A method for preparing a carbon nanotube / chemically transformed graphene / polyaniline composite film for a flexible solid-state supercapacitor

Abstract

The application discloses a preparation method of a carbon nanotube / chemical conversion graphene / polyaniline composite film for a flexible solid-state supercapacitor. First, graphene oxide is moderately reduced to prepare chemical conversion graphene (CCG) with partial reduction and high oxidation activity. Then, a three-dimensional network structure is constructed by adding carbon nanotubes (CNT) to the CCG intercalation to obtain a composite material CNT / CCG with a larger specific surface area and more active sites. Polyaniline is introduced into the CNT / CCG composite material through in-situ polymerization to obtain a carbon nanotube / chemical conversion graphene / polyaniline composite film (CNT / CCG / PANi). The electrochemical test results show that the specific capacitance of the CNT / CCG / PANi is 706 mF cm ‑2 at a current density of 0.1 mA cm ‑2 , and the specific capacitance is still 78% of the original value after 3000 cycles at 1 mA cm ‑2 . The energy density of the flexible supercapacitor prepared by using the CNT / CCG / PANi composite electrode material is as high as 245 mW cm ‑2 , and the power density is 124 mWh cm ‑2 . The flexible solid-state supercapacitor with the CNT / CCG / PANi electrode has a potential application prospect as an energy storage device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer material preparation, and particularly relates to a method for obtaining carbon material chemical conversion graphene by controlling reaction time to partially reduce graphene oxide. BACKGROUND

[0002] Supercapacitors are a new type of energy storage device between traditional capacitors and chemical power sources, which have the advantages of high specific capacitance, short charging time, long service life, good temperature characteristics, and green environmental protection. In today's society, with the increasing application of portable and wearable electronic devices in various fields such as intelligent devices, micro robots, medical monitoring, rehabilitation and motion detection, there is a growing demand for small, light, safe, mechanically durable, and electrochemically excellent flexible energy storage and conversion devices. Under this background, flexible supercapacitors have won people's favor due to their advantages of excellent flexibility, high safety, strong cycle performance and the like under different degrees of mechanical deformation. Flexible supercapacitors have bright application prospects in the fields of consumer electronics, solar energy power generation systems, smart grid systems, new energy vehicles, industrial energy-saving systems, pulse power systems and the like. The core component of the flexible supercapacitor is the electrode, and various electrode materials applied to supercapacitors include carbon materials, conductive polymers, metal oxides and their composite materials, among which carbon materials are considered to be one of the most promising and widely used electrode materials due to their good physical and chemical stability, wide source and good electrical conductivity.

[0003] Carbon materials have flexible structures, including one-dimensional (1D) carbon nanotubes (CNTs) and two-dimensional (2D) graphene, which have been applied in many fields such as catalysis, batteries and fuel cells. More importantly, carbon materials are suitable for building flexible supercapacitors due to their large surface area, high electrical conductivity and good chemical and mechanical stability; graphene is an exceptionally conductive form of carbon, consisting of single carbon atom planes arranged in a repeating two-dimensional hexagonal lattice. Using various graphene (graphene nanoplatelets, graphene oxide, porous graphene, etc.) as components, high-density carbon materials with controllable porous structures and high volumetric capacitance and good rate performance are obtained. Carbon nanotubes are essentially tubes formed by rolled graphene sheets, and carbon nanotubes have various geometric structures, only differing in thickness, length and layer number, have high specific surface area and excellent electrical conductivity, and carbon nanotubes have high freedom in surface modification functionalization. The present application realizes the establishment of a 3D carbon network structure by combining chemical conversion graphene with carbon nanotubes, which is conducive to the construction of pore structure, improves the specific surface area, and thus enhances the performance in energy storage.

[0004] The conductive polymers mainly include polyaniline (PANi), polypyrrole (PPy), polythiophene and derivatives thereof. As a pseudo-capacitive material, they have simple synthesis, good environmental stability, good conductivity and high pseudo-capacitance. Polyaniline is a conductive polymer, which has been widely studied and applied due to the characteristics of easy availability of raw materials, simple synthesis process, good chemical and environmental stability, etc. As a pseudo-capacitive material, it is applied to the preparation of electrode materials. The electrode material made of pure carbon material has excellent performance and cycle stability. However, the capacitance is still far lower than the estimated theoretical value. The conductive polymer stores and transports charges through reversible oxidation-reduction process. In the oxidation process, ions are transferred to the polymer main chain, while in the reduction process, ions are released into the solution. This makes the specific capacitance of the material larger, because the charging and discharging occurs in the whole body of the material, not just the surface phenomenon like metal oxide electrode materials. Therefore, they actually show higher specific capacitance than metal compounds, but due to the lack of stable redox sites or mechanical degradation caused by swelling and shrinking of the conductive polymer during ion intercalation / deintercalation process, which leads to poor cycle stability. The combination with carbon material can effectively improve the energy density of the composite material. In order to further pursue high capacitance, the conductive polymer has been developed and incorporated as a separate electrode. Not only the integrity of the carbon material can be ensured, but also the specific capacitance of the carbon material can be further improved, so that the carbon material has better electrochemical performance when used as an electrode material of supercapacitor. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a preparation method of carbon nanotube / chemically converted graphene / polyaniline composite film for flexible solid-state supercapacitor. By controlling the volume fraction of chemically converted graphene solution and carbon nanotube solution and the polymerization time of polyaniline, the establishment of 3D carbon material network structure and the introduction of pseudo-capacitive material are realized to optimize the electrochemical performance of the composite electrode.

[0006] The purpose of the present application is realized by the following technical scheme: a method for preparing carbon nanotube / chemically converted graphene / polyaniline film, the specific steps are as follows:

[0007] (1) a certain amount of graphite powder, nitrate and strong oxidizing agent are completely dissolved in deionized water for ice bath;

[0008] (2) a certain concentration of H2O2 solution is slowly added to the aqueous solution obtained in step (1) under mechanical stirring, and it is stirred at 500 rpm for 30 minutes; centrifuge several times with DI until the ion concentration is <10, to obtain black-brown solid;

[0009] (3) the black-brown solid obtained in step (2) is freeze-dried to obtain black product and ground; the black powder is formulated into 0.5mg·ml-1 Solution, and the multi-walled carbon nanotube is also prepared into a 0.5mg·ml -1 Solution, and the two solutions are mixed in proportion, heated and filtered into a film.

[0010] (4) The composite material obtained in step (3) is immersed in a certain amount of aniline solution, and after adding an oxidizing agent in an ice bath at 0°C, polymerization is carried out for 4 hours to obtain a carbon nanotube / chemically converted graphene / polyaniline (CNT / CCG / PANi) composite film.

[0011] The nitrate in step (1) is, but not limited to, NaNO3.

[0012] The oxidizing agent in step (1) is KMnO4.

[0013] The black powder in step (3) is graphene oxide (GO).

[0014] In step (3), the volume ratio of GO to CNT solution is 20:(2-10).

[0015] The oxidizing agent in step (4) is ammonium persulfate.

[0016] The beneficial effects of the present application are:

[0017] (1) Reduced graphene oxide (rGO) has excellent mechanical and electrochemical properties, however, the oxygen-containing functional groups possessed by rGO have low catalytic activity, which seriously affects its application in electrode materials. The method prepares chemically converted graphene (CCG) with higher oxidation activity by partially reducing graphene oxide.

[0018] (2) By constructing a 3D network structure, more electron transport channels are provided, and the electrochemical performance of the material is optimized. By adjusting the ratio of the chemically converted graphene dispersion and the carbon nanotube dispersion, the 3D network structure of the carbon material is effectively controlled, thereby improving the performance of the electrode material.

[0019] (3) The polymerization of aniline is introduced into the CCG / CNT material, and the CNT / CCG / PANi composite electrode material obtained has the characteristics of low reaction resistance and high stability, which not only ensures the integrity of the carbon material, but also further introduces a pore structure to form a multi-level pore structure to improve the specific capacitance of the carbon material, so that it has better electrochemical performance as an electrode material for supercapacitors. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1Scanning electron microscope images of Comparative Example 1, Example 1, Example 2, Example 3, Example 4; wherein (a-c) are Comparative Example 1; (d-f) are Example 1; (g-i) are Example 2; (j-l) are Example 3; (m-o) are Example 4; Figure 2 Galvanostatic charge-discharge curves, cyclic voltammograms, specific capacitance and impedance plots of Comparative Example 1, Example 1, Example 2, Example 3, Example 4; wherein:

[0021] a: galvanostatic charge-discharge curves; b: cyclic voltammograms; c: specific capacitance; d: impedance plots. DETAILED DESCRIPTION

[0022] The application is further described below in connection with specific embodiments but this application is not limited to only these embodiments.

[0023] Example 1

[0024] To a flask containing 5.0 g of graphite powder (99%) and 8 g of NaNO3(99.0%) was added 160 ml of H2SO4(98%); it was stirred at 250 rpm for 30 minutes. Next, the flask was placed in an ice bath (0°C) and 30 g of KMnO4was added slowly in portions and stirring was continued for 30 minutes; then, the solution was heated at 40°C for 24 hours. After the reaction, 200 ml of deionized water (DI) was slowly added to the mixture under magnetic stirring. Then, 150 ml of H2O2was slowly added to the suspension, converting the manganese oxide to manganese sulfate. The suspension was centrifuged at 10,000 rpm in portions, the solid was collected and 1000 ml of 5% HC1 was added; it was stirred at 500 rpm for 30 minutes. It was centrifuged several times with DI until the ionic concentration of the solution was <10. The GO was obtained as a black-brown solid and was subjected to lyophilization and ground into a powder. The obtained GO powder was prepared as a 0.5 mg ml -1 Dispersion. The CCG / CNT film used as an independent electrode was first prepared by a method of heating and filtering into a film from a stable CCG and CNT dispersion (0.5 mg ml -1 ) (CCG dispersion was dosed at 20 ml, and the volume of the CNT dispersion was 2 ml). The CCG / CNT film was cut into 1 x 1 cm 2The CCG / CNT dispersion solution was then immersed in 150 mL of 1.0 M aqueous HC1 solution containing 250 μL of aniline monomer. The solution was stored in an ice bath for 2 hours to allow the aniline monomer to be completely absorbed by the CCG / CNT film. Then, 10 mL of 1.0 M aqueous HC1 solution containing 150 mg of ammonium persulfate (APS) was poured into the above mixture solution and polymerization was carried out in an ice bath for 4 hours. After the polymerization was completed, the carbon nanotube / chemically converted graphene / polyaniline composite film (CNT / CCG / PANi) was completely washed with 1 M HC1 and deionized water.

[0025] Example 2: The specific experimental steps were the same as Example 1, and the ratio of the prepared CCG / CNT dispersion solution was 20:4.

[0026] Example 3: The specific experimental steps were the same as Example 1, and the ratio of the prepared CCG / CNT dispersion solution was 20:6.

[0027] Example 4: The specific experimental steps were the same as Example 1, and the ratio of the prepared CCG / CNT dispersion solution was 20:8.

[0028] Table 1 Data of the porous carbon materials prepared under different conditions

[0029]

[0030] The morphology characteristics of the prepared different samples of Comparative Example 1, Example 1, Example 2, Example 3 and Example 4 were observed by SEM. Figure 1 The scanning electron microscope images of the CNT / CCG / PANi films with the same CNT dispersion solution mass but different PANi in-situ polymerization times (1, 2, 4 and 6 hours) are shown. It can be clearly seen that both PANi and CNT are uniformly distributed on the CCG film. This uniform distribution can be attributed to the strong chemical bonds formed on the CCG surface by the aromatic aniline molecules through π-π interactions and electrostatic forces between aniline and other heteroatoms. However, the size and structure of PANi / CNT on the surface of the CCG film present different morphologies. Specifically, as the polymerization time is prolonged, the size of PANi / CNT also increases. As shown in FIG. 2, as the polymerization time increases from 0 hours to 4 hours, more PANi / CNT can be observed to be loaded on the composite film. However, when the polymerization time reaches 6 hours, PANi / CNT begins to connect with each other, forming a dense spatial network that can hinder the movement of electrons. Although PANi provides the composite film with pseudo-capacitance, an excess of loading can result in a lack of redox active sites, thereby destroying the network structure. When the polymerization time of aniline is 4 hours, the morphological structure of the composite film reaches the optimum. In this time period, the PANi / CNT on the film is evenly distributed and forms a three-dimensional interconnected network structure, maximizing the pseudo-capacitance and structural integrity. Figure 1 The scanning electron microscope images of the CNT / CCG / PANi films with the same CNT dispersion solution mass but different PANi in-situ polymerization times (1, 2, 4 and 6 hours) are shown. It can be clearly seen that both PANi and CNT are uniformly distributed on the CCG film. This uniform distribution can be attributed to the strong chemical bonds formed on the CCG surface by the aromatic aniline molecules through π-π interactions and electrostatic forces between aniline and other heteroatoms. However, the size and structure of PANi / CNT on the surface of the CCG film present different morphologies. Specifically, as the polymerization time is prolonged, the size of PANi / CNT also increases. As shown in FIG. 2, as the polymerization time increases from 0 hours to 4 hours, more PANi / CNT can be observed to be loaded on the composite film. However, when the polymerization time reaches 6 hours, PANi / CNT begins to connect with each other, forming a dense spatial network that can hinder the movement of electrons. Although PANi provides the composite film with pseudo-capacitance, an excess of loading can result in a lack of redox active sites, thereby destroying the network structure. When the polymerization time of aniline is 4 hours, the morphological structure of the composite film reaches the optimum. In this time period, the PANi / CNT on the film is evenly distributed and forms a three-dimensional interconnected network structure, maximizing the pseudo-capacitance and structural integrity.

[0031] The electrode material of Example 3 with the best electrochemical properties was subjected to electrochemical tests, and the CV and GCD thereof are shown in Figure 2 (a) and Figure 2 (b), Figure 2 (a) is the CV curve at a scan rate from 5 mV s -1 to 100 mV s -1 It can be found that, as the current density increases, the CV curves all have a pair of redox peaks, and the shapes keep good similarity, indicating that the electrode redox reaction is stable, and the capacitance keeps good stability, and the GCD curves Figure 2 (b) can also draw the same conclusion as the CV curves, as the current density increases, all the GCD curves have a typical battery-type electrode material charge-discharge platform, and the curve shape is not found to be deformed obviously. In addition, the charge-discharge platform potentials under different current densities are also different. According to the GCD curves, the specific capacitance of the electrode of Example 3 is calculated to be 706 mF cm -2 when the current density is 0.1 mA cm -2 When the current density is increased to 2 mA cm -2 , the capacitance retention rate of the electrode of Example 3 is 48%, which further proves the excellent rate performance of the electrode. Different CNT / CCG mass ratios will lead to different morphologies, Figure 2 (c) shows the change of the specific capacitance of the electrode materials of Example 1, Example 2, Example 3 and Example 4 under different current densities. Among them, the specific capacitance of Example 3 is the highest, and when the current density is increased to 20 times, the capacitance retention rate thereof is also the highest. Figure 2 (d) shows the EIS diagrams of the electrode materials of Comparative Example 1, Example 1, Example 2, Example 3 and Example 4. The charge transfer resistance and the internal resistance of the CNT / CCG / PANi 3-4 electrode material are the smallest, indicating that its electrochemical performance is the best.

[0032] The above only describes the preferred embodiments of the present application, and any changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a carbon nanotube / chemically transformed graphene / polyaniline composite film for a flexible solid-state supercapacitor, characterized by, Comprising the following steps: (1) graphite powder, nitrate and strong oxidant are completely dissolved in deionized water for ice bath; (2) H2O2 solution was slowly added to the aqueous solution obtained in step (1) under mechanical stirring, stirring at 500 rpm for 30 minutes; centrifuged several times with deionized water until the ionic concentration of the solution was <10 mg·L -1 , to obtain black-brown solid; (3) the black-brown solid obtained in step (2) is freeze-dried to obtain a black product and ground; The black powder was formulated into 0.5 mg·ml -1 solution; in the same way multi-walled carbon nanotubes were formulated into 0.5 mg·ml -1 solution, after mixing the two solutions in the right proportions, heating and filtering into a film. (4) the film obtained in step (3) is immersed in aniline solution and ice bathed at a temperature of 0°C, and after adding an oxidant, polymerization is carried out for 4 hours to obtain a carbon nanotube / chemically converted graphene / polyaniline composite film; The nitrate in step (1) comprises NaNO3; The strong oxidant in step (1) comprises KMnO4; The black powder in step (3) is graphene oxide, and the volume ratio of graphene oxide solution to multi-walled carbon nanotube solution is 20:(2-8).

2. The method of claim 1, wherein: The oxidant in step (4) comprises ammonium persulfate.

3. The use of the composite film prepared by the method of any one of claims 1-2 in the preparation of a flexible solid-state supercapacitor.

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