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

Abstract

The present invention relates to a lithium metal electrode and a method for manufacturing same. The lithium metal electrode of the present invention comprises a current collector and a protective layer disposed on at least one surface of the current collector, wherein the protective layer comprises a powder-form carbon-based material and powder-form metal particles, and the average particle diameter of the metal particles is 250 nm or less.

Description

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

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

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

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

[0004] Typically, lithium metal electrodes face challenges in manufacturing thin layers of lithium metal through commercial processes. Furthermore, uneven current density and dendrite growth caused by electrochemical reactions during the charging and discharging of secondary batteries pose challenges. This can lead to persistent side reactions with the electrolyte and even internal short circuits where the anode and cathode contact each other. This dendrite growth can also cause significant problems, including poor cycle life and stability. Consequently, the practical application of ultra-thin lithium metal anodes remains challenging.

[0005] Various methods have been proposed to suppress dendrite growth and extend battery life. However, achieving both high energy density through ultrathin lithium and sufficient battery life characteristics remains challenging. To address this issue, a method using a protective layer on a lithium metal electrode has been proposed. However, this method fails to achieve sufficient lithium deposition speed and charge / discharge cycle life characteristics.

[0006] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery improves lithium ion conductivity to increase a lithium stacking speed and provides a lithium secondary battery having improved charge / discharge life characteristics.

[0007] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode for a lithium secondary battery provides a method for manufacturing a lithium metal electrode for a lithium secondary battery having the advantages described above.

[0008] According to one embodiment of the present invention, a lithium metal electrode includes a current collector and a protective layer disposed on at least one surface of the current collector, wherein the protective layer includes a carbonaceous material in powder form and metal particles in powder form, and the average particle diameter of the metal particles may be 250 nm or less. In one embodiment, the electrode includes a metal layer disposed between the current collector and the protective layer, and the metal layer may include lithium.

[0009] In one embodiment, the metal particles in the protective layer may be included in an amount of 10 to 30 wt% based on 100 wt% of the total amount of the carbon-based material and the metal particles. In one embodiment, the thickness of the protective layer may be 3 to 7 μm.

[0010] In one embodiment, the carbonaceous material comprises amorphous carbon, and the amorphous carbon may comprise at least one selected from the group consisting of Acetylene Black, Super P Black, Carbon Black, Denka Black, Activated Carbon, Graphite, Hard Carbon, and Soft Carbon. In one embodiment, the metal particles may be lithium-philic metals. In one embodiment, the metal particles may comprise at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

[0011] In one embodiment, the metal particles may have an area of ​​30 to 50% based on 100% of an area of ​​17.5 μm × 22.5 μm in an SEM image of the protective layer. In one embodiment, the average particle diameter of the metal particles may be larger than the average particle diameter of the amorphous carbon. In one embodiment, the difference value between the average particle diameter of the metal particles and the average particle diameter of the amorphous carbon may be 10 to 250 nm.

[0012] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode includes the steps of preparing a current collector, and the steps of forming a protective layer by coating a slurry containing a powdery carbon-based material and powdery metal particles on at least one surface of the current collector, wherein the average particle diameter of the metal particles may be 250 nm or less.

[0013] In one embodiment, after the step of forming the protective layer, the method may include the step of positioning a current collector having the protective layer formed thereon in a plating solution, positioning a lithium source at a predetermined distance from the protective layer, and applying a current between the current collector and the lithium source to form a metal layer including a lithium alloy in which metal particles included in the protective layer and lithium precipitated from the lithium source are alloyed.

[0014] In one embodiment, after the step of forming the protective layer, the method 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 a current between the current collector and the lithium source to form a metal layer including a lithium alloy in which metal particles included in the protective layer and lithium precipitated from the lithium source are alloyed.

[0015] In one embodiment, in the step of forming the protective layer, the weight ratio of the metal particles to the carbon-based particles may be mixed in a range of 10:90 to 30:70. In one embodiment, in the step of forming the protective layer, the slurry may be coated in a range of 3 to 10 μm. In one embodiment, in the step of forming the protective layer, the slurry may further include a binder, and the content of the binder may include 1 to 15 parts by weight based on 100 parts by weight of the total amount of the carbon-based material and the metal particles.

[0016] According to one embodiment of the present invention, a lithium metal electrode for a lithium secondary battery is provided by mixing amorphous carbon and metal particles in a protective layer and controlling the average particle diameter and distribution of the metal particles, thereby improving lithium ion conductivity, increasing the lithium stacking speed, and providing a lithium secondary battery with improved charge / discharge life characteristics.

[0017] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode for a lithium secondary battery is provided, which comprises disposing a protective layer of a mixture of amorphous carbon and metal particles on a current collector, and laminating lithium on the lower surface of the protective layer so as not to introduce a separate lithium-philic metal layer, thereby shortening the process time and having the advantages described above.

[0018] Figure 1 illustrates a lithium metal electrode manufactured according to one embodiment.

[0019] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode of the present invention.

[0020] Figures 3a and 3b show the microstructure of the surface and cross-section when a protective layer is placed on the collector.

[0021] Figure 4 shows a metal layer formed on the lower surface of a protective layer by an electrodeposition process.

[0022] Figures 5a and 5b show the appearance of electrodeposition according to the maximum current density in the electrodeposition process according to the examples and comparative examples.

[0023] FIGS. 6A to 6C are EDS analysis photographs of a protective layer according to a comparative example of the present invention, and FIGS. 6D to 6F are EDS analysis photographs of a protective layer according to an embodiment of the present invention.

[0024] Figure 7 shows the cell life evaluation of an all-solid-state battery using an embodiment and a comparative example of the present invention.

[0025] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0027] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0028] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0029] FIG. 1 illustrates a lithium metal electrode (100) manufactured according to one embodiment.

[0030] Referring to FIG. 1, a lithium metal electrode (100) according to one embodiment includes a current collector (10) and a protective layer (30) disposed on at least one surface of the current collector.

[0031] The current collector (10) may be a member for electrical connection within a lithium secondary battery. The current collector (10) may have a foil form, but is not limited thereto, and may have, for example, a mesh, foam, rod, wire, or sheet made by weaving wire (fiber).

[0032] 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 any one or a combination of, for example, copper, nickel, titanium, stainless steel, iron, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, conductive polymers, and composite fibers coated with a conductive layer on a non-conductive polymer.

[0033] 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 weight of the battery increases, thereby lowering the energy density of the battery. If the thickness of the current collector (10) is excessively thin, there is a risk of overheating damage during high-current operation, and damage may occur due to tension during the battery manufacturing process.

[0034] The protective layer (30) is disposed on at least one surface of the current collector (10) and may include a carbonaceous material and metal particles. The carbonaceous material may include, for example, amorphous carbon. The amorphous carbon may be, for example, at least one selected from the group consisting of acetylene black, super P black, carbon black, denka black, activated carbon, graphite, hard carbon, and soft carbon, but is not limited thereto. The amorphous carbon may be in a powder form.

[0035] The metal particles may be, for example, a lithium-philic metal. The lithium-philic metal refers to a metal that can react with lithium from a lithium source during a lithium electrodeposition process to form a lithium alloy. The lithium-philic metal may be, for example, at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi. Specifically, the metal particles may be in a powder form rather than a liquid form. Since the metal particles are in a powder form rather than a liquid form, there is an advantage in that the size can be easily controlled and handled when applying the electrode.

[0036] In one embodiment, the metal particles may have an average particle diameter (D50) of 250 nm or less. Specifically, the average particle diameter (D50) of the metal particles may be 20 to 200 nm, more specifically, 20 to 100 nm, and even more specifically, 30 to 70 nm. The average particle diameter (D50) of the metal particles refers to a particle diameter corresponding to 50% of the volume accumulation of the particle size distribution of the metal particles.

[0037] When the average particle diameter (D50) of the metal particles satisfies the above-mentioned range, agglomeration of the metal particles is minimized, distribution is formed evenly, and thus, electrodeposition characteristics are excellent, which has the advantage of improving life characteristics. When the average particle diameter (D50) of the metal particles is outside the upper limit of the above-mentioned range, there is a problem that lithium is difficult to electrodeposit between the protective layer and the current collector because the metal particles themselves have too strong a force to attract lithium. When the average particle diameter (D50) of the metal particles is outside the lower limit of the above-mentioned range, there is a problem that it is disadvantageous in price competitiveness.

[0038] In one embodiment, the carbon-based material may have an average particle diameter D50 of 0.01 to 1 μm. Since the average particle diameter of the carbon-based material satisfies the above-mentioned range, the thickness of the protective layer can be freely adjusted and there is an advantage of excellent dispersibility. If the average particle diameter of the carbon-based material is outside the upper limit of the above-mentioned range, there is a problem that it is difficult to make the protective layer thin and it is difficult to control the degree of dispersibility. If the average particle diameter of the carbon-based material is outside the lower limit of the above-mentioned range, there is a problem that the particles are excessively small, which reduces the ease of workability.

[0039] In one embodiment, the average particle diameter of the metal particles can be confirmed to be larger than the average particle diameter of the amorphous carbon. The difference value between the average particle diameter of the metal particles and the average particle diameter of the amorphous carbon can be 10 to 250 nm. The difference value refers to an absolute value, and by satisfying the above-described range, the metal particles within the protective layer can be more uniformly dispersed.

[0040] In one embodiment, the metal particles in the protective layer (30) may be included in an amount of 10 to 30 wt% based on 100 wt% of the total amount of the carbon-based material and the metal particles. Specifically, the metal particles may be included in an amount of 15 to 25 wt%. More specifically, the weight ratio of the carbon-based material to the metal particles may be 90:10 to 70:30, specifically, 85:15 to 75 to 25. Since the metal particles are included in the protective layer (30) in the aforementioned range, there is an advantage in that lithium can be deposited at the interface between the current collector (10) and the protective layer (30).

[0041] If the metal particles are included in the protective layer (30) beyond the upper limit of the aforementioned range, not only will the cost of the metal particles increase, but if the metal particles are distributed too widely within the protective layer, there will be a problem that lithium will not be deposited under the protective layer. If the metal particles are included in the protective layer (30) beyond the lower limit of the aforementioned range, conversely, there will be a problem that lithium will be deposited on the upper surface of the protective layer because the force with which the metal particles attract lithium is too weak.

[0042] In one embodiment, the metal particles may have an area of ​​15 to 50% based on 22.5 μm × 17.5 μm in the SEM image of the protective layer (30), which is 100%. Specifically, the area may be 30 to 50%. As the metal particles are distributed in the above-described area, there is an advantage in that the metal particles can uniformly attract lithium and deposit lithium on the current collector.

[0043] If the above area is outside the upper limit of the above-mentioned range, it means that there are too many metal particles, so there is a problem that occurs when the metal particles are outside the upper limit of the above-mentioned range. If the above area is outside the lower limit of the above-mentioned range, it means that there are too few metal particles or they are clumped together due to poor dispersion, so there is a problem that occurs when the above-mentioned metal particles are outside the lower limit or when the average particle diameter of the metal particles is outside the upper limit.

[0044] In one embodiment, the lithium metal electrode may include a metal layer (20) disposed between a current collector (10) and a protective layer (30). Specifically, the metal layer (20) may be an alloy layer positioned on the current collector (10) and including lithium. Specifically, the metal layer (20) may be a layer including a lithium alloy in which a lithium-friendly metal included in the protective layer (30) and lithium precipitated from the lithium source (40) are alloyed on the current collector (10) by applying a current between the current collector (10) and the lithium source (40 in FIG. 2).

[0045] In this way, the lithium metal electrode of the present invention forms a lithium alloy layer through a reaction between metal particles in the protective layer (30) and a lithium source (40) without a process of coating a separate metal layer under the protective layer (30), thereby shortening the time required for the entire electrode manufacturing process and being economical. In addition, the lithium metal electrode includes a metal layer (20) including a lithium alloy, which is advantageous for lithium deposition and can improve battery life characteristics.

[0046] In one embodiment, the thickness of the metal layer (20) may be in the range of 3 to 25 μm, specifically, 5 to 20 μm. If the thickness of the metal layer (20) is excessively thick, when the lithium metal electrode of the present embodiment is applied to a secondary battery, there is a problem in that the weight and volume of the battery increase, resulting in a decrease in energy density. In addition, since the time and cost of the electrodeposition process increase in proportion to the thickness when forming the metal layer (20), the thickness of the metal layer (20) is preferably 20 μm or less.

[0047] When the thickness of the metal layer (20) is excessively thin, when the lithium metal electrode of the present embodiment is applied to a secondary battery, there is a problem that the charge / discharge life of the battery is reduced. Specifically, during charge / discharge of the battery, lithium in the battery is gradually consumed due to side reactions between lithium contained in the negative electrode active material layer, i.e., the metal layer of the present invention, and the electrolyte, so that the battery capacity is reduced, and the amount of lithium that can replenish the lithium consumed during charge / discharge is reduced, so that the charge / discharge life of the battery is reduced. Therefore, the thickness of the metal layer (20) is preferably 3 ㎛ or more.

[0048] In one embodiment, the thickness of the protective layer (30) may be 5 to 20 μm. Specifically, the thickness may be 5 to 10 μm. The thickness of the protective layer (30) may refer to the average thickness of the area excluding the metal layer (20) containing lithium. By satisfying the above-described range in thickness of the protective layer (30), an ultra-thin lithium metal electrode can be provided.

[0049] If the thickness of the protective layer (30) exceeds the upper limit of the aforementioned range, there is a problem that the protective layer becomes excessively thick and the conductivity decreases. If the thickness of the protective layer (30) exceeds the lower limit of the aforementioned range, there is a problem that it cannot properly perform its role as a protective layer.

[0050] In one embodiment, the protective layer (30) may include a binder. The binder may be an aqueous binder, and the aqueous binder may be, but is not limited to, one or more selected from the group consisting of a rubber-based binder selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), and acrylic rubber, and a group consisting of polymer resins such as hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinylidene fluoride.

[0051] Here, the binder may be added in an amount of 1 to 15 parts by weight, specifically 3 to 10 parts by weight, based on 100 parts by weight of the combined amount of the carbon-based material and the metal particles. When the content of the binder satisfies the above-mentioned range, the particles constituting the protective layer are efficiently bound together to form a protective layer with excellent performance without causing a decrease in battery energy density due to an increase in weight and volume, thereby further improving the life characteristics of the secondary battery.

[0052] If the content of the binder is excessively less than the above-mentioned range, there is a problem that the bonding force between particles is reduced when forming a protective layer, and if the content of the binder is excessively more than the above-mentioned range, there is a problem that not only does it cause a decrease in energy density, but also the resistance of the protective layer is greatly increased, hindering lithium ion conduction.

[0053] In one embodiment, the lithium metal electrode (100) may further include a film layer disposed on at least a portion of the protective layer (30). The film layer may be formed during the manufacturing process of the metal layer (20), by a reaction between the lithium metal of the electrodeposited lithium source (40) and the plating solution, etc. The thickness, composition, and characteristics of the film can be controlled by adjusting the composition of the plating solution used and the conditions of the electrodeposition process.

[0054] In one embodiment, the film layer may include at least a portion of LiF. By including at least a portion of LiF, the film layer can improve the lifespan and prevent dendrite growth during battery operation due to high ionic conductivity.

[0055] The thickness of the film layer may be 2 nm to 2 ㎛. Specifically, the thickness of the film layer may be specifically in the range of 10 nm to 500 nm. If the thickness of the film layer is excessively thick, the lithium ion conductivity decreases and the interfacial resistance increases, which causes a problem in that the charge / discharge characteristics deteriorate when applied to a battery. If the thickness of the film layer is excessively thin, the film layer may be easily lost during the process of applying the lithium metal electrode according to the embodiment to a battery. Therefore, the film layer may have a thin thickness within the range satisfying the above thickness range and may be uniformly and densely formed over the entire protective layer (30).

[0056] Figure 2 is a schematic diagram of a method for manufacturing a lithium metal electrode (100) of the present invention.

[0057] Referring to FIG. 2, a method for manufacturing a lithium metal electrode (100) according to one embodiment includes a step of preparing a current collector (10), and a step of forming a protective layer (30) by coating a slurry containing a carbon-based material and metal particles on at least one surface of the current collector (10) using a coating composition containing a lithium-philic component.

[0058] In the step of preparing the current collector (10), 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, one or a combination of copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, conductive polymers, and composite fibers coated with a conductive layer on a non-conductive polymer.

[0059] A protective layer (30) can be formed on the surface of a current collector (10) using a slurry containing a carbon-based material and metal particles. The protective layer (30) can be applied by mixing the amorphous carbon and a binder in water using at least one of a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush application method. The protective layer (30) can further include a binder. For a detailed description of the carbon-based material and the metal particles, reference can be made to the aforementioned FIG. 1.

[0060] In one embodiment, the step of forming a protective layer may be performed by mixing the metal particles and the carbon particles in a weight ratio of 10:90 to 30:70. Specifically, the weight ratio may be mixed in a weight ratio of 15:85 to 25:75. Advantages and problems according to the weight ratio may be referred to in the aforementioned FIG. 1.

[0061] In one embodiment, the step of forming a protective layer (30) may include coating a slurry in a range of 3 to 10 μm. Specifically, the coating may be in a range of 4 to 7 μm. As the slurry is coated in the aforementioned range, the ionic conductivity of the protective layer can be secured while easily performing its function.

[0062] If the slurry exceeds the upper limit of the aforementioned range, there is a problem in that it becomes difficult to ensure uniformity after drying. If the slurry exceeds the lower limit of the aforementioned range, there is a problem in that it cannot function as a protective layer.

[0063] In one embodiment, a method for manufacturing a lithium metal electrode includes, after a step of forming a protective layer (30), a step of positioning a current collector (10) on which a protective layer (30) is formed in a plating solution (50), and then positioning a lithium source (40) at a predetermined distance from the protective layer (30), and a step of applying a current between the current collector (10) and the lithium source (40) to form a metal layer (20) including a lithium alloy in which a lithium-friendly component included in the protective layer (30) and lithium precipitated from the lithium source (40) are alloyed.

[0064] Specifically, after positioning a current collector (10) having a protective layer (30) formed within a plating solution, a lithium supply source (40) is positioned at a predetermined distance from the protective layer (30). For example, the lithium supply source (40) may be lithium metal, a lithium alloy, a foil obtained by pressing the lithium metal or lithium alloy onto a current collector, a plating solution in which a lithium salt is dissolved, etc.

[0065] The plating solution (50) can be prepared by dissolving a lithium salt in a plurality of solvents. Specifically, the lithium salt can be LiCl, LiBr, LiI, LiCO3, LiNO3, LiFSI, LiTFSI, LiBF4, LiPF6, LiAsF6, LiClO4, LiN(SO2CF3)2, LiBOB, or a combination thereof. The concentration of the lithium salt can be 1.0 to 3.0 M based on the total electrolyte.

[0066] Specifically, in the present embodiment, the plating solution (50) is characterized in that it includes a nitrogen-based compound as at least one of the lithium salt and a plurality of solvents. The nitrogen-based compound may include, for example, one or more selected from the group consisting of lithium nitrate, lithium bis fluorosulfonyl imide, lithium bis trifluoromethane sulfonimide, e-caprolactam, N-methyl-e-caprolactam, triethylamine, and tributylamin.

[0067] Among the above nitrogen compounds, at least one of lithium nitrate, lithium bis fluorosulfonyl imide, and lithium bis trifluoromethane sulfonimide can be used as a lithium salt.

[0068] Among the above nitrogen compounds, at least one of caprolactam (e-caprolactam), methyl caprolactam (N-methyl-e-caprolactam), triethylamine, and tributylamin can be used as a non-aqueous solvent.

[0069] The plating solution (50) may be manufactured using only the nitrogen-based compound, but may include a general non-aqueous solvent as an auxiliary solvent in consideration of the viscosity of the plating solution (50), etc.

[0070] The auxiliary solvent may include, for example, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and 1,3,5-trioxane.

[0071] In one embodiment, the auxiliary solvent may be included in an amount of 5 to 70 wt%, preferably 10 to 60 wt%, based on 100 wt% of the total plating solution (50), but is not limited thereto. However, when the auxiliary solvent is included within the above range, the viscosity of the plating solution (50) may be appropriate, thereby shortening the deposition time, but is not limited thereto.

[0072] In one embodiment, the plating solution (50) may further include a fluorine-based compound. When the plating solution (50) further includes the fluorine-based compound, there is an advantage in that the properties of the film layer on the metal layer or protective layer can be improved.

[0073] The fluorine-based compounds include, for example, lithium difluoro phosphate, lithium hexafluorophosphate, lithium difluoro bisoxalato phosphate, lithium tetrafluoro oxalato phosphate, lithium difluoro oxalate borate, lithium difluoro oxalato borate, lithium tetrafluoro oxalato borate, fluoroethylene carbonate, difluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. It may include at least one selected from the group consisting of 2,2,3,3-Tetrafluoropropyl ether.

[0074] The above fluorine-based compound may be included in an amount of 0.1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on 100 wt% of the total plating solution (50). When the fluorine-based compound is included within the above range, the interaction between the nitrogen-based compound and the fluorine-based compound in the plating solution (50) is favorable, so there is an excellent advantage in that the film layer properties are improved. In addition, there is an advantage in that the electrochemical properties are excellent because excessive generation of LiF, etc. due to the direct reaction between the fluorine-based compound and lithium is suppressed.

[0075] Next, after positioning an insulating film between the current collector (10) and the lithium supply source (40), the current collector (10), the lithium supply source (40), and the insulating film can be laminated and restrained in both directions using a restraining device. The restraining device can be a non-limiting example, and can be a method commonly used in the art, such as a manual clamping method, a uniaxial pressurization method such as hydraulic pressure, or pneumatic pressure.

[0076] In the step of forming a metal layer (20) containing lithium on at least one surface of the current collector (10) by applying the above current, the current density of the current applied is 0.1 mA / cm 2 100 mA / cm 2 range, more specifically 0.2 mA / cm 2 50 mA / cm 2 Range, 5 mA / cm 2 30 mA / cm 2 range or 7 mA / cm 2 25 mA / cm 2 It could be a range.

[0077] 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.

[0078] In one embodiment, the step of applying the current to form a lithium metal layer on at least one surface of the current collector may be performed at least once at different current densities. The step of applying the current may be performed in multiple stages. Specifically, the step of applying the current in multiple stages may be performed by increasing the current density from a low current density to a high current density in predetermined time steps. For example, the step of applying the current may be performed at a current density of 0.1 to 0.3 mA / cm. 2 , 0.3 to 0.7 mA / cm 2 , and 0.8 to 1.5 mA / cm 2 It can be applied step by step and increased sequentially.

[0079] In one embodiment, the step of forming a metal layer (20) on at least one surface of the current collector (10) by applying the current is 6 to 12 mA / cm 2 A step of electrodeposition at a maximum current density of the range may be included. Specifically, the maximum current density is 8 to 12 mA / cm 2 It can be performed in the range. The above maximum current density means the limit of the current density at which lithium deposited in the electrodeposition process can precipitate lithium between the protective layer (30) and the current collector (10).

[0080] The step of electrodeposition at the above maximum current density may be a final step performed after the step of depositing in multiple stages, for example, for lithium deposition between the current collector (10) and the protective layer (30). By satisfying the above-described range, lithium is appropriately deposited between the current collector (10) and the protective layer (30), thereby providing the advantages of excellent battery life characteristics and bonding strength between the current collector (10) and the protective layer (30).

[0081] If the maximum current density exceeds the upper limit of the aforementioned range, lithium is deposited on the surface of the protective layer (30), which causes a problem in that the targeted stabilized electrode structure cannot be secured. If the maximum current density exceeds the lower limit of the aforementioned range, the time for lithium to be deposited increases, which causes a problem in that productivity decreases.

[0082] In one embodiment, in the step of forming a metal layer (20) including lithium on at least one surface of the current collector (10) by applying the current, the step of electrodepositing the deposited lithium to a thickness in the range of 5 to 15 μm may be included. Specifically, the thickness of the deposited lithium may be electrodeposited to a thickness in the range of 8 to 12 μm. The thickness of the deposited lithium may refer to the vertical height of the lithium disposed between the current collector (10) and the protective layer (30).

[0083] If the thickness of the precipitated lithium exceeds the upper limit of the aforementioned thickness, not only will the energy density of the battery decrease, but the process time and the amount of metal raw materials used in forming the metal layer will also increase. If the thickness of the precipitated lithium exceeds the lower limit of the aforementioned thickness, there will be problems such as a decrease in the initial coulombic efficiency due to the initial irreversibility and a decrease in the charge / discharge performance due to a lack of excess lithium.

[0084] In one embodiment, in the step of forming a metal layer (20) containing lithium on at least one surface of the current collector (10) by applying the current, the thickness of the metal layer (20) containing a lithium alloy can be controlled to 5 to 20 μm. For a detailed description of the thickness of the metal layer (20), reference may be made to the contents of the aforementioned FIG. 1.

[0085] According to another embodiment of the present invention, a lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte positioned between the positive electrode and the negative electrode. Here, the negative electrode may be a lithium metal electrode according to the present invention.

[0086] In one embodiment, a lithium secondary battery may include an electrode assembly including a positive electrode including a positive active material, a negative electrode which is a lithium metal electrode of the present invention, and a separator disposed between the positive electrode and the negative electrode. This electrode assembly may be wound or folded and accommodated in a battery case.

[0087] Thereafter, an electrolyte may be injected into the battery case and sealed to complete the secondary battery. At this time, the battery case may have a cylindrical, square, pouch-shaped, coin-shaped, etc. shape.

[0088] The positive electrode may include a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer may include, for example, a Li compound including at least one metal selected from the group consisting of Ni, Co, Mn, Al, Cr, Fe, Mg, Sr, V, La, and Ce, and at least one non-metallic element selected from the group consisting of O, F, S, P, and combinations thereof.

[0089] In one embodiment, a conductive material may be further added to the positive electrode active material layer. The conductive material may be, but is not limited to, carbon black, ultrafine graphite particles, fine carbon such as acetylene black, nano metal particle paste, etc.

[0090] The above-described positive electrode current collector serves to support the positive electrode active material layer. Examples of positive electrode current collectors that can be used include, but are not limited to, aluminum foil, nickel foil, or a combination thereof.

[0091] The electrolyte to be filled in the lithium secondary battery may be a non-aqueous electrolyte or a solid electrolyte. Specifically, the electrolyte may be a solid electrolyte. The non-aqueous electrolyte may include, for example, a lithium salt such as lithium hexafluorophosphate or lithium perchlorate, and a solvent such as ethylene carbonate, propylene carbonate, or butylene carbonate. In addition, the solid electrolyte may be, for example, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte, or an inorganic solid electrolyte such as LiI or Li3N.

[0092] The separator may be any membrane commonly used in lithium secondary batteries, as it separates the positive and negative electrodes and provides a passage for lithium ions to move. Specifically, the separator may be one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. The separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric. Meanwhile, when a solid electrolyte is used as the electrolyte, the solid electrolyte may also function as the separator.

[0093] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereby, and the present invention is defined only by the scope of the claims set forth below.

[0094]

[0095] <Experimental Example>

[0096] Manufacturing of cathodes for lithium secondary batteries

[0097] <Example 1>

[0098] <Manufacturing the entire house>

[0099] A nickel (Ni) current collector was prepared for use in the negative electrode of the lithium secondary battery of the present invention.

[0100]

[0101] <Protective layer formation>

[0102] A protective layer of approximately 5 μm was formed on the upper surface of both sides of the nickel current collector by slurry coating using a comma coater. Specifically, to prepare the slurry used to form the protective layer, amorphous carbon and metal particles were mixed. Additionally, a binder and a solvent were mixed. At this time, acetylene black was used as the amorphous carbon, and silver (Ag) was used as the metal particles. The weight ratio of amorphous carbon to metal particles was 80:20. At this time, the average particle diameter of the silver (Ag) particles, which are metal particles, was 65 nm.

[0103] Additionally, the mixed binder 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. In addition, the solvent was used so that water and ethylene glycol (EG) were in a weight ratio of 80:20. The total amount of the solvent was approximately 25 wt% of the total amount of amorphous carbon, metal particles, and binder to maintain an appropriate viscosity for coating.

[0104] Figures 3a and 3b show the microstructure of the surface and cross-section when a protective layer is placed on the collector.

[0105] Referring to FIGS. 3a and 3b, the surface and cross-sectional structure can be confirmed after the protective layer is placed.

[0106]

[0107] Lithium electrodeposition process

[0108] Afterwards, lithium was removed from the lithium source using an electrodeposition process to form a lithium alloy or pure lithium metal between the protective layer and the current collector, and lithium was deposited between the protective layer and the current collector. The plating solution used for this electrodeposition was prepared by adding 40 wt% and 5 wt% of lithium bis(fluorosulfonyl)imide and lithium nitrate, which are nitrogen compounds, based on 100 wt% of the plating solution, to a 1,2-dimethoxyethane solvent, and adding 5 wt% of fluoroethylene carbonate, which is a fluorine compound, based on 100 wt% of the plating solution.

[0109] 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) as a lithium source. After the lithium source and the current collector were electrically insulated and laminated in a plating solution, a power supply was used to apply current to the lithium source and the current collector as (+) and (-) electrodes, respectively, to deposit lithium between the current collector and the composite protective layer.

[0110] The current density of the electrodeposition process was 0.2 mA / cm 2 , 0.5 mA / cm 2 , 1 mA / cm 2 Increasing step by step in order, after 5 minutes of deposition, 10 mA / cm 2 The maximum current density was set. The deposition time at the maximum current density was calculated as the time required for a final accumulated lithium thickness of 10 ㎛ to be deposited, and was set variably depending on the size of the maximum current density.

[0111] Figure 4 shows a metal layer formed on the lower surface of a protective layer by an electrodeposition process.

[0112] Referring to Fig. 4, it was confirmed that a metal layer, which is an alloy layer containing lithium, was formed between the current collector and the protective layer by lithium provided from a lithium source.

[0113] Figures 5a and 5b show the appearance of electrodeposition according to the maximum current density in the electrodeposition process according to the examples and comparative examples.

[0114] Fig. 5a shows the appearance of the electrodeposition when electrodeposition is performed below the maximum current density, and Fig. 5b shows the appearance of the electrodeposition when electrodeposition is performed above the maximum current density. Referring to Figs. 5a and 5b, when electrodeposition is performed below the maximum possible current density, the precipitated lithium is deposited under the black protective layer, so that a black protective layer is visible in appearance. When electrodeposition is performed above the maximum possible current density, lithium is deposited on the upper surface of the protective layer, so that gray-colored lithium is deposited on the upper surface of the protective layer. Through this, the maximum current density is defined as the maximum possible current density for electrodeposition, which is the maximum current density at which lithium is deposited between the current collector and the protective layer in the electrodeposition process.

[0115]

[0116] All-solid-state battery manufacturing

[0117] Using the cathode manufactured according to the above-described example, an all-solid-state battery was fabricated, and its charge-discharge life was evaluated. To evaluate the all-solid-state battery cell, a pressurized, dedicated evaluation cell from Terraleader, capable of maintaining an inert atmosphere, was used. For the fabrication of the all-solid-state battery cell, a sulfide-based argyrodite (Li6P5Cl) solid electrolyte was used, and the electrolyte was in pellet form with a thickness of approximately 0.7 mm. To ensure a dense electrolyte, the cell was pressurized at a pressure of 370 MPa.

[0118] Lithium having a thickness of 0.5 mm was attached as a reference electrode on one side of the electrolyte, and the negative electrode manufactured according to the examples and comparative examples was attached on the opposite side. The reference electrode and the evaluation electrode were attached to the solid electrolyte at a pressure of 50 MPa, and during the charge and discharge evaluation, the pressure was applied to 16 MPa in a dedicated evaluation cell.

[0119]

[0120] <Example 2>

[0121] The same procedure as Example 1 was followed, except that the average particle size of the Ag particles used to prepare the slurry used to form the protective layer was 50 nm.

[0122]

[0123] <Example 3>

[0124] The same procedure as Example 1 was followed, except that the average particle size of the Ag particles used to prepare the slurry used to form the protective layer was 200 nm.

[0125]

[0126] <Comparative Example 1>

[0127] The same procedure as Example 1 was followed, except that the average particle size of the Ag particles used to prepare the slurry used to form the protective layer was 300 nm.

[0128]

[0129] <Comparative Example 2>

[0130] The same procedure as Example 1 was followed, except that the average particle size of the Ag particles used to prepare the slurry used to form the protective layer was 500 nm.

[0131]

[0132] <Comparative Example 3>

[0133] The same procedure as Example 1 was followed, except that the average particle size of the Ag particles used to prepare the slurry used to form the protective layer was 700 nm.

[0134]

[0135] <Comparative Example 4-5>

[0136] The same procedure as Example 1 was followed, except that the average particle diameters of the amorphous carbon particles used to prepare the slurry used to form the protective layer were 20 nm and 300 nm, respectively.

[0137]

[0138] <Evaluation Example>: Evaluation based on average particle size of metal particles

[0139] Table 1 below shows the distribution of metal particles in the protective layer, the maximum electrodeposition current, and the number of charge / discharge cycles when metal particles with different average particle diameters are included in forming the protective layer. The distribution of metal particles in the protective layer, the maximum electrodeposition current, and the number of charge / discharge cycles were measured using the following methods.

[0140] Distribution of metal particles within the protective layer: The protective coating layer was composed of a mixture of amorphous carbon and metal elements, and EDS analysis was performed on the protective layer sample before electrodeposition. During the EDS analysis, the distribution of each element was evaluated in mapping mode, and in particular, the parts that caused differences in brightness in the SEM analysis image were selected as points and further analysis was performed. If the distribution of metal particles within the protective layer was good through the above-mentioned method, it was marked with ○, if it was average, it was marked with △, and if it was poor, it was marked with ×.

[0141] Maximum current density (mA / cm 2 ): The maximum current density refers to the limit of the current density at which lithium deposited according to the above process can precipitate lithium between the ion concentration protective layer and the current collector, and the maximum current density was measured.

[0142] Charge / discharge performance number (cycles): The reference electrode and evaluation electrode were attached to the solid electrolyte at a pressure of 50 MPa, and the dedicated evaluation cell was pressurized at 16 MPa during the charge / discharge evaluation. The charge / discharge evaluation was performed at 2 mA / cm 2 Charge for 0.5 hours at constant current of 2 mA / cm 2 A 0.5-hour discharge at constant current was defined as one cycle. The charge-discharge life was defined as the end of the life when a short circuit occurred between the reference electrode and the evaluation electrode during the charge-discharge process or when the voltage between the two electrodes exceeded 2 V.

[0143] Distinction Amorphous carbon average particle size (nm) Average particle size of metal particles (nm) │Average particle size of metal particles - Average particle size of amorphous carbon │Distribution area of ​​metal particles (%) Metal particle distribution diagram in protective layer Maximum electrodeposition current (mA / cm) 2 ) Charge and discharge performance number of times (times) Example 130653546○8710 Example 230502049○8892 Example 33020017030△6594 Comparative example 13030027027×1122 Comparative example 23050047019×187 Comparative example 3307006709×--Comparative example 420654543△6575 Comparative example 52006513537×2279

[0144] Looking at Table 1 above, it was confirmed that Examples 1 to 3 had a larger distribution area of ​​metal particles and a superior metal particle distribution within the protective layer compared to Comparative Examples 1 to 3. In addition, it was confirmed that the Comparative Examples were inferior to the Examples in terms of charge-discharge performance characteristics. Specifically, it was confirmed that Comparative Examples 1 to 3, in which the average particle diameter of the metal particles was excessively large, had inferior metal particle distribution areas and metal particle distributions within the protective layers compared to the Examples. In addition, it was confirmed that Comparative Example 4, in which the average particle diameter of the amorphous carbon was excessively small, and Comparative Example 5, in which the average particle diameter was excessively large, also had inferior metal particle distribution areas and metal particle distributions within the protective layers compared to the Examples. FIGS. 6a to 6c are EDS analysis photographs of protective layers according to Comparative Examples of the present invention, and FIGS. 6d to 6f are EDS analysis photographs of protective layers according to Examples of the present invention.

[0145] Figures 6a to 6c are EDS analysis photographs of the protective layer according to Comparative Example 1. Specifically, Comparative Example 1 used Ag having an average particle size of about 300 nm, and when EDS analysis was performed on the sample with the protective layer coated on the current collector, C was detected in the amorphous carbon, which is the main component, and Ag contained in the protective layer. When the EDS results were examined by dividing the parts where the difference in brightness was clearly evident into S1, S2, and S3, the C signal was weak and the Ag signal was strong in the parts S1 and S2, which appeared bright and close to white in the SEM analysis image.

[0146] This means that Ag particles are clumped together in the part that appears white in the SEM. On the other hand, in the case of S3, which appears relatively black, the C signal appears strong and the Ag signal is detected very weakly. This means that, unlike S1 and S2, there are almost no Ag particles in the part that appears black in the SEM. Based on the analysis results, it can be confirmed that although most of the particles are black because they are mostly composed of amorphous carbon, a considerable number of white particles are clumped together and distributed.

[0147] Figures 6d to 6f are EDS analysis photographs of the protective layer according to Example 1. Specifically, Example 1 used Ag having an average particle size of about 65 nm. As a result of EDS analysis of the sample with the protective layer coated on the current collector, C was detected in the amorphous carbon, which is the main component, and Ag was detected in the Ag particles included in the protective layer. When a relatively white part in the SEM analysis image was selected as a point and the EDS analysis result of the same part was viewed, the C signal was weak and the Ag signal was strong, indicating that the white part has a high Ag content.

[0148] However, unlike Comparative Example 1, in Example 1, it can be confirmed that Ag particles rarely aggregate throughout the sample, and small Ag particles are evenly distributed.

[0149] Looking at Figures 6a to 6f and Table 1, it was confirmed that the examples in which the average particle diameter of the metal particles in the protective layer was 400 nm or less had an excellent distribution of the metal particles in the protective layer and an excellent number of charge / discharge cycles compared to the comparative examples in which the average particle diameter exceeded 400 nm. In the case of Comparative Example 3, in order to measure the maximum electrodeposition current, 0.5 mA / cm was measured under the existing experimental conditions. 2The experiment was conducted by lowering the current density to , but it was confirmed that lithium was deposited on the upper surface of the protective layer even at that current. Since lithium was deposited on the upper surface of the protective layer even at a sufficiently low current, it was difficult to quantify the maximum deposition current, so it was not indicated. In addition, in the case of Comparative Example 3, in terms of the number of charge / discharge performances, the protective layer is effective only when the cell is manufactured in a state where lithium is laminated on the lower surface of the protective layer. However, if lithium is deposited on the upper surface of the protective layer, it is difficult to conduct the experiment under the same conditions even if the cell is manufactured. When the cell was manufactured without a protective layer, about 80% of the cells did not perform normal cycles and an internal short circuit occurred, so it was not indicated.

[0150] In addition, among Examples 1 to 3, Example 2, having an average particle size of 100 nm or less, was found to have a superior metal particle distribution and a superior charge / discharge cycle performance compared to Example 3, having an average particle size of about 200 nm, and Example 2 was found to have a superior metal particle distribution and a superior charge / discharge cycle performance compared to Example 3.

[0151] Figure 7 shows the results of evaluating the charge / discharge life of a lithium metal electrode according to an embodiment and a comparative example of the present invention.

[0152] Referring to Figure 7, the charge / discharge life of Example 1 was 710 cycles, and the charge / discharge life of Comparative Example 1 was 122 cycles, confirming that the charge / discharge performance of Example 1, which has a smaller average particle size of metal particles in the protective layer, was superior to that of Comparative Example 1.

[0153]

[0154] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. The entire house; and Comprising a protective layer disposed on at least one surface of the above-mentioned housing, The above protective layer comprises a carbon-based material in powder form and metal particles in powder form, A lithium metal electrode wherein the average particle diameter of the above metal particles is 250 nm or less.

2. In paragraph 1, Including a metal layer disposed between the above-mentioned collector and the above-mentioned protective layer, The above metal layer is a lithium metal electrode containing lithium.

3. In paragraph 1, A lithium metal electrode comprising 10 to 30 wt% of the metal particles in the protective layer based on 100 wt% of the total amount of the carbon-based material and the metal particles.

4. In paragraph 1, A lithium metal electrode having a thickness of the protective layer of 3 to 7 ㎛.

5. In paragraph 1, The above carbon-based material contains amorphous carbon, A lithium metal electrode comprising the amorphous carbon at least one selected from the group consisting of acetylene black, super P black, carbon black, denka black, activated carbon, graphite, hard carbon, and soft carbon.

6. In paragraph 1, The above metal particles are lithium metal electrodes, which are lithium-philic metals.

7. In paragraph 1, A lithium metal electrode wherein the metal particles include at least one selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

8. In paragraph 1, The above metal particles are lithium metal electrodes having an area of ​​30 to 50% based on a 100% area of ​​17.5 ㎛ × 22.5 ㎛ in the SEM image of the above protective layer.

9. In paragraph 1, A lithium metal electrode wherein the average particle diameter of the metal particles is larger than the average particle diameter of the amorphous carbon.

10. In paragraph 1, A lithium metal electrode wherein the difference between the average particle diameter of the metal particles and the average particle diameter of the amorphous carbon is 10 to 250 nm.

11. Steps to prepare the entire house; and Comprising a step of forming a protective layer by coating a slurry containing a powdery carbon-based material and powdery metal particles on at least one surface of the above-mentioned collector, A method for manufacturing a lithium metal electrode, wherein the average particle diameter of the metal particles is 250 nm or less.

12. In paragraph 11, After the step of forming the above protective layer, A step of positioning a current collector having the protective layer formed thereon within a plating solution and then positioning a lithium supply source at a predetermined distance from the protective layer; and A method for manufacturing a lithium metal electrode, comprising the step of applying a current between the current collector and the lithium source to form a metal layer including a lithium alloy in which metal particles included in the protective layer and lithium precipitated from the lithium source are alloyed.

13. In paragraph 11, A method for manufacturing a lithium metal electrode, wherein the metal particles and the carbon particles are mixed in a weight ratio of 10:90 to 30:70 in the step of forming the protective layer.

14. In paragraph 11, A method for manufacturing a lithium metal electrode, wherein the step of forming the protective layer comprises coating the slurry in a range of 3 to 10 μm.

15. In paragraph 14, A method for manufacturing a lithium metal electrode, wherein the step of forming the protective layer further includes a binder in the slurry, and the content of the binder includes 1 to 15 parts by weight based on 100 parts by weight of the total amount of the carbon-based material and the metal particles.

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