Preparation method and application of silicon-based composite material

Abstract

The invention 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, then adding selenium dioxide, and uniformly stirring; then, a cobalt source, a nickel source and a reducing agent are added, pH is adjusted, and a precursor solution is obtained; carrying out hydrothermal reaction on the precursor solution, centrifuging, washing, filtering and drying to obtain a Si / NiyCo (1-y) Sex nanowire powder sample; and grinding and sieving the powder sample, then carrying out chemical vapor deposition, and growing a carbon nanotube on the surface of the nanowire to obtain the final silicon-based composite material. In the silicon-based composite material, the nickel-cobalt selenide nanowires and the carbon nanotubes are uniformly distributed on the surfaces of the nano silicon particles, the nickel-cobalt selenide nanowires and the carbon nanotubes are interwoven to form a cage-like conductive network structure, and the nano silicon particles are effectively coated and fixed, so that the overall electrochemical performance of the composite material is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a preparation method and application of a silicon-based composite material. BACKGROUND

[0002] Silicon-based materials are considered as one of the most potential next-generation high-energy-density lithium-ion battery anode materials due to their high specific capacity, low working potential and abundant reserves. However, the significant volume expansion effect, low intrinsic conductivity and slow lithium ion diffusion kinetics of silicon materials in the process of deintercalation / intercalation of lithium seriously restrict the commercialization process. Nanotechnology provides a new way to solve these problems. The current main research directions include nanoparticles, nanowires and nanosheets. Among them, nanoparticles can effectively improve the critical swelling stress threshold due to their geometric characteristics; nanosheets can significantly shorten the lithium ion transmission path due to their excellent electronic conductivity; and one-dimensional nanowire and nanotube structures can not only eliminate the lithium ion transmission barrier between particles, but also maintain the structural integrity due to their unique high aspect ratio characteristics, and the space between nanowires can effectively buffer the volume expansion and form an axial rapid lithium ion transmission channel, thereby exhibiting excellent cycle stability and high reversible specific capacity.

[0003] However, single nanostructure inevitably leads to a sharp increase in specific surface area and a decrease in tap density of the material, thereby making the first coulombic efficiency and volume specific capacity of the battery perform poorly, which seriously limits the actual application. Therefore, researchers are working to develop single nanostructure into a more complex hierarchical structure system. However, the complexity of the structure puts higher requirements on the preparation process and precursor, so it is crucial to develop a simple and efficient preparation method of hierarchical nanowires to promote the commercialization of silicon anodes. SUMMARY

[0004] The application provides a preparation method and application of a silicon-based composite material to solve the problems in the prior art, and starts from preparing ultrafine nanowires, uses in-situ self-assembly as a technical means to modify nickel-cobalt selenide nanowires and carbon nanotubes on the surface of nanosilicon powder, and designs the structure of Si material to achieve the purposes of buffering volume expansion and improving electrochemical performance.

[0005] In an aspect, the application provides a preparation method of a silicon-based composite material, which comprises the following steps: S1, dissolving a polydiallyldimethylammonium chloride (PDDA) solution in a mixture of water and ethanol, adding nanosilicon powder into the mixture, and then adding selenium dioxide and stirring uniformly; subsequently, adding a cobalt source, a nickel source and a reducing agent, adjusting the pH value to 9-14, and continuing to stir to obtain a precursor solution; S2, hydrothermal reaction of the precursor solution, centrifugation, washing, filtration, 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, surface growth of carbon nanotubes on Si / Ni y Co (1-y) Se x nanowires, to obtain Si / Ni y Co (1-y) Se x / CNTs composite material.

[0006] The step S1 is described in detail as follows: Preferably, the average particle size of the nanosilicon powder is 1-200 nm, further preferably 2-100 nm, and still further preferably 10-80 nm.

[0007] The nanosilicon powder has a large activity, but is prone to agglomeration during preparation. The addition of PDDA in the present application is conducive to uniform dispersion of the nanosilicon powder. Si adsorbs PDDA through electrostatic attraction, so that the surface of Si is positively charged, and the selenous acid ions generated by dissolving selenium dioxide in water are attracted, thereby solving the problem of easy agglomeration.

[0008] Preferably, the mass fraction of the polydiallyldimethylammonium chloride solution is 20-50 wt%.

[0009] Preferably, the weight average molecular weight Mw of the polydiallyldimethylammonium chloride is ≤100000.

[0010] Optionally, the ratio of the mass of the polydiallyldimethylammonium chloride solution to the volume of the mixed solution of water and ethanol is 1:10-100. In the mixed solution of water and ethanol, the mass ratio of water to ethanol is 0.8-1.5:1.

[0011] The nanosilicon powder is dispersed therein by ultrasonic dispersion, and the ultrasonic dispersion time is 0.5-2 h.

[0012] Preferably, the mass ratio of the nanosilicon powder to the polydiallyldimethylammonium chloride is 1:0.8-1.5.

[0013] Subsequently, selenium dioxide is added and stirred uniformly, the stirring speed is 100-800 rpm, and the stirring time is 10-60 min.

[0014] Preferably, the mass ratio of selenium dioxide to the nanosilicon powder is 1-10:1.

[0015] 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.

[0016] Preferably, the ratio of the molar amount of selenium dioxide to the total molar amount of the cobalt source and the nickel source is 0.5-5:1.

[0017] Preferably, the molar ratio of the cobalt source to the nickel source is 0.2-5:1.

[0018] By introducing different proportions of the Co source and the Ni source in the precursor, the Ni y Co （1-y） Se x nanowires.

[0019] Further preferably, the mass ratio of selenium dioxide to silicon nanowires is 3.5-4.5:1; the molar ratio of the cobalt source to the nickel source is 0.9-1.1:1; and the ratio of the molar amount of selenium dioxide to the total molar amount of the cobalt source and the nickel source is 1-3:1.

[0020] Preferably, the reducing agent is one or more of 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 of Se atom diffusion and growth. Further preferably, the reducing agent is xylose.

[0021] Preferably, the molar ratio of the reducing agent to selenium dioxide is 0.5-5:1.

[0022] 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 crystal during the reaction. Further preferably, the pH is adjusted to 9-11.

[0023] After the pH is adjusted, stirring is continued for 10-60 min.

[0024] Step S2 is described in detail as follows: Preferably, the hydrothermal reaction conditions of step S2 include a temperature of 120-200 ℃ and a time of 12-30 h. Further preferably, the hydrothermal reaction temperature is 160-180 ℃ and the reaction time is 20-25 h.

[0025] Preferably, the centrifugal washing conditions of step S2 include a centrifugal speed of 3000-10000 rpm, a centrifugal time of 5-30 min, and a washing number of 2-6 times. The excess PDDA and residual impurities are removed.

[0026] The drying conditions include: vacuum drying, drying temperature of 50-90 ℃, and drying time of 5-24 h.

[0027] In step (2), the Ni y Co （1-y） Se x nanowires with a diameter of 5-100 nm and a length of 1-50 μm are obtained.

[0028] The step S3 is described in detail as follows: Preferably, the mesh number in step S3 is 300-700.

[0029] The conditions of the chemical vapor deposition in step S3 include: temperature increasing rate of 1-10 ℃ / min, temperature of 700-1100 ℃, time of 0.5-5 h, and gas source of one or more of acetylene, methane, ethanol, ethylene and inert gas; the flow rate of each gas is 20-800 sccm; and the reaction gas pressure is 300-700 Pa. Further preferably, the temperature in the chemical vapor deposition process is 950-1050 ℃, and the time is 1-3 h.

[0030] The inert gas herein is nitrogen and / or argon.

[0031] A layer of carbon nanotubes is regrown on the surface of the original nanowires by chemical vapor deposition.

[0032] The second aspect of the present application provides a silicon-based composite material prepared by the above preparation method.

[0033] In the silicon-based composite material, the surface of the nanosilicon particles is uniformly distributed with nickel-cobalt selenide nanowires and carbon nanotubes, which are interwoven to form a cage-like conductive network structure.

[0034] The third aspect of the present application provides an application of a silicon-based composite material in a lithium ion battery, wherein the negative electrode sheet of the lithium ion battery comprises the silicon-based composite material.

[0035] Preferably, the raw material comprising the silicon-based composite material and a solvent are mixed to prepare a slurry, which is coated on a current collector, dried to obtain a negative electrode sheet.

[0036] Preferably, the raw material comprises the silicon-based composite material and a binder; and the mass ratio of the silicon-based composite material to the binder is (89-98):(2-11).

[0037] Preferably, the raw material comprises the silicon-based composite material, a conductive agent and a binder; and the mass ratio of the silicon-based composite material to the conductive agent to the binder is (87-97):(0.5-5):(2-10).

[0038] The conductive agent, the binder and the solvent are all common substances in the preparation process of the negative plate, and are not particularly limited herein.

[0039] Compared with the prior art, the present application has the following beneficial effects: The Si / Ni y Co (1-y) Se x / CNTs composite material is successfully constructed through the synergistic effect of a simple and efficient one-step hydrothermal method and a subsequent chemical vapor deposition (CVD) method.

[0040] 2、The present application realizes the multifunctional surface modification of the nano-silicon powder by introducing a polydiallyldimethylammonium chloride (PDDA) solution. +(CH3)2- ) and the surface oxide of silicon particles, forming a positively charged Si@PDDA complex. Thanks to the structural advantages of the linear molecular chain of PDDA, it can be closely arranged on the surface of silicon particles in a highly ordered manner, which can provide a more dense distribution of charged groups than branched surfactants, thereby producing a stronger Zeta potential difference. This uniform surface modification not only effectively prevents the agglomeration of nanosilicon, but also provides an ideal active interface for subsequent reactions. 2- Anions are directionally adsorbed on the positively charged Si@PDDA surface by electrostatic interaction, forming a regular active site array. More importantly, PDDA molecules can act as an efficient crystal face regulator, changing the relative surface energy of different crystal faces by selective adsorption, thereby precisely controlling the anisotropic growth kinetics of nickel-cobalt-selenium (NiCoSe NWs) crystals. This dual-action mechanism can precisely control the morphology and microstructure of NiCoSe nanomaterials. This innovative surface modification strategy not only solves the technical problem of nanosilicon dispersion, but also provides a new control dimension for building nanomaterials with specific morphology and structure, exhibiting significant multi-functional advantages.

[0041] 3、The present application uses xylose, fructose, sucrose and other polyhydroxy sugars as reducing agents, and the rich hydroxyl groups in their molecular structure can effectively promote the interaction between the reducing agent and the SeO3 2- adsorbed on Si@PDDA. During the reaction, these reducing agents undergo redox reactions with SeO3 2- , first generating amorphous selenium and uniformly coating the surface of silicon particles. Subsequently, under high-temperature hydrothermal conditions, amorphous selenium undergoes a crystallization transformation process to form black crystalline selenium, and through Se atom diffusion and self-assembly process, it finally grows into one-dimensional nanowire structure. It is worth noting that different reducing agents can control the orientation growth rate of selenium crystals due to their differences in reducing ability, thereby obtaining nanomaterials with different morphologies, including zero-dimensional nanoparticles, one-dimensional nanowires, and two-dimensional nanosheets.

[0042] 4、The present application uses ammonia as a pH regulator to precisely control the acidity and alkalinity of the precursor solution, providing favorable conditions for the preparation of one-dimensional nanowires with uniform size. The surface free energy of each crystal face of the crystal has a significant dependence on the pH value of the solution, and the crystal face with higher surface free energy is more conducive to the directional growth of nanowires. Through this pH control mechanism, the controllable synthesis of different morphologies of nanomaterials is successfully realized.

[0043] 5、The application prepares bimetallic nickel-cobalt selenide nanowires (NiCoSe NWs) with adjustable components by regulating the feeding ratio of cobalt source and nickel source. y Co (1-y) Se x nanowires. The nanowires have unique electronic transmission characteristics: the delocalization effect of lone pair electrons in selenium nanowires endows them with excellent anisotropic electron migration ability, which can significantly promote the directional transmission of electric charges; and stable active site anchoring: through the strong Se-M (M=Ni / Co) chemical bond between the surface of Se NWs and metal atoms, the active site is firmly fixed. Therefore, nickel-cobalt selenide nanowires can be used as suitable catalytic carriers to carry active sites while enhancing the charge transfer ability.

[0044] 6、The Si / Ni y Co (1-y) Se x / CNTs composite material prepared by the application can effectively improve the electrochemical activity and has high specific capacity, initial coulombic efficiency and cycle stability when used as a negative electrode material for lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The structure schematic diagram of the Si / Ni y Co （1-y） Se x / CNTs composite material provided by the application is shown in the figure; Figure 2 is a low-magnification scanning electron microscope image of the Si / Ni 0.5 Co 0.5 Se2 / CNTs composite material prepared in Example 1; Figure 3 is a high-magnification scanning electron microscope image of the Si / Ni 0.5 Co 0.5 Se2 / CNTs composite material prepared in Example 1; Figure 4 is a cycle curve diagram of the Si / Ni 0.5 Co 0.5 Se2 / CNTs composite material prepared in Example 1 as a lithium ion negative electrode material. DETAILED DESCRIPTION

[0046] In the description of the application, unless otherwise specified, the numerical range "a~b" represents a shorthand representation of any real combination between a and b, and a and b are included. A plurality includes two, three, four, five or more.

[0047] The technical solutions of the present application are further described and illustrated below by means of specific examples and drawings. It should be understood that the specific examples described herein are only used to help understand the present application and are not used to limit the present application. The drawings used herein are only used to better illustrate the disclosed content of the present application and do not limit the scope of protection. If not specifically stated, the raw materials used in the examples of the present application are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0048] 1. Example 1 Si / Ni y Co （1-y） Se x The preparation method of the Si / Ni (1) 3.0 g of polydiallyldimethylammonium chloride solution (PDDA, 38%, Mw<100000) was dissolved in 120 mL of a mixed solution of deionized water and ethanol (1:1 by weight), 1.0 g of silicon powder with an average particle size of 50 nm was ultrasonically dispersed for 1 h, and then 4.0 g of selenium dioxide (SeO2) was added. The mixture was stirred at room temperature and 600 rpm for 30 min, respectively, until a uniform solution was formed. Then, 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 were slowly added, and 10 mL of ammonia water (25 wt%) was added dropwise to adjust the pH of the solution to about 10, and the mixture was continuously stirred for 30 min.

[0049] (2) The above mixed solution was transferred to a 500 mL polytetrafluoroethylene-lined autoclave, and heated at 180°C for 24 h. After the reaction was completed, the sample was taken out after the autoclave was naturally cooled to room temperature, and was subjected to centrifugation, washing, and filtration with deionized water for 3 times and ethanol for 1 time. 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.

[0050] (3) After the dried powder sample was ground through a 325 mesh sieve and placed in a rotary furnace, chemical vapor deposition was carried out on the surface of the Si / Ni 0.5 Co 0.5 Se2 nanowire to grow carbon nanotubes, wherein the process parameters were set as follows: heating rate 1°C / min, reaction temperature 1000°C, reaction time 2 h, and the gases used were argon, methane, and acetylene, with gas flow rates of 300, 50, and 50 sccm, respectively, and the reaction gas pressure was 500 Pa. Si / Ni 0.5 Co0.5 Se2 / CNTs nanowire composite material.

[0051] Figure 1 Si / Ni y Co （1-y） Se x Structure diagram of Se2 / CNTs composite material: the surface of nano-silicon particles is uniformly distributed with nickel cobalt selenide nanowires (NiCoSe NWs) and carbon nanotubes (CNTs), which are interwoven to form a cage-like conductive network structure, thereby effectively coating and fixing the nano-silicon particles.

[0052] Figures 2-3 Si / Ni 0.5 Co 0.5 SEM image of Se2 / CNTs composite material, showing that the silicon particles are uniformly dispersed in a three-dimensional porous network structure constructed by nickel cobalt selenide nanowires and carbon nanotubes. In this structure, the carbon nanotubes exhibit the characteristics of bending and winding, short size, and rough surface, with an average diameter of about 40 nm; while the nickel cobalt selenide nanowires exhibit the characteristics of smooth surface, straight shape, and slender structure.

[0053] 2. Example 2 Example 2 differs from Example 1 in that Example 2 uses 30.4g sucrose instead of 13.4g xylose in Example 1, and the rest is the same as Example 1.

[0054] 3. Example 3 Example 3 differs from Example 1 in that Example 3 uses 3.37g sodium borohydride instead of 13.4g xylose in Example 1, and the rest is the same as Example 1.

[0055] 4. Example 4 Example 4 differs from Example 1 in that Example 4 uses 16g fructose instead of 13.4g xylose in Example 1, and the rest is the same as Example 1.

[0056] 5. Example 5 Example 5 differs from Example 1 in that Example 5 drops more ammonia water to make the solution pH value 12 instead of pH value 10 in Example 1, and the rest is the same as Example 1.

[0057] 6. Example 6 Example 6 differs from Example 1 in that Example 6 uses 5.2g cobalt nitrate hexahydrate instead of 2.6g cobalt nitrate hexahydrate in Example 1, and the rest is the same as Example 1.

[0058] 7. Example 7 Example 7 is different from Example 1 in that 2.0 g of nano-silicon powder is used instead of 1.0 g of nano-silicon powder in Example 1, and the rest is the same as Example 1.

[0059] 8. Example 8 Example 8 is different from Example 1 in that the step (2) of Example 8 is heated in the hydrothermal reactor for 30 h instead of 24 h in Example 1, and the rest is the same as Example 1.

[0060] 9. Example 9 Example 9 is different from Example 1 in that the coating process parameters of step (3) of Example 9 are set as follows: the heating rate is 1 ℃ / min, the reaction temperature is 800 ℃, the reaction time is 2 h, the gas used is argon, methane and acetylene, the gas flow is 300, 50 and 50 sccm respectively, and the reaction gas pressure is 500 Pa, and the rest is the same as Example 1.

[0061] Comparative Example 1 Comparative Example 1 is different from Example 1 in that no poly diallyl dimethyl ammonium chloride solution is added in Comparative Example 1, and the rest is the same as Example 1.

[0062] Comparative Example 2 The preparation method of the Si / CNTs nanowire composite material of Comparative Example 2 comprises the following steps: (1) 1.0 g of silicon powder with an average particle size of 50 nm is added to a mixed solution of 120 mL of deionized water and ethanol (1:1 by weight) and ultrasonically dispersed for 1 h, and then 0.5 g of cobalt powder and 0.5 g of nickel powder are added, and magnetic stirring is carried out at 80 ℃ and 600 rpm for 2 h until the slurry is viscous. Then, the uniformly dispersed slurry is vacuum dried at 100 ℃ for 6 h to obtain a mixed cobalt-nickel-containing silicon powder.

[0063] (2) After the dried powder sample is ground through a 325 mesh screen, it is placed in a rotary furnace for chemical vapor deposition to grow carbon nanotubes on the surface of the silicon powder, wherein the process parameters are set as follows: the heating rate is 1 ℃ / min, the reaction temperature is 1000 ℃, the reaction time is 2 h, the gas used is argon, methane and acetylene, the gas flow is 300, 50 and 50 sccm respectively, and the reaction gas pressure is 500 Pa, to obtain a Si / CNTs nanowire composite material.

[0064] Comparative Example 3 Comparative Example 3 is different from Example 1 in that no selenium dioxide is added in Comparative Example 3, and the rest is the same as Example 1.

[0065] Comparative Example 4 Comparative Example 4 is different from Example 1 in that no xylose is added in Comparative Example 4, and the rest is the same as Example 1.

[0066] Comparative Example 5 Comparative Example 5 is different from Example 1 in that Comparative Example 5 does not perform the carbon nanotube growth process of step (3), and is the same as Example 1 in other aspects.

[0067] Comparative Example 6 Comparative Example 6 is different from Example 1 in that Comparative Example 6 adds 1.14 g of polyvinylpyrrolidone instead of 3.0 g of polydiallydimethylammonium chloride solution of Example 1, and is the same as Example 1 in other aspects.

[0068] The composite materials prepared in Examples 1-9 and Comparative Examples 1-6 are mixed with Super P, single-walled carbon nanotubes (SWCNT), polyacrylic acid (PAA) and SBR according to a mass ratio of 94.55:1:0.15:1.3:3, and deionized water is added and stirred to form a uniform slurry. Subsequently, the slurry is coated on a copper foil and dried in a vacuum drying oven at 110°C for 12 hours, and finally punched to obtain negative electrode sheets with a diameter of 14 mm. A lithium metal sheet is used as the counter electrode, a polyethylene (PE) film is used as the separator, and an electrolyte is 1 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1, to assemble a coin cell. The coin cell is subjected to conventional electrochemical performance testing and four-probe powder resistance testing, and the results are shown in Table 1.

[0069] Table 1 Test results of Examples 1-9 and Comparative Examples 1-6

[0070] According to the data in the table and the attached Figure 4 It can be seen from the results that the Si / Ni 0.5 Co 0.5 The Si / Ni

[0071] Different reducing agents were used in Examples 2-4. The electrochemical performance of the composites prepared with other reducing agents was slightly worse than that of the composite prepared with xylose. Xylose has a higher reducing power than sucrose and fructose because it contains an aldehyde group, and sodium borohydride has the strongest reducing power. The difference in reducing power affects the diffusion and crystal growth behavior of selenium (Se) atoms. The strong reducing power of sodium borohydride results in a higher concentration of selenium atoms in the solution, and particles are more likely to collide and combine, thereby increasing the probability of crystal growth in non-preferred directions, resulting in shorter and thicker nanowire structures, and even irregular particles. In contrast, the reducing power of sucrose and fructose is weaker, and the concentration of selenium atoms is lower, and the atomic spacing is larger, which provides space for the growth of selenium atoms in the direction of higher surface free energy, making it easier to form nanostructures. However, the slow supply rate of selenium atoms leads to easy interruption of growth, and the final product is mostly nanorods.

[0072] In Example 5, by increasing the pH value of the precursor solution, the surface free energy of certain crystal planes (such as the a-axis non-polar plane) is increased, promoting the growth of selenium crystals in this direction. When the growth rate in the a-axis direction exceeds the polar c-axis (nanowire growth direction), it tends to form two-dimensional nanosheet structures.

[0073] Example 6 adjusts the ratio of Ni to Co, and Example 7 changes the content ratio between silicon and nanowires / carbon nanotubes, affecting the density of the cage-like conductive network structure, thereby reducing the cycle stability of the composite material. Example 8 examines the effect of hydrothermal reaction time, which has a decisive role in the morphology of nanowires and is directly related to the completion of the reaction. Prolonged reaction time can exacerbate Ostwald ripening, leading to thickening, shortening, or even breaking of the nanowires. Example 9 changes the growth conditions of carbon nanotubes, and lower temperatures reduce the crystallinity and conductivity of CNTs, weakening the bonding between silicon / nanowires, which is not conducive to the formation of a strong and highly conductive elastic network structure, thereby negatively affecting the electrochemical performance of the material in lithium-ion batteries.

[0074] In Comparative Example 1, polydiallyldimethylammonium chloride (PDDA) is not added, which on the one hand leads to uneven mixing of the material, resulting in a large amount of silicon powder agglomeration, thereby reducing the electrochemical performance, which is mainly due to the fact that PDDA can adjust the electron distribution at the interface, optimize the electron density, and promote charge transfer; on the other hand, PDDA as a crystal plane regulator can guide the nanowire structure to develop in a curved and slender direction, resulting in uniform product size, and plays a role in structure stabilization and guidance. When PDDA is not added, the nanorod morphology obtained in Comparative Example 1 is chaotic.

[0075] In Comparative Example 2, carbon nanotubes are directly grown on the surface of nanosilicon powder. Since the silicon powder is directly mixed with nickel and cobalt sources, it is easy to cause silicon powder agglomeration and uneven dispersion of catalytic active sites, resulting in CNTs that cannot be uniformly modified on the surface of silicon particles.

[0076] Comparative Example 3 did not add SeO2, and no nanowire structure was generated; Comparative Example 4 did not add a reducing agent, and could not induce the generation of a nanowire structure, and both showed poor electrochemical performance.

[0077] Comparative Example 5 did not perform the final growth of carbon nanotubes. Although the theoretical capacity of the nickel-cobalt selenide nanowires is higher than that of CNTs, the introduction of CNTs effectively improves the originally long, high-resistance, and easily agglomerated single nanowire network, and enhances the structural stability and compactness thereof. This fine hierarchical structure has a positive effect on improving the application performance of the composite material in lithium ion batteries.

[0078] Comparative Example 6 used a conventional dispersant instead of polydiallyldimethylammonium chloride, which had limited dispersing effect on the Si powder in the system of the present application, and could not control the growth kinetics of the nickel-cobalt selenide crystals, so that the nanowire morphology constructed thereby was not uniform.

[0079] In summary, the types of reducing agents, the pH value of the solution, the hydrothermal reaction time, the metal ratio, the component content, the pH adjustment, and the carbon nanotube growth conditions all affect the formation of the ultrafine nanostructure and the construction of the conductive network, and ultimately determine the electrochemical performance of the composite material in lithium ion batteries.

[0080] In the preparation method of the present application, the order of the steps is not limited to the order listed, and for those skilled in the art, changes in the order of the steps without creative labor are also within the protection scope of the present application. In addition, two or more steps or actions can be performed simultaneously.

[0081] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the embodiments of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways. Here, it is not necessary or possible to fully exemplify all embodiments. However, these obvious changes or variations within the spirit of the present application still fall within the protection scope of the present application, and any additional limitation is contrary to the spirit of the present application.

Claims

1. A method of preparing a silicon-based composite material, characterized by, The method comprises the following steps: S1, dissolving a polydiallyldimethylammonium chloride solution in a mixture of water and ethanol, adding nano-silicon powder and dispersing it, then adding selenium dioxide and stirring uniformly; subsequently, adding a cobalt source, a nickel source and a reducing agent, adjusting the pH value to 9-14, and continuing to stir to obtain a precursor solution; S2, the precursor solution is subjected to hydrothermal reaction, and after centrifugation, washing, filtration and drying, Si / Ni is obtained y Co (1-y) Se x nanowire powder sample; S3, after grinding and sieving the powder sample, chemical vapor deposition was carried out on Si / Ni y Co (1-y) Se x carbon nanotubes on the surface of nanowires, obtaining Si / Ni y Co (1-y) Se x / CNTs composite material.

2. The production method according to claim 1, characterized by, The mass fraction of the polydiallyldimethylammonium chloride solution is 20-50 wt%; the weight average molecular weight Mw of the 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; And / or, the reducing agent is one or more of xylose, fructose, glucose, sucrose, hydrazine hydrate, ascorbic acid, sodium borohydride and sodium thiosulfate.

4. The method of claim 1, wherein, The mass ratio of the nano-silicon powder to the polydiallyldimethylammonium chloride is 1:0.8-1.5; And / or, the mass ratio of the selenium dioxide to the nano-silicon powder is 1-10:1; And / or, the ratio of the molar amount of the selenium dioxide to the total molar amount of the cobalt source and the nickel source is 0.5-5:1; And / or, the molar ratio of the cobalt source to the nickel source is 0.2-5:1; And / or, the molar ratio of the reducing agent to the selenium dioxide is 0.5-5:

1.

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

1.

6. The method of claim 1, wherein, Ammonia water is added to adjust the pH value to 9-11.

7. The production method according to claim 1, characterized by, The hydrothermal reaction conditions of step S2 include a temperature of 120-200 ℃ and a time of 12-30 h.

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

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

10. Use of a silicon-based composite material according to claim 9 in a lithium-ion battery, characterized in that, The negative electrode sheet of the lithium ion battery comprises the silicon-based composite material.

Images