Ultralow-profile composite copper foil capable of being used for high-frequency circuit as well as preparation method and application of ultralow-profile composite copper foil

Abstract

The invention discloses an ultralow-profile composite copper foil capable of being used for a high-frequency circuit and a preparation method and application of the ultralow-profile composite copper foil. Wherein the composite copper foil comprises a copper foil and a graphene layer coated on the surface of the copper foil, the copper foil is prepared by an electro-deposition process, the graphene layer is prepared by an in-situ chemical vapor deposition process, and the copper foil is subjected to high-temperature annealing treatment in advance before the graphene layer is prepared. According to the invention, through high-temperature annealing of the copper foil and in-situ CVD growth of graphene, an atomic-scale flat graphene interface layer is successfully constructed on the surface of the macroscopic copper foil, a microscopic peak-valley profile formed by coarsening crystallization on the surface of the traditional copper foil is changed, and the surface roughness of a conductor is reduced to be close to a theoretical limit; therefore, skin effect loss and signal scattering in high-frequency signal transmission are inhibited to the greatest extent, and revolutionary improvement of signal transmission efficiency is realized.

Description

Technical Field

[0001] This invention relates to the field of copper foil technology, and in particular to a composite copper foil with ultra-low profile suitable for high-frequency circuits, its preparation method, and its application. Background Technology

[0002] High-frequency communication technology is rapidly developing towards millimeter waves, terahertz, and multilayer high-density integration, placing increasingly stringent demands on the signal transmission integrity, energy consumption control, and long-term reliability of circuit boards. As a key carrier for signal transmission, the surface profile and interface characteristics of copper foil directly determine the performance ceiling of high-frequency circuits. Although traditional low-profile electrolytic copper foil has reduced its profile to the micrometer level through optimized electrodeposition processes, microscopic grain boundaries and crystal surface undulations still exist on its surface. Signal loss caused by the "skin effect" in frequency bands above 10 GHz is still significant. At the same time, copper foil is easily oxidized in high-temperature and high-humidity environments to form insulating copper compounds, and copper atoms migrate after lamination with the dielectric layer, leading to a decrease in circuit insulation resistance and fluctuations in dielectric constant, which seriously affects phase stability and device lifespan.

[0003] To balance high-frequency performance and interface reliability, the industry has attempted to construct functional protective layers on the surface of copper foil, such as using electroless nickel-gold plating, blackening treatment, or depositing diamond-like carbon films. However, these coatings may introduce additional resistance due to insufficient conductivity, or peel off during subsequent processing due to uneven thickness and weak adhesion. They may even cause increased electromagnetic wave reflection due to dielectric constant mismatch, making it difficult to achieve an ideal balance between high frequency, high peel strength, and high oxidation resistance. Summary of the Invention

[0004] The main objective of this invention is to provide a composite copper foil with ultra-low profile that can be used in high-frequency circuits, as well as its preparation method and application, in order to solve at least one of the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides a composite copper foil with ultra-low profile suitable for high-frequency circuits, comprising a copper foil and a graphene layer covering the surface of the copper foil. The copper foil is prepared by an electrodeposition process, and the graphene layer is prepared by an in-situ chemical vapor deposition process. Furthermore, the copper foil is pre-treated with high-temperature annealing before the preparation of the graphene layer.

[0006] Furthermore, the thickness of the copper foil is 12–30 μm.

[0007] Furthermore, the graphene layer is a single layer or a double layer of graphene.

[0008] The present invention also provides a method for preparing the above-mentioned ultra-low profile composite copper foil that can be used in high-frequency circuits, comprising the following steps: (1) Preparation of copper foil by electrodeposition Copper sulfate was dissolved in water, then sulfuric acid was added, followed by sodium chloride aqueous solution. The mixture was stirred, and then sodium dithiopropane sulfonate aqueous solution, Janus Green B aqueous solution, and polyethylene glycol aqueous solution were added. After adding water to make up the volume, the electrolyte was obtained and then aged. Electrodeposition parameters were set and electrodeposition was performed. After deposition, the cathode with copper foil attached was washed with water, then immersed in benzotriazole aqueous solution, and finally dried to obtain copper foil. (2) Copper foil substrate pretreatment and high-temperature planarization The copper foil is first cleaned with an organic solvent, then immersed in dilute sulfuric acid, then rinsed with water, dried with nitrogen, and finally annealed at high temperature. (3) In-situ chemical vapor deposition growth of graphene layers In a mixed atmosphere of Ar and H2, copper foil that has undergone high-temperature annealing is placed in the reaction zone of an in-situ chemical vapor deposition (CVD) apparatus. Methane is used as the carbon source, and growth parameters are set for in-situ CVD. After growth is completed, the copper foil is moved to the cold zone of the furnace tube. After cooling, all gases are turned off, and high-purity Ar is introduced into the furnace tube to atmospheric pressure. The copper foil is then removed to obtain the composite copper foil.

[0009] Further, in step (1), the concentration of copper sulfate in the electrolyte is 140–180 g / L, the concentration of sulfuric acid is 60–100 g / L, the concentration of chloride ions is 30–70 mg / L, the concentration of sodium polydisulfide dipropane sulfonate is 5–50 mg / L, the concentration of Janus Green B is 10–50 mg / L, and the concentration of polyethylene glycol is 30 mg / L; the current density for the aging treatment is 5–15 A / dm³. 2 The time is 20 to 40 minutes.

[0010] Furthermore, in step (1), the electrodeposition parameters are: cathode current density 15–35 A / dm³. 2 The deposition time is 35–110 minutes, the cathode roller speed is 5–25 rpm, and the electrode spacing is 50–80 mm.

[0011] Furthermore, in step (2), the concentration of dilute sulfuric acid is 1 wt%, and the immersion time is 30 to 60 seconds.

[0012] Further, in step (2), the high-temperature annealing treatment is carried out in a mixed atmosphere of Ar and H2, with a gas flow rate of 400-600 sccm and a gas flow rate of 30-70 sccm. The heating rate of the high-temperature annealing treatment is 20-30°C / min, the annealing temperature is 950-1050°C, and the annealing time is 20-40 minutes.

[0013] Further, in step (3), the growth parameters are: growth temperature 980~1020°C, carbon source flow rate 3~15sccm, H2 flow rate 20~80sccm, Ar flow rate 500sccm, pressure 500~2000 Pa, and growth time 15~45 minutes.

[0014] The present invention also provides an application of the above-mentioned ultra-low profile composite copper foil, which can be used in high-frequency circuits, in high-frequency / high-speed communication equipment, lithium-ion batteries, automotive electronics, or high-end testing instruments.

[0015] The design principle of this invention is as follows: Through a synergistic process chain of "substrate optimization - in-situ growth - interface control," high-temperature annealing is used to achieve lattice restructuring and surface planarization on the precisely controlled surface of electrodeposited copper foil. Then, a large-area, high-quality graphene layer is grown in-situ using chemical vapor deposition (CVD) technology. This constructs a graphene-copper composite structure with atomically flat surface, excellent conductivity, superior oxidation / diffusion resistance, and strong interfacial bonding, meeting the extreme requirements of high-frequency, high-speed circuits for signal integrity and reliability. Specifically: I. Material System and Process Innovation This invention electrodeposits a copper substrate with specific crystal orientations suitable for graphene growth using a specific additive system; subsequently, high-temperature annealing is performed under a protective atmosphere to simultaneously achieve recrystallization and leveling of the copper foil and optimize its surface catalytic activity; finally, a carbon source is directly introduced to complete graphene growth without disrupting the vacuum and atmosphere. This process avoids contamination and oxidation in intermediate steps, ensuring the uniformity and stability of the final product's performance.

[0016] This invention abandons the complex traditional process of transferring graphene to copper foil. Instead, it directly grows high-quality graphene in situ on ultra-low profile copper foil prepared by precision electrodeposition, avoiding the pollution, damage, and interface impedance problems caused by the transfer process. This achieves strong chemical bonding and ultra-low contact resistance between graphene and copper substrate in the form of carbon atom intercalation, providing a near-ideal defect-free transmission channel for high-frequency signals.

[0017] II. Structural Design Innovation This invention successfully constructs an atomically smooth graphene interface layer on the macroscopic copper foil surface through high-temperature annealing and in-situ CVD growth of graphene. This changes the microscopic peak-valley profile formed by coarsened crystals on the traditional copper foil surface, reducing the surface roughness of the conductor to near the theoretical limit. This maximizes the suppression of skin effect loss and signal scattering in high-frequency signal transmission, achieving a revolutionary improvement in signal transmission efficiency.

[0018] Furthermore, through the graphene interface layer, several key properties were successfully achieved, including anti-oxidation, copper diffusion inhibition, maintaining high peel strength, and ensuring ultra-low profile. Graphene, with its physical barrier properties, simultaneously solved the long-term oxidation problem of copper foil and the ion migration problem in high-frequency boards. At the same time, the graphene layer can achieve ideal interfacial bonding with the upper resin (the "upper resin" is a resin-based dielectric layer that must be bonded to the composite copper foil in high-frequency circuit applications, such as epoxy resin, polyimide, etc.). While achieving an ultra-low profile, it still maintains peel strength higher than the industry standard, breaking through the technical barrier of the difficulty in achieving both "low roughness" and "high adhesion" in traditional technologies.

[0019] The beneficial effects of this invention are reflected in: The composite copper foil of this invention reduces the surface profile to near the theoretical limit, which can suppress the skin effect and signal scattering in high-frequency signal transmission, so that the conductor can still maintain extremely low insertion loss and excellent signal integrity in the ultra-high frequency band above 10 GHz, meeting the data transmission rate requirements of cutting-edge fields such as 5G / 6G communication and high-speed computing.

[0020] The in-situ grown dense graphene layer acts as a physical barrier layer, effectively preventing oxygen and moisture in the environment from contacting the copper substrate. This solves the problem of easy oxidation of traditional copper foil and improves storage and processing stability. At the same time, this layer strongly inhibits the migration of copper atoms to the dielectric layer under high electric field and high temperature conditions, preventing circuit short circuits and performance degradation caused by this, and greatly improving the long-term reliability and lifespan of high-end printed circuit boards (PCBs).

[0021] This invention optimizes the surface chemical state and structural integrity of the graphene layer by precisely controlling the fabrication process parameters of the composite copper foil (especially graphene growth-related parameters), thereby achieving ideal interfacial bonding with the upper resin layer. Simultaneously, it achieves peel strength far superior to traditional low-profile copper foils while obtaining an ultra-low surface profile. This resolves the long-standing dilemma in the field of high-frequency circuit materials: either sacrificing adhesion for low loss or accepting high loss for reliability, enabling circuit boards to possess both excellent electrical performance and mechanical reliability.

[0022] This invention avoids the problems of wrinkles, contamination, and damage caused by traditional graphene transfer technology. The process is simple, the product yield is high, and it is suitable for large-scale, low-cost production of high-performance high-frequency circuit copper foil. Attached Figure Description

[0023] Figure 1 This is a SEM schematic diagram of the ultra-low profile composite copper foil prepared in Example 1 that can be used in high-frequency circuits.

[0024] Figure 2 This is a schematic SEM image of the copper foil prepared in Comparative Example 1.

[0025] Figure 3 The surface profile / roughness test diagram is shown for the ultra-low profile composite copper foil prepared in Example 1 that can be used in high-frequency circuits.

[0026] Figure 4 The insertion loss test diagram is shown for the ultra-low profile composite copper foil prepared in Example 1 that can be used in high-frequency circuits.

[0027] Figure 5 This is a peel strength test diagram of the ultra-low profile composite copper foil prepared in Example 1 that can be used in high-frequency circuits.

[0028] Figure 6 This is a chemical resistance test diagram of the ultra-low profile composite copper foil prepared in Example 1, which can be used in high-frequency circuits. Detailed Implementation

[0029] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0030] Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art. Electrodeposition equipment, product series: lithium battery copper foil electroplating equipment, Kunshan Dongwei Technology Co., Ltd.; in-situ chemical vapor deposition equipment, model: FBCVD-100, Suzhou Newmte Co., Ltd.

[0031] Example 1 Ultra-low profile composite copper foil can be used in the fabrication of high-frequency circuits. (1) Preparation of copper foil by electrodeposition In a 2L PP beaker, add 1.5L of 50°C ultrapure water. While continuously stirring (300rpm), slowly add copper sulfate (CuSO4). After the copper sulfate is completely dissolved, slowly add electronic-grade sulfuric acid (H2SO4) dropwise, and finally add an aqueous solution of sodium chloride (NaCl). Continue stirring at 50°C for 30 minutes. Subsequently, add an aqueous solution of sodium polydithiopropane sulfonate (SPS, as a carrier), an aqueous solution of Janus Green B (JGB, as a leveling agent), and an aqueous solution of polyethylene glycol (PEG, molecular weight ~6000, as an inhibitor). Make up the volume to 2L with ultrapure water to obtain the electrolyte. The electrolyte concentrations are: copper sulfate 160g / L, sulfuric acid 80g / L, chloride ion 50mg / L, SPS 20mg / L, JGB 30mg / L, and PEG 30mg / L.

[0032] The electrolyte was aged under an aging process, with a current density of 10 A / dm³. 2 Aging time: 30 minutes.

[0033] Install the cathode roller (the substrate for depositing copper foil) and anode plate (titanium-based anode) into the preset positions of the electrolytic cell, ensuring the cathode roller can rotate; inject the prepared electrolyte into the assembled electrolytic cell, ensuring the electrodes are completely immersed in the electrolyte. Activate the temperature control device to heat the electrolyte to 50°C and maintain a constant temperature. Electrodeposition parameters: 1. Cathode current density (Jk): 25 A / dm 2 2. Cathode speed / stirring: Cathode roller speed 15 rpm; 3. Auxiliary air stirring flow rate 2 L / min; 4. Electrode spacing 60 mm. Start electrodeposition, deposition time 55 minutes.

[0034] Immediately after deposition, the cathode with copper foil attached is immersed in a flowing ultrapure water bath and ultrasonically cleaned (100W) for 1 minute to remove residual electrolyte. Then, it is immersed in a 1.5wt% benzotriazole (BTA) aqueous solution at 60°C for 20 seconds to form a temporary protective film. Finally, it is dried in a forced-air drying oven at 90°C for 3 minutes to obtain the copper foil substrate.

[0035] (2) Annealing treatment of copper foil The copper foil substrate obtained in step (1) was first ultrasonically cleaned in anhydrous ethanol and acetone for 8 min each to remove BTA and organic contaminants. Then it was immersed in 1 wt% dilute sulfuric acid for 45 seconds to remove oxides and activate the surface. It was rinsed with ultrapure water and dried with nitrogen. Then it was subjected to high-temperature annealing with the following parameters: 1. Atmosphere: Ar / H2 mixture; 2. Gas flow rate: Ar 500 sccm, H2 50 sccm; 3. Heating rate: 25°C / min; 4. Annealing temperature: 1000°C; 5. Annealing time: 30 min; 6. System pressure: 1000 Pa.

[0036] (3) In-situ chemical vapor deposition growth of graphene layers The copper foil substrate treated in step (2) was placed in a quartz boat under a continuous Ar / H2 (500 / 50 sccm) atmosphere and quickly and smoothly pushed to the isothermal center of the furnace tube reaction zone. Growth parameters were set as follows: 1. Growth temperature: 1000°C; 2. Carbon source: methane (CH4); 3. Carbon source flow rate: 5 sccm; 4. Hydrogen flow rate: 50 sccm; 5. Argon flow rate: 500 sccm; 6. System pressure: 1000 Pa; 7. Growth time: 30 minutes. Growth was started, and after growth, the CH4 valve was quickly closed. While maintaining the Ar / H2 atmosphere, the copper foil was quickly moved to the furnace tube cold zone. When the temperature dropped below 80°C, all gases were shut off, and high-purity Ar was introduced into the furnace tube to atmospheric pressure. The ultra-low profile composite copper foil suitable for high-frequency circuits was then quickly removed.

[0037] Comparative Example 1 Comparative preparation of composite copper foil The preparation method of this comparative example is basically the same as that of Example 1, except that the in-situ chemical vapor deposition growth of graphene layer in step (3) is omitted.

[0038] Comparative Example 2 Comparative preparation of composite copper foil The preparation method of this comparative example is basically the same as that of Example 1, except that the growth time in step (3) is adjusted to 5 minutes.

[0039] Comparative Example 3 Comparative preparation of composite copper foil The preparation method of this comparative example is basically the same as that of Example 1, except that in step (3), the flow rate of the carbon source methane is adjusted to 1 sccm.

[0040] Comparative Example 4 Comparative preparation of composite copper foil The preparation method of this comparative example is basically the same as that of Example 1, except that the copper foil annealing treatment in step (2) is omitted.

[0041] Comparative Example 5 Comparative preparation of composite copper foil The preparation method of this comparative example is basically the same as that of Example 1, except that the electrodeposition cathode current density in step (1) is adjusted to 10 A / dm. 2 .

[0042] Experimental Example 1 Copper foil performance testing Multiple performance tests were performed on the copper foils prepared in Example 1 and each comparative example, and the results were compared with commercially available ultra-low profile copper foils for high-frequency circuits (produced by Jiangxi Jiangtong, model: VLP copper foil). The test items and methods are shown in Table 1 below: Table 1

[0043] The test results are shown in Table 2: Table 2

[0044] Structural characterization (SEM observation results): Example 1: The graphene is a uniform monolayer with a domain size of 5-10 μm and an atomically flat surface without agglomeration or exposure; the copper foil substrate has refined grains (after annealing) and has no gaps at the interface with the graphene.

[0045] Comparative Example 1: No graphene, the copper foil surface is flat (after annealing), and uniform fine grains (size 2-5μm) are visible, with no obvious peaks and valleys.

[0046] Comparative Example 2: The graphene is discontinuous, with local monolayer coverage (coverage rate of about 60%), and the uncovered areas expose copper foil; the graphene crystal domains are small (2-3μm), with local micro-agglomerations.

[0047] Comparative Example 3: Graphene is mainly monolayer with local thin areas (due to insufficient carbon source), with a coverage of about 85%; the crystal domain size is 3-8μm, and there is no obvious agglomeration on the surface, with better continuity than Comparative Example 2.

[0048] Comparative Example 4: The graphene is a single layer but undulates with the copper foil substrate (no annealing resulted in coarse copper foil grains, size 10-20μm); there are tiny gaps at the interface between graphene and copper foil, and copper foil oxide spots are visible in some areas.

[0049] Comparative Example 5: The copper foil surface has coarse grains (10-30 μm), and the graphene monolayer is completely covered but has slight undulations with the substrate; there are no obvious graphene defects, and the interface bonding is relatively tight but weaker than in Example 1.

[0050] Commercially available VLP: Micron-level peaks and valleys (Rz 0.71 μm) are visible on the copper foil surface, with no graphene layer; grain size 5-15 μm, and slight oxidation marks on the surface.

[0051] As can be seen from the above: 1. A complete and uniform monolayer of graphene is the core component for improving the overall performance of VLP copper foil. Compared to Comparative Example 1 (without graphene), Example 1 (complete monolayer graphene) showed a significant reduction in surface roughness (Rz 0.42 μm vs 0.85 μm), a 46.5% decrease in 20 GHz insertion loss (0.412 dB / cm vs 0.768 dB / cm), a 41.7% increase in peel strength (8.5 lb / in vs 6.0 lb / in), and a substantial improvement in chemical resistance (oxidized area 1.2% vs 25.3%). This demonstrates that monolayer graphene can simultaneously achieve the synergistic effects of "reduced roughness, low loss, strong bonding, and corrosion resistance," which is key to inventing superior VLP copper foil compared to traditional graphene-free materials.

[0052] 2. Precise matching of graphene growth parameters is necessary to ensure film quality. The methane flow rate and growth time directly determine the continuity and integrity of graphene: Comparative Example 2 (insufficient growth time) has a graphene coverage of only 60%, while Comparative Example 3 (low methane flow rate) has a coverage of 85%. Both examples have weaker insertion loss and exfoliation strength than Example 1 (methane flow rate 10 sccm + growth time 30 min). Furthermore, Comparative Example 2 has a higher defect rate due to insufficient growth time, and its performance is inferior to Comparative Example 3. Experimental verification shows that only when the methane flow rate is 3-15 sccm and the growth time is 15-45 min can a uniform and dense monolayer graphene be formed, fully leveraging its performance advantages.

[0053] 3. High-temperature annealing pretreatment of copper foil is crucial for strengthening graphene bonding and optimizing surface smoothness. Compared with Example 1, Comparative Example 4 (without annealing) showed an increase in copper foil grain size from 2-5 μm to 10-20 μm, a doubling of surface roughness (Rz 1.10 μm vs 0.42 μm), and the appearance of gaps at the graphene layer-copper foil interface. This resulted in a 23.5% decrease in peel strength (6.5 lb / in vs 8.5 lb / in), and a significant deterioration in chemical resistance and insertion loss. This demonstrates that high-temperature annealing can refine copper foil grains, enhance surface activity, and eliminate the oxide layer, providing a smooth and suitable substrate for in-situ graphene growth. Simultaneously, it strengthens the interfacial bonding between graphene and copper foil, making it an indispensable pretreatment step.

[0054] 4. Electrodeposition current density affects the state of the copper foil substrate, indirectly regulating the performance of the graphene layer. Comparative Example 5 (Cathode current density 10 A / dm) 2 ) and Example 1 (cathode current density 25A / dm 2Compared to Example 1, copper foil has coarser grains (10-30 μm vs 2-5 μm) and higher surface roughness (Rz 0.95 μm vs 0.42 μm), which weakens the interfacial bonding of graphene. Consequently, its peel strength (7.0 lb / in vs 8.5 lb / in) and insertion loss are inferior to those of Example 1. Experiments have verified that the electrodeposition current density needs to be controlled within 15-35 A / dm². 2 Only by adhering to the patent scope can a copper foil substrate with fine grains and a smooth surface be prepared, laying the foundation for the subsequent graphene layer to achieve optimal performance.

[0055] Experiment Example 2 Application testing of composite copper foil in lithium metal batteries The ultra-low profile high-frequency circuit with controllable surface growth of graphene layer prepared in Example 1 was assembled into a lithium metal battery using copper foil, and the battery performance was tested as follows: (L1) Battery composition: Positive electrode: LiFePO4 was selected as the active material for the positive electrode. LiFePO4 (active material), SuperP (conductive agent), and PVDF (binder) were mixed in a mass ratio of 8:1:1, with N-methylpyrrolidone (NMP) as the solvent, and stirred for 2 hours to form a uniform slurry. The slurry was coated onto a 12μm thick aluminum foil and vacuum dried at 80℃ for 12 hours (vacuum degree -0.095MPa). Subsequently, it was rolled at a pressure of 5MPa using a roller press and cut into 12mm×12mm square electrode sheets. The active material loading was controlled at 1.5±0.1mg / cm³. 2 .

[0056] Negative electrode: The composite copper foil prepared in Example 1 was cut into square electrode sheets of 14mm × 14mm (larger than the positive electrode to avoid lithium dendrites piercing the separator); to supplement the lithium source, a 5μm thick lithium metal layer was deposited on the surface of the composite copper foil by vacuum evaporation (evaporation vacuum degree ≤ 5 × 10⁻⁶). -4 Pa, surface capacity 0.5 mAh / cm³ 2 The composite copper foil serves as the negative electrode for lithium metal batteries. The copper layer (20 μm thick) provides mechanical support, while the surface graphene layer (atomic-level flatness) inhibits lithium dendrite growth, blocks copper oxidation and migration, and maintains ultra-low interface impedance, thus meeting the high stability requirements of lithium metal batteries.

[0057] Electrolyte: 1 mol / L LiPF6 dissolved in EC / DEC / DMC (volume ratio 1:1:1), with 2 wt% fluoroethylene carbonate (FEC, to enhance lithium dendrite suppression) and 1 wt% imidazole compound (to adapt to the chemical properties of graphene surface and optimize interface compatibility). The electrolyte volume is 50±5 μL / cell.

[0058] Separator: Celgard 2400 polypropylene separator (25μm thickness, 0.1μm pore size) is selected and cut into 16mm×16mm pieces to ensure complete coverage of the positive and negative electrodes and avoid direct contact.

[0059] (L2) Assembly process: Environmental control: Operate in an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm) to prevent electrolyte hydrolysis, lithium metal oxidation and graphene layer contamination.

[0060] Stacking sequence: 2032 coin cell casing (positive electrode casing) → LiFePO4 positive electrode → separator (pre-wetting with 5μL electrolyte) → composite copper foil negative electrode (graphene layer facing lithium layer) → 0.1mm thick nickel sheet (auxiliary current collector) → spring sheet → gasket → negative electrode casing.

[0061] Packaging parameters: The battery is sealed using a button cell sealing machine at a pressure of 10±0.5MPa. After sealing, it is left to stand in a vacuum environment at 25℃ for 30 minutes to ensure that the electrolyte fully wets the electrodes and the separator, and at the same time, to form a stable interface between the graphene layer and the lithium layer, thus completing the battery activation.

[0062] (L3) Test method: Charge / discharge capacity and efficiency test: The Blue Electric CT2001A battery test system was used, with a voltage window of 2.5-3.6V (LiFePO4 standard window), and 150 cycles were performed at a current density of 0.1C (1C=170mA / g). The charge / discharge capacity and coulombic efficiency of each cycle were recorded, and the capacity retention rate after 150 cycles was calculated as (discharge capacity of the 150th cycle / discharge capacity of the 2nd cycle × 100%).

[0063] Rate performance test: In the same 2.5-3.6V window, discharge at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C in sequence (3 cycles per rate, charged to 3.6V at 0.1C), record the discharge capacity at each rate, calculate the 10C / 0.1C capacity ratio, and evaluate the advantages of high frequency and low impedance.

[0064] Electrochemical performance test under tensile conditions: The coin cell was fixed in the Instron 5967 universal material machine fixture and stretched to 8% strain at a rate of 1±0.05mm / min (the elongation at break of the composite copper foil is ≥10%, and 8% is the safety functional strain). Under the strain condition, it was charged and discharged for 5 cycles at a current density of 0.5C. The capacity and impedance changes without stretching were compared (impedance was tested with a Keysight 34461A multimeter).

[0065] Chemical resistance cycling test: The battery was stored in an 85℃ / 85% RH constant temperature and humidity chamber for 500 hours. After being removed, it was cycled 50 times at a current density of 0.1C to test the capacity decay rate and coulombic efficiency stability, and to evaluate the barrier protection effect of the graphene layer.

[0066] Thermal stability test: High-temperature cycling: Place a fully charged battery in a 100℃ constant temperature chamber and charge and discharge it at 0.5C for 20 cycles, then calculate the capacity decay rate; Temperature program: Using a NETZSCH STA 449 F3 thermal analyzer, the temperature was increased from 25°C to 300°C at a rate of 5±0.1°C / min, with a holding time of 20°C for 30 minutes. Voltage changes and battery appearance (whether there was leakage or bulging) were recorded.

[0067] Overcharge protection performance test: At 25℃, the battery was overcharged from 3.6V to 5V at a current density of 0.5C. The voltage curve and battery appearance were monitored in real time to assess whether there was a sudden voltage drop (internal short circuit) or safety hazard, and to verify the effect of graphene layer on suppressing lithium dendrite piercing.

[0068] Electrochemical impedance spectroscopy (EIS) testing: A CHI660E electrochemical workstation was used, with a test frequency range of 10... 5 ~10 -2 Hz, AC signal amplitude 5±0.05mV, tested after battery assembly (initial state), 50 cycles, 100 cycles, and after chemical resistance test; equivalent circuit was fitted using ZView software (R s (Solution impedance) - Rct (interfacial charge transfer impedance) - W (Warburg impedance)), extract the Rct value to analyze interfacial stability.

[0069] Characterization of lithium dendrite suppression: After 150 cycles, the battery was disassembled and the lithium deposition morphology on the surface of the composite copper foil was observed using scanning electron microscopy (SEM) to evaluate the suppression effect of the graphene layer on lithium dendrite growth.

[0070] (L4) Test Results As shown in Table 3 below, the control group used conventional 6μm electrolytic copper foil (Jiangxi Tongbo Technology Co., Ltd.), and the remaining battery composition (positive electrode, electrolyte, separator, etc.) was completely consistent with the composite copper foil battery in Example 1.

[0071] Table 3

[0072] Experimental Example 3 Solid-state battery application testing of composite copper foil The composite copper foil prepared in Example 1 was assembled into a solid-state battery for battery performance testing, as detailed below: (G1) Battery composition: Positive electrode: Formulation and slurry: based on NCM811 (LiN 0.8 Co 0.1 Mn 0.1 O2 (theoretical capacity 220mAh / g) was used as the positive electrode active material. NCM811, Super P (conductive agent), and PVDF (binder) were mixed at a mass ratio of 90:5:5, with N-methylpyrrolidone (NMP) as the solvent. The mixture was stirred at 300 rpm for 4 hours to form a uniform, particle-free slurry. Coating and molding: The slurry was coated onto a 12μm thick aluminum foil surface. The solvent was removed using a process of "pre-baking at 80℃ for 2 hours + vacuum drying at 120℃ for 12 hours (vacuum degree -0.095MPa)". Subsequently, the foil was rolled using a roller press at a pressure of 8MPa (controlling the electrode density to 3.6±0.1g / cm³). 3 The electrode was cut into 12mm × 12mm square sheets, and the active material loading was controlled at 4.0 ± 0.2 mg / cm³. 2 (Solid-state batteries typically operate under high loads, making them suitable for high-frequency circuits with high energy density requirements.)

[0073] Negative electrode: Composite copper foil pretreatment: Take the composite copper foil prepared in Example 1 (copper layer thickness 20μm, single layer of graphene on the surface), cut it into 14mm×14mm square electrode sheets (size larger than the positive electrode to avoid lithium dendrites piercing the solid electrolyte); and perform vacuum evaporation (evaporation vacuum degree ≤5×10). -4 A 5 μm thick lithium metal layer was deposited on the surface of a composite copper foil graphene substrate, with the areal capacity controlled to be 0.5 mAh / cm². 2 (Supplementing the lithium source for solid-state batteries and improving the lithium-solid electrolyte interface contact).

[0074] Structural advantages and compatibility: The copper layer provides mechanical support and basic conductivity, while the monolayer graphene (atomic-level flatness, Rz=0.42μm) can suppress lithium dendrite growth and block the diffusion of copper atoms into the solid electrolyte, while maintaining ultra-low interface impedance (suitable for high-frequency signal transmission), solving the core problems of high interface impedance and poor cycle stability of solid batteries.

[0075] Solid electrolyte: A sulfide-based composite solid electrolyte, Li3PS4-LiI-LiBr (molar ratio 70:25:5), was selected. After high-energy ball milling for 12 hours, it was pressed into discs with a diameter of 16 mm and a thickness of 150 μm (cold pressing pressure 200 MPa, holding pressure for 5 min). The room temperature ionic conductivity was ≥2.5 × 10⁻⁶. -3 S / cm; Before assembly, dry in an 80℃ vacuum drying oven (vacuum degree -0.095MPa) for 4 hours to remove residual moisture (avoid Li). +It reacts with H2O to generate byproducts, thus protecting the integrity of the graphene layer.

[0076] Interface modification layer: To reduce the interface impedance between the negative electrode and the solid electrolyte, a 5μm thick Li6PS5Cl nano-slurry (20wt% solid content, anhydrous ethanol as solvent) was spin-coated onto the surface of the composite copper foil lithium layer and vacuum dried at 60℃ for 2h to form a transition modification layer (to adapt the chemical compatibility between graphene and sulfide electrolyte and reduce the interface charge transfer resistance).

[0077] (G2) Battery Assembly: Environmental control: The entire process is carried out in an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm) to prevent the solid electrolyte from absorbing moisture and hydrolyzing, lithium metal from oxidizing, and graphene layer from contaminating.

[0078] Stacking sequence: 2032 coin cell case (positive electrode case) → NCM811 positive electrode sheet → solid electrolyte disc (pre-drop 5μL 1mol / L LiTFSI-acetonitrile solution to activate the interface and improve contact tightness) → interface modification layer / composite copper foil negative electrode (graphene layer facing solid electrolyte) → 0.1mm thick nickel sheet (auxiliary current collection, reducing contact resistance) → spring sheet → gasket → negative electrode case.

[0079] Encapsulation and activation: Encapsulation parameters: Encapsulate with a button cell sealing machine at a pressure of 15±1MPa (10MPa higher than that of liquid batteries to ensure close contact between the solid electrolyte and the positive and negative electrodes and eliminate interface gaps); Activation process: After encapsulation, stand in a vacuum environment at 60℃ (vacuum degree -0.09MPa) for 2 hours to promote the wetting of the electrolyte and electrode interface, so that the graphene layer and the modification layer form stable chemical bonds, thus completing the battery activation.

[0080] (G3) Test Method: Electrochemical impedance spectroscopy (EIS): A CHI660E electrochemical workstation was used, with a test frequency range of 10... 6 ~10 -2 Hz, AC signal amplitude 5±0.05mV; tested after battery assembly (initial state), 20 / 50 / 100 cycles, and high-temperature cycling; equivalent circuit fitted using ZView software (R s (Bulk impedance) - Rct (interfacial charge transfer impedance) - CPE (electric double layer capacitance) - W (Warburg impedance)), calculate the ion diffusion coefficient, and evaluate the interface stability.

[0081] Linear scanning voltammetry (LSV): Scan range 2.5–4.5V (adapted to NCM811 voltage window), scan rate 0.1mV / s, recording current changes; if the current density at 4.5V is <1×10⁻⁶. -5 A / cm2 The interface was determined to be electrochemically stable (without side reactions such as copper dissolution or electrolyte decomposition), verifying the compatibility between the composite copper foil and the solid electrolyte.

[0082] Static tensile test: The button cell was fixed in the Instron 5967 universal material handling machine fixture and stretched to 5%, 8%, and 10% strain at a rate of 1±0.05 mm / min (the elongation at break of the composite copper foil is ≥10%, and 10% is the ultimate functional strain); under the strain condition, it was charged and discharged for 10 cycles at a current density of 0.5C, and the capacity and impedance changes in the unstretched state were compared (impedance was tested using a Keysight 34461A multimeter); at the same time, the appearance of the battery after strain was observed to verify the structural integrity of the composite copper foil.

[0083] High-temperature cycling: The battery was placed in constant temperature chambers at 60℃, 80℃, and 120℃ (temperature control accuracy ±0.5℃) and charged and discharged for 20 cycles at a current density of 0.5C. The capacity decay rate was then calculated. Programmed temperature rise: The fully charged battery is heated from -40℃ to 200℃ at a rate of 5±0.1℃ / min, and held at 20℃ for 30min. Voltage changes are recorded using a voltage acquisition instrument (accuracy ±0.01V). Observe whether there is a voltage drop (interface peeling) or shell bulging, and evaluate the structural stability under extreme temperatures.

[0084] Damage simulation: A 0.5 mm deep and 3 mm long scratch was made on the surface of the composite copper foil negative electrode using a diamond scratcher (200 μm wide) (penetrating the copper layer to the graphene layer to simulate micro-damage during solid-state battery assembly / vibration), and the 0.1C charge-discharge performance after damage was tested (as a baseline). Needle penetration test: Use a φ1.0mm steel needle (puncture rate 5mm / s, penetrate the center of the battery), observe whether the battery short circuits or catches fire after the test, and record the voltage change; Extrusion test: A flatbed press (extrusion rate 1 mm / s, maximum pressure 10 kN, extruding until the battery thickness is reduced by 50%) is used. After the test, the battery integrity and electrochemical performance residual rate are evaluated (calculated as 0.1C discharge capacity / capacity before damage × 100%).

[0085] Charge-discharge cycle: voltage window 3.0~4.3V (NCM811 safety window), the first 3 cycles are activated at 0.1C, followed by 100 cycles at a current density of 1C; discharge capacity and polarization voltage (voltage at the end of charging - voltage at the beginning of discharging) are recorded every 10 cycles, and the capacity retention rate is calculated after 100 cycles; Post-cycle characterization: After 100 cycles, the battery was disassembled and the lithium deposition morphology (whether lithium dendrites are present) on the composite copper foil surface was observed using scanning electron microscopy (SEM). The content of interfacial byproducts (such as Li2S and Cu3P) was analyzed using X-ray photoelectron spectroscopy (XPS) to evaluate the barrier effect of the graphene layer.

[0086] (G4) Test Results The control group used conventional 6μm electrolytic copper foil (Jiangxi Tongbo Technology Co., Ltd.), and the remaining battery composition (positive electrode, solid electrolyte, interface modification layer, etc.) was completely consistent with the composite copper foil battery in Example 1. The test results are shown in Table 4 below: Table 4

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite copper foil with ultra-low profile suitable for high-frequency circuits, characterized in that, The invention includes a copper foil and a graphene layer covering the surface of the copper foil. The copper foil is prepared by an electrodeposition process, and the graphene layer is prepared by an in-situ chemical vapor deposition process. The copper foil is pre-treated with high-temperature annealing before the graphene layer is prepared.

2. The ultra-low profile composite copper foil for high-frequency circuits as described in claim 1, characterized in that, The thickness of the copper foil is 12–30 μm.

3. The ultra-low profile composite copper foil for high-frequency circuits as described in claim 1 or 2, characterized in that, The graphene layer is a single layer or a double layer of graphene.

4. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 1, 2, or 3, characterized in that, Includes the following steps: (1) Electrodeposition preparation of copper foil Copper sulfate was dissolved in water, then sulfuric acid was added, followed by sodium chloride aqueous solution. The mixture was stirred, and then sodium dithiopropane sulfonate aqueous solution, Janus Green B aqueous solution, and polyethylene glycol aqueous solution were added. After adding water to make up the volume, the electrolyte was obtained and then aged. Electrodeposition parameters were set and electrodeposition was performed. After deposition, the cathode with copper foil was washed with water, then immersed in benzotriazole aqueous solution, and finally dried to obtain copper foil. (2) Annealing treatment of copper foil The copper foil is first cleaned with an organic solvent, then immersed in dilute sulfuric acid, then rinsed with water, dried with nitrogen, and finally annealed at high temperature. (3) In-situ chemical vapor deposition growth of graphene layers In a mixed atmosphere of Ar and H2, copper foil that has undergone high-temperature annealing is placed in the reaction zone of an in-situ chemical vapor deposition (CVD) apparatus. Methane is used as the carbon source, and growth parameters are set for in-situ CVD. After growth is completed, the copper foil is moved to the cold zone of the furnace tube. After cooling, all gases are shut off, and high-purity Ar is introduced into the furnace tube to atmospheric pressure. The copper foil is then removed to obtain the composite copper foil.

5. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 4, characterized in that, In step (1), the concentration of copper sulfate in the electrolyte is 140-180 g / L, the concentration of sulfuric acid is 60-100 g / L, the concentration of chloride ion is 30-70 mg / L, the concentration of sodium polydithiobispropane sulfonate is 5-50 mg / L, the concentration of gentian violet B is 10-50 mg / L, and the concentration of polyethylene glycol is 30 mg / L; the current density for aging treatment is 5-15 A / dm 2 , and the time is 20-40 minutes.

6. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 4 or 5, characterized in that, In step (1), the electrodeposition parameters are: cathode current density 15–35 A / dm³. 2 The deposition time is 35–110 minutes, the cathode roller speed is 5–25 rpm, and the electrode spacing is 50–80 mm.

7. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 4 or 5, characterized in that, In step (2), the concentration of dilute sulfuric acid is 1 wt%, and the immersion time is 30 to 60 seconds.

8. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 4 or 5, characterized in that, In step (2), the high-temperature annealing treatment is carried out in a mixed atmosphere of Ar and H2, with a gas flow rate of 400-600 sccm and a gas flow rate of 30-70 sccm. The heating rate of the high-temperature annealing treatment is 20-30°C / min, the annealing temperature is 950-1050°C, and the annealing time is 20-40 minutes.

9. The method for preparing ultra-low profile composite copper foil suitable for high-frequency circuits as described in claim 4 or 5, characterized in that, In step (3), the growth parameters are: growth temperature 980-1020°C, carbon source flow rate 3-15 sccm, H2 flow rate 20-80 sccm, Ar flow rate 500 sccm, pressure 500-2000 Pa, and growth time 15-45 minutes.

10. The application of the ultra-low profile composite copper foil as described in claim 1, 2 or 3 for use in high-frequency circuits in high-frequency / high-speed communication equipment, lithium-ion batteries, automotive electronics or high-end test instruments.

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