Nano-silicon-doped porous carbon for silicon-carbon negative electrode, preparation method of nano-silicon-doped porous carbon, silicon-carbon negative electrode material and battery

Abstract

The invention discloses nano-silicon-doped porous carbon for a silicon-carbon negative electrode, a preparation method of the nano-silicon-doped porous carbon, a silicon-carbon negative electrode material and a battery, and the preparation method of the nano-silicon-doped porous carbon comprises the following steps: S1-1, placing substrate porous carbon in an adsorption device, and introducing inert gas to replace air; s1-2, introducing silane gas into the adsorption device until the adsorption is saturated; and S1-3, taking out the porous carbon, placing the porous carbon in a reaction container, and heating to perform in-situ cracking on the silane gas, thereby obtaining the nano-silicon doped porous carbon. On one hand, the mass transfer kinetics of silicon can be effectively improved, the mass transfer process and mass transfer resistance of silicon elementary substances are reduced, the CVD reaction time is shortened, the production efficiency is improved, the silane utilization rate is increased, and the production cost is reduced; on the other hand, silicon elementary substances generated by CVD are preferentially deposited and nucleated in situ in the pore channels, generation of aggregated silicon particles outside the porous carbon is reduced, the sizes of the silicon particles in the pore channels can be effectively controlled due to limitation of the nanoscale pore channels, and the purpose of improving the performance of the prepared silicon-carbon negative electrode is achieved.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and in particular to a nano-silicon-doped porous carbon for silicon-carbon anodes, its preparation method, silicon-carbon anode materials, and batteries. Background Technology

[0002] Silicon anodes have a high theoretical specific capacity and are the most promising next-generation anode material. Their lithium storage mechanism involves an alloying reaction with lithium, which causes a rapid expansion of silicon particles during charge and discharge. This volume change leads to material pulverization and detachment from the current collector, resulting in a rapid decrease in capacity. Furthermore, the surface changes cause the formation of an unstable SEI film, reducing coulombic efficiency. Another drawback of silicon is its relatively weak conductivity, which hinders the diffusion of electrons and lithium ions, negatively impacting the rate performance of the battery.

[0003] To overcome the above problems, several methods have been proposed. First, silicon can be combined with materials that have good conductivity, commonly carbon materials such as graphite, graphene, and carbon nanotubes. Second, the structure of silicon can be modified, for example, by designing core-shell or porous structures to improve its electrochemical performance. Third, silicon can be nanoscaled to reduce the negative effects caused by volume changes. Currently, the preparation of silicon-carbon anodes using chemical vapor deposition (CVD) has attracted widespread attention. This method uses silane as the silicon source and porous carbon as the substrate material. The decomposed silicon nanoparticles are introduced into the pore structure of the porous carbon using a fluidized bed CVD device. Subsequently, gases such as acetylene are introduced to cause pyrolysis, resulting in a thin carbon layer coating the surface. Differences in the surface chemical properties, pore size distribution, and specific surface area of ​​porous carbon all affect the silicon vapor deposition process, leading to variations in the performance of the prepared silicon-carbon anodes. Meanwhile, a large portion of the elemental silicon produced by pyrolysis does not spontaneously enter the pores of porous carbon, but instead deposits and agglomerates on the surface, forming larger silicon particles, which in turn reduces the initial efficiency and cycle life of the silicon-carbon anode.

[0004] In existing CVD methods, the porous carbon used cannot achieve controlled deposition of nano-silicon particles. This method first fluidizes the porous carbon and raises the temperature to a target temperature (typically 400-600°C), then switches the gas flow to silane, causing it to decompose. Due to the high temperature, the silane decomposes randomly and irregularly on the outside of the porous carbon, resulting in uncontrollable mass transfer of the generated elemental silicon. The generated elemental silicon, due to its large surface energy, spontaneously enters the pore structure of the porous carbon. However, due to the nano-effect, the silicon exists in two states: free and aggregated. The silicon inside the pores can be considered free, while a large portion aggregates and grows into large-diameter silicon particles under silicon-silicon interactions, randomly depositing outside the pores.

[0005] Existing CVD methods are limited by the mass transfer kinetics of silicon produced by pyrolysis, as elemental silicon needs to overcome a significant energy barrier to enter the channels of porous carbon. Therefore, to ensure a high silicon content, the deposition of elemental silicon onto porous carbon after silane pyrolysis often takes more than 5 hours, resulting in low efficiency. Furthermore, this process requires a continuous supply of excess silane gas, leading to low utilization of the silane gas.

[0006] Therefore, it is necessary to improve existing technologies to provide a more reliable solution. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a nano-silicon-doped porous carbon for silicon-carbon anodes, its preparation method, silicon-carbon anode materials, and batteries.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In its first aspect, the present invention provides a method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes, comprising the following steps:

[0009] S1-1. Place the porous carbon substrate inside the adsorption device and introduce inert gas to replace the air inside the adsorption device.

[0010] S1-2. Introduce silane gas into the adsorption device until the porous carbon substrate reaches saturation for adsorption.

[0011] S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Heat it to cause the silane gas to decompose in situ, and obtain the nano-silicon-doped porous carbon.

[0012] Preferably, the porous carbon substrate has a pore size in the range of 0.4–5 nm and a specific surface area in the range of 1028–2673 m². 2 Within the range of / g, the total pore volume is 0.4–1.2 cm³. 3 Within the range of / g.

[0013] Preferably, the minimum particle size Dmin of the porous carbon substrate is between 50 nm and 3 μm, and the D50 is between 7 and 13 μm; the compaction density of the porous carbon is 0.75-1.5 cm³. 3 / g;

[0014] The total content of nitrogen and oxygen in the porous carbon substrate is 7.6-12.7 wt%.

[0015] The Fe, Zn, K, Cr, and Ni metal elements in the porous carbon substrate are all less than 10 ppm, and the ash content is less than 0.3 wt%.

[0016] Preferably, in step S1-1, the inert gas introduced is one or more of nitrogen, argon, and helium, the flow rate is 3-20 L / min, and the introduction time is 0.5-2 h.

[0017] Preferably, in steps S1-2, the temperature is controlled to be between -20°C and 0°C, and the introduced silane gas is one or more of silane, silane, and dichlorosilane, with a flow rate of 100-500 mL / min.

[0018] Preferably, in steps S1-3, the pyrolysis temperature is 400-600℃, the temperature is controlled to rise to the required pyrolysis temperature within 1-10 seconds, and the pyrolysis time is 15-45 seconds.

[0019] Preferably, the method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes includes the following steps:

[0020] S1-1. Place the porous carbon substrate in the adsorption device and introduce inert gas into the adsorption device at a flow rate of 3-20 L / min for 0.5-2 hours to replace the air in the adsorption device.

[0021] S1-2. Control the temperature to -20 to 0℃, and introduce silane gas into the adsorption device at a flow rate of 100-500 mL / min. When the concentration of silane gas in the tail gas no longer changes, it is considered that the adsorption of the porous carbon substrate has reached saturation, and the adsorption ends.

[0022] S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Decompose it in situ at 400-600℃ for 1-10 seconds. After natural cooling, the nano-silicon doped porous carbon is obtained.

[0023] In a second aspect, the present invention provides a nano-silicon-doped porous carbon, which is prepared by the method described above.

[0024] A third aspect of the present invention provides a silicon-carbon anode, which is prepared by the following method:

[0025] S2-1. Add the nano-silicon-doped porous carbon as described above to the reaction vessel, and replace the air by introducing sufficient argon gas into the reactor at a flow rate of 5-20 L / min.

[0026] S2-2. Raise the temperature of the reaction vessel to 400-600℃ and introduce silane gas at a flow rate of 12.5-50L / min to deposit silicon for 2-4 hours.

[0027] S2-3. Maintain the temperature of the reaction vessel. After the deposition is completed, introduce acetylene at a flow rate of 10-40 L / min to perform carbon coating. The coating time is 1-4 h. After the coating is completed, allow it to cool naturally to obtain the silicon-carbon anode material.

[0028] In a fourth aspect, the present invention provides a battery comprising the silicon-carbon anode material as described above.

[0029] The beneficial effects of this invention are:

[0030] This invention provides a nano-silicon-doped porous carbon for silicon-carbon anodes, its preparation method, silicon-carbon anode materials, and batteries. On the one hand, this invention can effectively improve the mass transfer kinetics of silicon, reduce the mass transfer process and resistance of elemental silicon, shorten the CVD reaction time, improve the utilization rate of silane, and reduce production costs. On the other hand, the elemental silicon generated by CVD preferentially deposits and nucleates in situ inside the pores, reducing the generation of aggregated silicon particles on the outside of the porous carbon. Furthermore, due to the limitation of the nano-sized pores, the size of silicon particles inside the pores can also be effectively controlled, thereby improving the performance of the prepared silicon-carbon anode. Attached Figure Description

[0031] Figure 1 The silane adsorption breakthrough curves are for the porous carbon substrate used in Examples 1-4.

[0032] Figure 2 The image shows the XPS Si2p scan curve of the silicon-carbon anode in Example 1. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0034] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0036] This invention provides a method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes, comprising the following steps:

[0037] S1-1. Place the porous carbon substrate inside the adsorption device and introduce inert gas to replace the air inside the adsorption device.

[0038] S1-2. Introduce silane gas into the adsorption device until the porous carbon substrate reaches saturation for adsorption.

[0039] S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Heat it to cause the silane gas to decompose in situ, and obtain the nano-silicon-doped porous carbon.

[0040] In a preferred embodiment, the porous carbon substrate has a pore size in the range of 0.4–5 nm and a specific surface area in the range of 1028–2673 m². 2 Within the range of / g, the total pore volume is 0.4–1.2 cm³. 3 Within the range of / g.

[0041] In a preferred embodiment, the minimum particle size Dmin of the porous carbon substrate is between 50 nm and 3 μm, and the D50 is between 7 and 13 μm; the compaction density of the porous carbon is 0.75-1.5 cm³. 3 / g.

[0042] In a preferred embodiment, the total content of nitrogen and oxygen in the porous carbon substrate is 7.6-12.7 wt%.

[0043] In a preferred embodiment, the content of Fe, Zn, K, Cr, and Ni metal elements in the porous carbon substrate is less than 10 ppm, and the ash content is less than 0.3 wt%.

[0044] The specific surface area is calculated using the BET method, and the pore size distribution needs to be measured by one or more methods, such as the carbon dioxide isotherm adsorption-desorption curve at 0℃, the nitrogen isotherm adsorption-desorption at -196℃, and the helium isotherm adsorption-desorption at -186℃. The calculation model used is one or more of the following: multi-point BET, NLDFT, QSDFT, and BJH.

[0045] The porous carbon substrate is prepared using phenolic resin microspheres through conventional processes such as activation, acid washing, drying, and pulverization, but it is necessary to control it to meet the above parameter requirements.

[0046] In this invention, porous carbon with suitable pore size distribution, specific surface area and surface functional groups is selected as the doping substrate, which has a high silane adsorption capacity.

[0047] In a preferred embodiment, in step S1-1, the inert gas introduced is one or more of nitrogen, argon, and helium, the flow rate is 3-20 L / min, and the introduction time is 0.5-2 h.

[0048] In a preferred embodiment, in steps S1-2, the temperature is controlled to be -20 to 0°C, and the introduced silane gas is one or more of silane, silane, and dichlorosilane, with a flow rate of 100-500 mL / min.

[0049] In a preferred embodiment, in steps S1-3, the pyrolysis temperature is 400-600℃, and the temperature is raised to the desired pyrolysis temperature within 1-10 seconds, with a pyrolysis time of 15-45 seconds. Adsorption is an exothermic process; therefore, increasing the temperature will cause some of the adsorbed silane gas to desorb and leave the adsorption sites. Therefore, the heating time in the pyrolysis process needs to be controlled within 1-10 seconds. Excessive heating time will lead to a sharp decrease in the silicon content in the prepared doped porous carbon. More preferably, the heating time in this pyrolysis process is controlled within 3 seconds.

[0050] In a preferred embodiment, the method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes includes the following steps:

[0051] S1-1. Place the porous carbon substrate in the adsorption device and introduce inert gas into the adsorption device at a flow rate of 3-20 L / min for 0.5-2 hours to replace the air in the adsorption device.

[0052] S1-2. Control the temperature to -20 to 0℃, and introduce silane gas into the adsorption device at a flow rate of 100-500 mL / min. When the concentration of silane gas in the tail gas no longer changes, it is considered that the adsorption of the porous carbon substrate has reached saturation, and the adsorption ends.

[0053] S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Decompose it in situ at 400-600℃ for 1-10 seconds. After natural cooling, the nano-silicon doped porous carbon is obtained.

[0054] The present invention also provides nano-silicon-doped porous carbon, which is prepared by the method described above.

[0055] The present invention also provides a silicon-carbon anode, which is prepared by the following method:

[0056] S2-1. Add the nano-silicon-doped porous carbon as described above to the reaction vessel, and replace the air by introducing sufficient argon gas into the reactor at a flow rate of 5-20 L / min.

[0057] S2-2. Raise the temperature of the reaction vessel to 400-600℃ and introduce silane gas at a flow rate of 12.5-50L / min to deposit silicon for 2-4 hours.

[0058] S2-3. Maintain the temperature of the reaction vessel. After the deposition is completed, introduce acetylene at a flow rate of 10-40 L / min to perform carbon coating. The coating time is 1-4 h. After the coating is completed, allow it to cool naturally to obtain the silicon-carbon anode material.

[0059] Using the above method, the silicon-carbon anode provided by this invention has a silicon content of 20wt%-80wt%, a carbon coating content of 1wt%-5wt%, and the remainder is porous carbon. The silicon-carbon anode has a capacity of 1352mAh / g to 2071mAh / g and an initial efficiency greater than 90%.

[0060] The present invention also provides a battery comprising the silicon-carbon anode material as described above.

[0061] To address the limitations of current CVD silicon-carbon anodes, such as the inability to achieve controllable deposition of nano-silicon particles and slow mass transfer rates with porous carbon, and to improve deposition efficiency and reduce production costs, this invention provides a nano-silicon-doped porous carbon for CVD silicon-carbon anodes and its preparation method. The doped porous carbon described in this invention is based on the adsorption-in-situ pyrolysis doping principle: using porous carbon with high silane adsorption capacity as the substrate material, a fixed-bed adsorption device is used to adsorb a large amount of silane into the pores, followed by rapid heating to pyrolyze the silane, resulting in in-situ doping of nano-silicon.

[0062] When using the nano-silicon-doped porous carbon provided by this invention as a CVD deposition substrate, a large number of in-situ deposited nano-silicon particles exist inside the porous carbon channels. During the high-temperature CVD process, these nano-silicon particles can act as effective internal anchors. Through the silicon-silicon interaction forces, the elemental silicon generated by the cracking process can quickly break through the energy barrier at the channel interface and enter the channels. On the one hand, this can effectively improve the mass transfer kinetics of silicon, reduce the mass transfer process and resistance of elemental silicon, shorten the CVD reaction time, increase the utilization rate of silane, and reduce production costs. On the other hand, the generated elemental silicon preferentially deposits and nucleates in situ inside the channels, reducing the generation of aggregated silicon particles on the outside of the porous carbon. Furthermore, due to the limitation of the nano-sized channels, the size of the silicon particles inside the channels can also be effectively controlled, thereby improving the performance of the prepared silicon-carbon anode.

[0063] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0064] Example 1

[0065] A method for preparing nano-silicon-doped porous carbon includes the following steps:

[0066] S1-1. A certain mass of porous carbon substrate is placed in a fixed-bed adsorption device. The specific surface area of ​​the porous carbon substrate is 1524 m². 2 / g, the pore size distribution is concentrated in the range of 0.4 to 0.8 nm, and the total nitrogen and oxygen content is 9.1 wt%;

[0067] The porous carbon substrate is composed of phenolic resin microspheres (particle size 1-3 μm, specific surface area 5-30 m²).2 The precursor, made from phenolic resin microspheres (grade RMB-1) produced by Hunan Qixian New Material Technology Co., Ltd., is prepared through carbonization, activation, acid washing, and pulverization. Specifically: i) A certain mass of phenolic resin microspheres is placed in a tube furnace, and nitrogen gas is introduced at a flow rate of 5 L / min. After purging for 1 hour to remove air, the temperature is increased to 400℃ (heating rate set at 10℃ / min), and the mixture is held at this temperature for one hour before natural cooling to obtain the carbonized precursor; ii) The carbonized precursor is then reacted with potassium citrate (commonly available analytical grade CAS). 866-84-2) and urea (common commercial analytical grade CAS: 57-13-6) were mixed uniformly at a mass ratio of 1:2:1 and then placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 5 L / min and the mixture was purged for 1 hour. The temperature was then increased to 650°C at a heating rate of 10°C / min and held at that temperature for one hour. After natural cooling, the mixture was removed and added to a sufficient amount of 5 wt% hydrochloric acid solution. After stirring for 10 hours, the mixture was filtered, dried at 80°C for 24 hours, and then pulverized using an air jet mill to obtain the porous carbon substrate.

[0068] Nitrogen gas was introduced at a flow rate of 5 L / min and purged for 1 hour to remove air. After the nitrogen content in the exhaust gas was detected by mass spectrometry and found to be 100%, the air replacement was completed.

[0069] S1-2. Control the adsorption temperature to -20℃, switch the gas path and introduce silane at a flow rate of 500mL / min to start adsorption. When the mass spectrometer shows that the concentration of silane in the tail gas no longer changes, it is considered that the adsorption has reached saturation and the adsorption ends.

[0070] S1-3. Take out the porous carbon substrate and place it into a rapid Joule heating reaction vessel. Quickly raise the temperature to 450°C for in-situ pyrolysis. The heating time is 3s and the pyrolysis duration is 30s. After natural cooling, the nano-silicon doped porous carbon is obtained.

[0071] A silicon-carbon anode based on the above-mentioned nano-silicon doped porous carbon is prepared by the following method:

[0072] S2-1. Add a certain amount of the above-mentioned nano-silicon doped porous carbon to the reaction vessel, and replace the air with sufficient argon gas at a rate of 10 L / min. When the mass spectrometer detects that the argon content in the tail gas is 100%, it is considered that the replacement is complete.

[0073] S2-2. Raise the temperature of the reaction vessel to 500℃ and introduce silane gas at a rate of 25L / min to deposit silicon for 2 hours.

[0074] S2-3. After deposition is complete, maintain the reaction vessel temperature at 500℃ and introduce acetylene at a rate of 20L / min to perform carbon coating for 2 hours. After coating is completed, allow it to cool naturally to obtain the silicon-carbon anode material.

[0075] A coin cell based on the aforementioned silicon-carbon anode is fabricated as follows:

[0076] Silicon-carbon anode material, conductive agent, and binder were thoroughly mixed at a mass ratio of 8:1:1 and then evenly coated onto a clean copper foil with a scraper to serve as the anode of a lithium-ion battery. The mixture was then allowed to stand and dry at room temperature before being placed in a vacuum drying oven at 100°C for 12 hours. Subsequently, it was transferred to a glove box, where a circular lithium metal sheet was used as the positive electrode, a 1M LiPF6+EC / DEC (1:1) mixture was used as the electrolyte, a polyethylene / polypropylene composite membrane was used as the separator, and CR2023 was used as the anode battery casing. The mixture was then assembled into a coin cell in an argon atmosphere with a moisture and oxygen content of less than 1ppm.

[0077] Performance tests were conducted on the aforementioned silicon-carbon anode coin cells: The assembled lithium-ion coin cells were subjected to cyclic charge-discharge tests under constant current conditions using a battery testing system, with a charge-discharge cutoff voltage of 0.01–1.5V (vs. Li / Li). + The temperature is set to 25℃.

[0078] Example 2

[0079] The difference between Example 2 and Example 1 is that the porous carbon substrate used in this example is prepared by using phenolic resin microspheres with potassium citrate and urea in a ratio of 1:4:1, while the rest of the method remains the same, and its specific surface area is 2673 m². 2 / g, pore size distribution is concentrated in the range of 0.8 to 3.0 nm, and the total nitrogen and oxygen content is 7.6 wt%.

[0080] Example 3

[0081] The difference between Example 3 and Example 1 is that in this example, the porous carbon substrate used was subjected to plasma treatment with an oxygen flow rate of 150 mL / min, a nitrogen flow rate of 100 mL / min, and a treatment power of 250 W. After treatment, the specific surface area of ​​the porous carbon substrate was 1025 m². 2 / g, the pore size distribution is concentrated in the range of 0.4 to 0.8 nm, and the total nitrogen and oxygen content is 12.7 wt%.

[0082] Example 4

[0083] The difference between Example 4 and Example 1 is that the fixed-bed silane adsorption temperature is set to 0℃ in this example (steps S1-2).

[0084] Example 5

[0085] The difference between Example 5 and Example 1 is that in the pyrolysis of the porous carbon substrate in this example (steps S1-3), the heating time in the rapid Joule heating reaction vessel is 10s.

[0086] Comparative Example 1

[0087] A method for preparing nano-silicon-doped porous carbon includes the following steps:

[0088] S1. A certain mass of porous carbon substrate is placed in a CVD vapor deposition apparatus. The specific surface area of ​​the porous carbon substrate is 1024 m². 2 / g, the pore size distribution is concentrated in the range of 0.4 to 0.8 nm, and the total nitrogen and oxygen content is 9.1 wt%;

[0089] Sufficient argon gas was introduced at a rate of 10 L / min to replace the air. When the mass spectrometer detected that the argon content in the exhaust gas was 100%, the replacement was considered complete.

[0090] S2. Increase the temperature of the reaction vessel to 500℃ and introduce silane gas at a rate of 25L / min to deposit silicon for 2 hours.

[0091] S3. After deposition is complete, acetylene is introduced at a rate of 20 L / min to perform carbon coating for 2 hours. After coating, the silicon-carbon anode material is obtained by natural cooling.

[0092] A coin cell based on the aforementioned silicon-carbon anode is fabricated as follows:

[0093] The silicon-carbon anode, conductive agent, and binder were thoroughly mixed at a mass ratio of 8:1:1. The mixture was then evenly coated onto a clean copper foil using a scraper. After being left to dry at room temperature, the mixture was placed in a vacuum drying oven at 100°C for 12 hours. Subsequently, it was transferred to a glove box. A coin cell was assembled using a circular lithium metal sheet as the anode, a 1M LiPF6+EC / DEC (1:1) mixture as the electrolyte, a polyethylene / polypropylene composite membrane as the separator, and CR2023 as the anode battery casing in an argon atmosphere with a moisture and oxygen content of less than 1ppm.

[0094] Performance tests were conducted on the aforementioned silicon-carbon anode coin cells: The assembled lithium-ion coin cells were subjected to cyclic charge-discharge tests under constant current conditions using a battery testing system. The charge-discharge cutoff voltage was 0.01–1.5V (vs. Li / Li). + The temperature is set to 25℃.

[0095] Comparative Example 2

[0096] The difference between Comparative Example 2 and Comparative Example 1 is that the porous carbon substrate in this example was prepared by using phenolic resin microspheres with potassium hydroxide and urea in a ratio of 1:2:1, while the other methods remained unchanged, resulting in a specific surface area of ​​2673 m². 2 / g, pore size distribution is concentrated in the range of 0.8 to 3.0 nm, and the total nitrogen and oxygen content is 7.6 wt%.

[0097] Comparative Example 3

[0098] The difference between Comparative Example 3 and Comparative Example 1 is that: in this example, the porous carbon substrate used was subjected to plasma treatment with an oxygen flow rate of 150 mL / min, a nitrogen flow rate of 100 mL / min, and a treatment power of 250 W. After treatment, the specific surface area of ​​the porous carbon substrate was 995 m². 2 / g, the pore size distribution is concentrated in the range of 0.4 to 0.8 nm, and the total nitrogen and oxygen content is 12.7 wt%.

[0099] Comparative Example 4

[0100] The difference between Comparative Example 2 and Comparative Example 1 is that the CVD deposition time in step S2 of this example is 10 hours.

[0101] Performance characterization and testing

[0102] 1. Figure 1 The graph shows the silane adsorption breakthrough curves of the porous carbon substrate used in Examples 1-4 above, where the adsorption temperature for Examples 1-3 was -20℃ and the adsorption temperature for Example 4 was 0℃. The graph shows that the dynamic saturated adsorption capacities of silane in Examples 1-4 were 0.45, 0.27, 0.49, and 0.11 g / g, respectively. The results indicate that there is no direct positive correlation between the silane adsorption capacity and the specific surface area of ​​the porous carbon substrate; rather, it is closely related to the pore size distribution. The narrower pores (0.5–0.8 nm) in the micropore range are more conducive to the silane adsorption process. This is because in a fixed-bed adsorption device, the process of silane passing through the adsorption interface into the porous carbon channels falls under the category of physical adsorption, and the adsorption force is mainly provided by van der Waals forces. According to the basic principle of adsorption, when the pore size is less than 2-3 times the kinetic diameter of the silane (0.36 nm), the adsorption potential energy from adjacent pore walls will have a superposition effect, promoting the molecular filling process and thus improving the adsorption capacity. On the other hand, after plasma treatment of the porous carbon substrate, the content of nitrogen and oxygen functional groups on the surface of the porous carbon substrate increased to a certain extent, while the specific surface area decreased slightly, but the adsorption capacity of silane was slightly improved. This is because oxygen-containing functional groups such as carboxyl and hydroxyl groups, and nitrogen-containing functional groups such as pyridine and pyrrole, will form hydrogen bonds and electrostatic interactions with silane, thereby improving the adsorption effect. In addition, the silane adsorption capacity at an adsorption temperature of -20℃ is significantly higher than that at 0℃, because adsorption is an exothermic process, and the lower the temperature, the more favorable the adsorption process.

[0103] 2. Table 1 below shows the silicon content (converted to wt%) in the silicon-doped porous carbon of Examples 1-5 obtained by X-ray photoelectron spectroscopy (XPS). It can be seen that the higher the adsorption amount of silane, the higher the silicon content in the prepared silicon-doped porous carbon. However, it can also be seen that, based on the obtained silicon content, not all the silicon nanoparticles generated by the adsorbed silane are deposited in the substrate porous carbon. This is because some silane desorbs from the pores and escapes during rapid heating. This conclusion is also proven in Example 5, where the silicon content in the prepared silicon-doped porous carbon is only 2.6 wt% when the substrate porous carbon is heated in a rapid Joule heating reactor for 10 s. Therefore, the faster the heating time, the smaller the effect of silane desorption.

[0104] Table 1. Silicon content in nano-silicon-doped porous carbon in Examples 1-5

[0105] Test sample Carbon content (wt%) Silicon content (wt%) Example 1 80.1 10.8 Example 2 85.5 6.9 Example 3 75.8 11.5 Example 4 87.6 3.3 Example 5 88.3 2.6

[0106] 3. The silicon content of the silicon-carbon anodes prepared in Examples 1-5 and Comparative Examples 1-4 was tested by XPS. Figure 2 Table 2 shows the XPS Si2p scan curve for Example 1 and the silicon content data (converted to wt%) obtained from the test. As can be seen from the table, the silicon contents of the silicon-carbon anodes prepared in Examples 1-5 were 56.7, 32.8, 57.1, 29.4, and 24.4 wt%, respectively. This indicates that the higher the silicon content in the nano-silicon-doped porous carbon used, the higher the silicon content of the silicon-carbon anode obtained in the same CVD deposition time, and a deposition weight of over 50 wt% can be achieved in just 2 hours. The silicon contents of the silicon-carbon anodes prepared in Comparative Examples 1-3 were 18.3, 21.8, and 18.9 wt%, respectively, demonstrating a slower deposition rate and lower silicon content when the CVD deposition time was 2 hours. The silicon content of the silicon-carbon anode prepared in Comparative Example 4 was 54.1 wt%, indicating that the silicon content increased significantly after extending the deposition process time. In conclusion, the nano-silicon-doped porous carbon described in this invention can significantly reduce the time required for the CVD deposition process, achieving the effects of improving efficiency and reducing energy consumption.

[0107] Table 2 shows the silicon content in nano-silicon-doped porous carbon in Examples 1-5.

[0108] Test sample Carbon content (wt%) Silicon content (wt%) Example 1 34.2 56.7 Example 2 59.6 32.8 Example 3 30.2 57.1 Example 4 61.5 29.4 Example 5 66.5 24.4 Comparative Example 1 72.6 18.3 Comparative Example 2 70.2 21.8 Comparative Example 3 68.4 18.9 Comparative Example 4 36.8 54.1

[0109] 4. The silicon-carbon anode samples prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to performance tests according to the above-mentioned coin cell manufacturing and testing standards. The measured charge specific capacity and initial coulombic efficiency (1.5V) are shown in Table 3.

[0110] Table 3 Performance test results of the examples and comparative examples

[0111]

[0112]

[0113] As shown above, the initial discharge specific capacities of the silicon-carbon anodes prepared in Examples 1-5 were 2298, 1622, 2321, 1457, and 1279 mAh / g, respectively. This result is consistent with the trend of silicon content in the silicon-carbon anodes in Table 2, indicating that the higher the silicon content, the better the lithium storage performance of the prepared silicon-carbon anode material. The initial discharge specific capacities of the silicon-carbon anodes prepared in Comparative Examples 1-4 were 1700, 1098, 1142, and 2038 mAh / g, indicating that when the deposition time is 2 h, using the nano-silicon-doped porous carbon provided by this invention as the deposition base can significantly improve the electrochemical performance of the prepared silicon-carbon anode. Furthermore, by calculating the initial coulombic efficiency (1.5V) of the silicon-carbon anodes prepared in Examples 1-5 and Comparative Examples 1-4, it can be found that the silicon-carbon anode prepared using the nano-silicon-doped porous carbon provided by this invention has a higher initial coulombic efficiency. This is because the porous carbon channels prepared by the present invention based on the adsorption-in-situ pyrolysis doping principle contain a large number of nano-sized silicon particles, which can act as effective internal anchors during the high-temperature CVD process. Through the interaction force between silicon and silicon, the elemental silicon generated by pyrolysis can quickly break through the energy barrier of the channel interface and enter the channel. It preferentially deposits and nucleates in situ inside the channel, reducing the generation of aggregated silicon particles on the outside of the porous carbon. Furthermore, due to the limitation of the nano-sized channels, the size of the silicon particles inside the channels can also be effectively controlled, reducing the loss of lithium ions caused by the unrestricted growth and agglomeration of silicon particles after deposition outside the channels.

[0114] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes, characterized in that, Includes the following steps: S1-1. Place the porous carbon substrate inside the adsorption device and introduce inert gas to replace the air inside the adsorption device. S1-2. Introduce silane gas into the adsorption device until the porous carbon substrate reaches saturation for adsorption. S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Heat it to cause the silane gas to decompose in situ, and obtain the nano-silicon-doped porous carbon.

2. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 1, characterized in that, The porous carbon substrate has a pore size in the range of 0.4–5 nm and a specific surface area in the range of 1028–2673 m². 2 Within the range of / g, the total pore volume is 0.4–1.2 cm³. 3 Within the range of / g.

3. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 2, characterized in that, The minimum particle size Dmin of the porous carbon substrate is between 50 nm and 3 μm, and the D50 is between 7 and 13 μm; the compaction density of the porous carbon is 0.75-1.5 cm³. 3 / g; The total content of nitrogen and oxygen in the porous carbon substrate is 7.6-12.7 wt%.

4. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In step S1-1, the inert gas introduced is one or more of nitrogen, argon, and helium, the flow rate is 3-20 L / min, and the introduction time is 0.5-2 h.

5. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In steps S1-2, the temperature is controlled to be between -20°C and 0°C, and the introduced silane gas is one or more of silane, silane, and dichlorosilane, with a flow rate of 100-500 mL / min.

6. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 1, characterized in that, In steps S1-3, the pyrolysis temperature is 400-600℃, and the temperature is controlled to rise to the required pyrolysis temperature within 1-10 seconds, with a pyrolysis time of 15-45 seconds.

7. The method for preparing nano-silicon-doped porous carbon for silicon-carbon anodes according to claim 1, characterized in that, Includes the following steps: S1-1. Place the porous carbon substrate in the adsorption device and introduce inert gas into the adsorption device at a flow rate of 3-20 L / min for 0.5-2 hours to replace the air in the adsorption device. S1-2. Control the temperature to -20 to 0℃, and introduce silane gas into the adsorption device at a flow rate of 100-500 mL / min. When the concentration of silane gas in the tail gas no longer changes, it is considered that the adsorption of the porous carbon substrate has reached saturation, and the adsorption ends. S1-3. Take out the adsorbed saturated porous carbon and place it in a reaction vessel. Decompose it in situ at 400-600℃ for 1-10 seconds. After natural cooling, the nano-silicon doped porous carbon is obtained.

8. A nano-silicon-doped porous carbon, characterized in that, It is prepared by the method described in any one of claims 1-7.

9. A silicon-carbon anode, characterized in that, It is prepared by the following method: S2-1. Add the nano-silicon-doped porous carbon as described in claim 8 to the reaction vessel, and replace the air by introducing sufficient argon gas into the reactor at a flow rate of 5-20 L / min. S2-2. Raise the temperature of the reaction vessel to 400-600℃ and introduce silane gas at a flow rate of 12.5-50L / min to deposit silicon for 2-4 hours. S2-3. Maintain the temperature of the reaction vessel. After the deposition is completed, introduce acetylene at a flow rate of 10-40 L / min to perform carbon coating. The coating time is 1-4 h. After the coating is completed, allow it to cool naturally to obtain the silicon-carbon anode material.

10. A battery, characterized in that, It includes the silicon-carbon anode material as described in claim 9.

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