Preparation method of single-atom metal catalytic local graphitized carbon-based nanosheet

Abstract

The application discloses a preparation method and application of single-atom metal catalytic local graphitization carbon-based nanosheet. The preparation method comprises the following steps: (1) material preparation and ultrasonic treatment; (2) heating and washing; (3) post-treatment; and (4) pyrolysis. In the pyrolysis process, the local region of the carbon-based nanosheet is subjected to graphitization transformation by the catalysis of the single-atom metal, so that the conductivity and structural stability of the carbon-based nanosheet are improved, and the carbon-based nanosheet can maintain a high discharge capacity in a low-temperature environment. The technology provides a new idea for optimization of a sodium ion battery negative electrode material and has a wide application prospect in a low-temperature or high-rate charge-discharge scene.

Description

Technical Field

[0001] This invention belongs to the field of energy storage, and specifically relates to a method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets for use in sodium-ion battery anode materials and its application. Background Technology

[0002] With the continuous development of rechargeable battery technology, sodium-ion batteries have become a potential alternative to lithium-ion batteries due to their abundant resources and low cost. Sodium-ion batteries have broad application prospects in large-scale energy storage, electric vehicles, and consumer electronics. However, sodium-ion batteries suffer from relatively low specific capacity, poor cycle stability, and poor rate performance, thus limiting their application in high-performance energy storage systems. Therefore, developing sodium-ion battery anode materials with high specific capacity, good cycle stability, and high rate performance has become one of the current research hotspots.

[0003] In recent years, carbon-based materials have attracted widespread attention as anode materials for sodium-ion batteries. Among them, graphene and carbon nanotubes have been extensively studied due to their good conductivity, structural tunability, and high specific capacity. However, these materials often suffer from poor structural stability and low surface activity, which limits their application in high-efficiency sodium-ion batteries. To address these issues, researchers have proposed optimizing the electrochemical performance of carbon-based materials through doping and modification to improve their application in sodium-ion battery anodes. For example, nitrogen-doped vertical graphene nanosheets with Al2O3 coatings prepared by atomic layer deposition (refer to non-patent literature 1) have achieved good specific capacity and cycle stability. However, this study is based on performance at room temperature (around 25°C), and the prepared batteries may not be able to maintain good and stable electrochemical performance under low temperature or large temperature differences in all-weather conditions.

[0004] Single-atom metal catalysts are considered an effective method to improve the performance of carbon-based materials. Through single-atom metal catalysis, the formation of localized graphitized structures in carbon-based materials can be promoted, thereby improving the materials' conductivity, structural stability, and electrochemical performance. Especially at low temperatures, carbon-based materials with graphitized structures can significantly improve the specific capacity, cycle stability, and rate performance of sodium-ion batteries. However, optimizing single-atom metal-catalyzed carbon-based materials through simple and efficient synthesis methods remains a key technical problem that urgently needs to be solved.

[0005] Existing technology

[0006] Non-patent literature 1: Energy Environ. Mater. 2022, 5, 285-294 Summary of the Invention

[0007] To address the issues of high synthesis cost and insufficient electrochemical performance in existing sodium-ion battery anode materials, this invention discloses a single-atom metal-catalyzed locally graphitized carbon-based nanosheet and its application in sodium-ion battery anodes. This invention employs a low-temperature pyrolysis method catalyzed by a single-atom metal to synthesize carbon-based nanosheets, where the single-atom metal exists in a metal-OP coordination form, effectively promoting the formation of locally graphitized structures on the carbon-based nanosheets. Specifically, utilizing the catalytic effect of the single-atom metal, localized regions of the carbon-based nanosheets undergo graphitization during pyrolysis, thereby enhancing their conductivity and structural stability. The nanosheets exhibit a specific capacity exceeding 150 mAh / g in sodium-ion battery anodes, demonstrating good cycle stability and rate performance, especially maintaining a high discharge capacity even at low temperatures. Furthermore, the application of the carbon-based nanosheets in sodium-ion battery anode materials can effectively reduce the battery's internal resistance under high-rate charge-discharge conditions, improving its rate performance, while maintaining low capacity decay during long-term cycling. The local catalytic effect of single-atom metals not only improves the electrochemical performance of carbon-based materials, but also enhances their adaptability in low-temperature and high-rate applications, showing broad application prospects.

[0008] One technical solution of the present invention provides a method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets, the synthesis schematic diagram of which is shown below. Figure 1 As shown, the specific steps are as follows:

[0009] (1) Material preparation and ultrasonic treatment: First, carbon-based nanosheet dispersion and organometallic salt are added to an organic solvent at a certain mass ratio, and then the mixture is ultrasonically treated to ensure full dispersion.

[0010] (2) Heating and washing: The mixture after being fully dispersed in step (1) is rapidly heated to 250-350°C at a heating rate of 5-15°C / min and kept under reflux for 30 min. Then the mixture is allowed to cool naturally to room temperature. Subsequently, it is centrifuged and washed with a mixture of ethyl acetate and methanol to obtain the metal compound / carbon-based nanosheet composite.

[0011] (3) Post-processing: The metal compound / carbon-based nanosheet composite obtained in step (2) was redispersed in methanol and subjected to ultrasonic treatment. Then, the polymer precursor solution was slowly added to methanol and stirred continuously for 6 hours. The precipitate was then filtered and separated and dried under vacuum to obtain metal compound / carbon-based nanosheets@PZS.

[0012] (4) Pyrolysis: The metal compound / carbon-based nanosheets @PZS obtained in step (3) are heated to above 650°C in an argon atmosphere and maintained at this temperature to complete the pyrolysis, thereby obtaining locally graphitized carbon-based nanosheets (metal-HC nanosheets) catalyzed by a single atom metal.

[0013] In step (1) above,

[0014] The organometal salt is selected from acetylacetone metal salts, metal phosphonates, metal imidazole salts, etc., wherein the acetylacetone metal salt is one of iron (III) acetylacetone, copper (II) acetylacetone, platinum (II) acetylacetone, cobalt (II) acetylacetone, or zinc (II) acetylacetone.

[0015] The organic solvent is triethylene glycol.

[0016] Of course, the single-atom metal is selected from, but not limited to, one of platinum, gold, copper, iron, cobalt, nickel, manganese, and zinc.

[0017] The mass ratio of the carbon-based nanosheet dispersion to the organometallic salt is 0.0001 to 0.1.

[0018] The carbon-based nanosheets are one of graphene oxide, reduced graphene oxide, graphene doped with heterogeneous non-metallic elements, graphene co-doped with multiple heterogeneous non-metallic elements, or activated carbon nanosheets.

[0019] The dispersion medium for the dispersion of the carbon-based nanosheets is generally water.

[0020] In step (3), the vacuum drying is performed at 80°C for 8 to 12 hours.

[0021] The precursor solution is a solution containing 800 mg of phosphonyl chloride trimer and 1800 mg of 4,4'-dihydroxydiphenyl sulfone, which is formed by adding 2 mL of triethylamine dropwise with stirring.

[0022] In step (4), the pyrolysis is performed by heating to 650-900°C at a heating rate of 2-10°C / min and maintaining the temperature for 2-15 hours.

[0023] In the above preparation process, organometal salts first participate in the reaction as reactants, and the metal oxide / carbon-based nanosheets @PZS generated by the reaction then participate in the subsequent reaction process as single-atom metal catalyst precursors.

[0024] During pyrolysis, the single-atom metal catalysis in the metal compound / carbon-based nanosheets@PZS can effectively promote the formation of graphitized structures in local areas of carbon-based nanosheets, significantly improving their conductivity and structural stability, thereby enhancing their electrochemical performance in sodium-ion battery anodes.

[0025] This invention also provides an application in which the locally graphitized carbon-based nanosheets prepared above are used in anode materials for sodium-ion batteries. Such anode materials, due to their locally graphitized carbon-based nanosheets, exhibit excellent electrochemical performance, and their application in sodium-ion battery anodes results in the formation of stable anode materials.

[0026] Furthermore, the carbon nanosheets with such locally graphitized structures can achieve a specific capacity of over 150 mAh / g, thus exhibiting excellent cycle stability and rate performance, especially maintaining a high discharge capacity even at low temperatures. In other words, applying such locally graphitized carbon nanosheets to sodium-ion battery anode materials can effectively reduce the battery's internal resistance and improve its rate performance under high-rate charge-discharge conditions, while maintaining low capacity decay during long-term cycling.

[0027] The single-atom metal described in this invention achieves synergistic effects through a dual mechanism (structural coordination and catalytic activity): on the one hand, the metal-OP coordination structure formed in step (3) stabilizes the single-atom dispersion state, thereby preventing metal agglomeration; on the other hand, the high catalytic activity of its single metal atoms significantly reduces the energy required for graphitization of carbon-based materials, thus enabling the low-temperature synthesis of carbon-based nanosheets with high graphitization. Compared to traditional catalysts (such as metal particles or oxides), the atomic-level utilization of single-atom metals can maximize catalytic efficiency, thereby achieving a better conductive network construction under the same pyrolysis conditions (as in the following examples). Furthermore, by differentiating the d-band center positions of different metal catalysts (such as iron, copper, and cobalt), the degree of graphitization and electron transport paths can be controlled (as in the performance of the iron catalyst in the following examples), providing a flexible means for the targeted optimization of material performance.

[0028] The sodium-ion battery anode material of the present invention has the following technical effects:

[0029] (1) This invention improves the conductivity and structural stability of carbon-based nanomaterials through a local graphitization process catalyzed by a single-atom metal, effectively enhancing the specific capacity and cycle stability of sodium-ion batteries; (2) Under high-rate charge and discharge conditions, it reduces the internal resistance of the battery, optimizes the rate performance, and makes the material highly competitive in fast charge and discharge applications; (3) It maintains a high discharge capacity even at low temperatures, significantly improving the low-temperature performance of the battery and adapting to energy storage needs in different environments; (4) In addition, the preparation method of this invention is simple and easy to learn, and single-atom metal-catalyzed locally graphitized carbon-based nanosheets can be obtained through pyrolysis, which is also very economical. Therefore, this preparation method and the products obtained by this method have very broad application prospects. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the synthesis of locally graphitized carbon-based nanosheets catalyzed by metal single atoms.

[0031] Figure 2 The XRD patterns are those of the Fe3O4 / rGO@PZS precursor and the locally graphitized carbon-based nanosheets catalyzed by a single-atom metal in Example 1.

[0032] Figure 3 a) is a high-resolution transmission electron microscope image of locally graphitized carbon-based nanosheets catalyzed by a single atom metal in Example 1. Figure 3 b) is a high-angle annular dark-field scanned transmission image after aberration correction. Figure 3 c) is a transmission electron microscope image of locally graphitized carbon-based nanosheets catalyzed by a single-atom metal and the corresponding energy-dispersive X-ray spectra of carbon, iron, nitrogen, phosphorus and sulfur.

[0033] Figure 4 The high-resolution a)Fe 2p, b)O 1s and c)P 2p X-ray photoelectron spectra of the locally graphitized carbon-based nanosheets catalyzed by single-atom metals in Example 1 are shown.

[0034] Figure 5 a) is the iron K-edge X-ray absorption near-edge structure spectrum of locally graphitized carbon-based nanosheets and related reference materials (Fe foil, FePc, Fe3O4 and FePO4) catalyzed by single-atom metals. Figure 5 b) is the k of locally graphitized carbon-based nanosheets catalyzed by single-atom metals and related reference materials. 3 Weighted Fourier transform fine structure diagram of Fe K-side extended X-ray absorption; Figure 5 c) is the corresponding EXAFS fitting curve for iron-catalyzed locally graphitized carbon-based nanosheets (abbreviated as Fe-HC, the same below). Figure 5 d) is the k-factor of locally graphitized carbon-based nanosheets catalyzed by Fe foil, Fe3O4, and single-atom metals. 3 Wavelet transform of weighted extended X-ray absorption fine structure signal.

[0035] Figure 6 The room temperature rate performance of the single-atom metal-catalyzed locally graphitized carbon-based nanosheets (top) and conventional graphitized carbon-based nanosheets (bottom) of this invention are shown.

[0036] Figure 7 The room temperature cycling performance of the single-atom metal-catalyzed locally graphitized carbon-based nanosheets (top) and conventional graphitized carbon-based nanosheets (bottom) of this invention is shown.

[0037] Figure 8 The present invention describes the room temperature cycling performance of locally graphitized carbon-based nanosheets catalyzed by a single-atom metal at a current density of 0.5 A / g.

[0038] Figure 9 The low-temperature (-10°C) rate performance of the single-atom metal-catalyzed locally graphitized carbon-based nanosheets (top) and conventional graphitized carbon-based nanosheets (bottom) of the present invention is shown.

[0039] Figure 10 The low-temperature (-10℃) cycling performance of locally graphitized carbon nanosheets catalyzed by single-atom metals (top) and conventional graphitized carbon nanosheets (bottom) is shown. Detailed Implementation

[0040] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0041] The raw materials and instruments used in the examples are not subject to specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0042] Example 1

[0043] A method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets, the method specifically includes the following steps:

[0044] (1) Material preparation and ultrasonic treatment: Weigh 400 mg of iron(III) acetylacetone and 8 mL of graphene oxide dispersion (5 mg / mL) and add them to 50 mL of triethylene glycol, and ultrasonically treat for 30 min.

[0045] (2) Heating and washing: The above mixture was rapidly heated to 278°C at a heating rate of 8°C / min and kept under reflux for 30 min. After cooling to room temperature, it was washed five times by centrifugation with a mixture of ethyl acetate and methanol to obtain the Fe3O4 / reduced graphene oxide composite.

[0046] (3) Post-processing: The obtained Fe3O4 / reduced graphene oxide composite was redispersed in methanol and subjected to ultrasonic treatment. Then, the polymer precursor solution was slowly added to methanol and stirred continuously for 6 hours. The precipitate was then filtered and separated, and dried in a vacuum oven at 80°C for 12 hours to obtain Fe3O4 / reduced graphene oxide composite @PZS.

[0047] (4) Pyrolysis: The Fe3O4 / carbon-based nanosheets@PZS obtained in step (3) are heated to argon atmosphere at 750℃ at a rate of 5℃ / min and pyrolyzed for 2h to complete the graphitization process catalyzed by single-atom metal and finally obtain carbon-based nanosheets (Fe-HC nanosheets) catalyzed by single-atom metal.

[0048] In this embodiment, the XRD patterns and microstructures of the obtained locally graphitized carbon-based nanosheets are as follows: Figure 2 and 3 As shown, Figure 2 The XRD patterns of Fe3O4 / rGO@PZS precursor and Fe-HC, a partially graphitized carbon nanosheet catalyzed by single-atom metals, from Example 1 are shown. The characteristic peaks of graphene oxide (2θ≈10°) are weakened or disappear, while the characteristic peaks of graphite (2θ≈23°) are significantly enhanced, and the characteristic peaks of iron single atoms (2θ≈44.5°, 51.8°, 65.1°) appear. These changes indicate that the graphitization process has been successfully achieved, and iron single atoms play an important catalytic role in it. Figure 3 It shows the microstructure and elemental distribution of the material. Figure 3 In figure a), region I represents a localized graphitized area in the material. As can be seen in the magnified view on the right, this region exhibits a clear layered graphite structure with an interlayer spacing of approximately 0.34–0.42 nm (corresponding to the (002) crystal plane of graphite). This indicates a significant graphitization transformation in this region, with a high degree of order in the carbon layers. Region II represents a non-graphitized area in the material. No obvious layered structure was observed in this region; instead, a disordered carbon structure was observed. This suggests a lower degree of graphitization in this region, potentially containing numerous defects or incompletely graphitized carbon. The existence of this non-graphitized area indicates that the graphitization process is localized rather than complete. This localized graphitization structure helps to improve the material's conductivity and sodium-ion storage performance while maintaining a high specific surface area. Figure 3 In a), point III represents the distribution region of the single-atom metal catalyst in the material. Some bright spots or small particles can be seen in this region. These are the distribution locations of the single-atom metal, indicating that the single-atom metal catalyst is uniformly distributed in the carbon-based nanosheets and no metal agglomeration is formed. This uniform distribution is the key to achieving efficient catalysis and local graphitization. Figure 3 In a), point IV represents the interface region between the carbon-based nanosheets and the single-atom metal catalyst in the material. A clear interface structure can be seen in this region, such as the interaction between the carbon layer and the metal atoms. The presence of this interface structure indicates that there is a good interaction between the single-atom metal and the carbon matrix, which helps to improve the overall performance of the material.

[0049] This demonstrates that the single-atom metal catalyst successfully promoted local graphitization during pyrolysis, thereby improving the conductivity and structural stability of the material.

[0050] Figure 3 b) The distribution of single-atom metals in carbon-based nanosheets was demonstrated using high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM). Aberration correction techniques clearly revealed the uniform distribution of single-atom metals, the presence of localized graphitization structures, and a favorable interface structure. Figure 3 The bright spots in b) indicate that the single-atom metal is uniformly distributed within the carbon-based nanosheets without forming metal agglomerates. This demonstrates that the single-atom metal catalyst successfully achieved atomic-level dispersion during preparation. Furthermore, observation of the carbon structure surrounding these bright spots confirms the existence of localized graphitized regions. This is because the presence of the single-atom metal promotes the ordered arrangement of the carbon layers, forming localized graphitized structures. Figure 3 (b) The interfacial structure between the single-atom metal and the carbon matrix was also revealed. The existence of this interfacial structure indicates a good interaction between the single-atom metal and the carbon matrix, which helps to improve the overall performance of the material. These characteristics show that the single-atom metal catalyst successfully promoted the local graphitization of carbon-based nanosheets during pyrolysis, improved the conductivity and structural stability of the material, and thus significantly enhanced its electrochemical performance.

[0051] Figure 3 c) The microstructure of locally graphitized carbon-based nanosheets catalyzed by single-atom metals and the corresponding elemental distribution of carbon, iron, nitrogen, phosphorus, and sulfur were revealed using transmission electron microscopy (TEM) images and energy-dispersive X-ray spectroscopy (EDS) spectroscopy. The layered structure in the TEM images confirmed the presence of locally graphitized regions within the material. This locally graphitized structure contributes to improved conductivity and sodium ion diffusion. The EDS spectroscopy provided the distribution of different elements within the material. The distribution of carbon (C), iron (Fe), nitrogen (N), phosphorus (P), and sulfur (S) within the nanosheets was clearly visible. The uniform distribution of iron (Fe) in the EDS spectroscopy indicates that the single-atom metal catalyst is uniformly distributed within the carbon-based nanosheets without metal agglomeration; this uniform distribution is crucial for achieving efficient catalysis and localized graphitization. The distribution of nitrogen (N), phosphorus (P), and sulfur (S) in the EDS spectroscopy indicates that these elements were successfully doped into the carbon-based nanosheets. Atomic doping can modulate the electronic structure of carbon-based materials, improving their conductivity and sodium ion storage performance. Figure 3 c) The material characteristics show that the conductivity and sodium-ion storage performance of the material are significantly improved through single-atom metal catalysis and heteroatom doping, thereby significantly improving the electrochemical performance of the sodium-ion battery anode material.

[0052] Therefore, it is believed that the introduction of monatomic metallic iron and subsequent high-temperature treatment can significantly promote the local graphitization of carbon-based materials.

[0053] Figure 4 The high-resolution a)Fe 2p, b)O 1s and c)P 2p X-ray photoelectron spectra of the iron single-atom catalytic locally graphitized carbon-based nanosheets obtained in Example 1 are specifically the three spectra: a)Fe 2p, b)O 1s and c)P 2p. Figure 4 In the a) Fe 2p spectrum, the position and shape of the peaks indicate that iron atoms have formed stable chemical bonds with oxygen and phosphorus atoms: two main peaks appear in the figure, corresponding to the Fe 2p3 / 2 and Fe 2p1 / 2 orbitals respectively. The position and shape of the peaks indicate that iron atoms form stable chemical bonds with Fe atoms. 3+ or Fe 2+ The presence of multiple peaks in the O 1s spectrum indicates that oxygen atoms participate in the formation of Fe-O and OP bonds: one peak appears at approximately 531.5 eV, corresponding to the Fe-O bond, and another peak appears at approximately 533.2 eV, corresponding to the OP bond. These peaks demonstrate that oxygen atoms not only bond with iron atoms but also form chemical bonds with phosphorus atoms, further proving the existence of the metal (Fe)-OP coordination structure; the presence of multiple peaks in the P 2p spectrum indicates that phosphorus atoms participate in the formation of PC and PO bonds: in this spectrum, the P 2p peak is divided into two main peaks, corresponding to PC and PO bonds respectively. One peak appears at approximately 133.4 eV, corresponding to the PC bond, and another peak appears at approximately 134.5 eV, corresponding to the PO bond. These peaks demonstrate that phosphorus atoms not only bond with carbon atoms but also form chemical bonds with oxygen atoms, further proving the existence of the metal (Fe)-OP coordination structure. All these results collectively prove the formation of the metal-OP coordination structure.

[0054] Figure 5 X-ray absorption spectroscopy (XAS) analysis results of locally graphitized carbon-based nanosheets catalyzed by single-atom metals are presented, including iron K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis. Figure 5 a) X-ray absorption near-edge (XANES) spectrum of iron K-edge structure: The figure compares the absorption edge position of locally graphitized carbon nanosheets (Fe-HC) catalyzed by single-atom metal with the absorption edge positions of reference materials (such as Fe foil, FePc, Fe3O4, and FePO4). It is found that the absorption edge position of Fe-HC is close to that of FePO4, but significantly different from that of Fe foil or Fe3O4. This indicates that iron atoms in Fe-HC are in the form of Fe... 3+ or Fe 2+It exists in the form of oxygen and phosphorus and forms stable chemical bonds with them; Figure 5 b) is k 3 Weighted Fourier transform extended X-ray absorption fine structure (EXAFS) diagram of Fe K-side: The EXAFS spectrum of Fe-HC shows peaks similar to those of FePO4, but without the characteristic peaks of metal-metal bonds (such as Fe-Fe bonds) commonly found in Fe foil or Fe3O4. This indicates that iron atoms in Fe-HC are mainly coordinated with oxygen and phosphorus atoms, rather than forming metal aggregates. Figure 5 c) EXAFS fitting curve of Fe-HC: The EXAFS fitting curve of Fe-HC shows that iron atoms are mainly coordinated with oxygen and phosphorus atoms. The fitting results indicate that the coordination number of iron atoms is approximately 4.4, and the bond length is approximately... (Bond length with oxygen atom) and (Bond length with phosphorus atoms), these results further confirm the existence of the metal-OP coordination structure and show that iron atoms are uniformly distributed in the carbon-based nanosheets; Figure 5 d) shows the k of Fe foil, Fe3O4, and Fe-HC. 3 Wavelet transform of weighted extended X-ray absorption fine structure signal: The wavelet transform spectrum of Fe-HC is compared with that of Fe foil and Fe3O4. The wavelet transform spectrum of Fe-HC shows characteristic peaks similar to those of FePO4, but does not have the Fe-Fe bond features commonly found in Fe foil. This further proves that iron atoms in Fe-HC are mainly coordinated with oxygen and phosphorus atoms. The presence of this characteristic peak further confirms the formation of the metal-OP coordination structure.

[0055] Therefore, it can be seen that from Figure 4 High-resolution X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectra, extended X-ray absorption fine structure maps of (a) to (c) and Figure 5 The electronic structure and coordination environment of iron single atoms in (a) to (d) were analyzed by X-ray absorption spectroscopy (XAS), which further confirmed the uniform distribution of iron single atoms and the formation of metal-OP coordination structure.

[0056] Example 2

[0057] This embodiment demonstrates a method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets: the specific steps are as follows:

[0058] (1) Material preparation and ultrasonic treatment: According to the method of Example 1, copper(II) acetylacetone was selected as the catalyst. 400 mg of copper(II) acetylacetone and 8 mL of graphene oxide dispersion (5 mg / mL) were weighed, added to 50 mL of triethylene glycol, and ultrasonically treated for 30 min.

[0059] (2) Heating and washing: The above mixture was rapidly heated to 300°C at a heating rate of 8°C / min and kept under reflux for 30 min. After cooling to room temperature, it was centrifuged and washed five times with a mixture of ethyl acetate and methanol to obtain the Cu / reduced graphene oxide composite.

[0060] (3) Post-processing: The obtained Cu / reduced graphene oxide composite was redispersed in methanol solution and subjected to ultrasonic treatment. Then, the polymer precursor solution was slowly added to methanol and stirred continuously for 6 hours. The precipitate was then filtered and separated, and dried in a vacuum oven at 80°C for 10 hours to obtain Cu / carbon-based nanosheets@PZS.

[0061] (4) Pyrolysis: The Cu / carbon-based nanosheets @PZS obtained in step (3) are pyrolyzed in an argon atmosphere at 750℃ for 5 hours to complete the graphitization process catalyzed by a single atom metal, and finally carbon-based nanosheets (Cu-HC nanosheets) with local graphitization catalyzed by a single atom metal are obtained.

[0062] Example 3

[0063] This embodiment further verifies the electrochemical performance of the single-atom metal-catalyzed locally graphitized carbon-based nanosheets (Fe-HC nanosheets) obtained in Example 1 in a sodium-ion battery:

[0064] (1) Electrode preparation: Fe-HC nanosheets, conductive agent Super P and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) solvent was added to make a slurry. The slurry was coated on copper foil, dried and cut into electrode sheets with a diameter of 14 mm.

[0065] (2) Battery assembly: In an argon-filled glove box, the prepared electrode sheet, a sodium metal counter electrode, and an EC / PC (1:1, v / v) electrolyte containing 1M NaClO4 were assembled into a 2032 button cell.

[0066] (3) Electrochemical testing: such as Figure 6As shown in the figure, the room-temperature rate performance of the locally graphitized carbon-based nanosheets (top) catalyzed by the single-atom metal catalyst of the present invention reveals that the Fe-HC anode exhibits average discharge capacities of 394, 341, 318, 300, 280, 258, 206, and 141 mAh / g at current densities of 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively. In contrast, the HC anode exhibits discharge capacities of 310, 275, 253, 231, 200, 174, 143, and 89 mAh / g under the same conditions. When the current density is reduced back to 0.1 A / g, the discharge capacity of the Fe-HC anode recovers to 316 mAh / g, demonstrating good rate performance and verifying the cycling stability of the Fe-HC anode at current densities of 0.1 and 0.5 A / g.

[0067] It can perform charge-discharge cycle tests at a current density of 0.1 A / g, such as... Figure 7 As shown, the room temperature cycling performance of a sodium-ion battery using the Fe-HC anode material of the present invention (top) is compared with that using conventional graphitized carbon nanosheets HC (bottom). After 250 cycles, the Fe-HC anode maintained a reversible specific capacity of 281 mAh / g, which is much higher than the 225 mAh / g of the HC anode. The stable discharge capacity of the Fe-HC anode showed no significant decay. This demonstrates that the battery using the single-atom metal graphitized carbon nanosheets of the present invention as the anode material exhibits good cycle stability.

[0068] Charge-discharge cycle tests were performed at a high current density of 0.5 A / g, such as... Figure 8 As shown, the Fe-HC anode still exhibits a high discharge capacity of 209.6 mAh / g after 400 cycles, demonstrating its excellent long-cycle performance.

[0069] Example 4

[0070] This embodiment further verifies the electrochemical performance of the single-atom metal-catalyzed locally graphitized carbon-based nanosheets (Fe-HC nanosheets) obtained in Example 1 in a low-temperature sodium-ion battery. Rate and cycle tests were conducted at -10°C, as shown in the figure. Figure 9 and Figure 10 As shown, compared to the low-temperature (-10°C) rate performance of a battery using conventional graphitized carbon nanosheets (HC) as the anode material (bottom), the battery using the locally graphitized carbon nanosheets (Fe-HC) loaded with a single-atom metal (top) of this invention as the anode material exhibits superior rate performance and cycle performance. Furthermore, under cycle testing conditions of -10°C and a current density of 0.1 A / g, the locally graphitized carbon nanosheets, catalyzed by the single-atom metal, remained stable for 200 cycles, maintaining a specific capacity of 191 mAh / g.

[0071] Example 5

[0072] This embodiment explores the effect of synthesis conditions at different temperatures on the performance of single-atom metal-catalyzed locally graphitized carbon-based nanosheets:

[0073] (1) Material preparation and ultrasonic treatment: According to the method of Example 1, iron(III) acetylacetone was used as reactant and catalyst to prepare the catalytic reaction mixture.

[0074] (2) Pyrolysis temperature variation: The pyrolysis temperature in step 4 of Example 1 was adjusted to 650℃, 750℃ and 850℃ respectively, while other conditions remained unchanged, to observe the effect of different pyrolysis temperatures on the electrochemical performance of carbon-based nanosheets.

[0075] (3) Performance Evaluation: The obtained graphitized nanosheets were used to prepare the anode of a sodium-ion battery, and their charge-discharge performance at a current density of 0.1 A / g was tested. The results showed that the obtained Fe-HC nanosheets exhibited good electrochemical performance at pyrolysis temperatures above 750℃. Specifically, the electrochemical performance of the obtained Fe-HC nanosheets at pyrolysis temperatures of 650℃ or 850℃ decreased slightly. This indicates that the pyrolysis temperature has a certain influence on the degree of graphitization of the carbon-based nanosheets, resulting in different electrochemical performances.

[0076] Example 6

[0077] This embodiment demonstrates the effect of preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets at different atomic mass ratios:

[0078] (1) Select iron(III) acetylacetone, and mix graphene oxide and iron(III) acetylacetone at mass ratios of 0.0001, 0.01 and 0.1 respectively. The remaining steps are carried out according to Example 1.

[0079] (2) Performance evaluation: The prepared graphitized carbon-based nanosheets were used as anode materials for sodium-ion batteries, and their electrochemical performance was tested. The results showed that the locally graphitized carbon-based nanosheets obtained within the above mass ratio range all exhibited excellent electrochemical performance as anode materials for sodium-ion batteries, with an initial capacity of over 200 mAh / g. Under the condition of 1% mass ratio, the nanosheets showed the best performance, with an initial capacity of over 400 mAh / g.

[0080] Example 7

[0081] Exploring the effects of different types of single-atom metals (gold, iron, manganese) on the local graphitization of carbon-based nanosheets and their properties:

[0082] (1) Synthesis: Using the method of Example 1, platinum, gold and iron acetylacetone metal salts were used as single-atom metal precursors to prepare locally graphitized carbon-based nanosheets.

[0083] (2) Performance Evaluation: The obtained single-atom metal-catalyzed locally graphitized carbon nanosheets were used as anodes in sodium-ion batteries, and their electrochemical performance was tested. The results showed that the electrochemical performance of each single-atom metal-catalyzed locally graphitized carbon nanosheet was superior to that of HC, with specific capacities of 327, 335, and 350 mAh / g at a current density of 0.1 A / g, respectively. Among these metals, the obtained single-atom iron-catalyzed locally graphitized carbon nanosheet provided the best performance.

[0084] Example 8

[0085] This embodiment verifies the specific capacity performance of single-atom metal-catalyzed locally graphitized carbon-based nanosheets as anode materials for sodium-ion batteries:

[0086] Single-atom iron-catalyzed locally graphitized carbon-based nanosheets (Fe-HC nanosheets) were prepared using the method in Example 1. Electrodes were prepared and batteries were assembled using the method in Example 3.

[0087] Charge and discharge test: Constant current charge and discharge test was performed at a current density of 0.1 A / g, with a test voltage range of 0.01 to 3.0 V.

[0088] like Figure 6 As shown, the Fe-HC nanosheet anode exhibits an initial discharge capacity of 412 mAh / g and a capacity retention of 92% after 100 cycles. Compared to conventional graphitized carbon-based nanosheets (initial capacity of 125 mAh / g), the material of this invention demonstrates a significantly improved specific capacity and excellent cycling stability. Furthermore, at a high rate of 0.5 A / g ( Figure 8 Even with high-rate charge and discharge, Fe-HC nanosheets still provide a specific capacity of 238 mAh / g, fully demonstrating their applicability in high-rate charge and discharge scenarios.

[0089] Example 9

[0090] This embodiment studies the effect of different heating rates on the synthesis process:

[0091] The Fe3O4 / reduced graphene oxide composite was prepared in the same manner as in Example 1.

[0092] Changes in pyrolysis heating rate: The heating rate in the pyrolysis step was adjusted to 2℃ / min, 5℃ / min and 10℃ / min respectively, while other conditions remained unchanged.

[0093] Performance Evaluation: The obtained graphitized carbon-based nanosheets were used to prepare sodium-ion battery anodes, and their charge-discharge performance at a current density of 0.1 A / g was tested. The results showed that, at the above heating rates, their charge-discharge performance was superior to that of the HC anode, with corresponding initial capacities of 350, 337, and 325 mAh / g, respectively. However, at a heating rate of 2 °C / min, the Fe-HC nanosheets exhibited the best electrochemical performance, with an initial capacity of 350 mAh / g and a capacity retention of over 80% after 200 cycles.

[0094] As can be seen from the above embodiments, the single-atom metal-catalyzed locally graphitized carbon-based nanosheets of the present invention exhibit a specific capacity of over 150 mAh / g, thus demonstrating excellent cycle stability and rate performance, especially maintaining a high discharge capacity even at low temperatures. This significantly improves the low-temperature performance of the battery, adapting to energy storage requirements under various environments. Therefore, the single-atom metal-catalyzed locally graphitized carbon-based nanosheets of the present invention have a very broad application prospect in the field of sodium-ion batteries.

Claims

1. A method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets, characterized in that, The steps are as follows: (1) Material preparation and ultrasonic treatment: The carbon-based nanosheet dispersion and organometallic salt were added together to an organic solvent, and then the mixture was ultrasonically treated to ensure full dispersion; (2) Heating and washing: The mixture after being fully dispersed in step (1) is rapidly heated to 250~350℃ at a heating rate of 5~15℃ / min and kept under reflux for 30min. Then the mixture is allowed to cool naturally to room temperature. Subsequently, it is centrifuged and washed with a mixed solvent of ethyl acetate and methanol to obtain the metal compound / carbon-based nanosheet composite. (3) Post-processing: The metal compound / carbon nanosheet composite obtained in step (2) is redispersed in methanol and subjected to ultrasonic treatment. Then, a polymer precursor solution is slowly added to methanol and stirred continuously for 6 hours. Then, the precipitate is obtained by filtration and separation and dried under vacuum to obtain the polymer precursor-coated metal compound / carbon nanosheet. (4) Pyrolysis: The metal compound / carbon-based nanosheets coated with the polymer precursor obtained in step (3) are heated to above 650°C in an argon atmosphere and maintained at this temperature to complete pyrolysis, thereby obtaining single-atom metal-catalyzed locally graphitized carbon-based nanosheets. The single-atom metal is selected from one of platinum, gold, copper, iron, cobalt, nickel, manganese, and zinc. The organometal salt is selected from acetylacetone metal salts and metal phosphonates and metal imidazole salts, wherein the acetylacetone metal salt is one of iron (III) acetylacetone, copper (II) acetylacetone, platinum (II) acetylacetone, cobalt (II) acetylacetone or zinc (II) acetylacetone; In step (3), the polymer precursor solution is a solution containing 800 mg of phosphonyl chloride trimer and 1800 mg of 4,4'-dihydroxydiphenyl sulfone, which is formed by adding 2 mL of triethylamine dropwise under stirring. At this time, the metal compound / carbon nanosheet coated by the polymer precursor is a metal compound / carbon nanosheet coated with poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol), i.e., metal compound / carbon nanosheet@PZS.

2. The method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets according to claim 1, characterized in that, The mass ratio of the carbon-based nanosheet dispersion to the organometallic salt is 0.0001~0.

1.

3. The method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets according to claim 1, characterized in that, In step (1), the carbon-based nanosheets are selected from one of graphene oxide, reduced graphene oxide, graphene or activated carbon nanosheets co-doped with various heterogeneous non-metallic elements.

4. The method for preparing single-atom metal-catalyzed locally graphitized carbon-based nanosheets according to claim 1, characterized in that, In step (4), the pyrolysis is performed by heating to 650-900°C at a heating rate of 2-10°C / min and maintaining the temperature for 2-15 hours.

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