Preparation Method of Negative Electrode Material, Negative Electrode Material and Sodium Ion Battery

Abstract

The present invention discloses a negative electrode material, a preparation method thereof, and a sodium ion battery. In the present invention, a displacement reaction is carried out on copper-carbon nanofibers, and the copper element in the copper-carbon nanofibers is replaced by elemental tin nanoparticles through ion exchange, realizing the uniform dispersion of the elemental tin nanoparticles in the carbon nanofibers. Through the method of the present invention, a high proportion of the elemental tin nanoparticles can be incorporated into the carbon fibers, and at the same time, the microstructural stability of the elemental tin can be maintained, thereby obtaining a high reversible sodium storage capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and relates to a negative electrode material, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] With the rapid development of new energy, the demand for energy storage devices by people is increasing day by day. Common chemical energy storage systems include flow batteries, supercapacitors, secondary batteries, etc. As a secondary battery, sodium-ion batteries have received great attention in the field of energy storage due to their rich raw materials, low price, and relatively high energy density (Energy Stor. Mater. 2021, 21 - 44).

[0003] Among many negative electrode materials for sodium-ion batteries, tin (Sn) can undergo an alloying reaction with sodium ions, and the main process of the reaction is: Sn → NaSn3 (0.36V) → NaSn (0.19V) → Na9Sn4 (0.08V) → Na 15 Sn4 (0.035V), and the process of sodium ion deintercalation is: Na 15 Sn4 (0.14V) → NaSn (0.25V) → NaSn3 (0.53V) → Sn (0.58V). Benefiting from its multi-step sodium storage reaction, the tin negative electrode exhibits an extremely high theoretical sodium storage capacity (847 mAh g -1 )(J. Mater. Chem. A 2020, 2913 - 2933).

[0004] However, during the sodium storage process of the tin negative electrode, there is a huge volume expansion, resulting in serious structural damage and poor cycle performance. Summary of the Invention

[0005] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a negative electrode material, a preparation method thereof, and a sodium-ion battery.

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

[0007] In the first aspect, the present invention provides a preparation method of a negative electrode material, and the method includes the following steps:

[0008] Step (1): Provide copper-carbon nanofibers;

[0009] Step (2): Mix copper-carbon nanofibers, a tin salt, thiourea, a reducing agent, a pH value regulator and water, and react at 40 - 80 °C to obtain tin-carbon nanofibers.

[0010] Among them, the temperature of the reaction in step (2) above can be, for example, 40°C, 45°C, 48°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc. Within this temperature range, the copper in the copper-carbon nanofibers can be completely replaced by elemental tin nanoparticles, and the microstructure stability of the elemental tin can be maintained; if the temperature is too high, the solvent water will evaporate or even dry out prematurely, resulting in the premature end of the reaction and affecting the sodium storage performance of the product; if the temperature is too low, the reaction will be too slow, the replacement reaction will be insufficient, and the copper cannot be completely replaced.

[0011] To improve the sodium storage performance of tin anodes, researchers have conducted many explorations, such as size control, surface coating, etc. (Adv. Funct. Mater. 2019, 1900790). Among them, constructing nano-sized tin particles with a loose nano-structure can effectively alleviate the volume expansion during the sodium storage process of tin anodes and accelerate the sodium ion storage process; in addition, through the surface coating of carbon materials and TiO2, the microstructure of tin anodes can be better maintained during the sodium storage process, increasing the sodium storage stability of tin anodes.

[0012] It should be noted that due to the low melting point of tin, high-temperature treatment will damage its microstructure. To ensure the sodium storage performance of tin, it is necessary to evenly distribute the tin nanoparticles in the host material. However, in most of the currently prepared anode materials, to ensure the uniform dispersion of tin, the tin content is often low, making it difficult to exhibit the high-capacity advantage of tin.

[0013] To solve this problem, the present invention creatively conducts a replacement reaction on copper-carbon nanofibers, and through ion exchange, the copper in the copper-carbon nanofibers is replaced by elemental tin nanoparticles, achieving the uniform dispersion of elemental tin nanoparticles in carbon nanofibers. Through the method of the present invention, a high proportion of elemental tin nanoparticles can be incorporated into carbon fibers, and at the same time, the microstructure stability of elemental tin can be maintained, thereby obtaining a high reversible sodium storage capacity.

[0014] In the method of the present invention, the function of thiourea is to form a complex with copper, reducing the reduction potential so that copper can replace tin.

[0015] The method of the present invention is simple and easy to implement, with low preparation cost. The obtained tin-carbon nanofibers have excellent electrochemical sodium storage performance and have the value of further exploration and application.

[0016] The following are the preferred technical solutions of the present invention, but not a limitation to the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved.

[0017] Preferably, the preparation method of the copper-carbon nanofibers in step (1) includes the following steps: mixing a copper source, PVP and an organic solvent to prepare an electrospinning solution, and electrospinning to obtain a copper-carbon nanofiber precursor; annealing the copper-carbon nanofiber precursor to obtain copper-carbon nanofibers.

[0018] This method is simple and easy to implement. By combining the electrospinning and high-temperature annealing processes, elemental copper nanoparticles are obtained under the reduction of carbon during the high-temperature annealing process, and they are uniformly distributed in the carbon nanofibers. Due to the high annealing temperature experienced by the carbon fibers, they have a high degree of carbonization, good electronic conduction performance and sodium ion storage characteristics, which helps to improve the reversible sodium storage capacity.

[0019] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the copper source includes an organic copper source, preferably copper acetate.

[0020] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the organic solvent is DMF.

[0021] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the mass ratio of the copper source, PVP and the organic solvent is (0.2-1):1:20.

[0022] Preferably, in the process of preparing the copper-carbon nanofiber precursor, stirring is accompanied during the mixing process, the temperature of the mixing is 40-80 °C, such as 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C or 80 °C, etc.; the mixing time is 4-8 h, such as 4 h, 5 h, 6 h, 7 h, 7.5 h or 8 h, etc.

[0023] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the parameters of electrospinning are: the flow rate of the electrospinning solution is 5-20 μL / min, such as 5 μL / min, 8 μL / min, 10 μL / min, 12 μL / min, 13 μL / min, 15 μL / min, 18 μL / min or 20 μL / min, etc.; the voltage is 10-20 kV, such as 10 kV, 12 kV, 13 kV, 15 kV, 16 kV, 18 kV or 20 kV, etc.; the distance between the needle tip and the grounded plate is 10-20 cm, such as 10 cm, 12 cm, 13 cm, 14 cm, 16 cm, 18 cm or 20 cm, etc.

[0024] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the atmosphere of the annealing treatment is a protective atmosphere, and the protective gas in the protective atmosphere includes at least one of argon, helium, neon and nitrogen.

[0025] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the temperature of the annealing treatment is 600-1000 °C, such as 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C or 1000 °C, etc.; the time of the annealing treatment is 1-4 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc.

[0026] Preferably, in the process of preparing the copper-carbon nanofiber precursor, the heating rate of the annealing treatment is 4-8 °C / min, such as 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min or 8 °C / min, etc.

[0027] As a preferred technical solution of the method of the present invention, the tin salt in step (2) is stannous chloride.

[0028] Preferably, in step (2), the mass ratio of the copper-carbon nanofiber to the tin salt is (5-20):20, such as 5:20, 6:20, 8:20, 10:20, 12:20, 13:20, 15:20, 17:20 or 20:20, etc.

[0029] It should be noted that in the present invention, the amount of the tin salt used is excessive, and the purpose is to ensure that all the elemental copper in the copper-carbon nanofiber is replaced by elemental tin.

[0030] Preferably, the reducing agent in step (2) is sodium hypophosphite.

[0031] Preferably, the pH regulator in step (2) is hydrochloric acid.

[0032] In the present invention, the hydrochloric acid can be concentrated hydrochloric acid or dilute hydrochloric acid, and the purpose is to adjust the pH value.

[0033] In one embodiment, the hydrochloric acid is concentrated hydrochloric acid with a mass fraction of 37%.

[0034] In one embodiment, the addition amount of the pH regulator satisfies that the pH value of the system is adjusted to 1-2, such as 1, 1.5, 1.7 or 2, etc.

[0035] Preferably, the mass ratio of the copper-carbon nanofiber, stannous chloride, thiourea, sodium hypophosphite and water is (5-20):20:10:10:100, wherein the selection range of the copper-carbon nanofiber is 5-20, such as 5, 6, 7, 8, 9, 10, 13, 15, 17 or 20, etc.

[0036] Preferably, the reaction in step (2) is accompanied by stirring, and the stirring time is 4-24 h, such as 4 h, 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 22 h or 24 h, etc.

[0037] Preferably, after the reaction in step (2), a washing and separation step is carried out. The present invention does not limit the separation method, for example, it can be filtration or centrifugation.

[0038] In one embodiment, water washing and centrifugation are carried out. The sequential water washing and centrifugation are carried out as one cycle for water washing and centrifugation, and the number of times of water washing and centrifugation is 2 to 4 times.

[0039] As a further preferred technical solution of the method of the present invention, the method includes the following steps:

[0040] Step 1), Dissolve copper acetate and PVP in DMF, mix and stir at 60 °C for 6 h to completely dissolve them, and then obtain a copper-carbon nanofiber precursor through electrospinning;

[0041] Step 2), Anneal the copper-carbon nanofiber precursor in an argon atmosphere, and then grind the obtained powder for 2 min to obtain copper-carbon nanofibers;

[0042] Step 3), Add the copper-carbon nanofibers, stannous chloride, thiourea, sodium hypophosphite, and hydrochloric acid to deionized water, slowly stir at 60 °C to completely displace elemental copper with elemental tin, wash with water and centrifuge to obtain tin-carbon nanofibers, that is, the anode material.

[0043] In the second aspect, the present invention provides an anode material prepared by the method as described in the first aspect. The anode material has a nanofiber structure, and the composition of the anode material is tin nanoparticles and carbon fibers, and the tin nanoparticles are uniformly dispersed in the carbon fibers.

[0044] Preferably, the diameter of the carbon fibers in the nanofiber structure is 10 to 30 nm, such as 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 27 nm or 30 nm, etc.

[0045] Preferably, based on the total mass of the anode material being 100%, the content of elemental tin is 20 to 30%, such as 20%, 25%, 27%, 28%, 29% or 30%, etc.

[0046] In the third aspect, the present invention provides a sodium-ion battery, and the anode of the sodium-ion battery includes the anode material as described in the second aspect.

[0047] Compared with the existing technology, the present invention has the following beneficial effects:

[0048] The present invention performs a replacement reaction on copper-carbon nanofibers, replacing elemental copper nanoparticles in the copper-carbon nanofibers with elemental tin nanoparticles through ion exchange, thereby achieving uniform dispersion of the elemental tin nanoparticles in the carbon nanofibers. The method of the present invention can achieve a high proportion of elemental tin nanoparticles incorporated into carbon fibers while maintaining the microstructural stability of the elemental tin, thereby obtaining a higher reversible sodium storage capacity. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0050] Example 1

[0051] This embodiment provides a negative electrode material, and the preparation method thereof includes the following steps:

[0052] Step 1) Dissolve 0.5g of copper acetate and 1.5g of PVP in 20g of DMF and stir at 60°C for 6h to obtain a uniformly mixed solution. The resulting solution is then electrospun to obtain a copper-carbon nanofiber precursor. The electrospinning process is performed at a solution flow rate of 10uL / min, an applied voltage of 15kV, and a distance of 12cm between the needle tip and the grounded plate.

[0053] Step 2) annealing the copper-carbon nanofiber precursor under an argon atmosphere by heating it to 900°C at a rate of 5°C / min, maintaining it at 900°C for 2 hours, and then cooling it naturally to room temperature. The annealed powder was ground for 2 minutes to obtain copper-carbon nanofibers.

[0054] Step 3) Add 10 g of copper carbon nanofibers, 20 g of stannous chloride, 10 g of thiourea, 10 g of sodium hypophosphite, and 2 g of concentrated hydrochloric acid (mass fraction 37%) to 100 mL of deionized water to obtain a reaction system with a pH value of 1.7. Slowly stir at 60 ° C for 12 h to completely replace the elemental copper with tin ions. Then wash with water and centrifuge three times, and dry to obtain tin carbon nanofibers, i.e., the negative electrode material.

[0055] In the negative electrode material of this embodiment, the mass content of tin is 27.8%.

[0056] The mass content of tin in the tin-carbon composite negative electrode material can be tested using conventional testing methods in the art. In this embodiment, the mass content of tin is tested using an acid pickling method.

[0057] The present invention adopts a replacement reaction on the copper-carbon nanofibers to replace the copper in the copper-carbon nanofibers with elemental tin nanoparticles through ion exchange, thereby achieving a high proportion of incorporation of elemental tin nanoparticles. The content of elemental tin in the negative electrode material can reach 20-30%, wherein the mass content range of elemental tin can be adjusted by adjusting the mass content of elemental copper in the copper-carbon nanofibers.

[0058] Example 2

[0059] This example provides a negative electrode material, and its preparation method includes the following steps:

[0060] Step 1): Dissolve 0.8 g of copper acetate and 2 g of PVP in 20 g of DMF, and mix and stir at 70 °C for 4.5 h to obtain a uniformly mixed solution. Then, electrospin the obtained solution to obtain a copper-carbon nanofiber precursor. When electrospinning, the solution flow rate is 6 μL / min, the applied voltage is 12 kV, and the distance between the needle tip and the grounded flat plate is 15 cm.

[0061] Step 2): Anneal the copper-carbon nanofiber precursor in an argon atmosphere, heat it to 800 °C at a heating rate of 5 °C / min, and hold it at 800 °C for 3 h, and then naturally cool it to room temperature. Grind the annealed powder for 3 min to obtain copper-carbon nanofibers.

[0062] Step 3): Add 5 g of copper-carbon nanofibers, 20 g of stannous chloride, 10 g of thiourea, 10 g of sodium hypophosphite, and 2 g of concentrated hydrochloric acid (mass fraction 37%) to 100 mL of deionized water to obtain a reaction system with a pH value of 1.7. Slowly stir at 70 °C for 18 h to completely replace elemental copper with tin ions. Then, wash and centrifuge 3 times and dry to obtain tin-carbon nanofibers, which are the negative electrode material.

[0063] In the negative electrode material of this example, the mass content of tin is 26.5%.

[0064] Example 3

[0065] This example provides a negative electrode material, and its preparation method includes the following steps:

[0066] Step 1): Dissolve 0.3 g of copper acetate and 1 g of PVP in 20 g of DMF, and mix and stir at 80 °C for 5 h to obtain a uniformly mixed solution. Then, electrospin the obtained solution to obtain a copper-carbon nanofiber precursor. When electrospinning, the solution flow rate is 15 μL / min, the applied voltage is 18 kV, and the distance between the needle tip and the grounded flat plate is 18 cm.

[0067] Step 2): Anneal the copper-carbon nanofiber precursor in an argon atmosphere, heat it to 850 °C at a heating rate of 6 °C / min, and hold it at 850 °C for 4 h, and then naturally cool it to room temperature. Grind the annealed powder for 2 min to obtain copper-carbon nanofibers.

[0068] Step 3): Add 8 g of copper-carbon nanofibers, 20 g of stannous chloride, 10 g of thiourea, 10 g of sodium hypophosphite, and 2 g of concentrated hydrochloric acid (mass fraction 37%) into 100 mL of deionized water to obtain a reaction system with a pH value of 1.7. Stir gently at 75 °C for 15 h to completely replace elemental copper with tin ions. Then, wash and centrifuge three times, and dry to obtain tin-carbon nanofibers, which are the anode materials.

[0069] In the anode material of this example, the mass content of tin is 26.9%.

[0070] Example 4

[0071] The difference from Example 1 is that the addition amount of stannous chloride is 50 g.

[0072] Example 5

[0073] The difference from Example 1 is that the addition amount of stannous chloride is 5 g.

[0074] Example 6

[0075] The difference from Example 1 is that the addition amount of concentrated HCl is adjusted to make the pH value of the reaction system 2.

[0076] Example 7

[0077] The difference from Example 1 is that the addition amount of concentrated HCl is adjusted to make the pH value of the reaction system 1.

[0078] Comparative Example 1

[0079] This comparative example provides a preparation method of an anode material, including the following steps:

[0080] Step 1): Dissolve 0.7 g of tin acetate and 1 g of PVP in 20 g of DMF, and mix and stir at 60 °C for 6 h to obtain a uniformly mixed solution. Then, electrospin the obtained solution to obtain a tin-carbon nanofiber precursor. When electrospinning, the solution flow rate is 10 μL / min, the applied voltage is 15 kV, and the distance between the needle tip and the grounded flat plate is 12 cm.

[0081] Step 2): Anneal the tin-carbon nanofiber precursor in an argon atmosphere, heat it at a heating rate of 5 °C / min to 900 °C, and keep it at 900 °C for 2 h, and then cool it to room temperature naturally. Grind the annealed powder for 2 min to obtain tin-carbon nanofibers.

[0082] In this comparative example, the content of tin is the same as that in Example 1.

[0083] Comparative Example 2

[0084] The difference from Example 1 is that the temperature in Step 2) is adjusted to 500 °C.

[0085] Comparative Example 3

[0086] The difference from Example 1 is that the reaction temperature in step 3) is 25 °C.

[0087] Comparative Example 4

[0088] The difference from Example 1 is that the reaction temperature in step 3) is 95 °C.

[0089] Performance test:

[0090] Prepare the negative electrode using the negative electrode materials prepared in each of the examples and comparative examples. Sodium metal is used as the counter electrode, and 2032 button cells are assembled. Among them, the preparation method of the negative electrode is as follows: Mix the negative electrode material, PVDF, and super-P in a mass ratio of 8:1:1. Take 5 g of the mixture and add 6 g of NMP, stir to mix evenly, coat it on a copper foil, and dry it for use as the negative electrode.

[0091] When assembling the button cell, the electrolyte solute is NaClO4, the concentration of the electrolyte solute is 1 M, the electrolyte solvent is a mixed solution of PC, EC, and DEC in a volume ratio of 1:1:1, the electrolyte additive is 1.5 vol% VC, 1.5 vol% FEC, 1.5 vol% PS, the separator is glass fiber, and the battery should be left to stand for 24 h after assembly, and then its sodium storage reversible capacity is tested.

[0092] Sodium storage reversible capacity test:

[0093] At room temperature (25 °C), discharge the sodium-ion battery at 0.5C to 0.01V, let it stand for 1 min, then charge it at 0.5C to 3.0V, let it stand for 1 min, and cycle "discharge - stand - charge - stand" 3 times; according to its third charging capacity, obtain the reversible capacity of the sodium-ion battery.

[0094] Cycle performance test: At room temperature (25 °C), discharge the sodium-ion battery at 5C to 0.01V, let it stand for 1 min, then charge it at 5C to 3.0V, let it stand for 1 min, and calculate its capacity retention rate after cycling "discharge - stand - charge - stand" 500 times.

[0095] Table 1

[0096] Reversible capacity (mAh / g) Cyclic capacity retention rate (%) Example 1 430 73％ Example 2 422 76％ Example 3 425 74％ Example 4 431 73％ Example 5 360 76％ Example 6 428 74％ Example 7 433 73％ Comparative Example 1 392 45％ Comparative Example 2 380 72％ Comparative Example 3 402 71％ Comparative Example 4 378 70％

[0097] In Example 4, it basically does not affect the reaction result, indicating that an excessive amount of Sn will not further improve the performance but will instead increase the cost. However, in Example 5, if the amount of Sn is insufficient, the copper in the copper-carbon nanofibers cannot be completely displaced, affecting the tin content in the product and thus the sodium storage reversible capacity of the negative electrode.

[0098] From the comparison between Example 1 and Examples 6-7, it can be seen that the pH value has little effect, but the reaction needs to be carried out within a suitable pH range.

[0099] In Comparative Example 1, tin-carbon nanofibers were directly prepared by electrospinning. The high-temperature reaction would cause the tin element to dissolve and then precipitate on the surface of the carbon fiber, seriously affecting the sodium storage reversible capacity and cycle performance.

[0100] In Comparative Example 2, the carbonization temperature of the copper carbon nanofibers is low, and the carbon fibers contain more oxygen-containing groups, which affects the sodium storage performance of the negative electrode material finally obtained.

[0101] In Comparative Example 3, the replacement reaction temperature is low, the replacement reaction is insufficient, and the sodium storage performance is affected; in Comparative Example 4, the replacement reaction temperature is too high, which easily leads to premature evaporation of the reaction solvent and premature termination of the reaction, affecting the sodium storage performance.

[0102] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a negative electrode material, characterized in that: The method comprises the following steps: (1) providing copper carbon nanofibers; (2) mixing copper carbon nanofibers, tin salt, thiourea, a reducing agent, a pH regulator, and water, and reacting the mixture at 40-80° C. to obtain tin carbon nanofibers; The process of copper-carbon nanofiber in step (1) comprises the following steps: mixing a copper source, PVP and an organic solvent to prepare an electrospinning solution, and electrospinning to obtain a copper-carbon nanofiber precursor; and annealing the copper-carbon nanofiber precursor to obtain copper-carbon nanofiber.

2. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the copper source includes an organic copper source.

3. The preparation method according to claim 2, characterized in that In the process of preparing the copper-carbon nanofiber precursor, the copper source is copper acetate.

4. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the organic solvent is DMF.

5. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the mass ratio of the copper source, PVP and organic solvent is (0.2-1):1:

20.

6. The preparation method according to claim 1, characterized in that During the preparation of the copper-carbon nanofiber precursor, the mixing process is accompanied by stirring, the mixing temperature is 40 to 80° C., and the mixing time is 4 to 8 hours.

7. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the electrospinning parameters are: the flow rate of the electrospinning solution is 5-20 μL / min, the voltage is 10-20 kV, and the distance between the needle tip and the grounded plate is 10-20 cm.

8. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the atmosphere of the annealing treatment is a protective atmosphere, and the protective gas in the protective atmosphere includes at least one of argon, helium, neon and nitrogen.

9. The preparation method according to claim 1, characterized in that In the process of preparing the copper carbon nanofiber precursor, the temperature of the annealing treatment is 600-1000° C., and the time of the annealing treatment is 1-4 hours.

10. The preparation method according to claim 1, characterized in that During the preparation of the copper-carbon nanofiber precursor, the heating rate of the annealing treatment is 4-8° C. / min.

11. The preparation method according to claim 1, characterized in that The tin salt in step (2) is stannous chloride.

12. The preparation method according to claim 11, characterized in that In step (2), the mass ratio of the copper carbon nanofiber to stannous chloride is (5-20):

20.

13. The preparation method according to claim 1, characterized in that The reducing agent in step (2) is sodium hypophosphite.

14. The preparation method according to claim 1, characterized in that The pH regulator in step (2) is hydrochloric acid.

15. The preparation method according to claim 1, characterized in that The pH value of the reaction system in step (2) is in the range of 1 to 2.

16. The preparation method according to claim 13, characterized in that The mass ratio of the copper carbon nanofiber, stannous chloride, thiourea, sodium hypophosphite and water is (5-20):20:10:10:

100.

17. The preparation method according to claim 1, characterized in that The reaction in step (2) is accompanied by stirring, and the stirring time is 4 to 24 hours.

18. The preparation method according to claim 1, characterized in that The reaction in step (2) is followed by washing and separation steps.

19. The preparation method according to claim 1, characterized in that The method comprises the following steps: Step 1), copper acetate and PVP were dissolved in DMF, mixed and stirred at 60°C for 6 hours to completely dissolve them, and then copper carbon nanofiber precursors were obtained by electrospinning; Step 2), annealing the copper-carbon nanofiber precursor in an argon atmosphere, and then grinding the resulting powder for 2 minutes to obtain copper-carbon nanofibers; Step 3) Add the copper carbon nanofibers, stannous chloride, thiourea, sodium hypophosphite and hydrochloric acid into deionized water, slowly stir at 60°C to completely replace the elemental copper with elemental tin, wash with water and centrifuge to obtain tin carbon nanofibers, i.e., the negative electrode material.

20. A negative electrode material prepared by the method according to any one of claims 1 to 19, characterized in that: The negative electrode material is a nanofiber structure, and the negative electrode material is composed of tin nanoparticles and carbon fibers, wherein the tin nanoparticles are uniformly dispersed in the carbon fibers.

21. The negative electrode material according to claim 20, characterized in that The diameter of the carbon fibers in the nanofiber structure is 10 to 30 nm.

22. The negative electrode material according to claim 20, characterized in that Based on the total mass of the negative electrode material being 100%, the content of the single substance tin is 20-30%.

23. A sodium ion battery, characterized in that: The negative electrode of the sodium ion battery comprises the negative electrode material according to claim 21 or 22.