A double-layer coated porous silicon-carbon negative electrode material and its preparation method

Abstract

The present invention provides a double-layer coated porous silicon-carbon anode material and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing a carbon precursor and a doping precursor; introducing an inert gas into a chemical vapor deposition furnace, adjusting the temperature to 400-500°C, and simultaneously introducing a silicon source gas; and controlling the reaction time to be 500-1000 minutes to obtain a porous silicon-carbon skeleton, wherein the doping precursor includes a silicon source material; heating the porous silicon-carbon skeleton to 450-550°C, introducing an 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, and stirring at room temperature for 1-5 hours. After stirring, a polymer solution is added, and stirring is continued at room temperature for 1-5 hours to form a polymer layer on the oxygen-silicon layer. The double-layer coated porous silicon-carbon anode material is obtained after washing and drying. This effectively improves the cycle performance of the anode material.

Description

Technical Field

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

[0002] Various negative electrode materials with improved storage capacity and thermal stability have been proposed for lithium-ion batteries (LIBs) over the past decade. Silicon (Si) has been extensively studied as an anode active material in lithium-ion batteries due to its remarkable properties. The theoretical specific capacity of carbon active materials is 372 mAh / g based on an intercalation ratio of one lithium (Li) per six carbon atoms (C). Silicon and lithium alloys with higher lithium to silicon ratios can be formed in all-carbon materials using a lithium to C atom ratio of 1 / 6. Among these alloys, the Li / Si ratio ranges from 1.71 for the alloy phase (theoretical capacity of 1636 mAh / g) to 2.5 for the alloy phase Li. 15 The Li / Si ratio of Si4 (theoretical capacity is 3579 mAh / g) is 3.75. 22 The Si5 alloy has a specific capacity of 4.4 and a theoretical capacity of 4200mAh / g. In addition to its high specific capacity, silicon has a slightly higher voltage than the graphite platform, so it has attractive safety features. In addition, silicon is an abundant and inexpensive material, and lithium silicon is more stable than lithium graphite in typical lithium-ion battery electrolytes. However, silicon materials themselves have poor conductivity. At the same time, silicon-based materials currently have problems such as volume expansion of up to 400% during lithium insertion, low electronic conductivity, and difficulty in forming a stable solid electrolyte interface film (SEI), which seriously hinders its commercialization as a high-capacity negative electrode. Currently, this problem is mainly solved by nano-scaling, alloying, and silicon-carbon composites.

[0003] Because nano-silicon particles are small and easy to agglomerate, the related technology of silicon-carbon composite is ball milling, which can effectively disperse nano-silicon particles. However, nano-silicon particles have high chemical activity and are easily oxidized, resulting in low initial efficiency of the material. Carbon materials such as graphite have a small specific surface area, and nano-silicon particles agglomerate between and on the surface of graphite layers. The dispersion space provided by carbon materials is limited, making it difficult to improve the cycle 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 negative electrode material and a preparation method thereof, aiming to solve the problem that the cycle performance of the negative electrode material is difficult to improve.

[0005] To solve the above technical problems, the present invention is implemented as follows: the present invention provides a method for preparing a double-layer coated porous silicon-carbon negative electrode material for making a lithium-ion battery, the steps comprising:

[0006] S1. uniformly mixing a carbon precursor and a doping precursor, introducing an inert gas into a chemical vapor deposition furnace, adjusting the temperature to 400-500° C., introducing a silicon source gas, and controlling the reaction time to be 500-1000 minutes to obtain a porous silicon-carbon skeleton, wherein the doping precursor includes a silicon source material;

[0007] S2, heating the porous silicon-carbon skeleton to 450-550° C., introducing an 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;

[0008] S3. Disperse the porous silicon-carbon skeleton with the silicon oxide layer in a mixed solvent, add a modified coupling agent and a lithium salt, and stir at room temperature for 1 to 5 hours. After stirring, add a polymer solution and stir at room temperature for another 1 to 5 hours to generate a polymer layer on the silicon oxide layer. After washing and drying, a double-layer coated porous silicon-carbon negative electrode material is obtained.

[0009] In some embodiments of the present invention, the carbon precursor includes porous carbon spheres and a pitch matrix, and the doping precursor includes a silicon source material and a metal catalyst;

[0010] Step S1 includes:

[0011] S1.1, mixing the porous carbon spheres, the asphalt matrix, the silicon source material, and the metal catalyst in a predetermined ratio to obtain a mixture;

[0012] S1.2. Evenly spread the mixture on a high-purity ceramic substrate, place it in the reaction chamber of a chemical vapor deposition furnace, then introduce inert gas at a flow rate of 10-20 L / min, gradually increase the temperature to 400°C, and preheat at this temperature for 30 minutes;

[0013] S1.3, gradually increase the temperature to 400~500℃, ensuring that the heating rate is within the range of 5~10℃ / min,

[0014] After reaching the target temperature, the silicon source gas is slowly introduced into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5~6L / min while continuing to maintain the inert gas flow rate to obtain a porous silicon-carbon skeleton.

[0015] In some embodiments of the present invention, in step S1.1, the porous carbon balls include at least one of polyphenolic resin carbon balls, coconut shell activated carbon balls, and polyacrylonitrile modified carbon balls, the asphalt matrix includes at least one of petroleum asphalt, coal tar, and heavy oil asphalt, the silicon source material includes at least one of tetraethoxysilane, tetramethoxysilane, and diethoxysilane, the metal catalyst includes at least one of nano-scale iron catalyst, nano-scale nickel catalyst, and nano-scale cobalt catalyst, and the silicon source gas includes at least one of monosilane, disilane, and trimethoxysilane.

[0016] In some embodiments of the present invention, in step S1.1, calculated according to the 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).

[0017] In some embodiments of the present invention, step S2 includes:

[0018] S2.1. The porous silicon-carbon skeleton is evenly laid on a ceramic boat. First, pure nitrogen is introduced at a flow rate of 5-15 L / min for cleaning. The furnace temperature is gradually increased to 450-550°C and kept stable for 10-20 minutes.

[0019] S2.2. Introduction of oxygen-containing gas, reducing or increasing the gas flow rate of the oxygen-containing gas every 10 to 15 minutes, and controlling the reaction time to be 200 to 800 minutes. After the reaction is completed, the introduction of the oxygen-containing gas is stopped, and the furnace temperature is gradually lowered 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 skeleton.

[0020] 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.

[0021] In some embodiments of the present invention, the polymer solution includes a conductive polymer and an ion-conducting polymer;

[0022] Step S3 includes:

[0023] S3.1. Prepare a mixed solution of ethanol, deionized water, and isopropanol in a volume ratio of 1:1:0.5, add the porous silicon-carbon skeleton with the silicon oxide layer to the mixed solution, and treat in an ultrasonic cleaner for 15 to 30 minutes;

[0024] S3.2. Add the modified coupling agent and lithium salt and stir at room temperature using a magnetic stirrer for 1 to 5 hours.

[0025] S3.3. Add the conductive polymer and stir for 1 to 5 hours. Then add the ion-conducting polymer solution and continue stirring at room temperature for 1 to 5 hours. Wash and filter three times with ethanol / distilled water alternately, and dry in a vacuum drying oven at 80°C to obtain a double-layer coated porous silicon-carbon negative electrode material.

[0026] 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-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 skeleton: the modified coupling agent: the lithium salt: the polymer solution = 100:5:2:10.

[0027] The present invention provides a double-layer coated porous silicon-carbon negative electrode material, which is prepared by the above-mentioned preparation method of a double-layer coated porous silicon-carbon negative electrode material. The double-layer coated porous silicon-carbon negative electrode material comprises a porous silicon-carbon skeleton, an oxygen-silicon layer provided on the porous silicon-carbon skeleton, and a polymer layer provided on the oxygen-silicon layer; wherein,

[0028] The porous silicon-carbon skeleton is used to provide mechanical support and volume buffering, build an internal electron transport network, and ensure that the double-layer coated porous silicon-carbon negative electrode material works stably during the charge and discharge process;

[0029] The silicon oxide layer acts as a passivation layer to prevent side reactions between silicon and the electrolyte, while generating abundant hydroxyl functional groups, providing active sites for chemical bonding of the subsequent polymer layer and optimizing interface stability;

[0030] The polymer layer is used to enhance the electronic conduction and lithium ion conduction capabilities of the double-layer coated porous silicon-carbon negative electrode material, while alleviating the mechanical stress caused by volume expansion of silicon during the cycle and improving the cycle stability.

[0031] Compared with the prior art, the double-layer coated porous silicon-carbon negative electrode material and its preparation method in the present invention have the following advantages:

[0032] The silicon oxide layer forms a dense and functional passivation layer on the surface of the porous silicon-carbon skeleton. It not only prevents direct contact between silicon and the electrolyte, inhibiting adverse side reactions, but also mitigates mechanical damage caused by silicon's volume expansion. Simultaneously, the polymer layer grown on the silicon oxide layer acts as a buffer and fixation layer, ensuring that the negative electrode structure remains intact during charge and discharge, significantly improving cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the cycle of the double-layer coated porous silicon-carbon negative electrode material in one embodiment of the present invention.

[0034] Figure 2 This is an XRD pattern of a double-layer coated porous silicon-carbon negative electrode material in one embodiment of the present invention;

[0035] Figure 3 1 is a capacity-voltage diagram of a double-layer coated porous silicon-carbon negative electrode material according to an embodiment of the present invention;

[0036] Figure 4 This is an FT-IR analysis chart of a double-layer coated porous silicon-carbon negative electrode material in one embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 intended to limit the present invention.

[0038] The present invention provides a method for preparing a double-layer coated porous silicon-carbon negative electrode material for making a lithium-ion battery, comprising the following steps:

[0039] S1. The carbon precursor and the doping precursor are uniformly mixed, an inert gas is introduced into a chemical vapor deposition furnace (CVD), the temperature is adjusted to 400-500°C, and a silicon source gas is introduced at the same time. The reaction time is controlled at 500-1000 minutes to obtain a porous silicon-carbon skeleton, wherein the doping precursor includes a silicon source material.

[0040] The carbon precursor includes porous carbon spheres and a pitch matrix, and the doping precursor includes a silicon source material and a metal catalyst;

[0041] Step S1 includes:

[0042] S1.1. Porous carbon spheres, an asphalt matrix, a silicon source material, and a metal catalyst are mixed in predetermined proportions to obtain a mixture. In step S1.1, the porous carbon spheres include at least one of polyphenolic resin carbon spheres, coconut shell activated carbon spheres, and polyacrylonitrile-modified carbon spheres; the asphalt matrix includes at least one of petroleum asphalt, coal tar, and heavy oil asphalt; the silicon source material includes at least one of tetraethoxysilane, tetramethoxysilane, and diethoxysilane; the metal catalyst includes at least one of a nano-sized iron catalyst, a nano-sized nickel catalyst, and a nano-sized cobalt catalyst; and the silicon source gas includes at least one of monosilane, disilane, and trimethoxysilane. The mass ratio of porous carbon spheres: asphalt matrix: silicon source material: metal catalyst is (40-60): (20-40): (10-20): (0.5-2).

[0043] Through ball milling or ultrasonic treatment, the various components are evenly dispersed to ensure that during 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 asphalt matrix. Under subsequent high-temperature conditions, the silicon source material can decompose, releasing silicon precursors and, with the help of the metal catalyst, in situ depositing silicon nanoparticles in the carbon matrix; at the same time, the metal catalyst can also promote the partial recombination of the asphalt components to form a carbon nanotube structure that is conducive to electron transport. Achieving uniform distribution of the various precursors lays the foundation for the subsequent formation of a porous silicon-carbon skeleton. The metal catalyst is used to activate the silicon source reaction, promote the uniform deposition of silicon nanoparticles within the carbon skeleton, and generate local carbon nanotubes, thereby improving the conductivity and structural stability of the material.

[0044] S1.2. Evenly spread the mixture on a high-purity ceramic substrate, place it in the reaction chamber of a chemical vapor deposition furnace, and then introduce inert gas at a gas flow rate of 10-20 L / min. Gradually increase the temperature to 400°C and preheat at this temperature for 30 minutes.

[0045] Ensure uniform heating of the mixture within the furnace, avoiding local overheating or temperature variations that could lead to inconsistent reactions. The preheating stage helps remove moisture and volatile organic compounds (especially low-molecular-weight components in asphalt) from the mixture, providing a clean, stable substrate for subsequent high-temperature reactions. High-temperature CVD furnaces are equipped with precise temperature control systems and flow control devices to ensure uniform temperature and atmosphere. Preheating controls eliminate impurities and volatile components from the mixture, improving the efficiency of the subsequent silicon deposition reaction. This ensures uniform temperature distribution within the furnace and the structural consistency of the porous silicon-carbon framework, creating an ideal foundation for the formation of a highly conductive network.

[0046] S1.3, gradually increase the temperature to 400~500℃, ensuring that the heating rate is within the range of 5~10℃ / min,

[0047] After reaching the target temperature, the silicon source gas is slowly introduced into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5~6L / min while continuing to maintain the inert gas flow rate to obtain a porous silicon-carbon skeleton.

[0048] At 400-500°C, the silicon source gas thermally decomposes to produce silicon atoms or silicon precursors. Promoted by a metal catalyst, the silicon atoms are deposited on the surface of the carbon precursor to form nanoscale silicon particles. Trace metal catalysts not only catalyze silicon deposition but also promote the reorganization of some carbon components in the asphalt matrix, generating localized carbon nanotubes in situ to form an interconnected conductive network. Using a CVD furnace with precise gas flow control allows for precise mixing and uniform distribution of the silicon source gas and inert gas. Silicon nanoparticles are uniformly generated within the structure, enhancing the active lithium storage capacity of the skeleton. Catalytic action allows for self-assembly of embedded carbon nanotubes, improving the overall conductivity and structural stability of the skeleton. Precise gas and temperature control ensures good structural consistency and a highly conductive network, providing a solid foundation for subsequent process steps.

[0049] S1.1 The mixture preparation utilizes a combination of porous carbon spheres and an asphalt matrix, supplemented by silicon source materials and metal catalysts. Uniform mixing provides uniformly dispersed precursors for subsequent reactions, ensuring the coordinated progress of silicon deposition and carbon self-assembly reactions to form a basic porous skeleton. S1.2 Uniform laying and preheating eliminate volatile components and impurities in the mixture through precise control of the laying and preheating process, ensuring uniform temperature in the furnace and creating optimal conditions for high-temperature reactions. S1.3 High-temperature silicon source deposition utilizes the decomposition of silicon source gas under high temperature conditions to achieve uniform deposition of silicon nanoparticles under the action of metal catalysts, while simultaneously generating carbon nanotubes in situ to construct a porous silicon-carbon skeleton that is both highly active and highly conductive.

[0050] S2. The porous silicon-carbon skeleton is heated to 450-550° C. and an oxygen-containing gas is introduced therein for 200-800 minutes to form an oxygen-silicon layer deposited on the surface of the porous silicon-carbon skeleton. The oxygen-containing gas comprises at least one of carbon dioxide, pure oxygen, and an oxygen-nitrogen mixture, and the flow rate of the oxygen-containing gas is 0.5-2.5 L / min.

[0051] Step S2 includes:

[0052] S2.1. Evenly lay the porous silicon-carbon skeleton on a ceramic boat. First, introduce pure nitrogen at a flow rate of 5-15 L / min for cleaning. Gradually increase the furnace temperature to 450-550°C and maintain the temperature stable for 10-20 minutes.

[0053] Uniform deposition ensures consistent gas and temperature exposure across all regions during the subsequent oxidation process, resulting in uniform deposition of the silicon oxide layer. Purging with pure nitrogen, an inert gas, removes oxygen and moisture from the air, preventing uncontrolled oxidation or moisture-induced side reactions during the preheating phase. The surface activity of the porous silicon-carbon framework increases at temperatures between 450°C and 550°C. This temperature range is ideal for the reaction of silicon atoms with oxygen to form oxides, while also fostering the formation of a hydroxyl-rich surface structure, which provides active sites for chemical bonding in the subsequent polymer layer. The preheating phase also partially volatilizes residual organic components within the material, ensuring a purer surface for subsequent oxide layer deposition. This provides a clean, uniform, and thermally stable reaction environment, ensuring the subsequent oxidation reaction proceeds uniformly, resulting in a uniform and well-functioning silicon oxide layer. Temperature control and nitrogen purging eliminate moisture and impurities that could interfere with the oxidation reaction, improving the controllability and stability of the silicon oxide layer deposition.

[0054] S2.2. Introduce oxygen-containing gas, reduce or increase the gas flow rate of the oxygen-containing gas every 10 to 15 minutes, and control the reaction time to be 200 to 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 maintaining the flow of inert gas to obtain an oxygen-silicon layer deposited on the surface of the porous silicon-carbon skeleton.

[0055] Under conditions of 450-550°C, oxygen molecules or atoms in the oxygen-containing gas react chemically with free silicon atoms on the surface of the porous silicon-carbon skeleton, forming a SiOx oxide layer, or oxygen-silicon layer. At the same time, by dynamically regulating the gas flow rate, the oxygen supply rate can be precisely controlled, making the oxidation reaction more balanced and avoiding local overoxidation or oxygen deficiency, thereby forming an oxygen-silicon layer of uniform thickness rich in hydroxyl functional groups. The hydroxyl-rich oxygen-silicon layer provides active sites for chemical bonding between the subsequent polymer layer and the silicon-carbon skeleton, ensuring a strong interface and promoting the transmission of electrons and ions.

[0056] Carbon dioxide can also partially decompose at high temperatures to produce oxygen atoms, and this mild oxidation helps form a thin, uniform oxygen-silicon layer. Pure oxygen has a strong oxidizing ability and can quickly form an oxide layer, but care must be taken to control the flow rate to avoid over-oxidation. An oxygen-nitrogen mixture, by diluting the pure oxygen, ensures the oxidation reaction proceeds while reducing the risk of over-oxidation and facilitating control of the oxidation rate.

[0057] Adjusting the oxygen-containing gas flow rate every 10-15 minutes creates a periodic change in the oxygen supply. This dynamic regulation makes the oxidation reaction milder, avoiding localized, overly rapid oxidation caused by sustained high flow rates. It also activates surface defects and enhances the functionality of the SiOx layer. After the reaction, a cooling rate of 5°C / min is used to ensure that the silicon-oxygen layer does not develop cracks or structural defects due to thermal stress caused by rapid cooling. Maintaining the inert gas flow prevents external contamination and reoxidation of the oxide layer.

[0058] In one embodiment, the flow rate of the oxygen-containing gas is adjusted. For example, if the initial flow rate is set at 0.5 L / min, a control scheme is pre-set in the control system, which stipulates that the flow rate is increased by 0.5 L / min every 10 minutes until it reaches 2.5 L / min. Alternatively, the flow rate can be increased and then decreased within a single adjustment cycle, depending on actual needs. Using a digital control system, the system is programmed to automatically adjust the flow rate of the oxygen-containing gas every 10-15 minutes. The system can be pre-programmed, for example: Stage 1: Maintain 0.5 L / min from 0-10 minutes; Stage 2: Adjust to 1.0 L / min from 10-20 minutes; Stage 3: Adjust to 1.5 L / min from 20-30 minutes; Stage 4: Adjust to 2.0 L / min from 30-40 minutes; Stage 5: Adjust to 2.5 L / min from 40-50 minutes; and then decrease the flow rate in the reverse order, forming a cyclic control mode. In manual mode, the operator manually adjusts the flow rate every 10-15 minutes based on online monitoring data (e.g., oxidation status feedback from an online gas analyzer or temperature sensor). For example, if a particular area oxidizes rapidly, the flow rate can be reduced; if oxidation is slow, the flow rate can be increased to maintain uniform oxidation across the board.

[0059] Throughout the entire process, data is fed back by a real-time monitoring system (such as online FTIR or gas chromatography), allowing the operator or automatic control system to dynamically modify the preset control scheme based on the actual oxidation reaction rate and sample surface state to ensure uniform reaction.

[0060] By dynamically adjusting the flow rate of the oxygen-containing gas and controlling the oxidation reaction time, a uniform, dense, and surface-active silicon-oxygen layer rich in surface-active functional groups (such as hydroxyl groups) is formed. This effectively passivates the surface of the porous silicon-carbon skeleton, preventing direct reaction with the electrolyte and facilitating chemical bonding of the subsequent polymer layer. Selecting at least one of carbon dioxide, pure oxygen, and an oxygen-nitrogen mixture provides a flexible way to control the oxidation reaction, ensuring uniformity while avoiding over-oxidation, further improving interfacial stability and overall material performance.

[0061] In one embodiment, step S1 forms a silicon-carbon skeleton 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 an oxygen-silicon layer, the surface properties and interface stability also change. After these two steps are completed, the prepared porous silicon-carbon skeleton with an oxygen-silicon layer is subjected to electrochemical impedance spectroscopy (EIS) to determine the specific conditions of the lithium ion channel. The test-related calculation formula is:

[0062]

[0063] in, is the real part of impedance, derived 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: assemble the prepared porous silicon-carbon skeleton with an oxygen-silicon layer into a battery with the test positive electrode, diaphragm and electrolyte (or test the electrode separately), and ensure that the test environment (temperature, humidity, etc.) is stable. While applying a small sinusoidal AC voltage disturbance, scan a wider frequency range (from high frequency to low frequency) and record the voltage and current response data. Draw a data graph based on the test data (imaginary part versus real part). In the data graph, an intercept will appear in the high-frequency region, located on the far left 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, one or more semicircles will appear. The first semicircle (appearing in the high to medium frequency region) corresponds to the charge transfer process at the electrode interface, and the diameter of the semicircle represents the charge transfer resistance. By observing the data graph, find the high-frequency intercept and the low-frequency intercept of the semicircle. The diameter of the semicircle is By fitting the real part of the impedance and The relationship between the reflection coefficient can be obtained ( ), this parameter directly reflects the difficulty of lithium ions diffusing in the porous skeleton. A larger value means that the impedance increases faster when the frequency decreases. This reflects that lithium ions encounter greater resistance when diffusing inside the material, which is caused by narrow pores, low porosity, or high bends and defects in the porous skeleton, making diffusion more difficult. Conversely, a smaller value means that the impedance increases faster when the frequency decreases. The value indicates that the impedance increases less with decreasing frequency, which means that the resistance encountered by lithium ions during diffusion is lower, the pores are more unobstructed, and the structure is more conducive to ion transmission, thus helping to improve the rate performance of the material. Can be 0.5~50 .

[0064] like Too high, the silicon source gas flow rate of S1.3 is reduced from 0.5~6L / min to 0.5~2L / min to slow down the deposition rate and avoid pore clogging. The heating rate of S1.3 is slowed down from 5~10℃ / min to 5~7℃ / min to improve the nucleation stability of the pore structure. The CVD time of S1.3 is extended from 500~1000min to 800~1000min to form a continuous porous network. The oxygen-containing gas flow rate of S2.2 is reduced from 0.5~2.5L / min to 0.5~1.5L / min to slow down oxidation and avoid the formation of a barrier layer. The oxygen-containing reaction time of S2.2 is reduced from 200~800min to 200~300min to prevent the oxygen-silicon layer from being too thick and affecting diffusion.

[0065] S3. Disperse the porous silicon-carbon skeleton with the silicon oxide layer in a mixed solvent, add a modified coupling agent and a lithium salt, stir at room temperature for 1 to 5 hours, add a polymer solution after stirring, and stir at room temperature for another 1 to 5 hours to form a polymer layer on the silicon oxide layer. Wash and dry to obtain a double-layer coated porous silicon-carbon negative electrode material. The polymer solution includes a conductive polymer and an ion-conducting polymer. 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. The lithium salt includes at least one of lithium metaborate, lithium tetrafluoroborate, and lithium hexafluorophosphate. Calculated by mass ratio, the porous silicon-carbon skeleton: modified coupling agent: lithium salt: polymer solution = 100:5:2:10.

[0066] Step S3 includes:

[0067] S3.1. Prepare a mixed solution of ethanol, deionized water, and isopropyl alcohol in a volume ratio of 1:1:0.5. Add the porous silicon-carbon skeleton with an oxygen-silicon layer to the mixed solution and treat it in an ultrasonic cleaner for 15 to 30 minutes.

[0068] Ethanol and isopropanol have good organic solubility and help disperse carbon-based components. Deionized water can increase the polarity of the mixed system and improve the exposure of hydroxyl functional groups. The combined use of the three achieves the synergy of organic and polar environments, which is beneficial to the reaction between the oxygen-silicon layer and subsequent coupling agents and polymers. Ultrasonic cavitation is used to break up the agglomerates, so that the porous silicon-carbon particles are evenly distributed in the solution, exposing the active sites on the surface of the oxygen-silicon layer to the greatest extent, creating a reaction basis for the next coupling reaction and polymer attachment. It significantly improves the uniformity and interfacial activity of the reaction system, provides sufficient contact opportunities for the subsequent grafting and bonding reactions between the coupling agent and the polymer monomer, and improves the final coating uniformity and bonding strength.

[0069] S3.2. Add the modified coupling agent and lithium salt, and stir at room temperature for 1 to 5 hours using a magnetic stirrer.

[0070] The modified coupling agent's structure contains a hydrolyzable silane end and a reactive organic group (such as an amino group). The silane end, upon hydrolysis, generates -Si-OH groups, which condense with the -Si-OH groups on the surface of the silicon oxide layer to form a stable Si-O-Si bond, achieving chemical bonding. The organic group acts as a grafting anchor, guiding the orderly in situ polymerization of the subsequent conductive polymer at the interface. The lithium salt primarily provides lithium ions, pre-doping them into the interface and providing an ion source for establishing ion channels in the subsequent polymer layer. It also regulates the charge distribution on the surface of the silicon oxide layer, contributing to a tighter and more stable interfacial structure. The construction of a functionalized grafted interface and the formation of a strong chemical connection not only enhances the stability of subsequent polymer attachment but also, through the pre-doping of the lithium salt, guides the formation of a highly ion-conducting region at the interface, providing structural and chemical support for rapid ion transport.

[0071] S3.3. Add the conductive polymer and stir for 1 to 5 hours. Then add the ion-conducting polymer solution and continue stirring at room temperature for 1 to 5 hours. Wash and filter three times with ethanol / distilled water alternately, and dry in a vacuum drying oven at 80°C to obtain a double-layer coated porous silicon-carbon negative electrode material.

[0072] The polymer layer generated in step S3.3 includes a conductive polymer coating and an ion-conducting polymer coating. In solution, the conductive polymer is guided by a modified coupling agent to polymerize near the interface, generating polymer chains that polymerize in situ against the surface of the silicon-oxygen layer, forming a dense, continuous conductive polymer coating. This improves the efficiency of electron conduction across the entire silicon-carbon skeleton surface, prevents electron islanding in the active material, and enhances rate performance. The polymer molecules in the ion-conducting polymer coating are rich in carboxyl or hydroxyl groups, which can further condense or hydrogen bond / electrostatically interact with the chains in the conductive polymer coating, achieving strong interfacial anchoring. The flexible segments in its molecular structure enhance the overall strain adaptability of the interface while providing diffusion pathways for lithium ion migration. The inner conductive polymer coating provides electron pathways, while the outer ion-conducting polymer coating regulates lithium ion pathways. The two are coupled to form a three-dimensional conductive network, synergistically enhancing conductivity and ion diffusion rate. Washing removes unpolymerized monomers, residual lithium salts, and byproducts, preventing electrochemical side reactions. Vacuum drying solidifies the material structure, removes solvent moisture, and prevents the coating from cracking or shedding later. The construction of a dual-functional polymer structure that conducts electrons internally and ions externally greatly enhances the interfacial stability and transmission efficiency of the negative electrode material during cycling. The flexible structure of the polymer buffers silicon volume expansion, prevents structural breakage, and improves cycle life. The double-layer coating not only improves rate performance and cycle stability, but also significantly enhances the material's usability under extreme operating conditions such as high rate and low temperature.

[0073] Conductive polymers (such as aniline, pyrrole, or thiophene) are in situ polymerized on the silicon oxide layer to form a continuous film, effectively creating efficient electron transport channels. Combined with the inherently good conductivity of the porous carbon framework, this creates a multi-level conductive network. This network significantly reduces electron transport resistance and improves the rate performance of the negative electrode.

[0074] Ion-conducting polymers (such as lithium polyacrylate, polyethylene glycol, or polyvinyl alcohol) chemically bond with the silicon oxide layer, creating a continuous ion conduction channel at the interface. This layer not only promotes rapid lithium ion transport and reduces interfacial impedance, but also mitigates side reactions caused by direct contact between the electrolyte and silicon, ultimately improving the negative electrode's ion transport efficiency and stability.

[0075] In one embodiment, the double-layer coated porous silicon-carbon negative electrode material prepared in step S3 is subjected to an electrochemical impedance spectroscopy test again, and the obtained The diffusion coefficient D is calculated using the following formula:

[0076]

[0077] in, is the gas constant, R=8.314 , T is the thermodynamic temperature (K), T≈298K when tested at room temperature, B is the surface area of ​​the negative electrode (cm 2 ), refers to the surface area or geometric electrode area that can actually be contacted by the double-layer coated porous silicon-carbon negative electrode material in the electrolyte, which can be 1~2cm 2 Or larger / smaller (depending on the specific battery design). n is the number of electron transfers involved 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 When it is larger, will be smaller, that is, the diffusion rate of lithium ions is low and the diffusion process is hindered. When younger will be larger, indicating that the diffusion process is smoother and the ion transmission efficiency is higher. Can be 10 -8 ~10 -6 cm 2 ·s -1 . The unit is ,in, =V / A, V=J / C, A=C / s, that is The unit can be converted to J·s·C -2 .

[0078] like If it is too low, the concentration of the ion-conducting polymer in S3.3 should be reduced from 0.05~0.2g / mL to 0.02~0.1g / mL to avoid thick coating that blocks the ion channel.

[0079] The present invention provides a double-layer coated porous silicon-carbon negative electrode material, which is made by a preparation method of a double-layer coated porous silicon-carbon negative electrode material. The double-layer coated porous silicon-carbon negative electrode material includes a porous silicon-carbon skeleton, an oxygen-silicon layer provided on the porous silicon-carbon skeleton, and a polymer layer provided on the oxygen-silicon layer; wherein,

[0080] The porous silicon-carbon skeleton is used to provide mechanical support and volume buffering, build an internal electron transport network, and ensure the stable operation of the double-layer coated porous silicon-carbon negative electrode material during the charge and discharge process;

[0081] The silicon oxide layer acts as a passivation layer to prevent side reactions between silicon and the electrolyte. It also generates abundant hydroxyl functional groups, providing active sites for chemical bonding of the subsequent polymer layer and optimizing interface stability.

[0082] The polymer layer is used to enhance the electronic conduction and lithium ion conduction capabilities of the double-layer coated porous silicon-carbon negative electrode material, while alleviating the mechanical stress caused by volume expansion of silicon during the cycle and improving the cycle stability.

[0083] Example 1: 3000 g of porous carbon spheres and tetraethoxysilane were added to a CVD furnace, and nitrogen was introduced at a flow rate of 14 L / min for 60 minutes. The temperature in the CVD furnace was raised to 480°C, and monosilane was introduced at a flow rate of 2 L / min for 1000 minutes to obtain a porous silicon-carbon framework.

[0084] The porous silicon-carbon skeleton was added to a CVD furnace, and nitrogen was introduced at a flow rate of 14 L / min. The temperature in the CVD furnace was raised to 500°C, and carbon dioxide was introduced at a flow rate of 1 L / min for 500 minutes to form an oxygen-silicon layer deposited on the surface of the porous silicon-carbon skeleton.

[0085] 20 g of the porous silicon-carbon skeleton with an oxygen-silicon layer was weighed and added to a solvent (V ethanol: V deionized water = 1:1) and magnetically stirred for 30 minutes. 0.1 ml of a silane coupling agent and 0.5% of a lithium salt were added and stirred at room temperature for 3 hours. A certain amount of a 1 Mol / L phosphoric acid solution and 2 ml of aniline were added in sequence and stirred. Subsequently, a certain amount of an ammonium persulfate solution with a concentration of 1 Mol / L was slowly added dropwise to the above solution, and in situ polymerization was carried out for 2 hours. A certain amount of lithium polyacrylate (the amount of lithium polyacrylate was 0.25% of the mass of the porous silicon-carbon skeleton with an oxygen-silicon layer) solution was added to the above solution and stirred for 3 hours. After the reaction was completed, the obtained mixed solution was washed alternately with ethanol and deionized water and filtered three times, and then dried in a vacuum environment at 80°C for 10 hours to obtain a double-layer coated porous silicon-carbon negative electrode material.

[0086] 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 skeleton with the silicon oxygen layer.

[0087] Example 3: The same as Example 1, except that the amount of lithium polyacrylate is 1% of the mass of the porous silicon-carbon skeleton with the silicon oxygen layer.

[0088] Comparative Example 1: The same as Example 1, except that no polymer solution is added in step S3.

[0089] Comparative Example 2: The same as Example 1, except that step S3 is not performed.

[0090] Weigh the double-layer coated porous silicon-carbon anode material, conductive carbon black, and binder and add deionized water to prepare a homogenous slurry. The solids ratio of double-layer coated porous silicon-carbon anode material: conductive carbon black: binder CMC is 95:1.5:3.5. Samples are prepared using a homogenizer at 2000 rpm for 20 minutes. The slurry is sieved and evenly coated onto copper foil. Dry it in a 90°C vacuum drying oven. The dried electrode sheet is roller-pressed and cut into circular electrodes of a desired size. The electrode mass is recorded. In an argon atmosphere glove box, a lithium metal sheet is used as the counter electrode. The electrodes, separator, and gasket are assembled into button cells. A silicon-carbon electrolyte is used as the electrolyte.

[0091] In one embodiment, by performing CV tests at different scan rates, current-potential curves can be recorded. To distinguish pseudocapacitive behavior from diffusion-controlled behavior in cyclic voltammetry tests, the following empirical equation is used: Pseudocapacitive behavior refers to the energy storage phenomenon of the electrode material, in addition to the traditional ion insertion / deintercalation process, which is similar to that of a capacitor and is generated by a rapid surface or near-surface electrochemical reaction. Although this phenomenon is not a pure electric double-layer capacitor (EDLC), it exhibits characteristics such as fast charge and discharge speed and rapid response, which makes it exhibit capacitor-like behavior in cyclic voltammetry (CV) tests, hence the name pseudocapacitive behavior. In the negative electrode material, lithium ions need to diffuse into the material along the channels within the porous structure. When the pores are not smooth or there is a large diffusion resistance, the diffusion process of lithium ions becomes a bottleneck for the entire reaction, thus exhibiting diffusion-controlled behavior.

[0092]

[0093] in, 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 ( ), Can , For the current component related to diffusion-controlled behavior, data processing is performed on the CV curves at different scan rates (e.g., recording the peak current or transient current at a preset potential). At the same potential, the current at different scan rates is measured or read. .Will Fitting , thus obtaining and .

[0094] Obtained by fitting The value can be used to quantitatively determine how much current is provided by the surface fast reaction (pseudocapacitance) at this potential; This indicates the portion of the current that is due to limited ion diffusion. If the test results show If the item is large, it means that the material surface or coating design effectively promotes the rapid pseudocapacitive reaction, corresponding to excellent high rate performance, and can maintain or further enhance the conductivity and reactivity of the electrode surface, such as by increasing the content of conductive polymer. On the contrary, if If the proportion of the item is high, it indicates that the diffusion-controlled process is dominant and the porous structure or interface conductivity needs to be further improved. The addition ratio of porous carbon spheres can be increased to form a more continuous and porous skeleton.

[0095] After subjecting Examples 1-3 and Comparative Examples 1-2 to charge and discharge cycles, the experimental data obtained are shown in Table 1. As can be seen from Table 1, the abundant carboxyl groups in the polymer solution can connect with certain functional groups on the surface of the silicon material through hydrogen bonds, promoting the formation of the negative electrode solid electrolyte interface film (SEI film). This greatly improves the cycling performance of the silicon-based negative electrode and reduces battery capacity loss. The capacity retention rates of Examples 1, 2, and 3 are all higher than those of Comparative Examples 1 and 2, indicating that the double-layer coating material can form a protective film on the surface of the negative electrode material, enhancing the mechanical strength of the negative electrode material and reducing pulverization and shedding during charge and discharge. The polymer layer has electrical conductivity and ion conductivity. The introduction of conductive polymers and ion-conducting polymers helps improve the lithium ion transport capacity of the composite binder, thereby effectively constructing a double-layer conductive network, giving it high electronic conductivity, high lithium ion conductivity, and excellent mechanical properties. The first cycle 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 the double-layer coated porous silicon-carbon negative electrode material can improve the specific capacity and coulombic efficiency of the battery through improved conductivity and structural stability, thereby improving the electrochemical performance of the battery. The specific surface area of ​​Example 1, Example 2, Example 3 and Comparative Example 1 is less 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, which increases the specific surface area (SSA) of the double-layer coated porous silicon-carbon negative electrode material from 50 to 100 m 2 / g is reduced to 1~5m 2 / g. Reducing the specific surface area means reducing the contact area between the negative electrode material and the electrolyte, thereby reducing the excessive formation of the solid electrolyte interface (SEI) film, reducing electrolyte decomposition and irreversible side reactions. A lower specific surface area can reduce unnecessary electrochemical reactions, reduce initial coulombic efficiency loss and capacity decay, and help improve long-term cycling performance and overall energy efficiency.

[0096] Table 1. Charge and discharge cycle experimental data:

[0097]

[0098] Please refer to Figure 1 This figure shows the variation in specific capacity (left vertical axis, mAhg⁻¹) and coulombic efficiency (right vertical axis, %) over the first 100 charge-discharge cycles of the electrode materials for the comparative samples (Comparative Examples 1 and 2) and the implemented samples (Examples 1, 2, and 3) at a current density of 0.1Ag⁻¹. It can be seen that all examples have slightly higher initial specific capacities than the comparative examples at the beginning of the cycle, and the specific capacity decay is smaller during subsequent cycles. Furthermore, the coulombic efficiency rises rapidly after the first cycle and stabilizes between 98% and 100%, indicating that the coating significantly enhances the electrochemical stability and reversibility of the electrode materials.

[0099] Please refer to Figure 2 This figure shows the XRD diffraction patterns of the porous silicon-carbon skeleton sample before coating (black line) and after coating (red line) (2θ range 10° to 90°). 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 sample after coating is significantly increased, especially around 30°, where there is a slight peak shift or peak width change, indicating that after the double layer coating of silicon layer and 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 shows the voltage-specific capacity (V–mAhg⁻¹) curves for Comparative Examples 1 and 2 and Examples 1, 2, and 3 during the first cycle. Both the discharge process (voltage decreases from high to low) and the charge process (voltage increases from low to high) exhibit similar step and slope characteristics. Compared to the comparative examples, the curves for the examples show a higher capacity at the discharge plateau, and the shapes of the charge and discharge curves of the two examples largely overlap, indicating that the coating does not introduce significant polarization, but instead increases the reversible specific capacity, highlighting the coating's advantages in stabilizing the electrode interface and promoting rapid lithium ion transport.

[0100] Please refer to Figure 4This figure compares the FTIR transmittance spectra of the pristine sample (black line) and the double-layer coated sample (red line) in the wavenumber range of 4000–400 cm⁻¹. While the pristine sample exhibits only a weak C–H stretching vibration peak at approximately 2900 cm⁻¹, the coated sample exhibits a stronger characteristic absorption peak of the organic polymer in the same region. Furthermore, a new peak around 1100 cm⁻¹ corresponds to Si–O–Si bond vibration, confirming the presence of the oxygen-silicon layer. At 1600–1700 cm⁻¹, the coated sample also exhibits absorption peaks due to carboxyl or amide groups, reflecting the introduction of the lithium polyacrylate / aniline polymer. The overall spectral changes clearly demonstrate that the double-layer coating strategy successfully constructs an organic-inorganic composite protective layer on the electrode material surface. The four characteristic absorption peaks marked by gray dashed lines are located at approximately 1400 cm⁻¹, 1150 cm⁻¹, 1060 cm⁻¹, and 730 cm⁻¹, respectively. The peak at 1400 cm⁻¹ is associated with deformation vibrations of –CH2 / –CH3 hydroxyl groups or –C–N stretching vibrations; the peak at 1150 cm⁻¹ is attributed to Si–O–C or C–O–C stretching vibrations, suggesting coupling bonds between organic or siloxane segments; the main peak at 1060 cm⁻¹ is the Si–O–Si asymmetric stretching vibration, indicating the integrity of the siloxane backbone; and the peak around 730 cm⁻¹ corresponds to Si–O–Si swinging / bending vibrations, interspersed with C–H out-of-plane bending vibrations. These changes indicate the formation of a siloxane backbone (Si–O–Si) and silicon-oxygen-carbon bridges (Si–O–C) in the coating layer, accompanied by 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 a siloxane network on the material surface, but also retains or introduces organic side chains, collectively forming a new surface functional group environment.

[0101] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer coated porous silicon-carbon negative electrode material for making a lithium-ion battery, characterized in that: Steps include; S1. uniformly mixing a carbon precursor and a doping precursor, introducing an inert gas into a chemical vapor deposition furnace, adjusting the temperature to 400-500° C., introducing a silicon source gas, and controlling the reaction time to be 500-1000 minutes to obtain a porous silicon-carbon skeleton, wherein the doping precursor includes a silicon source material; S2, heating the porous silicon-carbon skeleton to 450-550° C., introducing an 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; S3. Disperse the porous silicon-carbon skeleton with the silicon oxide layer in a mixed solvent, add a modified coupling agent and a lithium salt, and stir at room temperature for 1 to 5 hours. After stirring, add a polymer solution and stir at room temperature for another 1 to 5 hours to generate a polymer layer on the silicon oxide layer. After washing and drying, a double-layer coated porous silicon-carbon negative electrode material is obtained.

2. The method for preparing a double-layer coated porous silicon-carbon negative electrode material according to claim 1, characterized in that: 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, mixing the porous carbon spheres, the asphalt matrix, the silicon source material, and the metal catalyst in a predetermined ratio to obtain a mixture; S1.

2. Evenly spread the mixture on a high-purity ceramic substrate, place it in the reaction chamber of a chemical vapor deposition furnace, then introduce inert gas at a flow rate of 10-20 L / min, gradually increase the temperature to 400°C, and preheat at this temperature for 30 minutes; S1.3, gradually increase the temperature to 400~500℃, ensuring that the heating rate is within the range of 5~10℃ / min, After reaching the target temperature, the silicon source gas is slowly introduced into the reaction chamber of the chemical vapor deposition furnace at a flow rate of 0.5~6L / min while continuing to maintain the inert gas flow rate to obtain a porous silicon-carbon skeleton.

3. The method for preparing a double-layer coated porous silicon-carbon negative electrode material according to claim 2, characterized in that: In step S1.1, the porous carbon balls include at least one of polyphenolic resin carbon balls, coconut shell activated carbon balls, and polyacrylonitrile modified carbon balls; the asphalt matrix includes at least one of petroleum asphalt, coal tar, and heavy oil asphalt; the silicon source material includes at least one of tetraethoxysilane, tetramethoxysilane, and diethoxysilane; the metal catalyst includes at least one of nano-scale iron catalyst, nano-scale nickel catalyst, and nano-scale cobalt catalyst; and the silicon source gas includes at least one of monosilane, disilane, and trimethoxysilane.

4. The method for preparing a double-layer coated porous silicon-carbon negative electrode material according to claim 3, characterized in that: In step S1.1, according to the mass ratio, the porous carbon sphere: the asphalt matrix: the silicon source material: the metal catalyst = (40-60): (20-40): (10-20): (0.5-2).

5. The method for preparing a double-layer coated porous silicon-carbon negative electrode material according to claim 1, characterized in that: Step S2 includes: S2.

1. The porous silicon-carbon skeleton is evenly laid on a ceramic boat. First, pure nitrogen is introduced at a flow rate of 5-15 L / min for cleaning. The furnace temperature is gradually increased to 450-550°C and kept stable for 10-20 minutes. S2.

2. Introduction of oxygen-containing gas, reducing or increasing the gas flow rate of the oxygen-containing gas every 10 to 15 minutes, and controlling the reaction time to be 200 to 800 minutes. After the reaction is completed, the introduction of the oxygen-containing gas is stopped, and the furnace temperature is gradually lowered 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 skeleton.

6. The method for preparing a double-layer coated porous silicon-carbon negative electrode 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 method for preparing a double-layer coated porous silicon-carbon negative electrode 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 of ethanol, deionized water, and isopropanol in a volume ratio of 1:1:0.5, add the porous silicon-carbon skeleton with the silicon oxide layer to the mixed solution, and treat in an ultrasonic cleaner for 15 to 30 minutes; S3.

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

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

8. The method for preparing a double-layer coated porous silicon-carbon negative electrode 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 skeleton: the modified coupling agent: the lithium salt: the polymer solution = 100:5:2:

10.

9. A double-layer coated porous silicon-carbon negative electrode material, characterized in that: The double-layer coated porous silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1 to 8, wherein the double-layer coated porous silicon-carbon negative electrode material comprises a porous silicon-carbon skeleton, an oxygen-silicon layer provided on the porous silicon-carbon skeleton, and a polymer layer provided on the oxygen-silicon layer; wherein, The porous silicon-carbon skeleton is used to provide mechanical support and volume buffering, build an internal electron transport network, and ensure that the double-layer coated porous silicon-carbon negative electrode material works stably during the charge and discharge process; The silicon oxide layer acts as a passivation layer to prevent side reactions between silicon and the electrolyte, while generating abundant hydroxyl functional groups, providing active sites for chemical bonding of the subsequent polymer layer and optimizing interface stability; The polymer layer is used to enhance the electronic conduction and lithium ion conduction capabilities of the double-layer coated porous silicon-carbon negative electrode material, while alleviating the mechanical stress caused by volume expansion of silicon during the cycle and improving the cycle stability.

Images