Electrode for lithium secondary battery and method for manufacturing same

Abstract

The present invention relates to an electrode for a lithium secondary battery and a method for manufacturing same, the electrode for a lithium secondary battery of the present invention comprising: a current collector; a metal layer disposed on the current collector and containing lithium; and a protective layer disposed on the metal layer and containing an oxide-based ceramic, wherein the protective layer comprises the oxide-based ceramic and a binder.

Description

Electrode for lithium secondary battery and method for manufacturing the same

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

[0002] This application claims priority to Korean Patent Application No. 10-2024-0191892, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003] Lithium metal batteries are attracting attention as next-generation energy storage devices due to their high energy density and excellent electrochemical properties. In particular, research on battery technologies using lithium metal as the anode is actively underway to meet the high energy density and long lifespan requirements of electric vehicles and large-capacity energy storage systems. While these lithium metal batteries can offer higher capacity and lower weight compared to conventional graphite-based lithium-ion batteries, they still face many technical challenges regarding stability and interfacial reaction characteristics.

[0004] Recently, research on semi-solid and all-solid-state batteries is actively underway to address the stability issues of liquid electrolytes. In particular, LLZTO (Li7LaZr2O2), an oxide-based electrolyte 12 LLZTO, which is LLZO doped with ) or Ta, is attracting attention as a promising electrolyte for next-generation all-solid-state batteries due to its excellent lithium-ion conductivity, chemical stability, and high mechanical strength. In addition, when such oxide-based electrolytes are used as a protective layer, they have the advantage of effectively suppressing direct reactions between the lithium metal anode and the electrolyte and preventing lithium dendrite growth.

[0005] However, when coating a protective layer based on LLZO or LLZTO on the surface of a lithium anode, there is a problem of adverse reactions with the solvent, which leads to a degradation of interfacial properties. These adverse reactions weaken the chemical stability of the protective layer and hinder the movement of lithium ions, acting as one of the main causes of reduced electrochemical performance and lifespan of the battery.

[0006] Therefore, a technical solution is required that can minimize adverse reactions between the lithium metal anode and the solvent while maintaining the advantages of LLZO or LLZTO-based protective layers.

[0007] The technical problem that the present invention aims to solve is to provide an electrode for a lithium secondary battery that improves the electrochemical performance of the battery by securing stable surface characteristics to prevent adverse reactions with a solvent when coating the lithium layer surface, thereby improving interfacial characteristics.

[0008] Another technical problem that the present invention aims to solve is to provide a method for manufacturing an electrode for a lithium secondary battery having the aforementioned advantages.

[0009] According to one embodiment of the present invention, an electrode for a lithium secondary battery comprises a current collector, a metal layer disposed on the current collector and containing lithium, and a protective layer disposed on the metal layer and containing an oxide-based ceramic, wherein the protective layer may include the oxide-based ceramic and a binder.

[0010] In one embodiment, a reaction layer may be included between the metal layer and the protective layer.

[0011] In one embodiment, the reaction layer may be an alloy layer containing lithium or an SEI layer.

[0012] In one embodiment, the reaction layer may include LiF, Li2CO3, Li2O, and combinations thereof.

[0013] In one embodiment, XPS analysis may include a peak of 682.0 to 688.0 eV.

[0014] In one embodiment, it may comprise Ag: 18 to 25 wt%, F: 1.5 to 5.0 wt%, and S: 2.5 to 5.0 wt% in weight%.

[0015] In one embodiment, the lithium-friendly metal layer containing lithium-friendly metal may be further included on the current collector.

[0016] In one embodiment, the lithium-friendly metal may be arranged in the form of an alloy.

[0017] In one embodiment, the binder may be an organic binder.

[0018] In one embodiment, the oxide-based ceramic may include at least one of garnet-type oxides, nasicon-type oxides (LATP, LAGP), and ricicon-type oxides (Li3PO4).

[0019] A method for manufacturing an electrode for a lithium secondary battery according to another embodiment of the present invention comprises the steps of preparing a current collector, forming a protective layer on the current collector using a slurry containing an oxide-based ceramic, and forming a metal layer containing lithium by electrodepositing lithium between the current collector and the protective layer, wherein a reaction layer may be formed between the metal layer and the protective layer.

[0020] In one embodiment, the step of forming the metal layer may include the step of positioning a current collector having the protective layer formed thereon in a plating solution and then positioning a lithium source at a predetermined distance from the protective layer, and the step of applying an electric current between the current collector and the lithium source so that a metal layer containing lithium is formed on the current collector.

[0021] In one embodiment, the step of forming the protective layer may involve mixing the oxide-based ceramic and the binder to form the slurry, and mixing the oxide-based ceramic and the binder in a weight percent ratio of 70:30 to 95:5 (oxide-based ceramic (wt%):binder (wt%)).

[0022] In one embodiment, in the step of forming the metal layer containing lithium on the current collector, the current density of the current is 0.1 to 100 mA / cm² 2 It can be authorized within the range.

[0023] In one embodiment, the oxide-based ceramic may include at least one of garnet-type oxides, nasicon-type oxides (LATP, LAGP), and ricicon-type oxides (Li3PO4).

[0024] In one embodiment, the step of forming the protective layer can control the thickness of the protective layer to 5 to 15 μm.

[0025] According to one embodiment of the present invention, an electrode for a lithium secondary battery includes an oxide-based protective layer obtained from a pre-coating process in which lithium is electrodeposited after coating a protective layer on a current collector, thereby increasing the stability of the interface and improving the electrodeposition performance of lithium and the electrochemical characteristics of the battery.

[0026] According to another embodiment of the present invention, a method for manufacturing an electrode for a lithium secondary battery can manufacture an electrode for a lithium secondary battery having the aforementioned characteristics by electrodepositing lithium between a current collector and a protective layer using an electrodeposition process rather than a rolling process.

[0027] FIG. 1 illustrates an electrode for a lithium secondary battery according to one embodiment of the present invention.

[0028] FIGS. 2a to 2c are SEM images of embodiments and comparative examples of the present invention.

[0029] FIGS. 3a and 3b are EDS component analysis photographs of an embodiment and a comparative example of the present invention, and FIGS. 3c and 3d are elemental component graphs of an embodiment and a comparative example of the present invention.

[0030] Figures 4a and 4b are XPS surface analysis photographs of an embodiment and a comparative example of the present invention.

[0031] Figure 5 is a graph showing the evaluation of the electrodeposition efficiency of an embodiment of the present invention.

[0032] Figure 6 is a graph showing the interfacial resistance of the embodiments and comparative examples of the present invention.

[0033] Figure 7 is a graph showing the evaluation of the electrodeposition efficiency of the embodiments and comparative examples of the present invention.

[0034]

[0035] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0036] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0037] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0038] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0039] FIG. 1 illustrates an electrode (100) for a lithium secondary battery according to one embodiment of the present invention.

[0040] Referring to FIG. 1, an electrode (100) for a lithium secondary battery according to one embodiment may have a current collector (10), a metal layer (20), and a protective layer (30) arranged sequentially. Specifically, the electrode (100) for a lithium secondary battery forms a metal layer (20) by electrodepositing lithium between a current collector (10) and a protective layer (30) including an oxide-based ceramic, thereby enabling uniform high-speed electrodeposition during the lithium electrodeposition process and increasing the bonding strength between the metal layer (20) and the protective layer (30), thereby improving electrochemical performance when applied to a battery.

[0041] The current collector (10) may be a component for electrical connection within a lithium secondary battery. The current collector (10) may have the form of a foil, but is not limited thereto, and may have the form of, for example, a mesh, foam, rod, wire, or a sheet woven from wire or fiber.

[0042] The current collector (10) may be made of a material that is electrically conductive and has limited reaction with lithium. Specifically, the material of the current collector (10) may be, for example, copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, a conductive polymer, or a composite fiber with a conductive layer coated on a non-conductive polymer, or a combination thereof. More specifically, the material of the current collector (10) may be a composite material of copper and gold.

[0043] In one embodiment, the thickness of the current collector (10) may be 1 μm to 50 μm. If the thickness of the current collector (10) 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 (10) is excessively thin, there is a risk of overheating damage during high-current operation and damage due to tension during the battery manufacturing process.

[0044] The metal layer (20) may be obtained from a lithium source described later. Specifically, the metal layer (20) may be a layer formed by electrodepositing lithium between the current collector (10) and the protective layer (30).

[0045] The metal layer (20) may be a metal layer containing lithium. By containing lithium, the metal layer (20) serves to store the charge of the battery and improve current conductivity. Specifically, in the metal layer (20), lithium ions recombine with electrons to be reduced to neutral lithium, and electrical energy is stored in this process. Specifically, the metal layer (20) can assist in allowing current to flow efficiently within the battery by having very high conductivity of the lithium layer.

[0046] In one embodiment, the metal layer (20) can serve as a buffer between the current collector (10) and the protective layer (30). Specifically, the metal layer (20) can form a mechanically stable structure to serve as a buffer between the current collector and the protective layer. Through this, the metal layer (20) can prevent damage to the current collector (10) and assist in facilitating the function of the protective layer (30).

[0047] In one embodiment, the metal layer (20) may comprise Ag: 18 to 25 wt%, F: 1.5 to 5.0 wt%, and S: 2.5 to 5.0 wt% in weight% based on EDS component analysis. In one embodiment, the metal layer (20) may comprise the remainder Li. The above-described EDS surface component analysis results are measured by the lithium alloy layer formed after lithium is electrodeposited.

[0048] In one embodiment, a lithium-friendly metal layer containing lithium-friendly metal may be further included on the current collector (10). Specifically, the lithium-friendly metal layer may serve to assist in the easy electrodeposition of lithium.

[0049] Specifically, it was confirmed that in the process of electrodepositing a metal layer containing lithium between a current collector (10) and a protective layer (30), a lithium-friendly metal and lithium can be alloyed, and the F component can be identified due to the SEI layer generated during electrodeposition. The alloyed metal may be, for example, Li-Ag.

[0050] The protective layer (30) is placed on the metal layer (20) and may include an oxide-based ceramic. Specifically, the oxide-based ceramic may include garnet-type oxides. The garnet-type oxide may include, for example, LLZO (Lithium Lanthanum Zirconium Oxide) or LLZTO (Lithium Lanthanum Zirconium Tantalum Oxide).

[0051] In one embodiment, the thickness of the protective layer (30) may be from 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. By satisfying the above-mentioned range, an ultra-thin electrode for a lithium secondary battery can be provided.

[0052] If the thickness of the protective layer (30) exceeds the upper limit of the aforementioned range, the resistance of the protective layer becomes excessively high, which can cause an increase in overvoltage during secondary battery operation and cause a decrease in battery energy density due to an increase in weight and volume. If the thickness of the protective layer (30) exceeds the lower limit of the aforementioned range, there is a problem that it cannot perform the function of a protective layer.

[0053] In one embodiment, the protective layer (30) may include a binder. The binder may be a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR) and acrylic rubber, a water-based binder selected from the group consisting of hydroxyethyl cellulose, carboxymethyl cellulose and polyvinylidene fluoride, or an organic-based binder selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0054] Specifically, the binder may be an organic binder, such as polyvinylidene fluoride. By forming a protective layer (30) with the oxide-based ceramic using the binder as an organic binder, there is an advantage in that a protective layer with increased interfacial stability can be formed.

[0055] In one embodiment, the weight ratio (oxide ceramic (wt%):binder (wt%)) of the oxide-based ceramic and the binder in the protective layer (30) may be 70:30 to 95:5. Specifically, the weight ratio may be 80:20 to 95:5. By satisfying the above-mentioned range, a protective layer (30) can be realized that has excellent adhesion to the current collector, increased interfacial stability, and easy electrodeposition of lithium.

[0056] When the oxide-based ceramic is included in an excess amount beyond the aforementioned range, the binder content is excessively low, which causes a problem of reduced inter-particle bonding strength when forming a protective layer. When the oxide-based ceramic is included in a small amount beyond the aforementioned range, the binder content is excessively high, which not only causes a decrease in energy density but also significantly increases the resistance of the protective layer, thereby hindering lithium ion conduction.

[0057] In one embodiment, the thickness of the protective layer (30) may be 5 to 10 μm. Specifically, the thickness of the protective layer (30) may be in the range of 7 to 9 μm. By satisfying the above-mentioned range, the possibility of detachment from the current collector (10) is minimized, resistance during cell operation can be minimized, and the loss of energy density of the cell can be minimized.

[0058] If the thickness of the protective layer (30) exceeds the upper limit of the aforementioned range, the resistance of the protective layer is excessively high, which may cause an increase in overvoltage during secondary battery operation and cause a decrease in battery energy density due to an increase in weight and volume. If the thickness of the protective layer (30) exceeds the lower limit of the aforementioned range, there is a problem that the effect caused by including the protective layer is insufficient.

[0059] In one embodiment, the electrode of the present invention may further include a reaction layer between the metal layer (20) and the protective layer (30). The reaction layer may be a layer formed by undergoing a pre-coating process, which is performed by coating the protective layer (30) on the current collector (10) and then electrodepositing a metal containing lithium onto the current collector (10).

[0060] In one embodiment, the reaction layer may be a lithium-containing alloy layer or an SEI layer. Specifically, the lithium-containing alloy layer or SEI layer may include, as a non-limiting example, a lithium-containing material such as LiF, Li2CO3, or Li2O. By including the reaction layer, the ion conductivity of the battery can be increased and the interfacial resistance can be lowered to improve interfacial characteristics.

[0061] In one embodiment, XPS analysis may include a peak of 682.0 to 688.0 eV. Specifically, the aforementioned peak may refer to a LiF peak. The LiF has high ionic conductivity and may be formed through a lithium electrodeposition process as in the present invention.

[0062] In this way, the present invention pre-coates a lithium layer (20) between a current collector (10) and a protective layer (30) by an electrodeposition process rather than rolling, thereby increasing interfacial stability and forming a lithium alloy and SEI layer in advance during electrodeposition, and improving initial efficiency and electrodeposition performance.

[0063] FIG. 2 illustrates an electrode (100) for a lithium secondary battery according to another embodiment of the present invention.

[0064] Referring to FIG. 2, in one embodiment, the metal layer (20) may include a lithium alloy layer (21) and a lithium metal layer (22). Specifically, when lithium electrodeposition is performed after coating metal particles on a current collector (10), the metal particles and lithium may be alloyed to form a lithium alloy layer (21) in part, and a lithium metal layer (22) may be formed in the remaining area where alloying was not performed. At this time, the bonding layer (20I) of FIG. 1 may be formed at the interface between the lithium metal layer (22) and the protective layer (30).

[0065] In one embodiment, the metal layer (20) may include a lithium-friendly metal. When forming a metal layer (20) including a lithium-friendly metal, the nucleation free energy can be lowered during the initial nucleation of lithium particles in the lithium electrodeposition process, so a metal layer having a coarse particle structure can be formed even under high current and high voltage conditions.

[0066] The metal layer (20) is located on the current collector (10) and may include a lithium alloy layer (21) containing a lithium alloy and a lithium metal layer (22) located on the lithium alloy layer (21). The lithium alloy layer (21) may be a layer comprising a lithium alloy in which the lithium-friendly metal contained in the metal layer (20) and the lithium precipitated from the lithium source are alloyed by applying current between the current collector (10) and the lithium source during the process of manufacturing an electrode for a lithium secondary battery.

[0067] When the electrodeposition process is carried out by applying a high current to increase the speed of electrodeposition when forming the metal layer (20), there is a problem that the performance of the lithium secondary battery is degraded. However, when the metal layer (20) 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 the excessive generation of fine lithium particles or the destruction of the protective layer (30) located on the lithium metal layer (22) already formed during the electrodeposition process.

[0068] Specifically, since the metal layer (20) 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 (22) on the lithium alloy layer (21), the lithium particles initially generated are induced to grow well so that particles with a coarse structure are formed, and at the same time, the lithium metal layer (22), and consequently the metal layer (20), can have a uniform surface.

[0069] In this embodiment, the lithium alloy layer (21) includes a lithium-friendly metal. 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. In this way, when the lithium alloy layer (21) includes a lithium-friendly metal, since it includes a lithium-friendly metal with high electron conductivity, electrons are smoothly supplied from the current collector, and lithium ions are reduced, thereby providing the advantage of easily performing electrodeposition of the lithium metal layer. The metal layer (20) plays a role in helping lithium to be deposited more effectively on the underside of the protective layer (30) during the charging process of the battery.

[0070] In one embodiment, the thickness of the metal layer (20) 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 (20) is excessively thick, when the electrode for a lithium secondary battery of this embodiment is applied to a secondary battery, there is a problem in that the weight and volume of the battery increase, and the energy density decreases. In addition, since the time and cost of the electrodeposition process increase in proportion to the thickness when forming the metal layer (20), it is preferable that the thickness of the metal layer (20) be 100 μm or less.

[0071] When the thickness of the metal layer (20) is excessively thin, there is a problem that the charge / discharge life of the battery is reduced when the electrode for the lithium secondary battery of this embodiment is applied to a secondary battery. Specifically, during the charge / discharge of the battery, lithium in the battery is gradually consumed due to side reactions between the lithium contained in the metal layer and the electrolyte, etc., and the battery capacity decreases. Since the amount of lithium available to replenish the lithium consumed during the charge / discharge decreases, the charge / discharge life of the battery is reduced. Therefore, it is preferable that the thickness of the metal layer (20) be 1 μm or more. In addition, the detailed description of the current collector (10), the bonding layer (20I), and the protective layer (30) is the same as that described in FIG. 1 to the extent that it does not contradict.

[0072] According to another embodiment of the present invention, a method for manufacturing an electrode (100) for a lithium secondary battery may include the steps of preparing a current collector (10), forming a protective layer (30) on the current collector (10) using a slurry containing an oxide-based ceramic, and forming a metal layer (20) containing lithium by electrodepositing lithium between the current collector (10) and the protective layer (30). In this way, after forming a protective layer (30) on the current collector (10), a metal layer (20) containing the aforementioned bonding layer (20I) can be formed by electrodepositing lithium between the current collector (10) and the protective layer (30).

[0073] In the step of preparing the current collector (10), the current collector (10) may be made of a material that has electrical conductivity and has limited reaction with lithium. Specifically, the material of the current collector (10) may be, for example, copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, a conductive polymer, a composite fiber with a conductive layer coated on a non-conductive polymer, or a combination thereof.

[0074] The step of forming a protective layer (30) on a current collector (10) using a slurry containing an oxide-based ceramic may be formed by mixing the oxide-based ceramic and a binder. The oxide-based ceramic may include at least one of garnet-type oxides, nasicon-type oxides (LATP, LAGP), and ricicon-type oxides (Li3PO4). The garnet-type oxide may include, for example, LLZO (Lithium Lanthanum Zirconium Oxide) or LLZTO (Lithium Lanthanum Zirconium Tantalum Oxide). Specifically, the oxide-based ceramic may be LLZTO.

[0075] The step of forming a protective layer (30) using the above slurry is a non-limiting example, and various coating methods such as doctor blade coating, slot die coating, roll coating, spray coating, slit coating, gravure coating, or curtain coating may be utilized. As a non-limiting example of the above coating method, the protective layer (30) can be formed by applying a slurry, such as doctor blade coating, to a certain thickness on a current collector and then spreading it flat with a blade.

[0076] In one embodiment, the content of the oxide-based ceramic may comprise 80 to 95 weight percent of solids based on 100 weight percent of the slurry. More specifically, the content of the oxide-based ceramic may comprise 85 to 95 weight percent of solids. The content of the oxide-based ceramic can be maintained identically not only in the slurry but also in the protective layer (30) of the final product, the electrode (100) for a lithium secondary battery.

[0077] By satisfying the aforementioned range of the oxide-based ceramic content, there is an advantage of increased electrodeposition ability due to the characteristic of high ionic conductivity. If the oxide-based content exceeds the upper limit of the aforementioned range, the excessive content of the oxide-based ceramic causes cracks to form easily due to the brittleness characteristic of the ceramic, and there is a problem of poor interfacial properties. If the oxide-based content exceeds the lower limit of the aforementioned range, there is a problem that the effect exhibited by including the oxide-based ceramic is insufficient.

[0078] In one embodiment, the binder may be a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), and acrylic rubber, a water-based binder selected from the group consisting of hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylidene fluoride, or an organic-based binder selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polyethylene oxide (PEO). Specifically, the binder may be an organic-based binder, specifically polyvinylidene fluoride.

[0079] In one embodiment, the content of the binder may be 5 to 15 weight% based on 100 weight% of the solid content slurry. Specifically, the content of the binder may be 8 to 12 weight% based on 100 weight% of the solid content slurry. As the content of the binder is included within the aforementioned range, oxide-based ceramics within the protective layer (30) can be easily bonded and arranged.

[0080] If the content of the above binder exceeds the upper limit of the aforementioned range, the excessively high content of the binder causes a decrease in energy density and significantly increases the resistance of the protective layer, thereby facilitating lithium ion conduction.

[0081] In one embodiment, the weight ratio of the oxide-based ceramic and the binder in the slurry may be 70:30 to 95:5 based on solid content. Specifically, it may be mixed in a ratio of 80:20 to 95:5 (oxide-based ceramic (wt%):binder (wt%)).

[0082] By satisfying the aforementioned range for the weight ratio, a protective layer with excellent adhesion to the current collector, increased interfacial stability, and easy electrodeposition of lithium can be realized. In addition, a substance such as a solvent in the slurry may be included, and this may be a slurry formed by mixing a general solvent.

[0083] In one embodiment, the step of forming the protective layer (30) may form the protective layer (30) with a thickness of 5 to 15 μm. Specifically, the protective layer (30) may be formed with a thickness of 7 to 13 μm. If the thickness exceeds the upper limit of the aforementioned range, there is a problem in that the weight of the battery increases and the energy density decreases. If the thickness exceeds the lower limit of the aforementioned range, there is a problem in that the physical properties deteriorate during repeated charging and discharging.

[0084] In one embodiment, the method for manufacturing an electrode for a lithium secondary battery may further include the step of forming a lithium-friendly metal layer before forming a protective layer (30). Specifically, the step of forming the lithium-friendly metal layer may be performed using at least one method among electrolytic and electroless plating, sputtering, electron beam, and thermal vapor deposition. For example, the step of forming the lithium-friendly metal layer may be coated by an electroless plating method.

[0085] The above lithium-friendly metal layer may include lithium-friendly metal. Specifically, the step of forming the above lithium-friendly metal layer may be a step of coating lithium-friendly metal on a current collector (10). More specifically, the step of forming the above lithium-friendly metal layer may be a step of coating or applying particles containing lithium-friendly metal on the current collector (10) in various ways. By forming the above lithium-friendly metal layer on the current collector (10), the electrodeposition of lithium may be facilitated in the lithium electrodeposition step described later. The above lithium-friendly metal layer may be formed by separating it into a lithium alloy layer (21) and a lithium metal layer (22) through the lithium electrodeposition step described later.

[0086] In one embodiment, the step of forming the metal layer may include the step of positioning a current collector having the protective layer formed thereon in a plating solution, then positioning a lithium source at a predetermined distance from the protective layer, and applying an electric current between the current collector and the lithium source to form a metal layer containing lithium on the current collector.

[0087] Specifically, a current collector (10) having a protective layer (30) formed thereon is positioned within the plating solution, and then a lithium source is positioned at a predetermined distance from the protective layer (30). The lithium source may be, for example, lithium metal, a lithium alloy, a plating solution in which the lithium metal or a lithium salt is dissolved.

[0088] The above plating solution can be prepared by dissolving a lithium salt in a plurality of solvents. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiCO3, LiNO3, LiFSI, LiTFSI, LiBF4, LiPF6, LiAsF6, LiClO4, LiN(SO2CF3)2, LiBOB, or a combination thereof. The concentration of the lithium salt may be 1.0 to 3.0 M based on the total electrolyte.

[0089] Specifically, in this embodiment, the plating solution is characterized by comprising 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.

[0090] Among the above nitrogen-based compounds, at least one of lithium nitrate, lithium bis fluorosulfonyl imide, and lithium bis trifluoromethane sulfonimide can be used as a lithium salt.

[0091] The above plating solution may be prepared using only the nitrogen-based compound, but may include a general non-aqueous solvent considering the viscosity of the plating solution, etc. The above-mentioned non-aqueous solvent may comprise, for example, one or more selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and 1,3,5-trioxane.

[0092] In one embodiment, the auxiliary solvent may be included in an amount of 5 to 70 weight%, preferably 10 to 60 weight%, based on 100 weight% of the total plating solution, but is not limited thereto. However, when the auxiliary solvent is included within the above range, the viscosity of the plating solution is appropriate, which can shorten the electrodeposition time, but is not limited thereto.

[0093] In one embodiment, the plating solution may further include a fluorine-based compound. When the plating solution (50) further includes the fluorine-based compound, a fluorine-based film layer can be formed on the protective layer to improve the properties of the electrode.

[0094] The above-mentioned fluorine compounds are, for example, lithium difluorophosphate, lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorooxalate borate, lithium difluorooxalatoborate, lithium tetrafluorooxalatoborate, fluoroethylene carbonate, difluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. It may include one or more selected from the group consisting of ether.

[0095] The above fluorine-based compound may be included in an amount of 0.1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on 100 weight% of the total plating solution. When the above fluorine-based compound is included within the above range, the interaction between the nitrogen-based compound and the above fluorine-based compound in the plating solution (50) is smooth, which has the advantage of excellent improvement in the properties of the film layer. In addition, it has the advantage of excellent electrochemical properties by suppressing the excessive generation of LiF, etc., caused by the direct reaction between the above fluorine-based compound and lithium.

[0096] Next, an insulating film is positioned between the current collector (10) and the lithium source, and then the current collector (10), the lithium source, and the insulating film can be stacked and constrained from both directions using a restraining device. The restraining device may use methods commonly used in the industry, such as manual clamping, hydraulic, pneumatic, or uniaxial pressure methods, as a non-limiting example.

[0097] The current density of the current applied in the step of forming a metal layer containing lithium on at least one surface of the current collector by applying the above current is 0.1 mA / cm² 2 Up to 100 mA / cm 2 Range, more specifically 0.2 mA / cm 2 Up to 50 mA / cm 2 Range, 5 mA / cm 2 Up to 30 mA / cm 2 Range or 7 mA / cm 2 Up to 25 mA / cm 2 It may be in the range. Specifically, 10 to 14 mA / cm 2 It can be performed within the range.

[0098] 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.

[0099] In one embodiment, the step of forming a metal layer containing lithium on at least one surface of the current collector by applying the current 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 0.1 to 0.3 mA / cm² 2 , 0.3 to 0.7 mA / cm 2 , and 0.8 to 1.5 mA / cm 2Electroplating can be performed by increasing the steps in order.

[0100] In one embodiment, the step of electrodepositing lithium on at least one surface of the current collector (10) by applying the current is 6 to 12 mA / cm 2 The method may include a step of electrodeposition at a maximum current density in the range of 8 to 12 mA / cm². Specifically, the maximum current density is 8 to 12 mA / cm². 2 It can be performed within a range. The maximum current density above refers to the limit of the current density at which lithium can be deposited between the protective layer (30) and the current collector (10) during the electrodeposition process.

[0101] The step of electrodeposition at the maximum current density described above may be a final step performed after a multi-stage deposition step for lithium deposition between the current collector (10) and the protective layer (30), for example. By satisfying the aforementioned range of maximum current density, lithium is properly deposited between the current collector (10) and the protective layer (30), thereby providing the advantage of excellent battery life characteristics and bonding strength between the current collector (10) and the protective layer (30).

[0102] If the above maximum current density exceeds the upper limit of the aforementioned range, there is a problem in that the target stabilized electrode structure cannot be secured because lithium is deposited on the surface of the protective layer (30). If the above maximum current density exceeds the lower limit of the aforementioned range, there is a problem of reduced productivity because the time for lithium to be electrodeposited increases.

[0103] In one embodiment, the step of forming a metal layer containing lithium on at least one surface of the current collector by applying the current may include the step of electrodepositing the thickness of the deposited lithium in the range of 5 to 15 μm. Specifically, the thickness of the deposited lithium may be electrodeposited in the range of 8 to 12 μm. The thickness of the deposited lithium may refer to the height in the vertical direction of the lithium disposed between the current collector (10) and the protective layer (30).

[0104] If the thickness of the precipitated lithium exceeds the upper limit of the aforementioned thickness, there is a problem in that not only is the energy density of the battery reduced, but the process time and the amount of metal raw material used increase during the formation of the metal layer. If the thickness of the precipitated lithium exceeds the lower limit of the aforementioned thickness, there is a problem in that the initial Coulomb efficiency is reduced due to initial irreversibility and the charge / discharge performance is reduced because there is a shortage of excess lithium.

[0105] According to another embodiment of the present invention, a lithium secondary battery comprises a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode. Herein, the negative electrode may be an electrode for a lithium secondary battery according to the present invention.

[0106] In one embodiment, a lithium secondary battery may include an electrode assembly comprising a positive electrode including a positive active material, a negative electrode which is an electrode for a lithium secondary battery according to the present invention, and a separator disposed between the positive electrode and the negative electrode. Such an electrode assembly may be wound or folded and accommodated in a battery case.

[0107] Subsequently, an electrolyte is injected into the battery case and sealed to complete the secondary battery. At this time, the battery case may have a shape such as a cylindrical, prismatic, pouch, or coin type.

[0108] The above-mentioned anode may include an anode active material layer and an anode current collector. The above-mentioned anode active material layer may include, for example, a Li compound comprising 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-metal element selected from O, F, S, P, and combinations thereof.

[0109] In one embodiment, a conductive material may be further added to the positive active material layer. The conductive material may be, for example, carbon black and ultrafine graphite particles, fine carbon such as acetylene black, nano metal particle paste, etc., but is not limited thereto.

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

[0111] The electrolyte filled in the above lithium secondary battery may be a non-aqueous electrolyte or a solid electrolyte. Specifically, the electrolyte may be a solid electrolyte. The above 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 above solid electrolyte may be, for example, a gel-type polymer electrolyte in which an electrolyte is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N.

[0112] The above-mentioned separator separates the positive and negative electrodes and provides a pathway for the movement of lithium ions; any separator commonly used in lithium secondary batteries may be used. Specifically, the separator may be one that has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. 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 nonwoven or woven fabric. Meanwhile, if a solid electrolyte is used as the electrolyte, the solid electrolyte may also serve as the separator.

[0113] 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, and the present invention is defined only by the scope of the claims set forth below.

[0114]

[0115] <Experimental Example 1>: Rolled / Electroplated Differential

[0116] Manufacturing of negative electrodes for lithium secondary batteries

[0117] <Example 1>

[0118] <Whole House Manufacturing>

[0119] A copper (Cu)-gold (Au) current collector was prepared for use as a negative electrode for a lithium secondary battery according to the present invention. At this time, the thickness of the current collector was approximately 10 μm.

[0120]

[0121] Formation of a protective layer

[0122] A protective layer of approximately 8 μm, which is an oxide-based ceramic protective layer, was formed on the above-mentioned current collector by slurry coating using a comma coater. Specifically, a slurry was prepared to form the protective layer. The slurry was prepared by mixing Lithium Lanthanum Zirconium Titanium Oxide (LLZTO) and PVdF, a binder, in amounts of 90 wt% and 10 wt%, respectively, based on solid content, resulting in a weight ratio of 90:10 relative to solid content. Additionally, a solvent was mixed to prepare the slurry. Furthermore, THF, an organic solvent, was used. The total amount of the solvent was set to approximately 25 wt% of the total amount of LLZTO and the binder to maintain a viscosity suitable for coating.

[0123]

[0124] <Lithium Electrodeposition Process>

[0125] Subsequently, to form a lithium alloy or pure lithium metal between the protective layer and the current collector, lithium was separated from the lithium source using an electrodeposition process and deposited between the protective layer and the current collector. The plating solution used for such electrodeposition was prepared by adding 40% by weight of lithium bis(fluorosulfonyl)imide and 5% by weight of lithium nitrate, which are nitrogen-based compounds, and 5% by weight of fluoroethylene carbonate, which is a fluorine-based compound, to 1,2-dimethoxyethane solvent, based on 100% by weight of the plating solution, and adding 5% by weight of fluoroethylene carbonate, which is a fluorine-based compound, based on 100% by weight of the plating solution.

[0126] A lithium metal plate with a purity of 99.9% or higher and a thickness of 500 μm was pressed onto a copper current collector (Cu Plate) and used as a lithium source. After stacking the lithium source and the current collector in an electrically insulated state within the plating solution, lithium was deposited between the current collector and the composite protective layer by applying current using a power supply, with the lithium source and the current collector serving as the (+) and (-) electrodes, respectively.

[0127] The current density of the electrodeposition process is approximately 12 mA / cm² 2 Electrodeposition was performed for 60 minutes. The electrodeposition time at the maximum current density was calculated as the time required to electrodeposit a final cumulative lithium thickness of 10 μm, and was set variably according to the magnitude of the maximum current density.

[0128]

[0129] Manufacturing of lithium metal cells

[0130] A lithium metal cell was fabricated by applying a lithium metal electrode prepared according to the above-described example. To manufacture the lithium metal cell, as a liquid electrolyte, lithium bis(fluorosulfonyl)imide and lithium nitrate, which are nitrogen-based compounds, were added to a 1,2-dimethoxyethane solvent at 40 wt% and 5 wt%, respectively, based on 100 wt% of the plating solution, and fluoroethylene carbonate, which is a fluorine-based compound, was added at 5 wt% based on 100 wt% of the plating solution.

[0131]

[0132] <Comparative Example 1> - Rolling instead of lithium electrodeposition

[0133] <Whole House Manufacturing>

[0134] A copper (Cu)-gold (Au) current collector was prepared for use as a negative electrode for a lithium secondary battery according to the present invention. At this time, the thickness of the current collector was approximately 10 μm.

[0135]

[0136] Lithium layer formation

[0137] A lithium foil of approximately 20 μm thickness was placed on a current collector and rolled using a roll pressing device to form a lithium layer.

[0138]

[0139] Formation of a protective layer

[0140] A protective layer of approximately 8 μm, which is an oxide-based ceramic protective layer, was formed on the above-mentioned current collector by slurry coating using a comma coater. Specifically, a slurry was prepared to form the protective layer. The slurry was prepared by mixing Lithium Lanthanum Zirconium Titanium Oxide (LLZTO) and PVdF, a binder, in amounts of 90 wt% and 10 wt%, respectively, based on solid content, at a weight ratio of 90:10 relative to solid content. Additionally, a solvent was mixed to prepare the slurry. Furthermore, THF was used as the solvent. The total amount of the solvent was set to approximately 25 wt% of the total amount of LLZTO and the binder to maintain a viscosity suitable for coating.

[0141]

[0142] <Evaluation Example 1>: SEM Analysis

[0143] FIGS. 2a to 2c are SEM images of embodiments and comparative examples of the present invention.

[0144] FIGS. 2a and 2b are SEM images showing the lithium surfaces of Example 1 and Comparative Example 1, and FIG. 2c is an SEM image of a cross-section of the electrode. The above SEM images were confirmed through Scanning Electron Microscopy.

[0145] Referring to FIGS. 2a to 2c, it can be seen that Example 1, in which electrodeposition was performed, forms a lithium electrodeposited layer of a more uniform size than Comparative Example 1, in which rolling was performed. It can be seen that Comparative Example 1 forms a rougher and non-uniform lithium layer compared to Example 1.

[0146]

[0147] <Evaluation Example 2>: EDS Component Analysis

[0148] FIGS. 3a and 3b are EDS component analysis photographs of an embodiment and a comparative example of the present invention, and FIGS. 3c and 3d are elemental component graphs of an embodiment and a comparative example of the present invention.

[0149] More specifically, FIGS. 3a and 3b are photographs of the EDS component analysis of Example 1 and Comparative Example 1 of the present invention, and FIGS. 3c and 3d show graphs of the EDS component analysis of Example 1 and Comparative Example 1 of the present invention.

[0150] Table 1 below shows the EDS component analysis results in Example 1 and Comparative Example 1.

[0151] wt%COFSZrAgLaTa Example 15.1958.823.383.610.6623.593.920.84 Comparative Example 111.7886.91-1.31----

[0152] Referring to Figures 3a to 3d and Table 1 above, in the case of Example 1, it can be confirmed that the Ag component is identified due to the formation of a Li-Ag alloy in the electrodeposited lithium layer, and the F component is derived due to the SEI layer formed during electrodeposition. In the case of the rolling system, it was confirmed that there is a problem in that components other than C and O, which are expected to be impurities, cannot be identified.

[0153]

[0154] <Evaluation Example 3>: XPS Analysis

[0155] Figures 4a and 4b are XPS surface analysis photographs of an embodiment and a comparative example of the present invention.

[0156] Figures 4a and 4b are XPS surface analysis photographs of Example 1 and Comparative Example 1 of the present invention. The XPS analyzes the surface characteristics of a protective layer by irradiating the surface of the protective layer with X-rays to emit photoelectrons from atoms of the protective layer and measuring the energy and intensity of the photoelectrons.

[0157] i) X-ray type: Al k alpha, 1486.68 eV, 900 ㎛ Beam size

[0158] ii) Analyzer: CAE (constant analyzer energy) Mode

[0159] iii) Number of scans: 50

[0160] iv) Pass energy: 20 eV

[0161] v) Dwell Time: 100ms

[0162]

[0163] Based on the EDS component analysis results, XPS analysis was performed to confirm whether the SEI layer was properly formed. In the case of Example 1, a peak corresponding to LiF (approx. 684.5 eV) can be observed.

[0164]

[0165] <Evaluation Example 4>: Evaluation of Electrodeposition Efficiency

[0166] Figure 5 is a graph showing the evaluation of the electrodeposition efficiency of an embodiment of the present invention.

[0167] Referring to Fig. 5, the electrodeposition efficiency during the initial electrodeposition to form a lithium metal anode for Example 1 was evaluated to confirm an irreversible reaction. It was confirmed that the first charge-discharge efficiency was 86.4% and the second charge-discharge efficiency was 90.8%. Through this, it can be indirectly confirmed that an irreversible layer, such as the SEI layer, was formed.

[0168]

[0169] <Evaluation Example 5>: EIS interface resistance

[0170] Figure 6 is a graph showing the interfacial resistance of the embodiments and comparative examples of the present invention.

[0171] Referring to Fig. 6, when the interfacial resistance of Example 1 (electrodeposited Li) and Comparative Example 1 (rolled Li) was measured, it was confirmed that Example 1 was lower than Comparative Example 1. In addition, it was confirmed that in the case of Comparative Example 1, the interfacial properties were degraded due to by-products resulting from unnecessary side reactions that may occur during the protective coating.

[0172]

[0173] <Evaluation Example 6>: Electrodeposition overvoltage

[0174] Figure 7 is a graph showing the evaluation of the electrodeposition efficiency of the embodiments and comparative examples of the present invention.

[0175] Referring to Fig. 7, it can be seen that the nucleation overpotential is low when charging (electrodepositing) the current collector with Example 1 (electrodeposited Li) and Comparative Example 1 (rolled Li). This confirms that the electrodeposited Li, having the same morphology, is more advantageous for repeated charge and discharge cycles because the charging (electrodepositing) is performed on lithium that has been pre-formed by electrodeposition.

[0176]

[0177] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Entire house; A metal layer containing lithium disposed on the above current collector; and A protective layer disposed on the above metal layer and comprising an oxide-based ceramic; Includes, The above protective layer is an electrode for a lithium secondary battery comprising the oxide-based ceramic and a binder.

2. In Paragraph 1, An electrode for a lithium secondary battery comprising a reaction layer between the metal layer and the protective layer.

3. In Paragraph 2, The above reaction layer is an electrode for a lithium secondary battery, which is an alloy layer containing lithium or an SEI layer.

4. In Paragraph 2, The above reaction layer is an electrode for a lithium secondary battery comprising LiF, Li2CO3, Li2O, and combinations thereof.

5. In Paragraph 1, An electrode for a lithium secondary battery containing a peak of 682.0 to 688.0 eV upon XPS analysis.

6. In Paragraph 1, An electrode for a lithium secondary battery comprising, in weight%, Ag: 18 to 25 wt%, F: 1.5 to 5.0 wt%, and S: 2.5 to 5.0 wt%.

7. In Paragraph 1, An electrode for a lithium secondary battery further comprising a lithium-friendly metal layer containing a lithium-friendly metal on the above-mentioned current collector.

8. In Paragraph 1, The above binder is an organic binder, an electrode for a lithium secondary battery.

9. In Paragraph 1, The above oxide-based ceramic is an electrode for a lithium secondary battery comprising at least one of garnet-type oxides, nasicon-type (LATP, LAGP), and ricicon-type (Li3PO4).

10. The stage of preparing the entire house; A step of forming a protective layer on the above current collector using a slurry containing an oxide-based ceramic; and The method includes the step of forming a metal layer containing lithium by electrodepositing lithium between the above current collector and the above protective layer. A method for manufacturing an electrode for a lithium secondary battery in which a reaction layer is formed between the metal layer and the protective layer.

11. In Paragraph 10, The step of forming the metal layer above is, A step of positioning a current collector having the protective layer formed thereon within a plating solution, and then positioning a lithium source at a predetermined distance from the protective layer; and A method for manufacturing an electrode for a lithium secondary battery, comprising the step of applying current between the current collector and the lithium source to form a metal layer containing lithium on the current collector.

12. In Paragraph 10, The step of forming the above protective layer is, The above oxide-based ceramic and binder are mixed to form the above slurry, and A method for manufacturing an electrode for a lithium secondary battery by mixing the oxide-based ceramic and the binder in a ratio of 70:30 to 95:5 (oxide-based ceramic (wt%):binder (wt%)) based on the solid content of the oxide-based ceramic and the binder.

13. In Paragraph 11, In the step of forming a metal layer containing the above lithium on the current collector, The current density of the above current is 0.1 to 100 mA / cm² 2 A method for manufacturing an electrode for a lithium secondary battery that is authorized within a certain range.

14. In Paragraph 10, A method for manufacturing an electrode for a lithium secondary battery, wherein the oxide-based ceramic comprises at least one of garnet-type oxides, nasicon-type oxides (LATP, LAGP), and ricicon-type oxides (Li3PO4).

15. In Paragraph 10, The step of forming the above protective layer is, A method for manufacturing an electrode for a lithium secondary battery, wherein the thickness of the protective layer is controlled to 5 to 15 μm.

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