Preparation method of porous carbon for silicon-carbon anode material

Abstract

The present invention provides a preparation method of porous carbon for silicon-carbon anode materials, belonging to the field of anode materials for lithium-ion batteries. The preparation method of the porous carbon for the silicon-carbon anode materials includes the following steps: crushing and grading, activation and pore formation, washing and purification, and high-temperature carbonization. The preparation method of the porous carbon for the silicon-carbon anode materials of the present invention, while solving the technical problems of difficult improvement in the yield of the porous carbon for the current silicon-carbon anode materials, difficult control in the activation process, low activation efficiency, poor activation effect, and high cost for preventing and controlling metal pollution, further improves the uniformity of the pore structure of the porous carbon for the silicon-carbon anode materials, improves the quality of the porous carbon, improves the production efficiency, and reduces the production cost.

Description

Technical Field

[0001] The present invention belongs to the field of anode materials for lithium-ion batteries, and particularly relates to a preparation method of porous carbon for silicon-carbon anode materials. Background Art

[0002] With the rapid development of industries such as lithium-ion vehicles and electronics, the requirement for battery energy density is getting higher and higher. Currently, due to the high theoretical specific capacity of silicon-based anode materials, they are considered as the first choice for the next-generation high-capacity lithium-ion battery anode materials. Among them, the embedded silicon-carbon anode is one of the earliest commercialized silicon-carbon anode materials, and silicon particles are usually embedded in a continuous carbon matrix. Therefore, the pore structure of the carbon matrix can effectively affect the structural stability and cycle life of the material.

[0003] As a kind of carbon matrix, porous carbon has the advantages of high specific surface area, pore volume, good chemical stability and cycle stability, and is widely used in the field of energy storage. The traditional porous carbon manufacturing process is mostly as follows: carbonize the selected biomass raw materials, and through high-temperature pyrolysis, convert the raw materials into carbon materials; crush the carbonized materials to less than 1 mm; the materials after coarse crushing need to be activated to increase their specific surface area and pore structure. The commonly used activation method is to react KOH, etc. with the carbon materials at high temperature in a rotary kiln to expand their pore diameters; after activation treatment, wash and purify the products to remove the residual impurities in the materials; under an inert atmosphere, calcine the washed and impurity-removed materials at high temperature to remove the possible functional groups, etc. in the materials and stabilize the pore structure; use air jet mills, mechanical mills, etc. to crush the materials and then screen out qualified products through classification.

[0004] However, with the practical application of the above method, some difficult-to-solve technical problems have also emerged: 1. The particle size of the material after coarse crushing is uneven, and the particle size, shape and specific surface area vary greatly between the particles. In order to ensure the activation effect during activation in the rotary kiln, the required activation time is long and the activation efficiency is low; during the long activation process, the material is prone to over-activation, that is, over-corrosion, resulting in the phenomenon of porous carbon pores, broken holes, perforations, etc., the activation effect is not good, and the product yield is directly reduced; further, if the material is crushed to a smaller particle size before activation, it will make it easier to over-activate in the subsequent activation, and the activation process is extremely difficult to control. 2. The particle size of the material after coarse crushing is uneven, and the particle size, shape and specific surface area vary greatly between the particles. Under the same activation time, it also leads to high uneven particle activation and poor activation effect; and in the subsequent processing of large particle materials after activation to the finished product particle size, the pore structure will inevitably be destroyed (such as broken holes, perforations, etc.) due to the crushing, which will further lead to a decrease in the uniformity of the pore structure of the porous carbon finished product and a decrease in the yield. 3. The activated material is still in the state of large particles, and it is not easy to remove impurities inside the particles during washing; and the center of the large particles may not be fully activated, resulting in low quality of the finished product after crushing. 4. Battery materials need to prevent metal contamination, so the lining of porous carbon crushing equipment generally needs to be ceramicized, and the equipment cost is high. However, as the crushing efficiency is higher than that of air flow mills and mechanical impact mills, it is difficult to achieve ceramic linings for equipment such as ring roller mills, so they are rarely used, and porous carbon cannot be processed efficiently and at low cost; 5. The particle size and particle size distribution requirements of general qualified products are very strict, so the requirements for the classifier are very high. When the particle size is very fine, the efficiency of the classifier will also be reduced accordingly, and the classification of fine particles of 2um and above will fail, that is, in order to remove fine particles of 2um and above, some coarse qualified particles of 2um and above will be lost; 6. The aforementioned traditional process defects limit the yield of porous carbon products to between 10-15%, which is relatively low and difficult to effectively improve.

[0005] Therefore, there is an urgent need to provide a method for preparing porous carbon for silicon-carbon negative electrode material to solve the above problems. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing porous carbon for silicon-carbon negative electrode materials, while solving the technical problems that the yield of porous carbon for silicon-carbon negative electrode materials is difficult to improve, the activation process is difficult to control, the activation efficiency is low, the activation effect is poor, and the cost of metal pollution prevention and control is high, while further improving the uniformity of the pore structure of porous carbon for silicon-carbon negative electrode materials, improving the quality of porous carbon, improving production efficiency, and reducing production costs.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method of porous carbon for silicon-carbon anode materials, comprising the following steps: crushing and grading, activation and pore formation, washing, and carbonization;

[0009] The method of crushing and grading is that the pyrolysis carbonized material is crushed and graded to obtain the crushed and graded material;

[0010] The pyrolysis carbonized material is prepared by using biomass raw materials and / or non-biomass raw materials;

[0011] The method of activation and pore formation is that in a fluidized bed device, in the presence of an activation gas, the crushed and graded material is subjected to activation and pore formation treatment to obtain the activated and pore-formed material.

[0012] Preferably, in the crushing and grading, the particle size specifications of the crushed and graded material are D10≥2um, D50: 5-10um, D90≤15um, Dmax≤25um.

[0013] Preferably, in the activation and pore formation, the activation gas is at least one of the following: water vapor, CO2.

[0014] Preferably, in the activation and pore formation, the activation and pore formation temperature is 800-1100°C, and the activation and pore formation time is 1-5h.

[0015] Furthermore, when the pyrolysis carbonized material is prepared by using non-biomass raw materials and / or biomass raw materials, before the crushing and grading step, there is also: pyrolysis carbonization;

[0016] The method of pyrolysis carbonization is that under the protection of an inert gas, the non-biomass raw material / or biomass raw material is subjected to pyrolysis carbonization treatment to obtain the pyrolysis carbonized material.

[0017] Furthermore, when the pyrolysis carbonized material is prepared by using biomass raw materials or by using biomass raw materials and non-biomass raw materials, before the crushing and grading step, there is also: steam explosion, pyrolysis carbonization;

[0018] The method of steam explosion is that in the presence of water vapor, the biomass raw material is subjected to steam explosion treatment to obtain the steam explosion material;

[0019] The method of pyrolysis carbonization is that under the protection of an inert gas, the steam explosion material is subjected to pyrolysis carbonization treatment to obtain the pyrolysis carbonized material; or the steam explosion material is mixed with the non-biomass raw material for pyrolysis carbonization treatment; to obtain the pyrolysis carbonized material.

[0020] Furthermore, when the pyrolysis carbonized material is prepared by using biomass raw materials, before the crushing and grading step, there is also: steam carbonization, steam explosion;

[0021] The method of steam carbonization is to perform steam carbonization treatment on biomass raw materials in the presence of water vapor;

[0022] The method of steam explosion is that after the steam carbonization is completed, the temperature of the steam carbonization is kept unchanged, and the pressure is released for steam explosion to obtain pyrolysis carbonized materials.

[0023] Furthermore, the activated pore-forming materials are washed and carbonized to prepare porous carbon for silicon-carbon anode materials.

[0024] Furthermore, the method of washing is to completely immerse the activated pore-forming materials in hydrochloric acid or a mixed acid solution, soak them after heating, wash them to neutrality, and dry them to obtain purified materials.

[0025] Preferably, the mass fraction of the hydrochloric acid solution is 5-20%.

[0026] Preferably, the mixed acid is at least two of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0027] Furthermore, the method of carbonization is to perform carbonization treatment on the purified materials obtained by washing under the protection of an inert gas, and control the high-temperature carbonization temperature to be not lower than 1000 °C to obtain porous carbon for silicon-carbon anode materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1)The preparation method of the porous carbon for the silicon-carbon anode material of the present invention uses a fluidized bed to replace the rotary kiln in the traditional process for the activation and pore-forming treatment of the pyrolyzed and carbonized material. In the fluidized bed, the carbon material particles are in a suspended motion state, greatly increasing the contact area between the particles and the gas. Moreover, the particles are constantly mixed and tumbled in the bed layer, prompting the activator to fully contact the material, thereby enhancing the diffusion rate of the activator into the interior of the material, making the activation reaction more complete, and improving the efficiency of the activation reaction. The intense movement of the particles in the fluidized bed makes the temperature distribution in the bed layer more uniform. On the one hand, the rapid heat exchange between the gas and the particles ensures that the particles can quickly obtain the heat required for the activation reaction, enabling the activation reaction to proceed under suitable temperature conditions. On the other hand, the uniform temperature distribution can avoid the occurrence of local overheating or overcooling phenomena, reduce the product quality differences caused by uneven temperature, and improve the stability of product quality. The fluidization state of the solid particles in the fluidized bed makes their distribution in the bed layer relatively uniform, and each particle has a similar motion trajectory and residence time. This makes the activation conditions experienced by each particle basically the same, including the concentration of the activator, reaction temperature, reaction time, etc., thus ensuring the uniformity of the activation reaction in the entire material system, and the quality of the final product is also more uniform and stable. Compared with the rotary kiln activation in the traditional process, the fluidized bed can effectively avoid phenomena such as material accumulation and blockage in the reactor, reduce the situation of local over-activation or under-activation caused by uneven material distribution, and improve the activation effect and quality stability of the product.

[0030] (2) When using a rotary kiln for activation and pore formation, there are problems such as uneven activation of materials in the rotary kiln and easy over-activation of materials. Therefore, before using a rotary kiln for activation and pore formation in the traditional process, only coarse crushing of the materials is carried out, and the particle size of the materials is relatively large to reduce the impact of over-activation. At the same time, due to the relatively large particle size of the materials, in order to improve the activation efficiency, potassium hydroxide is often used as the activator during activation. Even so, a relatively long activation time is still required to achieve a good activation effect, the activation efficiency is low, and since potassium hydroxide is used as the activator, a large amount of purified water is required in the subsequent washing and purification stage to wash it to neutral. To solve the inevitable problems of long activation time, low activation efficiency, large environmental pollution, and waste of water resources in the subsequent washing and purification process when using a rotary kiln for activation and pore formation, the present invention uses a fluidized bed for activation and pore formation. The activation reaction proceeds uniformly in the entire material system, effectively improving the control of the activation process. Therefore, the materials can be directly crushed and classified to a particle size close to that of the final porous carbon product before activation and pore formation, effectively avoiding the over-activation problem of the materials during activation. At the same time, the materials with a small particle size require relatively less energy during activation, and due to the increased reaction area, the activation and pore formation time is significantly shortened, improving the activation and pore formation efficiency. Therefore, when using a fluidized bed for activation and pore formation in the present invention, steam and / or carbon dioxide can be selected as the activator for activation and pore formation, which can improve the activation and pore formation efficiency, reduce the activation energy consumption, improve the activation effect, and avoid the waste of water resources in the washing and purification process.

[0031] (3) Based on the advantages of high activation and pore formation efficiency, short time, easy control of the activation process, low degree of over-activation, and good product uniformity of the fluidized bed, the present invention replaces the coarse crushing step in the traditional process with crushing and classification, and directly crushes and classifies the pyrolyzed and carbonized materials to a particle size close to the final particle size required for porous carbon. The materials after subsequent high-temperature carbonization no longer need to be crushed and classified, and the finished product can be directly obtained. In the traditional process, the crushing and classification step is the last step in the preparation of carbon materials. Since the requirement for the particle size of porous carbon materials is D0≥2μm, it is difficult for commonly used classification equipment to achieve. Therefore, if the particle size of the final product is to meet the requirements, a part of the materials that meet the particle size requirements and small particles that do not meet the particle size requirements must be removed together, and the classification efficiency is relatively low at this time, resulting in a reduction in the yield of the final product. In the process proposed by the present invention, because a part of the particles will be corroded during the activation and pore formation process, the particle size of the particles is further reduced. Therefore, the crushing and classification step only needs to crush to a particle size close to the requirements of the finished product. The materials that were originally close to the particle size requirements of the finished product can meet the particle size requirements of the finished product after the activation reaction. Thus, the classification requirements for the classification equipment are effectively reduced, thereby improving the crushing and classification efficiency and effectively increasing the yield of the final product.

[0032] (4) Since the crushing and classification step is advanced to before the washing and purification step, the selection of the crushing and classification equipment does not need to consider the contamination of the material by the equipment material. Because even if metal impurities are introduced, they can be removed by pickling in the washing and purification step. Therefore, equipment with high crushing and classification efficiency or more economical but not easily preventing metal contamination can be selected, such as ring roll mills, thereby further improving the yield of this step and the final output. In addition, advancing the crushing and classification step can also avoid the destruction of the pore structure such as broken pores and perforations during the subsequent crushing of the activated large particles to the particle size of the porous carbon finished product, effectively improving the pore structure uniformity of the porous carbon material and ensuring the quality and yield of the finished product.

[0033] (5) During the fluidized bed activation pore formation and washing and purification processes, ultrafine powders that do not meet the product particle size requirements (such as finer than 1um) can be further removed, thereby further improving the quality of the porous carbon product and the safety and final product quality of the subsequent production process of preparing silicon-carbon anode materials by chemical vapor deposition in a fluidized bed. Due to their small particle size and large specific surface area, these ultrafine powders have strong van der Waals forces and surface energy between particles, resulting in small particles tightly agglomerating together or adsorbing onto large particles. It is very difficult to remove them completely by means of air classification in the crushing and classification stage in traditional processes. The large specific surface area of these small particles can provide more active sites in the CVD reaction. These sites will catalyze chemical reactions, accelerating the reaction rate, and a large amount of reaction heat will be rapidly released in a short time, leading to a sharp rise in temperature and triggering a runaway temperature. In addition, during the CVD process, Si-C bonds will be formed between carbon and silicon, and a large amount of heat will be released during the bonding process. The heat transfer between the agglomerated small particles is blocked, and the reaction heat inside the agglomerates cannot be effectively dissipated, resulting in a high-temperature region inside the agglomerates and leading to a runaway temperature. This causes certain quality problems and safety problems in the CVD process. In addition, due to the certain classification effect during the fluidized bed activation pore formation and washing and purification processes, the crushing and classification step can reduce the requirements for the particle size distribution of the material, enabling a higher yield to be maintained in the crushing and classification stage;

[0034] (6) For pyrolysis carbonized materials prepared using biomass raw materials, pretreating the raw materials with steam explosion or steam explosion plus carbonization before pyrolysis carbonization will improve the reaction efficiency of the subsequent process, and can also improve the uniformity and stability of the cell structure of the biomass raw materials, effectively solving the disadvantage of poor batch stability of biomass raw materials, reducing the batch differences of products, and being conducive to ensuring the long-term quality of products.

[0035] Steam explosion improves the reaction efficiency of the subsequent process:

[0036] Place materials (such as biomass like lignocellulosic raw materials, straw, etc.) in a sealed container and introduce high-temperature and high-pressure steam. The steam will gradually penetrate into the internal pores of the materials and structures such as cell walls. Under the high-temperature and high-pressure environment, components such as lignin in the materials will soften, and the forces such as hydrogen bonds between cellulose molecules will also be weakened, making the overall structure of the materials become relatively loose, laying the foundation for the subsequent explosion process. For example, for wood raw materials, the originally dense and hard wood structure will become more easily damaged after the action of steam. When the materials are fully acted upon by steam in the sealed container for the set time, the pressure is suddenly released, and the internal high-pressure environment will rapidly change to an atmospheric pressure environment. At this time, due to the sudden release of steam pressure inside the materials, a huge pressure difference will be generated. This pressure difference is like triggering countless "micro-explosions" inside the materials, strongly damaging the organizational structure of the materials. Structures such as the cell walls of the materials will rupture and tear due to the rapid expansion of the internal steam, and the originally closely connected components such as fibers will be scattered and separated. The originally larger pieces of materials will break into smaller particles or fiber bundles, etc., forming a loose and fragmented physical structure, which has a larger specific surface area and increases the contact opportunities with external substances (such as enzymes, chemical reagents, etc.). Whether it is subsequent biological conversion, chemical modification, or other processing, the reaction efficiency will be significantly improved. Since the connections between cellulose, hemicellulose, and lignin are broken, part of the lignin will degrade into some small-molecule soluble substances, increasing the porosity and specific surface area of the biomass raw materials; steam explosion can also reduce the crystallinity of cellulose, increasing the mobility of cellulose molecular chains. These advantages make it easier for the materials to come into contact with and react with the materials during the subsequent pyrolysis carbonization and activation pore-forming processes, thereby improving the reaction efficiency.

[0037] Steam explosion improves the batch stability of raw materials:

[0038] During the steam explosion process, the hydrogen bond-breaking effect causes the tight connections between cellulose, hemicellulose, and lignin to be untied. After the hydrogen bonds are broken, lignin and hemicellulose can be more evenly dispersed around cellulose. The originally tightly aggregated cellulose molecular chains become loose, helping to make the internal structure of the raw materials more uniform. This uniform structure is beneficial for subsequent processing. For example, in the enzymatic hydrolysis process, enzymes can more evenly contact cellulose. Because after the hydrogen bonds are broken, the surface area of cellulose increases, and the interaction between enzymes and substrates becomes more uniform, thus improving the uniformity of the reaction. Although the hydrogen bonds are broken, during the steam explosion process, some new interactions will form between the components of the raw materials. For example, some products generated by the hydrolysis of hemicellulose may undergo chemical cross-linking reactions with cellulose or lignin. These new connection methods to a certain extent replace the original hydrogen bonds and form a more stable structure.

[0039] For different biomass raw materials, their original structures vary greatly, and there may be some areas with dense local structures and fewer pores. The powerful impact generated by steam explosion will damage the cell structure of the biomass raw material, tear and disperse the fiber tissues with different internal structures of the biomass raw material caused by factors such as growth environment and growth cycle. The originally uneven structure tends to form a more uniform state under this external force, forming a relatively uniform fibrous material. Moreover, the lignin in the biomass raw material will be redistributed around the cellulose to a certain extent, forming a relatively stable support structure, which is similar to building a stable framework around the pores, making the pores not easily collapse during subsequent processing (such as drying, storage or further chemical treatment). During the steam explosion process, the partial hydrolysis of hemicellulose and the modification of lignin contribute to stabilizing the chemical composition of the raw material. Hemicellulose plays a role in filling and connecting cellulose microfibrils in the cell wall structure of the raw material. Hydrolysis products of hemicellulose (such as xylose, etc.) during the steam explosion process can be released from the raw material to a certain extent, making the content and composition of hemicellulose more stable during subsequent processing, making the connection between cellulose microfibrils loose, and facilitating the formation of more uniformly distributed pores. The softening and partial degradation of lignin change its wrapping state of cellulose and hemicellulose, making the cellulose in the raw material more easily utilized. Moreover, this change in chemical structure reduces the impact of chemical composition differences of biomass raw materials due to different sources (such as different planting environments and different varieties of plant raw materials) on product quality to a certain extent.

[0040] Adjustment of the pore structure of carbon materials by steam explosion:

[0041] During the steam explosion process, high-temperature and high-pressure steam penetrates into the interior of the carbon material. When the pressure is released instantaneously, the impact force generated by the rapid expansion of the steam will cause new pores to form inside the carbon material. These new pores increase the specific surface area of the carbon material, resulting in more surface active sites, which is beneficial to improving the performance of the carbon material in adsorption, catalysis, etc.; the powerful force generated by the steam explosion can cause the original smaller pores in the carbon material to expand. On the one hand, the carbon material at the pore edge may be partially peeled off or stretched under the impact of the steam, increasing the pore diameter; on the other hand, the thermal effect during the steam explosion process will also cause a certain degree of softening and deformation of the carbon material structure, thus promoting the expansion of the original pores, further improving the pore structure of the carbon material and enhancing its adsorption and accommodation capacity for macromolecular substances; steam explosion can make the pore distribution of the carbon material more uniform. During the explosion process, the diffusion and expansion of steam inside the carbon material are relatively uniform, making the formation and expansion degree of pores in different parts of the carbon material tend to be consistent, thus optimizing the pore structure of the carbon material, enabling it to come into contact with external substances more fully during application, and improving the reaction efficiency and performance stability; the impact force and thermal effect of steam explosion will also change the shape of the pores in the carbon material. The originally irregular or narrow pores may become more rounded and regular under the action of steam explosion, reducing the resistance inside the pores and increasing the diffusion rate of substances in the pores, further enhancing the performance of the carbon material.

[0042] Influence of steam carbonization:

[0043] The moisture in the material is evaporated and removed under the heat provided by the steam. First, the free water is quickly removed. As the temperature further increases, the bound water will also gradually detach from the material structure. For example, a large amount of moisture originally contained in biomass raw materials (such as straw, etc.) turns into water vapor and is discharged after steam heating. This process helps the subsequent carbonization reaction to proceed more efficiently and can reduce the moisture content of the carbon generated subsequently to a certain extent; as the temperature continues to rise, the organic components in the material begin to pyrolyze. Macromolecular organic compounds (such as lignin, cellulose, hemicellulose, etc. in biomass) will break down into small-molecule volatile substances (including combustible gases such as carbon monoxide, methane, hydrogen, etc. and some organic volatiles) and solid carbon. In a steam environment, the steam can play a dilution role, timely carry away some of the volatile substances generated by pyrolysis, promote the pyrolysis reaction to proceed in the direction of generating more carbon, and at the same time is also conducive to the uniform distribution of heat and prevents local overheating and other situations; when steam participates in some processes aimed at preparing carbon materials with a high specific surface area and porous structure, the steam also plays an activation role. High-temperature steam can react with the initially formed carbon, for example, react with some active carbon atoms in the carbon, etch the surface of the carbon, make it form more pore structures, increase the specific surface area, and thus improve the adsorption performance and other related characteristics of the carbon. Commonly seen in processes such as activated carbon preparation, using steam activation can make activated carbon have stronger abilities to adsorb impurities, gases, etc.; the steam fills the carbonization environment and can displace air, reducing the chance of contact between the material and oxygen. Because if a large amount of oxygen exists during the carbonization process, the material is prone to oxidation reactions such as combustion, which is not conducive to the formation of carbon, and the relatively oxygen-isolated environment formed by the steam ensures that the carbonization process can proceed stably as expected, enabling the material to be mainly transformed according to reaction paths that are conducive to carbon formation such as pyrolysis. Description of the Drawings

[0044] Figure 1 Graph of the conductivity test results of the porous carbon materials for silicon-carbon anodes obtained in Examples 1-3 and Comparative Examples 1-2. Detailed Embodiments

[0045] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0046] The present invention provides a method for preparing porous carbon for a silicon-carbon anode material, which includes the following steps: crushing and grading, activation and pore formation, washing, and carbonization;

[0047] The method of crushing and classifying is as follows: the pyrolyzed and carbonized material is crushed and classified to obtain the crushed and classified material;

[0048] The pyrolyzed and carbonized material is prepared by using biomass raw materials and / or non-biomass raw materials;

[0049] The method of activating and creating pores is as follows: in a fluidized bed device, in the presence of an activating gas, the crushed and classified material is subjected to an activating and pore-creating treatment to obtain the activated and pore-created material;

[0050] The method of washing is as follows: the activated and pore-created material is completely immersed in hydrochloric acid or a mixed acid solution, soaked after heating, washed to neutrality, and dried to obtain the purified material;

[0051] The method of carbonization is as follows: under the protection of an inert gas, the purified material obtained by washing is carbonized, and the high-temperature carbonization temperature is controlled to be not lower than 1000 °C to obtain porous carbon for silicon-carbon anode materials.

[0052] On the basis of the foregoing technical solution, preferably, in the crushing and classification, the particle size specifications of the crushed and classified material are D10≥2um, D50: 5-10um, D90≤15um, Dmax≤25um.

[0053] On the basis of the foregoing technical solution, preferably, in the activating and pore-creating, the activating gas is at least one of the following: water vapor, CO2.

[0054] On the basis of the foregoing technical solution, preferably, in the activating and pore-creating, the activating and pore-creating temperature is 800-1100 °C, and the activating and pore-creating time is 1-5h.

[0055] On the basis of the foregoing technical solution, preferably, in the activating and pore-creating, the gas linear velocity of the activating gas in the fluidized bed is controlled to be 0.05-0.5m / s, and the fluidized bed pressure is maintained at 1-100KPa.

[0056] On the basis of the foregoing technical solution, preferably, in the washing, the mass fraction of the hydrochloric acid solution is 5-20%; the mixed acid is at least two of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0057] On the basis of the foregoing technical solution, as a preferred implementation manner, when the pyrolyzed and carbonized material is prepared by using non-biomass raw materials and / or biomass raw materials, before the crushing and classification step, it further includes: pyrolysis and carbonization;

[0058] The method of pyrolysis and carbonization is as follows: under the protection of an inert gas, the non-biomass raw materials and / or biomass raw materials are subjected to pyrolysis and carbonization treatment to obtain the pyrolyzed and carbonized material.

[0059] Preferably, the temperature of pyrolytic carbonization is 750 - 850 °C, the heating rate of pyrolytic carbonization is 3 - 8 °C / min, and the heat preservation time of pyrolytic carbonization is 1 - 3 h; more preferably, the temperature of pyrolytic carbonization is 800 °C, the heating rate of pyrolytic carbonization is 5 °C / min, and the heat preservation time of pyrolytic carbonization is 2 h.

[0060] In view of the situation of preparing pyrolytic carbonization materials using non-biomass raw materials and / or biomass raw materials, the present invention directly sets a pyrolytic carbonization step before comminution and classification, directly conducts pyrolytic carbonization treatment on the non-biomass raw materials and / or biomass raw materials to obtain pyrolytic carbonization materials; then uses the pyrolytic carbonization materials for subsequent comminution and classification treatment.

[0061] On the basis of the above technical solution, as a preferred parallel implementation manner, when the pyrolytic carbonization materials are prepared using biomass raw materials or using biomass raw materials and non-biomass raw materials, before the comminution and classification step, there are further included: steam explosion, pyrolytic carbonization;

[0062] The method of steam explosion is to conduct steam explosion treatment on biomass raw materials in the presence of water vapor to obtain steam explosion materials;

[0063] The method of pyrolytic carbonization is to conduct pyrolytic carbonization treatment on the steam explosion materials under the protection of inert gas to obtain pyrolytic carbonization materials; or mix the steam explosion materials with non-biomass raw materials for pyrolytic carbonization treatment; to obtain pyrolytic carbonization materials.

[0064] Preferably, the steam explosion temperature is 170 - 190 °C, the steam explosion pressure is 0.8 - 1.4 MPa, and the steam explosion pressure holding time is 5 - 15 min; more preferably, the steam explosion temperature is 180 °C, the steam explosion pressure is 1.0 MPa, and the steam explosion pressure holding time is 10 min.

[0065] Preferably, the temperature of pyrolytic carbonization is 750 - 850 °C, the heating rate of pyrolytic carbonization is 3 - 8 °C / min, and the heat preservation time of pyrolytic carbonization is 1 - 3 h; more preferably, the temperature of pyrolytic carbonization is 800 °C, the heating rate of pyrolytic carbonization is 5 °C / min, and the heat preservation time of pyrolytic carbonization is 2 h.

[0066] In view of the situation of preparing pyrolytic carbonization materials using biomass raw materials, before comminution and classification, first conduct steam explosion treatment on the biomass raw materials therein to obtain steam explosion materials; then conduct pyrolytic carbonization treatment on the steam explosion materials or the mixture of steam explosion materials and non-biomass raw materials to obtain pyrolytic carbonization materials; then use the pyrolytic carbonization materials for subsequent comminution and classification treatment.

[0067] On the basis of the foregoing technical solutions, as a preferred parallel implementation, when the pyrolytic carbonized material is prepared from biomass raw materials, before the crushing and classification steps, there are further included: steam carbonization and steam explosion;

[0068] The method of steam carbonization is to perform steam carbonization treatment on biomass raw materials in the presence of water vapor;

[0069] The method of steam explosion is that after the steam carbonization is completed, the steam carbonization temperature is kept unchanged, the pressure is released for steam explosion, and the pyrolytic carbonized material is obtained.

[0070] Preferably, the temperature of the steam carbonization is 210 - 240 °C, the steam carbonization pressure is 2.1 - 2.6 MPa, and the steam carbonization time is 40 - 60 min; more preferably, the temperature of the steam carbonization is 220 °C, the steam carbonization pressure is 2.4 MPa, and the steam carbonization time is 45 min.

[0071] In the case of preparing pyrolytic carbonized materials from biomass raw materials, the present invention performs steam carbonization and steam explosion treatment on biomass raw materials before crushing and classification to obtain pyrolytic carbonized materials; then the subsequent crushing and classification treatment is carried out using the pyrolytic carbonized materials.

[0072] The present invention will be further described by way of examples below, but the protection scope of the present invention is not limited to these embodiments.

[0073] Example 1

[0074] This example provides a method for preparing porous carbon for silicon-carbon anode materials, specifically as follows:

[0075] Step 1, pyrolytic carbonization: Place the cleaned and dried coconut shell (i.e., the pyrolytic carbonization raw material) in a pyrolytic carbonization furnace, introduce nitrogen as a protective gas, and heat it to 800 °C at a heating rate of 5 °C / min, keep it for pyrolytic carbonization for 2 h, and take it out after natural cooling to room temperature to obtain the pyrolytic carbonized coconut shell charcoal (i.e., the pyrolytic carbonized material);

[0076] Step 2, crushing and classification: Directly crush the pyrolytic carbonized coconut shell charcoal to the particle size specifications of the finished porous carbon, that is, crush it to D10≥2um, D50: 5 - 10um, D90≤15um, Dmax≤25um, to obtain the crushed and classified coconut shell charcoal (i.e., the crushed and classified material);

[0077] Step 3, activation and pore formation: Place 1 kg of the crushed and classified coconut shell charcoal in a fluidized bed, introduce water vapor for activation, control the activation and pore formation temperature to be 1000 °C, and the activation and pore formation time to be 2 h. After activation is completed, take it out after natural cooling to room temperature to obtain the activated coconut shell charcoal (i.e., the activation and pore formation material);

[0078] During the activation pore-forming process, control the gas linear velocity of water vapor to be 0.2 m / s, and keep the fluidized bed pressure within the range of 30 - 50 KPa.

[0079] Step 4, Washing: Completely immerse the activated coconut shell charcoal in a 10 wt% hydrochloric acid solution, heat it to 80 °C, keep it warm and soak for 2 h, then wash it with distilled water until the washing liquid is neutral, and dry it to obtain purified coconut shell charcoal (i.e., purified material).

[0080] Step 5, Carbonization: Place the purified coconut shell charcoal in a carbonization furnace, introduce nitrogen as a protective gas, and heat it to 1100 °C at a heating rate of 5 °C / min, keep it warm and carbonize for 2 h, then take it out after natural cooling to room temperature to obtain coconut shell porous carbon (i.e., porous carbon for silicon-carbon negative electrode material).

[0081] Example 2

[0082] This example provides a method for preparing porous carbon for silicon-carbon negative electrode material, specifically as follows:

[0083] Step 1, Steam explosion: Put the cleaned coconut shell (i.e., pyrolysis carbonization raw material) into a metal basket with dense small holes, then put it into a steam explosion kettle, close the kettle lid, introduce steam to start steam explosion, control the steam explosion temperature to be 180 °C, the steam explosion pressure to be 1.0 MPa, the steam explosion pressure holding time to be 10 min, relieve the pressure, and dry it to obtain steam explosion material.

[0084] Step 2, Pyrolysis carbonization: Place the steam explosion material in a carbonization furnace, introduce nitrogen as a protective gas, and heat it to 800 °C at a heating rate of 5 °C / min, keep it warm and pyrolyze carbonize for 2 h, then take it out after natural cooling to room temperature to obtain coconut shell charcoal after pyrolysis carbonization (i.e., pyrolysis carbonization material).

[0085] Step 3, Crushing and classification: Directly crush the coconut shell charcoal after pyrolysis carbonization to the particle size specification of the finished porous carbon, that is, crush it to D10 ≥ 2 um, D50: 5 - 10 um, D90 ≤ 15 um, Dmax ≤ 25 um to obtain coconut shell charcoal after crushing and classification (i.e., crushed and classified material).

[0086] Step 4, Activation pore-forming: Place 1 kg of coconut shell charcoal after crushing and classification in a fluidized bed, introduce water vapor for activation, control the activation pore-forming temperature to be 1000 °C, the activation pore-forming time to be 2 h, after activation is completed, take it out after natural cooling to room temperature to obtain activated coconut shell charcoal (i.e., activation pore-forming material).

[0087] During the activation pore-forming process, control the gas linear velocity of water vapor to be 0.3 m / s, and keep the fluidized bed pressure within the range of 45 - 65 KPa.

[0088] Step 5, Washing: Immerse the activated coconut shell charcoal completely in a 10 wt% hydrochloric acid solution, heat it to 80 °C, keep it soaked for 2 h, then wash it with distilled water until the washing liquid is neutral, and dry it to obtain purified coconut shell charcoal (i.e., the purified material).

[0089] Step 6, Carbonization: Place the purified coconut shell charcoal in a carbonization furnace, introduce nitrogen as the protective gas, heat it at a heating rate of 5 °C / min to 1100 °C, keep it carbonized for 2 h, cool it naturally to room temperature and then take it out to obtain coconut shell porous carbon (i.e., the porous carbon for silicon-carbon anode material).

[0090] Example 3

[0091] This example provides a preparation method of porous carbon for silicon-carbon anode material, specifically as follows:

[0092] Step 1, Steam carbonization: At room temperature, put the crushed coconut shell (i.e., the raw material for pyrolysis carbonization) into a metal basket with dense small holes, then put it into a steam explosion kettle, close the kettle lid and introduce steam to start steam carbonization. Control the steam carbonization temperature at 220 °C, the steam carbonization pressure at 2.4 MPa, and the steam carbonization time at 45 min.

[0093] Step 2, Steam explosion: After the steam carbonization is completed, keep the temperature of the steam carbonization unchanged, open the pressure relief valve on the steam explosion kettle for steam explosion, and then take out the material after steam explosion and add it to an oven for drying to obtain coconut shell charcoal after steam explosion (i.e., the material after steam explosion).

[0094] Step 3, Crushing and classification: Directly crush the coconut shell charcoal after steam explosion to the particle size specification of the finished porous carbon, that is, crush it to D10≥2 um, D50: 5 - 10 um, D90≤15 um, Dmax≤25 um to obtain the coconut shell charcoal after crushing and classification (i.e., the material after crushing and classification).

[0095] Step 4, Activation and pore formation: Place 1 kg of the coconut shell charcoal after crushing and classification in a fluidized bed, introduce water vapor for activation, control the activation and pore formation temperature at 1000 °C, the activation and pore formation time at 2 h. After the activation and pore formation are completed, cool it naturally to room temperature and then take it out to obtain the activated coconut shell charcoal (i.e., the material after activation and pore formation).

[0096] Step 5, Washing: Immerse the activated coconut shell charcoal completely in a 10 wt% hydrochloric acid solution, heat it to 80 °C, keep it soaked for 2 h, then wash it with distilled water until the washing liquid is neutral, and dry it to obtain purified coconut shell charcoal (i.e., the purified material).

[0097] Step 6. Carbonization: Place the purified coconut shell carbon in a carbonization furnace, introduce nitrogen as a protective gas, heat it at a heating rate of 5 °C / min to 1100 °C, keep it for carbonization for 2 h, naturally cool it to room temperature and then take it out to obtain coconut shell porous carbon (i.e., the porous carbon for silicon-carbon anode material).

[0098] Comparative Example 1

[0099] The preparation of the porous carbon in Comparative Example 1 adopts the traditional porous carbon preparation process, specifically as follows:

[0100] Step 1. Pyrolytic carbonization: Place the cleaned and dried coconut shell in a carbonization furnace, introduce nitrogen as a protective gas, heat it at a heating rate of 5 °C / min to 800 °C, keep it for pyrolytic carbonization for 2 h, naturally cool it to room temperature and then take it out to obtain the coconut shell carbon after pyrolytic carbonization;

[0101] Step 2. Coarse crushing: Crush the coconut shell carbon after pyrolytic carbonization to a particle size < 1 mm to obtain the coarsely crushed coconut shell carbon;

[0102] Step 3. Activation and pore formation: Place the coarsely crushed coconut shell carbon in a rotary kiln, introduce KOH for activation, the activation and pore formation temperature is 1000 °C, and the activation and pore formation time is 4 h. Naturally cool it to room temperature and then take it out to obtain the activated coconut shell carbon;

[0103] Step 4. Washing: Completely immerse the activated coconut shell carbon in a 10 wt% hydrochloric acid solution, heat it to 80 °C, keep it for soaking for 2 h, then wash it with distilled water until the washing liquid is neutral, and dry it to obtain the purified coconut shell carbon;

[0104] Step 5. Carbonization: Place the purified coconut shell carbon in a carbonization furnace, introduce nitrogen as a protective gas, heat it at a heating rate of 5 °C / min to 1100 °C, keep it for carbonization for 2 h, naturally cool it to room temperature and then take it out to obtain the coconut shell porous carbon after high-temperature carbonization;

[0105] Step 6. Crushing and classification: Use a jet mill to crush the coconut shell carbon after high-temperature carbonization, and after crushing, screen out the porous carbon with particle size meeting the requirements by classification, D10 ≥ 2 um, D50: 5 - 10 um, D90 ≤ 15 um, Dmax ≤ 25 um.

[0106] Comparative Example 2

[0107] The preparation of the porous carbon in Comparative Example 2 adopts the traditional porous carbon preparation process plus fluidized bed activation, specifically as follows:

[0108] Step 1. Pyrolytic carbonization: Place the cleaned and dried coconut shell in a carbonization furnace, introduce nitrogen as a protective gas, heat it at a heating rate of 5 °C / min to 800 °C, keep it for pyrolytic carbonization for 2 h, naturally cool it to room temperature and then take it out to obtain the coconut shell carbon after pyrolytic carbonization;

[0109] Step 2, Coarse crushing: Crush the pyrolyzed and carbonized coconut shell charcoal to a particle size < 1 mm to obtain the coarsely crushed coconut shell charcoal;

[0110] Step 3, Activation and pore formation: Place the coarsely crushed coconut shell charcoal in a fluidized bed, introduce steam for activation, the activation and pore formation temperature is 1000 °C, and the activation and pore formation time is 2 h. Take it out after natural cooling to room temperature to obtain the activated coconut shell charcoal;

[0111] Step 4, Washing: Completely immerse the activated coconut shell charcoal in a 10 wt% hydrochloric acid solution, heat to 80 °C, keep warm and soak for 2 h, then wash with distilled water until the washing liquid is neutral, and dry to obtain the purified coconut shell charcoal;

[0112] Step 5, Carbonization: Place the purified coconut shell charcoal in a carbonization furnace, introduce nitrogen as a protective gas, heat at a heating rate of 5 °C / min to 1100 °C, keep warm and carbonize for 2 h, take it out after natural cooling to room temperature to obtain the high-temperature carbonized coconut shell porous carbon;

[0113] Step 6, Crushing and classification: Use a jet mill to crush the high-temperature carbonized coconut shell charcoal, and after crushing, screen out the porous carbon with particle size meeting the requirements through classification. The particle size requirements for the porous carbon are D10 ≥ 2 μm, D50: 5 - 10 μm, D90 ≤ 15 μm, Dmax ≤ 25 μm.

[0114] Statistically calculate the yields of the porous carbon for silicon-carbon anodes obtained in Examples 1 - 3 and Comparative Examples 1 - 2, and detect the ash content, magnetic substances, tapped density, particle size D50, and pore parameters of each porous carbon for silicon-carbon anodes. The specific results are shown in the following table:

[0115]

[0116] Furthermore, test the electrical conductivities of the porous carbon for silicon-carbon anodes obtained in Examples 1 - 3 and Comparative Examples 1 - 2. The specific test results are as Figure 1 shown; it can be seen that within the test temperature range, the electrical conductivities of the porous carbon for silicon-carbon anodes obtained in Examples 1 - 3 are significantly better than those of Comparative Examples 1 - 2.

[0117] After performing silicon deposition and carbon coating treatments (silicon deposition content is 50 wt%, carbon coating content is 1 wt%) with the same process on Examples 1 - 3 and Comparative Examples 1 - 2, the obtained materials are made into button half-cells using the same assembly process, and the measured electrochemical performances are shown in the following table:

[0118]

[0119] It can be seen that, under the same test conditions, compared with the improvement in conductivity, the initial Coulomb efficiency of the examples is significantly better than that of the comparative examples, indicating that the porous carbon materials prepared by the method provided in this patent also have an improvement in their end-use performance.

[0120] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0121] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of porous carbon for silicon-carbon anode materials, characterized in that, It includes the following steps: steam carbonization, steam explosion, crushing and classification, activation and pore formation, washing, and carbonization; The method of the steam carbonization is to carry out steam carbonization treatment on the biomass raw material in the presence of water vapor; In the steam carbonization, the steam carbonization temperature is 210 - 240 °C, the steam carbonization pressure is 2.1 - 2.6 MPa, and the steam carbonization time is 40 - 60 min; The method of the steam explosion is that after the steam carbonization is completed, keeping the steam carbonization temperature unchanged, relieving the pressure for steam explosion to obtain the pyrolysis carbonization material; The method of the crushing and classification is that the pyrolysis carbonization material is crushed and classified to obtain the crushed and classified material; The particle size specifications of the crushed and classified material are D10 ≥ 2 μm, D50: 5 - 10 μm, D90 ≤ 15 μm, Dmax ≤ 25 μm; The method of the activation and pore formation is that in a fluidized bed device, controlling the gas linear velocity of the activation gas in the fluidized bed to be 0.05 - 0.5 m / s, keeping the fluidized bed pressure at 1 - 100 KPa, and carrying out activation and pore formation treatment on the crushed and classified material in the presence of the activation gas to obtain the activated and pore - formed material; In the activation and pore formation, the activation and pore formation temperature is 800 - 1100 °C, and the activation and pore formation time is 1 - 5 h; The method of the washing is to completely immerse the activated and pore - formed material in hydrochloric acid or a mixed acid solution, heat up and soak it, then wash it to neutrality and dry it to obtain the purified material; The method of the carbonization is to carry out carbonization treatment on the purified material under the protection of an inert gas, with a heating rate of 5 °C / min, heating up to 1100 °C to obtain the porous carbon for silicon - carbon anode materials; 2. The preparation method of the porous carbon for the silicon-carbon anode material according to claim 1, characterized in that, In the activation and pore formation, the activation gas is at least one of the following: water vapor, CO2.

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