Self-supporting silicon-carbon negative electrode material with coaxial structure as well as preparation method and application of self-supporting silicon-carbon negative electrode material

Abstract

The invention belongs to the field of lithium ion batteries, and relates to a negative electrode material, in particular to a self-supporting silicon-carbon negative electrode material with a coaxial structure and a preparation method and application of the self-supporting silicon-carbon negative electrode material. Carrying out modification treatment on the silicon nanoparticles by adopting a silane coupling agent to obtain modified silicon nanoparticles; uniformly mixing the modified silicon nanoparticles with a core layer polymer to obtain a modified core layer mixture; preparing the modified core layer mixture and the skin layer polymer into a composite nanofiber with a coaxial structure by using a coaxial electrostatic spinning method; and performing pyrolysis and carbonization on the composite nanofiber with the coaxial structure under an inert atmosphere condition to obtain the composite nanofiber with the coaxial structure. According to the preparation method disclosed by the invention, not only can the dispersity of the nano silicon particles in the silicon-carbon negative electrode material be improved, but also the volume expansion of silicon in the circulation process can be controlled, and the conductivity and the lithium ion diffusion rate can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, relates to a negative electrode material, and particularly relates to a self-supporting silicon-carbon negative electrode material with a coaxial structure, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or any form of implication that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] With the increasing global demand for high energy density, long cycle life, and high safety energy storage systems, lithium-ion batteries, which are mainly used in energy storage devices, have been widely applied to various electronic products, electric vehicles, and portable electronic devices. As the most widely used graphite anode at present, it has the advantages of low cost, long cycle life, rich reserves, etc. However, due to the low theoretical specific capacity of graphite of 372 mAh·g -1 , it limits the future development of commercial lithium-ion batteries. Different from the embedded graphite anode, the alloy-type silicon-based anode has a theoretical ultra-high specific capacity of 4200 mAh·g -1 , which is the highest known capacity anode and is 10 times the specific capacity of the commercial graphite anode. It is a very promising anode material for lithium-ion batteries.

[0004] However, while the silicon-based anode has an ultra-high specific capacity, it also has disadvantages such as low electrical conductivity, short cycle life, and severe capacity attenuation. This is because during the alloying-dealloying reaction of the alloy-type silicon-based anode, silicon will undergo a volume expansion and contraction of more than 300%, resulting in the pulverization of silicon and ultimately leading to cracking of the anode. The pulverization of silicon will also lead to an increase in the solid electrolyte interface (SEI) generated, consuming more Li + , resulting in an excessive amount of dead lithium. And the low electrical conductivity of silicon will hinder the transport of electrons of Li + , making the cycle stability poor.

[0005] To solve the above disadvantages of the silicon-based anode, combining a carbon material with good electrical conductivity with a silicon material is a viable solution. Constructing silicon / carbon composite materials has become the research focus of lithium-ion battery anode materials. In the silicon / carbon composite material, the introduction of the carbon material can alleviate the pulverization and volume expansion problems of the silicon anode. And the carbon material can also improve the electrical conductivity of the anode. Although some progress has been made, there are still many problems at present. These include insufficient alleviation of the volume expansion of silicon particles, limited improvement in electrical conductivity, and poor dispersion of nano-silicon particles, etc. Summary of the Invention

[0006] To address the deficiencies of the prior art, the objective of the present invention is to provide a self-supporting silicon-carbon anode material with a coaxial structure, its preparation method, and applications. The preparation method of the present invention can not only improve the dispersion of nano-silicon particles in the silicon-carbon anode material, but also control the volume expansion of silicon during cycling, and is also conducive to improving conductivity and the lithium-ion diffusion rate.

[0007] To achieve the above objective, the technical solution of the present invention is as follows:

[0008] In a first aspect, a preparation method of a self-supporting silicon-carbon anode material with a coaxial structure includes the following steps:

[0009] Modify silicon nanoparticles using a silane coupling agent to obtain modified silicon nanoparticles;

[0010] Mix the modified silicon nanoparticles uniformly with a core layer polymer to obtain a modified core layer mixture; wherein, the core layer polymer is one of polymethyl methacrylate, polyvinyl alcohol, polyvinylpyrrolidone, polycaprolactone, and polyethylene oxide;

[0011] Use the method of coaxial electrospinning to form a coaxial structure composite nanofiber from the modified core layer mixture and a skin layer polymer; wherein, the coaxial structure composite nanofiber is divided into two layers from the inside out, the inner layer is a core layer composed of the modified core layer polymer, and the outer layer is a skin layer composed of the skin layer polymer; the skin layer polymer is one of polyacrylonitrile, polyvinylidene fluoride, and polyimide;

[0012] Pyrolyze and carbonize the coaxial structure composite nanofiber under an inert atmosphere condition to obtain the product.

[0013] In the present invention, a coaxial structure composite nanofiber is formed from a core layer polymer and a skin layer polymer through the method of coaxial electrospinning, and then two layers of carbon fibers, namely a core layer + a skin layer, are formed through carbonization. By selecting the core layer polymer and the skin layer polymer, the carbon structure of the core layer of the carbon fiber after carbonization is relatively loose, and the carbon fiber structure of the skin layer is relatively dense, and is supported by the skin layer carbon; at this time, adding silicon nanoparticles to the core layer carbon structure can utilize the loose structure of the core layer carbon to avoid the volume expansion of silicon during cycling. However, silicon nanoparticles are an inorganic nano material, prone to agglomeration, and have poor compatibility with the core layer polymer, resulting in difficulty in more uniform dispersion of the silicon nanoparticles in the core layer carbon structure; although the loose structure of the core layer carbon has a certain volume margin to accommodate the expanded silicon nanoparticles, the agglomerated silicon nanoparticles are concentrated at one point or a part of the core layer carbon structure, resulting in the expanded volume exceeding the volume margin of the loose structure of the core layer carbon, thereby causing the fiber structure to rupture, and thus unable to solve the impact of silicon volume expansion on the anode material.

[0014] Therefore, the present invention uses a silane coupling agent to modify silicon nanoparticles, which not only destroys the surface energy of the silicon nanoparticles and reduces the aggregation of the silicon nanoparticles, but also the modified silicon nanoparticles can increase the compatibility with the core layer polymer, increasing the dispersibility of the modified silicon nanoparticles in the core layer of the coaxial structure composite nanofibers. As a result, the modified silicon nanoparticles are uniformly dispersed in the core layer, enabling the volume expansion of silicon during the cycling process to be accommodated by the volume margin of the loose structure of the overall core layer carbon, thereby solving the influence of silicon volume expansion on the anode material.

[0015] In a second aspect, a self-supporting silicon-carbon anode material with a coaxial structure is obtained by the above preparation method.

[0016] In a third aspect, there is provided an application of the above self-supporting silicon-carbon anode material with a coaxial structure in the preparation of an anode for a lithium-ion battery.

[0017] In a fourth aspect, a lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the active material of the negative electrode is the above self-supporting silicon-carbon anode material with a coaxial structure.

[0018] The beneficial effects of the present invention are as follows:

[0019] The coaxial electrospinning technical solution provided by the present invention is applied to the anode material of a lithium-ion electrode, having a very obvious coaxial structure, and the silicon nanoparticles are uniformly dispersed inside the carbon cortex, effectively suppressing the aggregation and volume expansion of the silicon nanoparticles.

[0020] The method for modifying silicon nanoparticles provided by the present invention can form a bridge between the silicon nanoparticles and the long-chain organic material, enhancing the interfacial bonding and increasing the stability of the silicon nanoparticles with a silane coupling agent on the surface in the polymer solution. The silane coupling agent can not only enhance the adhesion between silicon and carbon, buffer the volume expansion, reduce the particle detachment, thereby improving the cycle stability of the battery, but also reduce the aggregation phenomenon of the silicon nanoparticles, ensuring a uniform electrode structure, which helps to improve the conductivity and the lithium-ion diffusion rate.

[0021] The present invention provides a simple and effective method for preparing a silicon-carbon anode material for lithium-ion batteries. By using the coaxial electrospinning process, nanofibers with a very distinct coaxial structure are prepared. The silane coupling agent is used to improve the dispersion of silicon nanoparticles in the electrode material, enhance the adhesion force between the silicon-carbon materials, and improve the mechanical properties of the silicon-carbon anode material. Moreover, the surface of the silicon modified by the silane coupling agent is more hydrophobic, which can reduce the side reactions with the electrolyte and delay the capacity decay caused by the thickening of the SEI film. The combined action of the two inhibits the volume expansion of the silicon material during the capacity cycle, significantly improving the cycle stability and conductivity of the silicon-carbon anode. This method can effectively overcome some technical deficiencies of the existing silicon-carbon anodes, solve the problem of poor dispersion of nanoparticles resulting in a small addition amount, and the addition of the silane coupling agent can further increase the addition amount of silicon in the silicon-carbon anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which form a part of this specification, are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0023] Figure 1 It is a scanning electron microscope image of the silicon-carbon composite nanofibers prepared in Example 3 of the present invention.

[0024] Figure 2 It is an EDS diagram of the silicon-carbon composite nanofibers prepared in Example 3 of the present invention.

[0025] Figure 3 It is an XRD diagram of the silicon-carbon composite nanofibers prepared in Example 3 of the present invention.

[0026] Figure 4 It is a graph of the discharge specific capacity and cycle number of the coin cell with the silicon-carbon composite nanofibers prepared in Example 3 of the present invention as the electrode at 0.3 A·g -1 under. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] In view of the problems existing in the silicon / carbon composite materials prepared by the prior art, such as insufficient alleviation of the volume expansion of silicon particles, limited improvement in conductivity, and poor dispersion of nano-silicon particles, the present invention provides a self-supporting silicon-carbon anode material with a coaxial structure, a preparation method thereof, and an application thereof.

[0030] A typical embodiment of the present invention provides a method for preparing a self-supporting silicon-carbon anode material with a coaxial structure, comprising the following steps:

[0031] Modifying silicon nanoparticles with a silane coupling agent to obtain modified silicon nanoparticles;

[0032] Mixing the modified silicon nanoparticles with a core layer polymer uniformly to obtain a modified core layer mixture; wherein, the core layer polymer is one of polymethyl methacrylate, polyvinyl alcohol, polyvinyl pyrrolidone, polycaprolactone, and polyethylene oxide.

[0033] Using the method of coaxial electrospinning to make the modified core layer mixture and a skin layer polymer into a coaxial structure composite nanofiber; wherein, the coaxial structure composite nanofiber is divided into two layers from the inside out, the inner layer is a core layer composed of the modified core layer polymer, and the outer layer is a skin layer composed of the skin layer polymer; the skin layer polymer is one of polyacrylonitrile, polyvinylidene fluoride, and polyimide.

[0034] Pyrolyzing and carbonizing the coaxial structure composite nanofiber under an inert atmosphere condition to obtain the product.

[0035] The present invention gives full play to the modification effect of the silane coupling agent, combines silicon nanoparticles with carbon materials, combines electrospinning with a coaxial structure, prepares nanofibers with an obvious coaxial structure, and the two jointly inhibit the volume expansion of the anode material during the lithium insertion / delithium process, improve the cycling performance of the silicon-carbon material, and enhance the application prospect of the silicon-carbon material in the field of lithium-ion batteries.

[0036] In some embodiments, the silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. Research shows that better effects can be achieved by using this silane coupling agent.

[0037] In some embodiments, the added mass of the modified silicon nanoparticles is 5-40 wt% of the core layer polymer.

[0038] In some embodiments, the modification process is as follows: adding a silane coupling agent to an alcohol aqueous solution with a pH of 3 to 4 to prepare a coupling agent hydrolysis solution, and adding silicon nanoparticles to the coupling agent hydrolysis solution to fully react to obtain modified silicon nanoparticles. Specifically, in the alcohol aqueous solution, the mass ratio of ethanol to water is 90:10-80:20. Specifically, in the coupling agent hydrolysis solution, the amount of silane coupling agent added is 0.5-2wt%. Specifically, the time for full reaction is 10-24h.

[0039] In some embodiments, the modified silicon nanoparticles are uniformly mixed with a core layer polymer and a solvent to obtain a modified core layer mixture solution; the modified core layer mixture solution and the skin layer polymer solution are made into coaxial structure composite nanofibers by a coaxial electrospinning method. Specifically, in the modified core layer mixture solution, the concentration of the core layer polymer is 4-25wt%. Specifically, the concentration of the skin layer polymer solution is 10-25wt%.

[0040] In some embodiments, the parameters of the coaxial electrospinning method are: temperature of 25-35°C, humidity of 30-40%, voltage of 10-20 kV, and skin propulsion rate of 0.04-0.08 mm·min -1 , the core layer advancement rate is 0.02-0.05mm·min -1 , spinning time is 4-12h, drum speed is 500-1000r·min -1 , the receiving distance is 10-20cm.

[0041] In some embodiments, the temperature of pyrolysis carbonization is 600-1000° C. Specifically, the heating rate of pyrolysis carbonization is 1-10° C. min -1 Specifically, the pyrolysis carbonization time is 1-4h.

[0042] In some embodiments, the coaxial structure composite nanofibers are first heated to 150-300° C. in an air atmosphere for low temperature thermal stabilization, and then pyrolyzed and carbonized in an inert atmosphere. Specifically, the low temperature thermal stabilization time is 0.5-4 hours.

[0043] Specifically, the steps are as follows:

[0044] Step 1: Cleaning and drying the surface of silicon nanoparticles: soak the silicon nanoparticles with hydrofluoric acid to remove the silicon dioxide on the surface of the silicon nanoparticles, wash with deionized water and dry;

[0045] Step 2: preparing a coupling agent hydrolysis solution: adding a certain amount of deionized water to ethanol to obtain an alcohol-water solution; adding acid to the alcohol-water mixed solution to adjust the pH to 3-4; adding a silane coupling agent and mixing evenly to obtain a coupling agent hydrolysis solution;

[0046] Step 3: Modify silicon nanoparticles: Disperse silicon nanoparticles in an ethanol solution, mix it evenly with the hydrolyzed solution of the coupling agent, stir at a low speed for several hours to ensure a sufficient reaction, then centrifuge and wash, and obtain modified silicon nanoparticles after drying.

[0047] Step 4: Prepare the spinning precursor solution: Disperse the modified silicon nanoparticles in a spinning solvent, add the core layer polymer and completely dissolve it in the spinning solvent to obtain the core layer spinning solution; completely dissolve the skin layer polymer in the spinning solvent to obtain the skin layer spinning solution.

[0048] Step 5: Coaxial electrospinning: Under certain temperature and humidity conditions, use the coaxial electrospinning method to prepare coaxial structure composite nanofibers from the skin layer spinning solution and the core layer spinning solution.

[0049] Step 6: Heat treatment: Place the composite fiber film in the air for thermal stabilization for a period of time, and then place it in an inert gas for high-temperature carbonization to finally prepare one-dimensional uniform silicon-carbon composite nanofibers.

[0050] Another embodiment of the present invention provides a self-supporting silicon-carbon negative electrode material with a coaxial structure, which is obtained by the above preparation method.

[0051] The third embodiment of the present invention provides an application of the above self-supporting silicon-carbon negative electrode material with a coaxial structure in the preparation of a negative electrode of a lithium-ion battery.

[0052] The fourth embodiment of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the active material of the negative electrode is the above self-supporting silicon-carbon negative electrode material with a coaxial structure.

[0053] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments.

[0054] Example 1

[0055] A preparation method of silicon-carbon composite nanofibers is as follows:

[0056] Step 1: Clean and dry the surface of silicon nanoparticles: Immerse silicon nanoparticles in 30wt% hydrofluoric acid for 20 min to remove the silicon dioxide on the surface of the silicon nanoparticles, wash with deionized water and vacuum dry at 60 °C for 12 h.

[0057] Step 2: Prepare the hydrolyzed solution of the coupling agent: Add 4 ml of deionized water to 16 ml of ethanol to obtain an alcohol-water solution; add acid to the alcohol-water mixed solution to adjust the pH to 4; add 40 μl of γ-aminopropyltriethoxysilane and mix evenly to obtain the hydrolyzed solution of the coupling agent.

[0058] Step 3: Modify silicon nanoparticles: Disperse 0.3 g of silicon nanoparticles in 10 ml of ethanol solution, mix it evenly with the hydrolyzed coupling agent solution, stir at a low speed for 20 h to ensure full reaction, centrifuge and wash, and obtain modified silicon nanoparticles after drying.

[0059] Step 4: Prepare the spinning precursor solution: Disperse 0.2 g of modified silicon nanoparticles in 10 ml of N,N-dimethylformamide, add 1 g of polymethyl methacrylate and completely dissolve it in the spinning solvent to obtain the core layer spinning solution. Completely dissolve 2 g of polyvinylidene fluoride in 10 ml of N,N-dimethylformamide to obtain the skin layer spinning solution.

[0060] Step 5: Coaxial electrospinning: At 25 °C and a humidity of 30%, use the coaxial electrospinning method to prepare coaxial structure composite nanofibers from the skin layer spinning solution and the core layer spinning solution. The parameters of electrospinning are as follows: the voltage is 14 kV, the advancing rate of the skin layer is 0.04 mm·min -1 , the advancing rate of the core layer is 0.025 mm·min -1 , the spinning time is 11 h, the rotating speed of the roller is 500 r·min -1 , and the receiving distance is 15 cm.

[0061] Step 6: Heat treatment: Place the composite fiber film in the air at 230 °C for thermal stabilization for 4 h, then place it in argon gas at 700 °C for carbonization for 2 h, and the heating rate is 2 °C·min -1 , and finally prepare one-dimensional uniform silicon-carbon composite nanofibers.

[0062] Example 2

[0063] A preparation method of silicon-carbon composite nanofibers is as follows:

[0064] Step 1: Clean and dry the surface of silicon nanoparticles: Immerse silicon nanoparticles in 30 wt% hydrofluoric acid for 20 min to remove the silicon dioxide on the surface of the silicon nanoparticles, wash with deionized water and vacuum dry at 60 °C for 12 h.

[0065] Step 2: Prepare the hydrolyzed coupling agent solution: Add 3 ml of deionized water to 17 ml of ethanol to obtain an alcohol-water solution; add acid to the alcohol-water mixed solution to adjust the pH to 4; add 40 μl of γ-glycidoxypropyltrimethoxysilane and mix evenly to obtain the hydrolyzed coupling agent solution.

[0066] Step 3: Modify silicon nanoparticles: Disperse 0.3 g of silicon nanoparticles in 10 ml of ethanol solution, mix it evenly with the hydrolyzed coupling agent solution, stir at a low speed for 18 h to ensure full reaction, centrifuge and wash, and obtain modified silicon nanoparticles after drying.

[0067] Step 4: Prepare the spinning precursor solution: Disperse 0.3 g of modified silicon nanoparticles in 10 ml of N,N-dimethylformamide, and add 0.5 g of polyethylene oxide to completely dissolve it in the spinning solvent to obtain the core layer spinning solution. Dissolve 1.5 g of polyacrylonitrile completely in 10 ml of N,N-dimethylformamide to obtain the skin layer spinning solution.

[0068] Step 5: Coaxial electrospinning: At 25 °C and a humidity of 30%, use the coaxial electrospinning method to prepare coaxial structure composite nanofibers from the skin layer spinning solution and the core layer spinning solution. The parameters of electrospinning are as follows: the voltage is 16 kV, the skin layer feeding rate is 0.06 mm·min -1 , and the core layer feeding rate is 0.025 mm·min -1 , the spinning time is 10 h, the roller rotation speed is 500 r·min -1 , and the receiving distance is 15 cm.

[0069] Step 6: Heat treatment: Place the composite fiber film in air at 250 °C for thermal stabilization for 4 h, then place it in nitrogen gas at 1000 °C for carbonization for 1 h, and the heating rate is 5 °C·min -1 , and finally prepare one-dimensional uniform silicon-carbon composite nanofibers.

[0070] Example 3

[0071] A method for preparing silicon-carbon composite nanofibers comprises the following steps:

[0072] Step 1: Clean and dry the surface of silicon nanoparticles: Immerse the silicon nanoparticles in 40 wt% hydrofluoric acid for 20 min to remove the silicon dioxide on the surface of the silicon nanoparticles, wash them with deionized water and vacuum dry them at 60 °C for 12 h.

[0073] Step 2: Prepare the coupling agent hydrolysis solution: Add 2 ml of deionized water to 18 ml of ethanol to obtain an alcohol-water solution; add acid to the alcohol-water mixed solution to adjust the pH to 4; add 20 μl of γ-aminopropyltriethoxysilane and mix evenly to obtain the coupling agent hydrolysis solution.

[0074] Step 3: Modify the silicon nanoparticles: Disperse 0.3 g of silicon nanoparticles in 10 ml of ethanol solution, mix it evenly with the coupling agent hydrolysis solution, stir at low speed for 24 h to ensure complete reaction, centrifuge and wash, and obtain modified silicon nanoparticles after drying.

[0075] Step 4: Prepare the spinning precursor solution: Disperse 0.3 g of modified silicon nanoparticles in 10 ml of N,N-dimethylformamide, and add 1 g of polyvinylpyrrolidone to completely dissolve it in the spinning solvent to obtain the core layer spinning solution. Dissolve 1.5 g of polyacrylonitrile completely in 10 ml of N,N-dimethylformamide to obtain the skin layer spinning solution.

[0076] Step 5: Coaxial electrospinning: At 25 °C and a humidity of 30%, the skin spinning solution and the core spinning solution are used to prepare coaxial structure composite nanofibers by coaxial electrospinning. The parameters of electrospinning are as follows: the voltage is 15 kV, the advancing rate of the skin layer is 0.06 mm·min -1 , and the advancing rate of the core layer is 0.04 mm·min -1 , the spinning time is 11 h, and the rotating speed of the roller is 500 r·min -1 , and the receiving distance is 15 cm.

[0077] Step 6: Heat treatment: The composite fiber film is thermally stabilized in air at 260 °C for 2 h, and then carbonized in nitrogen gas at 800 °C for 4 h with a heating rate of 5 °C·min -1 , and finally one-dimensional uniform silicon-carbon composite nanofibers are prepared.

[0078] Figure 1 is a scanning electron microscope picture of the silicon-carbon composite nanofibers prepared in Example 3. Through Figure 1 , the cross-sectional morphology of a single fiber and the clear silicon nanoparticles wrapped inside the carbon shell can be clearly observed. The fiber cross-section has a very obvious coaxial structure, indicating that the prepared fiber belongs to the coaxial structure and has excellent conductivity. The silicon nanoparticles inside the carbon shell are evenly dispersed without obvious agglomeration.

[0079] Figure 2 is the EDS diagram of the silicon-carbon composite nanofibers prepared in Example 3. The carbon nanofiber skeleton can be clearly shown, and the silicon nanoparticles are evenly distributed inside the carbon nanofiber skeleton, further confirming that the silane coupling agent can reduce the agglomeration of silicon nanoparticles.

[0080] Figure 3 is the XRD diagram of the silicon-carbon composite nanofibers prepared in Example 3. The diffraction peaks at 2θ values of 28.5°, 47.4°, 56.3°, 69.2°, 76.4° and 88.0° are consistent with the standard XRD data (PDF no. 27-1402) of silicon nanoparticles, which once again proves that there are indeed nano-silicon powders in the sample, and the pre-oxidation carbonization process does not change the inherent structure of the silicon nanoparticles.

[0081] Figure 4 is a button cell with the silicon-carbon composite nanofibers prepared in Example 3 as the electrode at 0.3 A·g -1Discharge specific capacity and cycle number graph below. The electrochemical performance test was carried out using a standard 2032 type button battery. The sample of Example 3 was cut into a 12 mm circle and directly used as the working electrode without adding any conductive agent and binder. In a glove box filled with argon, the obtained electrode and lithium metal foil were assembled as the counter electrode. Ethylene carbonate (EC): Diethyl carbonate (DEC): Dimethyl carbonate (DMC) dissolved in 1.0 M LiPF6 in a ratio of 1:1:1 (v / v / v) was used as the electrolyte, and polypropylene was used as the separator. The constant current charge-discharge performance was tested on a NEWARE multi-channel battery measurement system (CT4008T, China) with a voltage range of 0.001 - 3V. After 900 cycles, 35.6% of the initial capacity was still retained. When the number of cycles reached about 100, the cycle capacity had stabilized, proving the stability of the SEI layer. At such a large number of cycles, the capacity retention rate confirmed that the coaxial structure could alleviate the volume expansion problem of silicon nanoparticles and stabilize the growth of the SEI film.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting silicon-carbon negative electrode material with a coaxial structure, characterized in that: The steps include: Modifying silicon nanoparticles by using a silane coupling agent to obtain modified silicon nanoparticles; The modified silicon nanoparticles are uniformly mixed with a core layer polymer to obtain a modified core layer mixture; wherein the core layer polymer is one of polymethyl methacrylate, polyvinyl alcohol, polyvinyl pyrrolidone, polycaprolactone, and polyethylene oxide; The modified core layer mixture and the skin layer polymer are made into coaxial structure composite nanofibers by coaxial electrospinning method; wherein the coaxial structure composite nanofibers are divided into two layers from inside to outside, the inner layer is a core layer composed of the modified core layer polymer, and the outer layer is a skin layer composed of the skin layer polymer; the skin layer polymer is one of polyacrylonitrile, polyvinylidene fluoride, and polyimide; The coaxial structure composite nanofiber is pyrolyzed and carbonized under inert atmosphere to obtain the composite nanofiber.

2. The preparation method according to claim 1, characterized in that: The silane coupling agent is one of γ-aminopropyl triethoxysilane, γ-glycidyloxypropyl trimethoxysilane and γ-methacryloxypropyl trimethoxysilane.

3. The preparation method according to claim 1, characterized in that: The added mass of the modified silicon nanoparticles is 5-40wt% of the core layer polymer.

4. The preparation method according to claim 1, characterized in that: The modification process is as follows: adding a silane coupling agent to an alcohol aqueous solution with a pH of 3 to 4 to prepare a coupling agent hydrolysis solution, and adding silicon nanoparticles to the coupling agent hydrolysis solution to fully react to obtain modified silicon nanoparticles.

5. The preparation method according to claim 1, characterized in that: The modified silicon nanoparticles are uniformly mixed with a core layer polymer and a solvent to obtain a modified core layer mixture solution; the modified core layer mixture solution and a skin layer polymer solution are made into coaxial structure composite nanofibers by a coaxial electrospinning method.

6. The preparation method according to claim 1, characterized in that: The parameters of the coaxial electrospinning method are: temperature 25-35°C, humidity 30-40%, voltage 10-20 kV, and cortical propulsion rate 0.04-0.08 mm·min -1 , the core layer advancement rate is 0.02-0.05mm·min -1 , spinning time is 4-12h, drum speed is 500-1000r·min -1 , the receiving distance is 10-20cm.

7. The preparation method according to claim 1, characterized in that: The temperature of pyrolysis carbonization is 600-1000℃; Alternatively, the coaxial structure composite nanofibers are first heated to 150-300° C. in an air atmosphere for low temperature thermal stabilization, and then pyrolyzed and carbonized under inert atmosphere conditions.

8. A self-supporting silicon-carbon negative electrode material with a coaxial structure, characterized in that: Obtained by the preparation method described in any one of claims 1 to 7.

9. Use of the self-supporting silicon-carbon negative electrode material with a coaxial structure as claimed in claim 8 in preparing a negative electrode for a lithium-ion battery.

10. A lithium ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein: The active material of the negative electrode is the self-supporting silicon-carbon negative electrode material with a coaxial structure as described in claim 8.

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