Rice hull-based capacitive carbon and method of making the same

Abstract

The application discloses a rice hull-based capacitive carbon and a preparation method thereof. The rice hull is pyrolyzed and carbonized, and then is pretreated by desiliconization with a NaOH aqueous solution; the pretreated rice hull is fully mixed with an ionic liquid solution of cellulose, and then is heated and treated; and finally, the heated and treated rice hull is mixed with NaOH and is activated at high temperature to obtain the rice hull-based capacitive carbon. The rice hull-based capacitive carbon obtained by the application has rich micropore structure, and the specific capacitance and cycle stability of the capacitive carbon are improved, which is beneficial to improving the electrochemical performance of a super capacitor.

Description

Technical Field

[0001] This invention relates to the field of capacitor electrode materials technology, and in particular to a rice husk-based capacitor carbon and its preparation method. Background Technology

[0002] Supercapacitors are a new type of energy storage device, characterized by high power density, fast charge / discharge speed, and long cycle life, attracting increasing attention. Electrode materials are a core component of supercapacitors, significantly influencing their performance. Among them, porous activated carbon materials, with their advantages of wide availability, low cost, and high specific surface area, have become one of the most widely researched and applied supercapacitor materials.

[0003] Rice husks are the outer shell residue left after rice is hulled or processed. As a common agricultural byproduct, they are abundant. Currently, the main method for preparing rice husk-based capacitor carbon is the carbonization-alkali dissolution method, which involves first performing pyrolysis carbonization, followed by alkali treatment for activation, to obtain capacitor carbon. However, the porous carbon materials prepared by this method generally suffer from uneven pore size and low density, resulting in low specific capacitance and energy density, which cannot meet the performance requirements of high-energy-density supercapacitors. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a rice husk-based capacitor carbon and its preparation method.

[0005] The present invention proposes a method for preparing rice husk-based capacitor carbon, comprising the following steps:

[0006] S1. Rice husks are pyrolyzed and carbonized under an inert atmosphere, and then cooled to obtain rice husk carbon material.

[0007] S2. The rice husk char material is added to an aqueous solution of NaOH with a concentration of 0.1-0.5 mol / L and dispersed evenly. Then, it is stirred for a period of time, filtered, and the filter cake is washed with deionized water and dried to obtain pretreated rice husk char material.

[0008] S3. Add lignocellulose to imidazole chloride ionic liquid, heat to dissolve fully, and cool to obtain cellulose ionic liquid solution; mix the pretreated rice husk char material with the cellulose ionic liquid solution, stir for a period of time, and then heat at 300-400℃ for 20-30 min under an inert atmosphere, and cool to obtain capacitor carbon precursor.

[0009] S4. The capacitor carbon precursor is mixed with NaOH and activated at high temperature under an inert atmosphere. After cooling, it is washed with deionized water and dried to obtain rice husk-based capacitor carbon.

[0010] Preferably, in S1, the pyrolysis carbonization temperature is 500-600℃ and the time is 1-2 hours.

[0011] Preferably, in S2, the ratio of the rice husk charcoal material to the NaOH aqueous solution is 1g: 5-10mL.

[0012] Preferably, in step S2, the stirring temperature is room temperature and the stirring time is 1 to 2 hours.

[0013] Preferably, in S3, the imidazole chloride ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, and 1-allyl-2-methylimidazolium chloride.

[0014] Preferably, in S3, the mass ratio of the lignocellulose to the imidazole chloride ionic liquid is 1:5 to 10.

[0015] Preferably, in S3, the heating and dissolving temperature is 60–90°C, and the time is 8–12 hours.

[0016] Preferably, in S3, the mass ratio of the pretreated rice husk charcoal material to the ionic liquid solution of cellulose is 1:0.1 to 0.2.

[0017] Preferably, in step S3, the stirring temperature is 30–50°C and the stirring time is 1–2 hours.

[0018] Preferably, in S4, the mass ratio of the capacitor carbon precursor to NaOH is 1:1.5 to 2.

[0019] Preferably, in step S4, the high-temperature activation step includes: first heating to 500-600°C and holding for 20-30 minutes, then heating to 700-800°C and holding for 1.5-2 hours.

[0020] In this invention, an inert atmosphere refers to an atmosphere formed by one or more inert gases, wherein the inert gas is a non-reactive gas, such as nitrogen, argon, or helium.

[0021] The present invention also proposes a rice husk-based capacitor carbon, which is prepared by the aforementioned method.

[0022] The beneficial effects of this invention are as follows:

[0023] In the preparation process of rice husk-based capacitor carbon of the present invention, rice husks are first pyrolyzed and carbonized, then pretreated with desilication using an aqueous solution of NaOH, thoroughly mixed with an ionic liquid solution of cellulose, heated, and then activated at high temperature with NaOH to obtain rice husk-based capacitor carbon. After the desilication pretreatment of rice husk carbon material, many large pores are formed in the carbon material. The present invention uses a method of mixing the carbon material with an ionic liquid solution of cellulose and activating it together with NaOH at high temperature. This allows the ionic liquid and the cellulose dissolved in the ionic liquid to penetrate into the large pores formed after the desilication of the rice husk carbon material. Cellulose, as the carbon skeleton, carbonizes together with the ionic liquid during the high-temperature activation process to form a rich microporous structure. This makes the micropores in the carbon material finer, more uniform, and has higher mechanical strength, and is less prone to collapse or damage during high-temperature treatment. This optimizes the pore structure, improves the specific capacitance and cycle stability of the capacitor carbon, and is beneficial to improving the electrochemical performance of supercapacitors. Detailed Implementation

[0024] The technical solution of the present invention will now be described in detail through specific embodiments.

[0025] Example 1

[0026] A method for preparing rice husk-based capacitor carbon includes the following steps:

[0027] S1. Rice husks are heated to 500°C in a muffle furnace under nitrogen atmosphere at a heating rate of 5°C / min, and held at that temperature for 2 hours for pyrolysis and carbonization. After cooling, rice husk carbon material is obtained.

[0028] S2. Disperse the rice husk char material evenly in a 0.1 mol / L NaOH aqueous solution, stir at room temperature for 2 hours, filter, wash the filter cake with deionized water, and dry to obtain the pretreated rice husk char material; wherein the ratio of rice husk char material to NaOH aqueous solution is 1 g: 5 mL.

[0029] S3. Lignocellulose was added to 1-butyl-3-methylimidazolium chloride at a mass ratio of 1:5 and heated to dissolve at 60°C for 12 hours. After cooling, an ionic liquid solution of cellulose was obtained. The pretreated rice husk char material and the ionic liquid solution of cellulose were mixed at a mass ratio of 1:0.1 and stirred at 30°C for 2 hours. Then, the mixture was placed in a muffle furnace and heated to 300°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was held for 30 minutes and then cooled to obtain the capacitor carbon precursor.

[0030] S4. The capacitor carbon precursor is mixed with NaOH at a mass ratio of 1:1.5 and placed in a muffle furnace for high-temperature activation under a nitrogen atmosphere. The high-temperature activation steps include: first, heating to 500℃ at a heating rate of 5℃ / min and holding for 30min; then heating to 700℃ at a heating rate of 5℃ / min and holding for 2h; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0031] Example 2

[0032] A method for preparing rice husk-based capacitor carbon includes the following steps:

[0033] S1. Rice husks are heated to 550°C in a muffle furnace under nitrogen atmosphere at a heating rate of 5°C / min, and held at that temperature for 1.5 hours for pyrolysis and carbonization. After cooling, rice husk char material is obtained.

[0034] S2. Disperse the rice husk char material evenly in a 0.2 mol / L NaOH aqueous solution, stir at room temperature for 1.5 h, filter, wash the filter cake with deionized water, and dry to obtain the pretreated rice husk char material; wherein the ratio of rice husk char material to NaOH aqueous solution is 1 g: 8 mL.

[0035] S3. Lignocellulose was added to 1-butyl-3-methylimidazolium chloride at a mass ratio of 1:8 and heated to dissolve at 70°C for 10 hours. After cooling, an ionic liquid solution of cellulose was obtained. The pretreated rice husk char material and the ionic liquid solution of cellulose were mixed at a mass ratio of 1:0.15 and stirred at 40°C for 1.5 hours. Then, the mixture was placed in a muffle furnace and heated to 350°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was held for 25 minutes and then cooled to obtain the capacitor carbon precursor.

[0036] S4. The capacitor carbon precursor is mixed with NaOH at a mass ratio of 1:1.8 and placed in a muffle furnace for high-temperature activation under a nitrogen atmosphere. The high-temperature activation steps include: first, heating to 550℃ at a heating rate of 5℃ / min and holding for 25min, then heating to 750℃ and holding for 1.5h; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0037] Example 3

[0038] A method for preparing rice husk-based capacitor carbon includes the following steps:

[0039] S1. Rice husks are heated to 600°C in a muffle furnace under nitrogen atmosphere at a heating rate of 5°C / min, and held at that temperature for 1 hour for pyrolysis and carbonization. After cooling, rice husk char material is obtained.

[0040] S2. Disperse the rice husk char material evenly in a 0.5 mol / L NaOH aqueous solution, stir at room temperature for 1 h, filter, wash the filter cake with deionized water, and dry to obtain the pretreated rice husk char material; wherein the ratio of rice husk char material to NaOH aqueous solution is 1 g: 10 mL.

[0041] S3. Lignocellulose was added to 1-butyl-3-methylimidazolium chloride at a mass ratio of 1:10 and heated to dissolve at 90℃ for 8 hours. After cooling, an ionic liquid solution of cellulose was obtained. The pretreated rice husk char material was mixed with the ionic liquid solution of cellulose at a mass ratio of 1:0.2 and stirred at 50℃ for 1 hour. Then, it was placed in a muffle furnace and heated to 400℃ at a heating rate of 5℃ / min under a nitrogen atmosphere. The temperature was held for 20 minutes and then cooled to obtain the capacitor carbon precursor.

[0042] S4. The capacitor carbon precursor is mixed with NaOH at a mass ratio of 1:2 and placed in a muffle furnace for high-temperature activation under a nitrogen atmosphere. The high-temperature activation steps include: first heating to 600℃ at a heating rate of 5℃ / min and holding for 20min, then heating to 800℃ and holding for 2h; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0043] Comparative Example 1

[0044] A conventional method for preparing rice husk-based capacitor carbon includes the following steps:

[0045] S1. Rice husks are heated to 550°C in a muffle furnace under nitrogen atmosphere at a heating rate of 5°C / min, and held at that temperature for 1.5 hours for pyrolysis and carbonization. After cooling, rice husk char material is obtained.

[0046] S2. Disperse the rice husk char material evenly in a 0.2 mol / L NaOH aqueous solution, stir at room temperature for 1.5 h, filter, wash the filter cake with deionized water, and dry to obtain the capacitor carbon precursor; wherein the ratio of rice husk char material to NaOH aqueous solution is 1 g: 8 mL.

[0047] S3. The capacitor carbon precursor is mixed with NaOH at a mass ratio of 1:3 and placed in a muffle furnace for high-temperature activation under a nitrogen atmosphere. The high-temperature activation steps include: heating to 750℃ at a heating rate of 5℃ / min and holding at that temperature for 1.5h; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0048] Comparative Example 2

[0049] The only difference between Comparative Example 2 and Example 2 is that an ionic liquid is used instead of the cellulose ionic liquid solution, specifically including the following steps:

[0050] S1. Rice husks are heated to 550°C in a muffle furnace under nitrogen atmosphere at a heating rate of 5°C / min, and held at that temperature for 1.5 hours for pyrolysis and carbonization. After cooling, rice husk char material is obtained.

[0051] S2. Disperse the rice husk char material evenly in a 0.2 mol / L NaOH aqueous solution, stir at room temperature for 1.5 h, filter, wash the filter cake with deionized water, and dry to obtain the pretreated rice husk char material; wherein the ratio of rice husk char material to NaOH aqueous solution is 1 g: 8 mL.

[0052] S3. The pretreated rice husk char material and 1-butyl-3-methylimidazolium chloride were mixed at a mass ratio of 1:0.15 and stirred at 40°C for 1.5 h. Then, the mixture was placed in a muffle furnace and heated to 350°C at a heating rate of 5°C / min under a nitrogen atmosphere. The temperature was held for 25 min and then cooled to obtain the capacitor char precursor.

[0053] S4. The capacitor carbon precursor was mixed with NaOH at a mass ratio of 1:1.8 and placed in a muffle furnace for high-temperature activation under a nitrogen atmosphere. The high-temperature activation steps included: first, heating to 550℃ at a heating rate of 5℃ / min and holding for 25 min; then heating to 750℃ and holding for 1.5 h; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0054] Test case

[0055] The rice husk-based capacitive carbon prepared in Examples 1-3 and Comparative Examples 1-2 were assembled into supercapacitors for performance testing. The electrolyte was a 6 mol / L KOH electrolyte, the test current density was 1 A / g, and the specific capacitance retention rate was the specific capacitance retention rate after 10,000 cycles of constant current charge-discharge testing. The test results are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] Comparing Examples 1-3 with Comparative Example 1 in Table 1, it can be seen that the rice husk-based capacitor carbon prepared by the method of the present invention can significantly improve the specific capacitance and cycle stability of the capacitor compared with the conventional carbonization-alkali dissolution method. Comparing Examples 1-3 with Comparative Example 2, it can be seen that compared with single ionic liquid-assisted activation, the rice husk-based capacitor carbon prepared by the present invention using cellulose ionic liquid solution for assisted activation has a significant improvement in specific capacitance and cycle stability. This is because the cellulose dissolved in the ionic liquid penetrates into the macropores formed after desilication of the rice husk carbon material during high-temperature activation, and together with the ionic liquid, forms a rich microporous structure during high-temperature activation, making the micropores in the carbon material finer, more uniform, and with higher mechanical strength, and less prone to collapse or damage during high-temperature treatment, thereby optimizing the pore structure and improving the electrochemical performance of the capacitor carbon.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing rice husk-based capacitor carbon, characterized in that, Includes the following steps: S1. Rice husks are pyrolyzed and carbonized under an inert atmosphere, and then cooled to obtain rice husk carbon material. S2. The rice husk char material is added to an aqueous solution of NaOH with a concentration of 0.1-0.5 mol / L and dispersed evenly. Then, it is stirred for a period of time, filtered, and the filter cake is washed with deionized water and dried to obtain pretreated rice husk char material. S3. Add lignocellulose to imidazole chloride ionic liquid, heat to dissolve fully, and cool to obtain cellulose ionic liquid solution; mix the pretreated rice husk char material with the cellulose ionic liquid solution, stir for a period of time, and then heat at 300-400℃ for 20-30 min under an inert atmosphere, and cool to obtain capacitor carbon precursor. S4. The capacitor carbon precursor is mixed with NaOH and activated at high temperature under an inert atmosphere. After cooling, it is washed with deionized water and dried to obtain rice husk-based capacitor carbon.

2. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S1, the temperature of the pyrolysis carbonization is 500-600℃, and the time is 1-2 hours.

3. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S2, the ratio of the rice husk charcoal material to the NaOH aqueous solution is 1g: 5-10mL; In S2, the stirring temperature is room temperature, and the stirring time is 1 to 2 hours.

4. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S3, the imidazole chloride ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, and 1-allyl-2-methylimidazolium chloride.

5. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S3, the mass ratio of the lignocellulose to the imidazole chloride ionic liquid is 1:5 to 10.

6. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S3, the heating and dissolution temperature is 60–90℃, and the time is 8–12 hours.

7. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S3, the mass ratio of the pretreated rice husk charcoal material to the ionic liquid solution of cellulose is 1:0.1 to 0.2; In S3, the stirring temperature is 30–50℃ and the stirring time is 1–2 hours.

8. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S4, the mass ratio of the capacitor carbon precursor to NaOH is 1:1.5 to 2.

9. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that, In S4, the high-temperature activation steps include: first heating to 500-600℃ and holding for 20-30 minutes, then heating to 700-800℃ and holding for 1.5-2 hours.

10. A rice husk-based capacitor carbon, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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