Coal-based activated carbon for super capacitor, and green and efficient preparation method and application of coal-based activated carbon

Abstract

The invention discloses coal-based activated carbon for a super capacitor and a green and efficient preparation method and application of the coal-based activated carbon. The invention belongs to the field of active carbon materials. The invention aims to solve the technical problems that the specific capacitance of the active carbon prepared by the existing activation method is not high and the activation method cannot give consideration to both environmental protection and high efficiency. The method comprises the following steps: uniformly mixing crushed raw material coal, structure enhancing additive powder and KOH powder, and then heating and activating in a mixed atmosphere of non-inert gas and inert gas. According to the method, the coal is used as the raw material, the coal-based activated carbon is prepared by adopting one-step activation, the process is simple, the reaction temperature is low, the cost is low, the operation is convenient, meanwhile, the dosage of an activating agent KOH and the dosage of acid for subsequent pickling are remarkably reduced, and the method is suitable for large-scale production and practical application. The obtained coal-based activated carbon has a relatively large specific surface area and a developed pore structure, is used as an electrode of a supercapacitor, has high specific capacitance and excellent rate capability, and can promote the application of a high-performance supercapacitor.

Description

Technical Field

[0001] The present invention belongs to the field of activated carbon materials, and particularly relates to a coal-based activated carbon for supercapacitors, a green and efficient preparation method thereof, and an application thereof. Background Art

[0002] Supercapacitors have the characteristics of high power density, fast charge and discharge rate, long cycle life, wide operating temperature range, and maintenance-free, and are widely used in portable electronic devices, vehicle starting power supplies, rail transit, national defense and military and other fields. The electrode material is one of the important factors affecting the performance of supercapacitors. Activated carbon has the advantages of low cost, large specific surface area, good chemical stability, high conductivity, etc., and is currently the most commonly used electrode material in supercapacitors. At present, the activated carbon materials used for supercapacitors are mainly prepared by high-temperature carbonization and activation of carbon-containing precursors (organic polymers, fossil fuels, biomass, etc.). Coal-based activated carbon has the advantages of high specific surface area, convenient pore size and structure regulation, excellent conductivity, etc. Therefore, the preparation of supercapacitor activated carbon from coal as raw material has received extensive attention in the academic and industrial fields.

[0003] At present, the methods for preparing activated carbon materials mainly include activation method, template method, direct carbonization method, etc. Among them, the template method is complex and cumbersome in the experimental process, and there may be problems such as residues when removing the template; although the direct carbonization method has simple steps, it limits the structural diversity of the activated carbon material, and the specific surface area of the prepared activated carbon is relatively low; the activation method is divided into chemical activation and physical activation. The chemical activation method has the advantages of low temperature, short time, developed pore structure, large specific surface area, and small density of the material, but subsequent pickling is required, and the acid-base waste water pollution is serious; although the physical activation method does not require subsequent treatment and is more environmentally friendly, it requires high temperature, long time, underdeveloped pore structure, small specific surface area, large material density, and at present, the activated carbon prepared by the existing activation method still has disadvantages such as poor rate performance and short cycle life. Therefore, in the preparation of supercapacitor activated carbon materials from coal as raw material, how to effectively regulate its specific surface area and pore structure is one of the technical problems that need to be solved urgently. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems that the specific capacitance of the activated carbon prepared by the existing activation method is not high and the activation method cannot take into account environmental protection and high efficiency, and to provide a coal-based activated carbon for supercapacitors, a green and efficient preparation method thereof, and an application thereof.

[0005] One of the purposes of the present invention is to provide a green and efficient preparation method of a coal-based activated carbon for supercapacitors, and the preparation method is carried out according to the following steps:

[0006] S1: Mix the pulverized raw coal and the structure enhancing auxiliary powder evenly to obtain a mixture, and add KOH powder and continue to mix until evenly distributed;

[0007] S2: Heat up and activate under a mixed atmosphere of non-inert gas and inert gas, then add the activated product to dilute hydrochloric acid, stir, filter by suction, wash until neutral, and dry to obtain coal-based activated carbon.

[0008] Further define that the raw coal in S1 is coal with ash content ≤ 10%.

[0009] Even further define that the coal with ash content ≤ 10% is selected from at least one of anthracite, bituminous coal, and lignite.

[0010] Further define that the raw coal in S1 is crushed to 50 - 400 mesh.

[0011] Further define that the structural reinforcement additive powder in S1 is selected from at least one of phenolic resin, coal tar pitch, petroleum pitch, and natural asphalt.

[0012] Further define that the mass ratio of the raw coal to the structural reinforcement additive in S1 is 1:(0.01 - 1).

[0013] Further define that the mass ratio of the mixture to KOH in S1 is 1:(0.1 - 5).

[0014] Further define that the volume ratio of the inert gas to the non-inert gas in S2 is 1:(0.1 - 10).

[0015] Further define that the inert gas in S2 includes nitrogen, argon, and helium.

[0016] Further define that the non-inert gas in S2 is water vapor or carbon dioxide.

[0017] Further define that the heating rate in S2 is 1 - 10 °C·min -1 , heat up to 500 - 1500 °C, and keep the temperature for 0.5 - 5 h.

[0018] Further define that the concentration of the dilute hydrochloric acid in S2 is 5 - 20 wt%.

[0019] The second object of the present invention is to provide a coal-based activated carbon prepared by the above method.

[0020] The third object of the present invention is to provide an electrode based on the above coal-based activated carbon, and the specific capacitance of the electrode > 180 F·g when the current density is 0.5 A·g -1 -1 .

[0021] The fourth object of the present invention is to provide a preparation method of an electrode based on the above coal-based activated carbon, and the method:

[0022] Mix the coal-based activated carbon, conductive agent, binder, and solvent evenly, and then directly press into tablets or coat onto a substrate to obtain the electrode.​

[0023] A fifth object of the present invention is to provide an application of an electrode based on the above-mentioned coal-based activated carbon in a supercapacitor.

[0024] The remarkable effects of the present invention compared with the prior art are as follows:

[0025] The present invention uses coal as a raw material and prepares coal-based activated carbon by one-step activation. The process is simple, the reaction temperature is low, the cost is low, and the operation is convenient. At the same time, the dosage of the activator KOH and the dosage of the acid used in subsequent pickling are significantly reduced, which is suitable for large-scale production and practical application.

[0026] The present invention uses low-ash coal and a structure-enhancing auxiliary material as raw materials, and mixes them in different ratios, which can effectively adjust the microscopic morphology and pore structure of the activated carbon, and at the same time improve the yield of the coal-based activated carbon. The obtained coal-based activated carbon has a large specific surface area and a developed pore structure. When used as an electrode of a supercapacitor, it has a high specific capacitance and excellent rate performance, which can promote the application of high-performance supercapacitors. Description of the Drawings

[0027] Figure 1 is the X-ray diffraction pattern (XRD) of the coal-based activated carbon prepared in Example 1;

[0028] Figure 2 is the N 2 adsorption / desorption isotherm;

[0029] Figure 3 is the galvanostatic charge-discharge curve of the coal-based activated carbon prepared in Example 1;

[0030] Figure 4 is the specific capacitance curve of the coal-based activated carbon prepared in Example 1 at different current densities;

[0031] Figure 5 is the Nyquist plot of the coal-based activated carbon prepared in Example 1. Detailed Embodiments

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in this field, and those skilled in the art can obtain them through commercial channels without special instructions.

[0034] The terms "comprising", "including", "having", "containing" or any other variation thereof used in the following embodiments are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus comprising the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0035] As used herein, "one embodiment" or "an embodiment" refers to a particular feature, structure, or characteristic that may be included in at least one implementation of the present invention. The appearances of "in one embodiment" in various places in this specification are not all referring to the same embodiment, nor are they separate or alternative embodiments that exclude other embodiments.

[0036] The endpoints and any values disclosed in the ranges of the invention are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, combinations can be made between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0037] Example 1:

[0038] (1) Weigh 1 g of anthracite with a 200-mesh ash content of <1% and 0.1 g of 200-mesh coal tar pitch, grind them in a mortar for 30 min, add 2 g of KOH powder, and continue grinding for 30 min to form a homogeneous mixture;

[0039] (2) Transfer the mixture to a tubular furnace and perform high-temperature activation treatment under a mixed atmosphere of steam / argon (v / v = 10 / 1). Heat it at a heating rate of 5 °C·min -1 to 750 °C, keep it at a constant temperature for 2 h, and after natural cooling to room temperature, obtain the activated product;

[0040] (3) Add the activated product to 100 mL of a 10% by mass dilute hydrochloric acid solution, stir magnetically for 12 h, then perform suction filtration and washing until the filtrate is neutral, and dry it under vacuum at 80 °C for 12 h to obtain coal-based activated carbon. The XRD pattern of the obtained activated carbon is as shown in Figure 1 As can be seen from Figure 1 two broad diffraction peaks appear at 22.1° and 43.3°, corresponding to the (002) and (100) crystal planes of the carbon material respectively. Among them, the (002) diffraction peak can be attributed to a typical characteristic peak of low graphitization degree, proving that the prepared coal-based capacitive carbon has a micrographitic structure, which is helpful for the transfer of charges during the charge and discharge process. In addition, the diffraction peak is strong at 2θ < 10°, indicating that the material contains a large number of micropores. The N 2 adsorption / desorption isotherm is as shown inFigure 2 As shown, from Figure 2 it can be seen that the adsorption / desorption isotherm belongs to the composite adsorption / desorption isotherm of type I and type IV. In the low-pressure range, the adsorption amount of N 2 increases rapidly with the increase of the relative pressure, corresponding to typical micropores. There is a hysteresis loop in the high-pressure region, indicating that mesopores are also present in the sample. The specific surface area of the sample is 1940 m 2 g -1 , and the pore volume is 1.04 cm 3 g -1 .

[0041] (4) Coal-based activated carbon, acetylene black, and binder (polytetrafluoroethylene, PFTE) are mixed in a mass ratio of 75:20:5, then anhydrous ethanol is added, and they are pressed into a uniform thin sheet, cut into circular electrode sheets with a diameter of 12 mm, and vacuum dried at 80 °C for 12 h to obtain electrode sheets.

[0042] Take two electrode sheets with the same mass and assemble them into a symmetric supercapacitor in a glove box (H 2 O ≤ 0.01 ppm, O 2 ≤ 0.01 ppm). The electrolyte is a 1 mol·L -1 tetraethylammonium tetrafluoroborate / acetonitrile solution (TEABF 4 / AN). Use an electrochemical workstation to perform constant current charge / discharge and cyclic voltammetry tests on the assembled capacitor. The test voltage range is 0 - 2.5 V, and the current density is 0.5 - 50 A·g -1 .

[0043] The constant current charge / discharge curves at different current densities are as Figure 3 shown. From Figure 3 it can be seen that the assembled symmetric capacitor exhibits symmetric charge / discharge curves, further proving that the prepared activated carbon has ideal electric double layer capacitance characteristics.

[0044] The specific capacitance curves at different current densities are as Figure 4 shown. From Figure 4 it can be seen that when the current density is 0.5 A·g -1 , the specific capacitance is 181.5 F·g -1 , and when the current density increases to 50 A·g -1 , the specific capacitance can still be maintained at 158.6 F·g -1 , and the rate is 87.4%.

[0045] Example 2:

[0046] (1) Weigh 1 g of anthracite with 200 mesh and ash content < 1% and 0.1 g of coal tar pitch with 200 mesh, grind them in a mortar for 30 min, add 2 g of KOH powder, and continue grinding for 30 min to form a homogeneous mixture;

[0047] (2) Transfer the mixture to a tubular furnace and carry out high-temperature activation treatment in a steam / argon (v / v = 1 / 10) atmosphere. Heat it up to 750 °C at a heating rate of 5 °C·min -1 and keep it at a constant temperature for 2 h. After natural cooling to room temperature, the activated product is obtained;

[0048] (3) Add the activated product to 100 mL of a 10% dilute hydrochloric acid solution, stir magnetically for 12 h, then carry out suction filtration and washing until the filtrate is neutral, and dry it in vacuum at 80 °C for 12 h to obtain coal-based activated carbon.

[0049] (4) Mix coal-based activated carbon, acetylene black, and a binder (polytetrafluoroethylene, PFTE) in a mass ratio of 75:20:5, then add absolute ethanol, press it into a uniform thin sheet, cut it into circular electrode sheets with a diameter of 12 mm, and dry it in vacuum at 80 °C for 12 h to obtain electrode sheets.

[0050] Take two electrode sheets with the same mass and assemble them into a symmetric supercapacitor in a glove box (H 2 O ≤ 0.01 ppm, O 2 ≤ 0.01 ppm). The electrolyte is a 1 mol·L -1 solution of tetraethylammonium tetrafluoroborate / acetonitrile (TEABF 4 / AN). Use an electrochemical workstation to conduct constant current charge-discharge and cyclic voltammetry tests on the assembled capacitor. The test voltage range is 0 - 2.5 V, and the current density is 0.5 - 50 A·g -1 . When the current density is 0.5 A·g -1 , the specific capacitance is 170.0 F·g -1 . When the current density increases to 50 A·g -1 , the specific capacitance can still be maintained at 152.7 F·g -1 (as Figure 4 shown).

[0051] Example 3:

[0052] (1) Weigh 1 g of anthracite with 200 mesh and ash content < 1% and 0.1 g of coal tar pitch with 200 mesh, grind them in a mortar for 30 min, add 3 g of KOH powder, and continue grinding for 30 min to form a homogeneous mixture;

[0053] (2) Transfer the mixture to a tubular furnace and carry out high-temperature activation treatment in a steam / argon (v / v = 10 / 1) atmosphere. Heat it up at a heating rate of 5 °C·min-1 Heat it up to 750 °C at a heating rate of, keep it at a constant temperature for 2 h, and then cool it naturally to room temperature to obtain the activated product;

[0054] (3) Add the activated product to 100 mL of a dilute hydrochloric acid solution with a mass concentration of 10%, stir magnetically for 12 h, then carry out suction filtration and washing until the filtrate is neutral, and dry it in vacuum at 80 °C for 12 h to obtain coal-based activated carbon.

[0055] (4) Mix coal-based activated carbon, acetylene black, and a binder (polytetrafluoroethylene, PFTE) in a mass ratio of 75:20:5, then add absolute ethanol, press it into a uniform thin sheet, cut it into circular electrode sheets with a diameter of 12 mm, and dry it in vacuum at 80 °C for 12 h to obtain electrode sheets.

[0056] Take two electrode sheets with the same mass and assemble them into a symmetric supercapacitor in a glove box (H 2 O ≤ 0.01 ppm, O 2 ≤ 0.01 ppm). The electrolyte is a 1 mol·L -1 tetraethylammonium tetrafluoroborate / acetonitrile solution (TEABF 4 / AN). Use an electrochemical workstation to conduct constant current charge and discharge and cyclic voltammetry tests on the assembled capacitor. The test voltage range is 0 - 2.5 V, and the current density is 0.5 - 50 A·g -1 . When the current density is 0.5 A·g -1 , the specific capacitance is 185.7 F·g -1 . When the current density increases to 50 A·g -1 , the specific capacitance can still be maintained at 166.0 F·g -1 (as Figure 4 shown).

[0057] Example 4:

[0058] (1) Weigh 1 g of lignite with a mesh size of 200 and an ash content of < 10%, add 5 g of KOH powder, and continue to grind for 30 min to form a uniform mixture;

[0059] (2) Transfer the mixture to a tube furnace and carry out high-temperature activation treatment under an argon atmosphere. Heat it up to 750 °C at a heating rate of 5 °C·min -1 , keep it at a constant temperature for 2 h, and then cool it naturally to room temperature to obtain the activated product;

[0060] (3) Add the activated product to 100 mL of a dilute hydrochloric acid solution with a mass concentration of 10%, stir magnetically for 12 h, then carry out suction filtration and washing until the filtrate is neutral, and dry it in vacuum at 80 °C for 12 h to obtain coal-based activated carbon.

[0061] (4) Coal-based activated carbon, acetylene black, and binder (polytetrafluoroethylene, PFTE) are mixed in a mass ratio of 75:20:5, then anhydrous ethanol is added, and they are pressed into a uniform thin sheet, cut into circular electrode sheets with a diameter of 12 mm, and vacuum dried at 80 °C for 12 h to obtain electrode sheets.

[0062] Take two electrode sheets of the same mass in a glove box (H 2 O≤0.01 ppm, O 2 ≤0.01 ppm) and assemble them into a symmetric supercapacitor. The electrolyte is a 1 mol·L -1 tetraethylammonium tetrafluoroborate / acetonitrile solution (TEABF 4 / AN). Use an electrochemical workstation to conduct constant current charge and discharge and cyclic voltammetry tests on the assembled capacitor. The test voltage range is 0 - 2.5 V, and the current density is 0.5 - 50 A·g -1 . When the current density is 0.5 A·g -1 , the specific capacitance is 140.6 F·g -1 . When the current density increases to 50 A·g -1 , the specific capacitance can still be maintained at 129.2 F·g -1 (as Figure 4 shown).

[0063] Example 5:

[0064] (1) Weigh 1 g of anthracite with a mesh size of 200 and an ash content of <2% and 0.1 g of coal tar pitch with a mesh size of 200, and grind them in a mortar for 30 min to form a uniform mixture;

[0065] (2) Transfer the mixture to a tubular furnace and conduct high-temperature activation treatment in a water vapor atmosphere. Heat it to 850 °C at a heating rate of 5 °C·min -1 , keep it at a constant temperature for 2 h, and naturally cool it to room temperature to obtain the activated product;

[0066] (3) Add the activated product to 100 mL of a dilute hydrochloric acid solution with a mass concentration of 15%, stir magnetically for 12 h, then perform suction filtration and washing until the filtrate is neutral, and vacuum dry it at 80 °C for 12 h to obtain coal-based activated carbon.

[0067] (4) Coal-based activated carbon, acetylene black, and binder (polytetrafluoroethylene, PFTE) are mixed in a mass ratio of 75:20:5, then anhydrous ethanol is added, and they are pressed into a uniform thin sheet, cut into circular electrode sheets with a diameter of 12 mm, and vacuum dried at 80 °C for 12 h to obtain electrode sheets.

[0068] Take two electrode sheets of the same mass in a glove box (H 2 O≤0.01 ppm, O 2≤ 0.01 ppm) were assembled into a symmetric supercapacitor, and the electrolyte was 1 mol·L -1 tetraethylammonium tetrafluoroborate / acetonitrile solution (TEABF 4 / AN). The assembled capacitor was subjected to constant current charge-discharge and cyclic voltammetry tests using an electrochemical workstation. The test voltage range was 0 - 2.5 V, and the current density was 0.5 - 50 A·g -1 . When the current density was 0.5 A·g -1 , the specific capacitance was 102.0 F·g -1 . When the current density increased to 50 A·g -1 , the specific capacitance could still be maintained at 80.5 F·g -1 (as Figure 4 shown).

[0069] As described above, these are only the preferred specific embodiments of the present invention. These specific embodiments are different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A green and efficient method for preparing coal-based activated carbon for supercapacitors, characterized in that: The method: S1: The crushed raw coal and the structure reinforcement additive powder are mixed evenly to obtain a mixture, and KOH powder is added and mixed until it is uniform; S2: Activate by heating in a mixed atmosphere of non-inert gas and inert gas, then add the activated product into dilute hydrochloric acid, stir, filter, wash to neutrality and dry to obtain coal-based activated carbon.

2. The method according to claim 1, characterized in that The raw coal in S1 is coal with an ash content of ≤10%, and the structure-enhancing auxiliary powder is selected from at least one of phenolic resin, coal tar, petroleum asphalt, and natural asphalt.

3. The method according to claim 2, characterized in that The coal with ash content ≤ 10% is selected from at least one of anthracite, bituminous coal and lignite.

4. The method according to claim 1, characterized in that: The mass ratio of raw coal to structural reinforcement additive in S1 is 1:(0.01-1), and the mass ratio of the mixture to KOH is 1:(0.1-5).

5. The method according to claim 1, characterized in that The volume ratio of inert gas to non-inert gas in S2 is 1:(0.1-10), the inert gas includes nitrogen, argon, helium, and the non-inert gas is water vapor or carbon dioxide.

6. The method according to claim 1, characterized in that The heating rate in S2 is 1~10℃·min -1 , raise the temperature to 500-1500°C, keep warm for 0.5-5h, and the concentration of dilute hydrochloric acid in S2 is 5-20wt%.

7. Coal-based activated carbon prepared by the method according to any one of claims 1 to 6.

8. The electrode based on coal-based activated carbon according to claim 7, characterized in that: The electrode is at a current density of 0.5 A·g -1 When the specific capacitance is greater than 180F·g -1 .

9. The method for preparing the electrode according to claim 8, characterized in that: The method: The coal-based activated carbon, conductive agent, binder and solvent are mixed evenly and then directly pressed into sheets or coated onto a substrate to obtain an electrode.

10. Use of the electrode according to claim 8 in a supercapacitor.

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