CN111477893A - Electrospun carbon nanofiber composite material with functional components distributed in longitudinal gradient manner, preparation method of electrospun carbon nanofiber composite material and application of electrospun carbon nanofiber composite material in vanadium battery - Google Patents
Electrospun carbon nanofiber composite material with functional components distributed in longitudinal gradient manner, preparation method of electrospun carbon nanofiber composite material and application of electrospun carbon nanofiber composite material in vanadium battery Download PDFInfo
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Abstract
The invention relates to an electrospun carbon nanofiber composite material with functional components distributed in a longitudinal gradient manner, a preparation method thereof and application thereof in a vanadium battery. The electrospun carbon nanofiber composite material is a positive carbon nanofiber material and a negative carbon nanofiber material which are prepared by an electrostatic spinning process; the positive carbon nanofiber material is characterized in that functional components are distributed in a longitudinal gradient mode, wherein the top layer is iridium oxide/PAN, the middle layer is iridium oxide + graphene/PAN, and the bottom layer is graphene/PAN; the cathode carbon nanofiber material is formed by longitudinal gradient distribution of functional components, wherein the top layer is made of metal bismuth/PAN, the middle layer is made of metal bismuth + graphene/PAN, and the bottom layer is made of graphene/PAN. When the electrospun carbon nanofiber composite material prepared by the invention is applied to positive and negative electrode materials of a vanadium battery, the electrochemical reaction polarization and ohmic polarization of the battery can be simultaneously reduced, the energy efficiency and the power density of the vanadium battery are effectively improved, and the electrospun carbon nanofiber composite material is simple and convenient to operate, flexible in design and universal.
Description
Technical Field
The invention relates to the technical field of battery materials and energy storage, in particular to an electrospun carbon nanofiber composite material with longitudinally-gradient-distributed functional components and application thereof in a vanadium battery.
Background
With the continuous development of new energy sources such as wind energy, solar energy and the like, corresponding energy storage matching equipment is paid more and more attention. The vanadium battery belongs to one of flow batteries, and the active substance of the vanadium battery is vanadium ions with different valence states, and the charging and discharging of the battery are completed through the conversion between chemical energy and electric energy. The vanadium battery has larger output power, longer cycle life and good safety, so that the vanadium battery has wide application prospect in the fields of power grid peak shaving and new energy power generation matching energy storage.
The standard electromotive force of a vanadium redox battery is about 1.26V. But the actual terminal voltage is far less than the standard electromotive force due to ohmic drop and electrochemical polarization. By selecting a proper vanadium battery electrode material, the polarization overpotential of the battery can be reduced to a certain extent, the voltage efficiency of the battery is improved, and the performance of the battery is finally improved. An excellent vanadium battery electrode material needs to have good chemical stability and mechanical strength, excellent conductivity and hydrophilic property, and certainly, excellent electrochemical reaction activity. The carbon material with lower cost, such as carbon felt, carbon paper and graphite felt, is widely applied to the field of vanadium battery electrode materials at present. They generally have good mechanical and chemical properties, large porosity, specific surface area and high electrical conductivity; however, the electrochemical activity of the electrode material to vanadium ions is poor, and the hydrophilicity is poor, so that the performance of the vanadium battery is limited.
The activation methods for carbon felt electrode materials mainly include heat treatment, acid treatment, catalyst modification, and the like, but these methods have a limited improvement in electrochemical activity and easily affect the electrical conductivity of the material. In addition, the catalyst modified on the surface of the carbon felt cannot exist stably and is easily washed away by flowing electrolyte, so that the performance of the electrode is reduced, and the circulation stability is reduced.
By utilizing the electrostatic spinning technology, the carbon fiber with the nanometer scale can be prepared, so that the specific surface area of the electrode is greatly increased. In addition, specific functionality can be endowed to the electrode material by introducing functional components into the electrospinning precursor solution, and the functional components are usually embedded into the fiber filaments, so that the bonding force of the two is enhanced. However, the conductivity and the reactivity of the electrode cannot be considered, so that the conductivity of the electrode is lost while the reactivity of the electrode is improved.
Disclosure of Invention
The invention aims to provide an electrospun carbon nanofiber composite material with functional components distributed in a longitudinal gradient manner, and the electrospun carbon nanofiber composite material is applied to positive and negative electrode materials of a vanadium battery, so that the electrochemical reaction activity and the conductivity can be improved, and meanwhile, the oxygen evolution and hydrogen evolution side reaction can be inhibited, the electrochemical polarization and the ohmic polarization are simultaneously reduced, the utilization rate of an electrolyte is improved, the stability of the battery is improved, and the efficiency of the battery is effectively improved.
In order to achieve the purpose, the invention adopts the technical scheme that: an electrospun carbon nanofiber composite material with functional components distributed in a longitudinal gradient manner is a positive carbon nanofiber material and a negative carbon nanofiber material which are prepared by an electrostatic spinning process; the positive carbon nanofiber material is characterized in that functional components are distributed in a longitudinal gradient mode, wherein the top layer is iridium oxide/PAN, the middle layer is iridium oxide + graphene/PAN, and the bottom layer is graphene/PAN; the cathode carbon nanofiber material is formed by longitudinal gradient distribution of functional components, wherein the top layer is made of metal bismuth/PAN, the middle layer is made of metal bismuth + graphene/PAN, and the bottom layer is made of graphene/PAN.
A preparation method of an electrospun carbon nanofiber composite material with longitudinally gradient distributed functional components comprises the following steps:
1) preparation of PAN/DMF electrospinning precursor solution: adding Polyacrylonitrile (PAN) powder into N, N-Dimethylformamide (DMF), and stirring at 80 ℃ for 6-7 h until the Polyacrylonitrile (PAN) powder is completely dissolved to prepare a PAN/DMF electrospinning precursor solution;
2) preparation of anode carbon nanofiber material
2.1) adding chloroiridic acid into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution I;
2.2) adding chloroiridic acid and graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution II;
2.3) adding graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution III;
2.4) sequentially sucking the positive electrode electrospinning precursor solution I, the positive electrode electrospinning precursor solution II and the positive electrode electrospinning precursor solution III into a sample injector of an electrospinning device, and carrying out continuous electrospinning to obtain a positive electrode polyacrylonitrile nanofiber membrane with a top layer of chloroiridic acid + PAN, a middle layer of chloroiridic acid + graphene + PAN and a bottom layer of graphene + PAN, wherein the functional components of the graphene + PAN are distributed in a longitudinal gradient manner;
2.5) pre-oxidation treatment: flattening the obtained positive polyacrylonitrile nano-fiber membrane by using a corundum plate, placing the flattened positive polyacrylonitrile nano-fiber membrane in a tubular furnace, and carrying out heat treatment for 0.5-2 h at the temperature of 250-350 ℃ in the air atmosphere;
2.6) carbonization treatment: heating a tubular furnace to 800-1500 ℃, carrying out heat treatment for 1-5 h in a nitrogen or argon atmosphere, and cooling to obtain a positive carbon nanofiber material with a top layer of iridium oxide/PAN, a middle layer of iridium oxide + graphene/PAN and a bottom layer of graphene/PAN functional components in longitudinal gradient distribution;
3) preparation of negative carbon nanofiber material
3.1) adding bismuth trichloride into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution I;
3.2) adding bismuth trichloride and graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution II;
3.3) adding the graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution III;
3.4) sequentially sucking the negative electrode electrospinning precursor solution I, the negative electrode electrospinning precursor solution II and the negative electrode electrospinning precursor solution III into a sample injector of an electrospinning device for continuous electrospinning to obtain a negative electrode polyacrylonitrile nanofiber membrane with a top layer of bismuth trichloride + PAN, a middle layer of bismuth trichloride + graphene + PAN and a bottom layer of graphene + PAN, wherein functional components of the graphene + PAN are distributed in a longitudinal gradient manner;
3.5) pre-oxidation treatment: flattening the obtained negative polyacrylonitrile nanofiber membrane by using a corundum plate, placing the flattened negative polyacrylonitrile nanofiber membrane in a tubular furnace, and carrying out heat treatment for 0.5-2 hours at the temperature of 250-350 ℃ in the air atmosphere;
3.6) carbonization treatment: heating the tubular furnace to 800-1500 ℃, carrying out heat treatment for 1-5 h in the nitrogen or argon atmosphere, and cooling to obtain the cathode carbon nanofiber material with the top layer of metal bismuth/PAN, the middle layer of metal bismuth + graphene/PAN and the bottom layer of graphene/PAN in longitudinal gradient distribution.
Further, in the preparation method, in the step 1), the PAN/DMF electrospinning precursor solution contains 7-16% of PAN by mass percentage concentration.
Further, in the preparation method, in the step 2.1), the positive electrode electrospinning precursor solution i contains 0.6-2.4% of chloroiridic acid by mass percentage concentration.
Further, in the preparation method, in the step 2.2), the positive electrode electrospinning precursor solution ii contains 0.3 to 1.2% of chloroiridic acid and 0.3 to 1.2% of graphene by mass percentage.
Further, in the preparation method, in step 2.3), the positive electrode electrospinning precursor solution iii contains 0.6-2.4% of graphene by mass percentage concentration.
Further, in the preparation method, in the step 3.1), the negative electrode electrospinning precursor solution i contains 0.6-2.4% of bismuth trichloride according to mass percentage concentration.
Further, in the preparation method, in the step 3.2), the negative electrode electrospinning precursor solution ii contains 0.3-1.2% of bismuth trichloride and 0.3-1.2% of graphene by mass percentage concentration.
Further, in the preparation method, in step 3.3), the negative electrode electrospinning precursor solution iii contains 0.6 to 2.4% of graphene by mass percentage concentration.
Further, in the preparation method, the molecular weight of the polyacrylonitrile PAN is 6-12 ten thousand.
Further, in the preparation method, the graphene has a size of 50-1000 nm, the number of layers is 1-5, and the surface resistance is 500-5000 omega.
Further, in the preparation method, in step 2.4), according to the volume ratio, the positive electrode electrospinning precursor solution iii, the positive electrode electrospinning precursor solution ii, the positive electrode electrospinning precursor solution i, 1, (2-5) and (2-5); in the step 3.4), the negative electrode electrospinning precursor solution III, the negative electrode electrospinning precursor solution II, the negative electrode electrospinning precursor solution I are 1, (2-5) and (2-5) according to the volume ratio.
Further, in the preparation method, the rotating speed of the yarn collector is 100-250 r/min, the voltage is 17-23 kV, the receiving distance is 8-15 cm, the spinning temperature is 20-40 ℃, the spinning humidity is 40-60% RH, and the pushing speed is 10-100 mu L/min.
The electrospun carbon nanofiber composite material with the functional components distributed in the longitudinal gradient manner, which is prepared by the invention, is applied to a vanadium battery as an electrode material.
Further, the method is as follows: the bottom graphene/PAN in the positive carbon nanofiber material is in contact with a current collector in the vanadium battery, and the top iridium oxide/PAN is in contact with a vanadium battery diaphragm; the bottom graphene/PAN layer in the negative carbon nanofiber material is in contact with a current collector in the vanadium battery, and the top metal bismuth/PAN layer is in contact with a vanadium battery diaphragm.
The invention has the beneficial effects that:
1. according to the prepared anode carbon nanofiber material, the top layer is iridium oxide/PAN (polyacrylonitrile), the top layer is a high-activity layer, the middle layer is iridium oxide + graphene/PAN, the middle layer is a transition layer, the bottom layer is graphene/PAN, and the middle layer is a high-conductivity layer, so that the electrode material with functional components distributed in a longitudinal gradient manner is formed; the prepared cathode carbon nanofiber material has a top layer of metal bismuth/PAN (polyacrylonitrile), a high-activity layer, a middle layer of metal bismuth + graphene/PAN, a transition layer and a bottom layer of graphene/PAN, and is a high-conductivity layer, so that the electrode material with functional components distributed in a longitudinal gradient manner is formed.
2. According to the invention, electrostatic spinning is carried out on the electrospinning precursor solution containing polyacrylonitrile with different functional components in sequence, firstly, positive and negative polyacrylonitrile nanofiber membranes with longitudinally gradient distribution of the functional components are obtained, and then, the electrospinning carbon nanofiber composite material with conductivity, reaction activity and side reaction inhibition property in longitudinal distribution can be obtained through pre-oxidation and carbonization treatment.
3. According to the electrospun carbon nanofiber composite material with the longitudinally-gradient-distributed functional components, the metal active components have high reactivity on vanadium ions and inhibition on oxygen evolution and hydrogen evolution side reactions, and the graphene has high conductivity. The electrospun carbon nanofiber composite material with the longitudinally gradient-distributed functional components is applied to vanadium battery electrodes, so that ohmic polarization and electrochemical polarization of the battery can be reduced, oxygen evolution and hydrogen evolution side reactions of positive and negative electrodes can be inhibited, and the battery performance and the electrolyte utilization rate can be effectively improved.
4. According to the invention, when the electrospun carbon nanofiber composite material with the longitudinally gradient distribution of functional components is applied to a vanadium battery electrode, the bottom graphene/PAN of the positive carbon nanofiber material is used as a conductive layer to be in contact with a current collector of the vanadium battery, and the top iridium oxide/PAN is used as a high-activity layer to be in contact with a diaphragm of the vanadium battery; the bottom graphene/PAN of the negative carbon nanofiber material is used as a conducting layer to be in contact with a current collector of the vanadium battery, and the top metal bismuth/PAN is used as a high-activity layer to be in contact with a diaphragm of the vanadium battery; so as to realize effective promotion of electrochemical activity and conductivity and effective inhibition of side reaction.
5. The invention realizes the longitudinal gradient distribution of functional components in the electrode material by utilizing the electrostatic spinning technology, has simple and controllable method and strong designability, and has guiding significance for the design and preparation of other related materials.
Drawings
Fig. 1 is a scanning electron micrograph of a bare carbon nanofiber (a) and a positive electrode carbon nanofiber material (b) prepared in example 1.
Fig. 2a is an electrochemical impedance spectrum of the blank carbon nanofiber and the positive electrode carbon nanofiber material prepared in example 1 in a positive electrode electrolyte.
Fig. 2b is an electrochemical impedance spectrum of the blank carbon nanofiber and anode carbon nanofiber materials prepared in example 1 in an anode electrolyte.
FIG. 3 shows the blank carbon nanofibers and the positive carbon nanofiber material prepared in example 1The charge-discharge curve of a single cell assembled by taking the material and the cathode carbon nanofiber material as the positive electrode and the negative electrode has the current density of 100mA/cm2。
Detailed Description
Example 1
Comparative example preparation of blank carbon nanofiber electrode Material
Polyacrylonitrile (PAN) powder with the molecular weight of 90000 is dissolved in N, N-Dimethylformamide (DMF), and the mixture is magnetically stirred for 5 hours at the temperature of 80 ℃ until the Polyacrylonitrile (PAN) powder is completely dissolved, so that a mixed solution (PAN/DMF solution) of the Polyacrylonitrile (PAN) and the N, N-Dimethylformamide (DMF) with the mass percentage concentration of 12 wt% of the Polyacrylonitrile (PAN) is obtained.
And (2) sucking the PAN/DMF solution into a sample injector of electrostatic spinning equipment, and carrying out electrostatic spinning to obtain the original blank polyacrylonitrile nano-fiber material, wherein the electrostatic spinning conditions comprise that the rotating speed of a filament collector is 100r/min, the voltage between a spray head and the filament collector is 20kV, the distance between the spray head and the filament collector is 14cm, the spinning temperature is 30 ℃, the spinning humidity is 50% RH, the pushing speed is 60 mu L/min, and the spinning time is 3 h.
Flattening the obtained original blank polyacrylonitrile nano-fiber material by using a corundum plate, and placing the flattened blank polyacrylonitrile nano-fiber material in a tubular furnace for pre-oxidation treatment, namely, carrying out heat treatment for 30min at 280 ℃ in air atmosphere. Then subjected to a carbonization treatment, i.e. at N2And (3) carrying out heat treatment at 1000 ℃ for 90min in the atmosphere to obtain the blank carbon nanofiber electrode material.
As shown in a in fig. 1, the diameter of the obtained blank carbon nanofiber electrode material is about 200nm, and the surface is smooth.
(II) preparation of electrospun carbon nanofiber composite material with longitudinally gradient distributed functional components
1. In this example, polyacrylonitrile PAN was used having a molecular weight of 90000. The size of the adopted graphene is 50-1000 nm, the number of layers is 1-5, and the surface resistance is 500-5000 omega.
The electrospun carbon nanofiber composite material with the functional components distributed in the longitudinal gradient manner is a positive carbon nanofiber material and a negative carbon nanofiber material prepared by an electrostatic spinning process; the positive carbon nanofiber material is characterized in that functional components are distributed in a longitudinal gradient mode, wherein the top layer is iridium oxide/PAN, the middle layer is iridium oxide + graphene/PAN, and the bottom layer is graphene/PAN; the cathode carbon nanofiber material is formed by longitudinal gradient distribution of functional components, wherein the top layer is made of metal bismuth/PAN, the middle layer is made of metal bismuth + graphene/PAN, and the bottom layer is made of graphene/PAN.
2. The preparation method comprises the following steps:
1) preparation of PAN/DMF electrospinning precursor solution: adding polyacrylonitrile Powder (PAN) into N, N-Dimethylformamide (DMF), and stirring at 80 ℃ for 6-7 h until the polyacrylonitrile powder is completely dissolved to prepare PAN/DMF electrospinning precursor solution; according to mass percentage, the composite material contains 12 percent of PAN.
2) Preparation of anode carbon nanofiber material
2.1) adding chloroiridic acid into the PAN/DMF electrospinning precursor solution, uniformly dispersing, and obtaining a positive electrode electrospinning precursor solution I (0.6 wt% chloroiridic acid +12 wt% PAN/DMF) by containing 0.6% chloroiridic acid according to the mass percentage concentration;
2.2) adding chloroiridic acid and graphene into the PAN/DMF electrospinning precursor solution, uniformly dispersing, and obtaining a positive electrode electrospinning precursor solution II (0.3 wt% chloroiridic acid, 0.3 wt% graphene and 12 wt% PAN/DMF) by mass percentage concentration, wherein the chloroiridic acid and the graphene are 0.3% by mass percentage;
2.3) adding graphene into the PAN/DMF electrospinning precursor solution, uniformly dispersing, and obtaining a positive electrode electrospinning precursor solution III (0.6 wt% of graphene and 12 wt% of PAN/DMF) according to the mass percentage concentration, wherein the graphene contains 0.6% of graphene;
2.4) sequentially sucking the positive electrode electrospinning precursor solution I, the positive electrode electrospinning precursor solution II and the positive electrode electrospinning precursor solution III into a sample injector of an electrospinning device according to the volume ratio of 1:2:2, and performing continuous electrospinning to obtain a positive polyacrylonitrile nanofiber membrane with a top layer of chloroiridic acid + PAN, a middle layer of chloroiridic acid + graphene + PAN and a bottom layer of graphene + PAN, wherein functional components of graphene and PAN are distributed in a longitudinal gradient manner;
continuous electrostatic spinning, wherein the technological parameters comprise the rotating speed of a filament collector of 100r/min, the voltage of 20kV, the receiving distance of 14cm, the spinning temperature of 30 ℃, the spinning humidity of 50 percent RH and the pushing speed of 60 mu L/min until all three kinds of positive electrode electro-spinning precursor solutions in a sample injector are spun;
2.5) pre-oxidation treatment: flattening the obtained polyacrylonitrile nanofiber membrane of the positive electrode by using a corundum plate, placing the flattened polyacrylonitrile nanofiber membrane into a tubular furnace, and carrying out heat treatment for 30min at 280 ℃ in air atmosphere;
2.6) carbonization treatment: and (3) heating the tubular furnace to 1000 ℃, carrying out heat treatment for 90min in a nitrogen atmosphere, and cooling to obtain the anode carbon nanofiber material with the top layer of iridium oxide/PAN, the middle layer of iridium oxide + graphene/PAN and the bottom layer of graphene/PAN in longitudinal gradient distribution.
As can be seen from b in fig. 1, the introduction of graphene has no significant effect on the fiber diameter, and the three-dimensional network structure of the fiber membrane is not destroyed.
3) Preparation of negative carbon nanofiber material
3.1) adding bismuth trichloride into the PAN/DMF electrospinning precursor solution, dispersing uniformly, and obtaining a negative electrode electrospinning precursor solution I (0.6 wt% of bismuth trichloride and 12 wt% of PAN/DMF) according to the mass percentage concentration and containing 0.6% of bismuth trichloride;
3.2) adding bismuth trichloride and graphene into the PAN/DMF electrospinning precursor solution, dispersing uniformly, and obtaining a negative electrode electrospinning precursor solution II (0.3 wt% of bismuth trichloride, 0.3 wt% of graphene and 12 wt% of PAN/DMF) according to the mass percentage concentration, wherein the bismuth trichloride and the graphene are 0.3% and 0.3% respectively;
3.3) adding graphene into the PAN/DMF electrospinning precursor solution, uniformly dispersing, and obtaining a positive electrode electrospinning precursor solution III (0.6 wt% of graphene and 12 wt% of PAN/DMF) according to the mass percentage concentration, wherein the graphene contains 0.6% of graphene;
3.4) according to the volume ratio, sequentially sucking the negative electrode electrospinning precursor solution I, the negative electrode electrospinning precursor solution II and the negative electrode electrospinning precursor solution III into a sample injector of electrospinning equipment for continuous electrospinning to obtain a negative electrode polyacrylonitrile nanofiber membrane with a top layer of bismuth trichloride + PAN, a middle layer of bismuth trichloride + graphene + PAN and a bottom layer of graphene + PAN, wherein functional components of graphene and PAN are distributed in a longitudinal gradient manner;
the continuous electrostatic spinning process comprises the process parameters of the spinning speed of a spinning receiver of 100r/min, the voltage of 20kV, the receiving distance of 14cm, the spinning temperature of 30 ℃, the spinning humidity of 50% RH and the pushing speed of 60 mu L/min until all three kinds of positive electrode electrospinning precursor solutions in a sample injector are spun.
3.5) pre-oxidation treatment: flattening the obtained negative polyacrylonitrile nano-fiber membrane by using a corundum plate, placing the flattened negative polyacrylonitrile nano-fiber membrane in a tubular furnace, and carrying out heat treatment at 280 ℃ for 30min in air atmosphere;
3.6) carbonization treatment: and (3) heating the tubular furnace to 1000 ℃, carrying out heat treatment for 90min in a nitrogen atmosphere, and cooling to obtain the cathode carbon nanofiber material with the top layer made of metal bismuth/PAN, the middle layer made of metal bismuth + graphene/PAN and the bottom layer made of graphene/PAN functional components in longitudinal gradient distribution.
Example 2 application
(1) Electrochemical impedance spectroscopy test
The carbon nanofiber material of the positive electrode and the carbon nanofiber material of the negative electrode prepared in the second step of the embodiment 1 are used as working electrodes, a saturated calomel electrode is used as a reference electrode, a platinum sheet electrode is used as a counter electrode to form a three-electrode system, and the three-electrode system is respectively arranged at the positive electrode of 0.1M V4++2M H2SO4Electrolyte solution and negative electrode 0.1M V3++2M H2SO4Electrochemical impedance tests were performed in the electrolyte.
And contacting the bottom graphene/PAN in the carbon nanofiber material of the anode with a titanium plate current collector, and contacting the top iridium oxide/PAN with the vanadium electrolyte of the anode. And contacting the bottom graphene/PAN in the negative carbon nanofiber material with a titanium plate current collector, and contacting the top metal bismuth/PAN with a negative electrolyte. Under the same conditions, a blank carbon nanofiber is used as a working electrode for a comparison experiment.
As shown in fig. 2a and fig. 2b, on the composite carbon nanofiber with the gradient distribution of functional components, the charge transfer resistance of the positive and negative electrode reactions is obviously lower than that of the blank carbon nanofiber. The positive and negative vanadium ions have better electrochemical reaction activity on the composite carbon fiber, the electrochemical polarization and the ohmic polarization of the electrode can be effectively reduced, and the utilization rate of the electrolyte is improved.
(2) Single cell charge and discharge test
The positive and negative carbon nanofiber materials prepared in the second step (1) are used as electrode materials to be applied to a vanadium battery.
And contacting the bottom graphene/PAN in the positive carbon nanofiber material with a current collector in the vanadium battery, and contacting the top iridium oxide/PAN with a vanadium battery diaphragm.
And contacting the bottom graphene/PAN in the negative carbon nanofiber material with a current collector in the vanadium battery, and contacting the top metal bismuth/PAN with a vanadium battery diaphragm.
And (3) performing a comparison experiment by taking the blank carbon nanofiber as a positive electrode and a negative electrode.
As shown in fig. 3, the single cell using the composite carbon nanofiber as an electrode showed a lower initial charge voltage and a higher initial discharge voltage, indicating that the cell had a lower polarization overpotential. Meanwhile, the battery capacity is obviously higher than that of a battery taking blank carbon nanofibers as electrodes, which shows that the composite electrode has better electrochemical reaction activity, higher electron transmission capability and inhibition on positive and negative side reactions, thereby effectively improving the utilization rate of the electrolyte of the battery.
Claims (10)
1. An electro-spinning carbon nanofiber composite material with functional components distributed in a longitudinal gradient manner is characterized in that: the electrospun carbon nanofiber composite material is a positive carbon nanofiber material and a negative carbon nanofiber material which are prepared by an electrostatic spinning process; the positive carbon nanofiber material is characterized in that functional components are distributed in a longitudinal gradient mode, wherein the top layer is iridium oxide/PAN, the middle layer is iridium oxide + graphene/PAN, and the bottom layer is graphene/PAN; the cathode carbon nanofiber material is formed by longitudinal gradient distribution of functional components, wherein the top layer is made of metal bismuth/PAN, the middle layer is made of metal bismuth + graphene/PAN, and the bottom layer is made of graphene/PAN.
2. The method for preparing the electrospun carbon nanofiber composite material with the longitudinally gradient distribution of the functional components as claimed in claim 1, which is characterized by comprising the following steps:
1) preparation of PAN/DMF electrospinning precursor solution: adding Polyacrylonitrile (PAN) powder into N, N-Dimethylformamide (DMF), and stirring at 80 ℃ for 6-7 h until the Polyacrylonitrile (PAN) powder is completely dissolved to prepare a PAN/DMF electrospinning precursor solution;
2) preparation of anode carbon nanofiber material
2.1) adding chloroiridic acid into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution I;
2.2) adding chloroiridic acid and graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution II;
2.3) adding graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a positive electrode electrospinning precursor solution III;
2.4) sequentially sucking the positive electrode electrospinning precursor solution I, the positive electrode electrospinning precursor solution II and the positive electrode electrospinning precursor solution III into a sample injector of an electrospinning device, and carrying out continuous electrospinning to obtain a positive electrode polyacrylonitrile nanofiber membrane with a top layer of chloroiridic acid + PAN, a middle layer of chloroiridic acid + graphene + PAN and a bottom layer of graphene + PAN, wherein the functional components of the graphene + PAN are distributed in a longitudinal gradient manner;
2.5) pre-oxidation treatment: flattening the obtained positive polyacrylonitrile nano-fiber membrane by using a corundum plate, placing the flattened positive polyacrylonitrile nano-fiber membrane in a tubular furnace, and carrying out heat treatment for 0.5-2 h at the temperature of 250-350 ℃ in the air atmosphere;
2.6) carbonization treatment: heating a tubular furnace to 800-1500 ℃, carrying out heat treatment for 1-5 h in a nitrogen or argon atmosphere, and cooling to obtain a positive carbon nanofiber material with a top layer of iridium oxide/PAN, a middle layer of iridium oxide + graphene/PAN and a bottom layer of graphene/PAN functional components in longitudinal gradient distribution;
3) preparation of negative carbon nanofiber material
3.1) adding bismuth trichloride into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution I;
3.2) adding bismuth trichloride and graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution II;
3.3) adding the graphene into the PAN/DMF electrospinning precursor solution, and uniformly dispersing to obtain a negative electrode electrospinning precursor solution III;
3.4) sequentially sucking the negative electrode electrospinning precursor solution I, the negative electrode electrospinning precursor solution II and the negative electrode electrospinning precursor solution III into a sample injector of an electrospinning device for continuous electrospinning to obtain a negative electrode polyacrylonitrile nanofiber membrane with a top layer of bismuth trichloride + PAN, a middle layer of bismuth trichloride + graphene + PAN and a bottom layer of graphene + PAN, wherein functional components of the graphene + PAN are distributed in a longitudinal gradient manner;
3.5) pre-oxidation treatment: flattening the obtained negative polyacrylonitrile nanofiber membrane by using a corundum plate, placing the flattened negative polyacrylonitrile nanofiber membrane in a tubular furnace, and carrying out heat treatment for 0.5-2 hours at the temperature of 250-350 ℃ in the air atmosphere;
3.6) carbonization treatment: heating the tubular furnace to 800-1500 ℃, carrying out heat treatment for 1-5 h in the nitrogen or argon atmosphere, and cooling to obtain the cathode carbon nanofiber material with the top layer of metal bismuth/PAN, the middle layer of metal bismuth + graphene/PAN and the bottom layer of graphene/PAN in longitudinal gradient distribution.
3. The preparation method according to claim 2, wherein in the step 1), the PAN/DMF electrospinning precursor solution contains 7-16% of PAN by mass percentage.
4. The preparation method according to claim 2, wherein in the step 2.1), the positive electrode electrospinning precursor solution I contains 0.6-2.4% by mass of chloroiridic acid; in the step 2.2), the positive electrode electrospinning precursor solution II contains 0.3-1.2% of chloroiridic acid and 0.3-1.2% of graphene according to mass percentage concentration; in the step 2.3), the positive electrode electrospinning precursor solution III contains 0.6-2.4% of graphene according to mass percentage concentration.
5. The preparation method according to claim 2, wherein in step 3.1), the negative electrode electrospinning precursor solution I contains 0.6-2.4% of bismuth trichloride by mass percentage; in the step 3.2), the negative electrode electrospinning precursor solution II contains 0.3-1.2% of bismuth trichloride and 0.3-1.2% of graphene according to mass percentage concentration; in the step 3.3), the negative electrode electrospinning precursor solution III contains 0.6-2.4% of graphene according to mass percentage concentration.
6. The preparation method according to claim 2, wherein the molecular weight of the polyacrylonitrile PAN is 6-12 ten thousand; the graphene is 50-1000 nm in size, 1-5 layers in number and 500-5000 omega in surface resistance.
7. The preparation method according to claim 2, wherein in step 2.4), the volume ratio of the positive electrode electrospinning precursor solution III to the positive electrode electrospinning precursor solution II to the positive electrode electrospinning precursor solution I is 1 (2-5) to (2-5); in the step 3.4), the negative electrode electrospinning precursor solution III, the negative electrode electrospinning precursor solution II, the negative electrode electrospinning precursor solution I are 1, (2-5) and (2-5) according to the volume ratio.
8. The preparation method of the polyester filament yarn as claimed in claim 2, wherein the continuous electrostatic spinning in the step 2.4) and the step 3.4) comprises the process parameters of the rotating speed of a filament winder of 100-250 r/min, the voltage of 17-23 kV, the receiving distance of 8-15 cm, the spinning temperature of 20-40 ℃, the spinning humidity of 40-60% RH and the pushing speed of 10-100 mu L/min.
9. The application of the electrospun carbon nanofiber composite with the longitudinal gradient distribution of the functional components as claimed in claim 1 as an electrode material in a vanadium battery.
10. Use according to claim 9, characterized in that the method is as follows: the bottom graphene/PAN in the positive carbon nanofiber material is in contact with a current collector in the vanadium battery, and the top iridium oxide/PAN is in contact with a vanadium battery diaphragm; the bottom graphene/PAN layer in the negative carbon nanofiber material is in contact with a current collector in the vanadium battery, and the top metal bismuth/PAN layer is in contact with a vanadium battery diaphragm.
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