Preparation method and application of silicon-based composite material

Abstract

The application belongs to the technical field of battery materials, and relates to a preparation method and application of a silicon-based composite material. The preparation method comprises the following steps: dissolving a PDDA solution in water and ethanol, adding nano-silicon powder, and then adding selenium dioxide and stirring uniformly; subsequently, a cobalt source, a nickel source and a reducing agent are added, and pH is adjusted to obtain a precursor solution; the precursor solution is subjected to hydrothermal reaction, and after centrifugation, washing, filtration and drying, a Si / Ni y Co (1‑y) Se x nanowire powder sample; after the powder sample is ground and sieved, chemical vapor deposition is performed to grow carbon nanotubes on the surface of the nanowires, and finally, the silicon-based composite material is obtained. In the silicon-based composite material, the surface of the nano-silicon particles is uniformly distributed with nickel-cobalt selenide nanowires and carbon nanotubes, the two are interwoven to form a cage-like conductive network structure, the nano-silicon particles are effectively coated and fixed, and therefore the overall electrochemical performance of the composite material is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a method for preparing and applying a silicon-based composite material. Background Technology

[0002] Silicon-based materials are considered one of the most promising next-generation high-energy-density lithium-ion battery anode materials due to their high specific capacity, low operating potential, and abundant reserves. However, significant volume expansion during lithium insertion / extraction, low intrinsic conductivity, and slow lithium-ion diffusion kinetics severely restrict their commercialization. Nanotechnology offers a new approach to solving these problems, with current research focusing on structures such as nanoparticles, nanowires, and nanosheets. Nanoparticles, with their geometric properties, can effectively increase the critical expansion stress threshold; nanosheets, due to their excellent electronic conductivity, can significantly shorten the lithium-ion transport path; and one-dimensional nanowires and nanotubes, with their unique high aspect ratio, can not only eliminate the lithium-ion transport barrier between particles, but their radial volume change characteristics also maintain structural integrity. Furthermore, the gaps between nanowires can effectively buffer volume expansion and form axial fast lithium-ion transport channels, thus exhibiting excellent cycle stability and high reversible specific capacity.

[0003] However, single nanostructures inevitably lead to a surge in specific surface area and a decrease in tap density, resulting in poor initial coulombic efficiency and volumetric specific capacity of the battery, severely limiting its practical applications. Therefore, researchers are working to develop single nanostructures into more complex hierarchical structures. However, increased structural complexity places higher demands on fabrication processes and precursors; thus, developing simple and efficient hierarchical nanowire fabrication methods is crucial for advancing the commercialization of silicon anodes. Summary of the Invention

[0004] This invention addresses the shortcomings of existing lithium batteries by providing a method for preparing and applying silicon-based composite materials. Starting with the preparation of ultrafine nanowires, in-situ self-assembly is used as a technical means to modify nickel cobalt selenide nanowires and carbon nanotubes on the surface of nano-silicon powder. Through structural design of the Si material, the aim is to buffer volume expansion and thus improve electrochemical performance.

[0005] One aspect of the present invention provides a method for preparing a silicon-based composite material, comprising the following steps:

[0006] S1. Dissolve polydiallyldimethylammonium chloride (PDDA) solution in a mixture of water and ethanol, add nano-silica powder to disperse it, then add selenium dioxide and stir evenly; subsequently, add cobalt source, nickel source and reducing agent, adjust the pH value to 9~14, and continue stirring to obtain precursor solution;

[0007] S2. The precursor solution was subjected to a hydrothermal reaction, followed by centrifugation, washing, filtration, and drying to obtain Si / Ni. y Co (1-y) Se x Nanowire powder sample;

[0008] S3. After grinding and sieving the powder sample, chemical vapor deposition is performed on the Si / Ni... y Co (1-y) Se x Carbon nanotubes are grown on the surface of nanowires to obtain Si / Ni y Co (1-y) Se x / CNTs composite materials.

[0009] The following is a detailed description of step S1:

[0010] Preferably, the average particle size of the nano-silicon powder is 1~200 nm, more preferably 2~100 nm, and even more preferably 10~80 nm.

[0011] Nano-silicon powder has high activity, but it is prone to agglomeration during the preparation process. The addition of PDDA in this invention helps to uniformly disperse the nano-silicon powder. Si attracts and adsorbs PDDA through electrostatic attraction, making its surface positively charged, attracting selenite ions generated by selenium dioxide dissolved in water, thus solving the problem of easy agglomeration.

[0012] Preferably, the mass fraction of the polydiallyldimethylammonium chloride solution is 20-50 wt%.

[0013] Preferably, the weight-average molecular weight (Mw) of polydiallyldimethylammonium chloride is ≤100,000.

[0014] Optionally, the mass ratio of the polydiallyldimethylammonium chloride solution to the volume ratio of the water and ethanol mixture is 1:10 to 100. In the water and ethanol mixture, the mass ratio of water to ethanol is 0.8 to 1.5:1.

[0015] Nano-silica powder is added and dispersed using ultrasonic dispersion for 0.5 to 2 hours.

[0016] Preferably, the mass ratio of nano-silicon powder to polydiallyldimethylammonium chloride is 1:0.8~1.5.

[0017] Then add selenium dioxide, stir evenly at a speed of 100-800 rpm for 10-60 minutes.

[0018] Preferably, the mass ratio of selenium dioxide to nano-silicon powder is 1~10:1.

[0019] Preferably, the cobalt source is one or more of cobalt nitrate or its hydrate, cobalt chloride, cobalt acetate or its hydrate; the nickel source is one or more of nickel nitrate or its hydrate, nickel chloride, nickel acetate or its hydrate.

[0020] Preferably, the molar ratio of selenium dioxide to the total molar ratio of cobalt and nickel sources is 0.5 to 5:1.

[0021] Preferably, the molar ratio of cobalt source to nickel source is 0.2 to 5:1.

[0022] By introducing different proportions of Co and Ni sources into the precursor, Ni with controllable composition can be prepared. y Co （1-y） Se x Nanowires.

[0023] Further optimizations include a selenium dioxide to nano-silicon powder mass ratio of 3.5 to 4.5:1; a cobalt source to nickel source molar ratio of 0.9 to 1.1:1; and a selenium dioxide molar amount to the total molar amount of cobalt and nickel sources ratio of 1 to 3:1.

[0024] Preferably, the reducing agent is one or more selected from xylose, fructose, glucose, sucrose, hydrazine hydrate (N2H4·H2O), ascorbic acid, sodium borohydride (NaBH4), and sodium thiosulfate. The type of reducing agent significantly affects the morphology of the nanowires; reducing agents with different reducing abilities result in different kinetics for the diffusion growth of Se atoms. More preferably, the reducing agent is xylose.

[0025] Preferably, the molar ratio of the reducing agent to selenium dioxide is 0.5 to 5:1.

[0026] Preferably, ammonia is added to adjust the pH. The pH of the precursor solution also affects the final morphology of the product and can regulate the surface freedom of the crystals during the reaction. More preferably, the pH is adjusted to 9-11.

[0027] After adjusting the pH value, continue stirring for 10-60 minutes.

[0028] The following is a detailed description of step S2:

[0029] Preferably, the hydrothermal reaction conditions in step S2 include: a temperature of 120~200 ℃ and a time of 12~30 h. More preferably, the hydrothermal reaction temperature is 160~180 ℃ and the reaction time is 20~25 h.

[0030] Preferably, the centrifugal washing conditions in step S2 include: a centrifugal speed of 3000~10000 rpm, a centrifugation time of 5~30 min, and 2~6 washes. This removes excess PDDA and residual impurities.

[0031] The drying conditions include: vacuum drying, drying temperature of 50~90 ℃, and drying time of 5~24 h.

[0032] Step (2) yields Ni particles with a diameter of 5~100 nm and a length of 1~50 μm. y Co （1-y） Se x Nanowires.

[0033] The following is a detailed description of step S3:

[0034] Preferably, the sieve mesh size in step S3 is 300~700 mesh.

[0035] The conditions for chemical vapor deposition in step S3 include: a heating rate of 1–10 °C / min, a temperature of 700–1100 °C, a time of 0.5–5 h, and a gas source consisting of one or more of acetylene, methane, ethanol, and ethylene, as well as an inert gas; a flow rate of 20–800 sccm for each gas; and a reaction pressure of 300–700 Pa. More preferably, the temperature during chemical vapor deposition is 950–1050 °C, and the time is 1–3 h.

[0036] The inert gases used in this article are nitrogen and / or argon.

[0037] A layer of carbon nanotubes is regrown on the surface of the original nanowires through chemical vapor deposition.

[0038] A second aspect of the present invention provides a silicon-based composite material prepared by the above-described preparation method.

[0039] In the silicon-based composite material, nickel cobalt selenide nanowires and carbon nanotubes are uniformly distributed on the surface of the nano-silicon particles, and the two intertwine to form a cage-like conductive network structure.

[0040] A third aspect of the present invention provides an application of a silicon-based composite material in a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the silicon-based composite material.

[0041] Preferably, the raw materials including the silicon-based composite material and the solvent are mixed to prepare a slurry, which is then coated onto the current collector and dried to obtain the negative electrode sheet.

[0042] Preferably, the raw materials include the silicon-based composite material and the binder; the mass ratio of the silicon-based composite material and the binder is (89~98):(2~11).

[0043] Preferably, the raw materials include the silicon-based composite material, the conductive agent, and the binder; the mass ratio of the silicon-based composite material, the conductive agent, and the binder is (87~97):(0.5~5):(2~10).

[0044] The conductive agent, binder, and solvent mentioned are all commonly used substances in the preparation of negative electrode sheets, and no special restrictions are imposed here.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention successfully constructs Si / Ni with a three-dimensional multi-level conductive network structure through the synergistic effect of a simple and efficient one-step hydrothermal method and a subsequent chemical vapor deposition (CVD) method. y Co (1-y) Se x / CNTs composite material. The preparation process mainly includes three key steps: (1) Controllable growth of selenium nanowires: Based on the unique hexagonal crystal structure and significant anisotropic growth characteristics of selenium atoms, they preferentially grow along the

[001] polar direction during crystallization, forming a helical chain structure through Se-Se covalent bonds, thereby spontaneously assembling into one-dimensional nanowires. By precisely controlling the type of reducing agent and the pH value of the precursor solution, the size and morphology of selenium nanowires (Se NWs) can be controlled. (2) In-situ conversion of metal selenides: Using oriented ultrafine selenium nanowires as flexible templates, transition metal atoms (Co, Ni, etc.) are combined with Se NWs through in-situ chemical conversion reactions, and completely converted into the corresponding selenide nanowires. The uniform modification of nickel cobalt selenide nanowires (NiCoSeNWs) on the surface of nano-silicon particles was successfully achieved by a one-step hydrothermal method. (3) Construction of the carbon nanotube network: The Co / Ni bimetallic component in the nickel-cobalt-selenide nanowires serves as a highly efficient catalyst, providing abundant active sites and inducing in-situ growth of carbon nanotubes under a methane / acetylene mixed atmosphere. These selenide nanowires not only act as structure-directing agents to connect silicon particles and carbon nanotubes, but also construct a unique "nanocage"-shaped multi-level conductive network. This three-dimensional multi-threaded interpenetrating network structure significantly reduces the interfacial electron transfer barrier between silicon and the conductive components, thereby greatly improving the overall electrochemical performance of the composite material. This design cleverly combines the structural advantages of each component, achieving a significant improvement in material performance through multi-scale synergistic effects.

[0047] 2. This invention achieves multifunctional surface modification of nano-silicon powder by introducing polydiallyldimethylammonium chloride (PDDA) solution. Its mechanism of action is mainly reflected in the following two aspects: (1) Uniform dispersion and surface modification of nano-silicon: Under ultrasonic assistance, the quaternary ammonium salt cation groups (-N) in PDDA molecules are uniformly dispersed and surface modified. +(CH3)2-) interacts electrostatically with the oxides on the surface of silicon particles to form a positively charged Si@PDDA complex. Thanks to the structural advantages of the linear molecular chain of PDDA, it can be arranged in a highly ordered and compact manner on the surface of silicon particles. Compared with branched surfactants, it can provide a denser distribution of charged groups, thereby generating a stronger Zeta potential difference. This uniform surface modification not only effectively prevents the aggregation of nano-silicon, but also provides an ideal active interface for subsequent reactions. (2) Crystal growth regulation and morphology control: The dissolved SeO2 generates H2SeO3 electrolyte solution, in which SeO3 2- Anions are directionally adsorbed onto the positively charged Si@PDDA surface via electrostatic interactions, forming a regular array of active sites. More importantly, PDDA molecules can act as a highly efficient crystal facet modifier, selectively adsorbing and altering the relative surface energy of different crystal faces, thereby precisely controlling the anisotropic growth kinetics of NiCoSe NWs crystals. This dual-action mechanism enables precise control over the morphology and microstructure of NiCoSe nanomaterials. This innovative surface modification strategy not only solves the technical challenge of dispersibility in nano-silicon but also provides a new dimension of control for constructing nanomaterials with specific morphologies and structures, demonstrating significant multifunctional advantages.

[0048] 3. This invention uses polyhydroxy sugars such as xylose, fructose, and sucrose as reducing agents. The abundant hydroxyl groups in their molecular structure can effectively promote the resorption of the reducing agent and the SeO3 adsorbed by Si@PDDA. 2- The interaction between them. During the reaction, these reducing agents react with SeO3. 2- A redox reaction occurs, initially generating amorphous selenium which uniformly coats the surface of silicon particles. Subsequently, under high-temperature hydrothermal conditions, the amorphous selenium undergoes a crystallization transformation, forming black crystalline selenium. Through the diffusion and self-assembly of Se atoms, it ultimately grows into a one-dimensional nanowire structure. Notably, different reducing agents, due to their varying reducing abilities, can modulate the orientational growth rate of selenium crystals, thereby obtaining nanostructures with diverse morphologies, including zero-dimensional nanoparticles, one-dimensional nanowires, and two-dimensional nanosheets.

[0049] 4. This invention uses ammonia as a pH adjuster, providing favorable conditions for the preparation of uniform one-dimensional nanowires by precisely controlling the acidity and alkalinity of the precursor solution. The surface free energy of each crystal facet is significantly dependent on the pH value of the solution, with crystal faces having higher surface free energies being more conducive to the directional growth of nanowires. Through this pH control mechanism, the controllable synthesis of nanostructures with different morphologies has been successfully achieved.

[0050] 5. This invention prepares bimetallic nickel-cobalt selenide nanowires (NiCoSe NWs) with tunable composition by controlling the feeding ratio of cobalt and nickel sources. An innovative one-step synthesis strategy is employed to simultaneously achieve Ni synthesis during the formation of selenium nanowires. y Co (1-y) Se x In-situ growth of nanowires. These nanowires possess unique electron transport properties: the delocalization effect of lone pair electrons in selenium nanowires endows them with excellent anisotropic electron migration capabilities, significantly promoting directional charge transport; on the other hand, they exhibit stable active site anchoring: the strong Se-M (M=Ni / Co) chemical bonds formed between the Se NWs surface and metal atoms achieve robust fixation of the active sites. Therefore, nickel-cobalt selenide nanowires can serve as suitable catalyst supports, enhancing charge transfer capabilities while supporting active sites.

[0051] 6. The Si / Ni prepared by this invention y Co (1-y) Se x When CNTs composite materials are used as anode materials for lithium-ion batteries, they can effectively improve electrochemical activity and exhibit high specific capacity, initial coulombic efficiency, and cycle stability. Attached Figure Description

[0052] Figure 1 The Si / Ni provided by the present invention y Co （1-y） Se x Schematic diagram of the CNTs composite material;

[0053] Figure 2 It is the Si / Ni prepared in Example 1 0.5 Co 0.5 Low-magnification scanning electron microscope image of Se2 / CNTs composite material;

[0054] Figure 3 The Si / Ni prepared in Example 1 0.5 Co 0.5 High-magnification scanning electron microscope image of Se2 / CNTs composite material;

[0055] Figure 4 It is the Si / Ni prepared in Example 1 0.5 Co 0.5 Cycle curves of Se2 / CNTs composite material as lithium-ion anode material. Detailed Implementation

[0056] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two, three, four, five, or more.

[0057] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0058] 1. Example 1

[0059] This embodiment uses Si / Ni y Co （1-y） Se x The preparation method of CNT nanowire composite materials includes the following steps:

[0060] (1) Dissolve 3.0 g of polydiallyldimethylammonium chloride solution (PDDA, 38%, Mw < 100000) in a 120 mL mixture of deionized water and ethanol (1:1 weight ratio), add 1.0 g of silicon powder with an average particle size of 50 nm and ultrasonically disperse for 1 h, then add 4.0 g of selenium dioxide (SeO2) and magnetically stir for 30 min at room temperature and 600 rpm respectively until a homogeneous solution is formed. Then, slowly add 2.6 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O 291), 2.6 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and 13.4 g of xylose, then add 10 mL of ammonia water (25 wt%) to adjust the pH of the solution to about 10, and continue to magnetically stir for 30 min.

[0061] (2) The above mixed solution was transferred to a 500 mL polytetrafluoroethylene-lined hydrothermal reactor and heated at 180 °C for 24 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The sample was then removed and subjected to centrifugation, washing, and filtration three times with deionized water and once with ethanol. The centrifugation parameters were set as follows: speed 5000 rpm, time 5 min. Finally, the precipitate was vacuum dried at 65 °C for 12 h to obtain Si / Ni. 0.5 Co 0.5 Se2 nanowire composite material.

[0062] (3) After the dried powder sample is ground and passed through a 325-mesh sieve, it is placed in a rotary kiln for chemical vapor deposition in Si / Ni 0.5 Co 0.5Carbon nanotubes were grown on the surface of Se2 nanowires. The process parameters were set as follows: heating rate 1℃ / min, reaction temperature 1000℃, reaction time 2h, using argon, methane, and acetylene at flow rates of 300, 50, and 50 sccm respectively, and a reaction pressure of 500 Pa. This yielded Si / Ni... 0.5 Co 0.5 Se2 / CNTs nanowire composite material.

[0063] Figure 1 The Si / Ni provided by the present invention y Co （1-y） Se x A schematic diagram of the CNT composite material: Nickel cobalt selenide nanowires (NiCoSe NWs) and carbon nanotubes (CNTs) are uniformly distributed on the surface of the nano-silicon particles. The two intertwine to form a cage-like conductive network structure, thereby effectively coating and fixing the nano-silicon particles.

[0064] Figures 2-3 The Si / Ni prepared in Example 1 0.5 Co 0.5 SEM images of the Se2 / CNTs composite material show that silicon particles are uniformly dispersed in a three-dimensional porous network structure composed of nickel cobalt selenide nanowires and carbon nanotubes. In this structure, the carbon nanotubes are characterized by being tortuous, short, and having a rough surface, with an average diameter of about 40 nm; while the nickel cobalt selenide nanowires are characterized by a smooth surface, straight shape, and slender structure.

[0065] 2. Example 2

[0066] The difference between Example 2 and Example 1 is that Example 2 uses 30.4g of sucrose instead of 13.4g of xylose in Example 1, while the rest is the same as Example 1.

[0067] 3. Example 3

[0068] The difference between Example 3 and Example 1 is that in Example 3, 3.37g of sodium borohydride is used instead of 13.4g of xylose in Example 1, while the rest is the same as in Example 1.

[0069] 4. Example 4

[0070] The difference between Example 4 and Example 1 is that Example 4 uses 16g of fructose instead of 13.4g of xylose in Example 1, while the rest is the same as Example 1.

[0071] 5. Example 5

[0072] The difference between Example 5 and Example 1 is that more ammonia is added in Example 5 to make the pH value of the solution 12 instead of the pH value of 10 in Example 1. Otherwise, they are the same as in Example 1.

[0073] 6. Example 6

[0074] The difference between Example 6 and Example 1 is that Example 6 uses 5.2g of cobalt nitrate hexahydrate instead of 2.6g of cobalt nitrate hexahydrate in Example 1, while the rest is the same as Example 1.

[0075] 7. Example 7

[0076] The difference between Example 7 and Example 1 is that Example 7 uses 2.0g of nano-silicon powder instead of 1.0g of nano-silicon powder in Example 1, while the rest is the same as Example 1.

[0077] 8. Example 8

[0078] The difference between Example 8 and Example 1 is that in Example 8, step (2) involves heating in a hydrothermal reactor for 30 hours instead of 24 hours in Example 1, while the rest is the same as in Example 1.

[0079] 9. Example 9

[0080] The difference between Example 9 and Example 1 is that the coating process parameters in step (3) of Example 9 are set as follows: the heating rate is 1℃ / min, the reaction temperature is 800℃, the reaction time is 2h, the gases used are argon, methane and acetylene, the gas flow rates are 300, 50 and 50 sccm respectively, the reaction pressure is 500Pa, and the rest are the same as in Example 1.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not include polydiallyldimethylammonium chloride solution, while the rest was the same as Example 1.

[0083] Comparative Example 2

[0084] The preparation method of the Si / CNTs nanowire composite material of Comparative Example 2 includes the following steps:

[0085] (1) 1.0 g of silicon powder with an average particle size of 50 nm was added to 120 mL of a mixed solution of deionized water and ethanol (1:1 weight ratio) and ultrasonically dispersed for 1 h. Then, 0.5 g of cobalt powder and 0.5 g of nickel powder were added, and the mixture was magnetically stirred at 80 °C and 600 rpm for 2 h until the slurry became viscous. Then, the uniformly dispersed slurry was vacuum dried at 100 °C for 6 h to obtain a uniformly mixed silicon powder containing cobalt and nickel.

[0086] (2) After the dried powder sample is ground through a 325-mesh sieve, it is placed in a rotary kiln for chemical vapor deposition to grow carbon nanotubes on the surface of silicon powder. The process parameters are set as follows: heating rate is 1℃ / min, reaction temperature is 1000℃, reaction time is 2h, the gases used are argon, methane and acetylene, the gas flow rates are 300, 50 and 50 sccm respectively, and the reaction pressure is 500 Pa to obtain Si / CNTs nanowire composite material.

[0087] Comparative Example 3

[0088] The difference between Comparative Example 3 and Example 1 is that no selenium dioxide was added in Comparative Example 3, but otherwise it is the same as Example 1.

[0089] Comparative Example 4

[0090] The difference between Comparative Example 4 and Example 1 is that xylose was not added in Comparative Example 4, but otherwise it is the same as Example 1.

[0091] Comparative Example 5

[0092] The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 did not perform the carbon nanotube growth process of step (3), but was otherwise the same as Example 1.

[0093] Comparative Example 6

[0094] The difference between Comparative Example 6 and Example 1 is that 1.14g of polyvinylpyrrolidone was added to Comparative Example 6 instead of 3.0g of polydiallyldimethylammonium chloride solution in Example 1, while the rest was the same as in Example 1.

[0095] The composite materials prepared in Examples 1-9 and Comparative Examples 1-6 were mixed with Super P, single-walled carbon nanotubes (SWCNTs), polyacrylic acid (PAA), and SBR at a mass ratio of 94.55:1:0.15:1.3:3, and added to deionized water. The mixture was stirred until a homogeneous slurry was formed. The slurry was then coated onto copper foil and dried in a vacuum drying oven at 110°C for 12 hours. Finally, a negative electrode sheet with a diameter of 14 mm was punched out. A coin cell was assembled using a lithium metal sheet as the counter electrode, a polyethylene (PE) membrane as the separator, and 1 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) at a volume ratio of 1:1:1. The battery was subjected to conventional electrochemical performance tests and four-probe powder resistivity tests. The results are shown in Table 1.

[0096] Table 1 Test results of Examples 1-9 and Comparative Examples 1-6

[0097]

[0098] Based on the data in the table and appendixFigure 4 The results show that the Si / Ni prepared in Example 1 of this invention 0.5 Co 0.5 Se2 / CNTs composite material exhibits excellent electrochemical performance as a negative electrode material for lithium-ion batteries. At a current density of 0.1C, the initial charge-discharge specific capacity of this material is 1269.8 mAh / g and 1105.9 mAh / g, respectively, with an initial efficiency of up to 87.1%. Furthermore, its capacity retention rate remains at 89.38% after 100 cycles. Simultaneously, this composite material exhibits high conductivity, with a powder resistivity of 0.992 Ω·cm at 20 MPa and only 0.193 Ω·cm at 100 MPa.

[0099] Different reducing agents were used in Examples 2-4. Compared with xylose, the electrochemical performance of the composite materials prepared using other reducing agents was slightly worse. Xylose, due to its aldehyde group, has a higher reducing power than sucrose and fructose, while sodium borohydride has the strongest reducing power. This difference in reducing power affects the diffusion of selenium (Se) atoms and crystal growth behavior. The strong reducing power of sodium borohydride leads to a higher concentration of selenium atoms in the solution, making it easier for particles to collide and combine, thereby increasing the probability of crystal growth along a non-preferred direction. The resulting nanowire structures are shorter and thicker, and even irregular particles appear. In contrast, sucrose and fructose have weaker reducing power, lower selenium atom concentrations, and larger interatomic distances, providing space for them to grow along directions with higher surface free energy, making it easier to form nanostructures. However, the slow selenium atom supply rate makes growth easy to interrupt, and the final products are mostly nanorods.

[0100] In Example 5, increasing the pH of the precursor solution increased the surface free energy of certain crystal planes (such as the a-axis nonpolar plane), promoting the growth of selenium crystals along this direction. When the growth rate along the a-axis exceeds that along the polar c-axis (the nanowire growth direction), a two-dimensional nanosheet structure tends to form.

[0101] Example 6 adjusted the Ni to Co ratio, while Example 7 changed the content ratio of silicon to nanowires / carbon nanotubes. The density of the cage-like conductive network structure was affected, leading to reduced cycle stability of the composite material. Example 8 investigated the effect of hydrothermal reaction time, a parameter that plays a decisive role in the morphology of the nanowires and directly relates to the degree of reaction completion. Excessive reaction time exacerbates Ostwald ripening, causing the nanowires to coarsen, shorten, or even break. Example 9 altered the growth conditions of carbon nanotubes. Lower temperatures reduced the crystallinity and conductivity of CNTs, weakening their bonding with silicon / nanowires and hindering the formation of a robust and highly conductive elastic network structure, thus negatively impacting the electrochemical performance of the material in lithium-ion batteries.

[0102] In Comparative Example 1, the absence of polydiallyldimethylammonium chloride (PDDA) resulted in uneven material mixing and a large amount of silicon powder agglomeration, thus reducing electrochemical performance. This is mainly because PDDA can regulate the electron distribution at the interface, optimize electron density, and promote charge transport. Furthermore, PDDA, as a crystal plane modifier, can guide the nanowire structure towards curvature and elongation, resulting in uniform product size and playing a role in structural stability and guidance. Without PDDA, the nanorods obtained in Comparative Example 1 exhibited disordered morphology.

[0103] In Comparative Example 2, carbon nanotubes were grown directly on the surface of nano-silicon powder. However, due to the direct mixing of silicon powder with nickel and cobalt sources, problems such as silicon powder agglomeration and uneven dispersion of catalytic active sites were easily caused, resulting in the inability of the grown CNTs to be uniformly modified on the surface of silicon particles.

[0104] Comparative Example 3 did not contain SeO2 and no nanowire structure was generated; Comparative Example 4 contained SeO2 but no reducing agent, so it could not induce the formation of nanowire structure and both showed poor electrochemical performance.

[0105] Comparative Example 5 did not undergo final carbon nanotube growth. Although the theoretical capacity of nickel cobalt selenide nanowires is higher than that of CNTs, the introduction of CNTs effectively improves the original long, high-resistivity, and easily agglomerated single nanowire network, enhancing its structural stability and density. This refined hierarchical structure has a positive effect on improving the performance of composite materials in lithium-ion batteries.

[0106] Comparative Example 6 uses a conventional dispersant instead of polydiallyldimethylammonium chloride, which has limited effect on dispersing Si powder in the system of this invention and cannot control the growth kinetics of nickel cobalt selenide crystals, resulting in non-uniform morphology of the constructed nanowires.

[0107] In summary, factors such as the type of reducing agent, solution pH, hydrothermal reaction time, metal ratio, component content, pH adjustment, and carbon nanotube growth conditions all affect the formation of ultrafine nanostructures and the construction of conductive networks, ultimately determining the electrochemical performance of composite materials in lithium-ion batteries.

[0108] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0109] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing a silicon-based composite material, characterized in that, Includes the following steps: S1. Dissolve polydiallyldimethylammonium chloride solution in a mixture of water and ethanol, add nano-silica powder to disperse it, then add selenium dioxide and stir evenly; subsequently, add cobalt source, nickel source and reducing agent, adjust the pH value to 9~14, and continue stirring to obtain precursor solution; S2. The precursor solution was subjected to a hydrothermal reaction, followed by centrifugation, washing, filtration, and drying to obtain Si / Ni. y Co (1-y) Se x Nanowire powder sample; S3. After grinding and sieving the powder sample, chemical vapor deposition is performed on the Si / Ni... y Co (1-y) Se x Carbon nanotubes are grown on the surface of nanowires to obtain Si / Ni y Co (1-y) Se x / CNTs composite materials; The reducing agent is one or more of xylose, fructose, glucose, sucrose, hydrazine hydrate, ascorbic acid, sodium borohydride, and sodium thiosulfate. The molar ratio of selenium dioxide to the total molar ratio of cobalt and nickel sources is 0.5 to 5:

1.

2. The preparation method according to claim 1, characterized in that, The mass fraction of the polydiallyldimethylammonium chloride solution is 20~50 wt%; the weight-average molecular weight of polydiallyldimethylammonium chloride is ≤100000; The average particle size of the nano-silicon powder is 1~200 nm.

3. The preparation method according to claim 1, characterized in that, The cobalt source is one or more of cobalt nitrate or its hydrate, cobalt chloride, cobalt acetate or its hydrate; And / or, the nickel source is one or more of nickel nitrate or its hydrate, nickel chloride, nickel acetate or its hydrate.

4. The preparation method according to claim 1, characterized in that, The mass ratio of nano-silica powder to polydiallyldimethylammonium chloride is 1:0.8~1.5; And / or, the mass ratio of selenium dioxide to nano-silicon powder is 1~10:1; And / or, the molar ratio of cobalt source to nickel source is 0.2~5:1; And / or, the molar ratio of reducing agent to selenium dioxide is 0.5~5:

1.

5. The preparation method according to claim 1, characterized in that, The mass ratio of selenium dioxide to nano-silicon powder is 3.5~4.5:1; the molar ratio of selenium dioxide to the total molar ratio of cobalt and nickel sources is 1~3:1; and the molar ratio of cobalt and nickel sources is 0.9~1.1:

1.

6. The preparation method according to claim 1, characterized in that, Add ammonia to adjust the pH to 9-11.

7. The preparation method according to claim 1, characterized in that, The hydrothermal reaction conditions for step S2 include: a temperature of 120~200 ℃ and a time of 12~30 h.

8. The preparation method according to claim 1, characterized in that, The conditions for chemical vapor deposition in step S3 include: a heating rate of 1~10 ℃ / min, a temperature of 700~1100 ℃, a time of 0.5~5 h, and a gas source of one or more of acetylene, methane, ethanol, ethylene, and an inert gas; a flow rate of 20~800 sccm for each gas; and a reaction pressure of 300~700 Pa.

9. A silicon-based composite material prepared by the preparation method according to any one of claims 1-8.

10. The application of a silicon-based composite material as described in claim 9 in a lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the silicon-based composite material.

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