Double-layer coated porous silicon carbon negative electrode material and preparation method thereof

Abstract

The invention provides a double-layer coated porous silicon carbon negative electrode material and a preparation method thereof.The preparation method comprises the steps that a carbon precursor and a doped precursor are evenly mixed, inert gas is introduced into a chemical vapor deposition furnace, the temperature is adjusted to 400-500 DEG C, meanwhile, silicon source gas is introduced, the reaction time is controlled to be 500-1000 minutes, and a porous silicon carbon framework is obtained, the doped precursor comprises a silicon source material; heating the porous silicon carbon skeleton to 450-550 DEG C, introducing oxygen-containing gas, and reacting for 200-800 minutes to obtain an oxygen-silicon layer deposited on the surface of the porous silicon carbon skeleton; dispersing the porous silicon carbon skeleton with the oxygen silicon layer in a mixed solvent, adding a modified coupling agent and a lithium salt, stirring for 1-5 hours at room temperature, adding a polymer solution after stirring, stirring for 1-5 hours at room temperature, generating a polymer layer on the oxygen silicon layer, and washing and drying to obtain the double-layer coated porous silicon carbon negative electrode material. Therefore, the cycle performance of the negative electrode material is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a double-layer coated porous silicon-carbon anode material and a preparation method thereof. Background Art

[0002] In the past decade, various anode materials for improving storage capacity and thermal stability have been proposed for lithium-ion batteries (LIBs). Silicon (Si) has been widely studied as an anode active material in lithium-ion batteries due to its remarkable properties. Based on the intercalation ratio of one lithium (Li) per six carbon atoms (C), the theoretical specific capacity of carbon active materials is 372 mA / g. A higher lithium-to-silicon ratio of silicon and lithium alloy can be formed by using a lithium-to-C atom ratio of 1 / 6 in all-carbon materials. In these alloys, the Li / Si ratio of the alloy phase (theoretical capacity of 1636 mAh / g) ranges from 1.71, and the Li / Si ratio of the alloy phase Li 15 Si4 (theoretical capacity of 3579 mAh / g) is 3.75. Among them, the most abundant Li 22 Si5 alloy phase ratio is 4.4, and the theoretical capacity is 4200 mAh / g. In addition to the high specific capacity, the voltage of silicon is slightly higher than that of the graphite platform, so it has remarkable safety characteristics. In addition, silicon is a rich and inexpensive material, and the lithium of silicon is more stable than the lithium of graphite in typical lithium-ion battery electrolytes. However, the silicon material itself has poor conductivity, and at the same time, there are problems such as a volume expansion of up to 400% of the material during the lithium intercalation process, low electronic conductivity, and difficulty in forming a stable solid electrolyte interface film (SEI) in silicon-based materials, which seriously hinder its commercialization process as a high-capacity anode. Currently, this problem is mainly solved by means such as nanosizing, alloying, and silicon-carbon composite.

[0003] Because the nano-silicon particles are small and easy to agglomerate, the related technology of silicon-carbon composite is that ball milling can effectively disperse the nano-silicon particles. However, the chemical activity of the nano-silicon particles is relatively high, and they are easy to be oxidized, resulting in a low initial efficiency of the material. The specific surface area of carbon materials such as graphite is small, and the nano-silicon particles agglomerate between and on the surface of the graphite layers. The dispersion space provided by the carbon materials is limited, and it is difficult to improve the cycling performance, and the improvement is not obvious. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a double-layer coated porous silicon-carbon anode material and a preparation method thereof, aiming to solve the problem that it is difficult to improve the cycling performance of the anode material.

[0005] To solve the above technical problem, the present invention is implemented as follows. The present invention proposes a preparation method for a double-layer coated porous silicon-carbon anode material for making lithium-ion batteries, and the steps include; S1. Mix the carbon precursor and the doping precursor uniformly. Introduce an inert gas into the chemical vapor deposition furnace, adjust the temperature to 400-500 °C, and simultaneously introduce the silicon source gas. Control the reaction time within 500-1000 minutes to obtain a porous silicon-carbon framework. Among them, the doping precursor includes a silicon source material; S2. Heat the porous silicon-carbon framework to 450-550 °C, introduce an oxygen-containing gas, and react for 200-800 minutes to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework; S3. Disperse the porous silicon-carbon framework with the oxygen-silicon layer in a mixed solvent, add a modified coupling agent and a lithium salt, stir at room temperature for 1-5 hours. After the stirring is completed, add a polymer solution and then stir at room temperature for 1-5 hours to form a polymer layer on the oxygen-silicon layer. After washing and drying, a double-coated porous silicon-carbon anode material is obtained.

[0006] In some embodiments of the present invention, the carbon precursor includes porous carbon spheres and an asphalt matrix, and the doping precursor includes a silicon source material and a metal catalyst; Step S1 includes: S1.1. Mix the porous carbon spheres, the asphalt matrix, the silicon source material, and the metal catalyst in a preset ratio to obtain a mixed material; S1.2. Uniformly spread the mixed material on a high-purity ceramic substrate, place it in the reaction chamber of the chemical vapor deposition furnace, and then introduce an inert gas with a gas flow rate of 10-20 L / min, gradually heat up to 400 °C, and preheat at this temperature for 30 minutes; S1.3. Gradually raise the temperature to 400-500 °C, ensuring that the heating rate is within the range of 5-10 °C / min, After reaching the target temperature, slowly introduce the silicon source gas into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5-6 L / min, and at the same time continue to maintain the inert gas flow rate to obtain a porous silicon-carbon framework.

[0007] In some embodiments of the present invention, in step S1.1, the porous carbon spheres include at least one of phenolic resin carbon spheres, coconut shell activated carbon spheres, and polyacrylonitrile-modified carbon spheres, the asphalt matrix includes at least one of petroleum asphalt, coal asphalt, and heavy oil asphalt, the silicon source material includes at least one of silane, disilane, and trimethoxysilane, the metal catalyst includes at least one of nanoscale iron catalysts, nanoscale nickel catalysts, and nanoscale cobalt catalysts, and the silicon source gas includes at least one of silane, disilane, and trimethoxysilane.

[0008] In some embodiments of the present invention, in step S1.1, calculated by mass ratio, the porous carbon spheres: the asphalt matrix: the silicon source material: the metal catalyst = (40 - 60):(20 - 40):(10 - 20):(0.5 - 2).

[0009] In some embodiments of the present invention, step S2 includes: S2.1, uniformly lay the porous silicon-carbon framework on a ceramic boat, first introduce pure nitrogen with a flow rate of 5 - 15 L / min for cleaning, gradually raise the furnace temperature to 450 - 550 °C, and keep the temperature stable for 10 - 20 minutes; S2.2, introduce an oxygen-containing gas. Every 10 - 15 minutes, increase or decrease the gas flow rate of the oxygen-containing gas. Control the reaction time within 200 - 800 minutes. After the reaction is completed, stop introducing the oxygen-containing gas, and gradually reduce the furnace temperature to room temperature at a cooling rate of 5 °C / min, while keeping an inert gas flowing, to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework.

[0010] In some embodiments of the present invention, the oxygen-containing gas includes at least one of carbon dioxide, pure oxygen, and an oxygen-nitrogen mixture, and the gas flow rate of the oxygen-containing gas is 0.5 - 2.5 L / min.

[0011] In some embodiments of the present invention, the polymer solution includes a conductive polymer and an ion-conductive polymer; Step S3 includes: S3.1, prepare a mixed solution with a volume ratio of ethanol, deionized water, and isopropanol of 1:1:0.5, add the porous silicon-carbon framework with an oxygen-silicon layer to the mixed solution, and process it with an ultrasonic cleaner for 15 - 30 minutes; S3.2, add a modified coupling agent and a lithium salt, and stir with a magnetic stirrer at room temperature for 1 - 5 hours; S3.3, add the conductive polymer and stir for 1 - 5 hours, then add the ion-conductive polymer solution, continue to stir at room temperature for 1 - 5 hours, wash and filter three times alternately with ethanol / distilled water, and dry in a vacuum drying oven at 80 °C to obtain a double-coated porous silicon-carbon anode material.

[0012] In some embodiments of the present invention, in step S3, the conductive polymer includes at least one of aniline, pyrrole, and thiophene, the ion-conducting polymer includes at least one of lithium polyacrylate, polyethylene glycol, and polyvinyl alcohol, the modified coupling agent includes at least one of 3-(2-aminoethylamino)propyltrimethoxysilane, vinyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane, and the lithium salt includes at least one of lithium metaborate, lithium tetrafluoroborate, and lithium hexafluorophosphate. Calculated by mass ratio, the porous silicon-carbon framework: the modified coupling agent: the lithium salt: the polymer solution = 100:5:2:10.

[0013] The present invention provides a double-coated porous silicon-carbon anode material, which is prepared by the preparation method of a double-coated porous silicon-carbon anode material as described above. The double-coated porous silicon-carbon anode material includes a porous silicon-carbon framework, an oxygen-silicon layer provided on the porous silicon-carbon framework, and a polymer layer provided on the oxygen-silicon layer; wherein, The porous silicon-carbon framework is used to provide mechanical support and volume buffering, construct an internal electron transport network, and ensure the stable operation of the double-coated porous silicon-carbon anode material during charge and discharge; The oxygen-silicon layer serves as a passivation layer to prevent side reactions between silicon and the electrolyte, and at the same time generates abundant hydroxyl functional groups, providing active sites for the chemical bonding of the subsequent polymer layer and optimizing the interface stability; The polymer layer is used to improve the electron conduction and lithium-ion conduction capabilities of the double-coated porous silicon-carbon anode material, and at the same time relieve the mechanical stress caused by the volume expansion of silicon during cycling, and improve the cycling stability.

[0014] Compared with the prior art, the double-coated porous silicon-carbon anode material and its preparation method in the present invention have the following beneficial effects: The oxygen-silicon layer forms a dense and functionalized passivation layer on the surface of the porous silicon-carbon framework. It not only prevents the direct contact between silicon and the electrolyte, inhibits adverse side reactions, but also relieves the mechanical damage caused by the volume expansion of silicon. At the same time, the polymer layer grown on the oxygen-silicon layer plays a buffering and fixing role, enabling the anode structure to better maintain integrity during charge and discharge, and significantly improving the cycling stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a cycling schematic diagram of the double-coated porous silicon-carbon anode material in an embodiment of the present invention; Figure 2 is an XRD pattern of the double-coated porous silicon-carbon anode material in an embodiment of the present invention; Figure 3 is a capacity-voltage diagram of the double-coated porous silicon-carbon anode material in an embodiment of the present invention; Figure 4 This is the FT-IR analysis diagram of the double-layer coated porous silicon-carbon anode material in an embodiment of the present invention. Detailed implementation manners

[0016] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] The present invention provides a preparation method for a double-layer coated porous silicon-carbon anode material for manufacturing a lithium-ion battery. The steps include: S1. Uniformly mix a carbon precursor and a doping precursor, introduce an inert gas into a chemical vapor deposition furnace (CVD), adjust the temperature to 400-500 °C, and simultaneously introduce a silicon source gas. Control the reaction time within 500-1000 minutes to obtain a porous silicon-carbon framework. Among them, the doping precursor includes a silicon source material.

[0018] The carbon precursor includes porous carbon spheres and a pitch matrix, and the doping precursor includes a silicon source material and a metal catalyst; Step S1 includes: S1.1. Mix the porous carbon spheres, the pitch matrix, the silicon source material, and the metal catalyst in a preset ratio to obtain a mixture. In step S1.1, the porous carbon spheres include at least one of phenolic resin carbon spheres, coconut shell activated carbon spheres, and polyacrylonitrile-modified carbon spheres; the pitch matrix includes at least one of petroleum pitch, coal pitch, and heavy oil pitch; the silicon source material includes at least one of tetraethoxysilane, tetramethoxysilane, and diethoxysilane; the metal catalyst includes at least one of nano-scale iron catalysts, nano-scale nickel catalysts, and nano-scale cobalt catalysts; the silicon source gas includes at least one of silane, disilane, and trimethoxysilane. Calculated by mass ratio, the porous carbon spheres: the pitch matrix: the silicon source material: the metal catalyst = (40-60):(20-40):(10-20):(0.5-2).

[0019] Through ball milling or ultrasonic treatment, each component is uniformly dispersed to ensure that in the subsequent gas-phase pyrolysis process, the silicon source material and the metal catalyst can play a synergistic role under the support of the porous carbon spheres and the pitch matrix. Under subsequent high-temperature conditions, the silicon source material can decompose, release silicon precursors, and with the help of the metal catalyst, in-situ deposit to form silicon nanoparticles in the carbon matrix; at the same time, the metal catalyst can also promote partial recombination of the pitch components to generate a carbon nanotube structure conducive to electron transport. Achieve the uniform distribution of each precursor, lay the foundation for the subsequent formation of the porous silicon-carbon framework, activate the silicon source reaction using the metal catalyst, promote the uniform deposition of silicon nanoparticles in the carbon framework, and generate local carbon nanotubes, thereby improving the conductivity and structural stability of the material.

[0020] S1.2. Uniformly spread the mixed material on a high-purity ceramic substrate, place it into the reaction chamber of a chemical vapor deposition furnace, then introduce an inert gas with a gas flow rate of 10 - 20 L / min, gradually heat up to 400 °C, and preheat at this temperature for 30 minutes.

[0021] Ensure that the mixed material is heated evenly in the furnace to avoid inconsistent reactions caused by local overheating or uneven temperature. The preheating stage helps to remove the moisture and organic volatile components (especially the low-molecular components in asphalt) in the mixed material in advance, providing a clean and stable substrate for subsequent high-temperature reactions. The high-temperature CVD furnace is equipped with a precise temperature control system and a flow control device to ensure uniform temperature and atmosphere. Through preheating regulation, impurities and volatile components in the mixed material are removed, the efficiency of subsequent silicon deposition reaction is improved, the temperature distribution in the furnace is ensured to be uniform, the structural consistency of the porous silicon-carbon skeleton is ensured, and a good premise for the formation of a highly conductive network is provided.

[0022] S1.3. Gradually raise the temperature to 400 - 500 °C, ensuring that the heating rate is within the range of 5 - 10 °C / min. After reaching the target temperature, slowly introduce the silicon source gas into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5 - 6 L / min, while continuing to maintain the inert gas flow rate to obtain a porous silicon-carbon skeleton.

[0023] Under the condition of 400 - 500 °C, the silicon source gas thermally decomposes to produce silicon atoms or silicon precursors. Under the promotion of a metal catalyst, silicon atoms deposit on the surface of the carbon precursor to form nanoscale silicon particles. The trace metal catalyst not only catalyzes silicon deposition but also promotes the recombination of some carbon components of the asphalt matrix to in-situ generate local carbon nanotubes, forming an interconnected conductive network. Using a CVD furnace with precise gas flow control can achieve the precise mixing and uniform distribution of the silicon source gas and the inert gas. Uniformly generate silicon nanoparticles inside to enhance the active lithium storage capacity of the skeleton, utilize the catalytic effect to realize the self-assembly of embedded carbon nanotubes, improve the overall conductivity and structural stability of the skeleton, and ensure that the skeleton structure has good consistency and a highly conductive network through precise gas and temperature control, providing a solid foundation for subsequent process steps.

[0024] S1.1 Mixing and Preparation: Using the combination of porous carbon spheres and asphalt matrix, supplemented with silicon source materials and metal catalysts, uniform mixing is carried out to provide a uniformly dispersed precursor for subsequent reactions, ensuring the coordinated progress of silicon deposition and carbon self-assembly reactions, and forming a basic porous framework. S1.2 Uniform Laying and Preheating: By precisely controlling the laying and preheating processes, volatile components and impurities in the mixture are removed, ensuring uniform temperature in the furnace and creating optimal conditions for high-temperature reactions. S1.3 High-temperature Silicon Source Deposition: Utilizing the decomposition of silicon source gas under high-temperature conditions, uniform deposition of silicon nanoparticles is achieved under the action of metal catalysts, and at the same time, carbon nanotubes are in-situ generated to construct a porous silicon-carbon framework with both high activity and high conductivity.

[0025] S2. Heat the porous silicon-carbon framework to 450 - 550 °C, introduce an oxygen-containing gas, and react for 200 - 800 minutes to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework. The oxygen-containing gas includes at least one of carbon dioxide, pure oxygen, and oxygen-nitrogen mixture, and the gas flow rate of the oxygen-containing gas is 0.5 - 2.5 L / min.

[0026] Step S2 includes: S2.1. Uniformly lay the porous silicon-carbon framework on a ceramic boat, first introduce pure nitrogen with a flow rate of 5 - 15 L / min for cleaning, gradually raise the furnace temperature to 450 - 550 °C, and keep the temperature stable for 10 - 20 minutes.

[0027] Uniform laying is beneficial to ensuring that each area is uniformly affected by gas and temperature during the subsequent oxidation process, thus realizing the uniform deposition of the oxygen-silicon layer. Introducing pure nitrogen for cleaning, the oxygen and moisture in the air are discharged by the inert gas to prevent uncontrolled oxidation or side reactions caused by moisture during the preheating stage. At a temperature of 450 - 550 °C, the surface activity of the porous silicon-carbon framework is enhanced. This temperature range is suitable for the reaction of silicon atoms with oxygen to form oxides, and at the same time helps to form a surface structure rich in hydroxyl groups, providing active sites for the chemical bonding of the subsequent polymer layer. The preheating stage can also promote the partial volatilization of residual organic components inside the material, ensuring a cleaner surface of the material during the subsequent deposition of the oxide layer. It provides a clean, uniform, and thermally stable reaction environment, ensuring that the subsequent oxidation reaction can proceed on a uniform basis to form a uniform and functionally good oxygen-silicon layer; by controlling the temperature and nitrogen cleaning, the moisture and impurities that may interfere with the oxidation reaction are eliminated, improving the controllability and stability of the deposition of the oxygen-silicon layer.

[0028] S2.2. Introduce the oxygen-containing gas. Every 10 - 15 minutes, increase or decrease the gas flow rate of the oxygen-containing gas, control the reaction time within 200 - 800 minutes. After the reaction is completed, stop introducing the oxygen-containing gas, and gradually lower the furnace temperature to room temperature at a cooling rate of 5 °C / min while keeping the inert gas flowing to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework.

[0029] Under the condition of 450 - 550 °C, oxygen molecules or oxygen atoms in the oxygen-containing gas react chemically with the free silicon atoms on the surface of the porous silicon-carbon framework to form a layer of SiOx oxide layer, namely the oxygen-silicon layer. At the same time, by dynamically regulating the gas flow rate, the supply rate of oxygen can be precisely controlled, making the oxidation reaction more balanced, avoiding local over-oxidation or oxygen deficiency, and thus forming an oxygen-silicon layer with a uniform thickness and rich in hydroxyl functional groups. The oxygen-silicon layer rich in hydroxyl groups provides active sites for the chemical bonding between the subsequent polymer layer and the silicon-carbon framework, ensuring a firm interface and being conducive to improving the electron and ion transport performance.

[0030] Carbon dioxide can also partially decompose to produce oxygen atoms at high temperatures, and the mild oxidation effect helps to form a thin and uniform oxygen-silicon layer. Pure oxygen has a strong oxidation ability and can quickly form an oxide layer, but it is necessary to pay attention to regulating the flow rate to avoid over-oxidation. The oxygen-nitrogen mixture dilutes pure oxygen through mixing, which not only ensures the progress of the oxidation reaction but also reduces the risk of over-oxidation and is convenient for regulating the oxidation rate.

[0031] Adjusting the flow rate of the oxygen-containing gas every 10 - 15 minutes can make the oxygen supply show a periodic change. This dynamic regulation can make the oxidation reaction more mild, avoid the too-fast local oxidation caused by continuous high flow rate, and at the same time can activate some surface defect areas and enhance the functionality of the SiOx layer. After the reaction, a cooling rate of 5 °C / min is adopted to ensure that the oxygen-silicon layer does not crack or have structural defects due to thermal stress caused by rapid cooling during the cooling process, and at the same time keep the inert gas flowing to prevent the oxide layer from being polluted or re-oxidized by the outside world.

[0032] In one embodiment, for the regulation of the flow rate of the oxygen-containing gas, for example, the initial flow rate is set to 0.5 L / min. A regulation scheme is preset in the control system. In the scheme, the flow rate is increased by 0.5 L / min every 10 minutes until it reaches 2.5 L / min; or according to actual needs, a change of first increasing and then decreasing is achieved within one regulation cycle. Using the digital regulation system, a program is set so that the system automatically adjusts the flow rate of the oxygen-containing gas every 10 - 15 minutes. The system can be pre-programmed. For example: Phase 1: Maintain 0.5 L / min from 0 to 10 minutes; Phase 2: Adjust to 1.0 L / min from 10 to 20 minutes; Phase 3: Adjust to 1.5 L / min from 20 to 30 minutes; Phase 4: Adjust to 2.0 L / min from 30 to 40 minutes; Phase 5: Adjust to 2.5 L / min from 40 to 50 minutes; then the flow rate is decreased in the reverse order to form a cyclic regulation mode. If the manual mode is adopted, the operator manually adjusts the value every 10 - 15 minutes according to the online monitoring data (such as the oxidation state feedback by the online gas analyzer or temperature sensor), thereby changing the flow rate. For example, when it is observed that the oxidation in a certain area is faster, the flow rate can be decreased; if the oxidation is slower, the flow rate can be appropriately increased to maintain the overall uniform oxidation effect.

[0033] Throughout the process, by the feedback data of the real-time monitoring system (such as online FTIR or gas chromatography), the operator or the automatic control system can dynamically modify the preset regulation scheme according to the actual oxidation reaction rate and the surface state of the sample to ensure the uniform progress of the reaction.

[0034] By dynamically adjusting the flow rate of the oxygen-containing gas and controlling the oxidation reaction time, a uniform, dense and oxygen-silicon layer rich in surface active functional groups (such as hydroxyl groups) is formed. It can not only effectively passivate the surface of the porous silicon-carbon framework to prevent direct reaction with the electrolyte, but also provide favorable conditions for the chemical bonding of the subsequent polymer layer. Selecting at least one of carbon dioxide, pure oxygen and oxygen-nitrogen mixture provides a flexible way to regulate the oxidation reaction, which not only ensures the oxidation uniformity but also avoids over-oxidation, further improving the interface stability and the overall material performance.

[0035] In one embodiment, step S1 forms a silicon-carbon framework with a three-dimensional porous structure by chemical vapor deposition. This structure provides a channel for the diffusion of lithium ions inside the electrode. When the material undergoes subsequent oxidation deposition (step S2) to generate the oxygen-silicon layer, the surface properties and interface stability also change accordingly. After these two steps are completed, the electrochemical impedance spectroscopy (EIS) test is carried out on the prepared porous silicon-carbon framework with the oxygen-silicon layer to judge the specific situation of the lithium ion channel. The relevant calculation formula for the test is:

[0036] Wherein, is the real part of impedance, from EIS test data (Ω), is the solution resistance during the test (Ω), is the charge transfer resistance (Ω), is the angular frequency (1 / s). The specific experimental steps of EIS are as follows: Assemble the prepared porous silicon-carbon framework with an oxygen-silicon layer, the test positive electrode, the separator, and the electrolyte into a battery (or test the electrode alone), ensuring the stability of the test environment (temperature, humidity, etc.). While applying a small-amplitude sinusoidal AC voltage perturbation, scan a wide frequency range (from high frequency to low frequency), and record the voltage and current response data. Draw a data graph (imaginary part vs. real part) based on the test data. In the data graph, there will be an intercept in the high-frequency region, located at the leftmost side of the graph, which is the intersection of the graph and the real axis. This intercept mainly reflects the ohmic impedance caused by the electrolyte and the contact interface, that is, the solution resistance . In the data graph, there will be one or more semi-circles. The first semi-circle (appearing in the high-frequency to medium-frequency region) corresponds to the charge transfer process at the electrode interface, and the diameter of the semi-circle represents the charge transfer resistance . By observing the data graph, find the high-frequency intercept and the low-frequency intercept of the semi-circle. The diameter of the semi-circle is . By fitting the relationship between the real part of impedance and , the reflection coefficient ( ) can be obtained. This parameter directly reflects the ease of lithium-ion diffusion in the porous framework. If the value measured in the EIS experiment is large, it means that the impedance increases faster when the frequency decreases. This reflects that there is a large resistance when lithium ions diffuse inside the material, due to narrow pores, low porosity, or high tortuosity and defects in the porous framework, resulting in increased diffusion difficulty. Conversely, a smaller value indicates that the growth rate of impedance with decreasing frequency is small, meaning that the resistance encountered by lithium ions during diffusion is low, the pores are more unobstructed, and the structure is more conducive to ion transport, thus helping to improve the rate performance of the material. Specifically, can be 0.5 - 50 .

[0037] If Too high, the flow rate of the silicon source gas in S1.3 is reduced from 0.5 - 6 L / min to 0.5 - 2 L / min to slow down the deposition rate and avoid pore blockage. The heating rate of S1.3 is slowed down from 5 - 10 °C / min to 5 - 7 °C / min to improve the nucleation stability of the pore structure. The CVD time of S1.3 is extended from 500 - 1000 min to 800 - 1000 min to form a continuous porous network. The flow rate of the oxygen-containing gas in S2.2 is reduced from 0.5 - 2.5 L / min to 0.5 - 1.5 L / min to slow down oxidation and avoid the formation of a barrier layer. The oxygen-containing reaction time of S2.2 is reduced from 200 - 800 min to 200 - 300 min to prevent the oxygen-silicon layer from being too thick and affecting diffusion.

[0038] S3. Disperse the porous silicon-carbon framework with an oxygen-silicon layer in a mixed solvent, add a modified coupling agent and a lithium salt, stir at room temperature for 1 - 5 hours. After stirring is completed, add a polymer solution and stir at room temperature for another 1 - 5 hours to form a polymer layer on the oxygen-silicon layer. After washing and drying, a double-layer coated porous silicon-carbon anode material is obtained. The polymer solution includes a conductive polymer and an ion-conductive polymer. The conductive polymer includes at least one of aniline, pyrrole, and thiophene. The ion-conductive polymer includes at least one of lithium polyacrylate, polyethylene glycol, and polyvinyl alcohol. The modified coupling agent includes at least one of 3-(2-aminoethylamino)propyltrimethoxysilane, vinyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. The lithium salt includes at least one of lithium metaborate, lithium tetrafluoroborate, and lithium hexafluorophosphate. Calculated by mass ratio, the porous silicon-carbon framework: modified coupling agent: lithium salt: polymer solution = 100:5:2:10.

[0039] Step S3 includes: S3.1. Prepare a mixed solution with a volume ratio of ethanol, deionized water, and isopropanol of 1:1:0.5. Add the porous silicon-carbon framework with an oxygen-silicon layer to the mixed solution and treat it with an ultrasonic cleaner for 15 - 30 minutes.

[0040] Ethanol and isopropanol have good organic solubility, which helps to disperse the carbon-based components. Deionized water can increase the polarity of the mixed system and improve the exposure degree of hydroxyl functional groups. The combined use of the three realizes the synergy of the organic and polar environments, which is beneficial to the reaction of the oxygen-silicon layer with the subsequent coupling agent and polymer. Using the ultrasonic cavitation effect, the agglomerates are broken up, so that the porous silicon-carbon particles are evenly distributed in the solution, and the surface active sites of the oxygen-silicon layer are exposed to the greatest extent, creating a reaction basis for the next coupling reaction and polymer attachment. Significantly improve the uniformity and interfacial activity of the reaction system, provide sufficient contact opportunities for the grafting and bonding reactions of the subsequent coupling agent and polymer monomers, and enhance the final coating uniformity and binding force.

[0041] S3.2. Add a modified coupling agent and a lithium salt, and stir for 1 - 5 hours at room temperature using a magnetic stirrer.

[0042] The modified coupling agent contains a hydrolyzable silane end and an active organic group (such as an amino group) in its structure. After hydrolysis, the silane end generates -Si-OH, which undergoes condensation with -Si-OH on the surface of the oxygen-silicon layer to form a stable Si-O-Si bond, achieving chemical bonding. The organic group serves as a grafting anchor point to guide the subsequent in-situ polymerization of the conductive polymer at the interface. The lithium salt mainly provides lithium ions, which are pre-doped into the interface to provide an ion source for establishing an ion channel in the subsequent polymer layer. At the same time, it has a regulating effect on the charge distribution on the surface of the oxygen-silicon layer, contributing to the formation of a denser and more stable interfacial layer structure. Constructing a functionalized graft interface to form a strong chemical connection not only improves the adhesion stability of the subsequent polymer but also guides the formation of a high-ion-conducting region at the interface through the pre-doping of the lithium salt, providing structural and chemical support for rapid ion transport.

[0043] S3.3. Then add the conductive polymer and stir for 1 - 5 hours. Next, add the ion-conducting polymer solution and continue to stir for 1 - 5 hours at room temperature. After washing and filtering alternately with ethanol / distilled water three times, dry in a vacuum drying oven at 80°C to obtain the double-layer coated porous silicon-carbon anode material.

[0044] The polymer layer formed in step S3.3 includes a conductive polymer coating layer and an ion-conducting polymer coating layer. In solution, the conductive polymer is guided by the modified coupling agent to polymerize near the interface, generating polymer chains that in-situ polymerize closely to the surface of the oxygen-silicon layer to form a dense and continuous conductive polymer coating layer. This improves the conduction efficiency of electrons on the entire silicon-carbon skeleton surface, prevents the electron island effect of active substances, and improves the rate performance. The polymer molecules in the ion-conducting polymer coating layer are rich in carboxyl or hydroxyl groups, which can continue to undergo condensation or hydrogen bond / electrostatic interactions with the chains of the conductive polymer coating layer to achieve strong interfacial anchoring. The flexible chain segments in its molecular structure can enhance the strain adaptability of the overall interface and at the same time provide a diffusion channel for lithium-ion migration. The inner conductive polymer coating layer provides an electron channel, and the outer ion-conducting polymer coating layer regulates the lithium-ion channel. The two are coupled to form a three-dimensional conduction network, synergistically improving the conductivity and ion diffusion rate. Washing can remove unpolymerized monomers, lithium salt residues, and by-products to avoid electrochemical side reactions. Vacuum drying shapes the material structure, removes solvent moisture, and prevents the coating layer from cracking or peeling off later. Constructing a dual-functional polymer structure that conducts electrons internally and ions externally greatly enhances the interfacial stability and transport efficiency of the anode material during cycling. The flexible structure of the polymer can buffer the volume expansion of silicon, avoid structural fragmentation, and improve the cycle life. The double-layer coating not only improves the rate performance and cycle stability but also significantly enhances the material's usability under extreme conditions such as high rate / low temperature.

[0045] Conductive polymers (such as aniline, pyrrole, or thiophene) are in-situ polymerized on the oxygen-silicon layer to form a continuous thin film, which can effectively construct an efficient electron transport channel. Coupled with the good conductivity of the porous carbon skeleton itself, a multi-level conductive network is formed. This network greatly reduces the electron transport resistance and improves the rate performance of the negative electrode.

[0046] Ion-conductive polymers (such as lithium polyacrylate, polyethylene glycol, or polyvinyl alcohol) construct a continuous ion conduction channel at the interface through chemical bonding with the oxygen-silicon layer. This layer can not only promote the rapid transport of lithium ions, reduce the interfacial impedance, but also reduce the side reactions caused by the direct contact between the electrolyte and silicon, overall improving the ion transport efficiency and stability of the negative electrode.

[0047] In one embodiment, the double-layer coated porous silicon-carbon negative electrode material prepared in step S3 is subjected to another electrochemical impedance test, and the value is used to calculate the diffusion coefficient D. The calculation formula is as follows:

[0048] Where, is the gas constant, R = 8.314 , T is the thermodynamic temperature (K). When tested at room temperature, T ≈ 298K. B is the surface area of the negative electrode (cm 2 ), which refers to the actual contact surface area or geometric electrode area of the double-layer coated porous silicon-carbon negative electrode material in the electrolyte, and can be 1 - 2 cm 2 or larger / smaller (depending on the specific battery design). n is the number of electrons transferred in the electrochemical reaction. For the insertion / extraction of a single lithium ion, = 1. is the Faraday constant, = 96485 . is the concentration of lithium ions in the electrode (mol·cm -3 ), can be 10 -3 ~10 -1 mol·cm -3 . is the diffusion coefficient (cm 2 ·s -1 ). When is larger, will be smaller, that is, the diffusion rate of lithium ions is low and the diffusion process is hindered. When is smaller will be larger, indicating that the diffusion process is smoother and the ion transport efficiency is higher. can be 10 -8 ~10 -6 cm 2·s -1 。 The unit of is, where = V / A, V = J / C, A = C / s, that is The unit of can be converted to J·s·C -2 。

[0049] If is too low, the concentration of the conductive ionic polymer in S3.3 is reduced from 0.05 - 0.2 g / mL by 0.02 - 0.1 g / mL to avoid thick coating from hindering the ion channels.

[0050] The present invention provides a double - coated porous silicon - carbon anode material, which is made by a preparation method of a double - coated porous silicon - carbon anode material. The double - coated porous silicon - carbon anode material includes a porous silicon - carbon framework, a silicon - oxygen layer provided on the porous silicon - carbon framework, and a polymer layer provided on the silicon - oxygen layer; where The porous silicon - carbon framework is used to provide mechanical support and volume buffering, construct an internal electron transport network, and ensure the stable operation of the double - coated porous silicon - carbon anode material during charge and discharge; The silicon - oxygen layer serves as a passivation layer to prevent side reactions between silicon and the electrolyte, and at the same time generates abundant hydroxyl functional groups, providing active sites for the chemical bonding of the subsequent polymer layer and optimizing the interfacial stability; The polymer layer is used to improve the electron conduction and lithium - ion conduction capabilities of the double - coated porous silicon - carbon anode material, and at the same time relieve the mechanical stress caused by volume expansion of silicon during cycling, and improve the cycling stability.

[0051] Example 1: Add 3000 g of porous carbon spheres and tetraethoxysilane to a CVD furnace, and introduce nitrogen at a flow rate of 14 L / min for 60 minutes. Raise the temperature in the CVD furnace to 480 °C, and introduce silane at a flow rate of 2 L / min for 1000 min to obtain a porous silicon - carbon framework.

[0052] Add the obtained porous silicon - carbon framework to the CVD furnace, and introduce nitrogen at a flow rate of 14 L / min. Raise the temperature in the CVD furnace to 500 °C, and introduce carbon dioxide gas at a flow rate of 1 L / min for 500 min to obtain a silicon - oxygen layer deposited on the surface of the porous silicon - carbon framework.

[0053] Weigh 20 g of the porous silicon-carbon framework with an oxygen-silicon layer and add it to a solvent (V ethanol:V deionized water = 1:1), then carry out magnetic stirring for 30 min. Add 0.1 ml of silane coupling agent and 0.5% lithium salt, and stir at room temperature for 3 h. Sequentially add a certain amount of 1 Mol / L phosphoric acid solution and 2 ml of aniline and stir; subsequently, slowly dropwise add a certain amount of 1 Mol / L ammonium persulfate solution to the above solution for in-situ polymerization for 2 h. Add a certain amount of lithium polyacrylate (the amount of lithium polyacrylate is 0.25% of the mass of the porous silicon-carbon framework with an oxygen-silicon layer) solution to the above solution and stir for 3 h. After the reaction ends, wash the obtained mixed solution with ethanol and deionized water alternately by suction filtration three times, and then dry it in a vacuum environment at 80 °C for 10 h to obtain a double-layer coated porous silicon-carbon anode material.

[0054] Example 2: The same as Example 1, except that the amount of lithium polyacrylate is 0.5% of the mass of the porous silicon-carbon framework with an oxygen-silicon layer.

[0055] Example 3: The same as Example 1, except that the amount of lithium polyacrylate is 1% of the mass of the porous silicon-carbon framework with an oxygen-silicon layer.

[0056] Comparative Example 1: The same as Example 1, except that no polymer solution is added in step S3.

[0057] Comparative Example 2: The same as Example 1, except that step S3 is not carried out.

[0058] Weigh the double-layer coated porous silicon-carbon anode material, conductive carbon black, and binder, add deionized water to prepare a uniform slurry. Among them, the solid content ratio of the double-layer coated porous silicon-carbon anode material:conductive carbon black:binder CMC is 95:1.5:3.5. Use a homogenizer to prepare the sample, with a rotation speed of 2000 rpm and a time of 20 min. After sieving the slurry, evenly coat it on a copper foil, and place it in a vacuum drying oven at 90 °C for drying. After the dried electrode sheet is roll-pressed, cut it into circular electrodes of a certain size, and record the electrode mass. In an argon atmosphere glove box, use a lithium metal sheet as the counter electrode, and assemble it into a button cell with the above-obtained electrode, separator, gasket, etc. The electrolyte uses a special electrolyte for silicon-carbon.

[0059] In one embodiment, by performing CV tests at different scan rates, current-potential curves can be recorded. To distinguish the pseudocapacitive behavior from the diffusion-controlled behavior in cyclic voltammetry tests, the following empirical equation is used. Pseudocapacitive behavior refers to the energy storage phenomenon that occurs in electrode materials during the energy storage process. In addition to the traditional ion insertion / extraction process, there is also a kind of energy storage phenomenon similar to that of a capacitor, which is caused by a fast surface or near-surface electrochemical reaction. Although this phenomenon is not a pure electric double layer capacitor (EDLC), its characteristics such as fast charge and discharge speed and rapid response make it exhibit capacitive-like behavior in cyclic voltammetry (CV) tests, so it is called pseudocapacitive behavior. In the negative electrode material, lithium ions need to diffuse along the channels inside the porous structure into the material. When the pores are not smooth enough or there is a large diffusion resistance, the diffusion process of lithium ions will become the bottleneck of the whole reaction, thus showing diffusion-controlled behavior.

[0060]

[0061] Wherein, is the peak current (A), is the scan rate (V / s), is the pseudocapacitive behavior coefficient (A·s / V), can be 10 -5 ~10 -3 A·s / V, is the current component related to pseudocapacitive behavior, is the diffusion-controlled behavior coefficient (A / (V / S) 0.5 ), can be 10 -5 ~10 -3 A / (V / S) 0.5 , k2v 0.5 is the current component related to diffusion-controlled behavior. By processing the data of the CV curves at different scan rates (for example, recording the peak current or instantaneous current at a preset potential). At the same potential, measure or read the currents at different scan rates . Fit to k1v + k2v 0.5 , so as to obtain and .

[0062] Through the value obtained by fitting, it can be quantitatively judged how much current is provided by the surface fast reaction (pseudocapacitance) at this potential; while illustrates the current part caused by the limited ion diffusion. If the test results show A larger value of this item indicates that the surface of the material or the coating design effectively promotes a rapid pseudocapacitive reaction, corresponding to excellent high-rate performance, and can maintain or further enhance the conductivity and reactivity on the electrode surface, such as by increasing the content of conductive polymers. On the contrary, if this item has a relatively high proportion, it indicates that the diffusion control process dominates, and it is necessary to further improve the porous structure or interface conductivity. The addition ratio of porous carbon spheres can be increased to form a more continuous and porous framework.

[0063] After performing charge-discharge cycles on Examples 1-3 and Comparative Examples 1-2, the experimental data obtained are shown in Table 1. It can be seen from Table 1 that the abundant carboxyl groups in the polymer solution can be connected to some functional groups on the surface of the silicon material through hydrogen bonds, and promote the formation of the solid electrolyte interface film (SEI film) on the negative electrode. This greatly improves the cycling performance of the silicon-based negative electrode and reduces the loss of battery capacity. The capacity retention rates of Example 1, Example 2, and Example 3 are all higher than those of Comparative Example 1 and Comparative Example 2, indicating that the double-layer coating material can form a protective film on the surface of the negative electrode material, enhance the mechanical strength of the negative electrode material, and reduce pulverization and shedding during charge and discharge. The polymer layer has conductivity and ion conductivity. Introducing conductive polymers and ion-conducting polymers is beneficial to improving the lithium-ion transport ability of the composite binder, thus effectively constructing a double-layer conductive network, making it have high electronic conductivity, high lithium-ion conductivity, and excellent mechanical properties. The initial capacity and efficiency of Example 1, Example 2, and Example 3 are all higher than those of Comparative Example 1 and Comparative Example 2, indicating that through improved conductivity and structural stability, the double-layer coated porous silicon-carbon negative electrode material can improve the specific capacity and Coulomb efficiency of the battery, thereby improving the electrochemical performance of the battery. The specific surface areas of Example 1, Example 2, Example 3, and Comparative Example 1 are all smaller than that of Comparative Example 2, indicating that the polymer layer forms a surface sealing layer, with the characteristics of conformal growth and a highly cross-linked molecular structure, reducing the specific surface area (SSA) of the double-layer coated porous silicon-carbon negative electrode material from 50-100 m 2 / g to 1-5 m 2 / g. Reducing the specific surface area means that the contact area between the negative electrode material and the electrolyte decreases, thereby reducing the excessive formation of the solid electrolyte interface (SEI) film, reducing the decomposition of the electrolyte and irreversible side reactions. A lower specific surface area can reduce unnecessary electrochemical reactions, reduce the initial Coulomb efficiency loss and capacity decay, and contribute to improving the long-term cycling performance and overall energy efficiency.

[0064] Table 1. Charge-discharge cycle experimental data: 。

[0065] Please refer to Figure 1, this figure shows the specific capacity (left vertical axis, mAh g⁻¹) and Coulombic efficiency (right vertical axis, %) of the electrode materials of the comparative samples (Comparative Example 1, Comparative Example 2) and the implementation samples (Example 1, Example 2, Example 3) during the first 100 charge-discharge cycles at a current density of 0.1 A g⁻¹ as a function of the number of cycles. It can be seen that all the examples have a slightly higher initial specific capacity than the comparative examples at the beginning of the cycle, and during the subsequent cycle process, the attenuation amplitude of the specific capacity is smaller; at the same time, the Coulombic efficiency rises rapidly after the first cycle and stabilizes between 98% and 100%, indicating that the coating layer has a significant effect on enhancing the electrochemical stability and reversibility of the electrode material.

[0066] Please refer to Figure 2 , this figure is the XRD diffraction pattern (2θ range from 10° to 90°) of the porous silicon-carbon skeleton samples before (black line) and after (red line) coating. It can be seen that both groups of samples show an amorphous peak of carbon material mainly at 26°, and the overall peak intensity of the coated samples increases significantly. In particular, there is a slight peak position shift or peak width change near 30°, indicating that after the double-layer coating of the silicon layer and the polymer, a new silicon-containing oxide structure is formed on the surface of the sample, which enhances the interlayer order of the material and increases the diffraction signal intensity. Please refer to Figure 3 , this figure gives the voltage-specific capacity (V–mAh g⁻¹) curves of Comparative Example 1, Comparative Example 2 and Example 1, 2, 3 at the 1st cycle. Both the discharge process (the voltage decreases from high to low) and the charge process (the voltage increases from low to high) show similar step and ramp characteristics. Compared with the comparative examples, the capacity of the example curves at the discharge plateau is higher, and the shapes of the charge-discharge curves of the two basically overlap, indicating that the coating layer does not introduce obvious polarization, but instead improves the reversible specific capacity, highlighting the advantages of the coating layer in helping to stabilize the electrode interface and enabling rapid lithium-ion transport.

[0067] Please refer to Figure 4, This figure compares the FTIR transmittance spectra of the original sample (black line) and the double-layer coated sample (red line) in the wavenumber range of 4000–400 cm⁻¹. The original sample only has a weak C–H stretching vibration peak at about 2900 cm⁻¹, while the coated sample shows stronger characteristic absorption peaks of organic polymers in the same region; in addition, the new peak near 1100 cm⁻¹ corresponds to the vibration of the Si–O–Si bond, confirming the existence of the oxygen-silicon layer; at 1600–1700 cm⁻¹, the coated sample also shows absorption peaks of carboxyl or amide groups, reflecting the introduction of lithium polyacrylate / aniline polymer. The overall spectral changes clearly demonstrate that the double-layer coating strategy has successfully constructed an organic–inorganic composite protective layer on the surface of the electrode material. As can be seen from the infrared spectrum, the four characteristic absorption peaks marked by the gray dotted line are located at about 1400 cm⁻¹, 1150 cm⁻¹, 1060 cm⁻¹, and 730 cm⁻¹ respectively. 1400 cm⁻¹ is related to the deformation vibration of –CH2 / –CH3 hydroxyl or the stretching vibration of –C–N; the 1150 cm⁻¹ peak belongs to the stretching vibration of Si–O–C or C–O–C, indicating the coupling bond of organic or siloxane segments; 1060 cm⁻¹ is the main peak of the asymmetric stretching vibration of Si–O–Si, characterizing the integrity of the silicon-oxygen skeleton; while near 730 cm⁻¹, it corresponds to the rocking / bending vibration of Si–O–Si, and also contains signals of out-of-plane bending vibration of C–H. These changes indicate that a silicon-oxygen skeleton (Si–O–Si) and silicon-oxygen-carbon bridging bonds (Si–O–C) are formed in the coating layer, along with the introduction of a small amount of organic alkyl or amino residues. In other words, the coating process not only deposits an inorganic or organic-inorganic hybrid layer rich in silicon-oxygen network on the material surface, but also retains or introduces organic side chains, jointly constituting a new surface functional group environment.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a double-layer coated porous silicon-carbon anode material for fabricating a lithium-ion battery, characterized in that, The steps include; S1. Uniformly mix a carbon precursor and a doping precursor, introduce an inert gas into a chemical vapor deposition furnace, adjust the temperature to 400 - 500 °C, and simultaneously introduce a silicon source gas. Control the reaction time within 500 - 1000 minutes to obtain a porous silicon-carbon framework. Among them, the doping precursor includes a silicon source material; S2. Heat the porous silicon-carbon framework to 450 - 550 °C, introduce an oxygen-containing gas, and react for 200 - 800 minutes to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework; S3. Disperse the porous silicon-carbon framework with the oxygen-silicon layer in a mixed solvent, add a modified coupling agent and a lithium salt, stir at room temperature for 1 - 5 hours. After stirring is completed, add a polymer solution and stir at room temperature for another 1 - 5 hours to form a polymer layer on the oxygen-silicon layer. After washing and drying, a double-coated porous silicon-carbon anode material is obtained.

2. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 1, wherein, The carbon precursor includes porous carbon spheres and an asphalt matrix, and the doping precursor includes a silicon source material and a metal catalyst; Step S1 includes: S1.

1. Mix the porous carbon spheres, the asphalt matrix, the silicon source material, and the metal catalyst in a preset ratio to obtain a mixture; S1.

2. Uniformly spread the mixture on a high-purity ceramic substrate, place it in the reaction chamber of a chemical vapor deposition furnace, and then introduce an inert gas with a gas flow rate of 10 - 20 L / min, gradually heat up to 400 °C, and preheat at this temperature for 30 minutes; S1.

3. Gradually raise the temperature to 400 - 500 °C, ensuring that the heating rate is within the range of 5 - 10 °C / min, After reaching the target temperature, slowly introduce the silicon source gas into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5 - 6 L / min, while continuously maintaining the inert gas flow rate to obtain a porous silicon-carbon framework.

3. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 2, characterized in that, In step S1.1, the porous carbon spheres include at least one of phenolic resin carbon spheres, coconut shell activated carbon spheres, and polyacrylonitrile-modified carbon spheres; the asphalt matrix includes at least one of petroleum asphalt, coal asphalt, and heavy oil asphalt; the silicon source material includes at least one of silane, disilane, and trimethoxysilane; the metal catalyst includes at least one of nanoscale iron catalysts, nanoscale nickel catalysts, and nanoscale cobalt catalysts; the silicon source gas includes at least one of silane, disilane, and trimethoxysilane.

4. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 3, characterized in that, In step S1.1, calculated by mass ratio, the porous carbon spheres: the asphalt matrix: the silicon source material: the metal catalyst = (40 - 60):(20 - 40):(10 - 20):(0.5 - 2).

5. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 1, wherein, Step S2 includes: S2.

1. Uniformly lay the porous silicon-carbon framework on a ceramic boat, first introduce pure nitrogen with a flow rate of 5 - 15 L / min for cleaning, gradually raise the furnace temperature to 450 - 550 °C, and keep the temperature stable for 10 - 20 minutes; S2.

2. Introduce an oxygen-containing gas. Every 10 - 15 minutes, increase or decrease the gas flow rate of the oxygen-containing gas. Control the reaction time within 200 - 800 minutes. After the reaction is completed, stop introducing the oxygen-containing gas, and gradually reduce the furnace temperature to room temperature at a cooling rate of 5°C / min while maintaining the flow of the inert gas to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon framework.

6. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 5, characterized in that, The oxygen-containing gas includes at least one of carbon dioxide, pure oxygen, and an oxygen-nitrogen mixture, and the gas flow rate of the oxygen-containing gas is 0.5 - 2.5 L / min.

7. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 1, characterized in that, The polymer solution includes a conductive polymer and an ion-conducting polymer; Step S3 includes: S3.

1. Prepare a mixed solution with a volume ratio of ethanol, deionized water, and isopropanol of 1:1:0.

5. Add the porous silicon-carbon framework with the oxygen-silicon layer to the mixed solution and treat it with an ultrasonic cleaner for 15 - 30 minutes; S3.

2. Add a modified coupling agent and a lithium salt, and stir at room temperature for 1 - 5 hours using a magnetic stirrer; S3.

3. Then add the conductive polymer and stir for 1 - 5 hours. Then add the ion-conducting polymer solution and continue to stir at room temperature for 1 - 5 hours. After washing and filtering three times alternately with ethanol / distilled water, dry in a vacuum drying oven at 80°C to obtain a double-layer coated porous silicon-carbon anode material.

8. The preparation method of a double-layer coated porous silicon-carbon anode material according to claim 7, characterized in that, In step S3, the conductive polymer includes at least one of aniline, pyrrole, and thiophene, the ion-conducting polymer includes at least one of lithium polyacrylate, polyethylene glycol, and polyvinyl alcohol, the modified coupling agent includes at least one of 3-(2-aminoethylamino)propyltrimethoxysilane, vinyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane, and the lithium salt includes at least one of lithium metaborate, lithium tetrafluoroborate, and lithium hexafluorophosphate. Calculated by mass ratio, the porous silicon-carbon framework: the modified coupling agent: the lithium salt: the polymer solution = 100:5:2:

10.

9. A double-layer coated porous silicon-carbon anode material, characterized in that, Prepared by the method for preparing a double-layer coated porous silicon-carbon anode material according to any one of claims 1 - 8, the double-layer coated porous silicon-carbon anode material includes a porous silicon-carbon framework, an oxygen-silicon layer provided on the porous silicon-carbon framework, and a polymer layer provided on the oxygen-silicon layer; wherein, The porous silicon-carbon framework is used to provide mechanical support and volume buffering, construct an internal electron transport network, and ensure the stable operation of the double-layer coated porous silicon-carbon anode material during charge and discharge; The oxygen-silicon layer serves as a passivation layer to prevent side reactions between silicon and the electrolyte, and at the same time generates abundant hydroxyl functional groups to provide active sites for chemical bonding of the subsequent polymer layer and optimize the interface stability; The polymer layer is used to improve the electron conduction and lithium ion conduction capabilities of the double-layer coated porous silicon-carbon anode material, and at the same time relieve the mechanical stress caused by volume expansion of silicon during cycling and improve the cycling stability.

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