CN114085377A

CN114085377A - Preparation of polyaniline/carbon nanotube composite material and application of polyaniline/carbon nanotube composite material in sodium-based dual-ion battery

Info

Publication number: CN114085377A
Application number: CN202111383159.2A
Authority: CN
Inventors: 焦丽芳; 孙志钦
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2021-11-22
Filing date: 2021-11-22
Publication date: 2022-02-25
Anticipated expiration: 2041-11-22
Also published as: CN114085377B

Abstract

Preparation of polyaniline/carbon nano tube composite material and application in sodium-based double-ion battery. The invention carries out the preparation of polyaniline/carbon nano tube composite material by a simple stirring method, firstly, aniline monomer and carbon nano tube are uniformly dispersed into a mixed solvent containing hydrofluoric acid and hydrochloric acid, and after cooling treatment, oxidant is added for in-situ polymerization. The preparation process is simple and easy to implement, the reaction conditions do not need high temperature and high pressure, the control is easy, and the cost of the adopted raw materials is low, so that the preparation method is suitable for large-scale production. The excellent conductivity and structural stability of the carbon nano tube can be complementary with the high-capacity advantage of polyaniline, and the electrochemical performance of the composite material for storing anions is comprehensively improved through introduction of fluorine and protonation.

Description

Preparation of polyaniline/carbon nanotube composite material and application of polyaniline/carbon nanotube composite material in sodium-based dual-ion battery

Technical Field

The invention belongs to the technical field of sodium-based dual-ion full batteries, and particularly relates to preparation of a positive electrode material, in particular to efficient storage of anions with large volume.

Background

Unlike the traditional rocking chair type metal ion battery, the Double Ion Battery (DIB) can realize high energy/power density output because the anions and cations can participate in the charge transfer reaction of the anode and the cathode at the same time. Due to the large volume of the anions, the structural stability of the positive electrode material is critical for the intercalation/deintercalation of the anions. For example, hexafluorophosphate (PF)₆ ^-) The volume is large, and the storage into the positive active material causes large volume expansion when the positive active material is under the action of an electric field. This significant volume expansion causes rapid performance loss while causing more irreversible electrochemical reactions to occur. To break this limitation, it is important to research a novel positive electrode having high stability, large capacity, and long life.

Disclosure of Invention

The invention aims to solve the problems of low specific capacity of the positive electrode material of the bi-ion battery to the storage of anions, poor reversibility and insufficient chemical kinetics, and provides a preparation method of a polyaniline/carbon nano tube composite material and application of the polyaniline/carbon nano tube composite material in a sodium-based bi-ion battery. Polyaniline has been widely studied as a battery material. The organic conductor has good oxidation-reduction reversibility and high stability, can show different electrochemical properties by using doping means in different modes, and is applied to the positive electrode of the highly reversible double-ion battery. In polyaniline, the protonation of nitrogen is a doping process (n-type doping) that promotes the uniformity of the number of electrons on the polymer chain. When polyaniline is contacted with a halogen acid, some of the nitrogen atoms are protonated, creating a positive charge that moves in the conjugated chain, while halogen anions are doped into the conjugated chain of the polyaniline. At the end of this process, the resulting polymer is in the form of a salt and can significantly affect the cell performance for anion storage. Carbon nanotubes are receiving attention for their excellent electrical conductivity and mechanical strength. When used as a matrix to be compounded with an active material, can bring about a great improvement in properties. Polyaniline is subjected to in-situ polymerization on the surface of the carbon nano tube, and halogen acid is used for effective modification, so that the problems of low specific capacity, poor reversibility and insufficient electrochemical kinetics of the positive electrode material of the double-ion battery can be solved.

The technical scheme of the invention is as follows:

the preparation method of the polyaniline/carbon nanotube composite material comprises the following preparation steps:

(1) firstly, preparing a precursor solution: uniformly dispersing aniline monomer, hydrofluoric acid, hydrochloric acid and carbon nano tubes (with the size of 60-100 nm) into a solvent, stirring and mixing uniformly at room temperature (20-30 ℃) for 5-8 h, and cooling a reaction system to below 5 ℃ in an ice bath.

(2) And adding an oxidant into the dispersion liquid, controlling the temperature of the mixed solution to be 3-5 ℃ in the whole process, and continuously stirring the mixed solution for 6-8 hours after the oxidant is added. After polymerization, the product is filtered and washed until the filtrate is colorless and clear, and is freeze-dried to obtain the final target product polyaniline/carbon nano tube composite material.

In the step, the mass ratio of the aniline monomer to the carbon nano tube is 1: 2-3; the solvent is ultrapure water, and the total volume of the final solution is 100 mL; the molar ratio of the aniline monomer to the hydrofluoric acid to the hydrochloric acid is 1: 10: 5; the oxidant is one of ammonium persulfate, potassium persulfate or sodium persulfate, and the molar ratio of the aniline monomer to the oxidant is 1: 1-1.5.

The invention also provides the application of the polyaniline/carbon nanotube composite material in the sodium-based double-ion battery, and the method comprises the following steps:

(3) assembling the battery: and uniformly mixing the final target product polyaniline/carbon nano tube, conductive carbon black (super P) and Polytetrafluoroethylene (PTFE) in ethanol according to the mass ratio of 7: 2: 1 or 8: 1, and stirring for 1-2 h. After the electrode paste is prepared into uniform electrode paste, evaporating ethanol, rolling the solid into a film, cutting the film into squares of 8 multiplied by 8mm, punching and fixing the squares on the surface of a titanium net, wherein the thickness of the titanium net load electrode is 75-100 mu m, and the diameter of the titanium net is 12 mm. After preparation, the mixture is dried for 2 hours in a vacuum drying oven at 60 ℃. And finally, forming a two-electrode system with sodium metal in a glove box, wherein the battery assembly model is a CR2032 button battery.

The invention has the advantages and beneficial effects that:

the preparation method has the advantages of simple preparation steps, no need of high temperature and high pressure for reaction conditions, easiness in control, low cost of adopted raw materials, suitability for large-scale production and high repeatability. The mixed halogen acid can be doped into the polyaniline conjugated chain in the monomer polymerization process. The acidic environment can provide sufficient hydrogen ions, which is beneficial to the generation of protonated polyaniline and has the effect of greatly improving the specific capacity. Meanwhile, the existence of fluorine ions in the conjugated chain can obviously play a key role in the long cycle life of the electrode. The addition of the carbon nanotube substrate can obviously improve the conductivity of the battery active material, and has a dispersing effect on the conductive polymer, thereby avoiding the agglomeration of the material to a great extent and buffering the problem of volume expansion of the electrode in the charging and discharging processes. The overall composite material exhibits an inter-crosslinked structure, which facilitates rapid kinetics of the anion during charge and discharge. Electrochemical tests show that the prepared material has high specific discharge capacity, excellent cycle stability and coulombic efficiency approaching 100 percent.

Drawings

FIG. 1 shows the IR spectra of the prepared polyaniline and polyaniline/carbon nanotube.

Fig. 2 is a content analysis of each element of the prepared polyaniline/carbon nanotube.

FIG. 3 is a TEM morphology of the prepared polyaniline/carbon nanotubes.

Fig. 4 is a TGA test of the prepared carbon nanotubes, polyaniline and polyaniline/carbon nanotubes.

Fig. 5 is a graph of the rate capability of the prepared polyaniline/carbon nanotube electrode, wherein (a) is a constant current charge-discharge curve of the polyaniline/carbon nanotube electrode under different current densities, and (b) is a graph of the rate of the electrode material.

FIG. 6 shows the cycle life performance of the polyaniline/carbon nanotube prepared, wherein (a) is the polyaniline/carbon nanotube electrode at 0.2 A.g^-1Performance under conditions for 250 weeks of cycling, (b) TEM topography after cycling of the electrode material.

Detailed Description

Example 1

In the step of preparing the polymeric precursor, the size of the carbon nanotube may be 60nm to 100 nm. Before aniline, hydrofluoric acid and hydrochloric acid are added, the mass fraction of the carbon nano tube in the solvent is not more than 15%, and the inventor finds that the composite material is more easily agglomerated and has poor effect when the concentration is higher than the mass fraction.

(1) Preparing a precursor solution: the total volume of the precursor mixed solution is 100mL, hydrofluoric acid, concentrated hydrochloric acid, aniline monomer and carbon nano tubes are uniformly dispersed in ultrapure water, and are mixed and stirred at room temperature (20-30 ℃) for 6 hours. Compared with other temperatures, the temperature range is more beneficial to the electrostatic attraction of the aniline monomer and the carbon tube. After stirring well, it was ice-cooled to reduce its temperature to 5 ℃. The mass ratio of the aniline monomer to the carbon nano tube is 1: 2; the molar ratio of the aniline monomer to the hydrofluoric acid to the hydrochloric acid is 1: 10: 5.

(2) Preparing a polyaniline/carbon nano tube composite material: in the polymerization step for preparing polyaniline/carbon nano tube, ammonium persulfate oxidant is added when the temperature of the precursor solution is reduced to 3 ℃. Researches show that the polymerization at lower temperature is favorable for improving the molecular weight of polyaniline and obtaining the polymer with narrower molecular weight distribution. The molar ratio of the added ammonium persulfate to the aniline monomer is 1: 1. The whole reaction temperature is 3-5 ℃, and the reaction time is 6 h.

Example 2

(1) Preparing a precursor solution: the total volume of the precursor mixed solution is 100mL, hydrofluoric acid, concentrated hydrochloric acid, aniline monomer and carbon nano tubes are uniformly dispersed in ultrapure water, and are mixed and stirred at room temperature (20-30 ℃) for 6 hours. Compared with other temperatures, the temperature range is more favorable for electrostatic attraction of the aniline monomer and the carbon tube. After stirring well, it was ice-cooled to reduce its temperature to 5 ℃. The mass ratio of the aniline monomer to the carbon nano tube is 1: 2; the molar ratio of the aniline monomer to the hydrofluoric acid to the hydrochloric acid is 1: 10: 5.

(2) Preparing a polyaniline/carbon nano tube composite material: in the polymerization step for preparing polyaniline/carbon nano-tube, potassium persulfate oxidant is added when the temperature of the precursor solution is reduced to 3 ℃. The molar ratio of the added potassium persulfate to the aniline monomer is 1.25: 1. The whole reaction temperature is 3-5 ℃, and the reaction time is 6 h.

Example 3

(1) Preparing a precursor solution: the total volume of the precursor mixed solution is 100mL, hydrofluoric acid, concentrated hydrochloric acid, aniline monomer and carbon nano tubes are uniformly dispersed into ultrapure water, and are mixed and stirred at room temperature (20-30 ℃) for 6 h. Compared with other temperatures, the temperature range is more beneficial to the electrostatic attraction of the aniline monomer and the carbon tube. After stirring well, it was ice-cooled to reduce its temperature to 5 ℃. The mass ratio of the aniline monomer to the carbon nano tube is 1: 2; the molar ratio of the aniline monomer to the hydrofluoric acid to the hydrochloric acid is 1: 10: 5.

(2) Preparing a polyaniline/carbon nano tube composite material: in the polymerization step for preparing polyaniline/carbon nano tube, ammonium sodium persulfate oxidant is added when the temperature of the precursor solution is reduced to 3 ℃. The molar ratio of the added sodium persulfate to the aniline monomer is 1.5: 1. The whole reaction temperature is 3-5 ℃, and the reaction time is 6 h.

Assembly of battery

Example 4:

(1) preparing electrode slurry, uniformly mixing the final target product polyaniline/carbon nano tube, conductive carbon black (super P) and Polytetrafluoroethylene (PTFE) in ethanol according to the mass ratio of 7: 2: 1, and stirring for 1 h. After the electrode paste is prepared into uniform electrode paste, ethanol is evaporated to be dry, the solid is rolled into a film, the film is cut into squares of 8 multiplied by 8mm and is punched and fixed on the surface of a titanium mesh, the thickness of the titanium mesh load electrode is 100 mu m, and the diameter of the titanium mesh is 12 mm. After preparation, the mixture is dried for 2 hours in a vacuum drying oven at 60 ℃.

(2) 5mmol NaPF is added into 5mL Propylene Carbonate (PC) as solvent of electrolyte₆. Glass fiber with the diameter of 16mm is used as a diaphragm, and a metal sodium sheet with the diameter of 14mm is used as a counter electrode. The whole process of assembling the CR2032 button cell battery is carried out in a glove box in an argon atmosphere, and the voltage testing range is 2.2-4.2V.

Fig. 1 is an infrared spectrum of polyaniline and polyaniline/carbon nanotube, and the infrared characteristic peaks of the two materials are shown to correspond to each other. At 1600 and 1500cm^-1The positions correspond to stretching vibration of the nitrogen-quinone ring and the nitrogen-benzene ring, respectively. At 1100 and 1300cm simultaneously^-1The protonized imine is corresponded, so that the prepared polyaniline composite material can be proved to have a reduction state, which is beneficial to the improvement of specific capacity.

Fig. 2 is an X-ray energy spectrum analysis (EDS) of the prepared polyaniline/carbon nanotube, from which it can be seen that fluorine is successfully doped into the conjugated main chain after aniline polymerization.

Fig. 3 is a TEM image of polyaniline/carbon nanotubes, which shows that polyaniline is uniformly coated on the surface of the carbon nanotubes and the thickness is about 100 nm.

Fig. 4 is a TGA test of polyaniline/carbon nanotube, and according to the test result, the mass fraction of polyaniline in the polyaniline/carbon nanotube composite material can be calculated to be 78%.

Fig. 5 is a constant current charge and discharge curve (a in fig. 5) of a sodium ion battery assembled with metallic sodium at different current densities. The multiplying power performance of the polyaniline/carbon nano tube shows that the current density is 0.2 A.g^-1The reversible capacity can reach 127 mAh.g^-1(ii) a When the current density increased to 3A g^-1The reversible capacity can still maintain about 75mAh g^-1(b in FIG. 5).

FIG. 6 shows the current density of the prepared polyaniline/carbon nanotube at 0.2 A.g^-1The prepared electrode material shows better cycling stability, namely the coulombic efficiency is more stable after 250 cycles, and the capacity can be maintained at about 101 mAh.g^-1。

Claims

1. The preparation method of the polyaniline/carbon nanotube composite material comprises the following preparation steps:

(1) firstly, preparing a precursor solution: uniformly dispersing hydrofluoric acid, hydrochloric acid, aniline monomer and carbon nano tubes into a solvent, uniformly mixing, then mixing and stirring at room temperature, wherein the treatment time is 5-8 h, and after uniformly stirring, carrying out ice bath to reduce the temperature to below 5 ℃;

(2) and (2) when the temperature of the dispersion liquid in the step (1) is reduced to below 5 ℃, adding an oxidant, controlling the whole reaction temperature to below 5 ℃ and the reaction time to be 6-8 h, performing suction filtration and washing for multiple times by using ultrapure water, and performing freeze drying to obtain the polyaniline/carbon nanotube composite material.

2. The preparation method of the polyaniline/carbon nanotube composite material according to claim 1, wherein in the step (1), the mass ratio of the aniline monomer to the carbon nanotube is 1: 2-3, and the molar ratio of the aniline monomer to the hydrofluoric acid to the hydrochloric acid is 1: 10: 5; the solvent is ultrapure water, the total volume of the reaction solution is 100mL, and the mass fraction of the carbon nano tube in the solvent is not more than 15%.

3. Use of the polyaniline/carbon nanotube composite prepared by the method of any one of claims 1-2 in a sodium-based bi-ion battery.