Preparation method and application of self-supporting sodium ion battery negative electrode material

Abstract

The invention discloses a preparation method and application of a self-supporting sodium ion battery negative electrode material, and belongs to the technical field of sodium ion batteries. According to the method, firstly, cobalt / nitrogen-doped porous carbon modified carbon nanofibers are obtained through spinning and calcination, the cobalt / nitrogen-doped porous carbon modified carbon nanofibers serve as a framework, and then CoSe2-NC-coated CNF is obtained through selenylation. According to the preparation method, the synergistic effect of a multi-component and multi-stage structure is realized, and the specific capacity, the rate capability and the cycling stability of the sodium-ion battery negative electrode material are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for preparing a self-supporting sodium-ion battery anode material and its application. Background Technology

[0002] Lithium-ion batteries, as a novel energy storage device, have become a research hotspot due to their advantages such as high specific energy, low self-discharge rate, long lifespan, no memory effect, and environmental friendliness. They are currently widely used in portable electronic devices and electric vehicles. However, with the widespread application of lithium-ion batteries, insufficient lithium resource reserves have become a key bottleneck restricting their development. Sodium-ion batteries, on the other hand, have attracted considerable attention due to their high resource abundance and low raw material cost.

[0003] However, anode materials, as a key link limiting their industrialization, still face severe challenges: traditional hard carbon materials have low reversible specific capacity, and their small interlayer spacing is unsuitable for sodium ion insertion / extraction, making them unsuitable as anode materials for sodium-ion batteries. Therefore, developing anode materials that combine high capacity, long cycle life, and low cost remains crucial for the commercialization of sodium-ion batteries. Electrospinning technology offers advantages such as low cost, multifunctionality, and high controllability. The three-dimensional nanofiber network structure constructed using this technology can effectively alleviate the problem of severe volume expansion. Therefore, nitrogen-doped carbon-based composite materials designed based on electrospinning technology can significantly improve the overall electrochemical performance of materials, providing a new path to solve the key technological bottlenecks of sodium-ion battery anode materials.

[0004] Chinese patent document CN110416546A discloses a three-dimensional self-supporting sodium-ion anode material. This material is prepared by ZIF-8, electrospinning, and high-temperature carbonization to obtain a nitrogen-doped three-dimensional self-supporting carbon material. It requires no binder and the method is simple. Compared to ZIF-67, which contains cobalt ions (Co... 2+ ) Variable valence state (Co) 2+ / Co 3+ In electrochemical reactions, it can act as a catalytic active center, promoting the adsorption / desorption and conversion reactions of sodium ions and zinc ions (Zn). 2+ Lacking multivalent redox activity, its derived carbon, although possessing high specific surface area and nitrogen doping characteristics, cannot provide additional catalytic sites, resulting in ion transport relying on physical diffusion rather than electrochemical catalysis, which limits its application at high rates. Although the reversible discharge specific capacity reaches 385 mAh / g at a current density of 0.1 A / g in the examples, its capacity is still relatively low compared to other high-performance carbon-based anodes (such as some transition metal compound / carbon composite materials with capacities exceeding 500 mAh / g).

[0005] Chinese patent document CN115939341A discloses a cobalt disulfide / boron-nitrogen-sulfur co-doped porous carbon composite material. Its core involves preparing a composite precursor using a metal-organic framework (ZIF-67), a nitrogen-containing carbon source, a boron source, and a confined solvent. The target material is then obtained through carbonization and sulfidation treatments and applied to the anode of a sodium-ion battery. However, the uniformity of the boron-nitrogen-sulfur co-doping depends on the precursor mixing and heat treatment processes. Inhomogeneous doping can lead to uneven distribution of active sites, affecting electrochemical reaction kinetics. Furthermore, its pore structure relies on pyrolysis and volatilization, easily resulting in uneven pore size distribution and the failure to form a continuous conductive fiber network, thus limiting its effectiveness in mitigating volume expansion.

[0006] Chinese patent document publication number 118281220A discloses a self-supporting sodium-ion battery anode material, its preparation method, and its application. Using carbon fiber as a substrate, carbon nanotubes are grown via electrodeposition of cobalt compounds and chemical vapor deposition, followed by sulfidation-loaded CoS2 to form a self-supporting composite material. The CoS2 used in this method has a low intrinsic conductivity (1.63 × 10⁻⁵ S / cm). -5 This can easily lead to slow ion / electron transport kinetics during sodium storage, resulting in insufficient rate performance and weakened sodium storage advantages. The interfacial bonding between carbon fiber and carbon nanotube depends on the quality of CVD growth. If the bonding is not strong, CNTs will fall off from the carbon fiber surface, leading to loss of active materials. The particle dispersion and interfacial bonding are not as good as those of the MOF derivation method. Furthermore, the electron transport channel constructed using carbon fiber / carbon nanotube composite materials has low transport efficiency, which in turn results in poor electrochemical performance of the battery anode material. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a self-supporting sodium-ion battery anode material and its application. This preparation method is simple, can effectively alleviate the volume expansion problem, and significantly improves the specific capacity, rate performance and cycle stability of the sodium-ion battery anode material.

[0008] To achieve the above objectives, the technical solution of the present invention includes the following steps: (1) Mix the aqueous solutions of cobalt salt, hexadecyltrimethylammonium bromide and dimethylimidazole to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash and dry solid A to obtain ZIF-67 powder. (2) Add pore-forming agent, ZIF-67 powder and carbon source to N,N-dimethylformamide to obtain spinning solution, and obtain fiber mat by electrospinning the spinning solution; (3) After drying the fiber felt, it was calcined under a protective atmosphere to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place the cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of the tube furnace and place the selenium powder in the upstream. Calcinate them for the second time under a protective gas atmosphere to obtain cobalt diselenide-nitrogen-doped porous carbon modified carbon nanofiber materials, which are the self-supporting sodium-ion battery anode materials.

[0009] Preferably, in step (1), the cobalt salt is either cobalt acetate or cobalt nitrate, the molar ratio of hexadecyltrimethylammonium bromide to cobalt salt is 1:20-30, the concentration of the cobalt salt aqueous solution is 0.05-0.15 mol / L, the concentration of the dimethylimidazole aqueous solution is 0.5-1 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:10-30.

[0010] Preferably, in step (2), the pore-forming agent is at least one of polystyrene or polymethyl methacrylate; the carbon source is at least one of polyacrylonitrile, polyimide or polyvinyl alcohol; and the mass ratio of N,N-dimethylformamide, ZIF-67 powder, carbon source and pore-forming agent is 6-9:0.5-2:0.5-3:1.

[0011] Preferably, in step (3), the protective gas is argon or nitrogen, the heating rate is 2-4℃ / min, the calcination temperature is 500-600℃, and the calcination time is 8-10h.

[0012] Preferably, in step (4), the mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 1-3:1, the protective gas is argon or nitrogen, the heating rate is 1-2℃ / min, the secondary calcination temperature is 600-700℃, and the secondary calcination time is 10-14h.

[0013] The present invention also provides the application of the prepared self-supporting sodium-ion battery anode material, applying the self-supporting sodium-ion battery anode material to the anode of a sodium-ion battery.

[0014] The beneficial effects of this invention are as follows: 1. The self-supporting sodium-ion battery anode material prepared by the method of the present invention is prepared by directly adding ZIF-67 powder to the spinning solution to prepare cobalt / nitrogen-doped porous carbon modified carbon nanofibers (Co-NC@CNF), forming a highly composite structure in one step: this material can not only serve as a self-supporting framework, but also be used directly as an independent electrode without the need for additional binders and conductive additives, effectively reducing the content of inactive materials, thereby improving the electrode energy density. Its integrated continuous conductive network structure significantly promotes electron conduction, while simplifying the electrode preparation process.

[0015] 2. This invention adds a pore-forming agent to the spinning solution, and the resulting pore structure after spinning and calcination can play multiple optimization roles: First, the pores provide Na+ for the active material during charging and discharging. +The volume expansion space caused by embedding effectively suppresses particle breakage and electrode pulverization; secondly, the high porosity structure significantly increases the interfacial contact area between the electrode and the electrolyte, accelerating the interfacial charge transfer kinetics; simultaneously, the interconnected pore network can significantly shorten the Na... + The diffusion path reduces ion transport resistance and significantly improves the response speed and rate performance of the electrode at high current densities.

[0016] 3. This invention achieves multiple benefits by adding ZIF-67 to the spinning solution, followed by calcination and selenization to form cobalt-nitrogen-doped porous carbon (CoSe2-NC). First, the nitrogen-doped porous carbon derived from ZIF-67 possesses regular and controllable channels, providing pathways for electrolyte penetration and enhancing electrolyte permeation and ion transport. The continuous conductive network constructed with cobalt / nitrogen-doped porous carbon-modified carbon nanofibers significantly enhances conductivity, reduces internal resistance, and, combined with the hierarchical pore structure, shortens the sodium ion diffusion path, accelerating ion transport kinetics and thus optimizing rate performance. Second, the nitrogen atoms in the ZIF-67 ligand, after calcination, are embedded in the carbon framework in the form of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, forming a conductive network while introducing a large number of defect states. These polar sites enhance the absorption of sodium ions through the formation of a conductive network. + Adsorption enhances electron conduction rate and reduces charge transfer impedance, achieving an initial coulombic efficiency of approximately 90%.

[0017] 4. This invention forms uniformly sized CoSe2 nanoparticles during the selenization process, which are tightly embedded in a nitrogen-doped porous carbon matrix. This effectively avoids the aggregation problem of CoSe2 in traditional methods, significantly increases the exposed area of ​​active sites, and shortens the time required for Na... + Diffusion pathway; simultaneously, the multi-electron transfer reaction of CoSe2 (CoSe2 + 4Na) + + 4e - → Co + 2Na2Se), not only achieves a high theoretical capacity (500 mAh / g), but also improves the actual sodium storage efficiency through surface adsorption effect. Furthermore, the NC layer derived from ZIF-67 coats the CoSe2 particles to reserve expansion space, forming a synergistic buffer system with the mechanical support of Co-NC@CNF to suppress volume changes during charging and discharging; the three-dimensional multi-level structure constructed by the two has both high specific surface area (245.8 m² / g) and confinement effect, fundamentally preventing the pulverization of active materials and structural collapse, and ensuring long-term cycling stability.

[0018] 5. The self-supporting sodium-ion battery anode material (CoSe2-NC@CNF) prepared in this invention has a first-cycle discharge specific capacity of 900-905.14 mAh / g at a current density of 0.2 A / g, 600-609.1 mAh / g at a current density of 1 A / g, and 350-356 mAh / g at a current density of 5 A / g. After 100 cycles at a current density of 1 A / g, the specific capacity retention rate is 85%-87%. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope (SEM) image of the CoSe2-NC@CNF material in Example 1; Figure 2 The N1s spectrum of the CoSe2-NC@CNF material in Example 1 is shown (where the horizontal axis represents binding energy and the vertical axis represents intensity). Figure 3 The cycling curve of the CoSe2-NC@CNF material in Example 1 at 1 A / g; Figure 4 The cycling curves of the CoSe2-NC@CNF material in Example 1 at different magnifications are shown. Detailed Implementation

[0020] The present invention will be described in detail below through embodiments. Example 1

[0021] (1) 2.8 mmol cobalt nitrate and 0.093 mmol hexadecyltrimethylammonium bromide were dissolved in 20 mL of distilled water, and 0.042 mol dimethylimidazole was dissolved in 80 mL of distilled water. The two solutions were mixed and stirred at room temperature for 12 h to prepare suspension A. Suspension A was centrifuged to obtain solid A. Solid A was washed and dried at 80 °C for 8 h to obtain ZIF-67 powder. The molar ratio of hexadecyltrimethylammonium bromide to cobalt nitrate was 1:30, the concentration of cobalt nitrate aqueous solution was 0.14 mol / L, the concentration of dimethylimidazole aqueous solution was 0.525 mol / L, and the molar ratio of cobalt salt to dimethylimidazole was 1:15. (2) Add 1g ZIF-67 powder, 1g polyacrylonitrile and 1g polystyrene to 12g N,N-dimethylformamide to obtain a spinning solution. The spinning solution is then electrospun to obtain fiber mat. The mass ratio of N,N-dimethylformamide, ZIF-67 powder, polyacrylonitrile and polystyrene is 12:1:1:1. The voltage of electrospinning is 11kV, the pushing speed is 0.0015mm / s and the receiving distance is 13cm. (3) After drying the fiber felt at 60°C for 7 hours, it was calcined at 500°C for 9 hours under an argon atmosphere by increasing the temperature at 2°C / min to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place 2g of cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of a tube furnace and place 2g of selenium powder in the upstream. The mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 1:1. Calcinate the carbon nanofibers in a nitrogen atmosphere at a temperature of 700℃ for 10h and a heating rate of 2℃ / min. The cobalt-nitrogen diselenide-doped porous carbon modified carbon nanofiber material is obtained, which is the self-supporting sodium-ion battery anode material. Example 2

[0022] (1) Dissolve 2 mmol cobalt nitrate and 0.08 mmol hexadecyltrimethylammonium bromide in 20 mL of distilled water, and dissolve 60 mmol dimethylimidazole in 100 mL of distilled water. Mix the two solutions and stir at room temperature for 18 h to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash solid A and dry it at 60 °C for 12 h to obtain ZIF-67 powder. The molar ratio of hexadecyltrimethylammonium bromide to cobalt nitrate is 1:25, the concentration of cobalt nitrate aqueous solution is 0.1 mol / L, the concentration of dimethylimidazole aqueous solution is 0.6 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:30. (2) Add 1g ZIF-67 powder, 1g polyimide, 1g polystyrene and 1g polymethyl methacrylate to 20g N,N-dimethylformamide to obtain a spinning solution. Electrospin the spinning solution to obtain fiber mat. The mass ratio of N,N-dimethylformamide, ZIF-67 powder, polyimide, polystyrene and polymethyl methacrylate is 10:0.5:0.5:1. The voltage of electrospinning is 8kV, the pushing speed is 0.0015mm / s and the receiving distance is 12cm. (3) After drying the fiber felt at 80℃ for 7.5h, it was calcined at 600℃ for 10h under a nitrogen atmosphere by raising the temperature at 2℃ / min to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place 2g of cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of a tube furnace and place 4g of selenium powder in the upstream. The mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 2:1. Calcinate the carbon nanofibers in a nitrogen atmosphere at a temperature of 700℃ for 14h and a heating rate of 1℃ / min. The cobalt diselenide-nitrogen-doped porous carbon modified carbon nanofiber material is obtained, which is the self-supporting sodium-ion battery anode material. Example 3

[0023] (1) Dissolve 3 mmol cobalt acetate and 0.1 mmol hexadecyltrimethylammonium bromide in 20 mL of distilled water, and dissolve 30 mmol dimethylimidazole in 60 mL of distilled water. Mix the two solutions and stir at room temperature for 16 h to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash solid A and dry it at 75 °C for 9 h to obtain ZIF-67 powder. The molar ratio of hexadecyltrimethylammonium bromide to cobalt nitrate is 1:30, the concentration of cobalt acetate aqueous solution is 0.15 mol / L, the concentration of dimethylimidazole aqueous solution is 0.5 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:10. (2) Add 2g ZIF-67 powder, 1g polyvinyl alcohol, and 1g polymethyl methacrylate to 15g N,N-dimethylformamide to obtain a spinning solution. Then, use electrospinning to obtain fiber mat. The mass ratio of N,N-dimethylformamide, ZIF-67 powder, polyvinyl alcohol, and polymethyl methacrylate is 15:2:1:1. The voltage of electrospinning is 6kV, the pushing speed is 0.001mm / s, and the receiving distance is 16cm. (3) After drying the fiber felt at 75°C for 8 hours, it was calcined at 600°C at 4°C / min under an argon atmosphere for 8 hours to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place 1g of cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of a tube furnace and place 3g of selenium powder in the upstream. The mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 3:1. Calcinate the carbon nanofibers for the second time in an argon atmosphere at a temperature of 650℃ for 13h and a heating rate of 1℃ / min. The cobalt diselenide-nitrogen-doped porous carbon modified carbon nanofiber material is obtained, which is the self-supporting sodium-ion battery anode material. Example 4

[0024] (1) Dissolve 1 mmol cobalt acetate and 0.05 mmol hexadecyltrimethylammonium bromide in 20 mL of distilled water, and dissolve 20 mmol dimethylimidazole in 20 mL of distilled water. Mix the two solutions and stir at room temperature for 14 h to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash solid A and dry it at 70 °C for 10 h to obtain ZIF-67 powder. The molar ratio of hexadecyltrimethylammonium bromide to cobalt nitrate is 1:20, the concentration of cobalt acetate aqueous solution is 0.05 mol / L, the concentration of dimethylimidazole aqueous solution is 1 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:20. (2) Add 1g ZIF-67 powder, 1g polyvinyl alcohol, 2g polyacrylonitrile, and 1g polymethyl methacrylate to 15g N,N-dimethylformamide to obtain a spinning solution. Electrospin the spinning solution to obtain fiber mat. The mass ratio of N,N-dimethylformamide, ZIF-67 powder, polyvinyl alcohol, polyacrylonitrile, and polymethyl methacrylate is 15:1:3:1. The voltage of electrospinning is 9kV, the pushing speed is 0.002mm / s, and the receiving distance is 14cm. (3) After drying the fiber felt at 60°C for 6 hours, it was calcined at 550°C for 9 hours under an argon atmosphere by raising the temperature at 3°C / min to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place 2g of cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of a tube furnace and place 4g of selenium powder in the upstream. The mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 2:1. Calcinate the carbon nanofibers for the second time in an argon atmosphere at a temperature of 600℃ for 10h and a heating rate of 2℃ / min. The cobalt-nitrogen diselenide-doped porous carbon modified carbon nanofiber material is obtained, which is the self-supporting sodium-ion battery anode material. Comparative Example 1

[0025] (1) Dissolve 2 mmol cobalt acetate and 0.08 mmol hexadecyltrimethylammonium bromide in 20 mL of distilled water, and dissolve 60 mmol dimethylimidazole in 100 mL of distilled water. Mix the two solutions and stir at room temperature for 18 h to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash solid A and dry it at 60 °C for 12 h to obtain ZIF-67 powder. The molar ratio of hexadecyltrimethylammonium bromide to cobalt nitrate is 1:25, the concentration of cobalt nitrate aqueous solution is 0.1 mol / L, the concentration of dimethylimidazole aqueous solution is 0.6 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:30. (2) Add 1g ZIF-67 powder, 1g polyimide, 1g polystyrene and 1g polymethyl methacrylate to 20g N,N-dimethylformamide to obtain a spinning solution. Electrospin the spinning solution to obtain fiber mat. The mass ratio of N,N-dimethylformamide, ZIF-67 powder, polyimide, polystyrene and polymethyl methacrylate is 10:0.5:0.5:1. The voltage of electrospinning is 8kV, the pushing speed is 0.0015mm / s and the receiving distance is 12cm. (3) After drying the fiber felt at 80℃ for 7h, it was calcined at 600℃ for 10h under a nitrogen atmosphere by raising the temperature at 2℃ / min to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. Comparative Example 2

[0026] (1) Add 1g of polyvinyl alcohol, 2g of polyacrylonitrile, and 1g of polymethyl methacrylate to 15g of N,N-dimethylformamide to obtain a spinning solution. Then, use electrospinning to obtain fiber mat. The mass ratio of N,N-dimethylformamide, polyvinyl alcohol, polyacrylonitrile, and polymethyl methacrylate is 15:3:1. The voltage of electrospinning is 9kV, the pushing speed is 0.002mm / s, and the receiving distance is 14cm. (2) After drying the fiber felt at 60°C for 6 hours, it was calcined at 550°C for 9 hours under an argon atmosphere at a rate of 3°C / min to obtain porous carbon nanofibers. (3) Place 2g of porous carbon nanofibers in the downstream of a tube furnace and 4g of selenium powder in the upstream. The mass ratio of selenium powder to porous carbon nanofibers is 2:1. The furnace is calcined twice in an argon atmosphere at a temperature of 600℃ for 10 hours at a heating rate of 2℃ / min to obtain selenium-modified carbon nanofiber materials. Comparative Example 3

[0027] This comparative example spinning solution did not contain a pore-forming agent, and the remaining steps were the same as in Example 1. The resulting sample was a cobalt diselenide / selenium-nitrogen doped porous carbon-modified carbon nanofiber material, which is a self-supporting sodium-ion battery anode material. This material has few pores. Comparative Example 4

[0028] The calcination temperature of step (4) in this comparative example is 500℃, and the remaining steps are the same as in Example 1. The resulting sample is a cobalt diselenide / selenium-nitrogen doped porous carbon modified carbon nanofiber material, which is a self-supporting sodium-ion battery anode material. Comparative Example 5

[0029] The calcination temperature of step (4) in this comparative example is 800℃, and the remaining steps are the same as in Example 1. The obtained sample is a cobalt diselenide / cobalt-nitrogen doped porous carbon modified carbon nanofiber material, which is a self-supporting sodium-ion battery anode material.

[0030] Table 1 summarizes the electrochemical performance of Examples 1-4 and Comparative Examples 1-5, as follows:

[0031] Figure 1The SEM image of Example 1 shows that the CoSe2-NC@CNF material exhibits a multi-level composite structure. First, a three-dimensional cross-linked carbon nanofiber network is constructed through electrospinning and calcination. Second, the selenization process promotes the uniform anchoring of CoSe2-NC particles on the fiber surface and within the pores, forming abundant mesoporous / microporous hierarchical channels, which significantly improves electrolyte wetting efficiency and electron transport dynamics. The multi-level structure formed by the CNF skeleton and CoSe2-NC effectively suppresses volume deformation during charging and discharging. At the same time, the synergistic effect of the continuous conductive carbon fiber network and the porous structure endows the material with excellent mechanical stability and charge transfer capability, providing an ideal microstructure basis for its application in the field of sodium-ion batteries. Figure 2 The N1s spectrum can be divided into three peaks: pyridine-type N, pyrrole-type N, and graphitic N. This is achieved through polar site enhancement of Na. + Adsorption increases electron conduction rate and reduces charge transfer impedance.

[0032] The samples obtained from Examples 1-4 and Comparative Examples 1-5 were used as negative electrode materials and assembled into CR2035 coin cells. The entire process was carried out in an argon-filled glove box (H2O and O2 content below 0.01 ppm), and their electrochemical performance was tested at rates of 0.2-5 A / g. As shown in Table 1, the discharge specific capacities of Example 1 at 0.2, 0.5, 1, 2, and 5 A / g were 900.63, 694.78, 600.19, 420.36, and 350.25 mAh / g, respectively. Figure 3 The cycling curve for Example 1 at 1A / g shows that the discharge specific capacity in the first cycle is 602.32mAh / g, and it can still maintain 523.73mAh / g after 100 cycles, with a specific capacity retention rate of 86.95% and a coulombic efficiency of 99.85% in the first cycle. Figure 4 The cycling curves for Example 1 are shown in the range of 0.2-10 A / g. Thanks to its hierarchical structure and multi-component design, the material still achieves a discharge specific capacity of 204.5 mAh / g at a high rate of 10 A / g. Compared to Example 1, Comparative Example 1 lacks the selenization process, and Comparative Example 2 lacks the nitrogen-doped porous carbon component. Nitrogen-doped porous carbon materials, due to their high specific surface area and regularly ordered porous structure, enhance the absorption of Na+ through polar sites. +The adsorption of CoSe2 improves electrolyte wettability. CoSe2 achieves a high theoretical capacity (approximately 500 mAh / g) through a multi-electron transfer reaction. Simultaneously, the surface adsorption effect synergistically enhances the actual sodium storage efficiency. Therefore, the discharge specific capacity of the comparative example at 0.2 A / g is only 450.5 mAh / g and 480.98 mAh / g. Comparative example 3, without the addition of a pore-forming agent, has fewer pores in the prepared cobalt diselenide-nitrogen-doped porous carbon-modified carbon nanofiber material, which cannot provide sufficient volume expansion space for the active material. Therefore, the discharge specific capacity of comparative example 3 at a current density of 0.2 A / g is only 496.12 mAh / g. The specific capacity of the selenization process in Comparative Example 4 was 490.36 mAh / g. The selenization process in Comparative Example 5 was 700℃. The high temperature would damage the conductive network and structural support, and the selenium powder would escape in the form of vapor, resulting in insufficient selenium actually participating in the reaction. The specific capacity of the discharge was only 460.75 mAh / g at a current density of 0.2 A / g.

[0033] The above embodiments are intended to illustrate the essential content of the present invention, but are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of protection of the present invention.

Claims

1. A method for preparing a self-supporting sodium-ion battery anode material, characterized in that, Includes the following steps: (1) Mix the aqueous solutions of cobalt salt, hexadecyltrimethylammonium bromide and dimethylimidazole to prepare suspension A. Centrifuge suspension A to obtain solid A. Wash and dry solid A to obtain ZIF-67 powder. (2) Add pore-forming agent, ZIF-67 powder and carbon source to N,N-dimethylformamide to obtain spinning solution, and obtain fiber mat by electrospinning the spinning solution; (3) After drying the fiber felt, it was calcined under a protective atmosphere to obtain cobalt / nitrogen-doped porous carbon modified carbon nanofibers. (4) Place the cobalt / nitrogen-doped porous carbon modified carbon nanofibers in the downstream of the tube furnace and place the selenium powder in the upstream. Calcinate them for the second time under a protective gas atmosphere to obtain cobalt diselenide-nitrogen-doped porous carbon modified carbon nanofiber materials, which are the self-supporting sodium-ion battery anode materials.

2. The method for preparing the self-supporting sodium-ion battery anode material according to claim 1, characterized in that, In step (1), the cobalt salt is cobalt acetate or cobalt nitrate, the molar ratio of hexadecyltrimethylammonium bromide to cobalt salt is 1:20-30, the concentration of the cobalt salt aqueous solution is 0.05-0.15 mol / L, the concentration of the dimethylimidazole aqueous solution is 0.5-1 mol / L, and the molar ratio of cobalt salt to dimethylimidazole is 1:10-30.

3. The method for preparing the self-supporting sodium-ion battery anode material according to claim 1, characterized in that, In step (2), the pore-forming agent is at least one of polystyrene or polymethyl methacrylate; the carbon source is at least one of polyacrylonitrile, polyimide or polyvinyl alcohol; and the mass ratio of N,N-dimethylformamide, ZIF-67 powder, carbon source and pore-forming agent is 6-9:0.5-2:0.5-3:

1.

4. The method for preparing the self-supporting sodium-ion battery anode material according to claim 1, characterized in that, In step (3), the protective gas is argon or nitrogen, the heating rate is 1-2℃ / min, the calcination temperature is 500-600℃, and the calcination time is 8-12h.

5. The method for preparing the self-supporting sodium-ion battery anode material according to claim 1, characterized in that, In step (4), the mass ratio of selenium powder to cobalt / nitrogen-doped porous carbon modified carbon nanofibers is 1-3:1, the protective gas is argon or nitrogen, the heating rate is 1-3℃ / min, the secondary calcination temperature is 600-700℃, and the secondary calcination time is 10-14h.

6. The application of a self-supporting sodium-ion battery anode material prepared by the method described in any one of claims 1-5, characterized in that, The self-supporting sodium-ion battery anode material described above is applied to the anode of a sodium-ion battery.

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