Iron-selenium double-monatomic nitrogen-doped carbon-based composite material as well as preparation method and application thereof

Abstract

The invention provides an iron-selenium double-monatomic nitrogen-doped carbon-based composite material and a preparation method and application thereof, the composite material comprises an N-doped carbon matrix, and Fe monatomic and Se monatomic distributed on the N-doped carbon matrix, and the Fe monatomic and the Se monatomic are anchored on the N-doped carbon matrix. The method comprises the following steps: preparing a Fe / Se / N-doped carbon-based precursor, and carrying out high-temperature carbonization on the Fe / Se / N-doped carbon-based precursor to obtain the iron-selenium double-monatomic nitrogen-doped carbon-based composite material. The preparation method overcomes the technical bottlenecks of low specific capacity, poor cycling stability, poor rate capability, complex preparation process, no environmental protection and the like of the existing sodium-ion battery negative electrode material. The composite material has high reversible capacity, excellent cycle stability and good rate capability, comprehensively improves the comprehensive electrochemical performance of the sodium-ion battery, provides a competitive high-performance material solution for the field of sodium-ion batteries, and practically meets the urgent demand of the current new energy field on high-performance battery materials.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery electrode material technology, and specifically relates to iron-selenium double single-atom nitrogen-doped carbon-based composite materials, their preparation methods and applications. Background Technology

[0002] Against the backdrop of a continuously rising global demand for clean energy, sodium-ion batteries, with their outstanding advantages such as abundant sodium resources and low cost, have shown broad application prospects in large-scale energy storage and electric vehicles, becoming a highly anticipated new battery system.

[0003] Carbon-based anode materials have long been a key research area for sodium-ion battery anode materials due to their high conductivity, low discharge / charge voltage plateau, cost-effectiveness, and environmental friendliness. However, their relatively low theoretical specific capacity has become a major bottleneck restricting the performance improvement and widespread application of sodium-ion batteries. To improve their electrochemical performance, current technologies mainly focus on defect engineering, morphology control, nanostructure design, and composite structure construction.

[0004] Patent CN119306199A discloses a method for preparing hard carbon anode materials using starch as a raw material. This method first uses a first crosslinking agent to crosslink starch particles, controlling the degree of crosslinking to keep the starch particles in a semi-fixed state, maintaining their original morphology while reserving space for pore shrinkage during secondary crosslinking. Subsequently, a second crosslinking agent is used for further treatment to shrink the pore structure, and finally, carbonization is performed to obtain the hard carbon anode material. Although the initial coulombic efficiency of this material is improved, its reversible capacity is only 280-340 mAh / g, indicating poor overall performance and limited practical application prospects. Anchoring highly dispersed atoms to carbon-based materials can maximize atom utilization (≈100%), promote reaction kinetics, and facilitate Na+ adsorption. For example, patent CN119143111A discloses a sodium-ion battery anode material loaded with metal single atoms and its preparation method. This method involves stepwise single-atom modification of biomass hard carbon materials, increasing the interlayer spacing of graphite nanodomains, optimizing the structure and concentration of defective functional groups, and lowering the diffusion kinetic energy barrier of sodium ions in the hard carbon materials. However, this method offers limited improvement to material performance; the assembled sodium-ion battery has a first-cycle capacity of only 342 mAh / g, and the synthesis process uses toxic solvents, which is detrimental to industrial applications.

[0005] Furthermore, the sodium storage capacity of hard carbon materials doped with a single atom has a physical limit, while multi-atom synergistic systems, through electronic coupling effects and steric hindrance modulation, are expected to achieve performance breakthroughs. For example, the paper "Asymmetric Coordination of Heterogeneous Fe-Se Dual-atom Sites Boosts CO2 Electroreduction" discloses a method for successfully preparing Fe-Se-NC composite materials on porous carbon nanofibers through electrospinning and in-situ gas-phase selenization strategies. The specific steps include dissolving Zn(NO3)2·6H2O and 2-methylimidazole in methanol and methanol respectively, stirring continuously for 2 hours, centrifuging and drying to obtain ZIF-8 white powder; adding the prepared ZIF-8NPs, Fe(acac)3, and PAN to DMF solvent and stirring for 24 hours to form a uniformly dispersed solution; then electrospinning the mixture; and finally drying the obtained Fe / Zn-ZIFs / PAN composite material under vacuum at 60°C overnight. The obtained Fe / Zn-ZIFs / PAN composite material was first pre-oxidized in air at 220℃ for 2 h, and then pyrolyzed at 900℃ under argon for 2 h to remove residual Zn or Fe nanoparticles, yielding Fe-NC. Se powder and the prepared Fe-NC sample were then sealed with a lid. The mixture was then heated in a tube furnace at 900℃ under argon / hydrogen conditions for 2 h to obtain the Fe-Se-NC composite material. Experimental data show that this Fe-Se-NC composite material possesses a bicentric asymmetric coordination structure, and its induced electronic hybridization effect effectively regulates the adsorption / desorption kinetics of key intermediates at the active sites. However, the preparation process of the Fe-Se-NC composite material obtained by this method is cumbersome, has a long production cycle, and generates a lot of toxic waste. These indicators are still far from meeting the requirements for commercial applications, severely limiting the application potential of this material.

[0006] Therefore, there is an urgent need to develop carbon-based anode materials for sodium-ion batteries that combine high specific capacity, excellent rate performance, and long cycle stability. This can be achieved by optimizing heteroatom doping strategies, innovating structural designs, and exploring green synthesis processes to meet the pressing demand for high-performance energy storage materials in the new energy field. Summary of the Invention

[0007] To address the problems mentioned in the background art, this application provides iron-selenium dual single-atom nitrogen-doped carbon-based composite materials, their preparation methods, and applications.

[0008] Firstly, this invention proposes an iron-selenium dual-single-atom nitrogen-doped carbon-based composite material. The composite material includes an N-doped carbon matrix and Fe and Se single atoms distributed on the N-doped carbon matrix, with the Fe and Se single atoms anchored on the N-doped carbon matrix. This structural design endows the material with unique electronic structure and surface properties. While introducing Se single atoms as active sites, Fe single atoms are used to regulate the charge distribution and spin state of the active sites. The atomically dispersed Fe and Se active sites ensure efficient charge transfer and effectively suppress volume expansion, thereby achieving excellent sodium storage performance.

[0009] In some specific embodiments, Fe-N-Se-C coordination bonds exist in the composite material. The formation of Fe-N-Se-C coordination bonds optimizes the electron cloud distribution of the material, enhances interatomic interactions, improves the material's conductivity, accelerates the charge transfer rate, and enables the sodium-ion battery to respond quickly during charging and discharging, thereby improving the battery's power density and charge / discharge efficiency.

[0010] In some specific embodiments, the carbon matrix is ​​amorphous carbon, and the composite material exhibits a wrinkled nanosheet morphology. The N-doped carbon matrix provides stable support for Fe and Se single atoms, while the wrinkled nanosheet morphology greatly increases the specific surface area of ​​the material, providing more sodium ion adsorption sites, which is beneficial for the rapid diffusion and storage of sodium ions. At the same time, this special structure can provide buffer space during charge-discharge volume changes, maintain structural integrity, and improve battery cycle stability.

[0011] In some specific embodiments, the mass fraction of Fe single atoms in the composite material is 2%-13%, preferably 4%-6%, and the mass fraction of Se single atoms in the composite material is 5%-6%. Within this mass fraction range, the optimal loading of Fe and Se single atoms on the carbon matrix can be achieved, which can ensure a sufficient number of active sites to improve sodium storage capacity, while avoiding agglomeration due to excessive single atom loading, thus ensuring the structural stability and consistency and stability of the material and its electrochemical performance.

[0012] In some specific embodiments, the mass percentage of N doping in the composite material is 5%-15%. Appropriate N doping can effectively regulate the electronic structure of the carbon matrix. The lone pair electrons of N atoms can optimize the charge distribution within the material, making the electron cloud distribution more uniform and reasonable. Simultaneously, N doping introduces additional active sites, increasing the material's adsorption capacity for sodium ions, which helps improve the specific capacity of the battery.

[0013] Secondly, this invention proposes a method for preparing an iron-selenium dual single-atom nitrogen-doped carbon-based composite material, comprising:

[0014] S1, preparing Fe / Se / N-doped carbon-based precursors;

[0015] S2, high-temperature carbonization of Fe / Se / N doped carbon-based precursors to obtain iron-selenium dual single-atom nitrogen doped carbon-based composite materials.

[0016] In the above technical solution, the preparation method employs a two-step process of first preparing a precursor and then high-temperature carbonization, which allows for precise control of the material structure and composition. The precursor preparation process enables uniform mixing and atomic-level dispersion of raw materials, while the high-temperature carbonization process forms a stable amorphous carbon-based structure and anchors single atoms, ensuring the repeatability and stability of material properties and facilitating industrial production.

[0017] In some specific embodiments, step S1 includes the following:

[0018] S11, melamine, L-alanine, selenium dioxide, ferric chloride and ZrO2 grinding media are mixed and ground until a uniform powder is formed to obtain a mixed powder;

[0019] S12, add an ethanol-hydrochloric acid mixed solution with a volume ratio of 5:1-10:1 to the mixed powder, continue grinding until the ethanol evaporates completely, and obtain the sample;

[0020] S13. Place the sample in an oven and dry it at 80-100℃ for 8-12 hours to obtain the Fe / Se / N doped carbon-based precursor.

[0021] In the above technical solution, the grinding process in S11 utilizes the mechanical force of ZrO grinding media to facilitate the initial dispersion and mixing of powders. Grinding plays a role in the formation of Fe and Se single atoms, providing a precursor basis for subsequent processes. In S12, the ethanol-hydrochloric acid mixed solution promotes the chemical reaction and uniform dispersion of raw materials. The drying step in S13 removes the solvent and initially fixes the precursor structure. The entire S1 step lays the foundation for the subsequent high-temperature carbonization to form a composite material with the target structure and properties.

[0022] In some specific embodiments, step S2 includes:

[0023] Fe / Se / N doped carbon-based precursors were placed in a tube furnace and heated to 550-600℃ at a heating rate of 5-10℃ / min, held for 2-4 hours, and then heated to 900-950℃ at a heating rate of 5-10℃ / min, held for 2-4 hours. The furnace was then cooled to obtain iron-selenium double monatomic nitrogen doped carbon-based composite materials.

[0024] In the above technical solution, the precisely controlled heating rate and segmented heat preservation process enable the precursor to undergo orderly physicochemical changes at different temperature stages, gradually forming an amorphous carbon-based structure and stably anchoring Fe and Se single atoms, avoiding structural defects or single-atom agglomeration caused by excessively rapid temperature changes, and ensuring that the composite material has excellent electrochemical performance.

[0025] In some specific embodiments, the mass ratio of melamine, L-alanine, selenium dioxide, and ferric chloride is 12:3:6:(0.010-0.045). This mass ratio allows for sufficient reaction between the raw materials, ensuring adequate carbon and nitrogen sources to form a stable N-doped carbon matrix. Simultaneously, it introduces and uniformly disperses appropriate amounts of Fe and Se atoms, avoiding waste of raw materials or material performance defects due to improper proportions, thus ensuring the stable and uniform performance of the prepared composite material.

[0026] Thirdly, this invention proposes an application of an iron-selenium double single-atom nitrogen-doped carbon-based composite material, wherein the iron-selenium double single-atom nitrogen-doped carbon-based composite material described in the first aspect or the iron-selenium double single-atom nitrogen-doped carbon-based composite material prepared by the method described in the second aspect is used as the negative electrode of a sodium-ion battery.

[0027] Compared with the prior art, the beneficial results of the present invention are as follows:

[0028] (1) This invention uses nano-hard carbon as the carbon matrix, and its wrinkled nanosheet structure endows the material with good mechanical stability. The raw materials used are widely available, easy to obtain, and inexpensive. The target product can be prepared by a simple grinding method and a one-step carbonization method, avoiding the use of high-risk reagents and fundamentally avoiding the safety risks and environmental hazards caused by hazardous chemicals. The preparation process is simple, energy-saving, environmentally friendly, and environmentally friendly.

[0029] (2) This invention employs a Fe / Se dual single-atom synergistic regulation strategy, leveraging the synergistic effect of Se atoms as active sites and Fe atoms' charge regulation to achieve dual optimization of the "structure-electronics" of hard carbon materials. The introduction of Fe atoms significantly modulates the spin state and charge distribution of Se sites, laying the foundation for the long-term application of the material in the battery field. Furthermore, the preparation process of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material is simple and efficient, possessing outstanding potential for large-scale production and effectively meeting the needs of industrial production.

[0030] (3) When the iron-selenium double single-atom nitrogen-doped carbon-based composite material of the present invention is used in sodium-ion batteries, it has high reversible capacity, stable cycle performance and excellent rate performance, which comprehensively improves the overall electrochemical performance of sodium-ion batteries, provides more competitive material options for the sodium-ion battery field, and effectively meets the current urgent demand for high-performance battery materials. Attached Figure Description

[0031] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. Other embodiments and many anticipated advantages of the embodiments will be readily recognized as they become better understood through reference to the following detailed description. Elements in the drawings are not necessarily to scale. The same reference numerals refer to corresponding similar parts.

[0032] Figure 1 This is a flowchart of a method for preparing an iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the synthesis of an iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to an embodiment of the present invention at the atomic level.

[0034] Figure 3 This is a scanning electron microscope (SEM) image of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to the present invention;

[0035] Figure 4 This is an X-ray diffraction (XRD) pattern of the iron selenium double single-atom nitrogen-doped carbon-based composite material according to Example 1 of the present invention;

[0036] Figure 5 These are microscopic analysis images of the iron-selenium double single-atom nitrogen-doped carbon-based composite material according to the present invention;

[0037] Figure 6 This is a synchrotron radiation diagram of the iron-selenium double single-atom nitrogen-doped carbon-based composite material according to the present invention;

[0038] Figure 7 The image shows an inductively coupled plasma (ICP) analysis of the iron-selenium double single-atom nitrogen-doped carbon-based composite material according to the present invention.

[0039] Figure 8 The XPS-C1s, XPS-N1s, XPS-Se3d and XPS-Fe2p spectra of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to the present invention are shown.

[0040] Figure 9 The diagram shows the cycling performance of the materials described in Examples 1, 2, 3, and 4 of this invention as negative electrode materials for sodium-ion batteries at a current density of 0.1 A / g.

[0041] Figure 10 This is a cycle performance diagram at a current density of 0.1 A / g when the present invention's Examples 1, 1, 2, and 3 are used as negative electrode materials for sodium-ion batteries.

[0042] Figure 11This is a cycle performance diagram of sodium-ion batteries when using Examples 1, 1, 2, and 3 of the present invention as negative electrode materials at a high current density of 8 A / g.

[0043] Figure 12 This is a rate performance diagram of the present invention when Examples 1, 1, 2, and 3 are used as negative electrode materials for sodium-ion batteries. Detailed Implementation

[0044] The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. Similar component reference numerals in the drawings represent similar components. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. 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.

[0045] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0046] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0047] This invention provides a flowchart of a method for preparing iron-selenium dual single-atom nitrogen-doped carbon-based composite materials, as shown in the embodiments below. Figure 1 As shown, the method includes:

[0048] S100 was used to prepare Fe / Se / N doped carbon-based precursors.

[0049] S200, the Fe / Se / N doped carbon-based precursor is subjected to high-temperature carbonization to obtain the iron-selenium dual single-atom nitrogen-doped carbon-based composite material.

[0050] In some specific embodiments, step S100 includes the following:

[0051] S101, melamine, L-alanine, selenium dioxide, ferric chloride and ZrO2 grinding media are mixed and ground into a uniform powder to obtain a mixed powder;

[0052] S102, add an ethanol-hydrochloric acid mixed solution with a volume ratio of 5:1-10:1 to the mixed powder, continue grinding until the ethanol evaporates completely, and obtain the sample;

[0053] S103, place the sample in an oven and dry at 80-100℃ for 8-12 hours to obtain Fe / Se / N doped carbon-based precursor.

[0054] Specifically, melamine, L-alanine, selenium dioxide, and ferric chloride in a mass ratio of 12:3:6:(0.010-0.045) were placed in a ball mill jar, ZrO grinding beads were added, and the mixture was ball-milled at room temperature for 120 min to obtain a mixed powder. 20 mL of an ethanol-hydrochloric acid mixed solution with a volume ratio of 5:1-10:1 was added to the powder, and the mixture was ball-milled for another 120 min to obtain a sample. The sample was then dried in an oven at 80-100℃ for 8-12 h to obtain a Fe / Se / N doped carbon-based precursor.

[0055] In some specific embodiments, step S200 includes placing the Fe / Se / N doped carbon-based precursor in a tube furnace, heating it to 550-600°C at a heating rate of 5-10°C / min, holding it at that temperature for 2-4 hours, and then continuing to heat it to 900-950°C at a heating rate of 5-10°C / min, holding it at that temperature for 2-4 hours; cooling it in the furnace to obtain the iron-selenium double single-atom nitrogen doped carbon-based composite material.

[0056] Specifically, the Fe / Se / N doped carbon-based precursor obtained in step S100 is placed in a tube furnace and heated at a heating rate of 5-10℃ / min. When the temperature reaches 550-600℃, it is maintained at this temperature for 2-4 hours. Subsequently, the temperature is raised to 900-950℃ at a heating rate of 5-10℃ / min and maintained at this temperature for 2-4 hours. After the holding period, the material in the tube furnace is allowed to cool naturally, and finally, the iron-selenium double single-atom nitrogen doped carbon-based composite material is obtained. The process involves heating from the initial temperature to 550-600℃ at a rate of 5-10℃ / min and holding at that temperature for 2-4 hours. This stage removes moisture, low-boiling-point organic solvents, and some volatile impurities from the precursor, initially stabilizing the material and forming a preliminary carbon network structure. The temperature is then further increased to 900-950℃ at the same rate and held for 2-4 hours to further solidify the carbon network structure. The controlled heating rate ensures the uniformity and stability of the carbonization process, contributing to improved quality of the carbon matrix and its bonding with other components. Simultaneously, the high-temperature treatment enhances the interaction between single atoms and carbon, improving the overall stability and electrochemical performance of the composite material, ultimately yielding a high-quality iron-selenium dual-single-atom nitrogen-doped carbon-based composite material with excellent structure and performance.

[0057] This invention also proposes an iron-selenium dual single-atom nitrogen-doped carbon-based composite material, with reference to... Figure 2 , Figure 2 A schematic diagram illustrating the atomic-level synthesis of an iron-selenium dual-single-atom nitrogen-doped carbon-based composite material according to an embodiment of the present invention is shown. As shown, raw materials containing elements such as Fe, Se, C, and N are placed together with ZrO grinding beads in a ball mill jar, and the raw materials are thoroughly mixed and refined through the ball milling process. The mechanical action of the ZrO grinding beads ensures thorough mixing of these raw materials, breaks up particle agglomeration, achieves uniform dispersion, and obtains a mixed powder. Subsequently, a mixed solution of 20 mL of ethanol and hydrochloric acid (volume ratio of 5:1-10:1) is added, and the mixture is ball-milled again for 120 min to obtain the sample. HCl plays multiple roles in the system, promoting chemical reactions between raw materials and helping to regulate the microstructure of the material. In this step, the interatomic interactions are further enhanced, and the atoms of each element begin to arrange themselves in an orderly manner at the microscopic level, gradually forming a precursor with a specific structure. Finally, through a high-temperature pyrolysis process, the precursor undergoes complex physicochemical changes. At the atomic level, elements such as C and N form an amorphous carbon-based framework, while Fe and Se atoms are precisely anchored to the N-doped carbon matrix in single-atom form (from...). Figure 2 The magnified area on the right shows the distribution of Fe single atoms and Se single atoms in the carbon-based hexagonal structure, which constructs a unique Fe-N-Se-C coordination structure, ultimately forming an iron-selenium dual single-atom nitrogen-doped carbon-based composite material.

[0058] This invention also proposes an application of an iron-selenium dual single-atom nitrogen-doped carbon-based composite material.

[0059] In some specific embodiments, firstly, the iron-selenium dual-monoatomic nitrogen-doped carbon-based composite material is thoroughly ground and mixed with conductive carbon SuperP to achieve uniform mixing. Then, sodium carboxymethyl cellulose (CMC) and deionized water are added and stirred to form a uniform and fluid slurry. Next, a doctor blade coating process is used to uniformly coat the slurry onto the copper foil surface, strictly controlling the electrode loading at 0.7-1.3 mg / cm³. 2 Within the specified range. After coating, it is dried. After drying, the electrode is cut into circular pieces with a diameter of 12mm. Finally, the cut circular pieces are used as electrodes to assemble a coin cell. The preferred mass ratio of negative electrode material, conductive carbon, sodium carboxymethyl cellulose, and deionized water is 8:1:1:80.

[0060] Example 1

[0061] A method for preparing an iron-selenium dual single-atom nitrogen-doped carbon-based composite material specifically includes the following steps:

[0062] Step 1: Precursor. Mix 12g melamine, 3g L-alanine, 6g selenium dioxide, 15mg ferric chloride, and ZrO2 ball milling beads, and ball mill for 2 hours to obtain a mixed powder. Add 20mL of a 5:1 volume ratio ethanol-hydrochloric acid mixed solution to the mixed powder, and ball mill again for 120 minutes at room temperature to obtain a sample. Place the sample in an oven and dry at 80℃ for 12 hours to obtain the Fe / Se / N doped carbon-based precursor.

[0063] Step 2: Composite material synthesis. The Fe / Se / N doped carbon-based precursor was placed in a tube furnace and heated to 550℃ at a heating rate of 5℃ / min, then held for 2 hours. Subsequently, it was heated to 900℃ at a heating rate of 5℃ / min and held for 2 hours. After the holding period, the material in the tube furnace was allowed to cool naturally, yielding the iron-selenium dual-monatomic nitrogen-doped carbon-based composite material. Analysis showed that the Fe mass fraction in this composite material was 4.33%, and the Se mass fraction was 5.21%.

[0064] Example 2

[0065] The difference from Example 1 is that the mass ratio of melamine, L-alanine, selenium dioxide and ferric chloride in step one is 12:3:6:0.01, while the other steps are the same as in Example 1, to prepare an iron-selenium dual single-atom nitrogen-doped carbon-based composite material, wherein the mass fraction of Fe is 2.75% and the mass fraction of Se is 5.01%.

[0066] Example 3

[0067] The difference from Example 1 is that the mass ratio of melamine, L-alanine, selenium dioxide and ferric chloride in step one is 12:3:6:0.03. The other steps are the same as in Example 1. Iron selenium double single-atom nitrogen-doped carbon-based composite material is prepared, wherein the mass fraction of Fe single atoms is 8.10% and the mass fraction of Se is 5.43%.

[0068] Example 4

[0069] The difference from Example 1 is that the mass ratio of melamine, L-alanine, selenium dioxide and ferric chloride in step one is 12:3:6:0.045. The other steps are the same as in Example 1. Iron selenium double single-atom nitrogen-doped carbon-based composite material is prepared, wherein the mass fraction of Fe single atoms is 12.70% and the mass fraction of Se is 5.71%.

[0070] Comparative Example 1

[0071] This comparative example provides the preparation process and performance testing of Fe single-atom anchored N-doped carbon-based composite materials. The specific preparation process is as follows:

[0072] S1, melamine, L-alanine and ferric chloride are ball-milled together with ZrO2 ball milling beads to obtain a uniform powder;

[0073] S2, add a mixed solution of ethanol and hydrochloric acid (volume ratio of 5:1) and continue ball milling until the ethanol has completely evaporated;

[0074] S3, The above sample is placed in an oven to dry, and Fe / N doped carbon-based precursor is obtained;

[0075] S4 was heated to 550℃ at a heating rate of 5℃ / min and held at 550℃ for 2 hours. Then it was heated to 900℃ at a heating rate of 5℃ / min and held for 2 hours. After cooling, Fe single-atom anchored N-doped carbon-based composite material was obtained.

[0076] S5: Subsequently, the obtained material was used as the negative electrode material for sodium-ion batteries to assemble coin cells. After 100 cycles at a current density of 0.1 A / g, the capacity was only 282.17 mAh / g; after 10,000 cycles at a current density of 8 A / g, the capacity was only 133.14 mAh / g, and the performance was far lower than that of Example 1.

[0077] Comparative Example 2

[0078] This comparative example provides the preparation process and performance testing of Se single-atom anchored N-doped carbon-based composite materials. The specific preparation process is as follows:

[0079] S1, melamine, L-alanine and selenium dioxide are ball-milled together with ZrO2 ball milling beads to obtain a uniform powder;

[0080] S2, add a mixed solution of ethanol and hydrochloric acid (volume ratio of 5:1) and continue ball milling until the ethanol has completely evaporated;

[0081] S3, The above sample is placed in an oven to dry, and Fe / N doped carbon-based precursor is obtained;

[0082] S4 was heated to 550℃ at a heating rate of 5℃ / min and held at 550℃ for 2 hours. Then it was heated to 900℃ at a heating rate of 5℃ / min and held for 2 hours. After cooling, Se single-atom anchored N-doped carbon-based composite material was obtained.

[0083] S5: Subsequently, the obtained material was used as the negative electrode material for sodium-ion batteries to assemble coin cells. After 100 cycles at a current density of 0.1 A / g, the capacity was only 310.86 mAh / g; after 10,000 cycles at a current density of 8 A / g, the capacity was only 153.78 mAh / g. The performance was far lower than that of Example 1.

[0084] Comparative Example 3

[0085] This comparative example provides the preparation process and performance testing of N-doped carbon-based composite materials. The specific preparation process is as follows:

[0086] S1, melamine and L-alanine are ball-milled together with ZrO2 ball milling beads to obtain a uniform powder;

[0087] S2, add a mixed solution of ethanol and hydrochloric acid (volume ratio of 5:1) and continue ball milling until the ethanol has completely evaporated;

[0088] S3, The above sample is placed in an oven to dry, and Fe / N doped carbon-based precursor is obtained;

[0089] S4 was heated to 550℃ at a heating rate of 5℃ / min and held at 550℃ for 2 hours. Then it was heated to 900℃ at a heating rate of 5℃ / min and held for 2 hours. After cooling, N-doped carbon-based composite material was obtained.

[0090] S5: Subsequently, the obtained material was used as the negative electrode material for sodium-ion batteries to assemble coin cells. After 100 cycles at a current density of 0.1 A / g, the capacity was only 231.51 mAh / g; after 10,000 cycles at a current density of 8 A / g, the capacity was only 103.98 mAh / g, and the performance was far lower than that of Example 1.

[0091] Further reference Figure 3 , Figure 3 A scanning electron microscope (SEM) image of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material prepared according to Example 1 of the present invention is shown. Figure 3 a and Figure 3 b shows scanning electron microscope (SEM) images of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material prepared in Example 1. As can be seen from the figures, the composite material exhibits a two-dimensional lamellar wrinkled microstructure under SEM. This structure possesses a large specific surface area, which can promote the diffusion and storage of sodium ions within the material, and has a positive significance for improving the electrochemical performance of sodium-ion batteries.

[0092] Figure 4 The X-ray diffraction (XRD) pattern of the iron-selenium dual-single-atom nitrogen-doped carbon-based composite material prepared according to Example 1 of the present invention is shown. As can be seen from the figure, no sharp, obvious characteristic diffraction peaks appear within the scanning range of 2θ from 10° to 80°; only broadened diffraction peaks of amorphous carbon are observed. This indicates that the iron-selenium dual-single-atom nitrogen-doped carbon-based composite material of Example 1 has an amorphous carbon structure, and that Fe and Se particles are absent from the system.

[0093] Figure 5Microscopic images of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material prepared according to Example 1 of the present invention are shown, including transmission electron microscopy (TEM) images, aberration-corrected scanning transmission electron microscopy (spherical aberration electron microscopy) images, and X-ray energy-dispersive spectroscopy (EDS) analysis images. Figure 5 a presents the overall morphology of the material, and the selected area electron diffraction (SAED) pattern in the inset shows diffuse diffraction rings, indicating that the material has an amorphous structure; Figure 5 b further reveals the microstructure of the material, showing its folded, lamellar morphology; EDS elemental distribution map ( Figure 5 c) indicates that the composite material is composed of C, N, O, Fe, and Se elements, and these elements are uniformly distributed on the material surface, verifying the feasibility of the Fe and Se anchoring strategy for N-doped carbon. At the same time, the uniformly dispersed Fe and Se single atoms ensure the full exposure of active sites, promote uniform charge transport, effectively suppress structural damage caused by local stress concentration during charging and discharging, enhance material stability, and extend the service life of sodium-ion batteries. Figure 5 Image d is a spherical aberration electron micrograph. The highlighted atomic sites (marked by red circles) in the image indicate that Fe and Se exist in the carbon-based material in the form of single atoms.

[0094] Figure 6 The synchrotron radiation spectrum of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material prepared according to Example 1 of the present invention is shown. Valence state analysis shows that the valence state of Fe is between Fe foil and Fe2O3, without obvious Fe-Fe bonds. The valence state of Se is between Se foil and SeO2, and there are no obvious Se-Se bonds, which also proves that Fe and Se are anchored to the carbon matrix in single-atom form. Coordination fitting analysis confirms that iron-nitrogen-selenium-carbon (Fe-N-Se-C) bonds are formed between Fe, Se, N, and C. Figure 6 The wavelet transform (WT) diagram on the right further verifies the above structural information, confirming the coordination environment and structural characteristics of atoms in the material from different dimensions.

[0095] The iron-selenium dual-monoatomic nitrogen-doped carbon-based composite material of this invention exhibits a wrinkled nanosheet structure, consisting of a layered matrix formed by stacking multiple tightly connected carbon nanosheets. Fe and Se monoatomic atoms are uniformly anchored within the wrinkled carbon nanosheet matrix through specific iron-nitrogen-selenium-carbon (Fe-N-Se-C) coordination bonds with nitrogen atoms, constructing an Fe-Se monoatomic-anchored N-doped structure. This structural design significantly increases the specific surface area of ​​the material, providing abundant sodium ion adsorption sites and effectively improving the sodium storage capacity of the battery. Simultaneously, the stable Fe-N-Se-C coordination bonds enhance the stability of the material structure, effectively suppressing structural collapse and volume expansion of the carbon nanosheets during charge and discharge, thereby significantly improving the cycle stability of the battery.

[0096] Figure 7 The inductively coupled plasma optical emission spectrometry (ICP-OES) analysis results of the iron-selenium dual-atom nitrogen-doped carbon-based composite materials prepared according to Examples 1, 2, 3, and 4 of the present invention are shown. The results indicate that the mass fraction of Fe in Example 1 is 4.33%, and the mass fraction of Se is 5.21%. The mass fraction of Fe in Example 2 is 2.75%, and the mass fraction of Se is 5.01%. The mass fraction of Fe single atoms in Example 3 is 8.10%, and the mass fraction of Se is 5.43%. The mass fraction of Fe single atoms in Example 4 is 12.70%, and the mass fraction of Se is 5.71%.

[0097] Continue to refer to Figure 8 , Figure 8 The XPS-C1s, XPS-N1s, XPS-Fe2p, and XPS-Se3d spectra of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material prepared according to Example 1 of the present invention are shown. As shown in the figure, the C 1s spectrum has a horizontal binding energy range of 281 eV to 292 eV, with intensity on the vertical axis. The peaks at 284.8 eV, 285.5 eV, and 288.6 eV correspond to C-C, CO, and O=C bonds, respectively, reflecting the different chemical environments of carbon in the material. The N 1s spectrum has a horizontal binding energy range of 395 eV to 407 eV. The peaks at 397.8 eV, 399.1 eV, 400.5 eV, and 402.1 eV correspond to pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, and nitrogen oxides, respectively, indicating that nitrogen is doped in carbon-based materials in multiple forms. The Fe 2p spectrum has a horizontal binding energy range of 705 eV to 735 eV, with the peaks at 709.8 and 714.8 eV corresponding to the 2p bonds of Fe(II) and Fe(III). 3 / 2 The peaks at 722.9 and 728.1 eV correspond to the 2p orbitals of Fe(II) and Fe(III), respectively. 1 / 2 The Se 3d spectrum shows a binding energy range of 51 eV to 62 eV along the horizontal axis, with two peaks at 52.7 eV and 55.1 eV corresponding to Se orbitals. 3- and Se 0 3D 5 / 2 The orbital; the two peaks at 53.6 eV and 56.3 eV correspond to Se, respectively. 3- and Se 0 3D 3 / 2 Orbits. These detailed spectra clearly show the bonding patterns of the elements.

[0098] Figure 9The cycling performance curves at a current density of 0.1 A / g are shown when the materials of Examples 1, 2, 3, and 4 according to the present invention are used as anode materials for sodium-ion batteries. As shown in the figure, Example 1 exhibits better cycling performance than Examples 2, 3, and 4. The results indicate that the preferred Fe single-atom mass fraction in the iron-selenium dual-single-atom nitrogen-doped carbon-based composite anode is 4%-6%.

[0099] Figure 10 The figure shows the cycling performance curves at a current density of 0.1 A / g when the materials of Examples 1, 1, 2, and 3 of this invention are used as anode materials for sodium-ion batteries. As shown in the figure, after 100 cycles, the specific capacity of the iron-selenium dual-single-atom nitrogen-doped carbon-based composite material (Fe-Sea@NC, orange curve) anode is 450.9 mAh / g, demonstrating its excellent sodium-ion storage performance and cycling stability. In comparison, the reversible capacity of the N-doped carbon-based composite material (bare NC, green curve) anode is 231.5 mAh / g; the reversible capacities of the Fe single-atom anchored N-doped carbon-based composite material (Fe@NC, blue curve) anode and the Se single-atom anchored N-doped carbon-based composite material (Sea@NC, red curve) anode are 282.2 mAh / g and 310.9 mAh / g, respectively. Although these are higher than the N-doped carbon-based composite material anode, they are still much lower than the iron-selenium dual-single-atom nitrogen-doped carbon-based composite material anode.

[0100] Figure 11 The following graphs show the cycle performance of sodium-ion batteries using Examples 1, 1, 2, and 3 of the present invention as negative electrode materials at a current density of 8 A / g. Figure 11 It can be seen that a small current of 0.1 A / g was used to activate the electrode in the first three cycles, and the current density was switched to 8 A / g from the fourth cycle onwards. After 10,000 cycles, the specific capacity of the iron-selenium dual single-atom nitrogen-doped carbon-based composite material remained at 179.8 mAh / g, with a capacity retention of 81.7%, demonstrating excellent cycling stability. Meanwhile, the specific capacities of the Fe single-atom anchored N-doped carbon-based composite material, the Se single-atom anchored N-doped carbon-based composite material, and the N-doped carbon-based composite material after 10,000 cycles at a current density of 8 A / g were 133.1 mAh / g, 153.78 mAh / g, and 103.9 mAh / g, respectively. The results indicate that the introduction of Fe and Se atoms effectively increased the active sites, and their synergistic effect further improved the Na+ storage performance of the material.

[0101] Figure 12 The rate performance diagrams of the negative electrode materials used in sodium-ion batteries according to Embodiment 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention are shown. Figure 12It can be seen that when the current density increases from 0.05 A / g to 8 A / g, the composite material exhibits capacities of 470.2, 435.9, 401.9, 339.3, 295.7, 252.2, 231.2, 215.2, and 201.8 mAh / g at current densities of 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 4 A / g, 6 A / g, and 8 A / g, respectively, demonstrating its excellent rate performance and good application potential. Furthermore, although the specific capacity decreases with increasing cycle number, it remains relatively stable at all current densities, further verifying its good cycling stability.

[0102] This application innovatively constructs an Fe / Se dual single-atom anchored N-doped carbon matrix structure. Firstly, this structure exhibits a wrinkled nanosheet morphology with a high specific surface area, facilitating Na+ adsorption and endowing the material with excellent sodium storage performance. The atomically dispersed Fe and Se active sites enable efficient charge transfer while effectively suppressing volume expansion during charge and discharge, significantly improving cycle performance and greatly extending the lifespan of sodium-ion batteries compared to existing technologies. Secondly, the iron-selenium dual single-atom nitrogen-doped carbon-based composite material significantly enhances ionic and electronic conductivity, improving rate performance. At different current densities, this composite material enables the battery to maintain excellent charge and discharge performance, overcoming the problem of rapid capacity decay at high current densities in existing similar materials.

[0103] In summary, the iron-selenium dual single-atom nitrogen-doped carbon-based composite material of the present invention combines high reversible capacity, stable cycle performance and good rate performance, comprehensively improving the overall electrochemical performance of sodium-ion batteries, providing a highly competitive material option for the sodium-ion battery field, and effectively meeting the current urgent need for high-performance battery materials.

[0104] It is evident that those skilled in the art can make various modifications and alterations to the embodiments of the present invention without departing from the spirit and scope of the invention. In this way, the invention is also intended to cover such modifications and alterations if they fall within the scope of the claims and their equivalents. The word "comprising" does not exclude the presence of other elements or steps not listed in the claims. The simple fact that certain measures are described in mutually different dependent claims does not indicate that a combination of these measures cannot be used for profit. Any reference numerals in the claims should not be considered as limiting the scope.

Claims

1. A carbon-based composite material with iron-selenium dual single-atom nitrogen doping, characterized in that, The composite material includes an N-doped carbon matrix, and Fe single atoms and Se single atoms distributed on the N-doped carbon matrix, wherein the Fe single atoms and the Se single atoms are anchored on the N-doped carbon matrix.

2. The iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 1, characterized in that, The composite material contains Fe-N-Se-C coordination bonds.

3. The iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 1, characterized in that, The carbon matrix is ​​amorphous carbon, and the composite material is in the form of wrinkled nanosheets.

4. The iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 1, characterized in that, The Fe single atom has a mass fraction of 2%-13% in the composite material, and the Se single atom has a mass fraction of 5%-6% in the composite material.

5. The iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 1, characterized in that, The mass fraction of Fe single atoms in the composite material is 4%-6%.

6. A method for preparing an iron-selenium dual single-atom nitrogen-doped carbon-based composite material, characterized in that, The preparation method includes: S1, preparing Fe / Se / N-doped carbon-based precursors; S2, the Fe / Se / N doped carbon-based precursor is subjected to high-temperature carbonization to obtain the iron-selenium dual single-atom nitrogen-doped carbon-based composite material.

7. The method for preparing the iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 6, characterized in that, The S1 step includes the following: S11, melamine, L-alanine, selenium dioxide, ferric chloride and ZrO2 grinding media are mixed and ground until a uniform powder is formed to obtain a mixed powder; S12, add an ethanol-hydrochloric acid mixed solution with a volume ratio of 5:1-10:1 to the mixed powder, continue grinding until the ethanol evaporates completely, and obtain a sample; S13, the sample is placed in an oven and dried at 80-100℃ for 8-12 hours to obtain the Fe / Se / N doped carbon-based precursor.

8. The method for preparing the iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 6, characterized in that, Step S2 includes: The Fe / Se / N doped carbon-based precursor was placed in a tube furnace and heated to 550-600℃ at a heating rate of 5-10℃ / min, held for 2-4 hours, and then heated to 900-950℃ at a heating rate of 5-10℃ / min, held for 2-4 hours. The furnace was then cooled to obtain the iron-selenium double single-atom nitrogen-doped carbon-based composite material.

9. The method for preparing the iron-selenium dual single-atom nitrogen-doped carbon-based composite material according to claim 7, characterized in that, The mass ratio of the melamine, L-alanine, selenium dioxide, and ferric chloride is 12:3:6:(0.010-0.045).

10. The application of the iron-selenium double-single-atom nitrogen-doped carbon-based composite material according to any one of claims 1-5, or the iron-selenium double-single-atom nitrogen-doped carbon-based composite material prepared by the preparation method of any one of claims 6-9, as a negative electrode material for sodium-ion batteries.

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