A method for preparing and applying an ultrathin copper current collector modified with a carbon nanotube composite coating.

Abstract

This invention belongs to the field of new energy storage materials technology, specifically relating to a method for preparing and applying an ultrathin copper current collector modified with a carbon nanotube composite coating. Addressing the problems of strong lithium repellency, uneven metal deposition, and short cycle life of copper current collectors in electrodeless lithium-ion batteries, this invention constructs a composite functional layer on an ultrathin copper foil, composed of zinc-based oxide rich in oxygen vacancies and carbon nanotubes. In this coating, the zinc-based oxide acts as a highly lithium-affinity site, effectively reducing the metal nucleation overpotential; the carbon nanotube network provides a rapid electron conduction path and alleviates deposition stress. The preparation process is environmentally friendly, employing an aqueous slurry system and a simple heat treatment process. This modified current collector, used in electrodeless lithium-ion batteries, can guide uniform and dense metal deposition, significantly improving the battery's coulombic efficiency and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of new energy storage materials technology, and in particular to a method for preparing and applying an ultrathin copper current collector modified with a carbon nanotube composite coating. Background Technology

[0002] Electrodeless lithium batteries achieve energy storage by directly depositing / dissolving lithium metal on copper current collectors, eliminating the need for traditional graphite or silicon-based anode materials, thus potentially pushing battery energy density to its limits. However, this technology faces significant challenges: on the one hand, the surface of commercial copper foil is inherently lithium-repellent, resulting in a high nucleation barrier for lithium metal and a tendency to form dendritic or moss-like uneven deposits; on the other hand, during repeated deposition / stripping processes, the large volume changes can easily cause the deposited layer to separate from the current collector, forming "dead lithium" that continuously consumes electrolyte, leading to rapid capacity decay and shortened cycle life.

[0003] Currently, research on the modification of copper current collectors mainly focuses on the following aspects: First, constructing a three-dimensional conductive framework (such as porous copper, carbon nanofiber membranes, etc.) on the copper surface to reduce local current density and provide deposition space. However, the preparation process of three-dimensional structures is often complex and increases the proportion of inactive materials. Second, modifying the copper surface with lithiophilic sites, such as introducing metal nanoparticles such as gold, silver, and tin through sputtering, chemical plating, etc. These methods are costly and the bonding force with the copper substrate needs to be strengthened. Third, using organic or metal-organic framework coatings to regulate interfacial ion flow. However, their electronic conductivity is usually low, which may increase interfacial impedance.

[0004] In particular, as batteries develop towards higher energy densities, current collectors are becoming increasingly thinner (e.g., ≤6µm). Ultra-thin copper foils have lower mechanical strength and are more prone to wrinkling or even breakage under the immense stress of lithium deposition, while also placing higher demands on the adhesion and functional integrity of the surface modification layer. Therefore, developing an interface layer that can firmly bond with ultra-thin copper foil, possessing excellent lithium affinity, high ionic / electron hybrid conductivity, and good mechanical buffering properties is crucial for promoting the practical application of electrodeless lithium batteries. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a method for preparing an ultrathin copper current collector modified with a carbon nanotube composite coating that is simple to prepare, low in cost, and has significant effects, as well as the modified current collector obtained by this method and its application in a cathodeless lithium battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing an ultrathin copper current collector modified with a carbon nanotube composite coating and applying it to a negative electrode-free lithium battery.

[0007] The method is achieved by constructing a composite functional layer composed of zinc-based oxide and carbon nanotubes.

[0008] The carbon nanotubes are acid-treated before use to increase surface functional groups, improve their dispersibility in aqueous systems, and form a three-dimensional conductive network that provides a fast electron transport path.

[0009] A water-based binder (polyacrylic acid or sodium carboxymethyl cellulose) is selected to ensure good compatibility with ether-based electrolytes commonly used in negative electrodeless batteries. This composite coating is achieved through slurry coating and optimized heat treatment processes, resulting in a strong bond with the copper substrate and ultimately an ultrathin copper current collector modified with a carbon nanotube composite coating.

[0010] In a preferred embodiment of the present invention, the ultrathin copper current collector uses copper foil with a thickness of 3~10µm.

[0011] In a preferred embodiment of the present invention, the zinc-based oxide is one of zinc oxide, zinc monoxide, and aluminum-doped zinc oxide, with zinc oxide being preferred.

[0012] In a preferred embodiment of the present invention, the final composite coating has a thickness of 5 to 20 µm and has a suitable porous structure to balance ion transport and deposition space.

[0013] In a preferred embodiment of the present invention, the heat treatment is carried out under argon protection at a temperature of 250-300°C for 2-3 hours. Under these conditions, the binder can form a stable cross-linked network without complete decomposition, while optimizing the oxygen vacancy concentration of the zinc-based oxide.

[0014] The second objective of this invention is to provide an ultrathin copper current collector modified with a carbon nanotube composite coating prepared by the above-mentioned method.

[0015] In a preferred embodiment of the present invention, the selected cathode material is at least one of NCM811, Ni85, and NCM622, with Ni85 being the preferred cathode material.

[0016] The third objective of this invention is to provide a high-energy-density, electrodeless lithium battery that uses an ultrathin copper current collector modified with the aforementioned carbon nanotube composite coating as the current collector on the negative electrode side, in conjunction with an ether-based electrolyte.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention creatively combines zinc-based oxides rich in oxygen vacancies with functionalized carbon nanotubes, achieving synergistic functional enhancement. Zinc-based oxides, as highly lithiophilic sites, significantly reduce the nucleation overpotential of metallic lithium (down to below 50 mV), guiding uniform nucleation; while the three-dimensional conductive network constructed by carbon nanotubes not only provides a rapid electron transport path, but its mechanical strength and flexibility also effectively buffer the volumetric stress during lithium deposition / stripping, suppressing damage to the electrode structure.

[0018] This invention innovatively introduces oxygen vacancies, significantly improving the ionic conductivity of the composite coating and optimizing interfacial ion transport kinetics. Combined with the high electronic conductivity and uniform current distribution brought by the carbon nanotube network, it ensures that lithium metal can be uniformly deposited in a dense, dendrite-free morphology, fundamentally solving the problems of low coulombic efficiency and short cycle life caused by dendrite growth and uneven deposition.

[0019] This invention employs an aqueous slurry system (using deionized water as a solvent and PAA or CMC-Na as a binder), making the entire preparation process environmentally friendly and easy to scale up for production. The selected binder exhibits excellent compatibility with ether-based electrolytes commonly used in negative electrode-free lithium batteries, avoiding the swelling problem of traditional PVDF binders in ether-based electrolytes and ensuring the stability of the battery interface during long-term cycling.

[0020] Applying the modified current collector prepared in this invention to electrodeless lithium batteries achieves an average coulombic efficiency exceeding 70% and stable cycling for over 100 cycles, significantly outperforming unmodified pure copper current collectors. This preparation method is flexible, allowing for adaptation to different performance requirements by adjusting parameters such as the ratio of zinc-based oxide to CNTs and coating thickness. It provides a reliable and efficient current collector solution for the development of high-energy-density, long-life electrodeless lithium batteries. Attached Figure Description

[0021] Figure 1 The graphs show the cycle performance of the ultrathin copper current collector modified with carbon nanotube composite coating prepared in Example 1 and Comparative Example 1 of this invention, and the solid-state battery with Ni85 cathode using commercial copper current collector, wherein the activation rate is 0.1C, the cycle rate is 0.5C, and the cathode loading is 7 mg cm-2. (a) Example 1; (b) Comparative Example 1.

[0022] Figure 2 The bar chart shows the capacity retention rate of the corresponding positive electrode cells of Examples 1-2 of the present invention and commercial copper current collectors after 100 cycles.

[0023] Figure 3The graph shows the rate performance of the ultrathin copper current collector modified with carbon nanotube composite coating prepared in Example 1 and Comparative Example 1, and the lithium battery with commercial copper current collector and Ni85 cathode. The cycle rates are 0.1C, 0.3C, 0.5C, 0.6C, 0.8C, 0.1C, and 0.3C, respectively, increasing and then decreasing. The cathode loading is 7 mg cm-2.

[0024] Figure 4 The images show scanning electron microscope (SEM) images of the copper current collectors prepared in Example 1 and Comparative Example 1 of the present invention. (a) Comparative Example 1; (b) Example 1.

[0025] Figure 5 The images show cross-sectional scanning electron microscope (SEM) images of the copper current collector-assembled lithium copper half-cells prepared in Example 1 and Comparative Example 1 of this invention after being discharged at a current density of 0.1 mA cm⁻² to deposit lithium with a surface capacity of 5 mAh cm⁻². (a) Comparative Example 1; (b) Example 1. Detailed Implementation

[0026] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0028] Compared with existing technologies, the high lithium-phobicity of copper current collectors in traditional electrodeless lithium batteries leads to uneven lithium metal deposition and dendrite growth, resulting in low coulombic efficiency and a sharp decline in cycle life. The ultrathin copper current collector modified with carbon nanotube composite coating prepared in this invention provides a stable and reliable deposition interface for electrodeless lithium batteries. By synergistically combining lithium-philic sites and a three-dimensional conductive network, it significantly improves the deposition uniformity and long-term cycle stability of lithium metal batteries.

[0029] Example 1 A method for preparing an ultrathin copper current collector modified with a carbon nanotube composite coating includes the following steps: S1. Cut the 6µm copper foil into 10×10 cm² sheets, and ultrasonically wash them for 5 minutes each with 0.1M dilute hydrochloric acid, acetone and ethanol in sequence to remove surface oxides and contaminants. Dry them with nitrogen gas for later use.

[0030] S2. Weigh 0.5g of commercial aluminum-doped zinc oxide (Al doping amount 2 at.%) nanoparticles, 0.5g of acid-treated multi-walled carbon nanotubes (outer diameter 10-20nm, length 10-20µm), and 0.1g of polyacrylic acid binder. Add 9ml of deionized water as a solvent and control the solid content to 10%. Stir the mixture in a planetary mixer at 500 rpm for 30 minutes, then at 1000 rpm for 2 hours to obtain a uniform black slurry.

[0031] S3. Use a coating machine to evenly coat the slurry onto the pretreated copper foil surface, controlling the coating thickness to be 10 µm and the coating speed to be 2 mm / s.

[0032] S4. The coated electrode is first vacuum dried at 80℃ for 12 hours, then transferred to a tube furnace and heated to 300℃ at 3℃ / min under argon protection. It is held at this temperature for 2 hours and then naturally cooled to room temperature to obtain an ultrathin copper current collector modified with a composite coating.

[0033] The preparation method of a negative electrode-free lithium battery includes the following steps: S5. Using the ultrathin copper current collector modified with the above carbon nanotube composite coating as the negative electrode current collector, matching it with a Ni 85 positive electrode of 1.4 mAh / cm², and selecting an ether electrolyte, a high energy density negative electrode-free lithium battery with an ultrathin copper current collector modified with carbon nanotube composite coating is obtained.

[0034] Example 2 A method for preparing an ultrathin copper current collector modified with a carbon nanotube composite coating includes the following steps: S1. Cut the 6µm copper foil into 10×10 cm² sheets and process them using the same cleaning and drying procedures as in Example 1.

[0035] S2. Weigh 0.3g of porous zinc oxide microspheres, 0.6g of multi-walled carbon nanotubes, and 0.1g of sodium carboxymethyl cellulose binder, add 8ml of deionized water as a solvent, and control the solid content to 10%. Prepare a uniform slurry using the same stirring procedure as in Example 1.

[0036] S3. Use a coating machine to evenly coat the slurry onto the pretreated copper foil surface, controlling the coating thickness to be 10 µm and the coating speed to be 2 mm / s.

[0037] S4. After the coated electrode is vacuum dried at 80℃ for 12 hours, it is heated to 250℃ at 5℃ / min under nitrogen protection and held for 1 hour to obtain an ultrathin copper current collector modified with composite coating.

[0038] The preparation method of a negative electrode-free lithium battery includes the following steps: S5. Using the ultrathin copper current collector modified with the above carbon nanotube composite coating as the negative electrode current collector, and matching it with a 2.0 mAh / cm² NCM811 positive electrode, and selecting an ether electrolyte, a high energy density negative electrode-free lithium battery with an ultrathin copper current collector modified with carbon nanotube composite coating is obtained.

[0039] Comparative Example 1 A method for preparing a negative electrode-free lithium battery includes the following steps: S1. Cut the 6µm copper foil into 10×10 cm² sheets, and ultrasonically wash them for 5 minutes each with 0.1M dilute hydrochloric acid, acetone and ethanol in sequence to remove surface oxides and contaminants. Dry them with nitrogen gas for later use.

[0040] S2. Commercial copper foil is punched into electrode sheets with a diameter of 16mm. These are then assembled with an NCM811 positive electrode with a surface capacity of 2.0mAh / cm² and an ether electrolyte in an argon-protected glove box to form a CR2032 coin cell. The water content and oxygen content are both below 0.1ppm, resulting in a negative electrode-free lithium battery.

[0041] In Examples 1 and 2 of this invention, ultrathin copper current collectors modified with carbon nanotube composite coatings and electrodeless lithium batteries with excellent electrochemical performance were prepared. The ultrathin copper current collectors of Examples 1 and 2 are compared with the commercially available copper current collector and electrodeless lithium battery of Comparative Example 1. The specific research methods and results are shown below: Using the ultrathin copper current collector of Example 1 and the commercial copper current collector of Comparative Example 1 as negative electrodes, and Ni 85 material with an areal capacity of 1.4 mAh / cm² as positive electrodes, their electrochemical stability was tested according to the following test methods, and the test results are as follows. Figure 1 As shown.

[0042] Test conditions: The battery was activated by charging and discharging at a rate of 0.1 C for the first three cycles, and then charged and discharged at a rate of 0.3 C for the cycle test. The Ni 85 cathode with a capacity of 1.4 mAh / cm² was used, and the charge and discharge voltage range was 3.0~4.3V.

[0043] And by Figure 1 The test results show that after 100 cycles, the battery assembled in Example 1 still has a capacity retention rate of 74.5%, which is a significant improvement compared to 56.5% in Comparative Example 1. This indicates that the metal-organic framework modified ultrathin copper current collector prepared by this process can significantly improve the cycle stability of the negative electrode-free lithium battery.

[0044] Figure 2 This is a bar chart showing the electrochemical stability. (From...) Figure 2It is evident that the addition of carbon nanotube composite coating significantly improves the electrochemical stability of the negative electrode side. For the negative electrode-free lithium battery with Ni85 and NCM811 as the positive electrode, it can still maintain 74.5% and 69.2% capacity retention respectively after 100 cycles at 0.3C, while the negative electrode-free lithium battery with commercial copper current collector as the negative electrode only has a capacity retention of 56.5%.

[0045] Figure 3 In this study, the ultrathin copper current collector of Example 1 and the commercial copper current collector of Comparative Example 1 were used as negative electrodes, and Ni 85 material with an areal capacity of 1.4 mAh / cm² was used as the positive electrode. Their cycle performance was tested according to the following test methods, and the test results are as follows: Figure 3 As shown.

[0046] Test conditions: Charge and discharge tests were conducted at current densities of 0.1C, 0.3C, 0.5C, 0.6C, 0.8C, 0.1C, and 0.3C, increasing first and then decreasing (1C=200mAh / g). The Ni 85 material used had a loading of 7 mg / cm2, and the charge and discharge voltage range was 3.0V~4.3V.

[0047] Depend on Figure 3 The test results show that the lithium battery assembled with the silicon-based negative electrode sheet pretreated in Example 1 has good rate performance and greatly improves the specific capacity of the lithium battery under high rate charge and discharge.

[0048] Figure 4 In this study, taking the ultrathin copper current collector electrode prepared in Example 1 and the commercial copper current collector electrode in Comparative Example 1 as examples, the microstructure of their negative electrode surfaces after lithium deposition was tested, and the test results are as follows: Figure 4 (a) and Figure 4 As shown in (b).

[0049] Depend on Figure 4 As can be seen, (a) shows commercial copper foil, while (b) shows the ultrathin copper current collector modified with carbon nanotube composite coating proposed in this invention, successfully transforming a two-dimensional plane into a multi-level synergistic three-dimensional functional interface. Macroscopically, this structure increases the specific surface area and enhances interfacial bonding through a uniformly rough surface; microscopically, the interwoven network of carbon nanotubes achieves uniform current distribution and provides elastic space to buffer volume changes; at the nanoscale, zinc-based oxide particles rich in oxygen vacancies serve as high-density lithiophilic sites, guiding uniform lithium nucleation. Through the synergistic effect of the conductive network and lithiophilic sites, the lithium nucleation overpotential is fundamentally reduced, dendrite growth is suppressed, and volume changes during the deposition process are accommodated. Ultimately, this significantly improves the metal deposition uniformity, coulombic efficiency, and cycle stability of electrodeless lithium batteries, solving the core pain points of commercial copper foil in this application.

[0050] Figure 5 Using the ultrathin copper current collector of Example 1 and the commercial copper current collector of Comparative Example 1 as negative electrodes, lithium-copper half-cells were assembled. Lithium with an areal capacity of 5 mAh cm⁻² was deposited at a current density of 0.1 mA cm⁻², and the cross-sections were photographed using scanning electron microscopy. As shown in Figures (a) and (b), the lithium deposited on the surface of the commercial copper current collector exhibits porosity and obvious lithium dendrite protrusions, while the lithium deposited on the surface of the ultrathin copper current collector modified with the carbon nanotube composite coating of Example 1 is dense and has a flat cross-section, proving that the composite coating can significantly improve the lithiophilicity of the copper current collector and guide uniform lithium deposition.

[0051] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0052] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an ultrathin copper current collector modified with a carbon nanotube composite coating, characterized in that, Includes the following steps: A coating slurry comprising zinc-based oxide, carbon nanotubes, a binder, and a solvent is prepared, wherein the binder is polyacrylic acid or sodium carboxymethyl cellulose, and the solvent is deionized water; The coating slurry is uniformly coated onto the surface of the ultrathin copper foil current collector; The coated copper foil is subjected to step drying and heat treatment: first, it is vacuum dried at 60~80℃ for 6~12 hours, and then heat treated at 200~350℃ for 1~3 hours in an inert atmosphere to form a zinc-based oxide / carbon nanotube composite coating on the surface of the copper foil.

2. The preparation method according to claim 1, characterized in that, The thickness of the copper foil current collector is 3~10 µm.

3. The preparation method according to claim 1, characterized in that, The zinc-based oxide is one of zinc oxide, zinc monoxide, and aluminum-doped zinc oxide.

4. The preparation method according to claim 1, characterized in that, The aluminum doping concentration in the aluminum-doped zinc oxide is 1-5%.

5. The preparation method according to claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes that have been refluxed with concentrated nitric acid for 2 to 4 hours; the mass ratio of zinc-based oxide to carbon nanotubes is 1:2 to 2:

1.

6. The preparation method according to claim 1, characterized in that, The coating slurry has a solid content of 15% to 25%, of which the binder accounts for 8% to 12% of the total solid mass.

7. The preparation method according to claim 1, characterized in that, The thickness of the composite coating is 5~20 µm.

8. An ultrathin copper current collector modified with a carbon nanotube composite coating, characterized in that, Prepared by the method described in any one of claims 1-7.

9. A negative electrode-free lithium battery, characterized in that, The ultrathin copper current collector modified with the carbon nanotube composite coating as described in claim 8 is used as the negative electrode current collector.

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