A copper foil and a method for manufacturing the same, and a circuit board and a current collector

Abstract

The application provides a copper foil and a preparation method thereof, and a circuit board and a current collector, relates to the technical field of copper foil preparation, and the microstructure of the copper foil contains nanodomains, and the distribution state of the nanodomains is one or more of the following states: in the grain interior, on the grain boundary, both in the grain interior and on the grain boundary. On the one hand, the nanodomains can effectively hinder dislocation movement, improve dislocation storage capacity, increase the strength of the copper foil and contribute to the elongation rate thereof; on the other hand, the nanodomains can hinder grain boundary migration, ensure the stability of the grain boundary, and the stable grain boundary can refine the grain to the nanometer level, further improving the strength of the copper foil.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of copper foil preparation, and particularly relates to a copper foil, a preparation method thereof, and a circuit board and a current collector. BACKGROUND

[0002] As the "nerve network" of signal and power transmission and communication of electronic products and the "current collector" of lithium ion batteries, copper foil is widely used in new electronic information industry, new energy automobile industry and national major projects such as aerospace. High-performance copper foil is a key material for manufacturing 5G communication high-frequency high-speed printed circuit boards and high-energy density lithium ion batteries. However, due to the constraints of copper foil production technology in China and the secrecy of foreign copper foil production technology, the development of copper foil production level in China is seriously restricted, resulting in overproduction of low-grade copper foil in China, while high-grade electrolytic copper foil production is lacking, especially high-grade ultra-thin electrolytic copper foil and high-performance electrolytic copper foil almost entirely rely on imports.

[0003] Electrolytic copper foil is a key material for manufacturing high-quality copper-clad plate and high-quality battery negative current collector. Under the harsh environment of circuit use and the demand for high load of battery negative electrode, the copper foil should have high tensile strength and elongation to ensure efficient signal transmission under the conditions of circuit board bending or rapid temperature change, and the copper foil current collector does not break or wrinkle during electrode coating and rolling process. Grain refinement can effectively improve the mechanical properties of electrolytic copper foil. In the production of electrolytic copper foil, a small amount of additives can greatly affect the grain size, brightness, flatness and internal stress of the coating. Currently, the improvement of electrolytic copper foil strength is essentially realized according to the traditional "grain refinement strengthening" principle. Therefore, in the research and development process of high-performance electrolytic copper foil, in addition to the progress of technical equipment, the development of new, stable and easy-to-control additives is also important.

[0004] Reducing the grain size of electrolytic copper foil can effectively improve the yield strength and thus the tensile strength. In the preparation process of electrolytic copper foil, by adding a certain amount of additives, the grain size is reduced from micrometer level to sub-micrometer level, and the tensile strength of electrolytic copper foil can be increased from about 280 MPa to about 400 MPa. When the grain size decreases, the resistance to dislocation movement in the deformation process of electrolytic copper foil increases, thereby improving its tensile strength. At the same time, the movement space and storage capacity of dislocations also decrease, resulting in a decrease in elongation (plasticity). In addition, when the grain size is reduced to nanometer level, the grain boundary of electrolytic copper foil becomes extremely unstable, and even at room temperature, the self-annealing phenomenon of grain growth occurs, and the grain size continues to increase with the extension of storage time until it reaches a stable state, making it difficult to maintain a high level of tensile strength. Therefore, it is difficult to obtain electrolytic copper foil with higher tensile strength through grain refinement strengthening. SUMMARY

[0005] Therefore, the present application provides a copper foil and a preparation method thereof, and a circuit board and a current collector, which can solve the technical problem that it is difficult to obtain an electrolytic copper foil with higher tensile strength in the prior art.

[0006] To solve the above problems, the present application provides a copper foil, which contains nanodomains in the microstructure of the copper foil, and the distribution state of the nanodomains is one or more of the following states: inside the crystal grains, on the grain boundaries, both inside the crystal grains and on the grain boundaries.

[0007] Further, the crystal grains are irregular in shape, and the ratio of the long axis to the short axis of the crystal grains is greater than 1 and less than or equal to 5; and / or

[0008] The crystal grains include columnar-like crystal grains and equiaxed-like crystal grains.

[0009] The ratio of the long axis to the short axis of the columnar-like crystal grains is greater than 1.5 and less than or equal to 3.

[0010] The ratio of the long axis to the short axis of the equiaxed-like crystal grains is 1-2.

[0011] Further, the size of the nanodomains is 1-50 nm; and / or

[0012] The average volume fraction of the nanodomains is greater than 0.01%.

[0013] Preferably, the nanodomains are distributed alternately and spaced apart in low-density regions and high-density regions; the volume fraction of the nanodomains in the low-density regions is not higher than the average volume fraction, and the volume fraction of the nanodomains in the high-density regions is higher than the average volume fraction.

[0014] Further, the composition of the copper foil is composed of only copper elements; or

[0015] The composition of the copper foil includes copper elements with a mass fraction of not less than 90% and one or more elements including carbon, oxygen, sulfur, nitrogen, chlorine, hydrogen, phosphorus, silver, nickel, iron, molybdenum, tungsten, chromium, cerium, and zinc.

[0016] Further, at room temperature, the tensile strength of the copper foil is 400-1000 MPa, and the elongation is higher than 3%; and / or

[0017] The surface roughness Rz of the copper foil is 0.1-3.0 μm; and / or

[0018] The thickness of the copper foil is 1-200 μm.

[0019] Preferably, when the thickness of the copper foil is 1-4 μm, the copper foil is used to form a carrier copper foil by compounding with a carrier.

[0020] In another aspect, the present application provides a method for preparing the copper foil as described in any of the above aspects, characterized in that the copper foil is prepared by direct current electrolytic deposition; wherein the electrolyte used comprises an additive; and the additive comprises gelatin, polyethylene glycol, hydroxyethyl cellulose, glucose, 2-mercaptobenzimidazole, sodium polydithiobis propane sulfonate, and thiourea.

[0021] Preferably, the deposition method is selected from the group consisting of flat plate deposition in an electrolytic cell and roller deposition in a foil generator; and if the flat plate deposition in an electrolytic cell is selected, the deposition time is 1-3 minutes.

[0022] Further, in the additive, the concentration of gelatin is 1-40 mg / L, the concentration of polyethylene glycol is 1-20 mg / L, the concentration of hydroxyethyl cellulose is 1-10 mg / L, the concentration of glucose is 10-300 mg / L, the concentration of 2-mercaptobenzimidazole is 0.5-5 mg / L, the concentration of sodium polydithiobis propane sulfonate is 1-20 mg / L, and the concentration of thiourea is 1-15 mg / L.

[0023] Preferably, the concentration of gelatin is 5-20 mg / L, the concentration of polyethylene glycol is 1-10 mg / L, the concentration of hydroxyethyl cellulose is 1-5 mg / L, the concentration of glucose is 50-200 mg / L, the concentration of 2-mercaptobenzimidazole is 2-5 mg / L, the concentration of sodium polydithiobis propane sulfonate is 5-15 mg / L, and the concentration of thiourea is 2-8 mg / L.

[0024] Further, the electrolyte further comprises copper sulfate pentahydrate, sulfuric acid H2SO4, hydrochloric acid HCl, and deionized water.

[0025] Preferably, the concentration of copper sulfate pentahydrate is 200-350 g / L, the concentration of sulfuric acid H2SO4 is 20-120 g / L, and the concentration of hydrochloric acid HCl is 5-50 mg / L.

[0026] Further, in the process of direct current electrolytic deposition, the current density is 10-110 A / dm 2 ; and the temperature is 10-60℃.

[0027] Preferably, the current density is 40-70 A / dm 2 ; and the temperature is 30-50℃.

[0028] Further, the present application is characterized in that the density of nanodomains, the size of nanodomains, and the average short axis size of crystal grains in the copper foil are regulated by adjusting the temperature of the electrolyte, the concentration of one or more components in the additive, and the current density in the process of direct current electrolytic deposition; and / or

[0029] The strength of the copper foil is regulated by adjusting one or more of the density of the nanodomains, the size of the nanodomains, the average short axis size of the grains, the proportion of twin structure, and the thickness of the twin lamella in the copper foil; and / or

[0030] The surface roughness of the copper foil is adjusted by adjusting one or more of the density of the nanodomains, the size of the nanodomains, and the average short axis size of the grains in the copper foil.

[0031] In still another aspect, the present application provides a circuit board, comprising a substrate and the copper foil according to any one of the above; wherein the copper foil is located on the substrate.

[0032] Preferably, the copper foil is bonded to the substrate.

[0033] In still another aspect, the present application provides a current collector, comprising graphite and the copper foil according to any one of the above; wherein the graphite is bonded to the copper foil.

[0034] Preferably, the current collector is applied in a lithium battery.

[0035] In still another aspect, the present application provides a method for electronic circuit packaging, wherein the method for preparing the copper foil according to any one of the above is used to deposit a copper foil in a blind hole of a circuit board to realize the electronic circuit packaging operation of circuit board wiring and interlayer interconnection.

[0036] Compared with the prior art, the present application has at least the following beneficial effects:

[0037] 1. The present application provides a copper foil, which has nanodomains in its microstructure. On the one hand, these nanodomains can effectively hinder dislocation movement, improve dislocation storage capacity, and thus improve the strength and ductility of the copper foil. On the other hand, these nanodomains can hinder grain boundary migration and ensure stable grain boundaries, which can refine the grains to the nanometer level and further improve the strength of the copper foil. For example, the average nanodomain size of the copper foil according to an embodiment of the present application is 3.1 nm, and the volume fraction is 2%. The room temperature tensile properties (tensile strength) of the copper foil are 778 MPa and the elongation is 4.1%. The strength of the copper foil far exceeds the requirements of the tensile strength (276 MPa) of the electronic circuit printed board IPC-4562 copper foil standard and the tensile strength (300 MPa) of the lithium ion battery SJ / T 11483-2014 copper foil standard, and also fully meets the requirements of the elongation in the standards. At the same time, the nanodomain copper foil has high thermal stability. After being placed at room temperature for 3 months or baked at 150 degrees Celsius for 10 minutes, the tensile strength attenuation is less than 5%, overcoming the self-annealing phenomenon (room temperature tensile strength attenuation exceeds 50%) of conventional copper foils.

[0038] 2. In another aspect, the present application provides a method for preparing a copper foil, wherein the copper foil is deposited by direct current electrodeposition; specifically, the selected additives include not only strong surfactants such as gelatin and hydroxyethyl cellulose, but also certain reducing additives such as glucose and 2-mercaptobenzimidazole, and additives with strong surface adsorption capacity such as sodium polydithiobispropyl sulfone and thiourea; the above multi-complex system has a good synergistic effect on the copper plating layer, can produce strong cathode polarization, and continuously generate high overpotential; for example, the coupling effect between the additives leads to uneven adsorption, and when the additives are locally adsorbed more, the overpotential in this area is higher; according to the theory of electrocrystallization, the increase of overpotential will greatly promote the generation of crystal nucleus; however, part of the additives will be quickly consumed or desorbed, resulting in a decrease in the overpotential in this area, so that the crystal nucleus cannot continue to grow, and therefore a nanodomain with extremely small size is formed. When the adsorption and consumption (or desorption) of the additives change periodically, the nanodomain will be periodically distributed.

[0039] 3. Further, the present application provides a method for preparing a copper foil, which has strong controllability and easy performance optimization. In this method, the size of the nanodomain, the volume fraction of the nanodomain, the grain size (average short axis size) in the copper foil can be adjusted by changing the current density, the concentration of each component of the additives, the temperature and other parameters, so as to further optimize the performance of the copper foil. For example, in the embodiments 1-2 of the present application, when the current density is increased from 65 A / dm 2 to 80 A / dm 2 , the average volume fraction of the nanodomain is increased from 2.3% to 3.7%, and the tensile strength of the copper foil is increased from 701 MPa to 883 MPa, the elongation at break is increased from 1.8% to 3.0%, and the surface roughness Rz is reduced from 0.98 μm to 0.32 μm.

[0040] 4. In addition, by changing the current density and the concentration of the additives, the distribution of the nanodomain in the copper foil of the present application can be effectively controlled, and not only random distribution but also periodic distribution (i.e. the nanodomain is distributed in the grain in the form of alternating low-density and high-density regions) can be achieved. Compared with the nanodomain with random distribution, the nanodomain with periodic distribution can contribute higher strength in the high-density nanodomain and higher elongation in the low-density nanodomain, so that the nanodomain with periodic distribution can combine the advantages of both. In addition, due to the different strengths, the deformation will be uncoordinated, further generating geometrically necessary dislocations, which further improves work hardening and increases strength and plasticity.

[0041] In conclusion, the copper foil and the preparation method thereof provided by the present application have the advantages of extremely high strength, high elongation, high stability, extremely low surface roughness, and extremely thin thickness, greatly meeting the development of current electronic products in the direction of miniaturization, light weight, thinness, multifunction, and high reliability, the high requirements of thin multi-layer printed circuit boards, thin double-sided copper-clad boards in performance, and the development requirements of high safety, high stability, high energy density, and low cost of high-performance lithium ion batteries and electronic circuits, and thus having great application prospects in the fields of new energy batteries and electronic circuits. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required to be used in the following embodiment or prior art description will be briefly introduced. The drawings in the following description are merely exemplary, and other embodiments can be derived from the provided drawings without creative labor for those skilled in the art.

[0043] Figure 1 It is a schematic diagram of the nano-domain distribution of the nano-domain copper foil;

[0044] Figure 2 It is a cross-sectional transmission electron microscope image of the copper foil in Example 1, wherein Fig. A is a TEM bright field image of the cross section of the copper foil, Fig. B is a high-magnification HRTEM image of the nano-domain in the grain, and Figs. C, D, and E are EELS distribution of C, O, and Cl elements in the nano-domain, respectively;

[0045] Figure 3 It is a cross-sectional transmission electron microscope bright field image of the copper foil in Example 2;

[0046] Figure 4 It is an electron microscope image of the cross section of the copper foil in Example 3, wherein Figs. 4A and 4B are scanning electron microscope and transmission electron microscope images, respectively;

[0047] Figure 5 It is a tensile engineering stress-strain curve of the copper foil sample in Examples 1-3. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required to be used in the following embodiment or prior art description will be briefly introduced. The drawings in the following description are merely exemplary, and other embodiments can be derived from the provided drawings without creative labor for those skilled in the art.

[0049] The present application provides a copper foil, the microstructure of the copper foil contains nanodomains; the distribution state of the nanodomains is one or more of the following states: inside the crystal grains, on the grain boundaries, both inside the crystal grains and on the grain boundaries.

[0050] The term "nanodomain" referred to in the present application refers to a nanoscale tiny region distributed on the (matrix) crystal grains, the crystal structure or / and the composition of the region is different from that of the (matrix) crystal grains; specifically, the average angle difference between the (111) face of the region under the (110) crystal band axis and the (111) face of the (matrix) crystal grains is 0-15°; compared with the matrix crystal grains, the nanodomain contains a small amount of enrichment of elements such as C and O (see Figure 2 ); wherein the size of the nanodomain is 1-50 nm, which is smaller than the size of the (matrix) crystal grains; there is an interface between the nanodomain and the (matrix) crystal grains, and there is an interface (i.e. grain boundary) between the (matrix) crystal grains.

[0051] The nanodomains can be randomly distributed or periodically distributed (see Figure 1 ). The periodic distribution refers to the alternative distribution of the volume fraction of the nanodomains along the thickness direction of the copper foil from the high-density region to the low-density region, and at least one period of distribution, that is, the low-density region and the high-density region are alternately and periodically distributed. The average volume fraction of the nanodomains in the present application is greater than 0.01%; wherein the volume fraction of the nanodomains in the low-density region is not higher than the average volume fraction, and the volume fraction of the nanodomains in the high-density region is higher than the average volume fraction. Compared with the randomly distributed nanodomains, the periodically distributed nanodomains make the copper foil have higher tensile strength and elongation. Among them, the high-density nanodomains can contribute to higher strength, and the low-density nanodomains can contribute to higher elongation, so the periodically distributed nanodomains can integrate the advantages of both.

[0052] Preferably, the crystal grains are irregular in shape, the ratio of the long axis to the short axis of the crystal grains is greater than 1 and less than or equal to 5; preferably 1.5-3; the crystal grains include columnar-like crystal grains and equiaxed-like crystal grains;

[0053] Among them, the ratio of the long axis to the short axis of the columnar-like crystal grains is greater than 1.5 and less than or equal to 3;

[0054] The ratio of the long axis to the short axis of the equiaxed-like crystal grains is 1-2.

[0055] Further, the crystal grains further include twin structures; and / or

[0056] Further, at room temperature, the tensile strength of the copper foil is 400-1000 MPa, and the elongation is higher than 3%; the surface roughness Rz of the copper foil is 0.1-3.0 μm; the thickness of the copper foil is 1-200 μm;

[0057] Preferably, when the thickness of the copper foil is 1-4 μm, the copper foil is used to form a carrier copper foil by being combined with a carrier; preferably, the thickness of the carrier is 6-30 μm; and preferably, the carrier is selected from one of a copper foil, an aluminum foil and an organic film.

[0058] The copper foil is composed of copper elements or contains copper elements with a mass fraction of not less than 90%; and further contains one or more of carbon, oxygen, sulfur, nitrogen, chlorine, hydrogen, phosphorus, silver, nickel, iron, molybdenum, tungsten, chromium, cerium and zinc. In addition to the elements added intentionally, the purity of the solution and the additives also affect the composition of the copper foil. When the copper foil is composed of multiple elements, the elements can play a role of solid solution strengthening, thereby improving the strength of the copper foil.

[0059] In another aspect, the application provides a method for preparing the copper foil described in any of the above aspects, characterized in that the copper foil is prepared by direct current electrolytic deposition; and the electrolyte used in the method contains additives, copper sulfate pentahydrate, sulfuric acid, hydrochloric acid and deionized water; and the additives include gelatin, polyethylene glycol, hydroxyethyl cellulose, glucose, 2-mercaptobenzimidazole, sodium polydithiopropyl sulfone and thiourea.

[0060] Preferably, the deposition method is selected from a flat plate deposition method using an electrolytic cell or a roller deposition method using a foil maker; and if the flat plate deposition method is used, the deposition time is 1-3 minutes.

[0061] In the process of direct current electrolytic deposition, the current density is 10-110 A / dm 2 ; and the temperature is 10-60℃.

[0062] Preferably, the current density is 40-70 A / dm 2 ; and the temperature is 30-50℃.

[0063] In the additives, the concentration of gelatin is 1-40 mg / L, the concentration of polyethylene glycol is 1-20 mg / L, the concentration of hydroxyethyl cellulose is 1-10 mg / L, the concentration of glucose is 10-300 mg / L, the concentration of 2-mercaptobenzimidazole is 0.5-5 mg / L, the concentration of sodium polydithiopropyl sulfone is 1-20 mg / L, and the concentration of thiourea is 1-15 mg / L.

[0064] Preferably, the concentration of gelatin is 5-20 mg / L, the concentration of polyethylene glycol is 1-10 mg / L, the concentration of hydroxyethyl cellulose is 1-5 mg / L, the concentration of glucose is 50-200 mg / L, the concentration of 2-mercaptobenzimidazole is 2-5 mg / L, the concentration of sodium polydithiopropyl sulfone is 5-15 mg / L, and the concentration of thiourea is 2-8 mg / L.

[0065] The concentration of copper sulfate pentahydrate is 200-350 g / L, the concentration of sulfuric acid H2SO4 is 20-120 g / L, and the concentration of hydrochloric acid HCl is 5-50 mg / L.

[0066] Further, the density of the nanodomains, the size of the nanodomains, the average short axis size of the grains, and / or the twin structure proportion and the twin lamella thickness in the copper foil are adjusted by adjusting the temperature of the electrolyte, the concentration of one or more components in the additive, and the current density in the direct current electrolytic deposition process.

[0067] The strength of the copper foil is adjusted by adjusting one or more of the density of the nanodomains, the size of the nanodomains, the average short axis size of the grains, the twin structure proportion, and the twin lamella thickness in the copper foil.

[0068] The surface roughness of the copper foil is adjusted by adjusting one or more of the density of the nanodomains, the size of the nanodomains, and the average short axis size of the grains in the copper foil.

[0069] Preferably, when the nanodomain size is 1-10 nm and the nanodomain density is 1-15%, the strength of the copper foil is 500-900 MPa.

[0070] Preferably, when the average short axis size of the grains is 10 nm-5 μm, the strength of the copper foil is 500-900 MPa.

[0071] Preferably, during the direct current electrolytic deposition process, by adjusting any one of the temperature, the current density, and the additive concentration or adjusting two or more of them simultaneously, the copper foil prepared can satisfy the following conditions: the nanodomain size is 1 nm-30 nm, the nanodomain spacing is 1 nm-50 nm, the average short axis size of the grains is 10 nm-5 μm, and the strength of the copper foil is 300-900 MPa. 2 Further preferably, the temperature is adjusted to 20-55 ℃, the current density is adjusted to 40-100 A / dm2, and the additive concentration is adjusted as follows: the concentration of gelatin is 5-20 mg / L, the concentration of polyethylene glycol is 1-10 mg / L, the concentration of hydroxyethyl cellulose is 1-5 mg / L, the concentration of glucose is 50-200 mg / L, the concentration of 2-mercaptobenzimidazole is 2-5 mg / L, the concentration of sodium polydithiopropyl sulfonate is 5-15 mg / L, and the concentration of thiourea is 2-8 mg / L.

[0072] It should be noted that the size, spacing, volume fraction of the nanodomains, and the average short axis size of the grains can be reduced by adjusting the temperature, the current density, and the additive concentration alone or by adjusting two or more of them simultaneously.

[0073] In another aspect, the application provides a circuit board comprising a substrate and the copper foil of any one of the above.

[0074] Preferably, the copper foil is adhered to the substrate.

[0075] In another aspect, the present application provides a current collector, which comprises graphite and the copper foil of any one of the above; wherein the graphite is adhered to the copper foil.

[0076] Preferably, the current collector is applied in a lithium battery.

[0077] In another aspect, the present application provides a method for electronic circuit packaging, wherein the copper foil is deposited in the blind hole of the circuit board by the method for preparing the copper foil of any one of the above to realize the electronic circuit packaging operation of the circuit board wiring and interlayer interconnection.

[0078] The present application is further illustrated below with specific examples and comparative examples.

[0079] Example 1

[0080] The present example provides a copper foil, wherein the nano-domains are randomly distributed, and the copper foil is prepared by using direct current electrolytic deposition technology, wherein:

[0081] The electrolytic deposition equipment is a direct current stabilized voltage and current power supply; the anode and the cathode are iridium tantalum titanium plate and pure titanium plate, respectively;

[0082] Requirements for the electrolyte used for electrolytic deposition: an analytical pure copper sulfate pentahydrate and pure water are used to prepare a copper sulfate solution, and the concentration thereof is about 300 g / L, then analytical pure concentrated sulfuric acid is added to make the concentration of H2SO4 be 100 g / L, and HCL is added to make the concentration of HCl be 15 mg / L, to form a basic solution for electrolytic deposition. Then additives are added, specifically, the concentration of gelatin is 8 mg / L, the concentration of polyethylene glycol is 4 mg / L, the concentration of hydroxyethyl cellulose is 6 mg / L, the concentration of glucose is 100 mg / L, the concentration of 2-mercaptobenzimidazole is 3 mg / L, the concentration of polydithiodipropyl sulfone sodium is 1 mg / L, and the concentration of thiourea is 3 mg / L;

[0083] Electrolytic deposition process parameters: direct current electrolysis is used to electroplate the copper foil, wherein the current density is 65 A / dm 2 ; the cathode and the anode are placed in parallel with a spacing of 15 mm, and the area size ratio of the cathode to the anode is 1:1; the electrolysis temperature is 53℃; a water pump is used for electrolyte circulation, and the water pump power is 2.2 m 3 / h; the preparation time (deposition time) is 70 seconds.

[0084] The area of the copper foil prepared in the present example is 180×70 mm 2 , and the thickness thereof is 9.0 μm measured by the weighing method.

[0085] Figure 2The cross-section bright field image of the copper foil prepared in this example under transmission electron microscope. Transmission electron microscope test shows that the copper foil prepared in this example is composed of nanocrystalline grains, the grains are irregular in shape, the ratio of long axis to short axis is between 1 and 4.5, the average value is 2.8, the average short axis grain size is 77 nm; some grains have random twin boundaries inside, the thickness of the twin lamella is below 100 nm, the twin lamella is parallel to the long axis direction of the grains; nanodomains are randomly distributed inside the grains and on the grain boundaries, the average size of the nanodomains is about 3.4 nm, the average volume fraction is about 2.3%, the EELS composition analysis by transmission electron microscope shows that the nanodomains have more C elements than the matrix. More C elements can play the role of solid solution strengthening.

[0086] The copper foil prepared in this example has high strength, can be smoothly and completely peeled off from the titanium plate, and has no pinholes and burrs.

[0087] The room temperature tensile results of the copper foil prepared in this example are shown in Table 1. Figure 5 The test conditions are as follows: the tensile test sample is cut by JDC-0.5-10 precision cutter, the length x width is 50 mm x 12 mm, the tensile properties are tested by tensile testing machine Instron 5848, the tensile rate is 50 mm / min. The test shows that the tensile strength of the nanotwinned copper foil prepared in this example is 701 MPa, and the elongation at break is 1.8%.

[0088] Example 2

[0089] This example provides a copper foil, which is prepared by direct current electrolytic deposition technology, and the difference from example 1 is that the current density is increased during direct current electrolytic deposition, and the concentration of each additive and the electrolytic deposition time are adjusted; the specific direct current electrolytic deposition parameters are as follows:

[0090] The electrolytic deposition equipment is a direct current stabilized voltage and current power supply; the anode and the cathode are iridium tantalum titanium plate and pure titanium plate respectively;

[0091] The requirements for the electrolyte used for electrolytic deposition are as follows: analytical pure copper sulfate pentahydrate and pure water are used to prepare copper sulfate solution, the concentration is about 300 g / L, then analytical pure concentrated sulfuric acid is added to make the concentration of H2SO4 be 100 g / L, HCl is added to make the concentration of HCl be 15 mg / L, forming the basic solution for electrolytic deposition. Then additives are added, specifically, the concentration of gelatin is 10 mg / L, the concentration of polyethylene glycol is 6 mg / L, the concentration of hydroxyethyl cellulose is 3 mg / L, the concentration of glucose is 150 mg / L, the concentration of 2-mercaptobenzimidazole is 2.5 mg / L, the concentration of polydithiodipropyl sulfone sodium is 5 mg / L, and the concentration of thiourea is 3 mg / L.

[0092] Electrolytic deposition process parameters: direct current electrolysis is used for copper foil plating, wherein the current density is 70 A / dm 2 ; the cathode and the anode are placed in parallel with a spacing of 15 mm, and the area size ratio of the cathode to the anode is 1:1; the electrolysis temperature is 53℃; a water pump is used for electrolyte circulation, and the water pump power is 2.2 m 3 / h; the preparation time (deposition time) is 60 seconds.

[0093] The thickness of the copper foil prepared in this embodiment is 9.8 μm, which is measured by the weighing method.

[0094] Figure 3 The cross-sectional bright field images of the copper foil prepared in this embodiment under the transmission electron microscope are shown in Figures 1 and 2. It is shown that the microstructure of the copper foil is mostly elongated columnar grains, the ratio of the long axis to the short axis is between 1-4, the average value is 2.7, and the average short axis grain size is 60 nm; it can be seen that the nanodomains are periodically distributed, i.e. alternatingly spaced with low density regions and high density regions. The columnar grains can grow across the nanodomains; the average size of the nanodomains is about 3 nm, and the average volume fraction of the nanodomains in the copper foil is about 3.7%; the nanodomains in the copper foil prepared in this embodiment are periodically distributed, wherein the volume fraction of the nanodomains in the low density region is about 1.2%, and the volume fraction of the nanodomains in the high density region is about 7.2%.

[0095] Compared with Example 1, by adjusting the current density and the concentration parameters of the various additives, the nanodomains in the copper foil prepared in this embodiment present a periodic distribution of high density regions and low density regions, the average spacing of the nanodomains is about 5.8 nm, and the average volume fraction increases to 3.7%.

[0096] The average short axis size of the grains of the copper foil prepared in this embodiment is reduced to 60 nm, and the grain size has a weak increasing trend along the thickness direction of the copper foil, the average short axis size of the grains near the lower surface (the smooth surface) is 125 nm, and the average short axis size of the grains near the upper surface (the rough surface) is 172 nm. In the copper foil prepared in this embodiment, part of the grains have twin boundaries.

[0097] Compared with Example 1, by actively regulating the current density and the concentration of the various additives, this embodiment realizes the reduction of the spacing of the nanodomains, the grain size (the average short axis size of the grains), and the volume fraction of the nanodomains, and the roughness of the copper foil is reduced to Rz=0.32 μm, Ra=0.14 μm.

[0098] The room temperature tensile test results of the copper foil prepared in this embodiment are as follows: Figure 5Compared with Example 1, the present embodiment reduces the distance between nano-domains, the grain size and the density of nano-domains by actively regulating the current density and the concentration of each additive, so that the tensile strength of the copper foil is increased to 883 MPa and the elongation is 3.0%. Moreover, the tensile strength and the elongation of the copper foil of the present embodiment remain basically unchanged (the change rate is less than 5%) after aging at room temperature for 1 year, which indicates that the copper foil prepared in the present embodiment has high room temperature stability.

[0099] Example 3

[0100] The present embodiment provides a copper foil, wherein nano-domains are randomly distributed in the grains, and the copper foil is prepared by using direct current electrolytic deposition technology. Different from Example 1, the current density is increased during direct current electrolytic deposition, and the concentration of each additive and the electrolytic deposition time are adjusted. The specific direct current electrolytic deposition parameters are as follows:

[0101] The electrolytic deposition equipment is a direct current stabilized voltage and current power supply; the anode and the cathode are iridium tantalum titanium plate and pure titanium plate respectively;

[0102] Requirements for the electrolyte used for electrolytic deposition: an analytical pure copper sulfate pentahydrate and pure water are used to prepare a copper sulfate solution with a concentration of about 300 g / L, then analytical pure concentrated sulfuric acid is added to make the concentration of H2SO4 be 100 g / L, and HCL is added to make the concentration of HCl be 15 mg / L, forming the basic solution for electrolytic deposition. Then additives are added, specifically, the concentration of gelatin is 16 mg / L, the concentration of polyethylene glycol is 8 mg / L, the concentration of hydroxyethyl cellulose is 2 mg / L, the concentration of glucose is 250 mg / L, the concentration of 2-mercaptobenzimidazole is 3 mg / L, the concentration of polydithiodipropyl sulfone sodium is 8 mg / L, and the concentration of thiourea is 6 mg / L.

[0103] Electrolytic deposition process parameters: direct current electrolysis is used to electroplate the copper foil, wherein the current density is 80 A / dm 2 ; the cathode and the anode are placed in parallel with a distance of 15 mm, and the area size ratio of the cathode to the anode is 1:1; the electrolysis temperature is 53℃; a water pump is used for electrolyte circulation, and the power of the water pump is 2.2 m 3 / h; and the preparation time (deposition time) is 55 seconds.

[0104] The thickness of the copper foil of the present embodiment is measured by the weighing method to be 10.2 μm.

[0105] The copper foil prepared in the present embodiment is tested by using a scanning electron microscope and a transmission electron microscope, and the results are shown in FIGS. 3 and 4. Figure 4As shown, the copper foil prepared in the embodiment has self-annealing behavior, most of the grains are equiaxed grains, the grain size is obviously increased to about 3.8 μm, some cross-section grains grow to the thickness direction of the entire copper foil; there are a large number of annealing twins, the twin lamella thickness is about 62 nm, and the length is about 766 nm; the grain interior grows nanodomains, the average size of the nanodomains is slightly increased to about 4.5 nm, and the volume fraction of the nanodomains is about 3.6%.

[0106] Compared with example 1, in the embodiment, the grain size of the copper foil is increased, the nanodomains in the grain are slightly increased, and the proportion and volume fraction of the twin boundaries are obviously increased, the annealing twin lamella thickness is about 62 nm and 86 nm, and the volume fraction is about 42% and 18% by adjusting the process parameters.

[0107] Compared with example 1, in the embodiment, the roughness of the copper foil is Rz=0.5 μm and Ra=0.12 μm by actively adjusting the current density and the concentration of each additive in the electrolyte.

[0108] The room temperature tensile test results of the copper foil prepared in the embodiment are shown in Figure 5 Compared with example 1, in the embodiment, the grain size and the twin density are greatly increased, the nanodomain size is slightly increased by actively adjusting the current density and the concentration of each additive, so that the tensile strength of the copper foil in the embodiment is 545 MPa, and the elongation is increased to 5.0%.

[0109] The mechanical property requirements of the printed board metal foil standard IPC-4562 for 17 μm thick standard electrolytic copper foil include: tensile strength ≥ 207 MPa, elongation ≥ 2%; when the tensile strength of 17 μm thick calendered wrought copper foil is ≥ 345 MPa, the elongation is ≥ 0.5%.

[0110] And the copper foil prepared in the embodiment of the present application not only has a thinner thickness, but also has a higher elongation and a lower surface roughness, because the grain size of the nanodomain copper foil is small, and the nanodomains grow in the grain interior.

[0111] The industry standard SJ / T 11483-2014 for electrolytic copper foil for lithium ion batteries requires that: for LBEC-01 type, when the thickness is 8-20 mu m, the tensile strength is greater than or equal to 294 MPa, the elongation is greater than or equal to 3%, and the roughness of the rough surface Rz is less than or equal to 3.0 mu m, measured at room temperature (23 DEG C); for LBEC-02, when the thickness is 8 mu m, 9 mu m, 10 mu m and 12 mu m, the tensile strength is greater than or equal to 300 MPa, the elongation is greater than or equal to 2.5%, and the roughness of the rough surface Rz is less than or equal to 3.0 mu m, 4.0 mu m, 4.5 mu m and 5.0 mu m, measured at room temperature (23 DEG C); for LBEC-03 type, when the thickness is 9 mu m, 10 mu m, 12 mu m, the tensile strength is greater than or equal to 300 MPa, the elongation is greater than or equal to 2.5%, and the roughness of the rough surface Rz is less than or equal to 4.0 mu m, 4.5 mu m and 5.0 mu m, measured at room temperature (23 DEG C); for LBEC-04 type, when the thickness is 10 mu m, 12 mu m, the tensile strength is greater than or equal to 300 MPa, the elongation is greater than or equal to 2.5%, and the roughness of the rough surface Rz is less than or equal to 5.0 mu m, 6.0 mu m, measured at room temperature (23 DEG C).

[0112] It is found through comparison that the tensile strength of the copper foil prepared in the embodiment of the application is much higher than the requirements of the electrolytic copper foil standards IPC-4562 and SJ / T11483-2014.

[0113] The embodiment of the application adopts an independently developed electrolytic copper foil deposition device, and the thickness, strength, elongation, surface roughness, etc. of the copper foil prepared by different additive ratios and current densities can greatly meet the industry standards for lithium battery electrolytic copper foil. The technical scheme of the application can control the size of the copper foil grain size, the proportion of the nano domain, the size of the nano domain, etc. by actively adjusting the process parameters such as current density, additive concentration and temperature, so as to further optimize the mechanical properties and surface roughness of the copper foil, thereby providing technical support for preparing copper foils with different performance requirements.

[0114] Comparative Example 1

[0115] Ding et al. (Master's degree thesis of Nanchang University, 2022) studied the electrolytic copper foil by using high current density, and the specific process parameters were: current density 70 A / dm 2 , Cu 2+The concentration was 80 g / L, the chloride ion concentration was 30 mg / L, the sulfuric acid concentration was 110 g / L, the electrodeposition temperature was 53°C, and no additives were used. The thickness of the prepared copper foil was 8 pm. Without any additives, the copper foil rough surface grain was coarse, blocky growth and the size of the grain was very uneven, the grain was not dense, the tensile strength was about 161 MPa, the elongation was about 1.77%, the roughness of the rough surface Ra = 0.51 pm, and the roughness of the smooth surface Ra = 0.4 pm. Comparative Example 1 did not use any additives, so that the reduction process of copper ions could not be hindered or the resistance was small, the degree of cathode polarization was low, the overpotential was low, the nucleation density of the coating was reduced, which was not conducive to the surface flatness and grain refinement, so that the nanodomain could not be formed in the grain, and therefore the tensile strength was low.

[0116] Comparative Example 2

[0117] He Tieshu et al. (Shandong Industry Technology, 2020 (6)) used hydroxyethyl cellulose, collagen, 3-mercapto-1-propane sulfonate, saccharin sodium, polyethylene glycol, polyoxyethylene alkyl ether and other additives to produce ultra-thin high safety performance lithium battery copper foil. The tensile strength of the produced copper foil was about 550 MPa, and the elongation was about 4%. In Comparative Example 2, the synergistic effect of the lack of reducing additives such as glucose and 2-mercaptobenzimidazole was reduced, the degree of cathode polarization was reduced, the overpotential of the entire solution system was reduced, the nanodomain could not be formed, and the grain could not be stabilized, so that the tensile strength was limited.

[0118] Meanwhile, the copper foil prepared by the embodiment of the present application has not only thinner thickness but also higher elongation and lower surface roughness, because the grain size of the copper foil with nano-domains is small, and nano-domains are randomly grown inside the grain, and high-density interfaces exist. The copper foil prepared by the embodiment of the present application is suitable for the current collector of the battery, and the significant tensile strength, elongation, surface roughness and other performance advantages meet the development trend of high-capacity, high-safety, high-stability and low-cost of high-performance lithium-ion batteries. The smaller the thickness of the lithium battery copper foil is, the lighter the weight of the battery will be. At the same time, the thinner lithium battery copper foil also means smaller resistance, and the performance of the battery will also be improved. Therefore, reducing the mass of the copper foil on the battery, reducing the cost of copper foil raw materials, and providing higher energy density have become the key to the copper foil for power lithium batteries. Meanwhile, in addition, thanks to the higher fatigue resistance, conductivity (up to 93% IACS), higher thermal stability, excellent anti-electromigration ability and weldability, the copper foil with nano-domains and the preparation method thereof of the present application are also suitable for circuit board manufacturing and electronic circuit packaging, respectively. In addition, the mechanical properties and surface roughness of the copper foil prepared by the embodiment of the present application have a wide range of changes, so that the copper foil has a wide range of uses. It is worth noting that the technical application can also actively control the size of the copper grain size, the spacing of the nano-domain, the size of the nano-domain, and the volume fraction of the nano-domain by increasing or decreasing the current density, the rotating speed, the temperature and other process parameters, such as increasing the current density to 80-100 A / dm 2 The average grain size of the copper foil is refined to below 50 nm, and the average size of the nano-domain also decreases slightly and the volume fraction increases significantly, so that a copper foil with excellent surface quality can be obtained, and the mechanical properties of the copper foil are further optimized, providing technical support for the preparation and manufacture of copper foils for different performance requirements. Therefore, it has great application potential and commercial value.

[0119] It is easy for those skilled in the art to understand that the advantageous technical features of the above-mentioned modes can be freely combined and superimposed without conflict.

[0120] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above description is only the preferred embodiment of the present application, and it should be pointed out that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications shall be regarded as the protection scope of the present application.

Claims

1. A copper foil, characterized by, The microstructure of the copper foil contains nanodomains, and the distribution state of the nanodomains is one or more of the following states: inside the grains, on the grain boundaries, both inside the grains and on the grain boundaries; The size of the nanodomains is 1-50 nm; and the average volume fraction of the nanodomains is greater than 0.01%. The nanodomains are alternately distributed in low-density regions and high-density regions; the volume fraction of the nanodomains in the low-density regions is not higher than the average volume fraction, and the volume fraction of the nanodomains in the high-density regions is higher than the average volume fraction.

2. The copper foil according to claim 1, characterized by, The grains are irregular in shape, and the ratio of the long axis to the short axis of the grains is greater than 1 and less than or equal to 5; and / or The grains include columnar-like grains and equiaxed-like grains; The ratio of the long axis to the short axis of the columnar-like grains is greater than 1.5 and less than or equal to 3; The ratio of the long axis to the short axis of the equiaxed-like grains is 1-2.

3. The copper foil according to claim 1, characterized by, The composition of the copper foil is composed of copper elements only; or The composition of the copper foil includes copper elements with a mass fraction of not less than 90% and one or more elements including carbon, oxygen, sulfur, nitrogen, chlorine, hydrogen, phosphorus, silver, nickel, iron, molybdenum, tungsten, chromium, cerium, and zinc.

4. The copper foil according to any one of claims 1 to 3, characterized by, At room temperature, the tensile strength of the copper foil is 400-1000 MPa, and the elongation is higher than 3%; and / or The surface roughness Rz of the copper foil is 0.1-3.0 μm; and / or The thickness of the copper foil is 1-200 μm.

5. The copper foil according to claim 4, characterized by At room temperature, when the thickness of the copper foil is 1-4 μm, the copper foil is used to form a carrier copper foil by being combined with a carrier.

6. A method of producing the copper foil as claimed in any one of claims 1 to 5, characterized by, The copper foil is deposited by a direct current electrolytic deposition method; the electrolyte used includes an additive; and the additive includes gelatin, polyethylene glycol, hydroxyethyl cellulose, glucose, 2-mercaptobenzimidazole, sodium polydithiopropanesulfonate, and thiourea.

7. The method of producing a copper foil according to claim 6, characterized in that, The deposition method is selected from a flat plate deposition method of an electrolytic cell or a roller deposition method of a foil maker; if the flat plate deposition method of the electrolytic cell is selected, the deposition time is 1-3 minutes.

8. The method of producing a copper foil according to claim 6, characterized by, In the additive, the concentration of gelatin is 1-40 mg / L, the concentration of polyethylene glycol is 1-20 mg / L, the concentration of hydroxyethyl cellulose is 1-10 mg / L, the concentration of glucose is 10-300 mg / L, the concentration of 2-mercaptobenzimidazole is 0.5-5 mg / L, the concentration of sodium polydithiopropanesulfonate is 1-20 mg / L, and the concentration of thiourea is 1-15 mg / L.

9. The method of producing a copper foil according to claim 8, characterized in that, The concentration of gelatin is 5-20 mg / L, the concentration of polyethylene glycol is 1-10 mg / L, the concentration of hydroxyethyl cellulose is 1-5 mg / L, the concentration of glucose is 50-200 mg / L, the concentration of 2-mercaptobenzimidazole is 2-5 mg / L, the concentration of sodium polydithiopropanesulfonate is 5-15 mg / L, and the concentration of thiourea is 2-8 mg / L.

10. The method of producing a copper foil according to claim 6, wherein The electrolyte further includes copper sulfate pentahydrate, sulfuric acid H2SO4, hydrochloric acid HCl, and deionized water; The concentration of copper sulfate pentahydrate is 200-350 g / L, the concentration of sulfuric acid H2SO4 is 20-120 g / L, and the concentration of hydrochloric acid HCl is 5-50 mg / L.

11. The method of producing a copper foil according to any one of claims 6 to 10, characterized in that, In the process of direct current electrolytic deposition, the current density is 10-110 A / dm 2 ; the temperature is 10-60℃.

12. The method of producing a copper foil according to claim 11, characterized in that, The current density is 40-70 A / dm 2 ; the temperature is 30-50°C.

13. The method of producing a copper foil according to any one of claims 11, characterized in that, The density of the nanodomains, the size of the nanodomains, the average short axis size of the grains in the copper foil are regulated by adjusting the temperature of the electrolyte, the concentration of one or several components in the additive, the current density in the direct current electrolytic deposition process; and / or The strength of the copper foil is regulated by adjusting one or several of the density of the nanodomains, the size of the nanodomains, the average short axis size of the grains, the proportion of twin structure, the thickness of the twin lamella in the copper foil. and / or The surface roughness of the copper foil is adjusted by adjusting one or several of the density of the nanodomains, the size of the nanodomains, the average short axis size of the grains in the copper foil.

14. A circuit board, characterized by The circuit board comprises a substrate and the copper foil according to any one of claims 1-4; wherein the copper foil is located on the substrate.

15. The circuit board of claim 14, wherein, The copper foil is bonded to the substrate.

16. A current collector characterized by comprising: The current collector comprises graphite and the copper foil according to any one of claims 1-4; wherein the graphite is bonded to the copper foil.

17. The current collector of claim 16, wherein The current collector is applied in a lithium battery.

18. A method of packaging an electronic circuit, characterized by In the packaging of electronic circuits, the method for preparing the copper foil according to any one of claims 6-13 is used to deposit the copper foil in the blind hole of the circuit board, so as to realize the electronic circuit packaging operation of the circuit board wiring and interlayer interconnection.

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