A method for preparing a self-supporting composite anode, a self-supporting composite anode, and a lithium-ion battery.

Abstract

This invention discloses a method for preparing a self-supporting composite anode, a self-supporting composite anode, and a lithium-ion battery. The preparation method includes: S1, pulverizing SiO powder, grinding and mixing an appropriate amount of multi-walled carbon nanotube dispersion with the pulverized SiO powder to obtain a modified SiO material; S2, uniformly mixing the modified SiO material and a PAN solution to obtain a spinning mixture; S3, electrospinning using the spinning mixture, and after spinning, removing and drying the obtained fiber felt to obtain SiO / PAN composite fibers; S4, sequentially pre-oxidizing and carbonizing the SiO / PAN composite fibers to obtain a SiO self-supporting composite anode fiber material. This invention has a simple process, low cost, and can prepare a self-supporting composite anode material with good electrochemical performance and stable mechanical structure.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery anode material technology, and in particular to a method for preparing a self-supporting composite anode, a self-supporting composite anode, and a lithium-ion battery. Background Technology

[0002] Structural-functional integrated lithium-ion battery technology introduces self-supporting and load-bearing characteristics into the battery, facilitating its shape-configurable and irregular design, and improving the space utilization efficiency of energy equipment. Existing methods for realizing structural batteries include designing embedded battery packs, constructing carbon fiber structural batteries, and fabricating one-dimensional linear fiber batteries, among others.

[0003] In the casting process of commercial lithium-ion battery negative electrode sheets, a relatively large copper foil is typically used as a current collector to support the active material in the electrode and facilitate electron transfer. However, the high mass density of copper foil significantly hinders the improvement of the negative electrode's energy density. Taking a common silicon-carbon composite electrode as an example, its active material specific capacity is 400 mAh / g to 500 mAh / g, and the surface density of the active material coating is 4 mg / cm³. 2 ~5mg / cm 2 In this case, the areal density of the attached copper foil current collector reaches 7-9 mg, therefore the overall energy density of the electrode is less than 300 mAh / g, and the areal capacity is only 1.5 mAh / cm³. 2 ~2mAh / cm 2 (0.05V~2.0V). Furthermore, the rigidity of copper foil electrodes is detrimental to their application in structurally integrated batteries. Therefore, the fabrication of self-supporting electrode materials is a key technology for improving the energy density of lithium-ion battery electrodes and realizing the structural design of batteries.

[0004] In existing self-supporting electrode material design and fabrication techniques, conductive properties and high active material loading are crucial. These methods include hydrothermal growth to synthesize active materials in situ on the surface of elastic, non-conductive polymers, filtration and impregnation to composite active particles (graphene or carbon nanotube sheets) into highly conductive carbon materials, and magnetron sputtering to bond active materials to the surface of a foamed metal matrix. However, all these methods suffer from low active material loading. Therefore, balancing electrode conductivity and active material loading is key to fabricating high-energy-density self-supporting electrode structures.

[0005] Silicon suboxide anode materials possess a high theoretical specific capacity of 2680 mAh / g, but during electrochemical reactions, the repeated insertion and extraction of lithium ions within the structure leads to a dramatic volume expansion (approximately 200%). Most studies have opted for in-situ SiO generation by adding tetraethyl orthosilicate to the PAN spinning solution and then heating and reducing the fiber precursor to obtain the product. However, the SiO loading in the materials obtained by this method is generally low, limiting the capacity utilization of the SiO fibers. Summary of the Invention

[0006] This invention provides a method for preparing a self-supporting composite anode, a self-supporting composite anode, and a lithium-ion battery, so as to balance electrode conductivity and active material loading.

[0007] To achieve the above objectives, this invention proposes a method for preparing a self-supporting composite negative electrode, comprising the following steps:

[0008] S1. The SiO powder is pulverized, and an appropriate amount of multi-walled carbon nanotube dispersion and the pulverized SiO powder are ground and mixed to obtain modified SiO material.

[0009] S2. Mix the modified SiO material and PAN solution evenly to obtain a spinning mixture;

[0010] S3. Electrospinning is performed using a spinning mixture. After spinning, the obtained fiber felt is removed and dried to obtain SiO / PAN composite fiber.

[0011] S4. The SiO / PAN composite fibers are pre-oxidized and carbonized sequentially to obtain SiO self-supporting composite anode fiber material.

[0012] The present invention also provides a self-supporting composite anode, which is prepared by the above preparation method; the self-supporting composite anode includes one-dimensional carbon nanofibers and silicon suboxide anode material particles; the one-dimensional carbon nanofibers are prepared by heat treatment of PAN;

[0013] During the electrospinning process, silicon suboxide anode material particles are uniformly embedded into the interior of one-dimensional carbon nanofibers, and a uniform heterogeneous interface is formed between the surface of silicon suboxide anode material particles and one-dimensional carbon nanofibers.

[0014] The diameter of the one-dimensional carbon nanofiber is 200nm to 400nm, and the mass ratio of the one-dimensional carbon nanofiber to the silicon suboxide anode material particles is (0.5 to 0.8):1.

[0015] The present invention also provides a lithium-ion battery comprising the SiO self-supporting composite negative electrode fiber material prepared by the above preparation method or the above self-supporting composite negative electrode.

[0016] The advantage of this invention over the prior art lies in:

[0017] 1. This invention modifies SiO using a multi-walled carbon nanotube dispersion: 1) Adding highly conductive carbon materials can significantly improve the conductivity of the heat-treated silicon suboxide / carbon fiber self-supporting composite anode material, greatly increasing the coulombic efficiency of the electrode; 2) Adding multi-walled carbon nanotubes can greatly improve the mechanical properties of the heat-treated silicon suboxide / carbon fiber self-supporting composite anode material, greatly improving the flexibility and toughness of the self-supporting electrode. The premise of a self-supporting electrode is that the electrode material itself has certain mechanical properties (such as tensile strength and bending strength) without the action of any current collector and binder; 3) Using a multi-walled carbon nanotube dispersion to modify SiO is beneficial for forming a fiber structure at a lower temperature.

[0018] 2. Compared with traditional flexible electrodes, the self-supported silica / carbon fiber composite anode prepared by electrospinning has the following advantages: 1) Uniform composition: The self-supported silica / carbon fiber composite anode prepared by electrospinning has a more uniform composition, which is beneficial to improving the electrochemical performance of the electrode; 2) Tunable structure: By controlling the electrospinning technology parameters, the diameter, shape, orientation and other structural parameters of the flexible fibers can be controlled, which provides more choices for optimizing the structure and performance of the electrode; 3) Excellent mechanical properties: The self-supported silica / carbon fiber composite anode prepared by electrospinning has excellent mechanical properties, such as high flexibility and stretchability, which makes the electrode more adaptable and durable in practical applications; 4) Simple preparation method: Electrospinning technology has the advantages of simple preparation process and large-scale production, which helps to reduce the manufacturing cost of the electrode and improve production efficiency. In summary, the self-supported silica / carbon fiber composite anode prepared by electrospinning has advantages in terms of uniform composition, tunable structure, mechanical properties and preparation method, making it a strong competitor to traditional flexible electrodes and with broad application prospects in many fields.

[0019] In summary, the preparation method of this invention proposes a technology for forming a flexible, highly conductive framework by electrospinning and coating electrode materials. This method has the advantages of simple process, low cost, and significant effect, and is conducive to industrial application.

[0020] 3. Compared with traditional electrodes, the silicon suboxide / carbon fiber self-supporting composite anode material prepared by this invention has the following advantages: 1) Reduced cost: The silicon suboxide / carbon fiber self-supporting composite anode can eliminate some or all of the current collector, thereby reducing the cost of the battery; 2) Simplified structure: The structure of the silicon suboxide / carbon fiber self-supporting composite anode is relatively simple and does not require an additional current collector, thus simplifying the battery structure; 3) Increased capacity: The silicon suboxide / carbon fiber self-supporting composite anode can provide a larger specific surface area of ​​active material, thereby increasing the battery capacity; 4) Improved battery stability: The silicon suboxide / carbon fiber self-supporting composite anode has high stability, which can reduce safety hazards during battery use.

[0021] In summary, the composite anode of this invention does not require copper metal current collectors as support, which significantly improves the energy density of the battery electrode. The composite anode has a simple preparation process, good electrochemical performance, and especially stable mechanical structure and high cycle capacity, making it highly valuable and promising for use in the preparation of lithium-ion batteries.

[0022] 4. The silicon suboxide / carbon fiber self-supporting composite anode prepared by this invention significantly improves the huge volume change of conventional silicon anodes during charging and discharging, which is beneficial to the stability of lithium-ion battery structure. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 These are microscopic images of the raw materials for the self-supporting silicon suboxide / carbon fiber composite anode material of the present invention; (a) is a SEM image of SiO raw material; (b) is a SEM image of SiO / PAN composite fiber; (c) is a TEM image of SiO / PAN composite fiber.

[0025] Figure 2 The images shown are scanning electron microscope (SEM) images and photographs of the silicon suboxide / carbon fiber self-supporting composite anode material of Example 1 of the present invention.

[0026] Figure 3 The images show the HRTEM image and elemental distribution of the silicon suboxide / carbon fiber self-supporting composite anode material of Example 1 of this invention.

[0027] Figure 4The image shows the XRD pattern of the silicon suboxide / carbon fiber self-supporting composite anode material of the present invention and its related raw materials and intermediate products.

[0028] Figure 5 The graphs show the cycle energy variation curves of the silicon suboxide / carbon fiber self-supporting composite anode material of Example 1 of the present invention, and the anode materials of Comparative Examples 1, 2 and 3 at different rates.

[0029] Figure 6 The graphs show the cycle energy variation curves of the silicon suboxide / carbon fiber self-supporting composite anode material of Example 1 of the present invention, and the anode materials of Comparative Examples 4 and 5 at different rates.

[0030] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0033] This invention proposes a method for preparing a self-supporting composite negative electrode, characterized by comprising the following steps:

[0034] S1. The SiO powder is pulverized, and an appropriate amount of multi-walled carbon nanotube dispersion and the pulverized SiO powder are ground and mixed to obtain modified SiO material.

[0035] S2. The modified SiO material and PAN solution are uniformly mixed to obtain a spinning mixture. Uniform mixing can be achieved using a homogenizer, wherein the homogenizer speed can be 350 rpm.

[0036] S3. Electrospinning is performed using a spinning mixture. After spinning, the obtained fiber felt is removed and dried to obtain SiO / PAN composite fibers. The spinning solution is contained in a syringe, and the solution is extruded from the syringe and passed through a flat-mouth needle into a high-voltage electric field. The droplets are stretched into nanocomposite fibers and collected on the surface of a roller. The spinning parameters can be set as follows: spinning environment at room temperature and 30% relative humidity, spinning speed of 1.5 mL / h, inner diameter of the flat-mouth needle of 5 mm, positive and negative high voltage of 11 kV and -2 kV respectively, and distance between the roller surface and the syringe of 8 cm.

[0037] S4. The SiO / PAN composite fibers are pre-oxidized and carbonized sequentially to obtain a SiO self-supporting composite negative electrode fiber material. The obtained SiO / PAN composite fibers can be sandwiched between perforated graphite plates and placed in a tube furnace for pre-oxidation, followed by furnace cooling and annealing, and then carbonization.

[0038] Preferably, in step S1, the pulverization is achieved by ball milling or grinding; wherein the ball milling speed is 400-500 rpm and the ball milling time is 2-3 h;

[0039] The dispersion of multi-walled carbon nanotubes has a mass fraction of 1–2%, and the solvent is one or both of N-methylpyrrolidone and DMF; the aspect ratio of the multi-walled carbon nanotubes is 10. 3 ~10 6 .

[0040] This invention uses multi-walled carbon nanotubes with a high aspect ratio to modify SiO, which is beneficial for the formation of fibrous structures in the composite material after heat treatment.

[0041] Preferably, in step S1, the mass ratio of the multi-walled carbon nanotube dispersion to the pulverized SiO powder is (1-5) g: 0.8 g. Too high a multi-walled carbon nanotube content will result in low negative electrode capacity, while too low a content will make it difficult to form the fibrous structure of the negative electrode material, reducing the flexibility of the self-supporting electrode. Furthermore, too low a multi-walled carbon nanotube content will reduce the conductivity of the electrode.

[0042] Preferably, in step S2, the PAN solution has a mass fraction of 5-20%, and the solvent is one or two of N,N-dimethylformamide and DMSO.

[0043] Preferably, in step S2, the mass ratio of modified SiO material to PAN solution is (0.8-1.4) g: 6 g.

[0044] Preferably, in step S3, the drying temperature is 100–110°C, and the holding time is 6–12 hours. If the temperature is too high, the fiber structure of the material will be damaged; if the temperature is too low, the organic solvent will be difficult to evaporate completely.

[0045] Preferably, in step S4, the pre-oxidation is carried out in a flowing air atmosphere; the carbonization is carried out in a reducing atmosphere; the reducing atmosphere is Ar / H2 gas.

[0046] Preferably, in step S4, the heating rate of the pre-oxidation is 2.5–3.5 °C / min, the holding temperature is 200–210 °C, and the holding time is 2–3 h;

[0047] The carbonization heating rate is 1.5–2℃ / min, the holding temperature is 600–700℃, and the holding time is 2–3h.

[0048] If the pre-oxidation temperature is too low, PAN will not be able to cross-link and cyclize to form carbon nanofibers; if the pre-oxidation temperature is too high, the material's toughness will deteriorate. If the carbonization temperature is too low, the material's electrical conductivity will be poor; if the carbonization temperature is too high, the material's brittleness will increase and its toughness will decrease. If the heating rate is too high, the material's thermal expansion will be too severe; if the heating rate is too low, the material's shrinkage will increase significantly.

[0049] The present invention also proposes a self-supporting composite anode, which is prepared by the above preparation method; the self-supporting composite anode includes one-dimensional carbon nanofibers and silicon suboxide anode material particles; the one-dimensional carbon nanofibers are obtained by heat treatment of PAN;

[0050] During electrospinning, silicon suboxide anode material particles are uniformly embedded into one-dimensional carbon nanofibers. A good interface structure is formed between the surface of the silicon suboxide anode material particles and the one-dimensional carbon nanofibers through the formation of a uniform heterogeneous interface, which can significantly improve the conductivity of the composite fiber material.

[0051] The diameter of the one-dimensional carbon nanofiber is 200nm to 400nm, and the mass ratio of the one-dimensional carbon nanofiber to the silicon suboxide anode material particles is (0.5 to 0.8):1.

[0052] The present invention also proposes a lithium-ion battery comprising a SiO self-supporting composite negative electrode fiber material prepared by the above-described preparation method or the above-described self-supporting composite negative electrode.

[0053] Example 1:

[0054] S1. First, commercial SiO powder was ball-milled at 400 rpm for 2 hours in a ball mill. Then, 0.8 g of the ball-milled powder was weighed and ball-milled in a planetary ball mill at 400 rpm with 1 g of 1% (w / w) multi-walled carbon nanotube dispersion (solvent: N-methylpyrrolidone, i.e., NMP) to obtain modified SiO material. At this time, the amount of silica added was 40%.

[0055] S2. Subsequently, the modified SiO material was mixed with 6g of PAN solution with a mass fraction of 16.7% (solvent being N,N-dimethylformamide, i.e., DMF), and mixed evenly at a speed of 350rpm to prepare a spinning mixture.

[0056] S3. The spinning solution is contained in a 10mL syringe. At room temperature and 30% relative humidity, the spinning solution is extruded from the syringe at a rate of 1.5mL / h, passing through a flat-mouthed needle with an inner diameter of 0.5mm and entering a high-voltage electric field. The positive and negative voltages of the electric field are 11kV and -2kV, respectively, stretching the droplets into nanocomposite fibers, which are collected on the surface of rollers 8cm apart. After spinning, the obtained fiber felt is removed and placed in a vacuum oven at 110℃ for 6 hours to dry excess solvent. The final product is a SiO / PAN composite fiber with a SiO content of 40%.

[0057] S4. Place the SiO / PAN composite fibers in a muffle furnace and ensure full contact with air. Pre-oxidize the spun fibers in air at 200℃ with a heating rate of 3℃ / min and a holding time of 2 hours, then anneal with furnace cooling. The pre-oxidized fiber anode materials are collectively referred to as SiO / cPAN. Place the SiO / cPAN obtained from the 200℃ pre-oxidation in a tube furnace under an Ar / H2 atmosphere, heat to 600℃ at a heating rate of 2℃ / min, and hold for 2 hours for carbonization, ultimately obtaining the carbonized SiO composite anode fiber material (SiO / CNF).

[0058] Comparative Example 1:

[0059] The only difference between Comparative Example 1 and Example 1 is that the amount of silicon suboxide added is 50%, that is, the powder after ball milling is 1.0g.

[0060] Comparative Example 2:

[0061] The only difference between Comparative Example 2 and Example 1 is that the amount of silicon suboxide added is 60%, that is, the powder after ball milling is 1.2g.

[0062] Comparative Example 3:

[0063] The only difference between Comparative Example 3 and Example 1 is that the amount of silicon suboxide added is 70%, that is, the powder after ball milling is 1.4g.

[0064] Comparative Example 4:

[0065] The only difference between Comparative Example 4 and Example 1 is that the carbonization temperature is 500°C.

[0066] Comparative Example 5:

[0067] The only difference between Comparative Example 5 and Example 1 is that the carbonization temperature is 700°C.

[0068] Characterization and performance testing

[0069] (1) The silicon suboxide / carbon fiber self-supporting composite anode material and its related raw materials and intermediates were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and elemental distribution. The results are as follows: Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown.

[0070] like Figure 1 As shown, SiO particles exhibit severe agglomeration, so ball milling was used to break them down and disperse the nanoparticles before spinning. The resulting SiO / PAN fibers after spinning interweave, forming a continuous, straight network of polymer matrix that effectively encapsulates the inorganic SiO anode particles. The diameter of a single fiber ranges from 200 to 400 nm, with the portion loaded with the active material reaching approximately 400 nm in diameter. It can be seen that the fiber material prepared by electrospinning effectively loads inorganic materials into the polyacrylonitrile polymer, forming a continuous interwoven network structure. The inorganic SiO particles in the fibers coexist in a continuous / semi-continuous manner, forming an organic / inorganic composite fiber.

[0071] Figure 2 This is a SEM image of the SiO / CNF material. Compared to... Figure 1 After carbonization, the fibers of SiO / cPAN undergo significant twisting and shrinkage, with the portion carrying active particles shrinking to 200–400 nm. From a macroscopic morphology perspective, the surface color of the fiber felt before carbonization is generally light gray; after pre-oxidation in air, the fibers turn brownish-yellow; and after carbonization, they turn brownish-black. It can be bent with a radius of curvature of 1 cm, indicating good bending resistance.

[0072] Figure 3 The image shows the HRTEM image of SiO / CNF and its mapping. Figure 3 In the carbon fiber and its supported active particles, neither obvious lattice fringes are observed, indicating an amorphous state, and a continuous contact interface is formed between the two materials. Beaded, discontinuously distributed aggregated particles, rich in Si and O elements, are also present in the fiber, forming aggregated SiO nanoparticles. The heat-treated carbon fiber exhibits a uniform distribution of N and C elements, demonstrating that N doping has been achieved in the carbon fiber.

[0073] Figure 4The XRD patterns of the composite fibers and their raw materials are shown. In the XRD pattern of pure SiO, mixed peaks of Si and SiO2 appear. The broad peak near 2θ = 23° belongs to amorphous SiO2 (JCPDS 46-1045), while the peaks at 2θ = 28.3°, 47.5°, and 56.0° belong to the (111), (220), and (310) planes of pure silicon (JCPDS 27-1402). The reason for these two mixed peaks is that when pure SiO is vigorously pulverized in a ball mill, a partial differentiation reaction occurs, resulting in Si and SiO2 with distinct crystal forms. The peak at 2θ = 16.9° of the original and peroxide fibers comes from the cyano groups (-C≡N) remaining in PAN before carbonization (JCPDS 48-2119). The carbonized composite fibers, coated with polyacrylonitrile-based carbon, are deposited on the SiO material. A broad peak appears only near 2θ = 25°, indicating a mixture of SiO and carbonized polyacrylonitrile fibers. This demonstrates that the SiO is coated with polyacrylonitrile-based carbon.

[0074] (2) The negative electrode materials of Comparative Examples 1, 2, 3, 4, 5, and 1 were used to prepare battery electrodes for electrochemical performance testing. The specific steps are as follows:

[0075] The electrochemical testing electrode is a 12mm diameter circular electrode, and it is a self-supporting electrode, requiring no additional components for support. The preparation process of this type of self-supporting electrode is as follows: The original composite fiber is placed in a 110℃ vacuum oven for 6 hours, then, using aluminum foil as a buffer layer, it is cut into self-supporting electrodes using a cutting machine. After removing the aluminum foil and weighing, it is transferred to a high-purity argon atmosphere glove box for assembly. Before chemical testing, the composite fiber electrode material needs to be mixed with a binder and a conductive agent to form a conductive slurry, ball-milled, and coated. The conductive agent is superconducting carbon SP, and the binder is PVDF. Before use, PVDF is dissolved in NMP to prepare a homogeneous solution with a mass fraction of 10%. The preparation process of this type of electrode is as follows: An appropriate amount of composite fiber electrode is cut and pulverized in a ball mill at a speed of 350 rpm. After extraction, SP and PVDF were added in a mass ratio of 8:1:1, along with an appropriate amount of NMP to achieve a suitable slurry viscosity. The slurry was then ball-milled for 30 minutes at a ball-to-material ratio of 3:1 until homogeneous. A 100-mesh stainless steel scraper was used to evenly coat the slurry. The slurry was then stored in a 110℃ forced-air drying oven until no obvious liquid solvent residue remained on the surface. It was then transferred to a 110℃ vacuum chamber and kept at that temperature for 6 hours. After being punched into 12mm diameter electrode sheets and weighed, the sheets were transferred to a high-purity argon atmosphere glove box for assembly.

[0076] Cycling and rate performance curves: At room temperature (25°C), the assembled coin cells were subjected to constant current charge-discharge and rate performance tests at a specific current density. The cutoff voltage range was 0.0 to 1.5V (vs Li+ / Li), and the charge-discharge rate ranged from 0.1C to 5C. Each cell was cycled 5 times at different rates.

[0077] Electrochemical test results as follows Figure 5 , Figure 6 As shown, Figure 5 Cycling and rate performance graphs of SiO / CNF composite fibers with different SiO addition amounts. Figure 5 As shown, the material exhibits a low capacity decay rate at low rates. In Example 1, the initial discharge capacity in the first and second cycles reaches 1500 mAh / g and 992 mAh / g, respectively, decaying to 775 mAh / g after 100 cycles, with a capacity retention rate of 78.1%, indicating acceptable cycle stability. Figure 5 As shown, in the rate test, after 5 cycles at a high rate of 5C, the capacity retention rate of the material in Example 1 was 65.1% (relative to the first cycle at 0.1C), while the capacity retention rates of Comparative Examples 3, 2, and 1 were 50.3%, 23.6%, and 39.5%, respectively. This indicates that Example 1 has better rate performance.

[0078] Figure 6 To assess the specific capacity performance of SiO / CNF fibers with different carbonization temperatures at various rates, the battery was cycled 5 times at each rate. At low rates of 0.1C and 0.2C, disregarding the rapid initial capacity decay, Sample 1 exhibited the best capacity performance, approximately 1240 mAh / g and 1040 mAh / g, respectively, while Comparative Examples 4 and 5 showed similar specific capacities, approximately 890 mAh / g and 960 mAh / g, respectively. At 0.2C, Sample 1's specific capacity was approximately 1035 mAh / g, significantly higher than the other two samples. After recovering to 0.1C following high-rate cycling, Sample 1's specific capacity recovered to 1067 mAh / g, indicating good stability.

[0079] In summary, this patent proposes a method for preparing a self-supporting composite fiber anode material using electrospinning and SiO2 as the active material. Starting with the influence of heat treatment process, component ratio, and heat treatment temperature on the composite fiber structure and electrochemical performance, optimal ratios and heat treatment conditions are proposed. Furthermore, a three-dimensional stable conductive network is constructed through impregnation and drying of carbon nanotube conductive slurry, improving the cycle stability and rate performance of the composite fiber anode material. The SiO / CNF self-supporting fiber felt prepared with 40% SiO2 addition and a carbonization temperature of 600℃ exhibits high active material loading capacity and good bending resistance. This is because the 40% SiO2 addition makes the active particles easier to disperse and maintains the inherent fiber morphology during carbonization, while the 600℃ carbonization temperature allows the fiber material to possess both high conductivity and bending ability. From an industrial application perspective, this patent eliminates the need for metal current collectors and large amounts of binders in traditional electrodes, showing broad commercial application prospects and potential.

[0080] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a self-supporting composite negative electrode, characterized in that, Includes the following steps: S1. The SiO powder is pulverized, and a multi-walled carbon nanotube dispersion with a mass ratio of (1~5) g: 0.8 g and the pulverized SiO powder are ground and mixed to obtain a modified SiO material, wherein the mass fraction of the multi-walled carbon nanotube dispersion is 1~2%; S2. Mix the modified SiO material and PAN solution evenly to obtain a spinning mixture; S3. Electrospinning is performed using a spinning mixture. After spinning, the obtained fiber felt is removed and dried to obtain SiO / PAN composite fiber. S4. The SiO / PAN composite fibers are pre-oxidized and carbonized sequentially. The heating rate of carbonization is 1.5~2℃ / min, the holding temperature is 600~700℃, and the holding time is 2~3h to obtain the SiO self-supporting composite negative electrode fiber material.

2. The preparation method according to claim 1, characterized in that, In step S1, pulverization is achieved by ball milling; wherein the ball milling speed is 400~500 rpm and the ball milling time is 2~3 h. The solvent is one or both of N-methylpyrrolidone and DMF; the aspect ratio of the multi-walled carbon nanotubes is 10. 3 ~10 6 .

3. The preparation method according to claim 1, characterized in that, In step S2, the PAN solution has a mass fraction of 5-20%, and the solvent is one or two of N,N-dimethylformamide and DMSO.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of modified SiO material to PAN solution is (0.8~1.4) g: 6 g.

5. The preparation method according to claim 1, characterized in that, In step S3, the drying temperature is 100~110℃, and the holding time is 6~12h.

6. The preparation method according to claim 1, characterized in that, In step S4, the pre-oxidation is carried out in a flowing air atmosphere; Carbonization is carried out in a reducing atmosphere, which is Ar / H2 gas.

7. The preparation method according to claim 1, characterized in that, In step S4, the heating rate of the pre-oxidation is 2.5~3.5℃ / min, the holding temperature is 200~210℃, and the holding time is 2~3h.

8. A self-supporting composite negative electrode, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7; The self-supporting composite anode comprises one-dimensional carbon nanofibers and silicon suboxide anode material particles; the one-dimensional carbon nanofibers are obtained by heat treatment of PAN. The silicon suboxide anode material particles are uniformly embedded into the interior of one-dimensional carbon nanofibers during electrospinning, and a uniform heterogeneous interface is formed between the surface of the silicon suboxide anode material particles and the one-dimensional carbon nanofibers. The diameter of the one-dimensional carbon nanofiber is 200 nm to 400 nm, and the mass ratio of the one-dimensional carbon nanofiber to the silicon suboxide anode material particles is (0.5~0.8):

1.

9. A lithium-ion battery, characterized in that, This includes the SiO self-supporting composite negative electrode fiber material prepared by the preparation method according to any one of claims 1 to 7, or the self-supporting composite negative electrode as described in claim 8.

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