CN113621998A

CN113621998A - Nano twin crystal copper foil and preparation method thereof

Info

Publication number: CN113621998A
Application number: CN202110498736.6A
Authority: CN
Inventors: 卢磊; 程钊; 金帅
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2021-05-08
Filing date: 2021-05-08
Publication date: 2021-11-09
Anticipated expiration: 2041-05-08
Also published as: CN113621998B

Abstract

The invention discloses a nanometer twin crystal copper foil and a preparation method thereof, belonging to the technical field of electrolytic copper foil preparation. The copper foil is prepared by using a direct-current electrolytic deposition technology, and the thickness of the copper foil is controllably adjusted within the range of 3-100 micrometers. The internal microstructure of the copper foil consists of columnar grains, and the size of the columnar grains is gradually increased from nanometer magnitude to micrometer magnitude from bottom to top; a twin crystal lamella with nanometer scale exists in the columnar crystal grains, and the orientation of the crystal grains is changed from random orientation to strong (111) texture. When the thickness of the nanometer twin crystal copper foil is 6 microns, the tensile strength of the nanometer twin crystal copper foil is higher than 500MPa, and meanwhile, the nanometer twin crystal copper foil has higher stability and conductivity and has better application prospect in the fields of lithium ion batteries and circuit boards.

Description

Nano twin crystal copper foil and preparation method thereof

Technical Field

The invention relates to the technical field of electrolytic copper foil preparation, in particular to a nanometer twin crystal copper foil and a preparation method thereof.

Background

Copper foil is one of basic materials in the electronic industry, and is mainly used in the fields of electronic circuits, lithium ion batteries and the like. With the rapid development in the fields of new energy, telecommunication equipment (5G), robots, flexible wearable devices, smart cars and the like, the requirement on the performance of copper foil is increasing day by day. However, most of the current copper foil materials are obtained by rolling or electrolytic deposition technology, and the high strength, high elongation, high conductivity and extremely thin thickness dimension are often difficult to be obtained, which seriously hinders the development of advanced electronic devices and high-performance batteries. For this reason, extra thin copper foil (less than 6 μm in thickness) has been the key new material by the Ministry of industry and communications.

At present, in the preparation process of the copper foil, the method for improving the strength of the copper foil is mostly based on the idea of grain refinement. For example, the strain amount is increased in the rolling process of the rolled copper foil, so that the grain size of the rolled copper foil is reduced; the grain size is also reduced for electrolytic copper foil by increasing the current density or increasing the degree of cathodic polarization using additives during the manufacturing process. The principle of fine grain strengthening is to increase the strength of the material by hindering the movement of dislocations through grain boundaries, as the Hall-Petch relationship describes that the strength of a metallic material is inversely proportional to the 0.5 th power of the grain size. However, since dislocation movement is restricted by grain boundaries during fine grain strengthening, the plasticity (ductility) of the metal material is significantly reduced, i.e., an inverse relationship of strength and plasticity is exhibited. Meanwhile, the grain boundary is a disordered and high-energy surface defect, and the refined grains tend to reduce the conductivity and the thermal stability of the copper foil material.

Compared with fine-grain strengthening, the nano twin-crystal strengthening can enable the pure copper material to have high strength, plasticity, conductivity and thermal stability at the same time. Strengthening and toughening of the nano twin crystal structure has been a hot problem in the field of material science since the discovery of the nano twin crystal structure in the early 21 st century. For example, the equiaxial nano twin crystal Cu prepared by pulse electrolytic deposition has the strength as high as 1000MPa, and simultaneously has good elongation (13%), excellent conductivity (97% IACS) and extremely low electric mobility; the columnar nano twin crystal Cu prepared by utilizing the direct current electrolytic deposition has excellent fatigue resistance besides excellent strength, plasticity and electrical properties. The reason why the nano twin crystal structure has such excellent mechanical and electrical properties is that coherent twin crystal boundaries can hinder dislocation movement to achieve the purpose of improving strength on one hand, and can react with dislocations and improve dislocation movement space to achieve the effect of keeping good plasticity on the other hand; the energy of the coherent twin crystal boundary is only one tenth of that of the common crystal boundary, so that the coherent twin crystal boundary has good thermal stability and electromigration resistance; the atoms near the twin boundary are aligned and have a low degree of electron scattering, and thus have good conductivity.

Disclosure of Invention

In order to solve the problem that the strength and the plasticity can not be simultaneously obtained in the existing copper foil material, the invention provides a nano-twin crystal copper foil and a preparation method thereof.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a nanometer twin crystal copper foil is composed of columnar crystal grains, the size of the crystal grains of a twin crystal sheet layer is gradually increased from bottom to top, and the size change range of a minor axis is 200-950 nm; the columnar crystal grains contain nanometer-scale twin crystal lamella, and the average thickness of the nanometer twin crystal lamella is below 100 nm.

The orientation of the columnar crystal grains is changed from random orientation to strong (111) texture from bottom to top.

The thickness of the nanometer twin crystal copper foil is 3-100 μm.

The performance of the nanometer twin crystal copper foil is as follows: the purity is 99.995 +/-0.005 at%, the tensile strength is more than 500MPa at room temperature, and the elongation is 1-5%.

The nanometer twin crystal copper foil is prepared by a direct current electrolytic deposition technology, wherein the direct current electrolytic deposition technology comprises the following used electrolyte components:

the electrolyte used preferably has the following composition:

the technological parameters of the direct current electrolytic deposition technology are as follows: adopting constant current mode with current density of 5-150mA/cm²The electrolytic deposition time is 3 min-20 h, and the temperature is 5-40 ℃; and adjusting the pH value of the electrolyte to 0.5-1.5 by using concentrated sulfuric acid.

In the direct-current electrolytic deposition process, an iridium tantalum titanium electrode is selected as an anode, a cathode is a pure Ti plate, the distance between the cathode and the anode is 60-140 mm, and the area ratio of the anode to the cathode is (1-10): 1.

The invention has the following advantages:

1. has unique microstructure

By utilizing reasonable process parameters, the nano twin crystal copper foil material obtains a unique internal microstructure: from bottom to top, the grain size gradually increases, and the average minor axis size variation range is 200-950 nm; twin crystal boundaries with high density exist in the columnar crystal grains, and the average thickness of the twin crystal lamella is below 100 nm; at the same time, the orientation of the grains changes from random orientation to a strong (111) texture.

2. Excellent mechanical property

In the invention, when the thickness of the copper foil material is 6 microns, the room temperature tensile property is 508 +/-24 MPa, which exceeds the requirements of the tensile strength (276MPa) of the standard copper foil in the printed board standard IPC-4562 and the tensile strength (300MPa) in the lithium ion battery electrolytic copper foil standard SJ/T11483-2014.

3. Application prospect

The nanometer twin crystal copper foil has controllable thickness, can meet the requirement of extremely thin copper foil, and has excellent application prospect in lithium ion batteries and circuit boards due to the excellent mechanical property.

4. The preparation method is simple and easy to control

The formation of the nanometer twin crystal is controlled by the additive, only the additive in the traditional electrolytic deposition technology needs to be slightly changed, and the method is suitable for industrial large-scale production.

Drawings

FIG. 1 is a sectional microscopic structure view of a nano-twin copper foil under a scanning electron microscope in example 1.

FIG. 2 is a scanning electron microscope backscattered electron diffraction (EBSD) pattern of example 1.

FIG. 3 is an engineering stress-strain curve of the nano-twin copper foil of examples 1-3.

FIG. 4 is a sectional microscopic structure view of a nano-twin copper foil under a scanning electron microscope in example 2.

FIG. 5 is a sectional microscopic structure view of a nano-twin copper foil under a scanning electron microscope in example 3.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

Example 1

1. Preparation of nano twin crystal copper foil by using direct current electrolytic deposition technology

An electrolytic deposition apparatus: a direct current voltage and current stabilization power supply;

the requirements of the electrolyte used for the electrowinning: CuSO₄The concentration is 100g/L, deionized water is used for preparing electrolyte, and analytically pure H is used₂SO₄The pH of the electrolyte was adjusted to 1.

The additives added into the electrolyte comprise: the analytically pure gelatin concentration was 30mg/L and the HCl concentration was 40 mg/L.

The anode and the cathode are respectively an iridium tantalum titanium plate and a pure titanium plate.

2. Parameters of the electrolytic deposition process: the direct current electrolysis type electroplated copper foil has a current density of 30mA/cm²(ii) a The distance between the cathode and the anode is 10cm, the cathodes and the anode are arranged in parallel and in centrosymmetry, and the area ratio of the anode to the cathode is 4: 1; the electrolysis temperature is 25 ℃ and is kept constant; adopting a water pump to circulate the electrolyte, wherein the power of the water pump is 30W; the DC electrodeposition time was 40 minutes.

The prepared nano twin crystal copper foil has the area of 200 x 300mm²After a portion 30mm from the edge was cut out, the thickness was measured by weighing to be 17.0. mu.m. The crystal grains below the copper foil and close to the titanium plate substrate are columnar, the size of the crystal grains is smaller, and the average minor axis size of the columnar crystal grains is 280nm measured by a line cutting method; as the thickness increases, the columnar grain size increases; the average minor axis size of columnar grains near the growth surface of the copper foil was increased to 730 nm. Each columnar crystal grain contains a high-density twin boundary inside, and the thickness of a twin crystal lamella is below 100 nanometers, as shown in figure 1. The copper foil has good toughness, can be directly taken down from the titanium plate substrate, and has no pin hole.

The columnar crystal orientation of the prepared nano twin crystal copper foil gradually transits to 111 texture orientation from random orientation, as shown in figure 2.

In this example, the room temperature stretching result of the nano twinned copper foil is shown as curve 1 in fig. 3. The test conditions were: the tensile test pattern was cut with a common blade, the length x width of which was 50mm x 12mm, and the tensile properties were tested with a universal tester 5848, the tensile rate being 50 mm/min. The performance of the nanometer twin crystal copper foil is as follows: the purity is 99.995 +/-0.005 at%, the tensile strength is 515 +/-12 MPa, and the elongation at break is 3.5 +/-0.8%.

Example 2

The difference from the embodiment 1 is that:

the concentration of analytically pure gelatin is 40mg/L, the concentration of HCl is 30mg/L, and the direct current electrolytic deposition time is 22 min.

The thickness of the prepared nano twin crystal copper foil is 11 μm by adopting a weighing method. The average minor axis size of columnar grains under the copper foil on the side close to the titanium substrate was 230 nm. The grain size gradually increased from bottom to top, and the average minor axis size at the growth surface of the copper foil was 660nm, as shown in fig. 4.

In this example, the room temperature tensile structure of the nano twin crystal copper foil is shown by curve 2 in fig. 3, and the purity is 99.995 ± 0.005 at%, the tensile strength is 524 ± 10MPa, and the elongation at break is 2.0 ± 0.3%.

Example 3

The difference from the embodiment 1 is that:

50mg/L of analytically pure gelatin, 30mg/L of HCl concentration and 40min of electrolytic deposition time,

the thickness of the prepared nano twin crystal copper foil is 6 mu m by adopting a weighing method. The average minor axis size of columnar grains below the copper foil on the side close to the titanium substrate was 270 nm. The grain size gradually increased from bottom to top, and the average minor axis size of the grains at the growth surface of the copper foil was about 550nm, as shown in fig. 5.

In this example, the room temperature tensile structure of the nano twin crystal copper foil is shown by curve 3 in fig. 3, and the purity is 99.995 ± 0.005 at%, the tensile strength is 508 ± 24MPa, and the elongation at break is 1.3 ± 0.3%.

Comparative example 1

In the printed board metal foil standard IPC-4562, the requirements for a standard electrolytic copper foil at room temperature (23 ℃) are as follows: when the thickness is 17.1 mu m, the tensile strength is 207MPa, and the elongation is 2 percent; when the thickness is 34.3 mu m, the tensile strength is 276MPa, and the elongation is 3 percent; when the thickness was 68.6. mu.m, the tensile strength was 276 μm and the elongation was 3%.

Comparative example 2

In the electrolytic copper foil industry standard SJ/T11483-2014 for the lithium ion battery, the requirements of the electrolytic copper foil at room temperature are as follows: the LBEC-01 double-sided smooth copper foil has the tensile strength of 294MPa and the elongation of 3.0 percent when the thickness is 8-20 mu m; the LBEC-02 single-sided smooth copper foil has the tensile strength of 300MPa and the elongation of 2.5 percent when the thickness is 8-12 mu m; the LBEC-03 double-sided rough copper foil has the tensile strength of 300MPa and the elongation of 2.5 percent when the thickness is 9-12 mu m.

The comparison shows that the strength of the nano-twin copper foil is far higher than the requirements of the electrolytic copper foil standards IPC-4562 and SJ/T11483-2014, which benefits from the strengthening effect of the nano-twin structure. In addition, the nanometer twin crystal structure often has excellent fatigue resistance, conductivity and thermal stability, and has great application prospect in the field of circuit boards and lithium ion batteries.

Claims

1. A nano twin crystal copper foil is characterized in that: the nanometer twin crystal copper foil is composed of columnar crystal grains, the size of the columnar crystal grains is gradually increased from bottom to top, and the size change range of the average minor axis is 200-950 nm; the columnar crystal grains contain nanometer-scale twin crystal lamella, and the average thickness of the nanometer twin crystal lamella is below 100 nm.

2. The nano twin crystal copper foil according to claim 1, characterized in that: the columnar crystal grain orientation is changed from random orientation to strong (111) texture from bottom to top.

3. The nano twin crystal copper foil according to claim 1, characterized in that: the thickness of the nanometer twin crystal copper foil is 3-100 μm.

4. The nano twin crystal copper foil according to claim 1, characterized in that: the performance of the nanometer twin crystal copper foil is as follows: the purity is 99.995 +/-0.005 at%, the tensile strength is more than 500MPa at room temperature, and the elongation is 1-5%.

5. The method for producing a nano twin copper foil according to claim 1, characterized in that: the nanometer twin crystal copper foil is prepared by a direct current electrolytic deposition technology, wherein the direct current electrolytic deposition technology comprises the following electrolyte:

6. the method for producing a nano twin copper foil according to claim 5, characterized in that: the electrolyte used had the following composition:

7. the method for producing a nano twin copper foil according to claim 5, characterized in that: the technological parameters of the direct current electrolytic deposition technology are as follows: adopting constant current mode with current density of 5-150mA/cm²The electrolytic deposition time is 3 min-20 h, and the temperature is 5-40 ℃; and adjusting the pH value of the electrolyte to 0.5-1.5 by using concentrated sulfuric acid.

8. The method for producing a nano twin copper foil according to claim 5, characterized in that: in the direct-current electrolytic deposition process, an iridium tantalum titanium electrode is selected as an anode, a cathode is a pure Ti plate, the distance between the cathode and the anode is 60-140 mm, and the area ratio of the anode to the cathode is (1-10): 1.