Electrolytic copper foil and method for producing the same, composite copper foil, and current collector

Abstract

The application relates to an electrolytic copper foil and a preparation method thereof, a composite copper foil and a current collector. The method comprises the following steps: supplying an electrolyte between an anode and a cathode, performing first electroplating treatment at a current density J1, and forming a seed copper layer on the cathode; adjusting a current parameter, performing second electroplating treatment at a current density J2, and forming a thickened copper layer on the seed copper layer; wherein J1J2. The method changes the crystal growth behavior by a step-by-step electroplating process and adjusts the current density to improve the mechanical properties and peelability of the copper foil. Moreover, the step-by-step electroplating process does not need to replace electrolytic equipment and an electrolyte system, is simple, efficient and low in cost, and is suitable for industrialization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foil production, more particularly to an electrolytic copper foil, a preparation method thereof, a composite copper foil and a current collector. BACKGROUND

[0002] In recent years, with the rapid development of 5G, consumer electronics, new energy vehicles, energy storage and other fields, the demand for metal foil has increased rapidly, especially the demand for copper foil has increased significantly.

[0003] As a key material for lithium battery negative current collector, the preparation method of copper foil mainly includes electrolysis method (ED) and rolling method (RA). Among them, the electrolytic copper foil (ED copper foil) is formed by electrolytic deposition of copper ions on the cathode, and the thickening copper layer is formed on the seed copper layer by controlling the current density, additives and other processes. The surface treatment (such as roughening, passivation, etc.) is made into finished product, which has the advantages of low cost, mature process, and can mass-produce ultra-thin copper foil with thickness ≤6μm. The rolling copper foil (RA copper foil) is made by physically rolling high-purity copper ingot, annealing, pickling and other processes, which has excellent ductility (such as elongation at break >10%), but the thickness is difficult to be less than 6μm, and the cost is high. At present, the market share of electrolytic copper foil is more than 90%, which dominates the application of lithium battery.

[0004] The current battery industry is developing towards lightness and high-end, but the copper foil has the problems of high production cost, large density, large weight ratio in the battery, leading to low energy density of the battery. Based on this, the industry has developed an extremely thin copper foil with a thickness of 4.5μm. With the decrease of the thickness of the copper foil, the mechanical properties of the copper foil decrease significantly, and the copper foil is prone to wrinkle during transportation, storage, handling, taking and placing, pressing and other processes. Even scratches, copper marks or concave points occur, and the subsequent processing performance also deteriorates, such as protrusions, holes and even breakage (broken belt) during the coating and rolling preparation process of the battery, which needs to be improved. SUMMARY

[0005] Based on this, the present application provides a new preparation method of electrolytic copper foil, which can improve the mechanical properties of ultra-thin copper foil, and is used for composite copper foil and current collector.

[0006] The technical scheme of the present application is a preparation method of electrolytic copper foil, comprising the following steps:

[0007] An electrolyte is supplied between the anode and the cathode, a first electroplating treatment is carried out at a current density J1, and a seed copper layer is formed on the cathode;

[0008] The current parameters are adjusted, a second electroplating treatment is carried out at a current density J2, and a thickening copper layer is formed on the seed copper layer;

[0009] Wherein, J1 < J2.

[0010] In one embodiment, J1 and J2 satisfy: J2 / J1≥1.5, and the units of J1 and J2 are both A / dm2.

[0011] In one embodiment, J1 and J2 satisfy: J2 / J1≥4.

[0012] In one embodiment, J1 and J2 satisfy: J1 is 2 A / dm2~20 A / dm2, and J2 is 30 A / dm2~75 A / dm2.

[0013] In one embodiment, J1 and J2 satisfy: J1 is 5 A / dm2~15 A / dm2, and J2 is 40 A / dm2~60 A / dm2.

[0014] In one embodiment, the power source used in the first electroplating process is direct current.

[0015] In one embodiment, the temperature of the electrolyte during the first electroplating process is 40℃~55℃.

[0016] In one embodiment, the power source used in the second electroplating process is direct current.

[0017] In one embodiment, the temperature of the electrolyte during the second electroplating process is 40℃~55℃.

[0018] In one embodiment, the thickness ratio of the seed copper layer to the thickened copper layer is 1:(2~100).

[0019] In one embodiment, the thickness of the seed copper layer is 0.02μm~0.5μm.

[0020] In one embodiment, the thickness of the thickened copper layer is≥1.5μm.

[0021] In one embodiment, the electrolyte comprises copper ions, sulfuric acid, and chloride ions, and the electrolyte further comprises one or more of a combination of brightener, leveler, leveler, wetter, and carrier type additives.

[0022] In one embodiment, the method for preparing an electrolytic copper foil further comprises the following steps:

[0023] Separating the copper foil comprising the seed copper layer and the thickened copper layer from the cathode.

[0024] The present application also provides an electrolytic copper foil prepared according to the method for preparing an electrolytic copper foil as described above.

[0025] The application also provides a composite copper foil, comprising an insulating layer and a copper foil layer arranged on at least one surface of the insulating layer, wherein the copper foil layer comprises the electrolytic copper foil as described above.

[0026] The application also provides a current collector, comprising the electrolytic copper foil as described above, or the composite copper foil as described above.

[0027] The application at least has the following beneficial effects:

[0028] The preparation method of the electrolytic copper foil provided by the application involves a step-by-step electroplating process. First, electroplating is performed at a low current density to form a seed copper layer with sparse crystal arrangement on the cathode. The seed copper layer has a large surface roughness and can provide more sites. Then, the current density is increased to form a thickened copper layer with fine and closely arranged crystals on the seed copper layer. The mechanical properties of the copper foil are significantly improved, and an ultrathin copper foil and an extremely thin copper foil with excellent mechanical properties and easy peeling are prepared. In addition, the step-by-step electroplating process of the application regulates crystal growth behavior by changing the current density to improve the mechanical properties of the copper foil. The electrolytic equipment and electrolyte system do not need to be replaced, which is simple, efficient, low in cost, and suitable for industrialization.

[0029] Tests show that the electrolytic copper foil prepared according to the step-by-step electroplating process of the application has a tensile strength of ≥260 MPa, an elongation at break of ≥3.0%, and is easy to peel, which can effectively avoid edge tearing and has excellent comprehensive performance. The electrolytic copper foil prepared by the application can be used for battery current collectors to reduce the weight of the battery and improve the energy density of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A flow chart of the preparation method of the electrolytic copper foil according to an embodiment of the application is shown.

[0031] Figure 2 An SEM image of the electrolytic copper foil with a total thickness of about 3 μm according to an embodiment of the application is shown. DETAILED DESCRIPTION

[0032] The technical solutions of the application will be described below in conjunction with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the application, not all the embodiments, and are only used to illustrate the application, and should not be regarded as limiting the scope of the application. In addition, the drawings are not drawn to scale 1:1, and the relative sizes of the elements are only drawn by example in the drawings to facilitate understanding of the application, but are not necessarily drawn according to the true scale, and the scale in the drawings does not constitute a limitation on the application.

[0033] The embodiments of the present application and the figures are only for illustrative purposes, and should not be understood as limiting the present application. The present application can be implemented in many different forms, and is not limited to the embodiments described in the present application. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0034] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the specification of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0035] In the present application, "and / or" includes any and all combinations of one or more of the associated listed items. The "comprise", "have", and "include" described in the present application are intended to cover non-exclusive inclusion, unless the explicit limiting language such as "only", "consisting of", etc. is used, otherwise another component can be added.

[0036] In the present application, "preferably", "more preferably", "preferably", "more preferably", etc. refer to the embodiments of the present application that can provide certain beneficial effects in certain cases. However, other embodiments can also be preferred in the same or other cases. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present application. That is, in the present application, "preferably", "more preferably", "preferably", "more preferably", etc. are only for describing the implementation or embodiment with better effect, but do not constitute a limitation on the scope of protection of the present application. Similarly, "further", "more further", "in particular", etc. are only for description purposes, indicating differences in content, but should not be understood as a limitation on the scope of protection of the present application.

[0037] In the present application, "A and B are independently selected from x, y or z" means that A and B are independent events, and event A does not affect the occurrence of event B, so when A is selected from x, B can be selected from any of x, y or z, when A is selected from y, B can be selected from any of x, y or z, and when A is selected from z, B can be selected from any of x, y or z.

[0038] When a numerical range is disclosed in the present application, the above range is considered to be continuous, and includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value. Further, when a range is referred to as an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in the present application should be understood to include any and all sub-ranges incorporated therein.

[0039] If there is no special description, all steps of the present application can be carried out in sequence, or randomly. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0040] In the present application, "above" or "below" includes the number itself. For example, 1 below includes 1.

[0041] In the present application, room temperature refers to 0℃~60℃, including but not limited to 10℃~40℃, or further 20℃~30℃.

[0042] In the present application, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features.

[0043] In the present application, the meaning of "several" or "several" is at least two, such as two, three, etc., unless otherwise specifically limited. The meaning of "several" is at least one, such as one, two, three, etc., unless otherwise specifically limited. "At least one" refers to any one, any two or any two or more. Unless otherwise mentioned, the singular form of the term can include the plural form, and cannot be understood as having a quantity of one.

[0044] In the present application, for orientation words, such as the terms "center", "transverse", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. The orientation and position relationship shown in the drawing is based on the orientation or position relationship shown in the drawing, only for the convenience of describing the present application and simplifying the description, and cannot be understood as indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and cannot be understood as limiting the specific protection scope of the present application.

[0045] In the present application, when describing positional relationships, unless otherwise specified, when an element such as a layer, film, or substrate is referred to as being "on" another film layer, it can be directly on the other film layer or intervening film layer(s) can also be present. Further, when a layer is referred to as being "under" another layer, it can be directly under the other layer, or one or more intervening layers can also be present. It will also be understood that when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers can also be present.

[0046] In the present application, the minimum molecular weight is denoted as Min, the maximum molecular weight is denoted as Max, and the interval between the minimum molecular weight and the maximum molecular weight Max is denoted as [Min, Max], including the minimum molecular weight Min and the maximum molecular weight Max.

[0047] In the present application, the test method for material tensile test (such as tensile strength and elongation at break) is well known to those skilled in the art, and the present application does not limit it. For example, the test method can refer to GB / T 29847-2013, SJ / T 11483-2014, or GB / T 1040.3-2006, and the test instrument can use a universal tensile testing machine (also known as a universal material testing machine or a tensile testing machine) to test the tensile strength and elongation at break of the sample.

[0048] In the present application, the viscosity of hydroxyethyl cellulose is the viscosity of a 2w% aqueous solution of the corresponding hydroxyethyl cellulose, measured by a Brookfield viscometer at 25°C, and the unit is mPa·s.

[0049] With the development of lithium battery technology, high energy density, lightweight, battery safety, and reducing battery cost have become the direction of lithium battery manufacturers. Traditional lithium batteries use electrolytic copper foil as the negative electrode current collector. The thickness of the mainstream electrolytic copper foil on the market is ≥6μm, its tensile strength is ≥330MPa, and the elongation at break is 3.0%~4.0%. Some enterprises have developed 4.5μm copper foil (which can be called ultra-thin copper foil), and its tensile strength is 280MPa~380MPa, and the elongation at break is 3.0%~4.0% (it can be understood that due to the use of different test standards and test conditions, the data is slightly different). With the further reduction of copper foil thickness, the mechanical properties of copper foil decrease significantly, so there are fewer reports in the industry about electrolytic ultra-thin or ultra-thin copper foil with a thickness less than or equal to 3.5μm.

[0050] In addition, in the process of electrolytic copper foil, the copper foil is usually directly peeled off from the cathode, and the thicker copper foil is not easy to tear during the peeling process, but as the thickness of the copper foil decreases, the tearing problem becomes more serious. In order to solve the problem of tearing of copper foil, the traditional method chooses to pre-treat or modify the structure of the cathode, or modify the anode, or change the composition of the additive, which is either complicated or high in equipment cost, or poor in electrolyte applicability or difficult to control the electrolysis parameters, unstable in copper foil performance, and large in batch difference, which is difficult to realize industrialization.

[0051] Therefore, it is of great significance to develop a new method capable of improving the mechanical properties of electrolytic copper foil and prepare ultra-thin / thin copper foil with excellent mechanical properties and easy peeling.

[0052] In order to solve the above problems, the present application provides a preparation method of electrolytic copper foil, as shown in Figure 1 The preparation method comprises the following steps:

[0053] S100: supplying an electrolyte between an anode and a cathode, performing first electroplating treatment at a current density J1, and forming a seed copper layer on the cathode;

[0054] S200: adjusting the current parameters, performing second electroplating treatment at a current density J2, and forming a thickened copper layer on the seed copper layer;

[0055] J1 < J2.

[0056] The preparation method of electrolytic copper foil provided by the present application involves a step-by-step electroplating process, first electroplating at a low current density to form a seed copper layer with sparse crystal arrangement on the cathode, and the seed copper layer has a larger roughness and a larger specific surface area. After increasing the current density, copper is deposited on the seed copper layer. Due to the large increase in the specific surface area of the seed copper layer, more sites are provided, and the number of copper crystal nuclei is greatly increased. As the electroplating proceeds, a thickened copper layer with fine crystals and close arrangement is formed on the seed copper layer, which significantly improves the mechanical properties of the copper foil.

[0057] In one embodiment, J1 and J2 satisfy: J2 / J1≥1.5, and the units of J1 and J2 are both A / dm². Controlling J2 / J1≥1.5 increases the structural gradient of the seed copper layer and the thickened copper layer, which is beneficial to improve the mechanical properties of the copper foil.

[0058] In one embodiment, J1 and J2 satisfy: J2 / J1≥4, which further increases the structural gradient of the seed copper layer and the thickened copper layer, which is more beneficial to improve the mechanical properties of the copper foil.

[0059] In one embodiment, J1 and J2 satisfy: J2 / J1 is 4-15, which is more beneficial to improve the mechanical properties and peeling properties of the copper foil.

[0060] In one embodiment, J1 and J2 satisfy: J1 is 2 A / dm2~20 A / dm2, and J2 is 30 A / dm2~75 A / dm2. Controlling J1 to be 2 A / dm2~20 A / dm2 can avoid the problems of too slow deposition speed of copper foil, too many bubbles in the deposition process, or too loose crystal arrangement on the seed copper layer, which cannot significantly increase the specific surface area and sites, and is not conducive to the deposition of the subsequent thickened copper layer, and the grains are not fine enough, which reduces the mechanical properties of the copper foil, such as reducing the tensile strength and elongation at break of the copper foil. Controlling J2 to be 30 A / dm2~75 A / dm2 can avoid the problems of coarse crystals, or burning, dendritic, and powdering of the copper foil, which results in not enough tightness between the grains, and deteriorates the mechanical properties of the copper foil, such as reducing the tensile strength and elongation at break of the copper foil.

[0061] In one embodiment, J1 and J2 satisfy: J1 is 5 A / dm2~15 A / dm2, and J2 is 40 A / dm2~60 A / dm2, which is more conducive to improving the mechanical properties and peelability of the copper foil.

[0062] It can be understood that the application does not have special restrictions on the anode and cathode used in the electrolysis process. For example, the anode can be selected from insoluble anodes, such as titanium (Ti) as a base material, and a noble metal oxide coating on the surface, and further, the coating composition can be selected from iridium-based coatings, such as IrO2-Ta2O5 (iridium oxide-tantalum oxide) and / or ruthenium-based coatings, such as RuO2-IrO2 (ruthenium oxide-iridium oxide); or, the anode can be selected from soluble anodes, such as electrolytic copper plates, such as phosphorus-containing copper, and the phosphorus content is 0.04wt%~0.06wt%. For example, the cathode can be selected from titanium or titanium alloy materials, such as titanium-palladium (Ti-Pd) alloy.

[0063] It can be understood that the application does not have special restrictions on the power source used in the electrolysis process. For example, the power source used in the first electroplating process and the second electroplating process is direct current, and the power source does not need to be replaced in the step-by-step electroplating process, which is simple and efficient.

[0064] It can be understood that the application does not have special restrictions on the temperature of the electrolyte. For example, during the first electroplating process and the second electroplating process, the temperature of the electrolyte is 40℃~55℃, the temperature range is wide, and the operation is simplified. In addition, the temperatures of the first electroplating process and the second electroplating process are independent of each other, and can be the same or different.

[0065] It is appreciated that the step-by-step electroplating process of the present application mainly regulates the crystal growth behavior by changing the current density to improve the mechanical properties of the copper foil, and the composition of the electrolyte is not specially limited in the present application, and the electrolyte can be a conventional formula or a self-made formula in the art; and the electrolytes used in the first electroplating process and the second electroplating process are independent of each other and can be the same or different. For example, the same electrolyte is used in the first electroplating process and the second electroplating process, which is more convenient, efficient and low in cost, and is suitable for industrialization.

[0066] In one embodiment, the electrolyte includes copper ions, sulfuric acid and chloride ions, and the electrolyte further includes one or more combinations of brightener, leveling agent, throwing agent, wetting agent and carrier additive. By adding one or more combinations of brightener, leveling agent, throwing agent, wetting agent and carrier additive, the performance of the copper foil is improved. It is appreciated that some raw materials have multiple functions, such as polyethylene glycol (PEG) which can be used as leveling agent, throwing agent, wetting agent and carrier.

[0067] Generally, the electrolyte includes an electrolyte mother liquor and an additive, the mother liquor includes copper ions and sulfuric acid, and chloride ions can be included as a mother liquor component or as an additive component. Chloride ions can activate sulfur-containing brighteners to form an active adsorption layer, refine grains, and improve the tensile strength of the copper foil; enhance the adsorption efficiency of leveling agents, fill the interstitial gaps of leveling agent molecules, enhance the uniformity of their coverage on the copper surface, and reduce the surface roughness of the copper foil; and regulate the copper deposition path, suppress side reactions, change the crystal orientation, improve the elongation at break of the copper foil, and protect insoluble anodes. It is appreciated that when chloride ions are added to the mother liquor, they can no longer be added to the additive.

[0068] In one embodiment, the electrolyte mother liquor includes:

[0069] Cu 2+ 60g / L~100g / L;

[0070] H2SO475g / L~140g / L.

[0071] The system as a whole is relatively stable, and after adding the additive, the electrolyte mother liquor and the additive can effectively play a role to prepare high-performance electrolytic copper foil.

[0072] In one embodiment, the electrolyte includes, in terms of concentration in the electrolyte, chloride ions 10ppm~60ppm, and it is appreciated that it includes but is not limited to 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, 55ppm or 60ppm, and preferably 15ppm~40ppm.

[0073] In one embodiment, the electrolyte further comprises a brightener. The brightener can be used to control the brightness of the copper foil surface, inhibit impurity formation, and ensure the weather resistance of the plated layer.

[0074] In one embodiment, the brightener comprises one or more of a combination of sulfur-containing organic brightener, 4-phenyl imidazole, 2-benzyl imidazoline, hexyl benzyl amine salt, and diphenyl vinyl pyridine. Further, the sulfur-containing organic brightener comprises one or more of a group consisting of sodium polydithiobis propane sulfonate (SPS), sodium thiazolinyl dithiobis propane sulfonate, sodium trimethyl formamide sulfonate, sodium N,N dimethyl dithioformamide propane sulfonate, sodium 3-mercapto-1-propane sulfonate (MPS), sodium diphenyl amine sulfonate, L-dithiothreitol, sodium 3 (benzothiazole 2 mercapto) propane sulfonate, sodium 2-hydroxy-3-mercapto thiosulfonate, tetrahydrothiazoline thione, sodium phenyl polydithiopropyl sulfonate, sodium alcohol thio propane sulfonate, sodium ethyl dithio carbonic acid propyl sulfonate, thiourea, polyisothiourethane propane sulfonate, or 2 hydroxy benzene thiourea.

[0075] In one embodiment, the electrolyte comprises, in terms of concentration in the electrolyte, 5 ppm to 20 ppm of the brightener.

[0076] In one embodiment, the electrolyte further comprises a wetting agent. The wetting agent is beneficial to better coverage of the workpiece surface by the plating liquid, reduction of air bubble production, and promotion of uniform distribution of the plating solution, thereby improving the uniformity and quality of the plated layer.

[0077] In one embodiment, the wetting agent comprises one or more of a combination of polyethylene glycol (PEG), octyl phenol polyoxyethylene ether (OPE), or polypropylene glycol (PPG).

[0078] In one embodiment, the electrolyte comprises, in terms of concentration in the electrolyte, 5 ppm to 20 ppm of the wetting agent.

[0079] In one embodiment, the electrolyte comprises the brightener and the wetting agent, and the brightener is sodium polydithiobis propane sulfonate and the wetting agent is polyethylene glycol.

[0080] In one embodiment, the electrolyte further comprises a leveling agent. The leveling agent can improve the surface flatness of the copper foil, refine the crystal grains, promote the preferred orientation of the crystal surface, reduce the warping degree, improve the oxidation resistance and corrosion resistance, and improve the mechanical properties and processing properties.

[0081] In one embodiment, the leveler comprises one or more of a nitrogen-containing organic leveler or agarose. Further, the nitrogen-containing organic leveler comprises one or more of the group consisting of diaminopolyglycols or amine organic compounds. Further, the amine organic compound comprises one or more of the group consisting of genamine, polyethyleneimine compounds, 1,1 dimethylpropargylamine, alkylated polyethyleneimine, quaternary ammonium salts or polyquaternary ammonium salts, benzotriazoles or arginine; and further, the polyethyleneimine compound comprises one or more of the group consisting of polyethyleneimine, polyethyleneimine alkyl compounds, N-acetyl ethyleneimine, polyethyleneimine alkyl or ethoxylated polyethyleneimine.

[0082] In one embodiment, the electrolyte comprises, in terms of concentration in the electrolyte, 0.01 ppm to 20 ppm of a leveler.

[0083] In one embodiment, the electrolyte further comprises a carrier additive. The carrier additive delays the consumption of the main additives (such as brightener and / or leveler) by physical coating / hydrogen bonding, stabilizes the activity of the main additives, prolongs the life of the additives, and maintains the concentration stable.

[0084] In one embodiment, the electrolyte comprises, in terms of concentration in the electrolyte, 20 ppm to 120 ppm of a carrier additive.

[0085] In one embodiment, the carrier additive comprises a combination of one or more of a protein and hydroxyethyl cellulose. With this type of additive, the electrolytic copper foil formed during the electrolysis process has improved mechanical properties in all aspects (such as tensile strength and elongation at break).

[0086] In one embodiment, the electrolyte comprises, in terms of concentration in the electrolyte, 20 ppm to 60 ppm (including but not limited to 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm or 60 ppm, preferably 20 ppm to 40 ppm) of a protein component comprising proteins of different molecular weights. Illustratively, the proteins of different molecular weights are distributed in a gradually increasing range of [molecular weight Min, molecular weight Max], and the proportion of the proteins of different molecular weights is normally distributed; or the proteins of different molecular weights are distributed in a gradually increasing range of [molecular weight Min, molecular weight Max], and the proportion of the proteins of different molecular weights is uniform.

[0087] Further, the molecular weights of the different molecular weight proteins can be increased in a stepwise manner; further, the difference (error) in the quantity ratio between the different molecular weight proteins in the protein component is less than or equal to 10%; the ratio refers to the quantity ratio in the overall protein component. Further, the molecular weight is the weight average molecular weight Mw.

[0088] When the protein mixture with different molecular weights according to the present application is used as an additive, the improvement effect on the mechanical properties of the electrolytic ultra-thin copper foil is remarkable, such as the elongation at break and tensile strength of the corresponding electrolytic copper foil can be significantly improved. The inventors speculate that this is because the adsorption sites of single molecular weight proteins are limited, so the improvement of the mechanical properties of the copper layer formed is limited, while different molecular weight proteins can provide multiple adsorption and binding sites, thereby further improving the flatness of the copper foil and the corresponding elongation at break and tensile strength.

[0089] In one embodiment, the molecular weight Min is greater than or equal to 180, and the molecular weight Max is less than or equal to 10,000. Further, the difference between the molecular weight Max and the molecular weight Min is greater than or equal to 1,800. Further, a protein component with a different molecular weight distribution width range can be used as an additive, which is not particularly limited in the present application. For example, [molecular weight Min, molecular weight Max] can be [1,000, 3,000], [3,000, 5,000], or [5,000, 10,000]. In one embodiment, the present application uses normally distributed proteins with different molecular weights in the interval [1,000, 3,000], and the electrolytic copper foil obtained has excellent mechanical properties.

[0090] In one embodiment, the protein component includes one or more combinations of collagen, gelatin, proteose peptone, and protein peptides. For example, the protein component is collagen or gelatin.

[0091] In one embodiment, the electrolyte includes, in terms of concentration in the electrolyte, 20 ppm to 60 ppm (including but not limited to 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, or 60 ppm, preferably 20 ppm to 40 ppm) of a hydroxyethyl cellulose mixture, the hydroxyethyl cellulose mixture including hydroxyethyl cellulose with different viscosities.

[0092] When the hydroxyethyl cellulose mixture containing hydroxyethyl celluloses with different viscosities is added to the electrolyte containing copper ions, the compactness and tensile strength of the copper foil produced by electrolysis are further enhanced. It is speculated that this may be due to the fact that the hydroxyethyl cellulose mixture contains hydroxyethyl celluloses with different viscosities (understandably, viscosity is related to molecular weight, and different viscosities in this application can be regarded as different molecular weights). With the combination of hydroxyethyl cellulose and copper ions, different molecular weight hydroxyethyl cellulose achieves the combination of copper ions in different directions and different distances. Through the combination of hydroxyethyl cellulose with different molecular weights, a complex copper ion distribution network can be formed, and a complex structure with a wide distribution and a high concentration of copper ions can be formed, thereby significantly improving the compactness and stability of the copper foil produced by electrolysis, and synergistically improving the tensile strength and elongation at break of the copper foil. On the other hand, by linking and combining copper ions with hydroxyethyl cellulose to improve the compactness of the copper foil, the number of pinholes can be significantly reduced and the light transmittance of the copper foil can be reduced.

[0093] Understandably, the proportion of hydroxyethyl celluloses with different viscosities in the hydroxyethyl cellulose mixture can be adjusted according to requirements. The component content of the additive in the electrolyte refers to the concentration of the additive in the overall electrolytic solution after the additive is added to the electrolyte.

[0094] In one embodiment, the viscosity of each of the hydroxyethyl celluloses is independently 15000 mPa·s to 100000 mPa·s, including but not limited to 15000 mPa·s, 20000 mPa·s, 24000 mPa·s, 25000 mPa·s, 30000 mPa·s, 35000 mPa·s, 40000 mPa·s, 45000 mPa·s, 50000 mPa·s, 55000 mPa·s, 60000 mPa·s, 65000 mPa·s, 70000 mPa·s, 75000 mPa·s, 80000 mPa·s, 85000 mPa·s, 90000 mPa·s, 95000 mPa·s, or 100000 mPa·s. The above hydroxyethyl cellulose components can better link and combine copper ions, thereby facilitating the improvement of the compactness of the corresponding copper foil, the reduction of pinholes, the reduction of light transmittance, and the significant improvement of the corresponding tensile strength.

[0095] In one embodiment, the hydroxyethyl cellulose mixture includes at least hydroxyethyl celluloses with different viscosities that differ by more than 1000 mPa·s. Further, the hydroxyethyl cellulose mixture includes at least hydroxyethyl celluloses with different viscosities that differ by more than 3000 mPa·s. When the different hydroxyethyl celluloses have a certain degree of viscosity / molecular weight difference, it is convenient to cross-link copper ions in a wider distance range, form a complex and wide cross-network, further improve the compactness and stability of the corresponding foil, and thereby improve the tensile strength of the copper foil.

[0096] In one embodiment, the hydroxyethyl cellulose mixture is formed by mixing two or more of hydroxyethyl cellulose with viscosity of 20000 mPa·s, 24000 mPa·s, 30000 mPa·s and 90000 mPa·s respectively. By using the above-mentioned several viscosity hydroxyethyl cellulose, the mechanical properties of the electrolytic copper foil are significantly improved.

[0097] In one embodiment, the additive described in the present application is composed of chloride ions, brighteners, wetting agents and carrier additives, and the carrier additives are compounded by protein components and hydroxyethyl cellulose mixtures. Exemplarily, the additive includes: chloride ions 15 ppm~40 ppm, brighteners 5 ppm~20 ppm, wetting agents 5 ppm~20 ppm, protein components 20 ppm~60 ppm, and hydroxyethyl cellulose mixtures 20 ppm~60 ppm, in terms of concentration in the electrolyte. By the cooperation of chloride ions, brighteners, wetting agents, protein components and hydroxyethyl cellulose mixtures, the performance of the electrolytic copper foil can be improved in many aspects, including flatness, density, tensile strength, elongation at break and surface brightness, etc. The comprehensive performance of the electrolytic ultra-thin copper foil is excellent, even if the thickness of the copper foil is less than 4.5 μm, or even less than 3 μm, it still has good mechanical properties and processability.

[0098] As described above, the composition of the electrolyte is not specially limited in the present application, in addition to the above-mentioned example formula, the electrolyte described in the present application can also be selected from commercially available products or published patent formulas, see the examples below.

[0099] For example, referring to CN109750334A, the concentration of copper ions in the copper sulfate electrolyte is 70 g / L~100 g / L, the concentration of sulfuric acid is 80 g / L~130 g / L, and the concentration of chloride ions is 25 ppm~35 ppm; the additive is composed of polyethylene glycol aqueous solution with concentration of 5 g / L~10 g / L, FESS aqueous solution with concentration of 2 g / L~5 g / L, low molecular glue aqueous solution with concentration of 4 g / L~8 g / L and polydithiodipropyl sulfonic acid sodium aqueous solution with concentration of 4 g / L~8 g / L. It can be understood that the additive is added according to the volume of the solution during use.

[0100] Alternatively, referring to CN119162619A, the concentration of copper ions in the electrolyte is 70 g / L~100 g / L, and the concentration of sulfuric acid is 90 g / L~140 g / L; the additives include polydithiopropane sulfonic acid sodium 10 g / L~100 g / L, 3-mercapto propane sulfonic acid sodium 30 g / L~70 g / L, 2-mercaptobenzimidazole 0~10 g / L, chloride ion 15 g / L~35 g / L, hydroxyethyl cellulose 5 g / L~25 g / L, polyacrylamide 0-10 g / L, polyethyleneimine and its derivatives 15 g / L~35 g / L, diethyl thiourea 30 g / L~60 g / L, tetrahydrothiazole thione-4-carboxylic acid 2 g / L~15 g / L. Understandably, the additive flow size is set as needed during use.

[0101] Alternatively, referring to CN110644021A, the electrolyte mother liquor has no special restrictions, and the additives include 2.5 g / L~3 g / L polyquaternary ammonium salt-10, 3.5 g / L~4 g / L polyquaternary ammonium salt-7, 2.5 g / L~3 g / L polyquaternary ammonium salt-51, 2 g / L~2.5 g / L polydithiopropane sulfonic acid sodium, 0.75 g / L~1.25 g / L alcohol sulfide propane sulfonic acid sodium, ≤0.5 g / L gelatin, ≤0.5 g / L basic crocein dye, ≤0.5 g / L N-butyl thiourea, 0.75 g / L~1.25 g / L sodium mercapto imidazole benzene sulfonate, and ≤0.75 g / L polyethylene glycol formaldehyde. Understandably, the additive flow size is set as needed during use.

[0102] In one embodiment, the thickness ratio of the seed copper layer to the thickened copper layer is 1:(2~100), which is more conducive to improving the mechanical properties and peelability of the copper foil. Understandably, the thickness ratio of the seed copper layer to the thickened copper layer includes but is not limited to 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22, 25, 28, 30, 35, 40, 45, 50, 60, 65, 70, 80, 90 or 100. Further, the thickness ratio of the seed copper layer to the thickened copper layer is 1:(2~50).

[0103] In one embodiment, the thickness of the seed copper layer is 0.02 μm~0.5 μm, including but not limited to 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm or 0.5 μm.

[0104] In one embodiment, the thickened copper layer has a thickness of ≥1.5 μm, including but not limited to 1.5 μm, 2.0 μm, 2.5 μm, 3 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, or 8.0 μm. In an exemplary embodiment, the thickened copper layer has a thickness of 2.0 μm to 5.5 μm. In a further exemplary embodiment, the thickened copper layer has a thickness of 2.0 μm to 4.0 μm.

[0105] In one embodiment, the method for preparing an electrolytic copper foil further comprises the following steps:

[0106] stripping the copper foil comprising the seed copper layer and the thickened copper layer from the cathode.

[0107] In addition, it is understood that the method for preparing an electrolytic copper foil described herein can comprise other conventional operations in the art, such as pre-treatment of the cathode, or subsequent roughening or passivation of the copper foil, in addition to the steps of step-by-step electroplating and stripping described above.

[0108] The present application also provides an electrolytic copper foil prepared according to the method described above.

[0109] As can be seen from the above, the present application first forms a seed copper layer with a sparse crystal structure at a low current, and then deposits a dense copper layer at a high current, thereby ensuring the mechanical properties of the copper foil body. According to the electrolytic method of the present application, an ultra-thin copper foil and an extremely thin copper foil with easy stripping and excellent mechanical properties can be prepared. Tests show that the electrolytic copper foil prepared by the present application has a tensile strength of ≥260 MPa, an elongation at break of ≥3.0%, and is easy to strip, thereby effectively avoiding edge tearing and having excellent comprehensive performance. In an exemplary embodiment, a 3 μm electrolytic copper foil prepared in some embodiments has a tensile strength of ≥320 MPa, an elongation at break of ≥4.0%, and is easy to strip. A 3 μm electrolytic copper foil prepared in some preferred embodiments has a tensile strength of ≥360 MPa, an elongation at break of ≥4.2%, and is easy to strip. In addition, an electrolytic copper foil with a thickness of ≥4 μm prepared in some embodiments has a tensile strength of ≥450 MPa, an elongation at break of ≥5.0%, and is easy to strip, and has very excellent comprehensive performance.

[0110] In addition, the step-by-step electroplating process of the present application adjusts the crystal growth behavior by changing the current density, thereby improving the mechanical properties of the copper foil. The present application does not require replacement of the electrolytic equipment and electrolyte system, and is simple, efficient, and low in cost, and is suitable for industrialization.

[0111] The present application also provides a composite copper foil comprising an insulating layer and a copper foil layer provided on at least one surface of the insulating layer, wherein the copper foil layer comprises the electrolytic copper foil described above. Since the electrolytic copper foil has excellent mechanical properties, the use of the electrolytic copper foil in the composite copper foil can significantly improve the mechanical properties of the composite copper foil.

[0112] It can be understood that the composite copper foil with copper foils arranged on both sides of the insulating layer is called double-sided composite copper foil, and the composite copper foil with copper foils arranged on one side of the insulating layer is called single-sided composite copper foil. The present application does not make special restrictions on the structure of the composite copper foil.

[0113] It can be understood that the present application does not make special restrictions on the insulating layer (including structure, material, thickness, length or width). For example, the insulating layer can be provided as one or more insulating functional layers. Alternatively, the insulating functional layer includes one or more combinations of a substrate layer, a support layer, an adhesive layer and a surface modification layer. Correspondingly, the composite copper foil is a two-layer composite copper foil, a three-layer composite copper foil, a four-layer composite copper foil, a five-layer composite copper foil, a six-layer composite copper foil, a seven-layer composite copper foil or the like.

[0114] In one embodiment, the structure of the composite copper foil can be a sandwiched layered structure, i.e., a first copper foil layer, an insulating layer and a second copper foil layer arranged in sequence. The insulating layer mainly plays a supporting role and reduces the weight and cost of the current collector, thereby improving the energy density of the battery. For example, the insulating layer can be a polymer substrate layer or an insulating functional layer capable of playing the same role, such as an adhesive layer having certain mechanical strength and adhesion. Alternatively, the adhesive layer is formed by curing an adhesive or an adhesive curing liquid.

[0115] In one embodiment, the structure of the composite copper foil can also be a four-layer or five-layer structure. For example, the insulating layer includes a polymer substrate layer and an adhesive layer arranged between the polymer substrate layer and the metal layer, which is used to enhance the bonding force between the polymer substrate layer and the metal layer and increase the peeling strength. For example, the adhesive layer is arranged between the first copper foil layer and the polymer substrate layer, and / or between the polymer substrate layer and the second copper foil layer. Alternatively, the adhesive layer is formed by curing an adhesive or an adhesive curing liquid.

[0116] In one embodiment, the structure of the composite copper foil can also be a six-layer or seven-layer structure. For example, the insulating layer includes the above-mentioned polymer substrate layer and adhesive layer, and a surface modification layer arranged between the polymer substrate layer and the adhesive layer, which is used to improve the bonding force between the polymer substrate layer and the adhesive layer.

[0117] In one embodiment, the thickness of the first copper foil layer is 0.8 μm to 10 μm. Further, the thickness of the first copper foil layer is 0.8 μm to 6 μm.

[0118] In one embodiment, the insulating layer is a polymer substrate layer. Further, the polymer substrate layer is made of one or more of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyimide (PI), polyamide (PA), polycarbonate (PC), polyvinyl chloride (PVC), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), acrylonitrile-styrene copolymer (SAN), acrylonitrile-butadiene-styrene terpolymer (ABS), poly aryl sulfone (PASF), polyethylene naphthalate (PEN), poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANI), and polypyrrole (PPy). Further, the polymer substrate layer is made of one or more of PET, PP, and PI. Further, the polymer substrate layer is made of one or more of PET and PP. For example, the polymer substrate layer is made of PET or PP.

[0119] In one embodiment, the insulating layer has a thickness of 1-15 μm. Further, the insulating layer has a thickness of 2-8 μm.

[0120] In one embodiment, the second copper foil layer has a thickness of 0.8-10 μm. Further, the second copper foil layer has a thickness of 0.8-6 μm.

[0121] The application also provides a current collector comprising the electrolytic copper foil as described above or the composite copper foil as described above. In view of the advantages of the electrolytic copper foil described above, the electrolytic copper foil is directly used as a current collector or is combined with an insulating material to form a composite copper foil which is further used as a current collector, thereby reducing the weight of the electrode plate and further reducing the weight of the battery and improving the energy density of the battery.

[0122] The application also provides a battery comprising the current collector as described above. In view of the excellent mechanical properties and processability of the current collector, the battery prepared using the current collector has the advantages of high energy density, good cycle performance, and safety and reliability.

[0123] Further, the battery is a lithium battery comprising a positive electrode plate, a separator, and a negative electrode plate. The lithium battery has the advantages of light weight, high energy density, good cycle performance, and safety and reliability.

[0124] In one embodiment, the positive electrode plate comprises a positive current collector and a positive active layer disposed on one side or both sides of the positive current collector. It can be understood that the application does not have special restrictions on the positive current collector and the positive active layer, such as the material and thickness of the positive current collector, and the components, amount, thickness, surface density, and compacted density of the positive active layer can be set according to the conventional requirements in the art.

[0125] In one embodiment, the negative electrode tab comprises a negative current collector and a negative active layer disposed on one side or both sides of the negative current collector, and the copper foil or composite copper foil described in the present application is used as the negative current collector. It can be understood that the negative active layer is not particularly limited in the present application, such as the components, amount, layer thickness, surface density and compaction density in the negative active layer, which can be set according to the conventional requirements in the art.

[0126] The shape of the battery is not particularly limited in the present application, which can be cylindrical, square or any other shape.

[0127] The preparation method of the battery is not particularly limited in the present application. Alternatively, the battery is prepared by a stacking process or by a winding process.

[0128] The present application also provides an energy storage device comprising the battery as described above, wherein the battery is used for storing or providing electrical energy. The energy storage device can be used in energy storage power stations, wind power systems, solar power systems, mobile power systems or temporary power supply systems (such as data center UPS power supply, communication base station backup battery) and the like. The energy storage device can store electrical energy as needed and output electrical energy at the appropriate time.

[0129] The present application also provides an electrical device comprising the battery as described above, wherein the battery provides electrical energy for the electrical device. Exemplarily, the electrical device comprises a vehicle, a lighting device, an industrial mechanical arm or robot, a medical device, a consumer electronics (such as a handheld appliance, a wearable electronics and a smart home) and the like.

[0130] The technical solutions of the present application will be described clearly and completely in the following with reference to the accompanying drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the embodiments, which are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, which are conventional products that can be purchased in the market.

[0131] Test method:

[0132] (1) The mechanical property test method of the copper foil or composite copper foil refers to GB / T29847-2013, and the test instrument is Dongguan Sitai ST-D200;

[0133] (2) Copper foil peelability: The electrolytic copper foil is peeled off from the cathode, and whether there is copper foil residue on the cathode is observed, and the percentage of the residual copper foil area on the cathode is divided into five levels, wherein, I level: no residue, very easy to peel; II level: 0 < residual copper foil area percentage ≤ 5%, easy to peel; III level: 5% < residual copper foil area percentage ≤ 20%, copper foil edge when peeling, poor peelability; IV level: 20% < residual copper foil area percentage ≤ 50%, poor peelability; V level: 50% < residual copper foil area percentage, very poor peelability.

[0134] Example 1

[0135] This embodiment provides a plurality of sets of electrolytic copper foils and a preparation method thereof, specifically as follows:

[0136] (1) The electrolyte is prepared according to the formula in Table 1;

[0137] Table 1 Electrolyte formula

[0138]

[0139] The protein used is collagen (P) and hydroxyethyl cellulose (HEC, unit: mPa·s), specifically, the protein component P has a weight average molecular weight of [1000, 3000] and a normal distribution of molecular weight distribution; the hydroxyethyl cellulose is a hydroxyethyl cellulose mixture formed by mixing hydroxyethyl cellulose with viscosities of 24000 mPa·s and 30000 mPa·s at a weight ratio of 1:1.

[0140] (2) The titanium plate coated with iridium-based coating IrO2-Ta2O5 on the surface is used as the anode, and the titanium substrate is used as the cathode, and the electrolyte is supplied between the anode plate and the cathode;

[0141] (3) The test group is subjected to first electroplating treatment under the conditions of electrolyte 50℃~55℃ and first current density J1 according to the parameters shown in Table 2, to form a seed copper layer on the titanium substrate;

[0142] (4) Adjust the current parameters, and perform second electroplating treatment under the condition of second current density J2 to form a thickened copper layer on the seed copper layer, to obtain an ultra-thin copper foil with a corresponding thickness; the control group uses one-step electroplating process to prepare electrolytic copper foil. Understandably, the thickness below refers to the average thickness, and there is an error within the range acceptable in the art due to the limitation of the measurement method.

[0143] The electrolytic copper foils obtained from the test group and the control group are subjected to performance tests, and the performance test results of the ultra-thin copper foils of each group are as shown in Table 2, and " / " indicates no.

[0144] Table 2 Main process parameters of electrolysis and copper foil performance data

[0145]

[0146] As can be seen from Table 2, compared with the one-step plating process of the control group, the electrolytic ultra-thin copper foil with a total thickness of about 3 μm prepared by the step-by-step plating process of the test group of the present application is superior in at least one aspect of tensile strength, elongation at break and peelability to the control group, and has better comprehensive performance. In particular, under low current density, the electrolytic copper foil prepared by the one-step plating process has extremely poor peelability and cannot be peeled off for testing mechanical properties; while increasing the current density, the peelability of the copper foil is improved, the elongation at break is moderate, but the tensile strength is poor.

[0147] Example 2

[0148] The present embodiment provides a plurality of groups of electrolytic copper foils and a preparation method thereof, specifically as follows:

[0149] (1) The electrolyte is prepared according to the formula in Table 1 above;

[0150] (2) A titanium plate coated with iridium-based coating IrO2-Ta2O5 on the surface is used as an anode, and a titanium substrate is used as a cathode, and the electrolyte is supplied between the anode plate and the cathode;

[0151] (3) The electrolyte is cycled for first plating treatment under the conditions of 50-55°C of the electrolyte and first current density J1 according to the parameters shown in Table 3, to form a seed copper layer on the titanium substrate;

[0152] (4) The current parameters are adjusted, the electrolyte is cycled for second plating treatment under the conditions of second current density J2, to form a thickened copper layer on the seed copper layer, to obtain ultra-thin copper foils with different thicknesses, and the obtained electrolytic copper foils are subjected to performance testing, and the performance test results of each group of ultra-thin copper foils are as shown in Table 3.

[0153] Table 3 Main process parameters of electrolysis and copper foil performance data

[0154]

[0155] As can be seen from Table 3, the electrolytic ultra-thin copper foils with different thicknesses prepared by the step-by-step plating process of the test group of the present application have a tensile strength of ≥260 MPa, an elongation at break of ≥3.0%, and are easy to peel off, which can effectively avoid edge tearing, and have excellent comprehensive performance; in addition, compared with commercially available copper foils with the same thickness, the electrolytic ultra-thin copper foils prepared by the present application have higher tensile strength, greater elongation at break, and better mechanical properties.

[0156] Example 3

[0157] The present embodiment provides a plurality of groups of electrolytic copper foils and a preparation method thereof, specifically as follows:

[0158] (1) The electrolyte is prepared according to Table 4;

[0159] Table 4 electrolyte formula

[0160]

[0161] (2) using a titanium plate coated with iridium-based coating IrO2-Ta2O5 as an anode, a titanium substrate as a cathode, and supplying an electrolyte between the anode plate and the cathode;

[0162] (3) performing first electroplating treatment on the titanium substrate under the conditions of electrolyte 45℃~55℃ and first current density J1 according to the parameters shown in Table 5, to form a seed copper layer;

[0163] (4) adjusting the current parameters, performing second electroplating treatment under the condition of second current density J2 to form a thickened copper layer on the seed copper layer, to obtain an ultra-thin copper foil with a corresponding thickness, and then performing performance testing on the obtained electrolytic copper foil, and the performance testing results of each group of ultra-thin copper foils are shown in Table 5.

[0164] Table 5 main process parameters of electrolysis and copper foil performance data

[0165]

[0166] As can be seen from Table 5, the step-by-step electroplating process of the present application is suitable for various electrolyte systems, and the electrolytic copper foils prepared by different electrolyte systems have excellent mechanical properties and are easy to peel, which can effectively avoid edge tearing and have excellent comprehensive performance.

[0167] Figure 2 The SEM results of the electrolytic copper foil with a total thickness of about 3 μm prepared by the test group 3 of the present application are shown in Figure 2, and it can be seen that the crystal grains are densely arranged, and the surface of the copper foil is relatively smooth and flat. Figure 2

[0168] In summary, the step-by-step electroplating process provided by the present application can regulate the crystal growth behavior by changing the current density, improve the mechanical properties and peelability of the copper foil, the prepared electrolytic copper foil has a tensile strength ≥260 MPa, an elongation at break ≥3.0%, is easy to peel, can effectively avoid edge tearing, has excellent comprehensive performance, and has a broad application prospect. Moreover, in the step-by-step electroplating process, the electrolytic equipment and electrolyte system can be replaced without changing the electrolytic equipment and electrolyte system, which is simple, efficient, low in cost, and suitable for industrialization.

[0169] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0170] ​The above-described embodiments only express several implementation manners of the present application, facilitate specific and detailed understanding of the technical solutions of the present application, but cannot be understood as a limitation on the patent protection scope of the present application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. It should be understood that, on the basis of the technical solutions provided by the present application, the technical solutions obtained by logical analysis, reasoning or limited experiments by the skilled person in the art all belong to the protection scope of the appended claims of the present application. Therefore, the patent protection scope of the present application should be subject to the content of the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A method for preparing electrolytic copper foil, characterized in that, Includes the following steps: An electrolyte is supplied between the anode and the cathode, and a first electroplating process is performed at a current density J1 to form a seed copper layer on the cathode. Adjust the current parameters to perform a second electroplating process with a current density of J2 to form a thickened copper layer on the seed copper layer. The power supply used for the first electroplating process and the second electroplating process is DC power, and J1 and J2 satisfy: J1 is 2A / dm²~20A / dm², and J2 is 30A / dm²~75A / dm². The thickness ratio of the seed copper layer to the thickened copper layer is 1:(10~100). The thickness of the seed copper layer is 0.02μm~0.5μm; the thickness of the thickened copper layer is ≥1.5μm; The electrolytic copper foil has a tensile strength ≥260MPa and an elongation at break ≥3.0%.

2. The method for preparing electrolytic copper foil according to claim 1, characterized in that, J1 and J2 satisfy: J2 / J1≥4.

3. The method for preparing electrolytic copper foil according to claim 1, characterized in that, J1 and J2 satisfy the following conditions: J1 is 5A / dm²~15A / dm², and J2 is 40A / dm²~60A / dm².

4. The method for preparing electrolytic copper foil according to claim 3, characterized in that, J1 is 10A / dm²~15A / dm².

5. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The thickness ratio of the seed copper layer to the thickened copper layer is 1:(10~50).

6. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The thickness of the seed copper layer is 0.02μm~0.2μm.

7. The method for preparing electrolytic copper foil according to claim 1, characterized in that, The thickness of the thickened copper layer is 2.0μm to 5.5μm.

8. The method for preparing electrolytic copper foil according to any one of claims 1 to 7, characterized in that, During the first and second electroplating processes, the temperature of the electrolyte is independently set to 40°C to 55°C.

9. The method for preparing electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The electrolyte includes copper ions, sulfuric acid and chloride ions, and further includes one or more of the following additives: brightener, leveling agent, positioning agent, wetting agent and carrier additive.

10. The method for preparing electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The resulting 3μm electrolytic copper foil has a tensile strength ≥320MPa, an elongation at break ≥4.0%, and is easy to peel off.

11. The method for preparing electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The resulting 3μm electrolytic copper foil has a tensile strength ≥360MPa, an elongation at break ≥4.2%, and is easy to peel off.

12. The method for preparing electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The resulting electrolytic copper foil with a thickness ≥4μm has a tensile strength ≥450MPa, an elongation at break ≥5.0%, and is easy to peel off.

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