Integrated structure of current collector and silicon-carbon material, and preparation method and application thereof

Abstract

This invention belongs to the field of battery technology, specifically relating to the integrated structure of current collector and silicon-carbon material, its preparation method, and applications. At least one surface of a copper foil substrate is sequentially subjected to corona etching, gradient carbon layer coating, silicon deposition, and carbon coating to obtain an integrated structure of current collector and silicon-carbon material. Through gradient functionalized carbon layer design, a composite structure with three functions—interfacial bonding, expansion buffering, and catalytic deposition—is constructed on the copper foil surface. Then, silicon nanoparticles are grown in situ in the pores of the carbon layer using a CVD process and coated with a carbon layer, achieving the integrated preparation of current collector and silicon-carbon material and improving the electrical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to the integrated structure of current collector and silicon-carbon material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have been widely used in portable electronic devices, electric vehicles, and energy storage systems. As a core component of the battery, the performance of the anode material directly determines the overall battery performance. Currently, commercial lithium-ion batteries mainly use graphite-based anode materials, but their theoretical specific capacity is relatively low (approximately 372 mAh / g), making it difficult to meet the ever-increasing demand for high energy density.

[0003] Silicon (Si) is considered one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries due to its extremely high theoretical specific capacity (approximately 4200 mAh / g), moderate lithium intercalation potential, and abundant resource reserves. However, silicon-based anode materials experience severe volume expansion (>300%) during charge and discharge, which leads to the following problems: 1) active material pulverization and detachment, resulting in loss of electrical contact; 2) the solid electrolyte interphase (SEI) film continuously breaks down and regenerates, consuming electrolyte and causing low coulombic efficiency and a sharp decline in cycle life; 3) the point contact or weak surface contact between traditional copper foil current collectors and silicon anode materials is difficult to withstand the huge volume change stress, making interface separation prone to occur. To address the aforementioned issues, various modification strategies have been proposed in existing technologies. For example, nanostructuring silicon materials, designing porous or core-shell structures, and preparing silicon / carbon composite materials can buffer volume expansion. In current collector design, common methods include chemical etching of the copper foil surface, electrodeposition roughening treatment, or coating with a conductive adhesive layer to enhance the bonding force between the active material and the current collector.

[0004] Furthermore, some studies have attempted to construct integrated structures of current collectors and anode materials. For example, silicon thin films are directly deposited on copper foil using methods such as chemical vapor deposition (CVD) or magnetron sputtering to form binder-free electrodes. However, due to the mismatch in thermal expansion coefficients and mechanical properties between silicon and copper, directly deposited silicon thin films are still prone to cracking and peeling off from the copper foil surface during cycling. Some technologies introduce a single intermediate buffer layer (such as a titanium, nickel, or carbon layer), but a single buffer layer has limited effectiveness in synergistically alleviating multilayer interfacial stress, regulating interfacial electron / ion transport, and suppressing copper-silicon interfacial side reactions (such as the formation of non-conductive copper-silicon alloys).

[0005] Constructing an integrated electrode structure that combines high interfacial bonding strength, excellent conductivity, and effective buffering of volume expansion is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide an integrated structure of current collector and silicon-carbon material, its preparation method, and its application.

[0007] First, this invention provides a method for preparing an integrated structure of current collector and silicon-carbon material, which involves sequentially performing corona etching, gradient carbon layer coating, silicon deposition, and carbon coating on at least one surface of a copper foil substrate. Specifically, it includes the following steps: Step S1, copper foil pretreatment: Provide a copper foil substrate and perform corona etching on at least one surface of the copper foil substrate.

[0008] Step S2, gradient carbon layer coating: an interface transition layer slurry, a buffer functional layer slurry, and a deposition catalytic layer slurry are sequentially coated on at least one surface of the copper foil substrate after corona etching to obtain a carbon-coated copper foil.

[0009] Step S3, Silicon deposition: Silicon nanoparticles are deposited in the coating layer of the carbon-coated copper foil using a chemical vapor deposition process.

[0010] Step S4, Surface carbon coating: A carbon coating layer is formed on the surface of the coating layer on which silicon nanoparticles have been deposited on the carbon-coated copper foil.

[0011] Furthermore, the copper foil substrate is an electrolytic copper foil with a thickness of 4.5~9.0μm.

[0012] Furthermore, the corona etching power is 300~600V. Etching the copper foil substrate helps to form a uniform micro-rough surface on the copper foil substrate, thereby improving the adhesion of the carbon layer.

[0013] Furthermore, after corona etching, the surface roughness Rz of the copper foil substrate reaches over 2.0 μm.

[0014] Furthermore, the components of the interface transition layer slurry, by mass percentage, include: 10-20% cyano-modified polyacrylate, 70-85% conductive carbon black, and 5-10% silane coupling agent. The interface transition layer can improve the adhesion between the carbon layer and the copper foil substrate, resulting in a peel strength ≥8 N / m.

[0015] Furthermore, the components of the buffer functional layer slurry, by mass percentage, include: 60-75% porous carbon microspheres, 15-25% carbon nanotubes, and 5-20% polyacrylic acid. The buffer functional layer can provide buffer space for the volume expansion of silicon materials during charging and discharging.

[0016] Furthermore, the pore size of the porous carbon microspheres is 20~50 nm.

[0017] Furthermore, the components of the deposited catalyst layer, by mass percentage, include: 80-90% nitrogen-doped graphene, 5-15% nano-copper catalyst, and 3-10% binder. The deposited catalyst layer can reduce the silicon deposition temperature during chemical vapor deposition and can regulate the uniform distribution of silicon grains.

[0018] Furthermore, the particle size of the nano-copper catalyst is 5~10 nm.

[0019] Furthermore, the binder in the deposited catalyst layer is a composite binder composed of polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

[0020] Furthermore, the mass ratio of styrene-butadiene rubber (SBR) to sodium carboxymethyl cellulose (CMC) in the composite adhesive is (1~3):1.

[0021] Further, in step S2, a coating machine is used to sequentially coat at least one surface of the copper foil substrate that has undergone corona etching with an interface transition layer slurry, a buffer functional layer slurry, and a deposition catalyst layer slurry. After each slurry is coated, the copper foil substrate is dried at 80-150°C for 3-5 minutes. After coating, it is thermally cured in a nitrogen atmosphere at 150-250°C for 1-4 hours to obtain a carbon-coated copper foil precursor.

[0022] Furthermore, in step S3, the temperature of the chemical vapor deposition process is 400-600℃, the silicon source is silane, and the deposition time is 30-120 min. Silicon nanoparticles are deposited and embedded in the pores of the buffer functional layer.

[0023] Furthermore, in step S4, the carbon coating layer is formed by the following process: a carbon coating layer is obtained by depositing a carbon source gas using a chemical vapor deposition process.

[0024] Furthermore, the thickness of the carbon coating layer is 5-20 nm.

[0025] Furthermore, the carbon source gas includes one or more of methane, ethane, ethylene, propylene, and propane.

[0026] Secondly, the present invention provides an integrated structure of current collector and silicon-carbon material prepared by the above preparation method.

[0027] Furthermore, the present invention provides a lithium-ion battery comprising an integrated structure of the aforementioned current collector and silicon-carbon material.

[0028] This invention constructs a composite structure on the surface of copper foil by designing a gradient functionalized carbon layer, which has the triple functions of interface bonding, expansion buffering and catalytic deposition. Then, silicon nanoparticles are grown in situ in the pores of the carbon layer by CVD process and coated with a carbon layer on the surface, so as to realize the integrated preparation of current collector and silicon-carbon material.

[0029] Compared with the prior art, the above-described one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: 1. This invention eliminates the traditional silicon-carbon anode processes such as powder preparation, slurry mixing, and electrode coating, shortening the process flow and significantly reducing process costs.

[0030] 2. The integrated structure of current collector and silicon-carbon material provided by this invention fundamentally solves the problem of interface peeling caused by silicon expansion.

[0031] 3. The battery using the integrated structure of current collector and silicon-carbon material provided by this invention has good electrochemical performance. Detailed Implementation

[0032] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] Example 1 An 8μm thick electrolytic copper foil was selected, and one surface was etched using a 400V corona discharge to obtain a copper foil substrate with a surface roughness Rz = 2.3μm. Three layers of carbon paste were then sequentially coated onto the corona-etched surface of the electrolytic copper foil. Interface transition layer slurry: 15% cyano-modified polyacrylate, 80% conductive carbon black, and 5% silane coupling agent. After coating, dry at 120℃ for 3 minutes.

[0036] Buffer functional layer slurry: 70% porous carbon microspheres (pore size 30nm), 20% carbon nanotubes, 10% polyacrylic acid. After coating, dry at 120℃ for 4 minutes.

[0037] The catalytic layer slurry consists of 85% nitrogen-doped graphene, 10% nano-copper catalyst (8 nm particle size), and 5% PVDF. After coating, it is dried at 120°C for 3 min.

[0038] After all coatings are completed, the copper foil is heat-treated at 180°C in a nitrogen atmosphere for 1.5 h to obtain carbon-coated copper foil.

[0039] Carbon-coated copper foil was fed into a continuous CVD furnace and heated to 400°C under argon protection. Silane gas was then introduced, and deposition was carried out for 60 minutes, resulting in the in-situ growth of silicon nanoparticles embedded in the pores of the buffer functional layer. Subsequently, the gas flow was switched to acetylene gas, with argon as the carrier gas, forming an 8 nm thick amorphous carbon coating layer on the surface. After cooling, an integrated structure of the current collector and silicon-carbon material was obtained.

[0040] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no interface transition layer slurry was applied to the surface of the electrolytic copper foil corona etched by corona treatment.

[0041] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no catalytic layer slurry was coated on the surface of the electrolytic copper foil corona etched by electrolysis.

[0042] Example 2 A 6μm thick electrolytic copper foil was selected, and one surface was etched using a 300V corona discharge to obtain a copper foil substrate with a surface roughness Rz = 2.2μm. Three layers of carbon paste were then sequentially coated onto the corona-etched surface of the electrolytic copper foil. Interface transition layer slurry: 10% cyano-modified polyacrylate, 80% conductive carbon black, and 10% silane coupling agent. After coating, dry at 100℃ for 3 minutes.

[0043] Buffer functional layer slurry: 70% porous carbon microspheres (pore size 20nm), 25% carbon nanotubes, 5% polyacrylic acid. After coating, dry at 100℃ for 4 minutes.

[0044] The catalytic layer slurry consists of 90% nitrogen-doped graphene, 5% nano-copper catalyst (8 nm particle size), and 5% composite binder (SBR and CMC in a 1:1 mass ratio). After coating, it is dried at 100°C for 5 minutes.

[0045] After all coating is completed, the copper foil is heat-treated at 200℃ in a nitrogen atmosphere for 2 hours to obtain carbon-coated copper foil.

[0046] Carbon-coated copper foil was fed into a continuous CVD furnace and heated to 500°C under argon protection. Silane gas was then introduced, and deposition was carried out for 40 minutes, resulting in the in-situ growth of silicon nanoparticles embedded in the pores of the buffer functional layer. Subsequently, the gas flow was switched to methane, with argon as the carrier gas, forming a 5 nm thick amorphous carbon coating layer on the surface. After cooling, an integrated structure of the current collector and silicon-carbon material was obtained.

[0047] Example 3 A 4.5 μm thick electrolytic copper foil was selected, and one surface was etched using a 300V corona discharge to obtain a copper foil substrate with a surface roughness Rz = 2.1 μm. Three layers of carbon paste were then sequentially coated onto the corona-etched surface of the electrolytic copper foil. Interface transition layer slurry: 20% cyano-modified polyacrylate, 70% conductive carbon black, and 10% silane coupling agent. After coating, dry at 150℃ for 3 minutes.

[0048] Buffer functional layer slurry: 60% porous carbon microspheres (50nm pore size), 15% carbon nanotubes, and 20% polyacrylic acid. After coating, dry at 150℃ for 3 minutes.

[0049] The catalytic layer slurry consisted of 82% nitrogen-doped graphene, 15% nano-copper catalyst (8 nm particle size), and 3% PVDF. After coating, it was dried at 150°C for 3 min.

[0050] After all coatings are completed, the copper foil is heat-treated at 250°C in a nitrogen atmosphere for 1 hour to obtain carbon-coated copper foil.

[0051] Carbon-coated copper foil was fed into a continuous CVD furnace and heated to 400°C under argon protection. Silane gas was then introduced, and deposition was carried out for 90 minutes, resulting in the in-situ growth of silicon nanoparticles embedded in the pores of the buffer functional layer. Subsequently, the gas flow was switched to acetylene gas, with argon as the carrier gas, forming a 12 nm thick amorphous carbon coating layer on the surface. After cooling, an integrated structure of the current collector and silicon-carbon material was obtained.

[0052] Example 4 A 9μm thick electrolytic copper foil was selected, and two surfaces were etched using a 600V corona discharge to obtain a copper foil substrate with a surface roughness Rz = 2.6μm. Three layers of carbon paste were then sequentially coated onto the corona-etched surface of the electrolytic copper foil. Interface transition layer slurry: 10% cyano-modified polyacrylate, 85% conductive carbon black, and 5% silane coupling agent. After coating, dry at 80℃ for 5 minutes.

[0053] Buffer functional layer slurry: 70% porous carbon microspheres (pore size 40nm), 15% carbon nanotubes, 15% polyacrylic acid. After coating, dry at 80℃ for 5 minutes.

[0054] The catalytic layer slurry consists of 80% nitrogen-doped graphene, 10% nano-copper catalyst (8 nm particle size), and 10% composite binder (SBR and CMC in a 3:1 mass ratio). After coating, it is dried at 80°C for 5 min.

[0055] After all coatings are completed, the copper foil is heat-treated at 180°C in a nitrogen atmosphere for 1.5 h to obtain carbon-coated copper foil.

[0056] Carbon-coated copper foil was fed into a continuous CVD furnace and heated to 600°C under argon protection. Silane gas was then introduced, and deposition was carried out for 120 minutes, resulting in the in-situ growth of silicon nanoparticles embedded in the pores of the buffer functional layer. Subsequently, the gas flow was switched to ethylene gas, with argon as the carrier gas, forming a 20 nm thick amorphous carbon coating layer on the surface. After cooling, an integrated structure of the current collector and silicon-carbon material was obtained.

[0057] The surface roughness mentioned in the above embodiments and comparative examples was tested using an image-guided microscope, referring to the GB / T 3505-2009 standard. The sample was cut to 100 mm × 100 mm, and 5 test points were selected. Each point was measured 3 times. Test parameters: probe pressure 2mg, scan speed 0.5mm / s, scan stroke 5mm; Record the height Rz values ​​of ten micro-irregularities, and take the average of five points as the final result.

[0058] The peel strength of the carbon-coated copper foil obtained in the above examples and comparative examples was tested using the 180° peel test method, referring to the GB / T 41511-2022 standard. Sampling: Cut slits of carbon foil or electrode sheets along the direction of mechanical movement (MD) to a size of 15 mm (length) × 200 mm (width).

[0059] Fixing: Apply double-sided tape to the material surface, and the other side to the stainless steel plate. Then fix the entire assembly to the two clamps of the universal tensile testing machine.

[0060] Test: Perform a 180° peel test at a peel speed of 50 mm / min, and operate according to the tensile testing machine operating procedures.

[0061] Results: Record the average peel force required for the peel strength test. Peel strength = average peel force ÷ sample width. Perform multiple parallel tests and take the arithmetic mean.

[0062] The test results are shown in Table 1.

[0063] Table 1 The integrated structure of current collector and silicon-carbon material obtained in the above embodiments and comparative examples is further assembled into a battery in the following manner.

[0064] Assemble CR2032 button cells in an argon-protected glove box (water and oxygen content <0.1ppm).

[0065] The integrated structure is cut into φ12mm round pieces as the working electrode, lithium metal sheets as the counter electrode, and PE diaphragm; Electrolyte: 1 mol / L LiPF6 dissolved in EC / DMC / EMC (volume ratio 1:1:1), with 5% fluoroethylene carbonate added; Assembly sequence: positive electrode shell → working electrode → electrolyte (100μL) → separator → electrolyte (50μL) → lithium sheet → nickel foam → negative electrode shell. After pressing and sealing, let stand for 12 hours before testing.

[0066] Testing the electrochemical performance of the battery: Initial Coulombic Efficiency / Discharge Capacity: Under 25℃ conditions, using the Blue Battery testing system, charge and discharge at a constant current of 0.1C with a voltage range of 0.01V~2.0V, and record the initial charge and discharge capacity. Initial Coulombic Efficiency = Initial Discharge Capacity ÷ Initial Charge Capacity × 100%; Cyclic performance: After 1500 cycles of constant current charge and discharge at 1C, the capacity retention rate is calculated as follows: Capacity at the 1500th discharge cycle ÷ Capacity at the first 1C discharge cycle × 100%; Rate performance: Discharged sequentially at currents of 0.2C, 0.5C, 1C, 2C, 5C, and 10C. Capacity retention rate at 10C rate = 10C discharge capacity ÷ 0.2C discharge capacity × 100%.

[0067] Volume expansion rate test: The electrode thickness change during the cycling process was monitored using an in-situ electrode expansion tester, referring to standard GB / T 44027.2-2024 Carbon materials - Determination of expansion rate - Part 2.

[0068] The test results are shown in Table 2.

[0069] Table 2 The battery assembled with the integrated structure obtained in Example 1 exhibits superior initial coulombic efficiency, initial discharge capacity, capacity retention after 1500 cycles at 1C, capacity retention at 10C rate, and volume expansion rate after 1500 cycles at 1C compared to the battery assembled with the integrated structure obtained in Comparative Example 1. The volume expansion rate of the battery assembled with the integrated structure in Comparative Example 1 after 1500 cycles at 1C is close to 50%, which is attributed to the lack of an interface transition layer, insufficient adhesion between the carbon layer and the copper foil substrate, carbon layer shedding during cycling, and silicon particle pulverization.

[0070] The battery assembled with the integrated structure obtained in Example 1 exhibits superior initial coulombic efficiency, initial discharge capacity, capacity retention after 1500 cycles at 1C, capacity retention after 10C rate, and volume expansion rate after 1500 cycles at 1C compared to the battery assembled with the integrated structure obtained in Comparative Example 2. In Comparative Example 2, the copper foil substrate lacked a deposited catalytic layer during the fabrication of the integrated structure. Under deposition conditions of 400°C, silane could slowly decompose to generate silicon atoms, but the reaction rate was low, making effective nucleation and growth difficult. Ultimately, only a sparse and large-particle silicon deposition layer could be formed, resulting in uneven particle distribution and insufficient pore filling. Furthermore, the lack of catalytically guided silicon deposition easily leads to the formation of free "floating silicon" on the coating surface, which has weak adhesion to the carbon matrix and rapidly pulverizes and detaches during cycling, causing electrode structure failure and deterioration in battery capacity, cycle performance, and rate performance.

[0071] The batteries assembled from the integrated structures obtained in Examples 2-4 exhibit excellent performance in terms of initial coulombic efficiency, initial discharge capacity, capacity retention after 1500 cycles at 1C, capacity retention at 10C rate, and volume expansion rate after 1500 cycles at 1C. This further demonstrates that constructing a composite structure on the copper foil surface, combining interfacial bonding, expansion buffering, and catalytic deposition functions, followed by in-situ growth of silicon nanoparticles in the carbon layer pores using CVD technology and surface coating with a carbon layer, achieves the integrated fabrication of the current collector and silicon-carbon material, thereby improving the battery's electrical performance.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an integrated structure of current collector and silicon-carbon material, characterized in that, The copper foil substrate is subjected to corona etching, gradient carbon layer coating, silicon deposition, and carbon coating sequentially on at least one surface, including the following steps: Step S1, copper foil pretreatment: Provide a copper foil substrate and perform corona etching on at least one surface of the copper foil substrate; Step S2, gradient carbon layer coating: an interface transition layer slurry, a buffer functional layer slurry, and a deposition catalytic layer slurry are sequentially coated on the first surface of the copper foil substrate after corona etching to obtain a carbon-coated copper foil. The components of the interface transition layer slurry, by mass percentage, include: 10-20% cyano-modified polyacrylate, 70-85% conductive carbon black, and 5-10% silane coupling agent. The components of the buffer functional layer slurry, by mass percentage, include: 60-75% porous carbon microspheres, 15-25% carbon nanotubes, and 5-20% polyacrylic acid; The components of the deposited catalyst layer slurry, by mass percentage, include: 80-90% nitrogen-doped graphene, 5-15% nano-copper catalyst, and 3-10% binder; Step S3, Silicon deposition: Silicon nanoparticles are deposited in the coating layer of the carbon-coated copper foil using a chemical vapor deposition process. Step S4, Surface carbon coating: A carbon coating layer is formed on the surface of the coating layer on which silicon nanoparticles have been deposited on the carbon-coated copper foil.

2. The preparation method according to claim 1, characterized in that, Includes at least one of the following technical features (1) to (4): (1) The copper foil substrate is an electrolytic copper foil with a thickness of 4.5~9.0μm; (2) After corona etching, the surface roughness Rz of the copper foil substrate reaches more than 2.0 μm; (3) The pore size of the porous carbon microspheres is 20~50 nm; (4) The particle size of the nano-copper catalyst is 5~10nm.

3. The preparation method according to claim 1, characterized in that, The binder in the components of the deposited catalyst layer slurry is a composite binder composed of polyvinylidene fluoride or styrene-butadiene rubber and sodium carboxymethyl cellulose.

4. The preparation method according to claim 3, characterized in that, The mass ratio of styrene-butadiene rubber to sodium carboxymethyl cellulose in the composite adhesive is (1~3):

1.

5. The preparation method according to claim 1 or 2, characterized in that, In step S2, a coating machine is used to sequentially coat at least one surface of the copper foil substrate that has been corona etched with an interface transition layer slurry, a buffer functional layer slurry, and a deposition catalyst layer slurry. After each type of slurry is applied, the copper foil substrate is dried at 80-150℃ for 3-5 minutes. After coating, heat cure in a nitrogen atmosphere at 150-250℃ for 1-4 hours.

6. The preparation method according to claim 1 or 2, characterized in that, In step S3, the temperature of the chemical vapor deposition process is 400~600℃, the silicon source is silane, and the deposition time is 30~120min.

7. The preparation method according to claim 1 or 2, characterized in that, In step S4, a carbon coating layer is formed through the following process: a carbon source gas is introduced using a chemical vapor deposition process to deposit the carbon coating layer.

8. The preparation method according to claim 1 or 7, characterized in that, The thickness of the carbon coating layer is 5-20 nm.

9. The preparation method according to claim 7, characterized in that, The carbon source gas includes one or more of methane, ethane, ethylene, propylene, and propane.

10. An integrated structure of current collector and silicon-carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

11. A lithium-ion battery, characterized in that, The integrated structure of current collector and silicon-carbon material as described in claim 10.

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