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

Abstract

The present invention relates to a lithium metal electrode and a method of making 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; a protective layer positioned on the metal layer; and a film layer positioned on a surface of the protective layer and at least partially containing LiF. When the lithium metal electrode is measured by X-ray photoelectron spectroscopy (XPS), the intensity of a peak appearing at 684 eV-686 eV is greater than the intensity of a peak appearing at 687 eV-689 eV.

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 using a single solvent during lithium deposition, the ionic conductivity of the electrolyte itself is high, but the salt decomposition reaction is performed first when supplying electrons, which reduces the life characteristics of the battery and causes excessive growth of dendrites.

[0007] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery provides a lithium metal battery that improves the life characteristics of the battery and prevents dendrite growth due to high ionic conductivity during battery operation.

[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, a protective layer positioned on the metal layer, and a film layer positioned on a surface of the protective layer and including at least a portion of LiF.

[0010] In one embodiment, the film layer of the lithium metal electrode can satisfy the following equation 1 when measured by X-ray photoelectron spectroscopy (XPS).

[0011] <Formula 1>

[0012] Imax(LiF) / Imax(FSO2) ≥ 1.5

[0013] (The intensity of the peak appearing at 684~686 eV in the above equation 1 is I max (LiF), and the intensity of the peak appearing at 687~689 eV is I max (called FSO2)

[0014] In one embodiment, the above equation 1 may be greater than or equal to 2.0.

[0015] In one embodiment, the film layer can satisfy the following equation 2 when measured by X-ray photoelectron spectroscopy (XPS).

[0016] <Formula 2>

[0017] [[Area(LiF)] / [Area(LiF) + Area(FSO2)] × 100 ≥ 55.0

[0018] (In the above equation 2, the area of ​​the peak appearing at 684~686 eV is called Area(LiF), and the area of ​​the peak appearing at 687~689 eV is called Area(FSO2))

[0019] In one embodiment, the film layer can satisfy the following equation 3 when measured by X-ray photoelectron spectroscopy (XPS).

[0020] <Formula 3>

[0021] I max (N-SO x ) / I max (NO3 - ) ≥ 0.30

[0022] (The intensity of the peak appearing at 399~401 eV in the above equation 3 is Imax(N-SO x ) and the intensity of the peak appearing at 407~409 eV is called Imax(NO3).

[0023] In one embodiment, the film layer can satisfy the following equation 4 when measured by X-ray photoelectron spectroscopy (XPS).

[0024] <Formula 4>

[0025] [[Area(N-SO x )] / [Area(N-SO x ) + Area(NO3 - )] × 100 ≥ 10.0

[0026] (The area of ​​the peak appearing at 399~401 eV in the above equation 4 is Area(N-SO x ) and the area of ​​the peak appearing at 407~409 eV is called Area(NO3))

[0027] In one embodiment, the total resistance (R) of the interface between the protective layer and the film layer total ) is 1.5 to 4.6 Ω·cm 2 may be. In one embodiment, the intensity of the peak appearing at 684 to 686 eV is I max (LiF) can be greater than 25,000. In one embodiment, the intensity of the peak appearing at 687 to 689 eV is I max (FSO2) can be less than 11,000.

[0028] In another embodiment of the present invention, 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-philic component, forming a protective layer on the surface of the coating layer, placing the current collector on which the coating layer and the protective layer are formed in a plating solution including a plurality of solvents and then positioning a lithium source at a predetermined distance from the protective layer, and 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, wherein at least one solvent among the plurality of solvents has a dielectric constant of 25 or more.

[0029] In one embodiment, at least one solvent among the plurality of solvents may have a dielectric constant of 25 to 80. In one embodiment, the content of the solvent having a dielectric constant of 25 or greater may be 3 to 40 mol% based on 100 mol% of the total solvent.

[0030] In one embodiment, the solvent having a dielectric constant of 25 or greater may be a sulfone-based solvent. In one embodiment, the sulfone-based solvent may include at least one of ethyl methyl sulfone (EMS), diphenyl sulfone (DPheS), sulfolane (SL), dimethyl sulfone, diethyl sulfone (DS), and methyl sulfone.

[0031] In one embodiment, a current is applied between the current collector and the lithium source to form a metal layer including a lithium alloy in which a lithium-friendly component included in the coating layer and lithium precipitated from the lithium source are alloyed, at a current of 6 to 12 mA / cm 2 It may be a step of electrodeposition at the maximum current density of the range.

[0032] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery includes a film layer located on the surface of a protective layer and containing at least a portion of LiF that induces electrodeposition, thereby providing a lithium metal electrode that improves the life characteristics of the battery and prevents dendrite growth.

[0033] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode for a lithium secondary battery includes a plurality of solvents in a plating solution during electrodeposition, and at least one solvent among the plurality of solvents has a high dielectric constant, thereby improving the degree of salt decomposition dissociation, thereby suppressing salt decomposition reaction during electrodeposition and promoting solvent decomposition reaction, thereby forming a film containing at least a portion of LiF, and providing a lithium metal electrode having the advantages described above.

[0034] Figures 1a to 1f illustrate lithium metal electrodes manufactured according to one embodiment.

[0035] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode of the present invention.

[0036] 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.

[0037] FIG. 4a is a scanning electron microscope (SEM) photograph of the surface when an ion concentration protective layer 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.

[0038] Figure 5 is a graph showing the lifespan evaluation of an all-solid-state battery cell using a lithium negative electrode according to an embodiment and a comparative example of the present invention.

[0039] Figure 6 is a graph comparing XPS surface analyses of the surface of an electrodeposited lithium negative electrode protective layer according to an embodiment and a comparative example of the present invention.

[0040] Figure 7 is a graph analyzing the impedance and resistance of electrodeposited lithium according to examples and comparative examples of the present invention.

[0041] 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 solely 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] FIGS. 1A to 1F illustrate a lithium metal electrode (100) manufactured according to one embodiment.

[0046] Referring to FIGS. 1A to 1C, 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).

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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).

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Here, the binder may be added in an amount of 1 to 15 parts by weight, specifically 3 to 10 parts by weight, based on the weight of the slurry formed by mixing the amorphous carbon and water. When the content of the binder satisfies the above-mentioned range, the particles constituting the protective layer are 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.

[0064] If the content of the binder is excessively less than the above-mentioned range, there is a problem that the bonding force between particles is reduced when forming a protective layer, and if the content of the binder is excessively more than the above-mentioned range, there is a problem that not only does it cause a decrease in energy density, but also the resistance of the protective layer is greatly increased, hindering lithium ion conduction.

[0065] 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.

[0066] 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.

[0067] In one embodiment, the lithium metal electrode may include a film layer (31) disposed within the protective layer (30), between the metal layer (12) and the protective layer (30), and at least a portion of the protective layer (30). Specifically, the film layer (31) may be disposed within at least a portion of the protective layer (30), between the metal layer (12) and the protective layer (30), may be disposed simultaneously within the protective layer (30) and between the metal layer (12) and the protective layer (30), and may be disposed above the protective layer (30).

[0068] The film layer (31) 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.

[0069] In one embodiment, the film layer (31) 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 (31) 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.

[0070] In one embodiment, the film layer (31) may have a peak intensity that appears at 684 to 686 eV greater than a peak intensity that appears at 687 to 689 eV when measured by X-ray photoelectron spectroscopy (XPS). Specifically, the peak intensity that appears at 684 to 686 eV refers to the peak intensity of LiF, and the peak intensity that appears at 687 to 689 eV refers to the peak intensity of FSO2. FSO2 is a product of salt decomposition reaction, which inhibits smooth movement of lithium ions on the electrode surface and may inhibit stable electrodeposition of lithium. In contrast, LiF is a main product of solvent decomposition reaction, which may alleviate additional electrolyte decomposition that occurs, smoothly assist Li ion conduction, reduce interfacial resistance, and contribute to stable electrodeposition of lithium. In this way, it was confirmed that the film layer (31) contributing to the stable electrodeposition of lithium was included, as the intensity of the Li peak was calculated to be greater than that of FSO2.

[0071] In one embodiment, the film layer (31) can satisfy the following equation 1 when measured by X-ray photoelectron spectroscopy (XPS).

[0072] <Formula 1>

[0073] Imax(LiF) / Imax(FSO2) ≥ 1.5

[0074] (The intensity of the peak appearing at 684~686 eV in the above equation 1 is I max (LiF), and the intensity of the peak appearing at 687~689 eV is I max (called FSO2)

[0075]

[0076] The above equation 1 is one of the indicators for the LiF production rate, and may be 1.5 or more. Specifically, the above equation 1 may be 2.0 or more, more specifically, 2.5 or more and 5.0 or less, and even more specifically, 2.5 or more and 3.1 or less.

[0077] In one embodiment, the film layer (31) can satisfy the following equation 2 when measured by X-ray photoelectron spectroscopy (XPS).

[0078] <Formula 2>

[0079] [[Area(LiF)] / [Area(LiF) + Area(FSO2)] × 100 ≥ 55.0

[0080] (In the above equation 2, the area of ​​the peak appearing at 684~686 eV is called Area(LiF), and the area of ​​the peak appearing at 687~689 eV is called Area(FSO2))

[0081] The above equation 2 is one of the indicators for the LiF production rate, and may be 55.0 or more. Specifically, the above equation 2 may be 60.0 or more, more specifically, 60.0 or more, more specifically, 70 or more and 100 or less, more specifically, 70 or more and 85 or less, and more specifically, 70 or more and 83 or less.

[0082] When the values ​​of the above equations 1 and 2 satisfy the above-mentioned range, it can be confirmed that LiF, which is the main product of the solvent decomposition reaction, is appropriately formed within the protective layer (30), and thus, when applied to a battery, the interfacial resistance can be reduced, contributing to more stable electrodeposition of lithium. When the values ​​of the above equations 1 and 2 do not satisfy the above-mentioned range, the content of the product of the salt decomposition reaction may become excessively large, which may hinder the smooth movement of lithium ions on the electrode surface, thereby hindering stable electrodeposition of lithium.

[0083] In one embodiment, the intensity of the peak appearing at 684 to 686 eV is I max (LiF) may be greater than or equal to 25,000. Specifically, the intensity of the peak may be greater than or equal to 27,500. More specifically, it may be greater than or equal to 28,000, and even more specifically, greater than or equal to 29,000.

[0084] If the intensity of the above peak exceeds the lower limit of the aforementioned range, there is a problem that the ionic conductivity and mechanical strength of the protective layer are reduced due to insufficient production of LiF, which is the main product of the solvent decomposition reaction.

[0085] In one embodiment, the intensity of the peak appearing at 687 to 689 eV is I max (FSO2) may be less than or equal to 11,000. Specifically, the intensity of the peak may be less than or equal to 10,500, more specifically less than or equal to 10,000.

[0086] If the intensity of the above peak exceeds the upper limit of the above-mentioned range, there is a problem in that the solvent decomposition reaction is suppressed, and therefore, its product, LiF, is not sufficiently produced.

[0087] In one embodiment, the film layer (31) can satisfy the following equation 3 when measured by X-ray photoelectron spectroscopy (XPS).

[0088]

[0089] <Formula 3>

[0090] I max (NO3 - ) / I max (N-SO x ) ≥ 0.30

[0091] (The intensity of the peak appearing at 399~401 eV in the above equation 3 is Imax(N-SO x ) and the intensity of the peak appearing at 407~409 eV is called Imax(NO3).

[0092]

[0093] The above equation 3 is one of the indicators for the solvent decomposition rate, and may be 0.30 or more. Specifically, the above equation 3 may be 0.32 or more, more specifically, 0.40 or more and 0.70 or less, and even more specifically, 0.45 or more and 0.60 or less.

[0094] In one embodiment, the film layer (31) can satisfy the following equation 4 when measured by X-ray photoelectron spectroscopy (XPS).

[0095] <Formula 4>

[0096] [Area(NO3 - )] / [Area(N-SO x ) + Area(NO3 - )] × 100 ≥ 10.0

[0097] (The area of ​​the peak appearing at 399~401 eV in the above equation 4 is Area(N-SO x ) and the area of ​​the peak appearing at 407~409 eV is called Area(NO3))

[0098]

[0099] The above equation 4 is one of the indicators for the solvent decomposition rate, and may be 10.0 or more. Specifically, the above equation 4 may be 20 or more, more specifically, 20 or more and 50 or less, and even more specifically, 20 or more and 25 or less.

[0100] NO3 in the above equations 3 and 4 - is a solvent decomposition product, and N-SO X may be a salt decomposition reaction product. By satisfying the above-mentioned ranges of Equations 3 and 4, it can be confirmed that the salt decomposition reaction is suppressed and the solvent decomposition reaction is promoted, thereby appropriately forming the main product by the solvent decomposition reaction, and thus, when applied to a battery, the interfacial resistance can be reduced, thereby contributing to more stable electrodeposition of lithium. If the values ​​of Equations 3 and 4 do not satisfy the above-mentioned ranges, the content of the product by the salt decomposition reaction may become excessively large, which may hinder the smooth movement of lithium ions on the electrode surface, thereby hindering stable electrodeposition of lithium.

[0101] In one embodiment, the total resistance (R) of the interface between the protective layer (30) and the film layer (31) total ) is 1.5 to 4.6 Ω·cm 2 It can be. Specifically, the total resistance is 1.5 to 3.5 Ω·cm 2 , more specifically, 1.8 to 3.1 Ω·cm 2 It could be.

[0102] In one embodiment, the charge transfer resistance (R) between the protective layer (30) and the film layer (31) ct ) is 0.5 to 1.5 Ω·cm 2 It can be. The charge transfer resistance is the resistance generated in the process of lithium ions moving through the electrolyte undergoing an oxidation-reduction reaction at the interface of the electrode material. The lower the resistance, the better the oxidation-reduction reaction of lithium ions occurs, which may mean that it is advantageous for electrodeposition. The charge transfer resistance is 0.8 to 1.5 Ω cm. 2 , more specifically, 1.0 to 1.3 Ω·cm 2 It could be.

[0103] In one embodiment, the solid electrolyte interphase resistance (R) of the SEI layer between the protective layer (30) and the film layer (31) SEI ) is 0.5 to 1.2 Ω·cm 2 It can be. The SEI layer resistance is a resistance to lithium ion conduction of the film layer (31), and the lower it is, the easier lithium ion conduction is. The SEI layer resistance is 0.6 to 1.0 Ω·cm. 2 , specifically, 0.7 to 0.9 Ω·cm 2 It could be.

[0104] If the resistance value mentioned above exceeds the upper limit of the above-mentioned range, the resistance to conduction of lithium ions and oxidation-reduction reaction of lithium ions increases excessively, so that overvoltage occurs during the electrodeposition process, or when configured as a secondary battery, overvoltage occurs during charging and discharging, which causes a problem of reduced battery life.

[0105] The thickness of the film layer (31) may be 2 nm to 2 ㎛. 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 (31) is excessively thick, the lithium ion conductivity decreases and the interfacial resistance increases, which causes a problem in that the charge / discharge characteristics deteriorate when applied to a battery. If the thickness of the film layer (31) is excessively thin, the film layer (31) may be easily lost during the process of applying the lithium metal electrode according to the embodiment to a battery. Therefore, the film layer (31) may have a thin thickness within the range satisfying the above thickness range and may be uniformly and densely formed on the entire surface of the metal layer (12) and the protective layer (30).

[0106] Referring to FIGS. 1D to 1F, 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).

[0107] 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.

[0108] 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.

[0109] 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).

[0110] 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.

[0111] 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 (31) on the inside and / or surface of the protective layer (30). For a detailed description of the protective layer (30) and the film layer (31), reference may be made to the description given above in FIG. 1A.

[0112] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode of the present invention.

[0113] 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.

[0114] 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.

[0115] In one embodiment, the step of forming the coating layer (20) may be performed using at least one of electrolytic plating, 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.

[0116] 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.

[0117] 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 to form the coating layer (20), so there is a problem that production efficiency and economic feasibility are reduced, and the weight and weight of the battery increase, resulting in a lower energy density. In this way, the coating layer (20) can form a metal layer (12) including a lithium alloy layer (21) through a lithium electrodeposition process. For example, the coating layer (20) can include a metal layer (12) including a lithium alloy layer (21) and a lithium metal layer (41), and can also include a metal layer (12) in which lithium and a lithium alloy are mixed and arranged. Detailed descriptions thereof can be found in FIGS. 1A to 1F.

[0118] A protective layer (30) can be formed on the surface of the coating layer (20) using a slurry containing amorphous carbon. The protective layer (30) can be applied by mixing the amorphous carbon and a binder in water 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. The protective layer (30) can further include a binder.

[0119] Meanwhile, in the step of forming the protective layer (30), the thickness of the lithium ion conductivity promoting 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] The plurality of solvents may include at least one solvent that is a high-k solvent having a dielectric constant of 25 or greater. In one embodiment, the high-k solvent may have a dielectric constant of 25 to 80, specifically, 28 to 45.

[0124] In the conventional case, when a single solvent is used, the ability to dissociate the salt is not complete, so the salt in the form of an incompletely dissociated ion pair exists in the plating solution. The ion pair easily dissociates by receiving electrons during the lithium electrodeposition process, and the decomposition product of the ion pair accumulates on the surface. The product of the salt decomposition reaction is FSO2 or N-SO X There is a problem that is relatively large in XPS analysis. The above FSO2 or N-SO X Such salt decomposition products have the problem of hindering the smooth movement of lithium ions on the electrode surface and consequently hindering the stable electrodeposition of lithium.

[0125] As in the present invention, by using a plurality of solvents, and mixing at least one of the plurality of solvents with a high-k solvent having a permittivity of 25 or higher, the salt can be sufficiently dissociated so that the incompletely dissociated ion pairs can be significantly attenuated. Accordingly, in the lithium electrodeposition process, electrons are mainly used for the dissociation of incomplete ion pairs when a single solvent is used as in the past, but in the composite solvent, they preferentially contribute to the reduction and decomposition of the solvent. Accordingly, the decomposition products of the solvent are excellently accumulated on the electrode surface. It can be confirmed that the main product of the solvent decomposition reaction, such as LiF, is relatively high in the XPS analysis. The source of the LiF may be formed from the dissociated Li+ ions and F in the FEC additive in the solvent.

[0126] In this way, by using a plurality of solvents and mixing and using a high-dielectric constant solvent having a dielectric constant of 25 or higher among the plurality of solvents, a film layer (31) containing LiF decomposition products in at least some areas is formed within the protective layer (30), thereby alleviating electrolyte decomposition, and at the same time facilitating Li ion conduction and reducing interfacial resistance, thereby enabling stable lithium deposition.

[0127] In one embodiment, the plurality of solvents may include a first solvent and a second solvent having a high dielectric constant. The first solvent may be a non-aqueous solvent, and 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.

[0128] The above second solvent may be a high-k solvent such as a sulfone-based solvent. The sulfone-based solvent is a high-k solvent and can facilitate the formation of a LiF layer inside and / or on the surface of the protective layer (30).

[0129] In one embodiment, the sulfone solvent may include at least one of Ethyl Methyl Sulfone (EMS), Diphenyl Sulfone (DPheS), Sulfolane (SL), Dimethyl Sulfone, Diethyl Sulfone (DS), and Methyl Sulfone.

[0130] In one embodiment, in the plurality of solvents, the content of the solvent having a dielectric constant of 25 or greater may be 3 to 40 mol% based on 100 mol% of the total solvent. Specifically, the content of the solvent having a dielectric constant of 25 or greater may be 5 to 35 mol%, and more specifically, 5 to 30 mol%.

[0131] If the content of the solvent having a dielectric constant of 25 or more exceeds the upper limit of the above-mentioned range, there is a problem of hindering the smooth movement of lithium ions due to an increase in the viscosity of the plating solution due to the high dielectric constant solvent. If the content of the solvent having a dielectric constant of 25 or more exceeds the lower limit of the above-mentioned range, there is a problem of a large amount of salt in the form of incompletely dissociated ion pairs existing in the plating solution because the ability to dissociate salts is not complete.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] In the step of forming a lithium metal layer on at least one surface of the current collector 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 2range or 7 mA / cm 2 25 mA / cm 2 It could be a range.

[0136] 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.

[0137] 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.

[0138] 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).

[0139] 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).

[0140] 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.

[0141] 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).

[0142] 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.

[0143] 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. 1.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0154]

[0155] <Experimental Example>

[0156] Manufacturing of cathodes for lithium secondary batteries

[0157] <Example 1>

[0158] <Formation of alloy material coating layer>

[0159] 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 lithium ion concentration protective layer thereon, and then forming a lithium or lithium alloy layer between the current collector and the protective layer through an electrodeposition method.

[0160] 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.

[0161] 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 coating layer (20) containing silver (Ag) was formed by plating to a thickness of about 300 nm on both sides of a copper current collector (11) using an electroless plating method.

[0162] <Protective layer formation>

[0163] FIG. 4a is a scanning electron microscope (SEM) photograph of the surface when a protective layer 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.

[0164] Referring to Figures 4a and 4b, a protective layer of approximately 5 μm was formed on a copper current collector having a silver-containing coating layer by slurry coating using a comma coater. Specifically, the protective layer was formed by mixing acetylene black, an amorphous carbon, and a binder. At this time, the binder was prepared by adding 3.0 wt% of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

[0165] Lithium electrodeposition process

[0166] Afterwards, lithium was removed from the lithium source (40) 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 40 wt% and 5 wt% of lithium bis(fluorosulfonyl)imide, which are nitrogen compounds, and lithium nitrate, respectively, based on 100 wt% of the plating solution, to a composite solvent in which 1,2-dimethoxyethane (DME) as the first solvent and sulfolane (SL) as the second solvent were mixed in a molar ratio of 90:10, and adding 5 wt% of fluoroethylene carbonate, which is a fluorine compound, based on 100 wt% of the plating solution. A lithium metal plate with a purity of 99.9% or higher and a thickness of 500 μm was used by pressing it onto a copper current collector plate (Cu Plate) as a lithium supply source (40).

[0167] After electrically insulating the lithium supply source (40) and the current collector within the plating solution, lithium was deposited between the current collector and the ion concentration protective layer by applying current using a power supply device with the lithium supply source (40) and the current collector as (+) and (-) electrodes, respectively.

[0168] The current density of the electrodeposition process was 0.2 mA / cm2 , 0.5 mA / cm 2 , 1 mA / cm 2 Increasing step by step in order, after 5 minutes of deposition, 12 mA / cm 2 The maximum current density was set. The deposition time at the maximum current density was calculated as the time required for a final accumulated lithium thickness of 10 ㎛ to be deposited, and was set variably depending on the size of the maximum current density.

[0169]

[0170] <Example 2>

[0171] The addition of ethylmethylsulfone (EMS) as a second solvent in the lithium electrodeposition process and the maximum possible electrodeposition current of 10 mA / cm 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0172]

[0173] <Example 3>

[0174] The addition of diphenyl sulfone (DPheS) as a second solvent in the lithium electrodeposition process and the maximum possible electrodeposition current of 10 mA / cm 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0175]

[0176] <Example 4>

[0177] In the lithium electrodeposition process, the molar ratio of the first solvent and the second solvent is 70:30 and the maximum electrodeposition current is 8 mA / cm. 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0178]

[0179] <Example 5>

[0180] A lithium metal electrode was manufactured in the same manner as in Example 1, except that the molar ratio of the first solvent and the second solvent in the lithium deposition process was 95:5.

[0181]

[0182] <Example 6>

[0183] In the lithium electrodeposition process, the molar ratio of the first solvent and the second solvent is 60:40 and the maximum electrodeposition current is 6 mA / cm. 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0184]

[0185] <Example 7>

[0186] In the lithium electrodeposition process, the molar ratio of the first solvent and the second solvent is 97:3 and the maximum possible electrodeposition current is 6 mA / cm. 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0187]

[0188] <Comparative Example 1>

[0189] In the lithium electrodeposition process, the second solvent is not used, and only 1,2-dimethoxyethane (DME), the first solvent, is used at 100 mol%, and the maximum electrodeposition current is 4 mA / cm. 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0190]

[0191] Comparative Example 2

[0192] In the lithium electrodeposition process, dipropyl sulfone (DProS) with a dielectric constant of 22.2 was used as the second solvent, and the maximum possible electrodeposition current was 4 mA / cm. 2 A lithium metal electrode was manufactured in the same manner as in Example 1, except for this point.

[0193]

[0194] All-solid-state battery manufacturing

[0195] 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 cells, a pressurized, dedicated evaluation cell from Terraleader, capable of maintaining an inert atmosphere, was used. For the fabrication of the all-solid-state battery cells, a sulfide-based argyrodite (Li6P5Cl) 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.

[0196] 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.

[0197] 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.

[0198]

[0199] <Evaluation Example 1>

[0200] Table 1 below shows data on the maximum electrodeposition current, LiF production, solvent decomposition, interfacial layer resistance, and charge / discharge performance of Example 1 using a composite solvent and Comparative Example 1 using a single solvent, based on the conditions of the solvent in the plating solution.

[0201] 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.

[0202] LiF formation: The components of the protective layer surface were analyzed using X-ray photoelectron spectroscopy (XPS) on the protective layer surface after the electrodeposition process. XPS analysis was performed using a Nexsa G2 device from Thermo Fisher (X-ray beam size: 400 μm, energy resolution: 0.59 eV, acceleration voltage: 12 kV / 10 mA, minimum analysis area: 10 μm, step size: 0.1 eV). In the F 1S spectrum obtained by XPS, the peak appearing at 684-686 eV was classified as a peak due to the LiF component, and the peak appearing at 687-689 eV was classified as a peak due to the FSO2 component.

[0203] The extent of formation of solvent decomposition products was compared by calculating Imax(LiF) / Imax(FSO2) from the maximum size of the LiF peak, which is a product of solvent decomposition, Imax(LiF), and the maximum size of the FSO2 peak, which is a product of salt decomposition, Imax(FSO2). In addition, the extent of formation of solvent decomposition products was compared by calculating [Area(LiF)] / [Area(LiF) + Area(FSO2)] × 100 from the area Area(LiF) and Area(FSO2) of each peak in XPS.

[0204] Meanwhile, the peak appearing at 399-401 eV in the N 1S spectrum obtained by XPS is N-SO x The peak appearing at 407-409 eV was classified as a peak due to the NO3 component, as it was a peak due to the combined component.

[0205] NO3, a product of dissolved decomposition - Maximum size of the peak I max (NO3 - ) and N-SO, a product of salt decomposition reaction X Maximum size of the peak Imax(N-SO X ) from Imax(NO3 - ) / Imax(N-SO X) was calculated and the degree of production of solvent decomposition products was compared.

[0206] Also, the area of ​​each peak in XPS is Area(NO3 - ) and Area(N-SO X ) from [Area(NO3 - )] / [Area(N-SO X )+Area(NO3 - )] × 100 to compare the degree of production of solvent decomposition products.

[0207] Resistance Analysis of the Protective Layer: Electrochemical Impedance Spectroscopy (XPS) was performed to analyze the interfacial resistance of the protective layer. For EIS analysis, symmetrical coin cells were fabricated using electrodeposited lithium containing the protective layers fabricated in the Examples and Comparative Examples. For the fabrication of the coin cells, a Celgard 2400 separator and an electrolyte containing 1 M lithium hexafluorophosphate (LiPF6), 1.5 wt% vinylene carbonate (VC), and 2 wt% fluoroethylene carbonate (FEC) in a 3 / 7 solvent of ethyl carbonate (EC) / ethyl methyl carbonate (EMC) were used.

[0208] EIS analysis was performed using a coin cell with a potentiostatic impedance meter (Biologic VSP300, measurement frequency: 1 MHz to 0.1 Hz, oscillation voltage: 10 mV), and charge transfer resistance (R) was calculated from the EIS curve. ct ), SEI layer resistance (Solid Electrolyte Interphase Resistance, R SEI ) and total resistance (R total ) was measured.

[0209] 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 / cm2 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.

[0210] Figure 5 is a graph showing the lifespan evaluation of an all-solid-state battery cell using a lithium negative electrode according to an embodiment and a comparative example of the present invention.

[0211] Referring to FIG. 5, it can be confirmed that Example 1 has superior battery cell life characteristics than Comparative Example 1, as the battery cell life of Example 1 is 811 cycles and the battery cell life of Comparative Example 1 is 418 cycles.

[0212] Figure 6 is a graph comparing XPS surface analyses of the surface of an electrodeposited lithium negative electrode protective layer according to an embodiment and a comparative example of the present invention.

[0213] Fig. 6 is an XRD surface analysis graph of Comparative Example 1 and Example 1, and it can be confirmed that the LiF peak value of Example 1 is higher than that of Comparative Example 1, and the XRD peak values ​​of FSO2, N-Sox, and NO3 are lower than that of Comparative Example 1.

[0214] Maximum current that can be deposited under solvent conditions within the plating solution [mA / cm 2 ]LiF production rate, solvent decomposition rate, charge / discharge performance, number of cycles, solvent 1, solvent 2, solvent 2, permittivity, solvent 1 content [mol%], solvent 2 content [mol%], formula 1 * Equation 2 ** Equation 3 *** Equation 4 **** Example 1 DMESL40.49010123.1830.5225811 Comparative Example 1 DME--100-40.4110.316418*: I max (LiF) / I max (FSO2)**: [Area(LiF)]+[Area(LiF) + Area(FSO2)] × 100 (%)***: Imax (NO3 - ) / I max (N-SO X )****: [Area(NO3 - )]+[Area(NO3 - ) + Area(N-SO X )] × 100 (%)

[0215] Referring to Table 1, FIG. 5, and FIG. 6, in the lithium electrodeposition process, compared to Comparative Example 1 in which a single solvent was used as the solvent in the plating solution, by using sulfolane, a sulfone-based high-k solvent, together with DME solvent, it was confirmed that the maximum electrodeposition current was high, and equations 1 to 4 related to LiF production and solvent decomposition had high values, and it was confirmed that the number of charge-discharge cycles of the battery was excellent.

[0216] Table 2 below shows the protection layer resistance analysis values ​​of Example 1 and Comparative Example 1, including charge transfer resistance (R ct ), SEI layer resistance (Solid Electrolyte Interphase Resistance, R SEI ) and total resistance (R total ) represents the measured value.

[0217] Figure 7 is a graph analyzing the impedance and resistance of electrodeposited lithium according to examples and comparative examples of the present invention.

[0218] R ct R SEI R total Example 11.20.82.0 Comparative Example 15.02.27.2

[0219] Referring to Table 2 and Figure 7 above, compared to Example 1, which is a composite solvent, Comparative Example 1, which is a single solvent, was confirmed to have higher charge transfer resistance, SEI layer resistance, and overall resistance of the electrodeposited lithium including the protective layer.

[0220] <Evaluation Example 2>

[0221] Table 3 below shows data on the maximum electrodeposition current, LiF production rate, solvent decomposition rate, interfacial layer resistance, and charge / discharge performance according to the type of sulfone-based high-k solvent in the second solvent.

[0222]

[0223] Maximum current that can be deposited under solvent conditions within the plating solution [mA / cm 2 ]LiF production rate, solvent decomposition rate, interface layer, total resistance [Ω.㎠], charge / discharge performance, number of cycles [times], first solvent, second solvent, second solvent, permittivity, first solvent content [mol%], second solvent content [mol%], formula 1 * Equation 2 ** Equation 3 *** Equation 4 **** Example 1 DMESL40.49010123.1830.52252.0811 Example 2 DMEEMS28.59010102.8750.48222.2755 Example 3 DMEDphes33.8901082.5700.45212.5810 Comparative Example 2 DMEDProS22.2901041.2480.35104.8503*: I max (LiF) / I max (FSO2)**: [Area(LiF)]+[Area(LiF) + Area(FSO2)] × 100 (%)***: I max (NO3 - ) / I max (N-SO X )****: [Area(NO3 - )]+[Area(NO3 - ) + Area(N-SO X )] × 100 (%)

[0224] Looking at Table 3 above, as in Comparative Example 2, when the dielectric constant of the second solvent is lower than 25, the maximum electrodeposition current is low, the values ​​of Equations 1 and 2, which are indices of LiF production, are low, and the values ​​of Equations 3 and 4, which are indices of solvent decomposition, are low compared to Examples 1 to 3. In the case of Examples 1 to 3, it was confirmed that the maximum electrodeposition current, LiF production, and solvent decomposition were high because the dielectric constant of the second solvent was satisfied to be 25 or higher.

[0225] <Evaluation Example 3> - Content ratio of first solvent and second solvent

[0226] Table 4 below shows data on the maximum electrodeposition current, LiF production, solvent decomposition, interfacial layer resistance, and charge / discharge performance according to the type of sulfone-based high-k solvent, depending on the content ratio of the first solvent and the second solvent.

[0227] Maximum current that can be deposited under solvent conditions within the plating solution [mA / cm 2 ]LiF production rate, solvent decomposition rate, interface layer, total resistance [Ω.㎠], charge / discharge performance, number of cycles [times], first solvent, second solvent, second solvent, permittivity, first solvent content [mol%], second solvent content [mol%], formula 1 * Equation 2 ** Equation 3 *** Equation 4 **** Example 1 DMESL40.490 101 23.18 30.52 25 2.08 11 Example 4 DMESL40.47 0 30 8 2.77 40.47 21 3.17 80 Example 5 DMESL40.49 5 5 102.67 20.46 20 1.88 23 Example 6 DMESL40.46 0 40 6 1.55 5 0.32 104.26 21 Example 7 DMESL40.49 7 36 1.85 8 0.35 124.55 98 Comparative Example 2 DMEDProS22.290 104 1.24 8 0.35 104.85 03*: I max (LiF) / I max (FSO2)**: [Area(LiF)]+[Area(LiF) + Area(FSO2)] × 100 (%)***: I max (NO3 - ) / Imax (N-SO X )****: [Area(NO3 - )]+[Area(NO3 - ) + Area(N-SO X )] × 100 (%)

[0228] Referring to Table 4 above, in Examples 1, 4, 5, 6, and 7, Example 6, in which the mol % of the second solvent was excessively high, and Example 7, in which the mol % of the second solvent was excessively low, the content of the sulfone-based high-k solvent was insufficient, so that the ability to dissociate salts was insufficient, and thus the decomposition products in the form of incompletely dissociated ion pairs in the plating solution accumulated on the electrode surface, thereby hindering the smooth movement of lithium ions. Therefore, the maximum electrodeposition current was somewhat lower than in Examples 1, 4, and 5, in which the mol % of the second solvent in the plating solution was within an appropriate range, and the values ​​of Equations 1 and 2, which are indices of the LiF production degree, and Equations 3 and 4, which are indices of the solvent decomposition degree, were somewhat lower.

[0229] Example 7, in which the molar % of the second solvent was excessively low, had a high viscosity of the second solvent, which hindered the smooth movement of lithium ions due to the effect of increased viscosity, and thus the maximum electrodeposition current was somewhat lower than that of Examples 1, 4, and 5, and the values ​​of Equations 1 to 4, which are indicators of the LiF production rate, were confirmed to be somewhat lower.

[0230] However, it was confirmed that Examples 6 and 7 had a higher maximum electrodeposition current and higher values ​​of Equations 1 to 4 compared to Comparative Example 2, which had a lower dielectric constant of the second solvent.

[0231]

[0232] 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, located on at least one surface of the above-mentioned collector; and A protective layer positioned on the above metal layer; and A film layer is disposed within the protective layer, between the metal layer and the protective layer, and at least in a portion of the protective layer, and includes at least a portion of LiF. When measuring X-ray photoelectron spectroscopy (XPS), A lithium metal electrode in which the intensity of the peak appearing at 684–686 eV is greater than that of the peak appearing at 687–689 eV.

2. In paragraph 1, The above film layer is, A lithium metal electrode satisfying the following equation 1 when measured by X-ray photoelectron spectroscopy (XPS). <Formula 1> Imax(LiF) / Imax(FSO2) ≥ 1.5 (The intensity of the peak appearing at 684–686 eV in the above equation 1 is I max (LiF), and the intensity of the peak appearing at 687–689 eV is I max (called FSO2) 3. In paragraph 2, The above formula 1 is a lithium metal electrode having a value of 2.0 or greater.

4. In paragraph 1, The above film layer is, A lithium metal electrode satisfying the following equation 2 when measured by X-ray photoelectron spectroscopy (XPS). <Formula 2> [[Area(LiF)] / [Area(LiF) + Area(FSO2)] × 100 ≥ 55.0 (In the above equation 2, the area of ​​the peak appearing at 684~686eV is called Area(LiF), and the area of ​​the peak appearing at 687~689eV is called Area(FSO2)) 5. In paragraph 1, The above film layer is, A lithium metal electrode satisfying the following equation 3 when measured by X-ray photoelectron spectroscopy (XPS). <Formula 3> I max (N-SO x ) / I max (NO3 - ) ≥ 0.30 (The intensity of the peak appearing at 399–401 eV in the above equation 3 is Imax(N-SO x ) and the intensity of the peak appearing at 407~409 eV is called Imax(NO3).

6. In paragraph 1, The above film layer is, A lithium metal electrode satisfying the following equation 4 when measured by X-ray photoelectron spectroscopy (XPS). <Formula 4> [[Area(N-SO x )] / [Area(N-SO x ) + Area(NO3 - )] × 100 ≥ 10.0 (The area of ​​the peak appearing at 399–401 eV in the above equation 4 is Area(N-SO x ) and the area of ​​the peak appearing at 407~409 eV is called Area(NO3).

7. In paragraph 1, The total resistance (R) of the interface between the protective layer and the film layer total ) is 1.5 to 4.6 Ω cm 2 Lithium metal electrode.

8. In paragraph 1, The intensity of the peak appearing at 684–686 eV above is I max (LiF) is a lithium metal electrode with a molecular weight of 25,000 or more.

9. In paragraph 1, The intensity of the peak appearing at 687–689 eV above is I max (FSO2) Lithium metal electrode with less than 11,000.

10. 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 on the surface of the coating layer; A step of positioning a current collector on which the coating layer and the protective layer are formed in a plating solution containing a plurality of solvents, and then positioning a lithium supply source (40) 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 producing a lithium metal electrode, wherein at least one solvent among the above plurality of solvents has a dielectric constant of 25 or higher.

11. In Article 10, A method for producing a lithium metal electrode, wherein at least one solvent among the above plurality of solvents has a dielectric constant of 25 to 80.

12. In paragraph 10, A method for producing a lithium metal electrode, wherein the content of the solvent having a dielectric constant of 25 or higher is 3 to 40 mol% based on 100 mol% of the total solvent.

13. In paragraph 10, A method for manufacturing a lithium metal electrode, wherein the solvent having a dielectric constant of 25 or higher is a sulfone solvent.

14. In paragraph 13, A method for producing a lithium metal electrode, wherein the sulfone solvent comprises at least one of Ethyl Methyl Sulfone (EMS), Diphenyl Sulfone (DPheS), Sulfolane (SL), Dimethyl Sulfone, Diethyl Sulfone (DS), and Methyl Sulfone.

15. In paragraph 10, In the step of applying a current between the above-described 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, 6 to 12 mA / cm 2 A method for manufacturing a lithium metal electrode, comprising the step of electrodepositing at a maximum current density in the range.

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