A method for surface modification of biomass supercapacitor activated carbon

Abstract

The present invention relates to the technical field of activated carbon, and discloses a surface modification method for 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 under an atmosphere of CO2, water vapor, or a mixture of CO2 and water vapor. By doping the activated carbon with a carbon and 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 cause less lattice distortion of the carbon material, thereby improving the conductivity and cycle stability of the capacitive carbon.

Description

Technical Field

[0001] The present invention relates to the technical field of activated carbon, and particularly 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. In a high-temperature environment with water vapor, CO2, and O2 atmospheres, a large number of oxygen-containing groups and defect sites are formed on the microporous surface of the activated carbon, and relatively stable saturated bonds are formed on the microporous surface of the activated carbon, thereby reducing the conductivity of the activated carbon. For organic supercapacitors based on this biomass activated carbon, when the working voltage exceeds 2.7V, the cycle performance significantly deteriorates, 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 at 600 - 800°C for 3 - 5 h in a CO2 atmosphere to first eliminate the passivating groups introduced by the activation step; 2) calcining at 300 - 350°C for 1 - 2 h in a reducing or protective atmosphere to secondarily remove the passivating groups introduced by the pickling step. However, methods such as reduction after pickling can achieve the effect of removing impurities and surface functional groups of the capacitor carbon, but they still bring surface defect problems of the activated carbon and reduce the conductivity.

[0004] Patent CN116588932A discloses a preparation method of coconut shell capacitor carbon for supercapacitors, as well as coconut shell capacitor carbon and its application. Asphalt powder is mixed with pickled porous carbon and then calcined. High-temperature carbonization is used to remove the surface functional groups caused by pickling, 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 capacitor carbon. However, the infiltration effect of liquid asphalt is limited by the rich microporous structure (<2nm) and complex pore structure of the activated carbon, and it 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 and 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 cause less lattice distortion of the carbon material, thereby improving the conductivity and cycle stability of the capacitor carbon.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] The present invention provides a method for surface modification of biomass supercapacitor activated carbon, comprising the following steps:

[0008] (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;

[0009] (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;

[0010] (3) Performing an activation reaction under an atmosphere of CO2, water vapor, or a mixture of CO2 and water vapor.

[0011] 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 simultaneously achieve carbon doping and nitrogen doping of the activated carbon. The doping of nitrogen atoms can result in less lattice distortion of the carbon material, showing 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 enhance 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.

[0012] 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, hydroxyl groups, etc.) 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. Subsequently, high-temperature activation treatment is beneficial to optimizing the pore size distribution, increasing mesopores and micropores, and helping to improve the electrochemical capacitance.

[0013] 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 under a CO2 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.

[0014] Preferably, the mass concentration of the aqueous solution containing the carbon and nitrogen source dopant is 2-10%.

[0015] Preferably, the hydrothermal carbonization is carried out at 120-300 °C in an inert atmosphere for 2-8 h.

[0016] Preferably, the heat treatment is carried out at 400-500 °C in an inert atmosphere for 10-14 h.

[0017] 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.

[0018] Preferably, the activation reaction is carried out at 800-1000 °C for 1-5 h.

[0019] Preferably, in the mixed gas of CO2 and water vapor, the volume ratio of CO2 to water vapor is 1-4:1.

[0020] Preferably, when the activation reaction is carried out in a mixed atmosphere of CO2 and water vapor, it is maintained at 800-850 °C for 1-5 h, and then heated to 950-1000 °C and maintained for 1-5 h.

[0021] The activation energy of the reaction between CO2 and carbon is high and the reaction rate is low, which is conducive to the formation of microporous structures; the activation energy of the reaction between water vapor and carbon is low and the reaction rate is fast, which is conducive to the formation of mesopores and macropores. By activating with a 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 heating to 950-1000 °C, CO2 starts to activate, and more micropores can be generated to realize the regulation of the pore size.

[0022] Preferably, after the activation reaction, it is switched to an inert atmosphere and cooled to room temperature.

[0023] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) By doping the activated carbon with a carbon and nitrogen source dopant, a carbon source and a nitrogen source can be introduced 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 surface of the internal pores, and making the dopant more dispersed in the activated carbon;

[0026] (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;

[0027] (3) High-temperature heat treatment in an inert atmosphere helps to remove free groups introduced during hydrothermal carbonization, including carboxyl groups, hydroxyl groups, amino groups, etc., ensuring the cycle stability of the capacitive carbon;

[0028] (4) High-temperature activation treatment realizes carbonization and nitrogen doping on the one hand, and on the other hand, is beneficial to optimizing the pore size distribution of the activated carbon for the secondary activity, increasing mesopores and micropores, which helps to improve the electrochemical capacity. Specific Embodiments

[0029] 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.

[0030] The surface modification method of the biomass supercapacitor activated carbon in the present invention includes the following steps:

[0031] (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.

[0032] (2) The carbon and nitrogen source dopant (glucosamine) is added to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 2 - 10%; the aqueous solution containing the carbon and nitrogen source dopant is sprayed onto the surface of the biomass supercapacitor activated carbon and completely infiltrated to ensure that the surface of the activated carbon is completely wetted in the aqueous solution;

[0033] (3) The activated carbon with a completely wetted surface is kept at 120 - 300 °C in an inert atmosphere for 2 - 8 h for hydrothermal carbonization; after carbonization, it is dried. First, it is dried in a blast at 100 - 120 °C for 10 - 14 h, and then dried in vacuo at 150 - 180 °C for 10 - 14 h;

[0034] (4) The dried activated carbon is heated from room temperature to 400 - 500 °C at a heating rate of 5 - 10 °C / min in an inert atmosphere and kept at 400 - 500 °C for 10 - 14 h for heat treatment;

[0035] (5) The heat-treated activated carbon is subjected to an activation reaction in an atmosphere of CO2, water vapor, or a mixture of CO2 and water vapor. It is heated from room temperature to 800 - 1000 °C at a heating rate of 5 - 10 °C / min and kept at 800 - 1000 °C for 1 - 5 h; after the activation reaction is completed, it is switched to an inert atmosphere and cooled to room temperature to obtain the surface-modified activated carbon;

[0036] (6) The surface-modified activated carbon is crushed to the required particle size.

[0037] 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 tubular furnace. After evacuating the tubular furnace with a vacuum pump, introduce nitrogen until normal pressure, and repeat 3 times. Then set the nitrogen flow rate to 60 mL / min, and increase the temperature at a 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 warm 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.

[0038] In a specific embodiment of the present invention, the volume ratio of CO2 to water vapor in the mixture of CO2 and water vapor is 1 - 4:1.

[0039] In a specific embodiment of the present invention, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0040] Example 1

[0041] The surface modification method of the biomass supercapacitor activated carbon includes the following steps:

[0042] (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;

[0043] (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;

[0044] (3) Keep the activated carbon with a completely wetted surface at 120 °C in a nitrogen atmosphere for 4 h for hydrothermal carbonization; After the carbonization is completed, carry out 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;

[0045] (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;

[0046] (5) Activate the heat-treated activated carbon in an atmosphere of a mixed gas of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1). Heat it from room temperature to 800 °C at a heating rate of 5 °C / min, hold it at 800 °C for 1 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and hold 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.

[0047] (6) Crush the surface-modified activated carbon to the required particle size.

[0048] Example 2

[0049] The difference from Example 1 lies in the different volume ratio of the CO2 and water vapor mixed gas and the different treatment conditions of the activation reaction.

[0050] The surface modification method of the biomass supercapacitor activated carbon includes the following steps:

[0051] (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.

[0052] (2) Add the carbon and nitrogen source dopant (glucosamine) to water to obtain an aqueous solution of the carbon and nitrogen source dopant with a mass concentration of 5%. Spray the aqueous solution of 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 soaked in the aqueous solution.

[0053] (3) Keep the activated carbon with a completely wetted surface at 120 °C in a nitrogen atmosphere for 4 h for hydrothermal carbonization. After the carbonization is completed, dry it. 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.

[0054] (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 hold it at 400 °C for 12 h for heat treatment.

[0055] (5) Activate the heat-treated activated carbon in an atmosphere of a mixed gas of CO2 and water vapor (the volume ratio of CO2 to water vapor is 1:1). Heat it from room temperature to 800 °C at a heating rate of 5 °C / min, hold it at 800 °C for 2 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and hold 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.

[0056] (6) Crush the surface-modified activated carbon to the required particle size.

[0057] Example 3

[0058] The difference from Example 1 lies in that an activation reaction is carried out in a CO2 atmosphere and the treatment conditions of the activation reaction are different.

[0059] The surface modification method of biomass supercapacitor activated carbon includes the following steps:

[0060] (1) Dry the biomass supercapacitor activated carbon at 150 °C in a nitrogen atmosphere for 6 h, and then cool it to room temperature;

[0061] (2) Add a 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;

[0062] (3) Hydrothermally carbonize the activated carbon with a completely wetted surface at 120 °C in a nitrogen atmosphere for 4 h; after carbonization, conduct drying, first dry it in a blast at 120 °C for 12 h, and then dry it in vacuo at 150 °C for 12 h;

[0063] (4) Heat-treat the dried activated carbon in an inert atmosphere, heat it from room temperature to 400 °C at a heating rate of 5-10 °C / min, and hold it at 400 °C for 12 h;

[0064] (5) Carry out an activation reaction on the heat-treated activated carbon in a CO2 atmosphere, heat it from room temperature to 1000 °C at a heating rate of 5 °C / min, and hold 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;

[0065] (6) Crush the surface-modified activated carbon to the required particle size.

[0066] Example 4

[0067] The difference from Example 1 lies in that an activation reaction is carried out in a steam atmosphere and the treatment conditions of the activation reaction are different.

[0068] The surface modification method of biomass supercapacitor activated carbon includes the following steps:

[0069] (1) Dry the biomass supercapacitor activated carbon at 150 °C in a nitrogen atmosphere for 6 h, and then cool it to room temperature;

[0070] (2) Add a 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;

[0071] (3) Hydrothermally carbonize the activated carbon after complete surface wetting at 120 °C under a nitrogen atmosphere for 4 h; after carbonization, carry out drying, first dry in a blast dryer at 120 °C for 12 h, and then dry in a vacuum dryer at 150 °C for 12 h;

[0072] (4) Heat-treat the dried activated carbon under an inert atmosphere, raise the temperature from room temperature to 400 °C at a heating rate of 5 - 10 °C / min, and hold at 400 °C for 12 h;

[0073] (5) Carry out an activation reaction on the heat-treated activated carbon under a steam atmosphere, raise the temperature from room temperature to 800 °C at a heating rate of 5 °C / min, and hold at 800 °C for 5 h; after the activation reaction, switch to a nitrogen atmosphere and cool to room temperature to obtain the surface-modified activated carbon;

[0074] (6) Crush the surface-modified activated carbon to the required particle size.

[0075] Example 5

[0076] The difference from Example 1 lies in: the concentration of the aqueous solution containing the carbon and nitrogen source dopant and the hydrothermal carbonization conditions are different.

[0077] The surface modification method of the biomass supercapacitor activated carbon includes the following steps:

[0078] (1) Dry the biomass supercapacitor activated carbon, dry it at 150 °C under a nitrogen atmosphere for 6 h, and then cool to room temperature;

[0079] (2) Add a 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;

[0080] (3) Hydrothermally carbonize the activated carbon after complete surface wetting at 200 °C under a nitrogen atmosphere for 3 h; after carbonization, carry out drying, first dry in a blast dryer at 120 °C for 12 h, and then dry in a vacuum dryer at 150 °C for 12 h;

[0081] (4) Heat-treat the dried activated carbon under an inert atmosphere, raise the temperature from room temperature to 400 °C at a heating rate of 5 - 10 °C / min, and hold at 400 °C for 12 h;

[0082] (5) The activated carbon obtained after heat treatment is subjected to an activation reaction in an atmosphere of a mixed gas of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1). 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 surface-modified activated carbon.

[0083] (6) The surface-modified activated carbon is crushed to the required particle size.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that only carbon source doping is carried out using a carbon source dopant (glucose).

[0086] The method for surface modification of biomass supercapacitor activated carbon includes the following steps:

[0087] (1) The biomass supercapacitor activated carbon is dried at 150 °C in a nitrogen atmosphere for 6 h and then cooled to room temperature.

[0088] (2) The carbon source dopant (glucose) is added to water to obtain an aqueous solution containing the carbon source dopant with a mass concentration of 5%. The aqueous solution containing the carbon source dopant is sprayed onto the surface of the biomass supercapacitor activated carbon and completely infiltrated to ensure that the surface of the activated carbon is completely wetted in the aqueous solution.

[0089] (3) The activated carbon with a completely wetted surface is hydrothermally carbonized at 120 °C in a nitrogen atmosphere for 4 h. After carbonization, it is dried. First, it is dried in a blast at 120 °C for 12 h, and then dried in a vacuum at 150 °C for 12 h.

[0090] (4) The dried activated carbon is heated from room temperature to 400 °C at a heating rate of 5 - 10 °C / min in an inert atmosphere and held at 400 °C for 12 h for heat treatment.

[0091] (5) The activated carbon obtained after heat treatment is subjected to an activation reaction in an atmosphere of a mixed gas of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1). 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 surface-modified activated carbon.

[0092] (6) The surface-modified activated carbon is crushed to the required particle size.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that only nitrogen source doping is carried out using a nitrogen source dopant (melamine).

[0095] The surface modification method of the biomass supercapacitor activated carbon includes the following steps:

[0096] (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;

[0097] (2) Add the 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;

[0098] (3) Hydrothermally carbonize the activated carbon with a completely wetted surface at 120 °C under a nitrogen atmosphere for 4 h; after carbonization, carry out drying, first dry it at 120 °C with forced air for 12 h, and then dry it under vacuum at 150 °C for 12 h;

[0099] (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 hold it at 400 °C for 12 h for heat treatment;

[0100] (5) Carry out an activation reaction on the heat-treated activated carbon under an atmosphere of a mixture of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1), heat it from room temperature to 800 °C at a heating rate of 5 °C / min, hold it at 800 °C for 1 h, and then heat it to 1000 °C at a heating rate of 5 °C / min and hold 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;

[0101] (6) Crush the surface-modified activated carbon to the required particle size.

[0102] Comparative Example 3

[0103] The difference from Example 1 is that ammonium citrate is used as the carbon and nitrogen source dopant.

[0104] The surface modification method of the biomass supercapacitor activated carbon includes the following steps:

[0105] (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;

[0106] (2) Add the carbon and nitrogen source dopant (ammonium citrate) 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;

[0107] (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 in a blast at 120 °C for 12 h, and then dry in vacuo at 150 °C for 12 h;

[0108] (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;

[0109] (5) Conduct an activation reaction on the heat-treated activated carbon under an atmosphere of a mixture of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1), heat 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 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 to room temperature to obtain the surface-modified activated carbon;

[0110] (6) Crush the surface-modified activated carbon to the required particle size.

[0111] Comparative Example 4

[0112] The difference from Example 1 is that in step (3), drying is carried out first and then carbonization.

[0113] The method for surface modification of biomass supercapacitor activated carbon includes the following steps:

[0114] (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 to room temperature;

[0115] (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;

[0116] (3) Dry the activated carbon with a completely wetted surface, first dry in a blast at 120 °C for 12 h, and then dry in vacuo at 150 °C for 12 h; after drying, keep it at 120 °C under a nitrogen atmosphere for 4 h for carbonization;

[0117] (4) The activated carbon obtained after carbonization is heated from room temperature to 400 °C at a heating rate of 5 - 10 °C / min under an inert atmosphere and held at 400 °C for 12 h for heat treatment;

[0118] (5) The activated carbon obtained after heat treatment is subjected to an activation reaction under an atmosphere of a mixture of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1). 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, the atmosphere is switched to a nitrogen atmosphere and cooled to room temperature to obtain the surface-modified activated carbon;

[0119] (6) The surface-modified activated carbon is crushed to the required particle size.

[0120] Comparative Example 5

[0121] The difference from Example 1 is that the heat treatment under an inert atmosphere in step (4) is not carried out.

[0122] The method for surface modification of biomass supercapacitor activated carbon includes the following steps:

[0123] (1) The biomass supercapacitor activated carbon is dried at 150 °C under a nitrogen atmosphere for 6 h and then cooled to room temperature;

[0124] (2) The carbon and nitrogen source dopant (glucosamine) is added to water to obtain an aqueous solution containing the carbon and nitrogen source dopant with a mass concentration of 5%. The aqueous solution containing the carbon and nitrogen source dopant is sprayed onto the surface of the biomass supercapacitor activated carbon and completely infiltrated to ensure that the surface of the activated carbon is completely wetted in the aqueous solution;

[0125] (3) The activated carbon with a completely wetted surface is hydrothermally carbonized at 120 °C under a nitrogen atmosphere for 4 h. After carbonization, it is dried. First, it is dried in a blast at 120 °C for 12 h, and then dried in a vacuum at 150 °C for 12 h;

[0126] (4) The dried activated carbon is subjected to an activation reaction under an atmosphere of a mixture of CO2 and water vapor (the volume ratio of CO2 to water vapor is 3:1). 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, the atmosphere is switched to a nitrogen atmosphere and cooled to room temperature to obtain the surface-modified activated carbon;

[0127] (5) The surface-modified activated carbon is crushed to the required particle size.

[0128] The surface-modified activated carbon (particle size D50 < 10 μm) obtained in Examples 1-5 and Comparative Examples 1-5 was used in a symmetric supercapacitor (button cell), and its preparation process is as follows:

[0129] 1) Prepare the slurry: Weigh 0.4 g of surface-modified activated carbon, 0.05 g of conductive carbon black, and 2.25 g of polyvinylidene fluoride (PVDF) glue (solid content 4%) using an analytical balance, with a mass ratio of 8:1:1. Stir with a degassing machine to obtain a uniform electrode slurry.

[0130] 2) Coating the electrode: Lay the aluminum foil flat on a glass plate, and use a four-sided coater (height 100 μm) to evenly coat the slurry on the surface of the aluminum foil.

[0131] 3) Drying the electrode: Place the aluminum foil coated with the slurry and the glass plate in a blast oven at 80 °C for 1 h, and then transfer to a vacuum oven at 120 °C for 12 h.

[0132] 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.

[0133] 5) In the glove box, stack the positive electrode case, activated carbon positive electrode, separator, activated carbon negative electrode, gasket, spring piece, and negative electrode case in sequence, use TEABF4 / ACN as the electrolyte, and seal with a battery encapsulation machine.

[0134] Table 1

[0135]

[0136] 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.

[0137] As shown in Table 1, in Examples 1-4, different atmospheres were used for activation treatment. Compared with a single CO2 atmosphere or steam atmosphere, the treatment effect was better when activated in a mixed atmosphere of CO2 and steam, and the obtained activated carbon had lower ohmic impedance and higher specific capacitance. However, generally speaking, the electrochemical capacity and cycle stability of the activated carbon in Examples 1-5 were higher than those in Comparative Examples 1-5.

[0138] 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 carbons 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-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.

[0139] 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 its 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.

[0140] In Comparative Example 5, there is no heat treatment process in an inert atmosphere 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 introduced in hydrothermal carbonization (such as carboxyl groups, hydroxyl groups, etc.), but the functional groups in the form of five-membered rings and six-membered rings are retained at high temperatures and structural doping is achieved, ensuring the cycling stability of the capacitive carbon.

[0141] 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 structural 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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