CN112017869A - A kind of self-supporting flexible composite film and preparation method thereof - Google Patents

Abstract

The invention relates to a self-supporting flexible composite film and a preparation method thereof, belonging to the field of supercapacitor electrode materials. The self-supporting flexible composite film of the present invention includes mixing pseudocapacitive materials and carbon materials in an aqueous solution by means of physical electrostatic adsorption, and then ultrasonically obtaining a uniform mixture of pseudocapacitive materials/carbon materials, and then mixing the pseudocapacitive materials/carbon materials The uniform mixed solution is vacuum filtered to obtain a pseudocapacitive material/carbon material composite material; the obtained pseudocapacitive material/carbon material composite material is heat-treated at 550 ℃-650 ℃ in a tube furnace under an ammonia atmosphere to perform nitrogen doping, and carbon The material is reduced under heat treatment at 550°C-650°C to finally obtain the self-supporting flexible composite film. The preparation method of the self-supporting flexible composite film of the invention realizes the removal of the conductive agent and the binder, fully utilizes the advantages of the molybdenum trioxide material and the graphene material, and has a good application prospect.

Description

A kind of self-supporting flexible composite film and preparation method thereof

technical field

The invention relates to a self-supporting flexible composite film and a preparation method thereof, belonging to the field of supercapacitor electrode materials.

Background technique

Supercapacitor electrode materials are usually composed of three parts: active material, conductive agent and binder. Due to the extremely low conductivity of the binder, the performance of the electrode material will be significantly reduced. How to remove the conductive agent and binder from the electrode? Material removal is a major direction of current research. Active materials play the most important role in electrode materials. In the selection of electrode active materials, mainly carbon materials with electric double layer energy storage mechanism, conductive polymers with pseudocapacitive energy storage mechanism, metal oxides, and metal sulfides. and other materials. Among them, the electric double layer material mainly realizes energy storage through the adsorption of positive and negative charges. Since this physical adsorption process only occurs on the surface of the electrode material, the energy density of this type of material is limited by the specific surface area of the material; pseudocapacitive materials Energy storage is achieved through a highly reversible redox reaction between electrolyte ions and electrode materials. This reaction can not only occur on the surface of the electrode material, but also the electrolyte ions can penetrate deep into the electrode material to react with it. Therefore, pseudocapacitive materials usually have higher energy density.

The traditional supercapacitor electrode materials are bulk solid materials. In order to further meet the needs of flexible wearable electronic devices, the electrode materials of supercapacitors are constantly developing towards flexibility and light weight. Flexible electrode materials for supercapacitors are currently mainly divided into two categories, flexible substrate structure electrodes and self-supporting flexible electrodes. Flexible substrate electrodes are electrode materials prepared on a flexible, stretchable or compressible flexible substrate, and the substrate is used as a deformation carrier. In the process of causing the deformation of the electrode material, the flexible substrate, as the main bearing part of the stress, largely alleviates the damage to the electrode material and keeps the electrode material stable in performance, but the substrate material often affects the electrode material. its own performance. Self-supporting flexible electrodes do not need to add additional substrate materials, which can greatly reduce the influence of other materials on the electrode material itself, and at the same time give full play to the advantages of the electrode material itself, improve the quality of the flexible electrode and improve the overall performance of the device. Self-supporting flexible electrodes are mainly prepared by chemical vapor deposition or vacuum filtration. Usually, the main electrode materials are one-dimensional nanowires and two-dimensional nanosheet structures. Similar nanomaterials are conducive to the formation of self-supporting thin film materials.

SUMMARY OF THE INVENTION

In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a self-supporting flexible composite film and a preparation method thereof, which have the advantages of simple process, flexible self-supporting, excellent electrochemical performance and the like.

To achieve the above object, the technical scheme adopted in the present invention is:

A preparation method of a self-supporting flexible composite film, comprising the following steps:

(1) mixing the pseudocapacitive material and the carbon material by physical means to obtain a mixed solution;

(2) vacuum-filtering the solution mixed with the pseudocapacitive material and the carbon material to obtain the pseudocapacitive material/carbon material composite material;

(3) The obtained pseudocapacitive material/carbon material composite material is heat-treated at 550°C-650°C in a tube furnace in an ammonia gas atmosphere to perform nitrogen doping, and the carbon material is reduced under heat treatment at 550°C-650°C, and finally the obtained The self-supporting flexible composite film.

Due to its unique pseudocapacitive energy storage mechanism, metal oxide materials have a larger theoretical specific capacitance and are often used as pseudocapacitive materials. The preparation of the material into a nanowire structure can make the material have a larger specific surface area, which is conducive to improving the material utilization, and the nanowire structure facilitates the formation of self-supporting flexible films. Due to its unique layered structure, α-MoO ₃ material forms an ion channel that is more conducive to the penetration of electrolyte ions into the electrode material, which can greatly improve the capacitance performance of the electrode material. Graphene oxide powder can be reduced to reduced graphene oxide material (rGO) after heat treatment. Graphene material has excellent electrical conductivity and mechanical properties. In composite materials, reduced graphene oxide can significantly improve the electron transfer rate, so Improve the rate capability of electrode materials. In addition, the presence of graphene material also greatly enhances the mechanical flexibility of the electrode material.

Preferably, the pseudocapacitive material is a metal oxide material.

Preferably, the pseudocapacitive material is selected from α-MoO ₃ having a layered structure.

Preferably, the α-MoO ₃ is a nanowire material.

Preferably, the α-MoO ₃ is prepared by a hydrothermal method.

Nanomaterials prepared by hydrothermal method tend to have higher purity, good dispersibility, good and controllable crystal shape, and low production cost.

Preferably, the carbon material is graphene oxide powder (GO).

Preferably, the physical method of mixing is to disperse the pseudocapacitive material in deionized water and then add a polydiene dimethyl ammonium chloride solution to make the surface of the pseudocapacitive material positively charged; and then add the carbon material dispersion to the pseudocapacitor In the material dispersion, the pseudocapacitive material and the carbon material are adsorbed by electrostatic action, and the ultrasonic wave is uniform.

This electrostatic adsorption interaction can make the pseudocapacitive material and the carbon material more uniformly composite, and form a microstructure in which the carbon material evenly coats the pseudocapacitive material.

Preferably, the nitrogen doping conditions are as follows: heat treatment at 550°C-650°C in an ammonia gas atmosphere, a heating rate of 2-5°C/min, a holding time of 30-120 minutes, and a natural cooling to room temperature after the heat treatment. .

Using this method for nitrogen doping, the process is simple, and nitrogen atoms can be uniformly doped into the MoO3 crystal structure, thereby realizing the improvement _of the electrical conductivity _of the MoO3 nanowire.

Compared with the prior art, the present invention has the following beneficial effects: (1) the process is simple, and a self-supporting flexible composite film is obtained by simple vacuum filtration and heat treatment; (2) the raw materials are environmentally friendly and will not pollute the environment (3) The electrochemical performance is superior, which has great advantages compared with the previously reported self-supporting flexible composite film materials.

Description of drawings

Figure 1 is the preparation process of the self-supporting flexible composite film of the present invention; wherein, (a) is the flow chart of the MoNO/rGO film material, and (b) is the actual picture of the MoO ₃ /GO composite film material.

Fig. 2 is the scanning electron microscope (SEM) diagram of α _- MoO under different magnifications in the present invention; wherein, (a) is 1k times magnification, (b) is 5k times magnification, (c) is 13k times magnification, (d) is a magnification of 30k.

FIG. 3 is an X-ray diffraction (XRD) pattern of α-MoO ₃ in the present invention.

Figure 4 (ad) is the characterization SEM image of the MoO ₃ /GO self-supporting flexible composite film in the present invention after heat treatment at 550 ℃-650 ℃ in ammonia gas, (e) is the X-ray energy dispersive analysis (EDS) image , (f) is a transmission electron microscope (TEM) image.

Fig. 5 is the electrochemical test result of MoNO/rGO flexible self-supporting composite film in 1M H ₂ SO ₄ aqueous electrolyte according to the present invention; wherein (a) is the cyclic voltammetry curve (CV curve) obtained under different scanning rates, (b) is the constant current charge-discharge curve at different current densities, (c) is the curve of area specific capacitance with current density, and (d) is the electrochemical impedance spectroscopy (EIS) test.

Detailed ways

In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Traditional supercapacitor electrode materials are bulk solid materials. In order to further meet the needs of flexible wearable electronic devices, supercapacitor electrode materials are constantly developing towards flexibility and light weight. The flexible substrate electrode is to prepare the electrode material on a flexible, stretchable or compressible flexible substrate, and use the substrate as a deformation carrier, but the substrate material often affects the performance of the electrode material itself. The self-supporting flexible electrode does not need to add additional substrate materials, which can greatly reduce the influence of other materials on the electrode material itself, and at the same time give full play to the advantages of the electrode material itself, improve the quality of the flexible electrode and improve the overall performance of the device. The invention provides a self-supporting flexible composite film in order to solve the deficiencies in the prior art.

Example 1

An embodiment of the preparation method of the self-supporting flexible composite film of the present invention, the preparation method of the self-supporting flexible composite film described in this embodiment is:

( ₁ ) Preparation of α-MoO : the molybdenum powder and the hydrogen peroxide solution are uniformly stirred in a certain proportion and then transferred to the reaction kettle, the reaction kettle is placed in the oven, and reacted at a reaction temperature of 180 ° C for 3 days, the reaction After the end, the reaction product was filtered and thoroughly washed with deionized water and absolute ethanol, and dried under vacuum at 70 °C for 12 h.

(2) Preparation of MoO ₃ /GO composite film: Dissolve an appropriate amount of α-MoO ₃ nanowires in deionized water. After stirring evenly, 0.5 ml of polydiene dimer was added dropwise during continuous stirring. based on ammonium chloride solution (PDDA) to positively charge the surface of α _- MoO3 nanowires. Excess PDDA was removed by centrifugation, washing and redispersion. After that, a certain amount of GO powder was weighed and added to the aqueous solution, and then ultrasonically dispersed with a probe sonicator to obtain a 1 mg/mL uniformly dispersed GO aqueous solution. Then, the previously prepared aqueous solution of positively charged MoO3 nanowires was added dropwise to the above ₁ mg/mL aqueous solution of negatively charged GO under the condition of sonication, and self _- assembled MoO3 was formed due to electrostatic interaction. /GO nanocomposite aqueous solution. After further ultrasonication, the MoO ₃ /GO nanocomposite aqueous solution obtained above was vacuum filtered through a filter membrane with a pore size of 220 nm, washed with deionized water for several times, and the membrane after suction filtration was placed in a freeze dryer. After freezing for 15 min, the MoO ₃ /GO film was finally removed from the filter membrane and dried under vacuum at 60 °C. Figure 1(b) is the actual picture of the MoO ₃ /GO composite film, and the diameter of the film is about 4 cm.

(3) Preparation of MoNO/rGO thin film: The obtained MoO ₃ /GO thin film was placed in a tube furnace for heat treatment at 550°C in an ammonia atmosphere, and the heating rate was 5°C/min; holding time: 120 minutes, the heat treatment was over After that, let the tube furnace cool down naturally and take out the sample.

Example 2

An embodiment of the preparation method of the self-supporting flexible composite film of the present invention, please refer to FIG. 1 for its process. The difference between the preparation method of the self-supporting flexible composite film in this embodiment and Embodiment 1 is that in this embodiment , the procedure of setting up the tube furnace in the preparation of step (3) MoNO/rGO film is as follows: heat treatment at 600°C in an ammonia atmosphere, the heating rate is 3°C/min, and the holding time is 80 minutes.

Example 3

An embodiment of the preparation method of the self-supporting flexible composite film of the present invention, the preparation method of the self-supporting flexible composite film described in this embodiment is different from the embodiment 1 in that: in this embodiment, step (3) MoNO/ In the preparation of rGO thin films, the procedure of setting the tube furnace is to perform heat treatment at 650 °C in an ammonia atmosphere, the heating rate is 2 °C/min, and the holding time is 30 minutes.

Please refer to Figure 2. Figure 2 is the SEM image of the α-MoO ₃ nanowires. It can be seen from the figure that the α-MoO ₃ nanowires are as long as several tens of microns, and the ultra-long α-MoO ₃ nanowires are flexible self-supporting films. The preparation of α-MoO ₃ provides the preconditions that through vacuum filtration, the α-MoO3 nanowires will be firmly entangled together to form a flexible film with good mechanical properties.

Please refer to Figure 3. Figure 3 is the XRD pattern of α-MoO ₃ nanowires. The XRD spectrum obtained by scanning is in good agreement with the PDF card of α-MoO ₃ , which indicates that the nanowire material we prepared is α-MoO ₃ .

Please refer to Figure 4, which is a characterization diagram of MoO ₃ /GO after heat treatment in ammonia gas. After high temperature annealing, the graphene oxide is fully reduced, and the nanowires still maintain the original structure and morphology after heat treatment, and the reduced graphene oxide is uniformly dispersed on the surface of the nanowires, forming a good conductive network, which greatly accelerates the electronic The transmission rate in the electrode material is beneficial to the improvement of the rate performance of the electrode material. Figure 4(f) is the TEM image of the MoNO/rGO composite film. It can be seen from the figure that although the composite film was ultrasonically dispersed before TEM analysis, the MoNO nanowires and rGO were still well combined, and the rGO was uniform. dispersed on the surface of MoNO nanowires, which is consistent with the previous SEM image analysis. Figure 4(e) is the EDS spectrum of the MoNO/rGO composite film, which proves that the composite film prepared by us contains Mo, N, O and C elements, and the Cu element comes from the copper mesh used in the TEM test.

Please refer to Figure 5, which demonstrates the electrochemical performance of the obtained thin film material. Among them, the CV curve of (a) proves that the MoNO/rGO material has good electrochemical performance. When the scan rate is increased from 5mV/s to 200mV/s, the CV curve has always maintained a very complete rectangle without distortion and deformation. , which indicates that the electrode material has good electrochemical reversibility. Figure 5(b) shows the constant current charge-discharge (GCD) curves of the MoNO/rGO self-supporting flexible composite film electrode at different current densities. It can be seen from the figure that the GCD curve has a symmetrical triangular feature, and the voltage varies with the charge-discharge time. The relationship is almost linear, indicating that this electrode material has good rate capability. At the same time, no obvious IR drop was observed in the discharge curve, which indicates that the transfer of electrons and the migration of electrolyte ions are very rapid. Figure 5(c) shows the calculated area specific capacitance of the electrode material as a function of current density, and its area specific capacitance is as high as 303 mF/cm ^{2 under the discharge current density of 2 mA/cm 2 .} With the further increase of the current density, the area specific capacitance decreases. The main reason may be that with the increase of the current density, the redox reaction on the electrode surface consumes a large amount of ions, which leads to the formation of the electrolyte near the electrode surface. The ion concentration of the electrolyte decreases, and the ion diffusion rate in the electrolyte is limited, and the ion concentration near the electrode surface cannot be balanced in time, resulting in concentration polarization. The charge transfer on the capacitor lags the corresponding voltage, causing a drop in capacitance. To further understand the kinetics of electrolyte ions and electrons during the electrochemical reaction, we tested the electrochemical impedance spectroscopy of the electrode material (Fig. 5(d)). From the measured electrochemical impedance spectroscopy results, the analysis can be carried out from the following three perspectives, namely:

(1) The intercept of the intersection of the X axis and the high frequency region indicates that the total equivalent series resistance (ESR) of the entire circuit is relatively small, about 0.1Ωcm ² ;

(2) The semicircular arc with a smaller radius at the mid-high frequency region indicates a smaller interfacial charge transfer resistance (R _ct ) between the electrode material and the electrolyte;

(3) In the low frequency region, the real part and imaginary part of the AC impedance curve are almost vertical, indicating that the electrode material has good capacitance performance.

Please refer to Table 1 to compare the area specific capacitance of the prepared MoNO/rGO electrode material with some other electrode materials reported so far.

Table 1 Comparison of the area specific capacitance of MoNO/rGO electrode material with that of some other electrode materials reported so far

As shown in Table 1, at a higher current density than other composite materials, the MoNO/rGO electrode material prepared by us can still maintain a large area specific capacitance, which shows that the composite film material prepared by us has the existence of performance. relatively obvious advantages.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should The technical solutions of the present invention may be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims (9)

1. A self-supporting flexible composite film and a preparation method thereof are characterized by comprising the following steps:

(1) mixing the pseudocapacitance material and the carbon material in a physical mode to obtain a mixed solution;

(2) carrying out vacuum filtration on a solution obtained by mixing the pseudocapacitance material and the carbon material to obtain a pseudocapacitance material/carbon material composite material;

(3) and carrying out heat treatment on the obtained pseudo-capacitance material/carbon material composite material at 550-650 ℃ in a tubular furnace under the atmosphere of ammonia gas for nitrogen doping, and reducing the carbon material at 550-650 ℃ under the heat treatment to finally obtain the self-supporting flexible composite film.

2. The method of claim 1, wherein the pseudocapacitive material is a metal oxide material.

3. The method of claim 2, wherein the metal oxide material is α -MoO with a layered structure₃。

4. The method of claim 3, wherein the α -MoO is in the form of a film₃Is a nanowire material.

5. The self supporting flexible composite sheet of claim 4Method for producing a membrane, characterized in that the alpha-MoO₃Is prepared by a hydrothermal method.

6. The method of claim 1, wherein the carbon material is graphene oxide powder.

7. The preparation method of the self-supporting flexible composite film according to claim 1, wherein the physical mixing is to disperse the pseudocapacitance material in deionized water and then add polydienedimethylammonium chloride solution to make the surface of the pseudocapacitance material positively charged; and adding the carbon material dispersion liquid into the pseudocapacitance material dispersion liquid, adsorbing the pseudocapacitance material and the carbon material through electrostatic interaction, and performing ultrasonic homogenization.

8. The method for preparing the self-supporting flexible composite film according to claim 1, wherein the nitrogen doping conditions are as follows: carrying out heat treatment at 550-650 ℃ in ammonia atmosphere, wherein the heating rate is 2-5 ℃/min, the heat preservation time is 30-120 min, and naturally cooling to room temperature after the heat treatment is finished.

9. A self-supporting flexible composite film prepared by the method of any one of claims 1 to 8.

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