Spore-like cobalt diselenide composite porous carbon nanofiber material as well as preparation method and application thereof

Abstract

The invention discloses a spore-like cobalt diselenide composite porous carbon nanofiber material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery electrode materials. A preparation method of a spore-like cobalt diselenide composite porous carbon nanofiber material comprises the following steps: performing electrostatic spinning on a spinning solution containing a cobalt source to obtain cobalt-containing nanofibers; the cobalt-containing nanofiber is subjected to pre-oxidation and calcination treatment, and cobalt-containing nitrogen-doped nanofiber is obtained; and performing high-temperature chemical vapor deposition treatment on the mixture of the cobalt-containing nitrogen-doped nanofiber and selenium powder to obtain the spore-like cobalt diselenide composite porous carbon nanofiber material. According to the preparation method disclosed by the invention, the structure of the finally prepared composite porous carbon nanofiber material is adjusted by controlling the addition amount of the selenium powder, the reaction temperature and the addition mode of the cobalt diselenide particles; the spore-like cobalt diselenide composite porous carbon nanofiber material prepared by the invention can significantly increase the contact area between an active material and an electrolyte, reduce ion diffusion paths and improve charge transfer efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery electrode materials, and in particular relates to a spore-shaped cobalt diselenide composite porous carbon nanofiber material and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasing depletion of fossil energy, the development and utilization of renewable and clean energy has become a hot topic. Efficient and flexible electrochemical energy storage technologies have therefore emerged as a research focus. Among these, lithium-ion batteries (LIBs) have been widely commercialized due to their advantages, such as high voltage (approximately 3.6V), lack of memory effect, and long cycle life. However, the relatively scarce and uneven distribution of lithium resources in the Earth's crust, coupled with the increasing demand for LIBs, has led to a gradual increase in their cost, which has, to some extent, hindered their further application.

[0003] Therefore, there is an urgent need to develop new battery energy storage products to replace LIBs and meet the growing energy demand. Sodium-ion batteries (SIBs) share similar reaction principles with lithium-ion batteries (LIBs). Furthermore, sodium resources are abundant, inexpensive, and highly safe. Therefore, they have been widely studied and show potential as a replacement for LIBs.

[0004] However, the radius of sodium ions is larger than that of lithium ions, which results in a lower ion transfer rate during the charge and discharge process. It also causes a significant volume expansion of the electrode material, which in turn leads to the shedding or even collapse of the electrode material, resulting in the capacity decay of SIBs. Summary of the Invention

[0005] In response to the current technical problem that active substances are embedded in carbon fiber materials, the exposed area of the active substances is low and the ion transfer rate is slow, thus affecting the charge and discharge performance of sodium ion batteries, the present invention proposes a spore-shaped cobalt diselenide composite porous carbon nanofiber material and its preparation method and application. Its "surface-interior" dual active site distribution reduces the ion diffusion path and increases the exposed area of the active substances. The stable anchoring of the carbon fiber matrix avoids particle agglomeration or shedding, improves the charge transfer efficiency, and further improves the electrochemical performance and stability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0009] electrospinning a spinning solution containing a cobalt source to obtain cobalt-containing nanofibers;

[0010] pre-oxidizing and calcining the cobalt-containing nanofibers to obtain cobalt-containing nitrogen-doped nanofibers;

[0011] The mixture of the cobalt-containing nitrogen-doped nanofibers and selenium powder is subjected to high-temperature chemical vapor deposition treatment to obtain the spore-shaped cobalt diselenide composite porous carbon nanofiber material.

[0012] Beneficial effects: The preparation method of the spore-shaped cobalt diselenide composite porous carbon nanofiber provided by the present invention can adjust the growth mode of cobalt diselenide nanoparticles according to actual application conditions. That is, the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared by the method of the present invention has a shorter ion diffusion path and a higher active material exposure area. In addition, the stable anchoring of the porous carbon fiber matrix avoids particle agglomeration or shedding, improves the charge transfer efficiency, and further improves the electrochemical performance. Furthermore, when the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared by the present invention is applied to the negative electrode material of sodium ion batteries, it can show good cycle stability.

[0013] Optionally, the spinning solution is obtained by mixing a cobalt source, polyacrylonitrile, a template and an organic solvent.

[0014] Furthermore, the cobalt source is cobalt acetate tetrahydrate; the template is polymethyl methacrylate; and the organic solvent is N,N-dimethylformamide.

[0015] Optionally, the mass ratio of the cobalt source, polyacrylonitrile and template agent is 1 to 3:1 to 3:1;

[0016] The mass ratio of the cobalt-containing nitrogen-doped nanofibers to the selenium powder is 1:1-3.

[0017] Beneficial Effects: In the present invention, the mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate is 1-3:1-3:1. Cobalt acetate tetrahydrate provides a cobalt source, polyacrylonitrile, as a spinning raw material, provides carbon and nitrogen, polymethyl methacrylate acts as a pore-forming agent, and selenium powder, as a selenium source, provides selenium to promote the selenization reaction. Insufficient reaction temperature or too little selenium powder can result in incomplete selenization, producing defective selenides. Excessive temperature or excessive selenium can cause elemental volatilization or stoichiometric imbalance.

[0018] Optionally, the electrospinning conditions are: temperature of 20°C to 40°C, humidity of 40% to 60%, inner diameter of the electrospinning needle of 0.21mm to 1.07mm, collection distance of 10cm to 25cm, voltage of 16kV to 25kV, and propulsion speed of 0.5mL / h to 1.5mL / h.

[0019] Beneficial Effects: To produce nanofibers of uniform size and similar properties, the electrospinning conditions are as follows: temperature of 20°C to 40°C, humidity of 40% to 60%, an electrospinning needle inner diameter of 0.21mm to 1.07mm, a collection distance of 10cm to 25cm, a voltage of 16kV to 25kV, and a propulsion speed of 0.5mL / h to 1.5mL / h. These are the required environmental conditions for spinning; if these conditions are not within these ranges, spinning will fail. Temperature and humidity affect the fiber's stretchability and toughness. Excessively high temperatures and low humidity lead to premature solvent evaporation during spinning; excessively low temperatures and high humidity prevent solvent evaporation during spinning, resulting in no polymerized fibers. Needle diameter, voltage, collection distance, and propulsion speed are the key spinning process parameters. Higher voltage results in smaller fiber diameters, while longer spray distances result in larger fiber diameters. The needle inner diameter determines the velocity and atomization of droplets ejected from the needle. A smaller inner diameter produces finer fibers but is more prone to clogging.

[0020] Optionally, the pre-oxidation and calcination conditions are: pre-oxidation in air at 200° C. to 250° C. for 2 hours, then heating to 500° C. to 1000° C., and calcining in a protective atmosphere for 2 hours to 5 hours.

[0021] Furthermore, the heating rate during the heating process is 1°C / min to 5°C / min.

[0022] Furthermore, the pre-oxidation and calcination conditions are: pre-oxidation at 200° C. in air for 2 h, then heating to 800° C. in a protective atmosphere at a heating rate of 5° C. / min, and then calcining at this temperature for 4 h.

[0023] Optionally, the high temperature chemical vapor deposition process is: heating the mixture to 300° C. to 600° C., and selenizing (calcining) the mixture at this temperature for 2 h to 5 h.

[0024] The second technical solution of the present invention:

[0025] A spore-shaped cobalt diselenide composite porous carbon nanofiber material is prepared by the above preparation method.

[0026] Beneficial effects: The cobalt diselenide composite porous carbon nanofiber material prepared by the above preparation method has a spore-like structure. In this structure, on the one hand, the "surface-interior" dual active site distribution reduces the ion diffusion path; on the other hand, the stable anchoring of the carbon fiber matrix avoids particle agglomeration or shedding, thereby jointly improving the charge transfer efficiency.

[0027] The third technical solution of the present invention:

[0028] Application of the above-mentioned spore-shaped cobalt diselenide composite porous carbon nanofiber material in the preparation of sodium ion battery negative electrode materials.

[0029] Optionally, the preparation process of the sodium ion battery negative electrode material is:

[0030] The spore-shaped cobalt diselenide composite porous carbon nanofiber material, conductive carbon black, and binder (polyvinylidene fluoride) were mixed, N-methylpyrrolidone was added, ground, and coated on copper foil, dried, and cut to obtain an electrode sheet with a diameter of 16 mm and a thickness of 0.1 mm.

[0031] Furthermore, the mass ratio of the spore-shaped cobalt diselenide composite porous carbon nanofiber material, the conductive carbon black, and the binder is 7 to 8:1 to 2:1.

[0032] The fourth technical solution of the present invention:

[0033] A sodium ion battery, wherein the negative electrode material is the spore-shaped cobalt diselenide composite porous carbon nanofiber material.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] The present invention provides a spore-shaped cobalt diselenide composite porous carbon nanofiber material and a preparation method and application thereof. According to the present invention, cobalt acetate tetrahydrate is used as a cobalt source, polyacrylonitrile is used as a spinning raw material, and polymethyl methacrylate is used as a template for a pore structure. The materials are dispersed in a spinning solution and spun to obtain cobalt-containing nanofibers. The nanofibers are pre-oxidized and calcined to obtain nitrogen-doped carbon fibers. Selenium powder is then subjected to high-temperature chemical vapor deposition treatment to obtain the spore-shaped cobalt diselenide composite porous carbon fiber material.

[0036] The present invention adjusts the structure of the composite material by controlling the growth mode of cobalt diselenide particles, and uses pre-oxidation and calcination to convert the polymer fibers obtained by electrospinning into carbon fibers, thereby improving the mechanical strength and stability of the fibers; wherein, pre-oxidation partially oxidizes the cobalt, hydrogen, oxygen and nitrogen elements in the polymer fibers to form oxides with a high oxygen content, thereby reducing the amount of gas released during fiber carbonization, reducing the internal stress and thermal shrinkage of the fibers during fiber carbonization, and improving carbonization efficiency. The pre-oxidized polymer fibers are then pyrolyzed into carbon fibers at high temperatures after carbonization (calcination). Then, by selenization, the cobalt ions and cobalt-containing oxides in the nanofibers are converted into cobalt diselenide nanoparticles embedded in the interior and surface of the fibers, thereby enabling the active substances to participate in the reaction faster. Compared with nano-carbon fibers grown with cobalt diselenide outside situ, the spore-shaped cobalt diselenide composite porous carbon nanofiber material of the present invention can significantly increase the contact area between the active material and the electrolyte, reduce the ion diffusion path, and improve the charge transfer efficiency. In addition, the stable anchoring of the carbon fiber matrix avoids particle agglomeration or shedding, further improving the electrochemical performance and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 This is a SEM image of the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention;

[0039] Figure 2 This is a TEM image of the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention;

[0040] Figure 3 This is an SEM image of the cobalt diselenide composite porous carbon nanofiber material prepared in Comparative Example 1;

[0041] Figure 4 TEM image of the cobalt diselenide composite porous carbon nanofiber material prepared in Comparative Example 1;

[0042] Figure 5 The sodium ion battery prepared by using the cobalt diselenide composite porous carbon nanofiber material prepared in Examples 1 to 4 and Comparative Examples 1 to 2 as the electrode material is -1 Cyclic comparison diagram under current density of ;

[0043] Figure 6 This is a comparison chart of the rate performance of sodium ion batteries prepared using the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 as electrode materials;

[0044] Figure 7 The electrochemical impedance spectroscopy graphs of the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 3 and Comparative Example 1;

[0045] Figure 8 The Warburg impedance slope graphs of the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 3 and Comparative Example 1;

[0046] Figure 9 This is a graph of sodium ion diffusion coefficients obtained during a single discharge process of the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 3 and Comparative Example 1 by electrochemical static intermittent titration technology;

[0047] Figure 10 This is a sodium ion diffusion coefficient diagram obtained during a single charge process of the cobalt diselenide composite porous carbon nanofiber material prepared in Examples 1 to 3 and Comparative Example 1 by electrochemical static intermittent titration technology. DETAILED DESCRIPTION

[0048] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0049] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0050] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0051] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0052] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0053] The embodiment of the present invention discloses a method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material, comprising the following steps:

[0054] Cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate are dissolved in N,N-dimethylformamide, stirred at 30°C to 60°C to obtain a spinning solution, and the spinning solution is electrospun to obtain cobalt-containing nanofibers;

[0055] The cobalt-containing nanofibers are pre-oxidized in air at 200°C to 250°C, and then heated to 500°C to 1000°C and calcined under a protective atmosphere to decompose the polymethyl methacrylate in the cobalt-containing nanofibers to obtain cobalt-containing nitrogen-doped nanofibers.

[0056] Cobalt-containing nitrogen-doped nanofibers are mixed with selenium powder, heated to 300°C to 600°C, and selenized under a protective atmosphere, that is, through high-temperature chemical vapor deposition treatment, spore-shaped cobalt diselenide composite porous carbon fiber materials are obtained.

[0057] In some optional embodiments, the mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 1-3:1-3:1.

[0058] In some optional embodiments, the mass ratio of selenium powder to cobalt-containing nitrogen-doped nanofibers is 1-3:1.

[0059] In some optional embodiments, the stirring time is 6 hours to 24 hours.

[0060] In some optional embodiments, the conditions for electrospinning are: temperature of 20°C to 40°C, humidity of 40% to 60%, inner diameter of the electrospinning needle of 0.21mm to 1.07mm, collection distance of 10cm to 25cm, voltage of 16kV to 25kV, and propulsion speed of 0.5mL / h to 1.5mL / h.

[0061] In some optional embodiments, the pre-oxidation time is 2 hours; the calcination time is 2 hours to 5 hours; and the selenization time is 2 hours to 5 hours.

[0062] In some optional embodiments, the heating rate is 1° C. / min to 5° C. / min.

[0063] The present invention discloses a spore-shaped cobalt diselenide composite porous carbon fiber material prepared by the above-mentioned preparation method; and application of the spore-shaped cobalt diselenide composite porous carbon fiber material in preparing a negative electrode material for a sodium ion battery.

[0064] In addition, the present invention also discloses a sodium ion battery negative electrode material, the preparation process of which is as follows:

[0065] The spore-shaped cobalt diselenide composite porous carbon fiber material, conductive carbon black, and binder (polyvinylidene fluoride) were mixed, N-methylpyrrolidone was added, ground, and coated on copper foil, dried, and cut to obtain an electrode sheet with a diameter of 16 mm and a thickness of 0.1 mm.

[0066] In some optional embodiments, the mass ratio of the spore-shaped cobalt diselenide composite porous carbon fiber material, the conductive carbon black, and the polyvinylidene fluoride is 7 to 8:1 to 2:1.

[0067] Unless otherwise specified, the "room temperature" in the present invention refers to 20-30°C.

[0068] The raw materials used in the present invention are all purchased from the market.

[0069] The technical solution of the present invention is further illustrated by the following examples.

[0070] Example 1

[0071] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0072] (1) Cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a spinning solution;

[0073] The mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 2:3:1;

[0074] (2) electrospinning the spinning solution of step (1) under the following conditions: temperature of 25° C., humidity of 55%, inner diameter of electrospinning needle of 0.6 mm, collection distance of 15 cm, voltage of 18 kV, and propulsion speed of 1 mL / h to obtain electrospun nanofibers;

[0075] (3) pre-oxidizing (carbonizing) and calcining the electrospun nanofibers of step (2) to obtain cobalt-containing nitrogen-doped nanofibers;

[0076] The pre-oxidation (carbonization) and calcination process is as follows: first, pre-oxidation at 200°C in air for 2 hours, then heating to 800°C at a heating rate of 5°C / min in a protective atmosphere, calcining at this temperature for 4 hours, and cooling to room temperature;

[0077] (4) selenizing the cobalt-containing nitrogen-doped nanofibers obtained in step (3) by high-temperature chemical vapor deposition, and then cooling and grinding to obtain a spore-shaped cobalt diselenide composite porous carbon nanofiber material;

[0078] The selenization process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 3:1, heated to 500°C at a heating rate of 5°C / min in a protective atmosphere, then calcined for 4 hours and cooled to room temperature.

[0079] Example 2

[0080] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0081] (1) Cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a spinning solution;

[0082] The mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 2:3:1;

[0083] (2) The spinning solution of step (1) was subjected to electrospinning under the following conditions: temperature of 25°C, humidity of 55%, inner diameter of electrospinning needle of 0.5 mm, collection distance of 17 cm, voltage of 20 kV, propulsion speed of 1.3 mL / h, to obtain electrospun nanofibers.

[0084] (3) pre-oxidizing (carbonizing) and calcining the electrospun nanofibers of step (2) to obtain cobalt-containing nitrogen-doped nanofibers;

[0085] The pre-oxidation (carbonization) and calcination process is as follows: first, pre-oxidation at 250°C in air for 2 hours, then heating to 700°C at a heating rate of 3°C / min in a protective atmosphere, calcining at this temperature for 3 hours, and cooling to room temperature;

[0086] (4) selenizing the cobalt-containing nitrogen-doped nanofibers obtained in step (3) by high-temperature chemical vapor deposition, and then cooling and grinding to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0087] The selenization process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 2:1, heated to 500°C at a heating rate of 3°C / min in a protective atmosphere, then calcined for 3 hours and cooled to room temperature.

[0088] Example 3

[0089] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0090] (1) Cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a spinning solution;

[0091] The mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 2:3:1;

[0092] (2) electrospinning the spinning solution of step (1) under the following conditions: temperature of 25° C., humidity of 55%, inner diameter of electrospinning needle of 0.67 mm, collection distance of 15 cm, voltage of 17 kV, and propulsion speed of 1.5 mL / h to obtain electrospun nanofibers;

[0093] (3) pre-oxidizing (carbonizing) and calcining the electrospun nanofibers of step (2) to obtain cobalt-containing nitrogen-doped nanofibers;

[0094] The pre-oxidation (carbonization) and calcination process is as follows: first, pre-oxidation at 250°C in air for 2 hours, then heating to 600°C at a heating rate of 3°C / min in a protective atmosphere, calcining at this temperature for 5 hours, and cooling to room temperature;

[0095] (4) selenizing the cobalt-containing nitrogen-doped nanofibers obtained in step (3) by high-temperature chemical vapor deposition, and then cooling and grinding to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0096] The selenization process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 1:1, heated to 400°C at a heating rate of 3°C / min in a protective atmosphere, then calcined for 3 hours and cooled to room temperature.

[0097] Example 4

[0098] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0099] (1) Cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a spinning solution;

[0100] The mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 2:3:1;

[0101] (2) electrospinning the spinning solution of step (1) under the following conditions: temperature of 25° C., humidity of 55%, inner diameter of electrospinning needle of 0.4 mm, collection distance of 20 cm, voltage of 25 kV, and propulsion speed of 1.7 mL / h to obtain electrospun nanofibers;

[0102] (3) pre-oxidizing (carbonizing) and calcining the electrospun nanofibers of step (2) to obtain cobalt-containing nitrogen-doped nanofibers;

[0103] The pre-oxidation (carbonization) and calcination process is as follows: first, pre-oxidation at 250°C in air for 2 hours, then heating to 900°C at a heating rate of 5°C / min in a protective atmosphere, calcining at this temperature for 4 hours, and cooling to room temperature;

[0104] (4) selenizing the cobalt-containing nitrogen-doped nanofibers obtained in step (3) by high-temperature chemical vapor deposition, and then cooling and grinding to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0105] The selenization process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 2:1, heated to 400°C at a heating rate of 5°C / min in a protective atmosphere, then calcined for 4 hours and cooled to room temperature.

[0106] Example 5

[0107] A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0108] (1) Cobalt acetate tetrahydrate, polyacrylonitrile, and polymethyl methacrylate were dissolved in N,N-dimethylformamide and stirred at 60°C for 12 hours to obtain a spinning solution;

[0109] The mass ratio of cobalt acetate tetrahydrate, polyacrylonitrile and polymethyl methacrylate is 2:3:1;

[0110] (2) electrospinning the spinning solution of step (1) under the following conditions: temperature of 25° C., humidity of 55%, inner diameter of electrospinning needle of 0.67 mm, collection distance of 15 cm, voltage of 18 kV, and propulsion speed of 1 mL / h to obtain electrospun nanofibers;

[0111] (3) pre-oxidizing (carbonizing) and calcining the electrospun nanofibers of step (2) to obtain cobalt-containing nitrogen-doped nanofibers;

[0112] The pre-oxidation (carbonization) and calcination process is as follows: first, pre-oxidation at 200°C in air for 2 hours, then heating to 800°C at a heating rate of 5°C / min in a protective atmosphere, calcining at this temperature for 2 hours, and cooling to room temperature;

[0113] (4) selenizing the cobalt-containing nitrogen-doped nanofibers obtained in step (3) by high-temperature chemical vapor deposition, followed by cooling and grinding to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0114] The selenization process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 3:1, heated to 400°C at a heating rate of 5°C / min in a protective atmosphere, then calcined for 4 hours and cooled to room temperature.

[0115] Comparative Example 1

[0116] A method for preparing a cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0117] (1) Calcinate cobalt acetate tetrahydrate in air at 500°C for 4 h to obtain Co3O4;

[0118] (2) dissolving the Co3O4, polyacrylonitrile and polymethyl methacrylate obtained in step (1) in N,N'-dimethylformamide and mixing to obtain a spinning solution;

[0119] Among them, the mass ratio of Co3O4, polyacrylonitrile and polymethyl methacrylate is 2:3:1, the stirring temperature is 60℃, and the stirring time is 12h.

[0120] (3) electrospinning the spinning solution of step (2) at a temperature of 25° C., a humidity of 55%, an electrospinning needle inner diameter of 1 mm, a collection distance of 15 cm, a voltage of 18 kV, and a propulsion speed of 1 mL / h to obtain electrospun nanofibers;

[0121] (4) carbonizing and calcining the electrospun nanofibers obtained in step (3) to obtain nitrogen-doped nanofibers containing Co3O4;

[0122] The carbonization and calcination process is as follows: first, pre-oxidation at 250 °C in air for 2 h, heating to 800 °C at a heating rate of 5 °C / min in a protective atmosphere, calcination for 4 h, and cooling to room temperature;

[0123] (5) selenizing and calcining the nitrogen-doped nanofibers containing Co3O4 in step (4), cooling and grinding the nanofibers to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0124] The selenization and calcination process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 3:1, heated to 500°C at a heating rate of 5°C / min in a protective atmosphere, calcined for 4 hours, and cooled to room temperature.

[0125] Comparative Example 2

[0126] A method for preparing a cobalt diselenide composite porous carbon nanofiber material comprises the following steps:

[0127] (1) 0.3 g of cobalt nitrate hexahydrate was added to 10 mL of deionized water and mixed uniformly by ultrasonication at room temperature for 10 minutes to obtain solution A; 4.54 g of 2-methylimidazole was added to 70 mL of deionized water and mixed uniformly by ultrasonication at room temperature for 10 minutes to obtain solution B;

[0128] (2) Solution A was slowly added dropwise to solution B under stirring and aged at room temperature for 24 h. The aged solution was centrifuged with deionized water at a speed of 8000 rpm for 5 min per centrifugation. The product was dried at 65°C for 24 h to obtain ZIF-67.

[0129] (3) dissolving the ZIF-67, polyacrylonitrile and polymethyl methacrylate obtained in step (2) in N,N'-dimethylformamide and mixing to obtain a spinning solution;

[0130] The mass ratio of ZIF-67, polyacrylonitrile and polymethyl methacrylate was 2:3:1, the stirring temperature was 60 °C, and the stirring time was 12 h.

[0131] (4) electrospinning the spinning solution of step (3) at a temperature of 25° C., a humidity of 55%, an electrospinning needle inner diameter of 0.67 mm, a collection distance of 15 cm, a voltage of 18 kV, and a propulsion speed of 1 mL / h to obtain electrospun nanofibers;

[0132] (5) carbonizing and calcining the electrospun nanofibers obtained in step (4) to obtain nitrogen-doped nanofibers containing ZIF-67;

[0133] The carbonization and calcination process is as follows: first, pre-oxidation at 200 °C in air for 2 h, then heating to 800 °C at a heating rate of 3 °C / min in a protective atmosphere, calcining for 4 h, and cooling to room temperature;

[0134] (6) selenizing and calcining the nitrogen-doped nanofibers containing ZIF-67 in step (5), cooling and grinding the nanofibers to obtain a cobalt diselenide composite porous carbon nanofiber material;

[0135] The selenization and calcination process is as follows: selenium powder is mixed with cobalt-containing nitrogen-doped nanofibers in a mass ratio of 3:1, heated to 500°C at a heating rate of 5°C / min in a protective atmosphere, calcined for 4 hours, and cooled to room temperature.

[0136] Effect verification

[0137] 1. Microstructure Characterization

[0138] The morphology of the cobalt diselenide composite porous carbon nanofiber materials prepared in Example 1 and Comparative Example 1 was characterized.

[0139] Figure 1 This is a SEM image of the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention;

[0140] Figure 2 This is a TEM image of the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention.

[0141] Depend on Figure 1 、 Figure 2 It can be seen that the cobalt diselenide composite porous carbon nanofibers prepared in the present invention have a three-dimensional spore-like structure, and nanoparticles are inlaid and distributed on the surface and inside.

[0142] Figure 3 This is an SEM image of the cobalt diselenide composite porous carbon nanofiber material prepared in Comparative Example 1;

[0143] Figure 4 This is the TEM image of the cobalt diselenide composite porous carbon nanofiber material prepared in Comparative Example 1.

[0144] Depend on Figure 3 and Figure 4 It can be seen that the cobalt diselenide active substance in the non-in-situ grown cobalt diselenide composite porous carbon nanofibers prepared in Comparative Example 1 is embedded in the interior of the carbon fibers.

[0145] 2. Electrochemical Effect

[0146] The cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were respectively made into working electrodes. The specific preparation process is as follows:

[0147] The cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were respectively mixed with conductive carbon black and binder polyvinylidene fluoride in a mass ratio of 8:1:1, and N-methylpyrrolidone solvent was added and fully ground. The mixture was evenly coated on a copper foil, and finally dried at 60°C and cut into electrode sheets with a diameter of 16 mm to obtain a working electrode.

[0148] Preparation of sodium ion battery: Sodium sheet as positive electrode, glass fiber separator, 1 mol / L NaPF6 electrolyte, and porous carbon fiber electrode sheet as negative electrode are assembled into button batteries in a glove box.

[0149] Among them, the ratio of sodium hexafluorophosphate electrolyte is: NaPF6 is dissolved in an organic solvent with a volume ratio of EC:PC:FEC of 47.5:47.5:5 and the concentration is 1 mol / L.

[0150] The performance of the sodium ion battery obtained above was tested.

[0151] Figure 5 The sodium ion battery prepared by using the cobalt diselenide composite porous carbon nanofiber material prepared in Examples 1 to 4 and Comparative Examples 1 to 2 as the electrode material is -1 Cyclic comparison diagram under current density of Figure 5 As shown, at a current density of 1 A / g, after 700 cycles, the specific capacity of Example 1 is 232 mAh g -1 The specific capacity of Example 2 is 142 mAh g -1 The specific capacity of Example 3 is 98 mAh g -1 The specific capacity of Example 4 is 194 mAh g -1 The specific capacity of comparative example 1 is 69 mAh g -1 The specific capacity of comparative example 2 is 54 mAh g -1 That is, the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention can significantly increase the contact area between the active material and the electrolyte, reduce the ion diffusion path, improve the charge transfer efficiency, and improve the electrochemical performance of the sodium ion battery.

[0152] Figure 6The figure is a comparison chart of the rate performance of sodium ion batteries prepared using the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 as electrode materials. Figure 6 It can be seen that after 10 cycles at different current densities, when the current density returns to 100 mAh g -1 The specific capacity of Example 1 is 306 mAh g -1 The specific capacity of Example 2 is 283 mAh g -1 The specific capacity of Example 3 is 258 mAh g -1 The specific capacity of Example 4 is 290 mAh g -1 The specific capacity of comparative example 1 is 176 mAh g -1 The specific capacity of comparative example 2 is 107 mAh g -1 , which proved that the spore-shaped cobalt diselenide composite porous carbon nanofibers have good rate performance.

[0153] Figure 7 The electrochemical impedance spectroscopy of the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1 to 3 and Comparative Example 1 is shown. -1 After circulating 100 times at a current density of , the electrochemical impedance spectrum obtained by EIS test using an electrochemical workstation is shown; the specific resistance value is obtained by fitting using the "ZView" software, or by observing the diameter of the semicircle in the figure. Among them, the charge transfer resistance of the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention is only 59.9Ω, the resistance of Example 2 is 105.8Ω, the resistance of Example 3 is 122.5Ω, and the resistance of Comparative Example 1 is 136.6Ω.

[0154] Figure 8 The Warburg impedance slope diagram of the cobalt diselenide composite porous carbon nanofiber material prepared in Examples 1 to 3 and Comparative Example 1. The larger the slope, the greater the ion diffusion resistance. Figure 8 It can be seen that the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention has the lowest slope and the highest ion transmission efficiency.

[0155] Figure 9 and Figure 10This graph shows the sodium ion diffusion coefficients of the cobalt diselenide composite porous carbon nanofiber materials prepared in Examples 1-3 and Comparative Example 1 during a single charge-discharge cycle, obtained using electrochemical static intermittent titration. The graph shows that the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared in Example 1 of the present invention has the highest sodium ion diffusion coefficient throughout the entire cycle, consistent with the results of EIS analysis. Therefore, all observations confirm that the spore-shaped cobalt diselenide composite porous carbon nanofibers prepared in the present invention possess fast reaction kinetics and rapid charging capability.

[0156] In summary, the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared by the present invention creates a synergistic interface by allowing cobalt diselenide nanoparticles to grow in situ inside and on the surface of the nanofibers, reducing the charge transfer resistance and improving the ion diffusion efficiency. The stable anchoring of the porous carbon fiber matrix prevents particle agglomeration or shedding, improves the charge transfer efficiency, and further improves the electrochemical performance. In addition, when the spore-shaped cobalt diselenide composite porous carbon nanofiber material prepared by the present invention is applied to the negative electrode material of sodium ion batteries, it exhibits good cycle stability.

[0157] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material, characterized in that: The following steps are involved: electrospinning a spinning solution containing a cobalt source to obtain cobalt-containing nanofibers; pre-oxidizing and calcining the cobalt-containing nanofibers to obtain cobalt-containing nitrogen-doped nanofibers; The mixture of the cobalt-containing nitrogen-doped nanofibers and selenium powder is subjected to high-temperature chemical vapor deposition treatment to obtain the spore-shaped cobalt diselenide composite porous carbon nanofiber material.

2. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 1, characterized in that: The spinning solution is obtained by mixing a cobalt source, polyacrylonitrile, a template agent and an organic solvent.

3. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 2, characterized in that: The cobalt source is cobalt acetate tetrahydrate; The template is polymethyl methacrylate; The organic solvent is N,N-dimethylformamide.

4. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 2, characterized in that: The mass ratio of the cobalt source, polyacrylonitrile and template is (1-3): (1-3): 1; The mass ratio of the cobalt-containing nitrogen-doped nanofibers to the selenium powder is 1:(1-3).

5. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 1, characterized in that: The electrospinning conditions are as follows: temperature of 20°C to 40°C, humidity of 40% to 60%, inner diameter of the electrospinning needle of 0.21mm to 1.07mm, collection distance of 10cm to 25cm, voltage of 16kV to 25kV, and propulsion speed of 0.5mL / h to 1.5mL / h.

6. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 1, characterized in that: The conditions of the pre-oxidation and calcination treatment are: pre-oxidation in air at 200° C. to 250° C. for 2 hours, then heating to 500° C. to 1000° C., and calcination in a protective atmosphere for 2 hours to 5 hours.

7. The method for preparing a spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 1, characterized in that: The high temperature chemical vapor deposition process is as follows: heating the mixture to 300° C. to 600° C. and selenizing at this temperature for 2 hours to 5 hours.

8. A spore-shaped cobalt diselenide composite porous carbon nanofiber material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the spore-shaped cobalt diselenide composite porous carbon nanofiber material according to claim 8 in preparing a negative electrode material for a sodium ion battery.

10. A sodium ion battery, characterized in that: The negative electrode material is the spore-shaped cobalt diselenide composite porous carbon nanofiber material as described in claim 8.

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