A flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material and its preparation and application

Abstract

The present invention discloses a flexible, self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material, its preparation, and application, belonging to the field of battery negative electrode materials. The present invention first prepares Sn-MOF, then adds it to a spinning solution to obtain a fiber membrane through electrospinning, and then places the cellulose membrane in a dopamine hydrochloride solution for reaction to obtain a composite material; finally, the composite material and sulfur powder are calcined together and cooled to room temperature to obtain a flexible, self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material. The flexible, self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared by the present invention has excellent cycle stability, high current charge and discharge capability, and good flexibility when applied to sodium ion batteries.

Description

Technical Field

[0001] The present invention relates to a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material and its preparation and application, belonging to the field of battery negative electrode materials. Background Art

[0002] With the development of science and technology, the demand for fossil energy such as oil, natural gas, and coal is also increasing. Fossil energy is a non-renewable energy source. The shortage of fossil energy will greatly restrict economic development in the future. Therefore, there is an urgent need to develop a sustainable energy source.

[0003] Lithium-ion batteries, as a primary energy storage device, have a mature manufacturing process and are environmentally friendly. However, my country relies heavily on imported lithium ore. Sodium-ion batteries, with similar properties to lithium-ion batteries, are considered a highly promising alternative. Compared to lithium, sodium boasts advantages such as abundant reserves and low cost. However, because sodium's ionic radius and relative atomic mass are much larger than those of lithium ions, it suffers from disadvantages such as lower energy density and greater volume expansion of the electrode material during charging and discharging compared to lithium-ion batteries. The anode material, a key component of sodium-ion batteries, significantly impacts their overall performance. However, the graphite anode material commonly used in lithium-ion batteries is unsuitable for use in sodium-ion batteries. Currently, research on sodium-ion battery anode materials is limited; therefore, there is an urgent need to find a suitable sodium-ion battery anode material.

[0004] Stannous sulfide is a low-cost, non-toxic, and abundant compound. As the negative electrode for sodium-ion batteries, it offers the advantage of high specific capacity. However, when used directly as the negative electrode, the charge and discharge processes produce significant volume changes, resulting in low cycle stability and poor rate performance. Summary of the Invention

[0005] [Technical Issues]

[0006] (1) There is little research on negative electrode materials for sodium ion batteries;

[0007] (2) The poor conductivity of tin sulfide negative electrode material and the volume change during charging and discharging lead to poor cycle stability.

[0008] [Technical solution]

[0009] To address at least one of the above issues, the present invention first prepares Sn-MOF, then adds it to a spinning solution and electrospins it to produce a fiber membrane. The cellulose membrane is then placed in a dopamine hydrochloride solution for reaction to produce a composite material. Finally, the composite material is calcined with sulfur powder and cooled to produce a flexible, self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material. The flexible, self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material prepared by the present invention exhibits excellent cycling stability, high current charge and discharge capabilities, and good flexibility.

[0010] The first object of the present invention is to provide a method for preparing a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material, comprising the following steps:

[0011] (1) Dissolve terephthalic acid and lithium hydroxide in water, then add stannous sulfate (SnSO4) solution dropwise to the above solution, and react at 0-100°C for 2-5 hours to obtain Sn-MOF (square structure);

[0012] (2) dispersing Sn-MOF in N,N-dimethylformamide to obtain a Sn-MOF solution; then adding polyacrylonitrile (PAN) to the Sn-MOF solution, stirring and mixing uniformly to obtain a spinning solution;

[0013] (3) electrospinning the spinning solution to obtain a Sn-MOF / PAN fiber membrane;

[0014] (4) soaking the Sn-MOF / PAN fiber membrane in a Tris-HCl buffer solution of dopamine hydrochloride for reaction, washing and drying after the reaction to obtain a hollow Sn-PDA / PDA-PAN composite material; wherein the concentration of dopamine hydrochloride in the Tris-HCl buffer solution of dopamine hydrochloride is 0.5 to 3 mg / mL, the reaction is carried out at room temperature (20 to 30°C) for 6 to 18 hours, and the number of reactions is 1 to 6;

[0015] (5) The hollow Sn-PDA / PDA-PAN composite material and sulfur powder were calcined together and cooled to room temperature to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

[0016] In one embodiment of the present invention, the mass ratio of terephthalic acid, lithium hydroxide and water in step (1) is 1-2:0.5-2:100.

[0017] In one embodiment of the present invention, the stannous sulfate solution in step (1) is an aqueous stannous sulfate solution with a concentration of 0.25M to 0.5M.

[0018] In one embodiment of the present invention, the volume ratio of the stannous sulfate solution to water in step (1) is 1:1-5.

[0019] In one embodiment of the present invention, the usage ratio of Sn-MOF, N,N-dimethylformamide and polyacrylonitrile (PAN) in step (2) is 1-5 g: 5-15 mL: 0.5-1.5 g.

[0020] In one embodiment of the present invention, the electrospinning parameters in step (3) are set as follows: voltage of 15 to 30 kV, spinning solution injection rate of 1.2 to 1.5 mL / h, spinning temperature of 25±2°C and humidity of 45±5%, and the distance between the needle tip and the receiver is 10 to 20 cm.

[0021] In one embodiment of the present invention, the number of reactions in step (4) is based on the number of times the mother solution is replaced for the reaction.

[0022] In one embodiment of the present invention, the concentration of the Tris-HCl buffer in step (4) is 10 mM, and the pH is 8.5.

[0023] In one embodiment of the present invention, the washing in step (4) is performed by using water and ethanol, and the drying is performed by placing the mixture in a vacuum oven at 50-70°C.

[0024] In one embodiment of the present invention, the bath ratio of the reaction in step (4) is 1:10-500.

[0025] In one embodiment of the present invention, the mass ratio of the hollow Sn-PDA / PDA-PAN composite material to sulfur powder in step (5) is 1:5-20.

[0026] In one embodiment of the present invention, the calcination in step (5) is pre-oxidation followed by sulfurization and carbonization. The pre-oxidation and calcination process is as follows: heating from room temperature to 220°C to 280°C at a heating rate of 2°C / min and holding time of 1 to 2 hours. The synchronous sulfurization and carbonization process is as follows: heating to 400°C to 800°C after pre-oxidation at a heating rate of 2°C / min and holding time of 1 to 4 hours.

[0027] The second object of the present invention is to provide a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared by the method described in the present invention.

[0028] The third object of the present invention is to use the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material described in the present invention in sodium ion batteries or wearable electronic devices.

[0029] The fourth object of the present invention is to provide a method for improving the cycle stability performance of sodium ion batteries, wherein the method adopts the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material described in the present invention.

[0030] [Beneficial Effects]

[0031] (1) The present invention utilizes Sn-MOF as a self-sacrificial template to prepare a hollow structure. Compared with other preparation methods, the present invention has mild synthesis conditions, simple operation, controllable conditions, and low cost. In addition, the hollow structure provides sufficient buffer space for volume expansion during the cycle, which can effectively improve the long-cycle stability and rate performance of the battery. Therefore, the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber prepared by the present invention has excellent high-current charge and discharge capacity and cycle stability for use as a negative electrode material in sodium ion batteries.

[0032] (2) The hollow MOF-SnS / C@nitrogen-doped carbon fiber prepared in the present invention has good flexibility and cycle stability, has application value as a negative electrode material for flexible sodium ion batteries, and can be used in wearable electronic devices.

[0033] (3) The present invention first prepares a square-structured Sn-MOF, which dissociates in a dopamine hydrochloride aqueous solution, releasing organic ligand molecules and Sn 2+ To produce a hollow structure, dopamine hydrochloride is in situ condensed into PDA and reacted with Sn 2+ Coordination reaction; by controlling the concentration of dopamine hydrochloride, reaction time, and number of reactions, the degree of Sn-MOF etching can be controlled, so that the Sn-MOF is completely etched away to form a Sn-PDA hollow structure; this method is simple, has a short process, and mild conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the structural characterization of Sn-MOF in Example 1.

[0035] Figure 2 This is the X-ray diffraction spectrum of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared in Example 1.

[0036] Figure 3 This is a transmission electron micrograph of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared in Example 1.

[0037] Figure 4 The flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared in Example 1 was subjected to a current density of 2A g -1 The cycle performance diagram below.

[0038] Figure 5 The flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material prepared in Example 1 was subjected to different current densities of 0.1 A g -1 , 0.5A g -1 、1A g -1 、2A g -1 、5A g -1 、10A g -1 , 0.1A g -1 The rate performance diagram below.

[0039] Figure 6 This is a flexibility test picture of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared in Example 1.

[0040] Figure 7 This is the structural characterization of Sn-MOF in Example 2.

[0041] Figure 8 This is the structural characterization of Sn-MOF in Example 3.

[0042] Figure 9 This is the structural characterization of Sn-MOF in Example 4.

[0043] Figure 10 The negative electrode materials formed by Sn-MOF prepared at different temperatures in Examples 1 to 4 were tested at a current density of 0.1 A g -1 The cycle performance diagram below.

[0044] Figure 11 The negative electrode materials formed by Sn-MOF prepared at different temperatures in Examples 1, 5 to 7 were tested at a current density of 0.1 A g -1 The cycle performance diagram below.

[0045] Figure 12 The negative electrode materials formed by Sn-MOF prepared in Examples 1 and 8 at different dopamine hydrochloride concentrations were tested at a current density of 0.1 A g -1 The cycle performance diagram below.

[0046] Figure 13 The negative electrode material of Comparative Example 1 is 0.1A g -1 The cycle performance diagram below; the solid area represents discharge and the hollow area represents charge.

[0047] Figure 14 The negative electrode material of Comparative Example 2 is -1 The cycle performance diagram below.

[0048] Figure 15 The negative electrode material of Comparative Example 3 is -1The cycle performance diagram below. DETAILED DESCRIPTION

[0049] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0050] Test method:

[0051] Cyclic performance test:

[0052] Before the test, the -1 Afterwards, the hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material and sodium sheet were assembled into a button-type sodium ion battery. -1 The cycle test was carried out at a current density of 100 nm and 25° C. The raw materials used in the examples are:

[0053] The concentration of Tris-HCl buffer was 10 mM, pH = 8.5.

[0054] The solutions involved in the examples without specifying the solvent are water, and the % involved without specifying the meaning is mass percentage.

[0055] Example 1

[0056] A method for preparing a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material comprises the following steps:

[0057] (1) 1.0 g of terephthalic acid and 0.5 g of lithium hydroxide were dissolved in 100 g of water, and 20 mL of 0.25 M stannous sulfate (SnSO4) aqueous solution was added dropwise. The mixture was reacted at 25 °C for 2 h to obtain Sn-MOF (such as Figure 1 , square structure, size 1 μm);

[0058] (2) 1.5 g of Sn-MOF was dispersed in 10 mL of N,N-dimethylformamide to obtain a Sn-MOF solution; 1 g of polyacrylonitrile (PAN) was then added to the Sn-MOF solution and stirred to obtain a spinning solution;

[0059] (3) The spinning solution was electrospun and received by a roller at a voltage of 15 kV, a spinning solution perfusion rate of 1.5 mL / h, a spinning temperature of 25 ± 2 °C, and a humidity of 45 ± 5%, and a distance between the needle tip and the receiver of 15 cm to obtain a Sn-MOF / PAN fiber membrane;

[0060] (4) 0.08 g of Sn-MOF / PAN fiber membrane was immersed in 40 mL of 2 mg / mL dopamine hydrochloride in Tris-HCl buffer and reacted at room temperature for 12 h. The reaction was repeated twice. After the reaction, it was washed with deionized water and ethanol three times and then dried in a vacuum oven at 60 °C to obtain a hollow Sn-PDA / PDA-PAN composite material.

[0061] (5) The hollow Sn-PDA / PDA-PAN composite material and sulfur powder were calcined in a mass ratio of 1:5 and cooled to room temperature to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material; the calcination was pre-oxidation followed by sulfurization and carbonization. The pre-oxidation calcination process was: under nitrogen protection, the temperature was raised from room temperature to 240°C at a heating rate of 2°C / min and the holding time was 2h. The synchronous sulfurization and carbonization process was: after pre-oxidation, the temperature was raised to 600°C at a heating rate of 2°C / min and the holding time was 2h.

[0062] The obtained flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material was subjected to performance testing, and the test results are as follows:

[0063] Figure 2 This is the X-ray diffraction spectrum of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material. Figure 2 It can be seen that the main phase of the sample is SnS, and its data is consistent with the standard data (JCPDS 39-0354). The carbon in it is amorphous carbon and no obvious diffraction peak can be seen.

[0064] Figure 3 Transmission electron microscopy image of flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material. Figure 3 It can be seen that when the addition amount of Sn-MOF is 1.5 g, the concentration of dopamine hydrochloride is 2 mg / mL, the reaction time is 12 h, and the number of reactions is 2 times, the composite material presents a hollow morphology.

[0065] Figure 4 Flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material as anode material for sodium ion batteries at a current density of 2A g -1 The cycle performance diagram below. Figure 4 It can be seen that after 3500 cycles, the discharge capacity is still 327mAh g -1 , indicating that the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material has excellent cycling stability.

[0066] Figure 5Flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber anode material as anode material for sodium ion batteries at different current densities of 0.1 A g -1 , 0.5A g -1 、1A g -1 、2A g -1 、5A g -1 、10A g -1 , 0.1A g -1 The rate performance diagram below. Figure 5 It can be seen that at 0.1A g -1 After 10 cycles, the discharge capacity is 464 mAh g -1 When the current density rises to 0.5A g -1 、1A g -1 、2A g -1 、5A g -1 、10A g -1 , the discharge capacity is 365mAh g -1 , 343mAh g -1 、325mAhg -1 , 252mAh g -1 , 130mAh g -1 After high current charge and discharge, the current density returned to 0.1A g -1 , still has up to 393mAh g -1 The discharge specific capacity shows that the hollow MOF-SnS@carbon fiber has excellent rate performance.

[0067] Figure 6 This is a flexible test picture of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material. Figure 6 It can be seen from the figure that no matter it is bent, wound, twisted, or folded, the negative electrode material can return to its original shape. This shows that the negative electrode material has good flexibility and can be directly used as a negative electrode material for sodium ion batteries.

[0068] Example 2

[0069] The reaction temperature in step (1) of Example 1 was adjusted to 0°C to prepare Sn-MOF with the structure shown in FIG. Figure 7 ;

[0070] Other aspects were consistent with Example 1, and a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material was obtained.

[0071] Example 3

[0072] The reaction temperature in step (1) of Example 1 was adjusted to 50°C to prepare Sn-MOF with the structure shown in FIG. Figure 8 ;

[0073] Other aspects were consistent with Example 1, and a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material was obtained.

[0074] Example 4

[0075] The reaction temperature in step (1) of Example 1 was adjusted to 100°C to prepare Sn-MOF with the structure shown in FIG. Figure 9 ;

[0076] Other aspects were consistent with Example 1, and a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material was obtained.

[0077] The performance of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material obtained in Examples 1 to 4 was tested, and the test results are as follows:

[0078] Figure 10 The negative electrode materials formed by Sn-MOF prepared at different temperatures in Examples 1 to 4 were tested at a current density of 0.1 A g -1 The cycle performance diagram below. Figure 10 It can be seen that after 100 cycles, the discharge capacity remains basically unchanged, among which Example 1 has the largest discharge capacity at 25°C, reaching 400 mAh g -1 above.

[0079] Example 5

[0080] The number of reactions in step (4) of Example 1 was adjusted to 4 times, and the other steps were kept consistent with Example 1 to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

[0081] Example 6

[0082] The number of reactions in step (4) of Example 1 was adjusted to 6 times, and the other steps were kept consistent with Example 1 to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

[0083] Example 7

[0084] The number of reactions in step (4) of Example 1 was adjusted to 1, and the other steps were kept consistent with Example 1 to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

[0085] The performance of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode materials obtained in Examples 1 and 5 to 7 was tested, and the test results are as follows:

[0086] Figure 11The negative electrode materials formed by Sn-MOF prepared at different temperatures in Examples 1, 5 to 7 were tested at a current density of 0.1 A g -1 The cycle performance diagram below. Figure 11 It can be seen that if the number of reactions is too small, the discharge capacity will decrease after a certain number of cycles; if the number of reactions is too large, the discharge capacity will also decrease.

[0087] Example 8

[0088] The concentration of dopamine hydrochloride in step (4) of Example 1 was adjusted to 1 mg / mL, and the other contents remained the same as in Example 1 to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

[0089] The performance of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode materials obtained in Examples 1 and 8 was tested, and the test results are as follows:

[0090] Figure 12 The negative electrode materials formed by Sn-MOF prepared in Examples 1 and 8 at different dopamine hydrochloride concentrations were tested at a current density of 0.1 A g -1 The cycle performance diagram below. Figure 12 It can be seen that a decrease in dopamine concentration will reduce the discharge specific capacity.

[0091] Comparative Example 1

[0092] The dopamine hydrochloride in step (4) of Example 1 was omitted, and only Tris-HCl buffer was used for the impregnation treatment. Other steps were the same as in Example 1 to obtain a negative electrode material.

[0093] The obtained negative electrode material was subjected to performance testing, and the test results are as follows:

[0094] Figure 13 The negative electrode material of Comparative Example 1 is 0.1A g -1 The cycle performance diagram below. Figure 13 It can be seen that the discharge specific capacity has been greatly reduced compared with that of Example 1.

[0095] Comparative Example 2

[0096] The polyacrylonitrile in step (2) of Example 1 was adjusted to polymethyl methacrylate, and the other parts were kept consistent with Example 1 to obtain a negative electrode material.

[0097] The obtained negative electrode material was subjected to performance testing, and the test results are as follows:

[0098] Figure 14 The negative electrode material of Comparative Example 2 is -1 The cycle performance diagram below. Figure 14 It can be seen that the discharge specific capacity has been greatly reduced compared with that of Example 1.

[0099] Comparative Example 3

[0100] The sulfur powder in step (5) of Example 1 was adjusted to thioacetamide, and the other steps were kept consistent with Example 1 to obtain a negative electrode material.

[0101] The obtained negative electrode material was subjected to performance testing, and the test results are as follows:

[0102] Figure 15 The negative electrode material of Comparative Example 3 is -1 The cycle performance diagram below. Figure 15 It can be seen that the discharge specific capacity has been greatly reduced compared with that of Example 1.

[0103] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material, characterized in that: The steps include: (1) Dissolving terephthalic acid and lithium hydroxide in water, then adding stannous sulfate (SnSO4) solution dropwise to the solution, reacting at 0-100°C for 2-5 hours to obtain Sn-MOF; the mass ratio of terephthalic acid, lithium hydroxide, and water is 1-2:0.5-2:100; the prepared Sn-MOF has a square structure; (2) dispersing Sn-MOF in N,N-dimethylformamide to obtain a Sn-MOF solution; then adding polyacrylonitrile to the Sn-MOF solution, stirring and mixing uniformly to obtain a spinning solution; the amount ratio of Sn-MOF, N,N-dimethylformamide and polyacrylonitrile is 1-5 g: 5-15 mL: 0.5-1.5 g; (3) electrospinning the spinning solution to obtain a Sn-MOF / PAN fiber membrane; (4) soaking the Sn-MOF / PAN fiber membrane in a Tris-HCl buffer solution of dopamine hydrochloride for reaction, washing and drying after the reaction to obtain a hollow Sn-PDA / PDA-PAN composite material; wherein the concentration of dopamine hydrochloride in the Tris-HCl buffer solution of dopamine hydrochloride is 0.5 to 3 mg / mL, the reaction is carried out at room temperature for 6 to 18 hours, and the number of reactions is 1 to 6; (5) The hollow Sn-PDA / PDA-PAN composite material and sulfur powder are calcined together, and the mass ratio of the hollow Sn-PDA / PDA-PAN composite material to sulfur powder is 1:5~20; cooled to room temperature to obtain a flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material.

2. The method according to claim 1, characterized in that In step (5), the calcination is performed by pre-oxidation followed by sulfurization and carbonization. The pre-oxidation and calcination process is as follows: the temperature is raised from room temperature to 220°C to 280°C at a heating rate of 2°C / min and the holding time is 1 to 2 hours. The synchronous sulfurization and carbonization process is as follows: the temperature is raised to 400°C to 800°C after pre-oxidation at a heating rate of 2°C / min and the holding time is 1 to 4 hours.

3. The method according to claim 1, characterized in that In step (1), the volume ratio of the stannous sulfate solution to water is 1:1-5.

4. A flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material prepared by the method according to any one of claims 1 to 3.

5. Use of the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material according to claim 4 in sodium ion batteries or wearable electronic devices.

6. A method for improving the cycle stability of a sodium ion battery, characterized in that: The method adopts the flexible self-supporting hollow MOF-SnS / C@nitrogen-doped carbon fiber negative electrode material described in claim 4.

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