Composite sodium-ion battery anode material and preparation method and application thereof

Abstract

The application relates to a composite sodium ion battery anode material and a preparation method and application thereof, and belongs to the technical field of sodium ion batteries. The preparation method comprises the following steps: S1, dissolving polyacrylonitrile and tetrabutyl titanate in a solvent II, uniformly mixing to obtain a shell layer solution; dissolving multi-walled carbon nanotubes and styrene-acrylonitrile copolymer in a solvent III, uniformly mixing to obtain a core layer solution; stirring and heating gallium, silicon and silicon dioxide, then adding a solvent I to obtain gallium-silicon nanoparticles through ultrasonic treatment, adding the gallium-silicon nanoparticles into the core layer precursor solution to obtain an intermediate layer solution; S2, performing three-axis electrostatic spinning on the three solutions through a concentrically shaped channel nozzle to obtain a composite film; and S3, carbonizing the composite film to obtain the composite sodium ion battery anode material. The composite sodium ion battery anode material can make the electrode have high capacity and excellent cycle stability, prolong the service life of the battery, and is a self-healing and self-repairing battery anode.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a composite sodium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] Sodium is abundant, making it a low-cost and high-potential material for sodium-ion batteries (NiBs). However, the inherently large ionic radius of sodium leads to slow kinetics and significant volume changes in electrode materials during charge and discharge, resulting in poor cycle and rate performance. Utilizing nanomaterials with high specific surface area, short ion transport paths, and rapid electron longitudinal transfer is an important way to improve the performance of sodium-ion batteries, and electrospinning is the fastest, most convenient, and simplest method for preparing nanomaterials.

[0003] Electrospinning is a common method for preparing hollow fibers to improve the anode of batteries, and triaxial electrospinning can provide more space when Si expands in volume, thus mitigating the effects of Na. + The volume expansion of liquid metal nanoparticles improves conductivity. The addition of liquid metal nanoparticles allows the large amount of heat released during battery operation to be absorbed by the nanoparticles, extending battery life. Patent CN 110416546 A discloses a three-dimensional self-supporting nitrogen-doped sodium carbonate ion anode material, which can be directly used as an electrode without a binder, but lacks sufficient space to mitigate volume expansion. Patent CN 102668194 A discloses a hollow carbon nanofiber precursor and active material for rechargeable lithium batteries, which can improve battery capacity density; however, this material easily generates heat during use, affecting battery performance. Patent CN 108246281 A discloses a carbon fiber@molybdenum dioxide nanoparticle core-shell composite structure and its preparation method; this fiber has high purity and good crystallinity, but low conductivity and poor electron transfer. Patent CN 111416159 A discloses a novel liquid metal battery with adjustable output voltage and current magnitude and direction, which can operate stably at room temperature, but is bulky, inconvenient to carry, and has low cycle stability. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a composite sodium-ion battery anode material, its preparation method, and its applications. The prepared composite sodium-ion battery anode material can be directly used as the anode of the battery without the need for a binder. The liquid metal Ga particles in the composite sodium-ion battery anode material can absorb heat from the battery at 40°C, extending the battery's lifespan. Simultaneously, Si and TiO2 / C can increase the battery's conductivity, reduce ion transport paths, and directly generate CNFs through electrospinning and carbonization, enhancing the pseudocapacitive behavior of the surface.

[0005] The first objective of this invention is to provide a method for preparing a composite sodium-ion battery anode material, comprising the following steps:

[0006] S1. Dissolve polyacrylonitrile and tetrabutyl titanate in solvent II and mix well to obtain a shell precursor solution.

[0007] Multi-walled carbon nanotubes and styrene-acrylonitrile copolymer were dissolved in solvent III and mixed to obtain a core layer precursor solution.

[0008] A mixture of gallium, silicon, and silicon dioxide is stirred and heated, and then solvent I is added for ultrasonic treatment to obtain gallium-silicon nanoparticles. The gallium-silicon nanoparticles are then added to the core layer precursor solution to obtain the intermediate layer precursor solution.

[0009] S2. Using a concentric irregular channel nozzle, triaxial electrospinning is performed on the shell precursor solution, intermediate layer precursor solution and core layer precursor solution described in S1 to obtain a composite film.

[0010] S3. Carbonize the composite film described in S2 in air or an inert atmosphere to obtain the composite sodium-ion battery anode material.

[0011] Wherein, solvent I is selected from acetone; solvent II is selected from dimethylformamide (DMF); and solvent III is selected from a mixture of dimethylformamide (DMF) and acetone.

[0012] In one embodiment of the present invention, in S1, the mass ratio of gallium (Ga), silicon (Si), and silicon dioxide (SiO2) is 80-87:12-17:1-3.

[0013] In one embodiment of the present invention, in S1, the temperature of the stirring and heating is 55°C-60°C, and the time is 55 min-60 min.

[0014] In one embodiment of the present invention, in S1, the conditions for ultrasonic treatment are: ultrasonic power of 70W-180W, temperature of 20℃-22℃, amplitude of 50μm-60μm, single ultrasonic treatment of 45min-55min, and repeated 5-7 times.

[0015] In one embodiment of the present invention, in S1, the mass-to-volume ratio of the polyacrylonitrile (PAN) and tetrabutyl titanate is 1 g: 1.4 mL - 1.5 mL.

[0016] In one embodiment of the present invention, in S1, the mass ratio of the multi-walled carbon nanotubes to the styrene-acrylonitrile copolymer is 1:50-55; the weight-average molecular weight of the styrene-acrylonitrile copolymer is 165,000-185,000, and the mass percentage of acrylonitrile in the styrene-acrylonitrile copolymer is 25%-30%.

[0017] In one embodiment of the present invention, in S1, the silicon particle size is 30nm-50nm, and the gallium-silicon nanoparticles have a particle size of 50nm-200nm. Because silicon materials exhibit high stress, smaller-sized silicon materials demonstrate superior performance as electrodes.

[0018] In one embodiment of the invention, in S1, the mass ratio of dimethylformamide (DMF) to acetone is 1:1. Because acetone is added to the intermediate layer precursor solution, the fact that PAN precipitates in acetone prevents mixing between the intermediate layer and the shell layer. Therefore, even if the shell layer solution is sprayed from the nozzle tip and immediately encounters the solution, PAN will precipitate at the intermediate layer interface of the fiber.

[0019] In one embodiment of the invention, in S1, the holding time of metallic gallium in the intermediate layer precursor solution is longer than that of most conventional phase change materials (PCMs). Mixing SiO2 with gallium helps reduce the significant overcooling of gallium, which facilitates the rapid return of the material to its original usable state and makes it easier for gallium to return to a solid state and continue absorbing heat. Silicon has outstanding energy density, but its volume change is significant; placing silicon in hollow fibers helps mitigate the effects of this volume change.

[0020] In one embodiment of the present invention, in S1, the MWCNTs in the intermediate layer precursor solution can not only significantly enhance electron transfer capability as a conductive network, but also prevent the aggregation of liquid metal nanoparticles.

[0021] In one embodiment of the present invention, in S2, the conditions for triaxial electrospinning are: voltage of 15kV-20kV, spinning distance of 15cm-18cm, temperature of 20℃-25℃, and humidity of 45%-47%.

[0022] The spinning speed of the shell layer is 1.5 mL / h-2 mL / h, the spinning speed of the middle layer is 0.15 mL / h-0.3 mL / h, and the spinning speed of the core layer is 0.8 mL / h-0.9 mL / h.

[0023] The needle sizes corresponding to the shell, intermediate layer, and core layer are selected from 12G-13G, 16G-17G, and 22G-23G, respectively.

[0024] In one embodiment of the present invention, in S2, the concentric irregularly shaped channel nozzle has an irregularly shaped channel in the intermediate layer (corresponding to the intermediate layer precursor solution). The cross-section of this irregularly shaped channel is triangular, allowing the solution to gradually flow out from the narrow to wide channel, preventing blockage. The irregularly shaped channel is composed of three irregularly shaped triangular blocks. The height of the arc rectangle in the irregularly shaped triangular block is 0.44 mm, the height of the cross-sectional triangle is 1.5 mm, and the central angle is 45 degrees.

[0025] In one embodiment of the present invention, in S3, the carbonization is divided into two stages: the first stage involves heating to 350°C-400°C in air at a rate of 5°C / min-8°C / min and holding for 1-1.5 hours; the second stage involves heating to 500°C-700°C in an inert atmosphere at a rate of 5°C / min-8°C / min and holding for 3-3.5 hours. After carbonization, tetrabutyl titanate forms TiO2 / C, C-, N-doped titanium dioxide (-TiO2), which exhibits significant sodium storage capacity. After carbonization, styrene-acrylonitrile copolymer (SAN) undergoes thermal decomposition to form hollow fibers with a hollow structure.

[0026] In one embodiment of the invention, in S3, the protective atmosphere is selected from nitrogen and / or argon.

[0027] A second objective of this invention is to provide a composite sodium-ion battery anode material prepared by the method described above.

[0028] A third objective of this invention is to provide an application of the aforementioned composite sodium-ion battery anode material in sodium-ion batteries.

[0029] The technical solution of the present invention has the following advantages compared with the prior art:

[0030] The preparation method described in this invention utilizes triaxial electrospinning to prepare nanoscale hollow fibers, which helps alleviate volume expansion. The triaxial core-shell structure of the fibers provides sufficient axial space when Ga-Si nanoparticles undergo volume expansion. Furthermore, this composite sodium-ion battery anode thin film material can be easily synthesized into a freestanding fiber anode without the need for auxiliary additives or metal current collectors. The N-doped carbon fiber structure facilitates the construction of a three-dimensional conductive system structure, increasing the specific surface area of ​​the electrode and ensuring rapid electron / ion transfer. Moreover, C- and N-doped titanium dioxide exhibits significant sodium storage capacity. Using concentric irregular channel nozzles for triaxial electrospinning allows the hollow fibers to form a hollow structure in the central layer, providing sufficient space in both the lateral and longitudinal directions to accommodate the volume expansion of silicon particles and liquid metal particles. The surface carbon fibers support the internal volume changes, and the fiber structure does not change significantly during sodium ion insertion or extraction, resulting in good cycle performance. The innermost hollow channel alleviates structural strain caused by sodium insertion / extraction, extending battery life; it also facilitates electron flow and improves electrochemical performance.

[0031] The Ga-Si nanoparticles in the composite sodium-ion battery anode material of this invention possess self-healing properties when in a liquid state, enabling the freestanding electrode to exhibit high capacity and excellent cycle stability. Si powder mitigates the drawback of gallium liquefying at room temperature, allowing gallium-based liquid metals to liquefy at around 40°C. Furthermore, the mixing of SiO2 with gallium helps reduce significant hypercooling of gallium, facilitating its return to a solid state and continued heat absorption. This ensures that the heat dissipated during battery operation is promptly absorbed by the liquid metal particles, extending battery life and resulting in a self-healing and self-repairing battery anode. Attached Figure Description

[0032] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0033] Figure 1 This is a schematic diagram of the concentric irregular channel nozzle used in this invention.

[0034] Figure 2 This is a flowchart illustrating the preparation process of gallium-silicon nanoparticles in Example 1 of the present invention.

[0035] Figure 3 This is a schematic diagram of the composite sodium-ion battery anode material of Embodiment 1 of the present invention;

[0036] Figure 4 This is a schematic diagram of the fiber structure of the composite sodium-ion battery anode material of Embodiment 1 of the present invention;

[0037] Figure 5This is a SEM image of the composite sodium-ion battery anode material of Example 1 of the present invention;

[0038] Figure 6 This is an electron microscope image of the composite sodium-ion battery anode material of Comparative Example 7 of the present invention;

[0039] Figure 7 The particle size distribution of Ga-Si nanoparticles in Example 1 and Comparative Example 3 of this invention is shown in the statistical diagram.

[0040] Figure 8 For the rate performance of the sodium-ion battery in Test Example 3 of this invention;

[0041] Figure 9 The charge-discharge curve of the sodium-ion battery in Test Example 3 of this invention;

[0042] Explanation of reference numerals in the attached figures: 1-Shell carbon fiber, 2-Intermediate layer four-channel structure, 3-Core layer hollow structure, 4-Ga-Si nanoparticles, 5-MWCNTs, 6-Concentric irregular channel nozzle, 61-Shell channel, 62-Intermediate layer channel, 63-Core layer channel, 64-Triangular irregular shape, 641-Circular arc rectangle, 642-Height of circular arc rectangle, 643-Central angle, 644-Height of cross-sectional triangle. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] In this invention, unless otherwise stated, the composite sodium-ion battery anode material is prepared by... Figure 1 The concentric irregular channel nozzle shown is implemented by a nozzle 6 consisting of three coaxial channels, including a shell channel 61, an intermediate channel 62, and a core channel 63; wherein the intermediate channel 62 contains four triangular irregularities 64. The cross-section of the triangular irregularity 64 is a circular arc rectangle 641, wherein the height 642 of the circular arc rectangle is 0.44mm, the central angle 643 is 45 degrees, and the height 644 of the triangular cross-section is 1.5mm.

[0045] In this invention, unless otherwise stated, all raw materials are commercially available or prepared by conventional methods in the art; PAN was purchased from Wuxi Yatai United Chemical Co., Ltd., CAS No. 85-85-8; DMF solution was purchased from Wuhan Kemike Biomedical Technology Co., Ltd., CAS No. 4637-24-5; gallium was purchased from Jiangsu Argon Krypton Xenon Materials Technology Co., Ltd., CAS No. 7440-55-3; silicon powder was purchased from Xiya Chemical Technology (Shandong) Co., Ltd., CAS No. 7440-21-3, with a particle size of 30nm-50nm; silicon dioxide was purchased from Foshan Orite New Materials Co., Ltd. Materials Technology Co., Ltd., CAS No. 14808-60-7; Acetone solution purchased from Guangzhou Jiangshun Chemical Technology Co., Ltd., CAS No. 53337-93-9; Tetrabutyl titanate purchased from UTP Technology Suzhou Co., Ltd., CAS No. 5593-70-4; Styrene-acrylonitrile copolymer (SAN) purchased from UTP Technology Suzhou Co., Ltd., CAS No. 9003-54-7, the weight average molecular weight of SAN is approximately 165,000, and the mass percentage of acrylonitrile in SAN is approximately 25%; Nitrogen gas purchased from Suzhou Tianping Crystal Gas Co., Ltd., CAS No. 7727-37-9. Example 1

[0046] The composite sodium-ion battery anode material and its preparation method of the present invention specifically include the following steps:

[0047] S1. Preparation of precursor solution

[0048] S11. Dissolve 1g of polyacrylonitrile (PAN) in 9mL of dimethylformamide (DMF), stir vigorously at room temperature, then add 1.5mL of tetrabutyl titanate, and stir vigorously at 40℃ for 12h to prepare a uniform shell precursor solution.

[0049] S12. Dissolve 5 mg of MWCNTs in 0.75 g of DMF and 0.75 g of acetone and sonicate for 3 h to obtain a uniform suspension. Add 0.25 g of styrene-acrylonitrile copolymer (SAN) and stir at 80 °C for 5 h to obtain a core layer precursor solution.

[0050] S13. Reference Figure 2As shown, gallium, silicon, and silicon dioxide were weighed in a ratio of 87:12:1. The weighed substances were placed in a three-necked flask, heated to 60°C in a water bath, and nitrogen gas was introduced. The mixture was mechanically stirred (magnetically stirred) for 60 minutes to obtain Ga-based liquid metal. 0.4 g of Ga-based liquid metal and 20 mL of acetone solution were added to a 25 mL beaker, and then placed in an ultrasonic cleaner (model SK3200HP, maximum power 180 W, frequency 53 kHz). The ultrasonic power was set to 180 W, the temperature to 20°C, and the amplitude to 50 μm. Each ultrasonic treatment lasted 50 minutes, and the treatment lasted for 6 hours to obtain a Ga microsphere suspension. After the Ga microsphere suspension was allowed to stand for 180 minutes, the supernatant was aspirated with a pipette and dropped onto a 30 mm × 30 mm silicon wafer to obtain Ga-Si nanoparticles.

[0051] S14. Add 150 mg of Ga-Si nanoparticles to the core layer precursor solution and sonicate for 12 h to obtain the intermediate layer precursor solution.

[0052] S2. Using concentric irregular channel nozzles, the shell precursor solution, intermediate layer precursor solution, and core layer precursor solution are injected into the triaxial electrospinning needle for triaxial electrospinning. The electrospinning voltage is set to 20kV, the spinning distance to 15cm, the temperature to 22℃, the humidity to 46%, the shell flow rate to 2mL / h, the intermediate layer flow rate to 0.3mL / h, and the core layer flow rate to 0.8mL / h. The needle sizes corresponding to the shell, intermediate layer, and core layer are 12G, 16G, and 22G, respectively, to obtain a composite film.

[0053] S3. Under a nitrogen atmosphere, the composite film was carbonized in stages. First, it was heated to 400℃ in air at a rate of 5℃ / min and held for 1 hour; then, it was heated to 700℃ in an inert atmosphere at a rate of 5℃ / min and held for 3.5 hours, resulting in the following: Figure 3 The composite sodium-ion battery anode material shown has a fiber structure as follows: Figure 4 As shown, the outer carbon fiber 1 serves as the supporting structure, and after carbonization, the middle layer is a four-channel structure 2. Ga-Si nanoparticles 4 and MWCNTs 5 are arranged relatively regularly in the four-channel structure 2, and the core layer disappears to form a hollow core structure 3. Comparative Example 1

[0054] The process is basically the same as in Example 1, except that triaxial electrospinning is replaced with coaxial electrospinning, and the core layer precursor solution is not used. Comparative Example 2

[0055] The process is basically the same as in Example 1, except that the tetrabutyl titanate in the shell precursor solution is replaced with styrene-acrylonitrile copolymer (SAN), which makes the film form a porous structure after carbonization. Comparative Example 3

[0056] The process is basically the same as in Example 1, except that silicon dioxide is not added during the preparation of Ga-Si nanoparticles. Comparative Example 4

[0057] The process is basically the same as in Example 1, except that silicon is replaced with tin in the preparation of Ga-Si nanoparticles. Comparative Example 5

[0058] The process is basically the same as in Example 1, except that acetone is not added to the intermediate layer precursor solution.

[0059] Because acetone is not added, the intermediate layer cannot bond with the outer solution, thus failing to form a perfect triaxial structure. Comparative Example 6

[0060] The process is basically the same as in Example 1, except that Ga-Si nanoparticles are not added to the intermediate layer precursor solution. Comparative Example 7

[0061] The process is basically the same as in Example 1, except that the flow rate of the shell layer is 2 mL / h, the flow rate of the intermediate layer is 0.3 mL / h, and the flow rate of the core layer is 1 mL / h.

[0062] Due to the high flow rate of the core layer, droplets are generated at the concentric nozzles, resulting in a large number of droplets in the prepared fiber membrane. Comparative Example 8

[0063] The process is basically the same as in Example 1, except that in preparing the outer precursor solution, 1 g of polyacrylonitrile (PAN) is dissolved in 9 mL of dimethylformamide (DMF), and 1.6 mL of tetrabutyl titanate is added to the above solution.

[0064] Because the outer solution is too thick, it can easily clog the needle and make spinning difficult.

[0065] Test Example 1

[0066] The sodium-ion battery anode materials prepared in Example 1 and Comparative Example 7 were characterized, and the results are as follows: Figure 5-6 As shown. From Figure 5 It can be seen that the sodium-ion battery anode material in Example 1 has a distinct hollow structure, indicating that the SAN core has essentially disappeared after carbonization treatment, and the uniform surface of the shell fibers is conducive to ion transport; from Figure 6 It can be seen that the sodium-ion battery anode material prepared in Comparative Example 7 has a high core layer flow rate and different viscosities of the three-layer solution, resulting in an imbalance in the spinning speed. This leads to the formation of droplets during the spinning process, which can easily clog the needles. As a result, the spun filaments are finer, while there are more droplets of varying sizes.

[0067] Test Example 2

[0068] Based on Example 1 and Comparative Example 3, the particle size distribution range of Ga-Si nanoparticles was scanned using a cold field emission scanning electron microscope (Hitachi-4700). The results are as follows: Figure 7 As shown. From Figure 7 It can be seen that the Ga-Si nanoparticles prepared by the ultrasonic method all have a particle size distribution within the nanometer range. The Ga-Si nanoparticles prepared in Example 1 have a particle size concentrated in the range of 50 nm to 150 nm, indicating that the size of the Ga-Si nanoparticles prepared by this method meets the requirements. The Ga-Si nanoparticles prepared in Comparative Example 3 have a more uniform particle size, with more particles around 300 nm. This is because silicon dioxide facilitates the condensation of liquid gallium metal, acting as a nucleating agent, resulting in a Ga-Si nanoparticle particle size distribution in the range of 50 nm to 200 nm.

[0069] Test Example 3

[0070] Electrochemical tests were performed on the sodium-ion battery anode materials prepared in the examples and comparative examples. The test methods or standards are as follows: According to the group standard "TQGCML 308-2022 Sodium-ion Battery Anode Materials", the sodium-ion battery anode materials were cut into circular electrode sheets with a diameter of 1 cm using a slicing machine. Sodium foil was used as the reference electrode, and the obtained circular electrode sheets were used as the working electrodes. Glass fiber (GF / D) was used as the separator, and 1 mol / L NaClO4 / EC (ethylene carbonate) + diethyl carbonate (DEC) was used as the electrolyte (NaClO4 was the solute in the electrolyte, and the volume ratio of the solvent EC + DEC was 1:1). 5% fluorinated ethylene carbonate (FEC) was used as an additive. The batteries were assembled into CR2032 button batteries in a glove box filled with high-purity argon gas. The batteries were sealed and placed for 12 hours before testing.

[0071] (1) According to the test method for rate performance in GB / T 31485-2015, the LAND battery tester (LAND CT3002A) was used to conduct the rate test, and the results are as follows: Figure 8 As shown. From Figure 8It can be seen that the discharge capacities of Example 1 at 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C are 1162.43, 927.98, 810.74, 677.20, 543.52, and 581.44 mA h / g, respectively. This indicates that Example 1 exhibits high capacity retention and good rate performance. Compared to other comparative examples, Example 1 shows a more stable discharge plateau voltage and a larger reversible capacity. It can also be seen that the anode of the battery prepared in Example 1 has more sodium storage sites than other methods. This is because the doping of titanium dioxide with nitrogen atoms and the subsequent preparation of a composite nanomaterial with carbon enhances electron transport efficiency; the nanostructured silicon enhances the battery's cycle life and reduces volume expansion; and the gallium-silicon nanoparticles effectively mitigate temperature changes, maintaining battery stability and improving efficiency during use.

[0072] (3) According to the "IEC 61960-3 2017 Standard for Performance Testing of Portable Secondary Lithium Batteries", the results of 30 constant current charge-discharge tests at a current density of 50 mA / g are as follows: Figure 9 As shown. From Figure 9 It can be seen that during charging, the voltage rise rate is slow and the charging platform is relatively flat; during discharging, the discharge cutoff voltage is low, which can prevent the battery from being over-discharged. In addition, the first charge and discharge capacities are 868.7 mA h / g and 887.6 mA h / g, respectively, indicating high charge and discharge efficiency.

[0073] The results above show that this invention utilizes a perfect combination of liquid metal particles and triaxial electrospun hollow fibers. The liquid metal particles are prepared using an ultrasonic method, and silica accelerates the solidification of the liquid metal, resulting in Ga-Si nanoparticles with a size of 50nm-200nm, which can alleviate battery heating and extend battery life. The Ga-Si nanoparticles utilize carbonization to form hollow fibers (styrene-acrylonitrile copolymer SAN undergoes thermal decomposition at temperatures exceeding 350℃, forming a hollow structure; SAN loses 96% of its weight during pyrolysis, and N functional groups are introduced into the carbon material during this process), buffering the volume change of the liquid metal particles during charging and discharging. Simultaneously, the hollow structure of the core layer and the porous structure of the outer layer provide Na… + It provides additional sites, increasing sodium storage capacity.

[0074] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a composite sodium-ion battery anode material, characterized in that, Includes the following steps: S1. Polyacrylonitrile and tetrabutyl titanate are dissolved in solvent II and mixed to obtain a shell precursor solution; the mass-to-volume ratio of polyacrylonitrile and tetrabutyl titanate is 1g:1.4mL-1.5mL. Multi-walled carbon nanotubes and styrene-acrylonitrile copolymer were dissolved in solvent III and mixed to obtain a core layer precursor solution; the mass ratio of multi-walled carbon nanotubes to styrene-acrylonitrile copolymer was 1:50-55; the weight average molecular weight of styrene-acrylonitrile copolymer was 165,000-185,000, and the mass percentage of acrylonitrile in styrene-acrylonitrile copolymer was 25%-30%; A mixture of gallium, silicon, and silicon dioxide is stirred and heated, then solvent I is added and ultrasonically treated to obtain gallium-silicon nanoparticles. The gallium-silicon nanoparticles are then added to the core layer precursor solution to obtain an intermediate layer precursor solution. The mass ratio of gallium, silicon, and silicon dioxide is 80-87:12-17:1-3. S2. Using a concentric irregular channel nozzle, triaxial electrospinning is performed on the shell precursor solution, intermediate layer precursor solution, and core layer precursor solution described in S1 to obtain a composite film. The conditions for triaxial electrospinning are: voltage 15kV-20kV, spinning distance 15cm-18cm, temperature 20℃-25℃, and humidity 45%-47%. The spinning speed of the shell layer is 1.5mL / h-2mL / h, the spinning speed of the intermediate layer is 0.15mL / h-0.3mL / h, and the spinning speed of the core layer is 0.8mL / h-0.9mL / h. The needle sizes corresponding to the shell layer, intermediate layer, and core layer are selected from 12G-13G, 16G-17G, and 22G-23G, respectively. S3. Carbonize the composite film described in S2 in air or an inert atmosphere to obtain the composite sodium-ion battery anode material. The carbonization is divided into two stages: the first stage is to heat the film in air at a rate of 5°C / min-8°C / min to 350°C-400°C and hold it for 1-1.5 hours; the second stage is to heat the film in an inert atmosphere at a rate of 5°C / min-8°C / min to 500°C-700°C and hold it for 3-3.5 hours. Wherein, solvent I is selected from acetone; solvent II is selected from dimethylformamide (DMF); and solvent III is selected from a mixture of dimethylformamide (DMF) and acetone.

2. The method for preparing the composite sodium-ion battery anode material according to claim 1, characterized in that, In S1, the stirring and heating temperature is 55℃-60℃, and the time is 55min-60min.

3. The method for preparing the composite sodium-ion battery anode material according to claim 1, characterized in that, In S1, the conditions for ultrasonic treatment are: ultrasonic power of 70W-180W, temperature of 20℃-22℃, amplitude of 50μm-60μm, single ultrasonic treatment of 45min-55min, and repeated 5-7 times.

4. A composite sodium-ion battery anode material prepared by the method according to any one of claims 1-3.

5. The application of the composite sodium-ion battery anode material according to claim 4 in a sodium-ion battery.

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