Doped electrode material based on porous silicon carbon and preparation method thereof

Abstract

The invention provides a doped electrode material based on porous silicon carbon and a preparation method thereof.The preparation method comprises the steps that a resin base material is smashed and then put into a high-temperature furnace to be subjected to a carbonization process, the carbonization temperature ranges from 300 DEG C to 1500 DEG C, an alkaline additive, a phosphorus source material and a nitrogen source material are sequentially added in the temperature interval, and phosphorus-nitrogen co-doped porous carbon is obtained; the preparation method comprises the following steps: mixing a silicon dioxide microsphere template into phosphorus-nitrogen co-doped porous carbon, adding a first coating carbon source to carry out first coating treatment, and etching the silicon dioxide microsphere template by using an etching solution to obtain a prefabricated object with a cavity structure; and putting the prefabricated object with the cavity structure into a fluidized bed reactor, introducing silicon source gas and a surface activation auxiliary agent, carrying out deposition at 400-550 DEG C, and then adding a second coating carbon source to carry out secondary coating treatment, thereby obtaining the doped electrode material based on porous silicon carbon. Therefore, the expansion coefficient of the electrode material is effectively reduced, and the rate capability is improved.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high specific energy, low self-discharge rate, relatively high working voltage, long cycle life, no memory effect, environmental friendliness, etc., and have been widely used in fields such as electric vehicles, portable electronic products, and medical devices. Currently, the most commonly used anode for lithium-ion batteries is graphite. However, the theoretical specific capacity of graphite anodes is only 372 mAh / g, which is far from meeting the current demand for energy density. Therefore, higher energy density requirements are put forward for lithium-ion batteries, and there is an urgent need to develop the next generation of new anodes with high energy density. Silicon anodes have an extremely high theoretical specific capacity, are environmentally friendly, and have rich reserves. However, silicon anodes also have great disadvantages. First of all, there is a large volume expansion during the charge and discharge process, which leads to material pulverization and the loss of electrical contact between the active silicon particles and the current collector, as well as the low electronic conductivity of the silicon anode.

[0003] In related technologies, in order to improve the reaction kinetics of silicon materials and thus improve the rate performance of silicon anodes to meet the need for fast charging, silicon materials and carbon materials are compounded to form silicon-carbon anodes to improve the overall conductivity. On the one hand, methods such as ball milling, spray drying, and pyrolytic carbon coating are used for compounding. However, these only simply mix carbon materials and silicon materials, and there is a certain improvement in the expansion problem but it is not enough. On the other hand, chemical vapor deposition technology is used to deposit silicon in the pores of porous carbon by the cracking of silane molecules to form porous silicon-carbon materials. Although it can effectively improve the volume expansion of silicon anodes, due to the fact that the silicon anode is inside the porous carbon, there are great obstacles to ion transport and the transport rate is slow, resulting in poor rate performance of vapor-phase silicon-carbon and not meeting the requirements for 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 carbide and a preparation method thereof, aiming to solve the problems of too high expansion coefficient and poor rate performance of the electrode material.

[0005] To solve the above technical problem, the present invention is implemented as follows. The present invention provides a preparation method of a doped electrode material based on porous silicon carbide, and the steps include: S1. After crushing the resin substrate, it is put into a high-temperature furnace for carbonization. The carbonization temperature is 300 - 1500 °C. While maintaining the temperature range, an alkaline additive, a phosphorus source material, and a nitrogen source material are sequentially added to obtain phosphorus and nitrogen co-doped porous carbon; S2. Mix silica microsphere templates into the phosphorus-nitrogen co-doped porous carbon, add a first carbon coating source for the first coating treatment, and then etch the silica microsphere templates with an etching solution to obtain a cavity structure preform; S3. Place the cavity structure preform in a fluidized bed reactor, introduce a silicon source gas and a surface activation aid, deposit at 400-550 °C, and then add a second carbon coating source for the second coating treatment to obtain a doped electrode material based on porous silicon carbon.

[0006] 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 basic additive includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate, the phosphorus source material includes at least one of sodium phosphate, inositol phosphate, and red phosphorus, the nitrogen source material includes at least one of melamine, polyethyleneimine, and 2-methylimidazole, and the mass ratio of resin substrate:basic additive:phosphorus source:nitrogen source is 10:5:(2-4):1.

[0007] In some embodiments, step S1 includes: S1.1. Crush the resin matrix into uniform particles with a particle size of 10-20 μm, and place them in an 80 °C constant temperature drying oven for drying for 6-8 hours; 50 S1.2. Load the dried resin matrix into a quartz boat, place it in a tube furnace with temperature program control and atmosphere regulation functions, introduce high-purity nitrogen, heat up to 300 °C and hold for 1 hour, then heat up to 700 °C and hold for 2-3 hours for the first-stage heat treatment to obtain a first-stage product; S1.3. Add the basic additive, phosphorus source material, and nitrogen source material to the carbonized product in an inert atmosphere and mix for 2 hours. After mixing, load it into the tube furnace again, heat up to 750-850 °C in a nitrogen atmosphere, perform the second-stage heat treatment, and hold for 1.5 hours to obtain a second-stage product; S1.4. Immerse the second-stage product in a 1 mol / L hydrochloric acid solution for 1 hour, stir with a magnetic stirrer during this period, and then repeatedly wash with deionized water until the pH value of the washing solution is 6.5-7.5. After washing, perform suction filtration and then put it into a vacuum drying oven. The vacuum drying oven is set at a temperature of 80 °C and dried for 10 hours to obtain phosphorus-nitrogen co-doped porous carbon. S1.4. Immerse the second-stage product in a 1 mol / L hydrochloric acid solution for 1 hour, stir with a magnetic stirrer during this period, and then repeatedly wash with deionized water until the pH value of the washing solution is 6.5-7.5. After washing, perform suction filtration and then put it into a vacuum drying oven. The vacuum drying oven is set at a temperature of 80 °C and dried for 10 hours to obtain phosphorus-nitrogen co-doped porous carbon.

[0008] In some embodiments, in step S2, the first carbon coating 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 complex solution.

[0009] In some embodiments, step S2 includes: S2.1. Mix silica microspheres with a particle size of 50 - 100 nm as a templating agent and phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:1, add an ethanol-water mixed solution, stir with a magnetic stirrer for 1 hour, perform ultrasonic treatment for 20 minutes, and then centrifuge and dry to obtain a composite; S2.2. Add a first carbon coating source to the composite, first heat to 50 - 70 °C, keep warm 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; S2.3. Add an etching solution to the first coated product, react at room temperature for 5 - 60 minutes, and use ultrasonic assistance for 5 minutes to obtain a cavity structure preform.

[0010] In some embodiments, in step S3, the second carbon coating 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 surface activation assistant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

[0011] In some embodiments, step S3 includes: S3.1. Load the cavity structure preform into a vertical quartz fluidized bed reactor under a nitrogen atmosphere, preheat to 400 - 550 °C, the reaction bed layer velocity is 0.02 - 0.08 m / s, introduce the silicon source gas and the surface activation assistant, and deposit at a reaction temperature of 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 buffer solution with a pH of 8.5, add the second carbon coating source with a concentration of 2 mg / mL, stir for 2 - 4 hours for the second coating treatment, and then carbonize at 700 - 800 °C for 2 hours under nitrogen protection 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.

[0012] The present invention provides a doped electrode material based on porous silicon carbon, which is prepared by the preparation method of a doped electrode material based on porous silicon carbon as described above.

[0013] Compared with the prior art, a doped electrode material based on porous silicon carbon and its preparation method in the present invention have the beneficial effects that: The doped electrode material based on porous silicon carbide proposed by the present invention constructs a cavity buffer structure and a double-carbon layer coating system. During the preparation process, silica microsphere templates are introduced, and cavities are formed between the center and the shell through etching processes, enabling the subsequently deposited silicon material to have free expansion space. When the volume expansion of silicon occurs due to the insertion of lithium ions, the cavity structure can effectively absorb the strain, preventing the rupture of the outer carbon layer and the structural disintegration, thereby significantly suppressing the macroscopic volume change and reducing the overall expansion coefficient of the electrode. In addition, the double-carbon layer coating system constructed on the basis of this cavity can synergistically relieve the accumulation of internal and external mechanical stresses during charge and discharge cycles and enhance the elasticity and integrity of the outer carbon shell, improving the volume stability of the electrode from a structural perspective.

[0014] In terms of rate performance, this electrode material also exhibits excellent characteristics, which stem from the synergistic regulation between doping modification and the porous framework. First, the co-doping of phosphorus and nitrogen elements introduces abundant defect sites and charge enrichment centers in the carbon matrix, significantly enhancing the electron migration rate and the conductivity of the carbon framework, enabling electrons to still be efficiently transported under high-rate conditions. Second, this material retains a high specific surface area and a through-network structure, forming fast ion diffusion channels, significantly shortening the lithium ion insertion path, and effectively reducing the ion transport impedance. Description of the Drawings

[0015] Figure 1 It is a chart showing the specific surface area, pore volume, and pore diameter of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention; Figure 2 It is a graph showing the resistivity-pressure relationship of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention; Figure 3 It is a graph showing the lithium ion diffusion coefficient of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention; Figure 4 It is a cycle graph of the rate performance of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention; Figure 5 It is a table showing the capacity retention rate of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention at 3C rate; Figure 6 It is a graph showing the long-cycle performance of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention; Figure 7 It is a table showing the capacity retention rate of the doped electrode material based on porous silicon carbide in the examples and comparative examples of the present invention after 100 cycles. Detailed Embodiments

[0016] To make the objectives, 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 used to limit the present invention.

[0017] The present invention provides a preparation method of a doped electrode material based on porous silicon carbide, and the steps include: S1. Crush the resin substrate and put it into a high-temperature furnace for carbonization process. The carbonization temperature is 300~1500°C. While maintaining the temperature range, add an alkaline additive, a phosphorus source material, and a nitrogen source material in sequence to obtain phosphorus and nitrogen co-doped porous carbon.

[0018] Step S1 includes: S1.1. Crush the resin matrix to uniform particles with a D 50 particle size of 10~20μm, and place it in an 80°C constant-temperature drying oven for drying for 6~8 hours.

[0019] By crushing the resin matrix to a particle size of 10~20μm and performing low-temperature constant-temperature drying for 6~8 hours, the pyrolysis uniformity and carbonization efficiency of the raw materials are significantly improved. The smaller-sized resin particles can transfer heat quickly and uniformly during subsequent heat treatment, avoiding the phenomena of shell carbonization and un-depolymerized core during the carbonization process, and contributing to the formation of a dense and continuous carbon skeleton network structure. In addition, the drying treatment effectively removes the adsorbed moisture in the raw materials, preventing the rapid volatilization of water vapor at high temperature from causing 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 basis with stable structure and uniform thermal behavior for subsequent pyrolysis and doping reactions.

[0020] S1.2. Load the dried resin matrix into a quartz boat, place it in a tube furnace with temperature program control and atmosphere regulation functions, introduce high-purity nitrogen, heat up to 300°C and keep it warm for 1 hour, then heat up to 700°C and keep it warm for 2~3 hours for the first-stage heat treatment to obtain the first-stage product.

[0021] Performing the first-stage carbonization treatment on the resin by program-controlled temperature in an inert atmosphere can not only remove low-molecular volatile organic components, but also gradually construct a primary porous carbon structure with a three-dimensional cross-linked aromatic ring skeleton. The constant-temperature treatment at 300°C helps to remove volatile components such as residual monomers of formaldehyde and phenol, while the high-temperature pyrolysis at 700°C promotes the breakage of carbon-hydrogen bonds and carbon-oxygen bonds, forming an aromatic ring stacking structure, thereby enhancing the thermal stability and 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 a diffusion channel for the subsequent entry of dopants into the pores of the carbon matrix, which is an important precursor step for constructing an efficient hetero-element doping structure.

[0022] In one embodiment, to precisely control the temperature of the first-stage heat treatment, it is necessary to set the heating rate for heating up to 700 °C. , the heating rate The calculation equation is: Wherein, is the heating rate (°C / min), and the empirical reference value is 5 - 20 °C / min. is the peak temperature of the thermal analysis (K). In thermogravimetric analysis (TGA) or differential scanning calorimetry (DSC) experiments, different values in the range of 5 - 20 °C / min are used for experiments to scan the samples. The peak temperature corresponding to the highest reaction rate in each scan read from the obtained TGA / DSC curve is the decomposition thermal analysis peak temperature corresponding to the value . R is the gas constant, which is 8.314 J·mol⁻¹·K⁻¹. is the reaction activation energy (J·mol⁻¹). The corresponding and data are organized into a table, and the and for each group are calculated. By plotting and linearly fitting, the slope and intercept respectively correspond to and C, and then and the constant C can be obtained. Then, substituting into and the constant C, calculate when it is 973 K (i.e., 700 °C), and the value, which is the optimal heating rate.

[0023] During the first-stage heat treatment, using the optimal heating rate calculated by the equation can make the temperature field in the carbonization bed layer 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 is more concentrated at this rate, which is beneficial to the formation of a connected microporous - mesoporous hierarchical network, significantly increasing the specific surface area and pore volume, and making the subsequent silicon source deposition and electrolyte infiltration more sufficient.

[0024] S1.3. Add an alkaline additive, a phosphorus source material, and a nitrogen source material to the carbonization product in sequence and mix them in an inert atmosphere for 2 hours. After mixing, load them into a tube furnace again, heat up to 750 - 850 °C in a nitrogen atmosphere, and carry out the second-stage heat treatment for 1.5 hours to obtain the second-stage product.

[0025] Introducing an alkaline additive, a phosphorus source material, and a nitrogen source material into the preliminary carbonization product and performing a second-stage high-temperature treatment can achieve the dual functions of co-doping and etching to create pores, thereby obtaining functionalized porous carbon with a hierarchical pore structure and uniform heteroatom distribution. The alkaline additive decomposes at high temperature to generate reactive alkali metal oxides, which react with carbon to release carbon monoxide / carbon dioxide while etching out regular pores. Phosphorus sources such as red phosphorus or sodium phosphate combine with the carbon structure during pyrolysis 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 lithium affinity of the carbon material. This step significantly enhances the specific surface area, conductivity, and interfacial anchoring ability of the carbon material, providing a stable and functionalized carbon substrate for subsequent silicon source deposition.

[0026] S1.4: Immerse the product of the second stage in a hydrochloric acid solution with a concentration of 1 mol / L for 1 hour, stir magnetically during this period, and then wash repeatedly with deionized water until the pH value of the washing solution is 6.5 - 7.5. After washing, perform suction filtration and then place it in a vacuum drying oven. The vacuum drying oven is set at a temperature of 80 °C and dried for 10 hours to obtain phosphorus and nitrogen co-doped porous carbon.

[0027] By immersing the doped and activated product in a hydrochloric acid solution and stirring and washing thoroughly, inorganic by-products and unreacted dopants remaining in the material can be efficiently removed, preventing side reactions or structural swelling during the electrochemical process. During the pickling process, hydrogen ions react with alkali metal salts to form soluble products, and magnetic stirring enhances the solute migration efficiency; subsequently, repeated washing with deionized water until neutral 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 micropore and surface functional group structure, avoiding the pyrolysis of functional groups at high temperatures, so that the finally formed phosphorus and 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.

[0028] 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, inositol phosphate, and red phosphorus. 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.

[0029] S2: Mix silica microsphere templates into the phosphorus and nitrogen co-doped porous carbon, add a first coating carbon source for the first coating treatment, and then etch the silica microsphere templates with an etching solution to obtain a cavity structure preform.

[0030] Step S2 includes: S2.1. Using silica microspheres with a particle size of 50 - 100 nm as a templating agent, mixing them with phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:1, adding an ethanol–water mixed solution, stirring with a magnetic stirrer for 1 hour, performing ultrasonic treatment for 20 minutes, and then centrifuging and drying to obtain a composite.

[0031] By mixing silica (SiO2) microspheres with a particle size of 50 - 100 nm and phosphorus-nitrogen co-doped porous carbon in a mass ratio of 1:1, and using magnetic stirring and ultrasonic synergistic dispersion in an ethanol–water mixed solution, the uniform embedding and directional distribution of the SiO2 template on the surface and in the pore structure of the porous carbon can be achieved. Ethanol–water as a dispersion medium not only has an appropriate surface tension to promote the entry of SiO2 particles into the porous carbon pores, but also has good volatility to avoid agglomeration. Magnetic stirring provides macroscopic hybrid power, while 20 minutes of ultrasonic treatment breaks up the SiO2 aggregates at the microscopic level, enhancing their interfacial contact with the carbon skeleton, thus ensuring the spatial controllability and uniformity of the subsequent formation of the cavity structure. The composite formed after centrifuging and drying not only has a uniform structure, but also the SiO2 particles are embedded in the key positions of the carbon material, which is beneficial to the formation of a complete coating during the subsequent growth of the carbon shell, and finally an ideal cavity conformal structure is obtained after template etching.

[0032] S2.2. Adding a first carbon coating source to the composite, first heating to 50 - 70 °C, holding for 1 - 2 hours, and then transferring to an inert atmosphere tubular furnace for carbonization at 600 - 700 °C for 2 hours to obtain a first coated product. The first carbon coating source includes at least one of 1,3,5-triethynylbenzene, dopamine, and polypyrrole. The used first carbon coating sources, including 1,3,5-triethynylbenzene, dopamine, and polypyrrole, are all precursors with strong structure-directing properties and high-quality carbonized products.

[0033] In one embodiment, when 1,3,5-triethynylbenzene is selected as the first carbon coating source, it is dissolved in anhydrous tetrahydrofuran, and an iron salt (such as FeCl3) is added as an oxidant for gas-phase or liquid-phase polymerization reaction to form a conjugated microporous polymer, which can provide a highly π-conjugated and high-density graphitized carbon layer after carbonization. Dopamine forms a nitrogen-rich functionalized carbon layer after carbonization at 700 °C; polypyrrole is a typical conductive polymer, which forms a flexible and conductive carbon shell after high-temperature carbonization. The key technical effect of this step is to construct a complete outer carbon shell without damaging the carbon–SiO2 composite structure, providing a solid support for retaining the cavity structure after subsequent etching, and at the same time providing a protective barrier with high electrochemical stability. Introducing the first carbon coating source into the composite and undergoing low-temperature heat treatment and high-temperature carbonization steps can construct a dense and continuous carbon shell structure on the outer surface of the SiO2-doped carbon composite particles.

[0034] S2.3. Add an etching solution to the first coating product, react at room temperature for 5 - 60 minutes, and use ultrasonic assistance for 5 minutes to obtain a preform of the cavity structure. The etching solution includes at least one of hydrofluoric acid solution, sodium hydroxide solution, and ammonia - sodium hydroxide compound solution.

[0035] Adding an etching solution to the first coating product and assisting with ultrasonic treatment can selectively remove the embedded silica template, thereby forming a stable cavity structure inside the carbon coating shell. The etching solutions used include: hydrofluoric acid solution, which has a strong ability to break Si - O bonds and is a traditional high - efficiency solution for etching SiO2; sodium hydroxide solution can also react with SiO2 under medium - strength alkaline conditions and is suitable for systems with high requirements for the carbon shell structure; ammonia - sodium hydroxide compound solution has good interfacial wettability and slow - release etching characteristics, which is beneficial to maintaining the stability of the carbon shell. Ultrasonic assistance helps to break the inert solution boundary layer on the surface of the SiO2 template, accelerate the etching reaction, and improve the pore - cavity formation efficiency. The core technical effect of this step is to construct a high - specific - volume and low - stress embedded cavity structure while keeping the outer shell intact, providing sufficient expansion space and stress buffering capacity for subsequent silicon deposition, and it is the key node for forming the core - cavity - shell sandwich structure.

[0036] In one embodiment, taking the hydrofluoric acid solution as an example of the etching solution, the following equation is proposed to control the etching effect: where r is the etching rate (nm / min), [HF] is the concentration of hydrofluoric acid (mol·L⁻¹), n is the reaction order, and the reaction order of hydrofluoric acid etching silica is between 0.8 and 1.2. Under the same temperature conditions, various [HF] (such as 1, 2, 5, 10 mol / L) are used for etching respectively, the corresponding etching rates r are measured, and then a linear fit of logr against log[HF] is made. The slope of the fitted straight line is the reaction order n. T is the temperature of the etching solution (K). is the activation energy for the reaction of hydrofluoric acid solution with silica and is a fixed value. R is the gas constant and T is the etching temperature.

[0037] In the system using silica microspheres as templates, completely removing the templates without damaging the carbon skeleton is crucial for the pore structure of the final electrode. First, by accurately predicting the etching rate r at a given HF concentration and temperature through a model, we can quantitatively evaluate the shortest time t required to remove the silica microspheres. For example, if the average diameter of the template microspheres is 100 nm, the solution is maintained at 10 wt% HF, and at room temperature, the etching rate is approximately 5 nm / min. Calculating t≈20 min can ensure that all silica particles are completely dissolved without residue and prevent the carbon matrix surface from being overly eroded due to long-term immersion. Second, online monitoring of the HF concentration and temperature and substituting the observed values into can dynamically correct the etching rate model to ensure that r remains stable throughout the process. Then, adjust the etching time in a timely manner according to the latest r value to achieve second-level precision control and prevent under-etching or over-etching. Finally, this quantitative etching strategy not only avoids uneven subsequent deposition or coating caused by the residue of silica microspheres but also maximally protects the original morphology and mechanical strength of the porous carbon structure, thereby significantly improving the batch consistency, electrochemical cycle stability, and initial Coulombic efficiency of the material.

[0038] S3. Place the cavity structure preform into a fluidized bed reactor, introduce the silicon source gas and the surface activation assistant, deposit at 400~550 °C, and then add the second carbon coating source for a second coating treatment to obtain a doped electrode material based on porous silicon carbon.

[0039] Step S3 includes: S3.1. Load the cavity structure preform into a vertical quartz fluidized bed reactor under a nitrogen atmosphere, preheat to 400~550 °C, with a reaction bed layer velocity of 0.02~0.08 m / s. Introduce the silicon source gas and the surface activation assistant, and deposit for 2~4 hours at a reaction temperature of 450 °C to obtain the deposited reactants; the silicon source gas includes at least one of isobutyltrichlorosilane, tetraethoxysilane, and trichlorosilane, and the surface activation assistant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

[0040] Load the cavity structure preform into a vertical quartz fluidized bed reactor, preheat it under a nitrogen protection atmosphere at 400 - 550 °C to form a stable bed state, and control the reaction bed velocity at 0.02 - 0.08 m / s, which can ensure that the particles are in a uniform fluidization state and effectively enhance the gas - solid interface reaction efficiency. Subsequently, introduce the silicon source gas and the surface activation assistant, and continuous silicon deposition can be achieved at about 450 °C. The selection of different silicon sources endows the reaction with different film - forming kinetic characteristics: isobutyltrichlorosilane has a lower decomposition temperature and a higher vapor pressure, which is conducive to the rapid deposition of nano - silicon particles; tetraethoxysilane can produce a controllable silicon - oxygen network structure at medium temperature, which helps to uniformly cover the inner wall and the shell; while trichlorosilane has a high decomposition efficiency at high temperature and can form Si - C interfacial bonding synergistically with the activation assistant. Activation assistants such as aluminum chloride and boron trifluoride are Lewis acids, which can adsorb on the surface of the carbon shell to form acidic centers, inducing the silicon source to preferentially grow at the active sites of the carbon skeleton, thereby constructing a nano - silicon layer with good structural continuity, controllable particle size, and stable attachment. This process effectively solves the problems of easy agglomeration, uneven coating, and interfacial shedding of nano - silicon, laying a structural foundation for improving the cycle life and rate performance.

[0041] S3.2. Cool the deposited reactants to room temperature and disperse them in a tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5, add a second carbon - coating source with a concentration of 2 mg / mL, stir for 2 - 4 hours for the second coating treatment, and then carbonize at 700 - 800 °C for 2 hours under nitrogen protection to obtain the second - coated product; the second carbon - coating source includes at least one of glucose, arabinose, and furfuryl alcohol - formaldehyde resin precursor.

[0042] The composite material after silicon deposition needs to be further treated by a second carbon - coating process to enhance the structural stability and interfacial protection ability of the silicon layer. After cooling the deposited reactants to room temperature, disperse them in a tris(hydroxymethyl)aminomethane (Tris) buffer solution with a pH of 8.5, which helps to stabilize the surface functional group state and improve the adhesion of the coating precursor. Under this condition, add a second carbon - coating source with a concentration of 2 mg / mL, such as glucose, arabinose, or furfuryl alcohol - formaldehyde resin precursor. After stirring for 2 - 4 hours, uniform coating in the solution can be achieved. Glucose and arabinose have a good self - polymerization tendency under weak alkaline conditions and form a flexible amorphous carbon film during the carbonization process, effectively buffering the silicon expansion; the furfuryl alcohol - formaldehyde resin carbon source can construct a hard carbon network, providing mechanical support for the outer shell and introducing controllable O / N doping sites. Subsequently, carbonize at 700 - 800 °C in a nitrogen atmosphere for 2 hours, and the second - layer carbon shell uniformly covers the silicon particles and their interfaces, forming a silicon core - first carbon shell - cavity - second carbon shell hierarchical composite structure. This multiple - layer structure can not only effectively buffer the volume expansion stress but also improve the electron continuity and SEI film stability, which is especially suitable for enhancing the rate response and cycle durability of electrode materials.

[0043] S3.3. Naturally cool the second coated product and screen it to obtain a doped electrode material based on porous silicon carbon.

[0044] Naturally cool the product after the second coating and carbonization, and perform screening treatment 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 rapid cooling, and help maintain the synergistic cooperation between the multi-layer coating shells. The screening process can remove agglomerated particles and irregular large lumps, improve the film-forming uniformity and slurry stability of the material, and provide a good particle size distribution for the subsequent preparation of electrode sheets. This final material has a central nano-Si that provides a high reversible specific capacity; the cavity structure buffers its expansion; the embedded phosphorus and nitrogen co-doped porous carbon improves the electron / ion transport ability; the double-layer carbon shell realizes long-term interface protection. The synergy of the four functions enables it to exhibit excellent performance in fast charging conditions, high-rate discharge, and long-cycle electrochemical cycling, and has significant application prospects.

[0045] In one embodiment, the preparation method of the doped electrode material based on porous silicon carbon further includes, after S3: S4. Place the doped electrode material based on porous silicon carbon in a deposition device. First, use tetramethylaluminum and water as precursors to deposit for 30 cycles at 120 °C to form a 3 nm alumina passivation layer. Subsequently, switch to tetraethoxytitanium and a water source and deposit for another 20 cycles to obtain a 2 nm titanium dioxide nanolayer. This passivation composite layer can construct a uniform inorganic passivation film on the electrode surface, effectively isolate the electrolyte erosion, slow down the silicon body expansion-cracking, and improve the initial Coulomb efficiency and long-cycle stability.

[0046] S5. Assemble the doped electrode material based on porous silicon carbon obtained in S4 into a half-cell, and perform three cycles at a rate of 0.05C in the voltage range of 0.01~1.5V. During the first cycle, charge at 0.8V for 30 min, and within 5 min at the end of the second cycle, charge with a mixed solution of 5 wt% ethylene carbonate and fluoroethylene carbonate. During the first cycle, charging at 0.8V for 30 min causes an in-situ SEI formation reaction on the electrode surface. Short-time charging with a mixed solution of 5 wt% ethylene carbonate and fluoroethylene carbonate at the end of the second cycle promotes the in-situ construction of a highly stable organic-inorganic composite SEI film on the silicon surface.

[0047] The present invention proposes a doped electrode material based on porous silicon carbon, which is made by a preparation method of a doped electrode material based on porous silicon carbon.

[0048] Example 1: S1. After crushing phenolic resin powder, put it into a high-temperature furnace for carbonization process. The carbonization temperature is 700 °C. Keep the temperature range and sequentially add potassium hydroxide, sodium phosphate, and melamine 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.

[0049] S2. Mix silica microsphere templates into the phosphorus-nitrogen co-doped porous carbon, add 1,3,5-triethynylbenzene for the first coating treatment, and then etch the silica microsphere templates with hydrofluoric acid solution to obtain a cavity structure preform. S3. Put the cavity structure preform into a fluidized bed reactor, introduce isobutyltrichlorosilane and aluminum chloride, deposit at 400 - 550 °C, and then add a furfuryl alcohol-formaldehyde resin precursor for the second coating treatment to obtain a doped electrode material based on porous silicon carbon.

[0050] Example 2: Prepare a doped electrode material based on porous silicon carbon by the same method as in Example 1, except that the mass ratio of phenolic resin powder: potassium hydroxide: sodium phosphate: melamine is 10:5:4:1.

[0051] Example 3: Prepare a doped electrode material based on porous silicon carbon by the same method as in Example 1, except that the carbonization temperature is 1000 °C.

[0052] Comparative Example 1: Compared with Example 1, no phosphorus source material was added in step S1.

[0053] Please refer to Figure 1 , which shows the physical parameters of Comparative Example 1 and the 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 in Examples 1, 2, and 3, the specific surface area and pore volume decreased slightly compared with Comparative Example 1, but the micropore size remained similar (about 1.6 - 1.7 nm), indicating that the material still retains a rich pore network after the cavity structure is constructed, which is suitable for the rapid diffusion of lithium ions. Especially in Example 1, although phosphorus was doped, its specific surface area still reached 2273 m² / g, indicating that reasonable doping will not significantly damage 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 interfacial stability.

[0054] Please refer to Figure 2, This figure illustrates the change trend of the compression resistivity of different samples under the compaction condition of 0 - 30 MPa. The resistivity of all samples decreases with the increase of pressure, reflecting the enhanced contact brought by pore compression. Among them, Example 2 has the best conductivity performance (the lowest resistivity), which is related to its higher phosphorus doping ratio (4 parts of sodium phosphate in Example 2). Phosphorus doping improves the electron migration rate by regulating the defect density and charge polarization in the carbon structure. In contrast, Comparative Example 1 (without phosphorus doping) always has the highest resistivity, indicating that phosphorus doping is one of the key factors to improve the conductivity of carbon materials.

[0055] Please refer to Figure 3 , This figure is a graph of the relationship between the lithium-ion diffusion coefficient and potential (logD vs V) obtained by pseudo-steady-state GITT or CV fitting, which is used to characterize the transport ability of Li⁺ in the electrode. The diffusion coefficients of Example 1 and Example 2 are generally higher than that of Comparative Example 1, and Example 2 has the best performance, indicating that phosphorus doping not only improves the electronic conductivity but also has a more significant effect on regulating the Li⁺ diffusion channel. In addition, the "dip - rise" characteristics of the logD curve at different potentials reflect the existence of interfacial impedance at the initial stage of lithium intercalation, and the buffer layer and cavity structure of the examples can effectively alleviate this problem, which is beneficial to high-rate applications.

[0056] Please refer to Figure 4 , This figure shows the change of the cycle capacity under the rate condition of 0.1C - 3C. Example 1 and Example 2 show high capacity and good rate adaptability throughout the rate range, especially maintaining obvious reversibility at the high rate of 3C. Comparative Example 1 decays rapidly at high rates, indicating that the structure of the undoped carbon material is difficult to buffer stress and maintain electron / ion co-conduction under rapid charge and discharge. The results in the figure reflect the significant advantages of phosphorus-nitrogen co-doping and cavity structure in supporting high-rate applications.

[0057] Please refer to Figure 5 , This figure will Figure 4 The degree of capacity decay under the 3C rate condition in is intuitively shown in the form of a percentage. The retention rate of Example 1 is 52.6%, far better than 29.2% of Comparative Example 1, indicating that the double carbon shell coating and P–N co-doping effectively alleviate the structural collapse and SEI film deterioration at high rates. Example 2 is the second best, but still significantly better than the control, verifying that the regulation of the phosphorus doping ratio can optimize the structural stability and interfacial integrity in high-speed reactions.

[0058] Please refer to Figure 6, this figure shows the 100-cycle long-cycle specific capacity performance of various samples at a constant rate (0.2 - 0.5C). Example 1 always remained on a high plateau (>1400 mAh / g), while Comparative Example 1 showed a significant attenuation, tending to be below 1200 mAh / g. This trend indicates that through the rational design of the porous - cavity - double carbon shell structure and phosphorus-nitrogen co-doping, not only the initial capacity is improved, but also the long-term structural integrity, interfacial stability, and electrochemical reversibility are significantly enhanced.

[0059] Please refer to Figure 7 , Figure 6 the summary table form of the data, highlighting that the 100-cycle capacity retention rate of Example 1 is as high as 87.5%, while that of Comparative Example 1 is only 66.3%, and the attenuation rate is nearly doubled. This table further numerically corroborates the durability and buffering efficacy of phosphorus-nitrogen co-doping and the cavity carbon shell structure, which is the key path to constructing high-stability anode materials.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a doped electrode material based on porous silicon carbide, characterized in that the steps Including: S1. Crush the resin substrate and put it into a high-temperature furnace for carbonization process. The carbonization temperature is 300~1500°C. Keep the temperature range and sequentially add an alkaline additive, a phosphorus source material, and a nitrogen source material to obtain phosphorus and nitrogen co-doped porous carbon; S2. Mix silica microsphere templates into the phosphorus and nitrogen co-doped porous carbon, add a first coating carbon source for the first coating treatment, and then etch the silica microsphere templates with an etching solution to obtain a cavity structure preform; S3. Put the cavity structure preform into a fluidized bed reactor, introduce a silicon source gas and a surface activation assistant, deposit at 400~550°C, and then add a second coating carbon source for the second coating treatment to obtain a doped electrode material based on porous silicon carbon.

2. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1, characterized in that, 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, inositol phosphate, and red phosphorus. 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.

3. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1 or 2, characterized in that, Step S1 includes: S1.

1. Crush the resin matrix into uniform particles with a particle size of D 50 of 10 - 20 μm, and place them in an oven at a constant temperature of 80°C for drying for 6 - 8 hours; S1.

2. Load the dried resin matrix into a quartz boat, place it in a tube furnace with temperature program control and atmosphere regulation functions, introduce high-purity nitrogen, heat up to 300°C and keep it warm for 1 hour, then heat up to 700°C, and keep it warm for 2~3 hours for the first-stage heat treatment to obtain a first-stage product; S1.

3. Sequentially add an alkaline additive, a phosphorus source material, and a nitrogen source material to the carbonized product and mix them in an inert atmosphere for 2 hours. After mixing, load them into the tube furnace again, heat up to 750~850°C in a nitrogen atmosphere, carry out the second-stage heat treatment, and keep it warm for 1.5 hours to obtain a second-stage product; S1.

4. Immerse the second-stage product in a hydrochloric acid solution with a concentration of 1mol / L for 1 hour, stir it magnetically during this period, then wash it repeatedly with deionized water until the pH value of the washing solution is 6.5~7.

5. After washing, carry out suction filtration and then put it into a vacuum drying oven. The temperature of the vacuum drying oven is set at 80°C and dried for 10 hours to obtain phosphorus and nitrogen co-doped porous carbon.

4. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1, characterized in that, In step S2, the first coating carbon source includes at least one of 1,3,5-triethynylbenzene, dopamine, and polypyrrole. The etching solution includes at least one of hydrofluoric acid solution, sodium hydroxide solution, and ammonia-sodium hydroxide compound solution.

5. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1 or 4, characterized in that, Step S2 includes: S2.

1. Use silica microspheres with a particle size of 50~100nm as a templating agent, mix them with the phosphorus and nitrogen co-doped porous carbon according to a mass ratio of 1:1, add an ethanol-water mixed solution, stir with a magnetic stirrer for 1 hour, carry out ultrasonic treatment for 20 minutes, and then carry out centrifugal drying to obtain a composite; S2.

2. Add the first coating carbon source to the composite, first heat up to 50~70°C and keep it warm for 1~2 hours, then transfer it to an inert atmosphere tube furnace and carbonize it at 600~700°C for 2 hours to obtain a first coating product; S2.

3. Add an etching solution to the first coating product, react at room temperature for 5 to 60 minutes, and use ultrasonic assistance for 5 minutes to obtain a cavity structure preform.

6. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1, characterized in that, In step S3, the second carbon source for coating 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; the surface activation assistant includes at least one of aluminum chloride, boron trifluoride, and zinc chloride vapor.

7. The preparation method of a doped electrode material based on porous silicon carbide according to claim 1 or 6, characterized in that, Step S3 includes: S3.

1. Load the cavity structure preform into a vertical quartz fluidized bed reactor under a nitrogen atmosphere, preheat to 400 to 550 °C, with a reaction bed layer velocity of 0.02 to 0.08 m / s, introduce the silicon source gas and the surface activation assistant, and deposit for 2 to 4 hours at a reaction temperature of 450 °C to obtain a deposited reactant; S3.

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

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

8. A doped electrode material based on porous silicon carbide, characterized in that, It is made by the preparation method of a doped electrode material based on porous silicon carbide according to any one of claims 1-7.

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