High-yield biomass-based porous carbon as well as preparation method and application thereof

Abstract

The invention discloses high-yield biomass-based porous carbon as well as a preparation method and application thereof, and belongs to the technical field of material preparation. The method comprises the following steps: carbonizing and depositing volatile components capable of forming tar in biomass on the surface of porous carbon at a low temperature by using a mixture of porous carbon and ferric salt, uniformly mixing residual biomass residues with a product obtained by low-temperature carbonization, and continuously carbonizing at a high temperature. According to the strategy, the yield of the biomass-based porous carbon can be remarkably improved, and the cost of commercial porous carbon and electrochemical energy storage devices is further reduced.

Description

A high-yield biomass-based porous char, its preparation method and application Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a high-yield biomass-based porous carbon, its preparation method, and its application. Background Technology

[0002] In response to the global challenges of limited crude oil storage and global warming, the development of advanced secondary energy storage devices is crucial for promoting future low-carbon and sustainable economic development. Lithium / sodium-ion hybrid capacitors have garnered widespread attention worldwide due to their combination of the high energy density of lithium-ion batteries and the high power density, long cycle life, and excellent safety performance of supercapacitors. As a core material, porous carbon, with its large specific surface area, high pore volume, abundant pore structure, and excellent physicochemical stability, is considered one of the key factors determining its electrochemical performance and cost. Therefore, the development of high-performance porous carbon is of great significance for promoting the commercial application of lithium-ion hybrid capacitors.

[0003] Currently, precursors for porous char mainly include biomass, polymers, and bitumen. Among these, biomass is widely available, abundant, and inexpensive. Therefore, using biomass as a raw material to prepare porous char can not only alleviate the shortage of fossil resources to some extent but also achieve the effective utilization of biomass resources and biomass waste. This is of great significance for social progress, environmental protection, and sustainable economic growth, thus attracting much attention from researchers. However, the low yield (<30%) of biomass-based porous char increases its production cost, which in turn restricts its application scope and scale to some extent. Therefore, developing effective strategies to further improve the yield of biomass-based porous char is of significant practical importance. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a high-yield biomass-based porous carbon, its preparation method and application, so as to solve the technical problems of poor rate performance and cycle stability of existing porous carbon materials.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for preparing high-yield biomass-based porous char, comprising the following steps: S1, mixing porous char, iron salt, and urea in a molar ratio of 8-12:3-5:5-7, then reacting at 170-190℃ for 7-9 hours, followed by drying at 80-110℃ to constant weight; S2, high-temperature segmented reaction; S21, placing biomass powder and the powder obtained in S1 into two separate ceramic boats, then placing them in a dual-temperature zone tube furnace, wherein the ceramic boat containing the biomass powder is adjacent to the low-temperature heating zone at the argon gas inlet, and the ceramic boat containing the powder obtained in S1 is placed in the high-temperature heating zone away from the argon gas inlet; S22, setting the target temperature of the low-temperature heating zone to 350-450℃ and the target temperature of the high-temperature heating zone to 800-950℃, when… After the low-temperature heating zone and the high-temperature heating zone are heated to the target temperature, they react for 1-5 hours respectively; the sum of the heating and reaction time in the high-temperature heating zone is greater than or equal to the sum of the heating and reaction time in the low-temperature heating zone; S23, the temperature of the low-temperature heating zone is raised to 550-650℃ and then held for 1 hour; the temperature of the high-temperature heating zone is kept constant and held for 1.5-5 hours; the holding time in the high-temperature heating zone is greater than or equal to the sum of the heating and holding times in the low-temperature heating zone; S3, the product obtained in the high-temperature heating zone S23 is washed sequentially with acid (to remove iron precursors and impurities) and water, then freeze-dried, and then mixed evenly with the product obtained in the low-temperature heating zone S23 at a mass ratio of 0.5-1.5:4-6, then soaked in alkaline solution for 2-4 hours, and finally carbonized at 650-900℃ for 1-3 hours to obtain the final product.

[0006] This invention utilizes the rich pore structure of porous carbon to effectively adsorb volatile organic components and tar vapors, as well as the role of iron-based materials in promoting carbonization reactions. Through a strategy of low-temperature vaporization followed by high-temperature carbonization, organic components that cannot be carbonized at low temperatures and are lost due to volatilization are first carbonized and deposited into the structure of the finished porous carbon product. Then, the remaining biomass residues are mixed evenly with the product obtained from low-temperature carbonization, and further activated and carbonized at high temperature. This strategy can significantly improve the yield of biomass-based porous carbon.

[0007] Based on the above technical solution, the present invention can be further improved as follows: further, the iron salt is ferric chloride.

[0008] Furthermore, the heating rate of the low-temperature heating zone is 2-3℃ / min, and the heating rate of the high-temperature heating zone is 8-10℃ / min; the heating rate of the high-temperature heating zone is greater than or equal to 3 times the heating rate of the low-temperature heating zone.

[0009] Furthermore, the acid solution is a hydrochloric acid solution with a concentration of 2-4 mol / L, and the alkali solution is a potassium hydroxide solution with a concentration of 5-7 mol / L.

[0010] Furthermore, the freeze-drying temperature is -50~-30℃, and the time is 10-12h.

[0011] The present invention also discloses a high-yield biomass-based porous carbon prepared by the above preparation method.

[0012] The present invention also discloses the application of the above-mentioned high-yield biomass-based porous carbon in the preparation of electrode materials.

[0013] The beneficial effects of this invention are as follows: 1. This invention first utilizes a mixture of porous carbon and iron salts to carbonize and deposit volatile and tar-forming components in biomass onto the surface of porous carbon at low temperature. Then, the remaining biomass residue is mixed evenly with the product obtained from low-temperature carbonization and carbonized again at high temperature. This strategy can significantly improve the yield of biomass-based porous carbon, thereby reducing the cost of commercial porous carbon and electrochemical energy storage devices.

[0014] 2. The biomass-based porous carbon prepared by the method of this invention exhibits higher capacity and electrochemical kinetics, and less polarization. The sodium-ion hybrid capacitor prepared using the biomass-based porous carbon of this invention was subjected to cycling performance verification at a current density of 1 A / g. It was found that after 2600 cycles, the sodium-ion hybrid capacitor constructed from the porous carbon prepared in Example 1 still maintained a capacity retention rate as high as 97.4%, significantly higher than the 88.8% of Comparative Example 1, demonstrating its excellent cycling stability. Attached Figure Description

[0015] Figure 1 shows the CV curves of the double-layer capacitor based on button batteries in Example 1 and Comparative Example 1 at a scan rate of 20 mV / s; Figure 2 shows the CV curves of the double-layer capacitor based on button batteries in Example 1 at different scan rates; Figure 3 shows the constant current charge-discharge curves of the double-layer capacitor based on pouch batteries in Example 1; Figure 4 shows the constant current charge-discharge curves of the double-layer capacitor based on pouch batteries in Comparative Example 1; Figure 5 shows the cycling performance of the sodium-ion hybrid capacitor based on pouch batteries in Example 1 and Comparative Example 1 at a current density of 1 A / g. Detailed Implementation

[0016] The specific embodiments of the present invention are described below to facilitate understanding of the invention by those skilled in the art. Unless otherwise specified, specific conditions are applied according to conventional conditions or the manufacturer's recommendations. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various modifications are obvious as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims. All inventions utilizing the concept of this invention are protected.

[0017] Example 1: A method for preparing high-yield biomass-based porous char, comprising the following steps: S1, mixing porous char, ferric chloride, and urea in a molar ratio of 10:4:6, then reacting at 180°C for 8 hours, followed by drying at 95°C to constant weight; S2, high-temperature segmented reaction; S21, placing biomass powder and the powder obtained in S1 into two ceramic boats respectively, and then placing them in a dual-temperature zone tube furnace, wherein the ceramic boat containing biomass powder is adjacent to the low-temperature heating zone at the argon gas inlet, and the ceramic boat containing the powder obtained in S1 is placed in the high-temperature heating zone away from the argon gas inlet; S22, starting heating from room temperature (25°C), the low-temperature heating zone is heated to 400°C at a heating rate of 2°C / min and the reaction is carried out. S23: The temperature of the high-temperature heating zone is increased to 850℃ at a heating rate of 10℃ / min and reacted for 3 hours. S24: The temperature of the low-temperature heating zone is increased to 650℃ at a heating rate of 2℃ / min and held for 1 hour. The temperature of the high-temperature heating zone is kept constant and held for 3.5 hours. S3: The product obtained in the high-temperature heating zone S23 is washed with hydrochloric acid solution (3mol / L), then washed with deionized water until neutral, freeze-dried at -40℃ for 11 hours, and then mixed with the product obtained in the low-temperature heating zone S23 at a mass ratio of 1:5. Then it is soaked in potassium hydroxide solution (6mol / L) for 3 hours, and finally carbonized at 700℃ for 2 hours under argon atmosphere protection to obtain the final product.

[0018] Example 2 differs from Example 1 in that the insulation temperature of the S23 low-temperature heating zone is replaced with 600℃ instead of 650℃, while the other implementation conditions are the same as in Example 1, resulting in high-yield biomass-based porous carbon.

[0019] Example 3 differs from Example 1 in that the reaction temperature of the S22 low-temperature heating zone is replaced with 420°C instead of 400°C, and the heat preservation temperature of the S23 low-temperature heating zone is replaced with 600°C instead of 650°C. The other implementation conditions are the same as in Example 1, and a high-yield biomass-based porous carbon is obtained.

[0020] Example 4 differs from Example 1 in that the heating rate of the high-temperature heating zone S22 is replaced by 8℃ / min, and the holding temperature of the low-temperature heating zone S23 is replaced by 600℃ instead of 10℃. The other implementation conditions are the same as in Example 1, resulting in high-yield biomass-based porous carbon.

[0021] Example 5 differs from Example 1 in that the heating rate of the low-temperature heating zone S22 is replaced by 3℃ / min, the heating rate of the high-temperature heating zone is replaced by 9℃ / min, and the holding temperature of the low-temperature heating zone S23 is replaced by 600℃ instead of 650℃. The remaining implementation conditions are the same as in Example 1, resulting in high-yield biomass-based porous carbon.

[0022] Example 6: A method for preparing high-yield biomass-based porous char, comprising the following steps: S1, mixing porous char, ferric chloride, and urea in a molar ratio of 8:5:5, then reacting at 170°C for 9 hours, followed by drying at 80°C to constant weight; S2, high-temperature segmented reaction; S21, placing biomass powder and the powder obtained in S1 into two ceramic boats respectively, and then placing them in a dual-temperature zone tube furnace, wherein the ceramic boat containing biomass powder is adjacent to the low-temperature heating zone at the argon gas inlet, and the ceramic boat containing the powder obtained in S1 is placed in the high-temperature heating zone away from the argon gas inlet; S22, starting heating from room temperature (25°C), the low-temperature heating zone is heated to 350°C at a heating rate of 3°C / min and then... S23: In the high-temperature heating zone, the temperature is increased to 800℃ at a rate of 10℃ / min and reacted for 2 hours. S24: The temperature of the low-temperature heating zone is increased to 550℃ at a rate of 3℃ / min and held for 1 hour. The temperature of the high-temperature heating zone is kept constant and held for another 2 hours. S3: The product obtained in the high-temperature heating zone S23 is washed with hydrochloric acid solution (2 mol / L), then washed with deionized water until neutral, freeze-dried at -50℃ for 10 hours, and then mixed with the product obtained in the low-temperature heating zone S23 at a mass ratio of 1:5. The mixture is then soaked in potassium hydroxide solution (5 mol / L) for 4 hours, and finally carbonized at 650℃ for 3 hours under argon atmosphere protection to obtain the final product.

[0023] Example 7: A method for preparing high-yield biomass-based porous char, comprising the following steps: S1, mixing porous char, ferric chloride, and urea in a molar ratio of 12:3:7, then reacting at 190°C for 7 hours, followed by drying at 110°C to constant weight; S2, high-temperature segmented reaction; S21, placing biomass powder and the powder obtained in S1 into two ceramic boats respectively, and then placing them in a dual-temperature zone tube furnace, wherein the ceramic boat containing biomass powder is adjacent to the low-temperature heating zone at the argon gas inlet, and the ceramic boat containing the powder obtained in S1 is placed in the high-temperature heating zone away from the argon gas inlet; S22, starting heating from room temperature (25°C), the low-temperature heating zone is heated to 450°C at a heating rate of 2°C / min and... The reaction was carried out for 1 hour. The temperature in the high-temperature heating zone was increased to 950℃ at a rate of 8℃ / min and reacted for 5 hours. In step S23, the temperature in the low-temperature heating zone was increased to 550℃ at a rate of 2℃ / min and held for 1 hour. The temperature in the high-temperature heating zone was kept constant and held for another 5 hours. In step S3, the product obtained in the high-temperature heating zone S23 was washed with hydrochloric acid solution (4 mol / L), then washed with deionized water until neutral, freeze-dried at -30℃ for 12 hours, and then mixed with the product obtained in the low-temperature heating zone S23 at a mass ratio of 1:5. The mixture was then soaked in potassium hydroxide solution (7 mol / L) for 2 hours, and finally carbonized at 900℃ for 1 hour under argon atmosphere protection to obtain the final product.

[0024] Comparative Example 1 differs from Example 1 in that: S2, biomass powder and the powder obtained in S1 are mixed at a mass ratio of 1:5, and then placed in a tube furnace, heated from room temperature to 850°C at a heating rate of 2°C / min, and reacted for 2.5 h; the remaining conditions are the same as in Example 1, and biomass-based porous carbon is obtained.

[0025] The difference between Comparative Example 2 and Example 1 is that the heating rate of the high-temperature heating zone S22 was changed from 10℃ / min to 2℃ / min, and the holding temperature of the low-temperature heating zone S23 was changed from 650℃ to 600℃. The other implementation conditions were the same as those in Example 1, and biomass-based porous carbon was obtained.

[0026] The difference between Comparative Example 3 and Example 1 is that the heating rate of the high-temperature heating zone S22 was changed from 10℃ / min to 3℃ / min, the holding temperature of the low-temperature heating zone S23 was changed from 650℃ to 600℃, and the holding time of the high-temperature heating zone S23 was changed from 3.5h to 3h. The other implementation conditions were the same as those in Example 1, and biomass-based porous carbon was obtained.

[0027] The difference between Comparative Example 4 and Example 1 is that the reaction time of the high-temperature heating zone S22 was replaced from 3h to 1h (the sum of the heating and reaction time of the high-temperature heating zone is less than the sum of the heating and reaction time of the low-temperature heating zone), and the heat preservation temperature of the low-temperature heating zone S23 was replaced from 650℃ to 600℃. The other implementation conditions were the same as those in Example 1, and biomass-based porous carbon was obtained.

[0028] The difference between Comparative Example 5 and Example 1 is that the reaction temperature of the S22 low-temperature heating zone was replaced from 400°C to 300°C, and the heat preservation temperature of the S23 low-temperature heating zone was replaced from 650°C to 450°C. The other implementation conditions were the same as those in Example 1, and biomass-based porous carbon was obtained.

[0029] The products prepared in Examples 1-5 and Comparative Examples 1-5 were used as material samples for the following experiments.

[0030] 1. Fabrication of Button Cells: Porous carbon material, conductive carbon black, and PVDF binder are mixed in a mass ratio of 80:5:15. 10 mL of 1-methyl-2-pyrrolidone (NMP) is then added. The mixture is ground into a paste in an agate mortar and coated onto aluminum foil. The paste is then dried in a vacuum oven at 120°C for 12 hours to obtain the positive and negative electrode sheets. These are transferred to an argon-filled glove box for button cell assembly. The button cell model is CR2032. The separator is glass fiber, and the electrolyte is a propylene carbonate solution containing 1 mol / L tetraethylammonium tetrafluoroborate. The assembled cells are left to stand for at least 12 hours before electrochemical performance testing is performed, with a voltage range of 0-2.7V.

[0031] Figure 1 shows the CV curves of the double-layer capacitors based on coin cells in Example 1 and Comparative Example 1 at a scan rate of 20 mV / s. The figure shows that compared to the porous carbon obtained by conventional methods (Comparative Example 1), the porous carbon obtained in Example 1 has a CV curve closer to a rectangle and a larger area, indicating that the biomass-based porous carbon prepared by the method of this invention has higher capacity and electrochemical kinetics, and less polarization.

[0032] Figure 2 shows the CV curves of the double-layer capacitor based on a coin cell in Example 1 at scan rates of 10 mV / s, 20 mV / s, 50 mV / s, 100 mV / s, and 150 mV / s. The figure shows that even at scan rates as high as 150 mV / s, the porous carbon obtained in Example 1 did not exhibit significant polarization, further demonstrating its excellent electrochemical kinetics and rate performance.

[0033] 2. Preparation of positive electrode sheet for soft-pack battery: Mix Na3V2(PO4)3 positive electrode, polyvinylidene fluoride (PVDF) and conductive carbon black evenly in a mass ratio of 85:10:5. Then add 10mL of N-methylpyrrolidone (NMP) solvent and stir thoroughly to make it evenly mixed. Finally, the resulting slurry is coated, baked, rolled and die-cut to obtain the positive electrode sheet.

[0034] Negative electrode sheet: Porous carbon material, conductive carbon black, PVDF binder are mixed with NMP at a mass ratio of 80:5:15. The resulting slurry is then coated, baked, rolled and die-cut to obtain the negative electrode sheet.

[0035] Battery assembly: The positive and negative electrode sheets are stacked on a Z-shaped stacking machine equipped with a separator, and then top and side sealed. Electrolyte is then injected to complete battery fabrication. Specifically, the positive and negative electrodes of the pouch double-layer capacitor are both porous carbon electrodes, and the electrolyte is a propylene carbonate solution containing 1 mol / L tetraethylammonium tetrafluoroborate. The positive electrode of the pouch sodium-ion mixed capacitor is a Na3V2(PO4)3 electrode, and the negative electrode is a porous carbon electrode. The electrolyte is a mixed solution of ethylene carbonate and dimethyl carbonate containing 1 mol / L NaPF6.

[0036] Figure 3 shows the constant current charge-discharge curve of the double-layer capacitor based on a pouch cell in Example 1, and Figure 4 shows the constant current charge-discharge curve of the double-layer capacitor based on a pouch cell in Comparative Example 1. It can be seen from the figures that, compared to Comparative Example 1 (Figure 4), the double-layer capacitor constructed from the porous carbon prepared in Example 1 has a higher capacity, a lower charging initiation voltage, and a higher discharging initiation voltage, indicating that the biomass-based porous carbon prepared using the method of this invention has less polarization.

[0037] Figure 5 shows the cycling performance of the sodium-ion hybrid capacitors based on pouch cells in Example 1 and Comparative Example 1 at a current density of 1 A / g. The figure shows that after 2600 cycles, the sodium-ion hybrid capacitor constructed from the porous carbon prepared in Example 1 still exhibits a capacity retention of up to 97.4%, significantly higher than the 88.8% of Comparative Example 1, demonstrating its excellent cycling stability.

[0038] 3. Performance data: The porous carbon materials prepared in Examples 1-5 and Comparative Examples 1-5 were tested for performance, and the results are shown in Table 1.

[0039] Table 1. Yield and performance data of porous carbon materials in Examples 1-5 and Comparative Examples 1-5

[0040] As can be seen from the table, the porous carbon prepared by the method of this invention has a significantly higher yield. Utilizing the adsorption properties of porous carbon and the role of iron-based materials in promoting the carbonization reaction, and through high-temperature segmented reaction, the reaction temperature, time, and heating rate in the high- and low-temperature heating zones are limited, significantly improving the yield of porous carbon. After 2600 cycles, the sodium-ion mixed capacitors constructed from the porous carbon prepared in Examples 1-5 still exhibit a capacity retention rate as high as 95.3%-97.4%, significantly higher than the 88.8%-90.8% of Comparative Examples 1-5, demonstrating their excellent cycling stability.

Claims

1. A method for preparing high-yield biomass-based porous char, characterized in that, Includes the following steps: S1. Mix porous carbon, iron salt, and urea in a molar ratio of 8-12:3-5:5-7, then react at 170-190℃ for 7-9 hours, and then dry at 80-110℃ to constant weight; S2. High-temperature segmented reaction; S21. Place the biomass powder and the powder obtained in S1 into two separate ceramic boats, and then place them in a dual-temperature zone tube furnace. The ceramic boat containing the biomass powder is placed next to the low-temperature heating zone at the argon inlet, and the ceramic boat containing the powder obtained in S1 is placed in the high-temperature heating zone away from the argon inlet; S22. Set the target temperature of the low-temperature heating zone to 350-450℃ and the target temperature of the high-temperature heating zone to 800-950℃. After the low-temperature heating zone and the high-temperature heating zone reach the target temperature, separate the reaction mixture into two separate containers. S23. The temperature of the low-temperature heating zone is raised to 550-650℃ and then kept at that temperature for 1 hour. The temperature of the high-temperature heating zone is kept constant and kept at that temperature for 1.5-5 hours. The holding time of the high-temperature heating zone is greater than or equal to the sum of the heating time and holding time of the low-temperature heating zone. S3. The product obtained in the high-temperature heating zone S23 is washed sequentially with acid and water, then freeze-dried, and then mixed evenly with the product obtained in the low-temperature heating zone S23 at a mass ratio of 0.5-1.5:4-6. The mixture is then soaked in alkaline solution for 2-4 hours and finally carbonized at 650-900℃ for 1-3 hours to obtain the final product.

2. The method for preparing high-yield biomass-based porous char according to claim 1, characterized in that, The iron salt is ferric chloride.

3. The method for preparing high-yield biomass-based porous char according to claim 1, characterized in that, The heating rate of the low-temperature heating zone is 2-3℃ / min, and the heating rate of the high-temperature heating zone is 8-10℃ / min; the heating rate of the high-temperature heating zone is greater than or equal to 3 times the heating rate of the low-temperature heating zone.

4. The method for preparing high-yield biomass-based porous char according to claim 1, characterized in that, The acid solution is a hydrochloric acid solution with a concentration of 2-4 mol / L, and the alkali solution is a potassium hydroxide solution with a concentration of 5-7 mol / L.

5. The method for preparing high-yield biomass-based porous char according to claim 1, characterized in that, The freeze-drying temperature is -50~-30℃, and the time is 10-12h.

6. A high-yield biomass-based porous char, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the high-yield biomass-based porous carbon according to claim 6 in the preparation of electrode materials.

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