A copper foil and a method for manufacturing the same and use thereof

Abstract

The application discloses a copper foil and a preparation method and application thereof, and belongs to the technical field of nano-structured metal material engineering. The copper foil comprises a nano-twin crystal structure inside the crystal grain; the nano-twin crystal structure comprises parallel twin crystal sheet layers and / or intersecting twin crystal sheet layers. The copper foil has stable mechanical properties and physical properties at room temperature. The stable performance means that the attenuation ratio of the mechanical properties is less than 10% after the green foil is treated by baking (150 DEG C, 10 min) or stored for 7 days at room temperature. The method is an improvement of a direct current electrolytic deposition copper foil method, the deposition process of copper is affected by changing the fluctuation amplitude of the output current, and finally, a high-density nano-twin crystal electrolytic copper foil with fine unit cells, uniform and small structures and intersecting twin crystal sheet layers in the crystal is obtained.

Description

Technical Field

[0001] This application relates to a copper foil, its preparation method, and its application, belonging to the field of nanostructured metallic materials engineering technology. Background Technology

[0002] The mechanical properties of electrolytic copper foil are a major bottleneck restricting its "ultra-thin" development. Traditional fine-grain strengthening theory holds that strength and plasticity cannot be simultaneously improved, while nanotwin strengthening offers a novel approach. On one hand, by utilizing the effective interaction between dislocations and twin boundaries, the strength and plasticity of electrolytic copper foil can be improved simultaneously. On the other hand, due to the weak electron scattering ability of twin boundaries, i.e., lower electrical resistance, high conductivity can be maintained. Research shows that reducing the thickness of twin lamellae to the nanometer level to increase twin density can effectively improve strength, plasticity, and conductivity.

[0003] Existing technologies for preparing copper foil with nanotwin structures include pulsed electrolytic deposition and direct current deposition methods. Lu Lei et al. prepared a copper foil structure with a strong (111) orientation, in which nanotwin lamellae are stacked along the (111) direction within longitudinally growing columnar crystals, dividing submicron-sized grains into nanoscale twin / matrix lamellar structures, which can significantly improve the tensile strength of the copper foil. However, the control of unidirectional twin structure growth is difficult, and there are strict requirements for deposition thickness, deposition time, and surface grain orientation of the substrate. In the application of ultrathin copper foil, the advantages of this structure are weakened because the thickness dimension of the copper foil is greatly reduced, the size of the (111) oriented columnar crystals is reduced, and the number of stackable twin lamellae within the crystals is greatly reduced, which leads to a decrease in the overall nanotwin density and very limited improvement in the performance of ultrathin copper foil.

[0004] Therefore, there is an urgent need to develop an easy-to-implement method for preparing copper foil with a high-density nanotwin structure that can be applied to actual production. Summary of the Invention

[0005] To address the problem of the inability to simultaneously achieve elongation, tensile strength, and conductivity in existing technologies for ultra-thin electrolytic copper foil, an electrolytic copper foil with a unique nanotwin structure and its preparation method are provided.

[0006] According to the first aspect of this application, an electrolytic copper foil is provided, which has stable and excellent mechanical and physical properties at room temperature. The stable properties mean that after the raw foil is baked (150°C, 10 min) or stored at room temperature for 7 days, the rate of decrease in mechanical properties is less than 10%. The copper foil has a uniform and fine grain structure, is equiaxed or nearly equiaxed, and has a random orientation or a (111) preferred orientation. The microstructure of the high-performance copper foil is characterized by a high-density nanotwin structure. The high-density nanotwin structure refers to the fact that the twin lamellae within the grain are parallel or intersecting, with a spatial angle between intersecting twin lamellae of 45°–90°, a lamellae thickness and spacing of 10–500 nm, and by controlling the process parameters, it is possible to achieve this twin structure in 50–80% of all grains, with twin boundaries accounting for as high as 80–90% of all grain boundaries.

[0007] A copper foil, wherein the interior of the copper foil grains comprises a nanotwin structure;

[0008] The nanotwin structure comprises parallel twin lamellae and / or intersecting twin lamellae.

[0009] The twin wafer layers can also interact and intersect with each other.

[0010] Optionally, the size of the grains is 0.5 μm to 5 μm.

[0011] Optionally, the orientation of the grains is random / specifically distributed.

[0012] Optionally, the included angle between intersecting twin wafer layers is 45° to 90°.

[0013] Optionally, the angle between intersecting twin wafer layers is 70° to 90°.

[0014] Optionally, the thickness of the twin wafer layer is 10 nm to 500 nm.

[0015] Optionally, the thickness of the twin wafer layer is independently selected from 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 220nm, 230nm, 240nm, etc. Any value or a range between any two of the following: 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, 420nm, 430nm, 440nm, 450nm, 460nm, 470nm, 480nm, 490nm, and 500nm.

[0016] Optionally, the spacing between the twin wafer layers is 10 nm to 500 nm.

[0017] Optionally, the spacing between the twin wafer layers is independently selected from 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 220nm, 230nm, 240nm, Any value or a range between any two of the following: 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, 420nm, 430nm, 440nm, 450nm, 460nm, 470nm, 480nm, 490nm, and 500nm.

[0018] Optionally, the thickness of the copper foil is 3μm to 100μm.

[0019] Optionally, the thickness of the copper foil is 4μm to 6μm.

[0020] Optionally, the thickness of the copper foil is independently selected from any value or a range between 3μm, 5μm, 7μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, and 100μm.

[0021] Optionally, along the thickness direction of the copper foil, from bottom to top, there exists a fine-grained region of 0μm to 0.5μm and the remaining equiaxed / nearly equiaxed grain regions.

[0022] Optionally, the grain structure of both the rough and smooth surfaces of the copper foil is equiaxed or approximately equiaxed.

[0023] Optionally, the grain structure of the copper foil surface and cross-section is equiaxed or approximately equiaxed.

[0024] Optionally, the grain structure orientation of the copper foil surface and cross-section is randomly / specifically distributed.

[0025] Optionally, grains containing nanotwins account for 50% to 80% of the total grain structure.

[0026] Optionally, the twin boundaries in the nanotwinned structure account for 80% to 90% of all grain boundaries.

[0027] Optionally, the percentage of grains containing nanotwins is independently selected from any value of 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any range between both.

[0028] Optionally, the proportion of twin boundaries to all grain boundaries in the nanotwinned structure is independently selected from any value of 80%, 82%, 84%, 86%, 88%, 90%, or any range between two.

[0029] According to a second aspect of this application, a method for preparing copper foil is provided. This method involves controlling the waveform and parameters of the output current fluctuation during the preparation of the raw foil. By utilizing minute but specific frequency current fluctuations to generate instantaneous tensile and relaxation stresses, the twinning nucleation rate under electrodeposition conditions is increased, resulting in parallel or intersecting twinned structures within the Cu deposited layer grains. This structure effectively controls the thickening of the twinned layer and grain growth. The minute fluctuations can be obtained by superimposing or paralleling multiple identical waveforms. The waveform of the output current is at least one of a sine wave, square wave, triangular wave, and sawtooth wave. The fluctuations have a frequency range of 0.1 Hz to 100 Hz. The current value difference between the peaks and troughs is 2-10% of the average current.

[0030] The preparation method randomly distributes the nucleation sites of twins, and the growth direction depends on the growth rate of each orientation crystal plane. It is particularly beneficial for the microstructure control and performance improvement of ultra-thin copper foils, and the method is simple and easy to control.

[0031] A method for preparing copper foil includes the following steps:

[0032] The copper foil is obtained by electrochemical reaction of a plating solution containing a copper source.

[0033] The output current used in the electrochemical reaction is direct current;

[0034] The DC current exhibits periodic, minute fluctuations near the average current.

[0035] The electrochemical reaction is electrolytic deposition.

[0036] The copper foil is obtained by electrolytically depositing metallic copper from a plating solution containing a copper source using electrochemical principles.

[0037] Further explanation is as follows:

[0038] A current pulse is a periodically repeating current with constantly varying intensity. It is equivalent to intermittently stopping the power supply; due to the intermittent interruption of the current, the cathode potential changes periodically over time.

[0039] The fluctuations differ from pulses in that, on the one hand, the degree of change in current intensity is smaller than that of pulses, and on the other hand, the power supply does not stop intermittently; that is, the intensity changes only around the average current, with only instantaneous changes in current strength.

[0040] Optionally, the copper source is a divalent copper salt.

[0041] Optionally, the divalent copper salt is selected from at least one of copper sulfate, copper chloride, and copper methanesulfonate.

[0042] Optionally, the plating solution contains sulfuric acid, chloride ions, and water.

[0043] Alternatively, Cu 2+ The concentration in the plating solution is 80 g / L to 100 g / L.

[0044] Optionally, when the copper source is copper sulfate pentahydrate, the content of the copper source in the plating solution is 350 g / L to 380 g / L.

[0045] Optionally, the concentration of chloride ions in the plating solution is 10 mg / L to 20 mg / L.

[0046] Optionally, the sulfuric acid content is 100 g / L to 130 g / L.

[0047] Optionally, the pH of the plating solution is 0.5 to 1.0.

[0048] Optionally, the conductivity of the plating solution is 150 mS / cm to 200 mS / cm.

[0049] Optionally, the fluctuation range of the output current is 2% to 10% of the average current.

[0050] The fluctuation range of the output current refers to the difference between the current values ​​at the peak and trough.

[0051] Optionally, the fluctuation range of the output current is independently selected from any value of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two.

[0052] Optionally, the frequency of the output current is 0.1Hz to 100Hz.

[0053] Optionally, the frequency of the output current is 0.1Hz to 2Hz.

[0054] Optionally, the frequency of the output current is independently selected from any value or a range between any two of 0.1Hz, 0.2Hz, 0.3Hz, 0.4Hz, 0.5Hz, 0.6Hz, 0.7Hz, 0.8Hz, 0.9Hz, 1Hz, 1.1Hz, 1.2Hz, 1.3Hz, 1.4Hz, 1.5Hz, 1.6Hz, 1.7Hz, 1.8Hz, 1.9Hz, 2Hz, 3Hz, 4Hz, 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, 10Hz, 12Hz, 14Hz, 16Hz, 18Hz, 20Hz, 25Hz, 30Hz, 35Hz, 40Hz, 45Hz, 50Hz, 55Hz, 60Hz, 65Hz, 70Hz, 75Hz, 80Hz, 85Hz, 90Hz, 95Hz, and 100Hz.

[0055] Optionally, the high-level ratio of the output current is 50% to 95%.

[0056] Optionally, the high-level ratio of the output current is 90% to 95%.

[0057] Optionally, the high-level ratio of the output current is independently selected from any value of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, or a range between any two.

[0058] Within a cycle, the proportion of time with current higher than the average current for the entire cycle:

[0059] High-level ratio = (time above average current / time of one cycle) × 100%.

[0060] Optionally, the waveform of the output current is at least one of a sine wave, a square wave, a triangular wave, and a sawtooth wave.

[0061] Optionally, the waveform of the output current is obtained by superimposing single or multiple waveforms and / or connecting them in parallel.

[0062] Alternatively, the conditions for the electrochemical reaction are as follows:

[0063] Current density is 50 A / dm2 ~70A / dm 2 .

[0064] Optionally, the current density is independently selected from 50 A / dm. 2 60A / dm 2 61A / dm 2 62A / dm 2 63A / dm 2 64A / dm 2 65A / dm 2 66A / dm 2 67A / dm 2 68A / dm 2 69A / dm 2 70A / dm 2 Any value in the range or any value between the two.

[0065] Optionally, the temperature of the plating solution is 52°C to 58°C.

[0066] Optionally, in the electrochemical reaction, a titanium / roller is used as the cathode, and a titanium plate with a titanium-iridium-tantalum coating is used as the anode. The area ratio of the cathode to the anode is 1:(1-2), and the distance between the cathode and anode is 10 mm to 20 mm.

[0067] Alternatively, the roughness of the titanium cathode is as follows:

[0068] Ra is 0.2μm~0.3μm;

[0069] Rz is 2.0μm to 2.5μm.

[0070] Optionally, the grain size of the titanium cathode surface is at least level 8 or higher.

[0071] According to one embodiment of this application, a method for preparing copper foil includes the following steps:

[0072] (1) Prepare a base plating solution of acid copper system free of impurities, set the plating solution temperature at 50℃~58℃, maintain the plating solution circulation, and maintain a flow rate of 0.1~5m. 3 / s, no copper particles precipitate in the plating solution. The pH of the plating solution is 0.5-1.0, and the conductivity of the plating solution is 150-200 mS / cm.

[0073] The base plating solution contains 300-380 g / L of copper sulfate, 100-130 g / L of sulfuric acid, and 10-20 mg / L of chloride ions.

[0074] (2) Place the prepared cathode (surface grain size greater than or equal to grade 8, surface Ra 0.2-0.3μm) and anode face to face into the plating solution. The area ratio of the cathode to the anode is 1:(1-2), and the distance between the cathode and anode is 10-20mm. Set the electrical parameters, and control the current density at 50-70 ASD (A / dm²). 2 Electrolytic deposition is used to prepare green foil. The power supply used in electrolytic deposition is a DC power supply, but the waveform of its output current has slight fluctuations and a certain frequency range. Preferably, this frequency range is 0.1Hz to 100Hz. The difference between the peak and trough current values ​​is 2-10% of the average current. The high-level ratio is 50% to 95%.

[0075] The high-level ratio refers to the proportion of time within a cycle that the current is higher than the average current for the entire cycle.

[0076] High-level ratio = (Time above average current / Time of one cycle) × 100%

[0077] (3) After a certain period of deposition, disconnect the circuit, rinse the prepared raw foil with dilute acid and pure water in sequence, blow dry, peel off, and then bake in a 150℃ oven for 10 minutes. After that, cool naturally to room temperature, or store at room temperature for 7 days to obtain a mature foil with stable performance at room temperature.

[0078] Test the tensile properties, surface roughness, and gloss of raw and cooked foils, and check for pinholes, warping, etc.

[0079] The method for calculating the mechanical attenuation ratio is as follows:

[0080] Mechanical attenuation percentage % = [(strength of baked foil or copper foil stored at room temperature for 7 days - strength of raw foil) / strength of raw foil] × 100%.

[0081] According to a third aspect of this application, an application of copper foil is provided.

[0082] The application of the copper foil described above and / or the copper foil obtained by the preparation method described above in lithium batteries.

[0083] During the deposition process, under the tensile and relaxation stresses generated by the fluctuating current, the twin structure within the grains rapidly nucleates and grows in a parallel or intersecting manner, obtaining a high-density nanotwin structure in a very short deposition time. This can significantly hinder the growth of twin wafers during copper foil baking, self-annealing at room temperature, and stress relief processes. Therefore, nanotwin copper foil with high elongation, high tensile strength, and high conductivity can be obtained.

[0084] The growth direction of the high-density nanotwin structure is not limited to the grain orientation of the matrix, but is anisotropic.

[0085] A further explanation suggests that when copper ions are deposited under completely direct current conditions, stress accumulates in the deposited layer as deposition progresses, easily leading to the formation of deformed grains. During the growth of these deformed grains within each layer, their higher energy causes them to develop around low-energy twin boundaries, reducing the number of large-angle grain boundaries and engulfing the deformed grains. The twinning region continuously expands and further engulfs the deformed grains, lowering the system energy. This results in a structure with large individual grains within the deposited layer and thicker twin layers, which is detrimental to performance improvement.

[0086] Copper ions are deposited under certain tensile and relaxation stresses, and the stress accumulated in each layer is released to a certain extent, reducing the nucleation of high-energy deformed grains. Twins can nucleate but are not large enough to grow, thus resulting in a finer twin lamellae structure.

[0087] The strength, elongation, surface roughness, and oxidation resistance of the copper foil will change depending on the choice of the waveform and the parameters of the fluctuation.

[0088] The beneficial effects that this application can produce include:

[0089] 1) This application provides a high-density nanotwinned electrolytic copper foil, which exhibits stable and excellent mechanical and physical properties at room temperature. This high-density nanotwinned electrolytic copper foil is free of pinholes and warping. The stable performance refers to the fact that after the raw foil is baked (150℃, 10 min) or stored at room temperature for 7 days, the rate of decrease in mechanical properties is less than 10%; the elongation of the 4μm to 6μm copper foil reaches 8±2%, and the tensile strength is not less than 330MPa.

[0090] 2) This application provides a method for preparing copper foil, which is an improvement on the DC electrolytic deposition method. By changing the fluctuation amplitude of the output current, the copper deposition process is influenced, ultimately obtaining a high-density nanotwinned electrolytic copper foil with fine cell structure, uniform and small microstructure, and parallel and intersecting intracrystalline twin layers. By changing the fluctuation amplitude, the elongation of the electrolytic copper foil can be significantly improved. This has an absolute advantage in the production of ultra-thin and even extremely thin copper foils. On the one hand, it utilizes the principle of pulses but avoids the risks associated with pulses, i.e., the instability of copper foil performance. On the other hand, it increases the nanotwin density in the microstructure of extremely thin copper foil from another perspective, without being limited by the dimensions in the thickness direction of the copper foil. This technology is of great significance to the development of thinner and lighter lithium-ion battery copper foils. Attached Figure Description

[0091] Figure 1 This is a schematic diagram of a rectangular wave waveform in this application, where I0 refers to the average current output by the rectifier, and I... max The maximum current, I min Refers to the minimum current value, (I max -I minThe percentage of I0 is 2% to 10%.

[0092] Figure 2 This is a schematic diagram of a triangular waveform for this application, where I0 refers to the average current output by the rectifier, and I... max The maximum current, I min Refers to the minimum current value, (I max -I min The percentage of I0 is 2% to 10%.

[0093] Figure 3 This is a schematic diagram of the sawtooth waveform of this application, where I0 refers to the average current output by the rectifier, and I... max The maximum current, I min Refers to the minimum current value, (I max -I min The percentage of I0 is 2% to 10%.

[0094] Figure 4 This is a schematic diagram of the sine wave waveform of this application, where I0 refers to the average current output by the rectifier, and I... max The maximum current, I min Refers to the minimum current value, (I max -I min The percentage of I0 is 2% to 10%.

[0095] Figure 5 This is a schematic diagram of the twin wafer layer structure with intersecting crystals on the rough surface of the copper foil in this application.

[0096] Figure 6 This is a SEM image of the intersecting twin wafer layer structure in Example 1.

[0097] Figure 7 This is an EBSD diagram of the cross-sectional structure of the intersecting twin wafer layers in Example 1.

[0098] Figure 8 This is a schematic diagram showing that the intracrystalline twin wafer layers in Comparative Example 1 do not intersect each other.

[0099] Figure 9 The image shows the EBSD diagram of the microstructure of the rough surface of the copper foil in Comparative Example 1.

[0100] Figure 10 The image shows the EBSD diagram of the cross-sectional structure of the copper foil in Comparative Example 1. Detailed Implementation

[0101] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0102] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0103] The analysis method in the embodiments of this application is as follows:

[0104] Copper foil with a width of 0.5 inches was cut using a double-edged cutter (JDC, THWING-ALBERT), and then the tensile properties of the copper foil were tested using a single tensile testing machine (LD22.502).

[0105] The surface roughness and gloss values ​​of copper foil were recorded using a roughness meter (Marfurf, PS10) and a miniature gloss meter (BYK4563).

[0106] The surface and cross-section of the copper foil were polished by electropolishing and argon ion polishing, respectively. Then, the surface and cross-section microstructure of the copper foil were observed by a high-performance field emission scanning electron microscope (Thermo Scientific, Apreo 2S), and EBSD analysis was performed using an OXFORD Symmetry S2 probe.

[0107] Example 1

[0108] (1) Prepare a base plating solution for an acid-copper system free of impurities. Set the solution temperature at 53℃ and maintain solution circulation at a flow rate of 0.5 m / s. 3 / s, no copper particles precipitated in the plating solution. The pH of the plating solution was 0.5, and the conductivity of the plating solution was 160 mS / cm.

[0109] The base plating solution contains 350 g / L copper sulfate, 120 g / L sulfuric acid, and 10 mg / L chloride ion.

[0110] (2) Place the prepared cathode (surface Ra 0.25μm) and anode face to face into the plating solution. The area ratio of the cathode to the anode is 1:1, and the distance between the cathode and anode is 10mm. Set the electrical parameters, and control the current density at 62A / dm³. 2 Electrolytic deposition is used to prepare green foil.

[0111] Fluctuation parameters of DC power supply output current: rectangular wave waveform ( Figure 1 As shown), the fluctuation frequency is 10Hz. Figure 1 (T = 100ms); the difference in current values ​​between the peak and trough is 10% of the average current ((I max -I min (I0 is 10%); high level ratio is 90% (t) Imax / T = 90%.

[0112] (3) After energizing for 30s, a raw foil with a thickness of 6μm was prepared. It was then rinsed with dilute acid and pure water, dried, peeled off, and placed in a 150℃ oven for 10min. After that, it was naturally cooled to room temperature to obtain a cooked foil with stable performance at room temperature.

[0113] Test tensile properties, surface roughness, gloss, and check for pinholes, surface discoloration, and warping before and after baking.

[0114] Depend on Figure 6 As can be seen, the twin crystalline structure can be clearly seen within the grains of the rough surface of the copper foil. In the figure, gray represents the substrate, and the black and white stripes are twin crystalline layers with different orientations. The thickness of the twin crystalline layer is 50-200nm. The twin crystalline layers are parallel to each other or intersect each other, with an included angle of 70° to 90°.

[0115] Depend on Figure 7 According to the cross-sectional EBSD results, the twinning ratio is approximately 80.8% at the (111)60° twin boundary.

[0116] Example 2

[0117] The difference between Example 2 and Example 1 is that the wave waveform is a sine wave, and the electrodeposition parameters are different, namely:

[0118] Fluctuation parameters of DC power supply output current: sine waveform ( Figure 4 As shown), the fluctuation frequency is 100Hz. Figure 1 (T = 10ms); the difference in current values ​​between the peak and trough is 10% of the average current ((I max -I min (I0 is 10%); high level ratio is 90% (t) 上 / T = 90%.

[0119] Current density controlled at 64 A / dm 2 Green foil was prepared by electrolytic deposition. After applying current for 25 seconds, a green foil with a thickness of 5 μm was prepared.

[0120] The other steps are the same as in Example 1.

[0121] Comparative Example 1

[0122] The difference between Comparative Example 1 and Example 1 is that the current is completely direct current, that is:

[0123] The DC power supply outputs a high-precision pure DC current without any minor fluctuations.

[0124] Current density controlled at 62A / dm 2 Green foil was prepared by electrolytic deposition. After applying current for 29 seconds, a green foil with a thickness of 6 μm was prepared.

[0125] Depend on Figure 9 It can be seen that twin crystalline layers also exist within the grains of the rough surface of the copper foil. In the figure, gray represents the matrix and black stripes represent twin crystalline layers. The twin crystalline layers are relatively thick, ranging from 500 to 1500 nm, and are parallel to each other, but without intersecting twins.

[0126] Depend on Figure 10 According to the cross-sectional EBSD results, the twinning ratio is approximately 62.8% at the (111)60° twin boundary.

[0127] Analysis example

[0128] Tensile properties, surface roughness, gloss, pinholes, and warping were tested on Examples 1, 2, and Comparative Example 1. The test methods were in accordance with GB / T 228.1-201 Metallic materials, tensile testing—Part 1: Tests at room temperature and GB / T 29847-2013 Test methods for copper foil for printed circuit boards.

[0129] Differences between Examples 1 and 2 and Comparative Example 1:

[0130] Example 1: Copper foil strength: 345 MPa, yield strength: 312 MPa, elongation: 8.4%;

[0131] Example 2: Copper foil strength: 332 MPa, yield strength: 298 MPa, elongation: 6.8%;

[0132] Comparative Example 1: Copper foil strength: 308 MPa, yield strength: 258 MPa, elongation: 4.5%.

[0133] After baking (150°C, 10 min) or storage at room temperature for 7 days, the mechanical properties of the raw foils in Examples 1 and 2 showed a decrease of less than 10%, specifically 8.4% and 8.0% respectively, as shown in Table 1.

[0134] After baking (150℃, 10 min) or storage at room temperature for 7 days, the mechanical properties of the raw foil in Comparative Example 1 decreased by more than 20%, specifically 20.6%, as shown in Table 1.

[0135] Table 1 Test Results

[0136]

[0137] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing copper foil, characterized in that, Includes the following steps: The copper foil is obtained by electrochemical reaction of a plating solution containing a copper source. The copper source is a divalent copper salt; The plating solution contains sulfuric acid, chloride ions, and water; Cu 2+ The concentration in the plating solution is 80 g / L ~ 100 g / L; The sulfuric acid content is 100 g / L ~ 130 g / L; The concentration of chloride ions in the plating solution is 10 mg / L ~ 20 mg / L; The output current used in the electrochemical reaction is direct current; The difference between the current values ​​at the peak and trough is 2-10% of the average current; The output current exhibits periodic, minute fluctuations near the average current. The fluctuation range of the output current is 2% to 10% of the average current; The frequency of the output current is 10 Hz ~ 100 Hz; The high-level ratio of the output current is 50% to 95%. The high-level ratio refers to the proportion of time within a cycle that is higher than the average current to the total cycle time. The conditions for the electrochemical reaction are as follows: The current density is 50 A / dm 2 ~ 70 A / dm 2 .

2. The preparation method according to claim 1, characterized in that, The divalent copper salt is selected from at least one of copper sulfate, copper chloride, and copper methanesulfonate.

3. The preparation method according to claim 1, characterized in that, When the copper source is copper sulfate, the content of the copper source in the plating solution is 350 g / L ~ 380 g / L; The mass of the copper sulfate is calculated as copper sulfate pentahydrate.

4. The preparation method according to claim 1, characterized in that, The pH of the plating solution is 0.5 to 1.

0.

5. The preparation method according to claim 1, characterized in that, The conductivity of the plating solution is 150 mS / cm ~ 200 mS / cm.

6. The preparation method according to claim 1, characterized in that, The waveform of the output current is at least one of sine wave, square wave, triangle wave, and sawtooth wave.

7. The preparation method according to claim 1, characterized in that, The waveform of the output current is obtained by superimposing single or multiple waveforms and / or connecting them in parallel.

8. The preparation method according to claim 1, characterized in that, The temperature of the plating solution is 52 ℃ ~ 58 ℃.

9. The preparation method according to claim 1, characterized in that, In the electrochemical reaction, titanium is used as the cathode and a titanium plate with a titanium-iridium-tantalum coating is used as the anode.

10. The preparation method according to claim 9, characterized in that, The surface roughness of the titanium cathode is as follows: Ra is 0.2 μm ~ 0.3 μm; Rz is 2.0 μm ~ 2.5 μm.

11. The preparation method according to claim 9, characterized in that, The grain size of the titanium cathode surface is greater than or equal to level 8.

12. A copper foil obtained by the preparation method according to any one of claims 1 to 11, characterized in that, The copper foil contains nanotwin structures within its grains; The nanotwin structure includes parallel twin lamellae and intersecting twin lamellae. The included angle between intersecting twin wafer layers is 45° ~ 90°; The thickness of the copper foil is 3 μm to 6 μm; The grain size is 0.5 μm ~ 5 μm; The thickness of the twin wafer layer is 10 nm to 500 nm; The spacing between the twin wafer layers is 10 nm to 500 nm.

13. The copper foil according to claim 12, characterized in that, The thickness of the copper foil is 4 μm to 6 μm.

14. The copper foil according to claim 12, characterized in that, The grains are randomly oriented or have a (111) preferred orientation.

15. The copper foil according to claim 12, characterized in that, The grains containing nanotwins account for 50% to 80% of the total grain structure.

16. The copper foil according to claim 12, characterized in that, The twin boundaries in the nanotwinned structure account for 80% to 90% of all grain boundaries.

17. The application of the copper foil obtained by the preparation method according to any one of claims 1 to 11 or the copper foil according to any one of claims 12 to 16 in a lithium battery.

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