Preparation method and application of high-performance biomass-based porous carbon material

Abstract

The present invention relates to the technical field of preparation and application of porous carbon materials, and specifically to a preparation method and application of a high-performance biomass-based porous carbon material. The preparation method comprises the following steps: crushing, drying and screening a biomass raw material to obtain a crushed material, carbonizing the obtained crushed material to obtain a carbonized material, mixing the obtained carbonized material with a coating material in proportion, coating the obtained material to obtain a precursor, activating the obtained precursor to obtain an activated product, washing and drying to obtain a biomass-based porous carbon material, coating the biomass material and then activating it to prepare a biomass-based porous carbon material that can control the proportion of macropores, has a high micropore volume and specific surface area, can provide more active sites for chemical vapor deposition of silicon, and improves deposition efficiency. The biomass-based porous carbon material can be used as a negative electrode material for a lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation and application of porous carbon materials, and in particular to a preparation method and application of a high-performance biomass-based porous carbon material. Background Art

[0002] In recent years, with the rapid development of portable electronic devices, electric vehicles, and hybrid vehicles, lithium-ion batteries have received increasing attention. Silicon materials are considered to be the most promising next-generation negative electrode materials for lithium-ion batteries due to their large theoretical capacity, low delithiation potential, and abundant resource reserves. However, due to the poor conductivity of silicon materials and the huge volume changes during the lithium ion lithiation and delithiation process, the commercial application of silicon materials in lithium-ion battery negative electrode materials is greatly restricted.

[0003] To solve this problem, scientists are constantly exploring new preparation processes and technologies. Among them, the new vapor-deposited silicon-carbon anode material has become a new generation of lithium battery anode material that has attracted much attention due to its high initial efficiency, excellent cycle performance, and low expansion rate. The synthesis and selection of porous carbon have a great influence on the performance of the final silicon-carbon anode material.

[0004] Porous carbon materials have become a research hotspot in the fields of chemistry, biology and materials due to their advantages such as high specific surface area, rich pore structure, high chemical stability and good conductivity.

[0005] Biomass is abundant in nature, renewable and non-toxic, so it has become the most ideal precursor for preparing porous carbon materials. At present, there are many literature reports on the preparation of porous carbon materials using cheap biomass resources, such as sucrose, glucose, cyclodextrin, cellulose, starch or biochar. Porous carbon prepared from biomass often has a developed pore structure and a large number of surface active sites. In the existing porous carbon preparation technology, only the specific surface area and pore volume of porous carbon are usually considered, while the existence of macropores is ignored. The existence of macropores is often not conducive to the subsequent preparation of silicon-carbon materials.

[0006] For example, in the Chinese patent application number 202111233748.2, a preparation method and application of a bio-based porous carbon material is specifically disclosed. Fresh plants are used as bio-based precursors and KOH is treated to prepare a bio-based porous carbon with a specific surface area of ​​1200-1800m 2 / g, pore volume 0.5-1cm 3 / g, and the pore size distribution is 1.5-2.5nm.

[0007] Although the above-mentioned invention patent has produced a bio-based porous carbon material with a pore size distribution of 1.5-2.5nm, it needs to use fresh plants as the bio-base, the source of raw materials is limited, and KOH is used for pre-treatment. When targeting some biomass, such as bamboo, leaves, fruit shells, peels and straw, which are widely available biomass, the etching and activation effects of KOH further increase the proportion of macropores in the prepared bio-based porous carbon.

[0008] Therefore, there is an urgent need to provide a porous, high-performance biomass-based carbon material that can improve the lithium storage performance of silicon-carbon materials by controlling and reducing the proportion of macropores, and improve the initial efficiency, power performance and compaction density of silicon-carbon materials. Summary of the invention

[0009] In response to the above problems, the present invention provides a method for preparing a high-performance biomass-based porous carbon material and its application. By coating the biomass material and then activating it, a biomass-based porous carbon material with controlled macropore proportion, high micropore volume and specific surface area can be prepared. The biomass-based porous carbon material can provide more active sites for chemical vapor deposition of silicon and improve deposition efficiency. The biomass-based porous carbon material can be used as a negative electrode material for lithium batteries.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0012] Step S1, crushing, crushing, drying and sieving the biomass raw materials to obtain crushed materials;

[0013] Step S2, carbonization, carbonizing the crushed material obtained in step S1 to obtain a carbonized material;

[0014] Step S3, coating, mixing the carbonized material obtained in step S2 with the coating material according to a mass ratio, and then coating to obtain a precursor;

[0015] Step S4, activation, the precursor obtained in step S3 is activated to obtain an activated product, which is washed and dried to obtain a biomass-based porous carbon material.

[0016] The present invention innovatively introduces a coating step in the preparation method of biomass-based porous carbon materials, and uses the coating material to cover and block the macropores of the carbonized material during the coating process, thereby reducing the volume proportion of macropores in the carbonized material. In addition, after the coating is completed, the precursor is activated to form more micropores and mesopores inside the carbon material, significantly increasing its specific surface area. These newly formed pores greatly increase the area of ​​contact between the material and external substances. Taking supercapacitor electrode materials as an example, porous carbon materials with high specific surface area can provide more active sites, so that ions in the electrolyte can be adsorbed and desorbed on the electrode surface, thereby increasing the capacitance.

[0017] At the same time, the prepared biomass-based porous carbon material has a hierarchical pore structure. Compared with the existing biomass-based porous carbon material, the hierarchical pore structure contains micropores, mesopores and macropores. The pore diameter of the micropores is less than 2nm, the pore diameter of the mesopores is 2-50nm; the pore diameter of the macropores is greater than 50nm. The biomass-based porous carbon material of the present invention, while minimizing the volume share of macropores, makes the specific surface area greater than 1390m² / g, the micropore specific surface area greater than 860m² / g, the pore volume greater than 0.67cm³ / g, the micropore volume greater than 0.35cm³ / g, the average pore diameter less than 2nm, and the microporosity is as high as more than 95%.

[0018] As an improvement, in step S1, the biomass raw material is one or more of bamboo, leaves, fruit shells, peels, straw, reeds, wood, loofah and starch, but the biomass raw materials of the present invention are not limited to the above-mentioned biomass raw materials. In addition, all biomass raw materials that meet the preparation requirements of the present invention are within the protection scope of the present invention, such as wood in lignocellulose, such as pine, poplar, eucalyptus, etc., coffee bean residues, rice husks, etc. in seeds, and microalgae in algae, etc.;

[0019] In the step S1, the crushed biomass raw material is sieved with a 50-200 mesh screen to ensure the uniformity of the biomass raw material particles, improve the uniformity of heat transfer and gas release of the biomass raw material during the carbonization process, and also promote the uniformity of activator contact and the consistency of reaction degree during the activation process.

[0020] Preferably, the present invention uses a 200-mesh screen for screening, and the obtained biomass raw material has a finer particle size.

[0021] As an improvement, in step S2, the heating rate of the carbonization treatment is 1-10°C / min; the carbonization temperature is 400-900°C, and the carbonization treatment time is 2-5h.

[0022] Preferably, the carbonization temperature of the biomass raw material of the present invention is 600° C., and the carbonization treatment time is 3 hours.

[0023] As an improvement, in the step S3, the coating material is one or more of asphalt-based and resin-based coating materials obtained by two-stage processes of oxidative crosslinking and high-temperature thermal polycondensation of a coating material precursor, and the softening point of the coating material is 200-300 °C.

[0024] Preferably, the softening point of the coating material of the present invention is 280 °C, and the β-resin content is 55 wt%.

[0025] Specifically, in the step S3, the coating material precursor is one or two of ethylene tar and catalytic cracking slurry;

[0026] When the coating material precursor is subjected to oxidative crosslinking, the temperature of the oxidation treatment is 300-500 °C, and the time is 3-8 h.

[0027] Preferably, the temperature of the oxidation treatment of the present invention is 500 °C, and the oxidation time is 5 h.

[0028] As an improvement, in the step S3, when the coating material precursor is subjected to high-temperature thermal polycondensation treatment, it is heated from room temperature to 200-250 °C at a rate of 5 °C / min under the protection of an inert gas, held for 2-5 h, and then heated to 300-400 °C at a rate of 2 °C / min and held for 5-8 h.

[0029] Preferably, when the coating material precursor is subjected to high-temperature thermal polycondensation treatment, it is heated from room temperature to 200 °C at a rate of 5 °C / min under the protection of an inert gas, held for 2 h, and then heated to 350 °C at a rate of 2 °C / min and held for 5 h.

[0030] The coating material obtained by the two-stage processes of oxidative crosslinking and high-temperature thermal polycondensation has the following advantages:

[0031] 1. During the oxidative crosslinking process, oxygen free radicals react fully with polycyclic aromatic hydrocarbon substances, hindering the regularization of polycyclic aromatic hydrocarbons, avoiding the formation of mesophase, and enabling the obtained coating material to have isotropy and good homogeneity, and achieving homogeneous coating;

[0032] 2. The purge of gas during the oxidative crosslinking process can remove residual light components with strong reaction activity, reduce the energy required for subsequent reactions, and also reduce the adverse effects of light components on the product performance, making the product performance more stable;

[0033] 3. Through high-temperature thermal polycondensation, the molecules in the asphalt are promoted to undergo polycondensation reactions to form a crosslinked structure, thereby significantly increasing the softening point of the asphalt-based coating material. The high softening point enables the coating material to maintain a stable form at high temperatures, not prone to flowing or deforming, which is beneficial to maintaining the integrity of the coating during subsequent processing and use;

[0034] 4. Make the asphalt molecules form a larger molecular structure, increase the molecular weight and carbonization rate of the material. A high carbonization rate means that more carbonaceous substances can be formed during the carbonization process, which is beneficial to improve the conductivity and mechanical strength of the material. For example, when used as a negative electrode coating material for lithium batteries, it can improve the battery's charge and discharge efficiency and cycle stability;

[0035] 5. The combination of the two-stage process can flexibly adjust the performance of the asphalt-based coating material by controlling the reaction conditions of oxidative cross-linking and high-temperature thermal polycondensation. For example, the softening point, residual carbon value, toluene insoluble content and other indicators of the material can be accurately adjusted according to different application requirements to better meet various specific usage requirements;

[0036] 6. Oxidative cross-linking is first performed and then high-temperature thermal polycondensation is performed, so that a more complex and stable network structure is formed inside the material. This structure not only improves the physical properties of the material, such as mechanical strength and thermal stability, but also improves its chemical stability and enhances its resistance to environmental factors;

[0037] 7. For raw materials such as ethylene tar and catalytic cracking oil slurry, the combination of the two-stage process can better utilize their composition characteristics. Ethylene tar and catalytic cracking oil slurry contain rich aromatic ring structures. Through oxidative cross-linking and high-temperature thermal polycondensation, these aromatic ring structures can be effectively converted into coating materials with good performance, which improves the utilization rate of raw materials, reduces production costs, and also reduces the impact on the environment.

[0038] In addition, during the oxidative cross-linking, a micro-positive pressure stirring operation is adopted to allow the coating material precursor to be oxidized and heated uniformly, so that the prepared coating material generates a suitable content of β resin.

[0039] In the present invention, β resin refers to a component that is insoluble in toluene but soluble in quinoline, that is, β resin content (%) = toluene insoluble content (TI) - quinoline insoluble content (QI).

[0040] The β-resin content is an important factor in determining the coating effect. The β-resin component has adhesion and is an efficient component that reacts and converts into solid carbon during heat treatment. Therefore, a suitable β-resin component is the key to having good bonding properties and is also a key factor in covering the macropores of biomass-based porous activated carbon materials. The content of the β-resin component of the coating material in the present invention is preferably 55wt%.

[0041] Specifically, when the β-resin content is higher than 55wt%, the coating material is prone to swelling or cracking. This is because too high a β-resin content will cause an imbalance in the internal structure of the material. The β-resin itself has certain physical and chemical properties, such as swelling under certain conditions. Excessive β-resin will cause the material to swell or crack during subsequent processing or use due to uneven internal stress. For example, when the temperature changes or when it comes into contact with certain solvents, excessive β-resin may absorb too much material (such as solvent molecules) and swell, or cause excessive stress inside the material due to its own volume change, thereby causing the coating material to crack.

[0042] As an improvement, in step S3, the carbonized material and the coating material are mixed by one or more of mechanical grinding, ball milling, and VC mixing;

[0043] In the step S3, the mixing ratio is 2-20% of the coating material to the carbonized material; the coating temperature is 300-600° C.; and the coating time is 2-6 hours.

[0044] Preferably, the mixing ratio is 10-20% of the coating material to the carbonized material, the coating temperature is 600° C., and the coating time is 3.5 h.

[0045] As an improvement, in step S3, the coating method is one of dry coating and melt coating.

[0046] As an improvement, in step S4, the activation method is one or both of chemical activation and physical activation;

[0047] During chemical activation, the chemical activator is one or more of potassium hydroxide and sodium hydroxide, and the weight ratio of the chemical activator to the precursor is (1-4):1. The precursor is placed in a protective atmosphere at 600° C.-1000° C., activated for 2-5 hours, and then washed multiple times with hydrochloric acid solution and distilled water in sequence;

[0048] During physical activation, the physical activation method is one or more of water vapor activation and carbon dioxide activation. The gas flow rate during activation is 600-900 L / h. The precursor is in an activation atmosphere at 600° C.-1000° C. for 2-10 hours.

[0049] Preferably, the weight ratio of the chemical activator to the precursor of the present invention is 3:1.

[0050] Preferably, when the chemical activation is performed in the present invention, the precursor is placed in a protective atmosphere and activated at 850° C. for 3 hours.

[0051] Preferably, when the physical activation is performed in the present invention, carbon dioxide activation is adopted, the gas flow rate is 800 L / h, the activation temperature is 700° C., and the activation time is 5 h.

[0052] In addition, the present invention also provides an application of the high-performance biomass-based porous carbon material prepared as above. The microporosity of the prepared high-performance biomass-based porous carbon material is as high as over 95%, which is more conducive to the preparation of new vapor-deposited silicon-carbon negative electrode materials.

[0053] The beneficial effects of the present invention are:

[0054] The present invention innovatively uses a coating material to coat the biomass-based porous carbon material, reduces the proportion of macropores on the biomass-based porous carbon material, and then activates it, thereby preparing a biomass-based porous carbon material that can control the proportion of macropores, has a higher micropore volume and specific surface area, can provide more active sites for chemical vapor deposition of silicon, and improves deposition efficiency. The biomass-based porous carbon material can be used as a negative electrode material for lithium batteries.

[0055] In addition, the coating material in the present invention is obtained by a two-step process of oxidative crosslinking and high-temperature thermal polycondensation of the coating material precursor, which can improve the isotropy and good uniformity of the coating material, achieve homogeneous coating, and appropriately increase the content of β resin in the coating material, so that the coating material has good viscosity, thereby improving the macroporous coating and covering ability of the biomass porous carbon material, and at the same time, the coating material has good chemical stability.

[0056] In summary, the biomass-based porous carbon material of the present invention has the advantages of a lower macropore ratio, higher micropore volume and specific surface area, can provide more active sites for chemical vapor deposition of silicon, and improve deposition efficiency, etc. It is particularly suitable for the preparation and application technology field of biomass-based porous carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram of the preparation method of the present invention;

[0058] Figure 2 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 1 of the present invention;

[0059] Figure 3 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 2 of the present invention;

[0060] Figure 4 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 3 of the present invention;

[0061] Figure 5 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 4 of the present invention;

[0062] Figure 6This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 5 of the present invention;

[0063] Figure 7 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 6 of the present invention;

[0064] Figure 8 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 7 of the present invention;

[0065] Fig. 9 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 8 of the present invention;

[0066] Fig.10 This is a scanning electron microscope photograph of the biomass-based porous carbon material of Example 9 of the present invention. DETAILED DESCRIPTION

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0069] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0070] Embodiment 1:

[0071] like Figure 1 As shown, a method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0072] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0073] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 600°C and the time is 3 hours;

[0074] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 280°C and a β resin content of 55wt%;

[0075] S4, coating: in a melt coating machine, the carbonized material is coated with 20% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0076] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 3:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 850° C., and the activation time is 3 hours;

[0077] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 2 .

[0078] Embodiment 2:

[0079] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0080] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0081] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 600°C and the time is 3 hours;

[0082] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 280°C and a β resin content of 55wt%;

[0083] S4, coating: in a melt coating machine, the carbonized material is coated with 20% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0084] S5, activation: the above precursor is physically activated to obtain an activated product, wherein the physical activation is carbon dioxide activation, the steam flow rate is 800L / h, the activation temperature is 700°C, the activation time is 5h, and the final high-performance biomass-based porous carbon material is obtained. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 3 .

[0085] Embodiment 3:

[0086] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0087] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0088] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 600°C and the time is 3 hours;

[0089] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 280°C and a β resin content of 55wt%;

[0090] S4, coating: in a melt coating machine, the carbonized material is coated with 10% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0091] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 3:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 850° C., and the activation time is 3 hours;

[0092] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 4 .

[0093] Embodiment 4:

[0094] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0095] S1. Crushing: crushing the biomass raw material to 200 meshes to obtain crushed material;

[0096] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 600°C and the time is 3 hours;

[0097] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 280°C and a β resin content of 55wt%;

[0098] S4, coating: in a dry coating machine, the carbonized material is coated with 20% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0099] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 3:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 850° C., and the activation time is 3 hours;

[0100] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 5 .

[0101] Embodiment 5:

[0102] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0103] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0104] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 900°C and the time is 3 hours;

[0105] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 280°C and a β resin content of 55wt%;

[0106] S4, coating: in a melt coating machine, the carbonized material is coated with 20% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0107] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 3:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 850° C., and the activation time is 3 hours;

[0108] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 6 .

[0109] Embodiment 6:

[0110] S1. Crushing: crushing the biomass raw material into 50 meshes to obtain crushed material;

[0111] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 400°C and the time is 2h;

[0112] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 300°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 300°C at 2°C / min and kept at that temperature for 5h; and further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 200°C and a β resin content of 38wt%;

[0113] S4, coating: in a melt coating machine, the carbonized material is coated with 2% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 300°C, and the time is 2h;

[0114] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 1:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 600° C., and the activation time is 1.5 h;

[0115] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Figure 7 .

[0116] Embodiment 7:

[0117] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0118] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 900°C and the time is 5 hours;

[0119] S3, preparation of coating material: in air atmosphere, catalytic cracking oil slurry was subjected to oxidation treatment at 500°C for 8h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 250°C at 5°C / min and kept at that temperature for 5h, and then further heated to 400°C at 2°C / min and kept at that temperature for 8h; and further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 300°C and a β resin content of 58wt%;

[0120] S4. Coating: In a melting coater, coat the carbonized material with 20% of the coating material to obtain a precursor; wherein, the atmosphere for the coating operation is nitrogen, the temperature is 600 °C, and the time is 6 h;

[0121] S5. Activation: Add an alkaline activator to the above-mentioned precursor for activation to obtain an activated product. Among them, the alkaline activator is potassium hydroxide, and its weight ratio to the carbonized product is 4:1. The atmosphere for the activation operation is nitrogen, the activation temperature is 1000 °C, and the activation time is 5 h;

[0122] S6. Post-treatment: Perform multiple pickling and water washing operations on the activated product in sequence to obtain a washed material. Among them, pickling is performed using dilute hydrochloric acid, and water washing is performed using distilled water; finally, perform hot air drying on the washed material to obtain the final high-performance biomass-based porous carbon material. The scanning electron microscope photograph of the biomass-based porous carbon material is shown in Figure 8 .

[0123] Example 8:

[0124] S1. Crushing: Crush the biomass raw material to 125 mesh to obtain a crushed material;

[0125] S2. Carbonization: Carbonize the crushed biomass after drying and sieving under a nitrogen atmosphere to obtain a carbonized material; wherein, the carbonization temperature is 600 °C, and the time is 3 h;

[0126] S3. Coating material preparation: Under an air atmosphere, perform an oxidation treatment on the catalytic cracking slurry at 400 °C for 5.5 h; then further under an inert gas atmosphere, heat the above-prepared material from room temperature to 225 °C at a rate of 5 °C / min and hold for 3.5 h, and further heat it to 350 °C at a rate of 2 °C / min and hold for 6.5 h; further perform extrusion and crushing operations to obtain a coating material product with a final softening point of 250 °C and a β-resin content of 46 wt%;

[0127] S4. Coating: In a melting coater, coat the carbonized material with 10% of the coating material to obtain a precursor; wherein, the atmosphere for the coating operation is nitrogen, the temperature is 450 °C, and the time is 4 h;

[0128] S5. Activation: Physically activate the above-mentioned precursor to obtain an activated product. Among them, the physical activation is carbon dioxide activation, the vapor flow rate is 900 L / h, the activation temperature is 1000 °C, and the activation time is 10 h to obtain the final high-performance biomass-based porous carbon material. The scanning electron microscope photograph of the biomass-based porous carbon material is shown in Fig. 9 .

[0129] Example 9:

[0130] A method for preparing a high-performance biomass-based porous carbon material comprises the following steps:

[0131] S1. Crushing: crushing the biomass raw material to 200 mesh to obtain crushed material;

[0132] S2, carbonization: the crushed biomass is dried and sieved, and then carbonized in a nitrogen atmosphere to prepare a carbonized material; wherein the carbonization temperature is 600°C and the time is 3 hours;

[0133] S3, preparation of coating material: in air atmosphere, ethylene tar was subjected to oxidation treatment at 500°C for 3h; then, in inert gas atmosphere, the obtained material was heated from room temperature to 200°C at 5°C / min and kept at that temperature for 2h, and then further heated to 350°C at 2°C / min and kept at that temperature for 5h; and further extrusion and crushing operation was performed to obtain a coating material product with a final softening point of 200°C and a β resin content of 29wt%;

[0134] S4, coating: in a melt coating machine, the carbonized material is coated with 20% of the coating material to obtain a precursor; wherein the coating operation atmosphere is nitrogen, the temperature is 600°C, and the time is 3.5h;

[0135] S5, activation: adding an alkaline activator to the above-mentioned precursor to activate it to obtain an activated product, wherein the alkaline activator is potassium hydroxide, and the weight ratio of potassium hydroxide to the carbonized product is 3:1, the atmosphere of the activation operation is nitrogen, the activation temperature is 850° C., and the activation time is 3 hours;

[0136] S6, post-treatment: the activated product is subjected to acid washing and water washing operations for multiple times in sequence to obtain a washed material, wherein dilute hydrochloric acid is used for the acid washing operation and distilled water is used for the water washing operation; finally, the washed material is subjected to hot air drying operation to obtain a final high-performance biomass-based porous carbon material. The scanning electron microscope photo of the biomass-based porous carbon material is shown in Fig.10 .

[0137] Comparative Example 1:

[0138] The same as Example 1, but different from Example 1 is that the carbon material of Example 1 is not coated.

[0139] Comparative Example 2:

[0140] The same as Example 1, but different from Example 1 is that, when coating the carbon material of Comparative Example 2, the coating material used is a conventional asphalt-based coating material, and the β-resin content of the conventional asphalt-based coating material is about 20%.

[0141] Comparative Example 3:

[0142] Meanwhile, Example 1 is the same as Example 1, except that the carbon material of Comparative Example 3 is not subjected to activation treatment after coating.

[0143] Analysis and summary: As shown in Table 1 below, by comparing Examples 1-4, 6, 8-9 with Comparative Examples 1-3, it can be seen that for the carbonized biomass-based porous carbon material of the present invention, after coating with a coating material having a β-resin content of 55 wt%, the macropores of the biomass-based porous carbon material can be effectively covered, the macropores can be eliminated, and the proportion of macropores in the biomass-based porous carbon material can be reduced. Moreover, by combining physical activation or chemical activation treatment, the number of pores can be increased, and at the same time, it has micropores, mesopores and a small amount of macropores, and has a high micropore volume and specific surface area, which can provide more active sites for chemical vapor deposition of silicon and improve the deposition efficiency.

[0144] As shown in Table 1 below, by comparing Examples 5-7 with Example 1 and Comparative Examples 1-3 respectively, it can be seen that in Example 5, the carbonization temperature is as high as 900 °C. Too high a carbonization temperature will cause the surface of the carbonized material to shrink and form an easily graphitized carbon layer, increasing the activation difficulty, and then resulting in a decrease in specific surface area, an increase in average pore diameter, and a decrease in microporosity; in Example 6, the factors leading to the decrease in specific surface area are: 1. The carbonization temperature is too low and the crushed material is not sufficiently carbonized; 2. In the preparation step of the coating material, the β-resin content of the prepared coating material is low, resulting in low viscosity of the coating material and unsatisfactory coating effect; 3. The weight ratio of the activator to the carbonized product is 1:1, and the amount of the activator used is small, resulting in unsatisfactory activation effect. The combined action of the above three groups of factors leads to a decrease in specific surface area and a corresponding decrease in microporosity in Example 6; in Example 7, the carbonization temperature is too high and the amount of the activator used is also high, deepening the etching degree of the carbon material, thus causing the generation of medium and large pores and a corresponding decrease in microporosity.

[0145] In summary, for the biomass-based porous carbon material in the present invention, through the combination of coating and activation treatment, while reducing the proportion of macropores by coating treatment, the number of pores is increased by activation treatment, thereby improving the lithium storage performance of the silicon-carbon material prepared from the biomass-based porous carbon material, and enhancing the first efficiency, power performance and tap density of the silicon-carbon material.

[0146] Moreover, the coating material used in the coating process needs to be pretreated to achieve the purpose of appropriately increasing the β-resin content, thereby enhancing the viscosity of the coating material and achieving the effect of improving the macropore coverage rate of the biomass-based porous carbon material.

[0147] Therefore, for the high-performance biomass-based porous carbon material prepared in the present invention, the microporosity is as high as more than 95%, and a suitable carbonization temperature, a suitable amount of activator used and a suitable coating material are required, and none of them can be missing.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0149] The specific surface area, micropore specific surface area, pore volume, micropore volume, average pore diameter and microporosity of the biomass-based porous carbon materials prepared in Examples 1-9 and Comparative Examples 1-3 were tested, and the average values ​​were taken and recorded in Table 1 below.

[0150] Table 1

[0151]

Claims

1. A method for preparing a high-performance biomass-based porous carbon material, characterized in that: The following steps are involved: Step S1, crushing, crushing, drying and sieving the biomass raw materials to obtain crushed materials; Step S2, carbonization, carbonizing the crushed material obtained in step S1 to obtain a carbonized material; Step S3, coating, mixing the carbonized material obtained in step S2 with the coating material according to a mass ratio, and coating to obtain a precursor, wherein the coating method is one of dry coating and melt coating, and the coating material is a resin-based coating material obtained by subjecting the coating material precursor to two-stage processes of oxidation crosslinking method and high-temperature thermal polycondensation method, wherein the coating material precursor is one or both of ethylene tar and catalytic cracking oil slurry, and the β resin content is 55wt%; Step S4, activation, the precursor obtained in step S3 is activated to obtain an activated product, which is washed and dried to obtain a biomass-based porous carbon material.

2. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S1, the biomass raw material is one or more of bamboo, leaves, fruit shells, fruit peels, straw, reeds, wood, loofah and starch; In the step S1, the crushed biomass raw material is sieved using a 50-200 mesh screen.

3. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S2, the heating rate of the carbonization treatment is 1-10°C / min; the carbonization temperature is 400-900°C, and the carbonization treatment time is 2-5h.

4. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S3, the softening point of the coating material is 200-300°C.

5. The method for preparing a high-performance biomass-based porous carbon material according to claim 4, characterized in that: In the step S3, when the coating material precursor is subjected to oxidative cross-linking, the oxidation treatment temperature is 300-500° C. and the time is 3-8 hours.

6. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S3, when the coating material precursor is subjected to high-temperature thermal polycondensation treatment, the temperature is raised from room temperature to 200-250°C at 5°C / min under inert gas protection, and kept warm for 2-5 hours, and then raised to 300-400°C at 2°C / min and kept warm for 5-8 hours.

7. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S3, the carbonized material and the coating material are mixed by one or more of mechanical grinding, ball milling, and VC mixing; In the step S3, the mixing ratio is 2-20% of the coating material to the carbonized material; the coating temperature is 300-600° C.; and the coating time is 2-6 hours.

8. The method for preparing a high-performance biomass-based porous carbon material according to claim 1, characterized in that: In step S4, the activation method is one or both of chemical activation and physical activation; During chemical activation, the chemical activator is one or more of potassium hydroxide and sodium hydroxide, and the weight ratio of the chemical activator to the precursor is (1-4):

1. The precursor is placed in a protective atmosphere at 600° C.-1000° C. for 1.5-5 hours, and then washed multiple times with hydrochloric acid solution and distilled water in sequence; During physical activation, the physical activation method is one or more of water vapor activation and carbon dioxide activation. The gas flow rate during activation is 600-900 L / h. The precursor is in an activation atmosphere at 600° C.-1000° C. for 2-10 hours.

9. An application of a high-performance biomass-based porous carbon material prepared by the method according to any one of claims 1 to 8, characterized in that: The microporosity of the prepared high-performance biomass-based porous carbon material is greater than 95%, and can be better applied to the preparation of vapor-deposited silicon-carbon negative electrode materials.

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