Preparation method of nitrogen-doped graphene carbon nanotube high-power composite electrode material

Abstract

The invention discloses a preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material. The material is prepared by taking graphene oxide and carboxylated multi-walled carbon nanotubes as precursors and urea as a nitrogen source through synergism of chemical reduction and a hydrothermal method. A three-dimensional porous network structure is constructed through solvent dispersion, ultrasonic compounding, high-temperature reduction and hydrothermal doping processes, and the nitrogen-doped graphene carbon nanotube composite hydrogel is obtained. The electronic structure of the carbon material is regulated and controlled through nitrogen atom doping, active sites such as pyridine nitrogen, pyrrole nitrogen and graphite nitrogen are introduced, and the surface wettability and the pseudocapacitance performance are improved. The prepared NGM5 electrode has a high specific surface area (197.91 m < 2 > / g) and a multilevel mesoporous structure. 37.0 wt% H2SO4 is used as an electrolyte to assemble a symmetric supercapacitor, the surface capacity of 498 mF cm <-2 > and the energy density of 69.03 mu Wh cm <-2 > are realized at room temperature of 1 mA cm <-2 >, the energy density of 57.51 mu Wh cm <-2 > is still kept at the extreme low temperature of-60 DEG C, and the capacitance retention rate exceeds 70% after 8000 times of charge and discharge cycles. The preparation process is simple, the cost is low, graphene stacking and carbon nanotube agglomeration are effectively inhibited, the problem of low-temperature performance degradation of a traditional carbon-based material is solved, and the method is suitable for industrial production of a high-power and wide-temperature-range supercapacitor electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage materials, and specifically relates to a preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material, and the application of this material in a low-temperature high-power supercapacitor. Background Art

[0002] Supercapacitors have become a research hotspot in the field of energy storage due to their high power density, fast charge and discharge ability, and long cycle life. However, traditional carbon-based electrode materials (such as graphene and carbon nanotubes) still have significant defects in practical applications: 1. Graphene sheet stacking: resulting in a reduction in specific surface area and hindering the ion transport of the electrolyte; 2. Carbon nanotube aggregation: affecting the dispersibility and conductivity of the material; 3. Poor low-temperature performance: In a low-temperature environment, the ionic conductivity of the electrolyte in a conventional supercapacitor decreases, and the activity of the electrode material decreases, resulting in a significant attenuation of capacitance and power density;

[0003] In the prior art, the electrochemical performance of carbon materials can be improved by heteroatom doping. Therefore, it is of great significance to develop a composite electrode material with high specific surface area, high conductivity, and low-temperature stability. Summary of the Invention

[0004] The present invention provides a nitrogen-doped graphene carbon nanotube composite hydrogel electrode material and its preparation method, and the application of this material in a low-temperature high-power supercapacitor. By optimizing the nitrogen doping process and material structure, the problem of performance decline of traditional carbon materials at low temperatures is solved, while its specific capacitance, power density, and cycle stability are improved.

[0005] A preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material provided by the present invention includes the following steps:

[0006] Step 1, Pretreatment: Dispersing graphene oxide (GO) in ultrapure water, adding 30% hydrogen peroxide, stirring at 90 °C for 5 hours, and centrifuging and washing to prepare a 2 mg / mL HGO dispersion. Treating multi-walled carbon nanotubes (MWCNTs) with a mixed acid of concentrated nitric acid and sulfuric acid (volume ratio 2:3) for 4 hours, and centrifuging and washing to prepare a 4 mg / mL s-MWCNTs dispersion.

[0007] Step 2, Preparation of composite hydrogel: Mixing HGO and s-MWCNTs at a volume ratio of 2:1, ultrasonically dispersing for 30 minutes; adding urea (mass ratio to the composite material 500:1), heating at 90 °C for 8 hours to form a self-assembled hydrogel; transferring the hydrogel to a reaction kettle, and performing a hydrothermal reaction at 180 °C for 12 hours to complete nitrogen doping.

[0008] Step 3: Electrode forming: Immerse the hydrogel in 37 wt% sulfuric acid electrolyte for solvent replacement; cut it into gel sheets with a thickness of 2.5 mm, and press them under a pressure of 2 MPa for 5 minutes to obtain the self-supporting electrode NGM5.

[0009] For the electrode material processed by the above method, specific capacitance: 1 mA / cm 2 The capacitance reaches 498 mF / cm under the following current density 2 ; Energy density: 0.5 mW / cm 2 The power density is 69.03 μWh / cm 2 ; Low-temperature adaptability: It still maintains an energy density of 57.51 μWh / cm at -60 °C 2 ; Cycle stability: The capacitance retention rate is > 70% after 8000 charge and discharge cycles. It is applicable to extreme low-temperature environments (-60 °C to 25 °C); no binder and current collector are required, which simplifies the device assembly process; it can be mass-produced with low cost. Brief Description of the Drawings

[0010] Figure 1 This is the technical roadmap of the present invention;

[0011] Figure 2 This is the SEM image of Example 1;

[0012] Figure 3 This is the energy-power density diagram of Example 1;

[0013] Figure 4 This is the SEM image of Comparative Example 1;

[0014] Figure 5 This is the energy-power density diagram of Comparative Example 1; Detailed Embodiments

[0015] The technical solutions of the present invention will be further described below in conjunction with the embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered within the protection scope of the present invention. For the process equipment or devices not specifically noted in the following embodiments, conventional equipment or devices in the art are used. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well-known to those skilled in the art.

[0016] Example 1

[0017] Pretreatment step: Prepare 300 mg of graphene oxide (GO) powder, add 90 ml of ultrapure water and mix, then perform dispersion treatment for 10 min. After ultrasonic treatment, add the oxidant to the system. The mixed oxidant is used. Stir magnetically at 90 °C for 5 h. Then, the prepared porous graphene oxide is centrifuged once at a rotational speed of 8000 r / min by a centrifuge to wash the H2O2 in the mixed system. The obtained thick liquid is ultrasonically treated by an ultrasonic cell disruptor for 10 min, and finally a 2 mg / mL HGO dispersion is prepared. Functionalize MWCNTs by an acid treatment method. Take 0.4 g of MWCNTs in a beaker, add 20 mL of concentrated nitric acid and 30 mL of sulfuric acid mixed solution, and stir magnetically at 70 °C for 4 h. After stirring, centrifuge the solution once at a rotational speed of 8000 r / min by itself, and wash with water 3 times. After drying the prepared carbon nanotubes, a 4 mg / mL s-MWCNT dispersion is prepared.

[0018] Hydrogel synthesis step: Pipette 4 mL of liquid from the 4 mg / mL s-MWCNT dispersion, and then pipette 8 mL of liquid from the 2 mg / mL HGO dispersion. Mix the two liquids in a 20 mL sample bottle and disperse for 30 min. Then add 10 g of urea to the dispersion, shake evenly and place in an oven at 90 °C for 8 h. During this period, the graphene-carbon nanotube hydrogel will gradually self-assemble into a black cylindrical shape through urea reduction. Subsequently, transfer the hydrogel to a reaction kettle and place it in an oven at 180 °C for hydrothermal doping for 12 h. Take out the reacted hydrogel and immerse it in 37.0 wt.% H2SO4 electrolyte for solvent replacement.

[0019] Electrode pressing step: After complete replacement, cut a small piece of the hydrogel and sandwich it between two smooth graphene sheets, and press it at a pressure of 2 MPa for 5 min. Then peel off the graphene sheets on both sides to obtain an independently supported nitrogen-doped graphene-carbon nanotube composite electrode.

[0020] After testing, the specific surface area of the doped electrode is 197.91 m 2 g -1 , when the current density is 1 mA cm -2 , the electrode material exhibits the best areal capacitance of 498 mF cm -2 , and its energy density is 69.03 μWh cm -2 . When the power density rises to 100 mW cm -2 , at -40 °C and -60 °C, its energy density can still reach 22.22 μWh cm -2 and 16.67 μWh cm -2 .

[0021] Example 2

[0022] Pretreatment step: Prepare 300 mg of graphene oxide (GO) powder, add 90 ml of ultrapure water and mix, then perform dispersion treatment for 10 min. After ultrasonic treatment, add the oxidant to the system. The mixed oxidant is used. Stir magnetically at 90 °C for 5 h, and then centrifuge the prepared porous graphene oxide once at a rotation speed of 8000 r / min to wash the H2O2 in the mixed system. The obtained thick liquid is ultrasonically treated with an ultrasonic cell disruptor for 10 min, and finally a 2 mg / mL HGO dispersion is prepared. Functionalize MWCNTs by an acid treatment method. Take 0.4 g of MWCNTs in a beaker, add 20 mL of concentrated nitric acid and 30 mL of sulfuric acid mixed solution, and stir magnetically at 70 °C for 4 h. After stirring, centrifuge the solution once at a rotation speed of 8000 r / min, and wash with water 3 times. Dry the prepared carbon nanotubes and then prepare a 4 mg / mL s-MWCNT dispersion.

[0023] Hydrogel synthesis step: Pipette 4 mL of liquid from the 4 mg / mL s-MWCNT dispersion, and then pipette 8 mL of liquid from the 2 mg / mL HGO dispersion. Mix the two liquids in a 20 mL sample bottle and disperse for 30 min. Then add 8 g of urea to the dispersion, shake well and place in an oven at 90 °C for 8 h. During this period, it will gradually self-assemble into a black cylindrical graphene carbon nanotube hydrogel through urea reduction. Subsequently, transfer the hydrogel to a reaction kettle and hydrothermally dope it in an oven at 180 °C for 12 h. Take out the reacted hydrogel and immerse it in 37.0 wt.% H2SO4 electrolyte for solvent replacement.

[0024] Electrode pressing step: After complete replacement, cut a small piece of the hydrogel and sandwich it between two smooth graphene sheets, and press it at a pressure of 2 MPa for 5 min. Then peel off the graphene sheets on both sides to obtain an independently supported nitrogen-doped graphene carbon nanotube composite electrode.

[0025] After testing, the specific surface area of the doped electrode is 197.91 m 2 g -1 , when the current density is 1 mA cm -2 , the electrode material exhibits the best areal capacity of 423 mF cm -2 , and its energy density is 48.75 μWh cm -2 . When the power density rises to 100 mW cm -2 , at -40 °C and -60 °C, its energy density can still reach 15.45 μWh cm -2 and 12.79 μWh cm -2 [[ID=2,6]].

[0026] Comparative Example 1

[0027] Pretreatment step: Prepare 300 mg of graphene oxide (GO) powder, add 90 ml of ultrapure water, mix, and perform dispersion treatment for 10 min. After ultrasonic treatment, add the oxidant to the system. The mixed oxidant is used. Stir magnetically at 90 °C for 5 h. Then, the prepared porous graphene oxide is centrifuged once by a centrifuge at a speed of 8000 r / min to wash the H2O2 in the mixed system. The obtained thick liquid is ultrasonically treated by an ultrasonic cell disruptor for 10 min, and finally, a 2 mg / mL HGO dispersion is prepared. Functionalize MWCNTs by an acid treatment method. Take 0.4 g of MWCNTs in a beaker, add 20 mL of a mixed solution of concentrated nitric acid and 30 mL of sulfuric acid, and stir magnetically at 70 °C for 4 h. After stirring, centrifuge the solution once by itself at a speed of 8000 r / min and wash it three times with water. Dry the prepared carbon nanotubes and prepare a 4 mg / mL s-MWCNT dispersion.

[0028] Hydrogel synthesis step: Pipette 4 mL of liquid from the 4 mg / mL s-MWCNT dispersion, and then pipette 8 mL of liquid from the 2 mg / mL HGO dispersion. Mix the two liquids in a 20 mL sample bottle, disperse for 30 min, add 60 mg of ascorbic acid, and heat in an oven at 90 °C for 8 h. During this period, it will gradually self-assemble into a black cylindrical graphene carbon nanotube hydrogel through urea reduction. Take out the reacted hydrogel and immerse it in a 37.0 wt.% H2SO4 electrolyte for solvent replacement.

[0029] Electrode pressing step: After complete replacement, cut a small piece of the hydrogel and sandwich it between two smooth graphene sheets, and press it at a pressure of 2 MPa for 5 min. Then peel off the graphene sheets on both sides to obtain an independently supported graphene carbon nanotube composite electrode.

[0030] After testing, the specific surface area of the doped electrode is 76.84 m 2 g -1 , when the current density is 1 mA cm -2 , the electrode material exhibits the best areal capacitance of 275 mF cm -2 , and its energy density is 36.74 μWh cm -2 . When the power density rises to 100 mW cm -2 , at -40 °C and -60 °C, its energy density can reach 8.76 μWh cm -2 and 9.62 μWh cm -2 respectively.

Claims

1. A preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material, characterized in that, Including the following steps: Pretreatment step: Prepare 300 mg of graphene oxide (GO) powder, add 90 ml of ultrapure water, mix, and perform dispersion treatment for 10 min. After ultrasonic treatment, add the oxidant to the system, using a mixed oxidant, stir magnetically at 90 °C for 5 h, and then centrifuge the prepared porous graphene oxide once at a rotation speed of 8000 r / min to wash the H2O2 in the mixed system. The obtained thick liquid is then ultrasonically treated with an ultrasonic cell disruptor for 10 min, and finally a 2 mg / mL HGO dispersion is prepared. Functionalize MWCNTs by an acid treatment method. Take 0.4 g of MWCNTs in a beaker, add 20 mL of a mixed solution of concentrated nitric acid and 30 mL of sulfuric acid, and stir magnetically at 70 °C for 4 h. After stirring, centrifuge the solution once at a rotation speed of 8000 r / min, and wash with water three times. Dry the prepared carbon nanotubes and prepare a 4 mg / mL s-MWCNT dispersion. Hydrogel synthesis step: Pipette 4 mL of liquid from the 4 mg / mL s-MWCNTs dispersion, and then pipette 8 mL of liquid from the 2 mg / mL HGO dispersion. Mix the two liquids in a 20 mL sample bottle and disperse for 30 min. Then add 10 g of urea to the dispersion, shake evenly, and place in an oven at 90 °C for 8 h. During this period, through urea reduction, it will gradually self-assemble into a black cylindrical graphene-carbon nanotube hydrogel. Subsequently, transfer the hydrogel to a reaction kettle and perform hydrothermal doping in an oven at 180 °C for 12 h. Take out the reacted hydrogel and immerse it in a 37.0 wt.% H2SO4 electrolyte for solvent replacement. Electrode pressing step: After complete replacement, cut a small piece of the hydrogel and sandwich it between two smooth graphene sheets, and press it at a pressure of 2 MPa for 5 min. Then peel off the graphene sheets on both sides to obtain an independently supported nitrogen-doped graphene-carbon nanotube composite electrode.

2. The preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material according to claim 1, wherein The mixed oxidant contains hydrogen peroxide and sulfuric acid.

3. The preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material according to claim 1, characterized in that, In the pretreatment step and the hydrogel synthesis step, the dispersion method is ultrasonic fragmentation in an ultrasonic cell disruptor.

4. The preparation method of a nitrogen-doped graphene carbon nanotube high-power composite electrode material according to claim 1, wherein, In the electrode pressing step, the thickness of the cut small piece of hydrogel is about 2.5 mm and the mass is about 5 mg.

5. The tablet electrode prepared by the method for preparing a nitrogen-doped graphene carbon nanotube high-power composite electrode material according to claim 1, wherein, The specific surface area of the electrode is 197.91 m 2 g -1 . When the current density is 1 mA cm -2 , the electrode material exhibits the best areal capacitance of 498 mF cm -2 , and its energy density is 69.03 μWh cm -2 . When the power density rises to 100 mW cm -2 , at -40 °C and -60 °C, its energy density can still reach 22.22 μWh cm -2 and 16.67 μWh cm -2 respectively.

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