Preparation method of high specific capacitance activated carbon for supercapacitor
By introducing nitrogen-doped mesoporous structures into coconut shell-based activated carbon, the problem of scarce active sites on the surface of biomass activated carbon was solved, thereby improving the specific capacitance and electrochemical performance of supercapacitors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUJIAN XINSEN CARBON
- Filing Date
- 2025-11-28
- Publication Date
- 2026-07-21
AI Technical Summary
Biomass-based activated carbon has few active sites on its surface and lacks additional pseudocapacitive contributions, resulting in reduced specific capacitance. Furthermore, its loose carbon skeleton structure and fragile pore walls make it difficult to achieve excellent performance in supercapacitors.
Using coconut shell as a precursor, a carbon skeleton is formed through carbonization, and a microporous structure is formed through pre-activation. Phenolic lignin-modified amine generated by the reaction of phenolic lignin, pyridine diamine and formaldehyde is cross-linked with dialdehyde on the inner wall of the pores of the pre-activated material to form a nitrogen-doped mesoporous carbon structure, which improves the ion transport rate and introduces pseudocapacitance.
High specific capacitance activated carbon was obtained, which avoided excessive etching and collapse of the initial pores, improved the effective specific surface area and electrochemical performance, and enhanced the electrochemical performance of the supercapacitor.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of activated carbon technology, specifically relating to a method for preparing high specific capacitance activated carbon for supercapacitors. Background Technology
[0002] Supercapacitors mainly consist of three parts: symmetrical electrodes, electrolyte, and separator. When an external voltage is applied to the electrode plates of the two symmetrical electrodes of a supercapacitor, electrostatic forces form a double layer of charges on the two electrode plates, resulting in the charging and discharging process. Supercapacitors are a new type of energy storage device that falls between traditional capacitors and batteries. They have advantages such as high power density, large capacity, long service life, maintenance-free operation, and economic and environmental friendliness, and are increasingly attracting keen attention from researchers.
[0003] Different electrode materials have a crucial impact on the performance of supercapacitors. Currently, the main electrode materials used are carbon materials, including activated carbon, graphene, template carbon, carbon nanotubes, onion-shaped carbon, etc. Among them, activated carbon is the most widely used electrode material due to its large specific surface area, good electrical / thermal conductivity, and wide availability of raw materials. For example, patent CN107215871B discloses a method for preparing activated carbon for supercapacitors, which includes the following steps: (1) material preparation; (2) carbonization; (3) pre-activation; (4) activation; (5) washing. Patent CN105923634B discloses coconut shell fiber-based activated carbon for supercapacitors and its preparation method. The method includes crushing pretreated coconut shell fibers, heating the mixture at a rate of 2-5℃ / min to 700-750℃, and holding it at that temperature for 1-1.5 hours to obtain a carbonized product; grinding and sieving the carbonized product; mixing the carbonized product with KOH at a mass ratio of 1:2 to 1:5; heating the mixture at a rate of 3-5℃ / min to 800-850℃ and holding it at that temperature for 1-1.5 hours to obtain an activated product; washing the activated product with water, acid washing, and then washing it again with water until the pH reaches 6-7; and drying it to prepare activated carbon. Patent CN107253720B discloses a high specific surface area mesoporous activated carbon, its preparation method, and its application in supercapacitors. The activated carbon is prepared by impregnating durian shell powder in an activating agent solution, drying it, and then carbonizing it at high temperature under a protective atmosphere, resulting in a specific surface area as high as 3712 m². 2 g -1 Activated carbon with a mesoporous content of 29% exhibits excellent electrochemical performance when used as an electrode material for supercapacitors.
[0004] The above describes the technology for preparing activated carbon using biomass such as coconut shells, durian shell powder, and coconut husks as raw materials. Biomass is the only renewable organic aromatic carbon resource in nature, with advantages such as abundant reserves, low price, and low pollution. However, activated carbon prepared from biomass has scarce active sites on its surface, resulting in a lack of additional pseudocapacitive contribution. Furthermore, due to the high O / H ratio and naturally porous structure of biomass, the resulting carbon skeleton has a loose structure and fragile pore walls, making the activated carbon surface prone to structural collapse. This leads to a reduction in effective specific surface area and active sites, further decreasing the specific capacitance of biomass-prepared activated carbon. Therefore, it is necessary to modify the biomass-based activated carbon preparation process to obtain a high specific capacitance activated carbon and expand its application in the field of supercapacitor electrode materials. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a method for preparing high specific capacitance activated carbon for supercapacitors. First, coconut shell is used as a precursor. The carbonization process removes volatiles, forming a carbon skeleton. Then, an alkaline activator penetrates the microcrystalline structure and natural pores within the coconut shell carbonized material, pre-etching out obvious initial pore channels to form a basic carbon skeleton dominated by micropores and possessing a large specific surface area. Next, phenolic lignin-modified amine and dialdehyde, generated by the reaction of phenolic lignin, pyridine diamine, and formaldehyde, are cured and cross-linked on the inner walls and surface of the pre-activated material's pores, forming a polymer thin layer. This polymer is then activated at high temperature, undergoing carbonization and etching to form a nitrogen-doped mesoporous carbon structure. This not only prevents the initial pores of the pre-activated material from collapsing into macropores due to excessive etching but also enhances the ion transport rate through surface mesoporous channels and introduces pseudocapacitance using nitrogen functional groups, resulting in high specific capacitance activated carbon.
[0006] To achieve the above objectives, the following technical solution is adopted: A method for preparing high specific capacitance activated carbon for supercapacitors includes the following steps: 1) Carbonize and crush coconut shells, mix the resulting carbonized and crushed material with an alkaline activator, pre-activate, and grind to obtain a pre-activated material; the pre-activation conditions are an inert atmosphere, 450-550℃, and maintained for 0.5-1.5h. 2) Dissolve phenolic lignin in alkaline solution, add pyridine diamine and formaldehyde solution, mix and react to obtain phenolic lignin-modified amine; 3) Add phenolic lignin-modified amine, dialdehyde, and catalyst to an organic solvent and mix well. Add pre-activated material and disperse ultrasonically. Heat and reflux to react and obtain coated modified pre-activated material. 4) Activate, acid wash, water wash and dry the coated modified pre-activated material to obtain high specific capacitance activated carbon for supercapacitors.
[0007] In step 1), the average particle size of the coconut shell is 10-20 mesh. The pulverization is performed until the average particle size is 20-50 mesh. The mass ratio of the carbonized pulverized material to the alkali activator is 1:3-5. The alkali activator is selected from one or a combination of potassium hydroxide and sodium hydroxide. The carbonization conditions are an inert atmosphere, 400-500℃, and maintained for 1-3 hours. The grinding is performed until the average particle size is 100-200 mesh.
[0008] In step 2), the reaction is carried out at 80-100℃ for 2-5 hours. The mass ratio of the phenolic lignin, pyridine diamine, and formaldehyde solution is 1:1.5-2:4.5-9.5. The pyridine diamine is selected from one or a combination of two or more of 2,5-diaminopyridine, 2,6-diaminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, and 3,5-diaminopyridine. The pH of the alkaline solution is 9-12. The alkaline solution is selected from one or a combination of two of sodium hydroxide and potassium hydroxide solutions.
[0009] Furthermore, the phenolic lignin-modified amine is prepared by the following steps: dissolving phenolic lignin in an alkaline solution, adding pyridine diamine and mixing, heating and reacting, adding formaldehyde solution dropwise, continuing to heat and react, and dehydrating under vacuum after the reaction is completed to obtain the phenolic lignin-modified amine.
[0010] Further, the heating reaction is carried out at 80-90℃ for 1-2 hours. The formaldehyde solution concentration is 37 wt%. The formaldehyde solution is added dropwise over 30-60 minutes. The continued heating reaction is carried out at 90-100℃ for 1-3 hours. After the continued heating reaction is completed, dehydration is carried out at 140-160℃ under a vacuum of 0.08 to 0.095 MPa.
[0011] Step 2) The phenolic lignin is prepared by phenolic treatment of alkali lignin, specifically by adding alkali lignin, phenol, and alkaline catalyst to water and stirring until dissolved, then heating to react and obtaining phenolic lignin.
[0012] Further, the mass ratio of alkali lignin, phenol, alkaline catalyst, and water is 1:0.35-0.55:0.05-0.10:1-3. The alkali lignin is prepared from black liquor of bamboo, oak, poplar, eucalyptus, birch, or Masson pine through acid precipitation. The alkaline catalyst is selected from one or a combination of sodium hydroxide and potassium hydroxide. The heating reaction conditions are 70-100℃ for 1-3 hours. After the heating reaction, the process includes acidification, filtration, washing, and drying. Acidification is performed with 1-2 mol / L hydrochloric acid to pH=2-3. Washing is performed 1-3 times with hot water at 80-100℃. Drying is performed at 60℃ to constant weight.
[0013] Step 3) The mass ratio of the phenolic lignin-modified amine, dialdehyde, catalyst, pre-activated material, and organic solvent is 1:0.2-0.35:0.01-0.02:4-9:40-60, preferably 1:0.2-0.35:0.01-0.02:5-8:40-60. The organic solvent is selected from one or a combination of two of DMF and DMSO. The dialdehyde is selected from one or a combination of two or more of o-phthalaldehyde, terephthalaldehyde, and iso-phthalaldehyde. The catalyst is selected from one or a combination of two or more of triethylamine, 4-dimethylaminopyridine, and N,N-dimethylaniline. The ultrasonic dispersion is performed at a wave power of 100-300W and a frequency of 30-50kHz for 30-60 minutes. The reflux reaction time is 3-5 hours. After the reaction, the process includes filtration, washing, and drying steps.
[0014] Step 4) The activation conditions are an inert atmosphere, 800-950℃, and maintained for 1-2 hours. The acid washing is performed by washing with 1-5wt% hydrochloric acid 1-5 times. The water washing is performed by washing with water until the pH value is 5.0-7.0.
[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention first uses coconut shell as a precursor, which undergoes carbonization to remove volatiles and form a carbon skeleton. Then, it undergoes pre-activation: an alkaline activator penetrates the microcrystalline structure and natural pores within the carbonized coconut shell material, pre-etching out obvious initial pore channels to form a basic carbon skeleton dominated by micropores and possessing a large specific surface area. Next, phenolic lignin-modified amines and dialdehydes, generated by the reaction of phenolic lignin, pyridine diamine, and formaldehyde, are cured and cross-linked on the inner walls and surface of the pre-activated material's pores, forming a polymer thin layer. This polymer is then activated at high temperature, undergoing carbonization and etching to form a nitrogen-doped mesoporous carbon structure. This not only prevents the initial pores of the pre-activated material from collapsing into macropores due to excessive etching, but also enhances the ion transport rate through surface mesoporous channels and introduces pseudocapacitance using nitrogen functional groups, resulting in high specific capacitance activated carbon. Detailed Implementation
[0016] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, all "parts" mentioned in the embodiments of the present invention are parts by weight. All reagents used are commercially available in the art.
[0017] Alkali lignin is an alkali lignin prepared by acid precipitation of black liquor from poplar alkali papermaking, and it comes from Shandong Yaotong Industrial Co., Ltd.
[0018] Example 1 1) Carbonize 20-mesh coconut shells at 500℃ for 3 hours under nitrogen atmosphere, pulverize them to an average particle size of 50 mesh, mix the resulting carbonized pulverized material with sodium hydroxide at a mass ratio of 1:5, pre-activate it at 550℃ for 0.5 hours under nitrogen atmosphere, and grind it to an average particle size of 200 mesh to obtain pre-activated material. 2) Add 1 part by mass of alkali lignin, 0.55 parts by mass of phenol, and 0.10 parts by mass of sodium hydroxide to 3 parts by mass of water and stir until dissolved. Heat to 100℃ and react for 1 hour. After the reaction, acidify with 1 mol / L hydrochloric acid to pH 3, filter, wash twice with 80℃ hot water, and dry at 60℃ to constant weight to obtain phenolic lignin. Dissolve 1 part by mass of phenolic lignin in sodium hydroxide solution with pH 12, add 2 parts by mass of 2,5-diaminopyridine and mix well. Heat to 80℃ and react for 1 hour. Add 9.5 parts by mass of 37wt% formaldehyde solution dropwise over 1 hour. Continue heating to 100℃ and react for 3 hours. After the reaction, dehydrate under vacuum at 140℃ and 0.08MPa for 1.5 hours to obtain phenolic lignin-modified amine. 3) Add 1 part by weight of phenolic lignin-modified amine, 0.35 parts by weight of terephthalaldehyde, and 0.02 parts by weight of triethylamine to 60 parts by weight of DMF and mix well. Add 5 parts by weight of pre-activated material and ultrasonically disperse for 30 min at a wave power of 300 W and a frequency of 30 kHz. Heat and reflux for 5 h. Filter, wash with water 3 times, and dry at 60 °C to constant weight to obtain the coated modified pre-activated material. 4) The coated and modified pre-activated material was activated at 950°C for 1 hour under a nitrogen atmosphere, washed twice with 3wt% hydrochloric acid, washed with water until the pH value was 7, and dried at 60°C to constant weight to obtain high specific capacitance activated carbon for supercapacitors.
[0019] Example 2 The rest is the same as in Example 1, except that in step 2), the amount of 2,5-diaminopyridine used is 1.5 parts by mass.
[0020] Example 3 The rest is the same as in Example 1, except that in step 2), the amount of 37wt% formaldehyde solution used is 4.5 parts by mass.
[0021] Example 4 The rest is the same as in Example 1, except that in step 3), the amount of terephthalaldehyde used is 0.2 parts by mass.
[0022] Example 5 The rest is the same as in Example 1, except that in step 3), the amount of pre-activated material is 8 parts by mass.
[0023] Example 6 The rest is the same as in Example 1, except that in step 3), the amount of pre-activated material is 9 parts by mass.
[0024] Example 7 The rest is the same as in Example 1, except that in step 3), the amount of pre-activated material is 4 parts by mass.
[0025] Example 8 The rest is the same as in Example 1, except that in step 1), the obtained carbonized pulverized material is mixed with sodium hydroxide at a mass ratio of 1:3.
[0026] Example 9 1) Carbonize 20-mesh coconut shells at 500℃ for 3 hours under nitrogen atmosphere, pulverize them to an average particle size of 50 mesh, mix the resulting carbonized pulverized material with sodium hydroxide at a mass ratio of 1:5, pre-activate it at 450℃ for 1.5 hours under nitrogen atmosphere, and grind it to an average particle size of 200 mesh to obtain pre-activated material. 2) Add 1 part by mass of alkali lignin, 0.35 parts by mass of phenol, and 0.10 parts by mass of sodium hydroxide to 3 parts by mass of water and stir until dissolved. Heat to 70℃ and react for 3 hours. After the reaction, acidify with 1 mol / L hydrochloric acid to pH 3, filter, wash twice with 80℃ hot water, and dry at 60℃ to constant weight to obtain phenolic lignin. Dissolve 1 part by mass of phenolic lignin in sodium hydroxide solution with pH 12, add 2 parts by mass of 2,5-diaminopyridine and mix well. Heat to 80℃ and react for 1 hour. Add 9.5 parts by mass of 37wt% formaldehyde solution dropwise over 1 hour. Continue heating to 100℃ and react for 3 hours. After the reaction, dehydrate under vacuum at 140℃ and 0.08MPa for 1.5 hours to obtain phenolic lignin-modified amine. 3) Add 1 part by weight of phenolic lignin-modified amine, 0.35 parts by weight of terephthalaldehyde, and 0.02 parts by weight of triethylamine to 60 parts by weight of DMF and mix well. Add 5 parts by weight of pre-activated material and ultrasonically disperse for 30 min at a wave power of 300 W and a frequency of 30 kHz. Heat and reflux for 3 h. Filter, wash with water 3 times, and dry at 60 °C to constant weight to obtain the coated modified pre-activated material. 4) The coated and modified pre-activated material was activated at 800℃ for 2 hours under a nitrogen atmosphere, washed twice with 3wt% hydrochloric acid, washed with water until the pH value reached 7, and dried at 60℃ to constant weight to obtain high specific capacitance activated carbon for supercapacitors.
[0027] Comparative Example 1 1) Carbonize 20-mesh coconut shells at 500℃ for 3 hours under nitrogen atmosphere, pulverize them to an average particle size of 50 mesh, mix the resulting carbonized pulverized material with sodium hydroxide at a mass ratio of 1:5, pre-activate it at 550℃ for 0.5 hours under nitrogen atmosphere, and grind it to an average particle size of 200 mesh to obtain pre-activated material. 2) The pre-activated material was activated at 950℃ for 1 hour under a nitrogen atmosphere, washed twice with 3wt% hydrochloric acid, washed with water until the pH value was 7, and dried at 60℃ to constant weight to obtain activated carbon.
[0028] Application examples Electrode sheet preparation: The activated carbon, PVDF binder, and acetylene black conductive agent are prepared in a mass percentage ratio of 80:12:8. First, the binder is dissolved in N-methylpyrrolidone to prepare a 0.02 g / ml solution. Then, the activated carbon and conductive agent are added to the binder solution and stirred until a paste is formed. The paste is coated onto a nickel foam current collector and then dried in a vacuum drying oven at 100°C for 12 h. The paste is then pressed into sheets at 20 MPa using a tablet press and cut into electrode sheets to obtain the electrode sheet.
[0029] Assemble the supercapacitor: Place the electrode sheet / porous polypropylene separator / electrode sheet into the button cell casing in sequence to form a sandwich structure with two electrodes, then add 3 mol / L KOH electrolyte and encapsulate it into a CR2032 type button supercapacitor.
[0030] The activated carbon and supercapacitors prepared in the above examples and comparative examples were subjected to the following performance tests: 1. Specific surface area and pore structure: Measured using a NOVA 1000e pore structure and specific surface area analyzer. Samples were degassed at 350℃ for 2 hours, using liquid nitrogen as the adsorption medium, at 77K and a relative pressure (P / P0) of 10. -6 N2 adsorption was measured within the range of -1, and the specific surface area and pore size distribution were obtained by the BET equation and the BJH equation, respectively.
[0031] 2. Constant current charge and discharge performance: The constant current charge and discharge test of the coin-type supercapacitor was carried out using the battery testing system (CT3001A) of Wuhan Landian Electronics Co., Ltd., and the specific capacitance at a current density of 1A / g was recorded.
[0032] 3. Cyclic performance: Long-term cycle performance was tested using the battery testing system (CT3001A) of Wuhan Landian Electronics Co., Ltd. At a current density of 1A / g, the supercapacitor underwent 10,000 constant current charge-discharge cycles, and the specific capacitance retention rate was calculated.
[0033] Table 1 Performance Test Results .
[0034] As can be seen from Table 1, the activated carbon prepared by this invention has high mesoporosity and specific capacitance. At a current density of 1 A / g, the supercapacitor retains more than 88% of its specific capacitance after 10,000 constant current charge-discharge cycles.
[0035] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.
Claims
1. A method for preparing high specific capacitance activated carbon for supercapacitors, characterized in that, Includes the following steps: 1) Carbonize and crush coconut shells, mix the resulting carbonized and crushed material with an alkaline activator, pre-activate, and grind to obtain a pre-activated material; the pre-activation conditions are an inert atmosphere, 450-550℃, and maintained for 0.5-1.5h. 2) Dissolve phenolic lignin in alkaline solution, add pyridine diamine and mix well, heat to 80-90℃ and react for 1-2 hours, add formaldehyde solution dropwise, continue to heat to 90-100℃ and react for 1-3 hours, dehydrate under vacuum after the reaction to obtain phenolic lignin modified amine. 3) Phenolic lignin-modified amine, dialdehyde, and catalyst are added to an organic solvent and mixed well. Pre-activated material is added and ultrasonically dispersed. The mixture is then heated under reflux to obtain a coated modified pre-activated material. The catalyst is selected from one or more of triethylamine, 4-dimethylaminopyridine, and N,N-dimethylaniline. 4) Activate, acid wash, water wash and dry the coated modified pre-activated material to obtain high specific capacitance activated carbon for supercapacitors; the activation conditions are inert atmosphere, 800-950℃, for 1-2 hours.
2. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 1), the pulverization is to pulverize to an average particle size of 20-50 mesh; the mass ratio of the carbonized pulverized material to the alkali activator is 1:3-5.
3. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 1), the carbonization conditions are an inert atmosphere, 400-500℃, and maintained for 1-3 hours; the grinding is grinding to an average particle size of 100-200 mesh.
4. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 2), the mass ratio of the phenolic lignin, pyridine diamine, and formaldehyde solution is 1:1.5-2:4.5-9.5; the pyridine diamine is selected from one or more combinations of 2,5-diaminopyridine, 2,6-diaminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, and 3,5-diaminopyridine.
5. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, The pH of the alkaline solution is 9-12.
6. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 2), the phenolic lignin is prepared by phenolic treatment of alkali lignin.
7. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 3), the mass ratio of the phenolic lignin-modified amine, dialdehyde, catalyst, pre-activated material, and organic solvent is 1:0.2-0.35:0.01-0.02:4-9:40-60.
8. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 7, characterized in that, In step 3), the mass ratio of the phenolic lignin-modified amine, dialdehyde, catalyst, pre-activated material, and organic solvent is 1:0.2-0.35:0.01-0.02:5-8:40-60.
9. The method for preparing high specific capacitance activated carbon for supercapacitors according to claim 1, characterized in that, In step 3), the organic solvent is selected from one or a combination of two of DMF and DMSO; the dialdehyde is selected from one or a combination of two or more of o-phthalaldehyde, terephthalaldehyde, and isophthalaldehyde.