Preparation method and application of nitrogen and oxygen co-doped coal pitch-based hierarchical porous carbon material

Abstract

The application discloses a preparation method and application of nitrogen and oxygen co-doped coal pitch-based hierarchical porous carbon material. The coal pitch is used as a carbon source and is pre-oxidized by an oxidizing agent, oxygen-containing functional groups are introduced by pre-oxidation, and the molecular structure is improved, so that more active sites are provided for subsequent reactions; the pre-oxidized product and a nitrogen-containing precursor are fully mixed, and pre-carbonization treatment is carried out, the nitrogen-containing precursor not only provides a stable nitrogen source for the system, realizes introduction of a nitrogen-doped structure, but also can promote rearrangement and stability of a carbon skeleton in a heat treatment process, and enhance the conductivity and structural stability of the material; finally, the pre-carbonized product and an activating agent are activated to obtain the nitrogen and oxygen co-doped hierarchical porous carbon material. The carbon material prepared by the application has nitrogen and oxygen co-doping and hierarchical pore structure, and the synergistic regulation can effectively improve the storage capacity and ion transmission kinetics of Zn 2+ , so that the rate performance and cycle stability of a device are improved, and an advantageous reference is provided for design and construction of a high-performance aqueous energy storage device.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, specifically relating to a nitrogen and oxygen co-doped coal tar pitch-based hierarchical porous carbon material, its preparation method, and its application in aqueous / quasi-solid-state zinc ion hybrid capacitors. Background Technology

[0002] With the rapid development of renewable energy and portable electronic devices, high-performance, low-cost, and highly safe energy storage devices have become a research hotspot. Aqueous zinc-ion hybrid capacitors (ZHCs) combine the high energy density of batteries with the high power density of supercapacitors, and are environmentally friendly and highly safe, making them very promising for large-scale energy storage and microelectronic devices.

[0003] Porous carbon materials are the mainstream cathode materials for zinc-ion mixed capacitors, but they generally suffer from problems such as simple pore structure, insufficient active sites, slow ion transport, and poor cycle stability. Traditional single KOH activation is difficult to achieve hierarchical pore construction and uniform heteroatom doping simultaneously; coal tar pitch-based carbon materials have high graphitization, few defects, and a lack of surface functional groups, leading to Zn... 2+ Insufficient storage sites, limited rate performance, and limited cycle life.

[0004] Currently, there is a lack of a low-cost, scalable method for preparing coal tar pitch-based carbon materials that can synergistically achieve nitrogen and oxygen co-doping, hierarchical porous, and ordered-disorder hybrid carbon frameworks. At the same time, there is a lack of integrated device solutions that support high-performance, high-stability, and flexible hydrogel electrolytes, making it difficult to meet the requirements of high-performance zinc-ion hybrid capacitors for high capacity, high rate capability, ultra-long cycle life, and flexible wearability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon materials, thereby solving the problems of unreasonable pore structure, few active sites, low doping efficiency, and poor rate capability and cycle performance of traditional coal tar pitch-based carbon materials. Simultaneously, a gel-GKPA hydrogel electrolyte is used as the cathode of a zinc-ion hybrid capacitor, exhibiting ultra-high specific capacitance, excellent rate capability, ultra-long cycle life, and good flexibility.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon materials, comprising the following steps: (1) Coal tar pitch and oxidant are pre-oxidized by heating and reflux to obtain oxidized coal tar pitch material; (2) After mixing the oxidized coal tar pitch material with the nitrogen-containing precursor solid phase, carbonize it under an inert atmosphere to obtain a pre-carbonized product; (3) After the pre-carbonized product is mixed evenly with the activator, it is activated at high temperature under an inert atmosphere, and then the carbon material is prepared by acid washing, water washing and drying.

[0007] Preferably, the reflux temperature in step (1) is 75~85℃, the reflux time is 8~10h, and the mass ratio of coal tar pitch to oxidant is 1:1~1:5.

[0008] Preferably, the oxidant in step (1) includes concentrated nitric acid, hydrogen peroxide, or ammonium persulfate.

[0009] Preferably, in step (2), the mass ratio of oxidized coal tar pitch material to nitrogen-containing precursor is 1:1 to 1:5, the carbonization temperature is 300 to 500°C, and the time is 90 to 150 min.

[0010] Preferably, the nitrogen-containing precursor in step (2) includes melamine cyanurate, urea, or melamine.

[0011] Preferably, the mass ratio of the pre-carbonized product to the activator in step (3) is 1:3 to 1:5, the activation temperature is 600 to 800°C, and the activation time is 120 to 150 min.

[0012] Preferably, the activator in step (3) includes one or more of potassium hydroxide, potassium phytate, or potassium carbonate.

[0013] The present invention also provides a method for preparing and applying the nitrogen- and oxygen co-doped coal tar pitch-based hierarchical porous carbon material obtained by the above preparation method.

[0014] This invention provides a nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon material and its preparation method, comprising the following steps: Coal tar pitch is used as a carbon source and pre-oxidized with an oxidant. Pre-oxidation introduces oxygen-containing functional groups and improves its molecular structure, providing more active sites for subsequent reactions. The pre-oxidized product is thoroughly mixed with a nitrogen-containing precursor for pre-carbonization treatment. The nitrogen-containing precursor not only provides a stable nitrogen source for the system, enabling the introduction of nitrogen-doped structures, but also promotes the rearrangement and stabilization of the carbon framework during heat treatment, enhancing the material's conductivity and structural stability. Finally, the pre-carbonized product is activated with an activator to obtain the nitrogen- and oxygen-co-doped hierarchical porous carbon material. The carbon material prepared by this invention possesses nitrogen- and oxygen-co-doped hierarchical porous structures, and their synergistic regulation can effectively enhance Zn... 2+ This improves the storage capacity and ion transport kinetics of the device, thereby enhancing its rate performance and cycle stability. Attached Figure Description

[0015] Figure 1 is an HRTEM image of the sample prepared in Example 2.

[0016] Figure 2 shows application examples 1, 2, 4, and 5 in the range of 0.1-30 Ag. -1 Rate performance within the current density range.

[0017] Figure 3 shows the charge-discharge cycle curves of Application Example 2.

[0018] Figure 4 shows application example 3 in the range of 0.1-30 Ag. -1 Rate performance within the current density range.

[0019] Figure 5 is a schematic diagram of graphite microcrystal extraction in Example 2 and Comparative Example 1.

[0020] Figure 6 shows the graphite crystallite length distribution of Example 2 and Comparative Example 1.

[0021] Figure 7 shows the N2 adsorption-desorption isotherms for Examples 1-3 and Comparative Example 1.

[0022] Figure 8 shows the XRD patterns of Examples 1-3 and Comparative Example 1.

[0023] Figure 9 shows the energy-power density curves for application examples 1, 2, 4, and 5. Detailed Implementation

[0024] To further illustrate the nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon material and its preparation method, and to achieve the intended purpose of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] The following will provide a more detailed description of the nitrogen- and oxygen co-doped coal tar pitch-based hierarchical porous carbon material and its preparation method, with reference to specific embodiments.

[0026] Example 1

[0027] 1 g of coal tar pitch was mixed with 3 g of 12 M concentrated nitric acid, refluxed at 80 °C for 8 h, cooled, washed, and dried to obtain oxidized coal tar pitch (OCTP). OCTP was then mixed uniformly with 3 g of melamine cyanurate (CAM) solid phase, placed in a tube furnace, and heated at 2 °C for 1 min under an argon atmosphere. -1The temperature was raised to 450 °C and held for 2 h, then allowed to cool naturally to obtain the pre-carbonized product. The pre-carbonized product was mixed with 3 g KOH and 3 g potassium phytate (KP) in a solid phase, and then heated at 5 °C for 1 min under an argon atmosphere. -1 The temperature was raised to the activation temperature of 600 °C and held for 2 h. The resulting activated product was then treated with 1 mol L... -1 The carbon material NOC-KP-600 was obtained by soaking in hydrochloric acid for 12 h, repeatedly washing with deionized water until neutral, and vacuum drying at 60 ℃ for 12 h.

[0028] Application Example 1

[0029] Carbon material NOC-KP-600, acetylene black, and polytetrafluoroethylene (PTFE) were weighed at a mass ratio of 8:1:1, and anhydrous ethanol was added for ultrasonic dispersion. After drying at 60 °C, the mixture was pressed into a disc electrode with a diameter of 12 mm and vacuum dried at 90 °C for 6 h. The active material loading was approximately 1.6 mg, and the areal loading was 1.4 mg·cm⁻¹. -2 ; A CR2032 button structure was used to fabricate a carbon electrode as the cathode, a zinc foil as the anode, and Whatman glass fiber as the diaphragm. 1 mol L -1 Using Zn(CF3SO3)2 aqueous solution as the electrolyte and graphite paper as the current collector, an aqueous Zn / / NOC-KP-600 ZHC device was assembled.

[0030] The water-based Zn / / NOC-KP-600 ZHC device assembled using Blue Electric Equipment in use case 1 operates at 0.1-30A g. -1 Rate performance was tested over a current density range, and the results showed that as the current density increased from 0.1 A g... -1 Increased to 30 A g -1 The specific capacity of the device increased from 137.7 mAh g. -1 Gradually decreased to 75.2 mAh g -1 When the current density recovers to 2 A g -1 At that time, the specific capacity basically recovered to 103.2 mAh g. -1 ( Figure 2 ).

[0031] Example 2

[0032] The only difference from Example 1 is that the activation temperature is 700 °C, while the other steps are exactly the same, resulting in sample NOC-KP-700.

[0033] Figure 1 shows the HRTEM image of the sample prepared in Example 2. As can be seen from the figure, the carbon layer exhibits a distinctly disordered carbon structure, accompanied by locally short-range ordered graphitization streaks, demonstrating the characteristics of an ordered / disordered hybrid carbon skeleton. The formation of this structure is closely related to the nitrogen source provided by melamine cyanurate during the pre-carbonization stage, which not only introduces nitrogen doping sites during the heat treatment process but also promotes the rearrangement and stabilization of the carbon skeleton.

[0034] Application Example 2

[0035] The only difference from Application Example 1 is that the carbon material mixed in the carbon electrode is NOC-KP-700. The rest of the steps are exactly the same, resulting in an aqueous Zn / / NOC-KP-700 ZHC device.

[0036] The aqueous Zn / / NOC-KP-700 ZHC device assembled using the Blue Electric equipment in use case 2 operates within the range of 0.1-30 A g. -1 Rate performance was tested over a current density range, and the results showed that as the current density increased from 0.1 A g... -1 Increased to 30 A g -1 The specific capacity of the device increased from 256.9 mAh g. -1 It gradually decreased to 102.2 mAh g. -1 When the current density recovers to 2 A g -1 At that time, the specific capacity basically recovered to 159.6 mAh g. -1 This indicates that the device possesses rapid ion transport capabilities and excellent electrochemical reversibility. Figure 2 ).

[0037] The long-cycle performance of the aqueous Zn / / NOC-KP-700 ZHC device was tested using Blue Electric Equipment. The results showed that the specific capacity of the device was approximately 108.6 mAh g⁻¹ during the initial cycle. -1 It still maintains 68.2 mAh g after 150,000 cycles. -1 The device exhibits a capacity retention of 62.80%, while maintaining a coulombic efficiency close to 100%. This result demonstrates the device's excellent cycle stability and reversibility, indicating that the NOC-KP-700 electrode material can maintain a stable structure during long-term charge-discharge processes, providing a solid performance foundation for the practical application of aqueous ZHC devices. Figure 3 ).

[0038] Application Example 3

[0039] Weigh 0.8 g of gelatin, add 10 mL of deionized water, and stir magnetically in a water bath at 60 ℃ for 1 h until completely dissolved to form a transparent solution; add 0.1 g of konjac mannan (KGM) to the transparent solution, and stir at 60 ℃ for 2 h until fully dissolved; add 2 g of acrylamide (AM) to the solution, and stir at 60 ℃ for 2 h until homogeneous; cool to room temperature, and add 3.635 g of zinc trifluoromethanesulfonate, 0.003 g of ammonium persulfate (APS), and 0.006 g of N,N-methylenebisacrylamide (MBAA) sequentially, and stir vigorously for 1 h to obtain a transparent precursor solution; pour the precursor solution into a glass mold, and heat in an oven at 60 ℃ for 30 min to polymerize, to obtain gel-GKPA hydrogel electrolyte.

[0040] The prepared NOC-KP-700 carbon material was used as the cathode, gel-GKPA hydrogel electrolyte as the electrolyte and separator, and zinc foil as the negative electrode to assemble a Zn / / gel-GKPA / / NOC-KP-700 quasi-solid-state ZHC device.

[0041] The Zn / / gel-GKPA / / NOC-KP-700 quasi-solid-state ZHC device assembled using Blue Electric Equipment in use case 3 operates within the range of 0.1-30 A g. -1 Rate performance was tested over a current density range, and the results showed that as the current density increased from 0.1 A g... -1 Increased to 30 A g -1 The specific capacity of the device increased from 185.1 mAh g. -1 Gradually decreased to 77.5 mAh g -1 When the current density recovers to 2 A g -1 At that time, the specific capacity basically recovered to 144.4 mAh g. -1 This indicates that NOC-KP-700 carbon material and gel-GKPA hydrogel electrolyte also have relatively good compatibility. Figure 4 ).

[0042] Comparative Example 1

[0043] The difference from Example 1 is that: only coal tar pitch is pre-oxidized to obtain OCTP; no melamine cyanurate is added, and no pre-carbonization is performed; only KOH is used as an activator, with a mass ratio of OCTP to KOH of 1:3, and activation is performed at 700 °C; under the same post-treatment conditions, the comparative sample OCTP-700 is obtained.

[0044] Figure 5 is a schematic diagram of graphite crystallization extraction in Example 2 and Comparative Example 1 of this invention. As can be seen from the figure, the sample in Example 2 contains more graphite crystallites, which are more uniformly distributed and exhibit more complex spatial orientation characteristics. This is mainly attributed to the fact that CAM provides a nitrogen source during carbonization, promoting the reconstruction of the carbon framework structure. Simultaneously, the synergistic activation effect of KP and KOH enhances the etching and rearrangement of the carbon layer, resulting in a richer graphite crystallite structure and defect sites within the material, thereby constructing a hybrid carbon framework where ordered and disordered structures coexist.

[0045] Figure 6 shows the graphite crystallite length distribution of Example 2 and Comparative Example 1 of this invention. As can be seen from the figure, the proportion of graphite crystallites in NOC-KP-700 significantly increases in the ranges of 1.2 ≥ L ≥ 0.1 nm and 2.3 ≥ L ≥ 1.2 nm. Longer graphite crystallites (3.3 ≥ L ≥ 2.3 nm) account for a higher proportion in OCTP-700, indicating that the combined effect of CAM and KP suppresses the excessive growth of long-range graphite structures and promotes the formation of more short-sized graphite crystallites. This more rational graphite crystallite distribution is beneficial for introducing more disordered structures and defect sites while maintaining a certain degree of graphitization to ensure electronic conductivity, thereby constructing ordered-disorder hybrid carbon materials with good conductivity and rich porosity, providing better ion transport channels and charge storage sites for ZHC devices.

[0046] Application Example 4

[0047] The only difference from Application Example 1 is that the carbon material mixed in the carbon electrode is OCTP-700. The rest of the steps are exactly the same, resulting in an aqueous Zn / / OCTP-700 ZHC device.

[0048] The aqueous Zn / / OCTP-700 ZHC device assembled using Blue Electric Equipment corresponding to use case 4 operates in the range of 0.1-30 Ag. -1 Rate performance was tested over a current density range, and the results showed that as the current density increased from 0.1 A g... -1 Increased to 30 A g -1 The specific capacity of the device increased from 144.3 mAh g⁻¹ -1 Gradually decreased to 73.1 mAh g -1 When the current density recovers to 2 A g -1 At that time, the specific capacity basically recovered to 100.7 mAh g. -1 ( Figure 2 ).

[0049] Example 3

[0050] The only difference from Example 1 is that the activation temperature is 800 °C, while the other steps are exactly the same, resulting in NOC-KP-800.

[0051] Figure 7 shows the N2 adsorption-desorption isotherms of Examples 1-3 and Comparative Example 1 of this invention. As can be seen from the figure, the NOC-KP-x series samples all exhibit typical microporous-mesoporous composite isotherm characteristics. In the low relative pressure region (P / P0 < 0.1), the adsorption capacity increases rapidly, indicating the presence of abundant microporous structures in the material. In the medium-to-high relative pressure region, a significant hysteresis loop appears, indicating the simultaneous presence of a certain proportion of mesoporous structures. The pore structure varies significantly at different activation temperatures. Compared with other materials, the sample in Example 2 (NOC-KP-700) exhibits the highest overall adsorption capacity and a more reasonable hysteresis loop morphology, indicating that it has a larger specific surface area and a more optimized hierarchical pore structure.

[0052] Figure 8 shows the XRD patterns of Examples 1-3 and Comparative Example 1 of the present invention. As can be seen from the figure, compared with other materials, the (002) peak of NOC-KP-700 is slightly broadened, indicating that the introduction of CAM and the synergistic activation effect of KP and KOH have a stronger etching and reconstruction effect on the carbon skeleton, making the material structure more porous and forming more structural defects, which is conducive to building a rich pore structure and improving the diffusion and transport capabilities of electrolyte ions.

[0053] Application Example 5

[0054] The only difference from Application Example 1 is that the carbon material mixed in the carbon electrode is NOC-KP-800. The rest of the steps are exactly the same, resulting in an aqueous Zn / / NOC-KP-800 ZHC device.

[0055] The aqueous Zn / / NOC-KP-800 ZHC device assembled using the Blue Electric equipment in use case 5 operates within the range of 0.1-30 A g. -1 Rate performance was tested over a current density range, and the results showed that as the current density increased from 0.1 A g... -1 Increased to 30 A g -1 The specific capacity of the device increased from 165.9 mAh g. -1 Gradually decreased to 72.1 mAh g -1 When the current density recovers to 2 A g -1 At that time, the specific capacity basically recovered to 106.3 mAh g. -1 ( Figure 2 ).

[0056] Figure 9 shows the energy-power density curves for application examples 1, 2, 4, and 5 of this invention. As can be seen from the figure, application example 2 achieves a power density of 92.1 W kg⁻¹. -1 It can achieve a power density of 187.9 Wh / kg. -1 Energy density; even when the power density increases to 26040.9 W kg -1 At that time, the energy density can still be maintained at 101.3 Wh kg. -1 This result demonstrates that the device maintains high energy density while still possessing excellent power output capability, exhibiting good energy-power balance characteristics.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon material, characterized in that, The hierarchical porous carbon material has an ordered-disorder hybrid structure. The proportion of graphite crystallites with a size in the range of 1.2 ≥ L ≥ 0.1 nm is 55%–59%, those in the range of 2.3 ≥ L ≥ 1.2 nm are 35%–37%, while the proportion of longer graphite crystallites with a size of 3.3 ≥ L ≥ 2.3 nm is only 4%–10%. This hierarchical porous carbon material exhibits relatively good compatibility with both aqueous and quasi-solid-state zinc ion mixed capacitors. It is prepared by the following method: (1) Coal tar pitch and oxidant are pre-oxidized by heating and reflux to obtain oxidized coal tar pitch material; (2) After mixing the oxidized coal tar pitch material with the nitrogen-containing precursor solid phase, carbonize it under an inert atmosphere to obtain a pre-carbonized product; (3) After the pre-carbonized product is mixed evenly with the activator, it is activated at high temperature under an inert atmosphere, and then the carbon material is prepared by acid washing, water washing and drying.

2. A method for preparing a nitrogen- and oxygen-co-doped coal tar pitch-based hierarchical porous carbon material, comprising the following steps: (1) Coal tar pitch and oxidant are pre-oxidized by heating and reflux to obtain oxidized coal tar pitch material; (2) After mixing the oxidized coal tar pitch material with the nitrogen-containing precursor solid phase, carbonize it under an inert atmosphere to obtain a pre-carbonized product; (3) After the pre-carbonized product is mixed evenly with the activator, it is activated at high temperature under an inert atmosphere, and then the carbon material is prepared by acid washing, water washing and drying.

3. The preparation method according to claim 2, characterized in that, The reflux temperature in step (1) is 75~85℃, the reflux time is 8~10h, and the mass ratio of coal tar pitch to oxidant is 1:1~1:

5.

4. The preparation method according to claim 2, characterized in that, The oxidant in step (1) includes concentrated nitric acid, hydrogen peroxide, or ammonium persulfate.

5. The preparation method according to claim 2, characterized in that, In step (2), the mass ratio of oxidized coal tar pitch material to nitrogen-containing precursor is 1:1 to 1:5, the carbonization temperature is 300 to 500°C, and the time is 90 to 150 min.

6. The preparation method according to claim 2, characterized in that, The nitrogen-containing precursor in step (2) includes melamine cyanurate, urea, or melamine.

7. The preparation method according to claim 2, characterized in that, The mass ratio of the pre-carbonized product to the activator in step (3) is 1:3 to 1:5, the activation temperature is 600 to 800°C, and the time is 120 to 150 min.

8. The preparation method according to claim 2, characterized in that, The activator in step (3) includes one or more of potassium hydroxide, potassium phytate, or potassium carbonate.

9. The application of coal tar pitch-based hierarchical porous carbon as described in claims 1 or 2-8 in zinc ion hybrid capacitors.

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