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. 10-2024-0191891, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003] To reduce the cost and increase the energy density of secondary batteries, it is essential to use lithium-ion battery electrodes as the negative electrodes. Specifically, all-solid-state batteries are recently attracting attention as next-generation batteries for high energy density applications, such as electric vehicles (EVs).

[0004] All-solid-state batteries have various advantages, such as excellent stability because they do not use liquid electrolytes, the ability to operate at high voltages, improved energy density of the battery pack due to the reduction of cooling and safety-related auxiliary materials, and the ability to operate over a wide temperature range. In order to practically achieve high energy density in such all-solid-state batteries, thick, low-capacity graphite-based anode materials must be replaced with thin, high-capacity lithium materials, and considering economic feasibility and energy density, electrodes for thin-film lithium secondary batteries with a thickness of 10 to 20 μm are practically required.

[0005] Generally, for electrodes used in lithium secondary batteries, there are difficulties in the technology for manufacturing thin lithium metal through commercialization processes, and dendrite growth caused by non-uniform current density and electrochemical reactions during the charging and discharging of the secondary battery is a problem. This can lead to continuous side reactions with the electrolyte and even internal short circuits where the anode and cathode come into contact. Such dendrite growth can also cause significant problems with low lifespan characteristics and stability.

[0006] Although various methods have been proposed to increase lifespan by suppressing the above-mentioned dendrite growth, it is still difficult to simultaneously achieve high energy density through lithium thinning and sufficient lifespan characteristics. Various methods have been proposed to suppress the above-mentioned dendrite growth, such as using amorphous carbon alone as a protective layer on the electrode for a lithium secondary battery or using composite materials with expensive lithium-friendly metals, but there is a problem in that sufficient lithium stacking speed and charge / discharge lifespan characteristics cannot be obtained.

[0007] According to one embodiment of the present invention, an electrode for a lithium secondary battery provides an electrode for a lithium secondary battery in which lithium is uniformly formed on a current collector to suppress dendrite growth and improve charge / discharge life characteristics.

[0008] According to another embodiment of the present invention, an electrode for a lithium secondary battery provides an electrode for a lithium secondary battery that can improve charge / discharge life characteristics by performing lithium electrodeposition uniformly at high speed and suppressing dendrite growth during lithium electrodeposition.

[0009] A method for manufacturing an electrode for a lithium secondary battery according to another embodiment of the present invention provides a method for manufacturing an electrode for a lithium secondary battery having the aforementioned advantages.

[0010] According to one embodiment of the present invention, an electrode for a lithium secondary battery may include a current collector and a protective layer disposed on the current collector, comprising an oxide-based ceramic and amorphous carbon.

[0011] In one embodiment, the protective layer may include a first protective layer disposed on the current collector and comprising the amorphous carbon, and a second protective layer disposed on the first protective layer and comprising the oxide-based ceramic.

[0012] In one embodiment, the second protective layer may include the oxide-based ceramic and the binder.

[0013] In one embodiment, the binder may be an organic binder.

[0014] In one embodiment, the weight ratio of the oxide-based ceramic and the binder in the second protective layer (oxide-based ceramic (wt%):binder (wt%)) may be 70:30 to 95:5.

[0015] In one embodiment, the oxide-based ceramic may be at least one of garnet-type oxides, nasicon-type oxides (LATP, LAGP), and ricicon-type oxides (Li3PO4).

[0016] In one embodiment, the ratio of the thickness of the first protective layer to the thickness of the second protective layer (thickness of the first protective layer (㎛):thickness of the second protective layer (㎛)) may be 1:2 to 1:6.

[0017] In one embodiment, the thickness of the first protective layer may be 1 to 10 μm.

[0018] In one embodiment, the thickness of the second protective layer may be 10 to 30 μm.

[0019] In one embodiment, a metal layer containing lithium may be included between the current collector and the protective layer.

[0020] A method for manufacturing an electrode for a lithium secondary battery according to another embodiment of the present invention may include the steps of preparing a current collector, forming a first protective layer on the current collector using a slurry containing amorphous carbon, and forming a second protective layer on the first protective layer using a slurry containing an oxide-based ceramic.

[0021] In one embodiment, the step of forming the second protective layer may involve mixing the oxide-based ceramic and the binder to form the slurry, and mixing them in a ratio of 7:3 to 9.5:0.5 (oxide-based ceramic (wt%):binder (wt%)) based on the solid content of the oxide-based ceramic and the binder.

[0022] In one embodiment, in the step of forming the first protective layer and the step of forming the second protective layer, the ratio of the thickness of the first protective layer to the thickness of the second protective layer (thickness of the first protective layer (㎛):thickness of the second protective layer (㎛)) can be formed to be 1:2 to 1:6.

[0023] In one embodiment, the step of forming the first protective layer may form the thickness of the first protective layer to 1 to 10 μm.

[0024] In one embodiment, the step of forming the second protective layer may form the thickness of the second protective layer to be 15 to 25 μm.

[0025] In one embodiment, after the step of forming the second protective layer, the method may include the step of positioning a current collector having a protective layer formed thereon, including the first protective layer and the second protective layer, 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 to form a metal layer comprising metal particles included in the protective layer and lithium precipitated from the lithium source.

[0026] According to one embodiment of the present invention, an electrode for a lithium secondary battery can be provided by including a protective layer comprising an oxide-based ceramic and amorphous carbon, thereby allowing lithium to be uniformly formed on a current collector to suppress dendrite growth and improve charge / discharge life characteristics.

[0027] Specifically, the electrode for a lithium secondary battery includes a first protective layer containing amorphous carbon and a second protective layer containing an oxide-based ceramic in sequence, thereby enabling the electrodeposition of lithium to be performed uniformly at a high speed and suppressing dendrite growth during lithium electrodeposition, and thus providing an electrode for a lithium secondary battery that can improve charge / discharge life characteristics.

[0028] A method for manufacturing an electrode for a lithium secondary battery according to another embodiment of the present invention provides a method for manufacturing an electrode for a lithium secondary battery having the aforementioned advantages.

[0029] FIG. 1 illustrates an electrode for a lithium secondary battery according to one embodiment of the present invention.

[0030] FIG. 2 illustrates an electrode for a lithium secondary battery according to another embodiment of the present invention.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] FIG. 1 illustrates an electrode (100) for a lithium secondary battery according to one embodiment of the present invention.

[0036] Referring to FIG. 1, an electrode (100) for a lithium secondary battery according to one embodiment includes a current collector (10) and a protective layer (20) disposed on at least one surface of the current collector (10). Specifically, the electrode (100) for a lithium secondary battery includes a protective layer (20) comprising an oxide-based ceramic and amorphous carbon on the current collector (10) so that uniform high-speed electrodeposition is possible during the lithium electrodeposition process and lithium dendrite formation can be suppressed during charging and discharging.

[0037] 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.

[0038] The current collector (10) may use 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 nickel and silver.

[0039] In one embodiment, the thickness of the current collector (10) may be 1 μm to 50 μm. Specifically, the thickness may be 5 to 20 μm, and more specifically, 10 to 15 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 it may be damaged by tension during the battery manufacturing process.

[0040] The protective layer (20) is disposed on at least one surface of the current collector (10) and may comprise oxide-based ceramic and amorphous carbon. Specifically, the oxide-based ceramic may comprise garnet-type oxides. The garnet-type oxide may comprise, for example, LLZO (Lithium Lanthanum Zirconium Oxide) or LLZTO (Lithium Lanthanum Zirconium Tantalum Oxide).

[0041] The above amorphous carbon may be, for example, one or more selected from the group consisting of acetylene black, super P black, carbon black, Denka black, activated carbon, graphite, hard carbon, and soft carbon, but is not limited thereto. The above amorphous carbon may be, for example, in the form of a powder.

[0042] In one embodiment, the thickness of the protective layer (20) may be from 0.01 μm to 50 μm. Specifically, the thickness of the protective layer (20) may be in the range of 10 μm to 35 μm. By satisfying the above-mentioned range, an ultra-thin electrode for a lithium secondary battery can be provided.

[0043] If the thickness of the protective layer (20) exceeds the upper limit of the aforementioned range, the resistance of the protective layer becomes excessively large, 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 (20) exceeds the lower limit of the aforementioned range, there is a problem that it cannot perform the function of a protective layer.

[0044] In one embodiment, the protective layer (20) may include a first protective layer (21) and a second protective layer (22). The first protective layer (21) may be disposed on the current collector (10) and may include the amorphous carbon. The second protective layer (22) may be disposed on the first protective layer (21) and may include the oxide-based ceramic.

[0045] In one embodiment, the second protective layer (22) 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).

[0046] Specifically, the binder may be an organic binder, such as polyvinylidene fluoride. By forming a second protective layer (22) with the oxide-based ceramic using the organic binder, a protective layer with increased interfacial stability can be formed.

[0047] In one embodiment, the weight ratio of the oxide-based ceramic and the binder in the second protective layer (22) (oxide-based ceramic (wt%):binder (wt%)) may be 70:30 to 95:5. Specifically, the weight ratio may be 80:20 to 95:5. By satisfying the aforementioned range of weight ratios, a second protective layer (22) with excellent adhesion to the current collector and high strength can be realized.

[0048] 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 the first 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.

[0049] In one embodiment, the thickness of the first protective layer (21) may be 1 μm to 10 μm. Specifically, the thickness of the first protective layer (21) may be in the range of 3 μm to 8 μm. By satisfying the aforementioned range, the possibility of detachment from the current collector (10) is minimized, and the interface can be stabilized by being positioned between the current collector (10) and the second protective layer (22).

[0050] If the thickness of the first protective layer (21) exceeds the upper limit of the aforementioned range, the resistance of the first protective layer is excessively high, which may cause an increase in overvoltage during operation of the secondary battery and cause a decrease in battery energy density due to an increase in weight and volume. If the thickness of the first protective layer (21) exceeds the lower limit of the aforementioned range, there is a problem that the effect caused by including the first protective layer is insufficient.

[0051] In one embodiment, the second protective layer (22) may be placed on the first protective layer (21). Specifically, the second protective layer (22) is placed on the first protective layer (21), so that the electrode (100) for a lithium secondary battery of the present invention is arranged in a structure in which the current collector (10), the first protective layer (21), and the second protective layer (22) are sequentially stacked, thereby enabling high-speed electrodeposition in the lithium electrodeposition process and allowing lithium to be electrodeposited uniformly, thereby suppressing the formation of lithium dendrites.

[0052] In one embodiment, the thickness of the second protective layer (22) may be 10 μm to 30 μm. Specifically, the thickness of the second protective layer (22) may be in the range of 15 μm to 25 μm. By satisfying the aforementioned range for the thickness of the second protective layer (22), the possibility of the protective layer (20) detaching from the current collector (10) is minimized, and peeling or detachment during charging and discharging can be suppressed with high mechanical strength.

[0053] If the thickness of the second protective layer (22) exceeds the upper limit of the aforementioned range, the resistance of the first 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 second protective layer (22) exceeds the lower limit of the aforementioned range, there is a problem that the effect caused by including the second protective layer is insufficient.

[0054] In one embodiment, the ratio of the thickness of the first protective layer to the thickness of the second protective layer (thickness of the first protective layer (㎛):thickness of the second protective layer (㎛)) may be 1:2 to 1:6. Specifically, the ratio may be 1:3 to 1:5. By satisfying the above-mentioned range, high-speed electrodeposition is possible during lithium electrodeposition, uniform electrodeposition can be induced, and the detachment of the protective layer can be minimized.

[0055] In the above ratio, if the thickness ratio of the first protective layer (21) is excessively large, there is a problem that it may act as a resistance layer that hinders uniform electrodeposition. In the above ratio, if the ratio of the first protective layer (21) is excessively small, there is a problem that the interface resistance and cell driving overvoltage increase due to disadvantages in securing interface stability.

[0056] In this way, according to one embodiment of the present invention, the electrode (100) for a lithium secondary battery has a first protective layer (21) comprising amorphous carbon disposed on a current collector (10) and a second protective layer (22) comprising an oxide-based ceramic and an organic binder stacked thereon, so that when lithium is electrodeposited between the current collector (10) and the protective layer (20) according to a lithium electrodeposition process or charging and discharging of the battery, it can induce uniform electrodeposition and suppress the formation of lithium dendrites.

[0057] FIG. 2 illustrates an electrode (100) for a lithium secondary battery according to another embodiment of the present invention.

[0058] Referring to FIG. 2, in one embodiment, the electrode (100) for a lithium secondary battery may further include a metal layer (30) disposed between a current collector (10) and a protective layer (20). The metal layer (30) may be a layer disposed between the current collector (10) and the protective layer (20) that facilitates electrodeposition when lithium is electrodeposited.

[0059] The metal layer (30) may include a lithium-friendly metal. When forming a metal layer (30) containing a lithium-friendly metal, the free energy of nucleation can be lowered during the initial nucleation of lithium particles in the lithium electrodeposition process, so a lithium metal layer having a coarse particle structure can be formed even under high current and high voltage conditions.

[0060] The metal layer (30) is located on the current collector (10) and may include a lithium alloy layer (31) containing a lithium alloy and a lithium metal layer (32) located on the lithium alloy layer (31). The lithium alloy layer (31) may be a layer comprising a lithium alloy in which the lithium-producing metal contained in the metal layer (30) 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.

[0061] When the electrodeposition process is carried out by applying a high current to increase the speed of electrodeposition when forming the metal layer (30), there is a problem that the performance of the lithium secondary battery is degraded. However, when the metal layer (12) is formed with a structure including a lithium alloy layer (31) 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 (20) located on the lithium metal layer (32) already formed during the electrodeposition process.

[0062] Specifically, since the metal layer (30) of one embodiment includes a lithium alloy layer (31) containing a lithium component, when a high current is applied in the electrodeposition process to form a lithium metal layer (32) on the lithium alloy layer (31), 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 (32), and consequently the metal layer (30), can have a uniform surface.

[0063] In this embodiment, the lithium alloy layer (31) 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 (31) 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 (30) plays a role in helping lithium to be deposited more effectively on the underside of the protective layer (20) during the charging process of the battery.

[0064] In one embodiment, the thickness of the metal layer (30) 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 (30) 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 (30), it is preferable that the thickness of the metal layer (30) be 100 μm or less.

[0065] When the thickness of the metal layer (30) 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, and the amount of lithium available to replenish the lithium consumed during the charge / discharge decreases. Therefore, it is preferable that the thickness of the metal layer (30) be 1 μm or more. In addition, the detailed description of the current collector (10) and the protective layer (20) is the same as that described in FIG. 1 to the extent that it does not contradict.

[0066] A method for manufacturing an electrode (100) for a lithium secondary battery according to another embodiment of the present invention includes the steps of preparing a current collector (10), forming a first protective layer (21) on the current collector (10) using a slurry containing an oxide-based ceramic, and forming a second protective layer (22) on the first protective layer (21) using a slurry containing amorphous carbon.

[0067] 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.

[0068] The step of forming a second protective layer (22) on a first protective layer (21) 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.

[0069] The step of forming the second protective layer (22) 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. The aforementioned coating methods are non-limiting examples, and the second protective layer (22) 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.

[0070] In one embodiment, the content of the oxide-based ceramic may be 80 to 95 weight% of solid content based on 100 weight% of the slurry. Specifically, the content of the oxide-based ceramic may include 88 to 92 weight% of solid content. The content of the oxide-based ceramic can be maintained equally not only in the slurry but also in the first protective layer (21) of the final product, the electrode (100) for a lithium secondary battery.

[0071] 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.

[0072] 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 first protective layer (21) can be easily bonded and arranged.

[0073] 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.

[0074] In one embodiment, the weight ratio of the oxide-based ceramic and the binder in the slurry may be mixed in a ratio of 7:3 to 9.5:0.5 (oxide-based ceramic (wt%):binder (wt%)) based on solid content. Specifically, the ratio may be mixed in a ratio of 8.5:1.5 to 9.5:0.5. As the oxide-based ceramic and the binder are included within the aforementioned ratio range, there is an advantage in that the strength of the protective layer is increased. In addition, a substance such as a solvent may be included in the slurry, and this may be a general solvent mixed to form the slurry.

[0075] In one embodiment, the step of forming the first protective layer (21) may form the first protective layer (21) with a thickness of 1 to 10 μm. Specifically, the thickness of the first protective layer (21) may be formed with a thickness of 3 to 8 μm. As the thickness is formed within the aforementioned range, it can be positioned between the current collector (10) and the second protective layer (22) to stabilize the interface.

[0076] If the thickness of the first protective layer (21) exceeds the upper limit of the aforementioned range, the resistance of the first protective layer becomes excessively large, 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.

[0077] In the step of forming a first protective layer (21) on a current collector (10) using a slurry containing amorphous carbon, the amorphous carbon may be one or more selected from the group consisting of, for example, acetylene black, super P black, carbon black, Denka black, activated carbon, graphite, hard carbon and soft carbon, but is not limited thereto.

[0078] The step of forming a first protective layer (21) on a current collector (10) using a slurry containing amorphous carbon may be a step of coating the current collector (10) with the aforementioned slurry containing amorphous carbon and a solvent. The step of forming the first protective layer (21) using the slurry may utilize various coating methods, such as doctor blade coating, slot die coating, roll coating, spray coating, slit coating, gravure coating, or curtain coating, as non-limiting examples. As a non-limiting example of the aforementioned coating method, the first protective layer (21) may be formed by applying a slurry, such as doctor blade coating, to the current collector (10) at a certain thickness and then spreading it flat with a blade.

[0079] In one embodiment, the step of forming the second protective layer (22) may have a thickness of 10 μm to 30 μm for the second protective layer (22). Specifically, the thickness of the second protective layer (22) may be in the range of 15 μm to 25 μm. By satisfying the aforementioned range for the thickness of the second protective layer (22), the possibility of the protective layer (20) detaching from the current collector (10) is minimized, and peeling or detachment during charging and discharging can be suppressed with high mechanical strength.

[0080] If the thickness of the second protective layer (22) exceeds the upper limit of the aforementioned range, the resistance of the first 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 second protective layer (22) exceeds the lower limit of the aforementioned range, there is a problem that the effect caused by including the second protective layer is insufficient.

[0081] In one embodiment, the method for manufacturing an electrode for a lithium secondary battery may further include the step of forming a metal layer (30) before forming a first protective layer (21). Specifically, the step of forming the metal layer (30) 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 metal layer (30) may be performed by coating using an electroless plating method.

[0082] The metal layer (30) may include a lithium-friendly metal. Specifically, the step of forming the metal layer (30) may be a step of coating a lithium-friendly metal on the current collector (10). More specifically, the step of forming the metal layer (30) may be a step of coating or applying particles containing a lithium-friendly metal on the current collector (10) in various ways. By forming the metal layer (30) on the current collector (10), the electrodeposition of lithium may be facilitated in the lithium electrodeposition step described later. The metal layer (30) may be formed by separating it into a lithium alloy layer (31) and a lithium metal layer (32) through the lithium electrodeposition step described later.

[0083] In one embodiment, a method for manufacturing an electrode for a lithium secondary battery comprises, after the step of forming a first protective layer (21) and a second protective layer (22), a current collector (10) having a protective layer (20) formed thereon including the first protective layer (21) and the second protective layer (22) is positioned in a plating solution, and a lithium source is positioned at a predetermined distance from the protective layer (20); and a step of applying a current between the current collector and the lithium source to form a metal layer comprising a lithium alloy in which the lithium-friendly component included in the coating layer and the lithium precipitated from the lithium source are alloyed.

[0084] Specifically, a current collector (10) having a protective layer (20) formed thereon is positioned within a plating solution, and then a lithium source is positioned at a predetermined distance from the protective layer (20). The lithium source may be, for example, lithium metal, a lithium alloy, a foil formed by pressing the lithium metal or lithium alloy onto a current collector, or a plating solution in which a lithium salt is dissolved.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 can be a range.

[0095] 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.

[0096] In one embodiment, the step of forming a lithium metal layer on at least one surface of the current collector by applying the current may 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 2 Electroplating can be performed by increasing the steps in order.

[0097] 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 above maximum current density refers to the limit of the current density at which lithium can be deposited between the protective layer (20) and the current collector (10) during the electrodeposition process.

[0098] 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 (20), for example. By satisfying the aforementioned range of maximum current density, lithium is properly deposited between the current collector (10) and the protective layer (20), thereby providing the advantage of excellent battery life characteristics and bonding strength between the current collector (10) and the protective layer (20).

[0099] 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 (20). 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.

[0100] In one embodiment, the step of forming a lithium metal layer on at least one surface of the current collector by applying the current may include 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 (20).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111]

[0112] <Experimental Example 1>: Difference between single and double layers

[0113] Manufacturing of negative electrodes for lithium secondary batteries

[0114] <Example 1>

[0115] <Whole House Manufacturing>

[0116] A nickel (Ni)-silver (Ag) 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 12 μm.

[0117]

[0118] <Formation of the first protective layer>

[0119] A second protective layer, which is a carbon-based protective layer, was formed on the above current collector by slurry coating using a comma coater to form a protective layer of about 5 μm. Specifically, a slurry was prepared to form the second protective layer, and the slurry was prepared by additionally mixing PVDF as a binder and a solvent with amorphous carbon.

[0120]

[0121] <Formation of a second protective layer>

[0122] A second protective layer, which is an oxide-based ceramic protective layer, was formed on the first protective layer using a slurry coating method with a thickness of approximately 20 μm. Specifically, a slurry was prepared to form the first 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, the solvent used was water and ethylene glycol (EG) in a weight ratio of 80:20. 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] At this time, Super-P was used as the amorphous carbon. Additionally, the binder to be mixed was prepared by adding carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) in amounts of 3 parts by weight and 6 parts by weight, respectively, based on the total amount of amorphous carbon and metal nitride. Furthermore, an NMP non-aqueous solvent was used as the solvent. The total amount of solvent was set to approximately 25% by weight of the total amount of amorphous carbon, metal particles, and binder to maintain a viscosity suitable for coating.

[0124]

[0125] <Lithium Electrodeposition Process>

[0126] 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.

[0127] 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.

[0128] 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.

[0129]

[0130] Manufacturing of lithium metal cells

[0131] 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.

[0132]

[0133] <Comparative Example 1> - Single layer (including only the first protective layer)

[0134] The procedure was performed in the same manner as Example 1, except that the second protective layer formation step was not included.

[0135]

[0136] <Comparative Example 2> - Single layer (including only the second protective layer)

[0137] The procedure was performed in the same manner as Example 1, except that the first protective layer formation step was not included.

[0138]

[0139] <Comparative Example 3> - Single layer (including mixed layer)

[0140] The procedure was performed in the same manner as Example 1, except that instead of proceeding with the first protective layer formation step and the second protective layer formation step separately, amorphous carbon and LLZTO were mixed simultaneously to form the protective layer.

[0141]

[0142] <Evaluation Example 1>: Electrodeposition Performance Evaluation

[0143] FIGS. 3a to 3d are SEM images according to the examples and comparative examples.

[0144] FIGS. 3a to 3d are cross-sectional SEM images of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0145] Figure 3 is a photograph of the electrodeposition performance evaluation according to an embodiment and a comparative example of the present invention.

[0146] Figure 4 shows photographs of the examples and comparative examples after electrodeposition and after three cycles of electrodeposition and desorption.

[0147] Figure 5 is an EDS component analysis photograph of an embodiment of the present invention.

[0148] Referring to FIGS. 3a to 3d, FIG. 4, and FIG. 5, in the case of Comparative Examples 1 to 3, which are single layers, complete peeling or partial cracking occurred after three cycles of deposition and desorption, but in the case of Example 1, which is a double layer, severe peeling did not occur due to the high mechanical properties of LLZTO.

[0149]

[0150] <Evaluation Example 2>: Initial electrodeposition efficiency

[0151] Figure 6 shows the initial electrodeposition efficiency according to the embodiments and comparative examples of the present invention.

[0152] Referring to Fig. 6, it can be seen that in the case of Example 1, the initial electrodeposition efficiency is 77.2% or higher, whereas Comparative Example 1 is 73.3% and Comparative Example 3 is 75.2%, which is lower than Example 1, and in the case of Comparative Example 2, an abnormal profile phenomenon can be observed.

[0153] It is determined that although the LLZTO component increases initial efficiency, in the case of Comparative Example 2, which has only a single LLZTO layer, an abnormality in the profile is found during the desorption process. In addition, it was confirmed that layers containing carbon generally have low efficiency due to the irreversible lithium consumed to form the Li-Ag alloy layer.

[0154]

[0155] <Evaluation Example 3>: Interface Resistance

[0156] FIG. 7 shows the interfacial resistance according to the embodiments and comparative examples of the present invention.

[0157] Referring to Figure 7, it can be seen that the interfacial resistance of LLZTO, which has poor interfacial stability, is reduced by configuring it in a double layer form with carbon, and in the case of layers that do not contain carbon, interfacial stability is generally increased.

[0158]

[0159] 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. The entire house; and A protective layer disposed on the above-mentioned current collector and comprising oxide-based ceramic and amorphous carbon; Electrode for a lithium secondary battery comprising 2. In Paragraph 1, The above protective layer is, A first protective layer disposed on the above-mentioned current collector and comprising the amorphous carbon; and A second protective layer disposed on the first protective layer and comprising the oxide-based ceramic; Electrode for a lithium secondary battery comprising 3. In Paragraph 2, The above second protective layer is an electrode for a lithium secondary battery comprising the oxide-based ceramic and a binder.

4. In Paragraph 3, The above binder is an organic binder, an electrode for a lithium secondary battery.

5. In Paragraph 3, An electrode for a lithium secondary battery in which the weight ratio of the oxide-based ceramic and the binder in the second protective layer (oxide-based ceramic (wt%):binder (wt%)) is 70:30 to 95:

5.

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

7. In Paragraph 2, An electrode for a lithium secondary battery in which the ratio of the thickness of the first protective layer to the thickness of the second protective layer (thickness of the first protective layer (㎛):thickness of the second protective layer (㎛)) is 1:2 to 1:

6.

8. In Paragraph 2, An electrode for a lithium secondary battery having a first protective layer with a thickness of 1 to 10 μm.

9. In Paragraph 2, An electrode for a lithium secondary battery having a second protective layer with a thickness of 10 to 30 μm.

10. In Paragraph 1, An electrode for a lithium secondary battery comprising a metal layer containing lithium between the above current collector and the above protective layer.

11. The stage of preparing the entire house; A step of forming a first protective layer on the above current collector using a slurry containing amorphous carbon; and A step of forming a second protective layer on the first protective layer using a slurry containing an oxide-based ceramic; A method for manufacturing an electrode for a lithium secondary battery comprising 12. In Paragraph 11, The step of forming the second 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 7:3 to 9.5:0.5 (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 the first protective layer and the step of forming the second protective layer, A method for manufacturing an electrode for a lithium secondary battery, wherein the ratio of the thickness of the first protective layer to the thickness of the second protective layer (thickness of the first protective layer (㎛):thickness of the second protective layer (㎛)) is formed to be 1:2 to 1:

6.

14. In Paragraph 11, A method for manufacturing an electrode for a lithium secondary battery, wherein the step of forming the first protective layer comprises forming the thickness of the first protective layer to 1 to 10 μm.

15. In Paragraph 11, After the step of forming the second protective layer, A step of positioning a current collector having a protective layer including the first protective layer and the second protective layer in 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 an electric current between the above-mentioned current collector and the above-mentioned lithium source to form a metal layer comprising metal particles included in the above-mentioned protective layer and lithium precipitated from the above-mentioned lithium source.

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