Preparation method of coal pitch-based compact porous carbon with ultrahigh specific surface area and application of coal pitch-based compact porous carbon in zinc ion hybrid capacitor

Abstract

The invention discloses a preparation method of coal pitch-based dense porous carbon with an ultrahigh specific surface area and application of the coal pitch-based dense porous carbon in a zinc ion hybrid capacitor, and belongs to the technical field of electrochemistry and new energy materials. The coal pitch is subjected to oxidation treatment through mixed acid, and oxidized coal pitch is obtained. The method comprises the following steps: mixing and dissolving oxidized coal pitch and biological polysaccharide in an acid solution to obtain a precursor solution; then, adding an activating agent into the solution, and uniformly stirring; and grinding the dried mixture into powder, and carrying out high-temperature carbonization and acid pickling treatment to obtain the coal pitch-based compact carbon with the ultrahigh specific surface area. When the compact carbon is applied to the positive electrode of the zinc ion hybrid capacitor, high specific capacitance and excellent rate capability are shown. Meanwhile, the material can realize high energy density and high power density under high surface load, and has a good comprehensive application prospect.

Description

Technical Field

[0001] The invention relates to a preparation method of ultra-high specific surface area coal tar pitch-based dense porous carbon and application thereof, belonging to the technical field of electrochemistry and new energy materials. Background Art

[0002] With the development of economy and society and the improvement of people's living standards, the demand for fossil fuels in human society is increasing. However, the depletion of traditional energy is getting worse and worse, and the uneven distribution of energy in the world has led to regional imbalances in consumption supply and demand. In addition, the mining of coal or oil frequently causes landslides or large-scale oil spills at sea, which not only bring huge economic losses, but also cause inestimable harm to the environment and human life safety. Therefore, it is imperative to develop renewable clean energy. Wind energy, hydropower, solar energy, etc. are all new energy sources that can be used. These renewable energy sources are intermittent, which makes the storage and transportation of energy problems need to be solved urgently. Energy storage has become a strategic emerging industry that countries are competing to develop.

[0003] Secondary batteries with high energy density and supercapacitors with high power density have wide applications in the energy storage market. However, with the rise of new energy vehicles, it is urgent to develop new energy storage devices with both high energy density and high power density. Metal ion capacitors combine the chemical reactions of batteries and the physical mechanisms of capacitors to achieve high energy density and high power output. Compared with traditional batteries, metal ion capacitors have the advantages of high power output, long life and high energy density. Compared with supercapacitors, metal ion capacitors have advantages such as higher energy density and voltage. Alkali metal capacitors represented by lithium ion capacitors need to operate in low water and low oxygen environments, and use flammable organic electrolytes for assembly. This makes its production and operation relatively complex, and the cost of these metals is high. Compared with hybrid ion capacitors based on monovalent cations, systems based on multivalent cations are more attractive. Although multivalent metals such as calcium and aluminum ions can provide more charges in a single charge transfer, their kinetic characteristics are relatively sluggish, limiting their performance in practical applications. Taking into account factors such as kinetics, electrochemical performance and safety, zinc ion hybrid capacitors are considered to be an ideal energy storage device. Zinc has some unique properties, such as high theoretical capacity, relatively low redox potential and high stability in water. Therefore, zinc ion hybrid capacitors are expected to meet various practical needs and have broad development prospects.

[0004] The positive electrode material of a zinc-ion hybrid capacitor is usually a carbon material, which stores charges through the electric double layer and pseudocapacitance on the surface. Achieving a zinc-ion hybrid capacitor with high energy, high power, and long life depends critically on the delicate balance of pore structure, heteroatom dopants, and micro / nano structures in the carbon cathode. The precise pore structure, doping, and micro / nano structures in carbon materials usually require complex material design and preparation, which incur high economic costs. Patent CN 117558563 A introduces a process for preparing coal-tar pitch-based porous carbon by air flash pyrolysis-low alkali activation. The specific surface area of the obtained coal-tar pitch-based porous carbon is 1300-1500m 2 g -1 , and its use as the positive electrode of a zinc-ion hybrid capacitor has a relatively low specific capacitance. Patent CN 113496825 A obtained N-PCD nanoparticles by calcining ZIF-8 nanoparticles, and then prepared nitrogen and sulfur co-doped porous carbon by mixing with a sulfur source and calcining. Its preparation process is complex and unfriendly to the environment. In addition, the reported positive electrode materials of zinc-ion hybrid capacitors are all tested at low loadings, thus showing relatively excellent electrochemical performance. However, in practical applications, the battery current collectors, separators, casings, and electrolytes that do not contribute to capacitance will greatly reduce the overall device performance. Secondly, as the loading increases, the thickness of the electrode also increases exponentially, resulting in an exponential increase in the impedance of the device, slow charge transfer process, and decreased utilization rate of active sites. Therefore, constructing a zinc-ion hybrid capacitor with ultrafast reaction kinetics and excellent electrochemical performance under high mass loading is a huge challenge.

[0005] Coal-tar pitch is a major by-product of the coal chemical industry, mainly composed of polycyclic aromatic hydrocarbons, and is characterized by high carbon content, low price, and large output. Converting coal-tar pitch into a carbon-based electrode material with excellent electrochemical performance can realize the high-value utilization of coal-tar pitch, which has important practical significance for the green development of the coal chemical industry. However, coal-tar pitch is prone to melting and agglomeration during high-temperature carbonization, and polycyclic aromatic hydrocarbons are prone to directional stacking through intermolecular π-π* bonds. Bio-polysaccharides (such as chitosan, starch, or carrageenan) are a kind of biomass polymer composed of polar segments, containing a large number of hydroxyl and amino groups, and are prone to pyrolysis. By coordinating two trends, namely the forced miscibility trend caused by the chemical bond between oxidized coal-tar pitch and bio-polysaccharide and the separation trend caused by the polarity difference, coal-tar pitch-based dense porous carbon can be obtained. Summary of the Invention

[0006] The objective of the present invention is to overcome the deficiencies and drawbacks of the prior art, promote the recycling of resources, simplify the traditional synthesis steps of porous carbon, and prepare a coal-tar pitch-based dense porous carbon with an ultra-high specific surface area for application in energy storage devices. The synthesis of this material utilizes microphase separation engineering and the "cesium effect" to highly utilize coal tar pitch, a major byproduct of coal chemical industry, and prepare a coal-tar pitch-based dense porous carbon with a high specific surface area. As the positive electrode material of a zinc-ion hybrid capacitor, it realizes high energy density and high power density of energy storage devices at high areal loadings.

[0007] The technical solution of the present invention:

[0008] A preparation method of a coal-tar pitch-based dense porous carbon with an ultra-high specific surface area, which uses mixed acids to oxidize coal tar pitch to obtain oxidized coal tar pitch with abundant hydrophilic functional groups, enabling it to be uniformly mixed with biological polysaccharides to obtain a precursor solution. The activator is mixed with the precursor and subjected to high-temperature carbonization treatment in an inert gas to obtain a coal-tar pitch-based dense porous carbon with a high specific surface area. After being oxidized by mixed acids, the abundant oxygen-containing groups on the surface of coal tar pitch can undergo covalent coupling / non-covalent hydrogen bonding with the hydroxyl and amino groups of biological polysaccharides, making the oxidized coal tar pitch and biological polysaccharides have a miscibility trend, while the non-polarity of coal tar pitch itself and the polarity difference of biological polysaccharides lead to a separation trend between the two, which is conducive to the construction of a conductive network and a porous structure. At the same time, there is no foaming behavior during the pyrolysis process of coal tar pitch, which helps to obtain a dense carbon structure and is beneficial to energy storage at high areal loadings. The cesium activator has a strong activation effect (superior to the commonly used potassium hydroxide), thus promoting the formation of a high specific surface area.

[0009] A preparation method of a coal-tar pitch-based dense porous carbon with an ultra-high specific surface area, comprising the following steps:

[0010] (1) Oxidize coal tar pitch with mixed acids to obtain oxidized coal tar pitch;

[0011] (2) Dissolve biological polysaccharides in an acidic solution or water, add oxidized coal tar pitch and stir evenly to obtain a precursor solution.

[0012] (3) Add the activator to the precursor solution to obtain a mixed solution.

[0013] (4) After drying the mixed solution in an oven, grind the mixture into powder. Place the powder in a tubular furnace for high-temperature carbonization, wash with acid and dry to obtain a coal-tar pitch-based dense porous carbon.

[0014] Further, in the step (1), the mixed acids are concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated sulfuric acid to the concentrated nitric acid is 2:1 - 3:1.

[0015] Further, the specific process of step (1) includes: mixing mixed acid with coal tar pitch, subjecting it to oxidation treatment at 40 - 50 °C for 4 - 6 h, then pouring the reaction mixture into deionized water to terminate the reaction; allowing it to stand until stable, filtering with suction and washing until neutral. Dissolve the obtained solid in an alkali solution, adjust the pH to be greater than 12, heat and stir at 70 - 80 °C for 1 - 2 h, and then perform suction filtration; adjust the pH of the filtrate to be less than 2, centrifuge, and dry the obtained solid at 80 - 110 °C to constant weight to obtain oxidized coal tar pitch.

[0016] Furthermore, the alkali in the alkali solution is sodium hydroxide or potassium hydroxide, and the concentration of the alkali solution is 1 - 3 M.

[0017] Furthermore, the acid in the acid solution for adjusting pH is hydrochloric acid or sulfuric acid, and the concentration of the acid solution is 1 - 3 M.

[0018] Furthermore, the volume - mass ratio of the mixed acid to coal tar pitch during mixing is 20 - 25 ml / g.

[0019] Further, the coal tar pitch in step (1) is medium - temperature coal tar pitch or high - temperature coal tar pitch as a by - product of coal coking.

[0020] Further, in step (2), the biological polysaccharide is one of chitosan, starch, and carrageenan. The acidic solution is a small - molecule organic acid such as formic acid, acetic acid, or lactic acid, and its concentration in the solution is 4 - 6 wt%. The added mass ratio of the biological polysaccharide to the oxidized coal tar pitch is 1:3 - 3:1; the mass percentage of the biological polysaccharide in the acidic solution or water is 0.1 - 2 wt%.

[0021] Further, in step (3), the activator is one of cesium hydroxide, cesium carbonate, cesium bicarbonate, or cesium acetate, and the mass ratio of cesium to the total amount of the biological polysaccharide and the oxidized coal tar pitch is 0.6:1 - 4:1.

[0022] Further, in step (4), the drying temperature is 80 - 110 °C; the conditions for high - temperature carbonization of the powder in a tubular furnace are as follows: heating at a heating rate of 2 - 5 °C / min to 250 - 300 °C and holding for 0.5 - 1 h, and then heating at a heating rate of 5 - 10 °C / min to 600 - 900 °C and holding for 1 - 2 h. The pickling is to add the product of high - temperature carbonization to 1 - 3 M HCl, stir for 12 - 24 h, then filter with suction and wash until neutral. The conditions for the drying treatment are 80 - 110 °C and the time is 12 - 24 h. -1 of the heating rate to 250 - 300 °C and holding for 0.5 - 1 h, and then at a heating rate of 5 - 10 °C / min -1 of the heating rate to heat to 600 - 900 °C and hold for 1 - 2 h. The pickling is to add the product of high - temperature carbonization to 1 - 3 M HCl, stir for 12 - 24 h, then filter with suction and wash until neutral. The conditions for the drying treatment are 80 - 110 °C and the time is 12 - 24 h.

[0023] The beneficial effects of the present invention are:

[0024] (1) Using low-cost coal tar pitch as the carbon material precursor, the high-value utilization of coal chemical by-products is realized. The preparation process is simple and easy to operate, which is suitable for industrial production.

[0025] (2) The prepared coal tar pitch-based dense porous carbon has a specific surface area of 1800 - 3100 m 2 g -1 , the nitrogen doping amount is 1 - 6 at%, and the oxygen doping amount is 6 - 11 at%, showing excellent zinc storage performance.

[0026] (3) The coal tar pitch-based dense porous carbon has good conductivity and a rich pore structure. When used as the positive electrode material of a zinc-ion hybrid capacitor, it exhibits a high specific capacitance and excellent rate performance. It also has a high energy density and high power density at a high areal loading, demonstrating its commercial value. Description of the Drawings

[0027] Figure 1 Scanning electron microscope photograph of HC-Cs-800 prepared in Example 1;

[0028] Figure 2 EDS element mapping picture of HC-Cs-800 prepared in Example 1;

[0029] Figure 3 XRD pattern of HC-Cs-800 prepared in Example 1;

[0030] Figure 4 XPS full spectrum of HC-Cs-800 prepared in Example 1;

[0031] Figure 5 Low-temperature nitrogen adsorption and desorption test results of HC-Cs-800 prepared in Example 1;

[0032] Figure 6 Pore size distribution of HC-Cs-800 prepared in Example 1;

[0033] Figure 7 Galvanostatic charge-discharge curves of the materials prepared in Examples 1, 2, 3, and 4;

[0034] Figure 8 Cyclic voltammograms of the materials prepared in Examples 1, 5, and the control example;

[0035] Figure 9 Rate performance curves of the materials prepared in Examples 1, 5, and the control example;

[0036] Figure 10 Rate performance graph of HC-Cs-800 prepared in Example 1 at different areal loadings. Detailed Embodiments

[0037] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following examples. The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described can be obtained from commercial sources unless otherwise specified.

[0038] Example 1:

[0039] 1.0 g of medium-temperature coal tar pitch was oxidized with 20 mL of a mixed acid (concentrated sulfuric acid: concentrated nitric acid volume ratio = 2.3:1), the oxidation temperature was 40 °C, and the reaction was carried out at a constant temperature for 5 h. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, and then filtered; the filtrate was adjusted to a pH less than 2 with 1 M hydrochloric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0040] 0.25 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until uniformly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. At a heating rate of 2 °C min -1 it was heated to 250 °C and held for 1 h, and then heated to 800 °C at a heating rate of 5 °C min -1 and held for 1 h. The sample was added to 3 M HCl, stirred for 12 h, then filtered and washed until neutral, and placed in an 80 °C oven for 24 h to obtain coal tar pitch-based dense porous carbon HC-Cs-800.

[0041] The coal tar pitch-based dense porous carbon material prepared in this example, acetylene black, and polytetrafluoroethylene (PTFE) were used to prepare a positive electrode material according to a mass ratio of 8:1:1. A zinc ion hybrid capacitor was assembled with a zinc sheet as the negative electrode and 2 M ZnSO4 solution as the electrolyte. Electrochemical performance tests were carried out on a CHI 660E electrochemical workstation, and it was measured that the sample could achieve 493.4 F g -1 (0.5 A g -1 ), 433.8 F g -1 (1.0 A g -1 ), 392.9 F g -1 (2.0 A g -1 ), 349.7 F g -1 (5.0 A g -1 ), 313.1 F g -1 (10.0 A g -1 ), 279.1 F g -1(20.0 Ag -1 ) and 155.3 F g -1 (100.0 Ag -1 ) specific capacitance; at a surface loading as high as 15.96 mg cm -2 , it can still achieve a high energy density of 146.2 Wh kg -1 and a high power density of 8.039 kW kg -1 .

[0042] Example 2:

[0043] 1.0 g of medium-temperature coal tar pitch was oxidized by 25 mL of mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2:1), the oxidation temperature was 40 °C, and the constant temperature reaction was carried out for 6 h. After the reaction of the oxidation treatment ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 2 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, and then filtered; the filtrate was adjusted to a pH less than 2 with 2 M hydrochloric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0044] 0.25 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until evenly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into powder and placed in a tubular furnace under an inert atmosphere. It was heated at a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then heated at a heating rate of 5 °C min -1 to 600 °C and held for 1 h. The sample was added to 1 M HCl, stirred for 24 h, then filtered and washed until neutral, and placed in an oven at 110 °C for 12 h to obtain coal tar pitch-based dense porous carbon HC-Cs-600.

[0045] The coal tar pitch-based dense porous carbon material prepared in this example, acetylene black, and PTFE were used to prepare the positive electrode material according to a mass ratio of 8:1:1. A zinc ion hybrid capacitor was assembled with a zinc sheet as the negative electrode and 2 M ZnSO4 solution as the electrolyte. Electrochemical performance tests were carried out on a CHI 660E electrochemical workstation, and it was measured that the sample could achieve 433.4 F g -1 (0.5 Ag -1 ), 392.5 F g -1 (1.0 Ag -1 ), 359 F g -1 (2.0 Ag -1 ), 323.75 F g -1 (5.0 Ag -1 ), 298.1 F g-1 (10.0 Ag -1 )、269.5 F g -1 (20.0 Ag -1 ) and 258.1 F g -1 (30.0 Ag -1 ) specific capacitances.

[0046] Example 3:

[0047] 1.0 g of medium-temperature coal tar pitch was oxidized by 20 mL of mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 3:1) at an oxidation temperature of 50 °C for 4 h of constant-temperature reaction. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 3 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 70 °C for 2 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 3 M hydrochloric acid solution, centrifuged, and dried at 110 °C to constant weight to obtain oxidized coal tar pitch.

[0048] 0.25 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until evenly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. It was heated at a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then heated at a heating rate of 5 °C min -1 to 700 °C and held for 1 h. The sample was added to 2 M HCl, stirred for 18 h, then filtered and washed until neutral, and placed in an oven at 90 °C for 18 h to obtain coal tar pitch-based dense porous carbon HC-Cs-700.

[0049] The coal tar pitch-based dense porous carbon material prepared in this example, acetylene black, and PTFE were used to prepare a positive electrode material according to a mass ratio of 8:1:1. A zinc ion hybrid capacitor was assembled with a zinc sheet as the negative electrode and 2 M ZnSO4 solution as the electrolyte. Electrochemical performance tests were carried out on a CHI 660E electrochemical workstation, and it was measured that the sample could achieve 461.2 F g -1 (0.5 Ag -1 )、415 F g -1 (1.0 Ag -1 )、377.1 F g -1 (2.0 Ag -1 )、334.1 F g -1 (5.0 Ag -1 )、306.2 F g -1 (10.0 Ag -1 )、280.6 F g-1 (20.0 Ag -1 ) and 267.9 F g -1 (30.0 Ag -1 ).

[0050] Example 4:

[0051] 1.0 g of medium-temperature coal tar pitch was oxidized with 22 mL of a mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1) at an oxidation temperature of 40 °C for 5 h under constant temperature. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M hydrochloric acid solution, centrifuged, and dried at 90 °C to constant weight to obtain oxidized coal tar pitch.

[0052] 0.25 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until uniformly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. It was heated at a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then heated at a heating rate of 5 °C min -1 to 900 °C and held for 1 h. The sample was added to 3 M HCl, stirred for 12 h, then filtered and washed until neutral, and placed in an 80 °C oven for 12 h to obtain coal tar pitch-based dense porous carbon HC-Cs-900.

[0053] The coal tar pitch-based dense porous carbon material prepared in this example, acetylene black, and PTFE were used to prepare a positive electrode material according to a mass ratio of 8:1:1. A zinc ion hybrid capacitor was assembled with a zinc sheet as the negative electrode and 2 M ZnSO4 solution as the electrolyte. Electrochemical performance tests were carried out on a CHI 660E electrochemical workstation, and it was measured that the sample could achieve 369.4 F g -1 (0.5 Ag -1 ), 324.4 F g -1 (1.0 Ag -1 ), 294.5 F g -1 (2.0 Ag -1 ), 265.3 F g -1 (5.0 Ag -1 ), 242.5 F g -1 (10.0 Ag -1 ), 219.6 F g -1 (20.0 Ag -1 ) and 205.9 F g-1 (30.0 Ag -1 )。

[0054] Example 5:

[0055] 1.0 g of medium-temperature coal tar pitch was oxidized with 20 mL of a mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1) at an oxidation temperature of 40 °C for 5 h under constant temperature. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M potassium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M sulfuric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0056] 0.25 g of starch was dissolved in 80 mL of water, 0.25 g of oxidized coal tar pitch was added, and it was stirred until uniformly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. It was heated at a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then heated at a heating rate of 5 °C min -1 to 800 °C and held for 1 h. The sample was added to 3 M HCl, stirred for 24 h, then filtered and washed until neutral, and placed in an oven at 80 °C for 12 h to obtain coal tar pitch-based dense porous carbon SHC-Cs-800.

[0057] The coal tar pitch-based dense porous carbon material prepared in this example, acetylene black, and PTFE were used to prepare a positive electrode material according to a mass ratio of 8:1:1. A zinc sheet was used as the negative electrode, and a 2 M ZnSO4 solution was used as the electrolyte to assemble a zinc-ion hybrid capacitor. Electrochemical performance tests were carried out on a CHI 660E electrochemical workstation, and it was measured that the sample could achieve 451.6 F g -1 (0.5 Ag -1 ), 395 F g -1 (1.0 Ag -1 ), 355 F g -1 (2.0 Ag -1 ), 314.7 F g -1 (5.0 Ag -1 ), 291.3 F g -1 (10.0 Ag -1 ), 269.1 F g -1 (20.0 Ag -1 ), and 257.5 F g -1 (30.0 Ag -1 ).

[0058] Example 6:

[0059] 1.0 g of medium-temperature coal tar pitch was oxidized with 20 mL of mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1), the oxidation temperature was 40 °C, and the constant-temperature reaction was carried out for 5 h. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M potassium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M hydrochloric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0060] 0.25 g of chitosan was dissolved in 200 mL of 4 wt% formic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until evenly dissolved. 0.81 g of cesium carbonate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. At a heating rate of 5 °C min -1 to 300 °C and held for 1 h, and then heated to 800 °C at a heating rate of 10 °C min -1 and held for 1 h. The sample was added to 3 M HCl, stirred for 12 h, then filtered and washed until neutral, and placed in an 80 °C oven for 12 h to obtain coal tar pitch-based dense porous carbon HC-lCs-800.

[0061] Example 7:

[0062] 1.0 g of medium-temperature coal tar pitch was oxidized with 20 mL of mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1), the oxidation temperature was 40 °C, and the constant-temperature reaction was carried out for 5 h. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M sulfuric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0063] 0.25 g of carrageenan was dissolved in 13 mL of 6 wt% lactic acid solution, 0.25 g of oxidized coal tar pitch was added, and it was stirred until evenly dissolved. 2.91 g of cesium bicarbonate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. At a heating rate of 2 °C min -1 to 300 °C and held for 0.5 h, and then heated to 800 °C at a heating rate of 5 °C min -1 and held for 1 h. The sample was added to 3 M HCl, stirred for 12 h, then filtered and washed until neutral, and placed in an 80 °C oven for 24 h to obtain coal tar pitch-based dense porous carbon HC-hCs-800.

[0064] Example 8:

[0065] 1.0 g of high-temperature coal tar pitch was oxidized with 20 mL of a mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1) at an oxidation temperature of 40 °C for 5 h under constant temperature. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M hydrochloric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0066] 0.125 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.375 g of oxidized coal tar pitch was added, and it was stirred until uniformly dissolved. 1.92 g of cesium acetate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. At a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then heated at a heating rate of 5 °C min -1 to 800 °C and held for 1 h. The sample was added to 1 M HCl, stirred for 24 h, then filtered and washed until neutral, and placed in an 80 °C oven for 24 h to obtain coal tar pitch-based dense porous carbon HC-Cs-1.

[0067] Example 9:

[0068] 1.0 g of high-temperature coal tar pitch was oxidized with 20 mL of a mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2:1) at an oxidation temperature of 40 °C for 4 h under constant temperature. After the oxidation reaction ended, the reaction mixture was poured into deionized water to terminate the reaction; it was left to stand until stable, and then filtered and washed until neutral. The obtained solid was dissolved in 1 M sodium hydroxide solution, the pH was adjusted to be greater than 12, and it was heated and stirred at 80 °C for 1 h, followed by filtration; the filtrate was adjusted to a pH less than 2 with 1 M hydrochloric acid solution, centrifuged, and dried at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0069] 0.375 g of chitosan was dissolved in 80 mL of 5 wt% acetic acid solution, 0.125 g of oxidized coal tar pitch was added, and it was stirred until uniformly dissolved. 1.77 g of cesium hydroxide monohydrate was added and stirred for 6 h. The precursor solution was dried at 110 °C. The mixture was ground into a powder and placed in a tubular furnace under an inert atmosphere. At a heating rate of 2 °C min -1 to 250 °C and held for 1 h, and then at a heating rate of 5 °C min -1Heat it to 800 °C at a heating rate and hold for 1 h. Add the sample to 3 M HCl, stir for 12 h, then filter and wash until neutral, and place it in an 80 °C oven for 24 h to obtain coal-tar pitch-based dense porous carbon HC-Cs-3.

[0070] Control example:

[0071] Oxidize 1.0 g of medium-temperature coal tar pitch with 20 mL of mixed acid (volume ratio of concentrated sulfuric acid: concentrated nitric acid = 2.3:1) at an oxidation temperature of 40 °C for 5 h under constant temperature. After the oxidation reaction ends, pour the reaction mixture into deionized water to terminate the reaction; let it stand until stable, then filter and wash until neutral. Dissolve the obtained solid in 1 M sodium hydroxide solution, adjust the pH to be greater than 12, heat and stir at 80 °C for 1 h, and then filter; take the filtrate and adjust the pH to be less than 2 with 1 M hydrochloric acid solution, centrifuge, and dry at 80 °C to constant weight to obtain oxidized coal tar pitch.

[0072] Dissolve 0.25 g of chitosan in 80 mL of 5 wt% acetic acid solution, add 0.25 g of oxidized coal tar pitch, and stir until evenly dissolved. Add 0.66 g of potassium hydroxide and stir for 6 h. Place the precursor solution in an oven at 110 °C to dry. Grind the mixture into powder and place it in a tube furnace under an inert atmosphere. At a heating rate of 2 °C min -1 heat to 250 °C at a heating rate of 2 °C min and hold for 1 h, then heat to 800 °C at a heating rate of 5 °C min -1 and hold for 1 h. Add the sample to 3 M HCl, stir for 12 h, then filter and wash until neutral, and place it in an 80 °C oven for 12 h to obtain coal-tar pitch-based dense porous carbon HC-K-800.

[0073] Prepare a positive electrode material by mixing the coal-tar pitch-based dense porous carbon material prepared in this example, acetylene black, and PTFE in a mass ratio of 8:1:1. Use a zinc sheet as the negative electrode and 2 M ZnSO4 solution as the electrolyte to assemble a zinc-ion hybrid capacitor. Perform electrochemical performance tests on a CHI 660E electrochemical workstation. It is measured that the sample can achieve 295 F g -1 (0.5 A g -1 ), 257.5 F g -1 (1.0 A g -1 ), 233.8 F g -1 (2.0 A g -1 ), 203.4 F g -1 (5.0 A g -1 ), 174.5 F g -1 (10.0 A g -1 ), and 140.3 F g -1 (20.0 A g -1 ).

[0074] The scanning electron microscopy of the coal tar pitch-based dense porous carbon material prepared in Example 1 is as shown in Figure 1 , and the carbon material presents a dense block structure. It can be obtained from EDS that the C, N, and O elements in the material are evenly distributed, as shown in Figure 2 . The XRD analysis of the carbon material is as shown in Figure 3 . There are relatively wide diffraction peaks near 23° and 43° of 2θ for the carbon material, indicating the existence of an amorphous carbon structure. At the same time, the diffraction peaks of the sample show an obvious upward trend in the small-angle (2θ less than 10°) range, confirming that the material has a high specific surface area. The XPS full spectrum of the sample ( Figure 4 ) confirms the doping of N and O elements in the material, where the N content is 1.88 at%, and the O content is 7.62 at%.

[0075] Figure 5 The nitrogen adsorption and desorption test results of the coal tar pitch-based dense porous carbon prepared in Example 1 are provided. It can be seen that the nitrogen adsorption and desorption curve of the prepared carbon material belongs to a typical type I curve. The BET specific surface area of the material calculated by DFT is 3128.7 m 2 g -1 . Figure 6 For the pore size distribution diagram, it can be obtained that the pore size distribution of the material is concentrated in the range of 1 - 2.5 nm, with both micropores and small mesopores.

[0076] Figure 7 The charge-discharge curves of the carbon materials prepared in Examples 1, 2, 3, and 4 at a current density of 0.5 Ag -1 are provided. It can be known that 800 °C is the optimal carbonization temperature.

[0077] Figure 8 The cyclic voltammetry curves of the carbon materials prepared in Examples 1, 5, and the control example at a scanning rate of 50 mV s -1 are provided. HC-Cs-800 shows a larger curve area than HC-K-800, proving that it has a larger specific capacitance. At the same time, the weak oxidation-reduction peaks on the cyclic voltammetry curve indicate that there is not only a double-layer capacitance but also a pseudocapacitance contribution brought by heteroatom doping during the energy storage process.

[0078] Figure 9 The rate performance of the carbon materials prepared in Examples 1, 5, and the control example is shown. HC-Cs-800 and SHC-Cs-800 perform excellently, significantly superior to the control example HC-K-800.

[0079] Figure 10 The rate performance of the carbon material prepared in Example 1 at three different areal loadings (1.05, 10.58, 15.96 mg cm -2 ) is provided, indicating that the material has a comprehensive application prospect.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon, characterized in that: The following steps are involved: (1) using mixed acid to oxidize coal tar pitch to obtain oxidized coal tar pitch; (2) dissolving the biopolysaccharide in an acidic solution or water, adding oxidized coal tar pitch and stirring evenly to obtain a precursor solution; (3) adding an activator to the precursor solution to obtain a mixed solution; (4) After the mixed solution is placed in an oven to dry, the mixture is ground into powder; the powder is placed in a tube furnace for high-temperature carbonization, and after acid washing and drying, a coal tar-based dense porous carbon is obtained.

2. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: The mixed acid in step (1) is concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated sulfuric acid to the concentrated nitric acid is 2:1-3:1; the coal tar pitch in step (1) is medium-temperature coal tar pitch or high-temperature coal tar pitch which is a by-product of coal coking.

3. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: The specific process of step (1) comprises: mixing the mixed acid and coal tar pitch, oxidizing the mixture at 40-50°C for 4-6 hours, pouring the reaction mixture into deionized water to terminate the reaction; standing it until it is stable, filtering and washing it to neutrality; dissolving the obtained solid in alkaline solution, adjusting the pH to greater than 12, heating and stirring at 70-80°C for 1-2 hours, and then filtering; taking the filtrate and adjusting the pH to less than 2, centrifuging, and drying the obtained solid at 80-110°C to constant weight to obtain oxidized coal tar pitch.

4. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 3, characterized in that: The alkali in the alkali solution is sodium hydroxide or potassium hydroxide, and the alkali solution concentration is 1-3M; the acid in the acid solution for adjusting pH is hydrochloric acid or sulfuric acid, and the acid solution concentration is 1-3M; the volume mass ratio of the mixed acid and coal tar is 20-25ml / g.

5. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: In the step (2), the biopolysaccharide is one of chitosan, starch and carrageenan; the acidic solution is formic acid, acetic acid or lactic acid, and the solution concentration is 4-6wt%.

6. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: In the step (2), the added mass ratio of the biopolysaccharide to the oxidized coal tar pitch is 1:3-3:1; the mass percentage of the biopolysaccharide in the acidic solution or water is 0.1-2wt%.

7. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: The activator in step (3) is one of cesium hydroxide, cesium carbonate, cesium bicarbonate or cesium acetate, wherein the mass ratio of cesium to the total amount of biopolysaccharide and oxidized coal tar pitch is 0.6:1-4:

1.

8. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: In the step (4), the drying temperature is 80-110°C; the acid washing is to add the high temperature carbonized product to 1-3M HCl, stir for 12-24 hours, filter and wash until neutral; the drying treatment condition is 80-110°C for 12-24 hours.

9. The method for preparing ultra-high specific surface area coal-tar pitch-based dense porous carbon according to claim 1, characterized in that: In the step (4), the powder is placed in a tube furnace for high temperature carbonization at a temperature of 2-5°C min -1 The heating rate is 250-300℃ and kept at this temperature for 0.5-1h, then 5-10℃ min -1 Heat to 600-900℃ at a heating rate and keep warm for 1-2h.

10. Application of a coal tar pitch-based dense porous carbon with ultra-high specific surface area prepared by the preparation method according to any one of claims 1 to 9 in positive electrode materials of zinc ion hybrid capacitors.

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