Film for punching lithium metal and method for punching lithium metal using same

Abstract

The present invention provides a film for punching lithium metal and a method for punching lithium metal using the same, the film for punching lithium metal being easily separated because the lithium metal does not adhere to a lower release film provided below the lithium metal when punching lithium metal by an ultrasonic cutting method, and a method for punching lithium metal using the same. When the lithium metal is ultrasonically cut, the film for punching the lithium metal is positioned at the lower part of the lithium metal, and the film comprises a PET substrate and a silicone coating layer positioned on the surface of the PET substrate.

Description

Technical Field

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0084812, filed on June 30, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a release film disposed under a lithium metal when punching the lithium metal using an ultrasonic cutting device. More particularly, the present invention relates to a film for punching lithium metal and a method of punching lithium metal using the film, such that when punching the lithium metal using an ultrasonic cutting method, the lithium metal does not adhere to the lower release film disposed under the lithium metal. Background Art

[0003] As the interest in energy storage technologies continues to grow, and as their applications expand to energy sources for mobile phones, tablet computers, laptop computers, and video cameras, as well as electric vehicles (EVs) and hybrid electric vehicles (HEVs), research and development of electrochemical devices have been increasing. In this regard, electrochemical devices have received the most attention, among which lithium-based secondary batteries (such as rechargeable lithium-sulfur batteries, lithium-ion batteries, and lithium-ion polymer batteries) have become the focus of attention, and recently, research and development of new electrode and battery designs have been initiated to improve the capacity density and specific energy of these batteries.

[0004] These lithium-based secondary batteries generally include lithium metal with an extremely high energy density as a negative electrode active material. In order to use lithium metal as a negative electrode active material, it is first necessary to punch the lithium metal into a certain size. Generally, there are a contact method and a non-contact method for punching lithium metal. In the case of the contact method, it can be divided into a die method using a punch shaped like an electrode and an ultrasonic horn method shaped like an electrode. In the case of the contact method, a part of the material and the device are in direct contact, so the material may be damaged, and the device may be contaminated with part of the material or debris. The non-contact method includes laser punching, which allows cutting without directly contacting the material, thereby minimizing damage to the material and minimizing the possibility of the material or debris remaining on the device. However, depending on the material used, laser cutting may cause oxidation or generate dust.

[0005] For the materials used in the present invention, in order to minimize damage to the materials, the laser cutting method is preferred. However, since the lithium metal may be oxidized during laser irradiation and dust may be generated in the area in contact with the material, for safety reasons, the laser cutting method is not a suitable method for punching. Therefore, it is necessary to eliminate the above problems by using ultrasonic punching. Ultrasonic punching is in direct contact with the material, but can effectively minimize the problem of material adhesion to the device and cause less damage to the material.

[0006] Figure 1Schematic diagram of the method for ultrasonic blanking of lithium metal. Among them, as Figure 1 shown, release films (upper film, lower film) are respectively placed above and below the lithium metal, and the lithium metal is cut with ultrasonic waves (a mold in the shape of an electrode is placed above the upper film).

[0007] The upper film is used to prevent the lithium metal from adhering to the ultrasonic horn. The lower film is used to prevent ultrasonic waves from penetrating the lithium metal and damaging the bottom platform during the cutting of the lithium metal. However, in this case, the lithium metal will adhere to the lower film during the ultrasonic cutting process and is not easily separated. Therefore, a method is needed to prevent the lithium metal from adhering to the lower film when cutting the lithium metal using the ultrasonic cutting method, so that the lithium metal can be easily separated. Summary of the Invention

[0008] [Technical Problem]

[0009] Therefore, the purpose of the present invention is to provide a film for lithium metal blanking and a method for blanking lithium metal using the film, such that when blanking lithium metal by ultrasonic cutting, the lithium metal does not adhere to the lower release film provided below the lithium metal.

[0010] [Technical Solution]

[0011] To achieve the above purpose, the present invention provides a film for lithium metal blanking located below the lithium metal when cutting lithium metal with ultrasonic waves. The film includes: a PET substrate; and a silicone coating located on the surface of the PET substrate.

[0012] The present invention also provides a method for blanking lithium metal, which includes: (a) sequentially stacking the above-mentioned film for lithium metal blanking (or lower release film), lithium metal, one or more molds, and an upper release film; and (b) spacing ultrasonic horns on the upper surface of the upper release film, and then irradiating with ultrasonic waves to cut the lithium metal into a shape identical to the shape of the mold.

[0013] [Beneficial Effects]

[0014] According to the lithium metal release film and the method for blanking lithium metal using the film of the present invention, when blanking lithium metal by ultrasonic cutting, the lithium metal does not adhere to the lower release film provided below the lithium metal, and the film has the advantage of being easily separated. Description of the Drawings

[0015] Figure 1 Exploded view of ultrasonic blanking of lithium metal.

[0016] Figure 2 (a) of is an image of the blanking form after the lithium metal is separated from the lower film in Example 1, Figure 2(b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Example 1.

[0017] Figure 3 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Example 2. Figure 3 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Example 2.

[0018] Figure 4 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 1. Figure 4 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 1.

[0019] Figure 5 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 2. Figure 5 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 2.

[0020] Figure 6 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 3. Figure 6 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 3.

[0021] Figure 7 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 4. Figure 7 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 4.

[0022] Figure 8 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 5. Figure 8 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 5.

[0023] Figure 9 (a) is the image of the blanking form after the lithium metal and the lower film are separated in Comparative Example 6. Figure 9 (b) is the image of the lower film after the lithium metal and the lower film are separated after blanking in Comparative Example 6. Detailed Description of the Invention

[0024] The present invention will now be described in detail.

[0025] The film for lithium metal blanking of the present invention comprises a PET substrate and a silicone coating on the surface of the PET substrate, and the film is located below the lithium metal when ultrasonic cutting of the lithium metal is performed.

[0026] Lithium secondary batteries generally contain lithium metal with extremely high energy density as the negative electrode active material. In order to use lithium metal as the negative electrode active material, it is first necessary to blank the lithium metal into a certain specification. Generally, there are a contact method and a non-contact method for blanking lithium metal. In the case of the contact method, it can be divided into a die method using a punch similar in shape to an electrode and a horn method similar in shape to an electrode. In the case of the contact method, a part of the material is in direct contact with the equipment, so the material may be damaged, and the equipment may be contaminated with part of the material or debris. The non-contact method includes laser blanking, which allows cutting without direct contact with the material, thus minimizing damage to the material and minimizing the possibility of the material or debris remaining on the equipment. However, depending on the material used, laser cutting may cause oxidation or generate dust.

[0027] For the materials used in the present invention, in order to minimize damage to the materials, the laser cutting method is preferred. However, since lithium metal may be oxidized during laser irradiation and dust may be generated in the area in contact with the material, for safety reasons, the laser cutting method is not a suitable method for blanking. Therefore, it is necessary to eliminate the above problems by using ultrasonic blanking. Ultrasonic blanking is in direct contact with the material, but minimizes the problem of the material adhering to the equipment and causes less damage to the material.

[0028] In the method of ultrasonic blanking of lithium metal, as Figure 1 shown, release films (upper film, lower film) are respectively placed above and below the lithium metal, and the lithium metal is cut with ultrasonic waves (an electrode-shaped die is placed on the upper film). In this case, the upper film is made of polypropylene (PP) for the purpose of preventing the lithium metal from adhering to the ultrasonic horn. The lower film is mainly made of polyethylene terephthalate (PET) for the purpose of preventing ultrasonic waves from penetrating the lithium metal and damaging the bottom platform during cutting of the lithium metal. However, in this case, since the ultrasonic horn not only penetrates the lithium metal but also penetrates the lower film during ultrasonic cutting, the lithium metal adheres to the lower film during ultrasonic cutting and is not easily separated. Therefore, the applicant of the present invention has invented a method for preventing the lithium metal from adhering to the lower film during cutting of the lithium metal by using the ultrasonic cutting method, so that the lithium metal can be easily separated.

[0029] The film for lithium metal blanking of the present invention, more specifically, the "lower film for lithium metal blanking", is located below the lithium metal during ultrasonic cutting of the lithium metal. The film comprises a PET (polyethylene terephthalate) substrate and a silicone coating on the surface of the PET substrate.

[0030] The PET substrate constitutes a conventional "lower film for punching lithium metal", while the "lower film for punching lithium metal" of the present invention has a silicone coating on the surface of the PET substrate. In other words, when the surface of the PET substrate is coated with silicone as described above, when ultrasonic cutting is used to punch lithium metal, the lithium metal does not adhere to the lower (release) film provided below the lithium metal.

[0031] The silicone coating may be located only on a part of the surface of the PET substrate or on the entire surface of the PET substrate. However, it is preferred that the silicone coating is located on the entire surface of the PET substrate, so that the lithium metal can be easily separated without adhesion.

[0032] Relative to the total weight of the film for punching lithium metal, the silicone content in the silicone coating may be 4% by weight to 50% by weight, preferably 4% by weight to 30% by weight, more preferably 5% by weight to 20% by weight. If the silicone content in the silicone coating is less than 4% by weight relative to the total weight of the film for punching lithium metal, the benefits of coating the substrate with silicone cannot be achieved. In addition, if the silicone content in the silicone coating is greater than 50% by weight based on the total weight of the film for punching lithium metal, no further effects can be seen.

[0033] In addition, based on the thickness of the 50-μm PET substrate, the thickness of the silicone coating may be 0.01 μm to 25 μm, preferably 0.02 μm to 20 μm, more preferably 0.03 μm to 20 μm. If the thickness of the silicone coating is less than 0.01 μm based on the thickness of the 50-μm PET substrate, the benefits of coating the substrate with silicone cannot be obtained. In addition, if the thickness of the silicone coating exceeds 25 μm based on the thickness of the 50-μm PET substrate, no further effects will occur.

[0034] The silicone contained in the silicone coating may be selected from aqueous silicone, acetic acid type oil-based silicone, non-acetic acid type oil-based silicone, biological silicone, heat-resistant silicone, and polyurethane silicone. In addition, for the purpose of achieving the object of the present invention, one or more of vinyl polysiloxane and hydrogen polysiloxane may be very advantageous.

[0035] In addition, the surface of the silicone coating may be flat or in a embossed form with a plurality of protrusions. However, considering the need for uniform cutting characteristics when cutting lithium metal, a silicone coating with a flat surface may be preferred.

[0036] Meanwhile, the silicone coating may further contain a crosslinking agent as needed. When the silicone coating contains a crosslinking agent, the content of the crosslinking agent may be from 0.001 parts by weight to 0.8 parts by weight relative to the total weight of 100 parts by weight of the film for lithium metal blanking. Depending on the degree of crosslinking, the surface characteristics and peeling tendency of the film may also vary. For a silicone release film with a relatively high crosslink density, it is possible to prevent the physical penetration of the adhesive, thereby preventing an increase in the change of the peeling force over time. However, due to the relatively hard surface, it may not be able to absorb impacts well during peeling and may exhibit an unstable peeling tendency. On the other hand, for a release film with a relatively low crosslink density, a relatively soft surface is formed, which enables smooth absorption of impacts during the peeling process and a stable peeling tendency. However, due to the physical penetration of the adhesive, the change in the peeling force over time increases, which may cause problems.

[0037] Hereinafter, a method for blanking lithium metal using the film for lithium metal blanking of the present invention will be described. The method for blanking lithium metal using the above-mentioned film for lithium metal blanking includes: (a) sequentially stacking the above-mentioned film for lithium metal blanking (or lower release film), lithium metal, one or more dies, and an upper release film; and (b) arranging a horn at an interval above the upper release film, and then irradiating with ultrasonic waves to cut the lithium metal into a shape identical to the die shape.

[0038] In the method for blanking lithium metal using the film for lithium metal blanking of the present invention, the stacking order of each layer and the ultrasonic irradiation process are not different from those of the conventional method. However, as described above, the present invention is different from the conventional lower film. In addition, the method for blanking lithium metal using the film for lithium metal blanking has a key feature in terms of the ultrasonic irradiation depth (horn depth), which will be described below.

[0039] In other words, in the past, when using ultrasonic waves to blank lithium metal, the depth of the ultrasonic waves was generally about 0.1 mm, and so far, there has been no attempt to increase or decrease the depth of the ultrasonic waves. This is because the problem of lithium metal adhesion caused by the ultrasonic irradiation depth has not been recognized. However, the applicant of the present invention has obtained the optimal ultrasonic irradiation depth through repeated and diverse methods and attempts.

[0040] In the present invention, the ultrasonic irradiation depth is from 0.075 mm to 0.080 mm. If the ultrasonic irradiation depth is less than 0.075 mm, the ultrasonic irradiation depth is insufficient, and when removing the blanked lithium metal, the lithium metal may be torn instead of being separated according to the die shape. In addition, if the ultrasonic irradiation depth exceeds 0.080 mm, due to the excessive irradiation depth, even if the lithium metal is separated according to the die shape, the lithium metal is easily torn, and there is also a problem that the lithium metal adheres to the lower film, which may cause burrs at the electrode edge.

[0041] Therefore, by using the lithium metal release film of the present invention (i.e., the lower release film) and irradiating it with ultrasonic waves having a depth of 0.075 mm to 0.080 mm, lithium metal will not further adhere to the lower release film, making it easier to separate the lithium metal.

[0042] The lithium metal produced by the above "method for blanking lithium metal" can be used as the negative electrode active material of a lithium secondary battery. However, it is obvious that the present invention can also be applied to other fields that require blanking of lithium metal outside the battery field.

[0043] Based on the case where the lithium metal produced by the above "method for blanking lithium metal" is used as the negative electrode active material in a lithium secondary battery, the related secondary battery is described below.

[0044] If the lithium secondary battery is a lithium-sulfur battery, sulfur can be included as the positive electrode active material, and a sulfur-carbon composite material containing a carbon material can also be used as the positive electrode active material. If the lithium secondary battery is a lithium-ion battery, the positive electrode active material can include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), and lithium nickel cobalt manganese-based positive electrode active materials (or lithium NCM-based positive electrode active materials, or NCM-based lithium composite transition metal oxides, or high-Ni positive electrode materials). In addition to the above positive electrode active materials, the positive electrode can also include a binder and a conductive material.

[0045] The binder is a component that helps the adhesion of the positive electrode active material and the conductive material and the adhesion to the current collector. For example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(methyl)acrylate, poly(ethyl)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butene rubber, fluorinated rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof can be used, but are not limited thereto.

[0046] Relative to 100 parts by weight of the total weight of the positive electrode, the addition amount of the binder is usually 1 part by weight to 50 parts by weight, preferably 3 parts by weight to 15 parts by weight. If the content of the binder is less than 1 part by weight, the adhesion of the positive electrode material to the current collector may be insufficient, while if the content is greater than 50 parts by weight, although the adhesion can be improved, the content of the positive electrode active material decreases accordingly, resulting in a reduction in the cell capacity.

[0047] There is no particular limitation on the conductive material contained in the positive electrode, as long as it has excellent electrical conductivity, does not cause side reactions in the internal environment of the battery, and does not cause any chemical changes in the battery. Graphite or conductive carbon can be used as representatives. For example, one or a mixture of two or more of the following can be used, but it is not limited thereto: graphite, such as natural graphite, artificial graphite, etc.; carbon black, such as carbon black, acetylene black, Ketjen black, Denka black, thermal cracking carbon black, channel black, furnace black, lamp black, etc.; carbon-based materials having a crystal structure of graphene or graphite; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives.

[0048] With respect to 100 parts by weight of the total weight of the positive electrode, the addition amount of the conductive material is generally 0.5 parts by weight to 50 parts by weight, preferably 1 part by weight to 30 parts by weight. If the content of the conductive material is too small, less than 0.5 parts by weight, it is difficult to expect the effect of improving electrical conductivity, or the electrochemical characteristics of the battery may deteriorate. If the content of the conductive material is too high, more than 50 parts by weight, the amount of the positive electrode material can be relatively small, resulting in a decrease in capacity and energy density. The method of adding the conductive material to the positive electrode is not limited, and any conventional method known in the art can be used, such as coating the positive electrode material. Additionally, if necessary, a second conductive coating can be added to the positive electrode material instead of adding the above-mentioned conductive material.

[0049] In addition, the positive electrode can optionally add a filler as a component to suppress its swelling. Such fillers are not particularly limited as long as they can suppress the swelling of the electrode without causing chemical changes in the battery, and can be, for example, olefin polymers, such as polyethylene or polypropylene; fibrous materials, such as glass fibers or carbon fibers; and so on.

[0050] The positive electrode can be manufactured by dispersing and mixing the positive electrode material, binder, and conductive material in a dispersant (solvent) to form a slurry, coating it on the positive electrode current collector, and then drying and rolling it. NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, and their mixtures can be used as the dispersant, but it is not limited thereto.

[0051] The positive current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), In-doped SnO2 (ITO), F-doped SnO2 (FTO), and their alloys, as well as aluminum (Al) or stainless steel whose surface is treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not limited thereto. The positive current collector can be in the form of foil, film, sheet, blanked form, porous form, foam form, etc.

[0052] The negative electrode can be prepared according to conventional methods known in the art. For example, the negative electrode can be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and optionally a filler in a dispersant (solvent) to form a slurry, coating it on the negative current collector, and then drying and rolling. As the negative electrode active material, the punched lithium metal of the present invention can be applied, and a compound capable of reversibly inserting and extracting lithium can be used simultaneously. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc.; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal compounds capable of doping or dedoping lithium, such as SiO β (where 0 < β < 2), SnO2, vanadium oxide, or lithium vanadium oxide; or a composite material containing a metal compound and a carbonaceous material, such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof can be used. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, planar, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbead, mesophase pitch, and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0053] In addition, the binder and conductive material used for the negative electrode can be the same as those used for the positive electrode above. The negative current collector can include but is not limited to platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO2), FTO (F-doped SnO2), and their alloys, as well as copper (Cu) or stainless steel whose surface is treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The negative current collector can be in the form of foil, film, sheet, blanked form, porous form, foam form, etc.

[0054] As the separator, an olefin polymer (e.g., polyethylene, polypropylene) or glass fiber can be used, and its form can be a sheet, multi-layer, microporous membrane, woven fabric or non-woven fabric, but it is not limited thereto. However, porous polyethylene or a porous glass filter can be preferably used as the separator, and a porous glass filter is even more preferably used as the separator.

[0055] On the other hand, when using a solid electrolyte (e.g., an organic solid electrolyte or an inorganic solid electrolyte), such as a polymer, as the electrolyte, the solid electrolyte can also be used as the separator. Specifically, an insulating film having high ion permeability and mechanical strength is used. The pore diameter of the separator can generally be in the range of 0.01 μm to 10 μm, and the thickness can generally be in the range of 5 μm to 300 μm, but they are not limited thereto.

[0056] The electrolyte or electrolytic solution can include, but is not limited to: carbonates, esters, ethers or ketones as non-aqueous electrolytes (non-aqueous organic solvents), which are used alone or as a mixture of two or more. For example, non-amphoteric organic solvents such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, triphosphate, dibutyl ether, N-methyl-2-pyrrolidone, 1,2-dimethoxyethane, tetrahydrofuran derivatives (e.g., 2-methyltetrahydrofuran), dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate or ethyl propionate can be used, but it is not limited thereto.

[0057] A lithium salt (so-called non-aqueous electrolyte containing a lithium salt) can also be further added to the above electrolyte. The lithium salt includes lithium salts known in the art and well-dissolved in the non-aqueous electrolyte, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, and lithium imide, but not limited thereto. To improve charge and discharge characteristics, flame retardancy, etc., the (non-aqueous) electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, glycol diether compounds, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazoline, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. Optionally, it may also contain a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene to impart non-flammability, or it may also include carbon dioxide gas to improve high-temperature storage performance.

[0058] Alternatively, the secondary battery can be manufactured according to methods known in the art. For example, it can be manufactured by placing a porous separator between the positive electrode and the negative electrode and adding a non-aqueous electrolyte. The secondary battery of the present invention can be applied to a single cell to be used as a power source for small devices, and is particularly suitable as a unit cell in a battery module that is used as a power source for medium and large devices. In this regard, the present invention also provides a battery module that includes two or more secondary batteries electrically connected (in series or in parallel). Of course, the number of secondary batteries contained in the battery module can be changed considering the use and capacity of the battery module.

[0059] In addition, according to the technology in the art, the present invention provides a battery pack electrically connected to the battery module. The battery module and the battery pack can be used as a power source for one or more of the following medium and large devices: power tools; electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV); electric trucks; electric commercial vehicles; or power storage systems.

[0060] Although the present invention has been described with reference to the above preferred examples, those skilled in the art will readily understand that the present invention is not limited thereto and various modifications and changes can be made as long as they do not depart from the concepts and scope of the following patent claims.

[0061] [Example 1] Blanking lithium metal using a lower film coated with silicone

[0062] First, stack a 75-μm-thick lower release film (wherein, the entire surface of the PET substrate is coated with silicone), lithium metal (GF-60, Mg 3%), and a 40-μm-thick upper release film (PP) in sequence. Then, an ultrasonic horn is installed above the upper release film at intervals, and ultrasonic irradiation (Demo device, frequency: 28.5 KHz, horn deep: 0.075 mm) is carried out to blank the lithium metal. Among them, based on the total weight of 100% by weight of the lower release film, the PET substrate is coated with 5% by weight of silicone.

[0063] [Example 2] Blanking lithium metal using a lower film coated with silicone

[0064] The lithium metal is blanked in the same method as in Example 1 above, except that the ultrasonic irradiation depth (horn depth) is changed from 0.075 mm to 0.080 mm.

[0065] [Comparative Example 1] Blanking lithium metal using a conventional lower film

[0066] The lithium metal is blanked in the same method as in Example 1 above, except that the lower release film is replaced with a release film named 75OS-IR01 (Osung RF).

[0067] (*75OS-IR01: The composition is the same as that in Example 1 above, but based on the total 100% by weight of the lower release film, the silicone content coating the PET substrate is 1% by weight).

[0068] [Comparative Example 2] Blanking lithium metal using a conventional lower film

[0069] The lithium metal is blanked in the same method as in Comparative Example 1 above, except that the ultrasonic irradiation depth is changed from 0.075 mm to 0.080 mm.

[0070] [Comparative Example 3] Blanking lithium metal using a conventional lower film

[0071] The lithium metal is blanked in the same method as in Example 1 above, except that the lower release film is replaced with a release film named 75OS-PE-LH04 (Osung R.F.).

[0072] (*75OS-PE-LH04: The composition is the same as that in Example 1 above, but based on the total 100% by weight of the lower release film, the silicone content coating the PET substrate is 3% by weight).

[0073] [Comparative Example 4] Blanking lithium metal using a conventional lower film

[0074] The lithium metal was blanked in the same manner as in Comparative Example 3 above, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.080 mm.

[0075] [Comparative Example 5] Blanking lithium metal using a lower film coated with silicone

[0076] The lithium metal was blanked in the same manner as in Example 1 above, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.070 mm.

[0077] [Comparative Example 6] Blanking lithium metal using a lower film coated with silicone

[0078] The lithium metal was blanked in the same manner as in Example 1 above, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.090 mm.

[0079] [Experimental Example 1] Measurement of Peel Force

[0080] To measure the peel force of the lower release film itself used in Examples 1 and 2 and Comparative Examples 1 to 6 (i.e., the peel force between the PET substrate and the coating), each film was measured multiple times, and the results are shown in Table 1 below. For the measurement of the peel force, the AR-1000 product of chem.Instrument was used.

[0081] [Table 1]

[0082] Peeling force (gf / in) Example 1 8 to 12 Example 2 8 to 12 Comparative Example 1 60 to 80 Comparative Example 2 60 to 80 Comparative Example 3 30 to 40 Comparative Example 4 30 to 40 Comparative Example 5 8 to 12 Comparative Example 6 8 to 12

[0083] The measurement results show that the peel force of the lower release films used in Examples 1 and 2 and Comparative Examples 5 and 6 is 8 gf / in to 12 gf / in. After blanking the lithium metal, the lithium metal is easily separated from the lower film without adhering to the lower film. In other words, by measuring the peel force between the PET substrate and the coating on the lower release film, it was confirmed that coating the PET substrate with silicone prevented the lithium metal from adhering to the lower release film, even after blanking the lithium metal.

[0084] On the other hand, in Comparative Examples 1 to 4, it was observed that when a release film with a high peel force of 30 gf / in to 80 gf / in was used as the lower release film, the lithium metal and the bottom release film adhered and stuck together and were not easily detached.

[0085] Based on the above peel force measurement results, it can be seen that by using a lower release film with a silicone coating having a specific content to reduce the peel force, the lithium metal is not stuck even after ultrasonic irradiation and is thus easily peeled off.

[0086] [Example 2] Observation of Adhesion of Lithium Metal

[0087] In Examples 1 and 2 and Comparative Examples 1 to 6, after punching the lithium metal, the lithium metal was separated from the upper film and the lower film, and whether the lithium metal adhered to the upper film and the lower film was visually observed. The results are shown in Table 2 below.

[0088] [Table 2]

[0089] Upper film adhesion Lower film adhesion Edge shrinkage Blankable (detachable) Example 1 × × ○ ○ Example 2 × × ○ ○ Comparative Example 1 × ○ △ ○ Comparative Example 2 × ○ ○ ○ Comparative Example 3 × ○ ○ ○ Comparative Example 4 × ○ ○ ○ Comparative Example 5 × × × × Comparative Example 6 ○ ○ ○ ×

[0090] It was observed that in Example 1 and Example 2, when punching the lithium metal using the silicone-coated lower film, the lithium metal did not adhere to the upper film and the lower film, which was beneficial for separation. Figure 2 (a) in is the image of the lithium metal separated from the lower film in Example 1, Figure 2 and (b) in is the image of the lower film after the lithium metal is separated from the lower film in Example 1. Figure 3 (a) in is the image of the punching shape of the lithium metal separated from the lower film in Example 2, Figure 3 and (b) in is the image of the lower film after the punched lithium metal is separated from the lower film in Example 2, as Figure 2 and Figure 3 shown. When the lithium metal was separated from the lower film, good separation was confirmed, no stains appeared, and it was observed that there was no problem with punching.

[0091] In the case of Comparative Examples 5 and 6, when punching the lithium metal using the same silicone-coated lower film as in Examples 1 and 2, the ultrasonic irradiation depth exceeded the scope of the present invention, and the lithium metal adhered to the film, or even if it did not adhere, the lithium metal could not be normally separated from the film. Figure 8 (a) in is the image of the punching shape of the lithium metal separated from the lower film in Comparative Example 5, Figure 8 and (b) in is the image of the lower film after the lithium metal is separated from the lower film in Comparative Example 5. Figure 9 (a) in is the image of the punching shape of the lithium metal separated from the lower film in Comparative Example 6, Figure 9 and (b) in is the image of the lower film after the lithium metal is separated from the lower film in Comparative Example 6.

[0092] As Figure 8 shown, in Comparative Example 5, the lithium metal was well separated from the lower film, no stains appeared, but the ultrasonic irradiation depth was insufficient, and the lithium metal could not be properly punched. This resulted in a tearing phenomenon when removing the punched lithium metal, and it was not separated according to the shape of the mold (electrode). As Figure 9 shown, in Comparative Example 6, the ultrasonic irradiation depth was too deep, resulting in the lower film and the lithium metal adhering to each other, and burrs appeared at the edge of the electrode. In addition, it was observed that the lithium metal adhered to the lower film and was not separated from the lower film. Moreover, when attempting to manually separate the lithium metal from the lower film, the lithium metal was easily torn.

[0093] In Comparative Examples 1 to 4, a conventional lower film was used, and there were common problems of lithium metal adhering to the lower film. Figure 4 (a) in it is an image of the blanking shape after the separation of lithium metal and the lower film in Comparative Example 1. Figure 4 (b) in it is an image of the lower film after the separation of lithium metal and the lower film in Comparative Example 1. Figure 5 (a) in it is an image of the blanking shape after the separation of lithium metal and the lower film in Comparative Example 2. Figure 5 (b) in it is an image of the lower film after the separation of lithium metal and the lower film in Comparative Example 2. Figure 6 (a) in it is an image of the blanking shape after the separation of lithium metal and the lower film in Comparative Example 3. Figure 6 (b) in it is an image of the lower film after the separation of lithium metal and the lower film in Comparative Example 3. Figure 7 (a) in it is an image of the blanking shape after the separation of lithium metal and the lower film in Comparative Example 4. Figure 7 (b) in it is an image of the lower film after the separation of lithium metal and the lower film in Comparative Example 4.

[0094] As Figure 4 shown, in Comparative Example 1, the separation effect after blanking was good, but it can be seen that part of the lithium metal adhered to the lower film. As Figure 5 shown, in Comparative Example 2, a large amount of lithium metal after blanking adhered to the lower film and was particularly difficult to remove, while the remaining lithium metal adhered to the upper film and was separable. As Figure 6 and Figure 7 shown, Comparative Examples 3 and 4 confirmed that even when the ultrasonic irradiation depth was within the scope of the present invention, the lithium metal still adhered to the lower film. Therefore, it can be seen that even if the substrate is coated with a silicone coating, the purpose of the present invention can only be achieved by coating within the content range of the present invention.

Claims

1. A lithium metal punching film, which is disposed under the lithium metal when the lithium metal is cut using ultrasonic waves, the film comprising a PET substrate and a silicone coating on a surface of the PET substrate.

2. The lithium metal punching film according to claim 1, wherein The content of silicone in the silicone coating layer is 4 wt % to 50 wt % based on the total weight of the lithium metal punching film.

3. The lithium metal punching film according to claim 1, wherein Based on the thickness of the PET substrate of 50 μm, the thickness of the silicone coating layer is 0.01 μm to 25 μm.

4. The lithium metal punching film according to claim 1, wherein The silicone coating includes at least one of alkenyl polysiloxane and hydrogen polysiloxane.

5. The lithium metal punching film according to claim 1, wherein The surface of the silicone coating is flat or in an embossed form with a plurality of protrusions.

6. The lithium metal punching film according to claim 1, wherein The silicone coating also includes a cross-linking agent.

7. A method for punching lithium metal, comprising the following steps: (a) stacking the lithium metal punching film according to claim 1, lithium metal, one or more molds and an upper release film in sequence; as well as (b) An ultrasonic horn is disposed above the upper release film at intervals, and then ultrasonic irradiation is performed to cut the lithium metal into a shape identical to that of the mold.

8. The method for punching lithium metal according to claim 7, wherein: The ultrasonic irradiation depth is 0.075 mm to 0.080 mm.

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