CN108808021A - Mo2C/C nanocomposites and preparation method thereof and lithium carbon dioxide anode and preparation method thereof comprising the material - Google Patents

Abstract

The invention relates to a Mo ₂ C/C nanocomposite material and a preparation method thereof, a positive electrode of a lithium carbon dioxide battery containing the material and a preparation method thereof, and belongs to the technical field of electrochemical energy. The invention uses ammonium molybdate as a molybdenum source, citric acid as a carbon source, and utilizes the reducing property of _hydrogen to prepare Mo2C/C nanometer composite material. The positive electrode sheet of lithium carbon dioxide battery is prepared by coating method, and the Mo ₂ C/C nanocomposite material is mixed with PVDF to form a coating film slurry and coated on the current collector to obtain a lithium carbon dioxide battery containing Mo ₂ C/C nanocomposite material positive electrode. The positive electrode of the lithium carbon dioxide battery containing Mo ₂ C/C nanocomposite materials effectively alleviates the polarization problem of the positive electrode of the battery, reduces the charging overpotential of the lithium carbon dioxide battery, and enables the lithium carbon dioxide battery to operate stably and efficiently.

Description

Mo2C/C nanocomposite material and its preparation method and lithium dioxide comprising the material Carbon battery positive electrode and preparation method thereof

technical field

The invention relates to a Mo ₂ C/C nanocomposite material and a preparation method thereof, a positive electrode of a lithium carbon dioxide battery containing the material and a preparation method thereof, and belongs to the technical field of electrochemical energy.

Background technique

With the rapid development of human society and the burning of tens of thousands of tons of fossil fuels (coal, natural gas and petroleum products) every year, the emission of carbon dioxide in the atmosphere is increasing year by year. Carbon dioxide is the main greenhouse gas, and the increase in carbon dioxide concentration has caused severe climate change, and there is an urgent need to reduce carbon dioxide emissions into the atmosphere. However, since the carbon atoms in CO2 are in the highest oxidation state, converting CO2 into other chemical substances requires a lot of energy, which will inevitably lead to additional pollution. Therefore, how to achieve ecologically efficient and environmentally friendly carbon dioxide capture and utilization has become a worldwide challenge, and researchers are constantly exploring technologies to achieve carbon dioxide conversion through various strategies. However, these methods all require additional continuous supplementary energy, which in turn leads to the generation and emission of more carbon dioxide on the basis of conventional technologies. In conventional CO2 capture and utilization strategies, we obtain various products including carbon monoxide, methane, ethylene, formic acid and methanol. However, the storage and transportation of these liquid or gaseous products require further compression or liquefaction procedures, resulting in additional energy consumption. Therefore, the traditional capture and utilization of carbon dioxide still requires more energy and produces more pollution. Therefore, introducing CO2 into a battery system can not only reduce CO2 emissions, but also convert CO2 into a renewable energy source.

Compared with lithium-air batteries, lithium-carbon dioxide batteries have the following advantages: (1) carbon dioxide gas is easier to compress and store than oxygen; (2) in organic solvents, the solubility of carbon dioxide is 50 times greater than that of oxygen, which is beneficial to discharge during discharge. Carbon dioxide is consumed on the cathode, and carbon dioxide may have better kinetic characteristics than oxygen; (3) The battery can not only consume greenhouse gases, but also alleviate the energy crisis.

Although lithium carbon dioxide battery is an attractive new energy system, at present, lithium carbon dioxide battery is still in the laboratory research stage, and the further development of lithium carbon dioxide battery system still needs to overcome many problems. For example, the instability of the electrolyte, the generation of lithium dendrites, and the electrochemical polarization of the positive electrode. The use of suitable catalyst materials can greatly reduce the electrochemical polarization of the positive electrode of the battery and improve the performance of the battery. Catalyst materials can stabilize intermediate products and discharge products, increase the discharge capacity of the battery, reduce the charging platform and improve the energy conversion efficiency of the battery. At present, the commonly used catalysts for lithium-carbon dioxide batteries are mainly carbon materials and metal ruthenium nanoparticles. Due to the high cost of the noble metal ruthenium, it is not conducive to practical application, and the effect of carbon material catalysts on reducing the polarization of the positive electrode is not significant. Therefore, finding a suitable catalyst to reduce the electrochemical polarization of the cathode and improve the energy conversion efficiency is one of the technical problems to be solved in the field of lithium carbon dioxide batteries.

Contents of the invention

The object of the present invention is to provide a Mo ₂ C/C nanocomposite material and its preparation method, a lithium carbon dioxide battery positive electrode containing the material and its preparation method. The positive electrode of lithium carbon dioxide battery uses Mo ₂ C/C nanocomposite material as the catalyst, and the positive electrode of lithium carbon dioxide battery containing Mo ₂ C/C nanocomposite material can effectively alleviate the polarization problem of the positive electrode of the battery, reduce the charging overpotential of lithium carbon dioxide battery, and improve the The cycle life of the battery.

The present invention is realized by adopting the following technical solutions:

A preparation method of Mo ₂ C/C nanocomposite material, comprising the following steps:

(1) ammonium molybdate, citric acid and sodium chloride are dissolved in deionized water, and stirred to obtain a uniform aqueous solution;

(2) freeze-drying the aqueous solution obtained in step (1) to obtain a mixture;

(3) reducing the mixture obtained in step (2) in a mixed atmosphere of argon and hydrogen;

(4) Wash and dry the mixture reduced in step (3) with deionized water to obtain Mo ₂ C/C nanocomposite material.

Further, the mass ratio of ammonium molybdate and citric acid in the step (1) is 1:1-1.5.

Further, the volume ratio of hydrogen to argon in the step (3) is 5:95.

Further, the heating rate of the reduction process in the step (3) is 1-5°C/min, the target temperature is 700-1000°C, and the holding time is 1-3h.

A Mo ₂ C/C nanocomposite material prepared by the method described above.

A lithium carbon dioxide battery positive electrode prepared from the above-mentioned materials.

A method for preparing a positive electrode of a lithium carbon dioxide battery as described above, comprising the steps of:

(1) Mo ₂ C/C nanocomposite material and PVDF are mixed and ground in proportion, dissolved in NMP solution, and stirred to obtain coating slurry;

(2) Coating the coating film slurry on the current collector and drying in vacuum to obtain the positive electrode of the lithium carbon dioxide battery.

Further, the amount of PVDF used in the step (1) is 10-20% of the mass of the coating slurry.

Further, the current collector in the step (2) is carbon paper, and the diameter of the current collector is 12-16mm.

Further, in the step (2), the drying temperature is 80-120° C., and the drying time is 10-12 hours.

The Mo ₂ C/C nanocomposite material of the present invention is used as a catalyst for the positive electrode of the lithium carbon dioxide battery, which can ease the polarization of the positive electrode of the lithium carbon dioxide battery and reduce the charging voltage platform.

A non-hydrophilic lithium carbon dioxide battery is assembled using the positive electrode of the lithium carbon dioxide battery of the present invention, the battery includes a metal lithium negative electrode, a non-aqueous electrolyte, a diaphragm and a catalyst positive electrode, wherein the battery assembly process is carried out in a glove box filled with high-purity argon of. Preferably adopt the lithium metal sheet of 16mm diameter as the anode of battery, glass fiber filter paper is as the diaphragm of battery, electrolyte uses bistrifluoromethanesulfonylimide lithium as solute, tetraethylene glycol dimethyl ether as solvent, O in the glove box ₂ <0.1ppm and _H20 <0.1ppm.

Compared with prior art, the beneficial effect of the present invention is:

(1) The Mo ₂ C/C nanocomposite material of the present invention is a three-dimensional porous hierarchical structure with both micropores and mesopores, which is beneficial to the transmission of ions in the electrolyte and the diffusion of carbon dioxide gas.

(2) The Mo ₂ C/C nanocomposite material of the present invention has a large specific surface area and good electrical conductivity, and the preparation method is simple and the process cost is low.

(3) The Mo ₂ C/C nanocomposite material of the present invention is used as a positive electrode catalyst of a lithium carbon dioxide battery, which can alleviate the positive electrode polarization of the lithium carbon dioxide battery, reduce the charging voltage platform, and have a remarkable catalytic effect.

Description of drawings

Fig. ₁ is the SEM figure of Mo2C/C nanocomposite material in the embodiment one of the present invention;

Fig. 2 is the SEM figure of commercial BP2000 carbon powder in comparative example one of the present invention;

Fig. 3 is the X-ray diffraction spectrum of the Mo2C/C nanocomposite material in Example ₁ of the present invention;

Fig. 4 is a comparison chart of charge and discharge curves of the lithium carbon dioxide battery in Example 4 of the present invention and Comparative Example 1 at a current of 20 μA;

FIG. 5 is a curve showing the variation of the capacity of the lithium-carbon dioxide battery with the current in Example 4 of the present invention.

Detailed ways

In order to make the purpose and technical solution of the present invention clearer, the present invention will be further described in detail through the following examples.

Embodiment one :

(1) ammonium molybdate, citric acid and sodium chloride are dissolved in deionized water, and magnetically stirred to obtain a uniform aqueous solution, wherein the mass ratio of ammonium molybdate and citric acid is 1:1;

(2) freeze-drying the aqueous solution obtained in step (1) to obtain a mixture;

(3) The mixture obtained in step (2) is reduced in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen and argon in the argon-hydrogen mixture is 5:95, and the heating rate of the reduction process is 3° C./min, The target temperature for reduction is 800°C and kept for 3 hours;

(4) Wash and dry the mixture reduced in step (3) with deionized water to obtain Mo ₂ C/C nanocomposite material.

Embodiment two :

(1) Ammonium molybdate, citric acid and sodium chloride are dissolved in deionized water, and magnetically stirred to obtain a uniform aqueous solution, wherein the mass ratio of ammonium molybdate and citric acid is 1:1.2;

(2) freeze-drying the aqueous solution obtained in step (1) to obtain a mixture;

(3) The mixture obtained in step (2) is reduced in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen and argon in the argon-hydrogen mixture is 5:95, and the heating rate of the reduction process is 5° C./min, The target temperature for reduction is 750°C and kept for 3 hours;

(4) Wash and dry the mixture reduced in step (3) with deionized water to obtain Mo ₂ C/C nanocomposite material.

Embodiment three :

(1) Ammonium molybdate, citric acid and sodium chloride are dissolved in deionized water, and magnetically stirred to obtain a uniform aqueous solution, wherein the mass ratio of ammonium molybdate and citric acid is 1:1.5;

(2) freeze-drying the aqueous solution obtained in step (1) to obtain a mixture;

(3) The mixture obtained in step (2) is reduced in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen and argon in the argon-hydrogen mixture is 5:95, and the heating rate of the reduction process is 5° C./min, The target temperature for reduction is 900°C and kept for 3 hours;

(4) Wash and dry the mixture reduced in step (3) with deionized water to obtain Mo ₂ C/C nanocomposite material.

Embodiment four :

Preparation of positive electrode of lithium carbon dioxide battery:

(1) Mix and grind the Mo ₂ C/C nanocomposite material prepared in Example 1 and PVDF in a ratio of 9:1, dissolve in the NMP solution, and stir magnetically to obtain a coating slurry;

(2) Coating the coating film slurry on carbon paper, and drying in vacuum at 100° C. for 12 hours to obtain the positive electrode of the lithium carbon dioxide battery.

Assembly of lithium carbon dioxide battery:

The assembly of the battery is carried out in a glove box filled with high-purity argon gas. In the glove box, O ₂ <0.1ppm and H ₂ O<0.1ppm, the positive electrode is the positive electrode of the lithium carbon dioxide battery prepared above, and the negative electrode is a lithium metal sheet with a diameter of 16mm. The diaphragm is a glass fiber filter paper, and the electrolyte is a TEGDME solution of 1M/L LiTFSI. First place the shrapnel, the gasket and the lithium sheet in sequence on the negative electrode shell of the battery, place the separator on the lithium sheet, then add the electrolyte dropwise and put in the positive electrode sheet. Before the test, the assembled battery was left to stand in a carbon dioxide atmosphere for 10 h.

Embodiment five :

Preparation of positive electrode of lithium carbon dioxide battery:

(1) Mix and grind Mo ₂ C/C nanocomposite material and PVDF in a ratio of 8:2, dissolve in NMP solution, and stir magnetically to obtain coating slurry;

(2) Coating the coating film slurry on the current collector, and drying in vacuum at 100° C. for 12 hours to obtain the positive electrode of the lithium carbon dioxide battery.

Assembly of lithium carbon dioxide battery:

The assembly of the battery is carried out in a glove box filled with high-purity argon gas. In the glove box, O ₂ <0.1ppm and H ₂ O<0.1ppm, the positive electrode is the positive electrode of the lithium carbon dioxide battery prepared above, and the negative electrode is a lithium metal sheet with a diameter of 16mm. The diaphragm is a glass fiber filter paper, and the electrolyte is a TEGDME solution of 1M/L LiTFSI. First place the shrapnel, the gasket and the lithium sheet in sequence on the negative electrode shell of the battery, place the separator on the lithium sheet, then add the electrolyte dropwise and put in the positive electrode sheet. Before the test, the assembled battery was left to stand in a carbon dioxide atmosphere for 10 h.

Comparative example one :

Preparation of positive electrode of lithium carbon dioxide battery:

Mix and grind commercial BP2000 carbon powder and PVDF in a ratio of 9:1, dissolve in NMP solution, and stir magnetically to obtain a coating slurry;

The coating slurry was coated on carbon paper, and vacuum-dried at 100° C. for 12 hours to obtain the positive electrode of the lithium-carbon dioxide battery.

Assembly of lithium carbon dioxide battery:

The assembly of the battery is carried out in a glove box filled with high-purity argon gas. In the glove box, O ₂ <0.1ppm and H ₂ O<0.1ppm, the positive electrode is the positive electrode of the lithium carbon dioxide battery prepared above, and the negative electrode is a lithium metal sheet with a diameter of 16mm. The diaphragm is a glass fiber filter paper, and the electrolyte is a TEGDME solution of 1M/L LiTFSI. First place the shrapnel, the gasket and the lithium sheet in sequence on the negative electrode shell of the battery, place the separator on the lithium sheet, then add the electrolyte dropwise and put in the positive electrode sheet. Before the test, the assembled battery was left to stand in a carbon dioxide atmosphere for 10 h.

The SEM (scanning electron image) of the Mo ₂ C/C nanocomposite material prepared in Example 1 and the BP2000 carbon powder in Comparative Example 1 are shown in Fig. 1 and Fig. 2 respectively. The X-ray diffraction pattern of the Mo ₂ C/C nanocomposite prepared in Example ₁ is shown in Figure 3. This pattern shows the successful preparation of the Mo ₂ C/C nanocomposite and illustrates that Nanocomposites have good crystallinity. The Mo ₂ C/C nanocomposite material prepared in Example 1 and BP2000 carbon powder were respectively used as a cathode catalyst for a lithium carbon dioxide battery to prepare a lithium carbon dioxide battery, and a constant current charge and discharge test was performed in a pure carbon dioxide atmosphere. Figure 4 is the deep charge and discharge curves of the lithium carbon dioxide battery prepared in Example 4 and Comparative Example 1 at a current of 20 μA, the charging platform of the lithium carbon dioxide battery in Example 4 and the charging platform of the lithium carbon dioxide battery in Comparative Example 1 Compared with that, it is reduced by 1V, indicating that the Mo ₂ C/C nanocomposite material can effectively alleviate the positive polarization of the lithium carbon dioxide battery and reduce the charging overpotential of the lithium carbon dioxide battery.

The variation curve of the capacity of the lithium carbon dioxide battery with the current in Example 4 is shown in FIG. 5 . It can be seen that the discharge capacity of the carbon dioxide battery gradually decreases with the increase of the current.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. All equal modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the present invention. covered by the patent.

Claims (10)

1. A preparation method of Mo ₂ C/C nanocomposite, characterized in that, comprising the following steps: (1) ammonium molybdate, citric acid and sodium chloride are dissolved in deionized water, and stirred to obtain a uniform aqueous solution; (2) freeze-drying the aqueous solution obtained in step (1) to obtain a mixture; (3) reducing the mixture obtained in step (2) in a mixed atmosphere of argon and hydrogen; (4) Wash and dry the mixture reduced in step (3) with deionized water to obtain Mo ₂ C/C nanocomposite material. 2. preparation method according to claim 1, is characterized in that, in described step (1), the mass ratio of ammonium molybdate and citric acid is 1:1-1.5. 3. preparation method according to claim 1, is characterized in that, in described step (3), the volume ratio of hydrogen and argon is 5:95. 4. The preparation method according to claim 1 or 3, characterized in that, the heating rate of the reduction process in the step (3) is 1 to 5°C/min, the target temperature is 700 to 1000°C, and the holding time is 1 ~3h. 5. _A Mo2C/C nanocomposite material prepared by the method according to any one of claims 1-4. 6. A lithium carbon dioxide battery positive electrode prepared from the material according to claim 5. 7. a preparation method of lithium carbon dioxide battery positive pole as claimed in claim 6, is characterized in that, comprises the steps: (1) Mo ₂ C/C nanocomposite material and PVDF are mixed and ground in proportion, dissolved in NMP solution, and stirred to obtain coating slurry; (2) Coating the coating film slurry on the current collector and drying in vacuum to obtain the positive electrode of the lithium carbon dioxide battery. 8. The preparation method according to claim 7, characterized in that the amount of PVDF in the step (1) is 10-20% of the mass of the coating slurry. 9. The preparation method according to claim 7, characterized in that the current collector in the step (2) is carbon paper, and the diameter of the current collector is 12-16 mm. 10. The preparation method according to claim 7, characterized in that, in the step (2), the drying temperature is 80-120° C., and the drying time is 10-12 hours.