxalate borate, lithium difluoro oxalato borate, lithium tetrafluoro oxalato borate, fluoroethylene carbonate, difluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. It may include at least one selected from the group consisting of 2,2,3,3-Tetrafluoropropyl ether.

[0107] The above fluorine-based compound may be included in an amount of 0.1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on 100 wt% of the total plating solution (50). When the fluorine-based compound is included within the above range, the interaction between the nitrogen-based compound and the fluorine-based compound in the plating solution (50) is favorable, so that there is an excellent advantage in improving the properties of the film layer formed on the lithium metal layer (12). In addition, there is an advantage in that the electrochemical properties are excellent because excessive generation of LiF, etc. due to the direct reaction between the fluorine-based compound and lithium is suppressed.

[0108] Next, after positioning an insulating film between the current collector (11) and the lithium supply source (40), the current collector (11), the lithium supply source (40), and the insulating film can be laminated and restrained in both directions using a restraining device. The restraining device can be a non-limiting example, and can be a method commonly used in the art, such as a manual clamping method, a uniaxial pressurization method such as hydraulic or pneumatic.

[0109] In the step of forming a lithium metal layer on at least one surface of the current collector (11) by applying the above current, the current density of the current applied is 0.1 mA / cm 2 100 mA / cm 2 range, more specifically 0.2 mA / cm 2 50 mA / cm 2 Range, 5 mA / cm 2 30 mA / cm 2 range or 7 mA / cm 2 25 mA / cm 2 It could be a range.

[0110] In one embodiment, the time for applying 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.

[0111] In one embodiment, the step of applying the current to form a lithium metal layer on at least one surface of the current collector may be performed at least once at different current densities. The step of applying the current may be performed in multiple stages. Specifically, the step of applying the current in multiple stages may be performed by increasing the current density from a low current density to a high current density in predetermined time steps. For example, the step of applying the current may be performed at a current density of 0.1 to 0.3 mA / cm. 2 , 0.3 to 0.7 mA / cm 2 , and 0.8 to 1.5 mA / cm 2 It can be applied step by step and increased sequentially.

[0112] In one embodiment, the step of forming a lithium metal layer (12) on at least one surface of the current collector (11) by applying the current is 6 to 12 mA / cm 2 A step of electrodeposition at a maximum current density of the range may be included. Specifically, the maximum current density is 8 to 12 mA / cm 2 It can be performed in the range. The above maximum current density means the limit of the current density at which lithium deposited in the electrodeposition process can precipitate lithium between the protective layer (30) and the current collector (11).

[0113] The step of electrodeposition at the above maximum current density may be a final step performed after the step of depositing in multiple stages, for example, for lithium deposition between the current collector (11) and the protective layer (30). By satisfying the above-described range, lithium is appropriately deposited between the current collector (11) and the protective layer (30), thereby providing advantages such as excellent battery life characteristics and bonding strength between the current collector (11) and the protective layer (30).

[0114] If the maximum current density exceeds the upper limit of the aforementioned range, there is a problem in that the targeted stabilized electrode structure cannot be secured because lithium is deposited on the surface of the protective layer (30). If the maximum current density exceeds the lower limit of the aforementioned range, there is a problem in that the productivity decreases because the time for lithium to be deposited increases.

[0115] In one embodiment, the step of forming a lithium metal layer on at least one surface of the current collector by applying the current may include a step of electrodepositing the deposited lithium to a thickness in the range of 5 to 15 μm. Specifically, the thickness of the deposited lithium may be electrodeposited to a thickness in the range of 8 to 12 μm. The thickness of the deposited lithium may refer to the vertical height of the lithium disposed between the current collector (11) and the protective layer (30).

[0116] If the thickness of the precipitated lithium exceeds the upper limit of the aforementioned thickness, not only will the energy density of the battery decrease, but there will also be problems such as increased process time and metal raw material usage during metal layer formation. If the thickness of the precipitated lithium exceeds the lower limit of the aforementioned thickness, there will be problems such as decreased initial coulombic efficiency due to initial irreversibility and decreased charge / discharge performance due to insufficient excess lithium.

[0117] In one embodiment, in the step of forming a lithium metal layer (12) on at least one surface of the current collector (11) by applying the current, the thickness of the metal layer (12) including a lithium alloy can be controlled to 1 to 100 μm. For a detailed description of the thickness of the metal layer (12), reference may be made to the contents of the aforementioned FIG. 1a.

[0118] In this way, in this embodiment, a lithium metal electrode (100) can be manufactured in which a metal layer including a lithium metal layer (12) having a coarse particle structure is formed by preventing excessive generation of fine lithium particles even under high current conditions and inducing the initially generated lithium particles to grow well. In addition, the metal layer manufactured in this way also has excellent surface uniformity.

[0119] According to another embodiment of the present invention, a lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte positioned between the positive electrode and the negative electrode. Here, the negative electrode may be a lithium metal electrode according to the present invention.

[0120] In one embodiment, a lithium secondary battery may include an electrode assembly including a positive electrode including a positive active material, a negative electrode which is a lithium metal electrode of the present invention, and a separator disposed between the positive electrode and the negative electrode. This electrode assembly may be wound or folded and accommodated in a battery case.

[0121] Thereafter, an electrolyte may be injected into the battery case and sealed to complete the secondary battery. At this time, the battery case may have a cylindrical, square, pouch-shaped, coin-shaped, etc. shape.

[0122] The positive electrode may include a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer may include, for example, a Li compound including 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 non-metallic element selected from the group consisting of O, F, S, P, and combinations thereof.

[0123] In one embodiment, a conductive material may be further added to the positive electrode active material layer. The conductive material may be, but is not limited to, carbon black, ultrafine graphite particles, fine carbon such as acetylene black, nano metal particle paste, etc.

[0124] The above-described positive electrode current collector serves to support the positive electrode active material layer. Examples of positive electrode current collectors that can be used include, but are not limited to, aluminum foil, nickel foil, or a combination thereof.

[0125] The electrolyte to be filled in the lithium secondary battery may be a non-aqueous electrolyte or a solid electrolyte. Specifically, the electrolyte may be a solid electrolyte. 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. In addition, 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 Li3N.

[0126] The separator may be any membrane commonly used in lithium secondary batteries, as it separates the positive and negative electrodes and provides a passage for lithium ions to move. Specifically, the separator may be one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. The separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric. Meanwhile, when a solid electrolyte is used as the electrolyte, the solid electrolyte may also function as the separator.

[0127] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereby, and the present invention is defined only by the scope of the claims set forth below.

[0128]

[0129] <Experimental Example>

[0130] Manufacturing of cathodes for lithium secondary batteries

[0131] <Example 1>

[0132] <Formation of alloy material coating layer>

[0133] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery is formed by forming a coating layer of an alloy material on a current collector, forming a protective layer thereon, and then forming a lithium or lithium alloy layer between the current collector and the protective layer through an electrodeposition method.

[0134] In order to manufacture a lithium metal electrode for a lithium secondary battery according to one embodiment of the present invention, a coating layer containing silver (Ag) was formed by plating to a thickness of about 300 nm on both sides of a copper current collector using an electroless plating method.

[0135] FIG. 3 is a scanning electron microscope (SEM) photograph of a cross-section when an alloy material coating layer is formed on a current collector according to one embodiment of the present invention.

[0136] Referring to FIG. 3, in order to manufacture a lithium metal electrode for a lithium secondary battery according to one embodiment of the present invention, a silver (Ag)-containing alloy material coating layer was formed by plating to a thickness of about 300 nm on both sides of a copper current collector using an electroless plating method.

[0137]

[0138] <Protective layer formation>

[0139] FIG. 4a is a scanning electron microscope (SEM) photograph of the surface when a protective layer (30) of the present invention is formed on a current collector coated with an alloy material according to one embodiment of the present invention, and FIG. 4b is a scanning electron microscope (SEM) photograph of a cross-section.

[0140] Referring to FIGS. 4a and 4b, a protective layer of about 5 μm was formed on a copper current collector having a coating layer including silver (Ag) by slurry coating using a comma coater. Specifically, the slurry for forming the protective layer was mixed with a first solvent of H2O, a second solvent of EG (Ethylene Glycol), a binder, and amorphous carbon in amounts of 70.4 wt%, 17.6 wt%, 1 wt%, and 11.0 wt%, respectively, based on 100 wt% of the slurry. Specifically, 32 g of the first solvent, 8 g of the second solvent of EG, 0.15 g of carboxymethylcellulose (CMC) as a binder, 0.3 g of styrene butadiene rubber (SBR), and 5 g of acetylene black (Acetylene Black) as an amorphous carbon were mixed. At this time, the ratio of the first solvent and the second solvent was mixed at a ratio of 80:20 when the total amount of the first solvent and the second solvent was 100. In addition, the content of the binder was mixed at 9 wt% when the total amount of amorphous carbon was 100.

[0141]

[0142] Lithium electrodeposition process

[0143] Afterwards, lithium was removed from the lithium source using an electrodeposition process to form a lithium alloy or pure lithium metal between the protective layer and the current collector, and lithium was deposited between the protective layer and the current collector. The plating solution used for this electrodeposition was prepared by adding lithium bis(fluorosulfonyl)imide, a nitrogen-based compound, and lithium nitrate, in amounts of 40 wt% and 10 wt%, respectively, based on 100 wt% of the total plating solution, to a 1,2-dimethoxyethane solvent, and adding fluoroethylene carbonate, a fluorine-based compound, in an amount of 10 wt% based on 100 wt% of the total plating solution.

[0144] A lithium metal plate having a purity of 99.9% or higher and a thickness of 500 μm was used by pressing it onto a copper current collector (Cu Plate) as a lithium source (40). After the lithium source and the current collector were electrically insulated and laminated in a plating solution, a power supply was used to apply current by making the lithium source and the current collector serve as (+) and (-) electrodes, respectively, to deposit lithium between the current collector and the protective layer.

[0145] Specifically, the current density of the electrodeposition process was 0.2 mA / cm 2 , 0.5 mA / cm 2 , 1 mA / cm 2 Increasing step by step in order, after 5 minutes of deposition, 10 mA / cm 2 The maximum current density was set. The electrodeposition time at the maximum current density was calculated as the time for the final accumulated lithium thickness of 10 ㎛ to be deposited, and was variably set according to the size of the maximum current density. In addition, at this time, the reduction and decomposition reaction of the plating solution on the surface of the current collector and the reaction between the electrodeposited lithium metal layer and the plating solution were controlled to form a film layer on the surface of the lithium metal layer.

[0146] Figures 5a to 5f represent the microstructure and pore image mapping of the cross-section of the protective layer of the embodiment and comparative example of the present invention.

[0147] To measure the porosity of the protective layer cross-sections of FIGS. 5A to 5F, a mirror-finishing process was performed using an Ilion 697 machining device from Gatan, and the microstructure was observed using a GEMINI-500 scanning electron microscope from ZEISS. The porosity within the protective layer was measured as a two-dimensional plane porosity using the ImageJ image program developed by the National Institute of Health (NIH) based on photographs observed with a scanning electron microscope.

[0148] FIGS. 5a and 5b show the microstructure and pore image mapping of the cross-section of the protective layer of Example 1 of the present invention, and the pore area ratio was measured to be approximately 48.4%. FIGS. 5c and 5d show the microstructure and pore image mapping of the cross-section of the protective layer of Comparative Example 1 of the present invention, and the pore area ratio was measured to be approximately 27.4%. FIGS. 5e and 5f show the microstructure and pore image mapping of the cross-section of the protective layer of Comparative Example 3 of the present invention, and the pore area ratio was measured to be approximately 60.5%.

[0149]

[0150] <Example 2>

[0151] The procedure was the same as Example 1 except that the ratio of the first solvent to the second solvent was controlled to 90:10 in the protective layer formation step.

[0152]

[0153] <Example 3>

[0154] The procedure was the same as Example 1 except that the ratio of the first solvent to the second solvent was controlled to 60:40 in the protective layer formation step.

[0155]

[0156] <Example 4>

[0157] In the protective layer formation step, ethanol was used as the first solvent, and NMP was used as the second solvent. In addition, after slurry coating, the solvent was dried in two stages. The first drying was performed at 90°C, which is higher than the boiling point of the first solvent, ethanol, for 30 minutes, and the second drying was performed at 210°C, which is higher than the boiling point of the second solvent, NMP, for 30 minutes.

[0158]

[0159] <Comparative Example 1>

[0160] In adding a solvent in the protective layer formation step, the second solvent was not added, 100% of the first solvent was used, water was used as the first solvent, and drying of the solvent after coating was performed in the same manner as in Example 1, except that drying was performed for 30 minutes at 110°C, which is higher than the boiling point of water.

[0161]

[0162] Comparative Example 2

[0163] The process was performed in the same manner as in Comparative Example 1, except that the binder content was 3 wt% in the protective layer formation step.

[0164]

[0165] <Comparative Example 3>

[0166] The protective layer formation step was performed in the same manner as Example 1, except that EGME (Ethylene glycol monomethyl ether) was used as the second solvent and the binder content was 8 wt%.

[0167]

[0168] All-solid-state battery manufacturing

[0169] All-solid-state batteries were fabricated using the cathodes manufactured according to the aforementioned examples and comparative examples, and their charge-discharge cycle life was evaluated. To evaluate the all-solid-state battery cell, a pressurized, dedicated evaluation cell from Terraleader, capable of maintaining an inert atmosphere, was used. For the fabrication of the all-solid-state battery cell, a sulfide-based argyrodite (Li6PS5Cl) solid electrolyte was used, and the electrolyte was in pellet form with a thickness of approximately 0.7 mm. To ensure a dense electrolyte, the electrolyte was pressurized at a pressure of 370 MPa.

[0170] Lithium having a thickness of 0.5 mm was attached to one side of the electrolyte as a reference electrode, and the negative electrode manufactured according to the examples and comparative examples was attached to the opposite side. The reference electrode and the evaluation electrode were pressurized at a pressure of 50 MPa.

[0171] Lithium having a thickness of 0.5 mm was attached as a reference electrode to one side of the electrolyte, and the negative electrode manufactured according to the examples and comparative examples was attached to the opposite side.

[0172]

[0173] <Evaluation Example 1> - Content range of the first solvent and the second solvent

[0174] Table 1 below presents data on the porosity, bonding strength, maximum electrodeposition current, and charge / discharge characteristics of the protective layer according to the type of solvent in the slurry and the binder content conditions during protective layer formation. The porosity, bonding strength, maximum electrodeposition current, and charge / discharge characteristics of the protective layer were measured using the following methods.

[0175] Porosity (%) of the protective layer: The surface was polished using a Gatan llion 697 machining device, and the microstructure was observed using a ZEISS GEMINI-500 scanning electron microscope. The porosity within the protective layer was measured in a two-dimensional plane using the ImageJ image program developed by the National Institute of Health (NIH) based on the images observed with the scanning electron microscope. The pore area ratio was confirmed through the measured image values.

[0176] Bonding strength (mN / cm): A 10 mm wide polyimide tape (No. 360A, thickness: 0.08 mm, adhesive strength: 4.4 N / 19 mm) from Nitto was adhered to the protective layer, and the bonding strength was measured through a tensile test using a peel strength measuring device (AND, MCT-2150W). The tensile speed was 50 mm / min, and the tensile test distance was set to within 200 mm in total. The bonding strength was calculated as the average strength over a 100 mm section starting from the 50 mm point in the tensile test.

[0177] Maximum current density (mA / cm 2): The maximum current density refers to the limit of the current density at which lithium deposited according to the above process can precipitate lithium between the ion concentration protective layer and the current collector, and the maximum current density was measured.

[0178] Charge / discharge performance number (cycles): The reference electrode and evaluation electrode were attached to the solid electrolyte at a pressure of 50 MPa, and the dedicated evaluation cell was pressurized at 16 MPa during the charge / discharge evaluation. The charge / discharge evaluation was performed at 2 mA / cm 2 Charge for 0.5 hours at constant current of 2 mA / cm 2 A 0.5-hour discharge at constant current was defined as one cycle. The charge-discharge life was defined as the end of the life when a short circuit occurred between the reference electrode and the evaluation electrode during the charge-discharge process or when the voltage between the two electrodes exceeded 2 V.

[0179] Classification 1 Solvent 2 Solvent Binder Content [%] Type Boiling point [℃] Content [wt%] Type Boiling point [℃] Content [wt%] Example 1 Water 100 80 EG 198 209 Example 2 Water 100 90 EG 198 109 Example 3 Water 100 60 EG 198 409 Example 4 Ethanol 78 80 NMP 202 209 Comparative Example 1 Water 100 100 --- 9 Comparative Example 2 Water 100 100 --- 3 Comparative Example 3 Water 100 80 EG ME 125 209 EG: Ethylene glycol EGME: Ethylene glycol monomethyl ether

[0180] Porosity (%), Bonding strength [mN / cm], Maximum possible electrodeposition current [mA / cm] 2 ]Charge and discharge characteristics [times] Example 245.3558817 Example 351.85812872 Example 447.26210717 Comparative example 127.4534476 Comparative example 252.41110481 Comparative example 338.2516566

[0181] Looking at Tables 1 and 2 above, it was confirmed that it is difficult to implement a structure with both a high binder content and high porosity when using a single solvent slurry. Specifically, a single solvent slurry, such as Comparative Example 1, has a problem in that the solvent in the protective layer simultaneously escapes, and the solid content settles while the solvent escapes, making it difficult to obtain a structure with high porosity. In the case of a slurry containing a complex solvent, as in the examples, first, the low-temperature solvent is preferentially escaped near the volatilization point of the low-temperature solvent, and until then, the high-temperature solvent does not escape but remains in the slurry. Second, when drying is performed near the volatilization point of the high-temperature solvent, the high-temperature solvent escapes, and it was confirmed that a structure including a protective layer with high porosity can be obtained because the space where the high-temperature solvent escapes remains as pores.

[0182] In addition, looking at the examples and comparative example 1, it was confirmed that when the second solvent, which is a high-boiling-point solvent, was not used at all and the binder content was added within an appropriate range, the porosity was excessively low and the maximum current density that could be deposited was low. Looking at the examples and comparative example 2, it was confirmed that when the second solvent was not used and the binder content was low, the porosity was appropriate but the binder content was low, which caused a problem of low bonding strength.

[0183] Figure 6 shows the bonding strength of the protective layer measured using a peel strength measuring device in examples and comparative examples of the present invention.

[0184] Referring to FIG. 6, the bonding strength of Example 1 and Comparative Example 2 of the present invention was measured through a tensile test using a peel strength measuring device (AND Corporation, MCT-2150W) after a 10 mm wide polyimide tape (No. 360A, thickness: 0.08 mm, adhesive strength: 4.4 N / 19 mm) from Nitto was adhered on the protective layer. At this time, the tensile speed was 50 mm / min, and the tensile test distance was set to be within 200 mm in total. The bonding strength was obtained as the average strength of a 100 mm section from the 50 mm point in the tensile test. It was confirmed that the bonding strength of Example 1 was superior to the bonding strength of Comparative Example 2.

[0185] FIGS. 7a and 7b are photographs comparing the appearance of electrodeposition between a current collector and an ion concentration protective layer when electrodeposited at the maximum current density according to one embodiment of the present invention.

[0186] Figure 7a is a photograph showing the appearance after electrodeposition of Example 1, in which lithium is deposited between the current collector and the protective layer when electrodeposition is performed at the maximum current density. Figure 7b shows a comparison of the appearance when lithium is deposited on the protective layer when electrodeposition is performed at a current density exceeding the maximum current density.

[0187]

[0188] FIG. 8 illustrates a cross-sectional structure in which lithium is deposited between a protective layer and a current collector by an electrodeposition process according to one embodiment of the present invention.

[0189] Referring to Figure 8, a cross-sectional structure in which lithium is deposited between the protective layer and the current collector through a lithium deposition process can be confirmed.

[0190] Figure 9 shows the charge / discharge life results of examples and comparative examples of the present invention.

[0191] Referring to Figure 9, it can be confirmed that the charge / discharge life evaluation result of Example 1 is high at 902 cycles, but the charge / discharge life evaluation result of Comparative Example 2 is low at 481 cycles.

[0192]

[0193] <Evaluation Example 2> - Binder Content Range

[0194] <Example 5>

[0195] In the protective layer formation step, the ratio of the first solvent:second solvent was controlled to 80:20, and the binder content was controlled to 6 wt%, except that the same procedure as Example 1 was performed.

[0196]

[0197] <Example 6>

[0198] The same procedure as Example 4 was followed, except that the binder content was controlled to 12 wt% in the protective layer formation step.

[0199]

[0200] <Comparative Example 3>

[0201] The protective layer formation step was performed in the same manner as Example 1, except that the binder content was controlled to 3 wt%.

[0202]

[0203] Comparative Example 4

[0204] The protective layer formation step was performed in the same manner as Example 1, except that the binder content was controlled to 18 wt%.

[0205]

[0206] Table 4 below shows the porosity, bonding strength, maximum deposition current, and charge / discharge characteristics of the protective layer according to the binder content.

[0207] Classification 1 Solvent 2 Solvent Binder Content [%] Type Boiling point [℃] Content [wt%] Type Boiling point [℃] Content [wt%] Example 1 Water 10080 EG 198209 Example 5 Water 10080 EG 198206 Example 6 Water 10080 EG 1982012 Comparative Example 3 Water 10080 EG 198203 Comparative Example 4 Water 10080 EG 1982018

[0208] Porosity (%), Bonding strength [mN / cm], Maximum possible electrodeposition current [mA / cm] 2 ]Charge / Discharge Characteristics [Times] Example 148.46610902 Example 550.54810820 Example 643.7758728 Comparative Example 360.52312359 Comparative Example 425.7854416

[0209] Looking at Tables 3 and 4 above, when the binder content is within the scope of the present invention, as in Examples 1, 5, and 6, it was confirmed that the bonding strength, maximum electrodeposition current, and charge / discharge characteristics were superior compared to Comparative Examples 3 and 4. When the binder content exceeded the lower limit, as in Comparative Example 3, it was confirmed that the porosity, bonding strength, and charge / discharge characteristics were inferior, and when the binder content exceeded the upper limit, as in Comparative Example 4, it was confirmed that the porosity, maximum electrodeposition current, and charge / discharge characteristics were inferior.

[0210] In this way, it was confirmed that it is advantageous to use a solvent with a high boiling point to obtain a structure with a high binder content and high porosity.

[0211]

[0212] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Whole house; A metal layer comprising a lithium alloy and located on at least one surface of the above-described collector; and A protective layer comprising amorphous carbon and a binder, positioned on the metal layer, The porosity of the above protective layer is 30 to 60%, A lithium metal electrode having a binder content of 5 to 15 wt% based on 100 wt% of the total amorphous carbon in the protective layer.

2. In paragraph 1, A lithium metal electrode having a bonding strength between the entire body and the protective layer of 30 to 80 mN / cm.

3. In paragraph 1, The above metal layer is a lithium metal electrode including a lithium alloy layer including an alloy composed of lithium and a lithium-friendly metal.

4. In paragraph 3, A lithium metal electrode wherein the lithium-friendly metal is at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

5. In paragraph 4, The above metal layer is a lithium metal electrode including a lithium metal layer positioned on a lithium alloy layer.

6. In paragraph 1, The above protective layer is a lithium metal electrode further comprising ceramic particles.

7. In paragraph 6, A lithium metal electrode having a weight ratio of the amorphous carbon and ceramic particles in the protective layer of 97:3 to 70:

30.

8. A step of forming a coating layer on at least one surface of a current collector using a coating composition containing a lithium-friendly component; A step of forming a protective layer by applying slurry on the surface of the coating layer; A step of positioning a current collector having the coating layer and protective layer formed in the plating solution and then positioning a lithium supply source at a predetermined distance from the protective layer; and A step of applying a current between the current collector and the lithium source to form a metal layer including a lithium alloy in which the lithium-friendly component included in the coating layer and lithium precipitated from the lithium source are alloyed, A method for manufacturing a lithium metal electrode, comprising a step of mixing a first solvent and a second solvent having different boiling points in the slurry in the step of forming a protective layer on the surface of the coating layer.

9. In paragraph 8, A method for producing a lithium metal electrode wherein the second solvent has a higher boiling point than the first solvent.

10. In paragraph 8, A method for producing a lithium metal electrode, wherein the ratio of the first solvent to the second solvent is 60:40 to 90:

10.

11. In paragraph 8, A method for manufacturing a lithium metal electrode, wherein the amorphous carbon in the slurry is 5 to 15 wt% based on 100 wt% of the total amorphous carbon in the step of forming a protective layer on the surface of the coating layer.

12. In paragraph 8, A method for manufacturing a lithium metal electrode, wherein the difference in boiling points between the first solvent and the second solvent is 50° C. or more in the step of forming a protective layer on the surface of the coating layer.

13. In paragraph 8, The step of forming a protective layer on the surface of the coating layer includes a step of drying a solvent, A method for producing a lithium metal electrode, wherein the step of drying the solvent comprises a first drying step and a second drying step.

14. In paragraph 13, A method for manufacturing a lithium metal electrode, wherein in the step of forming the protective layer, the drying step is performed at a temperature higher than the boiling point of the first solvent.

15. In paragraph 13, A method for manufacturing a lithium metal electrode, wherein the first drying step is performed at a temperature range of 90° C. or higher.

16. In paragraph 13, A method for producing a lithium metal electrode, wherein the second drying step is performed at a temperature range of 185° C. or higher.

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