A method for directional preparation of porous carbon for silicon-carbon negative electrode and application

Abstract

The application relates to the technical field of lithium ion battery negative electrode material preparation, and discloses a directional preparation method and application of porous carbon for a silicon-carbon negative electrode, which comprises the following steps: S1, adding a carbon source and a binder, stirring and mixing, and filtering to obtain a directional composite blank; S2, directional compression molding to obtain a directional molded blank; S3, high-temperature carbonization under the protection of an inert atmosphere to obtain a carbonized blank; S4, high-temperature activation under the protection of an inert atmosphere to obtain an activated porous blank; S5, chemical vapor deposition to obtain a carbon-coated porous blank; and S6, obtaining a silicon-carbon negative electrode porous carbon finished product. The precursor is forced to be oriented and formed through a mold with a directional guide structure, the template agent particles are regularly arranged along the preset direction, the template agent is etched and removed after carbonization and shaping, the silicon-carbon negative electrode material with directional through macro-pore channels is obtained, and the problems of a narrow process window, high sensitivity of pore structure to freezing conditions and difficult large-scale production are solved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material preparation technology, specifically to a method for the directional preparation and application of porous carbon for silicon-carbon anodes. Background Technology

[0002] Silicon-carbon anode materials have become key materials for next-generation high-energy-density lithium-ion batteries due to silicon's theoretical specific capacity being far higher than that of graphite. However, silicon undergoes dramatic volume expansion during charge and discharge, leading to material pulverization and electrode structure damage. To address this issue, the industry typically disperses nano-silicon within a porous carbon matrix, utilizing the pores to buffer volume strain. The oriented pores not only provide low-torsion ion transport paths to improve rate capability but also offer anisotropic buffering space for volume expansion, preventing stress concentration. Therefore, achieving the oriented fabrication of pore structures is a key technological direction for synergistically improving the capacity, rate capability, and cycle stability of silicon-carbon anodes.

[0003] Existing technologies mainly employ the ice crystal template method to prepare oriented porous carbon, which utilizes temperature gradients to induce oriented ice crystal growth as a sacrificial template, followed by freeze-drying and carbonization to obtain oriented channels. However, the problem is that the morphology of ice crystal growth is extremely sensitive to freezing conditions, resulting in a narrow process window, poor batch-to-batch consistency, and difficulty in obtaining stable and controllable oriented structures. At the same time, the freeze-drying process is time-consuming and energy-intensive, fundamentally limiting the large-scale industrial application of this technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for the directional preparation and application of porous carbon for silicon-carbon anodes, solving the problems of narrow process window, high sensitivity of pore structure to freezing conditions, and difficulty in scale-up production.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for the directional preparation and application of porous carbon for silicon-carbon anodes, comprising the following steps: S1, Precursor preparation: Nano-silicon powder is selected as the silicon source, purified and mixed with a directional template agent, a dispersant is added and ball milled to obtain a directional template precursor; then a carbon source and binder are added, stirred and mixed, and filtered to obtain a directional composite preform; S2, Oriented Forming: The oriented composite preform obtained in S1 is placed in a mold with an oriented guiding structure and orientedly pressed to obtain an oriented preform; S3, carbonization treatment: The oriented preform obtained in S2 is first pre-fired at low temperature under inert atmosphere protection to obtain a pre-fired preform; then carbonized at high temperature under inert atmosphere protection to obtain a carbonized preform. S4, Pore Forming and Activation: The carbonized preform obtained in S3 is immersed in an etchant to remove the template agent. After washing, a porous preform is obtained. The porous preform is then mixed with an activator and activated at high temperature under an inert atmosphere to obtain an activated porous preform. S5, Carbon coating treatment: The activated porous preform obtained in S4 is subjected to chemical vapor deposition in an atmosphere containing carbon gas source and carrier gas to obtain a carbon-coated porous preform. S6, Washing and Drying: The carbon-coated porous preform obtained in S5 is washed and dried to obtain the silicon-carbon anode porous carbon product.

[0006] By adopting the above technical solution, and using solid nano-oxides as directional templates, combined with the precursor design using polyolefin waste plastics as carbon sources, a material foundation is laid for subsequent mechanical forced orientation and waste plastic resource utilization. This achieves the effect of directional control of pore structure and significant reduction in raw material costs.

[0007] Preferably, in step S1, the directional template agent is a nano-oxide with a particle size of 30-100 nm; The mass ratio of nano-silica powder to directional template agent is 1:0.3-0.8; The dispersant is a mixture of ethanol and deionized water, with a volume ratio of ethanol to deionized water of 1:1-2:1. The amount of dispersant added is 1.5-3 times the total mass of the nano-silica powder and the directional template agent. The ball mill speed is 200-300 rpm, the ball milling time is 1-2 hours, and the ball-to-material ratio is 5:1-10:1.

[0008] By adopting the above technical solution, the particle size of the nano-oxide template agent and the process parameters of ball milling dispersion are limited, thus ensuring that the template agent particles are uniformly dispersed in the precursor and form uniform composite particles with nano-silicon powder. This avoids the channel defects caused by template agent agglomeration and achieves the effect of uniform channel distribution and consistent orientation.

[0009] Preferably, in step S1, the carbon source is polyolefin waste plastic, which is added after being crushed to a particle size of 50-200μm, and the mass ratio of the carbon source to the directional template precursor is 1:1.2-2.0; the binder is a mixture of cellulose ether and styrene-butadiene rubber binder, and the amount added is 3-8% of the total mass of the directional template precursor and the carbon source.

[0010] By adopting the above technical solution, and using polyolefin waste plastics as a carbon source and a specific ratio of mixed binder, the problem of waste plastic resource utilization is solved, and the mixture is guaranteed to have good formability in subsequent compression molding, thus achieving the effect of suitable green strength and effective solidification of waste.

[0011] Preferably, in step S2, the directional guiding structure of the mold is a parallel arrangement of strip grooves; the directional pressing pressure is 5-15 MPa, and the temperature is 60-100℃.

[0012] By adopting the above technical solution, and using a mold with parallel strip grooves, and pressing and molding under specific temperature and pressure, the macroscopic orientation structure of the mold is forced to be replicated inside the blank by mechanical force, replacing the traditional ice crystal template method that relies on temperature gradient to induce orientation. This achieves a stable process and macroscopic orientation channel prefabrication effect that is not affected by environmentally sensitive factors.

[0013] Preferably, in step S3, the inert atmosphere is argon or nitrogen; the low-temperature pre-firing temperature is 200-350℃, and the holding time is 2-4h; the high-temperature carbonization temperature is 600-900℃, and the holding time is 1-4h.

[0014] By adopting the above technical solution, a low-temperature pre-calcination step is introduced before high-temperature carbonization, and a specific temperature window is set. This causes the polyolefin carbon source molecular chain to undergo thermo-oxidative stabilization and pre-crosslinking at this stage, forming a heat-resistant intermediate structure. This overcomes the technical bias of easy melting and flow at high temperatures, and achieves the effect that the carbon skeleton can still maintain the preset oriented pore structure completely under high-temperature treatment.

[0015] Preferably, in step S4, the etching agent is selected according to the type of directional template agent used in step S1: when the template agent is nano-alumina, an alkali metal hydroxide solution is selected; when the template agent is nano-silicon oxide, a hydrofluoric acid solution is selected.

[0016] By adopting the above technical solution, since the selection of the etchant precisely corresponds to the chemical properties of the template agent, the template agent can be removed efficiently and selectively while minimizing damage to the carbon skeleton and silicon active material, thus achieving the effect of clean and unobstructed macropore channels with high structural integrity.

[0017] Preferably, in step S4, the activator is an alkali metal hydroxide, and the mass ratio of the porous preform to the activator is 1:2-1:4; the high-temperature activation temperature is 700-900℃, and the holding time is 1-3h.

[0018] By adopting the above technical solution, after the macropores are formed by template elution, a chemical activation process is further introduced. Therefore, by utilizing the etching effect of alkali metal hydroxide, a large number of micropores and mesopores are generated in situ on the carbon wall surface of the macropores. This achieves a significant synergistic improvement in the tiered distribution of macropores, mesopores, and micropores, as well as the specific surface area and lithium storage active sites.

[0019] Preferably, in step S4, the high-temperature activation is carried out under an inert atmosphere, which is argon or nitrogen.

[0020] By adopting the above technical solution, since the activation process is carried out in an inert atmosphere throughout, the oxidation and ablation of the carbon skeleton at high temperature is effectively prevented, ensuring the stability and controllability of the activation and pore-forming process, and achieving the effect of abundant active sites and maintained structural strength.

[0021] Preferably, in step S5, the carbon-containing gas source is at least one of acetylene, methane, or ethylene, and the carrier gas is argon or nitrogen; the temperature of chemical vapor deposition is 700℃-1000℃, and the processing time is 0.5-4 hours.

[0022] By adopting the above technical solution, an amorphous carbon layer is deposited on the surface of the multi-level porous structure through vapor deposition. This effectively repairs the surface defects of the carbon skeleton that may be caused by the activation process and prevents direct contact between the electrolyte and the internal silicon, thus achieving the effect of first-time improvement in coulombic efficiency and enhanced cycle interface stability.

[0023] Preferably, in step S6, the washing is completed to neutral, and the drying temperature is 80-120°C.

[0024] By adopting the above technical solution, the porous preform after carbon coating is thoroughly washed and dried, thus completely removing impurities such as alkali metal ions and fluoride ions that may remain in the entire preparation process, and strictly controlling the moisture content of the finished product, resulting in high product purity and safe and stable storage and use.

[0025] This invention provides a method for the directional preparation and application of porous carbon for silicon-carbon anodes. It offers the following advantages: 1. This invention employs a solid nano-oxide template agent combined with a mold mechanical pressing and orientation technique. The precursor is forcibly oriented using a mold with a directional guiding structure, causing the template agent particles to align regularly along a preset direction. After carbonization and shaping, the template agent is etched away, resulting in a silicon-carbon anode material with directional, interconnected macropore channels. This technique achieves controllable pore orientation, high process stability, and insensitivity to environmental conditions. Compared to the existing ice crystal template method, which relies on temperature gradient-induced directional ice crystal growth, this invention solves the problems of narrow process window, high sensitivity of pore structure to freezing conditions, and difficulty in scaling up production.

[0026] 2. This invention employs a technical solution that uses polyolefin waste plastics as a carbon source and combines it with low-temperature pre-calcination stabilization treatment. A low-temperature pre-calcination step is introduced before high-temperature carbonization, causing the polyolefin molecular chains to undergo thermo-oxidative stabilization and pre-crosslinking, forming a heat-resistant intermediate structure. This maintains the shape of the green body and the orientation of internal particles during the subsequent high-temperature carbonization stage. This technical solution achieves the technical effect of converting waste plastics into high-quality oriented porous carbon skeletons while simultaneously realizing the resource utilization of waste. Compared to the existing technical bias that polyolefin plastics are unsuitable as a carbon source for porous carbon materials due to their tendency to melt and flow at high temperatures, this invention solves the problem of green body deformation and collapse during the carbonization process of waste plastics, which prevents the maintenance of the predetermined pore structure.

[0027] 3. This invention employs a two-stage tandem pore-forming technique of template elution and chemical activation coupled with chemical vapor deposition for carbon coating. First, solid template agent is selectively etched to remove the solid template agent to form directional macropores. Then, chemical activation is used to etch micropores and mesopores in situ on the pore wall. Finally, a uniform amorphous carbon coating layer is formed on the pore wall surface by chemical vapor deposition. This technique achieves the synergistic control of the distribution of macropores, mesopores, and micropores, and simultaneously repairs surface defects of the carbon skeleton. Compared with existing technologies where a single template method can only form macropores without micropores or mesopores, or a single activation method cannot construct directional through-holes, this invention solves the problems of single pore structure hierarchy, difficulty in balancing ion transport efficiency and lithium storage active sites, and large irreversible capacity loss caused by surface defects after activation. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the steps of a method for the directional preparation of porous carbon for silicon-carbon anodes according to the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see the appendix Figure 1 The technical solution of the present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited thereto: Example 1: This embodiment of the invention provides a method for the directional preparation of porous carbon for silicon-carbon anodes, comprising the following steps: S1: 50g of 80nm nano-silicon powder was selected and ultrasonically cleaned with 8wt% sodium hydroxide solution for 20min to remove the surface oxide layer. It was then repeatedly washed with deionized water until the pH of the filtrate reached 7, and dried at 70℃ for 5h to complete the purification process. The purified nano-silicon powder was mixed with 50nm nano-alumina template agent at a mass ratio of 1:0.5, i.e., the amount of template agent used was 25g. 150g of a mixed dispersant prepared with ethanol and deionized water at a volume ratio of 1.5:1 was added, and the mixture was placed in a planetary ball mill and ball-milled at 250rpm for 1.5h with a ball-to-material ratio of 8:1 to obtain a uniformly mixed directional template precursor.

[0031] The recycled low-density polyethylene waste plastic was crushed and sieved, and powder with a particle size of 100μm to 150μm was used as the carbon source. The above-mentioned oriented template precursor and polyolefin carbon source were mixed at a mass ratio of 1:1.5, i.e., the amount of carbon source used was 112.5g. Then, a mixed binder of CMC and SBR at a mass ratio of 1:1.5 was added, at a rate of 5% of the total mass of the precursor and carbon source, i.e., 9.4g. After stirring and mixing for 40 minutes, the mixture was filtered to obtain a density of 1.35g / cm³. 3 directional composite preform.

[0032] S2: The oriented composite preform is filled into a mold with parallel strip grooves. The grooves are 40 μm deep, 80 μm wide, and 150 μm apart. Oriented pressing is performed under 10 MPa pressure and 80°C for 20 min. After demolding, the oriented preform is obtained.

[0033] S3: The oriented preform is placed in a tube furnace, and 99.995% pure argon gas is introduced as a protective atmosphere at a flow rate of 80 ml / min. First, the temperature is increased to 280℃ at a rate of 3℃ / min and held for 3 hours for low-temperature pre-firing to allow the polyolefin carbon source to undergo thermal-oxidative stabilization. Then, the temperature is increased to 750℃ at a rate of 5℃ / min and held for 2 hours for high-temperature carbonization. After natural cooling, the carbonized preform is obtained.

[0034] S4: The carbonized preform was immersed in a 20wt% KOH solution and etched at 60℃ for 6 hours with stirring to remove the alumina template agent. It was repeatedly washed with deionized water until the pH of the filtrate reached 7. The washed porous preform was mixed with KOH powder at a mass ratio of 1:3 and placed in a tube furnace. Under argon protection, the temperature was increased to 800℃ at 3℃ / min and held for 2 hours for chemical activation. After cooling, the residual KOH was neutralized with dilute hydrochloric acid, and the preform was washed with deionized water until neutral to obtain the activated porous preform.

[0035] S5: The activated porous preform is placed in a CVD furnace, and a mixture of acetylene and argon gas with a volume flow rate ratio of 1:8 is introduced. The preform is treated at 850°C for 2 hours to deposit a uniform amorphous carbon coating layer on the pore wall surface.

[0036] S6: Wash the carbon-coated product thoroughly with deionized water and dry it at 100℃ for 8 hours to obtain the silicon-carbon anode porous carbon product.

[0037] The silicon-carbon anode porous carbon prepared by the method in this embodiment has internal channels that are oriented in the same direction as the pressing direction, with a total porosity of 68%; macropores account for approximately 15%, mesopores for approximately 40%, and micropores for approximately 45%; and the specific surface area reaches 2850 m². 2 / g, pore volume 1.8cm 3 / g. When tested as a negative electrode material for lithium-ion batteries, it showed a reversible specific capacity of 1680 mAh / g at a current density of 0.1 A / g, an initial coulombic efficiency of 82%, and a capacity retention of 91% after 100 cycles.

[0038] Example 2: This embodiment of the invention provides a method for the directional preparation of porous carbon for silicon-carbon anodes, comprising the following steps: S1: 60g of 50nm nano-silicon powder was selected, purified, and then mixed with 80nm nano-silica template agent at a mass ratio of 1:0.6, i.e., the amount of template agent used was 36g. The dispersant, ball milling, and other conditions were the same as in Example 1 to obtain a directional template precursor. High-density polyethylene waste plastic powder was used as the carbon source, and the mass ratio of carbon source to precursor was 1:1.8. The binder was added at 6% of the total mass, and the remaining steps were the same as in Example 1 to obtain a directional composite preform.

[0039] S2: The directional compression molding parameters are the same as in Example 1.

[0040] S3: The low-temperature pre-firing temperature is 300℃, and the holding time is 2.5h; the high-temperature carbonization temperature is 850℃, and the holding time is 1.5h. The rest is the same as in Example 1.

[0041] S4: The template agent is silicon dioxide, and the etchant is a 15wt% HF solution. The etching is carried out by stirring at 40℃ for 8 hours. After thorough washing, the porous preform is mixed with KOH at a mass ratio of 1:3.5 and activated at 850℃ for 1.5 hours.

[0042] S5: The carbon coating treatment parameters are the same as in Example 1.

[0043] S6: Washing and drying conditions are the same as in Example 1.

[0044] Example 3: This embodiment of the invention provides a method for the directional preparation of porous carbon for silicon-carbon anodes, comprising the following steps: S1: Nano-silicon powder with a particle size of 100nm and nano-alumina template agent were used at a mass ratio of 1:0.4. The carbon source was waste polypropylene plastic, and the mass ratio of carbon source to precursor was 1:1.3. The remaining conditions were the same as in Example 1.

[0045] S2: The pressing pressure is 12 MPa, and the temperature is 90°C. The rest is the same as in Example 1.

[0046] S3: Low-temperature pre-firing temperature 320℃, hold for 2 hours; high-temperature carbonization temperature 800℃, hold for 2 hours. The rest is the same as in Example 1.

[0047] S4: The template etching is the same as in Example 1; the activator dosage ratio is 1:2.5, the activation temperature is 780℃, and the holding time is 2.5h.

[0048] S5-S6: Same as Example 1.

[0049] Comparative Example 1: The oriented preform obtained in S2 was not subjected to low-temperature pre-firing. Instead, it was directly heated to 750°C at a rate of 5°C / min for carbonization. All other steps were the same as in Example 1.

[0050] Because it did not undergo a low-temperature pre-calcination stabilization treatment, the polyolefin carbon source experienced severe melting and flow during high-temperature carbonization, resulting in significant shrinkage and deformation of the green body. The oriented arrangement of the template agent formed by pressing was also disrupted. The final product did not exhibit a regular, oriented porous carbon structure; the pore orientation was disordered, and the specific surface area was only 1250 m². 2 / g. Under the same test conditions, its reversible specific capacity of 0.1A / g is only 1120mAh / g, and the capacity retention rate after 100 cycles is only 65%.

[0051] Comparative Example 2: Without adding nano-oxide template agent, purified nano-silicon powder was directly mixed with carbon source, pressed, carbonized, and then skipped the template etching step, directly proceeding to KOH activation and subsequent steps. The rest was the same as in Example 1.

[0052] Due to the lack of directional macropores provided by a template agent, the product, although possessing a high specific surface area of ​​approximately 2200 m², suffers from poor performance. 2 While the pore structure of this sample is composed entirely of micropores and mesopores generated by KOH activation, it lacks directional, interconnected macropores. Its rate performance is poor, with a capacity retention of only 42% at 2 A / g compared to 0.1 A / g, while Example 1 retains 68% of its capacity at the same rate. This indicates that directional macropore channels are crucial for the rapid transport of lithium ions.

[0053] Comparative Example 3: No chemical activation or carbon coating was performed. After etching and washing with the template agent, the product directly entered the drying step. The rest was the same as in Example 1.

[0054] The product mainly consists of macropores left after the template agent is removed, with a specific surface area of ​​only about 380 m². 2 / g. Although it has oriented channels, it lacks the large number of lithium storage active sites provided by micro-mesopores, and its reversible specific capacity is only about 850 mAh / g.

[0055] The performance differences between Examples 1-4 and Comparative Examples 1-3 will be further illustrated below with experimental examples: Example 1: Specific surface area detection, performed according to GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method", using a specific surface area and pore size analyzer. Weigh 0.1-0.5 g of the sample after vacuum degassing at 200℃ for 6 h, place it in a sample tube, and measure the adsorption-desorption isotherm within a relative pressure range at liquid nitrogen temperature using high-purity nitrogen as the adsorbate. Calculate the specific surface area within a relative pressure range of 0.05-0.30 using the BET equation. Perform the test in triplicate for each sample group, record the specific surface area value for each test, and take the average value as the sample's specific surface area. Judgment criterion: The specific surface area should reach 1000-3500 m². 2 The preset target value within the range of / g.

[0056] Example 2, pore volume and pore size distribution detection, was performed according to GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method" (in conjunction with BJH method and DFT method), using a specific surface area and pore size analyzer; Based on the adsorption-desorption isotherms obtained from specific surface area measurements, the BJH method was used to analyze the desorption branch data to obtain the mesopore size distribution, and the DFT method was used to analyze the adsorption branch data to obtain the pore size distribution and total pore volume across the entire pore size range. Each sample was tested in triplicate, and the total pore volume and the proportion of each pore size range were recorded for each test. The average value was taken as the sample's pore volume and pore size distribution results. Judgment criterion: The total pore volume should reach 0.8-2.5 cm³. 3 The preset target value is within the range of / g; the pore size distribution is as follows: micropores account for 35-55%, mesopores account for 30-45%, and macropores account for 10-20%.

[0057] Experiment Example 3: First coulombic efficiency test, performed according to Appendix O of GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" and GB / T38823-2020 "Silicon-Carbon", using a coin cell assembly system and a charge-discharge tester; A porous silicon-carbon anode sample was prepared into an anode slurry by mixing a conductive agent and a binder in a specific mass ratio. This slurry was coated onto a copper foil current collector, dried, rolled, and cut into sheets to serve as the working electrode. A lithium metal sheet was used as the counter electrode to assemble a CR2032 coin cell. An initial constant current charge-discharge test was conducted at 25±1℃ with a current density of 0.1 A / g. The discharge cutoff voltage was 0.01 V, and the charge cutoff voltage was 1.5 V. The initial lithium insertion capacity and lithium extraction capacity were recorded and calculated using the formula: Initial coulombic efficiency = Initial lithium extraction capacity / Initial lithium insertion capacity × 100%. Three cells were tested in parallel for each sample group, and the average value was taken as the initial coulombic efficiency of the sample. The judgment criterion was that the initial coulombic efficiency should reach 80% or higher.

[0058] Example 4, Cycle retention rate test, was conducted in accordance with Appendix O of GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" and GB / T38823-2020 "Silicon-Carbon", using a charge-discharge tester; Using the same coin-cell half-cell system as the initial coulombic efficiency test, multiple constant-current charge-discharge cycles were performed at 25±1℃ with a current density of 0.1 A / g, and the charge-discharge voltage range was 0.01V-1.5V. The discharge capacity of each cycle was recorded, and the cycle retention rate was calculated using the formula: Cycle Retention Rate = (Nth discharge capacity / Initial discharge capacity) × 100%. Three cells were tested in parallel for each sample group, and the average value was taken as the cycle retention rate of the sample. The judgment criterion was that the capacity retention rate should reach more than 80% after 100 cycles.

[0059] Example 5, moisture content detection, was performed according to GB / T6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method" and Appendix B of GB / T24533-2019, using a Karl Fischer moisture analyzer. Weigh approximately 0.5-2.0 g of accurately measured sample in a dry environment and quickly transfer it to a moisture evaporation apparatus. Heat the sample at 150°C to fully release the moisture. Titrate the released moisture using Karl Fischer coulometric titration and calculate the moisture content based on the amount of electricity consumed. Perform three parallel tests on each sample, recording the moisture content from each test. Take the average value as the sample moisture content. Judgment criterion: Moisture content should be ≤0.5 wt%.

[0060] Example 6, Electrolyte contact angle detection, refers to GB / T30447-2014 "Method for measuring contact angle of nanofilm surface" and GB / T30693-2014 "Measurement of contact angle between plastic film and water", using an optical contact angle measuring instrument; Porous carbon silicon-carbon anode samples are pressed into flat sheets or coated into uniform films and placed on the sample stage of an optical contact angle measuring instrument. Using lithium-ion battery electrolyte as the test liquid, 2-5 μL droplets are added to the sample surface via a micro-syringe. Image acquisition is completed within 3-5 seconds after the droplet contacts the sample surface. Image analysis software is used to fit the droplet profile and calculate the contact angle value. Each sample is tested five times in parallel at different locations. The maximum and minimum values ​​are removed, and the average value is taken as the sample electrolyte contact angle. Judgment criterion: The electrolyte contact angle should be ≤30°.

[0061] Table 1, Performance Test Data Table

[0062] Based on the differences between Examples 1-3 and Comparative Examples 1-3 and the performance test data table, it can be seen that the synergistic process of precursor preparation, directional molding, carbonization treatment, pore-forming activation, carbon coating treatment, washing and drying in this invention has a significant impact on the specific surface area, initial coulombic efficiency, cycle retention rate and pore orientation of silicon-carbon anode porous carbon, thus achieving the dual goals of directional porous carbon preparation and electrochemical performance improvement.

[0063] Comparative Example 1 eliminated the low-temperature pre-calcination step, and the carbon source polyolefin waste plastics were directly carbonized at high temperature, resulting in the lack of pre-curing of the carbon skeleton, the inability to maintain the orientation of the template agent, and a decrease in specific surface area to 1250 m². 2 / g, the initial coulombic efficiency drops to 65%, the cycle retention rate drops to 65%, the overall performance is the worst, and it cannot form regular oriented porous carbon.

[0064] Comparative Example 2 omitted the template agent addition and template elution steps, and the product lacked oriented macropores, although the specific surface area remained at approximately 2200 m². 2 / g, but the rate performance is significantly reduced, with the capacity retention rate at a current density of 2A / g being only 42% of that at 0.1A / g, which is much lower than the 68% in Example 1.

[0065] Comparative Example 3, without chemical activation and carbon coating treatment, produced a product containing only macropores after template removal, resulting in a sharp drop in specific surface area to approximately 380 μm². 2 / g, the initial coulombic efficiency dropped to 58%, the cycle retention rate dropped to 70%, and the reversible specific capacity was only about 850mAh / g. The unrepaired surface defects led to a large irreversible capacity loss.

[0066] The silicon-carbon anode porous carbon prepared in Examples 1-3 exhibits excellent performance: specific surface area of ​​2630-2850 m². 2 / g, initial coulombic efficiency 80%-82%, capacity retention 89%-91% after 100 cycles, pore volume 1.6-2.0 cm³ 3 / g, with electrolyte contact angles all ≤30°, achieving synergistic control of directional porous carbon and cascade pore distribution.

[0067] Among them, Example 1 has the best overall performance, with a specific surface area of ​​2850 m². 2 / g, initial coulombic efficiency 82%, cycle retention rate 91%, suitable for nano-alumina template agent and waste polyethylene carbon source system; compared with Comparative Example 1, specific surface area increased by 128%, initial coulombic efficiency increased by 17 percentage points, and cycle retention rate increased by 26 percentage points. Example 2 is suitable for nano-silica template agent system, and Example 3 is suitable for waste polypropylene carbon source system, broadening the applicable range of raw materials.

[0068] The core processes achieve a deep synergistic effect: precursor preparation and orientation molding work together to ensure uniform particle dispersion and orientation; orientation molding and carbonization work together to ensure the integrity of the template agent's orientation structure during the high-temperature carbonization stage through forced orientation using molds and low-temperature pre-calcination stabilization; carbonization and pore-forming activation work together to first construct a complete carbon skeleton and then etch the template agent, combined with chemical activation to achieve a macropore-mesopore-micropore tiered distribution; pore-forming activation and carbon coating work together to develop micro-mesopores and then deposit a carbon layer to repair surface defects and improve conductivity; and carbon coating and washing and drying work together to remove residual impurities and control moisture content.

[0069] Comparative Examples 1-3 showed that the lack of a single process step led to the breakage of the synergistic chain: Comparative Example 1 disrupted the synergy between carbon source stabilization and orientation maintenance; Comparative Example 2 lost the ability to construct directional macropores; Comparative Example 3 disrupted the synergy between micro-mesopore generation and defect repair. All of these examples demonstrate the irreplaceable nature of the process steps and parameter selections in this invention.

[0070] In summary, through synergistic optimization of each step, this invention effectively solves the technical problems of narrow process window, difficulty in pore size control, and difficulty in using waste plastics as a carbon source in the ice crystal template method. It achieves precise preparation of directional porous carbon and significant improvement in electrochemical performance, while overcoming the technical bias of utilizing waste plastics as a carbon source and reducing raw material costs.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for the directional preparation of porous carbon for silicon-carbon anodes, characterized in that, Includes the following steps: S1, Precursor preparation: Nano-silicon powder is selected as the silicon source, purified and mixed with a directional template agent, a dispersant is added and ball milled to obtain a directional template precursor; then a carbon source and binder are added, stirred and mixed, filtered to obtain a directional composite preform; S2, Oriented Forming: The oriented composite preform obtained in S1 is placed in a mold with an oriented guiding structure and orientedly pressed to obtain an oriented preform; S3, carbonization treatment: The oriented preform obtained in S2 is pre-fired at a low temperature under an inert atmosphere to obtain a pre-fired preform; Then, under the protection of an inert atmosphere, high-temperature carbonization is carried out to obtain a carbonized green body; S4, Pore Forming and Activation: The carbonized preform obtained in S3 is immersed in an etchant to remove the template agent. After washing, a porous preform is obtained. The porous preform is then mixed with an activator and activated at high temperature under an inert atmosphere to obtain an activated porous preform. S5, Carbon coating treatment: The activated porous preform obtained in S4 is subjected to chemical vapor deposition in an atmosphere containing carbon gas source and carrier gas to obtain a carbon-coated porous preform. S6, Washing and Drying: The carbon-coated porous preform obtained in S5 is washed and dried to obtain the silicon-carbon anode porous carbon product.

2. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In S1, the directional template agent is a nano-oxide with a particle size of 30-100 nm; The mass ratio of nano-silica powder to directional template agent is 1:0.3-0.8; The dispersant is a mixture of ethanol and deionized water, with a volume ratio of ethanol to deionized water of 1:1-2:

1. The amount of dispersant added is 1.5-3 times the total mass of the nano-silica powder and the directional template agent. The ball mill speed is 200-300 rpm, the ball milling time is 1-2 hours, and the ball-to-material ratio is 5:1-10:

1.

3. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In S1, the carbon source is polyolefin waste plastic, which is added after being crushed to a particle size of 50-200μm, and the mass ratio of the carbon source to the directional template precursor is 1:1.2-2.0; the binder is a mixture of cellulose ether and styrene-butadiene rubber binder, and the amount added is 3-8% of the total mass of the directional template precursor and the carbon source.

4. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In S2, the directional guiding structure of the mold is a parallel arrangement of strip grooves; the directional pressing pressure is 5-15MPa and the temperature is 60-100℃.

5. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S3, the inert atmosphere is argon or nitrogen; the low-temperature pre-burning temperature is 200-350℃, and the holding time is 2-4h; the high-temperature carbonization temperature is 600-900℃, and the holding time is 1-4h.

6. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S4, the etching agent is selected according to the type of directional template agent used in step S1: when the template agent is nano-alumina, an alkali metal hydroxide solution is selected; when the template agent is nano-silicon oxide, a hydrofluoric acid solution is selected.

7. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S4, the activator is an alkali metal hydroxide, and the mass ratio of the porous preform to the activator is 1:2-1:4; the high-temperature activation temperature is 700-900℃, and the holding time is 1-3h. High-temperature activation is carried out under an inert atmosphere, which is argon or nitrogen.

8. The method for directional preparation and application of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S5, the carbon-containing gas source is at least one of acetylene, methane, or ethylene, and the carrier gas is argon or nitrogen; the temperature of chemical vapor deposition is 700℃-1000℃, and the processing time is 0.5-4 hours.

9. The method for directional preparation of porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S6, the material is washed until neutral and dried at a temperature of 80-120°C.

10. The application of the porous carbon product for silicon-carbon anode prepared by any one of claims 1 to 9 in lithium-ion battery anode materials.

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