Porous silicon / carbon nanofiber negative electrode material and preparation method thereof

Abstract

This invention discloses a porous silicon-carbon nanofiber anode material. It uses a silicon-based material as the core, with a three-dimensional porous carbon framework coating the surface of the silicon-based material to form a core-shell composite structure. The nanofiber anode material has hollow cavities and porous structures. The hollow porous structure facilitates rapid lithium-ion transport and sufficient electrolyte wetting, and provides internal buffer space for the huge volume expansion generated during charging and discharging, effectively suppressing the crushing of active materials and the damage to the electrode structure. It also exhibits excellent conductivity and rate capability. Furthermore, the three-dimensional porous carbon framework on the silicon-based surface provides a stable conductive network, further enhancing the structural stability of the electrode. This material is prepared by electrospinning solid carbon and solid oxygen. The synergistic effect of the carbon coating layer and reduced graphene oxide forms a porous carbon network coating, which not only provides better coating performance but also effectively promotes electrolyte penetration, lithium-ion diffusion, and improves the material's conductivity.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode materials, specifically to a porous silicon-carbon nanofiber anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and relatively low self-discharge rate, have become a key technology in portable electronic devices, electric vehicles, and grid energy storage systems, profoundly impacting the development of modern society. However, with the increasing global demand for higher energy density, faster charging speeds, and longer battery life, the performance of traditional lithium-ion batteries, especially those relying on graphite anodes, is gradually approaching their theoretical limit (372 mAh / g), restricting further improvements in overall battery energy density. Therefore, silicon (Si), as a potential alternative to next-generation lithium-ion battery anode materials, has attracted considerable attention due to its extremely high theoretical specific capacity (approximately 4200 mAh / g), abundant reserves, environmental friendliness, and low operating potential. Despite the promising prospects of silicon-based anode materials, they undergo a massive volume change of approximately 300% to 400% during lithiation / delithiation, leading to the fragmentation of active materials, damage to the electrode structure, loss of electrical contacts, and consequently, rapid capacity decay and poor cycle stability. Furthermore, its low conductivity results in slow lithium-ion and electron transport dynamics, leading to low rate performance. Studies have found that carbon coating provides mechanical support for silicon particles and absorbs and disperses the stress generated by silicon expansion through its flexibility, effectively inhibiting the crushing and shedding of active materials. However, its rate performance has not been significantly improved. Furthermore, the thickness of the carbon layer has a significant impact; an excessively thick carbon layer increases the diffusion resistance of lithium ions, while an excessively thin carbon layer affects the absorption of expansion stress. In addition, existing carbon-coated silicon-based materials are mostly in powder form, such as nano-silicon powder. While this is beneficial for carbon coating, the final product is in powder form, which can lead to agglomeration.

[0003] Therefore, it is necessary to effectively solve the problem of volume expansion of silicon during lithiation, while also enhancing the structural stability of the electrode and improving the overall conductivity of the negative electrode. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a porous silicon-carbon nanofiber anode material and its preparation method, which can effectively alleviate the volume expansion of silicon during lithiation, enhance the structural stability of the electrode, and improve the overall conductivity of the anode.

[0005] This invention discloses a porous silicon-carbon nanofiber anode material. The nanofiber anode material has a core-shell composite structure with a silicon-based material as the core and a three-dimensional porous carbon skeleton coated on the surface of the silicon-based material. The nanofiber anode material has hollow cavities and porous holes.

[0006] Furthermore, the nanofiber anode material is prepared by electrospinning using solid carbon source, solid oxygen source and nano-silicon as raw materials.

[0007] This invention also discloses a method for preparing porous silicon-carbon nanofiber anode materials, comprising the following steps:

[0008] S1, a solid carbon source and a template agent are dissolved in a solvent to prepare a shell spinning solution;

[0009] S2, solid oxygen source, nano-silicon and template agent are dissolved in solvent to prepare core spinning solution;

[0010] S3, using the outer shell spinning solution and the inner shell spinning solution for electrospinning, then pre-oxidizing the product and then carbonizing it at high temperature;

[0011] Furthermore, the solid carbon source is a polymer carbon source, the solid oxygen source is graphene oxide, the mass ratio of the solid carbon source to the solid oxygen source is 3 to 7:1, and the mass ratio of the nano-silicon to the solid oxygen source is 4 to 6:1.

[0012] Furthermore, the polymer carbon source is one or a mixture of two or more of polyacrylonitrile, polyurethane acrylate, polyvinyl alcohol, phenolic resin, and polyvinylpyrrolidone;

[0013] Furthermore, the template agent is polymethyl methacrylate, and the solvent is N-dimethylformamide;

[0014] Furthermore, in step S2, the solid oxygen source and nano-silicon are first dissolved in a solvent and ultrasonically dispersed before the template agent is added.

[0015] Furthermore, in step S3, during electrospinning, the flow rate of the outer shell spinning solution is not less than the flow rate of the inner shell spinning solution.

[0016] Furthermore, in step S3, the temperature for pre-oxidation of the product is 260–300°C;

[0017] Furthermore, in step S3, the high-temperature carbonization temperature is 680–720°C.

[0018] The beneficial effects of this invention are as follows: This invention provides a porous silicon-carbon nanofiber anode material and its preparation method. The composite fiber is a silicon-based structure coated with a porous carbon network. This hollow porous structure facilitates rapid lithium-ion transport and sufficient electrolyte wetting, and provides internal buffer space for the significant volume expansion during charging and discharging, effectively suppressing the pulverization of the active material and the damage to the electrode structure. It also exhibits excellent conductivity and rate capability. Furthermore, the three-dimensional porous carbon framework on the silicon-based surface provides a stable conductive network, further enhancing the structural stability of the electrode. This nanofiber anode material is prepared by electrospinning solid carbon and solid oxygen to create hollow nanofibers. The synergistic effect of the carbon coating layer and reduced graphene oxide forms a porous carbon network coating, which not only provides better coating properties but also effectively promotes electrolyte penetration, lithium-ion diffusion, and improves the material's conductivity.

[0019] Instruction manual illustrations

[0020] Figure 1 SEM image of the sample prepared in Example 1;

[0021] Figure 2 SEM and EDS images of the sample prepared in Example 1;

[0022] Figure 3 The XRD pattern of the sample prepared in Example 1;

[0023] Figure 4 CV curve of the sample prepared in Example 1;

[0024] Figure 5 The EIS image is of the sample prepared in Example 1;

[0025] Figure 6 The GCD image of the sample prepared in Example 1;

[0026] Figure 7 This is a graph showing the long-cycle performance of the sample prepared in Example 1;

[0027] Figure 8 This is a rate performance graph of the sample prepared in Example 1. Detailed Implementation

[0028] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0030] This embodiment discloses a porous silicon-carbon nanofiber anode material. The nanofiber anode material has a core-shell composite structure with a silicon-based material as the core and a three-dimensional porous carbon skeleton covering the surface of the silicon-based material. The nanofiber anode material has hollow cavities and porous holes. The nanofiber anode material has a core-shell structure with a porous hollow structure. The core is a silicon-based material and the outer shell is a carbon skeleton with a three-dimensional porous structure. These structures facilitate the rapid transport of lithium ions and the full wetting of the electrolyte. They also provide an internal buffer space for the huge volume expansion generated during charging and discharging, thereby effectively suppressing the crushing of active materials and the damage to the electrode structure.

[0031] In this embodiment, the nanofiber anode material is prepared by electrospinning using solid carbon source, solid oxygen source, and nano-silicon as raw materials to form a "coated-composite-micro-nano structure". The porous carbon network coating formed by the synergistic effect of the carbon coating layer and reduced graphene oxide can effectively promote the penetration of electrolyte, promote lithium ion diffusion, improve the conductivity of the material, and effectively suppress the volume expansion problem of silicon. The nanofibers with hollow structures prepared by electrospinning provide an internal buffer space for the huge volume expansion of the active material during charging and discharging, thereby effectively suppressing the crushing of the active material and the damage to the electrode structure. The three-dimensional (3D) porous carbon skeleton constructed by carbon nanofibers not only effectively alleviates volume expansion, but also provides a stable conductive network, further enhancing the structural stability of the electrode.

[0032] This embodiment also discloses a method for preparing porous silicon-carbon nanofiber anode material, including the following steps:

[0033] S1, a solid carbon source and a template agent are dissolved in a solvent to prepare a shell spinning solution;

[0034] S2, solid oxygen source, nano-silicon and template agent are dissolved in solvent to prepare core spinning solution;

[0035] S3 utilizes electrospinning with both outer shell and inner shell spinning solutions, followed by pre-oxidation and high-temperature carbonization of the product. The template agent, acting as a pore-forming aid, decomposes during high-temperature carbonization, leaving pores. Since both the inner and outer shells contain the template agent after spinning, pores remain in both after high-temperature carbonization, contributing to the formation of hollow cavities and porous structures. The inner and outer shells together form a three-dimensional porous spatial network structure. Electrospinning technology, as an effective method for preparing nanofibers, can produce continuous one-dimensional (1D), two-dimensional (2D), and other multi-dimensional nanofibers with diameters ranging from tens of nanometers to several micrometers. This unique nanofiber structure has a high aspect ratio, providing a larger surface area for active materials, which is beneficial for rapid lithium-ion transport and sufficient electrolyte wetting. Furthermore, controlling the flow rate allows for the rapid and convenient preparation of composite materials with different proportions, saving time and material costs, and providing a convenient means to explore composite materials with the best performance ratios. A core-shell silicon-carbon nanofiber composite material was constructed using electrospinning technology to address the common problems of volume expansion and insufficient conductivity in silicon anode materials used in lithium-ion batteries. Polymethyl methacrylate (PMMA) was preferably used as the template agent, and N-dimethylformamide (NDM) was preferably used as the solvent.

[0036] In this embodiment, the solid carbon source is a polymer carbon source, the solid oxygen source is graphene oxide, and the mass ratio of the solid carbon source to the solid oxygen source is 3-7:1 (solid carbon source: solid oxygen source = 3-7:1); the mass ratio of the nano-silicon to the solid oxygen source is 4-6:1 (nano-silicon: solid oxygen source = 4-6:1); the polymer carbon source is one or a mixture of two or more of polyacrylonitrile, polyurethane acrylate, polyvinyl alcohol, phenolic resin, and polyvinylpyrrolidone; polyacrylonitrile is preferred as the polymer carbon source because it has good dispersibility in the electrospinning solution. When using other polymer carbon sources, a certain amount of dispersant can also be added to improve the electrospinning effect.

[0037] In this embodiment, in step S2, the solid oxygen source and nano-silicon are first dissolved in a solvent and ultrasonically dispersed before the template agent is added; the composite of nano-silicon and solid oxygen source graphene oxide utilizes the high conductivity of graphene to improve the overall electron transport efficiency of the material and alleviate the polarization problem of silicon particles during charging and discharging.

[0038] In this embodiment, in step S3, during electrospinning, the flow rate of the outer shell spinning solution is not less than the flow rate of the core spinning solution; for example, if the outer shell solution flow rate is 15 μL / min, then the core solution flow rate can be 12, 9 μL / min, or 15 μL / min, to facilitate the formation of the core-shell structure. In electrospinning (especially coaxial spinning), the spinning speed (usually referring to the feed rate of the injection pump) of the "core" (i.e., the core layer) and the "outer shell" (i.e., the sheath layer) are key parameters affecting the fiber structure, diameter, and integrity. Fiber morphology is typically controlled by adjusting the ratio of these two speeds. This is because the outer shell layer needs to provide sufficient volume to encapsulate the core while forming a stable jet structure. If the speed is too low, it may fail to encapsulate the core, leading to fiber breakage or core exposure. The speed of the core layer is usually set slower than that of the outer shell to prevent the core liquid flow rate from being too high and breaking through the outer shell encapsulation layer. In this invention, the core solution flow rate can be selected to be the same as the outer shell solution flow rate, which has no significant impact on the formation of the core-shell structure. The velocity ratio between the core and the shell is the core factor determining whether a fiber forms a uniform core-shell structure. If the core velocity is too high, it may break through the shell's coverage, causing protrusions or unevenness on the fiber surface, or even forming a "fuzzy" structure. If the shell velocity is too high, the overall fiber diameter will increase, and the fiber wall may become thinner, affecting mechanical properties and porosity. If the shell and core velocities are similar, the fiber is prone to uneven delamination or blurred interfaces, which may prevent the formation of an ideal core-shell structure.

[0039] In this embodiment, the pre-oxidation temperature of the product in step S3 is 260–300°C; this is a crucial step in the conversion of polyacrylonitrile (PAN) into carbon fibers. By slowly heating at 260–300°C, the cyano groups (-CN) in the PAN molecular chain undergo a cyclization reaction, forming a conjugated hexagonal ring structure (similar to the structure of a benzene ring), and then undergo an oxidation reaction with oxygen (introducing oxygen-containing groups such as carboxyl and hydroxyl groups). These cyclization and cross-linking reactions greatly improve the thermal stability of the polymer, preventing it from melting or burning during the subsequent high-temperature carbonization process, thus preserving the fiber morphology.

[0040] In this embodiment, in step S3, the high-temperature carbonization temperature is 680–720°C. At this high temperature, the pre-oxidized polyacrylonitrile further decomposes, removing non-carbon elements (such as hydrogen, nitrogen, and oxygen), ultimately leaving a carbonized product mainly composed of carbon elements. This step not only transforms the outer shell solution into a robust conductive carbon-based network but also reduces graphene (graphene oxide is converted into graphene) through high temperature, thereby further improving conductivity. Simultaneously, polymethyl methacrylate (PMMA) decomposes and evaporates at high temperatures (PMMA is a polymer that is easily pyrolyzed), and this "flammable" characteristic leaves a large number of porous structures inside the carbonized product. These pores not only help buffer the expansion of silicon particles but also increase the specific surface area of ​​the material, improving the permeability of the electrolyte and the diffusion rate of lithium ions.

[0041] Example 1

[0042] The preparation method of the porous silicon-carbon nanofiber anode material in this embodiment includes the following steps:

[0043] S1, Preparation of spinning solution for shell material: Add 0.5g polyacrylonitrile and 1.2g polymethyl methacrylate to 10mL N,N-dimethylformamide and stir continuously for 12 hours until completely and uniformly dissolved.

[0044] S2, Preparation of spinning solution for core material: Add 0.5g of nano-silicon and 0.1g of graphene oxide to 10mL of N,N-dimethylformamide and then ultrasonically disperse for 2h. Then add 1.1g of polymethyl methacrylate to the above solution and stir for 12 hours to ensure uniform dissolution.

[0045] S3, Electrospinning of Nanofiber Composite Materials: The well-stirred solution is placed in a syringe for spinning. The spinning conditions are: receiver rotation speed 400 r / min; voltage 16 kV; outer shell solution flow rate 15 μL / min; core solution flow rate 12 μL / min.

[0046] Pre-oxidation of the product: The product was heated from room temperature to 280°C at a rate of 1°C / min in a muffle furnace and held at 280°C for 1 hour, and then allowed to cool naturally to room temperature.

[0047] Carbonization of the product: The temperature was increased from room temperature to 700°C at 5°C / min in an argon atmosphere using a tube furnace, and held at 700°C for two hours. The product was then naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0048] Example 2

[0049] The preparation method of the porous silicon-carbon nanofiber anode material in this embodiment includes the following steps:

[0050] S1, Preparation of spinning solution for shell material: Add 0.3g polyacrylonitrile and 0.8g polymethyl methacrylate to 8mL N,N-dimethylformamide and stir continuously for 12 hours until completely and uniformly dissolved.

[0051] S2, Preparation of spinning solution for core material: Add 0.6g of nano-silicon and 0.1g of graphene oxide to 10mL of N,N-dimethylformamide and then ultrasonically disperse for 2h. Then add 1.2g of polymethyl methacrylate to the above solution and stir for 12 hours to ensure uniform dissolution.

[0052] S3, Electrospinning of Nanofiber Composite Materials: The well-stirred solution is placed in a syringe for spinning. The spinning conditions are: receiver rotation speed 410 r / min; voltage 16 kV; outer shell solution flow rate 15 μL / min; core solution flow rate 12 μL / min.

[0053] Pre-oxidation of the product: The product was heated from room temperature to 260°C at a rate of 1°C / min in a muffle furnace and held at 260°C for 1 hour, and then allowed to cool naturally to room temperature.

[0054] Carbonization of the product: The temperature was increased from room temperature to 680°C at 5°C / min in an argon atmosphere using a tube furnace, and held at 680°C for two hours. The product was then naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0055] Example 3

[0056] The preparation method of the porous silicon-carbon nanofiber anode material in this embodiment includes the following steps:

[0057] S1, Preparation of spinning solution for shell material: Add 0.6g polyacrylonitrile and 1.4g polymethyl methacrylate to 13mL N,N-dimethylformamide and stir continuously for 12 hours until completely and uniformly dissolved.

[0058] S2, Preparation of spinning solution for core material: Add 0.6g of nano-silicon and 0.1g of graphene oxide to 10mL of N,N-dimethylformamide and then ultrasonically disperse for 2h. Then add 1.5g of polymethyl methacrylate to the above solution and stir for 12 hours to ensure uniform dissolution.

[0059] S3, Electrospinning of Nanofiber Composite Materials: The well-stirred solution is placed in a syringe for spinning. The spinning conditions are: receiver rotation speed 400 r / min; voltage 16 kV; outer shell solution flow rate 15 μL / min; core solution flow rate 9 μL / min.

[0060] Pre-oxidation of the product: The temperature was increased from room temperature to 300°C at 1°C / min in a muffle furnace and held at 300°C for 1 hour, followed by natural cooling to room temperature.

[0061] Carbonization of the product: The temperature was increased from room temperature to 720°C at 5°C / min in an argon atmosphere using a tube furnace, and held at 720°C for two hours. The product was then naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0062] Example 4

[0063] The preparation method of the porous silicon-carbon nanofiber anode material in this embodiment includes the following steps:

[0064] S1, Preparation of spinning solution for shell material: Add 0.6g of polyurethane acrylate and 1.2g of polymethyl methacrylate to 10mL of N,N-dimethylformamide and stir continuously for 12 hours until completely and uniformly dissolved.

[0065] S2, Preparation of spinning solution for core material: Add 0.8g of nano-silicon and 0.2g of graphene oxide to 18mL of N,N-dimethylformamide and then ultrasonically disperse for 2h. Then add 2.1g of polymethyl methacrylate to the above solution and stir for 12 hours to ensure uniform dissolution.

[0066] S3, Electrospinning of Nanofiber Composite Materials: The well-stirred solution is placed in a syringe for spinning. The spinning conditions are: receiver rotation speed 400 r / min; voltage 16 kV; outer shell solution flow rate 15 μL / min; core solution flow rate 12 μL / min.

[0067] Pre-oxidation of the product: The product was heated from room temperature to 280°C at a rate of 1°C / min in a muffle furnace and held at 280°C for 1 hour, and then allowed to cool naturally to room temperature.

[0068] Carbonization of the product: The temperature was increased from room temperature to 700°C at 5°C / min in an argon atmosphere using a tube furnace, and held at 700°C for two hours. The product was then naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0069] Example 5

[0070] The preparation method of the porous silicon-carbon nanofiber anode material in this embodiment includes the following steps:

[0071] S1, Preparation of spinning solution for shell material: Add 0.4g polyvinyl alcohol and 1.2g polymethyl methacrylate to 10mL N,N-dimethylformamide and stir continuously for 12 hours until completely and uniformly dissolved.

[0072] S2, Preparation of spinning solution for core material: Add 0.5g of nano-silicon and 0.1g of graphene oxide to 10mL of N,N-dimethylformamide and then ultrasonically disperse for 2h. Then add 1.1g of polymethyl methacrylate to the above solution and stir for 12 hours to ensure uniform dissolution.

[0073] S3, Electrospinning of Nanofiber Composite Materials: The well-stirred solution is placed in a syringe for spinning. The spinning conditions are: receiver rotation speed 400 r / min; voltage 16 kV; outer shell solution flow rate 14 μL / min; core solution flow rate 10 μL / min.

[0074] Pre-oxidation of the product: The product was heated from room temperature to 270°C at a rate of 1°C / min in a muffle furnace and held at 270°C for 1 hour, and then allowed to cool naturally to room temperature.

[0075] Carbonization of the product: The temperature was increased from room temperature to 710°C at 5°C / min in an argon atmosphere using a tube furnace, and held at 710°C for two hours. The product was then naturally cooled to room temperature to obtain a silicon-carbon composite material.

[0076] In the above embodiments, the electrospinning flow rate ultimately determines the carbon-silicon ratio in the finished product of the prepared silicon-carbon nanofiber composite material. For example, in Example 1, the carbon-silicon ratio of the composite material is 5:4, denoted as P@Si-G(5:4). The silicon-carbon nanofibers prepared in Example 1 were subjected to various performance analyses, and the results are as follows:

[0077] (I) Morphological and structural characterization

[0078] Depend on Figure 1 As can be seen, commercial silicon nanoparticles are densely distributed and exhibit obvious agglomeration, while the SEM image of the P@Si-G(5:4) composite material shows a spherical core-shell structure compared to silicon nanoparticles, indicating good coating. Simultaneously, the P@Si-G(5:4) composite material possesses a significant porous and mesoporous structure. These structures facilitate rapid lithium-ion transport, sufficient electrolyte wetting, and provide internal buffer space for the significant volume expansion during charging and discharging, thereby effectively suppressing the fragmentation of active materials and the damage to the electrode structure.

[0079] To investigate the elemental composition of the P@Si-G(5:4) composite material, EDS testing was performed. The corresponding EDS mapping is as follows: Figure 2 As shown, this further proves the uniform distribution of C, Si, and O elements in P@Si-G.

[0080] Figure 3 The image shows the XRD pattern of the P@Si-G(5:4) composite material. By comparing it with the standard card of Si, diffraction peaks with high compatibility with Si are shown, which appear at 2θ = 28.4°, 47.3°, 56.1°, 69.2° and 76.3°, respectively, corresponding to the (111), (220), (311), (400) and (331) crystal planes of silicon. This indicates that the crystal structure of silicon was not damaged after the synthesis process.

[0081] (II) Electrochemical performance characterization

[0082] (1) Battery preparation: The nanofiber material for lithium battery anode obtained in the example was ground evenly and used as anode active material. It was mixed with conductive agent (acetylene black) and binder (sodium alginate) at a mass ratio of 8:1:1. Deionized water was added to make a slurry, which was uniformly coated on copper foil current collector. After drying and rolling, it was made into anode sheet. The anode sheet was cut into pieces after vacuum drying at 80°C for 12 hours. The lithium-ion battery anode was obtained by cutting the sheet. The lithium metal sheet was used as the counter electrode, the glass fiber membrane was used as the separator, and the electrolyte was a mixed solution of 1 mol / L LiFP6, ethylene carbonate and dimethyl carbonate (the volume ratio of ethylene carbonate and dimethyl carbonate was 1:1). The battery was assembled into a button cell in a glove box under an argon atmosphere.

[0083] (2) Results analysis:

[0084] The electrochemical behavior of P@Si-G(5:4) composite materials in the voltage window of 0.01–1.5 V (vs. Li+ / Li) was systematically investigated by cyclic voltammetry (CV) testing (data were recorded starting from the second cycle of the cyclic voltammetry test). Figure 4 As shown. At 0.1mVs −1 At the scan rate, three distinct peaks appeared in the first five cycles of the CV test. The reduction peak at 0.19 V corresponds to the silicon alloying reaction (Si→LixSi) and is related to the lithium intercalation process. The oxidation peaks, associated with the delithiation process, appeared at 0.34 V and 0.53 V, corresponding to the dealloying reaction (LixSi→Si). Furthermore, the intensity of both the oxidation and reduction peaks gradually increased with the number of scan cycles, indicating that the activation process continued.

[0085] The interfacial charge transfer kinetics of the P@Si-G(5:4) composite material were investigated by electrochemical impedance spectroscopy (EIS), such as... Figure 5 As shown in the figure, the semicircle in the high-frequency region and the sloping straight line in the low-frequency region constitute the entire Nyquist curve. It can be seen from the figure that the Rct values ​​of P@Si-G are 56Ω, 70Ω and 88Ω, respectively, while the Rct resistance of uncoated SiNPs reaches 105Ω. This indicates that the synergistic coating of rGO and PAN-derived carbon significantly improves the conductivity of the material, while alleviating the particle fragmentation caused by silicon volume expansion, thereby greatly reducing the charge transfer resistance.

[0086] Figure 6 P@Si-G(5:4) at 0.1Ag −1The charge-discharge curves for the voltage window of 0.01~1.5V at current density show two distinct discharge plateaus during the first cycle. The plateau around 1.3V is mainly related to the formation of the SEI film, while the flatter and longer plateau around 0.2V is related to the lithium-silicon alloy reaction. In subsequent cycles, the first voltage plateau disappears with increasing cycle number, indicating the formation of a relatively stable SEI film on the electrode material surface.

[0087] like Figure 7 The figure shows the cycling performance of Si and P@Si-G in different ratios. As can be seen from the figure, Si exhibits extremely poor cycling performance, with a capacity decay of 0% after 80 cycles. The P@Si-G (5:4) composite material, on the other hand, exhibits better electrochemical performance, with a coulombic efficiency as high as 101% in the first cycle at 1 A g. −1 At a current density of 391 mAh g, its first-cycle reversible capacity reaches 391 mAh g. −1 After 100 cycles, the reversible capacity remained stable at 231 mAh g. −1 It exhibits excellent cycle performance with a capacity retention rate of up to 59.8%.

[0088] like Figure 8 As shown, different proportions of Si and P@Si-G are used in 0.1Ag. −1 0.5Ag −1 1Ag −1 and 2Ag −1 Rate performance at current density. The figure shows that P@Si-G(5:4) exhibits excellent rate performance; although its capacity decreases with increasing current density, it remains high at 2 A g. −1 Even at high current density, the average capacity remains as high as 296 mAhg. −1 When the current density changes from 2Ag −1 Restored to 1Ag −1 When the current density is high, the capacity is rapidly recovered and gradually stabilizes. These results indicate that P@Si-G(5:4) has excellent rate performance and maintains a large reversible capacity even at high current densities.

[0089] (3) Cause Analysis: The superior performance of the example lies in the multiple roles of coaxially spun polyacrylonitrile as the carbon source and graphene oxide as the oxygen source: the synergistic effect of the carbon coating layer and the reduced graphene oxide. The formed porous carbon network coating can effectively promote the penetration of electrolyte, promote lithium ion diffusion, improve the conductivity of the material, and effectively suppress the volume expansion problem of silicon. Electrospinning prepares nanofibers with hollow structures. These structures provide internal buffer space for the huge volume expansion generated by the active material during charging and discharging, thereby effectively suppressing the crushing of the active material and the destruction of the electrode structure; the three-dimensional (3D) porous carbon skeleton constructed by carbon nanofibers can not only effectively alleviate the volume expansion, but also provide a stable conductive network, further enhancing the structural stability of the electrode.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A porous silicon-carbon nanofiber anode material, characterized in that: The nanofiber anode material has a core-shell composite structure with a silicon-based material as the core and a three-dimensional porous carbon skeleton coated on the surface of the silicon-based material. The nanofiber anode material has hollow cavities and porous holes.

2. The porous silicon-carbon nanofiber anode material according to claim 1, characterized in that: The nanofiber anode material is prepared by electrospinning using solid carbon source, solid oxygen source and nano-silicon as raw materials.

3. The method for preparing porous silicon-carbon nanofiber anode material according to claim 1, characterized in that: Includes the following steps: S1, a solid carbon source and a template agent are dissolved in a solvent to prepare a shell spinning solution; S2, solid oxygen source, nano-silicon and template agent are dissolved in solvent to prepare core spinning solution; S3 utilizes the outer shell spinning solution and the inner shell spinning solution for electrospinning, and then pre-oxidizes the product before high-temperature carbonization.

4. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: The solid carbon source is a polymer carbon source, the solid oxygen source is graphene oxide, the mass ratio of the solid carbon source to the solid oxygen source is 3 to 7:1, and the mass ratio of the nano-silicon to the solid oxygen source is 4 to 6:

1.

5. The method for preparing porous silicon-carbon nanofiber anode material according to claim 4, characterized in that: The polymer carbon source is one or a mixture of two or more of polyacrylonitrile, polyurethane acrylate, polyvinyl alcohol, phenolic resin, and polyvinylpyrrolidone.

6. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: The template agent is polymethyl methacrylate, and the solvent is N-dimethylformamide.

7. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: In step S2, the solid oxygen source and nano-silicon are first dissolved in a solvent and ultrasonically dispersed before the template agent is added.

8. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: In step S3, during electrospinning, the flow rate of the outer shell spinning solution is not less than the flow rate of the inner shell spinning solution.

9. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: In step S3, the pre-oxidation temperature of the product is 260–300 °C.

10. The method for preparing porous silicon-carbon nanofiber anode material according to claim 3, characterized in that: In step S3, the high-temperature carbonization temperature is 680–720°C.

Images