CN113593932B

CN113593932B - Preparation method of supercapacitor based on two-dimensional carbon material and product thereof

Info

Publication number: CN113593932B
Application number: CN202110762124.3A
Authority: CN
Inventors: 冯光; 莫唐明; 王祯祥
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2021-07-06
Filing date: 2021-07-06
Publication date: 2023-03-24
Anticipated expiration: 2041-07-06
Also published as: CN113593932A

Abstract

The invention belongs to the related technical field of supercapacitors and discloses a preparation method of a supercapacitor based on a two-dimensional carbon material and a product thereof. The preparation method comprises the following steps: s1, selecting porous graphite alkyne as a matrix, and doping a non-metallic element in the matrix to enable the porous graphite alkyne to become a conductor; doping a non-metal element in the matrix means that non-metal atoms are used for replacing carbon atoms in the matrix; the non-metal element is one of boron, nitrogen, oxygen or sulfur; the doping mode is quadrivalent doping; the porous graphite alkyne is one of hydrogen substituted graphite monoalkyne, hydrogen substituted graphite diyne or halogen substituted graphite alkyne in the porous graphite alkyne; and S2, forming the supercapacitor by taking the conductive porous graphite alkyne in the step S1 as an electrode and the ionic liquid as an electrolyte. By the invention, the problem of low energy density of the super capacitor is solved.

Description

Preparation method of supercapacitor based on two-dimensional carbon material and product thereof

Technical Field

The invention belongs to the related technical field of super capacitors, and particularly relates to a preparation method of a super capacitor based on a two-dimensional carbon material and a product thereof.

Background

The super capacitor has the advantages of high power density, high charging and discharging speed and long cycle life, but the energy density is lower compared with that of a battery. Increasing its energy density without decreasing its power density can expand the application range of supercapacitors. At present, three-dimensional nano porous carbon materials such as activated carbon, carbide derived carbon and the like are generally used as electrodes of super capacitors to improve the energy density of the super capacitors. But because of the disordered structure of the carbon electrode, the ion channel is complicated in a winding way, and the power density of the super capacitor is reduced. Therefore, development of novel supercapacitor electrode materials is necessary.

The porous graphite alkyne is a two-dimensional porous carbon material, has the advantages of regular pore structure, accurate regulation and control of pore diameter, large specific surface area and the like, has potential application to the electrode of the supercapacitor, but has low conductivity so as to limit the application; in the aspect of electrolyte, the room-temperature ionic liquid is a low-melting-point liquid completely composed of anions and cations, has the advantages of high voltage window (usually more than 3.5V), stable electrochemical performance, wide working temperature range and the like, and is very suitable for super capacitor electrolyte. Therefore, the conductivity of the two-dimensional porous graphdine is improved, and the supercapacitor with high energy density and high power density can be designed by combining the ionic liquid.

Disclosure of Invention

Aiming at the defects or the improvement requirements of the prior art, the invention provides a preparation method of a supercapacitor based on a two-dimensional carbon material and a product thereof, and solves the problem of low energy density and power density of the supercapacitor.

To achieve the above objects, according to one aspect of the present invention, there is provided a method for manufacturing a supercapacitor based on a two-dimensional carbon material, the method comprising the steps of:

s1, selecting porous graphite alkyne as a matrix, and doping a non-metallic element in the matrix to enable the porous graphite alkyne to become a conductor;

and S2, forming the supercapacitor by taking the conductive porous graphite alkyne in the step S1 as an electrode and the ionic liquid as an electrolyte.

Further preferably, in step S1, the doping of the non-metal element in the matrix means that the non-metal element is used to replace the carbon element in the matrix.

Further preferably, the method for doping the non-metal element in the matrix is adsorption doping and lattice doping. Further preferably, in step S1, the non-metal element is one of boron, nitrogen, oxygen or sulfur.

Further preferably, the doping manner is tetravalent doping.

Further preferably, in step S1, after doping the non-metal element in the porous graphdiyne, a density functional theory is further adopted to optimize the porous graphdiyne structure doped with the non-metal element, so as to ensure that the porous graphdiyne structure doped with the non-metal element is a conductor. .

Further preferably, when the doped element is boron, the mass fraction of the doped element is 3.7-22.6%; when the doped element is nitrogen, the mass fraction is 4.7% -28%; when the doped element is oxygen, the mass fraction is 5.4-30%; when the doped element is sulfur, the mass fraction is 10.2% -46.4%.

Further preferably, in step S2, the ionic liquid is one or more of imidazolium ionic liquid, pyridinium ionic liquid, quaternary ammonium salt ionic liquid and quaternary phosphonium salt ionic liquid.

Further preferably, in step S1, the porous graphdiyne is one of hydrogen-substituted graphdiyne, and halogen-substituted graphdiyne in the porous graphdiyne.

According to another aspect of the invention, the super capacitor prepared by the preparation method is provided.

Generally, compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the porous graphite alkyne adopted in the invention is a two-dimensional ordered porous structure, compared with a three-dimensional disordered porous electrode material, the two-dimensional pore channel can shorten the transmission path of ions and accelerate the charging speed of a super capacitor, thereby obtaining higher power density; compared with the common graphite alkyne, the porous graphite alkyne can obtain a larger specific surface area value due to the pore structure, and according to an energy formula: e =1/2ACV ² (E is energy, A is specific surface area, C is capacitance, V is working voltage), a larger energy density can be obtained; the capacity and the conductivity of the electrode can be improved by doping non-metallic elements in the porous graphite alkyne; the ionic liquid is used, because the organic solvent can obtain a larger voltage window compared with the aqueous solution, and the energy density of the obtained super capacitor is larger according to an energy density formula;

2. in the invention, the porous graphite alkyne is doped with the non-metallic elements because valence electrons of carbon atoms in the original porous graphite alkyne are all involved in forming covalent bonds, so that carriers are lacked to participate in conduction, and the conductivity of the original porous graphite alkyne is very low; boron, nitrogen, oxygen or sulfur atoms can be doped to introduce holes or free electrons, and the holes or the free electrons can be used as carriers to participate in electric conduction, so that the doped porous graphite alkyne becomes a conductor;

3. the inventor dopes non-metal elements such as boron, nitrogen, oxygen or sulfur, because the outermost layer of boron has one electron less than carbon, holes can be formed by adopting quadrivalent doping; nitrogen has one more electron than carbon, oxygen or sulfur has two more electrons than carbon, and the adoption of tetravalent doping of nitrogen, oxygen or sulfur elements can form free electrons, so that the conductivity of the porous graphite alkyne can be improved, and the porous graphite alkyne is converted into a conductor from a semiconductor after tetravalent doping;

4. when the mass fraction of the doped elements is selected, the lowest value for ensuring the mass rheumatism is that each graphdine unit is doped with a non-metallic element, and the porous graphdine can be ensured to be converted into a conductor only if the value is greater than the lowest value; the maximum value is that three sites on each benzene ring are substituted by non-metallic elements, and if excessive doping is carried out, the graphdine structure is unstable, and the maximum value is given so that the conductivity and the performance of the supercapacitor are good enough, and higher proportion is difficult to realize in practice.

Drawings

FIG. 1 is a flow diagram of the design of a supercapacitor constructed in accordance with a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of the molecular structure of a raw hydrogen-substituted graphdine without doping;

fig. 3 is a schematic structural diagram of hydrogen-substituted grapyne molecules doped with boron or nitrogen in different proportions, wherein (a) is a schematic structural diagram of nitrogen doping at site No. 1, (b) is a schematic structural diagram of nitrogen doping at site No. 2, (c) is a schematic structural diagram of nitrogen doping at high proportion, (d) is a schematic structural diagram of boron doping at site No. 1, (e) is a schematic structural diagram of boron doping at site No. 2, and (f) is a schematic structural diagram of boron doping at high proportion, constructed according to a preferred embodiment of the present invention;

FIG. 4 is a graph of the electron state density of virgin hydrogen-substituted graphyne without doping;

FIG. 5 is a graph of hydrogen substituted graphyne electron state densities doped with nitrogen in varying proportions constructed in accordance with a preferred embodiment of the present invention;

FIG. 6 is a diagram of differential capacitance of a supercapacitor made up of an ionic liquid 1-methyl-3-methylimidazolium tetrafluoroborate ([ EMIM ] [ BF4 ]) as an electrolyte with different ratios of nitrogen doped hydrogen substituted graphdiynes as electrodes constructed in accordance with a preferred embodiment of the present invention;

FIG. 7 is a graph of boron element doped hydrogen substituted graphyne electron state densities at different ratios constructed in accordance with a preferred embodiment of the present invention;

FIG. 8 is a schematic diagram of the differential capacitance of a supercapacitor made up of hydrogen substituted graphdiynes doped with boron elements in different proportions as electrodes and ionic liquid [ EMIM ] [ BF4] as electrolyte, constructed in accordance with a preferred embodiment of the present invention;

FIG. 9 is a schematic diagram of the charge time of a supercapacitor with a boron doped hydrogen substituted graphdiyne as the electrode and an ionic liquid [ EMIM ] [ BF4] as the electrolyte as constructed in accordance with a preferred embodiment of the present invention as a function of voltage;

FIG. 10 is a graph of the intra-pore ion transport resistance of a supercapacitor with boron-doped hydrogen-substituted graphdiyne as the electrode and an ionic liquid [ EMIM ] [ BF4] as the electrolyte, as a function of voltage, constructed in accordance with a preferred embodiment of the present invention;

FIG. 11 is a graph of specific mass energy density and power density of a supercapacitor made up of boron doped hydrogen substituted graphdiyne as an electrode and ionic liquid [ EMIM ] [ BF4] as an electrolyte, constructed in accordance with a preferred embodiment of the present invention;

FIG. 12 shows the specific volume energy density and power density of a supercapacitor with boron-doped hydrogen-substituted graphdiyne as an electrode and an ionic liquid [ EMIM ] [ BF4] as an electrolyte.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the respective embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in figure 1, the invention designs a two-dimensional carbon material and ionic liquid super capacitor with high performance. The method comprises the following specific steps:

s1, predicting the crystal structure of porous graphite alkyne under different doping conditions through a density functional theory; the calculation is realized by Vienna ab-initio simulation package software, a Perew-Burke-Ernzerhof exchange correlation function with generalized gradient approximation is adopted, and Grimmer's D dispersion correction is added; the interaction between nuclei and electrons is described by the projection infix wave method; and analyzing the electron state density result to obtain the porous graphite alkyne structure with the conductor property.

S2, taking porous graphite alkyne with different doping elements and different doping proportions as an electrode and ionic liquid as electrolyte, calculating the electric double layer capacitance of the device by using molecular dynamics simulation, calculating the electrode quantum capacitance by using a density functional, calculating the differential capacitance performance of the supercapacitor by combining the electric double layer capacitance and the quantum capacitance, and screening a better doping method.

And S3, performing charge-discharge simulation on the screened doped porous graphite alkyne electrode by using molecular dynamics simulation, amplifying the electrode to a macroscopic device by combining a transmission line model, and calculating the specific mass/specific volume energy density and power density of the device.

The invention will be further illustrated with reference to specific examples.

Example 1

As shown in fig. 2, in this embodiment, hydrogen substituted graphyne is used as a doping target, hydrogen substituted graphyne doped with nitrogen at position No. 1 is used as an electrode, and as shown in (a) of fig. 3, ionic liquid [ EMIM ] [ BF4] is used as an electrolyte.

Fig. 2 is a schematic of a pristine hydrogen-substituted graphdiyne in which the larger atoms are carbon atoms and the smaller atoms are hydrogen atoms. Depending on the position of the carbon atoms, four types of carbon atoms can be distinguished, as indicated by the numbers 1-4 in the figures. This example was performed by doping site No. 1 with nitrogen atoms, and is shown as light gray atoms in the circled circle in fig. 3 (a).

Next we calculate the electron density of states using density functional theory. The results show that, as shown in fig. 4, there is a large band gap (about 1.4 eV) near the fermi level for the undoped pristine hydrogen-substituted graphyne, indicating that the pristine hydrogen-substituted graphyne is a semiconductor and its lower conductivity is not suitable for use as an electrode in a supercapacitor. After doping, as shown in fig. 5, there is a greater distribution of electrons near the fermi level, indicating that the material has been converted from a previous semiconductor to a conductor.

As shown in fig. 6, the differential capacitance was calculated for the original hydrogen-substituted graphdine and the hydrogen-substituted graphdine nitrogen-doped at position No. 1, and it was found that the capacitance value at the negative electrode was low for the original hydrogen-substituted graphdine, which may limit its practical application. The capacitance of the cathode after doping is obviously improved and can reach 184F/g at most near-1V.

This case demonstrates that nitrogen doping of raw graphdiyne can increase its conductivity and improve the capacitive performance of the supercapacitor.

Example 2

As shown in fig. 3 (b), in this example, a hydrogen substituted graphdine in which nitrogen is doped at position No. 2 is used as an electrode, and an ionic liquid [ EMIM ] [ BF4] is used as an electrolyte.

Analysis of the electron density state of site No. 2 shows that site No. 2 doping results similar to site No. 1 doping, with a more electron distribution near the fermi level, as shown in fig. 5, indicating that the material has been converted from a previous semiconductor to a conductor. The capacitance performance is similar to that of the site doping of No. 1, and as shown in FIG. 6, the capacitance of the cathode is obviously improved compared with that of the original hydrogen substituted graphite alkyne.

The case shows that the conductivity of the original graphite alkyne nitrogen doping at different sites can be improved, and the capacitance performance of the super capacitor is improved.

Example 3

As shown in fig. 3 (c), this example dopes hydrogen-substituted graphdiyne with nitrogen element at a higher concentration (28% by mass) at site No. 1 and uses it as an electrode and an ionic liquid [ EMIM ] [ BF4] as an electrolyte.

As shown in fig. 5, analysis of the electron density states indicated a higher proportion of doping with a much greater distribution of electrons near the fermi level, indicating that this material has better conductivity. The capacitance of the negative electrode is obviously improved relative to the low-proportion doping, and as shown in FIG. 6, the maximum capacitance can reach 210F/g.

This case demonstrates that increasing the doping ratio can further increase the porous graphitic alkyne conductivity and further increase the capacitive performance of the supercapacitor.

Example 4

As shown in fig. 2, in this embodiment, hydrogen-substituted graphyne is used as a doping target, and as shown in fig. 3 (d), hydrogen-substituted graphyne doped with boron at the site No. 1 is used as an electrode, atoms in a circle in the figure are boron atoms, and ionic liquid [ EMIM ] [ BF4] is used as an electrolyte.

Similar to nitrogen doping, the electron density results indicate that boron-doped hydrogen substituted graphyne has a more electron distribution near the fermi level, as shown in fig. 7, indicating that this material has been converted from a previous semiconductor to a conductor. When different from nitrogen doping, nitrogen doping shifts electrons toward the cathode, and boron doping shifts electrons toward the anode. Therefore, compared with nitrogen doping, boron doping is used as an electrode, and the capacitance of the positive electrode is larger than that of the graphite alkyne doped with nitrogen (170F/g can be obtained at 1V), as shown in FIG. 8, but the negative electrode is slightly smaller than that of the graphite alkyne doped with nitrogen.

This case illustrates that boron doping of the pristine graphdine can also improve its conductivity and improve the capacitive performance of the supercapacitor.

Example 5

As shown in fig. 3 (e), in this example, hydrogen substituted graphyne doped with boron at position No. 2 is used as an electrode, and ionic liquid [ EMIM ] [ BF4] is used as an electrolyte.

Analysis of the electron density state of boron element at site No. 2 shows that boron doping at site No. 2 has similar results to boron doping at site No. 1, and has more electron distribution near the Fermi level, as shown in FIG. 7, which shows that the material has been converted from a previous semiconductor into a conductor, as shown in FIG. 8, and the capacitance performance is also similar to that of boron doping at site No. 1.

This case demonstrates that doping with pristine graphitic boron-alkyne at different sites can increase its conductivity and improve the capacitive performance of the supercapacitor.

Example 6

As shown in fig. 3 (f), in this example, hydrogen-substituted graphdiyne was doped with boron at a higher concentration (22.6% by mass) at site No. 1, and used as an electrode and an ionic liquid [ EMIM ] [ BF4] as an electrolyte.

Analysis of the electron density states indicated a higher proportion of the doping with a much greater electron distribution near the fermi level, as shown in figure 7, indicating that this material has better conductivity. The capacitance of the material at the positive and negative electrodes is improved more obviously relative to the doping with a low proportion, and as shown in fig. 8, the maximum capacitance can reach 200F/g at both the positive and negative electrodes.

In combination with cases 1-6, it is shown that high proportion of boron element can obtain better capacitance performance when doped in positive and negative electrodes, and the method is a better scheme as an electrode. Then, high proportion boron element doped hydrogen replaces graphite alkyne to be used as an electrode, ionic liquid [ EMIM ] [ BF4] is used as electrolyte, and the electrode is established to have the size diameter of 16mm and the thickness of 165 mu m; a supercapacitor device with a separator diameter of 16mm and a thickness of 25 μm.

The charging process is calculated by molecular dynamics simulation, the device performance is calculated by simulink simulation by using a transmission line model, as shown in fig. 9, the charging time is 15-45 s, and the charging of the three-dimensional porous carbon electrode needs dozens of minutes.

As shown in FIG. 10, the ion transport resistance in the hole of the supercapacitor device was calculated to be 8-30. Omega. Cm ² 。

As shown in FIG. 11, the energy density and power density of the supercapacitor device at room temperature were calculated to be 58.71Wh/kg and 70.5kW/kg, respectively, at 3V applied voltage and 98.50Wh/kg and 71.87kW/kg, respectively, at 4V applied voltage, and to be 60.86Wh/L and 44.41kW/L, respectively, at 4V applied voltage, as shown in FIG. 12. The specific mass energy density is far higher than that of a commercial super capacitor by 4-9Wh/kg (the specific volume energy density is 5-7 Wh/L), the specific mass power density is about 20kW/kg at most (the specific volume power density is about 1.8kW/L at most), and the specific mass energy density also far exceeds the Chinese 2025 manufacturing requirement (30 Wh/kg and 5 kW/kg)

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A preparation method of a supercapacitor based on a two-dimensional carbon material is characterized by comprising the following steps:

s1, selecting porous graphite alkyne as a matrix, and doping a non-metallic element in the matrix to enable the porous graphite alkyne to become a conductor; the non-metal element is boron or nitrogen, and the doping mode is quadrivalent doping; after doping the non-metal elements in the porous graphdiyne, optimizing a porous graphdiyne structure doped with the non-metal elements by adopting a density functional theory so as to ensure that the porous graphdiyne structure doped with the non-metal elements is a conductor; the porous graphite alkyne is hydrogen-substituted graphite diyne in the porous graphite alkyne, and the molecular structure of the non-doped original hydrogen-substituted graphite alkyne is as follows:

wherein the larger atoms are carbon atoms and the smaller atoms are hydrogen atoms;

2. The method for preparing a supercapacitor based on a two-dimensional carbon material according to claim 1, wherein in step S1, the doping of the matrix with the non-metal element means replacing carbon element in the matrix with the non-metal element.

3. The method for preparing the supercapacitor based on the two-dimensional carbon material, according to claim 2, wherein the doping of the nonmetal elements in the matrix is performed by adsorption doping and lattice doping.

4. The method for preparing the supercapacitor based on the two-dimensional carbon material according to claim 1, wherein when the doped element is boron, the mass fraction of the doped element is 3.7-22.6%; when the doped element is nitrogen, the mass fraction is 4.7-28%.

5. The method for preparing the supercapacitor based on the two-dimensional carbon material according to claim 1, wherein in the step S2, the ionic liquid is one or more of imidazolium ionic liquid, pyridinium ionic liquid, quaternary ammonium salt ionic liquid and quaternary phosphonium salt ionic liquid.

6. A supercapacitor prepared by the method of any one of claims 1 to 5.