Porous carbon microsphere, silicon-carbon negative electrode material, and preparation method therefor
By preparing porous carbon microspheres with internal framework support and depositing elemental silicon within the pores, the problems of cumbersome synthesis and easy breakage of porous carbon microspheres were solved, thus improving the cycle stability and rate performance of silicon-based anode materials.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SHANGHAI SHANSHAN NEW MATERIAL CO LTD
- Filing Date
- 2024-11-15
- Publication Date
- 2026-05-21
AI Technical Summary
The existing porous carbon microsphere synthesis process is cumbersome, and the surface carbon coating layer is prone to cracking, resulting in volume expansion and poor conductivity of silicon-based anode materials in lithium-ion batteries, which affects cycle stability and rate performance.
A water-in-oil emulsion is formed by mixing solvent-based resin with framework-based carbon material. Porous carbon microspheres with internal framework support are prepared through carbonization and activation treatment, and elemental silicon is deposited in the pores to form a silicon-carbon anode material.
The preparation process of porous carbon microspheres was simplified, the strength and conductivity of the material were improved, the volume expansion of silicon-based anode materials was effectively alleviated, and the cycle stability and rate performance were enhanced.
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Figure CN2024132316_21052026_PF_FP_ABST
Abstract
Description
Porous carbon microspheres, silicon-carbon anode materials and their preparation methods Technical Field
[0001] This application relates to the field of lithium-ion batteries, and in particular to a porous carbon microsphere, a silicon-carbon anode material, and a method for preparing the same. Background Technology
[0002] With the rapid development of the power battery market, the demand for high-energy-density batteries is becoming increasingly apparent. However, the specific capacity of graphite is nearing its theoretical limit, making significant breakthroughs difficult. Silicon-based anode materials possess high theoretical capacity (4200 mAh / g) and a low voltage plateau (0.4 V vs. Li / Li). + Silicon-based anode materials are promising. However, during lithium insertion and extraction, silicon-based anode materials experience significant volume expansion (~300%) and contraction, leading to particle breakage and pulverization. This results in continuous damage and regeneration of the SEI film, causing a decline in battery performance. Furthermore, the poor conductivity of silicon also hinders the rapid development of silicon-based anode materials.
[0003] Employing porous carbon matrices can effectively mitigate the volume expansion of silicon-based anode materials. For example, porous carbon microspheres with abundant pores provide ample space for the volume expansion of silicon-based anode materials. However, the synthesis process of existing porous carbon microspheres is relatively cumbersome, hindering mass production. Furthermore, the carbon coating layer on the surface of porous carbon microspheres is a rigid structure, which will still break after repeated charge and discharge cycles, causing the porous carbon microspheres to deactivate. In addition, the strength of porous carbon matrices is reduced, which is not conducive to high-pressure compaction, and the intrinsic resistivity also increases with the increase of pore size in the carbon matrix.
[0004] Therefore, new methods for preparing porous carbon microspheres are needed. Summary of the Invention
[0005] This application provides a simple and rapid method for synthesizing porous carbon microspheres with high strength and low resistivity, and applies it to silicon-carbon materials, which can effectively alleviate the volume expansion of silicon-carbon materials and improve the cycle stability and rate performance of silicon-carbon materials.
[0006] One aspect of this application provides a method for preparing porous carbon microspheres, comprising: dissolving a solvent-based resin in a first organic solvent to form a first oil phase solution, wherein the first organic solvent is immiscible with water; mixing and uniformly dispersing the first oil phase solution with a framework-type carbon material; dissolving a surfactant in water as a first aqueous phase solution, wherein the surfactant includes both hydrophilic and hydrophobic groups; mixing the first aqueous phase solution and the first oil phase solution to form an oil-in-water emulsion system, wherein the volume ratio of the first aqueous phase solution to the first oil phase solution is greater than 1; removing water and the first organic solvent from the emulsion system to form resin microspheres with internal framework support; carbonizing the resin microspheres under oxygen-free conditions to form carbon microspheres with internal framework support; and activating the carbon microspheres to form the porous carbon microspheres.
[0007] In some embodiments of this application, the solid content in the solvent-based resin is 60-80%, and the volume ratio of the solvent-based resin to the first organic solvent is 1:1-3.
[0008] In some embodiments of this application, the solid content in the solvent-based resin is 60-80%, and the volume ratio of the solvent-based resin to the first organic solvent is 1:1-3.
[0009] In some embodiments of this application, the first organic solvent includes at least one selected from methyl acetate, ethyl acetate, n-propyl acetate, dichloromethane, carbon tetrachloride, 1,1-dichloroethane, 1,1,1-trichloroethane, benzene, and cyclohexane.
[0010] In some embodiments of this application, the framework carbon material includes at least one of carbon nanotubes and graphene, and the length of the framework carbon material is less than or equal to 10 μm.
[0011] In some embodiments of this application, the mass ratio of the surfactant to water is 1 to 4:100, and the surfactant includes at least one of PVA, sodium dodecyl sulfate, sodium benzenesulfonate, sodium dodecylbenzenesulfonate, sodium stearate, polyoxyethylene fatty acid ester, and polyoxyethylene fatty alcohol ether.
[0012] In some embodiments of this application, the volume ratio of the first aqueous phase solution to the first oil phase solution is 5 to 15:1.
[0013] In some embodiments of this application, the first aqueous phase solution and the first oil phase solution are added to an emulsifier for mixing, and the emulsion system is formed by the emulsifier. The time for forming the emulsion system is 0.5 to 3 minutes, and the shear rate of the emulsifier is 5000 to 20000 rpm.
[0014] In some embodiments of this application, the carbonization process is carried out under vacuum or inert atmosphere, and the carbonization temperature is 500-800°C, with a carbonization time of 1-3 hours.
[0015] In some embodiments of this application, the activation temperature of the activation treatment is 800-1000°C, the activation time is 6-12 hours, and the activation gas includes at least one of water vapor, carbon dioxide, and oxygen.
[0016] In some embodiments of this application, the skeleton volume accounts for 10% to 50% of the total volume of the porous carbon microspheres.
[0017] This application also provides a porous carbon microsphere, formed by any of the above methods, comprising: a porous carbon matrix and a framework, wherein the framework is embedded in the porous carbon matrix.
[0018] In some embodiments of this application, the skeleton volume accounts for 10% to 50% of the total volume of the porous carbon microspheres.
[0019] In some embodiments of this application, the framework includes at least one of carbon nanotubes and graphene, and the length of the framework is less than or equal to 10 μm.
[0020] This application also provides a method for preparing a silicon-carbon anode material, comprising: using any of the above-described porous carbon microspheres as a matrix, allowing silicon-containing gas to diffuse and adsorb into the pores of the porous carbon microspheres and undergo a cracking reaction within the pores, and depositing elemental silicon on the pore walls.
[0021] In some embodiments of this application, the method further includes forming a carbon coating layer on the surface of the silicon-carbon anode material.
[0022] In some embodiments of this application, the silicon-containing gas includes at least one of silane, silicon tetrachloride, trichlorosilane, dichlorosilane, and chlorosilane.
[0023] In some embodiments of this application, after elemental silicon is deposited in the pores of the porous carbon microspheres, the mass percentage content of the elemental silicon is 40-60%.
[0024] This application also provides a silicon-carbon anode material, comprising porous carbon microspheres as described in any one of the above; and elemental silicon located within the pores of the porous carbon microspheres.
[0025] In some embodiments of this application, a carbon coating layer is also formed on the surface of the porous carbon microspheres.
[0026] In some embodiments of this application, the mass percentage content of the elemental silicon is 40-60%.
[0027] Compared with the prior art, the porous carbon microspheres and their preparation method of this application have the following advantages:
[0028] By mixing and emulsifying the first oil phase solution and the first liquid phase solution to form an oil-in-water emulsion, resin microspheres with internal skeleton support are then prepared. The particle size of the resin microspheres can be adjusted by shear rate and feed rate, achieving micron- to millimeter-level control. The process is fast, the equipment is mature, and it is suitable for industrial production.
[0029] The activated porous carbon microspheres possess an excellent porous structure, providing effective space for silicon deposition and effectively mitigating silicon volume expansion. Their spherical particles are isotropic, effectively avoiding stress concentration, allowing them to withstand greater compressive stress and increasing compaction density.
[0030] The porous carbon microspheres contain a supporting framework, which can effectively improve the overall compressive strength of the particles and prevent particle breakage and pore damage during compression. Furthermore, the supporting framework is an excellent conductor material such as carbon nanotubes or graphene, which can ensure the rapid transmission of electrons inside the particles.
[0031] The carbon coating on the surface of the porous carbon microspheres can avoid side reactions caused by direct contact between the material surface and the electrolyte, and its amorphous structure can also ensure rapid ion transport, which can effectively improve the rate capability and cycle stability of the material. Attached Figure Description
[0032] The following accompanying drawings describe in detail the exemplary embodiments disclosed in this application. The same reference numerals denote similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting and exemplary, and the drawings are for illustrative purposes only and are not intended to limit the scope of this application. Other embodiments may similarly fulfill the inventive intent of this application. It should be understood that the drawings are not drawn to scale. Wherein:
[0033] Figure 1 is a schematic flowchart of the preparation method of porous carbon microspheres according to an embodiment of this application;
[0034] Figure 2 is a schematic diagram of the structure of porous carbon microspheres according to an embodiment of this application;
[0035] Figure 3 is a schematic diagram of the structure of the silicon-carbon anode material according to an embodiment of this application. Detailed Implementation
[0036] The following description provides specific application scenarios and requirements for this application, intended to enable those skilled in the art to make and use the content of this application. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.
[0037] Referring to Figure 1, the method for preparing porous carbon microspheres according to an embodiment of this application includes the following steps:
[0038] Step S1: Dissolve the solvent-based resin in a first organic solvent, then add the framework carbon material and disperse it evenly to form a first oil phase solution, wherein the first organic solvent is immiscible with water;
[0039] Step S2: Dissolve the surfactant in water to form a first aqueous solution, wherein the surfactant includes both hydrophilic and hydrophobic groups;
[0040] Step S3: Mix the first aqueous solution and the first oil solution to form an oil-in-water emulsion system, wherein the volume ratio of the first aqueous solution to the first oil solution is greater than 1;
[0041] Step S4: Remove water and the first organic solvent from the emulsion system to form resin microspheres with an internal skeleton support;
[0042] Step S5: Carbonize the resin microspheres under oxygen-isolated conditions to form carbon microspheres with an internal skeleton support.
[0043] Step S6: Activate the carbon microspheres to form the porous carbon microspheres.
[0044] Referring to step S1: The solvent-based resin is dissolved in a first organic solvent, and then a framework carbon material is added and uniformly dispersed to form a first oil phase solution, wherein the first organic solvent is incompatible with water; the embodiments of this application use a first organic solvent that is incompatible with water to form an oil-in-water emulsion system in subsequent processes.
[0045] In some embodiments of this application, the solvent-based resin includes at least one selected from phenolic resin, polyester resin, polyamide resin, melamine resin, urea-formaldehyde resin, and epoxy resin. The solid content of the solvent-based resin is 60-80%, which is the percentage by mass of the remaining portion after the emulsion or coating has been dried under specified conditions. For example, the solvent-based resin may be phenolic resin, a mixture of phenolic resin and polyamide resin, or a mixture of phenolic resin, polyester resin, and melamine resin.
[0046] The solvent-based resin described in this application is liquid at room temperature and solidifies upon curing. The volume ratio of the solvent-based resin to the first organic solvent is 1:1 to 3. In some embodiments of this application, the first organic solvent includes at least one selected from methyl acetate, ethyl acetate, n-propyl acetate, dichloromethane, carbon tetrachloride, 1,1-dichloroethane, 1,1,1-trichloroethane, benzene, and cyclohexane.
[0047] In some embodiments of this application, the framework carbon material includes at least one of carbon nanotubes and graphene; optionally, the framework carbon material is carbon nanotubes. In some embodiments of this application, the length of the framework carbon material is less than or equal to 10 μm. To ensure that the final porous carbon microspheres have a particle size D50 of 7–8 μm, and that the framework carbon material is mostly or entirely embedded within the porous carbon, considering the existence of bending points in carbon nanotubes or graphene, the length of the carbon nanotubes or graphene used is less than or equal to 10 μm. If excessively long or large carbon nanotubes / graphene are used, the solvent-based resin will adhere to them, resulting in excessively large particle sizes, or the carbon nanotubes / graphene will penetrate the entire particle, exhibiting a sea urchin-like shape, causing continuous compression of the particle surface during battery charging and discharging, thus damaging the SEI film.
[0048] Referring to step S2: The surfactant is dissolved in water to form a first aqueous phase solution, wherein the surfactant includes both hydrophilic and hydrophobic groups; in the embodiments of this application, the hydrophilic group includes at least one of carboxylic acid, sulfonic acid, or amino group; the hydrophobic group includes at least one of hydroxyl, alkyl, or phenyl group. Using a surfactant that includes both hydrophilic and hydrophobic groups allows the oil phase solution to be uniformly dispersed in the aqueous phase solution to form an emulsion.
[0049] In some embodiments of this application, the surfactant includes at least one selected from polyvinyl alcohol (PVA), sodium dodecyl sulfate, sodium benzenesulfonate, sodium dodecylbenzenesulfonate, sodium stearate, polyoxyethylene fatty acid ester, and polyoxyethylene fatty alcohol ether. In some embodiments of this application, the mass ratio of the surfactant to water is (1-4):100.
[0050] This application does not limit the execution order of steps S1 and S2.
[0051] Referring to step S3: The first aqueous phase solution and the first oil phase solution are mixed to form an oil-in-water emulsion system, wherein the volume ratio of the first aqueous phase solution to the first oil phase solution is greater than 1. In this embodiment, in order to form an oil-in-water emulsion system, the volume ratio of the first aqueous phase solution to the first oil phase solution is greater than 1, that is, the volume of the first aqueous phase solution must be greater than the volume of the first oil phase solution to ensure that water is a continuous external phase.
[0052] In some embodiments of this application, the first aqueous solution and the first oil phase solution are simultaneously fed into an emulsifier for mixing. After being subjected to high-speed shearing by the emulsifier, an oil-in-water emulsion system is formed. Through the high-speed shearing of the emulsifier, the continuously distributed solution in the first oil phase solution is separated to form small spherical solutions. Whether the molecules of the first oil phase solution are uniformly dispersed in the molecules of the first aqueous phase solution, or the molecules of the first aqueous phase solution are uniformly dispersed in the first oil phase solution, the oil-in-water emulsion system can be formed.
[0053] In some embodiments of this application, the volume ratio of the first aqueous phase solution to the first oil phase solution is (5-15):1, and the shearing speed of the emulsifier is 5000-20000 rpm. For example, the volume ratio of the first aqueous phase solution to the first oil phase solution is 7:1, 10:1, or 12:1, etc., and the shearing speed of the emulsifier is 5000-20000 rpm, such as 8000 rpm, 10000 rpm, 12000 rpm, or 18000 rpm, etc.
[0054] In some embodiments of this application, the volume ratio of the first aqueous solution to the first oil solution affects the size of the prepared porous carbon microspheres to a certain extent. As the volume of the first oil solution increases, the difficulty of dispersing the first oil solution in the first aqueous solution also increases, because a larger volume makes it easier to form a continuous phase, making it difficult to shear into small oil droplets. Shearing is the main process for dividing and uniformly dispersing the first oil solution in the first aqueous solution. The faster the shearing speed, the greater the shearing force on the first oil solution, making it easier to shear the first oil solution into small droplets, resulting in a better dispersion effect on the solution.
[0055] Referring to step S4: Remove water and the first organic solvent from the emulsion system to form resin microspheres with an internal skeleton support;
[0056] In other words, by evaporating the water and the first organic solvent in the emulsion system until the water and the first organic solvent in the emulsion system are completely removed, resin microspheres with internal skeleton support can be obtained, and the diameter of the resin microspheres is adjustable from 5 to 100 μm.
[0057] In the process of removing water and the first organic solvent from the emulsion system, the water-in-oil emulsion system is dried at 60°C to 80°C. During the drying process, the water evaporates, the solvent-based resin slowly solidifies, and the solvent-based resin molecules are encapsulated with skeletal carbon materials during the solidification process.
[0058] Referring to step S5: The resin microspheres are carbonized under oxygen-isolated conditions to form carbon microspheres with an internal framework support. During the carbonization process, the resin molecules in the resin microspheres undergo a carbonization reaction and are transformed into carbon microspheres. The carbonization reaction process includes the breaking of macromolecular C-C and CH bonds, the cleavage of oxygen- and nitrogen-containing functional groups, and then a series of complex physical and chemical processes such as cyclization and aromatization to transform them into carbon microspheres. The structure of the carbon microspheres contains a certain amount of porosity, which is beneficial for subsequent activation.
[0059] In some embodiments of this application, the carbonization process can be carried out under vacuum conditions or an inert atmosphere, wherein the inert atmosphere can be an inert atmosphere formed by at least one of nitrogen, argon or helium; the carbonization equipment used in the carbonization process can be a box furnace, a vacuum furnace, a pusher kiln or a rotary kiln; the carbonization temperature is 500-800℃ and the carbonization time is 1-3h.
[0060] Referring to step S6: The carbon microspheres are activated to form the porous carbon microspheres.
[0061] The activation treatment includes physical activation and chemical activation, with physical activation being preferred. The activation temperature is 800–1000℃, the activation time is 6–12 hours, and the activation gas includes at least one of water vapor, carbon dioxide, and oxygen.
[0062] The activation treatment aims to form a rich porous structure within the carbon microspheres. The activation process involves the reaction of an activator with the carbon microspheres. During this continuous reaction, some carbon atoms are consumed, leaving pores at those locations. Through the selective reaction of the active sites within the carbon microspheres with the activating gas, porous carbon microspheres with a multi-level (including microspheres and mesopores) pore structure are formed. The framework structure is stable and does not readily react with the activating gas, thus preserving its original structure well.
[0063] The porous carbon microspheres prepared in this embodiment have a specific surface area of 1300–2000 m². 2 / g, pore volume 0.6~1.0cm³ 3 / g, with micropores accounting for 60-95% and mesopores accounting for 5-40%, porous carbon microspheres with different pore size distributions can be obtained by adjusting the activation parameters, with a preferred specific surface area of 1800-2000 m². 2 / g, pore volume 0.8~1.0cm³ 3 / g, porous carbon microspheres with 90-95% micropores and 5-10% mesopores.
[0064] In the preparation method of porous carbon microspheres provided in this application embodiment, the framework is difficult to activate, which will also affect the pore size distribution. If the proportion of carbon nanotubes inside the porous carbon microsphere is high, activation will be difficult, and the specific surface area and pore volume will be low, which is not conducive to subsequent silicon deposition. If the proportion of carbon nanotubes (CNTs) inside the porous carbon microsphere is low, the strength and conductivity of the porous carbon microsphere cannot be effectively improved.
[0065] In this embodiment, the skeleton volume accounts for 10% to 50% of the total volume of the porous carbon microspheres, preferably 20% to 30%. The skeleton volume can be obtained by dividing the mass of the added carbon nanotubes by the density of the carbon nanotubes, and the mass of the added carbon nanotubes can be calculated by multiplying the mass of the added carbon nanotube slurry by the solid content, wherein the carbon nanotube slurry is a raw material.
[0066] The total volume of the porous carbon microspheres can be calculated by dividing the total mass of the resin microspheres by the particle density. Since all solvent-based resin solutions produce resin microspheres, the mass of the resin microspheres can be obtained by multiplying the mass of the first oil phase solution by the solid content of the first oil phase solution. The density of CNTs is 0.1 g / cm³. 3 The density of the resin microspheres is 0.3-0.5 g / cm³. 3 .
[0067] Referring to Figure 2, which is a schematic diagram of the structure of porous carbon microspheres formed in an embodiment of this application, the porous carbon microspheres include a porous carbon matrix 10 and a framework 11. The framework 11 is embedded in the porous carbon matrix 10, and the volume of the framework 11 accounts for 10% to 50% of the total volume of the porous carbon microsphere particles. In some embodiments of this application, the framework is a framework-type carbon material, which is uniformly and interwoven in the porous carbon matrix; the porous carbon matrix includes a plurality of pores 101, which include micropores and mesopores, with a pore volume of 0.6 to 1.0 cm³. 3 / g, with a microporous content of 60-95% and a mesoporous content of 5-40%. The framework carbon material includes at least one of carbon nanotubes and graphene, optionally, the framework carbon material is carbon nanotubes. In some embodiments of this application, the length of the framework carbon material is less than or equal to 10 μm, and the framework carbon material is mostly or entirely embedded in the porous carbon matrix.
[0068] In this embodiment, the particle size D50 of the porous carbon microspheres is 7-8 μm. The particle size of the porous carbon microspheres directly affects the particle size of the silicon-carbon anode material formed using these microspheres. The particle size of the silicon-carbon anode material has a significant impact on the performance of the final battery product. Excessively large particle sizes result in poor battery kinetics, longer transport paths, and poor rate performance; excessively small particle sizes lead to low efficiency, low capacity utilization, and also affect the homogenization process. Therefore, controlling the appropriate particle size is crucial for the performance of the final product.
[0069] This application also provides a method for preparing a silicon-carbon anode material, comprising: using any of the porous carbon microspheres described in the embodiments of this application as a matrix, allowing silicon-containing gas to enter the pores of the porous carbon microspheres through diffusion adsorption and undergo a cracking reaction in the pores, and depositing elemental silicon on the pore walls.
[0070] In some embodiments of this application, the silicon-containing gas includes at least one of silane, silicon tetrachloride, trichlorosilane, dichlorosilane, and chlorosilane. In some embodiments of this application, the porous carbon microspheres are used as a matrix and fed into a fluidized bed or CVD furnace. A silicon-containing gas, silane, is introduced and diffuses into the pores. Silicon is then deposited on the pore walls of the porous carbon microspheres via high-temperature pyrolysis to obtain a silicon-carbon material. The pyrolysis temperature of the silicon-containing gas is 400–900°C, and after the deposition of elemental silicon in the pores of the porous carbon microspheres, the mass percentage (wt%) of the elemental silicon is 40–60%.
[0071] In some embodiments of this application, the method further includes the step of carbon coating the surface of porous carbon microspheres deposited with elemental silicon within the pores to form a carbon coating layer. The method for forming the carbon coating layer includes gas-phase coating and liquid-phase coating, with gas-phase coating being preferred. The gas-phase coating method includes: subjecting a carbon-containing gas to high-temperature pyrolysis, thereby forming the carbon coating layer on the surface of the porous carbon microspheres deposited with elemental silicon within the pores. The carbon-containing gas includes any one or more of alkanes, alkenes, or alkynes. For example, one or more of methane, ethylene, and acetylene are introduced into a reactor, and high-temperature pyrolysis forms a uniform carbon coating layer on the entire surface of the silicon-carbon anode material. The temperature for forming the carbon coating layer is 500–800°C, and the coating time is 2–6 hours.
[0072] Referring to Figure 3, which is a schematic diagram of the structure of the silicon-carbon anode material formed in an embodiment of this application, the silicon-carbon anode material includes porous carbon microspheres 200 and elemental silicon 201 located within the pores of the porous carbon microspheres. Optionally, the mass percentage content of the elemental silicon is 40% to 60%.
[0073] In some embodiments of this application, the silicon-carbon anode material further includes a carbon coating layer 202 covering the surface of the porous carbon microspheres.
[0074] Example 1
[0075] Preparation of porous carbon microspheres:
[0076] Step S1: Add 20ml of phenolic resin (70% solid content, solvent is methanol) to 50ml of 1,1,1-trichloroethane (first organic solvent), stir until it is evenly dissolved, then add 200g of framework carbon material CNT slurry (solid content 0.4%), the length of the framework carbon material is controlled at about 10μm, and continue to disperse until uniform to form the first oil phase solution;
[0077] Step S2: Add 10g of sodium dodecyl sulfate (surfactant) to 500ml of deionized water and stir until completely dissolved to form the first aqueous phase solution;
[0078] Step S3: The first aqueous phase solution and the first oil phase solution formed in steps S1 and S2 are simultaneously injected into the emulsifier using a peristaltic pump. The first aqueous phase solution and the first oil phase solution are added within 1 minute. The shearing speed of the emulsifier is 10,000 rpm to obtain an oil-in-water emulsion system.
[0079] Step S4: Place the emulsion system obtained in step S3 into an 80°C water bath and evaporate it to dryness while stirring. After most of the solution has evaporated, transfer the material to a forced-air drying oven to dry it thoroughly and obtain resin microspheres.
[0080] Step S5: Place the resin microspheres into a rotary kiln, heat to 600℃ at 5℃ / min under nitrogen protection, and hold for 2 hours to obtain carbon microspheres;
[0081] Step S6: Under nitrogen protection, the temperature is increased to 900℃ at 5℃ / min, high-temperature water vapor is introduced, and the nitrogen is cut off at the same time. The temperature is maintained for 6 hours. After the temperature maintenance is completed, the high-temperature water vapor is cut off, and nitrogen is introduced at the same time until the temperature drops to room temperature, thus obtaining porous carbon microspheres.
[0082] Preparation of silicon-carbon anode materials:
[0083] The porous carbon microspheres formed in step S6 are fed into a fluidized bed, and silane is introduced into the fluidized bed at a rate of 5 L / min. After holding at 500℃ for 6 h, the silane gas is stopped to obtain silicon-carbon material (Si / C).
[0084] A methane-acetylene mixture (1:2) was introduced at a flow rate of 3 L / min and kept at 600 °C for 5 h. After the mixture was stopped, it was allowed to cool naturally to room temperature to obtain carbon-coated silicon-carbon material (Si / C@C).
[0085] Example 2
[0086] In step S3, the first aqueous phase solution and the first oil phase solution are added within 30 seconds. The remaining steps are completely consistent with those in Example 1.
[0087] Example 3
[0088] In step S3, the first aqueous phase solution and the first oil phase solution are added within 2 minutes. The remaining steps are completely consistent with those in Example 1.
[0089] Example 4
[0090] In step S3, the shearing speed of the emulsifier is 5000 rpm, and the remaining steps are completely consistent with those in Example 1.
[0091] Example 5
[0092] In step S3, the shearing speed of the emulsifier is 20,000 rpm, and the remaining steps are completely consistent with those in Example 1.
[0093] Example 6
[0094] In step S1, the amount of CNT slurry with a framework type carbon material added is 100g, and the remaining steps are completely consistent with those in Example 1.
[0095] Example 7
[0096] In step S1, the amount of CNT slurry with a framework type is 500g, and the remaining steps are completely consistent with those in Example 1.
[0097] Example 8
[0098] In step S1, the length of the framework carbon material CNT is approximately 30 μm, and the remaining steps are completely consistent with those in Example 1.
[0099] Comparative Example 1
[0100] This example does not add CNTs; the remaining steps are exactly the same as in Example 1.
[0101] Table 1 shows the particle size distribution data of the porous carbon microspheres formed in Examples 1-7 and the comparative examples. As can be seen from Table 1, the particle size of the obtained material can be controlled by adjusting the shear rate of the emulsifier in step S3 and the feed rate of the first aqueous phase solution and the first oil phase solution in step S3. As the shear rate increases, the particle size decreases, and vice versa. A faster feed rate results in a weaker shearing effect and a larger particle size, and vice versa. Long-diameter carbon nanotubes also cause a slight increase in particle size because the carbon nanotubes cannot be completely embedded inside the porous carbon, resulting in excessive external exposure and thus an increased particle size.
[0102] Table 1
[0103] Table 2
[0104] Table 2 shows a comparison of the electrical performance data of the silicon-carbon anode materials formed in the embodiments of this application. It can be seen that the compaction and rate performance of the material with the skeleton structure are better than those of the conventional structure, and the cycle stability is also greatly improved. This is because, in addition to the porous structure accommodating silicon expansion, the embedded skeleton structure can also further restrain and alleviate particle breakage caused by expansion.
[0105] Finally, it should be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments of this application. Other modified embodiments are also within the scope of this application. Therefore, the embodiments disclosed herein are merely examples and not limitations. Those skilled in the art can implement the applications in this application by adopting alternative configurations based on the embodiments in this application. Therefore, the embodiments of this application are not limited to those embodiments precisely described in the application.
Claims
1. A method for preparing porous carbon microspheres, characterized by, include: Solvent-based resin is dissolved in a first organic solvent, and then a framework carbon material is added and uniformly dispersed to form a first oil phase solution, wherein the first organic solvent is immiscible with water; A surfactant is dissolved in water to form a first aqueous phase solution, wherein the surfactant includes both hydrophilic and hydrophobic groups. The first aqueous solution and the first oil solution are mixed to form an oil-in-water emulsion system, wherein the volume ratio of the first aqueous solution to the first oil solution is greater than 1. Water and the first organic solvent are removed from the emulsion system to form resin microspheres with an internal skeletal support. The resin microspheres are carbonized under oxygen-free conditions to form carbon microspheres with an internal skeleton support. The carbon microspheres are activated to form the porous carbon microspheres.
2. The method of claim 1, wherein the porous carbon microspheres are prepared by the steps of: The solid content of the solvent-based resin is 60-80%, and the volume ratio of the solvent-based resin to the first organic solvent is 1:1-3.
3. The method of claim 2, wherein the porous carbon microspheres are prepared by the steps of: The first organic solvent includes at least one selected from methyl acetate, ethyl acetate, n-propyl acetate, dichloromethane, carbon tetrachloride, 1,1-dichloroethane, 1,1,1-trichloroethane, benzene, and cyclohexane.
4. The method of claim 1, wherein the porous carbon microspheres are prepared by the steps of: The framework carbon material includes at least one of carbon nanotubes and graphene, and the length of the framework carbon material is less than or equal to 10 μm.
5. The method of claim 1, wherein the porous carbon microspheres are prepared by the steps of: The mass ratio of the surfactant to water is 1 to 4:100, and the surfactant includes at least one of PVA, sodium dodecyl sulfate, sodium benzenesulfonate, sodium dodecylbenzenesulfonate, sodium stearate, polyoxyethylene fatty acid ester, and polyoxyethylene fatty alcohol ether.
6. The method of claim 1, wherein the porous carbon microspheres are prepared by the steps of: The volume ratio of the first aqueous phase solution to the first oil phase solution is 5 to 15:
1.
7. The method for preparing porous carbon microspheres according to claim 1, characterized in that, The first aqueous phase solution and the first oil phase solution are added to an emulsifier and mixed, and the emulsion system is formed by the emulsifier. The time for forming the emulsion system is 0.5 to 3 minutes, and the shear rate of the emulsifier is 5000 to 20000 rpm.
8. The method for preparing porous carbon microspheres according to claim 1, characterized in that, The carbonization process is carried out under vacuum or inert atmosphere, with a carbonization temperature of 500–800°C and a carbonization time of 1–3 hours.
9. The method for preparing porous carbon microspheres according to claim 1, characterized in that, The activation temperature of the activation treatment is 800-1000℃, the activation time is 6-12h, and the activation gas includes at least one of water vapor, carbon dioxide and oxygen.
10. The method for preparing porous carbon microspheres according to claim 1, characterized in that, The skeleton volume accounts for 10% to 50% of the total volume of the porous carbon microspheres.
11. A porous carbon microsphere formed using any one of the methods of claims 1 to 10, comprising: A porous carbon matrix and a framework, wherein the framework is embedded in the porous carbon matrix.
12. The porous carbon microspheres according to claim 11, characterized in that, The volume of the skeleton accounts for 10% to 50% of the total volume of the porous carbon microspheres.
13. The porous carbon microspheres according to claim 11, characterized in that, The framework includes at least one of carbon nanotubes and graphene, and the length of the framework is less than or equal to 10 μm.
14. A method for preparing a silicon-carbon negative electrode material, characterized by, include: Using the porous carbon microspheres according to any one of claims 11 to 13 as a matrix, silicon-containing gas is introduced into the pores of the porous carbon microspheres through diffusion and adsorption, and a cracking reaction occurs in the pores, thereby depositing elemental silicon on the pore walls.
15. The method of claim 14, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The method further includes forming a carbon coating layer on the surface of the silicon-carbon anode material.
16. The method of claim 14, wherein the silicon-carbon negative electrode material is prepared by a process comprising: The silicon-containing gas includes at least one of silane, silicon tetrachloride, trichlorosilane, dichlorosilane, and chlorosilane.
17. The method of producing a silicon-carbon negative electrode material according to claim 14, characterized by, The mass percentage content of the elemental silicon in the porous carbon microspheres is 40-60%.
18. A silicon-carbon negative electrode material, characterized in that, Comprise: The porous carbon microspheres according to any one of claims 11-13; And the elemental silicon in the pores of the porous carbon microspheres.
19. The silicon-carbon negative electrode material of claim 18, wherein, The surface of the porous carbon microspheres is further formed with a carbon coating layer.
20. The silicon-carbon negative electrode material of claim 18, wherein, The mass percentage content of the elemental silicon is 40-60%.