Method for manufacturing aluminum thin film, aluminum thin film, positive electrode including the same, and lithium secondary battery

Abstract

The method for producing an aluminum thin film according to the present invention includes the steps of: (A) cutting an aluminum thin film and winding up the cut aluminum thin film in one direction; and (B) heat-treating a cut surface of the wound aluminum thin film roll, including the cut portion of the aluminum thin film, wherein the heat treatment can be carried out so as to satisfy the following formula (1), where T (unit: °C) is the heat treatment temperature and t (unit: seconds) is the heat treatment time. Formula (1): -0.21t+150≦T≦-0.21t+210

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0184417, filed December 26, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing an aluminum thin film, an aluminum thin film, a positive electrode including the same, and a lithium secondary battery, and more particularly to a method for manufacturing an aluminum thin film that is heat-treated over a specific temperature and time range so as to have a desired tensile strength and average residual stress value, an aluminum thin film, a positive electrode including the same, and a lithium secondary battery. [Background technology]

[0003] As technological development and demand for electric vehicles and energy storage systems (ESS) increases, the demand for batteries as energy sources is rapidly increasing, and research into batteries that can meet various needs is being conducted. In particular, research into lithium secondary batteries that have high energy density, excellent lifespan, and cycle characteristics as power sources for such devices is being actively conducted.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. The positive electrode may have a structure in which a positive electrode current collector and a positive electrode active material layer are sequentially stacked, and the positive electrode current collector is typically an aluminum thin film.

[0005] The aluminum thin film is used after being slit to a desired width, but at this time, a considerable pressure is applied to the slit portion, which may leave residual stress in the slit portion, which may cause microcracks in processes performed after slitting, making the film vulnerable to fracture.When the film is subjected to a high-speed roll-to-roll process, the residual stress in the slit portion may cause breakage during the rolling process. Therefore, there is a need for techniques to reduce the residual stresses in the cut portion. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and aims to provide a method for manufacturing an aluminum thin film in which the aluminum thin film is heat-treated over a specific temperature and time range to have a desired tensile strength and average residual stress value, an aluminum thin film, a positive electrode including the same, and a lithium secondary battery. [Means for solving the problem]

[0007] In one aspect, there is provided a method for producing an aluminum thin film, comprising: (A) cutting an aluminum thin film and winding the cut aluminum thin film in one direction; and (B) heat-treating a cut surface of the wound aluminum thin film roll, including the cut portion of the aluminum thin film, wherein the heat treatment is carried out so as to satisfy the following formula (1), where T (unit: °C) is a heat treatment temperature and t (unit: seconds) is a heat treatment time: Formula (1): -0.21t+150≦T≦-0.21t+210

[0008] The heat treatment temperature T may be in the range of 25°C to 200°C. The heat treatment time t may be in the range of 50 seconds to 650 seconds. Step (B) can reduce residual stress at the cut portion.

[0009] In the step (B), the cut surface can be heated using a heating device having a cross-sectional area larger than the area of ​​the cut surface. The heating device may include a heat treatment performing portion having a cross-sectional area larger than an area of ​​the cut surface.

[0010] The heating device includes an inductively coupled coil arranged to heat the cutting surface, and the cutting surface can be heated using an induced current from the inductively coupled coil.

[0011] The heating device includes a heating wire arranged to heat the cutting surface, and the cutting surface can be heated by the heating wire. The heating device may be disposed spaced apart from the aluminum thin film roll.

[0012] In another embodiment, the thickness is 10 μm to 20 μm, and the tensile strength in the MD direction is 20.0 kgf / mm 2 ~30.4kgf / mm 2 and the stretching ratio in the MD direction is 1.8% to 2.6%. The average residual stress of the end portion arranged along the MD direction of the aluminum thin film may be −18.5 MPa to −12.0 MPa.

[0013] In another aspect, there is provided a positive electrode comprising the aluminum thin film and a positive electrode active material layer disposed on at least one surface of the aluminum thin film. In yet another aspect, there is provided a lithium secondary battery comprising the positive electrode, a negative electrode, and an electrolyte. [Effects of the Invention]

[0014] According to the present invention, the cut surface of the aluminum thin film roll is heat-treated at a specific temperature and for a specific time range to soften the aluminum thin film, thereby manufacturing an aluminum thin film having a desired tensile strength, which can prevent microcracks that may occur during charge and discharge.

[0015] According to the present invention, the cut surface of the aluminum thin film roll is heat-treated at a specific temperature and for a specific time range, thereby reducing the residual stress at the end of the unwound aluminum thin film, which can prevent breakage during the rolling process. DETAILED DESCRIPTION OF THE INVENTION

[0016] The advantages and features of the present invention, as well as methods for achieving them, will become apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided solely to ensure that the disclosure of the present invention is complete and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined solely by the claims. The same reference numerals refer to the same elements throughout the specification.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in the sense that they can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless they are clearly defined otherwise.

[0018] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified. The terms "including," "having," and "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0019] In this specification, when a part is said to include a certain component, this does not mean that it may further include other components, unless otherwise specified.

[0020] In this specification, the phrase "A and / or B" means A or B, or A and B. In this specification, "%" means % by weight unless expressly indicated otherwise.

[0021] In this specification, the "tensile strength" of an aluminum thin film refers to the stress immediately before the aluminum thin film breaks. Specifically, the aluminum thin film, including the heat-treated portion, was punched out to a size of 12.7 mm x 150 mm, and both ends of the aluminum thin film were fastened to the upper and lower fixtures of a Universal Testing Machine (UTM, Zwick). The aluminum thin film was then pulled vertically at a speed of 20 mm / min to measure the maximum tensile strength immediately before the aluminum thin film broke.

[0022] In this specification, the surface residual stress of the aluminum thin film was measured by X-ray diffraction using a μ-X360 device manufactured by Pulstec. In this specification, the MD (Machine Direction) direction means the direction parallel to the length direction of the aluminum thin film, and the TD (Transverse Direction) direction means the width direction of the aluminum thin film, i.e., the direction perpendicular to the MD direction.

[0023] Aluminum thin film manufacturing method The method for producing an aluminum thin film according to the present invention will now be described. The method for manufacturing an aluminum thin film according to the present invention includes the steps of cutting an aluminum thin film, winding the cut aluminum thin film in one direction, and heat-treating the cut surfaces of the wound aluminum thin film roll, including the cut portions of the aluminum thin film. The heat treatment can be performed so as to satisfy the following formula (1), where T (unit: °C) is the heat treatment temperature and t (unit: seconds) is the heat treatment time: Formula (1): -0.21t+150≦T≦-0.21t+210

[0024] The heat treatment temperature T may be 25°C to 200°C, preferably 50°C to 200°C, and more preferably 50°C to 180°C. The heat treatment time t may be 50 seconds to 650 seconds, preferably 100 seconds to 600 seconds, and more preferably 120 seconds to 600 seconds.

[0025] When the heat treatment temperature and heat treatment time are within the above ranges, the aluminum thin film can be softened to produce an aluminum thin film having a desired tensile strength, which can prevent microcracks that may occur during charge and discharge.

[0026] The heat treatment can reduce residual stress at the cut portion, which can prevent breakage during a rolling process due to residual stress present at the cut portion when the wire is subjected to a high-speed roll-to-roll process. The heat treatment can be performed by heating the cut surface using a heating device having a cross-sectional area larger than the area of ​​the cut surface.

[0027] The heating device may include a heat treatment execution portion having a cross-sectional area larger than the area of ​​the cut surface, so that the entire cut surface of the aluminum thin film roll is heated by the heating device to reduce residual stress.

[0028] The heating device includes an inductively coupled coil arranged to heat the cutting surface, and the cutting surface can be heated using an induced current from the inductively coupled coil. The heating device includes a heating wire arranged to heat the cutting surface, and the cutting surface can be heated by the heating wire.

[0029] The heating device may be disposed at a distance from the aluminum thin film roll. Specifically, the heating device may be disposed so as to face the cut surface of the aluminum thin film roll. Specifically, two or more heating devices may be disposed when heat treating one aluminum thin film roll. The distance between the heating device and the cut surface of the aluminum thin film roll may be 1 mm to 500 mm, preferably 1 mm to 100 mm, and more preferably 1 mm to 50 mm.

[0030] Aluminum Thin Film Next, the aluminum thin film according to the present invention will be described. The aluminum thin film according to the present invention has a thickness of 10 μm to 20 μm and a tensile strength in the MD direction of 20.0 kgf / mm 2 ~30.4kgf / mm 2 The stretching ratio in the MD direction is 1.8% to 2.6%.

[0031] The aluminum thin film according to the present invention may have a thickness of 10 μm to 20 μm, preferably 12 μm to 18 μm, and more preferably 13 μm to 17 μm. The tensile strength of the aluminum thin film in the MD direction is 20.0 kgf / mm 2 ~30.4kgf / mm 2 , preferably 22.0 kgf / mm 2 ~30.4kgf / mm 2 , more preferably 26.0 kgf / mm 2 ~30.2kgf / mm 2 When the tensile strength of the aluminum thin film satisfies the above-mentioned range, microcracks that may occur during charging and discharging can be prevented. In addition, the aluminum thin film has excellent mechanical properties against external forces and can be excellent in durability. When the tensile strength of the aluminum thin film satisfies the above-mentioned range, microcracks that may occur during charging and discharging can be prevented. In addition, the aluminum thin film has excellent mechanical properties against external forces and can be excellent in durability. 2 If it is less than 30.4 kgf / mm, breakage may occur during the rolling process, and the tensile strength may be less than 30.4 kgf / mm. 2 If the temperature is higher than 1000 MPa, poor welding may occur during the ultrasonic welding process of the electrode tabs.

[0032] The elongation ratio of the aluminum thin film in the MD direction may be 1.8% to 2.6%, preferably 1.9% to 2.6%, and more preferably 2.0% to 2.6%. If the elongation ratio of the aluminum thin film is less than 1.8%, wire breakage may occur during the electrode rolling process, and cracks may occur due to electrode expansion during electrode charge and discharge. If the elongation ratio is more than 2.6%, the tensile strength of the aluminum thin film may be lower than desired.

[0033] The average residual stress of the end portions of the aluminum thin film arranged along the MD direction may be -18.5 MPa to -12.0 MPa, preferably -18.5 MPa to -13.0 MPa, and more preferably -18.3 MPa to -13.5 MPa. If the average residual stress of the aluminum end portions is less than -18.5 MPa, an aluminum thin film having the desired tensile strength cannot be obtained, and if the average residual stress exceeds -12.0 MPa, the aluminum thin film may become excessively hardened and brittle, and may be prone to cracking.

[0034] positive electrode Next, the positive electrode according to the present invention will be described. The positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, and the positive electrode current collector includes the aluminum thin film according to the present invention. Since the aluminum thin film has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0035] The positive electrode active material layer may optionally contain a conductive material and a binder, as well as a positive electrode active material, if necessary. The positive electrode active material can include a compound capable of reversible intercalation and deintercalation of lithium, specifically, a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, examples of the lithium metal oxide include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (such as Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1), or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate salts (such as Li1+a Fe 1-x M x (PO 4-b )X b (wherein M is one or more selected from Al, Mg, and Ti, and X is one or more selected from F, S, and N, and -0.5≦a≦0.5, 0≦x≦0.5, 0≦b≦0.1), and the compound may contain any one or more of these compounds.

[0036] Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2), or lithium iron phosphate (e.g., LiFePO4), or a mixture of any one or more of these may be used. The positive electrode active material may be included in an amount of 60 wt % to 99 wt %, preferably 70 wt % to 99 wt %, and more preferably 80 wt % to 98 wt %, based on the total weight of the positive electrode active material layer.

[0037] The conductive material is used to impart conductivity to the electrode and can be any material that exhibits electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 0.01% to 10% by weight, preferably 0.1% to 9% by weight, and more preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0038] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethylmethacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen atoms in these polymers are substituted with Li, Na, or Ca, and various copolymers thereof. These may be used singly or in combination. The binder may be contained in an amount of 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, and more preferably 1% by weight to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0039] The positive electrode according to the present invention can be manufactured by a conventional method for manufacturing a positive electrode, except that the aluminum thin film according to the present invention is used as a positive electrode current collector. Specifically, the positive electrode can be manufactured by coating at least one surface of the aluminum thin film with a positive electrode slurry composition prepared by dissolving or dispersing a positive electrode active material, and optionally a binder, a conductive material, and a dispersant in a solvent, followed by drying and rolling.

[0040] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the production yield, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a cathode.

[0041] Alternatively, the positive electrode can be produced by casting the positive electrode slurry composition on a separate support, peeling the composition from the support, and laminating the resulting film on at least one surface of an aluminum thin film.

[0042] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described. Specifically, the lithium secondary battery includes the positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as that described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0043] The lithium secondary battery may further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0044] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0045] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material. The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0046] The negative electrode active material may be included in an amount of 80 wt % to 99 wt %, 82 wt % to 99 wt %, or 84 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0047] The binder is a component that helps bind the conductive material, active material, and current collector together, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0048] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be contained in an amount of 1 wt % to 30 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt % relative to the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. Examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0049] The negative electrode active material layer can be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition can be cast on a separate support, and then peeled off from the support to obtain a film, which can be laminated on the negative electrode current collector.

[0050] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitation. It is particularly preferred that the separator exhibits low resistance to ion migration and excellent electrolyte humidification. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0051] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0052] Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0053] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitation. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used at a concentration of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. When the lithium salt concentration is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance and enabling effective migration of lithium ions.

[0054] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 10.0 wt % based on the total weight of the electrolyte.

[0055] As described above, the lithium secondary battery including the aluminum thin film according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0056] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0057] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0058] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative to aid in understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present description, and it goes without saying that such changes and modifications are within the scope of the appended claims.

[0059] Examples and Comparative Examples Example 1 An aluminum thin film (product name: A1100H18, width 1310 mm, diameter 200 mm, thickness 15 μm) was prepared and cut to a width of 1100 mm. The cut aluminum thin film was wound up in one direction.

[0060] The cut surface of the wound aluminum thin film roll was heat-treated at a temperature of 50°C for 600 seconds using a heating device disposed 10 mm away from the cut surface including the cut portion of the aluminum thin film, to produce an aluminum thin film roll.

[0061] Example 2 An aluminum foil roll was manufactured in the same manner as in Example 1, except that the cut surface was heat-treated at 100° C. for 500 seconds.

[0062] Example 3 An aluminum foil roll was manufactured in the same manner as in Example 1, except that the cut surface was heat-treated at 125° C. for 120 seconds.

[0063] Example 4 An aluminum foil roll was manufactured in the same manner as in Example 1, except that the cut surface was heat-treated at a temperature of 180° C. for 120 seconds.

[0064] Comparative Example 1 An aluminum thin film roll was produced in the same manner as in Example 1, except that the cut surface was not heat-treated.

[0065] Comparative Example 2 An aluminum foil roll was manufactured in the same manner as in Example 1, except that the cut surface was heat-treated at a temperature of 220° C. for 180 seconds.

[0066] Comparative Example 3 An aluminum foil roll was manufactured in the same manner as in Example 1, except that the cut surface was heat-treated at a temperature of 180° C. for 700 seconds.

[0067] Experimental Example 1 - Evaluation of tensile strength and elongation rate The tensile strength and elongation in the MD direction of the aluminum thin films unwound from the aluminum thin film rolls produced in Examples 1 to 4 and Comparative Examples 1 to 3 were measured. Specifically, the aluminum thin film rolls were unwound, and the unwound aluminum thin film, including the heat-treated portion, was punched out to a size of 12.7 mm x 150 mm. Both ends of the aluminum thin film were fastened to the upper and lower jigs of a Universal Testing Machine (UTM, Zwick), respectively, and the aluminum thin film was pulled from the top and bottom at a speed of 20 mm / min to measure the maximum tensile strength just before the aluminum thin film broke. The measurement results are shown in Table 1 below.

[0068] [Table 1]

[0069] As shown in Table 1, the aluminum thin films unwound from the aluminum thin film rolls of Examples 1 to 4, which were produced by heat-treating the cut surface of the aluminum thin film roll at temperatures ranging from 25°C to 200°C for 100 to 600 seconds, exhibited reduced MD tensile strength and elongation compared to the unheat-treated aluminum thin film roll of Comparative Example 1. Meanwhile, the aluminum thin films unwound from the aluminum thin film rolls of Comparative Examples 2 and 3, which exceeded the heat treatment temperature or time range, exhibited excessively reduced MD tensile strength and elongation compared to the aluminum thin films of Examples 1 to 4. This suggests that heat-treating the cut surface of the aluminum thin film roll within a specific temperature and time range softens the relevant portion, preventing microcracks that may occur during charge and discharge, resulting in high tensile strength and preventing wire breakage during the rolling process.

[0070] Experimental Example 2 - Evaluation of average residual stress The average residual stress of the aluminum thin film unwound from the aluminum thin film roll produced in each of Examples 1 to 4 and Comparative Examples 1 to 3 was measured. Specifically, the aluminum thin film roll was unwound, and the end portion of the unwound aluminum thin film arranged along the MD was punched out to a size of 2 mm x 16 mm, and then measured by X-ray diffraction using a μ-X360 device from Pulstec. The measurement results are shown in Table 2 below.

[0071] [Table 2]

[0072] As shown in Table 2, it was confirmed that the aluminum thin films unwound from the aluminum thin film rolls of Examples 1 to 4 and Comparative Examples 2 and 3, which were manufactured by heat-treating the cut surfaces of the aluminum thin film rolls, had a reduced average residual stress at the end portion compared to the unheat-treated aluminum thin film roll of Comparative Example 1. Therefore, when the cut surfaces of the aluminum thin film roll are heat-treated, the average residual stress is reduced, and the risk of breakage due to residual stress is reduced. However, as seen in Experimental Example 1, it can be inferred that the cut surfaces of the aluminum thin films of Comparative Examples 2 and 3 are excessively softened, resulting in low tensile strength and making it difficult to prevent microcracks or increasing the risk of breakage during the rolling process.

Claims

1. (A) cutting an aluminum thin film and winding the cut aluminum thin film in one direction; (B) heat-treating the cut surface of the aluminum thin film, including the cut portion, in the wound aluminum thin film roll; The heat treatment is carried out so as to satisfy the following formula (1), where T (unit: ° C.) is the heat treatment temperature and t (unit: seconds) is the heat treatment time: Formula (1): -0.21t+150≦T≦-0.21t+210 A method for producing an aluminum thin film.

2. 2. The method for producing an aluminum thin film according to claim 1, wherein the heat treatment temperature T is in the range of 25°C to 200°C.

3. 2. The method for producing an aluminum thin film according to claim 1, wherein the heat treatment time t is in the range of 50 seconds to 650 seconds.

4. The method for producing an aluminum thin film according to claim 1 , wherein the step (B) reduces residual stress in the cut portion.

5. The method for producing an aluminum thin film according to claim 1 , wherein the step (B) heats the cut surface using a heating device having a cross-sectional area larger than an area of ​​the cut surface.

6. The method for producing an aluminum thin film according to claim 5 , wherein the heating device includes a heat treatment execution part having a cross-sectional area larger than an area of ​​the cut surface.

7. The method for producing an aluminum thin film according to claim 5 , wherein the heating device includes an inductively coupled coil arranged to heat the cut surface, and the cut surface is heated using an induced current from the inductively coupled coil.

8. The method for producing an aluminum thin film according to claim 5 , wherein the heating device includes a heat wire arranged so as to heat the cut surface, and the cut surface is heated by the heat wire.

9. The method for producing an aluminum thin film according to claim 5 , wherein the heating device is disposed at a distance from the aluminum thin film roll.

10. A thickness of 10 μm to 20 μm; 20.0kgf / mm ２ ~30.4kgf / mm ２ tensile strength in the MD direction of An aluminum thin film having an MD stretch ratio of 1.8% to 2.6%.

11. The aluminum thin film according to claim 10, wherein the average residual stress of the end portion arranged along the MD direction of the aluminum thin film is −18.5 MPa to −12.0 MPa.

12. The aluminum thin film according to claim 10 or 11, a positive electrode active material layer disposed on at least one surface of the aluminum thin film.

13. The positive electrode according to claim 12; a negative electrode; and an electrolyte.

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