Preparation method of coal-based activated carbon with high specific capacitance

Abstract

The invention provides a preparation method of coal-based activated carbon with high specific capacitance, which belongs to the technical field of carbon materials and comprises the following steps: uniformly mixing raw coal and monopotassium phosphate according to a mass ratio of 1: (2-3), pre-carbonizing at 350-450 DEG C in a muffle furnace in a nitrogen atmosphere, calcining at 750-850 DEG C for 1-2 hours, cooling and washing to be neutral to obtain the coal-based activated carbon with high specific capacitance. The high-specific-capacitance coal-based activated carbon is obtained. The coal-based activated carbon prepared by the invention has the advantages of simple preparation method and high specific capacitance.

Description

Technical Field

[0001] The invention relates to the technical field of carbon materials, and in particular to a method for preparing high specific capacitance coal-based activated carbon. Background Art

[0002] Supercapacitor is a new type of energy storage device between conventional capacitors and secondary batteries, and has the advantages of high power density of conventional capacitors and high energy density of secondary batteries. Activated carbon has the advantages of high specific surface area, good chemical stability, high porosity and adjustable size, high conductivity, good electrolyte wettability, and wide potential window, making it an ideal supercapacitor electrode material.

[0003] The preparation process of coal-based activated carbon mainly includes the steps of grinding, molding, carbonization, activation, etc. Activation is the process of forming most of the pore structure of activated carbon, which is the core process in the production of activated carbon. It can be carried out by physical activation (such as steam activation or carbon dioxide activation) and chemical activation (such as acid activation, alkali activation and oxidation activation). These activation methods have high requirements on equipment, or usually activation and doping need to be carried out separately (for example, CN 109195907A, CN113903598A), and the preparation process is complicated.

[0004] Therefore, it is necessary to develop a preparation method for high specific capacitance coal-based activated carbon. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a high specific capacitance coal-based activated carbon, using potassium dihydrogen phosphate as an activator and a dopant, and preparing a coal-based activated carbon with a high specific capacitance by adjusting the process.

[0006] The technical solution of the present invention is achieved in this way: The present invention provides a method for extracting and preparing ultra-low ash coal using coal as raw material, comprising the following steps: The raw coal and potassium dihydrogen phosphate are mixed evenly in a mass ratio of 1:2-3, placed in a muffle furnace, pre-carbonized at 350-450°C under a nitrogen atmosphere, calcined at 750-850°C for 1-2h, cooled and washed to neutrality to obtain high specific capacitance coal-based activated carbon.

[0007] As a further improvement of the present invention, the heating rate of the pre-carbonization is 4-6°C / min.

[0008] As a further improvement of the present invention, the pre-carbonization temperature is 400°C.

[0009] As a further improvement of the present invention, the pre-carbonization time is 0.5-1.5h.

[0010] As a further improvement of the present invention, the heating rate of the calcination is 6-8°C / min.

[0011] As a further improvement of the present invention, the specific capacitance of the high specific capacitance activated carbon is 260-316 F / g.

[0012] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, potassium dihydrogen phosphate is selected as an activator, which is further decomposed at high temperature to generate metal K and heteroatoms P / O. Metal K atoms can effectively enrich the pore structure, and P / O heteroatoms can promote the formation of functional groups, doping and modifying the activated carbon, enhancing the surface wettability and conductivity of the carbon material, and significantly improving the specific capacitance of the coal-based activated carbon. Different from the strong base activator, the activator belongs to a green and environmentally friendly fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 This is the CV test chart of the coal-based activated carbon prepared in Example 3 of the present invention.

[0015] Figure 2 This is a cycle life cycle test chart of the coal-based activated carbon prepared in Example 3 of the present invention.

[0016] Figure 3 It is the GCD test chart of the coal-based activated carbon prepared in Examples 1-3 of the present invention and Comparative Examples 1-4.

[0017] Figure 4 XRD spectra of coal-based activated carbons prepared in Examples 1-3 and Comparative Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Test conditions: The sample was mixed with PTFE and carbon black in a weight ratio of 8:1:1 to prepare an active material mixture (with anhydrous ethanol as a dispersant). Then, the mixture (about 1 mg) was pressed onto 1×2.5 cm nickel foam (collector) using a tablet press to prepare a working electrode. The measurement process adopted a three-electrode system with 6M KOH aqueous electrolyte. The measurement process included cyclic voltammetry (CV), constant current charge and discharge (GCD), and cycle life test. CV and GCD were used to calculate the specific capacitance of the electrode material.

[0020] The specific surface area of ​​the samples was tested using a Micromeritics ASAP 2460 multi-station fully automatic specific surface area and pore size analyzer.

[0021] In the present invention, the element analysis of the raw coal used is shown in Table 1: Table 1

[0022] The invention is further described below through specific examples.

[0023] Example 1

[0024] After 3g of raw coal and 6g of potassium dihydrogen phosphate were mixed evenly, they were placed in a square crucible boat, a little nitrogen was introduced and sealed. Then they were placed in a muffle furnace, heated to 400℃ at a heating rate of 5℃ / min and kept warm for 1h, then heated to 750℃ at a heating rate of 7℃ / min and kept warm for 1h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.46g of doped modified activated carbon with a specific capacitance of 261.21F / g.

[0025] Example 2

[0026] After mixing 3g of raw coal and 6g of potassium dihydrogen phosphate evenly, put them into a square crucible boat, pass a little nitrogen gas and seal it. Then put it into a muffle furnace, heat it to 400℃ at a heating rate of 5℃ / min and keep it warm for 1h, then heat it to 750℃ at a heating rate of 7℃ / min and keep it warm for 2h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.46g of doped modified activated carbon with a specific capacitance of 316.3F / g, such as Figure 2 As shown, the capacitance retention rate is as high as 97.73% after 6000 cycles at 10 A / g.

[0027] Example 3

[0028] After 3g of raw coal and 9g of potassium dihydrogen phosphate were mixed evenly, they were placed in a square crucible boat, a little nitrogen was introduced and the crucible was sealed. Then it was placed in a muffle furnace, heated to 400℃ at a heating rate of 4℃ / min and kept warm for 1h, then heated to 800℃ at a heating rate of 7℃ / min and kept warm for 1h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.61g of doped modified activated carbon with a specific capacitance of 301.2F / g.

[0029] Comparative Example 1 After 3g of raw coal and 3g of potassium dihydrogen phosphate were mixed evenly, they were placed in a square crucible boat, a little nitrogen was introduced and sealed. Then they were placed in a muffle furnace, heated to 400℃ at a heating rate of 5℃ / min and kept warm for 1h, then heated to 750℃ at a heating rate of 7℃ / min and kept warm for 1h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.50g of doped modified activated carbon with a specific capacitance of 208.2F / g.

[0030] Comparative Example 2 After 6g of raw coal and 12g of potassium phosphate are mixed evenly, they are placed in a square crucible boat, a little nitrogen is introduced and the crucible is sealed. Then it is placed in a muffle furnace, heated to 400℃ at a heating rate of 5℃ / min and kept warm for 1h, then heated to 850℃ at a heating rate of 7℃ / min and kept warm for 1h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product is washed with water until neutral and then dried to obtain 2.33g of doped modified activated carbon with a specific capacitance of 209.1F / g.

[0031] Comparative Example 3 After 3g of raw coal and 6g of potassium dihydrogen phosphate were mixed evenly, they were placed in a square crucible boat, a little nitrogen was introduced and sealed. Then they were placed in a muffle furnace and heated to 750℃ at a heating rate of 7℃ / min for 2h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.12 doped modified activated carbon with a specific capacitance of 199.3F / g.

[0032] Comparative Example 4 After 3g of raw coal and 9g of diammonium phosphate were mixed evenly, they were placed in a square crucible boat, a little nitrogen was introduced and the crucible was sealed. Then it was placed in a muffle furnace, heated to 400℃ at a heating rate of 5℃ / min and kept warm for 1h, then heated to 800℃ at a heating rate of 7℃ / min and kept warm for 2h, with a nitrogen range of 200ml / min. After cooling to room temperature, the obtained product was washed with water until neutral and then dried to obtain 1.45g of doped modified activated carbon with a specific capacitance of 161.2F / g.

[0033] Figure 1The CV curve of the coal-based activated carbon prepared in Example 3 maintains a symmetrical rectangle at different scanning rates (5-200 mv / s), indicating that its electrochemical performance is stable.

[0034] like Figure 2 As shown, the capacitance retention rate of the coal-based activated carbon prepared in Example 3 is as high as 97.73% under 6000 cycles (current density is 10 A / g), which indicates that the coal-based activated carbon prepared in the embodiment of the present invention has good cycle performance.

[0035] like Figure 3 As shown, under the condition of current density of 0.5A / g, the specific capacitance of activated carbon in Comparative Example 1 is only 208.2F / g, because the dosage of potassium dihydrogen phosphate is too low, resulting in poor P / O element doping effect, and it can also be found from the XRD curve that its functional group position is offset and small. The dosage of potassium dihydrogen phosphate is doubled, and it can be seen in Example 1 that the specific capacitance has increased by nearly 25%. In Comparative Example 2, the specific capacitance of activated carbon is only 209.1F / g, while in Example 2, the specific capacitance of activated carbon is as high as 316.3F / g. It is shown that the preparation effect of potassium dihydrogen phosphate under the same conditions is much higher than that of potassium phosphate, because the molar mass of potassium phosphate is higher than that of potassium dihydrogen phosphate, resulting in more K atoms in potassium phosphate of the same mass. Although it can more effectively optimize the pore structure, it will rob the expansion effect and is not conducive to the doping of P / O. On the other hand, potassium dihydrogen phosphate will dissolve at 400°C, which plays an auxiliary role in the phase change process. The specific capacitance of the activated carbon in Comparative Example 3 is only 199.3 F / g. This is because no 400°C heat preservation phase change pretreatment was performed, which greatly reduced the contact area between potassium dihydrogen phosphate and the carbon skeleton.

[0036] from Figure 4 It can be seen that the XRD spectra of Examples 1, 2, and 3 have obvious convex parts, indicating that the heteroatom doping effect is good and new functional groups are introduced. The functional group diffraction peak misalignment in Comparative Example 1 is due to the weak doping effect caused by the low amount of potassium dihydrogen phosphate. Comparative Examples 2, 3, and 4 have similar gentle diffraction peaks, indicating that the doping effect is general.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing high specific capacitance coal-based activated carbon, characterized in that: The following steps are involved: The raw coal and potassium dihydrogen phosphate are mixed evenly in a mass ratio of 1:2-3, placed in a muffle furnace, pre-carbonized at 350-450°C under a nitrogen atmosphere, calcined at 750-850°C for 1-2h, cooled and washed to neutrality to obtain high specific capacitance coal-based activated carbon.

2. The method according to claim 1, characterized in that The heating rate of the pre-carbonization is 4-6°C / min.

3. The method according to claim 1, characterized in that The pre-carbonization temperature is 400°C.

4. The method according to claim 1, characterized in that: The pre-carbonization time is 0.5-1.5h.

5. The method according to claim 1, characterized in that: The heating rate of the calcination is 6-8°C / min.

6. The method according to claim 1, characterized in that The specific capacitance of the high specific capacitance activated carbon is 260-316 F / g.

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