Electro-deposited copper foil and current collector for lithium ion secondary battery and lithium ion secondary battery

Abstract

An electrolytic copper foil for a lithium-ion secondary battery has a deposition surface and a roller surface with opposite sides. The texture factor TC(220) of the electrolytic copper foil is ≥1.36 on the (220) crystal plane and TC(311) ≥0.79 on the (311) crystal plane. This disclosure also provides a current collector for a lithium-ion secondary battery and a lithium-ion secondary battery.

Description

Technical Field

[0001] This invention relates to an electrolytic copper foil, and more particularly to an electrolytic copper foil used in lithium-ion secondary batteries. Prior Technology

[0002] With the widespread adoption of portable electronic devices (PEDs), electric vehicles (EVs), hybrid electric vehicles (HEVs), and energy storage systems (ESS), lithium-ion rechargeable batteries, which combine advantages such as high capacity, high energy density, fast charging, and no memory effect, are being actively developed to meet the booming market demand. In lithium-ion rechargeable batteries, copper foil can be used as both a current collector and an electrode.

[0003] Lithium-ion rechargeable batteries generate heat during charging and discharging, which can cause thermal degradation of the copper foil, such as a significant decrease in mechanical strength. Furthermore, the expansion and contraction of the active materials during charging and discharging repeatedly apply stress to the copper foil. Therefore, if the copper foil structure and its tolerance to these harsh environments are insufficient, it is prone to damage due to performance degradation, reducing the reliability and lifespan of the lithium-ion rechargeable battery. Summary of the Invention

[0004] In view of the above, there is a need for electrolytic copper foil with high tolerance and strength to solve the above problems. This disclosure provides an electrolytic copper foil for lithium-ion secondary batteries, wherein the texture factor TC(220) of the (220) crystal plane is ≥1.36 and the texture factor TC(311) of the (311) crystal plane is ≥0.79.

[0005] In one specific embodiment, the TC (220) of the electrolytic copper foil is between 1.36 and 2.75, and the TC (311) of the electrolytic copper foil is between 0.79 and 1.10.

[0006] In one specific embodiment, the TC (311) of the electrolytic copper foil is between 0.85 and 1.05.

[0007] In one specific embodiment, after electrolytic copper foil was vacuum heated at 200°C for 5 hours, the change rate of TC(220) was <5%.

[0008] In a specific embodiment, after electrolytic copper foil was vacuum heated at 200°C for 5 hours, the change rate of TC(311) was <6%.

[0009] In a specific embodiment, the tensile strength of the electrolytic copper foil is ≥50 kg / mm².

[0010] In one specific embodiment, after electrolytic copper foil was vacuum heated at 200℃ for 5 hours, its tensile strength was ≥50kg / mm2.

[0011] In one specific embodiment, after electrolytic copper foil was vacuum heated at 200°C for 5 hours, the tensile strength degradation rate was ≤10%.

[0012] In one specific embodiment, the electrolytic copper foil is a surface-treated copper foil comprising a copper foil body and a rust-preventive layer.

[0013] In one specific embodiment, at least one surface of the electrolytic copper foil has a rust-preventive layer, which may be formed of organic or inorganic materials.

[0014] In one specific embodiment, the inorganic material used to form the rust-preventive layer comprises at least one selected from the group consisting of chromium, nickel, zinc, cobalt, manganese and tin.

[0015] In one specific embodiment, the organic material used to form the rust-preventive layer comprises at least one selected from the group consisting of carbon, oxygen, nitrogen, sulfur and silicon.

[0016] In one specific embodiment, the organic material used to form the anti-rust layer comprises at least one of the group consisting of porphyrin group, silane group, benzotriazole and triazine trithiol.

[0017] This disclosure also provides a current collector for lithium-ion secondary batteries, comprising the electrolytic copper foil described in this disclosure.

[0018] This disclosure also provides a lithium-ion secondary battery comprising the current collector described herein.

[0019] This disclosure reveals that by regulating the crystal orientation of the electrolytic copper foil, specifically at the high degree of preferential orientation of the (220) crystal plane and the (311) crystal plane, electrolytic copper foils with high tensile strength and only smaller tensile strength decay rate in the thermal state are obtained, i.e., with high dimensional stability. Brief explanation of the schema

[0020] Embodiments of the present invention are illustrated by illustrative reference drawings.

[0021] Figure 1 shows a schematic diagram of the flow of preparing the present disposable electrolytic copper foil, which includes optionally anti-rust treatment.

[0022] Figure 2 shows a side view schematic of this exposed electrolytic copper foil. Implementation

[0023] The embodiment of this disclosure is illustrated below by resorting to specific specific embodiments, which in the technical field are commonly known other advantages and efficacy of this disclosure that the weavers can easily understand from the content revealed herein.

[0024] Note that all ranges and values ​​in this paper are included and mergeable. This disclosure reveals many scopes, any value or point falling within the range described herein is also covered by this disclosure, and any value or point falling within the range described herein can be derived as a minimum or maximum value of the lower range, which is also covered by this disclosure.

[0025] When used herein, the terms “contains,” “includes,” “contains,” or “has” a particular element may include other elements, components, structures, regions, parts, devices, systems, steps, or connection relationships, unless otherwise stated, to the exclusion of such other elements. In other words, the claimed invention “contains,” “includes,” “contains,” or “has” a particular element, in effect permits other unspecified elements, whether or not that element is necessary.

[0026] The terms “above” and “below” are used herein to facilitate the articulation of specific embodiments of the present invention and not to limit the scope of the present invention, and adjustments, interchanges and alterations of their relative positions and relationships shall be considered to be implemented in the absence of substantial changes to the technical content of the present invention.

[0027] Unless otherwise expressly stated herein, the singular forms “a” and “the” used herein include the plural forms, and the word “or” used herein is interchangeable with “and / or”.

[0028] [<Electrolytic Copper Foil>]

[0029] This disclosure discloses an electrolytic copper foil, which can be manufactured by electrodeposition (or electrolysis, electrolytic deposition, electroplating), and an exemplary manufacturing method will be described below. The electrolytic copper foil has two opposing sides, one of which is the drum side, referring to the side of the electrolytic copper foil that is in contact with the cathode roller before being peeled off from the cathode roller; the other is the deposition side, which, relative to the drum side, refers to the side of the electrolytic copper foil that is not in contact with the cathode roller before being peeled off from the cathode roller.

[0030] The electrolytic copper foil disclosed herein is mainly composed of copper, for example, the copper content can be 99 wt% or more. The electrolytic copper foil disclosed herein has a thickness of 3 to 20 μm or 4 to 10 μm, and a surface roughness Rz (JIS 0601B-1994) of less than 2 μm. The first aspect of this disclosure is to provide an electrolytic copper foil for lithium-ion secondary batteries, having a deposition surface and a roller surface, and the texture coefficient TC(220) of the electrolytic copper foil on the (220) crystal plane is ≥1.36, and the texture coefficient TC(311) on the (311) crystal plane is ≥0.79.

[0031] In this technical field, the texture coefficient refers to a measure of the crystal structure or crystal orientation distribution of a material. Texture refers to the similar crystal orientation of most grains in a polycrystalline material, while the texture coefficient represents the relative distribution degree of texture on a certain crystal plane. For example, the texture coefficient TC(220) of the (220) crystal plane refers to the relative distribution degree of the (220) crystal plane in a polycrystalline material. The texture coefficient of the electrolytic copper foil on a specific crystal plane is obtained by performing X-ray diffraction (XRD) analysis on the electrolytic copper foil when it is in a stable state and substituting the analysis results into equation (I).

[0032] In equation (I), TC(hkl) represents the texture factor of the (hkl) crystal plane; the larger the TC value, the higher the degree of preferred orientation of the crystal plane. I(hkl) represents the diffraction intensity of the (hkl) crystal plane of the specimen. I0(hkl) represents the diffraction intensity of the (hkl) crystal plane of standard copper powder as defined by ASTM PDF#040836. n represents the number of diffraction peaks within a specific diffraction angle (2θ).

[0033] The stable state can be achieved by letting the electrolytic copper foil stand for a period of time after preparation, such as more than 1 day, more than 3 days, or more than 7 days. Alternatively, the electrolytic copper foil can be aged after preparation, such as by letting it stand for 3 days at 35 to 45°C and 10 to 25% humidity.

[0034] In this paper, electrolytic copper foil was vacuum heated at 200℃ for 5 hours to simulate a thermal state in order to observe the crystallization changes of electrolytic copper foil under thermal conditions. After vacuum heating at 200℃ for 5 hours, the texture coefficients of the electrolytic copper foil on the (220) crystal plane and the (311) crystal plane can be expressed as TC'(220) and TC'(311), respectively. The change rate of TC(220) can be obtained by the difference between TC(220) and TC'(220). Similarly, the change rate of TC(311) can be obtained by the difference between TC(311) and TC'(311).

[0035] Generally, the crystal orientations in polycrystalline materials should be randomly distributed. However, by controlling certain factors, most grains in the material can have similar crystal orientations, thus giving the material anisotropy. The inventors of this case discovered that when the crystals of copper foil are at a specific texture coefficient, its mechanical properties, such as tensile strength and the rate of tensile strength decay under thermal conditions, are significantly improved, and the rate of tensile strength decay under thermal conditions is also significantly slowed down, thereby improving the battery's tolerance.

[0036] Through dedicated research, the inventors of this case have discovered that the texture of electrolytic copper foil is related to its tensile strength and the rate of tensile strength degradation under thermal conditions (thermal stability). If the rate of tensile strength degradation of electrolytic copper foil under thermal conditions is severe, the electrolytic copper foil is prone to wrinkling or cracking. The inventors of this case have found that by simultaneously controlling the texture coefficients TC(220) and TC(311) of the electrolytic copper foil, such that the texture coefficient TC(220) of the (220) crystal plane is ≥1.36 and the texture coefficient TC(311) of the (311) crystal plane is ≥0.79, the desired high tensile strength can be obtained, and the electrolytic copper foil can have only a small rate of tensile strength degradation under thermal conditions. Specifically, when the electrolytic copper foil has the aforementioned texture coefficient, it will have a high tensile strength of greater than or equal to 50 kg / mm2, and after being vacuum heated at 200°C for 5 hours, the tensile strength can still be maintained at greater than or equal to 50 kg / mm2; that is, after being vacuum heated at 200°C for 5 hours, the tensile strength decay rate can be maintained at less than or equal to 10%.

[0037] In one specific embodiment, the TC (220) of the electrolytic copper foil is between 1.36 and 2.75, and the TC (311) of the electrolytic copper foil is between 0.79 and 1.10.

[0038] In one specific embodiment, the TC (311) of the electrolytic copper foil is between 0.85 and 1.05. Within this range, the rate of decrease in tensile strength of the copper foil under hot conditions is further suppressed, for example, the rate of decrease in tensile strength can be less than or equal to 5%.

[0039] In one specific embodiment, after the electrolytic copper foil was vacuum heated at 200°C for 5 hours, the change rate of TC(220) was <5%. In another specific embodiment, after the electrolytic copper foil was vacuum heated at 200°C for 5 hours, the change rate of TC(311) was <6%. This disclosure stabilizes the crystal structure of the electrolytic copper foil by controlling the texture coefficient of the electrolytic copper foil in both the stable and hot states, specifically by controlling the change rate of the texture coefficient TC(220) to be less than or equal to 5% and the change rate of TC(311) to be less than or equal to 6%, thereby enabling the electrolytic copper foil to still exhibit high tensile strength under high heat, thus improving the defect of mechanical property degradation of copper foil due to heat in the prior art.

[0040] In one specific embodiment, the electrolytic copper foil may be processed to be multilayered. For example, at least one surface of the electrolytic copper foil has a rust-preventive layer, which may be formed of organic or inorganic materials. In one specific embodiment, the rust-preventive layer may be formed by plating chromium, nickel, zinc, cobalt, manganese, tin, or mixtures thereof, such as a chromium-plated rust-preventive layer. In one specific embodiment, at least one surface of the electrolytic copper foil may be coated with an organic compound containing at least one element selected from carbon, oxygen, nitrogen, sulfur, silicon, etc. The organic compound includes, for example, porphyrin group, silane group, benzotriazole, triazine trithiol, and combinations thereof. If a rust-preventive layer is present, its thickness is typically from 0.2 nm to 100 nm, but is not limited thereto. For example, in order to apply it to sulfur-based solid-state batteries, a corrosion-resistant metal can be appropriately selected and the thickness of the anti-rust layer can be increased to resist the corrosion of the electrolyte. For example, a nickel layer with a thickness of more than 0.5 μm can be used as an anti-rust layer.

[0041] The electrolytic copper foil disclosed herein, as shown in Figure 1, may include a copper layer 51, and at least one surface of the copper layer 51 has a rust-preventive layer. The example in Figure 1 shows rust-preventive layers 52 and 53 on both the deposition surface 511 and the roller surface 512 of the copper layer, but this is not a limitation. The rust-preventive layer of the electrolytic copper foil disclosed herein may also use different materials on the two surfaces, for example, a nickel rust-preventive layer and a chromium rust-preventive layer on the two surfaces, but this is not a limitation.

[0042] [Methods for Manufacturing Electrolytic Copper Foil]

[0043] The electrolytic copper foil disclosed herein can be manufactured by the exemplary manufacturing method described below, but is not limited thereto. As shown in FIG2, the equipment for producing electrolytic copper foil 50 includes an electrolytic deposition apparatus 10, an optional rust prevention treatment apparatus 20, and a series of guide rollers 30. The electrolytic deposition apparatus 10 includes a cathode roller 11, an insoluble anode plate 12, and a copper electrolyte 13. The cathode roller 11 is a rotatable titanium cathode roller. The insoluble anode plate 12 is an iridium oxide coated titanium plate, which is disposed below the cathode roller 11 and generally surrounds the lower half of the cathode roller 11, and has an anode surface facing the cathode roller. The cathode roller 11 and the insoluble anode plate 12 are spaced apart from each other to accommodate the copper electrolyte 13. After the copper electrolyte 13 is filled, a portion of the cathode roller 11 is immersed in the copper electrolyte 13. A current is then applied between the cathode roller 11 and the insoluble anode plate, causing the copper electrolyte 13 to electrodeposit on the surface of the cathode roller 11 to form an electrolytic copper foil 50. Subsequently, the electrolytic copper foil 50 is peeled off from the surface of the cathode roller 11 and optionally subjected to further processing. This subsequent processing may include a rust-prevention treatment, which forms a rust-prevention layer on at least one surface of the electrolytic copper foil using a rust-prevention treatment device 20. The rust-prevention treatment device 20 includes a rust-prevention treatment tank 21 and an electrode plate 210 disposed therein. The electrolytic copper foil 50 can be conveyed via a series of guide rollers 30, including conveying the electrolytic copper foil 50 peeled off from the surface of the cathode roller 11 to the rust-prevention treatment device 20 for rust-prevention treatment, and also passing the rust-prevention treated electrolytic copper foil 50 through an air knife 40 to remove excess rust and other substances from the surface. The electrolytic copper foil 50 can finally be wound up on the last guide roller.

[0044] By controlling the composition of the copper electrolyte (e.g., the concentrations of copper ions, sulfuric acid, chloride ions, and additives), current density, and temperature during electrodeposition, the crystal growth of electrolytic copper foil can be controlled. This disclosure allows for adjustment of the electrolytic deposition parameters during the electrolytic copper foil manufacturing process as needed. In one embodiment, the copper electrolyte formulation in the electrodeposition step may include copper sulfate, sulfuric acid, chloride ions, and additives, but is not limited thereto. In one embodiment, the copper sulfate (CuSO4‧5H2O) concentration may be from 200 g / L to 400 g / L, the sulfuric acid concentration may be from 80 g / L to 150 g / L, the chloride ion concentration may be from 20 ppm to 100 mg / L, and the additive concentration may be less than 90 ppm.

[0045] Examples of additives mentioned above include gelatin, polyethylene glycol, cellulose-based water-soluble polymers, polyethyleneimine, and polyacrylamide, but are not limited to these. From the perspective of controlling TC(220) and TC(311), the polymer and its pyrolysis products can be used as additives. Based on the overall copper electrolyte, the polymer content is 20 to 50 ppm, the pyrolysis product content is 5 to 20 ppm, and the ratio of pyrolysis product to polymer is 0.2 to 0.5. The molecular weight of the unpyrolyzed polymer can be selected between 20,000 and 100,000, but can be adjusted as needed.

[0046] The pyrolysis product can be obtained by electrolyzing the aforementioned polymer. For example, an aqueous solution containing the polymer is added between a titanium plate (positive electrode) and a copper plate (negative electrode), and then electrolyzed with direct current. In addition to the aforementioned polymer, the aqueous solution may contain excipients such as sodium thiosulfate, potassium sulfide, sodium 3-mercapto-1-propanesulfonate (MPS), or sodium bisulfide (SPS). Electrolysis conditions can be 5–30 amperes per square decimeter (A / dm²) of direct current, and the electrolysis time can be 8–15 seconds. The excipient content, based on the total copper electrolyte, is less than 50 ppm.

[0047] Rust prevention treatment, as shown in Figure 2, involves immersing electrolytic copper foil 50 in a rust prevention treatment tank 21 filled with rust-preventive liquid, and forming a rust-preventive layer on the surface of the electrolytic copper foil 50 by electrode deposition via electrode plate 210. Alternatively, the electrolytic copper foil can be immersed in rust-preventive liquid to allow molecules to adsorb and bond to the surface of the electrolytic copper foil. The material of the rust-preventive layer can be selected according to requirements. The rust-preventive liquid used can be an organic rust-preventive liquid containing azole compounds, or an inorganic rust-preventive liquid such as chromium rust-preventive liquid, nickel rust-preventive liquid, zinc rust-preventive liquid, or tin rust-preventive liquid.

[0048] In one embodiment, the rust inhibitor may be a chromium rust inhibitor, the concentration of chromium trioxide (CrO3) may be 1.5 g / L to 5.0 g / L, the current density may be 0.5 A / dm2 to 6.0 A / dm2, the liquid temperature of the chromium rust inhibitor may be 20℃ to 40℃, and the rust prevention treatment time may be 2 seconds to 4 seconds, but is not limited thereto.

[0049] In one embodiment, the rust inhibitor may be a nickel rust inhibitor, the concentration of nickel sulfate (NiSO4) may be 1.5 g / L to 5.0 g / L, the concentration of boric acid (H3BO3) may be 15 g / L to 40 g / L, the concentration of chloride ions may be 10 to 30 ppm, the current density may be 0.3 A / dm2 to 0.8 A / dm2, the temperature of the nickel rust inhibitor may be 15℃ to 50℃, the pH value may be 3 to 4, and the rust prevention treatment time may be 2 seconds to 20 seconds, but is not limited thereto.

[0050] In one embodiment, the rust inhibitor may be a zinc rust inhibitor, the zinc sulfate (ZnSO4) concentration may be 8.0 g / L to 12.0 g / L, the current density may be 0.2 A / dm2 to 0.5 A / dm2, the liquid temperature of the zinc rust inhibitor may be 15℃ to 20℃, the pH value may be 12 to 14, and the rust prevention treatment time may be 2 seconds to 20 seconds, but is not limited thereto.

[0051] [Current collector for lithium-ion secondary batteries]

[0052] A second aspect of this disclosure is to provide a current collector for a lithium-ion secondary battery, comprising the electrolytic copper foil disclosed herein. At least one side of the electrolytic copper foil is coated with at least one layer of active material to form a current collector and electrode for a lithium-ion secondary battery. The current collector may be a positive current collector and / or a negative current collector; the electrode may be a positive electrode and / or a negative electrode.

[0053] Active materials can be categorized into positive electrode active materials and negative electrode active materials. Negative electrode active materials contain negative electrode active substances, which can be carbon-containing substances, silicon-containing substances, silicon-carbon composites, metals, metal oxides, metal alloys, or polymers; preferably carbon-containing or silicon-containing substances, but not limited to these. Specifically, the carbon-containing substances can be mesophase graphite powder (MGP), non-graphitizing carbon, coke, graphite, glassy carbon, carbon fiber, activated carbon, carbon black, or calcined polymers, but not limited to these; wherein, coke includes pitch coke, needle coke, or petroleum coke, etc.; the calcined polymers are obtained by carbonizing polymers such as phenol-formaldehyde resin or furan resin at appropriate temperatures. The silicon-containing material possesses excellent ability to form alloys with lithium ions and excellent ability to extract lithium ions from the alloyed lithium. Furthermore, 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 (Co), iron (Fe), tin (Sn), nickel (Ni), copper (Cu), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), chromium (Cr), ruthenium (Ru), molybdenum (Mo), or combinations thereof, to form alloy materials. The metal or metal alloy elements may be selected from the group consisting of: 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 oxides are ferric oxide, magnetite, ruthenium dioxide, molybdenum dioxide, and molybdenum trioxide, but are not limited thereto. Examples of the polymers mentioned are polyacetylene and polypyrrole, but are not limited thereto.

[0054] The active material may be supplemented with auxiliary additives as needed. These auxiliary additives may be binders and / or weak acid reagents, but are not limited thereto. Preferably, the binder may be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly(acrylic acid), PAA, polyacrylonitrile (PAN), or polyacrylate, and the weak acid reagent may be oxalic acid, citric acid, lactic acid, acetic acid, or formic acid.

[0055] [Lithium-ion secondary batteries]

[0056] A third aspect of this disclosure is to provide a lithium-ion secondary battery, including the current collector / electrode disclosed herein.

[0057] According to this disclosure, depending on the composition of different cathode slurries, the lithium-ion secondary batteries disclosed herein may be lithium cobalt batteries (LiCoO2 battery), lithium nickel batteries (LiNiO2 battery), lithium manganese batteries (LiMn2O4 battery), lithium cobalt nickel batteries (LiCoXNi1-XO2 battery), or lithium iron phosphate batteries (LiFePO4 battery), but are not limited thereto.

[0058] According to this disclosure, a lithium-ion secondary battery includes an electrolyte, which may contain solvents, electrolytes, or additives as appropriate. Solvents in the electrolyte include non-aqueous solvents, such as cyclic carbonates like ethylene carbonate (EC) or propylene carbonate (PC); chain carbonates like dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC); or sultones, but are not limited thereto; the aforementioned solvents may be used alone or in combination of two or more solvents. Electrolytes include, but are not limited to, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalate)borate, and lithium bis(trifluoromethanesulfonamide).

[0059] In one specific embodiment, the lithium-ion secondary battery may use solid electrolytes instead of the aforementioned electrolyte. For example, the solid electrolyte may be a crystalline electrolyte, a glassy 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 LISICON type or argyrodite type; or an oxide solid electrolyte such as a garnet type, perovskite type, or NASICON type, but is not limited thereto. The glassy electrolyte may be a glassy solid electrolyte such as an oxide or sulfide, but is not limited thereto. Polymer electrolytes can be pure solid polymer electrolytes such as polyethylene oxide-based (PEO system) and polypropylene oxide-based (PPO system); or colloidal polymer electrolytes such as polyacrylonitrile-based (PAN system), poly(methyl methacrylate)-based (PMMA system), poly(vinyl chloride)-based (PVC system), and poly(vinylidene fluoride)-based (PVDF system), but are not limited thereto.

[0060] According to this disclosure, a lithium-ion secondary battery can be a stacked lithium-ion secondary battery comprising a negative electrode and a positive electrode stacked through 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, the lithium-ion secondary battery disclosed herein can be used in notebook computers, mobile phones, electric vehicles, and energy storage systems, and can be manufactured as, for example, cylindrical secondary batteries, prismatic secondary batteries, pouch secondary batteries, or button-type secondary batteries, but is not limited thereto.

[0061] The details are further illustrated by the following embodiments. However, the interpretation of this disclosure should not be limited to the description of the following embodiments.

[0062] [Example]

[0063] A copper electrolyte is prepared using the following materials, causing a titanium cathode roller to rotate at a constant speed and contact the copper electrolyte. An electric current (i.e., the following electrolytic deposition conditions) is applied to the titanium cathode roller and the insoluble anode plate, causing the copper electrolyte to deposit on the surface of the titanium cathode roller to form an electrolytic copper foil. The electrolytic copper foil is then peeled off and guided onto a series of guide rollers. [Copper Electrolyte Formulation] Copper sulfate (CuSO4‧5H2O): 320g / l Sulfuric acid: 85g / l Chloride ions: 77 ppm Additives: Gelatin (Mw 40,000 to 60,000, purchased from Hiroei Chemical Co., Ltd.) 20 to 50 ppm Gelatin lysis products (Mw 12,000 to 16,000) 5 to 20 ppm The ratio of gelatin pyrolysis products to gelatin is 0.2 to 0.5. Sodium thiosulfate 5 to 20 ppm Gelatin pyrolysis products are prepared and used as follows: Gelatin and sodium thiosulfate are mixed in water to prepare an aqueous solution containing 20 g / L gelatin and 20 g / L sodium thiosulfate. A titanium plate is set as the positive electrode and a copper plate as the negative electrode. Electrolysis is performed for 10 seconds at a direct current of 20 A / dm² to produce small molecule gelatin pyrolysis products (Mw 12,000~16,000). This aqueous solution contains gelatin pyrolysis products and an equal amount of sodium thiosulfate. When using, an appropriate amount of the aforementioned aqueous solution is added to the copper electrolyte, taking the entire solution as the basis. [Electrodeposition conditions] Temperature: 48℃ Current density: 44A / dm2 Electrolytic copper foil thickness: 4~10μm

[0064] Next, the electrolytic copper foil is conveyed to the rust prevention treatment device via a series of guide rollers for rust prevention treatment. The electrolytic copper foil is immersed in a rust prevention treatment tank filled with rust-preventive liquid, and a rust-preventive layer is formed on both surfaces of the electrolytic copper foil by electrodeposition using two sets of electrode plates. [Rust Inhibitor Formula] Chromium trioxide (CrO3), concentration: 1.5 g / L [Rust prevention treatment conditions] Temperature: 25℃ Current density: 0.5 A / dm² Electroplating time: 2 seconds

[0065] After the rust-proofing treatment is completed, the rust-proofed electrolytic copper foil is guided to a series of guide rollers. An air knife is used to remove excess rust-proofing liquid and other substances from the surface, and the foil is dried before being wound up to obtain the electrolytic copper foil. The electrolytic copper foils prepared in Examples 1-7 are shown in Table 1 below.

[0066] [Comparative Example]

[0067] Comparative Examples 1-5 are electrolytic copper foils. Except for the manufacturing parameters shown in Table 1, the other manufacturing procedures are the same as those in the Examples.

[0068] Table 1

[0069] Test methods

[0070] XRD analysis was performed on the electrolytic copper foils prepared in the examples and comparative examples to observe the structure and texture of the electrolytic copper foils. [XRD Analysis] Instrument: Bruker D2 PHASFR Target material: copper tube Radiation: Cu-Kα (1.5418 Å) Voltage: 45kV Current: 40mA Scan range: 2θ is 40~95° Scan rate: 0.2° / second

[0071] The texture factor of each electrolytic copper foil is calculated using the following formula (I):

[0072] In equation (I), TC(hkl) represents the texture factor of the (hkl) crystal plane; the larger the TC value, the higher the degree of preferred orientation of the crystal plane. I(hkl) represents the diffraction intensity of the (hkl) crystal plane of the specimen. I0(hkl) represents the diffraction intensity of the (hkl) crystal plane of standard copper powder as defined by ASTM PDF#040836. n represents the number of diffraction peaks within a specific diffraction angle (2θ).

[0073] The prepared electrolytic copper foil was placed at 35-45℃ and RH 10-25% for 3 days to stabilize it. The texture coefficients of each crystal plane (TC(111), TC(200), TC(220) and TC(311)) of each electrolytic copper foil in the stable state and the texture coefficients of each crystal plane (TC'(220) and TC'(311)) in the hot state (simulated by annealing at 200℃ for 5 hours under vacuum) were obtained by XRD analysis of the deposition surface of the electrolytic copper foil. [Annealing treatment] Instrument: DENG YNG DOV-30 drying oven Vacuum degree: 760 mmHg Temperature: 200℃ Time: 2 hours

[0074] In addition, the tensile strength of each electrolytic copper foil and whether wrinkles and cracks occur were tested. The standards and parameters used are as follows. Tensile strength Standard: IPC-TM-650 2.4.18 Instrument: Shimadzu AG-I Universal Tensile Testing Machine Test piece size: 100mm (TD) x 12.7mm (MD) Temperature: 25℃ Chuck distance: 50mm Stretching speed: 50mm / min Does the electrolytic copper foil produce wrinkles or cracks? Continuously produce 10,000 meters of electrolytic copper foil and rewind it. Visually inspect the entire length of electrolytic copper foil to see if there are wrinkles and / or cracks that can be easily seen with the naked eye.

[0075] The results of texture coefficient, texture coefficient change rate, tensile strength, tensile strength decay rate, and whether wrinkles and cracks were obtained for each electrolytic copper foil through the above test methods are listed in Table 2 below.

[0076] Table 2

[0077] The results above show that the electrolytic copper foil disclosed in this study has high tensile strength and a low rate of tensile strength degradation under hot conditions, and no wrinkling or cracking of the electrolytic copper foil occurred during the preparation process. Furthermore, this study found that the TC(220) and TC(311) of the electrolytic copper foil are related to its tensile strength and the rate of tensile strength degradation under hot conditions. Specifically, the higher the TC(220) of the electrolytic copper foil, the higher its tensile strength; conversely, the lower the TC(220) and the higher the TC(311), the lower its tensile strength. In this study, the TC(220) and TC(311) of the electrolytic copper foil can be controlled by additives. These results fully confirm that by controlling the crystal orientation of the electrolytic copper foil, the system has a higher degree of crystal orientation on the (220) and (311) crystal planes, which enables the electrolytic copper foil to have excellent mechanical properties (e.g., high tensile strength) and to withstand thermal conditions without easily deteriorating mechanical properties (e.g., only a small rate of tensile strength degradation under thermal conditions). Thus, the electrolytic copper foil can be effectively used in lithium-ion secondary batteries to avoid thermal degradation caused by the charging and discharging process.

[0078] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Anyone skilled in the art can modify and alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of this invention should be as set forth in the following patent claims.

[0079] 10: Electrolytic deposition apparatus 11: Cathode Roller 12: Insoluble anode plate 13: Copper electrolyte 20: Rust prevention treatment device 21: Rust Prevention Treatment Tank 210: Plate 30: Guide roller 40: Air Knife 50: Electrolytic copper foil 51: Copper layer 511: Sedimentary surface 512: Roller surface 52, 53: Rust-proof coating

Claims

1. An electrolytic copper foil for lithium-ion secondary batteries, having a deposition surface and a roller surface opposite each other, wherein the texture coefficient TC(220) of the electrolytic copper foil is ≥1.36 on the (220) crystal plane and the texture coefficient TC(311) of the (311) crystal plane is ≥0.

79.

2. The electrolytic copper foil as described in claim 1, wherein, The TC (220) is between 1.36 and 2.75, and the TC (311) is between 0.79 and 1.

10.

3. The electrolytic copper foil as described in claim 1, wherein, After being vacuum heated at 200°C for 5 hours, the TC(220) change rate of the electrolytic copper foil was <5%.

4. The electrolytic copper foil as described in claim 1, wherein, After being vacuum heated at 200°C for 5 hours, the TC(311) change rate of the electrolytic copper foil was <6%.

5. The electrolytic copper foil as described in claim 1, wherein, The tensile strength of this electrolytic copper foil is ≥50 kg / mm².

6. The electrolytic copper foil as described in claim 1, wherein, The electrolytic copper foil, after being vacuum heated at 200℃ for 5 hours, has a tensile strength ≥50kg / mm2.

7. The electrolytic copper foil as described in claim 2, wherein, After being vacuum heated at 200°C for 5 hours, the electrolytic copper foil exhibited a tensile strength degradation rate of ≤10%.

8. The electrolytic copper foil as described in claim 1 is a surface-treated copper foil comprising a copper foil body and a rust-proof layer.

9. The electrolytic copper foil as claimed in claim 1, wherein, At least one surface of the electrolytic copper foil has a rust-preventive layer, which may be formed of organic or inorganic materials.

10. The electrolytic copper foil as claimed in claim 9, wherein, The inorganic material comprises at least one of the group consisting of chromium, nickel, zinc, cobalt, manganese and tin.

11. The electrolytic copper foil as claimed in claim 9, wherein, The organic material comprises at least one element selected from the group consisting of carbon, oxygen, nitrogen, sulfur, and silicon.

12. The electrolytic copper foil as claimed in claim 11, wherein, The organic material comprises at least one of the groups selected from porphyrin group, silane group, benzotriazole and triazine trithiol.

13. A current collector for a lithium-ion secondary battery, comprising an electrolytic copper foil as described in any one of claims 1 to 12.

14. A lithium-ion secondary battery comprising a current collector as described in claim 13.

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