Porous carbon, silicon-carbon negative electrode material and preparation method thereof

Abstract

This invention relates to the field of battery anode material technology, specifically disclosing a porous carbon and silicon-carbon anode material and its preparation method. The invention involves primary oxidation of modified asphalt, followed by secondary oxidation at 280℃~320℃ with the addition of a titanium-containing sensitizer; gradient negative pressure carbonization of the resulting pre-oxidized coal tar pitch, adding an activator to the resulting carbonized asphalt, and supercritical CO2 melting and mixing; then primary activation at 500℃~750℃; followed by secondary activation at 800℃~1000℃ with the introduction of supercritical CO2 and O2 to obtain porous carbon. The invention utilizes radio frequency oxygen plasma gradient oxidation to provide uniform anchoring points, supercritical technology to achieve precise pore formation and Ti impurity removal, electrochemical pulse oxidation-reduction to form a defect-free buffer layer, and a one-step gradient carbon coating to enhance structural stability. The synergistic effect of these four factors results in a silicon-carbon anode material with significantly superior overall performance compared to existing technologies.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, and in particular to a porous carbon / silicon-carbon anode material and its preparation method. Background Technology

[0002] With the explosive growth of the new energy vehicle and energy storage industries, the demand for high-energy-density, long-cycle-life, and low-volume-expansion anode materials for lithium-ion batteries is becoming increasingly urgent. Silicon-based materials, with their theoretical specific capacity (4200 mAh / g) far exceeding that of traditional graphite (372 mAh / g), have become the core direction for next-generation anode materials. Coal tar pitch, as a byproduct of coal chemical industry, possesses natural advantages such as wide availability, low cost, high carbon yield, and tunable molecular structure, making it an ideal precursor for preparing high-performance silicon-carbon anode carbon supports. The combination of silicon-based materials and coal tar pitch has become the mainstream technical route for the research and development of silicon-carbon anode materials.

[0003] The current preparation process for pitch-based silicon-carbon anodes has formed a basic framework of pre-oxidation → carbonization → activation and pore formation → silicon deposition → coating. In the pre-oxidation process, the reaction rate, depth, and uniformity of traditional gas-phase and liquid-phase oxidation are uncontrollable. The industry has begun to introduce plasma oxidation technology to achieve solvent-free, homogeneous oxidation; simultaneously, there are existing technologies that lower the oxidation reaction energy barrier and improve the uniformity of oxygen group regulation by adding sensitizers during oxygen heating. However, sensitizers suffer from incomplete in-situ self-removal, leading to impurities poisoning the silicon deposition interface and carbon support pores. In the supercritical CO2 activation and pore formation process, supercritical CO2, with its excellent permeability and dissolving ability, facilitates the uniform adsorption and deposition of silanes in porous carbon. However, its functional applications are still limited by the compatibility of conventional equipment, and it suffers from poor controllability of the carbon support pore structure, thus affecting the rate performance and cycle stability of the silicon-carbon anode. In the SiO coating process, SiO acts as a buffer layer for silicon-based materials, effectively suppressing volume expansion during lithium insertion / extraction. However, traditional vapor-phase pulse oxidation processes cannot precisely control the oxidation depth and reduction degree, leading to uneven SiO coating thickness and uncontrolled proportions. Carbon coating is key to improving the conductivity and structural stability of silicon-carbon anodes. Traditional coatings either only coat conductive carbon, resulting in cumbersome processes and poor interfacial adhesion, or create a dense structure or a buffer gradient layer, requiring additional processes to achieve the doping effect. It is impossible to achieve the triple effect of dense carbon + conductive carbon + elemental doping in a single coating process.

[0004] Therefore, there is an urgent need to develop a method for preparing silicon-carbon anode materials in order to achieve the preparation of ultra-high performance silicon-carbon anode materials. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a porous carbon and silicon-carbon anode material and its preparation method. It employs radio frequency oxygen plasma gradient oxidation to provide uniform anchoring points, supercritical technology to achieve precise pore formation and Ti impurity removal, electrochemical pulse oxidation-reduction to form a defect-free buffer layer, and a one-step gradient carbon coating to enhance structural stability. The synergistic effect of these four methods results in a silicon-carbon anode material with significantly superior overall performance compared to existing technologies.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing porous carbon, comprising the following steps: S1. Under radio frequency plasma conditions, the modified pitch is subjected to primary oxidation at 240℃~260℃, and then the temperature is raised to 280℃~320℃. A titanium-containing sensitizer is added for secondary oxidation to obtain pre-oxidized coal tar pitch. S2. The pre-oxidized coal tar pitch is subjected to primary negative pressure carbonization at 500℃~750℃, and then the temperature is raised to 800℃~1000℃ for secondary negative pressure carbonization to obtain carbonized pitch. S3. Add an activator to the carbonized asphalt, and introduce CO2 to 5MPa~10MPa for melting and mixing; then introduce N2 and supercritical CO2 for primary activation at 500℃~750℃; then raise the temperature to 800℃~1000℃ and introduce supercritical CO2 and O2 for secondary activation to obtain porous carbon.

[0007] Compared to existing technologies, the porous carbon preparation method provided by this invention utilizes oxygen free radicals generated by radio frequency plasma to gently etch the surface of modified bitumen at 240℃~260℃, causing C / C bonds to break and simultaneously introducing oxygen groups such as -OH and -C=O, providing uniform anchoring sites for silicon deposition. The addition of a titanium-containing sensitizer at 280℃~320℃ lowers the oxygen free radical reaction energy barrier, enhancing oxidation uniformity. Simultaneously, its ligands volatilize upon heating, leaving residual amorphous TiO₂. x In the subsequent negative pressure gradient carbonization stage, the carbon matrix is ​​carbothermally reduced to Ti atoms (C+TiO). x →Ti+CO↑), Ti atoms are vaporized under high temperature and negative pressure (about 1 kPa) of 800℃~1000℃ and discharged by N2 during the negative pressure gradient carbonization process; the remaining trace Ti (<100ppm) is efficiently extracted by supercritical CO2 in the supercritical CO2 melting and mixing-gradient activation stage of the tube furnace, and finally achieves Ti residue ≤40ppm, without impurity interference.

[0008] After being carbonized under negative pressure gradient, pre-oxidized coal tar pitch gradually condenses to form a stable carbon skeleton, while initially creating pores. In the supercritical CO2 melting and mixing stage, supercritical CO2, with its excellent permeability, evenly penetrates the activator into the interior of the carbonized pitch particles. In the supercritical gradient activation stage, the first-stage activation and gentle etching form a large number of micropores, while the second-stage activation, with supercritical CO2 and O2 working together to etch, connects the micropores into a mesoporous-macroporous hierarchical structure. This provides ample space for silicon deposition, ensures unobstructed lithium-ion transport channels, and further extracts and removes trace Ti impurities.

[0009] Preferably, in S1, the softening point of the modified asphalt is 100℃~280℃.

[0010] Preferably, in S1, the particle size of the modified asphalt is ≤3mm.

[0011] For example, in S1, the modified bitumen needs to be dried at 80°C and -0.09MPa vacuum for 12 hours before oxidation etching.

[0012] Preferably, in S1, the first-stage oxidation step includes: placing the modified asphalt into a radio frequency plasma reactor, first introducing a mixed gas of Ar and O2, wherein the volume fraction of O2 in the mixed gas is 5%~20%, then evacuating to 8Pa~12Pa, and then heating to 240℃~260℃ for first-stage oxidation.

[0013] More preferably, in S1, the flow rate of the mixed gas is 20 sccm to 200 sccm.

[0014] It should be noted that the secondary oxidation process maintains this oxidizing atmosphere.

[0015] Preferably, in S1, the conditions for the primary oxidation include: the power of the radio frequency power supply is 80W~120W (more preferably 90W~110W), the temperature is increased to 240℃~260℃ at a rate of 2.5℃ / min~3.5℃ / min, and the reaction time is 50min~70min.

[0016] This invention replaces traditional hydrogen peroxide liquid-phase oxidation with oxygen plasma free radicals, using free radical etching to modify the surface of asphalt, gently introducing -OH and -C=O without corroding the internal skeleton of the modified asphalt, while providing uniform anchoring points for subsequent silicon deposition.

[0017] Preferably, in S1, the titanium-containing sensitizer includes titanium acetylacetonate.

[0018] Preferably, in S1, the mass ratio of the titanium-containing sensitizer to the modified asphalt is (0.6~1.5):100, and more preferably (0.8~1.2):100.

[0019] In this invention, titanium chelates can lower the reaction energy barrier of oxygen free radicals, making oxidation more uniform and controllable. At 280℃~320℃, the acetylacetone ligand can spontaneously volatilize and be removed, leaving only trace amounts of TiO₂. x It is dispersed on the surface. That is, secondary oxidation can simultaneously achieve sensitization and pre-removal of acetylacetonate titanium oxide.

[0020] Preferably, in S1, the conditions for the secondary oxidation include: heating to 280°C to 320°C at a rate of 1.5°C / min to 2.5°C / min, and a reaction time of 50 min to 70 min.

[0021] Preferably, in S1, the content of oxygen groups in the pre-oxidized coal tar pitch is 18.8 at% to 19.2 at%.

[0022] Through extensive experiments, this invention has discovered that 19.0 at% is the optimal point for the strongest bonding and highest initial efficiency of silicon deposition. If the content of oxygen groups is too low, the bonding force with subsequent Si is weak, and Si is prone to detachment; if the content of oxygen groups is too high, it will reduce the initial efficiency of the prepared silicon-carbon anode material and increase the irreversible capacity.

[0023] For example, in S2, the first-stage negative pressure carbonization process includes: placing pre-oxidized coal tar pitch into a tubular furnace, first evacuating to 480 Pa~520 Pa, then backfilling with N2 to an absolute pressure of 0.9 kPa~1.1 kPa, with an N2 flow rate of 70 sccm~90 sccm, and then performing first-stage negative pressure carbonization at 500℃~750℃. The second-stage negative pressure carbonization maintains this atmosphere.

[0024] Preferably, S2 specifically includes the following steps: heating the pre-oxidized coal tar pitch to 500℃~750℃ at a rate of 7℃ / min~10℃ / min for primary negative pressure carbonization, holding for 1h~2h, then heating to 800℃~1000℃ at a rate of 4℃ / min~6℃ / min for secondary negative pressure carbonization, holding for 2h~4h, to obtain the carbonized asphalt.

[0025] In this invention, pre-oxidized coal tar pitch undergoes condensation into a stable carbon framework during primary negative pressure carbonization, and TiO is reduced via carbothermal reduction during secondary negative pressure carbonization. x The Ti atoms are metallic Ti atoms; the Ti atoms are vaporized at high temperature and can be carried away by negative pressure + N2 purging. This step is the main removal step of the titanium sensitizer. After negative pressure gradient carbonization, the Ti content of carbonized asphalt is <100ppm.

[0026] For example, in S2, after the secondary negative pressure carbonization is completed, it also includes: crushing, sieving, and obtaining carbonized asphalt.

[0027] Preferably, in S2, the particle size of the carbonized asphalt is ≤75μm.

[0028] In this invention, the carbonized asphalt needs to pass through a 200-mesh sieve to ensure uniform particle size, which provides a basis for the uniform mixing with the activator and the uniformity of silicon deposition.

[0029] Preferably, in S3, the activator comprises potassium carbonate and sodium carbonate in a mass ratio of (1.1~2):1.

[0030] Preferably, in S3, the particle size of the activator is ≤30μm.

[0031] Preferably, in S3, the mass ratio of the carbonized asphalt to the activator is 1:(1~3), and more preferably 1:(1~2).

[0032] This invention uses a composite activator and limits its dosage. The dual-salt eutectic process can achieve a mild activation temperature and uniform pore formation without local burn-through.

[0033] For example, in S3, after adding the surfactant, the vacuum is first evacuated to 10Pa~1000Pa before charging CO2.

[0034] Preferably, the melting and mixing temperature in S3 is 30°C to 50°C higher than the softening temperature of the modified asphalt in S1.

[0035] Preferably, in S3, during the first-stage activation, the flow rate of N2 is 60 sccm to 80 sccm, and the flow rate of supercritical CO2 is 4 sccm to 6 sccm.

[0036] Preferably, in S3, during the secondary activation, the flow rate of supercritical CO2 is 17.5 sccm to 19.1 sccm, and the flow rate of O2 is 0.9 sccm to 2.5 sccm.

[0037] Preferably, S3 specifically includes the following steps: adding an activator to the carbonized asphalt, charging CO2 to 7MPa~9MPa, heating to 140℃~320℃ at a rate of 3℃ / min~5℃ / min, and performing melt mixing for 1.7h~2.3h; then introducing N2 and supercritical CO2, heating to 500℃~750℃ at a rate of 1.5℃ / min~2.5℃ / min for primary activation, and holding at this temperature for 1h~2h; then heating to 800℃~1000℃, introducing supercritical CO2 and O2 for secondary activation, and holding at this temperature for 1.7h~2.5h to obtain the porous carbon.

[0038] During the supercritical CO2 melting and mixing stage, supercritical CO2, with its excellent permeability, uniformly penetrates the activator into the pores of the carbonized asphalt particles, while simultaneously extracting residual trace amounts of Ti, achieving deep Ti removal. In the primary activation stage, the molten carbides are slowly etched by the activator, forming numerous micropores that provide space for silicon deposition. In the secondary activation stage, the micropores in the carbides are connected into mesoporous-macroporous channels, accelerating ion transport and providing ample expansion space; simultaneously, the high temperature and gas flow completely remove trace amounts of Ti, resulting in a Ti content of ≤40 ppm in the porous carbon.

[0039] Preferably, in step S3, after the secondary activation is completed, the process further includes: N2 cooling, crushing, washing, and drying to obtain the porous carbon.

[0040] For example, in S3, deionized water and ethanol with a volume ratio of 3:1 are used for washing, the liquid-to-solid ratio is 10:1, the washing temperature is 60°C, and the washing is repeated until the pH is neutral; the drying is carried out by vacuum drying at a temperature of 80°C for 12 hours.

[0041] Through the above post-processing steps, the present invention can effectively remove activator salt ions, avoiding electrolyte decomposition or reduction of initial efficiency.

[0042] Preferably, in S3, the particle size of the porous carbon is ≤50μm.

[0043] Secondly, the present invention provides a porous carbon, which is prepared by the aforementioned method for preparing porous carbon.

[0044] The porous carbon prepared by the present invention through a specific method not only has a mesoporous-macroporous hierarchical structure, but also has a thorough removal of Ti containing titanium sensitizer, with Ti residue ≤40ppm, and no impurities interfering with / poisoning the subsequent silicon deposition interface or the pores of the porous carbon.

[0045] Thirdly, the present invention provides an application of the porous carbon described above in the preparation of silicon-carbon anode materials.

[0046] Fourthly, the present invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: S4. Under magnetically confined plasma conditions, the porous carbon is subjected to silicon deposition to obtain silicon-supported carbon material; S5. Under an inert atmosphere, at 580℃~620℃ and constant voltage pulse, the silicon-supported carbon material is subjected to in-situ electrochemical pulse oxidation; then, the reverse voltage is switched and H2 is introduced to carry out a reduction reaction to obtain SiO-coated silicon-supported carbon material. S6. By controlling the flow rates of C2H2, B(CH3)3 and NH3, the SiO-coated silicon-supported carbon material is subjected to boron-nitrogen co-doping gradient carbon coating to sequentially form a dense sub-outer layer and a buffer outer layer, thereby obtaining a silicon-carbon anode material.

[0047] The method for preparing silicon-carbon anode materials provided by this invention involves silicon deposition using magnetically confined plasma technology to load a silicon layer onto porous carbon. Constant-pressure pulse oxidation at a specific temperature oxidizes the silicon surface to SiO, while inert gas purging intervals prevent over-oxidation. Subsequent hydrogen reduction removes peroxide impurities from the SiO, forming a dense, defect-free SiO buffer layer, which effectively buffers volume expansion during silicon lithium insertion / extraction, improving the material's cycle stability. The one-step boron-nitrogen co-doped gradient carbon coating stage, by controlling the flow rates of C2H2, B(CH3)3, and NH3, achieves boron-nitrogen co-doped gradient carbon coating in one step, sequentially forming a dense sub-outer layer and a buffer outer layer.

[0048] Preferably, in step S4, before silicon deposition, the porous carbon is further pretreated to remove moisture from it.

[0049] More preferably, in S4, the pretreatment is carried out in an N2 atmosphere, and the flow rate of N2 is 90 sccm to 110 sccm.

[0050] More preferably, in S4, the pretreatment temperature is 440℃~460℃, and the pretreatment time is 50min~70min.

[0051] Water decomposes SiH4 to produce SiO2 impurities, which must be removed through pretreatment.

[0052] Preferably, in step S4, the silicon deposition step includes: placing the porous carbon into a deposition furnace, applying an axial magnetic field, introducing SiH4 and Ar in a volume ratio of 1:(4~20), and turning on the radio frequency power supply to perform silicon deposition.

[0053] More preferably, in S4, the magnetic confinement plasma conditions for silicon deposition include: the power of the radio frequency power supply is 60W~80W, the strength of the axial magnetic field is 0.25T~0.35T, the temperature is 340℃~360℃, and the deposition time is 2.5h~3.5h.

[0054] In this invention, an axial magnetic field confines SiH4 plasma within the pores of porous carbon. By limiting the magnetically confined plasma deposition conditions, atomic-level deposition is achieved, resulting in no agglomeration, no pore blockage, and extremely uniform silicon distribution.

[0055] Preferably, in S4, the silicon content in the silicon-supported carbon material is 56.5wt%~57.5wt%.

[0056] Through extensive testing, this invention has found that 57.0 wt% is the balance point between capacity and cycle life. If the Si content is too low, the capacity will be insufficient; if the Si content is too high, it will easily expand and explode.

[0057] For example, in S4, silicon deposition is monitored using LIBS+QCM linkage (response time < 3s, automatic silane cut-off) to ensure that the silicon content in the silicon-supported carbon material is within a specific range.

[0058] In step S4 of this invention, within the magnetically confined plasma deposition furnace (referring to a thin-film deposition device combining magnetically confined plasma technology), an axial magnetic field of specific intensity confines the SiH4 and Ar mixture, while a specific radio frequency power plasmaifies the SiH4, causing it to break down into Si atoms. Under the influence of the magnetic field, the Si atoms are uniformly deposited within the micropores and mesopores of porous carbon, achieving atomic-level dispersion and preventing silicon agglomeration. LIBS (laser-induced breakdown spectroscopy) monitors the characteristic Si spectral line (288.16 nm) in real time, and QCM (quartz crystal microbalance) monitors the deposition quality increment in real time. Dual closed-loop linkage controls the gas flow rate to ensure the silicon content remains stable at 57.0 wt% ± 0.5 wt%.

[0059] Preferably, in step S5, the inert atmosphere includes Ar, and the flow rate of Ar is 45 sccm to 55 sccm.

[0060] Preferably, in S5, the voltage of the constant voltage pulse is +1.1V to +1.3V, the pulse duration is 18s / time to 22s / time, and the cycle is 28 to 32 times.

[0061] Preferably, in S5, the voltage of the reduction reaction is -0.7V to -0.9V, and the reduction reaction time is 8min to 12min.

[0062] Preferably, S5 specifically includes the following steps: placing the silicon-supported carbon material in an electrochemical vapor furnace, introducing Ar, heating to 580℃~620℃ at a rate of 0.3℃ / min~0.7℃ / min, performing in-situ electrochemical pulse oxidation under constant voltage pulse, purging with Ar, and cycling 28~32 times; then switching the reverse voltage, introducing H2 to carry out a reduction reaction, cooling with Ar, to obtain the SiO-coated silicon-supported carbon material.

[0063] More preferably, in S5, the flow rate of H2 is 4.5 sccm to 5.5 sccm.

[0064] Preferably, in S5, the SiO content in the SiO-coated silicon-supported carbon material is 21wt%~23wt%.

[0065] Preferably, in S5, the thickness of the SiO coating layer in the SiO-coated silicon-supported carbon material is 2.5 nm to 3.5 nm.

[0066] This invention enables the oxidation of only a very thin layer of silicon to form SiO on the surface by limiting the conditions of in-situ electrochemical pulse oxidation, and locks the SiO content by in-situ Raman spectroscopy; by limiting the conditions of the reduction reaction, the peroxide is reduced, thereby forming a dense, defect-free SiO buffer layer, which can suppress expansion, improve cycling, and prevent silicon powdering.

[0067] Preferably, in step S6, the specific steps of the gradient carbon coating include: placing the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introducing N2, and heating it to 680℃~720℃ at a rate of 8℃ / min~12℃ / min; then controlling the flow ratio of C2H2, B(CH3)3 and NH3 to be (23~27):1:(1.8~2.2), with a total flow rate of 110sccm~130sccm, and forming a dense sub-outer layer after 23min~27min; then controlling the flow ratio of C2H2, B(CH3)3 and NH3 to be (4.5~5.5):1:(0.7~1.3), with a total flow rate of 190sccm~210sccm, and forming a buffer outer layer after 23min~27min; and cooling with N2 to obtain the silicon-carbon anode material.

[0068] More preferably, in S6, the flow rate of N2 is 230 sccm to 270 sccm.

[0069] In this invention, a high proportion of C2H2 reacts with a small amount of B(CH3)3 and NH3 to form a dense boron-nitrogen co-doped carbon sub-outer layer, which firmly encapsulates the SiO-coated silicon-supported carbon material and prevents silicon particle migration. Reducing the proportion of C2H2 and increasing the total gas flow rate can form a loose and highly conductive carbon outer layer, improving the conductivity of the material. The doping of boron and nitrogen elements further optimizes the electron transport performance of the carbon layer and enhances the compatibility between the carbon layer and the electrolyte. "Dense coating + enhanced conductivity + element doping" can be achieved in one step.

[0070] Fifthly, the present invention provides a silicon-carbon anode material, which is prepared by the method described above.

[0071] The silicon-carbon anode material provided by this invention has excellent overall performance, with an initial coulombic efficiency of ≥93.0%, a capacity retention rate of ≥89% after 1000 cycles, and a volume expansion rate of ≤14%, which fully meets the requirements of high-energy-density power batteries for anode materials.

[0072] The present invention has the following beneficial effects: The method for preparing silicon-carbon anode materials (including the method for preparing porous carbon) provided by this invention achieves precise parameter control throughout the entire process, solves the problem of poor batch stability caused by the wide range of parameters in existing technologies, and has small batch fluctuations, enabling direct and stable industrial mass production.

[0073] This invention achieves thorough in-situ self-removal of titanium-containing sensitizers, eliminating the risk of impurity poisoning. Through a three-step in-situ synergistic removal process involving ligand pre-volatilization, carbothermal reduction, and supercritical CO2 extraction, the residual Ti in porous carbon is ≤40 ppm, below the allowable impurity threshold (<50 ppm) for lithium-ion battery anodes. This fundamentally avoids the poisoning effect of impurities on the silicon deposition interface, carbon pore structure, and electrochemical performance. This invention simultaneously performs titanium oxyacetylacetonate oxidation with secondary oxidation. While completing the pre-removal of sensitizer ligands at 280℃~320℃, it further strengthens the pitch cross-linking structure, achieving sensitization-enhanced oxidation and in-situ ligand removal. This provides a foundation for subsequent deep Ti removal, reduces process steps, lowers energy consumption, and ensures oxidation uniformity and continuous removal of titanium-containing sensitizers.

[0074] This invention uses synchrotron infrared real-time locking at 3400 cm. -1 The -OH characteristic peak precisely stabilizes the oxygen group content in pre-oxidized coal tar pitch within an extremely narrow range of 19.0at%±0.2at%, providing uniform and sufficient anchoring points for silicon atoms, thus improving the stability of silicon-carbon bonding, while avoiding side reactions caused by excessive oxygen groups, ensuring the core performance foundation of the material.

[0075] This invention clarifies that supercritical melting and mixing, as well as supercritical gradient activation, are both completed within the same high-pressure tube furnace. This eliminates the need for material transfer and additional equipment, perfectly adapting to the limitations of industrial production equipment and addressing the core pain point of the difficulty in scaling up supercritical technology. Through primary activation to form a microporous foundation and secondary activation to connect the micropores and form hierarchical channels, this invention precisely controls the pore structure distribution, ensuring that the specific surface area and pore size distribution of the carbon carrier perfectly match the atomic-level deposition requirements of silicon. Simultaneously, it improves the rate performance and cycle stability of the material.

[0076] This invention endows supercritical CO2 with three core functions: ① Permeation and pore formation: Supercritical CO2, with its excellent permeability, uniformly carries the composite activator into the interior of carbonized asphalt particles, and combined with gradient temperature-controlled activation, forms a hierarchical porous carbon structure of micropores-mesopores-macropores, which provides sufficient deposition space for silicon atoms and ensures lithium ion transport; ② Deep extraction: Simultaneously completes the extraction of trace Ti species, complementing the previous carbothermal reduction removal, and ultimately achieving Ti residue ≤40 ppm; ③ Uniform mixing: Replaces traditional mechanical mixing, avoids activator agglomeration, and improves the uniformity of the carbon carrier pore structure.

[0077] This invention precisely locks the SiO ratio at 22.0% ± 1.0% and controls the coating thickness at 3 nm ± 0.5 nm through in-situ electrochemical constant-voltage pulse oxidation + hydrogen reduction, perfectly matching the optimal buffer threshold for silicon volume expansion. Compared with existing technologies, this significantly reduces the expansion problem caused by uneven coating, achieving a material volume expansion rate of ≤14%. This invention employs in-situ synergistic regulation of electrochemical oxidation-reduction. The oxidation stage precisely generates a thin layer of high-purity SiO, while the reduction stage thoroughly removes peroxide impurities, forming a dense, defect-free SiO buffer layer. This avoids SiO layer cracking and detachment during lithium insertion / extraction, strengthens the interfacial bonding between the silicon core and the coating, and extends the material's cycle life. This invention completes the entire oxidation-reduction process within the same electrochemical vapor furnace, eliminating the need for sample transfer. It adapts to the silicon core structure characteristics in real time, improving the bonding strength between the SiO coating and the silicon core, while reducing process energy consumption and operational complexity.

[0078] Existing gradient carbon coating methods typically involve a two-step process of splicing a dense sub-outer layer followed by a conductive outer layer. This invention employs a one-step in-situ boron-nitrogen co-doping gradient carbon coating process, continuously completed within the same furnace and at the same temperature. By adjusting the gas ratio and flow rate in real time, in-situ doping of boron and nitrogen atoms and the construction of a dense, buffered gradient carbon layer are achieved simultaneously. This one-step simultaneous doping method ensures that boron and nitrogen atoms are uniformly dispersed within the carbon framework, forming a BNC synergistic conductive structure. This significantly improves the conductivity of the carbon layer (reducing internal resistance) and enhances the compatibility between the carbon layer and the electrolyte, reducing side reactions and further improving the material's rate performance and cycle stability. The dense sub-outer layer strengthens the bond between silicon particles and the carbon layer, preventing silicon particle migration and aggregation. The buffered outer layer utilizes a loose buffer structure to alleviate volume expansion during silicon lithium insertion / extraction, while also improving overall conductivity. This dual-function synergy significantly improves the material's overall performance, achieving a capacity retention of ≥89% after 1000 cycles. Detailed Implementation

[0079] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0080] In the current field of silicon-carbon anode material preparation, the following technical problems exist: (1) Incomplete removal of sensitizer, residual impurities poison the material. In existing technologies, the sensitization removal process is cumbersome, energy-intensive, and cannot guarantee the continuity and thoroughness of titanium species removal. Sensitizers such as acetylacetone titanium oxide rely solely on high-temperature volatilization or simple washing, which cannot completely remove residual TiO2. xIn lithium-ion batteries, residual Ti content is typically >100 ppm, far below the permissible impurity threshold (<50 ppm) for anode materials. Residual metal oxides / particles can clog carbon support pores, hinder uniform silane deposition, and trigger side reactions that consume electrolyte, leading to reduced initial coulombic efficiency and accelerated cycle degradation.

[0081] (2) Insufficient precision in the regulation of oxygen groups affects the stability of silicon bonding. Conventional plasma oxidation lacks precise online monitoring and closed-loop control methods, resulting in large fluctuations in the oxygen group atomic fraction (usually ±1 at% or more). This can easily lead to insufficient oxygen groups (weak bonding between silicon and carbon, easy detachment) or excessive oxygen groups (causing side reactions and reducing first-efficiency), failing to meet the interface requirements of silicon atomic-level deposition.

[0082] (3) Insufficient precision in pore structure control, unable to meet silicon deposition requirements. Conventional supercritical activation lacks gradient temperature control and synergistic gas regulation, resulting in carbon pore structures dominated by single micropores or mesopores. It fails to form a hierarchical porous structure of micropores-mesopores-macropores, thus failing to provide sufficient deposition space for silicon atoms and hindering lithium-ion transport, thereby limiting the material's rate performance and cycle stability. Furthermore, current technologies only use supercritical CO2 for a single pore-forming or extraction stage, leading to uneven activator distribution, poor pore structure controllability, and an inability to simultaneously achieve deep removal of titanium-containing sensitizers.

[0083] (4) Poor precision and controllability of SiO coating layer Traditional vapor-phase pulsed oxidation relies on time and flow rate control, failing to provide real-time feedback on oxidation depth and reduction degree. This results in large fluctuations in the SiO ratio (typically ±3% or more), uneven coating thickness (deviation >1nm), and an inability to stabilize within the optimal buffer zone of 20wt%~25wt%, leading to poor volume expansion suppression. Vapor-phase oxidation without electrochemical control easily produces peroxide residues, and impurities cannot be completely removed during the reduction stage, resulting in lattice defects in the SiO coating. This makes it prone to cracking and detachment during lithium insertion / extraction, hindering long-term structural stability. Furthermore, current technologies do not achieve in-situ synchronous control of oxidation-reduction, requiring equipment replacement or process interruption. This leads to weak interfacial adhesion of the coating and an inability to precisely match the structural characteristics of the silicon core, reducing the overall cycle life of the material.

[0084] (5) The efficiency of boron-nitrogen co-doping is low and the synergistic effect is not realized. Traditional stepwise doping (B first then N or N first then B) results in B and N atoms not being able to enter the carbon framework evenly, failing to form a BNC synergistic structure. This leads to limited improvement in the conductivity and interfacial compatibility of the carbon layer and cannot effectively buffer the expansion of silicon particles.

[0085] To address the above problems, this invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: S1. Under radio frequency plasma conditions, the modified pitch is subjected to primary oxidation at 240℃~260℃, and then the temperature is raised to 280℃~320℃. A titanium-containing sensitizer is added for secondary oxidation to obtain pre-oxidized coal tar pitch. S2. The pre-oxidized coal tar pitch is subjected to primary negative pressure carbonization at 500℃~750℃, and then the temperature is raised to 800℃~1000℃ for secondary negative pressure carbonization to obtain carbonized pitch. S3. Add an activator to the carbonized asphalt, and introduce CO2 to 5MPa~10MPa for melting and mixing; then introduce N2 and supercritical CO2 for primary activation at 500℃~750℃; then raise the temperature to 800℃~1000℃ and introduce supercritical CO2 and O2 for secondary activation to obtain porous carbon. S4. Under magnetically confined plasma conditions, the porous carbon is subjected to silicon deposition to obtain a silicon-supported carbon material; S5. Under an inert atmosphere, at 580℃~620℃ and constant voltage pulse, the silicon-supported carbon material is subjected to in-situ electrochemical pulse oxidation; then, the reverse voltage is switched and H2 is introduced to carry out a reduction reaction to obtain SiO-coated silicon-supported carbon material. S6. By controlling the flow rates of C2H2, B(CH3)3 and NH3, the SiO-coated silicon-supported carbon material is subjected to boron-nitrogen co-doping gradient carbon coating to sequentially form a dense sub-outer layer and a buffer outer layer, thereby obtaining a silicon-carbon anode material.

[0086] In this embodiment of the invention, the modified asphalt needs to be dried at 80°C and under a vacuum of -0.09 MPa for 12 hours before oxidative etching, and then crushed into particles with a particle size ≤3 mm; the activators potassium carbonate and sodium carbonate both have a particle size ≤30 μm. Unless otherwise specified, all materials used in this embodiment of the invention can be obtained commercially or prepared by conventional methods in the art. Unless otherwise specified, the operating steps or dosages in this embodiment of the invention can be performed in accordance with conventional practices in the art.

[0087] To better illustrate the present invention, further examples and application examples are provided below.

[0088] Example 1 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1. Place 100g of modified asphalt with a softening point of 180℃ into a radio frequency plasma reactor. First, introduce a mixed gas of Ar and O2 (flow rate of 100 sccm), with the volume fraction of O2 in the mixed gas being 5%. Then, evacuate to 10 Pa, start the radio frequency power supply (power 100W), and heat to 250℃ at a rate of 3℃ / min for primary oxidation. After 60 min, turn off the radio frequency power supply and heat to 300℃ at a rate of 2℃ / min. Add 1.0g of acetylacetone titanium oxide for secondary oxidation. Synchrotron infrared real-time lock at 3400 cm⁻¹. -1 -OH characteristic peak, after 61 min, pre-oxidized coal tar pitch with an oxygen group content of 19.0 at% was obtained.

[0089] It should be noted that infrared detection can detect various oxygen-containing groups such as -OH, -COOH, and C=O, with -OH being the most prevalent, and the detection range is 3400 cm⁻¹. -1 The -OH characteristic peak is the easiest to identify, and the hydroxyl content is also highly linearly correlated with the total oxygen content. Therefore, monitoring -OH can represent the total oxygen content.

[0090] S2. Place the pre-oxidized coal tar pitch into a tubular furnace, first evacuate to 500 Pa, then backfill with N2 (flow rate of 80 sccm) until the absolute pressure is 1.0 kPa, heat to 650 °C at a rate of 8 °C / min for primary negative pressure carbonization, hold for 1.5 h, then heat to 850 °C at a rate of 5 °C / min for secondary negative pressure carbonization, hold for 3 h, then crush and pass through a 200 mesh sieve to obtain carbonized pitch.

[0091] S3. In a tubular furnace, add 15g of activator (potassium carbonate and sodium carbonate in a mass ratio of 1.5:1) to 100g of carbonized pitch, evacuate to 600Pa, introduce CO2 to 8MPa, heat to 220℃ at a rate of 4℃ / min, and melt mix at 600rpm for 2h; then introduce N2 (flow rate of 70sccm) and supercritical CO2 (flow rate of 5sccm), heat to 650℃ at a rate of 2℃ / min for primary activation, hold for 1.5h; then heat to 860℃, introduce supercritical CO2 (flow rate of 18sccm) and O2 (flow rate of 2sccm) for secondary activation, hold for 2h, cool N2 to room temperature, crush, pass through a 300-mesh sieve, wash, and vacuum dry to obtain porous carbon.

[0092] S4. The porous carbon was placed in a magnetically confined plasma deposition furnace, and N2 (flow rate of 100 sccm) was introduced. It was pretreated at 450°C for 60 min to remove moisture from the porous carbon. Then, the temperature was lowered to 350°C, an axial magnetic field of 0.3T was applied, and SiH4 and Ar with a volume ratio of 1:12 were introduced. The radio frequency power supply (power of 70W) was turned on to carry out plasma deposition. LIBS+QCM linkage was used for monitoring. After 3 h, silicon-loaded carbon material with a silicon content of 57.0 wt% was obtained.

[0093] S5. Place the silicon-supported carbon material in an electrochemical vapor furnace, introduce Ar (flow rate 50 sccm), and heat to 600℃ at a rate of 0.5℃ / min. Perform in-situ electrochemical pulse oxidation under a constant voltage pulse of +1.2V (20s / cycle), purge with Ar for 40s, cycle 30 times, and lock the SiO content to 22.0wt% in situ using Raman spectroscopy. Then switch the voltage to -0.8V, introduce H2 (flow rate 5 sccm) for reduction reaction, and after 10min, cool Ar to room temperature to obtain SiO-coated silicon-supported carbon material (SiO coating thickness is 3.0nm).

[0094] S6. Place the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introduce N2 (flow rate of 250 sccm), and heat to 700℃ at a rate of 10℃ / min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 25:1:2, with a total flow rate of 120 sccm, and form a dense sub-outer layer after 25 min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 5:1:1, with a total flow rate of 200 sccm, and form a buffer outer layer after 25 min; cool the N2 to room temperature to obtain the silicon-carbon anode material.

[0095] Example 2 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1. Place 100g of modified asphalt with a softening point of 120℃ into a radio frequency plasma reactor. First, introduce a mixed gas of Ar and O2 (flow rate of 60 sccm), with the volume fraction of O2 in the mixed gas being 18%. Then, evacuate to 8 Pa, start the radio frequency power supply (power 90W), and heat to 240℃ at a rate of 2.5℃ / min for primary oxidation. After 50 min, turn off the radio frequency power supply and heat to 280℃ at a rate of 1.5℃ / min. Add 0.8g of acetylacetone titanium oxide for secondary oxidation. Synchrotron infrared real-time lock at 3400 cm⁻¹. -1 -OH characteristic peak, after 52 min, pre-oxidized coal tar pitch with an oxygen group content of 18.8 at% was obtained.

[0096] S2. Place the pre-oxidized coal tar pitch into a tubular furnace, first evacuate to 480 Pa, then backfill with N2 (flow rate of 70 sccm) until the absolute pressure is 0.9 kPa, heat to 550 °C at a rate of 7 °C / min for primary negative pressure carbonization, hold for 2 h, then heat to 800 °C at a rate of 4 °C / min for secondary negative pressure carbonization, hold for 3.8 h, then crush and pass through a 200-mesh sieve to obtain carbonized asphalt.

[0097] S3. In a tubular furnace, add 12g of activator (potassium carbonate and sodium carbonate in a mass ratio of 1.1:1) to 100g of carbonized pitch, evacuate to 50Pa, introduce CO2 to 7MPa, heat to 155℃ at a rate of 3℃ / min, and melt mix at 600rpm for 1.7h; then introduce N2 (flow rate of 60sccm) and supercritical CO2 (flow rate of 6sccm), heat to 550℃ at a rate of 1.5℃ / min for primary activation, hold for 1.2h; then heat to 800℃, introduce supercritical CO2 (flow rate of 17.5sccm) and O2 (flow rate of 2.5sccm) for secondary activation, hold for 1.8h, cool N2 to room temperature, crush, pass through a 300-mesh sieve, wash, and vacuum dry to obtain porous carbon.

[0098] S4~S5 are the same as S4~S5 in Example 1, and will not be described again.

[0099] S6. Place the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introduce N2 (flow rate of 235 sccm), and heat to 680℃ at a rate of 8℃ / min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 23:1:1.8, with a total flow rate of 110 sccm, and form a dense sub-outer layer after 23 min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 4.5:1:0.7, with a total flow rate of 190 sccm, and form a buffer outer layer after 27 min; cool the N2 to room temperature to obtain the silicon-carbon anode material.

[0100] Example 3 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1. Place 100g of modified asphalt with a softening point of 250℃ into a radio frequency plasma reactor. First, introduce a mixed gas of Ar and O2 (flow rate of 160 sccm), with the volume fraction of O2 in the mixed gas being 10%. Then, evacuate to 12 Pa, start the radio frequency power supply (power 110W), and heat to 260℃ at a rate of 3.5℃ / min for primary oxidation. After 70 min, turn off the radio frequency power supply and heat to 320℃ at a rate of 2.5℃ / min. Add 1.2g of acetylacetone titanium oxide for secondary oxidation. Synchrotron infrared real-time lock at 3400 cm⁻¹. -1-OH characteristic peak, after 69 min, pre-oxidized coal tar pitch with an oxygen group content of 19.2 at% was obtained.

[0101] S2~S6 are the same as S2~S6 in Example 1, and will not be described again.

[0102] Example 4 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1 is the same as S1 in Example 1, and will not be described again.

[0103] S2. Place the pre-oxidized coal tar pitch into a tubular furnace, first evacuate to 520 Pa, then backfill with N2 (flow rate of 90 sccm) until the absolute pressure is 1.1 kPa, heat to 720 °C at a rate of 10 °C / min for primary negative pressure carbonization, hold for 1 h, then heat to 950 °C at a rate of 6 °C / min for secondary negative pressure carbonization, hold for 2 h, then crush and pass through a 200-mesh sieve to obtain carbonized pitch.

[0104] S3. In a tubular furnace, add 20g of activator (potassium carbonate and sodium carbonate in a mass ratio of 2:1) to 100g of carbonized pitch, evacuate to 900Pa, introduce CO2 to 9MPa, heat to 225℃ at a rate of 5℃ / min, and melt mix at 600rpm for 2.3h; then introduce N2 (flow rate of 80sccm) and supercritical CO2 (flow rate of 4sccm), heat to 720℃ at a rate of 2.5℃ / min for primary activation, hold for 2h; then heat to 950℃, introduce supercritical CO2 (flow rate of 19.1sccm) and O2 (flow rate of 0.9sccm) for secondary activation, hold for 2.5h, cool N2 to room temperature, crush, pass through a 300-mesh sieve, wash, and vacuum dry to obtain porous carbon.

[0105] S4. The porous carbon was placed in a magnetically confined plasma deposition furnace, and N2 (flow rate of 90 sccm) was introduced. It was pretreated at 440℃ for 70 min to remove moisture from the porous carbon. Then, the temperature was lowered to 340℃, an axial magnetic field of 0.35T was applied, and SiH4 and Ar with a volume ratio of 1:18 were introduced. The radio frequency power supply (power of 62W) was turned on for plasma deposition. LIBS+QCM linkage was used for monitoring. After 2.5 h, silicon-supported carbon material with a silicon content of 56.5 wt% was obtained.

[0106] S5~S6 are the same as S5~S6 in Example 1, and will not be described again.

[0107] Example 5 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1~S3 are the same as S1~S3 in Example 1, and will not be described again.

[0108] S4. The porous carbon was placed in a magnetically confined plasma deposition furnace, and N2 (flow rate of 110 sccm) was introduced. It was pretreated at 460°C for 50 min to remove moisture from the porous carbon. Then, the temperature was lowered to 360°C, an axial magnetic field of 0.25T was applied, and SiH4 and Ar with a volume ratio of 1:6 were introduced. The radio frequency power supply (power of 78W) was turned on for plasma deposition. LIBS+QCM linkage was used for monitoring. After 3.5 h, silicon-loaded carbon material with a silicon content of 57.5 wt% was obtained.

[0109] S5~S6 are the same as S5~S6 in Example 1, and will not be described again.

[0110] Example 6 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1~S4 are the same as S1~S4 in Example 1, and will not be described again.

[0111] S5. The silicon-supported carbon material was placed in an electrochemical vapor furnace, and Ar (flow rate of 45 sccm) was introduced. The temperature was increased to 580℃ at a rate of 0.4℃ / min. In-situ electrochemical pulse oxidation was performed under a constant voltage pulse of +1.1V (22s / time). Ar was purged for 40s and the cycle was repeated 28 times. The in-situ Raman lock-in SiO content was 21wt%. Then the voltage was switched to -0.7V, and H2 (flow rate of 4.5 sccm) was introduced to carry out the reduction reaction. After 12min, Ar was cooled to room temperature to obtain SiO-coated silicon-supported carbon material (SiO coating thickness of 2.7nm).

[0112] S6. Place the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introduce N2 (flow rate of 270 sccm), and heat to 720℃ at a rate of 12℃ / min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 27:1:2.2, with a total flow rate of 130 sccm, and form a dense sub-outer layer after 27 min; then control the flow ratio of C2H2, B(CH3)3 and NH3 to 5.5:1:1.3, with a total flow rate of 210 sccm, and form a buffer outer layer after 23 min; cool the N2 to room temperature to obtain the silicon-carbon anode material.

[0113] Example 7 This embodiment provides a method for preparing a silicon-carbon anode material, including the following steps: S1~S4 are the same as S1~S4 in Example 1, and will not be described again.

[0114] S5. The silicon-supported carbon material was placed in an electrochemical vapor furnace, and Ar (flow rate of 55 sccm) was introduced. The temperature was increased to 620℃ at a rate of 0.6℃ / min. In-situ electrochemical pulse oxidation was performed under a constant voltage pulse of +1.3V (18s / time). Ar was purged for 40s and the cycle was repeated 32 times. The in-situ Raman lock-in SiO content was 23wt%. Then the voltage was switched to -0.9V, and H2 (flow rate of 5.5 sccm) was introduced to carry out the reduction reaction. After 8min, Ar was cooled to room temperature to obtain SiO-coated silicon-supported carbon material (SiO coating thickness of 3.3nm).

[0115] S6 is the same as S6 in Example 1, and will not be described again.

[0116] Comparative Example 1 This comparative example provides a method for preparing silicon-carbon anode material (traditional liquid-phase hydrogen peroxide oxidation), including the following steps: S1. Place 100g of modified pitch with a softening point of 180℃ into a reactor, introduce N2 (flow rate of 50sccm), heat to 300℃ at a rate of 5℃ / min, add 30mL of 30wt% hydrogen peroxide, and after 60min of oxidation reaction, obtain pre-oxidized coal tar pitch with an oxygen group content of 18.0at%.

[0117] S2~S6 are the same as S2~S6 in Example 1, and will not be described again.

[0118] Comparative Example 2 This comparative example provides a method for preparing silicon-carbon anode materials (retaining only simple volatilization, without secondary negative pressure carbonization or supercritical CO2 melting and mixing), including the following steps: S1 is the same as S1 in Example 1, and will not be described again.

[0119] S2. Place the pre-oxidized coal tar pitch into a tubular furnace, first evacuate to 500Pa, then backfill with N2 (flow rate of 80sccm) to an absolute pressure of 1.0kPa, heat to 650℃ at a rate of 8℃ / min for primary negative pressure carbonization, hold for 1.5h, then crush and pass through a 200-mesh sieve to obtain carbonized pitch.

[0120] S3. In a tubular furnace, add 15g of activator (potassium carbonate and sodium carbonate in a mass ratio of 1.5:1) to 100g of carbonized pitch, and introduce N2 (flow rate of 70sccm) and supercritical CO2 (flow rate of 5sccm). Heat to 650℃ at a rate of 2℃ / min for primary activation. After holding at this temperature for 1.5h, cool the N2 to room temperature, crush, pass through a 300-mesh sieve, wash, and vacuum dry to obtain porous carbon.

[0121] S4~S6 are the same as S4~S6 in Example 1, and will not be described again.

[0122] Comparative Example 3 This comparative example provides a method for preparing silicon-carbon anode materials (conventional mechanical mixing + high-temperature activation), including the following steps: S1~S2 are the same as S1~S2 in Example 1, and will not be described again.

[0123] S3. In a tube furnace, add 15g of activator (potassium carbonate and sodium carbonate in a mass ratio of 1.5:1) to 100g of carbonized pitch and mix at 600rpm for 30min. Then, introduce N2 (flow rate of 75sccm) and activate at 850℃ for 3.5h. Cool the N2 to room temperature, crush, pass through a 300-mesh sieve, wash, and vacuum dry to obtain porous carbon.

[0124] S4~S6 are the same as S4~S6 in Example 1, and will not be described again.

[0125] Comparative Example 4 This comparative example provides a method for preparing silicon-carbon anode materials (traditional gas-phase pulse oxidation, without voltage regulation), including the following steps: S1~S4 are the same as S1~S4 in Example 1, and will not be described again.

[0126] S5. Place the silicon-supported carbon material in an electrochemical vapor furnace, introduce Ar (flow rate 50 sccm), heat to 600℃ at a rate of 0.5℃ / min, introduce O2 (flow rate 5 sccm) for 20s for vapor-phase pulse oxidation, purge with Ar for 40s, and cycle 30 times; then introduce H2 (flow rate 5 sccm) for reduction reaction for 10min, and cool Ar to room temperature to obtain SiO-coated silicon-supported carbon material.

[0127] S6 is the same as S6 in Example 1, and will not be described again.

[0128] Comparative Example 5 This comparative example provides a method for preparing a silicon-carbon anode material (two-step boron-nitrogen co-doping coating), including the following steps: S1~S5 are the same as S1~S5 in Example 1, and will not be described again.

[0129] S6. Place the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introduce N2 (flow rate 250 sccm), and heat to 700℃ at a rate of 10℃ / min; control the flow ratio of C2H2 and B(CH3)3 to be 25:1, with a total flow rate of 120 sccm. After 25 min, a dense sub-outer layer is formed. Then transfer to another furnace, introduce N2 (flow rate 250 sccm), and heat to 700℃ at a rate of 10℃ / min; control the flow ratio of C2H2, B(CH3)3, and NH3 to be 5:1:1, with a total flow rate of 200 sccm. After 25 min, a buffer outer layer is formed; cool the N2 to room temperature to obtain the silicon-carbon anode material.

[0130] Verification test The performance of the silicon-carbon anode materials provided in Examples 1-7 and Comparative Examples 1-5 was tested respectively, and the results are shown in Table 1.

[0131] The preparation method of 2032 coin cells includes the following steps: S100. Each silicon-carbon anode material is compounded with graphite at a mass ratio of 1:9 to obtain anode samples.

[0132] S200: Mix the negative electrode sample, Super C and polyvinylidene fluoride (PVDF) at a mass ratio of 95.5:2.5:2, and dilute with N-methylpyrrolidone (NMP) to form a uniform slurry.

[0133] S300: The slurry is coated onto copper foil and dried at 80°C for 12 hours to serve as the working electrode.

[0134] The S400, using a lithium metal sheet as the counter electrode and a Celgard 2500 separator, was assembled together with the working electrode in an Ar-filled glove box to obtain the CR2016 coin cell. The electrolyte was a 1 mol / L LiPF6 solution dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 1:1:1), with 0.04 mL of electrolyte used per cell.

[0135] 2032 coin cell performance test: Test charging and discharging conditions: In the 0~2.0V range, first apply a constant current of 0.1C to 2.0V, then apply a constant voltage of 2.0V until the current is less than 0.02C. After 2 cycles, change to 1.0CC / 1.0CD and continue the cycle for 200 cycles before removing the tamper.

[0136] Characterization methods for each parameter: (1) Residual Ti content in porous carbon (ppm): The Ti content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). After the sample was digested by microwave, the intensity of the characteristic spectral lines of Ti was detected, and the residual content was calculated by combining the calibration curve. The detection accuracy was ±1ppm.

[0137] (2) Silicon content (wt%) in silicon-supported carbon materials: Laser-induced breakdown spectroscopy (LIBS) combined with inductively coupled plasma spectroscopy (ICP) was used for calibration. LIBS was used to detect the characteristic spectral line of Si (288.16nm) in real time, and ICP was used for offline calibration. The detection accuracy was ±0.1wt%.

[0138] (3) Uniformity of silicon deposition in silicon-supported carbon materials (%): Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to select 5 different regions to detect the uniformity of Si element distribution, calculate the uniformity percentage, and the detection accuracy was ±0.1%.

[0139] (4) The proportion of SiO in the SiO-coated silicon-supported carbon material (%): determined by in-situ Raman spectroscopy, detecting the characteristic peak of SiO (500 cm⁻¹). -1 ~550cm -1 ) and Si characteristic peak (520cm) -1 The strength ratio of SiO2 is calculated by combining the calibration curve, and the detection accuracy is ±0.5%.

[0140] (5) Thickness of SiO coating layer in SiO-coated silicon-supported carbon material (nm): 20 SiO-coated silicon-supported carbon material particles were randomly selected by transmission electron microscopy (TEM) to measure the coating layer thickness and take the average value. The measurement accuracy was ±0.1nm.

[0141] (6) Initial Coulombic Efficiency (%): Using the Blue Battery Testing System, CR2032 coin cells were assembled. The ratio of the initial charge and discharge capacity at 0.1C rate is the initial coulombic efficiency, with a test accuracy of ±0.1%.

[0142] (7) Capacity retention rate after 200 cycles (%): The ratio of the discharge capacity after the 200th cycle to the discharge capacity after the first cycle is obtained by using the Blue Battery test system at 0.5C rate for 200 cycles. The test accuracy is ±0.1%.

[0143] (8) Volume expansion rate (%): The volume change of the battery before and after charging and discharging was determined by the water displacement method. The volume expansion rate = (volume after lithium intercalation - volume before lithium intercalation) / volume before lithium intercalation × 100%, with a test accuracy of ±0.1%.

[0144] Table 1. Performance test results of silicon-carbon anode materials and 2032 coin cells in the examples and comparative examples.

[0145] The results in the table above show that the Ti residue in the silicon-carbon anode material provided by this invention is ≤40 ppm, the silicon content is stable at 56.5wt%~57.5wt%, the silicon deposition uniformity is 98.2%~98.6%, the SiO ratio is stable at 21.0%~23.0%, and the SiO coating thickness is controlled at 2.7nm~3.3nm, demonstrating the advantage of "precise parameter control throughout the entire process" of this invention. The initial coulombic efficiency of the 2032 coin cell provided by this invention is 92.6%~93.2%, the capacity retention rate after 200 cycles is 88.0%~89.2%, and the volume expansion rate is 13.7%~14.5%, proving that the process of this invention has extremely strong stability and parameter tolerance, and can achieve stable industrial mass production.

[0146] Example 4 (the holding time for supercritical secondary activation was extended to 2.5 h) reduced Ti residue to 30 ppm, with the best performance in all aspects (first-time efficiency 93.2%, cycle retention rate 89.2%, volume expansion rate 13.7%), verifying the effectiveness of supercritical gradient activation in the final removal of titanium-containing sensitizers.

[0147] In Comparative Example 1, the silicon content and SiO ratio of the silicon-carbon anode material were reduced, and the SiO coating layer was thickened and uneven. Compared with Example 1, the first efficiency and cycle retention rate were significantly reduced, and the volume expansion rate was increased. This proves that the radio frequency oxygen plasma oxidation + precise oxygen group control provided by the present invention is superior to the traditional liquid phase oxidation, and can improve the uniformity of silicon deposition and material performance.

[0148] The silicon-carbon anode material in Comparative Example 2 had a Ti residue as high as 180 ppm, and its performance in terms of first-time efficiency, cycle retention rate, and volume expansion rate was the worst. This proves that the three-step in-situ self-removal process of titanium-containing sensitizer provided by this invention is the key to solving the problem of impurity residue and improving material performance.

[0149] In Comparative Example 3, the silicon content of the silicon-carbon anode material decreased, the SiO coating thickness increased, and the cycle retention rate and silicon deposition uniformity decreased. This demonstrates that the supercritical CO2 melt mixing + gradient activation provided by this invention can achieve uniform penetration of the activator and precise pore formation, which is superior to conventional activation processes.

[0150] The SiO content (18.3%) of the silicon-carbon anode material in Comparative Example 4 was relatively low, resulting in a significant decrease in first-efficiency and cycle retention rates, and a significant increase in volume expansion rate. This demonstrates that the in-situ electrochemical pulse oxidation-reduction provided by this invention can achieve precise control of the SiO coating layer, resulting in better buffering effect and stronger structural stability.

[0151] The carbon coating layer of the silicon-carbon anode material in Comparative Example 5 was uneven, resulting in a decrease in first-efficiency and cycle retention rates and an increase in volume expansion rate. This demonstrates that the one-step boron-nitrogen co-doped gradient carbon coating method provided by this invention is superior to the two-step splicing process, which can improve the bonding force between the carbon layer and the SiO-coated silicon-loaded carbon material, thereby enhancing conductivity and stability.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon, characterized by: Includes the following steps: S1. Under radio frequency plasma conditions, the modified pitch is subjected to primary oxidation at 240℃~260℃, and then the temperature is raised to 280℃~320℃. A titanium-containing sensitizer is added for secondary oxidation to obtain pre-oxidized coal tar pitch. S2. The pre-oxidized coal tar pitch is subjected to primary negative pressure carbonization at 500℃~750℃, and then the temperature is raised to 800℃~1000℃ for secondary negative pressure carbonization to obtain carbonized pitch. S3. Add an activator to the carbonized asphalt, and introduce CO2 to 5MPa~10MPa for melting and mixing; then introduce N2 and supercritical CO2 for primary activation at 500℃~750℃; then raise the temperature to 800℃~1000℃ and introduce supercritical CO2 and O2 for secondary activation to obtain porous carbon.

2. The method for producing porous carbon according to claim 1, wherein: In S1, the oxygen group content in the pre-oxidized coal tar pitch is 18.8 at%~19.2 at%; In S1, the softening point of the modified asphalt is 100℃~280℃; in S3, the melting and mixing temperature is 30℃~50℃ higher than the softening temperature of the modified asphalt in S1. In S1, the titanium-containing sensitizer includes titanium acetylacetonate, and the mass ratio of the titanium-containing sensitizer to the modified asphalt is (0.6~1.5):100; In S3, the activator comprises potassium carbonate and sodium carbonate in a mass ratio of (1.1~2):1, and the mass ratio of carbonized pitch to activator is 1:(1~3).

3. The method for preparing porous carbon according to claim 1, wherein: In S1, the first-stage oxidation step includes: placing the modified asphalt into a radio frequency plasma reactor, first introducing a mixed gas of Ar and O2, wherein the volume fraction of O2 in the mixed gas is 5%~20%, then evacuating to 8Pa~12Pa, and then heating to 240℃~260℃ for first-stage oxidation; In S1, the conditions for the first-stage oxidation include: a radio frequency power supply of 80W~120W, a temperature increase to 240℃~260℃ at a rate of 2.5℃ / min~3.5℃ / min, and a reaction time of 50min~70min; the conditions for the second-stage oxidation include: a temperature increase to 280℃~320℃ at a rate of 1.5℃ / min~2.5℃ / min, and a reaction time of 50min~70min. In S3, during the first-stage activation, the flow rate of N2 is 60 sccm to 80 sccm, and the flow rate of supercritical CO2 is 4 sccm to 6 sccm; during the second-stage activation, the flow rate of supercritical CO2 is 17.5 sccm to 19.1 sccm, and the flow rate of O2 is 0.9 sccm to 2.5 sccm.

4. The method for producing porous carbon according to any one of claims 1 to 3, wherein: S2 specifically includes the following steps: heating the pre-oxidized coal tar pitch to 500℃~750℃ at a rate of 7℃ / min~10℃ / min for primary negative pressure carbonization, holding for 1h~2h, then heating to 800℃~1000℃ at a rate of 4℃ / min~6℃ / min for secondary negative pressure carbonization, holding for 2h~4h, to obtain the carbonized asphalt; S3 specifically includes the following steps: adding an activator to the carbonized asphalt, charging CO2 to 7MPa~9MPa, heating to 140℃~320℃ at a rate of 3℃ / min~5℃ / min, and performing melt mixing for 1.7h~2.3h; then introducing N2 and supercritical CO2, heating to 500℃~750℃ at a rate of 1.5℃ / min~2.5℃ / min for primary activation, and holding at this temperature for 1h~2h; then heating to 800℃~1000℃, introducing supercritical CO2 and O2 for secondary activation, and holding at this temperature for 1.7h~2.5h to obtain the porous carbon.

5. A porous carbon, characterized in that: It is prepared by the method for preparing porous carbon according to any one of claims 1 to 4.

6. A method for preparing a silicon-carbon anode material, characterized in that: Includes the following steps: S4. Under magnetically confined plasma conditions, the porous carbon described in claim 5 is subjected to silicon deposition to obtain a silicon-supported carbon material. S5. Under an inert atmosphere, at 580℃~620℃ and constant voltage pulse, the silicon-supported carbon material is subjected to in-situ electrochemical pulse oxidation; then, the reverse voltage is switched and H2 is introduced to carry out a reduction reaction to obtain SiO-coated silicon-supported carbon material. S6. By controlling the flow rates of C2H2, B(CH3)3 and NH3, the SiO-coated silicon-supported carbon material is subjected to boron-nitrogen co-doping gradient carbon coating to sequentially form a dense sub-outer layer and a buffer outer layer, thereby obtaining a silicon-carbon anode material.

7. The method for preparing the silicon-carbon anode material as described in claim 6, characterized in that: In S4, the silicon content in the silicon-supported carbon material is 56.5 wt% to 57.5 wt%. In S5, the SiO content in the SiO-coated silicon-supported carbon material is 21wt%~23wt%, and the thickness of the SiO coating layer is 2.5nm~3.5nm.

8. The method for preparing the silicon-carbon anode material as described in claim 6, characterized in that: In S4, the silicon deposition step includes: placing the porous carbon into a deposition furnace, applying an axial magnetic field, introducing SiH4 and Ar in a volume ratio of 1:(4~20), and turning on the radio frequency power supply to perform silicon deposition; the magnetic confinement plasma conditions for silicon deposition include: the power of the radio frequency power supply is 60W~80W, the strength of the axial magnetic field is 0.25T~0.35T, the temperature is 340℃~360℃, and the deposition time is 2.5h~3.5h; In S5, the voltage of the constant voltage pulse is +1.1V to +1.3V, the pulse time is 18s / time to 22s / time, and the cycle is 28 to 32 times; the voltage of the reduction reaction is -0.7V to -0.9V, and the reduction reaction time is 8min to 12min.

9. The method for preparing the silicon-carbon anode material according to any one of claims 6 to 8, characterized in that: In S6, the specific steps of the gradient carbon coating include: placing the SiO-coated silicon-supported carbon material into a vapor-phase self-assembly furnace, introducing N2, and heating it to 680℃~720℃ at a rate of 8℃ / min~12℃ / min; then controlling the flow ratio of C2H2, B(CH3)3 and NH3 to be (23~27):1:(1.8~2.2), with a total flow rate of 110sccm~130sccm, and forming a dense sub-outer layer after 23min~27min; then controlling the flow ratio of C2H2, B(CH3)3 and NH3 to be (4.5~5.5):1:(0.7~1.3), with a total flow rate of 190sccm~210sccm, and forming a buffer outer layer after 23min~27min; and cooling with N2 to obtain the silicon-carbon anode material.

10. A silicon-carbon anode material, characterized in that: It is prepared by the method for preparing silicon-carbon anode material according to any one of claims 6 to 9.

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