Method for manufacturing concentration gradient-type anode current collector using pulse electroplating, anode current collector manufactured thereby, and anode-free lithium metal battery including same

Abstract

The present invention relates to a method for manufacturing a concentration gradient-type anode current collector using pulse electroplating, an anode current collector manufactured thereby, and an anode-free lithium metal battery including same. In the present invention, a magnesium (Mg) seed having high affinity for lithium and high binding energy with lithium ions is deposited in a gradient form on a lower portion of a current collector having a three-dimensional structure by using pulse electroplating, thereby inducing lithium to be uniformly electrodeposited from the lower portion of the current collector. Accordingly, the present invention can solve a top growth problem occurring in conventional three-dimensional current collectors and suppress dendrite formation, thereby enabling efficient and stable electrodeposition of lithium. When the anode current collector of the present invention is applied to an anode-free lithium metal battery, cycle stability, lifespan, and energy density of the battery can be effectively improved.

Description

Method for manufacturing a concentration gradient type negative current collector using pulsed electroplating, a negative current collector manufactured thereby, and a negative-electrode lithium metal battery including the same

[0001] The present invention relates to a method for manufacturing a concentration gradient type negative current collector using pulsed electroplating, a negative current collector manufactured thereby, and a negative-electrode lithium metal battery including the same. More specifically, the invention relates to a method for manufacturing a negative current collector capable of suppressing dendritic growth and upward growth of lithium by depositing magnesium seeds in a concentration gradient type on porous copper by pulsed electroplating, a negative current collector manufactured thereby, and a negative-electrode lithium metal battery including the same.

[0002] Lithium Metal Batteries (LMBs) use lithium metal as the negative electrode and offer advantages over lithium-ion batteries, such as theoretically higher energy density, faster charging speeds, and lighter weight. Since conventional lithium-ion batteries suffer from short driving ranges when applied to electric vehicles due to their theoretical capacity limitations, the technology of utilizing lithium metal batteries is attracting attention to improve the driving range of EVs.

[0003] However, the anodes applied to lithium metal batteries face critical problems: mass production in ambient conditions is difficult due to the high reactivity of lithium metal; unlike conventional graphite anodes, the absence of a host material capable of reversibly storing lithium ions results in low lifespan characteristics; and internal short circuits can occur due to the growth of lithium dendrites. Therefore, the development of technologies to improve battery stability and lifespan is required for the practical application of lithium metal batteries.

[0004] As an example, research is being conducted on anode-free lithium metal batteries (AFLMBs) that use only a negative current collector without initial lithium metal. In these anode-free batteries, a multidimensional structure is used as the negative current collector; however, due to the high electrical conductivity of the current collector, the current concentrates at the top, causing lithium metal to be deposited from the outer surface rather than from the interior of the collector. In other words, for conventional anode-free batteries, the "top growth" phenomenon, where lithium is preferentially deposited from the top of the current collector, has been a major problem. Consequently, the large internal space of the current collector is not properly utilized, and dendrite formation is promoted, leading to shortened battery life and stability issues.

[0005] As a technology to solve such problems, Korean Registered Patent Publication No. 10-2559762 describes a technology that suppresses dendritic growth during lithium electrodeposition by using a negative electrode current collector containing a transition metal dichalcogenide layer. Additionally, Korean Published Patent Publication No. 10-2024-0144823 discloses a technology that suppresses side reactions between a lithium thin film and a metal salt by optimizing the electrolyte.

[0006] However, while the aforementioned technologies improve stability by inhibiting the dendritic growth of lithium, the development of technologies capable of solving the problem of lithium upstream growth remains insufficient.

[0007] Accordingly, there is a need to develop technology that can effectively improve the cycle stability and lifespan of lithium metal batteries as a multidimensional current collector capable of suppressing dendritic and top growth of lithium.

[0008] One objective of the present invention is to provide a negative electrode current collector that can be used in a negative electrode lithium metal battery to prevent problems of dendritic growth and top growth of lithium.

[0009] Another objective of the present invention is to provide a method for manufacturing the cathode current collector.

[0010] Another objective of the present invention is to provide a cathode-free lithium metal battery with improved cycle stability and lifespan, including the cathode current collector.

[0011] To achieve the above objective, the present invention provides a method for manufacturing a negative electrode current collector comprising the step of manufacturing a negative electrode current collector in which magnesium seeds are deposited in a gradient form such that the concentration decreases toward the upper direction of the porous copper by depositing magnesium (Mg) on ​​porous copper using pulsed electroplating.

[0012] In the present invention, the porous copper can be manufactured through a dealloying process that removes metals other than copper from a copper-containing alloy.

[0013] In the present invention, the copper-containing alloy is of the chemical formula Cu x M 1-x It is represented as such, where M is zinc (Zn), tin (Sn), or nickel (Ni), and x can be 0.5 to 0.8.

[0014] In the present invention, the dealolysis process can be performed through a chemical dealolysis process in which a copper-containing alloy is immersed in an acid solution to remove metals other than copper.

[0015] In the present invention, the immersion may be performed for 6 to 18 hours.

[0016] In the present invention, the porosity of the porous copper may be 40 to 70%.

[0017] In the pulse electroplating step of the present invention, the current interruption time (off-time, t) off ) can be 0.1 to 5.0 seconds.

[0018] In the pulse electroplating step of the present invention, the peak current density (PCD) is 200 to 800 mA / cm² 2 It could be.

[0019] In the pulse electroplating step of the present invention, the area capacity is 2 to 10 mAh / cm² 2 It could be.

[0020] In the present invention, the pulse electroplating step may be performed through the steps of: preparing a cell comprising a porous copper cathode, an electrolyte for magnesium deposition, and a magnesium anode; and applying a pulse current to the cell to deposit a magnesium seed on the porous copper.

[0021] In the present invention, the particle size of the deposited magnesium seed may be 100 nm to 2 µm.

[0022] In the present invention, the content of the deposited magnesium seed may be 2 to 10 weight percent with respect to the total weight of the negative current collector.

[0023]

[0024] The present invention also provides a cathode current collector manufactured by the above method.

[0025] The cathode current collector of the present invention comprises porous copper; and a magnesium (Mg) seed deposited on the surface of the porous copper, wherein the magnesium seed may be formed in the form of a concentration gradient in which the content decreases in the upward direction of the porous copper.

[0026]

[0027] The present invention also provides a cathode-free lithium metal battery comprising the above-mentioned cathode current collector.

[0028] The negative electrode lithium metal battery of the present invention may include the negative electrode current collector, the positive electrode, the electrolyte, and the separator.

[0029] In the present invention, the electrolyte comprises a lithium salt and a solvent, and the solvent may be a mixed solvent comprising two or more solvents selected from the group consisting of carbonate-based solvents, ether-based solvents and fluorinated substituents thereof.

[0030] In the present invention, by using pulsed electroplating to electrodeposit magnesium (Mg) seeds, which have high lithium affinity and high binding energy with lithium ions, in a gradient shape on the bottom of a current collector with a three-dimensional structure, it is possible to induce the uniform deposition of lithium starting from the bottom of the current collector. Accordingly, by using the present invention, the problem of top growth occurring in conventional 3D current collectors can be solved and dendrite formation can be suppressed, and efficient and stable electrodeposition of lithium is possible. When the negative current collector of the present invention is applied to a negative-electrode lithium metal battery, the cycle stability, lifespan, and energy density of the battery can be effectively improved.

[0031] Figure 1 illustrates a magnesium deposition process according to one embodiment of the present invention and a form in which the manufactured current collector is applied to a battery.

[0032] Figure 2 is a conceptual diagram showing the difference in magnesium deposition behavior using DC electroplating and pulsed electroplating.

[0033] Figure 3 shows the behavior of lithium electrodeposition when a negative electrode current collector according to one embodiment of the present invention is used as a negative electrode current collector of a lithium metal battery.

[0034] Figure 4 illustrates a process for manufacturing a cathode current collector according to one embodiment of the present invention.

[0035] FIG. 5 shows Cu according to reaction time in a dealolysis reaction according to one embodiment of the present invention. 0.65 Zn 0.35 This shows the color change of the alloy.

[0036] FIG. 6 shows Cu according to reaction time in a dealolysis reaction according to one embodiment of the present invention.0.65 Zn 0.35 This shows the weight change of the alloy.

[0037] FIG. 7 shows Cu according to reaction time in a dealolysis reaction according to an embodiment of the present invention. 0.65 Zn 0.35 This shows an SEM image of the alloy.

[0038] Figure 8 shows the difference in X-ray diffraction (XRD) patterns according to reaction time in a dealolysis reaction according to one embodiment of the present invention.

[0039] FIG. 9 shows an optical image and a scanning electron microscope (SEM) image of porous copper produced by a dealolysis reaction according to one embodiment of the present invention.

[0040] Figure 10 shows the BET analysis results of porous copper produced by a dealolysis reaction according to one embodiment of the present invention.

[0041] Figure 11 shows the EDS analysis results of porous copper produced by a dealolysis reaction according to one embodiment of the present invention.

[0042] FIG. 12 shows the batch / strip test results according to the electrolyte in a Li / P-Cu cell according to one embodiment of the present invention.

[0043] Figure 13 shows the XPS analysis results of the magnesium deposition surface in an MGP-Cu structure manufactured according to one embodiment of the present invention.

[0044] Figure 14 shows the XRD analysis results of the magnesium deposition surface in an MGP-Cu structure manufactured according to one embodiment of the present invention.

[0045] Figure 15 shows an SEM image of a structure when DC electroplating is used in one embodiment of the present invention.

[0046] FIGS. 16a and 16b respectively show a cross-sectional SEM image and an EDS image of an Mg deposited surface formed using DC electroplating (a) and PC electroplating (b) in one embodiment of the present invention.

[0047] FIG. 17 shows optical images, scanning electron microscope (SEM) images, and EDS mapping results of an MGP-Cu magnesium deposition surface according to maximum current density (PCD) in one embodiment of the present invention.

[0048] FIG. 18 shows optical images, scanning electron microscope (SEM) images, and EDS mapping results of the opposite side of the MGP-Cu magnesium deposition according to the maximum current density (PCD) in one embodiment of the present invention.

[0049] Figure 19 shows the results of an analysis of the average particle size of Mg seeds according to the maximum current density (PCD) in one embodiment of the present invention.

[0050] FIG. 20 is a current interruption time (t) in one embodiment of the present invention. off This shows the change in the concentration gradient inside MGP-Cu according to the control.

[0051] FIG. 21 shows a current interruption time (t) in one embodiment of the present invention. off This shows the change in particle size of Mg seeds according to the control.

[0052] FIG. 22 shows a current density of 1 mA / cm² according to one embodiment of the present invention. 2 Scanning electron microscope (SEM) images of P-Cu and MGP-Cu according to area capacity during lithium electrodeposition under certain conditions are shown.

[0053] FIG. 23 shows a current density of 2 mA / cm² according to one embodiment of the present invention. 2 This shows optical microscope (OM) images of P-Cu and MGP-Cu cross-sections according to area capacity during lithium electrodeposition under certain conditions.

[0054] FIG. 24 shows a current density of 1 mA / cm² according to one embodiment of the present invention. 2, area capacity 1mAh / cm² 2 This compares the Li electrodeposition behavior of P-Cu and MGP-Cu after 10 cycles under conditions.

[0055] FIG. 25 shows the results of measuring the nucleation overpotential of B-Cu, P-Cu, and MGP-Cu structures according to one embodiment of the present invention.

[0056] FIG. 26 shows a Tafel plot of P-Cu and MGP-Cu structures according to one embodiment of the present invention.

[0057] FIG. 27 shows the Coulomb efficiency (CE) and detailed time-voltage graphs of MGP-Cu, P-Cu, and B-Cu structures in a Li electrodeposition / discharge test according to one embodiment of the present invention.

[0058] FIG. 28 shows the time-voltage profile for a symmetric cell fabricated in one embodiment of the present invention.

[0059] FIG. 29 shows 0.1 to 5 mA / cm for a symmetric cell fabricated in one embodiment of the present invention. 2 This shows the time-voltage profile under the conditions.

[0060] FIG. 30 shows the results of a charge / discharge cycle analysis under 0.5C conditions for a full cell fabricated in one embodiment of the present invention.

[0061] Specific embodiments of the present invention will be described in more detail below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which the present invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0062]

[0063] The present invention relates to a method for manufacturing a concentration gradient type negative current collector using pulsed electroplating, a negative current collector manufactured thereby, and a negative-electrode lithium metal battery comprising the same.

[0064] In the present invention, by using pulsed electroplating to deposit magnesium (Mg) seeds, which have high lithium affinity and high binding energy with lithium ions, in a gradient shape on the lower part of a current collector with a three-dimensional structure, lithium can be induced to grow uniformly from the lower part of the current collector.

[0065] Accordingly, by using the present invention, the problem of top growth occurring in conventional 3D current collectors can be solved and dendrite formation can be suppressed, and efficient and stable electrodeposition of lithium is possible. In addition, when applied to lithium metal batteries, the battery life and energy density can be improved, and in particular, high electrical efficiency and cycle life can be provided in non-anode lithium metal batteries.

[0066] The cathode current collector of the present invention can be manufactured by depositing a magnesium seed on porous copper using pulsed electroplating. At this time, magnesium is deposited while forming a concentration gradient on the porous copper, and when the magnesium-deposited porous copper is used as a current collector, the magnesium-deposited surface functions as the upper part of the current collector, and the surface opposite to the magnesium-deposited surface functions as the lower part of the current collector.

[0067] Accordingly, the negative current collector of the present invention comprises porous copper; and a magnesium (Mg) seed deposited on the surface of the porous copper, wherein the magnesium seed is formed in the form of a concentration gradient in which the content decreases in the upward direction of the porous copper.

[0068] In the present invention, the term "gradient shape" refers to a shape in which the content / concentration of a substance decreases as it moves in one direction.

[0069] In the present invention, the surface of porous copper is interpreted to include not only the outer surface of the porous copper structure but also the surface within the pores, unless specifically described otherwise.

[0070] Figure 1 illustrates a magnesium deposition process for manufacturing a current collector of the present invention (left) and a form in which the manufactured current collector is applied to a battery (right).

[0071] When pulse electroplating, magnesium deposition begins from the side facing magnesium in the porous copper. In describing the present invention, the side where magnesium deposition is performed in this manner and has a high magnesium density is referred to as the "magnesium deposition surface," and the opposite side where magnesium density is low due to the concentration gradient deposition is referred to as the "magnesium deposition opposite surface."

[0072] In this manner, when a structure in which magnesium deposition is completed is used as a negative current collector, the magnesium deposition surface is positioned so as to be located at the bottom of the current collector, and the opposite side of the magnesium deposition surface is positioned so as to be located at the top of the current collector. In describing the present invention, the surface facing the anode direction in the current collector is referred to as the upper surface (top), and the opposite side is referred to as the lower surface (bottom).

[0073] In the present invention, the porous copper can be used as a negative electrode current collector and serves as a structure for depositing magnesium seeds, so that magnesium can penetrate not only the outer surface of the porous copper structure but also the inner surface of the pores to form seeds.

[0074] In the present invention, the porosity of the porous copper may be 40 to 70%, preferably 50 to 65%. Additionally, the average size (diameter) of the pores may be 1 to 10 μm. Under these conditions, magnesium seeds can be deposited smoothly, and when used as a current collector, the undergrowth of lithium is possible.

[0075] In the present invention, the porous copper can be manufactured by dealloying a copper-containing alloy to remove metals other than copper.

[0076] In the present invention, the copper-containing alloy has the chemical formula Cu x M 1-x It can be expressed as such, wherein M can be a metal other than copper, for example, zinc (Zn), tin (Sn), or nickel (Ni), and x can be 0.5 to 0.8, preferably 0.6 to 0.7.

[0077] In the present invention, the dealloying may be performed through a heat treatment process in which a copper-containing alloy is heat-treated at a high temperature of 600 to 800°C to vaporize metals other than copper; or through a chemical process in which a copper-containing alloy is immersed in an acid solution to remove metals other than copper.

[0078] In the above chemical dealloying process, one or more of hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and acetic acid (CH3COOH) may be used as the acid solution. In addition, the concentration of the acid solution may be 5 to 15 M, preferably 8 to 12 M.

[0079] In the present invention, the chemical dealloying process (i.e., acid solution immersion process) can be performed for 6 to 18 hours, preferably for 10 to 18 hours, and more preferably for 12 to 14 hours. If the time is shorter than this, non-copper metals may not be properly removed, and if the time is extended too much, it may be disadvantageous in terms of process efficiency because the amount of change in non-copper metals is very small after a certain time.

[0080] In the present invention, the temperature of the chemical dealloying process can be controlled to 40 to 80°C, for example, 50 to 70°C. In addition, it is preferable to wash and dry the porous copper formed after dealloying before use.

[0081] In the present invention, the weight per unit area of ​​the porous copper is 30 to 45 mg / cm² 2 It may be, preferably 32 to 40 mg / cm² 2 It is possible. Under the above conditions, magnesium seeds can be smoothly deposited within porous copper, and when used as a current collector, the undergrowth of lithium is possible.

[0082] In the present invention, the thickness of the porous copper may vary depending on the size of the battery, but for example, it may be 20 μm to 1 mm, specifically 50 to 200 μm. In describing the present invention, the upper and lower portions of the porous copper are set based on the thickness direction.

[0083] The negative current collector of the present invention comprises a magnesium (Mg) seed deposited on a porous copper surface, wherein the magnesium seed is formed in the form of a concentration gradient in which the concentration decreases toward the upper direction of the porous copper.

[0084] In the case of porous copper current collectors, growth of dendritic lithium (lithium dendrite) is likely to occur on the top surface that is closely exposed to the electrolyte, whereas the current collector of the present invention has magnesium seeds with lithium affinity formed in a concentration gradient, so lithium growth is induced from the bottom of the current collector by these magnesium seeds, effectively filling the pores of the porous copper and preventing growth on the top.

[0085] In the present invention, the magnesium seed can be formed by depositing magnesium on porous copper using pulsed electroplating.

[0086] Unlike conventional direct current (DC) electroplating, pulse current (PC) electroplating has an off-time during which the current is cut off after flowing for a certain period of time. The deposition process can be controlled through a repetitive cycle of such on-time and off-time.

[0087] Figure 2 is a conceptual diagram showing the deposition behavior of magnesium in DC and PC electroplating methods, where the dashed arrows and gray spheres represent the ion pathways and nucleation seeds, respectively.

[0088] When using the DC electroplating method, a constant current is applied to grow Mg seeds in a direction that increases in size, whereas when using the PC electroplating method, many small Mg seeds grow depending on the current application and interruption times, which can increase the exposed surface area of ​​the Mg seeds and improve the efficiency of lithium affinity utilization.

[0089] In the pulse electroplating step above, the current application time (on-time, t) on ) refers to the time during which an actual plating reaction occurs by applying current, and the current cutoff time (off-time, t off ) refers to the time during which the target material penetrates into the current collector without the application of current. In the present invention, unlike the DC electroplating method which has no penetration time by applying a constant current, pulse electroplating is used to penetrate Mg seeds into the inside of the current collector, thereby enabling the production of a current collector with a concentration gradient.

[0090] In the pulse electroplating step of the present invention, the current application time (on-time, t) on ) can be 0.01 to 1.0 seconds, specifically 0.05 to 0.2 seconds.

[0091] In the pulse electroplating step of the present invention, the current interruption time (off-time, t) off ) may be 0.1 to 5.0 seconds, preferably 0.1 to 2.0 seconds, and more preferably 0.5 to 1.0 seconds. Within the above range, it is preferable because the magnesium seed is small and can penetrate into the pores of the porous copper structure.

[0092] In the pulse electroplating step of the present invention, the total plating time may be 4 to 10 minutes, specifically 5 to 7 minutes. Within this range, magnesium seeds may be sufficiently deposited on the deposition surface and may be sufficiently deposited in a gradient shape along the pores of the porous teeth.

[0093] In the pulsed electroplating step above, the peak current density (PCD) is 200 to 800 mA / cm² 2 , preferably 300 to 700 mA / cm 2 , preferably 400 to 600 mA / cm 2 It may be possible. Within the above range, the size of the magnesium seeds may be formed small, and the magnesium may penetrate to the pore surface of the porous copper structure so that the seeds are formed uniformly.

[0094] In the pulse electroplating step above, the area capacity is 2 to 10 mAh / cm² 2 , for example, 4 to 6 mAh / cm² 2 It could be.

[0095] In the present invention, pulse electroplating for magnesium deposition can be performed through the steps of: preparing a cell comprising a porous copper cathode, an electrolyte for magnesium deposition, and a magnesium anode; and applying a pulsed current to the cell to deposit a magnesium seed on the porous copper.

[0096] The above-mentioned electrolyte for magnesium deposition contains magnesium ions, specifically may contain magnesium salts and solvents, and may additionally include additives, pH adjusters, etc.

[0097] In an exemplary embodiment of the present invention, the magnesium salt may be magnesium chloride, magnesium sulfate, a salt represented by the formula R-Mg-X, or a complex of these with an aluminum salt. In the formula R-Mg-X, R may be methyl, ethyl, propyl, butyl, cyclohexyl, or phenyl, and X may be Cl, Br, or I. For example, the magnesium salt may include one or more selected from the group consisting of ethyl magnesium bromide (EtMgBr), ethyl magnesium chloride (EtMgCl), an EtMgCl-(EtAlCl2)2 complex, and a PhMgCl-AlCl3 complex.

[0098] In the present invention, water or an organic solvent, such as tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc), methanol, ethanol, acetone, etc., may be used as the solvent for the electrolyte for magnesium deposition.

[0099] The particle size of the magnesium seed formed in the present invention may be 100 nm to 2 µm, preferably 200 nm to 1 µm, and more preferably 300 nm to 800 nm. If the size of the magnesium seed is too large, the total surface area is small, so the lithium-friendly properties of magnesium may not be fully exhibited, and if the size of the seed is too small, a problem may occur in which the initial irreversible capacity of lithium deposition increases.

[0100] The content of the magnesium seed formed in the present invention may be 2 to 10 weight%, specifically 3 to 8 weight%, based on the total weight of the negative current collector.

[0101] In the present invention, magnesium seeds can be deposited while forming a concentration gradient by depositing magnesium on porous copper using pulsed electroplating. When such a structure is used as a negative electrode current collector for a lithium metal battery, due to the lithium-friendly nature of magnesium, lithium is electrodeposited from the magnesium deposition site (i.e., the bottom of the current collector) on the current collector, thereby preventing problems of upper growth and dendritic growth of lithium.

[0102]

[0103] Accordingly, the negative current collector of the present invention can be effectively used in lithium metal batteries, particularly anode-free lithium metal batteries (AFLMB).

[0104] Specifically, a negative electrode lithium metal battery according to one embodiment of the present invention may include a negative electrode current collector; a positive electrode; an electrolyte; and a separator.

[0105] Figure 3 shows the behavior of lithium electrodeposition when porous copper (P-Cu) and a structure (MGP-Cu) in which magnesium is deposited in a concentration gradient according to the present invention are used as negative electrode current collectors of a lithium metal battery.

[0106] In the case of porous copper current collectors, lithium dendrite growth is likely to occur on the top surface that is closely exposed to the electrolyte, whereas in the current collector of the present invention, lithium growth is induced from the bottom by magnesium seeds formed in a concentration gradient shape, effectively filling the pores of the porous copper and preventing growth on the top.

[0107] In the present invention, the anode comprises an anode active material and an anode current collector, and the anode active material may be applied in the form of a slurry comprising an anode active material, a binder, and a conductive material.

[0108] The above-mentioned positive active materials include LiCoO2, LiMnO2, LiNiO2, LiMn2O4, and LiNi 1-x Co xOne or more of lithium transition metal oxides such as O2, LiFePO4, LiMnPO4, and LiCoPO4 can be used.

[0109] The above positive current collector may be made of aluminum foil (Al foil) or aluminum mesh (Al mesh).

[0110] The conductive material used in the above-mentioned positive electrode active material slurry is used to impart conductivity to the electrode, and one or more types of carbon-based materials such as graphite, carbon black, super P, acetylene black, ketjen black, graphene, carbon nanotubes, and channel black; metals such as copper, nickel, aluminum, and silver; and conductive metal oxides such as titanium oxide may be used.

[0111] The binder used in the above-mentioned positive active material slurry is intended to provide adhesion between the active material and the conductive material, and one or more types such as polyvinylidene fluoride (PVdF), polyimide (PI), fluoropolyimide (FPI), polyacrylic acid (PAA), and polyvinyl alcohol (PVA) may be used.

[0112] In the battery of the present invention, the electrolyte may include a lithium salt and a mixed solvent, and as the lithium salt, one or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiN(FSO2)2, LiCl, LiI, LiSCN, LiB(C2O4)2, LiF2BC2O4, LiPF4(C2O4), LiPF2(C2O4)2, and LiP(C2O4)3 may be used.

[0113] In the present invention, the mixed solvent of the electrolyte may include two or more selected from the group consisting of carbonate-based solvents, ether-based solvents, and fluorinated substituents thereof. One or more of the following may be used as the carbonate-based solvent: ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, etc., and one or more of the following may be used as the ether-based solvent: dimethyl ether, ethyl methyl ether, diethyl ether, propyl methyl ether, propyl ethyl ether, dipropyl ether, dipropyl ether, isopropyl methyl ether, isopropyl ethyl ether, etc.

[0114] Preferably, in the present invention, the mixed solvent of the electrolyte may include one or more carbonate-based solvents and fluorinated carbonate-based solvents. By using a fluorinated carbonate-based solvent in this way, the overvoltage can be lowered and the circulating properties of the battery can be improved.

[0115] In the present invention, the separator may be a porous polymer membrane made of polyethylene or polypropylene, and may also be coated with a ceramic material.

[0116] The lithium metal battery of the present invention uses porous copper in which magnesium seeds are formed in a concentration gradient as a negative electrode current collector, thereby inducing lithium growth at the bottom of the negative electrode current collector during lithium deposition that occurs during the charging and discharging process and suppressing the formation of dendritic lithium. Accordingly, the overvoltage of the lithium metal battery can be lowered, and cycle stability and cyclicity, i.e., lifespan, can be improved.

[0117]

[0118] Examples

[0119]

[0120] The present invention will be explained in more detail through the following examples. However, these examples represent some experimental methods and configurations to illustrate the invention, and the scope of the invention is not limited to these examples.

[0121]

[0122] Preparation Example 1: Fabrication of MGP-Cu Structure Using Pulse Electroplating

[0123]

[0124] According to the process shown in Figure 4, porous copper was fabricated by chemical dealloying, and then magnesium was deposited in a concentration gradient form by pulse plating.

[0125] Cu 0.65 Zn 0.35 An alloy brass sheet (Brass sheet, Nilaco Co.) was cut to a size of 30×50 mm and washed with ethanol. Then, a chemical dealloying reaction was performed by immersing it in a 10 M hydrochloric acid solution at 60°C for 12 hours, and then it was washed several times with deionized water and ethanol.

[0126] Porous copper (P-Cu) was obtained by placing the sample in a tube furnace at 60°C under an argon gas atmosphere for 2 hours and drying it in a vacuum oven at 60°C for 10 hours. The thickness of the formed P-Cu was 100 μm, identical to that of the brass sheet prior to dealloying, and its weight decreased by 56.4% compared to the brass sheet, resulting in a weight per area of ​​36.3 mg / cm². 2 It was measured as.

[0127] Next, to prepare the all-phenyl-complex (APC) electrolyte used for magnesium deposition, AlCl3 was slowly dissolved in THF and stirred for 12 hours, then mixed with a PhMgCl solution and stirred for an additional 12 hours.

[0128] After deairing, an Mg disc (diameter 1.4 cm) was ground with a blade in a glove box filled with argon gas (O2 and H2O <0.1 ppm). The components were then assembled into a coin cell (P-Cu / APC / Mg) with a wattage of 5 mAh / cm². 2 Capacity and maximum current density (PCD) of 500 mA / cm² 2Pulse electroplating was performed under the condition of pulse electroplating. At this time, the current application time (t on ) is 0.1 seconds, current interruption time (t off The time was set to 0.9 seconds, and plating was performed for a total of 6 minutes.

[0129] After disassembling the cell, the manufactured structure (MGP-Cu) was rinsed several times with DMC and dried in a vacuum for 2 hours.

[0130]

[0131] Preparation Example 2: Cell fabrication using MGP-Cu electrode

[0132]

[0133] For the half-cell test, each structure and Li foil were used as the working electrode and reference electrode. For the symmetrical and full cells, each substrate was set to 5 mAh / cm² prior to the test. 2 It was lithiated to a capacity of . Prior to the test, the half cell and symmetrical cell were 1 mAh / cm². 2 With a capacity of 0.1mA / cm 2 Three cycles of precycling were performed, and the full cell was precycled at 0.1C.

[0134] In the case of a full cell, the active material Li(Ni) is added to an N-methylpyrrolidone (NMP) solution. 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by mixing O2 (NCM622), Super P as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder using a Thinky mixer. In the cathode slurry, the weight ratio of active material:binder:conductive additive was adjusted to 90:5:5.

[0135] Then, NCM622 at 10.08 mg / cm² on the aluminum thin film 2Slurry casting was performed at the loading level. Polyethylene (PE) was used as the separator, and as the electrolyte (Dongwha Co.), 1M lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC), DMC, and fluoroethylene carbonate (FEC) in a volume ratio of 45:45:10. 100 μL of electrolyte was used for the half cell and symmetric cell, and 80 μL of electrolyte was used for the full cell.

[0136]

[0137] Experimental Example 1: Analysis of Structural Changes According to Dealoalloy Time

[0138]

[0139] A porous copper structure was fabricated using the method of the manufacturing example, but with the reaction time during dealloying adjusted to 0 to 16 hours, and the change in physical properties over time was confirmed.

[0140] Figures 5 and 6 show Cu according to dealolysis reaction time, respectively. 0.65 Zn 0.35 This shows the color and weight changes of the alloy. As a result of checking the weight changes at intervals, it was confirmed that the total weight decreased by an average of 56.4% and 58.6% after 12 and 16 hours, respectively, during the dealloying process. These results indicate that the weight change after 12 hours is not significant, meaning that 12 hours of acid treatment is sufficient.

[0141] Figure 7 shows Cu according to dealolysis reaction time. 0.65 Zn 0.35 The image shows an SEM image of the alloy, and it can be confirmed from the SEM image that a porous structure is formed as dealolysis progresses. In addition, the pore size and porosity can be controlled by adjusting the dealolysis reaction time, and since the porosity in the SEM image after 12 hours remains constant, it was confirmed that 12 hours is the optimal reaction time.

[0142]

[0143] Experimental Example 2: Analysis of compositional changes according to dealloying time

[0144]

[0145] A porous copper structure was fabricated using the method of the manufacturing example, but with the reaction time during dealloying adjusted to 0 to 16 hours, and changes in elemental composition were confirmed through X-ray diffraction (XRD) analysis.

[0146] Figure 8 shows the difference in X-ray diffraction (XRD) patterns according to the dealloying reaction time. In Figure 8, starting from the bottom line, Cu in order 0.65 Zn 0.35 The results of the alloy, 4-hour acid treatment, 8-hour acid treatment, 12-hour acid treatment, and 16-hour acid treatment are shown. There is no significant change between the 12-hour and 16-hour acid treatments, and in particular, it can be confirmed that the peaks at 49.5° and 72.5° remain unchanged even after 12 hours. From this, it was determined that 12 hours is an appropriate dealloying reaction time.

[0147]

[0148] Experimental Example 3: Analysis of Structure and Composition of Porous Copper After Dealolysis

[0149]

[0150] The structure and composition of porous copper produced through dealolysis according to the manufacturing example were specifically identified.

[0151] Figure 9 shows optical and scanning electron microscope (SEM) images of porous copper prepared by a 12-hour dealolysis reaction. From this, it was confirmed that the porous copper has pores with a maximum diameter of 10 μm.

[0152] Figure 10 shows the BET analysis results of the fabricated porous copper. The average pore size distribution calculated from this was 1.6 nm, and the porosity calculated based on the Cu density after dealloying was 58.6%, with an estimated capacity of 12.085 mAh / cm² when lithium completely fills the pores. 2It can be estimated as such. In addition, Figure 11 shows the EDS analysis results of the manufactured porous copper, and by referring to this, it can be confirmed that zinc has been sufficiently removed.

[0153]

[0154] Experimental Example 4: Analysis of Electrical Characteristics of Li / P-Cu Cells According to Electrolyte

[0155]

[0156] The method of Manufacturing Examples 1 and 2 was used, but the cell was fabricated excluding FEC from the electrolyte, and then the difference in performance according to the presence or absence of FEC in the electrolyte was confirmed.

[0157] Figure 12 shows the batch / strip test results for the selection of an electrolyte for a Li / P-Cu cell. Referring to this, it was confirmed that when FEC was added to the electrolyte, it exhibited low overpotential and excellent cycling performance in the voltage-time profile. From this, it was found that it is desirable for the electrolyte to contain FEC.

[0158]

[0159] Experimental Example 5: Component Analysis After Magnesium Deposition

[0160]

[0161] For the porous copper structure with magnesium deposited according to Preparation Example 1, the magnesium component was confirmed through X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis.

[0162] Figure 13 shows the results of XPS analysis of the magnesium deposition surface. Referring to the XPS spectrum, the formation of MgO, Mg(OH)2, and MgCO3 on the deposition surface can be confirmed, and from this, it was found that Mg reacted with carbonates to form compounds such as MgO, Mg(OH)2, and MgCO3.

[0163] Figure 14 shows the XRD analysis results of the magnesium deposited surface. Referring to the XRD pattern, a metallic Mg peak is observed, confirming that the interior of the Mg seed is composed of metallic Mg. Additionally, it was found that the Mg content within the structure is significantly high at approximately 5 wt%, and that it exists in the form of a nano-seed, resulting in a large active surface area.

[0164]

[0165] Experimental Example 6: Analysis of Structural Differences According to Magnesium Deposition Method

[0166]

[0167] The method of Preparation Example 1 was used, but the magnesium deposition method was changed to a direct current (DC) method, and the difference in magnesium characteristics according to the deposition method was confirmed.

[0168] Figure 15 shows SEM images of the structure according to DC deposition and changes in conditions, respectively. During DC deposition, large Mg particles grew randomly, and it was confirmed that during DC deposition, rather than the nucleation of Mg, there was a tendency for the Mg seed particles to grow larger. Additionally, it was confirmed that at high current densities, the seed size decreased, but the excessive current induced dendritic growth of Mg.

[0169] Figures 16a and 16b show cross-sectional SEM and EDS images of the Mg deposition surface using DC electroplating (a) and PC electroplating (b), respectively. When using DC electroplating, Mg crystals grow mainly on the top surface of the porous copper, whereas when using PC electroplating, Mg nanoseeds penetrate into the porous copper and are gradually deposited.

[0170]

[0171] Experimental Example 7: Analysis of Structural and Compositional Differences According to PCD Conditions

[0172]

[0173] MGP-Cu structures were fabricated using the method of Preparation Example 1, but with different maximum current densities (PCD) in the pulse electroplating process, and differences in structure and composition were confirmed.

[0174] Figure 17 shows optical images, scanning electron microscope (SEM) images, and EDS mapping results of MGP-Cu deposited surfaces on various PCDs.

[0175] Referring to the experimental results, although the same amount of Mg seed was deposited electrically, the PCD ranged from 100 to 700 mA / cm² 2 As the value increased, the Mg element decreased on the Mg deposition surface of MGP-Cu. Accordingly, it was confirmed that Mg penetrates deeply into the porous copper, and it was found that the gradient slope can be controlled by adjusting the PCD. At a PCD of 500 mA / cm² 2 From the result that the Mg content does not change significantly in the above case, 500 mA / cm² under PCD conditions 2 It was found that this is desirable. In addition, referring to the EDS mapping results, it can be confirmed that Mg is very abundant on the Mg deposited surface.

[0176] Meanwhile, Figure 18 shows optical images, scanning electron microscope (SEM) images, and EDS mapping results of the opposite side of the MGP-Cu deposition in various PCDs. Referring to the experimental results, it can be confirmed that the amount of Mg on the opposite side of the Mg deposition surface is very small.

[0177] Referring to the EDS mapping results of the deposition surface and the opposite surface of the MGP-Cu structure above, it can be seen that nano-level Mg seeds are deposited in a gradient shape with a slope during PC deposition.

[0178] In addition, Figure 19 shows the results of the analysis of the average particle size of Mg seeds according to PCD conditions. Referring to the Mg seed particle size measurement results, it was found that as PCD increased, the Mg seed particle size decreased from the 2000 nm level to the 500 nm level. These experimental results indicate that PC is advantageous for both controlling the size of Mg seeds and controlling the distribution of the internal pore surface of the three-dimensional structure during deposition.

[0179]

[0180] Experimental Example 8: Analysis of Concentration Gradient and Seed Size Changes According to Current Interruption Time

[0181]

[0182] MGP-Cu structures were fabricated using the method of Preparation Example 1, but with different current interruption times of 0.1, 0.9, and 9.9 s in the pulse electroplating process.

[0183] FIG. 20 shows the current interruption time (t off This shows the change in the concentration gradient inside MGP-Cu according to the control of ), and Fig. 21 shows the current interruption time (t off This shows the change in particle size of Mg seeds according to the control.

[0184] Referring to the experimental results, as the current interruption time increases, more ion penetration time can be secured in pulsed electroplating, and thus the degree of the Mg seed concentration gradient inside the current collector can be controlled using this. However, in the present invention, when the current interruption time was extended to 9.9s, a result was observed in which the size of the Mg seed increased.

[0185] Therefore, it is important to control the current cutoff time within a certain range to form seeds of an appropriate size while controlling the Mg seed concentration gradient, and it was confirmed that about 0.9s is optimal.

[0186]

[0187] Experimental Example 9: Analysis of Differences in Lithium Electroplating (Li plating) Depending on Magnesium Deposition

[0188]

[0189] Electroplating was performed on the MGP-Cu of the preparation example by connecting it to lithium, and differences in shape were observed as the plating progressed. For comparison, the same experiment was performed on porous copper (P-Cu) without magnesium deposition, and the results were compared.

[0190] Figure 22 shows a current density of 1 mA / cm² 2 Scanning electron microscope (SEM) images of P-Cu and MGP-Cu according to areal capacity during lithium electrodeposition under certain conditions are shown.

[0191] Experimental results showed that in the initial P-Cu, no morphological difference was observed between the top and bottom sections, and a distinctive porous structure was clearly visible. When Li electrodeposition began, it was observed that lithium filled the pores in the top section without any change in the bottom section. Furthermore, as Li electrodeposition increased, the pores in the top section became almost completely blocked, and dendritic growth of lithium was observed, whereas no change was observed in the bottom section. From this, it was determined that when porous copper is used as a current collector in a lithium metal battery, the internal space is not utilized, leading to the occurrence of upper and dendritic growth of lithium.

[0192] On the other hand, in the case of MGP-Cu, the area capacity is 4 mAh / cm² 2 Even under these conditions, there was no change in the pores at the top, and lithium electrodeposition occurred at the bottom, resulting in continuous lithium electrodeposition at the bottom as the area capacity increased. Accordingly, it was confirmed that lithium electrodeposition is induced at the bottom by the Mg seed, allowing for effective storage of lithium starting from the bottom pores.

[0193] Figure 23 shows a current density of 2 mA / cm² 2The optical microscope (OM) images of the cross-sections of P-Cu and MGP-Cu according to areal capacity during lithium electrodeposition under the specified conditions are shown. Referring to these images, in the case of P-Cu, lithium begins to grow from the top, and as the areal capacity increases, dendritic growth of lithium becomes dominant and topward growth is observed. On the other hand, in the case of MGP-Cu, no dendritic growth was observed; instead, a phenomenon was observed where lithium accumulated while filling the internal pores at the bottom.

[0194] Figure 24 shows a current density of 1 mA / cm² 2 , area capacity 1mAh / cm² 2 The Li electrodeposition behavior of P-Cu and MGP-Cu was compared after 10 cycles under the conditions, and it was confirmed that the bottom growth phenomenon of MGP-Cu continued even after several cycles.

[0195]

[0196] Experimental Example 10: Analysis of Electrochemical Characteristics of Half Cells Depending on Magnesium Deposition

[0197]

[0198] A Li half cell was fabricated using MGP-Cu according to Preparation Example 2, and its electrochemical characteristics were compared with those of half cells using B-Cu (bare Cu) and P-Cu.

[0199] Figure 25 shows the results of measuring the nucleation overpotential of B-Cu, P-Cu, and MGP-Cu structures. In the case of MGP-Cu, the lowest nucleation overpotential was observed during Li electrodeposition due to the Mg seed.

[0200] Figure 26 shows Tafel plots for P-Cu and MGP-Cu structures. Upon checking the exchange current density of each cell, it was confirmed that the exchange current density was higher when using MGP-Cu. Accordingly, it was found that charge transfer was accelerated by Mg nanoseeds and the energy barrier of Li electrodeposition / discharge was reduced. From this, it was found that when using MGP-Cu, uniform and high-density lithium growth can be promoted by the gradient-shaped Mg seeds.

[0201] Figure 27 shows the Coulomb efficiency (CE) and detailed time-voltage graphs of MGP-Cu, P-Cu, and B-Cu structures in a Li electrodeposition / discharge test. The Li || MGP-Cu cell exhibited the highest cyclicity compared to the other cells.

[0202] Table 1 below shows the average Coulomb efficiency (CE) of each cell, and the cell with MGP-Cu applied showed the highest CE and circulation.

[0203]

[0204]

[0205]

[0206] Experimental Example 11: Analysis of Electrochemical Characteristics of Symmetric Cells Depending on Magnesium Deposition

[0207]

[0208] A Li symmetric cell was fabricated using MGP-Cu according to the method of Preparation Example 2, and its electrochemical properties were compared with those of symmetric cells fabricated using B-Cu (bare Cu) and P-Cu.

[0209] Figure 28 shows the time-voltage profile for each symmetric cell. It was confirmed that while both B-Cu and P-Cu cells showed significant overvoltage and rapid fluctuations after 80 hours, the MGP-Cu cell maintained a stable voltage curve for over 300 hours and recorded a low overvoltage (25mV).

[0210] FIG. 29 shows 0.1 to 5 mA / cm for each symmetric cell. 2 The time-voltage profile is shown under conditions, where the number at the top of the graph represents the current density. Experimental results showed that at low current densities, there was almost no difference in overvoltage among the three structures, but as the current density increased, the overvoltage in the B-Cu and P-Cu cells rose significantly, whereas the MGP-Cu maintained a low overvoltage.

[0211]

[0212] Experimental Example 12: Analysis of Electrochemical Characteristics of a Full Cell Depending on Magnesium Deposition

[0213]

[0214] A Li pool cell was fabricated using MGP-Cu, and its electrochemical characteristics were compared with those of pool cells fabricated using B-Cu (bare Cu) and P-Cu.

[0215] Figure 30 shows the results of the charge-discharge cycle analysis for each full cell under 0.5C conditions. While all cells exhibited similar initial capacities of ~160 mAh / g at 0.5C, the NCM622 || B-Cu cell showed a sharp decrease in capacity after 60 cycles due to increased interface resistance caused by the lithium dendrites at the top. P-Cu showed slightly better performance than B-Cu, but the results showed a sharp decrease in capacity after 120 cycles. On the other hand, the NCM622 || MGP-Cu cell exhibited nearly 1.5 times higher cycleability than the P-Cu cell and maintained a stable voltage curve for 180 cycles.

[0216]

[0217] Foregoing, specific parts of the content of the present invention have been described in detail. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the present invention. Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a negative electrode current collector comprising the step of manufacturing a negative electrode current collector having magnesium seeds deposited in a gradient form in which the concentration decreases toward the upper direction of the porous copper by depositing magnesium (Mg) on ​​porous copper using pulsed electroplating.

2. In Paragraph 1, A method for manufacturing a negative current collector in which the above-mentioned porous copper is produced through a dealloying process that removes metals other than copper from a copper-containing alloy.

3. In Paragraph 2, The above copper-containing alloy has the chemical formula Cu x M 1-x It is displayed as, In the above formula, M is zinc (Zn), tin (Sn), or nickel (Ni), and A method for manufacturing a negative current collector, wherein x is 0.5 to 0.

8.

4. In Paragraph 2, A method for manufacturing a cathode current collector, wherein the above dealolysis process is performed through a chemical dealolysis process in which a copper-containing alloy is immersed in an acid solution to remove metals other than copper.

5. In Paragraph 4, A method for manufacturing a cathode current collector, wherein the above immersion is performed for 6 to 18 hours.

6. In Paragraph 1, A method for manufacturing a negative current collector in which the porosity of the porous copper is 40 to 70%.

7. In Paragraph 1, In the pulse electroplating step above, the current interruption time (off-time, t off A method for manufacturing a negative current collector in which ) is 0.1 to 5.0 seconds.

8. In Paragraph 1, In the above pulsed electroplating step, the peak current density (PCD) is 200 to 800 mA / cm² 2 Phosphorus, method for manufacturing a negative current collector.

9. In Paragraph 1, In the pulse electroplating step above, the area capacity is 2 to 10 mAh / cm² 2 Phosphorus, method for manufacturing a negative current collector.

10. In Paragraph 1, The above pulse electroplating step, A step of preparing a cell comprising a porous copper cathode, an electrolyte for magnesium deposition, and a magnesium anode; and Step of depositing magnesium seeds on porous copper by applying a pulsed current to the above cell A method for manufacturing a cathode current collector, performed through 11. In Paragraph 1, A method for manufacturing a negative current collector, wherein the particle size of the deposited magnesium seeds is 100 nm to 2 μm.

12. In Paragraph 1, A method for manufacturing a cathode current collector, wherein the content of the deposited magnesium seed is 2 to 10 weight percent based on the total weight of the cathode current collector.

13. A negative current collector comprising porous copper; and a magnesium (Mg) seed deposited on the surface of the porous copper, A cathode current collector in which the magnesium seed is formed in the form of a concentration gradient in which the content decreases in the upward direction of the porous copper.

14. A negative electrode lithium metal battery comprising a negative electrode current collector, a positive electrode, an electrolyte, and a separator according to claim 13.

15. In Paragraph 14, The above electrolyte includes a lithium salt and a solvent, and A non-anode lithium metal battery, wherein the solvent is a mixed solvent comprising two or more solvents selected from the group consisting of carbonate-based solvents, ether-based solvents, and fluorinated substituents thereof.

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