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

Abstract

Disclosed are a film for lithium metal punching and a lithium metal punching method using same, wherein the film facilitates the separation of a lithium metal by preventing the lithium metal from adhering to a lower release film provided below the lithium metal when the lithium metal is punched by ultrasonic cutting. The film for lithium metal punching is positioned below the lithium metal when the lithium metal is subjected to ultrasonic cutting, and comprises: a PET base material; and a silicon coating layer positioned on the surface of the PET base material.

Description

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

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0084812, filed June 30, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a release film provided on the lower part of lithium metal when lithium metal is punched out using ultrasonic cutting equipment, and more specifically, to a lithium metal punching film that prevents lithium metal from sticking to a lower release film provided on the lower part of lithium metal when lithium metal is punched out using an ultrasonic cutting method, and a lithium metal punching method using the same.

[0003] As interest in energy storage technology grows, its applications expand to include the energy storage of mobile phones, tablets, laptops, and camcorders, as well as electric vehicles (EVs) and hybrid electric vehicles (HEVs). Consequently, research and development on electrochemical devices are steadily increasing. Electrochemical devices are receiving the most attention in this regard, and within these fields, the development of rechargeable lithium-based secondary batteries, such as lithium-sulfur batteries, lithium-ion batteries, and lithium-ion polymer batteries, has become a focus of interest. Recently, research and development on novel electrode and battery designs has been focused on improving capacity density and specific energy.

[0004] Lithium secondary batteries typically include lithium metal, which has a very high energy density, as the anode active material. To apply lithium metal as the anode active material, a process is required to stamp the lithium metal into a specific size. There are two general methods for stamping lithium metal: contact and non-contact. Contact stamping can be categorized into a mold stamping method, which uses a punch in the form of an electrode, and a method using an ultrasonic horn in the form of an electrode. Contact stamping requires caution, as the material and the equipment come into direct contact. This can damage the material and / or contaminate the equipment. Non-contact stamping methods include laser stamping, which cuts without directly contacting the material, minimizing material damage and contamination. However, depending on the material used, laser cutting can cause oxidation and dust generation.

[0005] For the materials used in the present invention, laser cutting is preferred to minimize material damage. However, due to safety concerns, laser cutting is not an appropriate punching method because lithium metal can oxidize and generate dust at the point of contact with the material during laser irradiation. Therefore, conditions are required to eliminate the above problems by utilizing an ultrasonic punching method that allows direct contact but minimizes material contamination on the equipment and causes less material damage.

[0006] Figure 1 is a schematic diagram illustrating a method for punching lithium metal using ultrasonic waves. That is, the punching method using ultrasonic waves cuts lithium metal using ultrasonic waves while positioning release films (upper film, lower film) on the upper and lower portions of the lithium metal, respectively, as illustrated in Figure 1 (an electrode-shaped mold is placed on top of the upper film).

[0007] At this time, the upper film is used to prevent lithium metal from sticking to the ultrasonic horn. Furthermore, the lower film is used to prevent ultrasonic waves from penetrating the lithium metal and damaging the lowermost stage when cutting the lithium metal. However, in this case, the lithium metal sticks to the lower film during ultrasonic cutting, making it difficult to separate. Therefore, there is a need to find a method for cutting lithium metal using ultrasonic cutting, but preventing the lithium metal from sticking to the lower film, thereby facilitating its separation.

[0008] Accordingly, the purpose of the present invention is to provide a lithium metal punching film that does not allow lithium metal to stick to a lower release film provided on the lower side of the lithium metal when punching lithium metal using an ultrasonic cutting method, and a lithium metal punching method using the same.

[0009] In order to achieve the above object, the present invention provides a lithium metal punching film comprising a PET base material, which is positioned below the lithium metal when the lithium metal is ultrasonically cut; and a silicon coating layer positioned on the surface of the PET base material.

[0010] In addition, the present invention provides a method for punching lithium metal, comprising the steps of: (a) sequentially stacking the lithium metal punching film (or lower release film), lithium metal, one or more molds, and an upper release film; and (b) positioning an ultrasonic horn spaced apart from the upper portion of the upper release film and then irradiating ultrasonic waves to cut the lithium metal into a shape identical to the shape of the mold.

[0011] According to the lithium metal punching film and the lithium metal punching method using the same according to the present invention, when the lithium metal is punched using an ultrasonic cutting method, the lithium metal does not stick to the lower release film provided at the bottom of the lithium metal, so that the lithium metal can be easily separated.

[0012] Figure 1 is a schematic diagram showing the process for striking lithium metal using ultrasound.

[0013] Figure 2a is an image of the punched shape after the lithium metal of Example 1 is separated from the lower film, and Figure 2b is an image of the lower film after the punched lithium metal of Example 1 is separated from the lower film.

[0014] Figure 3a is an image of the punched shape after the lithium metal of Example 2 is separated from the lower film, and Figure 3b is an image of the lower film after the punched lithium metal of Example 2 is separated from the lower film.

[0015] Figure 4a is an image of the punched shape after the lithium metal of Comparative Example 1 is separated from the lower film, and Figure 4b is an image of the lower film after the punched lithium metal of Comparative Example 1 is separated from the lower film.

[0016] Figure 5a is an image of the punched shape after the lithium metal of Comparative Example 2 is separated from the lower film, and Figure 5b is an image of the lower film after the punched lithium metal of Comparative Example 2 is separated from the lower film.

[0017] Figure 6a is an image of the punched shape after the lithium metal of Comparative Example 3 is separated from the lower film, and Figure 6b is an image of the lower film after the punched lithium metal of Comparative Example 3 is separated from the lower film.

[0018] Figure 7a is an image of the punched shape after the lithium metal of Comparative Example 4 is separated from the lower film, and Figure 7b is an image of the lower film after the punched lithium metal of Comparative Example 4 is separated from the lower film.

[0019] Figure 8a is an image of the punched shape after the lithium metal of Comparative Example 5 is separated from the lower film, and Figure 8b is an image of the lower film after the punched lithium metal of Comparative Example 5 is separated from the lower film.

[0020] Figure 9a is an image of the punched shape after the lithium metal of Comparative Example 6 is separated from the lower film, and Figure 9b is an image of the lower film after the punched lithium metal of Comparative Example 6 is separated from the lower film.

[0021] Hereinafter, the present invention will be described in detail.

[0022] A lithium metal cutting film according to the present invention is positioned below the lithium metal when the lithium metal is ultrasonically cut, and includes a PET base material and a silicon coating layer positioned on the surface of the PET base material.

[0023] Lithium secondary batteries typically include lithium metal, which has a very high energy density, as the anode active material. To apply lithium metal as the anode active material, it must first be pressed into a specific size. Methods for pressing lithium metal include contact and non-contact pressing. Contact pressing can be categorized into a die pressing method, which uses a punch (an electrode-shaped tool) to press the metal, and a method using an ultrasonic horn (an electrode-shaped tool). Contact pressing requires careful processing, as the material and the equipment come into direct contact. This can damage the material and potentially contaminate the equipment. Non-contact pressing methods include laser pressing, which cuts the material without direct contact, minimizing material damage and contamination. However, depending on the material used, laser cutting can cause oxidation and dust generation.

[0024] For the materials used in the present invention, laser cutting is preferred to minimize material damage. However, due to safety concerns, laser cutting is not an appropriate punching method because lithium metal can oxidize and generate dust at the point of contact with the material during laser irradiation. Therefore, conditions are required to eliminate the above problems by utilizing an ultrasonic punching method that allows direct contact but minimizes material contamination on the equipment and causes less material damage.

[0025] The ultrasonic punching method, as illustrated in Fig. 1, cuts the lithium metal using ultrasonic waves while positioning release films (upper film, lower film) on the upper and lower portions of the lithium metal, respectively (an electrode-shaped mold is placed on top of the upper film). At this time, the upper film is made of polypropylene (PP) to prevent the lithium metal from sticking to the ultrasonic horn. The lower film is mainly made of polyethylene terephthalate (PET) to prevent the ultrasonic waves from penetrating the lithium metal and damaging the lowermost stage when cutting the lithium metal. However, in this case, since the ultrasonic horn penetrates not only the lithium metal but also the lower film during ultrasonic cutting, there is a problem that the lithium metal is smeared on the ultrasonic horn or the lithium metal sticks to the lower film and is not easily separated. Therefore, the present applicant has developed a method for cutting the lithium metal using an ultrasonic cutting method, but preventing the lithium metal from sticking to the lower film, thereby making it easy to separate the lithium metal.

[0026] A film for lithium metal cutting according to the present invention, more specifically, a 'lower film for lithium metal cutting', is positioned below the lithium metal when the lithium metal is ultrasonically cut, and includes a PET (polyethylene terephthalate) base material and a silicon coating layer positioned on the surface of the PET base material.

[0027] The above PET base material constitutes a conventional 'lower film for lithium metal punching', and the 'lower film for lithium metal punching' of the present invention is characterized by having a silicone coating layer positioned on the surface of the PET base material. That is, when the surface of the PET base material is coated with silicone as described above, when the lithium metal is punched using an ultrasonic cutting method, the lithium metal does not stick to the lower (release) film provided on the lower side of the lithium metal.

[0028] The above silicone coating layer may be located on only a portion of the surface of the PET base material or may be located on the entire surface of the PET base material. However, in order to prevent lithium metal from sticking and to allow easy separation, it is preferable that the silicone coating layer be located on the entire surface of the PET base material.

[0029] The content of silicon included in the silicon coating layer may be 4 to 50 wt%, preferably 4 to 30 wt%, and more preferably 5 to 20 wt%, based on the total weight of the lithium metal punching film. If the content of silicon included in the silicon coating layer is less than 4 wt% based on the total weight of the lithium metal punching film, the advantage obtained by coating silicon on the base material may not appear. In addition, if the content of silicon included in the silicon coating layer exceeds 50 wt% based on the total weight of the lithium metal punching film, no further effect may appear.

[0030] In addition, the thickness of the silicone coating layer may be 0.01 to 25 ㎛, preferably 0.02 to 20 ㎛, and more preferably 0.03 to 20 ㎛, based on a thickness of 50 ㎛ of the PET base material. If the thickness of the silicone coating layer is less than 0.01 ㎛ based on a thickness of 50 ㎛ of the PET base material, the advantage obtained by coating silicone on the base material may not appear. In addition, if the thickness of the silicone coating layer exceeds 25 ㎛ based on a thickness of 50 ㎛ of the PET base material, no further effect may appear.

[0031] The silicone included in the above silicone coating layer may be selected from the group consisting of water-based silicone, acetic acid-based oil-based silicone, non-acetic acid-based oil-based silicone, bio-silicone, heat-resistant silicone, and urethane silicone. In addition, at least one of alkenyl polysiloxane and hydrogen polysiloxane may be most advantageous in achieving the purpose of the present invention.

[0032] In addition, the surface of the silicon coating layer may be flat or may have an embossed shape with multiple protrusions formed. However, considering that uniform cutting characteristics are required when cutting lithium metal, it may be more desirable to form the surface of the silicon coating layer flat.

[0033] Meanwhile, the silicone coating layer may further include a cross-linking agent as needed. When the cross-linking agent is included in the silicone coating layer, the cross-linking agent may be included in an amount of 0.001 to 0.8 parts by weight based on 100 parts by weight of the total weight of the lithium metal stamping film. At this time, the surface properties and peeling tendency of the film may vary depending on the degree of cross-linking. In the case of a silicone release film with a high cross-linking density, the physical penetration of the adhesive can be blocked, thereby preventing the phenomenon of an increase in peeling force variation over time. However, since the film is hard, shock absorption is not smooth during peeling, and an unstable peeling tendency may be exhibited. On the other hand, in the case of a release film with a low cross-linking density, a relatively soft film is formed, so shock absorption is smooth during peeling and a stable peeling tendency is exhibited, but a problem may occur due to an increase in peeling force variation over time due to physical penetration of the adhesive.

[0034] Next, a method for punching lithium metal using a lithium metal punching film according to the present invention will be described. The method for punching lithium metal using the lithium metal punching film includes (a) a step of sequentially stacking the lithium metal punching film (or lower release film) of the present invention described above, lithium metal, at least one mold, and an upper release film, and (b) a step of positioning an ultrasonic horn spaced apart from the upper portion of the upper release film and then irradiating ultrasonic waves to cut the lithium metal into a shape identical to the shape of the mold.

[0035] In the method for punching lithium metal using the lithium metal punching film of the present invention, the order of laminating the substrates and the process of irradiating ultrasonic waves are no different from conventional methods. However, as previously explained, the present invention differs from conventional methods in that it is applied as a lower film. In addition, the method for punching lithium metal using the lithium metal punching film also has a key feature in the depth of ultrasonic irradiation (horn deep), which will be described below.

[0036] In other words, when using ultrasound to strike lithium metal, the ultrasound irradiation depth was generally set to approximately 0.1 mm, and to this day, no attempt has been made to increase or decrease the ultrasound irradiation depth. This is because the problem of lithium metal sticking according to the ultrasound irradiation depth is not recognized. However, the present applicant has derived the optimal ultrasound irradiation depth through repeated and diverse approaches and trials.

[0037] In the present invention, the ultrasonic irradiation depth is 0.075 to 0.080 mm. If the ultrasonic irradiation depth is less than 0.075 mm, the depth of the ultrasonic waves is not sufficient, and when the punched lithium metal is removed, the lithium metal may tear instead of being separated according to the shape of the mold. In addition, if the ultrasonic irradiation depth exceeds 0.080 mm, the irradiation depth is excessively deep, and even if the lithium metal is separated according to the shape of the mold, it may be easily torn, and furthermore, the lithium metal may stick to the lower film, and burrs may occur throughout the electrode edge.

[0038] Therefore, by irradiating ultrasonic waves at a depth of 0.075 to 0.080 mm while using the lithium metal plating film (i.e., the lower release film) of the present invention, the lithium metal is prevented from sticking to the lower release film, so that the lithium metal can be separated more easily.

[0039] Furthermore, the lithium metal produced through the above "lithium metal stamping method" can be applied as an anode active material for lithium-based secondary batteries. However, it should be noted that the present invention can also be applied to fields other than batteries where lithium metal stamping is necessary.

[0040] Below, a description is given of a related secondary battery based on the case where lithium metal produced through the above 'lithium metal punching method' is applied as an anode active material of a lithium-based secondary battery.

[0041] If the above lithium secondary battery is a lithium-sulfur battery, the positive electrode active material may include sulfur, and a sulfur-carbon composite including carbon material may also be applied as the positive electrode active material. If the above lithium secondary battery is a lithium ion battery, the positive electrode active material may 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 material (or lithium NCM-based positive electrode active material, or NCM-based lithium composite transition metal oxide, or High Ni positive electrode material). In addition, the positive electrode further includes a binder and a conductive material in addition to the positive electrode active material.

[0042] The above binder is a component that assists in the bonding of the positive electrode active material and the conductive material and the bonding to the current collector, and includes, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, One or more selected from the group consisting of hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof may be used, but is not necessarily limited thereto.

[0043] The above binder is typically added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the binder is less than 1 part by weight, the adhesive strength between the positive electrode material and the current collector may become insufficient, and if it exceeds 50 parts by weight, the adhesive strength may be improved, but the content of the positive electrode material may be reduced accordingly, which may lower the battery capacity.

[0044] The conductive material included in the above positive electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the battery, does not cause chemical changes in the battery, and has excellent electrical conductivity. Representative examples thereof include graphite or conductive carbon, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, and lamp black; carbon-based materials having a crystal structure of graphene or graphite; conductive fibers such as carbon fiber and metal fiber; fluorinated carbon; metal powder such as aluminum powder and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; which may be used alone or in combination of two or more thereof, but are not necessarily limited thereto.

[0045] The conductive material is typically added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is too low, less than 0.5 parts by weight, it is difficult to expect an effect of improving electrical conductivity or the electrochemical characteristics of the battery may deteriorate. If the content of the conductive material is too high, exceeding 50 parts by weight, the amount of positive electrode material is relatively small, which may result in a decrease in capacity and energy density. The method of including the conductive material in the positive electrode is not particularly limited, and conventional methods known in the art, such as coating the positive electrode material, may be used. In addition, if necessary, the addition of the conductive material as described above may be replaced by adding a second conductive coating layer to the positive electrode material.

[0046] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes to the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0047] The positive electrode can be manufactured by dispersing and mixing the above positive electrode material, binder, and conductive material in a dispersion medium (solvent) to make a slurry, applying the slurry on a positive electrode current collector, and then drying and rolling. The dispersion medium may include, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof.

[0048] As the positive electrode current collector, 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), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited thereto. The positive electrode current collector may have a form such as a foil, a film, a sheet, a punched form, a porous body, or a foam body.

[0049] The negative electrode can be manufactured according to a conventional method known in the art. For example, a slurry may be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and, if necessary, a filler in a dispersion medium (solvent), and then applying the slurry on a negative electrode current collector, followed by drying and rolling to manufacture the negative electrode. As the negative electrode active material, the lithium metal formed by the present invention may be applied, and a compound capable of reversible intercalation and deintercalation of lithium may be used together. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic 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; SiO β (0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, the carbon material may be both low-crystalline carbon and high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0050] In addition, the binder and conductive material used in the negative electrode may be the same as those described above for the positive electrode. As the negative electrode current collector, 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 alloys thereof, as well as copper (Cu) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but are not necessarily limited thereto. The form of the negative electrode current collector may be in the form of a foil, a film, a sheet, a punched body, a porous body, a foam, etc.

[0051] As a separation membrane, olefin polymers such as polyethylene and polypropylene, glass fibers, etc. can be used in the form of sheets, multi-layer films, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber non-woven fabric (glass filter) as a separation membrane, and it may be more preferable to use porous glass filter (glass fiber non-woven fabric) as a separation membrane.

[0052] Meanwhile, when a solid electrolyte such as a polymer (e.g., an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also function as a separator. Specifically, a thin insulating film with high ion permeability and mechanical strength is used. The pore diameter of the separator may generally range from 0.01 to 10 μm, and the thickness may generally range from 5 to 300 μm, but is not limited thereto.

[0053] As the above electrolyte or electrolyte solution, a non-aqueous electrolyte (non-aqueous organic solvent) such as carbonate, ester, ether or ketone may be used alone or in a mixture of two or more, but is not necessarily limited thereto. For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, propionic acid Non-protic organic solvents such as ethyl may be used, but are not necessarily limited thereto.

[0054] The above electrolyte can be used by adding a lithium salt (so-called lithium salt-containing non-aqueous electrolyte), and the lithium salt may be a known one that is easy to dissolve in a non-aqueous electrolyte, for example, 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 carboxylic acid, lithium tetraphenylborate, lithium imide, etc., but are not necessarily limited thereto. For the purpose of improving charge / discharge characteristics, flame retardancy, etc., the above (non-aqueous) electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, glyme compounds, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. If necessary, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluorooxide may be further included to provide incombustibility, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

[0055] Meanwhile, secondary batteries can be manufactured according to conventional methods in the art. For example, they can be manufactured by inserting a porous separator between the positive and negative electrodes and injecting a non-aqueous electrolyte. The secondary battery according to the present invention can be applied to battery cells used as power sources for small devices, and is particularly suitable for use as a unit cell of a battery module, which is a power source for medium- to large-sized devices. In this regard, the present invention also provides a battery module including two or more secondary batteries electrically connected (in series or parallel). The number of secondary batteries included in the battery module can be adjusted in various ways, taking into account the purpose and capacity of the battery module, etc.

[0056] Furthermore, the present invention provides a battery pack in which the battery modules are electrically connected according to conventional techniques in the field. The battery modules and battery packs can be used as power sources for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric trucks; electric commercial vehicles; or power storage systems, but are not necessarily limited thereto.

[0057] Although the present invention has been described through preferred embodiments as described above, it will be readily understood by those skilled in the art that the present invention is not limited thereto, and various modifications and variations are possible without departing from the concept and scope of the patent claims set forth below.

[0058] [Example 1] Lithium metal plating using a silicon-coated lower film

[0059] First, a 75 ㎛ thick lower release film coated with silicone over the entire surface of a PET base material, lithium metal (GF-60, Mg 3%), and a 40 ㎛ thick upper release film (PP) were sequentially laminated. Next, an ultrasonic horn was positioned spaced apart from the upper part of the upper release film and then ultrasonic waves were irradiated (Demo equipment, frequency: 28.5 KHz, horn depth: 0.075 mm) to pierce the lithium metal. Meanwhile, the silicone was coated on the PET base material in an amount of 5 wt% based on 100 wt% of the total weight of the lower release film.

[0060] [Example 2] Lithium metal plating using a silicon-coated lower film

[0061] Lithium metal was smelted in the same manner as in Example 1, except that the ultrasonic irradiation depth (Horn deep) was changed from 0.075 mm to 0.080 mm.

[0062] [Comparative Example 1] Lithium metal stamping using a conventional lower film

[0063] Lithium metal was stamped in the same manner as in Example 1, except that the lower release film was changed to a release film having the product name 75OS-IR01 (Osung RF).

[0064] (* 75OS-IR01: The components are the same as in Example 1 above, but the content of silicone coated on the PET base material is 1 wt% based on 100 wt% of the total weight of the lower release film.)

[0065] [Comparative Example 2] Lithium metal stamping using a conventional lower film

[0066] Lithium metal was pierced in the same manner as in Comparative Example 1, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.080 mm.

[0067] [Comparative Example 3] Lithium metal stamping using a conventional lower film

[0068] Lithium metal was stamped out in the same manner as in Example 1, except that the lower release film was changed to a release film having the product name 75OS-PE-LH04 (Osung RF).

[0069] (* 75OS-PE-LH04: The components are the same as in Example 1 above, but the content of silicone coated on the PET base material is 3 wt% based on 100 wt% of the total weight of the lower release film.)

[0070] [Comparative Example 4] Lithium metal stamping using a conventional lower film

[0071] Lithium metal was pierced in the same manner as in Comparative Example 3, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.080 mm.

[0072] [Comparative Example 5] Lithium metal plating using a silicon-coated lower film

[0073] Lithium metal was smelted in the same manner as in Example 1, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.070 mm.

[0074] [Comparative Example 6] Lithium metal plating using a silicon-coated lower film

[0075] Lithium metal was smelted in the same manner as in Example 1, except that the ultrasonic irradiation depth was changed from 0.075 mm to 0.090 mm.

[0076] [Experimental Example 1] Measurement of the peel strength of a different type

[0077] In order to determine the release peel strength of the lower release film itself (i.e., the release peel strength between the PET base material and the coating layer) used in Examples 1 and 2 and Comparative Examples 1 to 6, each was measured several times, and the results are shown in Table 1 below. The AR-1000 product from Chem. Instrument was used to measure the peel strength.

[0078] Peeling force (gf / in) Examples 18-12 Examples 28-12 Comparative Examples 160-80 Comparative Examples 260-80 Comparative Examples 330-40 Comparative Examples 430-40 Comparative Examples 58-12 Comparative Examples 68-12

[0079] As a result of the measurement, the lower release film used in Examples 1 and 2 and Comparative Examples 5 and 6 had a release peel strength of 8 to 12 gf / in, which means that the lithium metal did not stick to the lower film after the lithium metal was punched out and was easily separated. That is, as a result of measuring the release peel strength between the PET base material and the coating layer on the lower release film, it was confirmed that when silicone was coated on the PET base material, the lithium metal and the lower release film did not stick well even after the lithium metal was punched out.

[0080] On the other hand, Comparative Examples 1 to 4 had a release strength of 30 to 80 gf / in, and when a release film with a high release strength was used as the lower release film, it was confirmed that the lithium metal and the lower release film were adhered and adhered together and did not come off easily.

[0081] Through the above results of the measurement of the release force, it can be seen that when a lower release film with a lower release force through a silicone coating of a specific content is used, lithium metal does not stick even after ultrasonic irradiation, making it easy to peel.

[0082] [Experimental Example 2] Observation of Lithium Metal Adhesion

[0083] After the lithium metal was formed in Examples 1 and 2 and Comparative Examples 1 to 6, the lithium metal was separated from the upper and lower films, and whether the lithium metal was adhered to the upper and lower films was observed with the naked eye. The results are shown in Table 2 below.

[0084] Upper film adhesion Lower film adhesion Edge shrinkage Punching possible (separation) Example 1××○○ Example 2××○○ Comparative example 1×○△○ Comparative example 2×○○○ Comparative example 3×○○○ Comparative example 4×○○○ Comparative example 5×××× Comparative example 6○○○×

[0085] As a result of the observation, Examples 1 and 2, in which lithium metal was punched out using a silicon-coated lower film, showed that the lithium metal did not stick to either the upper or lower film, making separation easy. Fig. 2a is an image of the punched shape after the lithium metal of Example 1 was separated from the lower film, and Fig. 2b is an image of the lower film after the punched lithium metal of Example 1 was separated from the lower film. Fig. 3a is an image of the punched shape after the lithium metal of Example 2 was separated from the lower film, and Fig. 3b is an image of the lower film after the punched lithium metal of Example 2 was separated from the lower film. As shown in Figs. 2 and 3, it was confirmed that the lithium metal was well separated without any smearing when separated from the lower film, and it was also observed that there was no problem with the punching.

[0086] In Comparative Examples 5 and 6, in which lithium metal was punched out using a lower film coated with silicone in the same manner as Examples 1 and 2, the depth of ultrasonic irradiation was outside the scope of the present invention, and the lithium metal was adhered to the film, or even if it was not adhered, it was impossible to normally separate the lithium metal from the film. Fig. 8(a) is an image of the punched shape after the lithium metal of Comparative Example 5 was separated from the lower film, and Fig. 8(b) is an image of the lower film after the punched lithium metal of Comparative Example 5 was separated from the lower film. Fig. 9(a) is an image of the punched shape after the lithium metal of Comparative Example 6 was separated from the lower film, and Fig. 9(b) is an image of the lower film after the punched lithium metal of Comparative Example 6 was separated from the lower film.

[0087] As shown in Fig. 8, in Comparative Example 5, when the lithium metal was peeled off from the lower film, it was well separated without any sticking, but the depth of ultrasonic irradiation was not deep enough, so the lithium metal was not normally punched out. In addition, because the depth of ultrasonic irradiation was not deep enough, when peeling off the punched lithium metal, it was not separated according to the shape of the mold (electrode), so a tearing phenomenon occurred. As shown in Fig. 9, in Comparative Example 6, the depth of ultrasonic irradiation was excessively deep, so the lower film and the lithium metal were stuck together, and as a result, burrs occurred throughout the electrode edge. In addition, it was confirmed that the lithium metal was not separated from the lower film but was stuck together. In addition, when the lithium metal was tried to be separated from the lower film by hand with force, the lithium metal was easily torn.

[0088] All of Comparative Examples 1 to 4 using a conventional lower film had a common problem in that the lithium metal was adhered to the lower film. Fig. 4(a) is a punched shape image after the lithium metal of Comparative Example 1 was separated from the lower film, and Fig. 4(b) is a lower film image after the punched lithium metal of Comparative Example 1 was separated from the lower film. Fig. 5(a) is a punched shape image after the lithium metal of Comparative Example 2 was separated from the lower film, and Fig. 5(b) is a lower film image after the punched lithium metal of Comparative Example 2 was separated from the lower film. Fig. 6(a) is a punched shape image after the lithium metal of Comparative Example 3 was separated from the lower film, and Fig. 6(b) is a lower film image after the punched lithium metal of Comparative Example 3 was separated from the lower film. Figure 7a is an image of the punched shape after the lithium metal of Comparative Example 4 is separated from the lower film, and Figure 7b is an image of the lower film after the punched lithium metal of Comparative Example 4 is separated from the lower film.

[0089] As shown in Fig. 4, in Comparative Example 1, separation was relatively good after punching, but it was confirmed that some lithium metal was attached to the lower film. As shown in Fig. 5, in Comparative Example 2, a large amount of the punched lithium metal was attached to the lower film, and there were parts that were particularly difficult to separate, and the remaining lithium metal was attached to the upper film and could be separated. As shown in Figs. 6 and 7, in Comparative Examples 3 and 4, it was confirmed that lithium metal was attached to the lower film even though the ultrasonic irradiation depth was within the scope of the present invention. Therefore, it can be seen that even if a silicone coating is applied to the base material, the coating must be done in an amount within the scope of the present invention to achieve the purpose of the present invention.

Claims

1. A film for cutting lithium metal, comprising a PET base material and a silicon coating layer located on the surface of the PET base material, which is positioned below the lithium metal when cutting the lithium metal with ultrasonic waves.

2. A lithium metal punching film according to claim 1, characterized in that the content of silicon included in the silicon coating layer is 4 to 50 wt% with respect to the total weight of the lithium metal punching film.

3. A film for lithium metal punching, characterized in that, in claim 1, the thickness of the silicone coating layer is 0.01 to 25 ㎛ based on a thickness of 50 ㎛ of the PET base material.

4. A film for lithium metal plating, characterized in that the silicon coating layer comprises at least one of alkenyl polysiloxane and hydrogen polysiloxane according to claim 1.

5. A film for lithium metal stamping, characterized in that the surface of the silicone coating layer according to claim 1 is flat or has an embossed shape with a plurality of protrusions formed thereon.

6. A film for lithium metal plating, characterized in that the silicon coating layer further comprises a crosslinking agent according to claim 1. 7.(a) A step of sequentially laminating the lithium metal film of claim 1, lithium metal, one or more molds, and the upper release film; and (b) A method for punching lithium metal, comprising the step of: positioning an ultrasonic horn at a distance from the upper portion of the upper release film and then irradiating ultrasonic waves to cut the lithium metal into a shape identical to the shape of the mold.

8. A method for punching lithium metal, characterized in that the ultrasonic irradiation depth in claim 7 is 0.075 to 0.080 mm.

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