Carbon-based current collector for sodium metal negative electrode as well as preparation method and application of carbon-based current collector

Abstract

The invention discloses a carbon-based current collector for a sodium metal negative electrode and a preparation method and application of the carbon-based current collector. A mesoporous carbon plate with a two-dimensional plane structure and rich mesoporous channels is prepared and coated on a current collector base material to serve as the sodium metal negative electrode. The rich open mesopores of the mesoporous carbon plate prepared by the invention provide a large number of short paths for sodium ion transmission, and the ion migration rate is obviously improved; uniform electric field distribution is ensured by a regular plane structure, and the local current density is effectively reduced; the structure synergistically promotes rapid surface diffusion and uniform nucleation of sodium ions, and dendritic crystal growth is significantly inhibited. And meanwhile, the excellent mechanical strength of the carbon plate provides stable framework support for the electrode, and the volume change in the circulation process is effectively buffered.

Description

Technical Field

[0001] This invention relates to the field of sodium battery technology, and in particular to a carbon-based current collector for sodium metal anodes, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries boast high energy density and energy conversion efficiency, but their energy density remains difficult to improve due to inherent limitations in their charge-discharge mechanisms. With the development of electric vehicles and various electronic products, current energy and power densities are insufficient to meet all requirements, making the research and development of new high-energy-density rechargeable batteries an urgent priority.

[0003] Sodium belongs to the same group as lithium in the periodic table, so they share similar physicochemical properties. Furthermore, sodium resources have unique advantages over lithium, including abundant reserves (2.74%) and low development costs. Moreover, sodium metal batteries theoretically have about three times the capacity of lithium-ion batteries and exhibit low redox potential and high energy density. Based on these advantages, rechargeable sodium metal batteries have attracted considerable attention for the sustainable development of next-generation high-energy-density batteries.

[0004] However, safety is paramount in rechargeable batteries, and the safety hazards of sodium metal anodes are evident. During continuous deposition / stripping, dendrites can form on the sodium anode due to uneven deposition. The uncontrolled growth of these dendrites can potentially puncture the separator, causing a short circuit between the positive and negative electrodes, leading to battery overheating and even fire. Furthermore, sodium dendrites isolated from the bulk sodium metal anode become "dead sodium" due to loss of electron contact, resulting in battery capacity loss and shortened cycle life. Additionally, the presence of side reactions causes continuous SEI (electrolyte interphase) breakage and regeneration, fundamentally leading to electrolyte consumption and reduced coulombic efficiency. Despite decades of significant efforts to improve the electrochemical performance of lithium metal anodes, research on sodium metal anodes remains in its early stages. Developing highly reversible sodium metal anodes is one of the major challenges in developing next-generation rechargeable sodium metal batteries.

[0005] Numerous research efforts have addressed the challenges of sodium metal anodes. Among these approaches, constructing reliable host structures is currently a primary focus, as 3D conductive frameworks can significantly reduce current density and promote the formation of Na+ anodes. + Uniform deposition of carbon nanofibers, carbon foams, and aerogels, which are lightweight and have good conductivity, has made them excellent choices for negative electrode current collectors. However, regardless of whether it is carbon nanotubes or nanofibers, there are always many intersecting gaps in their intersecting regions that cannot cover the entire current collector surface, resulting in less than ideal deposition performance under high current. Summary of the Invention

[0006] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a carbon-based current collector for sodium metal anodes, its preparation method and application.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a carbon-based current collector for sodium metal anode, comprising a current collector substrate and a functional coating coated on the current collector substrate, wherein the functional coating comprises a mesoporous carbon sheet, a conductive material, and a binder, wherein the mesoporous carbon sheet is a two-dimensional planar structure and mesoporous channels are distributed on the mesoporous carbon sheet.

[0008] A method for preparing a carbon-based current collector for sodium metal anodes, comprising the following steps: Step 1: Add the aqueous solution of graphene oxide and polyvinylpyrrolidone to a mixture of ethanol and deionized water to obtain a mixed solution. Add ammonia and tetraethoxysilane to the mixed solution and stir to react to obtain nanosheets. Step 2: Disperse the nanosheets in a mixture of deionized water and ethanol, add resorcinol, formaldehyde, ethylenediamine and tetraethoxysilane, stir the reaction and centrifuge to separate the product, carbonize the obtained solid product at high temperature and treat it with hydrofluoric acid to obtain mesoporous carbon sheets. Step 3: Mix the mesoporous carbon sheet and binder obtained in step 2 in a certain proportion and put them into the ball mill of a planetary ball mill to obtain a slurry. Coat the slurry evenly on the surface of the current collector substrate and dry it to obtain a carbon-based current collector.

[0009] In the above-mentioned method for preparing a carbon-based current collector for sodium metal anodes, the stirring reaction temperature in step 1 is 30℃-40℃.

[0010] In the above-mentioned method for preparing a carbon-based current collector for sodium metal anodes, the stirring reaction temperature in step 2 is 30℃-50℃.

[0011] In the above-mentioned method for preparing a carbon-based current collector for sodium metal anodes, the mass ratio of mesoporous carbon sheet to binder in step 3 is 9:1.

[0012] The preparation method of the carbon-based current collector for sodium metal anode described above, wherein the slurry in step 3 further includes a conductive material.

[0013] In the above-mentioned method for preparing a carbon-based current collector for sodium metal anodes, the mass ratio of mesoporous carbon sheet, conductive material, and binder in step 3 is 8:1:1.

[0014] An application of a carbon-based current collector for a sodium metal anode, wherein the carbon-based current collector described above or prepared using the preparation method described above is used as the sodium metal anode in a sodium metal battery.

[0015] The beneficial effects of this invention are that it uses a carbon sheet with a two-dimensional planar structure and abundant mesoporous channels as a sodium metal carrier. On the one hand, its abundant open mesopores provide numerous short paths for sodium ion transport, significantly improving the ion migration rate. On the other hand, the regular planar structure ensures a uniform electric field distribution, effectively reducing local current density. This structure synergistically promotes rapid surface diffusion and uniform nucleation of sodium ions, significantly suppressing dendrite growth. Simultaneously, the excellent mechanical strength of the carbon sheet provides stable skeletal support for the electrode, effectively buffering volume changes during cycling. Attached Figure Description

[0016] Figure 1 This is a SEM image of the mesoporous carbon sheet of the present invention; Figure 2 This is a SEM image of a single mesoporous carbon sheet of the present invention; Figure 3 This is a top view of the electrode sheet made of the mesoporous carbon sheet of the present invention; Figure 4 This is a cross-sectional view of the electrode sheet made of the mesoporous carbon sheet of the present invention; Figure 5 This invention is based on a current density of 5 mA / cm². 2 Cycle performance of Na|| carbon sheet half-cell; Figure 6 This invention is based on a current density of 10 mA / cm². 2 Na@carbon sheet || Na@carbon sheet symmetric cell performance; Figure 7 This invention is based on a current density of 30 mA / cm². 2 Performance of Na@carbon sheet || Na@carbon sheet symmetrical battery. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This embodiment discloses a carbon-based current collector, comprising a current collector substrate and a functional coating applied to the current collector substrate. The functional coating includes a mesoporous carbon sheet, a conductive material, and a binder. The mesoporous carbon sheet has a two-dimensional planar structure with mesoporous channels distributed on it. In this embodiment, the current collector substrate is a copper foil, but the substrate can also be an aluminum foil, a carbon-coated aluminum foil, or a carbon-coated copper foil. The morphology of the mesoporous carbon sheet is as follows: Figure 1-2As shown, the mesoporous carbon sheet exhibits a paper-like structure with dimensions ranging from a few micrometers to tens of micrometers. A carbon sheet with a two-dimensional planar structure and abundant mesoporous channels is used as the sodium metal carrier. On one hand, its abundant open mesopores provide numerous short paths for sodium ion transport, significantly improving the ion migration rate. On the other hand, the regular planar structure ensures a uniform electric field distribution, effectively reducing local current density. This structure synergistically promotes rapid surface diffusion and uniform nucleation of sodium ions, significantly suppressing dendrite growth. Simultaneously, the excellent mechanical strength of the carbon sheet provides stable skeletal support for the electrode, effectively buffering volume changes during cycling. Ultimately, the sodium metal anode based on this mesoporous carbon sheet current collector exhibits excellent cycling stability, with the half-cell reaching 5 mA / cm². 2 It can stably cycle for more than 1300 cycles at a current density, and the symmetric cell can cycle at 30 mA / cm². 2 Stable cycling for more than 150 hours at ultra-high current density (e.g.) Figure 5 (As shown).

[0019] This embodiment also discloses a method for preparing a carbon-based current collector, which specifically includes the following steps: Step 1, Preparation of mesoporous carbon sheets: 10 mL of graphene oxide (GO) aqueous solution (6 mg / L) and 0.6 g of polyvinylpyrrolidone (PVP) were added to a mixture of 230 mL of ethanol and 20 mL of deionized water. Then, 12 mL of ammonia and 6 mL of tetraethoxysilane (TEOS) were added to the mixture. After stirring at 30 °C for 6 hours, GO@SiO2 nanosheets were obtained and dispersed in 60 mL of deionized water. 12 mL of the GO@SiO2 nanosheet aqueous dispersion was added to a mixture of 60 mL of ethanol and 120 mL of deionized water and stirred continuously. 0.4 g of resorcinol, 0.6 mL of formaldehyde, 0.6 mL of ethylenediamine, and 1.2 mL of TEOS were added to the above GO@SiO2 dispersion. After stirring overnight at 40 °C, the product was centrifuged. The obtained solid product was carbonized at 800 °C for 4 hours under a N2 atmosphere. Mesoporous carbon nanosheets were obtained after treatment with a 10% HF aqueous solution.

[0020] Step 2, Electrode preparation: Commercial copper foil is cut into circular pieces with a diameter of 13 / 15 mm using an air press. The pieces are soaked in ethanol and acetone and ultrasonically treated to remove surface impurities and dust. The ethanol and acetone solutions are then discarded, and the pieces are placed in an oven for vacuum drying. Mesoporous carbon sheet material, conductive carbon black (super P), and binder CMC are mixed together in a mass ratio of 8:1:1. Depending on the specific situation, a few drops of ultrapure water and ethanol are added. The mixed slurry is ball-milled in a planetary ball mill for 6 hours. The slurry is then evenly coated onto the surface of the copper foil and dried overnight in a vacuum drying oven at 60 °C.

[0021] In step 2, conductive carbon black can be omitted when preparing the slurry. That is, only mesoporous carbon sheet material and binder are added to the slurry, and the mass ratio of mesoporous carbon sheet material to binder is 9:1.

[0022] After adding conductive carbon black and binder to a slurry to form an electrode, the SEM top view of the electrode is shown below. Figure 3 As shown in the figure, mesoporous carbon sheets are evenly spread on the copper foil. Figure 4 The image shows a cross-sectional SEM image of the mesoporous carbon sheet electrode. As can be seen from the image, the mesoporous carbon sheet is spread layer by layer on the copper foil. The mesoporous channels enable the rapid transport of sodium ions, which allows for long-term stable cycling under high current.

[0023] The aforementioned carbon-based current collector was used as the sodium metal anode in a sodium metal battery to assemble a coin cell. The specific process was as follows: With the water and oxygen content in the glove box below 1 ppm, the dried stainless steel electrode shell, electrode sheets, and separator were placed inside the glove box. The positive electrode shell, electrode sheets, and separator were arranged in that order, followed by 35 μL of electrolyte (1M NaPF6, diethylene glycol dimethyl ether). The negative electrode shell was then placed on top and compacted using a tablet press. Performance tests were performed on the battery, and the results are as follows: Figure 5-7 As shown, at a current density of 5 mA / cm² 2 The half-cell cycle performance of the Na+ and mesoporous carbon sheet composition exceeded 1300 hours, with the coulombic efficiency consistently maintained above 99%. This was achieved at a current density of 10 mA / cm². 2 The symmetric battery composed of a carbon sheet with sodium deposited on it exhibits stable cycling performance, exceeding 300 hours at a current density of 30 mA / cm². 2 The symmetrical battery composed of a carbon sheet with sodium deposited on it exhibits stable cycling performance exceeding 150 hours. This demonstrates that the carbon-based current collector in this embodiment significantly improves the cycling performance of the sodium metal anode.

[0024] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and spirit, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A carbon-based current collector for sodium metal anodes, comprising a current collector substrate and a functional coating applied to the current collector substrate, characterized in that, The functional coating includes a mesoporous carbon sheet, a conductive material, and a binder. The mesoporous carbon sheet has a two-dimensional planar structure and mesoporous channels are distributed on the mesoporous carbon sheet.

2. A method for preparing a carbon-based current collector for sodium metal anodes, characterized in that, The method for preparing the carbon-based current collector as described in claim 1 comprises the following steps: Step 1: Add the aqueous solution of graphene oxide and polyvinylpyrrolidone to a mixture of ethanol and deionized water to obtain a mixed solution. Add ammonia and tetraethoxysilane to the mixed solution and stir to react to obtain nanosheets. Step 2: Disperse the nanosheets in a mixture of deionized water and ethanol, add resorcinol, formaldehyde, ethylenediamine and tetraethoxysilane, stir the reaction and centrifuge to separate the product, carbonize the obtained solid product at high temperature and treat it with hydrofluoric acid to obtain mesoporous carbon sheets. Step 3: Mix the mesoporous carbon sheet and binder obtained in step 2 in a certain proportion and put them into the ball mill of a planetary ball mill to obtain a slurry. Coat the slurry evenly on the surface of the current collector substrate and dry it to obtain a carbon-based current collector.

3. The method for preparing a carbon-based current collector for a sodium metal anode according to claim 2, characterized in that, The temperature of the stirring reaction in step 1 is 30℃-40℃.

4. The method for preparing a carbon-based current collector for a sodium metal anode according to claim 2, characterized in that, The stirring reaction temperature in step 2 is 30℃-50℃.

5. The method for preparing a carbon-based current collector for a sodium metal anode according to claim 2, characterized in that, In step 3, the mass ratio of the mesoporous carbon sheet to the binder is 9:

1.

6. The method for preparing a carbon-based current collector for a sodium metal anode according to claim 2, characterized in that, The slurry in step 3 also includes a conductive material.

7. The method for preparing a carbon-based current collector for a sodium metal anode according to claim 6, characterized in that, In step 3, the mass ratio of the intermediate porous carbon sheet, conductive material, and binder is 8:1:

1.

8. An application of a carbon-based current collector for sodium metal anodes, characterized in that, The carbon-based current collector according to claim 1 or the carbon-based current collector prepared by any one of the preparation methods according to claims 2-7 is used as the sodium metal anode of a sodium metal battery.

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