Method for preparing lithium metal negative electrode from which surface oxide layer is removed, and lithium metal negative electrode prepared thereby

Abstract

The present invention relates to a method for preparing a lithium metal negative electrode from which a surface oxide layer is removed by physically removing the surface oxide layer formed on the surface of lithium metal by using a cutting tool, and to a lithium metal negative electrode prepared by the method. According to the present invention, since there is no surface oxide layer causing non-uniformity of the surface of the lithium metal negative electrode, overvoltage is reduced at the interface between the negative electrode and an electrolyte, thereby enabling rapid and uniform transport. It is possible to inhibit dendritic growth on the surface of the negative electrode as a nucleus is not locally formed, and a generally flat and uniform electrodeposition shape is exhibited. In addition, the number of cycles is increased, and the formation of a lithium porous layer and dead lithium, which are factors degrading the performance of a lithium metal battery, is reduced, thereby improving cycle performance.

Description

Method for manufacturing a lithium metal anode with a surface oxide layer removed and a lithium metal anode manufactured by the method

[0001] The present invention relates to a method for manufacturing a lithium metal negative electrode having a surface oxide layer removed by physically removing a surface oxide layer formed on a lithium metal surface using a cutting tool, and to a lithium metal negative electrode manufactured by the method.

[0002]

[0003] Recently, the severity of climate change and the rise in global temperatures caused by greenhouse gas emissions have become increasingly apparent. Carbon-neutral policies are being implemented around the world to reduce carbon dioxide emissions, and this trend is driving rapid growth in the electric vehicle market, which does not use fossil fuels.

[0004] The batteries used in electric vehicles, which run on electricity, typically use lithium-ion batteries. Lithium-ion batteries consist of a cathode (-), an anode (+), an electrolyte, and a separator. Materials used as the cathode include lithium metal and graphite. Lithium metal possesses a capacity that surpasses that of graphite, the current cathode material used in commercial electric vehicle batteries, making it essential for the commercialization of high-energy-density batteries.

[0005] However, lithium metal anodes suffer from dendrite growth. Lithium metal is highly reactive and reacts with trace amounts of oxygen and moisture, forming a surface oxide layer (native layer). This surface oxide layer increases the surface unevenness of the lithium metal.

[0006] To address this issue, research has been conducted on changes to the lithium metal manufacturing process and methods for reacting lithium oxide through chemical reactions using solvents. However, conventional technologies require the design of new process lines and are unsuitable for large-area electrodes and mass production due to their wasteful use of solvents.

[0007] Accordingly, in the present invention, the surface oxide layer that causes unevenness of the lithium metal surface, which is mentioned as one of the main causes of dendritic growth of the metal negative electrode, was removed by a simple method to induce uniform and high-density electrodeposition, thereby improving the performance of a lithium metal battery.

[0008]

[0009] The present invention is intended to solve the problems of the prior art, and provides a method for manufacturing a lithium metal negative electrode from which a surface oxide layer that increases surface unevenness of lithium metal is removed, and a lithium metal negative electrode manufactured by the method.

[0010]

[0011] A method for manufacturing a lithium metal negative electrode with a surface oxide layer removed according to the present invention comprises the steps of (S1) laminating a lithium metal foil on one surface of a current collector; and (S2) removing the surface oxide layer of the lithium metal foil. In step (S2), the removal of the surface oxide layer may be characterized by physically removing the surface of the lithium metal foil using a cutting tool.

[0012] In the method for manufacturing a lithium metal negative electrode with a surface oxide layer removed according to the present invention, lamination can be performed in the step (S1) by applying a pressure of 1 to 10 MPa at a temperature of 60 to 160°C for 10 to 80 minutes.

[0013] In the method for manufacturing a lithium metal negative electrode with a surface oxide layer removed according to the present invention, the current collector may be a thin film made of a metal material including at least one selected from the group consisting of copper, aluminum, and nickel.

[0014] In the method for manufacturing a lithium metal negative electrode from which a surface oxide layer has been removed according to the present invention, the cutting tool may be a soldering iron blade or wire.

[0015] In the method for manufacturing a lithium metal negative electrode from which a surface oxide layer has been removed according to the present invention, the cutting tool can be heated to a temperature of 140 to 220°C.

[0016] In the method for manufacturing a lithium metal negative electrode with a surface oxide layer removed according to the present invention, the surface of the lithium metal foil can be removed by cutting at a speed of 10 to 100 m / min in the step (S2).

[0017] In the method for manufacturing a lithium metal negative electrode from which a surface oxide layer has been removed according to the present invention, the surface of the lithium metal foil can be removed by 3 to 30 μm in the step (S2).

[0018] A lithium metal negative electrode having a surface oxide layer removed according to the present invention includes a current collector and a lithium metal foil laminated to one surface of the current collector, and the lithium metal foil may have a surface oxide layer removed.

[0019] In the lithium metal negative electrode from which the surface oxide layer according to the present invention has been removed, the thickness of the lithium metal foil may be 10 to 200 μm.

[0020]

[0021] According to the present invention, the surface oxidation layer that causes unevenness on the surface of the lithium metal anode is eliminated, thereby reducing the overvoltage at the anode-electrolyte interface, enabling rapid and uniform transport. Local nuclei are not formed, and an overall flat and uniform electrodeposition shape is observed, thereby suppressing dendritic growth on the anode surface. Furthermore, as the cycle count increases, the formation of lithium porous layers and dead lithium, factors that deteriorate the performance of lithium metal batteries, is reduced, thereby improving cycle performance.

[0022] In particular, unlike conventional technologies, it is suitable for large-area and mass production essential in actual processes, and is advantageous in controlling lithium surface chemistry regardless of the type of initial lithium.

[0023]

[0024] Figure 1 is a flowchart showing the manufacturing process of a method for manufacturing a lithium metal negative electrode from which a surface oxide layer of the present invention has been removed.

[0025] FIG. 2 is a conceptual diagram illustrating a method for removing a surface oxide layer of a lithium laminate copper thin film using a heated wire according to one embodiment.

[0026] FIG. 3 is a conceptual diagram illustrating a method for removing a surface oxide layer of a lithium metal foil using a soldering iron blade according to one embodiment.

[0027] Figure 4 shows the surface shapes of Example 1 and Comparative Example 1.

[0028] Figure 5 shows the ether electrolyte of Example 1 and Comparative Example 1 at 0.5 mA / cm. 2 , 1.0 mAh / cm 2 This shows the deposition voltage when electrodeposited.

[0029] Figure 6 shows the ether electrolyte of Example 1 and Comparative Example 1 at 0.5 mA / cm. 2 , 3.0 mAh / cm 2 This shows the surface shape when deposited.

[0030] Figure 7 shows the reversible characteristics of the symmetric cell in the ether electrolyte of Example 1 and Comparative Example 1 at a current density of 1.0 mA / cm. 2 , capacity density 1.0 mAh / cm 2 It shows the results confirmed under the conditions.

[0031] Figure 8 shows the reversible characteristics of the symmetric cell in the carbonate-based electrolyte of Example 1 and Comparative Example 1 at a current density of 1.0 mA / cm. 2 , capacity density 1.0 mAh / cm 2 It shows the results confirmed under the conditions.

[0032] Figure 9 shows 2.2 mAh / cm in the ether electrolyte of Example 1 and Comparative Example 1. 2The results are shown when the positive electrode of the loading is used and the driving is performed in an ether electrolyte.

[0033]

[0034] The embodiments described herein may be modified in various different forms, and the technology according to one embodiment is not limited to the embodiments described below. In addition, the embodiments of one embodiment are provided to more completely explain the present disclosure to a person with average knowledge in the relevant technical field. In this case, unless there is a different definition for the technical and scientific terms used, they have the meaning commonly understood by a person with ordinary skill in the technical field to which this invention belongs, and in the following description and the attached drawings, descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention are omitted.

[0035] Additionally, the singular forms used in this specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0036] Additionally, in this specification and the appended claims, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0037] Additionally, in this specification and the appended claims, when a part such as a film (layer), region or component is said to be located “on,” “above,” “upper,” “below,” “lower,” or “lower” another part, this includes not only cases where one part is in contact with another part, but also cases where another part exists between the two parts.

[0038] In addition, the terms "about," "substantially," and the like used in this specification and the appended claims are used in a meaning that is at or close to the numerical value when manufacturing and material tolerances inherent in the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly utilizing the disclosure in which exact or absolute values ​​are stated to aid in the understanding of this specification and the appended claims.

[0039] Additionally, the numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of upper and lower limits of numerical ranges defined in different shapes.

[0040] Furthermore, terms such as “include” or “have” in this specification and the appended claims mean that a feature or component described in the specification exists, and unless specifically limited, do not preclude the possibility that one or more other features or components may be added.

[0041]

[0042] Hereinafter, a method for manufacturing a lithium metal negative electrode from which a surface oxide layer of the present invention has been removed and a lithium metal negative electrode manufactured by the method will be described in detail with reference to the attached drawings.

[0043]

[0044] Lithium is a silvery-white alkali metal in Group 1 of the periodic table, with atomic number 3. It is the lightest metal and has the lowest density of all solid elements. It reacts readily with water and oxygen to form compounds such as LiOH, Li2O, and Li2O3. Lithium has a variety of applications, but its primary industrial application is lithium-ion batteries. Lithium-ion batteries are lighter and can be manufactured with larger capacities than conventional batteries, and are therefore used in virtually all portable electronic devices. Lithium-ion batteries are also used in electric vehicles.

[0045]

[0046] Lithium metal batteries, hailed as the next-generation battery to succeed lithium-ion batteries, use lithium metal itself as the anode instead of graphite. Lithium metal batteries using lithium as the anode can theoretically achieve a capacity ten times higher than that of graphite, the currently commercialized anode material.

[0047]

[0048] However, when lithium metal is used as a battery negative electrode, the battery is generally manufactured by attaching lithium foil on a flat current collector. However, since lithium is an alkali metal and has a high reactivity, it reacts explosively with water and also reacts with oxygen in the air, which makes it difficult to manufacture and use in general environments. In particular, when lithium metal is exposed to the air, it forms an oxide film such as LiOH, Li2O, Li2O3 as a result of oxidation. When this surface oxide film (native layer) exists on the surface, the oxide film acts as an insulating film, lowering the electrical conductivity and hindering the smooth movement of lithium ions, which causes the electrical resistance to increase.

[0049]

[0050] Because of this, the lithium surface quality rapidly deteriorates, forming dendrites, which are branch-like growths of lithium during the charge and discharge process. Dendrites are branch-like crystals that form when using metal-ion batteries. Dendrites, which are branch-like crystals, grow by spreading out branches in all directions after a metal nucleus is formed in a solution where the metal is dissolved. In particular, dendrites formed when lithium metal is deposited are known to penetrate the separator and induce a short circuit between the positive and negative electrodes, causing a rapid temperature rise and explosion problems.

[0051]

[0052] For this reason, in order to suppress the formation of a surface oxide film in manufacturing a lithium anode, attempts have been made to manufacture a thin film by electrochemically depositing lithium ions on a copper current collector, to manufacture a lithium anode with a reduced thickness of a surface oxide film by blocking contact with the atmosphere, or to manufacture a lithium metal anode with an oxide layer removed chemically using a solvent and electrolyte.

[0053]

[0054] Accordingly, the present invention sought to physically remove a surface oxide layer that affects the formation of dendritic crystals of a lithium metal negative electrode by using a cutting tool, both mechanically and thermally.

[0055]

[0056] The present invention provides a method for manufacturing a lithium metal negative electrode from which a surface oxide layer is removed, and the method for manufacturing a lithium metal negative electrode from which a surface oxide layer is removed includes: (S1) a step of laminating a lithium metal foil on one surface of a current collector; and (S2) a step of removing a surface oxide layer of the lithium metal foil.

[0057]

[0058] Figure 1 is a flowchart showing the manufacturing process of a method for manufacturing a lithium metal negative electrode from which a surface oxide layer of the present invention has been removed.

[0059]

[0060] (S1) Step of laminating lithium metal foil on one side of the entire collector.

[0061]

[0062] Lamination is a technique that protects the surface and increases strength and stability by covering the target object with one or more thin layers. It firmly bonds the coating material to the target object by applying high temperature and pressure.

[0063]

[0064] A lithium laminate current collector thin film is manufactured by applying a pressure of 1 to 10 MPa to a negative electrode assembly including a lithium metal foil and a current collector at a temperature of 60 to 160°C for 10 to 80 minutes.

[0065]

[0066] The temperature is preferably 80 to 140°C, more preferably 100 to 120°C, the pressure is preferably 3 to 8 MPa, more preferably 5 to 6 MPa, and the time is preferably 30 to 60 minutes, more preferably 40 to 50 minutes.

[0067]

[0068] If the temperature and pressure are not controlled consistently, bubbles, wrinkles, or cracks may occur, and the space between the lithium metal foil and the current collector may not be attached and may be empty, allowing dust to enter the interior.

[0069]

[0070] The current collector is a thin film material, usually several tens of micrometers thick, located inside the battery and acts as a passage for electrons to flow smoothly when charging and discharging the battery.

[0071]

[0072] The above current collector is a thin film made of a metal material including at least one selected from the group consisting of copper, aluminum, and nickel, and a copper thin film is most preferred as the negative current collector. It may also be coated with an oxidation-resistant metal or alloy film to prevent oxidation.

[0073]

[0074] (S2) Step of removing the surface oxide layer of lithium metal foil

[0075]

[0076] Milling is a metalworking method that uses a cutting tool to cut the surface of a metal into a specific shape. In the present invention, the surface oxide layer formed on the surface of a lithium metal foil is physically removed by applying heat using a heated cutting tool.

[0077]

[0078] The above cutting tool is a soldering iron blade or wire, and the heating temperature is 140 to 220°C, preferably 160 to 200°C, and more preferably 180°C, which is the melting point of lithium.

[0079]

[0080] FIG. 2 is a conceptual diagram illustrating a method for removing a surface oxide layer of a lithium laminate copper thin film using a heated wire according to one embodiment.

[0081]

[0082] The lithium laminate current collector thin film manufactured in the above step (S1) is supplied to the heated cutting tool at a speed of 10 to 100 m / min, preferably 30 to 80 m / min, more preferably 50 to 60 m / min, while the surface of the lithium metal foil is removed to manufacture a lithium metal negative electrode with a surface oxide layer removed.

[0083]

[0084] Figure 3 is a conceptual diagram illustrating a method for removing a surface oxide layer of a lithium metal foil using a soldering iron blade according to one embodiment. The soldering iron blade is used to push and remove the surface of the lithium metal foil, and a step for thickness control is applied to both sides of the blade to adjust the thickness so that only the uppermost portion of the lithium metal foil can be removed.

[0085]

[0086] The surface of the lithium metal foil is removed by about 3 to 30 μm, preferably about 5 to 20 μm, and more preferably about 10 to 15 μm. If the surface of the lithium metal foil is removed too much, not only the surface oxide layer but also the lithium metal foil may be removed.

[0087]

[0088] The lithium metal negative electrode from which the surface oxide layer has been removed includes a current collector and a lithium metal foil laminated to one surface of the current collector, the lithium metal foil having a surface oxide layer removed, and the thickness of the lithium metal foil is 10 to 200 ㎛, preferably 50 to 150 ㎛, and more preferably 100 to 120 ㎛.

[0089]

[0090] Hereinafter, specific examples and experimental examples will be described. However, the examples and experimental examples described below are only illustrative, and the technology described in this specification is not limited thereto.

[0091]

[0092] <Example 1>

[0093]

[0094] The surface of a lithium metal foil was milled to about 20 ㎛ using a soldering iron blade at 180 ℃ at a speed of 50 m / min to remove the surface oxide layer, and then punched into a circle with a diameter of 12 pi and a thickness of 0.1 mm, and used as both electrodes of a symmetric cell to manufacture Example 1. The entire process was carried out in a glove box under argon gas, and 18 pi PE was used as the separator.

[0095]

[0096] <Comparative Example 1>

[0097]

[0098] The entire process was carried out in a glove box under argon gas, and 18pi PE was used as the separator. It was punched into a circle with a diameter of 12pi and a thickness of 0.1 mm, and used as both electrodes of a symmetric cell to manufacture Comparative Example 1.

[0099]

[0100] <Experimental Example 1> Comparison of Example 1 and Comparative Example 1

[0101]

[0102] Example 1, in which the surface oxide layer was removed, and Comparative Example 1, in which the surface oxide layer was not removed, were compared.

[0103]

[0104] Figure 4 shows the surface morphology of Example 1 and Comparative Example 1. In Comparative Example 1, microcracks induced in the surface oxide layer were observed, whereas Example 1 showed a flat surface morphology.

[0105]

[0106] Figure 5 shows the ether electrolyte of Example 1 and Comparative Example 1 at 0.5 mA / cm. 2 , 1.0 mAh / cm 2 This shows the deposition voltage when electrodeposited. Comparative Example 1 showed an overvoltage due to a surface oxide layer, but Example 1 showed almost no nucleation overvoltage and was confirmed to have less overvoltage.

[0107]

[0108] Figure 6 shows the ether electrolyte of Example 1 and Comparative Example 1 at 0.5 mA / cm. 2 , 3.0 mAh / cm 2 This shows the surface shape when electrodeposited. In Comparative Example 1, the lithium metal surface shows a shape in which electrodeposition occurs sparsely like islands, but in Example 1, it can be confirmed that electrodeposition occurs densely.

[0109]

[0110] <Experimental Example 2> Reversible Characteristics of Symmetric Cells

[0111]

[0112] Figure 7 shows the reversible characteristics of the symmetric cell in the ether electrolyte of Example 1 and Comparative Example 1 at a current density of 1.0 mA / cm. 2 , capacity density 1.0 mAh / cm 2 The results are shown under the conditions. Comparative Example 1 showed a voltage modification with increasing polarization after 80 hours, whereas Example 1 showed significantly higher reversibility and lower polarization for over 220 hours.

[0113]

[0114] Figure 8 shows the reversible characteristics of the symmetric cell in the carbonate-based electrolyte of Example 1 and Comparative Example 1 at a current density of 1.0 mA / cm. 2 , capacity density 1.0 mAh / cm 2 The results are shown under the conditions. Comparative Example 1 shows a voltage change in which polarization increases after 30 hours and completely dissipates after about 100 hours, whereas Example 1 shows a remarkably high reversibility and low polarization for over 220 hours.

[0115]

[0116] Figure 9 shows 2.2 mAh / cm in the ether electrolyte of Example 1 and Comparative Example 1. 2The results are shown when the loading electrode was used and operated in an ether electrolyte. In Comparative Example 1, performance degradation was observed after 100 cycles or more, but in Example 1, no performance degradation was observed even after 500 cycles or more.

[0117]

[0118] As described above, the lithium metal negative electrode with the surface oxide layer removed according to the embodiment of the present invention has the effect of improving battery life characteristics by suppressing dendritic growth and having excellent capacity retention rate according to cycles by physically removing the surface oxide layer using a cutting tool.

[0119]

[0120] Although the present invention has been described in this specification with specific details and limited examples, these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art to which the present invention pertains can make various modifications and variations based on these descriptions. Therefore, the ideas described in this specification should not be limited to the described examples, and all things that are equivalent or equivalent to the claims below, as well as the claims, are considered to fall within the scope of the ideas described in this specification.

Claims

1. (S1) A step of laminating a lithium metal foil on one side of the entire body; and, (S2) a step of removing the surface oxide layer of the lithium metal foil; A method for manufacturing a lithium metal negative electrode, characterized in that the surface oxide layer is removed in the above step (S2) by physically removing the surface of the lithium metal foil using a cutting tool.

2. In paragraph 1, A method for manufacturing a lithium metal negative electrode, wherein lamination is performed by applying a pressure of 1 to 10 MPa at a temperature of 60 to 160° C. for 10 to 80 minutes in the above step (S1).

3. In paragraph 1, A method for manufacturing a lithium metal negative electrode, wherein the above-mentioned current collector is a thin film made of a metal material including at least one selected from the group consisting of copper, aluminum, and nickel.

4. In paragraph 1, The above cutting tool is a method for manufacturing a lithium metal negative electrode, which is a soldering iron blade or wire.

5. In paragraph 4, The above cutting tool is a method for manufacturing a lithium metal negative electrode heated to a temperature of 160 to 220°C.

6. In paragraph 1, A method for manufacturing a lithium metal negative electrode, wherein the surface of the lithium metal foil is removed by cutting at a speed of 10 to 100 m / min in the above step (S2).

7. In paragraph 1, A method for manufacturing a lithium metal negative electrode, wherein the surface of the lithium metal foil is removed by 3 to 30 μm in the above step (S2).

8. A lithium metal negative electrode manufactured by the method of any one of claims 1 to 7, comprising a current collector and a lithium metal foil laminated to one surface of the current collector, wherein the lithium metal foil has a surface oxide layer removed.

9. In paragraph 8, A lithium metal negative electrode having a thickness of the lithium metal foil of 10 to 200 μm.

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