A doped electrode material based on porous silicon carbon and its preparation method

Abstract

The present invention provides a doped electrode material based on porous silicon-carbon and a preparation method thereof. The preparation method comprises the following steps: crushing a resin substrate and placing it in a high-temperature furnace for carbonization at a temperature of 300-1500°C. An alkaline additive, a phosphorus source material, and a nitrogen source material are sequentially added while maintaining the temperature range to obtain phosphorus-nitrogen co-doped porous carbon; mixing a silica microsphere template into the phosphorus-nitrogen co-doped porous carbon, adding a first coating carbon source for a first coating treatment, and etching the silica microsphere template with an etching solution to obtain a cavity structure preform; placing the cavity structure preform in a fluidized bed reactor, introducing a silicon source gas and a surfactant, and depositing the material at 400-550°C. Finally, adding a second coating carbon source for a second coating treatment to obtain the doped electrode material based on porous silicon-carbon. This effectively reduces the electrode material's coefficient of expansion and improves rate performance.

Description

Technical Field

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

[0002] Lithium-ion batteries have advantages such as high specific energy, low self-discharge rate, high operating voltage, long cycle life, no memory effect, and environmental friendliness. They have been widely used in electric vehicles, portable electronic products, medical devices, and other fields. Currently, the most commonly used negative electrode in lithium-ion batteries is graphite, but the theoretical specific capacity of graphite negative electrodes is only 372mAh / g, which is far from enough to meet the current energy density requirements. Therefore, higher energy density requirements are placed on lithium-ion batteries, and the development of new next-generation high-energy density negative electrodes is urgently needed. Silicon negative electrodes have extremely high theoretical specific capacity, are environmentally friendly, and have abundant reserves. However, silicon negative electrodes also have significant disadvantages. The first is the large volume expansion during the charge and discharge process, which leads to material pulverization and loss of electrical contact between the active silicon particles and the current collector. In addition, the silicon negative electrode has low electronic conductivity.

[0003] In order to improve the reaction kinetics of silicon materials and thus improve the rate performance of silicon negative electrodes to meet the needs of fast charging, silicon materials and carbon materials are compounded to form silicon-carbon negative electrodes to improve the overall conductivity. On the one hand, ball milling, spray drying, pyrolysis carbon coating, etc. are used for compounding, but these are just simple mixing of carbon materials and silicon materials, which has a certain improvement on the expansion problem but is not enough. On the other hand, chemical vapor deposition technology is used to deposit silicon in the pores of porous carbon through the cracking of silane molecules to form porous silicon-carbon materials. Although it can effectively improve the volume expansion of the silicon negative electrode, since the silicon negative electrode is inside the porous carbon, there is a large obstacle to ion transmission and the transmission rate is slow, resulting in poor rate performance of gas-phase silicon-carbon, which cannot meet the requirements of the fast charging performance of the battery. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a doped electrode material based on porous silicon carbon and a preparation method thereof, aiming to solve the problems of excessively high expansion coefficient and poor rate performance of the electrode material.

[0005] To solve the above technical problems, the present invention is implemented as follows: the present invention provides a method for preparing a doped electrode material based on porous silicon carbon, the steps comprising:

[0006] S1. The resin substrate is crushed and placed in a high-temperature furnace for carbonization process at a carbonization temperature of 300-1500°C. An alkaline additive, a phosphorus source material, and a nitrogen source material are sequentially added while maintaining the temperature range to obtain phosphorus-nitrogen co-doped porous carbon;

[0007] S2, using a silica microsphere template mixed into phosphorus and nitrogen co-doped porous carbon, adding a first coating carbon source to perform a first coating treatment, and then etching the silica microsphere template with an etching solution to obtain a cavity structure preform;

[0008] S3. Place the cavity structure preform into a fluidized bed reactor, introduce silicon source gas and surfactant, and perform deposition at 400-550° C. Then, add a second coating carbon source for a second coating treatment to obtain a doped electrode material based on porous silicon-carbon.

[0009] In some embodiments, in step S1, the resin substrate includes at least one of phenolic resin powder, resorcinol-formaldehyde resin, and benzothiazole-modified phenolic resin, the alkaline additive includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate, the phosphorus source material includes at least one of sodium phosphate, phosphoinositide, and red phosphorus, and the nitrogen source material includes at least one of melamine, polyethyleneimine, and 2-methylimidazole. The mass ratio of resin substrate: alkaline additive: phosphorus source: nitrogen source is 10:5:(2~4):1.

[0010] In some embodiments, step S1 includes:

[0011] S1.1. Crush the resin matrix to D 50 Uniform particles with a particle size of 10-20 μm are placed in a constant temperature drying oven at 80°C and dried for 6-8 hours;

[0012] S1.2. Place the dried resin matrix in a quartz boat and place it in a tube furnace with temperature program control and atmosphere adjustment functions. Flow high-purity nitrogen gas and heat it to 300°C and hold it for 1 hour. Then heat it to 700°C and hold it for 2-3 hours to perform the first stage heat treatment to obtain the first stage product.

[0013] S1.3, adding an alkaline additive, a phosphorus source material, and a nitrogen source material to the carbonized product in sequence and mixing them under an inert atmosphere for 2 hours. After mixing, the product is again placed in a tube furnace and heated to 750-850°C under a nitrogen atmosphere for a second stage heat treatment. The temperature is kept at this temperature for 1.5 hours to obtain a second stage product;

[0014] S1.4. Soak the product of the second stage in a 1 mol / L hydrochloric acid solution for 1 hour with magnetic stirring, and then wash repeatedly with deionized water until the pH value of the washing solution is 6.5-7.5. After washing, filter and place in a vacuum drying oven with the temperature set at 80°C. Dry for 10 hours to obtain phosphorus-nitrogen co-doped porous carbon.

[0015] In some embodiments, in step S2, the first coated carbon source includes at least one of 1,3,5-triethynylbenzene, dopamine, and polypyrrole, and the etching solution includes at least one of hydrofluoric acid solution, sodium hydroxide solution, and ammonia-sodium hydroxide compound solution.

[0016] In some embodiments, step S2 includes:

[0017] S2.1. Silica microspheres with a particle size of 50-100 nm were mixed as a template with phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:1. An ethanol-water mixture was added, and the mixture was stirred using a magnetic stirrer for 1 hour. The mixture was ultrasonically treated for 20 minutes, and then centrifuged and dried to obtain a composite.

[0018] S2.2, adding a first coating carbon source to the composite, first raising the temperature to 50-70°C, keeping the temperature for 1-2 hours, then transferring to an inert atmosphere tube furnace, and carbonizing at 600-700°C for 2 hours to obtain a first coating product;

[0019] S2.3. Add etching solution to the first coated product, react at room temperature for 5 to 60 minutes, and use ultrasonic assistance for 5 minutes to obtain a cavity structure preform.

[0020] In some embodiments, in step S3, the second coating carbon source includes at least one of glucose, arabinose, and furfuryl alcohol-formaldehyde resin precursor, the silicon source gas includes at least one of isobutyltrichlorosilane, tetraethoxysilane, and trichlorosilane, and the surfactant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

[0021] In some embodiments, step S3 includes:

[0022] S3.1. Place the cavity structure preform into a vertical quartz fluidized bed reactor in a nitrogen atmosphere, preheat to 400-550°C, with a bed velocity of 0.02-0.08 m / s. Silicon source gas and a surfactant are introduced, and deposition is carried out at a reaction temperature of 450°C for 2-4 hours to obtain a deposition reactant.

[0023] S3.2. The deposited reactant was cooled to room temperature and dispersed in a tris (hydroxymethyl)aminomethane) buffer solution with a pH of 8.5. A second coating carbon source was added at a concentration of 2 mg / mL and stirred for 2-4 hours for a second coating treatment. The reactant was then carbonized at 700-800°C under nitrogen for 2 hours to obtain a second coated product.

[0024] S3.3. Naturally cool the second coated product and sieve it to obtain a doped electrode material based on porous silicon carbon.

[0025] The present invention provides a doped electrode material based on porous silicon carbon, which is prepared by the above-mentioned method for preparing a doped electrode material based on porous silicon carbon.

[0026] Compared with the prior art, the porous silicon-carbon-based doped electrode material and its preparation method in the present invention have the following advantages:

[0027] The porous silicon-carbon-based doped electrode material proposed in the present invention constructs a cavity buffer structure and a double-carbon layer coating system. A silica microsphere template is introduced during the preparation process, and a cavity between the center and the shell is formed through an etching process, so that the subsequently deposited silicon material has free expansion space. When lithium ion embedding causes the volume expansion of silicon, the cavity structure can effectively absorb its strain, avoid the rupture and structural disintegration of the outer carbon layer, thereby significantly suppressing the macroscopic volume change and reducing the overall expansion coefficient of the electrode. In addition, the double-layer carbon coating system constructed on the basis of this cavity can synergistically alleviate the accumulation of internal and external mechanical stresses during the charge and discharge cycle, and enhance the elasticity and integrity of the outer carbon shell, thereby improving the volume stability of the electrode from a structural perspective.

[0028] In terms of rate performance, this electrode material also exhibits excellent characteristics, the root of which lies in the synergistic regulation between doping modification and porous skeleton. First, the co-doping of phosphorus and nitrogen elements introduces abundant defect sites and charge-rich centers into the carbon matrix, significantly improving the electron migration rate and the conductivity of the carbon skeleton, allowing electrons to be efficiently transmitted under high-rate conditions. Second, the material retains a high specific surface area and a through-network structure, forming a fast ion diffusion channel, significantly shortening the lithium ion embedding path, and effectively reducing the ion transmission impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 1 is a graph showing the specific surface area, pore volume and pore diameter of the porous silicon carbon-based doped electrode materials in the embodiments and comparative examples of the present invention;

[0030] Figure 2 1 is a resistivity-pressure relationship diagram of the doped electrode material based on porous silicon carbon in the embodiment of the present invention and the comparative example;

[0031] Figure 3 Graph showing the lithium ion diffusion coefficient of the porous silicon-carbon-doped electrode material in the embodiments of the present invention and the comparative example;

[0032] Figure 4 1 is a rate performance cycle diagram of the porous silicon carbon doped electrode material in the embodiment of the present invention and the comparative example;

[0033] Figure 5 This is a table showing the capacity retention rate at 3C rate of the porous silicon carbon-doped electrode materials in the embodiments of the present invention and the comparative examples;

[0034] Figure 6 1 is a graph showing the long cycle performance of the porous silicon-carbon-based doped electrode material in the embodiments of the present invention and the comparative example;

[0035] Figure 7 This is a table showing the 100-cycle capacity retention rate of the porous silicon-carbon-based doped electrode materials in the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0036] 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.

[0037] The present invention proposes a method for preparing a doped electrode material based on porous silicon carbon, the steps comprising:

[0038] S1. The resin substrate is crushed and placed in a high-temperature furnace for carbonization process at a carbonization temperature of 300-1500°C. While maintaining the temperature range, alkaline additives, phosphorus source materials, and nitrogen source materials are sequentially added to obtain phosphorus-nitrogen co-doped porous carbon.

[0039] Step S1 includes:

[0040] S1.1. Crush the resin matrix to D 50 Uniform particles with a particle size of 10-20 μm are placed in a constant temperature drying oven at 80°C and dried for 6-8 hours.

[0041] By crushing the resin matrix to a particle size of 10-20 μm and drying it at a low temperature constant temperature for 6-8 hours, the pyrolysis uniformity and carbonization efficiency of the raw materials are significantly improved. Resin particles with smaller particle sizes can transfer heat quickly and evenly during subsequent heat treatment, avoiding the phenomenon of shell carbonization and core non-depolymerization during the carbonization process, and helping to form a dense and continuous carbon skeleton network structure. In addition, the drying process effectively removes the adsorbed moisture in the raw materials, preventing the rapid volatilization of water vapor at high temperatures, which causes the expansion and cracking of the carbon structure, thereby enhancing the integrity and controllability of the initial structure of the material. This treatment provides a foundation for structural stability and uniform thermal behavior for subsequent pyrolysis and doping reactions.

[0042] S1.2. Place the dried resin matrix into a quartz boat, place it in a tubular furnace with temperature program control and atmosphere adjustment functions, introduce high-purity nitrogen, raise the temperature to 300°C and keep it warm for 1 hour, then raise the temperature to 700°C and keep it warm for 2-3 hours to perform the first stage heat treatment to obtain the first stage product.

[0043] The first stage of carbonization of the resin in an inert atmosphere, using programmed temperature control, not only removes low-molecular-weight volatile organic components but also gradually constructs a primary porous carbon structure with a three-dimensional cross-linked aromatic ring skeleton. Constant temperature treatment at 300°C helps remove volatile components such as residual monomers like formaldehyde and phenol, while high-temperature pyrolysis at 700°C promotes the breakage of carbon-hydrogen and carbon-oxygen bonds, forming an aromatic ring stacking structure, thereby improving the thermal stability and electrical conductivity of the carbon skeleton. The pre-activated structure formed in this process not only retains some heterocyclic sites (such as nitrogen and phosphorus sites in benzothiazole) but also provides diffusion channels for dopants to subsequently enter the pores of the carbon matrix, making it an important precursor step in constructing efficient heterogeneous element-doped structures.

[0044] In one embodiment, in order to accurately control the temperature of the first stage heat treatment, it is necessary to set the heating rate to 700°C. , heating rate The calculation equation is:

[0045]

[0046] in, is the heating rate (℃ / min), and the empirical reference value is 5~20℃ / min. is the thermal analysis peak temperature (K), which is measured at different speeds of 5-20°C / min in thermogravimetric analysis (TGA) or differential scanning calorimetry (DSC) experiments. The experiment is carried out with the value of 1, and the sample is scanned. The peak temperature of the curve corresponding to the highest reaction rate of each scan is read from the obtained TGA / DSC curve, which is the corresponding Decomposition thermal analysis peak temperature R is the gas constant, which is 8.314 J·mol⁻¹·K⁻¹. is the reaction activation energy (J·mol⁻¹), and the corresponding and The data were organized into tables and the and , draw a graph and perform a linear fit, the slope and intercept correspond to With C, we can get and constant C. Substitute and constant C, calculate At 973K (700℃) The value is the optimal heating rate.

[0047] During the first stage of heat treatment, the optimal heating rate calculated by the equation can make the temperature field in the carbonization bed more uniform, reduce thermal hysteresis and thermal stress concentration, thereby inhibiting the generation of microcracks and ensuring the structural integrity of the porous carbon matrix; at the same time, the activation energy distribution of the carbonization reaction at this rate is more concentrated, which is conducive to the formation of a connected micropore-mesopore hierarchical network, significantly increasing the specific surface area and pore volume, and making the subsequent silicon source deposition and electrolyte infiltration more sufficient.

[0048] S1.3. Alkaline additives, phosphorus source materials and nitrogen source materials are sequentially added to the carbonized product and mixed under an inert atmosphere for 2 hours. After mixing, the product is again loaded into a tubular furnace and heated to 750-850°C under a nitrogen atmosphere for a second stage heat treatment. The temperature is kept at this temperature for 1.5 hours to obtain a second stage product.

[0049] Introducing an alkaline additive, a phosphorus source, and a nitrogen source into the initial carbonization product and performing a second high-temperature treatment achieves the dual functions of synergistic doping and etching pore formation, resulting in functionalized porous carbon with a hierarchical pore structure and uniform heterogeneous atomic distribution. The alkaline additive decomposes at high temperature to form active alkali metal oxides, which react with carbon to release carbon monoxide / carbon dioxide while simultaneously etching regular pores. During pyrolysis, phosphorus sources such as red phosphorus or sodium phosphate combine with the carbon structure to form P–C bonds and P–O–C bridging structures, enhancing the electronic polarizability of the carbon material. Nitrogen sources such as melamine or 2-methylimidazole can be converted into graphitic nitrogen and pyridinic nitrogen, improving the electronic conductivity and lithiophilicity of the carbon material. This step significantly increases the specific surface area, electrical conductivity, and interfacial anchoring ability of the carbon material, providing a stable, functionalized carbon substrate for the subsequent deposition of a silicon source.

[0050] S1.4. Soak the product of the second stage in a 1 mol / L hydrochloric acid solution for 1 hour with magnetic stirring, and then wash repeatedly with deionized water until the pH value of the washing solution is 6.5-7.5. After washing, filter and place in a vacuum drying oven with the temperature set at 80°C. Dry for 10 hours to obtain phosphorus-nitrogen co-doped porous carbon.

[0051] By immersing the doped and activated product in a hydrochloric acid solution and stirring and washing it thoroughly, the residual inorganic byproducts and unreacted dopants in the material can be efficiently removed to prevent them from inducing side reactions or causing structural expansion during the electrochemical process. During the pickling process, hydrogen ions react with alkali metal salts to form soluble products, and the solute migration efficiency is enhanced by combining magnetic stirring; it is then repeatedly washed with deionized water until neutral, which helps to stabilize the surface chemical environment of the material and reduce the interference of residual acid on subsequent coating reactions. The drying process uses low-temperature vacuum drying to retain the micropores and surface functional group structure, avoiding thermal decomposition of functional groups at high temperatures, so that the final phosphorus-nitrogen co-doped porous carbon has both excellent physical pore structure and electrochemically active interface, and its overall performance is significantly better than that of unwashed or undoped carbon materials.

[0052] The resin base material includes at least one of phenolic resin powder, resorcinol-formaldehyde resin, and benzothiazole-modified phenolic resin; the alkaline additive includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate; the phosphorus source material includes at least one of sodium phosphate, phosphoinositide, and red phosphorus; the nitrogen source material includes at least one of melamine, polyethyleneimine, and 2-methylimidazole; and the mass ratio of resin base material: alkaline additive: phosphorus source: nitrogen source is 10:5:(2~4):1.

[0053] S2. Use a silica microsphere template to mix into phosphorus and nitrogen co-doped porous carbon, add a first coating carbon source to perform a first coating treatment, and then etch the silica microsphere template with an etching solution to obtain a cavity structure preform.

[0054] Step S2 includes:

[0055] S2.1. Silica microspheres with a particle size of 50-100 nm were used as a template and mixed with phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:1. An ethanol-water mixed solution was added, and the mixture was stirred using a magnetic stirrer for 1 hour. The mixture was ultrasonically treated for 20 minutes and then centrifuged and dried to obtain a composite.

[0056] By mixing silica (SiO2) microspheres with particle sizes of 50-100 nm with phosphorus-nitrogen co-doped porous carbon in a 1:1 mass ratio and dispersing them in an ethanol-water mixture using magnetic stirring and ultrasonic synergistic dispersion, the SiO2 template was uniformly embedded and distributed throughout the porous carbon surface and pore structure. The ethanol-water dispersion medium possesses both an appropriate surface tension to facilitate the integration of SiO2 particles into the porous carbon pores and good volatility to prevent aggregation. Magnetic stirring provides macroscopic mixing, while 20 minutes of ultrasonic treatment breaks up SiO2 aggregates at the microscopic level, enhancing interfacial contact with the carbon framework and ensuring spatially controllable and uniform formation of the subsequent cavity structure. The resulting composite, after centrifugal drying, exhibits not only a uniform structure but also embeds SiO2 particles at key locations within the carbon material, facilitating complete encapsulation during subsequent carbon shell growth. Ultimately, the ideal conformal cavity structure is achieved after template etching.

[0057] S2.2. Add a first coating carbon source to the composite, first raise the temperature to 50-70°C, maintain the temperature for 1-2 hours, then transfer to an inert atmosphere tube furnace and carbonize at 600-700°C for 2 hours to obtain a first coated product. The first coating carbon source includes at least one of 1,3,5-triethynylbenzene, dopamine, and polypyrrole. The first coating carbon sources used include 1,3,5-triethynylbenzene, dopamine, and polypyrrole, all of which are precursors with strong structural orientation and high-quality carbonized products.

[0058] In one embodiment, 1,3,5-triethynylbenzene is used as the first coating carbon source. It is dissolved in anhydrous tetrahydrofuran and an iron salt (such as FeCl₃) is added as an oxidant for vapor- or liquid-phase polymerization to form a conjugated microporous polymer. Carbonization provides a highly π-conjugated, dense graphitized carbon layer. Dopamine forms a nitrogen-rich functionalized carbon layer upon carbonization at 700°C. Polypyrrole, a typical conductive polymer, forms a flexible, conductive carbon shell upon high-temperature carbonization. The key technical effect of this step is the construction of a complete outer carbon shell without destroying the carbon-SiO₂ composite structure. This provides a solid support for the cavity structure after subsequent etching and a protective barrier with high electrochemical stability. By introducing the first coating carbon source into the composite, followed by low-temperature heat treatment and high-temperature carbonization, a dense and continuous carbon shell is constructed on the outer surface of the SiO₂-doped carbon composite particles.

[0059] S2.3. Add an etching solution to the first coated product and allow the reaction to proceed at room temperature for 5 to 60 minutes, with ultrasonic assistance for 5 minutes, to obtain a preformed cavity structure. The etching solution comprises at least one of a hydrofluoric acid solution, a sodium hydroxide solution, and an ammonia-sodium hydroxide solution.

[0060] Adding an etching solution to the first coating product, supplemented by ultrasonic treatment, selectively removes the embedded silica template, thereby forming a stable cavity structure within the coated carbon shell. The etching solutions used include: hydrofluoric acid, which has a strong Si–O bond-breaking ability and is a traditional, efficient SiO2 etching solution; sodium hydroxide, which can also undergo a dissolution reaction with SiO2 under moderately alkaline conditions and is suitable for systems with high requirements for carbon shell structures; and an ammonia-sodium hydroxide mixture, which exhibits good interfacial wettability and slow-release etching properties, which helps maintain carbon shell stability. Ultrasonic treatment helps break down the inert solution boundary layer on the SiO2 template surface, accelerating the etching reaction and improving cavity formation efficiency. The core technical effect of this step is to construct a high-specific-volume, low-stress embedded cavity structure while maintaining the integrity of the outer shell. This provides ample expansion space and stress buffering capacity for subsequent silicon deposition, and is a key node in the formation of the core-cavity-shell sandwich structure.

[0061] In one embodiment, the etching solution is a hydrofluoric acid solution. To control the etching effect, the following equation is proposed:

[0062]

[0063] Where r is the etch rate (nm / min). [HF] is the hydrofluoric acid concentration (mol·L⁻¹). n is the reaction order, which ranges from 0.8 to 1.2 for hydrofluoric acid etching of silicon dioxide. Under the same temperature conditions, etching is performed using various [HF] concentrations (e.g., 1, 2, 5, and 10 mol / L). The corresponding etch rates, r, are measured. A linear fit is then performed against log[HF] using logr. The slope of the fitted line is the reaction order, n. T is the temperature of the etching solution (Kelvin). is the activation energy of the reaction between hydrofluoric acid solution and silicon dioxide, which is a fixed value. R is the gas constant, and T is the etching temperature.

[0064] In a system using silica microspheres as templates, it is crucial to completely remove the template without damaging the carbon skeleton for the pore structure of the final electrode. First, by accurately predicting the etching rate r at a given HF concentration and temperature through the model, we can quantitatively evaluate the minimum time t required to remove the silica microspheres. For example, if the average diameter of the template microspheres is 100nm, the solution is maintained at 10wt% HF, and room temperature, the etching rate is about 5nm / min, and t≈20min is calculated. At this time, it can ensure that all silica particles are completely dissolved without residue, and the carbon substrate surface will not be excessively eroded due to long-term immersion. Secondly, monitor the HF concentration and temperature online and bring the observed values ​​into In the process, the etching rate model can be dynamically modified to ensure that r is stable throughout the entire process. The etching time can then be adjusted in real time based on the latest r value, achieving second-level precision control to eliminate under- or over-etching. Finally, this quantitative etching strategy not only avoids residual silica microspheres causing subsequent deposition or uneven coating, but also maximizes the protection of the original morphology and mechanical strength of the porous carbon architecture, thereby significantly improving the batch consistency, electrochemical cycling stability, and first coulombic efficiency of the material.

[0065] S3. Place the cavity structure preform into a fluidized bed reactor, introduce silicon source gas and surfactant, and perform deposition at 400-550° C. Then, add a second coating carbon source for a second coating treatment to obtain a doped electrode material based on porous silicon-carbon.

[0066] Step S3 includes:

[0067] S3.1. Place the cavity structure preform into a vertical quartz fluidized bed reactor in a nitrogen atmosphere, preheat to 400~550℃, with a reaction bed velocity of 0.02~0.08m / s, introduce silicon source gas and surfactant, and deposit for 2~4 hours at a reaction temperature of 450℃ to obtain a deposited reactant; the silicon source gas includes at least one of isobutyltrichlorosilane, tetraethoxysilane, and trichlorosilane, and the surfactant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

[0068] The cavity structure preform was loaded into a vertical quartz fluidized bed reactor and preheated at 400-550°C under a nitrogen atmosphere to achieve a stable bed state. The bed velocity was controlled between 0.02 and 0.08 m / s to ensure uniform fluidization of the particles, effectively enhancing the efficiency of the gas-solid interface reaction. Subsequently, a silicon source gas and a surfactant were introduced, enabling continuous silicon deposition at approximately 450°C. The choice of different silicon sources imparted distinct film-forming kinetics to the reaction: isobutyltrichlorosilane, with its low decomposition temperature and high vapor pressure, facilitated the rapid deposition of silicon nanoparticles; tetraethoxysilane, at moderate temperatures, produced a controllable silicon-oxygen network, facilitating uniform coverage of the inner wall and shell; and trichlorosilane, which decomposes efficiently at high temperatures and synergistically with the surfactant to form Si-C interfacial bonds. Activating agents such as aluminum chloride and boron trifluoride are Lewis acids that adsorb on the carbon shell surface to form acidic centers, inducing the preferential growth of silicon sources on the carbon skeleton active sites. This results in the construction of a nano-silicon layer with good structural continuity, controllable particle size, and stable adhesion. This process effectively solves problems such as easy agglomeration of nano-silicon, uneven coating, and interfacial shedding, laying the structural foundation for improving cycle life and rate performance.

[0069] S3.2. Cool the deposition reactant to room temperature and disperse it in a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5. Add a second coating carbon source with a concentration of 2 mg / mL and stir for 2 to 4 hours for a second coating treatment. Then, carbonize at 700 to 800°C for 2 hours under nitrogen protection to obtain a second coating product; the second coating carbon source includes at least one of glucose, arabinose, and furfuryl alcohol-formaldehyde resin precursor.

[0070] After silicon deposition, the composite material undergoes a second carbon coating treatment to enhance the structural stability and interfacial protection of the silicon layer. The deposited reactants are cooled to room temperature and then dispersed in a tris (hydroxymethyl)aminomethane (Tris) buffer solution at pH 8.5. This helps stabilize the surface functional groups and improves the adhesion of the coating precursor. Under these conditions, a second coating carbon source, such as glucose, arabinose, or a furfuryl alcohol-formaldehyde resin precursor, is added at a concentration of 2 mg / mL and stirred for 2–4 hours to achieve uniform coating in the solution. Glucose and arabinose exhibit a strong tendency to self-polymerize under weakly alkaline conditions, forming a flexible amorphous carbon film during carbonization that effectively buffers silicon expansion. The furfuryl alcohol-formaldehyde resin carbon source constructs a rigid carbon network, providing mechanical support for the shell and introducing controllable O / N doping sites. Subsequent carbonization at 700–800°C in a nitrogen atmosphere for 2 hours uniformly coats the silicon particles and their interfaces with a second carbon shell, forming a hierarchical composite structure consisting of a silicon core-first carbon shell-cavity-second carbon shell. This multiple structure can not only effectively buffer volume expansion stress, but also improve electronic continuity and SEI film stability. It is particularly suitable for improving the rate response and cycle durability of electrode materials.

[0071] S3.3. Naturally cool the second coated product and sieve it to obtain a doped electrode material based on porous silicon carbon.

[0072] The product after the second coating carbonization is naturally cooled and sieved to obtain a doped porous silicon-carbon electrode material with uniform particle size and complete structure. Natural cooling can prevent thermal stress cracking or structural distortion caused by sudden cooling, and helps to maintain the synergy between the multiple coating shells. The screening process can remove agglomerated particles and irregular large agglomerates, improve the film formation uniformity and slurry stability of the material, and provide good particle grading for subsequent electrode sheet preparation. The final material has a central nano-Si to provide high reversible specific capacity; a cavity structure to buffer its expansion; embedded phosphorus and nitrogen co-doped porous carbon to enhance electron / ion transport capabilities; and a double-layer carbon shell to achieve long-term interface protection. The synergy of the four functions enables it to exhibit excellent performance under fast charging conditions, high-rate discharge and long-cycle electrochemical cycles, and has significant application prospects.

[0073] In one embodiment, the method for preparing a doped electrode material based on porous silicon carbon further comprises, after S3:

[0074] S4. A porous silicon-carbon-doped electrode material was placed in a deposition apparatus. Using tetramethylaluminum and water as precursors, 30 deposition cycles were performed at 120°C to form a 3nm aluminum oxide passivation layer. Subsequently, tetraethoxytitanium and water were switched to form a 2nm titanium dioxide nanolayer. This passivation composite layer formed a uniform inorganic passivation film on the electrode surface, effectively insulating it from electrolyte corrosion, slowing silicon expansion and cracking, and improving initial Coulombic efficiency and long-term cycling stability.

[0075] S5. The porous silicon-carbon-doped electrode material obtained in S4 was assembled into a half-cell and cycled three times at a 0.05C rate within a voltage range of 0.01–1.5 V. During the first cycle, the cell was charged at 0.8 V for 30 minutes, and a 5 wt% mixed solution of ethylene carbonate and fluoroethylene carbonate was added within 5 minutes at the end of the second cycle. During the first cycle, the cell was charged at 0.8 V for 30 minutes to induce in situ SEI formation on the electrode surface. At the end of the second cycle, a 5 wt% mixed solution of ethylene carbonate and fluoroethylene carbonate was briefly added to promote the in situ construction of a highly stable organic-inorganic composite SEI film on the silicon surface.

[0076] The present invention provides a doped electrode material based on porous silicon carbon, which is prepared by a preparation method of a doped electrode material based on porous silicon carbon.

[0077] Example 1:

[0078] S1. Phenolic resin powder is crushed and placed in a high-temperature furnace for carbonization process at a carbonization temperature of 700°C. Potassium hydroxide, sodium phosphate and melamine are added in sequence while maintaining the temperature range to obtain phosphorus-nitrogen co-doped porous carbon; the mass ratio of phenolic resin powder: potassium hydroxide: sodium phosphate: melamine is 10:5:2:1.

[0079] S2, using a silica microsphere template mixed into phosphorus and nitrogen co-doped porous carbon, adding 1,3,5-triethynylbenzene for a first coating treatment, and then etching the silica microsphere template with a hydrofluoric acid solution to obtain a cavity structure preform;

[0080] S3. Place the cavity structure preform into a fluidized bed reactor, introduce isobutyltrichlorosilane and aluminum chloride, and deposit at 400-550°C. Then, add furfuryl alcohol-formaldehyde resin precursor for a second coating treatment to obtain a doped electrode material based on porous silicon carbon.

[0081] Example 2:

[0082] A doped electrode material based on porous silicon carbon was prepared by the same method as in Example 1, except that the mass ratio of phenolic resin powder: potassium hydroxide: sodium phosphate: melamine was 10:5:4:1.

[0083] Example 3:

[0084] A doped electrode material based on porous silicon carbon was prepared by the same method as in Example 1, except that the carbonization temperature was 1000°C.

[0085] Comparative Example 1:

[0086] Compared with Example 1, no phosphorus source material is added in step S1.

[0087] Please refer to Figure 1 , showing the physical parameters of comparative example 1 and three examples in terms of porous structure, including specific surface area, pore volume and average pore diameter. After adding a phosphorus source or optimizing the carbonization conditions, Examples 1, 2 and 3 slightly reduced the specific surface area and pore volume compared with Comparative Example 1, but maintained a similar micropore size (about 1.6~1.7nm), indicating that after the cavity structure is constructed, the material still retains a rich pore network, which is suitable for the rapid diffusion of lithium ions. In particular, Example 1, although doped with phosphorus, its specific surface area still reaches 2273m² / g, indicating that reasonable doping will not significantly destroy the pore structure. The slight pore size shrinkage may be attributed to the coating and the P element occupying the pore wall defects, which helps to enhance the structural rigidity and interface stability.

[0088] Please refer to Figure 2 , this figure illustrates the trend of compression resistivity changes of different samples under compression conditions of 0~30MPa. The resistivity of all samples decreases with increasing pressure, reflecting the contact enhancement brought about by pore compression. Among them, Example 2 has the best electrical conductivity (lowest resistivity), which is related to its higher phosphorus doping ratio (sodium phosphate is 4 parts in Example 2). Phosphorus doping improves the electron migration rate by regulating the defect density and charge polarization in the carbon structure. In contrast, the resistivity of Comparative Example 1 (no phosphorus doping) is always the highest, indicating that phosphorus doping is one of the key factors in improving the electrical conductivity of carbon materials.

[0089] Please refer to Figure 3 This figure shows the lithium ion diffusion coefficient-potential relationship (logD vs V) obtained through pseudo-steady-state GITT or CV fitting, which is used to characterize the Li⁺ transport capacity in the electrode. The diffusion coefficients of Examples 1 and 2 are generally higher than those of Comparative Example 1, with Example 2 performing the best. This demonstrates that phosphorus doping not only improves electronic conductivity but also significantly regulates the Li⁺ diffusion channel. Furthermore, the "depression-rise" characteristics of the logD curves at different potentials reflect the presence of interfacial impedance during the initial lithium insertion phase. The buffer layer and cavity structure of the examples can effectively alleviate this problem, facilitating high-rate applications.

[0090] Please refer to Figure 4, which shows the change in cycle capacity under 0.1C~3C rate conditions. Examples 1 and 2 show high capacity and good rate adaptability in the entire rate range, especially at a high rate of 3C, they still maintain obvious reversibility. Comparative Example 1 decays rapidly at high rates, indicating that the undoped carbon material structure is difficult to buffer stress and maintain electron / ion cooperative conduction under rapid charge and discharge. The results in the figure reflect the significant advantages of phosphorus and nitrogen co-doping and cavity structure in supporting high-rate applications.

[0091] Please refer to Figure 5 , this figure will Figure 4 The degree of capacity decay at medium 3C rates is intuitively displayed as a percentage. Example 1 achieved a retention rate of 52.6%, significantly superior to the 29.2% of Comparative Example 1, demonstrating that the dual carbon shell coating and P–N synergistic doping effectively mitigate structural collapse and SEI degradation at high rates. Example 2 performed second best, but still significantly better than the control, demonstrating that regulating the phosphorus doping ratio can optimize structural stability and interface integrity during high-rate reactions.

[0092] Please refer to Figure 6 The figure shows the specific capacity performance of each sample over 100 cycles at a constant rate (0.2-0.5C). Example 1 consistently maintains a high plateau (>1400mAh / g), while Comparative Example 1 exhibits a significant decrease, trending below 1200mAh / g. This trend demonstrates that the rational design of the porous-cavity-double-carbon-shell structure and phosphorus-nitrogen co-doping not only improves initial capacity but also significantly enhances long-term structural integrity, interfacial stability, and electrochemical reversibility.

[0093] Please refer to Figure 7 , Figure 6 The data is summarized in a tabular format, highlighting that Example 1 maintains a high 100-cycle capacity of 87.5%, compared to only 66.3% for Comparative Example 1, representing nearly double the decay rate. This table further demonstrates the durability and buffering effectiveness of phosphorus-nitrogen co-doping and the hollow carbon shell structure, demonstrating that they are key to developing highly stable anode materials.

[0094] 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 doped electrode material based on porous silicon carbon, characterized in that: The steps include: S1. The resin substrate is crushed and placed in a high-temperature furnace for carbonization process at a carbonization temperature of 300-1500°C. An alkaline additive, a phosphorus source material, and a nitrogen source material are sequentially added while maintaining the temperature range to obtain phosphorus-nitrogen co-doped porous carbon; Step S1 includes: S1.

1. Crush the resin matrix to D 50 Uniform particles with a particle size of 10-20 μm are placed in a constant temperature drying oven at 80°C and dried for 6-8 hours; S1.

2. Place the dried resin matrix in a quartz boat and place it in a tube furnace with temperature program control and atmosphere adjustment functions. Flow high-purity nitrogen gas and heat it to 300°C and hold it for 1 hour. Then heat it to 700°C and hold it for 2-3 hours to perform the first stage heat treatment to obtain the first stage product. S1.3, adding an alkaline additive, a phosphorus source material, and a nitrogen source material to the carbonized product in sequence and mixing them under an inert atmosphere for 2 hours. After mixing, the product is again placed in a tube furnace and heated to 750-850°C under a nitrogen atmosphere for a second stage heat treatment. The temperature is kept at this temperature for 1.5 hours to obtain a second stage product; S1.

4. Soak the product of the second stage in a 1 mol / L hydrochloric acid solution for 1 hour with magnetic stirring, then rinse repeatedly with deionized water until the pH of the rinse solution reaches 6.5-7.

5. After rinsing, filter and place in a vacuum drying oven at 80°C for 10 hours to obtain phosphorus-nitrogen co-doped porous carbon. S2, using a silica microsphere template mixed into phosphorus and nitrogen co-doped porous carbon, adding a first coating carbon source to perform a first coating treatment, and then etching the silica microsphere template with an etching solution to obtain a cavity structure preform; Step S2 includes: S2.

1. Silica microspheres with a particle size of 50-100 nm were mixed as a template with phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:

1. An ethanol-water mixture was added, and the mixture was stirred using a magnetic stirrer for 1 hour. The mixture was ultrasonically treated for 20 minutes, and then centrifuged and dried to obtain a composite. S2.2, adding a first coating carbon source to the composite, first raising the temperature to 50-70°C, keeping the temperature for 1-2 hours, then transferring to an inert atmosphere tube furnace, and carbonizing at 600-700°C for 2 hours to obtain a first coating product; S2.

3. Add an etching solution to the first coated product and react at room temperature for 5 to 60 minutes, and use ultrasonic assistance for 5 minutes to obtain a cavity structure preform; The etching solution is hydrofluoric acid solution, and the equation controlling the etching effect is: Where r is the etching rate in nm / min, [HF] is the hydrofluoric acid concentration in mol / L, n is the reaction order, which is unitless. The reaction order of hydrofluoric acid etching silicon dioxide is between 0.8 and 1.

2. T is the etching solution temperature in K. is the activation energy of the reaction between hydrofluoric acid solution and silica, in J / mol, which is a fixed value, R is the gas constant, in J / mol·K, and k is in nm·min -1 ·(mol·L -1 ) -n ; S3. Place the cavity structure preform into a fluidized bed reactor, introduce silicon source gas and surfactant, and perform deposition at 400-550° C. Then, add a second coating carbon source for a second coating treatment to obtain a doped electrode material based on porous silicon-carbon.

2. The method for preparing a doped electrode material based on porous silicon carbon according to claim 1, characterized in that: In step S1, the resin base material includes at least one of phenolic resin powder, resorcinol-formaldehyde resin, and benzothiazole-modified phenolic resin; the alkaline additive includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate; the phosphorus source material includes at least one of sodium phosphate, phosphoinositide, and red phosphorus; the nitrogen source material includes at least one of melamine, polyethyleneimine, and 2-methylimidazole; and the mass ratio of resin base material: alkaline additive: phosphorus source: nitrogen source is 10:5:(2-4):

1.

3. The method for preparing a doped electrode material based on porous silicon carbon according to claim 1, characterized in that: In step S2, the first coated carbon source includes at least one of 1,3,5-triethynylbenzene, dopamine, and polypyrrole.

4. The method for preparing a doped electrode material based on porous silicon carbon according to claim 1, characterized in that: In step S3, the second coating carbon source includes at least one of glucose, arabinose, and furfuryl alcohol-formaldehyde resin precursor, the silicon source gas includes at least one of isobutyltrichlorosilane, tetraethoxysilane, and trichlorosilane, and the surfactant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

5. The method for preparing a doped electrode material based on porous silicon carbon according to claim 1 or 4, characterized in that: Step S3 includes: S3.

1. Place the cavity structure preform into a vertical quartz fluidized bed reactor in a nitrogen atmosphere, preheat to 400-550°C, set the bed velocity at 0.02-0.08 m / s, introduce silicon source gas and surfactant, and deposit at 450°C for 2-4 hours to obtain a deposited reactant. S3.

2. Cool the deposited reactant to room temperature and disperse it in a tris (hydroxymethyl)aminomethane (pH 8.5) buffer solution. Add a second coating carbon source at a concentration of 2 mg / mL and stir for 2-4 hours for a second coating treatment. Then, carbonize the reactant at 700-800°C under nitrogen for 2 hours to obtain a second coated product. S3.

3. Naturally cool the second coated product and sieve it to obtain a doped electrode material based on porous silicon carbon.

6. A doped electrode material based on porous silicon carbon, characterized in that: The porous silicon carbon doped electrode material is prepared by the method for preparing the porous silicon carbon doped electrode material according to any one of claims 1 to 5.

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