Copper foil, current collector, and lithium ion secondary battery

Abstract

The present disclosure provides a copper foil containing 2 ppm to 21 ppm of silver, 0.5 ppm to 5.5 ppm of titanium, and 2 ppm to 80 ppm of sulfur, in which the orientation index of the (220) plane of the copper foil is between 2.05 and 3.08. The present disclosure further provides a current collector for a lithium ion secondary battery and a lithium ion secondary battery.

Description

Technical Field

[0001] The present disclosure relates to a copper foil having a wide range of uses and being particularly suitable for use in lithium-ion secondary batteries. Background Art

[0002] Lithium-ion secondary batteries, due to their small size, high energy density, long life, fast charging, minimal memory effect, and low cost, are widely used in various portable electronic devices such as mobile phones, laptops, tablets, and cameras, as well as in electric vehicles and energy storage systems, making them indispensable in modern life. To achieve higher energy density and achieve high energy density in a small package, technologies to improve the performance of lithium-ion secondary batteries continue to develop and innovate.

[0003] In lithium-ion secondary batteries, copper foil serves as the negative electrode current collector because it is a good conductor of current. However, if the copper foil itself has poor mechanical properties and becomes loose, wrinkles develop after coating with carbon- or silicon-based active materials, or cracks develop due to the inability to adapt to the thermal expansion and contraction of the lithium-ion secondary battery during charging and discharging, these factors can affect the battery's reliability and lifespan. Therefore, improvements are needed to meet these demands in copper foil for lithium-ion secondary batteries. Summary of the Invention

[0004] In view of this, the present disclosure provides a copper foil with excellent electrical conductivity, low sagging resistance, and low wrinkling after coating with substances such as active materials. Furthermore, when used in lithium-ion secondary batteries, the copper foil of the present disclosure can adapt to thermal expansion and contraction during charging and discharging, and is less likely to crack.

[0005] The copper foil disclosed herein contains 2 ppm to 21 ppm of silver, 0.5 ppm to 5.5 ppm of titanium, and 2 ppm to 80 ppm of sulfur, wherein the orientation index of the (220) plane of the copper foil is between 2.05 and 3.08.

[0006] In one embodiment, the copper foil contains 5 ppm to 20 ppm of silver. In another embodiment, the copper foil contains 0.5 ppm to 5 ppm of titanium. In yet another embodiment, the copper foil contains 5 ppm to 70 ppm of sulfur.

[0007] In one embodiment, the ratio of the orientation index of the copper foil (220) side to the orientation index of the copper foil (111) side is between 2.77 and 5.40. In another embodiment, the orientation index of the copper foil (111) side is between 0.57 and 0.87.

[0008] In one embodiment, the tensile strength of the copper foil is between 45 kg / mm 2 Up to 85kg / mm 2 In another embodiment, the tensile strength of the copper foil is between 60 kg / mm2 Up to 80kg / mm 2 between.

[0009] In one embodiment, the electrical conductivity of the copper foil is 80% or higher of the International Annealed Copper Standard (IACS).

[0010] In one embodiment, the copper foil has a first surface and an opposite second surface, and the ten-point average roughness Rz of the first surface and the second surface of the copper foil is respectively 2.5 μm or less.

[0011] In one embodiment, the copper foil has an elongation of 1% to 15%.

[0012] In one embodiment, the copper foil has a thickness of 3 μm to 35 μm.

[0013] In one embodiment, the copper foil comprises a copper layer and a handle layer.

[0014] In one embodiment, the treatment layer of the copper foil is formed on at least one surface of the copper layer, and the treatment layer is formed of an organic material or an inorganic material.

[0015] In one embodiment, the inorganic material comprises at least one selected from the group consisting of chromium, nickel, zinc, cobalt, manganese, and tin.

[0016] In one embodiment, the organic material comprises at least one selected from the group consisting of carbon, oxygen, nitrogen, sulfur, and silicon.

[0017] In one embodiment, the organic material includes at least one selected from the group consisting of a porphyrin compound, a silane compound, a benzotriazole compound, and a triazine trithiol compound.

[0018] The present disclosure also provides a current collector for a lithium ion secondary battery, comprising the copper foil described in the present disclosure.

[0019] The present disclosure also provides a lithium ion secondary battery, which includes the current collector described in the present disclosure.

[0020] The present disclosure mainly controls the content of non-copper elements in the copper foil, specifically the content of elements such as silver, titanium, and sulfur, and controls the crystal orientation of the copper foil, specifically the orientation index of the (220) plane, so that the copper foil can have excellent electrical conductivity and mechanical properties. The present disclosure also controls the tensile strength of the copper foil within a specific range to further improve the performance of the copper foil. Through the technical means described in the present disclosure, the copper foil has good electrical conductivity, is not easy to relax, and is not easy to wrinkle after coating substances such as active materials. In addition, it is found that when the copper foil of the present disclosure is used in lithium-ion secondary batteries, it can adapt to thermal expansion and contraction during charging and discharging and is not easy to crack.

[0021] The foregoing summary is not intended to represent each specific embodiment or every aspect of the present disclosure. Rather, the foregoing summary merely provides examples of the novel aspects and features herein. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present disclosure through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the description herein.

[0023] It should be noted that all ranges and values ​​herein are inclusive and combinable. If a numerical range is provided, each value between and including the upper and lower limits of the range is deemed to be disclosed herein. It should be understood that any numerical range cited herein is intended to include all subranges encompassed by that range. For example, a range of "1 to 10" is intended to include all subranges between and including the stated minimum value of 1 and the maximum value of 10; in other words, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values.

[0024] When the terms "comprise," "include," "contain," or "have" specific elements as used herein, unless otherwise specified, these terms may further include other components, elements, structures, regions, parts, devices, systems, steps, or connections, rather than excluding such other elements. In other words, when an invention claims to "comprise," "include," "contain," or "have" specific elements, these terms may actually allow for other unspecified elements, whether or not they are essential.

[0025] The terms "upper" and "lower" described herein are only used to illustrate the specific embodiments of the present invention and are not used to limit the scope of the present invention. Adjustments, interchanges and changes in their relative positions and relationships should be regarded as within the scope of the present invention without substantially changing the technical content of the present invention.

[0026] Unless otherwise expressly stated herein, the singular forms "a", "an" and "the" herein include plural forms as well, and "or" and "and / or" herein are used interchangeably.

[0027] The first aspect of the present disclosure provides a copper foil, which is mainly composed of copper (for example, containing >99.5wt% copper, more preferably containing >99.9wt% copper) and contains trace amounts of non-copper elements. In some embodiments, the copper foil can be prepared by electrolysis (that is, as an electrolytic copper foil). During the electrolysis process, other non-copper elements in the electrolyte may be precipitated together with the copper or attached to the copper foil by adhesion, deposition, etc., so the electrolytic copper foil contains trace amounts of non-copper elements. The present disclosure controls the trace amounts of non-copper elements so that the copper foil contains 2ppm to 21ppm of silver, 0.5ppm to 5.5ppm of titanium and 2ppm to 80ppm of sulfur. The element content can be measured using known methods, including but not limited to measurement by inductively coupled plasma analysis (ICP).

[0028] The copper foil of the present disclosure contains 2 ppm to 21 ppm of silver, more preferably 5 ppm to 20 ppm of silver, for example, 2 ppm, 2.5 ppm, 3 ppm, 3.5 ppm, 4 ppm, 4.5 ppm, 5 ppm, 5.5 ppm, 6 ppm, 6.5 ppm, 7 ppm, 7.5 ppm, 8 ppm, 8.5 ppm, 9 ppm, 9.5 ppm, 10 ppm, 11 ppm, 12 ppm, 13 ppm, 14 ppm, 15 ppm, 16 ppm, 17 ppm, 18 ppm, 19 ppm, 20 ppm, or 21 ppm of silver. The copper foil of the present disclosure contains 0.5 ppm to 5.5 ppm of titanium, more preferably 0.5 ppm to 5 ppm of titanium, for example, 0.5 ppm, 1 ppm, 1.5 ppm, 2 ppm, 2.5 ppm, 3 ppm, 3.5 ppm, 4 ppm, 4.5 ppm, 5 ppm, or 5.5 ppm of titanium. The copper foil of the present disclosure contains 2 ppm to 80 ppm of sulfur, more specifically 5 ppm to 70 ppm of sulfur, for example, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, 60 ppm, 65 ppm, 70 ppm, 75 ppm, or 80 ppm of sulfur.

[0029] The crystal orientation of the copper foil disclosed herein is controlled. Specifically, the orientation index of the (220) plane of the copper foil is controlled. The orientation index of a certain crystal plane refers to the ratio of the following two values: (i) the value obtained by dividing the X-ray diffraction intensity of a certain crystal plane of the tested sample by the sum of the X-ray diffraction intensities of each crystal plane of the tested sample, and (ii) the value obtained by dividing the X-ray diffraction intensity of a certain crystal plane of the standard sample by the sum of the X-ray diffraction intensities of each crystal plane of the standard sample. Therefore, the orientation index M(220) of the (220) plane can be expressed by the following formula:

[0030]

[0031] Wherein, I(200) represents the X-ray diffraction intensity of the (220) crystal plane of the copper foil sample under test; ΣI(hkl) represents the sum of the X-ray diffraction intensities of each crystal plane of the copper foil sample under test; IF(220) represents the X-ray diffraction intensity of the (220) crystal plane of the standard sample; and ΣIF(hkl) represents the sum of the X-ray diffraction intensities of each crystal plane of the standard sample; and the X-ray diffraction intensity of each crystal plane of the standard sample is the diffraction intensity of the (hkl) crystal plane of the j6 standard copper powder developed by the American Society for Testing and Materials (ASTM) (PDF#040836). In some embodiments, ΣI(hkl) represents the sum of the X-ray diffraction intensities of the (111), (200), (220), and (311) crystal planes of the copper foil sample under test, and ΣIF(hkl) represents the sum of the X-ray diffraction intensities of the (111), (200), (220), and (311) crystal planes of the standard sample.

[0032] In some embodiments, the crystal orientation index of the copper foil can be measured on any surface of the copper foil. When the copper foil is prepared by electrolysis, the surface can be a roller surface or a deposition surface. In some embodiments, when the copper foil is prepared by electrolysis, the crystal orientation index of the copper foil is measured on the deposition surface of the copper foil.

[0033] In some embodiments, the orientation index of the (220) plane of the copper foil is between 2.05 and 3.08, such as 2.05, 2.10, 2.20, 2.25, 2.30, 2.37, 2.40, 2.41, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.08. In some embodiments, the orientation index of the (111) plane of the copper foil is between 0.57 and 0.87, such as 0.57, 0.58, 0.60, 0.62, 0.69, 0.70, 0.80, 0.87. In some embodiments, the ratio of the orientation index of the (220) plane of the copper foil to the orientation index of the (111) plane is between 2.77 and 5.40, for example, 2.77, 2.80, 2.90, 3.00, 3.10, 3.20, 3.26, 3.30, 3.31, 3.40, 3.43, 3.50, 3.60, 3.70, 3.80, 3.90, 4.00, 4.10, 4.20, 4.30, 4.31, 4.40, 4.50, 4.60, 4.70, 4.80, 4.90, 5.00, 5.10, 5.20, 5.30, 5.40.

[0034] In addition to controlling the content of non-copper elements in the copper foil, the present disclosure also observes the tensile strength. The copper foil of the present disclosure is controlled to have a tensile strength between 45 kg / mm 2 Up to 85kg / mm 2 The tensile strength is between 60kg / mm 2 Up to 80kg / mm 2 In some embodiments, the tensile strength refers to the transverse direction (TD) tensile strength. 2 Up to 85kg / mm 2 Tensile strength between, for example, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85 kg / mm 2 .

[0035] In some embodiments, the electrical conductivity of the copper foil is tested and is above 80% IACS, e.g., 80% IACS, 81% IACS, 82% IACS, 83% IACS, 84% IACS, 85% IACS, 86% IACS, 87% IACS, 88% IACS, 89% IACS, 90% IACS.

[0036] In some embodiments, the copper foil has a first surface and an opposite second surface, and the ten-point average roughness Rz of the first surface and the second surface of the copper foil is respectively less than 2.5 μm, more specifically, Rz is respectively less than 2.0 μm, for example, 2.5 μm, 2.4 μm, 2.3 μm, 2.2 μm, 2.1 μm, 2.0 μm, 1.9 μm, 1.8 μm, 1.7 μm, 1.6 μm, 1.5 μm, 1.4 μm, 1.3 μm, 1.2 μm, 1.1 μm, and 1.0 μm.

[0037] In some embodiments, the copper foil may have a thickness of 3 μm to 35 μm; in some specific applications or considering desired mechanical properties, the copper foil may have a thickness of 3 μm to 10 μm. The copper foil thickness is, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or 35 μm.

[0038] The preparation of the copper foil of the present disclosure is illustrated below. In some embodiments, the copper foil can be prepared by electrolysis. Electrolytic copper foil can be made by electrolysis (also known as electrodeposition, electrolytic deposition or electroplating) using a foil making machine. The foil making machine may include at least a roller as a cathode, a pair of insoluble metal anode plates, and an electrolyte feed pipe. The roller is a rotatable metal roller with a mirror-polished surface. The metal anode plate can be detachably fixed to the lower half of the roller to surround the lower half of the roller. The feed pipe can be fixed directly below the roller and located between the two metal anode plates. The roller surface of the electrolytic copper foil is the surface that contacts the roller used during the electrolysis process; and the deposition surface is the opposite side of the roller surface, or the surface that contacts the electrolyte during the electrolysis process. The method for manufacturing electrolytic copper foil includes partially immersing a rotating roller assembly in an electrolyte containing copper ions and non-copper element ions. Then, under the action of an electric current, the ions are attracted to the roller and reduced to cover the roller surface, thereby forming copper foil (i.e., electrolytic copper foil) on the roller surface. In a continuous process, the roller rotates and the electrolytic copper foil thereon is rolled out, and new electrolytic copper foil continues to be formed on the roller surface that is no longer covered by the electrolytic copper foil. The rolled out is separated from the roller, for example, by an external force, and then passes through or through the downstream roller. In some embodiments, the roller surface is equivalent to the first surface, and the deposition surface is equivalent to the second surface.

[0039] In addition to the main copper ions, the electrolyte also contains additives. In one embodiment, the additives can be inorganic additives and / or organic additives, such as silver-containing additives, titanium-containing additives, sulfur-containing additives, and other additives. In one embodiment, silver-containing additives include, but are not limited to, silver salts such as silver nitrate, silver sulfate, and silver chloride; titanium-containing additives include, but are not limited to, titanium salts such as titanium sulfate; and sulfur-containing additives include, but are not limited to, thiourea, ethylenethiourea, 3-sulfur-isothiuronium propyl sulfonate (UPS), sodium disulfide (bis-(sodium sulfopropyl)-disulfide, SPS), sodium 3-mercapto-1-propanesulfonate (MPS), etc. In one embodiment, other additives can include polymers such as gelatin, polyethylene glycol, cellulose-based water-soluble polymers, polyethyleneimine, and polyacrylamide. Lysates of the aforementioned polymers, such as gelatin lysates, can also be added as additives. The polymer lysate can be prepared by electrolyzing the polymer, for example, in a system comprising a titanium plate as a positive electrode, a copper plate as a negative electrode, a 10 g / L to 50 g / L aqueous solution containing the polymer, and a 0 g / L to 50 g / L auxiliary agent (such as sodium thiosulfate, potassium sulfide, etc.), at 5 A / dm 2 Up to 30A / dm 2 Electrolysis is performed at a current density of 100 nm for 8 to 15 seconds to obtain a pyrolysis product of the polymer. The weight average molecular weight (Mw) of the polymer is 20,000 to 100,000, and the weight average molecular weight (Mw) of the pyrolysis product of the polymer is 6,000 to 30,000, but can be adjusted as needed.

[0040] In one embodiment, when the copper foil is prepared by electrolysis, the composition and performance of the copper foil can be controlled by regulating the composition of the electrolyte during the electrolysis process (e.g., the concentration of copper ions, non-copper element ions and other substances) and various operating parameters (e.g., current density, electrolyte temperature, processing time, etc.). In one embodiment, as a means of regulating the content of non-copper elements in the electrolytic copper foil, the composition of the electrolyte can be exemplarily listed. According to this scheme, the various components in the electrolyte can be regulated. For example, when the composition of the electrolyte includes copper sulfate, sulfuric acid, chloride ions and additives, the concentrations of these components can be regulated to regulate the content of non-copper elements in the electrolytic copper foil. In another embodiment, the concentration of copper sulfate (CuSO4.5H2O) can be regulated to be 200g / L to 400g / L, the concentration of sulfuric acid is 80g / L to 150g / L, the concentration of chloride ions is 20ppm to 100ppm, and the concentration of additives is 10ppm to 300ppm. In another embodiment, as a means of further regulating the content of non-copper elements in the electrolytic copper foil, regulating the concentration of additives can be exemplified.

[0041] The present disclosure has discovered that regulating the content of non-copper elements in copper foil can improve its performance. For example, regulating the silver content to above 2 ppm and the sulfur content to above 2 ppm can reduce wrinkles generated during processing, while regulating the sulfur content to above 2 ppm can easily cause wrinkles. These wrinkles make the copper foil uneven, which is not conducive to application. Especially when there is a coating material on the copper foil surface, these wrinkles will lead to insufficient contact between the copper foil and the coating material, increasing the risk of peeling. For another example, regulating the titanium content to above 0.5 ppm can prevent the copper foil from sagging, while regulating the titanium content to above 0.5 ppm can not. Furthermore, the present disclosure has discovered that in the case of lithium-ion secondary batteries, regulating the silver content to 2 to 21 ppm, the titanium content to 0.5 to 5.5 ppm, and the sulfur content to 2 to 80 ppm can significantly reduce the cracks generated after charging and discharging. The present disclosure speculates that when the silver content and sulfur content are below 2 ppm, the surface condition or mechanical properties of the copper foil may be poor, resulting in wrinkles during processing; and when the titanium content is below 0.5 ppm, the mechanical properties of the copper foil may also be poor. Furthermore, non-copper elements such as silver, titanium, and sulfur are present at the grain boundaries of copper foil. Excessive amounts of these elements, such as silver, titanium, and sulfur, can weaken the crystal structure and make the copper foil brittle. Furthermore, excessive silver or titanium content can lead to decreased electrical conductivity.

[0042] The present disclosure also discovered that regulating the orientation index of the (220) side of the copper foil can improve the performance of the copper foil. When the orientation index of the (220) side (i.e., M(220)) or the ratio of the orientation index of the (220) side to the orientation index of the (111) side (i.e., M(220) / M(111)) is too low, the copper foil is prone to wrinkling after being coated with substances such as active materials.

[0043] In some embodiments, the copper foil may have a multilayer structure, for example, the copper foil comprises a copper layer and a treatment layer. In some embodiments, the treatment layer is a layer formed on the surface of the copper layer by further treating the copper layer. In some embodiments, the treatment layer is formed on at least one surface of the copper layer. When the copper layer is prepared by electrolysis, the surface may be a roller surface or a deposition surface. The treatment layer may protect the copper layer from external factors, such as from oxidation or corrosion that may cause degradation of the copper foil. In some embodiments, the treatment layer is, for example, an anti-rust treatment layer. The treatment layer may be prepared by any known method, including immersing the copper layer in or passing through a solution containing a material that will become the treatment layer, or plating the material that will become the treatment layer (for example, by an electroplating bath) on the copper layer, and the process may be continuous and part of the overall process for preparing surface-treated copper foil. The thickness of the treatment layer may be 0.2 nm to 100 nm.

[0044] In some embodiments, the treatment layer is formed of an organic material or an inorganic material. In some embodiments, the inorganic material comprises at least one member selected from the group consisting of chromium, nickel, zinc, cobalt, manganese, and tin. In some embodiments, the organic material comprises at least one member selected from the group consisting of carbon, oxygen, nitrogen, sulfur, and silicon. In some embodiments, the organic material comprises at least one member selected from the group consisting of porphyrin compounds, silane compounds, benzotriazole compounds, and tripolysulfide compounds.

[0045] In some embodiments, the rust preventive liquid may be a chromium rust preventive liquid, the main component of the chromium rust preventive liquid is chromium trioxide (CrO3), the concentration of chromium trioxide may be 1.5 g / L to 5.0 g / L, the temperature of the rust preventive liquid may be 20° C. to 40° C., and the current density of the rust preventive treatment may be 0.5 A / dm 2 Up to 6.0A / dm 2 The anti-rust treatment time may be 2 seconds to 4 seconds, but is not limited thereto.

[0046] A second aspect of the present disclosure provides a current collector for a lithium ion secondary battery, comprising the copper foil of the present disclosure.

[0047] At least one layer of active material is coated on at least one side of the copper foil of the present invention to make a collector and an electrode of a lithium-ion secondary battery, the collector can be a positive electrode collector and / or a negative electrode collector; the electrode can be a positive electrode and / or a negative electrode. The active material can be divided into a positive electrode active material and a negative electrode active material. The negative electrode active material contains a negative electrode active material, which can be a carbonaceous substance, a silicon-containing substance, a silicon-carbon composite, a metal, a metal oxide, a metal alloy or a polymer; preferably a carbonaceous substance or a silicon-containing substance, but not limited thereto. Specifically, the carbonaceous substance can be mesophase graphite carbon microbeads (mesophase graphite powder, MGP), non-graphitizing carbon (non-graphitizing carbon), coke, graphite, glassy carbon, carbon fiber, activated carbon, carbon black or a high polymer calcined product, but not limited thereto; wherein, coke includes pitch coke, needle coke or petroleum coke, etc.; the high polymer calcined product is obtained by burning a high polymer such as phenolic resin or furan resin at an appropriate temperature so as to be carbonated. The silicon-containing material has an excellent ability to form alloys with lithium ions and an excellent ability to extract lithium ions from the alloyed lithium. Moreover, when used in lithium-ion secondary batteries, the silicon-containing material can achieve the advantage of high energy density. The silicon-containing material can be used in combination with cobalt, iron, tin, nickel, copper, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, chromium, ruthenium, molybdenum, or a combination thereof to form an alloy material. The elements of the metal or metal alloy can be selected from the following group: cobalt, iron, tin, nickel, copper, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, chromium, ruthenium, and molybdenum, but are not limited thereto. Examples of the metal oxide are, but are not limited to, ferric oxide, ferric oxide, ruthenium dioxide, molybdenum dioxide, and molybdenum trioxide. Examples of the polymer are, but are not limited to, polyacetylene and polypyrrole.

[0048] The active material may be added with auxiliary additives as needed, and the auxiliary additives may be, but are not limited to, a binder and / or a weak acid reagent. For example, the binder may be polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, or polyacrylate, and the weak acid reagent may be oxalic acid, citric acid, lactic acid, acetic acid, or formic acid.

[0049] A third aspect of the present disclosure provides a lithium ion secondary battery including the current collector of the present disclosure.

[0050] According to the present disclosure, the lithium-ion secondary battery of the present disclosure can be a lithium cobalt battery (LiCoO2 battery), a lithium nickel battery (LiNiO2 battery), a lithium manganese battery (LiMn2O4 battery), a lithium cobalt nickel battery (LiCo X Ni1-XO2 battery) or lithium iron phosphate battery (LiFePO4 battery), but not limited thereto.

[0051] According to the present disclosure, a lithium-ion secondary battery includes an electrolyte, which may include a solvent, an electrolyte, or optionally added additives. The solvent in the electrolyte includes a non-aqueous solvent, for example: cyclic carbonates such as ethylene carbonate or propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate; or sultones (sultone), but not limited thereto; the aforementioned solvents can be used alone or in combination of two or more solvents. Electrolytes include: lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethylsulfonate, lithium bis(oxalatoborate), and lithium bis(trifluoromethylsulfonylimide), but not limited thereto.

[0052] In one embodiment, the lithium-ion secondary battery may use a solid electrolyte (solid electrolytes) instead of the above-mentioned electrolyte. For example, the solid electrolyte may be a crystalline electrolyte, a glass electrolyte, a glass ceramic electrolyte, or a polymer electrolyte, but is not limited thereto. Specifically, the crystalline electrolyte may be a sulfide solid electrolyte such as a lithium superion conductor (LISICON) type or an argyrodite type; or an oxide solid electrolyte such as a garnet structure type (garnet type), a perovskite structure type (peroskite type), a NASICON structure type, but is not limited thereto. The glass electrolyte may be a glassy solid electrolyte such as an oxide or a sulfide, but is not limited thereto. The polymer electrolyte may be a pure solid polymer electrolyte such as polyethylene oxide-based (PEO) or polypropylene oxide-based (PPO); or a colloidal polymer electrolyte such as polyacrylonitrile-based (PAN), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF). However, the present invention is not limited thereto.

[0053] According to the present disclosure, a lithium-ion secondary battery can be a stacked lithium-ion secondary battery comprising a negative electrode and a positive electrode stacked with a separator, or a spirally wound stacked lithium-ion secondary battery comprising a continuous electrode and a separator spirally wound together, but is not limited thereto. Depending on the application product, the lithium-ion secondary battery of the present disclosure can be used in notebook personal computers, mobile phones, electric vehicles, and energy storage systems in the form of cylindrical secondary batteries, prismatic secondary batteries, soft-pack secondary batteries, or button-type secondary batteries, but is not limited thereto.

[0054] The following examples further illustrate the details. However, the interpretation of this disclosure should not be limited to the following examples. It should be understood that within the scope of this disclosure, the technical features mentioned above and below (such as the embodiments) can be freely combined with each other to form new or preferred technical solutions, which are omitted for brevity.

[0055] Example

[0056] A copper electrolyte is prepared using the following materials. A cathode titanium roller is rotated at a constant speed and in contact with the copper electrolyte. An electric current is applied between the cathode titanium roller and an insoluble anode plate (i.e., the following electrolysis conditions), causing the copper electrolyte to deposit on the surface of the cathode titanium roller to form an electrolytic copper foil. The electrolytic copper foil is then peeled off and guided onto a series of guide rollers.

[0057] [Copper electrolyte formula]

[0058] Copper sulfate (CuSO4·5H2O): 320g / L

[0059] Sulfuric acid: 85g / L

[0060] Chloride ion: 77ppm

[0061] [Electrolysis conditions]

[0062] Temperature: 48°C

[0063] Current density: 44A / dm 2

[0064] Electrolytic copper foil thickness: 4-10μm

[0065] Next, the electrolytic copper foil is transported to the anti-rust treatment device through a series of guide rollers for anti-rust treatment. The electrolytic copper foil is immersed in the anti-rust treatment tank filled with anti-rust treatment liquid, and an anti-rust layer is formed on the surface of the electrolytic copper foil through two sets of electrode plates.

[0066] [Rust-proof treatment liquid formula]

[0067] Chromium trioxide (CrO3): 1.5g / L

[0068] [Rust prevention treatment conditions]

[0069] Temperature: 25℃

[0070] Current density: 0.5A / dm 2

[0071] Plating time: 2 seconds

[0072] After the anti-rust treatment is completed, the anti-rust treated electrolytic copper foil is continued to be guided to a series of guide rollers, and the excess anti-rust treatment liquid and other substances on the surface are removed by an air knife, and the foil is dried and then rolled up to obtain the electrolytic copper foil.

[0073] Example 1

[0074] In addition to the copper sulfate, sulfuric acid, and chloride ions mentioned above, the copper electrolyte also contains the following additives: 20 ppm gelatin (Mw 40,000 to 60,000, purchased from Koei Chemical Co., Ltd.), 10 ppm gelatin lysate (Mw 12,000 to 16,000), 2 ppm thiourea, 35 ppm silver nitrate, and 10 ppm titanium sulfate. The gelatin lysate is prepared by first adding gelatin and sodium thiosulfate to water to form an aqueous solution containing 20 g / L gelatin and 20 g / L sodium thiosulfate. Electrolysis is then performed using a titanium plate as the positive electrode and a copper plate as the negative electrode at a current density of 20 A / dm 2 Electrolysis is performed for 10 seconds at 40°C to produce an aqueous solution containing a small-molecule gelatin lysate. An appropriate amount of the gelatin lysate, calculated relative to the total copper electrolyte solution, is added to the copper electrolyte solution. The copper electrolyte solution is then electrolyzed under the aforementioned conditions to form an electrolytic copper foil on the roller surface, which serves as the copper layer. Anti-rust treatment is then performed to form an anti-rust layer on both surfaces of the electrolytic copper foil. Excess anti-rust treatment solution and other substances are removed, and the foil is dried to produce an electrolytic copper foil with a thickness of 6 μm.

[0075] Example 2

[0076] A copper electrolyte was prepared according to Example 1, but the gelatin content was adjusted to 24 ppm and the gelatin lysate content was adjusted to 6 ppm. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0077] Example 3

[0078] A copper electrolyte was prepared according to Example 1, except that the gelatin, gelatin lysate, thiourea, silver nitrate, and titanium sulfate contents were adjusted to 24 ppm, 6 ppm, 45 ppm, and 15 ppm, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0079] Example 4

[0080] A copper electrolyte was prepared according to Example 1, but the thiourea content was adjusted to 1 ppm. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0081] Example 5

[0082] A copper electrolyte was prepared according to Example 1, but the gelatin content was adjusted to 24 ppm and the gelatin lysate content was adjusted to 6 ppm. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 4 μm.

[0083] Example 6

[0084] A copper electrolyte was prepared according to Example 1, but the gelatin content was adjusted to 24 ppm and the gelatin lysate content was adjusted to 6 ppm. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 10 μm.

[0085] Comparative Example 1

[0086] A copper electrolyte was prepared according to Example 1, but without adding silver nitrate and titanium sulfate. The copper electrolyte was further prepared into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm according to Example 1.

[0087] Comparative Example 2

[0088] A copper electrolyte was prepared according to Example 1, except that the gelatin content was adjusted to 24 ppm and the gelatin lysate content was adjusted to 6 ppm, and silver nitrate and titanium sulfate were not added. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0089] Comparative Example 3

[0090] A copper electrolyte was prepared according to Example 1, but without adding titanium sulfate, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0091] Comparative Example 4

[0092] A copper electrolyte was prepared according to Example 1, but without adding silver nitrate, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0093] Comparative Example 5

[0094] A copper electrolyte was prepared according to Example 1, except that the gelatin, silver nitrate, and titanium sulfate contents were adjusted to 30 ppm, 5 ppm, and 1 ppm, and no gelatin lysate was added. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0095] Comparative Example 6

[0096] A copper electrolyte was prepared according to Example 1, except that the gelatin, gelatin lysate, silver nitrate, and titanium sulfate contents were adjusted to 24 ppm, 6 ppm, 50 ppm, and 20 ppm, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0097] Comparative Example 7

[0098] A copper electrolyte was prepared according to Example 1, except that the gelatin, gelatin lysate, silver nitrate, and titanium sulfate contents were adjusted to 24 ppm, 6 ppm, 100 ppm, and 40 ppm, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0099] Comparative Example 8

[0100] A copper electrolyte was prepared according to Example 1, but the thiourea content was adjusted to 5 ppm. The copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0101] Comparative Example 9

[0102] A copper electrolyte was prepared according to Example 1, but without adding thiourea, and the copper electrolyte was further prepared according to Example 1 into an electrolytic copper foil having an anti-rust layer on both sides and a thickness of 6 μm.

[0103] Testing and evaluation methods

[0104] (I) Metal element content analysis

[0105] 70% nitric acid was diluted with deionized water to prepare 50 mL of 30% nitric acid. The 30% nitric acid was placed in a 250 mL PFA bottle, and 5.4 g of the electrolytic copper foil sample was added. After dissolution was complete, 85 mL of deionized water was added to obtain a total volume of 135 mL of sample solution. The concentration of non-copper metal elements (silver and titanium in the examples shown below) in the sample solution was analyzed using an inductively coupled plasma optical emission spectrometer (ThermoScientific iCAP 7400 ICP-OES). The measured values ​​were expressed in "mg metal / 1 L of sample solution." Since 135 mL of sample solution actually contained 5.4 g of electrolytic copper foil sample, and 1 L of sample solution contained 40 g of electrolytic copper foil sample, the measured values ​​expressed in "mg metal / 1 L of sample solution" were equivalent to "mg metal / 40 g of electrolytic copper foil sample," which, after further conversion, yielded "mg metal * 25 / 1 kg of electrolytic copper foil sample," or ppm.

[0106] (II) Analysis of sulfur content

[0107] First, bake a ceramic crucible at 1350°C for 15 minutes. Then, place 1 gram of electrolytic copper foil and 1 gram of flux (Copper Metal Accelerator, CAS No. 7440-50-8, manufactured by LECO Corporation) in the crucible. The crucible is then placed on the autosampler of a sulfur analyzer (Model: LECO S744) for sampling and analysis. The measured value, expressed in %, is multiplied by 10,000 to obtain the sulfur content in ppm.

[0108] (III) Orientation index

[0109] Method: X-ray diffraction

[0110] Instrument: Bruker D8 ADVANCE ECO

[0111] Test conditions:

[0112] Tested on the deposited surface of the electrolytic copper foil sample

[0113] Target: Co-Kα

[0114] Voltage: 40kV

[0115] Current: 25mA

[0116] Scanning range: 2θ = 40 to 120°

[0117] Scan rate: 0.39° / s

[0118] After obtaining the X-ray diffraction intensities of the (111), (200), (220), and (311) planes, the X-ray diffraction intensity of each crystal plane is divided by the sum of the X-ray diffraction intensities of each crystal plane to obtain the orientation index of each crystal plane.

[0119] (IV) Tensile strength

[0120] Standard: IPC-TM-650

[0121] Instrument: AG-I tensile testing machine manufactured by SHIMADZU

[0122] Test piece size: 100mm long x 12.7mm wide

[0123] Test temperature: 25℃

[0124] Chuck distance: 50mm

[0125] Stretching speed: 50mm / min (stretching along TD)

[0126] (V) Degree of relaxation

[0127] Electrolytic copper foil samples with a width of 1,380 mm were fed between two horizontal, fixed guide rollers spaced 700 mm apart in a slitting machine. The guide rollers were then rotated to apply varying tensions to the foil samples. The foil samples were then visually inspected for signs of slack and evaluated for the presence and degree of slack according to Table 1 below. Without tension applied, the foil samples were visually inspected. If the foil appeared unslacked, the slackness rating was "0." If the foil appeared unslacked, further tension was applied and the foil was re-inspected for signs of slack. If the foil appeared unslacked after applying 5 kg of tension, the slackness rating was "1," indicating slight slack. If the foil remained unslacked, the tension was further applied to 10 kg. If the foil remained unslacked after applying 10 kg of tension, the slackness rating was "2," indicating moderate slack. If the foil remained unslacked, the slackness rating was "3," indicating severe slack.

[0128] Table 1

[0129] Applied tension (kg) Appearance of copper foil after tension is applied Relaxation level 0 Not relaxed 0 (good) 5 Not relaxed 1 (mild) 10 Not relaxed 2 (moderate) 10 relaxation 3 (severe)

[0130] (VI) Wrinkle degree

[0131] A negative electrode slurry was prepared using water as the solvent, using the negative electrode materials listed in Table 2 below at a solid-to-liquid ratio of 73 wt% (100 g of negative electrode material: 73 g of water). A 130 μm thick layer of the negative electrode slurry was applied to the surface of an electrolytic copper foil sample at a speed of 5 m / min. The sample was then dried in an oven at 160°C and rolled using a roller press (rollers made of high-carbon chromium bearing steel (SUJ2)) at a speed of 1 m / min and a pressure of 3000 psi. The copper foil was then visually inspected for wrinkles. If no wrinkles were present at the interface between the negative electrode slurry and the electrolytic copper foil sample, the wrinkle grade was "A," indicating good wrinkling. If the wrinkle width accounted for more than 0% and less than 10% of the total copper foil width, the wrinkle grade was "B," indicating mild wrinkling. If the wrinkle width accounted for more than 10% of the total copper foil width, the wrinkle severity was "C," indicating severe wrinkling.

[0132] Table 2

[0133]

[0134] (VII) Conductivity

[0135] The conductivity was measured using a YOKOGAWA 2752 Double Bridge instrument according to ASTM B193-16.

[0136] (VIII) Crack degree after charge and discharge test

[0137] The present disclosure further applies electrolytic copper foil to lithium-ion secondary batteries. The preparation method for the lithium-ion secondary battery is as follows. Using N-methylpyrrolidone (NMP) as a solvent, the positive electrode materials listed in Table 3 below were mixed at a solid-to-liquid ratio of 195 wt% (100 g positive electrode material: 195 g NMP) to prepare a positive electrode slurry. Separately, using water as a solvent, the negative electrode materials listed in Table 2 above were mixed at a solid-to-liquid ratio of 73 wt% (100 g negative electrode material: 73 g water) to prepare a negative electrode slurry.

[0138] Table 3

[0139]

[0140] The positive electrode slurry is coated on the aluminum foil, and the negative electrode slurry is coated on the electrolytic copper foil sample, and then dried in an oven at 160°C to evaporate the solvent. Then, a roller press (the roller material is high carbon chromium bearing steel (SUJ2)) is used to roll at a speed of 1m / min and a pressure of 3000psi, and then stripped into a certain size to make positive and negative electrode sheets. Before assembling into a lithium-ion secondary battery, the negative electrode sheet is placed in an oven and baked at 140°C for 5 hours to remove moisture. The positive electrode sheet and the separator are placed in an oven at 140°C for 5 hours to remove moisture. The negative electrode sheet and the negative electrode sheet were wound together, placed in a container (18650 standard cylindrical size), injected with the following electrolyte, and sealed. The resulting lithium-ion secondary battery was charged and discharged 300 times under the following charge and discharge conditions. The battery was then disassembled and the degree of cracking in the electrolytic copper foil was visually inspected. The results are shown in Table 4.

[0141] Electrolyte: 1M lithium hexafluorophosphate (LiPF6) and 2wt% vinylene carbonate (VC) were added to a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2.

[0142] Charge and discharge conditions:

[0143] Room temperature (25℃)

[0144] Constant current constant voltage (CCCV) mode charging, charging voltage 4.2V, charging current 1C

[0145] Constant current (CC) mode discharge, discharge voltage 2.8V, discharge current 1C

[0146] The results of the silver content, titanium content, sulfur content, M(111), M(220), M(220) / M(111), tensile strength, relaxation degree, presence of wrinkles and electrical conductivity of each electrolytic copper foil obtained by the above test method are listed in Table 4 below.

[0147] Table 4

[0148]

[0149] From the above results, it can be seen that the electrolytic copper foil disclosed in the present invention can show the outstanding effects of high conductivity, no relaxation, and not easy to wrinkle after coating with active materials by controlling the content of silver, titanium and sulfur elements and controlling the orientation index of the (220) plane. Moreover, when the electrolytic copper foil is used in lithium-ion secondary batteries, it is not easy to crack even after repeated charging and discharging of the battery. In contrast, the silver content of Comparative Examples 1, 2, 4 and 5 is too low, and the copper foil is prone to wrinkles after coating with active materials; the silver content of Comparative Examples 6 and 7 is too high, and the copper foil is prone to cracks after repeated charging and discharging; the titanium content of Comparative Examples 1, 2, 3 and 5 is too low, and the copper foil is prone to relaxation; the titanium content of Comparative Examples 6 and 7 is too low, and the copper foil is prone to cracks after repeated charging and discharging; the sulfur content of Comparative Example 9 is too low, and the copper foil is prone to wrinkles after coating with active materials; the sulfur content of Comparative Example 8 is too high, and the copper foil is prone to cracks after repeated charging and discharging. Moreover, the M(220) and M(220) / M(111) of Comparative Examples 2, 5, and 9 are too low, and the copper foil is prone to wrinkles after coating the active material; the sum of the silver element content and the titanium element content of Comparative Example 7 is too high, resulting in the electrical conductivity of the copper foil being lower than 80% IACS.

Claims

1. A copper foil comprising 2 ppm to 21 ppm of silver, 0.5 ppm to 5.5 ppm of titanium, and 2 ppm to 80 ppm of sulfur, wherein: The orientation index of the (220) plane of the copper foil is between 2.05 and 3.

08. 2 . The copper foil according to claim 1 , comprising 5 ppm to 20 ppm of silver. The copper foil according to claim 1 , comprising 0.5 ppm to 5 ppm of titanium. The copper foil according to claim 1 , comprising 5 ppm to 70 ppm of sulfur.

5. The copper foil according to claim 1, wherein the ratio of the orientation index of the (220) plane to the orientation index of the (111) plane is between 2.77 and 5.

40. The copper foil according to claim 5 , wherein the orientation index of the (111) plane is between 0.57 and 0.

87.

7. The copper foil according to claim 1, having a tensile strength of 45 kg / mm 2 Up to 85kg / mm 2 between.

8. The copper foil according to claim 7, having a tensile strength of 60 kg / mm 2 Up to 80kg / mm 2 between. 9 . The copper foil according to claim 1 , wherein the electrical conductivity is 80% IACS or higher. The copper foil according to claim 1 , comprising a first surface and an opposite second surface, wherein the ten-point average roughness Rz of the first surface and the second surface of the copper foil is respectively 2.5 μm or less. The copper foil according to claim 1 , having an elongation of 1% to 15%. 12 . The copper foil according to claim 1 , having a thickness of 3 μm to 35 μm.

13. The copper foil of claim 1, comprising a copper layer and a treatment layer.

14. The copper foil according to claim 13, wherein The treatment layer is formed on at least one surface of the copper layer, and the treatment layer is formed of an organic material or an inorganic material.

15. The copper foil according to claim 14, wherein The inorganic material includes at least one selected from the group consisting of chromium, nickel, zinc, cobalt, manganese, and tin.

16. The copper foil according to claim 14, wherein The organic material includes at least one selected from the group consisting of carbon, oxygen, nitrogen, sulfur, and silicon.

17. The copper foil according to claim 14, wherein The organic material includes at least one selected from the group consisting of a porphyrin compound, a silane compound, a benzotriazole compound, and a tripolysulfide compound. 18 . A current collector for a lithium ion secondary battery, comprising the copper foil according to claim 1 . 19 . A lithium ion secondary battery comprising the current collector according to claim 18 .

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