Rice hull-based capacitor carbon and preparation method thereof

Abstract

The preparation method comprises the following steps: pyrolyzing and carbonizing rice hulls, then carrying out desilicication pretreatment by using an aqueous solution of NaOH, fully mixing with an ionic liquid solution of cellulose, carrying out heating treatment, mixing with NaOH, and carrying out high-temperature activation to obtain the rice hull-based capacitor carbon. The rice hull-based capacitor carbon obtained by the invention has a rich microporous structure, the specific capacitance and cycling stability of the capacitor carbon are improved, and the electrochemical performance of a supercapacitor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of capacitor electrode materials, and in particular to a rice husk-based capacitor carbon and a preparation method thereof. Background Art

[0002] Supercapacitor is a new type of energy storage device, which has the characteristics of high power density, fast charge and discharge speed and long cycle life, and has attracted more and more attention. Electrode material is the core component of supercapacitor and has a key influence on the performance of supercapacitor. Among them, porous activated carbon material has the advantages of wide source, low price and high specific surface area, and has become one of the most widely studied and applied supercapacitor materials.

[0003] Rice husk is the shell residue left after rice is husked or processed. As a common agricultural and sideline product, it is very abundant in source. At present, the main preparation method of rice husk-based capacitor carbon is carbonization-alkali dissolution method, that is, it is first subjected to pyrolysis carbonization treatment, and then activated by alkali treatment to obtain capacitor carbon. Since the porous carbon materials prepared by this method generally have problems such as uneven pores and low density, the specific capacitance and energy density of the capacitor carbon are low, 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 a preparation method thereof.

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

[0006] S1, pyrolyzing and carbonizing rice husk under an inert atmosphere, and obtaining rice husk charcoal material after cooling;

[0007] S2, adding the rice husk carbon material to an aqueous solution of NaOH with a concentration of 0.1 to 0.5 mol / L and dispersing the mixture evenly, stirring the mixture for a period of time, filtering the mixture, washing the filter cake with deionized water, and drying the mixture to obtain a pretreated rice husk carbon material;

[0008] S3, adding wood cellulose to imidazolium chloride ionic liquid, fully heating to dissolve, and cooling to obtain a cellulose ionic liquid solution; mixing the pretreated rice husk carbon material with the cellulose ionic liquid solution, stirring for a period of time, and then heating at 300-400° C. for 20-30 minutes under an inert atmosphere, and cooling to obtain a capacitor carbon precursor;

[0009] S4. After mixing the capacitor carbon precursor with NaOH, the mixture is activated at high temperature in an inert atmosphere, cooled, washed with deionized water, and dried to obtain rice husk-based capacitor carbon.

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

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

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

[0013] Preferably, in S3, the imidazolium 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 imidazolium chloride ionic liquid is 1:5-10.

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

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

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

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

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

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

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

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

[0023] In the preparation process of the rice husk-based capacitor carbon of the present invention, the rice husk is first pyrolyzed and carbonized, and then pre-treated with desiliconization using an aqueous solution of NaOH, fully mixed with an ionic liquid solution of cellulose, heated, and then mixed with NaOH for high-temperature activation to obtain the rice husk-based capacitor carbon. After the desiliconization pre-treatment of the rice husk carbon material, many macropores are formed in the carbon material, and the present invention adopts a mixed treatment of the carbon material and the ionic liquid solution of cellulose, and high-temperature activation with NaOH, so that the ionic liquid and the cellulose dissolved in the ionic liquid penetrate into the macropores formed after the desiliconization of the rice husk carbon material, and the cellulose as the carbon skeleton is carbonized together with the ionic liquid during the high-temperature activation process to form a rich microporous structure, so that the micropores in the carbon material are more fine, uniform, and have high mechanical strength, and are not easy to collapse or destroy during high-temperature treatment, so that the pore structure is optimized, the specific capacitance and cycle stability of the capacitor carbon are improved, and it is beneficial to improve the electrochemical performance of the supercapacitor. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described in detail below through specific embodiments.

[0025] Example 1

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

[0027] S1. In a muffle furnace, the rice husk is heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, and kept at this temperature for 2 hours for pyrolysis and carbonization, and then cooled to obtain a rice husk carbon material;

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

[0029] S3, adding wood cellulose to 1-butyl-3-methylimidazolium chloride at a mass ratio of 1:5, heating and dissolving at 60°C for 12 hours, and obtaining an ionic liquid solution of cellulose after cooling; mixing the pretreated rice husk carbon material and the ionic liquid solution of cellulose at a mass ratio of 1:0.1, stirring at 30°C for 2 hours, and then placing in a muffle furnace, heating to 300°C at a heating rate of 5°C / min under a nitrogen atmosphere, keeping the temperature for 30 minutes, and obtaining a capacitor carbon precursor after cooling;

[0030] S4. After mixing the capacitor carbon precursor and NaOH in a mass ratio of 1:1.5, place the mixture in a muffle furnace and perform high-temperature activation under a nitrogen atmosphere. The steps of high-temperature activation include: first heating the temperature to 500°C at a heating rate of 5°C / min, keeping the temperature for 30 minutes, then heating the temperature to 700°C at a heating rate of 5°C / min, and keeping the temperature for 2 hours; after cooling, wash with deionized water, and dry to obtain rice husk-based capacitor carbon.

[0031] Example 2

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

[0033] S1. In a muffle furnace, the temperature of the rice husk is raised to 550° C. at a heating rate of 5° C. / min under a nitrogen atmosphere, and the temperature is kept for 1.5 h for pyrolysis and carbonization, and the rice husk carbon material is obtained after cooling;

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

[0035] S3, adding wood cellulose to 1-butyl-3-methylimidazolium chloride in a mass ratio of 1:8, heating and dissolving at 70°C for 10 hours, and obtaining an ionic liquid solution of cellulose after cooling; mixing the pretreated rice husk carbon material and the ionic liquid solution of cellulose in a mass ratio of 1:0.15, stirring at 40°C for 1.5 hours, and then placing in a muffle furnace, heating to 350°C at a heating rate of 5°C / min under a nitrogen atmosphere, keeping the temperature for 25 minutes, and obtaining a capacitor carbon precursor after cooling;

[0036] S4. After mixing the capacitor carbon precursor and NaOH in a mass ratio of 1:1.8, place it in a muffle furnace and perform high-temperature activation under a nitrogen atmosphere. The steps of high-temperature activation include: first heating to 550°C at a heating rate of 5°C / min, keeping warm for 25 minutes, then heating to 750°C, keeping warm for 1.5 hours; after cooling, wash with deionized water, and dry to obtain rice husk-based capacitor carbon.

[0037] Example 3

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

[0039] S1. In a muffle furnace, the rice husk is heated to 600°C at a heating rate of 5°C / min under a nitrogen atmosphere, and kept at this temperature for 1 hour for pyrolysis and carbonization, and then cooled to obtain a rice husk carbon material;

[0040] S2, adding the rice husk carbon material to a 0.5 mol / L NaOH aqueous solution and dispersing the mixture evenly, then stirring the mixture at room temperature for 1 hour, filtering the mixture, washing the filter cake with deionized water, and drying the mixture to obtain a pretreated rice husk carbon material; wherein the ratio of the rice husk carbon material to the NaOH aqueous solution is 1 g: 10 mL;

[0041] S3, adding wood cellulose to 1-butyl-3-methylimidazolium chloride in a mass ratio of 1:10, heating and dissolving at 90°C for 8 hours, and obtaining an ionic liquid solution of cellulose after cooling; mixing the pretreated rice husk carbon material and the ionic liquid solution of cellulose in a mass ratio of 1:0.2, stirring at 50°C for 1 hour, and then placing in a muffle furnace, heating to 400°C at a heating rate of 5°C / min under a nitrogen atmosphere, keeping the temperature for 20 minutes, and obtaining a capacitor carbon precursor after cooling;

[0042] S4. After mixing the capacitor carbon precursor and NaOH in a mass ratio of 1:2, place the mixture in a muffle furnace and perform high-temperature activation under a nitrogen atmosphere. The steps of high-temperature activation include: first heating the temperature to 600°C at a heating rate of 5°C / min, keeping the temperature for 20 minutes, then heating the temperature to 800°C, and keeping the temperature for 2 hours; after cooling, wash with deionized water, and dry to obtain rice husk-based capacitor carbon.

[0043] Comparative Example 1

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

[0045] S1. In a muffle furnace, the temperature of the rice husk is raised to 550° C. at a heating rate of 5° C. / min under a nitrogen atmosphere, and the temperature is kept for 1.5 h for pyrolysis and carbonization, and the rice husk carbon material is obtained after cooling;

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

[0047] S3. After mixing the capacitor carbon precursor and NaOH in a mass ratio of 1:3, the mixture is placed in a muffle furnace and activated at high temperature under a nitrogen atmosphere. The steps of high temperature activation include: heating to 750°C at a heating rate of 5°C / min and keeping the temperature for 1.5 hours; after cooling, washing with deionized water and drying to obtain rice husk-based capacitor carbon.

[0048] Comparative Example 2

[0049] The difference between Comparative Example 2 and Example 2 is that the ionic liquid solution of cellulose is replaced by an ionic liquid, and specifically comprises the following steps:

[0050] S1. In a muffle furnace, the temperature of the rice husk is raised to 550° C. at a heating rate of 5° C. / min under a nitrogen atmosphere, and the temperature is kept for 1.5 h for pyrolysis and carbonization, and the rice husk carbon material is obtained after cooling;

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

[0052] S3, mixing the pretreated rice husk carbon material with 1-butyl-3-methylimidazolium chloride in a mass ratio of 1:0.15, stirring at 40°C for 1.5h, then placing in a muffle furnace, heating to 350°C at a heating rate of 5°C / min under a nitrogen atmosphere, keeping the temperature for 25min, and cooling to obtain a capacitor carbon precursor;

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

[0054] Test example

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

[0056] Table 1

[0057]

[0058]

[0059] By comparing Examples 1 to 3 in Table 1 with Comparative Example 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; by comparing Examples 1 to 3 with Comparative Example 2, it can be seen that compared with the single ionic liquid-assisted activation, the present invention uses an ionic liquid solution of cellulose for auxiliary activation, and the specific capacitance and cycle stability of the prepared rice husk-based capacitor carbon are greatly improved. This is because the cellulose dissolved in the ionic liquid penetrates into the macropores formed after the desiliconization of the rice husk carbon material during high-temperature activation, and forms a rich microporous structure together with the ionic liquid during the high-temperature activation process as a carbon skeleton, so that the micropores in the carbon material are more dense, uniform, and have high mechanical strength, and are not easy to collapse or destroy during high-temperature treatment, thereby optimizing the pore structure and improving the electrochemical properties of the capacitor carbon.

[0060] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing rice husk-based capacitor carbon, characterized in that: The following steps are involved: S1, pyrolyzing and carbonizing rice husk under an inert atmosphere, and obtaining rice husk charcoal material after cooling; S2, adding the rice husk carbon material to an aqueous solution of NaOH with a concentration of 0.1 to 0.5 mol / L and dispersing the mixture evenly, stirring the mixture for a period of time, filtering the mixture, washing the filter cake with deionized water, and drying the mixture to obtain a pretreated rice husk carbon material; S3, adding wood cellulose to imidazolium chloride ionic liquid, fully heating to dissolve, and cooling to obtain a cellulose ionic liquid solution; mixing the pretreated rice husk carbon material with the cellulose ionic liquid solution, stirring for a period of time, and then heating at 300-400° C. for 20-30 minutes under an inert atmosphere, and cooling to obtain a capacitor carbon precursor; S4. After mixing the capacitor carbon precursor with NaOH, the mixture is activated at high temperature in an inert atmosphere, cooled, 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°C and the time is 1-2h.

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 carbon material to the aqueous solution of NaOH is 1 g: 5-10 mL; In S2, the stirring temperature is room temperature and the 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 imidazolium 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 imidazolium chloride ionic liquid is 1:5-10.

6. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that: In S3, the temperature of heating and dissolving is 60 to 90° C., and the time is 8 to 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 carbon material to the ionic liquid solution of cellulose is 1:0.1-0.2; In S3, the stirring temperature is 30 to 50°C and the stirring time is 1 to 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 1:1.5-2.

9. The method for preparing rice husk-based capacitor carbon according to claim 1, characterized in that: In S4, the high temperature activation step includes: firstly heating to 500-600°C, keeping the temperature for 20-30 minutes, then heating to 700-800°C, keeping the temperature for 1.5-2 hours.

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

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