A lithium metal electrode for a lithium secondary battery and a manufacturing method thereof

Abstract

The present invention relates to a lithium metal electrode and a method of manufacturing the same. The lithium metal electrode of the present invention includes a current collector and a protective layer disposed on at least one surface of the current collector, the protective layer including a carbon-based substance in a powder form and metal particles in a powder form, the metal particles having an average particle diameter of 250 nm or less.

Description

Technical Field

[0001] This invention relates to a lithium secondary battery, and more specifically, to a lithium metal electrode for a lithium secondary battery and a method for manufacturing the same. Background Technology

[0002] To achieve both low cost and high energy density in secondary batteries, lithium metal electrodes must be used as the negative electrode. Specifically, in recent years, all-solid-state batteries have attracted much attention as a new generation of batteries that meet the high energy density requirements of electric vehicles (EVs).

[0003] Because all-solid-state batteries do not use liquid electrolytes, they offer excellent safety, can operate at high voltages, and allow for increased energy density by reducing the need for cooling and safety-related auxiliary materials. They also operate over a wide temperature range, providing advantages in several aspects. To practically achieve high energy density in all-solid-state batteries as described above, it is necessary to replace the thick, low-capacity graphite-based anode material with thin, high-capacity lithium. Considering both economics and energy density, a thin-film lithium metal electrode with a thickness of 10 to 20 μm is practically required.

[0004] Typically, there are difficulties in manufacturing thin lithium metal electrodes using commercial processes. Furthermore, dendrite growth due to uneven current density and electrochemical reactions during the charging and discharging of secondary batteries is also a problem. This can lead to continuous side reactions with the electrolyte and may even cause internal short circuits due to contact between the negative and positive electrodes. Such dendrite growth can also significantly impact low lifespan and safety. Therefore, the practical application of ultrathin lithium metal anodes is challenging.

[0005] Various methods have been proposed to suppress dendrite growth and improve lifespan, but the challenge remains in simultaneously achieving high energy density and sufficient lifespan characteristics through lithium ultrathinning. To address this issue, a method using a protective layer on the lithium metal electrode has been proposed; however, this still fails to achieve sufficient lithium stacking speed and charge / discharge lifespan characteristics. Summary of the Invention

[0006] (a) Technical problems to be solved According to an embodiment of the present invention, a lithium metal electrode for a lithium secondary battery provides a lithium secondary battery that improves lithium stacking speed and charge-discharge cycle life characteristics by increasing lithium-ion conductivity.

[0007] According to another embodiment of the present invention, a method for manufacturing a lithium metal electrode for a lithium secondary battery is provided, which has the above-mentioned advantages.

[0008] (II) Technical Solution According to one embodiment of the present invention, a lithium metal electrode may include: a current collector and a protective layer disposed on at least one surface of the current collector, the protective layer comprising a carbon-based material in powder form and metal particles in powder form, the metal particles having an average particle size of less than 250 nm. In one embodiment, a metal layer disposed between the current collector and the protective layer may be included, the metal layer comprising lithium.

[0009] In one embodiment, the protective layer may contain 10 to 30% by weight of the metal particles relative to 100% by weight of the total amount of the carbonaceous 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 carbon-based material comprises amorphous carbon, which may include one or more selected from the group consisting of acetylene black, super P black, carbon black, superconducting denka black, activated carbon, graphite, hard carbon, and soft carbon. In one embodiment, the metal particles may be a lithium-philic metal. In one embodiment, the metal particles may include one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

[0011] In one embodiment, the metal particles may occupy 30 to 50% of the area relative to 100% of the 17.5 μm × 22.5 μm area in the SEM image of the protective layer. In one embodiment, the average particle size of the metal particles may be larger than the average particle size of the amorphous carbon. In one embodiment, the difference between the average particle size of the metal particles and the average particle size 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 may include: a step of preparing a current collector, and a step of coating at least one surface of the current collector with a slurry comprising a carbon-based material in powder form and metal particles in powder form to form a protective layer, wherein the average particle size of the metal particles may be less than 250 nm.

[0013] In one embodiment, after the step of forming the protective layer, the process may include: placing a current collector for forming the protective layer after a plating bath, and configuring a lithium supply source and the protective layer at a predetermined interval; and forming a metal layer comprising a lithium alloy by applying an electric current between the current collector and the lithium supply source, the lithium alloy being formed by alloying metal particles contained in the protective layer with lithium deposited from the lithium supply source.

[0014] In one embodiment, after the step of forming the protective layer, the process may include: placing a current collector for forming the protective layer after a plating bath, and configuring a lithium supply source and the protective layer at a predetermined interval; and forming a metal layer comprising a lithium alloy by applying an electric current between the current collector and the lithium supply source, the lithium alloy being formed by alloying metal particles contained in the protective layer with lithium deposited from the lithium supply source.

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

[0016] (III) Beneficial Effects According to an embodiment of the present invention, a lithium metal electrode for a lithium secondary battery is provided, which improves the lithium-ion conductivity by mixing amorphous carbon and metal particles in a protective layer and controlling the average particle size and distribution of the metal particles, thereby increasing the lithium stacking speed and improving the charge-discharge cycle 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 has the above-mentioned advantages. A protective layer mixed with amorphous carbon and metal particles is provided on the current collector, and lithium is stacked on the lower surface of the protective layer. There is no need to introduce a separate lithium-loving metal layer, thereby shortening the process time. Attached Figure Description

[0018] Figure 1 A lithium metal electrode manufactured according to one embodiment is shown.

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

[0020] Figure 3a and Figure 3b The surface and cross-sectional microstructure of the current collector when a protective layer is applied is shown.

[0021] Figure 4 The metal layer formed on the underside of the protective layer by an electrodeposition process is shown.

[0022] Figure 5a and Figure 5bThe electrodeposition appearance as a function of maximum current density is shown in the examples and comparative examples.

[0023] Figures 6a to 6c These are EDS analysis images of the protective layer according to a comparative example of the present invention. Figures 6d to 6f This is an EDS analysis photograph of the protective layer according to an embodiment of the present invention.

[0024] Figure 7 Battery life assessments of all-solid-state batteries using embodiments and comparative examples of the present invention are shown. Detailed Implementation

[0025] The terms "first," "second," and "third," etc., can be used to describe various parts, components, regions, layers, and / or segments, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or segment from another. Therefore, hereinafter, without departing from the scope of the invention, a first part, component, region, layer, or segment may be referred to as a second part, component, region, layer, or segment.

[0026] The technical terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise expressly stated, the singular forms used herein also include the plural forms. The term "comprising" as used in the specification means specifically describing a particular feature, region, integer, step, action, element, and / or component, and does not exclude the presence or addition of other features, regions, integers, steps, actions, elements, and / or components.

[0027] When one part is located "above" or "on top of" another part, it can be directly on the other part, or there can be other parts between them. Conversely, when one part is "directly on" another part, there are no other parts between them.

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

[0029] Figure 1 This is a diagram showing a lithium metal electrode 100 manufactured according to one embodiment.

[0030] Reference Figure 1 According to one embodiment, a lithium metal electrode 100 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 can be a component used for electrical connection within a lithium secondary battery. The current collector 10 can have a film (Foil) form, but is not limited to this; for example, it can also have a mesh, foam, rod, wire, or sheet form woven from wire (fiber).

[0032] The current collector 10 can be made of a material that is conductive and has limited reactivity with lithium. Specifically, the material of the current collector 10 can be any one or a combination of copper, nickel, titanium, stainless steel, iron, gold, platinum, silver, tantalum, ruthenium and their alloys, 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 can be from 1 μm to 50 μm. When the current collector 10 is too thick, the battery weight increases, resulting in a decrease in the battery's energy density. When the current collector 10 is too thin, there is a risk of overheating and damage during high-current operation, and it may be damaged due to tension during the battery manufacturing process.

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

[0035] The metal particles can be, for example, a lithiophilic metal. A lithiophilic metal is a metal that can react with lithium from the lithium supply source during lithium deposition to form a lithium alloy. The lithiophilic metal can be, for example, one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi. Specifically, the metal particles can be in powder form rather than liquid form. Because the metal particles have a non-liquid powder form, they have the advantages of easy size adjustment and easy handling when applied to electrodes.

[0036] In one embodiment, the average particle size (D50) of the metal particles may be less than 250 nm. Specifically, the average particle size (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 size (D50) of the metal particles refers to the particle size corresponding to 50% of the cumulative volume of the particle size distribution.

[0037] Since the average particle size (D50) of the metal particles meets the above-mentioned range, the agglomeration of the metal particles is minimized, resulting in a uniform distribution. This provides advantages such as excellent electrodeposition characteristics and improved lifetime performance. When the average particle size (D50) of the metal particles exceeds the upper limit of the above-mentioned range, there is a problem that the metal particles themselves have an excessively strong attraction to lithium, making it difficult to electrodeposit lithium between the protective layer and the current collector. When the average particle size (D50) of the metal particles exceeds the lower limit of the above-mentioned range, there is a problem that is detrimental to cost competitiveness.

[0038] In one embodiment, the average particle size (D50) of the carbon-based material can be from 0.01 to 1 μm. Since the average particle size of the carbon-based material meets the above range, it has the advantages of allowing free adjustment of the protective layer thickness and excellent dispersibility. When the average particle size of the carbon-based material exceeds the upper limit of the above range, it becomes difficult to reduce the protective layer thickness and adjust the dispersibility. When the average particle size of the carbon-based material exceeds the lower limit of the above range, the particles are too small, leading to a decrease in operational convenience.

[0039] In one embodiment, it can be confirmed that the average particle size of the metal particles is greater than the average particle size of the amorphous carbon. The difference between the average particle size of the metal particles and the average particle size of the amorphous carbon can be between 10 and 250 nm. The difference refers to an absolute value, and when the difference meets the above range, the metal particles in the protective layer can be more uniformly dispersed.

[0040] In one embodiment, the protective layer 30 may contain 10 to 30% by weight of the metal particles relative to 100% by weight of the total amount of the carbon-based material and the metal particles. Specifically, it may contain 15 to 25% by weight of the metal particles. 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 75:25. Since the metal particles are contained in the protective layer 30 in the above-mentioned range, it has the advantage of enabling lithium-ion batteries to be deposited at the interface between the current collector 10 and the protective layer 30.

[0041] When the content of the metal particles in the protective layer 30 exceeds the upper limit of the aforementioned range, it not only leads to an increase in the cost of the metal particles, but also causes the problem that lithium cannot be electrodeposited below the protective layer when there are too many metal particles distributed in the protective layer. Conversely, when the content of the metal particles in the protective layer 30 exceeds the lower limit of the aforementioned range, the problem of lithium being deposited on the upper surface of the protective layer will occur because the attraction of the metal particles to lithium is too weak.

[0042] In one embodiment, the metal particles occupy 15% to 50% of the area in the SEM image of the protective layer 30, with the total area of ​​the 22.5μm × 17.5μm region as 100%. Specifically, the area can be 30% to 50%. Because the metal particles are distributed with the above-mentioned area, they have the advantage of uniformly attracting lithium, thereby depositing lithium on the current collector.

[0043] When the area exceeds the upper limit of the aforementioned range, it means there are too many metal particles, thus causing problems when the metal particles exceed the upper limit of the aforementioned range. When the area exceeds the lower limit of the aforementioned range, it means there are too few metal particles or poor dispersion leading to agglomeration, thus causing problems when the metal particles exceed the lower limit or the average particle size of the metal particles exceeds the upper limit.

[0044] In one embodiment, the lithium metal electrode may include a metal layer 20 disposed between the current collector 10 and the protective layer 30. Specifically, the metal layer 20 is located on the current collector 10 and may be an alloy layer containing lithium. Specifically, the metal layer 20 may be formed by passing the current collector 10 and a lithium supply source (… Figure 2 A current is applied between the lithium-loving metal contained in the protective layer 30 and the lithium deposited from the lithium supply source 40 on the current collector 10 to form a lithium alloy layer.

[0045] As described above, the lithium metal electrode of the present invention forms a lithium alloy layer through the reaction between the metal particles in the protective layer 30 and the lithium supply source 40, without the need for a process of coating an additional metal layer under the protective layer 30. This shortens the time required for the entire electrode manufacturing process, making it economical. Furthermore, by including a metal layer 20 containing a lithium alloy in the lithium metal electrode, it facilitates lithium deposition and improves battery life characteristics.

[0046] In one embodiment, the thickness of the metal layer 20 can be 3 to 25 μm, specifically 5 to 20 μm. When the thickness of the metal layer 20 is too thick, when the lithium metal electrode of this embodiment is applied to a secondary battery, there will be an increase in battery weight and volume, leading to a decrease in energy density. Furthermore, since the time and cost of the electrodeposition process increase with 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 too thin, the battery's charge-discharge lifespan will decrease when the lithium metal electrode of this embodiment is applied to a secondary battery. Specifically, during the battery's charge-discharge process, lithium within the battery is gradually consumed due to side reactions between the lithium contained in the negative electrode active material layer (i.e., the metal layer of this invention) and the electrolyte, resulting in a decrease in battery capacity. Furthermore, the amount of lithium reserves available to replenish the lithium consumed during charge-discharge is reduced, thus decreasing the battery's charge-discharge lifespan. Therefore, the thickness of the metal layer 20 is preferably 3 μm or more.

[0048] In one embodiment, the thickness of the protective layer 30 can be from 5 to 20 μm. Specifically, the thickness can be from 5 to 10 μm. The thickness of the protective layer 30 can refer to the average thickness of the region excluding the lithium-containing metal layer 20. When the thickness of the protective layer 30 meets the above range, an ultra-thin lithium metal electrode can be provided.

[0049] When the thickness of the protective layer 30 exceeds the upper limit of the above range, there will be a problem of reduced conductivity due to excessive thickness of the protective layer; when the thickness of the protective layer 30 is lower than the lower limit of the above range, there will be a problem of the protective layer not being able to fully play its role.

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

[0051] Here, relative to 100 parts by weight of the total amount of the carbon-based material and the metal particles, 1 to 15 parts by weight of the binder can be added, specifically 3 to 10 parts by weight. When the content of the binder meets the above range, the particles constituting the protective layer can be effectively bonded without reducing the energy density of the battery due to an increase in weight and volume, thereby forming a protective layer with excellent performance and further improving the life characteristics of the secondary battery.

[0052] When the content of the adhesive is too low, the bonding force between particles is reduced when the protective layer is formed. When the content of the adhesive is too high, not only is the energy density reduced, but the resistance of the protective layer is also significantly increased, which hinders 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 of the metal layer 20 by a reaction between lithium metal from the lithium supply source 40 and the plating bath. The thickness, composition, and characteristics of the film layer can be controlled by adjusting the composition of the plating bath and the electrodeposition process conditions.

[0054] In one embodiment, the film layer may at least partially comprise LiF. Because the film layer at least partially comprises LiF, its lifespan is improved and dendrite growth is prevented during battery operation due to its higher ionic conductivity.

[0055] The thickness of the film layer can be from 2 nm to 2 μm. Specifically, the thickness of the film layer can be in the range of 10 nm to 500 nm. When the thickness of the film layer is too thick, the lithium-ion conductivity decreases and the interface resistance increases, resulting in a decrease in charge-discharge characteristics when applied to a battery. When the thickness of the film layer is too thin, the film layer may easily be lost during the application of the lithium metal electrode according to the embodiment to the battery. Therefore, the film layer can have a relatively thin thickness within the thickness range and be uniformly and densely formed on the surface of the metal layer 12 or throughout the entire protective layer 30.

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

[0057] Reference Figure 2 A method for manufacturing a lithium metal electrode 100 according to an embodiment includes the steps of preparing a current collector 10 and coating at least one surface of the current collector 10 with a coating composition containing a lithium-based material and metal particles to form a protective layer 30.

[0058] In the step of preparing the current collector 10, the current collector 10 can be made of a material that is conductive and has limited reactivity with lithium. Specifically, the material of the current collector 10 can be any one or a combination of, for example, copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium and its alloys, 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 the current collector 10 using a slurry containing carbon-based materials and metal particles. The protective layer 30 is applied to the slurry formed by mixing the amorphous carbon and a binder in water using at least one of the following methods: doctor blade coating, dip coating, reverse roller coating, direct roller coating, gravure coating, extrusion, and brush coating. The protective layer 30 may also include a binder. Detailed descriptions of the carbon-based materials and the metal particles can be found above. Figure 1 .

[0060] In one embodiment, during the step of forming the protective layer, the metal particles and the carbon-based particles can be mixed in a weight ratio of 10:90 to 30:70. Specifically, the weight ratio can be 15:85 to 25:75. Regarding the advantages and disadvantages of this weight ratio, please refer to the above. Figure 1 .

[0061] In one embodiment, during the step of forming the protective layer 30, the slurry can be coated to a range of 3 to 10 μm. Specifically, the coating range can be 4 to 7 μm. When the slurry is coated to the above range, the function of the protective layer can be facilitated while ensuring the ionic conductivity of the protective layer.

[0062] When the slurry exceeds the upper limit of the above range, it is difficult to ensure uniformity after drying. When the slurry exceeds the lower limit of the above range, it may fail to function as a protective layer.

[0063] In one embodiment, a method for manufacturing a lithium metal electrode includes: after forming a protective layer 30, placing a current collector 10 with the protective layer 30 formed thereon in a plating bath 50, and then separating a lithium supply source 40 from the protective layer 30 at a predetermined interval; and forming a metal layer 20 comprising a lithium alloy by applying an electric current between the current collector 10 and the lithium supply source 40, the lithium alloy being formed by alloying a lithiophilic component contained in the protective layer 30 with lithium deposited from the lithium supply source 40.

[0064] Specifically, the current collector 10 with the protective layer 30 formed thereon is placed in the plating solution, and then the lithium supply source 40 is separated from the protective layer 30 by a predetermined interval. For example, the lithium supply source 40 may be lithium metal, lithium alloy, a foil material with the lithium metal or lithium alloy pressed onto the current collector, or a plating solution containing dissolved lithium salts.

[0065] The plating solution 50 can be manufactured by dissolving a lithium salt in several 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 relative to the entire electrolyte can be from 1.0 to 3.0 M.

[0066] Specifically, in this embodiment, the plating solution 50 is characterized in that it contains a nitrogen-based compound as the lithium salt and at least one of a plurality of solvents. For example, the nitrogen-based compound may contain one or more selected from the group consisting of lithium nitrate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethane sulfonimide, e-caprolactam, N-methyl-e-caprolactam, triethylamine, and tributylamine.

[0067] Among the nitrogen-based compounds, at least one of lithium nitrate, lithium bisfluorosulfonyl imide, and lithium bis trifluoromethanesulfonimide can be used as a lithium salt.

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

[0069] The plating solution 50 may also be manufactured using only the nitrogen-based compound; however, considering the viscosity of the plating solution 50, it may contain a general non-aqueous solvent as an auxiliary solvent.

[0070] For example, the auxiliary solvent may comprise one or more of the following: 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 comprise 5 to 70% by weight of 100% of the total amount of plating solution 50, preferably 10 to 60% by weight, but is not limited thereto. However, when the auxiliary solvent is contained within the range, the viscosity of plating solution 50 is appropriate, thus enabling a shorter electrodeposition time, but is not limited thereto.

[0072] In one embodiment, the plating solution 50 may also contain a fluorine-based compound. When the plating solution 50 also contains the fluorine-based compound, it has the advantage of improving the properties of the film layer on the metal layer or protective layer.

[0073] For example, the fluorinated compound may comprise one or more of the following groups: lithium difluorophosphate, lithium hexafluorophosphate, lithium difluoro bisoxalato phosphate, lithium tetrafluoro oxalato phosphate, lithium difluoro oxalate borate, lithium difluoro oxalato borate, lithium tetrafluorooxalato borate, fluoroethylene carbonate, difluoroethylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0074] The plating bath 50 may contain 0.1 to 30% by weight of the fluorine-based compound, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to 100% by weight of the total amount of the plating bath 50. When the fluorine compound is contained within the range described above, the interaction between the nitrogen-based and fluorine-based compounds in the plating bath 50 is smooth, thus resulting in excellent improvement in film properties. Furthermore, it suppresses the excessive formation of LiF due to the direct reaction between the fluorine-based compounds and lithium, thereby exhibiting excellent electrochemical properties.

[0075] Next, after an insulating film is placed between the current collector 10 and the lithium supply source 40, the current collector 10, the lithium supply source 40, and the insulating film are stacked using a constraint device and constrained in both directions. As a non-limiting example, the constraint device can employ methods commonly used in the art, such as manual clamping, hydraulic clamping, pneumatic clamping, or other uniaxial pressurization methods.

[0076] In the step of forming a lithium-containing metal layer 20 on at least one surface of the current collector 10 by applying the current, the current density of the applied current may be 0.1 mA / cm². 2 Up to 100mA / cm 2 The range, more specifically, can be 0.2 mA / cm. 2Up to 50mA / cm 2 The range can be 5mA / cm 2 Up to 30mA / cm 2 Range or 7mA / cm 2 Up to 25mA / cm 2 scope.

[0077] In one embodiment, the duration of the applied current can range from 0.05 hours to 50 hours, and more specifically, from 0.25 hours to 25 hours.

[0078] In one embodiment, the step of forming a lithium metal layer on at least one surface of the current collector by applying the current can be performed more than once at different current densities. The current application step can be performed in a multi-stage manner. Specifically, the multi-stage current application step can be performed by gradually increasing the current density from low to high in stages over a predetermined time period. For example, the current application step can be performed at a rate of 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 Sequential, phased addition and electrodeposition.

[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 may include at a current of 6 to 12 mA / cm². 2 The electrodeposition step is performed using the maximum current density within a certain range. Specifically, the maximum current density can be between 8 and 12 mA / cm². 2 The maximum current density refers to the limit of the current density that allows the electrodeposited lithium to deposit between the protective layer 30 and the current collector 10 during the electrodeposition process.

[0080] For example, the electrodeposition step at the maximum current density can be a final step performed after lithium has been deposited between the current collector 10 and the protective layer 30 through a multi-stage deposition step. Since the maximum current density meets the above range, lithium can be appropriately deposited between the current collector 10 and the protective layer 30, thus providing the advantages of battery life characteristics and excellent bonding strength between the current collector 10 and the protective layer 30.

[0081] When the maximum current density exceeds the upper limit of the aforementioned range, lithium deposits on the surface of the protective layer 30, resulting in the inability to obtain the desired stable electrode structure. When the maximum current density exceeds the lower limit of the aforementioned range, the lithium deposition time increases, leading to a decrease in production efficiency.

[0082] In one embodiment, the step of forming a lithium-containing metal layer 20 on at least one surface of the current collector 10 by applying the current may include an electrodeposition step of controlling the thickness of the deposited lithium to be 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 vertical height of the lithium disposed between the current collector 10 and the protective layer 30.

[0083] When the thickness of the deposited lithium exceeds the upper limit mentioned above, it not only leads to a decrease in the energy density of the battery, but also increases the processing time and the amount of metal raw materials used in forming the metal layer. When the thickness of the deposited lithium exceeds the lower limit mentioned above, the initial coulombic efficiency decreases due to initial irreversibility and insufficient remaining lithium, thus resulting in a decrease in charge-discharge performance.

[0084] In one embodiment, during the step of forming a lithium-containing metal layer 20 on at least one surface of the current collector 10 by applying the current, the thickness of the lithium alloy-containing metal layer 20 can be controlled to be between 5 and 20 μm. A detailed description of the thickness of the metal layer 20 can be found above. Figure 1 The content.

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

[0086] In one embodiment, the lithium secondary battery may include an electrode assembly comprising: a positive electrode containing a positive active material; a negative electrode, serving as the lithium metal electrode of the present invention; and a separator disposed between the positive and negative electrodes. This electrode assembly can be housed within a battery casing by winding or folding.

[0087] Next, electrolyte is injected into the battery casing and sealed, thus completing the secondary battery. At this time, the battery casing can have a cylindrical, prismatic, pouch, or button-shaped shape.

[0088] The positive electrode may include a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may contain a Li compound, which contains at least one metal selected from 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, the positive electrode active material layer may further contain a conductive material. For example, the conductive material may be carbon black, ultrafine graphite particles, fine carbon such as acetylene black, or nano-metal particle slurry, but is not limited to these.

[0090] The positive electrode current collector serves to support the positive electrode active material layer. For example, aluminum foil, nickel foil, or a combination thereof can be used as the positive electrode current collector, but it is not limited to these.

[0091] The electrolyte used to fill the lithium secondary battery can be a non-aqueous electrolyte or a solid electrolyte. Specifically, the electrolyte can be a solid electrolyte. The non-aqueous electrolyte may contain lithium salts such as lithium hexafluorophosphate and lithium perchlorate, and solvents such as ethylene carbonate, propylene carbonate, and butylene carbonate. Alternatively, the solid electrolyte may be a gel polymer electrolyte in which the electrolyte is impregnated in a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N.

[0092] The separator is used to separate the positive and negative electrodes and provide a channel for lithium ion movement. Any separator commonly used in lithium secondary batteries can be used. Specifically, the separator can have low resistance and excellent electrolyte retention capabilities for electrolyte ion movement. The separator can be, for example, selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof, and can be in the form of non-woven or woven fabric. Alternatively, when a solid electrolyte is used, the solid electrolyte can also serve as the separator.

[0093] Hereinafter, implementation examples of the present invention will be described in detail. However, these are merely examples and are not intended to limit the present invention, which is defined only by the scope of the following claims.

[0094] <Experimental Example> Manufacturing negative electrodes for lithium secondary batteries <Example 1> <Manufacturing Current Collectors> Preparations are made to apply the nickel (Ni) current collector to the negative electrode of the lithium secondary battery of the present invention.

[0095] <Forming a protective layer> A slurry is applied to both surfaces of the nickel current collector using a comma coater to form a protective layer of approximately 5 μm. Specifically, to prepare the slurry for forming the protective layer, amorphous carbon and metal particles are mixed. A binder and solvent are further mixed in. Here, the amorphous carbon is acetylene black, and the metal particles are silver (Ag). The weight ratio of amorphous carbon to metal particles is 80:20. At this point, the average particle size of the silver (Ag) particles is 65 nm.

[0096] Furthermore, the mixed binder is manufactured by adding 3 parts by weight of carboxymethyl cellulose (CMC) and 6 parts by weight of styrene-butadiene rubber (SBR) relative to the total amount of amorphous carbon and metal nitrides. Additionally, the solvent used is water and ethylene glycol (EG) in an 80:20 weight ratio. The total amount of solvent is approximately 25% by weight of the total amount of amorphous carbon, metal particles, and binder to maintain a suitable viscosity for coating.

[0097] Figure 3a and Figure 3b The fine structure of the surface and cross-section when a protective layer is disposed on the current collector is shown.

[0098] Reference Figure 3a and Figure 3b This allows us to confirm the surface and cross-sectional structure after the protective layer is applied. <Lithium Electrodeposition Process> Subsequently, in order to form a lithium alloy or pure lithium metal between the protective layer and the current collector, an electrodeposition process is used to remove lithium from the lithium supply source and deposit lithium between the protective layer and the current collector. The plating solution used for the electrodeposition as described above is prepared by adding 40% by weight of lithium bis(fluorosulfonyl)imide and 5% by weight of lithium nitrate as nitrogen compounds, respectively, relative to 100% by weight of the plating solution, and adding 5% by weight of fluoroethylene carbonate as a fluorine compound, relative to 100% by weight of the plating solution.

[0099] As a lithium supply source, a lithium metal plate with a purity of 99.9% or higher and a thickness of 500 μm is pressed onto a copper current collector (Cu plate). After the lithium supply source and the current collector are stacked in an electrically insulating state in the plating solution, a current is applied to the lithium supply source and the current collector as (+) electrodes and (-) electrodes, respectively, using a power supply device, thereby causing lithium to precipitate between the current collector and the composite protective layer.

[0100] In the electrodeposition process, the current density is set to 0.2 mA / cm². 2 0.5mA / cm 2 1mA / cm 2 The order of electrodeposition was gradually increased, and after 5 minutes of electrodeposition at each stage, the maximum current density was set to 10 mA / cm². 2 The electrodeposition time at the maximum current density is calculated as the time required to deposit a final cumulative lithium thickness of 10 μm, and is set variably according to the magnitude of the maximum current density.

[0101] Figure 4 The metal layer formed on the underside of the protective layer by an electrodeposition process is shown.

[0102] Reference Figure 4 It was confirmed that a lithium-containing alloy layer, i.e. a metal layer, was formed between the current collector and the protective layer, consisting of lithium supplied by a lithium source.

[0103] Figure 5a and Figure 5b The electrodeposition appearance according to the maximum current density is shown in the electrodeposition process according to the embodiments and comparative examples.

[0104] Figure 5a This refers to the appearance of electrodeposited material when electrodeposition is performed below the maximum current density. Figure 5b This refers to the appearance of electrodeposition when electrodeposition is performed at current densities exceeding the maximum. (See reference.) Figure 5a and Figure 5b When electrodeposition is performed below the maximum depositable current density, the deposited lithium is confirmed to be stacked under the black protective layer, which is therefore visible. However, when electrodeposition is performed above the maximum depositable current density, the lithium is confirmed to be stacked on the upper surface of the protective layer, resulting in gray lithium deposits on the upper surface of the protective layer. Therefore, the maximum current density at which lithium deposits between the current collector and the protective layer during the electrodeposition process is defined as the maximum depositable current density.

[0105] Manufacturing all-solid-state batteries All-solid-state batteries were fabricated using the negative electrodes manufactured according to the above embodiments and comparative examples, and their charge-discharge life was evaluated. For evaluating the all-solid-state battery cell, a pressurized evaluation battery from Teraleader capable of maintaining an inert atmosphere was used. To fabricate the all-solid-state battery cell, a sulfide-based nitrogen-containing heterocyclic magnesium aluminate (Li6P5Cl) solid electrolyte was used, and the electrolyte was formed into a sheet with a thickness of approximately 0.7 mm. To obtain a dense electrolyte, a pressure of 370 MPa was applied.

[0106] A 0.5 mm thick lithium electrode was attached to one side of the electrolyte as a reference electrode, and a negative electrode manufactured according to the examples and comparative examples was attached to the other side. The reference electrode and the evaluation electrode were attached to the solid electrolyte at a pressure of 50 MPa, and in the charge-discharge evaluation, the battery was pressurized at 16 MPa.

[0107] <Example 2> Except that the average particle size of the Ag particles used to make the slurry for forming the protective layer is 50 nm, the process is carried out in the same manner as in Example 1.

[0108] <Example 3> Except that the average particle size of the Ag particles used to make the slurry for forming the protective layer is 200 nm, the process is carried out in the same manner as in Example 1.

[0109] <Comparative Example 1> Except that the average particle size of the Ag particles used to make the slurry for forming the protective layer is 300 nm, the process is carried out in the same manner as in Example 1.

[0110] <Comparative Example 2> Except that the average particle size of the Ag particles used to make the slurry for forming the protective layer is 500 nm, the process is carried out in the same manner as in Example 1.

[0111] <Comparative Example 3> Except that the average particle size of the Ag particles used to make the slurry for forming the protective layer is 700 nm, the process was carried out in the same manner as in Example 1.

[0112] <Comparative Examples 4-5> Except that the average particle sizes of the amorphous carbon particles used to make the slurry for forming the protective layer were 20 nm and 300 nm, respectively, the process was carried out in the same manner as in Example 1.

[0113] <Evaluation Example>: Evaluation of the average particle size of metal particles Table 1 below shows the distribution of metal particles, maximum electrodeposition current, and number of charge-discharge cycles within the protective layer when it contains metal particles of different average particle sizes. The distribution of metal particles, maximum electrodeposition current, and number of charge-discharge cycles within the protective layer were measured using the following methods.

[0114] Distribution of metal particles within the protective layer: A protective coating was constructed by mixing amorphous carbon and metal elements, and EDS analysis was performed on the protective layer sample before electrodeposition. During EDS analysis, an elemental distribution mapping model was used to confirm the distribution of each element, with additional analysis performed on areas showing differences in brightness and darkness in the SEM images. Using this method, a good distribution of metal particles within the protective layer was marked with ○, a moderate distribution with △, and a poor distribution with ×.

[0115] Maximum current density (mA / cm) 2 The maximum current density refers to the limit of the current density that allows electrodeposited lithium to be deposited between the ion concentration protective layer and the current collector according to the process described. The maximum current density was measured.

[0116] Charge-discharge cycle count (times): The reference electrode and evaluation electrode were attached to the solid electrolyte at a pressure of 50 MPa. During the charge-discharge evaluation, the electrode was pressurized at 16 MPa in a dedicated evaluation battery. One charge-discharge evaluation was defined as one cycle under the following conditions: at 2 mA / cm². 2 Constant current charging for 0.5 hours, and at 2mA / cm 2 The constant current discharge lasts for 0.5 hours. The charge-discharge life is defined as the end of the life when a short circuit occurs between the reference electrode and the evaluation electrode or the voltage between the two electrodes exceeds 2V during the charge-discharge process.

[0117] Table 1 Referring to Table 1, Examples 1 to 3 exhibit a higher metal particle distribution area and superior metal particle distribution uniformity within the protective layer compared to Comparative Examples 1 to 3. Meanwhile, the charge / discharge performance characteristics of the Comparative Examples are confirmed to be inferior to those of the Examples. Specifically, Comparative Examples 1 to 3, with excessively large average metal particle size, show poorer metal particle distribution area and metal particle distribution uniformity within the protective layer compared to the Examples. Furthermore, Comparative Example 4, with excessively small amorphous carbon average particle size, and Comparative Example 5, with excessively large amorphous carbon average particle size, also exhibit poorer performance in terms of metal particle distribution area and metal particle distribution within the protective layer compared to the Examples. Figures 6a to 6c These are EDS analysis images of the protective layer corresponding to the comparative examples of the present invention. Figures 6d to 6f These are EDS analysis images of the protective layer corresponding to embodiments of the present invention.

[0118] Figures 6a to 6c The image shown is an EDS analysis photograph of the protective layer corresponding to Comparative Example 1. Specifically, Comparative Example 1 used Ag with an average particle size of approximately 300 nm. In this sample, EDS analysis after coating the current collector showed that C element was detected in the main component, amorphous carbon, and Ag element was also detected in the protective layer. The areas with more obvious differences in brightness were classified as S1, S2, and S3. Analysis of their EDS results showed that in the bright areas S1 and S2, which appeared almost white in the SEM images, the C signal was weak, while the Ag signal was strong.

[0119] This indicates that Ag particles have aggregated in the white areas of the SEM images. On the other hand, in S3, which appears relatively dark, the C signal is strong, while the Ag signal is detected as very weak. This means that, unlike S1 and S2, the black areas in the SEM images contain almost no Ag particles. Based on the above analysis, it can be concluded that the majority of the image is composed of amorphous carbon, hence the predominantly black color, but it is still confirmed that a large number of white particles are aggregated and distributed within it.

[0120] Figures 6d to 6fThis is an EDS analysis image of the protective layer corresponding to Example 1. Specifically, Example 1 used Ag with an average particle size of approximately 65 nm. EDS analysis of this sample with a protective layer coated on the current collector showed that C was detected in the main component, amorphous carbon, and Ag was detected in the Ag particles contained within the protective layer. Analysis of the EDS results for the relatively white areas in the SEM image revealed that the C signal was weaker and the Ag signal was stronger in these areas, indicating a higher Ag content in the white areas.

[0121] However, unlike Comparative Example 1, in Example 1 it was confirmed that the aggregation of Ag particles within the entire sample was relatively rare, and the smaller Ag particles were evenly distributed throughout the sample.

[0122] Reference Figures 6a to 6f As shown in Table 1, examples with an average metal particle size of 400 nm or less within the protective layer demonstrate superior metal particle distribution and charge-discharge cycle life compared to comparative examples with a particle size exceeding 400 nm. In Comparative Example 3, to determine the maximum electrodeposition current, the current density was reduced to 0.5 mA / cm² under existing experimental conditions. 2 Experiments were conducted, but it was confirmed that lithium deposition still occurred on the upper surface of the protective layer even under the specified current conditions. Lithium continued to electrodeposit on the upper surface of the protective layer even under sufficiently reduced current conditions, making it difficult to quantify the maximum electrodeposition current; therefore, it was not indicated. Furthermore, in Comparative Example 3, regarding the number of charge-discharge cycles, the effect of the protective layer was only evident when the battery was fabricated with lithium stacked in layers on the lower surface of the protective layer. However, when lithium electrodeposited on the upper surface of the protective layer, it was difficult to conduct experiments under the same conditions, even if a battery was fabricated. When batteries were fabricated without the protective layer, approximately 80% of the batteries failed to cycle normally and experienced internal short circuits; therefore, this was not indicated.

[0123] Furthermore, it can be confirmed that among Examples 1 to 3, compared with Example 3, which has an average particle size of about 200 nm, Example 2, which has an average particle size of less than 100 nm, has excellent uniformity of metal particle distribution and excellent charge-discharge cycle count. Moreover, compared with Example 3, Example 2 has excellent uniformity of metal particle distribution and excellent charge-discharge cycle count.

[0124] Figure 7 The charge-discharge lifetime evaluation results of the lithium metal electrodes corresponding to the embodiments and comparative examples of the present invention are shown.

[0125] Reference Figure 7It can be confirmed that the charge-discharge life of Example 1 is 710 cycles, while that of Comparative Example 1 is 122 cycles. The charge-discharge performance of Example 1, which has a smaller average particle size of metal particles in the protective layer, is better than that of Comparative Example 1.

[0126] This invention is not limited to the embodiments described, and can be manufactured in various different forms. Those skilled in the art should understand that it can be implemented in other specific forms without altering the technical concept or basic characteristics of the invention. Therefore, the above embodiments should be understood in all respects as exemplary, not limiting.

Claims

1. A lithium metal electrode, characterized in that, include: Current collector, and A protective layer is disposed on at least one surface of the current collector; The protective layer comprises carbon-based materials in powder form and metal particles in powder form. The average particle size of the metal particles is below 250 nm.

2. The lithium metal electrode according to claim 1, characterized in that, Includes a metal layer disposed between the current collector and the protective layer. The metal layer contains lithium.

3. The lithium metal electrode according to claim 1, characterized in that, The protective layer comprises 10 to 30% by weight of the metal particles relative to 100% by weight of the total amount of the carbonaceous material and the metal particles.

4. The lithium metal electrode according to claim 1, characterized in that, The thickness of the protective layer is 3 to 7 μm.

5. The lithium metal electrode according to claim 1, characterized in that, The carbon-based substances include amorphous carbon. The amorphous carbon comprises one or more selected from the group consisting of acetylene black, super P black, carbon black, superconducting acetylene carbon black, activated carbon, graphite, hard carbon, and soft carbon.

6. The lithium metal electrode according to claim 1, characterized in that, The metal particles are lithium-loving metals.

7. The lithium metal electrode according to claim 1, characterized in that, The metal particles comprise one or more selected from the group consisting of In, Ag, Sn, Zn, Si, Al, and Bi.

8. The lithium metal electrode according to claim 1, characterized in that, The metal particles occupy 30 to 50% of the area relative to 100% of the 17.5 μm × 22.5 μm area in the SEM image of the protective layer.

9. The lithium metal electrode according to claim 1, characterized in that, The average particle size of the metal particles is greater than the average particle size of the amorphous carbon.

10. The lithium metal electrode according to claim 1, characterized in that, The difference between the average particle size of the metal particles and the average particle size of the amorphous carbon is 10 to 250 nm.

11. A method for manufacturing a lithium metal electrode, characterized in that, include: The steps for preparing a current collector; and The step of coating at least one surface of the current collector with a slurry comprising carbon-based material in powder form and metal particles in powder form to form a protective layer; The average particle size of the metal particles is below 250 nm.

12. The method for manufacturing a lithium metal electrode according to claim 11, characterized in that, After the step of forming the protective layer, the following is included: The steps of placing the current collector for forming the protective layer after the plating solution, and configuring the lithium supply source at a predetermined interval from the protective layer; and The step of forming a metal layer comprising a lithium alloy by applying an electric current between the current collector and the lithium supply source, wherein the lithium alloy is formed by alloying metal particles contained in the protective layer with lithium deposited from the lithium supply source.

13. The method for manufacturing a lithium metal electrode according to claim 11, characterized in that, In the step of forming the protective layer, the metal particles and the carbon-based particles are mixed in a weight ratio of 10:90 to 30:

70.

14. The method for manufacturing a lithium metal electrode according to claim 11, characterized in that, In the step of forming the protective layer, the slurry is coated in a range of 3 to 10 μm.

15. The method for manufacturing a lithium metal electrode according to claim 14, characterized in that, In the step of forming the protective layer, the slurry further includes a binder, comprising 1 to 15 parts by weight of the binder relative to 100 parts by weight of the total amount of the carbonaceous material and the metal particles.

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