A self-supporting Si / C nanofilm material and its preparation method and application

Abstract

The present invention discloses an ultra-tough self-supporting Si / C nanofilm material, its preparation method, and application, belonging to the field of lithium-ion battery electrode materials. The preparation method comprises the following steps: S1. adding silicon powder and sodium dodecylbenzenesulfonate to deionized water and mixing them evenly, then adding melamine, heating to 60°C and adding acrylic acid, heating to 80-120°C and adding an initiator, keeping the temperature for 6-16 hours, washing, filtering, and drying to obtain a Si@PAA precursor; S2. dissolving PAN in a solvent, then adding sodium dodecyl sulfate and the Si@PAA precursor obtained in step S1, stirring to obtain a spinning solution, and then electrospinning the spinning solution to obtain a Si@PAA / PAN film; S3. pre-curing the Si@PAA / PAN film obtained in step S2, then calcining it under a protective gas atmosphere, and cooling it naturally to obtain the product. The ultra-tough self-supporting Si / C nanofilm material prepared by the present invention has excellent cycle stability and rate performance when used as a negative electrode material for lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery electrode materials, and in particular to a self-supporting Si / C nanofilm material and a preparation method and application thereof. Background Art

[0002] Compared with traditional negative electrode material graphite, silicon has an absolute high capacity advantage. Its theoretical capacity (4200mAh g -1 ) is graphite (372mAh·g -1 ) ten times; at the same time, silicon materials also have the advantages of abundant reserves and environmental friendliness, and are one of the most promising next-generation high-energy-density lithium battery negative electrode materials. However, silicon materials have a huge volume expansion effect (volume change rate of up to 300%) in the process of lithium ion extraction / insertion, which leads to problems such as SEI film instability, electrode material crushing and falling off from the current collector, resulting in low coulombic efficiency, poor cycle performance and rate performance when used as a negative electrode material, limiting the commercial application of silicon-based materials. In response to its failure mechanism, the modification method of silicon negative electrode materials is mainly to construct Si / C composite materials with various structures, including core-shell structure, yolk-shell structure, porous structure and embedded structure. A large number of studies have shown that the core-shell structure that completely encapsulates silicon particles can effectively improve the cycle life. During the cycle process, the carbon material as the shell layer has the triple effect of alleviating the volume expansion effect of the silicon material, maintaining the integrity of the SEI layer, and improving the conductivity, thereby greatly improving the cycle performance.

[0003] In recent years, electrospinning has garnered widespread attention for its ability to effectively produce self-supporting nanomaterials. As a nanofiber production technique, electrospinning offers advantages such as high efficiency and controllability, making it a standout among numerous nanofiber production methods. Compared to traditional electrode materials, the self-supporting electrode materials produced by this method do not require copper as a current collector, significantly reducing the overall battery mass and significantly increasing the overall energy density. Furthermore, for silicon materials, the lack of a rigid copper current collector allows silicon to expand in all directions, rather than being confined to a single direction. This helps mitigate the volume expansion effect and improves cycling performance. For example, Chinese patent CN111900411A discloses a self-supporting silicon-carbon anode material and its preparation method. The method comprises the following steps: first, mixing silicon powder, a surfactant, and polyacrylonitrile to obtain a spinning solution; second, electrospinning the spinning solution to produce composite nanofibers; and finally, drying the composite nanofibers and subjecting them to pre-oxidation and carbonization to produce a self-supporting composite electrode material. The prepared self-supporting silicon-carbon anode material can be directly used in lithium-ion batteries, exhibiting improved cycling performance in Si / C battery anodes. However, the patent only demonstrates cycling stability up to 30 cycles; the capacity begins to slowly decline after 25 cycles, indicating a very low cycle life. Furthermore, the self-supporting Si / C nanomembranes prepared by this method still have several issues: ① The rate performance is still poor. Since the porosity of carbon materials is much lower than that of copper, the overall porosity of the material is low, resulting in poor rate performance. ② Nano-silicon and polyacrylonitrile have poor compatibility, making it difficult to achieve a perfect core-shell structure, resulting in poor cycling performance. Ideally, the goal would be to completely encapsulate silicon particles within carbon nanofibers through electrospinning, creating a perfect core-shell structure that increases porosity and thus suppresses the volume expansion effect of the silicon material. However, in practice, problems such as large silicon particles, poor dispersion in solution, and shrinkage during carbonization of the carbon fibers often result in silicon particles being exposed on the carbon fiber surface, resulting in poor cycling performance. Some researchers have adopted coaxial static spinning to achieve complete encapsulation of silicon particles; Si / C fibers prepared using this method exhibit good cycling stability. However, this method reduces the silicon content, ultimately resulting in a decrease in the specific capacity of the overall material. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of the present invention is to provide a method for preparing a self-supporting Si / C nanofilm material.

[0005] The objectives of the present invention are achieved through the following technical solutions.

[0006] A method for preparing a self-supporting Si / C nanofilm material comprises the following steps:

[0007] S1. Silica powder and sodium dodecylbenzenesulfonate were added to deionized water and mixed evenly. Melamine was then added and the mixture was heated to 60°C. Acrylic acid was added and stirred evenly. The mixture was heated to 80-120°C and then the initiator was added. The mixture was kept warm for 6-16 hours, washed, filtered, and dried to obtain the Si@PAA precursor.

[0008] S2. PAN is dissolved in a solvent, and then sodium dodecyl sulfate and the Si@PAA precursor obtained in step S1 are added, and the mixture is stirred to obtain a spinning solution, which is then electrospun to obtain a Si@PAA / PAN film.

[0009] S3. The Si@PAA / PAN film obtained in step S2 is pre-cured, and then calcined under a protective gas atmosphere, and then naturally cooled to obtain the self-supporting Si / C nanofilm material.

[0010] The preparation method of the present invention uses acrylic acid as a monomer, an initiator to initiate polymerization, and silicon powder is added during the polymerization process to obtain a Si@PAA precursor, in which PAA perfectly wraps the silicon particles; then mixed with polyacrylonitrile, since PAA and polyacrylonitrile are both organic materials and have good compatibility with polyacrylonitrile, using PAA to wrap the silicon particles can greatly improve the compatibility of the materials, help the silicon particles to be completely wrapped in carbon nanofibers, and significantly optimize the microstructure of the material; further, after high-temperature calcination, Si@PAA / PAN becomes a Si / C composite material with appropriate porosity, which helps to alleviate the volume expansion effect of nano-silicon materials and solve the volume expansion problem of nano-silicon during lithium insertion and extraction. Therefore, the self-supporting Si / C nanofilm material obtained by the preparation method of the present invention has excellent cycle stability during charge and discharge as the negative electrode material of lithium-ion batteries.

[0011] The role of melamine in acrylic polymerization is to act as a cross-linking agent to obtain a polymer with a network structure, thereby improving the heat resistance, water resistance and mechanical strength of acrylic resin.

[0012] In the preparation method of the present invention, since step S1 is an aqueous system and step S2 is an organic system, in order to achieve better compatibility, the present invention uses different surfactants in the two steps.

[0013] Preferably, in step S1, the mass volume ratio of the silicon powder, sodium dodecylbenzenesulfonate, melamine, initiator and acrylic acid is (0.3-0.8) g:0.12 g:(1-3) g:(0.05-0.5) g:(0.5-5) mL.

[0014] Further preferably, the mass volume ratio of the silicon powder, sodium dodecylbenzenesulfonate, melamine, initiator and acrylic acid is 0.4g:0.12g:1.26g:0.08g:1.37mL.

[0015] Preferably, in step S1, the initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0016] Preferably, in step S1, the particle size of the silicon powder is 30-50 nm.

[0017] Preferably, in step S2, the mass ratio of PAN to solvent is 1:(5-15).

[0018] Preferably, in step S2, the mass ratio of PAN to Si@PAA precursor is (1.5-5): 1. Further preferably, the mass ratio of PAN to Si@PAA precursor is 2.5:1.

[0019] Preferably, in step S2, the mass ratio of the Si@PAA precursor to sodium dodecyl sulfate is (5-15):1.

[0020] Preferably, in step S3, the temperature of the pre-curing treatment is 180-380°C, the heating rate is 1-5°C / min, and the holding time is 1-3 hours.

[0021] Preferably, in step S3, the calcination temperature is 600-1000° C., the heating rate is 1-5° C. / min, and the holding time is 1-3 h.

[0022] Preferably, in step S2, the electrospinning parameters are: high voltage 16-18 kV, low voltage -2.3 kV, and injection speed 1-5 mL / h.

[0023] Another object of the present invention is to provide a self-supporting Si / C nanofilm material prepared by the preparation method.

[0024] Another object of the present invention is to provide an application of the self-supporting Si / C nanofilm material prepared by the preparation method in the preparation of negative electrode materials for lithium-ion batteries.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention uses PAA to wrap silicon particles, greatly improving the compatibility of silicon particles in the material. In the resulting Si / C nanofilm, the silicon particles are completely wrapped by carbon nanofibers, greatly improving the material's cyclic stability. In addition, the Si / C nanofilm prepared by the present invention has a suitable porosity, which helps to inhibit the volume expansion of silicon. The Si / C nanofilm also has excellent structural strength. As a negative electrode material for lithium-ion batteries, it has excellent cyclic stability and rate performance. After 100 cycles, the material has a discharge specific capacity of 1244.3 mAh / g.

[0027] 2. When the self-supporting Si / C nanofilm material prepared by the present invention is used as the negative electrode material of a lithium-ion battery, inactive materials such as a rigid current collector, a binder and a conductive agent can be completely eliminated, thereby greatly improving the overall energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the self-supporting Si / C nanofilm material prepared in Example 1;

[0029] Figure 2 This is a scanning electron microscope image of the Si / C nanofilm material prepared in Comparative Example 1;

[0030] Figure 3 The electronic photos of the prepared Si / C nanofilm materials are shown, where (a) is the Si / C nanofilm material prepared in Comparative Example 1, and (b) is the self-supporting Si / C nanofilm material prepared in Example 1;

[0031] Figure 4 The self-supporting Si / C nanofilm material prepared in Example 1 and the Si / C nanofilm material prepared in Comparative Example 1 were tested at 0.1 A·g -1 Cycling performance diagram under current density;

[0032] Figure 5 These are rate performance diagrams of the self-supporting Si / C nanofilm material prepared in Example 1 and the Si / C nanofilm material prepared in Comparative Example 1 at different current densities. DETAILED DESCRIPTION

[0033] The applicant will now further describe the method of the present invention in detail with reference to specific examples, with the goal of enabling those skilled in the art to clearly understand the present invention. However, the following examples should not be construed as limiting the scope of protection of the claims of the present invention to any extent.

[0034] In the following examples and comparative examples, the particle size of silicon powder is 30-50 nm; the weight average molecular weight of polyacrylonitrile is 150,000; and the purity of polyacrylonitrile, N,N-dimethylformamide, acrylic acid, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate is not less than chemical purity.

[0035] Example 1

[0036] This embodiment provides a method for preparing a self-supporting Si / C nanofilm material, comprising the following steps:

[0037] S1. 0.4 g of silicon powder and 0.12 g of sodium dodecylbenzenesulfonate were added to a three-necked flask and stirred uniformly. The mixture was ultrasonically treated for 10 min, and then 1.26 g of melamine was added and stirred for 10 min. The mixture was heated to 60°C, 1.37 mL of acrylic acid was added, and stirred for 10 min. The mixture was then heated to 100°C in a water bath, and 2 mL of ammonium persulfate (4 wt% aqueous solution) was added. The mixture was incubated for 10 h. The product was washed, filtered, and dried to obtain a Si@PAA precursor.

[0038] S2. 1.5 g of polyacrylonitrile (PAN) was dissolved in 12 g of N,N-dimethylformamide, followed by the addition of 0.06 g of sodium dodecyl sulfate and 0.6 g of the Si@PAA precursor obtained in step S1. The mixture was ultrasonicated for 30 min and stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was then poured into a syringe and pushed onto the needle for later use. The electrospinning machine parameters were set as follows: high voltage 16 kV, low voltage -2.3 kV, syringe propulsion speed 1.2 mL / h, and the minimum distance between the needle tip and the drum surface 18 cm. The Si@PAA / PAN film was obtained after electrospinning.

[0039] S3. The Si@PAA / PAN film obtained in step S2 is placed in a muffle furnace, heated to 280°C at a heating rate of 2°C / min, and then kept warm for 2 hours for pre-curing treatment. After naturally cooling to room temperature, it is placed in a tubular furnace, heated to 800°C at a heating rate of 2°C / min, and calcined under nitrogen protection for 2 hours. Then, it is naturally cooled to room temperature to obtain a self-supporting Si / C nanofilm material.

[0040] Figure 1 This is the SEM image of the self-supporting Si / C nanofilm material prepared in this example. It can be seen from the image that the material fibers are uniform in thickness and have a smooth surface, indicating that the particles are completely wrapped inside the carbon nanofibers.

[0041] Example 2

[0042] This embodiment provides a method for preparing a self-supporting Si / C nanofilm material, comprising the following steps:

[0043] S1. 0.3 g of silicon powder and 0.12 g of sodium dodecylbenzenesulfonate were added to a three-necked flask and stirred uniformly. The mixture was ultrasonically treated for 10 min, and then 1 g of melamine was added and stirred for 10 min. The mixture was heated to 60°C, 0.5 mL of acrylic acid was added, and stirred for 10 min. The mixture was then heated to 80°C in a water bath, and 1 mL of ammonium persulfate (4 wt% aqueous solution) was added. The mixture was incubated for 16 h. The product was washed, filtered, and dried to obtain a Si@PAA precursor.

[0044] S2. 1.5 g of polyacrylonitrile (PAN) was dissolved in 10 g of N,N-dimethylformamide, followed by the addition of 0.06 g of sodium dodecyl sulfate and 0.4 g of the Si@PAA precursor obtained in step S1. The mixture was ultrasonicated for 30 min and stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was then poured into a syringe and pushed onto the needle for later use. The electrospinning machine parameters were set as follows: high voltage 16 kV, low voltage -2.3 kV, syringe propulsion speed 1.2 mL / h, and the minimum distance between the needle tip and the drum surface 18 cm. The Si@PAA / PAN film was obtained after electrospinning.

[0045] S3. The Si@PAA / PAN film obtained in step S2 is placed in a muffle furnace, heated to 180°C at a heating rate of 2°C / min, and then kept warm for 3 hours for pre-curing treatment. After naturally cooling to room temperature, it is placed in a tubular furnace, heated to 1000°C at a heating rate of 5°C / min, and calcined under nitrogen protection for 1 hour. Then, it is naturally cooled to room temperature to obtain a self-supporting Si / C nanofilm material.

[0046] Example 3

[0047] This embodiment provides a method for preparing a self-supporting Si / C nanofilm material, comprising the following steps:

[0048] S1. 0.8 g of silicon powder and 0.12 g of sodium dodecylbenzenesulfonate were added to a three-necked flask and stirred uniformly. The mixture was ultrasonically treated for 10 min, and then 3 g of melamine was added and stirred for 10 min. The mixture was heated to 60°C, 5 mL of acrylic acid was added, and stirred for 10 min. The mixture was then heated to 80°C in a water bath, and 5 mL of ammonium persulfate (4 wt% aqueous solution) was added. The mixture was incubated for 6 h. The product was washed, filtered, and dried to obtain a Si@PAA precursor.

[0049] S2. 1.5 g of polyacrylonitrile (PAN) was dissolved in 15 g of N,N-dimethylformamide, followed by the addition of 0.06 g of sodium dodecyl sulfate and 0.8 g of the Si@PAA precursor obtained in step S1. The mixture was ultrasonicated for 30 min and stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was then poured into a syringe and pushed onto the needle for later use. The electrospinning machine parameters were set as follows: high voltage 16 kV, low voltage -2.3 kV, syringe propulsion speed 1.2 mL / h, and the minimum distance between the needle tip and the drum surface 18 cm. The Si@PAA / PAN film was obtained after electrospinning.

[0050] S3. The Si@PAA / PAN film obtained in step S2 is placed in a muffle furnace, heated to 380°C at a heating rate of 3°C / min, and then kept warm for 1 hour for pre-curing treatment. After naturally cooling to room temperature, it is placed in a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and calcined under nitrogen protection for 3 hours. Then, it is naturally cooled to room temperature to obtain a self-supporting Si / C nanofilm material.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing a self-supporting Si / C nanofilm material, comprising the following steps:

[0053] S1. 1.5 g of polyacrylonitrile was dissolved in 12 g of N,N-dimethylformamide, followed by the addition of 0.6 g of silicon powder and 0.06 g of sodium lauryl sulfate. The mixture was ultrasonicated for 30 min and stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was then poured into a syringe and pushed onto the needle for later use. The electrospinning machine parameters were set as follows: high voltage 16 kV, low voltage -2.3 kV, syringe propulsion speed 1.2 mL / h, and the minimum distance between the needle tip and the drum surface 18 cm. A precursor film was obtained after electrospinning.

[0054] S2. Place the precursor film obtained in step S1 in a muffle furnace, heat it to 280°C at a heating rate of 2°C / min, keep it warm for 2 hours, perform pre-curing treatment, cool it naturally to room temperature, then place it in a tubular furnace, heat it to 800°C at a heating rate of 2°C / min, calcine it under nitrogen protection for 2 hours, and then cool it naturally to room temperature to obtain a self-supporting Si / C nanofilm material.

[0055] Figure 2 This is a scanning electron microscope image of the self-supporting Si / C nanomembrane material prepared in Comparative Example 1; it can be seen from the figure that the shape of the fiber is very uneven, and a large number of silicon particles are attached to the surface. The silicon particles are exposed on the surface of the carbon fiber, indicating that the particles are not wrapped inside the fiber.

[0056] Figure 3 (a) is an electronic photograph of the Si / C nanofilm material prepared in Comparative Example 1 after being artificially bent 90°. As can be seen from the figure, there are obvious cracks on the surface of the material; Figure 3 (b) is an electronic photograph of the self-supporting Si / C nanofilm material prepared in Example 1 after being artificially bent 90°; it can be seen from the figure that there are no obvious cracks on the surface of the material, indicating that the Si / C nanofilm material prepared by the method of the present invention has excellent structural strength.

[0057] Comparative Example 2

[0058] This comparative example provides a method for preparing a self-supporting Si / C nanofilm material, comprising the following steps:

[0059] S1. 0.4 g of silicon powder and 0.12 g of sodium dodecylbenzenesulfonate were added to a three-necked flask and stirred uniformly. Ultrasonic treatment was performed for 10 min, and then 1.2 mL of polyacrylic acid (average Mw ~250,000, 35 wt.% in H2O) was added. The mixture was stirred for 10 min and dried to obtain a Si-PAA blend.

[0060] S2. 1.5 g of polyacrylonitrile (PAN) was dissolved in 12 g of N,N-dimethylformamide, followed by the addition of 0.06 g of sodium lauryl sulfate and 0.6 g of the Si-PAA blend obtained in step S1. The mixture was ultrasonicated for 30 min and stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was then poured into a syringe and pushed onto the needle for later use. The electrospinning machine parameters were set as follows: high voltage 16 kV, low voltage -2.3 kV, syringe propulsion speed 1.2 mL / h, and the minimum distance between the needle tip and the drum surface 18 cm. The Si-PAA / PAN film was obtained after electrospinning.

[0061] S3. The Si-PAA / PAN film obtained in step S2 is placed in a muffle furnace, heated to 280°C at a heating rate of 2°C / min, and then kept warm for 2 hours for pre-curing treatment. After naturally cooling to room temperature, it is placed in a tubular furnace, heated to 800°C at a heating rate of 2°C / min, and calcined under nitrogen protection for 2 hours. Then, it is naturally cooled to room temperature to obtain a self-supporting Si / C nanofilm material.

[0062] Comparative Example 3

[0063] This comparative example is basically the same as Example 1, except that step S1 is as follows: 0.4 g of silicon powder and 0.12 g of sodium dodecylbenzenesulfonate are added to a three-necked flask and stirred evenly, ultrasonically treated for 10 minutes, then 1.26 g of melamine is added, stirred for 10 minutes, heated to 60° C., 6 mL of acrylic acid is added, and stirred for 10 minutes. Then, the mixture is placed in a water bath and heated to 100° C., and then 2 mL of ammonium persulfate (4 wt % aqueous solution) is added. The mixture is kept warm for 10 hours. The product is washed, filtered, and dried to obtain a Si@PAA precursor. Steps S2 and S3 are the same as in Example 1.

[0064] Application Examples

[0065] The nanofilm materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were respectively assembled into lithium-ion button batteries for electrochemical performance measurement. The specific method is as follows: the nanofilms prepared in Examples and Comparative Examples were dried under vacuum at 80°C, then cut into electrode sheets, and then the positive electrode shell, electrode sheet, diaphragm, lithium sheet, nickel foam and negative electrode shell were stacked in sequence in a glove box, and packaged after adding an appropriate electrolyte; the battery shell used was CR2016 type, the diaphragm was Celgard2400, and the electrolyte was a mixed electrolyte of ethylene carbonate (EC) and diethyl carbonate (DEC) containing 1M LiPF6 (the volume ratio of EC and DEC in the mixed electrolyte was 1:1). The cycle performance test was then carried out, and the electrochemical performance test was carried out on a Blue Electric CT2001A battery testing system (produced by Wuhan Blue Electric Electronics Co., Ltd.).

[0066] Figure 4 The self-supporting Si / C nanofilm material prepared in Example 1 and the Si / C nanofilm material prepared in Comparative Example 1 were tested at 0.1 A·g -1 The cycle performance diagram under current density shows that the first discharge specific capacity of the self-supporting Si / C nanofilm material of Example 1 can reach 1656.5 mAh / g. -1 At a current density of 0.1A·g, the specific capacity is still 1244.3mAh / g after 100 cycles, which has excellent cycle stability. -1 At this current density, the specific capacity is only 92.19 mAh / g after 100 cycles.

[0067] Figure 5 The rate performance diagram of the self-supporting Si / C nanofilm material prepared in Example 1 and the Si / C nanofilm material prepared in Comparative Example 1 at different current densities can be seen from the figure. The self-supporting Si / C nanofilm material in Example 1 has a higher current density than the self-supporting Si / C nanofilm material in Comparative Example 1 at 0.1 A·g -1 The current density can reach 1635.4 mAh g -1 The specific capacity at 2A·g -1 Even at high current, there is still 778mAh·g -1 The above specific capacity, and when it is restored to a low current, the capacity is not lost, indicating that the composite material of the present invention has excellent rate performance. The Si / C nanofilm material of Comparative Example 1 is -1 The current density can reach 1612.9 mAh g -1 The specific capacity of -1 Under high current, only 370.4mAh·g -1 The specific capacity is only 641.6 mAh g -1, the capacity loss is obvious.

[0068] The self-supporting Si / C nanofilm materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were -1 The specific capacity after 100 cycles at a current density of is shown in Table 1.

[0069] Table 1 Electrochemical properties of lithium-ion batteries

[0070] Example <![CDATA[Initial discharge specific capacity (mAh·g -1 )]]> <![CDATA[Specific capacity (mAh·g) after 100 cycles -1 )]]> Example 1 1656.5 1244.3 Example 2 1321.3 1040.9 Example 3 1967.6 968.5 Comparative Example 1 1598.2 92.19 Comparative Example 2 1432.2 120.5 Comparative Example 3 720.3 350.5

[0071] From the data in Table 1, it can be seen that when the self-supporting Si / C nanofilm material prepared by the present invention is used as an electrode material for lithium-ion batteries, the -1 After 100 cycles at the current density, the specific capacity retention rate is high, showing excellent cycle stability. Compared with Example 1, Comparative Example 1 does not use PAA to wrap the silicon particles. The carbon nanofibers cannot completely wrap the silicon particles, and the silicon particles stick to the surface of the carbon fibers, resulting in a significant decrease in specific capacity after 100 cycles and a significant deterioration in cycle stability. Comparative Example 2 directly compounds polyacrylic acid with silicon powder. Polyacrylic acid cannot evenly wrap the silicon powder, and the wrapping effect deteriorates, resulting in a deterioration in the compatibility of silicon particles with PAN, and ultimately resulting in the silicon particles being unable to be well wrapped by carbon nanofibers, and the cycle stability of the battery deteriorates. In Comparative Example 3, the amount of acrylic acid used is too high, resulting in a low proportion of silicon powder, which results in a significant decrease in the initial discharge specific capacity of the battery. This indicates that the ratio of silicon powder to acrylic acid must be within the specified range of the present invention in order to simultaneously have a high initial discharge specific capacity and excellent cycle stability.

[0072] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a self-supporting Si / C nanofilm material, characterized in that: The following steps are involved: S1. Silica powder and sodium dodecylbenzenesulfonate were added to deionized water and mixed evenly. Melamine was then added and the mixture was heated to 60°C. Acrylic acid was added and stirred evenly. The mixture was heated to 80-120°C and then the initiator was added. The mixture was kept warm for 6-16 hours, washed, filtered, and dried to obtain the Si@PAA precursor. S2. PAN is dissolved in a solvent, and then sodium dodecyl sulfate and the Si@PAA precursor obtained in step S1 are added, and the mixture is stirred to obtain a spinning solution, which is then electrospun to obtain a Si@PAA / PAN film. S3. The Si@PAA / PAN film obtained in step S2 is pre-cured, and then calcined under a protective gas atmosphere, and then naturally cooled to obtain the self-supporting Si / C nanofilm material.

2. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S1, the mass volume ratio of the silicon powder, sodium dodecylbenzenesulfonate, melamine, initiator and acrylic acid is (0.3-0.8) g:0.12 g:(1-3) g:(0.05-0.5) g:(0.5-5) mL.

3. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S1, the initiator includes at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

4. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S2, the mass ratio of PAN to Si@PAA precursor is (1.5-5):

1.

5. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S2, the mass ratio of the Si@PAA precursor to sodium dodecyl sulfate is (5-15):

1.

6. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S3, the temperature of the pre-curing treatment is 180-380° C., and the time is 1-3 hours.

7. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S3, the calcination temperature is 600-1000° C. and the calcination time is 1-3 hours.

8. The method for preparing a self-supporting Si / C nanofilm material according to claim 1, characterized in that: In step S2, the electrospinning parameters are: high voltage 16-18 kV, low voltage -2.3 kV, and injection speed 1-5 mL / h.

9. A self-supporting Si / C nanofilm material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the self-supporting Si / C nanofilm material according to claim 9 in preparing negative electrode materials for lithium-ion batteries.

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