Method for manufacturing a negative electrode current collector, a negative electrode current collector, a negative electrode including the same, an electrode assembly, and a secondary battery

Abstract

The method for producing a negative electrode current collector according to the present invention can include the steps of (A) preparing an electrolytic copper foil, and (B) applying compressive residual stress to both end portions in the MD direction of the electrolytic copper foil.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182377, filed December 22, 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 a negative electrode current collector, a negative electrode current collector, a negative electrode including the same, an electrode assembly, and a 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, lithium secondary batteries are classified into cylindrical and prismatic batteries, in which an electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries, in which an electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet, depending on the shape of the battery case. The electrode assembly is a rechargeable power-generating element consisting of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. These batteries are classified into jelly-roll types, in which a long sheet-like positive electrode and negative electrode coated with an active material are wound up with a separator interposed between them, and stack types, in which multiple positive and negative electrodes of a predetermined size are stacked one on top of the other with a separator interposed between them. The negative electrode may have a structure in which a negative electrode active material layer is laminated on one or both sides of a negative electrode current collector, and the negative electrode current collector is typically made of a copper foil (hereinafter referred to as "copper foil").

[0005] Types of copper foil include rolled copper foil, which is produced by a rolling process, and electrolytic copper foil, which is produced by an electroplating process. Rolled copper foil has advantages over electrolytic copper foil in terms of physical properties, as the rolling process imparts workability to the metal. However, it has disadvantages, such as high manufacturing costs and poor quality uniformity across the width, due to the need for multiple rolling processes to produce a thin film. In contrast, electrolytic copper foil has the advantage of being easily manufactured at extremely thin thicknesses of around 6 μm to 8 μm. However, due to the process characteristics of electrolytic copper foil, crystalline grains are grown by electrolytic deposition, which can lead to the formation of tensile residual stress on the surface of the copper foil. Tensile residual stress is the main cause of fatigue failure in metals. Fatigue failure refers to the breakage of a material when stress is repeatedly applied at a level far lower than its tensile strength.

[0006] FIG. 1 is a diagram showing the locations where breakage occurs in a conventional jelly-roll type electrode assembly. Referring to FIG. 1, a conventional jelly-roll electrode assembly includes a positive electrode 2, a negative electrode 3, and a separator 1 disposed between the positive and negative electrodes. The negative electrode 3 includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. Due to the contraction and expansion of the electrode during the charge and discharge process of a battery, a weak stress is continuously applied to the negative electrode current collector disposed at the outermost portion of the electrode assembly, i.e., the end portion of the negative electrode current collector disposed on the side of the battery can housing the electrode assembly, which can further concentrate tensile residual stress. This can increase fatigue fracture at specific locations, causing fractures at stresses far lower than the tensile strength of the negative electrode current collector, resulting in reduced battery life. Therefore, there is a need for technological development to improve fatigue failure at the end portion of the negative electrode current collector. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention addresses the above-mentioned problems and provides a method for manufacturing a negative electrode current collector that can improve fatigue fracture at an end portion of the negative electrode current collector disposed at the outermost portion of an electrode assembly, a negative electrode current collector, a negative electrode including the same, an electrode assembly, and a secondary battery. [Means for solving the problem]

[0008] In one aspect, the present invention provides a method for producing a negative electrode current collector, the method comprising the steps of: preparing an electrolytic copper foil; and applying a compressive residual stress to both end portions in a MD direction of the electrolytic copper foil.

[0009] The step of applying the compressive residual stress may be performed by sandblasting. The sandblasting can be carried out with particles having a particle size of 30 μm or less.

[0010] The particles can include at least one of Al2O3, melamine, and aminoaldehyde. The sandblasting may be performed at a projection distance of 20 mm to 100 mm. The sandblasting may be performed at an air pressure of 0.10 MPa to 0.30 MPa.

[0011] The sandblasting may be performed at a nozzle moving speed of 5M / s to 10M / s. In the step of applying the compressive residual stress, the tension of the electrolytic copper foil may be controlled by a transfer roll.

[0012] In another aspect, the present invention provides a negative electrode current collector comprising an electrolytic copper foil having a plastic deformation layer formed on both end portions in the MD direction, and having an average residual stress of 0 MPa or less when measuring the surface residual stress.

[0013] The area where compressive residual stress is formed when measuring the surface residual stress of the negative electrode current collector may be 70.0% to 99.5% of the total measured area. The area where tensile residual stress is formed when measuring the surface residual stress of the negative electrode current collector may be 0.5% to 10.0% of the total measurement area. The plastic deformation layer may have a compressive residual stress.

[0014] In yet another aspect, the present invention provides a negative electrode comprising the negative electrode current collector described above. In yet another aspect, the present invention provides an electrode assembly including the negative electrode described above. The plastic deformation layer may include an end portion of a negative electrode current collector disposed on the outermost side of the electrode assembly.

[0015] In yet another aspect, the present invention provides a secondary battery including the above-described electrode assembly, a battery can that houses the electrode assembly, and a cap assembly that seals an upper opening of the battery can. [Effects of the Invention]

[0016] According to the present invention, by selectively applying compressive residual stress to specific regions on the surface of an electrodeposited copper foil, the tensile residual stress concentrated at the end portion of the negative electrode current collector disposed at the outermost portion of the electrode assembly can be offset, thereby suppressing the occurrence of breakage due to fatigue fracture and achieving improved life characteristics.

[0017] When compressive residual stress is applied by sandblasting as in the present invention, surface damage to the electrolytic copper foil is minimized and the occurrence of fracture due to fatigue fracture can be reduced. [Brief explanation of the drawings]

[0018] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to facilitate a better understanding of the technical concept of the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to only the matters depicted in such drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer description. [Figure 1] 1A and 1B are diagrams showing positions where breakage occurs in a conventional jelly roll-type electrode assembly. [Figure 2] FIG. 2 is a diagram showing a position where compressive residual stress is applied in an electrolytic copper foil according to one embodiment of the present invention. [Figure 3] 1 is a diagram showing a secondary battery according to an embodiment of the present invention; [Figure 4] 1 is a diagram showing a secondary battery according to an embodiment of the present invention; [Figure 5] 1 is a residual stress contour image showing the measurement results of the surface residual stress of the negative electrode current collector according to Example 1 of the present invention. [Figure 6] 10 is a residual stress contour image showing the measurement results of the surface residual stress of the negative electrode current collector according to Comparative Example 1 of the present invention. [Figure 7] 10 is a residual stress contour image showing the measurement results of the surface residual stress of a negative electrode current collector according to Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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 scope of the claims. Throughout the specification, the same reference symbols refer to the same elements.

[0020] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless clearly defined otherwise.

[0021] 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 in the text. The words "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0022] 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.

[0023] 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.

[0024] In this specification, the surface residual stress of the negative electrode current collector can be measured by the cos α method using a Pulstec u-X360 device. In the present invention, the MD direction (machine direction) means the length direction of the electrolytic copper foil, and the TD direction (transverse direction) means the width direction of the electrolytic copper foil.

[0025] <Method of manufacturing negative electrode current collector> A method for producing the negative electrode current collector according to the present invention will be described. The method for producing a negative electrode current collector according to the present invention may include the steps of preparing an electrolytic copper foil and applying a compressive residual stress to a partial region of a surface of the electrolytic copper foil.

[0026] Due to processing characteristics, conventional electrodeposited copper foils have residual tensile stresses on their surfaces, which are a major cause of metal fatigue failure. In the case of conventional electrode assemblies wound in one direction, weak stresses are continuously applied to the end portion of the negative electrode current collector, which is located on the outermost side of the electrode assembly, i.e., the battery can side that houses the electrode assembly, due to the contraction and expansion of the electrodes during the charge and discharge process of the battery, which can further concentrate the residual tensile stress. This acts as a factor that increases fatigue failure at the end portion of the negative electrode current collector, which is located on the outermost side of the electrode assembly, and fracture occurs at a stress much lower than the tensile strength of the negative electrode current collector, resulting in a problem of reduced battery life.

[0027] As a result of extensive research to solve the above problems, the inventors have found that selectively applying compressive residual stress to specific regions on the surface of an electrodeposited copper foil can offset the tensile residual stress concentrated at the end portion of the negative electrode current collector disposed at the outermost portion of the electrode assembly, thereby suppressing the occurrence of breakage due to fatigue fracture and achieving improved life characteristics, which led to the completion of the present invention. Each step of the method for producing a negative electrode current collector according to the present invention will be described in more detail below.

[0028] (1) Step of preparing electrolytic copper foil The method for producing a negative electrode current collector according to the present invention begins with a step of preparing an electrolytic copper foil. In this case, the electrolytic copper foil may be prepared by purchasing a commercially available electrolytic copper foil or by using an electrolytic plating process well known in the art.

[0029] For example, copper foil can be manufactured by an electrolytic plating process. Electrolytic plating is advantageous in terms of process flexibility and cost because it is easy to adjust the thickness of the plating film by adjusting the magnitude of the applied current, the current application time, the temperature, etc. Furthermore, when an electrolytic plating process is used, a copper foil with a thin thickness can be realized, thereby improving the energy density of the battery.

[0030] For example, a method for producing copper foil by an electrolytic plating process is as follows. First, a reaction vessel is prepared, which is provided with a negative electrode rotating drum and a positive electrode plate disposed opposite the negative electrode rotating drum, and the reaction vessel is filled with an electrolyte containing copper ions and water. Next, the negative electrode rotating drum is rotated while applying electricity to the negative electrode rotating drum and the positive electrode plate, and copper is electrodeposited on the surface of the negative electrode rotating drum. Finally, the electrodeposited copper is continuously removed from the reaction vessel, thereby finally producing the copper foil.

[0031] (2) Applying compressive residual stress to specific regions on the surface of the electrolytic copper foil Next, a compressive residual stress is applied to a specific region on the surface of the electrodeposited copper foil prepared above. FIG. 2 is a diagram showing positions where compressive residual stress is applied in an electrolytic copper foil according to one embodiment of the present invention.

[0032] 2, the regions to which the compressive residual stress is applied are both end portions A in the MD direction of the electrolytic copper foil 15. Specifically, the regions may be regions that form the end portions of the negative electrode current collector after the electrolytic copper foil 15 is cut.

[0033] The end portion A of the negative electrode current collector may be disposed at the outermost portion of the electrode assembly, and by applying compressive residual stress to the end portion A of the negative electrode current collector and reducing tensile residual stress, it is possible to suppress the occurrence of fracture due to fatigue fracture.

[0034] Compressive residual stress can be applied to a portion of the surface of the prepared electrolytic copper foil by sandblasting. When compressive residual stress is applied by sandblasting, surface damage to the electrolytic copper foil can be minimized and fracture due to fatigue fracture can be suppressed.

[0035] The fine particles may have a particle size of 30 μm or less, specifically 5 μm to 25 μm, more specifically 10 μm to 20 μm. In the present invention, when the fine particles have a particle size within the above range, compressive residual stress can be selectively applied only to the partial region without damaging the surface of the electrodeposited copper foil. The particles may include, but are not limited to, at least one of Al2O3, melamine, and aminoaldehyde.

[0036] During the sandblasting, the projection distance, air pressure, and nozzle moving speed may vary depending on the type and physical properties of the electrolytic copper foil used. For example, the sandblasting may be performed at a projection distance of 20 mm to 100 mm, specifically 20 mm to 50 mm, and more specifically 20 mm to 30 mm.

[0037] For example, the sandblasting may be performed at an air pressure of 0.10 MPa to 0.30 MPa, specifically 0.10 MPa to 0.20 MPa, and more specifically 0.10 MPa to 0.15 MPa.

[0038] For example, the sandblasting may be performed at a nozzle moving speed of 5 M / s to 10 M / s, specifically 5 M / s to 8 M / s, and more specifically 5 M / s to 6 M / s. In the present invention, when the projection distance, air pressure, and / or nozzle moving speed satisfy the above ranges, compressive residual stress can be selectively applied to only the partial region without damaging the surface of the electrodeposited copper foil.

[0039] As shown in Fig. 2, the tension of the electrodeposited copper foil 15 prepared above can be controlled by a transfer roll 25. In the present invention, by controlling the tension of the electrodeposited copper foil 15 by the transfer roll 25, it is possible to selectively apply compressive residual stress to only the partial region without damaging the surface of the electrodeposited copper foil 15.

[0040] The sandblasting can plastically deform the partial region of the electrolytic copper foil, resulting in the formation of a portion with compressive residual stress and a portion with tensile residual stress on the surface of the electrolytic copper foil.

[0041] <Negative electrode current collector> The negative electrode current collector according to the present invention includes an electrolytic copper foil having plastic deformation layers formed at both end portions in the MD direction, and may have an average residual stress of 0 MPa or less, specifically −30 MPa to 0 MPa, more specifically −25 MPa to −10 MPa, when the surface residual stress is measured. When the average residual stress is within the above range, the occurrence of fracture due to fatigue failure at the end portions of the negative electrode current collector can be suppressed.

[0042] When measuring the surface residual stress, the area where compressive residual stress is formed may be 70.0% to 99.5%, specifically 90% to 99.5%, more specifically 95.0% to 99.5% of the total measured area, and the area where tensile residual stress is formed may be 0.5% to 10.0%, specifically 2.0% to 8.0%, more specifically 2.0% to 7.0% of the total measured area.

[0043] If the area ratio where compressive residual stress is formed is less than 70.0%, work hardening may occur during sandblasting, resulting in wrinkles due to differences in physical properties between the uncoated and coated areas, while if it exceeds 99.5%, the area where compressive residual stress is formed becomes too large, resulting in disconnection and damage to the current collector.When the area ratio where tensile residual stress is formed satisfies the above range, the strength of the stress field formed around microcracks on the surface of the negative electrode current collector is reduced, thereby improving fatigue failure.

[0044] The plastic deformation layer may have compressive residual stress. To change the residual stress on the surface of the negative electrode current collector, plastic deformation must occur only on the outer surface of the negative electrode current collector, with almost no plastic deformation occurring inside the negative electrode current collector.

[0045] The surface of the negative electrode current collector according to the present invention may contain both compressive and tensile residual stresses. For example, FIG. 5 is a residual stress contour image showing the measurement results of the surface residual stress of the negative electrode current collector according to Example 1 of the present invention. As shown in FIG. 5, the negative electrode current collector may include a compressive residual stress (shown in blue) and a tensile residual stress (shown in red). In this case, the compressive residual stress and the tensile residual stress may each be separated into one or more regions and scattered on the surface of the negative electrode current collector. As a result, the tensile residual stress concentrated at the outermost end of the negative electrode current collector due to the contraction and expansion of the electrode during the charge and discharge process of the battery is offset, thereby suppressing the occurrence of fatigue fractures and achieving improved life characteristics.

[0046] The negative electrode current collector according to the present invention can be used as a negative electrode current collector because it does not cause chemical changes in the battery and has conductivity. In addition, the negative electrode current collector according to the present invention can be manufactured by an electrolytic plating method, which has the advantage of relatively reducing manufacturing costs.

[0047] The thickness of the negative electrode current collector according to the present invention may be 3 μm to 500 μm, specifically 5 μm to 100 μm, and more specifically 6 μm to 12 μm. When the thickness of the negative electrode current collector satisfies the above range, the durability of a battery produced from the negative electrode current collector according to the present invention can be improved.

[0048] <Negative electrode> The negative electrode according to the present invention may include the negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector.

[0049] The negative electrode according to the present invention may include a coating portion on which a negative electrode active material layer is formed, and a plain portion on which no negative electrode active material layer is formed. The negative electrode active material layer contains a negative electrode active material, and may further contain a conductive material, a binder, and the like, as necessary.

[0050] The negative electrode active material can contain at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal, or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and undoping lithium, and a transition metal oxide.

[0051] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, any carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these may be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0052] As the metal or an alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn or an alloy of these metals and lithium may be used.

[0053] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li z Fe2O3(0≦x≦1), Li x WO2(0≦x≦1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) may be used.

[0054] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x ≤ 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. Also, at least one of these may be mixed with SiO2 and used. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0055] The negative electrode active material may be contained at 60% to 99% by weight, preferably 70% to 99% by weight, more preferably 80% to 98% by weight based on the total weight of the negative electrode active material layer.

[0056] The negative electrode conductive material is a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fiber or metal fiber; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0057] The negative electrode conductive material may be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of the negative electrode active material layer.

[0058] The negative electrode binder is a component that helps to bond the negative electrode conductive material, negative electrode active material, and negative electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0059] Typically, the negative electrode binder may be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of the negative electrode active material layer.

[0060] <Electrode assembly> The present invention provides an electrode assembly including the negative electrode. The plastic deformation layer may include an end portion of a negative electrode current collector disposed at the outermost side of the electrode assembly according to the present invention.

[0061] The electrode assembly is provided by winding the negative electrode, the positive electrode, and the separator interposed between the negative electrode and the positive electrode in one direction. Since the negative electrode has been described above, only the remaining components excluding the negative electrode will be described below.

[0062] (positive electrode) The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0063] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like.

[0064] The positive electrode current collector may have a thickness of 3 μm to 500 μm, and may have fine irregularities formed on its surface to enhance adhesion to the positive electrode active material layer. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0065] The positive electrode active material layer contains a positive electrode active material, and may further contain a conductive material, a binder, and the like, as necessary. The positive electrode active material may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum as a compound capable of reversible intercalation and deintercalation of lithium. More specifically, the lithium metal oxide may include lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn YO2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., 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 (e.g., 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 (e.g., 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, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≦ a ≦ 0.5, 0 ≦ x ≦ 0.5, 0 ≦ b ≦ 0.1), etc.), and any one or two or more of these compounds can be included.

[0066] 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 the like, and a mixture of any one or more of these may be used.

[0067] The positive electrode active material may be contained in an amount of 60% to 99% by weight, preferably 70% to 99% by weight, and more preferably 80% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0068] The positive electrode conductive material is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fiber or metal fiber; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0069] Typically, the positive electrode conductive material may be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0070] The positive electrode binder is a component that assists in binding the active material and conductive material to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0071] Typically, the positive electrode binder may be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0072] (separator) On the other hand, a separator can be disposed between the negative electrode and the positive electrode. Any separator that is generally used as a separator in a lithium secondary battery can be used without any particular limitation, and it is particularly preferable that the separator has low resistance to ion migration of the electrolyte and has excellent ability to absorb the electrolyte solution.

[0073] For example, the separator may be a porous polymer film containing 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. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used as the separator.

[0074] <Secondary battery> The present invention provides a secondary battery including the electrode assembly. 3 and 4 are diagrams illustrating a secondary battery according to an embodiment of the present invention. The secondary battery may include the electrode assembly 120, a battery can 130 that houses the electrode assembly, and a cap assembly 140 that seals the top opening of the battery can. Since the electrode assembly has been described above, only the remaining components excluding the electrode assembly will be described below.

[0075] (electrolyte) The secondary battery according to the present invention may include an electrolyte. In this case, the electrolyte may be a non-aqueous electrolyte. The non-aqueous electrolyte may include an organic solvent and a lithium salt commonly used in the art, and is not particularly limited.

[0076] The organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, 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; and carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0077] Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having 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.

[0078] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be 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 contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0079] Meanwhile, the non-aqueous electrolyte according to the present invention may further contain an additive, although this is not essential, to further improve the physical properties of the secondary battery. Examples of such additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, nitrile compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0080] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinyl ethylene carbonate (VEC). The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0081] The nitrile compound may be, for example, succinonitrile, adiponitrile, hexanetricyanide, 1,4-dicyano-2-butene, or the like. The sultone compound may be, for example, 1,3-propane sultone, 1,3-propene sultone, or the like.

[0082] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0083] The phosphate-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0084] The borate-based compound may be, for example, tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or the like. The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0085] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalatoborate) (LiB(C2O4)2)), and LiBF4.

[0086] On the other hand, the additives may be used alone or in combination of two or more. The total amount of the additives may be 1 wt % to 20 wt %, preferably 1 wt % to 15 wt %, based on the total weight of the electrolyte. When the additives are contained within the above range, a stable coating is formed on the electrode, which can suppress ignition during overcharge, and can prevent side reactions from occurring during the initial activation process of the secondary battery, or residue or precipitation of the additives.

[0087] (battery can) The battery can 130 is a container for accommodating the electrode assembly 120 and the electrolyte, has an opening at the top, and is made of a conductive metal material such as aluminum or steel. The battery can 130 accommodates the electrode assembly 120 and the electrolyte in its inner space through the opening at the top.

[0088] If necessary, the battery can 130 may include a beading portion 60 and a crimping portion 70. The beading portion 60 may be formed by pressing the outer circumferential surface of the battery can 130. The beading portion 60 prevents the electrode assembly 120 housed inside the battery can 130 from slipping out through the upper opening of the battery can 130 and may function as a support portion on which the cap assembly 140 is placed.

[0089] The crimping portion 70 may be formed on the upper portion of the beading portion 60 and has an extended and bent shape to surround the outer circumferential surface and a part of the upper surface of the cap assembly 140 disposed on the beading portion 60.

[0090] (Cap Assembly) Next, the cap assembly 140 is for sealing the top opening of the battery can, and includes a top cap 10, a safety vent 20, and a CID filter 30, as shown in FIG.

[0091] The top cap 10 protrudes to form a positive electrode terminal and is perforated with an exhaust port (not shown). A safety vent 20 is located at the bottom of the top cap 10. A portion of the top surface of the CID filter 30 is connected to the safety vent 20, and a portion of the bottom surface is connected to the electrode of the electrode assembly 120. When gas is generated from the electrode assembly 120 due to overcharging, high temperature, etc., and the internal pressure increases, the safety vent 20 reverses shape and protrudes upward, venting the gas. At this time, the CID filter 30 also moves upward, breaking the notch portion (T) and cutting off the current flow. This prevents further overcharging and battery explosion.

[0092] The cap assembly 140 may also include an insulating gasket 32 ​​that provides airtightness between the top cap 10 and the battery can 130. The top cap 10 may be crimped onto a beading portion 60 formed on the battery can 130 and fixed by a crimping portion 70. The top cap 10 is a component made of a conductive metal material and covers the top opening of the battery can 130. The top cap 10 is electrically connected to the positive electrode of the electrode assembly 120 and is electrically insulated from the battery can 130 via the gasket 32. Therefore, the top cap 10 may function as a positive electrode terminal of the secondary battery. The top cap 10 may have a protrusion formed upward at its center, and the protrusion may be in contact with an external power source so that current can be applied from the external power source.

[0093] 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.

[0094] Example 1 A reaction vessel containing a negative electrode rotating drum and a positive electrode plate facing the negative electrode rotating drum was prepared, and the reaction vessel was filled with an electrolyte containing copper sulfate and water. Next, the negative electrode rotating drum was rotated while an electric power source was applied to the negative electrode rotating drum and the positive electrode plate, and copper was electrodeposited on the surface of the negative electrode rotating drum. The electrodeposited copper was then continuously removed from the reaction vessel to obtain an 8 μm thick electrolytic copper foil.

[0095] The electrolytic copper foil obtained above was polished by sandblasting using Al2O3 with a particle size of 30 μm as an abrasive under the conditions of a projection distance of 20 mm, a transfer speed of 10 m / s, and an air pressure of 0.10 MPa. The position of the polishing process is shown as region A in Figure 2. After the polishing process, the electrolytic copper foil was slit and sheeted to prepare a negative electrode current collector.

[0096] Comparative Example 1 A negative electrode current collector was produced in the same manner as in Example 1, except that the electrolytic copper foil obtained above was not subjected to a polishing treatment.

[0097] Comparative Example 2 A negative electrode current collector was manufactured in the same manner as in Example 1, except that the entire surface of the electrolytic copper foil obtained above was polished with sandpaper using 10 μm silicon carbide as an abrasive.

[0098] [Experimental Example 1 - Measurement of Residual Stress on the Surface of the Negative Electrode Current Collector] The residual stress on the surface of the negative electrode current collectors manufactured in Example 1 and Comparative Examples 1 and 2 was measured. Specifically, the residual stress on the surface of the negative electrode current collectors was measured by the cos α method using a Pulstec u-X360 device. The measurement results are shown in Table 1 below and Figures 5 to 7.

[0099] The average residual stress in [Table 1] was measured at intervals of 0.2 mm, and the average residual stress was calculated by dividing the measured value by the total variable. FIG. 5 is a residual stress contour image showing the residual stress formed on the surface of the negative electrode current collector manufactured according to Example 1 of the present invention.

[0100] FIG. 6 is a residual stress contour image showing the residual stress formed on the surface of the negative electrode current collector manufactured according to Comparative Example 1 of the present invention. FIG. 7 is a residual stress contour image showing the residual stress formed on the surface of the negative electrode current collector manufactured according to Comparative Example 2 of the present invention.

[0101] As shown in FIGS. 5 to 7, the negative electrode current collector can include a portion where compressive residual stress is formed (shown in blue) and a portion where tensile residual stress is formed (shown in red).

[0102] [Table 1]

[0103] As shown in Table 1, it can be seen that in Example 1, in which the surface of the electrolytic copper foil was sandblasted, the average residual stress was lower than in Comparative Example 1, in which the surface of the electrolytic copper foil was not polished, and Comparative Example 2, in which the surface of the electrolytic copper foil was polished using a grinder. From this, it can be inferred that when a secondary battery manufactured from a negative electrode current collector including the electrolytic copper foil of Example 1 is operated, cracks do not occur at the end of the negative electrode current collector.

Claims

1. (A) preparing an electrolytic copper foil; (B) applying a compressive residual stress to both end portions in the MD direction of the electrodeposited copper foil; A method for producing a negative electrode current collector, comprising:

2. The method for producing a negative electrode current collector according to claim 1 , wherein the step (B) is performed by sandblasting.

3. The method for producing a negative electrode current collector according to claim 2 , wherein the sandblasting is performed by blasting particles having a particle size of 30 μm or less.

4. The particles are Al ２ O ３ 4. The method for producing a negative electrode current collector according to claim 3, wherein the additive comprises at least one of methylcellulose, melamine, and aminoaldehyde.

5. The method for producing a negative electrode current collector according to claim 3, wherein the sandblasting has a projection distance of 20 mm to 100 mm.

6. The method for producing a negative electrode current collector according to claim 3, wherein the sandblasting is performed at an air pressure of 0.10 MPa to 0.30 MPa.

7. The method for producing a negative electrode current collector according to claim 3, wherein the sandblasting is performed at a nozzle moving speed of 5 M / s to 10 M / s.

8. The method for producing a negative electrode current collector according to claim 1 , wherein in step (B), the tension of the electrolytic copper foil is controlled by a transfer roll.

9. The electrolytic copper foil includes an electrodeposited copper foil having a plastic deformation layer formed on both end portions in the MD direction, A negative electrode current collector having an average residual stress of 0 MPa or less when the surface residual stress is measured.

10. The negative electrode current collector according to claim 9, wherein an area where compressive residual stress is formed when measuring the surface residual stress of the negative electrode current collector is 70.0% to 99.5% of the total measured area.

11. The negative electrode current collector according to claim 9, wherein an area where tensile residual stress is formed when measuring the surface residual stress of the negative electrode current collector is 0.5% to 10.0% of the total measured area.

12. The negative electrode current collector according to claim 9 , wherein the plastic deformation layer has a compressive residual stress.

13. A negative electrode comprising the negative electrode current collector according to claim 9 .

14. 14. An electrode assembly according to claim 13, in which the negative electrode, the positive electrode, and the separator interposed between the negative electrode and the positive electrode are wound in one direction.

15. The electrode assembly according to claim 14 , wherein the plastic deformation layer comprises an end portion of a negative electrode current collector disposed on the outermost side of the electrode assembly.

16. The electrode assembly according to claim 14; a battery can that houses the electrode assembly; a cap assembly that seals the top opening of the battery can.

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