Surface modification method of biomass supercapacitor activated carbon

Abstract

The invention relates to the technical field of activated carbon, and discloses a surface modification method of biomass super-capacitor activated carbon, which comprises the following steps: (1) spraying an aqueous solution containing a carbon and nitrogen source dopant onto the surface of the biomass super-capacitor activated carbon and realizing complete infiltration, the carbon and nitrogen source dopant being glucosamine; (2) carrying out hydrothermal carbonization at 120-300 DEG C in an inert atmosphere, and then drying; then carrying out heat treatment at 400-500 DEG C in an inert atmosphere; and (3) carrying out activation reaction in the atmosphere of CO2, water vapor or mixed gas of CO2 and water vapor. According to the preparation method, the activated carbon is doped by adopting the carbon and nitrogen source doping agent, meanwhile, hydrothermal carbonization is carried out, surface functional groups of biomass activated carbon are removed, defect sites in the structure of the biomass activated carbon are repaired through carbon doping, structured doping is achieved, lattice distortion of the carbon material can be small through nitrogen doping, and then the conductivity and cycling stability of the capacitor carbon are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of activated carbon, and in particular to a method for surface modification of biomass supercapacitor activated carbon. Background Art

[0002] Activated carbon materials for biomass supercapacitors are usually prepared by activating and creating pores using biomass such as coconut shell charcoal as raw materials. In a high-temperature and water vapor, CO 2 , O 2 atmosphere environment, a large number of oxygen-containing groups and defect sites are formed on the surface of the activated carbon micropores, and relatively stable saturated bonds are formed on the surface of the activated carbon micropores, thereby reducing the conductivity of the activated carbon. For the organic supercapacitor based on this biomass activated carbon, when its working voltage exceeds 2.7V, the cycle performance significantly decreases, and the quality and performance consistency need to be improved.

[0003] Patent CN109592681B discloses a method for gradually purifying coconut shell-based supercapacitor carbon. Under a protective or reducing atmosphere, it is calcined at 300°C for 1-2 h to remove the passivating groups in the surface structure. Patent CN109850892B discloses a two-step activation industrial preparation method for high-conductivity coconut shell activated carbon for supercapacitors, including: 1) reacting in a CO 2 atmosphere at 600-800°C for 3-5 h to eliminate the passivating groups introduced by the activation step for the first time; 2) calcining at 300-350°C for 1-2 h under a reducing or protective atmosphere to remove the passivating groups introduced by the pickling step for the second time. However, methods such as reduction after pickling can achieve the effect of removing impurities and surface functional groups of capacitive carbon, but they will still bring surface defect problems of activated carbon and reduce the conductivity.

[0004] Patent CN116588932A discloses a preparation method of coconut shell capacitive carbon for supercapacitors, as well as coconut shell capacitive carbon and its application. The asphalt powder is mixed with the pickled porous carbon and then calcined. The surface functional groups caused by pickling are removed by high-temperature carbonization, and at the same time, taking advantage of the excellent fluidity of asphalt near the softening point, the porous carbon is coated to reduce the surface defects of the obtained coconut shell capacitive carbon. However, the infiltration effect of liquid asphalt is limited by the rich microporous structure (<2nm) and complex pore structure of activated carbon, and has the defect of unstable performance. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for surface modification of biomass supercapacitor activated carbon. By doping the activated carbon with a carbon-nitrogen source dopant and simultaneously performing hydrothermal carbonization, the surface functional groups of the biomass activated carbon are removed, carbon doping repairs the defect sites in its structure, and structural doping is achieved. Nitrogen doping can make the lattice distortion of the carbon material smaller, thereby improving the conductivity and cycle stability of the capacitive carbon.

[0006] The object of the present invention is achieved by the following technical solutions: The present invention provides a method for surface modification of biomass supercapacitor activated carbon, comprising the following steps: (1) Spraying an aqueous solution containing a carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon to achieve complete wetting, wherein the carbon and nitrogen source dopant is glucosamine; (2) Performing hydrothermal carbonization at 120 - 300 °C under an inert atmosphere, and then drying; thereafter, performing heat treatment at 400 - 500 °C under an inert atmosphere; (3) Performing an activation reaction in an atmosphere of CO 2 , water vapor or a mixture of CO 2 and water vapor.

[0007] In the present invention, the activated carbon is doped with a carbon and nitrogen source dopant. Since the carbon and nitrogen source dopant contains both a carbon source and a nitrogen source, it can achieve simultaneous carbon doping and nitrogen doping of the activated carbon. The doping of nitrogen atoms can result in a smaller lattice distortion of the carbon material, and it has particularly excellent performance in the fields of electrocatalysis and energy storage. Carbon doping can repair the defect sites on the surface of the activated carbon and improve the conductivity. At the same time, the carbon and nitrogen source dopant used in the present invention can improve the wettability of the aqueous solution containing the carbon and nitrogen source dopant in the hydrophobic microregions and pores on the surface of the activated carbon, making the dopant more dispersed in the activated carbon. Subsequently, hydrothermal carbonization helps to improve the penetration rate of the carbon source and nitrogen source in the structure of the activated carbon. During the carbonization process, more active groups such as carboxyl groups and hydroxyl groups can be generated on the surface of the activated carbon, and at the same time, unsaturated carbon-carbon bonds can be repaired to a cyclic structure; during the nitridation process, active groups such as amino groups and amines can be generated on the surface of the activated carbon, thereby achieving an increase in the abundance of active functional groups on the surface of the activated carbon after hydrothermal carbonization.

[0008] However, a large number of oxygen-containing groups on the microporous surface of the activated carbon can, to a certain extent, increase the charge-discharge voltage, but will reduce the cycle performance. Therefore, heat treatment under an inert atmosphere helps to remove the free groups (such as carboxyl groups and hydroxyl groups) introduced during hydrothermal carbonization, but the functional groups in the form of five-membered rings and six-membered rings are retained at high temperatures and achieve structural doping, ensuring the cycle stability of the capacitive carbon. Then, high-temperature activation treatment is carried out, which is beneficial to optimizing the pore size distribution, increasing mesopores and micropores, and helping to improve the electrochemical capacitance.

[0009] Preferably, the biomass supercapacitor activated carbon is obtained by pre-activating and pickling coconut shell carbonized material; the pre-activation is carried out by performing activation treatment in a CO 2 atmosphere at a temperature of 800 - 1000 °C for 4 - 8 h; the pickling is carried out using hydrochloric acid and cleaning at room temperature for 8 - 15 h.

[0010] Preferably, the mass concentration of the aqueous solution containing the carbon and nitrogen source dopant is 2-10%.

[0011] Preferably, the hydrothermal carbonization is as follows: maintaining at 120-300 °C under an inert atmosphere for 2-8 h.

[0012] Preferably, the heat treatment is as follows: maintaining at 400-500 °C under an inert atmosphere for 10-14 h.

[0013] Preferably, the drying is carried out by vacuum drying at 150-180 °C for 10-20 h; or, first by blowing air drying at 100-120 °C for 10-14 h, and then by vacuum drying at 150-180 °C for 10-14 h.

[0014] Preferably, the activation reaction is as follows: maintaining at 800-1000 °C for 1-5 h.

[0015] Preferably, the CO 2 and the volume ratio of CO 2 and water vapor in the water vapor mixture is 1-4:1.

[0016] Preferably, when the activation reaction is carried out under a mixed atmosphere of CO 2 and water vapor, maintain at 800-850 °C for 1-5 h, and then raise the temperature to 950-1000 °C and maintain for 1-5 h.

[0017] CO 2 has a high activation energy for the reaction with carbon and a low reaction rate, which is conducive to the formation of microporous structures; water vapor has a lower activation energy for the reaction with carbon and a fast reaction rate, which is conducive to the formation of mesopores and macropores. Through activation with the mixed gas, the pore size distribution can be further finely adjusted. By activating at 800-850 °C first, the water vapor reacts preferentially and is exhausted, completing the erosion of the activated carbon, and then raising the temperature to 950-1000 °C, CO 2 starts to activate, and more micropores can be generated to realize the regulation of the pore size.

[0018] Preferably, after the activation reaction, switch to an inert atmosphere and cool to room temperature.

[0019] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) By doping the activated carbon with a carbon and nitrogen source dopant, it is possible to introduce a carbon source and a nitrogen source simultaneously, simplifying the steps of modifying the activated carbon; moreover, the addition of the carbon and nitrogen source dopant helps to improve the wettability of the dopant aqueous solution in the hydrophobic region of the activated carbon, making it easier to wet the surface of the dry activated carbon particles and the inner pore surface, and making the dopant more dispersed in the activated carbon; (2) After doping with a carbon and nitrogen source dopant and then performing hydrothermal carbonization, the defective sites of the activated carbon are repaired, enabling structural doping on the surface of the activated carbon, mainly including five-membered rings and six-membered rings; (3) High-temperature heat treatment in an inert atmosphere helps remove free groups introduced during hydrothermal carbonization, including carboxyl groups, hydroxyl groups, amino groups, etc., ensuring the cycle stability of the capacitive carbon; (4) High-temperature activation treatment realizes carbonization and nitrogen doping on the one hand, and is beneficial for optimizing the pore size distribution of the activated carbon on the other hand, increasing mesopores and micropores, which helps improve the electrochemical capacity. Specific implementation mode

[0021] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0022] The surface modification method of the biomass supercapacitor activated carbon in the present invention includes the following steps: (1) The biomass supercapacitor activated carbon is dried at 120 - 160 °C in an inert atmosphere for 2 - 8 h, and then cooled to room temperature.

[0023] (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 2 - 10%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Keep the activated carbon with a completely wetted surface at 120 - 300 °C in an inert atmosphere for 2 - 8 h for hydrothermal carbonization; after carbonization, perform drying, first dry in a blast at 100 - 120 °C for 10 - 14 h, and then dry in vacuum at 150 - 180 °C for 10 - 14 h; (4) Heat-treat the dried activated carbon in an inert atmosphere, heat it from room temperature to 400 - 500 °C at a heating rate of 5 - 10 °C / min, and keep it at 400 - 500 °C for 10 - 14 h; (5) Activate the heat-treated activated carbon in an atmosphere of CO 2 , water vapor or a mixture of CO 2 and water vapor, heat it from room temperature to 800 - 1000 °C at a heating rate of 5 - 10 °C / min, and keep it at 800 - 1000 °C for 1 - 5 h; after the activation reaction is completed, switch to an inert atmosphere and cool to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0024] In a specific embodiment of the present invention, the biomass supercapacitor activated carbon is obtained by pre-activating and pickling coconut shell carbonized material, and specifically includes the following steps: Weigh 30 g of coconut shell carbonized material into a crucible, and place the crucible into a tube furnace. After evacuating the tube furnace with a vacuum pump, introduce nitrogen until normal pressure, and repeat this process 3 times. Then set the nitrogen flow rate to 60 mL / min, and heat up at a heating rate of 10 °C / min to the set temperature of 800 °C. After reaching the temperature set value, switch the nitrogen to carbon dioxide gas, and adjust the flow rate to the set value of 600 mL / min. Keep it at this temperature for 6 h in a carbon dioxide atmosphere, and then cool it to room temperature with the furnace. Take out the pre-activated activated carbon, place it in dilute hydrochloric acid with a mass concentration of 5% and wash for 12 h, and then rinse it multiple times with deionized water to obtain the biomass supercapacitor activated carbon.

[0025] In a specific embodiment of the present invention, CO 2 and the mixture of water vapor and CO 2 in the mixture of water vapor and CO have a volume ratio of 1 - 4:1.

[0026] In a specific embodiment of the present invention, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0027] Example 1 The surface modification method of the biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C in a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; Spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Keep the activated carbon with a completely wetted surface at 120 °C in a nitrogen atmosphere for 4 h for hydrothermal carbonization; After carbonization, conduct drying. First, dry it in a blast at 120 °C for 12 h, and then dry it in a vacuum at 150 °C for 12 h; (4) Under an inert atmosphere, heat the dried activated carbon from room temperature to 400 °C at a heating rate of 5 - 10 °C / min, and keep it at 400 °C for 12 h for heat treatment; (5) Conduct an activation reaction on the activated carbon obtained after heat treatment in a mixture of CO 2 and water vapor (the volume ratio of CO 2 and water vapor is 3:1). Heat it from room temperature to 800 °C at a heating rate of 5 °C / min, keep it at 800 °C for 1 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and keep it at this temperature for 4 h; After the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0028] Example 2 It is different from Example 1 in that: the volume ratio of the CO 2 and water vapor mixture is different, and the treatment conditions of the activation reaction are different.

[0029] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Keep the activated carbon with completely wetted surface at 120 °C under a nitrogen atmosphere for 4 h for hydrothermal carbonization; after carbonization, carry out drying, first dry it in a blast at 120 °C for 12 h, and then dry it under vacuum at 150 °C for 12 h; (4) Under an inert atmosphere, heat the dried activated carbon from room temperature to 400 °C at a heating rate of 5-10 °C / min, and keep it at 400 °C for 12 h for heat treatment; (5) The activated carbon obtained after heat treatment is in a mixed gas of CO 2 and water vapor (the volume ratio of CO 2 and water vapor is 1:1) atmosphere for activation reaction, heat it from room temperature to 800 °C at a heating rate of 5 °C / min, keep it at 800 °C for 2 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and keep it for 3 h; after the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0030] Example 3 It is different from Example 1 in that: use a CO 2 atmosphere for activation reaction, and the treatment conditions of the activation reaction are different.

[0031] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting to ensure that the surface of the activated carbon is completely immersed in the aqueous solution; (3) Keep the activated carbon with a completely wetted surface at 120 °C under a nitrogen atmosphere for 4 h for hydrothermal carbonization; after carbonization, conduct drying. First, dry it in a blast dryer at 120 °C for 12 h, and then dry it in a vacuum dryer at 150 °C for 12 h; (4) Under an inert atmosphere, heat the dried activated carbon from room temperature to 400 °C at a heating rate of 5 - 10 °C / min and keep it at 400 °C for 12 h for heat treatment; (5) Conduct an activation reaction on the activated carbon obtained after heat treatment in a CO 2 atmosphere. Heat it from room temperature to 1000 °C at a heating rate of 5 °C / min and keep it at 1000 °C for 5 h; after the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0032] Example 4 The difference from Example 1 is that a steam atmosphere is used for the activation reaction and the treatment conditions of the activation reaction are different.

[0033] The method for surface modification of biomass supercapacitor activated carbon includes the following steps: (1) Conduct a drying treatment on the biomass supercapacitor activated carbon. Dry it at 150 °C under a nitrogen atmosphere for 6 h and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting to ensure that the surface of the activated carbon is completely immersed in the aqueous solution; (3) Keep the activated carbon with a completely wetted surface at 120 °C under a nitrogen atmosphere for 4 h for hydrothermal carbonization; after carbonization, conduct drying. First, dry it in a blast dryer at 120 °C for 12 h, and then dry it in a vacuum dryer at 150 °C for 12 h; (4) Under an inert atmosphere, heat the dried activated carbon from room temperature to 400 °C at a heating rate of 5 - 10 °C / min and keep it at 400 °C for 12 h for heat treatment; (5) Conduct an activation reaction on the activated carbon obtained after heat treatment in a steam atmosphere. Heat it from room temperature to 800 °C at a heating rate of 5 °C / min and keep it at 800 °C for 5 h; after the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0034] Example 5 The difference from Example 1 lies in that the concentration of the aqueous solution containing the carbon and nitrogen source dopant and the hydrothermal carbonization conditions are different.

[0035] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 8%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Carry out hydrothermal carbonization on the activated carbon with a completely wetted surface at 200 °C under a nitrogen atmosphere for 3 h; after carbonization, carry out drying, first dry it by blowing air at 120 °C for 12 h, and then dry it under vacuum at 150 °C for 12 h; (4) Under an inert atmosphere, heat the dried activated carbon from room temperature to 400 °C at a heating rate of 5 - 10 °C / min, and keep it at 400 °C for 12 h for heat treatment; (5) Heat the activated carbon obtained after heat treatment in a mixed gas of CO 2 and water vapor (the volume ratio of CO 2 and water vapor is 3:1) for an activation reaction, heat it from room temperature to 800 °C at a heating rate of 5 °C / min, keep it at 800 °C for 1 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and keep it for 4 h; after the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0036] Comparative Example 1 The difference from Example 1 lies in that only carbon source doping is carried out using a carbon source dopant (glucose).

[0037] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon source dopant (glucose) to water to obtain an aqueous solution containing the carbon source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Hydrothermally carbonize the activated carbon after complete surface wetting at 120 °C under a nitrogen atmosphere for 4 h; after carbonization, conduct drying, first blow-dry at 120 °C for 12 h, and then vacuum-dry at 150 °C for 12 h; (4) Under an inert atmosphere, heat-treat the dried activated carbon by heating from room temperature to 400 °C at a heating rate of 5 - 10 °C / min and maintaining at 400 °C for 12 h; (5) For the activated carbon obtained after heat treatment, conduct an activation reaction in a mixed gas of CO 2 and water vapor (the volume ratio of CO 2 and water vapor is 3:1), heat from room temperature to 800 °C at a heating rate of 5 °C / min, maintain at 800 °C for 1 h, and then heat to 1000 °C at a heating rate of 5 °C / min and maintain for 4 h; after the activation reaction, switch to a nitrogen atmosphere and cool to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0038] Comparative Example 2 The difference from Example 1 is that only nitrogen source doping is carried out using a nitrogen source dopant (melamine).

[0039] The method for surface modification of biomass supercapacitor activated carbon includes the following steps: (1) Conduct drying treatment on the biomass supercapacitor activated carbon, dry at 150 °C under a nitrogen atmosphere for 6 h, and then cool to room temperature; (2) Add a nitrogen source dopant (melamine) to water to obtain an aqueous solution containing the nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely immersed in the aqueous solution; (3) Hydrothermally carbonize the activated carbon after complete surface wetting at 120 °C under a nitrogen atmosphere for 4 h; after carbonization, conduct drying, first blow-dry at 120 °C for 12 h, and then vacuum-dry at 150 °C for 12 h; (4) Under an inert atmosphere, heat-treat the dried activated carbon by heating from room temperature to 400 °C at a heating rate of 5 - 10 °C / min and maintaining at 400 °C for 12 h; (5) For the activated carbon obtained after heat treatment, conduct an activation reaction in a mixed gas of CO 2 and water vapor (the volume ratio of CO 2The activation reaction was carried out in an atmosphere of 3:1 (volume ratio of water vapor to water vapor), the temperature was raised from room temperature to 800°C at a heating rate of 5°C / min, maintained at 800°C for 1 hour, and then raised to 1000°C at a heating rate of 5°C / min and maintained for 4 hours; after the activation reaction, the atmosphere was switched to nitrogen and cooled to room temperature to obtain surface-modified activated carbon; (6) Grind the surface-modified activated carbon into the desired particle size.

[0040] Comparative Example 3 The difference from Example 1 is that ammonium citrate is used as the carbon and nitrogen source dopant.

[0041] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon at 150°C in a nitrogen atmosphere for 6 hours, and then cool it to room temperature; (2) adding a carbon-nitrogen source dopant (ammonium citrate) into water to obtain an aqueous solution containing the carbon-nitrogen source dopant at a mass concentration of 5%; spraying the aqueous solution containing the carbon-nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieving complete infiltration, ensuring that the surface of the activated carbon is completely immersed in the aqueous solution; (3) The activated carbon with completely wetted surface is kept at 120°C in a nitrogen atmosphere for 4 hours for hydrothermal carbonization; after carbonization, it is dried, first at 120°C for 12 hours, and then at 150°C for 12 hours in vacuum; (4) The activated carbon obtained after drying is heated from room temperature to 400°C at a heating rate of 5-10°C / min under an inert atmosphere, and maintained at 400°C for 12 hours for heat treatment; (5) The activated carbon obtained after heat treatment is heated to 2 and water vapor mixture (CO 2 The activation reaction was carried out in an atmosphere of 3:1 (volume ratio of water vapor to water vapor), the temperature was raised from room temperature to 800°C at a heating rate of 5°C / min, maintained at 800°C for 1 hour, and then raised to 1000°C at a heating rate of 5°C / min and maintained for 4 hours; after the activation reaction, the atmosphere was switched to nitrogen and cooled to room temperature to obtain surface-modified activated carbon; (6) Grind the surface-modified activated carbon into the desired particle size.

[0042] Comparative Example 4 The difference from Example 1 is that in step (3), drying is performed first and then carbonization is performed.

[0043] The surface modification method of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon at 150°C in a nitrogen atmosphere for 6 hours, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Dry the activated carbon with a completely wetted surface. First, dry it in a forced-air oven at 120 °C for 12 h, and then dry it in a vacuum oven at 150 °C for 12 h; after drying, keep it at 120 °C under a nitrogen atmosphere for 4 h for carbonization; (4) Under an inert atmosphere, heat the activated carbon obtained after carbonization from room temperature to 400 °C at a heating rate of 5 - 10 °C / min, and keep it at 400 °C for 12 h for heat treatment; (5) The activated carbon obtained after heat treatment is placed in a mixed gas of CO 2 and water vapor (the volume ratio of CO 2 and water vapor is 3:1) and carry out an activation reaction. Heat it from room temperature to 800 °C at a heating rate of 5 °C / min, keep it at 800 °C for 1 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and keep it for 4 h; after the activation reaction, switch to a nitrogen atmosphere and cool it to room temperature to obtain the surface-modified activated carbon; (6) Crush the surface-modified activated carbon to the required particle size.

[0044] Comparative Example 5 The difference from Example 1 is that the heat treatment under an inert atmosphere in step (4) is not carried out.

[0045] The method for surface modification of biomass supercapacitor activated carbon includes the following steps: (1) Dry the biomass supercapacitor activated carbon. Dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool it to room temperature; (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%; spray the aqueous solution containing the carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon and achieve complete wetting, ensuring that the surface of the activated carbon is completely soaked in the aqueous solution; (3) Keep the activated carbon with a completely wetted surface at 120 °C under a nitrogen atmosphere for 4 h for hydrothermal carbonization; after carbonization, carry out drying. First, dry it in a forced-air oven at 120 °C for 12 h, and then dry it in a vacuum oven at 150 °C for 12 h; (4) The dried activated carbon is placed in a mixed gas of CO 2 and water vapor (CO 2The activation reaction is carried out in an atmosphere with a volume ratio of 3:1 of [substance] and water vapor. It is heated from room temperature to 800 °C at a heating rate of 5 °C / min, held at 800 °C for 1 h, and then heated to 1000 °C at a heating rate of 5 °C / min and held for 4 h. After the activation reaction, it is switched to a nitrogen atmosphere and cooled to room temperature to obtain the surface-modified activated carbon. (5)Crush the surface-modified activated carbon to the required particle size.

[0046] The surface-modified activated carbon (particle size D50 < 10 μm) obtained in Examples 1-5 and Comparative Examples 1-5 is used for a symmetric supercapacitor (button cell), and its preparation process is as follows: 1) Prepare the slurry: Weigh 0.4 g of the surface-modified activated carbon, 0.05 g of conductive carbon black, and 2.25 g of polyvinylidene fluoride (PVDF) glue (solid content 4%) respectively using an analytical balance. The mass ratio is 8:1:1, and a uniform electrode slurry is obtained by stirring with a degassing machine.

[0047] 2) Coating the electrode: Lay the aluminum foil flat on a glass plate, and use a four-sided coater (height 100 μm) to uniformly coat the slurry on the surface of the aluminum foil.

[0048] 3) Drying the electrode: Place the aluminum foil coated with the slurry and the glass plate in a blast drying oven at 80 °C for 1 h, and then transfer it to a vacuum drying oven at 120 °C for 12 h.

[0049] 4) Cutting the electrode: Use a slicing machine to cut the dried electrode into circular pieces (φ = 12 mm), weigh them, and place them in a glove box for later use.

[0050] 5) In the glove box, stack the positive electrode case, activated carbon positive electrode, separator, activated carbon negative electrode, gasket, shrapnel, and negative electrode case in sequence, use TEABF4 / ACN as the electrolyte, and seal it with a battery encapsulation machine.

[0051] Table 1

[0052] Note: The number of cycles is the number of cycles when the capacity remains 80% or more of the original capacity under the condition of 3.0 V.

[0053] As shown in Table 1, in Examples 1-4, different atmospheres were used for activation treatment. Compared with a single CO 2 atmosphere or water vapor atmosphere, the treatment effect is better when carrying out the activation treatment in a mixed atmosphere of CO 2 and water vapor, and the obtained activated carbon has lower ohmic impedance and higher specific capacitance. Generally speaking, however, the electrochemical capacity and cycle stability of the activated carbon in Examples 1-5 are higher than those in Comparative Examples 1-5.

[0054] Specifically, Comparative Example 1 involves single carbonization using a carbon source dopant, and Comparative Example 2 involves single nitridation using a nitrogen source dopant. Compared with Examples 1-5, the specific capacitance and cycling performance of the activated carbon obtained in Comparative Examples 1-2 are both poor. At the same time, in Comparative Example 3, ammonium citrate is used to replace glucosamine as the carbon and nitrogen source dopant. Although ammonium citrate also contains a carbon source and a nitrogen source, the ohmic impedance of the obtained activated carbon increases significantly and the number of cycles decreases significantly, indicating that the carbon and nitrogen source dopant used in the present invention can achieve a better carbon and nitrogen co-doping effect and can realize the structural doping of five-membered rings and six-membered rings, ensuring the cycling stability of the capacitive carbon.

[0055] In Comparative Example 4, carbonization is carried out after drying. When the obtained activated carbon is used in a capacitor, its ohmic impedance increases significantly, and the specific capacitance and cycling performance decrease, indicating that the hydrothermal carbonization in the present invention helps to improve the penetration rate of the carbon source and nitrogen source in the structure of the activated carbon, thereby improving the electrochemical capacity.

[0056] In Comparative Example 5, the heat treatment process in an inert atmosphere is not carried out after hydrothermal carbonization. Since the surface functional group abundance of the activated carbon after hydrothermal carbonization increases, the cycling performance of the activated carbon obtained in Comparative Example 5 decreases. However, the heat treatment in an inert atmosphere helps to remove the free groups (such as carboxyl groups, hydroxyl groups, etc.) introduced in hydrothermal carbonization, but the functional groups in the form of five-membered rings and six-membered rings are retained at high temperatures and achieve structural doping, ensuring the cycling stability of the capacitive carbon.

[0057] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A surface modification method for biomass supercapacitor activated carbon, characterized in that: The steps include: (1) spraying an aqueous solution containing a carbon and nitrogen source dopant onto the surface of the biomass supercapacitor activated carbon to achieve complete infiltration, wherein the carbon and nitrogen source dopant is glucosamine; (2) Hydrothermal carbonization at 120-300°C in an inert atmosphere, followed by drying; followed by heat treatment at 400-500°C in an inert atmosphere; (3) The activation reaction is carried out in an atmosphere of CO2, water vapor or a mixture of CO2 and water vapor.

2. The surface modification method of biomass supercapacitor activated carbon according to claim 1, characterized in that: The mass concentration of the aqueous solution containing the carbon and nitrogen source dopant is 2-10%.

3. The surface modification method of biomass supercapacitor activated carbon according to claim 1 or 2, characterized in that: The biomass supercapacitor activated carbon is obtained by pre-activating and acid-washing coconut shell carbonized material.

4. The surface modification method of biomass supercapacitor activated carbon according to claim 1, characterized in that: The hydrothermal carbonization is carried out at 120-300° C. and in an inert atmosphere for 2-8 hours.

5. The surface modification method of biomass supercapacitor activated carbon according to claim 1, characterized in that: The heat treatment is: maintaining at 400-500° C. in an inert atmosphere for 10-14 hours.

6. The surface modification method of biomass supercapacitor activated carbon according to claim 1, 4 or 5, characterized in that: The drying is vacuum drying at 150-180°C.

7. The surface modification method of biomass supercapacitor activated carbon according to claim 1, characterized in that: The activation reaction is: maintaining at 800-1000° C. for 1-5 hours.

8. The surface modification method of biomass supercapacitor activated carbon according to claim 1 or 7, characterized in that: The volume ratio of CO2 to water vapor in the mixed gas of CO2 and water vapor is 1-4:

1.

9. The surface modification method of biomass supercapacitor activated carbon according to claim 1, characterized in that: After the activation reaction, the atmosphere was switched to an inert atmosphere and the mixture was cooled to room temperature.

10. The surface modification method of biomass supercapacitor activated carbon according to claim 1 or 9, characterized in that: The inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

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